Logic-controlled flow compensation circuit for operating single-rod hydrostatic actuators

Abstract

A single-rod hydrostatic actuator or pump-controlled actuator, comprises a hydrostatic pump connected in a closed circuit to a single-rod hydraulic cylinder where the cylinder velocity is directly controlled by the pump flow, without the need of intermediary valves. Due to the absence of throttling losses, the efficiency of hydrostatic actuators is considerably superior to the efficiency of conventional valve-controlled circuits. However, because of the differential areas at the cap and rod sides of the cylinder, the flows coming into and out of the cylinder do not match. Several attempts have been made to this date to produce a stable, robust and reliable circuit that can be used in everyday applications but no circuit has ever been conceived to reach the high standards of reliability and robustness required by industry. The current invention solves the problem of the differential flows with a design that is reliable, oscillation-free and robust. The present conception is based on the correction of a misstated theory concerning the modus operandi of hydrostatic actuators. The resulting design can be translated into different embodiments using electronic or hydraulic technologies and uses only logical combinations of the pressure readings at the cap and rod-sides of the circuit.