Gears and steering devices

Abstract

A gear (22) comprises a resin sleeve (26) which is formed into a disk shape and a resin tooth portion (25) which covers an outer circumferential portion (262) of the sleeve (26) and includes a plurality of gear teeth (31) arranged at equal intervals in the circumferential direction. The sleeve (26) is provided with a plurality of protruding portions (264) arranged on an outer circumferential surface at equal intervals in the circumferential direction and a plurality of rib portions (270) arranged at equal intervals in the circumferential direction at positions on the inside of the protruding portions (264) in the radial direction. A first provision location number L of the protruding portions (264) in the circumferential direction and a second provision location number M of the rib portions (270) in the circumferential direction are the same number and are an integer multiple of a third provision location number N of the gear teeth (31) in the circumferential direction.

Description

[Technical field]

[0001] The present invention relates to a gear and a steering device. [Background technology]

[0002] For example, a known reducer provided in an automobile steering device has a worm and a gear serving as a worm wheel that meshes with the worm. In this type of gear, a disk-shaped resin sleeve and a resin tooth portion that covers the entire outer periphery of the sleeve and has a plurality of gear teeth are integrally molded (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-82860 A Summary of the Invention [Problem to be solved by the invention]

[0004] Here, when manufacturing a gear, a sleeve made of reinforced resin material is molded first, and then the teeth are molded with non-reinforced resin material while the sleeve is inserted. At this time, it is necessary to increase the dwell pressure in the mold to improve the precision of the gear teeth. However, if the dwell pressure is increased, the sleeve will be heated by the molten resin, reducing the rigidity of the sleeve and causing slight deformation of parts of the sleeve due to thermal contraction. This deformation ultimately reduces the precision of the gear (meshing runout).

[0005] An object of the present invention is to suppress deterioration of gear accuracy. [Means for solving the problem]

[0006] In order to solve the above problems, a gear according to one embodiment of the present invention comprises a resin sleeve formed in a disk shape, and a resin tooth portion covering the outer periphery of the sleeve and having a plurality of gear teeth arranged at even intervals in the circumferential direction, the sleeve comprising a plurality of convex portions arranged on the outer periphery surface at even intervals in the circumferential direction, and a plurality of rib portions arranged at even intervals in the circumferential direction at positions radially inward from the convex portions, the number of first installation locations in the circumferential direction on the convex portions and the number of second installation locations in the circumferential direction on the rib portions being the same number and being an integer multiple of the number of third installation locations in the circumferential direction on the gear teeth.

[0007] Furthermore, a steering device according to one embodiment of the present invention includes an electric motor that is driven based on steering of a steering member, and a reducer that includes the above-mentioned gear and reduces the output rotation of the electric motor by the gear and transmits it to a steering mechanism. Effect of the Invention

[0008] According to the present invention, deterioration of gear accuracy can be suppressed. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a steering device according to an embodiment. [Diagram 2] FIG. 2 is a perspective view of a gear according to an embodiment, as viewed from the front side. [Diagram 3] FIG. 2 is a plan view of the front side of the gear according to the embodiment. [Figure 4] FIG. 4 is a plan view of the rear side of the gear according to the embodiment. [Diagram 5] FIG. 4 is a partial front view of a part of the sleeve according to the embodiment, as viewed from the front side. [Figure 6] 4 is a partial cross-sectional view of a tooth portion and a part of a sleeve according to an embodiment, as viewed from the X-axis direction. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the present invention. Furthermore, among the components in the following embodiments, components that are not described in the independent claims showing the highest concept will be described as optional components.

[0011] The drawings are schematic diagrams in which emphasis, omissions, and ratios have been appropriately adjusted in order to illustrate the present invention, and may differ from the actual shapes, positional relationships, and ratios.

[0012] In the following description and drawings, the axial direction of the gear is defined as the Y-axis direction. The X-axis direction is perpendicular to the Y-axis direction, and the Z-axis direction is perpendicular to both the Y-axis direction and the X-axis direction. In the following description, for example, the positive X-axis direction indicates the direction of the X-axis arrow, and the negative X-axis direction indicates the opposite side to the positive X-axis direction. The same applies to the Y-axis and Z-axis directions. Furthermore, expressions indicating relative directions, attitudes, or positions, such as parallel, perpendicular, and coincident, may also include cases where the directions, attitudes, or positions are not strictly the same. For example, two straight lines being coincident with each other does not only mean that the two straight lines are completely coincident with each other, but also means that the two straight lines are substantially coincident with each other, that is, they include a difference of, for example, about several percent.

[0013] [Steering device] Fig. 1 is a schematic diagram of a steering device 1 according to an embodiment. As shown in Fig. 1, the steering device 1 is an electric power steering device, which includes a steering mechanism 6 and a turning mechanism 4, and steers steered wheels 3 based on the steering (steering operation) of a steering wheel 2 (steering member) by a driver. The steering mechanism 6 includes an assist mechanism 5 that assists the steering operation of the driver.

[0014] The steering mechanism 6 has an input shaft 8, an output shaft 9, an intermediate shaft 7, and a pinion shaft 15. The input shaft 8 is connected to the steering wheel 2. The output shaft 9 is connected to the input shaft 8 via a torsion bar 10. The intermediate shaft 7 is connected to the pinion shaft 15 having a pinion 15a via a universal joint.

[0015] The steering mechanism 4 has a rack shaft 16 and a tie rod 17. The rack shaft 16 has a rack 16a meshing with the pinion 15a. The tie rod 17 has one end connected to the rack shaft 16 and the other end connected to the steered wheels 3.

[0016] When the steering wheel 2 is rotated in response to the operation of the steering wheel 2 by the driver, the pinion shaft 15 rotates via the input shaft 8, the output shaft 9, and the intermediate shaft 7. The rotation of the pinion shaft 15 is converted by the steering mechanism 4 into reciprocating motion in the axial direction of the rack shaft 16. The reciprocating motion of the rack shaft 16 in the axial direction changes the steering angle of the steered wheels 3.

[0017] The assist mechanism 5 includes a torque sensor 11, an ECU (Electronic Control Unit) 12, an electric motor 19, and a reducer 20. The reducer 20 includes a worm 21, a gear 22 configured as a worm wheel meshing with the worm 21, and a housing 23 that accommodates the worm 21 and the gear 22. The worm 21 is connected to a rotating shaft (not shown) of the electric motor 19. The gear 22 is connected to the output shaft 9 so as to be rotatable integrally therewith.

[0018] When the steering wheel 2 rotates in response to the steering of the driver, the torque sensor 11 detects the amount of torsion between the input shaft 8 and the output shaft 9. The ECU 12 determines the assist torque based on the steering torque T obtained from the amount of torsion detected by the torque sensor 11, the vehicle speed V detected by the vehicle speed sensor 13, and the like. The electric motor 19 is driven and controlled by the ECU 12. The electric motor 19 driven in this manner based on the steering of the steering wheel 2 transmits the output rotation to the worm 21 to rotate the worm 21. Then, the gear 22 meshed with the worm 21 rotates at a slower speed than the worm 21, and the gear 22 and the output shaft 9 rotate integrally. In this manner, the reduction gear 20 reduces the speed of the output rotation of the electric motor 19 by the gear 22 and transmits it to the output shaft 9 of the steering mechanism 6 as an assist torque. This assists the steering operation of the steering wheel 2 by the driver.

[0019] [gear] Next, the gear 22 will be described in detail. Fig. 2 is a perspective view of the gear 22 according to the embodiment as seen from the front side. Fig. 3 is a plan view of the front side of the gear 22 according to the embodiment. Fig. 4 is a plan view of the rear side of the gear 22 according to the embodiment. In Figs. 3 and 4, the outline of the sleeve 26 provided on the gear 22 is shown by a dashed line.

[0020] 2 to 4, the gear 22 is formed in a disk shape. As described above, the Y-axis direction is the axial direction of the gear 22, which can also be said to be the thickness direction of the gear 22. The central axis C of the gear 22 extends in the Y-axis direction passing through the circular center of the gear 22. The negative Y-axis direction is the front side of the gear 22, and the positive Y-axis direction is the back side of the gear 22.

[0021] The gear 22 has a circular through hole 221 penetrating the gear 22 along the Y-axis direction at the center of the circle. The gear 22 is connected to the output shaft 9 so as to be rotatable together with the output shaft 9 by press-fitting the through hole 221. A plurality of gear teeth 31 meshing with the worm 21 are formed on the entire outer peripheral surface of the gear 22 at equal intervals in the circumferential direction of the gear 22. Here, the installation locations of the gear teeth 31 in the circumferential direction are referred to as third installation locations. The third installation locations are arranged at equal intervals in the circumferential direction. In this embodiment, a case is illustrated in which the total number of third installation locations (number of third installation locations N) is 41. One gear tooth 31 is sufficient in each third installation location. However, two or more gear teeth 31 may be arranged in the axial direction (Y-axis direction) in one third installation location.

[0022] The gaps between adjacent gear teeth 31 are formed as grooves cut in the Y-axis direction in the outer periphery of the gear 22. When the worm 21 rotates with the gear teeth 31 meshing with the worm 21, the gear 22 rotates in the circumferential direction.

[0023] The gear 22 has a collar 24, a teeth portion 25, and a sleeve 26. The collar 24 is a cylindrical metal member having a central axis coinciding with the central axis C. The through hole 221 of the gear 22 is defined by the inner peripheral surface of the collar 24. The teeth portion 25 is a resin member made of, for example, a non-reinforced resin, and constitutes a plurality of gear teeth 31. The teeth portion 25 is formed in an annular shape, and continuously covers the entire outer periphery of the outer periphery 262 of the sleeve 26. The plurality of gear teeth 31 are formed on the outer periphery surface of the teeth portion 25.

[0024] The sleeve 26 is a member that is coaxially fitted onto the collar 24. The sleeve 26 is formed in a disk shape, and is a resin member that is entirely made of resin. More specifically, the sleeve 26 is made of reinforced resin mixed with glass fiber, for example.

[0025] The sleeve 26 is integrally provided with an inner circumferential portion 261 located at the radially innermost position, an outer circumferential portion 262 located at the radially outermost position, and a connecting portion 263 disposed between the inner circumferential portion 261 and the outer circumferential portion 262 and connecting the inner circumferential portion 261 and the outer circumferential portion 262.

[0026] The inner peripheral portion 261 is formed in an annular shape having a central axis coinciding with the central axis C. The collar 24 is fitted to the inner peripheral surface of the inner peripheral portion 261. The outer peripheral portion 262 is formed in an annular shape and is arranged coaxially with the inner peripheral portion 261. On the outer peripheral surface of the outer peripheral portion 262, a plurality of convex portions 264 protruding radially outward are formed side by side at equal intervals in the circumferential direction of the outer peripheral portion 262. In Figs. 3 and 4, the plurality of convex portions 264 are illustrated by dashed lines. Here, the space between a pair of adjacent convex portions 264 is referred to as a concave portion 265. For this reason, a plurality of concave portions 265 are provided on the outer peripheral surface of the outer peripheral portion 262. The plurality of concave portions 265 are arranged side by side at equal intervals in the circumferential direction of the outer peripheral portion 262.

[0027] The installation location of each protrusion 264 in the circumferential direction is referred to as a first installation location. The first installation locations are arranged at equal intervals in the circumferential direction. In this embodiment, a case where the total number of first installation locations (number of first installation locations L) is 41 is illustrated. Each first installation location only requires one protrusion 264. However, two or more protrusions 264 may be arranged in the axial direction (Y-axis direction) in one first installation location.

[0028] The connecting portion 263 is an annular portion disposed between the inner peripheral portion 261 and the outer peripheral portion 262 so as to continuously connect the inner peripheral portion 261 and the outer peripheral portion 262 over the entire circumference. A plurality of rib portions 270 are arranged at equal intervals in the circumferential direction in the connecting portion 263. Since the connecting portion 263 is a portion radially inward from the outer peripheral portion 262, the plurality of rib portions 270 are disposed radially inward from the plurality of protruding portions 264.

[0029] 3, a plurality of first rib portions 271, which are part of the plurality of rib portions 270, are arranged at equal intervals in the circumferential direction on a first main surface 263a on the front side of the connecting portion 263. A first hole portion 281 is formed between the plurality of first rib portions 271 in the circumferential direction. That is, the plurality of first rib portions 271 and the plurality of first hole portions 281 are arranged alternately in the circumferential direction. Each of the first hole portions 281 has the same shape in a plan view (when viewed in the Y-axis direction) and is an oblong hole that is long in the radial direction.

[0030] 4, in the connecting portion 263, a plurality of second rib portions 272, which are part of the plurality of rib portions 270, are arranged at equal intervals in the circumferential direction on the second main surface 263b on the back side. Second hole portions 282 are provided between the plurality of second rib portions 272 in the circumferential direction. In other words, the plurality of second rib portions 272 and the plurality of second hole portions 282 are arranged alternately in the circumferential direction. The second hole portions 282 and the first hole portions 281 are lightening holes for reducing the weight of the sleeve 26.

[0031] Each second hole 282 has the same shape as each first hole 281 in a plan view (Y-axis direction view). In addition, each second hole 282 is disposed at a position corresponding to each first hole 281. Therefore, it can be said that each second rib portion 272 also has the same shape as each first rib portion 271 and is disposed at a position corresponding to each first rib portion 271. In other words, the corresponding first rib portion 271 and second rib portion 272 are disposed at the same position. This mounting position is called a second mounting position. The second mounting positions are arranged at equal intervals in the circumferential direction. In each second mounting position, it is sufficient to have one pair of the first rib portion 271 and the second rib portion 272. In this embodiment, a case is illustrated in which the total number of second mounting positions (number of second mounting positions M) is 41. In other words, the number of first mounting positions L, the number of second mounting positions M, and the number of third mounting positions N are the same.

[0032] During manufacturing, the mold is filled with molten resin that will become the teeth portion 25, with the sleeve 26 previously molded being placed in the mold. At this time, the heat from the molten resin and the pressure in the mold reduce the rigidity of the sleeve 26, and some parts may be slightly deformed. Here, since the number of first mounting locations L and the number of second mounting locations M match, and a certain pressure is applied in the mold, it is possible to generate slightly deformed parts in each of the protrusions 264 and each of the rib portions 270 at positions synchronized in the circumferential direction. Furthermore, since the number of third mounting locations N of each of the gear teeth 31 in the teeth portion 25 matches the number of first mounting locations L and the number of second mounting locations M, each slightly deformed part of the sleeve 26 and each of the gear teeth 31 are in a position synchronized in the circumferential direction. Therefore, even if each gear tooth 31 is also slightly deformed due to each slightly deformed part of the sleeve 26, the deformed parts of each gear tooth 31 will also be generated at approximately the same position. If different parts of each gear tooth 31 are deformed, it can cause fluctuations that differ from the meshing period or undulations in the rotation period; however, in the present embodiment, if the deformed parts of each gear tooth 31 are in roughly the same position, these problems can be suppressed.

[0033] Next, the positional relationship between each recess 265 in the sleeve 26 and each rib portion 270 (each first rib portion 271 and each second rib portion 272) will be described. As described above, each first rib portion 271 and each second rib portion 272 have the same shape and are disposed at corresponding positions, so the first rib portion 271 will be illustrated and described, and the second rib portion 272 will be omitted. In addition, the positional relationship between one recess 265 and one first rib portion 271 will be illustrated and described, but the positional relationship between the other recesses 265 and the other first rib portions 271 is similar.

[0034] 5 is a partial front view of a part of the sleeve 26 according to the embodiment, seen from the front side. As shown in FIG. 5, a center line C1 (shown by a dashed line) in the circumferential direction of the recess 265 coincides with a center line C2 (shown by a dashed line) in the circumferential direction of the first rib portion 271. Specifically, the center line C1 is a bisector of the circumferential width H1 of the recess 265, and is a straight line passing through the central axis C. Similarly, the center line C2 is a bisector of the circumferential width H2 of the first rib portion 271, and is a straight line passing through the central axis C. This makes it possible to make the radial rigidity of each first rib portion 271 as uniform as possible. This is also true for each second rib portion 272.

[0035] Moreover, it is preferable that the circumferential width H2 of the first rib portion 271 is larger than the circumferential width H1 of the recess 265. In this case, it is possible to increase the circumferential rigidity of the first rib portion 271. The same applies to each of the second rib portions 272.

[0036] Next, the positional relationship between the tooth portion 25 and the sleeve 26 will be described. FIG. 6 is a partial cross-sectional view of the tooth portion 25 and a part of the sleeve 26 according to the embodiment, as viewed from the X-axis direction. FIG. 6 illustrates the positional relationship between a pair of the first hole portion 281 and the second hole portion 282 and one gear tooth 31 corresponding to the pair, but the positional relationship between the other pair of the first hole portion 281 and the second hole portion 282 and the other gear teeth 31 corresponding to the other pair is similar. As shown in FIG. 6, a center line C3 (illustrated by a two-dot chain line) between the pair of the first hole portion 281 and the second hole portion 282 in the axial direction (Y-axis direction) coincides with a center line C4 (illustrated by a one-dot chain line) in the axial direction of the gear tooth 31. Specifically, the center line C3 is a bisector of the length H3 in the Y-axis direction between the bottom of the first hole portion 281 and the bottom of the second hole portion 282, and is a straight line parallel to the Z-axis direction. Similarly, the center line C4 is a bisector of the length H4 of the gear tooth 31 in the Y-axis direction, and is a straight line parallel to the Z-axis direction. This makes it possible to minimize the inclination of the first rib portion 271 and the second rib portion 272 in the axial direction.

[0037] [Effects, etc.] As described above, in the gear according to the present embodiment, the number L of the first mounting locations, the number M of the second mounting locations, and the number N of the third mounting locations are the same, so that the locations of the sleeve 26 that were slightly deformed during manufacturing are in circumferentially synchronized positions with the gear teeth 31. Therefore, even if the gear teeth 31 are also slightly deformed due to the locations of the sleeve 26 that were slightly deformed, the deformed locations of the gear teeth 31 can be generated in approximately the same positions. This makes it possible to suppress fluctuations that differ from the meshing cycle and waviness relative to the rotation cycle, and as a result, to suppress deterioration in the accuracy of the gear 22.

[0038] Since the center line C1 of the recess 265 in the circumferential direction coincides with the center line C2 of the rib portion 270 (the first rib portion 271, the second rib portion 272) in the circumferential direction, it is possible to make the radial rigidity of each rib portion 270 as uniform as possible. This makes it possible to reduce the number of locations in the sleeve 26 that are slightly deformed. Therefore, it is possible to further suppress deterioration in the accuracy of the gear 22.

[0039] Since the center line C3 between the first hole portion 281 and the second hole portion 282 in the axial direction coincides with the center line C4 in the axial direction of the gear teeth 31, it is possible to minimize the inclination of the first rib portion 271 and the second rib portion 272 in the axial direction. This makes it possible to suppress waviness with respect to the rotation period, and further suppress deterioration of the precision of the gear 22.

[0040] In the gear 22 used in the steering device 1, the decrease in accuracy is suppressed as described above, so that the operation of the steering device 1 can be stabilized.

[0041] [others] While the gear and steering device according to the present invention have been described based on the above embodiment, the present invention is not limited to the above embodiment.

[0042] For example, in the above embodiment, the first number of mounting locations L and the second number of mounting locations M are the same as the third number of mounting locations N. However, the first number of mounting locations L and the second number of mounting locations M may be the same and may be an integer multiple of the third number of mounting locations N. For example, even if the first number of mounting locations L and the second number of mounting locations M are each equal to or greater than Q times the third number of mounting locations N (Q is an integer of N), deformation locations of each gear tooth 31 caused by each minutely deformed location of the sleeve 26 can be generated at positions that are somewhat close to each other. In other words, even in this case, deterioration of the precision of the gears can be suppressed.

[0043] In the above embodiment, the case has been exemplified in which the center line C1 of the recess 265 coincides with the center line C2 of the rib portion 270. However, it is sufficient that the center line C1 of the recess 265 is contained within the circumferential width of the rib portion 270. Even in this case, it is possible to make the radial rigidity of each rib portion 270 uniform to some extent.

[0044] In the above embodiment, the case has been exemplified in which the center line C3 between the first hole portion 281 and the second hole portion 282 in the axial direction coincides with the center line C4 of the gear teeth 31. However, it is sufficient that the center line C4 of the gear teeth 31 is disposed at a position between the first hole portion 281 and the second hole portion 282 in the axial direction. Even in this case, it is possible to suppress the inclination of the first rib portion 271 and the second rib portion 272 in the axial direction to some extent.

[0045] In the above embodiment, the pair of first hole 281 and second hole 282 each have a bottom. However, the pair of first hole 281 and second hole 282 may have their bottoms penetrate each other in the axial direction. This can further reduce the weight of gear 22.

[0046] In the above embodiment, a case has been exemplified in which a plurality of first rib portions 271 are provided on the first main surface 263a of the connecting portion 263, and a plurality of second rib portions 272 are provided on the second main surface 263b. However, a plurality of rib portions may be provided on only one of the first main surface and the second main surface of the connecting portion.

[0047] In the above embodiment, the output shaft 9 is press-fitted into the through hole 221 of the collar 24 of the gear 22 to connect the gear 22 to the output shaft 9 so as to be rotatable together with the gear 22. However, serrations may be provided on the inner peripheral surface of the collar and the outer peripheral surface of the output shaft, and the collar and the output shaft may be fitted together by serrations. Also, the gear may not require a collar. In this case, the sleeve is directly connected to the output shaft.

[0048] In addition, the present invention also includes forms obtained by applying various modifications to the embodiments that a person skilled in the art may conceive, and forms realized by arbitrarily combining the components and functions of the embodiments and modifications within the scope that does not deviate from the spirit of the present invention. [Industrial Applicability]

[0049] The present invention is applicable to gears used in speed reducers. [Explanation of symbols]

[0050] 1...Steering device 2...Steering wheel 3...Steering wheel 4...Steering mechanism 5...Assist mechanism 6...Steering mechanism 7...Intermediate shaft 8...Input shaft 9...Output shaft 10...Torsion bar 11...Torque sensor 12...ECU 13...Vehicle speed sensor 15...Pinion shaft 15a...Pinion 16...Rack shaft 16a...Rack 17...Tie rod 19...Electric motor 20...Reduction gear 21...Worm 22...Gear 23...Housing 24...Collar 25...Tooth portion 26...Sleeve 31...Gear tooth 221...Through hole 261...Inner circumference 262...Outer circumference 263...Connecting portion 263a...First main surface 263b...Second main surface 264...Convex portion 265...Concave portion 270...Rib portion 271...First rib portion 272...Second rib part 281...First hole part 282...Second hole part C...Center axis C1, C2, C3, C4...Center line H1, H2...Width H3, H4...Length T...Steering torque V...Vehicle speed

Claims

1. A disk-shaped resin sleeve; A resin tooth portion having a plurality of gear teeth arranged at equal intervals in the circumferential direction and insert-molded to cover the outer circumferential portion of the sleeve, The sleeve is A plurality of protrusions arranged on an outer peripheral surface at equal intervals in a circumferential direction; a plurality of rib portions arranged at equal intervals in a circumferential direction at a position radially inward from the protruding portion, The number of first mounting locations on the convex portion in the circumferential direction is equal to the number of second mounting locations on the rib portion in the circumferential direction, and is an integer multiple of the number of third mounting locations on the gear teeth in the circumferential direction. gear.

2. The first number of installation locations and the second number of installation locations are equal to the third number of installation locations.

2. The gear of claim 1.

3. The center lines in the circumferential direction of the recesses present between the plurality of protrusions in the circumferential direction are contained within the circumferential width of the rib portion. A gear according to claim 1 or 2.

4. A circumferential center line of the recess coincides with a circumferential center line of the rib portion.

4. The gear of claim 3.

5. The plurality of rib portions include a plurality of first rib portions provided on one main surface of the sleeve and a plurality of second rib portions provided on the other main surface of the sleeve, A center line of the gear teeth in the axial direction is disposed at a position between a first hole portion present between the plurality of first rib portions in the circumferential direction and a second hole portion present between the plurality of second rib portions in the circumferential direction. A gear according to any one of claims 1 to 4.

6. A center line between the first hole portion and the second hole portion in the axial direction coincides with a center line of the gear teeth in the axial direction.

6. A gear according to claim 5.

7. an electric motor that is driven based on the steering of a steering member; 7. A steering device comprising: a gear according to claim 1; and a reducer that reduces the output rotation of the electric motor by the gear and transmits the reduced speed to a steering mechanism.

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