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

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

capable of providing power to all its wheels, whether full-time or on-demand. The most common forms of all-wheel drive are: ;1x1 : All unicycles
Reflecting one axle with one wheel capable of being powered. ; 2x2 : Some motorcycles and bikes
Reflecting two axles with one wheel on each capable of being powered. ;

4×4 Four-wheel drive, also called 4×4 ("four by four") or 4WD, refers to 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 ...

(also, four-wheel drive and 4WD): Reflecting two axles with both wheels on each capable of being powered. ; 6×6 (also, six-wheel drive and 6WD): Reflecting three axles with both wheels on each capable of being powered. ; 8×8 (also, eight-wheel drive and 8WD): Reflecting 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 (also, part-time): One axle is permanently connected to the drive, the other is being connected as needed ;Full-time (also, 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.

Usage of the terminology

Particularly in North America for several decades, the designation ''AWD'' has been used and marketed - distinctly from "4X4" 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 ABS. However, the designations ''AWD'' and ''all-wheel drive'' long predated the trend, with

Associated Equipment Company Associated Equipment Company (AEC) was a British vehicle manufacturer that built buses, motorcoaches and trucks from 1912 until 1979. The name Associated Equipment Company was hardly ever used; instead it traded under the AEC and ACLO brands. ...

(AEC) producing AWD trucks in 1929 in conjunction with the British subsidiary of the pioneering American firm,

Four Wheel Drive Auto Company Four-wheel drive, also called 4×4 ("four by four") or 4WD, refers to 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 ...

. Additionally, General Motors 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.

Characteristics

When tire grip is good during road driving, a differential is used between the axles to avoid

driveline windup Driveline windup is also known as "axle binding" or "driveline binding". Mechanical components in the drivetrain of vehicles may bind and wear, which may occur when tires of varying sizes are used on one vehicle. It is a particular issue in 4WD ...

. 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 A dog clutch (also known as a positive clutch or dog gears) is a type of clutch that couples two rotating shafts or other rotating components by engagement of interlocking teeth or dogs rather than by friction. The two parts of the clutch are de ...

in the transfer case, rather than a differential. For this reason, most early off-road vehicles used that system; e.g., Jeep, Land Rover. 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 The Jensen FF is a four-wheel drive grand tourer produced by British car manufacturer Jensen Motors between 1966 and 1971. It was the first non all-terrain production car equipped with four-wheel drive and an anti-lock braking system. The powe ...

followed by the

AMC Eagle AMC may refer to: Film and television * AMC Theatres, an American movie theater chain * AMC Networks, an American entertainment company ** AMC (TV channel) ** AMC+, streaming service ** AMC Networks International, an entertainment company *** ...

Subaru Leone The Subaru Leone is a compact car produced by the Japanese 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 Impreza. Al ...

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 with the use of

viscous coupling A viscous coupling is a mechanical device which transfers torque and rotation by the medium of a viscous fluid. Design Rotary viscous couplings with interleaved, perforated plates and filled with viscous fluids are used in automotive system ...

s and differentials to provide a safe and drivable car. The first off-road / on-road hybrids such as the

Range Rover Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to ...

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 mis-used, 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 Off-road vehicles Car layouts Drivetrain

Usage of the terminology

Characteristics

See also

References