
15 Layshaft gearboxes
15.1 PURPOSE AND ELEMENTS OF THE
GEARBOX
The need for a gearbox
A gearbox is incorporated in the vehicle transmission
system for the following reasons:
1 To assist the engine to do its work.
2 To enable the vehicle to be reversed.
3 To provide a ready means of disconnecting the engine
from the transmission system.
The first reason merits closer examination. In the same
sense that man is often required to perform physical
tasks beyond his unaided strength, so too can the
performance demanded of a motor vehicle exceed the
turning effort available at the engine crankshaft to
drive the road wheels.
In practice the turning