Post on 15-Jul-2015
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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