speed reduction mechanism

Abstract

Provided is a speed reduction mechanism that sufficiently increases the engagement strength of a first gear and a second gear, improves the power transmission efficiency of both, and can easily deal with a larger reduction ratio. When viewed in the axial direction of a pinion, the center of a pinion body and the center of a helical tooth are offset from each other, the diameter of the helical tooth is larger than the diameter of the pinion body, and a portion of the pinion body protrudes to the outside of an imaginary circle that forms the outline of the helical tooth. The cross-sectional shape of the pinion can be a non-circular shape that causes a portion of the pinion body to protrude to the outside of the imaginary circle that forms the outline of the helical tooth. The diameter of the pinion can be inhibited from increasing, the strength of the pinion can be improved, the strength of both the pinion and the helical gear can be improved, and the power transmission efficiency of both can be improved. Thus, a larger reduction ratio can be easily dealt with.

Description

Technical Field

[0001] The present invention relates to a speed reduction mechanism including a first gear and a second gear. Background Technology

[0002] Conventionally, drive sources for windshield wiper systems or power window systems mounted in automobiles and other vehicles have been equipped with reduction gears to achieve large outputs despite their small size. Such reduction gears used in vehicle-mounted drive sources are described, for example, in Patent Document 1.

[0003] The reduction mechanism described in Patent Document 1 includes a pinion (first gear) with a single helical tooth and a helical gear (second gear) with multiple helical teeth. By engaging the helical tooth with the multiple helical teeth, the high-speed rotation of the pinion is converted into the low-speed rotation of the helical gear. Thus, a reduction mechanism that further increases the reduction ratio and includes gears with appropriate meshing shapes is realized.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-184060 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Furthermore, in order to achieve the technology described in Patent Document 1, for example, it is considered to make the pinion, which is a slender part, out of steel, and the helical gear, which is a large disc-shaped part, out of resin. Based on this, in order to easily obtain a relatively large reduction ratio, the reduction mechanism including these pinion and helical gears needs to have sufficient meshing strength between the two.

[0009] However, in the technology described in Patent Document 1, the portion (core circle) where the rotation center of the pinion is located is arranged radially inside an imaginary circle (tooth profile circle) forming the helical teeth in a direction intersecting the axial direction. Therefore, when forming a reduction mechanism with the same volume as before, for example, if the helical teeth of the helical gear are made thick-walled and correspondingly, conversely, the helical teeth become small-diameter, and consequently, the portion (core circle) located at the rotation center of the pinion also becomes thinner. That is, ensuring the strength of the helical gear and ensuring the strength of the pinion are mutually balanced.

[0010] The purpose of this invention is to provide a reduction mechanism that ensures sufficient meshing strength between the first gear and the second gear, improves the power transmission efficiency of both, and can easily handle larger reduction ratios.

[0011] Technical means to solve the problem

[0012] In one embodiment of the present invention, a speed reduction mechanism is provided, including a first gear and a second gear. The speed reduction mechanism is characterized in that the first gear has: a first body portion, the cross-section of which is circular in the direction intersecting the axial direction of the first gear; and a helical tooth, which is helically disposed around the first body portion, the cross-section of which is crescent-shaped in the direction intersecting the axial direction of the first gear. The second gear has: a second body portion, the cross-section of which is circular in the direction intersecting the axial direction of the second gear; and a plurality of helical teeth, which are disposed around the second body portion for meshing with the helical tooth. When viewed axially from the first gear, the center of the first body portion is offset from the center of the helical tooth, the diameter of the helical tooth is larger than the diameter of the first body portion, and a portion of the first body portion extends to the outside of the imaginary circle forming the shape of the helical tooth.

[0013] The effects of the invention

[0014] With this invention, when viewed axially, the first gear can be shaped such that a portion of the first body (core circle) extends beyond the outer edge of an imaginary circle (tooth profile circle) forming the spiral teeth (non-circular). This allows for the suppression of excessive diameter in the first gear while simultaneously increasing its strength. Consequently, the strength of both the first and second gears is improved, thereby enhancing their power transmission efficiency. Consequently, larger reduction ratios can be easily accommodated. Attached Figure Description

[0015] Figure 1 This is a perspective view of the motor with a speed reduction mechanism, viewed from the side of the connector connection.

[0016] Figure 2 This is a 3D view of a motor with a reduction gear mechanism, viewed from the output shaft side.

[0017] Figure 3 This is a three-dimensional diagram illustrating the internal structure of a motor with a speed reduction mechanism.

[0018] Figure 4 It is a magnified three-dimensional view of the meshing part of the speed reduction mechanism.

[0019] Figure 5 yes Figure 4 A-direction view.

[0020] Figure 6 of (a), Figure 6 (b) is a cross-sectional view illustrating the design concept of the speed reduction mechanism.

[0021] Figure 7 This is a cross-sectional view illustrating the simulation-based fine-tuning.

[0022] Figure 8 This is a cross-sectional view illustrating the specifications (data of each part) of the pinion.

[0023] Figure 9 (a)~ Figure 9 (e) is an explanatory diagram illustrating the operation of the speed reduction mechanism.

[0024] Explanation of symbols

[0025] 10: Motor with a speed reduction mechanism

[0026] 11: Cover

[0027] 12: Shell

[0028] 12a: Bottom wall portion

[0029] 12b: Side wall portion

[0030] 12c: Shell flange

[0031] 12d: Protrusion

[0032] 12e: Reinforcing Rib

[0033] 12f: Bearing component housing

[0034] 12g: Stop ring

[0035] 13: Cover component

[0036] 13a: Body part

[0037] 13b: Cover flange

[0038] 13c: Motor Housing Section

[0039] 13d: Connector connection part

[0040] 13e: Terminal component

[0041] 20: Brushless motor

[0042] 21: Stator

[0043] 21a: Coil

[0044] 22: Rotor

[0045] 22a: Rotor body

[0046] 22b: Permanent magnet

[0047] 30: Speed ​​reduction mechanism

[0048] 31: Small gear (first gear)

[0049] 31a: Installation Department

[0050] 31b: Pinion body (first body section)

[0051] 31c: Spiral teeth

[0052] 31d: Weld overlay section

[0053] 31e: Depression

[0054] 31f: Another weldment

[0055] 32: Helical gear (second gear)

[0056] 32a: Gear body (second body section)

[0057] 32b: Cylindrical part

[0058] 32c: Helical teeth

[0059] 32d: Engagement recess

[0060] 33: Ball bearing

[0061] 34: Output shaft

[0062] AL: Auxiliary lines

[0063] BC1: Reference circle

[0064] BC2: Tooth root round

[0065] C1: Center of pinion body 31b

[0066] C2: Center of spiral tooth 31c

[0067] CP: Contact part

[0068] LN1: Outline of the pinion body 31b

[0069] LN2: Outline of the spiral teeth 31c

[0070] LN3: Circular tangent line

[0071] VC: Imaginary circle (tooth-shaped circle) Detailed Implementation

[0072] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0073] Figure 1 This is a perspective view of a motor with a speed reduction mechanism, viewed from the side of the connector connection. Figure 2 This is a perspective view of a motor with a reduction gear mechanism, viewed from the output shaft side. Figure 3 A perspective view illustrating the internal structure of a motor with a speed reduction mechanism. Figure 4 This is a three-dimensional view showing an enlarged view of the meshing part of the speed reduction mechanism. Figure 5 express Figure 4 View from direction A, Figure 6 of (a), Figure 6 (b) is a cross-sectional view illustrating the design concept of the reduction mechanism. Figure 7 This is a cross-sectional view illustrating the simulation-based fine-tuning portion. Figure 8 A cross-sectional view illustrating the specifications (data for each part) of the pinion. Figure 9 (a)~ Figure 9 (e) represents an explanatory diagram illustrating the operation of the speed reduction mechanism.

[0074] Figure 1 and Figure 2 The motor 10 with a reduction gear shown is used, for example, as a drive source for a windshield wiper unit (not shown) mounted on a vehicle such as an automobile. Specifically, the motor 10 with the reduction gear is disposed on the front side of the front glass (not shown) and causes the windshield wiper member (not shown), which is oscillating freely on the front glass, to oscillate within a predetermined wiping range (between the downward reversing position and the upward reversing position).

[0075] The motor 10 with a reduction gear includes a housing 11 forming its outer contour. For example... Figure 3 As shown, a brushless motor 20 and a reduction gear 30 are rotatably housed inside the casing 11. Here, as... Figure 1 and Figure 2 As shown, the casing 11 is formed by an aluminum casing 12 and a plastic cover member 13.

[0076] The shell 12 is formed into a generally bowl shape by injection molding of molten aluminum material. Specifically, the shell 12 includes a bottom wall portion 12a, a side wall portion 12b integrally disposed around it, and a shell flange 12c provided on the opening side (left side in the figure) of the shell 12.

[0077] At approximately the center of the bottom wall portion 12a, a cylindrical protrusion 12d is integrally provided to rotatably support the output shaft 34. On the radially inner side of the protrusion 12d, a cylindrical bearing member (not shown), referred to as a sliding bearing, is installed, thereby allowing the output shaft 34 to rotate smoothly relative to the protrusion 12d without wobbling.

[0078] Furthermore, a plurality of reinforcing ribs 12e are integrally provided on the radially outer side of the protrusion 12d, extending radially from the protrusion 12d as the center. These reinforcing ribs 12e are disposed between the protrusion 12d and the bottom wall portion 12a, forming a roughly triangular shape. These reinforcing ribs 12e improve the fixing strength of the protrusion 12d to the bottom wall portion 12a and prevent undesirable conditions such as the protrusion 12d tilting relative to the bottom wall portion 12a.

[0079] Furthermore, a bearing component receiving portion 12f is integrally provided at a position offset from the protrusion 12d on the bottom wall portion 12a. The bearing component receiving portion 12f is formed into a bottomed cylindrical shape and protrudes in the same direction as the protrusion 12d. Inside the bearing component receiving portion 12f, a ball bearing 33 (see reference) that rotatably supports the front end side of the pinion 31 is housed. Figure 3 ).

[0080] Here, as Figure 2 As shown, a retaining ring 12g is provided between the protrusion 12d and the output shaft 34. This prevents the output shaft 34 from axially wobbling in the protrusion 12d. Therefore, sufficient quietness is ensured for the motor 10 with the reduction gear mechanism.

[0081] The cover member 13 forming the housing 11 is formed into a generally flat plate shape by injection molding of a resin material such as plastic. Specifically, the cover member 13 includes a body portion 13a and a cover flange 13b integrally disposed therearound. The cover flange 13b abuts against the housing flange 12c via a sealing member such as an O-ring (not shown). This prevents rainwater or dust from entering the interior of the housing 11.

[0082] Additionally, a brushless motor 20 is integrally housed in the main body 13a of the cover member 13 (see reference). Figure 3 The motor housing 13c is formed as a bottomed cylindrical section and protrudes to the side opposite to the housing 12. With the cover member 13 installed on the housing 12, the motor housing 13c faces the bearing member housing 12f of the housing 12. Furthermore, the stator 21 of the brushless motor 20 (see reference 12f) is fixed inside the motor housing 13c. Figure 3 ).

[0083] Furthermore, a connector connection portion 13d is integrally provided on the body portion 13a of the cover member 13 for connection to an external connector (not shown) on the vehicle side. Inside the connector connection portion 13d, multiple terminal members 13e (for supplying drive current to the brushless motor 20) are located. Figure 1 Only one end of the brushless motor 20 is shown in the diagram. Drive current is supplied from the external connector to the brushless motor 20 via these terminal components 13e.

[0084] Furthermore, a control board (not shown) is provided between the other end of the plurality of terminal members 13e and the brushless motor 20 to control the rotation state (speed or direction of rotation, etc.) of the brushless motor 20. As a result, the wiper member fixed to the front end of the output shaft 34 swings within a predetermined wiping range on the windshield. Additionally, the control board is fixed to the inside of the body portion 13a of the cover member 13.

[0085] like Figure 3 As shown, the brushless motor 20 housed inside the housing 11 includes an annular stator 21. The stator 21 is fixed to the motor housing portion 13c of the cover member 13 in an anti-rotation state (see reference). Figure 1 and Figure 2 (the interior of)

[0086] The stator 21 is formed by stacking multiple thin steel plates (magnetic bodies), and has multiple teeth (not shown) on its radially inner side. Furthermore, multiple turns of U-phase, V-phase, and W-phase coils 21a are wound around these teeth using methods such as concentrated winding. Thus, by alternately supplying drive current to each coil 21a at predetermined times, the rotor 22, located radially inner side of the stator 21, is rotated in a predetermined direction with a predetermined drive torque.

[0087] A rotor 22 is provided radially inside the stator 21, rotating freely through a tiny gap (air gap). The rotor 22 includes a rotor body 22a formed by stacking multiple thin steel plates (magnetic bodies) into a generally cylindrical shape. Furthermore, a cylindrical permanent magnet 22b is mounted on the outer periphery of the rotor body 22a. Here, the permanent magnet 22b is magnetized with its N poles and S poles alternating in its circumferential direction. The permanent magnet 22b is also firmly fixed to the outer periphery of the rotor body 22a using an adhesive or the like.

[0088] Thus, the brushless motor 20 of this embodiment is a brushless motor with a surface permanent magnet (SPM) structure in which a permanent magnet 22b is fixed on the outer peripheral portion (surface) of the rotor body 22a. However, it is not limited to a brushless motor with an SPM structure; a brushless motor with an interior permanent magnet (IPM) structure in which multiple permanent magnets are embedded in the rotor body 22a may also be used.

[0089] Alternatively, instead of a single cylindrical permanent magnet 22b, multiple permanent magnets with arc-shaped cross-sections intersecting the axis of the rotor body 22a can be fixed at equal intervals to the surface of the rotor body 22a in an alternating manner with alternating magnetic poles. Furthermore, the number of poles of the permanent magnet 22b can be arbitrarily set to two poles or more, depending on the specifications of the brushless motor 20.

[0090] like Figure 3 As shown, the reduction mechanism 30 housed inside the casing 11 includes a pinion (first gear) 31 formed in the shape of a rod and a helical gear (second gear) 32 formed in the shape of a disc. Here, the axis of the pinion 31 is parallel to the axis of the helical gear 32. Thus, compared with a worm gear reducer that includes a worm and a worm wheel with mutually orthogonal axes, the reduction mechanism 30 can be made more compact.

[0091] Furthermore, the pinion 31 is disposed on the brushless motor 20 side (drive source side) of the motor 10 with the reduction mechanism, and the helical gear 32 is disposed on the output shaft 34 side (drive object side) of the motor 10 with the reduction mechanism. That is, the reduction mechanism 30 reduces the high-speed rotation of the pinion 31 with fewer teeth to the low-speed rotation of the helical gear 32 with more teeth.

[0092] Here, the base end of the pinion 31 is firmly fixed to the rotation center of the rotor body 22a by pressing or the like, and the pinion 31 rotates integrally with the rotor body 22a. That is, the pinion 31 is driven to rotate by the rotor 22. Moreover, the front end of the pinion 31 is rotatably supported by the ball bearing 33. Furthermore, at the rotation center of the helical gear 32, the base end of the output shaft 34 is firmly fixed by pressing or the like, and the output shaft 34 rotates integrally with the helical gear 32.

[0093] The pinion 31 forming the reduction mechanism 30 is made of steel (metal). Figures 4 to 9 The shape is as shown. Specifically, cylindrical mounting portions 31a are provided on the base end side and the front end side of the pinion 31. The mounting portion 31a on the base end side is fixed to the rotor body 22a, and the mounting portion 31a on the front end side is rotatably supported by the ball bearing 33. That is, the center C1 of the pinion 31 (mounting portion 31a) coincides with the rotation center of the rotor body 22a and the ball bearing 33.

[0094] The pinion 31 includes a pinion body 31b extending along the axial direction of the pinion 31. The pinion body 31b corresponds to the first body portion in this invention, and its cross-section in the direction intersecting the axial direction of the pinion 31 (orthogonal direction) is circular. Furthermore, the pinion body 31b forms the "core" portion of the pinion 31 and rotates around a center C1. The rigidity (bending strength, etc.) of the pinion 31 is influenced by the thickness of the pinion body 31b. In this embodiment, to match the volume of the motor 10 with the reduction mechanism, the thickness of the pinion body 31b (core circle) is as follows: Figure 8 The figure shows a radius r1 ≒ 1.7 mm (diameter 2 × r1 ≒ 3.4 mm).

[0095] Furthermore, the pinion 31 includes a single helical tooth 31c that meshes with the helical teeth 32c of the helical gear 32. The helical tooth 31c corresponds to the first tooth portion in this invention and is integrally disposed around the pinion body 31b in a helical manner. Additionally, the cross-section of the helical tooth 31c in the direction intersecting the axial direction of the pinion 31 (orthogonal direction) is formed in a crescent shape. Figure 8 (The grid portion). The helical teeth 31c are connected in a helical shape along the axial direction of the pinion body 31b, and the number of teeth is "1". The rigidity of the helical teeth 31c, i.e., the efficiency of power transmission, is affected by the thickness of the helical teeth 31c. In this embodiment, the size of the imaginary circle (tooth circle) VC forming the helical teeth 31c is matched with the volume of the motor 10 with the reduction mechanism, as shown in the figure. Figure 8 The figure shows a radius r2 ≒ 2.0 mm (diameter 2 × r2 ≒ 4.0 mm) (r2 > r1).

[0096] Here, as Figure 8 As shown, the center C2 of the helical tooth 31c (the center C2 of the imaginary circle VC) is eccentric (offset) relative to the center C1 of the pinion body 31b by a predetermined interval distance L1. Furthermore, in this embodiment, the interval distance L1 is a value obtained by adding the reference eccentricity (≒1.0 mm) to the eccentricity correction amount (≒0.8 mm) (L1 ≒1.8 mm). That is, when viewed axially from the pinion 31... Figure 4 When the arrow points in the direction of A, the center C1 of the pinion body 31b and the center C2 of the helical tooth 31c are offset from each other. Furthermore, the diameter of the helical tooth 31c (imaginary circle VC) is larger than the diameter of the pinion body 31b. Moreover, a portion of the pinion body 31b extends beyond the outer side (upper side in the figure) of the imaginary circle VC that forms the shape of the helical tooth 31c.

[0097] Therefore, when viewed axially, the cross-sectional shape of the pinion 31 is set to be approximately oval (non-circular), which can sufficiently ensure the strength of the pinion body 31b and the helical teeth 31c without increasing the volume of the motor 10 with the reduction mechanism.

[0098] Here, when viewed axially, the outline line LN1 of the pinion body 31b and the outline line LN2 of the helical tooth 31c are connected by a pair of arc-shaped tangents LN3 that convex outwards radially from the pinion 31. Therefore, the shape of the pinion 31 is formed by smooth curves of various curvatures, which allows the pinion 31 to be manufactured with good precision using the "cyclone milling method (outer diameter cyclone milling)".

[0099] In addition, such as Figure 8 As shown, in the portion of a pair of arc-shaped tangents LN3 of the pinion 31, a weld overlay portion 31d is provided in such a way as to fill the recessed portion between the pinion body 31b and the helical teeth 31c.

[0100] In this way, the overall strength of the pinion 31 can be fully ensured, thus improving the power transmission efficiency of the reduction mechanism 30. Here, the center C2 of the helical tooth 31c (imaginary circle VC) follows the rotation trajectory RT as the pinion body 31b rotates. In other words, the rotation trajectory RT becomes the reference circle of the helical tooth 31c.

[0101] In addition, such as Figure 8 As shown, if an auxiliary line AL is drawn from the center C1 of the pinion body 31b toward the center C2 (downwards in the figure) of the helical tooth 31c, and the auxiliary line AL is further extended to the surface of the helical tooth 31c, then the auxiliary line AL intersects the surface of the helical tooth 31c. The intersection point becomes the vertex TP of the helical tooth 31c.

[0102] Next, use Figure 6 of (a), Figure 6 (b) to Figure 8 The design concept of pinion 31 will be explained.

[0103] Consider motor 10 with a reduction gear (refer to) Figure 1 and Figure 2 Based on the volume of the gear, the size of the motor 10 with the reduction gear is kept as small as possible, while increasing the strength of the pinion 31. Specifically, such as... Figure 6As shown in (a), the pinion body 31b with a diameter of 2×r1 is eccentrically positioned relative to the helical teeth 31c with a diameter of 2×r2 by a predetermined interval distance L2. In this design phase, the interval distance L2 between the center C2 of the helical teeth 31c and the rotation center C1 of the pinion body 31b is a reference eccentricity amount (≒1.0 mm). This allows for an increase in the strength of the pinion 31 without significantly increasing the volume of the motor 10 with the reduction gear mechanism.

[0104] On the other hand, such as Figure 6 As shown in (a), when the reduction mechanism 30 is operating, in order to prevent interference between the pinion body 31b and the helical teeth 32c of the helical gear 32, the helical teeth 32c need to be retracted by a retraction dimension BK. That is, the tooth height H of the helical teeth 32c needs to be shortened by the retraction dimension BK. In this arrangement, the meshing depth between the helical teeth 31c and the helical teeth 32c becomes shallower, and the meshing strength between the helical teeth 31c and the helical teeth 32c decreases. Therefore, the power transmission efficiency of the reduction mechanism 30 is reduced.

[0105] To avoid this situation, in the deceleration mechanism 30 of this embodiment, such as Figure 6 As shown in (b), to ensure sufficient tooth height H of the helical teeth 32c, the pinion body 31b with a diameter of 2×r1 is recessed (offset) radially outward of the helical teeth 32. Specifically, the pinion body 31b with a diameter of 2×r1 is eccentrically positioned relative to the helical teeth 31c with a diameter of 2×r2 by a predetermined interval distance L1. The difference between the interval distance L1 and the interval distance L2 in this case is the eccentricity correction amount (≒0.8mm). Thus, sufficient meshing strength between the helical teeth 31c and the helical teeth 32c is achieved without significantly increasing the volume of the motor 10 with the reduction mechanism.

[0106] In the subsequent design phase (final stage), simulations using the finite element method (FEM analysis, etc.) were conducted to confirm whether the reduction mechanism 30 could actually operate, and other adverse conditions were discovered. Specifically, in Figure 6 In the design phase shown in (b), the helical teeth 31c with a diameter of 2×r2 enter the meshing recess 32d between adjacent helical teeth 32c of the helical gear 32 with virtually no clearance. In this state, as Figure 7 As shown, it was determined that if the reduction mechanism 30 is operated in the simulation, the tip portion of the helical tooth 31c ( Figure 8 The portion near the vertex TP) and the portion of the tip of the helical tooth 32c ( Figure 7 Interference occurs on the upper part (the grid part in the figure).

[0107] Therefore, in this embodiment, as Figure 8As shown, the tip of the helical tooth 31c is cut into an arc shape with a minimal amount of cutting (fine-tuning) D to the extent that it does not interfere with the tip of the helical tooth 32c. Specifically, as... Figure 8 As shown by the double-dotted line, the tip of the helical tooth 31c has a recessed portion 31e that is further radially inward than the imaginary circle VC of the helical tooth 31c. Thus, by providing the recessed portion 31e, interference between the helical tooth 31c and the helical tooth 32c is prevented. Consequently, the reduction mechanism 30 can operate smoothly.

[0108] However, if the strength of the pinion 31 decreases due to the recess 31e, then there can be a space with extra room around the pinion 31. Specifically, for example... Figure 8 As shown, on the outer side of the pinion body 31b, for example, another weld overlay portion 31f (the dotted line portion in the figure) with a thickness dimension G is provided. In this case, the outline of the portion forming the other weld overlay portion 31f also becomes convex and arc-shaped radially outward of the pinion 31. As a result, the pinion 31 can be manufactured easily and with high precision using the "cyclone milling machining method (outer diameter cyclone milling)".

[0109] As described above, regarding the cross-sectional shape of the pinion 31, the diameter of the helical tooth 31c is made larger than the diameter of the pinion body 31b, and the portion of the tip of the helical tooth 31c (near the vertex TP) is cut by a minimum amount D to avoid interference. Therefore, the contact state between the helical tooth 31c and the helical tooth 32c is deemed sufficiently reasonable. More specifically, as... Figure 9 (a) and Figure 9 As shown in (e), the helical tooth 31c is in a state where it contacts the helical tooth 32c at the contact portion CP on a roughly lateral side, and the direction of the load F applied from the helical tooth 31c is roughly the same as the rotation direction Rb of the helical gear 32. In other words, the "pressure angle" of the helical tooth 31c relative to the helical tooth 32c becomes smaller.

[0110] Thus, the strength of both the pinion 31 and the helical gear 32 becomes sufficient, and the helical teeth 31c will not interfere with the helical teeth 32c. Therefore, it is determined that the power transmission efficiency of the reduction mechanism 30 is sufficiently improved.

[0111] like Figures 3 to 7As shown, the helical gear 32 forming the reduction mechanism 30 is formed into a generally disc-shaped form by injection molding of a resin material such as plastic. Specifically, the helical gear 32 includes a gear body 32a, the cross-section of which is circular in the direction (orthogonal direction) intersecting the axial direction of the helical gear 32. The gear body 32a corresponds to the second body portion in this invention. Furthermore, the base end of the output shaft 34 is fixed to the rotation center of the gear body 32a, and a cylindrical portion 32b extending axially along the output shaft 34 is integrally provided on the outer periphery of the gear body 32a.

[0112] On the radially outer side of the cylindrical portion 32b, that is, around the gear body 32a, a plurality of helical teeth (second teeth) 32c are integrally provided in a manner arranged circumferentially on the cylindrical portion 32b. These helical teeth 32c are inclined at a predetermined angle relative to the axial direction of the helical gear 32, and are engaged by the helical teeth 31c of the pinion 31. Thus, the helical gear 32 rotates along with the rotation of the helical teeth 31c. Furthermore, the number of teeth of the helical teeth 32c of the helical gear 32 is "40". That is, in this embodiment, the reduction ratio of the reduction mechanism 30 is "40", and if the pinion 31 rotates 40 revolutions, the deceleration of the helical gear 32 can be obtained by rotating one revolution.

[0113] Furthermore, a meshing recess 32d is provided between adjacent helical teeth 32c for the helical teeth 31c of the pinion 31 to enter. That is, the meshing recess 32d, like the helical teeth 32c, is inclined at a predetermined angle relative to the axial direction of the helical gear 32. Moreover, the center of curvature C3 of the meshing recess 32d is located on the reference circle BC1 of the helical gear 32. Additionally, the helical teeth 31c with radius r2 (… Figure 8 The mesh portion enters the meshing recess 32d almost without gaps.

[0114] Here, the tooth height H of the helical tooth 32c is the height from the root circle BC2 through the deepest part of the meshing recess 32d to the reference circle BC1 (refer to...). Figure 5 In addition, the number of teeth of the helical gear 32 is "40", and the number of meshing recesses 32d is also "40". Therefore, in this embodiment, the angle formed by adjacent meshing recesses 32d is "9 degrees".

[0115] Next, the operation of the reduction mechanism 30 formed as described above, namely the meshing operation of the pinion 31 and the helical gear 32, will be explained in detail using the accompanying drawings.

[0116] like Figure 9 As shown in (a), when the pinion 31 passes through the brushless motor 20 (refer to...) Figure 3When the gear rotates in the direction of arrow Ra, driven by the helical gear 31c meshes with the helical gear 32c. Thus, in the contact portion CP, the driving force (load F) from the helical gear 31c is transmitted to the side of the helical gear 32c. This meshing action of the helical gear 31c relative to the helical gear 32c (contact portion CP) accompanies the rotation of the pinion 31 and the helical gear 32, gradually moving along the axial direction of the pinion 31 and the helical gear 32. Furthermore, the helical gear 32c is tilted relative to the axial direction of the helical gear 32, causing the helical gear 32 to rotate at a reduced speed compared to the pinion 31.

[0117] Here, as Figure 9 (a)~ Figure 9 As shown in (e), if we only consider a portion of the axial direction of the pinion 31 and the helical gear 32, then rotating the pinion 31 one revolution in the direction of arrow Ra, as shown in (e). Figure 9 (a)~ Figure 9 As shown in (e), the helical tooth 31c passes over a helical tooth 32c (marked with an asterisk in the figure). Thus, as... Figure 9 As shown in (e), the helical tooth 31c, after one revolution, meshes with the next helical tooth 32c (marked with an asterisk in the figure). Furthermore, as... Figure 9 (b) Figure 9 As shown in (d), when a portion of the helical teeth 31c in the axial direction of the pinion 31 is not engaged with the helical teeth 32c, the helical teeth 31c in the axial direction of the other portion of the pinion 31 are engaged with the helical teeth 32c.

[0118] Thus, when the helical tooth 31c rotates one revolution, the helical gear 32 rotates by the amount of one helical tooth 32c (refer to the movement of the helical tooth 32c marked with an asterisk in the diagram). That is, during the period when the pinion 31 rotates one revolution, the helical gear 32 rotates 9 degrees. In other words, by rotating the pinion 31 40 revolutions, the helical gear 32 gradually rotates one revolution (reduction ratio 40). Therefore, the helical gear 32 rotates with a rotational torque (high torque) 40 times that of the pinion 31.

[0119] As detailed above, according to this embodiment, when viewed axially, the center C1 of the pinion body 31b and the center C2 of the helical tooth 31c are offset from each other, the diameter of the helical tooth 31c is larger than the diameter of the pinion body 31b, and a part of the pinion body 31b extends to the outside of the imaginary circle VC that forms the shape of the helical tooth 31c.

[0120] Therefore, when viewed axially, the pinion 31 can be shaped (cross-sectional shape) such that a portion of the pinion body 31b (core circle) extends beyond the outer side of the imaginary circle (tooth profile circle) VC that forms the helical teeth 31c (approximately oval, non-circular). This allows for the suppression of excessive diameter increase in the pinion 31 while simultaneously improving its strength. Consequently, the strength of both the pinion 31 and the helical gear 32 can be increased, improving their power transmission efficiency. Furthermore, it allows for easier handling of larger reduction ratios.

[0121] Furthermore, according to this embodiment, when viewed axially, the outline line LN1 of the pinion body 31b and the outline line LN2 of the helical tooth 31c are connected to each other by a pair of arc-shaped tangents LN3 that are convex outward from the radial side of the pinion 31.

[0122] Therefore, the shape of the pinion 31 can be formed by smooth curves of various curvatures, and the pinion 31 can be easily and accurately manufactured using the "cyclone milling machining method (outer diameter cyclone milling)".

[0123] Furthermore, according to this embodiment, the spiral teeth 31c are provided with a recessed portion 31e that is further radially inward than the imaginary circle VC of the spiral teeth 31c.

[0124] This prevents interference between the helical teeth 31c and the helical teeth 32c, enabling smooth operation of the reduction mechanism 30, i.e., smooth meshing of the helical teeth 31c and the helical teeth 32c. Consequently, the power transmission efficiency of the reduction mechanism 30 can be improved, thereby suppressing the power consumption of the brushless motor 20, which serves as the drive source.

[0125] Furthermore, according to this embodiment, the strength of the pinion 31 and helical gear 32 can be sufficiently ensured to achieve a long service life, and the power consumption of the brushless motor 20, which serves as the drive source, can be suppressed. Therefore, energy saving related to manufacturing and operation can be achieved. Consequently, it can particularly contribute to Goal 7 (ensuring access to appropriate, reliable, sustainable and modern energy) and Goal 13 (taking urgent measures to address climate change and its impacts) of the United Nations-led Sustainable Development Goals (SDGs).

[0126] This invention is not limited to the described embodiments, and various modifications can be made without departing from its spirit. For example, in the described embodiment, the deceleration mechanism 30 is shown as being applied to the drive source of a windshield wiper unit mounted on a vehicle, but the invention is not limited thereto and can also be applied to other drive sources such as the drive source of an electric window unit, the drive source of a sunroof unit, and the drive source of a seat lift unit.

[0127] Furthermore, in the described embodiment, a case is shown in which a brushless motor 20 is used to drive the reduction mechanism 30, but the present invention is not limited to this, and a brushed motor or the like may be used instead of a brushless motor 20 for driving.

[0128] In addition, the material, shape, size, quantity, and placement of each component in the above embodiments are arbitrary as long as they enable the implementation of the present invention, and are not limited to the above embodiments.

Claims

1. A speed reduction mechanism, comprising a first gear and a second gear, characterized in that, The first gear has: The first body portion has a circular cross-section in the direction intersecting the axial direction of the first gear; and A spiral tooth is spirally arranged around the first body portion, and its cross-section in the direction intersecting the axial direction of the first gear is crescent-shaped. The second gear has: The second body portion has a circular cross-section in the direction intersecting the axial direction of the second gear; and Multiple helical teeth are disposed around the second body portion for engagement by the helical teeth. When viewed axially from the first gear, The center of the first body portion is offset from the center of the helical teeth. The diameter of the spiral teeth is larger than the diameter of the first body portion. A portion of the first body portion extends to the outside of an imaginary circle forming the shape of the spiral teeth, wherein, The imaginary circle is a reference circle formed by the rotational trajectory followed by the center of the spiral teeth as the first body rotates.

2. The speed reduction mechanism according to claim 1, characterized in that, When viewed axially from the first gear, the outline of the first body portion and the outline of the helical teeth are connected to each other by an arc-shaped tangent that is convex to the radially outward side of the first gear.

3. The speed reduction mechanism according to claim 1 or 2, characterized in that, The spiral teeth have a recessed portion that is further radially inward than the imaginary circle of the spiral teeth.

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