PREVOST GKN AXLES LIMITED KIRKSTALL DIVISION, Руководство по обслуживанию

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Section 16: SUSPENSION
16-12
9. FRONT KNEELING AND HI-
BUOY SYSTEM (IF
APPLICABLE)
The kneeling system is used to lower front of ve-
hicle. This allows passengers to board the vehicle
with greater ease. The kneeling action is achieved
by exhausting air from the front air springs (bel-
lows). This system bypasses the height control
valve to provide a fast up and down movement of
the front suspension. Only five seconds are re-
quired to lower vehicle from normal level to the
lower position, and approximately nine seconds to
raise it. This quick response is achieved by the
kneeling air tank installed in front of steering (for
exact position, refer to Section 12, paragraph "2.1
Location and Function"). This tank provides suffi-
cient air supply to the kneeling system for some
successive operations.
FIGURE 14: KNEELING/HI-BUOY PANEL (STEERING
COMPARTMENT)
16031
The system is provided with two safety features;
first, a speed switch will enable the kneeling sys-
tem to work only under 5 mph (8 km/h). Secondly,
the parking brake is automatically applied, and a
limit switch will keep it applied as long as the vehi-
cle 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
passengers to board the vehicle with greater
ease. It is also used to allow an extra ground
clearance for particular situations. In normal con-
ditions, the height control valve is in operation and
only the hi-buoy can be operated.
9.1 Principle of Operation
Refer to the system pneumatic diagram annexed
in the technical publication box provided with the
vehicle.
DOWN:
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 (Fig. 14).
UP:
Only the bellows control solenoid valve is ener-
gized, so the air coming from the kneeling air tank
is routed through air control valves, and up to front
air springs (Fig. 14). The height control valve is
bypassed until the kneeling proximity switch sig-
nals 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.
HI-BUOY FUNCTION:
Only the bellows control solenoid valve is ener-
gized, so the air coming from the kneeling air tank
is routed through air control valves, and up to front
air springs (Fig. 14). The height control valve is
bypassed during the up motion. However, the
down motion is achieved through the height con-
trol 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 along with the appropriate
system pneumatic diagram annexed in the
technical publication box provided with the
vehicle.