Automotive Transmission

U5AUA11 By. B.HARISH BABU asst.prof ,vtu.

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 drivingwheels to drive the vehicle on the road.

4

Requirement of Transmission System

• To provide for disconnecting the engine from thedriving wheels

• When engine is running , connect the drivingwheels to engine smoothly without shock

• Leverage between engine and driving wheels tobe varied

• Enable the driving wheels to rotate at differentspeeds.

• Provide relative movement between engine anddriving 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

ClutchRequirement 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 toclutch cover assembly.

• Clutch Cover assembly is bolted tothe flywheel.

• Clutch springs placed betweenPressure plate & Cover plate, pressthe Pressure plate against theclutch plate.

• Thus Clutch plate is squeezedbetween 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 orHydraulic)

- Actuation spring (Helicalor Diaphragm)

• Centrifugal clutch

11

Clutch Engaged & Disengaged• Clutch is always is in

engaged state.

• It can be disengaged bypressing of Clutch pedal.

Disengagement is effectedby non - contact of Clutchplate both with Flywheelface & Pressure plate face.

• Frictional heat isdissipated by openingspresent in Clutch housing& Cover

12

Clutch Material

13

Need of Gear Box

14

Gear Box• Gear box varies the leverage

(speed ratio & hence torqueratio) between the engine &driving wheels.

• It is located between Clutch &Propeller shaft.

• It is provided with either 4speed or 5 speed ratios or more

depending on design.

• Gear ratio is varied by Gearshift 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 toengage them.

• The two elements are friction clutch and toothedclutch.

• Lock the positive engagement until speeds aresynchronized .

• Establish the positive engagement and power flow.

• Synchronizer is splined on the shaft Cone on thegear (blue) fits into cone-shaped area in the collar.

• Friction between the cone and collar synchronizethe collar & gear.

• The outer portion of the collar (sleeve) then slidesso that the dogteeth engage the gear.

17

Synchromesh Gearbox

1.I speed gear2.II speed gear

3.main shaft4.outer engaging unit5.inner engaging unit

6.top gear engaging teeth7.main drive gear

8.top gear synchronizing cones9.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 theclutch pedal

• This operates a single clutch, which disconnects theengine from the gearbox and interrupts power flow to thetransmission

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

• Devices called synchronizers match the gears beforethey are engaged to prevent grinding

• Once the new gear is engaged, the driver releases theclutch 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 withmanufacturing infrastructure

• Gives control to the driver

• But driver comfort an issue with increasing trafficdensity

Hence automation must be considered

20

Automated Manual Transmission (AMT)• Automation of

Clutch and Gearshifting operations

• Elimination of ClutchPedal

• Modification of GearShifting lever

• Minimummodifications inmanual transmission

21

AMT Features• Automation of Clutch operation and Gearshifting.

• Clutch slip control during starting

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

• Necessary fail safe systems such as suddenshifting 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 isin neutral position

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

- When engine speed exceeds a specified rpm, ECUengages clutch gradually

• Vehicle Start

- On pressing the accelerator pedal, ECU controlsthe clutch

- actuator travel and clutch engagement

24

Clutch Actuation Control• Gear Change

- While engaging the clutch after gearshift, the ECU determines clutch actuatortravel based on shifted gear position andaccelerator pedal stroke

• Clutch disengagement

- While gear shifting and when acceleratorpedal is released,

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

disengages clutch

25

Advantages of AMT• Reduced driver effort

• Improved Clutch life

• Utilization of existing manufacturing facilitiesfor manual transmission

• Lower production cost than automatictransmissions

• Higher efficiency than automatictransmissions

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 thehousing via oil-tight seals.

• The input turbine is connected to the powersupply, typically an electric or ICE.

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

• Mineral oil is used

28

Fluid Coupling: Working• Standstill

- The entire operating fluid in thecoupling 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 istransmitted. Large degree of slip inthe unit. O/p shaft is rotating slowlythan input shaft.

• Medium to High Speed- Oil force is sufficient to transmit full

power. O/p shaft rotating at about98% 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 ConvertorVehicle 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 alsoconnected to Multi-disk clutch

• Sun gear is connected to a Drum(Yellow), which can be lockedby brake band (Red). It is also connected to the other half ofClutch

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

Planetary Gear System: Operation

• 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

Planetary Gear System: Operation• In High Gear (Direct drive)

• Band is released.• Lock any two members

• Clutch is engaged so that the sun gear and planetcarrier 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

Planetary Gear System: Operation

• 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 improvementsBetter control algorithms

Torque converter lock up

Most useable transmissions based on a couple of

standard arrangementsRavigneaux

Lepelletier

42

Continuously Variable Transmission(CVT)

• CVT provides infinitenumber of gear ratios

(between a minimum & amaximum).

• Shifts automatically with aninfinite number of ratios

• Seamless powerdelivery, no torque

interruption & power loss

43

CVT: Construction

Uses a pair of axiallyadjustable sets of

pulley halves(Variators)

Both pulleys have onefixed and oneadjustable pulley halve

A “belt” is used totransfers the engine'spower from one shaft

to another

44

CVT: Functioning• The transmission ratio is varied by

adjusting the spacing between thepulleys in line with the circumference

of the tapered pulley halves.• The variators are adjusted

hydraulically.

• When one pulley is varied, the otherpulley must adapt itself inversely sincethe 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 clutchpedal. 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 withoutinterrupting 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 steelend fittings- Renault)

Cold rolled and seamwelded

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 engineto 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 topspeed

• Torque carrying capacity requirements

• Plunge requirements (suspension travel)

• Assembly requirements

52

Universal joints• Designed to eliminate

torque and speedfluctuations (constant

velocity joints)

• If only one universal joint isused, speed fluctuationswill not be neutralized.

• To maintain uniformmotion, two universal jointsare used with yoke lugs in

phase.

53

Universal joints

54

Hooke s Joint‟

Condition for Constant velocity drive with two Hooke’s joint55

Differential• To transfer the

engine power to thewheels

• To act as the finalgear reduction inthe vehicle

• To make the wheelsto rotate at different

speeds whilenegotiating a turn.

56

Differential: In Straight Ahead Motion

Input torque is applied tothe ring gear, which turns

the entirecarrier, providing torqueto both side gears, whichin turn may drive the leftand right wheels.

If the resistance at bothwheels is equal, thepinion gear does not

rotate, and both wheelsturn at the same rate.

57

Differential: In a Turn

• If the left side gear(red) encounters

resistance, the piniongear(green) rotatesabout the left sidegear, in turn applyingextra rotation to the

right side gear(yellow).

58

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

Changes torsional direction from longitudinal totransverse

Provides speed reduction and torquemultiplication

Provides a differential action to permit vehiclecornering

Provides mounting points for suspension andbrakes

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 TrendPassenger Car Transmission in India

Manual transmission is more dominant in India as compared to other types oftransmissions. 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 T’s.

Source: Mahr GmbH, Germany

Global Transmission TrendEstimated global market share (%) for passenger car transmission types

1%

46%

1% 2%

6%MT

AT

50% CVT

4% 2%

47%

MT

AT

CVTDCT 41% DCT

AMT AMT

2005 2010

3%

7% 10%

43%

37%

MT

AT

CVT

DCT

AMT

2015

Requirements of the TransmissionDesign Process

Product Life Cycle

• Product Life Cycle must be developed to deliverCompany goals

New Product Introduction

Feasibility Studies/New Concepts

PrototypeTransmission Production Ready

Design Development Transmission

Manufacturing,Product support

anddevelopment

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 knowledgeProduct Design Specification Standards

Load data Customer specific requirements

(PDS)

- The PDS contains all the specification data and designtargets

• This document should be approved before work startson concept design

- The PDS is a „live document‟• This means that changes can be made to it, providingall parties agree to them

66

Project Set UpTo be included in the Product Design Specification:

• Understanding the customerneeds/wants from -

- Customer PDS(Vehicle/Transmission)

- Market Understanding

- Prior Design Experience

• General Requirements

- Number of gear ratios and theirvalues

- Packaging envelope constraints

- Weight

- Application specifics

- Duty cycle

- Interfaces

• Gear ratio must be defined.

• Special considerations

- Review all validation testingfor unusual manoeuvres

• Rig

• Vehicle• Special environmental operation

conditions, eg:

- Very high or very low ambienttemperature conditions

- Extremely tight vehiclepackaging space

• Special operational cycles, eg:

- Unusual off-road usage- Occasional vehicle overload

operation

67

Project Set Up• To be included in the Product Design Specification:

- 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 UpTo be included in the Product Design Specification:

• Design Loads & Duty Cycles

- A design load case may be comprised of a series of loads andcycles/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 engineapplication: 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 generallybased 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 loadcaseMaterial

PropertiesOperatingConditions

SelectRequiredReliability

ComponentGeometry

AppliedLoads (Duty

Cycle)

Analysis topredictstress

Operating Analysis toStresses predict life

70

Project Set Up: Duty Cycle• 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

- “Miner s 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

Project Set Up: Duty Cycle• In-service Loads must be converted into a dutycycle for design and testing

DurabilityIn-Service Loads

Time/torquehistory for the 95th

centile

CalculationTo derive the

damage for eachcomponent in the

transmission

Design Duty CycleEquivalent duty cycle

appropriate fortransmission design

Test Duty CycleEquivalent duty

cycle appropriatefor rig testing

72

Concept Design

• Activities within Concept Design (part A)

Inputs fromPDS:

•Gear rat ios•Engine

torque andduty cycle

•3Dpackaging

space

Design gearteeth andblanks anddog teeth

Createinitial

gearboxconcept

Synchroniserdesign, sizingand

packaging

I terat ive Designof the GearboxConcept

Splinedesign

andrating

Canratios

andpackagin

g beachieved

?No

Yes Output:Proposedconceptlayout

Define Defineshaft rollersections bearings

73

Concept Design• Generation of Design Options (Layouts/ Topology)

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

Option A Option B Option C

Option D Option E Option F

74

Concept DesignIterative 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 torqueratio

- Bearings• Durability

• Misalignment targets

- Spline• Stress

75

Concept Design• Activities within Concept Design (part B)

CasingDesign andDifferent ial

Proposed Concept LayoutShif t

MechanismCheck for compatibi l i tywith other componentsand with vehicle

packaging; Check forAssembly

Iterate on i tems defined inConcept Design Part A if

necessary

CompletedConceptDesign

Rank againstPDS, other

designs

• Once the concepts have been modelled and analysed, their strengthsand 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 thespecification

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

• Determine what objective measures can be takenfrom concept model

• Weight

• Number of parts

• Safety factors

77

Concept Selection

• Concept scoring• Assign a score to each concept according to theextent to which it meets each requirement

• Multiply each score by the appropriate weightingfactor

• The best scoring concept will then form the basis forthe detail design

78

Detailed DesignActivities within Detailed Design

• Focus on system deflections and gear micro-geometrydesign

DifferentialDetail ing

Gear Micro-geometry Design

Completed

Completed Concept Design Casing Detail ing

Detai led Design andAnalysis of Other

Components;Lubrication system

FE, System Deflectionand Gear ToothContact Detailed

Analysis

Check forcompatibi l i ty withother components

DetailedDesign, al l

NominalDimensionsComplete

Iterate on Concept DesignParts A and B i f necessary

79

Detailed Design

• Calculation of System Deflections

Loaddistribution

Shaftdeflection

Load distributionfactor

ContactStress

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 affectother 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 gearboxperformance

- Some parameters are needed to define otherparameters

- 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

• Hierarchy of Design Parameters- Other parameters have a smaller effect on gearboxperformance

- They are dependent on preceding parameters beingdefined

- e.g. gear micro-geometry

Gear centre distance

Housing designand stiffness

Gear tangential load

Gear tooth contactand transmission

error

Gear misalignment

Gear macro-geometry

Gear micro-geometry

Analysis Methods

• Hierarchy of Design Parameters- Other parameters have little effect on thegearbox performance- They can be estimated

- e.g. seal design

Shaft design

Sealdesign

Gearbox packaging

Engineering Drawings and Tolerancing

• Activities within Engineering Drawings and Tolerancing

- Major issues should be resolved

Complete Drawings

Completed Detailed Design

ConfirmMaterial

Specif ication

Identify AllTolerance

Stack Loops

Define Tolerances

for Components. Sub-Assembly and General

Arrangement, withAssembly Instructions

Carry out alltolerance stackcalculation and

assess

I f tolerance stacks aproblem, adjust

tolerances ifnecessary

If major problemiterate on Detai ledDesign if necessary

DeliverCompletedDrawings

86

Engineering Drawings and Tolerancing

• Applying Manufacturing Tolerances- Tolerances applied to components based onknowledge of manufacturing process

• e.g. turning, grinding etc

- Functionally critical features identified

- Initial tolerances applied based on experience

• These will be updated during the toleranceanalysis

87

Engineering Drawings and Tolerancing• Tolerance Stacks

Identifychecks required

Create masterdimension sheet

Create tolerancestacks for eachshaft assembly

Check result No

Yes

Create tolerancestacks for shaft to

shaft clearances

Gear and shaftdeflections from

analysis

Revise dimensionson master No

dimension sheet

No

Check result Yes

Final design

Yes

Check result

Create housingtolerance stacks

88

Engineering Drawings and TolerancingPotential 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

Engineering Drawings and TolerancingPotential 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 systemdeflections, at all tolerances, thermal extremes etc.

• Bill of Materials and material selection list confirmed

• 3D models complete with all components defined to nominaldimensions

• 2D drawings of all components defined with tolerances

• 2D drawings of sub-assemblies and assemblies, withassembly instructions

91

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