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.
The plastic sleeve bearings have a diffenent 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 diffficult 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 of controlled deformation. This then minimizes the requirement to perform post assembly operation 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 is 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 effecting the interior bearing surface.
U.S. Pat. No. 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. Pat. Nos. 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.
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.