US2597299A - Spring structure - Google Patents

Description

May 20, 1952 N. A. CRITES ET AL SPRING STRUCTURE Filed May 27, 1947 Patented May 20, 1952 UNITED STATES PATENT OFFICE SPRING STRUCTURE Application May 27, 1947, Serial No. 750,838

8 Claims. (Cl. 267-47) This invention relates to spring structures and particularly to spring structures comprising 1n combination peened spring leaves and interleaf v spacers.

It has long been the object of improvements in the spring manufacturing art to obtain springs A having greater life. Early in the twentieth century, interleaf spacers became the subject of considerable investigation and a number of patents were led thereon. While these interleaf .spacers contribute materially to quieting the action of the springs, they are without eifect in prolonging the life of the spring. Peened spring leaves have somewhat greater life than the unpeened leaves when tested singly, but the increase in life is not particularly significant in the normal spring assembly in which the leaves are allowed to rub on each other.

It is an object of this invention to provide spring structures having unexpectedly greatly increased life as compared With known spring structures having either peened leaves or interleaf spacers taken singly.

Another object of this invention is to provide spring structures which have improved spring life and which may be constructed with but little variation from present day manufacturing procedures.

Still another object of this invention is to provide a spring structure characterized by quiet action in combination with increased spring life.

A further object of this invention is to provide an improved leaf spring structure capable of wide variation so as to be adaptable for many different applications.

Other objects and advantages of the present invention Will become apparent from the following detailed description thereof when read in conjunction with the accompanying drawings in which Figure 1 is a side elevation of a typical automobile spring,

Figure 2 is a side elevation of a spring similar to that shown in Figure l Which is so drawn as to illustrate the manner of assembling the spring, and

Figures 3, 4, and 5 are plan views of several interleaf spacers suitable for use in the present invention.

In general, the present invention comprises spring structures in which peened spring leaves are separated by spacers. g

As above pointed out, interleaf spacers, by themselves, do not in any manner add to the life o f the spring, and only a moderate increase in life is obtained by peening the leaves. An altogether new and unexpected result is obtained, however, by peening the spring leaves and spacing them from one another by means of suitable spacers. This is illustrated in the following Table 1 which sets forth data obtained by testing four parabolic nonblockt springs having a drawre finish:

l Testing machine is standard flexing machine having 4-inch stroke with movement originating at the center of the spring with the eyes of the main leaf held relatively stationary.

Sample No. 0 63 shows failure at slightly fewer cycles than Sample No. O-62. This discrepancy is within the range of experimental error, however, and does not mean that the spacers actually decrease spring life. By peening the spring leaves, some increase in spring life may be obtained in certain instances, as shown by a comparison of Sample Nos. O-62 and O-76, although frequently no change at all in spring life is eiected. This increase of about 100,000 cycles before failure resulting 'from shot peening the individual spring leaves is insignificant in comparison with the more than 2,000,000 cycles increase effected by combining shot vpeened leaves with interleaf spacers. Actually, the increase effected by this combination was much more than 2,000,000 cycles, since there was no failure at the 2,500,000- cycle mark. Such an increase in spring life cannot in any manner be attributed merely to the additive eiect of shot peening and spacers, but is the result of a new combination of elements.

In order to illustrate the present invention more clearly, reference is now made to the accompanying drawings in which the particular embodiment disclosed in Figure 1 represents a typical automobile spring. Such a sp-ring l0 is composed of a plurality of leaves Il-I I, which may vary in number from 6 to 10 generally. The longest leaf I2 is termed the main leaf and is subjected to the greatest amount of ilexing and movement as respects the adjacent leaf. It is customary in the art to identify the spring leaves with number, beginning with the main leaf as No. l and continuing downwardly therefrom. The main leaf I2 is bent back on itself at both ends to form eyes I4-I4 by means of which the springs are attached to the chassis of the automobile. '.lhe center of the spring is attached to the axle ofthecar by U-bolts I5-I5, so that in operation the center of the spring moves up and down while the ends remain relatively stationary. This causes the upper side IB of the leaf I2 to be put in tension and the under side I8 to be put in compression. The amount of camber in each leaf will determine the locationand magnitude of the initial bending lstresses in the assembled spring unit. Spacers lil-IS, as shown particularly in Figure 2, are usually composed of such materials as wood, pressboard, canvas, etc., impregnated with, or covered by, graphite and a suitable grease or similar lubricant. Spacers may also be made of soft bearing metals, and, in 'some cases, 'certain 'plastics may be adequate. These spacers 'may `take -a variety'ofsforms as is shownfin Figures 3,`4,"and 5. Figure' represents a'conventional 'single-piece pressboard spacer Il', whereas the` 'spacer 'in Figure 4 vcontains slots "-2 Il in which lubricants Such as graphite may be placed. The 'spacers'hown in Figure 5 contains a plurality of holes 2I2I which may be filled with lubricant and, when held tightly bet'wntwo spring 1`eaves,will retain the lubricant thereinv so as to form self-lubricating springs. These vand a large variety of other forms of intereaf'spacers may besatisfactorily employed. Instead of a strip spacer running the length of thespring leaf, the tip of the leaf and the center under the U-bolts maybe supported by interleaf spacers With nothing butair space existing between the Ubolt and the tips.

Inactual operation, the ends of the leaves I 4- |4 attached tothe chassis are held in a relatively stationary position and the middle of the spring moves up and -downas the shock is transmitted by the 'road to the wheel, through the axle, "and to the spring. Pulling or tension stressesa'e 'exerted upon'the inner or upper side -of the spring 'leaf when'its center is bent upwardlyandfsimultaneously, pushing-together or compression vstresses"are'e'xerted upon the lower 'drouter side "of 'the leaf. In'fatigue failures of leaf springs, tlecompression stresses appear to play a 'very minor part, whereas the tension strssesaremajor -'factors in'causing failures be- Hca'u'se 'th'yfgiv'e rise to surface cracks or separations. The interleaf 'spacers lS-S extend slightly ov'er the 'end of the leaves I-l so as to preventaiiy-rubbing of one leaf upon the other to nproduce f retfmarlts or other surface defects. Thus, Vthe interle'afspacers 'lubricate the movement of the spring leaves 'with `respect to one `anothers'o as ftojreduceor eliminate squeaking, kwhile at the fsain'e time preventing any inter- 'action betweenthesurfaces of the spring `leaves so as lto damage ea'nother.

Peenin`g maybe rtechnically defined as a process of striking the surface of a metal with a 'very large numberfbf light blows. For purposes 'of this inventionfshotpeening and grit blasting lare equivalent processesfso that the word peenin`g, as used throughout the present specificajtionfand the accompanying claims, includes the `process of b lastin'g'a'metal surface with grit or angular vmetal `vparticles as `Well as shot or jroun'd'edmetal particles. Grit blasting is pref er 1fed, however, where' there is considerable'- scale 'on thesprngleanbecause the grit removes Vmore metal than does the shot. The size of the shot or grit employed is apparently immaterial as long as a thorough and uniform cold working of the surface to be treated is effected. Furthermore, the hardness of the metal particles employed is not critical, as long as they aresufliciently hard to effectively cold work the metal siufacc to be peened.

The most critical feature of the peening operation in the present invention is that there be complete coverage, and coverage is a function of shot or grit size, velocity or impact force, and time of exposure. By coverage is meant the peenin'g of the metal surface to such an extent that thecompressive stresses raised by the peening operation penetrate below the decarburized layer on the surface of the metal. The usual spring leaf has this decarburized layer of amorphous metal crystals which comprises a weak area in which cracks may originate and ultimately penetrate the entire leaf unless this layer is removed or altered by cold Workingfsueh as peening. The peening factors will vary'from'one type of spring leaf to another, but the accompanying examples indicate certain optimuni'c'onditionsforgiven springs. The entire spring leaf should be'peen'ed Whenever the leaf will be "sbject to reverse stresses, as in the first'thr'ee leaves of the normal nine-leaf automobile spring, but experience has shownthat only vthe 'edges and the tension side of the leaves Whichare not'subjected tovtensi'o'n stresses on theirjcompressioh sides need to lbe peenedto obtainthebptimum results. More particularly stated, o'njly `those surfaces 2 need be 'peened that are subjected to tensionfstresses beyondith'e'ir endurance liifiitjbe they drawre finished or otherwise. Peeiiirigo'f the edges of the spring leaf counteractstheftension stresses extending from the tensin 'side in the direction `of vtheunde'r side or compression side. The number of leaves of each'sprirr'gthat are p'referably'completely peened depends '-po'n the number and length of thespring leaves, "as well as the type Vo f spring involved. In'autoinotive springscontaining eight 'orni'ne le'avesfcm'- plete peening of the first Ithree leaves, Nos 1, 2, and 3, has been showntobe adequate. 'Agen'- eral rule to u se as aguidein applying the'pre'se'nt inventionV is Vto peen Iall jsu'rface's Kwhich 'are put into tension duringtheus'eofthe spring.

The particularmaterial,size,'shape,"or location of the spacers, vor the particular lubricant "mployed thereini'simmatrial Va'slo'r'ig as thelsprin'g leaves are prevented-from rubbingjonbne an'- other. It is obvious, of course, that these" paceirs cannot be made of 'a hard metal, 'sincetheywbilld damage thespring jleaves; however, :a Ivariety of metals Which-are sufficiently"softor'beainglike so they wouldnot damage thesprin'gleaves and which have no other detrimental effect 'u'po'n the spring can be used.

In order to better enable those-skilledfinthe 'art to practice the present invention, tliefollwing detailed examples thereof "are given. 'It v4's to be understood, however, that 'the following examples are merelyillustrative of theinven'tion and that the jpresent 'nvention isfappllcable to widely different spring structurs, including variations in typeof spring, size of leaves,`sp`aeers, and peening treatmentof the'leaves.

Example 1 tangulansectins and composed of 'SAE No. 9260 steel, was blocktted and then each leaf completely grit blasted manually in an aspirating air lift type sandblast machine. Grade 60 grit was projected at 90 pounds per sq. in. air pressure onto the individual leaves by means of a rubber hose. Approximately seconds of continuous blasting was required to completely cover a given spot. The spring was assembled using vulcanized fiber center spacers with steel tips attached to the outer ends of the leaves, the center spacers i and steel tips being lubricated with a mixture of flake graphite and heavy grease, such as Marfax No. 3. The spring thus constructed passed 1,000,000 cycles on the testing machine heretofore described in connection With Table 1.

Example 2 Example 3 This spring was constructed in a manner identical to that of the spring described in Example 2, with the exceptions that the leaves were of parabolic section and that the peening operation was carried out in a commercial, automatic apparatus. A mixture of No. shot and No. 45 grit was thrown against the spring leaves at an air stream pressure of approximately 125 p. s. i., and the leaves moved past this stream at the rate of about 25 feet per minute. As in Example 2, this spring passed 1,000,000 cycles on the spring assembly testing machine without failure.

Example 4 A nonblockiit spring having leaves of parabolic section was constructed in a manner otherwise identical to, and with materials similar to, the spring set forth in Example 2. Upon testing, this spring passed 1,000,000 cycles without failure.

Example 5 A spring was constructed similar to the one described in Example 3, except that the leaves were manually grit blasted only on the tension side instead of being peened all over in a commercial peening machine with a mixture 0f grit and shot. This spring ran 867,000 cycles on the testing machine before failing. Failure occurred on the compression side of No. 1 leaf.

A comparis-on of Example 1 with Examples 2, 3, and 4 shows that complete peening of all of the spring leaves is no improvement over peening completely just the rst three leaves and only the tension side and edges of the remaining leaves. Test measurements had shown that only in the rst three leaves of the eightand nineleaf springs tested were there tension stresses on the compression sides, so that there was no need to peen the compression sides of the remaining leaves.

The present invention applies equally to rectangular and parabolic section springs, as shown by a comparison of Examples 2 and 3, which examples also disclose that the employment of widely different peening operations does not affect the life of the resultant spring. The pressboard spacers used in the springs shown in all '6 of the examples other than r1 appeared to be equivalent to the greatly diiferent steel tip-center spacer arrangement used on the Example 1 spring.

Blockt and nonblockt springs proved to be 'equally good after being constructed in accordance with the present invention, as seen by a comparison of Examples 2 and 4. A very important difference was apparent, however, when all of the spring leaves were merely peened on their tension side, as in Example 5. It is signincant that the failure of the spring in Example 5 occurred on. the unpeened compression side of the main leaf, undoubtedly due to tension stresses caused by reversals of th`e main leaf. In'summarizing the above comments on the examples set forth, it appears that the peening operation may be varied widely without detrimentally affecting the'life of the spring. Nor does it appear that there is anything critical in the particular shape of the leaf or particular spacing means.

It is apparent that the present invention comprises spring structures which include the combination of peened spring leaves and interleaf spacers. By practicing the present invention, the life of the spring structure is greatly improved whether it be a blockt or nonblockt type spring,

A number of variations from the above-detailed description of this invention may be made without departing from the scope of the following claims. For example, a variety of spacers of different sizes, shapes, and materials may be employed as long as they perform the essential function of preventing the rubbing of one leaf upon another. Several dierent methods of throwing shot and grit are now in commercial use and any of them may be employed in the present invention as long as adequate coverage is obtained. Flat springs, such as heavy tractor springs, and other types of leaf springs may be constructed in accordance with the present invention.

What is claimed is:

l. A leaf spring structure comprising in combination spring leaves having all surfaces subject to tension stresses completely peened, said peened surfaces being such that the compression stresses resulting from the peening operation penetrate below the decarburized layer, and means, spacing said leaves from each other, interposed between at least those leaves having peened surfaces, and adjacent said peened surfaces.

2. A leaf spring structure comprising a plurality of leaves, each leaf having essentially its entire surface peened, and spacers interposed between adjacent spring leaves to prevent frictional action of any leaf upon another.

3. A multiple leaf spring structure comprising at least one leaf having all of its surfaces completely peened and the remaining leaves having their tension side and edges peened, and spacing means interposed between ajacent leaves.

4. A leaf spring structure comprising a plurality of leaves, each of which has the tension side and edges thereof peened, and means interposed between adjacent leaves for spacing one from the other.

5. A leaf spring structure comprising a plurality of leaves, each of which has the tension side thereof peened and lubricating spacers interposed between adjacent spring leaves to prevent frictional action of any leaf upon another.

6. A semi-elliptical leaf spring structure for automotive vehicles comprising approximately eight to ten leaves, the three longest leaves being completely peened on all surfaces and the other leaves being peened on the tension side and edges thereof, and lubricating spacers interposed between adjacent spring leaves.

'7. A leaf spring structure comprising a plurality of leaves, each of which has all of the surfaces peened which will be subjected to tension strains beyond their endurance limits, and means, for preventing damaging frictional action of one leaf upon another, interposed betweenv at least those leaves having peened surfaces, and adjacent such peened surfaces.

8. An automotive vehicle spring of the multiple leaf type, which comprises a completely peened main leaf, additional leaves peened on their tension side and edges, and lubricated pressedboard spacers. for preventing damaging fictional engagement of the leaves, interposed between at 8 least those leaves having peened surfaces, and adjacent such peened surfaces.

NELSON A. CRITES. NATHANIEL C. FICK.

REFERENCES CITED The following references are of record in the rileY 4of this patent:

UNITED 'STATES PATENTS Number Name Date 1,219,592 Schwarz Mar. 20, 1917 1,946,340 Vorwerk Feb. 6, 1934 2,107,455 Thompson Feb. 8, 1938 FOREIGN PATENTS Number Country Date France June 26, 1922

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