Transmission play an important role in the improvement in vehicle
performance and fuel economy.
Two basic main function of transmission are-
Disconnect the engine from the drive while the car has stopped, thus
allowing the engine to keep idling while the wheels aren’t.
Provide a range of gear ratios that allow quick acceleration from a stop.
3. Automatic transmission control is one of the key elements for the
improvement of vehicle safety, comfort and performance together
with the reduction of fuel consumption and emission in modern
Different approaches such as automatic,continuosly variable and
automated manual transmission have been pursued.The AMT
represents an important solution for the automobile industry.
Manual transmission has an overall efficiency of 96.2 % which is
highest in all types. Belt driven CVT have overall efficiency of
84.6%. Automatic transmission has efficiency of 86% whereas
automated manual transmission has efficiency par with manual
4. AMT has the advantage of lower weight and higher efficiency compared
with other automatic transmissions.
AMT is directly derived from manual transmission with the integration of
servo-actuators into existing devices, thus the development and production
costs are generally lower compared to other transmission technique.
5. What is AMT(Working principle)
AMT consists of a multi speed gearbox and a clutch both equipped
with electro hydraulic actuators controlled by an Electronic Control
The AMT can work in two different ways:
1)Semiautomatic-Where the gear shifting is requested by the driver by
means of proper levers.
2)Fully automatic-Here the ECU attends to the selection of gears
depending on various engine and driving conditions.
In both these situations, clutch and gearbox actuators must be properly
controlled in order to perform the gear shift.
7. Clutch actuation system
Automated manual transmission can be divided on the basic of the clutch
They are divided as single clutch and dual clutch automated manual
Single clutches were used in the earlier models, modern day vehicles make
use of dual clutch automated manual transmission.
8. Electro-hydraulically operated single clutch
When no external force is applied, clutch disks are pressed together by
preload springs, in this way clutch is locked and engine torque can be
Force applied to the piston is provided by an electro-hydraulic actuator.
To disengage the clutch, the hydraulic piston pushes the release bearing
10. The figure shows electronically operated clutch actuator.
It makes use of the rotary movement of the electric motor which is
transformed via a toothed gear segment into a linear movement.
This helps to open the clutch with the help of the release levers and release
This is an older, lurch prone and generally unpleasent, only smart forkwo
and exotic cars use them. 10
Electronically operated clutch actuator
11. Dual clutch automated manual transmission
Dual clutch transmission has two separate manual gearboxes
contained within one housing and working as one unit.
Sophisticated electronics and hydraulics control the clutches. One
clutch would control the odd gears while the other control the even
13. Transmission actuation system
The actuator system can be divided into three main subsystems-
Pressure control valves
14. Pressure control valves
The servo valves used for gear
engagement are single stage
pressure control valve
Consists of a valve , diaphragm
and a sensing unit which monitors
the required pressure as required.
Pipelines are long flexible pipes of
about 0.7m length.
Pipelines are provided for connection
between pressure control valve and
Pipelines are used because the above
connections may not be easy to make due
to vehicle layout constraints
16. Hydraulic actuators
The selection of the necessary gear ratios is performed by locking a
set of gears to the shafts by means of electro-hydraulic actuator.
The actuator used comprises of a piston joined with a fork on which
opposite axial forces can be applied by means of two distinct
hydraulic circuit. 16
17. The left and right movement corresponds to engaged odd and even
gears respectively, while middle position corresponds to neutral.
Oil pressures on actuator chambers are controlled by means of two single
stage pressure control valves connected to the actuator with two flexible
18. Electronic and transmission control unit
In this portion the automated manual transmission consists of a
transmission control unit(TCU) and a elecronic control unit(ECU).
The transmission control unit receives input signals from various
sensors like gear position sensor, clutch position sensor, brake
position sensor, transmission output speed.
20. It also collects vehicle related signals like torque requirement, engine speed
and throttle position from ECU(Electronic control unit).
The TCU has a control strategy, which on receiving the input signals,
generate the necessary output signal for the clutch actuator and gear shifting
22. Recent developments
Zero shift automated manual transmission allows a manual transmission to
shift gears in zero seconds.
It is easy to manufacture and is cost effective compared to alternative
Compared to existing AMT, zero shift provides uninterrupted torque path
from the engine to the vehicle which allows a seamless gearshift
23. Recent developments (cont’d)
Shift control algorithm without clutch operation in automated manual
transmission in hybrid electric vehicles.
Shift control without clutch operation is possible because both engine and
motor can control the speed of input shaft.
The shift control algorithm is said to increase the shift quality of vehicle
and prolongs the life of the clutch.
An optimum control strategy is the key to successful working of AMT.
AMT allows to provide driving comfort and gear shift quality.
AMT has the advantage of lower weight and higher efficiency with respect
to other automatic transmission.
Production cost is generally lower compared to other transmission
AMT has proved to provide 10% decrease in fuel consumption and also
decrease in CO2 emissions.
Lucente, Marcello Montanare, Carlo Rossi, G. Lucente, ‘Modeling of an
automated manual transmission
R.P.G Heath and A.J. Child, ‘Zeroshift Automated Manual
Transmission(AMT)’ ,SAE Paper No. 2007-26-061,(2007),pp.693-
Liao Chenglin, Zhang Junzhi, Zhu Haitao, ‘ A Study of Shift Control
Algorithm without Clutch Operation for Automated Manual Transmission in
the Parallel Hybrid Electric Vehicle’ ,SAE of China, Fiesta , World
Automobile Congress, Barcelona, February 13. 2004.