Hydraulic system for forklift

A hydraulic system for a forklift in which hydraulic fluid is supplied from a hydraulic pump to a power steering cylinder for steering wheels in accordance with rotational operation of a handle, said system comprising:

• a handle angle sensor for outputting a rotational angle signal indicative of a rotational angle of a handle;
• a wheel angle sensor for outputting a wheel angle signal indicative of a steering angle of wheels;
• a steering valve connected between the hydraulic pump and the power steering cylinder;
• a solenoid valve for bypassing the hydraulic fluid supplied to the power steering cylinder through said steering valve;
• a main controller for calculating the rotation angular velocity of the handle based on the rotational angle signal from the handle angle sensor in a predetermined time period to control a discharge flow rate of the hydraulic pump;
• and
• a knob position controller for controlling said solenoid valve so as to converge into zero a deviation between a rotation angle of the handle from its neutral position obtained on the basis of the rotational angle signal and a wheel steering angle obtained on the basis of the wheel angle signal,
• said handle angle sensor outputting first and second pulse signals having a phase differential therebetween every time when the handle is rotated at a predetermined angle, and a third pulse signal when the handle is rotated one turn,
• said knob position controller detecting the neutral position of the handle based on the third pulse signal and the wheel angle signal from said wheel angle sensor, detecting a rotational direction of the handle based on the first and second pulse signals, and calculating a rotational angle of the handle from the neutral position.