1. GEAR BOX
A gearbox is a transmission device which is used
between engine’s output shaft and the final drive in
order to transfer required torque and power to the
wheels of the vehicle, a gearbox consists of the set of
gears( i.e. spur, helical, bevel, worm and epicycle
depending on the types of gearbox used )which are
arranged in a special fashion in order to provide
required gear or speed ratios to the final drive of the
vehicle, a gearbox usually comes with the specification
i.e.5-speed transmission with a reverse, and an
automatic transmission.
https://www.youtube.com/watch?v=auQgOtveQi0
2. https://www.youtube.com/watch?v=auQgOtveQi0
Purpose
• Provides speed and torque conversions because of the limitations of internal combustion
engines.
• Also facilitates change of direction of output shaft for reversing
• Automotive gearboxes are used to reduce load on the engine by manipulating torque and
speed. They have the option to select one of several different gear ratios.
• Once the engine has reached a number of revolutions per minute, it is advisable to increase
the gear to reduce the engine rpm to reduce wear on the engine, allow more control, and
greater speeds, better acceleration, and better fuel economy.
• Most gearboxes are used to increase torque & reduce the speed of a output shaft. This
produces a mechanical advantage
• Automotive gearbox also have the provision to do the opposite ie provide an increase in
output shaft speed with a reduction of torque (overdrive).
3. Main components of gearbox
1.Clutch shaft
Clutch shaft OR driving shaft is a shaft which takes power from engine to further supply to other
shafts. As the name suggests, the driving shaft is connected via clutch & when the clutch is
engaged, the driving shaft also rotates. The clutch shaft has only one gear fixed on it and it rotates
with same speed as engine crankshaft. Also, the driving shaft and main shaft are in the same line.
2.Counter shaft/Lay shaft
Counter shaft is longest among the 3 in the gearbox. It has multiple gears of various sizes which is
able to produce a wide range of torque. The counter shaft rotates at a different but constant speed
just like the clutch shaft.
3.Main shaft
The main shaft OR output shaft is which rotates at different speed and also provides the required
torque to the vehicle. The output shaft is a splined shaft so that gears or synchronizers could be
moved in order to engage or disengage. The neutral gear is the position in which no gear on output
shaft is engaged with counter shaft. The output end is connected to the differential of the vehicle
via double Hooke’s joint.
4.Bearings
Bearings are mounted on both ends of every shaft. They serve 2 purposes- Provide support &
Minimize frictional losses, so that maximum power can be delivered.
4. 4.Gears
Gears are used to transmit power from one shaft to
another. The amount of torque transmitted via gears
depend on the number of teeth and size of the
gear. Higher the gear ratio, higher the
torque/acceleration and lesser the speed. If the ratio
is greater than 1, the vehicle will possess a high
acceleration & if the ratio is greater than 1, it will
travel at high speed.
5.Gear selector fork
Gear selectors are just simple devices which uses a
lever to select a gear for engaging in disengaging
mechanism. The motion of the lever slides the
engaging part on the shaft.
Approximate Gear ratios
1st gear – 3:1
2nd gear – 2:1
3rd gear – 1.5:1
4th gear – 1:1
5th gear – 0.8 : 1
Reverse gear – -3.2:1
5. Types of Gearbox
1. Manual transmission or manual gearbox
(i) Sliding Mesh Gearbox
(ii) Constant Mesh Gearbox
(iii) Synchromesh Gearbox
2. Automatic transmission or automatic gearbox
(i) Automatic transmissions using planetary gears
(ii) Continuously variable transmission(cvt)
6. 1. Manual Transmission
A manual transmission is the types of gearbox used in most of the vehicle on the
road due to its low cost. It is the type of gearbox in which there are limited gear or
speed ratios i.e. maximum of 6- speed and 1- reverse is there, and the shifting of
gears is a manual task performs by the driver by pushing or pulling the gear lever in
a predefined fashion. Manual transmission always requires the use of clutch.
7. (i) Sliding Mesh Gearbox
It is the oldest types of gearbox used, in sliding mesh gearbox the gears of main shaft
and layshaft are not in mesh i.e. independent, only a single gear is in continuous mesh
with the gear on the clutch shaft that rotates the lay-shaft and the meshing of gears
with the appropriate gear on the layshaft occurs due to the left or right siding of the
gears of the main shaft.
Note – Sliding mesh requires special technique for shifting of gears which is known as
double-de-clutching.
First Gear
Mesh: 5-6
10. (ii) Constant Mesh Gearbox
It is the modified gearbox introduced to overcome the limitations of the sliding mesh
gearbox. In this types of gearbox, all the gears of the lay-shaft, main-shaft and clutch shaft
are in constant mesh with each other and the shifting of gear is obtained by the sliding of
dog clutches over the splined main shaft in order to obtain high speed or torque output.
Note – Constant mesh gearbox overcomes the problem of double-de-clutching but the
shifting of gear is noisy and still not smooth because the speed of the layshaft, main-shaft
and clutch shaft is not same at the time of shifting.
11.
12. (iii) Synchromesh Gearbox
This is the latest of all types of manual gearbox which provides the smooth and quiet shifting of
gears due to the use of special devices known as synchromesh devices, these devices helps in
bringing the speed of all the shafts to the same (using frictional contact) before the meshing of
the appropriate gears which causes less wear and tear to the gears.
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14. 2. Automatic Transmission or Gearbox
It is used in high-end cars due to its high cost, in this types of gearbox infinite gear ratios
can be obtained by just pressing the accelerator, the driver just need to select the
mode of the drive i.e. forward or reverse, park, neutral, drive and sport, and the required
gear ratios along with the timing of the meshing is obtained automatically. Automatic
gearbox doesn’t require clutch pedal, so all the cars with automatic transmissions
comes with only 2 pedals.
15. (i) Automatic transmissions using planetary gears
HOW PLANETARY GEARS WORK
• A gear set in which all of the gears are grouped
around each other like
the planets around the sun.
• The central gear is called sun gear. In mesh with it is a
circular
grouping of gears, called planet gears, mounted on a
rotating carrier.
• By holding any one of the three gear elements
motionless, different ratios can be produced between
the other two. Planetary gear sets are common in
automatic transmissions.
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20. TORQUE CONVERTOR
• Takes the place of the clutch found on standard shift
vehicles
• It uses oil or transmission fluid to transmit power
• Torque converter can be divided into 3 main
members:
a. Pump/impeller: It is the driving member and rotates
with the engine.
b. Turbine: The impeller vanes pick up fluid in the
converter housing and direct it toward the turbine.
c. Stator: Fluid flow drives the turbine, and the turbine
rotates and turns the transmission input shaft.
21. (ii) Continuously variable transmission(CVT)
CVT
Continuously
Variable
Transmission
https://youtu.be/PEq5_b4LWNY
A continuously variable transmission is an automatic
transmission that can change seamlessly through a
continuous range of gear ratios.
22. Working
A CVT gearbox has a relatively simple arrangement of two cone-shaped pulleys with a
V-shaped drive belt connecting them. One pulley is attached to the engine, while the
other is joined to the wheels. When you press the accelerator, the engine revs and the
cone moves according to the amount of power asked for. The other cone adjusts
accordingly so that the drive belt maintains the same tension, and this is what
determines how the car accelerates.
