Page 393 - Manual Oficina Polaris Sportsman 570 2014 a 2016

P. 393

PVT SYSTEM

PVT SYSTEM OVERVIEW

GENERAL OPERATION toward the outer diameter of the drive clutch sheaves
and downward into the sheaves of the driven clutch. This
WARNING action, which increases the driven clutch speed, is called
upshifting.
All PVT maintenance or repairs should be performed Should the throttle setting remain the same and the
only by a certified Polaris Master Service Dealer (MSD) vehicle is subjected to a heavier load, the drive belt
technician who has received the proper training and rotates back up toward the outer diameter of the driven
understands the procedures outlined in this manual. clutch and downward into the sheaves of the drive clutch.
Because of the critical nature and precision This action, which decreases the driven clutch speed, is
balance incorporated into the PVT components, it is called backshifting.
absolutely essential that no disassembly or repair
be made without factory authorized special tools In situations where loads vary (such as uphill and
and service procedures. 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
The Polaris Variable Transmission (PVT) consists of PVT system should hold engine RPM at the peak of the
three major assemblies:
power curve. This RPM should be maintained during
1) The Drive Clutch clutch upshift and backshift. In this respect, the PVT
2) The Driven Clutch system is similar to a power governor. Rather than vary
throttle position, as a conventional governor does, the 5
3) The Drive Belt
PVT system changes engine load requirements by either
The internal components of the drive clutch and driven upshifting or backshifting.
clutch control engagement (initial vehicle movement),
clutch upshift and backshift. During the development of a MAINTENANCE / INSPECTION
Polaris ATV, the PVT system is matched first to the
engine power curve; then to average riding conditions Under normal use the PVT system will provide years of
and the vehicle’s intended usage. Therefore, trouble free operation. Periodic inspection and
modifications or variations of components at random are maintenance is required to keep the system operating at
never recommended. Proper clutch setup and careful peak performance. The following list of items should be
inspection of existing components must be the primary inspected and maintained to ensure maximum
objective when troubleshooting and tuning. performance and service life of PVT components. Refer
to the troubleshooting checklist at the end of this chapter
DRIVE CLUTCH OPERATION for more information.
Drive clutches primarily sense engine RPM. The two 1. Belt Inspection, Drive to Driven Clutch
major components which control its shifting function are Alignment, and Clutch Center Distance.
the shift weights and the coil spring. Whenever engine 2. Drive and Driven Clutch Buttons and Bushings,
RPM is increased, centrifugal force is created, causing Drive Clutch Shift Weights and Pins, Drive Clutch
the shift weights to push against rollers on the moveable Spider Rollers and Roller Pins, Drive and Driven
sheave, which is held open by coil spring preload. When Clutch Springs.
this force becomes higher than the preload in the spring,
the outer sheave moves inward and contacts the drive 3. Sheave Faces. Clean and inspect for wear.
belt. This motion pinches the drive belt between the 4. PVT System Sealing. Refer to appropriate
spinning sheaves and causes it to rotate, which in turn illustrations on the following pages. The PVT system
rotates the driven clutch. At lower RPM, the drive belt is air cooled by fins on the drive clutch stationary
rotates low in the drive clutch sheaves. As engine RPM sheave. The fins create a low pressure area in the
increases, centrifugal force causes the drive belt to be crankcase casting, drawing air into the system
forced upward on drive clutch sheaves.
through an intake duct. The opening for this intake
duct is located at a high point on the vehicle (location
DRIVEN CLUTCH OPERATION varies by model). The intake duct draws fresh air
through a vented cover. All connecting air ducts (as
Driven clutches primarily sense torque, opening and
closing according to the forces applied to it from the drive well as the inner and outer covers) must be properly
belt and the transmission input shaft. If the torque sealed to ensure clean air is being used for cooling
resistance at the transmission input shaft is greater than the PVT system and also to prevent water and other
the load from the drive belt, the drive belt is kept at the contaminants from entering the PVT area. This is
especially critical on units subjected to frequent
outer diameter of the driven clutch sheaves.
water fording.
As engine RPM and horsepower increase, the load from
the drive belt increases, resulting in the belt rotating up

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