ABS modulation: Notes

The diagram shows ABS modulation

Fig 1: Identifying ABS Modulation Graph

Courtesy of SAAB-SCANIA OF AMERICA, INC.

1. Speed 
2. Braking force 
3. Road speed 
4. Wheel rotation speed 

1. Modulation phase 1; inlet valve open, outlet valve closed 
2. Modulation phase 2; Inlet valve closed, outlet valve open 
3. Modulation phase 3; Outlet valve closed, pump activated 

When the control unit detects excessive retardation (speed decrease) for one of the wheels, it modulates the brake pressure to the wheel in three phases:

• PHASE 1 Pressure increase
• PHASE 2 Pressure holding
• PHASE 3 Pressure decrease