Arrangement for control of a continuously variable transmission

Abstract

An arrangement for controlling a variator in a continuously variable transmission such as a vehicle transmission is described. The arrangement comprises a user operable ratio control part such as a lever and a device for operatively coupling the ratio control part to a movable torque transfer part of the variator such as its rollers. The coupling device is, in the particular embodiment described, a hydro-mechanical arrangement. By moving the user operable ratio control part, the user exercises control over the variator ratio. In accordance with the invention the arrangement further comprises a torque release device such as a valve which is operable by the user to decouple the ratio control part from the movable torque transfer part. By doing so, the torque release device offers functionality which is in some ways analogous to that of a clutch in a conventional stepped ratio vehicle transmission.

Description

technical field [0001] The invention relates to the control of continuously variable transmissions. Background technique [0002] Conventional motor vehicle transmissions with manual, step-ratio transmissions typically have a user-operable clutch between the engine and transmission for engaging / disengaging the engine and transmission. When the vehicle starts, that is, when it leaves a standstill, there is inevitably an initial mismatch in speed between the transmission input and the engine output, and by causing the clutch to slip during this phase, the driver applies torque to the transmission so that the vehicle can be accelerated without imposing an unbearable load on the engine that would cause the engine to stall. With conventional automatic, stepped-ratio transmissions, the initial mismatch of speeds is accommodated through a torque converter. Clutches and torque converters are examples of what is referred to herein as a "launch device." [0003] In some continuousl...

AI Technical Summary

Problems solved by technology

In practice, except for very light vehicles, the required forces related to the torque to which the transmission is subjected prove to be too large to be comfortably provided by the user

Achieving gear neutral in such a configuration can also be problematic because any slight deviation in the position of the torque transmitting components from that required for gear neutral can cause the transmission to use very low gear ratios, even at low wheel speeds Also potentially causing large "slip torque"

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