Patent ID: 7435200

Claim:
A hydraulic pressure control apparatus of a belt-drive continuously variable transmission for an automotive vehicle, which employs a primary variable-width pulley of a driving pulley side, a secondary variable-width pulley of a driven pulley side, and a drive belt running in the primary and secondary pulleys, and whose shift is made by changing a radius of a contact circle of the drive belt of the driving pulley side and a radius of a contact circle of the drive belt of the driven pulley side by a primary pulley thrust, created by at least a primary pulley pressure applied to an adjustable flange of the primary pulley, and a secondary pulley thrust, created by at least a secondary pulley pressure applied to an adjustable flange of the secondary pulley, comprising: a vehicular information detector that detects engine-and-vehicle operating conditions; a hydraulic actuator that regulates the primary and secondary pulley pressures; and a control unit being configured to be electrically connected to the vehicular information detector and the hydraulic actuator, for calculating a command value of the primary pulley thrust and a command value of the secondary pulley thrust based on information about the engine-and-vehicle operating conditions, and for automatically controlling the hydraulic actuator responsively to the primary-pulley-thrust command value and the secondary-pulley-thrust command value; the control unit comprising a processor programmed to perform the following, (a) calculating a desired transmission ratio based on the information about the engine-and-vehicle operating conditions; (b) calculating a primary-pulley slip-limit pulley thrust, which is defined as a lower limit of the primary pulley thrust enabling torque transmission between the primary and secondary pulleys without slippage of the drive belt, and a secondary-pulley slip-limit pulley thrust, which is defined as a lower limit of the secondary pulley thrust enabling torque transmission between the primary and secondary pulleys without slippage of the drive belt, based on the information about the engine-and-vehicle operating conditions; (c) setting the primary-pulley-thrust command value to the primary-pulley slip-limit pulley thrust and calculating a desired secondary pulley thrust based on the desired transmission ratio, when a pulley ratio of the primary and secondary pulleys is greater than or equal to 1; and (d) setting the secondary-pulley-thrust command value to the secondary-pulley slip-limit pulley thrust and calculating a desired primary pulley thrust based on the desired transmission ratio, when the pulley ratio is less than 1.