Lexus ES300 (2002 year). Manual - part 108

CHASSIS – BRAKE

CH-54

182CH56

Rear
Brake
Force

Rear
Brake
Force

Ideal Brake Force
Distribution

EBD Control

Front Brake Force

Front Brake Force

EBD Control

Ideal Brake Force Distribution

without Load in Rear

with Load in Rear

181CH56

Front / Rear Wheels Brake Force Distribution

If the brakes are applied while the vehicle is moving straight forward, the transfer of the road reduces the
load that is applied to the rear wheels. The skid control ECU determines this condition by way of the signals
from the speed sensor, and the brake actuator regulates the distribution of the brake force of the rear wheels
to optimally control.
For example, the amount of the brake force that is applied to the rear wheels during braking varies whether
or not the vehicle is carrying a load. The amount of the brake force that is applied to the rear wheels also
varies in accordance with the extent of the deceleration.
Thus, the distribution of the brake force to the rear is optimally controlled in order to effectively utilize the
braking force of the rear wheels under these conditions.

 EBD Control Concept 



Right / Left Wheels Brake Force Distribution (During Cornering Braking)

When the brakes are applied while the vehicle is
cornering, the load that applied to the inner
wheel decreases to the outer wheel increases.
The skid control ECU determines this condition
by way of the signals from the speed sensor, and
the brake actuator regulates the brake force in
order to optimally control the distribution of the
brake force to the inner wheel and outer wheel.

CHASSIS – BRAKE

CH-55

211CH29

ABS Warning Light

Brake System
Warning Light Combination Meter

Speed Sensors

Speed Sensors

Brake Actuator

 Skid Control ECU

Stop Light Switch

4. Layout of Component

5. Function of Component

Component

Function

Combination

ABS Warning Light

Lights up to alert the driver when the skid control ECU detects the
malfunction in the ABS.

Combination
Meter

Brake System
Warning Light

Lights up together with the ABS warning light to alert the driver
when the skid control ECU detects the malfunction in the EBD
control.

Brake Fluid Level Warning Switch

Detects the brake fluid level.

Stop Light Switch

Detect the brake pedal depressing signal.

Speed Sensors

Detect the wheel speed of each four wheels.

Brake
Actuator

Actuator Portion

Charges the fluid path based on the signals from the skid control
ECU during the operation of the ABS with EBD system, in order
to control the fluid pressure that is applied to the wheel cylinders.

Actuator

Skid Control ECU

Judges the vehicle driving condition based on signals from each
sensor, and sends brake control signal to the brake actuator.

CHASSIS – BRAKE

CH-56

211CH30

Actuator
Portion

Skid Control
ECU

208CH25

Brake Actuator

Front Left

Rear Right

Rear Left

Front Right

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

6. Brake Actuator

General

The brake actuator consists of actuator portion
and skid control ECU.

Actuator Portion

1) Construction

The brake actuator consists of 8 two-position solenoid valves, 1 motor, 2 pumps and 2 reservoirs.
The 8 two-position solenoid valves consists of 4 pressure holding valves [(1), (2), (3), (4)], and 4 pressure
reduction valves [(5), (6), (7), (8)].

 Hydraulic Circuit 



CHASSIS – BRAKE

CH-57

169CH56

169CH55

169CH54

Port A

Pressure Holding Valve

Port B

Pressure
Reduction Valve To Wheel

Cylinder

To
Reservoir
and Pump

From Wheel
Cylinder

2) ABS with EBD Operation

Based on the signals received from the 4 wheel speed sensors, 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

Increase Mode

Holding Mode

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