Symmetrical All Wheel Drive

Last updated April 30, 2024

Subaru XV Symmetrical AWD logo

The Symmetrical All-Wheel Drive (also known as Symmetrical AWD or SAWD) is a full-time four-wheel drive system developed by the Japanese automobile manufacturer Subaru. The system consists of a longitudinally mounted boxer engine coupled to a symmetrical drivetrain with equal length half-axles. The combination of the symmetrical layout with a flat engine and a transmission balanced over the front axle provides optimum weight distribution with low center of gravity, improving the steering characteristics of the vehicle.^[1] Ever since 1986, most of the Subaru models sold in the international market are equipped with the SAWD system by default, with the rear wheel drive BRZ and kei cars as the exceptions.^[2]

History

The earliest version of the Subaru SAWD debuted in September 1972 as an optional part-time mechanical four-wheel drive system for the first-generation Subaru Leone Wagon.^[3] In 1986, the automatic non-turbocharged version of the Subaru XT was equipped with the first full-time SAWD system, with an electronically controlled version introduced in 1987. Variable Torque Distribution (VTD) AWD was first presented in 1991, with the addition of Vehicle Dynamics Control (VDC) in 1998, allowing for better control of the all-wheel drive system.^[4] Modern implementations of SAWD are used in conjunction with VDC, ABS, and traction control for enhanced handling performance.

Variants

Active torque split AWD

First introduced in 1987 for the Subaru XT, the active torque split AWD variant uses an electronically controlled multi-plate transfer clutch for a default torque distribution of 60% front, 40% rear ratio. Torque distribution is adjusted up to a 50:50 split in real time with input from the throttle, transmission, engine control unit and wheel speed sensors.^[1] Active torque split AWD is paired with 4-speed automatic transmissions and Subaru's chain-driven Lineartronic continuously variable transmission (CVT).^[5]

Variable torque distribution AWD

The 1991 Subaru SVX was equipped with the first version of variable torque distribution (VTD) AWD with a normal torque split of 36% front, and 64% rear, later implementations of VTD use a torque split of 45% front, and 55% rear. The rear biased torque distribution reduces understeer, which occurs in AWD vehicles. VTD AWD uses a multi-plate clutch in conjunction with planetary gears in the center differential and a viscous coupling rear differential to distribute torque up to a 50:50 ratio. With the addition of VDC, all torque can be sent to a single wheel.^[1]^[4]^[5]

Viscous centre differential AWD

Subaru vehicles equipped with manual transmissions use a viscous limited slip centre differential (VCD) AWD system, which by default distributes torque evenly between the front and rear axles.^[1]^[5]

Multi-mode Driver Control Centre Differential AWD

The Subaru WRX STI exclusively uses the Multi-mode Driver Control Centre Differential (DCCD) AWD system, it uses a torque sensing mechanical limited slip differential (LSD) with an electronic LSD to distribute torque with a 41% front and 59% rear split. Multi-mode DCCD AWD is able to operate in automatic mode or manual mode, where the driver is able to adjust the center differential lockup on the fly.^[6]^[7]

Related Research Articles

The Subaru Forester is a compact crossover SUV that has been manufactured by Subaru since 1997. The first generation was built on the platform of the Impreza in the style of a taller station wagon, a style that continued to the second generation, while the third-generation model onwards moved towards a crossover SUV design. A performance model was available for the second-generation Forester in Japan as the Forester STi.

The Subaru Outback is an automotive nameplate used by the Japanese automaker Subaru for two different SUV-themed vehicles: a Legacy-derived crossover station wagon, the Outback, and an Impreza-derived off-road themed hatchback, the Outback Sport (1994–2011).

A four-wheel drive, also called 4×4 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 providing an additional output drive shaft and, in many instances, additional gear ranges.

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

<span class="mw-page-title-main">Transfer case</span> Drivetrain used in four-wheel drive vehicles

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 drivetrain, it employs drive shafts to mechanically deliver motive power. The transfer case 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.

The Subaru Alcyone SVX, marketed outside Japan as the Subaru SVX, is a two-door, front-engine, all- or front-wheel drive coupé manufactured and marketed by Subaru from 1991 to 1996 over a single generation.

4Matic is the marketing name of an all-wheel drive system developed by Mercedes-Benz. It is designed to increase traction in slippery conditions. With the introduction of the 2017 E 63 S sedan, Mercedes-AMG announced a performance-oriented variant of the system called AMG Performance 4MATIC+.

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.

Torque steer is the unintended influence of engine torque on the steering, especially in front-wheel-drive vehicles. For example, during heavy acceleration, the steering may pull to one side, which may be disturbing to the driver. The effect is manifested either as a tugging sensation in the steering wheel, or a veering of the vehicle from the intended path. Torque steer is directly related to differences in the forces in the contact patches of the left and right drive wheels. The effect becomes more evident when high torques are applied to the drive wheels because of a high overall reduction ratio between the engine and wheels, high engine torque, or some combination of the two. Torque steer is distinct from steering kickback.

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.

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

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.

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 follows,

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.

The first generation Subaru Legacy is a mid-size family car / wagon developed by Fuji Heavy Industries. The Legacy was an all new model, and was considered a notable departure from Subaru products in the past.

The second-generation Subaru Legacy was marketed in Japan from October 1993, and July 1994 marked the second generation in North America with a full body and chassis revision. The exterior was designed by Olivier Boulay in 1991, during his tenure at Subaru. The tail light appearance on both the sedan and wagon was influenced by the taillights on the SVX.

Subaru launched the third generation Japanese and world-market Legacy in June 1998, while the North American model was introduced in May 1999 for the 2000 model year. In all markets except for the United States, production lasted through 2002, with a limited production Blitzen model sold mid-cycle under the 2003 model year in Japan. Production in the United States lasted through 2004.

Individual-wheel drive (IWD) is a wheeled vehicle with a drivetrain that allows all wheels to receive torque from several motors independent of each other. The term was coined to identify those electric vehicles whereby each wheel is driven by its own individual electric motor, as opposed to conventional differentials.

Torque vectoring is a technology employed in automobile differentials that has the ability to vary the torque to each half-shaft with an electronic system; or in rail vehicles which achieve the same using individually motored wheels. This method of power transfer has recently become popular in all-wheel drive vehicles. Some newer front-wheel drive vehicles also have a basic torque vectoring differential. As technology in the automotive industry improves, more vehicles are equipped with torque vectoring differentials. This allows for the wheels to grip the road for better launch and handling.

The second generation of the Subaru Impreza compact car was introduced in 2000 and manufactured up to 2007 by Subaru in Ota, Gunma, Japan, in both sedan and five-door wagon bodystyles, as well as two intermediate facelifts throughout its lifespan.

References

1 2 3 4 "Subaru Technology Overview". Subaru Global. Fuji Heavy Industries. October 6, 2008. Archived from the original on December 25, 2014. Retrieved November 19, 2014.
↑ "Subaru History Book" (PDF). Fuji Heavy Industries. Archived from the original (PDF) on December 25, 2014. Retrieved November 19, 2014.
↑ "Subaru History". Subaru Global. Fuji Heavy Industries. Archived from the original on December 11, 2014. Retrieved November 19, 2014.
1 2 "Symmetrical AWD" (in German). Subaru Deutschland GmbH. Archived from the original on March 18, 2012. Retrieved November 19, 2014.
1 2 3 "Symmetrical AWD". Subaru Global. Fuji Heavy Industries. October 6, 2008. Archived from the original on December 10, 2014. Retrieved November 19, 2014.
↑ "Multi-Mode DCCD". Subaru Global. Fuji Heavy Industries. Archived from the original on December 10, 2014. Retrieved November 19, 2014.
↑ "Subaru Commemorates the 40th Anniversary of Its AWD Vehicles" (PDF). Subaru Global. Fuji Heavy Industries. February 10, 2012. Retrieved November 19, 2014.

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.

[sub_tech-1] 1 2 3 4 "Subaru Technology Overview". Subaru Global. Fuji Heavy Industries. October 6, 2008. Archived from the original on December 25, 2014. Retrieved November 19, 2014.

[sub_hist_book-2] "Subaru History Book" (PDF). Fuji Heavy Industries. Archived from the original (PDF) on December 25, 2014. Retrieved November 19, 2014.

[sub_hist-3] "Subaru History". Subaru Global. Fuji Heavy Industries. Archived from the original on December 11, 2014. Retrieved November 19, 2014.

[sawd_ger-4] 1 2 "Symmetrical AWD" (in German). Subaru Deutschland GmbH. Archived from the original on March 18, 2012. Retrieved November 19, 2014.

[sub_sawd-5] 1 2 3 "Symmetrical AWD". Subaru Global. Fuji Heavy Industries. October 6, 2008. Archived from the original on December 10, 2014. Retrieved November 19, 2014.

[6] "Multi-Mode DCCD". Subaru Global. Fuji Heavy Industries. Archived from the original on December 10, 2014. Retrieved November 19, 2014.

[7] "Subaru Commemorates the 40th Anniversary of Its AWD Vehicles" (PDF). Subaru Global. Fuji Heavy Industries. February 10, 2012. Retrieved November 19, 2014.

[1]

[2]

[3]

[4]

[5]

[6]

[7]