9928487 R01 - 2018 RANGER XP 1000 Service Manual
© Copyright Polaris Industries Inc.
5.5
PVT SYSTEM OVERVIEW
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
spinning 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
resistance 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.
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 hour break-in period as recommended.
Refer to
Engine Break-In Period, page 3.8
for break-in
example). Pull only light loads. Avoid aggressive
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.
Periodic
inspection
and
maintenance is required to keep the system operating at
peak performance. The following list of items should be
inspected
and
maintained
to
ensure
maximum
performance and service life of PVT components. Refer
to
“PVT Troubleshooting”, page 5.35
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 illus-
tration (s) on the following pages. The PVT system is
air cooled by fins on the drive and driven clutch sta-
tionary 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 es-
pecially critical on units subjected to frequent water
forging.
