STEERING COLUMN FOR A MOTOR VEHICLE

Abstract

An electromechanical power steering system for a motor vehicle includes a worm shaft which can be driven by an electric motor and which meshes with a worm wheel coupled to a steering shaft. The worm shaft is rotatably mounted in a bearing which has at least one bearing ring fitted in a retainer that can be displaced relative to the worm wheel. In order to specify an electromechanical power steering system having an improved retainer, which has higher dimensional stability and increased stiffness, according to the invention the retainer has a main body of plastic, which is injection-molded onto the bearing ring as an injection-molded part.

Claims

1.-11. (canceled)

12. An electromechanical power steering system for a motor vehicle, comprising: a steering shaft; an electric motor; a worm shaft configured to be driven by the electric motor; and a worm wheel coupled to the steering shaft and operatively meshed with the worm shaft; wherein the worm shaft is rotatably mounted in a bearing which has at least one bearing ring fitted in a retainer that is configured to displace relative to the worm wheel; and wherein the retainer has a main body of plastic, which is injection-molded onto the bearing ring as an injection-molded part.

13. The power steering system of claim 12 wherein the main body is formed as an eccentric lever, which has a pivoting bearing with a pivot axis which is at a distance from an axis of the bearing.

14. The power steering system of claim 13 wherein the pivot axis is substantially parallel to the axis of the worm shaft.

15. The power steering system of claim 13 wherein the pivoting bearing has a bearing element injection-molded onto the main body.

16. The power steering system of claim 13 wherein at least one injection-molding point is disposed in the region between the bearing and the pivoting bearing.

17. The power steering system of claim 12 wherein the bearing ring forms an outer ring of the bearing formed as a rolling bearing.

18. The power steering system of claim 12 wherein the retainer has a damper element projecting outwardly, which is formed from an elastomer that is different from the plastic of the injection-molded part.

19. The power steering system of claim 18 wherein the damper element is injection-molded onto the main body.

20. The power steering system of claim 19 wherein the damper element is injection-molded into a concave recess of the main body.

21. The power steering system of claim 12 wherein the worm shaft and the worm wheel are arranged in a gear mechanism housing, on which the retainer is movably mounted.

22. The power steering system of claim 12 comprising a preloading element that elastically preloads the retainer in the direction of the worm wheel.

Description

DESCRIPTION OF THE DRAWINGS

[0025] Advantageous embodiments of the invention will be explained in more detail below by using the drawings, in which:

[0026] FIG. 1 shows a power steering system for a motor vehicle in a schematic perspective illustration,

[0027] FIG. 2 shows the drive of the power steering system according to FIG. 1 in a schematic illustration and without housing,

[0028] FIG. 3 shows a schematic partial view of the power steering system according to FIG. 2,

[0029] FIG. 4 shows a retainer of the power steering system according to FIGS. 1 to 3 in an axial view in the direction of the bearing axis,

[0030] FIG. 5 shows the retainer of the power steering system according to FIGS. 1 to 3 in an opposite axial view.

EMBODIMENTS OF THE INVENTION

[0031] In the various figures, the same parts are always provided with the same designations and are therefore as a rule also respectively named or mentioned only once.

[0032] FIG. 1 shows a power steering system 1 which is attached to a steering shaft 2, which is rotatably mounted about its longitudinal axis L, the steering shaft axis. The steering shaft 2 is co-rotationally but adjustably in the direction of the longitudinal axis L in a rear steering shaft part 21, as indicated by the double arrow, in order to adjust a steering wheel attached to a fixing section 22, not illustrated here, in the longitudinal direction.

[0033] The power steering system has a gear mechanism housing 11, which has been left out in the exploded illustration of FIGS. 2 and 3. In the gear mechanism housing 11, a worm wheel 12, which is co-rotationally connected to the steering shaft 2, is rotatably mounted about the longitudinal axis L. A worm shaft 13 meshes with the toothing of the worm wheel 12 to form a worm gear mechanism.

[0034] The worm shaft 13 is rotatably mounted in the gear mechanism housing 11 about an axis A, the worm wheel axis, and can be driven in rotation by an electric motor 3 flange-mounted on the gear mechanism housing 11. The electric motor 3 has a motor shaft which is co-rotationally coupled to the worm shaft 13 via a coupling 31, which consists of two coupling parts. For this purpose, the worm shaft 13 has a cylindrical bearing bush, into which a coupling part is inserted. On the side close to the motor, the worm shaft 11 adjacent to the coupling 31 is mounted in a bearing 14, preferably a rolling bearing, which is accommodated in the housing 11. Between the gear mechanism housing 11 and the bearing arrangement 14 close to the motor, a seal element 230 can be provided, which is arranged on one side of the bearing arrangement 14 adjacent to the coupling part or on both sides of the bearing arrangement 14. The rolling bearing 14 comprises an inner ring, rolling elements and an outer ring. The rolling elements run in grooves between the inner ring and the outer ring. The outer ring is accommodated relative to the axis of rotation in a pivoting ring 33. On the outer circumferential side, the outer ring has a spherical surface, which is curved convexly and which forms a contact surface relative to a contact surface on the pivoting ring 33. The contact surface of the pivoting ring 33 is curved convexly, so that the outer ring is pivotable as a pivotable bearing element in the pivoting ring 33 about a pivot axis located perpendicular to the worm shaft axis A. The pivot axis in the unloaded state extends centrally through the bearing arrangement 14, so that two spring elements 34 are pierced centrally by the pivot axis 22. As a result, the spring elements 34 thus produce only low forces, in a range of less than 5%, as compared with an adjustable preload, for example via a preloading device on a side of the worm shaft 13 remote from the motor. At the end remote from the motor, the worm shaft 13 is mounted in a retainer 4, which is formed as a pivoting lever and is explained in more detail in the illustration of FIGS. 3 to 5.

[0035] The exploded illustration of FIG. 3 reveals that a bearing 15 is arranged on the side of the worm shaft 13 that is remote from the motor, which bearing is preferably formed as a rolling bearing, for example as a deep groove ball bearing, and has an outer bearing region 16. The bearing 15 is fitted in the retainer 4 so as to be displaceable relative to the worm wheel 12.

[0036] The retainer 4 has a main body 41, which is formed as an injection-molded part made of thermoplastic polymer. The bearing region 16 is connected to the main body 41 by overmolding, as can be seen in FIGS. 4 and 5, which show axial views from opposite axial directions of the axis A.

[0037] Formed in the main body 41 of the retainer 4 is a pivoting bearing 42, having a bearing opening that is continuous in the direction of a pivot axis S. The pivot axis S extends at a distance r, the pivoting radius, substantially parallel to the axis A.

[0038] In the pivoting bearing 42, the retainer 4 is rotatably mounted about a bearing pin 43, which is attached to a bearing cover 17 connected to the housing. As a result, the bearing 15, which is fixed in the main body 41 by overmolding the bearing region 16 and the axis A of which is at a distance from the pivot axis S by the pivoting radius defined by the distance r, can be moved toward the longitudinal axis L by pivoting by a pivot angle a about the pivot axis S, as illustrated in FIGS. 4 and 5. As a result, the worm shaft 13 can be moved in the direction of the tooth engagement with the worm wheel 12 that can be rotated about the longitudinal axis L.

[0039] Arranged on the bearing pin 43 is a spring 5, which is formed as a leg spring. The spring 5 is supported by one leg on the gear mechanism housing 11, the other leg rests with the spring force on the retainer 4, and loads the arm of the pivoting bearing that accommodates the bearing 15 in the direction of the longitudinal axis L. As result, the worm shaft 13 is loaded elastically without play in mesh with the toothing of the worm wheel 12.

[0040] The bearing ring 16 is overmolded with the thermoplastic polymer of the main body 41. To this end, the bearing 15 is arranged in the cavity of an injection mold of the main body 41, into which the plastic melt is injected via a nozzle arranged at an injection point 44. As can be seen clearly in FIG. 5, the injection point 44 is arranged in the main body 41 between the bearing ring 16 and the pivoting bearing 42, for example approximately centrally, as in the embodiment shown. This ensures that the bearing ring 16 is overmolded uniformly with the plastic, and also the pivoting bearing 42 can be injection-molded with low production tolerances as a result of the short flow path of the melt.

[0041] Arranged on the outside of the main body 41 is a damper element 45. The latter is flat or convex, as illustrated in FIG. 5, and is formed at right angles to the worm shaft axis A.

[0042] The damper element 45 is made of a thermoplastic elastomer which is softer and more elastic than the polymer of the main body 41. To connect it to the damper element 45, the main body 41 has a concave recess 46 in the form of a cylindrical blind hole. In the example shown, two injection openings 47 are arranged in the wall of the recess 46, through which openings the elastomer material for forming the damper element 45 is injected in molten form in the injection molding. As a result, the damper element 45 is connected integrally and in a form-fitting manner in the recess 45 by injection molding with the main body 41. The damper element 45 cooperates with a substantially cylindrical preloading element 48 made of plastic. The preloading element 48 preloads the worm shaft 13 radially via the retainer 4 with a preloading force, by which means the worm shaft 13 is urged in the direction of the worm wheel 12, which contributes to improving the engagement between worm shaft 13 and worm wheel 12. It is conceivable and possible that the preloading element 48 is injection-molded directly into the recess 46 of the retainer 4 and therefore forms the damper element. The latter is substantially cylindrical and extends radially outward with respect to the longitudinal axis L from the main body 41, to be specific in the opposite direction as seen from the longitudinal axis L, as shown schematically in FIG. 4.

[0043] In the installed state, the preloading element 48 is supported on the gear mechanism housing 11 in the direction opposite to the tooth engagement, and ensures high smooth running as a result of reliable attenuation of vibrations.

[0044] By means of the bearing ring 16 connected to the main body 41 by injection molding according to the invention, long-term stable, rigid attachment of the bearing 15 to the retainer 4 is achieved. The damper element 45, likewise injection-molded onto the retainer 4, is connected firmly and reliably to the retainer over the entire service life.

LIST OF DESIGNATIONS

[0045] 1 Power steering system

[0046] 11 Housing

[0047] 12 Worm wheel

[0048] 13 Worm shaft

[0049] 14 Bearing

[0050] 15 Bearing

[0051] 16 Bearing ring

[0052] 17 Bearing cover

[0053] 2 Steering shaft

[0054] 21 Steering shaft part

[0055] 22 Fixing section

[0056] 3 Electric motor

[0057] 31 Coupling

[0058] 32 Sealing element

[0059] 33 Pivoting ring

[0060] 34 Spring element

[0061] 4 Retainer

[0062] 41 Main body

[0063] 42 Pivoting bearing

[0064] 43 Bearing pin

[0065] 44 Injection point

[0066] 45 Damper element

[0067] 46 Recess

[0068] 48 Preloading element

[0069] 5 Spring

[0070] L Longitudinal axis

[0071] A Axis (worm shaft axis)

[0072] S Pivot axis

[0073] r Distance

[0074] Pivot angle