All Mechanical CVT for the 21st Century

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A New Approach to a Continuously Variable Transmission


Totally mechanical design holds promise for improved

performance


Totally mechanical design holds promise for improved performance

Randy Frank, Contributing Editor -- Design News, February 25, 2008

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Dating back to the late 19th century, continuously variable transmissions have started to appear on several recent vehicles. Most designs rely on two V-shaped groove pulleys, one movable and one fixed, and hydraulic actuation to change the space between the grooves on the movable pulley. The belt rising from a low to a higher position changes the gear ratio providing a stepless change. This stepless motion provides better alignment to the engine's operating curve and results in higher fuel economy, the driving force for today's increased CVT usage. Inventor John Pellegrino has a concept for a totally mechanical design he says has several advantages over belt-driven CVTs, including better efficiency and reliability.
Pellegrino's design consists of a spur gear with arms that are capable of moving to maintain the proper pitch at the engagement point of the output gear. A cam-driven mechanism changes the spacing between the arms of the spur gear by using tapered pins that are inserted or withdrawn to adjust the spacing between each of the arms. To produce the desired mechanical movement, a series of cams will move using ball bearings or cam followers to reduce friction. The cam-driven mechanism operates by using the gearshift lever to move the tapered pins to the appropriate position and achieve continuous variation without engaging a different gear set.
The purely mechanical design does not require additional electrical or hydraulic mechanisms or interfaces that would decrease its efficiency. Preliminary analysis by the inventor and external reviews indicate this approach could provide an alternative to existing belt design CVTs. “It's cam operated, the cam followers are all ball bearing or roller bearing devices, which have extremely good efficiency ratings,†says Pellegrino. “The crux of the design is the design of the cam mechanisms that will produce the desired result. That's the tricky part.†Although this part is not easy, Pellegrino insists he has a pretty good scheme for how the cam mechanism should work. It just needs the development effort.
Currently not covered by patent protection, Pellegrino says he feels that with the support of a major player in the industry, high-level patent protection could be awarded that would avoid the work-arounds that can easily occur from an individually patented design. Pellegrino's objective is to get that support, develop a working prototype and move forward.
A single gear set, A, consisting of an adjustable input spur gear that meshes with a non-adjustable internal tooth ring gear provides the basis for a totally mechanical continuously variable transmission. The diameter of the spur gear changes as tapered pins are inserted or withdrawn, B.