Patent ID: 7041018

Claim:
A hydraulic control system for a belt-drive continuously variable transmission (CVT) of a vehicle, the CVT including a belt, the hydraulic control system comprising: an oil pump operative to produce an oil pressure and an oil flow amount which are supplied to the CVT; a pressure regulator valve operative to regulate the oil pressure produced by the oil pump; a belt lubricating oil supply passage for supplying oil to the belt on a downstream side of the pressure regulator valve; engine operating condition detecting means for detecting an engine operating condition and generating an engine operating condition signal, the engine operating condition detecting means including an oil temperature sensor operative to: detect a temperature of the oil in the CVT; and generate an oil temperature signal indicative of the oil temperature detected; an oil cooler disposed on a downstream side of the pressure regulator valve; a lubricating oil supply path for supplying the oil to lubrication parts in the CVT, the lubricating oil supply path being disposed on a downstream side of the oil cooler and including the belt lubricating oil supply passage; line pressure detecting means for: detecting a line pressure between the oil pump and the pressure regulator valve; and generating a line pressure signal indicative of the line pressure detected; and a controller for controlling the oil flow amount based on the engine operating condition signal, which is generated based on the oil temperature signal and the line pressure signal, the controller being programmed to: calculate a CVT input torque based on the engine operating condition signal; calculate a required belt lubricating oil flow amount to be supplied to the belt on the basis of the engine operating condition signal and the CVT input torque; calculate a required cooler oil flow amount to be supplied to the oil cooler from the required belt lubricating oil flow amount on the basis of a predetermined oil distribution ratio of an oil flow amount to be supplied to the belt lubricating oil supply passage to an oil flow amount to be supplied to the lubricating oil supply path; calculate a cooler input pressure required to supply the oil to the oil cooler on the basis of the required cooler oil flow amount; determine a minimum speed of the oil pump that is required to provide the cooler input pressure, on the basis of the oil temperature signal and the line pressure signal; and control the oil pump at the minimum speed.