Engine braking system for continuously variable transmission

Abstract

A continuously variable transmission (CVT) is disclosed which is operable in a first direction to transfer power from a power source to ground engaging members of a vehicle, and in a second direction where the ground engaging members brake and/or drive the engine. The CVT has a braking assembly having a thrust member positioned over a drive clutch shaft and adjacent an outer sheave of the drive clutch. A flanged sleeve is operatively coupled to the drive clutch shaft and generally positioned intermediate the inner and outer sheaves of the drive clutch, with a portion of the flanged sleeve being adjacent the thrust member. The flanged sleeve is fixed relative to the drive clutch shaft when operating in the first direction and is cooperable with the thrust member to move the flanged member axially relative to the drive clutch shaft and towards the inner sheave when operating in the second direction.

What is claimed is: 
     
         1 . A continuously variable transmission (CVT), comprising:
 a drive clutch having inner and outer sheaves rotatably coupled to a drive clutch shaft;   a driven clutch having inner and outer sheaves rotatably coupled to a driven clutch shaft;   one of the sheaves having a helix fixed to the sheave, the helix having helical surfaces, and the other of the sheaves having engagement members cooperating with the helical surfaces to effect movement of the two sheaves relative to each other; and   the one sheave being comprised of a first material having a density lower than 4 gr/cc and the helix is comprised of a second material having a density greater than 4 gr/cc.   
     
     
         2 . The CVT of  claim 1 , wherein the one sheave is cast aluminum. 
     
     
         3 . The CVT of  claim 1 , wherein the helix is forged steel. 
     
     
         4 . The CVT of  claim 3 , wherein the helix is coupled to the one sheave. 
     
     
         5 . The CVT of  claim 2 , further comprising a driven clutch shaft coupled to the outer sheave of the driven clutch. 
     
     
         6 . The CVT of  claim 5 , wherein the driven clutch shaft is steel and the one sheave is cast to the driven clutch shaft.