BEARING ARRANGEMENT WITH BEARING SLEEVE

Abstract: A pressed sleeve bearing (10) is disclosed which is moldable out of plastic and which will provide a superior retaining characteristic, while at the same time will retain the designed interior diameter of the bearing, unaffected from the pressing forces and deformation. The region of engagement (22) between the bearing and the supporting part is displaced axially from the bearing region (20) so that any deformation of the sleeve will not be communicated to the bearing surface. The interior of the sleeve in the region of engagement is relieved to provide clearance for the shaft (24) that will be inserted into the bearing.

Description: This invention relates to a bearing arrangement and more specifically to bearing arrangements, which include a bearing sleeve that may be pressed into the bore of a supporting part or member. BACKGROUND OF THE INVENTION Press fit sleeve bearings of both plastic and metal are well known. Metal sleeve bearings are typically pressed into a bore and then machined to the final internal dimension to accommodate the shaft that is intended to operate within the bearing. The post insertion machining is expensive and disrupts the normal flow of assembly of the product. An illustration of such a metal bearing is shown in DE-C-935520. This is a rather complex assembly including a first sleeve cooperating with the internal bore in which the shaft is to be mounted and a second sleeve, placed intermediate said first sleeve and the shaft. The structure of both sleeves and their connection is so as to allow both some radial and angular movements of the shaft. As mentioned above, this is a complex and expensive solution. The plastic sleeve bearings have a different drawback. In order for the sleeve to remain in the bore, there must be sufficient deformation in the bearing material to create the forces needed to retain the bearing in the bore. In plastics of the type used for bearings, the required deformation may be quite significant and therefore result in the deformation of the interior dimension. Since it is very difficult to accurately predict the amount of internal deformation, due to variations in the tolerances of the bore hole and the exterior sleeve dimensions, it is preferable to form the bearing such that the bearing structure permits controlled deformation. This then minimizes the requirement to perform post assembly operations on the bearing material. It is not very practical to perform a post insertion machining operation on the plastic bearing, since machining of plastic may not be precise and it is difficult to secure smooth bearing surfaces on plastic by machining. The molded skin of a plastic piece provides a superior bearing surface than that of a machined surface. Prior attempts to overcome the problem of using plastic materials as bearing sleeves have followed the approach of accommodating the compression of the bearing exterior without unduly affecting the interior bearing surface. U.S. Patent 3,359,685 to L. M. Hodgen discloses a bearing sleeve which provides the bearing surface in a series of alternating lands with intermediate grooves, parallel to the axis of the bearing. The lands provide the bearing surface, while the grooves provide flexural relief to accommodate the compression of the material. The exterior of the sleeve is likewise a series of alternating lands and grooves. The lands of the exterior surface are radially aligned to the grooves of the interior surface, thereby permitting the distortion to be accommodated in the region of the groove of the interior surface with a minimum distortion of the bearing surface. U.S. Patents 1,555,214 to C. W. Johnson and 3,515,417 to J. H. Bowman both use serrations or splines on the exterior surface of the bearing to accept the deformation caused by the insertion of the bearing into the bore of another member. In both of the patents, the splines or serrations extend the full length of the bearing. In the case of the Johnson patent, the bearing is lined with a split sleeve which defines the interior dimension of the bearing. This sleeve may contract or expand. Dimensional stability is thereby sacrificed in the Johnson bearing. The Bowman bearing appears more dimensionally stable on the interior but uses the flexure of the splines to effect a centering of the bearing surface. JP-A-59 166 711 discloses a bearing arrangement according to the preamble of the sole claim and comprising a bush which has peripheral side elastic contact face parts on its peripheral surfaces in both end parts in the axial direction and an internal peripheral side elastic contact face part on its internal peripheral side in the central part, in the expanded part of a rack housing. The bush is secured in the housing through a pin and hole assembly. At one end, the elastic contact is obtained by flexible axially extending fingers capable of bending in case of shaft tilting. At the other end the elastic contact is simply due to the elastic properties of the bush itself. For precision applications involving relatively light loads, plastic bearings are desirable since they may be molded to very tight tolerances. Cost is very reasonable, particularly if the molded dimensions may be used without further operations in the finally assembled product. SUMMARY OF THE INVENTION The present invention concerns a bearing arrangement as defined in the sole claim. DRAWINGS Fig. 1 is an oblique view of the bearing, in accordance with this invention. Fig. 2 is a partial sectional view of two of the bearings in bores of a supporting part and with the associated shaft inserted in the bearings. Fig. 3 is a frontal sectional view of the bearing, shaft and bore. Fig. 4 illustrates an alternative embodiment of the bearing having positioning regions which have a continuous flange and/or absence of a flange. DETAILED DESCRIPTION OF THE INVENTION Referring to Figs. 1-3, where like numbers denote like portions, the bearing 10 is illustrated in its unstressed condition, in which it is a cylinder 12 of substantially uniform outside diameter. The diameter is sized to be a loose fit with the interior of the bore 14 into which it is intended to be inserted. Arranged about the circumference of the cylinder 12 and at the cylinder ends 16 are a plurality of projections 18 which may be described as segments 18 of an interrupted flange. These protrusions or flange segments 18 engage the interior of the bore 14 and are dimensioned such that the diametral dimension of the flange segments 18 is larger than the diameter of the bore 14, by an amount that will result in the deflection of the cylinder 12 at the ends and thus create the outward restore force which then acts to hold the cylinder 12 in the bore 14. In the center, axially of the cylinder 12, is a continuous projecting cylinder 20 dimensioned to engage shaft 24. The interior of the cylinder 12 is, in effect, three subcylinders, positioned end to end, best seen in Fig. 3. One subcylinder is the bearing cylinder 20, the other two being the larger interior diameter of the end or positioning cylinders 22. The bearing cylinder 20 accepts the shaft 24 of the device being supported either rotationally or axially. The positioning cylinders 22 have an inside diameter 26 which is sufficiently larger than the diameter of the shaft 24 so that the portion underlying the segments 18 of the flange will not contact the shaft 24 when the bearing 10 is in place within the bore 14. The flange segments 18, when forced inwardly toward the axis of the bearing 10, will tend to cause the positioning cylinders 22 to partially collapse or distort and at the same time cause the segments 28 of the cylinder 12 intermediate the flange segments 18 to tend to bow outward. The natural tendency of the cylindrical structure is to return to an undeformed state. This tendency causes the flange segments 18 to be forced outwardly toward the surface of bore 14 and engage the bore 14 with sufficient force to retain the bearing 10 in the bore 14. The deflection of the cylinder 12 at and between the flange segments 18 will have no undesirable effect on the cylindrical shape of the bearing cylinder 20, since the flexing occurs in the thinner cylinder walls 30 (Fig. 3) between the end of the cylinder 12 and the bearing cylinder 20,. The suspension of the bearing cylinder 20 by and between the positioning regions 22 of the bearing 10 allows some limited additional flexing of the cylinder walls 30, thereby resulting in a self-aligning bearing 10 with a limited degree of alignment capability. The bearing 10 is molded of the desired plastic material and the bearing 10 is then inserted into the bore 14 of the part 32 in which the bearing 10 will reside. During insertion, the flange segments 18 will be forced inwardly sufficiently to permit entry into the bore 14 and in so doing the cylinder of the positioning region 22 will be deformed. The deformation of the cylinder 12 will act to create the outward restorative force that, when exerted against the bore 14, will be sufficient to hold the bearing 10 in bore 14 during normal use. Substantial deflection or distortion of the cylinder is necessary due to the relatively low forces generated by the plastic in its effort to restore to the non-distorted shape. The molded bearing surface of the bearing cylinder 20 is left undisturbed by post assembly finishing operations and the dimensional control is enhanced since it may be best and more consistently controlled in the molding operation. An alternative embodiment which is not covered by the sole claim of the bearing 10 is illustrated as technical background in Fig. 4. Referring to Fig. 4, the external flange 40 is continuous on the one end of the bearing 10 and a smaller, smooth cylindrical shape 42 extends around the entire end of a smooth cylindrical positioning region 44. This structure functions in a similar manner to the bearing of Figs. 1-3. The reduction in the diameter of the interior of cylindrical shape 42 and flange 40 at positioning regions 44 and 46 is accommodated by the interior diameter of cylindrical shape 42 and flange 40 being larger than the diameter of the shaft 24 intended for the bearing 10. Where the positioning region 44 is of the smooth cylinder configuration, the bore 14 of the accepting machine part 50 should be formed to concentrate the engaging force on the positioning region 44 in a limited band 52 around the circumference of the positioning region 44, while leaving a portion 54 of the positioning region 44 unconstrained in a radial direction, to eliminate the stresses of positioning region 44 being transferred to the bearing region 56. Bearing region 56 is functionally equivalent to cylinder 20 of the first embodiment. The embodiment disclosed in Fig. 4 is useful when the interior bore 14 is not symmetrical.

Claims: A bearing arrangement including a bearing sleeve (10) for insertion into a bore (14) to support a shaft (24) which comprises: a generally cylindrical body (12) having an inside diameter and an outside diameter, a bearing portion (20) for said shaft, the inside diameter of which is less than the inside diameter of said body and is substantially identical with the external diameter of said shaft, and the axial length of which is less than the length of said body, and frictionally engaging radially extending flanges (18) positioned about the exterior surface of said body and proximate both ends of said body, designed to engage said bore, the thickness of said bearing portion in the radial direction and the thickness of said flange being less than the difference between the internal radius of said bore and the radius of said shaft, said body being a unitary member, said flanges (18) having an axial length less than the distance from the end of said body to the relative end of said bearing portion, and the external diameter of said flanges is higher than the internal diameter of said bore, said flanges (18) being deflectable inwardly when inserted into said bore to thereby create a retaining force against said bore with the internal surface of said bearing portion being unaffected by said deflection, characterized in that both said flanges are made of a plurality of protusions (18) regularly distributed about the circumference of said cylindrical portion (30), and said protrusions (18) located at one end of said cylindrical portion have a different, complementary, angular orientation with respect to those protrusions located at the other end of said cylindrical portion.

Inventors: KOMPLIN, STEVEN ROBERT
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1987
Main classification: F16C27
IPC codes: F16C35, F16C27