Importance

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Abstract

The invention concerns an arrangement for control of a continuously variable transmission. The transmission includes a variator (10) having a movable torque transfer part (rollers 18) whose position corresponds to a variator drive ratio. A hydraulic actuator (28) is arranged to exert an adjustable force on the torque transfer part. The transmission further comprises a flow control arrangement which is arranged to receive as control inputs (a) the current position of the torque transfer part and (b) a demanded position for it. The demanded position may for example be determined by driver input. The flow control arrangement is adapted to supply through a supply outlet which communicates with the hydraulic actuator a flow of fluid which is modulated in accordance with an error between the two control inputs. The flow of fluid increases with increasing error. A relief passage (110) leads from the said outlet to a pressure sink and is constricted so that fluid flow through it results in a pressure at the hydraulic actuator which is greater than that of the sink by an amount which corresponds to the rate of flow through the relief passage. The result is a mode of control of the transmission which possesses some of the advantages of both torque and ratio control.

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First Claim