Traction control
From Wikipedia, the free encyclopedia
Traction control systems, on current production vehicles, are typically (but not necessarily) electro-hydraulic systems designed to prevent loss of traction (and therefore the control of the vehicle) when excessive throttle or steering is applied by the driver. Although similar to Electronic Stability Control systems, Traction Control systems do not have the same goal.
The intervention can consist of any, or all, of the following:
- Retard or suppress the spark to one or more cylinders
- Reduce fuel supply to one or more cylinders
- Brake one or more wheels
- Close the throttle, if the vehicle is fitted with drive by wire throttle.
Typically, the Traction Control system shares the brake actuator and the wheel speed sensors with the anti-lock braking system.
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[edit] History of Traction Control
The predecessor of modern electronic traction control systems can be found in high-torque, high-power rear-wheel drive cars as a limited slip differential, known as Positraction. As this system worked mechanically to transfer power to the individual rear wheel slipping the most, it still allowed some wheel spin to occur.
General Motors was among the first to bring electronic traction control it to market. In 1971, the Buick division of GM introduced MaxTrac, which used an early computer system to detect rear wheel spin and modulate engine power to those wheels to provide the most traction. A Buick-exclusive at the time, it was an option on all fullsize models, including the Riviera, Estate Wagon, Electra 225, Centurion, and popular LeSabre family sedan.
[edit] Use of traction control
- In road cars: Traction Control has traditionally been safety feature in high-performance cars, which would otherwise need very sensitive throttle input to keep them from spinning when accelerating, especially in wet or snowy conditions. In recent years, Traction Control systems have become widely available non-performance cars, minivans, and light trucks.
- In race cars: Traction Control is used as a performance enhancement, allowing maximum traction under acceleration without wheel spin. When accelerating out of turn, it keeps the tyres at the optimum slip angle.
- In off road vehicles: Traction Control is used instead or in addition to the mechanical limited slip or locking differential. It is often implemented with an electronic limited slip differential, as well as other computerized controls of the engine and transmission. Spinning wheel is slowed down with short applications of brakes, diverting more torque to the non-spinning wheel. This form of traction control has an advantage over a locking differential as steering and control of a vehicle is easier, so the system can be continuosly enabled. It also creates less stress on the drivetrain, which is particularly important to the vehicles with an independent suspension that is generally weaker compared to solid axels. On the other hand, only half of the available torque will be applied to a wheel with traction, compared to a locked differential, and handling is less predictable.
It is widely thought that TC removes some skill and control from the driver. As such it is unpopular with many motorsports fans. Some motorsports series have given up trying to outlaw TC. With current state of technology, it is possible to implement TC as a part of software in ECU, and as such it is very hard to detect by scrutineers. In Formula One, an effort to ban TC has lead to the change of rules for 2008: every car must have a standard (but custom mappable) ECU, issued by FIA, which is relatively basic and does not have TC capabilities.
[edit] Traction control in cornering
Traction control is not just used for moving a vehicle from stationary without slippage. During hard maneuvers in a front wheel drive car there is a point where the wheels cannot both steer and drive the car at the same time without losing traction. With traction control, it's less likely for this loss of control to occur. There is a limit though, when the tires lose grip. The car will not corner as sharply as indicated by the front wheels, this is Understeer. In some front wheel drive cars, Traction Control can induce Lift Off Oversteer due to its throttle retarding capabilities. This can keep some cars stable in long maneuvers. In rear wheel drive cars, traction control can prevent Oversteer
All car manufacturers strongly point out in vehicle manuals that the Traction Control system is not to be taken for granted and that its presence should not encourage dangerous driving or situations beyond the driver's control.
