US1937192A - Control mechanism for hydraulic motors - Google Patents

Description

' Nov. 28, 1933.

Filed Nov. 24, 1950 2 Sheets-Sheet l (IttornegS,

Nov. 28, 1933. w. ERNST ET AL CONTROL MECHANISII FOR HYDRAULIC MOTORS 2 Sheets-Sheet 2 Filed NOV. 24, 1950 Q Q i IJMI .Qm w w w mm mm M I lllllll Patented Nov. 28, 1933 PATENT OFFICE CONTROL MECHANISM FOR HYDRAULIC MOTORS Walter Ernst and Howard F. MaeMillin, Mount Gilead, Ohio, assignors to The Hydraulic Press Manufacturing Company, Mount Gilead, Ohio Application November 24, 1930 Serial No. 497,911

13 Claims.

This invention relates to control mechanism for hydraulic motors and more particularly to control mechanism for such motors as are operated by fluid delivered under pressure by a reversible pump.

In the patent to Walter Ernst No. 1,711,378, issued April 30, 1929, there is disclosed a control mechanism of the general character referred to. The present invention embodies improvements over the arrangement shown in the patent and also includes certain changes which make the mechanism better adapted for large installations.

In the patented arrangement a reversible radial pump is provided for delivering fluid under pressure. The cross-head of the pump is adapted to occupy three positions; in one of which positions fluid is supplied to the press in a direction to efiect a pressing operation; in another of which positions the direction of fluid travel is supplied to the press in a direction to effect a return stroke of the press platen, and in the remaining of which positions the discharge of the pump is reduced to zero, and the press ram and platen are maintained at rest. Mechanical control linkage is connected between the press and pump for effecting the desired movement of the cross-head to the three positions referred to. This arrangement has been found to be satisfactory when the size of the press and pump is such that the pump may be conveniently placed near the press. However, in some large installations it is not always possible to locate the press and pump close together, and the mechanical connecting linkage is not well adapted to such installations.

An object of the present invention is to provide control means more especially adaptable to such installations as render the use of mechanical connections between the press and pump undesirable. Other objects will become apparent as the description proceeds.

In accordance with the invention the crosshead or other movable device controlling the direction of discharge of the pump is adapted to 45 occupy only two definite positions. Means responsive to the pressure inv the circuit is operable for moving the cross-head to one of these two positions, and manually controlled means is provided for moving the cross-head to its other position. It will be observed that the cross-head is not moved to and retained in a neutral position, and in order to provide for bringing the press ram to rest, means is provided in the hydraulic circuit for by-passing pump fluid from the press cylinder during continued discharge of the pump when it is desired to maintain the ram at rest.

The invention may be embodied in various types of hydraulic motors and associated circuits. A practical embodiment of the invention 30 is illustrated in the accompanying drawings, in

which Figure 1 is a front elevational view of a hydraulic press, a radial pump and associated control mechanism, certain parts being shown in 5 section and the hydraulic connections between the pump and press being shown somewhat diagrammatically;

Figure 2 is a longitudinal, vertical, sectional view through a part of the control mechanism; 7

Figure 3 is a longitudinal, vertical, sectional view of a by-pass valve, and

Figure 4 is a diagrammatic view showing a modiflcation in the control mechanism.

In the drawings is shown a press A including a base 1, a press head 2 connected to the base by strain rods 3, a reciprocatory platen 4 mounted to perform working and return strokes, and a cylinder 5. A double acting ram 6 is mounted in the cylinder 5 and is connected to the platen by a so rod 7. For reciprocating the ram to effect working and return strokes thereof, fluid under pressure is introduced to a work chamber 8 in thecylinder and above the ram 6, and then into a return chamber 9 in the cylinder and below the ram 6.

The fluid delivered to the chambers in the cylinder 5 is furnished by a reversible radial pump, for example, of the kind shown in Patent No. 1,250,170 toHele-Shaw, et a1. Generally speaking, in such pumps the direction of travel of the fluid discharged may be reversed by reciprocating the cross-head or similar device from one position to another. This cross-head is connected to a floating ring which, by movement of the crosshead, may be shifted off center with relation to other elements of the pump. When this floating ring is ofi center in one direction fluid will be discharged under pressure in one direction and will be discharged in the opposite direction when the floating ring is moved ofi center to the opposite side.

.It is unnecessary to set forth the specific construction of the pump in further detail, and such construction is, therefore, not illustrated in detail herein, since the present invention relates to novel control mechanism interposed between the pump and the press whereby the operation of the pump Will be controlled through the shifting of the cross-head from one position to the other and vice versa.

A pump of this kind is indicated in the drawings at B, being preferably mounted upon a tank C. As shown in Figure 2, the pump is provided with the usual cross-head 10 which is movable horizontally to effect reversal of fluid flow in the pump in the manner previously set forth. The pump is provided with two pipe connections 11 and 12. each of which constitutes a combined pump discharge connection and intake connection depending upon the setting or positioning of the pump cross-head.

Means forming a reversible flow hydraulic circuit with the pump and press includes a pipe line 13 connected between the pipe connection 11 and the ram return chamber 9 of the press cylinder, and a pipe line 14 connected between the pipe connection 12 of the pump and the work chamber 8 in the cylinder. When the cross-head is in the position shown in Figure 2 the pump will take in fluid through the pipe connection 11 and will discharge through the pipe connection 12. Fluid will be delivered under pressure to the work chamber 8 and will be exhausted from the work chamber 9 through the pipe line 13. This will effect a pressing or working stroke of the ram and platen. When the cross-head is moved to the left from the position shown in Figure 2, the direction of flow of fluid through the pump will be reversed and fluid will be exhausted from the work chamber 8 through the pipe line 14 and will be delivered under pressure through the pipe line 13 to the ram-returning chamber 9, thus effecting a return stroke of the ram.

It will be observed that due to the displacement of the rod '7, the change in volume in the ramreturning chamber for a given amount of ram movement will be considerably less than the change in volume in the work chamber for the same movement of the ram. In order to compensate for this condition a make-up or differential valve D is provided. This valve includes a casing 15 formed with a central chamber 16 and with end chambers 1"! and 18 separated from the central chamber by partitions l9 and 20. These partitions are respectively provided with openings 21 and 22 which are adapted to be covered and uncovered by means of valve heads 23 and 24 mounted on the ends of a reciprocable valve stem 25. The central chamber 16 is in constant communication with the tank C by means of a pipe 26 and the chambers 17 and 18 communicate with the pipe line 13 and with the pipe line 14, respectively, by means of branch pipe connections 27 and 28. Assuming that the pump is discharging through the pipe line 14 during a working stroke, fluid will be drawn from the returning chamber 9 through the pipe line 13 and the connection 11 on the pump. This fluid, however, will not be sufficient alone to flll the more rapidly changing volume of the work chamber. The amount of fluid necessary to be added to the fluid removed from the returning chamber will, however, be supplied from the tank 0 through the medium of the pipe 26, the valve chamber 16, the valve chamber 1'7 and the pipe 2'7. It will be noted that the valve 25 will be shifted to and held in its Figure 1 position during a working stroke of the ram by the high pressure in the pipe line 14 which is active upon the valve head 24.

During a return stroke of the ram the valve 25 will be shifted so as to close the opening 21 and to open the opening 22, thereby providing a passage through which the excess fluid in the work chamber will be in part exhausted.

It will be understood that when the working stroke has been completed the pump cross-head 10 will be moved to the left as viewed in Figure 2 to reverse the discharge of the pump and to effect a return stroke of the ram. In order to provide for bringing the ram to rest at the end of a return stroke, a by-pass valve E mounted on the press head by means of a bracket 29 is connected between the pipe line 13 and the tank C through the medium of a branch pipe 30 communicating with the valve and pipe 13, and an exhaust pipe 31 communicating with the valve and with the tank C. The by-pass valve E is normally closed, but when the ram has reached a predetermined point during its upward movement, the valve will be opened in a manner to be described. When opened, the valve will by-pass fluid discharged through the pipe line 13 back to the tank by means of the pipes 30 and 31 so that the upward movement of the ram will be arrested. It is important that one side of the bypass valve be connected to communicate with the ram returning chamber 9, as in the present instance through the medium of the pipe 30 and the pipe 13; but it will be apparent that for the purposes of the invention the other side of the lay-pass valve may communicate with an exhaust in various ways. As shown, the by-pass valve communicates directly with the tank 6 by means of the pipe 31, but it will be apparent that, if the pipe 31 were connected, for instance, to the pipe 14, it would communicate with the tank during a return stroke since the opening 22 of the compensating valve D would be uncovered.

With more particular reference to the construction of the by-pass valve, this valve, as shown in Figure 3, includes a casing 32 formed with a valve chamber 33 in which a piston valve 34 is mounted for sliding movement. The piston valve 34 includes spaced heads 35 and 36' connected by a reduced portion or stem 3'7. A long valve operating stem 38 is formed integrally with the lower end of the piston valve and extends through 120 an apertured ring 39 positioned in a bore 40, the ring being held in place against a shoulder 40 by means of packing 41 interposed between the ring and a gland 42 urged upwardly against the packing by means of a hollow nut 43 having threaded 125 connection with the valve casing. The upper end of the valve casing is formed with a longitudinal recess 44 in which is positioned a spring 45 interposed between the valve head 36 and a plug 46 having threaded connection to the interior of 130 the recess 44 and closing the upper end thereof. The spring 45 constantly urges the valve 34 to its lower-most position, the downward movement of the valve being limited by contact of the head 35 with the ring 39. The valve 34 is pro- 135 vided with a drilled passage 47 extending from end to end and serving to afford communication between the recess 44 and the lower end of the valve chamber 33 whereby the valve is balanced as to pressure. The pipe 31 is adapted to com- 140 municate with the valve chamber by means of a port 48 when the piston valve is moved upwardly, and the pipe 30 is in constant communication with the valve chamber by means of a port 49.

The long stem 38 on the piston valve extends 145 down through 2, lug 50 secured to the press platen, this lug being adapted to slide freely on the rod 38 until, during upward movement of the platen, the lug engages a collar 51 secured to the stem 150 38, at which time the stem and the piston valve Cal 34 will be raised, thereby affording communication between the pipes 30 and 31' and by-passing fluid from the pipe 13 back in tank C. In operation, the platen will continue to ascend until the by-pass valve has been opened to such an extent that the throttling of the fluid caused by a somewhat restrictedvalve opening will be sufiicient to produce a back pressure just high enough to support the ram and connected parts in their elevated positions.

The controlmechanism for effecting the desired movements of the pump cross-head to produce the working and return strokes of the ram set forth above is generally designated F. Referring to Figure 2, it will be seen that a stem 52 is connected to the cross-head 10, and is mounted to slide freely in a bore 53 formed in a sleeve 54. A head 55 on the stem 52 is arranged for sliding movement in a hollow portion 56 in the sleeve, and a spring 5'7 is interposed between the head 55 and another stem 58 which has threaded connection with the interior of the sleeve 54. The outer end 59 of the stem 58 is mounted for sliding movement in a guide sleeve 60, threaded into a fixed frame 61 secured to the pump casing, the inner end 62 of the guidesleeve serving as an abutment for cooperation with a flange 63 on the stem for limiting the movement of the stem 58 toward the left. A strong spring 64 isinterposed between a flange 65 on the sleeve 54 and a flange 66 on a fixed sleeve 67 through which the stem 52 extends. This spring constantly urges the sleeve 54 and the stem 52 to the left. The spring 57 serves to cushion the connection between the sleeve 54 and the stem 52 when the sleeve and stem are moved to the right.

The movement of the cross-head 10 is controlled by means of a control lever 68which is fulcrumed as at 69 to the frame 61 and which is pivoted to the stem 58 as at 70. The upper end of this lever has a nose '71 adapted to be engaged by a trip '72 which is pivoted to a slidable frame '74 as at '73. The frame '74 is mounted to slide on the fixed frame 61 and such sliding movement is effected by the turning of a hand wheel fixed to a shaft '76 journalled in the fixed frame 61 and held against longitudinal movement, the inner end of the shaft 76 having threaded connection with the slide frame 74.

The slide frame carries a small cylinder '77 having a chamber '78 in constant communication with the pipe line 14 through the medium of a pipe '79. Mounted in the cylinder is a plunger 80 having a stem 81 pivoted to the trip '72 as at 82. The trip 72 is urged to the left by a spring 83 interposed between a screw 84 on the trip and a spring seat 85 on a threaded shaft '86 screw-threaded in a lug 87 on the cylinder. The compression of the spring may be adjusted by rotation of a hand wheel 88 secured to the shaft 86, and the shaft and spring may be locked in adjusted position by means of a set screw 89.

Assuming that the parts are in the positions shown in Figure 2, the pump will discharge through the pipe line 14 and will thus effect a pressing stroke of the ram. When the platen encounters the work, pressure will build up in the work chamber 8, the pipe line 14 and consequently in the chamber '78 of the cylinder '77. When the pressure has built up to a predetermined point, the plunger 80 will be moved to the right, as viewed in Figure 2, and the trip '72 will be disengaged from the nose '71 of the lever 68. When the lever has been thus released from its Figure 2 position in which it was previously retained by the trip, the spring 64 will move the sleeve 54 and the stem 52 to the left, and the discharge of the pump will be reversed so as to produce a return stroke of the platen. When it is desired to return the parts to their Figure 2 positions, the control lever is moved to such position by means to be later described. This will move the stem 58, the stem 52 and the'crosshead to the right, that is, to their Figure 2 positions. When such movement has been compieted, the trip 72 will be swung in a counterclockwise direction by means of the spring 83, thus again engaging the'nose '71 of the lever 68 and retaining the latter in its Figure 2 position until pressure again builds up to the chamber '78. It will be observed that the lever 68 constitutes a flow control device movable to two positions to effect reversal of fiuid flow through the pump and circuit.

The spring 57 permits a little overtravel of the stem 58 after the stem 52 has completed its stroke in order that the nose 71 may move far enough to insure its being retained by the trip 72. The amount of movement of the lever 68 and the stem 58 will be governed by the position of the trip '72. If the fulcrum '73 is moved by means of the hand wheel '75 toward the left the trip will engage the control lever nose '71 at an earlier point of its movement so that the stem 58 will be moved only through a part of its full stroke which will result in the pump delivering only a partial amount of the fluid, therefore imparting slower speed to the press. The hand wheel '75 may be set for any speed desired. The tension of the spring 83 may be varied by means of the hand wheel 88, thus varying the pressure at which the control mechanism will be operated and consequently varying the maximum pressure to be exerted by the press.

For moving the lever 68 to the left, that is to say, to its Figure 2 position, to effect a working stroke of the ram, power operated means is provided. One practical arrangement for accomplishing this purpose is shown in Figures 1 and 2. A cylinder 90 is mounted on a bracket 91 secured to the fixed frame 61 of the control mechanism F. This cylinder is open at its outer end as shown in Figure 1, and is closed at its other end. A piston 92 is mounted in the cylinder and is provided with a stem 93 which extends through an opening in the closed end of the cylinder, the outer end of "the stem 93 being pivotally connected to the lower end of the control lever 68 as at 94. Packing 95 maintained in place by a gland nut 96 maintains a fluid tight seal at the closed end of the cylinder. For moving the piston 92 to the left as viewed in Figure 1 the cylinder is connected to a source of fluid pressure, such as a compressed air tank 9'7. The connections between the cylinder and the tank comprise a pipe 98 connected to the tank and to a manually operable control valve 99 mounted on the press base, and a pipe 100 connected between the control valve and the cylinder. The control valve may be of any'suitable two-way type. The valve illustrated is of the rotary plug kind, and includes, a casing 101 and a rotary valve plug 102 mounted within the casing and having a passage 103. The valve casing is also provided with an exhaust passage 104. When the valve passage is in the position shown in dotted lines in Figure l compressed air from the tank 97 will be introduced into cylinder 90 through the medium of the pipe 98, the passage 103 in the valve plug and the pipe 100. The pressure fluid l-lO thus introduced into the cylinder will move the piston 92 to the left. When the valve plug is rotated to bring the passage 103 to its full line position, the pipe 100 and consequently the cylinder will be connected to the exhaust passage 104, thus relieving the pressure in the cylinder.

It will be noted that when pressure fluid is introduced into the cylinder 90, the piston 92 being thereby moved to the left will rock the control lever 68 in a clockwise direction against the urgeof the spring 64 until the control lever is latched in its Figure 2 position in the manner already described. After this, the valve plug is moved to bring the passage 103 to its full line position, thus relieving the pressure in the cylinder. Subsequently, when the trip '72 is disengaged from the nose '71 of the control lever in the manner already described, the spring 64 will move the sleeve 54, the stem 52, and the cross-head 10 to the right.

If desired, the movement of the control lever to the Figure 1 position may be effected by means of electrically operated means instead of the compressed air means described above. In the modification shown in Figure 4 an electric solenoid 105 is used in place of the cylinder 90, being mounted on the frame 61 by means of a bracket 106. The solenoid is provided with a plunger 107 pivoted at its outer end to the lever 68 as at 108. The solenoid is adapted to be energized from a supply line 109, and the energizing is controlled by means of a manually operable push-button switch 110 preferably mounted on the press base and being adapted to open and close the circuit through the solenoid. When the push-button switch is momentarily closed, the solenoid will be energized and the plunger 107 will be moved to the left. This will move the control lever 68 to its Figure 2 position in which it will be latched in the manner described above.

Operation The construction and arrangement of the various parts of the control mechanism having been described, a complete cycle of operation will now be set forth in order that the sequence of operation of the variouscontrol elements may be clearly understood.

Assuming that the several parts are in the positions shown in the drawings, the pump-crosshead 10 will be in its right-hand position and will be maintained in such position by means of the trip 72 retaining the control lever 68 in its Figure 2 position. In this position of the pumpcross-head, fluid will be delivered from the pump through the pipe line 14 to the work chamber 8 and the platen and ram will perform a working stroke. When the platen has encountered resistance to its travel, pressure will build up in the work chamber and in the chamber '78 of the cylinder '77 on the control device, resulting in the disengagement of the trip '72 from the control lever 68. The spring 64 will then move the sleeve 54 and the stem 58 to the left, and will swing the control lever in a counter-clockwise direction. Simultaneously the pump cross-head will be moved to the left and the direction of fluid travel through the pump will be reversed so that fluid will then be delivered to the ram-returning chamber 9, thus causing a return stroke to be performed. When the ram approaches the end of the return stroke, lug 50 will engage the collar 51 on the long stem 38 and will move the piston valve 34 upwardly to provide communication between the pipes 30 and 31, which will effect a bypass of the fluid discharged by the pump. This by-passing of fluid will bring the ram to rest, and the ram will be maintained at rest while the cross-head remains in its left hand position. When it is desired that the ram perform another working stroke, the manually operable valve is moved to its Figure 1 dotted line position, whereby compressed air will be admitted to the cylinder 90, moving the piston 92 to the left which results in returning the cross-head and associated parts to the right hand or Figure 2 position, at which time the direction of fluid travel through the pump will be reversed and another complete working and return stroke will take place in the manner set forth above.

When the ram is at rest in its uppermost position, the lower end of the control lever will be to the right of the position shown in Figure 2 and the cross-head will be to the left of the position shown in Figure 2. In other words, these are the positions occupied by the lever and crosshead when the press is inactive but in readiness to perform a pressing operation. These positions are therefore the first positions occupied by the parts referred. to. When the cross-head and lever 68 are moved to their Figure 2 positions to effect a working stroke, each will be in its second position.

In operating the press when equipped with the solenoid shown in Figure 4, the switch 110 is momentarily closed to start a pressing stroke. This produces the same effect as the opening of the valve 99 shown in Figures 1 and 2.

Although for the purpose of illustration the invention has been described as being embodied in a hydraulic press including a platen especially adapted for performing pressing operations, it is also applicable to hydraulic motors of other kinds which have movable rams equipped with tools other than platens such, for instance, as dies, punches, or shears.

We claim:

1. The combination with a hydraulic motor having a working chamber and a ram returning chamber including ram means mounted to perform working and return strokes; of a reversible flow radial pump having a movable cross head adapted to occupy two positions for selectively effecting flow through said pump in both directions; means forming a reversible flow hydraulic circuit with said motor and said pump; means connected to said pump cross head and automatically operable when the ram approaches the end of a working stroke for moving the cross head to one of its positions to reverse the direction of fluid travel; a normally closed by-pass valve connected to said ram returning chamber; and means connected to said ram means and adapted to open said valve when the ram approaches the end of a return stroke to thereby bring said ram to rest during continued discharge of said pump.

2. The combination with a hydraulic motor having a working chamber and a ram returning chamber including ram means mounted to perform working and return strokes; of a reversible flow radial pump having a movable cross head adapted to occupy two positions for selectively effecting flow through said pump in both directions; means forming a reversible flow hydraulic circuit with said motor and said pump; means connected to said pump cross head and automatically operable when the ram approaches the end of a working stroke for moving the cross head to one of its positions to reverse the direction of fluid travel; a normally closed by-pass valve connected to said ram returning chamber; means connected to said ram means and adapted to open said valve when the ram approaches the end of a return stroke to thereby bring said ram to rest during continued discharge of said pump; and manually controlled means for moving the pump cross head to its other position.

3. A control mechanism adapted to be operatively connected to a hydraulic circuit including a reversible pump, a hydraulic motor having working and ram returning cylinder chambers and reciprocable ram means, and a normally closed by-pass valve connected to said ram returning chamber and being interposed between the latter and an exhaust; said mechanism comprising a fiow control device associated with said pump and adapted to occupy two positions; means for moving said device from the first to the second position to cause the pump to discharge so as to produce a working stroke of the ram means; pressure controlled means for thereafter moving said device from the second position to the first position to reverse the discharge of the pump and produce a return stroke of the ram means; and means for thereafter automatically opening said by-pass valve to bring the ram means to rest during continued discharge of the pump.

4. A control mechanism adapted to be operatively connected to a hydraulic circuit including a reversible pump, a hydraulic motor having working and ram returning cylinder chambers and reciprocable ram means, and a normally closed by-pass valve connected to said ram returning chamber and being interposed between the latter and an exhaust; said mechanism comprising a flow control device associated with said pump and adapted to occupy two positions; manually controlled means for moving said device from the first to the second position to cause the pump to discharge so as to produce a working stroke of the ram means; means responsive to built up pressure in the circuit during a working stroke for thereafter moving said device from the second position to the first position to reverse the discharge of the pump and produce a return stroke of the ram means; and means for thereafter automatically opening said by-pass valve when the ram reaches a predetermined point on its return stroke to bring the ram means to rest during continued discharge of the pump.

5. A control mechanism adapted to be operatively connected to a hydraulic circuit including a reversible pump, a hydraulic motor having working and ram returning cylinder chambers and reciprocable ram means, and a normally closed by-pass valve connected to said ram returning chamber and being interposed between the latter and an exhaust; said mechanism comprising a flow control device associated with said pump and adapted to occupy two positions; means for moving said device from the first to the second position to cause the pump to discharge so as to produce a working stroke of the ram means; means for detaining the device in such position, means responsive to built up pressure in the circuit for releasing said detaining means; means for moving said device when releasedlfrom the detaining means from the second to the first position to produce a return movement of the ram means; and means connected to the ram means and adapted to automatically open said by-pass valve when the ram means reaches a predetermined position on its return stroke to bring the ram means to rest while said device remains in said first position and during continued discharge of said pump.

6. A control mechanism adapted to be operatively connected to a hydraulic circuit including a reversible pump, a hydraulic motor having working and ram returning cylinder chambers and reciprocable ram means; and a normally closed by-pass valve connected to said. ram returning chamber and being interposed between the latter and an exhaust; said mechanism comprising a shiftable pump element adapted to occupy two positions to control the direction of flow through the pump; power operated means operable independently of movement of said ram means for moving said shiftable element from the first position to the second position to cause the pump to discharge so as to produce a working stroke of the ram means, manually operable means for controlling the operation of said power operated means; means for moving said shiftable pump element device from the second position to the first position to reverse the discharge of the pump and produce a return stroke of the ram means; and means for thereafter automatically opening said by-pass valve to bring the ram means to rest while said device remains in its first position and during continued discharge of said pump.

7. A control mechanism adapted to be operatively connected to a hydraulic circuit including a reversible pump, a hydraulic motor having working and ram returning cylinder chambers and reciprocable ram means, and a normally closed by-pass valve connected to said ram returning chamber and being interposed between the latter and an exhaust; said mechanism comprisin; a shiftable pump element adapted to occupy two positions to control the direction of fiow through the pump; a fluid pressure actuated piston connected to said device and being operable independently of movement of said ram means for moving said shiftable element from the first position to the second position to cause the pump to discharge so as to produce a working stroke of the ram means, a manually operable valve for controlling the application of pressure to said piston; means .for moving said shiftable element from the second position to the first position to reverse the discharge of the pump and produce a return stroke of the ram means; and means for thereafter automatically opening said by-pass valve to bring the ram means to rest while said device remains in its first position and during continued discharge of said pump.

8. A control mechanism adapted to be operatively connected to a hydraulic circuit including a reversible pump, a hydraulic motor having working and ram returning cylinder chambers and reciprocable ram means, and a normally closed by-pass valve connected to said ram returning chamber and being interposed between the latter and an exhaust; said mechanism comprising a shiftable pump element adapted to occupy two positions to control the direction of fiow through the pump; an electric solenoid having a plunger connected to said device and being operable independently of movement of said ram means for moving said shiftable element from the first position to the second position to cause the pump to discharge so as to produce a working stroke of the ram means, a manually operable electric switch for controlling the energizing of said solenoid; means for moving said shiftable element from the second position to the first position to reverse the discharge of the pump and produce a return stroke of the ram means; and means for thereafter automatically opening said by-pass valve to bring the ram means to rest while said device remains in its first position and during continued discharge of said pump.

9. The combination with a hydraulic motor including working and ram returning cylinder chambers and ram means mounted to perform working and return strokes; of a reversible pump; means forming with the pump and the motor a reversibleflow hydraulic circuit; means responsive to built-up pressure in said circuit during a working stroke for reversing said pump to thereby effect the start of a return stroke; a normally closed valve connected to said ram returning chamber and being interposed between the latter and a fluid exhaust, said valve being adapted to be automatically opened when the ram approaches the end of a return stroke whereby fluid will be by-passed from said ram returning chamber and said ram means will be brought to rest during continued discharge of said pump; and manually controlled means for then reversing said pump to effect the start of a working stroke.

10. The combination with a hydraulic motor including working and ram returning cylinder chambers and reciprocable ram means adapted to perform working and return strokes; of a reversible pump; hydraulic connections forming a reversible flow hydraulic circuit with said motor and said pump; means associated with said pump for reversing the direction of fluid travel in said pump and circuit to thus eiiect working and return strokes of the ram means; and a normally closed valve connected to said ram returning chamber and being interposed between the latter and a fluid exhaust and adapted to be automatically opened when said ram means has reached a predetermined position during its return stroke, to thereby by-pass fluid from said ram returning chamber and bring the ram means to rest during continued discharge of said pump.

11. The combination with a hydraulic motor including a cylinder having working and ram returning chambers and a ram mounted to perform working and return strokes; of a reversible pump; means forming a reversible flow hydraulic circuit with said motor cylinder chambers and said pump; means associated with said pump and automatically operable when the ram approaches the limit of a working stroke for reversing the direction of fluid travel in said pump and circuit; a by-pass valve connected to said ram returning chamber and being interposed between the latter and an exhaust; means connected to said ram and adapted to open said valve when the ram approaches the end of a return stroke whereby said ram will be brought to rest during continued discharge by the pump; and manually controlled means associated with said pump and operable when the ram is at the end of a return stroke to reverse the direction of fluid travel in said pump and circuit.

12. The combination with a hydraulic motor including a cylinder having working and ram returning chambers and a reciprocable doubleacting ram; of a reversible pump; means forming a reversible flow fluid circuit with said motor cylinder chambers and said pump; means associated with said pump and responsive to an increase in pressure in said circuit for reversing the direction of flow thru said pump and circuit; a normally closed valve connected to said ram returning chamber and being interposed between the latter and an exhaust and adapted when open to by-pass fluid from said ram returning chamber; and means connected to said ram and operable to open said valve when the ram reaches a predetermined position during one of its strokes to thereby bring said ram to rest during continued discharge of said pump.

13. The combination with a hydraulic motor including a cylinder having working and ram returning chambers and a ram mounted for vertical downward working strokes and upward return strokes; of a reversible flow pump having a shiftable pump element adapted to occupy two positions for selectively efiecting flow through said pump in both directions; means forming a reversible flow circuit with said pump and motor cylinder chambers; means connected to said shiftable element and being automatically operable when the ram approaches the end of a working stroke for shifting said shiftable element to one of its positions to reverse the direction of fluid travel and thereby produce a return stroke; a normally closed by-pass valve connected to said ram returning chamber and being interposed between the latter and an exhaust; and means connected to said ram and being adapted during upward movement of the ram to effect a throttled opening of the valve, whereby to provide a by-pass of fluid from the circuit and to simultaneously maintain suificient pressure therein to sustain the weight of the ram and associated parts during continued discharge of the pump.

WALTER ERNST. HOWARD F. MACMILLIN.

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