Worm reducer and method for manufacturing worm reducer

Abstract

The present application relates to a worm reducer and a method for manufacturing a worm reducer. In one aspect, a worm reducer is provided, which includes a worm shaft (164); a worm wheel (163); a housing (153) that accommodates the worm shaft (164) and the worm wheel (163); a bearing that holds the worm shaft (164) in the housing (153); a coil spring (170) that contacts the outer peripheral surface of the bearing and applies a thrust toward the worm wheel (163); and a preload member (155) that is screwed into the housing (153) and fixed on the housing (153) and pressurizes the coil spring (170). The winding direction of the coil spring (170) is different from the winding direction of the thread of the preload member (155), and the contact resistance between the coil spring (170) and the preload member (155) is greater than the contact resistance between the coil spring (170) and the bearing.

Description

Technical Field

[0001] The invention relates to a worm reducer, wherein a worm shaft is pushed toward a worm wheel. Background Art

[0002] To prevent backlash, there is a worm reducer in which a worm is pushed toward a worm wheel by the elastic force of a coil spring (for example, see Japanese Patent Application Publication No. 2015-123769 (JP2015-123769A)). This worm reducer can suppress, for example, the occurrence of a knocking sound between a bearing housing that houses a bearing and a gearbox. Summary of the Invention

[0003] However, the inventors of the present invention have discovered that some worm reducers including coil springs produce an abnormal sound that is different from a knocking sound. After further experiments and research, the inventors discovered that the abnormal sound is a stick-slip sound between the coil spring and the bearing, discovered a positional relationship between the bearing and the coil spring that produces little stick-slip sound, and discovered a structure and manufacturing method that can easily arrange the coil spring in a position with a high probability of producing little stick-slip sound relative to the bearing without increasing the number of parts and without requiring a complex structure.

[0004] The present invention has been accomplished based on the above-mentioned findings of the inventors, and provides a worm reducer and a method for manufacturing the worm reducer that can suppress the generation of stick-slip sound with a high probability.

[0005] A first aspect of the present invention relates to a worm reducer comprising a worm shaft; a worm wheel; a housing accommodating the worm shaft and the worm wheel; a bearing holding the worm shaft within the housing; a coil spring contacting the outer peripheral surface of the bearing and applying a thrust toward the worm wheel; and a preload member threaded into and fixed to the housing to apply pressure to the coil spring. The coil spring is wound in a direction different from the direction of rotation of threads of the preload member, and the contact resistance between the coil spring and the preload member is greater than the contact resistance between the coil spring and the bearing.

[0006] A second aspect of the present invention relates to a method for manufacturing a worm reducer, comprising a worm shaft, a worm wheel, a housing accommodating the worm shaft and worm wheel, a bearing holding the worm shaft within the housing, a coil spring contacting the outer circumferential surface of the bearing and applying a thrust toward the worm wheel, and a preload member threaded into and secured to the housing to apply pressure to the coil spring. The method comprises: arranging the coil spring so that one end of the coil spring, in the direction of its winding axis, contacts the bearing; and threading the preload member into the housing. The coil spring has a winding direction that differs from the direction of rotation of the threads of the preload member. In the initial stage of threading the preload member into the housing, the coil spring rotates together with the preload member. In the final stage of threading the preload member into the housing, the position of a first distal end portion of a wire forming the coil spring is fixed within a predetermined range so that the distal end is located to one side of the bearing, and the preload member and the coil spring slide relative to each other, thereby attaching the preload member to the housing.

[0007] With the worm reducer and the method for manufacturing the worm reducer according to the above-described aspects of the present invention, the distal end of the wire rod of the coil spring can be arranged at a position within a predetermined range relative to the bearing with a high probability, thereby increasing the probability of suppressing the occurrence of stick-slip noise between the coil spring and the bearing. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals denote like elements, and wherein:

[0009] Figure 1 is a diagram showing the overall configuration of a steering system;

[0010] Figure 2 is a cross-sectional view showing the internal structure of the worm speed reducer according to the present embodiment;

[0011] Figure 3 is a perspective view showing a coil spring according to the present embodiment, a bearing in contact with the coil spring, and the vicinity of the bearing;

[0012] Figure 4 is a plan view showing a positional relationship of a first distal end portion of a coil spring relative to a bearing according to the present embodiment; and

[0013] Figure 5 It is a plan view showing the positional relationship of the first distal end portion of the right-hand coil spring relative to the bearing. DETAILED DESCRIPTION

[0014] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that all embodiments described below illustrate comprehensive or specific examples of the present invention. The numerical values, shapes, materials, components, arrangement positions and connection forms of components, steps, step sequences, etc. shown in the following embodiments are merely examples and are not intended to limit the present invention. Among the components in the following embodiments, components that are not described in the independent claims representing the most general concepts are described as optional components.

[0015] The drawings are schematic diagrams in which emphasis, omission, and ratio adjustment have been appropriately performed to illustrate the present invention and may be different from actual shapes, positional relationships, and ratios.

[0016] First, the overall configuration of a steering system 100 provided with a worm speed reducer according to an embodiment of the present invention will be described. Figure 1 is a diagram schematically showing the overall configuration of a steering system.

[0017] like Figure 1 As shown, the steering system 100 is a power steering system that assists the driver's force to rotate a steering member 110, such as a steering wheel, for steering. The steering system 100 includes a steering shaft 130 that rotates according to the rotation of the steering member 110; a rack and pinion device 140 that converts the rotation of the steering shaft 130 into reciprocating motion of a turning shaft 141; a sensor device 120 configured to detect the steering torque generated by the steering member 110; and a worm reducer 150 configured to apply a steering assist force to the steering shaft 130 based on a signal from the sensor device 120.

[0018] The worm speed reducer 150 is connected to the motor 152 and is a device that applies an assist force for assisting steering to the steering shaft 130 by using the motor 152 as a driving source. Note that the motor 152 is controlled by an electronic control unit (ECU) (not shown), and the assist force to be applied to the steering shaft 130 is appropriately adjusted.

[0019] The steering shaft 130 includes three shafts, namely a column shaft 131, an intermediate shaft 132, and a pinion shaft 133, which are arranged in the order described from the steering member 110 side. In the power steering system, the attachment position of the worm reducer 150 is not particularly limited, but in the case of this embodiment, the worm reducer 150 is coupled to the pinion shaft 133.

[0020] Figure 2 1 is a cross-sectional view showing the internal structure of the worm reducer. As shown in the figure, the worm reducer 150 includes a worm shaft 164, a worm wheel 163, a housing 153, a bearing 161, a coil spring 170 and a preload member 155.

[0021] The housing 153 is a box-shaped structural member that accommodates the worm shaft 164 and the worm wheel 163, and is provided with a hole 154 extending through the housing 153 and an engaging portion 156 arranged outside the hole 154. A coil spring 170 is arranged in the hole 154. A preloading member 155 that pressurizes the coil spring 170 is attached to the engaging portion 156.

[0022] The hole 154 is a through hole extending from the outside of the housing 153 to the inside of the housing 153 in the radial direction of the bearing 161. The shape of the hole 154 is not particularly limited, but in the case of the present embodiment, the shape is cylindrical.

[0023] The engaging portion 156 is a cylindrical portion provided coaxially with the hole 154 and is provided with an internal thread on its inner peripheral surface.

[0024] The preloading member 155 is a member having external threads on its outer periphery that threadably engage with the engagement portion 156 of the housing 153. The preloading member 155 is fixed by being screwed into the engagement portion 156, and pressurizes the coil spring 170. Although the shape of the preloading member 155 is not particularly limited, in the present embodiment, the preloading member 155 is a cylindrical member (in other words, a columnar member). The preloading member 155 has a surface that contacts the coil spring 170, and this surface is a plane perpendicular to the winding axis of the coil spring 170 (the Z-axis direction in the figure).

[0025] Although there is no particular limitation on the manufacturing method of the preload member 155, in the case of the present embodiment, the preload member 155 is a forged product made of an iron material such as SS400 or S15C, and the surface of the preload member 155 that contacts the coil spring 170 is formed by forging and is not subjected to finishing such as cutting.

[0026] Worm shaft 164 is rotatably held in the worm shaft housing by bearing 161 and a second end bearing 162. Worm shaft 164 is tiltably held about second end bearing 162 and is urged toward worm wheel 163 by the urging force of coil spring 170. In this embodiment, worm shaft 164 is coupled to motor 152 and rotates at high speed about its axis.

[0027] The worm wheel 163 is rotatably held in the worm housing portion. In the present embodiment, the worm wheel 163 is coupled to the pinion shaft 133 and amplifies torque input to the worm shaft 164 to apply assist torque to the pinion shaft 133.

[0028] Bearing 161 holds one end of worm shaft 164 within housing 153. Bearing 161 is held so as to be reciprocatingly movable relative to housing 153 in a direction toward worm wheel 163 (Z-axis direction in the figure), and can tilt worm shaft 164 relative to other-end bearing 162 that holds the other end of worm shaft 164.

[0029] The material constituting the bearing 161 is not particularly limited, but in the case of the present embodiment, bearing steel (SUJ2 or the like) is used as the material of at least the outer ring of the bearing 161 .

[0030] Figure 3 This is a perspective view showing a coil spring, a bearing in contact with the coil spring, and the vicinity of the bearing. As shown in the figure, coil spring 170 is a compression spring that contacts the outer peripheral surface of bearing 161 and applies a force that pushes worm shaft 164 toward worm wheel 163 (toward the negative Z-axis direction in the figure) relative to preload member 155 screwed and fixed into housing 153.

[0031] One end of the coil spring 170 is supported by a preload member 155 screwed into a hole 154 of the housing 153, and the coil spring 170 presses the bearing 161 provided in the housing 153 by a thrust force. The material of the wire constituting the coil spring 170 is not particularly limited, but in the case of this embodiment, so-called music wire (SWP-B wire) is used.

[0032] The winding direction of coil spring 170 is set to the opposite direction of the winding direction of the thread of preload member 155. In the case of this embodiment, preload member 155 is provided with a right-handed thread on its outer peripheral surface. When preload member 155 rotates to the right (i.e., clockwise) relative to housing 153, preload member 155 moves toward bearing 161. Conversely, coil spring 170 is left-handed (i.e., the winding direction is left-handed). When the wire of coil spring 170 is viewed from preload member 155 toward bearing 161, the wire rotates to the left, in other words, the wire is wound to the left (in a counterclockwise direction).

[0033] The contact resistance between coil spring 170 and preload member 155 is greater than the contact resistance between coil spring 170 and the outer peripheral surface of the outer ring of bearing 161. In other words, when preload member 155 is screwed into housing 153, coil spring 170 rotates together with preload member 155 and is brought into a sliding state on bearing 161.

[0034] As described above, the positional relationship of the first distal end portion 171 of the coil spring 170, which is formed as the distal end of the wire of the coil spring (170), relative to the bearing 161 may fall within the range shown below. Figure 4As shown, it is assumed that in a plane (the XY plane in the figure) perpendicular to the urging direction of coil spring 170 (i.e., the direction in which coil spring 170 exerts its thrust), the point where the winding axis of coil spring 170 and the plane intersect is called vertex O. It is also assumed that the side of ridge line 169 on the outer circumferential surface of bearing 161 relative to vertex O (the right side in the figure) is defined as 0°, while the other side of ridge line 169 (the left side in the figure) is defined as 180°, and the angle increases counterclockwise. In this case, when the winding direction of coil spring 170 is counterclockwise toward bearing 161, there is a high probability that first distal end portion 171 will be arranged at an angle within the range of 0° < θ ≤ 135° (θ1 in the figure) or 180° < θ ≤ 315° (θ2 in the figure).

[0035] In the case of manufacturing the worm reducer 150 having the above-described configuration, the coil spring 170 wound in a direction opposite to the winding direction of the thread provided on the outer periphery of the preloading member 155 is inserted into the hole 154. Then, the preloading member 155 is screwed into the engagement portion 156 of the housing 153, thereby determining the position of the first distal end portion 171 relative to the ridge line 169 of the bearing 161, and the coil spring 170 is brought into a preloaded state. At the final stage of screwing the preloading member 155 into the housing 153, the preloading member 155 and the coil spring 170 slide relative to each other, whereby the preloading member 155 is attached to the housing 153.

[0036] Furthermore, coil spring 170, supported by preload member 155, pushes worm shaft 164 toward the worm wheel via bearing 161. The movement of pressurized bearing 161 causes worm shaft 164 to tilt relative to other-end bearing 162, and then meshes with worm wheel 163 while maintaining the interaxial distance between worm shaft 164 and worm wheel 163. This interaxial distance suppresses backlash between the two. This provides the so-called anti-backlash system (ABLS) of this embodiment.

[0037] Specifically, worm shaft 164 and the output shaft of motor 152 are connected via a rubber spring made of an elastic material, allowing worm shaft 164 to tilt relative to the output shaft of motor 152. Bearing 162 on the other end of the motor 152 side supporting worm shaft 164 is a rolling bearing. This bearing 162 has an outer ring fixed to housing 153 and an inner ring connected to worm shaft 164. The inner ring is allowed to tilt relative to the outer ring. Meanwhile, bearing 161 on the opposite side of the worm shaft 164 is located in housing 153, allowing movement in the direction in which bearing 161 contacts and separates from worm wheel 163 (the Z-axis direction in the figure). The outer ring of bearing 161 is a rolling bearing, which is urged toward worm wheel 163 by the elastic force of coil spring 170.

[0038] With the worm reducer 150 having the above-described configuration, even when vibration is applied to the coil spring 170 or the coil spring 170 is repeatedly extended, the position of the first distal end portion 171 can be maintained and stick-slip noise generated between the coil spring 170 and the bearing 161 can be continuously suppressed simply by setting the coil spring 170 at a predetermined position and screwing the preload member 155 into the housing 153. Furthermore, since the worm shaft 164 is tilted about the other-end bearing 162 and the optimal interaxial distance between the worm shaft 164 and the worm wheel 163 is maintained, even when a sudden torque is generated in the worm shaft 164, a hitting sound can be suppressed.

[0039] Note that the present invention is not limited to the above embodiments. For example, another embodiment achieved by arbitrarily combining the components described in this specification or by excluding some components may be considered an embodiment of the present invention. The present invention includes modified examples that can be obtained by making various modifications to the above embodiments that occur to those skilled in the art without departing from the scope of the present invention.

[0040] For example, in a case where the preloading member 155 has a left-handed thread on its outer periphery and the preloading member 155 advances toward the bearing 161 when rotated leftward (in a counterclockwise direction) relative to the housing 153, the coil spring 170 is right-handed (i.e., the winding direction is a right-handed direction), and when the wire of the coil spring 170 is observed from the preloading member 155 toward the bearing 161, the wire is rotated to the right, i.e., the wire is wound to the right (in a clockwise direction).

[0041] In this case, if Figure 5 As shown, the winding direction of the coil spring 170 is clockwise toward the bearing 161. Therefore, there is a high possibility that the first distal portion 171 is arranged in an angular range of 45°≤θ<180° (θ3 in the figure) or 225°≤θ<360° (θ4 in the figure).

[0042] The surface of the preload member 155 in contact with the coil spring 170 can be a plane or a rotation surface with the winding axis of the coil spring 170 as the rotation axis, such as a conical surface (i.e., a conical surface) or a hemispherical surface (i.e., a hemispherical surface).

[0043] The present invention is applicable to a worm reducer including a coil spring as a component of an anti-backlash system.

Claims

1. A worm reducer, characterized in that: include: worm shaft (164); worm gear (163); a housing (153), the housing (153) accommodating the worm shaft (164) and the worm wheel (163); a bearing that holds the worm shaft (164) within the housing (153); a coil spring (170) that contacts an outer peripheral surface of the bearing and applies a thrust toward the worm gear (163); as well as a preloading member (155) which is screwed into the housing (153) and fixed to the housing (153) and which pressurizes the coil spring (170), wherein the winding direction of the coil spring (170) is different from the winding direction of the thread of the preloading member (155), and the contact resistance between the coil spring (170) and the preloading member (155) is greater than the contact resistance between the coil spring (170) and the bearing, The position of the first distal end portion as the distal end of the wire forming the coil spring (170) is arranged within a predetermined circumferential range centered on the winding axis of the coil spring so that the distal end is located on one side of the bearing.

2. The worm reducer according to claim 1, characterized in that: The preloading member (155) has a surface in contact with the coil spring (170), and the surface is a plane perpendicular to the winding axis of the coil spring (170) or a rotation surface with the winding axis as the rotation axis.

3. A method for manufacturing a worm reducer, the worm reducer comprising: A worm shaft (164), a worm wheel (163), a housing (153) accommodating the worm shaft (164) and the worm wheel (163), a bearing holding the worm shaft (164) in the housing (153), a coil spring (170) contacting an outer peripheral surface of the bearing and applying a thrust toward the worm wheel (163), and a preloading member (155) screwed into and fixed to the housing (153) and pressurizing the coil spring (170), The method is characterized by comprising: arranging the coil spring (170) so that one end of the coil spring (170) in the winding axis direction contacts the bearing; and Screwing the preload member (155) into the housing (153), wherein the winding direction of the coil spring (170) is different from the winding direction of the thread of the preloading member (155), The contact resistance between the coil spring (170) and the preload member (155) is greater than the contact resistance between the coil spring (170) and the bearing, wherein, in the initial stage of screwing the preloading member (155) into the housing (153), the coil spring (170) rotates together with the preloading member (155), and In which, in the final stage of screwing the preloading member (155) into the housing (153), the position of the first distal end portion of the wire forming the distal end of the coil spring (170) is configured within a predetermined circumferential range centered on the winding axis of the coil spring, so that the distal end is located on one side of the bearing, and the preloading member (155) and the coil spring (170) slide relative to each other in the circumferential direction, whereby the preloading member (155) is attached to the housing (153) toward the bearing.

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