All-wheel drive

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The Jeep Wrangler is a 4x4 four-wheel drive vehicle equipped with a low-range gearbox, which provides the driver with a selection between low range or high range gearing Jeep Wrangler TJ.jpg
The Jeep Wrangler is a 4×4 four-wheel drive vehicle equipped with a low-range gearbox, which provides the driver with a selection between low range or high range gearing
Hayes WHDX 70-170 6x6 tractor Hayes Arbegui 2010.JPG
Hayes WHDX 70-170 6×6 tractor
The 8x8 tractor unit of the HETS (heavy equipment transport system) M1070 HET in Fort Knox.jpg
The 8×8 tractor unit of the HETS (heavy equipment transport system)

An all-wheel drive vehicle (AWD vehicle) is one with a powertrain capable of providing power to all its wheels, whether full-time or on-demand.

Contents

The most common forms of all-wheel drive are:

4×4 (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 [1] and all-wheel drive [2] 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 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. 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. [3] Selectable 4WD also avoids this problem and requires only a simple dog clutch 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 followed by the AMC Eagle, Subaru Leone 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 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 mis-used, which can then cause damage due to wind-up, they have tended to be replaced by automatic locking through the viscous couplers.

See also

Related Research Articles

A traction control system (TCS), also known as ASR, is typically a secondary function of the electronic stability control (ESC) on production motor vehicles, designed to prevent loss of traction of the driven road wheels. TCS is activated when throttle input and engine power and torque transfer are mismatched to the road surface conditions.

Four-wheel drive Type of drivetrain with four driven wheels

Four-wheel drive, also called 4x4 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 providing an additional output drive shaft and, in many instances, additional gear ranges.

Limited-slip differential

A limited-slip differential (LSD) is a type of differential that allows its two output shafts to rotate at different speeds but limits the maximum difference between the two shafts.

Quattro (four-wheel-drive system)

quattro is the sub-brand used by the car brand Audi to indicate that all-wheel drive (AWD) technologies or systems are used on specific models of its Audi automobiles.

Transfer case

A transfer case is a part of the drivetrain of four-wheel-drive, all-wheel-drive, and other multiple powered axle vehicles. The transfer case transfers power from the transmission to the front and rear axles by means of drive shafts. It also synchronizes the difference between the rotation of the front and rear wheels, and may contain one or more sets of low range gears for off-road use.

Locking differential Forcing two transaxial wheels to spin together

A locking differential is designed to overcome the chief limitation of a standard open differential by essentially "locking" both wheels on an axle together as if on a common shaft. This forces both wheels to turn in unison, regardless of the traction available to either wheel individually.

Drive wheel

A drive wheel is a wheel of a motor vehicle that transmits force, transforming torque into tractive force from the tires to the road, causing the vehicle to move. The powertrain delivers enough torque to the wheel to overcome stationary forces, resulting in the vehicle moving forwards or backwards.

Viscous coupling unit

A viscous coupling is a mechanical device which transfers torque and rotation by the medium of a viscous fluid.

BMW xDrive

BMW xDrive is the marketing name for the all-wheel drive system found on various BMW models since 2003. The system uses an electronically-actuated clutch-pack differential to vary the torque between the front and rear axles. Models with the DPC torque vectoring system also have a planetary gearset to overdrive an axle or rear wheel as required.

ATTESA is a four-wheel drive system used in some automobiles produced by the Japanese automaker Nissan, including some models under its luxury marque Infiniti.

Jeep uses a variety of four-wheel drive systems on their vehicles. These range from basic part-time systems that require the driver to move a control lever to send power to four wheels, to permanent four-wheel systems that monitor and sense traction needs at all four wheels automatically under all conditions.

Super Handling-All Wheel Drive (SH-AWD) is a full-time, fully automatic, all-wheel drive traction and handling system combining front-rear torque distribution control with independently regulated torque distribution to the left and right rear wheels to freely distribute the optimum amount of torque to all four wheels in accordance with driving conditions." The system was announced in April 2004, and first introduced in the North American market in the second generation 2005 model year Acura RL, and in Japan as the fourth generation Honda Legend.

The layout of a motorised vehicle such as a car is often defined by the location of the engine and drive wheels.

All-Trac

All-Trac was a proprietary full-time four-wheel drive system used on a variety of Toyota badged models from 1988 to 2000. It was considered a revolutionary advance for four wheel drive automobiles into the mainstream consumer market and its electronic/vacuum controlled locking center differential was rare in a passenger car. The system originated in Japan under the GT-Four name in 1986, but was not released in the U.S. until 1988 under the All-Trac name.

Super Select

Super Select is the brand name of a four-wheel drive system produced by Mitsubishi Motors, used worldwide except for North America, where it was initially known as Active-Trac. It was first introduced in 1991 with the then-new second generation of the Mitsubishi Pajero.

ControlTrac four-wheel drive is the brand name of a selectable automatic full-time four-wheel drive system offered by Ford Motor Company. The four-wheel drive system was designed and developed at BorgWarner under its TorqTransfer Systems division in the mid 1980s. BorgWarner calls the system Torque-On-Demand (TOD). ControlTrac was the first automatic system to use software control and no planetary or bevel geared center differential. Instead of a planetary or bevel geared center differential, the system uses a variable intelligent locking center multi-disc differential.

Front-engine, four-wheel-drive layout

In automotive design, an F4, or front-engine, four-wheel drive (4WD) layout places the internal combustion engine at the front of the vehicle and drives all four roadwheels. This layout is typically chosen for better control on many surfaces, and is an important part of rally racing, as well as off-road driving. In terms of racing purposes, whether it be on-road or off-road, can be described as followed, "A team that pursues the Weak LS4WD architecture will minimize the development cost of the front-wheel drive system at the expense of having a larger rear powertrain. The Weak architecture produces a vehicle with a large powersplit between the front and rear powertrains, while the Strong architecture recommends a vehicle with more similar power and torque requirements for the front and rear."

S-AWC is the brand name of an advanced full-time four-wheel drive system developed by Mitsubishi Motors. The technology, specifically developed for the new 2007 Lancer Evolution, the 2010 Outlander, the 2014 Outlander, the Outlander PHEV and the Eclipse Cross have an advanced version of Mitsubishi Motors' AWC system. Mitsubishi Motors first exhibited S-AWC integration control technology in the Concept-X model at the 39th Tokyo Motor Show in 2005. According to Mitsubishi Motors, "the ultimate embodiment of the company's AWC philosophy is the S-AWC system, a 4WD-based integrated vehicle dynamics control system".

All Wheel Control (AWC) is the brand name of a four-wheel drive (4WD) system developed by Mitsubishi Motors. The system was first incorporated in the 2001 Lancer Evolution VII. Subsequent developments have led to S-AWC, developed specifically for the new 2007 Lancer Evolution. The system is referred by the company as its unique 4-wheel drive technology umbrella, cultivated through its motor sports activities and long history in rally racing spanning almost half a century.

FWD Model B 3-ton truck

The FWD Model B was an American built four-wheel drive truck produced by the Four Wheel Drive Auto Company that saw widespread service with American and British forces during the First World War.

References

  1. Allisons.org Automotive History "1929: AEC started to build AWD trucks in conjunction with FWD (UK)"
  2. MEYER, DONALD E. THE FIRST CENTURY OF GMC TRUCK HISTORY "By December [1939], GMC had orders for more than 4,400 all-wheel-drive military trucks."
  3. Ware, Pat (1994). In National Service. Warehouse Publications. p. 118. ISBN   0-9525563-0-8.