Ratio limiting arrangement
View Patent ↗An arrangement is disclosed for providing an “end-stop” function for a variator in a continuously variable transmission. The variator ( 8 ) needs some arrangement for preventing its own drive ratio from going beyond a ratio limit. In accordance with the present invention, this is provided by means of a one-way clutch ( 22 or 24 ). The one-way clutch is coupled to both the variators input and its output, and is arranged to engage (lock up) when the variator reaches its ratio limit, so that the variator is prevented from going beyond the limits. The invention is particularly suited to use with transmissions which provide two regimes and a synchronous change between them.
1. A continuously variable transmission comprising a rotary transmission input and a rotary transmission output, a variator having a rotary variator input and a rotary variator output between which it is adapted to transfer drive at a continuously variable variator ratio, gearing forming a first drive path which couples the transmission input via the variator to a first shaft so that a first speed ratio, between the transmission input and the first shaft, is a function of the variator ratio and decreases with increasing variator ratio, and gearing forming a second drive path which couples the transmission input via the variator to a second shaft so that a second speed ratio between the transmission input and the second shaft, is a function of the variator ratio and increases with increasing variator ratio, there being a certain variator ratio (“synchronous variator ratio”) at which the speeds of the first and second shafts are equal, the transmission further comprising a selector arrangement to selectively couple either the first shaft or the second shaft to the rotary transmission output to provide first and second transmission regimes, and a one-way clutch arrangement which prevents the speed of the first shaft from exceeding the speed of the second shaft, and so prevents the variator drive ratio from going beyond the synchronous ratio.
2. A continuously variable transmission as claimed in claim 1 in which the selector arrangement comprises at least one regime clutch and the one-way clutch arrangement comprises at least one one-way clutch connected across the regime clutch to prevent a reversal in the relative rotation of its input and output.
3. A continuously variable transmission as claimed in claim 1 in which the selector arrangement comprises a first regime clutch for selectively coupling the first shaft to the transmission output shaft, and a second clutch for selectively coupling the second shaft to the transmission output shaft, the one-way clutch arrangement comprising a first one-way clutch connected across the first regime clutch and a second one-way clutch connected across the second regime clutch.
4. A continuously variable transmission as claimed in claim 1 in which the first drive path incorporates an epicyclic gear.
5. A continuously variable transmission as claimed in claim 1 in which both drive paths incorporate a torque limiting clutch.