JP2016068765A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which is suitable for performing running-in operation of a worm gear and a worm wheel efficiently.SOLUTION: An electric power steering device comprises: a worm gear 3 rotated by a motor; a worm wheel engaging with the worm gear 3 and externally fitted and fixed to a steering shaft; a gear housing for accommodating the worm gear 3 and the worm wheel; and a column tube for supporting the steering shaft rotatably. The gear housing and the column tube are fixed by bolt fastening. A fitting position of the column tube to the gear housing can be selectively changed between a first position where a distance between a rotation axis O1 of the worm gear 3 and a center axis O2 of the column tube is relatively far and a second position where a distance between the rotation axis O1 and the center axis O2 is relatively near.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an electric power steering device for an automobile.

  Conventionally, an electric power steering apparatus using a motor as a drive source has been used as a power steering apparatus for reducing the steering force of a steering wheel. As for the transmission of the assist force in the electric power steering apparatus, there is known a structure in which, for example, a worm gear rotated by a steering assist motor is transmitted to a worm wheel attached to a steering shaft. As described above, in a gear reduction mechanism using a worm gear and a worm wheel, generally, an allowance called backlash is provided at the meshing portion of the gear. By providing the backlash, the meshing of the teeth of the worm gear and the worm wheel can be made favorable, and the rotation of the worm gear and the worm wheel can be made smooth.

  For the worm gear and the worm wheel, for example, a break-in operation is performed after assembling to the gear housing. The running-in operation of the worm gear and the worm wheel is performed by rotating the motor back and forth at short time intervals. By this running-in operation, the meshing portion of the gear is moderately worn and an appropriate backlash is ensured (see, for example, Patent Document 1).

  In Patent Document 1, a missing tooth portion is provided at one end of a rack that is output from a steering shaft via a pinion gear. The worm gear and the worm wheel are acclimated in a state where the missing tooth portion is arranged so as to correspond to the pinion gear and the pinion gear is idling. According to such a configuration, it is not necessary to move the rack during the break-in operation, but the mutual rotation operation of the worm gear and the worm wheel itself has to be performed as before.

JP 2006-15948 A

  The present invention has been conceived under the circumstances described above, and an object thereof is to provide an electric power steering apparatus suitable for efficiently performing a running-in operation of a worm gear and a worm wheel.

  In order to solve the above problems, the present invention employs the following technical means.

  An electric power steering apparatus provided by the present invention includes a worm gear that is rotated by a motor, a worm wheel that meshes with the worm gear and is externally fixed to the steering shaft, and a gear housing that houses the worm gear and the worm wheel. A column tube that rotatably supports the steering shaft, wherein the gear housing and the column tube are fixed by bolt fastening, wherein the column tube is attached to the gear housing. Is selectively changed to a first position where the distance between the rotation axis of the worm gear and the center axis of the column tube is relatively far and a second position where the distance between the rotation axis and the center axis is relatively close. Can be configured It is characterized in that.

  Preferably, a plurality of screw holes for screwing bolts on either side of the gear housing and the column tube are provided around the central axis, and a plurality of bolt holes for passing bolts on the other side. Is provided around the central axis, and the mounting position of the column tube with respect to the gear housing is changed to the first position by changing the relative positions of the plurality of screw holes and the plurality of bolt holes and tightening the bolts. And the second position.

  Preferably, the worm wheel includes an annular member made of synthetic resin in which a plurality of teeth are formed over the entire circumference of the outer peripheral edge, and a metal core member fixed to the inner edge side of the annular member.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

1 is a partial sectional view schematically showing an example of an electric power steering apparatus according to the present invention. It is sectional drawing which follows the II-II line | wire of FIG. It is the figure which represented typically an example of arrangement | positioning of several screw holes and several bolt holes, and is the III-III arrow directional view in FIG. It is the figure which represented typically the other example of arrangement | positioning of a some screw hole and a some bolt hole, and was the figure seen in the direction similar to FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a sectional view schematically showing a part of an electric power steering apparatus according to the present invention. 2 is a cross-sectional view taken along line II-II in FIG. An electric power steering apparatus A1 shown in FIGS. 1 and 2 includes an annular worm wheel 2 mounted on a steering shaft 1, a worm gear 3 meshing with the worm wheel 2, a gear housing 5, a column tube 6, The rotational driving force of the assisting motor 4 is transmitted to the steering shaft 1 via the speed reduction mechanism by the worm gear 3 and the worm wheel 2. The steering shaft 1 is inserted into the gear housing 5 and the column tube 6 and is connected to a steering wheel (not shown). The worm wheel 2 and the worm gear 3 are accommodated in the gear housing 5. The gear housing 5 and the column tube 6 are fastened by a plurality of bolts 7. FIG. 1 shows a state cut along a plane perpendicular to the rotation axis O1 of the worm gear.

  As shown in FIG. 1, in the present embodiment, the steering shaft 1 includes an upper shaft 11 and a lower shaft 12. The upper shaft 11 is mainly inserted into the column tube 6 and supported by the column tube 6 via a bearing 61. The lower shaft 12 is mainly inserted into the gear housing 5 and supported by the gear housing 5 via a bearing 51. The upper shaft 11 and the lower shaft 12 are connected so as not to rotate relative to each other. With such a configuration, the steering shaft 1 (the upper shaft 11 and the lower shaft 12) is rotatably supported by the column tube 6 and the gear housing 5 via the bearings 61 and 51.

  As shown in FIG. 2, in the present embodiment, the worm wheel 2 includes an annular member 21 and a core member 22. The annular member 21 is made of, for example, a synthetic resin having a predetermined strength such as a polyamide resin, and a plurality of teeth (not shown) are formed over the entire circumference of the outer peripheral edge. The core member 22 is made of, for example, a metal made of mild steel, and is fixed to the inner edge portion of the annular member 21. The fixing structure of the annular member 21 and the core member 22 is obtained by insert injection molding, for example. A through hole 22 a is provided in the approximate center of the core member 22. The core member 22 and the lower shaft 12 are fitted in the through hole 22a. With this configuration, the worm wheel 2 is externally fixed to the steering shaft 1 (lower shaft 12).

  The worm gear 3 is made of, for example, a metal material having a predetermined strength, and a helical tooth surface (not shown) that meshes with the teeth of the worm wheel 2 is formed on the outer peripheral portion. The worm gear 3 has a worm shaft 31 extending to both ends in the axial direction, and both ends of the worm shaft 31 are supported by the gear housing 5 via bearings 53 and 54. Thereby, the worm gear 3 can rotate around the rotation axis O1. One end of the worm shaft 31 in the axial direction is connected to the output shaft 41 of the motor 4.

  As shown in FIG. 1, in the present embodiment, the gear housing 5 includes a housing body 5A and a connecting member 5B. The housing body 5 </ b> A accommodates the worm wheel 2 and the worm gear 3. The housing body 5A has an opening 510 on the right side in FIG. The connecting member 5B has a cylindrical portion 520 on the left side in the drawing. The cylindrical portion 520 is fitted in the opening 510, and thereby the housing body 5A and the connecting member 5B are integrated.

  A plurality of screw holes 530 for fastening bolts are provided at the right end of the connection member 5B. The plurality of screw holes 530 are provided around the central axis O <b> 2 of the column tube 6. The screw portion of the bolt 7 is screwed into each screw hole 530.

  As shown in FIG. 1, in this embodiment, the column tube 6 includes a cylindrical portion 6A and a flange portion 6B connected to the left end of the cylindrical portion 6A in the drawing. The flange portion 6B is provided with a plurality of bolt holes 630 for bolt passage. The plurality of bolt holes 630 are provided around the central axis O <b> 2 of the column tube 6. The plurality of bolt holes 630 are disposed at positions corresponding to the plurality of screw holes 530, respectively.

  In the present embodiment, the arrangement of the plurality of screw holes 530 provided on the gear housing 5 side and the arrangement and shape of the plurality of bolt holes 630 provided on the column tube 6 side have the characteristics described below. Thus, the mounting position of the column tube 6 with respect to the gear housing 5 is configured to be changeable.

  FIG. 3 schematically shows an example of the arrangement of the screw holes 530 and the bolt holes 630 when viewed in the direction along the central axis O <b> 2 of the column tube 6. In FIG. 3, the screw holes 530 are hatched to distinguish them from the bolt holes 630. In the same figure, the position of the worm gear 3 is indicated by a virtual line. The worm gear 3 is located above the screw hole 530 and the bolt hole 630.

  In the example shown in FIG. 3, four screw holes 530 and four bolt holes 630 are provided. FIG. 3A shows a state where the column tube 6 is attached to the gear housing 5 at a normal attachment position (first position). The screw hole 530 and the bolt hole 630 are provided at respective positions in the upper, lower, left and right directions in the drawing. The distance (Ra) from the center axis O2 of the column tube 6 to the center of the lower screw hole 530 is shorter than the distance (Rb) from the center axis O2 to the center of the upper screw hole 530. The distances from the central axis O2 to the centers of the left and right screw holes 530 are equal.

  As for the bolt holes 630, those located above and below have the same center position as the corresponding screw holes 530, and have substantially the same inner diameter as that of the screw holes 530. That is, the distance (Ra) from the center axis O2 of the column tube 6 to the center of the lower bolt hole 630 is shorter than the distance (Rb) from the center axis O2 to the center of the upper bolt hole 630. The bolt holes 630 positioned on the left side and the right side overlap with the corresponding screw holes 530 and are elongated in the vertical direction.

  FIG. 3B shows an attachment position when the column tube 6 is attached to the gear housing 5 by rotating 180 degrees around the central axis O2 with respect to the attachment position of the column tube 6 shown in FIG. Show. In the state shown in FIG. 3B, the upper and lower positions of the bolt holes 630 on the column tube 6 side are switched as compared with the state shown in FIG. Thereby, in the state shown in FIG. 3B, the distance from the bolt hole 630 located above to the central axis O2 is Ra, and the difference between the distance Rb and the distance Ra is more than that in the state shown in FIG. Only the position of the center axis O2 is shifted upward. 3A, the column tube 6 is attached at a position where the distance between the rotational axis O1 of the worm gear 3 and the center axis O2 of the column tube 6 is relatively far. (First position). The attachment position of the column tube 6 shown in FIG. 3B is a position where the distance between the rotation axis O1 of the worm gear 3 and the center axis O2 of the column tube 6 is relatively close (second position).

  FIG. 4 schematically shows another example of the arrangement of the screw holes 530 and the bolt holes 630 when viewed in the direction along the central axis O2 of the column tube 6. In FIG. 4, the screw holes 530 are hatched to distinguish them from the bolt holes 630. In the same figure, the position of the worm gear 3 is indicated by a virtual line. The worm gear 3 is located above the screw hole 530 and the bolt hole 630.

  In the example shown in FIG. 4, three screw holes 530 and three bolt holes 630 are provided. FIG. 4A shows a state where the column tube 6 is attached to the gear housing 5 at a normal attachment position (first position). The screw hole 530 and the bolt hole 630 are provided at each of the upper, lower right, and lower left positions in the drawing. The distance (Ra) from the center axis O2 of the column tube 6 to the center of the lower right screw hole 530 is shorter than the distance (Rb) from the center axis O2 to the center of the upper screw hole 530. The angle formed by the line connecting the center axis O2 and the center of the lower right screw hole 530 and the line connecting the center axis O2 and the center of the upper screw hole 530 is 120 °. The bolt hole 630 corresponding to each of the lower right and upper screw holes 530 has a central position that is the same as that of the screw hole 530 and has an inner diameter that is substantially the same as the diameter of the screw hole 530. That is, the distance (Ra) from the center axis O2 of the column tube 6 to the center of the lower right bolt hole 630 is shorter than the distance (Rb) from the center axis O2 to the center of the upper bolt hole 630.

  With respect to the screw hole 530 at the lower left, when the column tube 6 is attached by rotating 120 ° counterclockwise from the state shown in FIG. 4A (see FIG. 4B), in FIG. In the state where the bolt hole 630 located at the upper position is located at the lower left, the bolt hole 630 at the lower left is provided at a position where the center position coincides.

  The lower left bolt hole 630 shown in FIG. 4 (a) overlaps with the corresponding lower left screw hole 530, and the column tube 6 is rotated 120 ° counterclockwise from the state shown in FIG. 4 (a). When it is rotated and attached (see FIG. 4B), it is provided so as to overlap with the screw hole 530 at the lower right. In the example shown in FIG. 4A, the bolt hole 630 located at the lower left is made long.

  FIG. 4B shows the attachment position when the column tube 6 is attached to the gear housing 5 by rotating it 120 degrees counterclockwise with respect to the attachment position of the column tube 6 shown in FIG. ing. In the state shown in FIG. 4B, the bolt hole 630 located at the lower right in FIG. 4A is located above, and the bolt hole 630 located above in FIG. 4A is located at the lower left. To do. Thereby, in the state shown in FIG. 4B, the distance from the bolt hole 630 located above to the central axis O2 is Ra, and the difference between the distance Rb and the distance Ra is more than that in the state shown in FIG. Only the position of the center axis O2 is shifted upward. 4A, the column tube 6 is attached at a position where the distance between the rotation axis O1 of the worm gear 3 and the center axis O2 of the column tube 6 is relatively far. (First position). The column tube 6 mounting position shown in FIG. 4B is a position where the distance between the rotation axis O1 of the worm gear 3 and the center axis O2 of the column tube 6 is relatively short (second position).

  Next, the operation of the above-described electric power steering apparatus A1 will be described.

  According to this embodiment, when performing the running-in operation of the worm gear 3 and the worm wheel 2, as shown in FIG. 3B and FIG. The column tube 6 is attached so that the distance between the rotation axis O1 of the worm gear 3 and the center axis O2 of the column tube 6 is relatively close (second position). The worm wheel 2 supported by the column tube 6 via the steering shaft 1 is closer to the worm gear 3 than the normal mounting position (the state shown in FIGS. 3A and 4A). Become. At this time, since the meshing portion of the worm gear 3 and the worm wheel 2 becomes more clogged than in the normal attachment position, wear of the meshing portion accompanying the rotation operation of the worm gear 3 and the worm wheel 2 is great. Therefore, if the running-in operation is performed in such a state, the gear meshing portion is appropriate even if the number of rotations of the worm gear 3 and the worm wheel 2 is reduced compared to the case where the running-in operation is performed at the normal mounting position. To wear. Therefore, according to the present embodiment, the time required for the break-in operation is shortened, and the break-in operation of the worm gear 3 and the worm wheel 2 can be performed efficiently.

  After the running-in operation of the worm gear 3 and the worm wheel 2 is finished, the column tube 6 is once removed from the gear housing 5 and rotated around the central axis O2, and the relative position of the bolt hole 630 with respect to the screw hole 530 is changed. The housing 5 and the column tube 6 are fastened with bolts 7. Thereby, as shown in FIGS. 3A and 4A, the distance between the rotation axis O1 of the worm gear 3 and the center axis O2 of the column tube 6 is a relatively far position (second position). It can be a normal attachment position. In this normal mounting position, the worm wheel 2 supported by the column tube 6 is located farther from the worm gear 3 than during the break-in operation, and an appropriate backlash is ensured at the gear meshing portion. According to the present embodiment, it is possible to easily switch between the state in which the running-in operation is performed and the normal attachment state by simply changing the attachment position of the column tube 6 with respect to the gear housing 5 by bolt fastening. Therefore, parts for exclusive use of running-in are not necessary, and the efficiency of running-in can be improved at low cost.

  The worm wheel 2 includes a synthetic resin-made annular member 21 having a plurality of teeth formed on the entire circumference of the outer peripheral edge, and a metal core member 22 fixed to the inner edge of the annular member 21. According to this configuration, residual stress may remain in resin molding of the annular member 21. On the other hand, when the break-in operation is performed in a state where the meshing portions of the worm gear 3 and the worm wheel 2 are clogged as described above, a large amount of heat is generated when the gear meshing portion slides, and the teeth of the annular member 21 become relatively small. It becomes high temperature. As a result, an annealing process for relaxing the residual stress is not required for the annular member 21 made of synthetic resin. Therefore, according to the present embodiment, the electric power steering apparatus A1 including the worm wheel 2 having the synthetic resin teeth can be manufactured at a low cost.

  Although the embodiment of the present invention has been described above, the technical scope of the present invention is not limited to the above-described embodiment. The specific configuration of each part of the present invention can be variously changed.

A1 Electric power steering apparatus 1 Steering shaft 11 Upper shaft 12 Lower shaft 2 Worm wheel 21 Annular member 22 Core member 22a Through hole 3 Worm gear 31 Worm shaft 4 Motor 41 Output shaft 5 Gear housing 5A Housing body 5B Connecting members 51, 53, 54 Bearing 510 Opening 520 Cylindrical part 530 Screw hole 6 Column tube 6A Cylindrical part 6B Flange part 61 Bearing 630 Bolt hole 7 Bolt

Claims (3)

A worm gear rotated by a motor;
A worm wheel that meshes with the worm gear and is externally fixed to the steering shaft;
A gear housing that houses the worm gear and the worm wheel;
A column tube that rotatably supports the steering shaft,
An electric power steering device in which the gear housing and the column tube are fixed by bolt fastening,
The column tube is attached to the gear housing at a position where the distance between the rotation axis of the worm gear and the center axis of the column tube is relatively far from the position where the distance between the rotation axis and the center axis is relatively short. An electric power steering apparatus configured to be selectively changeable to a second position. Among the gear housing and the column tube, a plurality of screw holes for screwing bolts are provided around the central axis on either side, and a plurality of bolt holes for passing bolts are provided on the other side. Around the axis,
The mounting position of the column tube with respect to the gear housing takes the first position and the second position by changing the relative positions of the plurality of screw holes and the plurality of bolt holes and tightening the bolts. The electric power steering apparatus according to 1.   The said worm wheel is provided with the synthetic resin annular member in which the several tooth | gear was formed over the perimeter of an outer periphery, and the metal core member fixed to the inner edge side of this annular member. 2. The electric power steering apparatus according to 2.

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