Editing Continuously variable transmission (section)

=== Ratcheting ===
A ratcheting CVT uses a series of one-way [[clutch]]es or [[Ratchet (device)|ratchets]] that rectify and sum only "forward" motion. The on-off characteristics of a typical ratchet means that many of these designs are not continuous in operation (i.e. technically not a CVT), but in practice, there are many similarities in operation, and a ratcheting CVT is able to produce a zero-output speed from any given input speed (as per an Infinitely Variable Transmission). The drive ratio is adjusted by changing linkage geometry within the oscillating elements so that the summed maximum linkage speed is adjusted, even when the average linkage speed remains constant.

Ratcheting CVTs can transfer substantial torque because their static friction actually increases relative to torque throughput, so slippage is impossible in properly designed systems. Efficiency is generally high because most of the dynamic friction is caused by very slight transitional clutch speed changes. The drawback to ratcheting CVTs is the vibration caused by the successive transition in speed required to accelerate the element, which must supplant the previously operating and decelerating power-transmitting element.

The design principle dates back to before the 1930s, with the original design intended to convert [[Rotation around a fixed axis|rotary motion]] to [[Oscillation|oscillating motion]] and back to rotary motion using roller clutches.<ref>{{cite book |last1=Franklin |first1=D. |title=Ingenious mechanisms for designers and inventors ... |date=1930 |publisher=Industrial Press |isbn=0-8311-1084-8 |pages=343–345 |edition=1st}}</ref> This design remains in production as of 2017, for use with low-speed electric motors.<ref>{{cite web |url=http://www.zero-max.com/products/drives/drivesmain.asp |title=drives |website=zero-max.com |access-date=19 September 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090301191004/http://www.zero-max.com/products/drives/drivesmain.asp |archive-date=1 March 2009}}</ref> An example prototyped as a bicycle transmission was patented in 1994.<ref>{{cite web |title=US patent US5516132A: Variable-speed transmission |url=https://patents.google.com/patent/US5516132 |access-date=17 July 2020 |language=en |date=22 July 1994}}</ref> The operating principle for a ratcheting CVT design, using a [[Scotch yoke]] mechanism to convert rotary motion to oscillating motion and [[non-circular gear]]s to achieve uniform input to output ratio, was patented in 2014.<ref>{{cite web |title=US patent US9970520B2: Continuous variable transmission with uniform input-to-output ratio that is non-dependent on friction |url=https://patents.google.com/patent/US9970520B2 |access-date=17 July 2020 |language=en |date=18 March 2014}}</ref>