Worm reduction gear equipped electric motor and electric power steering device

Abstract

To provide an electric motor with a worm speed reducer which achieves further downsizing, and to provide an electric power steering device.SOLUTION: An electric motor with a worm speed reducer includes: a first housing which houses a worm wheel; and a second housing which houses a worm shaft. The worm shaft includes: rotors located at one end and the other end as seen in a second direction relative to a shaft tooth part and each having a recessed part which is open toward the second direction; bearings respectively housed in the recessed parts of the rotors; and pins each including a body fitted in an inner periphery of the bearing and a protruding part protruding from the body in the second direction. The second housing is provided with slits in each of which the protruding part of the pin is fitted.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to an electric motor with a worm reduction gear and an electric power steering device. [Background technology]

[0002] The electric power steering device of Patent Document 1 includes an electric motor with a worm reduction gear, which has a worm shaft and a worm wheel. The worm shaft meshes with the worm wheel, and the worm wheel also rotates when the worm shaft is driven to rotate by a motor. The worm wheel is housed in a first housing, and the worm shaft is housed in a second housing.

[0003] The worm shaft extends in the axial direction of the central axis. The worm shaft has a shaft tooth portion, a rotor, a bearing, and a shaft. The shaft tooth portion is located in the center in the axial direction and meshes with the wheel tooth portion of the worm wheel. A rotor is located on both sides of the shaft tooth portion in the axial direction, and a bearing is located on both sides of the rotor in the axial direction. The shaft extends in the axial direction from the shaft tooth portion and fixes the rotor. In addition, both ends of the shaft are rotatably supported by bearings fixed to the second housing. As a result, the worm shaft is rotatably supported relative to the second housing via the bearings. In this way, since the worm shaft extends long in the axial direction of the central axis, the second housing that accommodates the worm shaft is also large. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-192787 A Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for a more compact electric motor with a worm reduction gear and an electric power steering device.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and has an object to provide an electric motor with a worm reduction gear and an electric power steering device that are more compact. [Means for solving the problem]

[0007] In order to achieve the above object, an electric motor with a worm reduction gear or an electric power steering device according to one embodiment includes a worm wheel rotatable about a central axis extending in a first direction and having a wheel tooth portion, a first housing that accommodates the worm wheel and rotatably supports the worm wheel, a worm shaft that has a shaft tooth portion that meshes with the wheel tooth portion and is rotatable about a central axis extending in a second direction intersecting the first direction, and a second housing that accommodates the worm shaft, rotatably supports the worm shaft, and supports the worm shaft in a first direction. the worm shaft is provided with a rotor located at one end and the other end in the second direction with respect to the shaft teeth portion and having a recess opening toward the second direction, a bearing accommodated in the recess of the rotor, and a pin including a main body portion fitted into the inner periphery of the bearing and a protrusion protruding from the main body portion in the second direction, the stator is disposed facing the outer periphery of the rotor, and the second housing has a fitting portion into which the protrusion of the pin fits.

[0008] As described above, in the worm shaft of Patent Document 1, the rotor is located on both axial sides of the shaft tooth portion, the bearing is located on both axial sides of the rotor, and the bearing is fixed inside the second housing. The shaft tooth portion and the rotor are separated in the axial direction, and the rotor and the bearing are separated in the axial direction. Therefore, the worm shaft and the second housing are long in the axial direction, and the electric motor with a worm reducer including the second housing is large.

[0009] In contrast, in the worm shaft according to the present disclosure, the bearing is housed in a recess provided on the inside of the rotor. Therefore, the worm shaft according to the present disclosure has a shorter axial length than the worm shaft of Patent Document 1, and the second housing is smaller. As described above, according to the present disclosure, it is possible to provide a more compact electric motor with a worm reduction gear and an electric power steering device.

[0010] As a desirable aspect, the second housing includes a first frame-shaped member located on the first housing side and extending along an edge of the first housing, and a second frame-shaped member extending from portions of the first frame-shaped member on one side and the other side in the second direction in a third direction intersecting both the first direction and the second direction, and the second frame-shaped member is provided with a slit that extends along the third direction and opens on the first housing side, and the slit is the fitting portion of the second housing.

[0011] In this way, since the second housing includes the first frame member and the second frame member, it has fewer openings than the box-shaped second housing of Patent Document 1. Therefore, the second housing of the present disclosure is lighter than the second housing of Patent Document 1. In addition, since the second frame member is provided with a slit that opens to the first housing side, when assembling the worm shaft to the second housing, it is only necessary to insert the protruding portion of the pin into the slit and move it in the third direction, so that the assembling work is easy. On the other hand, when the fitting portion of the second housing is an annular member having a through hole, it may be necessary to, for example, tilt the attitude of the worm shaft or push the second frame member to deform it in order to insert the protruding portion of the pin into the through hole of the annular member.

[0012] In a preferred embodiment, the protrusion of the pin is an elongated irregular columnar portion whose width in the first direction is smaller than its height in the third direction, and the protrusion cannot rotate when the protrusion is fitted into the slit. In this specification, the "irregular columnar portion" refers to a columnar portion having a shape other than a cylindrical shape, such as a rectangular column.

[0013] The protruding portion of the pin has a vertically elongated shape with a width in the first direction smaller than its height in the third direction, and therefore the width of the slit into which the protruding portion fits is smaller than that of a horizontally elongated protruding portion whose width in the first direction is greater than its height in the third direction, thereby further reducing the size of the second housing.

[0014] In a preferred embodiment, the bearing is a needle bearing or a plain bearing. A needle bearing or a plain bearing has a smaller outer diameter than, for example, a rolling bearing, and therefore the bearing can be made smaller, thereby further reducing the size of the second housing. Effect of the Invention

[0015] According to the present disclosure, it is possible to provide a more compact electric motor with a worm reduction gear and an electric power steering device. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of an electric power steering device according to an embodiment. [Diagram 2] FIG. 2 is a schematic perspective view of the electric motor with a worm reduction gear according to the embodiment, as viewed from the output shaft side of the first steering shaft. [Diagram 3] FIG. 3 is a side view of FIG. [Figure 4] FIG. 4 is a schematic perspective view of the worm reduction gear equipped electric motor according to the embodiment, as viewed from the input shaft side of the first steering shaft. [Diagram 5] FIG. 5 is a schematic front view of the electric motor with a worm reduction gear according to the embodiment, as viewed from the output shaft side of the first steering shaft. [Figure 6]FIG. 6 is an exploded perspective view of FIG. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. [Figure 8] FIG. 8 is a schematic exploded view of the worm shaft according to the embodiment. [Figure 9] FIG. 9 is a cross-sectional view that diagrammatically shows the cross section of FIG. [Figure 10] FIG. 10 is a schematic cross-sectional view of a worm reduction gear equipped electric motor according to a modified example, and corresponds to FIG. 7 of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A detailed description of the embodiment of the present invention will be given with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. The components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. The components described below can be appropriately combined. The same reference numerals are used for parts with the same structure, and the description is omitted. In the three-dimensional coordinate system, the X direction indicates the front-rear direction of the vehicle body, the Y direction indicates the width direction of the vehicle, and the Z direction indicates the up-down direction. Furthermore, the X1 side indicates the output shaft side of the first steering shaft 82, and the X2 side indicates the input shaft side. The Y1 side indicates the left side in the width direction of the vehicle, and the Y2 side indicates the right side. The Z1 side indicates the upper side, and the Z2 side indicates the lower side.

[0018] In the following description, the "first direction" refers to the axial direction of the central axis AX1 of the worm wheel 11, and the "second direction" refers to the axial direction of the central axis AX2 of the worm shafts 12, 12A. The "second direction" intersects with the "first direction." Furthermore, the "third direction" refers to a direction that intersects with both the "first direction" and the "second direction."

[0019] Here, in the following embodiment, for ease of understanding, the X direction coincides with the first direction, the Y direction coincides with the second direction, and the Z direction coincides with the third direction. The X1 side is also referred to as one side of the first direction, the X2 side as the other side of the first direction, the Y1 side as one side of the second direction, the Y2 side as the other side of the second direction, the Z1 side as one side of the third direction, and the Z2 side as the other side of the third direction. However, in the present invention, the "first direction" is not limited to the "X direction", the "second direction" is not limited to the "Y direction", and the "third direction" is not limited to the "Z direction".

[0020] [Embodiment] Hereinafter, an embodiment will be described. FIG. 1 is a schematic diagram of an electric power steering device according to an embodiment. FIG. 2 is a schematic perspective view of an electric motor with a worm reduction gear according to an embodiment, as viewed from the output shaft side of a first steering shaft. FIG. 3 is a side view of FIG. 2. FIG. 4 is a schematic perspective view of an electric motor with a worm reduction gear according to an embodiment, as viewed from the input shaft side of a first steering shaft. FIG. 5 is a schematic front view of an electric motor with a worm reduction gear according to an embodiment, as viewed from the output shaft side of a first steering shaft. FIG. 6 is an exploded perspective view of FIG. 4. FIG. 7 is a cross-sectional view taken along line VII-VII of FIG. 4. FIG. 8 is a schematic view of an exploded worm shaft according to an embodiment. FIG. 9 is a cross-sectional view showing a cross section of FIG. 8.

[0021] 1, the first steering shaft 82 includes an input shaft 82a and an output shaft 82b. One end of the input shaft 82a is connected to the steering wheel 81, and the other end of the input shaft 82a is connected to the output shaft 82b. One end of the output shaft 82b is connected to the input shaft 82a, and the other end of the output shaft 82b is connected to the first universal joint 84.

[0022] 1, the second steering shaft 85 connects the first universal joint 84 and the second universal joint 86. One end of the second steering shaft 85 is connected to the first universal joint 84, and the other end of the second steering shaft 85 is connected to the second universal joint 86. One end of the third steering shaft 87 is connected to the second universal joint 86, and the other end of the third steering shaft 87 is connected to a steering gear 88.

[0023] As shown in Fig. 1, the steering gear 88 includes a pinion 88a and a rack 88b. The pinion 88a is connected to a third steering shaft 87. The rack 88b meshes with the pinion 88a. The steering gear 88 converts the rotational motion transmitted to the pinion 88a into linear motion by the rack 88b. The rack 88b is connected to a tie rod 89. The angle of the wheels changes as the rack 88b moves.

[0024] 1, the steering force assist mechanism 83 includes a worm reduction motor 100. The worm reduction motor 100 applies an auxiliary steering torque to the output shaft 82b. The worm reduction motor 100 will be described in detail later.

[0025] As shown in Fig. 1, the electric power steering device 80 includes an electric motor 100 with a worm reduction gear, an ECU (Electronic Control Unit) 90, a torque sensor 94, and a vehicle speed sensor 95. The electric motor 100 with a worm reduction gear, the torque sensor 94, and the vehicle speed sensor 95 are electrically connected to the ECU 90. The torque sensor 94 outputs the steering torque transmitted to the input shaft 82a to the ECU 90 by CAN (Controller Area Network) communication. The vehicle speed sensor 95 detects the traveling speed (vehicle speed) of the vehicle body on which the electric power steering device 80 is mounted. The vehicle speed sensor 95 is provided on the vehicle body, and outputs the vehicle speed to the ECU 90 by CAN communication.

[0026] The ECU 90 controls the operation of the motor unit 3 (see FIG. 2) of the electric motor 100 with a worm reduction gear. The ECU 90 acquires signals from a torque sensor 94 and a vehicle speed sensor 95. When an ignition switch 98 is on, the ECU 90 is supplied with power from a power supply device 99 (e.g., an on-board battery). The ECU 90 calculates an auxiliary steering command value based on the steering torque and the vehicle speed. The ECU 90 adjusts the value of power supplied to the motor unit 3 based on the auxiliary steering command value. The ECU 90 acquires information on induced voltage from the motor unit 3 or information output from a resolver or the like provided in the motor unit 3. The force required to operate the steering wheel 81 is reduced by the ECU 90 controlling the motor unit 3.

[0027] As shown in Fig. 2 to Fig. 7, the electric motor 100 with a worm reduction gear includes a first structure 110 and a second structure 120. The first structure 110 and the second structure 120 are arranged in the vertical direction. The first structure 110 is located on the lower side (Z2 side), an elastic member 5 (see Fig. 5) is arranged on the first structure 110, and the second structure 120 is arranged above the first structure 110 and the elastic member 5. That is, the first structure 110 and the second structure 120 sandwich the elastic member 5 from above and below. The worm wheel 11 and the worm shaft 12 form the worm reduction gear 1 (see Fig. 4).

[0028] As shown in FIG. 2 to FIG. 7, the first structure 110 has a first housing 21 and a worm wheel 11. The first housing 21 has a main body 211 and a cover 212, and houses the worm wheel 11. The main body 211 is located on the X1 side in the front-rear direction (X direction), and the cover 212 covers an opening on the X2 side of the main body 211. The worm wheel 11 extends in the first direction. In other words, the worm wheel 11 extends in the axial direction of the central axis AX1. The worm wheel 11 is rotatable in a direction around the central axis AX1. In addition, as shown in FIG. 7, the first housing 21 has a first opening 213 to which the worm wheel 11 is exposed, and a peripheral portion 213a of the first opening 213.

[0029] As shown in FIG. 2 and FIG. 3, the main body 211 has a first peripheral surface portion 211a, a rear wall surface portion 211b, a second peripheral surface portion 211c, a flange 211d, a disk portion 211e, a spline shaft 211f, and a flange portion 211g. The first peripheral surface portion 211a is a cylindrical surface extending in a circumferential direction around a central axis AX1. The rear wall surface portion 211b extends radially inward from an end of the first peripheral surface portion 211a on the X1 side. The second peripheral surface portion 211c is a cylindrical surface extending in a circumferential direction. The second peripheral surface portion 211c extends from an end of the rear wall surface portion 211b on the radially inner side toward the X1 side. The disk portion 211e is fitted to the inner peripheral side of the second peripheral surface portion 211c. The flange 211d extends radially inward from the end of the second circumferential surface portion 211c on the X1 side. The spline shaft 211f is rotatably supported by the disk portion 211e, and the spline shaft 211f is connected to the worm wheel 11. The spline shaft 211f is integral with a protruding portion 212d, which will be described later. The output shaft 82b of the first steering shaft 82 is connected to the spline shaft 211f, and the input shaft 82a of the first steering shaft 82 is connected to the protruding portion 212d.

[0030] As shown in FIG. 4, the cover body portion 212 has a front surface portion 212a, a cylindrical portion 212b, a plate portion 212c, and a protruding portion 212d. The front surface portion 212a extends radially inward. The peripheral edge portion of the front surface portion 212a faces the X2 side end of the first peripheral surface portion 211a. The cylindrical portion 212b extends cylindrically from the radially inner end of the front surface portion 212a toward the X1 side. The plate portion 212c is fitted to the inner peripheral side of the cylindrical portion 212b. The cylindrical protruding portion 212d protrudes toward the X2 side from the plate portion 212c.

[0031] Further, the worm wheel 11 shown in FIG. 7 is disposed between the plate portion 212c and the disk portion 211e. That is, as shown in FIG. 7, the worm wheel 11 includes a core metal 11a located at the center in the radial direction and a wheel tooth portion 11b located on the outer circumferential side of the core metal 11a. The core metal 11a is formed to be thicker in the X direction than the wheel tooth portion 11b. A spline shaft 211f is connected to the core metal 11a. The wheel tooth portion 11b meshes with the shaft tooth portion 12b of the worm shaft 12 at a meshing portion 200.

[0032] As shown in FIG. 6, a groove is provided on the upper surface 21a of the first housing 21, and the elastic member 5 is fitted into the groove. The elastic member 5 is, for example, rubber. The upper surface 21a is also a peripheral portion 213a (see FIG. 7) of the first opening 213. That is, the upper surface 21a (peripheral portion 213a) extends along the edge of the first housing 21. The upper surface 21a of the first housing 21 is provided with curved portions 21c and 21d. A flange portion 211g is provided at the top of each of the curved portions 21c and 21d. In other words, the flange portion 211g protrudes toward the upper side (Z1 side) from the top of the curved portions 21c and 21d located at the center in the Y direction. The flange portion 211g has a plate shape, and a first through hole 211h is provided to penetrate the flange portion 211g. The first through hole 211h has a generally elliptical shape that is elongated in the vertical direction (Z direction). The first through hole 211h is a hole of an irregular shape.

[0033] Next, the second structure 120 will be described. As shown in Fig. 2 to Fig. 7, the second structure 120 includes a second housing 22, a worm shaft 12, and a motor unit 3. A central axis AX2 of the worm shaft 12 extends in the Y direction (second direction).

[0034] As shown in FIGS. 2 and 6, the second housing 22 includes a frame-shaped member 220 and a cover .

[0035] 2 covers the worm shaft 12. The cover 23 prevents foreign matter such as metal powder from adhering to the worm shaft 12.

[0036] As shown in FIG. 6, the frame-shaped member 220 has a first frame-shaped member 221, a second frame-shaped member 222, legs 225, and a flange 223.

[0037] As shown in FIG. 6, the first frame-shaped member 221 extends along the upper surface 21a (peripheral edge portion 213a) which is the edge of the first housing 21. The first frame-shaped member 221 has a substantially rectangular annular shape when viewed from the upper side (Z1 side). The first frame-shaped member 221 has a flat portion 221a, a curved portion 221b, and a curved portion 221c. The curved portion 221b has a curved shape that is convex toward the upper side (Z1 side). The curved portion 221b connects the flat portion 221a on the Y1 side to the flat portion 221a on the Y2 side on the X2 side of the first frame-shaped member 221. The curved portion 221c connects the flat portion 221a on the Y1 side to the flat portion 221a on the Y2 side on the X1 side of the first frame-shaped member 221. As shown in FIG. 7, the first frame-shaped member 221 has a second opening 224 through which the worm shaft 12 is exposed, and a peripheral edge 224a of the second opening 224.

[0038] Furthermore, a convex portion 221d is provided at the apex of each of the curved portions 221b and 221c. In other words, the convex portion 221d protrudes upward (to the Z1 side) at the apex located at the center in the Y direction of the curved portions 221b and 221c. The convex portion 221d has a semicircular shape that is convex upward when viewed from the X direction, and a second through hole 221e is provided penetrating the convex portion 221d. The second through hole 221e is circular when viewed from the X direction. The second through hole 221e is a circular hole.

[0039] The second frame member 222 extends upward (Z1 side) from the Y1 side and Y2 side portions of the first frame member 221. Specifically, the second frame member 222 is provided in a pair at the center in the X direction of the Y1 side portion of the first frame member 221 and at the center in the X direction of the Y2 side portion of the first frame member 221. The second frame member 222 has a first pillar portion 222a and a second pillar portion 222b. The first pillar portion 222a and the second pillar portion 222b extend upward (Z1 side) from the flat portion 221a. The first pillar portion 222a extends upward (Z1 side) from an end 221f of the flat portion 221a. The second pillar portion 222b extends upward (to the Z1 side) from an end 221g of the flat portion 221a. The first pillar portion 222a and the second pillar portion 222b are spaced apart in the X direction. Therefore, a slit 222c extending in the up-down direction (Z direction) is provided between the first pillar portion 222a and the second pillar portion 222b.

[0040] The slit 222c is open at the lower end on the first housing 21 side. The first pillar portion 222a and the second pillar portion 222b are connected at the top portion 222d. The position of the top portion 222d in the Z direction is approximately half the height of the frame-shaped member 220 in the Z direction. The first pillar portion 222a, the second pillar portion 222b and the top portion 222d are approximately U-shaped when viewed from the Y direction. The leg portion 225 extends upward (to the Z1 side) from the top portion 222d. The upper end of the leg portion 225 on the Y1 side and the upper end of the leg portion 225 on the Y2 side are connected via the flange 223. The flange 223 extends in the Y direction.

[0041] As shown in FIG. 3, the motor unit 3 includes a stator 31 and a rotor 250. The stator 31 includes teeth 33 and a coil 240. The stator 31 is formed by winding the coil 240 around the teeth 33. The stator 31 is fixed to the inner circumference of the support plate 37. The rotor 250 is disposed on the inner circumference side of the stator 31. The rotor 250 will be described later. As shown in FIG. 2, the support plate 37 includes an upper end flange 37a, an arc portion 37b, and a lower end flange 37c. The upper end flange 37a is fastened to the flange 223 with a bolt. The lower end flange 37c is fastened to the flat portion 221a of the first frame member 221 with a bolt. The arc portion 37b connects the upper end flange 37a and the lower end flange 37c. The stator 31 is provided on the inner circumference of the arc portion 37b.

[0042] Next, a configuration of the worm shaft 12 will be described. As shown in Fig. 8 and Fig. 9, the worm shaft 12 includes a shaft tooth portion 12b, a rotor 250, a needle bearing 122, and a pin 123. In the embodiment, the needle bearing 122 is an example of a bearing, and the bearing is not limited to the needle bearing 122 in the present invention.

[0043] As shown in Figures 8 and 9, the shaft teeth portion 12b is provided at the center of the worm shaft 12 in the Y direction. The shaft teeth portion 12b meshes with the wheel teeth portion 11b of the worm wheel 11. Therefore, when the worm shaft 12 rotates in the circumferential direction about the central axis AX2, the worm wheel 11 rotates in the axial direction about the central axis AX1. The worm shaft 12 extends in the second direction. In other words, the worm shaft 12 extends in the axial direction of the central axis AX2.

[0044] As shown in FIG. 8 and FIG. 9, the rotor 250 is located at the end on the Y1 side and the end on the Y2 side with respect to the shaft tooth portion 12b. As shown in FIG. 9, the rotor 250 includes a shaft portion 12a and a magnet 251. The shaft portion 12a is cylindrical and extends in the circumferential direction around the central axis AX2. The shaft portion 12a is provided with a recess 12c that opens in the Y direction. An annular magnet 251 is fitted to the outer periphery of the shaft portion 12a. Therefore, the outer periphery surface 12d of the shaft portion 12a contacts the inner periphery surface 251a of the magnet 251. The outer periphery surface 251b of the magnet 251 has a tapered surface 251c and a cylindrical surface 251d. The diameter of the tapered surface 251c becomes smaller as it goes inward in the axial direction (toward the center of the axial direction of the worm shaft 12). In other words, in a cross section including the central axis AX2, the tapered surface 251c approaches the central axis AX2 as it approaches the center of the axial direction of the worm shaft 12. The magnet 251 is manufactured by stacking thin plates such as electromagnetic steel plates and cold-rolled steel plates. A permanent magnet can also be used. The permanent magnet may be manufactured by, for example, providing magnet insertion holes in a plurality of stacked thin plates in advance and inserting the permanent magnet into the insertion holes. Alternatively, the permanent magnet may be manufactured by sintering magnetic powder.

[0045] As shown in Fig. 8 and Fig. 9, the needle bearing 122 is fitted and housed in the recess 12c of the shaft portion 12a. The needle bearing 122 is an annular member extending along the circumferential direction of the central axis AX2, and includes a retainer 122a and needles 122b, and a through hole 122c is provided in the needle bearing 122. A plurality of needles 122b are rotatably provided on the inner circumference of the retainer 122a. Note that the bearing is not limited to the needle bearing 122, and various bearings can be applied. Therefore, for example, a sliding bearing may be applied instead of the needle bearing 122.

[0046] As shown in Figs. 8 and 9, the pin 123 includes a main body 123a and a protruding portion 123b. The main body 123a and the protruding portion 123b are integral with each other. The main body 123a is a solid annular member extending along the circumferential direction of the central axis AX2. The main body 123a has a cylindrical shape. The main body 123a is fitted into a through hole 122c on the inner circumference of the needle bearing 122. The protruding portion 123b protrudes from the main body 123a in the Y direction. As shown in Fig. 6, the protruding portion 123b is a deformed columnar portion.

[0047] The thickness of the protruding portion 123b in the X direction is smaller than the height in the Z direction. That is, when the protruding portion 123b is viewed from the Y direction, it has a vertically long, approximately rectangular shape. The protruding portion 123b fits into the slit 222c of the second frame-shaped member 222. In other words, the slit 222c of the second frame-shaped member 222 is a fitting portion into which the protruding portion 123b fits. In a state in which the protruding portion 123b fits into the slit 222c, the pin 123 including the protruding portion 123b cannot rotate. Therefore, the pin 123 and the rotor 250 can rotate relative to each other via the needle bearing 122. As a result, the rotor 250 shown in FIG. 7 is rotatable with respect to the stator 31. Also, as shown in FIG. 7, for example, the end face in the Y direction of the rotor 250 and the end face in the Y direction of the stator 31 may be located at the same position in the Y direction.

[0048] Next, the procedure for assembling the electric motor 100 with a worm reduction gear will be briefly described. First, the worm shaft 12 is assembled. As shown by the arrow in FIG. 9, the pin 123 is fitted into the needle bearing 122. Specifically, the main body 123a of the pin 123 is fitted into the through hole 122c on the inner periphery of the needle bearing 122. Next, the pin 123 and the needle bearing 122 are fitted into the recess 12c of the shaft portion 12a. Specifically, the needle bearing 122 is fitted into the recess 12c. In this state, the protrusion 123b protrudes from the side surface 250a of the rotor 250 as shown in FIG. 6.

[0049] Next, as shown in FIG. 6, the two protrusions 123b of the worm shaft 12 are fitted into the slits 222c of the second frame member 222. Specifically, after the protrusions 123b are inserted into the lower end of the slits 222c, the worm shaft 12 is moved upward (toward the Z1 side) and abutted against the inner surface of the top 222d, thereby assembling the worm shaft 12 to the frame member 220. The first pillar portion 222a and the second pillar portion 222b are elastic, and the width of the slit 222c in the X direction is smaller than the width of the protrusions 123b in the X direction. Therefore, the worm shaft 12 is held in the frame member 220 with the two protrusions 123b of the worm shaft 12 pressed in the X direction by the first pillar portion 222a and the second pillar portion 222b.

[0050] After that, the frame-shaped member 220 to which the worm shaft 12 is attached is attached to the first housing 21. Specifically, as shown in FIG. 6, the first frame-shaped member 221 is placed on the upper surface 21a (peripheral edge portion 213a) of the first housing 21, and the second through-hole 221e of the convex portion 221d of the frame-shaped member 220 is aligned with the first through-hole 211h of the flange portion 211g, and then the support pin 300 is inserted and fitted into the first through-hole 211h and the second through-hole 221e. Specifically, the cylindrical portion 301 of the support pin 300 is fitted into the second through-hole 221e, and the irregular column portion 302 is fitted into the first through-hole 211h. The irregular column portion 302 has a cross section that is substantially elliptical in the vertical direction (Z direction). Therefore, in a state where the deformed column portion 302 is fitted into the first through hole 211h, the deformed column portion 302 cannot rotate with respect to the first through hole 211h. Therefore, the second housing 22 can swing with respect to the first housing 21 around the support pin 300.

[0051] As described above, the electric motor 100 with a worm reducer according to this embodiment includes the worm wheel 11 that is rotatable around a central axis AX1 extending in the X direction (first direction) and has wheel tooth portion 11b, a first housing 21 that houses the worm wheel 11 and rotatably supports the worm wheel 11, the worm shaft 12 that has shaft tooth portion 12b that meshes with the wheel tooth portion 11b and is rotatable around a central axis AX2 extending in the Y direction (second direction), and the second housing 22 that houses the worm shaft 12, rotatably supports the worm shaft 12, and is attached to the first housing 21. The worm shaft 12 is provided with a rotor 250 having recesses 12c located at one end (Y1 side) and the other end (Y2 side) in the Y direction (second direction) with respect to the shaft teeth portion 12b and opening toward the Y direction (second direction), a needle bearing 122 accommodated in the recesses 12c of the rotor 250, and a pin 123 including a main body portion 123a fitted into the inner periphery of the needle bearing 122 and a protrusion 123b protruding from the main body portion 123a in the Y direction (second direction). The second housing 22 is provided with a fitting portion into which the protrusion 123b of the pin 123 fits.

[0052] As described above, in the worm shaft of Patent Document 1, the rotor is located on both axial sides of the shaft tooth portion, the bearing is located on both axial sides of the rotor, and the bearing is fixed inside the second housing. The shaft tooth portion and the rotor are separated in the axial direction, and the rotor and the bearing are separated in the axial direction. Therefore, the worm shaft and the second housing are long in the axial direction, and the electric motor with a worm reducer including the second housing is large.

[0053] In contrast, in the worm shaft 12 according to this embodiment, the needle bearing 122 is housed in a recess 12c provided on the inside of the rotor 250. Therefore, the axial length of the worm shaft 12 according to this embodiment is shorter than that of the worm shaft of Patent Document 1, and the second housing 22 and the electric motor with a worm reduction gear including the second housing 22 are made smaller.

[0054] The second housing 22 includes a first frame member 221 located on the first housing 21 side and extending along the peripheral portion 213a (edge) of the first housing 21, and a second frame member 222 extending in the Z direction (third direction) from the Y1 side (one side) and the Y2 side (the other side) in the Y direction (second direction) of the first frame member 221. The second frame member 222 is provided with a slit 222c extending along the Z direction (third direction) and opening on the first housing 21 side, and the slit 222c is a fitting portion for the second housing 22.

[0055] In this way, the second housing 22 includes the first frame member 221 and the second frame member 222, and therefore has fewer openings than the box-shaped second housing as in Patent Document 1. Therefore, the second housing 22 of the embodiment is lighter than the second housing of Patent Document 1. In addition, the second frame member 222 is provided with a slit 222c that opens to the first housing 21 side, so that when the worm shaft 12 is assembled to the second housing 22, the protruding portion 123b of the pin 123 is inserted into the slit 222c and moved upward, making the assembly work easy. On the other hand, when the fitting portion of the second housing 22 is an annular member having a through hole, it may be necessary to perform an operation of, for example, tilting the attitude of the worm shaft 12 or expanding and deforming the second frame member 222 in order to insert the protruding portion 123b of the pin 123 into the through hole of the annular member.

[0056] Furthermore, the protrusion 123b of the pin 123 is a vertically elongated irregular column whose width in the X direction (first direction) is smaller than its height in the Z direction (third direction), and when the protrusion 123b is engaged with the slit 222c, the protrusion 123b cannot rotate.

[0057] The protruding portion 123b of the pin 123 has a vertically elongated shape in which the width in the X direction (first direction) is smaller than the height in the Z direction (third direction). Therefore, the width of the slit 222c into which the protruding portion 123b fits is smaller than that of a horizontally elongated shape in which the width in the X direction (first direction) is larger than the height in the Z direction (third direction), and the second housing is further reduced in size.

[0058] The bearing may be a needle bearing 122 or a plain bearing. The needle bearing 122 or the plain bearing has a smaller outer diameter than, for example, a rolling bearing, and therefore the bearing is smaller, so that the second housing can be made even more compact.

[0059] [Variations] Next, a modified example will be described. Fig. 10 is a schematic cross-sectional view of an electric motor with a worm reduction gear according to a modified example, and corresponds to Fig. 7 of the embodiment.

[0060] The electric motor with a worm reduction gear 100A according to the modified example is different from the electric motor with a worm reduction gear 100 according to the embodiment in terms of a second structure 120A, which will be described in detail below.

[0061] As is clear from a comparison of FIG. 7 and FIG. 10, in the worm shaft 12A, a pair of motor units 3A are disposed apart from the shaft tooth unit 12b on the Y1 side and Y2 side. The motor unit 3A includes a stator 31A and a rotor 250A. The stator 31A has teeth 33A and a coil, and is formed by winding the coil around the teeth 33A. The rotor 250A is disposed on the inner peripheral side of the stator 31A. The worm shaft 12A extends in the second direction. In other words, the worm shaft 12A extends in the axial direction of the central axis AX2.

[0062] The rotor 250A is located at an end on the Y1 side and an end on the Y2 side with respect to the shaft tooth portion 12b. As shown in FIG. 10, the rotor 250A includes a shaft portion 12Aa and a magnet 251A. The shaft portion 12Aa is cylindrical and extends in the circumferential direction around the central axis AX2. A recess 12c is provided in the shaft portion 12Aa. An annular magnet 251A is fitted to the outer periphery of the shaft portion 12Aa. The shaft portion 12Aa is connected to the shaft tooth portion 12b via the shaft 121. That is, the shaft 121 extends in the axial direction from the shaft tooth portion 12b, and the end of the shaft 121 is fixed to the shaft portion 12Aa.

[0063] The needle bearing 122 is fitted and housed in the recess 12c of the shaft portion 12Aa. The needle bearing 122 includes a retainer 122a and a needle 122b. The pin 123A is fitted to the inner circumference of the needle 122b. The protruding portion 123Ab at the tip of the pin 123A is fitted to the slit 222c of the second frame member 222. When the protruding portion 123Ab is fitted to the slit 222c, the pin 123A including the protruding portion 123Ab cannot rotate. Therefore, the pin 123A and the rotor 250A can rotate relative to each other via the needle bearing 122. As a result, the rotor 250A is rotatable with respect to the stator 31A.

[0064] As described above, in the worm shaft 12A according to the modified example, the needle bearing 122 is housed in the recess 12c provided on the inside of the rotor 250A. Therefore, the axial length of the worm shaft 12A according to the modified example is shorter than that of the worm shaft of Patent Document 1, and the second housing 22 and the worm reduction gear-equipped electric motor 100A including the second housing 22 are made smaller.

[0065] In addition, since the pair of motor parts 3A are disposed away from the shaft tooth part 12b on the Y1 side and on the Y2 side, a space (gap) is generated between the shaft tooth part 12b and the motor part 3A. Therefore, it becomes possible to place another new part or the like in the space (gap).

[0066] The present invention is not limited to the above-described embodiment, and can be applied to various speed reduction mechanisms of electric power steering (EPS) devices, speed reduction mechanisms of steering reaction devices in so-called steer-by-wire systems, etc. Examples of EPS devices include a so-called column-type EPS device in a steering column, a so-called pinion-type EPS device, and a so-called dual pinion-type EPS device.

[0067] The column-type EPS device applies assist power to a steering shaft rotatably supported inside a steering column. The pinion-type EPS device applies assist power to a steering pinion shaft of a steering gear unit. The dual-pinion-type EPS device applies assist power to an assist pinion shaft provided in the steering gear unit and separate from the steering pinion shaft. The reduction mechanism of the steering reaction force device in the steer-by-wire system applies a steering reaction force in accordance with the vehicle driving conditions to a steering shaft rotatably supported inside a steering column that is not mechanically connected to the steering gear unit.

[0068] In addition, in the reduction mechanism of the steering reaction force device in the steer-by-wire system, the reaction force to be applied is set to be relatively small compared to the auxiliary power in the EPS device, so that even greater effects can be expected in the form of a more compact electric motor with a worm reduction gear, which is the problem to be solved by the present application. [Explanation of symbols]

[0069] 1 Worm reducer 3, 3A motor section 5 Elastic member 11 Worm wheel (worm reducer) 11a Core metal 11b Wheel tooth part 12, 12A Worm shaft (worm reducer) 12a Shaft 12b Shaft teeth 12c Recess 12d Outer surface 21 1st Housing 21a Top side 21c, 21d Curved section 22 Second Housing 23 Cover 31 Stator 33 Teeth 37 Support Plate 37a Upper flange 37b Arc section 37c Lower flange 80 Electric power steering device 81 Steering Wheel 82 First steering shaft 82a Input shaft 82b Output shaft 83 Steering force assist mechanism 84 First universal joint 85 Second steering shaft (steering shaft) 86 Second universal joint 87 Third steering shaft 88 Steering gear 88a Pinion 88b Rack 89 Tie rod 90 ECU(Electronic Control Unit) 94 Torque Sensor 95 Vehicle speed sensor 100, 100A worm gear motor 110 First structure 120, 120A Second structure 121 Shaft 122 Needle bearing (bearing) 122a retainer 122b Needle 122c through hole 123 pin 123a Main body 123b Protrusion 200 Meshing part 211 Main body 211a First circumferential surface part 211b Rear wall section 211c Second peripheral part 211d flange 211e Disk Section 211f spline shaft 211g Flange 211h 1st through hole 212 Lid body 212a Front part 212b Cylindrical part 212c Plate section 212d Projection part 213 First Opening 213a Periphery 220 Frame-shaped member 221 First frame-shaped member 221a Flat area 221b, 221c curved section 221d Convex 221e 2nd through hole 221f edge 221g edge 222 Second frame-shaped member 222a First pillar 222b Second pillar 222c Slit (fitting part) 222d Top 223 Flange 224 Second Opening 224a Periphery 225 Legs 240 Coil 250, 250A rotor 250a side 251 Magnet 251a Inner surface 251b Outer surface 251c Tapered surface 251d Cylindrical surface 300 Support pin 301 Cylinder 302 Irregular column part AX1, AX2 center axis

Claims

1. a worm wheel rotatable around a central axis extending in a first direction and having wheel teeth; a first housing that accommodates the worm wheel and rotatably supports the worm wheel; a worm shaft having a shaft tooth portion that meshes with the wheel tooth portion and is rotatable in a direction around a central axis that extends in a second direction that intersects with the first direction; a second housing that accommodates the worm shaft, rotatably supports the worm shaft, and is attached to the first housing; a stator attached to the second housing; Equipped with The worm shaft is a rotor having a recess located at one end and the other end in the second direction with respect to the shaft teeth portion and opening toward the second direction; a bearing received in the recess of the rotor; a pin including a main body portion fitted to an inner periphery of the bearing and a protrusion portion protruding from the main body portion in the second direction, The stator is disposed opposite to an outer circumferential side of the rotor, The second housing includes: a fitting portion into which the protrusion of the pin fits, Electric motor with worm gear reducer.

2. The second housing includes: a first frame-shaped member located on the first housing side and extending along an edge of the first housing; a second frame-shaped member extending from portions of the first frame-shaped member on one side and the other side in the second direction in a third direction intersecting both the first direction and the second direction, the second frame member is provided with a slit extending along the third direction and opening toward the first housing, The slit is the fitting portion of the second housing.

2. An electric motor with a worm reduction gear according to claim 1.

3. The protruding portion of the pin is a vertically elongated irregular column portion having a width in the first direction smaller than a height in the third direction, When the protrusion is fitted into the slit, the protrusion cannot rotate.

3. An electric motor with a worm reduction gear according to claim 2.

4. The bearing is a needle bearing or a plain bearing. The electric motor with a worm reduction gear according to any one of claims 1 to 3.

5. A worm reduction gear-equipped electric motor according to any one of claims 1 to 4, Electric power steering device.

Images