Speed control valve for a hydraulic motor speed controlled by pressure between throttle and motor

摘要

A control block, having few moving parts and few bores, for the hydraulic drive of an airplane control surface comprises a primary spool valve 2 which is shifted by two electromagnetic valves I, II to determine the direction of rotation of a hydraulic motor 18. A prolongation 20 of primary spool valve 2 is located in a pressure chamber D and bears two annular pistons 22, 24 which are always a minimum distance apart. Space 26 is adapted to be connected via a control valve 34 with the return line of the hydraulic system. The position of slide 36 of control valve 34 is influenced by an electromagnetic valve III to change the pressure of the fluid in space 26 and thereby move the primary spool valve either into a position in which the fluid lines are completely opened (for the "fast speed" mode), or to move it into a position in which the fluid lines are throttled (for the "creep speed" mode). When there is a pressure drop, control valve 34 also reacts by moving the primary spool valve into a throttling position, so that the pressure is increased at a given hydraulic output and throttled flow rate. If the flow rate is too high, e. g. when the slats or landing flaps are retracting-- the aerodynamic forces have a supporting effect here--, a throttling and thus a restriction of the flow rate and the speed is obtained.