GB682223A - Electro-mechanical stroke limit control for hydraulic motor - Google Patents

Abstract

682,223. Hydraulic machines. BENDIX AVIATION CORPORATION. Jan. 4, 1951 [Jan. 10, 1950], No. 368/51. Class 69 (ii). In a hydraulic system in which a hydraulic motor is to be actuated through a desired fraction of its full stroke and automatically stopped when it has moved the desired distance and comprising a motor cylinder 10 containing a piston 11 having a piston rod 12 projecting from the cylinder, a valve 16 for controlling fluid flow to and from the cylinder to move the piston rod in either direction, a trigger 33 on the cylinder and a trigger actuator 35 frictionally engaging the piston rod for actuating the trigger in response to predetermined movement of the rod into the cylinder, and means responsive to actuation of the trigger for closing the valve to stop the piston rod, there is provided an energizable magnet structure including a stationary electro-magnet 40 and an armature 38b on the actuator for holding the actuator against the electro-magnet despite the frictional drag of the piston rod during outward movement thereof, the trigger 33 being so proportioned as to be actuated by the actuator 35 to stop the rod 12 during inward movement thereof prior to contact of the armature 38b with the electro-magnet 40, and means providing limited free movement between portions of the magnet structure for providing a closed paramagnetic flux path between the electro-magnet and the armature in response to energization of the electro-magnet. The cylinder contains normally closed limit switches 27 and 30 which are connected to ground and via conductors 28 and 31 respectively to solenoids 19, 20 for actuating the valve 16, current being supplied by a battery 36 which is also connected via contacts 24a and a conductor 39 to the electro-magnet 40. Closing a switch 23 energises the solenoid 19 so that fluid flows through the valve 16 into a line 15 to move the piston 11 to the left until the actuator 35 depresses the trigger 33 to open the limit switch 30, thereby breaking the electric circuit and closing the valve to stop the piston. Similarly closing a switch 22 energises the solenoid 20 ; fluid flows into a line 14 to move the piston 11 of the right until a cam surface 11a thereon engages a lever arm 27c to open the limit switch 27, thereby breaking the electric circuit to close the valve and stop the piston. Switches 24 and 25 are connected to ground so that closing the switch 25 energises the solenoid 19 and causes the piston to move to the left even if the limit switch 30 is open. Similarly closing the switch 24 energises the solenoid 20 and causes the piston to move to the right even if the limit switch 27 is open. Closing the switch 24 also bridges the contacts 24a, thereby energising the electro-magnetic 40 to attract the armature 38b so that the actuator 35 is drawn along the piston rod. The trigger actuator comprises a helical spring 37 encircling and gripping the piston rod 12 and housed in a groove in an element 38 on which is mounted the armature 38b.