Base Brake Mode (Non Antilock Brake Mode)

Under normal operating conditions, the brake system will operate using conventional braking by means of brake pedal force, the vacuum booster and the master cylinder. Each front channel consists of a motor, solenoid, Expansion Spring Brake (ESB), ball screw, piston, and check valve. As illustrated in figures, under normal operating conditions (base braking), the piston is held in the upmost or "home" position and the solenoid is open (not energized). This is accomplished by the ball screw via the motor to drive the nut upwards. Once at the upmost position, the piston is held by an ESB.

Two paths are available to transfer brake fluid to the calipers: (1) through the modulator, around the open check valve and out to the caliper, and (2) through the modulator, through the normally open solenoid and out to the caliper. The solenoid in the front circuits provides an alternate brake fluid pressure path to the caliper. With this arrangement, if the ABS were to lose power or malfunction with the piston out of the "home" position, a redundant brake fluid path is available. The rear channel operates in a similar manner except no solenoid is used.