Anti-lock Brake System (ABS)
Features/Gonstruction (cont'd)
ABS Modulator
The ABS modulator consists of the inlet solenoid valve, outlet solenoid valve, reservoir, pump, pump motor and thedampjng chamber.
The modulator reduces the caliper fluid pressure directly. lt is a circulating-type modulator because the brake fluid circulatesthrough the caliper, reservoir and the master cylinder.The hydraulic control has three modes: pressure reduction, pressure retaining and pressure intensifying modes.The hydraulic circuit is the independent four channel-type, one channel for each wheel.
SOLENOID VALVE
t-
Pressure intensifying mode: Inlet valve open, outlet valve closed,
Pressure retaining mode:
Pressure reduction mode:
Motor operation mode:
Master cylinder fluid is pumped out to the caliper.Inlet valve closed, outlet valve closed.
Caliper fluid is retained by the inlet valve and outlet valve.Inlet valve closed, outlet valve ooen
Caliper fluid flows through the outlet valve to the reservoir.When starting the pressure reduction mode. the pump motor is ON.When stopping ABS operation, the pump motor is OFF.The reservoir fluid is pumped out by the pump, through the damping chamber, to the mastercylinder.
PUMP MOTOR
19-30
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Wheel Sensor
The wheel sensors are the magnetic contactless type. As the gear pulser teeth rotate past the wheel sensor's magnetic
coil, AC current is generated. The AC frequency changes in accordance with the wheel speed. The ABS control unit detects
the wheel sensor signal frequency and thereby detects the wheel speed
at LOW SPEED
wheel Sp€od and Modulatot Control
VEHICLE SPEED
VEHICLE SPEED
WHEEL SPEED
PRESSU
OUTLETVALVE ON
OFF
INLETVALVE ON
OFF
MOTOR
ON
OFF
When the wheel speed drops sharply below the vehicle speed, the outlet valve opens momentarily to reduce the caliper
fluid pressure. The pump motor starts at this time. As the wheel speed is restored. the inlet valve opens momentarily to
increase the caliDer fluid oressure.
F
GEAR PULSER
19-31
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