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The predecessor of modern electronic traction control systems can be found in high-torque, high-power rear-wheel drive cars as a . A limited slip differential is a purely mechanical system that transfers a relatively small amount of power to the non-slipping wheel, while still allowing some wheel spin to occur.
In 1971, 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 item at the time, it was an option on all full-size models, including the , , , , and .
Cadillac introduced the Traction Monitoring System (TMS) in 1979 on the redesigned Eldorado.
Use of traction control
- In road cars: Traction control has traditionally been a safety feature in premium high-performance cars, which otherwise need sensitive throttle input to prevent spinning driven wheels when accelerating, especially in wet, icy or snowy conditions. In recent years, traction control systems have become widely available in non-performance cars, minivans, and light trucks and in some small hatchbacks.
- In : Traction control is used as a performance enhancement, allowing maximum traction under acceleration without wheel spin. When accelerating out of a turn, it keeps the tires at optimal .
- In : Traction control for production motorcycles was first available with the in 1988. HONDA offered Traction Control as an option, along with ABS on their ST1100 beginning about 1992. By 2009, traction control was an option for several models offered by and , and the model year 2010 (1400GTR).
- In vehicles: Traction control is used instead of, or in addition to, the mechanical limited slip or . It is often implemented with an , as well as other computerized controls of the engine and transmission. The spinning wheel is slowed down with short applications of brakes, diverting more torque to the non-spinning wheel; this is the system adopted by in 1993, for example. ABS brake traction control has several advantages over limited-slip and locking differentials, such as steering control of a vehicle is easier, so the system can be continuously enabled. It also creates less stress on powertrain and driveline components, and increases durability as there are fewer moving parts to fail.
When programmed or calibrated for off-road use, traction control systems like ’s four-wheel electronic traction control (ETC) which is included with AdvanceTrac, and ’s four-wheel automatic brake differential (ABD), can send 100 percent of torque to any one wheel or wheels, via an aggressive brake strategy or “brake locking”, allowing vehicles like the and to keep moving, even with two wheels (one front, one rear) completely off the ground.
Controversy in motorsports
Very effective yet small units are available that allow the driver to remove the traction control system after an event if desired. In , an effort to ban traction control led to a change of rules for 2008: every car must have a standard (but custom mappable) ECU, issued by the , which is relatively basic and does not have traction control capabilities. In 2008, NASCAR suspended a driver, crew chief, and car owner for one race and disqualified the team after finding questionable wiring in the ignition system, which could have been used to implement traction control.
Components of traction control
Generally, the main hardware for traction control and ABS are mostly the same. In many vehicles traction control is provided as an additional option to ABS.
- Each wheel is equipped with a sensor which senses changes in its speed due to loss of traction.
- The sensed speed from the individual wheels is passed on to an (ECU).
- The ECU processes the information from the wheels and initiates braking to the affected wheels via a cable connected to an automatic traction control (ATC) valve.
In all vehicles, traction control is automatically started when the sensors detect loss of traction at any of the wheels.
The basic idea behind the need for a traction control system is the loss of road grip that compromises steering control and stability of vehicles because of the difference in traction of the drive wheels. Difference in slip may occur due to turning of a vehicle or varying road conditions for different wheels. When a car turns, its outer and inner wheels rotate at different speeds; this is conventionally controlled by using a . A further enhancement of the differential is to employ an that can vary the amount of power being delivered to outer and inner wheels as needed. For example, if outward slip is sensed while turning, the active differential may deliver more power to the outer wheel in order to minimize the (essentially the degree to which the front and rear wheels of a car are out of line.)
Active differential, in turn, is controlled by an assembly of electromechanical sensors collaborating with a traction control unit.
When the traction control computer (often incorporated into another control unit, such as the ABS module) detects one or more driven wheels spinning significantly faster than another, it invokes the ABS to apply brake friction to wheels spinning with lessened traction. Braking action on slipping wheel(s) will cause power transfer to wheel axle(s) with traction due to the mechanical action within the differential. (AWD) vehicles often have an electronically controlled coupling system in the or engaged (active part-time AWD), or locked-up tighter (in a true full-time set up driving all wheels with some power all the time) to supply non-slipping wheels with torque.
This often occurs in conjunction with the powertrain computer reducing available engine torque by electronically limiting throttle application and/or fuel delivery, retarding ignition spark, completely shutting down engine cylinders, and a number of other methods, depending on the vehicle and how much technology is used to control the engine and transmission. There are instances when traction control is undesirable, such as trying to get a vehicle unstuck in snow or mud. Allowing one wheel to spin can propel a vehicle forward enough to get it unstuck, whereas both wheels applying a limited amount of power will not produce the same effect. Many vehicles have a traction control shut-off switch for such circumstances.
Traction control in cornering
Traction control is not just used for improving acceleration under slippery conditions. It can also help a driver to corner more safely. If too much throttle is applied during cornering, the drive wheels will lose traction and slide sideways. This occurs as in front wheel drive vehicles and in rear wheel drive vehicles. Traction control can prevent this from happening by limiting power to the wheels. It cannot increase the limits of grip available and is used only to decrease the effect of driver error or compensate for a driver’s inability to react quickly enough to wheel slip.
Automobile manufacturers state in vehicle manuals that traction control systems should not encourage dangerous driving or encourage driving in conditions beyond the driver’s control.