Springer STME User Manual
Springer Tracts in Mechanical Engineering
Yong Chen
Automotive
Transmissions
Design, Theory and Applications
Springer Tracts in Mechanical Engineering
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Yong Chen
Automotive Transmissions
Design, Theory and Applications
123
Yong Chen
Hebei University of Technology
Tianjin, China
ISSN 2195-9862 ISSN 2195-9870 (electronic)
Springer Tracts in Mechanical Engineering
ISBN 978-981-15-6702-5 ISBN 978-981-15-6703-2 (eBook)
https://doi.org/10.1007/978-981-15-6703-2
Jointly published with China Machine Press
The print edition is not for sale in China (Mainland). Customers from China (Mainland) please order the
print book from: China Machine Press.
ISBN of the Co-Publisher’s edition: 978-7-111-59945-6
© China Machine Press and Springer Nature Singapore Pte Ltd. 2021
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Singapore
Foreword
Professor Chen Yong has been engaged in the research and development of
automotive transmissions for a long time. He worked in the world famous automatic transmission company (JATCO) of Nissan Motor for 19 years, and completed
the development and mass production of many automatic transmission products;
after that, he worked in domestic automobile enterprises for nine years, leading the
independent research and development of manual and automatic transmissions of
Geely Automobile, and achieved fruitful results; now, he is devoted to academic
study in colleges and universities and committed to sorting out and systematically
refining his practical experience and technical accumulation of transmission
research over 30 years, and sharing it with others so as to benefit the industry and
help the development and progress of China’s automotive transmission business.
The book Theory, Design and Application of Automotive Transmissions of the
leading coauthor Chen Yong accumulates the profound knowledge and valuable
experience of first-class transmission experts and scholars at home and abroad,
elaborates the international advanced technology and development trend of automotive transmissions and emphatically explains the mature design theory in the
automotive transmission field and the latest international research and application
progress. It can be used as an engine ering technical book for automotive and
transmission R&D engineers and a reference book for graduates and undergraduates to learn basic theories and carry out academic research. It is a rare masterpiece
of both theory and practice.
Zhao Fuquan
Rotating Chairman of FISITA (2018–2020)
President of Automotive Industry
and Technology Strategy Institute
Tsinghua University, China
v
Preface
In order to change the output torque and speed of the engine and other power
systems, it is usually necessary to install a transmission in the transport machinery.
This book deals mainly with the transmissions of road vehicles. Under different
driving conditions, such as standing start, climbing, turning and acceleration, the
torque and speed required by the driving wheel of the vehicle are constantly
changing, while the range of torque and speed change that the engine can provide is
limited. The transmission is to adjust the performance of the engine by changing the
gear ratio and transfer the engine power to the wheels smoothly, reliably and
economically, so as to adapt well to the demands of external load and road conditions and achieve the best match between the characteristic field provided by the
engine and that required by the vehicle.
The automotive transmission is a high technology and process level of typical
products in mass production, and its development and design shall be oriented to
market demands while meeting environmental and regulatory requirements.
Regulatory requirements (such as energy conservation and emissions policies) and
user requirements must be fully considered. The main design objective of the
automotive transmission is to achieve the optimal transformation from engine or
motor power to the vehicle driving force within the wide speed range of the vehicle,
so as to ensure the dynamic property, acceleration and fuel economy of the vehicle.
Meanwhile, the application reliability and service life of new technologies and
processes shall be considered. The transmission design will be increasingly challenging given the increasing demand for fuel consumption, emissions and driveability, especially shift comfort and response speed. The current types of
transmission for passenger vehicles, including Manual Transmission (MT),
Automatic Transmission (AT), Dual Clutch Transmission (DCT), Continuously
Variable Transmission (CVT) and Automated Mechanical Transmission
(AMT) will remain largely unchanged for a long time. However, the application of
hybrid transmissions will grow substantially. The first author of this book worked
as a senior technician in the AT&CVT R&D in the R&D center of JATCO in Japan
for 19 years and was in charge of the R&D of AT and MT in Geely Automobile for
a long time after returning from abroad. He was deeply aware of the rapid progress
vii
viii Preface
of transmission technology and accelerated R&D cycle brought by computer
simulation techno logy, and also deeply aware of the urgent demand for systematic
explanation of the transmission development technology in the research and
development.
Therefore, the main purpose of this book is to systematically summarize the
main technical areas of the MT and AT development technology based on practical
development experience, comprehensively elaborate the theory and development
characteristics of the transmissions and display the main development processes
of the transmissions. In particular, many development processes are based on the
experience of trial and error. As a reference book providing main technical information for the research and development of transmission technology, this book is
suitable for engineers working in the field of automobiles and related power
transmission machines and graduate students at school. I would also like to thank
Dr. Guo Lishu, senior technical expert of Geely Commercial Vehicle Research
Institute, Dr. Gao Bingzhao of the College of Automotive Engineering, Jilin
University, for their hard work in this book. I would like to thank Dr. Tian Hua
from SGM Powersoon Research Institute, my doctoral student Zang Libin, Qiu
Zizhen, Li Guangxin, Wei Changyin, my assistant Cao Zhan and other graduate
students from the NEV Research Center of the Hebei University of Technology, as
well as others who have worked hard for this book. I would like to thank the Tianjin
Science and Technology Association for subsidizing this book.
Tianjin, China Yong Chen
Contents
1 Introduction .......................................... 1
1.1 Transmission Functions and Requirements
1.2 Types, Advantages and Disadvantages of Transmissions
1.3 Basic Structure of Transmission
........................ 12
1.4 Development Status and Trend of Transmission
Bibliography
.......................................... 21
................ 2
...... 3
............ 14
2 Manual Transmission
2.1 Overview
................................... 23
........................................ 23
2.2 Transmission Drive Mechanism
2.3 Synchronizer
..................................... 26
2.4 Transmission Operating Mechanism
2.5 Determination of Gear Ratio
.......................... 42
2.6 Joint Working of Engine and Transmission
2.7 Shift Performance Evaluation
2.8 New Technologies of MT
Bibliography
.......................................... 60
3 Automatic Transmission
3.1 Overview
........................................ 61
................................. 61
......................... 54
............................ 54
3.2 Composition and Control Principle of AT
3.3 Mechanical Structure of AT
.......................... 66
3.4 AT Speed Change Process Analysis
3.5 Hydraulic Control System of AT
3.6 Electronic Control System of aT
3.7 AT Performance Tests
3.8 Development Direction of aT
Bibliography
.......................................... 108
............................... 99
......................... 103
........................ 23
..................... 38
............... 49
................ 63
..................... 78
....................... 84
....................... 98
ix
x Contents
4 Continuously Variable Transmission ........................ 109
4.1 Overview
4.2 Composition of CVT
........................................ 109
............................... 111
4.3 Composition and Drive Theory of VDT Belt .............. 117
4.4 Composition and Principle of Hydraulic Control System
4.5 CVT Electronic Control System
4.6 Control of CVT
................................... 145
4.7 Main Performance Tests of Metal Belt CVT
4.8 CVT Upgrade
Bibliography
..................................... 148
.......................................... 153
........................ 140
............... 145
...... 129
5 Dual Clutch Transmission
................................ 155
5.1 Overview ........................................ 155
5.2 System Composition and Working Principle of DCT
5.3 Typical Design Scheme of DCT
5.4 Dual Clutch
5.5 Select-Shift Actuator
...................................... 162
................................ 177
5.6 Hydraulic Control System
5.7 Control System Hardware Design
5.8 Control System Software Design
....................... 159
............................ 180
...................... 190
....................... 195
........ 157
Bibliography .......................................... 199
6 Automated Mechanical Transmission
6.1 Overview
........................................ 201
....................... 201
6.2 Composition and Working Principle of AMT Control
System
.......................................... 202
6.3 Shifter .......................................... 207
6.4 Clutch
6.5 Select-Shift Actuator
6.6 Hydraulic Control System
6.7 AMT Control Strategy
6.8 AMT Performance Evaluation Indexes
Bibliography
7 Transmission for New Energy Vehicle
7.1 Overview
7.2 Power and Economy Performance of HEV
7.3 AMT Hybrid Transmission
7.4 AT Hybrid Transmission
7.5 CVT Hybrid Transmission
7.6 DCT Hybrid Transmission
7.7 Planetary Gear Hybrid Transmission
7.8 Electric Vehicle Transmission
7.9 Other Hybrid Power Plants
Bibliography
.......................................... 210
................................ 214
............................ 217
.............................. 222
................... 227
.......................................... 232
...................... 233
........................................ 233
................ 235
........................... 240
............................. 243
............................ 248
............................ 254
.................... 257
......................... 261
........................... 267
.......................................... 271
Contents xi
8 Transmission Design .................................... 273
8.1 Gear Design
8.2 Shaft Design
...................................... 273
...................................... 292
8.3 Bearing Selection and Design ......................... 297
8.4 Case Design
8.5 Parking Mechanism Design
8.6 Synchronizer Design
8.7 Selection of Seals
8.8 Transmission Ventilation Design
8.9 Transmission Tests
Bibliography
...................................... 300
........................... 308
................................ 328
.................................. 345
....................... 350
................................. 351
.......................................... 356
9 Transmission Fluid
9.1 MTF
9.2 ATF
........................................... 357
............................................ 358
9.3 CVTF
9.4 DCTF
..................................... 357
.......................................... 358
.......................................... 360
9.5 Performance Requirements and Tests for Transmission
Fluid
........................................... 362
9.6 Selection of Transmission Fluid
........................ 366
Bibliography .......................................... 369
10 Design of Hydraulic Torque Conve rter
...................... 371
10.1 Working Principle and Characteristics of Hydraulic Torque
Converter
10.2 Pre-design of Hydraulic Torque Converter
........................................ 371
................ 383
10.3 Blade Shape Design ................................ 391
10.4 Numerical Simulation and Analysis of Internal Flow Field
of Hydraulic Torque Converter
10.5 Parameter Adjustment of Hydraulic Torque Converter
10.6 Hydraulic Torque Converter Matching with Engine
Bibliography
11 Planetary Gear Drive
.......................................... 435
................................... 437
........................ 409
........ 428
......... 432
11.1 Theoretical Calculation of Transmission Efficiency
of Planetary Gear Train
11.2 Transmission Efficiency Test of Planetary Gear Train
.............................. 439
........ 454
11.3 Theoretical Calculation of Vibration and Noise
of Planetary Gear Train
11.4 Vibration and Noise Test of Planetary Gear Train
Bibliography
.......................................... 483
.............................. 464
........... 470
12 Electronic Control System of Auto matic Transmission
12.1 Introduction to AT Electronic Control System
12.2 AT Control System Development
...................... 488
............. 485
.......... 485
xii Contents
12.3 Validation of System Validity ......................... 503
12.4 Control Strategies of AT
............................. 506
12.5 Modeling of Hydraulic Torque Converter with Lockup
Clutch
12.6 Lockup Clutch Oil Circuit
.......................................... 507
............................ 508
12.7 Study on Control Strategies for Lockup Process of Lockup
Clutch
Bibliography
.......................................... 510
.......................................... 532
13 Automobile and Transmission Vibration and Noise
13.1 Vibration and Noise Foundation
13.2 Automobile Vibration and Noise
....................... 533
....................... 537
............ 533
13.3 Typical Automobile Vibration and Noise ................. 545
13.4 Analysis of Transmission Vibration and Noise
13.5 Typical Transmission Vibration and Noise Control
Bibliography
.......................................... 569
............. 553
.......... 563
Chapter 1
Introduction
Since the small torque range of the automobile engine cannot adapt to the requirements of automobile driving under various road conditions, the transmission that can
change the speed ratio and drive torque is adopted in the automotive drivetrain to
make the torque and speed output by the engine and other power systems vary in
a considerable range. This book deals mainly with the transmissions of road vehicles. Under different driving conditions, such as standing start, climbing, turning
and acceleration, the torque and speed required by the driving wheel of the vehicle
are constantly changing, while the range of torque and speed change that the engine
can provide is limited. The transmission is to adjust the performance of the engine
by changing the gear ratio and transfer the engine power to the wheels smoothly,
reliably and economically, so as to adapt well to the demands of external load and
road conditions and achieve the best match between the characteristic field provided
by the engine and that required by the vehicle.
The automotive transmission is a high technology and process level of typical
products in mass production, and its development and design shall be oriented to
market demands and fully consider the user requirements while meeting environmental and regulatory requirements (such as energy conservation and emissions
policies), as shown in Fig. 1.1. The main design objective of the automotive transmission is to achieve the optimal transformation from engine or motor power to the
vehicle driving force within the wide speed range of the vehicle, so as to ensure
the dynamic property, acceleration and fuel economy of the vehicle. Meanwhile,
the application reliability and service life of new technologies and processes shall
be considered. The transmission design will be increasingly challenging given the
increasing demand for fuel consumption, emissions and driveability, especially shift
comfort and response speed. The current types of transmission for passenger vehicles, including manual transmission (MT), automatic transmission (AT), continuously variable transmission (CVT), dual clutch transmission (DCT) and automated
mechanical transmission (AMT) will remain largely unchanged for a long time.
However, the hybrid transmissions will be more widely used and their number will
increase dramatically. The author of this book worked as a senior technician in the
© China Machine Press and Springer Nature Singapore Pte Ltd. 2021
Y. C h e n, Automotive Transmissions, Springer Tracts in Mechanical Engineering,
https://doi.org/10.1007/978-981- 15-6703-2_1
1
2 1 Introduction
Consumer demands: comfort and economy
Apply more advanced and efficient technology
Wide speed ratio and
multiple gears
Shift smoothness and economy
Fig. 1.1 Transmission design requirements
Shift strategy
optimization
Regulatory requirements: low-carbon,
efficient and environmentally friendly
Improve transmission
efficiency
Low-carbon, efficient and environmentall
Lightweight design
y friendly
AT&CVT R&D in the R&D center of JATCO in Japan for 19 years and was in charge
of the R&D of AT and MT in Geely Automobile for a long time after returning from
abroad. He was deeply aware of the rapid progress of transmission technology and
accelerated R&D cycle brought by computer simulation technology, and also deeply
aware of the urgent demand of the R&D personnel for systematic explanation of the
transmission development technology.
Based on the author’s over 30 years of practical experience in the development of
automotive transmissions at home and abroad, this book systematically summarizes
the main technical areas of the MT and AT development technology, comprehensively elaborates the theory and development characteristics of the transmissions
and displays the main development processes of the transmissions. Many development processes are based on the experience of trial and error. As a reference book
providing main technical information for the research and development of transmission technology, this book is suitable for engineers in the field of automobiles and
related power transmission machines and graduate students at school.
1.1 Transmission Functions and Requirements
The function of the transmission is to change the torque and speed of the engine
according to the requirements of the vehicle in different driving conditions, so that
the vehicle has the right traction and speed, and keeps the engine working in the most
favorable working conditions. To ensure the vehicle reversing and the powertrain
separation, the transmission must have forward as well as reverse and neutral. When
power output is required, power output devices shall also be provided.
Main requirements for the transmission:
(1) Guarantee good dynamic and economic indicators of the vehicle. This require-
ment is met by choosing the appropriate transmission gear number and gear
ratio according to the vehicle dead weight capacity, engine performance parameters, tire performance parameters and vehicle use requirements in the overall
vehicle design.
1.1 Transmission Functions and Requirements 3
(2) Reliable work and easy control. Automatic gear dropping, gear mixing and
shift impact are not allowed in the transmission during the vehicle driving.
(3) High safety. Guarantee the safe and reliable vehicle driving in any working
conditions.
(4) Small in size and light in weight. This requirement is met by reasonable use of
engineering plastics and other non-metallic materials, and the use of advanced
material forming technology and heat treatment technology.
(5) Low cost. Minimize the cost under the premise of meeting the vehicle
requirements for the transmission.
(6) High transmission efficiency. In order to reduce the gear engagement loss and
bearing friction loss, it is necessary to improve the manufacture and assembly
quality of components and reduce the gear churning loss. For example, the
proper lubricating oil and installed capacity can be selected to reduce the
churning loss and friction loss, thus improving the transmission efficiency.
(7) Low noise. This requirement can be met by adopting helical gears, selecting
a reasonable modification coefficient, making the axial modification and
profile modification and improving the manufacturing accuracy and assembly
stiffness.
(8) Meet the maximum input torque requirements.
(9) Meet the drive mode requirements.
(10) Meet the vehicle layout and installation requirements.
(11) Meet the reliable ramp parking requirements except for the MT.
(12) Meet the limp home requirements.
(13) With respect to the electrical controlled transmission, the hardware of the
control system shall meet the requirements of electromagnetic compati-
bility and anti-interference, and the software shall meet the requirements of
ISO26262, ASPICE, AUTOSAR and other standards.
(14) Consider factors such as driving pleasure and shift comfort and minimize the
shift impact.
1.2 Types, Advantages and Disadvantages of Transmissions
I. Types of automotive transmissions
Depending on the fixation of the gear ratio, the transmission may be classified into
stepped transmission and continuously variable transmission (CVT). The stepped
transmission, with fixed gear ratio, including ordinary transmission and planetary
transmission, is gear-driven and mostly widely used; the CVT, with the gear ratio
changing in a certain range, includes electric and hydraulic types. The variable speed
drive component of the electric CVT is DC series motor and the drive component of
the hydraulic CVT is hydraulic torque converter. The CVT can overcome the sudden
shift, slow throttle response, high fuel consumption and other shortcomings of the
AT and is mostly used in trolley buses and heavy-duty vehicles.
4 1 Introduction
The transmissions used in the passenger vehicles currently include MT, AT, CVT,
DCT, AMT and VIT, as well as the BEV transmission and HEV transmission evolved
on the basis of the above transmissions, as shown in Fig. 1.2.
1. Manual transmission
Manual transmission (MT) is also known as mechanical transmission. The engaging
position of the gears in the transmission is changed by moving the gear shift lever
by hand, thus changing the gear ratio to achieve variable speed. It take a place
in the transmission family because of its high transmission efficiency, high torque
transfer, easy manufacture, low cost, simple structure, low fuel consumption, short
acceleration time and short development cycle. The current MT is mainly 5 speed or
6 speed MT, covering SUV, middle-sized vehicles and compact vehicles. In order to
reduce fuel consumption and improve driving pleasure, the transfer torque increases
MT
Drive
system
AT
NEV
transmi
ssion
HEV transmission BEV transmission
Fig. 1.2 Main types of transmissions for passenger vehicles
AMT CVT
DCT
AT
1.2 Types, Advantages and Disadvantages of Transmissions 5
step by step and the 6 speed transmission in the MT will become the mainstream.
ZF and BMW are developing the 7 speed MT currently.
2. Automatic transmission
The automatic transmission (AT) is also known as stepped AT. According to the
different arrangement modes of shafts, AT can be divided into fixed shaft AT and
rotating shaft AT. Due to the large space occupied by the fixed shaft (parallel shaft),
it is impossible to achieve more gears (limited to 5-speed and 6-speed), which is
currently the main technology of Honda. The vastmajority of transmission companies
use the rotating shaft technology solutions. AT may be divided into 4AT, 5AT, 6AT,
7AT, 8AT and 9AT by gear. GM, Volkswagen and other automotive companies have
begun to develop 10AT. With mature technology and small size, 4AT is still the main
AT carried by small cars, although its comfort and economy are poor; 5AT is slightly
better than 4ATin terms of comfort and economy,but has still obvious abrupt shift and
limited late development space; 6AT has relatively superior economy and comfort
and has become a mainstream trend for small, compact and middle-sized vehicles;
7AT and 8AT have been adopted by Lexus, BMW, Audi, Benz and other highend imported models. 8AT has been successfully developed by domestic Shengrui
Transmission Co., Ltd. and installed in Landwind; 9AT represents the innovation of
science and technology has been developed successfully by ZF and Aisin Seiki.
3. Continuously variable transmission
The continuously variable transmission (CVT) becomes an important branch of automotive automatic transmission field since it can produce continuously changing gear
ratio, achieve the best match between the engine and powertrain, simplify the operation, reduce the driver’s labor intensity, increase driving safety, driving smoothness
and comfort and improve emission. CVT is classified into metal pushing V-belt type
CVT, chain type CVT and KRG. With light weight, small volume, simple s tructure,
smooth shift, relatively high cost, inconvenient maintenance and limited carrying
capacity, the metal pushing V-belt type CVT is used in small and compact cars and
has more room for improvement because of its unparalleled comfort. The chain type
CVT is the main technology of Schaeffler in terms of CVT and has higher transmission efficiency and more compact structure than the metal pushing V-belt type CVT,
but its disadvantage is that the protruding pin on the side of the chain will produce
noise when it comes into contact with the pulley point. At present, the KRG may be
unfamiliar to most people, but this kind of transmission may become the mainstream
transmission for low-emission vehicles in the future. Its low cost, high efficiency,
simple structure and multiple advantages in function and comfort deserve people’s
attention.
4. Dual clutch transmission
The dual clutch transmission (DCT), as a new AT, arranges the transmission gears by
odevity respectively on the two input shafts connected with two clutches, completes
6 1 Introduction
the shift process and achieves power shift through the alternate switching of clutches.
DCT has the advantages of AT and AMT. With high transmission efficiency, simple
structure and low production cost, it guarantees the dynamic and economy performance of the vehicle and greatly improves the vehicle operating comfort. DCT is
divided into DDCT and WDCT. DDCT is also divided into electro-hydraulic DDCT
and electric DDCT. The former is complicated in structure, needs to be improved
in reliability and is used in Volkswagen vehicles; the latter is simple and reliable
in structure and will become the mainstream trend in the development of small and
medium torque AT in the future. With large carrying capacity, WDCT will be used
greatly in the intermediate class and above vehicles.
5. Automated mechanical transmission
The automated mechanical transmission (AMT), based on the traditional fixed shaft
transmission, controls the hydraulic or electric actuating system through the electronic control unit by use of the electronic technology and automatic transmission
theory to achieve the clutch disengagement and engagement, gear selecting and
shifting, so as to achieve the automatic control of start and shift. AMT has a certain
development space in mini and small cars due to its high transmission efficiency,
easy manufacturing and low cost, but it has not much development space in models
above the compact level due to power failure in the shift process.
The AMT usually consists of electrically controlled hydraulic AMT and electrically driven AMT. The AMT with the core of electro-hydraulic actuator in the
electrically controlled hydraulic AMT has been widely applied in Chery QQ3, Riich
M1, Chevrolet Sail, SAIC MG3 and other models; compared with the electrically
controlled hydraulic AMT, the electrically driven AMT has simpler structure, better
reliability and lower cost and is the mainstream trend of AMT development.
6. Vit
VIT is a new concept of high-power and high-efficiency mechanical CVT successfully developed on the basis of the meshing principle of sliding vane CVT movable
teeth. The working surface of the sliding vane CVT movable teeth is overlapped by
a series of sliding vanes and any shape of meshed tooth profile can be formed by
free stepless slip of the sliding vanes. This design idea is equivalent to the “differentiation and reintegration” of the gears. That is, any required tooth profile, i.e. the
sliding vane CVT movable teeth can be formed by organic combination of multiple
elements. Since the slip direction of the sliding vanes is different from the force direction, the sliding vanes are free to deform with the current meshed tooth profile, while
the force direction is perpendicular to the free slip direction or the angle between
them is self-locking in the equivalent friction angle during the power transmission.
Therefore, the sliding vanes will not change the shape of the tooth profile when
bearing force. With the “rigid and flexible fusion, and movable teeth solidification”
effect, high carrying capacity and transmission efficiency, VIT is the true sense of
“movable teeth meshing CVT” and is applied in saloon cars, passenger cars, trucks
and other high-power and high-torque vehicles.
1.2 Types, Advantages and Disadvantages of Transmissions 7
7. BEV transmission
The BEV transmission mainly includes single reduction gear, multi-speed transmission and the wheel-side drive motor integrating reducer and motor. At present,
the single speed reducer with fixed speed ratio is mostly used in the small electric vehicles. This drive mode has simple structure and low manufacturing cost, but
it puts forward higher requirements for the traction motor that the traction motor
shall provide higher instantaneous torque in the constant torque area and higher
running speed in the constant power area, so as to meet the vehicle acceleration
performance requirements and maximum speed design requirements. Meanwhile,
the single speed reducer with fixed speed ratio has the problem of low motor utilization efficiency. In order to ensure the maximum vehicle speed, the speed ratio of
the reducer is often relatively small, which makes the traction motor in a longterm high torque and high current working condition, and relatively low motor efficiency, thus wasting the battery energy and reducing the driving range. The electric
vehicle drivetrain tends to be multi-speed to make the electric vehicles better meet
their dynamic performance and reduce their requirements for traction motors and
batteries. Oerlikon Graziano developed a two-speed transmission to match small
electric vehicles. Antonov designed a new efficient 3 speed AT for BEV that optimizes the powertrain size, weight and development costs while improving the energy
efficiency and guaranteeing the dynamic performance.
8. HEV transmission
(1) Hybrid drive type: before introducing the HEV transmission, it is important
to know the hybrid drive type. As shown in Fig. 1.3, the hybrid drive mainly
includes tandem hybrid drive, parallel hybrid drive, power-split hybrid drive
and other hybrid drive.
Hybrid drive types
Tandem hybrid drive
P0 hybrid P4 hybrid
Fig. 1.3 Hybrid drive types
Parallel hybrid drive
P1 hybrid
Power-split hybrid drive
P2 hybrid
Other hybrid drive
P3 hybrid
8 1 Introduction
(1) Tandem hybrid drive. The engine is completely decoupled from the driving
wheel and simply drives the generator to charge the power battery, which
drives another motor through the motor controller to keep the vehicle
moving. This scheme has low overall efficiency due to many power drive
links, but it is comfortable because the engine is completely decoupled
from the driving wheel.
(2) Parallel hybrid drive. Depending on the motor arrangement on the whole
vehicle, it is divided into P0 (BSG), P1 (ISG), P2, P3 and P4 structural
hybrid drives. In P0 structural hybrid drive, the motor is integrated in the
position of the generator of the traditional engine, playing the role of power
generation, assistance and starting, and acting as the generator in energy
recovery to recover the braking energy; in P1 structural hybrid drive, the
motor is integrated at the output end of the engine crankshaft, playing the
role of power generation, assistance and starting, and acting as the generator
in energy recovery to recover the braking energy; in P2 structural hybrid
drive, the motor is also integrated between the engine and the transmission.
The difference is that the motor is connected to the engine and transmission separately through the clutch, playing the role of power generation,
assistance and starting, and acting as the generator in energy recovery to
recover the braking energy. The motor drives the vehicle alone, either fully
hybrid or plug-in hybrid, which is one of the main forms of hybrid drive;
in P3 structural hybrid drive, the motor is integrated at the output end of
the transmission, playing the role of assistance and power generation, and
acting as the generator in energy recovery to recover the braking energy.
The motor drives the vehicle alone, either fully hybrid or plug-in hybrid;
in P4 structural hybrid drive, the engine drives a drive axle and the motor
drives the other drive axle. The motor plays the role of assistance and
power generation and acts as the generator in energy recovery to recover
the braking energy. The motor can also drive the vehicle alone, either fully
hybrid or plug-in hybrid.
(3) Power-split hybrid drive. It integrates the engine and two motors by means
of the planetary gear train to achieve various functions of the hybrid drive.
A typical example is Toyota Prius HEV, also known as the eCVT because
of the use of planetary gear train and motors to shift the output end of the
engine and planetary gear train.
(4) Other hybrid drive. A typical example is Honda Fit 7DCTH hybrid drive,
in which, the motor is connected to an input shaft of 7DCT through the
drive mechanism, forming a new and unique drive form. In this scheme, the
motor needs to be synchronously tracked in shift of each gear connected
with the motor input shaft, so as to reduce the difference between the active
and passive speeds of the synchronizer and prolong the service life of the
response synchronizer.
1.2 Types, Advantages and Disadvantages of Transmissions 9
(2) Common transmissions on HEV: the traditional automotive transmissions are
used in HEVs, among which AT is more widely used, as follows:
The AMT is the ideal choice for HEV transmissions. The electrically driven transmission based on AMT is characterized by coupling the motor used in the NEV
with AMT through high-intensity silent chain drive, which solves the power failure
problem during shift. This new electrically driven transmission fully combines the
advantages of the motor and the AMT to significantly reduce fuel consumption. The
7H-AMT hybrid transmission developed by FEM based on AMT i s characterized by
that the drive motor transfers power through other gears and outputs a certain torque
in the upshift to eliminate the impact caused by power failure during shift.
The application schemes of AT in HEV include coupling the motor at the input
end of the transmission and coupling the motor at the output end of the transmission.
The recent new scheme is to replace the hydraulic torque converter of the AT with
motor.In these schemes, the lubrication system shall be improved and the mechanical
fuel pump of the traditional AT is replaced with an electronic fuel pump or a new
electronic fuel pump is added; otherwise, the EV mode will be difficult to meet the
system lubrication requirements and fast start-stop requirements.
CVT is most frequently used in the mass produced HEVs. The HEV AT is characterized by powertrain integration. That is, the motor is integrated with the transmission, making the system structure more compact, power drive more stable and
control performance better.
The applications of DCT in HEV mainly include that the drive motor is connected
to the input shaft 1 of the transmission through the reducing gear, that the drive motor
is connected to the input shaft 2 of the transmission through the reducing gear and
that the drive motor is connected to the input shaft of the transmission through the
reducing gear. The advantage of the first two schemes is that the motor drive can
change the speed, but the disadvantage is that the motor needs to be synchronously
tracked in the synchronous engagement of the gear of the input shaft connected to the
motor; the advantage of the latter scheme is that the motor may not be synchronously
tracked in the shift, but the disadvantage is that the motor drive cannot change speed.
In addition, the PRIUS hybrid power system is a typical example of PSHEV. The
biggest feature of this system is to use a planetary gear train to couple two motors
and an engine together, so that a single planetary gear train can realize the functions
of CVT. See Table 1.1 for typical hybrid transmission applications.
II. Advantages and disadvantages of transmissions
The transmission, as an important part of the vehicle powertrain system, determines
the power output of the vehicle and has a direct impact on the fuel economy, comfort
and reliability of the vehicle. Different types of transmissions have different characteristics. The advantages and disadvantages of mainstream transmissions in today’s
market are shown in Table 1.2.
10 1 Introduction
Table 1.1 Typical hybrid transmission applications
Structure Manufacturer Model Transmission
Start-stop-BSG Buick LaCrosse 6AT
Chevrolet Malibu 6AT
Chery A5 BSG Original transmission
ISG (E-M-C-T) Honda Fit Hybrid MT/LVT
Honda CIVIC Hybrid (II) CVT
Honda CIVIC Hybrid (III) CVT
Honda Insight CVT
Honda CR-Z MT/LVT
BMW BMW 7 Hybrid 8AT
Benz Benz S400 Hybrid 7AT
ISG (E-C-M-T) Hyundai Hyundai Sonata hybrid
6AT
power
Nissan Nissan Fuga 7AT
Audi Audi A6 Hybrid 8AT
Audi Q5 Hybrid quattro 8AT
Audi Q7 Hybrid (EOL)
Porsche Porsche Panamero S
8AT
Hybrid
Volkswagen Volkswagen Touareg 8AT
Parallel rear axle drive Peugeot Peugeot 3008 6AMT
Series-parallel/dual-motor
single
planetary gear train
Toyota Toyota Prius Single reduction gear
Nissan Nissan Altimn Hybrid Single reduction gear
Ford Fusion Hybrid –
Ford Escape Hybrid
Ford C-MAX Hybrid
Series-parallel/dual-motor
dual
Lexus RX400h/HighlanSer
Hybrid
Single reduction gear
planetary gear train
Series-parallel/dual-motor
three-planetary gear train
Lexus GS450h/LS600h Single reduction gear
BMW BMW X6 7AT
Benz Benz ML450 7AT
1.2 Types, Advantages and Disadvantages of Transmissions 11
Unlimited
power
Unlimited
application
power
Unlimited
cost
power
Limited
cost
power
Limited
cost
power
Limited
cost
cost
Life Cost Scope of
Good Low Unlimited
Emission
performance
economy
Reliability Fuel
smoothness
good
High Unlimited
Relatively
good
good
Good Bad Relatively
uninterrupted
power
Good Bad High Limited
Relatively
good
Relatively
good
interruption
High Unlimited
good
Good Relatively
Relatively
good
Relatively
good
approximately
without
interruption
Relatively
low
Relatively
good
good
Power failure Bad Good Relatively
good
Torque Efficiency Comfort Shift
Large High Poor Power failure Good Good Relatively
Transmission
form
Table 1.2 Advantages and disadvantages of transmissions
MT Stepped
manual
Large Low Good Approximately
automatic
AT Stepped
Limited Low Best Power without
CVT Stepless
automatic
Large High Good Power
automatic
DCT Stepped
Large High Relatively
automatic
AMT Stepped
12 1 Introduction
1.3 Basic Structure of Transmission
The transmission consists of a case, a drive part and a shift control device.
1. Case
As the basic part, the case is used to mount and support all parts of the transmission
and to store the lubricating oil, above which, there is a precise bore for mounting
the bearing. The transmission bears variable load, so the case shall be rigid enough,
with complex ribs on the inner, most of which are castings (made of gray cast iron,
commonly HT200), as shown in Fig. 1.4.
For the convenience of installation, the transmission part and the shift control
device are often made into split type, and the transmission cover is bolted to the case
and positioned reliably. The case is provided with refueling and fuel drain hole and
fuel level inspection ruler hole, and the heat dissipation should also be considered.
2. Drive part
The drive part consists of the transmission gears, shaft, bearing and other driving
media. The geometric dimensions of the shaft are determined by the checking calculation of the strength and stiffness; the material is selected mainly depending on
whether its stiffness meets the requirements. The carbon steel has nearly equal elasticity modulus with the alloy steel, so the shaft is generally made of carbon steel
(usually steel 45) and the alloy steel is used only when the gear and shaft are integrated or when the bearing is under heavy load. The gears are usually made of low
carbon alloy steel (e.g. 20CrMnTi and 20MnCrS). The shaft is mostly splined with
the gears and has the advantages of good centering, reliable transmission of power
and small extrusion stress. The spline part and the bearing mounting site of the shaft
are surface hardened. The shaft is mainly supported by a rolling bearing, with simple
lubrication, high efficiency, small radial clearance and reliable axial positioning and
Controller mounting hole
Fig. 1.4 Transmission case
Flange plate
Bearing hole
1.3 Basic Structure of Transmission 13
Case
3 speed gear
Input shaft
3 speed gear
Fig. 1.5 Transmission profile
2speed gear
Output shaft
Countershaft
2speed gear
is mainly lubricated by splash lubrication (v>25 m/s, thrown to the wall as long as
the viscosity is appropriate). The transmission profile is shown in Fig. 1.5.
3. Shift control device
In MT, the driver controls the shift, while in AT, the electronic actuating system
completes shift partly or entirely relying on a lot of automation technology. The
neutral, reverse and park are still completed by the driver by controlling the shift
control device. The elements in the shift control device are selected according to the
transmission type and vehicle type. The engaging elements of the transmission for
passenger vehicles mainly include:
(1) Internal engaging elements: shift f ork (Fig. 1.6a), shift synchronizer (Fig. 1.6b),
locking device, multi-disk clutch and brake.
(2) External engaging elements: shift level system, inhaul cable and gear shift lever
14 1 Introduction
Fig. 1.6 (b) Shift
synchronizer
1.4 Development Status and Trend of Transmission
I. Development status of transmissions
The demand for transmissions varies greatly from region to region. The CVT has
benefited to a certain extent from the continued demand among Japanese users for
small cars that change speeds automatically, making it the best-selling AT type in
Japan. Figure 1.7 shows the demand for transmissions in Japan. The main transmis-
sion enterprises in Japan develop to the high gears (8 and 9) AT. Moreover, the CVT
is developing fast and gradually developing towards high torque.
AT possesses absolute advantage in the US, mainly because the consumers require
simple control and comfortable driving of vehicles but are not sensitive to fuel
consumption, thus forming the AT-dominated AT market in the US. Figure 1.8 shows
the demand for transmissions in the US. The main transmission enterprises in the
US are currently targeting the 6AT. With the continuous development of the wet
clutch technology of BorgWarner, the WDCT will also grow rapidly in the US. The
700
10,000 units
600
500
400
300
200
100
0
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
3-5 speed AT 6 speed AT 8-9 speed AT CVT DCT&AMT
Fig. 1.7 Demand for transmission in Japan
Year
1.4 Development Status and Trend of Transmission 15
100%
80%
60%
40%
20%
0%
2015 2020 2025 2030
EV DHT CVT AT9/10 AT6/7/8 DCT MT
Fig. 1.8 Demand for transmission in the US
Year
higher gear AT produced by the European transmission company is adopted for the
high-grade vehicles.
The European consumers pay attention to driving experience and driving pleasure, like the feeling brought by manual control of the machinery, and think a great
deal of fuel consumption. Therefore, after emergence, the DCT with energy saving
and kinetic characteristics immediately became the darling of the European market.
Figure 1.9 shows the demand for transmissions in Europe. The main transmission
enterprises in Europe have developed towards the high speed (8 and 9) AT and
DCT, and the engineering companies are also pushing the hybrid power technology
vigorously.
600
10,000 units
500
400
300
200
100
0
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
3-5 speed AT 6 speed AT 8-9 speed AT CVT DCT&AMT
Fig. 1.9 Demand for transmission in Europe
Year
16 1 Introduction
10,000 units
AT CVT DCT AMT
Fig. 1.10 Demand for transmission in China
In China, an emerging auto market, the traditional AT was the main choice for
previously automatic transmission vehicles. However, in recent years, the biggest
factors influencing consumers’ decision to buy cars are “price” factors (vehicle
fuel consumption and vehicle price). The number of vehicles assembled with DCT
has increased significantly, and the share of vehicles assembled with CVT has also
increased. Figure 1.10 shows the demand for transmissions in China. Due to accumulated experience in MT development and good process inheritance of AMT and DCT,
the transmission technology develops rapidly in recent years with the involvement
of the engineering companies with outstanding transmission development capability,
and the companies are also trying to make breakthroughs in the AT and CVT fields.
As AT continues to be multi-speed, DCT grows most and the demand for the AT
is increasing year by year. Figure 1.11 shows the demand for AT.
The carrying status of the AT in the passenger vehicles in China is shown in
Fig. 1.12. The 4 speed and 5- speed ATs are mainly assembled in 1.3–1.6 L small
cars and compact cars; the 6-7-8 speed ATs are mainly assembled in the vehicles with
the displacement of 2.0 L and above; the CVT (without hydraulic torque converter) is
mainly assembled in 1.5–1.8 L compact cars; the CVT (hydraulic torque converter)
is mainly assembled in 1.5–2.5 L vehicles; the DDCT is mainly assembled in the
vehicles with the displacement of 2.0 L and below and the WDCT in the vehicles with
the displacement above 2.0 L; the number of applications of turbocharged engine
and DCT combination will increase rapidly.
II. Development trend of transmissions
Energy conservation, environmental protection, safety and high efficiency is the
theme of the development of automotive transmissions, with the pursuit of comfort,
economy and safety from the perspective of consumers and the pursuit of high efficiency, low carbon and environmental protection from the perspective of regulations.
Thus, the transmission companies are required to apply advanced and efficient design,
manufacturing and control technologies and advanced materials to achieve wide gear
1.4 Development Status and Trend of Transmission 17
60
Million units
50
40
30
20
10
0
2013 2015 2017 2018 2019 2020
AT AMT CVT DCT
Fig. 1.11 Demand for AT
Torque /(N.m)
Year
5-6 speed AMT 4-5 speed AT 6~8 speed AT CVT DDCT WDCT
Fig. 1.12 Carrying status of the AT in the passenger vehicles in China
ratio and multi-speed of transmission, optimization of the shift strategy,improvement
of the transmission efficiency and light weight of transmissions.
1. Development trend of MT
(1) Multi-speed and large gear ratio of transmission: the three-axis 6 speed
transmission was gradually replacing the dual-axis 5 speed transmission
under thedominance of some European, American and Japanese companies
from twoor three years ago. The 7speed MT supplied by ZF for Porsche 911
Carrera and Carrera S was used in the passenger vehicles for the first time.
18 1 Introduction
With increased low speed gear ratio and more reasonable gear, it achieves
the comprehensive optimization of dynamic and economy performance.
(2) High efficiency and reduced NVH: the following measures can be taken
to improve the transmission efficiency: multi-speed transmission; reduce
the immersion height of the differential mechanism in the lubricating oil
and change the lubricating mode from traditional gear splash lubrication
to combination of gear splash lubrication and oil guide lubrication, so as to
reduce the churning loss of the lubricating oil; replace the traditional conical
bearing with ball bearing and roller bearing to reduce the bearing friction
loss; use efficient transmission lubricating oil. To meet the requirement
of noise reduction, the best match of the clutch and transmission shaft
with the transmission shall be considered in addition to the corresponding
measures taken for the transmission, such as precise control of the backlash
in circular tooth of the transmission matching gear, selection of appropriate
gear material, application of low noise bearing and full consideration to the
impact of the gear engagement on the transmission structure in the design
phase.
(3) Light weight and low cost: the light weight and low cost can be achieved
by use of advanced forming technology, reasonable plastics and other nonmetallic materials. The lightweight design of the transmission case based
on CAE can shorten the development cycle, reduce the development cost
and improve the product competitiveness.
(4) Further reduce the space occupied by the transmission and optimize the
space and size of all parts. Due to the application of the start-stop system,
a highly integrated solution with low cost and high reliability that can
identify the neutral and reverse is applied through the detection of reliable
neutral position signals.
2. Development trend of AT
(1) Development trend of hydraulic torque converter: flattened hydraulic torque
converter, increasing torque ratio, extended locking range and sliding friction
range and improved hydraulic torque converter range. With the application of
the engine supercharging technique, the engine torque is increasing and higher
requirements are put forward for the vibration reduction of the transmissions.
The torque converter with centrifugal pendulum vibration absorber and the
torque converter with turbine vibration absorber are presented, significantly
improving the vibration damping performance of the torque converter. The
hydraulic part is optimized to improve the hydraulic torque converter capacity
and optimize the axial space.
(2) Multi-speed AT. The 6~9 speed AT is gradually replacing the 4 or 5 speed trans-
mission. With the increased gears, the transmission may have a larger gear ratio
range and a reasonable gear ratio distribution. ZF has successfully developed
9AT and some companies are already working on 10AT.
(3) AT modular design. The modular design is very obvious in AT, including modu-
larization of hydraulic torque converter, modularization of hydraulic valve body,
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