US3490757A - Externally-retracted reciprocatory hydraulic spring - Google Patents

Description

Jan. 20, 1970 A. u. HAANES 3,490,757

EXTERNALLY-RETRACTED RECIPROCATORY HYDRAULIC SPRING Filed Sept. 13, 1967 INVENTOR ARNT u. 'HAANES BY' W ATTORNEYS United States Patent US. Cl. 2671 Claims ABSTRACT OF THE DISCLOSURE This reciprocatory hydraulic spring for replacing metallic springs such as are used in die sets for gripping a workpiece blank during forming, as in a press, utilizes an external source of hydraulic pressure fluid to retract the plunger after a working stroke has been completed, thereby achieving a much more compact device by eliminating the space required for the metal helical spring employed in prior self-contained hydraulic springs for retraction of the plunger. The plunger has a hollow piston head with a fluid passageway therethrough, this head being slidable along a piston rod provided with concavo-convex spring washers and an adjustment screw for varying their pressure. During a working stroke, as the press platen descends, the fluid subjected to pressure in the downwardly' moving cylinder escapes through this passageway to an external accumulator which is maintained under pneumatic pressure by compressed air from the factory compressed air supply line. During the upward stroke of the press platen, retraction of the plunger is brought about by the pressure of the hydraulic fluid returning to the rearward side of the piston head in response to the pressure exerted thereon by the accumulator.

In he drawings,

FIGURE 1 is a central vertical section through an externally-retracted reciprocatory hydraulic spring, according to one form of the invention, with the moving parts in their positions occupied at the beginning of a working stroke;

FIGURE 2 is a view similar to FIGURE 1 but with the moving parts in the positions occupied at the beginning of a retraction stroke; and

FIGURE 3 is a cross-section taken along the line 33 in FIGURE 1, showing the retaining nut construction with its fluid passageways.

Referring to the drawing in detail, FIGURES l and 2 show an externally-retracted reciprocatory hydraulic spring according to the invention, generally designated 10, as consisting generally of a plunger 12 reciprocable relatively to and mounted within a cylinder 14. The latter is ordinarily adapted to be subjected to a pressure in response to the descent of a press platen which is engaged in closing the components of a die set operating upon a metal blank yieldingly held or supported by one or more of the hydraulic springs 10 of the present invention. The cylinder 14 is provided with a cylinder bore 16 which,

with its upper end surface 17 containing a counterbored recess 18, defines a hydraulic fluid working chamber 19. At its lower end, an annular cylinder head 20 is bolted to the cylinder 14 and provided with a central bore 22 and annular recess 24 with packing 26 for the passage and sealing respectively of the hollow piston rod 28 of the plunger 12 carrying the hollow sliding piston head 30.

The cylinder 14 adjacent the cylinder head 20 is provided with a threaded .port 32 in the side wall 31 thereof remote from the cylinder upper end surface 33 of the end wall 34 containing the recess 18. The port 32, during use, is connected by piping to a conventional hydraulic accumulator (not shown) which in turn is connected to ice a compressed air line of the factory. Such compressed air line ordinarily carries compressed air under pressure of approximately pounds per square inch. This in turn exerts pneumatic pressure upon the hydraulic fluid, ordinarily hydraulic oil, which is forced into the accumulator during the working stroke of the press and expelled from the accumulator by the pneumatic pressure to achieve retraction of the hydraulic plunger 12 in the manner explained below. Adjacent the cylinder head 20 at the lower end of the cylinder bore 16 is a hydraulic lower or fluid retraction chamber 35 beneath the piston head 30 which has annular retraction piston areas 37, 39 and 106 thereon, the latter being the lower end of the head.

The piston rod 28 of the hydraulic plunger 12 has inner and outer end faces 36 and 38 respectively, the inner face 36 being formed on the end of a slight enlargement 40 of the piston rod 28 providing an annular abutment shoulder 42 engageable with the counterbored central inner face 44 of the cylinder head 20 as a stop. The outer end face 38 is provided with diametrally-aligned spanner notches 46 on opposite sides of a threaded central outer bore 48 containing a threaded screw closure plug 50. The closure plug 50 has an inwardly-extending integral cylindrical nose 52 which snugly engages a reduced diameter bore 54 annular recessed to receive a conventional sealing O-ring 56. The inner end of the nose 52 is tapered for ease of passage through the O-ring 56. The closure plug 50 is hexagonally recessed for the reception of a conventional Allen wrench (not shown) for its insertion orremoval.

The hollow piston rod 28 is provided with an inner threaded bore 58 extending from the reduced diameter bore 54 to the inner end face 36 thereof and containing a hexagonally-recessed-pressure-adjusting screw 60 which is locked in its adjusted position by a hexagonally-bored lock nut 62, both being adjusted by meansof a conventional Allen wrench. The adjusting screw 60 on the inner end of its outer threaded portion 64 is provided with a smooth cylindrical intermediate diameter portion 66 extending inward and upward from the threaded outer portion 64. The latter in turn terminates in a reduced diameter threaded inner end portion 68 with a top surface 69. Stacked upon the intermediate portion 66 are multiple convexo-concave spring washers 70, the lowermost of which engages the annular shoulder 72 between the adjusting screw portions 64 and 66. The uppermost spring washer 70 acts as a movable valve member in the manner described below, and is retained in position by a retaining nut 74 threaded upon the inner end portion 68. The nut 74 has a tubular interally-threaded shank 76 terminating in a cross-shaped head 78 (FIGURE 3) which has arms 80 separated from one another by arcuate cutaway portions 82 providing fluid passageways 84.

The outer ends 86 of the arms 80 of the retaining nut 74 extend radially outward beyond a central bore 88 in the hollow piston head 30 sufliciently to overhang (FIG- URE 1) and during operation engage (FIGURE 2) an annular shoulder 92 between the bore 88 and a counterbore 94 (FIGURE 1) extending downward from the inner end face 96 of the hollow piston head 30. The latter below the bore 88 has an annular beveled shoulder 98 which serves as a valve seat for the uppermost spring Washer 70 and extends from the bore 88 to an enlarged bore 100. From the lower end of the bore 100 an annular beveled shoulder 102 extends downward to a lower bore 104 which in turn extends downward to the annular lower face 106 of the piston head 30. The bores and bevel portions 100, 98 and 102 define an intermediate spring chamber 108 containing the spring washers 70, the upper ends of which engage the bevel surface 98 as a valve seat and the lower ends the annular shoulder 72 on the pressure-adjusting screw 60. The spring washers 70 during the retraction stroke of the hydraulic plunger 12 (FIG- URE 2) are loose and relaxed, whereas upon a working stroke (FIGURE 1) they are in a state of compression. The spring chamber 108 has an inclined fluid port 110 communicating with the cylinder port 32 through the side wall of the hollow piston head 30.

In the installation of the invention, let it be assumed that one or more of the reciprocatory hydraulic springs of the present invention are mounted either in the press bed or die set or in the press platen or ram itself of a metal forming press, such as in suitable vertical bores therein snugly receiving the cylinders 14 with the axes of their cylinder bores 16 parallel to the direction of travel of the platen. In a typical installation, the piston rods 28 extend downward from the cylinders 14 toward the holddown pad, blank holder or other portion of the die set or machine element upon which pressure is to be exerted by the lower end faces 38 of the piston rods 28. Let it also be assumed that the threaded ports 32 at the l wer ends of the cylinders 14 have been connected by suitable piping (not shown) to a hydraulic accumulator which in turn is connected to a compressed air supply line for supplying the pneumatic pressure above the hydraulic fluid, such as oil, in the storage chamber of the accumulat r. Let it finally be assumed that the press ram or platen is in its raised position and that each hydraulic spring 10 is in its open position shown in FIGURE 1, ready for the performance of a working stroke.

In the operation of the invention, as the press platen or ram (not shown) descends to perform a working stroke and moves the cylinders 14 downward by exerting pressure on the upper end surface 33 of each cylinder 14, the hydraulic fluid in the working chamber 19'transmits this pressure to the upper end surfaces 92 and 96 of the piston head 30, forcing the latter downward and at the same time compresses the spring washers 70 while flexing the uppermost spring washer 70 downward away from its valve seat 98. The piston rod 28 moves downward through the short distance represented by the gap between the surfaces 106 and 36 (FIGURE 2) until the arms 80 of the retaining nut 74 (FIGURE 3) engage the annular shoulder 92 and it is brought to a halt against the blank holder or other part upon which it is intended to exert pressure.

As the cylinder 14 continues to be pushed downward by the press ram or platen, it forces hydraulic fluid from the the chamber 19 past the cutout portions 82 of the retaining nut 74 FIGURE 3) and through the counterbore 94 and bore 88 past the peripheries of the flexed spring washers 70 and through the spring chamber 108 and the fluid port 110 into the lower chamber 35 and thence out through the cylinder side wall port 32 to the accumulator (not shown) where the rising level of the hydraulic fluid further compresses the air above it. This action continues until the cylinder 14 has descended to its full extent so that the upper end surface 96 of the piston head 30 comes to rest against the end surface 17 of the hydraulic working chamber 19. At the same time, the lower end 106 of the piston head 30 has remained in abutting engagement with the upper end surface 36 of the hollow piston rod 28, as shown in FIGURE 1, with the spring washers 70 in their compressed condition.

When the press platen or ram has reached the end of its downward stroke (FIGURE 2) and the hydraulic spring 10 has reached its fully closed position, the reversal of the press and the consequent beginning or the upward stroke causes hydraulic fluid under the pressure of the compressed air in the upper part of the hydraulic accumulator (not shown) to move through the cylinder side wall port 32 into the lower end chamber or retraction chamber 35 of the cylinder bore 16 beneath the piston head 30, where it acts against the area 36 to move the piston rod 28 downward. At the same time, the fluid also flows through the inclined port 110 and spring chamber 108, past the space between the spring washers 70 and the valve seat 98, through the bore 88 and counterbore 94 into the recess 18 to refill the working chamber 19 of the cylinder 14. The frictional drag of the piston head sealing ring 114 in the piston head groove 112 causes the piston head 30 to resist downward motion until forcibly pulled downward by the piston rod 28 when the ends of the arms of the retaining nut 74 move into engagement with the annular shoulder 92 (FIGURES 2 and 3). This downward or opening motion continues until the plunger 12 reaches its fully extended position shown in FIGURE 1, whereupon the hydraulic spring 10 is ready for the performance of another working stroke. In the meantime, the die set (not shown) operated by the press platen or ram (a so not shown) has completed the forming operation on the workpiece blank and the formed workpiece is ready to be ejected from the die set in the usual manner, by a knockout device or other conventional ejection device.

The pressure at which hydraulic fluid will be discharged from the working chamber 19 through the hollow piston head 30 into the retraction chamber 35 and thence through the cylinder port 32 to the hydraulic accumulator is adjusted by adjusting the pressure exerted by the convexo-concave spring washer 70. To make such an adjustment, the sealing plug 50 is first unscrewed by means of an Allen wrench and removed from the bores 48 and 54. The lock nut 62 is then rotated reversely by means of an Allen wrench to loosen the grip upon the pressure adjusting screw 60, whereupon the latter is screwed inward or outward, as desired, within its threaded bore 58 to cause the annular shoulder 72 to move inward or outward relatively to the inner end surface 36 of the hollow piston rod 28 of the plunger 12, as most clearly shown in FIGURE 2. While this is being done, the hollow piston rod 28 is held against rotation by means of a spanner inserted in the notches 46 in its outer end. When the desired adjustment has been accomplished, the lock nut 62 is retightened against the adjusting screw 60 and the cl sure plug 50 is then replaced and screwed into its bore 48, sealing the bore 54 by its engagement with the O-ring 56.

The term externally-retracted as used herein will be understood to mean that the source of pressure which effects return of the plunger 12 and cylinder 14 from their closed position of FIGURE 2 to their open position of FIGURE 1 is located externally of the hydraulic spring 10. This is in contradistinction to the use of mechanical springs located internally of the cylinder itself for effecting such retraction, as in the hydraulic spring discl sed and claimed in my co-pending application Ser. No. 499,442 filed Oct. 21, 1965 for Self-Contained Reciprocatory Hydraulic Spring, now US. Patent No. 3,350,087 issued Oct. 31, 1967.

I claim:

1. An externally-retracted spring, comprising:

a cylinder having a hydraulic working chamber adjacent one end thereof and a hydraulic retraction chamber adjacent the opposite end thereof with a cylinder port near said opposite end adapted to be connected to an external pressurized hydraulic fluid accumulator, and

a plunger reciprocably mounted in said cylinder and having a piston rod extending through said opposite end of said cylinder to the exterior thereof and a hollow piston head movably mounted on said piston rod for sliding motion relatively thereto,

said hollow piston head having a fluid passageway therethrough leading from said working chamber to said retraction chamber,

said plunger having Spring-pressed valve means normally closing said piston head passageway and responsive to the attainment of a predetermined pressure in said working chamber for opening communication therethrough from said working chamber through said retraction chamber to said cylinder port whereby to discharge reciprocatory hydraulic hydraulic fluid from said working chamber through said cylinder port.

2. An externally-retracted reciprocatory hydraulic spring, according to claim 1, wherein said hollow piston head has a valve seat communicating with said passageway, and wherein said valve means includes a spring washer movable into and out of fluid flow impeding engagement with said valve seat.

3. An externally-retracted reciprocatory hydraulic spring, according to claim 2, wherein said washer is a concavo-convex spring washer adapted to flex into and out of engagement with said valve seat.

4. An externally-retracted reciprocatory hydraulic spring, according to claim 1, wherein said piston rod has a bore therethrough threaded along at least part of its length, wherein a correspondingly-threaded springpressure adjusting screw threadedly engages the threaded portion of said bore and has an enlargement on the inner end thereof, and wherein said spring-pressed valve means includes a spring assembly mounted on said adjusting screw between said enlargement and said piston rod whereby relative rotation between said adjusting screw and said piston rod varies the compressing force of said washer.

5. An externally-retracted reciprocatory hydraulic spring, according to claim 4, wherein said enlargement includes a threaded member threaded into the inner end of said adjusting screw.

6. An externally-retracted reciprocatory hydraulic spring, according to claim 5, wherein said threaded member comprises an internally-threaded nut having a head provided with a fluid flow opening there past.

7. An externally-retracted reciprocatory hydraulic spring, according to claim 4, wherein said spring assembly includes a spring-pressed valve member yieldingly engaging said valve seat.

8. An externally-retracted reciprocatory hydraulic spring, according to claim 7, wherein said spring assembly also includes a plurality of eonvexo-concave spring washers disposed in stacked relationship on said adjustin g screw.

9. An externally-retracted reciprocatory hydraulic spring, according to claim 1, wherein said fluid passage- Way includes a fluid port in said hollow piston head communicating with said retraction chamber.

10. An externally-retracted reciprocatory hydraulic spring, according to claim 4, wherein said enlargement extends laterally into overhanging relationship with said piston head, and wherein said piston head is movable into and out of engagement with said enlargement.

References Cited UNITED STATES PATENTS JAMES B. MARBERT, Primary Examiner

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