Legacy Brighton Wagon AWD F4-2.2L SOHC (1997)
Hydraulic Control Assembly - Antilock Brakes: Description and Operation
ABS Only
DESCRIPTION
The Hydraulic Control Unit (H/U) is a fluid pressure controller comprising a motor, solenoid valve, housing, relay, etc. It constitutes two
diagonally independent brake fluid circuits for a cross piping vehicle.
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The pump motor rotates an eccentric cam to let the plunger pump generate a hydraulic pressure.
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The housing accommodates the pump motor, solenoid valve, reservoir, etc., and also constitutes a brake fluid passage.
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The plunger pump is a hydraulic pump which drains off the brake fluid which, when the pressure is reduced, is discharged to the reservoir, and
sends it toward the master cylinder.
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The solenoid valve is a 2-position type solenoid valve which switches the brake fluid passages between the wheel and master cylinder and
reservoir sides in response to an instruction from the ABS Control Module (ABSCM).
For each wheel cylinder, a pair of normally-closed and -opened solenoid valves are provided.
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The inlet solenoid valve is duty-controlled to reduce brake fluid pulsation for lower ABS operation noise.
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The reservoir is a fluid chamber which temporarily stores the brake fluid to be discharged from the wheel cylinder when the pressure is
reduced.
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The damper chamber suppresses the pulsation of the brake fluid which, when the pressure is reduced, is discharged from the plunger pump,
thereby minimizing the kickbacks to the brake pedal.
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The valve relay controls the solenoid valve and motor relay energizing power supply in response to an instruction from the ABSCM. In normal
(ignition ON) condition, the relay is actuated to supply power to the solenoid valve and motor relay. When an error occurs in the system, the
valve relay is forced to OFF to keep the fluid pressure circuit in the normal mode (normal brake mode) and also constitute the ABS warning
light operating circuit.
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The motor relay supplies power to the pump motor to operate the plunger pump in response to an instruction from the ABSCM in the ABS
control mode.
FOUR OPERATING MODES
The H/U has four operating modes; normal mode (control OFF: normal brake mode), "increase", "hold" and "decrease" modes (control ON in all
the three modes).
