JP2020098017A - Worm speed reducer and electric power steering device - Google Patents

Abstract

To provide a worm speed reducer which can inhibit occurrence of abnormal noise between a buffer member and an outer peripheral surface of a bearing.SOLUTION: A worm speed reducer 40 includes: a housing 42; a worm shaft 44 which has a first end part 56 and a second end part 58; a worm wheel 50 which engages with the worm shaft 44; a second bearing 48 which rotatably supports the second end part 58 of the worm shaft 44; a biasing member 52 which biases the second end part 58 of the worm shaft 44 to the worm wheel 50 side; and a buffer member 54 which is disposed between the housing 42 and an outer peripheral surface of the second bearing 48. An inner peripheral surface 66a of the buffer member 54 is formed with a rough surface part 72 for releasing air between the inner peripheral surface 66a and the outer peripheral surface 48a of the second bearing 48. Surface roughness Ra of the rough surface part 72 ranges from 2.5 μm or more to 50 μm or less.SELECTED DRAWING: Figure 4

Description

The present invention relates to a worm speed reducer and an electric power steering apparatus including the worm speed reducer.

A worm speed reducer is mounted on the electric power steering device. A worm reducer includes a housing, an electric motor supported by the housing, a worm shaft connected to the electric motor, a worm wheel that meshes with the worm shaft, a bearing that supports the tip of the worm shaft, and a tip of the worm shaft. And a coil spring for urging the portion toward the worm wheel. The coil spring is for removing backlash between the worm shaft and the worm wheel.

The bearing described above is not fixed to the housing. Therefore, when each of the worm shaft and the worm wheel rotates, a load acts on the tip portion of the worm shaft from the worm wheel, and the tip portion of the worm shaft is displaced in a direction away from the worm wheel. At this time, due to the collision between the housing and the outer peripheral surface of the bearing, a tapping sound is generated between the housing and the outer peripheral surface of the bearing. In order to reduce the hitting sound, in the worm speed reducer disclosed in Patent Document 1, a cushioning member made of rubber or the like is interposed between the housing and the outer peripheral surface of the bearing.

JP, 2005-182597, A

However, in the conventional worm reducer described above, when the tip end of the worm shaft is displaced in the direction away from the worm wheel, the air existing between the cushioning member and the outer peripheral surface of the bearing bursts, resulting in abnormal noise. There is a problem that (plosive sound of air) is generated.

The present invention is intended to solve the above-described problems, and an object thereof is to provide a worm speed reducer capable of suppressing generation of abnormal noise between the cushioning member and the outer peripheral surface of the bearing, and a worm speed reducer including the same. To provide an electric power steering device.

In order to achieve the above object, a worm speed reducer according to an aspect of the present invention includes a housing, a worm shaft disposed inside the housing, and a first end connected to an electric motor. A worm shaft having a second end opposite to the first end; a worm wheel rotatably supported inside the housing and meshing with the worm shaft; A bearing that rotatably supports the second end, a biasing member that biases the second end of the worm shaft toward the worm wheel, and an intervening member between the housing and the outer peripheral surface of the bearing. And a buffer member having a contact surface facing the outer peripheral surface of the bearing, wherein the second end portion of the worm shaft is displaced with respect to the worm wheel on the contact surface of the buffer member. By doing so, when the outer peripheral surface of the bearing comes into contact with the contact surface, a rough surface portion is formed for allowing air between the contact surface and the outer peripheral surface of the bearing to escape to the outside, and The surface roughness Ra of the rough surface portion is 2.5 μm or more and 50 μm or less.

According to the worm speed reducer and the like according to the aspect of the present invention, it is possible to suppress generation of abnormal noise between the cushioning member and the outer peripheral surface of the bearing.

1 is a schematic diagram showing a configuration of an electric power steering device according to a first embodiment. FIG. 3 is a cross-sectional view showing the configuration of the worm speed reducer according to the first embodiment. FIG. 3 is a cross-sectional view of the worm reducer according to the first embodiment taken along the line III-III in FIG. 2. FIG. 3 is a perspective view showing a cushioning member according to the first embodiment. FIG. 5 is a perspective view showing a cushioning member according to Embodiment 1 when viewed from an angle different from FIG. 4. 5 is a graph showing the results of a sensory evaluation test for confirming the effects obtained by the worm speed reducer according to the first embodiment. FIG. 7 is a perspective view showing a cushioning member according to the second embodiment. It is a perspective view which shows the buffer member which concerns on Embodiment 3. It is a perspective view which shows the buffer member which concerns on Embodiment 4.

Next, embodiments of a worm speed reducer and an electric power steering device according to the present invention will be described with reference to the drawings. It should be noted that each of the embodiments described below shows a comprehensive or specific example. Numerical values, shapes, materials, components, arrangement positions and connection forms of components, steps, order of steps, and the like shown in the following embodiments are examples, and are not intended to limit the present invention. Further, among the constituent elements in the following embodiments, the constituent elements that are not described in the independent claim indicating the highest concept are described as arbitrary constituent elements.

In addition, the drawings are schematic diagrams in which the present invention is appropriately emphasized or omitted, and the ratios are adjusted, and may differ from the actual shapes, positional relationships, and ratios.

(Embodiment 1)
First, the configuration of the electric power steering device 2 according to the first embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing a configuration of an electric power steering device 2 according to the first embodiment.

The electric power steering device 2 according to the first embodiment is mounted in a vehicle such as an automobile. As shown in FIG. 1, the electric power steering apparatus 2 includes a steering shaft 6 connected to a steering wheel 4, an intermediate shaft 10 connected to the steering shaft 6 via a universal joint 8, and a universal joint to the intermediate shaft 10. A pinion shaft 14 connected via 12 and a rack bar 16 meshing with the pinion shaft 14 are provided.

The steering shaft 6 includes a first steering shaft 18 connected to the steering wheel 4, a second steering shaft 20 connected to the intermediate shaft 10 via a universal joint 8, a first steering shaft 18 and a second steering shaft 18. And a torsion bar 22 that rotatably connects the steering shaft 20 and the steering shaft 20 on the same straight line.

The rack bar 16 is arranged so as to be capable of reciprocating in the left-right direction with respect to a vehicle body (not shown). Both ends of the rack bar 16 are connected to a pair of steered wheels 26 via a pair of tie rods 24. A pinion 28 is provided at the end of the pinion shaft 14, and a rack 30 that meshes with the pinion 28 is provided at the rack bar 16. The pinion 28 and the rack 30 constitute a steering mechanism for steering the pair of steered wheels 26.

When the driver steers the steering wheel 4, the steering shaft 6 rotates. The rotation of the steering shaft 6 is transmitted to the pinion shaft 14 via the intermediate shaft 10 and then converted into a linear motion of the rack bar 16 in the left-right direction by the pinion 28 and the rack 30. As a result, the pair of steered wheels 26 are steered.

The electric power steering device 2 further includes a torque sensor 32, an ECU (Electronic Control Unit) 34, a drive circuit 36, an electric motor 38, and a worm speed reducer 40.

The torque sensor 32 detects the steering torque of the steering wheel 4 based on the relative rotational displacement amount between the first steering shaft 18 and the second steering shaft 20. The torque sensor 32 outputs the detected steering torque to the ECU 34.

The ECU 34 is an electronic control unit for controlling the drive circuit 36. The ECU 34 generates a control signal based on the steering torque from the torque sensor 32, and outputs the generated control signal to the drive circuit 36.

The drive circuit 36 is a circuit for driving the electric motor 38. The drive circuit 36 drives the electric motor 38 based on a control signal from the ECU 34 to control the rotation amount, the rotation direction, and the like of the electric motor 38.

The electric motor 38 is a drive source that generates a drive force for assisting the steering of the steering wheel 4.

The worm reducer 40 reduces the rotation of the electric motor 38. The rotation of the electric motor 38 is reduced by the worm speed reducer 40, and then transmitted to the pinion shaft 14 via the second steering shaft 20 and the intermediate shaft 10 of the steering shaft 6 to linearly move the rack bar 16 in the left-right direction. Is converted to. This assists the driver in steering the steering wheel 4.

Next, the configuration of the worm reducer 40 according to the first embodiment will be described with reference to FIGS. 2 and 3. FIG. 2 is a cross-sectional view showing the configuration of the worm speed reducer 40 according to the first embodiment. FIG. 3 is a cross-sectional view of the worm reducer 40 according to the first embodiment taken along the line III-III in FIG.

As shown in FIG. 2, the worm reducer 40 includes a housing 42, a worm shaft 44, a first bearing 46, a second bearing 48 (an example of a bearing), a worm wheel 50, and a biasing member 52. And a cushioning member 54.

The housing 42 is formed in a hollow shape and is fixed to the vehicle body. The electric motor 38 described above is supported inside the housing 42.

The worm shaft 44 extends linearly along the first axial direction (X-axis direction) and is arranged inside the housing 42. The worm shaft 44 includes a first end portion 56, a second end portion 58 opposite to the first end portion 56 in the first axial direction, a first end portion 56 and a second end portion. 58 and a meshing portion 60 formed on the outer peripheral surface thereof. The meshing portion 60 has a plurality of teeth (not shown) that spirally extend along the first axial direction. The first end 56 of the worm shaft 44 is connected to the electric motor 38 and is fixed to the inside of the housing 42 via the first bearing 46. The second end 58 of the worm shaft 44 is not fixed inside the housing 42 via the second bearing 48, and is displaceable in the radial direction with respect to the worm wheel 50. That is, the worm shaft 44 projects from the electric motor 38 in the shape of a cantilever. The worm shaft 44 rotates around the first axial direction by the driving force of the electric motor 38.

Each of the first bearing 46 and the second bearing 48 is, for example, a ball bearing, and is formed in an annular shape. The first bearing 46 is fixed inside the housing 42 and rotatably supports the first end portion 56 of the worm shaft 44. The second bearing 48 is not fixed inside the housing 42, but rotatably supports the second end portion 58 of the worm shaft 44. As shown in FIG. 3, a gap 62 is formed between the outer peripheral surface 48 a of the second bearing 48 and the inner surface 42 a of the housing 42. As a result, the second end portion 58 of the worm shaft 44 is displaceable with respect to the worm wheel 50 in a direction away from the worm wheel 50 and a direction approaching the worm wheel 50.

The worm wheel 50 is formed in an annular shape and is rotatably supported inside the housing 42. The worm wheel 50 is rotatably connected integrally with the second steering shaft 20 (see FIG. 1) of the steering shaft 6. A tooth portion 64 having a plurality of teeth (not shown) is formed on the outer peripheral surface of the worm wheel 50. The teeth of the tooth portion 64 mesh with the teeth of the meshing portion 60 of the worm shaft 44. The rotation of the electric motor 38 is transmitted to the worm wheel 50 via the worm shaft 44. As a result, the worm wheel 50 rotates around the second axial direction (Y-axis direction), and the second steering shaft 20 of the steering shaft 6 rotates integrally with the worm wheel 50. The rotation of the electric motor 38 is decelerated when being transmitted from the worm shaft 44 to the worm wheel 50.

The urging member 52 is for removing backlash between the meshing portion 60 of the worm shaft 44 and the tooth portion 64 of the worm wheel 50, and constitutes a so-called ABLS (Anti-Backlash System) structure. The biasing member 52 is formed of, for example, a coil spring, and is arranged between the outer peripheral surface 48 a of the second bearing 48 and the inner surface 42 a of the housing 42. As shown by an arrow P in FIG. 2, the biasing member 52 biases the second end portion 58 of the worm shaft 44 toward the worm wheel 50 via the second bearing 48. As a result, the meshing portion 60 of the worm shaft 44 is pressed against the tooth portion 64 of the worm wheel 50 by the urging force of the urging member 52, so that the meshing portion 60 of the worm shaft 44 and the tooth portion 64 of the worm wheel 50 are separated from each other. The backlash can be eliminated.

The buffer member 54 is a damper for suppressing the collision between the inner surface 42a of the housing 42 and the outer peripheral surface 48a of the second bearing 48, and is made of an elastic material such as rubber or elastomer. As shown in FIG. 3, the cushioning member 54 is interposed in the gap 62 between the inner surface 42 a of the housing 42 and the outer peripheral surface 48 a of the second bearing 48.

Here, the configuration of the cushioning member 54 will be described in detail with reference to FIGS. 2 to 5. FIG. 4 is a perspective view showing cushioning member 54 according to the first embodiment. FIG. 5 is a perspective view showing the cushioning member 54 according to the first embodiment when viewed from an angle different from that in FIG.

As shown in FIGS. 4 and 5, the cushioning member 54 has a cushioning portion 66 and a connecting portion 68. The buffer portion 66 and the connecting portion 68 are integrally formed.

As shown in FIGS. 4 and 5, the buffer portion 66 is formed in a semi-cylindrical shape (an example of a semi-cylindrical shape). As shown in FIG. 3, the buffer portion 66 is interposed in the gap 62 between the inner surface 42 a of the housing 42 and the outer peripheral surface 48 a of the second bearing 48. The inner peripheral surface 66a (an example of a contact surface) of the buffer portion 66 is arranged on the side opposite to the worm wheel 50 with respect to the second bearing 48, and arranged so as to face the outer peripheral surface 48a of the second bearing 48. To be done. As shown in FIG. 3, in a state where the second end portion 58 of the worm shaft 44 is not displaced with respect to the worm wheel 50 in the direction away from the worm wheel 50, the inner peripheral surface 66a of the buffer portion 66 and the second end portion 58 are not moved. An air layer 70 is formed between the outer surface 48 a of the second bearing 48.

As shown in FIG. 4, a rough surface portion 72 having a large number of minute irregularities is formed on the inner peripheral surface 66a of the buffer portion 66. In the rough surface portion 72, the second end portion 58 of the worm shaft 44 is displaced with respect to the worm wheel 50 in a direction away from the worm wheel 50, so that the outer peripheral surface 48 a of the second bearing 48 is an inner peripheral surface of the buffer portion 66. This is for allowing the air existing in the air layer 70 to escape to the outside when it comes into contact with the surface 66a. The surface roughness Ra of the rough surface portion 72 is 2.5 μm or more and 50 μm or less. For convenience of description, in FIGS. 4 and 5, the rough surface portion 72 is shown as a mesh pattern. Although the rough surface portion 72 is formed on the inner peripheral surface 66a of the buffer portion 66 in the present embodiment, the rough surface portion may be formed on the entire surface of the buffer member 54.

As shown in FIGS. 4 and 5, a semi-circular cutout portion 74 is formed on the side edge of the central portion of the cushioning portion 66 in the circumferential direction to avoid interference between the biasing member 52 and the cushioning portion 66. Has been done. As shown in FIGS. 2 and 3, the biasing member 52 is arranged in a state of being released into the cutout portion 74. Further, on the outer peripheral surface 66b of the cushioning portion 66 (the surface on the side opposite to the inner peripheral surface 66a in the thickness direction of the cushioning portion 66), there is formed a rotation restricting projection 76 that projects radially outward. As shown in FIG. 2, the rotation restricting projection 76 is engaged with the rotation restricting recess 78 formed on the inner surface 42 a of the housing 42. As a result, circumferential rotation of the cushioning member 54 with respect to the housing 42 is restricted.

As shown in FIGS. 4 and 5, the connecting portion 68 connects between both ends of the buffer portion 66 in the circumferential direction. As shown in FIG. 2, the connecting portion 68 is arranged so as to face the end surface 58 a of the second end portion 58 of the worm shaft 44. As shown in FIG. 2, the connecting portion 68 is sandwiched between the end cover 80 attached to the opening of the housing 42 and the end surface 58a of the second end portion 58 of the worm shaft 44. As a result, the movement of the buffer member 54 with respect to the housing 42 in the first axial direction (X-axis direction) is restricted.

The effects obtained by the worm speed reducer 40 according to the first embodiment will be described below. As indicated by an arrow Q in FIG. 3, when the worm shaft 44 and the worm wheel 50 rotate, a load acts from the worm wheel 50 to the second end portion 58 of the worm shaft 44, thereby causing the worm shaft 44 to move. A second end 58 of the worm wheel is displaced relative to the worm wheel 50 in a direction away from the worm wheel 50. As a result, the outer peripheral surface 48a of the second bearing 48 contacts the inner peripheral surface 66a of the buffer portion 66, and the air layer between the inner peripheral surface 66a of the buffer portion 66 and the outer peripheral surface 48a of the second bearing 48 is formed. 70 is crushed.

At this time, as described above, since the rough surface portion 72 having the surface roughness Ra of 2.5 μm or more and 50 μm or less is formed on the inner peripheral surface 66 a of the buffer portion 66, the inner peripheral surface 66 a of the buffer portion 66. A large number of minute gaps are formed between and the outer peripheral surface 48a of the second bearing 48. As a result, the air existing in the air layer 70 between the inner peripheral surface 66a of the buffer portion 66 and the outer peripheral surface 48a of the second bearing 48 escapes to the outside through the numerous minute gaps described above without bursting. Will be As a result, it is possible to suppress generation of abnormal noise (burst of air) between the inner peripheral surface 66a of the buffer portion 66 and the outer peripheral surface 48a of the second bearing 48.

When the surface roughness Ra of the rough surface portion 72 is less than 2.5 μm, when the second end portion 58 of the worm shaft 44 is displaced with respect to the worm wheel 50 in the direction away from the worm wheel 50, A minute gap is hardly formed between the outer peripheral surface 48a of the second bearing 48 and the inner peripheral surface 66a of the buffer portion 66. As a result, the air existing in the air layer 70 between the inner peripheral surface 66a of the buffer portion 66 and the outer peripheral surface 48a of the second bearing 48 bursts without being released to the outside, and abnormal noise is generated. When the surface roughness Ra of the rough surface portion 72 exceeds 50 μm, the contact position of the second shaft portion 48 with respect to the inner peripheral surface 66a (rough surface portion 72) of the buffer portion 66 varies as described later. At this time, the noise level of the abnormal noise varies. The surface roughness Ra of the rough surface portion 72 is preferably 2.5 μm or more and 50 μm or less, and more preferably 4.5 μm or more and 16 μm or less.

In order to confirm the effects described above, the following sensory evaluation test was performed. In the worm reducer, the worm reducer was operated while sequentially exchanging a plurality of types of cushioning members having different surface roughness Ra. At that time, the subject was placed in the vicinity of the worm reducer, and sensory evaluation was performed by the subject based on the criteria of “abnormal noise was generated” and “abnormal noise was not generated”.

The result of the sensory evaluation test was as shown in FIG. FIG. 6 is a graph showing the results of a sensory evaluation test for confirming the effect obtained by the worm speed reducer 40 according to the first embodiment. 6, the horizontal axis represents the surface roughness Ra (μm) of the cushioning member, and the vertical axis represents the noise level (dB(A)) of the sound generated from the worm speed reducer.

As shown in FIG. 6, when the surface roughness Ra was less than 2.5 μm, abnormal noise was generated from the worm speed reducer, but when the surface roughness Ra was 2.5 μm or more, abnormal noise was not generated from the worm speed reducer. From this, it was confirmed that by setting the surface roughness Ra of the cushioning member to 2.5 μm or more and 50 μm or less, generation of abnormal noise from the worm speed reducer can be suppressed.

Here, an advantageous effect obtained by the worm speed reducer 40 according to the first embodiment when compared with the worm speed reducer disclosed in Patent Document 1 will be described.

In the worm speed reducer disclosed in Patent Document 1, a plurality of relatively large protrusions are formed on the inner peripheral surface of the buffer member (see FIG. 11(d) of Patent Document 1). However, such a configuration has the following problems. When the cushioning member is assembled to the housing, a cushioning member assembly error occurs in the circumferential direction (rotational direction). Further, a processing error occurs when processing a plurality of protrusions on the inner peripheral surface of the cushioning member. Further, when a load is applied from the worm wheel to the second end of the worm shaft, the direction in which the second end of the worm shaft is displaced with respect to the worm wheel is not constant. As a result, the contact position of the second shaft portion with respect to the cushioning member varies, so that the second shaft portion contacts, for example, the position of the protrusion of the cushioning member, or is located at a position between two adjacent protrusions. Contact them. As a result, the noise level of the abnormal noise generated from the worm speed reducer varies, and the durability of the cushioning member is not stable.

On the other hand, in the worm speed reducer 40 according to the first embodiment, as described above, the inner peripheral surface 66a of the buffer portion 66 has the rough surface portion 72 having the surface roughness Ra of 2.5 μm or more and 50 μm or less. Has been formed. As a result, even if the contact position of the second shaft portion 48 with respect to the inner peripheral surface 66a (rough surface portion 72) of the buffer portion 66 varies, the inner peripheral surface 66a of the buffer portion 66 and the second bearing. A large number of minute gaps formed between the outer peripheral surface 48a of 48 are substantially constant. As a result, it is possible to effectively suppress the generation of abnormal noise from the worm speed reducer 40 and stabilize the durability of the cushioning member 54.

(Embodiment 2)
Next, the configuration of the cushioning member 54A according to the second embodiment will be described with reference to FIG. FIG. 7 is a perspective view showing a cushioning member 54A according to the second embodiment. In addition, in each of the following embodiments, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 7, in the cushioning member 54A according to the second embodiment, a plurality of protrusions 82 are provided on the inner peripheral surface 66a of the cushioning section 66A, in addition to the rough surface section 72 described in the first embodiment. Has been formed.

The plurality of protrusions 82 are arranged at intervals along the circumferential direction of the cushioning portion 66A. In addition, each of the plurality of protrusions 82 extends linearly along the width direction (X-axis direction) of the buffer portion 66A. The surface roughness Ra of each of the plurality of protrusions 82 is 2.5 μm or more and 50 μm or less, like the rough surface portion 72.

When the second end portion 58 (see FIG. 2) of the worm shaft 44 is displaced with respect to the worm wheel 50 (see FIG. 2) in the direction away from the worm wheel 50, the outer peripheral surface 48a of the second bearing 48 (see FIG. 2) comes into contact with the inner peripheral surface 66a of the buffer portion 66A. At this time, since the outer peripheral surface 48a of the second bearing 48 contacts the plurality of protrusions 82, the air layer 70 is formed between the inner peripheral surface 66a of the buffer portion 66A and the outer peripheral surface 48a of the second bearing 48. A gap for letting air existing in (see FIG. 3) escape to the outside is formed. As a result, it is possible to suppress generation of abnormal noise between the inner peripheral surface 66a of the buffer portion 66A and the outer peripheral surface 48a of the second bearing 48.

(Embodiment 3)
Next, the configuration of the cushioning member 54B according to the third embodiment will be described with reference to FIG. FIG. 8 is a perspective view showing a cushioning member 54B according to the third embodiment.

As shown in FIG. 8, in the buffer member 54B according to the third embodiment, a plurality of recesses 84 are formed on the inner peripheral surface 66a of the buffer portion 66B in addition to the rough surface portion 72 described in the first embodiment. Has been done.

The plurality of concave portions 84 are arranged at intervals along the circumferential direction of the buffer portion 66B. Further, each of the plurality of recesses 84 extends linearly along the width direction (X-axis direction) of the buffer portion 66B. The surface roughness Ra of each of the plurality of recesses 84 is 2.5 μm or more and 50 μm or less, like the rough surface portion 72.

When the second end portion 58 (see FIG. 2) of the worm shaft 44 is displaced with respect to the worm wheel 50 (see FIG. 2) in the direction away from the worm wheel 50, the outer peripheral surface 48a of the second bearing 48 (see FIG. 2) comes into contact with the inner peripheral surface 66a of the buffer portion 66B. At this time, the air existing in the air layer 70 (see FIG. 3) between the inner peripheral surface 66a of the buffer portion 66B and the outer peripheral surface 48a of the second bearing 48 is allowed to escape to the outside through the plurality of recesses 84. Become. As a result, it is possible to suppress the generation of abnormal noise between the inner peripheral surface 66a of the buffer portion 66B and the outer peripheral surface 48a of the second bearing 48.

(Embodiment 4)
Next, the configuration of the cushioning member 54C according to the fourth embodiment will be described with reference to FIG. FIG. 9 is a perspective view showing a buffer member 54C according to the fourth embodiment.

As shown in FIG. 9, a plurality of slits 86 are formed in the buffer portion 66C of the buffer member 54C according to the fourth embodiment. The rough surface portion 72 described in the first embodiment is formed on the inner peripheral surface 66a of the buffer portion 66C.

The plurality of slits 86 are arranged at intervals along the circumferential direction of the buffer section 66C. In addition, each of the plurality of slits 86 penetrates from the inner peripheral surface 66a to the outer peripheral surface 66b of the cushioning portion 66C and extends linearly along the width direction (X-axis direction) of the cushioning portion 66C.

When the second end portion 58 (see FIG. 2) of the worm shaft 44 is displaced with respect to the worm wheel 50 (see FIG. 2) in the direction away from the worm wheel 50, the outer peripheral surface 48a of the second bearing 48 (see FIG. 2) comes into contact with the inner peripheral surface 66a of the buffer portion 66C. At this time, the air existing in the air layer 70 (see FIG. 3) between the inner peripheral surface 66a of the buffer portion 66C and the outer peripheral surface 48a of the second bearing 48 is allowed to escape to the outside through the plurality of slits 86. Become. As a result, it is possible to suppress the generation of abnormal noise between the inner peripheral surface 66a of the buffer portion 66C and the outer peripheral surface 48a of the second bearing 48.

Although the rough surface portion 72 is formed on the inner peripheral surface 66a of the buffer portion 66C in the present embodiment, the rough surface portion 72 may be omitted. Even in the case of such a configuration, the same effect as described above can be obtained.

(Modifications, etc.)
The present invention is not limited to the above embodiments. For example, another embodiment realized by arbitrarily combining the constituent elements described in this specification or excluding some of the constituent elements may be an embodiment of the present invention. Further, the present invention is also a modified example obtained by applying various modifications to the above-described embodiments to the gist of the present invention, that is, a range that does not deviate from the meaning indicated by the wording described in the claims. include.

The worm reducer according to the present invention is applicable to, for example, an electric power steering device.

2: Electric power steering device, 4: Steering wheel, 6: Steering shaft, 8, 12: Universal joint, 10: Intermediate joint, 14: Pinion shaft, 16: Rack bar, 18: First steering shaft, 20: No. 2 steering shaft, 22: torsion bar, 24: tie rod, 26: steered wheel, 28: pinion, 30: rack, 32: torque sensor, 34: ECU, 36: drive circuit, 38: electric motor, 40: worm deceleration Machine, 42: housing, 42a: inner surface, 44: worm shaft, 46: first bearing, 48: second bearing, 48a, 66b: outer peripheral surface, 50: worm wheel, 52: biasing member, 54, 54A , 54B, 54C: buffer member, 56: first end portion, 58: second end portion, 58a: end surface, 60: meshing portion, 62: gap, 64: tooth portion, 66, 66A, 66B, 66C: Buffer part, 66a: Inner peripheral surface, 68: Connection part, 70: Air layer, 72: Rough surface part, 74: Notch part, 76: Rotation restriction projection, 78: Rotation restriction recess, 80: End cover, 82: protrusion, 84: recess, 86: slit

Claims (7)

Housing,
A worm shaft disposed inside the housing, the worm shaft having a first end coupled to an electric motor and a second end opposite to the first end. ,
A worm wheel that is rotatably supported inside the housing and that meshes with the worm shaft;
A bearing that rotatably supports the second end of the worm shaft;
A biasing member that biases the second end of the worm shaft toward the worm wheel;
A cushioning member interposed between the housing and the outer peripheral surface of the bearing and having a contact surface facing the outer peripheral surface of the bearing,
When the second end of the worm shaft is displaced with respect to the worm wheel, the contact surface of the cushioning member contacts the contact surface when the outer peripheral surface of the bearing contacts the contact surface. A rough surface portion is formed for allowing air between the surface and the outer peripheral surface of the bearing to escape to the outside,
The surface roughness Ra of the rough surface portion is 2.5 μm or more and 50 μm or less. Worm reducer. The contact surface of the buffer member is further provided with a protrusion for releasing air between the contact surface and the outer peripheral surface of the bearing to the outside when the outer peripheral surface of the bearing contacts the contact surface. The worm reducer according to claim 1, wherein a portion is formed. In the contact surface of the buffer member, when the outer peripheral surface of the bearing comes into contact with the contact surface, a recess for releasing air between the contact surface and the outer peripheral surface of the bearing to the outside. The worm reducer according to claim 1, wherein the worm reducer is formed. The cushioning member is a slit that penetrates from the contact surface to a surface opposite to the contact surface, and when the outer peripheral surface of the bearing contacts the contact surface, the contact surface and the contact surface The worm speed reducer according to claim 1, wherein a slit is formed to allow air between the bearing and the outer peripheral surface to escape to the outside. The cushioning member,
A semi-cylindrical buffer portion arranged so that the inner peripheral surface faces the outer peripheral surface of the bearing, the buffer portion in which the contact surface is formed on the inner peripheral surface,
5. A connecting portion that connects between both ends in the circumferential direction of the buffer portion and that is arranged so as to face the end surface of the second end portion of the worm shaft. Worm reducer described in. Housing,
A worm shaft disposed inside the housing, the worm shaft having a first end coupled to an electric motor and a second end opposite to the first end. ,
A worm wheel that is rotatably supported inside the housing and that meshes with the worm shaft;
A bearing that rotatably supports the second end of the worm shaft;
A biasing member that biases the second end of the worm shaft toward the worm wheel;
A cushioning member interposed between the housing and the outer peripheral surface of the bearing,
The cushioning member,
A semi-cylindrical cushioning portion having an inner peripheral surface facing the outer peripheral surface of the bearing,
A connecting portion that connects between both end portions in the circumferential direction of the buffer portion and that is arranged so as to face an end surface of the second end portion of the worm shaft,
The buffer portion is a slit penetrating from the inner peripheral surface to a surface opposite to the inner peripheral surface, and the second end portion of the worm shaft is displaced with respect to the worm wheel. When the outer peripheral surface of the bearing comes into contact with the inner peripheral surface of the buffer portion, a slit is formed to release air between the inner peripheral surface and the outer peripheral surface of the bearing to the outside. Worm reducer. An electric power steering device comprising the worm speed reducer according to claim 1.

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