Abs/Atc System - Holiday Rambler Imperial 2008 Owner's Manual

charge from the spring brake air chambers on
the rear drive axle. In this case, the park brakes
will automatically apply at approximately
30 psi. This safety backup system acts as an
automatic emergency brake system.
Another backup safety is the air system
separation of the front and rear brakes,
implemented by using two air tanks. One tank
is located in the front and the other is located
in the rear. This separation allows the front air
tank to operate the front brakes; the rear tank
operates the rear drive axle brakes and tag axle
brakes. This tank division gives reassurance
in case one tank experiences the failure of an
accessory air item that allows the compressed
air to escape.
Accessory air items are other pneumatically
operated items such as the air horn, vacuum
generator, etc. The accessory air items operate
only when air tank pressures exceed 65 psi.
This is done with pressure protection valves.
Should an accessory air item fail, the pressure
protection valve (PPV) reserves the remaining
air pressure of 65 psi for braking. This will
leave the motorhome with one air tank fully
charged for safety backup.
The rear air tank also has a safety backup - the
safety inversion valve. The inversion valve senses
the absence of rear air tank pressure. In this case
the inversion valve will allow the operator to make
a modulated spring brake application, which is
made in conjunction with the emergency spring
brake relay valve. The inversion valve allows
the front air tank pressure to recharge the rear
brake chambers after the modulated spring brake
application has been made. This backup system
implements use of all the brakes, allowing the
operator to bring the motorhome a safe stop. In
case of all compressed air charge escaping from
the front air tank, the operator will still have full
use of the rear brakes.

ABS/ATC SYSTEM

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 magnetic tone ring mounted to the hub.
Revolving with the wheel, the magnetic tone
ring is polarized, giving positive and negative
pulsations. A stationary sensor is mounted
adjacent to the tone ring to monitor magnetic
pulses. The pulses are monitored by the ABS
electronic control unit (ECU).
The ECU monitors all 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 effi ciency. It is possible
under certain conditions to have the wheel(s)
skid with a normally functioning ABS system.
20 0 8 I M P E R I AL
CHASSIS INFORMATION — 10
The ABS itself does not apply additional
braking power. The purpose of the ABS is to
limit wheel lock and decrease stopping distance.
Cautious driving practices and maintaining a
safe distance 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
cannot overcome naturally occurring
laws of physics. The ABS/ATC system,
combined 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.
The ECU receives the speed sensor
signal pulses to calculate 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 are operated in the
Air, Release or Hold modes to regulate
air pressure to the brake chambers.
Braking force is applied at a level that
minimizes stopping distance while
maintaining as much lateral stability as
possible.
090307
221