150
150
Service Training Meeting Guide 682 SESV1682 March 1997 TECHNICAL PRESENTATION 793C OFF-HIGHWAY TRUCK
-
Upload
jorge-canipa -
Category
Documents
-
view
100 -
download
6
Transcript of 150
Service TrainingMeeting Guide 682 SESV1682
March 1997
TECHNICAL PRESENTATION
793C OFF-HIGHWAY TRUCK
793C OFF-HIGHWAY TRUCKMEETING GUIDE 682 SLIDES AND SCRIPT
AUDIENCE
Level II - Service personnel who understand the principles of machine systems operation, diagnostic
equipment, and procedures for testing and adjusting.
CONTENT
This presentation provides basic maintenance information and describes the systems operation of the
engine, power train, steering, hoist and the air system and brakes for the 793C Off-highway Truck. The
Automatic Retarder Control (ARC) and the Traction Control System (TCS) are also discussed.
OBJECTIVES
After learning the information in this meeting guide, the serviceman will be able to:
1. locate and identify the major components in the engine, power train, steering, hoist and the air
system and brakes;
2. explain the operation of the major components in the systems; and
3. trace the flow of oil or air through the systems.
REFERENCES
793C Off-highway Truck Service Manual SENR1440
793C Off-highway Truck Parts Book SEBP2503
Vital Information Management System (VIMS) Service Manual SENR6059
Fluid Power Graphic Symbols User's Guide SENR3981
PREREQUISITES
Interactive Video Course "Fundamentals of Mobile Hydraulics" TEVR9001
Interactive Video Course "Fundamentals of Electrical Systems" TEVR9002
STMG 546 "Graphic Fluid Power Symbols" SESV1546
Estimated Time: 8 Hours
Visuals: 184 (2 X 2) Slides
Serviceman Handouts: 4 Data Sheets
Form: SESV1682
© 1997 Caterpillar Inc. Date: 3/97
- 3 -STMG 682
3/97
SUPPLEMENTAL MATERIAL
Specification Sheets
793B Off-highway Truck AEHQ5061
793C Off-highway Truck AEHQ5186
Salesgrams
Vital Information Management System (VIMS) TELQ4478
793B Rear Axle Improvements TELQ3736
785B/789B/793B Introduction TELQ3725
789B/793B Feature Status TELQ4477
Video Tapes
793C Off-highway Truck--Service Introduction SEVN4016
793C Marketing Introduction AEVN3742
3500 EUI Service Introduction SEVN2241
Intelligence of Powerful Connections AEVN2974
Suspension Cylinder Charging TEVN2155
TPMS Management/Technical Information AEVN2211
TPMS Operating Tips AEVN2212
Automatic Electronic Traction Aid (AETA) Introduction SEVN9187
Service Training Meeting Guides
STMG 625 "793 Off-highway Truck" SESV1625
STMG 660 "785B/789B/793B Off-highway Trucks--Maintenance" SESV1660
STMG 681 "3500B Engine Controls--Electronic Unit Injection (EUI)" SESV1681
Technical Instruction Modules
Vital Information Management System--785B/789B/793B Off-highway Trucks SEGV2610
Vital Information Management System--Introduction SEGV2597
3500 Electronic Engine Controls--Introduction SEGV2588
3500 Electronic Engine Controls--Off-highway Trucks SEGV2589
Electronic Programmable Transmission Control (EPTC II) SEGV2584
769C - 793B Off-highway Trucks--Torque Converter
and Transmission Hydraulic Systems SEGV2591
785B/789B/793B Off-highway Trucks--Steering System SEGV2587
769C - 793B Off-highway Trucks--Hoist System SEGV2594
769C - 793B Off-highway Trucks--Air System and Brakes SEGV2595
Automatic Retarder Control System SEGV2593
Automatic Electronic Traction Aid SEGV2585
769C - 793B Off-highway Trucks--Suspension System SEGV2599
- 4 -STMG 682
3/97
SUPPLEMENTAL MATERIAL (Continued)
Booklets
Know Your Cooling System SEBD0518
Diesel Fuels and Your Engine SEBD0717
Oil and Your Engine SEBD0640
Special Instructions
Using the ECAP NEXG4521 Machine Functions Service Program Module SEHS9343
Using the 8T8697 Electronic Control Analyzer Programmer (ECAP) SEHS8742
Using the 7X1700 Communication Adapter Group SEHS9264
Use of 6V3000 Sure-Seal Repair Kit SMHS7531
Use of CE Connector Tools SEHS9065
Servicing DT Connectors SEHS9615
Use of 8T5200 Signal Generator/Counter Group SEHS8579
Repair of 4T8719 Bladder Accumulator Group SEHS8757
Suspension Cylinder Servicing SEHS9411
Using 1U5000 Auxiliary Power Unit (APU) SEHS8715
Using the 1U5525 Attachment Group SEHS8880
Brochures
Caterpillar Vital Information Management System (VIMS) AEDK2946
Caterpillar Electronic Technician NEHP5614
Caterpillar DataView NEHP5622
Diesel Engine Oil (CG4) Product Data Sheet PEHP5026
How to Take a Good Oil Sample PEHP6001
Air Filter Service Indicator PEHP9013
Intelligence of Powerful Connections AEDK2966
Caterpillar Fully Automatic Transmission AEDQ0066
Caterpillar Oil-cooled Multiple Disc Brakes AEDK2546
Caterpillar Automatic Retarder Control AEDK0075
Miscellaneous
Electronic Diagnostic Code Pocket Card NEEG2500
Pressure Conversion Chart SEES5677
793B Transmission Assembly Wall Chart SENR6834
793B Final Drive Assembly Wall Chart SENR8602
Improved Transmission/Drive Train Oil (IRM) PELE0179
- 5 -STMG 682
3/97
TABLE OF CONTENTS
INTRODUCTION ........................................................................................................................7
WALK AROUND INSPECTION...............................................................................................11
OPERATOR'S STATION............................................................................................................36
ENGINE......................................................................................................................................49
Cooling System.....................................................................................................................66
Lubrication System ...............................................................................................................77
Fuel System...........................................................................................................................80
Air Induction and Exhaust System .......................................................................................85
POWER TRAIN .........................................................................................................................90
Power Train Components......................................................................................................91
Power Train Hydraulic System...........................................................................................103
Electronic Programmable Transmission Control (EPTC II)...............................................120
STEERING SYSTEM ..............................................................................................................128
HOIST SYSTEM......................................................................................................................157
AIR SYSTEM AND BRAKES ................................................................................................177
Operator Controls................................................................................................................179
Air Charging System...........................................................................................................182
Parking and Secondary Brake System ................................................................................188
Service and Retarder Brake System....................................................................................195
AUTOMATIC RETARDER CONTROL (ARC) .....................................................................206
TRACTION CONTROL SYSTEM (TCS)...............................................................................211
CONCLUSION.........................................................................................................................221
SLIDE LIST..............................................................................................................................222
SERVICEMAN'S HANDOUTS...............................................................................................224
- 6 -STMG 682
3/97
INSTRUCTOR NOTES
- 7 -
• 3516B DITA engine
1
STMG 682
3/97
793C OFF-HIGHWAY TRUCK
C 1997 Caterpillar Inc.
INTRODUCTION
This presentation provides an introduction to the Caterpillar
793C Off-highway Truck. Included in this package is a walk around
inspection which provides information about daily service requirements
and identifies the locations of the major components. The major systems
of the truck will also be discussed. The major systems include the engine,
power train, steering, hoist, and the air system and brakes.
The 793C is the largest rigid frame truck produced by Caterpillar. The
793C is equipped with a Caterpillar 3516B engine rated at 1716 kW
(2300 gross hp) and 1616 kW (2166 flywheel hp). The load carrying
capacity is 218 Metric tons (240 tons) at a Gross Machine Weight (GMW)
of 376488 kg (830000 lbs.).
This slide shows a view of the left side of the truck. Notice that the body
canopy is extended over the cab to protect the front of the truck from
falling objects.
The fuel tank is located on the left side of the truck.• Fuel tank
• Extended bodycanopy
- 8 -
2
STMG 682
3/97
Shown is the right side of the truck. The large air tank on the right
platform supplies air for starting the truck and for the service and retarder
brake system.
The main hydraulic tank is also visible. The hydraulic tank supplies oil
for the hoist system and the brake system.
On the 793B truck, torque converter oil is also supplied from the main
hydraulic tank. A transmission oil supply tank is located in front of the
main hydraulic tank.
The 793C now uses the torque converter case as the supply tank for the
torque converter and the transmission.
• Main system air tank:
- Air starting
- Service/retarderbrakes
• Main hydraulic tank:
- Hoist system
- Brake system
• Torque converter caseused as sump forconverter andtransmission
- 9 -
• 789B and 793C aresimilar
• 793C has four airfilters
3
STMG 682
3/97
The 793C is similar in appearance to the 789B and may be difficult to
recognize from a distance. The 793C can be recognized by the four air
filters and the diagonal access ladder. The 789B has only two air filters
mounted in the same locations and is equipped with two vertical ladders.
- 10 -
• Truck body
4
STMG 682
3/97
The truck body has a dual-slope main floor and a "vee" bottom to center
the load and reduce spills. The steel used to construct the body has a
yield strength of 6205 bar (90000 psi).
The rear suspension cylinders absorb bending and twisting stresses rather
than transmitting them to the main frame.
• Rear suspensioncylinders
5
- 11 -STMG 682
3/97
• Read the Operationand MaintenanceManual
793C MAINTENANCE
793C Service
Procedure
WALK AROUND INSPECTION
WALK AROUND INSPECTION
Before working on or operating the truck, read the Operation and
Maintenance Manual (Form SEBU6995) thoroughly for information on
safety, maintenance and operating techniques.
Safety precautions and Warnings are provided in the manual and on the
truck. Be sure to identify and understand all symbols before starting the
truck.
The first step to perform when approaching the truck is to make a
thorough walk around inspection. Look around and under the truck for
loose or missing bolts, trash build-up and for coolant, fuel or oil leaks.
Look for indications of cracks. Pay close attention to high stress areas as
shown in the Operation and Maintenance Manual.
- 12 -
• Front wheel bearinginspection plug(arrow)
6
STMG 682
3/97
The front wheel bearing oil level is checked and filled by removing the
plug (arrow) in the center of the wheel bearing cover. The oil should be
level with the bottom of the plug hole.
Check the tire inflation pressure. Operating the truck with the wrong tire
inflation pressure can cause heat build-up in the tire and accelerate tire
wear.
NOTE: Care must be taken to ensure that fluids are contained while
performing any inspection, maintenance, testing, adjusting and
repair of the machine. Be prepared to collect the fluid in suitable
containers before opening any compartment or disassembling any
component containing fluids. Refer to the "Tools and Shop Products
Guide" (Form NENG2500) for tools and supplies suitable to collect
and contain fluids in Caterpillar machines. Dispose of fluids
according to local regulations and mandates.
• Tire inflation
- 13 -
1. Front wheel bearingaxle housingbreather
7
STMG 682
3/97
1
2
Inspect the condition of the front wheel bearing axle housing breather (1).
The breather prevents pressure from building up in the axle housing.
Pressure in the axle housing may cause brake cooling oil to leak through
the Duo-Cone seals in the wheel brake assemblies.
Two grease outlet fittings (2) are located on the front of each suspension
cylinder. The grease supply line for the Auto Lubrication System is
located at the rear of the suspension cylinder. No grease outlet fittings
should be located on the same side of the suspension cylinder as the
grease fill location. Having an outlet fitting on the same side of the
suspension cylinder as the grease fill location will prevent proper
lubrication of the cylinder.
Make sure that grease is flowing from the outlet fittings to verify that the
suspension cylinders are being lubricated and that the pressure in the
cylinders is not excessive.
2. Suspension cylindergrease outlet fittings
• Make sure greaseflows from outletfittings
- 14 -
1. Rear brake oilcoolers
2. Parking brakerelease filter
3. Torque convertercharging filter
4. Automaticlubrication injectorbank
8
STMG 682
3/97
4
2
1
3
Located behind the right front tire are the rear brake oil coolers (1), the
parking brake release filter (2), and the torque converter charging
filter (3).
One of the three injector banks (4) for the automatic lubrication system is
also in this location. These injectors are adjustable and regulate the
quantity of grease that is injected during each cycle (approximately once
per hour).
A solenoid air valve provides a controlled air supply for the automatic
lubrication system. The solenoid air valve is controlled by the Vital
Information Management System (VIMS), which energizes the solenoid
ten minutes after the machine is started. The VIMS energizes the
solenoid for 75 seconds before it is de-energized. Every 60 minutes
thereafter, the VIMS energizes the solenoid for 75 seconds until the
machine is stopped (shut down). These settings are adjustable through the
VIMS keypad in the cab.
INSTRUCTOR NOTE: For more detailed information on servicing
the automatic lubrication system, refer to the Service Manual Module
"Automatic Lubrication System" (Form SENR4724).
- 15 -
• Hoist and brakehydraulic tank
• Oil level sight gauges(arrows)
9
STMG 682
3/97
Shown is the hoist and brake hydraulic tank and the oil level sight gauges
(arrows). The oil level is normally checked with the upper sight gauge.
The oil level should first be checked with cold oil and the engine stopped.
The level should again be checked with warm oil and the engine running.
The lower sight gauge can be used to fill the hydraulic tank when the
hoist cylinders are in the RAISED position. When the hoist cylinders are
lowered, the hydraulic oil level will increase. After the hoist cylinders are
lowered, check the hydraulic tank oil level with the upper sight gauge as
explained above.
- 16 -
• Final drives
• Check magnetic plugs(arrow) for metal
10
STMG 682
3/97
The rear axles are equipped with double reduction planetary final drives.
The magnetic plug (arrow) should be removed from the final drives at
regular intervals and checked for metal particles. For some conditions,
checking the magnetic plug is the only way to identify a problem which
may exist.
The rear axle is a common sump for the differential and both final drives.
If a final drive or the differential fails, the other final drive components
must also be checked for contamination and then flushed. Failure to
completely flush the rear axle after a failure can cause a repeat failure
within a short time.
NOTICE
The rear axle is a common sump for the differential and both final
drives. If a final drive or the differential fails, the other final drive
components must also be checked for contamination and then
flushed. Failure to completely flush the rear axle after a failure can
cause a repeat failure within a short time.
• Flush all axlecomponents after afailure
- 17 -
1. Differential oil levelsight glass
11
STMG 682
3/97
22
4
1
5
3
The differential oil level is checked by viewing the oil level sight
glass (1). The oil should be level with the bottom of the inspection hole.
Two oil level sensors (2) provide input signals to the VIMS which
informs the operator of the rear axle oil level.
A rear axle oil filter (3) is used to remove contaminants from the rear axle
housing.
Check the charge condition of the rear suspension cylinders when the
truck is empty and on level ground.
The second of three injector banks (4) for the automatic lubrication
system is mounted on the top rear of the differential housing.
Above the lubrication injectors is a breather (5) for the rear axle. Inspect
the condition of the breather at regular intervals. The breather prevents
pressure from building up in the axle housing. Excessive pressure in the
axle housing can cause brake cooling oil to leak through the Duo-Cone
seals in the wheel brake assemblies.
INSTRUCTOR NOTE: For more detailed information on servicing
the suspension system, refer to the Special Instruction "Suspension
Cylinder Servicing" (Form SEHS9411).
2. Rear axle oil levelsensors
3. Rear axle housing oilfilter
• Rear suspensioncylinders
4. Automaticlubrication injectorbank
5. Rear axle breather
- 18 -
• Cable holds body up
12
STMG 682
3/97
The cable that holds the body up is stored below the rear of the body.
Whenever work is to be performed while the body is raised, the safety
cable must be connected between the body and the rear hitch to hold the
body in the raised position.
The space between the body and the frame becomes a zero clearance
area when the body is lowered. Failure to install the cable can result
in injury or death to personnel working in this area.
WARNING
- 19 -
• Fuel tank
13
STMG 682
3/97
The fuel tank is located on the left side of the truck. The fuel level sight
gauge (arrow) is used to check the fuel level during the walk around
inspection.• Fuel level sight gauge
(arrow)
- 20 -
1. Primary fuel filter
14
STMG 682
3/97
2
3
1
The primary fuel filter (1) is located on the inner surface of the fuel tank.
Open the drain valve (2) to remove condensation from the fuel tank.
A fuel level sensor (3) is also located on the fuel tank. The fuel level
sensor provides input signals to the VIMS which informs the operator of
the fuel level.
3. Fuel level sensor
2. Condensation drainvalve
- 21 -
15
STMG 682
3/97
1
2
Supply oil for the torque converter and the transmission is contained in
the torque converter case. Sight gauges (1) are used to check the oil level
for the torque converter and the transmission.
Torque converter and transmission oil is added at the fill tube (2).
When filling the torque converter and transmission oil sump after an oil
change, fill the sump with oil to the top of the upper sight gauge. Turn off
the engine manual shutdown switch (see slide No. 23) so the engine will
not start. Crank the engine for approximately 15 seconds. The oil level
will decrease as oil fills the torque converter and transmission system.
Add more oil to the sump to raise the oil level to the FULL COLD mark.
Crank the engine for an additional 15 seconds. Repeat this step as
required until the oil level stabilizes.
Turn off the engine manual shutdown switch and start the engine. Warm
the torque converter and transmission oil. Add more oil to the sump as
required to raise the torque converter and transmission oil level to the
FULL WARM mark.
NOTICE
Failure to correctly fill the torque converter and transmission oil
sump after an oil change may cause transmission clutch damage.
1. Torque converterand transmission oillevel sight gauges
2. Torque converterand transmission oilfill tube
• Torque converter andtransmission oil fill
procedure
- 22 -
16
STMG 682
3/97
1
4
2
3
Shown is the location of the torque converter outlet screen (1). Oil flows
from the torque converter outlet relief valve through the torque converter
outlet screen to the torque converter and transmission oil cooler located
on the right side of the engine. Oil from the torque converter and
transmission oil cooler returns to the torque converter housing.
Shown is the location of the transmission charging filter (2).
Transmission charging oil flows through the transmission charging filter
to the transmission control valves on top of the transmission and to the
torque converter lockup clutch valve located on top of the torque
converter.
The scavenge screen for torque converter and transmission oil is located
behind the cover (3).
Torque converter and transmission oil samples can be taken at the
Scheduled Oil Sampling (S•O•S) tap (4).
1. Torque converteroutlet screen
2. Transmissioncharging filter
3. TC/Transmissionscavenge screen
4. TC/TransmissionS•O•S tap
- 23 -
• Brake cylinderbreather (arrow)
17
STMG 682
3/97
Inspect the condition of the two breathers (arrow, one visible) for the
brake cylinders. The second breather is located behind the cross tube.
Oil should not leak from the breathers. Oil leaking from the breathers is
an indication that the oil piston seals in the brake cylinder need
replacement. Air flow from the breathers during a brake application is an
indication that the brake cylinder air piston seals need replacement.
- 24 -
• Front brake oil coolerfilters (arrow)
18
STMG 682
3/97
Located in front of the fuel tank are the front brake oil cooler filters
(arrow). Oil not used to raise or lower the hoist cylinders flows from the
hoist valve through the front brake oil filters to the front brake oil cooler
located above the torque converter.
The third injector bank for the automatic lubrication system is also
located in this area.
• Automatic lubricationinjector bank
- 25 -
• Front suspensioncylinder
19
STMG 682
3/97
1
2
Check the charge condition of the front suspension cylinders when the
truck is empty and on level ground.
The air dryer (1) is located in front of the left front suspension cylinder.
The air system can be charged from a remote air supply through a ground
level connector (2) inside the left frame.
INSTRUCTOR NOTE: For more detailed information on servicing
the suspension system, refer to the Special Instruction "Suspension
Cylinder Servicing" (Form SEHS9411).
1. Air dryer
2. Remote air supplyconnector
- 26 -
• Engine oil filters
1. Engine oil fill tube
2. Engine oil dipstick
20
STMG 682
3/97
2
1
3
4
The engine oil filters are located on the left side of the engine.
Engine oil should be added at the fill tube (1) and checked with the
dipstick (2).
Engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S)
tap (3).
The engine lubrication system is equipped with two oil pressure
sensors (4). A sensor is located on each end of the oil filter base. One
sensor measures engine oil pressure before the filters. The other sensor
measures oil pressure after the filters. The sensors provide input signals
to the second generation Advanced Diesel Engine Management
(ADEM II) engine Electronic Control Module (ECM). The ECM
provides input signals to the VIMS which informs the operator of the
engine oil pressure. Together, these sensors inform the operator if the
engine oil filters are restricted.
4. Engine oil pressure
sensor
3. Engine oil S•O•S tap
- 27 -
1. High speed oilchange connector
21
STMG 682
3/97
1 3
2
Engine oil can be added through the high speed oil change connector (1)
located in the left front corner of the oil pan.
Two engine oil level switches (2 and 3) provide input signals to the
engine ECM. The engine ECM provides an input signal to the VIMS,
which informs the operator of the engine oil level.
If the truck is equipped with the engine oil renewal system attachment,
the upper oil level switch (2) tells the operator when engine oil must be
added. The ADD ENG OIL message is a Category 1 Warning.
The lower oil level switch (3) tells the operator when the engine oil level
is low and it is unsafe to operate the truck without causing damage to the
engine. The ENG OIL LEVEL LOW message is a Category 2 or 3
Warning.
2. Add engine oil levelswitch
3. Engine oil level lowswitch
- 28 -
• Secondary fuel filters
• Fuel priming pump(arrow)
22
STMG 682
3/97
The secondary fuel filters and the fuel priming pump (arrow) are located
above the engine oil filters on the left side of the engine.
NOTE: If the fuel system requires priming, it may be necessary to
block the fuel return line during priming to force the fuel into the
injectors.
- 29 -
1. Manual engineshutdown switch
23
STMG 682
3/97
3 5
6
1
2
4
Before climbing the truck ladder, make sure that the manual engine
shutdown switch (1) is OFF. The engine will not start if the manual
shutdown switch is ON. If necessary, the switch can be used to stop the
engine from the ground level.
The toggle switches (2) control the lights in the engine compartment and
above the access ladder.
The RS-232 service connector (3) is used to connect a laptop computer
with VIMS PC software to upload new source and configuration files,
view real time data or download logged information from the VIMS.
The battery disconnect switch (4) and VIMS service connector key switch
(5) must be in the ON position before the laptop computer with VIMS
software will communicate with the VIMS.
The blue service lamp (6) is part of the VIMS. The service lamp will turn
on to notify service personnel that the VIMS has an active machine or
system event. The service lamp flashes to indicate when an event is
considered abusive to the machine.
2. Engine and accessladder light switches
3. RS-232 connector for
VIMS
4. Battery disconnectswitch
5. Key switch for VIMSservice connector
6. VIMS service lamp
- 30 -
• Inspect radiator
• Check air cleanerindicators (arrow)
24
STMG 682
3/97
While climbing the ladder, make a thorough inspection of the radiator. Be
sure that no debris or dirt is trapped in the cores. Check the air cleaner
indicators (arrow) located on both sides of the truck. If the yellow pistons
are in the red zone (indicating that the filters are plugged), the air cleaners
must be serviced.
- 31 -
• Engine coolingsystems:
- Jacket water coolingsystem
- Aftercooler coolingsystem
1. Engine coolantshunt tank
2. Coolant level gauges
3. Coolant level sensor
25
STMG 682
3/97
3
2
1
The cooling system on the 793C is divided into two systems. The two
systems are the jacket water cooling system and the aftercooler cooling
system. These two systems are not connected. When servicing the
cooling systems, be sure to drain and fill both systems separately.
The engine cooling system shunt tank (1) is located on the hood above the
radiator. The coolant levels are checked at the shunt tank. Use the
gauges (2) on top of the shunt tank to check the two coolant levels.
A coolant level sensor (3) is located on each side of the shunt tank to
monitor the coolant level of both cooling systems (guard removed for
viewing sensor). The coolant level sensors provide input signals to the
VIMS which informs the operator of the engine coolant levels.
- 32 -
26
STMG 682
3/97
2
3
1
Located on the right platform are the automatic lubrication system grease
tank (1), the main air system tank (2) and the steering system tank (3).
Check the level of the grease in the automatic lubrication system tank
with the grease level indicator located on top of the tank.
A drain valve is located at the bottom right of the main air system
tank. Drain the condensation from the air tank each morning.
1. Automaticlubrication tank
2. Main air system tank
3. Steering system tank
- 33 -
27
STMG 682
3/97
6
3
7
1
2
5
4
The oil level for the steering system tank is checked at the upper sight
gauge (1) when the oil is cold and the engine is stopped. After the engine
is started, the oil level will decrease as the oil fills the steering
accumulators.
After the accumulators are filled, the oil level should be checked again at
the lower sight gauge (2). When the engine is running and the
accumulators are fully charged, the oil level should not be below the
ENGINE RUNNING marking of the lower gauge. If the ENGINE
RUNNING level is not correct, check the nitrogen charge in each
accumulator. A low nitrogen charge will allow excess oil to be stored in
the accumulators and will reduce the secondary steering capacity.
Before removing the cap to add oil to the steering system, be sure that the
engine was shut off with the key start switch, and the steering oil has
returned to the tank from the accumulators. Then, depress the pressure
release button (3) on the breather to release any remaining pressure from
the tank.
Also located on the tank are the main steering oil filter (4) and the
steering pump case drain filter (5).
1. Upper sight gauge
2. Lower sight gauge
4. Main steering oilfilter
5. Steering pump casedrain filter
3. Steering tankpressure releasebutton
- 34 -STMG 682
3/97
If the steering pump fails or if the engine cannot be started, the
connector (6) is used to attach an Auxiliary Power Unit (APU). The APU
will provide supply oil from the steering tank at the connector (6) to
charge the steering accumulators. Steering capability is then available to
tow the truck.
The steering oil temperature sensor (7) provides an input signal to the
VIMS which informs the operator of the steering system oil temperature.
INSTRUCTOR NOTE: For more detailed information on servicing
the steering accumulators, refer to the Service Manual Module "793C
Off-highway Truck Steering System" (Form SENR1452) and the
Special Instruction "Repair of 4T8719 Bladder Accumulator Group"
(Form SEHS8757). For more information on using the APU, refer to
the Special Instructions "Using 1U5000 Auxiliary Power Unit (APU)"
(Form SEHS8715) and "Using the 1U5525 Attachment Group"
(Form SEHS8880).
6. APU supplementalsteering connector
7. Steering oiltemperature sensor
- 35 -
1. Parking/secondarybrake air tank drainvalve (arrow)
28
STMG 682
3/97
2
1
Another small air tank (not visible) is located behind the cab (see Slide
No. 156). The air tank behind the cab supplies air to the parking and
secondary brakes. Drain the moisture from the tank daily with the drain
valve (1).
Check the fluid level of the windshield washer reservoir (2).2. Windshield washer
fluid reservoir
- 36 -
• Transmission shiftlever
- Six speedsFORWARD
- One speed REVERSE
• Back-up light switch(arrow)
29
STMG 682
3/97
OPERATOR’S STATION
At the front of the center console is the transmission shift lever. The
793C transmission has six speeds FORWARD and one speed REVERSE.
To the right of the shift lever is the back-up light switch (arrow).
INSTRUCTOR NOTE: In this section of the presentation,
component locations inside the operator’s station will be shown.
Many of the components shown in this section will be further
explained in the sections that follow.
- 37 -
• Center consolecomponents:
1. Throttle back-upswitch
2. Manual ether startaid switch
3. Key start switch
4. TCS switch
5. Parking brakeswitch
6. Windshield washerand wiper switch
7. Cigarette lighter
8. Brake retractionswitch
- Service hourmeter
30
STMG 682
3/97
5 6 7 8
1 2 3 4
Shown is the center console. In the center of the console are the throttle
back-up switch (1), manual ether start aid switch (2), key start switch (3)
and the Traction Control System (TCS) switch (4).
The throttle back-up switch (1) increases the engine speed to 1300 rpm if
the engine ECM detects that the throttle sensor signal is invalid.
The manual ether start aid switch (2) allows the operator to manually
inject ether when the coolant temperature is below 10°C (50°F) and
engine speed is below 1200 rpm.
The Traction Control System (TCS) switch (4) is used to test the
operation of the TCS (formerly referred to as the "Automatic Electronic
Traction Aid").
Shown below these components are the parking brake switch (5), the
windshield washer and wiper switch (6), the cigarette lighter (7) and the
brake retraction switch (8).
The brake retraction switch (8) is used to release the parking brakes when
towing the truck.
The service hourmeter is located toward the rear of the center console.
- 38 -
• Overhead lightswitches:
1. Headlights andparking/taillights
2. Panel lights
3. Interior cab light
4. Front flood/ladderlights
5. Fog lights
31
STMG 682
3/97
2 34 51
Located above the operator's head are several light switches:
1. Headlights and parking/taillights
2. Panel lights
3. Interior cab light
4. Front flood/ladder lights
5. Fog lights
- 39 -
1. Gauge clustermodule:
- Engine coolanttemperature
- Brake oiltemperature
- System air pressure
- Fuel level
2. Speed/tach module:
- Analog tachometer
- Ground speed
- Transmission actualgear
3. Dash backlitindicators:
- Left and right turnsignals
- High beam indicator
- Action light
- Service/retarderbrakes ENGAGEDlight
32
STMG 682
3/97
21
3
Located on the front dash are two of the VIMS output components. They
are the gauge cluster module (1) and the speedometer/tachometer
module (2).
The four gauges in the gauge cluster module (from left to right and top to
bottom) are:
- Engine coolant temperature
- Brake oil temperature
- System air pressure
- Fuel level
The speedometer/tachometer module consists of an analog tachometer
and a display window which shows the ground speed and the transmission
actual gear.
Several backlit indicators will appear in the upper area (3) of the display
when they are active. The backlit indicators are:
- Left and right turn signals
- High beam indicator
- Action light
- Service/retarder brakes ENGAGED light
- 40 -
1. Automatic RetarderControl (ARC)ON/OFF switch
2. Message centermodule:
- Alert indicator
- Universal gauge
- Message displaywindow
33
STMG 682
3/97
3
2
1
To the right of the steering column is the Automatic Retarder Control
(ARC) ON/OFF switch (1).
To the right of the ARC switch are two more components of the VIMS.
They are the message center module (2) and the keypad
module (3).
The message center module consists of an alert indicator, a universal
gauge and a message display window. The alert indicator flashes when a
Category 1 Warning is present. The universal gauge displays the status of
the sensor selected for viewing by depressing the GAUGE key on the
keypad. The message display window shows various types of text
information to the operator.
- 41 -
3. Keypad module
STMG 682
3/97
The keypad module allows the operator or a service technician to interact
with the VIMS. Some of the functions that can be performed by the
keypad are:
- Scroll parameters monitored by VIMS by depressing the GAUGE key.
- Payload Monitor ON/OFF PAYLOAD 7295623
- Calibrate Payload Monitor PAYCAL 729225
- Payload Resettable Totals TOT 868
- Reset Displayed Data RESET 73738
- Display Self Test TEST 8378
- Reset Service Light SVCLIT 782548
- Set Lube Cycle Times LUBSET 582738
- Manual Lube LUBMAN 582626
- Show Acknowledged Events EACK 3225
- Show Event Statistics ESTAT 37828
- Show Event List ELIST 35478
- Start Event Recorder EREC 3732
- Start/Stop Data Logger DLOG 3564
- Reset Data Logger DLRES 35737
- Odometer Set/Reset ODO 636
(requires VIMS PC connection)
- Machine Status MSTAT 67828
- Change Language LA 52
- Change Units UN 86
- Change Backlight BLT 258
- Change Display Contrast CON 266
(requires Updated Message Center)
INSTRUCTOR NOTE: For more detailed information on the VIMS,
refer to the Service Manual Module "Vital Information Management
System (VIMS)" (Form SENR6059).
34
- 42 -STMG 682
3/97
• VIMS
SENSORS
ADEM IICONTROL
SERVICELAMP
MESSAGE CENTERMODULE
GAUGE CLUSTERMODULE
KEYPADMODULE
SENSORS
VIMSINTERFACE
MODULE
VIMSINTERFACE
MODULE
SENSORS
VIMSSERVICE TOOL
ANDSOFTWARE
CAT DATA LINK
SERVICEKEYSWITCH
ACTIONLAMP
ACTIONALARM
ELECTRONICTECHNICIAN/ECAP
VIMS MAIN MODULE
DISPLAY DATA LINK
VIMSRS-232PORT
AUTO RETARDERCONTROL
CAT DATA LINK
TRANSMISSIONCONTROL
VITAL INFORMATIONMANAGEMENT SYSTEM
(VIMS)
SPEEDOMETER/TACHOMETER
MODULE
3F12MPHkm/h
KEYPADDATA LINK
As shown in some of the previous slides, the 793C is equipped with the
VIMS which receives input signals from many sensors and also
communicates with other electronic controls on the machine. The VIMS
provides the operator and the service technician with a complete look at
the current and past conditions of all the systems on the truck.
- 43 -
• Behind the operator'sseat are:
- Fuse panel
- ECAP/ET diagnosticconnector (arrow)
35
STMG 682
3/97
Behind the operator’s seat are the fuse panel and the ECAP/ET diagnostic
connector (arrow). The ECAP/ET diagnostic connector is used to connect
the Electronic Control Analyzer Programmer (ECAP) or a laptop
computer with the Electronic Technician (ET) software installed.
While VIMS monitors all of the systems on the truck, the ECAP or ET is
used for programming, running diagnostic tests and retrieving logged
information from the engine, transmission and automatic retarder
controls.
- 44 -
• Electronic Technician(ET)
36
STMG 682
3/97
Shown is the communication adapter and a laptop computer with the
Electronic Technician (ET) diagnostic software installed. The
communication adapter is connected to the diagnostic connector shown in
the previous slide.
- 45 -
• VIMS connector(arrow)
37
STMG 682
3/97
Shown is a laptop computer with the VIMS PC diagnostic software
installed. The laptop computer is connected to the VIMS diagnostic
connector (arrow).
- 46 -
• Hoist control lever(arrow)
38
STMG 682
3/97
The operator controls include the hoist lever (arrow) which is located to
the left of the operator’s seat. The four positions are RAISE, HOLD,
FLOAT and LOWER.
The truck should normally be operated with the hoist lever in the FLOAT
position. Operating with the hoist lever in the FLOAT position allows the
hoist valve to provide some downward hydraulic pressure on the hoist
cylinders and prevents an empty body from bouncing on rough haul
roads.
The 793C hoist system is different from previous trucks. The hoist
system is electronically controlled.
INSTRUCTOR NOTE: The hoist system will be explained in more
detail in the HOIST SYSTEM section of this presentation.
• Electronicallycontrolled hoistsystem
• Hoist lever in FLOATfor normal operation
- 47 -
• Operator controls:
- Secondary brakelever (red)
- Retarder lever(black)
1. Tilt steering lock
2. Turn signal andhazard switch
39
STMG 682
3/97
2
1
The operator controls on the steering column are the secondary brake
lever (red), the retarder lever (black), the tilt steering lock (1) and the turn
signal and hazard switch (2).
- 48 -
1. Service brake pedal
2. Throttle pedal
3. Throttle positionsensor
40
STMG 682
3/97
2
1
3
On the floor to the right of the steering column are the service brake
pedal (1) and the throttle pedal (2). A throttle position sensor (3) is
attached to the throttle pedal. The throttle position sensor provides the
throttle position input signals to the engine ECM.
The engine ECM provides an elevated engine idle speed of 1300 rpm
when the coolant temperature is below 60°C (140°F). Above 60°C
(140°F), the elevated idle rpm is gradually reduced until the coolant
temperature reaches 71°C (160°F). Above 71°C (160°F), the engine will
idle at 700 rpm.
Increasing the low idle speed helps prevent incomplete combustion and
overcooling. To temporarily reduce the elevated idle speed, the operator
can depress the throttle momentarily, and the idle speed will decrease to
700 rpm for 10 minutes.
On the floor to the left of the steering column are the horn button and the
high beam switch (not shown).• Horn button and high
beam switch (notshown)
• Elevated low idlereduced with throttlepedal
- 49 -
• 793C uses 3516Bengine
41
STMG 682
3/97
ENGINE
The 793C is equipped with the Caterpillar 3516B engine with a gross
power rating of 1715 kW (2300 hp) and a net flywheel power rating of
1615 kW (2166 hp) at 1750 rpm.
42
- 50 -STMG 682
3/97
• 3516B electroniccontrol systemcomponent diagram
A/C PRESSURESWITCH
CRANKCASEPRESSURE
GROUND LEVELSHUTDOWN SWITCH
FUEL FILTERSWITCH
PRE-LUBRICATIONRELAY
OIL LEVELSWITCH (LOW)
OIL LEVELSWITCH (ADD)
FANFAN SPEED SENSOR
FAN CLUTCHSOLENOID
SERVICE TOOLEPTC II
ARCVIMS
CAT DATA LINK
ENGINE COOLANT TEMPERATURE
ADEM IICONTROLMODULE
GROUNDBOLT
15 AMPBREAKER
MAINPOWER RELAY
KEY STARTSWITCH
SPEED/TIMING SENSOR
ENGINE OIL PRESSURE(UNFILTERED)
COOLANT FLOW SWITCH
TIMING PROBECONNECTOR
ETHER SOLENOID
DISCONNECT SWITCH
3516B ELECTRONIC CONTROLSYSTEM COMPONENT DIAGRAM
ELECTRONIC UNITINJECTORS
TURBO OUTLET PRESSURE (BOOST)
RIGHT TURBO INLET PRESSURE
ATMOSPHERIC PRESSURE
ENGINE OIL PRESSURE (FILTERED)
THROTTLE
ENGINE OILRENEWAL SOLENOID
SHUTTER SOLENOID
REAR AFTERCOOLER TEMPERATURE
LEFT TURBO INLET PRESSURE
RIGHT TURBO EXHAUST
LEFT TURBO EXHAUST
THROTTLE OVERRIDESWITCH
MANUAL ETHERSWITCH
EXHAUSTWASTEGATE
SOLENOID
24 V
Shown is the electronic control system component diagram for the 3516B
engine used in the 793C. Fuel injection is controlled by the second
generation Advanced Diesel Engine Management (ADEM II) engine
Electronic Control Module (ECM).
Many electronic signals are sent to the ADEM II ECM by sensors,
switches and senders. The engine ECM analyzes these signals and
determines when and for how long to energize the injector solenoids.
When the injector solenoids are energized determines the timing of the
engine. How long the solenoids are energized determines the engine
speed.
- 51 -
• ECM (arrow)
43
STMG 682
3/97
Fuel injection is controlled by the ADEM II ECM (arrow) located on the
right front of the engine.
The previous ECM had one 70-pin connector. The ADEM II ECM has
two 40-pin connectors.
The engine ECM is cooled by fuel. Fuel flows from the fuel transfer
pump through the ECM to the secondary fuel filters.
• ECM has two 40-pinconnectors
• ECM cooled by fuel
- 52 -
44
STMG 682
3/97
The atmospheric pressure sensor (arrow) is located adjacent to the engine
ECM. Formerly, this sensor was located in the compartment behind the
cab. The engine ECM uses the atmospheric pressure sensor as a reference
for calculating boost and air filter restriction and for derating the engine at
high altitudes.
The engine ECM also uses the atmospheric pressure sensor as a reference
when calibrating all the pressure sensors.
• Atmospheric pressuresensor (arrow)
45
- 53 -STMG 682
3/97
• 3516B improvements
3516B IMPROVEMENTSINPUT SWITCHES AND SENSORS
• COOLANT FLOW
• REAR AFTERCOOLER TEMPERATURE
• ENGINE OIL LEVEL
• TURBOCHARGER TEMPERATURE
• ENGINE OIL FILTER PRESSURE/RESTRICTION
• ENGINE FAN SPEED
• FUEL FILTER RESTRICTION
• AIR CONDITIONER COMPRESSOR PRESSURE
• CRANKCASE PRESSURE
The 3516B engine has many improvements over the original 3516 engine.
Some of the improvements are accomplished by adding additional switch
and sensor inputs to the engine ECM. Adding additional inputs to the
engine ECM allows the ECM to control the engine more precisely.
Additional inputs to the 3516B ECM are:
- Coolant flow is monitored.
- Rear aftercooler temperature is measured.
- Engine oil level is monitored.
- Two turbocharger temperature sensors measure exhaust temperatures.
- Two engine oil pressure sensors are located on the oil filter base to
measure oil pressure and oil filter restriction.
- Engine fan speed is measured (with variable fan speed attachment).
INSTRUCTOR NOTE: The following slides will show some of the
engine ECM input components. The remaining inputs to the engine
ECM will be discussed when the systems they monitor are shown.
• Additional inputs
- 54 -
46
STMG 682
3/97
2
1
Fuel filter restriction is monitored with a fuel filter bypass switch (1)
located on the fuel filter base. The fuel filter bypass switch provides an
input signal to the engine ECM. The ECM provides a signal to the VIMS
which informs the operator if the secondary fuel filters are restricted.
If the fuel filter restriction exceeds 138 kPa (20 psi), a fuel filter
restriction event is logged. No factory password is required to clear this
event.
An air conditioner compressor switch (2) is located at the rear of the air
conditioner compressor. If the truck is equipped with the variable fan
speed attachment, the air conditioner compressor switch informs the
engine ECM when the air conditioner system is ON. When the air
conditioner system is ON, the ECM sets the variable speed fan at
MAXIMUM rpm.
Disconnecting the air conditioner compressor switch will also signal the
ECM to set the fan speed at MAXIMUM rpm.
1. Fuel filter bypassswitch
2. Air conditionercompressor switch
• Fuel filter restrictionevent
- 55 -
• Crankcase pressuresensor (arrow)
47
STMG 682
3/97
The crankcase pressure sensor (arrow) is located on the right side of the
engine above the engine oil cooler. The crankcase pressure sensor
provides an input signal to the engine ECM. The ECM provides the
signal to the VIMS which informs the operator of the crankcase pressure.
High crankcase pressure may be caused by worn piston rings or cylinder
liners.
If crankcase pressure exceeds 3.6 kPa (.5 psi), a high crankcase pressure
event will be logged. No factory password is required to clear this event.• Crankcase pressure
event
48
- 56 -STMG 682
3/97
3516B IMPROVEMENTSPREVIOUS LOGGED EVENTS
• AIR FILTER RESTRICTION
• LOW OIL PRESSURE
• HIGH COOLANT TEMPERATURE
• ENGINE OVERSPEED
The 3500B ECM logs the four events of the previous 3500 engine plus
some additional events. The four events logged by the 3500 ECM and the
3500B ECM are:
Air filter restriction: Greater than 6.25 kPa (25 in. of water). Maximum
derate of 20%.
Low oil pressure: From less than 100 kPa (15 psi) at LOW IDLE to less
than 300 kPa (44 psi) at HIGH IDLE.
High coolant temperature: Greater than 107°C (226°F).
Engine overspeed: Greater than 2200 rpm.
NOTE: Factory passwords are required to clear all the events listed
above.
• Events logged by 3500ECM and 3500B ECM
49
- 57 -STMG 682
3/97
• Additional loggedevents
3516B IMPROVEMENTS
ADDITIONAL LOGGED EVENTS
• OIL FILTER RESTRICTION • HIGH CRANKCASE PRESSURE
• FUEL FILTER RESTRICTION • LOW COOLANT FLOW
• HIGH EXHAUST TEMPERATURE • USER DEFINED SHUTDOWN
• HIGH AFTERCOOLER TEMPERATURE • LOW BOOST PRESSURE
• ENGINE OIL LEVEL LOW • HIGH BOOST PRESSURE
Additional events logged by the 3500B ECM are:
Oil filter restriction: Greater than 70 kPa (10 psi). No factory password
required. Greater than 200 kPa (29 psi). Factory password required.
Fuel filter restriction: Greater than 138 kPa (20 psi). No factory
password required.
Exhaust temperature high: Greater than 760°C (1400°F). Maximum
derate of 20%. Factory password required.
Aftercooler coolant temperature high: Greater than 107°C (226°F).
Factory password required.
Engine oil level low: No factory password required.
Crankcase pressure high: Greater than 3.6 kPa (.5 psi). No factory
password required.
Coolant flow low: Factory password required.
User defined shutdown: Parameters determined by the user.
Boost pressure high: 20 kPa (3 psi) greater than desired. Maximum
derate of 10%. No factory password required.
Boost pressure low: 30 kPa (4 psi) lower than desired. Maximum derate
of 10%. No factory password required.
50
- 58 -STMG 682
3/97
3516B IMPROVEMENTSSYSTEMS CONTROLLED BY ECM
• ETHER INJECTION
• RADIATOR SHUTTER CONTROL
• COLD CYLINDER CUTOUT
• ENGINE START FUNCTION
• ENGINE OIL PRE-LUBRICATION
• VARIABLE SPEED FAN CONTROL
• ENGINE OIL RENEWAL SYSTEM
• EXHAUST BYPASS AT HIGH BOOST
The engine ECM also regulates other systems by energizing solenoids or
relays. Some of the other systems controlled by the ECM are:
Ether Injection: Ether injection is controlled by the engine ECM or
manually. The engine ECM will energize the ether injection relay only if:
- The coolant temperature is below 10°C (50°F).
- Engine speed is below 1200 rpm.
Radiator Shutter Control: On trucks that operate in cold weather,
shutters can be added in front of the radiator. Installing shutters in front of
the radiator allows the engine to warm up to operating temperature
quicker. If a truck is equipped with the attachment radiator shutter
control, the shutters are controlled by the engine ECM.
• Engine ECM controlsother systems
• Ether injection
• Radiator shuttercontrol
- 59 -STMG 682
3/97
Cold Cylinder Cut-out: The 3508B engine uses a cold cylinder cut-out
function to reduce white exhaust smoke after start-up and during extended
idling in cold weather.
After the engine is started and the automatic ether injection system has
stopped injecting ether, the engine ECM will cut out one cylinder at a
time to determine which cylinders are firing. The ECM will disable some
of the cylinders that are not firing.
The ECM can identify a cylinder which is not firing by monitoring the
fuel rate and engine speed during a cylinder cut-out. The ECM averages
the fuel delivery and analyzes the fuel rate change during a cylinder
cut-out to determine if the cylinder is firing.
Disabling some of the cylinders during Cold Mode operation will cause
the engine to run rough until the temperature increases above the Cold
Mode temperature. This condition is normal, but the operator should be
aware it exists to prevent unnecessary complaints.
Engine Start Function: The Engine Start function is controlled by
ADEM II and the Electronic Programmable Transmission Control
(EPTC II). The engine ECM provides signals to the EPTC II regarding
the engine speed and the condition of the engine pre-lubrication system.
The EPTC II will energize the starter relay only when:
- The shift lever is in NEUTRAL.
- The parking brake is ENGAGED.
- The engine speed is 0 rpm.
- The engine pre-lubrication cycle is complete or turned OFF.
NOTE: To protect the starter, the starter is disengaged when the
engine rpm is above 300 rpm.
INSTRUCTOR NOTE: The remaining improvements are described
in the slides that follow.
• Cold cylinder cut-out
• Engine runs roughduring cold mode
• Engine start function
- 60 -
51
STMG 682
3/97
2
1
Engine Oil Pre-lubrication: Engine oil pre-lubrication is controlled by
the ADEM II and EPTC II. The EPTC II signals the ADEM II when to
energize the pre-lubrication pump relay (1). The ADEM II signals
EPTC II to crank the engine when:
- Engine oil pressure is 27 kPa (5 psi) or higher.
- The pre-lubrication pump (2) has run for 15 seconds. (If the
system times out after 15 seconds, a pre-lubrication fault is
logged in the ADEM II.)
- The engine has been running in the last 2 minutes.
- Coolant temperature is above 50°C (122°F).
NOTE: The ECAP and ET can enable or disable the pre-lubrication
feature in the ADEM II. On some trucks, the pre-lubrication pump is
located near the right front of the engine.
• Engine oilpre-lubrication
1. Pre-lubrication pumprelay
2. Pre-lubrication pump
- 61 -
• Variable speed fancontrol:
52
STMG 682
3/97
1
3
2
Variable Speed Fan Control: If the engine is equipped with a variable
speed fan, the engine ECM regulates the fan speed. Fan speed varies
according to the temperature of the engine. The ECM sends a signal to
the variable speed fan control solenoid valve (1) and engine oil pressure
engages a clutch as needed to change the speed of the fan.
The jacket water coolant temperature sensor (2) is located in the jacket
water temperature regulator (thermostat) housing. The ECM uses the
coolant temperature sensor information as the main parameter to control
the fan speed. The aftercooler temperature sensors, air conditioner
pressure sensor and brake cooling oil temperature sensors are also used as
inputs to determine the required fan speed. A speed sensor (not shown) is
located behind the fan pulley and informs the ECM of the current fan
speed.
The variable speed fan feature can be turned off using the ECAP or ET
service tool. Turning off the variable speed fan feature will set the fan
speed at MAXIMUM rpm. Disconnecting the air conditioning
compressor switch will also signal the ECM to set the fan speed at
MAXIMUM rpm.
The turbocharger outlet pressure sensor (3) sends an input signal to the
ECM. The ECM compares the value of the turbo outlet pressure sensor
with the value of the atmospheric pressure sensor and calculates boost
pressure.
INSTRUCTOR NOTE: For more information on the variable speed
fan, refer to the Service Manual "Variable Speed Fan Clutch"
(Form SENR8603).
1. Fan control solenoidvalve
• Fan speed sensor
(not shown)
• Fan speed overrides
3. Turbo outletpressure sensor
2. Jacket water coolanttemperature sensor
- 62 -
• Engine oil renewalsystem components:
1. Oil filter
2. Oil renewalsolenoid
3. Fuel pressureregulator
• Oil mixes with fuel infuel tank
53
STMG 682
3/97
1
3
2
Engine Oil Renewal System: Located on the right side of the engine are
the components of the engine oil renewal system. Engine oil flows from
the engine block through an oil filter (1) to the engine oil renewal
solenoid (2). A small amount of oil flows from the engine oil renewal
solenoid into the return side of the fuel pressure regulator (3). The engine
oil returns to the fuel tank with the return fuel.
The engine oil mixes with the fuel in the tank and flows with the fuel to
the EUI injectors to be burned.
When the engine oil renewal system is used, the operator must pay close
attention to the ADD OIL message that the VIMS provides to the operator
when makeup oil must be added (see Slide No. 54).
The oil does not have to be changed when using the engine oil renewal
system. When the engine oil renewal system is used, the engine oil
filters, the engine oil renewal system filter, the primary fuel filter and the
secondary fuel filters must all be changed at 500 hour intervals.
Engine oil samples must be taken regularly to ensure that the soot level of
the engine oil is in a safe operating range.• Sample engine oil to
check soot level
- 63 -
• Oil injection controlledby engine ECM
• Engine oil renewalsystem parameters
STMG 682
3/97
The ECM regulates the amount of oil that is injected by the engine oil
renewal solenoid. Several parameters must be met before the ECM will
allow the injection of oil through the engine oil renewal system. The
parameters that must be met are:
- Fuel position is greater than 10.
- Engine rpm is between 1300 and 1850 rpm.
- Jacket water temperature is between 63°C (145°F) and
107°C (225°F).
- Oil filter differential pressure at high idle with warm oil is less than
70 kPa (10 psi).
- Fuel filter differential pressure is less than 140 kPa (20 psi).
- Engine oil level switches are sending a valid signal to the ADEM II
control.
- Engine has been running more than five minutes.
The engine oil renewal system can be turned ON or OFF with the ECAP
or ET service tool. The amount of oil injected can also be adjusted by
programming the ECM with the ECAP or ET service tool. The factory
setting shown in the service tool is "0" and is equivalent to a 0.5% oil to
fuel ratio. The ratio can be changed with the service tool from minus 50
(-50) to plus 50 (+50), which is equivalent to 0.25% to 0.75% oil to fuel
ratios.
• Oil renewal adjustedwith ECAP or ET
- 64 -
54
STMG 682
3/97
1
2
The engine oil level switches (1 and 2) provide input signals to the engine
ECM. The ECM provides an input signal to the VIMS which informs the
operator of the engine oil level.
If the truck is equipped with the engine oil renewal system attachment,
the upper oil level switch (1) will tell the operator when makeup oil must
be added. The ADD ENG OIL message is a Category 1 Warning.
The lower oil level switch (2) will tell the operator when the engine oil
level is low and it is unsafe to operate the truck without causing damage
to the engine. The ENG OIL LEVEL LOW message is a Category 2 or 3
Warning.
If the engine ECM detects a low oil level condition (oil level below the
lower switch), the ECM will log a low oil level event. No factory
password is required to clear this event.
1. Add engine oil levelswitch
2. Engine oil level low
switch
• Low oil level event
- 65 -
1. Exhaust bypassvalve
55
STMG 682
3/97
1
2
Exhaust Bypass Control: An exhaust bypass (wastegate) valve (1)
prevents excessive boost pressure by diverting exhaust gasses away from
the turbochargers. The bypass valve is controlled by the engine ECM.
Brake system air pressure is reduced to 380 kPa (55 psi) by a valve
located outside the right rear of the cab and is supplied to the wastegate
solenoid valve (2). If boost pressure exceeds a predetermined value, the
ECM will open the wastegate solenoid and send air pressure to open the
exhaust bypass valve. When the exhaust bypass valve is open, exhaust at
the turbine side of the turbochargers is diverted through the muffler.
Diverting the turbine exhaust pressure decreases the speed of the
turbochargers which reduces the boost pressure to the cylinders.
The wastegate solenoid valve can be controlled with the ECAP or ET
service tool for diagnostic purposes. Connect a multimeter to the
wastegate solenoid and set the meter to read DUTY CYCLE. Using the
service tool, override the wastegate solenoid valve and use the multimeter
to measure the corresponding duty cycle.
If the actual boost pressure is 20 kPa (3 psi) higher than the desired boost
pressure calculated by the ECM, a high boost pressure event will be
logged. If the actual boost pressure is 30 kPa (4 psi) lower than the
desired boost pressure calculated by the ECM, a low boost pressure event
will be logged. If the ECM detects a high or low boost condition, the
ECM will derate the fuel delivery (maximum derating of 10%) to prevent
damage to the engine.
2. Wastegate solenoidvalve
- Controlled by engineECM
• Engine wastegatesolenoid checked withECAP or ET
• Boost pressure events
- 66 -
1. Cooling systemshunt tank
• Engine coolingsystems:
- Jacket water coolingsystem
- Aftercooler coolingsystem
56
STMG 682
3/97
3
1
4
2
Cooling System
The 793C is equipped with a shunt tank (1) to increase the cooling
capacity. The shunt tank provides a positive pressure at the coolant pump
inlets to prevent cavitation during high flow conditions.
The cooling system is divided into two systems. The two systems are the
jacket water cooling system and the aftercooler cooling system. The only
connection between these two systems is a small hole in the separator
plate in the shunt tank. The small hole in the shunt tank prevents a
reduction of coolant from either of the two systems if leakage occurs in
one of the separator plates in the radiator top or bottom tank. When
servicing the cooling systems, be sure to drain and fill both systems
separately.
The coolant levels are checked at the shunt tank. Use the gauges (2) on
top of the shunt tank to check the coolant level.
A coolant level sensor (3) is located on each side of the shunt tank to
monitor the coolant level of both cooling systems (guard removed for
viewing sensor). The coolant level sensors provide input signals to the
VIMS which informs the operator of the engine coolant levels.
Pressure relief valves (4) prevent the cooling systems from becoming over
pressurized.
4. Pressure reliefvalves
3. Coolant level sensor
2. Coolant level gauges
- 67 -
57
STMG 682
3/97
The jacket water cooling system uses 17 of the 30 cores on the right side
of the radiator (approximately 60% of the total capacity). The jacket
water cooling system temperature is controlled by temperature regulators
(thermostats).
The aftercooler cooling system uses 13 of the 30 cores on the left side of
the radiator (approximately 40% of the total capacity). The aftercooler
cooling system does not have thermostats in the circuit. The coolant
flows through the radiator at all times to keep the turbocharged inlet air
cool for increased horsepower.
• Aftercooler coolingsystem
• Jacket water coolingsystem
- 68 -
1. Jacket water pump
2. Bypass tube
3. Jacket waterthermostat housing
58
STMG 682
3/97
2
1
3
The jacket water pump (1) is located on the right side of the engine. The
pump draws coolant from the bypass tube (2) until the temperature
regulators (thermostats) open. The thermostats are located in the
housing (3) at the top of the bypass tube. When the thermostats are open,
coolant flows through the radiator to the water pump inlet.
If the jacket water cooling system temperature increases above 107°C
(226°F), the engine ECM will log an event that requires a factory
password to clear.
• High coolanttemperature event
- 69 -
• Coolant flow warningswitch (arrow)
59
STMG 682
3/97
Coolant flows from the jacket water pump, past the coolant flow warning
switch (arrow), and through the various system oil coolers (engine, torque
converter/transmission and rear brake).
The coolant flow switch sends an input signal to the engine ECM. The
ECM provides the input signal to the VIMS which informs the operator of
the coolant flow status.
If the ECM detects a low coolant flow condition, a low coolant flow event
will be logged. A factory password is required to clear this event.• Low coolant flow
event
- 70 -
1. Engine oil cooler
2. Torque converter/transmission oilcooler
60
STMG 682
3/97
1
2
Shown is the right side of the engine. The engine oil cooler (1) and the
torque converter and transmission oil cooler (2) are visible in this view.
The coolant flows through these coolers to the rear brake oil coolers
located on the outside right frame.
- 71 -
• Rear brake oil coolers(arrow)
61
STMG 682
3/97
Jacket water coolant flows from the rear brake oil coolers (arrow) to both
sides of the engine cylinder block. Coolant flows through the engine
block and through the cylinder heads. From the cylinder heads, the
coolant returns to the temperature regulators and either goes directly to
the water pump through the bypass tube or to the radiator (depending on
the temperature of the coolant).
62
- 72 -STMG 682
3/97
• Jacket water coolingsystem circuit
ENGINE OIL COOLER
TORQUE CONVERTER/TRANSMISSION OIL COOLER
ENGINEBLOCK
JACKET WATER COOLANT FLOW
REAR BRAKEOIL COOLERS
THERMOSTATHOUSING
RADIATOR
JACKETWATER PUMP
SHUNTTANK
Shown is the jacket water cooling system circuit. Coolant flows from the
jacket water pump through the coolers to the engine block. Coolant flows
through the engine block and the cylinder heads. From the cylinder
heads, the coolant returns to the temperature regulators (thermostats) and
either goes directly to the water pump through the bypass tube or to the
radiator (depending on the temperature of the coolant).
The shunt tank increases the cooling capacity and provides a positive
pressure at the coolant pump inlet to prevent cavitation during high flow
conditions.
In this illustration and those that follow, the colors used to identify the
various pressures in the systems are:
Red - Supply oil/water pressureGreen - Drain or reservoir oil/waterRed and White Stripes - Reduced supply oil pressureBrown - Lubrication or cooling pressureOrange - Pilot or load sensing signal pressureBlue - Blocked oilYellow - Moving componentsPurple - Air pressure
- 73 -
1. Aftercooler waterpump
2. Shunt tank supplytube
3. Aftercooler circuitcoolant tubes
63
STMG 682
3/97
3
12
The auxiliary (aftercooler) water pump (1) for the aftercooler cooling
system is located on the left side of the engine. Coolant enters the
aftercooler water pump from the radiator or the shunt tank supply
tube (2). Coolant flows from the pump to the aftercooler cores through
the large tubes (3)
- 74 -
• Rear aftercoolertemperature sensor(arrow)
64
STMG 682
3/97
Located in a tube at the rear of the aftercooler is the rear aftercooler
temperature sensor (arrow). The rear aftercooler temperature sensor
provides an input signal to the engine ECM. The engine ECM uses the
rear aftercooler temperature sensor signal with the jacket water
temperature sensor signal to control the variable speed fan attachment.
The ECM also provides the input signal to the VIMS which informs the
operator of the aftercooler coolant temperature.
If the rear aftercooler temperature increases above 107°C (226°F), the
engine ECM will log an event that requires a factory password to clear.
Another aftercooler temperature sensor is located in a tube at the front of
the aftercooler. The front aftercooler temperature sensor does not send an
input signal to the engine ECM. The front aftercooler temperature sensor
provides an input signal directly to the VIMS.
• Front aftercoolertemperature sensor
• Rear aftercoolertemperature event
- 75 -
1. Front brake oilcooler
65
STMG 682
3/97
2
1
Coolant flows through the aftercooler cores to the front brake oil
cooler (1) located at the rear of the engine.
Coolant flows through the front brake oil cooler to the aftercooler section
of the radiator. The aftercooler cooling system does not have temperature
regulators (thermostats) in the circuit.
When the service or retarder brakes are ENGAGED, the front brake oil
cooler diverter valve (2) allows brake cooling oil to flow through the front
brake oil cooler.
Normally, front brake cooling oil is diverted around the cooler and goes
directly to the front brakes. Diverting oil around the cooler provides
lower temperature aftercooler air during high power demands (when
climbing a grade with the brakes RELEASED, for example).
• Aftercooler coolingcircuit does not havethermostats
2. Front brake oilcooler diverter valve
66
- 76 -STMG 682
3/97
• Aftercooler coolingsystem circuit
AFTERCOOLER COOLANT FLOW
FRONT BRAKEOIL COOLER
RADIATOR
AFTERCOOLERWATER PUMP
SHUNTTANK
AFTERCOOLER
Shown is the aftercooler cooling system circuit. Coolant flows from the
aftercooler water pump through the aftercooler.
Coolant flows through the aftercooler cores to the front brake oil
cooler located at the rear of the engine.
Coolant then flows through the front brake oil cooler to the aftercooler
section of the radiator. The aftercooler cooling circuit does not have
temperature regulators (thermostats) in the circuit.
The shunt tank increases the cooling capacity and provides a positive
pressure at the aftercooler water pump inlet to prevent cavitation during
high flow conditions.
- 77 -
1. Engine oil pump
2. Engine oil pumprelief valve
67
STMG 682
3/97
3
4
1
2
Lubrication System
The engine oil pump (1) is located behind the jacket water pump on the
right side of the engine. The pump draws oil from the oil pan through a
screen. The relief valve (2) for the lubrication system is located on the
pump.
The engine also has a scavenge pump at the rear of the engine to transfer
oil from the rear of the oil pan to the main sump.
Oil flows from the pump through an engine oil cooler bypass valve (3) to
the engine oil cooler (4). The bypass valve for the engine oil cooler
permits oil flow to the system during cold starts when the oil is thick or if
the cooler is plugged.
3. Engine oil coolerbypass valve
4. Engine oil cooler
- 78 -
• Engine oil filters
68
STMG 682
3/97
2
4
3
1
Oil flows from the engine oil cooler to the oil filters on the left side of the
engine. The oil flows through the filters and enters the engine cylinder
block to clean, cool and lubricate the internal components and the
turbochargers.
Engine oil is added at the fill tube (1) and checked with the
dipstick (2). A bypass valve for each filter is located in each oil filter
base.
Engine oil samples can be taken at the Scheduled Oil Sample (S•O•S)
tap (3).
The engine has two oil pressure sensors. One sensor is located on each
end of the oil filter base. The front sensor measures engine oil pressure
before the filters. The rear sensor (4) measures oil pressure after the
filters. The sensors send input signals to the engine ECM. The ECM
provides the input signal to the VIMS which informs the operator of the
engine oil pressure. Used together, the two engine oil pressure sensors
inform the operator if the engine oil filters are restricted.
If the engine oil pressure is less than 100 kPa (15 psi) at low idle to less
than 300 kPa (44 psi) at high idle, the engine ECM will log an event that
requires a factory password to clear.
If the oil filter restriction exceeds 70 kPa (10 psi), a low oil filter
restriction event will be logged. No factory password is required to clear
this event. If the oil filter restriction exceeds 200 kPa (29 psi), a high oil
filter restriction event will be logged. A factory password is required to
clear this event.
4. Engine oil pressuresensors
• Engine oil filterrestriction events
• Engine oil pressureevent
3. Engine oil S•O•S tap
1. Engine oil fill tube
2. Engine oil dipstick
69
- 79 -STMG 682
3/97
• Engine oil system
ENGINEBLOCK
ENGINE OIL SYSTEM
ENGINEOIL COOLER
ENGINEOIL FILTERS
ENGINEOIL PUMP
SCAVENGEPUMP
BYPASSVALVE
ENGINEOIL RENEWAL
SYSTEM SOLENOID
TO FUELSYSTEM
The engine oil pump draws oil from the oil pan through a screen.
The engine also has a scavenge pump at the rear of the engine to transfer
oil from the rear of the oil pan to the main sump.
Oil flows from the pump through an engine oil cooler bypass valve to the
engine oil cooler. The bypass valve for the engine oil cooler permits oil
flow to the system during cold starts when the oil is thick or if the cooler
is plugged.
Oil flows from the engine oil cooler to the oil filters. The oil flows
through the filters and enters the engine cylinder block to clean, cool and
lubricate the internal components and the turbochargers.
Some trucks are equipped with an engine oil renewal system. Engine oil
flows from the engine block through an oil filter to an engine oil renewal
system manifold. A small amount of oil flows from the engine oil
renewal system manifold into the return side of the fuel pressure regulator.
The engine oil returns to the fuel tank with the return fuel (see Slides
No. 53 and 74).
• Engine oil renewalsystem
- 80 -
• Fuel heater(not shown)
• Primary fuel filter(arrow)
70
STMG 682
3/97
Fuel System
The fuel tank is located on the left side of the truck. Fuel is pulled from
the tank through the fuel heater (not shown), if equipped, and through the
primary fuel filter (arrow) by the fuel transfer pump located on the right
side of the engine behind the engine oil pump.
- 81 -
1. Fuel transfer pump
2. Fuel transfer pumpbypass valve
71
STMG 682
3/97
21
The fuel transfer pump (1) contains a bypass valve (2) to protect the fuel
system components from excessive pressure. The bypass valve setting is
higher than the setting of the fuel pressure regulator which will be shown
later. Fuel flows from the transfer pump through the engine ECM to the
secondary fuel filters located on the left side of the engine.
- 82 -
• Secondary fuel filters
1. Fuel priming pump
72
STMG 682
3/97
1
2
The secondary fuel filters and the fuel priming pump (1) are located
above the engine oil filters on the left side of the engine.
The fuel priming pump is used to fill the filters after they are changed.
A fuel filter bypass switch (2) is located on the fuel filter base. The fuel
filter bypass switch sends an input signal to the engine ECM. The ECM
provides the input signal to the VIMS which informs the operator if the
secondary fuel filters are restricted.
If fuel filter restriction exceeds 138 kPa (20 psi), a fuel filter restriction
event will be logged. No factory password is required to clear this event.
Fuel flows from the fuel filter base through the Electronic Unit Injection
(EUI) fuel injectors and the fuel pressure regulator and then returns to the
fuel tank. The injectors receive 4 1/2 times the amount of fuel needed for
injection. The extra fuel is used for cooling.
NOTE: If the fuel system requires priming, it may be necessary to
block the fuel return line during priming to force the fuel into the
injectors.
2. Fuel filter bypassswitch
• Fuel flows to EUIinjectors
• Extra fuel used to coolinjectors
• Fuel filter restrictionevent
- 83 -
1. Fuel pressure tubesto injectors
2. Fuel pressureregulator
73
STMG 682
3/97
1
2
Fuel flows from the fuel filter base through the steel tubes (1) to the EUI
fuel injectors. Return fuel from the injectors flows through the fuel
pressure regulator (2) before returning to the fuel tank. Fuel pressure is
controlled by the fuel pressure regulator.
74
- 84 -STMG 682
3/97
• Fuel system circuit
FUELTANK
PRIMARYFUEL
FILTER
SECONDARYFUEL FILTERS
ENGINEBLOCK
ENGINE OILRENEWAL
SYSTEM SOLENOID
FUELPRESSURE
REGULATOR
FUELTRANSFER
PUMP
FUELHEATER
ADEM IICONTROL
CYLINDERHEAD
FUEL SYSTEM
Fuel is pulled from the tank through a fuel heater, if equipped, and
through the primary fuel filter by the fuel transfer pump. Fuel flows from
the transfer pump through the ADEM II control to the secondary fuel
filters.
Fuel flows from the fuel filter base through the fuel injectors in the
cylinder heads. Return fuel from the injectors flows through the fuel
pressure regulator before returning through the fuel heater to the fuel tank.
Engine oil flows from the engine block through an oil filter to the engine
oil renewal system manifold. A small amount of oil flows from the
engine oil renewal system manifold into the return side of the fuel
pressure regulator. The engine oil returns to the fuel tank with the return
fuel.
The engine oil mixes with the fuel in the tank and flows with the fuel to
the injectors to be burned.
- 85 -
• Air filter restrictionindicators (arrow)
75
STMG 682
3/97
Air Induction and Exhaust System
The engine receives clean air through the four air filters located on the
front of the truck. Any restriction caused by plugged filters can be
checked at the filter restriction indicators (arrow). If the yellow piston is
in the red zone, the filters must be cleaned or replaced.
- 86 -
1. Turbocharger inletpressure sensor
76
STMG 682
3/97
2
1
The turbocharger inlet pressure sensor (1) is located in a tube between the
air cleaners and the turbochargers. The engine ECM uses the
turbocharger inlet pressure sensor in combination with the atmospheric
pressure sensor to determine air filter restriction. The ECM provides the
input signal to the VIMS which informs the operator of the air filter
restriction.
If air filter restriction exceeds 6.25 kPa (25 in. of water), an air filter
restriction event will be logged, and the ECM will derate the fuel delivery
(maximum derating of 20%) to prevent excessive exhaust temperatures.
A factory password is required to clear this event.
If the truck is equipped with an ether start system, the ECM will
automatically inject ether from the ether cylinders (2) during cranking.
The operator can also inject ether manually with the ether switch in the
cab on the center console (see Slide No. 30). Ether will be injected only
if the engine coolant temperature is below 10°C (50°F) and engine speed
is below 1200 rpm.
2. Ether cylinders
• Air filter restrictionevent
- 87 -
• Series turbochargersystem
1. Low pressureturbochargers
2. High pressureturbochargers
77
STMG 682
3/97
1
12
2
The 793C engine is equipped with a series turbocharger system. The
clean air from the filters enters the larger low pressure turbochargers (1).
The compressed air from the low pressure turbochargers flows to the inlet
of the smaller high pressure turbochargers (2). After additional
compression by the high pressure turbochargers, the air flows to the
aftercoolers. After the air is cooled by the aftercoolers, the air flows to
the cylinders and combines with the fuel for combustion.
The turbochargers are driven by the exhaust gasses from the cylinders.
The exhaust gasses first enter the smaller high pressure turbochargers.
The exhaust from the high pressure turbochargers flows to the larger low
pressure turbochargers. The exhaust gasses then flow through the low
pressure turbochargers, the exhaust piping, and the mufflers.
- 88 -
• Exhaust temperaturesensor (arrow)
78
STMG 682
3/97
An exhaust temperature sensor (arrow) is located in each exhaust
manifold before the turbochargers. The two exhaust temperature sensors
provide input signals to the engine ECM. The ECM provides the input
signal to the VIMS which informs the operator of the exhaust
temperature.
Some causes of high exhaust temperature may be faulty injectors, plugged
air filters, or a restriction in the turbochargers or the muffler.
If the exhaust temperature is above 760°C (1400°F), the engine ECM will
derate the fuel delivery (maximum derate of 20%) to prevent excessive
exhaust temperatures. The ECM will also log an event that requires a
factory password to clear.
• Causes of highexhaust temperature
• High exhausttemperature deratesengine and logs event
79
- 89 -STMG 682
3/97
• Turbocharger speedreduced when exhaustbypass valve opens
EXHAUST BYPASS VALVE
MUFFLER
HIGH PRESSURETURBOCHARGER
LOW PRESSURETURBOCHARGER
FROM AIRFILTER
AFTERCOOLER
FROM BRAKEAIR SYSTEM
WASTEGATESOLENOID
VALVE
EXHAUST SYSTEM
PRESSUREREDUCING
VALVE
This schematic shows the air flow through the air induction system. If
boost pressure exceeds a predetermined value programmed in the engine
ECM, the ECM will open the wastegate solenoid valve and send brake air
pressure to open the exhaust bypass valve. The exhaust bypass valve will
vent the exhaust gasses before they reach the turbochargers. Less exhaust
gasses will flow through the turbochargers, and the turbocharger speed
will decrease. The slower turbochargers reduce the boost pressure until
the bypass valve closes and the exhaust gasses are again directed through
the turbochargers.
80
- 90 -STMG 682
3/97
• Power traincomponents:
1. Torque converter
2. Transfer gears
3. Transmission
4. Differential
5. Final drives
793C
POWER TRAIN
POWER TRAIN
Power flows from the engine to the rear wheels through the power train.
The components of the power train are:
1. Torque converter
2. Transfer gears
3. Transmission
4. Differential
5. Final drives
INSTRUCTOR NOTE: In this section of the presentation, component
locations and a brief description of the component functions are
provided. For more detailed information on the Electronic
Programmable Transmission Control (EPTC II), torque converter and
ICM (Individual Clutch Modulation) transmission, refer to the
Technical Instruction Modules "Electronic Programmable
Transmission Control (EPTC II)" (Form SEGV2584-01) and
"769C - 793B Off-highway Trucks--Torque Converter and Transmission
Hydraulic System" (Form SEGV2591).
- 91 -
• Torque converter:
- Provides a fluidcoupling
- Multiplies torque
- Provides direct driveoperation
1. Inlet relief valve
2. Outlet relief valve
3. Lockup clutchcontrol valve
4. Outlet temperaturesensor
81
STMG 682
3/97
3
4
2 1
Power Train Components
The first component in the power train is the torque converter. The torque
converter provides a fluid coupling that permits the engine to continue
running with the truck stopped. In converter drive, the torque converter
multiplies torque to the transmission. At higher ground speeds, a lockup
clutch engages to provide direct drive. The NEUTRAL and REVERSE
ranges are converter drive only. FIRST SPEED is converter drive at low
ground speed and direct drive at high ground speed. SECOND through
SIXTH SPEEDS are direct drive only. The torque converter goes to
converter drive between each shift (during clutch engagement) to provide
smooth shifts.
Mounted on the torque converter are the inlet relief valve (1), the outlet
relief valve (2) and the torque converter lockup clutch control valve (3).
A torque converter outlet temperature sensor (4) provides an input signal
to the VIMS which informs the operator of the torque converter outlet
temperature.
82
- 92 -STMG 682
3/97
• CONVERTER DRIVE
- Output shaft rotatesslower than enginerpm
- Torque is increased
• Torque convertercomponents:
- Lockup clutch
- Impeller
- Turbine
- Stator
STATOR
TORQUE CONVERTERCONVERTER DRIVE
LOCKUP PISTON
TORQUE CONVERTERLOCKUP OIL PASSAGE
TURBINE IMPELLER
FREEWHEELASSEMBLY
TORQUE CONVERTERINLET OIL
This sectional view shows a torque converter in CONVERTER DRIVE.
The lockup clutch (yellow piston and blue discs) is not engaged. During
operation, the rotating housing and impeller (red) can rotate faster than the
turbine (blue). The stator (green) remains stationary and multiplies the
torque transfer between the impeller and the turbine. The output shaft
rotates slower than the engine crankshaft, but with increased torque.
83
- 93 -STMG 682
3/97
• DIRECT DRIVE
- Lockup clutchengaged
- Output shaft rotatesat engine rpm
- Stator freewheels
STATOR
TORQUE CONVERTERDIRECT DRIVE
LOCKUP PISTON
TORQUE CONVERTERLOCKUP OIL PASSAGE
TURBINE IMPELLER
STATOR
FREEWHEELASSEMBLY
TORQUE CONVERTERINLET OIL
In DIRECT DRIVE, the lockup clutch is engaged by hydraulic pressure
and locks the turbine to the impeller. The housing, impeller, turbine, and
output shaft then rotate as a unit at engine rpm. The stator, which is
mounted on a freewheel assembly, is driven by the force of the oil in the
housing and will freewheel at approximately the same rpm.
- 94 -
1. Transfer gears
2. Transmission
3. Differential
84
STMG 682
3/97
2
1
3
Power flows from the torque converter through a drive shaft to the
transfer gears (1). The transfer gears are splined to the transmission.
The transmission (2) is located between the transfer gears and the
differential (3). The transmission is electronically controlled and
hydraulically operated like all other ICM (Individual Clutch Modulation)
transmissions in Caterpillar rigid frame trucks.
The differential is located in the rear axle housing behind the
transmission. Power from the transmission flows through the differential
and is divided equally to the final drives in the rear wheels. The final
drives are double reduction planetaries.
85
- 95 -STMG 682
3/97
• Transmission is powershift planetary design
1 2 3
4
5 6
POWER SHIFT PLANETARY TRANSMISSION
The transmission is a power shift planetary design which contains six
hydraulically engaged clutches. The transmission provides six
FORWARD speeds and one REVERSE speed.
- 96 -
1. Rear axle oil pump
86
STMG 682
3/97
1
2
3
4
Shown is the differential removed from the rear axle housing. The rear
axle cooling and filter system starts with a rear axle oil pump (1) that is
driven by the differential. Since the pump rotates only when the machine
is moving, no oil flow is produced when the machine is stationary.
Cooling oil flow increases with ground speed to provide cooling when it
is most needed.
The rear axle pump pulls oil from the bottom of the rear axle housing
through a suction screen (2). Oil flows from the pump through a
temperature and flow control valve located on top of the differential
housing to a filter mounted on the rear of the axle housing. Oil then flows
from the filter back to the valve located on top of the differential housing.
Oil then flows from the valve to the rear wheel bearings and the
differential bearings.
Oil flows through tubes (3) to the differential bearings.
The fiberglass shroud (4) reduces the temperature of the rear axle oil on
long hauls by reducing the oil being splashed by the bevel gear.
2. Rear axle suctionscreen
3. Differential bearingoil tubes
4. Fiberglass shroud
- 97 -
1. Differential oiltemperature sensor
2. Rear axletemperature andflow control valve
87
STMG 682
3/97
2
4
1
3
Oil flows from the pump past the differential oil temperature sensor (1) to
the rear axle temperature and flow control valve (2). The differential oil
temperature sensor provides an input signal to the VIMS.
The temperature sensor input signal is used to warn the operator of a high
rear axle oil temperature condition or to turn on the attachment rear axle
cooling fan (if equipped).
Oil flows from the temperature and flow control valve to the differential
oil filter (3) mounted on the rear of the axle housing. Oil then flows from
the filter back to the temperature and flow control valve. Some of the oil
that flows from the temperature and flow control valve flows through the
small supply hose (4) to the differential bearings.
3. Differential oil filter
4. Differential bearingoil supply hose
- 98 -
1. Differential oil filterrestriction switch
2. Rear axle oil levelswitches
88
STMG 682
3/97
2
1
32
The differential oil filter restriction switch (1) and the two rear axle oil
level switches (2) provide input signals to the VIMS.
The differential oil filter restriction switch signal is used to warn the
operator when the differential oil filter is plugged.
The rear axle oil level switch input signals are used to warn the operator
when the rear axle oil level is LOW.
When the truck is initially put into operation, a 1R0719 (40 micron) filter
is installed. This filter removes the rust inhibitor used during
manufacturing. The 40 micron filter should be changed after the first
50 hours of operation and replaced with a 4T3131 (13 micron) filter. The
13 micron filter should be changed every 500 hours.
A differential carrier thrust pin is located behind the small cover (3). The
thrust pin prevents movement of the differential carrier during high thrust
load conditions.
3. Differential carrierthrust pin cover
• Differential oil filterservice information
- 99 -
1. Differential oilpressure sensor
89
STMG 682
3/97
12
The differential oil pressure sensor (1) provides an input signal to the
VIMS. The differential oil pressure sensor signal is used to warn the
operator of a HIGH or LOW rear axle oil pressure condition.
A LOW oil pressure warning is provided if the pressure is below
35 kPa (5 psi) when the differential oil temperature is above 52°C
(125°F) and the ground speed is higher than 24 km/h (15 mph).
A HIGH oil pressure warning is provided if the pressure is above 690 kPa
(100 psi) when the differential oil temperature is above 52°C (125°F).
The temperature and pressure control valve (2) prevents high oil pressure
when the rear axle oil is cold. When the oil temperature is below 43°C
(110°F), the valve is OPEN and allows oil to flow to the rear axle
housing. When the oil temperature is above 43°C (110°F), the valve is
CLOSED and all the oil flows through the filter to a flow control valve
located in the temperature and flow control valve. The temperature and
pressure control valve is also the system main relief valve. If the pressure
exceeds 690 kPa (100 psi), the temperature and pressure control valve
will open to prevent high oil pressure to the rear axle oil filter.
The flow control valve distributes the oil flow to the rear wheel bearings
and the differential bearings.
2. Temperature andpressure controlvalve
90
- 100 -STMG 682
3/97
• Rear axle oil coolingand filter system
OIL COOLER OILFILTER
TEMPERATURE/PRESSURE
CONTROL VALVE
REAR AXLEOIL COOLING AND FILTER SYSTEM
FLOW CONTROL VALVE
DIFFERENTIALOIL PUMP
SUCTIONSCREEN
REAR AXLE
Shown is a schematic of the rear axle oil cooling and filter system. The
differential oil pump pulls oil from the bottom of the rear axle housing
through a suction screen. Oil flows from the pump through a temperature
and flow control valve located on top of the differential housing.
The temperature and pressure control valve, which is part of the
temperature and flow control valve, prevents high oil pressure when the
rear axle oil is cold. When the oil temperature is below 43°C (110°F), the
valve is OPEN and allows oil to flow to the rear axle housing. When the
oil temperature is above 43°C (110°F), the valve is CLOSED and all the
oil flows through the differential oil filter and the oil cooler (if equipped)
to a flow control valve, which is also part of the temperature and flow
control valve.
• Temperature andpressure control valve
- 101 -
• Temperature andpressure control valveis main relief
STMG 682
3/97
The temperature and pressure control valve is also the system main relief
valve. If the pressure exceeds 690 kPa (100 psi), the temperature and
pressure control valve will open to prevent high oil pressure to the rear
axle oil filter.
The flow control valve distributes the oil flow to the rear wheel bearings
and the differential bearings. At high ground speeds, excess oil flow is
diverted to the axle housing to prevent overfilling the wheel bearing and
final drive compartments.
• Flow control valveprevents overfillingwheel bearingcompartment
91
- 102 -STMG 682
3/97
• Double reductionplanetary gear finaldrive
FIRST REDUCTIONRING GEAR
SECOND REDUCTIONRING GEAR SECOND REDUCTI
CARRIER
SECOND REDUCSUN GEAR
SECOND REDUCTPLANETARY GE
FIRST REDUCTIONPLANETARY GEAR
FIRST REDUCTIONSUN GEAR
FIRST REDUCTIONCARRIER
FINAL DRIVE
Shown is a sectional view of the double reduction planetary gear final
drive. Power flows from the differential through axles to the sun gear of
the first reduction planetary set. The ring gears of the first reduction
planetary set and the second reduction planetary set cannot rotate. Since
the ring gears cannot rotate, the first reduction sun gear causes rotation of
the first reduction planetary gears and the first reduction carrier.
The first reduction carrier is splined to the second reduction sun gear. The
second reduction sun gear causes rotation of the second reduction
planetary gears and the second reduction carrier. Since the second
reduction carrier is connected to the wheel assembly, the wheel assembly
also rotates.
The wheel assembly rotates much slower than the axle shaft but with
increased torque.
- 103 -
• Torque converterhousing is oil sump
• Four section pump:
1. Transmissionscavenge
2. Torque convertercharging
3. Transmissioncharging
4. Transmission lube
5. Transmission oilreturn screen
92
STMG 682
3/97
14 3 2
5
Power Train Hydraulic System
The torque converter housing is the oil sump for the torque converter and
transmission oil supply.
A four section torque converter and transmission pump is located at the
rear of the torque converter. The four sections (from front to rear) are:
1. Transmission scavenge
2. Torque converter charging
3. Transmission charging
4. Transmission lube
The transmission scavenge section pulls oil through the magnetic screens
located at the bottom of the transmission. The scavenged oil from the
transmission is transferred into the torque converter housing through the
transmission oil return screen located behind the cover (5).
- 104 -
• Transmissionmagnetic scavengescreens (arrow)
93
STMG 682
3/97
Shown is the location of the transmission magnetic scavenge
screens (arrow). These screens should always be checked for debris if a
problem with the transmission is suspected.
Oil is scavenged from the transmission by the first section of the pump
(shown in Slide No. 92).
- 105 -
• Torque converter/transmission suctionscreen cover (arrow)
94
STMG 682
3/97
The three rear sections of the torque converter and transmission pump
pull oil from the torque converter housing sump. Most of the required oil
supply is pulled directly from the torque converter and transmission oil
cooler return oil. The remaining required oil supply is drawn through a
suction screen located behind the cover (arrow).
- 106 -
1. Torque convertercharging filter
2. Torque converterinlet relief valve
95
STMG 682
3/97
2
1
Oil flows from the torque converter charging section of the torque
converter and transmission pump to the torque converter charging filter
(1) located on the front of the hydraulic tank.
Oil flows from the torque converter charging filter to the torque converter
inlet relief valve (2).
- 107 -
• Torque converter inletrelief valve (arrow)
96
STMG 682
3/97
Oil flows from the torque converter charging filter to the inlet relief
valve (arrow) mounted on the torque converter. The inlet relief valve
controls the maximum pressure of the supply oil to the torque converter.
The torque converter inlet relief pressure can be measured at this valve by
removing a plug and installing a pressure tap.
Oil flows through the inlet relief valve and enters the torque converter.
- 108 -
1. Torque converteroutlet relief valve
2. Outlet relief valvepressure tap
97
STMG 682
3/97
1
5
2
4
3
Torque converter charging oil either drops to the bottom of the housing or
flows through the torque converter outlet relief valve (1). The outlet
relief valve limits the pressure inside the torque converter. The outlet
relief pressure can be measured at the tap (2) on the outlet relief valve.
All the oil from the torque converter outlet relief valve flows through the
torque converter outlet screen (3) to the torque converter and transmission
oil cooler located on the right side of the engine (see Slide No. 60). Oil
flows from the torque converter and transmission oil cooler back to the
torque converter housing.
A torque converter outlet screen bypass switch (4) provides an input
signal to the VIMS which informs the operator if the torque converter
outlet screen is restricted.
A torque converter outlet temperature sensor (5) provides an input signal
to the VIMS which informs the operator of the torque converter outlet
temperature.
3. Torque converteroutlet screen
4. Torque converteroutlet screen bypassswitch
5. Torque converteroutlet temperaturesensor
- 109 -
1. Transmissioncharging filter
98
STMG 682
3/97
23
1
Oil flows from the transmission charging section of the torque converter
and transmission pump to the transmission charging filter (1).
A transmission charging filter bypass switch (2) sends an input signal to
the VIMS which informs the operator if the transmission charging filter is
restricted.
Transmission charging oil flows in two directions from the transmission
charging filter:
- Transmission charging oil flows to the torque converter lockup
clutch valve located on top of the torque converter.
- Transmission charging oil also flows to the transmission control
valves located on top of the transmission.
Torque converter and transmission oil samples can be taken at the
Scheduled Oil Sample (S•O•S) tap (3).
2. Filter bypass switch
• Transmissioncharging oil flows in
two directions:
- To torque converterlockup clutch valve
- To transmissioncontrol valves
3. S•O•S tap
- 110 -
1. Torque converterlockup clutch valvesupply port
99
STMG 682
3/97
21
3
The transmission charging pump supplies oil to the torque converter
lockup clutch valve through the inlet port (1). When the lockup clutch
solenoid (located on the transmission housing) is energized by the
transmission control, the lockup clutch valve supplies oil to ENGAGE the
lockup clutch in the torque converter.
Torque converter lockup clutch pressure can be measured at the tap (2).
Torque converter lockup clutch pressure should be 2205 ± 70 kPa
(320 ± 10 psi) at 1300 rpm or higher. Do not check the torque converter
lockup clutch pressure below 1300 rpm.
The transmission control uses a dual stage relief valve for clutch supply
pressure. At high idle in torque converter drive, transmission charging
pressure should be 3065 kPa (445 psi) maximum. At low idle in torque
converter drive, transmission charging pressure should be 2480 kPa
(360 psi) minimum.
During torque converter lockup (DIRECT DRIVE), clutch supply
pressure is reduced to extend the life of the transmission clutch seals.
At high idle in direct drive, the clutch supply pressure should be
1620 + 240 - 100 kPa (235 + 35 - 15 psi). The corresponding
transmission charge pressure is reduced to 2205 ± 70 kPa (320 ± 10 psi).
2. Torque converterlockup clutchpressure tap
• Do not test converterlockup pressurebelow 1300 rpm
- 111 -STMG 682
3/97
The torque converter output speed (TCO) sensor (3) sends an input signal
to the Electronic Programmable Transmission Control (EPTC II). The
EPTC II memory also contains the engine rpm and the Transmission
Output Speed (TOS) for each gear of the transmission. The EPTC II
provides all these input signals to the VIMS.
Using the information from the EPTC II, the VIMS calculates if any
slippage exists in the torque converter lockup clutch or any of the
transmission clutches and stores this information in the VIMS main
module. This information can be downloaded from the VIMS with a
laptop computer.
3. Torque converteroutput speed (TCO)sensor
• Clutch slippage isrecorded in VIMS
100
- 112 -STMG 682
3/97
• Lockup clutch valveoperation
LOCKUPSOLENOID
ON
FROMTRANSMISSION
CHARGEPUMP
RELAY VALVE
LOCKUPREDUCING
VALVE
LOCKUPMODULATION
VALVE
LOCKUP CLUTCHPILOT OIL
PRESSURE
TO LOCKUPCLUTCH
FROMTRANSMISSION
CHARGEPUMP
TORQUE CONVERTER LOCKUP CLUTCH CONTROLDIRECT DRIVE
SHUTTLEVALVE
SELECTORPISTON
TOTRANSMISSION
LUBE PUMP
TOSTATION
"D"
Shown is a sectional view of the torque converter lockup clutch valve in
DIRECT DRIVE. Supply oil from the transmission charging pump is
used to provide lockup clutch oil and has two functions:
1. Supply pressure is reduced to provide pilot pressure.
2. When the solenoid is energized, supply pressure is reduced by the
modulation reduction valve to provide lockup clutch pressure.
The lockup solenoid has been energized and directs pump supply pressure
to the relay valve. Before moving the selector piston, pilot oil moves a
shuttle valve to the right which closes the drain and opens the check
valve. Oil then flows to the selector piston. Moving the selector piston
blocks the drain passage and the load piston springs are compressed.
• Lockup solenoidenergized startsclutch modulation
- 113 -STMG 682
3/97
Compressing the load piston springs moves the modulation reduction
valve spool down against the force of the inner spring. This initial
movement opens the supply passage (from the transmission charge pump)
and permits pressure oil to flow to the clutch. As the clutch fills, pressure
oil opens the ball check valve and fills the slug chamber at the top of the
reduction valve spool. At the same time, oil flows through the load piston
orifice and fills the chamber between the end of the load piston and the
selector piston. The load piston orifice provides a pressure drop and time
delay in the flow of oil to the load piston chamber. The load piston orifice
helps control the rate of modulation. Filling the load piston chamber is
made possible when the selector piston covers the drain passage at the
decay orifice.
The load piston has now moved completely down against the stop. The
modulation cycle is completed and the clutch pressure is at its maximum
setting. Because this is a modulation reduction valve, the maximum
pressure setting of the clutch is lower than the transmission charge
pressure. At the end of the modulation cycle, the pressure in the slug
chamber moves the reduction valve a small distance up to restrict the flow
of supply oil to the clutch. This is the "metering position" of the
reduction valve spool. In this position, the valve maintains precise
control of the clutch pressure.
Primary pressure is adjusted with shims in the load piston. Final lockup
clutch pressure is not adjustable. If the primary pressure is correct and
final lockup clutch pressure is low, the load piston should be checked to
make sure that it moves freely in the selector piston. If the load piston
moves freely, the load piston springs should be replaced.
• Lockup clutch atmaximum pressure
- 114 -
101
STMG 682
3/97
1
3
4
5
2
The transmission charging pump supplies oil to the transmission
hydraulic control valve and the shift solenoids through the inlet port (1).
Excess transmission charging oil either drops to the bottom of the housing
to be scavenged or flows back to the torque converter housing through the
outlet hose (2).
The torque converter lockup clutch solenoid (3) is energized by the EPTC
II when DIRECT DRIVE (lockup clutch ENGAGED) is required.
Transmission charge pump supply oil flows through the small hose (4) to
the lockup clutch control valve. The lockup clutch control valve then
engages the lockup clutch.
The transmission charging pressure relief valve is part of the transmission
hydraulic control valve. The relief valve limits the maximum pressure in
the transmission charging circuit. Transmission charging pressure can be
measured at the tap (5).
1. Transmissioncontrol valve supplyport
2. Transmissioncharging oil returnport
3. Torque converterlockup clutchsolenoid
4. Lockup clutch pilotoil hose
5. Transmissioncharging pressuretap
- 115 -
1. Transmission clutchpressure taps
102
STMG 682
3/97
32
1
Shown is the Individual Clutch Modulation (ICM) transmission hydraulic
control valve. Transmission clutch pressures are measured at the pressure
taps (1).
The transmission hydraulic control valve contains a priority valve. The
priority valve controls the pressure that is directed to the selector pistons
in each of the clutch stations. The transmission priority valve pressure
has been increased from 1720 kPa (250 psi) to 2585 kPa (375 psi).
Increasing the priority valve pressure also increases the charging pressure
available to the lockup clutch valve.
The "D" Station (2) is used to control the dual stage relief valve setting
for the clutch supply pressure (shown on next slide).
The transmission lube pressure relief valve (3) limits the maximum
pressure in the transmission lube circuit.
2. "D" Station controlsdual stage reliefvalve
• Priority valve pressureincreased
3. Transmission luberelief valve
103
- 116 -STMG 682
3/97
• ICM transmissionhydraulic controlvalve
DOWNSHIFTSOLENOID
UPSHIFTSOLENOID
LOCKUPSOLENOID
F
G
H
A
B
C
TRANSMISSIONCHARGING
FILTER
ROTARYSELECTOR
SPOOL
NEUTRALIZERVALVEPRIORITY
REDUCTIONVALVE
DOWNSHIFTPRESSURE
UPSHIFTPRESSURE
TRANSMISSION CASE
TORQUE CONVERTERHOUSING
CHARGINGPUMP
LUBEPUMP
SCAVENGEPUMP
COOLERBYPASSVALVE
OILCOOLER
LUBRICATIONRELIEF VALVE
PUMPPRESSURE
TO TORQUE CONVERTERRELAY VALVE
SELECTOR VALVE GROUPRELIEF VALVE
TRANSMISSION ICMHYDRAULIC SYSTEM
LOCKUP DUALSTAGE RELIEF VALVE
LUBEPRESSURE
ON
PRESSURE CONTROLGROUP
PILOT OILPRESSURE
D
E
ROTARY ACTUATOR
N1
3
The transmission control group uses a dual stage relief valve for clutch
supply pressure. At high idle in torque converter drive, transmission
charging pressure should be 3065 kPa (445 psi) maximum. At low idle in
torque converter drive, transmission charging pressure should be
2480 kPa (360 psi) minimum.
Shown is a sectional view of the ICM transmission hydraulic control
valve group. The rotary selector spool is in a position that engages two
clutches. Pump supply oil from the lockup solenoid flows to the selector
piston in station "D." Station "D" reduces the pump supply pressure, and
the reduced pressure flows to the lower end of the relief valve. Providing
oil pressure to the lower end of the relief valve reduces the clutch supply
pressure.
During torque converter lockup (DIRECT DRIVE), clutch supply
pressure is reduced to extend the life of the transmission clutch seals.
At high idle in direct drive, clutch supply pressure should be
1620 + 240 - 100 kPa (235 + 35 - 15 psi). The corresponding
transmission charge pressure is reduced to 2205 ± 70 kPa (320 ± 10 psi).
• Dual stage relief valve
- 117 -
1. Transmission lubesupply hose
104
STMG 682
3/97
3
1
2
Oil flows from the transmission lube section of the torque converter and
transmission pump to the transfer gears through a hose (1). Transmission
lube oil flows through the transfer gears and the transmission to cool and
lubricate the internal components.
The transmission lube oil temperature sensor (2) provides an input signal
to the VIMS which informs the operator of the temperature of the
transmission lube oil.
The transmission lube pressure relief valve is in the transmission case
near the transmission hydraulic control valve. The relief valve limits the
maximum pressure in the transmission lube circuit. Transmission lube oil
pressure can be measured at the tap (3).
At HIGH IDLE, the transmission lube pressure should be 110 to 207 kPa
(16 to 30 psi). At LOW IDLE, the transmission lube pressure should be
5 to 65 kPa (.5 to 10 psi).
2. Transmission lubeoil temperaturesensor
3. Transmission lubeoil pressure tap
105
- 118 -STMG 682
3/97
• Torque converter/transmissionhydraulic system
• Four section pump:
1. Transmissionscavenge
2. Torque convertercharging
3. Transmissioncharging
4. Transmission lube
SUCTIONSCREEN
RETURNSCREEN
TC LOCKUPVALVE
TC INLETRELIEFVALVE
TC OUTLETRELIEFVALVE
TC/TRANSPUMPS
TC OUTLETSCREEN
TORQUE CONVERTER/TRANSMISSION COOLER
TC LOCKUPVALVE
TC CHARGINGFILTER
TRANSMISSIONCHARGING
FILTER
TRANSMISSIONMAGNETICSCREENS
RETURNSCREEN
TORQUE CONVERTER ANDTRANSMISSION HYDRAULIC SYSTEM
Shown is the torque converter and transmission hydraulic system. A four
section torque converter and transmission pump is located at the rear of
the torque converter. The four sections (from front to rear) are:
1. Transmission scavenge
2. Torque converter charging
3. Transmission charging
4. Transmission lube
The transmission scavenge pump pulls oil through the magnetic screens
located at the bottom of the transmission. The scavenged oil from the
transmission is transferred into the torque converter housing through the
transmission oil return screen.
The three rear sections of the torque converter and transmission pump pull
oil from the torque converter housing sump. Most of the required oil
supply is pulled directly from the torque converter and transmission oil
cooler return oil. The remaining required oil supply is drawn through a
suction screen located in the bottom of the torque converter housing.
- 119 -
• Torque convertercharging section
STMG 682
3/97
Oil from the torque converter charging section of the torque converter and
transmission pump flows through the torque converter charging filter to
the inlet relief valve mounted on the torque converter. The inlet relief
valve limits the maximum pressure of the supply oil to the torque
converter.
Torque converter charging oil either drops to the bottom of the housing or
flows through the torque converter outlet relief valve. The outlet relief
valve limits the pressure inside the torque converter.
Most of the oil from the torque converter outlet relief valve flows through
the torque converter outlet screen to the torque converter and transmission
oil cooler located on the right side of the engine. Oil from the torque
converter and transmission oil cooler returns to the torque converter
housing.
Oil from the transmission charging section of the torque converter and
transmission pump flows through the transmission charging filter. From
the filter, transmission charging oil flows in two directions:
- Transmission charging oil flows to the torque converter lockup clutch
valve located on top of the torque converter.
- Transmission charging oil also flows to the transmission control
valves located on top of the transmission.
Excess transmission charging oil to the transmission control valves either
drops to the bottom of the housing to be scavenged or flows back to the
torque converter housing.
When the torque converter lockup clutch solenoid is energized, pump
supply oil flows to the lockup clutch control valve. The lockup clutch
control valve then engages the lockup clutch.
Oil flows from the transmission lube section of the torque converter and
transmission pump to the transfer gears. Transmission lube oil flows
through the transfer gears and the transmission to cool and lubricate the
internal components.
• Transmissioncharging section
• Transmission lubesection
106
- 120 -STMG 682
3/97
• EPTC II shifts thetransmissionelectronically
STARTER SOLENOID
A11
A12
A13
A14
A15
A16
B10
B9
A17
A18
A19
A36
A37
A10 A21 A22 A23 A24 A25
TOS
TRANSMISSION
A26 A3 A4 A5
EPTC II
A - 37 PIN CONNECTORB - 10 PIN SURE-SEAL CONNECTOR
A9
B1
B6
B7
A29
A30
A27
B5
A6
A20
A28
892 - BR
893 - GN
306 - GNE750 - PU
706 - BR
720 - PU
707 - PU
711 - BR
712 - WH
713 - OR
714 - YL
715 - GN
716 - BU
307 - OR
D996 - PU
D997 - YL
218- BK
217 - BK
219 - BK
227 - BK
280 - BK
709 -
OR
710 -
GN
721 -
BR
722 -
WH
723 -
OR
724 -
YL
725 -
GN
726 -
BU
703 -
BU
704 -
GY
705 -
PK
DATA LINK
UP, DOWN,LOCKUPSOLENOIDS
450 - YL
452- PU
2
10
12
3 4 5
11
6 7 8 9
13
D1 D2 D3
BACK-UP ALARMRELAY
B2 321- BR
MACHINEID CODE
RAISE SOLENOIDA31 G714 - PU
FLOAT SOLENOIDA32 G711 - BR
LOWER SOLENOIDG712- GNA33
SHIFTLEVERSWITCH
SERVICE "SET" AND"CLEAR" SWITCHES
CONVERTERSPEED
ENGINESPEED
KEY STARTSWITCH
BODY UP
SECONDARYBRAKE
HOISTLEVER
SERVICE/RETARDER
BRAKE
TRANSMISSIONGEAR SWITCH
Electronically Programmable Transmission Control (EPTC II)
The purpose of the EPTC II is to determine the desired transmission gear
and energize solenoids to shift the transmission up or down as required
based on information from both the operator and machine.
The EPTC II receives information from various input components such as
the shift lever switch, Transmission Output Speed (TOS) sensor,
transmission gear switch and the hoist lever switch.
Based on the input information, the EPTC II determines whether the
transmission should upshift, downshift, engage the lockup clutch or limit
the transmission gear. These actions are accomplished by sending signals
to various output components.
• Shifts controlled byelectrical signals
- 121 -STMG 682
3/97
Output components include the upshift, downshift and lockup solenoids,
the back-up alarm and others.
The EPTC II also provides the service technician with enhanced
diagnostic capabilities through the use of onboard memory, which stores
possible diagnostic codes for retrieval at the time of service.
With the use of a set of service switches, the service technician can access
the different modes to gather the stored diagnostic codes or set the
adjustable transmission gear limit functions.
Input and output components on the block diagram are accompanied with
a letter and number. The letter A corresponds with the 37 pin connector
and the letter B corresponds with the 10 pin Sure-Seal connector that are
attached to the transmission control. The numbers next to the letters
correspond to the pin numbers in the connector. For example, the shift
lever switch is connected to the transmission control through six wires in
the 37 pin connector at pin locations 11 through 16.
The Advanced Diesel Engine Management (ADEM II) engine control, the
Automatic Retarder Control (ARC), the Vital Information Management
System (VIMS) and the EPTC II all communicate with each other
through the CAT Data Link. Communication between the electronic
controls allows the sensors of each system to be shared. Many additional
benefits are provided, such as Controlled Throttle Shifting (CTS). CTS
occurs when the EPTC II tells the engine ECM to reduce engine fuel
during a shift to lower stress to the power train.
The EPTC II is also used to control the hoist system on the 793C. Several
changes have been made to the input and output signals through the EPTC
II 37 pin CE connector. The changes are:
1. The bed raise switch has been eliminated and an input signal is no
longer transmitted through Pin 7.
2. A Pulse Width Modulation (PWM) type position sensor provides
the hoist lever input signal to Pin 28.
3. A raise solenoid output signal has been added to Pin 31. The
output is a ground signal to a relay which sends +24 Volts to the
raise solenoid.
4. A float solenoid output signal has been added to Pin 32. The
output is a ground signal to a relay which sends +24 Volts to the
float solenoid.
5. A power down solenoid output signal has been added to Pin 33.
The output is a ground signal to a relay which sends +24 Volts to
the power down solenoid.
• Benefits of electroniccommunication
• EPTC II used tocontrol hoist system
• EPTC II connectorsand pin numbers
• EPTC II outputs
- 122 -
• Transmissionelectronic control
107
STMG 682
3/97
Shown is the Electronic Programmable Transmission Control (EPTC II).
The EPTC II is located to the right of the operator’s seat in the center
console. The control contains a diagnostic window with 12 Light
Emitting Diodes (LED’s) and a three digit numeric display.
The service switches (arrow) are used to interrogate the EPTC II for
stored diagnostic information, event information and to program the
transmission top gear limit functions. The switches are labeled with an
"S" for "SET" and a "C" for "CLEAR."
The DIAGNOSTIC MODE of the Electronic Control is changed by
DEPRESSING and HOLDING both service switches (SET and CLEAR).
When the desired mode is shown on the display, the switches can be
released. By following the instructions in the Service Manual, the
serviceman can determine if the transmission electronic control system is
operating correctly.
• Service switches(arrow)
• Diagnostic modeschanged with serviceswitches
108
- 123 -STMG 682
3/97
EPTC II DIAGNOSTIC WINDOW
D1 D2 D3
2
10
12
3 4 5
11
6 7 8 9
13
The onboard diagnostic window houses 12 status LED's along with a
three digit numeric display.
The functions of the three digit display and the status LED's are:
1. Three digits (D1, D2, D3) display numbers and letters or indicate
circuit conditions.
2. DIAG PRESENT--A RED LED which indicates that the Electronic
Control has detected a fault for which a diagnostic code has been
stored in memory. The LED is ON if the fault is still present.
3. BODY UP--An AMBER LED which is ON when the body up switch
is in use as sensed by a ground from the body up switch.
• EPTC II diagnosticwindow:
- 12 status LED's
- Three digit display
- 124 -STMG 682
3/97
4. RETARDER--An AMBER LED which is ON when the service brake
or retarder is in use as sensed by a ground from the service/retarder
brake pressure switch.
5. BRAKE--An AMBER LED which is ON when the secondary or
parking brake is in use as sensed by an open from the
secondary/parking brake pressure switch.
6. BODY RAISE--An AMBER LED which is ON when the hoist lever
sensor is providing a signal to the electronic control.
7. HOLD--An AMBER LED which is ON when the hold pedal or
switch is in use as sensed by a ground from the hold pedal or switch.
(Not used on Trucks.)
8. CONT FAILURE--A RED LED which is ON or FLASHING when
the electronic control has FAILED and should be replaced.
9. POWER--A GREEN LED which is ON when a nominal 24 Volts is
available between pins 1 and 2 of the electronic control 37 pin
connector.
10. TOS--An AMBER LED which is ON when the Transmission Output
Speed (TOS) sensor is providing a signal to the electronic control.
11. TCO--An AMBER LED which is ON when the Torque Converter
Output (TCO) speed sensor is providing a signal to the electronic
control.
12. EOS--An AMBER LED which is ON when the Engine Output Speed
(EOS) sensor is providing a signal to the electronic control.
13. MODE 1--An AMBER LED which is ON when the electronic
control is NOT in Mode 0.
NOTE: The small LED at the bottom right of the three digit display
has no diagnostic function. The small LED will always be ON.
Service personnel should always view the diagnostic window with the
small LED at the bottom right of the three digit display. When the
small LED is at the bottom right of the three digit display, service
personnel know that the window is being viewed in the correct
orientation.
- 125 -
109
STMG 682
3/97
The Electronic Control Analyzer Programmer (ECAP) and the Electronic
Technician (ET) Service Tools can be used in place of the EPTC II
diagnostic window. The ECAP and ET perform the same functions as the
EPTC II diagnostic window and are capable of several additional
diagnostic functions that the EPTC II window does not display.
Additional diagnostic functions that the service tools can perform are:
- Display the EPTC II internal clock hour reading.
- Display the hour reading of the first and last occurrence for each
logged diagnostic code.
- Display the definition for each logged diagnostic code.
- Display logged events.
- Display the lockup clutch engagement counter.
- Display the transmission gear shift counter.
• ECAP and ET servicetools
- 126 -
1. Transmission gearswitch
110
STMG 682
3/97
4
3
2
1
Shown is an example of one input component to the EPTC II and three
output components from the EPTC II.
The transmission gear switch (1) provides input signals to the EPTC II.
The transmission gear switch inputs (also referred to as the actual gear
inputs) are comprised of six wires. Five of the six wires provide a code to
the EPTC II. The code is unique for each position of the transmission
gear switch. Each transmission gear switch position will result in two of
the five wires sending a ground signal to the EPTC II. The other three
wires will remain open (ungrounded). The pair of grounded wires is
unique for each gear position. The sixth wire is known as the "Ground
Verify" wire, which is normally grounded. The "Ground Verify" wire is
used by the EPTC II to verify that the transmission gear switch is
connected to the transmission control. The "Ground Verify" wire allows
the EPTC II to distinguish between loss of the transmission gear switch
signals and a condition in which the transmission gear switch is between
gear detent positions.
Earlier transmission gear switches use a wiper contact assembly that does
not require a power supply to Pin 4 of the switch. Present transmission
gear switches are Hall-Effect type switches. A power supply is required
to power the switch. A small magnet passes over the Hall cells which
then provide a non-contact position switching capability. The Hall-Effect
type switches use the same 10-Volt power supply as the transmission
output speed sensor.
- 127 -STMG 682
3/97
The solenoid outputs provide + Battery voltage to the upshift solenoid (2)
or the downshift solenoid (3) based on the input information from the
operator and the machine. The solenoids are energized until the
transmission actual gear switch signals the EPTC II that a new gear
position has been reached. The length of time that the solenoid is
energized is usually about 0.1 seconds when a single gear upshift is
desired.
The lockup solenoid output provides + Battery voltage to the lockup
clutch solenoid (4). The lockup solenoid is energized by the EPTC II
when in a DIRECT DRIVE gear. In FIRST gear, the solenoid will be
energized when the Transmission Output Speed (TOS) reaches a
predetermined value. When the machine is in CONVERTER DRIVE, the
solenoid is de-energized by the EPTC II.
2. Upshift solenoid
3. Downshift solenoid
4. Lockup clutchsolenoid
111
- 128 -STMG 682
3/97
793C
STEERING
STEERING SYSTEM
This section of the presentation explains the operation of the steering
system. As on other Caterpillar Off-highway Trucks, the steering system
uses hydraulic force to change the direction of the front wheels. The
system has no mechanical connection between the steering wheel and the
steering cylinders.
- 129 -
• Steering tank
1. Upper sight gauge
2. Lower sight gauge
112
STMG 682
3/97
6
3
7
1
2
5
4
The steering tank is located on the right platform. Two sight gauges are
on the side of the tank. When the engine is shut off and the oil is cold, the
oil should be visible between the FULL and ADD OIL markings of the
upper sight gauge (l). When the engine is running and the accumulators
are fully charged, the oil level should not be below the ENGINE
RUNNING marking of the lower sight gauge (2). If the ENGINE
RUNNING level is not correct, check the nitrogen charge in each
accumulator. A low nitrogen charge will allow excess oil to be stored in
the accumulators and will reduce the secondary steering capacity.
A combination vacuum breaker/pressure relief valve is used to limit the
tank pressure. Before removing the fill cap, be sure that the engine was
shut off with the key start switch and the oil has returned to the tank from
the accumulators. Depress the pressure release button (3) on the breather
to vent any remaining pressure from the tank.
Supply oil for the steering system is provided by a piston-type pump.
Case drain oil from the pump returns to the tank through the filter (4).
The remaining steering system oil returns to the tank through the main
steering filter (5). Both filters are equipped with bypass valves to protect
the system if the filters are plugged or during cold oil start-up.
4. Case drain oil filter
5. Main steering filter
3. Combinationvacuum breaker/relief valve andpressure releasebutton
- 130 -STMG 682
3/97
If the steering pump fails or if the engine cannot be started, the
connector (6) is used to attach an Auxiliary Power Unit (APU). The APU
will provide supply oil from the steering tank at the connector (6) to
charge the steering accumulators. Steering capability is then available to
tow the truck.
The steering oil temperature sensor (7) provides an input signal to the
VIMS which informs the operator of the steering system oil temperature.
INSTRUCTOR NOTE: For more detailed information on servicing
the steering accumulators, refer to the Service Manual Module "793C
Off-highway Truck Steering System" (Form SENR1452) and the
Special Instruction "Repair of 4T8719 Bladder Accumulator Group"
(Form SEHS8757). For more information on using the APU, refer to
the Special Instructions "Using 1U5000 Auxiliary Power Unit (APU)"
(Form SEHS8715) and "Using the 1U5525 Attachment Group"
(Form SEHS8880).
6. APU supplementalsteering connector
7. Steering oiltemperature sensor
- 131 -
113
STMG 682
3/97
2
4
3
1
The 793C is equipped with a load sensing, pressure compensated,
piston-type pump (1). The steering pump is mounted to the pump drive.
The pump drive is located on the inside of the right frame rail near the
torque converter.
The steering pump operates only when the engine is running and provides
the necessary flow of oil to the accumulators for steering system
operation. The steering pump contains a load sensing controller (2) that
works with an accumulator charging valve to monitor and control steering
pump output.
The steering pump will produce flow at high pressure until the steering
accumulators are charged with oil and the pressure increases to
21400 ± 345 kPa (3100 ± 50 psi) at LOW IDLE. This pressure is referred
to as the CUT-OUT pressure. When the CUT-OUT pressure is reached,
the accumulator charging valve reduces the load sensing signal pressure
to the pump load sensing controller, and the pump will destroke to the
LOW PRESSURE STANDBY position. During LOW PRESSURE
STANDBY, the pressure should be between 2410 and 3445 kPa
(350 and 500 psi).
The pump operates at minimum swashplate angle to supply oil for
lubrication, leakage and Hand Metering Unit (HMU) "thermal bleed."
Because of the normal leakage in the steering system, the pressure in the
accumulators will gradually decrease to 19200 ± 315 kPa (2785 ± 45 psi).
This pressure is referred to as the CUT-IN pressure.
1. Steering pump
• CUT-OUT pressure
• LOW PRESSURESTANDBY
2. Load sensingcontroller
• CUT-IN pressure
- 132 -STMG 682
3/97
When the pressure in the accumulators decreases to the CUT-IN pressure,
the accumulator charging valve blocks the load sensing signal line to the
load sensing controller from returning to the tank, and the pump will
upstroke to maximum displacement (full flow).
A pressure tap (3) is located on the pump pressure switch manifold. If
steering pump pressure is measured at this tap during LOW PRESSURE
STANDBY, a gauge acceptable for testing maximum steering system
pressure must be used to avoid damaging the gauge when the steering
pump upstrokes to provide maximum oil flow.
Two pressure switches monitor the condition of the steering system on the
793C. One switch (4) monitors the output of the steering pump. The
purpose of this switch is to monitor pump supply pressure during LOW
PRESSURE STANDBY. The VIMS refers to this switch as the "low
steering pressure" switch.
The other steering pressure switch is mounted on the solenoid and relief
valve manifold, which is located on the front frame rail below the engine.
This switch monitors the steering system accumulator pressure. The
VIMS refers to this switch as the "high steering pressure" switch.
Both steering pressure switches provide input signals to the VIMS which
informs the operator of the condition of the steering system. A steering
system warning is only displayed if the ground speed is above 8 km/h
(5 mph).
4. Low steeringpressure switch
4. High steeringpressure switch
• Steering pressurewarnings only above8 km/h (5 mph)
3. LOW PRESSURESTANDBY pressuretap
- 133 -
114
STMG 682
3/97
5
4
6
2
13
Steering pump supply oil flows through a check valve (1) to the solenoid
and relief valve manifold (2). The solenoid and relief valve manifold
connects the steering pump to the accumulator charging valve (3), the
accumulators and the steering directional valve (4). The solenoid and
relief valve manifold also provides a path to drain for the steering oil.
When checking the steering system CUT-OUT and CUT-IN pressures, a
gauge can be connected at the pressure tap (5).
Steering system oil samples can be taken at the steering system Scheduled
Oil Sampling (S•O•S) tap (6).
1. Check valve
2. Solenoid and reliefvalve manifold
3. Accumulatorcharging valve
4. Steering directionalvalve
5. Steering systempressure tap
6. Steering systemS•O•S tap
- 134 -
115
STMG 682
3/97
3
2
1
Shown is a closer view of the accumulator charging valve (1). Steering
system CUT-OUT pressure is adjusted at the upper valve (2). Steering
system CUT-IN pressure is adjusted at the lower valve (3).
Steering pump supply pressure increases until the accumulator pressure
acting on the accumulator charging valve shifts the cut-out and cut-in
pressure valves. Together, the cut-out and cut-in pressure valves reduce
the Load Sensing (LS) signal pressure (feedback pressure) to slightly
above tank pressure. The pump is destroked to LOW PRESSURE
STANDBY (CUT-OUT).
When the pressure in the accumulators decreases, the cut-in and cut-out
pressure valves shift again and block the load sensing signal pressure
from the tank. The pump load sensing signal pressure becomes equal to
pump pressure, and the steering pump returns to the FULL FLOW
position (CUT-IN).
1. Accumulatorcharging valve
2. CUT-OUT pressurevalve
3. CUT-IN pressurevalve
116
- 135 -STMG 682
3/97
• Steering pumpoperation
• Actuator pistondrained duringmaximum flow
PUMP OUTPUT
LOAD SENSINGPRESSURE
ACTUATOR PISTON
LOAD SENSINGCONTROLLER
SWASHPLATEPISTON
FLOWCOMPENSATOR
DURING CHARGING (CUT-IN)
STEERING PUMP
ACCUMULATORCHARGING VALVE
TO ACCUMULATORS
FROM ACCUMULATORSCUT-OUTVALVE
CUT-INVALVE
HIGH PRESSURECUTOFF VALVE
After the engine is started, pressure increases in the steering accumulators.
The pump load sensing controller is spring biased to vent the actuator
piston pressure to drain. Venting pressure from the load sensing controller
and the actuator piston positions the spring biased swashplate to
maximum displacement (full flow).
As pressure increases in the accumulators, pump supply pressure is sensed
in the accumulator charging valve and on both ends of the flow
compensator. When pressure is present on both ends of the flow
compensator, the swashplate is kept at maximum angle by the force of the
spring in the pump housing and pump discharge pressure on the
swashplate piston. The pistons travel in and out of the barrel and
maximum flow is provided through the outlet port. Since the pump is
driven by the engine, engine rpm also affects pump output.
NOTE: Because the signal lines are sensing pump supply pressure
and not a "load" pressure, the steering system does not operate the
same as other load sensing systems with a margin pressure.
117
- 136 -STMG 682
3/97
• Accumulator chargingvalve shifts
• Signal pressuredecreases
PUMP OUTPUT
LOAD SENSINGPRESSURE
LOAD SENSINGCONTROLLER
FLOWCOMPENSATOR
SWASHPLATEPISTON
ACTUATORPISTON
LOW PRESSURE STANDBY (CUT-OUT)
STEERING PUMP
TO ACCUMULATORS
FROM ACCUMULATORS
ACCUMULATORCHARGING
VALVE
CUT-OUTVALVE
CUT-INVALVE
HIGH PRESSURECUTOFF VALVE
Pump supply pressure will increase until the accumulator pressure acting
on the accumulator charging valve shifts the cut-out and cut-in valves, and
the load sensing signal pressure is reduced to slightly above tank pressure.
The cut-out and cut-in valves shift when the pump outlet pressure is
approximately 21400 ± 345 kPa (3100 ± 50 psi) at LOW IDLE.
Pump oil (at LOW PRESSURE STANDBY) flows past the lower end of
the displaced flow compensator spool to the actuator piston. The actuator
piston has a larger surface area than the swashplate piston. The oil
pressure at the actuator piston overcomes the spring force of the
swashplate piston and moves the swashplate to destroke the pump. The
pump is then at LOW PRESSURE STANDBY (cut-out). Pump output
pressure is equal to the setting of the flow compensator. The LOW
PRESSURE STANDBY setting is between 2410 and 3445 kPa
(350 and 500 psi).
• Pump at LOWPRESSURE STANDBY
- 137 -STMG 682
3/97
In the NEUTRAL or NO STEER position, demand for oil from the
accumulators is low. The pump operates at minimum swashplate angle to
supply oil for lubrication, leakage and HMU "thermal bleed." Because of
the normal leakage in the steering system, the pressure in the
accumulators will gradually decrease to 19200 ± 315 kPa (2785 ± 45 psi).
When the pressure in the accumulators decreases to 19200 ± 315 kPa
(2785 ± 45 psi), the accumulator charging valve cut-in and cut-out valves
shift and block the load sensing signal line pressure from the tank. Pump
oil pressurizes the load sensing signal line. The load sensing signal shifts
the flow compensator spool and drains the actuator piston. Draining the
actuator piston positions the spring biased swashplate to maximum
displacement and full flow (CUT-IN).
At LOW lDLE in the NEUTRAL or NO STEER position, the pump will
cycle between the cut-out and cut-in conditions in intervals of 30 seconds
or more. Connecting a pressure gauge to the pressure tap below the
steering directional valve will indicate these steering system pressures. If
the pump pressure cycles in less than 30 seconds, leakage exists in the
system and must be corrected. Typical sources of leakage can be the
accumulator bleed down solenoid or the back-up relief valve located on
the solenoid and relief valve manifold. If a machine has an HMU with
the thermal bleed orifice removed, the cycle time between cut-out and
cut-in will be between 6 and 7 minutes.
If the accumulator charging pressure cannot be adjusted within
specifications, an adjustment of the high pressure cutoff valve is required.
The high pressure cutoff valve is part of the load sensing controller
mounted on the steering pump. The high pressure cutoff setting is
23100 ± 345 kPa (3350 ± 50 psi) at HIGH IDLE. The high pressure
cutoff setting must be a minimum of 350 kPa (50 psi) higher than the
accumulator charging (cut-out) valve setting at HIGH IDLE.
To adjust the high pressure cutoff valve on the load sensing controller,
turn the cut-out valve adjustment screw completely in and count the
number of turns so it can be returned to its original position later. With
the engine at HIGH IDLE, adjust the high pressure cutoff valve to
23100 ± 345 kPa (3350 ± 50 psi). Return the cut-out valve adjustment
screw to its original position and re-test the cut-out and cut-in valve
pressures.
NOTE: When testing or adjusting any steering system pressure
settings, always allow the accumulator charge cycle to occur at least
ten times before measuring the pressure. Failure to allow the
charging cycle to occur ten times will result in inaccurate readings.
• Accumulator pressuredecreases
• Cut-in and cut-outvalves shift
• Pump returns to fullflow
• High pressure cutoffvalve adjustment
• Cycle time betweenCUT-OUT and CUT-IN:
- With thermal bleedorifice, 30 secondsor more
- Without thermalbleed orifice,between 6 and 7minutes
118
- 138 -STMG 682
3/97
• Accumulator chargingvalve
FROM PUMP TO PUMP CONTROLSIGNAL PORT
CUT-OUT VALVE
CUT-IN VALVE
FROMACCUMULATOR
TO TANK
FEEDBACK ORIFICE
ACCUMULATOR CHARGE VALVEDURING CHARGING (CUT-IN)
Shown is a sectional view of the accumulator charging valve during
CHARGING (CUT-IN).
During CHARGING, the cut-out spool is held to the right by the spring.
The cut-out spool blocks the pump and load sensing signal passages from
the feedback orifice. Signal pressure is equal to pump pressure and the
high signal pressure causes the pump to upstroke to maximum
displacement (full flow).
As accumulator pressure increases, the cut-out spool will move to the left
against the spring force. When accumulator pressure reaches the cut-out
setting, the cut-out spool will open the pump and load sensing signal
passages to the feedback orifice. The feedback orifice reduces the load
sensing signal pressure to slightly more than tank pressure.
119
- 139 -STMG 682
3/97
• Accumulator chargingvalve
FROM PUMP TO PUMP CONTROLSIGNAL PORT
CUT-OUT VALVE
CUT-IN VALVE
FROMACCUMULATOR
TO TANK
FEEDBACK ORIFICE
ACCUMULATOR CHARGE VALVELOW PRESSURE STANDBY (CUT-OUT)
Shown is a sectional view of the accumulator charging valve in the LOW
PRESSURE STANDBY (CUT-OUT) position.
In the CUT-OUT position, accumulator pressure has increased to the cut-
out setting and both the cut-in and cut-out stems are fully shifted against
the springs. The pump and load sensing signal passages are open to the
feedback orifice. The feedback orifice reduces the signal pressure to
slightly more than tank pressure.
The feedback orifice is only required to initiate and maintain CUT-OUT.
As the accumulator pressure decreases, the feedback pressure holds the
cut-out spool to the left until the cut-in valve opens and vents the feedback
pressure to the tank. The feedback pressure during CUT-OUT assists
shifting against the spring. At the beginning of CUT-IN, the feedback
pressure assists the spring force.
120
- 140 -STMG 682
3/97
• Accumulator chargingvalve
FROM PUMP TO PUMP CONTROLSIGNAL PORT
CUT-OUT VALVE
CUT-IN VALVE
FROMACCUMULATOR
TO TANK
FEEDBACK ORIFICE
ACCUMULATOR CHARGE VALVEBEGINNING STAGE OF CUT-IN
Shown is a sectional view of the accumulator charging valve in the
beginning stage of CUT-IN.
When accumulator pressure decreases to the cut-in pressure, the cut-in
spool will move to the right and allow feedback pressure into the cut-in
valve and cut-out valve spring chambers. The feedback pressure assists
the cut-out and cut-in valve springs with shifting the cut-out and cut-in
spools to the right.
The cut-in spool continues to move to the right and blocks the center
passage to the cut-out spool. When the center passage to the cut-out spool
is blocked, signal pressure becomes equal to pump pressure.
CUT-IN will occur when the cut-out spool shifts to a position in which the
pump load sensing signal is no longer vented to feedback pressure. Signal
pressure becomes equal to pump pressure, the pump upstrokes and the
charging cycle begins.
- 141 -
1. Check valve
121
STMG 682
3/97
1
6
2
1
3
45
Steering pump supply oil flows through a check valve (1) to the solenoid
and relief valve manifold. The solenoid and relief valve manifold
connects the steering pump to the accumulator charging valve, the
accumulators and the steering directional valve. The solenoid and relief
valve manifold also provides a path to drain for the steering oil.
A steering accumulator pressure switch (2), an accumulator bleed down
solenoid (3), a back-up relief valve (4), a steering system Scheduled Oil
Sampling (S•O•S) tap (5) and a supplemental steering connector (6) are
located on the solenoid and relief valve manifold.
The check valve (1) prevents accumulator oil from flowing back to the
steering pump when the pump destrokes to LOW PRESSURE
STANDBY.
The steering accumulator pressure switch (2) monitors the steering
accumulator pressure. The VIMS refers to this switch as the "High
Steering Pressure" switch.
The steering accumulator pressure switch provides an input signal to the
VIMS which informs the operator of the steering system condition. A
steering system warning is displayed only if the ground speed is above
8 km/h (5 mph).
2. Steeringaccumulatorpressure switch
3. Accumulator bleeddown solenoid
4. Back-up relief valve
5. Steering systemS•O•S tap
6. Supplementalsteering connector
• Steering pressurewarnings only above8 km/h (5 mph)
- 142 -STMG 682
3/97
The accumulator bleed down solenoid (3) is used to drain pressure oil
from the accumulators when the truck is not in operation.
The back-up relief valve (4) is used to drain pressure oil if the steering
pump high pressure cutoff valve does not open.
Steering system oil samples can be taken at the steering system Scheduled
Oil Sampling (S•O•S) tap (5)
To operate the steering circuit on a disabled truck, an Auxiliary Power
Unit (APU) connects to the supplemental steering connector (6) on the
solenoid and relief valve manifold and to a suction port on the hydraulic
tank (see Slide No. 112). The APU will provide supply oil to charge the
accumulators. Steering capability is then available to tow the truck.
122
- 143 -STMG 682
3/97
• Solenoid and reliefvalve manifold
BACK-UP RELIEF VALVE
BLEED DOWNSOLENOID
TO TANK
SUPPLY FROM PUMPAND ACCUMULATORS
SOLENOID AND RELIEF VALVE MANIFOLD
Shown is a sectional view of the solenoid and relief valve manifold. The
accumulator bleed down solenoid is activated by the bleed down solenoid
shutdown control when the key start switch is moved to the OFF position.
The bleed down solenoid shutdown control holds the solenoid open for
70 seconds.
Pressure oil from the accumulators is sensed by the bleed down solenoid.
When the solenoid is energized, the plunger moves and connects the
pressure oil to the drain passage. Pressure oil flows through an orifice,
past the plunger, to the tank. The orifice limits the return oil flow from
the accumulators to a rate which is LOWER than the flow limit
(restriction) of the steering oil filter in the hydraulic tank. When the
solenoid is de-energized, spring force moves the plunger and pressure oil
cannot go to drain.
• Bleed down solenoiddrains accumulators
- 144 -
• Back-up relief valveprotects system ifpump does notdestroke
STMG 682
3/97
The back-up relief valve protects the steering system if the steering pump
malfunctions (fails to destroke). Pressure oil from the steering pump
works against the end of the back-up relief valve and the spring. The
relief valve unseats (opens) if oil pressure reaches approximately
26000 ± 400 kPa (3775 ± 60 psi) at a flow of 8 ± 2 L/min. (2 ± .5 gpm).
Oil then flows past the relief valve and drains to the tank.
The back-up relief valve must only be adjusted on a test bench. The
pressure setting of the back-up relief valve can be changed by adjusting
the spring force that keeps the relief valve seated (closed). To change the
relief valve setting, remove the protective cap and turn the adjustment
screw clockwise to increase or counterclockwise to decrease the pressure
setting. One revolution of the setscrew will change the pressure setting
3800 kPa (550 psi).
A functional test of the back-up relief valve can be performed on the
machine by installing a manual hydraulic pump at the location of the
Auxiliary Power Unit (APU) connector and installing blocker plates to
prevent oil from flowing to the accumulators. See the service manual for
more detailed information.
NOTE: Using the functional test procedure to adjust the back-up
relief valve will provide only an approximate setting. Accurate
setting of the back-up relief valve can only be performed on a
hydraulic test bench.
• Adjust back-up reliefvalve on test benchonly
• Functional test ofback-up relief valve(on machine)
- 145 -
1. Steering directionalvalve
123
STMG 682
3/97
2
1
The steering directional valve (1) is pilot operated from the HMU in the
operator’s station. Five pilot lines connect these two components. The
pilot lines send pilot oil from the HMU to shift the spools in the steering
directional valve. The spools control the amount and direction of pressure
oil sent to the steering cylinders. Four pilot lines are used for pump
supply, tank return, left turn and right turn. The fifth pilot line is for the
load sensing signal.
When checking the steering system cut-out and cut-in pressures, a gauge
can be connected at the pressure tap (2).
2. Steering system
pressure tap
124
- 146 -STMG 682
3/97
• Steering directionalvalve components:
- Priority spool
- Amplifier spool withcombiner/checkspool
- Directional spool
- Relief/makeup valves
- Back pressure valve
RELIEF/MAKEUPVALVE
LEFT TURNCYLINDER
BACK PRESSUREVALVE
LEFT TURN PILOT OIL
AMPLIFIER SPOOL
RIGHT TURN PILOT OIL
COMBINER/CHECKSPOOL
LOAD SENSING PORT
FROMACCUMULATOR
PRIORITY SPOOL
STEERING DIRECTIONAL VALVE
RIGHT TURNCYLINDER
RELIEF/MAKEUPVALVE
HAND METERINGUNIT SUPPLY ANDTHERMAL BLEED
NO TURN
TO TANK
Shown is a sectional view of the steering directional valve. The main
components of the steering directional valve are: the priority spool, the
amplifier spool with internal combiner/check spool, the directional spool,
the relief/makeup valves and the back pressure valve.
Pressure oil from the accumulators flows past the spring biased priority
spool and is blocked by the amplifier spool. The same pressure oil flows
through an orifice to the right end of the priority spool. The orifice
stabilizes the flow to the priority spool and must be present to open and
close the priority spool as the flow demand changes. The same pressure
oil flows to the HMU. After all the passages fill with pressure oil, the
priority spool shifts to the left, but remains partially open. In this
position, the priority spool allows a small amount of oil flow (thermal
bleed) to the HMU and decreases the pressure to the HMU supply port.
The lower pressure prevents the HMU from sticking.
- 147 -STMG 682
3/97
With the truck in the NEUTRAL or NO TURN position, all four working
ports (supply, tank, right turn and left turn) are vented to the tank through
the HMU. The directional spool is held in the center position by the
centering springs.
125
- 148 -STMG 682
3/97
• Steering directionalvalve during a RIGHTTURN
AMPLIFIER SPOOL
BACK PRESSURE VALVE
LEFT TURN PILOT OILRIGHT TURN PILOT OIL
COMBINER/CHECK SPOOL
LOAD SENSING PORT
FROMACCUMULATOR
HAND METERINGUNIT SUPPLY ANDTHERMAL BLEED
PRIORITY SPOOL
STEERING DIRECTIONAL VALVERIGHT TURN
RELIEF/MAKEUP VALVE
LEFT TURNCYLINDER
RIGHT TURNCYLINDER
RELIEF/MAKEUP VALVE
TO TANK
When the steering wheel is turned to the RIGHT, the "thermal bleed" and
venting of the four work ports to the tank is stopped. The increased
supply pressure flows to the HMU and the load sensing pilot line. The
load sensing pilot line directs cylinder pressure to the priority spool in the
directional valve. Cylinder pressure is present in the HMU because pilot
oil combines with accumulator oil in the combiner/check valve spool in
the directional valve. The increased pressure in the load sensing line
causes the priority spool to move to the right and allows more oil to flow
to the HMU through the supply line. The load sensing pump supply
pressure varies with the steering load. The priority spool moves
proportionally, allowing sufficient oil flow to meet the steering
requirements.
Pilot oil flows through a stabilizing orifice to the right turn pilot port of
the directional valve and moves the directional spool. Movement of the
directional spool allows pilot oil to flow to the amplifier and
combiner/check spools.
• Pilot oil movesdirectional spool
• Load sensing pilotpressure movespriority spool
- 149 -
• Pilot oil movesamplifier spool
STMG 682
3/97
The pilot oil divides at the amplifier spool. Pilot oil flows through a
narrow groove around the combiner/check spool. The pilot oil is
momentarily blocked until the amplifier spool moves far enough to the
right to allow partial oil flow through one of eight orifices.
Pilot oil also flows through a connecting pin hole and a stabilizing orifice
to the left end of the amplifier spool and causes the amplifier spool to
move to the right. Accumulator oil at the spring end (right end) of the
amplifier spool flows through a mid-connecting pin to the left end of the
amplifier spool and also causes the amplifier spool to move to the right.
When the amplifier spool moves to the right, accumulator oil flows to the
inner chamber, forcing the combiner/check spool to the left. Accumulator
oil then flows through seven of the eight orifices. Pilot and accumulator
oil combine. Oil flows across the directional spool (which has already
shifted) for a RIGHT TURN.
The faster the steering wheel is turned, the farther the directional spool
and the amplifier spool are shifted. A higher flow rate is available, which
causes the truck to turn faster. The ratio of pilot and pump supply oil that
combine is always the same because one orifice is dedicated to pilot flow
and seven orifices are dedicated to accumulator supply flow.
Return oil from the cylinders flows across the directional spool, around
the relief/makeup valve, forces the back pressure valve open and returns
to the tank.
During a turn, if a front wheel strikes a large obstruction that cannot
move, oil pressure in that steering cylinder and oil line increases. Oil
flow to the cylinder is reversed. This pressure spike is felt in the
amplifier spool. The combiner/check spool moves to the right and blocks
the seven pump supply oil orifices to the steering cylinders. The
amplifier spool moves to the left and blocks the pilot oil orifice. Pilot oil
flow to the steering cylinders stops. The pressure spike is not felt at the
HMU. If the pressure spike is large enough, the relief/makeup valve
drains the pressure oil to the tank as previously described.
• Turning steeringwheel faster providesmore flow to cylinders
• Pressure spike movescombiner/check spooland blocks flow to
HMU
• Pilot and accumulatoroil combine incombiner/check spool
- 150 -
• HMU (arrow)
126
STMG 682
3/97
The Hand Metering Unit (HMU) (arrow) is located at the base of the
steering column behind a cover at the front of the cab. The HMU is
connected to the steering wheel and controlled by the operator.
The HMU meters the amount of oil sent to the steering directional valve
by the speed at which the steering wheel is turned. The faster the HMU is
turned, the higher the flow sent to the steering cylinders, and the faster the
wheels will change direction.
• Meters oil todirectional valve
![dl.mitsubishielectric.co.jp · 1113/ h 500 clit250, 500 2000 —5000 1000 —2000 150 800 —800 150 150 150 150 150 150 80 80 lb- clkx4 lpb-ûkx4 lb-cidf6 lgh-nc]rs2 lgh-nclrs2d](https://static.fdocuments.net/doc/165x107/5e3f6ee9f762ab228f08e1f1/dl-1113-h-500-clit250-500-2000-a5000-1000-a2000-150-800-a800-150-150-150.jpg)
