Sunday, December 8, 2013
The Components of a 4 Wheel Drive System
Four-wheel drive vehicles receive torque from the engine in all four wheels at the same time. The original concept was to be able to maintain traction to either haul extra weight or drive in tough road conditions, or both. There are two modes of 4-wheel drives. The part-time mode is used for off-road driving or loose road surfaces. The driver is able to switch from 2-wheel drive to 4-wheel drive as needed. Full-time mode is used in all road conditions all of the time.
Differentials
The 4-wheel drive has a differential between the two front wheels and another between the back wheels. During a turn, all wheels are going at different speeds while at the same time, the inside wheels are following a different path than the outside wheels. The differentials allow front, back, left and right wheels to spin at different speeds during a turn by sending the power from the engine to the wheels. The differentials slow the transmissions rotational speed before it hits the wheels. In this manner it behaves as the last gear reduction of the vehicle.
Transfer Case
The transfer case is said to be the component that defines a vehicle as 4-wheel drive. This device splits power between all four axles on the vehicle. The transfer case is used to lock the front and rear axle drive shafts to force the wheels to have the same speed when they are turning. On part-time 4-wheel drive systems, transfer cases have an extra set of gears. These gears give a low range to the vehicle, providing extra torque.
Drive Shaft
Drive shafts enable the transfer case to transmit power from the drive to the front and back axles. The drive shafts are enclosed inside axle housings and transmit the drive to the tires. In part-time 4-wheel drive vehicles the drive is transmitted through the front axle drive only when the driver uses 4-wheel drive.
Locking Hubs
Every vehicles wheels are bolted to a hub. Part-time 4-wheel drive vehicles are equipped with locking hubs that are designed to disconnect front wheels from the front differential when 4-wheel drive is not engaged. The locking hubs also disconnect the front wheels from the drive shaft when a car is in 2-wheel drive.
Electronics
Electronically controlled clutches are used on some 4-wheel drive vehicles. This type of clutch controls torque transfer between the tires in a much more effective manner than older clutch mechanisms. Many 4-wheel drive systems use Anti Lock Brake Systems (ABS). The ABS systems provide brake-traction control when the tires begin to skid.
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