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4. Hydraulic Circuit
The hydraulic circuit of the Nippondenso and Bosch systems are the same.
5. Operation
The hydraulic system of the ABS has 4 circuits. Although the hydraulic circuit described below is 1 circuit, it is
applicable to other circuits as well.
During Normal Braking (ABS not activated)
During normal braking, the ABS is not activated
and the ECU does not send control signal. When the
brake pedal is depressed, the fluid pressure in the
master cylinder rises, brake fluid passes from port
A to port B, and then flows to the brake wheel
cylinder. When the brake pedal is released, brake
fluid returns from the brake wheel cylinder to the
master cylinder through port B to port A and the No.
1 Check Valve.
Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS ECUOperation
Pressure
Holding ValveOFFPort AOpen
Pressure
Reduction
Valve
OFFPort DClosed
Pump MotorOFFRotating
Hydraulic Circuit
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During Normal Braking (ABS not activated)
1) Pressure Reduction Mode
When the wheel is about to lock, the control signal
from the ECU causes port A to close, port D to open,
thus engaging the pressure reduction mode.
At this time, the brake fluid flows from the wheel
cylinder, through ports C and D, to the reservoir,
reducing the wheel cylinder pressure. At the same
time, the brake fluid is pumped and returned to the
master cylinder.
Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS ECUOperation
Pressure
Holding ValveONPort AClosed
Pressure
Reduction
Valve
ONPort DOpen
Pump MotorONRotating
2) Pressure Holding Mode
After the fluid pressure in the wheel cylinder is
reduced or increased to the required pressure, a
control signal fromt he ECU causes ports A and D
to close. As a result, the system engages in the
pressure holding mode to maintain the fluid
pressure in the wheel cylinder.
Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS ECUOperation
Pressure
Holding ValveONPort AClosed
Pressure
Reduction
Valve
OFFPort DClosed
Pump MotorONRotating
Hydraulic Circuit
Hydraulic Circuit
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68CHASSISÐBRAKES
3) Pressure Increase Mode
When the fluid pressure in the wheel cylinder needs
to be increased in order to apply more braking force,
a control signal from the ECU causes port A to open,
port D to close, thus engaging in the pressure
increase mode.
Accordingly, the circuit will be in the same state as
in normal braking, in chich the brake fluid is sent
from the master cylinder to the wheel cylinder to
increase the fluid pressure in the wheel cylinder.
The fluid pressure increase rate is controlled by
repetition of the pressure increase and pressure
holding mode.
Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS ECUOperation
Pressure
Holding ValveOFFPort AOpen
Pressure
Reduction
Valve
OFFPort DClosed
Pump MotorONRotating
Hydraulic Circuit
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69 CHASSISÐBRAKES
ABS & TRAC SYSTEM
1. General
The ABS & TRAC system totally controls the engine torque control through the fuel cutoff and the braking of the
driving wheels (front wheels). If helps to avoid slippage of the driving wheels that tends to happen during starting
and acceleration and to maintain an optimal driving force according to the road surface conditions. The system
eliminates the need for a subtle accelerator pedal opeation and ensures vehicle stability when starting, accelerating
or turning on slippery roads.
2. System Diagram
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3. Wiring Diagram
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4. Layout of Components
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5. Function of Components
No.ComponentFunction
1Slip Indicator LightBlinks to inform the driver when the TRAC system is operated.
2TRAC OFF Indicator Light
Lights to inform the driver when the TRAC system is turned OFF by
the by the TRAC OFF switch. And, blinks to alert the driver when
the ECU detects the malfunction in the TRAC system.
3ECM
Sends signals to the ABS & TRAC ECU, such as the throttle
valve opening angle, specific volume of intake air signal, etc.
Controls the engine output and shift timing in accordance with
the fuel cutoff request and shift timing request that are output by
the ABS & TRAC ECU.
4ABS & TRAC ECU
Judges the vehicle driving condition based on signals from 4 speed
sensors and signals from ECM, and sends fuel cut and shift timing
demand signals to the ECM and brake control signal to the ABS &
TRAC actuator.
5ABS & TRAC Actuator
Controls the brake fluid pressure to each brake wheel cylinder
of the driving wheel (front wheel) by signals from the ABS &
TRAC ECU.
ABS & TRAC
Solenoid RelayDirects electricity to the solenoid valves in the actuator.
6ABS & TRAC
RelayPump Motor
RelayControls the pump motor operation in the actuator.
7Speed Sensors (Front and Rear)Detect the wheel speed of each of four wheels.
8Throttle Position SensorDetects the throttle valve opening angle.
9TRAC OFF SwitchTurns the TRAC system inoperative.
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6. Construction and Operation of Components
TRAC OFF Switch and Indicator Light
1) TRAC OFF Switch
When pressing, this switch turns the TRAC system to be inoperative. Pressing it again changes it to be operative.
When turning the ignition switch from ªOFFº to ªONº, TRAC system always becomes operative.
2) TRAC OFF Indicator Light
This light comes on when the TRAC system is set inoperative by the TRAC OFF switch, and informs the driver
accordingly. And blinks to alert the driver when a malfunction has occurred in the engine and TRAC system.
3) Slip Indicator Light
When the TRAC system is operative, the light blinks and informs the driver accordingly.
ABS & TRAC Actuator
1) Construction
The ABS & TRAC actuator consists of 12 two±position solenoid valves, 1 motor, 2 pumps 2 reservoirs and 2 pressure
regulator valves.
The 12 two±position solenoid valves consists of 2 master cut solenoid valves, 2 reservoirs cut solenoid valves, 4
pressure holding valves, and 4pressure reduction valves.
Pressure regulator valve is assembled into the master cut solenoid valve.
The basic construction and operation of the pump, reservoir, pressure holding valve, and pressure reduction valve
are shared with ABS.
a. Master Cut Solenoid Valve
When the TRAC system is active, a signal from the ABS & TRAC ECU causes the master cut solenoid valve to turn
ON in order to shut off the circuit between the master cylinder and the front brake wheel cylinder.