Bendix Commercial Vehicle Systems EC-80 ABS ATC SD - Manual (Page 8)

8
Normal Braking
During normal braking, brake pressure is delivered through
the ABS PMV and into the brake chamber. If the ECU
does not detect excessive wheel slip, it will not activate
ABS control, and the vehicle stops with normal braking.
Retarder Brake System Control
On surfaces with low traction, application of the retarder can
lead to high levels of wheel slip at the drive axle wheels,
which can adversely affect vehicle stability.
To avoid this, the Bendix EC‑80 controller switches off the
retarder as soon as a lock‑up is detected at one (or more)
of the drive axle wheels.
When the ECU is placed in the ABS off‑road mode, it will
switch off the retarder only when ABS is active on a steer
axle wheel and a drive axle wheel.
Optional HSA Mode
As a driver begins to move a vehicle forward when stopped
facing up an incline (or backs‑up a vehicle when facing
down a slope), vehicles without Bendix Hill Start Aid/Assist
(HSA) may experience rolling downhill during the delay
between the release of the brakes and providing enough
torque to move the vehicle up the slope.
For vehicles with Bendix HSA, the ECU receives a J1939
message from the transmission when it will need the
assistance of the brakes to avoid the vehicle rolling. The
HSA components apply brake pressure to select wheel‑end
brakes. After three (3) seconds from the driver brake
release, the HSA system releases the brake pressure.
The three‑second delay allows the drive‑line components
to activate while the vehicle is held in place.
When using the HSA function, the ABS off-road
function and the Retarder Relay output are temporarily
disabled.
Optional ABS Off-Road Mode
On some road conditions, particularly when the driving
surface is soft, the stopping distance with ABS may be
longer than without ABS. This can occur when a locked
wheel on soft ground plows up the road surface in front of
the tire, changing the rolling friction value. Although vehicle
stopping distance with a locked wheel may be shorter than
corresponding stopping distance with ABS control, vehicle
steerability and stability is reduced.
Bendix
® EC‑80 ™ ATC controllers have an optional control
mode that more effectively accommodates these soft road
conditions to shorten stopping distance while maintaining
optimal vehicle steerability and stability.
The ABS off-road mode should not be used on normal,
paved road surfaces because vehicle stability and
steerability may be reduced. The flashing ABS
indicator lamp communicates the status of this mode
to the driver.
The vehicle manufacturer should provide the optional
ABS off‑road function only for vehicles that operate on
unpaved surfaces or that are used in off‑road applications.
The vehicle OEM is responsible for ensuring that
vehicles equipped with the ABS off‑road function meet all
FMVSS‑121 requirements and have adequate operator
indicators and instructions.
The vehicle operator activates the off‑road function with a
switch on the dash panel. A flashing ABS indicator lamp
indicates to the driver that the ABS off‑road function is
engaged. To exit the ABS off‑road mode, depress and
release the switch.
All-Wheel Drive (AWD) Vehicles
AWD vehicles with an engaged interaxle differential (steer
axle to rear axle)/AWD transfer case may have negative
effects on ABS performance. Optimum ABS performance
is achieved when the lockable differentials are disengaged,
allowing individual wheel control.
Bendix EC‑80 ATC controllers can be programmed
specifically for this configuration to control the differential
lock/unlock solenoid in the AWD transfer case. When
programmed to do so, the ECU will disengage the locked
interaxle/AWD transfer case during an ABS event and
reengage it once the ABS event has ended.
ATC OPERATION
ATC Functional Overview
Just as ABS improves vehicle stability during braking,
ATC improves vehicle stability and traction during vehicle
acceleration. The Bendix EC‑80 ATC controller’s ATC
function uses the same wheel speed information and
modulator control as the ABS function. The ECU detects
excessive drive wheel speed; compares the speed of the
front, non‑driven wheels; and reacts to help bring the wheel
spin under control. The ECU can be configured to use
engine torque limiting and/or differential braking to control
wheel spin. For optimal ATC performance, both methods
are recommended.
ATC Lamp Operation
The ATC lamp illuminates:
1. During power‑up (e.g. when the vehicle is started for
approximately 2.5 seconds) and turns off after the
self‑test is completed, providing no Diagnostic Trouble
Codes are present.
2. When ATC is disabled for any reason.