CONTINUOUSLY VARIABLE TRANSMISSION

摘要

The present invention provides a continuously variable transmission having a variator (5) comprising input discs (2) coupled to an input shaft (12) and an output disc (3) providing a rotary variator output. The input and output discs are mounted for rotation about a common axis and at least one roller (4) is arranged between the discs to transfer drive from one to the other at a continuously variable variator drive ratio. The roller is mounted in a carrier (30) in a manner which permits it to spin about its own axis and to tilt relative to the disks to vary the variator drive ratio. A hydraulic actuator (22) is arranged to apply to the carrier (30) a reaction force determined by a hydraulic pressure difference acting on the actuator. The reaction force opposes a traction force applied to the roller (4) by the action of the discs (2, 3). Power-recirculation gearing (6), preferably in the form of planetary gearing, receives as inputs the rotation of the input shaft (12) and the rotary variator output, and produces an output speed which is a function of both its inputs. The transmission further comprises a low / high switching mechanism (10) which comprises a low clutch L and a high clutch H and which serves to switch between (a) a low regime in which the low clutch is engaged and the output of the power- recirculation gearing is transmitted to an output shaft and (b) a high regime in which the high clutch is engaged and rotation of the variator output is transmitted to the output shaft. The direction of the reaction force of the hydraulic actuator is reversed during switching between low and high regime. In accordance with the invention, the transmission further comprises an engagement control (37) which begins to engage the disengaged clutch (H or L) when the transmission reaches a condition at which regime change is to be initiated. A reaction force switching control (38) begins reversal of the direction of the reaction force while the disengaged clutch is being engaged. A rapid and potentially smooth regime change is achieved. In a particularly preferred embodiment, a one-way clutch is provided between the input-side member of the high clutch and an input-side member of the low clutch, ensuring that the speed of the latter cannot become greater than the speed of the former.