7.9
CLUTCHING
CENTRIFUGAL DRIVE SYSTEM
THEORY OF OPERATION
The graph illustrates what occurs in a properly tuned
snowmobile drive system during an idle speed to WOT (wide
open throttle) pull. Note that the shift out overrev occurs for a
brief amount of time and drops back to the desired engine
operating RPM. The low and high ratio lines are a function of
component design.
NOTE: Shift out overrev is not detrimental to overall
efficiency of the drive system as long as the RPM
drop does not fall below the desired operating RPM.
The use of the new drive system technologies,
tighter tolerance components and refined drive
system calibration in Polaris snowmobiles has
virtually eliminated shift out overreving.
DRIVE CLUTCH
OPERATION
The drive, or primary, clutch is an RPM sensing device. The
main functions of the drive clutch is to control the neutral
RPM speed, initial engagement RPM, and desired engine
operating RPM. The drive clutch works by using the principle
of centrifugal force to react to engine RPM. At idle speed, the
moveable sheave is held open by the drive spring pre-load
force. As engine speed increases, the centrifugal force
generated by the clutch weights will overcome the drive spring
pre-load force, and begin to close the moveable sheave. This
action engages, or “pinches" the drive belt.
In a properly tuned clutch, the desired operating RPM should
be reached immediately after clutch engagement under full
throttle (WOT) conditions. The desired engine operating RPM
is the recommended operating RPM listed for each model.
This information can be found in each models' general
specification table. To ensure optimum power, the
recommended operating RPM must be maintained throughout
the upshift and backshift modes.
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