Acura CSX. Manual — part 401
03
02
ABS Features
Anti-lock control
Grip force of tire and road surface
Main Control
19-109
COEFFICIENT OF
FRICTION
TARGET SLIP RATE
ROTATIONAL
DIRECTION
RADIAL
DIRECTION
OF THE
ROTATIONAL
DIRECTION
SLIP RATE
LEFT-REAR
WHEEL SPEED
SENSOR
RIGHT-REAR
WHEEL SPEED
SENSOR
LEFT-FRONT
WHEEL SPEED
SENSOR
RIGHT-FRONT
WHEEL SPEED
SENSOR
Select Low
Speed Wheel
Detect
Vehicle Speed
Drive
Solenoid
RIGHT-REAR
SOLENOID
LEFT-REAR
SOLENOID
RIGHT-FRONT
SOLENOID
LEFT-FRONT
SOLENOID
CONTROL UNIT
ABS
Control
Reference
Slip Rate
Drive
Solenoid
ABS
Control
Drive
Solenoid
ABS
Control
Drive
Solenoid
ABS
Control
RIGHT-FRONT
LEFT-FRONT
Detect
Wheel Speed
Detect
Slip Rate
RIGHT-REAR
LEFT-REAR
Detect
Slip Rate
Detect
Slip Rate
Detect
Slip Rate
Detect
Wheel Speed
Detect
Wheel Speed
Detect
Wheel Speed
Without ABS, when the brake pedal is pressed while driving, the wheels sometimes lock before the vehicle comes to a
stop. In such an event, the maneuverability of the vehicle is reduced if the front wheels are locked, and the stability of
the vehicle is reduced if the rear wheels are locked, creating an extremely unstable condition. With ABS, the system
precisely controls the slip rate of the wheels to ensure maximum grip force from the tires, and it thereby ensures
maneuverability and stability of the vehicle. The ABS calculates the slip rate of the wheels based on the four wheel
speeds, and then it controls the brake fluid pressure to reach the target slip rate.
The control unit detects the wheel speed based on the wheel speed sensor signals it receives, then it calculates the
vehicle speed based on the detected wheel speed. The control unit detects the vehicle speed during deceleration
based on the wheel speeds.
The control unit calculates the slip rate of each wheel, and transmits the control signal to the modulator unit solenoid
valve when the slip rate is high.
The hydraulic control has three modes: Pressure intensifying, pressure reducing, and pressure retaining.
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05
06
EBD Features
TCS Features
19-110
VSA System Components
REAR WHEEL
BRAKE PRESSURE
With EBD under HEAVY LOAD
at REAR WHEELS
With EBD under LIGHT LOAD
at REAR WHEELS
Without EBD
FRONT WHEEL BRAKE PRESSURE
ANTI-POWER of BRAKE FORCE
TOTAL TRACTION
DRIVING POWER
TOTAL TRACTION
BRAKE FORCE
SLIPPERY ROAD SURFACE
NORMAL ROAD SURFACE
The electronic brake distribution (EBD) feature helps control vehicle braking by adjusting the rear brake force in
accordance with the rear wheel load before the ABS operates. Based on the wheel speed sensor signals, the control
unit uses the modulator to control the rear brakes individually. When the rear wheel speed is less than the front wheel
speed, the VSA modulator-control unit retains the current rear brake fluid pressure by closing the inlet valve in the
modulator. As the rear wheel speed increases, and approaches the front wheel speed, the VSA modulator-control unit
increases the rear brake fluid pressure by momentarily opening the inlet valve. This whole process is repeated very
rapidly. While this is happening, kickback may be felt at the brake pedal.
When a drive wheel loses traction on a slippery road surface and starts to spin, the VSA modulator-control unit applies
brake pressure to the spinning wheel, and sends an engine torque control request to the ECM/PCM to slow the
spinning wheel and keep traction.
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07
03
VSA System Features
Oversteer control
Understeer control
19-111
with VSA
without VSA
The brake makes the yaw rate opposite
to the turning direction
with VSA
without VSA
The brake increases the yaw rate toward
the turning direction
The throttle control effect;
• reduces vehicle speed
• increases cornering force
Applies the brake to the front and rear outside wheels
• Applies the brake to the rear inside wheel
• Controls the engine torque when accelerating
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09
Brake Assist Features
19-112
VSA System Components
Pressure
Threshold
Brake Assist
Begins
Time
Threshold
Brake Pedal
Effort Reduced
Panic Stop with Brake Assist
Time
Pressure
Panic Stop without Brake Assist
Normal Stop
Brake assist helps ensure that any driver can achieve the full braking potential of the vehicle by increasing brake
system pressure in a panic situation, bringing the vehicle into a full ABS stop.
If during a panic stop the VSA modulator-control unit determines that the brake system pressure increases above a
threshold in less than a certain amount of time, the VSA modulator-control unit engages brake assist.
Because the brake system pressure crossed the pressure threshold before the time threshold had expired, the VSA
modulator-control unit goes into brake assist mode.
08/08/21 15:04:54 61SNR030_190_0112
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