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20 08 CONTESSA
CHASSIS INFORMATION — 10
If the motorhome is allowed continued
operation, the pneumatic emergency spring
brake relay valve, installed in the air system,
senses the low air pressure condition and will
release the air 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. 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.
BRAKE - AUXILIARY
The auxiliary braking systems is designed to
supplement the standard wheel braking system.
It is not designed to bring the motorhome
to a complete stop; however, it can assist in
controlling the speed of the motorhome. Use of
the auxiliary braking system can extend service
life of brake linings.
Exhaust Brake
The red brake switch (located on the
driver’s console) activates the auxiliary brake
integrated in the variable nozzle turbocharger.
The dash mounted switch will operate the
auxiliary brake when the dash switch is ON
and throttle is released.
When the auxiliary brake is activated, exhaust
pressure increases within the engine. Increased
exhaust back pressure slows the engine speed,
resulting in engine braking action. The amount
of engine braking power developed is related to
engine speed (RPM).
When the auxiliary brake is activated going
down a hill, it will help control road speed
or sufciently slow the road speed until the
transmission can automatically downshift to the
next lower gear. Downshifting automatically
occurs from high gear down to second gear.
Certain road conditions and engine speeds may
require the transmission be manually down
shifted in order to generate adequate engine
RPM and increase the engine brake effect.
NOTE:
The brake lights will illuminate while
the Exhaust Brake is applied.
NOTE:
Activating the Exhaust Brake switch
will cancel the cruise control.
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).
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