21st Century Overview - Drive Train

Drive Train (power train) transmits engine power to the wheels and tires.   Engine power is transferred first to the transmission, which has many gears that change to assist the engine move the wheels as it gradually increases power.   The drive shaft (driveline, propeller shaft) transmits power from the transmission to the differential.   The two universal joints (U-Joints, UJs) allow the drive shaft to move vertically and horizontally without damage when the car tires hits irregularities in the road (bumps and holes).   The differential transmits power from the drive shaft to the axles.   The axle transmits power from the differential to the wheels and tires.   The differential is a complicated set of gears that allow each rear wheel to turn at different speeds when the car turns a corner.

Drive train for a rear-wheel drive (RWD).   Note that the drive train is long to connect the transmission, located in front, to the differential, located in the rear.

Rear axle viewed from the top showing how the drive shaft connects to the differential, shaft and wheels.

Drive train for a front-wheel drive (FWD).   Note that the drive train is short because the engine, diffeential, and driving wheels are close together.

Drive train for a front-wheel drive (FWD) from a rear view.

Drive train for a four-wheel drive (4WD) and all-wheel drive (AWD).   The engine powers both the front and rear wheels by means of a transfer case.

Drive train for a four-wheel drive (4WD) and all-wheel drive (AWD) viewed from the top.

Wheel and tire assembly enables the car to move.   The tire has two functions: (1) absorb shocks by road irregularities, and (2) grip the road, which enables the car to move.   The wheel holds the tire and provides a braking surface.