A ball bearing for an automobile wheel hub

Abstract: In a ball bearing for an automobile wheel hub comprising a double set of balls, the inner race is composed of two half-races to allow mounting of one of the two sets of balls. A first set of balls (2) is located between an outer race (3) and a facing portion of the hub (4). A second set of balls (5) is located between the outer race (3) and an inner half-race (6) fixed onto the hub (4). The inner half-race (6) is secured by an ring-like end portion (9) of the hub (4) folded by cold forming. A substantially flat washer (10) is interposed between said inner half-race (6) and the ring-like end portion (9).

Description: Field of the invention The present invention refers to a ball bearing for an automobile wheel hub, of the type comprising a double set of balls in angular contact, the inner race being composed of two half-races to allow mounting of one of the two sets of balls. Description of prior art There are known various methods of locking together the two inner races of a ball bearing or, generally, two metal rings slipped or screwed one on the other, wherein one abuts the other. Among these methods, the most common is that of using a bolt inserted axially in one of the two races, the head of the bolt urging axially against a side face of the other race. This method, although being very simple, implies a number of operations which render it expensive. Moreover, it only allows a slight reduction of the inner diameter of the inner race and, consequently, of the overall weight and dimensions of the bearing. The reason of this is that it is impossible to narrow the wall in which the tread for the bolt is provided over a certain extent, otherwise it would easily collapse. A second method, disclosed in DE-A-41 34 434, consists in cold forming a first inner half race so as to create a front wall for abutting the outer face of the second outer half race. This method, besides allowing to reduce the number of operations required and therefore production costs, it does not allow to reduce the overall diameter of the inner race. In fact, the cold forming process generates strain within the second half-race which are likely to deform the race on which the balls roll. It is therefore necessary that such second half-race has a relatively high thickness in order to prevent said deformation from occurring. As a consequence, the overall diameter remains of considerable dimensions with no chances of reducing it, also because the machine carrying out cold forming requires an axial bore in the first half race which cannot be reduced in its diameter below a certain level. In an embodiment illustrated in DE-A-19 15 932, forming concerns an inner half race for a wheel hub bearing, in which the other half-race inserted thereon is kept in position by a threaded flange. Forming of the inner half race is in this case intended for guaranteeing positioning of the second half-race, which is attained by providing said threaded flange. Forming in this instance concerns only a minimum portion of the inner half race and does not generate strains therein which could cause deformation of the ball races. However, the number of working operations remains high and in addition it is a particular application making use of a flange that has no general use. EP-B-0 475 792 discloses the application of a tapered ring for axial support axially interposed between one of the half-races and a collar obtained by folding the end portion of the hub. Said tapered ring is heated before mounting to the bearing. As it cools, the ring contracts radially. Radial contraction of the tapered section transmits an axial load to the bearing. US-A-4 893 960, which represents the closest prior art according to the preamble of claim 1, discloses the application of a intermediate ring for transmitting torque axially interposed between one of the half-races and a collar obtained by folding the end portion of the hub. Said intermediate ring is made of a material not suitable to collapse so that the thrusts due to the folding of the hub are transmitted directly to the bearing. Summary of the invention It is an object of the present invention to provide a wheel hub ball bearing which on one hand allows to reduce the number of operations and assembly costs and on the other hand provides for considerable reduction of the overall diameter of the bearing without jeopardizing its reliability. The above and further objects which will be more apparent hereinafter are attained according to the present invention by the provision of a ball bearing for an automobile wheel hub, of the type comprising a double set of balls in angular contact, the inner race being composed of two half-races to allow mounting of one of the two sets of balls, of which the first set of balls is located between an outer race and a facing portion of the hub, and the second set of balls is located between the outer race and an inner half-race fixed onto said hub, said inner half-race being secured by an ring-like end portion of said hub folded by cold forming, characterized in that a substantially flat washer is interposed between said inner half-race and said ring-like end portion; the washer being of a less harder material than that of said inner half-race to prevent the latter from thrusts and deformations due to the cold forming of said ring-like end portion. Brief description of the drawings For a better understanding of the present invention, reference is made to the following detailed description of various exemplary embodiments considered in combination with the accompanying drawings in which: FIG. 1 is a partial axial sectional view of a bearing arranged in accordance with the present invention; FIGS. 2 to 4 show alternative embodiments of a washer that this invention proposes to use. Description of preferred embodiments With reference to FIG. 1, numeral 1 designates overall a ball bearing for an automobile wheel hub, of the type with a double set of balls. The race of the first set of balls 2 is formed in the outer ring 3 and the portion of hub 4 being part of the inner race of the bearing. The outer race 3 also contains the race for the second set of balls 5. These balls roll on a separate inner ring 6 which is interference fitted on the protruding portion 7 of hub 4. Protruding portion 7 provides an axial bore 8. Due to this arrangement, the bearing surely has to resist high axial forces, whereby the separate ring 6 must be securely fixed to protruding portion 7 of hub 4. Fixing is attained by cold forming of the end ring 9 of protruding portion 7. It is achieved by inserting a tool in axial bore 8. In order to avoid cracks in ring 9 while performing cold forming, and especially to prevent race 6 from undergoing deformations which could jeopardize correct operation of the bearing and shorten its lifetime, according to the present invention a substantially flat washer 10 is fitted with slight interference on protruding portion 7 of hub 4 and against the outer face of said race 6. Washer 10, which is preferably made of a less harder material than that of race 6, is so sandwiched between race 6 and the folded portion of end ring 9 after cold forming. In this way, most of axial and radial thrusts due to cold forming are absorbed by the washer without prejudice to race 6 on which the balls roll. Race 6 can therefore be suitably sized so as to reduce overall diameter of the bearing with appreciable advantages. This is made possible because the thickness of race 6 is considerably less than what could be achieved without employing washer 10. Preferably, the radial width "w" will be greater that its axial thickness "t". More preferably, the W/T ratio will be of about 2:1. The same results will obviously be attained also where the race for the first set of balls consists of a separate ring not being obtained integral from hub 4. Still according to the present invention, an axial or radial toothing can be provided on washer 10 in order to act as an impulse ring for a revolving speed gauging device. For example, as illustrated in FIG. 2, an axial toothing 11 is provided on the peripheral part of the washer 10. In the embodiment of FIG. 3, a radial toothing 11 is provided. In a still different embodiment, schematically shown in FIG. 4, a magnetized ring 12 is applied to the peripheral part of washer 10 through a mounting metal insert 13.

Claims: A ball bearing for an automobile wheel hub, of the type comprising a double set of balls in angular contact, the inner race being composed of two half-races to allow mounting of one of the two sets of balls, of which the first set of balls (2) is located between an outer race (3) and a facing portion of the hub (4), and the second set of balls (5) is located between the outer race (3) and an inner half-race (6) fixed onto said hub (4), said inner half-race (6) being secured by an ring-like end portion (9) of said hub (4) folded by cold forming, characterized in that a substantially flat washer (10) is interposed between said inner half-race (6) and said ring-like end portion (9); the washer (10) being of a less harder material than that of said inner half-race (6) to prevent the latter from thrusts and deformations due to the cold forming of said ring-like end portion (9). A ball bearing for an automobile wheel hub as claimed in claim 1, characterized in that the washer (10) is so shaped as to act as an impulse ring for a rotating speed sensing device. A ball bearing for an automobile wheel hub as claimed in claim 2, characterized in that said washer has an axially or radially directed toothed peripheral portion. A ball bearing for an automobile wheel hub as claimed in claim 2, characterized in that a magnetized ring (12) is applied to the peripheral part of said washer (10) through a mounting metal insert (13). A ball bearing for an automobile wheel hub as claimed in claim 1, characterized in that the radial width (w) of said washer (10) is greater that its axial thickness (t). A ball bearing for an automobile wheel hub as claimed in claim 5, characterized in that w/t ratio is of about 2:1.

Inventors: BERTETTI PAOLO, PICCA MAURO, BERTETTI, PAOLO, PICCA, MAURO
Applicants: SKF IND SPA, SKF INDUSTRIE S.P.A.
Application year: 1996
Main classification: B60B27
IPC codes: F16C35, B60B27, F16C19, F16C43