Joint device and motor

A joint device includes a drive rotor fixed to a drive shaft, a driven rotor fixed to a driven shaft, and a ring-shaped buffer located between the drive rotor and the driven rotor. The drive rotor includes a drive engagement portion that projects toward the driven rotor in an axial direction. The driven rotor includes a driven engagement portion that projects toward the drive rotor in the axial direction. The buffer includes an outer surface, which includes a first engagement recess and a second engagement recess that are recessed toward a radially inner side. An outer diameter of a bottom surface of the second engagement recess is smaller than an inner diameter of the driven engagement portion or an outer diameter of a bottom surface of the first engagement recess is smaller than an inner diameter of the drive engagement portion.

BACKGROUND ART

The present invention relates to a joint device and a motor.

Japanese Laid-Open Patent Publication No. 2002-364713 describes a prior art example of a motor in which a drive shaft of a motor body and a driven shaft (referred to as “worm shaft” in the publication) are coupled by a joint device so that the rotation generated by the motor body is transmitted from the drive shaft to the driven shaft by the joint device.

The above joint device includes a drive rotor fixed to the drive shaft of the motor body, a driven rotor fixed to the driven shaft, and a ring-shaped buffer (rubber member) located between the drive rotor and the driven rotor. The drive rotor and the driven rotor each include an engagement portion. The engagement portions project in an axial direction toward each other. The outer surface of the buffer includes a first engagement recess and a second engagement recess respectively receiving the drive engagement portion and the driven engagement portion. The drive engagement portion contacts the first engagement recess of the buffer in the rotation direction, and the driven engagement portion contacts the second engagement recess of the buffer in the rotation direction. This transmits a rotation force from the drive engagement portion to the driven engagement portion through the buffer. Thus, the buffer absorbs the impact produced when rotation is transmitted in the joint device.

However, if coupling tolerances result in misalignment between the drive shaft and the driven shaft, resistance that occurs between the drive engagement portion and the driven engagement portion in the joint device may hinder the smooth transmission of rotation. Although the above publication describes that the elasticity of the buffer allows for misalignment between the drive shaft and the driven shaft, rotation cannot be smoothly transmitted only by the elasticity of the buffer.

SUMMARY OF THE INVENTION

It is an object of the present invention is to provide a joint device and a motor capable of smoothly transmitting rotation even when a drive shaft and a driven shaft are misaligned.

To achieve the above object, a joint device of one embodiment of the present invention includes a drive rotor fixed to a drive shaft, a driven rotor fixed to a driven shaft, and a ring-shaped buffer located between the drive rotor and the driven rotor. The drive rotor includes a drive engagement portion that projects toward the driven rotor in an axial direction. The driven rotor includes a driven engagement portion that projects toward the drive rotor in the axial direction. The buffer includes an outer surface, which includes a first engagement recess and a second engagement recess that are recessed toward a radially inner side. The drive engagement portion is inserted into the first engagement recess engageable in a rotation direction. The driven engagement portion is inserted into the second engagement recess engageable in the rotation direction. An outer diameter of a bottom surface of the second engagement recess is smaller than an inner diameter of the driven engagement portion or an outer diameter of a bottom surface of the first engagement recess is smaller than an inner diameter of the drive engagement portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of a motor will now be described.

As shown inFIG. 1, the motor of the present embodiment is configured so that the rotation output of a motor body11can be transmitted by a joint device12to a reduction drive13.

The motor body11includes a yoke housing14, a drive shaft15accommodated in the yoke housing14, and an armature16that rotates integrally with the drive shaft15. The drive shaft15is supported by two bearings17that are supported by the yoke housing14.

The reduction drive13includes a gear housing21coupled to the yoke housing14, a worm shaft22(driven shaft) accommodated in the gear housing21, and a worm wheel23that meshes with the worm shaft22. The worm shaft22is supported by two bearings24, which are supported by the gear housing21, coaxially with the drive shaft15of the motor body11. The worm shaft22and the drive shaft15are coupled by the joint device12, which is accommodated in the gear housing21. Thus, the rotation of the drive shaft15can be transmitted to the worm shaft22via the joint device12. The worm wheel23transmits the rotation of the worm shaft22to an output shaft (not shown) of the motor.

Joint Device

As shown inFIGS. 2, 3A and 3B, the joint device12includes a drive rotor30fixed to the drive shaft15, a driven rotor40fixed to the worm shaft22, and a ring-shaped rubber buffer50located between the drive rotor30and the driven rotor40.

The drive rotor30includes a fixing portion31, in which a distal end of the drive shaft15having two flat opposing surfaces is fitted and fixed so that relative rotation is prohibited, and a disk32formed integrally with the fixing portion31. The disk32is disk-shaped and orthogonal to the axis L1of the drive shaft15, and the fixing portion31is located at a portion of the disk32closer to the motor body11. The disk32has a circular shape, the center of which is the axis L1of the drive shaft15.

The disk32includes an end surface32a, which is located at the opposite side of the fixing portion31. The central portion of the end surface32aincludes a cylindrical projection33that projects toward the opposite side of the fixing portion (opposite side of the motor body) in the axial direction. The cylindrical projection33has a circular shape, the center of which is the axis L1of the drive shaft15. That is, the center axis of the cylindrical projection33and the axis L1of the drive shaft15are coaxial.

The surrounding portion (radially outer portion) of the cylindrical projection33includes three projections34, each of which projects from the end surface32aof the disk32in the same direction (axial direction) as the cylindrical projection33. Each projection34is substantially T-shaped as viewed from the axial direction. The projection34includes a rotation transmission portion35(drive engagement portion), which is located at the circumferentially middle portion of the projection34, and two drive contact portions36, which extend from the rotation transmission portion35toward the two circumferential sides.

The rotation transmission portion35has a sectoral shape, the center of which is the axis L1of the drive shaft15as viewed from the axial direction. The rotation transmission portion35is widened toward the radially outer side. The two circumferential end surfaces of the rotation transmission portion35extend in the radial direction of the axis L1of the drive shaft15. That is, the two circumferential end surfaces of the rotation transmission portion35are each planar and orthogonal to the rotation direction of the drive shaft15and the drive rotor30.

The rotation transmission portions35are arranged at equal intervals (120-degree intervals) in the circumferential direction. The radially inner end surface of each rotation transmission portion35is arcuate, the center of which is the axis L1of the drive shaft15. The rotation transmission portions35are set to have the same inner diameter, that is, the same radius from the axis L1of the drive shaft15to the radially inner end surface of the rotation transmission portion35.

The drive contact portion36is formed on the radially outer portion of the rotation transmission portion35. That is, the rotation transmission portion35projects toward the inner side in the radial direction from the drive contact portion36. The drive contact portion36is arcuate, the center of which is the axis L1of the drive shaft15.

The driven rotor40includes a disk41orthogonal to an axis L2of the worm shaft22. The central portion of the disk41includes a fixing hole41a, in which the end of the worm shaft22having two flat opposing surfaces is fitted and fixed so that relative rotation is prohibited. The disk41has a circular shape, the center of which is the axis L2of the worm shaft22. The disk41of the driven rotor40opposes the disk32of the drive rotor30in the axial direction.

The disk41includes an axially inner surface41b(end surface located closer to the drive rotor30). The axially inner surface41bincludes three rotation reception portions42(driven engagement portions), which are arranged at equal intervals (120-degree intervals) in the circumferential direction. The rotation reception portions42project toward the drive rotor30in the axial direction. The rotation reception portions42are arranged along the outer edge of the disk41.

Each rotation reception portion42has a sectoral shape, the center of which is the axis of the driven rotor40as viewed from the axial direction (coaxial with the axis L2of the worm shaft22). The rotation reception portion42is widened toward the radially outer side. The two circumferential end surfaces of the rotation reception portion42extend in the radial direction of the driven rotor40. That is, the two circumferential end surfaces of the rotation reception portion42are each planar and orthogonal to the rotation direction of the driven rotor40.

The radially inner end surface of the rotation reception portion42is arcuate, the center of which is the axis L2of the worm shaft22. The rotation reception portions42are set to have the same inner diameter, that is, the same radius from the axis L2of the worm shaft22to the radially inner end surface of the rotation reception portion42. The rotation reception portion42is set to have the same inner diameter as the rotation transmission portion35of the drive rotor30. When the joint device12is coupled, the rotation reception portions42are arranged in the circumferential direction between the rotation transmission portions35of the drive rotor30.

The ring-shaped rubber buffer50is arranged between the disk32of the drive rotor30and the disk41of the driven rotor40. The central portion of the buffer50includes a through hole50a, into which the cylindrical projection33of the drive rotor30is inserted.

The outer surface of the buffer50includes first engagement recesses51respectively corresponding to the rotation transmission portions35and second engagement recesses52respectively corresponding to the rotation reception portions42. The first engagement recesses51and the second engagement recesses52are alternately formed in the circumferential direction. The number of the first engagement recesses51is the same as that of the rotation transmission portions35(three in the present embodiment). The number of the second engagement recesses52is the same as that of the rotation reception portions42(three in the present embodiment).

The first and second engagement recesses51and52are recessed from the outer surface of the buffer50to the radially inner side. The first engagement recess51and the second engagement recess52are sectoral and widened toward the radially outer side. The circumferential side surfaces of the first and second engagement recesses51and52are formed in the radial direction. That is, the two circumferential end surfaces of each of the first and second engagement recesses51and52are each planar and orthogonal to the rotation direction.

As shown inFIG. 3A, the rotation transmission portions35are fitted in the first engagement recesses51without any gaps between the rotation transmission portions35and the first engagement recesses51. More specifically, the circumferential width W1of each rotation transmission portion35is set to be substantially equal to the circumferential width W2of each first engagement recess51. The inner diameter D1of the rotation transmission portion35is set to be substantially equal to the outer diameter D2of the bottom surface of the first engagement recess51. That is, the arcuate surface of the first engagement recess51has a radius substantially equal to the arcuate surface of the opposing rotation transmission portion.

Thus, the cylindrical projection33and each rotation transmission portion35of the drive rotor30stably hold the buffer50so that the buffer50is not misaligned relative to the drive rotor30in the radial direction.

The rotation reception portions42are loosely fitted in the second engagement recesses52of the buffer50so that gaps are formed between the rotation reception portions42and the corresponding second engagement recesses52. More specifically, the circumferential width W3of each rotation reception portion42is set to be smaller than the circumferential width W4of each second engagement recess52. This forms a gap in the circumferential direction between the rotation reception portion42and the second engagement recess52. The inner diameter D3of the rotation reception portion42is set to be larger than the outer diameter D4of the bottom surface of the second engagement recess52. That is, the arcuate surface of the second engagement recess52has a smaller radius than that of the arcuate surface of the opposing rotation reception portion42. This forms a gap in the radial direction between the rotation reception portion42and the second engagement recess52.

When the joint device12is coupled, the projections of the buffer50between the first engagement recesses51and the second engagement recesses52are arranged in the circumferential direction between the rotation transmission portion35and the rotation reception portion42. Thus, the rotation transmission portions35do not directly contact the rotation reception portions42in the rotation direction.

When the motor body11drives and rotates the drive shaft15(clockwise inFIGS. 3A and 3B), the drive rotor30of the joint device12rotates integrally with the drive shaft15. When the rotation transmission portions35of the drive rotor30engage the first engagement recesses51, the buffer50rotates integrally with the drive rotor30.

As shown inFIG. 3A, when the drive shaft15and the worm shaft22are aligned (that is, the axes L1and L2are in conformance), the side surfaces of the three second engagement recesses52respectively contact the side surfaces of the three rotation reception portions42in the rotation direction. Thus, the rotation of the drive rotor30(rotation transmission portion35) is transmitted to the driven rotor40(rotation reception portion42) by the buffer50. During transmission of rotation, the drive rotor30, which has high rigidity, does not directly contact the driven rotor40, which has high rigidity. This limits the generation of noise.

If excessive load applied to the worm shaft22locks and stops the rotation of the driven rotor40during the transmission of rotation, the drive contact portion36of each projection34of the drive rotor30contacts the rotation reception portion42in the rotation direction as shown inFIG. 3B. This stops the rotation of the drive shaft15of the motor body11. Thus, when the worm shaft22is locked, direct contact of the drive rotor30and the driven rotor40limits compression of the buffer50caused by a strong force. That is, the buffer50is not further compressed by the rotation transmission portions35and the rotation reception portions42from the locations where the drive contact portions36contacts the rotation reception portions42. This reduces wear of the buffer50.

For example, coupling tolerances of the yoke housing14of the motor body11and the gear housing21of the reduction drive13may result in misalignment of the axis L1of the drive shaft15and the axis L2of the worm shaft22when coupling the drive rotor30and the driven rotor40.

As shown inFIG. 4, this misaligns the drive rotor30and the driven rotor40in the joint device12. The buffer50, which is held by the drive rotor30, is coaxial with the drive rotor30and misaligned relative to the driven rotor40. The rotation reception portions42of the driven rotor40, loosely fitted in the second engagement recesses52of the buffer50with gaps formed between the rotation reception portion42and the second engagement recess52, allows for misalignment in the radial direction.

When the axis L1of the drive shaft15and the axis L2of the worm shaft22are misaligned, rotation is transmitted by one or two of the three sets of the rotation reception portion42and the second engagement recess52as shown inFIGS. 4 and 5. When rotation is transmitted under a misaligned state, the side surfaces of the second engagement recesses52and the side surfaces of the rotation reception portions42repeatedly contact and separate as they move. In the present embodiment, the rubber buffer50contacts the rotation reception portions42. This limits the generation of noise when the rotation reception portions42contacts the buffer50.

The advantages of the present embodiment will now be described.

(1) The drive rotor30includes the rotation transmission portions35that project toward the driven rotor40in the axial direction. The driven rotor40includes the rotation reception portions42that projects toward the drive rotor30in the axial direction. The outer surface of the buffer50includes the first engagement recesses51, which are engageable with the rotation transmission portions35in the rotation direction, and the second engagement recesses52, which are engageable with the rotation reception portion42in the rotation direction. The outer diameter D4of the bottom surface of each second engagement recess52is set to be smaller than the inner diameter D3of the rotation reception portion42. Since this structure forms a gap in the radial direction between the bottom surface of the second engagement recess52and the rotation reception portion42, misalignment of the drive shaft15and the worm shaft22is allowed in the radial direction. Thus, rotation can be smoothly transmitted even when the drive shaft15and the worm shaft22are misaligned.

(2) The outer diameter D2of the bottom surface of each first engagement recess51is set to be substantially equal to the inner diameter D1of each rotation transmission portion35. This does not form a gap in the radial direction between the bottom of the first engagement recess51and the rotation transmission portion35. In this manner, the buffer50has gaps for the driven rotor40to allow for misalignment in the radial direction but does not have gaps in the radial direction for the drive rotor30, to stably hold the drive rotor30.

(3) The circumferential width W2of the first engagement recess51is substantially equal to the circumferential width W1of the rotation transmission portion35. The circumferential width W4of the second engagement recess52is set to be larger than the circumferential width W3of the rotation reception portion42. This structure allows for integral rotation of the buffer50and the drive rotor30and further stably holds the buffer50. This structure also forms gaps in the circumferential direction between the rotation reception portions42and the second engagement recesses52. Thus, misalignment is allowed in the radial direction between the buffer50and the driven rotor40in a further preferable manner.

(4) The drive contact portions36of the drive rotor30contacts the rotation reception portions42in the rotation direction when the load of the driven rotor40is greater than or equal to a predetermined level. In this structure, the drive contact portions36directly contact the rotation reception portions42in the rotation direction when excessive load is applied to the worm shaft22during the rotation of the drive shaft15. Thus, the buffer50is not compressed more than necessary. This reduces wear of the buffer50.

The above embodiment may be modified as follows.

In the above embodiment, the drive rotor30does not have to include the drive contact portions36that contact the rotation reception portions42in the rotation direction when the worm shaft22is locked. For example, the drive contact portion36may be omitted from the drive rotor30so that the driven rotor40includes a driven contact portion extending in the circumferential direction from the rotation reception portion42. The drive contact portion36may be separated from the rotation transmission portion35so that the drive contact portion36and the rotation transmission portion35are different bodies.

In the above embodiment, the circumferential width W3of the rotation reception portion42does not have to be set to be smaller than the circumferential width W4of the second engagement recess52. For example, the circumferential width W3may be set to be substantially equal to the circumferential width W4.

In the above embodiment, the rotation transmission portions35are fitted in the first engagement recesses51without any gaps between the rotation transmission portions35and the first engagement recesses51, and the rotation reception portions42are loosely fitted in the second engagement recesses52with gaps between the rotation reception portion42and the second engagement recess52. Instead, as shown inFIG. 6, the rotation transmission portion35may be loosely fitted in the first engagement recess51with gaps between the rotation transmission portion35and the first engagement recess51, and the rotation reception portion42may be fitted in the second engagement recess52without any gaps between the reception portion42and the second engagement recess52. For example, the circumferential width W1of each rotation transmission portion35is set to be smaller than the circumferential width W2of each first engagement recess51, and the inner diameter D1of each rotation transmission portion35is set to be larger than the outer diameter D2of the bottom surface of each first engagement recess51. The circumferential width W3of each rotation reception portion42is set to be substantially equal to the circumferential width W4of each second engagement recess52. The inner diameter D3of each rotation reception portion42is set to be substantially equal to the outer diameter D4of the bottom surface of each second engagement recess52. That is, the arcuate surface of the first engagement recess51has a radius smaller than that of the opposing rotation transmission portion35. The arcuate surface of the second engagement recess52has a radius substantially equal to that of the rotation reception portion42. Thus, the buffer50is held by the driven rotor40and can be misaligned relative to the drive rotor30. It is preferable that the cylindrical projection33be formed on the driven rotor40, not on the drive rotor30.