How Does Mazdas Active Torque Split All Wheel Drive Work?

by Joshua Bailey
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The purpose of any all-wheel-drive system is to increase traction, thereby enhancing the driving characteristics of the vehicle it gives power to in varying road conditions. Mazda's patented Active Torque Split All Wheel Drive system is no different. Found in such vehicles as the CX-7, CX-9 and MazdaSpeed 6, this system was designed to balance the performance and safety of all-wheel drive with the economic and practicality of front drive. Using multiple sensors and driver input, this AWD system can effectively "decide" which wheel to transfer the engines torque to and how much to supply.

Torque Transfer

Different driving conditions call for different characteristics from a vehicles drivetrain. Normal driving conditions with mild turning and acceleration only necessitate front drive. This increases fuel economy and prevents wear on certain drivetrain components. More aggressive driving requires more torque to be transferred to the rear wheels. This increases oversteer during cornering and prevents slippage during acceleration. In snowy conditions, torque is transferred to all wheels, but limiting transfer to the rear wheels aids in traction in this case as the engine is mounted over the front wheels.

The System

Through an array of sensors, the Mazda system determines which of three computer-controlled modes---normal, sport and snow---to provide the car with optimum traction in all conditions. These sensors measure parameters such as steering angle, body roll, lateral acceleration, engine status and throttle positions. A computer-controlled active torque coupler acts as the center differential, transferring as much as 50 percent of the engine's torque to the rear wheels depending on sensor reading.

For example, under heavy acceleration with large lateral forces, the computer would assume the driver is making an aggressive turn in pleasant driving conditions. Weight is shifted to the rear of the vehicles, so the center differential would then transfer maximum torque to the rear wheels, accelerating the rear end of the vehicle out of the turn. During normal driving, sensors would be reading mild acceleration and small steering angles. Under these conditions, the computer would transfer 100 percent of torque to the front wheels. Power to the rear drivetrain would be redundant, being that there is no tire slippage and most of the vehicle's weight is over the front wheels. In snowy conditions, the computer would sense apprehensive acceleration and perhaps wheel slippage. Torque would be welcomed to the rear wheels, but only enough to maintain control. Too much torque to the rear end, and the wheels would slip under its relatively light weight.

This system is capable of acting as a front drive or all-wheel drive vehicle---or anywhere in between. When combined with a limited slip rear differential, Mazda's AWD system is capable of a sporty drive, yet can easily save fuel by only powering the front axle. When poor driving conditions arise, the system can keep the vehicle moving and keep its passengers safe.

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