Auto 5sem ATE

Automotive Transmission

UNIT I

Contents

Introduction

Transmission Systems

Manual

Automated Manual Automatic

Continuously variable Dual Clutch

Propeller Shaft

2

Contents

Universal joints Differential

Requirements of the Transmission Design Process

Product Life Cycle

Stages in the Design Process

Project Set Up

Concept Design

Detailed Design

Engineering Drawings and Tolerancing

3

Transmission System

Function of transmission:

- It is used to transmit engine torque to the driving wheels to drive the vehicle on the road.

4

Requirement of Transmission System

To provide for disconnecting the engine from the driving wheels

When engine is running , connect the driving wheels to engine smoothly without shock

Leverage between engine and driving wheels to be varied

Enable the driving wheels to rotate at different speeds.

Provide relative movement between engine and driving wheels

5

Transmission System - Layout

6

Transmission Types

7

Clutch

Function of clutch

Clutch is used to disengage and engage the engine with rest of the transmission systems.

To disengage while starting the engine and while changing gear ratio.

To engage after starting of the engine and gear shift operation.

8

Clutch

Requirement of Clutch

Transmit maximum torque of the engine.

Engage gradually to avoid sudden jerks.

Dissipate maximum amount of heat.

Damp the vibrations and noise.

Dynamically balanced.

As small as possible.

Easy to operate.

9

Clutch Unit

Flywheel also acts as a driving member

Pressure plate is connected to clutch cover assembly.

Clutch Cover assembly is bolted to the flywheel.

Clutch springs placed between Pressure plate & Cover plate, press the Pressure plate against the clutch plate.

Thus Clutch plate is squeezed between Flywheel & Pressure plate.

Classification of Clutch

Cone clutch

Flat Plate clutch

- Dry or Wet type clutch

- No. of friction plates (Single or Multiple)

- Actuation mode (Cable or Hydraulic)

- Actuation spring

(Helical

or Diaphragm)

Centrifugal clutch

11

Clutch Engaged & Disengaged

Clutch is always is in

engaged state.

It can be disengaged by pressing of Clutch pedal.

Disengagement is effected

by non - contact of Clutch

plate both with Flywheel face & Pressure plate face.

Frictional

heat

is

dissipated by openings

present in Clutch housing & Cover

12

Clutch Material

13

Need of Gear Box

14

Gear Box

Gear box varies the leverage (speed ratio & hence torque ratio) between the engine & driving wheels.

It is located between Clutch & Propeller shaft.

It is provided with either4

speed or 5 speed ratios or more

depending on design.

Gear ratio is varied by Gear shift lever.

15

Manual Transmission - Types

16

UNIT II

Synchronizers

A device used to bring two adjacent members to the same speed before allowing the sleeve to engage them.

The two elements are friction clutch and toothed

clutch.

Lock the positive engagement until speeds are

synchronized .

Establish the positive engagement and power flow.

Synchronizer is splined on the shaft Cone on the

gear (blue) fits into cone-shaped area in the collar.

Friction between the cone and collar synchronize the collar & gear.

The outer portion of the collar (sleeve) then slides so that the dogteeth engage the gear.

17

Synchromesh Gearbox

1.I speed gear

2.II speed gear

3.main shaft

4.outer engaging unit

5.inner engaging unit

6.top gear engaging teeth

7.main drive gear

8.top gear synchronizing cones

9.counter shaft

18

How Manual Transmission Work?

When a driver wants to change from one gear to another in a standard stick-shift car, he first presses down the clutch pedal

This operates a single clutch, which disconnects the engine from the gearbox and interrupts power flow to the transmission

Then the driver uses the stick shift to select a new gear, a process that involves moving a toothed collar from one gear wheel to another gear wheel of a different size

Devices called synchronizers match the gears before they are engaged to prevent grinding

Once the new gear is engaged, the driver releases the clutch pedal, which re-connects the engine to the

gearbox and transmits power to the wheels.

19

Manual Transmission

Cheap to make

Durable, efficient

Easy to install

Established in marketplace and with manufacturing infrastructure

Gives control to the driver

But driver comfort an issue with increasing traffic density

Hence automation must be considered

20

Automated Manual Transmission (AMT)

Automation

of

Clutch and Gear

shifting operations

Elimination of Clutch Pedal

Modification of Gear Shifting lever

Minimum

modifications

in

manual transmission

21

AMT Features

Automation of Clutch operation and Gear shifting.

Clutch slip control during starting

Hill start aid system which will assist the driver in hold and move the vehicle in hill slope

Necessary fail safe systems such as sudden shifting from higher gear to lowest gear and vice

versa

22

System Block Diagram

23

Clutch Actuation Control

Engine Start

- Starter should be operated only when the gear is in neutral position

- When engine is not running and in power on, ECU will disengage clutch

- When engine speed exceeds a specified rpm, ECU engages clutch gradually

Vehicle Start

- On pressing the accelerator pedal, ECU controls the clutch

- actuator travel and clutch engagement

24

Clutch Actuation Control

Gear Change

- While engaging the clutch after gear shift, the ECU determines clutch actuator

travel based on shifted gear position and accelerator pedal stroke

Clutch disengagement

- While gear shifting and when accelerator pedal is released,

- if the vehicle speed is lower than a set speed for select gear position, the ECU

disengages clutch

25

Advantages of AMT

Reduced driver effort

Improved Clutch life

Utilization of existing manufacturing facilities for manual transmission

Lower production cost than automatic transmissions

Higher efficiency than automatic transmissions

26

Automatic Transmission (AT)

Conventional Definition

Moving away from rest - Torque converter

Achieving ratio change - Planetary gear sets

No power interruption

Mechanism for ratio change

- Wet plate clutches and brakes

Control of ratio change

- Normally automatic timing and actuation

27

Fluid Coupling

Converts or transmits rotating mechanical energy or power.

Basic components.

- outer shell or housing,

- impeller or pump and turbine or runner

Both of these units are contained within the housing via oil-tight seals.

The input turbine is connected to the power supply, typically an electric or ICE.

The output turbine is connected to the drive train of the vehicle or the drive system of a machine.

Mineral oil is used

28

Fluid Coupling: Working

Standstill

- The entire operating fluid in the coupling is at rest

Idling

- In sufficient centrifugal force for the oil to turn the turbine

Low to medium speed:

- Centrifugal force pushes oil into turbine and some turning effort is transmitted. Large degree of slip in the unit. O/p shaft is rotating slowly than input shaft.

Medium to High Speed

- Oil force is sufficient to transmit full power. O/p shaft rotating at about 98% of speed of I/p shaft (2% slip).

29

UNIT III

Torque Convertor

Serves as automatic clutch which transmits engine torque to the transmission input shaft

Multiplies torque generated by the engine

Absorbs torsional vibration of engine

Acts as a flywheel and smoothes out engine rotation

Drives oil pump

A torque converter consists of

- Impeller

- Turbine

- Stator

- and transmission fluid

30

Torque Convertor - Sectional View

31

Impeller

32

Turbine

33

Stator

34

Working of Torque Convertor

Vehicle accelerates

35

Planetary Gear System

36

Planetary Gear System: Construction

Input shaft is connected to Ring gear(Blue)

Output shaft is connected to Plane carrier(Green) which is also connected to Multi-disk clutch

Sun gear is connected to a Drum(Yellow), which can be locked by brake band (Red). It is also connected to the other half of Clutch

37

Planetary Gear System: Operation

In Neutral

Both band and clutch sets are released

Planets assembled to carrier with NRB

Ring gear only drive planet gear not the planet carrier

(Output shaft)

The planet gears drive the sun gears to spin freely

38


In Low Gear (forward reduction)

Band locks the sun gear by locking the drum

Planets walk around the sun gear

Planet carrier to spin in same direction as ring gear

Gear ratio= sun & ring teeth/no of teeth of ring gear

39


In High Gear (Direct drive)

Band is released.

Lock any two members

Clutch is engaged so that the sun gear and planet carrier is locked to act as a rigid member

Planets has to walk around the ring gear,

Ring Gear (Input shaft) will spin at the same speed as the Planet Carrier (Output shaft)

40


Reverse Gear

Planet carrier is locked

Ring gear (Input shaft) will cause the sun gear (Output Shaft) to turn in the opposite direction

41

UNIT IV

Automatic Transmission (AT)

Advantages

The only option for comfortable automatic shifting Cost issue mitigated by high volume manufacturing

Disadvantages

Cost for development and manufacturing Fuel economy due to torque converter

Lack of control by the driver

Modern improvements

Better control algorithms Torque converter lock up

Most useable transmissions based on a couple of standard arrangements

Ravigneaux

Lepelletier

42

Continuously Variable Transmission

(CVT)

CVT provides infinite number of gear ratios

(between a minimum & a maximum).

Shifts automatically with an infinite number of ratios

Seamless power

delivery, no torque

interruption & power loss

43

CVT: Construction

Uses a pair of axially adjustable sets of

pulley halves

(Variators)

Both pulleys have one fixed and one

adjustable pulley halve

A belt is used to

transfers the engine's power from one shaft

to another

44

CVT: Functioning

The transmission ratio is varied by adjusting the spacing between the

pulleys in line with the circumference

of the tapered pulley halves.

The

variators

are

adjusted

hydraulically.

When one pulley is varied, the other pulley must adapt itself inversely since the length of the belt is fixed.

Dual Clutch Transmission (DCT)

46

DCT: Construction

Basic Dual Wet Clutch

How DCT Works?

In a conventional manual transmission, there is not a continuous flow of power from the engine to the wheels. Instead, power delivery changes from ON to OFF to ON during gearshift, causing a phenomenon known as "shift shock" or

"torque interrupt

A dual-clutch transmission uses two clutches, but has no clutch pedal.

Sophisticated electronics and hydraulics control the clutches, just as they do in a standard automatic transmission. In a DCT, however, the clutches operate independently One clutch controls the odd gears(first, third, fifth and reverse), while the other controls the even gears (second, fourth and sixth)

Using this arrangement, gears can be changed without interrupting the power flow from the engine to the transmission

49

Propeller Shaft

Single piece

Two piece

Front engine rear wheel drive Reduction in car height (lowering of body)

Crash energy management Material

Aluminum steel

Composite (75% carbon, 25% glass-fibre with bonded steel end fittings- Renault)

Cold rolled and seam welded

50

Propeller Shaft

It propels the vehicle forward, so called propeller shaft

A Propeller Shaft connects a gearbox to a Differential.

It is used to transmit the drive force generated by the engine to the axles.

It is strong enough to handle maximum low gear torque

It is provided with two U-joints to maintain constant velocity and positioning of differential at different plane.

It is provided with a slip joint to take care of the change in length.

Shaft diameter and its thickness decides the torque carrying capacity and angle of operation.

51

Propeller Shaft

Design requirements

Critical speed is at least 15% above top speed

Torque carrying capacity requirements

Plunge requirements (suspension travel)

Assembly requirements

52

Universal joints

Designed to eliminate

torque

and

speed

fluctuations

(constant

velocity joints)

If only one universal joint is used, speed fluctuations will not be neutralized.

To

maintain

uniform

motion, two universal joints

are used with yoke lugs in

phase.

53

Universal joints

54

Hookes Joint

Condition for Constant velocity drive with two Hookes joint

55

Differential

To

transfer

the

engine power to the

wheels

To act as the final gear reduction in the vehicle

To make the wheels to rotate at different

speeds

while

negotiating a turn.

56

Differential: In Straight Ahead Motion

Input torque is applied to

the ring gear, which turns

the

entire

carrier, providing torque to both side gears, which in turn may drive the left and right wheels.

If the resistance at both wheels is equal, the pinion gear does not

rotate, and both wheels

turn at the same rate.

57

Differential: In a Turn

If the left side gear

(red)

encounters

resistance, the pinion gear(green) rotates about the left side gear, in turn applying extra rotation to the

right

side

gear

(yellow).

58

Axle

Transmits rotary motion and torque from the engine-transmission-driveshaft to the wheels

Changes torsional direction from longitudinal to transverse

Provides speed reduction and torque multiplication

Provides a differential action to permit vehicle cornering

Provides mounting points for suspension and brakes

59

Transmission Troubleshooting

Leaking Transmission Fluid

Slipping of Transmission

Damaged Transmission Fluid

Surging of Transmission

Gear Problems

Fluid Leaking

Spilling out of Fluid

Erratic Gear Shifting

Overheating of Transmission

60

Transmission Trend

Passenger Car Transmission in India

Manual transmission is more dominant in India as compared to other types of transmissions.

Majority of the MT are using 5speed GB as compared to 6 speed GB.

But many of the luxurious car manufactures are now using AMT or Ts.

Source: Mahr GmbH, Germany

Global Transmission Trend

Estimated global market share (%) for passenger car transmission types

1%

46%

1%

2%

6%

MT

AT

50%CVT

4%

2%

47%

MT

AT

CVT

DCT

41%

DCT

AMT

AMT

2005

2010

3%

7%10%

43%

37%

MT

AT

CVT

DCT

AMT

2015

Requirements of the Transmission Design Process

Product Life Cycle

Product Life Cycle must be developed to deliver Company goals

New Product Introduction

Feasibility Studies/

New Concepts

Prototype

TransmissionProduction Ready

DesignDevelopmentTransmission

Manufacturing,

Product support and

development

Market feedback, Market research,

Technical Development, Application experience

Research

64

Stages in the Design Process

Timeline

Project set up

Concept design

Detail design

Tolerancing & drawings

Prototype testing

65

UNIT V

Project Set Up

- The first stage of the design process is to set targets Market research

Existing product knowledge

Product Design Specification

Standards

Load data Customer specific requirements

(PDS)

- The PDS contains all the specification data and design targets

This document should be approved before work starts on concept design

- The PDS is a live document

This means that changes can be made to it, providing all parties agree to them

66

Project Set Up

To be included in the Product Design Specification:

Understandingthecustomer

needs/wants from -

- Customer PDS

(Vehicle/Transmission)

- Market Understanding

- Prior Design Experience

General Requirements

- Number of gear ratios and their values

- Packaging envelope constraints

- Weight

- Application specifics

- Duty cycle

- Interfaces

Gear ratio must be defined.

Special considerations - Review all validation testing

for unusual manoeuvres Rig

Vehicle

Special environmental operation conditions, eg:

- Very high or very low ambient temperature conditions

- Extremelytightvehicle

packaging space

Special operational cycles, eg: - Unusual off-road usage

- Occasional vehicle overload operation

67

Project Set Up


- It may not be possible to meet all requirements, so define the hierarchy of importance, normally (approximately):

Packaging within the vehicle

Assemble-ability

Durability

Ratio

Weight

Cost

Gear shift quality

Noise

68

Project Set Up


Design Loads & Duty Cycles

- A design load case may be comprised of a series of loads and cycles/time at those loads combined into a duty cycle definition

Design loads are typically modified somewhat

- Maximum net engine output torque including

Reserve capacity for enhanced engine torque or larger engine application: 0% to 10% typical

Factor for unusually high engine torsionals output: 0% to 5% typical

- Maximum vehicle skid torque

Max skid torque in each gear for operation on dry, new concrete

Usually only significant in lowest ratios (eg: 1st, Reverse)

- Maximum transient overload torque (static overload only)

Factors vary according to specific vehicle and are generally based off of historical vehicle test results

Typical values range from 1.5x to 2.5x maximum engine torque

69

Project Set Up: Duty Cycle

A key component of the targets is the Duty Cycle.

What is a Duty Cycle?

- Calculation of Component Reliability - single loadcase

Material

Properties

Operating

Conditions

Select

Required Reliability

Component

Geometry

Applied

Loads (Duty Cycle)

Analysis to

predict

stress

OperatingAnalysis to

Stressespredict life

70


A Duty Cycle is a collection of loadcases

- All automotive transmissions are loaded with multiple loadcases

- Multiple ratios

- Different torque levels for each ratio

10%, 20%, 30% 100% torque

Accounting for Multiple-loadcases - Damage

- Miners Rule (Linear Damage Hypothesis)

To combine the effect of different loadcases

Damage Fraction & Percentage

We need to account for the effect of these many loadcases

71


In-service Loads must be converted into a duty cycle for design and testing

Durability

In-Service Loads

Time/torque

history for the 95th centile

Calculation

To derive the

damage for each

component in the transmission

Design Duty Cycle

Equivalent duty cycle appropriate for

transmission design

Test Duty Cycle

Equivalent duty

cycle appropriate

for rig testing

72

Concept Design

Activities within Concept Design (part A)

Inputs from

PDS:

Gear ratios

Engine

torque and duty cycle

3D

packaging

space

Design gear teeth and blanks and dog teeth

Create

initial

gearbox

concept

Synchroniser design, sizing and

packaging

Iterative Design of the Gearbox Concept

Spline

design

and

rating

Can

ratios

and

packagin

g be

achieved

?

No

YesOutput:

Proposed

concept

layout

Define

Define

shaft

roller

sections

bearings

73

Concept Design

Generation of Design Options (Layouts/ Topology)

- Create as many different design layouts as possible to meet the ratio and packaging requirements

Option A

Option B

Option C

Option D

Option E

Option F

74

Concept Design

Iterative Design, Analysis and Optimisation, by CAE:

- Gears

Tooth numbers

Rating to ISO 6336

Contact Ratio targets

Misalignment targets

- Shaft

Durability

Deflection

- Synchronizers

Shift force

Cone to index torque ratio

- Bearings

Durability

Misalignment targets

- Spline

Stress

75

Concept Design

Activities within Concept Design (part B)

Casing

Design and Differential

Proposed Concept Layout

Shift

Mechanism

Check for compatibility with other components

and with vehicle packaging; Check for

Assembly

Iterate on items defined in Concept Design Part A if

necessary

Completed

Concept

Design

Rank against

PDS, other

designs

Once the concepts have been modelled and analysed, their strengths and weaknesses can be evaluated

The selected concept will then form the basis for the detailed design

76

Concept Selection

Evaluation criteria

List all the requirements for the design from the specification

Apply a weighting importance to each requirement (e.g. 1-5)

Determine what objective measures can be taken from concept model

Weight

Number of parts

Safety factors

77

Concept Selection

Concept scoring

Assign a score to each concept according to the extent to which it meets each requirement

Multiply each score by the appropriate weighting factor

The best scoring concept will then form the basis for the detail design

78

Detailed Design

Activities within Detailed Design

Focus on system deflections and gear micro-geometry design

Differential Detailing

Gear Micro-

geometry Design

Completed

Completed Concept Design

Casing Detailing

Detailed Design and Analysis of Other

Components; Lubrication system

FE, System Deflection and Gear Tooth

Contact Detailed Analysis

Check for

compatibility with other components

Detailed Design, all

Nominal

Dimensions Complete

Iterate on Concept Design Parts A and B if necessary

79

Detailed Design

Calculation of System Deflections

Load

distribution

Shaft

deflection

Load distribution factor

Contact

Stress

Stress

Calculation of Durability

80

Detailed Design

Accurate analysis is required to determine whether targets are met

Simple methods do not give accurate results

- Increased risk of problems later in product life cycle

- Lack of clear direction for optimisation

Detailed analysis methods have their own issues

- Many design options

- Do we have to calculate everything before we make a decision?

- How do we manage these methods in the design process?

81

Analysis Methods

Principles

- Hierarchy of design parameters

Understand how design parameters affect other design parameters and transmission

performance

Understand the

hierarchy of design

parameters

Define the most important ones first

Analysis Methods

Hierarchy of Design Parameters

- Some parameters have a big effect on gearbox performance

- Some parameters are needed to define other parameters

- e.g. gear centre distance

Gear centre distance

Gear tangential load

Gear stress

Gear durability

Bearing load

Bearing durability

Housing design

Housing stiffness

Gear misalignment

Analysis Methods


- Other parameters have a smaller effect on gearbox performance

- They are dependent on preceding parameters being defined

- e.g. gear micro-geometry

Gear centre distance

Housing design and stiffness

Gear tangential load

Gear tooth contact and transmission

error

Gear misalignment

Gear macro-geometry

Gear micro-geometry

Analysis Methods


- Other parameters have little effect on the gearbox performance

- They can be estimated

- e.g. seal design

Shaft design

Seal

design

Gearbox packaging


Activities within Engineering Drawings and Tolerancing

- Major issues should be resolved

Complete Drawings

Completed Detailed Design

Confirm

Material

Specification

Identify All

Tolerance Stack Loops

Define Tolerances

for Components. Sub- Assembly and General

Arrangement, with Assembly Instructions

Carry out all tolerance stack calculation and

assess

If tolerance stacks a problem, adjust

tolerances if necessary

If major problem

iterate on Detailed Design if necessary

Deliver

Completed

Drawings

86


Applying Manufacturing Tolerances

- Tolerances applied to components based on knowledge of manufacturing process

e.g. turning, grinding etc

- Functionally critical features identified

- Initial tolerances applied based on experience

These will be updated during the tolerance analysis

87


Tolerance Stacks

Identify

checks required

Create master dimension sheet

Create tolerance

stacks for each

shaft assembly

Check resultNo

Yes

Create tolerance stacks for shaft to

shaft clearances

Gear and shaft deflections from

analysis

Revise dimensions on masterNo

dimension sheet

No

Check resultYes

Final design

Yes

Check result

Create housing

tolerance stacks

88


Potential Problems

Form and functionality at tolerance extremes

- Symptom (example):

At tolerance extremes, transmission does not assemble or there is a foul (at zero load)

- Action:

Small iteration: Redefine the tolerances

Large iteration: Nominal dimensions are redefined

89


Potential Problems

Form and functionality at tolerance, temperature extremes, under load

- Symptom (example): Transmission does not assemble or there is a foul at:

Tolerance extremes

Temperature extremes

Load (i.e. deflected shapes)

- Example: Gears clash due to thermal expansion and axial movement due to compliance of

bearings, housing etc.

- Action (as before)

90

Output of Design Process

A layout that satisfies the key requirements of the PDS

All durability targets are met, including the effect of system deflections, at all tolerances, thermal extremes etc.

Bill of Materials and material selection list confirmed

3D models complete with all components defined to nominal

dimensions

2D drawings of all components defined with tolerances

2D drawings of sub-assemblies and assemblies, with

assembly instructions

91

THANK YOU

*

Auto 5sem ATE

Documents

Transcript of Auto 5sem ATE