GB1410422A - Hydraulic control system - Google Patents

Abstract

1410422 Programme control SANDERS ASSOCIATES Inc 29 Jan 1973 [13 March 1972] 4469/73 Heading F2V [Also in Division G3] A die-casting machine 21, Fig. 1, is operated by a ram 22 controlled first by a valve 25 to have the velocity characteristic shown at 44 in Fig. 2 and then by a valve 26 to produce the pressure characteristic 48, control being transferred to the valve 26 when the ram has reached a predetermined point in its travel to operate a switch in a bank 24 and the pressure in the ram has reached a predetermined value 45. An electronic signal source 32 capable of generating and repeating a wide variety of output signals energizes a force motor 31, Fig. 4, controlling a pilot valve 88 through a flapper valve 85, the signal from the pilot being applied through a conduit 58 to the right hand end of a spool 53 in the valve 25, Fig. 3. The spool is displaced until the pilot pressure is exactly opposed by a spring 56 and source pressure P acting against the left hand end of the spool which is now in a position to provide the required rate of flow through conduits 27, 28. When control is to be transferred to the valve 26, a solenoid 145, Fig. 6, energized by a ram-actuated switch in the bank 24 lifts a valve 136 to connect the space below a valve spool 109 to a return line 124 so that the spool may be depressed when pressure in the conduit 27 is great enough to compress a spring 118. The movement of the spool connects a space 61 to a pressure source Pc through passages 62, 65 so that a part 59b of the spool 53 is moved relatively to the remainder of the spool against a spring 67 to close the connections between the flow control valve 25 and the ram. Simultaneously, a switch 115 de-energizes the motor 31, energizes a signal source 34, similar to the source 32, for a force motor 33 in the pressure control valve 26 and starts a programme timer 37. The motor 33 displaces a flapper 93 against a piston 102 subjected to the pressure in the conduit 27 until an equilibrium position is reached. A fluid actuated spool 94 controlled by the flapper connects the conduit 27 with pressure and return lines Pc and R by the amount required to provide the required pressure in the ram. This pressure is eventually relieved by the timer de-energizing the force motor 33 and allowing the spool 94 to connect the conduit 27 only with the return line R. The fall in pressure in conduit 27 allows the spool 109 to be returned by the spring 118 to the position in which passage 65 is again connected with the return line 124 so that the parts of the spool 53 return to the positions shown in Fig. 3. Further signals from the timer energize the motor 31 to cause fluid to enter the ram at a slow rate and eject the die, and after this movement has been arrested by a switch in the bank 24, to reverse the ram.