JP7570991B2 - Reduction mechanism - Google Patents

Description

The present invention relates to a reduction mechanism.

Conventionally, a reduction mechanism has been provided in the drive source of a wiper device, a power window device, etc., mounted on a vehicle such as an automobile, in order to obtain a large output while being compact. A reduction mechanism used in such an in-vehicle drive source is described, for example, in Patent Document 1.

The reduction gear mechanism described in Patent Document 1 includes a pinion gear (first gear) with one helical tooth and a helical gear (second gear) with multiple helical teeth. By meshing one helical tooth with the multiple helical teeth, the high-speed rotation of the pinion gear becomes the low-speed rotation of the helical gear. This makes it possible to achieve a larger reduction ratio while also achieving a smaller and lighter gear.

JP 2019-190614 A

In the technology described in the above-mentioned Patent Document 1, various shapes of the helical teeth are devised to suppress problems caused by the meshing of the helical teeth with a circular cross section and the helical teeth of the helical gear, i.e., large changes in pressure angle (large variations in power transmission efficiency) caused by deviations in the center-to-center pitch between the first gear and the second gear due to dimensional errors, etc.

However, the technology described in Patent Document 1 still had a large variation in power transmission efficiency (fluctuations in pressure angle) that made it difficult to commercialize the product, and it became necessary to further improve the power transmission efficiency between the helical teeth and helical teeth so that it could withstand mass production.

The object of the present invention is to provide a reduction mechanism that can stabilize the pressure angle at a small value even if the center pitch between the first gear and the second gear varies, and thus can improve the power transmission efficiency without variation between products.

In one aspect of the present invention, a reduction mechanism is provided with a first gear and a second gear, the first gear having a main body portion with a circular cross section in a direction intersecting the axial direction of the first gear, and one helical tooth provided around the main body portion, extending helically in the axial direction of the first gear, and having a crescent-shaped cross section in a direction intersecting the axial direction of the first gear, the second gear having a plurality of helical teeth with which the helical teeth mesh, the helical teeth having a tooth tip portion provided at the tip side of the helical teeth, a tooth bottom portion provided at the base end side of the helical teeth, and a meshing portion provided between the tooth tip portion and the tooth bottom portion with which the helical teeth mesh, the meshing portion being formed in the shape of an involute curve recessed in the tooth thickness direction of the helical teeth when viewed in the axial direction of the second gear.

According to the present invention, a meshing portion where the helical teeth mesh is provided between the tooth tip and tooth base that form the helical teeth, and when viewed in the axial direction of the second gear, the shape of the meshing portion is formed into the shape of an involute curve that is recessed in the tooth thickness direction of the helical teeth.

As a result, even if the center pitch between the first gear and the second gear varies, the pressure angle can be stabilized at a small value, and it is possible to improve the power transmission efficiency without variation between products. This makes it possible to realize a reduction mechanism that can withstand mass production.

2 is a perspective view of the motor with a reduction mechanism as viewed from the connector connection portion side. FIG. FIG. 2 is a perspective view of the motor with a reduction mechanism as viewed from the output shaft side. FIG. 2 is a perspective view illustrating an internal structure of a motor with a reduction mechanism. FIG. 4 is an enlarged perspective view of a meshing portion of the reduction mechanism. 5 is a cross-sectional view taken along line AA in FIG. 4. FIG. 2 is a cross-sectional view illustrating the shape of a helical gear's helical teeth. FIG. 2 is a schematic diagram illustrating an involute curve. FIG. 11 is a diagram illustrating the relationship between the deviation amount of the center pitch and the change in pressure angle (present invention). FIG. 13 is a diagram illustrating the relationship between the deviation amount of the center pitch and the change in pressure angle (comparative example). 1 is a graph comparing changes in pressure angle between the present invention and a comparative example. 4 is a graph showing the relationship between power transmission efficiency and pressure angle. FIG. 7 is a diagram showing a second embodiment of the present invention and corresponds to FIG. 6 .

The first embodiment of the present invention will be described in detail below with reference to the drawings.

Figure 1 shows a perspective view of a motor with a reduction gear mechanism seen from the connector connection side, Figure 2 shows a perspective view of a motor with a reduction gear mechanism seen from the output shaft side, Figure 3 shows a perspective view explaining the internal structure of the motor with a reduction gear mechanism, Figure 4 shows an enlarged perspective view of the meshing portion of the reduction gear mechanism, Figure 5 shows a cross-sectional view along line A-A in Figure 4, Figure 6 shows a cross-sectional view explaining the shape of the helical gear's helical teeth, Figure 7 shows a schematic diagram explaining an involute curve, Figure 8 shows a diagram explaining the relationship between the deviation in the center pitch and the pressure angle (present invention), Figure 9 shows a diagram explaining the deviation in the center pitch and the pressure angle (comparative example), Figure 10 shows a graph comparing the changes in pressure angle between the present invention and the comparative example, and Figure 11 shows a graph showing the relationship between power transmission efficiency and pressure angle.

The motor with speed reduction mechanism 10 shown in Figures 1 and 2 is used, for example, as a drive source for a wiper device (not shown) mounted on a vehicle such as an automobile. Specifically, the motor with speed reduction mechanism 10 is disposed in front of the windshield (not shown) and swings a wiper member (not shown) that is swingably mounted on the windshield within a predetermined wiping range (between a lower reversal position and an upper reversal position).

The motor 10 with a reduction gear mechanism has a housing 11 that forms its outer shell. Inside the housing 11, as shown in FIG. 3, the brushless motor 20 and the reduction gear mechanism 30 are housed so that they can rotate freely. Here, the housing 11 is formed from an aluminum casing 12 and a plastic cover member 13.

As shown in Figures 1 and 2, the casing 12 is formed in a roughly bowl shape by injection molding molten aluminum material. Specifically, the casing 12 has a bottom wall portion 12a, a side wall portion 12b integrally formed around the bottom wall portion 12a, and a case flange 12c provided on the opening side of the casing 12 (the left side in Figures 1 and 2).

A cylindrical boss 12d that rotatably holds the output shaft 34 is integrally provided at approximately the center of the bottom wall 12a. A cylindrical bearing member (not shown), known as a metal, is attached to the radially inner side of the boss 12d, allowing the output shaft 34 to rotate smoothly without rattling relative to the boss 12d.

In addition, multiple reinforcing ribs 12e are integrally provided on the radial outside of the boss portion 12d, extending radially from the boss portion 12d. These reinforcing ribs 12e are arranged between the boss portion 12d and the bottom wall portion 12a, and have a roughly triangular appearance. The reinforcing ribs 12e increase the fixing strength of the boss portion 12d to the bottom wall portion 12a, and prevent the boss portion 12d from tilting relative to the bottom wall portion 12a.

Furthermore, a bearing member accommodating portion 12f is provided integrally at a position eccentric to the boss portion 12d of the bottom wall portion 12a. The bearing member accommodating portion 12f is formed in a bottomed cylindrical shape and protrudes in the same direction as the boss portion 12d. As shown in FIG. 3, a ball bearing 33 that rotatably supports the tip side of the pinion gear 31 is accommodated inside the bearing member accommodating portion 12f.

As shown in FIG. 2, a retaining ring 12g is provided between the boss portion 12d and the output shaft 34. This prevents the output shaft 34 from rattling in the axial direction of the boss portion 12d. This ensures quiet operation of the reduction gear motor 10.

The cover member 13 that forms the housing 11 is formed in a generally flat plate shape by injection molding molten plastic material. Specifically, the cover member 13 comprises a main body 13a and a cover flange 13b that is integrally provided around the main body 13a. The cover flange 13b is abutted against the case flange 12c via a sealing member (not shown) such as an O-ring. This prevents rainwater and the like from entering the housing 11.

The main body 13a of the cover member 13 is integrally provided with a motor housing 13c that houses a brushless motor 20 (see FIG. 3). The motor housing 13c is formed in a bottomed cylindrical shape and protrudes on the side opposite the casing 12. When the cover member 13 is attached to the casing 12, the motor housing 13c faces the bearing member housing 12f of the casing 12. The stator 21 (see FIG. 3) of the brushless motor 20 is fixed inside the motor housing 13c.

Furthermore, a connector connection portion 13d is integrally provided on the main body portion 13a of the cover member 13 to which an external connector (not shown) on the vehicle side is connected. One end side of a plurality of terminal members 13e (only one is shown in FIG. 1) that supply drive current to the brushless motor 20 is exposed inside the connector connection portion 13d. Drive current is supplied from the external connector to the brushless motor 20 via these terminal members 13e.

A control board (not shown) that controls the rotation state (rotation speed, rotation direction, etc.) of the brushless motor 20 is provided between the other ends of the multiple terminal members 13e and the brushless motor 20. This causes the wiper member fixed to the tip end of the output shaft 34 to oscillate within a predetermined wiping range on the windshield. The control board is fixed to the inside of the main body portion 13a of the cover member 13.

As shown in FIG. 3, the brushless motor 20 housed inside the housing 11 has an annular stator 21. The stator 21 is fixed in the motor housing portion 13c (see FIG. 1) of the cover member 13 in a non-rotatable state.

The stator 21 is formed by laminating multiple thin steel plates (magnetic material), and multiple teeth (not shown) are provided on its radially inner side. U-phase, V-phase, and W-phase coils 21a are wound multiple times around these teeth using concentrated winding or the like. As a result, by alternately supplying a drive current to each coil 21a at a predetermined timing, the rotor 22 provided on the radially inner side of the stator 21 rotates with a predetermined drive torque in a predetermined rotational direction.

The rotor 22 is rotatably mounted on the radial inside of the stator 21 via a small gap (air gap). The rotor 22 has a rotor body 22a formed into a roughly cylindrical shape by laminating multiple thin steel plates (magnetic material), and a cylindrical permanent magnet 22b is provided on its outer periphery. The permanent magnet 22b is magnetized so that the north and south poles are arranged alternately in the circumferential direction. The permanent magnet 22b is fixed to the rotor body 22a with an adhesive or the like.

In this way, the brushless motor 20 according to this embodiment is a brushless motor with an SPM (Surface Permanent Magnet) structure in which the permanent magnet 22b is fixed to the surface of the rotor body 22a. However, the present invention is not limited to a brushless motor with an SPM structure, and it is also possible to use a brushless motor with an IPM (Interior Permanent Magnet) structure in which multiple permanent magnets are embedded in the rotor body 22a.

In addition, instead of a single cylindrical permanent magnet 22b, multiple permanent magnets with a roughly arc-shaped shape along a direction intersecting the axis of the rotor body 22a may be arranged at equal intervals so that the magnetic poles are arranged alternately around the circumference of the rotor body 22a. Furthermore, the number of poles of the permanent magnet 22b can be set arbitrarily, such as two poles or four poles or more, depending on the specifications of the brushless motor 20.

As shown in FIG. 3, the reduction mechanism 30 housed inside the housing 11 includes a pinion gear (first gear) 31 formed in a generally rod shape and a helical gear (second gear) 32 formed in a generally disk shape.

Here, the axis of the pinion gear 31 and the axis of the helical gear 32 are parallel to each other. This allows the reduction mechanism 30 to be more compact in size than a worm reduction gear equipped with a worm and a worm wheel whose axes intersect.

The pinion gear 31 is disposed on the input side (drive source side) of the motor 10 with a reduction mechanism, and the helical gear 32 is disposed on the output side (driven object side) of the motor 10 with a reduction mechanism. In other words, the reduction mechanism 30 reduces the high-speed rotation of the pinion gear 31, which has a small number of teeth, to the low-speed rotation of the helical gear 32, which has a large number of teeth.

Here, the base end side of the pinion gear 31 is fixed to the center of rotation of the rotor body 22a by press fitting or the like, and the pinion gear 31 rotates integrally with the rotor body 22a. In other words, the pinion gear 31 functions as the drive shaft of the motor with reduction mechanism 10.

The tip end of the pinion gear 31 is rotatably supported by a ball bearing 33. Furthermore, the base end of the output shaft 34 is fixed to the center of rotation of the helical gear 32 by press fitting or the like, and the output shaft 34 rotates integrally with the helical gear 32.

The pinion gear 31 forming the reduction gear mechanism 30 is made of metal and has a shape as shown in Figs. 3 to 5 and 8. Specifically, the pinion gear 31 has fixed parts 31a formed in a substantially cylindrical shape on both axial sides. The fixed part 31a on the axial base end side is fixed to the rotor body 22a, and the fixed part 31a on the axial tip side is rotatably supported by the ball bearing 33. In other words, the rotation center C1 of the pinion gear 31 (fixed part 31a) coincides with the rotation center of the rotor body 22a and the ball bearing 33.

As shown in FIG. 5, the pinion gear 31 has a pinion body 31b centered on the center of rotation C1. The pinion body 31b forms the core of the pinion gear 31 and corresponds to the main body in the present invention. The pinion body 31b has a circular cross section in a direction intersecting the axial direction of the pinion gear 31, and is formed in a generally cylindrical shape with a smaller diameter than the fixed portion 31a. Specifically, the radius R1 of the pinion body 31b is approximately half the radius R2 of the fixed portion 31a (R1 ≒ R2/2).

The pinion body 31b also has spiral teeth 31c formed integrally on the radial outside thereof, which mesh with the helical gear 32. The spiral teeth 31c extend spirally in the axial direction of the pinion gear 31, and the cross section in the direction intersecting the axial direction of the pinion gear 31 is formed in a crescent shape (see the shaded portion in FIG. 5). In other words, as shown in FIG. 5, the portion of the pinion gear 31 excluding the pinion body 31b, which has a circular cross section, forms the crescent-shaped spiral teeth 31c.

Here, the helical teeth 31c extend continuously in a helical manner in the axial direction of the pinion body 31b, and the pinion gear 31 is provided with only one helical tooth 31c. In other words, the number of teeth of the pinion gear 31 is "1". Here, the radius R3 of the helical teeth 31c is smaller than the radius R2 of the fixed portion 31a and larger than the radius R1 of the pinion body 31b (R1<R3<R2).

The center C2 of the helical tooth 31c is eccentric (offset) by a predetermined distance L with respect to the center of rotation C1 of the pinion gear 31 (pinion body 31b). As a result, the center C2 of the helical tooth 31c follows a path OC as the pinion gear 31 rotates. In other words, the path OC of the center C2 of the helical tooth 31c forms a reference circle for the helical tooth 31c.

Furthermore, as shown in FIG. 5, if an auxiliary line AL is drawn from the center of rotation C1 of the pinion gear 31 toward the center C2 of the helical tooth 31c (toward the bottom in the figure) and the auxiliary line AL is further extended to the surface of the helical tooth 31c, the auxiliary line AL intersects with the surface of the helical tooth 31c. This intersection point becomes the apex BP of the helical tooth 31c. As a result, a part of the helical tooth 31c including the apex BP enters between the adjacent helical teeth 32c of the helical gear 32 and meshes with them.

In this way, because one helical tooth 31c extends continuously in a helical manner in the axial direction of the pinion body 31b, the vicinity of the apex BP of the helical tooth 31c in the axial direction of the pinion body 31b successively enters and meshes with the helical teeth 32c, and the helical gear 32 rotates at a reduced speed. Note that FIG. 5 shows the helical tooth 31c and the helical tooth 32c meshing with each other.

The helical gear 32 forming the reduction mechanism 30 is made of plastic and has a shape as shown in Figures 3 to 8. Specifically, the helical gear 32 has a gear body 32a formed in a substantially disk shape, and the base end side of the output shaft 34 is fixed to the center part of the gear body 32a by press fitting or the like. In addition, a cylindrical part 32b extending in the axial direction of the output shaft 34 is integrally provided on the radial outer side of the gear body 32a.

A number of helical teeth 32c are integrally provided on the radially outer side of the cylindrical portion 32b, aligned in the circumferential direction of the cylindrical portion 32b, with which the helical teeth 31c mesh. These helical teeth 32c are inclined at a predetermined angle with respect to the axial direction of the pinion gear 31, so that the helical gear 32 rotates as the helical teeth 31c rotate.

Here, the number of helical teeth 32c provided on the helical gear 32 is "40." That is, in this embodiment, the reduction ratio of the reduction mechanism 30 consisting of the pinion gear 31 and the helical gear 32 is "40."

5 and 6, the helical tooth 32c has a tooth tip 32c1 provided at the tip side (upper side in the figure) of the helical tooth 32c, a tooth bottom 32c2 provided at the base end side (lower side in the figure) of the helical tooth 32c, and a meshing portion 32c3 provided between the tooth tip 32c1 and the tooth bottom 32c2 and meshing with the helical tooth 31c of the pinion gear 31. Specifically, as shown in FIG. 6, one helical tooth 32c has one tooth tip 32c1, a pair of tooth bottoms 32c2 and a pair of meshing portions 32c3 arranged on both sides of the tooth tip 32c1. In FIG. 6, a boundary line BL (dotted line) is drawn at the boundary between the tooth tip 32c1, the tooth bottom 32c2, and the meshing portion 32c3.

As shown in FIG. 6, the outline L1 (dashed line in the figure) that forms the tooth tip 32c1 forms part of the tooth tip circle of the helical gear 32 and extends in an approximately straight line in the circumferential direction of the helical gear 32. The outline L2 (dashed line in the figure) that forms the tooth bottom 32c2 is formed by an arc of radius R4. Here, the radius R4 of the outline L2 of the tooth bottom 32c2 is slightly larger than the radius R3 of the helical tooth 31c (R4>R3). This allows the helical tooth 31c to mesh securely with the helical tooth 32c, and the backlash (play) β (see FIG. 8) can be small.

The shape of the outline L3 (solid line in the figure) that forms the meshing portion 32c3, i.e., the shape of the meshing portion 32c3 when viewed in the axial direction of the helical gear 32, is formed in the shape of an involute curve that is recessed in the tooth thickness direction of the helical tooth 32c (left and right direction in the figure). Specifically, it is formed in the shape of a curve that connects arcs a1, a2, a3, a4, and a5 that gradually increase in length and radius.

The "involute curve" refers to the curve shown in FIG. 7, which indicates the curve drawn by the tip of the thread when the thread is wound around a cylinder and unwound without slack. In FIG. 7, the cylinder CC is divided into 12 equal parts at 30 degree intervals around the center Ct, and the tips of the thread (normal line) are shown by dashed circles 1 to 12. The arcs a1 (arc between dashed circles 6-7), a2 (arc between dashed circles 7-8), a3 (arc between dashed circles 8-9), a4 (arc between dashed circles 9-10), and a5 (arc between dashed circles 10-11) that form the involute curve shown in FIG. 7 correspond to the arcs a1 to a5 in FIG. 6, respectively.

That is, as shown in FIG. 6, the arc a1 side of the outline L3 that forms the meshing portion 32c3, which is the shortest and has the smallest radius, is connected to the outline L1 that forms the tooth tip 32c1. In contrast, the arc a5 side of the outline L3 that forms the meshing portion 32c3, which is the longest and has the largest radius, is connected to the outline L2 that forms the tooth bottom 32c2. The outlines L1 to L3 are connected to each other smoothly so that no corners are formed.

In this way, by making the shape of the meshing portion 32c3 of the helical teeth 32c with which the helical teeth 31c mesh (the shape of the external line L3) into the shape of an involute curve, the meshing state of the helical teeth 31c and the helical teeth 32c is made equivalent to that of an involute gear. As a result, even if there is an error in the distance between the rotation center C1 of the pinion gear 31 and the rotation center C3 of the helical gear 32 (see FIG. 3), the pressure angle α (see FIG. 8) can be made approximately constant from the start to the end of the meshing between the helical teeth 31c and the helical teeth 32c, and thus it is possible to suppress the decrease in power transmission efficiency. Therefore, the occurrence of defects such as wear of the plastic helical teeth 32c is also effectively suppressed.

Here, regardless of the presence or absence of an error in the distance between the rotation center C1 of the pinion gear 31 and the rotation center C3 of the helical gear 32 (see FIG. 3), as shown in FIG. 5, when the helical teeth 31c and the helical teeth 32c are in meshing state, a predetermined gap S is formed between the apex BP of the helical teeth 31c and the tooth bottom 32c2 of the helical teeth 32c. The gap S contains lubricating oil G (shown only in FIG. 5) that smooths the operation of the reduction gear mechanism 30. In other words, the gap S functions as a lubricating oil retaining portion that retains the lubricating oil G. Also, in FIG. 5 and FIG. 8, the black dot on the meshing portion 32c3 indicates the meshing point EP between the helical teeth 31c and the helical teeth 32c.

Next, the changes in pressure angle α and backlash β caused by displacement of meshing point EP in the reduction mechanism 30 formed as described above when the distance between the rotation center C1 of pinion gear 31 and the rotation center C3 of helical gear 32 (see Figure 3) varies will be described in detail with reference to the drawings.

The distance between the rotation center C1 of the pinion gear 31 and the rotation center C3 of the helical gear 32 (see Figure 3) is defined as the "center pitch", and the reference value of the center pitch (≒design value) is defined as "±0". A deviation in the direction in which the center pitch becomes wider is defined as a deviation in the "+" direction, and a deviation in the direction in which the center pitch becomes narrower is defined as a deviation in the "-" direction.

Figure 9 shows a comparative example, in which the pinion gear 31 is the same as that of the present invention, and the helical gear 100 has a tooth bottom and meshing portion that form the helical teeth 101, both of which are formed in an arc shape with the same radius R. In other words, the helical gear 100 does not have a meshing portion in the shape of an involute curve as in the present invention, but has a meshing portion that is a simple arc shape. Note that the radius R is slightly larger than the radius R3 of the helical teeth 31c (R>R3).

[When center pitch is ±0 (no misalignment)]
When the deviation in the center pitch is 0 mm, the meshing point EP in the present invention is located at a portion close to the tooth tip 32c1 of the meshing portion 32c3, as shown in the middle of Fig. 8. In contrast, the meshing point EP in the comparative example is also located at a portion close to the tooth tip of the helical tooth 101, as shown in the middle of Fig. 9.

Here, in Figures 5, 8, and 9, the meshing point EP is located on the left side of the pinion gear 31 in the figures, because Figures 5, 8, and 9 respectively show the cases where the pinion gear 31 rotates in the clockwise direction and the helical gear 32 rotates in the counterclockwise direction. In other words, when the pinion gear 31 rotates in the counterclockwise direction and the helical gear 32 rotates in the clockwise direction, the meshing point EP is located on the right side of the pinion gear 31 in the figures.

In the middle of Figures 8 and 9, the pressure angle α, as shown in Figure 10, is approximately 30 degrees in both the present invention (solid line) and the comparative example (dashed line) (α ≒ 30 degrees). In contrast, the backlash β, as shown in Figures 8 and 9, is smaller in the present invention than in the comparative example. When the pressure angle α is approximately 30 degrees, as shown in Figure 11, the power transmission efficiency is 85% or more (approximately 86.5%), and it was found that in both the present invention and the comparative example, a highly efficient reduction mechanism that can withstand sufficient use can be realized.

[When the center pitch is in the negative direction (with deviation)]
When the deviation in the center-to-center pitch is in the negative direction, specifically -0.05 mm, the meshing point EP in the present invention is located approximately in the center of the meshing portion 32c3 (the portion of arc a4 in FIG. 6) as shown in the lower part of Fig. 8. In contrast, the meshing point EP in the comparative example is significantly displaced and located closer to the deepest part of the tooth bottom as shown in the lower part of Fig. 9.

In the lower part of Figures 8 and 9, the pressure angle α in the present invention (solid line) was approximately 29 degrees (α ≒ 29 degrees), as shown in Figure 10. On the other hand, in the comparative example (dashed line), it was approximately 40 degrees (α ≒ 40 degrees). In addition, as shown in Figures 8 and 9, the backlash β in the present invention was smaller than that in the comparative example. Furthermore, as shown in Figure 11, in the present invention (α ≒ 29 degrees), the power transmission efficiency was sufficient at 85% or more (approximately 87%), while in the comparative example (α ≒ 40 degrees), the power transmission efficiency was below 80% (approximately 76%), indicating that the power transmission efficiency was insufficient.

[When the center pitch is in the positive direction (with deviation)]
When the deviation in the center pitch is in the + (plus) direction, specifically +0.11 mm, the meshing point EP in the present invention is located at a portion of the meshing portion 32c3 closer to the tooth tip 32c1 than when the deviation in the center pitch is 0 mm, as shown in the upper part of Fig. 8. In contrast to this, the meshing point EP in the comparative example is also located at a portion closer to the tooth tip of the helical tooth 101, as shown in the upper part of Fig. 9.

In the upper part of Figures 8 and 9, the pressure angle α showed a value of about 31 degrees in the present invention (solid line) (α ≒ 31 degrees) as shown in Figure 10. On the other hand, the comparative example (dashed line) showed a value of about 24 degrees (α ≒ 24 degrees). In addition, as shown in Figures 8 and 9, the backlash β showed a value slightly smaller in the present invention than in the comparative example. Furthermore, as shown in Figure 11, it was found that the power transmission efficiency showed a sufficient value of about 85% in the present invention (α ≒ 31 degrees), and the power transmission efficiency showed a sufficient value of over 90% (about 91%) in the comparative example (α ≒ 24 degrees).

As described above, when the center-to-center pitch between the pinion gear 31 and the helical gear 32 varies due to manufacturing errors or the like, the pressure angle α varies widely between approximately 24 degrees and 40 degrees in the comparative example, whereas in the present invention it is stable (does not vary) between approximately 29 degrees and 31 degrees (see Figure 10). Furthermore, in the reduction mechanism 30 of the present invention, the backlash (play) β also changes to a smaller value side compared to the reduction mechanism of the comparative example (see Figures 8 and 9).

The power transmission efficiency that is sufficient for practical use is preferably 80% or more, in accordance with the specifications of the brushless motor 20 that drives the reduction mechanism 30 (such as the output required for the drive source of the wiper device). However, if the tooth depth of the helical teeth is increased to reduce the pressure angle simply to increase the power transmission efficiency, then the pinion body 31b of the pinion gear 31 will interfere with the helical teeth 32c of the helical gear 32 when the reduction mechanism 30 is in operation. In other words, the meshing between the pinion gear 31 and the helical gear 32 will no longer be established. Therefore, an investigation was conducted into the pressure angle α that establishes the meshing between the pinion gear 31 and the helical gear 32, and it was found that a pressure angle of 10 degrees or more is desirable.

In other words, the necessary conditions for forming the reduction gear mechanism 30 are that the pinion gear 31 and the helical gear 32 are meshed with each other and that the power transmission efficiency between them is 80% or more. In summary, it was found that the reduction gear mechanism 30 should be formed so that the pressure angle α between the helical teeth 31c and the helical teeth 32c falls within the range of the reference region AR1 (see the shaded area) in which it is between 10 degrees and 33 degrees, as shown in Figure 11.

As described above, the reduction gear mechanism 30 in this embodiment has a pressure angle α fluctuation range of approximately 29 degrees to 31 degrees, which is within the range of the reference area AR1 (pressure angle α = 10 degrees to 33 degrees). In the NG area AR2 where the pressure angle exceeds 33 degrees, sufficient power transmission efficiency cannot be obtained, and in the NG area AR3 where the pressure angle is below 10 degrees, it becomes difficult to achieve meshing between the pinion gear 31 and the helical gear 32.

As described above in detail, in the first embodiment, the meshing portion 32c3 with which the helical tooth 31c meshes is provided between the tooth tip 32c1 and tooth bottom 32c2 that form the helical tooth 32c, and when viewed in the axial direction of the helical gear 32, the shape of the meshing portion 32c3 is formed into the shape of an involute curve that is recessed in the tooth thickness direction of the helical tooth 32c.

As a result, even if the center-to-center pitch between the pinion gear 31 and the helical gear 32 varies, the pressure angle α can be stabilized at a small value, and it is possible to improve the power transmission efficiency without variation between products. This makes it possible to realize a reduction gear mechanism 30 that can withstand mass production.

In addition, in the first embodiment, the pressure angle α between the helical teeth 31c and the helical teeth 32c is 10 degrees to 33 degrees, so in a reduction mechanism 30 having one helical tooth 31c and multiple helical teeth 32c, the helical teeth 31c (pinion gear 31) and the helical teeth 32c (helical gear 32) can be meshed with each other and the power transmission efficiency between them can be 80% or more. This makes it possible to use it as a drive source for a wiper device.

Furthermore, in the first embodiment, it is possible to suppress variations in power transmission efficiency between products, and thus suppress the occurrence of defective products, thereby making it possible to reduce the energy required for manufacturing. This can contribute to the Sustainable Development Goals (SDGs) led by the United Nations, particularly to Goal 7 (Ensure access to affordable, reliable, sustainable and modern energy) and Goal 13 (Take urgent action to combat climate change and its impacts).

Next, the second embodiment of the present invention will be described in detail with reference to the drawings. Note that parts having the same functions as those in the first embodiment described above will be given the same reference numerals, and detailed descriptions thereof will be omitted.

Figure 12 shows a diagram corresponding to Figure 6 showing embodiment 2.

As shown in FIG. 12, in the reduction gear mechanism 40 of the second embodiment, only the shape of the helical teeth 32c of the helical gear 32 is different from that of the first embodiment. Specifically, the helical teeth 32c have a tooth tip 32c1 provided at the tip side (upper side in the figure) of the helical teeth 32c, and a tooth bottom 41 provided at the base end side (lower side in the figure) of the helical teeth 32c. The helical teeth 32c also have a meshing portion 42 that is provided between the tooth tip 32c1 and the tooth bottom 41 near the tooth tip 32c1 and meshes with the helical teeth 31c of the pinion gear 31, and an arc-shaped connecting portion 43 that is provided between the tooth tip 32c1 and the tooth bottom 41 near the tooth bottom 41 and smoothly connects the tooth bottom 41 and the meshing portion 42.

More specifically, as shown in FIG. 12, each helical tooth 32c has one tooth tip 32c1, a pair of tooth bottoms 41 arranged on both sides of the tooth tip 32c1, a pair of meshing portions 42, and a pair of arc-shaped connecting portions 43.

The shape of the outline L4 (solid line in the figure) forming the meshing portion 42, i.e., the shape of the meshing portion 42 when viewed in the axial direction of the helical gear 32, is formed in the shape of an involute curve recessed in the tooth thickness direction (left and right direction in the figure) of the helical tooth 32c, as in the first embodiment (see FIG. 6). However, in the second embodiment, the connection relationship is reversed compared to the first embodiment. That is, the arc a5 side of the outline L4 forming the meshing portion 42, which has the longest length and the largest radius, is connected to the outline L1 forming the tooth tip portion 32c1. On the other hand, the arc a1 side of the outline L4 forming the meshing portion 42, which has the shortest length and the smallest radius, is connected to the outline L5 forming the arc-shaped connection portion 43.

The tooth bottom 41 extends linearly in the direction of rotation of the helical gear 32. The outline L6 forming the tooth bottom 41 is positioned closer to the helical teeth 31c of the pinion gear 31 by the height dimension H than the outline L2 forming the tooth bottom 32c2 in the first embodiment. This makes it possible to increase the thickness of the tooth bottom 41 of the helical gear 32 in the second embodiment compared to the first embodiment, thereby increasing the rigidity of the helical teeth 32c.

In addition, in the second embodiment, the outline lines L1, L4, L5, and L6 are also smoothly connected to each other so that no corners are formed.

The second embodiment formed as described above can also achieve the same effect as the first embodiment. In addition, the second embodiment has a tooth bottom portion 41 that extends linearly in the rotation direction of the helical gear 32, so that the rigidity of the helical teeth 32c of the helical gear 32 can be increased. In addition, an arc-shaped connection portion 43 that smoothly connects the meshing portion 42 and the tooth bottom portion 41 is provided between them, so that it is not necessary to provide corners in the mold used to mold the helical gear 32, and it is possible to extend the life of the mold (improved mass productivity). However, the effect (improved mass productivity) can also be achieved in the first embodiment (see FIG. 6) in which the arc-shaped meshing portion 32c3 and the arc-shaped tooth bottom portion 32c2 are smoothly connected.

The present invention is not limited to the above-mentioned first and second embodiments, and it goes without saying that various modifications can be made without departing from the scope of the present invention. In the first embodiment, as shown in FIG. 6, the arc a1 side of the outline L3 forming the meshing portion 32c3, which has the shortest length and smallest radius, is connected to the outline L1 forming the tooth tip 32c1, and the arc a5 side of the outline L3 forming the meshing portion 32c3, which has the longest length and largest radius, is connected to the outline L2 forming the tooth bottom 32c2. However, the present invention is not limited to this, and the connection relationship of the outline L3 forming the meshing portion 32c3 may be reversed, as in the second embodiment.

In addition, in the second embodiment, as shown in FIG. 12, the arc a5 side of the outline L4 that forms the meshing portion 42, which has the longest length and the largest radius, is connected to the outline L1 that forms the tooth tip portion 32c1, and the arc a1 side of the outline L4 that forms the meshing portion 42, which has the shortest length and the smallest radius, is connected to the outline L5 that forms the arc-shaped connection portion 43. However, the present invention is not limited to this, and the connection relationship of the outline L4 that forms the meshing portion 42 may be reversed, as in the first embodiment.

In addition, in the second embodiment, the tooth bottom portion 41 is formed in a shape that extends linearly in the rotational direction of the helical gear 32, but the present invention is not limited to this. For example, the tooth bottom portion 41 may be formed in an arc shape with a radius larger than the radius R4 (the radius of the outline L2 that forms the tooth bottom portion 32c2).

In addition, in the first and second embodiments, the reduction mechanism 30, 40 (motor 10 with reduction mechanism) is applied to the drive source of a wiper device mounted on a vehicle, but the present invention is not limited to this, and can also be applied to other drive sources such as a power window device, a sunroof device, and a seat lifter device.

Furthermore, in the first and second embodiments, a motor 10 with a reduction mechanism is shown in which the reduction mechanism 30, 40 is driven by a brushless motor 20, but the present invention is not limited to this, and a brushed motor can be used instead of the brushless motor 20 to drive the reduction mechanism 30, 40.

The materials, shapes, dimensions, numbers, installation locations, etc. of each component in the above-mentioned first and second embodiments are arbitrary as long as they can achieve the present invention, and are not limited to the above-mentioned first and second embodiments.

10: Motor with reduction mechanism, 11: Housing, 12: Casing, 12a: Bottom wall, 12b: Side wall, 12c: Case flange, 12d: Boss, 12e: Reinforcement rib, 12f: Bearing member housing, 12g: Retaining ring, 13: Cover member, 13a: Main body, 13b, Cover flange, 13c: Motor housing, 13d: Connector connection, 13e: Terminal member, 20: Brushless motor, 21: Stator, 21a: Coil, 22: Rotor, 22a: Rotor body, 22b: Permanent magnet, 30: Reduction mechanism, 31: Pinion gear (first gear), 31a: Fixed part, 31b: Pinion body (main body), 31c: Spiral teeth, 32: Helical gear (second gear), 32a: Gear body, 32 b: cylindrical portion, 32c: helical teeth, 32c1: tooth tip, 32c2: tooth bottom, 32c3: meshing portion, 33: ball bearing, 34: output shaft, 40: reduction mechanism, 41: tooth bottom, 42: meshing portion, 43: arc-shaped connection portion, 100: helical gear, 101: helical teeth, AL: auxiliary line, AR1: reference area, AR2, AR3: NG area, BL: boundary line, BP: Vertex, C1: center of rotation of pinion gear 31, C2: center of helical teeth 31c, C3: center of rotation of helical gear 32, CC: cylinder, Ct: center of cylinder CC, EP: meshing point, G: lubricant, L1-L6: outline, OC: trajectory of center C2 of helical teeth 31c, S: gap, a1-a5: arc of involute curve, α: pressure angle, β: backlash

Claims (4)

A reduction mechanism including a first gear and a second gear,
The first gear is
a main body portion having a circular cross section in a direction intersecting an axial direction of the first gear;
one helical tooth provided around the main body portion, extending helically in the axial direction of the first gear, and having a crescent-shaped cross section in a direction intersecting the axial direction of the first gear;
having
the second gear has a plurality of helical teeth with which the helical teeth mesh,
The helical teeth are
a tooth tip portion provided on a tip side of the helical tooth;
A tooth bottom portion provided on a base end side of the helical tooth;
a meshing portion provided between the tooth tip portion and the tooth bottom portion, with which the helical teeth mesh;
Equipped with
When viewed in the axial direction of the second gear,
The shape of the meshing portion is formed into an involute curve shape recessed in a tooth thickness direction of the helical teeth.
Reduction mechanism. The tooth bottom portion extends linearly in a rotational direction of the second gear.
The reduction mechanism according to claim 1 . 3. The reduction mechanism according to claim 2,
An arc-shaped connection portion is provided between the meshing portion and the tooth bottom portion, smoothly connecting the meshing portion and the tooth bottom portion.
Reduction mechanism. The pressure angle between the helical teeth and the helical teeth is from 10 degrees to 33 degrees.
The reduction mechanism according to any one of claims 1 to 3.

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