The document discusses the operation of different types of vehicle transmissions, including automatic and manual transmissions. It describes the main components of transmissions like the torque converter, gear sets, clutches, and shafts. The relationships between gear ratios, angular velocity, and shaft work are analyzed from a thermodynamic perspective. Both automatic and manual transmissions are compared in terms of their components and how power is transferred from the engine to the wheels.

1. The Transmission
Contents
Abstract 3
Introduction 3
Discussion 3
(Automatic-transmission) 3
(Manual Transmission) 5
(Type of Gears) 6
(Gear Ratios) 7
(Transmission and Shaft work) 8
Relative-Motion (Analysis: Velocity) 9

2. Conclusion 10
References 11
Abstract
The aim of this report is to introduce the types of transmissions
and how they operate. A description of the internal parts and
external parts are included to guide the reader better understand
the system. Since the report is based on a thermodynamic
perspective, some basic equations will also be presented. The
relationship between thermodynamics and transmission system
is mainly in the shaft work.Introduction
To overcome inertia, the automobile engine develops power that
is transmitted as torque from the engine crankshaft to the
wheels. In order to achieve a smooth and gradual transfer of
power, we use a clutch friction unit to engage and disengage the
power flow. The use of clutches are actually found in both
transmissions, however, the location is different. The
transmission is used to best choose the gear ratio according to
the power and speed. It is also present to provide the proper
gear ratio for the car in different conditions, such as when the
car is accelerating, stopping, maintaining speed, or reversing.
The basic components necessary to deliver power to the drive
wheels are the clutches, control linkages, flywheel (only in
manual) or flexplate (only in automatic), torque converter
(automatic), and the transmission. The relationship between
thermodynamics and transmission system is mainly in the shaft

3. work.Discussion
(Automatic-transmission)
To begin, it is important to understand that all transmissions
are different. There is the automatic, semi-automatic, and
manual (standard) transmission. The one that will first be
introduced is the more common type— the automatic
transmission.
The automatic transmission is called “automatic” because the
gear ratios are changed automatically without the driver’s
required input, typically using hydraulics o select ears
depending on the pressure exerted by the fluid within the
transmission assembly.. It is said that the clutch is replaced by a
mechanism called the torque converter. This torque converter is
located in front of the transmission housing as shown. The
torque converter is a mechanical device that transfers power
from engine to the transmission. (Note that the torque converter
is only found in automatic transmissions). Inside the torque
converter there is an impeller (pump), stator, and a turbine as
shown. The impeller is connected directly to the engine. The
impeller is responsible for moving the turbine. The movement
of the impeller accompanied with the transmission fluid forces
the turbine to rotate. This rotation causes the kinetic energy to
be transferred to the input shaft, and later to the inside of the
transmission. Lastly, there is small mechanism that is called the
stator. This component is in mounted in the center of the
impeller and turbine. Its usage is to prevent the transmission
fluid from being redirected to the impeller. This is caused
because the stator moves in the opposite direction, causing the
“fluid to change directions as it hits the
blades.”(Howstuffworks.com).
Figure 3: Planetary Gear
Figure 2 Torque Converter Diagram
Figure 1: Transmission and Torque Converter
The automatic transmission contains a special kind of gear set

4. called the planetary gear set. It consists of the sun gear, planet
gear, and ring gear. The sun gear is the gear that is at the center
of the ring gear. It is surrounded by other smaller gears like the
solar system. Unlike the manual transmission, where gears are
always shifting into different gears, the gears of the automatic
transmission are always in contact with the same gears. Any
gear change made will be accomplished by locking and
unlocking the gears.
(Manual Transmission)
It is said that the simplest transmission is the manual
transmission mainly because the driver has to change the gear
ratios on his own. The manual transmission, unlike the
automatic, works by manually changing gears using the stick
shift (lever). The online article found on howrah.org states that
in order for a smooth gear shift, “a clutch is provided to
disengage the engine from the transmission”. The commonly
used dry single disk clutch has a steel disk with a friction lining
that is sandwiched between a flywheel on the engine shaft and a
pressure plate on the transmission input shaft. To understand
the clutch we must first dissect it. The clutch is made up of
three components; the pressure plate, the clutch disk, and throw
out bearing. The clutch disk is inside the pressure plate. The
pressure plate is required, because with the use of the throw out
bearing, it will disengage or engage the clutch. For example,
when you depress the clutch pedal, the throttle bearing will
push on the pressure plate. When the teeth of the pressure plate
are pressed, pressure plate will actually move in the opposite
direction of the force applied, causing the pressure plate to
momentarily be disengaged from clutch. This means that when
you press the clutch pedal you disconnect the engine from the
wheels, allowing you to change the gear ratios. For a novice
driver, it is important to note, that whenever a change in gear is
to be made in a manual transmission car, one must first press
the clutch pedal. This suggestion was made clear in the article
How to Drive a Manual.

5. Figure 4 Clutch
Figure 5: Clutch Pedal
(Type of Gears)
A gear is a mechanical element responsible for converting the
speed of a shaft from one speed to another. The application of
the gear is to transmit power from one shaft to the other is
usually made up of two or more gears mounted together on a
frame so that the teeth of the gears engage. The shafts in may be
aligned in parallel or at any skew axis. The unique thing about
gears is that when they transfer power, they do it with a very
high efficiency (up to 99% in the case of parallel shafts). Gears
work by rotating on each other using their teeth. Therefore, the
shape and the number of the teeth are very important, since it
determines how smooth the transfer of motion is.
Gears have different kind; the first one is parallel gear shafts.
The parallel gear shafts are like spur gears, helical gears, and
herring one gears. This type of gear shaft offer maximum
transmission of power and efficiency. Furthermore, they have
higher road capacity and make less noise. On the other hand,
they are more expensive to manufacture and created axial
thrust. These gear shafts are wildly used for manual
transmission.
Figure 6: Parallel Gear shafts
Then there are the intersecting shaft gears which as the
name suggests, have intersecting shafts. These include bevel
gears, straight bevel gears, zero bevel gears, and spiral gears.
The intersecting shaft gears are efficient transmitters of power
and motion between intersecting shafts at an angle. We use
them instead of the parallel gear shafts because they are cheaper
and have high strength. These gears are commonly used in
automobiles.
Figure 5: Spiral Bevel Gear

6. Finally, we have the hypoid gears. The hypoid gears are neither
intersecting nor parallel; these include crossed helical gears and
worm gears. The hypoid gears require high-ratio speed
reduction in a limited space using non-intersecting shafts. Their
efficiency can be easily increased by lowering their ratios.
Their advantage is that they are the cheapest of all gears, and
they are also used in automobiles.
A gear train is usually made up of two or more gears mounted
together on a frame so that the teeth of the gears engage. The
first kind of gear train is the simple gear train which is when
there is only one gear on each shaft, these are typically spur
gears. The simple gear train consists of two gears the rotate on
the same direction, on is called the driver and one is the
follower, and the idler gear, which is only function is to change
the direction of rotation.
(Gear Ratios)
Gear ratios are very important. To understand, let us first be
introduced to the simplest gear—the spur gear. To understand
gear ratios let’s assume we have a gear train example like the
one pictured below. Assume the little gear is the “drive gear”,
gear in motion. And the “driven gear” the bigger gear. Assume
also that the drive gear has twenty teeth and the other gear has
thirty gears. The ratio is calculated by dividing . In this case
the gear ratio would be 30/20 which is 1.5. This means the drive
gear must move one complete revolution plus a half so that the
bigger gear can complete one revolution. This ratio is typically
written as 1.5 : 1.
Figure 6 Gear Ratio
The gear ratios are chosen depending on the vehicle weight,
expected loaded weight, and the size of the engine. Today’s
transmission systems can have four, five or six speeds forward.
However, since the engine rotates in only one direction, the

7. reversing procedure must be accomplished inside the
transmission, and it is usually one speed. The fifth gear in a
five-speed transmission is usually an overdrive. This gear is
used for higher speed driving where little load is placed on the
engine. This gear ratio rests the engine since the RPM is
lowered to maintain a specific speed. The input shaft rotates
only 0.87 of a turn, while the output shaft rotates one
revolution, resulting in the output shaft rotating faster than the
input shaft.
(Transmission and Shaft work)
As mentioned above, the shaft from the engine is connected to
the transmission which choses the best gear ratio and transfers
the power to the wheels. Transferring energy using rotating
shaft is extremely common in engineering. The engine and the
gearbox are bolted together, with the clutch between them to
allow the disconnection while switching gears as shown in the
figure below. In order to find out how much work is transmitted
to the gearbox, we use the equation of the shaft work from
thermodynamics.
The shaft work is measured in kJ, while the power transmitted
via the shaft per unit time is measured in kW. The shaft work
that engine provides to the transmission is then adjusted by
using the appropriate gear ratios and transferred to the wheel.
Obviously, as any mechanical system, energy is being lost
during the process as heat during to friction, which can be
reduced by reducing the friction.
Figure 7
Relative-Motion (Analysis: Velocity)
An exercise that is practical for this topic is to determine the
angular velocity of a planetary gear. The figure below taken
from the textbook titled Dynamics by R. C. Hibbeler, shows a

8. planetary gear. The exercise says the ring gear (outer gear) is
stationary. The planetary gears and sun gears are implied to be
moving. The question is to find the angular velocity of the
planetary gear. First, we must draw a free body diagram. In this
case, a rough diagram of the velocity vectors has been provided.
Since the ring gear is stationary, there is no velocity at point B.
Thus, the velocity at Va does exist. We calculate the velocity at
point A, by using the expression V=rw, where “r” is the radius
and “w” is the angular velocity. The sun gear has a radius of 80
mm and a given angular velocity of 5 rad/s. With this, we can
simply plug in the numbers to Va=rw (V=5*80) and obtain 400
mm/s. We have acquired two points A and B where velocities
may exist. When this is the case, a special formula Vb=Va +W x
rb/a. We know Vb is “0”and we know Va is 400mm/s. The
angular velocity W is 5 rad/s (rotating around the k-axis) and is
crossed with the relative position vector r b/a. This vector is
called “relative” because it takes into account the point of
interest B, with respect to point A. So the vector that was
omitted in the diagram below travels from point B to point A.
After all set and done, we should end up with 0=(-400i)+(wk)x
(80 j). This is reduced to w=5 rad/s. Notice that in order for the
cross product to work , a consideration of the unit vectors must
be taken into account.
Conclusion
In a standard transmission, in order to transfer power from the
engine crankshaft to the transmission, the clutch and pressure
plates are locked together by friction. When that happens, the
clutch shaft rotates with the engine crankshaft. When the power
in transferred to the transmission, the power is routed through
different gear ratios to obtain the best speed and power to start
and keep vehicle moving. The crankshaft transfers the power to
the transmission with the clutch in between. In the transmission,
the best gear is chosen to provide the most suitable gear ratio
according to the speed of the vehicle.
The study of mechanical engineering revolves around the use

9. of many different gears. Thus an extensive study of the
transmission has provided a clearer understanding of how
internal components mechanically interact together. The shaft
work is perhaps the most well-known formula for
thermodynamics. Hopefully, after completing this report, we
can better explain and even recognize the differences between a
manual and automatic transmissions.
References
Hibbeler, R.C. 2012 Mechanics for Engineers: Dynamic.
Singapore: Pearson Education
Toboldt, William. 2006. Automotive Encyclopedia. USA.
GoodHeart William Company
The Stator - HowStuffWorks. (n.d.). Retrieved from
http://auto.howstuffworks.com/auto-parts/towing/towing-
capacity/information/torque-converter3.htm
Clutch and Manual Transmission/Transaxle. (n.d.). Retrieved
from
http://www.procarcare.com/icarumba/resourcecenter/encycloped
ia/icar_resourcecenter_encyclopedia_manualtran.asp
Performance Transmission: Increase The Power of Your Ride.
(n.d.). Retrieved from http://www.howrah.org/transmission.html
How to Drive Manual: 15 Steps (with Pictures) - wikiHow.
(n.d.). Retrieved April 5, 2015, from
http://www.wikihow.com/Drive-Manual
"Performance Transmission." : Increase The Power of Your
Ride. N.p., n.d. Web. 06 Apr. 2015.
"Clutch and Manual Transmission/Transaxle." Clutch and
Manual Transmission/Transaxle. N.p., n.d. Web. 06 Apr. 2015.