JP2012167734A - Worm wheel, method of manufacturing the same, and electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and inexpensive worm wheel small having excellent strength and durability.SOLUTION: The worm wheel 31 includes teeth 32 made of metal, and a circumferential groove 34 crossing the central parts of the teeth 32 in the axial direction X1. The central parts of tooth faces 37 in the axial direction X1 are cut by the circumferential groove 34. The tooth faces 37 of the teeth 32 are formed by forging. The circumferential groove 34 reaches tooth bottoms 36, and the tooth faces 37 are divided into pairs of portions 37a, 37a on the opposite sides of the circumferential groove 34. Using the circumferential groove 34 as a lubricant supply path, the lubricant is supplied plentifully from the circumferential groove 34 to the pairs of portions 37a, 37a of the tooth faces 37.

Description

  The present invention relates to a worm wheel, a manufacturing method thereof, and an electric power steering apparatus.

There has been proposed a reduction mechanism for an electric power steering device in which a worm wheel as a reduction gear is constituted by a cored bar and a resin gear part disposed on the outer periphery of the cored bar (see, for example, Patent Documents 1 and 2). ).
In order to reduce rattling noise caused by backlash, in Patent Document 1, the gear portion is divided into a pair of halves that are divided in the axial direction and can be moved relative to each other in the axial direction. It is energizing in the approaching direction. Further, in Patent Document 2, the entire worm wheel is constituted by a pair of halves that are divided in the axial direction and are relatively movable in the axial direction, and the halves are urged toward each other by a biasing member. Yes.

JP 2001-355700 A JP 2004-26102 A

  With the recent increase in output of electric power steering devices, the speed reduction mechanism has become larger, and the layout of electric power steering devices on vehicles has become very strict. As in Patent Documents 1 and 2, when resin is used as the gear portion of the worm wheel, the worm wheel tends to be large in order to satisfy the strength. In addition, a resin that can withstand high strength is expensive, and the manufacturing cost increases.

  Therefore, it is conceivable to use a metal gear. However, when a cylindrical worm (for example, JIS3 type whose cross section tooth profile is trapezoidal) and a drum-shaped worm wheel (whose cross section tooth shape is involute) are meshed, the contact line of both gears and the sliding direction of the worm There is a problem that the lubricating oil film is likely to be cut off in a region where the angle (crossing angle) between the two is small (substantially equivalent to the axial central portion of the tooth surface of the worm wheel). Therefore, there is a problem that wear or heat generation occurs in the region of the worm wheel, resulting in poor durability.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a worm wheel that is small, inexpensive, and excellent in strength and durability, a manufacturing method thereof, and an electric power steering device. is there.

In order to achieve the object, the invention of claim 1 includes a metal tooth portion (32; 132; 332) including a tooth surface (37; 137; 337) and a central portion in the axial direction (X1) of the tooth portion. And a worm wheel (31; 131; 231; 331) in which the axial central portion of the tooth surface is missing by the circumferential groove. .
Further, as in claim 2, the angle (B) formed by the worm wheel tooth profile formed by the tooth surface and the contact line (CL) of the worm (20) and the sliding direction (S1) of the worm. The region (E1) where is less than or equal to the threshold value (B1) (B ≦ B1) may be missing due to the circumferential groove.

According to a third aspect of the present invention, the tooth portion may be integrally formed of a single material, and the tooth surface may be formed by forging.
According to a fourth aspect of the present invention, the metal tooth portion is composed of a pair of halves (51, 52) divided in the axial direction, interposed between the pair of halves, and both halves. In some cases, the circumferential groove is formed between the pair of halves.

Further, as in claim 5, the circumferential groove reaches a tooth bottom (36; 336), and the tooth surface is a pair of portions (37a, 37b; 137a, 137) disposed on both sides of the circumferential groove. 137b; 337a, 337b).
Further, as in claim 6, the circumferential groove may include a wide portion (138; 338) whose width increases toward the tooth bottom.

The invention of claim 7 provides an electric power steering device (1) for reducing the rotation of the electric motor (18) via the speed reduction mechanism (19) including the worm wheel and the worm described above.
The invention according to claim 8 includes a tooth portion made of metal that is integrally formed of a single material, including a tooth surface formed by forging, and a circumferential groove that crosses a central portion in the axial direction of the tooth portion. The tooth surface is missing a central portion in the axial direction by the circumferential groove, and the circumferential groove is a method of manufacturing a worm wheel including a wide portion that becomes wider toward the tooth bottom. Then, by pressing the tooth tip (M3) of the tooth part (M2) of the manufacturing intermediate (M), the width of the inlet of the peripheral groove (M1) of the manufacturing intermediate is narrowed, and the wide part is A method for manufacturing a worm wheel is provided.

  In the above description, numbers in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

  According to the invention of claim 1, since the metal tooth portion is used, high strength can be achieved at low cost. In addition, a circumferential groove is provided in the axial central portion of the tooth surface, which is likely to cause a lubricating oil film breakage, and the circumferential groove serves as a lubricant supply path, so that from the circumferential groove to the remaining portion of the tooth surface. Lubricant is supplied abundantly. Therefore, the lubricity is improved. Since the lubricity is improved, the durability can be improved without increasing the size, and the size can be reduced as much as possible. Further, the size can be further reduced by reducing the material by forming the circumferential groove.

  According to the invention of claim 2, the peripheral groove lacks a region where the angle between the worm wheel tooth profile and the contact line of the worm and the sliding direction of the worm is not more than a threshold value. In a region other than this region, the angle formed by the contact line and the sliding direction exceeds the threshold value, so that the oil film is hardly cut off as a whole tooth surface, and smooth lubrication can be ensured. Therefore, wear can be suppressed over a long period of time, and the durability can be remarkably improved.

Further, according to the invention of claim 3, since the portion that may be undercut at the time of forging from one direction is omitted, the tooth surface can be easily formed by forging.
According to the invention of claim 4, the tooth portion is constituted by a pair of halves that are divided in the axial direction and connected by an elastic body, and the circumferential groove is formed between the pair of halves. The tooth portion can be easily formed by forging from the axial direction, and a worm wheel having a circumferential groove across the tooth portion can be easily formed. The elastic body may be a resin that is fixed to a pair of halves during injection molding.

According to the fifth aspect of the present invention, the tooth surface is completely divided into a pair of portions on both sides of the circumferential groove, while a sufficient amount of lubricant can be stored in the deep circumferential groove reaching the tooth bottom. As a result, the lubricant can be supplied from the circumferential groove to the tooth surface divided into two.
According to the invention of claim 6, sufficient lubricant can be held in the circumferential groove having the wide portion, and the lubricity can be further improved.

Further, according to the invention of claim 7, it is possible to realize an electric power steering device which is small, inexpensive, excellent in strength and durability.
According to the invention of claim 8, the width of the inlet of the circumferential groove is narrowed and the wide portion is easily formed by pressurizing the tooth tip of the tooth portion of the manufacturing intermediate body in which the circumferential groove is formed. be able to.

It is a mimetic diagram showing a schematic structure of an electric power steering device to which a worm wheel concerning one embodiment of the present invention is applied. It is an expansion perspective view of the principal part of a worm wheel. It is sectional drawing of the principal part of a worm wheel. It is typical sectional drawing as a reference figure which shows the meshing state of a worm wheel and a worm when not providing a recessed part. It is sectional drawing of the principal part of the worm wheel which concerns on another embodiment of this invention. It is sectional drawing which shows one manufacturing process of the worm wheel of FIG. It is sectional drawing of the principal part of the worm wheel which concerns on another embodiment of this invention. It is sectional drawing of the principal part of the worm wheel which concerns on another embodiment of this invention.

Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a schematic diagram of an electric power steering apparatus 1 to which a worm wheel according to an embodiment of the present invention is applied. Referring to FIG. 1, an electric power steering device 1 assists steering by a steering wheel 2 as a steering member, a steering mechanism 4 that steers the steered wheels 3 in conjunction with rotation of the steering wheel 2, and a driver. A steering assist mechanism 5 is provided. The steering wheel 2 and the steering mechanism 4 are mechanically connected via a steering shaft 6 and an intermediate shaft 7.

In the present embodiment, a description will be given according to an example in which the steering assist mechanism 5 applies assist force (steering assist force) to the steering shaft 6. However, the present invention can also be applied to a structure in which the steering assist mechanism 5 applies assist force to the pinion shaft described later.
The steering shaft 6 includes an input shaft 8 connected to the steering wheel 2 and an output shaft 9 connected to the intermediate shaft 7. The input shaft 8 and the output shaft 9 are connected via a torsion bar 10 so as to be relatively rotatable on the same axis.

  A torque sensor 11 disposed around the steering shaft 6 detects the steering torque input to the steering wheel 2 based on the relative rotational displacement amounts of the input shaft 8 and the output shaft 9. The torque detection result of the torque sensor 11 is input to an ECU (Electronic Control Unit) 12 as a motor control device for assisting steering. Further, the vehicle speed detection result from the vehicle speed sensor 90 is input to the ECU 12. The intermediate shaft 7 connects the steering shaft 6 and the steering mechanism 4.

The steering mechanism 4 includes a rack and pinion mechanism including a pinion shaft 13 and a rack shaft 14 as a steered shaft. A steered wheel 3 is connected to each end of the rack shaft 14 via a tie rod 15 and a knuckle arm (not shown).
The pinion shaft 13 is connected to the intermediate shaft 7. The pinion shaft 13 rotates in conjunction with the steering of the steering wheel 2. A pinion 16 is provided at the tip (lower end in FIG. 1) of the pinion shaft 13.

  The rack shaft 14 extends linearly along the left-right direction of the automobile. A rack 17 that meshes with the pinion 16 is formed in the middle of the rack shaft 14 in the axial direction. By the pinion 16 and the rack 17, the rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. The steered wheel 3 can be steered by moving the rack shaft 14 in the axial direction.

When the steering wheel 2 is steered (rotated), this rotation is transmitted to the pinion shaft 13 via the steering shaft 6 and the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into an axial movement of the rack shaft 14 by the pinion 16 and the rack 17. Thereby, the steered wheel 3 is steered.
The steering assist mechanism 5 includes a steering assist electric motor 18 and a speed reduction mechanism 19 as a transmission mechanism for transmitting the output torque of the electric motor 18 to the steering mechanism 4. The reduction mechanism 19 includes a worm 20 as a drive gear and a worm wheel 31 as a reduction gear meshing with the worm 20. The speed reduction mechanism 19 is accommodated in the gear housing 21. In the gear housing 21, at least a meshing region between the worm 20 and the worm wheel 31 is filled with a lubricant such as grease, and the lubricant is interposed between the tooth surfaces of the worm 20 and the worm wheel 31. Yes.

The worm 20 is connected to a rotating shaft (not shown) of the electric motor 18 via a joint (not shown). The worm 20 is rotationally driven by the electric motor 18. Further, the worm wheel 31 is connected to the steering shaft 6 so as to be integrally rotatable.
When the electric motor 18 rotationally drives the worm 20, the worm wheel 31 is rotationally driven by the worm 20, and the worm wheel 31 and the steering shaft 6 rotate integrally. The rotation of the steering shaft 6 is transmitted to the pinion shaft 13 via the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. Thereby, the steered wheel 3 is steered. That is, the steered wheels 3 are steered by rotating the worm 20 by the electric motor 18.

  The electric motor 18 is a three-phase brushless motor, and is controlled by the ECU 12 as a motor control device. The ECU 12 controls the electric motor 18 based on the torque detection result from the torque sensor 11, the vehicle speed detection result from the vehicle speed sensor 90, and the like. Specifically, the ECU 12 determines a target assist amount using a map in which the relationship between the torque and the target assist amount is stored for each vehicle speed, and controls the assist force generated by the electric motor 18 to approach the target assist amount. To do.

As shown in FIG. 2, the worm wheel 31 includes tooth portions 32 and tooth spaces 33 arranged alternately. The tooth groove 33 is open in the radially outward direction R1, but is not open in the axial direction X1.
The worm wheel 31 includes a circumferential groove 34 that crosses the central portion of the tooth portion 32 in the axial direction X1 over the entire circumference of the worm wheel 31. The circumferential groove 34 extends from the tooth tip 35 of each tooth portion 32 to the tooth bottom 36. Thereby, the tooth surface 37 of each tooth part 32 is divided | segmented into a pair of part 37a, 37b arrange | positioned at the both sides of the circumferential groove 34. FIG.

Since the worm wheel 31 has an advance angle, the tooth line direction W1 is inclined with respect to the axial direction X1. The central portion of the tooth portion 32 in the axial direction X1 also corresponds to the central portion of the tooth line direction W1.
The entire worm wheel 31 including the plurality of tooth portions 32 is integrally formed of a single material (for example, steel such as S25C). The tooth surface 37 is formed by forging.

According to the present embodiment, since the metal tooth portion 32 is used, high strength can be achieved at low cost. In addition, a circumferential groove 34 is provided in the central portion of the tooth surface 37 in the axial direction X1 where the lubricating oil film is likely to be cut, and the circumferential groove 34 serves as a lubricant supply path. The lubricant is abundantly supplied to the pair of portions 37a and 37b which are the remaining portions of 37.
Therefore, the lubricity of the tooth surface 37 is improved. Since the lubricity is improved, the durability can be improved without increasing the size, and the worm wheel 31 can be made as small as possible. Further, by reducing the material by forming the circumferential groove 34, the worm wheel 31 can be further downsized. As a result, the speed reduction mechanism 19 and the electric power steering apparatus 1 that are small, inexpensive, and excellent in strength and durability can be realized.

  FIG. 4 is a schematic cross-sectional view as a reference view showing a meshed state of the worm 20 and the worm wheel 31 ′ including the tooth surface 37 ′ having a worm wheel tooth profile when the circumferential groove 34 is not provided. In FIG. 4, the contact line CL between the worm wheel tooth profile which is the tooth profile shape of the tooth surface 37 ′ and the worm 20 meshing with the tooth profile is indicated by a solid line. Further, the sliding direction S1 of the worm 20 is indicated by a one-dot chain line as a concentric circle with the central axis of the worm 20 as the center.

In FIG. 4, an angle B formed by the contact line CL and the sliding direction S1 is equal to or less than a threshold value B1 (B ≦ B1. The threshold value B1 is set to a value within a range of 5 to 10 °, for example, 10 °). In this region E1, it is difficult to form an oil film with a lubricant.
Therefore, it is preferable that the circumferential groove 34 of the present embodiment is formed so as to include the region E1. As a result, the circumferential groove 34 avoids meshing between the central portion of the tooth surface 37 in the axial direction X1 and the worm 20. Further, in the tooth surface 37, in the portions 37a and 37b on both sides of the circumferential groove 34, the angle B formed by the contact line CL and the sliding direction S1 of the worm 20 becomes a value exceeding the threshold value B1 (B ≧ B1). The tooth surface 37 as a whole is less prone to oil film breakage, and smooth lubrication can be ensured. Therefore, wear can be suppressed over a long period of time, and the durability can be remarkably improved.

Although the threshold value B1 is not shown, when the cylinder corresponding to the worm is brought into line contact with the tooth shape of the worm wheel and the cylinder is slid at an angle corresponding to the threshold value B1, the oil film in the tooth shape of the worm wheel is formed. It is determined to be a preferable value by experimentally determining the formation state.
Moreover, in the worm wheel 31, since the part (center part of the axial direction X1 of the tooth surface 37) which may be undercut at the time of forging from one direction is missing, the tooth surface 37 is formed by forging. It can be formed easily.

  Next, FIG. 5 is a cross-sectional view of a main part of a worm wheel according to another embodiment of the present invention. The configuration of this embodiment different from that of FIG. 3 is as follows. That is, in the embodiment of FIG. 3, the width is substantially constant regardless of the depth of the circumferential groove 34 (strictly speaking, since there is a draft angle of the forging die, the width gradually decreases as the depth increases). State). On the other hand, in the present embodiment, the circumferential groove 134 of the worm wheel 131 has a wide portion 138 that increases in width as the depth increases.

The worm wheel 131 is integrally formed of a single material (for example, steel such as S25C). The worm wheel 131 has a tooth gap 133. A tooth surface 137 of the tooth portion 132 of the worm wheel 131 is divided into a pair of portions 131 a and 131 b on both sides of the circumferential groove 134.
Specifically, as shown in FIG. 6, by pressing the tooth tip M3 of the tooth portion M2 of the manufacturing intermediate M in which the circumferential groove M1 having a constant width regardless of the depth is formed, In the middle, as shown by the one-dot chain line, both walls of the circumferential groove M1 are pushed inward to narrow the width of the inlet of the circumferential groove M1, and the worm wheel 131 having the wide portion 138 as shown in FIG. 5 is obtained. Although not shown in FIG. 6, the end surface in the axial direction X1 of the manufacturing intermediate M needs to be pressed from both sides so that the manufacturing intermediate M does not expand in the axial direction X1.

In the present embodiment, as in the embodiment of FIG. 3, it is possible to realize a worm wheel 131 that is small, inexpensive, excellent in strength and durability. Moreover, sufficient lubricant can be held in the circumferential groove 134 having the wide portion 138, and the lubricity can be further improved. Moreover, the wide part 138 can be easily formed in the circumferential groove 134 by forging.
Next, FIG. 7 is a cross-sectional view of a main part of a worm wheel according to still another embodiment of the present invention. The present embodiment is different from the embodiment of FIG. That is, in the embodiment of FIG. 5, the tooth groove 133 of the worm wheel 131 is not open in the axial direction X1. On the other hand, in the present embodiment, the tooth gap 233 of the worm wheel 231 is open on both sides in the axial direction X1. The worm wheel 231 is integrally formed of a single material (for example, steel such as S25C).

  In the constituent elements of this embodiment, the same constituent elements as those of the embodiment of FIG. 5 are denoted by the same reference numerals as those of the constituent elements of the embodiment of FIG. According to the present embodiment, as in the embodiment of FIG. 5, it is possible to realize a worm wheel 231 that is small, inexpensive, excellent in strength and durability. Moreover, the worm wheel 231 can be further downsized in the axial direction X1. Further, since the tooth groove 233 is open in the axial direction X1, the lubricant is supplied into the tooth groove 233 not only from the circumferential groove 134 but also from both sides in the axial direction X1. Accordingly, the lubricity is further improved.

  Next, FIG. 8 shows still another embodiment of the present invention. This embodiment is different from the embodiment of FIG. 5 as follows. That is, in the embodiment of FIG. 5, the worm wheel 131 is integrally formed of a single material (for example, steel such as S25C). On the other hand, in the present embodiment, the worm wheel 331 is configured by the elastic body 40 that is connected to the output shaft 9 so as to be able to rotate along with the output shaft 9 and an annular tooth portion 332. The tooth part 332 includes a pair of half halves 51 and 52 divided in the axial direction X1. The pair of halves 51 and 52 are symmetrical to each other and are disposed on both sides of the circumferential groove 334.

  That is, a circumferential groove 334 is formed between the pair of halves 51 and 52. The circumferential groove 334 reaches below the tooth root 336 that is the bottom of the tooth groove 333 from the tooth tip 335. The circumferential groove 334 has a wide portion 338 whose width increases as the depth increases. The tooth surface 337 of the worm wheel 331 is divided into a pair of portions 337 a and 337 b disposed on both sides of the circumferential groove 334. One portion 337 a of the tooth surface 337 is disposed on one half 51, and the other portion 337 b is disposed on the other main body 52.

  The elastic body 40 includes an annular main body 41 and an annular plate 42 extending from the central portion of the main body 41 in the axial direction X1 to the radially outer side R1. The annular plate 42 is interposed between the pair of halves 51 and 52. The elastic body 40 includes connecting portions 43 and 44 that extend from the annular plate 42 to both sides and connect the corresponding half bodies 51 and 52, respectively. The bottom of the circumferential groove 334 is partitioned by the outer periphery of the annular plate 42 of the elastic body 40.

  Each connection part 43 and 44 of the elastic body 40 has large diameter parts 43a and 44a and small diameter parts 43b and 44b. Each half 51, 52 has connection holes 53, 54 into which corresponding connection portions 43, 44 are fitted. The connecting holes 53 and 54 are respectively fitted with large-diameter portions 53a and 54a in which large-diameter portions 43a and 44a of the corresponding connecting portions 43 and 44 are fitted, and small-diameter portions 43b and 44b in the corresponding connecting portions 43 and 44. Small diameter portions 53b and 54b.

The elastic body 40 is made of a molding resin fixed to the pair of halves 51 and 52 during injection molding. Specifically, as the elastic body 40, it is preferable to use polyamide such as 66 nylon that can secure a sufficient amount of elastic deformation and has excellent durability.
According to the present embodiment, it is possible to realize a worm wheel 331 that is small, inexpensive, excellent in strength and durability. Moreover, the annular tooth portion 332 is constituted by a pair of halves 51 and 52 that are divided in the axial direction X1 and connected by the elastic body 40, and a circumferential groove 334 is formed between the pair of halves 51 and 52. Therefore, regardless of the presence or absence of the undercut portion, the tooth surface 337 of the metal tooth portion 332 can be formed by forging in the axial direction. Further, the worm wheel 331 having the circumferential groove 334 that crosses the tooth portion 332 can be easily formed.

Further, since the elastic body 40 is elastically deformed, it is possible to absorb the accuracy error and the assembly error of the tooth profile, so that an appropriate tooth contact can be ensured. In particular, the impact and vibration received by the tooth surface 337 can be absorbed by the elastic body 40, and the rattling noise can be significantly reduced.
The present invention is not limited to the above embodiment. For example, in the embodiment of FIG. 8, the positions of the pair of halves 51, 52 are shifted in the rotational direction of the worm wheel 331. Or may be shifted in the axial direction C1. In these cases, the elastic body 40 is elastically deformed when the worm wheel 331 is engaged with the worm 20. Due to the restoring force of the elastic body 40, the portions 337a and 337b of the tooth surface 337 can be reliably pressed against the tooth surface of the worm 20 without any gap, and the occurrence of uneven contact can be prevented.

  In addition, the present invention can be variously modified within the scope of the claims.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 4 ... Steering mechanism, 5 ... Steering assist mechanism, 6 ... Steering shaft, 18 ... Electric motor, 19 ... Deceleration mechanism, 20 ... Worm, 31; 131; 231; 331 ... Worm wheel, 32; 132; 332 ... tooth part, 33; 133; 233; 333 ... tooth gap, 34; 134; 334 ... circumferential groove, 35; 335 ... tooth tip, 36; 336 ... tooth bottom, 37; 137; 337 ... tooth surface, 37a, 37b; 137a, 137b; 337a, 337b ... (a pair of) parts, 138; 338 ... wide part, 40 ... elastic body, 43, 44 ... connecting part, 43a, 44a ... large diameter part, 43b, 44b ... small diameter Part, 51, 52 ... (a pair) half body, 53, 54 ... connection hole, 53a, 54a ... large diameter part, 53b, 54b ... small diameter part, B ... angle, B1 ... threshold, CL ... contact line, M ... Manufacturing Intermediate, M1 ... peripheral groove, M2 ... teeth, M3 ... addendum, S1 ... slip direction, X1 ... axial direction, W1 ... tooth trace direction

Claims (8)

Metal teeth including tooth surfaces;
A circumferential groove that crosses the axial central portion of the tooth portion, and
A worm wheel in which a central portion in the axial direction of the tooth surface is missing by the circumferential groove.   In Claim 1, The area | region where the angle which the worm wheel tooth profile and worm contact line which the said tooth surface makes, and the contact line of the worm and the sliding direction of the said worm make is less than a threshold is missing in the said tooth surface by the said circumferential groove. Worm wheel. In Claim 1 or 2, the tooth part is integrally formed of a single material,
The tooth surface is a worm wheel formed by forging. In claim 1 or 2,
The metal tooth portion is composed of a pair of halves divided in the axial direction,
An elastic body interposed between the pair of halves and connecting the halves;
A worm wheel in which the circumferential groove is formed between the pair of halves. In any one of Claim 1 to 4, the said circumferential groove has reached the tooth bottom,
The tooth surface is a worm wheel divided into a pair of portions disposed on both sides of the circumferential groove.   6. The worm wheel according to claim 1, wherein the circumferential groove includes a wide portion whose width increases toward a tooth bottom.   An electric power steering device that reduces the rotation of the electric motor via the speed reduction mechanism including the worm wheel and the worm according to any one of claims 1 to 6. Including a tooth surface formed by forging, and a metal tooth portion integrally formed of a single material;
A circumferential groove that crosses the axial central portion of the tooth portion, and
The axial center of the tooth surface is missing by the circumferential groove,
The circumferential groove is a method of manufacturing a worm wheel including a wide portion that becomes wider toward the tooth bottom,
A method of manufacturing a worm wheel, wherein the width of the inlet of the circumferential groove of the manufacturing intermediate is reduced by pressurizing the tooth tip of the tooth of the manufacturing intermediate to obtain the wide portion.

Images