System Operation

SYSTEM OPERATION
All four wheels at right-front, left-front, right-rear and left-rear are subject to anti-lock control of this ABS. The following description of operation, however, describes only one of four wheels which are controlled independently and it is applicable to other three wheels.

When ABS is not Operating (Normal braking operation)





As no signal is fed from ABS control module and the solenoid valve is not energized, the solenoid valve and the flow control valve are pushed by the spring and prevented from operating. In this state, the fluid pressure from the master cylinder passes through the passage in the flow control valve (through Port 1 and Port 2) to the wheel cylinder as it is.

When ABS is Operating (Reduced pressure mode)





When the wheel is about to lock, ABS control module opens the solenoid valve. At this time the brake fluid which remained under the orifice flows through Port 4 into the reservoir. Then, the pressure under the orifice becomes lower than that above it and the flow control valve is pushed down. As a result, Port 2 is closed to shut off the fluid pressure (fluid flow) to the wheel cylinder for an instant.





And, when the difference between pressures under and above the orifice continues to increase further than that in previous state, the flow control valve is pushed lower and Port 3 opens. Then the brake fluid in the wheel cylinder flows through Port 3 and Port 4 into the reservoir. (The fluid pressure in the wheel cylinder is reduced.) As the pump is constantly operating while ABS is operating, the brake fluid stored in the reservoir is drawn out by the pump and sent back to the master cylinder.

When ABS is Operating (increased pressure mode)





When a higher pressure of the fluid in the wheel cylinder is needed, ABS control module closes the solenoid valve. As the flow control valve is at a lower position (as shown below) at this time, the brake fluid from the master cylinder passes through Port 1 and Port 3 into the wheel cylinder and increases the fluid pressure in it. At this time, the flow control valve operates so that the pressure difference between above and below the orifice will become constant. In this way, opening of the passage Port 1 from the master cylinder varies and the fluid pressure to the wheel cylinder is increased at a constant rate.