Cvt System; Cvt Maintenance / Inspection; Drive Clutch Operation; Driven Clutch Operation - Polaris PREDATOR 50 2009 Manual

CVT SYSTEM

CVT SYSTEM
All CVT maintenance or repairs should be
performed only by a certified Polaris Master
Service Dealer (MSD) technician who has
received the proper training and understands
the procedures outlined in this manual. Because
of the critical nature and precision balance
incorporated into the CVT components, it is
absolutely essential that no disassembly or
repair be made without factory authorized
special tools and service procedures.
The Polaris Variable Transmission (CVT) consists of three
major assemblies: 1) The Drive Clutch; 2) The Driven Clutch;
and 3) The Drive Belt. The internal components of the drive
clutch and driven clutch control engagement (initial vehicle
movement), clutch upshift and backshift. During the
development of a Polaris ATV, the CVT system is matched first
to the engine power curve; then to average riding conditions and
the vehicle's intended usage. Therefore, modifications or
variations of components at random are never recommended.
Proper clutch setup and careful inspection of existing
components must be
troubleshooting and tuning.

CVT Maintenance / Inspection

Under normal operation the CVT 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 CVT
components. See "CVT Overheating / Diagnosis" on page 7.3.
for more information.
1. Drive clutch rollers and bushings. Driven clutch rollers,
pins, and spring.
2. Clutch sheave faces. Clean and inspect for wear.
3. CVT system sealing. The CVT system on 90cc models is
air cooled by fins on the drive clutch. The fins create a low
pressure area around the drive clutch, drawing fresh air in
through the intake duct. The opening for this intake duct is
located at a high point on the vehicle. All connecting air
ducts, as well as the clutch cover, must be sealed to ensure
clean air is being used for cooling the CVT system. This
also reduces the chance of water and other contaminants
entering the CVT area.
7.2
WARNING
the primary objective

Drive Clutch Operation

Drive clutches primarily sense engine RPM. The major
component which controls shifting function are the shift
centrifugal weights (rollers) inside the moveable sheave.
Whenever engine RPM is increased, centrifugal force is created,
causing the rollers to push against the cam plate and force the
moveable sheave toward 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. If belt speed is sufficient,
centrifugal friction shoes on the driven clutch overcome their
return spring pressure and swing outward against the
transmission drive hub, and the vehicle (if in gear) begins to
move.
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, changing
the ratio of the drive to driven clutch from low to high.

Driven Clutch Operation

CVT driven clutches primarily sense torque, but also react to
RPM, applying and retracting the friction shoes according to the
forces applied to it from the drive belt, while at the same time
reacting to the torque at the transmission input shaft. If the
torque resistance at the transmission input shaft is greater than
when
the load from the drive belt, the drive belt is kept at the outer
diameter of the driven clutch sheaves (low ratio).
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 torque sensing driven clutch will
close, forcing the drive belt back up toward the outer diameter
of the driven clutch. This also forces the belt downward into the
sheaves of the drive clutch. This action, which decreases the
driven clutch speed, is called backshifting.
In situations where loads vary and throttle settings are constant,
the drive and driven clutches are continually shifting to maintain
optimum engine RPM. At full throttle a perfectly matched CVT
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 CVT system is similar to a power
governor. Rather than vary throttle position, as a conventional
governor does, the CVT system changes engine load
requirements by either upshifting or backshifting.