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automobile,self-propelled vehicle used for travel on land. The term is commonly applied to a four-wheeled vehicle designed to carry two to six passengers and a limited amount of cargo, as contrasted with a trucktruck,
automotive vehicle designed primarily for the transportation of goods. A truck is constructed on the general lines of the automobile but uses larger and heavier parts. It may be powered by a gasoline internal-combustion engine or a diesel engine.
..... Click the link for more information. , which is designed primarily for the transportation of goods and is constructed with larger and heavier parts, or a busbus
[Lat. omnibus=for all], large public conveyance. A horse-drawn urban omnibus was introduced in Paris in 1662 by Blaise Pascal and his associates, but it remained in operation for only a few years. The omnibus reappeared c.
..... Click the link for more information. (or omnibus or coach), which is a large public conveyance designed to carry a large number of passengers and sometimes additionally small amounts of cargo. For operation and technical features of automobiles, differentialdifferential,
in the automobile, a set of gears used on the driving (usually rear) axle. The two wheels on the driving axle must be interconnected in order to receive their energy from the same source, the driving shaft; at the same time they must be free to revolve at different
..... Click the link for more information. ; fuel injectionfuel injection,
system in an internal-combustion engine that delivers fuel or a fuel-air mixture to the cylinders by means of pressure from a pump. It was originally used in diesel engines because of diesel fuel's greater viscosity and the need to overcome the high pressure of
..... Click the link for more information. ; ignitionignition,
apparatus for igniting a combustible mixture. The German engineer Nikolaus A. Otto, in his first gas engine, used flame ignition; another method was heating a metal tube to incandescence.
..... Click the link for more information. ; internal-combustion engineinternal-combustion engine,
one in which combustion of the fuel takes place in a confined space, producing expanding gases that are used directly to provide mechanical power.
..... Click the link for more information. ; lubricationlubrication,
introduction of a substance between the contact surfaces of moving parts to reduce friction and to dissipate heat. A lubricant may be oil, grease, graphite, or any substance—gas, liquid, semisolid, or solid—that permits free action of mechanical devices
..... Click the link for more information. ; mufflermuffler,
in automobiles, device designed to reduce the noise from the exhaust of an internal-combustion engine. When the exhaust gases from an internal-combustion engine are released directly into the atmosphere, they create a loud noise, caused by the passage of the exhaust
..... Click the link for more information. ; odometerodometer
, instrument provided in an automotive vehicle to indicate the total number of miles that have been traveled. The odometer generally shares a housing with the vehicle's speedometer and is driven by a cable that the two share.
..... Click the link for more information. ; shock absorbershock absorber,
device for reducing the effect of a sudden shock by the dissipation of the shock's energy. On an automobile, springs and shock absorbers are mounted between the wheels and the frame.
..... Click the link for more information. ; speedometerspeedometer,
instrument that indicates speed. A cable from an automotive speedometer is attached to the rear of the transmission of an automobile; the cable turns at a rate proportional to the speed of the car.
..... Click the link for more information. ; steering systemsteering system,
in automobiles, steering wheel, gears, linkages, and other components used to control the direction of a vehicle's motion. Because of friction between the front tires and the road, especially in parking, effort is required to turn the steering wheel.
..... Click the link for more information. ; suspensionsuspension,
in automobiles, system of springs used to suspend the frame, body, engine, and power train above the wheels. Its principal purpose is to lessen the jarring of the automobile that is caused by irregularities in the roads traveled.
..... Click the link for more information. ; tachometertachometer
, instrument that indicates the speed, usually in revolutions per minute, at which an engine shaft is rotating. Some tachometers, especially those used in automobiles, are similar in construction and operation to automotive speedometers.
..... Click the link for more information. ; tiretire,
device made of rubber and fabric and attached to the outer rim of a vehicle wheel. Solid rubber tires were in limited use before 1850; they are still used in some special applications, e.g., for industrial trucks in factories.
..... Click the link for more information. ; transmissiontransmission,
in automobiles, system of parts connecting the engine to the wheels. Suitable torque, or turning force, is generated by the engine only within a narrow range of engine speeds, i.e., rates at which the crankshaft is turning.
..... Click the link for more information. .
Automobile Propulsion Systems
Reciprocating Internal-Combustion Engines
The modern automobile is usually driven by a water-cooled, piston-type internal-combustion engineinternal-combustion engine,
one in which combustion of the fuel takes place in a confined space, producing expanding gases that are used directly to provide mechanical power.
..... Click the link for more information. , mounted in the front of the vehicle; its power may be transmitted either to the front wheels, to the rear wheels, or to all four wheels. Some automobiles use air-cooled engines, but these are generally less efficient than the liquid-cooled type. In some models the engine is carried just forward of the rear wheels; this arrangement, while wasteful of space, has the advantage of better weight distribution. Although passenger vehicles are usually gasoline fueled, diesel enginesdiesel engine,
type of internal-combustion engine invented by the German engineer Rudolf Diesel and patented by him in 1892. Although his engine was designed to use coal dust as fuel, the diesel engine now burns fuel oil.
..... Click the link for more information. (which burn a heavier petroleum oil) are employed both for heavy vehicles, such as trucks and buses, and for a small number of family sedans. Both diesel and gasoline engines generally employ a four-stroke cycle.
The Wankel Engine
For some years, it was hoped that the Wankel engine, a rotary internal-combustion engine developed by Felix Wankel of Germany in 1954, might provide an alternative to the reciprocating internal-combustion engine because of its low exhaust emissions and feasibility for mass production. In this engine a three-sided rotor revolves within an epithrochoidal drum (combustion chamber) in which the free space contracts or expands as the rotor turns. Fuel is inhaled, compressed, and fired by the ignition system. The expanding gas turns the rotor and the spent gas is expelled. The Wankel engine has no valves, pistons, connecting rods, reciprocating parts, or crankshaft. It develops a high horsepower per cubic inch and per pound of engine weight, and it is essentially vibrationless, but its fuel consumption is higher than that of the conventional piston engine.
Alternative Fuels and Engines
Internal-combustion engines consume relatively high amounts of petroleum, and contribute heavily to air pollution; therefore, other types of fuels and nonconventional engines are being studied and developed. An alternative-fuel vehicle (AFV) is a dedicated flexible-fuel vehicle (one with a common fuel tank designed to run on varying blends of unleaded gasoline with either ethanol or methanol) or a dual-fuel vehicle (one designed to run on a combination of an alternative fuel and a conventional fuel) operating on at least one alternative fuel. An advanced-technology vehicle (ATV) combines a new engine, power train, and drive train system to significantly improve fuel economy. It is estimated that more than a half million alternative-fuel vehicles were in use in the United States in 2002; 50% of these operate on liquefied petroleum gasliquefied petroleum gas
mixture of gases, chiefly propane and butane, produced commercially from petroleum and stored under pressure to keep it in a liquid state.
..... Click the link for more information. (LPG, or propanepropane,
CH3CH2CH3, colorless, gaseous alkane. It is readily liquefied by compression and cooling. It melts at −189.9°C; and boils at −42.2°C;.
..... Click the link for more information. ) and almost 25% use compressed natural gasnatural gas,
natural mixture of gaseous hydrocarbons found issuing from the ground or obtained from specially driven wells. The composition of natural gas varies in different localities.
..... Click the link for more information. (CNG).
The ideal alternative-fuel engine would burn fuel much more cleanly than conventional gasoline-powered internal-combustion engines and yet still be able to use the existing fuel infrastructure (i.e., gas stations). Compressed natural gas, propane, hydrogen, and alcohol-based substances (gasoholgasohol,
a gasoline extender made from a mixture of gasoline (90%) and ethanol (10%; often obtained by fermenting agricultural crops or crop wastes) or gasoline (97%) and methanol, or wood alcohol (3%).
..... Click the link for more information. , ethanolethanol
or ethyl alcohol,
CH3CH2OH, a colorless liquid with characteristic odor and taste; commonly called grain alcohol or simply alcohol. Properties
Ethanol is a monohydric primary alcohol. It melts at −117.
..... Click the link for more information. , methanolmethanol,
or wood alcohol,
CH3OH, a colorless, flammable liquid that is miscible with water in all proportions. Methanol is a monohydric alcohol. It melts at −97.8°C; and boils at 67°C;.
..... Click the link for more information. , and other "neat" alcohols) all have their proponents. However, although these fuels burn somewhat cleaner than gasoline, the use of all of them involves trade-offs. For example, because they take up more space per mile driven, these alternatives require larger fuel capacities or shorter distances between refueling stops. In addition, conventional automobiles may require extensive modifications to use alternative fuels; for example, to use gasohol containing more than 17% ethanol, the spark plugs, engine timing, and seals of an automobile must be modified; since 1998, however, many U.S. automobiles have been manufactured with equipment that enables them to run on E85, a mixture of 85% ethanol and 15% gasoline. Fuels derived from plant materials, such as ethanol, are a popular concept because they do not deplete the world's oil reserves; in various locations, "biodiesel" test cars have run on fuel similar to sunflower-seed oil. Similarly, dual-fuel (gasoline-diesel and gasoline-propane) and water-fuel-emulsion cars are being tested.
Alternative propulsion systems are also being studied. Steam engines, which were once more common than gasoline engines, are being experimented with now because they give off fewer noxious emissions; they are, however, less efficient than internal-combustion engines. Battery-powered electric engines, used in some early automobilies and later mainly for local delivery vehicles, are now used in automobiles capable of highway speeds, but they are restricted to shorter trips because of limitations on the storage batteries that power the motors and the time required to recharge the batteries. A true mass-market all-electric automobile was first sold to consumers in late 2010.
Some engineers worry that widespread adoption of electric cars might actually generate more air pollution, because additional electric power plants would be needed to recharge their batteries. Therefore, design and research work has also intensified on solar batteries, but they are generally not yet powerful enough to power such vehicles. The most promising technology for electric engines is the fuel cellfuel cell,
electric cell in which the chemical energy from the oxidation of a gas fuel is converted directly to electrical energy in a continuous process (see oxidation and reduction).
..... Click the link for more information. , but fuel cells currently are too expensive for practical applications.
Hybrid vehicles, or hybrid electric vehicles (HEVs), are powered by two or more energy sources, one of which is electricity, to produce a high-miles-per-gallon, low-emission drive. There are two types of HEVs, series and parallel. In a series hybrid, all of the vehicle power is provided from one source. For example, an electric motor drives the vehicle from the battery pack and the internal combustion engine powers a generator that charges the battery. In a parallel hybrid, power is delivered through both paths, both the electric motor and the internal combustion engine powering the vehicle. Thus, the electric motor may help power the vehicle while idling and during acceleration. The internal combustion engine takes over while cruising, powering the drive train and recharging the electric motor's battery. Some hybrids can operate in electric-only mode. Automobiles with gasoline-electric hybrid engines first appeared on the consumer market in 1999; unhampered by the AFV's limitations, sales of these vehicles increased steadily at the beginning of the 21st cent.
Automobiles and the Environment
Pollutants derived from automobile operation have begun to pose environmental problems of considerable magnitude. It has been calculated, for example, that 70% of the carbon monoxide, 45% of the nitrogen oxides, and 34% of the hydrocarbon pollution in the United States can be traced directly to automobile exhausts (see air pollutionair pollution,
contamination of the air by noxious gases and minute particles of solid and liquid matter (particulates) in concentrations that endanger health. The major sources of air pollution are transportation engines, power and heat generation, industrial processes, and the
..... Click the link for more information. ). In addition, rubber (which wears away from tires), motor oil, brake fluid, and other substances accumulate on roadways and are washed into streams, with effects nearly as serious as those of untreated sewage. A problem also exists in disposing of the automobiles themselves when they are no longer operable.
In an effort to improve the situation, the U.S. government has enacted regulations on the use of the constituents of automobile exhaust gas that are known to cause air pollution. These constituents fall roughly into three categories: hydrocarbons that pass through the engine unburned and escape from the crankcase; carbon monoxide, also a product of incomplete combustion; and nitrogen oxides, which are formed when nitrogen and oxygen are in contact at high temperatures. Besides their own toxic character, hydrocarbons and nitrogen oxides undergo reactions in the presence of sunlight to form noxious smogsmog
[smoke+fog], dense, visible air pollution. Smog is commonly of two types. The gray smog of older industrial cities like London and New York derives from the massive combustion of coal and fuel oil in or near the city, releasing tons of ashes, soot, and sulfur
..... Click the link for more information. . Carbon monoxide and hydrocarbons are rather easily controlled by the use of high combustion temperatures, leaner fuel mixtures, and lower compression ratios in engines. Unfortunately, the conditions that produce minimum emission of hydrocarbons tend to raise emission of nitrogen oxides. To some extent this difficulty is solved by adding recycled exhaust gas to the fuel mixture, thus avoiding the oversupply of oxygen that favors formation of nitrogen oxides.
The introduction of catalytic converters in the exhaust system has provided a technique for safely burning off hydrocarbon and carbon-monoxide emissions. The fragility of the catalysts used in these systems required the elimination of lead compounds previously used in gasoline to prevent engine knock. California, which has the most stringent air-pollution laws in the United States, requires further special compounding of gasoline to control emissions, and several states have mandated that ethanol be mixed with gasoline; as with the elimination of lead, measures taken to control air pollution have a negative impact on fuel efficiency. In 2009 the United States adopted more stringent mileage and emission standards (effective in 2012 and based on California's standards), which were designed to produce the first significant increases in vehicle efficiency and decreases in vehicle pollution since the mid-1980s.
Fatalities due to automobile accidents have stimulated improvements in automotive safety design. The first innovation involves creating a heavy cage around the occupants of the automobile, while the front and rear of the car are constructed of lighter materials designed to absorb impact forces. The second safety system uses seat belts to hold occupants in place. This was largely ineffective until states in the United States began passing laws requiring seat belt use. The third system is the air bag; within a few hundredths of a second after a special sensor detects a collision, an air bag in the steering wheel or dashboard inflates to prevent direct human impact with the wheel, dashboard, or windshield (newer vehicles sometimes include side air bags, to protect occupants from side collisions). Other advances in vehicle safety include the keyless ignition, which makes it impossible for a driver to start a car while under the influence of alcohol (over half of all vehicle fatalities involve at least one driver who has used alcohol) and antilock braking systems, which prevent an automobile's wheels from locking during braking.
Development of the Automobile
The automobile has a long history. The French engineer Nicolas Joseph Cugnot built the first self-propelled vehicle (Paris, 1789), a heavy, three-wheeled, steam-driven carriage with a boiler that projected in front; its speed was c.3 mph (5 kph). In 1801 the British engineer Richard Trevithick also built a three-wheeled, steam-driven car; the engine drove the rear wheels. Development of the automobile was retarded for decades by over-regulation: speed was limited to 4 mph (6.4 kph) and until 1896 a person was required to walk in front of a self-propelled vehicle, carrying a red flag by day and a red lantern by night. The Stanley brothers of Massachusetts, the most well-known American manufacturers of steam-driven autos, produced their Stanley Steamers from 1897 until after World War I.
The development of the automobile was accelerated by the introduction of the internal-combustion engine. Probably the first vehicle of this type was the three-wheeled car built in 1885 by the engineer Karl Benz in Germany. Another German engineer, Gottlieb Daimler, built an improved internal-combustion engine c.1885. The Panhard car, introduced in France by the Daimler company in 1894, had many features of the modern car. In the United States, internal-combustion cars of the horseless buggy type were manufactured in the 1890s by Charles Duryea and J. Frank Duryea, Elwood Haynes, Henry Ford, Ransom E. Olds, and Alexander Winton. Many of the early engines had only one cylinder, with a chain-and-sprocket drive on wooden carriage wheels. The cars generally were open, accommodated two passengers, and were steered by a lever.
The free growth of the automobile industry in the early 20th cent. was threatened by the American inventor George Selden's patent, issued in 1895. Several early manufacturers licensed by Selden formed an association in 1903 and took over the patent in 1907. Henry Ford, the leader of a group of independent manufacturers who refused to acknowledge the patent, was engaged in litigation with Selden and the association from 1903 until 1911, when the U.S. Circuit Court of Appeals ruled that the patent, although valid, covered only the two-cycle engine; most cars, including Ford's, used a four-cycle engine. The mass production of automobiles that followed, and the later creation of highways linking cities to suburbs and region to region, transformed American landscape and society.
Since 2010 there has been an increased focus on developing a practical automobile in which a computerized driving system either greatly aids or completely replaces the human driver. Although the technology for an automated vehicle has been explored since the 1920s, real work on semiautonomous and autonomous vehicles did not progress until the 1980s and the development of microcomputers, and even then the technology was not commercially practical. In the early 21st cent. an increasing number of automobile manufacturers begin including automatic safety equipment that activates when the vehicle's computerized systems sense conditions such as impending vehicle instability or collision and takes measures, such as automated braking, to avoid crashes and passenger injury. Significant advances also have been made in the development of self-driving vehicles, a number of which have been road-tested successfully in public traffic since 2010. In some cases, autonomous driving capabilities have been incorporated into cars that are commercially available.
See D. L. Lewis and L. Goldstein, The Automobile and American Culture (1983); J. J. Flink, The Automobile Age (1988); B. Olsen and J. Cabadas, The American Auto Factory (2002); P. Wollen and J. Kerr, ed., Autopia (2003); S. Parissien, The Life of the Automobile (2014).
A self-propelled land vehicle, usually having four wheels and an internal combustion engine, used primarily for personal transportation. Other types of motor vehicles include buses, which carry large numbers of commercial passengers, and medium- and heavy-duty trucks, which carry heavy or bulky loads of freight or other goods and materials. Instead of being carried on a truck, these loads may be placed on a semitrailer, and sometimes also a trailer, forming a tractor-trailer combination which is pulled by a truck tractor.
The automobile body is the assembly of sheet-metal, fiberglass, plastic, or composite-material panels together with windows, doors, seats, trim and upholstery, glass, and other parts that form enclosures for the passenger, engine, and luggage compartments. The assembled body structure may attach through rubber mounts to a separate or full frame (body-on-frame construction), or the body and frame may be integrated (unitized-body construction). In the latter method, the frame, body parts, and floor pan are welded together to form a single unit that has energy-absorbing front and rear structures, and anchors for the engine, suspension, steering, and power-train components. A third type of body construction is the space frame which is made of welded steel stampings. Similar to the tube chassis and roll cage combination used in race-car construction, non-load-carrying plastic outer panels fasten to the space frame to form the body. See Composite material
The frame is the main structural member to which all other mechanical chassis parts and the body are assembled to make a complete vehicle. In older vehicle designs, the frame is a separate rigid structure; newer passenger-car designs have the frame and body structure combined into an integral unit, or unitized body. Subframes and their assembled components attach to the side rails at the front and rear of the unitized body. The front subframe carries the engine, transmission or transaxle, lower front suspension, and other mechanical parts. The rear subframe, if used, carries the rear suspension and rear axle.
The suspension supports the weight of the vehicle, absorbs road shocks, transmits brake-reaction forces, helps maintain traction between the tires and the road, and holds the wheels in alignment while allowing the driver to steer the vehicle over a wide range of speed and load conditions. The action of the suspension increases riding comfort, improves driving safety, and reduces strain on vehicle components, occupants, and cargo. The springs may be coil, leaf, torsion bar, or air. Most automotive vehicles have coil springs at the front and either coil or leaf springs at the rear. See Automotive suspension
The steering system enables the driver to turn the front wheels left or right to control the direction of vehicle travel. The rotary motion of the steering wheel is changed to linear motion in the steering gear, which is located at the lower end of the steering shaft. The linear motion is transferred through the steering linkage to the steering knuckles, to which the front wheels are mounted. Steering systems are classed as either manual steering or power steering, with power assist provided hydraulically or by an electric motor.
A brake is a device that uses a controlled force to reduce the speed of or stop a moving vehicle, or to hold the vehicle stationary. The automobile has a friction brake at each wheel. When the brake is applied, a stationary surface moves into contact with a moving surface. The resistance to relative motion or rubbing action between the two surfaces slows the moving surface, which slows and stops the vehicle.
The engine supplies the power to move the vehicle. The power is available from the engine crankshaft after a fuel, usually gasoline, is burned in the engine cylinders. Most automotive engines are located at the front of the vehicle and drive either the rear wheels or the front wheels through a drive train or power train made up of gears, shafts, and other mechanical and hydraulic components. Most automotive vehicles are powered by a spark-ignition four-stroke-cycle internal combustion engine. The inline four-cylinder engine and V-type six-cylinder engine are the most widely used, with V-8 engines also common. Other automotive engines have three, five, ten, and twelve cylinders. Some passenger cars and trucks have diesel engines. Some automotive spark-ignition and diesel engines are equipped with a supercharger or turbocharger. See Automotive engine, Diesel engine, Engine, Ignition system, Turbocharger
Most automotive engines have electronic fuel injection instead of a carburetor. A computer-controlled electronic engine control system automatically manages various emissions devices and numerous functions of engine operation, including the fuel injection and spark timing. This allows optimizing power and fuel economy while minimizing exhaust emissions. See Carburetor, Control systems, Fuel injection
The power available from the engine crankshaft to do work is transmitted to the drive wheels by the power train, or drive train. In the front-engine rear-drive vehicle, the power train consists of a clutch and manual transmission, or a torque converter and an automatic transmission; driveshafts and Hooke (Cardan) universal joints; and rear drive axle that includes the final drive, differential, and wheel axle shafts. In the typical front-engine front-drive vehicle, the power train consists of a clutch and manual transaxle, or a torque converter and an automatic transaxle. The final drive and differential are designed into the transaxle, and drive the wheels through half-shafts with constant-velocity (CV) universal joints. See Clutch, Gear
The transmission is the device in the power train that provides different forward gear ratios between the engine and drive wheels, as well as neutral and reverse. The two general classifications of transmission are manual transmission, which the driver shifts by hand, and automatic transmission, which shifts automatically. To shift a manual transmission, the clutch must first be disengaged. However, some vehicles have automatic clutch disengagement for manual transmissions, while other vehicles have a limited manual-shift capability for automatic transmissions. See Automotive transmission
In the power train, the final drive is the speed-reduction gear set that drives the differential. The final drive is made up of a large ring gear driven by a smaller pinion, or pinion gear. This provides a gear reduction of about 3:1; the exact value can be tailored to the engine, transmission, weight of the vehicle, and performance or fuel economy desired.
In drive axles, the differential is the gear assembly between axle shafts that permits one wheel to rotate at a speed different from that of the other (if necessary), while transmitting torque from the final-drive ring gear to the axle shafts. When the vehicle is cornering or making a turn, the differential allows the outside wheel to travel a greater distance than the inside wheel; otherwise, one wheel would skid, causing tire wear and partial loss of control. See Differential
A wheel is a disc or a series of spokes with a hub at the center and a rim around the outside for mounting of the tire. The wheels of a vehicle must have sufficient strength and resiliency to carry the weight of the vehicle, transfer driving and braking torque to the tires, and withstand side thrusts over a wide range of speed and road conditions. Wheel size is primarily determined by the load-bearing strength of the tire.
The use of solid-state electronic devices in the automobile began during the 1960s, when the electromechanical voltage regulator of the alternator, was replaced by a transistorized voltage regulator. This was followed in the 1970s by electronic ignition, fuel injection, and cruise control. Since then, electronic devices and systems on the automobile have proliferated. These include engine and power train control, air bags, antilock braking, traction control, suspension and ride control, remote keyless entry, memory seats, driver information and navigation systems, cellular telephone and mobile communications systems, and onboard diagnostics. See Feedback circuit
The self-diagnostic capability of the vehicle computer, power-train or engine control module, or system controller may be aided by a memory that stores information about malfunctions that have occurred and perhaps temporarily disappeared. When recalled from the memory, this information can help the service technician diagnose and repair the vehicle more quickly, accurately, and reliably.