COMPARATIVE STUDY OF
VARIOUS TRANSMISSION SYSTEM
A Seminar Report Submitted
in Partial Fulfilment of the Requirements
for the Degree of
BACHELOR OF TECHNOLOGY
in
Mechanical Engineering
By
ANIKET TRIPATHI
(Roll No. 1616440024)
Under the Supervision of
MR. GURMEET SINGH ARORA
PROFESSOR
Department of Mechanical Engineering
Pranveer Singh Institute Of Technology, Kanpur
ABDUL KALAM TECHNICAL UNIVERSITY LUCKNOW
September 2018
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CERTIFICATE
Certified that Mr Aniket Tripathi (Roll Number :1616440024) has carried out the
research work presented in this thesis entitled “COMPARATIVE STUDY OF VARIOUS
TRANSMISSION SYSTEM” for the award of Bachelor of Technology from Abdul Kalam
Technical University, Lucknow under my supervision. The seminar embodies results of
original work, and studies are carried out by the student himself and the contents of the seminar
do not form the basis for the award of any other degree to the candidate or to anybody else
from this or any other University/Institution.
(MR. GURMEET SINGH ARORA)
Professor
Department of Mechanical Engineering
PSIT. Kanpur
Date:
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ABSTRACT
Transmission in automobiles is a unit which supplies the power from the clutch to the
differential. The simplest transmissions are manual transmissions which consist of a set of
gears which are in mesh when transmitting power. Manual transmission requires frequent shift
between gears especially while driving in cities. Each time it requires engaging and
disengaging clutch while shifting gears. This is a tiresome task. In order to make this task
easier, automatic transmissions are evolved. The automatic transmission no more consists of a
clutch unit. Thus there are two big differences between a manual transmission and an automatic
transmission. They are:


There is no clutch pedal in automatic transmission car.
There is no gear shift in automatic transmission car. Once you put the transmission in
the drive, everything else is automatic.
Both the automatic and manual transmissions accomplish exactly the same thing, but they
do it in totally different ways. Further, learning in a vehicle fitted with an automatic
transmission is very easy. But even now the vehicles with automatic transmissions are not very
popular in India. This is because the cost of such vehicles is comparatively high and low fuel
economy. When automatic transmissions were introduced in India it was mainly used by
persons having some kind of disable ness. Now that mind set has been changing rapidly
because of many technological advancements making such vehicles more powerful and more
economical ones.
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ACKNOWLEDGEMENT
I wish to express my sincere gratitude to Mr. Gurmeet Singh Arora, Professor, Department
of Mechanical Engineering, Pranveer Singh Institute of Technology, for providing me kind
guidance, continuous encouragement, extend help and support during my thesis work.
I wish to express my sincere gratitude to Prof. Nitin Srivastava, Head of Department of
Mechanical Engineering, Pranveer Singh Institute of Technology, Kanpur for providing me
kind guidance, continuous encouragement, extend help and support during my work.
I would also like to offer thanks to Dr. Ajit Kumar N. Shukla, Director, PSIT, Kanpur, for
allowing me to do this work.
I am also thankful to all the faculty members of PSIT Kanpur, for providing me various kind
of support and help directly or indirectly, during my present work.
Finally, I am extending my thanks to my parents, my sister, friends, a n d m y t e a c h e r s
for their blessings, strong support, encouragement and love that helped me to complete this work.
Date:
(Aniket Tripathi)
Roll No. 1616440024
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TABLE OF CONTENTS
Page No.
Abstract
iii
List of Table
vii
List of Figure
viii
ix
List of Symbols
Chapter 1 INTRODUCTION ABOUT TRANSMISSION
08-09
1.1
Introduction
08
1.2
Explanation
08
1.3
Use
08-09
Chapter 2 TYPES OF TRANSMISSION
Chapter 3 AUTOMATIC TRANSMISSION
10
11-17
3.1
INTRODUCTION
11-12
3.2
PARTS AND OPERATION
12-15
3.3
EFFECTS ON VEHICLE CONTROL
3.4 ADVANTAGES,DISADVANTAGES AND EFFICIENCY
16
16-17
Chapter 4 MANUAL TRANSMISSION
4.1
4.2
4.3
4.4
OVERVIEW
INTERNALS
CLUTCH
BENEFITS AND DRAWBACKS
18
18-19
19-22
22-23
23-26
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Chapter 5 CONTINUOUSLY VARIABLE TRANSMISSION
5.1
OVERVIEW
27-34
27-28
5.2
THEORY AND DESIGN
28-31
5.3
BACKGROUND AND HISTORY
31-34
Chapter 6 CONCLUSION AND FUTURE WORK
6.1
35
Conclusion
35
REFERENCES
36
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LIST OF FIGURE
Description
Page No
FIG 1. 8 GEAR AUTOMATIC TRANSMISSION SYSTEM…….............................11
FIG. 2 TORQUE CONVERTER ……………………………………….…………....12
FIG 3. CUT-AWAY MODEL OF TORQUE CONVERTER……………….……….13
FIG 4.
PLANATERY GEAR SETS ………………………………………….….…..14
FIG 5.
MANUAL TRANSMISSION……………………………………….….……15
FIG 6.
SHAFT……………………………………………………………….….…...19
FIG 7.
DOG CLUTCH……………………………………………….…….……...….20
FIG 8.
SYNCHROMESH………………………………………………………….....21
FIG 9.
CVT TRANSMISSION………………………………………………...…….28
FIG 10.
PUSH BELT……………………………………………………………...….28
FIG 11. TOROIDAL CVT……………………………………………………….…....29
FIG12. VARIABLE DIAMETER BELT ……………………………………….……..30
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CHAPTER 1: INTRODUCTION
A transmission is a machine in a power transmission system, which provides controlled
application of the power. Often the term transmission refers simply to the gearbox that
uses gears and gear trains to provide speed and torque conversions from a rotating power
source to another device.
In British English, the term transmission refers to the whole drivetrain, including clutch,
gearbox, prop shaft (for rear-wheel drive), differential, and final drive shafts.
In American English, however, the term refers more specifically to the gearbox alone, and
detailed usage differs.
The most common use is in motor vehicles, where the transmission adapts the output of
the internal combustion engine to the drive wheels. Such engines need to operate at a
relatively high rotational speed, which is inappropriate for starting, stopping, and slower
travel. The transmission reduces the higher engine speed to the slower wheel speed,
increasing torque in the process. Transmissions are also used on pedal bicycles, fixed
machines, and where different rotational speeds and torques are adapted.
Often, a transmission has multiple gear ratios (or simply "gears") with the ability to switch
between them as speed varies. This switching may be done manually (by the operator) or
automatically. Directional (forward and reverse) control may also be provided. Single-ratio
transmissions also exist, which simply change the speed and torque (and sometimes
direction) of motor output.
In motor vehicles, the transmission generally is connected to the engine crankshaft via a
flywheel or clutch or fluid coupling, partly because internal combustion engines cannot run
below a particular speed. The output of the transmission is transmitted via the driveshaft to
one or more differentials, which drives the wheels. While a differential may also provide gear
reduction, its primary purpose is to permit the wheels at either end of an axle to rotate at
different speeds (essential to avoid wheel slippage on turns) as it changes the direction of
rotation.
Conventional gear/belt transmissions are not the only mechanism for speed/torque adaptation.
Alternative mechanisms include torque converters and power transformation (e.g. dieselelectric transmission and hydraulic drive system). Hybrid configurations also exist.
Automatic transmissions use a valve body to shift gears using fluid pressures in response to
speed and throttle input.
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1.1 Explanation
Early transmissions included the right-angle drives and other gearing in windmills, horsepowered devices, and steam engines, in support of pumping, milling, and hoisting.
Most modern gearboxes are used to increase torque while reducing the speed of a prime
mover output shaft (e.g. a motor crankshaft). This means that the output shaft of a gearbox
rotates at a slower rate than the input shaft, and this reduction in speed produces a mechanical
advantage, increasing torque. A gearbox can be set up to do the opposite and provide an
increase in shaft speed with a reduction of torque. Some of the simplest gearboxes merely
change the physical rotational direction of power transmission.
Many typical automobile transmissions include the ability to select one of several gear ratios.
In this case, most of the gear ratios (often simply called "gears") are used to slow down the
output speed of the engine and increase torque. However, the highest gears may be
"overdrive" types that increase the output speed.
1.2 Uses
Gearboxes have found use in a wide variety of different—often stationary—applications,
such as wind turbines.
Transmissions are also used
in agricultural, industrial, construction, mining and automotive equipment. In addition to
ordinary transmission equipped with gears, such equipment makes extensive use of the
hydrostatic drive and electrical adjustable-speed drives.
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CHAPTER 2: TYPES OF TRANSMISSION

Automatic Transmission (AT)
This is a transmission that uses a torque converter, planetary gearset and clutches or bands to
shift through a vehicle's forward gears automatically. Some automatics allow the driver a
limited amount of manual control over the vehicle (aside from choosing a forward, reverse or
neutral mode) -- for example allowing the driver to control upshifts and downshifts by
utilizing buttons or paddles on the steering wheel or the gear selector. Common names for
such transmissions are "shiftable automatic," "Tiptronic" and "autostick." To learn more,
see Automatic Transmissions: What Makes Them Work.

Manual Transmission (MT)
With a manual transmission, the driver selects all gears manually using both a movable gear
selector and a driver-operated clutch. This type of transmission is also known as a "stick
shift" or a "standard" transmission. See Manual Transmission Basics for more information.

Continuously Variable Transmission (CVT)
This transmission has a continuously variable drive ratio (as opposed to conventionally
stepped gear ratios) and uses belts, pulleys and sensors rather than gears to maintain a steady
acceleration curve with no pauses for gear changes. Because of this, a CVT can keep the
engine in its optimum power range, thereby increasing efficiency and gas mileage. You can
get more information from CVT Enters the Mainstream.
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CHAPTER 3: AUTOMATIC TRANSMISSION
3.1 INTRODUCTION
A transmission is a device that is used to provide a set of discrete angular velocity outputs
from a constant velocity source. It is connected to the output of the engine and delivers the
power from the engine to the drive wheels. The transmission uses gears to make more effective
use of the engines torque and to keep the engine operating at an appropriate speed
An automobile engine runs at its best efficiency at a certain Revolutions Per Minute
(RPM) range and it is the transmission's job to make sure that the power is delivered to the
wheels while keeping the engine within that range. It does this through various gear
combinations. In first gear, the engine turns much faster in relation to the drive wheels, while
in high gear the engine is loafing even though the car may be travelling at higher speeds. In
addition to the various forward gears, a transmission also has a neutral position which
disconnects the engine from the drive wheels, and reverse, which causes the drive wheels to
turn in the opposite direction allowing to reverse the direction of the car
An automatic transmission is much easier to drive than a manual transmission,
because they do not have a clutch pedal or gearshift lever. An automatic transmission does the
work all by itself. The first automatic transmission appeared in 1939. Automatic transmissions
automatically change to higher and lower gear ratios with changes in the speed of the car and
the load on the engine. These transmissions are also aware of how far down the accelerator
have been pushed, and shift accordingly.
FIG. 1 An 8-gear automatic transmission
An automatic transmission, also called auto, self-shifting transmission, n-speed
automatic (where n is its number of forward gear ratios), or AT, is a type of motor
vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing
the driver from having to shift gears manually. Like other transmission systems on vehicles, it
allows an internal combustion engine, best suited to run at a relatively high rotational speed,
to provide a range of speed and torque outputs necessary for vehicular travel. The number of
forward gear ratios is often expressed for manual transmissions as well (e.g., 6-speed
manual).
The most popular form found in automobiles is the hydraulic automatic transmission. Similar
but larger devices are also used for heavy-duty commercial and industrial vehicles and
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equipment. This system uses a fluid coupling in place of a friction clutch, and accomplishes
gear changes by hydraulically locking and unlocking a system of planetary gears. These
systems have a defined set of gear ranges, often with a parking pawl that locks the output
shaft of the transmission to keep the vehicle from rolling either forward or backward. Some
machines with limited speed ranges or fixed engine speeds, such as some forklifts and lawn
mowers, only use a torque converter to provide a variable gearing of the engine to the wheels.
Besides the traditional hydraulic automatic transmissions, there are also other types of
automated transmissions, such as a continuously variable transmission(CVT) and semiautomatic transmissions, that free the driver from having to shift gears manually, by using the
transmission's computer to change gear, if for example the driver were redlining the engine.
Despite superficial similarity to other transmissions, traditional automatic transmissions differ
significantly in internal operation and driver's feel from semi-automatics and CVTs. In
contrast to conventional automatic transmissions, a CVT uses a belt or other torque
transmission scheme to allow an "infinite" number of gear ratios instead of a fixed number of
gear ratios. A semi-automatic retains a clutch like a manual transmission, but controls the
clutch through electrohydraulic means. The ability to shift gears manually, often via paddle
shifters, can also be found on certain automated transmissions (manumatics such
as Tiptronic), semi-automatics (BMW SMG, VW Group DSG), and CVTs (such
as Lineartronic).
3.2 PARTS AND OPERATION
1) Torque converter
FIG 2 TORQUE CONVERTER
A type of fluid coupling, hydraulically connecting the engine to the transmission. This takes
the place of a friction clutch in a manual transmission.[8] It transmits and decouples the engine
power to the planetary gears, allowing the vehicle to come to stop with the engine still
running without stalling.
A torque converter differs from a fluid coupling, in that it provides a variable amount
of torque multiplication at low engine speeds, increasing breakaway acceleration. A fluid
coupling works well when both the impeller and turbine are rotating at similar speeds, but it
is very inefficient at initial acceleration, where rotational speeds are very different. This
torque multiplication is accomplished with a third member in the coupling assembly known
as the stator, which acts to modify the fluid flow depending on the relative rotational speeds
of the impeller and turbine. The stator itself does not rotate, but its vanes are so shaped that
when the impeller (which is driven by the engine) is rotating at a high speed and the turbine
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(which receives the transmitted power) is spinning at a low speed, the fluid flow hits the
vanes of the turbine in a way that multiplies the torque being applied. This causes the turbine
to begin spinning faster as the vehicle accelerates (ideally), and as the relative rotational
speeds equalize, the torque multiplication diminishes. Once the impeller and turbine are
rotating within 10% of each other's speed, the stator ceases to function and the torque
converter acts as a simple fluid coupling.
FIG 3 CUT-AWAY MODEL OF TORQUE CONVERTER
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2) Planetary gears train
FIG 4 PLANATERY GEAR SETS
Consisting of planetary gear sets as well as clutches and bands. These are the mechanical
systems that provide the various gear ratios, altering the speed of rotation of the output shaft
depending on which planetary gears are locked.
To effect gear changes, one of two types of clutches or bands are used to hold a particular
member of the planetary gearset motionless, while allowing another member to rotate,
thereby transmitting torque and producing gear reductions or overdrive ratios. These clutches
are actuated by the valve body , their sequence controlled by the transmission's internal
programming. Principally, a type of device known as a sprag or roller clutch is used for
routine upshifts/downshifts. Operating much as a ratchet, it transmits torque only in one
direction, free-wheeling or "overrunning" in the other. The advantage of this type of clutch is
that it eliminates the sensitivity of timing a simultaneous clutch release/apply on two
planetaries, simply "taking up" the drivetrain load when actuated, and releasing automatically
when the next gear's sprag clutch assumes the torque transfer. The bands come into play for
manually selected gears, such as low range or reverse, and operate on the planetary drum's
circumference. Bands are not applied when drive/overdrive range is selected, the torque being
transmitted by the sprag clutches instead. Bands are used for braking; the GM TurboHydramatics incorporated this.
3) Hydraulic controls
Uses special transmission fluid sent under pressure by an oil pump to control various clutches
and bands modifying the speed of the output depending on the vehicle's running condition.
Not to be confused with the impeller inside the torque converter, the pump is typically a gear
pump mounted between the torque converter and the planetary gearset. It draws transmission
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fluid from a sump and pressurizes it, which is needed for transmission components to operate.
The input for the pump is connected to the torque converter housing, which in turn is bolted
to the engine's flexplate, so the pump provides pressure whenever the engine is running and
there is enough transmission fluid, but the disadvantage is that when the engine is not
running, no oil pressure is available to operate the main components of the transmission, and
is thus impossible to push-start a vehicle equipped with an automatic transmission. Early
automatic transmissions also had a rear pump for towing purposes, ensuring the lubrication of
the rear-end components.
The governor is connected to the output shaft and regulates the hydraulic pressure depending
on the vehicle speed. Modern designs have replaced the mechanical governor with an
electronic speed sensor and computer software. The engine load is monitored either by
a throttle cable or a vacuum modulator.]Modern designs have replaced these mechanical
devices with an electronic signal transmitted via a CAN bus. The valve body is the hydraulic
control center that receives pressurized fluid from the main pump operated by the fluid
coupling/torque converter. The pressure coming from this pump is regulated and used to run
a network of spring-loaded valves, check balls and servo pistons. The valves use the pump
pressure and the pressure from a centrifugal governor on the output side (as well as hydraulic
signals from the range selector valves and the throttle valve or modulator) to control which
ratio is selected on the gearset; as the vehicle and engine change speed, the difference
between the pressures changes, causing different sets of valves to open and close. The
hydraulic pressure controlled by these valves drives the various clutch and brake band
actuators, thereby controlling the operation of the planetary gearset to select the optimum
gear ratio for the current operating conditions. However, in many modern automatic
transmissions, the valves are controlled by electro-mechanical servos which are controlled by
the electronic [engine control unit] (ECU) or a separate transmission control unit (TCU, also
known as transmission control module (TCM).
The hydraulic & lubricating oil, called automatic transmission fluid (ATF), provides
lubrication, corrosion prevention, and a hydraulic medium to convey mechanical power (for
the operation of the transmission). Primarily made from refined petroleum, and processed to
provide properties that promote smooth power transmission and increase service life, the
ATF is one of the few parts of the automatic transmission that needs routine service as the
vehicle ages.
The multitude of parts, along with the complex design of the valve body, originally made
hydraulic automatic transmissions much more complicated (and expensive) to build and
repair than manual transmissions. In most cars (except US family, luxury, sport-utility
vehicle, and minivan models) they have usually been extra-cost options for this reason. Mass
manufacturing and decades of improvement have reduced this cost gap.
In some modern cars, computers use sensors on the engine to detect throttle position, vehicle
speed, engine speed, engine load, etc. to control the exact shift point. The computer transmits
the information via solenoids that redirect the fluid the appropriate clutch or servo to control
shifting.
3.3 EFFECTS ON VEHICLE CONTROL
1) Cornering
Unexpected gear changes can affect the attitude of a vehicle in marginal conditions.
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2) Maintaining constant speed
Torque converters and CVT transmissions make changes in vehicle speed less apparent by
the engine noise, as they decouple the engine speed from vehicle speed.
Lockup torque converters that engage and disengage at certain speeds can make these
speeds unstable — the transmission wastes less power above the speed at which the torque
converter locks up, usually causing more power to the wheels for the same throttle input.
3) Controlling wheelspin
Torque converters respond quickly to loss of traction (torque) by an increased speed of the
driving wheels for the same engine speed. Thus, under most conditions, where the static
friction is higher than the kinetic friction, the engine speed must be brought down to
counteract wheelspin when it has occurred, requiring a stronger or quicker throttle reduction
by the driver than with a manual transmission, making wheelspin harder to control. This is
most apparent in driving conditions with much higher static friction than kinetic, such as
packed hard snow (that turns to ice by friction work), or snow on top of ice.
4) Climbing steep slippery slopes
In situations where a driver with a manual transmission can't afford a gearshift, in fear of
losing too much speed to reach a hilltop, automatic transmissions are at a great advantage —
whereas driving a manual car depends on finding a gear that is not too low to enter the
bottom of the hill at the necessary speed, but not too high to stall the engine at the top of the
hill, sometimes an impossible task, this is not an issue with automatic transmissions, not just
because gearshifts are quick, but they typically maintain some power on the driving wheels
during the gear change.
3.4 ADVANTAGES, DISADVANTAGES AND EFFICIENCY
1) ADVANTAGES
1.Smooth and quiet shifting
2. Ease of use due to the absence of gear lever and clutch
A computerized automatic transmission has different shifting programs for different
requirements for instance, if you select Sport mode, the gearbox up shift at higher engine speed
to make better use of power band hence enhances acceleration. On the contrary, choosing
Economy mode will ease the pressure to the engine, thus enhance smoothness, quietness and
save fuel.
2) DISADVANTAGES
1. Because it employs a lot of planetary gears and clutches inside, it is considerably heavier
and several folds more expensive then manual gearbox.
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2. The use of torque converter instead of clutch makes them less responsive than manual
gearbox, moreover, they used to offer one less ratio, thus offer poorer acceleration and consume
slightly more fuel.
3) Energy efficiency
Earlier hydraulic automatic transmissions were almost always less energy efficient
than manual transmissions due mainly to viscous and pumping losses (parasitic losses), both
in the torque converter and the hydraulic actuators. 21% is the loss on a 3 speed Chrysler
Torqueflite compared to a modern GM 6L80 automatic. A relatively small amount of energy
is required to pressurise the hydraulic control system, which uses fluid pressure to determine
the correct shifting patterns and operate the various automatic clutch mechanisms. However,
with technological developments some modern continuously variable transmissions are more
fuel efficient than their manual counterparts and modern 8-speed automatics are within 5% as
efficient as a manual gearbox.
Manual transmissions use a mechanical clutch to transmit torque, rather than a torque
converter, thus avoiding the primary source of loss in an automatic transmission. Manual
transmissions also avoid the power requirement of the hydraulic control system, by relying on
the human muscle power of the vehicle operator to disengage the clutch and actuate the gear
levers, and the mental power of the operator to make appropriate gear ratio selections. Thus
the manual transmission requires very little engine power to function, with the main power
consumption due to drag from the gear train being immersed in the lubricating oil of the
gearbox.
The on-road acceleration of an automatic transmission can occasionally exceed that of an
otherwise identical vehicle equipped with a manual transmission in turbocharged diesel
applications. Turbo-boost is normally lost between gear changes in a manual whereas in an
automatic the accelerator pedal can remain fully depressed. This however, is still largely
dependent upon the number and optimal spacing of gear ratios for each unit, and whether or
not the elimination of spooldown/accelerator lift off represent a significant enough gain to
counter the slightly higher power consumption of the automatic transmission itself.
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CHAPTER 4 MANUAL TRANSMISSION
4.1 OVERVIEW
Manual transmissions often feature a driver-operated clutch and a movable gear stick. Most
automobile manual transmissions allow the driver to select any forward gear ratio ("gear") at
any time, but some, such as those commonly mounted on motorcycles and some types of
racing cars, only allow the driver to select the next-higher or next-lower gear. This type of
transmission is sometimes called a sequential manual transmission.
In a manual transmission, the flywheel is attached to the engine's crankshaft and spins along
with it. The clutch disk is in between the pressure plate and the flywheel, and is held against
the flywheel under pressure from the pressure plate. When the engine is running and the
clutch is engaged (i.e., clutch pedal up), the flywheel spins the clutch plate and hence the
transmission. As the clutch pedal is depressed, the throw out bearing is activated, which
causes the pressure plate to stop applying pressure to the clutch disk. This makes the clutch
plate stop receiving power from the engine, so that the gear can be shifted without damaging
the transmission. When the clutch pedal is released, the throw out bearing is deactivated, and
the clutch disk is again held against the flywheel, allowing it to start receiving power from
the engine.
Manual transmissions are characterized by gear ratios that are selectable by locking selected
gear pairs to the output shaft inside the transmission. Conversely, most automatic
transmissions feature epicyclic(planetary) gearing controlled by brake bands and/or clutch
packs to select gear ratio. Automatic transmissions that allow the driver to manually select
the current gear are called manumatics. A manual-style transmission operated by computer is
often called an automated trnsmission rather than an automatic, even though no distinction
between the term
FIG 5. MANUAL TRANSMISSION
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4.2 INTERNALS
1)SHAFTS
FIG 6 SHAFT
1 — middle housing, 2 — rear housing, 3 — main shaft, 4 — countershaft, 5 — power take
shaft, 6 — planet carrier of demultiplicator (range selector), 7 — planet wheel, 8 — epicycle
(ring gear)
Like other transmissions, a manual transmission has several shafts with various gears and
other components attached to them. Typically, a rear-wheel-drive transmission has three
shafts: an input shaft, a countershaft and an output shaft. The countershaft is sometimes
called a layshaft.
In a rear-wheel-drive transmission, the input and output shaft lie along the same line, and
may in fact be combined into a single shaft within the transmission. This single shaft is called
a mainshaft. The input and output ends of this combined shaft rotate independently, at
different speeds, which is possible because one piece slides into a hollow bore in the other
piece, where it is supported by a bearing. Sometimes the term mainshaft refers to just the
input shaft or just the output shaft, rather than the entire assembly.
In many transmissions the input and output components of the mainshaft can be locked
together to create a 1:1 gear ratio, causing the power flow to bypass the countershaft. The
mainshaft then behaves like a single, solid shaft: a situation referred to as direct drive.
Even in transmissions that do not feature direct drive, it's an advantage for the input and
output to lie along the same line, because this reduces the amount of torsion that the
transmission case has to bear.
Under one possible design, the transmission's input shaft has just one pinion gear, which
drives the countershaft. Along the countershaft are mounted gears of various sizes, which
rotate when the input shaft rotates. These gears correspond to the forward speeds and reverse.
Each of the forward gears on the countershaft is permanently meshed with a corresponding
gear on the output shaft. However, these driven gears are not rigidly attached to the output
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shaft: although the shaft runs through them, they spin independently of it, which is made
possible by bearings in their hubs. Reverse is typically implemented differently; see the
section on Reverse.
2) DOG CLUTCH
Among many different types of clutches, a dog clutch provides non-slip coupling of two
rotating members. It is not at all suited to intentional slipping, in contrast with the footoperated friction clutch of a manual-transmission vehicle.
The gear selector does not engage or disengage the actual gear teeth which are permanently
meshed. Rather, the action of the gear selector is to lock one of the freely spinning gears to
the shaft that runs through its hub. The shaft then spins together with that gear. The output
shaft's speed relative to the countershaft is determined by the ratio of the two gears: the one
permanently attached to the countershaft, and that gear's mate which is now locked to the
output shaft.
Locking the output shaft with a gear is achieved by means of a dog clutch selector. The dog
clutch is a sliding selector mechanism which is splined to the output shaft, meaning that its
hub has teeth that fit into slots (splines) on the shaft, forcing that shaft to rotate with it.
However, the splines allow the selector to move back and forth on the shaft, which happens
when it is pushed by a selector fork that is linked to the gear lever. The fork does not rotate,
so it is attached to a collar bearing on the selector. The selector is typically symmetric: it
slides between two gears and has a synchromesh and teeth on each side in order to lock either
gear to the shaft.
FOG 7 DOG CLUTCH
3) SYNCHROMESH
The synchronizer has to overcome the momentum of the entire input shaft and clutch disk
when it is changing shaft rpm to match the new gear ratio. It can be abused by exposure to the
momentum and power of the engine, which is what happens when attempts are made to select
a gear without fully disengaging the clutch. This causes extra wear on the rings and sleeves,
reducing their service life. When an experimenting driver tries to "match the revs" on a
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synchronized transmission and force it into gear without using the clutch, the synchronizer
will make up for any discrepancy in RPM. The success in engaging the gear without
clutching can deceive the driver into thinking that the RPM of the layshaft and transmission
were actually exactly matched. Nevertheless, approximate rev. matching with clutching can
decrease the difference in rotational speed between the layshaft and transmission gear shaft,
therefore decreasing synchro wear.
Synchronizing rings are made of metal and can be provided with anti-wear coatings called a
friction lining. Common metals for synchronizer rings are brass and steel. The linings
typically consist of molybdenum, iron, bronze or carbon. The synchronizing rings are
produced either by massive forming (common forging) or sheet metal shaping. The latter
involves the stamping of the blank out of a sheet metal strip and the subsequent machining
with follow-on composite tools or transfer tools. A friction lining usually consists of
thermally splashed molybdenum. Alternatively, iron or bronze sinter friction layers can be
used. Carbon-coated synchronizer rings are particularly wear resistant and offer very good
friction behavior. Due to their higher price, these are reserved for high-performance
transmissions.
FIG 8 SYNCHROMESH
4) REVERSE
The previous discussion normally applies only to the forward gears. The implementation of
the reverse gear is usually different, implemented in the following way to reduce the cost of
the transmission. Reverse is also a pair of gears: one gear on the countershaft and one on the
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output shaft. However, whereas all the forward gears are always meshed together, there is a
gap between the reverse gears. Moreover, they are both attached to their shafts: neither one
rotates freely about the shaft. When reverse is selected a small gear, called an idler
gear or reverse idler, is slid between them. The idler has teeth which mesh with both gears,
and thus it couples these gears together and reverses the direction of rotation without
changing the gear ratio.
In other words, when reverse gear is selected, it is in fact actual gear teeth that are being
meshed, with no aid from a synchronization mechanism. For this reason, the output shaft
must not be rotating when reverse is selected: the vehicle must be stopped. In order that
reverse can be selected without grinding even if the input shaft is spinning inertially, there
may be a mechanism to stop the input shaft from spinning. The driver brings the vehicle to a
stop, and selects reverse. As that selection is made, some mechanism in the transmission
stops the input shaft. Both gears are stopped and the idler can be inserted between them.
There is a clear description of such a mechanism in the Honda Civic 1996–1998 Service
Manual, which refers to it as a "noise reduction system":
Whenever the clutch pedal is depressed to shift into reverse, the mainshaft continues to rotate
because of its inertia. The resulting speed difference between mainshaft and reverse idler gear
produces gear noise [grinding]. The reverse gear noise reduction system employs a cam plate
which was added to the reverse shift holder. When shifting into reverse, the 5th/reverse shift
piece, connected to the shift lever, rotates the cam plate. This causes the 5th synchro set to
stop the rotating mainshaft.
4.3 CLUTCH
In all vehicles using a transmission (virtually all modern vehicles), a coupling device is used
to separate the engine and transmission when necessary. This is because most internalcombustion engines must continue to run when in use, although a few modern vehicles shut
off the engine when the vehicle is stationary. The clutch accomplishes this in manual
transmissions. Without it, then other than when the transmission is in neutral, the engine and
wheels would at all times be inextricably linked, and any time the vehicle stopped, the engine
would stall. Without the clutch, changing gears would be very difficult, even with the vehicle
moving already: deselecting a gear while the transmission is under load requires considerable
force (and risks significant damage), but can still be done with much less force if the driver
releases the accelerator just prior to attempting a shift as if there were no clutch disengaged.
Selecting a gear requires the revolution speed of the engine to be held at a very precise value
which depends on the vehicle speed and desired gear–the speeds inside the transmission have
to match. In a 4+-wheeled vehicle, the clutch is usually operated by a pedal; on a motorcycle,
a lever on the left handlebar serves the purpose.



When the clutch pedal is fully depressed, the clutch is fully disengaged, and no torque is
transferred from the engine to the transmission (and by extension to the drive wheels). In
this uncoupled state it is possible to select gears or to stop the vehicle without stopping
the engine.
When the clutch pedal is fully released, the clutch is fully engaged and all of the engine's
torque is transferred. In this coupled state, the clutch does not slip, but rather acts as rigid
coupling to transmit power to the gearbox.
Between these extremes of engagement and disengagement the clutch slips to varying
degrees. When slipping it still transmits torque despite the difference in speeds between
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

the engine crankshaft and the transmission input. Because this torque is transmitted by
means of friction rather than direct mechanical contact, considerable power is wasted as
heat (which is dissipated by the clutch). Properly applied, slip allows the vehicle to be
started from a standstill, and when it is already moving, allows the engine rotation to
gradually adjust to a newly selected gear ratio.
Learning to use the clutch efficiently requires the development of muscle memory and a
level of coordination.
A rider of a highly tuned motocross or off-road motorcycle may "hit" or "fan" the clutch
when exiting corners to assist the engine in revving to the point where it delivers the most
power. It can be done to a lesser extent, with cars.
The clutch is typically disengaged by a thrust bearing that makes contact with pressure petals
on the clutch ring plate and pushes them inward to release the clutch pad friction. Normally
the bearing remains retracted away from the petals and does not spin. However, the bearing
can be "burned out" and damaged by using the clutch pedal as a foot rest, which causes the
bearing to spin continuously from touching the clutch plates.
4.4 BENEFITS AND DRAWBACKS
1) Benefits

Fuel economy
The manual transmission couples the engine to the transmission with a rigid clutch instead of
the torque converter on an automatic transmission or the v-belt of a continuously variable
transmission,[13] which slip by nature. Manual transmissions also lack the parasitic power
consumption of the automatic transmission's hydraulic pump. Because of this, manual
transmissions generally offer better fuel economy than automatic or continuously variable
transmissions; however the disparity has been somewhat offset with the introduction of
locking torque converters on automatic transmissions.[14] Increased fuel economy with a
properly operated manual transmission vehicle versus an equivalent automatic transmission
vehicle can range from 5% to about 15% depending on driving conditions and style of
driving. The lack of control over downshifting under load in an automatic transmission,
coupled with a typical vehicle engine's greater efficiency under higher load, can enable
additional fuel gains from a manual transmission by allowing the operator to keep the engine
performing under a more efficient load/RPM combination. This is especially true as between
manual and automatic versions of older models, as more recent advances including variable
valve timing reduce the efficiency disadvantages of automatic transmissions by allowing
better performance over a broader RPM range. In recognition of this, many current models
(2010 and on) come with manual modes, or overrides on automatic models, although the
degree of control varies greatly by the manufacturer. Also, manual transmissions do not
require active cooling and because they are, mechanically, much simpler than automatic
transmissions, they generally weigh less than comparable automatics, which can improve
economy in stop-and-go traffic. However this gap in economy is being rapidly closed, and
many mid- to higher-end model automatic vehicles now get better economy than their
standard-spec counterparts.This is in part due to the increasing impact of computers coordinating multiple systems, particularly in hybrid models in which the engine and drive
motors must be managed, as well as using different automatic technology such as CVTs and
dual-clutch automatics.

Longevity
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Because manual transmissions are mechanically simpler, are more easily manufactured, and
have fewer moving parts than automatic transmissions, they require less maintenance and are
easier as well as cheaper to repair. Due to their mechanical simplicity, they often last longer
than automatic transmissions when used by a skilled driver. Typically, there are no electrical
components, pumps and cooling mechanisms in a manual transmission, other than an internal
switch to activate reversing lighting. These attributes become extremely vital with a vehicle
stuck in mud, snow, etc. The back and forth rocking motion of the vehicle drivers use to
dislodge a stuck vehicle can destroy automatic transmissions. Clutches are a wear item that
may need to be replaced at some point in the vehicle's lifespan, however the service life of
the clutch depends on the operating conditions that it is subjected to.

Lubrication
Most manual transmissions rely on splash lubrication although some five speed Rover
gearboxes did incorporate an oil pump. The problem with splash lubrication is that it is speed
dependent. There are centrifugal effects, hydrodynamic effects and effects from the gears
working as pumps. If a gearbox is fitted with Perspex windows and run on a test rig these
effects can be observed. As the gearbox is run through its rev range, the oil jets will switch
over and move around. Research on the Austin Maxi 1500 gearbox showed that one of the
ball races was running dry at 80 miles per hour (130 km/h). The solution was to alter the
casting to include a small projection that would intercept the main oil jet that was present at
80 mph and disperse it. This small modification enabled the later Maxi 1750 gearbox to be
relatively trouble free. Four speed gearboxes seldom show these problems because at top
speed (and maximum power) they are basically a solid shaft and the gears are not
transmitting power.

Engine braking
In contrast to most manual gearboxes, most automatic transmissions have far less effective
engine-braking. This means that the engine does not slow the vehicle as effectively when the
automatic transmission driver releases the engine speed control. This leads to more usage of
the brakes in vehicles with automatic transmissions, bringing shorter brake life. Brakes are
also more likely to overheat in hilly or mountainous areas, causing reduced braking
ability, brake fade, and the potential for complete failure with the automatic transmission
vehicle.

Push starting
Vehicles with a manual transmission can often be push started when the starter motor is not
operational, usually due to a low battery.
2) DRAWBACKS

Shifting speed
Automatic transmissions can typically shift ratios faster than a manual gear change can be
accomplished, due to the time required for the average driver to push the clutch pedal to the
floor and move the gearstick from one position to another. This is especially true in regards
to dual-clutch transmissions, which are specialized computer-controlled automatic
transmissions that mechanically operate more like a manual transmission than a traditional
automatic one.
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
Ease of use
Because manual transmissions require the operation of an extra pedal, and keeping the
vehicle in the correct gear at all times, they require more concentration, especially in heavy
traffic situations. The automatic transmissions, on the other hand, simply require the driver to
speed up or slow down as needed, with the vehicle doing the work of choosing an appropriate
gear. Manual transmissions also place a greater workload on the driver in heavy traffic
situations, when the driver must operate the clutch pedal quite often. Because the clutch pedal
can require a substantial amount of force, especially on large trucks, and the long pedal travel
compared to the brake or accelerator requires moving the entire leg, not just the foot near the
ankle, a manual transmission can cause fatigue, and is more difficult for injured people to
drive. Additionally, because automatic transmissions can be driven with only one foot, people
with one leg that is missing or impaired can still drive, unlike the manual transmission that
requires the use of two feet at once. Likewise, manual transmissions require the driver to
remove one hand periodically from the steering wheel while the vehicle is in motion, which
can be difficult or impossible to do safely for people with a missing or impaired arm, and
requires increased coordination, even for those with full use of both hands.
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CHAPTER 5 CONTINUOUSLY VARIABLE TRANSMISSION
5.1 OVERVIEW
After more than a century of research and development, the internal combustion
(IC) engine is nearing both perfection and obsolescence: engineers continue to
explore the outer limits of IC efficiency and performance, but advancements in fuel
economy and emissions have effectively stalled. While many IC vehicles meet
Low Emissions Vehicle standards, these will give way to new, stricter government
regulations in the very near future. With limited room for improvement,
automobile manufacturers have begun full-scale development of alternative power
vehicles. Still, manufacturers are loath to scrap a century of development and
billions or possibly even trillions of dollars in IC infrastructure, especially for
technologies with no history of commercial success. Thus, the ideal interim
solution is to further optimize the overall efficiency of IC vehicles.
One potential solution to this fuel economy dilemma is the continuously variable
transmission (CVT), an old idea that has only recently become a bastion of hope to
automakers. CVTs could potentially allow IC vehicles to meet the first wave of
new fuel regulations while development of hybrid electric and fuel cell vehicles
continues. Rather than selecting one of four or five gears, a CVT constantly
changes its gear ratio to optimize engine efficiency with a perfectly smooth torquespeed curve. This improves both gas mileage and acceleration compared to
traditional transmissions.
Although CVTs have been used in automobiles for decades, limited torque
capabilities and questionable reliability have inhibited their growth. Today,
however, ongoing CVT research has led to ever-more robust transmissions, and
thus ever-more-diverse automotive applications. As CVT development continues,
manufacturing costs will be further reduced and performance will continue to
increase, which will in turn increase the demand for further development. This
cycle of improvement will ultimately give CVTs a solid foundation in the world’s
automotive infrastructure.
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FIG 9 CVT TRANSMISSION
5.2 THEORY AND DESIGN
Today’s automobiles almost exclusively use either a conventional manual or
automatic transmission with “multiple planetary gear sets that use integral clutches
and bands to achieve discrete gear ratios”. A typical automatic uses four or five such
gears, while a manual normally employs five or six. The continuously variable
transmission replaces discrete gear ratios with infinitely adjustable gearing through
one of several basic CVT designs.

Push Belt
This most common type of CVT uses segmented steel blocks stacked on a steel
ribbon, as shown in Figure (1). This belt transmits power between two conical
pulleys, or sheaves, one fixed and one movable. With a belt drive:
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FIG 10 PUSH BELT
In essence, a sensor reads the engine output and then electronically
increases or decreases the distance between pulleys, and thus the tension of the drive
belt. The continuously changing distance between the pulleys—their ratio to one
another—is analogous to shifting gears. Push-belt CVTs were first developed
decades ago, but new advances in belt design have recently drawn the attention of
automakers worldwide.

Toroidal Traction-Drive
These transmissions use the high shear strength of viscous fluids to transmit torque
between an input torus and an output torus. As the movable torus slides linearly,
the angle of a roller changes relative to shaft
FIG 11 TOROIDAL CVT
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
Variable Diameter Elastomer Belt
This type of CVT, as represented in Figure (2), uses a flat, flexible belt mounted on
movable supports. These supports can change radius and thus gear ratio. However,
the supports separate at high gear ratios to form a discontinuous gear path, as seen
in Figure (3). This can lead to the problems with creep and slip that have plagued
CVTs for years.
FIG 12 VARIABLE DIAMETER BELT
This inherent flaw has directed research and development toward push belt
CVTs.

Other CVT Varieties
Several other types of CVTs have been developed over the course of automotive
history, but these have become less prominent than push belt and toroidal CVTs. A
notating traction drive uses a pivoting, conical shaft to change “gears” in a CVT. As
the cones change angle, the inlet radius decreases while the outlet radius increases,
or vice versa, resulting in an infinitely variable gear ratio. A variable geometry CVT
uses adjustable planetary gear-sets to change gear ratios, but this is more akin to a
flexible traditional transmission than a conventional CVT.
5.3 BACKGROUND AND HISTORY
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To say that the continuously variable transmission (CVT) is nothing new would be
a gross understatement: Leonardo Da Vinci sketched his idea for a CVT in 1490. In
automotive applications, CVTs have been around nearly as long as cars themselves,
and certainly as long as conventional automatics. General Motors actually developed
a fully toroidal CVT in the early 1930s and conducted extensive testing before
eventually deciding to implement a conventional, stepped-gear automatic due to cost
concerns. General Motors Research worked on CVTs again in the 1960s, but none
ever saw production. British manufacturer Austin used a CVT for several years in
one of its smaller cars, but “it was dropped due to its high cost, poor reliability, and
inadequate torque transmission”. Many early CVTs used a simple rubber band and
cone system, like the one developed by Dutch firm Daft in 1958.
However, the Daft CVT could only handle a 0.6 L engine, and problems
with noise and rough starts hurts its reputation. Uninspired by these early failures,
automakers have largely avoided CVTs until very recently, especially in the United
States.
Inherent Advantages & Benefits
Certainly, the clunk of a shifting transmission is familiar to all drivers. By
contrast, a continuously variable transmission is perfectly smooth—it naturally
changes “gears” discreetly and minutely such that the driver or passenger feels only
steady acceleration. In theory, a CVT would cause less engine fatigue and would be
a more reliable transmission, as the harshness of shifts and discrete gears force the
engine to run at a less-than-optimal speed.
Because the CVT allows an engine to run at this most efficient point
virtually independent of vehicle speed, a CVT equipped vehicle yields fuel economy
benefits when compared to a conventional transmission.
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Moreover, the CVT was more than one second faster in 0-60 mph
acceleration tests . The potential for fuel efficiency gains can also be seen in the CVT
currently used in Honda’s Civic. A Civic with a traditional automatic averages 20
km per litre city/highway, while the same car with a CVT gets 26 kmpl city/highway
. Honda has used continuously variable transmissions in the Civic for several years,
but these are 1.6 liter cars with limited torque capabilities. Ongoing research and
development will inevitably expand the applicability of CVTs to a much broader
range of engines and automobiles.
Challenges & Limitations
CVT development has progressed slowly for a variety of reasons, but much of the
delay in development can be attributed to a lack of demand: conventional manual
and automatic transmissions have long offered sufficient performance and fuel
economy. Thus, problems encountered in CVT development usually stopped said
progress. “Designers have … unsuccessfully tried to develop [a CVT] that can
match the torque capacity, efficiency, size, weight, and manufacturing cost of stepratio transmissions”. One of the major complaints with previous CVTs has been
slippage in the drive belt or rollers.
This is caused by the lack of discrete gear teeth, which form a rigid mechanical
connection between to gears; friction drives are inherently prone to slip, especially
at high torque. With early CVTs of the 1950s and 1960s, engines equipped with
CVTs would run at excessively high RPM trying to “catch up” to the slipping belt.
This would occur any time the vehicle was accelerated from a stop at peak torque:
“For compressive belts, in the process of transmitting torque, micro slip occurs
between the elements and the pulleys. This micro slip tends to increase sharply
once the transmitted torque exceeds a certain value …”
For many years, the simple solution to this problem has been to use CVTs only in
cars with relatively low-torque engines. Another solution is to employ a torque
converter (such as those used in conventional automatics), but this reduces the
CVT’s efficiency.
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Perhaps more than anything else, CVT development has been hindered by cost.
Low volume and a lack of infrastructure have driven up manufacturing costs,
which inevitably yield higher transmission prices. With increased development,
most of these problems can be addressed simply by improvements in
manufacturing techniques and materials processing. For example, Nissan’s Extroid
“is derived from a century-old concept, perfected by modern technology,
metallurgy, chemistry, electronics, engineering, and precision manufacturing”.
In addition, CVT control must be addressed. Even if a CVT can operate at the
optimal gear ratio at any speed, how does it “know” what ratio to select? Manual
transmissions have manual controls, where the driver shifts when he or she so
desires; automatic transmissions have relatively simple shifting algorithms to
accommodate between three and five gears. However, CVTs require far more
complex algorithms to accommodate an infinite division of speeds and gear ratios.
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CHAPTER 6 CONCLUSION
The following points can be made in summary:
1)The choice of the transmission system can be judged on the following basis:



High torque apllications- Manual transmissions eg. Tractor,truck
Where continuity is the main concern-CVT eg. Light vehicles,cars
Required several ratios which are needed to be switched quickly-Automatic
transmission eg performance cars like mustang,camero.
2) Automatic transmission vehicles are easier to drive as they don’t contain a clutch pedal.
3) All the cars in india are shifting from manual to automatic transmission.They are better
than manual transmission in both performance and in pickup in normal roads and hill
climbing.
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3.
4.
5.
6.
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Musial, W.; Butterfield, S.; McNiff, B. (May 2007), Improving Wind TurbineGearbox
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"Experts predict nine-, 10-speed transmissions to dominate in North America".
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Theory of machines, R S Khurmi
Automobile engineering ,S Shrinavasan
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