US2738971A - Liquid spring - Google Patents

Description

March 20, 1956 P H. TAYLOR LIQUID SPRING Filed Sept. 28. 1953 EXPANS/QN Ofz ornefi Patented Mar. 20, 1956 fiice LIQUID SPRING Paul H. Taylor, Grand Island, N. Y., assignor to Wales- Strippit Corporation, North Tonawanda, N. Y., a corporation of New York Application September 28, 1953, Serial No. 382,532

' 4 Claims. (11. 267-64) The present invention relates to liquid springs,that is, to devices in which the compressibility of a confined liquid is utilized to effect resilient action and to cushion the movement of one part toward another under working load or force so that upon release of the working load or force the movable part will be restored to its initial position.

There are many requirements in the machine tool and other industries for a resilient cushioning device which is capable of providing resistance to movement in one direction but in which the energy stored up during such movement is decreased or dissipated on the return stroke of the device so that the return stroke may take place under less force than has been stored up during the working stroke. Obviously conventional mechanical springs are unsuited for this purpose for the energy which they store up, when being compressed, is almost exactly the same as the force they exert as they expand after the force of compression is released. This is true of all mechanical springs and is one reason why in many instances mechanical springs cannot be used satisfactorily.

Where one way operation with reduced force has been desirable, it has heretofore been the practice to employ air or liquid operating against air, the air being compressed upon the cushioning stroke and being valved on the return stroke so as to relieve the pressure to the extent and with the rapidity desired. One such application of this type is in the air cushion of a metal-working press where metal drawing is accomplished. In this type of apparatus a one-way operation is obtained by the valving action which eliminates the resilient force upon completion of the compression stroke. This makes certain that upon the withdrawal of the pressure of the press ram on the work-piece, the pressure of the air cushion does not cause a reversal of the metal draw in the workpiece and does not cause the workpiece to be restored to its original shape by virtue of continuance of the resisting spring pressure. Many like uses for springs, which have a high cushioning spring force but a return pressure that drops off rapidly, abound in various mechanical fields, but these possible uses are particularly prevalent in the field of metal-working. One specific application is to the cushion pad employed in drawing operations in the metal-working or drawing of metal objects. It is to this field that the present invention has particular application.

In many press operations it has heretofore been virtually impossible to obtain sufficient pressure to accomplish the desired operation in a single stage with the air cushioning means heretofore available. In fact, the lack of sufficient pressure within an air or mechanical cushioning device of a given volume is one of the reasons why several stage dies and a complex series of operations are often used.

Liquid springs such as disclosed in the Wales et al. application Serial No. 180,966, filed August 23, 1950, now

Pat. 2,708,109, issued May 10, 1955,.and in the Zumwalt application Serial No; 228,215, filed March 12, 1952, now- Pat. 2,711,313, issued June 21, 1955, and in the Wales application Serial No. 228,245, filed May 25, 1951, now Pat. 2,729,440, issued January 3, 1956, enable extremely high pressures to be attained in a cushioning device of relatively small volume. However, these liquid springs, as heretofore constructed, are primarily a substitute for the mechanical springs used previously in metal-working operations. In other Words, their main advantage lies in the fact that they are capable of developing forces of six to ten times greater than conventional steel springs for a given volume. Through this ability alone, they are better for die operations than mechanical springs because they permit elimination of the extra stages of drawing required where conventional mechanical springs are normally used. However, where it is necessary for the cushioning medium to provide a high spring cushioning force in one direction that will drop oif rapidly in the other direction, then liquid springs as previously constructed are unsuitable. It has still continued to be necessary to use pressure pads in presses for drawing operations, for instance. This, of course, has meant that such metal-working operations have had to be restricted to those presses in a factory or shop which are equipped with pressure pads and which have the pressure pad tonnage adapted to the work.

Many factories find it is impossible to schedule their work so as to have a continuous steady volume of drawing operations and another steady volume of punching or blanking operations. It is either a feast or famine, that is, many types of metal working operations require draw and pressure pad operations and some require none at all, with the net result that all the presses in a factory must be equipped with pressure pads in order to handle the feast of drawing operations, whereas none need be so equipped if the factory were doing all perforating or blanking. This presents a serious problem, in that high expenditures for capital equipment must be made in the average metal working shop to be assured that the shop will at all times have sufiicient presses equipped with pressure pads to enable it to do the complicated drawing operations which may be part of its work. Obviously a press equipped with a pressure pad having pressure pins extending through holes in its bed is a more expensive proposition than a simple stamping press having no pressure pad incorporated therein.

But aside from the disadvantage of having capital tied up in press equipment that is really merely for stand-by usage, dies with pressure pads require the piping of air, and the use of accumulators and other kindred devices, which in themselves are often troublesome and the cause of greatly increased costs.

Another disadvantage of dies with pressure pads is the necessity for excessive press down-time, because the dies must be mounted over the pressure pins which must then be connected to the portion of the die on which the pressure is to be exerted to effect the satisfactory operation of the draw. This down-time is a serious problem because it means that an expensive piece of machinery may be tied up as long as three or four hours while the die setup is being made in a given press.

Obviously much of the loss of time could beeliminated of it were possible to have a self-contained die apparatus in which the pressure pad means is incorporated into the die itself so that a drawing die could be installed or removed from the press as a unit rather than requiring costly and intricate setup attachment to the press. Ob} viously, also, the liquid springs in press working machines and the like could be greatly expanded if they were capable of one way operation, for then the need for pressure pads would be eliminated.

In my pending application Serial No. 378,575, filed September 4, 1953, I have disclosed a liquid spring which is capa Providing hi pri g forc in one dir tion and a lesser force on its return stroke.

A primary object of the present invention is to provide an improved liquid spring capable of providing a high spring force when compressed and producing a lesser force on its return stroke.

Another object of the invention is to provide a spring of the character described which is self-contained.

Another object of the invention is to provide a liquid spring Whose rate of resistance or compressive force varies as the spring is compressed.

A further object of the invention is to provide a liquid spring whose rate of return also varies as the spring expands after the compression is released.

A further object of this invention is to provide a compact spring of the character described, which may easily be installed in a die to make the die a self-contained and a working ass mbly which is not dependent for operation upon attachment to external sources of power.

Other objects of this invention will be apparent hereinafter from the disclosure and from the recital of the appended claims.

In the drawing:

Fig. l is an axial section of a liquid spring constructed according to one embodiment of this invention;

Fig. 2 is a fragmentary axial section of this spring on an enlarged scale but with the spring in compressed condition;

Fig. 3 is a section on the line 3-3 of Fig. 2 looking in the direction of the arrows; and

Fig. 4 is a graph showing typical compression and expansion strokes of a spring built according to this invention.

The spring shown in the drawing comprises a container or housing which is filled with a compressible liquid L such as silicone oil. The container is closed at one end by a head 11 that is welded or otherwise secured to it against leakage. The head 11 is formed with a central tubular portion 12 that extends internally into the chamber and that forms a cylinder in which a piston 14 reciprocates.

The cylinder 12 opens at its inner end into. the con tainer or housing 10 but the head 11 is formed with a front wall portion 15 which acts as a stop for limiting outward movement of the piston. The piston rod or shank 16, which is integral with the, piston, projects outwardly of the container 19. through the hole 17 in this front wall portion. A seal 18, which is mounted in a recess 19 in the head serves to prevent leakage of liquid from the container along the piston rod, A cap 2t), which is secured to. the head by screws 21 serves to retain the seal in position.

The container is provided at its opposite end with a generally cylindrical protruding portion 27. This protruding portion 27 is provided with a cylindrical bore 26 which is aligned axially with the bore 28 of the cylinder 12 and which is of substantially the same diameter as bore 28. The piston 14 is inserted into cylinder 12 through the bore 26. After insertion of the piston into the cylinder, the bore 26 is effectively closed by a stub piston 30.

This piston carries a seal 31 of nylon or the like which engages and efi'ectively seals the bore 26 Piston is held in position by a nut 32 which threads on the outer end of the container projection 25.. i v I The piston 14 itself is of reduced diameter adjacent its inner end and is formed with a shoulder 35. It has a seal 34 mounted on it and seating against shoulder 35 and in effect forming the piston head. The seal. 34. shown 37 which is mounted in this notch. Sleeve 36 is of a imension to fit tightly in the bore 28 of cylinder 12, and may even be made a few ten-thousandths of an inch oversize so that it has to be compressed to insert it in this bore. A similar seal may be provided on stub piston 30.

The piston 14 is of progressively decreasing diameter forwardly of its shoulder 35, having a frustro-conical outer surface 38 forwardly of shoulder 35. Surface 38 tapers to the beveled front end surface 39 of the piston 14.

There is a hole 40 drilled in the cylinder 12 at a point which will preferably be slightly forward of the shoulder 35 of the piston 14 when the piston is in its forward position. This hole cooperates with the tapered, conical peripheral surface 38 of the piston 14 to provide the varia' tion in compressive resistance of the piston which is the object of the present invention.

As the piston 14 is forced inwardly into the cylinder 12 the liquid L in the container 10 will be compressed. In the initial part of the stroke of the piston the effective orifice of duct 40 is practically closed, but as the piston travels inwardly, due to the tapered conical shape of the forward end of the piston, the effective orifice 40 between the container and the cylinder is increased; there is progressively more and more space provided around the piston into which the liquid can flow. The rate of resistance to movement of the piston 14 varies, therefore, as the piston moves inwardly of the cylinder 12.

The rate of resistance to travel of the piston varies in proportion to the orifice or difference in clearance between the piston 14 and the bore 28 of the cylinder 12 at duct 40 due to the tapering conical shape of the forward end of the piston. In use, of course, as the piston 14 is pushed inwardly in the cylinder, its force and rate of travel is governed by the velocity of the press ram or whatever it is that actuates it. In the initial part of the stroke, the practically closed orifice can provide a relatively heavy spring load if the spring is hit suddenly as will be the case if the spring is being used, for instance, in a mechanical press. Then as the piston continues to travel inwardly the load curve does not go up as rapidly at this given ram velocity because liquid is being by-passed through the orifice 40, and because it is the smaller seal 18 around the piston rod 16 that is confining the liquid not the larger seal 34.

Upon release of the compressive force as soon as the press ram or other actuating part begins its return stroke, the energy stored up in the compressed liquid L effects the return stroke of the piston 14. On the return stroke, the velocity of travel of the piston 14 is governed by the effective orifice at the particular part of its return stroke. The efiective orifice, of course, varies during the return stroke because of the conical shape of the forward end of the piston. The liquid in the space S between seal 34 and wall 15 or seal 18 exerts during the return stroke, of course, a resisting pressure, causing the effective pressure on the inner side of seal 34 to be diminished in proportion to the pressure exerted at any instance against the outer face of the seal 34. Since the full force of the compressed liquid is acting on the inner face of the seal 34, however, the liquid in front of the seal 34 by-passes through hole 40. Thus, the piston is gradually slowed down a stop, the effective orifice for escape of the liquid trapped between the front face 42 of the piston and the front end wall 15 of the cylinder decreasing as the piston moves forward returning to its initial position.

Typical compression and expansion curves for a liquid spring constructed according to this invention are shown in Fig. 4. The size of hole 40 and the taper of the conical surface 38 of the piston govern these curves, of

course.

Should it be desired to vary the preload on the spring or to compensate for any liquid leakage from the spring, force adjustments can be effected by putting washers. or pa r w en otel and the opposed end: face of the j t e P n 2 he-e t ner- While the invention has been described in connection with different embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains, and as may be applied to the essential features hereinbefore set forth and as fall within the scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

l. A liquid spring comprising a closed container filled with a compressible liquid, a cylinder fixed to one end of said container and mounted to extend inwardly into :said container and opening thereinto at one end and effectively closed at its opposite end, said cylinder having a duct therethrough connecting the container with the in- .terior of the cylinder, a piston reciprocable in said cylinder and having a surface opposed to said duct which is inclined to the axis of the piston, whereby to vary the .space between the periphery of said piston and the opposed inside wall of said cylinder as the piston reciprocates.

2. A liquid spring comprising a closed container filled with a compressible liquid, a cylinder fixed to one end of said container and mounted to extend inwardly into said container and opening thereinto at one end and effectively closed at its opposite end, said cylinder having a duct therethrough connecting the container with the interior of the cylinder, a piston reciprocable in said cylinder and having a conical peripheral surface whose axis coincides with the longitudinal center line of said piston, whereby progressively to vary the space between the periphery of said piston and the opposed inside wall of the cylinder as the piston reciprocates.

3. A liquid spring comprising a closed container filled with a compressible liquid, a cylinder fixed to one end of said container and mounted to extend inwardly into said container and opening thereinto at one end, a piston reciprocable in said container, said piston having a head portion of uniform diameter slidable in said cylinder, a shank portion of reduced diameter which projects outwardly of said container through the other end of said cylinder, and a conical portion connecting said head portion with said shank portion, the axis of said conical portion coinciding with the longitudinal axis of said piston, and said cylinder having a duct therethrough through which liquid may pass between said container and said cylinder.

4. A liquid spring comprising a closed container filled with a compressible liquid, a cylinder fixed to one end of said container and mounted to extend inwardly into said container and opening thereinto at one end, a piston rcciprocable in said container, said piston having a head portion of uniform diameter slidable in said cylinder, a shank portion of reduced diameter which projects outwardly of said container through the other end of said cylinder, and a conical portion connecting said head portion with said shank portion and decreasing in diameter toward said shank portion, said cylinder having a duct therethrough through which liquid may pass between said container and said cylinder, said duct being disposed to open into said cylinder at a point between the head of said piston and the shank thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,554,807 Bingham May 29, 1951 2,581,856 Gruss Ian. 8, 1952 FOREIGN PATENTS 105,053 Great Britain Mar. 21, 1917 609,008 Great Britain Sept. 23, 1948 615,549 Great Britain Ian. 7, 1949

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