Section 16: SUSPENSION
PA1562
39
9. FRONT KNEELING SYSTEM
The kneeling system is used to lower front of
vehicle. This allows passengers to board the
vehicle with greater ease. The kneeling action is
achieved by exhausting air from the front air
springs (bellows). This system bypasses the
height control valve to provide a fast up and
down movement of the front suspension. Only
seven seconds are required to lower vehicle
from normal level to the lowered position, and
approximately the same time to raise the vehicle
back to normal level. The quick response is
achieved by an auxiliary air tank installed beside
the secondary air reservoir (for exact position,
refer to Section 12, “Brake and Air System”).
This tank provides sufficient air supply to the
kneeling system for some successive
operations.
The system is provided with two safety features;
first, a speed switch will enable the kneeling
system to work only at less than 5 mph (8 km/h).
Secondly, the parking brake is automatically
applied, and a limit switch will keep it applied as
long as the vehicle has not returned to a certain
height where the driver will be able to manually
remove the parking brake.
The purpose of the hi-buoy function in this
system is to raise the front end of the vehicle to
allow an extra ground clearance for particular
situations. In driving condition, the height control
valve is in operation and only the hi-buoy can be
operated.
9.1 PRINCIPLE OF OPERATION
Refer to the air system schematic diagram
annexed at the end of Section 12, “Brake and
Air System”.
DOWN (FRONT KNEELING):
Both the bellows control and bellows exhaust
solenoid valves are energized, so the air control
valves release air from front air springs. The
height control valve is bypassed to ensure no air
is forwarded to air springs while lowering the
front suspension.
UP (FRONT HIGH-BUOY):
Only the bellows control solenoid valve is
energized, so the air coming from the kneeling
air tank is routed through air control valves, and
up to front air springs.
The height control valve is bypassed until the
kneeling proximity switch signals the kneeling
module to cut off the bellows control solenoid
valve, about 1" (25 mm) below normal ride
height. The final height adjustment is achieved
by the height control valve.
9.2 MAINTENANCE
Since the kneeling action is issued from both the
air system and electrical system, refer to
Section: 12, “Brake and Air System” and Section
06, “Electrical System”.
For diagnosis and understanding of the system,
refer to wiring diagrams, and to the appropriate
air system schematic diagram annexed to
Section 12, “Brake and Air System”.
9.3 BELLOWS CONTROL SOLENOID
VALVES
9.3.1 Removal and installation
1. On the rear side of steering compartment,
locate both the bellows control and bellows
exhaust solenoid valves.
2. Identify hoses and wires to ease
reinstallation. Disconnect solenoid wires and
the three flexible black hoses from solenoid
valves.
3. Unscrew and remove the control solenoid
valve and exhaust solenoid valve assembly.
Place on a clean working place.
Reverse removal procedure to reinstall.
CAUTION
Any cable tie that has been cut during removal
procedure should be replaced with a new one.
10. HIGH-BUOY SYSTEM
The purpose of the rear high-buoy system is to
raise the entire vehicle body about 4” (100 mm)
in order to increase ground clearance to board a
ferryboat, to jump a curb, etc. This system can
be put into service during normal vehicle
operation.
10.1 PRINCIPLES OF OPERATION
The rear high-buoy system is added over the
front kneeling (with front high-buoy). The front
end uses the same valves as the front kneeling
(with front high-buoy). A solenoid valve is added
to send air to the double shuttle valves for the
rear end. It uses the same dash switch as the
kneeling (with front high-buoy).
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