JP2008284891A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of easily mounting a steering column to an auxiliary steering mechanism regardless of flatness, squareness and a thickness. <P>SOLUTION: This electric power steering device comprises a steering shaft 3 mounted to a steering wheel 2, a steering column 4 for rotatably holding the steering shaft 3, and a steering support mechanism 5 mounted to the steering column 4. The device has such a constitution that the steering column 4 is press-fitted and held in a housing 11a of the steering support mechanism 5 to secure a collapse stroke. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus including a steering shaft on which a steering wheel is mounted, a steering column that rotatably holds the steering shaft, and a steering assist mechanism that is attached to the steering column.

As this electric power steering device, for example, the lower column previously proposed by the present applicant, the upper column guided by the lower column at the time of a secondary collision and movable to collapse forward, and rotatable to the upper column Is formed integrally with the lower column at the lower end of the lower column to connect the steering shaft on which the steering wheel is mounted on the rear side of the vehicle body and the vehicle body front side of the lower column and the housing of the electric assist mechanism. There is known a steering column device that includes a flange and a rib formed around the flange (see, for example, Patent Document 1).
JP 2006-69483 A (2nd page, FIG. 2)

  However, in the conventional example described in Patent Document 1, a flange formed integrally with the lower column is provided at the lower end of the lower column, and this flange is bolted to the housing of the electric assist mechanism. Therefore, in order to integrally form the flange at the lower end of the lower column, the lower column is plastically deformed to form a rectangular flange, and a rib is formed on the outer periphery of the flange to ensure rigidity. Yes. However, in order to fix the flange to the housing, high precision flatness is required for the flange, and high precision squareness to the lower column is required. There is an unresolved problem that it is necessary to keep the plate thickness for maintaining rigidity.

  Therefore, the present invention has been made paying attention to the unsolved problems of the conventional example described in Patent Document 1 above, and considering the flatness, perpendicularity and plate thickness of the steering column as an auxiliary steering mechanism. It is an object of the present invention to provide an electric power steering device that can be easily mounted without any problem.

  To achieve the above object, an electric power steering apparatus according to a first aspect of the present invention includes a steering shaft on which a steering wheel is mounted, a steering column that rotatably holds the steering shaft, and a steering assist that is attached to the steering column. An electric power steering apparatus comprising a mechanism, wherein the steering column is press-fitted and held in a housing of the steering assist mechanism so as to ensure a collapse stroke.

  The electric power steering apparatus according to claim 2 is characterized in that, in the invention according to claim 1, the housing is provided with a holding plate for press-fitting and holding the steering column on an end face for press-fitting the steering column. Yes.

  Furthermore, the electric power steering apparatus according to a third aspect is characterized in that, in the invention according to the second aspect, the holding plate has a cylindrical portion formed by burring at the press-fitting portion of the steering column.

  Furthermore, in the electric power steering apparatus according to claim 4, in the invention according to claim 2 or 3, a protrusion that increases an initial sliding resistance is formed in a sliding portion of the steering column with the holding plate. It is characterized by.

According to the present invention, the steering column is press-fitted and held in the steering assist mechanism housing so as to ensure a collapse stroke. Therefore, when the steering column is mounted on the steering assist mechanism, the steering column is simply press-fitted and held in the steering assist mechanism. There is no need to consider flatness and perpendicularity, and the effect that it can be easily mounted is obtained.
At this time, by attaching a holding plate for press-fitting and holding the steering column to the housing of the steering assist mechanism, it is not necessary to form a high-precision press-fitting holding portion on the housing, and the sliding contact portion of the steering column is formed with the thickness of the holding plate. Thus, the sliding resistance can be kept substantially constant throughout the entire collapse stroke of the steering column.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 is an overall configuration diagram showing a first embodiment of the present invention, FIG. 2 is a cross-sectional view of a steering column and a gear housing of FIG. 1, FIG. 3 is a cross-sectional view taken along the line AA of FIG. 2 is a cross-sectional view showing the collapsed state of FIG. 2, and FIG. 5 is a characteristic diagram showing the relationship between the collapse stroke and the collapse load.

In the figure, reference numeral 1 denotes an electric power steering apparatus for steering a vehicle. The electric power steering apparatus 1 includes a steering wheel 2 and a steering shaft on which the steering wheel 2 is mounted at the rear end (right end in FIG. 1). 3 and a steering column 4 that rotatably holds the steering shaft 3.
At the front ends (left end in FIG. 1) of the steering shaft 3 and the steering column 4, a worm speed reducer 11 that applies a steering assist torque to the steering shaft 3, and an electric motor that generates a steering assist torque attached to the worm speed reducer 11. A steering assist mechanism 5 composed of a motor 12 is connected.

The output shaft 13 of the worm speed reducer 11 is connected to a pinion shaft 18 constituting the rack and pinion type steering gear mechanism 6 via a universal joint 17. A rack shaft (not shown) of the steering gear mechanism 6 is connected to the steered wheels via a tie rod (not shown).
Here, as shown in FIG. 2, the steering shaft 3 includes an outer shaft 7 on which the steering wheel 2 is mounted and an inner shaft 8 fitted inside the outer shaft 7. The rear end portion of the shaft 8 is serrated and connected, and the outer shaft 7 is disposed in a rolling bearing 9 fixed to the steering column 4 on the inner peripheral surface of the steering wheel 2 side end and a gear housing 11a described later. It is rotatably held by a rolling bearing (not shown).

Here, the outer shaft 7 includes a solid portion 7a on which the steering wheel 2 is mounted and a hollow portion 7b connected to the vehicle front side end of the solid portion 7a. The hollow portion 7b is on the steering wheel 2 side. The large-diameter portion 7c having tapered portions at both ends thereof and the small-diameter portion 7e formed with a serration groove portion 7d on the inner peripheral surface on the gear housing 11a side.
The inner shaft 8 includes a small-diameter solid shaft portion 8b in which a serration shaft portion 8a is formed on the outer peripheral surface of the steering wheel side end portion formed on the steering wheel 2 side, and a large-diameter solid portion that is connected to the small-diameter solid shaft portion 8b. It is comprised with the part 8c.

  The small-diameter solid portion 8b of the inner shaft 8 is serrated to the small-diameter portion 7e of the hollow portion 7b of the outer shaft 7 with the serration groove portion 7d engaged with the serration shaft portion 8a. Here, the coupling between the small-diameter solid portion 8b of the inner shaft 8 and the small-diameter portion 7e of the hollow portion 7b of the outer shaft 7 is not limited to serration coupling, and may be press-fit fitting or clearance fitting.

  Further, the steering column 4 inserted through the steering shaft 3 is formed in a cylindrical shape, and an intermediate portion thereof is supported by the vehicle body side mounting bracket 10 through the mounting bracket 4a so as to be detachable at the time of collapse. The portion is press-fitted into the worm speed reducer 11 so as to ensure a collapse stroke, and when an impact is applied in the axial direction toward the front of the vehicle body, a so-called collapsible structure is formed in which the total length is reduced while absorbing energy from the impact.

  As shown in FIG. 2, the gear housing 11 a of the worm speed reducer 11 is formed with a center opening 11 b extending from the vehicle front side end surface to the rear end side and passing through the inner shaft 7 of the steering shaft 3. At the same time, the steering column 4 can be inserted from the vehicle rear side end surface to the front end surface side of the center opening 11b, and the inner diameter becomes smaller toward the vehicle front end side for ensuring a predetermined collapse stroke of the steering column 4, and the deepest portion A tapered column insertion portion 11 c having an inner diameter set substantially equal to the outer diameter of the steering column 4 is formed.

The gear housing 11a is formed with a seal housing portion 11e for housing and holding a seal 11d whose lip portion contacts the inner shaft 7 at the vehicle rear side end portion of the column insertion portion 11c, and at the vehicle rear side end surface. A holding plate 11f is provided for press-fitting and holding the vehicle front side end of the steering column 4 so as to be slidable during collapse.
As shown in FIG. 3, the holding plate 11 f is configured by a substantially triangular plate portion. A center opening 11 g for press-fitting and holding the steering column 4 is formed at the center portion, and a bolt insertion hole 11 h is formed at each top portion. Is formed.

The holding plate 11f is screwed into a female screw 11j formed in the gear housing 11a with the center point of the center opening 11g aligned with the center point of the center opening 11b of the gear housing 11a. The vehicle housing is fixed to the rear end surface of the gear housing 11a, and the front end of the steering column 4 is press-fitted and held in the center opening 11g so as to be slidable during the collapse.
Furthermore, the vehicle body mounting bracket 21 fixed to the vehicle body side member 20 is fixed to the gear housing 11a at the vehicle front side end.

Next, the operation of the first embodiment will be described.
To assemble the electric power steering apparatus 1 having the above-described configuration, first, the inner shaft 8 is connected to the outer shaft 7 so as to be slidable in the axial direction and integrally rotated in the circumferential direction.
On the other hand, a rolling bearing 9 is fitted into the steering column 4 on the inner peripheral surface of the vehicle rear side end portion, and the vehicle front side end portion is press-fitted into the holding plate 11f so as to be slidable during collapse.

  Then, with the steering shaft 3 inserted into the steering column 4 and the steering shaft 3 fitted in the rolling bearing 9, the vehicle front side of the steering shaft 3 is opened to the center opening in the gear housing 11 a of the steering assist mechanism 5. The holding plate 11f into which the steering column 4 is press-fitted while being inserted into 11b is mounted on the end surface of the gear housing 11a so that the center of the center opening 11e substantially coincides with the center of the center opening 11b of the gear housing 11a. In this state, the bolt 11i is screwed into the female screw 11j through the bolt insertion hole 11h of the holding plate 11f and tightened to fix the holding plate 11f to the gear housing 11a.

  In this manner, the vehicle body mounting bracket 21 attached to the gear housing 11a is bolted to the vehicle body side member 20 in a state where the steering shaft 3 and the steering column 4 are integrally formed with the gear housing 11a of the steering assist mechanism 5. And mounting the electric power steering device 1 to the vehicle body is completed by supporting the mounting bracket 4a of the steering column 4 to the vehicle body side mounting bracket 10 so as to be detachable during the collapse.

  At this time, when the worm speed reducer 11 constituting the steering assist mechanism 5 of the steering column 4 is attached to the gear housing 11a, the holding plate 11f is bolted to the gear housing 11a with the bolt 11i in a state where the steering column 4 is press-fitted into the holding plate 11f. Therefore, the assembly can be easily performed. Further, when the steering column 4 is press-fitted into the holding plate 11f, the perpendicularity between the holding plate 11f and the steering column 4 may be adjusted. As in the conventional example, a flange is formed integrally with the steering column 4. In addition, it is not necessary to adjust the flatness and perpendicularity of the flange portion with high accuracy, and it is not necessary to increase the thickness of the steering column in order to ensure the configuration of the flange portion.

  In this way, the steering torque transmitted to the steering wheel 1 is not shown by the driver of the steering shaft 3 steering the steering wheel 1 in a state where the assembly of the electric power steering device 1 to the vehicle body is completed. The electric motor 12 detects the vehicle speed with a vehicle speed sensor (not shown) and generates an optimum steering assistance force in a steering state with a steering assistance control device (not shown) based on the steering torque and the vehicle speed. Is controlled.

  Therefore, the steering assist force generated by the electric motor 12 is transmitted to the steering shaft 3 via the worm speed reducer 11. By transmitting the steering assist force to the steering shaft 3 in this way, a large steering torque is output from the output shaft 13 of the worm speed reducer 11, and this is transmitted to the steering gear mechanism 6 via the universal joint 17 and the pinion shaft 18. Is done. In the steering gear mechanism 6, the rotational motion transmitted from the pinion shaft 18 is converted into a linear motion in the vehicle width direction by a pinion constituting the steering gear and a rack meshing with the pinion, and transmitted to the steered wheels via a tie rod (not shown). Then, this steered wheel is steered.

  At this time, since the optimum steering assist force corresponding to the steering torque transmitted to the steering wheel 1 is generated by the electric motor 12 of the steering assist mechanism 5, the steering wheel 1 can be lightly steered.

  By the way, when a secondary collision or the like occurs and an impact load F in the axial direction of the steering shaft 3 is applied to the steering wheel 2 as shown in FIG. 4, the impact load is greater than or equal to a preset collapse load. Then, first, the vehicle body side mounting bracket 10 and the mounting bracket 4a of the steering column 4 are detached, whereby the steering column 4 and the outer shaft 7 of the steering shaft 3 are moved in the axial direction toward the steering assist mechanism 5.

  At this time, in the steering shaft 3, since the outer shaft 7 is slidably coupled to the inner shaft 8, the outer shaft 7 slides along the inner shaft 8 toward the steering assist mechanism 5 as shown in FIG. Move.

  On the other hand, with respect to the steering column 4, the holding plate 11f is bolted to the gear housing 11a of the steering assist mechanism 5, so that the steering column 4 absorbs an impact load while the vehicle is in front of the center opening 11e of the holding plate 11f. Will slide to the side. At this time, the vehicle front side end portion of the steering column 4 is first inserted into the column insertion portion 11c while the lip portion of the seal 11d is bent toward the vehicle front side. When the front end of the steering column 4 is inserted into the column insertion portion 11c in this way, the column insertion portion 11c is formed in a tapered shape whose inner diameter gradually decreases toward the vehicle front side. It is possible to move smoothly without being caught in the column insertion portion 11c while being guided and centered in the above, and a predetermined collapse stroke can be ensured. The relationship between the collapse stroke and the collapse load at this time is as shown in FIG. 5, in which the collapse load increases steeply at the initial stage of the collapse stroke, and then maintains a substantially constant collapse load regardless of the increase of the collapse stroke. be able to.

In addition, during the movement of the collapse stroke, the steering column 4 is not supported by the vehicle body side member when the mounting bracket 4a of the steering column 4 is completely detached from the vehicle body side mounting bracket 10. In this state, the steering column is not supported. 4 is inserted into the column insertion portion 11c of the gear housing 11a. Therefore, the steering column 4 can be supported by the gear housing 11a, and the steering column 4 can be prevented from dropping.
Further, since the steering column 4 itself does not need to have a double structure of an inner column and an outer column as in the conventional example, the number of parts can be reduced and the number of assembly steps can be reduced.

Next, a second embodiment of the present invention will be described with reference to FIGS.
In the second embodiment, the steering column 4 can be reliably press-fitted and held by the holding plate 11f.
That is, in the second embodiment, as shown in FIG. 5, the first embodiment described above except that the holding plate 11f is formed with a cylindrical portion 11k protruding to the steering wheel 2 side by burring. The components corresponding to those in the first embodiment have the same reference numerals as those in FIG. 2 and will not be described in detail.

  According to the second embodiment, as in the first embodiment described above, the steering column 4 can be inserted into the column insertion portion 11c of the gear housing 11a during the collapse as shown in FIG. 8 to ensure a collapse stroke. The same effect as the first embodiment can be obtained, and the cylindrical portion 11k is formed in the holding plate 11f, and the tip of the steering column 4 is press-fitted and held in the cylindrical portion 11k. The holding rigidity of the steering column 4 by the plate 11f can be improved.

  In the second embodiment, since the cylindrical portion 11k is formed on the holding plate 11f, the length of the cylindrical portion 11k when the steering column 4 slides in the cylindrical portion 11k to the vehicle front side during the collapse. As the sliding resistance increases in accordance with the increase in the sliding resistance, the press-fitting allowance between the cylindrical portion 11k and the steering column 4 is adjusted in accordance with the increase in the sliding resistance, as in the first embodiment described above. The relationship between the collapse stroke and the collapse load shown in FIG. 5 can be obtained.

  In the first and second embodiments, the case where the seal 11d attached to the gear housing 11a has only the lip portion has been described. However, the present invention is not limited to this, and the core metal that reinforces the lip portion. Is preferably set so that the inner diameter of the mandrel is larger than the outer diameter of the steering column so as not to prevent the steering column 4 from sliding during collapse.

  In the first and second embodiments, as shown in FIG. 5, the relationship between the collapse stroke and the collapse load at the time of collapse is substantially constant after the collapse load increases sharply in the initial state of the collapse stroke. Although the case where the load is applied has been described, the present invention is not limited to this, and as shown in FIGS. Protruding portions 4b that protrude outwardly at positions slightly spaced from the portion toward the steering wheel 4 may be formed to protrude on the circumference at intervals of 90 degrees. In this case, as shown in FIG. 10, the relationship between the collapse stroke and the collapse load at the time of the collapse is such that the protrusion 4b slides on the central opening 11g or the cylindrical portion 11k of the holding plate 11f in the initial state of the collapse stroke. The total increase amount of the collapse load in the initial stage of the collapse stalk is increased as compared with the above-described characteristics of FIG. Similar to the collapse load in the embodiment, it can be returned to a collapse load that is substantially constant regardless of an increase in the collapse stroke. Here, the increase amount of the collapse load in the initial state of the collapse stroke can be adjusted by selecting the number of protrusions formed on the circumference of the steering column 4 and the length of the protrusions in the circumferential direction. .

  In the first and second embodiments, the case where the holding plate 11f is mounted on the gear housing 11a of the steering assist mechanism 5 has been described. However, the present invention is not limited to this, and the holding plate is omitted. Thus, the steering column 4 that is directly connected to the gear housing 11a may be press-fitted and held in a retractable storage.

1 is an overall configuration diagram showing a first embodiment of the present invention. It is sectional drawing of the steering column and gear housing of FIG. It is sectional drawing on the AA line of FIG. It is sectional drawing similar to FIG. 2 at the time of the collapse of 1st Embodiment. It is a characteristic diagram which shows the relationship between a collapse stroke and a collapse load. It is sectional drawing of the steering column and gear housing which show the 2nd Embodiment of this invention. It is sectional drawing on the BB line of FIG. It is sectional drawing similar to FIG. 6 at the time of the collapse in 2nd Embodiment. It is a figure which shows the modification of the steering column which can be applied to this invention, Comprising: (a) is a side view which makes a part of steering column a cross section, (b) is sectional drawing on the CC line of (a). is there. FIG. 10 is a characteristic diagram showing a relationship between a collapse stroke and a collapse load in the configuration of FIG. 9.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering wheel, 3 ... Steering shaft, 4 ... Steering column, 5 ... Steering assist mechanism, 6 ... Steering gear mechanism, 7 ... Outer shaft, 8 ... Inner shaft, 11 ... Worm speed reducer, 11a ... gear housing, 11b ... center opening, 11c ... column insertion part, 11d ... seal, 11e ... seal housing part, 11f ... holding plate, 11g ... center opening, 11h ... bolt insertion hole, 11i ... bolt, 11j ... female screw, 11k ... cylindrical portion, 12 ... electric motor, 17 ... universal joint, 18 ... pinion shaft

Claims (4)

An electric power steering apparatus comprising a steering shaft equipped with a steering wheel, a steering column for rotatably holding the steering shaft, and a steering assist mechanism attached to the steering column,
An electric power steering apparatus, wherein the steering column is press-fitted and held in a housing of the steering assist mechanism so as to ensure a collapse stroke.   2. The electric power steering apparatus according to claim 1, wherein a holding plate for press-fitting and holding the steering column is attached to an end surface of the housing for press-fitting the steering column.   The electric power steering apparatus according to claim 2, wherein the holding plate has a cylindrical portion formed by burring at a press-fitting portion of the steering column.   The electric power steering device according to claim 2 or 3, wherein a protrusion for increasing an initial sliding resistance is formed on a sliding portion of the steering column with the holding plate.

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