Motor unit and vehicle steering device

Abstract

[Problem] To provide a motor unit, a vehicle steering device, and a motor mounting structure capable of inhibiting vibrations generated by a motor from being transmitted to a mounting body even while retaining support stiffness of the motor by mounting a motor case to the mounting body by using a fastening member. [Solution] Mounting a motor case 44 of a motor 4, in which a stator 41 and a rotor 42 are accommodated in the motor case 44, to a housing 6, that serves as a mounting body, by using a bolt 7. The motor case 44 includes: a cylindrical part 441 that accommodates the stator 41; and a bottom part 443 that is provided so as to protrude radially inward from one end of the cylindrical part 441. A fastening part 445 for receiving the bolt 7 is provided to the bottom part 443 inward of the outer circumferential surface 441a of the cylindrical part 441.

Description

[Technical Field]

[0001] The present invention relates to a motor unit and a vehicle steering device. [Background technology]

[0002] Conventionally, electric power steering devices for vehicles that generate steering assist force by a motor have been known. The applicant has proposed an electric power steering device described in Patent Document 1 that has a structure for suppressing transmission of vibrations generated by the motor to a housing that is an attached body.

[0003] The motor of the electric power steering device described in Patent Document 1 has a rotor, a stator, an output shaft that rotates together with the rotor, and a motor case that houses the rotor and the stator. The motor case is attached to a housing that houses a worm reduction mechanism, and the motor output shaft is connected to a worm that is the input gear of the worm reduction mechanism. The torque of the motor amplified by the worm reduction mechanism is applied to the steering shaft as steering assist force.

[0004] The motor case is composed of a case body formed in a cylindrical shape with a bottom and a plate fixed to the case body. The case body integrally includes a cylindrical portion to which the stator is fixed on the inner peripheral surface and an annular bottom portion extending radially inward from one end of the cylindrical portion. The bottom portion is provided with a housing portion for housing a bearing supporting the output shaft. The plate integrally includes a base portion facing the bottom portion of the case body and a pair of mounting portions extending radially outward from the outer peripheral edge of the base portion. The base portion is provided with a fitting portion that is press-fitted into the outer periphery of the housing portion provided on the bottom portion of the case body, and the plate is fixed to the case body by the press-fit of the fitting portions. Each of the pair of mounting portions of the plate is formed with a through hole, and a fastening bolt is threaded through the through hole into a bolt hole formed in the housing. A small gap is formed between the outer peripheral portion of the fitting portion of the base portion and the bottom portion of the case body, and between the base portion and the housing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-090496 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the electric power steering device described in Patent Document 1, vibrations generated in the stator are damped by the plate of the motor case, and vibrations transmitted to the housing are suppressed. However, due to the structure, the support rigidity of the case body and the stator relative to the housing is low, and the output shaft is prone to tilt due to G forces (acceleration) in the front-rear, left-right, and up-down directions when the vehicle is running.

[0007] Therefore, the present invention aims to provide a motor unit and a vehicle steering device that can maintain the supporting rigidity of the motor by attaching the motor case to the mounting body using fastening members, while suppressing the transmission of vibrations generated by the motor to the mounting body. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the present invention provides a motor unit comprising: a motor having a stator, a rotor arranged inside the stator, an output rotating shaft that rotates integrally with the rotor, and a motor case that houses the stator; a worm reduction mechanism having a worm connected to the output rotating shaft and a worm wheel that meshes with the worm; a housing that houses the worm and the worm wheel; and a fastening member that fastens the motor case to the housing, wherein the motor case has a cylindrical portion that houses the stator and a bottom portion that protrudes radially inward from one end of the cylindrical portion, and the bottom portion is provided with a fastening portion that receives the fastening member, an inner annular convex portion provided on the bottom portion of the motor case is fitted inside an outer annular convex portion provided on the housing, the fastening portion is provided inside the outer peripheral surface of the inner annular convex portion, the height of the outer annular convex portion is set smaller than the axial length of the inner annular convex portion, and the tip surface of the outer annular convex portion does not contact the motor case.

[0010] In addition, in order to achieve the above-mentioned object, the present invention provides a vehicle steering device that steers the steered wheels of the vehicle by axially moving a steering shaft extending in the vehicle width direction, and that uses the above-mentioned motor unit as a driving source that generates a moving force that moves the steering shaft axially. [Effects of the Invention]

[0011] According to the motor unit and vehicle steering device of the present invention, by attaching the motor case to the mounting body using fastening members, it is possible to maintain the support rigidity of the motor while suppressing the transmission of vibrations generated by the motor to the mounting body. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing a configuration example of a steering device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram showing a column shaft, a column tube, a sensor case, a bracket, and a motor unit of the steering device. [Figure 3] FIG. 2 is a cross-sectional view of the motor unit. [Figure 4] FIG. [Figure 5] FIG. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] FIG. [Figure 9A] FIG. 10 is an explanatory diagram showing the expansion / contraction vibration of the motor in an exaggerated manner. [Figure 9B] FIG. 10 is an explanatory diagram showing the expansion / contraction vibration of the motor in an exaggerated manner. [Figure 10A] 9B is a cross-sectional view of the motor case taken along line CC in FIG. 9A. [Figure 10B] FIG. 9C is a cross-sectional view of the motor case taken along line DD in FIG. 9B. [Figure 11] FIG. 10 is a cross-sectional view showing a motor unit of a steering device according to a conventional example. [Figure 12] 10 is a graph showing the amount of displacement generated in the bracket when a predetermined drive current is supplied to the motor in a steering device using the motor unit according to the embodiment and a comparative example. [Figure 13] FIG. 10 is an external view of a motor case according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Embodiment Mode] The following description of the preferred embodiments of the present invention will be made with reference to the accompanying drawings. The embodiments described below are presented as preferred examples of the present invention, and while some of the embodiments specifically exemplify various technically preferred aspects, the technical scope of the present invention is not limited to these specific embodiments.

[0014] (Configuration of electric power steering device) Fig. 1 is a schematic diagram showing an example of the configuration of a steering device for a vehicle according to an embodiment of the present invention. Fig. 1 shows the steering device as seen from the front of the vehicle, with the left side of Fig. 1 corresponding to the right side of the vehicle, and the right side of Fig. 1 corresponding to the left side of the vehicle.

[0015] The steering device 1 includes a steering shaft 2 connected to a steering wheel 10 that is steered by the driver, a rack shaft 12 as a steering shaft that steers the left and right front wheels 11, which are the steerable wheels of the vehicle, by axial movement accompanying the rotation of the steering shaft 2, a torque sensor 13 that detects the steering torque applied to the steering wheel 10, a motor unit 3 that generates a steering assist force according to the detected steering torque, and a controller 30 that controls the motor unit 3.

[0016] The steering shaft 2 is composed of a column shaft 21 to the tip of which the steering wheel 10 is fixed, a pinion shaft 23 having pinion teeth 231 that mesh with the rack teeth 121 of the rack shaft 12, an intermediate shaft 22 interposed between the column shaft 21 and the pinion shaft 23, a universal joint 24 that connects the column shaft 21 and the intermediate shaft 22, and a universal joint 25 that connects the intermediate shaft 22 and the pinion shaft 23.

[0017] The column shaft 21 has an upper shaft 211 and a lower shaft 212 spline-fitted to allow telescopic adjustment, a torsion bar 213 connected to the rear end of the lower shaft 212, and an output shaft 214 connected to the rear end of the torsion bar 213. The torsion bar 213 has the flexibility to transmit steering torque to the output shaft 214 while twisting due to the steering torque applied to the steering wheel 10. The torque sensor 13 detects the steering torque from the amount of twist of the torsion bar 213.

[0018] Rack shaft 12 is housed in a cylindrical rack housing 14 and extends in the vehicle width direction. Ball joint sockets 15 are fixed to both ends of rack shaft 12, and tie rods 16 connected to rack shaft 12 by these ball joint sockets 15 steer the left and right front wheels 11 via knuckle arms (not shown). Bellows 17 made of bellows-like rubber or resin are arranged on the outer periphery of ball joint socket 15.

[0019] When the steering wheel 10 is steered, the pinion shaft 23 connected to the steering wheel 10 via the column shaft 21 and the intermediate shaft 22 rotates, and the rack shaft 12 moves in the axial direction due to the meshing of the pinion teeth 231 with the rack teeth 121. Then, due to this axial movement of the rack shaft 12, the left and right front wheels 11 are steered via the tie rods 16.

[0020] The motor unit 3 includes a motor 4 that receives a drive current from the controller 30 and generates torque, a worm reduction mechanism 5 having a worm 51 and a worm wheel 52, a housing 6 that accommodates the worm 51 and the worm wheel 52, and a fastening member (described later) for attaching the motor 4 to the housing 6. The worm 51 rotates due to the torque of the motor 4. The worm wheel 52 is engaged with the worm 51 and rotates at a slower rotational speed than the worm 51.

[0021] An output shaft 214 is fixed to the worm wheel 52, and the torque of the motor 4 amplified by the worm reduction gear mechanism 5 is transmitted to the output shaft 214 as a steering assist force. This steering assist force is transmitted to the pinion shaft 23 via the intermediate shaft 22 and becomes a moving force that moves the rack shaft 12 in the axial direction. In other words, the steering device 1 uses the motor unit 3 as a drive source that generates a moving force that moves the rack shaft 12 in the axial direction.

[0022] 2 is a schematic diagram showing the column tube 26 that houses the column shaft 21, upper shaft 211, and lower shaft 212, the sensor case 27 that houses the torque sensor 13, the bracket 8 that supports the column tube 26 relative to the vehicle body, and the motor unit 3. The column shaft 21, the column tube 26, the sensor case 27, the bracket 8, and the motor unit 3 make up the steering column device 20. In the following description, "above" and "below" refer to the up-down direction in the vertical direction when the steering device 1 is mounted on a vehicle. FIG. 2 shows the steering column device 20 as seen obliquely from above, perpendicular to the column shaft 21.

[0023] The column tube 26 has an outer tube 261 and an inner tube 262, and a portion of the inner tube 262 on the steering wheel 10 side is housed inside the outer tube 261. The rear end of the inner tube 262 is fitted and fixed to the sensor case 27. The upper shaft 211 is rotatably supported relative to the outer tube 261 by a bearing 28.

[0024] Bracket 8 has a pair of fixing plates 81 fixed to outer tube 261, a clamping member 82 having a pair of clamping plates 821 that clamp the pair of fixing plates 81 in the vehicle width direction and a top plate 822 arranged above outer tube 261, an operating lever 83 for releasing the clamped state of fixing plates 81 by clamping member 82, a plate 84 that is fixed to top plate 822 of clamping member 82 and extends in the vehicle width direction, and a pair of capsules 85 detachably attached to both ends of plate 84. The pair of capsules 85 are fixed to the vehicle body side by bolts (not shown) inserted into bolt insertion holes 850.

[0025] When the driver of the vehicle adjusts the tilt and telescopic position of the steering wheel 10, he operates the operating lever 83 to release the clamping state of the fixed plate 81 by the clamping members 82. Furthermore, when a secondary collision occurs with the steering wheel 10 caused by the driver's collision with the vehicle, the plate 84 separates from the pair of capsules 85, and the pair of fixed plates 81, the clamping members 82, the outer tube 261, and the upper shaft 211 move toward the front of the vehicle together with the steering wheel 10.

[0026] Fig. 3 is a cross-sectional view of the motor unit 3. Fig. 4 is a cross-sectional view of the motor 4. The motor 4 has a stator 41 that generates a magnetic field by a drive current supplied from the controller 30, a rotor 42 arranged inside the stator 41, an output rotating shaft 43 that rotates integrally with the rotor 42, a cylindrical motor case 44 with a bottom that houses the stator 41, a cover 45 arranged above the motor case 44 and covering an opening 40 at one end of the motor case 44, and first and second bearings 46 and 47.

[0027] As shown in Fig. 4, the stator 41 is configured by windings 412 around a plurality of teeth 411 arranged in an annular shape. In this embodiment, twelve teeth 411 are arranged in an annular shape. The rotor 42 has a rotor core 421 and a plurality of magnets 422 fixed to the rotor core 421. In this embodiment, ten magnets 422 are arranged on the outer periphery of the rotor core 421. The plurality of teeth 411 and the rotor core 421 are configured by laminating a plurality of electromagnetic steel plates.

[0028] The output rotating shaft 43 is inserted through the center of the rotor core 421, and one end thereof protruding downward from the rotor core 421 is supported by a first bearing 46, while the other end thereof protruding upward from the rotor core 421 is supported by a second bearing 47. The first bearing 46 is disposed between the output rotating shaft 43 and the motor case 44, and the second bearing 47 is disposed between the output rotating shaft 43 and the cover 45. The first and second bearings 46, 47 have outer rings 461, 471 and inner rings 462, 472, and a plurality of rolling elements 463, 473 disposed between the outer rings 461, 471 and the inner rings 462, 472.

[0029] Fig. 5 is a perspective view showing the motor case 44. Fig. 6 is a perspective view showing the housing 6. Fig. 7 is an external view of the motor case 44 as seen from the direction of the rotation axis O1 of the output rotation shaft 43. Fig. 8 is an external view of the housing 6 as seen from the direction of the rotation axis O2 of the worm 51. Fig. 3 shows a cross section of the motor case 44 taken along line AA in Fig. 7 and a cross section of the housing 6 taken along line BB in Fig. 8.

[0030] The motor case 44 is made of die-cast aluminum alloy and integrally includes a cylindrical portion 441 that houses the stator 41, a plurality of flanges 442 for fixing the cover 45, and a bottom portion 443 that protrudes radially inward from one end of the cylindrical portion 441. The cover 45 is fixed to the motor case 44 with a plurality of bolts 90 that screw into the flanges 442. The stator 41 is fixed to the inside of the cylindrical portion 441. A retaining hole 400 that holds an outer ring 461 of the first bearing 46 is formed in the center of the bottom portion 443 and penetrates the bottom portion 443, and the output rotation shaft 43 is inserted into an inner ring 462 of the first bearing 46.

[0031] The bottom portion 443 is provided with an inner annular protrusion 444 formed to protrude downward toward the housing 6, and a plurality of fastening portions 445 with threaded holes 440 formed therein. The inner annular protrusion 444 is formed in an annular shape centered on the rotation axis O1 of the output rotation shaft 43. When the motor case 44 is viewed from the bottom portion 443 side along the rotation axis O1 as shown in FIG. 7, the fastening portions 445 are provided inside an outer circumferential surface 441a of the cylindrical portion 441 that corresponds to the outer circumferential side of the stator 41. Furthermore, the fastening portions 445 are formed to protrude inward from an inner circumferential surface 444a of the inner annular protrusion 444, and are provided inside an outer circumferential surface 444b of the inner annular protrusion 444.

[0032] The diameter of the outer circumferential surface 444b of the inner annular convex portion 444 (outer diameter D1 of the inner annular convex portion 444) is smaller than the diameter of the inner circumferential surface 441b of the cylindrical portion 441 to which the stator 41 is fixed (inner diameter D2 of the cylindrical portion 441). The tip surface 444c of the inner annular convex portion 444 is a flat surface perpendicular to the rotation axis O1 of the output rotation shaft 43. The screw hole 440 extends parallel to the rotation axis O1.

[0033] In this embodiment, the controller 30 is disposed above the lid 45 and is integrated with the motor 4. The controller 30 is configured by a substrate 31 fixed to the lid 45 and a plurality of electronic components 32 mounted on the substrate 31. The plurality of electronic components 32 are, for example, switching elements such as power transistors, a CPU (Central Processing Unit), etc. The substrate 31 is covered from above with a cover 33 attached to the lid 45. The controller 30 may be disposed between the stator 41 and the bottom 443 of the motor case 44. The controller 30 may also be separate from the motor 4.

[0034] The controller 30 supplies a driving current of a magnitude corresponding to the steering torque and vehicle speed detected by the torque sensor 13 to the windings 412 of the stator 41. The driving current supplied by the controller 30 is a three-phase alternating current that generates a rotating magnetic field in the stator 41. The rotor 42 rotates following the rotating magnetic field due to the attractive and repulsive forces acting between each tooth 411 and the magnet 422.

[0035] The worm 51 is arranged coaxially with the output rotation shaft 43 of the motor 4, and is connected to the output rotation shaft 43 via a coupling 91. The output shaft 214 is inserted through the center of the worm wheel 52, and the relative rotation between the worm wheel 52 and the output shaft 214 is regulated by a key 92.

[0036] The housing 6 integrally includes a main body 61 that accommodates the worm wheel 52, a cylindrical portion 62 that accommodates the worm 51, a mounting portion 63 that faces the bottom 443 of the motor case 44, an outer annular protrusion 64 that is provided in an annular shape on the outer periphery of the mounting portion 63, and a supported portion 65 that has formed therein a pair of tilt bolt insertion holes 650 through which tilt bolts (not shown) that serve as the tilt center during tilt adjustment are inserted. The main body 61 of the housing 6 is provided with a plurality of flange portions 611 that have formed therein screw holes 610 through which bolts 93 (see FIG. 2) for fixing the sensor case 27 are threadedly engaged.

[0037] The cylindrical portion 62 accommodates a pair of bearings 94, 95 that rotatably support the worm 51. The mounting portion 63 is formed in a disk shape and protrudes from one upper end of the cylindrical portion 62 in a direction perpendicular to the rotation axis O2 of the worm 51. An upper surface 63a of the mounting portion 63 serves as a contact surface against which a tip surface 444c of an inner annular protrusion 444 of the motor case 44 abuts. The outer annular protrusion 64 protrudes above the upper surface 63a of the mounting portion 63. The protruding height of the outer annular protrusion 64 from the upper surface 63a of the mounting portion 63 is set to a dimension such that the tip surface 64a of the outer annular protrusion 64 does not contact the motor case 44. In other words, the height of the outer annular protrusion 64 from the mounting portion 63 is set to be shorter than the axial length of the inner annular protrusion 444. As a result, when the motor case 44 is attached to the housing 6, a gap 300 of a predetermined size is created between the tip surface 64a of the outer annular protrusion 64 and the motor case 44 in the direction of the rotation axis O1.

[0038] The motor 4 is attached to a housing 6, which serves as an attachment target, by a mounting structure using bolts 7 as fastening members. The bolts 7 have a threaded portion 71 with a male thread 711 and a head portion 72 with a larger diameter than the threaded portion 71. A mounting portion 63 of the housing 6 is formed with a plurality of bolt insertion holes 630 through which the threaded portions 71 of the bolts 7 are inserted. The bolt insertion holes 630 penetrate the mounting portion 63 parallel to the rotation axis O2 of the worm 51 and open to an upper surface 63a of the mounting portion 63 and a lower surface 63b of the mounting portion 63 opposite the upper surface 63a. The lower surface 63b is a part of the outer surface of the housing 6. In this embodiment, the plurality of bolt insertion holes 630 are formed so as to appear circular when the mounting portion 63 is viewed parallel to the rotation axis O2. However, the plurality of bolt insertion holes 630 may be formed as arc-shaped grooves or radially extending grooves centered on the rotation axis O2.

[0039] In this embodiment, the motor case 44 is fastened to the housing 6 by three bolts 7. Three fastening portions 445 corresponding to the three bolts 7 are provided on the bottom 443 of the motor case 44 along the circumferential direction of the inner annular protrusion 444. Each fastening portion 445 receives the bolt 7 by threading the male threads 711 of the bolt 7 into the threaded hole 440. Tightening the bolt 7 generates an axial force in the bolt 7, and the motor case 44 is fastened to the housing 6.

[0040] Three bolt insertion holes 630 corresponding to the three bolts 7 are formed in the mounting portion 63 of the housing 6 along the circumferential direction of the outer annular protrusion 64. The threaded portion 71 of each bolt 7 is inserted into the bolt insertion hole 630 from the lower surface 63b side toward the upper surface 63a side of the mounting portion 63, and is screwed into the threaded hole 440 of the motor case 44. The head 72 of the bolt 7 abuts against the lower surface 63b of the mounting portion 63. A washer may be sandwiched between the head 72 and the lower surface 63b.

[0041] The motor case 44 and the housing 6 are positioned by fitting the inner annular protrusion 444 of the motor case 44 inside the outer annular protrusion 64 of the housing 6. The outer diameter of the inner annular protrusion 444 is slightly smaller than the diameter (the inner diameter of the outer annular protrusion 64) of the inner circumferential surface 64b of the outer annular protrusion 444, which faces the outer circumferential surface 444b of the inner annular protrusion 444. When attaching the motor 4 to the housing 6, the inner annular protrusion 444 is fitted into the outer annular protrusion 64 to align the rotation axis O1 of the output rotation shaft 43 with the rotation axis O2 of the worm 51, and then the housing 6 and the motor 4 are rotated relative to each other about the rotation axes O1 and O2, thereby easily bringing the multiple bolt insertion holes 630 of the housing 6 into communication with the multiple screw holes 440 of the motor case 44.

[0042] Next, the operation of the mounting structure described above, which suppresses the expansion / contraction vibrations generated in the motor 4 due to the rotation of the rotor 42 and the transmission of these expansion / contraction vibrations to the housing 6, will be described with reference to Figures 9A, 9B, 10A, and 10B.

[0043] 9A and 9B are explanatory diagrams showing the expansion and contraction vibration of the motor 4 in an exaggerated manner. FIG. 9A shows the stator 41 and the cylindrical portion 441 of the motor case 44 expanding in the left-right direction and contracting in the up-down direction. FIG. 9B shows the stator 41 and the motor case 44 expanding in the up-down direction and contracting in the left-right direction. Also, in FIGS. 9A and 9B, arrow F1 indicates the attractive force that the teeth 411 of the stator 41 receive from the magnets 422, and arrow F2 indicates the repulsive force that the teeth 411 receive from the magnets 422. The two-dot chain lines in FIGS. 9A and 9B indicate the shape of the outer edge of the cylindrical portion 441 when no current is supplied to the windings 412. FIG. 10A is a cross-sectional view of the motor case 44 taken along line CC in FIG. 9A. FIG. 10B is a cross-sectional view of the motor case 44 taken along line DD in FIG. 9B.

[0044] The stator 41 expands in the direction in which it receives a repulsive force from the magnet 422 and contracts in the direction in which it receives an attractive force. As a result, the shape of the outer circumferential surface 441a of the cylindrical portion 441 of the motor case 44 expands and contracts into an elliptical shape relative to the shape indicated by the two-dot chain line in FIGS. 9A and 9B. The major and minor axes of this elliptical shape rotate together with the rotor 42 around the rotation axis O1. As the cylindrical portion 441 expands and contracts, the bottom 443 of the motor case 44 also flexes, as shown in FIGS. 10A and 10B. This flexure of the bottom 443 is small near the center portion close to the retaining hole 400 and large near the outer edge.

[0045] If such expansion / compression vibrations of cylindrical portion 441 are transmitted from motor case 44 to housing 6, and further from housing 6 via sensor case 27 to column tube 26 or bracket 8, the sound generated by this vibration may be heard as an abnormal noise by the driver or passengers, causing discomfort. Furthermore, if the amplitude of the expansion / compression vibration is large, there is also the risk that the vibrations may be transmitted from column tube 26 via bearing 28 to upper shaft 211 or steering wheel 10.

[0046] In this embodiment, by providing the fastening portion 445 radially inward of the outer peripheral surface 441a of the cylindrical portion 441 corresponding to the outer peripheral side of the stator 41, the bending vibration of the bottom portion 443 caused by the expansion / contraction vibration of the cylindrical portion 441 is suppressed from being transmitted to the housing 6. Also, in this embodiment, the reinforcing effect of the inner annular convex portion 444 of the bottom portion 443 increases the rigidity of the portion of the bottom portion 443 that is inner than the outer peripheral surface 444b of the inner annular convex portion 444, and by providing the fastening portion 445 in this portion with increased rigidity, the expansion / contraction vibration of the cylindrical portion 441 is further suppressed from being transmitted to the housing 6.

[0047] Furthermore, while the tip surface 444c of the inner annular protrusion 444 of the motor case 44 abuts against the upper surface 63a of the mounting portion 63 of the housing 6, the tip surface 64a of the outer annular protrusion 64 of the housing 6 does not contact the motor case 44, thereby preventing the deflection of the bottom 443 of the motor case 44, which is greater toward the outer edge, from being transmitted to the housing 6.

[0048] Figure 11 is a cross-sectional view showing a motor unit 3A of a steering device according to a comparative example. This motor unit 3A is configured similarly to the motor unit 3 according to the above embodiment, except for the mounting structure of the motor 4A to the housing 6A. In Figure 11, components that are common to those described in the above embodiment are assigned the same reference numerals as those in Figure 3.

[0049] The motor case 44A of the motor 4A has a flat bottom portion 446 that protrudes radially inward from the end of the cylindrical portion 441, and a pair of flange portions 447 that are provided on the outer periphery of the bottom portion 446. The housing 6A has a flat mounting portion 66 that faces the bottom portion 446, and a pair of flange portions 67 that are provided on the outer periphery of the mounting portion 66. The pair of flange portions 447 of the motor case 44A are fastened to the pair of flange portions 67 of the housing 6A with bolts 96, respectively.

[0050] 12 is a graph showing the magnitude of the displacement that occurs in the central portion 840 (see FIG. 2) of the plate 84 of the bracket 8 when a predetermined drive current is supplied to the motor 4 with the capsule 85 fixed to the fixed member in the steering device 1 using the motor unit 3 according to the above embodiment, and the magnitude of the displacement that occurs in the central portion 840 of the plate 84 of the bracket 8 when the motor unit 3 is replaced with a motor unit 3A according to a comparative example. Note that the magnitude of the displacement shown in FIG. 12 shows the maximum amount of displacement from the reference position during one rotation of the rotor 42 relative to the stator 41, with the position of the central portion 840 of the plate 84 in the non-energized state where no drive current is supplied to the stator 41 being set as the reference position.

[0051] When expansion / contraction vibrations generated in the motors 4, 4A are transmitted from the housing 6 through the sensor case 27 and column tube 26 to the bracket 8, elastic deformation occurs in each component of the bracket 8, and the position of the center portion 840 of the plate 84 is displaced from the reference position. As shown in FIG. 12, when the motor unit 3 according to the above embodiment is used, the amount of displacement generated in the plate 84 of the bracket 8 is suppressed to about one-tenth of the amount when the motor unit 3A according to the comparative example is used. This shows that the vibrations transmitted from the motor 4 to the housing 6 are significantly suppressed in this embodiment.

[0052] (Effects of the embodiment) As described above, the motor unit 3 according to the above embodiment and the steering device 1 using the same can suppress the transmission of expansion / contraction vibrations generated in the motor 4 to the housing 6. This prevents the sound generated by the expansion / contraction vibrations of the motor 4 from being heard as an abnormal noise by the driver and passengers, causing discomfort. Furthermore, by attaching the motor case 44 to the housing 6 with a plurality of bolts 7, the supporting rigidity of the motor 4 relative to the housing 6 is ensured.

[0053] According to the above embodiment, the motor case 44 is attached to the housing 6 with three bolts 7, which is more effective in suppressing vibration transmission from the motor 4 to the housing 6 than, for example, when the motor case 44 is attached to the housing 6 with two bolts 7 arranged symmetrically about the rotation axis O1 of the output rotation shaft 43. In other words, when the motor case 44 is attached to the housing 6 with two bolts 7 arranged symmetrically about the rotation axis O1, the deflection of the bottom 443 of the motor case 44 increases simultaneously at the two fastening portions 445 when the major axis direction of the cylindrical portion 441, which has become elliptical due to the attractive and repulsive forces of the multiple magnets 422 of the rotor 42, coincides with the arrangement direction of the two bolts 7, and displacement due to vibration is more likely to be transmitted from the motor 4 to the housing 6. On the other hand, in this embodiment, three fastening portions 445 are provided along the circumferential direction of the inner annular convex portion 444, thereby shifting the phase of the deflection of the bottom 443 of the motor case 44 from the phase of the fastening portions 445, thereby suppressing the transmission of vibration from the motor 4 to the housing 6.

[0054] Furthermore, even in a configuration in which two fastening portions 445 are fixed with two bolts 7, the transmission of vibration from the motor 4 to the housing 6 can be suppressed by offsetting the two fastening portions 445 by a predetermined angle from positions symmetrical about the rotation axis O1. For example, one of the three fastening portions 445 shown in FIG. 7 may be omitted, and the motor case 44 may be configured as shown in FIG. 13. The two fastening portions 445 shown in FIG. 13 are provided in positions that are offset by a predetermined angle θ in the circumferential direction of the inner annular convex portion 444 from position P, where one fastening portion 445 is symmetrical about the rotation axis O1 with respect to the other fastening portion 445. In this case, the transmission of vibration from the motor 4 to the housing 6 can be suppressed more effectively than when the two fastening portions 445 are provided at positions symmetrical about the rotation axis O1.

[0055] Note that four or more fastening portions 445 may be provided along the circumferential direction of the inner annular convex portion 444. That is, the number of fastening portions 445 is preferably two or more, and more preferably three or more. Furthermore, if the vibration mode of the side surfaces of the stator 41 and motor case 44 due to expansion / contraction vibrations generated in the motor 4 is not elliptical but is an N-sided polygon with more than one triangle (N is a natural number greater than or equal to 3) in shape, the transmission of vibration from the motor 4 to the housing 6 can be suppressed by arranging the fastening portions 445 in the circumferential direction at an angular pitch slightly offset from 360 degrees divided by N.

[0056] (Addendum) The present invention has been described above based on the embodiments, but these embodiments do not limit the scope of the invention as claimed. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. Furthermore, the present invention can be appropriately modified and implemented by omitting some components or adding or substituting components within the scope of the spirit of the invention. Furthermore, the present invention can also be modified, for example, as follows:

[0057] In the above embodiment, the present invention has been described as being applied to a column-assist steering device 1 that applies a steering assist force to the column shaft 21. However, the configuration of the steering device is not limited to the column-assist type, and the present invention can be applied to various types of known steering devices, such as a dual-pinion type in which two pinion gear shafts are meshed with a rack shaft, one of the pinion gear shafts is connected to a steering wheel via a universal joint or the like, and steering assist force is applied to the other pinion gear shaft, or a rack-parallel type in which a motor is arranged in parallel to the rack shaft and the torque of the motor is applied to the rack shaft as axial steering assist force via a belt and ball screw mechanism.

[0058] In the above embodiment, the bolt 7 having the threaded portion 71 and the head portion 72 is used as the fastening member, but the present invention is not limited to this. For example, a stud bolt having male threads at both ends may be screwed into the motor case 44 and combined with a nut to be used as the fastening member. Also, a rivet may be used as the fastening member.

[0059] The present invention can also be applied to a steering device of an autonomous vehicle that can travel autonomously without human intervention. Furthermore, the present invention can be applied not only to steering devices but also to various other machinery such as industrial machinery equipped with a motor, and is particularly suitable for use in machinery that requires a high level of low vibration, such as semiconductor manufacturing equipment. [Explanation of symbols]

[0060] 1...Steering device 11...Front wheels (steered wheels) 12...Rack shaft (steering shaft) 3...Motor unit 4...Motor 41...Stator 42...Rotor 43...Output rotating shaft 44...Motor case 440...screw hole 441...Cylindrical part 443…Bottom 444...Inner annular convex part 444b…Outer surface 445... Fastening part 5...Worm reduction mechanism 51...Warm 52...worm wheel 6. Housing 61...Main body 62...Cylindrical part 63...Mounting part 630...Bolt insertion hole 64...Outer annular convex part 7...Bolt (fastening member)

Claims

1. a motor including a stator, a rotor disposed inside the stator, an output rotary shaft that rotates integrally with the rotor, and a motor case that houses the stator; a worm reduction mechanism having a worm connected to the output rotation shaft and a worm wheel meshing with the worm; a housing that accommodates the worm and the worm wheel; a fastening member that fastens the motor case and the housing together, the motor case has a cylindrical portion that houses the stator, and a bottom portion that protrudes radially inward from one end of the cylindrical portion, The bottom portion is provided with a fastening portion that receives the fastening member, an inner annular protrusion provided on the bottom of the motor case is fitted inside an outer annular protrusion provided on the housing, the fastening portion is provided inside an outer circumferential surface of the inner annular convex portion, a height of the outer annular convex portion set to be smaller than an axial length of the inner annular convex portion, and a tip end surface of the outer annular convex portion is not in contact with the motor case; Motor unit.

2. the housing has a mounting portion formed with an insertion hole through which the fastening member is inserted, the mounting portion faces the bottom portion of the motor case; The motor unit according to claim 1 .

3. the fastening member is a bolt, A threaded hole into which the bolt is screwed is formed in the fastening portion, The bolt is inserted into the insertion hole of the mounting portion and is screwed into the screw hole. The motor unit according to claim 2 .

4. the housing has a main body portion that accommodates the worm wheel and a cylindrical portion that accommodates the worm, and the mounting portion is formed by protruding from one end of the cylindrical portion in a direction perpendicular to the rotation axis of the worm. The motor unit according to claim 2 .

5. Two or more of the fastening portions are provided along the circumferential direction of the inner annular convex portion. The motor unit according to claim 1 .

6. Two fastening portions are provided on the bottom portion, and the two fastening portions are provided at positions shifted by a predetermined angle from positions symmetrical with respect to the rotation axis of the motor. The motor unit according to claim 5 .

7. When a vibration mode of the stator and the cylindrical portion of the motor case due to expansion / contraction vibration generated in the motor is not an ellipse but an N-sided shape with more than one triangle (N is a natural number of 3 or more), the two or more fastening portions are arranged along the circumferential direction, each shifted by a predetermined angle from an angular pitch obtained by dividing 360 degrees by N. The motor unit according to claim 5 .

8. A vehicle steering device that steers steered wheels of a vehicle by axially moving a steering shaft extending in a vehicle width direction of the vehicle, The motor unit according to claim 1 is used as a drive source for generating a moving force for moving the steering shaft in the axial direction. A steering device for a vehicle.

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