ABS Operating Modes
ABS OPERATING MODES1. When ABS is not operated
Operating condition.
In ordinary brakes, each solenoid valve is turned OFF when electricity is turned on from ABS ECU to the solenoid valve IN, OUT.
As for solenoid valve at this time, IN is opened and OUT is closed by spring action. If brake pedal is pushed down, master cylinder liquid pressure passes the solenoid valve and arrives at wheel cylinder, and the brake acts. Afterwards if brake pedal is released, the liquid pressure passes IN and check valve to return to master cylinder, then brake is released.
2. Dump mode-Brake pressure decreasing
Operating condition.
If wheels are about to be locked at sudden braking, ABS ECU outputs the signal decreasing the liquid pressure in solenoid valve, and each solenoid valve is turned ON.
At this time the solenoid valve IN is shut and interrupts the liquid channel from master cylinder. And solenoid valve OUT is opened and releases the liquid channel from wheel cylinder to the reservoir therefore the liquid pressure in wheel cylinder passes the solenoid valve OUT to arrive at reservoir so that pressure is decreased.
3. Hold mode-Brake pressure maintained
Operating condition.
If wheel cylinder liquid pressure is decreased to the ultimate state, ABS ECU outputs the signal maintaining the liquid pressure in solenoid valve, so that solenoid valve IN is turned ON and OUT is turned OFF.
Then wheel cylinder liquid because solenoid valve in and out are both shut so that liquid channel is interrupted.
4. Rise mode-Brake pressure increasing
Operating condition.
If it is judged that there is no lock phenomenon in wheels, then ABS ECU interrupts electricity in solenoid valve therefore each solenoid valve is turned OFF and the liquid pressure by motor pump passes the solenoid valve IN to arrive at wheel cylinder so that pressure is increased.
Fail-safe function
If failure occurred in ABS ECU system and the hydraulic, then the fail-safe circuit turns off the relay that supplies electricity to solenoid valve, stopping the control signal output, lighting the warning lamp at the same time to inform ABS failure to driver, in which case the ordinary brake function is secured under same condition as vehicles without ABS system.