traction control

A traction control system (TCS), also known as ASR (from German: Antriebsschlupfregelung, lit. 'drive slippage regulation'), is typically (but not necessarily) a secondary function of the electronic stability control (ESC) on production motor vehicles, designed to prevent loss of traction (i.e., wheelspin) of the driven road wheels. TCS is activated when throttle input and engine power and torque transfer are mismatched to the road surface conditions.
The intervention consists of one or more of the following:

Brake force applied to one or more wheels
Reduction or suppression of spark sequence to one or more cylinders
Reduction of fuel supply to one or more cylinders
Closing the throttle, if the vehicle is fitted with drive by wire throttle
In turbocharged vehicles, a boost control solenoid is actuated to reduce boost and therefore engine power.Typically, traction control systems share the electrohydraulic brake actuator (which does not use the conventional master cylinder and servo) and wheel-speed sensors with ABS.
The basic idea behind the need for a traction control system is the loss of road grip can compromise steering control and stability of vehicles. This is the result of the difference in traction of the drive wheels. The difference in slip may occur due to the 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 differential. A further enhancement of the differential is to employ an active differential 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 yaw (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.

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