Torque Vectoring For Improved Driving

By Author: Rob Parker
Total Articles: 311
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No one doubts that all-wheel drive gives you the best possible vehicle control when you're driving in elemental weather. Whether you're dealing with flood, snow, or sand, dropping engine torque as low as it can go and having four tires working together instead of two improves traction no matter what you drive, but new technology soon to be appearing as a feature of the performance car of your choice takes all-wheel drive one step further. It's called "torque vectoring," and it's a system that enables the instantaneous and seamless distribution of torque to one specific wheel at a time.

Most recent-model all-wheel drive vehicles (cars and SUVs) already come with some kind of computer-managed system in order to boost fuel efficiency. The onboard computer will sense a wheel that might be straying from the intended path, or rotating faster than it should, and it will engage the opposite drive axle and apply torque as a corrective measure. If that isn't enough, engine torque will be reduced, or brakes applied until the problem is solved.

More recently, however, this technology has been vastly improved. Car manufacturers ...
... have re-designed both front and rear differentials to make it possible for the engine's torque to be vectored, or passed to each corner of the car. Put simply, traditional torque distribution systems in all-wheel drive cars can transfer engine torque only from the front axle to the rear axle and back, but with torque vectoring, it can be distributed from right to left, as well. An article in Popular Mechanics compared the technology to having "computer-controlled, super-speed limited slip differential in each axle." What this means is that vehicles will not only handle extremely well in bad driving conditions, but will offer impressive handling in normal conditions as well.

So, where can this technology be found? Look to Acura, Mitsubishi, and BMW for the most refined versions. Acura has offered a version of torque vectoring in it's Super Handling All-Wheel Drive system for several years. The system monitors vehicle speed, gear position, steering angle, wheel speed, yaw rate and lateral G forces as well as a number of other types of data, and automatically adds torque to the outside rear wheel during cornering, for smoother, more stable turns. The system includes a set of electromagnetic clutches in the rear differential to handle lateral torque transfers, and while the default distribution is 90% to the front / 10% to the rear, it will automatically change to a 50/50 split on hard turns and acceleration.

Mitsubishi, which was long been a pioneer when it comes to torque vectoring specifically and traction control in general offers a system similar to Acura's. Known as "Active Yaw Control" it's been part of the rear axle of their Evolution performance sedan since the late 1990s, while Audi and BMW are taking the technology further: Acura's system only works on the real axle of a vehicle that normally uses front-wheel drive, but these two makers are using technology from British automotive supplier Ricardo and German supplier ZF that can distribute torque to all four tires at once.

Ricardo's system, found in the Audi A4 and A5, uses wet clutches and planetary gearsets, as well as electromechanical controls to offer a response time of 0.1 seconds from accelerator push to delivery of up to 90% of available torque, and passes it both front to back and side to side with lightning-fast accuracy. The German system used by BMW has branded their system "VectorDrive" and it can pass torque to each of the rear wheels individually, for improved cornering and excellent stability in less-than-excellent driving conditions.

While torque vectoring is not yet an industry standard, it is growing in use, and, when married to existing systems like anti-lock braking and rollover prevention, will eventually give every driver the ability to drive safely through wind, snow, rain, and sleetnot to mention sunshine and dry roads.