Патент USA US2082379код для вставки
June 1, 1937. , R_ J_ BRITTMN. JR 2,082,379 PRESS FITTING Filed April 11, 1934 FIG. 3 ‘ ' FIG- 7 /NVENTOR.,' RICHARD J BB/TTA/N,JB., BY FIG. 4 ‘ _ FIG: 8 _ € ' H/S Arfo/e/wsw Patented June 1, 1937 2,082,379 UNITED STATES PATENT OFFICE_ 2,082,379 PRESS FITTING Richard J. Brittain, Jr., Bloom?eld, N. L, as signor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application April 11, 1934, Serial No. 720,147 8 Claims. This invention relates to press-?tting and com prises all of the features and aspects of novelty herein disclosed. An object of the invention is to provide an improved method of press-?tting parts, 5 such as sleeves or the like on shafts. Another object is to provide improved means of avoiding shaft failure, as when a hollow member is pressed upon a rotatable shaft and transmits load thereto. Another object is to provide an improved shaft 10 and sleeve combination. To these ends and also to improve generally upon methods and devices of this character, the invention further consists in the various matters hereinafter described and claimed. 15 In its broader aspects, the invention is not necessarily limited to the speci?c constructionv and method steps selected for illustration in the accompanying drawing in which Figs. 1 to 4 are sectional views indicating some 20 what diagrammatically certain forces and condi ‘ tions arising when sleeves and shafts are com bined. . Fig. 5 is a sectional view of portions of the improved shaft and sleeve combination, certain 25 small dimensions being exaggerated. Fig. 6 is a sectional view with the sleeve pressed on the shaft and showing certain conditions of stress. Fig. '7 is a sectional view of a modi?cation. Fig. 8 is a sectional view of a sleeve. 30 When mounting bushings, bearing race rings and the like upon shafts, it is common practice to use press ?ts in order that such bushing or ring may be securely held and supported. Some times the bore of the bushing is provided with a comparatively steep chamfer at one end to pro vide a lead when pressing the bushing on the shaft. So far as I am aware, however, the bore of the bushing or ring has been of uniform di 40 ameter or straight except at the chamfer and the surface stresses due to the press ?t have been substantially uniform along the shaft. In any (01. 287-52) point l8 where the chamfer begins and the straight bore terminates. Fig. 2 indicates a condition which occurs when load is applied. For this load, there must be a corresponding tension stress in the upper ?bres of 5 the shaft and a corresponding compression stress in the lower ?bres, all as indicated by the arrows. Both tension and compression stresses are maxi mum at top and bottom in the line of the load but are continually reversing as the shaft rotates. 10 Thus when the shaft turns 180°, the portion initially having maximum tension stress comes under maximum compressive stress and the por tion initially having maximum compressive stress comes under maximum tension stress. 15 These bending stresses are‘ to a great extent , localized in the plane where the straight bore l4 terminates because of the press ?t and the abrupt termination of surface stress. - I The condition of the loaded and rotating shaft 20 is further illustrated in exaggerated degree in Fig. 3. For every load, the shaft has a corre sponding de?ection or bending and the deflection is concentrated at the point of greatest stress which is at the bore termination. As the shaft 25 de?ects, the pressed-on race sleeve tends to in dent the shaft at the lower side. Due to shaft rotation, this tendency to indent is effective for the entire circumference and a minute shoulder 20 forms on the shaft where the bore l4 ter- 30 minates. This indenting increases the effect of stress localization produced by the press ?t. As a result, the metal in the shaft is subjected to gradual surface fatigue which progresses until a circumferential surface crack starts in the shaft where the bore l4 terminates or at the shoulder 20. This crack becomes a progressive fractvure which ultimately results in shaft breakage. Fig. 4 shows a shaft H0 with an enlarged por tion H2 terminating with a sharp corner H8. 5% The condition is directly comparable to that " shown in the preceding ?gures, except that the' event, there has been an abrupt termination of height of the enlargement H2 would be somewhat the magnitude of the stress at the end of the less than the thickness of the race sleeve l2 to 45 bushing, and shaft failure under load has fre produce the same effect. , In order to overcome the bad effects noted quently occurred at this point. The condition is above, the present invention provides exceedingly illustrated in Fig. 1 wherein the numeral l0 rep simple means for preventing localized stress. In resents a shaft, such as a railway axle, on which Fig. 5, dimension A represents the inside diameter is pressed the inner race ring or sleeve [2 of a 50 _ of a sleeve 212 to be mounted with a press ?t on 50 roller bearing, the sleeve having a straight bore v a shaft 2| 0 of diameter B. The difference be l4 extending to a steep chamfer IS. The arrows tween these diameters is determined by the de indicate the substantially uniform pressure or sired amount of press ?t. Dimension C is the stress between sleeve and shaft and it is apparent radial allowance for the press ?t and is exag 65 that the stress terminates very abruptly at the gerated in the drawing. In practice it would 55 2 10 15 20 25 2,082,370 frequently be only about two thousandths of an the shaft and having its bore of uniform size, the inch. If the sleeve bore were made to dimen sion A for its entire length, the bad conditions illustrated in Figs. 1 and 2 would occur. If the bore were made to dimension A plus 2C, there would be zero stress between the shaft and the shaft having one portion of uniform size and larger than the bore by the amount of the press sleeve. In the actual construction shown, the tially as described. 2. The combination with a shaft of a member race bore has a straight portion 2“ meeting at 222 a slightly angled or tapered portion 224 which has an axial length D and joins a chamfer 2". When this sleeve M2 is pressed‘ on the shaft, the conditions illustrated in Fig. 6 are secured. Here the surface stress between the sleeve and the shaft is indicated by the arrows. For a consider able distance, the stress is uniform and maximum. From the arrow 222 to the point 2l8, along a distance corresponding to the dimension D of Fig. 5, the stress gradually decreases and fades out to zero. Thus there is no abrupt change in surface stress as in Fig. l and the localized tension' and compression stresses indicated in Fig. 2 are avoided. One effect of the internal taper and the press ?t is that the outer surface of the sleeve 2|2 will become slightly tapered near the end as indicated at 226. This external taper is less than dimen fit, and another portion of the shaft being tapered down and engaging the bore with decreasing stress along the end portion thereof; substan having an elongated bore tightly ?tting said shaft, said member having the end portions of its bore 10 ?ared for a substantial distance but slightly enough to maintain contact with said shaft and thereby gradually reduce the tightness of the ?t of said member on said shaft. 3. The combination with a shaft of an inner 15 raceway member of a roller bearing thereon, said inner raceway member having an axial bore with radiused ends, the middle portion of the wall of said bore having a press ?t on said shaft of from .003" to .005" tight and said ?t decreasing grad ually from an end of such middle portion for a substantial distance to nothing at a radiused end. 4. The combination with a shaft of an inner raceway member of a roller bearing having an elongated bore tightly ?tting said shaft, said roller bearing because the rollers, of which one is indicated at 228, usually terminate short of raceway member having the end portions of its bore ?ared a substantial distance but slightly enough to maintain contact with said shaft and sion C and does no harm even in the case of a the end of the race sleeve and the usual cage, a thereby gradually reduce the tightness of the ?t portion of which is indicated at 230, overlies the tapered end portion of the sleeve. The length of of said member on said shaft. 5. The combination with a shaft, of a member the internal taper or dimension D may be in creased to any desired extent to get a more grad 35 ual change in stress when the length of the ex ternal taper at 226 is of no consequence. It is shaft, said member having an end portion of its bore ?ared for a substantial distance but slightly enough to maintain contact with said ‘shaft and preferred to make dimension C slightly greater thereby gradually reduce the tightness of the ?t than the radial press ?t allowance in order to of said member on said shaft. 6. The combination with a shaft, of an inner raceway member of a roller hearing or the like 40 thereon, said inner raceway member having an be sure and have the press ?t terminate or fade 40 out in the tapered portion. Fig. 7 illustrates a modi?cation wherein the same results are obtained in a different way. is having an elongated bore’ tightly ?tting said The ring or sleeve 3l2 has its bore wall initially straight except for a chamfer SIB. The shaft ‘III is straight from its end to the region of the arrow 322 and then tapers down or decreases in diam eter so that the press ?t stress becomes zero at axial bore with a chamfered end, the middle por tion of the wall of said here having a tight ?t on said shaft, and said ?t decreasing gradually from the point 3I8. Dimension C is the radial allow an end of said middle portion for a substantial 45 distance to nothing at a chamfered end. 7. The combination with a shaft, of an inner raceway member of a roller bearing or the like ance for the press ?t as before. The exterior having an elongated bore tightly ?tting said shaft, end portion 326 of the sleeve will become tapered said raceway member having an end portion of its bore uniformly tapered for a substantial dis tance but slightly enough to maintain contact as well as the interior portion between points 3|. and 322 because in those regions the sleeve has less than maximum stretching ‘under the press ?t. Thus, paradoxically, the shaft becomes 55 stronger and less liable to failure by thinning it down. As indicated in Fig. 8, the sleeve 2| 2 of Figs. 5 and 6 may be provided with a chamfer “8 formed by a radius merging smoothly with the tapered 60 surface 224. I claim: 1. In a device of the‘ character described, a shaft, a hollow member adapted to be pressed on with said shaft and thereby gradually reduce the tightness of the ?t of said member on said shaft. 8. The combination with a shaft member, of a member having a bore tightly ?tting the shaft member, one of said members being tapered throughout an end portion of the region of ?t so as to gradually reduce the grip of the member on the shaft member from a maximum to a mini mum adjacent the end of said region to avoid abrupt changes in stress. ' RICHARD J. BRI'I'TAIN, Jl.