Four-wheel drive
Four-wheel drive (also known as 4WD or 4×4) is a vehicle in which all the four wheels are allowed to receive torque from the engine at the same time. The term is widely associated with off-road driving. In fact, by powering all of the four wheels at the same time, a normal car has a better control on most surfaces. The term four-wheel drive describe cars in which the driver has to manually switch between two wheel drive (for streets) and four-wheel drive (for adverse conditions such as snow, ice, mud, gravel). AWD (All Wheel Drive) is a “full-time” four-wheel drive.
The best way to have 4WD on a car is to have differentials mounted. The differential allows one input shaft to drive two output shafts at different speeds. It distributes the angular force (called torque) evenly, while distributing angular velocity (turning speed) such that the average of the two output shafts is equal to that of the input shaft. Note that each of the powered axles requires a differential to distribute the power between the left side and the right side. When all the four wheels are used, a third differential can be used to distribute the power between the front and the rear axles. This would be the best way to use differentials at maximum efficiency. This system distributes the power evenly and smoothly between the wheels, and also makes slippage very unlikely. However, if the car slips, recovery can be a difficult thing. This is where the Traction Control helps us. If the car uses a traction control system, brake is automatically applied to the wheel that spins out of control. This prevents the wheel from spinning freely and the power is divided between the pavement for the non-slipping wheel and the brake for the slipping wheel. This is a very useful system that greatly helps drivers all over the world. Another way of stopping slippage is the Locking differentials system. This temporarily locks together the differential’s output shafts, thus causing all four wheels to turn at the same rate. This provides additional torque in the case of slippage. The third approach in order to limit slippage is the use of Torsen differential. This system allows the output shafts to receive different amounts of torque.
Some four-wheel drive engine cars (like the Bugatti Type 53, and Team Lotus’s 4WD-Lotus 63) were tried on the racing track. The cars behaved well, but inferior to the Rear-Wheel Drive (RWD) cars. The advent of aerodynamic downforce meant that adequate traction could be obtained in a lighter and more mechanically efficient manner. Although Lotus tried repeatedly, the idea of a four-wheel drive car on a racing circuit was discontinued.
The true inventor of four-wheel drive is not really known because the history was not well recorded. The first sign of the 4WD was in 1893, before the establishment of the modern automotive industry in Britain. Back then, Joeseph Bramah Diplock, an English engineer, created a four wheel drive system for the traction engine. The system included four-wheel steering and three differentials. Diplock’s system was subsequently built. The vehicle displayed the ability to drive on bad terrain and on adverse conditions. Since then, many renowned car producers managed to produce their own four-wheel drive cars. The ability to drive over rough terrain was, and still is, of great importance.
If you consider buying a 4WD car, you should carefully read its technical documentation. You should see if the car fits you needs and also see how it works. You should know that a four-wheel drive car is less fuel efficient than a two-wheel drive one. However, for the higher fuel consumption, it provides increased control over most surfaces. When driving on snow, ice, gravel, or mud, the four-wheel drive is excellent, as it provides additional security in case of slipping.
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