Automobile

A

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.

B

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.

VI

Electrical System

The automobile depends on electricity for fuel ignition, headlights, turn signals, horn, radio, windshield wipers, and other accessories. A battery and an alternator supply electricity. The battery stores electricity for starting the car. The alternator generates electric current while the engine is running, recharging the battery and powering the rest of the car’s electrical needs.

Early automotive electrical systems ran on 6 volts, but 12 volts became standard after World War II (1939-1945) to operate the growing number of electrical accessories. Eventually, 24- or 48-volt systems may become the standard as more computers and electronics are built into automobiles.

A

Ignition System

The ignition system supplies high-voltage current to spark plugs to ignite fuel vapor in the cylinders. There are many variations, but all gasoline-engine ignition systems draw electric current from the battery, significantly increase the current’s voltage, then deliver it to spark plugs that project into the combustion chambers. An electric arc between two electrodes at the bottom of the spark plug ignites the fuel vapor.

In older vehicles, a distributor, which is an electrical switching device, routes high-voltage current to the spark plugs. The distributor’s housing contains a switch called the breaker points. A rotating shaft in the distributor causes the switch to open and close, interrupting the supply of low-voltage current to a transformer called a coil. The coil uses electromagnetic induction (see Electricity: Electromagnetism) to convert interruptions of the 12-volt current into surges of 20,000 volts or more. This high-voltage current passes back to the distributor, which mechanically routes it through wires to spark plugs, producing a spark that ignites the gas vapor in the cylinders. A condenser absorbs excess current and protects the breaker points from damage by the high-voltage surge. The distributor and other devices control the timing of the spark-plug discharges.

In modern ignition systems, the distributor, coil, points, and condenser have been replaced by solid-state electronics controlled by a computer. A computer controls the ignition system and adjusts it to provide maximum efficiency in a variety of driving conditions.

VII

Safety Features

Manufacturers continue to build lighter vehicles with improved structural rigidity and ability to protect the driver and passengers during collisions.

Bumpers evolved as rails or bars to protect the front and rear of the car’s body from damage in minor collisions. Over the years, bumpers became stylish and, in some cases, not strong enough to survive minor collisions without expensive repairs. Eventually, government regulations required bumpers designed to withstand low-speed collisions with less damage. Some bumpers can withstand 4-km/h (2.5-mph) collisions with no damage, while others can withstand 8-km/h (5-mph) collisions with no damage.

Modern vehicles feature crumple zones, portions of the automobile designed to absorb forces that otherwise would be transmitted to the passenger compartment. Passenger compartments on many vehicles also have reinforced roll bar structures in the roof, in case the vehicle overturns, and protective beams in the doors to help protect passengers from side impacts.

Seat belt and upper-body restraints that relax to permit comfort but tighten automatically during an impact are now common. Some car models are equipped with shoulder-restraint belts that slide into position automatically when the car’s doors close.

An air bag is a high-speed inflation device hidden in the hub of the steering wheel or in the dash on the passenger’s side. Some automobiles have side-impact air bags, located in doors or seats. At impact, the bag inflates almost instantaneously. The inflated bag creates a cushion between the occupant and the vehicle’s interior. Air bags first appeared in the mid-1970s, available as an optional accessory. Today they are installed on all new passenger cars sold in the United States.

Air bags inflate with great force, which occasionally endangers a child or infant passenger. Some newer automobile models are equipped with switches to disable the passenger-side air bags when a child or infant is traveling in the passenger seat. Automakers continue to research ways to make air-bag systems less dangerous for frail and small passengers, yet effective in collisions.

	More from Encarta
	•  Presidential Myths Quiz •  Coffee break: Recharge your brain