Drivetrain

Hiroyuki Shioiri1）
1）Toyota Motor

1 Introduction 3 Manual Transmission Trends

Improving vehicle fuel efficiency has become an in- The Porsche 911 uses the world s first 7-speed manual
creasingly important development theme in recent transmission (MT) for a passenger vehicle (gear ratio
years as a result of active measures being implemented range: 5.50, manufactured by ZF Friedrichshafen AG).
around the world to combat global warming by reduc- This transmission shares the gear arrangement of the
ing CO2 emissions, in addition to energy issues created ZF 7-speed dual-clutch transmission (DCT) and adopts a
by increasing crude oil demand in emerging markets as gear-select mechanism that enables an H-type shift pat-
vehicle markets expand. Global vehicle sales around the tern for MTs (4). As an example of a loss-reduction tech-
world have increased from 77.9 million in 2011 to 81.7 nology, a 300 Nm input torque class transverse 6-speed
(1)
million in 2012 . In the same time frame, sales of so- MT has been developed with ball bearings on the dif-
(5)
called next-generation vehicles, such as hybrid, electric, ferential side by enhancing lubrication at low speeds .
and plug-in electric vehicles (HEVs, EVs, and PHEVs) Furthermore, as an example of a technology for improv-
(2)
increased by 80% from 960,000 to 1.73 million . These ing shifting feel, Mazda has developed a new structure
vehicles now make up 2.1% of the overall vehicle mar- for the selecting mechanism that moves the control rods
ket. With this background, current drivetrain trends in- up and down with the aim of reducing the effort re-
clude the reduction of component losses, increases in the quired to shift up. This structure uses the weight of the
number of shift speeds and wider gear ratio ranges for upper control rod parts to move the rods down when the
conventional transmissions that also consider the goal of driver shifts up by arranging the first and second gear
commonization, and the evolution and popularization of select positions in an upward position (Fig. 1) (6).
fuel efficiency improvement technologies such as idling For commercial vehicles, Hino has developed a 9-speed
stop systems. Next-generation automotive transmissions MT for the large Profia 25-ton class truck to help im-
have been developed with single-motor systems shared prove fuel and installation efficiency by enabling a wider
with conventional transmissions, as well as dual-motor gear ratio range and increasing the number of shift
systems with driving modes with a fixed gear ratio. speeds. This was achieved by reducing the size and
Technologies have also been developed to help enhance weight of the unit while achieving a wider gear ratio
driving enjoyment, including measures to improve shift
operability and continuous advances in technology to Select lever

boost perceived performance such as accelerator and Control rod

shift response. Shift fork (reverse)

2 Clutch Trends
A torque converter with a built-in centrifugal pendu-
lum vibration absorber was adopted in a vehicle with Shift fork (1st and 2nd gear)
a cylinder deactivation mechanism (the Mercedes Benz Shift fork (3rd and 4th gear)
SLK55 AMG). The pendulum order is applied when the Shift fork
(5th and 6th gear)
V8 engine is in 4-cylinder mode (3).
Fig. 1 Mazda 6-speed MT shift mechanism.

Copyright© 2013 Society of Automotive Engineers of Japan, Inc. All rights reserved
 Fig. 2 Section view of 9-speed MT (M009) for the Hino Profia（7）. Fig. 4 Section view of the Subaru Legacy Lineartronic
CVT for high-torque applications（15）.

9-speed AT (gear ratio range: 9.84) has been designed

with a completely modularized configuration. The gear
shifting portions are common for all variants, allowing
the adoption of various starting mechanisms and hybrid
(10)
systems . Getrag has developed a transverse 7-speed
wet-clutch DCT (the 7DCT300) with a gear ratio range of
8.6. This transmission is compatible with idling stop and
coasting functions. Getrag has also developed a 1-mo-
tor type hybrid specification transmission based on the
(11)
7DCT300 called the 7HDT300 .

Fig. 3 Section view of 6-speed AT for the Lexus RX.

For enhanced driving enjoyment, the 6-speed AT in-
stalled in the Mazda Atenza and CX-5 uses a kick-down
range compared to the conventional 7-speed transmis- switch in the shift control to improve shifting control-
sion. This 9-speed MT has a high/low switchover func- lability by the driver (12)
. The Toyota Crown 8-speed AT
tion using a planetary gear-type auxiliary transmission features a control that suppresses unnecessary up-shifts
(Fig. 2). while cornering using a G-sensor to determine the decel-
eration and cornering force. This function optimizes the
4 Automatic Transmission Trends (25)
engine braking and drive force when exiting a turn .
The number of shift speeds is also being increased for
5 Continuously Variable Transmission
automatic transmissions (ATs). The Lexus RX350 FS-
PORT features the world s first transverse 8-speed AT
(CVT) Trends
(gear ratio range: 7.58). This transmission is the same CVTs with wider gear ratio ranges and chain-driven
size as the conventional 6-speed AT due to a compact CVTs that increase torque and efficiency are being de-
configuration using one additional clutch (Fig. 3). veloped. In the case of belt-driven CVTs, the Honda Step
Idling stop mechanisms are also becoming more wide- Wagon features a 250 Nm input torque class CVT with
spread. For conventional ATs, the BMW 8-speed AT a gear ratio range of 6.54 (compared to the conventional
(gear ratio range: 7.06) has been installed on the X3 and 5.48) by adopting measures such as a wider interval be-
X1, the 3-Series and 5-Series diesel variants, the 7-Series, tween pulleys (increased from 170 mm to 180 mm) (13)
.
and so on. In the 7-Series, the transmission and the en- The CVT in the Nissan Altima features a gear ratio
gine are automatically disengaged when the driver re- range of 7.0 (compared to the conventional 6.0), which
leases the accelerator at speeds above 50 km/h to allow was achieved by reducing the diameter of the pulley
(8)
the vehicle to coast and reduce driving resistance . For shafts (14)
. For chain-driven CVTs, the adoption of short
DCTs, the VW Golf, Polo, and other models use a dry- pitch chains is expanding and the Subaru Legacy fea-
clutch 7-speed DCT, and the Tiguan uses a wet-clutch tures a 400 Nm input torque class CVT with a gear ratio
6-speed DCT. In addition, the VW up! uses a MT-based range of 6.44 (compared to 6.3 with the standard chain)
5-speed transmission with an automatic shifting mode (9). (Fig. 4). In addition, the Nissan Altima features a 380
As an example of the trend to commonize convention- Nm input torque class CVT with a gear ratio range of 6.3
al and next-generation transmissions, the ZF transverse (compared to 5.4 with the conventional belt) (14)
.

Copyright© 2013 Society of Automotive Engineers of Japan, Inc. All rights reserved
 Illustration of stepped shift control

Acceleration

Engine
speed
Time
Sport mode
Normal mode in conventional vehicle
Normal mode

Fig. 5 Illustration of shift control in the Auris CVT（25）.

HEV motor
HEV CL1 (clutch)
The adoption of CVTs with auxiliary transmissions Carryover parts

with a wide gear ratio range of 7.28 has expanded in New HEV parts

compact vehicles, such as the Mitsubishi Mirage, Nissan

Note and Latio, and Suzuki Wagon R.
Fig. 6 Jatco CVT8 Hybrid.
More vehicles are also using idling stop mechanisms
with an electric oil pump, such as the Honda Step Wag-
6 HEV Drivetrain Trends
on, Toyota Corolla and Auris, Mitsubishi Mirage and
Outlander, Nissan Note and Latio, Suzuki Wagon R, and On example of a drivetrain that combines a single
Subaru Impreza. Engine-stop mechanisms that facilitate motor with a conventional transmission is the system
re-starting from engine coasting are also becoming more used in the BMW 3-, 5-, and 7-Series that mates a ZF-
widespread in vehicles such as the Impreza, Corolla, Au- manufactured 1-motor 2-clutch mechanism to an 8-speed
(8)
ris, Wagon R, and the like. These use a tandem solenoid AT . Jatco has also developed a system that combines
starter that enables extrusion of the pinion gear and in- a 1-motor 2-clutch mechanism with a CVT (Fig. 6). The
dependent application of power to the motor. Mercedes Benz E300 Blue Tec combines a diesel engine
(17)
Loss-reduction technology is also making advances. with a 1-motor 7-speed AT through a clutch . The
The oil pump is responsible for the largest proportion of VW Jetta HV features a system that also combines an
energy loss in a CVT. Technology to reduce the drive engine with a 1-motor 7-speed DCT through a clutch. In
torque of the oil pump includes the adoption of two out- all cases, these transmissions automatically disengage the
let ports in a single oil pump and a mechanism to switch transmission and engine when the driver releases the ac-
the flow between them (13)
. This mechanism has a new celerator pedal at high speeds.
low-pressure port for lubrication in addition to the con- HEV drive systems with two motor-generators (MGs)
ventional high-pressure port (16)
. use a planetary gear mechanism to control the engine
Shifting control-related technology for enhancing and two MGs simultaneously. Examples include those
driving enjoyment has been adopted in the CVT in the used in the Toyota Prius and Ford Fusion HV. In con-
Subaru Legacy. This CVT increases the number of shift trast, another type of system has been developed without
speeds in manual mode and also enables the selection a planetary gear mechanism. In this system, the engine
of an 8-speed mode (15)
. The Toyota Wish, Corolla, and and generator, and the motor and differential are directly
Auris feature a control that suppresses unnecessary up- connected by fixed gear ratios. A clutch is provided be-
shifts during cornering after a downshift to enter a cor- tween the engine and differential. Engaging this clutch
ner, using a G-sensor to detect deceleration and corner- activates a parallel driving mode at a fixed gear ratio
ing force. The CVT control in the Auris also emphasizes suitable for high-speed driving. This system is used on
the up-shift feeling when the driver depresses the accel- the Mitsubishi Outlander PHEV and Honda Accord PHV
erator through a stepped shifting mode that feels like a (Fig. 7).
conventional transmission (Fig. 5). In the commercial vehicle field, the Isuzu Erga HV is
installed with a parallel hybrid system designed for route
transit buses that connects the engine with a MG and

Copyright© 2013 Society of Automotive Engineers of Japan, Inc. All rights reserved
 Generator shaft Engine shaft

Generator Generator Generator

Engine Engine
Engine Primary reduction Primary reduction
gear gear
Engine shaft Clutch shaft
Differential Differential Secondary reduction gear
Differential
Secondary
reduction Clutch
Counter shaft Counter shaft Counter shaft
gear
Primary
reduction
Front motor gear Front motor Front motor

Motor shaft Motor shaft Motor shaft

(a) EV mode (b) Series driving mode (c) Parallel driving mode
（18）
Fig. 7 Driving modes of Mitsubishi Outlander PHEV .

Input shaft integrated with

motor shaft
Press-fit intermediate gear
on intermediate shaft

Laser welded ring gear on

differential housing

Ball bearings

Dog clutch disconnect

Fig. 8 Appearance of transmission for Isuzu Erga HV（24）. Helical gears

Fig. 10 Section view of Peugeot 3008 rear unit.

member of the dual clutch system (the even-number

gear side) (Fig. 9). Both cases use a conventional starter.

7 Four-Wheel Drive Device Trends

The Peugeot 3008 Hybrid4 includes an electric motor
drive unit manufactured by GKN plc for driving the rear
wheels. The engagement mechanism for the differential
housing on the input side driven by the electric motor
Fig. 9 Transmission for Mitsubishi Fuso Canter HV. and the pinion pin supporting member on the output
side uses a dog clutch to reduce loss when disconnected
6-speed automated MT (manufactured by Eaton Corpo- (Fig. 10).
ration) through a clutch. This system is specifically de-
8 Drivetrain Research Trends
signed for buses that have frequent starts and stops and
allows motor drive on start ups and energy regeneration For half-toroidal CVTs, research is aiming to ex-
when stopping (Fig. 8) (19)
. pand the gear ratio range by reducing the pressing
The Hino 195h small truck uses a parallel hybrid sys- force between the disc and power roller, improving
tem (manufactured by Aisin Seiki Co., Ltd.) that connects the accuracy of contact point prediction, improving
the engine with a MG and 6-speed AT through a clutch. the oil traction coefficient, and the like. It may be
The Mitsubishi Canter is installed with a parallel hybrid possible in the future to expand the gear ratio range
(20)
system that adds a motor (40 kW, 200 Nm) to the outside from 4.33 to 8.0 . In addition, a new model was

Copyright© 2013 Society of Automotive Engineers of Japan, Inc. All rights reserved
 proposed for estimating the temperature within the (M009) for Heavy-duty Commercial Vehicles (20124724), JSAE
Symposium, The Latest Technology of Power Transmission Sys-
oil film for improving the accuracy of traction coef- tem 2012, No. 02-12, p. 27 ─ 30
ficient estimation. The improvement in estimation （8） BMW Website, Press Release (2012)
(21) （9） VW Website, Press Release (2012)
accuracy was then confirmed by verification tests .
（10） ZF Webiste, Press Release (January 14 , 2013)
Research is also aiming to improve the quietness and （11） Green Car Congress (2012 .9 .26)
reliability of a planetary gear type torque-sensing lim- （12） Mazda Website, SKYACTIVE TECHNOLOGY
（13） Inukai, et al.: Development of New CVT for Midsize Vehicle
ited slip differential (LSD) during differential operation. (20124725), JSAE Symposium, The Latest Technology of Power
The µ -v characteristics of the positive gradient can be Transmission System 2012, No. 02-12, p. 31 ─ 35
（14） Imai, et al.: Development of Variator System for JATCO CVT8
maintained by applying the appropriate surface rough- and CVT8 High Torque (20124726), JSAE Symposium, The Lat-
ness to the sliding portions, adopting a carbon-based est Technology of Power Transmission System 2012, No. 02-12 ,
p. 36 ─ 39
hard coating, and keeping the surface pressure of the
（15） Introduction of New SUBARU LEGACY and OUTBACK, Subaru
(22)
sliding portions below the ideal threshold . Another Technical Review, No. 39, p. 122─ 139 (2012)
report describes a measure related to the automation of （16） Ohgata, et al.: Development of CVT for 1.5 L-class FWD-vehicle
(20125753), JSAE Annual Congress Proceegings, No. 146 ─ 12
the enormous amount of calibration operations required （17） Mercedes-Benz Website, LifeCycle, March 2012, 05, 09
for shift control systems as the gear ratio range of ATs （18） Mitsubishi Outlander PHEV New Model Technical Description
（19） Isuzu Motors Website, Press Release (August 9 , 2012)
expands and the number of shift speeds increases to im- （20） Oishi, et al.: Development of Wide Ratio Coverage Half-toroidal
(23)
prove fuel efficiency and driveability . CVT (20125126), JSAE Annual Congress Proceegings, No. 26-12,
p. 1 ─ 4
References （21） Sano, et al.: Prediction method of maximum traction coefficient
（ 1 ） International Organization of Motor Vehicle Manufacturers for traction drive type CVT, JSAE Symposium, The Latest
(OICA) Website, Sales Statistics Technology of Power Transmission System 2012 , No. 02-12 , p. 7
（ 2 ） Fuji-Keizai Group, Press Release, No. 13018 (March 1 , 2013) ─ 12
（ 3 ） Mercedes-Benz Website, Press Release (May 9 , 2012) （22） JSAE Symposium, The Latest Technology of Power Transmis-
（ 4 ） ZF Webiste, Press Release (May 9 , 2012) sion System 2012, No. 02-12, p. 31 ─ 35
（ 5 ） Honda R&D Technical Review, Vol. 24, No. 2, p.53 ─ 60 (October （23） Hibino, et al.: Robust Design Method for Automatic Calibration of
2012) Automatic Transmission Shift Control System (20125266), JSAE
（ 6 ） Ishii, et al.: Introduction of SKYACTIV-MT, Mazda Technical Annual Congress Proceedings, No. 27-12, p. 5 ─ 10
Review, No. 30, p. 24 ─ 27 (2012) （24） Eaton Catalogue
（ 7 ） Yamazaki, et al.: Development of New 9 Speed Transmission （25） Toyota Motor Website

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