CN111542467A

CN111542467A - Worm gear and worm transmission mechanism

Info

Publication number: CN111542467A
Application number: CN201880085287.9A
Authority: CN
Inventors: J-U.哈费马尔茨; S.施瓦策尔; D.菲克泽尔; A.韦茨
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2018-01-04
Filing date: 2018-12-17
Publication date: 2020-08-14
Anticipated expiration: 2038-12-17
Also published as: CN111542467B; DE102018200090A1; WO2019134815A1

Abstract

A worm gear for an electric power steering device, having a worm (102) which is in engagement with a worm wheel (104), wherein the worm (102) is supported in the region of a first end (162) by means of a fixed bearing (160) and in the region of a second end (164) opposite the first end (162) by means of a floating bearing (166), wherein the fixed bearing (160) is arranged such that the worm (102) can be pivoted about an axis which is orthogonal to the rotational axis (118) of the worm wheel (104).

Description

Worm gear and worm transmission mechanism

Technical Field

The present invention relates to a worm gear and an electric power steering apparatus having the worm gear.

Background

A worm gear drive, also called a helical gear drive, is a gear hobbing drive. These worm and worm gears typically include a helical worm and a worm wheel. Upon a rotational movement of the worm, the worm engages in the worm wheel. In general, torque is introduced into the worm gear by the worm and is transmitted to the worm wheel.

Since the worm is usually mounted in a helically meshing but fixed manner, high axial forces occur. Therefore, depending on the operating conditions, it may be necessary to adequately support the worm on both sides by means of axial bearings. Furthermore, it should be noted that the worm is also subjected to bending stresses, so that the support structure must be designed correspondingly elastic or angle-compensated.

DE 102008001878 a1 discloses a worm gear mechanism which is designed for use in a power steering system. The gear train comprises a worm which is arranged in the gear train housing and is in engagement with the worm wheel. In order to improve the engagement, the worm is pivotably supported. For this purpose, the worm is mounted pivotably by means of a bearing ring mounted in a universal manner in the gear housing. The bearing ring is designed as a pivot ring. Furthermore, a prestressing device is provided in order to radially load the worm with a prestressing force. The described worm gear drive enables a pivotable movement of the worm perpendicular to the axis of rotation and in the direction of the worm wheel. Thus, the axis about which the worm pivots is parallel to the axis of rotation of the worm wheel.

Disclosure of Invention

Against this background, a worm gear according to claim 1 and an electric power steering device having the features of claim 11 are proposed. Embodiments emerge from the dependent claims and the description.

The proposed worm-gear drive comprises a shaft provided with one or more pitches (schraubenganging), a worm and a bevel gear, a worm wheel, meshing therein. In most cases, the axes of the two are 90 ° offset. A worm is a special form of a helical gear. The angle of the oblique toothing is selected to be so large that a tooth winds around the axle in a multiple spiral. Typically, the worm is connected to the drive shaft of the electric drive motor.

It is now provided that the worm is mounted in the gear housing, for example, in such a way that it is mounted in the region of a first end by means of a fixed bearing and in the region of a second end opposite the first end by means of a floating bearing, wherein the fixed bearing is arranged in such a way that the worm pivots about an axis that is orthogonal to the axis of rotation of the worm wheel.

The special support structure of the worm therefore allows its movement in the direction of the tooth width of the worm wheel.

The worm is supported in the design by means of two bearings, namely a fixed bearing and a floating bearing. In this way, a rotation of the worm is achieved with simultaneously defined positions in space. In the fixed-floating bearing arrangement realized here, the absorption of axial forces, i.e. forces acting in the direction of the axis of rotation of the worm, is undertaken by the fixed bearing. The fixed bearing, in addition to axially guiding the worm, also bears its radial support.

For example, plain bearings and rolling bearings, for example ball bearings, are considered for the fixed bearings.

The proposed worm gear and the electric power steering device described thereby comprising such a worm gear also have a series of advantages at least in some embodiments. Thus, in design, the worm may easily move (leichtg ä ngig) about two pivot axes (particularly referred to herein as the y-axis and z-axis in connection with the drawings). The clamping guide can be used on a floating bearing point by means of easy movement possibilities about two axes. In principle, new floating bearing solutions can be realized. The decoupling of the pivoting and elastic means (anderon) is achieved by two structural elements, eliminating the conflict of objectives, namely:

slightly pivotable means a small cross-section,

the small cross-section results in a reduced service life of the elastic means.

The now possible more robust embodiment of the pivot geometry results in a high service life and furthermore prevents cracking.

Furthermore, the use of larger ball bearings is allowed, which results in a longer service life under higher gear loads. The use of robust pivot geometry provides advantages in terms of crack-free and ability to withstand higher gear loads. Furthermore, the spring rate for compensating the basic play can be easily applied independently of the service life requirement. Furthermore, the spring characteristic for compensating the basic play can be set in a simple manner. Progressive or decreasing characteristics or different spring rates are associated with the deflection.

Other advantages and design aspects of the invention will appear from the description and the accompanying drawings.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or individually without leaving the scope of the invention.

Drawings

Fig. 1 shows an embodiment of a worm gear according to the prior art.

Fig. 2 shows an embodiment of the proposed worm gear in two views.

Detailed Description

The invention is illustrated schematically by means of embodiments in the figures and is described in detail below with reference to the figures.

Fig. 1 shows an embodiment of a worm gear according to the prior art. The worm drive is generally indicated by reference numeral 10. The illustration shows the worm gear mechanism 10 in an overall view 10a on the one hand and in a purely schematic view 10b on the other hand. Coordinate systems 12, in which the axes, namely x-axis 14, y-axis 16 and z-axis 18, are respectively assigned to the two views. Furthermore, a spring element 36 for spring action is provided.

In this illustration, a worm 20 and a worm wheel 22 are shown with cylindrical running toothing, which cooperate to transmit a force or a torque and engage into one another for this purpose. Further, the illustration shows a fixed bearing seat or fixed bearing 30 with a point of rotation and a floating bearing seat or floating bearing 32 with a stop 34.

It should be noted that in the worm or helical pinion currently used, the fixed bearing 30 is constituted comprising elastic means. This allows for small movements about the axis of the fixed bearing 30, which is referred to as the y-axis 16 in fig. 1. Movement of the worm 20 about the vertical axis (in this case the z-axis 18) is almost impossible. This can be a disadvantage in the case of corresponding embodiments of the floating bearing point, in particular in the clamping guide.

Fig. 2 shows an embodiment of the proposed worm gear, which is designated in general by reference numeral 100. The illustration shows the worm on the left side in a plan view and the worm gear 100 on the right side in a side view, with the worm 102 and the worm wheel 104 engaging into one another. Further, an x-axis 110, a y-axis 112, and a z-axis 114 are depicted in the illustration. The z-axis 114 is an axis that is directed orthogonal to the axis of rotation 118 of the worm gear 104. The pivoting of the worm 102 about the z-axis 114 means a movement of the worm 102 in the tooth width direction of the worm wheel 104.

The illustration also shows a first ring 140 having a ball bearing 141 that moves about a pivot axis. One possibility consists in placing the pivot axis at the level of the tooth axis. Thereby resulting in better kinematics. Further, a second ring 142 is provided. Furthermore, an eccentric element 146 for compensating for play in the teeth to generate a lever arm about the y-axis and a spring element 148 for applying a spring force 150 are provided.

The two

rings

140 and 142 allow the worm 102 to pivot about the y-axis 112 and the z-axis 114, and thus about an axis oriented perpendicular to the axis of rotation 118 of the worm gear 104. The two

rings

140 and 142 provide a double gimbal (doppelkardanisch) support structure. This dual gimbaled support structure is a fixed bearing 160. The fixed bearing 160 is arranged in the region of the first end 162 of the worm 102. A floating bearing 166 is provided at a second end 164 of the worm 102 opposite the first end 162.

The second ring 142 surrounds the first ring 140. In this illustration, the two

rings

140 and 142 are arranged coaxially with each other. The y-axis 112 in turn extends perpendicular to the z-axis 114 and in this embodiment parallel to the axis of rotation 118 of the worm gear 104. This is the case when the worm 102 and the worm wheel 104 are parallel to each other and thus the y-axis 112 and the worm wheel axis are also parallel to each other. If a shaft angle of 75 ° exists between the worm 102 and the worm wheel 104, the y-axis 112 and the worm wheel axis 118 are not parallel, but are inclined to one another if necessary.

Instead of the spring element 148, in principle an elastic element, for example a layer made of an elastomer, can be used. Furthermore, the worm 102 can be mounted in the gear housing. A stationary bearing 160 is then typically arranged in the gear housing.

In the described worm gear drive 100, the worm fixing bearing can be pivoted very easily about the two pivot axes of the worm 102. The pivoting of the worm screw about the y-axis 112 and the z-axis 114 is here effected with cylindrical pins between the first ring and the second ring and between the second ring and the housing or the further ring, respectively.

The illustration further shows a cylindrical pin 170, which in this case causes the worm screw 102 to pivot about two axes.

The pivoting of the worm screw about the y-axis can be achieved here with a horizontal cylindrical pin 170. These cylindrical pins are fixedly connected to the first ring 140. At the same time, in the two horizontal cylindrical pins 170, a force is applied by a lever arm, for example by means of a spring or similar element. The torque about the longitudinal axis of the pin generated in this way enables the worm 102 to be pressed into the worm wheel 104 and the backlash to be compensated. At the same time, the end stop can be integrated into the spring action mechanism.

Possible play compensation in the cylindrical pin engagement on the second ring 142 can also be achieved, in particular in embodiments with a small play fit, by optionally additional elastic means. The cylindrical pin 170 that allows pivoting about the y-axis 112 may be mounted directly on a ball bearing outer ring or in a ring with a fixed bearing.

In such an embodiment, pivoting about the z-axis 114 may also be accomplished with two cylindrical pins 170. These cylindrical pins are fixedly connected with the second ring 142 and have a small clearance fit in the transmission housing or another ring. The gap compensation can also be used here by means of additional elastic means.

More than two cylindrical pins 170 may be provided, respectively.

In fig. 2, a worm gear drive 100 is shown in one embodiment, which enables pivoting of the worm 102 about a y-axis 112 and a z-axis 114. In principle, the worm gear set proposed here is characterized in that in the worm gear set the worm 102 can be pivoted about the z-axis 114 and thus about an axis oriented orthogonally to the axis of rotation 118 of the worm wheel 104.

Claims

1. A worm gear for an electric power steering device, having a worm (102) which is in engagement with a worm wheel (104), wherein the worm (102) is supported in the region of a first end (162) by means of a fixed bearing (160) and in the region of a second end (164) opposite the first end (162) by means of a floating bearing (166), wherein the fixed bearing (160) is arranged such that the worm (102) can be pivoted about an axis which is orthogonal to the rotational axis (118) of the worm wheel (104).

2. The worm drive according to claim 1, wherein the at least sections are accommodated in a drive housing in which the fixed bearing (160) is arranged.

3. The worm gear according to claim 1 or 2, wherein the stationary bearing (160) has a second ring (142).

4. The worm gear drive according to claim 3, wherein two cylindrical pins (170) are provided which are fixedly connected with the second ring (142).

5. The worm gear according to any of claims 1 to 4, wherein the fixed bearing (160) is formed by a gimbal bearing structure.

6. The worm gear according to any of claims 1 to 5, wherein the worm (102) is supported such that it can pivot about another axis which is oriented parallel and/or oblique to the axis of rotation (118) of the worm wheel (104).

7. Worm and worm gear according to any of claims 1 to 6, wherein the integrated elastic means is provided with at least one eccentric element (146).

8. The worm gear according to any of claims 1 to 7, wherein a first ring (140) is provided.

9. The worm gear transmission according to claim 8, wherein a first cylindrical pin (170) is provided which is fixedly connected with the first ring (140).

10. The worm gear according to any of claims 5 to 9, wherein the worm (102) is supported with a double gimbal support structure.

11. An electric power steering apparatus for a motor vehicle having a worm gear (100) according to any one of claims 1 to 10.