Read all of SAFETY and this section before attempting any procedure. Pay particular attention to Notices, Cautions, Warnings and Dangers.
99
Repair and Service Manual
668061
CONTINUOUSLY VARIABLE TRANSMISSION (CVT)
GENERAL
Power is transfered from the engine to the rear axle by
the Continuously Variable Transmission (CVT). The CVT
consists of two matched clutch units joined by a trans-
mission belt. The engine mounted primary clutch is a
centrifugal unit that responds to engine speed. The rear
axle mounted secondary clutch is a load sensing unit.
CLUTCHES
Primary Clutch
When the accelerator is pressed, the engine speed
increases which causes the cam weights within the cen-
trifugal primary clutch to move outward. This forces the
movable sheave inward. The transmission belt is
engaged by the clutch sheaves and begins to rotate. At
this point, the ratio between primary and secondary
clutch is approximately 3:1.
As the engine speed rises, the primary clutch sheave
continues to move inward forcing the transmission belt to
the outer diameter of the primary clutch sheaves which
increases the speed of the belt. The ratio is greatly
decreased and provides maximum speed.
When the accelerator is released, the engine speed
decreases and the cams exert less pressure on the mov-
able sheave, which is forced outward against the cams
by a compression spring. The transmission belt disen-
gages from the clutch sheave when engine speed is
reduced to the point where the cams exert less force
than the spring.
Secondary Clutch
The secondary clutch sheaves are closed at rest which
results in the transmission belt being held at the outer
diameter of the secondary clutch. The secondary clutch
has no weights but is held closed by a torsion spring
which is joined to the movable secondary assembly.
As the transmission belt starts to rotate, the secondary
clutch starts to rotate. As the speed of the primary clutch
increases and the belt starts to climb the sheaves, the
secondary clutch responds by being forced open in order
to permit the belt to ride lower in the secondary clutch
sheaves. The sheaves overcome the pressure exerted
by the torsion spring and cam.
As the secondary clutch slows, the belt rides lower in the
primary clutch sheaves. The secondary clutch compen-
sates by closing in response to the torsion spring and
cam.
Increased Load
When a vehicle traveling at governed speed begins to
climb a grade or is subjected to other increased load con-
ditions, a change in wheel speed is detected by the
clutch system and the transmission belt seeks a position
where it can achieve adequate friction to overcome the
load change. The belt moves outward on the secondary
clutch, which closes due to the torsion spring moving the
movable sheave against the torque ramps. The move-
ment of the transmission belt overcomes some of the
centrifugal force exerted by the cams in the primary
clutch. This forces the belt lower into the primary clutch
which increases the drive ratio. This ‘down shifting’
applies more torque to the rear axle without a significant
change to the engine speed.
Equilibrium
The CVT functions because the primary and secondary
clutches maintain equilibrium. Clutch sets are tuned to
the vehicle that they are designed to operate. Changes in
vehicle weight or desired performance characteristics
require that both clutches be tuned to the needs of the
vehicle and remain compatible with each other.
Summary of Contents for Stampede 900 2017
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