Mounting for steering column

Abstract: A steering column assembly includes two bearing seats (46,48) for angular contact bearings (42,44), each bearing seat being tapered so that the diameter of a bore (52) of a housing (40) for the bearings tapers radially inwardly and a third bearing seat (54) associated with a column shaft (38) is also tapered to seat one of two inner rings (60) of the respective bearings, which are pre-loaded and axially aligned with the bearing seats. This construction eliminates the need for the press fit while still meeting the application requirements. Other designs reduce the rotational effort and torque variation of the system and facilitate assembly. The mating tapers give the bearings freedom to self-align and thereby avoid common "clicking" noise.

Description: This invention relates generally to the mounting of a rotatable shaft within a housing and, more particularly, to a mounting suitable for a steering column shaft. The features of the preamble of claim 1 belong to the common knowledge of the skilled person in the technical field. Typically, automotive upper tilt steering columns require a spring preload to eliminate axial free play and a tolerance ring to eliminate radial free play. Currently, a steel coil spring or wave type spring is used in combination with a steel or plastics tolerance ring. This mounting arrangement requires a great amount of axial space and introduces vibrations in torque-to-rotate. Additionally, such mounting arrangements allow transmission of noise and vibration to or from the shaft, through the bearing. Angular contact ball bearings used in such steering columns must be fixed axially and have no radial free play. Currently, the outer rings of the bearings are pressfit into a housing against a stepped shoulder. The interference fit eliminates the outer ring-housing clearance, and the step gives a positive stop for the bearing to seat against. However, the large range of interference causes raceway distortion due to the nonuniform wall thickness of the housing, and, as a result, does not allow the outer raceway to self-align. More specifically, many steering column housings of this type are cast, having wall sections around the bearings that are relatively thin with strengthening gussets in a few locations. When a round outer ring is pressed into a round housing bore with varying wall thickness as described above, the resulting raceway is distorted. The distortion is proportional to the amount of interference. Typically, the bearing rings and housing bores are formed or machined without tight tolerances. Since such steering column housings are formed of magnesium or aluminium, with a higher coefficient of thermal expansion than the steel outer ring, additional interference is designed into the system to maintain an interference fit throughout a temperature range. The large stack-up can result in an interference of .007 inch (0.178mm) or more. This large amount of interference distorts the installed outer raceway due to the varying housing wall thickness which increases and induces variation in the rotational effort of the system. In addition, a "click" may occur due to misaligned raceways. According to the present invention, there is provided a steering column assembly comprising a housing having a bore with first and second bearing seats axially spaced along an axis, first and second angular contact bearings having first and second outer rings seated on the first and second bearing seats, respectively, and having first and second inner rings respectively, a shaft extending through the bore of the housing and biasing means for biasing at least one of said first and second angular contact bearings such that the angular contact bearings are preloaded; characterised in that each bearing seat is tapered such that the diameter of the bore tapers radially inwardly in the axially inward direction, the shaft has a third tapered bearing seat located such that one of the first and second inner rings is seated on the third tapered bearing seat and the biasing means causes the angular contact bearings to be axially aligned with the three tapered bearing seats. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example to the accompanying drawings, in which:- Fig. 1 is a sectional view of a shaft mounted within a housing illustrating the prior art; Fig. 2 is an end view of a steering column housing illustrating the prior art; Fig. 3 is a graphical representation indicating the roundness of an outer ring of a bearing installed in the steering column housing of Fig. 2; Fig. 4 is a sectional view of a shaft mounted within a housing, illustrating a first embodiment of the present invention; and Figs. 5 to 10 are sectional views of a shaft mounted within a housing, illustrating alternative embodiments of the present invention. Figure 1 illustrates a shaft 10 mounted within a housing 12 by angular contact bearings 14 and 16. A steel tolerance ring 18 is split or segmented so that it can close radially inwardly against the shaft 10 and under a tapered portion of a bearing inner ring 20 of the angular contact bearing 14 to reduce radial free play between the shaft 10 and bearing inner ring 20. A steel coil spring 22 provides an axial preload on the angular contact bearings 14 and 16 by pressing axially against the steel tolerance ring 18. Figure 2 illustrates one particular prior art steering column housing 24 having a central bore 26 and openings 28, 30, 32 and 34 to accommodate various components. The housing 24 is cast of aluminium or magnesium with strengthening ribs and mounting supports of various configurations. Crush bushings (not illustrated) may be formed in the bore to facilitate an interference fit with a bearing outer ring with a minimum of distortion of the outer ring. Figure 3 is a graphical representation of the distortion of an outer ring of a bearing when pressed into the housing 24. The elongated portions of the graph at approximately 30 degrees and 180 degrees correspond to thin sections of the wall of the housing 24. A first embodiment of the present invention is illustrated in Figure 4, in which a shaft 38 is mounted within a housing 40 by angular first and second angular contact bearings 42 and 44. First and second bearing seats 46 and 48 of the housing 40 are axially spaced along an axis 50 and are tapered such that the diameter of a bore 52 tapers radially inwardly in the axially inward direction. The shaft 38 extends through the bore 52 of the housing 40 and has a third bearing seat 54 that is tapered radially inwardly in a direction toward the axial centre of the housing 40. The angular contact bearings 42 and 44 have first and second outer rings 56 and 58 seated on the first and second bearing seats 46 and 48, respectively, and a first inner ring 60 seated on the third bearing seat 54. A helical coil spring 62 abuts a snap ring 64 and applies an axially inward (with respect to the housing 40) force on a split tolerance ring 66. As a result of this force, the angular contact bearings 42 and 44 are axially aligned with the three tapered bearing seats 46, 48 and 54 and are preloaded. Preferably, the angular contact bearings 42 and 44 have inner and outer rings with tapered surfaces corresponding to the tapered bearing seats on which they are positioned, as illustrated in this first embodiment. Such configuration may be formed by coining or machining, for example. However, at least some of the benefits of the tapered bearing seat may be realised with inner or outer rings having rounded (not conically tapered) surfaces that engage the tapered bearing seats. Figure 5 illustrates a second embodiment of the present invention similar to that of Figure 4 but having a shaft 70 with a third bearing seat 72 formed of an elastomeric polymer, such as urethane, for example, and an alterative biasing means. A mounting ring 74, formed of an elastomeric polymer such as urethane, for example, is compressed axially between a snap ring 76 and inner ring 68, in place of the helical spring 62, to provide the desired force to align and preload the angular contact bearings 42 and 44. The third embodiment illustrated in Figure 6 is similar to the embodiment of Figure 5, including the resilient third bearing seat 72, but has resilient mounting ring 78 of a different configuration. Instead of being recessed within a shaft 80, the mounting ring 78 is positioned over a cylindrical portion of the shaft 80 that is in alignment with a fourth bearing seat 82. The mounting ring 78 is formed of an elastomeric polymer, such as urethane, for example, and includes a wedge shaped portion 84 for engaging a corresponding tapered portion of an inner ring 68. The embodiment illustrated in figure 7 is similar the embodiment of Figure 4, but includes a thin layer or film 84 and 86 of elastomeric polymer, such as urethane, for example, on the inner rings 60 and 68 and includes an alternative arrangement for the biasing spring. A helical spring 88 is not recessed within the shaft 90, as in the earlier embodiment, but is on a cylindrical portion of the shaft 90 in alignment with a fourth bearing seat 92. The helical spring 88 is compressed axially between a snap ring 94 and split wedge ring 96 to supply the desired axial force to align and preload the angular contact bearings 42 and 44. Figure 8 illustrates that the configuration of Figure 6 may be utilised with first and second angular contact bearings 98 and 100 with first and second outer rings 102 and 104, respectively, having a rounded portion engaging an intermediate diameter of the tapered bearing seats 46 and 48. As stated earlier, the use of such bearings may achieve at least part of the advantages that may be achieved with the preferred bearings having tapered portions engaging the tapered bearing seats. Figures 9 and 10 illustrate alternative embodiments in which the biasing means is positioned in the housing, exerting an axially outward force on at least one of the angular contact bearings, instead of on the shaft, exerting an axially inward force on one of the angular contact bearings. In Figure 9, a helical coil spring 106, mounted on a housing 108, exerts an axial force on a wedge ring 110 that engages outer ring 58. A snap ring 112, having a round cross section, provides a portion of a bearing seat for the angular contact bearing 44 and facilitates alignment of the inner ring 68. As in Figure 7, film 84 and 86 is provided on the inner rings 60 and 68. The embodiment of Figure 10 utilises resilient mounting rings 114 and 116 similar to the mounting ring 78 of the embodiment of Figures 6 and 8, but they are positioned on a housing 118 instead of on the shaft. The mounting rings 114 and 116 abut stop surfaces 120 and 122, respectively, of the housing 118 and provide axially outward force on both angular contact bearings 42 and 44. Wedge shaped portions 124 and 126 engage the outer rings 56 and 58 to centre and align the bearings, isolating them from the housing. These embodiments result in many advantages over the prior art. The large chamfer on the outer race that mates with a matching angular step in the housing bore eliminates the need for the press fit while still meeting the application requirements. These designs can reduce the rotational effort and torque variation of the system and facilitate assembly. The mating tapers give the bearing freedom to self-align and thereby avoid common "clicking" noise. Also, a secondary machining operation on the housing bore, end grinding of the outer ring, and a formed counterbore in the outer ring can, potentially, be eliminated.

Claims: A steering column assembly comprising a housing (40) having a bore (52) with first and second bearing seats (46,48) axially spaced along an axis (50), first and second angular contact bearings (42,44) having first and second outer rings (56,58) seated on the first and second bearing seats, respectively, and having first and second inner rings (60,68) respectively, a shaft (38) extending through the bore (52) of the housing and biasing means (62) for biasing at least one of said first and second angular contact bearings such that the angular contact bearings are preloaded; characterised in that each bearing seat (46,48) is tapered such that the diameter of the bore (52) tapers radially inwardly in the axially inward direction, the shaft (38) has a third tapered bearing seat (54) located such that one of the first and second inner rings (60,68) is seated on the third tapered bearing seat and the biasing means (62) causes the angular contact bearings (42,44) to be axially aligned with the three tapered bearing seats (46,48,54). A steering column assembly according to claim 1, wherein the biasing means (62) is mounted on a reduced diameter portion of the shaft (38). A steering column assembly according to claim 1 or 2, wherein said third bearing seat (54) is tapered radially inwardly in a direction toward the axial centre of the housing (40). A steering column assembly according to claim 1, 2 or 3, wherein the biasing means includes a helical spring (62) positioned over the shaft (38) and engaging a tolerance ring (66). A steering column assembly according to claim 1, 2 or 3, wherein the biasing means includes a mounting ring (74) of elastomeric polymer positioned over the shaft (70) and engaging said other of the first and second inner rings. A steering column assembly according to claim 1, 2 or 3, wherein the biasing means is a helical spring (106) mounted in the housing between the first and second bearing seats (46,48). A steering column assembly according to claim 1, 2 or 3, wherein the biasing means (74,78) is mounted on a reduced diameter portion of the shaft (70,80) and biases one of the inner rings (68) axially inwardly. A steering column assembly according to any one of the preceding claims, wherein the third tapered bearing seat is formed of an elastomeric polymer (72) positioned over the shaft. A steering column assembly according to any one of claims 1 to 7, further comprising a layer (84,86) of elastomeric polymer between at least one of the tapered bearing seats and the respective angular contact bearing (42,44). A steering column assembly according to any one of the preceding claims, further comprising a fourth tapered bearing seat (92), movably mounted on the shaft such that the biasing means biases the fourth tapered bearing seat axially inwardly. A steering column assembly according to any one of the preceding claims, wherein at least one of the inner bearing rings (60,68) has a tapered surface corresponding to the tapered bearing seat on which it is seated. A steering column assembly according to any one of the preceding claims, wherein at least one of the outer bearing rings (56,58) has a tapered surface corresponding to the tapered bearing seat (46,48) on which it is seated. A steering column assembly according to any one of claims 1 to 10, wherein at least one of the inner bearing rings has a rounded surface engaging an intermediate diameter of the tapered bearing seat on which it is seated. A steering column assembly according to any one of claims 1 to 10 or 13, wherein at least one of the outer bearing rings (102,104) has a rounded surface engaging an intermediate diameter of the tapered bearing seat on which it is seated. A steering column assembly according to claim 1, 2 or 3, wherein one of the first and second bearing seats (110) is movably mounted on the housing (108,118) and wherein the biasing means (106,116) biases said bearing seat axially outwardly against the outer ring of the angular contact bearing seated on said bearing seat. A steering column assembly according to any one of the preceding claims, wherein at least one of the first and second bearing seats (110) is made of an elastomeric polymer. A steering column assembly according to any one of the preceding claims, further comprising a snap ring (112) on a or the reduced diameter portion of the shaft preventing axially outward movement of said other of the first and second inner rings.

Inventors: BEAMAN MICHAEL D, BEAMAN, MICHAEL D.
Applicants: TORRINGTON CO, THE TORRINGTON COMPANY
Application year: 1998
Main classification: B62D1
IPC codes: B62D1, F16C25, F16C23, F16C35