ABS modulation: Notes

Fig 1: ABS Modulation Graph

Courtesy of SAAB-SCANIA OF AMERICA, INC.

1. Speed
2. Braking force
3. Road speed
4. Rotational speed of wheel
5. Inlet valve open, outlet valve closed
6. Inlet valve closed, outlet valve closed
7. Outlet valve open, return pump actuated

The TC/ABS control module continuously monitors the rotational speed of the wheels. When any wheel exceeds the slip threshold, the control module activates the ABS function and modulates brake pressure to the wheel or wheels in 3 phases. The front wheels are modulated individually but rear-wheel brake pressure is the same on both wheels, being controlled by the wheel having the lowest friction (greatest degree of slip).