Patent GB-516966-A (GB)
Title: Improvements in or relating to hydraulic actuator systems
IPC: B23Q5/26
Filed: 1938-05-10
Abstract: 516,966. Hydraulic apparatus. WAHLMARK, G. A. May 10, 1938, No. 13919. Convention date, May 15, 1937. [Class 69 (ii)] . A hydraulic system for actuating a member, e.g., the reciprocating bed of a milling machine. comprises a pump for supplying a motor for actuating the member, valve mechanism for controlling the volume, pressure and direction of the pump discharge and a pilot valve for controlling the operation of the valve mechanism, the valve mechanism having a first position in which all liquid drawn from a reservoir is returned to the reservoir, a second position in which a part of the liquid is passed by the pump to the motor at a higher pressure and a third position in which all the liquid passes to the motor. The pumping and valve mechanisms described are in the form of a unit of the construction described in Specification 516,565 and comprising a constant output pump 13, a variable output pump 14, valves 61, 70 for controlling the volume of liquid supplied by the pump 13 to the pump 14, a valve 85 for controlling the stroke of the pump 14, a reversible valve 106 for controlling the liquid supply to the motor 10, and a valve 118 for controlling the exhaust from the motor 10, the pumps and valves being enclosed in a casing. The control means comprises a pilot valve 135 for controlling the movements of the machine bed 216 from a central position in either direction at a number of different speeds, a solenoid actuated valve 137 for causing a dwell at each end of the stroke of the bed prior to reversal, and a solenoid actuated valve 136 by which the movements of the bed may be arrested at any time by the operator. The valve 137 when actuated closes communication between two normally connected pipe lines # 6 and # 6<1>and the duration of such closure is determined by a timing relay 204 in circuit with the solenoid 193 of the valve. The pilot valve 135 comprises a piston valve 138 working in a bore 142 and two piston valves 139, 140 normally held by springs in raised position shown in which pressure liquid from the outlet passage 25 of the pump 13 can pass through pipes #6, #6<1>, 6<1> to ports 168 connected by channels in the valves 139, 140 and their casing to the ends of the bore 142. The valve 138, which is operable manually or by dogs moving with the machine bed, can assume any of five positions viz@ a central "stop" position shown in which the bed is stationary in central position, an extreme " traverse " position on either side in which the bed is moved at high speed, and a mid " feed " position on either side at which the bed is moved at a feed speed which may be a fast feed speed or a slow feed speed according to the position of the co-operating valve 139 or 140. In the " stop " position of the valve 138 shown, the rear of the valve 61 communicates by pipe# 1 passages 1", 1<1>, groove 151 in casing of valve 138, radial and axial ports in the valve 138 to a large recess 156 open to the tank 20 so that, in the manner described in the prior Specification above referred to all the output from the pump 13 is discharged to the tank and the motor 10 is inoperative. In any of the other positions of the valve 138, the groove 151 is blocked so that the valve 61 is held closed to render the pump 13 effective. The rear of the valve 70 is connected by a pipe # 2 to a groove 153 which, in the " stop " and " feed " positions of the valve 138 is open to the tank 20 through radial and axial passages in the valve and the recess 156. In the " traverse " positions of the valve, however, the groove 153 is blocked so that the valve 70 is held closed and the whole of the output of the pump 13 passes through the pump 14 for 'high speed actuation of the motor 10 and bed 216. In either " feed " position the valve 70 is opened by the pressure liquid against the action of its spring 71 and part only of the pump output passes to the pump 14 which then drives, the bed at fast feed speed. In the " feed position to the right, the valve 106 is reversed by pressure liquid passing from the left hand end of the bore 142 through pipe 5A, the opposite end of valve 106 connecting to exhaust through pipe #5. The valves 139, 140 are movable by compound dogs 148 into a partly depressed and then into a fully depressed position. When the valve 138 is in "feed" position to the right and the valve 139 is partly depressed, the pipe 6<1> is put into communication with a passage 3<11> so that pressure liquid passes through pipe # 3 to operate valve 85, and thus, as described in the prior Specification, reduce the stroke of the pump 14 to actuate the bed 216 at slow feed speed. Complete depression of the valve 139 puts the left hand end of bore 142 to exhaust through groove 172 and radial and axial ports in the valve, passage 179 and pipe # 8. At about the same time a dog 208 closes a switch 207 to cause actuation of valve 137 for a time determined by the relay 204, to delay passage of pressure liquid from pipe # 6to pipe #6<1> and thus to the right hand end of the bore 142 so that a dwell occurs before the reversal of the valve 138 by liquid pressure to " traverse " left position. The order in which the movements of the valve 138 occur are determined by the positions and numbers of the actuating dogs. Thus, dogs 221, 226 may move the valve to "stop" position at the mid position of the table in either direction, or may be omitted so that the table moves continuously through the mid position, or the dogs may be so arranged that only fast feed or only slow feed may be obtained. In a modification, the compound dogs 143 are replaced by single dogs which move the valves 139, 140 only to fully depressed position. The slow feed speed is thus eliminated but the pipe # 3 instead of being connected to passage 3" is connected to a further port in valve 137 this port being normally connected to the exhaust but when the valve is actuated the port is connected to the pressure pipe # 6 so that the stroke of the pump 14 is reduced during the dwell of the bed 216 at the ends of its stroke.