Wheel bearing assembly

Abstract: A wheel bearing assembly is provided which can prevent lowering of the bearing life due to entry of muddy water into the bearing through the gap between fitting surfaces of a first inner member (11) and a second inner member (21). These members are rotatably supported by mounting rolling elements between double-row raceways formed on the inner peripheral surface of the outer member and raceways formed on the outer peripheral surfaces of the first (11) and second (21) inner members. A stem (23) formed on the second (21) inner member is inserted into a hole formed in the first inner member and the tip of the stem (23) is caulked to hold the first and second inner members in a coupled state. An annular groove is formed in the outer periphery of the stem. A seal ring is mounted in the annular groove.

Description: BACKGROUND OF THE INVENTION This invention relates to a wheel bearing assembly for supporting a vehicle wheel, and particularly to an arrangement for sealing the fitting surfaces of first and second inner members. As a wheel bearing assembly for a driving wheel, one shown in Fig. 9 is known. It comprises an outer member 1, a first inner member 11 and a second inner member 21, and double-row rolling elements 31 for supporting the outer member 1 and the first and second inner members 11 and 21 so as to be rotatable relative to each other. The outer member 1 has on its outer periphery a flange 2 for mounting to a vehicle body and on its inner periphery double-row raceways 3a, 3b. The first inner member 11 is formed on its outer periphery with a wheel-mounting flange 12 for supporting a driving wheel and a raceway 13 opposing one of the double-row raceways 3a, 3b. Also, the first inner member 11 is formed with a stem-inserting hole 14 extending therethrough. The hole 14 comprises a fitting hole portion 14a and a spline hole portion 14b. The second inner member 21 comprises an outer joint member of a constant-velocity joint provided with a stem 23 at a closed end of its mouth portion 22. On the outer periphery of the second inner member 21, a raceway 27 is formed so as to oppose the other of the double-row raceways 3a, 3b. Also, the second inner member 21 has the stem 23 which is formed with a fitting shaft portion 23a fitted in the fitting hole portion 14a, and a spline shaft portion 23b fitted in the spline hole portion 14b. The stem 23 of the second inner member 21 is inserted in the stem-inserting hole 14 of the first inner member 11, and by caulking the tip of the stem 23, the first and second inner members 11 and 21 are coupled together. Numeral 26 shows the caulked portion. The double-row rolling elements 31 are mounted between the double-row raceways 3a, 3b and the raceways 13, 27 of the first and second inner members 11 and 21. By caulking the tip of the stem 23 with a pre-load applied between the double-row rolling elements 31 and the raceways 3a, 3b, 13, 27, the wheel bearing assembly is assembled. Seal members 41 are mounted at both ends of the outer member 1 on its inner periphery. The seal members 41 provides seal between the outer member 1 and the first and second inner members 11 and 21 to prevent muddy water and foreign matter from invading into the bearing. Automobiles, particularly RVs (recreational vehicles), provided with conventional wheel bearing assembly sometimes travel on snow-covered road, mountain roads and bad roads. In such a case, although seal is provided between the opposed portions of the outer member 1 and the first and'second inner members 11 and 21 by the seal members 41, it is necessary to take measures to prevent entry of muddy water or dirt into the bearing through fitting surfaces of the first inner member 11 and the second inner member 21. A wheel bearing assembly according to the preamble of claim 1 is known from FR-A-2 795 021. The object of this invention is to provide a bearing assembly which is superior in sealing properties and prevents entry of muddy water, thereby increasing the bearing life. SUMMARY OF THE INVENTION According to this invention, there is provided a wheel bearing assembly according to claim 1. By providing the sealing means for sealing between the fitting surfaces of the first and second inner members, it is possible to prevent entry of muddy water into the bearing through the gap between the fitting surfaces. Thus, traveling on a bad road having much muddy water in an RV will not lower the bearing life. The sealing means may comprise an annular groove formed in at least one of fitting surfaces between the first inner member and the second inner member, and a seal ring mounted in the annular groove so as to be in resilient contact with the other of the fitting surfaces, or may comprise a sealing member mounted on one of the opposed end faces of the first and second inner members and having a plurality of seal lips in resilient contact with the other end face. With the seal using a seal member, since it is possible to seal at the contact portions between the plurality of seal lips and the end face, an extremely high degree of sealing is assured. Also, the seal means may comprise a seal cap mounted on one end of the second inner member protruding outwardly beyond the outer end face of the first inner member, the seal cap having a seal lip in resilient contact with the outer end face of the first inner member to cover an opening of a hole formed in the first inner member. With this arrangement, since the seal cap can be mounted after the wheel bearing assembly has been assembled, assembling work is easy. Further, a sealing agent may be applied to fitting surfaces between the first and second inner members. With the seal using a sealing agent, since it is possible to fill the gap at the fitting portion, high degree of sealing is achieved. In the wheel bearing assembly according to this invention, the second inner member may be an outer joint member of a constant-velocity joint having a stem formed with a fitting shaft portion pressed into a fitting hole portion of a stem-inserting hole formed in the first inner member and a spline shaft portion inserted into a spline hole portion of the stem-inserting hole. If the outer joint member is the second inner member, since it is integrated with a constant-velocity joint, it is possible to reduce the weight and axial length of the wheel bearing assembly. In the wheel bearing assembly according to this invention, the second inner member may be an inner ring pressed on a small-diameter bearing ring fitting surface formed on the outer periphery of the first inner member at one end thereof. Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical sectional front view of a wheel bearing assembly of a first embodiment of this invention; Fig. 2 is an enlarged sectional view showing a portion of the same; Fig. 3 is a sectional view showing the sealing means of a second embodiment; Figs. 4A to 4C are sectional views of the sealing means of a third embodiment; Figs. 5A to 5C are sectional views of the sealing means of a fourth embodiment; Fig. 6 is a vertical sectional front view showing the wheel bearing assembly of a fifth embodiment; Fig. 7 is a sectional view showing the sealing means of a sixth embodiment; Fig. 8 is a sectional view showing the sealing means of a seventh embodiment; and Fig. 9 is a vertical sectional front view showing a conventional wheel bearing assembly. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinbelow, the embodiments of this invention will be described with reference to Figs. 1 through 8. Fig. 1 shows the first embodiment of the wheel bearing assembly according to this invention. It comprises an outer member 1, a first inner member 11, a second inner member 21 and double-row rolling elements 31. The outer member 1 has on its outer periphery a flange 2 to be mounted to a vehicle body. On the inner periphery thereof, double-row raceways 3a and 3b are formed. The first inner member 11 comprises a hub ring. On its outer peripheral surface, a wheel-mounting flange 12 and a raceway 13 opposing the one raceway 3a of the double-row raceways 3a and 3b on the outer member 1 are formed. Also, the first inner member 11 has an axial stem-inserting hole 14 extending therethrough from its inner side end to its outer side end. The stem-inserting hole 14 consists of a fitting hole portion 14a and a spline hole portion 14b. The inner side refers to the side located inwardly in the width direction of a vehicle body with the wheel bearing assembly mounted on the vehicle body, and is on the right side of each figure. Conversely, the outer side refers to the side located outwardly in the width direction and is on the left side of each figure. The second inner member 21 comprises an outer joint member of a constant-velocity joint provided with a stem 23 on a closed end of its mouth portion 22. Curved track grooves 25 are formed in a spherical inner surface 24 formed on the mouth portion 22. The stem 23 is provided with a spline shaft portion 23b and a fitting shaft portion 23a which is pressed into the fitting hole portion 14a formed in the first inner member 11. On the other hand, the spline shaft portion 23b is fitted in the spline hole portion 14b. The first inner member 11 and the second inner member 21 are held in a coupled state by caulking the tip of the stem 23 at a portion 26. A raceway 27 is provided on the outer periphery of the closed end portion of the mouth portion 22 of the second inner member 21 so as to oppose the other raceway 3b of the outer member 1. The double-row rolling elements 31 are mounted between the raceways 3a, 3b of the outer member 1 and the raceways 13 and 27 formed on the first and second inner members 11 and 21. By caulking the tip of the stem 23 with a pre-load imparted between the rolling elements 31 and the raceways 3a, 3b, 13 and 27, the wheel bearing assembly is assembled. Seal members 41 are mounted at both ends of the outer member 1 on its inner periphery. The seal members 41 provides seal between the opposed portions of the outer member 1 and the first and second inner members 11 and 21 to prevent entry of muddy water and foreign matter into the bearing. Because the first inner member 11 and the second inner member 21 are connected together by fitting the stem 23 provided on the second inner member 21 into the stem-inserting hole 14 formed in the first inner member 11, reliability of seal between the fitting surfaces is not high, so that muddy water may enter through the gap between the fitting surfaces and lower the bearing life. In order to avoid such trouble, sealing means for sealing between the fitting surfaces is provided between the first inner member 11 and the second inner member 21. As the sealing means, as shown in Fig. 2, an annular groove 51 is formed in the outer peripheral surface of the fitting shaft portion 23b of the stem 23, and a seal ring 52 mounted in the annular groove 51 is resiliently brought into contact with the inner peripheral surface of the fitting hole portion 14a formed in the first inner member 11. The seal ring 52 is preferably formed of a material that is less likely to deteriorate and is superior in durability so that a seal between the fitting surfaces of the first inner member 11 and the second inner member 21 can be maintained for a long time. As such materials, nitrile rubber, fluororubber, acrylic rubber, silicone rubber, chloroprene rubber, etc. may be used. As described above, by mounting the seal ring 52 in the annular groove 51 formed in the outer peripheral surface of the fitting shaft portion 23a to seal between the fitting surfaces of the first and second inner members 11 and 21, entry of muddy water into the bearing through the gap between the fitting surfaces can be prevented to avoid lowering of the bearing life. In the embodiment shown in Fig. 1, the seal ring 52 is mounted on the fitting shaft portion 23a of the stem 23 of the second inner member 21. But it may be mounted in an annular groove formed in the inner peripheral surface of the fitting hole portion 14a of the first inner member 11. The first inner member 11 is formed by forging carbon steel whose carbon content is preferably 0.45-1.10 wt%, more preferably 0.45-0.75 wt%. After forming, its surface is subjected to hardening treatment such as induction hardening, carburizing hardening or laser hardening to increase hardness. Numeral 15 shows the hardened layer. Hardening is carried out over the range from the surface of the root portion of the wheel-mounting flange 12 to the inner-side end of the first inner member 11. The surface hardness should be about Hv 500-900. Also, the hardened depth of the hardened layer 15 is preferably about 0.7-4 mm at the raceway 13, and about 0.3-3 mm at other portions. By providing the hardened layer 15 deep in the hardened depth at the position of the raceway 13, rolling fatigue life of the raceway 13 can be assured. The rolling fatigue life is assured by hardening the first inner member 11 made of carbon steel having the carbon content of 0.45 wt% or over. If it is made of carbon steel having the carbon content of less than 0.45 wt%, required hardness could not be obtained even if hardening treatment is carried out. Also, by hardening the surface at the root portion of the wheel-mounting flange 12, the wheel-mounting flange can be prevented from deforming or running out due to moment loads from the wheel mounted on the wheel-mounting flange. Also, the frictional resistance at the contact positions of the seal members 41 decreases, so that the expected sealing effects reveal and the wear resistance improves. The second inner member 21 is made of carbon steel having the carbon content of preferably 0.45-1.10 wt%, more preferably 0.45-0.75 wt%, and is hardened after forming by forging. It is hardened for the range from the shoulder portion of the mouth portion 22 to the tip of the stem 23 and the entire inner surface of the track grooves 25 formed in the mouth portion 22. Its surface hardness is about Hv 500-900. Numeral 28 shows the hardened layer. The tip of the stem 23 is subjected to caulking. If the surface hardness of the tip is over Hv 300, when the tip is caulked, cracks may develop in the caulked portion 26 or the coupling force to the first and second inner members 11, 21 may be insufficient because of poor caulking. Thus, the tip of the stem 23 is left unhardened. Specifically, by keeping the surface hardness within the range of Hv 200-300, ductility is ensured to permit caulking. The hardened depth of the hardened layer 28 is about 0.7-4 mm at the positions of the track grooves 25 and the raceway 27, and shallower at other portions, e.g. about 0.3-3 mm. By providing the deeply hardened layer 28 at the positions of the track grooves 25 and the raceway 27, the rolling fatigue life of the surface of the track grooves 25 and the raceway 27 can be assured. By hardening the surface of the stem 23 by hardening, it is possible to prevent torsional deformation of the stem 23 during torque transmission and to improve the creep resistance and the fretting resistance of the fitting shaft portion 23a and the spline shaft portion 23b. With the wheel bearing assembly of the first embodiment shown in Fig. 1, by caulking the tip of the stem 23, the first inner member 11 and the second inner member 21 are held in a coupled state. But the coupling means is not limited thereto. For example, by providing a threaded portion at the tip of the stem 23 and tightening a nut on the threaded portion, the first inner member and the second inner member may be coupled. Figs. 3 through 5 are enlarged views of the sealing means in the second to fourth embodiments of the wheel bearing assembly according to this invention. Since the second to fourth embodiments differ from the wheel bearing assembly shown in Fig. 1 only in the sealing means for sealing between the fitting surfaces of the first inner member 11 and the second inner member 21, only the sealing means will be described below. With the sealing means of the wheel bearing assembly in the second embodiment shown in Fig. 3, a seal-mounting recess 53 is formed in the inner periphery of the first inner member 11 at its inner-side end, a seal member 54 is mounted in the seal-mounting recess 53 e.g. with an adhesive, and a plurality of seal lips 54a formed on the seal member 54 are resiliently brought into contact with an arcuate surface 23c formed at the root of the stem 23. Also, as means other than bonding, the seal member 54 may be fitted in the seal-mounting recess 53 with a slight interference provided between the inner periphery of the seal-mounting recess 53 and the seal member 54. As the seal member 54, one made of nitrile rubber, fluororubber, acrylic rubber, silicone rubber, chloroprene rubber, etc. may be used. In the figure, two seal lips 54a are provided on the seal member 54, but one or two radially extending seal lips may be added. With the sealing means of the wheel bearing assembly in the third embodiment shown in Figs. 4A to 4C, an annular protrusion 55 is provided on the outer periphery of the caulked portion 26 formed at the tip of the stem 23, and a seal cap 56 is mounted on the protrusion 55. The seal cap 56 comprises a resilient seal member 56b such as rubber fixed by baking or bonding to the surface of a cap body 56a in the form of a metal plate, an inwardly extending engaging piece 56c formed at the open end of the cap body 56a, and a seal lip 56d provided on the open end of the seal member 56b. As shown in Fig. 4B, the seal lip 56d may be one, or as shown in Fig. 4C, two, or may be three though not shown. The seal cap 56 is fitted on the caulked portion 26 and is held in a mounted state by the engagement of the engaging piece 56c with the protrusion 55. Also, it covers the entire opening of the outer-side end of the stem-inserting hole 14 formed in the first inner member 11 by resilient contact of the seal lip 56d with the outer end face of the first inner member 11 to seal the fitting surfaces between the first inner member 11 and the stem 23. With the sealing means of the wheel bearing assembly in the fourth embodiment shown in Figs. 5A to 5C, a sealing agent 57 is applied to the outer periphery of the stem 23 at its tip and the outer periphery of the fitting shaft portion 23a to seal between the fitting surfaces between the stem 23 and the first inner member 11. Fig. 5B is an enlarged view of the tip of the stem 23, and Fig. 5C is an enlarged view of the fitting shaft portion 23a of the stem 23. In these figures, the thickness of the sealing agent 57 is shown rather exaggeratedly. As the sealing agent 57, a resin adhesive is preferable, and an anaerobic room temperature curing type adhesive is more preferable. If a resin adhesive is employed as the sealing agent 57, since it completely fills fine recesses produced due to surface roughness of the stem 3 and the inner peripheral surface of the stem-inserting hole 14, extremely high sealing properties can be achieved. Also, since an anaerobic room temperature curing type adhesive is slow in the curing speed even in contact with air, but cures quickly at room temperature even without contacting air, it is possible to reduce the fitting interference between the fitting hole portion 14a of the first inner member 11 and the fitting shaft portion 23a of the stem 23. Thus the assembly is easier to assemble. As the anaerobic room temperature curing type adhesive, Loctite lifting compound 680 and Loctite 603 made by Henkel Japan Ltd. may be used. The sealing agent 57 may be applied only to the outer periphery of the tip of the stem 23 of Fig. 5B, or it may be applied only to the outer periphery of the fitting shaft portion 23a of Fig. 5C. Further, although not shown, it may be applied to the stem-inserting hole 14, or it may be applied to the outer periphery of the spline shaft portion 23b. With any of the sealing means shown in Figs. 3-5, seal is assured between the fitting surfaces of the first inner member 11 and the stem 23 formed on the second inner member 21. Thus, entry of e.g. muddy water into the bearing through the gap between the fitting surfaces is prevented. Fig. 6 shows the fifth embodiment of the wheel bearing assembly according to this invention. It differs from the wheel bearing assembly shown in Fig. 1 in only the second inner members 21'. It comprises an inner ring 30 having a raceway 29 on its outer periphery. The inner ring 30, which is the second inner member 21', is pressed onto a small-diameter bearing ring fitting surface 16 formed on the outer periphery of the inner end of the first inner member 11', and integrally coupled to the first inner member 11' by caulking the inner end of the first inner member 11'. With the wheel bearing assembly having such a structure, an annular groove 58 is formed in the bearing ring fitting surface 16, and a seal ring 59 mounted in the annular groove 58 is resiliently brought into contact with the inner peripheral surface of the second inner member 21' to seal between the fitting surfaces of the first inner member 11' and the inner ring 30, which is the second inner member 21'. As the material for the seal ring 59, one for the seal ring 52 shown in Fig. 2 may be used. A seal may be provided between the fitting surfaces of the first inner member 11' and the second inner member 21' by forming an annular groove in the inner periphery of the second inner member 21' and mounting a seal ring in the annular groove. The material and heat treatment for the first inner member 11' of this wheel bearing assembly are substantially the same as those of the first inner member 11 shown in Fig. 1. But in order to caulk the inner end, heat treatment is carried out within the range of from the surface at the root of the wheel-mounting flange 2 to the bearing ring fitting surface of the first inner member 11', and its inner end to be caulked is left unhardened. Figs. 7 and 8 are enlarged views of sealing means of the sixth and seventh embodiments of the wheel bearing assembly according to this invention. These embodiments differ from the wheel bearing assembly shown in Fig. 6 only in the sealing means between the fitting surfaces. Thus, only the sealing means will be described. With the sealing means of the wheel bearing assembly in the sixth embodiment shown in Fig. 7, a seal-mounting recess 60 is formed in the inner peripheral portion of the outer end of the second inner member 21', a seal member 61 is fixed in the seal-mounting recess 60 e.g. with an adhesive, and a plurality of seal lips 61a provided on the seal member 61 are brought into contact with the outer periphery of the first inner member 11' to seal between the fitting surfaces of the first and second inner members 11' and 21'. Also, as means other than bonding, the seal member 61 may be fitted in the seal-mounting recess 60 with a slight interference between the inner wall of the seal-mounting recess 60 and the seal member 61. For the material of the seal member 61, one shown for the seal member 54 of Fig. 3 may be used. With the sealing means of the wheel bearing assembly in the seventh embodiment shown in Fig. 8, a sealing agent 62 is applied between the fitting surfaces of the first inner member 11' and the second inner member 21' to seal therebetween. The thickness of the sealing agent is exaggerated in the figure. As the sealing agent 62, as with the sealing agent 57 shown in Figs. 5A to 5C, a resin adhesive is preferable, and an anaerobic room temperature curing type adhesive is more preferable. Any of the sealing means shown in Figs. 6-8 can seal between the fitting surfaces of the first inner member 11' and the second inner member 21'. Thus entry of e.g. muddy water into the bearing through the space between the fitting surfaces is prevented. In the embodiment shown in Fig. 6, a wheel bearing assembly for a driving wheel is shown which has the stem-inserting hole 14 in the form of a spline hole into which a stem of a constant-velocity joint (not shown) is inserted. But the wheel bearing assembly is not limited thereto, and may be a wheel bearing assembly for a non-driving wheel in which the first inner member 11' is formed with a circular hole or has no hole but is solid. Also in Fig. 6, a wheel bearing assembly in which the inner end of the first inner member 11' is caulked is shown. But it may be a wheel bearing assembly in which the caulked portion 17 is omitted with the inner ring 30 simply pressed onto the bearing ring fitting surface on the first inner member. With a wheel bearing assembly for a non-driving wheel, instead of the caulked portion 17, the first inner member 11' and the inner ring 30, which is the second inner member 21', may be held in a coupled state by providing a threaded shaft on the inner end of the first inner member 11' and tightening a nut on the threaded shaft. Also, in any of the embodiments, the rolling elements in the form of balls are shown but not limited to balls. They may be tapered rollers. According to this invention, by providing the sealing means for sealing between the fitting surfaces of the first inner member and the second inner member, it is possible to prevent entry of muddy water into the bearing through the gap between the fitting surfaces, thus suppressing lowering of the bearing life.

Claims: A wheel bearing assembly comprising an outer member (1) having a flange (2) for mounting to a vehicle body on its outer periphery and formed with two raceways (3a, 3b) on its inner periphery, a first inner member (11) having on its outer periphery a wheel-mounting flange (12) and a raceway (13) opposing one (3a) of said two raceways (3a, 3b) on said outer member (1), a second inner member (21) having on its outer periphery a raceway (27) opposing the other (3b) of said two raceways (3a, 3b) and coupled to said first inner member (11), double-row rolling elements (31) mounted between said outer member (1) and said first and second inner members (11, 21), and a pair of seal members (41) for sealing between both ends of the inner periphery of said outer member (1) and the outer peripheries of said first and second inner members (11, 21), characterized in that a sealing means (52) is provided for sealing between the fitting surfaces of said first inner member (11) and said second inner member (21). A wheel bearing assembly as claimed in claim 1 wherein said second inner member (21) comprises an outer joint member of a constant-velocity joint, said outer joint member having a stem (23) formed with a fitting shaft portion (23a) and a spline shaft portion (23b), said first inner member (11) being formed with a stem-inserting hole (14) which has a fitting hole portion (14a) and a spline hole portion (14b), said fitting shaft portion (23a) being pressed into said fitting hole portion (14a) of a stem-inserting hole (14) formed in said first inner member (11), and said spline shaft portion (23b) being fitted in said spline hole portion (14b) of said stem-inserting hole (14). A wheel bearing assembly as claimed in claim 1 wherein said second inner member (21) comprises an inner ring (30) pressed on a small-diameter bearing ring fitting surface (16) formed on the outer periphery of said first inner member (11) at one end thereof. A wheel bearing assembly as claimed in any of claims 1-3 wherein said sealing means comprises an annular groove (51) formed in at least one of fitting surfaces between said first inner member (11) and said second inner member (21), and a seal ring (52) mounted in said annular groove (51) so as to be in resilient contact with the other of the fitting surfaces. A wheel bearing assembly as claimed in claim 1 or 2 wherein said sealing means comprises a sealing member (54) mounted on the inner periphery of the inner end of said first inner member (11) and having a plurality of seal lips (54a) in resilient contact with the surface of said second inner member (21). A wheel bearing assembly as claimed in claim 1 or 3 wherein said sealing means comprises a sealing member (61) mounted on the inner peripheral portion of the outer end of said second inner member (21') and having a plurality of seal lips (61a) in resilient contact with the surface of said first inner member (11'). A wheel bearing assembly as claimed in claim 1 or 2 wherein said seal means comprises a seal cap (56) mounted on one end of said second inner member (21) protruding outwardly beyond the outer end face of said first inner member (11), said seal cap (56) having a seal lip (56d) in resilient contact with the outer end face of said first inner member (11) to cover an opening of a hole (44) formed in said first inner member (11'). A wheel bearing assembly as claimed in any of claims 1-3 wherein said seal means comprises a sealing agent (57) applied to fitting surfaces between said first and second inner members (11, 21).

Inventors: TAJIMA EIJI, TAKAKI MASUO, TORII AKIRA, TAJIMA, EIJI, TAKAKI, MASUO, TORII, AKIRA
Applicants: NTN TOYO BEARING CO LTD, NTN CORPORATION
Application year: 2001
Main classification: B60B27
IPC codes: B60B35, B60K17, F16C33, F16D3, F16C19, B60B27, F16D1