An all-wheel drive vehicle (AWD vehicle) is one with a

powertrain In a motor vehicle, the powertrain comprises the main components that generate engine power, power and deliver that power to the road surface, water, or air. This includes the internal combustion engine, engine, transmission (mechanics), trans ...

capable of providing power to all its wheels, whether full-time or on-demand.

Types

The most common forms of all-wheel drive are: ;1x1 : All

unicycle A unicycle is a vehicle that touches the ground with only one wheel. The most common variation has a frame with a saddle, and has a pedal-driven direct-drive. A two speed hub is commercially available for faster unicycling. Unicycling is prac ...

s
Reflects one axle with one wheel capable of being powered. ; 2x2 : Some motorcycles and bikes
Reflects two axles with one wheel on each capable of being powered. ;

4×4 A four-wheel drive, also called 4×4 ("four by four") or 4WD, is a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer case pro ...

(also, four-wheel drive or 4WD): Reflects two axles with both wheels on each capable of being powered. ; 6×6 (also, six-wheel drive or 6WD): Reflects three axles with both wheels on each capable of being powered. ;

8×8 Eight-wheel drive, often notated as 8WD or 8×8, is a drivetrain configuration that allows all eight wheels of an eight-wheeled vehicle to be drive wheels simultaneously. Unlike four-wheel drive drivetrains, the configuration is largely confined ...

(also, eight-wheel drive or 8WD): Reflects four axles with both wheels on each capable of being powered. Vehicles may be either part-time all-wheel drive or full-time: ;On-demand or Part-time: One axle is permanently connected to the drive, the other is connected as needed ;Full-time or Permanent: All axles are permanently connected, with or without a differential. ;Independent: The wheels are driven, but not dependent on a central mechanical power coupling.

Terminology

Particularly in North America for several decades, the designation ''AWD'' has been used and marketed – distinctly from ''4×4'' and ''4WD'' – to apply to vehicles with drive train systems that have permanent drive, a differential between the front and rear drive shafts, and active management of torque transfer, especially following the advent of the

anti-lock braking system An anti-lock braking system (ABS) is a Automotive safety, safety anti-Skid (automobile), skid Brake, braking system used on aircraft and on land motor vehicle, vehicles, such as cars, motorcycles, trucks, and buses. ABS operates by preventing t ...

(ABS). However, the designations ''AWD'' and ''all-wheel drive'' long predated the trend, with Associated Equipment Company (AEC) producing AWD trucks in 1929 in conjunction with the British subsidiary of the pioneering American firm Four Wheel Drive Auto Company. Additionally,

General Motors General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. The company is most known for owning and manufacturing f ...

began manufacturing a line as "all-wheel drive" as early as the late 1930s. This distinction in terminology is not generally used outside North America. In the context of hybrid and

electric vehicles An electric vehicle (EV) is a motor vehicle whose propulsion is powered fully or mostly by electricity. EVs encompass a wide range of transportation modes, including road vehicle, road and rail vehicles, electric boats and Submersible, submer ...

, the North American designation of 'all-wheel-drive' may differ. In some hybrid vehicles, the combustion engine is only mechanically connected to the front wheels, while the rear wheels are powered independently by an electric motor; this may be marketed as ''eAWD''. Furthermore, many electric vehicles have individual, unconnected motors powering each axle, or even each individual wheel, also without any center differential.

Characteristics

When tire grip is good during road driving, a differential is used between the axles to avoid driveline windup. This is not required off-road, as the limited grip allows the tires to slip. All-wheel drive vehicles designed for extensive off-road use may not have such a differential, and so they suffer from wind-up when used on-road. Selectable 4WD also avoids this problem and requires only a simple dog clutch in the

transfer case A transfer case is an intermediate gearbox that transfers power from the transmission of a motor vehicle to the driven axles of four-wheel-drive, all-wheel-drive, and other multi-axled on- and off-road machines. A part of the vehicle's drivetr ...

, rather than a differential. For this reason, most early off-road vehicles used that system; e.g.,

Jeep Jeep is an American automobile brand, now owned by multi-national corporation Stellantis. Jeep has been part of Chrysler since 1987, when Chrysler acquired the Jeep brand, along with other assets, from its previous owner, American Motors Co ...

Land Rover Land Rover is a brand of predominantly four-wheel drive, off-road capable vehicles, owned by British multinational car manufacturer Jaguar Land Rover (JLR), since 2008 a subsidiary of India's Tata Motors. JLR builds Land Rovers in Brazil ...

. As vehicles became more sophisticated and tires gave better winter performance in the 1960s, there was an interest in giving the benefits of all-wheel drive to conventional cars: not for off-road use but for winter use in snow or on wet roads. Exotic vehicles such as the high-powered Jensen FF followed by the

AMC Eagle The AMC Eagle is a compact four-wheel drive passenger vehicle manufactured and marketed in a single generation by American Motors Corporation (AMC) for model years 1980 through 1987 and continued by Chrysler, Chrysler Corporation following it ...

Subaru Leone The Subaru Leone is a compact car produced by the Japanese automaker, car manufacturer Subaru from 1971 to 1994. The word ''leone'' is Italian for lion. It was released as a replacement for the Subaru 1000 and was the predecessor of the Subaru Im ...

and Audi Quattro series were the first to offer all-wheel drive in a high-speed road-based car. These, particularly the Quattro, would extensively develop this

drivetrain A drivetrain (also frequently spelled as drive train or sometimes drive-train) or transmission system, is the group of components that deliver mechanical power from the prime mover to the driven components. In automotive engineering, the driv ...

with the use of viscous couplings and differentials to provide a safe and drivable car. The first off-road / on-road hybrids such as the Range Rover also chose the permanent all-wheel-drive system rather than manual selection. Selectable 4WD has both axles rigidly coupled together, which has some advantages in very poor off-road conditions. To gain the same advantage in a permanent AWD system with a differential, the differential can be locked manually with a differential lock. As this control is frequently misunderstood and misused, which can then cause damage due to wind-up, they have tended to be replaced by automatic locking through the viscous couplers.

References

{{DEFAULTSORT:All-Wheel Drive Vehicle Off-road vehicles Car layouts Drivetrain

Types

Terminology

Characteristics

See also

References