Worm gear

Abstract

Worm gear for an electric power steering system with a worm (102) which engages 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 pivoting of the worm (102) about an axis which is orthogonal to an axis of rotation (118) of the worm wheel (104) is made possible, characterized by that the fixed bearing (160) has a first ring (140) wherein two cylindrical pins (170) are provided which are firmly connected to the first ring (140); that the fixed bearing (160) has a second ring (142) wherein two cylindrical pins (170) are provided which are firmly connected to the second ring (142); wherein the axis of the cylindrical pins (170) on the first ring (140) and the axis of the cylindrical pins (170) on the second ring (142) intersect each other at right angles, thus forming a gimbal bearing.

Description

[0001] The invention relates to a worm gear and an electric power steering system with such a worm gear. State of the art

[0002] Worm gears, also known as helical gears, are a type of helical gear. They typically consist of a helical worm and a worm wheel. As the worm rotates, it engages with the worm wheel. Typically, torque is introduced into the worm gear via the worm and transmitted to the worm wheel.

[0003] Since the screw is typically helically toothed but rigidly mounted, high axial forces occur. Therefore, depending on the operating conditions, it may be necessary to adequately support the screw on both sides with axial bearings. Furthermore, it should be noted that the screw is also subjected to bending stresses, and consequently, the mounting must be designed to be correspondingly elastic or angle-compensating.

[0004] From German patent application DE 10 2008 001 878 A1, a worm gear is known that is designed for use in an auxiliary power steering system. The gear comprises a worm arranged in a gear housing and meshing with a worm wheel. To improve the meshing, the worm is pivotably mounted. For this purpose, the worm is pivotally mounted by means of a bearing ring that is cardanically mounted in the gear housing. The bearing ring is designed as a pivot ring. In addition, a preloading device is provided to apply a radial preload force to the worm. The described worm gear allows the worm to pivot perpendicular to the axis of rotation and in the direction of the worm wheel. The axis about which the worm pivots is therefore parallel to the axis of rotation of the worm wheel.

[0005] DE 10 2009 054 655 A1 discloses a worm gear for a steering system, wherein the worm is held by a fixed bearing and a floating bearing. The rolling bearing on the fixed bearing side is held by a spring plate. The spring plate has recesses that form pivoting webs, so that the worm is springed into the helical gear by torsion.

[0006] Such spring plate holders form a solid-state joint. Slight pivoting is only possible with narrow pivoting webs. However, a small cross-section of the pivoting webs leads to a shorter service life of the spring mechanism.

[0007] However, if a clamping guide is provided at the loose bearing, a slight pivoting motion at the fixed bearing is very important.

[0008] The object of the invention is therefore to provide a worm gear in which the described conflict of objectives is resolved. The fixed bearing should allow for easy pivoting, while the spring mechanism should have a long service life. Disclosure of the invention

[0009] The problem is solved by a worm gear according to claim 1 and an electric power steering system with the features of claim 3. Further details are provided in the dependent claims and the description.

[0010] The worm gear presented here comprises a shaft with one or more helical threads, the worm, and a meshing helical gear, the worm wheel. The axes of the two are, in most cases, offset by 90°. The worm is a special type of helical gear. The angle of the helical teeth is chosen so that each tooth winds multiple times around the gear axis in a helical fashion. Typically, the worm is connected to a drive shaft of an electric drive motor.

[0011] It is now provided that the worm gear is mounted, for example, in a gearbox housing in such a way that it is mounted in the area of ​​a first end by means of a fixed bearing and in the area 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 it is possible to pivot the worm gear about an axis that is orthogonal to an axis of rotation of the worm wheel.

[0012] Thus, the special mounting of the worm allows it to move in the tooth width direction of the worm wheel.

[0013] The screw is supported by two bearings: a fixed bearing and a floating bearing. This allows the screw to rotate while maintaining a defined position in space. In this fixed-floating bearing arrangement, the fixed bearing absorbs axial forces, specifically forces acting along the screw's axis of rotation. In addition to providing axial guidance, the fixed bearing also supports the screw radially.

[0014] For the fixed bearing, for example a plain bearing and a rolling bearing, e.g. a ball bearing, are suitable.

[0015] The presented worm gear, and thus also the described electric power steering system incorporating such a worm gear, offers a number of advantages, at least in some of its embodiments. For example, one design allows for smooth movement of the worm around both pivot axes, which are referred to here, particularly in conjunction with the figures, as the y-axis and z-axis. This smooth movement around both axes enables the use of a clamping guide at the floating bearing point. Fundamentally new floating bearing concepts can be implemented. The decoupling of pivoting and spring action by means of two design elements is achieved, thus resolving the conflicting objectives, namely: - easily swiveling means small cross-sections, Small cross-sections result in a shorter service life for the spring mechanism. A now possible more robust design of the pivot geometry leads to longer service lives and also prevents cracking.

[0016] Furthermore, the use of larger ball bearings is enabled, resulting in increased service life under higher gearbox loads. The use of a robust swivel geometry offers advantages in terms of crack resistance and increased strength for higher gearbox loads. Additionally, a spring rate for backlash compensation can be easily applied, independent of service life requirements. Moreover, a spring characteristic curve for backlash compensation can be easily set. A progressive or degressive characteristic curve, or different spring rates, can be selected depending on the deflection.

[0017] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0018] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention. Brief description of the drawings Fig. Figure 1 shows a state-of-the-art design of a worm gear. Fig. Figure 2 shows two illustrations of an embodiment of the presented worm gear. Embodiments of the invention

[0019] The invention is schematically illustrated with reference to embodiments in the drawings and is described in detail below with reference to the drawings.

[0020] In Fig. Figure 1 shows an embodiment of a worm gear according to the prior art, designated in its entirety by the reference numeral 10. The illustration shows the worm gear 10 in an overall view 10a and in a purely schematic view 10b. Each of the two views is also associated with a coordinate system 12, in which axes are labeled, namely an x-axis 14, a y-axis 16, and a z-axis 18. An elastic element 36, which serves for spring suspension, is also provided.

[0021] The illustration shows a worm 20 with cylindrical teeth and a worm gear 22, which interact to transmit a force or moment and mesh together for this purpose. The illustration also shows a fixed bearing seat or fixed bearing 30 with a pivot point and a floating bearing seat or floating bearing 32 with a stop 34.

[0022] It should be noted that in currently used worm gears or screw pinions, the fixed bearing 30 includes a spring-loaded mechanism. This allows small movements around an axis of the fixed bearing 30, which are Fig. 1 is designated as the y-axis 16. Movement of the worm 20 around the vertical axis, in this case the z-axis 18, is virtually impossible. This can prove to be a disadvantage depending on the design of the floating bearing point, especially with a clamping guide.

[0023] Fig. Figure 2 shows an embodiment of the presented worm gear, designated by the reference numeral 100. The illustration shows a top view of a worm on the left and a side view of the worm gear 100 on the right, with the worm 102 and a worm wheel 104 meshing together. The illustration also includes an x-axis 110, a y-axis 112, and a z-axis 114. The z-axis 114 is an axis perpendicular to a rotation axis 118 of the worm wheel 104. Pivoting the worm 102 about the z-axis 114 moves the worm 102 in the tooth width direction of the worm wheel 104.

[0024] The illustration further shows a first ring 140 with a ball bearing 141 moving about a pivot axis. One possibility is to position the pivot axis at the same height as the gear axis. This results in improved kinematics. A second ring 142 is also provided. Additionally, offset elements 146, which create a lever arm around the y-axis for backlash compensation in the gearing, and a spring element 148 for applying a spring force 150 are provided.

[0025] The two rings 140 and 142 allow the worm 102 to pivot about both the y-axis 112 and the z-axis 114, and thus about an axis perpendicular to the axis of rotation 118 of the worm gear 104. The two rings 140 and 142 provide a double-cardan bearing. This double-cardan bearing constitutes a fixed bearing 160. This fixed bearing 160 is located at a first end 162 of the worm 102. A floating bearing 166 is provided at a second end 164 of the worm 102, which is opposite the first end 162.

[0026] The second ring 142 surrounds the first ring 140. In this representation, the two rings 140 and 142 are arranged coaxially. The y-axis 112 is perpendicular to the z-axis 114 and, in this configuration, runs parallel to the axis of rotation 118 of the worm gear 104. This is the case if and only if the worm 102 and worm gear 104 are parallel, and therefore the y-axis 112 and the worm gear axis are also parallel to each other. If there is an axial angle of 75° between the worm 102 and the worm gear 104, then the y-axis 112 and the worm gear axis 118 are not parallel, but may be skew to each other.

[0027] Instead of the spring element 148, an elastic element, e.g., a layer of elastomer, can be used. Furthermore, the worm 102 can be mounted in a gearbox housing. The fixed bearing 160 is typically located in this gearbox housing.

[0028] In the described worm gear 100, the worm fixed bearing can be pivoted very smoothly about both pivot axes of the worm 102. The pivoting of the worm about the y-axis 112 and the z-axis 114 is achieved by means of dowel pins between the first ring and the second ring, as well as between the second ring and the housing or another ring.

[0029] The illustration also shows cylindrical pins 170, which in this case allow the worm 102 to pivot about two axes.

[0030] The pivoting of the worm about the y-axis is made possible by horizontal cylindrical pins 170. These are rigidly connected to the first ring 140. Simultaneously, a force, for example by means of a spring or similar element, is applied to these two horizontal cylindrical pins 170 via a lever arm. The resulting moment about the longitudinal axis of the pins enables the worm 102 to be pressed into the worm gear 104 and the backlash to be compensated. At the same time, an end stop can be integrated into the spring mechanism.

[0031] Any play compensation in the cylindrical pin fits on the second ring 142, particularly in a design with a small clearance fit, can be achieved by an additional spring element if necessary. The cylindrical pins 170, which allow pivoting about the y-axis 112, can be mounted directly on the outer ball bearing race or in a ring with a fixed bearing.

[0032] In this version, pivoting about the z-axis 114 is also achieved using two cylindrical pins 170. These are rigidly connected to the second ring 142 and have a small play adjustment in the gearbox housing or another ring. Here, too, play compensation can be achieved by means of an additional spring mechanism.

[0033] It is also possible to provide more than two cylinder pins 170.

[0034] In Fig. Figure 2 shows the worm gear 100 in a version that allows the worm 102 to pivot about both the y-axis 112 and the z-axis 114. The worm gear presented here is fundamentally characterized by the fact that it allows the worm 102 to pivot about the z-axis 114, and thus about an axis that is orthogonal to the axis of rotation 118 of the worm wheel 104.

Claims

[1] Worm gear for an electric power steering system with a worm (102) which engages 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 it is possible to pivot the worm (102) about an axis which is orthogonal to an axis of rotation (118) of the worm wheel (104), characterized by , that the fixed bearing (160) has a first ring (140) wherein two cylindrical pins (170) are provided which are firmly connected to the first ring (140); that the fixed bearing (160) has a second ring (142) wherein two cylindrical pins (170) are provided which are firmly connected to the second ring (142); wherein the axis of the cylindrical pins (170) on the first ring (140) and the axis of the cylindrical pins (170) on the second ring (142) intersect each other at right angles, thus forming a gimbal bearing. [2] Worm gear drive according to claim 1, wherein an integral spring is provided with at least one disaxation element (146). [3] Electric power steering for motor vehicles with a worm gear (100) according to one of claims 1 to 2.

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