JP2009051354A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device of low noise capable of achieving a high output without involving an increase of a size. <P>SOLUTION: This electric power steering device is provided with a speed reduction gear to reduce the speed of rotation of an electric motor for steering assistance. The speed reduction gear includes a worm wheel 24 including a tooth part forming body 30 as a sintered part constituting a tooth part 32. The tooth part forming body 30 includes a finishing rolling machining layer 35 as an outer peripheral surface layer forming each surface 37 (the surface 37 includes a tooth surface 37a, a tooth end surface 37b and a tooth bottom surface 37c) of a plurality of teeth 32a constituting the tooth part 32 and an internal part layer 36. The finishing rolling machining layer 35 has a higher concentration and higher strength than the internal part layer 36. By finishing rolling machining, the dimensional accuracy of the tooth part 32 is improved and the surface 37 of each tooth 32a becomes smooth. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus.

Some electric power steering devices include a reduction gear. For example, Patent Document 1 below discloses an electric power steering device including a speed reduction device including a worm and a worm wheel. The worm wheel in Patent Document 1 is composed of an annular cored bar and a synthetic resin member that surrounds the cored bar and has teeth formed on the outer periphery.
JP 2006-175891 A

Incidentally, in recent years, there has been a demand for mounting an electric power steering device on a large displacement automobile. Therefore, it is necessary to increase the output of the electric power steering device, and it is necessary to increase the allowable maximum load of the reduction gear.
However, in the reduction gear described in Patent Document 1, since the tooth portion of the worm wheel is made of synthetic resin, the worm wheel must be made large in order to increase the allowable maximum load of the reduction gear. When the worm wheel becomes large, the speed reduction device becomes large, and it becomes difficult to mount the electric power steering device on the vehicle.

  The present invention has been made based on such a background, and an object of the present invention is to provide a low noise electric power steering apparatus capable of increasing the output without increasing the size.

  The present invention for achieving the above object includes a reduction gear (19) for reducing the rotation of the electric motor (18) for assisting steering, and the reduction gear includes a worm wheel (24, 124, 224). The worm wheel includes at least a sintered part (30, 130, 224) constituting the tooth part (32), and the sintered part is a surface for forming at least a tooth surface (37a) of the tooth part. The electric power steering device (1, 1a) includes a finish rolling process layer (35) and an inner layer (36) as layers, and the finish rolling process layer has a higher density and higher strength than the inner layer. , 1b).

  According to the present invention, at least a tooth part of the worm wheel is constituted by a sintered part, and the sintered part is a finish rolling processed layer as a surface layer that forms at least a tooth surface of the tooth part. Therefore, the strength of the tooth portion of the worm wheel is improved as compared with the case where the tooth portion is made of synthetic resin. Therefore, the allowable maximum load of the reduction gear can be improved without increasing the size. As a result, it is possible to increase the output of the electric power steering device without increasing the size.

  Since the sintered part has higher vibration damping characteristics than a normal metal member (a metal member other than a sintered body), generation of rattling noise can be suppressed. Furthermore, since the tooth surface of the tooth portion is smoothed by finish rolling, it is possible to reduce sliding noise generated by sliding between the worm and the worm wheel. In this way, the noise reduction of the electric power steering apparatus is achieved.

  The worm wheel is interposed between the boss portion (29), the annular tooth portion forming body (30) surrounding the boss portion and having the tooth portions formed thereon, and the boss portion and the tooth portion forming body. An elastic body (31), the tooth part forming body includes the sintered part, and the boss part and the tooth part forming body are alternately arranged in the circumferential direction (Z1) of the worm wheel to mutually connect the elastic body. In some cases, there are teeth (33, 34) meshing with each other (claim 2).

  In this case, since the elastic body is interposed between the boss portion and the tooth portion forming body, it is possible to reduce the sound transmitted from one of the boss portion and the tooth portion forming body to the other. Therefore, it is possible to suppress the noise generated at the meshing portion between the worm and the worm wheel from being transmitted to the driver via the boss portion or the like. Thereby, further noise reduction of the electric power steering device is achieved.

Moreover, since the boss part and the tooth part forming body each have teeth that mesh with each other via the elastic body, even if a large torque is input to one of the boss part and the tooth part forming body, Torque can be reliably transmitted from one to the other.
The worm wheel is interposed between the boss portion (129), the annular tooth portion forming body (130) surrounding the boss portion and having the tooth portions formed thereon, and the boss portion and the tooth portion forming body. An elastic body (131), the tooth part forming body includes the sintered part, and a protrusion (38) formed on one of the boss part and the tooth part forming body is formed on a concave part (39 ) Is inserted with a predetermined play in the circumferential direction of the worm wheel, and the relative rotation between the boss portion and the tooth portion forming body is restricted by the engagement between the protrusion and the concave portion. (Claim 3).

In this case, as described above, since the elastic body is interposed between the boss portion and the tooth portion forming body, the sound transmitted from one of the boss portion and the tooth portion forming body to the other can be reduced. . Thereby, further noise reduction of the electric power steering device is achieved.
Further, since the protrusion formed on one of the boss part and the tooth part forming body is inserted into the concave part formed on the other side with a predetermined play in the circumferential direction of the worm wheel, the boss part and the tooth Even when a large torque is input to one of the part forming bodies, the relative rotation between the boss part and the tooth part forming body is restricted by the engagement between the protrusion and the recess, and the torque is applied to the other side. Reliable transmission.

  The electric power steering device includes a housing (20) that houses the speed reducer, a driven shaft (207) that supports the worm wheel so as to be able to rotate along and move in the axial direction (X1), and a worm wheel. A pair of bearings (53, 54) held by the housing on both sides sandwiched so as to rotatably support the driven shaft, inner rings (53a, 54a) of the bearings and corresponding end surfaces (224a, 224b) of the worm wheel And an annular elastic member (40, 41) that elastically supports the worm wheel in the axial direction (claim 4).

In this case, since the vibration of the worm wheel in the axial direction is absorbed by the elastic member, the generation of noise due to the vibration of the worm wheel is prevented, and further noise reduction of the electric power steering apparatus is achieved.
In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an electric power steering apparatus 1 according to an embodiment of the present invention. FIG. 2 is a schematic partial sectional view of the electric power steering apparatus 1 taken along the line II-II in FIG. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, and a rack and pinion mechanism connected to the steering shaft 3 via an intermediate shaft 4 or the like. The steering mechanism 5 is provided.

  The steering shaft 3 is divided into an input shaft 6 connected to the steering member 2 and an output shaft 7 connected to the steering mechanism 5. The input shaft 6 and the output shaft 7 are connected via a torsion bar 8 so as to be relatively rotatable on the same axis. A torque sensor 9 disposed around the steering shaft 3 detects the steering torque input to the steering member 2 based on the amount of relative rotational displacement between the input shaft 6 and the output shaft 7 via the torsion bar 8. And this torque detection result is input into ECU10 (Electronic Control Unit: Electronic control unit).

  The steering mechanism 5 includes a pinion shaft 11 coupled to the intermediate shaft 4 so as to be able to rotate along with the intermediate shaft 4, and a rack bar 12 that meshes with the pinion shaft 11. The rack bar 12 is supported by the housing 13 so as to be movable in the axial direction. Further, steered wheels 15 are connected to both ends of the rack bar 12 via tie rods 14 and knuckle arms (not shown). The steered wheels 15 are steered by moving the rack bar 12 in the axial direction.

When the steering member 2 is operated to rotate the steering shaft 3 and the intermediate shaft 4, the pinion shaft 11 rotates, and the rotation of the pinion shaft 11 is converted into the axial motion of the rack bar 12 by the pinion 16 and the rack 17. Thereby, the turning of the steered wheel 15 is achieved.
Referring to FIGS. 1 and 2, ECU 10 drives and controls steering assisting electric motor 18 based on a torque detection result input from torque sensor 9 or a vehicle speed detection result input from a vehicle speed sensor (not shown). To do. The output rotation of the electric motor 18 is decelerated by the reduction gear 19 and transmitted to the output shaft 7 in a state where the torque is amplified. The output rotation of the electric motor 18 transmitted to the output shaft 7 is converted into the axial movement of the rack bar 12 by the pinion 16 and the rack 17. In this way, the driver's steering is assisted.

  The reduction gear 19 is accommodated in the housing 20. The speed reducer 19 is engaged with the worm shaft 23 as a drive gear connected to the rotating shaft 22 of the electric motor 18 via the joint 21 so as to be able to transmit power, and rotates together with the output shaft 7 along with the worm shaft 23. And a worm wheel 24 as a follower gear connected in a possible manner. The output rotation of the electric motor 18 is transmitted to the worm shaft 23 and further transmitted from the worm shaft 23 to the worm wheel 24. By transmitting the rotation from the worm shaft 23 to the worm wheel 24, the output rotation of the electric motor 18 is decelerated and the torque is amplified.

  Referring to FIG. 2, the worm shaft 23 includes a worm 25 and a pair of shaft portions 26 and 27 that are respectively disposed at the axial ends of the worm 25. As the worm 25, for example, a cylindrical gear having a three-threaded shape is used. A lubricant such as grease is applied to the outer peripheral surface of the worm 25. Further, bearings 51 and 52 are attached to the outer circumferences of the pair of shaft portions 26 and 27, respectively. The worm shaft 23 is rotatably held by the housing 20 through the pair of bearings 51 and 52.

The shaft portion 26 includes a bearing mounting portion 26 a to which the bearing 51 is mounted, and a rotating shaft connecting portion 26 b that is connected to the rotating shaft 22 through the joint 21. The worm 25 and the pair of shaft portions 26 and 27 are arranged coaxially. Further, the worm shaft 23 and the rotating shaft 22 are coaxially connected.
Referring to FIGS. 1 and 2, the worm wheel 24 includes an annular boss portion 29, and an annular tooth portion forming body 30 that has a tooth portion 32 that meshes with the worm 25 and that surrounds the boss portion 29. And an annular elastic body 31 interposed between the outer peripheral surface of the boss portion 29 and the inner peripheral surface of the tooth portion forming body 30.

The boss portion 29 is coaxially connected to the output shaft 7 by press-fitting, for example. The output shaft 7 is rotatably supported on the housing 20 via a pair of bearings 53 and 54 held on the housing 20 on both sides of the boss portion 29 in the axial direction X1 of the worm wheel 24. As each bearing 53, 54, for example, a radial rolling ball bearing is used.
The boss 29 is immovable with respect to the output shaft 7 in the axial direction X1 and the circumferential direction Z1 of the worm wheel 24. The boss portion 29 is formed of a metal material such as iron, for example. Further, a lubricant such as grease is applied to the outer peripheral surface of the tooth portion forming body 30. The boss portion 29 and the tooth portion forming body 30 have teeth (external teeth 33, internal teeth 34) that are alternately arranged in the circumferential direction Z1 of the worm wheel 24 and mesh with each other via the elastic body 31.

  That is, as shown in FIG. 2, a plurality of external teeth 33 are formed along the circumferential direction Z <b> 1 of the worm wheel 24 on the outer peripheral portion of the boss portion 29. A plurality of internal teeth 34 corresponding to the plurality of external teeth 33 of the boss portion 29 are formed side by side in the circumferential direction Z1 of the worm wheel 24. The plurality of external teeth 33 of the boss portion 29 and the plurality of internal teeth 34 of the tooth portion forming body 30 are engaged with each other with the elastic body 31 sandwiched therebetween. Torque input to one of the boss portion 29 and the tooth portion forming body 30 is transmitted to the other while compressing and deforming the elastic body 31 between the tooth surfaces of the outer teeth 33 and the inner teeth 34.

  In the present embodiment, since the boss portion 29 and the tooth portion forming body 30 have the outer teeth 33 and the inner teeth 34 that mesh with each other via the elastic body 31, there is a large gap between the boss portion 29 and the tooth portion forming body 30. Torque can be transmitted reliably. Further, the elastic body 31 for torque transmission is mainly subjected to compressive deformation between the external teeth 33 of the boss portion 29 and the internal teeth 34 of the tooth portion forming body 30, so the durability of the elastic body 31 is high.

  In the present embodiment, since the elastic body 31 is interposed between the boss portion 29 and the tooth portion forming body 30, the sound transmitted from one of the boss portion 29 and the tooth portion forming body 30 to the other is reduced. can do. Accordingly, noise generated at the meshing portion between the worm 25 and the worm wheel 24 (for example, so-called rattling noise or sliding noise generated by sliding between the worm 25 and the worm wheel 24) is generated by the boss portion 29 or the steering shaft 3. It is possible to suppress transmission to the driver through the like. Thereby, the noise reduction of the electric power steering apparatus 1 is achieved.

  Further, the elastic body 31 absorbs vibration of the boss portion 29 and the tooth portion forming body 30 (vibration in the circumferential direction Z1 of the worm wheel 24) and is transmitted from one of the boss portion 29 and the tooth portion forming body 30 to the other. Vibration can be reduced. Therefore, for example, even when the boss portion 29 vibrates in the circumferential direction Z1 of the worm wheel 24 due to reverse input from the road surface, vibration transmitted from the boss portion 29 to the tooth portion forming body 30 can be reduced. Thereby, generation | occurrence | production of the rattling sound resulting from the reverse input from a road surface can be suppressed, and the further noise reduction of the electric power steering apparatus 1 can be achieved.

  FIG. 3 is an enlarged cross-sectional view schematically showing a part of the tooth portion 32 of the tooth portion forming body 30. With reference to FIG. 3, the feature of the present embodiment is that the tooth portion forming body 30 is a sintered body, and the entire tooth portion forming body 30 functions as a “sintered portion”. The tooth part forming body 30 is a finishing process in which a sintering process for sintering a powder material containing metal powder and a finish rolling process is performed on the outer peripheral part of a sintered body (not shown) obtained by the sintering process. It is obtained through a rolling process. The finish rolling process is a process in which the outer peripheral portion of the sintered body having a gear shape is pressed with a roller having an uneven shape adapted to the outer peripheral portion to increase the density and strength of the outer peripheral surface of the sintered body. .

  The tooth portion 32 of the tooth portion forming body 30 includes a finish rolled layer 35 as an outer peripheral surface layer and an inner layer 36. The finished rolled layer 35 has a higher density and strength than the inner layer 36. Each surface 37 of the plurality of teeth 32a constituting the tooth portion 32 (the surface 37 includes a tooth surface 37a, a tooth tip surface 37b, and a tooth bottom surface 37c) is formed by the finish rolling process layer 35. Yes.

  In the present embodiment, the tooth portion forming body 30 is formed of a powder material containing a metal powder, and each surface 37 of the plurality of teeth 32 a constituting the tooth portion 32 is formed by the finish rolling process layer 35. Therefore, compared with the case where a tooth part is a synthetic resin, the intensity | strength of the tooth part 32 is improved, for example. Therefore, the allowable maximum load of the reduction gear 19 can be improved without increasing the size. As a result, it is possible to increase the output of the electric power steering apparatus 1 without increasing the size.

In the present embodiment, since the dimensional accuracy of the tooth portion 32 of the tooth portion forming body 30 is improved by finish rolling, the meshing accuracy between the worm 25 and the worm wheel 24 is improved. Thereby, the reduction gear 19 can transmit a bigger torque. As a result, the electric power steering apparatus 1 has a higher output.
Furthermore, since the sintered body has higher vibration damping characteristics than a normal metal member (metal member other than the sintered body), generation of rattling noise is suppressed. Further, since the surface 37 of each tooth 32a constituting the tooth portion 32 of the tooth portion forming body 30 is smoothed by finish rolling, the sliding sound generated by sliding between the worm 25 and the worm wheel 24 is performed. Has been reduced. Thereby, further noise reduction of the electric power steering apparatus 1 is achieved.

  By smoothing the surface 37 of each tooth 32a, it is possible to reduce the harsh steering feel unique to the case where the speed reducer 19 is made of a metal gear, and to improve the steering feeling. Furthermore, by forming the tooth part forming body 30 through the sintering process and the finish rolling process, compared to a tooth part forming body formed by a conventional method (for example, a method of forming a tooth part by cutting). The material and the process can be reduced, and the cost can be greatly reduced.

  In the present embodiment, the case where the boss portion 29 is formed of a metal material such as iron has been described. However, the boss portion 29 may be formed of a sintered body, similarly to the tooth portion forming body 30. Good. Moreover, although the case where the whole tooth part formation body 30 was a sintered body was demonstrated in this embodiment, it is not restricted to this, The tooth part formation body 30 should just be that the tooth part 32 is a sintered compact. Furthermore, although this embodiment demonstrated the case where the surface 37 of each tooth | gear 32a which comprises the tooth | gear part 32 was formed with the finish rolling process layer 35, it is not restricted to this, At least tooth surface 37a of each tooth | gear 32a. May be formed by the finish rolling process layer 35.

  FIG. 4 is a schematic partial sectional view of an electric power steering apparatus 1a according to another embodiment of the present invention. FIG. 5 is a schematic enlarged sectional view of a part of the worm wheel 124 taken along the line VV in FIG. FIG. 6 is an enlarged view of a part of FIG. 4 to 6, the same components as those shown in FIGS. 1 to 3 described above are denoted by the same reference numerals as those in FIGS. 1 to 3 and description thereof is omitted.

  Referring to FIG. 4, this embodiment is mainly different from the above-described embodiment in that worm wheel 124 has an annular boss portion 129, and tooth portion 32 that meshes with worm 25 is formed on the outer peripheral portion. An annular tooth portion forming body 130 that surrounds the periphery of 129, and an outer peripheral surface of the boss portion 129 and an inner portion of the tooth portion forming body 130 interposed between the outer peripheral surface of the boss portion 129 and the inner peripheral surface of the tooth portion forming body 130. The annular elastic body 131 is fixed to the peripheral surface by adhesion or the like, and a projection 38 protruding outward in the radial direction Y1 of the worm wheel 124 is formed on the outer peripheral portion of the boss portion 129. The recessed portion 39 to be inserted is formed in the inner peripheral portion of the tooth portion forming body 130.

  The boss portion 129 is coaxially connected to the output shaft 7 of the steering shaft 3 by press fitting, for example. The boss portion 129 is immovable with respect to the output shaft 7 in the axial direction X1 (direction perpendicular to the paper surface in FIG. 4) of the worm wheel 124 and the circumferential direction Z1. The boss portion 129 is formed of a metal material such as iron. Further, the tooth part forming body 130 is a sintered body, and the whole tooth part forming body 130 functions as a “sintered part”.

  Referring to FIGS. 5 and 6, the protrusion 38 is inserted into the recess 39 with play in the circumferential direction Z <b> 1 of the worm wheel 124. As shown in FIG. 5, the protrusion 38 protrudes outward in the radial direction Y1 of the worm wheel 124 from the outer peripheral portion of the boss portion 129, and the concave portion 39 is a tooth portion forming body facing the outer peripheral portion of the boss portion 129. 130 is formed in the inner periphery. The concave portion 39 has a pair of first inner wall surfaces 39a and 39a facing the protrusion 38 at an interval with respect to the axial direction X1 of the worm wheel 124 (in FIG. 5 and FIG. 6, one of the first inner wall surfaces 39a and 39a). Only the inner wall surface 39a is shown.) Further, as shown in FIG. 6, the recess 39 has a pair of second inner wall surfaces 39 b and 39 b that face the protrusion 38 at an interval with respect to the circumferential direction Z <b> 1 of the worm wheel 124. Torque is transmitted from one of the boss portion 129 and the tooth portion forming body 130 to the other through the elastic body 131 or through the elastic body 131, the protrusion 38 and the recess 39.

That is, torque is transmitted from one of the boss portion 129 and the tooth portion forming body 130 to the other via the elastic body 131, but when the torque input to the one is equal to or greater than a predetermined value. The torque is transmitted not only from the elastic body 131 but also from the one side to the other side by the projection 38 and the recess 39.
Specifically, when a large torque is input to one of the boss part 129 and the tooth part forming body 130, the boss part 129 and the tooth part forming body 130 are relatively rotated by the bending of the elastic body 131, and the relative rotation angle is When the angle corresponding to the play is exceeded, the protrusion 38 engages with the corresponding second inner wall surface 39b of the recess 39, and relative rotation between the boss portion 129 and the tooth portion forming body 130 is restricted. The torque input to one of the boss portion 129 and the tooth portion forming body 130 is reliably transmitted to the other through the elastic body 131 and the engaging portion between the protrusion 38 and the concave portion 39. In the present embodiment, the pair of second inner wall surfaces 39b, 39b functions as a relative rotation amount restricting portion that restricts the relative rotation amount between the boss portion 129 and the tooth portion forming body 130.

  When the boss portion 129 and the tooth portion forming body 130 move relative to one side (downward in FIG. 5) in the axial direction X1 of the worm wheel 124 by a predetermined amount (a distance between the protrusion 38 and the first inner wall surface 39a) or more. The protrusion 38 is engaged with the corresponding first inner wall surface 39a of the recess 39, and the relative movement of the boss portion 129 and the tooth portion forming body 130 to the one side is restricted. The first inner wall surface 39a functions as an axial movement amount regulating portion that regulates the relative movement amount between the boss portion 129 and the tooth portion forming body 130 with respect to one side of the worm wheel 124 in the axial direction X1. .

  As described above, in the present embodiment, by providing the projection 38 and the recess 39, a large torque can be reliably transmitted from one of the boss portion 129 and the tooth portion forming body 130 to the other. Further, by providing the protrusion 38 and the recess 39, the amount of bending of the elastic body 131 in the circumferential direction Z1 of the worm wheel 124 can be regulated. Thereby, the durability of the elastic body 131 is improved.

  In addition, since the elastic body 131 is interposed between the boss portion 129 and the tooth portion forming body 130, it is possible to reduce the sound transmitted from one of the boss portion 129 and the tooth portion forming body 130 to the other. Therefore, it is possible to suppress the noise generated at the meshing portion between the worm 25 and the worm wheel 124 from being transmitted to the driver. Thereby, the noise reduction of the electric power steering apparatus 1a is achieved.

  The elastic body 131 absorbs vibrations of the boss part 129 and the tooth part forming body 130 (vibration in the circumferential direction Z1 of the worm wheel 124) and is transmitted from one of the boss part 129 and the tooth part forming body 130 to the other. Vibration can be reduced. Therefore, for example, even when the boss portion 129 vibrates in the circumferential direction Z1 of the worm wheel 124 due to reverse input from the road surface, vibration transmitted from the boss portion 129 to the tooth portion forming body 130 can be reduced. Thereby, generation | occurrence | production of the rattling sound resulting from the reverse input from a road surface can be suppressed, and the further noise reduction of the electric power steering apparatus 1a can be achieved.

  In the present embodiment, the case where a pair of protrusions 38 and recesses 39 are provided has been described, but a plurality of pairs of protrusions 38 and recesses 39 may be provided. Further, in the present embodiment, the case where the protrusion 38 is provided on the boss portion 129 and the concave portion 39 is provided on the tooth portion forming body 130 has been described, but the concave portion 39 is provided on the boss portion 129 and the tooth portion forming body 130 is provided. A protrusion 38 may be provided on the surface.

  FIG. 7 is a schematic cross-sectional view showing a schematic configuration of an electric power steering apparatus 1b according to still another embodiment of the present invention. FIG. 8 is a schematic partial cross-sectional view of the electric power steering apparatus 1b taken along line VIII-VIII in FIG. FIG. 9 is an enlarged cross-sectional view schematically showing the outer periphery of the worm 25. 7 to 9, the same components as those shown in FIGS. 1 to 3 described above are denoted by the same reference numerals as those in FIGS. 1 to 3 and the description thereof is omitted.

  7 and 8, the present embodiment is mainly different from the embodiment shown in FIGS. 1 to 3 in that the worm wheel 224 can be rotated along with the output shaft 207 as a driven shaft, and The worm wheel 224 is supported so as to be movable in the axial direction X1, and the inner rings 53a and 54a of the pair of bearings 53 and 54 that rotatably support the output shaft 207 and the corresponding end surfaces of the worm wheel 224 (axial direction) A pair of annular elastic members 40 and 41 for elastically supporting the worm wheel 224 in the axial direction X1 are interposed between the end surfaces 224a and 224b). Hereinafter, the electric power steering apparatus 1b according to the present embodiment will be specifically described.

  The worm wheel 224 according to the present embodiment is configured by a single sintered body. That is, the entire worm wheel 224 according to the present embodiment functions as a “sintered portion”. The worm wheel 224 includes a sintering process for sintering a powder material including metal powder, and a finish rolling process in which a finish rolling process is performed on an outer peripheral portion of a sintered body (not shown) obtained by the sintering process. It is obtained through a process and has a tooth portion 32. Although not shown, the tooth portion 32 includes a finish rolling layer 35 and an inner layer 36 (see FIG. 3).

  Further, as shown in FIG. 7, annular covers 42 and 42 for preventing lubricant discharge are attached to the pair of axial end faces 224a and 224b of the worm wheel 224, respectively. The outer diameter of each cover 42 is made larger than the outer diameter of the worm wheel 224 within a range where it does not contact the worm 25. Each cover 42 is made of, for example, metal, synthetic resin, synthetic rubber, or the like. Each cover 42 is coaxially fixed to the worm wheel 224 by using, for example, bonding, screws, or a band.

  As shown in FIG. 7, with the pair of covers 42, 42 attached to the worm wheel 224, the tooth portion 32 of the worm wheel 224 is sandwiched between the pair of covers 42, 42 in the axial direction X 1 of the worm wheel 224. ing. The lubricant applied to the tooth portion 32 of the worm wheel 224 is prevented from being discharged from the outer peripheral surface of the worm wheel 224 by the pair of covers 42 and 42. Thereby, poor lubrication of the meshing portion between the worm 25 and the worm wheel 224 is prevented, and the wear resistance of the worm 25 and the worm wheel 224 is improved. Moreover, good steering feeling is maintained by preventing poor lubrication.

  The spline processing corresponding to each other is performed on the outer peripheral surface of the intermediate portion in the axial direction of the output shaft 207 and the inner peripheral surface of the worm wheel 224. The output shaft 207 is splined to the inner periphery of the worm wheel 224. Thereby, the worm wheel 224 is supported by the output shaft 207 so as to be able to rotate along with the worm wheel 224 and to be movable in the axial direction X1 of the worm wheel 224.

  In a state where the output shaft 207 is fitted to the inner periphery of the worm wheel 224, the elastic member 40 is interposed between the inner ring 53a of the bearing 53 and the axial end surface 224a of the worm wheel 224. It is interposed between the inner ring 54 a of the bearing 54 and the axial end surface 224 b of the worm wheel 224. Thereby, the worm wheel 224 is elastically supported in the axial direction X1.

  When the worm wheel 224 is elastically supported by the pair of elastic members 40 and 41, for example, when the vehicle travels on a rough road or the like, the worm wheel in the axial direction X1 transmitted from the output shaft 207 via the intermediate shaft 4 or the like. The vibration of 224 can be absorbed by the pair of elastic members 40 and 41, and the worm 25 and the worm wheel 224 can be prevented from colliding with each other in the meshing portion. Thereby, generation | occurrence | production of a rattling sound is suppressed and the noise reduction of the electric power steering apparatus 1b is achieved.

  Referring to FIGS. 8 and 9, a pair of bands 43 and 43 for preventing lubricant discharge are attached to the outer periphery of worm 25. Each band 43 is annular, and is attached to the worm 25 on both sides of the mesh portion between the worm 25 and the worm wheel 224 with respect to the axial direction X2 of the worm 25. Each band 43 is formed of, for example, metal, synthetic resin, synthetic rubber, or the like. As shown in FIG. 8, each band 43 is attached to the worm 25 so as to intersect the tooth trace direction of the worm 25.

  As shown in FIG. 9, a convex portion 44 corresponding to the tooth groove of the worm 25 is formed on the inner periphery of each band 43. With each band 43 attached to the worm 25, the convex portion 44 of each band 43 is fitted in the tooth groove of the worm 25. Further, in a state where each band 43 is attached to the worm 25, the outer peripheral portion of each band 43 protrudes outward in the radial direction of the worm 25 from the outer peripheral surface of the worm 25.

  By attaching the pair of bands 43, 43 to the worm 25, the lubricant applied to the region sandwiched between the pair of bands 43, 43 on the outer peripheral surface of the worm 25 causes the worm 25 to rotate. It can be prevented that the worm 25 moves in the axial direction X2 along the tooth trace direction and is discharged from the region. Thereby, poor lubrication of the meshing portion between the worm 25 and the worm wheel 224 is prevented, and the wear resistance of the worm 25 and the worm wheel 224 is further improved. Further, as described above, good steering feeling is maintained by preventing poor lubrication.

The present invention is not limited to the contents of the above embodiments, and various modifications can be made within the scope of the claims. For example, in the above-described embodiment, the tooth portion 32 may be heat-treated to further improve the strength of the tooth portion 32 and further increase the output of the electric power steering devices 1, 1a, 1b.
Moreover, in each above-mentioned embodiment, since the tooth | gear part 32 is comprised with the sintered compact, you may make the tooth | gear part 32 impregnate lubricating oil. In this case, the lubrication state of the meshing portion between the worm 25 and the worm wheels 24, 124, and 224 is maintained better.

1 is a schematic cross-sectional view showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is a schematic partial cross-sectional view of the electric power steering apparatus taken along line II-II in FIG. 1. It is an expanded sectional view showing a part of tooth part of a tooth part formation object concerning the above-mentioned one embodiment. FIG. 4 is a schematic partial cross-sectional view of an electric power steering device according to another embodiment of the present invention. FIG. 5 is a schematic enlarged cross-sectional view of a part of a worm wheel taken along line VV in FIG. 4. It is the figure which expanded a part of FIG. It is an illustration sectional view showing a schematic structure of an electric power steering device concerning still another embodiment of the present invention. FIG. 8 is a schematic partial cross-sectional view of the electric power steering apparatus taken along line VIII-VIII in FIG. 7. It is an expanded sectional view which shows the outer peripheral part of the worm concerning another embodiment of the above illustration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a, 1b ... Electric power steering device, 18 ... Electric motor, 19 ... Deceleration device, 20 ... Housing, 24 ... Worm wheel, 29 ... Boss part, 30 ... -Tooth part forming body (sintered part), 31 ... elastic body, 32 ... tooth part, 33 ... external tooth (tooth), 34 ... internal tooth (tooth), 35 ... finish Rolling layer, 36 ... inner layer, 37a ... tooth surface, 38 ... projection, 39 ... concave, 40 ... elastic member, 41 ... elastic member, 53 ... bearing 53a ... Inner ring, 54 ... Bearing, 54a ... Inner ring, 124 ... Worm wheel, 129 ... Boss part, 130 ... Tooth part forming body (sintered part), 131 ... -Elastic body, 207 ... Output shaft (driven shaft), 224 ... Worm wheel (sintered part), 224a ... Axial direction Plane (corresponding end face of the worm wheel), 224b · · · axial end face (corresponding end face of the worm wheel), Z1 · · · circumferentially, X1 · · · axis

Claims (4)

A reduction device for reducing the rotation of the electric motor for assisting steering;
The speed reducer includes a worm wheel,
The worm wheel includes at least a sintered part constituting a tooth part,
This sintered portion includes a finish-rolled processed layer as a surface layer for forming at least the tooth surface of the tooth portion, and an inner layer,
An electric power steering device in which the finished rolled layer is formed with higher density and higher strength than the inner layer. 2. The worm wheel according to claim 1, wherein the worm wheel includes: a boss portion; an annular tooth portion forming body that surrounds the boss portion and formed with the tooth portion; and an elastic body interposed between the boss portion and the tooth portion forming body. The tooth part forming body includes the sintered part,
The electric power steering apparatus, wherein the boss part and the tooth part forming body have teeth that are alternately arranged in the circumferential direction of the worm wheel and mesh with each other via the elastic body. 2. The worm wheel according to claim 1, wherein the worm wheel includes: a boss portion; an annular tooth portion forming body that surrounds the boss portion and formed with the tooth portion; and an elastic body interposed between the boss portion and the tooth portion forming body. The tooth part forming body includes the sintered part,
A protrusion formed on one of the boss part and the tooth part forming body is inserted into a concave part formed on the other side with a predetermined play in the circumferential direction of the worm wheel,
An electric power steering device characterized in that the relative rotation between the boss portion and the tooth portion forming body is restricted by the engagement between the protrusion and the concave portion.   The housing according to any one of claims 1 to 3, wherein the housing accommodates the speed reducer, a driven shaft that supports the worm wheel so as to be able to rotate along and move in the axial direction, and both sides sandwiching the worm wheel. A pair of bearings rotatably supported by the driven shaft, and an annular elastic member interposed between an inner ring of each bearing and a corresponding end surface of the worm wheel, and elastically supporting the worm wheel in the axial direction. An electric power steering apparatus comprising:

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