초록 ▼

System and method for controlling a continuously variable transmission having a pair of variable-diameter pulleys disposed on input and output shafts, and a corresponding pair of hydraulic cylinders to change effective diameters of the pulleys. A speed ratio control valve assembly is used to control

System and method for controlling a continuously variable transmission having a pair of variable-diameter pulleys disposed on input and output shafts, and a corresponding pair of hydraulic cylinders to change effective diameters of the pulleys. A speed ratio control valve assembly is used to control flows of a fluid to and from one of the cylinders. The control valve assembly is selectively placed in one of three states consisting of a first state for feeding the fluid to the one cylinder, a second state for discharging the fluid from the one cylinder, and a third state for restricting the flow to or from the one cylinder. The first and third states are alternately established while a ratio of an operating time in the first state to that in the third state is changed, for controlling a rate of flow of the fluid into the one cylinder, and the second and third states are alternately established while a ratio of operating time in the second state to that in the third state is changed, for controlling a rate of flow of the fluid from the one cylinder, whereby the speed ratio of the transmission is continuously varied by the one cylinder under control of the speed-ratio control valve assembly.

대표청구항 ▼

A hydraulic control system for controlling a speed ratio of a hydraulically-operated continuously variable transmission of a vehicle, having (1) an input shaft operatively connected to an engine of the vehicle (2) an output shaft operatively connected to an engine of the vehicle, (3) a pair of varia

A hydraulic control system for controlling a speed ratio of a hydraulically-operated continuously variable transmission of a vehicle, having (1) an input shaft operatively connected to an engine of the vehicle (2) an output shaft operatively connected to an engine of the vehicle, (3) a pair of variable-diameter pulleys mounted on the input and output shafts, respectively, (4) a transmission belt connecting the pair of variable-diameter pulleys, and (5) a pair of hydraulic cylinders for changing an effective diameter of the pair of pulleys, respectively, the hydraulic control system including a speed-ratio control valve assembly associated with one of said hydraulic cylinders, the control valve assembly being selectively placed in one of three states of operation consisting of a first state in which a pressurized fluid is fed to said one of the hydraulic cylinders, a second state in which the fluid is discharged from said one hydraulic cylinder, and a third state in which the feed or discharge flow of the fluid to or from said one hydraulic cylinder is restricted, wherein the improvement comprises: detecting means for detecting an actual value of a variable to be controlled, such as a speed of the engine or a speed ratio of the transmission; first determining means for determining a target value of said variable, based at least on a currently required output of the engine and according to a predetermined relation between said target value and said required output; second determining means for determining a difference between said target value and said actual value of said variable to be controlled; and control means for controlling the operation of said speed-ratio control valve assembly so that said difference is reduced; said speed-ratio control valve assembly comprising a first and a second solenoid connected to said control means, said control means controlling both of said first and second solenoids to establish said third state, said control means selectively controlling said first solenoid to select one of said first and second states, and selectively controlling said second solenoid to permit a flow of said fluid to or from said one of the hydraulic cylinders in said first or second state, or restrict said flow in said third state, said control means establishing said first and third states in an alternate fashion while changing a ratio of an operating time in said first state to that in said third state, for controlling a rate of flow of said fluid into said one hydraulic cylinder in accordance with said difference, said control means establishing said second and third states in an alternate fashion while changing a ratio of an operating time in said second state to that in said third state in accordance with said difference, for controlling a rate of flow of said fluid from said one hydraulic cylinder, whereby the speed ratio of said continuously variable transmission is continuously varied by said one hydraulic cylinder under control of said speed-ratio control valve assembly.