Lexus RX300 (MCU15). Manual — part 57
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CHASSIS — BRAKES
101
Item
Brake Assist
Not Activated
Brake Assist
Activated
(2)
Master Cylinder Cut Solenoid Valve
(Front)
OFF
OFF
(7)
Port: (A), (F)
Open
Open
(3)
Master Cylinder Cut Solenoid Valve
(Front, Rear)
OFF
ON
(6)
Port: (B), (E)
Open
Close
(4)
Reservoir Cut
Solenoid Valve
OFF
ON
(5)
Port: (C), (D)
Close
Open
(8), (9)
Pressure Holding Valve
(Front, Rear)
OFF
OFF
(10), (11)
Port: (G), (H), (I), (J)
Open
Open
(12), (13)
Pressure Reduction Valve
(Front, Rear)
OFF
OFF
(14), (15)
Port: (K), (L), (M), (N)
Close
Close
Skid Control ECU
1) Vehicle Stability Control
Based on the 4 types of sensor signals received from the speed sensors, yaw rate sensor, deceleration
sensor and steering sensor, the skid control ECU calculates the amount of vehicle condition.
If a strong understeer or oversteer tendency is created during an emergency avoidance maneuver or corner-
ing, and the skid control ECU determines that the amount of vehicle condition exceeds a prescribed
value, it controls the engine torque control through fuel cutoff and the brake fluid pressure according
to the amount of the vehicle condition.
Start to Fuel Cutoff Control
Start to Brake Control
Brake Control Completed
Fuel Cutoff
Control Completed
→ Time
Brake Wheel
Cylinder Fluid
Pressure*
Engine Torque
Level of Strong
Under Steering
or Over Steering
Amount of
Vehicle
Condition
↑
↔
↑
151CH31
Open
Close
High
*: The wheel cylinder that activates varies depending on the condition of the vehicle.
CHASSIS — BRAKES
102
2) Initial Check
After the ignition is turned ON, and the vehicle attains an approximate speed of 6 km/h (4 mph) or
more only at first time, the skid control ECU performs an initial check.
The functions of each solenoid valve and pump motor in the actuator are checked in order.
3) Self-Diagnosis
If the skid control ECU detects a malfunction in the VSC system, the warning light that corresponds
to the function in which the malfunction has been detected lights up, as indicated in the table below,
to alert the driver of the malfunction. The ECU will also store the codes of the malfunctions. The
DTCs (Diagnostic Trouble Codes) can be accessed through the blinking of the VSC warning light or
the use of a hand-held tester. For details, see the LEXUS RX300 Chassis & Body Repair Manual (Pub.
No. RM785E).
Item
ABS
TRC
VSC
EBD
Brake
Assist
ABS Warning Light
f
—
—
—
f
Brake System Warning Light
—
—
—
f
—
VSC Warning Light
f
f
f
—
—
4) Fail Safe
In the event of a malfunction in the skid control ECU turns on the ABS warning light and the VSC
warning light and prohibits the ABS, TRC, VSC and Brake Assist control. In the case of the malfunction
that the EBD control can not be carried out, the ECU also turns on the brake system warning light and
prohibits the EBD control.
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CHASSIS — STEERING
103
STEERING
JDESCRIPTION
The engine revolution sensing type rack and pinion power steering is used. In addition, the same tilt mecha-
nism and energy absorbing mechanism are used.
187CH22
RHD Model
" Specifications A
Item
RHD
LHD
Gear Ratio (Overall)
15.7
16.0
No. of Turns Lock to Lock
2.82
2.60
Rack Stroke
mm (in.)
137.2 (5.40)
126.4 (4.98)
Fluid Type
ATF Type DEXRON
R
II or III
z
CHASSIS — STEERING
104
JENERGY ABSORBING MECHANISM
The energy absorbing mechanism in the steering column consists of a lower bracket, breakaway bracket,
energy absorbing plate and a contractile main shaft. The steering column is mounted onto the instrument
panel reinforcement via a lower bracket and breakaway bracket which is supported via a capsule and energy
absorbing plate. The steering column and the steering gear box are connected with a contractile intermediate
shaft. Operational examples of this mechanism are follows.
When the steering gear box moves during a collision (primary collision), the main shaft and the intermediate
shaft contract, thus reduce the chance that the steering column and the steering wheel protrude into the
cabin.
When an impact is transmitted to the steering wheel in a collision (secondary collision), the steering wheel
and the driver airbag help absorb the impact. In addition, the breakaway bracket and the lower bracket
separate, causing the entire steering column to move foward.
At this time, the energy absorbing plate becomes deformed to help absorb the impact of the secondary
collision.
Energy
Absorbing Plate
Deform
Primary
Collision
Secondary
Collision
Breakaway Bracket
Lower Bracket
187CH23
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