Torque vectoring

Torque vectoring is a new technology employed in automobile differentials. A differential transfers engine torque to the wheels. Torque vectoring technology provides the differential with the ability to vary the power to each wheel. This method of power transfer has recently become popular in all-wheel drive vehicles.^[1] 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

History

The torque vectoring idea builds on the basic principles of a standard differential. A torque vectoring differential performs basic differential tasks while also transmitting torque independently between wheels. This torque transferring ability improves handling and traction in almost any situation. Torque vectoring differentials were originally used in racing. Mitsubishi rally cars were some of the earliest to use the technology.^[2] The technology has slowly developed and is now being implemented in a small variety of production vehicles. The most common use of torque vectoring in automobiles today is in all-wheel drive vehicles.

Functional description

The idea and implementation of torque vectoring are both complex. The main goal of torque vectoring is to independently vary torque to each wheel. Differentials generally consist of only mechanical components. A torque vectoring differential requires an electronic monitoring system in addition to standard mechanical components. This electronic system tells the differential when and how to vary the torque. Due to the number of wheels that receive power, a front or rear wheel drive differential is less complex than an all-wheel drive differential.

Front/Rear Wheel Drive Vectoring

Torque vectoring differentials on front or rear wheel drive vehicles are less complex, yet share many of the same benefits as all-wheel drive differentials. The differential only varies torque between two wheels. The electronic monitoring system only monitors two wheels, making it less complex. A front-wheel drive differential must take into account several factors. It must monitor rotational and steering angle of the wheels. As these factors vary during driving, different forces are exerted on the wheels. The differential monitors these forces, and adjusts torque accordingly. Many front-wheel drive differentials can increase or decrease torque transmitted to a certain wheel.^[3] This ability improves a vehicle’s capability to maintain traction in poor weather conditions. When one wheel begins to slip, the differential can reduce the torque to that wheel, effectively braking the wheel. The differential also increases torque to the opposite wheel, helping balance the power output and keep the vehicle stable. A rear-wheel drive torque vectoring differential works the same way as a front-wheel drive differential.

All-Wheel Drive Vectoring

Most torque vectoring differentials are on all-wheel drive vehicles. A basic torque vectoring differential varies torque between the front and rear wheels. This means that under normal driving conditions, the front wheels receive a set percentage of the engine torque, and the rear wheels receive the rest. If needed, the differential can transfer more torque between the front and rear wheels to improve vehicle performance.

For example, a vehicle might have a standard torque distribution of 90% to the front wheels and 10% to the rear. Under harsh conditions, the differential changes the distribution to 50/50. This new distribution spreads the torque more evenly between all four wheels. Having more even torque distribution increases the vehicle’s traction.^[4]

There are more advanced torque vectoring differentials as well. These differentials build on basic torque transfer between front and rear wheels. They add the capability to transfer torque between individual wheels. This provides an even more effective method of improving handling characteristics. The differential monitors each wheel independently, and distributes available torque to match current conditions. Acura’s Super Handling All-Wheel Drive (SH-AWD) can transfer power between front and rear and vary the amount of torque transmitted to each rear wheel. The front wheels, however, do not receive different amounts of torque.^[5] Audi produced a torque vectoring system capable of varying the torque received by any wheel of the vehicle: quattro with torque vectoring. This allows each wheel to receive independent torque amounts to increase the overall performance of the vehicle.

Torque Vectoring in Electric Vehicles

In an electric vehicle all-wheel drive can be implemented with two independent electric motors, one for each axle. In this case the torque vectoring between the front and rear axles is just a matter of electronically controlling the power distribution between the two motors, which can be done on a millisecond scale.^[6]

Torque vectoring is even more effective if it is actuated through two electric motor drives located on the same axle, as this configuration can be used for shaping the vehicle understeer characteristic and improving the transient response of the vehicle,.^[7][8] In case of electric vehicles with four electric motor drives, the same total wheel torque and yaw moment can be generated through an infinite number of wheel torque distributions. Energy efficiency can be used as a criterion for allocating the torques among the individual wheels,.^[9][10]

In 2012, Mercedes introduced the SLS AMG Electric Drive. Mercedes engineers were able to make the system work with a higher traction torque level on the outer wheels than on the inner wheels during cornering, in order to tighten the turning radius.^[11][12]

List of systems capable of active left-right torque vectoring

• Acura's SH-AWD TL, TLX, MDX, RL
• Audi's quattro with Sport Differential
• BMW's Active M Differential
• BMW's xDrive with Dynamic Performance Control
• Honda's SH-AWD
• Kia's Dynamax™ AWD
• Land Rover's All New Range Rover Sport HSE and Autobiography Dynamics models ^[13]
• Mercedes-Benz's SLS AMG Electric Drive combined with active front-back torque vectoring
• Mitsubishi's Active Yaw Control
• Nissan GT-R's ATTESA E-TS Pro (rear wheels only)
• Nissan Juke
• Saab's XWD
• Ford on several models
• Porsche on several models, when torque vectoring added as an option
• Holden Special Vehicles Gen-F GTS^[14]
• Volvo's drive e (front wheel drive systems)
• Hyundai Veloster
• Subaru's Active Torque Vectoring, ATV - 2015 and later Outback, Legacy, WRX, and STi. Applies braking in inner front wheel in a turn in addition to front-rear transfer.^[15]

See also

• Differential

References