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Drive Clutch Operation
Drive clutches primarily sense engine RPM. The two
major components which control its shifting function are
the shift weights and the coil spring. Whenever engine
RPM is increased, centrifugal force is created, causing
the shift weights to push against rollers on the moveable
sheave, which is held open by coil spring preload. When
this force becomes higher than the preload in the spring,
the outer sheave moves inward and contacts the drive
belt. This motion pinches the drive belt between the spin-
ning sheaves and causes it to rotate, which in turn
rotates the driven clutch.
At lower RPM, the drive belt rotates low in the drive clutch
sheaves. As engine RPM increases, centrifugal force
causes the drive belt to be forced upward on drive clutch
sheaves.
Driven Clutch Operation
Driven clutches primarily sense torque, opening and
closing according to the forces applied to it from the drive
belt and the transmission input shaft. If the torque resis-
tance at the transmission input shaft is greater than the
load from the drive belt, the drive belt is kept at the outer
diameter of the driven clutch sheaves.
As engine RPM and horsepower increase, the load from
the drive belt increases, resulting in the belt rotating up
toward the outer diameter of the drive clutch sheaves and
downward into the sheaves of the driven clutch. This
action, which increases the driven clutch speed, is called
upshifting.
Should the throttle setting remain the same and the
vehicle is subjected to a heavier load, the drive belt rotates
back up toward the outer diameter of the driven clutch and
downward into the sheaves of the drive clutch. This action,
which decreases the driven clutch speed, is called
backshifting.
9924096 - 2013 RANGER RZR XP 900 / RZR XP 4 900 Service Manual
© Copyright 2012 Polaris Sales Inc.
CLUTCHING (PVT)
In situations where loads vary (such as uphill and downhill)
and throttle settings are constant, the drive and driven
clutches are continually shifting to maintain optimum
engine RPM. At full throttle a perfectly matched PVT
system should hold engine RPM at the peak of the power
curve. This RPM should be maintained during clutch
upshift and backshift. In this respect, the PVT system is
similar to a power governor. Rather than vary throttle
position, as a conventional governor does, the PVT
system changes engine load requirements by either
upshifting or backshifting.
PVT Break-In (Drive Belt / Clutches)
A proper break-in of the clutches and drive belt will ensure
a longer life and better performance. Break in the clutches
and drive belt by operating at slower speeds during the 10
hours as recommended (see Chapter 3 "Engine Break-In
Period"
for
break-in
example).
acceleration and high speed operation during the break-in
period.
Maintenance / Inspection
Under normal use the PVT system will provide years of
trouble
free
operation.
maintenance is required to keep the system operating at
peak performance. The following list of items should be
inspected
and
maintained
performance and service life of PVT components. Refer to
the troubleshooting checklist at the end of this chapter for
more information.
1. Belt Inspection.
2. Drive and Driven Clutch Buttons and Bushings,
Drive Clutch Shift Weights and Pins, Drive Clutch
Spider Rollers and Roller Pins, Drive and Driven
Clutch Springs.
3. Sheave Faces. Clean and inspect for wear.
4. PVT System Sealing. Refer to the appropriate
illustration(s) on the following pages. The PVT system
is air cooled by fins on the drive and driven clutch
stationary sheaves. The fins create a low pressure
area in the crankcase casting, drawing air into the
system through an intake duct. The opening for this
intake duct is located at a high point on the vehicle
(location varies by model). The intake duct draws
fresh air through a vented cover. All connecting air
ducts (as well as the inner and outer covers) must be
properly sealed to ensure clean air is being used for
cooling the PVT system and also to prevent water and
other contaminants from entering the PVT area. This
is especially critical on units subjected to frequent
water forging.
Avoid
aggressive
Periodic
inspection
and
to
ensure
maximum
6.3
6
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