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Novel Fixed Pitch Continuously Variable Transmission for High Torque Applications

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.




I don't see this as "continuously variable" but rather more like incrementally variable. If I understand the design from the brief description, it is clever and should handle more torque.

Kenneth Hawthorn

To the comment above, I invite you to look more closely at the design, it is in fact,continuously variable. I would be happy to walk anyone through the design. My phone numbver is four zero eight four eight zero two nine zero two. The website with design notes is -Ken Hawthorn


Thank you for your response, I have no need to find out more, but perhaps others on here will take you up on your offer.



I browsed quickly the text and images from the web site, and PDF of the patent, almost the same, and cannot figure out how you actually change the ratio when there is no load on output (say all wheels off the ground).
What part (position Nr on some image) has to be moved to what direction in order to increase or decrease transmission ratio - this is the purpose of every variable transmission.
What is the expected maximum range of transmission ratios, compared to existing automatic transmission of comparable volume for a comparable engine power/torque?
That range is currently obicno about 3.4 for 1st gear, and 0.7 for 5th or 6th gear, ie Max/Min Ratio is about 5 (3.4/0.7).
In your text it only mentions transmission ratio change due to load, when it self-adjusts.

Is it possible at all with this transmission to set say 6 fixed transmission ratios, like some current CVTs allow (CVT on new Mitsu Lancer for one)?

Kenneth Hawthorn

I should clarify that to make the patent application as simple as possible I have removed any outside actuation of ratios from the drawings as they are not part of the IP. This omission is to keep the patent as broad as possible. There are only two new things in the FPCVT idea:
1) Using separate pitch lines to transmit power
2) The idea of the externally actuatable two way locking/freewheeling mechanism.
These two ideas together allow the use of standard roller chain in a CVT that can change rations under load.
In order to use the FPCVT in cars I would expect outside actuation to be necessary (I am happy to share a few ideas, but I think this is pretty straight forward). The purpose of the curved and straight slots is to as close as possible mimic the engine efficiency curve to reduce the size of the actuator required. You are quite correct that, as drawn, the FPCVT, without an external actuator, would not change ratios while the car was up on a stand with the tires off of the ground (except for a small change that would react to the inertia of the wheels). Does that answer both of your questions above?

Right now an I am trying to put together a few thousand dollars to prototype this idea (sans actuator) to prove that the design works. It is my hope to attract some interest in this design as early as possible to gain some engineering help, or some financial backing, so I can buy some engineering help. I don’t have any formal engineering training. I will proceed to build the prototype in any case, but feedback like yours is definitely appreciated. Anyone can contact me at four zero eight four eight zero two nine zero two.

Thank You for your comments, I am happy to carry on a conversation here or at the phone number above.

Kenneth Hawthorn

On your question of max ratios: The prototype will likely have a ratio range of 2:1 to 1:2. The max ratio change is a function of the allowable package size and the load. The reason the load comes into play is the length of the moment arm from the locking rollers to the centerline of the axle the sprocket spins on needs to be as large as possible while I am using softer materials on the prototype. The max ratio range would jump to 4:1 to 1:4 when I can shrink that sprocket diameter and use the same materials that are found in other roller ramp style overrunning clutches on the market today.
I think the ideal test bed for a full scale prototype would be a front wheel drive diesel. That configuration allows for easy placement of the FPCVT and would work nicely with the higher torque loads and lower rpm speeds in diesels.

Account Deleted

hi,Separate creator Ken Bush has been issued a US papers (Patent 7,713,154) on a Geosynchronous Adapt Continuously Inconstant Gear (FPCVT) premeditated for higher force applications. The FPCVT is the eldest positively engaging wheel that uses prescriptive roll chain that can modification diameters patch meshed, Bush says.
Fixed Rate ISA

gotto besaid

So simple now we see it - great work. The only thisng I would suggest is to try and have more point increments touching to enabel the design to be smalle for the same power and increase it,s life.
One again great idea hope it goes well from this stage - the hard stage of getting to market. Dave mc

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