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A JOURNAL OF COMPOSITION THEORY ISSN : 0731-6755
Transmission System in Automobiles:A Review
Anand Sharma
Department of Mechanical Engineering,
UIET, Panjab University, Chandigarh, India
Email-
Parveen Goyal
Department of Mechanical Engineering,
UIET, Panjab University, Chandigarh, India
Email- pgoyal@pu.ac.in
Abstract- This paper presents an overview of transmission system with a focus on the major classification, need of
transmission, torsen differential’s prospects, electric vehicular transmission, CVT, factors for providing driving
simplification. A little of electric drive tracked vehicles is researched and laid out in this template. The need for effective
& efficient transmission with causing less driver fatigue and providing more pleasurable drive is the hot research area
now a days, and several researches has been going on the subject.
Keywords –Electric drive, Optimization, Transmission, torsen differential,
I. INTRODUCTION
The transmission is that crucial part of an automobile system which is involved in transferring the power generated by the engine
all the way to the driving axles through the gearbox and differential. The power developed by the engine is provided to
transmission through a rotating crankshaft and that output power is reached to one or more differential via driveshaft.
There are mainly two main types of transmissions to be discussed in this part namely manual transmission and automatic
transmission. Manual transmission works on the simple principle of gear ratio. The main shaft gears have a synchronized cone
teeth arrangement. A hub is fixed to the shaft. A sleeve that is free to slide over the hub is also used in this system. It is clear that
if the sleeve gets connected with the teeth of the synchronizer cone, the gears and shaft will turn together or the desire locking
action can be achieved. But during the gearbox operation the shaft and gear will be rotating in different speeds. A synchronizer
ring helps to match the speed of the gear with that of the shaft. The synchronizer ring is capable of rotating along with the hub but
it is free to slide in actual fact. The input and output shaft are connected through a counter shaft. The technique we use now a
days is known as constant mesh transmission as all of the gears mounted on the input and output shaft always remain in contact.
It is interested to know that in the highest gear the input and output shaft are almost directly connected.
.
Figure 1. Transmission parts [2]
Automatic transmission was developed to overcome the power discontinuation problem in manual transmission and uses a
planetary gear set arrangement rather than a simple gear pair. The hydraulic automatic transmission is the most popular form. It
has three main components– fluid coupling, planetary gear train set and hydraulic controls. This system uses a fluid coupling in
place of a friction clutch and accomplishes gear change by locking and unlocking a system of planetary gears. A simple planetary
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A JOURNAL OF COMPOSITION THEORY ISSN : 0731-6755
gear set consists of a sun gear, a planet carrier and a ring gear. Each of these components can be input, the output or can be held
stationery. Choosing which component plays which role will determine the gear ratio. For e.g. in first gear the torque converter
which is driven by the engine, drives the sun gear. The multi plate brake holds the ring gear stationery. The planet carrier is
connected to the output and thus drive the wheels of the vehicle. In the fifth or the highest gear, the torque converter drives the
planet carrier. The sun gear is held stationery and the ring gear is connected to the output which drives the wheels of the car and
thus in this arrangement the output speed becomes faster than the input speed and it is also known as overdrive. It selects an
appropriate gear ratio without the driver’s intervention. There is no gearshift in the car as once we put an automatic transmission
vehicle into drive, everything will be automatic [1] [3].
II. NEED FOR TRANSMISSION
The power generated by the engine flows to the transmission before reaching the drive wheels. The basic question is why do we
need transmission? An internal combustion engine produces useful torque and power only during a certain speed range. Due to tis
inherent problem of IC engine, controlling the he drive wheels speed by directly connection them to the engine is not a clever
idea. Such an approach will give the engine a very low efficiency. Rather we need a transmission in between so that the engines
can always be in the maximum efficiency range. The transmission takes care of the speed variation of the drive wheels. The
function mainly performed by the transmission is to have a control on the speed and torque available to the drive wheels to be
used in driving conditions which differs from each other. For example if one wants to climb an upward slope he will obtain more
torque by decreasing the speed at the transmission and that high torque is achievable for the same power input. Conversely, if the
torque demand is low like in straight road or downslope condition, we can increase the transmission speed [3].
III. Torsen Differential Prospects in Transmission System
Now a days, manufacturers are busy in developing those techniques which will be helpful in improving performance and handling
of new and advanced four wheel drives. In this context, a most important component of the transmission system is studied known
as differential. A differential is comprised of a gear train which is in simple planetary form, are nothing but a set of gears that
transfer power to the wheels and provide them the ability to rotate at speeds while they are turning. The outer wheels always cover
a longer path and the inner wheels cover a shorter path simultaneously while rotating at different speeds. Thus the importance of
Torsen differential among the available differentials of similar compatibility is felt more. This differential has properties like it is a
type of self-locked, requires lesser maintenance etc[4] [5].
Figure 2. Torsen differential [4]
3.1 Methodology of Torsen Differential –
Torsen differential uses the assembly of worm and worm gear in its operation which makes it unique. In its
operation a worm gear (bigger in size to that of worm wheel) is able to rotate the worm wheel but the rotating worm
wheel will not be able to spin the worm gear. This characteristic of torsen differential makes it different from other
differentials and makes it to respond quickly when any change in the torque output occurs. The pair of worm wheels
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A JOURNAL OF COMPOSITION THEORY ISSN : 0731-6755
have helical teeth and they are connected with the help of spur gears. Three types of gears are used namely parallel
gears, helical gears and planetary gears. For maintaining the suitable amount of torque distribution that must be at
rear, front and center position, the torsen differential can be used.
3.2 Torsion differential’s working –
In straight road conditions, the torque over the two wheels is equally distributed and thus no technical problem does
occur. In situations of slippery and muddy roads, the appropriate torque and speed distribution to be provided on the
wheels gets complicated. The outer and inner wheels should rotate with a bit different speed. The torque division is
needed between the drive axles at a bias ratio to serve as a precondition. As we know in an ordinary differential
suppose the left wheel is stuck in mud, it will rotate more as it is having greater resistance to move linearly. The
maximum of power generated by the transmission which is then transferred by differential hub to the axles is gone
to that wheel which was stuck in mud and the other i.e. right wheel would not get the necessary torque to rotate itself
and help the vehicle in moving forward. This drawback is eliminated in the case of torsen differential. It transfer the
toque in proportion to both the wheels which helps the wheel (which is not stuck in mud) to rotate and subsequently
contribute in the movement of the vehicle. By the method of its working this differential is popular now a days, as it
helps in reducing driver fatigue that would allow more attention on roads[4] [5] [6].
IV. HYBRID ELECTRIC VEHICLE TRANSMISSION
th
For decreasing the emission levels in our atmosphere, electric vehicles were developed early in 20 century. Electric vehicles run
on electric transmission system which uses an electric motor device. The transmission system is of three types namely pure
electric vehicles (PEV), hybrid electric vehicles (HEV) and fuel cell electric vehicles (FCEV). PEVs have very high initial cost
and their driving range is often short. That’s the reason they are not suitable to the general consumers need. FCEVs have brighter
future as they have zero emission and a well comparative driving range. But the thing is, the development is under process and is
difficult to find or discover low cost fuel cells and their refueling system. HEV is concluded as the interim solution between these
three. In the most cases, HEV mainly consists of a battery and an internal combustion engine (ICE).
4.1 Function & issues of HEV transmission –
It is similar to a conventional vehicle’s transmission but it employs a motor which is used to store a part of the kinetic energy in
battery (battery is attached to the wheels) while braking occurs. The braking cause the wheels to lose all of the kinetic energy into
friction and we can use this energy to get stored in the battery. A statistic says, by employing this technique we can save one third
of the total energy and get it stored in the battery which could have been all lost in the friction as the braking occurs.
The main issues in hybrid electric vehicle transmission is how to make the ICE operate at maximum efficiency. How one can
regulate the output power from the battery to meet the required power to the vehicle and give it a supplement? How one can
obtain the better fuel economy by optimizing the power flow also known as energy management. These are the issues need to be
addressed [7] [8] [9].
V. DESIGN OF THE AUTOMATIC GEARBOX PROVIDING DRIVING SIMPLIFICATION
The design of gearboxes used in the vehicles is studied. Simple design of gearboxes increase the work intensity of driver
especially in urban areas due to gear shifting and in clutch release. So the new designs of gearboxes are to be made in such a way
which would reduce the driver fatigue and enhances the concentration of drivers on the roads which ultimately lead to
improvement in the traffic safety.
Several types of gearboxes are reviewed. Mechanical gearboxes with automatic clutch provides less driver fatigue but their price
is twice as high as that of the gearbox with manual shifting. The ones having hydro mechanical transmission with electronic
control use a torque converter on high gears with hydraulic pump drive for compressing clutch disks but again the thing is its
price is thrice as high as compared to mechanical gearboxes. Similar is the case for Variators which reduces driver fatigue due to
continuously variable transmission. This type of gearbox has bigger mass and smaller efficiency coefficient.
5.1 Reducing Driver Fatigue –
The new design and principle of a step by step gearbox shifts gears automatically and the clutch is used by the driver only during
start of the vehicle and is not necessary during stopping. This design provides for decrease of work intensity for driver and also
cause to reduce in clutch operation and gearbox costs. Driver can now rely on the smooth operation of clutches. They must be
happy that their workload would be significantly decreased which would improve their attention on roads and ensure their safety
[10] [11] [12].
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A JOURNAL OF COMPOSITION THEORY ISSN : 0731-6755
VI. CONTINUOUSLY VARIABLE TRANSMISSION (E- DRIVE)
Continuously variable transmission i.e. CVT provides a very large number of gear ratios which makes the operation of gear
changing a nice experience. Two conical pulleys and a steel belt make up a basic CVT. The belt is turned by the input pulley and
then the output pulley is turned by the belt. The space between the cones ascertains the effective diameter of the pulley and for
that configuration the speed of the input pulley is always more than that of the output pulley. With the decrease in gap the
effective diameter of the pulley decreases. This simple mechanism forms the basic operation of the CVT. According to the
driving conditions, a transmission control unit will be responsible for adjusting the width between these cones and as a result of
this the speed change would be smooth and unnoticeable which doesn’t occur in any other transmission.
Rising concerns about the depleting air quality in the environment due to increasing emission levels, we often feel that there’s a
need of more use of bicycles over gasoline or diesel powered vehicles. It will provide a cleaner and sustainable transportation in
urban areas. A bicycle is a maneuverable, lightweight and is efficient to operate kind of vehicle. Recently, efforts have been made
in the direction of CVT technology to be adapted in light weight drive like bicycle. The e-drive is accommodated on the rear
wheel of a bicycle. Components consist of a shifter, computer and drive assembly. The shifter can be integrated in a brake handle
or handle bar grip, and the computer would be wore by the bicyclist. The Fig. 2 shows the e-Drive assembly. A housing made up
of plastic which is transparent in nature, is used to make tight the drive assembly and preserve it from the invasion of water and
dust [13] [14] [15][22].
Figure 3. E-Drive assembly on bicycle in operation with a close-up of the assembly (right)[14].
Sequence of the functions of e-drive:
(a) rotational power is transmitted to the drive input, (b) power is transmitted to the rear wheel output from a variable diameter
pulley, (c) a command signal in wireless form is sent to the transmitter receiver to the servo which actuates a displacement of the
pulley segments, and a resulting change in the transmission input–output ratio. The prototype tests these essential functions.
VII. Optimization of Electric Transmission Drive Tracked Vehicles
The electric transmission of drive tracked vehicles has packed together the electrical machines and power converters which gives
its drive a smooth continuously variable speed and good acceleration performance. Optimization in these vehicles has the purpose
to obtain maximum efficiency in the transmission. When we steer the vehicle, the speed and resistance of high
speed side track would become more, so the motor is expected to supply larger power. The regenerative power gets produced in
the side track moving with the lower speed. And what happens is when a person steer the car with smaller radius the previously
generated regenerative power gets absorbed by the side motor running at a lower speed. If that regenerative power could be
transmitted to the side track running at a higher speed then the requirement of power for its motor would be brought down by a
greater amount which results in increase in efficiency of the system. The efficiency of transmission depends on the power loss of
the motor and power loss which occurred mechanically. To improve the efficiency of transmission system, the most effective
way is to cut down the power of the motor. The results of the analysis and simulation shows that when we keep the steering
radius bigger, the efficiency of the system reduces with the increment of the torque of the motor and for the case of vehicle driven
with their steering radius being kept smaller, the efficiency increases with increase of the torque of the motor [15] [16] [17] [20].
Volume XII Issue VII JULY 2019 Page No: 696
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