Lexus ES300 (1997 year). Manual — part 19

74

CHASSIS — SUSPENSION

2) Function of Electric Modulated Suspension

This suspension system performs the controls described below in order to constantly maintain an optimal
vehicle posture, thus realizing excellent riding comfort, stability, and controllability.

Control

Function

e

Control

Float and
Pitch
Control

Estimates the relative speed between the vehicle body
and wheels based on the vehicle body vertical
acceleration rate detected by the acceleration sensor and
performs a (front/rear wheel independent) semi-active
control* of the shock absorbers’ damping force. As a
result, a damping force that is constantly optimal to the
road surface deviation is attained.
*: For details, see the next page.

R

oad-Sensitiv

e

Thumping
Sensitive
Control

When the road surface condition does not require a
damping force, this function controls the shock
absorbers so that their damping force will not increase.

R

Unsprung
Vibration
Control

If unsprung resonance is detected, this function controls
so that the damping force will not decrease below a
certain level, in order to reduce the unsprung resonance.

Anti-Roll
Control

During cornering, this function makes the damping force
firmer, thus restraining the body roll speed in order to
realize excellent stability and controllability.

Anti-Dive
Control

During braking, this function makes the damping force
firmer to restrain the body dive, thus ensuring excellent
stability and controllability.

Anti-Squat
Control

During acceleration, this function makes the damping
force firmer to minimize the changes in the vehicle body
posture.

High Speed
Control

This function varies the variable range of the damping
force according to vehicle speed in order to realize a soft
.and comfortable ride and a stable driving condition.
The damping force is controlled at a softer variable range
at low speeds, and at a firmer variable range at high
speeds.

Control by
Absorber
Control Switch

As shown on the left, the absorber control switch
enables the driver to select a desired damping force from
the 4 modes.

75

CHASSIS — SUSPENSION

3) Semi-Active Control

Based on the sprung mass and the direction of the shock absorber’s movement, the semi-active control
determines the conditions which assist and suppress the vibration in terms of the shock absorber’s sprung
mass. Thus, the semi-active control controls the damping force so that the shock absorber will only apply
an effective suppressing force against sprung mass.
Let us take an example of vehicle overcoming a gentle bump and separate it into 4 basic stages (stages

to

).

Starting uphill (1st stage)

According to the variation in the road surface,
the shock absorber contracts and the body
moves upward. At this time, the damping
force of the shock absorber is applied in the
direction which assists the body movement.

Ascending (2nd stage)

By inertia, the body keeps moving upward
causing the shock absorber to elongate
gradually. At this time, the damping force of
the shock absorber is applied in the direction
which restrains the movement of the body.

Starting Downhill (3rd stage)

The shock absorber deeps elongating along
with the variation of the road surface, but the
body starts moving downward. At this time,
the damping force of the shock absorber is
applied in the direction which assists the body
movement.

76

CHASSIS — SUSPENSION

Descending (4th stage)

By inertia, the body keeps moving downward
causing the shock absorber to contract
gradually. At this time, the damping force of
the shock absorber is applied in the direction
which restrains the movement of the body.

Thus, during stages

and

the shock absorbers assist the vibration to create a softer damping force,

and during stages

and

the shock absorber suppress the vibration to create a hard damping force, the

shock absorbers are minutely controlled to suppress the vibration to restrain the movement of the body
and of the shock absorbers.
The above processes are performed independently between the front and rear wheels in order to stabilize
the vehicle to a flat posture.

4) Self-Diagnosis

If a malfunction occurs in any of the sensors or actuators, the diagnostic code of that malfunction is stored
in memory. However, once the ignition switch is turned OFF, the diagnostic code is erased.
For diagnostic code check method, diagnostic code and diagnostic code clearance, see the 1997 ES300
Repair Manual (Pub. No. RM511U).

5) Fail-Safe

If a malfunction occurs in any of the sensors or actuators, the control of the damping force will be limited.

77

CHASSIS — STEERING

STEERING

DESCRIPTION

An engine revolution sensing type rack and pinon power steering is used on all models.

A compact and lightweight tilt steering is used on all models.

An energy absorbing mechanism has been changed.

Along with the discontinuance of the electronically controlled hydraulic cooling fan system, a single type
power steering pump has been adopted.

Specifications

Model

New

Previous

Item

New

Previous

Gear Ratio (Overall)

17.4 :1

15.9: 1

No. of Turn Lock to Lock

3.0

2.7

Rack Stroke mm (in)

145 (5.71)

←

Fluid Type

ATF Type DEXRON



II or III

←