Automobile

Article Outline

Introduction; Power System; Drivetrain; Support Systems; Control Systems; Electrical System; Safety Features; History; Automobiles in the 20th Century; New Technologies

Front- and Rear-Wheel Drive

Depending on the vehicle’s design, engine power is transmitted by the transmission to the front wheels, the rear wheels, or to all four wheels. The wheels receiving power are called drive wheels: They propel the vehicle forward or backward. Most automobiles either are front-wheel or rear-wheel drive. In some vehicles, four-wheel drive is an option the driver selects for certain road conditions; others feature full-time, all-wheel drive.

The differential is a gear assembly in an axle that enables each powered wheel to turn at different speeds when the vehicle makes a turn. The driveshaft connects the transmission’s output shaft to a differential gear in the axle. Universal joints at both ends of the driveshaft allow it to rotate as the axles move up and down over the road surface.

In rear-wheel drive, the driveshaft runs under the car to a differential gear at the rear axle. In front-wheel drive, the differential is on the front axle and the connections to the transmission are much shorter. Four-wheel-drive vehicles have drive shafts and differentials for both axles.

Support Systems

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Automobiles would deliver jolting rides, especially on unpaved roads, without a system of shock absorbers and other devices to protect the auto body and passenger compartment from severe bumps and bounces.

Suspension System

The suspension system, part of the undercarriage of an automobile, contains springs that move up and down to absorb bumps and vibrations. In one type of suspension system, a long tube, or strut, has a shock absorber built into its center section. Shock absorbers control, or dampen, the sudden loading and unloading of suspension springs to reduce wheel bounce and the shock transferred from the road wheels to the body. One shock absorber is installed at each wheel. Modern shock absorbers have a telescoping design and use oil, gas, and air, or a combination to absorb energy.

Luxury sedans generally have a soft suspension for comfortable riding. Sports cars and sport-utility vehicles have firmer suspensions to improve cornering ability and control over rough terrain.

Older automobiles were equipped with one-piece front axles attached to the frame with semielliptic leaf springs, much like the arrangement on horse-drawn buggies. Front wheels on modern cars roll independently of each other on half-shafts instead of on a common axle. Each wheel has its own axle and suspension supports, so the shock of one wheel hitting a bump is not transferred across a common axle to the other wheel or the rest of the car. Many rear-axle suspensions for automobiles and heavier vehicles use rigid axles with coil or leaf springs. However, advanced passenger cars, luxury sedans, and sports cars feature independent rear-wheel suspension systems.

Active suspensions are computer-controlled adjustments of the downward force of each wheel as the vehicle corners or rides over uneven terrain. Sensors, a pump, and hydraulic cylinders, all monitored and controlled by computer, enable the vehicle to lean into corners and compensate for the dips and dives that accompany emergency stops and rapid acceleration.

Wheels and Tires

Wheels support the vehicle’s weight and transfer torque to the tires from the drivetrain and braking systems. Automobile wheels generally are made of steel or aluminum. Aluminum wheels are lighter, more impact absorbent, and more expensive.

Pneumatic (air-filled) rubber tires, first patented in 1845, fit on the outside rims of the wheels. Tires help smooth out the ride and provide the automobile’s only contact with the road, so traction and strength are primary requirements. Tire treads come in several varieties to match driving conditions.

Control Systems