Power transmission mechanism and motor with speed reducer

Abstract

This power transmission mechanism (10) for transmitting rotational driving force of a driving body (5) to a driven body (6) comprises: a first protruding part (11) that is provided so as to protrudes from one among the driving body (5) and the driven body (6) in a first axial direction (C1) in the axial direction; and a second protruding part (12) that is provided so as to protrude from the other among the driving body (5) and the driven body (6) in a second axial direction (C2). The first protruding part (11) has a first side surface (11a) facing the circumferential direction. The second protruding part (12) has a second side surface (12a) that is in surface contact with the first side surface (11a) in a power transmission state in which the rotational driving force is transmitted to the driven body (6). In a power transmission starting state immediately before the power transmission state is reached, only an outer end part of the second side surface (12a) that is located on the outside in the radial direction abuts the first side surface (11a).

Description

Power transmission mechanism and motor with reducer

[0001] The present invention relates to a power transmission mechanism that transmits the rotational driving force of a driver to a driven body, and a motor with a reducer to which the power transmission mechanism is applied.

[0002] Conventionally, a power transmission mechanism that transmits the rotational driving force of a driver to a driven body arranged coaxially with the driver includes a mechanism that transmits the rotational driving force by abutting protrusions protruding from the driver and driven body against each other.

[0003] For example, Patent Document 1 discloses a connecting member (power transmission mechanism) that connects an armature shaft and a worm shaft so that they can rotate together, and that includes an armature shaft side connecting member and a worm shaft side connecting member. In the connecting member disclosed in Patent Document 1, the armature shaft side connecting member (driver) has three protrusions extending radially from its main body, and the worm shaft side connecting member (driven member) has three protrusions protruding in the axial direction. The protrusions of the worm shaft side connecting member fit into and connect with each other, and as the armature shaft rotates, the protrusions of the armature shaft side connecting member approach (abut) the protrusions of the worm shaft side connecting member, thereby transmitting the rotational force of the armature shaft to the worm shaft.

[0004] JP 2010-124620 A

[0005] In the connecting member disclosed in Patent Document 1, the protrusions of both the armature shaft-side connecting member and the worm shaft-side connecting member are formed in a generally fan-like shape centered on the axis of each member, so that the side surfaces located on both circumferential sides of each protrusion extend along a diametric line passing through the axis. In this manner, in conventional power transmission mechanisms, the side surfaces of the protrusions of both the driver and driven members are shaped to match each other (shapes that are rotationally symmetric about the axis), and the rotational driving force is transmitted through surface contact between the two side surfaces. However, in such power transmission mechanisms, when the rotational driving force is transmitted, the side surfaces of the protrusions of both the driver and driven members simultaneously abut over the entire radial area. Therefore, when the rotational driving force is transmitted, stress concentrates on the radially inner portion of the side surface of each protrusion, which is close to the axis. Repeated transmission of the rotational driving force can cause deformation of the protrusions. In other words, conventional power transmission mechanisms have room for improvement in the durability of the protrusions.

[0006] The power transmission mechanism and motor with a reducer of the present invention were devised in consideration of these problems, and one of the objects thereof is to improve the durability of the protrusion that transmits the rotational driving force of the driver to the driven body. However, in addition to this object, another object of the present invention is to achieve effects that cannot be obtained by conventional techniques, which are derived from the configurations shown in the below-mentioned detailed description of the invention.

[0007] The disclosed power transmission mechanism and motor with a reducer can be realized as the following disclosed aspects (application examples), which solve at least part of the above-mentioned problems.

[0008] The disclosed power transmission mechanism transmits a rotational driving force of a driver to a driven body coaxially disposed with the driver, and includes: a first protrusion protruding from one of the driver and the driven body toward a first axial direction along which the axis of the driver extends; and a second protrusion protruding from the other of the driver and the driven body toward a second axial direction opposite to the first axial direction. The first protrusion has a first side surface facing a circumferential direction around the axis, and the second protrusion has a second side surface that is in surface contact with the first side surface in a power transmission state in which the rotational driving force is transmitted to the driven body, and in a power transmission start state immediately before entering the power transmission state, only an outer end of the second side surface that is located radially outward from the axis abuts against the first side surface.

[0009] The disclosed motor with a reducer comprises a motor section having a motor shaft and a reducer section integrally assembled to the motor section, the reducer section comprising a worm that rotates integrally with the motor shaft of the motor section, a worm wheel that meshes with the worm, and an output shaft that is configured to be rotatable together with the worm wheel, and a power transmission mechanism including the above aspects is applied to the worm wheel as the driver and the output shaft as the driven body.

[0010] According to the disclosed power transmission mechanism and motor with a reducer, it is possible to improve the durability of the protrusion for transmitting the rotational driving force of the driver to the driven body.

[0011] 1 is a plan view of a reducer-equipped motor to which a power transmission mechanism according to an embodiment is applied; FIG. 2 is an axial cross-sectional view (cross-sectional view taken along the X-X arrow in FIG. 1) of a reducer unit included in the reducer-equipped motor of FIG. 1; FIG. 3 is an exploded perspective view of a worm wheel, an output shaft, and a buffer member provided in the reducer unit of FIG. 2; FIG. 4 is a perspective view of the output shaft of FIG. 3 as seen from the second axial direction; FIG. 5 is a radial cross-sectional view (corresponding to the Y-Y cross-sectional view in FIG. 2) of a state in which the output shaft and buffer member are assembled to the worm wheel of FIG. 3 (in a neutral state); FIG. 6 is an enlarged view of a portion Z of FIG. 5; FIG. 7 is a partial enlarged view (corresponding to FIG. 6) of a radial cross-section of the worm wheel and output shaft of FIG. 5 in a tight contact state; FIG. 8 is a partial enlarged view (corresponding to FIG. 6) of a radial cross-section of the worm wheel and output shaft of FIG. 5 in an abutting state.

[0012] A power transmission mechanism and a motor with a reducer will be described as an embodiment with reference to the drawings. The embodiment described below is merely an example, and is not intended to exclude various modifications and applications of techniques not explicitly described in the embodiment. Each configuration of the embodiment can be modified in various ways without departing from the spirit thereof.

[0013] [1. Configuration] Fig. 1 is a plan view (viewed from the axial direction of the output shaft 6 of the reducer unit 3) of a motor 1 with a reducer (hereinafter simply referred to as "motor 1") to which a power transmission mechanism 10 (see Fig. 2) of this embodiment is applied. The motor 1 is used as a drive source for external devices (not shown), such as a power window device for a vehicle or a closure device such as a back door or a sliding door. As shown in Fig. 1, the motor 1 includes a motor unit 2 as a drive source and a reducer unit 3 that reduces the rotational speed of the motor unit 2 and outputs the reduced speed.

[0014] The motor unit 2 is, for example, a brushed DC motor, and has a rotor 22 and a stator 23 housed in a housing 21, and a motor shaft 24 that rotates integrally with the rotor 22. The motor unit 2 is assembled integrally with the reducer unit 3 by connecting the housing 21 to a gear box 7 of the reducer unit 3. One end of the motor shaft 24 is rotatably supported by the housing 21, and the other end extends from the housing 21 and is disposed inside the gear box 7.

[0015] The reducer unit 3 includes a worm 4 that rotates integrally with the motor shaft 24, a worm wheel 5 that meshes with the worm 4, and an output shaft 6 that is configured to be rotatable together with the worm wheel 5. The worm 4 and the worm wheel 5 are housed in a gear box 7 and sealed with a cover 8. One end of the output shaft 6 is disposed inside the gear box 7, and the other end extends from the cover 8 and is disposed outside the gear box 7.

[0016] The worm 4 is a screw gear made of, for example, rolled steel (e.g., low-carbon steel). The worm wheel 5 is a resin helical gear (external gear) formed by injection molding of, for example, polyacetal resin (POM). The rotation of the motor shaft 24 is transmitted to the worm wheel 5 via the worm 4, causing the worm wheel 5 to rotate about an axis C perpendicular to the rotation center S of the worm 4.

[0017] Hereinafter, the direction of the axis C of the worm wheel 5 will be referred to as the axial direction. Within the axial direction, the direction in which the output shaft 6 is disposed relative to the worm wheel 5 will be referred to as the first axial direction C1, and the direction opposite to the first axial direction C1 will be referred to as the second axial direction C2. Furthermore, a direction perpendicular to the axial direction and away from the axis C will be referred to as the radially outward direction, and a direction perpendicular to the axial direction and towards the axis C will be referred to as the radially inward direction; when no distinction is made between inside and outside, they will simply be referred to as the radial direction. A direction perpendicular to the axial direction and circumferential around the axis C will be referred to as the circumferential direction.

[0018] 2 and 3 , the worm wheel 5 has a substantially annular rim 51 with external teeth formed thereon, a substantially cylindrical hub 52 with a smaller diameter than the rim 51, and a flat portion 53 connecting the rim 51 and the hub 52. The flat portion 53 is a flat plate-like portion that forms a plane 53f facing the first axial direction C1. A first protrusion 11 and a third protrusion 13 (described later) of the power transmission mechanism 10 are protruded from the flat surface 53f, and a buffer member 15 (described later) of the power transmission mechanism 10 is placed on the flat surface 53f. For example, the axial dimension of the flat portion 53 is set smaller than the axial dimension of the rim 51, and the flat portion 53 extends radially inward from an axially intermediate portion of the rim 51 to connect to the hub 52.

[0019] The hub 52 extends from the radially inner end of the flat portion 53 toward the first axial direction C1. This forms a space recessed toward the second axial direction C2 between the rim 51 and the hub 52 of the worm wheel 5. The inner diameter of the hub 52 is set slightly larger than the outer diameter of a fixed shaft 72 (described later) of the gearbox 7, and the outer diameter of the hub 52 is set slightly smaller than the inner diameter of the buffer member 15 of the power transmission mechanism 10.

[0020] The gearbox 7 has a portion (hereinafter referred to as the "accommodation portion 71") that accommodates the worm wheel 5 and a fixed shaft 72. As shown in FIG. 2, the accommodation portion 71 is generally cylindrical with a bottom, and the fixed shaft 72 is columnar and protrudes from the bottom of the accommodation portion 71 along the axis C in the first axial direction C1. The worm wheel 5 is supported by the gearbox 7 so as to be rotatable about the axis C with the hub 52 loosely fitted onto the fixed shaft 72. The cover 8 is a resin lid member that closes the opening of the accommodation portion 71, and a through hole 8h through which the output shaft 6 is inserted is formed on its radially inner side. The cover 8 may be provided with a generally annular bulge 81 that bulges toward the second axial direction C2 from a surface facing the second axial direction C2.

[0021] The output shaft 6 is a shaft member made of, for example, nylon resin, and has a substantially cylindrical shaft portion 61 that is loosely fitted onto the fixed shaft 72, and an output plate 63 that extends radially outward from the shaft portion 61. The shaft portion 61 extends in the axial direction and passes through the through-hole 8h of the cover 8. With the shaft portion 61 loosely fitted onto the fixed shaft 72, the output shaft 6 is disposed coaxially with the worm wheel 5 and is supported rotatably about the axis C relative to the gearbox 7.

[0022] The inner and outer diameters of the end of the shaft portion 61 on the second axial direction C2 side (hereinafter referred to as the "drive-side end 62") are set to be equal to the inner and outer diameters of the hub 52 of the worm wheel 5, and the end abuts against the hub 52 from the second axial direction C2 side. An output pinion (see FIG. 3) that transmits the rotational driving force output from the output shaft 6 to an external device may be provided at the end of the shaft portion 61 on the first axial direction C1 side. As shown in FIG. 2, an O-ring may be sandwiched between the inner circumferential surface of the shaft portion 61 and the outer circumferential surface of the fixed shaft 72 to seal the gap between them.

[0023] The output plate 63 is a portion extending radially outward from the first axial direction C1 side of the drive-side end 62 and forms a surface facing the flat surface 53f of the worm wheel 5. The output plate 63 of this embodiment has a substantially annular inner surface portion 64 extending radially outward from the first axial direction C1 side of the drive-side end 62, and an outer cylindrical portion 65 extending radially outward from the inner surface portion 64 and toward the second axial direction C2 side. The outer cylindrical portion 65 has a substantially cylindrical shape with a larger diameter than the drive-side end 62 when viewed from the axial direction. With this configuration, the output shaft 6 forms a space recessed toward the first axial direction C1 side between the drive-side end 62 and the outer cylindrical portion 65 in the portion on the second axial direction C2 side thereof.

[0024] As shown in FIG. 2 , the inner surface portion 64 forms an inner opposing surface 64f facing the flat surface 53f, closer to the first axial direction C1 than the driving-side end portion 62. The outer tubular portion 65 forms an outer opposing surface 65f facing the flat surface 53f, closer to the second axial direction C2 than the inner opposing surface 64f. As shown in FIG. 4 , a fourth protrusion 14 (described later) of the power transmission mechanism 10 is provided on the inner opposing surface 64f, and a second protrusion 12 (described later) of the power transmission mechanism 10 is provided on the outer opposing surface 65f. Note that, as shown in FIG. 2 , a portion of the outer opposing surface 65f where the second protrusion 12 is not provided may abut against a first protrusion 11 protruding from the worm wheel 5. As shown in the figure, an O-ring may be sandwiched between the outer peripheral surface of the outer tubular portion 65 and the inner peripheral surface of the bulge portion 81 of the cover 8 to seal the gap therebetween.

[0025] 2 to 8, the power transmission mechanism 10 will be described in detail. The power transmission mechanism 10 according to this embodiment is applied to the worm wheel 5 and the output shaft 6. The power transmission mechanism 10 transmits the rotational driving force of the worm wheel 5, which serves as a driver, to the output shaft 6, which serves as a driven body. The output shaft 6 is configured to be rotatable together with the worm wheel 5 via the power transmission mechanism 10.

[0026] 3 and 5 , the power transmission mechanism 10 includes a first protrusion 11 and a second protrusion 12 as elements for transmitting the rotational driving force of the worm wheel 5 to the output shaft 6. Furthermore, the power transmission mechanism 10 of this embodiment includes a third protrusion 13, a fourth protrusion 14, and a buffer member 15 as elements for suppressing impacts when the rotational driving force is transmitted from the worm wheel 5 to the output shaft 6.

[0027] 5 and 6 (enlarged view of portion Z in FIG. 5 ) are cross-sectional views of the worm wheel 5 and the output shaft 6 in a state where no rotational driving force is transmitted from the motor shaft 24 to the worm wheel 5 and no external force is acting on the output shaft 6 from an external device. Hereinafter, this state will be referred to as the "neutral state." The neutral state can also be referred to as the initial state before the external device is assembled to the motor 1. In the following description of the power transmission mechanism 10, the neutral state will be assumed unless otherwise specified. Note that the rim 51 of the worm wheel 5 is not shown in FIG. 5 . Furthermore, in FIG. 6 and FIGS. 7 and 8 (described later), the hatching of the first protrusion 11 and the second protrusion 12 is partially omitted.

[0028] The first protrusion 11 is an element (part) for transmitting the rotational driving force of the worm wheel 5 to the output shaft 6, and protrudes in one axial direction from either the worm wheel 5 or the output shaft 6. In the present embodiment, as shown in FIG. 2 , the first protrusion 11 protrudes from the flat surface 53 f of the worm wheel 5 in the first axial direction C1 to a position where it abuts against the outer opposing surface 65 f of the output shaft 6. As shown in FIG. 3 , six first protrusions 11 may be provided on the worm wheel 5. The first protrusions 11 have the same shape and are spaced apart at equal intervals in the circumferential direction.

[0029] As shown in FIG. 5 , the first protrusion 11 has a substantially partial annular (or substantially trapezoidal) outer shape extending in the circumferential direction when viewed from the axial direction. The first protrusion 11 has, at both circumferential ends thereof, first side surfaces 11a that extend from the flat surface 53f and face the circumferential direction. In this embodiment, the first side surfaces 11a extend in directions perpendicular to the circumferential direction, i.e., in the axial and radial directions. Specifically, the first side surfaces 11a extend parallel to the axis C in the axial direction, and extend radially on a diameter line D that passes through the axis C, as shown in FIGS. 5 and 6 .

[0030] In this embodiment, the inner circumferential surface 11b connecting the radially inner edges of the two first side surfaces 11a of the first protruding portion 11 extends from the plane 53f in the axial direction, as shown in FIGS. 2 and 3 . On the other hand, the outer circumferential surface 11c connecting the radially outer edges of the two first side surfaces 11a extends from the plane 53f in a direction inclined radially inward with respect to the axial direction. Note that, in order to increase the rigidity of the first protruding portion 11, the first side surface 11a, the inner circumferential surface 11b, and the outer circumferential surface 11c may have rounded surfaces formed at their base ends on the second axial direction C2 side (the plane 53f side), as shown in FIG. 3 . This increases the thickness of the base end of the first protruding portion 11, thereby improving rigidity.

[0031] The second protrusions 12 are elements (parts) that, together with the first protrusions 11, transmit the rotational driving force of the worm wheel 5 to the output shaft 6. The second protrusions 12 protrude from the other of the worm wheel 5 and the output shaft 6 (the side where the first protrusions 11 are not provided) toward the other axial direction (the opposite direction to the protruding direction of the first protrusions 11), and are disposed adjacent to the first protrusions 11 in the circumferential direction. In the present embodiment, as shown in FIG. 4 , the second protrusions 12 protrude from the outer opposing surface 65f of the output shaft 6 toward the second axial direction C2. The output shaft 6 may be provided with six second protrusions 12, the same number as the first protrusions 11. The second protrusions 12 have the same shape and are disposed at equal intervals in the circumferential direction while being spaced apart from each other. As shown in FIG. 5 , the first protrusions 12 are disposed with gaps between adjacent first protrusions 11 in the circumferential direction. As a result, the first protrusions 11 and the second protrusions 12 are disposed alternately in the circumferential direction.

[0032] The second protruding portion 12 has, for example, a substantially partially annular (or substantially trapezoidal) outer shape extending in the circumferential direction when viewed in the axial direction, and has second side surfaces 12a at both circumferential ends. The second side surface 12a is erected from the outer opposing surface 65f and faces the first side surface 11a of the first protruding portion 11. The second side surface 12a may extend parallel to the axis C in the axial direction, similar to the first side surface 11a. When the worm wheel 5 rotates, the first protruding portion 11 moves toward the second protruding portion 12, and the first side surface 11a and the second side surface 12a come into surface contact with each other as shown in FIG. 7 , thereby transmitting the rotational driving force of the worm wheel 5 to the output shaft 6. Hereinafter, the state in which the first side surface 11a and the second side surface 12a are in surface contact (close contact) with each other (the state shown in FIG. 7 ) will be referred to as the "close contact state." When the power transmission mechanism 10 is in a tight contact state, the rotational driving force of the worm wheel 5 is transmitted to the output shaft 6, so the tight contact state can also be referred to as a power transmission state.

[0033] As described above, the first side surface 11a extends on the diameter line D. In contrast, as shown in FIG. 6 , the second side surface 12a does not extend on the diameter line D in the neutral state. As shown in FIG. 8 , just before the close contact state is reached, only the outer end portion 12ao located radially outward abuts the first side surface 11a. Hereinafter, the state in which the first side surface 11a and the second side surface 12a are partially in contact with each other (the state shown in FIG. 8 ) will be referred to as the “contact state.” When the worm wheel 5 starts to rotate in conjunction with the rotation of the motor shaft 24 from the neutral state, the power transmission mechanism 10 moves the first protrusion 11 toward the second protrusion 12, entering the contact state and ultimately reaching the close contact state. Therefore, the contact state can also be referred to as a power transmission start state. Furthermore, since the first protrusion 11 and the second protrusion 12 are not in contact with each other in the neutral state, the neutral state can also be referred to as a non-contact state.

[0034] In this embodiment, both the first side surface 11 a and the second side surface 12 a extend parallel to the axis C. Therefore, in the abutting state, an outer end portion 12 ao of the second side surface 12 a is in line contact with the first side surface 11 a. In the abutting state, as shown in the figure, a small gap is formed between an inner end portion 12 ai located radially inside the second side surface 12 a and the first side surface 11 a.

[0035] In this embodiment, only the outer end 12ao contacts the first side surface 11a in the contact state. As shown in FIG. 6 , the second side surface 12a of this embodiment is tapered in the radial direction, inclined toward the first side surface 11a by a predetermined angle α as it extends radially outward. For example, the second side surface 12a extends along an inclined line F, which is inclined from the diameter line D toward the first side surface 11a by the predetermined angle α, with an inclined line starting point E on the diameter line D passing near the inner end 12ai as the center. The predetermined angle α is set to a small angle (e.g., 1 degree) that allows the inner end 12ai to contact the first side surface 11a in the close contact state. The inclined line starting point E defining the inclined line F is preferably located radially inward of the inner end 12ai in order to incline the second side surface 12a with respect to the diameter line D throughout the entire area from the inner end 12ai to the outer end 12ao.

[0036] 4, the second side surface 12a may have a rounded surface formed at a base end portion thereof on the first axial direction C1 side (the outer opposing surface 65f side) from the viewpoint of increasing the rigidity of the second protruding portion 12. This increases the thickness of the base end portion of the second protruding portion 12, thereby improving the rigidity.

[0037] The third protrusion 13 is an element (part) that suppresses impact when transmitting a rotational driving force, and protrudes from one of the worm wheel 5 and the output shaft 6 (the side where the first protrusion 11 is provided) toward one axial direction (the same direction as the protruding direction of the first protrusion 11) at a radial position different from that of the first protrusion 11. In the present embodiment, as shown in FIG. 3 , the third protrusion 13 protrudes from a flat surface 53 f of the worm wheel 5 toward the first axial direction C1, radially inward of the first protrusion 11. As shown in FIG. 5 , the third protrusion 13 is provided in the radial direction in a range from the outer peripheral surface of the hub 52 to near the inner peripheral surface 11 b of the first protrusion 11. The protrusion amount of the third protrusion 13 from the flat surface 53 f is set to be, for example, equal to or greater than the axial length of the buffer member 15.

[0038] The third protruding portion 13 has, for example, a substantially partial annular (or substantially trapezoidal) outer shape extending in the circumferential direction when viewed in the axial direction. The circumferential length of the third protruding portion 13 may be set, for example, to be greater than the circumferential length of the second protruding portion 12 and less than the circumferential length between circumferentially adjacent first protruding portions 11. As shown in FIG. 3 , the third protruding portion 13 may have a groove 13g formed by cutting out a radially inner portion thereof toward the second axial direction C2. A connecting portion 15Q (described later) of the buffer member 15 is disposed in the groove 13g.

[0039] The fourth protrusion 14, together with the third protrusion 13 and the buffer member 15, is an element (part) that suppresses impact when transmitting a rotational driving force. The fourth protrusion 14 protrudes from the other of the worm wheel 5 and the output shaft 6 (the side where the first protrusion 11 is not provided) toward the other axial direction (the opposite direction from the protruding direction of the first protrusion 11). The fourth protrusion 14 is provided at the same position as the third protrusion 13 in the radial direction. In this embodiment, as shown in FIG. 4 , the fourth protrusion 14 protrudes from the inner opposing surface 64f of the output shaft 6 toward the second axial direction C2. As shown in FIGS. 4 and 5 , the fourth protrusion 14 is provided in a range from the outer circumferential surface of the drive-side end 62 of the output shaft 6 to near the inner circumferential surface 11b of the first protrusion 11, corresponding to the radial arrangement of the third protrusion 13. The protrusion amount of the fourth protrusion 14 from the inner opposing surface 64f is set to, for example, be equal to or greater than the axial length of the buffer member 15.

[0040] As shown in Fig. 5 , the fourth protruding portion 14 has an outer shape that is generally partially annular (or generally trapezoidal) and extends circumferentially when viewed from the axial direction. The circumferential length of the fourth protruding portion 14, like the third protruding portion 13, may be set to be greater than the circumferential length of the second protruding portion 12 and smaller than the circumferential length between circumferentially adjacent first protruding portions 11. As shown in Fig. 4 , the fourth protruding portion 14 may have a groove 14g formed by cutting out a radially inner portion thereof toward the first axial direction C1. A connecting portion 15Q of the buffer member 15 is disposed in the groove 14g.

[0041] As shown in Figures 3 to 5, the worm wheel 5 may be provided with three third protrusions 13, and the output shaft 6 may be provided with three fourth protrusions 14, the same number as the third protrusions 13. The third protrusions 13 have the same shape but are positioned in different circumferential directions (phases). The fourth protrusions 14 also have the same shape but are positioned in different circumferential directions (phases). The three third protrusions 13 and the three fourth protrusions 14 are spaced apart from each other and alternately positioned in the circumferential direction, as shown in Figure 5.

[0042] In this embodiment, as shown in FIG. 4 , the output shaft 6 has six second protrusions 12 and three fourth protrusions 14, and the fourth protrusions 14 are located radially inward of three second protrusions 12 that are located alternately in the circumferential direction. The second protrusions 12 and the fourth protrusions 14 that are located at the same circumferential position are connected to each other and can be said to form a single large protrusion. As shown in FIG. 3 , the worm wheel 5 has six first protrusions 11 and three third protrusions 13, and of the six spaces formed between adjacent first protrusions 11 in the circumferential direction, the third protrusions 13 are located radially inward of three spaces that are located alternately in the circumferential direction. Since the second protrusions 12 are arranged in these six spaces, as shown in FIG. 5 , the third protrusions 13 can be said to be located radially inward of three second protrusions 12 that are located alternately in the circumferential direction. The third protruding portions 13 are disposed adjacent to the radially inner side of three of the six second protruding portions 12 that do not have a fourth protruding portion 14 radially inner thereto. Six substantially partial annular spaces are formed circumferentially between the third protruding portion 13 and the fourth protruding portion 14, partitioned by these protruding portions 13, 14, the inner circumferential surface 11b of the first protruding portion 11, and the hub 52.

[0043] The buffer member 15 is a member formed of a circumferentially expandable material (e.g., rubber such as nitrile rubber (NBR)). As shown in FIG. 2 , it is interposed between the worm wheel 5 and the output shaft 6. As shown in FIG. 5 , the buffer member 15 has six buffer blocks 15P interposed between the third protrusion 13 and the fourth protrusion 14. Each buffer block 15P has a shape (here, a substantially partial ring shape) that fills the space between the third protrusion 13 and the fourth protrusion 14 when viewed in the axial direction. Note that, as shown in FIG. 2 , the buffer blocks 15P do not necessarily fill the space between the flat surface 53f and the inner facing surface 64f in the axial direction. By providing a gap between the buffer blocks 15P and the inner facing surface 64f, axial expansion of the buffer blocks 15P is permitted when the buffer blocks 15P are compressed and deformed in the circumferential direction.

[0044] As described above, when the worm wheel 5 starts to rotate from the neutral state in response to the rotation of the motor shaft 24, the first protrusion 11 moves toward the second protrusion 12 and enters the abutting state. When the power transmission mechanism 10 enters the abutting state from the neutral state, the third protrusion 13 moves together with the first protrusion 11, causing the buffer block 15P to undergo compressive deformation. As a result, the shock generated when the rotational driving force is transmitted from the worm wheel 5 to the output shaft 6 is absorbed and suppressed by the buffer member 15.

[0045] 3, the buffer member 15 may be configured in an annular shape as a whole by connecting the radially inner portions of six buffer blocks 15P with connecting portions 15Q. By connecting multiple buffer blocks 15P together in this manner, assembly is facilitated.

[0046] [3. Actions and Effects] (1) In the power transmission mechanism 10 described above, when the worm wheel 5 starts to rotate from the neutral state in conjunction with the rotation of the motor shaft 24, the first protrusion 11 moves toward the second protrusion 12 and enters an abutting state, and finally enters a tightly contacted state. When the power transmission mechanism 10 enters the tightly contacted state, it transmits the rotational driving force of the worm wheel 5 to the output shaft 6.

[0047] In the abutting state, only the outer end 12ao of the second side surface 12a of the second protruding portion 12 abuts against the first side surface 11a, as shown in Fig. 8. In this manner, in the power transmission mechanism 10, just before the start of transmission of the rotational driving force, only the outer end 12ao abuts against the first side surface 11a before the inner end 12ai. This allows the power transmission mechanism 10 to move the position of the abutment point between the first protruding portion 11 and the second protruding portion 12 just before the start of transmission of the rotational driving force farther from the axis C, thereby mitigating the impact force (stress) generated when the first protruding portion 11 and the second protruding portion 12 abut.

[0048] Furthermore, in the power transmission mechanism 10, the outer end 12ao of the second side surface 12a and the portion of the first side surface 11a that contacts the outer end 12ao are elastically compressed during the process of transitioning from the abutting state to the close contact state. As a result, in the close contact state, the second side surface 12a is in surface contact with the first side surface 11a over the entire area from the inner end 12ai to the outer end 12ao, as shown in Fig. 7. This allows the rotational driving force transmitted from the worm wheel 5 to be dispersed over the surface. This allows the stress generated in both the first protruding portion 11 and the second protruding portion 12 to be alleviated.

[0049] Therefore, with the above-described power transmission mechanism 10, stress on the first protruding portion 11 and the second protruding portion 12 is alleviated in both the abutting state and the close contact state, thereby improving the durability of both the first protruding portion 11 and the second protruding portion 12. Furthermore, with the above-described power transmission mechanism 10, no major specification or size changes are required to improve the durability of the protruding portions 11, 12, making it possible to reduce the size and weight of the motor 1. In addition, with the above-described power transmission mechanism 10, no additional parts or material changes are required to improve the durability of the protruding portions 11, 12, making it possible to reduce the cost of the motor 1.

[0050] (2) In the power transmission mechanism 10 described above, the first side surface 11 a of the first protruding portion 11 extends in the radial direction, and the second side surface 12 a of the second protruding portion 12 is tapered in the radial direction, inclined toward the first side surface 11 a by a predetermined angle α as it moves radially outward. This allows the entire second side surface 12 a to be in surface contact with the first side surface 11 a in a tight contact state, thereby further alleviating stress generated in both the first protruding portion 11 and the second protruding portion 12.

[0051] (3) The power transmission mechanism 10 described above is provided with the buffer member 15, which undergoes compressive deformation between the neutral state and the abutting state. This allows the buffer member 15 to absorb and suppress the impact during transmission of the rotational driving force, thereby further improving the durability of the first protrusion 11 and the second protrusion 12. Furthermore, because the buffer member 15 absorbs the impact during transmission of the rotational driving force, damage to the various gears of the speed reducer unit 3 can be suppressed and the quietness of the motor 1 can be improved.

[0052] (4) In the above-described power transmission mechanism 10, the same number (six each) of first protrusions 11 and second protrusions 12 are provided, and the same number (three each) of third protrusions 13 and fourth protrusions 14 are provided. In addition, the number of first protrusions 11 and second protrusions 12 is set to be equal to or greater than the number of third protrusions 13 and fourth protrusions 14.

[0053] In this way, by setting the number of the first protruding portions 11 and the second protruding portions 12 to be equal to or greater than the number of the third protruding portions 13 and the fourth protruding portions 14, the rotational driving force transmitted from the worm wheel 5 can be more dispersed, thereby further alleviating stress generated in both the first protruding portions 11 and the second protruding portions 12. Furthermore, by setting the number of the third protruding portions 13 and the fourth protruding portions 14 to be equal to or less than the number of the first protruding portions 11 and the second protruding portions 12, a space for arranging the buffer member 15 between the third protruding portions 13 and the fourth protruding portions 14 can be easily secured.

[0054] (5) When six first protrusions 11 and six second protrusions 12 are provided and three third protrusions 13 and three fourth protrusions 14 are provided, space for arranging the buffer members 15 can be secured more appropriately (in a balanced manner), and the rotational driving force transmitted from the worm wheel 5 can be distributed to the six first protrusions 11 and six second protrusions 12, thereby achieving further stress relief.

[0055] [4. Other] The configurations of the power transmission mechanism 10 and the motor 1 described above are merely examples and are not limited to the above. In the power transmission mechanism 10 described above, the first protrusion 11 and the third protrusion 13 are provided on the worm wheel 5, and the second protrusion 12 and the fourth protrusion 14 are provided on the output shaft 6. However, the first protrusion 11 and the third protrusion 13 may be provided on the output shaft 6, and the second protrusion 12 and the fourth protrusion 14 may be provided on the worm wheel 5. In other words, the "first protrusion" described in the claims may be a portion protruding from the output shaft 6 as the driven body, and the "second protrusion" described in the claims may be a portion protruding from the worm wheel 5 as the driver. The first axial direction C1 and the second axial direction C2 in the power transmission mechanism 10 described above are merely examples, and these directions may be reversed.

[0056] The second side surface 12a of the second protrusion 12 is not limited to the above-described shape, and may have any shape as long as at least the outer end 12ao abuts against the first side surface 11a in the abutting state and is in surface contact with the first side surface 11a in a close contact state. For example, the second side surface 12a may be a curved surface that curves with respect to the inclined line F shown in Fig. 6, or may be a bent flat surface or a curved surface that extends on the diameter line D from the inner end 12ai to a radially intermediate portion and is inclined with respect to the diameter line D from the intermediate portion to the outer end 12ao.

[0057] The first side surface 11a of the first protruding portion 11 need only be a surface facing at least in the circumferential direction and need not have the above-described shape. For example, the first side surface 11a may not extend on the diameter line D in the radial direction but may extend at a slight inclination relative to the diameter line D. Furthermore, the first side surface 11a may not extend parallel to the axis C in the axial direction but may extend at a slight inclination relative to the axis C. In this case, the second side surface 12a of the second protruding portion 12 may have a shape that corresponds to the extension direction of the first side surface 11a and abuts against the first side surface 11a from the radially outer side.

[0058] In the power transmission mechanism 10, at least, it is sufficient that only the outer end portion 12ao of the second side surface 12a abuts against the first side surface 11a in the abutting state, and that the first side surface 11a and the second side surface 12a are in surface contact in the close contact state, and it does not matter whether the first side surface 11a or the second side surface 12a deforms in the process from the abutting state to the close contact state.

[0059] In the above-described power transmission mechanism 10, the first protrusion 11 has two first side surfaces 11a and the second protrusion 12 has two second side surfaces 12a, but if the motor shaft 24 rotates in only one direction, the first protrusion 11 may have one first side surface 11a (provided on only one circumferential side) and the second protrusion 12 may have one second side surface 12a (provided on only the other circumferential side).

[0060] In the power transmission mechanism 10 described above, both the first protruding portion 11 and the second protruding portion 12 have a substantially partial annular shape when viewed in the axial direction, but the shapes of the first protruding portion 11 and the second protruding portion 12 are not limited to this. The first protruding portion 11 may have a shape that forms at least the first side surface 11a facing the circumferential direction, and the second protruding portion 12 may have a shape that forms at least the second side surface 12a described above. Similarly, the third protruding portion 13 and the fourth protruding portion 14 do not have to have a partial annular shape as long as they have a shape that allows the buffer member 15 to be interposed between them.

[0061] The number of first protrusions 11 and the number of second protrusions 12 do not have to be the same. For example, the power transmission mechanism 10 may be configured to have two first protrusions 11 protruding from the worm wheel 5 and one second protrusion 12 protruding from the output shaft 6 and interposed between the two first protrusions 11. Similarly, the number of third protrusions 13 and the number of fourth protrusions 14 do not have to be the same. Furthermore, the number of first protrusions and second protrusions protruding from the driver and the number of driven bodies may each be one, and the number of third protrusions 13 and fourth protrusions 14 may also be one.

[0062] The third protruding portion 13 and the fourth protruding portion 14 only need to be provided at a position different from at least the first protruding portion 11 and the second protruding portion 12 in the radial direction, and may be provided radially outward of the first protruding portion 11 and the second protruding portion 12, or may not be disposed adjacent to the first protruding portion 11 and the second protruding portion 12. Note that the power transmission mechanism 10 does not need to include the third protruding portion 13, the fourth protruding portion 14, and the buffer member 15 if the function of suppressing impact when the rotational driving force is transmitted from the worm wheel 5 to the output shaft 6 is not required.

[0063] The motor section 2 of the motor 1 does not have to be a brushed DC motor. The power transmission mechanism 10 may be applied to devices other than the motor 1 that include a member that serves as a driver and a member that serves as a driven member, as long as it transmits the rotational driving force of a driver to a driven member that is coaxially arranged with the driver.

[0064] REFERENCE SIGNS LIST 1 Motor (motor with reducer) 2 Motor section 3 Reducer section 4 Worm 5 Worm wheel (driver) 6 Output shaft (driven body) 10 Power transmission mechanism 11 First protrusion 11a First side surface 12 Second protrusion 12a Second side surface 12ao Outer end portion 13 Third protrusion 14 Fourth protrusion 15 Buffer member 24 Motor shaft C Axis C1 First axial direction C2 Second axial direction α Predetermined angle

Claims

1. A power transmission mechanism that transmits the rotational driving force of a driver to a driven body arranged coaxially with the driver, comprising: a first protrusion protruding from one of the driver and the driven body toward a first axial direction among axial directions in which the axis of the driver extends; and a second protrusion protruding from the other of the driver and the driven body toward a second axial direction opposite to the first axial direction, wherein the first protrusion has a first side surface facing in a circumferential direction around the axis, and the second protrusion has a second side surface that comes into surface contact with the first side surface in a power transmission state in which the rotational driving force is transmitted to the driven body, and wherein in a power transmission start state immediately before entering the power transmission state, only an outer end of the second side surface that is located radially outward from the axis line abuts against the first side surface.

2. A power transmission mechanism as described in claim 1, characterized in that the first side surface extends in the radial direction, and the second side surface is tapered in the radial direction, inclining at a predetermined angle toward the first side surface as it moves radially outward.

3. A power transmission mechanism as described in claim 1, further comprising: a third protrusion protruding from one of the driver and the driven body toward the first axial direction at a position different from the first protrusion in the radial direction; a fourth protrusion protruding from the other of the driver and the driven body toward the second axial direction at the same position in the radial direction as the third protrusion; and a buffer member interposed between the third protrusion and the fourth protrusion in the circumferential direction, and compressively deforming during a transition from a neutral state in which the first protrusion and the second protrusion are not in contact to the power transmission start state.

4. A power transmission mechanism as described in claim 3, characterized in that the first protrusions and the second protrusions are provided in equal numbers and are arranged alternately in the circumferential direction, the third protrusions and the fourth protrusions are provided in equal numbers and are arranged alternately in the circumferential direction, and the number of the first protrusions and the second protrusions is equal to or greater than the number of the third protrusions and the fourth protrusions.

5. A power transmission mechanism according to claim 4, characterized in that the number of said first protrusions and said second protrusions is six, and the number of said third protrusions and said fourth protrusions is three.

6. A motor with a reducer, comprising: a motor section having a motor shaft; and a reducer section integrally assembled to the motor section, wherein the reducer section comprises a worm that rotates integrally with the motor shaft of the motor section, a worm wheel that meshes with the worm, and an output shaft that is configured to be rotatable together with the worm wheel, wherein a power transmission mechanism according to any one of claims 1 to 5 is applied to the worm wheel as the driver and the output shaft as the driven body.

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