Lexus ES300 (1997 year). Manual — part 18

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4. Layout of Components

5. Function of Components

No.

Component

Function

Steering Sensor

Detects the steering direction and angle of the steering wheel.

ECM

Sends the engine signal from the crankshaft position sensor to
the absorber control ECU.

ABS ECU

Converts the wheel speed signal from the speed sensors and
sends it to the absorber control ECU.

Shock Absorber and Actuator

Switches the damping force of the shock absorber based on the
control signal received from the absorber control ECU.

Speed Sensors (Front and Rear)

Detects the wheel speed of each wheels.

Crankshaft Position Sensor

Detects the engine revolution speed.

Stop Light Switch

Detects the brake condition.

Absorber Control ECU with
Acceleration Sensor

Determines the condition of the vehicle based on the signals

received from the sensors and switches and sends a control
signal to the actuator located in the shock absorber.

Uses an internal acceleration sensor to detect the vehicle’s

vertical acceleration rate.

Absorber Control Switch

Selects the damping force of the shock absorber.

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6. Construction and Operation of Components

Absorber Control Switch

The absorber control switch uses a rotary type
switch and is located in front of the rear console
box.
By operating this switch, the driver can select
four types of damping forces of the shock
absorbers.

Steering Sensor

The steering sensor is fitted to the turn signal switch assembly and detects the steering direction and angle.
The sensor includes a slotted disc that rotates with the steering wheel and a pair of photo interrupters. Each
photo interrupter consists of an LED (Light Emitting Diode) and a photo transistor, located facing each other.
It converts the change in the light radiation between the two elements to on/off signals. The slotted disc
rotates between the LED and photo transistor. As the steering wheel is turned, the slotted disc rotates with
the wheel and controls the light transmission between the two elements. The pair of photo interrupters are
phased and the absorber control ECU detects the steering direction and angle based on the changes of each
output.

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Front and Rear Shock Absorber and Actuators

The piston rod of the shock absorber is equipped with an internal actuator. The actuator consists of a step
motor, a screw mechanism (which converts the rotational movement to a linear movement) and a spool
valve. Also, the piston rod is equipped with a soft damping force valve and a hard damping force valve.
Signals from the absorber control ECU activate the actuator causing the spool valve to switch the oil passage.
Thus, the volume of oil that passes through each valve is varied in order to control the damping force in 16
steps.

Front Shock Absorber

Rear Shock Absorber

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Flow of the Oil

Absorber Control ECU

1) General

The absorber control ECU, which is located in the instrument panel, is equipped with an internal
acceleration sensor to detect the vehicle’s vertical movement.
Based on the signals received from the acceleration sensor enclosed in the absorber control ECU and other
sensors, the absorber control ECU detects the driving conditions and the vertical movement of the vehicle
body (as caused by bumpy roads).
According to the sky-hook theory, the absorber control ECU performs a front/rear wheel control of the
damping force of the shock absorbers independently to realize excellent riding comfort, stability, and
controllability.

— REFERENCE —

In order to maintain the vehicle posture fiat and stable, the sky-hook theory is a theory that renders as
ideal condition of a vehicle in which only the wheels move up and down when the bumpy road conditions
are transmitted to the vehicle body, while the body remains suspended in space via the shock absorbers.
In order to attain the movements that are as close as possible to those of the sky-hook theory, the new
model minutely controls the shock absorbers’ clamping force in response to bumpy roads.