Transmission and Driveline
The transmission has different pairs of gears in a housing. These gears
allow a car to drive at different speeds. The tramsission oil lubricates
and cools the gears. A low gear moves a car from stop. Other higher gears
heep the engine speed to proper levels while accelerating. A car can go
at a less maximum speed in a lower gear, but it has greater accelerating
ability and hill-climbing ability. To save fuel for highway driving,
most cars have overdrive gears which decrease enginge speeds to minimum
practical levels. Overdrives should be used for constant speed driving
on level roads but should not be used for trailer-towing, hill-climbing
and accelerating to pass another car.
Manual transmission has a clutch which is controlled by the clutch pedal.
When a driver depresses the clutch pedal by foot, the clutch disengages
the engine from the transmission, and the driver can shift the gears, start
or stop the car. When the foot is off the clutch pedal, the engine transmits
power through the clutch to transmission to the drive wheels.
Automatic transmission selects the proper gear by itself. Instead of
using a clutch, the automatic tramsimission uses a torque converter or
fluid coupling to disconnect the engine and transmission during shifting
and starting. Automatic transmission fluid is used to operate and lubricate
the transmission gears.
When a car turns a corner, the differential allows one drive wheel to
turn faster than another but splits the driving force between both wheels.
The differential is housed in the transaxle with the tramsmission in front
wheel drive cars. In rear wheel drive cars, the differential is part of
the rear axle assembly.