Patent ID: 6840466

Claim:
A hydraulic control valve comprising: a piezoelectric actuator including a deformable element made of a material which produces a mechanical deformation under application of a voltage, said piezoelectric actuator being so designed that an increase in output force of said piezoelectric actuator results in a decrease in allowable applied energy to said piezoelectric actuator, which is caused by production of charges in said piezoelectric actuator as a function of the increase in output force of said piezoelectric actuator; and a hydraulic valve mechanism working to convert the deformation of said piezoelectric actuator into a hydraulic pressure to move a valve member hydraulically for opening and closing a fluid port selectively, said hydraulic valve mechanism being so designed that said piezoelectric actuator produces a maximum output force working to develop the hydraulic pressure when opening the fluid port through the valve member, the maximum output force decreasing after the fluid port is opened, said hydraulic valve mechanism including a first and a second piston, the first piston working to convert the deformation of said piezoelectric actuator into the hydraulic pressure which acts on the second piston to move the valve member, a diameter ratio of the first piston to the second piston being so determined that the maximum output force of said piezoelectric actuator when opening the fluid port is set smaller than one-half of the maximum possible output force of said piezoelectric actuator under application of a maximum working voltage to said piezoelectric actuator.