Traction Control Systems
Traction control systems are designed to prevent wheel spin in the power mode. Traction control attempts to regain traction by braking the spinning wheels, and sometimes throttling back engine power. Unlike an ABS, traction control can automatically apply the brakes. The driver does not need to depress the brake pedal for traction control to engage.
Traction control electronics are integrated into the ABS ECU. The system applies the brakes on the spinning wheel(s) when the wheel speed sensors tell the ECU that a wheel is accelerating at a much faster speed than the wheel on the other end of the axle. It does this by energizing a solenoid valve, which directs reservoir pressure to the relay valve and simultaneously activates the modulator valves to keep air pressure from the brake chambers. The ECU then directs the modulator valve to open, and pulse air into the brake chamber on the spinning wheel until wheel speed balance is regained.
On some systems, the ECU will throttle back engine power if both wheels are spinning too fast. If all the drive wheels on a tractor are spinning too fast, the tractor can become unstable, spin or jackknife. Traction control is especially valuable when a light drive wheel load might allow the wheels to spin under power, or when a tractor is pulling multiple trailers.
