Chassis Information --- Section 10
The Executive 2005
439
ABS/ATC SYSTEM
(Anti-lock Brakes)
The motorhome is equipped with an anti-lock braking system (ABS) and automatic traction
control system (ATC). The ABS system monitors wheel rotation speeds by using a 100-tooth mag-
netic tone ring mounted to the hub. Revolving with the wheel, the magnetic tone ring is polarized giv-
ing positive and negative pulsations. A stationary sensor is mounted adjacent to the tone ring moni-
toring the magnetic pulses. The pulses are monitored by the ABS electronic control unit (ECU).
The ECU monitors all available wheel sensors at the rate of 100 times per second. The ECU
controls Pressure Modulator Valves. Pressure Modulator Valves have two electric over air solenoids, a
hold solenoid and a release solenoid. The modulator valves are open under normal braking, allowing a
straight through air signal from the treadle valve to the brake chamber. Should a wheel lose traction
under a braking application, the ECU will energize the hold solenoid of the Pressure Modulator Valve
to interrupt the air signal from the treadle valve to the brake chamber. The release solenoid vents the
existing air signal, at the brake chamber to the atmosphere, allowing the skidding tire to regain traction.
Skidding tires have less tractive efficiency. It is possible, under certain conditions, to have the wheel(s)
skid with a normal functioning ABS system.
The ABS itself does not apply additional braking power. The purpose of the ABS is limiting brake
torque to prevent wheel locking that results in the loss of lateral stability, and increased stopping dis-
tances. Cautious driving practices and maintaining adequate safe distances when following vehicles is
the key to safe vehicle operation.
WARNING:
The ABS/ATC system is designed to increase tire to road surface traction but can-
not overcome naturally occurring laws of physics. The ABS/ATC system, com-
bined with safe driving practices, will reduce the possibility of wheel skid and loss
of lateral stability.
ABS Component Function:
• Speed sensors and tone rings on each wheel monitor wheel rotation.
• Each speed sensor communicates wheel rotation pulses to the
Electronic Control Unit.
• ECU receives the speed sensor inputs, interprets the signal puls-
es, calculates speed and acceleration rates of each wheel.
• Based on the speed sensor input, the ECU detects impending
wheel lock and operates the ABS Modulator Valves required for
proper control. The Modulator Valves can be operated in the air,
release or hold modes to regulate air pressure to the brake chambers.
• The braking force is applied at a level which minimizes the
stopping distances while maintaining as much lateral stability as
possible.
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