Engine Running, Vehicle in Motion
Frequency of AC voltage generated at each sensor is directly proportional to the speed of the wheel. With light or no brake application, controller does not function. When brakes are applied with greater force, controller, based on wheel sensor signals, determines rate at which each wheel is decelerating. If lock-up is imminent, controller sends signal to modulator which controls braking for wheel or wheels concerned. Signal closes by-pass valve shutting off vacuum to front of chamber, air valve opens venting front of chamber to atmosphere resulting in pressure imbalance to diaphragm, moving diaphragm and displacement plunger rearward. Calipers or cylinders are isolated from master cylinder and pressure reduced to release brakes. Controller senses wheel speed increase signal, and by controlling air and by-pass valves, determines rate at which hydraulic pressure increases and brakes are re-applied. Cycle is repeated until vehicle speed is reduced to approximately 5 MPH or brakes are released. At end of brake stop, diaphragm plate and displacement plunger should always move forward enough to open hydraulic shut-off in pressure modulator. When this happens, brake pedal may drop slightly.