ABS modulation: Notes

Fig 1: ABS Modulation - Graph

Courtesy of SAAB-SCANIA OF AMERICA, INC.

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

The ABS control module continuously measures wheel speed. When any wheel exceeds the limit of optimum slip, the control module activates the ABS function and regulates the brake pressure applied to the wheel or wheels in 3 phases. The front wheels are regulated individually but the brake pressure applied to the rear wheels is the same on both, controlled by the wheel having the lowest friction (greatest slip).