GEAR ASSEMBLY AND STEERING SYSTEM

Abstract

The disclosure specifies a gear assembly for an electric-motor assisted steering system, comprising an electric motor, a worm shaft which can be driven by the electric motor and which meshes with a worm wheel. The worm shaft has a recess on an end face which faces the electric motor, in which recess there is arranged an elastic element which applies an axial force to the worm shaft in the direction away from the electric motor. In the axial direction, the elastic element is supported by one end on an adjustment element, which is formed in such a way that it permits expansion of the elastic element in the axial direction when the axial force on the worm shaft exceeds a defined threshold value, and limits expansion of the elastic element when the axial force on the worm shaft lies below the defined threshold value.

Claims

1. A gear assembly for an electric-motor assisted steering system, comprising an electric motor, a worm shaft which can be driven by the electric motor and which meshes with a worm wheel, wherein the worm shaft has a recess on an end face which faces the electric motor, in which recess there is arranged an elastic element which applies an axial force to the worm shaft in a direction away from the electric motor, wherein, in the axial direction, the elastic element is supported by one end on an adjustment element, which is formed in such a way that it permits expansion of the elastic element in an axial direction when the axial force on the worm shaft exceeds a defined threshold value, and limits expansion of the elastic element when the axial force on the worm shaft lies below the defined threshold value.

2. The gear assembly as claimed in claim 1, wherein the adjustment element permits expansion of the elastic element when the axial force effected by the elastic element exceeds 250 N.

3. The gear assembly as claimed in claim 1, wherein the adjustment element is pressed into the recess, wherein the press fit is designed in such a way that the adjustment element is displaceable in the recess when the threshold value is exceeded.

4. The gear assembly as claimed in claim 3, wherein the adjustment element is arranged between the elastic element and a bottom of the recess.

5. The gear assembly as claimed in claim 1, wherein a bush is inserted into the recess, wherein the adjustment element is pressed onto the bush in such a way that the adjustment element is displaceable relative to the bush when the threshold value is exceeded.

6. The gear assembly as claimed in claim 5, wherein the adjustment element and/or the bush is a deep-drawn part.

7. The gear assembly as claimed in claim 5, wherein the bush is slit.

8. The gear assembly as claimed in claim 5, wherein the bush is accommodated without play in the recess.

9. The gear assembly as claimed in claim 1, wherein the worm shaft is rotatably mounted by a fixed bearing, and a drive shaft of the electric motor is coupled to the worm shaft in a torque-transmitting manner via a coupling device, wherein the coupling device is supported on the fixed bearing and is loaded axially against the fixed bearing by the axial force effected by the elastic element.

10. A steering system for a motor vehicle having a gear assembly as claimed in claim 1.

11. The gear assembly as claimed in claim 2, wherein the adjustment element is pressed into the recess, wherein the press fit is designed in such a way that the adjustment element is displaceable in the recess when the threshold value is exceeded.

12. The gear assembly as claimed in claim 2, wherein is inserted into the recess, wherein the adjustment element is pressed onto the bush in such a way that the adjustment element is displaceable relative to the bush when the threshold value is exceeded.

13. The gear assembly as claimed in claim 6, wherein the bush is slit.

14. The gear assembly as claimed in claim 7, wherein the bush is accommodated without play in the recess.

15. The gear assembly as claimed in claim 5, wherein the worm shaft is rotatably mounted by a fixed bearing, and a drive shaft of the electric motor is coupled to the worm shaft in a torque-transmitting manner via a coupling device, wherein the coupling device is supported on the fixed bearing and is loaded axially against the fixed bearing by the axial force effected by the elastic element.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0028] Further advantages and features can be gathered from the following description and from the appended drawings, to which reference is made. In the drawings:

[0029] FIG. 1 shows part of a steering system according to the disclosure having a gear assembly according to the disclosure,

[0030] FIG. 2 shows a further steering system according to the disclosure having a further gear assembly according to the disclosure, and

[0031] FIG. 3 shows part of a gear assembly according to the disclosure according to yet another exemplary arrangement.

DETAILED DESCRIPTION

[0032] FIG. 1 shows part of an electric-motor assisted steering system 10. The steering system 10 comprises a steering column 12, which can be rotated by a user by a steering wheel, not illustrated, in order to maneuver a vehicle.

[0033] To simplify a steering operation, a gear assembly 14 is provided for the electric-motor assistance of the steering system 10.

[0034] The gear assembly 14 comprises an electric motor 16, a worm shaft 18, which can be driven by the electric motor 16, and a worm wheel 20, with which the worm shaft 18 is in engagement, more specifically in toothed engagement.

[0035] To drive the worm shaft 18, a drive shaft 22 of the electric motor 16 is coupled to the worm shaft 18 in a torque-transmitting manner via a coupling device 24.

[0036] The worm wheel 20 is firmly coupled to the steering column 12.

[0037] Consequently, the steering column 12 is rotated by the worm wheel 20 when the worm shaft 18 is driven by the electric motor 16.

[0038] The worm shaft 18 is rotatably mounted by a fixed bearing 26. The fixed bearing 26 is a rolling-contact bearing having rolling elements 25 and bearing rings 27.

[0039] The coupling device 24 is supported in the axial direction on the fixed bearing 26. In addition, the coupling device 24 is positioned radially inside and axially in the region of the fixed bearing.

[0040] In addition, to support the worm shaft 18, there is a loose bearing 28, wherein the fixed bearing 26 and the loose bearing 28 are arranged in opposite end sections of the worm shaft 18.

[0041] The loose bearing 28 is loaded laterally by a spring 30, in order to keep the loose bearing 28 in the position shown in FIG. 1.

[0042] Due to the spring 30, reliable engagement between the worm shaft 18 and the worm wheel 20 is ensured.

[0043] Furthermore, there is an elastic element 32, a coil spring in the exemplary arrangement, which applies an axial force to the worm shaft 18 in a direction away from the electric motor 16.

[0044] As a result of the axial loading, the rolling elements 25 of the fixed bearing 26 are in contact with bearing rings 27 of the fixed bearing 26.

[0045] In addition, the elastic element 32 is used to compensate for tolerances.

[0046] On an end face 34 facing the electric motor 16, the worm shaft 18 has a recess 36, in which the elastic element 32 is arranged.

[0047] The elastic element 32 is supported in the axial direction with one end on an adjustment element 38.

[0048] In the exemplary arrangement illustrated in FIG. 1, the adjustment element 38 is a bush, which is pressed into the recess 36.

[0049] The adjustment element 38 is arranged between the elastic element 32 and a bottom 37 of the recess 36.

[0050] The adjustment element 38 can be a milled part or a deep-drawn part.

[0051] The elastic element 32 is supported by the other end on a further bush 40, which is accommodated without play in the recess and is displaceably mounted.

[0052] The bush 40 is a milled part in the exemplary arrangement according to FIG. 1.

[0053] Formed on the bush 40 is an extension 41, onto which the elastic element 32 is pushed. As a result, assembly of the gear assembly 14 is simplified. In addition, the extension 41 prevents buckling of the elastic element 32.

[0054] In addition, the elastic element 32 is accommodated a little way in the adjustment element 38.

[0055] Because the elastic element 32 is accommodated in the adjustment element 38 and is additionally pushed onto the extension 41, the elastic element 32 is supported stably over its entire length.

[0056] Both the bush 40 and the adjustment element 38 have a circular cross section in the exemplary arrangement. However, other cross sections are also conceivable, for example an oval cross section or an angular cross section.

[0057] At an end opposite to the elastic element 32, the bush 40 has a recess 42, in which an end section of the drive shaft 22 is accommodated.

[0058] The elastic element 32 thus firstly forces the bush 40 against the drive shaft 22 of the electric motor 16 and secondly forces the worm shaft 18 away from the drive shaft 22. In this way, an axial tolerance chain is compensated.

[0059] In addition, the coupling device 24 is loaded axially against the fixed bearing 26 by the axial force effected by the elastic element 32.

[0060] According to the disclosure, the adjustment element 38 is formed in such a way that it permits expansion of the elastic element 32 in the axial direction when the axial force on the worm shaft 18 exceeds a defined threshold value, and limits expansion of the elastic element 32 when the axial force on the worm shaft 18 lies below the defined threshold value.

[0061] For example, an axial force effected by the elastic element 32 should not exceed 280 N, preferably 250 N. In the event of higher axial forces, high friction in the gear assembly 14 would occur, as a result of which the latter becomes stiff.

[0062] For this purpose, the press fit of the adjustment element 38 in the recess 36 is designed in such a way that the adjustment element 38 is displaced in the recess 36 when the axial force exceeds the threshold value.

[0063] This means that if the elastic element 32 is compressed so highly because of an unfavorable tolerance situation that the axial force on the worm shaft 18 exceeds the threshold value, the adjustment element 38 is displaced in the recess 36.

[0064] As a result of a displacement of the adjustment element 38, in particular in the direction of the bottom 37 of the recess 36, the elastic element 32 can relax, which reduces the axial force.

[0065] If the axial force is reduced to such an extent that the threshold value is no longer exceeded, the adjustment element 38 is not displaced further.

[0066] The press fit is influenced by a diameter of the adjustment element 38 and of the recess 36, the diameters being matched to each other.

[0067] In addition, ribs can be molded on the adjustment element 38 or in the recess 36 and/or the adjustment element 38 can be slit in order to optimize the press fit.

[0068] FIG. 2 shows a further exemplary arrangement of an electric-motor assisted steering system 10. The steering system 10 according to FIG. 2 differs from the steering system 10 according to FIG. 1 in the arrangement of the elastic element 32 and of the adjustment element 38.

[0069] In particular, the adjustment element 38 according to the exemplary arrangement illustrated in FIG. 2 is pressed onto the bush 40 in such a way that the adjustment element 38 is displaceable relative to the bush 40 when the threshold value is exceeded.

[0070] More specifically, the adjustment element 38 is pressed onto the extension 41 of the bush 40.

[0071] In this case, the elastic element 32 is arranged between the bottom 37 of the recess 36 and the adjustment element 38.

[0072] The adjustment element 38 is, for example, a deep-drawn part.

[0073] The functional principle of the gear assembly 14 does not change, however.

[0074] This means that if the elastic element 32 is compressed so highly because of an unfavorable tolerance situation that the axial force on the worm shaft 18 exceeds a threshold value, the adjustment element 38 is displaced on the bush 40, in particular on the extension 41, so that the elastic element 32 can relax, specifically to such an extent that the axial force no longer exceeds the threshold value.

[0075] In the bottom 37 of the recess 36 in the exemplary arrangement according to FIG. 2, there is an additional recess 44, in which the elastic element 32 is accommodated a little way in. As a result, the elastic element 32 is particularly stably supported.

[0076] FIG. 3 shows a section through a gear assembly 14 for a steering system 10 according to a further exemplary arrangement.

[0077] The exemplary arrangement illustrated in FIG. 3 corresponds substantially to the exemplary arrangement illustrated in FIG. 2, with the difference that both the bush 40 and the adjustment element 38 are formed as deep-drawn parts.

[0078] In addition, the adjustment element 38 illustrated in FIG. 3 is pot-shaped, and the elastic element 32 is partly accommodated in the adjustment element 38. This is used for improved guidance of the elastic element 32.