Patent ID: 8240241

Claim:
A method of diagnosing and controlling a hydraulic drive system comprising: measuring hydraulic fluid pressure in a hydraulic fluid supply conduit between a hydraulic pump and a hydraulic drive unit; switching hydraulic fluid flow direction to said hydraulic drive unit or stopping hydraulic fluid flow to said hydraulic drive unit to end a drive cycle when measured hydraulic fluid pressure crosses a predetermined pressure threshold value; adjusting said predetermined pressure threshold value, to a corrected pressure threshold value as a function of measured resistance transmitted to said hydraulic drive unit from machinery that is coupled to and driven by said hydraulic drive unit and hydraulic pump speed; calculating an amount of mechanical work done by said hydraulic drive unit in said drive cycle as a function of said measured hydraulic fluid pressure and at least one of hydraulic, pump speed during said drive cycle, time to complete said drive cycle, and the volume displaced by a hydraulic piston in said hydraulic drive unit during said drive cycle; and warning an operator or limiting hydraulic fluid flow rate to said hydraulic drive unit when said calculated mechanical work for said drive cycle is less than an expected amount of mechanical work by a predetermined margin, said expected amount of mechanical work being calculated as function of an expected peak hydraulic system pressure.