Engine Braking System (Ebs); One-Way Clutch; Driven Clutch Spring; High Elevation Setup - Polaris Magnum 2x4 Service Manual

Theory Of Operation
CLUTCHES
Engine Braking System (EBS)
The Engine Braking System (EBS) combines the standard "no-shift" feature of the Polaris Variable Transmission
(PVT) system with the added benefit of engine braking. Outwardly, both drive and driven clutch resemble those
used in a standard PVT system, however, there are some important differences in the EBS clutches:
• Belt Deflection - It's important to note that the belt is always "tight" in an EBS system. Belt deflection is not
adjustable. Consequently, there are no shims in the driven clutch for changing drive belt deflection.
• Special Drive Belt - The bottom side of the belt is grooved for better contact with the one-way clutch (A).
• One-Way Clutch One-way clutch (A) located on the drive clutch shaft is the key to system operation.
In a standard PVT system, engine braking occurs briefly on deceleration until engine RPM falls below belt
engagement speed and the drive clutch returns to the neutral position (sheaves open). At this point the drive
belt is no longer engaged with the drive clutch, and no further engine braking occurs.
Drive clutch operation is the same on a machine equipped with EBS at engine speeds above belt engagement.
However, the difference with EBS is evident when engine RPM is below engagement speed and the drive clutch
sheaves are open in the neutral position. In a standard PVT system, the belt is loose on the drive clutch shaft
when the clutch is disengaged due to the nominal belt deflection of 1
1/4"
(loose belt). If the vehicle is moving
downhill or coasting, the belt simply freewheels on the drive clutch shaft and engine braking does not occur.
With EBS, the belt is tight and engaged with the one-way clutch. If the vehicle is moving downhill or coasting,
the drive train turns the driven clutch, belt, and one way clutch in the direction of engine rotation. When
the one-way clutch rotational speed exceeds drive clutch rotational speed, the one-way clutch locks to the
drive clutch shaft, and engine braking occurs. Essentially, the driven clutch has become the "driving" clutch.
Engine braking will continue until drive clutch speed exceeds one-way clutch speed, or until the throttle is
applied and engine RPM reaches clutch engagement speed, lifting the belt off the one-way clutch.
When the engine is idling and the vehicle is at rest, the one-way clutch simply "freewheels" on the drive clutch
shaft.
One-way clutch locks to shaft
in forward direction only.
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Drive Clutch Rotation
When the forward rotational speed of the one-way
clutch (A) exceeds the speed of the engine (and
drive clutch), the one-way clutch locks to the drive
clutch shaft, and engine braking occurs.
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• Driven Clutch Spring - Unlike a standard PVT driven clutch spring, the EBS driven clutch spring has no
torsional wind. It is a compression spring only. The only difference between a 2-stroke and a 4-stroke EBS
kit is the color (and tension) of the driven spring. Like the EBS drive clutch, the driven clutch also utilizes a
one-way clutch, which locks to the shaft during engine braking. To check it, remove the belt and try to rotate
the stationary sheave counterclockwise (as viewed from the left side of the machine). The sheave should lock
to the shaft when rotated counterclockwise, and turn freely when rotated clockwise.
• High Elevation Setup - As with a standard PVT system, calibration changes are required for optimum
performance at elevations above 3000 feet (900 meters). EBS clutch setup is the same as a standard PVT
system for a given model. For example, if you install an EBS kit on a Magnum 4x4, use the drive clutch setup
information provided for a Magnum 4x4 with standard PVT. Disregard the driven clutch setup information (the
EBS driven spring has no torsional wind).
5/98 6.31
Polaris Industries Inc.