JP2011255818A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of increasing bonding strength between an elastic member reducing the rattling sound and a worm shaft supporting the elastic member.SOLUTION: In the electric power steering device 1, output of an electric motor is transmitted to a steered wheel through a worm reduction gear 21. The worm shaft 23 of the worm reduction gear 21 includes a plurality of tooth parts 57 and 58, and a plurality of groove parts 59 and 60 formed by the tooth parts 57 and 58. The elastic member 55 connected to the worm shaft 23 includes tooth bottom spiral parts 63 and 64 arranged on bottom surfaces 59c and 60c of the groove parts 59 and 60 at least in an engagement region 35 and capable of being abutted to a worm wheel 24, and cylindrical parts 61 and 62 mutually connecting the tooth bottom spiral parts 63 and 64 in a position separated from the engagement region 35.

Description

  The present invention relates to an electric power steering apparatus.

  The electric power steering apparatus includes, for example, a small gear that is rotated by an electric motor and a large gear that meshes with the small gear (see, for example, Patent Documents 1 and 2). The large gear is connected to the steering shaft. The rotation of the output shaft of the electric motor is transmitted to the steering shaft via the small gear and the large gear. This assists the driver's steering.

JP 2008-44426 A JP 2008-162352 A

  An appropriate backlash is provided between the small gear and the large gear, and the meshing resistance of both gears is reduced. However, noise due to the provision of backlash may be a problem. Specifically, when a force from the road surface is input to the large gear via the steered wheel and the steering shaft (in the reverse input), the large gear causes minute vibration corresponding to the backlash with respect to the small gear. Thereby, a rattling sound (rattle sound) as noise is generated.

In Patent Document 2, a rubber elastic body is provided on the tooth bottom surface of the small gear. The elastic body is always in contact with the tooth tip surface of the large gear. As a result, a frictional resistance is imparted to the large gear, and the minute vibration of the large gear is suppressed ([0019] paragraph, [0024 paragraph]).
That is, the elastic body receives a frictional resistance from the large gear. Since the elastic body receives a force (shearing force) in a direction substantially parallel to the tooth bottom surface of the small gear when the large gear is rotating, the elastic body may be detached from the small gear. In order to prevent this, it is necessary to sufficiently increase the coupling force between the elastic body and the small gear.

Such a problem is remarkable when a worm shaft having a plurality of teeth is used as a small gear. When the worm shaft has multiple teeth, the frictional resistance that the elastic body receives from the teeth of the worm wheel (the amount of worm wheel feed when the worm shaft makes one revolution) This is because the shearing force is increased.
Moreover, there are a plurality of tooth gaps between the plurality of teeth. The work of winding the elastic body around the respective tooth bottom surfaces of the plurality of tooth spaces is troublesome because it takes time and effort.

  The present invention has been made under such a background, and it is possible to increase the coupling force between an elastic member for reducing rattling noise and a worm shaft that supports the elastic member, and the elastic member is used as a worm. An object of the present invention is to provide an electric power steering device that can reduce the time and effort required to be assembled to a shaft.

  To achieve the above object, the present invention is capable of meshing with an electric motor (20), a worm shaft (23) connected to the electric motor so as to be able to transmit power, and a predetermined meshing region (35) of the worm shaft. A worm reduction gear (21) including a worm wheel (24) and an elastic member (55) coupled to the worm shaft, the worm shaft including a plurality of teeth (57, 58), and these A plurality of grooves (59, 60) formed by a plurality of teeth, and the elastic member is disposed on each bottom (59c, 60c) of the plurality of grooves at least in the meshing region. A plurality of spiral portions (63, 64; 63A, 64A) that can contact the cylinder, and a cylinder that connects the plurality of spiral portions to each other at a position separated from the meshing region (61, 62) and an electric power steering apparatus characterized by comprising providing (1) (claim 1).

  According to the present invention, frictional resistance is imparted to the worm wheel by the contact between the spiral portion of the elastic member and the worm wheel. For example, when the force from the road surface is input to the worm wheel via the steered wheels and the steering shaft (in reverse input), the worm wheel can be suppressed from causing minute vibrations corresponding to the backlash with respect to the worm shaft. . Therefore, the rattling noise (rattle noise) due to the collision between the worm wheel and the worm shaft can be suppressed.

  The cylindrical portion has a function of reinforcing each spiral portion by connecting the spiral portions to each other. Thereby, the intensity | strength of each part of an elastic member is raised. Moreover, the cylindrical portion can contact the worm shaft over the entire circumferential direction of the worm shaft. As a result, the coupling force between the elastic member and the worm shaft can be increased. Accordingly, it is possible to suppress the displacement of the spiral portion with respect to the worm shaft due to frictional contact between the spiral portion and the worm wheel when the worm shaft is rotationally driven. In particular, in the present invention, the worm shaft has a plurality of teeth, and the lead of the worm shaft (the feed amount of the worm wheel when the worm shaft makes one revolution) is large. Accordingly, the load (shearing force) that the elastic member receives from the teeth of the worm wheel is large. However, since the strength of the coupling between the elastic member and the worm shaft is sufficiently high, the elastic member can be reliably prevented from shifting with respect to the worm shaft. In addition, the spiral portion is disposed not at the tooth portion of the worm shaft but at the tooth bottom, and the cylindrical portion is disposed at a position separated from the meshing region of the worm shaft. Thereby, an elastic member can be prevented from intervening in the power transmission portion between the teeth of the worm shaft and the teeth of the worm wheel. Therefore, the elastic member is not strongly compressed, and deterioration of the elastic member can be suppressed.

  Further, the plurality of spiral portions are connected by the cylindrical portion. Thereby, a some spiral part and a cylindrical part can be handled as one member. As a result, the elastic member can be assembled to the worm shaft by assembling one member to the worm shaft. Therefore, the trouble of assembling the elastic member to the worm shaft can be reduced. In this case, the elastic member and the worm shaft are separately formed and the elastic member is wound around the worm shaft, and the worm shaft is inserted into the molding die of the elastic member and the elastic member is integrally formed with the worm shaft. Including both to do.

  When the elastic member and the worm shaft are formed separately and the elastic member is wound around the worm shaft, since the plurality of spiral portions are connected by the cylindrical portion, the spiral portions are assembled together in each of the plurality of groove portions. Can do. That is, as compared with the case where separate spiral portions that are not connected to each other are wound around the corresponding groove portions, the labor for assembling the elastic member to the worm shaft can be reduced, so that workability can be improved.

In the present invention, the end of the cylindrical portion may be provided with an engaging portion (67, 68) that engages with the worm shaft (claim 2). In this case, the coupling force between the cylindrical portion of the elastic member and the worm shaft can be further increased.
The worm shaft includes a worm shaft main body on which the tooth portion is formed, and a support shaft extending from an end of the worm shaft main body and having a smaller diameter than the worm shaft, and the engaging portion is formed on the worm shaft main body. It may be engaged with the end. In this case, the elastic member can be more reliably restricted from coming off the worm shaft.

The present invention may further include bearings (41, 42) for rotatably supporting the worm shaft, and the engagement portion may be sandwiched between the worm shaft and the bearing. ). In this case, it is possible to more reliably regulate the displacement of the elastic member in the axial direction of the worm shaft with respect to the worm shaft.
Moreover, in this invention, the groove part (78) may be formed in the outer periphery of the said elastic member (Claim 4). In this case, the groove portion can be used as a lubricant reservoir for storing a lubricant such as grease. Thereby, the lubricant in the groove can be supplied to the worm shaft and the worm wheel. Therefore, the lubricant can be more reliably supplied to the meshing region of the worm shaft. Moreover, the ease of bending of the elastic member can be easily adjusted by adjusting the shape such as the depth of the groove.

In the present invention, there may be further provided a bearing that rotatably supports the worm shaft, and the cylindrical portion may include a seal portion (81; 83) for sealing the bearing. In this case, the elastic member can be used as a seal member for the bearing by providing the elastic member with the seal portion. Thereby, the number of parts can be reduced.
In addition, in the above, the numbers in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

It is a mimetic diagram showing a schematic structure of an electric power steering device concerning one embodiment of the present invention. It is a partial cross section figure of the principal part around the reduction gear of FIG. It is an enlarged view of the worm shaft and elastic member periphery of FIG. It is a side view which shows a part of worm shaft in cross section. It is sectional drawing of the principal part of another embodiment of this invention. It is sectional drawing of the principal part of another embodiment of this invention. It is sectional drawing of the principal part of another embodiment of this invention. It is sectional drawing of the principal part of another embodiment of this invention.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus 1 according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering device 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, an intermediate shaft 5 connected to the steering shaft 3 via a universal joint 4, A pinion shaft 7 connected to the intermediate shaft 5 via a universal joint 6 and a rack shaft 10 are provided. The rack shaft 10 forms a rack 9 that meshes with a pinion 8 provided at the tip of the pinion shaft 7, and extends in the left-right direction of the vehicle.

  Tie rods 11 are connected to both ends of the rack shaft 10, and each tie rod 11 is connected to a corresponding steered wheel 12 via a corresponding knuckle arm (not shown). When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is transmitted to the pinion 8 via the intermediate shaft 5 and the like, and the straight line of the rack shaft 10 along the left-right direction of the vehicle is driven by the pinion 8 and the rack 9. Converted into movement. Thereby, the turning of the steered wheels 12 is achieved.

The steering shaft 3 has a first steering shaft 13 as an input shaft connected to the steering member 2 and a second steering shaft 14 as an output shaft connected to the universal joint 4. The first and second steering shafts 13 and 14 are coaxially connected to each other via a torsion bar 15.
A torque sensor 16 is provided in the vicinity of the torsion bar 15. The torque sensor 16 detects the amount of relative rotational displacement between the first steering shaft 13 and the second steering shaft 14 due to the torsion bar 15 being twisted. The detection signal of the torque sensor 16 is given to the control unit 17. The control unit 17 calculates the steering torque applied to the steering member 2 based on the detection signal from the torque sensor 16. Then, the control unit 17 controls the driving of the steering assisting electric motor 20 via the driver 19 based on the calculated steering torque, the vehicle speed detection signal from the vehicle speed sensor 18 and the like. As a result, the electric motor 20 is driven, and its output rotation (power) is decelerated by the worm worm reducer 21 and further transmitted to the second steering shaft 14. The power transmitted to the second steering shaft 14 is further transmitted to the steering mechanism 22 including the rack shaft 10, the tie rod 11, the knuckle arm and the like via the intermediate shaft 5 and the like to assist the driver's steering.

The worm speed reducer 21 includes a worm shaft 23 as a drive gear driven by the electric motor 20, a worm wheel 24 as a driven gear, and a housing 25 that houses the worm shaft 23 and the worm wheel 24.
The worm shaft 23 is coupled to the output shaft 20a of the electric motor 20 so that power can be transmitted. The worm wheel 24 meshes with the worm shaft 23. The worm wheel 24 is connected to the second steering shaft 14 so as to be integrally rotatable. The worm wheel 24 is connected to the steering mechanism 22 via the second steering shaft 14 and the intermediate shaft 5.

FIG. 2 is a partial cross-sectional view of the main part around the worm reduction gear 21 of FIG. Referring to FIG. 2, electric motor 20 includes an output shaft 20a and a motor housing 20b that rotatably supports output shaft 20a. The motor housing 20 b is fixed to the housing 25.
The housing 25 is formed using an aluminum alloy. The housing 25 includes a cylindrical worm shaft housing portion 27 that houses the worm shaft 23, and a worm wheel housing portion 28 that houses the worm wheel 24.

A flange portion 29 is formed at one end of the worm shaft housing portion 27. The motor housing 20 b is fixed to the flange portion 29.
The worm shaft 23 is formed using, for example, a metal such as iron, and extends from a worm shaft main body 32 including a tooth portion 31 that meshes with the worm wheel 24 and a pair of end portions 32 a and 32 b of the worm shaft main body 32. And a pair of support shafts 33 and 34 having a smaller diameter than the worm shaft main body 32.

  A meshing region 35 is provided in the approximate center of the worm shaft main body 32 in the axial direction X1 of the worm shaft 23. The tooth portion 31 of the worm shaft 23 meshes with the tooth portion 24 c of the worm wheel 24 in the meshing region 35. A lubricant is accommodated in the housing 25, and the lubricant is supplied to the meshing region 35 of the worm shaft 23. The lubricant is, for example, grease.

  One support shaft 33 includes a bearing connecting portion 33a adjacent to the worm shaft main body 32 and a joint connecting portion 33b adjacent to the bearing connecting portion 33a. The joint connecting portion 33b is connected to the output shaft 20a of the electric motor 20 via a joint 36 such as a spline joint so as to be integrally rotatable. The bearing connecting portion 33a of the one support shaft 33 and the other support shaft 34 are provided with first and second bearings 41 and 42 that rotatably support the worm shaft 23, respectively.

The first bearing 41 and the second bearing 42 are rolling bearings such as ball bearings, and are disposed in the worm shaft housing portion 27. The inner rings 41a and 42a of the first bearing and the second bearing 41 and 42 are fitted to the corresponding support shafts 33 and 34, respectively.
The outer ring 41 b of the first bearing 41 is fitted in a first bearing holding portion 43 formed in the worm shaft housing portion 27 with relative rotation being restricted. The outer ring 42 b of the second bearing 42 is fitted in a second bearing holding portion 44 formed in the worm shaft housing portion 27 with relative rotation being restricted.

  The first bearing 41 and the second bearing 42 are seal bearings. Specifically, a pair of seal members 45 and 46 are fixed to the outer ring 41 b of the first bearing 41. The pair of seal members 45 and 46 seals between the inner ring 41 a and the outer ring 41 b of the first bearing 41. A pair of seal members 45 and 46 are fixed to the outer ring 42 b of the second bearing 42. The pair of seal members 45 and 46 seals between the inner ring 42 a and the outer ring 42 b of the second bearing 42.

The worm wheel 24 is a metal cored bar 24a fitted to the second steering shaft 14 so as to be rotatable integrally with the second steering shaft 14 but not relatively movable in the axial direction, and a synthetic resin member 24b integrally provided on the outer periphery of the cored bar 24a. And have. The tooth portion 24 c formed on the outer peripheral portion of the synthetic resin member 24 b meshes with the tooth portion 31 of the worm shaft 23.
An appropriate backlash is provided between the tooth portion 31 of the worm shaft 23 and the tooth portion 24c of the worm wheel 24 so that the meshing resistance of both the tooth portions 24c and 31 is reduced.

  The first and second bearings 41 and 42 are preloaded. Specifically, the outer ring 42 b of the second bearing 42 is in contact with an annular step 48 formed at one end of the worm shaft housing portion 27, thereby being positioned with respect to the axial direction X <b> 1. The inner ring 42 a of the second bearing 42 is received by an annular step portion 49 formed between the other support shaft 34 of the worm shaft 23 and the worm shaft main body 32.

The inner ring 41 a of the first bearing 41 is in contact with a step portion 50 formed between the one support shaft 33 and the worm shaft main body 32. The outer ring 41b of the first bearing 41 is urged toward the second bearing 42 by a screw member 51 for preload adjustment.
The screw member 51 is preloaded to the first and second bearings 41 and 42 by being screwed into a screw hole formed adjacent to the first bearing holding portion 43 of the housing 25. A lock nut 53 is coupled to the screw member 51 in order to fix the screw member 51 after the preload adjustment.

  FIG. 3 is an enlarged view around the worm shaft 23 and the elastic member 55 shown in FIG. 2, and a part thereof is shown in cross section. With reference to FIG. 3, one of the features of the present embodiment is that an elastic member 55 is coupled to the worm shaft 23. By the elastic contact between the elastic member 55 and the worm wheel 24, the impact of the collision between the tooth portion 31 of the worm shaft 23 and the tooth portion 24c of the worm wheel 24 is suppressed.

  Next, details of the worm shaft main body 32 of the worm shaft 23 and details of the elastic member 55 will be described. FIG. 4 is a side view showing a part of the worm shaft 23 in cross section. Referring to FIG. 4, tooth portion 31 of worm shaft main body 32 includes first and second tooth portions 57 and 58 as tooth portions of a plurality of strips (two strips in the present embodiment). The worm shaft main body 32 includes first and second groove portions 59 and 60 as a plurality of groove portions formed by the first and second tooth portions 57 and 58. Although one tooth portion 57 and 58 and one groove portion 59 and 60 are provided, in FIGS. 3 and 4, for convenience, the tooth portions 57 and 58 and the groove portions 59 and 60 are denoted by reference numerals at a plurality of locations. Yes.

  The first and second tooth portions 57 and 58 each extend in a spiral shape, and are formed over substantially the entire area of the worm shaft main body 32 in the axial direction X1. The first and second tooth portions 57 and 58 are arranged with a phase difference of 180 ° with respect to the circumferential direction of the worm shaft 23. The first and second tooth portions 57 and 58 are each formed in, for example, a mountain-shaped cross section when viewed in the tooth trace direction, and are formed in the same shape as each other.

  Each of the first and second groove portions 59 and 60 extends in a spiral shape, and is formed over substantially the entire area of the worm shaft main body 32 in the axial direction X1. The first and second groove portions 59 and 60 are formed in the same shape. In FIG. 4, the pair of end surfaces 59a and 59b of the first groove portion 59 are represented by solid lines, and the pair of end surfaces 60a and 60b of the second groove portion 60 are represented by dotted lines.

The pair of end portions 32a and 32b of the worm shaft main body 32 include cylindrical portions 32c and 32d, respectively. The curvature radii of the cylindrical portions 32c and 32d are substantially the same.
Referring to FIG. 3, the elastic member 55 is an integrally molded product formed using an elastic member such as rubber. The thickness (wall thickness) of the elastic member 55 is, for example, about 1 mm. The elastic member 55 is formed into a single product state by injection molding or the like, and then coupled to the worm shaft 23 by being assembled to the worm shaft main body 32. The worm shaft 23 may be inserted into the mold during the injection molding of the elastic member 55, and the injection molding of the elastic member 55 and the connection to the worm shaft 23 may be performed collectively.

The elastic member 55 is coupled to the worm shaft main body 32 by, for example, vulcanization adhesion. In the worm shaft 23, the coupling surface with the elastic member 55 may be subjected to processing for increasing the surface roughness of the coupling surface, such as knurling. Thereby, peeling of the elastic member 55 from the worm shaft 23 can be suppressed more reliably.
The elastic member 55 includes a pair of cylindrical portions 61 and 62, a plurality of root spiral portions 63 and 64, and a plurality of tooth tip spiral portions 65 and 66. Although one tooth root spiral portion 63 and 64 and one tooth tip spiral portion 65 and 66 are provided, FIG. 3 shows a plurality of tooth root spiral portions 63 and 64 and tooth tip spiral portions 65 and 66 for convenience. Reference numerals are given to the places.

  The cylindrical portion 61 is fitted into the cylindrical portion 32 c of the worm shaft main body 32. An engaging portion 67 is provided at one end of the cylindrical portion 61 adjacent to the first bearing 41. The engaging portion 67 is formed in an annular shape protruding from the cylindrical portion 61 toward the inside in the radial direction of the cylindrical portion 61. The engaging portion 67 is engaged with the end surface of the cylindrical portion 32 c of the worm shaft main body 32, and is sandwiched between the cylindrical portion 32 c and the inner ring 41 a of the first bearing 41. Thereby, the engaging part 67 is elastically compressed.

  The cylindrical part 62 is formed in the same shape as the cylindrical part 61. The cylindrical portion 62 is fitted into the cylindrical portion 32 d of the worm shaft main body 32. An engaging portion 68 is provided at one end of the cylindrical portion 62 adjacent to the second bearing 42. The engaging portion 68 is formed in an annular shape that protrudes from the cylindrical portion 62 inward in the radial direction of the cylindrical portion 62. The engaging portion 68 is engaged with the end surface of the cylindrical portion 32 d of the worm shaft main body 32, and is sandwiched between the cylindrical portion 32 d and the inner ring 42 a of the second bearing 42. Thereby, the engaging part 68 is elastically compressed.

The tooth bottom spiral portions 63 and 64 are provided to make frictional contact with the tooth tip surface 24 d of the tooth portion 24 c of the worm wheel 24.
The tooth bottom spiral portion 63 is formed in a spiral shape, and extends along the bottom surface 59 c (the tooth bottom) of the first groove portion 59. The one end 63 a of the tooth bottom spiral portion 63 and the cylindrical portion 61 are continuous via the connection portion 69. The connecting portion 69 extends along the one end surface 59 a of the first groove portion 59. The other end 63 b of the tooth bottom spiral portion 63 and the cylindrical portion 62 are continuous via the connection portion 70. The connecting portion 70 extends along the other end surface 59 b of the first groove portion 59.

  The tooth bottom spiral portion 64 is formed in the same shape as the tooth bottom spiral portion 63. Specifically, the tooth bottom spiral portion 64 is formed in a spiral shape, and extends along the bottom surface 60 c (the tooth bottom) of the second groove portion 60. The one end 64 a of the tooth bottom spiral portion 64 and the cylindrical portion 61 are continuous via a connection portion 71 similar to the connection portion 69. The other end 64 b of the tooth bottom spiral portion 64 and the cylindrical portion 62 are continuous via a connection portion 72 similar to the connection portion 70.

The tooth tip spiral portions 65 and 66 are provided to make frictional contact with the tooth bottom surface 24e of the tooth portion 24c of the worm wheel 24.
The tooth tip spiral portion 65 is formed in a spiral shape and extends along the tooth tip surface (tip surface) of the first tooth portion 57. One end 65 a of the tooth tip spiral portion 65 is connected to the cylindrical portion 61. The other end 65 b of the tooth tip spiral portion 65 is connected to the cylindrical portion 62.

The tooth tip spiral portion 66 is formed in the same shape as the tooth tip spiral portion 65. Specifically, the tooth tip spiral portion 66 is formed in a spiral shape, and is along the tooth tip surface (tip surface) of the second tooth portion 58. One end 66 a of the tooth tip spiral portion 66 is connected to the cylindrical portion 61. The other end 66 b of the tooth tip spiral portion 66 is connected to the cylindrical portion 62.
With the above configuration, the tooth bottom spiral portions 63 and 64 and the tooth tip spiral portions 65 and 66 of the elastic member 55 are arranged in the meshing region 35 of the worm shaft 23. Further, the cylindrical portions 61 and 62 of the elastic member 55 are disposed on the cylindrical portions 32 c and 32 d of the worm shaft main body 32 that are separated from the meshing region 35 of the worm shaft 23.

The cylindrical portion 61 of the elastic member 55 connects the ends 63 a and 64 a of the root bottom spiral portions 63 and 64. The cylindrical portion 61 connects the ends 65 a and 66 a of the tooth tip spiral portions 65 and 66.
The cylindrical portion 62 of the elastic member 55 connects the other ends 63b and 64b of the tooth bottom spiral portions 63 and 64 to each other. Further, the cylindrical portion 62 connects the other ends 65b and 66b of the tooth tip spiral portions 65 and 66 to each other.

With the above configuration, the tooth surfaces of the first and second tooth portions 57 and 58 of the worm shaft 23 and the tooth surface of the tooth portion 24 c of the worm wheel 24 are in direct contact with each other. Therefore, the elastic member 55 is not interposed in the meshing portion (torque transmission portion) between the worm shaft 23 and the worm wheel 24.
With reference to FIG. 1, in the electric power steering apparatus 1 having the above-described schematic configuration, for example, consider a case where the vehicle is traveling straight on a road and the electric motor 20 and the worm shaft 23 are stopped. At this time, if the road is a stone pavement or the like, a reaction force (reverse input) from the road is transmitted to the worm wheel 24 via the steered wheel 12 and the steering shaft 3 and the like. As a result, the worm wheel 24 generates minute vibrations. This minute vibration occurs because a backlash is provided between the worm wheel 24 and the worm shaft 23.

  At this time, as shown in FIG. 3, in the meshing region 35 of the worm shaft 23, at least one of the tooth root spiral portions 63 and 64 of the elastic member 55 (for example, the tooth bottom spiral portion 63 in FIG. 3) The 24 tooth portions 24c are in frictional contact with the tooth tip surfaces 24d while being elastically compressed. Further, in the meshing region 35 of the worm shaft 23, at least one of the tooth tip spiral portions 65 and 66 of the elastic member 55 (for example, the tooth tip spiral portion 66 in FIG. 3) is the tooth bottom surface 24e of the tooth portion 24c of the worm wheel 24. In frictional contact with the elastically compressed state.

  As described above, since at least one of the tooth bottom spiral portions 63 and 64 of the elastic member 55 and at least one of the tooth tip spiral portions 65 and 66 are in frictional contact with the worm wheel 24, Vibration is damped. As a result, the impact (collision speed) when the tooth portion 24 c of the worm wheel 24 contacts the first and second tooth portions 57 and 58 of the worm shaft 23 is alleviated, and the contact between the worm shaft 23 and the worm wheel 24 is reduced. Noise (gap sound) is reduced.

  On the other hand, when the electric motor 20 is driven to apply the steering assist force to the steered wheels 12, when the worm shaft 23 and the worm wheel 24 are engaged with each other, the engaging portion 67 or 68 of the elastic member 55 is Due to the reaction force from the wheel 24, the worm shaft main body 32 and the corresponding bearings 41, 42 are elastically compressed. Thereby, the impact at the time of mesh | engagement with the worm shaft 23 and the worm wheel 24 is relieved. As a result, it is possible to improve the steering feeling including the steering feeling (neutral feeling) in the steering neutral state (straight vehicle traveling state).

  As described above, according to the present embodiment, the contact between the tooth bottom spiral portions 63 and 64 of the elastic member 55 and the tooth portion 24c of the worm wheel 24 and between the tooth tip spiral portions 65 and 66 and the worm wheel 24 are achieved. Friction resistance is given to the worm wheel 24 by the contact. For example, when a force from the road surface is input to the worm wheel 24 via the steered wheels 12 and the steering shaft 3 (reverse input), the worm wheel 24 causes minute vibration corresponding to the backlash to the worm shaft 23. It can suppress waking. Therefore, the rattling noise (rattle noise) due to the collision between the worm wheel 24 and the worm shaft 23 can be suppressed.

  Further, the cylindrical portions 61 and 62 of the elastic member 55 have a function of reinforcing the tooth bottom spiral portions 63 and 64 by connecting the tooth bottom spiral portions 63 and 64 to each other. Similarly, the cylindrical portions 61 and 62 have a function of reinforcing the tooth tip spiral portions 65 and 66 by connecting the tooth tip spiral portions 65 and 66 to each other. Thereby, the intensity | strength of each part of the elastic member 55 is raised. Moreover, the cylindrical portions 61 and 62 are in contact with the cylindrical portions 32 c and 32 d of the worm shaft main body 32 over the entire circumferential direction of the worm shaft 23. As a result, the coupling force between the elastic member 55 and the worm shaft 23 can be increased. Accordingly, the root bottom spiral portions 63 and 64 are peeled off from the worm shaft 23 due to frictional contact between the root bottom spiral portions 63 and 64 and the worm wheel 24 when the worm shaft 23 is rotationally driven. This can be suppressed. Similarly, it is possible to prevent the tooth tip spiral portions 65 and 66 from peeling off from the worm shaft 23.

  In particular, in this embodiment, the worm shaft 23 has first and second tooth portions 57 and 58 as a plurality of teeth, and the lead of the worm shaft 23 (the worm when the worm shaft 23 makes one rotation) The feed amount of the tooth portion 24c of the wheel 24) is large. Accordingly, the load (shearing force) received by the tooth bottom spiral portions 63 and 64 and the tooth tip spiral portions 65 and 66 of the elastic member 55 from the tooth portion 24c of the worm wheel 24 is large. However, since the strength of the coupling between the elastic member 55 and the worm shaft 23 is sufficiently high, the elastic member 55 can be reliably prevented from shifting with respect to the worm shaft 23.

  Moreover, the root spiral portions 63 and 64 are arranged on the bottom surfaces 59c and 60c of the first and second groove portions 59 and 60 instead of the tooth surfaces of the first and second tooth portions 57 and 58 of the worm shaft 23, The tooth tip spiral portions 65 and 66 are arranged on the tooth tip surfaces instead of the tooth surfaces of the first and second tooth portions 57 and 58, and the cylindrical portions 61 and 62 are meshing regions of the worm shaft 23. It is arranged at a position separated from 35. Thus, the elastic member 55 is not interposed in the power transmission portion between the first and second tooth portions 57 and 58 of the worm shaft 23 and the tooth portion 24c of the worm wheel 24. Therefore, the elastic member 55 is not strongly compressed, and deterioration of the elastic member 55 can be suppressed.

  Further, the plurality of tooth bottom spiral portions 63 and 64 are connected by the cylindrical portions 61 and 62. Thereby, the plurality of tooth bottom spiral parts 63 and 64 and the cylindrical parts 61 and 62 can be handled as one member. As a result, the elastic member 55 can be assembled to the worm shaft 23 by assembling one member to the worm shaft 23. Therefore, the trouble of assembling the elastic member 55 to the worm shaft 23 can be reduced.

  When the elastic member 55 is wound around the worm shaft 23, since the plurality of tooth bottom spiral portions 63 and 64 are connected by the cylindrical portions 61 and 62, the tooth bottom is collectively applied to each of the first and second groove portions 59 and 60. The spiral portions 63 and 64 can be assembled. That is, as compared with the case where the separate root spiral portions that are not connected to each other are wound around the corresponding groove portions, the labor for assembling the elastic member 55 to the worm shaft 23 can be reduced, so that workability can be improved. Such an effect of improving workability is further improved by connecting the plurality of tooth tip spiral portions 65 and 66 by the cylindrical portions 61 and 62.

In addition, the cylindrical portions 61 and 62 of the elastic member 55 are provided with engaging portions 67 and 68 that engage with the worm shaft main body 32. Thereby, the strength of the coupling between the cylindrical portions 61 and 62 of the elastic member 55 and the worm shaft 23 can be further increased.
Further, the engaging portions 67 and 68 are in contact with the end surfaces of the corresponding cylindrical portions 32 c and 32 d of the worm shaft main body 32. Thereby, it can control more reliably that elastic member 55 comes off from worm shaft 23.

Further, the engaging portions 67 and 68 of the elastic member 55 are sandwiched between the bearings 41 and 42 corresponding to the worm shaft main body 32. Thereby, it can control more reliably that the elastic member 55 shifts | deviates with respect to the worm shaft 23 in the axial direction X1.
Even if a mechanism for suppressing the rattling noise between the worm shaft 23 and the worm wheel 24 is provided, the performance of the electric power steering device 1 does not change. For example, consider a case where a configuration in which a worm shaft is pressed against a worm wheel in order to suppress rattling noise is employed. In this case, a configuration in which the other end of the worm shaft (the end far from the electric motor) is urged toward the worm wheel by a biasing member such as a spring is conceivable. Thereby, a worm axis | shaft is pressed by a worm wheel and the backlash between both is packed. As a result, minute vibrations of the worm wheel are suppressed, and rattling noise is suppressed. However, in this case, since the central axis of the worm shaft is inclined from the state before the worm shaft is urged by the urging member, the central axis of the output shaft (rotor) of the electric motor is also inclined together. For this reason, since the rotor of the electric motor is inclined with respect to the stator, the cogging torque of the electric motor is increased, and the performance of the electric power steering device is changed (deteriorated). In particular, this phenomenon appears remarkably when the output shaft of the electric motor and the worm shaft are integrally formed.

  On the other hand, in this embodiment, the minute vibration of the worm wheel 24 is suppressed by the frictional resistance between the elastic member 55 provided on the worm shaft 23 and the tooth portion 24c of the worm wheel 24. It is not configured to tilt. Therefore, the central axis of the worm shaft 23 and the output shaft 20a (rotor) of the electric motor 20 is not inclined. Therefore, the cogging torque of the electric motor 20 does not increase. Therefore, it is possible to suppress the performance of the electric power steering device 1 from being deteriorated regardless of whether the output shaft 20a of the electric motor 20 and the worm shaft 23 are formed separately or integrally formed.

  Moreover, when the electric power steering device 1 is used for a long period of time, the backlash between the worm shaft 23 and the worm wheel 24 increases, and the amplitude of minute vibrations of the worm wheel 24 increases. The effect of attenuating minute vibrations of the worm wheel 24 can be reliably maintained. Therefore, it is possible to suppress the rattling noise caused by the minute vibration of the worm wheel 24 over a long period of time.

Further, since the elastic member 55 is integrally formed, the elastic member 55 can be formed at a low cost. In addition, the elastic member 55 can be easily bonded to the worm shaft 23, and the strength of the coupling between them can be further increased.
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, as shown in FIG. 5, the engaging portion 67 may be provided with the claw portion 75, the groove 76 may be provided on the end surface of the cylindrical portion 32 c, and the groove 76 may be fitted into the claw portion 75. Thereby, it can suppress more reliably that the elastic member 55 remove | deviates from the worm shaft 23. FIG. The claw portion 75 and the groove 76 may be cylindrical or arcuate. Also, the engaging portion 68 may be provided with a claw portion 75 and a groove 76.

Further, in place of the tooth bottom spiral portions 63 and 64, as shown in FIG. 6, tooth bottom spiral portions 63A and 64A may be provided. The root bottom spiral portions 63A, 64A are (1) the cross-sectional shape perpendicular to the extending direction (tooth line direction) of the first and second groove portions 59, 60 is formed in a concave shape that is recessed toward the center. (2) The point which has the groove part 78 differs from the root spiral part 63,64.
A plurality of groove portions 78 are provided on the outer periphery of the root spiral portions 63A, 64A at least in the meshing region 35. A plurality of grooves 78 are provided in each of the root spiral portions 63A and 64A. The depth of each groove 78 may be different or may be constant.

  According to this configuration, immediately before the tooth portion 24 c of the worm wheel 24 contacts the first and second tooth portions 57 and 58 of the worm shaft 23, the tooth corresponding to the tooth tip surface 24 d of the tooth portion 24 c of the worm wheel 24. The bottom spiral portions 63A and 64A come into contact with each other. Thereby, since the impact of the contact between the worm wheel 24 and the worm shaft 23 can be more reliably mitigated, the rattling noise can be further reduced. Further, a lubricant such as grease can be stored in the groove 78. Thereby, since the lubricant in the groove 78 can be supplied to the worm shaft 23 and the worm wheel 24, the lubrication in the meshing region 35 of the worm shaft 23 can be more reliably performed. Therefore, the durability of the electric power steering device 1 can be improved. Further, by adjusting the shape such as the depth of the groove 78, the ease of bending of the elastic member 55 can be easily adjusted.

  Further, as shown in FIG. 7, an annular seal portion 81 for sealing between the inner ring 41 a and the outer ring 41 b of the first bearing 41 may be provided in the cylindrical portion 61. The seal portion 81 is integrally formed with the cylindrical portion 61 using a single material. The seal portion 81 closes between the inner ring 41a and the outer ring 41b at one end of the first bearing 41. The seal part 81 is provided with lips 81a and 81b. The lip 81a is slidably in contact with the inner peripheral surface of the outer ring 41b of the first bearing 41. The lip 81b is slidably in contact with one end surface of the outer ring 41b of the first bearing 41.

According to this configuration, the elastic member 55 can also be used as a seal member for the first bearing 41 by providing the elastic member 55 with the seal portion 81. Thereby, the number of parts of the electric power steering apparatus 1 can be reduced. Manufacturing costs can be reduced through a reduction in the number of parts.
Further, as shown in FIG. 8, a groove 41c is provided on the inner peripheral surface of the outer ring 41b of the first bearing 41, and a seal portion 83 having a lip 82 of the elastic member 55 is slidably contacted with the groove 41c. Good. Thereby, sealing performance can be improved more.

Note that a seal portion similar to the seal portions 81 and 83 may be provided in the cylindrical portion 62 of the elastic member 55. As a result, the same effect as that of providing the seal portions 81 and 83 on the first bearing 41 can be exerted on the second bearing 42.
Moreover, in each said embodiment, although the worm axis | shaft 23 demonstrated the structure which has the two teeth parts 57 and 58, it is not limited to this. For example, a worm shaft having three or more teeth may be used.

  Further, the cylindrical portions 61 and 62 of the elastic member 55 may be located at a position separated from the meshing region 35 of the worm shaft 23, and may not be disposed at the end portions 32 a and 32 b of the worm shaft main body 32. Furthermore, it is not necessary to provide both the cylindrical portions 61 and 62, and the cylindrical portion 61 or the cylindrical portion 62 may be eliminated.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 20 ... Electric motor, 21 ... Worm speed reducer, 23 ... Worm shaft, 24 ... Worm wheel, 35 ... Meshing area | region, 41, 42 ... Bearing, 55 ... Elastic member, 57 ... 1st tooth part (Tooth portion of worm shaft), 58 ... second tooth portion (tooth portion of worm shaft), 59 ... first groove portion, 59c ... bottom surface (bottom of groove portion), 60 ... second groove portion, 60c ... bottom surface (bottom of groove portion) ), 61, 62 ... cylindrical portion, 63, 64, 63A, 64A ... tooth root spiral portion (spiral portion), 67, 68 ... engagement portion, 78 ... groove portion (outer periphery of elastic member), 81, 83 ... seal Department.

Claims (5)

An electric motor;
A worm shaft coupled to the electric motor to transmit power, a worm wheel meshable with a predetermined meshing region of the worm shaft, and a worm speed reducer including an elastic member coupled to the worm shaft,
The worm shaft includes a plurality of teeth and a plurality of grooves formed by these teeth.
The elastic member is disposed at the bottom of each of the plurality of grooves at least in the meshing region, and connects the plurality of spirals that can contact the worm wheel and the plurality of spirals at a position spaced from the meshing region. An electric power steering apparatus comprising:   2. The electric power steering apparatus according to claim 1, wherein an engagement portion that engages with the worm shaft is provided at an end of the cylindrical portion. The bearing according to claim 2, further comprising a bearing rotatably supporting the worm shaft,
The electric power steering apparatus, wherein the engaging portion is sandwiched between the worm shaft and the bearing.   4. The electric power steering apparatus according to claim 1, wherein a groove is formed on an outer periphery of the elastic member. The bearing according to any one of claims 1 to 4, further comprising a bearing that rotatably supports the worm shaft,
The electric power steering apparatus according to claim 1, wherein the cylindrical portion includes a seal portion for sealing the bearing.

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