Automobile

I

Introduction

Automobile, self-propelled vehicle used primarily on public roads but adaptable to other surfaces. Automobiles changed the world during the 20th century, particularly in the United States and other industrialized nations. From the growth of suburbs to the development of elaborate road and highway systems, the so-called horseless carriage has forever altered the modern landscape. The manufacture, sale, and servicing of automobiles have become key elements of industrial economies. But along with greater mobility and job creation, the automobile has brought noise and air pollution, and automobile accidents rank among the leading causes of death and injury throughout the world. But for better or worse, the 1900s can be called the Age of the Automobile, and cars will no doubt continue to shape our culture and economy well into the 21st century.

Automobiles are classified by size, style, number of doors, and intended use. The typical automobile, also called a car, auto, motorcar, and passenger car, has four wheels and can carry up to six people, including a driver. Larger vehicles designed to carry more passengers are called vans, minivans, omnibuses, or buses. Those used to carry cargo are called pickups or trucks, depending on their size and design. Minivans are van-style vehicles built on a passenger car frame that can usually carry up to eight passengers. Sport-utility vehicles, also known as SUVs, are more rugged than passenger cars and are designed for driving in mud or snow.

Auto manufacturing plants in 40 countries produced a total of 63.9 million vehicles, including 42.8 million passenger cars, in 2004, according to Ward’s Auto, an auto industry analyst. About 16.2 million vehicles, including 6.3 million passenger cars, were produced in North America in 2004. For information on the business of making cars, see Automobile Industry.

The automobile is built around an engine. Various systems supply the engine with fuel, cool it during operation, lubricate its moving parts, and remove exhaust gases it creates. The engine produces mechanical power that is transmitted to the automobile’s wheels through a drivetrain, which includes a transmission, one or more driveshafts, a differential gear, and axles. Suspension systems, which include springs and shock absorbers, cushion the ride and help protect the vehicle from being damaged by bumps, heavy loads, and other stresses. Wheels and tires support the vehicle on the roadway and, when rotated by powered axles, propel the vehicle forward or backward. Steering and braking systems provide control over direction and speed. An electrical system starts and operates the engine, monitors and controls many aspects of the vehicle’s operation, and powers such components as headlights and radios. Safety features such as bumpers, air bags, and seat belts help protect occupants in an accident.

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II

Power System

Gasoline internal-combustion engines power most automobiles, but some engines use diesel fuel, electricity, natural gas, solar energy, or fuels derived from methanol (wood alcohol) and ethanol (grain alcohol).

Most gasoline engines work in the following way: Turning the ignition key operates a switch that sends electricity from a battery to a starter motor. The starter motor turns a disk known as a flywheel, which in turn causes the engine’s crankshaft to revolve. The rotating crankshaft causes pistons, which are solid cylinders that fit snugly inside the engine’s hollow cylinders, to move up and down. Fuel-injection systems or, in older cars, a carburetor deliver fuel vapor from the gas tank to the engine cylinders.

The pistons compress the vapor inside the cylinders. An electric current flows through a spark plug to ignite the vapor. The fuel mixture explodes, or combusts, creating hot expanding gases that push the pistons down the cylinders and cause the crankshaft to rotate. The crankshaft is now rotating via the up-and-down motion of the pistons, permitting the starter motor to disengage from the flywheel.

A

Engine

The basic components of an internal-combustion engine are the engine block, cylinder head, cylinders, pistons, valves, crankshaft, and camshaft. The lower part of the engine, called the engine block, houses the cylinders, pistons, and crankshaft. The components of other engine systems bolt or attach to the engine block. The block is manufactured with internal passageways for lubricants and coolant. Engine blocks are made of cast iron or aluminum alloy and formed with a set of round cylinders.

The upper part of the engine is the cylinder head. Bolted to the top of the block, it seals the tops of the cylinders. Pistons compress air and fuel against the cylinder head prior to ignition. The top of the piston forms the floor of the combustion chamber. A rod connects the bottom of the piston to the crankshaft. Lubricated bearings enable both ends of the connecting rod to pivot, transferring the piston’s vertical motion into the crankshaft’s rotational force, or torque. The pistons’ motion rotates the crankshaft at speeds ranging from about 600 to thousands of revolutions per minute (rpm), depending on how much fuel is delivered to the cylinders.

Fuel vapor enters and exhaust gases leave the combustion chamber through openings in the cylinder head controlled by valves. The typical engine valve is a metal shaft with a disk at one end fitted to block the opening. The other end of the shaft is mechanically linked to a camshaft, a round rod with odd-shaped lobes located inside the engine block or in the cylinder head. Inlet valves open to allow fuel to enter the combustion chambers. Outlet valves open to let exhaust gases out.

A gear wheel, belt, or chain links the camshaft to the crankshaft. When the crankshaft forces the camshaft to turn, lobes on the camshaft cause valves to open and close at precise moments in the engine’s cycle. When fuel vapor ignites, the intake and outlet valves close tightly to direct the force of the explosion downward on the piston.

B

Engine Types

The blocks in most internal-combustion engines are in-line designs or V designs. In-line designs are arranged so that the cylinders stand upright in a single line over the crankshaft. In a V design, two rows of cylinders are set at an angle to form a V. At the bottom of the V is the crankshaft. In-line configurations of six or eight cylinders require long engine compartments found more often in trucks than in cars. The V design allows the same number of cylinders to fit into a shorter, although wider, space. Another engine design that fits into shorter, shallower spaces is a horizontally opposed, or flat, arrangement in which the crankshaft lies between two rows of cylinders.

Engines become more powerful, and use more fuel, as the size and number of cylinders increase. Most modern vehicles in the United States have 4-, 6-, or 8-cylinder engines, but car engines have been designed with 1, 2, 3, 5, 12, and more cylinders.

Diesel engines, common in large trucks or buses, are similar to gasoline internal-combustion engines, but they have a different ignition system. Diesels compress air inside the cylinders with greater force than a gasoline engine does, producing temperatures hot enough to ignite the diesel fuel on contact. Some cars have rotary engines, also known as Wankel engines, which have one or more elliptical chambers in which triangular-shaped rotors, instead of pistons, rotate.

Electric motors have been used to power automobiles since the late 1800s. Electric power supplied by batteries runs the motor, which rotates a driveshaft, the shaft that transmits engine power to the axles. Commercial electric car models for specialized purposes were available in the 1980s. General Motors Corporation introduced a mass-production all-electric car in the mid-1990s.

Automobiles that combine two or more types of engines are called hybrids. A typical hybrid is an electric motor with batteries that are recharged by a generator run by a small gas- or diesel-powered engine. These hybrids are known as hybrid electric vehicles (HEVs). By relying more on electricity and less on fuel combustion, HEVs have higher fuel efficiency and emit fewer pollutants. Several automakers have experimented with hybrids.

In 1997 Toyota Motor Corporation became the first to mass-produce a hybrid vehicle, the Prius. It became available in Japan in 1997 and in North America in 2000. The first hybrid available for sale in North America, the Honda Insight, was offered by Honda Motor Co., Ltd., in 1999. Honda later introduced a hybrid version of the Honda Civic. In August 2004 the Ford Motor Company became the first U.S. automaker to release a hybrid vehicle when it began production of the Ford Escape Hybrid, the first hybrid sport- utility vehicle (SUV). The Escape Hybrid was released for the 2005 model year.

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