Bendix Commercial Vehicle Systems EC-30 ABS/ATC CONTROLLER 2/08 - Manual (Page 7)

7
ABS OPERATION
Bendix ABS uses wheel speed sensors, ABS modulators
and an ECU to control either four or six wheels. By
monitoring the wheel slip during braking, and adjusting
the brake pressure at each wheel, the EC-30
™ controller
is able to optimize slip between the tire and the road
surface. When excessive wheel slip is detected, the
EC-30
™ controller will activate ABS. The EC-30 ™ controller
controls the ABS modulators to simulate a driver pumping
the brakes. However, the EC-30
™ controller is able to pump
each brake on the vehicle independently, and with greater
speed and accuracy than a driver.
Front Axle Control
Although both steering-axle wheels are controlled by
individual ABS modulators, the EC-30
™ controller does
not control them completely independently. The EC-30 ™
controller uses a Modifi ed Individual Regulation (MIR)
philosophy which blends the applied braking force between
the two steering axle brakes. MIR is used to minimize
steering wheel pull while ABS is active on an uneven road
surface (e.g. ice and asphalt).
Single Rear Axle Control
On vehicles with a single rear axle (4x2), the rear axle
wheels are controlled independently. Therefore, brake
application pressure at each wheel is adjusted according
to the wheel behavior on the road surface.
Dual Rear Axle Control
For vehicles with dual rear axles (6x2 or 6x4), one ABS
modulator controls both right wheels and the other
modulator controls both left wheels. Both wheels on each
side receive equal brake pressure during an ABS stop. In
the case of only four wheel speed sensors, the two rear
sensors are located on the lighter rear axle.
Normal Braking
During normal braking, brake pressure is delivered through
the ABS modulator and into the brake actuator. If the wheel
speed sensors do not detect an excessive slip, the EC-30
™
controller does not activate ABS control and the vehicle
stops with normal braking.
ATC OPERATION
Just as ABS improves vehicle stability during braking,
ATC improves vehicle stability and traction during vehicle
acceleration. By adding an ATC modulator and/or engine
communication, the EC-30
™ controller ATC function uses
the same wheel speed information and modulator control
as the ABS function. The EC-30
™ controller detects
excessive drive wheel speed, compares the speed of the
front, non-driven, wheels, and reacts to bring the wheel spin
under control. The EC-30
™ controller can be confi gured
to use engine torque limiting and/or differential braking to
control wheel spin. For optimal ATC performance, both
methods are recommended.
During ATC activation, the EC-30 ™ controller will blink the
ATC active/warning lamp to advise the driver that drive-
wheel spin is occurring. When ATC is no longer active, the
ATC active/warning lamp turns off.
Engine Torque Limiting ATC
The engine torque limiting feature allows the EC-30 ™
controller to reduce engine torque to a suitable level, in
relation to the amount of available traction. When the
engine torque is controlled, wheel slip can be optimized,
producing more traction between the wheel and road
surface. Engine torque limiting is especially benefi cial in
avoidance of a power jackknife and when all drive wheels
are on an equally slippery surface. The EC-30
™ controller
will verify that the driver is pressing the accelerator (using
J1939 or J1922) prior to initiating an ATC event.
In order for the engine torque limiting ATC feature to be
used, the vehicle must be equipped with an electronically
controlled engine and throttle. When configured for
engine torque limiting ATC, the EC-30
™ controller must be
connected to an electronic engine via the SAE J1939 or
J1922 serial communications links.
Differential Braking ATC
Differential braking ATC allows the EC-30 ™ controller
to gradually apply the brake on a spinning drive wheel.
Since the vehicle’s differential tends to drive the wheel
that presents the least resistance (the wheel on the most
slippery surface), a slight brake application to this wheel
forces the differential to drive the wheel on the opposite
side. The EC-30
™ controller applies brake pressure to both
rear-axle ABS modulators by energizing the ATC modulator.
The EC-30
™ controller can then apply pressure only to the
spinning wheel by controlling the ABS modulators.
Differential braking ATC can be activated only when vehicle
speed is under 25 mph and one drive wheel is spinning
faster than the others.
In the event that differential braking, ATC is active for an
excessive time period, the EC-30
™ controller will disable
ATC to prevent overheating and fading of brakes. The
EC-30
™ controller will re-enable ATC after a short period
of time. The ATC active/warning lamp will be on while the
ATC is disabled.
In order for the differential braking control to be used, the
vehicle must be equipped with an antilock/traction relay
(ATR) valve (ATR-1 or ATR-2). The vehicle also must have
an electronically controlled engine throttle.
ATC Enable/Disable Switch
The ATC enable/disable switch allows the operator to
enable or disable the ATC feature as necessary. ATC can
be disabled while the vehicle is stationary or in motion.
However, ATC will not re-enable until the vehicle comes
to a complete stop, even with the switch in the enable
position. The ATC active/warning lamp will be on while the
ATC is disabled.