GB944366A - Hydraulically controlled air cylinder - Google Patents

Abstract

944,366. Fluid-pressure servomotor control systems. K. & H. EQUIPMENT Ltd. Jan. 29, 1962 [Feb. 6, 1961], No. 3368/62. Heading G3P. [Also in Divisions B4 and F1] An hydraulically-controlled air cylinder structure for operating a door or supporting a rock drill comprises a tubular piston rod 6, Fig. 1, fixed to an air piston 5 in a cylinder 1, the rod having alternate extension and retraction strokes in response to air pressure on the piston, and hydraulic means for controlling and adjusting the speed of the strokes consisting of a hydraulic piston 16 in the rod 6 providing a forward hydraulic chamber 27 on one side of the hydraulic piston and a rear hydraulic chamber on the other side of the piston, the capacity of the chambers being responsive to movement of the piston rod relative to the hydraulic piston, means 26,29 providing a hydraulic fluid passageway from one of the chambers to the other, and means 36, 38 controlling the flow through the passageway. The hydraulic piston is secured to a tube 17 fixed to an end wall 3 of the structure and a tube 26 is also secured to the piston and to the end wall to provide an annular space 29 connecting the rear chamber 30 to a passage 34, the interior of the tube 26 connecting the forward chamber 22 to a passage 33. Each passage 33, 34 has a check valve 37, 39 and an adjustable throttle valve 36, 38 and communicates with a reservoir 19 having a movable wall 20. A flexible tube 21 connects an air inlet or outlet port 10 to one side of the air piston 5 and an air inlet or outlet port 9 communicates with the other side of the piston. In operation, when air is supplied to port 10 to extend the rod 6, the piston 5 moves to the left and hydraulic fluid in the forward chamber 27 passes through the tube 26,pas-. sage 33 and valve 38 to the reservoir 19, the speed of the piston 5 being controlled by the valve 38. Hydraulic fluid from the reservoir at the same time passes without restriction through the check valve 37, passage 34 and annular space 29 to the rear chamber 30, the difference in volumes in the fluid flowing from chamber 27 and to chamber 30 being compensated by movement of the wall 20 of the reservoir 19. When air is supplied to the port 9 to retract the rod, the speed of the piston is controlled by the valve 36. In another embodiment, the movement of the rod is controlled by a regulated air pressure. Each throttle valve 49, 51, Fig. 3, is secured to a piston 53, 60 on one side subjected to the pressure of a balancing spring 56, 63, and on the other side, to the regulated air pressure supply 86. The latter supply also acts on a piston 66 movable against a balancing spring 69 to control a valve 75 which in turn controls valves controlling the supply of air to the ports 9, 10. When the supply pressure at 86 is low, valves 51 and 75 are closed and valve 49 is open to permit hydraulic fluid from the forward chamber to pass to the reservoir so that the piston rod is retracted. If the supply pressure at 86 is gradually increased, valve 49 gradually closes and flow between the forward and rear chambers is prevented thus holding the air piston in a locked position. As the supply pressure increases further, the piston 66 rises to unseat valve 75 so that pressure at an inlet 82 can pass to a passage 83 and operate a main valve to reverse the connection of the air supply and exhaust to the ports 9, 10. No movement of the piston rod occurs, however, until such time as there is a further increase in pressure at 86 resulting in the gradual opening of the valve 51 to permit the air pressure supplied to the inlet 10 to extend the piston rod. In a further embodiment in which the speed of movement of the piston varies with its piston relative to the cylinder 1, the rate of flow of hydraulic fluid from the forward or rear chambers is controlled by tapered valves 97, 100, Fig. 4, which co-operate with orifices 99, 102 to control the flow to a control reservoir 94 and are secured to a piston 103 separating the control reservoir from a make-up reservoir 115 supplied with hydraulic fluid from the reservoir 19 by a passage 116. As the air piston is moved by air supplied through the ports 9 or 10, the hydraulic fluid flows to and from the forward or rear chambers through the passages 92, 93 at a rate controlled by the restriction of the valves 97, 100 at the orifices 99, 102 to or from the control reservoir 94, the quantity of hydraulic fluid in the latter varying because of the difference in volume of the chambers to move the piston 103 by an amount corresponding to the movement of the air piston 5 and vary the relative positions of the valves 97, 100 and orifices 99, 100. In the event of leakage of hydraulic fluid, when the piston rod is fully extended, the control piston is moved to its forward position so that a rod 114 can unseat a valve 113 to permit fluid from the makeup reservoir 115 to pass to the control reservoir 94. In another embodiment in which for each valve of a control pressure supplied to an inlet 205, Fig. 6, there is a corresponding locked position of the air piston, the passages 158, 159 leading from the chambers to the front and rear of the hydraulic piston are controlled by valves 163, 166 closed by fluid pressure supplied to a port 173 under the control of a solenoid-operated valve 174, other valves 215, 217 controlling the supply of air pressure to the ports 9, 10 for moving the air piston. With the control pressure at the inlet 205 at a low valve and the air piston in its retracted position, a piston 192 subjected to the control pressure is held in a balanced position against a spring 200 and an extension 194 of the piston is displaced from a switch 195 controlling the solenoids so that the valves 174, 215, 217 are positioned to permit air pressure to both ports 9, 10 and the port 173 whereby both valves 163, 166 are closed and the air piston is locked in position. If a control pressure is increased a predetermined amount, the control piston 192 moves and closes contacts 209, 211 of switch 195 whereby valves 213, 174 exhaust port 9 and 173 to atmosphere permitting valves 163,166 to open and the air pressure at port 10 to move the air piston until such time as the change in volume between the chambers to the front and rear of the hydraulic piston causes a corresponding change in the volume of fluid in chamber 160. The change moves the piston 181 and compresses the spring 200 to balance the control pressure supplied at 205 resulting in the control piston moving to disengage the contacts 209, 211 so that the valves 174, 217 reconnect the supply to the ports 9 and 173 locking the air piston in its new position. In other embodiments the speed of extension of the piston rod may be controlled and the speed of retraction uncontrolled, the control being effected by a valve either in the air piston to permit rapid passage of air in one direction from one side to the other and/or by a valve in the hydraulic piston which permits rapid passage of hydraulic fluid from the forward to the rear chamber. In the latter case, the valve may be constituted by movement of the hydraulic piston on its rod.