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10 Posts
Discussion Starter · #1 ·
Trying to figure out an issue............

How does the secondary clutch work?
What is it's purpose with regards to the CVT and speed?
Does the belt force the sheaves open and engage the clutch or does the opposite happen?

Thanks so much.

21 Posts
I'll take a quick, simplified stab at it.

The drive system consists of the primary sheaves, belt, secondary sheaves, clutch and final drive.

  • The primary sheaves are connected to the engine crankshaft, as such they always spin the same speed as the crank.
  • The belt connects the primary (drive) sheaves to the secondary (driven) sheaves, it transfers power to the secondary sheaves any time the engine is running.
  • The secondary (driven) sheave also spins any time the engine is running.
  • The clutch is mounted on the secondary sheave, again it is always spinning when the engine is running.
  • The clutch housing (sometimes called the clutch bell) is splined to the input shaft of the final drive. It is stationary until the vehicle is moving.
  • Engine off or at idle the Primary sheave is "open", this is the position that provides lowest gear ratio (like a small front sprocket on a bicycle). There are weights (rollers or sliders) in the sheave near the center. As engine RPM increases centrifugal force sends the weights towards the outer circumference of the sheave. The weights ride on ramps within the sheave, as they move outward they close the sheave making the diameter the belt rides on larger (like shifting the front sprocket on a 10 speed bicycle).
  • Engine off or at idle the Secondary sheave is closed, again the position that provides the lowest gear ratio (like a large rear sprocket on a bicycle). The sheaves are held closed by a coil spring. As engine RPM increases and the front sheaves begin closing, the drive belt forces the rear sheaves to open resulting in a smaller diameter.
  • In summary, when the centrifugal force of the weights moving outward in the primary sheaves overcomes the spring in the secondary sheaves the ratio changes (upshifts).
  • As stated the clutch is mounted to the secondary sheave. The clutch shoes are each pinned to the body on one end and held down by a spring on the other end. At low RPM the shoes are not in contact with the clutch housing and not transmitting any torque. As the PRM of the rear sheave increases, centrifugal force drives the shoes outward and into contact with the clutch housing. Since the housing is splined to the input shaft of the final drive, torque is transmitted to the rear wheel and you're on your way.
  • The belt simply transfers power from the primary to secondary sheaves as well as facilitating the ratio change on the secondary sheave.
Hope this helps, what's the issue you're trying to figure out?

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