Hydraulic pressure control device for continuously variable transmission

1. A hydraulic fluid pressure control device comprising:

a hydraulic pressure regulating section that selectively supplies hydraulic pressure to a clutch operatively disposed between an engine and a continuously variable transmission to selectively transmit torque from the engine to a primary pulley of the continuously variable transmission;

a rotational movement detecting section that detects a rotational movement of the primary pulley when the hydraulic pressure acting on the clutch by the hydraulic pressure regulating section reaches a torque transmission point in which the clutch switches from an engaged state to a disengaged state such that the primary pulley stops rotating, and that outputs a signal during a change of the clutch from the engaged state to the disengaged state to indicate the torque transmission point; and

a control section that estimates a clutch engagement hydraulic pressure at which the clutch is switched to the disengaged state when a vehicle is stopped and in a running range based on the hydraulic pressure acting on the clutch by the hydraulic pressure regulating section when the rotational movement detecting section initially detects the torque transmission point,

the control section further controls the hydraulic pressure to change the clutch from the engaged state to the disengaged state when the vehicle is stopped and in the running range, so that the torque from the engine does not rotate a secondary pulley of the continuously variable transmission via a drive belt wrapped around the primary pulley and the secondary pulley.

2. The hydraulic fluid pressure control device according to claim 1 , wherein

the control section is further configured to repeat estimating of the clutch engagement hydraulic pressure for a prescribed number of times prior to setting a final value for the clutch engagement hydraulic pressure.

3. A hydraulic pressure control method comprising:

selectively supplying hydraulic pressure to a clutch operatively disposed between an engine and a continuously variable transmission to selectively transmit torque from the engine to a primary pulley of the continuously variable transmission;

detecting rotational movement of the primary pulley when the hydraulic pressure acting on the clutch reaches a torque transmission point in which the clutch switches from an engaged state to a disengaged state such that the primary pulley stops rotating;

outputting a signal during a change of the clutch from the disengaged state to the engaged state so that the signal indicates the torque transmission point in which initial movement of the primary pulley of the continuously variable transmission occurs;

estimating a clutch engagement hydraulic pressure at which the clutch is switched to the from the engaged state to disengaged state when the vehicle is stopped and in the running range based on the hydraulic pressure acting on the clutch when the signal is initially detected indicating the torque transmission point; and

controlling the hydraulic pressure to the clutch to a designated pressure that is no greater than the clutch engagement hydraulic pressure corresponding to the torque transmission point, when the vehicle is stopped and in the running range based on the clutch engagement hydraulic pressure that was estimated so that the torque from the engine does not rotate a secondary pulley of the continuously variable transmission via a drive belt wrapped around the primary pulley and the secondary pulley.