Lexus RX300 (MCU15). Manual — part 55
CH
BO
CHASSIS — BRAKES
Pressure
Reduction Valve
Port A
Pressure Holding Valve
Port B
To Wheel
Cylinder
To
Reservoir
and Pump
From
Wheel
Cylinder
169CH54
169CH55
169CH56
93
3) ABS with EBD Operation
Based on the signals received from the 4 wheel speed sensors and deceleration sensor, the skid control
ECU calculates each wheel speed and deceleration, and checks wheel slipping condition. And according
to the slipping condition, the ECU controls the pressure holding valve and pressure reduction valve in
order to adjust the fluid pressure of each wheel cylinder in the following 3 modes: pressure reduction,
pressure holding, and pressure increase modes.
Not Activated
Normal Braking
—
—
Activated
Pressure Increase Mode
Pressure Holding Mode
Pressure Reduction Mode
Hydraulic
Circuit
Pressure
Holding Valve
(Port A)
OFF
(Open)
ON
(Close)
ON
(Close)
Pressure
Reduction Valve
(Port B)
OFF
(Close)
OFF
(Close)
ON
(Open)
Wheel Cylinder
Pressure
Increase
Hold
Reduction
CHASSIS — BRAKES
94
4) TRC Operation
The fluid pressure that is generated by the pump is regulated by the pressure regulator valve to the required
pressure. Thus, the wheel cylinder of the drive wheels are controlled in the following 3 modes: pressure
reduction, pressure holding, and pressure increase modes, to restrain the slippage of the drive wheels.
The diagram below shows the hydraulic circuit in the pressure increase mode when the TRC system
is activated.
In other operating modes, the pressure holding valve and the pressure reduction valve are turned ON/OFF
according to the ABS operation pattern described on the previous page.
161ES36
Master
Cylinder
(1)
(1)
(2)
(3)
(1)
(4)
(5)
(6)
(7)
(1)
(8)
(9)
(12)
(13)
(14)
(15)
(10)
(11)
Front Right
Wheel Cylinder
Rear Left
Wheel Cylinder
Rear Right
Wheel Cylinder
Front Left
Wheel Cylinder
Reservoirs
Pumps
Port (A)
Port (H)
Port (G)
Port (L)
Port (K)
Port (F)
Port (I)
Port (J)
Port (M)
Port (N)
Port (B)
Port (C)
Port (D)
Port (E)
Increase Mode
" System Diagram A
187CH41
Speed Sensor
Skid
Control
ECU
Engine ECU
Brake
Actuator
Slip Indicator
Light
CH
BO
CHASSIS — BRAKES
Mode
Solenoid Valves
95
TRC Activated
TRC Not
Activated
Pressure
Increase
Mode
Pressure
Holding
Mode
Pressure
Reduction
Mode
(2)
Master Cylinder Cut Solenoid Valve
(Front)
OFF
ON
ON
ON
(7)
Port: (A), (F)
Open
Close
Close
Close
(3)
Master Cylinder Cut Solenoid Valve
(Front, Rear)
OFF
OFF
OFF
OFF
(6)
Port: (B), (E)
Open
Open
Open
Open
(4)
Reservoir Cut
Solenoid Valve
OFF
ON
ON
ON
(5)
Port: (C), (D)
Close
Open
Open
Open
(8)
Pressure Holding Valve
(Front)
OFF
OFF
ON
ON
(11)
Port: (G), (J)
Open
Open
Close
Close
(9)
Pressure Holding Valve
(Rear)
OFF
OFF
OFF
OFF
(11)
Port: (H), (J)
Open
Open
Open
Open
(12)
Pressure Reduction Valve
(Front)
OFF
OFF
OFF
ON
(15)
Port: (K), (N)
Close
Close
Close
Close
(13)
Pressure Reduction Valve
(Rear)
OFF
OFF
OFF
OFF
(14)
Port: (L), (M)
Close
Close
Close
Close
Wheel Cylinder
Front wheels
—
Increase
Hold
Reduction
Wheel Cylinder
Pressure
Rear wheels
—
—
—
—
5) VSC Operation
a. General
The VSC system, by way of solenoid valves, controls the fluid pressure that is generated by the pump
and applies it to the brake wheel cylinder of each wheel in the following 3 modes: pressure reduction,
pressure holding, and pressure increase modes. As a result, the tendency to understeer or oversteer
is restrained.
b. Understeer Restraining Control
In understeer restraining control, the brakes of the front wheels and rear wheel of the inner side of
the turn is applied.
Also, depending on whether the brake is ON or OFF and the condition of the vehicle, there are circum-
stances in which the brake might not be applied to the wheels even if those wheels are targeted for
braking.
The diagram below shows the hydraulic circuit in the pressure increase mode, as it restrains an understeer
condition while the vehicle makes a right turn.
In other operating modes, the pressure holding valve and the pressure reduction valve are turned ON/OFF
according to the ABS operation pattern.
CHASSIS — BRAKES
96
Port (A)
Port (H)
Port (G)
Port (L)
Port (K)
Port (F)
Port (I)
Port (J)
Port (M)
Port (N)
Port (B)
Port (C)
Port (D)
Port (E)
Increase Mode
161ES37
Master
Cylinder
(1)
(1)
(2)
(3)
(1)
(4)
(5)
(6)
(7)
(1)
(8)
(9)
(12)
(13)
(14)
(15)
(10)
(11)
Front Right
Wheel Cylinder
Rear Left
Wheel Cylinder
Rear Right
Wheel Cylinder
Front Left
Wheel Cylinder
Reservoirs
Pumps
" System Diagram A
187CH42
Speed Sensor
Skid
Control
ECU
Engine ECU
Brake
Actuator
Slip Indicator
Light
Stop Light
Switch
Steering Angle
Sensor
Yaw Rate
Sensor
Deceleration
Sensor
VSC Warning
Light
VSC Warning
Buzzer
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