US2608752A

US2608752A - Method of making single leaf springs

Info

Publication number: US2608752A
Application number: US785763A
Authority: US
Inventors: Schilling Robert
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1947-11-13
Filing date: 1947-11-13
Publication date: 1952-09-02
Anticipated expiration: 1969-09-02

Description

Sept. 2, 1952 R. SCHILLING 2,608,752

METHOD OF MAKING SINGLE LEAF SPRINGS Filed NOV. 15, 1947 2 SHEETSSHEET l A6352 5 flak/Jaw] an WIW G0 rornegs R. SCHILLING METHOD OF MAKING SINGLE LEAF SPRINGS Sept. 2, 1952 2 SHEETS-SHEET 2 Filed NOV. 13, 1947 Zhwentor @iq/ iii/4', W 'u/ (Ittornegs Patented Sept. 2, 1952 METHODUFM'AKING SINGLEIEAFSPRING'S Robert Schilling; 'Birmingham 'MiclL, assignct to" General Motors" Corporation, netroih Mic'hl a cnrporation of Delaware Applibatibn November, 13; 1947, seriarivorvss vts" 16 Claims. (Cl.29-17 3') :1"v Y 'TYiis inventionJreIetes generally to springs an i' thelmanufecture thereoflandji's more particularly concerned with l'eafis-prings .an'd thet p'roc essing thereof.

Conventional leafsprings are laminated and consist of a piurality ofhl'ades. fIn coritra'stgthe leaifv spring ofthe presentlinvention is made out oifasingiebiade:

order to arrive at a; minimum weighte Iea'f sprfi-ig mustloedes'ignedso'that' the operating stresses are the same ateupoints; Consequently a, single leaf spring must then have either a variable width, a variable thickness or both. 'A studyofithese possibflitieshas shown that a single l'eaf' spr'ingi w01 substantially constant width and, with e. variable thicknessis most practicable. The .pre'ferredi'form of. Single l'eafsnringJin eccordance with "thisinventiontherefore is of .constant o'rsuostantially constant width and varies in'tnickr' jessffrom a'maximum' at the center toua minimum atlipoints' adjacentthe two ends thereof; fit nas'a oout the semelength and width as e conventional laminated spring but is much thinner; The design ibeoomeypossibl'e because novefprocessing permitslth'e use of. much jliigher operating stressestlianis"present practice;

The cross section ofthespring blade of the invention may take" various "forms, Ordinarily it i's'of rectangular cross section with slightly rounded edges ('COIHGY" radius" i 'to inch). However; special: sections such as" center groove or paraboli'c edgesarealso possible; V

The single leaf spring of this invention "is espeoiallywelisuit'edfor rear suspensions of ijpas senger' ears; It'Tllay'b'e used" also for "front; suspensions although it does not show somany-edvant' agesin'suchinstances;

The"fasteningstotheaxle'end'chassis-aresimilar *to" those :empl'oye'd with conventional' lami natedsprings: -It ispreferred not'to' usea direct meta l to 'metal :olamp' atthe' spring center, because 'suchi'a clamp causes a certain amount of clia'fing which may lead to "failures" at the high stressesused. A liner offl'exible or plastic materialis -used between'the sprineblede endiciamp; to insure unif'ormsurface pressures andfprevent chafing. '-It is-preferred-also to avoid-the conventionai oenter bolt'hoie, and toiuse instead 2; pair 0f grooves a't the-side of the spring at the neutralaxis for the purpose of centering :the spring 'gintitaking longitudinal loads. Itis 1pos= sible to omit the grooves tend locate the spring by cementing it'to therirbberseatioads;

one important advantage of "the-single leaf spring of -'thisinvention- :compared with" a laminated'lea-f spring; is its -greatlyfreduoed weight. This is brought about-by theincre'ased' operating infull lines andthe'maximum gload position stress and the'redu'cti' n "of inective spfingimae teriai'. The manufacturing cost-is reduced in proportiontothe lower raiwmaterial weightrand to'th'e'smell'er number of parts to-beprooessedi In operation an important advantage-751s tile elimination of static friction of 'laminatedfleaf springs; Spring covers or liners'are not-needed and the spring requires no servicing; The-ride doies not change because the 'veriable frietion nolonger'present. l

The'primary' objects of'the invention are-to provide-asingle leaf'spring having'the edvanteges outlined above andto provide? an improved method 'or' methods of processing I such spring; Another object is 'to'p'rovide ran im-proved step or steps in a method of spring processing-which is applicable also tootherspringsthan single leaf springs; Other obj eets and eidvan te'gesQof the invention will :bee-ppetrent from the descriptieri which-follows; 5 Reference -isjiierewlth mad'e to' the accompany ing= drawingsillustraiting ai-single leaf spring-=arid the processing-thereof in accord' ance witli-e' p rf ferred-em'bodiment of theinventionn Inthe drawings: v i 3 I Figure 1-is a=view' illustrating the*-step of of; rolling a steel springblank of substantiallyauniform widthand-of avariabletliiokness. 1 Figurefl'illustratesthe step of for-m'i-ngtli eyes on-the; ends of the'springhlank off Figur Figure 3 il1ustrates: the step of quenching the spring on acurved-fixture in the hardening opelation. 7

Figure-4 illustrates the sho't peeriing of a lieet treat'edspri'ng while the spring 'i's under 1mm; Figure 5- is a; diagrammatic view of the idjdl contour of a semi-elliptic springof uni form width 'eind va'riable thickness having uniform op eratingstresse's-at all sections', the spring thi'c ness' being shownon ailargersettlethemis tlie length. 1'

Figure 'fi is a diagrammatic view; showing a; m'odificaition of theideal-contbur of Figure- 5} the spring" thickness being shown-on a; ilaii'ger scale than "is the length.- Figure 7 showsone form of appartus'wviiili' is used for prestressingthe-spring after itih'azs been sliot-peened. 'i

fi ed s tes a l rros o 1 sistan-t coating to "protest thespring f iomi'o'or;

rosl'onin-service; V I I Figure 9 isjiwcomposit'e view ofthetdifferent positionsor shapes of tli-e spring at difie' rent points-in the processing'andyor operatingioycles; Figure 10 is-a view sliowingthe spring'installefdj the-static'load position'of the "spring being the unloaded position being shown in dotted lines.

In forming the single leaf spring, steel or other spring material is hot formed as by rolling or otherwise into the required shape such that the operating stress will be the same or substantially the same at all sections. In Figure 1 is.diagrammatically shown the operation of hot rolling a spring blank [0. The blank shown is of constant width and of variable thickness with the portion of maximum thickness at the center of the blank where the spring will be attached to the axle. The bottom face of the spring blank is fiat and the upper face is of a contour such that the operating stresses will be substantially equal at all sections.

The ideal contour of a semi-elliptic spring of constant width having uniform operating stresses at all sections is diagrammatically shown in Figure 5. The bottom face H is fiat and the upper face is formed of two parabolic contours l2 and I3. Figure 6 shows diagrammatically the manner in which the ideal contour of Figure 5 is modified in the design illustrated in the several drawings herein.- 'At the center the two parabolas of Figure 5 are faired by a circular arc H which slightly reduces the thickness within the spring length which will be clamped by the center clamp. At the ends l5, I5 the thickness is held constant at a minimum value in order to provide sumcient stock to form eyes. In Figures 5 and 6 the thickness of the spring is shown on an enlarged scale as compared with the spring length in order to illustrate more clearly the contour or the single leaf spring.

The rolling operation may be carried out in any desired way. For example, the rolling may be accomplished in a single pass and in continuous strip form at the steel mill. Thisinay be done at the last pass of the strip rolling process, so that no separate heating is required. The rolllng also may be carried out in a number of successive passes in a manner analogous to the taper rolling on blades for laminated springs. V

Figure 2 illustrates the step of eye forming. This step is similar to that on the main leaf oi? laminated springs. The eyes are shown at [8.

After forming the eyes the blade is heat treated. In this operation the spring steel blade is heated to a hardening temperature above AC3. It is then mounted on a quench form such as shown in Figure 3 so shaped as to impart a desired curvature to the heated spring. The fixture shown comprises a lower portion l-l and an upper portion I8 between which the heated spring is held. It is then quenched with oil or by other suitable means to harden the spring. The quench form is designed to allow for changes in shape during subsequent processing steps so that the spring will have the desired shape and standing height in service. The hardened spring is then removed from the quench form and tempered without restraint. This operation consists in reheating the hardened spring to a spring tempering temperature considerably lower than that employed in the hardening operation. The tempering treatment does not change the curved shape of the spring resulting from quenching the spring in the curved fixture. The hardening and tempering temperatures may be the same as those employed in heat treating conventional springs. As a specific example of heat treatment, the spring may be heated to 1600 F. and held at this temperature for about two hours. It is then quenched in oil to harden the same. It is thereafter reheated to a tempering temperature on the 4 order of 750-920 F., the lower tempering temperatures being employed with steel of lower carbon content and the higher temperatures with spring steel of higher carbon content.

After being hardened and tempered the single blade is shct-peened while under load. The spring blade which is curved when free, is clamped to a form or fixture so that it is approximately fiat and under a stress between 125,000 and 200,000 lbs. per square inch (mostly about 175,000 lbs. per square inch) with the tension side exposed. In general the shot-peening is carried out while the spring is loaded in the direction of service loading to a tensile stress on the order of about 60% to of its yield point. The shot-peening is carried out by causing hardened steel shot to impinge upon the tension surface of the spring blade. The shot may be directed by a high velocity air stream against the tension surface, or the shot may be thrown from the periphery of a wheel which is rotating at high speed and caused to impinge upon the tension surface. The spring is passed through the shot-peening machine so that the entire tension side isthoroughly shot-peened. Best results are obtained when the corners adjacent the tensile side are also shotpeened. The shot are caused to travel at such high speed that they effect a cold working of the spring surfaces contacted thereby. Since the spring is already stressed near to its yield point the effect of the peening is more severe and penetrates more deeply than it would on an unstressed spring, The peening greatly improves the load carrying capacity and the endurance of the spring. At the same time the spring takes a considerable set during peening which must be allowed for when designing the quench form. One means for carrying out the shot-peening operation on the tension side of the spring is illustrated in Figure 4. In this figure, 20 represents a form to which the spring is clamped by means of similar clamps 22. Shot-peening nozzles are shown at 24. For peening the corners adjacent the tension side, the nozzle or nozzles may be arranged at an angle; for example, very efiective peening is obtained when the nozzles are at an angle of 45 to the vertical. The peening operation may be carried out in one or more passes through the machine. So far as I am aware, the operation of shot-peening while under load, is novel per se. It can beused also in treating other springs than single leaf springs in order to improve greatly the endurance and load carrying capacity thereof.

After the shot-peening operation the single leaf spring is preset by deflecting it in the directionof service loading without application of heat by an amount which is in excess of the maximum service deflection by between ten and thirty per cent. During presetting the spring takes a further set which also must be considered and taken into account in designing the quench form. The presetting accomplishes two main purpose (1) it minimizes subsequent settling in serviee and (2) it allows a readjustment of standing height, so that variations due to material and processing can be corrected. One form of apparatus for carrying out the presetting operation is illustrated in Figure 7. In this figure, 30 represents a form against which the spring is deflected by loading means 32. The presetting also may be performed by clamping the blade between male and female terms, or simply by loading it with a load which 1s in excess of the maximum service load by between ten and thirty per cent.

After presetting the spring has the correct free shape, which shows less curvature than that of the quench form.

The spring preferably is coated after presettmg with an anticorrosion coating, such as one of the hosphate treatments (Parkerizing, bonderizing) or painting. The coating operation is illustrated in Figure 8 in which the spring i shown immersed in a coating solution 38 in a tank 38.

Figure 9 is a view showing the various shapes of the spring during processing and operating superimposed. In this figure A illustrates the shape after hardening and tempering, B illustrates the shape after shot-peening, C represents the free shape of the finished spring, D represents the approximate shape at static load, E represents the shape at maximum service load and F represents the shape to which the spring is preset. The difference between shapes A and B is that due to the shot-peeping, and the difference between shapes B and C is the set due to presetting. The operating range extends from the free shape of the finished spring (shape C) to the shape at maximum load (position E). The difference between the shape at maximum load (position E) and the shape to which preset (position F) is the margin by which presetting exceeds the maximum operating deflection.

Figure 10 illustrates the single leaf spring as installed, The ends of the spring are shown connected to the chassis 48 in the same general manner as conventional laminated leaf springs. The center of the spring is clamped by the clamp 59 to axle 52. The full line position of the spring shows it in its static load position. The upper broken line position is the maximum load position, while the lower broken line is the unloaded position.

Load capacity and endurance of a spring may be increased if the shot-peening operation is repeated after the presetting of the spring. This can be done with a spring in the free shape condition or in a stressed condition asshown in Figure 4. Best results have been obtained when during the second shot-peening operation the spring was held under approximately the same stress as in the first shot-peening operation. The additional settling of the spring during this operation must also be allowed for in the quenched shape of the spring.

While I have shown what I consider to be a preferred embodiment of my invention, it will be understood that various modifications and rearrangements may be made therein without departing from the spirit and scope of the invention.

I claim:

1. The method of making a. single leaf spring characterized by high load carrying capacity and endurance which comprises providing a hardened and tempered steel leaf spring of substantially uniform width and of variable thickness ranging from a maximum at a point substantially midway between the ends to a minimum adjacent each end, flexing said leaf spring to produce a tensile stress on the order of 60% to 100% of its yield point on the tension side of said leaf spring; shotpeening the tension side and adjacent corners of said leaf spring while it is under said tensile stress and then presetting said leaf spring by de fleeting it in excess of maximum service deflection by between ten and thirty per cent.

2. The method of making a single leaf spring characterized by high load carrying capacity and endurance whichcomprises, providing a hardened and tempered steel leaf spring, loading said leaf spring to produce a tensile stress on the order of 125,000 to 200,000 pounds per square inch on the tension side of said leaf spring, shot-peenlng the tension side of said leaf spring while it is under said tensile stress and subsequently presetting said leaf spring by deflecting it in excess of the maximum service deflection by between ten and thirty per cent.

3. The method of making a single leaf spring characterized by high load carrying capacity and endurance which comprises, providing a hardened and tempered steel spring blade of substantially uniform width and of variable thickness ranging from a maximum at a point substantially midway between the, ends to a minimum adjacent each end, flexing said spring blade to produce a tensile stress on the order of 60% to of its yield point on the tension side of said spring blade and shot-peening the tension side and adjacent corners of the spring blade while it is under said tensile stress.

4. The method of treating spring which comprises shot-peening a steel spring while it is loaded in the direction of service loading to a tensile stress on the order of 60% to of its yield point.

5. A method as in claim 1 in which the spring also is subjected to a shot-peening operation after the presetting of the spring.

6. The method of making a single leaf spring characterized by high load carrying capacity and endurance which comprises hot forming steel into a single leaf spring of substantially uniform width and of variable thickness ranging from a maxmum at a point substantially midway between the ends to a minimum adjacent each end whereby said steel spring will have substantially uniform operating stresses at all sections, heating said steel spring to a hardening temperature, quenching said heated steel spring to harden the same while the spring is held in a fixture to impart a curvature thereto, reheating the hardened and curved leaf spring to a tempering temperature, flexing said leaf spring to produce a tensile stress on the order of 60% to 100% of its yield point on the tension side of said leaf spring then shot-peening the tension side and adjacent corners of said leaf spring while it is under said tensile stress, andthereafter presetting said leaf spring by deflecting it in excess of maximum service deflection by between ten and thirty per cent.

ROBERT SCHILLING.

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

UNITED STATES PATENTS Numb er August 1945, pages l41-149.