US2337848A - Hydraulic press - Google Patents

Description

A Dc. 28, 1943. .R. EIDAVIS 2,

HYDRAULIC mass r Filed Nov. 25, 1940 zsneet's-sheet -1 INVENTOR.

HmHARu E. DAVIS ATTORNEY;

Patented Dec. 28, "1943 HYDRAULIC PRESS Richard 'Davis, Milwaukee, Wis., assignor to I The'Oilgear Company, Milwaukee, Wis., a corporation of Wisconsin Application November 25,1940, Serial No. 366,963-

11 Claims. 01. 60-52) This invention relates to the control of reciprocating hydraulic motors ofv the type having large capacity working chambers and small capacity return chambers. For the. purpose of I illustration, the invention will be explained as applied 5 to a hydraulic press but it is not limited tosuch The force exerted by a press ram during its working stroke causes the pressure of the motive liquid to rise and the liquid in the working chaml ber to be compressed. If this compressed-liquid is suddenly released, an undesirable shock will result. If the'pump which powers the press is connected into a closed circuit with the working 9 and return chambers, reversal of flow in the cirl cuit will not cause the ram to be retracted until after the pump has pumped enough liquid from the working chamber to reduce the pressure therein to a low value, thereby causing a delay in reversingthe ram.. If the press is of the type in which the working chamber is connected to a surge tank through a surge valve, the high pressure in the working chamber at the end of the working stroke will make opening the surge valve dimcult and some types of surge valves will not open until the pressurein the working chamber has been reduced. If the press is of the downward acting type, means must be pro,- vided for supporting the ram when the press is idle and this means is ordinarily a resistance valve through which liquid from the return'chamber is forced during the working stroke, thereby causing power to be wasted and the motive liquid to become heated. 1

The invention has as an object to provide a 5 press with a novel control having means for re.- ducing the pressure in the working chamber after a working stroke of the ram has been completed and before a return stroke is initiated.

Another object is to provide a press of the 40 downward acting type with a novel control having means for supporting the ram when the press is idle and with means for automatically rendering the supporting means ineffective during at least a part of the working stroke or the ram.

Other'objects andadvantages will appear from the description hereinafter given or a hydraulic press in which the invention is embodied.

According to the invention in its general aspect and as ordinarily embodied in practice-the working chamber of a press is opened to drain atthe end oi the working stroke oi the rain, the fiow in the circuit is simultaneously reduced to zero and maintained at zero until the pressure in the working chamber has been reduced tov a low I value and then the flow in the circuit is reversed to effect reversal of the ram.

The invention also provides the press with a pressure responsive valve which when effective offers suiiicient resistance to the discharge of liquid from the return chamber to support the ram when the press is idle and which is rendered ineflective to support the ram in response to liquid being. directed .to the working chamber to advance. the ram.

The invention is exemplified by the press shown schematically in the accompanying drawings in which the views are as follows:

Fig, 1 is a diagram of the hydraulic circuit of a press in which the invention is embodied, the parts being shown in the positions occupied when the press is idle. 1

Fig. 2 is a diagram'ofthe electric circuit of the press shown in Fig. 1.

Fig. 3 is a view showing the pump control valve in the position occupied during a working stroke of the press ram.

Fig. 4 is a view showing the pump control valve in. the position occupied during a. return stroke of the'press ram.

Fig. 5 is a view showing the surgevalve in position to direct motive liquid to the main press 1 cylinder.

For the purpose of illustration, the invention has been shown applied toa downward acting speed press butit is not limited to presses of this type. Since such presses are well known and in extensive use, only so much or the press has been shown as is necessary to an explanation oi the invention.

As shown, the press includes a stationary head or die block l-for supporting a stationary die 2 and a movable head or platen 3 for moving a die I into and out of contact with a work piece W arranged upon die 2.

Platen 3 isadapted to be moved upward and is supported in its upper position by liquid supplied to the lowerends-ot two stationary rapid traverse cylinders 5 andv 5 having pistons 6 and 6 fitted therein and connected by rods land 1 to platen 3'upon opposite, sides of a large ram 8 fitted in a stationary main cylinder 9. It is adapted to be moved downward first at high speed either by gravity or by liquid supplied to the upper .ends of cylinders 5 and 5 and it is then moved downward at afslow' speed and upper die 4 is caused to exert a pressing force upon work W by liquid supplied to the upper ends of cylinders 5, I and I which constitute workto deliver liquid into oneand to supply pump.2l

' 26 with a reservoir 3| through and a low pressure resistance valve 33. Each of 7 liver liquid into channel 25.

I heads or pistons formed upon itsends and closely ing chambers while the lower ends of cylinders and 5 constitute return chambers.

Cylinder 9 is connected 'at its upper end with a surge valve casing I!) having a valve member [I fitted in the bore I2 thereof to control communication betweenwa pressure port l3 and a large annular groove or port l4, which is formed in the wall of bore l2 and communicates with the upper end of cylinder 9, and between port l4 and a passage |5'which connects one end of bore l2 to a surge tank |6.

When surge valve II is in Fig. 1, communication between port I3 and cylinder 9 is blocked and liquid will 'be drawn from tank |6 through passage l5 and valve casing l0 into. cylinder 9 by ram 8 as it moves downward and liquid will be expelled from cylinder 9 into tank I6 by ram 6 as it moves upward.

Whensurge valve H is shifted to the position shown in Fig. 5, communication between tank I6 may be of the rolling piston type fully illustrated 30 and described in Patent No. 2,074,068. It is deemed suflicient to state herein that pump 2| has its cylinders arranged radially in a cylinder barrel 22 which is .joumaled upon a stationary valve shaft or pintle 23 having ports and pas- 35 sages formed therein through which liquid flows to and from the cylinders, that the outer ends of the pistons react against the annular inner sur-' faceof a reaction member carried bya thrust discharged by pump 2| when slide block 24 is in its central or neutral position at which-time itsaxis coincides with the axis of cylinder barrel 22,

and that pump 2| will deliver liquid in a direction and at a rate dependent upon the direction 45 24 is shifted from its pump 2| is adapted have liquid returned to it through the other of two channels 25 and 26 and distance slide block neutral position. As shown,

which are connected'to pintle 23 in communica-- 60 tion with the passages formed therein.

Channel 25 is connected to the upperends of cylinders 5 and 5?- and has a branch 25"- thereof connected to. port-|3 in surge valve casing l0.

I described.

Since motors 5-6 and 5F-6 are of the differential type so that, when operating, liquid is discharged therefrom at rates which are either in excess of-orless than the rate required with liquid, channels 25 and 26 communicate at points intermediate their ends with the passages inpintl 23 and have their lower ends connected, grooves or ports 21 and 28 formed in the wall of 'a bore. 29 which is formed in a valve casing 30 and connected at a point between ports 21fand a check valve 32 channels 25 and 26 is also connected to a'high pressure relief valve which has been omitted from the drawings to avoid crowding the view.

Bore 29 contains a differential valve 34 having in the position shown member or slide block 24, that no liquid will be. 40

' .connected toor in engagement with slide block 24 and is fitted in a stationary cylinder 4| carried .Channel 26 is connected to the lower ends of 55 fitted in bore 29 to block one or the'other of ports 21 and 28, and opposite ends of bore 29 are connected by channels 35 and 36 to'channels 25 and 26 respectively.

The arrangement is such'that, when pump 2| discharges liquid into'channel 26 to raise pistons 6 and 6, pressure will extend through channel 36 to the left end of bore 29 and shift valve 34 toward the right to the position shown to block the end of channel 26 and uncover the end of channel 25 so that the liquid expelled from cylinders 5 and 5 by pistons 6 and 6 in excess of the volume required ,by pump 2| may be discharged through resistance valve 33 into reservoir 3| and, when pump-2| discharges liquid into channel 25 to cause pistons 6 and 6 to descend, pressure will extend through channel 35 to the right end of bore 29 and shift valve 34 toward the left to block the end of channel 25 and uncover the end of channel 26 so that pump 2| may draw liquid from reservoir 3| through check valve 32.

v In order that surgevalve may be shifted automatically to the position shown in Fig. -5 when pressure rises due to die 4 engaging work W, channel 25 is connected through a resistance valve 31 and a channel 38 to the left end of servo-motor cylinder l1 and, in order that piston 18 may 'eject liquid from cylinder |1 when surge valve II is shifted to the position shown in Fig. 1, channel 38 is connected through a check valve 39 to channel 25.

When slide block 24 is shifted toward the right liquid returned to it through channel 25.

Slide block |4 isatall times urged toward the right by liquid acting upon a piston 40 which is by the casing of pump 2|.

An adjusting screw 42 is threaded through the head of cylinder 4| to limit the movement of .piston 40 and slide block 24 toward the left. Turning screw 42 will adjust the rate at which pump 2| will, discharge liquid into channel 26.

Slide block 24 is adapted to be moved toward the left by liquid acting upon' a piston 43, which engages slide block 24 and is fitted in a stationary cylinder 44 carried by the pump casing, and by liquid acting upon a piston 45 which is fitted in cylinder 44 and adapted to engage the outer face of piston 43.

The movement of piston 45 toward the left is limited by a collar 46 fixed on a stop rod 41 which always 60 respectively, to two annular an adjusting screw 49 which is threaded through extends loosely through pistons 43 and 45 and through the head. of cylinder 44. The inner end of rod 41 is .adapted to engage slide block 24 and the outer end of rod 41 is provided with a nut 48 which is adjusted to so position collar 46 that piston 45 when energized will move slide block 24 exactly to its neutral position. The outer end of rod 41 is adapted to engage a cap 50 fixed to the head of cylinder 45. Turning screw 49 adjusts the distance rod 41 and slide block 24 may be moved toward the right tethereby determine the rate at which pump 2| will de- Pistons 43 and 45 arelarger than piston 40 so that slide block 24 will be moved toward the left when liquid is simultaneously supplied to both of 76 cylinders 4| and 44 at the same pressure.

equal to the resistance of relief Supply channel 52 has one of its branches connected to the outer end of cylinder 4| so that piston 48 is constantly urged toward the right by a constant force which is proportional to gear pump pressure.

Delivery of liquid from gear pump 5| to cylinder 44 is under the control of a pump control bore 83. A light spring 88 arranged in the right valve 56-having a valve member or plunger 51 I fitted in a valve casing 58 to control communication between four annular grooves or ports 59, 68,.6l and 62 formed in valve casing 58.

Port 59 has another-branch of supply-channel 62 connected'thereto. Port 68 is connected by a channel 63 to cylinder 44 at or near the outer end thereof. Port 6| is connected by a channel 64 to cylinder44 at a point between pistons 43 and 45. v Port 62 is connected to a drain channel 65 which discharges into reservoir 3|.

When valve member 51 is in its central position as shown in Fig. 1 pressure extends from channel 52 through valve casing 58 and channel 63 to the right end of cylinder 44 and holds piston 45 against collar 46 on stop rod 41, the space between pistons 43 and 45 communicates through channel 64 and valvecasing 58' to drain channel 66 so that the pressure in cylinder 4| will cause piston 48 to hold slide block 24 against piston 43 and piston 43 against piston 45 in which position of slide block, 24 pump 2| is at zero stroke and no liquid will be delivered thereby.

When valve member 51 is shifted toward the left to the position shown in Fig.3, port 59 is blocked and channels 63 and 64 are open to drain channel 65 so that liquid supplied by gear pump 5| to cylinder 4| can cause piston 48 to move slide block 24 toward the right until rod 41 abuts adjusting screw 49 at'which time pump 2| will discharge liquid into channel 25 at a rate determined by the adjustment of screw 49. i I

When valve memberf51 is shifted toward the right to the position shown in Fig. 4, port 62 is blocked and channels 63 and 64 are open to port 58 so that liquid from gear pump 5| can flow through channel 52, valve casing 58 and channels 63 and 64-to cylinder 44 and causepistons' 43 and 45 to move slide block 24 toward the left until piston 48 abuts adjusting screw 42 at which time pump 2| will discharge liquid into channel 26 at a rate determined by;the adjustment of screw 42.

Valve member 51 is normally held in its central or neutral position by two springs 66 and 61 arranged, respectively, in two chambers 68 and 69 which are formed in opposite ends of valve casing 58. Chamber 68 is connected to drain channel 65 and chamber 69 is connected to a drain channel 18 which discharges into reservoir 3|.

Valve member 51 is adapted to .be shifted in one direction or the other by one or the other 01' two solenoids H and 12 the cores of which are connected, respectively, to valve stems 13 and 14 which are fixed to opposite ends of valve meni-v ber 51 and extend outward through chambers 68- 76 to a position to open port 4 to port ||3 by a '70 channel 65 connected thereto.

and 69. Solenoids 1| and 12 are controlled in a manner to be presently described.

The other end of channel, 26 is connected to a port 88 formed in the casing 8| of a resistance v valve 82 which prevents platen 3 from descending when the press is idle.

Valve casing 8| has an axial bore 83 formedtherein and an annulargroove or port 84 formed in the wall of bore 83 at the left endthereof. Port 84 is connected to the lower ends of cylinders 5 and 5 by a branched channel 85, and a branch 85 thereof is connected to the right end of servo-motor cylinder l1.

Communication between ports 88 and 84 is controlled by a valve 86 fixed to a piston 81 which is larger in diameter than valve 85 and fitted in end of bore 83 urges piston 81 toward the left to hold valve 86 in contact with a valve seat 89 which is. formed around port 88 in the end wall of bore 83.

Spring 88 has sufficient strength to overcome the friction oi piston 81 and move it toward the left until valve 86 engages valve seat 89 butlt is incapable of holding valve 86 against valve seat 89 when the end of valve 86 or the end of pis-' ten .81 is subjected to an appreciable amount of unbalanced pressure.

Resistance valve 82 is controlled in part by a pressure responsivevalve 98 arranged in the bore 9| of a valve casing 92 and provided with two spaced apart heads or pistons 93 and 94 which are closely fitted in bore 9| to control communication between three annular grooves or ports 95, 96 and 91 formed in the wall of bore 9|. Piston 93 has at least one small tapered groove 98 tormedin its peripheral surface to provide a restricted passage. from port 95 to port 96 when valve 98 is in the position shown, in which position it is normally held by a spring 99 which is arranged in the right end of bore 9| and it is adapted to have its tension adjusted by means of a screw I88 Port 91"and the right end of bore 9| have drain channel 65 connected thereto, port 96 is con nected by a channel IN to the right end of bore 83 in resistance valve casing 8|, and port is open at all times to channel 85.as by being connected by a channel I82 to port 84 in resistance valve casing 8|.

In order that liquid may be expelled from the right end of bore 83 when piston 81 is moved toward the right by pressure applied to the end of valve 86, the right end of bore 83 is connected to port 84 through a check valvel83 which has been shown connected between channels |8| and I82. In order that piston 81 may draw liquid into the. right end of bore 83 when it moves toward the left, the right endof'bore 83 is connected to drain channel 65 through a check valve |84 which is shown connected to channel I8 I.

Resistance valve 82 is also controlled in part by a pilot valve 8 which is arranged in the bore III of a valve casing H2 and controls com-' munication between two annular grooves or ports 3 and I I4 formed in the wall of bore Port 4 is connected by a channel 5 and a throttle valve 6 to the right end of,.bore 83 while port 3 and the lower end of bore have drain Valve 8 is normally held in position to block port 4 by a spring 1 arranged in the lower end Of bore ill, and it is adapted to be moved reduced to zero.

. three switch decompression valve I which is 'operated in response to the displacement of pump 2I being As shown, valve I20has fitted in the bore I22 ofavalve casing I23 to control communication between two annular grooves or ports- I24 and I25-which are formed in the wall of bore I22 and-connected, respectively, to drain channel 65 and a branch 25 of channel 25. .7

Valve member I2I i normally held-in a position to block port I25 and thereby prevent escape of liquidirom channel 25 into channel 65 by a valve member I2I horizontally but vertically so that, when the magnets are deenergized, the switches will open by gravity to the positions shown.

In order that the press may time, a normally closed manually operable stop switch S2 is connected into one side of the circuit and, in order that platen 3 may be retracted either when it reaches a given point in its ad- 10 vanced movement or when the pressure incylinder 9 reaches a given maximum, a manually operable selector switch S3 is connected between switches 182 and PS2.

As shown, stop switch S2 has one of its termi- 5 nals connected to power conductor I3I by anona spring I26 arranged in one end of bore I22.

The other end'oi' bore I22 is connected by a'channel I2I to port 60 in pump control valve 56 so that. when valve member 51 is shifted to the position shown inFig. 1 to cause the displacement of pump 2I to be reduced to zero as previously explained, liquid will flow from gear pump 5| 25 a through channel 52,'valve 56 and channel I21:

to the end'oi bore-I22 and move valve member I2I far enough to uncover port I25 so that liquid can escape from ram cylinder 9 and thereby reduce the pressure therein. The rate at which liquid may escape from cylinder 9 is preferably limited such as by providing a throttle valve I28 "in channel I21 to limit the rate at which valve member III, is moved and by providing suitable tapered grooves. in the periphery. of valve member I2I so that the rate 'oi flow through I valve I20 is gradually increased as valve member I2 I moves toward the left.

H The electric circuit Referring now more particularly to Fig; 2. current for energizing solenoids II, I2 and H0 issupplied thereto from a power line shown as con sisting' or two conductors I30 and I3I.' Solenoid II is controlled by a contactor switch A having- AI, A2 and A3 and a magnet A4 for operating its switches.

Solenoid I2 is controlled in part by a con,-

tactor switch B which consists of two switches .50 to the fourth be al of limit switch LS2, to

BI and B2. and a magnet 33 for. operating its switches, and in part by a pressure switch PSI which is connected to channel 25 as shown in Fig. 1 and adapted switch A and in part by a limit switch LSI which is adapted to be operated near the end of a other terminal of switch SI is connected by a.

' conductor I-39to one end of the winding of magnet A4 the other end of which is connected to power conductor I30 by a conductor I40 so that,

' when switch SI is closed, magnet A4 will be energized and close switches Al, A2 and A3.

SwitchAI has one of its terminals connected by aconductor I4I to conductor I30 and its other terminal connected by a conductor I42 to one end of each or the windings oi! solenoids II and 0.. Switch A2 has one of its terminals con- .nected by a conductor I43 toconductor I3I and its other terminal connected by a conductor I44 to the other'end oi the winding of *solenoidll and to one terminal of limit switch LSIthe other terminal oiwhich is connected by a conductor I45 tothe other end of the winding of solenoid II8.

Switch A'3 has one of its terminals connected by a conductor I46 to conductor I39 and its other terminalconnected by a conductor 141 to one terminal of selector switch S3. A second terminal of switch S3 is connected by a conductor I40 45 to the third terminal of limit switch LS2, and

a third-terminal of switch S3 is connected by a conductor I40 to the third terminal of pressure switch PS2.

Switch B2 .has 'its other terminal connected obof the winding of magnet B3 the other end of down stroke of ram 8 by an actuator I32 which is carried by platen 3 as shown in Fig. 1.

Contactor switch A is controlled 'in part by a normally open manually operable starting switch SI and in part either by a. limit switch LS2,

which is adapted to be operated at the end of a down stroke of ram 8 by an actuator I33 (Fig. 1) carried by platen 3', or by a pressure-switch PS2 which is connected to channel 25 through a shut-off valve I34 as shown in Fig. 1.

Contactor switch B is controlled in part either by limit switch LS2 or'by pressure switch PS2 and in part by a limit switch LS3 which is adapted to be operated at the end of an up stroke of ram 0 by an actuator I35 (Fig. 1) carried-by platen 3.

In order to simplify the drawings, contactor switches A and B have been shown arranged which is connected to conductor I30 by a conductor I52.

Switch BI has one of its terminals connected to conductor I31 by a, conductor I53 and its other terminal connected to one end of the winding of solenoid I2 by a conductor I54; The other end of the winding of solenoid I2 is connected by a conductor I55 to one terminal of pressure switch PSI the other terminal of which is connected by a conductor I56 to conductor I30.

Operation If platen 3 is to be reversed when it has advanced die i to a given point, selector switch S3 is adjusted as shown in full lines, shut-oil valve 15- worir W, selector switch S3 is adjusted as shown in practice they are arranged be stopped at any through LS2-I48S3 and I41 to A3; I

I Closing switch AI and A2 establishes a oiruit (I38-I4I-=-AI--I42--lI-I44-A2-I43--I3I) to asaaacs:

in dotted lines. actuator I33 is-so adjusted that it will notoperate limit switch LS2 and shutofl.'

valve I34 is opened so that pressure switch PS2 will be operated when the pressure in cylinder 9 reaches a predetermined maximum.-

When the press is idle, the parts are in the positions shown in Fig. 1 and the weight of platen I 3 and the parts movable therewith cause pistons 8 and 8 to create pressure in the lower ends of cylinders 5 and 5 and this pressure will extend through channel 85 to port 84 in resistance valve 82 and tend to move piston 81 toward the right due to the pressure acting upon the left'end thereof.

However, the pressure also extends from port 84 through channel I82, port 95, groove 98, port ance of force acting upon the right end of piston 81 will hold valve 88 against seat 89 so that platen3 is positively prevented from descending.

When pumps 2i and 5 -I (are started, pressure will extend from gear pump 2| to'the right end of control cylinder 44 and hold pump 2| at zero stroke so that no liquid is delivered thereby as previously explained, and liquid from gear pump 5|. will flow through channel 52, valve casing plunger I2I time. v I

To start the press, starting switch SI is closed to establish a circuit (I 3I--I38S2--I3ISI- I 39-A4I 4Il-I3ll) to energize magnet A4 which willhave no effect at this which closes switches Al, A2 and A3. Closing switch A3 establishes a holding circuit to keep A4 energized and switches AI, A2 and A3 closed. If platen 3 is to be reversed when it "has advanced die 4 to a given point, the holdingcircuit will extend from power conductor I3I through I36---S2 I 3'I-LS2- I 48S3 I 4'IA3:

,-I46-I39A4 and M to power conductor I38, If platen 3 is to 'bereversed when die 4'has ex'- erted a predetermined force upon work W,-the

holding circuit will -be the same except that from conductor I31 it will extend through I38.

energize solenoid II and alsojestablishes a cir- A2I43I3I) to energize solenoid Ha;

control valve member 51 to the position shown in Fig; 3, thereby causing-pump- 2I.- to discharge liquid into channel 25 andto receive liquid from a l 60 differential valve 34 is in the position shown in channel 26 as previously explained. Shifting control valve member 511 to theposition shownin-Fig. 3'also opens channel'l 2'l to drain channel-65 to permit spring I26to move decompres- ..sion valvemember/2I toward the right to block channel 25.

Energizing-solenoid II8will cause it to shift'- pilot valve H8 to open port II 4 to port H3 and then the pressure created by pistons 6 and 6= due 'to the'weight of p1atenj3 .and associated"-- i v 4 l If limit switch LSI is not operated before die parts will act upon the left-end of plunger 81.

and move it and valve 88 towardthe right, only a low pressure being required to move'plunger at grate-determined by valve I I6 which is provided' to prevent plunger 81 from moving too rapidly. l

As soon'as valve 88 moves away from its seat 89, the pressure acts upon the combined areas A of valve 86 and piston 81 so that only a very low pressure is required to move valve 86 so far from seat 89 that'it offers no resistance to the flow of liquid through resistance valve 82.

10 If the resistance to the downward movement of platen 3 is sumcientto prevent it from descending by gravity; pump 2| will tend to discharge through resistance valve 33 the resistance of which will cause pressure to rise and liquid to flow through channel 35 to the right end of bore 29 and shift valve 34 toward the left to block port 28 and uncover port 21. The liquid discharged by pump 2I will then flow through channel 25 to the upper ends of cylinders 5 and 5 and cause pistons 6 and I5 to move platen 3 downward at a high speed which is. proportional .to' the displacement of .pump. 2I. Pistons 8 and 8 will expel liquid from cylinder 5 and 5 through channel 85, resistance valve 82 and l channel 26 to pump 2I which will draw the additional liquid it requires from reservoir 3I through check valve 32, bore 29 and channel 26.

If platen 3 and the parts movable therewith have suflicient weight to cause descent by grav-. v 30 ity pistons '6 and (i willexpel liquid from cyl- 58 and channel 121 to valve I20 and shift its inderj5 and 5 through channel 85 and resistance valve 82 into channel 26 and a part of this liquid .will tend to flow through bore 29 and resist-- ance valve 33 into reservoir 3| but difierential 35 valve at this time blocks port 2'Iand prevents the discharge of liquid into resrvoir 3I', thereby causing pump 2| to meter the discharge from cylinders 5 and 5 so that platen 3 descends at a high speed :which is proportional to the displacement of pum 2I.- Liquid to make up the difierence between the volume discharged by pump 2| and the volume required to fill, the upper ends of cylinders 5 and 5 is drawn from reservoir 3| through check valve 32 and bore 29 into channel25.

will continue downward at high speed until die '4 engages work W unless work W is of such nature. that it might be damaged by die 4 striking it at high speed .in which case actuator I32 v and limit switch LS I are so arranged that actuator I32'will open switch LSI, justibeforeldie 4 engagesworkW. If,.platen.3 is descending by gravity so that Fig. 1, the engagement ofdie 4 with work W or the closing of valve-86 due to the operationof limit switch LSI will cause pump 2| to tend to discharge through resistance valve-33 the resistance of'whichywill cause pressure to rise and liquid. to 'fiowthrough manna as to ,the right end of bore 29 and shift differential valve 34,to ward the left to block port &28 and uncoverport (S-channel 38110 cylinder l1; and cause piston .l8'to shift surge valve II to the position shown in Fig. to block communication between cylinder Sand surge tank l6 and to open cylinder 9 to port IS. The liquid from pump 28 will then flow Opening switches A2 and as breaks the circuit through solenoid 'Il to-deenergize it. If limit 1 switch LSI is not employed or has not'been operated, opening switches Aland A2 will also deenthrough channel 'and 25" and surge valve 5 ergize solenoid 8 to permit pilot valve H8 to casing III to cylinder 8 so'that platen 8 is moved downward at a slow speed by liquid acting upon the combined areas .of ram 8 and pistons 8 and 6.

If limit switch LSI engages work W, it will deenergize solenoid H8 and thereby permit spring I H to shift pilot valve l h! upward to block port Ill. The pressure prevailing' in channel 85 and port 84 will then extend through channel 102, port 85, slot 88 in 15 pressure responsive valve 88, port Y98 and channel l0! to the right end of bore 83 so that p ston 81 is hydrostatically balanced and spring 88 is then able to move valve 86 against its seat 88 to close port Bil. I

With port 80 closed, the downward movement of pistons 6 and 6* causes the pressure in port 84 to rise and extend through channel 2 and act" upon piston 98 of pressure responsive valve 90.

The pressure will continue to rise untilit becomes 5 high enough to overcome the resistance of spring 99 and then it will move valve 98 toward the right until port 91 is opened to port 86, thereby opening the right end of bore 88 to drain and permiting the pressure in port 84 to move piston 81 0 and valve 88 toward the right to open port 80 so that liquid can flow from the lower ends ofcylinders 5 and 5 through channel 85 and resistance valve 82 into return channel 26.

The pressure required to shift valve 98 is at least as great as the pressure required to open resistance valve 31 so that valve 81 opens and permits liquid to flow therethrough and shift surge valve H to direct liquid from pump 2| to cylinder 9 and cause platen 8 to move downward at slow speed before resistance valve 82 opens.

In order that solenoid 12 may not be operated and initiate an upstroke of platen 8 when limit switch LS2 orpressure switch PS2 is operated at the end of the down stroke, pressure switch FBI is so adjusted that it will open and the" I connection between solenoid I2 and'powr conductor I38 before the pressure becomes high enough to open resistance valve 81.

is operated before die 4 10 close as previously explained.

Deenergizing solenoid H permits spring 66 to shift control valvemember 51 to the position shown in Fig. 1 so that'the displacement of pump 2| is reduced to zero as previously explained and liquid from gear pump 2| may flow through channel52 valve casing 58 and channel I21 to bore I22 and shift valve member l2! to open channel 25 to drain channel 55. Liquid may now escape-from cylinder 9 through surge valve casing Ill, channels 2.": and 25 and decompression valve I28 into drain channel until the pressure in cylinder 9 drops suiiiciently to permit pressure switch PSI to close.

20 Closing pressure switch PSI establishes a'ciri55--PSII56I88) to energize solenoid 12.

which will shift control valve member 51 to the position shown in Fig. 4 to thereby cause pump 2! to discharge liquid-into channel 26 as previously explained. The liquid discharged by pump 2! shift diiferential valve 86 to the position shown in Fig. 1 and then it will flow through channel 26, open resistance valve 82 and flow therethrough and through channel 85 to the lower ends of cylinders 5 and 5 and tend to raise pistons 6 and 6 but the weight of platen 8 and associated parts will cause pressure to rise and liquid to flow through channel 85? to cylinder l1 and cause piston I8 to shift surge valve H to the position shown in Fig. 1, thereby blocking port 13 and opening port M to passage B5. The liqu d delivered to the lower ends of cylinders'fi and 5 will then cause pistons 8 and 6 toraise platen 3, g and ram 8 will eject liquid freely from cylinder 9 through surgevalve casing i0 and passage l5 into tank i6.

It pressure switch PS2 is efiective, it will operthat magnet B8is kept energized by the circuit Platen 3 will continue speed th switch AS p 3 moves upward,

and cause die 4 to operate upon work W until either limit switch LS2 or pressure switch PS2 is operated depending upon the adjustment of the press as previously explained.

Operating limit switch LS2or pressure switch 55 PS2 will cause magnet l38 to be energized and close switches BI and .82. If limit switch LS2 is operated, the circuit (l8 l-I 38 S2-| 8'I-LS2- l50--LS3--l5l-B3-|52I88) for energizing magnet B3 will extend therethrough. If pressure switch PS2 is operated, .the circuit for energizing magnet B3 will be the same except that it will extend therethrough and through conductor 588 instead of through limit switch LS8.

Closing switch B2 establishes a I30) to keepmagnet B8 energized and switches Bi and B2 closed. \Closing switch Bl has no eflect for the reason that pressure switch PS9 is open.

Operating limit switch LS2 or pressure switch 88 PS2 also breaks the circuit through magnet A l to deenergize it and thereby permit switches Al, A2 and A3 to open. Opening switch Al vhas no eiiect as the circuit therethrough was broken by limit switch LS2 or' by pressure switch actuator 588 permits limit" switch L8! to close but it cannot cause solenoid M8 to be energized I for the reason that switches Al and A2 are open. When platen 3 reaches the end of its up stroke,

be reduced to zero so that no liquid is delivered thereby as previously e rplained. The press has circuit 65 now completed a. cycle of operation and it comes to rest with thparts in the positions shown in Fig. 1 except that, as soon as valve member 51 is shifted to its neutral position, decompression valve (128 is opened by gear pump liquid and held open thereby until another cycle of operation is initiated or the pump is stopped;

The inventionhereim set forth is susceptible of various modifications and adaptations wlthout departing from the scope thereof as herepsg r5 after claimed.

will. first I k 3 starts upward but solenoid 18 will not be deenergized for the reason actuator l "opens limit switch LS8 to deener- The invention is hereby claimed as follows:

1. The combination with cylinder means having a work chamber and a return chamber, ram means mounted in said cylinder means'and a U pump connectedtoboth of said chambers, of

means including a. central valve for controlling thedelivery of liquid to said chambers, means for operating said control means to direct liquid therein, means including said control valve for directing liquid to said decompression valve to openv the same upon said control means beingfrom said pump to said work chamber and from said return chamber to said pump to effect a working stroke of said ram means, means operable at the end of said working stroke for efiecting operation of said control means to stop de-- livery of liquid to said work chamber, a normally closed decompression valve adapted when opened to permit liquid to escape from said work chamber to reduce the pressuretherein, means including saidcon'trol valve for directingliquld to said I decompression valve to open the same upon said control means being operated to-stop delivery of liquid to said cylinder means, means responsive to a reduction in pressure in said work chamber from said,pump to said return chamber to efiect a return stroke of said ram means, and means responsive to said ram means reaching the end of. said return stroke for operating said control means to stop delivery of liquid to said return chamber and bring said ram means to rest.

2. The combination with cylinder means having a work chamber and a return chamber, ram means mounted in said cylinder means and a pump connected to both of said chambers, of means including a'control valve for controlling the delivery of liquid to said chambers, means for operating said control means to direct liquid from said pump to said work chamber and from said return chamber to said pump to effect a operated to stop delivery of liquid to said cylinder means, means responsive to a reduction in pressure in said work chamber for operating said control means to direct liquid from said pump to said return chamber to effect a return stroke of said ram means, and means responsive to said ram means reaching the end-of said return stroke -for operating said control means to stop delivery of liquid to said return chamber and bring said ram means torest.

4. In a downward acting hydraulic press pro-- vided with cylinder means having a work chamber and a return chamber and ram means mounted in said cylinder means,a surge tank, a normally open surge valve for controlling communication between said tank and said work chamber, anda I for operating said control means to direct liquid servo-motor for operating said surge valve, the combination of a reversible pump having oneside thereof connected to said work chamber and the other side thereof connected to said return chamber and being adjustable to deliver liquid to one or the other of said chambers or to have its delivery reduced to zero, means for, causing said pump to deliver liquid in a direction toi'eflect a working stroke of said ram means, means for causing said servo-motor to close said surge valve in response to said ram means approaching the end of said working stroke to thereby enable said pump to create pressure in said work chamber, ,means operable at the end of said working Stroke for causing the delivery of said pump to be reduced to zero, means responsive to operation of said last named means for permitting liquid to escape from said work chamber to, re-

- duce the pressure therein, means operable after working stroke'of said ram means, means responsive to the pressure in said work chamber reaching a predetermined maximum during said working stroke for eifecting operation of said control means to stop delivery of liquid to said work chamber, a normally closed decompression valve adapted when opened to permit liquid to escape said last named means has .beenoperated for causing liquid from said pump to flow to said servo-motor and cause'it to open said surge valve and then flow to said return chamber and effect a return stroke of said. ram means, and means operable in response to'said ram means reaching from said work chamber to reduce the pressure therein, means including said control valve for directing liquid to said decompression valve to open the same upon said control means being operated to stop delivery of liquid to-said cylinder means, means responsive to a reduction in pressure in said work'chamber for operating said control means to direct liquid from said pump to said return chamber to effect a return stroke of said ram means, and means responsive to said ram means reaching the'end of said return 1 stroke for operating'said control means to stop delivery of liquid to said return chamber and bring said ram means to rest.

3. The combination with cylinder means having a work chamber and a return chamber, rain means mounted in said cylinder means and a pump connected to both of said-chambers, of

from said work chamber to reduce the pressure the end of said return stroke for causingthe delivery of said pump to be reduced to zero" to thereby bring said ram means to rest.

5. In 'a .downward acting hydraulic press provided with cylinder means having a work cham-,

ber and a return chamber and "ram means mounted in said cylindernieans, a surge tank, a'normally open surge valve for controlling communication betweensaid tank and said work chambenand a servo-motor for operating said surge valve, the combination of a reversible pump having one side thereof connected to said work chamberand theother side thereof connected to said return chamber and being adjustable to deliver liquid to one or the other of said cham bers or tohave its delivery reduced to zero, means for causing said pump to deliver liquid :ina di rection to effect a working stroke of 'said ram means, means for causing said servo-motor .to

close said surge valve in response to said ram means approaching the end of said working stroke to thereby-enable said pump tocreate pressure in said work chamber, means operable at the end of said working stroke for causing the delivery of said pump to be reduced tozero, 2

means responsive to operation of said last named.

means for permitting liquid to escape'from said work chamber to reduce the pressure therein, means "responsive to the pressure in said'work chamber reaching a predetermined, minimum for causing liquid from said pump to flowto said it effects reduction of pump delivery to zero and servo-motor and cause it to open said surge valve and then-flow to said return chamber and eflect a return stroke or said ram means, and means operable in response to said ram means reach ma the end of said return stroke for causing the delivery-of said pump to be reduced to zeroto thereby bring said ranr means to rest.

6. The combination, with cylinder means having' a work chamber and a return chamber and ram means mounted in said cylinder means, of

--a reversible pump having one side thereof con-v nected to said work chamber and the other side thereof coniiected to-said return chamber and having control means adjustable to ,cause it to deliver liquid to one or the other of said chambers or to have its delivery reduced to zero, a normally closed decompression valve adapted when open to permit liquid to escape from said work chamber to reduce the pressure therein,

saidcontrol means" including a control valve which is normally in a neutral position in which simultaneously directs'liquid to said decompresslon valve to open the same and which is shiftable to one or the other oitwo positions to cause said pump to deliver liquid too'ne or the/other of said chambers, means for shifting said control valve to-a position to cause said pump to having; control means adjustable to cause it todeliver liquid to one or the other of'said cham- 1 deliver liquid to said work chamber and to draw liquid from said returnchamber to effect a working stroke of said ram means, means operable at the endof said working stroke for-returning said control valve to neutral to cause the delivery of said pump to be reduced to zero and to simultaneously cause said decompression valve to open, means operable after said decompression valve has opened for shifting said control valve to a position to cause said pump to deliver liquid to said return-chamber to efiect a retum stroke 'of said ram means, and means operable at the end of said. return stroke for returning said control.

valve to neutral to cause the delivery oi said pump-to be reduced to zero to thereby bring said ram means to rest. i 7. The combination, with cylinder means havinga work chamber and a return chamber'and' ram means mounted in said cylinder means, of

a reversible pump having one side thereof, connected to said workbhainber and the other side thereof connected to said return chamber and bers=or tohave its delivery reduced to zerof a normally closed decompression valve adapted when open to permit liquid to escape from said work chamber, to reduce the pressure therein,

, said control means including a control valve I which is normally in a neutral position in which it effects reductionof pump delivery to zero and simultaneously directs liquid to said decompression valve to'open the same and whichis shift able to one-orthe other of two positions to cause said pumpto deliver liquid to one or the other of said chambersAneans for shifting said con-f trol'valve toa position to cause said pump to f deliver liquid to said work chamber and to drawv liquid from said return chamber to effect a work ing stroke of said ram means meansoperable at the end-of said working stroke 'for returning 7 stroke for returning said control valve to neutral said control valve to neutral to cause the delivery Io'f said pump-to be reduced to zeroand to-simultaneously cause saiddecompression valve to open,

for shifting said control valve to a position .to

20v which is'nor mally in a neutral 65 trol valve to cause 'saidrpumpto deliver liquid to said return chamber to effect a return stroke of said ram means; and means operable at the end of said return stroke Iorreturning said valve to neutral to cause the delivery-of said pump to be reduced a reversible pump having-one side thereof connected to said work chamber and the other side thereof connected-to said return chamber and having control means adjustable to cause it to deliver liquid'to one or the other of said chamnormally closed decompression valve adapted when open to permit liquid to escape from said work chamber to reduce the pressure therein, said control means including a control valve positionv in 'which it affects reduction o'f pump' delivery to zero and simultaneously directs liquid to said decompressionvalv to open the same and which is shiftable to one or the other of two "positions to cause 5 said pump to deliverliquid to one or the other of said chambers, means for shifting said control valve to a position to cause said pump to deliver I liquid to said work chamber and to draw liquid Irom said return chamber to effect a working stroke of said ram means, meansre'sponsive to the pressure in said work chamber reaching a predetermined maximum during said working stroke for returning said control valve to neutral to cause the delivery of said pump to be reduced to zero and to simultaneously cause, said de'com pression valve to open, means operable after said decompression valve has opened for shifting said control valve to a position to cause said pump to deliver liquid to said return chamber to effect a 4 return stroke of said ram means, and means oprable'at the end of said return stroke for retuming said control valve to neutralto cause the delivery of said pump to be reduced to zero to thereby bring said ram means to rest.

m 9. The combination, with cylinder means hav- IammeansmOunted in said cylinder means, of irreversible pump having one side thereof connected to said work chamber andthe other'side "oothereof connected to said retum chamber and having control means adjustable to cause it to deliver liquid 'to one or v bers or'to have its delivery reduced to zero, a

normallyclosed decompression valve adapted. when open to permit liquid to escape. from said work chamber to reduce the pressure therein, said control .means including a icontrolo valve which is normally in a'neutral position in which it effects reduction of pump delivery to zero and 6 simultaneously directs liquid to ,said decompression valve to open the same and which is shiftable to one or the other of two positions to cause 1 said pump to deliver liquid to one or the other of said chambers, means for shifting said cona position to cause said pump to deliver liquidvto said work chamber andsto draw liquid from said return chamber to eiject a workmg stroke of said ram means, means operable by said ram means at the end of said working to cause the delivery of said pump to be reduced .to zero and tosimultaneously cause said decompression valve to open, means operable after said bars or to have its delivery reduced to zero, a

the other of said chain-i to deliver liquid to said return chamber to efiect a return stroke of said ram means, and means operable at the end of said return stroke for returning said control valve to neutral to cause the delivery of said pump to be reduced to zero to thereby bring said ram means to rest.

10. In a downward acting hydraulic press, the combination with cylinder means having a work chamber and a return chamber, ram means mounted in said cylinder. means and a pump connected toboth'of said chambers, of means for controlling the delivery of liquid .to said' chambers, a normally closed resistance valve connected in series with said return chamber, means responsive to pressure in, said return chamber for holding said resistance valve closed to prevent the discharge of liquid from said return chamber and thereby support said ram means when said press is idle, means for operating said control means to direct liquid from said pump to said work chamber to effect a working stroke of said ram means, means operable in unison with said control means for rendering said holding means inefiective to therebypermit said resistance valve to open, means operable at the end of said working stroke for effecting operation of said control means to stop delivery of liquid to said work chamber, means responsive to operation of said last named means for permitting liquid to escape from said work chamber to reduce the pressure therein, means responsive to a reduction in pressure in said work chamber for operating said control means to direct liquid from said pump to said return chamber to efiect a return stroke of said ram means, and means responsive to said ram means reaching the end of said return stroke for operating said control means to stop delivery of liquid to said return chamber and bring said ram means to rest.

11. In a downward acting hydraulic press, the combination with cylinder means having a work chamber and a return chamber, ram means mounted in said cylinder means and a pump con nected to both of said chambers, of means for controlling the delivery of liquid to said chambers, a normally closed resistance valve connected in series with said return chamber, means responsive to pressure in said return chamber for holding said resistance valve closed to prevent the discharge of liquid from-said return chamber and thereby support said ram means when said press is idle, means 'for operating said control means to direct liquid from said pump to said work chamber to efiect a working stroke of said ram means, means operable in unison with said control means for rendering said holding means ineffective to thereby permit said resistancevalve to open, means responsive to' said ram means reaching a given point during said working stroke for rendering said holding means effective and thereby cause said resistance valve to offer resistance v.to further downward movement of said ram means, means operable at the end of said working stroke for efiecting opera-' to a reduction in pressure in said work-chamber for operating said control means to direct liquid fromsaid pump to said return chamber to efiect 'a return stroke of said ram means, and means I responsive to said ram means reaching the end of said return stroke for operating said control 12. The combination, with cylinder means having a work chamber and a return chamber and ram means mounted in said cylinder means,

of a reversible pump having one side thereof connected to said work chamber and the other side thereof connected to said return chamber and being adjustable to deliver liquid to one or the other of said chambers or to have its delivery reduced to zero, a normally closed resistancevalve connected in series with said return chamber, means responsive to pressure in said return chamber for holding said resistance valve closed to prevent the discharge of liquid from said return chamber and thereby support said ram means when said press is idle, means for causing said pump to deliver liquid to said work chamber to efiect a working stroke of said ram means, means operable in unison "with said last named means for rendering said holding means ineffective to thereby permit said resistance valve to open, a normally .closed decompression valve adapted when open to permit liquid to escape from said work chamber=to reduce the pressure therein, means operable at the end of said working stroke for causing the delivery of said pump to be reduced to zero and for simultaneously causing said decompression valve to open and permit liquid to escape from said work chamber to thereby reduce the pressure therein, means responsive to the pressure in said work chamber reaching a predetermined minimum for causing said pump to deliver liquidto said return chamher to eii'ect a return stroke of said ram means, and means operable at the end oisaid return stroke for causing the delivery of said pump to be reduced to zero to thereby bring said ram means to rest.

13. The combination, with cylinder -means having a work chamber and a return chamber and ram means mounted in said cylinder means, of a reversible pump having one side thereof connected to said work'chamber and the other side thereof connected to said return chamber and being adjustable to deliver liquid to one or to effect a working stroke of said ram means,

means-operable in unison with said last named means for rendering said holding means inefi'ective to thereby permit said resistance valve-to open, means responsive to said ram means reaching a given point during said working stroke for rendering said holding. means efiective and thereby cause said resistance valve toofier resistance to further downward movement of said ram means, a normally closed decompression valve adaptcd'when open to permit liquid to escape from said work chamber to reduce the pressure therein, means operable at the end of said working stroke for causing the delivery of said pump to be reduced to zero and for simultaneously causing said decompression valve to open and permit liquid to escape from said work chamber to thereby reduce the pressure therein,

means responsive to the pressure in said work chamber reaching a predetermined minimum for causing said pump to deliver liquid to said return chamber to effect a return stroke of said ram means, and means operable at the end of means, the combination of a resistance valve connected in series with said return chamber,

means for holding said resistance valve closed to prevent the discharge of'liquid from said return chamber and thereby support said ram means when said press is idle, means operated in response to said control means being operated to direct liquid to said work chamber for rendering said holding means ineffective to thereby permit said resistance valve to open, and means responsive to said ram means reaching a given point during said working stroke for rendering said holding means effective and thereby cause said resistance valve to offer resistance to further downward movement of said ram means.

15. In a downward acting hydraulic press having cylinder means including a work chamber and a return chamber, ram means mounted in said cylinder means, means including a pump for supplying motive liquid to said cylinder means, and control means fordirecting liquid from said pump to said chambers selectively to effect working and return strokes of said ram means, the combination of a resistance valve having an axial bore closed at one end and an axial port and a peripheral port arranged at the other end of said bore, a piston fitted in said bore, a valve member fixed to said piston to control communication between said ports, a spring normally urging said valve member against said axial port to close the same, fluid channels con-' necting said axial port and said peripheral port to said pump andsaidreturn chamber respectively, channel means connecting said peripheral port to the closed end of saidbore to thereby cause the pressure in saidperipheral port to act upon said piston and urge said valve member against said axial port, choke means arranged in said channel means for limiting the flow of liquid therethrough; a normally closed pilot valve connected to the closed end of said bore and adapted when open to permit liquid to-escape therefrom and thereby permit the pressure in said peripheral port to shift said valve member and open communication between said ports, and means operated in response to said control means being operated to direct'liquid to said work chamber for opening said pilot valve.

16. -In a downward acting hydraulic press having cylinder means including a work chamber and a return chamber, ram means mounted in .said cylinder means, means including a pump for supplying motive liquid to said cylinder means, and control means for directing liquid from said pump to said chambers selectively to effect working and return strokes of said ram means, the combination of a resistance valve having an axial bore closed atone end and an axial port and a peripheral port arranged at the other end of said bore, a piston fitted in said bore,

a valve member fixed to said piston to control communication between said ports, a spring normally urging said valve member against said axial port to close the same, fluid channels connecting said axial port and said peripheral port to said pump and said return chamber respectively, channel means connecting said peripheral port to the closed end of said bore to thereby cause the pressure in said peripheral port to act upon said piston and urge saidvalve member against said axial port, choke means arranged in said channel means for limiting the flow of liquid therethrough, a normally closed pilot valve connected to the closed end of said bore and adapted when open to permit liquid to escape therefrom and thereby permit the pressure in said peripheral port to shift said valve member and open communication between said ports, means operated in response to said control means being operated to direct liquid to said work chamber for opening said pilot valve, means responsive to said ram means reaching a given point during a working stroke for closing said pilot valve to thereby cause said valve member to close said axial port, and pressureresponsive means for permitting said valve member to be moved away from said seat upon the pressure in said peripheral port reaching a predetermined maximum.

1'7. In a downward acting hydraulic press having cylinder means including a work chamber and a return chamber, ram means mounted in said cylindermeans, means including .a pump for supplying motive liquid to said cylinder means, and control means for directing liquid from said pump to said chambers selectively to efiect working and return strokes of said ram means, the combination of a resistance valve having an axial bore closed atone end and an axial port and a peripheral port arranged at the other end of said bore, a piston fitted in said bore, a valve member fixed to said piston to control communication between said ports, a

spring normally urging said valve member against said axial port to 'close the same iiuid channels connecting said axial port and said peripheral port to said pump and said return chamber respectively, channel means connecting said peripheral port to the closed end of said bore to thereby cause the pressure in said peripheral port to act upon said piston and urge said valve member againstsaid axial port, a pressure responsive valve arranged in said channel means and providing a choke for limiting the flow of liquid from said peripheral port to the closed end r of said bore, a normally closed pilot valve con- I nectedto the closed end of said bore and adapted when open to permit liquid to escape therefrom and thereby permit the pressure in said peripheral port to shift said valve member and open communication between said ports, means operated in response to said control means being operated to direct liquid to said work'chamber for opening said pilot valve, and means responsive to said ram means reaching a given point during a working stroke for closingsaid pilot valve to thereby cause said valve member to close said axial port, said pressure responsive valve being adapted to open the closed end of said bore to drain in response to the pressure in said peripheral port reaching a predetermined maximum to thereby permit the pressure in said peripheral port to move said valve member away from said axialport so that liquid from said return chamber may flow therethrough.-

- RICHARD E. DAVIS.

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