ME597-lecture5-13

Dr. Monika IvantysynovaMAHA Professor Fluid Power Systems

Design and Modeling of Fluid Power SystemsME 597/ABE 591 Lecture 5

MAHA Fluid Power Research CenterPurdue University

Dr. Monika Ivantysynova Design and Modeling of Fluid PowerSystems, ME 597/ABE 5912

Axial piston pump design solutions (swash plate and bent axis)

Radial piston pumps and motors piston support

Gear Pumps internal and external axial and radial gap compensation

Vane pumps advantage and disadvantage of this design

Displacement Machines

Study different design principles and learn about the following topics

Aim: - To be able to select the right design for your system application! - Knowledge about limitations of each basic design - To apply models on system level for each design

Please study the appropriate chapters in Ivantysyn, J. and Ivantysynova, M. (2001), Hydrostatic Pumps and Motors.Akademia Books International. New Dehli. ISBN-81-85522-16-2


Displacement Machines

Fixed displacement machines Variable displacement machines

Piston Machines

Gear Machines

Screw Machines others

Axial Piston Machines

Radial Piston Machines

In-line Piston Machineswith external piston support

Swash Plate Machines

Bent Axis machines

Annual Gear

F

F

F

6

with internal piston support

External Gear

Internal Gear

Vane Machines


Bent axis axial piston pumps

18

Synchronization of cylinder block

Using a universal joint

Using a bevel gear

Cylinder blockDriving flange


Bent axis axial piston pumps

19

Cardan joint

Synchronization of cylinder block connecting rod

Synchronization by pistons

piston

Piston rod

Synchronization by piston rod


Kinematics of bent axis pumps

20

Frame (1)

Driving flange (2)

Piston (3)

Cylinder (4)

Four link 3D mechanism

Assuming a fixed connection between link 2 and link 4, achieved by synchronizationmechanism has finally two degreesof freedom

Five link 3D mechanism

Frame (1) Cylinder (4)

Piston (3)

Driving flange (2)

Piston rod (5)

the mechanism has finally threedegrees of freedom

Piston can rotate about z 3 -axisPiston can rotate about z3-axis and piston rod can rotate about z5-axis


Piston Design

16

Short piston with piston rod

Spherical piston with piston ring

Long piston with piston rod

Conical piston with piston rings

Synchronization by universal joint or bevel gear

Synchronization by pistons or piston rods


Design Examples

22

Driving flange bearings

Spherical valve plate

Pump control device


Design Examples

23

Conical piston

Spherical valve plate

Driving flange bearings Fixed displacement pump


Radial Piston Pumps

with external piston support with internal piston support

eccentricity

Suction

Delivery

Stroke ring

Rotating cylinder body

29

Stationary cylinder body

Rotating cam or crankshaft

Suction

Delivery

Displacement volume adjustable by changing eccentricity e


Radial Piston Pumps

30

with external piston support

Multiple stroke radial piston pumps

Stationary stroke ring

Rotating cylinder bodywith internal piston support

Stationary cylinder body

Rotating cam

Only fixed displacement pumps realizable!


Piston support on outer stroke ring

16

Stroke ring

Stroke ring Plane valve plate

Rotating cylinder body

Piston

Piston rotation enforcedby friction force Ff



17

Stroke ring borne in roller bearings

Stroke ring

Piston roller guide

Piston

Piston sliding bearing



18

Ball joint inside the piston

Slipper support Stroke ring

Hydrostaticallybalanced slipper

Hydrodynamicallybalanced slipperSlipper pocket


Stroke ring support

19

Using a sliding carriage supported using line contact

Stroke ring mounted on a pivot

Change of eccentricity by pivotingthe stroke ring about pivot axis


Design Example

Control journal

Slipper

Stroke ring

Piston

Pump control system


External gear pump

13

Basic principle

Inlet Outlet

Driving gear

Driven gear

Housing

Axial gaps between housing and the gear pair must be very small to seal thedisplacement chamber

Radial gaps between teeth addendum circle and housing

Qe = V n -Qs


Two stage gear pump

14

Driving gear

Driven gearDriven gear

Inlet 1

Inlet 2

Outlet 2

Outlet 1

Outlet 1 and inlet 2 can be connected

or the pump can have two separate outlets

p1

p2

p4

p3

p2 = p3

p1 = p3the driving gear is pressure balanced!


Internal gear pump

15

PinionInternal gear (ring gear)

Suction zonePressure zone

Crescent shaped divider

Using teeth of standard involute design requires a combination where thepinion has two or more fewer teeth than the ring gear! Pinion and ring gearare then separated by a crescent shaped divider.

Advantages:Better suction ability

Higher efficiencyMore compact designLess noise emission

Longer duration of teeth meshing leads to better sealing function


Internal gear pump

16

Many different tooth profiles have been applied in the recent past.

Crescent shaped divider


Annular gear pumps

Applying specially generated tooth curves it can be achieved, that the innerrotor (the pinion) has only one tooth less than the ring gear, thus eliminating thecrescent-shaped divider.

Gerotor pump

Each tooth of the pinion maintainscontinuous sliding contact with atooth of the ring gear, providingfluid tight engagement.

Relative sliding velocity betweenpinion and ring gear is very small

quiet operation and longservice life

Outlet Inlet

Ring gear (z2)

Pinion (z1)


Annular gear pump Orbit principle

Ring gear (z2) fixed

Displacement volume isgiven by z1 times z2 toothspaces

Multiple delivery ofeach tooth space

Rotatingdistributor

Inlet OutletRotating pinion (z1)

2 Pressure port

1 Suction port

18


Pressure compensated axial gaps

Sealing ring

Sliding bearing

Gear pair

Bearing bushings

Shaft seal

End cap Front coverhousing

Pressurized area A

Only one direction of shaft rotation possible!

FZ FZ

Axial gap


Pressure compensated axial gaps

19

Pressurized areaDriving gear

Driven gearSliding bearings

Sealing

Axial gap pressure compensated

Improved volumetric efficiency

2FZ


Pressure compensated radial gaps

Radial gap compensation

Pressurized areaAxial gap compensation

Bearing bushing

Small pressure zone achievable


Gear pump design example

Shaft seal

Bearing bushing performing a radial and axial gap compensation

Driving gear

Driven gear

inletoutlet


Internal gear pump- design example

Ring gear Pinion special shaped divider

Internal gear pump with axial and radial gap compensation

inlet

outletMoveable bearing shellPressurized area

Radial gap compensation


Screw Pumps

With two meshing screws

inlet

outlet

With two meshing screws


Screw Pumps

With three meshing screws

outlettthread pitch

inletoutlet


Vane PumpsClassification of vane pumps

Unbalanced vane pump

RotorStatorBalanced vane pump

Only fixed displacement pumpFixed and variable pump design


Vane pumps- basic working principle

37

inlet

inlet

outlet

Single stroke vane pump variabledisplacement volume

Large radial forces exerted on the rotor

Limitation of max. operating pressure (20 MPa)

Overcenter pump the direction of flow can be re-versed by change of eccentricity, i.e. without changing the direction of rotation of the drive shaft

outlet

no flow!Relatively high friction between axial moveable vanes and rotor

&between vanes and stator


Vane pumpsclassification

Multiple stroke vane pump

Rotor

Rigid vane pump


Fluid distribution

Internal fluid distributionExternal fluid distribution

inlet

outlet

Distributor - fixed control journal

rotor

stator


Rigid vane pump

vane

Rotor

Stator ringDisplacement volume:

1st rotor 2nd rotor

Pulsation free flow

ME597-lecture5-13

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