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Automobile, small, 4-wheeled vehicle that carries passengers. The 4 major components of an automobile are its power plant, drive system, control system, and body.

Power plant

Almost all automobiles are powered by internal combustion engines, usually with 4–8 cylinders attached to a crankshaft. In the internal combustion engine, gasoline from the fuel tank is mixed with air in the carburetor and fed to the cylinders. The highly explosive mixture is ignited by the spark plugs and, as it explodes, expands rapidly .The piston within the cylinder is forced downward, turning the crankshaft. The heavy metal flywheel attached to one end of the crankshaft moves the piston back up the cylinder to its original position. The order in which the spark plugs fire is controlled by the distributor. In most engines, the gasoline vapor simply enters the cylinder through a valve at the beginning of the downstroke, but some automobiles have fuel-injection systems that greatly increase efficiency.

Drive system

In most cars, the drive is supplied by the rear wheels. The motion of the crankshaft must therefore be transmitted by a driveshaft to the rear axle, where a system of cogs turns the wheels. The rotation of the crankshaft is transmitted to the driveshaft by the clutch, which consists of 2 circular plates, one attached to the driveshaft, the other to the crankshaft. When the plates are in contact, both rotate. When one plate is drawn back, the crankshaft rotates without affecting the driveshaft, and the engine can “turn over” without moving the car. Gears alter the number of turns required from the engine to achieve a single turn of the drive wheels. The gear box also makes reverse movement possible. When cars are equipped with automatic transmission, manual control of the gears or clutch is not required.

The controls

Steering is controlled by a steering wheel, attached to horizontal track rods between the two front wheels. The movement of these rods turns the wheels. In heavy cars, power steering uses hydraulic pressure to assist the driver in turning the wheel. The pedal-operated brake system uses either the pressure of brake shoes against brake drums attached to the wheels or the more efficient disk brakes. The handbrake, which clamps onto the driveshaft or one set of wheels, is used as an emergency brake or for parking. The gas pedal is connected to the carburetor and controls the amount of gasoline vapor that enters the cylinders of the engine. The greater the quantity of vapor, the more powerful the explosion and the greater the speed of the automobile.


The chassis of the car is the large steel frame that supports the engine and the control and running mechanisms. It may be a solid piece of stamped metal or a series of metal parts welded together. In cars that do not have a chassis, the body may simply be the framework that links the mechanical parts. The weight of the car is supported at the front and rear axles by metal springs, or sometimes by a hydraulic mechanism, to absorb shocks transmitted from the road and ensure a smooth ride.

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21st Century Webster's Family Encyclopedia21st Century Webster's Family Encyclopedia - Augusta to Barlach, Ernst