Troubleshooting guide

35
www.bendix.com 1-800-AIR-BRAKE (1-800-247-2725)
Section 6: Antilock Braking Systems
Premium ECUs have a drag torque control feature
which reduces driven-axle wheel slip (due to driveline
inertia) by communicating with the engine’s controller
and increasing the engine torque.
Electronic Stability Program (ESP)
Recent Bendix ABS advances include ESP
®
functionality
which has the ability to apply brakes to individual wheel
ends, and the trailer, to counteract the trailer “push”
during maneuvers that may lead to loss of control or
jackknifes on low to high friction surfaces (snow, rain,
asphalt, concrete, etc.)
Roll Stability Program (RSP)
The Bendix Roll Stability Program (RSP), is an all-axle
ABS solution that helps reduce vehicle speed by applying
all vehicle brakes as needed, reducing the tendency to
roll over. RSP focuses on reducing the vehicle’s speed
below the critical roll threshold during direction-
changing maneuvers such as exit ramps and obstacle
avoidance on dry, high friction surfaces.
Trailer ABS
See page 42 for more information on trailer ABS
systems and components.
Bendix
®
Antilock Braking Systems (ABS) use
wheel speed sensors, ABS pressure modulator valves,
and an Electronic Control Unit (ECU) to control
either four or six wheels of a vehicle. Bendix ECUs
are able to optimize slip between the tire and the road
surface by monitoring individual wheel turning motion
during braking, and adjust or pulse the brake pressure
at the wheel end. When excessive wheel slip, or wheel
lock-up, is detected, the ECU will activate the Pressure
Modulator Valves similar to a driver pumping the brakes.
The ECU, however, is able to pump the brakes on
individual wheels (or pairs of wheels), independently,
and with greater speed and accuracy than a driver.
In addition to the ABS function, premium models of
the ECUs provide an Automatic Traction Control
(ATC) feature. Bendix ATC can improve vehicle
traction during acceleration, and lateral stability while
driving through curves. ATC utilizes Engine Torque
Limiting where the ECU communicates with the
engine’s controller and/or Differential Braking
where individual wheel brake applications are used to
improve vehicle traction.
ABS Components
Typical ABS components (for trucks and tractors) are:
• Wheel speed sensors (such as the Bendix
®
WS-24
™
wheel speed sensors shown on this page). Each
sensor is installed with a Bendix Sensor Clamping
Sleeve. Vehicles have an exciter ring (or “tone ring”)
as part of the wheel assembly, and as the wheel
turns, the teeth of the exciter ring pass the wheel
speed sensor, generating an alternating current (AC)
signal, which varies in voltage and frequency as the
wheel speed changes. The ECU receives the AC
signal and can then monitor how fast the wheel is
turning.
• Pressure Modulator Valves (PMV) (such as the
Bendix
®
M-32
™
or M-32QR
™
pressure modulator
valves - shown on this page). PMVs use solenoids
with the ability to apply, hold, or release the air
pressure being delivered to the brakes to optimize
brake performance. Four, five, or six of these valves
may be used depending on ECU model and vehicle
configuration.
Antilock Braking Systems
90° Speed
Sensors
Straight Speed
Sensors
Sensor
Clamping
Sleeve
Bendix
®
WS-24
™
Wheel Speed Sensors
Bendix
®
M-32
™
and
M-32QR
™
Modulators
Delivery
Supply
Exhaust
Electrical
Connector
M-32QR
™
Modulator
M-32
™
Modulator
Supply