Abs Actuator
The actuator controls the brake fluid pressure to the rear brake wheel cylinders through signals from the ECU.
Power steering fluid pressure is fed to the ABS actuator. The pressure regulator controls power steering fluid pressure acting internally in the actuator, based on fluid pressure generated in the master cylinder. See Fig 1. This pressure is used during rear ABS operation to control rear brake application and release.
The actuator solenoid valve is normally off, with the plunger in the down position. This applies regulated power steering pressure to the by-pass and pressure reduction pistons. The cut valve will be in the open position.
If the ECU senses the rear brakes are about to lock, it energizes the actuator solenoid valve. When energized, the actuator solenoid valve plunger moves up. This action allows power steering fluid to return to the reservoir, allowing the pressure reduction piston to move to the left. the cut valve will now close. Brake fluid pressure in the rear wheel cylinders will accumulate in the actuator. This releases pressure in the rear wheel cylinders.
During ABS mode, the ECU turns the actuator solenoid valve on and off, controlling the flow of power steering pressure to the pressure reduction piston. This, in turn, controls the application and release of the rear brakes.
If the power steering system loses pressure because of a leak, the by-pass piston will move to the left. This action opens a by-pass port in the by-pass valve. In this mode, normal braking will be returned to the rear brakes.