Four-Wheel Drives And How They Operate
April 2nd, 2009 Muscle Cars
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Four-Wheel Drives And How They Operate
Four-wheel drive allows even the inexperienced driver to conquer slippery roads and treacherous weather conditions. But, understanding how it works makes it easier to operate safely. In general, a 4WD system distributes power to every tire on the car, not just the front or rear set. This broad definition also suggests that every car manufacturer has a unique four-wheel drive system with different power distribution to match.
In this article, we’ll take a closer look at how the power is distributed. We’ll explain how the parts which contribute to its operation work together so you’ll have an appreciation for the system.
Differentials And Locking Hubs
A four-wheel drive has three basic units: the differentials, transfer case, and locking hubs. The differentials are assemblies that take the torque from the transmission and route it to the tires. In addition, differentials allow the wheels to spin independently of one another when turning.
Locking hubs are devices used to preserve the front wheels. In every car, each tire is bolted to a hub, but in a 4WD vehicle when the front wheels are not receiving power, the differential and half-shafts are still spinning. With locking hubs, the front tires are disconnected so they avoid causing undue wear and tear on the drive shaft, differential, and half-shafts. A sliding collar is employed that connects the hub to the half-shaft and is moved depending upon whether the car is in two-wheel drive or not.
Many years ago, locking hubs were manually operated. If you wanted to switch to 2WD mode, you needed to exit your vehicle and manipulate a knob on the front tires to lock and disengage them. Today, the mechanism is completely automatic and can be activated when the car is moving.
The Transfer Case
The transfer case is responsible for splitting the power between the front and rear tires. These can vary depending upon whether your car is all-wheel drive (which means all wheels are permanently activated) or part-time. In a part-time vehicle, the transfer case binds both the front and rear axles together so everything spins at the same speed. However, this is not usually recommended on dry concrete or otherwise stable road surfaces as it will cause your tires to slip, needlessly wearing them down.
In some transfer case systems, the mechanism contains a set of gears known as a low range. The low range transfers large amounts of torque while operating at a very low speed. This is especially useful when driving in very slippery conditions or on steep roads.
Most motorists enjoy driving their 4WD vehicles without realizing how they operate. Long-time readers know that I always recommend learning as much as you can about the parts under your car’s hood. When the time comes to visit a mechanic, you’ll have a deeper understanding about your vehicle.
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Tags: 4W Drive, Cars, Four Wheel Drives