Patent ID: 7308789

Claim:
A hydraulic cylinder suspension method for use in a hydraulic drive system comprised of a hydraulic cylinder driving a working equipment and having a large chamber and a small chamber to which hydraulic fluid from a hydraulic pump is supplied, a control valve allowing the hydraulic fluid in the hydraulic pumps to be supplied to the hydraulic cylinder and returning the hydraulic fluid from the hydraulic cylinder to a tank, an operation lever for generating an operation signal to drive the working equipment, a controller changing the operational signal and generating a control signal for controlling the control valve, a valve drive unit controlling the control valve according to the control signal from the controller, and a pressure detection means mounted on the large chamber of the hydraulic cylinder and detecting operational pressure on the large chamber, the method comprising the steps of: receiving the operation signal of the operation lever and determining whether the hydraulic cylinder makes a sudden stop; receiving a pressure signal from the pressure detection means mounted on the large chamber of the hydraulic cylinder; if the hydraulic cylinder makes the sudden stop, determining whether the hydraulic cylinder is being extended or compressed; and if the hydraulic cylinder makes the sudden stop while the hydraulic cylinder is being extended, supplying the hydraulic fluid to the large chamber of the hydraulic cylinder for a predetermined amount of time starting from a point where the pressure signal reached a minimum for the first time, and returning the hydraulic fluid in the small chamber to the tank, while supplying the hydraulic fluid to the small chamber of the hydraulic cylinder for a predetermined amount of time starting from a point where the pressure signal reached a maximum for the first time, and returning the hydraulic fluid in the large chamber to the tank; if the hydraulic cylinder makes the sudden stop while the hydraulic cylinder is being compressed, supplying the hydraulic fluid to the small chamber of the hydraulic cylinder for a predetermined amount of time starting from a point where the pressure signal reached a maximum for the first time, and returning the hydraulic fluid in the large chamber to the tank.