working of gear box

1. Topic for the class: Transmission system
Unit 4 : Title: Transmission & Suspension system
Date & Time :10-Nov-2020
Dr. C Kodanda Rama Rao
Assistant Professor
Department of Mechanical Engineering
GITAM Institute of Technology (GIT)
Visakhapatnam – 530045
Email: kchebatt@gitam.edu

2. Objective of today class
To learn about different types of
Transmission system for
automobiles
5 April 2022
Department of Mechanical Engineering, GIT EME-401 Automobile Engineering
2

3. Out come of the class
By the end of the class the
student will be able to
identify different types of
Transmission system for
automobiles
5 April 2022
Department of Mechanical Engineering, GIT EME-401 Automobile Engineering
3

4. Transmission

5. •Mechanism which provides us
with suitable variation of the
engine torque at the road
wheels, whenever required

6. Functions
• To provide a means to vary the leverage or torque
ratio between the engine and the road wheels as
required
• To provide a neutral position to the vehicle
• To back the car by reversing the direction of rotation

7. Necessity of transmission
• Variation of resistance to the vehicle motion at
various speeds
• Variation of tractive effort of the vehicle available at
various speeds

8. Total resistance to the
vehicle motion
It consists of
• Resistance due to wind α speed2
• Resistance due to gradient = constant
• Vehicle weight parallel to the plane of the road
• Miscellaneous
• Type of road
• Tyre friction

10. • At start more acceleration is needed to gain speed quickly
• Then we may shift into higher gears

11. Principle of gear box
Driving gear
Driven gear

12. TWO SPEED
TRANSMISSION
FIRST GEAR
Neutral

13. Sliding mesh type gear box
Simplest type

15. First gear Second gear
Third gear
Reverse gear

16. Constant mesh gear box

17. Neutral 1st Gear
2nd Gear 3rd Gear
4th Gear Reverse
Collar

20. Double declutching
• The purpose of the double clutch is to match the
speed of the rotating parts of the gearbox for the
gear you wish to select to the speed of the input
shaft being driven by the engine.
• Once the speeds are matched, the gear will engage
smoothly.
• If the speeds are not matched, the gears will "crash"
as they come into mesh.
• A modern synchromesh gearbox accomplishes this
automatically.

21. SYNCHROSIZATION

22. Synchromesh gears
• Now all modern cars use.
• Two synchromesh gears can engage with one another
[running at different speeds] without any jerking.
• Where as non-synchromesh gears will cause jerking unless
their mating speeds are equal.
• Synchromesh is nothing but "helical" gears - which gradually
transfers mating speed from the periphery of gears towards
its inside mesh.
• Some old buses don't have synchromesh gears - so often
double declutching is necessary to match the speeds of
mating gears.
• Needless to say, synchromesh gears are always better

26. Synchromesh gear box

29. Selector mechanism
• Gear shift lever is mounted on the top of transmission case
• Gear shift lever is mounted on the steering column

30. Gear lever on top of transmission case
•Simple linkages
•More space
occupies
•Preferred and
universally used
type

32. Gear lever on steering column
• Occupies less
space
• Linkage is
complicated

34. AUTOMATIC TRANSMISSIONS
•An automatic transmission is an
automobile gearbox that can change
gear ratios automatically as the vehicle
moves, freeing the driver from having to
shift gears manually.
•Similar but larger devices are also used
for heavy-duty commercial and
industrial vehicles and equipment.

35. • SEMI AUTOMATIC
• Only the clutch is operated automatically
• The driver still has to select the gears
• FULLY AUTOMATIC
• Even the gears are changed automatically by a control
mechanism which is actuated by accelerator pedal only
• Employed in modern cars

36. AUTOMATIC TRANSMISSIONS
• Torque converter
• Epicyclic gear box
Automatic transmissions operate basically by controlling
vehicle speed and engine load.

37. Epicyclic gear box

38. 6 possible speeds
Forward, fast output speed–
• Planet carrier is driving
• Ring gear is driven
• Sun gear is stationary
(Stationary)

39. Forward, very fast output speed –
– Planet is driving
– Sun gear is driven
– Ring gear is stationary
(Stationary)

40. Forward, slow output speed –
– Ring gear is driving
– Planet carrier is driven
– Sun gear is stationary
(Stationary)

41. Forward, very slow output speed –
– Sun gear is driving
– Planet carrier is driven
– Ring gear is stationary
(Stationary)

42. Reverse, slow output speed –
– Sun gear is driving
– Ring gear is driven
– Planet carrier is stationary
(Stationary)

43. Reverse, fast output speed –
– Ring gear is driving
– Sun gear is driven
– Planet carrier is stationary
(Stationary)

49. OVERDRIVE
• To step up the
gear ratio in the
car
• Fitted between
transmission and
propeller shaft
• Generally fitted
on top gear only
• Operated
manually or
automatically

50. Overdrive…
• The overdrive consists of an electrically or hydraulically operated epicyclic
gear train bolted behind the transmission unit.
• It can either transfer the input drive shaft directly to the output shaft,
called a propshaft (1:1), or increase the propshaft speed so that it turns
faster than the input shaft (1:1 + n). Thus, in overdrive the gear ratio is less
than unity, i.e., propeller shaft rotates at a speed higher than the engine
speed.
• Thus the propshaft may be "overdriven" relative to the input shaft.
• It is actuated by a knob or button, often incorporated into the gearshift
knob, and does not require operation of the clutch.

51. Overdrive
3-synchro overdrive
gearbox of an MGB
Roadster 1968 model

52. Overdrive…
• This gearbox is provided with two ratios, i.e., unity and less than unity and
when second ratio is brought into action, this redcuces all the ratios of the
main gearbox, making it suitable for all types of use.
• If the main gearbox is having four ratios, by bringing the auxillary box in
connection with the main box another four ratios can be obtained. This is
due to less than unity ratio of the auxilary gearbox.
• To maintain eight ratios a large gearbox would be required. While here,
with the existing small gearbox, eight ratios can be obtained, by bringing
overdrive into action in conjunction with the main box.The auxiliary box
may be either a conventional one or the epicyclic type.
• To make gear changing easy, these are mostly the epicyclic type and are
fitted behind the main box.

53. TORQUE CONVERTER
• Similar to fluid flywheel
• An additional stator is
located
• Increases the torque in
ration about 2:1 to 3:1
• Torque variation is
continuous
• Efficiency is high only
within a narrow limits of
speed
Converter pressure 200-1200 kPa

55. APPLICATIONS ON PARTS FOR AUTOMOBILE – AUTO-TRANSMISSION
USAGE OF MAIN PRODUCTS
[ Driven Plate ]
 Torque Converter
- Application : Auto T/M
- Specification : SPFH540, SPFH590
[ Sepa / Plate ]
Front Cover
Lock-up Clutch
Turbine Runner
Pump Impeller
Stator

56. Torque Convertors…
• To maintain eight ratios a large gearbox would be required. While here,
with the existing small gearbox, eight ratios can be obtained, by bringing
overdrive into action in conjunction with the main box. The auxiliary box
may be either a conventional one or the epicyclic type.
• To make gear changing easy, these are mostly the epicyclic type and are
fitted behind the main box.
• The blades of the turbine are curved. This means that the fluid, which
enters the turbine from the outside, has to change direction before it exits
the center of the turbine.
• It is this directional change that causes the turbine to spin. As the turbine
causes the fluid to change direction, the fluid causes the turbine to spin.
• The turbine causes the transmission to spin, which basically moves the
car.

57. Connected to road wheels Fixed to the frame through freewheel

58. Torque Convertors…
The housing of the torque
converter is bolted to the
flywheel of the engine, so it turns
at whatever speed the engine is
running at.
The fins that make up the pump
of the torque converter are
attached to the housing, so they
also turn at the same speed as
the engine.
The cutaway below shows how
everything is connected inside
the torque converter.

59. Torque Convertors… The pump inside a torque
converter is a type of centrifugal
pump. As it spins, fluid is flung to
the outside, much as the spin cycle
of a washing machine flings water
and clothes to the outside of the
wash tub. As fluid is flung to the
outside, a vacuum is created that
draws more fluid in at the center.
The fluid then enters the blades of
the turbine, which is connected to
the transmission.

60. Advantages
Advantages of Automatic Transmission over Manual Transmission:
• Better fuel efficiency upto 15% increase.
• No loss of torque transmission from the engine to the driving wheels during gear shifts.
• Very smooth gear-shift operations
• Appeals to drivers due to overall fast shifts and rapid responses, along with the latest technology.

61. Disadvantages
Disadvantages of Automatic Transmission over Manual Transmission:
• Its mechanical efficiency is very less than that of a manual transmission type.
• Its requires a specialized transmission fluid/lubricants which is expensive and need to be changed
regularly.
• Its expensive to manufacture.
• It is heavier than an conventional manual transmission gearbox.
• It has much higher rate of failure due to complexity.

62. Continuously Variable Transmission
The Continuously Variable
Transmission (CVT) is a
transmission in which the
ratio of the rotational speeds
of two shafts, as the input
shaft and output shaft of a
vehicle or other machine, can
be varied continuously within
a given range, providing an
infinite number of possible
ratios.

63. Continuously Variable Transmission
The other mechanical transmissions
described above only allow a few different
gear ratios to be selected, but this type of
transmission essentially has an infinite
number of ratios available within a finite
range.

64. Continuously Variable Transmission
The continuously variable transmission allows the
relationship between the speed of the engine and
the speed of the wheels to be selected within a
continuous range.
This can provide even better fuel economy if the engine
is constantly running at a single speed.
The transmission is in theory capable of a better user
experience, without the rise and fall in speed of an
engine, and the jerk felt when changing gears.

65. Automobile Differential Gear Train

66. The function:
The device which reduces the
speed of the inner wheels and
increase the speed of the outer
wheels when taking a turn
It should at the same time keep
the speeds of all the wheels same
when going straight ahead

67. Automobile Differential Gear Train
• The above schematic diagram shows basically how the automobile
differential works.
• It only comes into play when one wheel needs to rotate differentially with
respect to its counterpart.
• When the car is moving in a straight line, the differential gears do not rotate
with respect to their axes.
• When the car negotiates a turn, however, the differential allows the two
wheels to rotate differentially with respect to each other.

68. Automobile Differential Gear Train
• One problem with an automotive differential is that if one wheel is held
stationary, the counterpart wheel turns at twice its normal speed as can be
seen by examining the complete scheme of automobile differential.
• This can be problematic when one wheel does not have enough traction,
such as when it is in snow or mud.
• The wheel without traction will spin without providing traction and the
opposite wheel will stay still so that the car does not move.
• This is the reason for a device known as a "limited slip differential" or
"traction control".

70. The clearance
between the teeth
of two meshing
gears is called
back lash

72. Differential
• The distance
traveled by outer
wheels is greater
than the inner
wheels

77. Propeller shaft
• Transmits the drive from the transmission to the bevel
pinion or worm of final drive in front engine, rear wheel
drive vehicles
• Also called drive shaft

78. •A drive shaft, driving shaft, propeller
shaft, or Cardan shaft is a mechanical
component for transmitting torque
and rotation, usually used to connect
other components of a drive train
that cannot be connected directly
because of distance or the need to
allow for relative movement between
them.

79. A Drive shaft consists of
•Shaft
• Tubular cross section
•One or two universal joints
• For the up and down movements of the
rear axle
•Slip joint
• To adjust the length of the propeller
shaft

84. Universal Joint
• It is a connection between two shafts, whose axes are
inclined to each other

88. Thank You