Contents:
What is a Gearbox?
- An automobile gearbox Is an assemblage of gears and shafts, which is used to control the output speed & torque of a machine/vehicle.
- The engine provides a fixed speed for a certain amount of power & If it is directly coupled to the output shaft then it will give the fixed velocity of the vehicle.
- In the case of a vehicle running on a straight road with a higher speed, It doesn’t require a higher amount of torque because of the momentum of the vehicle. Hence it can run with less amount of torque.
- In Another case, when the vehicle is climbing the heel, It requires a higher amount of torque.
- Therefore the power transmission depends upon the Running condition of the vehicle.
- The vehicle also requires neutral condition even the engine is started
- Therefore gearbox is needed for a vehicle to control output speed & torque.
- It is located between the clutch & propeller shaft
- As per the need of the vehicle, different speeds or torque we can achieve with the help of a gearbox.
- For Example – In the case of the tractor which requires higher torque & lower speed hence reduction ratio is higher.
- While in the case of Racing vehicles which require higher speeds with less torque. In this case reduction ratio is lower.
- It has N number of speed steps & one reverse step.
Gearbox diagram:

Working principle:
The gearbox works on the following principle:-
- When Smaller gear meshes with Larger gear, low speed & high torque will obtain at output shaft.
- When larger gear meshes with Smaller gear, high speed & low torque will obtain at output shaft.
Construction:
The gearbox consists of an engine shaft, Lay shaft, Output shaft (Externally Splined), Clutch gear, Gears (1, 2, 3, 4, A, B, C), Idler gear etc.
Necessity/Significance of gearbox:
- To Control Output Torque.
- To Control Output Speed.
- To Achieve Neutral Position.
- To Achieve Reverse Gear transmission.
Types of automobile gearbox:
A) Manual Transmission:-
B) Automatic Transmission:-
- Torque Converter
- Epicyclic Gear Transmission
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