Cherry Hill, N.J. - February 24, 2014 - Subaru produces passenger cars, SUVs and crossovers equipped as standard with Symmetrical All-Wheel Drive. (The Subaru BRZ sports car is rear-wheel drive.) Symmetrical All-Wheel Drive is a comprehensive system that includes a lightweight horizontally opposed Subaru BOXER engine and the full-time automatic torque distribution system. Rather than take a "one type fits all" approach, Subaru tailors its four different versions of Symmetrical All-Wheel Drive to a particular powertrain or model.

VTD: Variable Torque Distribution
DCCD: Driver Controlled Center Differential
BRZ sports car is rear-wheel drive.

All-Wheel Drive Built In, Not Added On

Subaru develops vehicles around Symmetrical All-Wheel Drive – it does not simply adapt AWD components to a front- or rear-wheel drive vehicle. All versions of Subaru Symmetrical All-Wheel Drive distribute torque to all four wheels all the time, reducing the load on each wheel and reducing and even helping to prevent tire slip, especially on slippery or loose surfaces.

In contrast, some AWD systems on the market function passively, transferring torque away from the main drive wheels only when they slip. When there is no slippage, vehicles equipped with such systems essentially operate in two-wheel drive. Although such automatic "part-time" or "on-demand" systems can help a vehicle traverse a snow-covered road, for example, they may not provide the all-road handling benefits of a true full-time All-Wheel Drive system.

Vehicle Dynamics Control Augments All-Wheel Drive Capability

The Vehicle Dynamics Control (VDC) stability and four-wheel traction control system (TCS) is standard on every 2014 and 2015 Subaru model (the BRZ has VDC and rear-wheel traction control). The VDC system uses an array of sensors to compare where the vehicle is heading to where the driver is steering it. If corrective action is needed to help keep the vehicle on course, VDC can apply momentary brake pressure at individual wheels and can also reduce torque at the wheels via the electronic throttle control system. It is important to note that traction control functions as a second line of defense against wheel slip, after torque distribution by Symmetrical All-Wheel Drive.

BOXER Engine: Compact and Light

Subaru introduced its horizontally opposed (BOXER) engine more than 40 years ago and today remains a staunch adherent to this engine configuration. The Subaru BOXER engine is ideal for an All-Wheel Drive application, because it is inherently compact. The layout concentrates the engine's mass in a small area and helps provide a lower center of gravity, which contributes to responsive handling and steering. Aluminum-alloy construction of the engine and transmission case results in a lightweight drivetrain.

Mounting the BOXER engine longitudinally allows the transmission to be located directly behind it and within the vehicle's wheelbase. Torque travels in a straight, near-horizontal line to the rear differential, minimizing frictional loss. This symmetrical, uniform layout also provides excellent left-right balance. By comparison, in a vehicle with a transverse-mounted engine, an All-Wheel Drive system requires additional transfer gearing to reroute the torque from transverse to longitudinal orientation. Such a system can cause more friction and can add extra weight on one side of the vehicle.

In addition, the horizontally opposed layout yields an inherently smooth-running engine, because the motion of the pistons from one cylinder bank (and the vibration the motion creates) cancels the vibrations of the opposing bank. Lower vibration contributes to durability, a Subaru hallmark.

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