AUTOMOBILE RUNNING SYSTEM AND POWER TRAIN 8. TRANSMISSION GEARBOX
In the last lesson we studied the clutch. The clutch, as we saw, normally remains in the engaged position and transmits engine power to the next component in the transmission system, the transmission gearbox. The gearbox then has the function to transform this power according to requirement i.e. either give more torque at low speed or decrease the torque and increase the speed at the output. These days we have gearboxes having gear ratio lower than 1 i.e. the rpm at the output of the gearbox is greater than the input i.e. the rpm of the engine. Such is called the overdrive and helps the car to move at very high speed. Gearbox also serves to drive the car in reverse.
8.0
Objectives After going through this lesson, you will be able to:
i. Describe a gear and recognize its various types. ii. Differentiate between the various types of gearboxes and give the advantage of the synchromesh gearbox. iii. Describe the working of the synchronizer. iv. Describe the working of the gear shift mechanism.
8.1
Introduction
The gearbox is placed in the transmission system after the clutch. It enables the vehicle to be driven at different speeds and at the same time providing differing torque values. When we start the car from rest, we need greater torque to make the car start to move. At this time we use the first gear. Next we change into the second, then third gear and so on. Also, in the city a vehicle is driven at a slower speed than on a highway. All this is achieved through the gearbox. The gearbox is also used to reverse the car. In the reverse gear the engine continues to rotate in the same direction but the car moves backward.
Self-check Questions 1. Give the functions of the gearbox 2. What is overdrive? 3. When is greatest torque required?