JP2007216721A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact electric power steering device. <P>SOLUTION: The electric power steering device is provided with a worm shaft 20 and a worm wheel 21 as a reduction gear 19, and an input shaft 9 and an output shaft 10 as steering shafts. The worm wheel 21 has an annular core metal 24 and a synthetic resin member 25 for surrounding the annular core metal 24 and formed with teeth 25b in the peripheral surface 25a thereof. The output shaft 10 has a first and a second divided bodies divided in the axial direction Y and fitted to each other freely to integrally rotate. The core metal 24 and the first divided body 22 are integrally formed with each other from single material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric power steering device that generates a steering assist force by an electric motor.

  A reduction gear is used in an electric power steering system (EPS) for a vehicle. For example, an electric power steering device that amplifies the output of the electric motor and transmits it to the steering mechanism by a worm shaft and worm wheel as a reducer decelerating the rotation of the output shaft of the electric motor, and torque assists the steering operation. Proposed.

The output shaft of the steering shaft is press-fitted into the inner periphery of the worm wheel. Thereby, the worm wheel is connected to the output shaft of the steering shaft so as to be integrally rotatable and immovable in the axial direction. (For example, refer to Patent Document 1).
JP 2005-280601 A

By the way, in the electric power steering apparatus as described above, in recent years, there has been a demand for higher functions such as increasing the shock absorption stroke at the time of a vehicle collision, or mounting an electric tilt adjustment mechanism or a telescopic adjustment mechanism. . Accordingly, it is required to reduce the size of the reduction gear of the electric power steering device.
However, between the worm wheel of the speed reducer and the output shaft press-fitted into the worm wheel, a fitting length of a predetermined length or more is necessary in order to transmit the output from the electric motor to the output shaft without slipping. Therefore, the reduction gear cannot be reduced in size.

  The present invention has been made based on such a background, and an object thereof is to provide an electric power steering apparatus that can achieve miniaturization.

  In order to achieve the above object, the present invention is configured to connect an input shaft (9) connected to the steering member (2), the input shaft so as to be relatively rotatable, and transmit power to the steering mechanism (A). Output shaft (10), a drive gear (20) driven by an electric motor (18) for assisting steering, and a driven gear (21) meshing with the drive gear, at least a part of the driven gear ( 24, 224, 326) is an electric power steering device (1) characterized in that it is formed integrally with the output shaft from a single material.

According to the present invention, since the axial length of the coupling portion between the driven gear and the output shaft can be shortened, an electric power steering device that is miniaturized in the axial direction can be obtained. An example of a method for forming an integrally formed product of at least a part of the driven gear and the output shaft is forging.
In the present invention, the output shaft includes first and second divided bodies (22, 122; 23, 123) that are divided in the axial direction and fitted together so as to be integrally rotatable. Either one of the two divided bodies may include a plurality of specifications having different axial lengths. In this case, parts can be shared between different specifications of the reduction gear. As a result, the cost of the entire electric power steering apparatus having a large number of specifications can be reduced.

Further, at least a part of the first divided body and the driven gear is integrally formed of a single material, and the bearing that rotatably supports the output shaft sandwiches the driven gear in the axial direction (Y1). The first and second bearings may include first and second bearings (32, 33) disposed on opposite sides, and the first and second bearings may support the first divided body.
In addition, at least a part of the first divided body and the driven gear are integrally formed of a single material, and the second divided body is a fitting that is fitted to the outer periphery of the first divided body. The bearing including the portion (140) and rotatably supporting the output shaft includes first and second bearings disposed on both sides sandwiching the driven gear in the axial direction, and the first bearing includes the second bearing The fitting portion of the divided body may be supported, and the second bearing may support the first divided body.

  In the present invention, the driven gear includes a worm wheel (21). The worm wheel includes a metal member (24, 224) integrally formed of a single material with the output shaft, and an outer peripheral surface (25a). ) And a synthetic resin member (25) in which teeth (25b) are formed, and the metal member extends axially downward from the annular plate portion (26, 226, 326) and the outer peripheral portion of the annular plate portion. The synthetic resin member may be coupled to the outer periphery (27a) of the cylindrical portion. In this case, the length of the coupling portion between the worm wheel and the output shaft can be shortened while ensuring the axial length of the teeth formed on the outer periphery of the synthetic resin member. Therefore, the output from the electric motor can be reliably transmitted to the worm wheel, and the axial dimension of the reduction gear can be shortened.

  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 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 apparatus 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, a pinion shaft 5 connected to the steering shaft 3 via an intermediate shaft 4, and a pinion shaft. The rack bar 7 has a rack tooth 7 that meshes with the pinion tooth 6 formed in the wheel 5, and a rack bar 8 as a steered shaft extending in the left-right direction of the automobile. The pinion shaft 5 and the rack bar 8 constitute a rack and pinion mechanism A as a steering mechanism.

The steering shaft 3 is divided into an input shaft 9 connected to the steering member 2 and an output shaft 10 connected to the pinion shaft 5. The input shaft 9 and the output shaft 10 are connected via a torsion bar 11 so as to be relatively rotatable on the same axis.
The rack bar 8 is supported by the housing 12 so as to be linearly reciprocable via a bush and a guide member (not shown). Both ends of the rack bar 8 protrude to both sides of the housing 12, and steered wheels 14 are connected to the ends via tie rods 13 and knuckle arms (not shown), respectively.

By operating the steering member 2, the steering shaft 3 rotates. The rotation of the steering shaft 3 is converted into a linear reciprocating motion of the rack bar 8 in the left-right direction of the vehicle body via the pinion teeth 6 and the rack teeth 7. Thereby, steering of the steering wheel 14 is achieved.
The steering torque applied to the steering member 2 is detected by a torque sensor 15 provided in the vicinity of the torsion bar 11 based on the relative rotational displacement between the input shaft 9 and the output shaft 10. The torque value detected by the torque sensor 15 is given to an ECU 16 (Electronic Control Unit). The ECU 16 drives and controls the steering assisting electric motor 18 via the drive circuit 17 based on a torque value, a vehicle speed given from a vehicle speed sensor (not shown), or the like. The drive circuit 17 is housed in the housing of the ECU 16.

The rotational force of the electric motor 18 output by the control of the ECU 16 is amplified by the speed reducer 19 and transmitted to the output shaft 10 of the steering shaft 3. The force transmitted to the output shaft 10 is transmitted to the rack bar 8 via the pinion shaft 5. This assists steering.
FIG. 2 is a cross-sectional view showing the configuration of the speed reducer 19 provided in the electric power steering apparatus 1 of FIG. 1 and the vicinity thereof. Referring to FIG. 2, the speed reducer 19 includes a worm shaft 20 as a drive gear that is rotationally driven by an electric motor 18, and a worm wheel 21 as a driven gear that meshes with the worm shaft 20. Further, the output shaft 10 of the steering shaft 3 includes a cylindrical first divided body 22 formed integrally with a part of the worm wheel 21 and a cylinder fitted to the first divided body 22 so as to be integrally rotatable. Second divided body 23. A part of the worm wheel 21 and the first divided body 22 are integrally formed, for example, by forging.

Although not shown, the worm shaft 20 is disposed on the same axis as the output shaft of the electric motor 18 and is connected to be able to transmit power through a joint. Thereby, the worm shaft 20 is rotationally driven.
The worm wheel 21 includes an annular cored bar 24 and a synthetic resin member 25 having teeth 25b formed on the outer peripheral surface 25a. The core metal 24 and the first divided body 22 of the output shaft 10 are integrally formed of a single material. The cored bar 24 includes an annular plate part 26 and a cylindrical part 27. The annular plate portion 26 protrudes outward in the radial direction X1 from the outer periphery of the first divided body 22, and the cylindrical portion 27 extends from the outer peripheral portion 26a of the annular plate portion 26 in the axially lower direction Z1. . A synthetic resin member 25 is connected to the outer periphery 27a of the cylindrical portion 27, and the cylindrical portion 27 and the synthetic resin member 25 are connected by, for example, injection molding. Thereby, the worm wheel 21 is connected to the output shaft 10 so as to be able to rotate integrally and not to move in the axial direction.

  The worm shaft 20 and the worm wheel 21 are accommodated in a space defined by a cylindrical gear housing 28 and a cylindrical sensor housing 29 in which an end portion 29a is fitted to an end portion 28a of the gear housing 28. ing. In addition, the region including the meshing portion of the worm shaft 20 and the worm wheel 21 is filled with a lubricant, whereby wear between the tooth surfaces of the worm shaft 20 and the worm wheel 21 is reduced.

  The first divided body 22 of the output shaft 10 has a first end portion 30 and a second end portion 31, and the worm wheel 21 is located at an intermediate portion between the first and second end portions 30 and 31. Is provided. A first bearing 32 is disposed at the first end 30, and a second bearing 33 is disposed at the second end 31. For example, rolling bearings are used as the first and second bearings 32 and 33.

  The outer ring 32 a of the first bearing 32 is held in the holding hole 50 of the gear housing 28, and the inner ring 32 b is fitted to the outer periphery of the first end 30. The inner ring 32 b of the first bearing 32 is connected to a first annular step portion 34 formed at the base end of the first end portion 30 and a screw portion 35 formed on the outer periphery of the first end portion 30. It is clamped in the axial direction Y1 by a nut 36 to be screwed. The outer ring 32 a of the first bearing 32 is disposed between an end wall 51 formed at one end of the holding hole 50 and an annular retaining ring 52 fitted in the groove of the holding hole 50. The outer ring 32 a is restricted from moving upward in the axial direction by the retaining ring 52, and is restricted from moving downward in the axial direction by the end wall 51.

  The outer ring 33 a of the second bearing 33 is held by the sensor housing 29, and the inner ring 33 b is fitted on the outer periphery of the second end portion 31. Further, the inner ring 33 b of the second bearing 33 is supported by a second annular step portion 37 formed at the base end of the second end portion 31, and is restricted from moving downward in the axial direction. The movement of the outer ring 33 a of the second bearing 33 in the axial direction is restricted by the sensor housing 29. In this way, the first divided body 22 is rotatably held by the gear housing 28 and the sensor housing 29 via the first and second bearings 32 and 33.

  The second divided body 23 includes a cylindrical connecting portion 39 connected to the torsion bar 11 via the pin 11 a and a cylindrical fitting portion 40. By fitting the outer periphery of the fitting portion 41 provided at the first end 30 of the first divided body 22 and the inner periphery of the fitting portion 40 of the second divided body 23, the first and second The 2nd division bodies 22 and 23 are connected so that integral rotation is possible. Examples of a method for connecting the fitting portion 41 of the first divided body 22 and the fitting portion 40 of the second divided body 23 include serration press fitting, welding, and pin coupling.

  As described above, according to this embodiment, the core metal 24 of the worm wheel 21 and the first divided body 22 of the output shaft 10 are integrally formed of a single material. Thereby, even if the length in the axial direction Y1 of the coupling portion between the worm wheel 21 and the output shaft 10 is shortened, the mutual coupling strength can be maintained at a predetermined value. Therefore, the length in the axial direction Y1 of the coupling portion between the worm wheel 21 and the output shaft 10 can be shortened, and the dimension in the axial direction Y1 of the speed reducer 19 can be shortened. As a result, the electric power steering device 1 can be downsized in the axial direction Y1.

In addition, by reducing the size of the electric power steering device 1 in the axial direction Y1, a space in the axial direction is created in the device, so that an impact absorption stroke can be increased, and an electric tilt adjustment mechanism, a telescopic adjustment mechanism, and the like can be easily performed. The electric power steering apparatus 1 can be enhanced in function.
Further, an integrally formed product of the cored bar 24 and the first divided body 22 reduced in size in the axial direction Y1 can be obtained. Therefore, when this integrally formed product is formed by forging, the synthetic resin member 25 and the integrally molded product. Are easy to process when they are connected by injection molding.

  Moreover, since the cylindrical part 27 of the metal core 24 is extended from the outer peripheral part 26a of the annular plate part 26 in the axially lower Z1, even when the annular plate part 26 becomes thin, The length in the axial direction Y1 can be ensured. Thereby, the length of the axial direction Y1 of the synthetic resin member 25 connected to the outer periphery 27a of the cylindrical part 27 and the tooth | gear 25b formed in the synthetic resin member 25 is securable. Therefore, the output of the electric motor 18 can be reliably transmitted to the output shaft 10 between the tooth surfaces of the worm shaft 20 and the worm wheel 21.

  Further, according to this embodiment, the output shaft 10 is divided in the axial direction Y1 into the first and second divided bodies 22 and 23 that are fitted to each other so as to be integrally rotatable. As a result, for example, among the reduction gears 19 having a large number of different specifications such as the outer diameter of the worm wheel 21 and the shaft length of the output shaft 10, parts can be shared with respect to each of the first and second divided bodies 22 and 23. Can be planned. Therefore, the cost of the speed reducer 19 can be reduced. Since the second divided body 23 has a simpler structure than the first divided body 22, the axial length dimension of the second divided body 23 is changed, and various output shafts 10 having different length dimensions can be obtained. Easy to meet specifications.

FIG. 3 is a cross-sectional view showing a configuration of the speed reducer 19 and its vicinity according to another embodiment of the present invention. 3, the same components as those shown in FIGS. 1 and 2 described above are denoted by the same reference numerals as those in FIGS. 1 and 2, and description thereof is omitted.
Referring to FIG. 3, this embodiment is mainly different from the embodiment of FIG. 2 in that the second divided body 123 is fitted on the outer periphery of the fitting portion 141 of the first divided body 122. The portion 140 is fitted, and the inner ring 32 b of the first bearing 32 is fitted on the outer periphery of the fitting portion 140 of the second divided body 123. On the outer periphery of the fitting portion 140 of the second divided body 123, a screw portion 135 that is screwed into the nut 36 is formed following the bearing holding portion formed of a cylindrical surface.

As described above, the inner ring 32 b of the first bearing 32 is fitted to the outer periphery of the fitting portion 140 of the second divided body 123, and the inner ring 32 b of the first bearing 32 is fitted to the first divided body 122. The first annular step 134 formed adjacent to the base end of the fitting portion 141 and the nut 36 are sandwiched in the axial direction Y1.
According to this embodiment, an effect equivalent to that of the embodiment shown in FIG. 2 can be obtained. Moreover, it arrange | positions so that at least one part of the axial direction position of the fitting parts 141 and 140 of both the division bodies 122 and 123 and the 1st bearing 32 may mutually overlap, and, thereby, the electric power steering apparatus 1 is axial direction. The size is reduced to Y1.

FIG. 4 is a cross-sectional view showing the configuration of the speed reducer 19 and its vicinity according to still another embodiment of the present invention. In FIG. 4, the same components as those shown in FIGS. 1 and 2 described above are denoted by the same reference numerals as those in FIGS. 1 and 2, and description thereof is omitted.
Referring to FIG. 4, this embodiment is mainly different from the embodiment of FIG. 2 in that sensor housing 29 is in a state where first and second bearings 32 and 33 maintain their relative positions. Is closer to the axial direction Y1 than the torque sensor 15 accommodated in the interior. Further, in order to prevent shortening of the fitting length between the end portions 28a and 29a of the gear housing 28 and the sensor housing 29 and the reduction in the thickness of the end portion 29a of the sensor housing 29, the annular plate of the cored bar 224 is prevented. A middle portion of the portion 226 is bent stepwise in the axially downward Z1, and a part of the gear housing 28 is moved in the axially downward Z1.

  The annular plate portion 226 of the cored bar 224 includes a first portion 42 that protrudes outward in the radial direction X1 from the outer periphery of the first divided body 22, one end connected to the first portion 42, and an outer periphery of the first portion 42. The second portion 43 extends downward in the axial direction Z1, and the third portion 44 is connected to the other end of the second portion 43 at one end and extends outward in the radial direction X1. One end of the cylindrical portion 27 of the cored bar 224 is connected to the other end of the third portion 44, and extends from the outer periphery of the third portion 44 to the axially lower Z 1.

Further, the outer peripheral surface of the first facing portion 46 facing the worm wheel 21 of the gear housing 28 in the axial direction Y1, and the outer peripheral surface of the second facing portion 47 facing the first bearing 32 of the gear housing 28 in the axial direction Y1. Is formed at the same position in the axial direction Y1.
According to this embodiment, an effect equivalent to that of the embodiment shown in FIG. 2 can be obtained. Further, by shortening the distance in the axial direction Y1 between the first and second bearings 32 and 33 and the torque sensor 15, the electric power steering device 1 can be further downsized in the axial direction Y1.

In the above-described embodiment, the example in which the first portion 42 of the cored bar 224 and the cylindrical portion 27 are connected via the stepped portion has been described, but instead of this, The cylindrical part 27 may be connected to each other through a linear part. Moreover, the 1st part 42 and the cylindrical part 27 may be mutually connected through the curved part like a circular arc, for example.
FIG. 5 is a cross-sectional view showing the configuration of the speed reducer 19 and the vicinity thereof according to still another embodiment of the present invention. 5, the same components as those shown in FIGS. 1 and 2 described above are denoted by the same reference numerals as those in FIGS. 1 and 2, and the description thereof is omitted.

Referring to FIG. 5, this embodiment is mainly different from the embodiment of FIG. 2 in that a cored bar 324 has an annular plate portion 326 and a cylindrical portion 327 joined to the annular plate portion 326. Therefore, it is formed integrally.
The annular plate portion 326 is formed integrally with the first divided body 22 from a single material. In other words, the annular plate portion 326 protrudes outward in the radial direction X1 from the outer periphery of the first divided body 22, and the first and second annular step portions that support the first and second bearings 32 and 33, respectively. It extends to a length that can secure 34 and 37. And the cylindrical part 327 is fitted by the outer peripheral part 326a of the cyclic | annular board part 326, and it mutually joined. Examples of the method for joining the annular plate portion 326 and the cylindrical portion 327 include welding, fastening with a bolt, and press-fitting.

Further, the teeth 25b of the synthetic resin member 25 are formed after the annular plate portion 326, the cylindrical portion 327, and the synthetic resin portion 25 are joined.
According to this embodiment, an effect equivalent to that of the embodiment shown in FIG. 2 can be obtained. In addition, the annular plate portion 326 and the cylindrical portion 327 of the cored bar 324 are configured as separate members and integrated with each other. Thereby, it is possible to reduce the outer diameter of the portion formed integrally with the first divided body 22 from a single material (in this embodiment, only the annular plate portion 326 and not the cylindrical portion 327). it can. Therefore, it is possible to prevent the yield of the material of the integrally formed product of the first divided body 22 and the annular plate portion 326 from being deteriorated, and to suppress an increase in cost. Furthermore, the teeth 25b of the synthetic resin member 25 are formed after the annular plate portion 326, the cylindrical portion 327, and the synthetic resin portion 25 are joined, so that the teeth 25b are accurately affected without being affected by the respective assembly errors. Can be formed.

  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.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment of the present invention. It is sectional drawing which shows the structure of the reduction gear with which the electric power steering apparatus of FIG. 1 was equipped, and its vicinity. It is sectional drawing which shows the reduction gear concerning another embodiment of this invention, and the structure of the vicinity. It is sectional drawing which shows the reduction gear concerning another embodiment of this invention, and the structure of the vicinity. It is sectional drawing which shows the reduction gear concerning another embodiment of this invention, and the structure of the vicinity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering member, 9 ... Input shaft, 10 ... Output shaft, 18 ... Electric motor, 20 ... Worm shaft (drive gear), 21 ..Worm wheel (driven gear), 22, 122 ... first divided body, 23, 123 ... second divided body, 24, 224, 324 ... core metal (metal member, driven gear) 25) synthetic resin member, 25a ... outer peripheral surface, 25b ... teeth, 26, 226, 326 ... annular plate part, 27, 327 ... cylindrical part (of metal member) Part), 27a ... outer periphery, 32 ... first bearing, 33 ... second bearing, 40 ... fitting part (part of second divided body), A ... Rack and pinion mechanism (steering mechanism), Y1 ... Axial direction

Claims (5)

An input shaft coupled to the steering member;
An output shaft that is coupled to the input shaft so as to be relatively rotatable and transmits power to the steering mechanism;
A drive gear driven by an electric motor for assisting steering;
A driven gear meshing with the drive gear,
An electric power steering apparatus, wherein at least a part of the driven gear is integrally formed with the output shaft from a single material.   In Claim 1, the output shaft includes first and second divided bodies that are divided in the axial direction and fitted so as to be integrally rotatable with each other, and any one of the first and second divided bodies includes: An electric power steering apparatus comprising a plurality of specifications having different shaft lengths. In claim 2, at least a part of the first divided body and the driven gear are integrally formed of a single material,
The bearing that rotatably supports the output shaft includes first and second bearings disposed on both sides sandwiching the driven gear in the axial direction,
The electric power steering apparatus, wherein the first and second bearings support the first divided body. In claim 2, at least a part of the first divided body and the driven gear are integrally formed of a single material,
The second divided body includes a cylindrical fitting portion fitted on the outer periphery of the first divided body,
The bearing that rotatably supports the output shaft includes first and second bearings disposed on both sides sandwiching the driven gear in the axial direction,
An electric power steering apparatus, wherein the first bearing supports the fitting portion of the second divided body, and the second bearing supports the first divided body. In any one of Claims 1-4, the said driven gear contains a worm wheel,
The worm wheel includes a metal member formed integrally with the output shaft and a single material, and a synthetic resin member having teeth formed on the outer peripheral surface,
The metal member includes an annular plate portion and a cylindrical portion extending axially downward from the outer peripheral portion of the annular plate portion, and a synthetic resin member is coupled to the outer periphery of the cylindrical portion. Electric power steering device.

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