Control Systems

Control Systems

A driver controls the automobile’s motion by keeping the wheels pointed in the desired direction, and by stopping or slowing the speed at which the wheels rotate. These controls are made possible by the steering and braking systems. In addition, the driver controls the vehicle’s speed with the transmission and the gas pedal, which adjusts the amount of fuel fed to the engine.

Steering

Automobiles are steered by turning the front wheels, although a few automobile types have all-wheel steering. Most steering systems link the front wheels together by means of a tie-rod. The tie-rod insures that the turning of one wheel is matched by a corresponding turn in the other.

When a driver turns the steering wheel, the mechanical action rotates a steering shaft inside the steering column. Depending on the steering mechanism, gears or other devices convert the rotating motion of the steering wheel into a horizontal force that turns the wheels.

Manual steering relies only on the force exerted by the driver to turn the wheels. Conventional power steering uses hydraulic pressure, operated by the pressure or movement of a liquid, to augment that force, requiring less effort by the driver. Electric power steering uses an electric motor instead of hydraulic pressure.

Brakes

Brakes enable the driver to slow or stop the moving vehicle. The first automobile brakes were much like those on horse-drawn wagons. By pulling a lever, the driver pressed a block of wood, leather, or metal, known as the shoe, against the wheel rims. With sufficient pressure, friction between the wheel and the brake shoe caused the vehicle to slow down or stop. Another method was to use a lever to clamp a strap or brake shoes tightly around the driveshaft.

A brake system with shoes that pressed against the inside of a drum fitted to the wheel, called drum brakes, appeared in 1903. Since the drum and wheel rotate together, friction applied by the shoes inside the drum slowed or stopped the wheel. Cotton and leather shoe coverings, or linings, were replaced by asbestos after 1908, greatly extending the life of the brake mechanism. Hydraulically assisted braking was introduced in the 1920s. Disk brakes, in which friction pads clamp down on both sides of a disk attached to the axle, were in use by the 1950s.

An antilock braking system (ABS) uses a computer, sensors, and a hydraulic pump to stop the automobile’s forward motion without locking the wheels and putting the vehicle into a skid. Introduced in the 1980s, ABS helps the driver maintain better control over the car during emergency stops and while braking on slippery surfaces.

Automobiles are also equipped with a hand-operated brake used for emergencies and to securely park the car, especially on uneven terrain. Pulling on a lever or pushing down on a foot pedal sets the brake.