GB940942A - Hydraulic control apparatus - Google Patents

Abstract

940,942. Hydraulic presses. AMERICAN BRAKE SHOE CO. Sept. 30, 1960, No. 33643/60. Heading B5F. [Also in Division F1] A control system for a fluid-operated reversible device such as an hydraulic press 23, comprises a pressure control means 14, a solenoidoperated reversing valve 16 and a separatelyoperated reversing valve 18 between a pressure source 10 and the device 23, the solenoid 74 of the valve 16 being connected to an electric circuit including switch means 69 operated with the valve 18, an electric valve 62, and means 59 responsive to a pressure condition in the control means 14, for actuating the electric valve. The pressure source consists of a pump 10 connected to the pressure control means 14 which has a through bore 31 connected by line 15 to the valves 16, 18 and the cylinder 23 of the press. A piston-device 27, 28 in the bore 31 is arranged to be operated when the force of the pressure acting on the under surface of the piston 27 exceeds the force acting in a chamber 48 above the piston to open a by-pass 32 leading to a reservoir 11. The chamber 48 is connected to the bore 31 by passages 43, 44, 45, restricting passages in a piston 36 and a passage 48, and when the pressure in the bore 31 exceeds a predetermined value, the piston 36 displaces a conical valve 37 against a spring to by-pass fluid to a line 46. leading to the reservoir, so reducing the pressure in chamber 48 to permit the device 27, 28 to open the by-pass 32. The bore 31 in the valve also communicates with both sides of a magnetic member 54 movable against a spring 55 in a cylinder of non-magnetic material, the bore being connected to the righthand side of the member by a line 53 and to the left-hand side by a line 51, groove 47, the restricting passages in the piston 36 and passages 43, 44, 45. When the valve 14 is closed, the pressure on both sides of the member 54 is equal and the member is urged to the position shown so that the voltage induced in a secondary coil 59 from a primary coil 58 connected to a power source by lines 60, 61 is at a maximum. The induced voltage is applied to the grid 77 of the electric valve which is in the form of a thyratron to prevent the thyratron from passing current and energizing a solenoid 86 having a normally-open switch 63 controlling a second solenoid 66. having a switch 72 controlling the solenoid 74 of the valve 16. The solenoid 66 can only be operated when the switch 69 is closed by a lever 21 secured to the valve 18. When the valve 18 is moved downwardly by the lever, the switch 69 is closed and fluid pressure is supplied to the cylinder 23 to move the piston 89 of the cylinder downwardly. At the end of the stroke, or when the piston engages the workpiece with a predetermined force, the pressure in the control valve 14 increases to a value sufficient to cause the piston 36 to displace the valve 37 and open the by-pass line 46 to reduce the pressure in chamber 48 permitting the device 27, 28 to open the by-pass 32. The consequential reduction in pressure in line 51 permits the pressure in line 53 to move the member 54 to the left so reducing the induced voltage in the coil 59. The reduced voltage enables the thyratron to pass current and energize the solenoid 86 which, in turn, energizes solenoid 66 and thus solenoid 74 to move valve 16 to its alternative position and raise the piston 89. When the piston reaches its upper position, the increase in pressure in bore 31 again causes the device 27, 28 to open the by-pass 32 to connect the pump to the reservoir. The valve 28 has a neutral position between its two operative positions whereby flow to and from the cylinder 23 is prevented to hydraulically lock the piston 89 in position. The thyratron may alternatively control a visual or audible signal device. In another embodiment, the electric valve is in the form of a toroid or saturable reactor having one coil connected to the secondary coil 59 and a second coil connected to the solenoid 86.