Grove
Published 01-14-2021 Control # 707-01
8-59
TMS9000-2 SERVICE MANUAL
CARRIER
8
ATC System Description
Just as ABS improves vehicle stability during braking, ATC
improves vehicle stability and traction during vehicle
acceleration. The Electronic Control Unit (ECU) 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 is configured to use engine torque limiting
and differential braking to control wheel spin. The ATC
system is controlled by the ABS ECU. It helps improve
traction on slippery or unstable driving surfaces by
preventing excessive wheel spin. ATC also enhances vehicle
stability by prevention of initial loss of traction.
ATC Operation
During periods of wheel slip, the Electronic Control Unit
enters an Automatic Traction Control mode. There are
various modes of Automatic Traction Control.
System Operation
•
At speeds above 40 km/h (25 mph), the engine is
throttled back via the data link to control spin out.
•
At speeds below 40 km/h (25 mph), both engine control
and differential brake control are activated as required to
control wheel slip. Once triggered, differential braking
mode remains active regardless of vehicle speed.
•
The off-road switch allows greater wheel spin (more
torque) when activated. It is intended for adverse
conditions, usually off-highway. The switch is
programmed for momentary operation. ATC reverts to
normal operation when the switch is cycled a second
time and whenever the system goes through a power-up
cycle.
ATC Valve
During normal operation, air is delivered to the ATC valve
treadle port (3), (Figure 8-62) from the Brake Pedal Control
Valve, which in turn supplies the air from the air delivery port
(2), (Figure 8-62) to the Rear Service Brake Relay Valve.
When traction control is utilized, the ATC valve is activated,
diverting supply tank air from the air supply port (1),
(Figure 8-62) to the Modulator Valves on the drive axle(s) by
way of the air delivery port (2), (Figure 8-62). The Electronic
Control Unit then activates the appropriate solenoids in order
to apply a brake force to the spinning wheel. The Automatic
Traction Control System cannot increase traction to a
particular wheel; it can only utilize the available traction.
FIGURE 8-61
1
2
9288
Fo
r
Reference
Only