|A Fixed Pitch Continuously Variable Transmission (FPCVT) assembly with two FPCVT units connected in series. Source: Ken Hawthorn. Click to enlarge.
Independent inventor Ken Hawthorn has been issued a US patent (Patent# 7,713,154) on a Fixed Pitch Continuously Variable Transmission (FPCVT) designed for higher torque applications. The FPCVT is the first positively engaging sprocket that uses standard roller chain that can change diameters while engaged, Hawthorn says.
Earlier attempts to use this approach have been frustrated by the inability to have multiple points of engagement on a sprocket that carries a roller chain and is still able to expand and to contract smoothly. The sprocket will force the chain to skip when the sprocket contracts in pitch diameter and it will not be able expand in pitch diameter at all because it is locked into the chain.
Further, even if the sprocket was able to expand and contract smoothly in pitch diameter, while engaged with a chain, its teeth would not be able to reengage the chain smoothly on each rotation if there was any ratio change while those teeth were unengaged
To address these problems, the FPCVT has only two points of contact per chain, one on the power side and one on the load side allowing for ratio shifts while positively engaged. Multiple chains provide multiple contact points to keep the power and load sides connected during a complete rotation. The Power Sprocket design also allows for smooth re-engagement of the chain.
While most push belt type CVTs fail at around 300 N·m (221 lb-ft) of torque, he says, the FPCVT in this patent will be best suited for the market of 300 N·m+ engines. This is exactly the market that has been affected least by drive train innovations in the last decades and would benefit the most from CVT technology.
Hawthorn is looking for funding and support to build a prototype.