2. ABS operation (pressure decrease) condition (Table 3-2 and Fig. 3-4).
Table 3-2
Solenoid valve Electricity Solenoid valve condition
Normally opened valve On Closed
Normally closed valve On Open
Fig. 3-4
If a vehicle is equipped with ABS and the braking pressure is too large, the friction coefficient will
be decreased and the wheel speed will be decreased much quickly than the vehicle body. Finally
the wheel will be locked, which makes ECU send HCU a signal of pressure decrease to wheel. In
order to decrease the pressure of wheel slave cylinder, the normally opened valve will close and
the normally closed valve will open. Then the brake oil from wheel slave cylinder will return to low
pressure accumulator (LPA) temporarily, and return to master pump with the oil pump started by
the motor. High pressure accumulator (HPA) between LPA and master pump will decrease the
high pressure pulse produced by oil pump with the help of metering jet fluid resistance.
3. ABS operation (maintaining) condition (Table 3-3 and Fig. 3-5).
Table 3-3
Solenoid valve Electricity Solenoid valve condition
Normally opened valve On Closed
Normally closed valve Off Closed
Fig. 3-5
The pressure of wheel slave cylinder is maintained by the closed normally opened valve and
normally closed valve, when proper pressure is applied to the salve cylinder through increase or
decrease of pressure.
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