US2419235A - Control system for hydraulic motors - Google Patents

Description

April 22, 1947. T. F. STACY CONTROL SYSTEM FOR HYDRAULIC MOTORS File d May 20, 1942 INVENrUR.

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Patented Apr. 22, 1947 CONTROL SYSTEM FOR HYDRAULIC MOTORS Thomas F. Stacy, Piqua, Ohio, assignor to The French Oil Mill Machinery Company, Piqua,

Ohio

Application May 20, 1942, Serial No. 443,766

Claims.

This invention relates to control systems for hydraulic motors such as hydraulic presses, and is in the nature of a continuation in part of my prior copending application No. 262,709, filed March 18, 1939, now Patent No. 2,367,241, issued January 16, 1945.

It has been proposed to have a pilot system operate a main valve which controls the advance and retraction of a working member, such as a hydraulic ram or platen, in which the pilot system includes a valve that is internally balanced as to pressure, and which directs the pilot oper ating fluid to hydraulic means for operating the main valve. When the advancing pressure on the working member reaches a predetermined pressure, a pressure responsive hydraulic device is utilized to move the pilot valve in a direction to reverse the direction of travel of the working member, but as the pressure builds up gradually, the pilot valve is operated gradually. Since the pressures at the time of reversal are relatively high, injury to the pilot and main valves by such gradual operation often results, and the action is not as prompt as it should be.

An object of the invention is to improve and simplify pilot operated controls for hydraulic motors, and particularly for hydraulic presses,

with which danger of injury to the valves through slow movement thereof will be avoided, which will require a minimum number of parts, which will have maximum flexibiilty of control, and which will be relatively trouble-free and relatively simple and inexpensive.

Another object of the invention is to provide an improved control system for hydraulic motors and presses, which will eliminate the'use of mechanical latches and slowly opening contacts in electrical circuits, which will give maximum freedom and flexibility of control, and which will avoid shock in the hydraulic control system upon reversal of the direction of travel of the Working member, when the reversal occurs immediately after a relatively high pressure has been exerted on the working member.

Another object is to provide an improved control system in which the delivery of the pump will be automatically reduced during a reversal In the drawing:

Fig. 1 is a sectional elevation showing, somewhat diagrarmnatically and schematically, parts of a hydraulic motor, and a control and operating system therefor constructed in accordance with this invention; and

Fig. 2 is a fragmentary diagram illustrating a slight modification of the system shown in Fig. 1, in which a bleeder port is substituted in place of a check valve.

In the embodiment of the invention illustrated in Fig. l, the hydraulic motor is in the nature of a hydraulic press having a head I open at its lower end to slidingly receive a ram or piston 2 which terminates within the head I in a piston head 3 that closely fits and reciprocates in the chamber within the head I. The chamber 4 at the upper end of the head I may be considered an advancing cylinder for forcing the piston head 3 downwardly or in an advancing direction, and the chamber 5 below the piston head 3 may be considered as a retracting cylinder for forcing the piston head 3 upwardly or retracting it. The chamber 5 is also sometimes called a pull-back cylinder and it may be a separate ram entirely outside the chamber within the head I, but connected to the working member or plate 6 which is carried on the piston or ram 2. In the particular illustration, the platen B descends during an advancing stroke or movement, and is elevated when retracted or returned to its initial position.

Any suitable source of operating fluid or liquid under pressure may be employed for operating the hydraulic motor, but preferably the source of operating fluid is a pump 1 of the variable delivery type which is connected at its intake side by a pipe 8 to a reservoir 9 for fluid such as oil. The output side of the pump 1 is connected by a pipe ID to a port H in the casing of a main valve I2. The valve [2 includes a valve chamber 13 in which reciprocates a valve element I4 having spaced lands l5 and It within the chamber l3.

A helical compression spring ll acting between one end of the chamber l3 and the land I6 yieldingly urges the valve element [4 in one direction from the position shown by dot and dash lines to the position shown by dash lines in Fig. l. The valve element M has an extension, rod or piston portion ['8 extending exteriorly of the chamber 13 and into another and separate chamber IS in a part which may be integrally attached to the housing of the valve [3. The chamber l9 and rod portion I8 constitute a hydraulic device which, when fluid pressure is applied to chamber l9, applies a moving force to valve element l4 tending to shift it upwardly in Fig. 1, against the action of the spring l1, into the upper position shown by dot and dash lines in Fig. 1. The position of the valve element as shown by full lines in Fig. 1 is its intermediate position, that is, intermediate the two positions which have just been described. The port H is intermediate the lands l5 and it when the valve element is in its intermediate position, and the land I6 is beveled at its periphery, as shown in Fig. 1.

When the valve element I l is in the intermediate position, the beveled edge of the land I6 will be alined with an annular port 26, and the fluid delivered through the port I I from the pipe it) may pass around the land 56 at the annular port 28 and reach an outwardly disposed port 2!, which is connected by a pipe 22 to the reservoir 9.

The port 29 is connected by a pipe 23 to the ad- 2 3 which is bridged and covered by the land l5 when the valve element i4 is in its intermediate position shown by full lines in Fig. 1, and this port 24 isconnected by a pipe 25 to the pullback or retracting chamber or cylinder 5. The end ofthe chamber l3 opposite from the spring I! is provided with a port 26 which is also connected to the pipe 22 leading to the reservoir 9.

The pipe ill is provided with a choke valve 21 through which all of the fluid reaching the chamber I3 of valve l2 must pass, and this choke may be of any suitable type which creates just sufficient back pressure to provide a working pressure on the pump at all times. A simple pressure relief valve set for a relatively low pressure but opening to pass fluid away from the pump is very suitable for this purpose. When the valve element I4 is in its intermediate position, fluid from the pump 1 passes through the pipe to the chamber 53 of the valve l2, thence back by pipe 22 to the reservoir. Fluid in the retracting cylinder 5 is held against escape by the closing of the port 24 by the land l5.

When the valve element It is moved upwardly in Fig. 1, the land l5 will move into a position between the ports I l and 2d nd will uncover port '24, and land I 6 will move into a position between ports 26 and 2i and cut off direct communication between those ports. The fluid delivered by the pipe II] from the pump 1 will then pass through chamber iii of valve I2 into pipe 23 and thence to the advancing cylinder 4 to cause an advance or descent of the working member or platen 6. When element i4 is in its upper position, the port 24 is uncovered and fluid from the retracting chamber 5 may escape through pipe 25, port 2 lower end of chamber l3, port 26 and pipe 22 back to reservoir 9. The platen B will descend under its own weight aided by the fluid delivered from the pump through the pipe 23, and to provide a more rapid advance or descent, a pilot operated, preflll check valve 28 is connected by pipe 29 'to the chamber 4 and by a pipe 30 to reservoir 9. The valve element 3| in the check valve opens automatically by reason of the suction in the chamber e, and fluid is drawn from the reservoir 9 through pipe to, valve 28, and pipe 29 to fill the space in head I that increased with the descent of the piston head 3, as usual in hydraulic presses of this type.

Manual means for operating the valve element l4 may be' provided such as by extending the "valve element ['4 outwardly of the housing of'the 4 valve l2 and providing spaced collars 32 thereon between which the forked end of a lever 33 operates. The lever 33 is pivoted at 3 1, and by rocking the lever 33, the valve element l4 may be shifted upwardly to cause an advance or descent of the platen E, or downwardly to cause a return of the platen. Any other manual control for element i i may be employed. Such manual operation of valve element i4 is advantageously employed when the platen is being inched or advanced by small increments as in setting up dies or work in the press, or wherever a close control of the press for obtaining small move- 7 ments of the platen is desired. When a full, ad-

vance operation of the platen 6 is desired, the Valve element Hi is operated against the action of the spring I! into its upper or advancing position, by the application of fluid under pressure to the chamber l9. Fluid in chamber 19 acts on the extension i8 and hydraulically shifts the valve element l i upwardly into its advancing position, which is one of its end or limit positions.

The chamber i9 is connected by a pipe 35 to a pilot valve 35 having therein a valve element 3? which is internally balanced as to pressure, so that this valve element will remain in either of its positions into which it may be moved and the pressure of the operating fluid therein will not move the Valve element in either direction. The pipe 35; opens into the housing of the valve 33 through a port 33, and'a pipe 39, leading from the pipe ll? between the choke valve 21 and the pump 7, opens into the chamber of the valve 36 through a port it. The valve element 31 carries spaced lands ll and d2, and when it is in one end position, such as shown in full lines in Fig. 1, the land ll will be disposed between the ports 33 and ii), and the land .2 will be on the opposite side of the port ii). A drain pipe 43 opens into the ends of the chamber of the valve 36 and leads to the reservoir 9.

When the valve element 3'5 is in the position shown in Fig. 1, fluid under pressure from the pump passes through pipes it and 3d and port iii into the chamber of the valve 35 between the lands and 1:12, and since the lands are the same size, the pressure exerted on the valve element will be equal in both directions and will cause no movement of the valve element. Since the land M is between the ports 33 and 43, there will be no escape for the fluid delivered to the pilot valve, the port 33 will be in communication with the adjacent end port to which drain pipe 43 is connected, and there will be no fluid pressure in the chamber IQ of the valve. If now the valve element is moved to the left in Fig. 1, so as to place the lands 6! and 42 in the positions shown by dash lines, then the land ll will be between the port 33 and the adjacent connection to the pipe thereby preventing escape of fluid from chamber iii to pipe t3, and the ports 38 and ii) will be connected to one another by the space between the lands ll and 42. Fluid from the pump will then pass through the pilot valve 35 to chamber is and force the valve element i l upwardly against the action of spring I "i into the advancing position to cause a descent or advance of the platen 6. Since the valve element 3? of the pilot valve is internally balanced, it will remain in this position and the pressure of the pump will hold the'valve element la in this elevated position.

Any suitable means forv operating the pilot valve element 37 into the dasheline position to cause an'advance' of the platen 6 may be employed, but for convenience, this may be accomplished by disposing the core 44 of an electromagnet or solenoid 45 in a position endwise against the valve element 3?, so that when the solenoid 45 is energized, the core 4 1 will be moved endwise and will shift the pilot valve element 31 from the full line to the dash line position in Fig. 1. Current for the solenoid i5 is supplied from line wires L and L the circuit being controlled by a normally open switch 25, which is closed and held closed only long enough for the solenoid to move the valve element 3? into the dotted or dash line positions, after which the switch 46 is released and will be automatically opened.

The switch it or the circuit of the solenoid 45 may be controlled by any suitable automatic mechanism that one may desire, but since the details of such controls are no part of the present invention, only a simple circuit for the solenoid 45 has been illustrated.

. To operate the pilot valve element 31 from the dash line position tothe full line position at the end of a desired movement of the platen 6, a fluid responsive device has been provided. For this purpose, a plunger il is disposed endwise in axial alinernent with the valve element 3?, and at the end opposite from the solenoid 135. This plunger is yieldingly urged into retracted position by a suitable retracting means such as by a spring as acting between a collar lie on the plunger ill and the end of a housing 59 having therein an auxiliary chamber or cylinder Si through which the plunger ll extends endwise. The plunger ll at a point within the chamber 5| is provided with a head 52 which acts as a piston therein. A pipe 53 is connected to the chamber 5| behind the head 52 so that when fluid pressure is supplied to chamber 5! by pipe 53, it will force the plunger t! to the right and carry the pilot valve element it? from the dash line position to the full line position, thus returning the pilot valve element to its normal, initial position. This same movement serves to move the core 44 of the solenoid 45 back into its retracted position. v

The pipe 53 is connected to the outlet side of a pressure relief valve s4, and the other or inlet side of that valve is connected by a pipe 55 to the pipe 23 leading to the advancing cylinder :3 of the hydraulic motor or press. The pressure relief valve 54 opens to pass fluid from the pipe 23 to the pipe 53, thence to'the chamber 5|, automatically when the pressure in the pipe 23 exceeds a predetermined pressure for which the .pressure relief valve is set, and closes automatically to prevent flow of fluid in the opposite direction therethrough. Since the fluid in the pipe 23 will be under substantially the same pressure as that in the advancing chamber or cylinder 4, the result is that the valve 54 automatically opens when the pressure in the advancing chamber or cylinder l exceeds a predetermined value for which the valve 54 is set. When valve 54 opens, fluid passes through valve 5 into the auxiliary cylinder 5i behind the head 52 and forces it to the right against the action of the spring 58 to shift the pilot valve element 3'! into the full line position in Fig. l, where it disconnects the pipes 35 and 39, and vents the pipe 35, thus releasing pressure from chamber :9.

The spring N then urges the valve element I l of the main valve downwardly in Fig. 1 and toward a position in which the land it is between .ports H and 28 and land I5 is between ports .24. a 5- Th sld s en eoi t ep pe w o the advancing chamber 15 and connects the pipe 23 to the port 2!,thus allowing release of fluid from the main or advancing cylinder and its movement back to the reservoir 9. This causes a return of the platen 6 to its elevated position. It is undesirable to have the valve element l4 pass through the intermediate position and into reverse position without stopping, because this causes a severe shock to the hydraulic system, owing to sudden release of the high pressure in the advancing chamber. Such pressures in the advancing chamber often amount to as much as 2500 or 8000 pounds per square inch and the sudden release or" such a high pressure, accompanied by the simultaneous application of fluid under the same pressure as received from the pump through pipe 19 to the retracting chamber 5, produces objectionable shocks. This shock is avoided by having the valve element It automatically restrained momentarily in the intermediate position and then allowed to continue its movement into reverse position.

Means for accomplishing this shock prevention will now be described. A two-way valve 56 has a chamber 51 in which a valve element 58 reciprocates, The element 58 extends through the housing of that valve along the path of travel of the platen t, as an outward rod or extension 59. The latter carries a collar 56 slidable therealong but secured thereon in any position, such as by a set screw, so as to be adjustable into different selected positions along the rod 59. The platen B has an extension 6! which moves along the rod 59 and at a selected point in the return travel of the platen 6, which position is determined by the setting of the collar Bil, the extension 6| picks up the collar 61! and through it shifts the valve element 58 into the position shown in full lines in Fig. 1 against the action of a spring 62. When the platen moves downwardly, the released valve element 58 is shifted downwardly by the spring 62 into its other position.

The housing of the main valve l2 extends beyond the chamber f! so as to p e co d chamber 63 which is alined with the chamber IS. A piston 64 slidingly extends through the partition wall 65 between the chambers 63 and I9, so as to abut against the end of the extension 18 of the valve element I4. The end of the piston 54 which is within the chamber 63 is provided with a head 66, which by engagement with the wall 65 limits the movement of the piston 64 into the chamber IE! beyond the position shown in Fig. 1. The piston 64 can thus shift the valve element I4 into the intermediate position shown in Fig. 1 against the action of the spring H, but no farther. A rod 51 extends outwardly of chamber 63 from the head 66 of piston 63 and at its outer end carries an adjustable nut 58. A spring 69 is compressed between the nut 68 and the part of the housing in which the chamber 63 is located, so as to yieldingly urge the piston 64 in a direction away from the valve element M.

A pipe 10 is connected to the outer end of the chamber 63 and to an intermediate port in the valve 56. The valve element 58 carries a pair of spaced lands "H and 12 arranged on opposite sides of the port opening into th pipe H3. A pipe 13 leads from the pipe 25 to the chamber 51 at a zone immediately adjacent the land 12 when the valve element 51 is in its position shown in full lines in Fig. l, but in a position to be closed by the land 12 when the valve element 51 is released by the platen 6 and moved by the springl62 into its otherposition, v.

Another pipe 14 opens into the chamber 5'! of valve 56 in a position to be closed by the land H when the valve element 58 is in its full line position, but in a position to be uncovered by the land H and placed in communication with the opening to pipe 1G, when the Valve element 58 is released and moves downwardly by the action of spring 62. The pipe 74 leads to the pipe 23, which is in communication with the advancing chamber 4. This valve 56 is a two-way valve internally balanced as to pressure, and yieldingly urged into one position when released by the platen but moved into its other position by the platen as the latter approaches a selected position in its return movement. When the platen 6 is retracted and operates the valve element 53 into the position shown in full lines, it places the pipes l and 73 in communication with one another so that the pressure in the retracting chamber will be in communication with the chamber 63, This pressure forces the piston E l upwardly as far as it will go, and thus forcibly shifts the valve element is of the main valve l2 into the intermediate position shown in full lines.

The fluid in the chamber 5 will be under pressure at this time because the weight of the platen 6 and piston 2 will tend to carry the platen 6 downwardly, but escape of fluid from the chamber 5 is substantially prevented by the land l5 which closes the port '24. Thus the chamber $53 and its piston B l which may be aptly designated as a, pressure responsive means, serves to move the valve element i l into its intermediate position and hold it in that position.

When the platen 6 has descended to some exten and released the Valve element 58, the latter is then moved to connect the pipes Hi and it so that thereafter until the platen 6 returns, the chamber '53 will be subjected to the pressure in the main advancing chamber 4. During the early part of the descent of the platen B after valve '56 operates, there is little pressure in chamber 4- and any fluid in the chamber 63 can escape into the advancing chamber 4 through the valve 56, During descent of the platen E, valve element M is held in its upper position by fluid pressure in chamber l9, and this same pressure in that chamber aids spring 69 in retracting piston fi l as soon as valve element 58 is released by platen t and operated by spring 62.

As soon as substantial resistance is encountered by th platen 5, it will not continu to fall of its own weight, but the pump will continue to deliver operating fluid to th-echamber 3, the valve element 3| in the check valve 28 will close automatically and pressure will build up in the chamber 4. This pressure is, of 'course, communicated to the chamber 53 but at that time, the valve element It is still held in its upper position by the pressure in th chamber is, The chamber '63 will have the same pressure as that in the advanc'ing chamber l. When the pressure in'the advancing chamber 4 is suficient to force the pressure relief valve 54 open, fluid will pass through that valve into the auxiliary cylinder 5% and force the plunger 37 in a direction to operate the pilot valve element 3? and release the hydraulic pressure holding the valve element id in its upper position in which it has compressed the spring H.

The spring I! then urges the valve element i l toward its other position, but when element it reaches the intermediate posit-ion, it is stopped by theyplunger 64 which is now held in its full line position by the pressure in chamber 63, and

leading to the reservoir 9.

hence element M will be held in this position momentarily While the fluid under pressure in the chamber 3 escapes through the pipe 23 and ports 2!) and 21 of main valve [2 to the pipe 22 As soon as the pressure in chamber 4 falls sufficiently, the-pressure in the chamber 63 which also falls to the same extent, will be overcome by the spring I! and the valve element [4 will be moved automatically into the reversing position. The platen 6 is then elevated, and the plunger 64 will remain retracted, because the chamber 4 is then under very little pressure, until the platen 6 engages collar 6!! and operates the valve 56 to reconnect the pipes i0 and 13, which then places the chamber 63 under the pressure in the retracting chamber. This pressure of the retracting chamber then forces the piston 64 against the valve element [4 and carries the latter into the intermediate position which stops the retraction of platen 6.

After an operation of the plunger 41, it is important to release the fluid from behind the piston head 5'2, so that the spring 48 can retract it, and this may be accomplished in a simple manner by connecting across the pressure relief valve an ordinary free check valve 75, see Fig. 1, which opens to pass fluid in a direction from the pipe 53 to the pipe 55 but closes automatically to prevent reverse flow. After an operation of the plunger; ll, the valve element I4 is operated to cause a retraction of the platen E5 and at such time, the chamber 4 is vented so that there will be no substantial pressure therein. Hence, the fluid from the auxiliary cylinder to can escape through th valv '15 and allow retraction of plunger 4'! by spring 48.

In Fig, 2, in place of the check valve i5, I have placed a bleeder valve 15a and connection l5?) from the pipe 53 to the reservoir so as to allow the escape of fluid from the auxiliary cylinder 50, but of course, such escape is less than the rate of supply through the pipe 53 and valve 54. This is less desirable than the check valve 15.,

A pipe '56 connects the pipe 25, to a pilot chamber l! in the check valve 28, so that when pressure is applied to the retracting chamber 5, the same pressure will be transmitted to the pilot chamber 11. A piston 78 in the chamber 11 is normally retracted by a suitable spring, but when the piston '68 is operated by fluid received from pipe 76, it engages and opens the valve element 3!, and hence during the retraction or elevation of the platen 6, fluid can escape not only from the chamber 4 through the valve 12, but the major portion of it can escape through the valve 23 and return directly to the reservoir 9.

A pipe it connects the pipe 53 to a pilot chamber provided in the pump 1. A piston 8| reciprocating in the cylinder Bil bears against and operates a yok shifting lever 82 which is pivoted at 83 to the pump frame and at 84 to one end of a yoke rod 85. The rod 85 is connected to the yoke within the pump, and when the rod 85 is shifted to the right in Fig. 1, it decreases the rate of delivery. A yoke 86 is pivotally connected at the ends of its arms by a pin 81 to the lever 82, and the base of the yoke has an aperture through which loosely passes a rod '88. The connections B4 and 8'? are, of course, loose connections which enable the pins 8 3 and 81 to pursue arcuate paths while shifting the rod 85-and yoke 35 in straight lines. Within the yoke 86, the rod 88 carries an adjustable nut 89, and a spring 9'0 is compressed between the nut 89 and the cross part of the yoke 86. The rod 88 passes loosely through an abutment or boss 9| ofthe pump frame, and a hand wheel 92 is threaded upon the outer end of the rod 83. By rotating the hand wheel 92, the rod 88 may be shifted endwise in either direction to compress or release the spring 98, and the spring 90 yieldingly urges the lever 82 clockwise in Fig. 1 to carry the piston 8| to the right.

When the pressure in the advancing chamber 4 is sufficient to overcome the pressure relief valve 54, the fluid passing this valve 54 not only moves the plunger 41 to shift the pilot valve element 31 into a position to reverse the direction of travel of the platen, but some of it passes through the pipe 19 to the pilot chamber 85 where it forces the piston 8| to the left, and rocks the lever 82 to shift the yoke rod 85 to the rightand decrease the rate of delivery of the pump, until the pressure has fallen in the chamber 4 Sllfficiently, and then spring 90 returns the pump yoke to full delivery position. Thus at the critical time, when the pressure in th advancing chamber 4 is being lowered, the delivery of the pump is decreased preferably to practically no delivery, and then the pump automatically resumes full delivery at the proper time. This aids in preventing shock in the hydraulic system at the time of reversal of travel of the working member.

The pressure at which the pump pilot control operates to cut down the rate of delivery of the pumpmay be varied by turning the hand wheel 92 to increase or decrease the compression of the spring 90, but the pressure at which the pump will return to full stroke may advantageously be made considerably less than the pressure at which the relief valve 54 will operate, because there will be no operation of the yokerod 85 to reduce delivery until after the relief valve 54 is opened. If the spring 9|! does not require a heavy pressure to overcome it, it will hold the pump l on no, or small, stroke until the pressure in the chamber 4 has fallen to the desired extent. The pilot chamber 80 remains responsive to the pressure in the chamber 4 during this fall of pressure in the chamber 4 because at that time, the valve 15 is open, which places the chamber 80 in direct communication with the chamber 4. This give a decidedly smooth and shockless operation to the control system, when the reversal occurs following the building up of a relatively high pressure in the advancing chamber 4.

It is believed that the operation of the control system will be clear from the foregoing description, but it will be briefly summarized as follows:

Assuming that the parts are'in the idle position shown in Fig. 1, an advance or descent of the platen 6 may be started by rocking the hand lever 33, but since the valve element M will re turn to the intermediate position when the handle 33 is released, this is only a temporary control. When one desires to cause a regular cycle of operation of the motor or press, the switch 46 is closed and held closed a moment until the solenoid 45 operates its core 44 and shifts the pilot valve element 37 from the full to the dash line position in Fig. 1. This causes delivery of the fluid from the pump through the pilot valve 36 to the chamber l9, and the pressure in chamber l9 forces the valve element [4 against the action of spring into its upper position to cause an advance of the platen 6. The valve element l4 in that position connects the pipes in and 23, and vents the pipe 25 leading to the retracting cham- 10 ber 5. When this occurs, fluid is released from the chamber 5 and the platen 6 begins its descent. During a small initial movement, the platen releases collar 60 and the valve element 51 is shifted into a position to connect the chamber'63 to the advancing chamber 4.

The check valve 28 will open automatically and fill the chamber 4 with fluid added from the reservoir in addition to the fluid which is delivered by the pump through the pipe 23. When the platen 6 encounters substantial resistance, the valve 28 closes and the platen then continues to advance at a slower rate with a building up of pressure. The pressure in the chamber 4 is, of course, transmitted to the chamber 63, and the same pressure is applied to the chamber 19, but

piston 65 being of greater area than piston 64,

piston 66 will be elevated to the full line position.

When the pressure in the advancing chamber has reached that for which the pressure relief valve 54 is set, the latter opens and passes fluid to the pilot chamber 89 of the pump control and to the auxiliary cylinder 50. The pressure in the latter causes an advance of the plunger 41 and an operation of the pilot valve element 31 back into the full line position.

This releases the pressure in the chamber l9,

and thereupon the spring ll begins to move the valve element 14 downwardly in Fig. 1 towards the position in which it reverses the direction of travel of the platen 5, but piston 54 stops it in the intermediate position until the pressure in chamber 4 has fallen sufficiently to be overcome .by the combined pressures of springs l1 and 69,

whereupon the Valve element |4 automatically continues its movement into full reversing position.

The pressure in the pilot chamber 8|! sets the pump for little or no delivery of the pump, so that the full capacity of the return pipes 22 and 23 is available for the escape of fluid from the advancing chamber 4 through the valve l2. Then when the valve element l4 continues its movement into the reverse position the absence of substantial pressure in chamber 4 transmitted to cylinder allows spring so to return the pump to full stroke or full delivery. The fluid from the pump then passes at full rate to the chamber 5 to cause retraction of the platen 6. When the platen 6 reaches a selected position in its return, for which collar 55 is set, it operates the valve element 58 to place the pipes 10 and 13 again in communication, and this pressure then forces piston 64 upwardly and through it moves the Valve element |4 into the intermediate position, where the delivery of fluid to the retracting chamber 5 is discontinued, and escape of fluid from the chamber 5 at the port 24 prevented. This completes a cycle of operation. It Will be understood that during the retraction of the platen 6, however, pressure is transmitted from the retraction chamber 5 to the pilot chamber ll of the valve 28 which opens the valve 3| to expedite the escape of fluid from chamber 4 and hence aid in retraction of the platen 6.

It will be understood that various changes in' the details and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art Within the principle and scope of the invention as expressed in the appended claims.

1. A control system for a hydraulic motor of the type having a working member and hydraulic 11 means for reciprocating'said member including advancing and retracting cylinders, which system comprises a variable delivery pump for supplying operating fluid under pressure, a main valve having a valve element movable between two limit positions through an intermediate position, means connecting said pump, valve and said cylinders, and operable when said valve element is in one limit position for connecting said pump to said advancing cylinder and venting said retracting cylinder, when in its other limit position for venting said advancing cylinder, and connecting said pump to said retracting chamber, and when in said intermediate position for closing said retracting cylinder to prevent escape of operating fluid therefrom, venting said advancing cylinder, and bypassing fluid from the said pump back to the pump, a hydraulic device operable on saidvalve element for shifting the latter into. said one position and holding it in that position, a hydraulic circuit for said device and havingtherein a two-way pilot valve with a valve element internally balanced as to pressure and operable when in' one position for deliveringfluid under pressure to said device and when in its, other po sition for discontinuing such delivery and venting said device, selectively controlled means for moving said pilot valve element into a position to cause delivery of'fiuid to said device, a plunger for shifting said pilot valve element back into its initial position in which it interrupts the delivery of fluid to said device and vents the. latter, an auxiliary cylinder in which said plunger moves, a conduit connecting said auxiliary cylinder behind said plunger to, said advancing cylinder, a pressure relief valve included in series in said con duit and opening to pass fluid in a direction from said advancing cylinder.= toward said auxiliary cylinder: when a predetermined pressure is. reached in said advancing cylinder, said pump having a pilot cylinder and means operated by said pilot cylinder for setting said pump for reduced, delivery when a predetermined pressure in said pilot cylinder is, reached, means for connecting said pilot cylinder to the discharge side of said pressure. relief valve, whereby when said fluid passes to; said auxiliary cylinder tomove said pilot valve element into position to reverse the direction travel of said member, fluid under the same pressure, will pass: to said pilot cylinder and set said pump for reduced delivery until the pressure in said auxiliary cylinder falls below that for which said pilot cylinder operated means is set, and a check: valve connected in parallel across said pressure relief valve and opening to pass fluid freely in the; opposite direction from that passed by the pressure relief valve.

2. A control system for a hydraulic motor of the type having a working member and cylinders for causing advances and retractions of said member, which system comprises a variable de livery pump of the type havingv a pilot control cylinder and a control operable therefrom. which reduces the rate of delivery of the pump automatically when the pressure in said cylinder is above a predetermined pressure, means supplied with operating fluid from said pump and deliveringit to. said cylinders of said. motor to, cause movements ofsaid member selectively in opposite directions, pilot means controlling said last named means and having a valve element operable between two positions to determine the direction of movement of said member, means for moving said element into one of said positions,

fluid Operated means for moving said member into the other of said positions, aconduit connecting said last means to said advancing cylinder of said motor a pressurerelief valve in said conduit and opening to pass fluid to said fluid operated means when a predetermined pressure is reached, a check valve connected in parallel across said pressure relief valve and opening to pass fluid in the opposite directions from that passed by said relief valve, and mean connecting said pilot control cylinder to said conduit at the outgoing side of said pressure relief valve, whereby when said pressure relief valve opens said pump will automatically reduce its rate of delivery until the pressure in said advancing cylinder falls below said predetermined pressure for which the pump control is. set.

3. In a control system for a hydraulic. motor of the type havingta working member, a variable delivery pump and a reversing valve connected to said motor and pump in a hydraulic circuit for controlling the delivery of fluid from saidpump to said motor to determine the direction of travel of said member, the improved control for said valve which comprises a pilot valve,

a source of pilot operating fluid connected to said pilot valve, hydraulically controlled means operatively connected to said pilot Valve and said reversing valve for causing movements of the latter between two motor controlling positions and in turn controlled by fluid from said pilot valve, means for causing movement of said pilot valve in one direction, a resiliently retracted, fluid operated device for moving said pilot valve in the other direction, a pipe connected to said circuit and responsive to the fluid pressure urging said member in one direction and connected to said'fluid operated device, a pressure relief valve in series in said pipe for passing fluid to said device only when a selected pressure is reached that is greater than that necessary to move said device away from retracted position, whereby movement of said pilot valve when started will be rapid, and means connected to said pipe between said pressure relief valve and said fluid operated device for setting said pump to a decreased rate of delivery upon opening of said pressure relief valve and until the pressure on said working member which opened said relief valve has fallen to a selected extent.

4. In a. control system for a hydraulic motor of the type having a working member, a variable delivery pump, and a reversing valve connected to said motor and pump in a hydraulic circuit for controlling the delivery of fluid from said pump to said motor to determine the direction of travel of said member, the improved control of. said valve which comprises a pilot valve, a source of pilot operating fluid connected to said pilot valve, hydraulically controlled means operatively connected to said pilot; valve and said reversing valve for causing movements of the latter between two. motor controlling positions and in turn controlled by fluid from said pilot valve, means for causing movement of said pilot valve in one direction, aresiliently retracted fluid operated device for moving said pilot valve in the other direction, a pipe connected to said circuit and responsive to the fluid pressure urging said member in one direction and conn cted to said fluid operated device, a pressure relief valve in series in said pipe for passing fluid to said device only when a selected pressure is reached that i greater than that necessary to move said device away from retracted position, whereby movement. of, said pilot valve when started will be rapid, means connected to said pipe between said pressure relief valve. and said fluid operated device for setting said pump to a decreased rate of delivery upon opening of said pressure relief valve and until the pressure on said working member which opened said relief valve has fallen to a selected extent, and means for releasing pressure from said fluid operated device after an operation thereof and said pressure relief valve has closed.

5. In a control system for a hydraulic motor of the type having a working member and advancing and retracting cylinders in which said member moves, means for delivering fluid under pressure alternately to each of said cylinders and releasing pressure from the other cylinder to determine the direction of travel of said member, the improved control for said delivering means which comprises a pilot valve, a source of operating fluid connected to said pilot valve, a hydraulic motor for operating said delivering means and in turn operated by fluid from said source and controlledby said pilot valve to determine the direction of travel of said member, means for causing movement of said pilot valve in one direction, a resiliently retracted, fluid operated device for moving said pilot valve in the other direction, a pipe connected to said delivering means and responsive to the fluid pressure urging said member in one direction and connected to and operating said fluid operated device, a pressure relief valve in series in said pipe for passing fluid to said device only when a selected pressure is reached that is greater than is necessary to move said device away from retracted position, and means connected to said pipe between said pressure relief valve and said fluid operated device for modifying said delivering means to cause a decreased rate of delivery upon opening of said relief valve until the pressure on said working member which opened said relief valve has fallen to a. selected extent.

THOMAS F. STACY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,113,161 Caborne .Apr. 5, 1938 2,070,720 Ernst Feb. 16, 1937 2,029,708 Douglas Feb. 4, 1936 2,219,896 Harrington Oct. 29, 1940 2,253,617 Grifiith Aug. 26, 1941 2,200,998 Schnuck May 14, 1940 2,009,608 Douglas July 30, 1935 2,320,759 Stacy June 1, 1943 2,072,488 Stacy Mar. 2, 1937

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