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 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
or Diaphragm)
(Helical
• 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 either
4
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
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 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
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 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
Hooke‟s Joint
Condition for Constant velocity drive with two Hooke’s 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 T’s.
Source: Mahr GmbH, Germany
Global Transmission Trend
Estimated global market share (%) for passenger car transmission types
1%
1% 2%
4%
6%
2%
MT
MT
AT
50%
AT
47%
CVT
DCT
46%
41%
AMT
DCT
AMT
2005
2010
3%
7%
CVT
MT
10%
43%
AT
CVT
37%
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
Transmission
Design
Development
Production Ready
Transmission
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
Standards
Load data
Customer specific requirements
Product Design Specification
(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:
• Understanding
the
needs/wants from -
customer
- 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
• Special considerations
- Review all validation testing
for unusual manoeuvres
• Rig
• Vehicle
• Special environmental operation
conditions, eg:
- Very high or very low ambient
temperature conditions
- Extremely
tight
vehicle
packaging space
• Special operational cycles, eg:
- Unusual off-road usage
- Occasional vehicle overload
operation
• Gear ratio must be defined.
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 Up
To be included in the Product Design Specification:
• 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
Analysis to
predict
stress
Operating
Stresses
Analysis to
predict life
Applied
Loads (Duty
Cycle)
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 duty
cycle for design and testing
In-Service Loads
Time/torque
history for the 95th
centile
Durability
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
Spline
design
and
rating
Iterative Design
of the Gearbox
Concept
Define
shaft
sections
Define
roller
bearings
Can
Yes Output:
ratios
Proposed
and
concept
packagin
layout
g be
achieved
?
No
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 D
Option B
Option E
Option C
Option F
74
Concept Design
Iterative Design, Analysis and Optimisation, by CAE:
- Gears
• Tooth numbers
• Rating to ISO 6336
• Contact Ratio targets
• Misalignment targets
- Synchronizers
• Shift force
• Cone to index torque
ratio
- Bearings
- Shaft
• Durability
• Deflection
• 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
Completed Concept Design
Casing Detailing
Detailed Design and
Analysis of Other
Components;
Lubrication system
Gear Microgeometry Design
FE, System Deflection
and Gear Tooth
Contact Detailed
Analysis
Completed
Detailed
Design, all
Nominal
Dimensions
Complete
Check for
compatibility with
other components
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
parameters
„hierarchy‟ of design
• 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
Bearing load
Housing design
Housing stiffness
Gear durability
Bearing durability
Gear misalignment
Analysis Methods
• Hierarchy of Design Parameters
- 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
Gear tangential load
Gear tooth contact
and transmission
error
Housing design
and stiffness
Gear misalignment
Gear macro-geometry
Gear micro-geometry
Analysis Methods
• Hierarchy of Design Parameters
- Other parameters have little effect on the
gearbox performance
- They can be estimated
Shaft design
- e.g. seal design
Seal
design
Gearbox packaging
Engineering Drawings and Tolerancing
• Activities within Engineering Drawings and Tolerancing
- Major issues should be resolved
Confirm
Material
Specification
Completed Detailed Design
Identify All
Tolerance
Stack Loops
Define Tolerances
Complete Drawings
for Components. SubAssembly and General
Arrangement, with
Assembly Instructions
Deliver
Completed
Drawings
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
86
Engineering Drawings and Tolerancing
• 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
Engineering Drawings and Tolerancing
• Tolerance Stacks
Identify
checks required
Gear and shaft
deflections from
analysis
Create master
dimension sheet
Final design
Create tolerance
stacks for each
shaft assembly
Check result
Yes
No
Revise dimensions
on master
dimension sheet
Yes
No
Create tolerance
stacks for shaft to
shaft clearances
Check result
No
Yes
Check result
Create housing
tolerance stacks
88
Engineering Drawings and Tolerancing
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
Engineering Drawings and Tolerancing
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
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