Page E-1
Repair and Service Manual
B
B
CONTINUOUSLY VARIABLE TRANSMISSION (CVT)
Read all of Section B and this section before attempting any procedure. Pay particular attention to Notices, Cautions, Warnings and Dangers.
Fig. 1 Continuously Variable Transmission System (CVT)
GENERAL
Power transmission from the engine to the rear axle is
by means of a continuously variable transmission (CVT).
The CVT consists of two matched clutch units joined by
a drive belt (Ref. Fig. 1). The engine mounted drive
clutch is a centrifugal unit that responds to engine speed
and the rear axle mounted driven clutch is a load sens-
ing unit.
CLUTCHES
Drive Clutch
When the accelerator is depressed, the engine speed is
increased which causes the cams (weights) within the
centrifugal drive clutch to move outwards and force the
moveable sheave inwards. The drive belt is engaged by
the clutch sheaves and begins to rotate. At this point,
the ratio between drive and driven clutch is approxi-
mately
3:1.
As the engine speed continues to rise, the drive clutch
sheave continues to move inwards forcing the drive belt
to the outer diameter of the drive 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 is
decreased and the cams exert less pressure on the
moveable sheave which is forced outwards against the
cams by a compression spring. The drive belt disen-
gages from the clutch sheave when engine speed is
reduced to the point where the cams exert less force
than the spring.
Driven Clutch
The driven clutch sheaves are closed at rest which
results in the drive belt being held at the outer diameter
of the driven clutch. The driven clutch has no weights
but is held closed by a torsion spring which is joined to
the moveable sheave and a torque ramp (cam) that is
attached to the fixed sheave. The moveable sheave
slides against the cam with the three points of contact
provided by low friction ‘buttons’.
As the drive belt starts to rotate, the driven clutch starts
to rotate. As the speed of the drive clutch increases and
the belt starts to climb the sheaves, the driven clutch
responds by being forced open in order to permit the
belt to ride lower in the driven clutch sheaves. The
sheaves overcome the pressure exerted by the torsion
spring and cam.
As the driven clutch slows, the belt rides lower in the
drive clutch sheaves. The driven clutch compensates by
closing in response to the torsion spring and cam.
Starter/Generator Belt
Drive Clutch
Driven Clutch
Summary of Contents for 625619 2012
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