JP2007145061A - Steering shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain both of a shock absorption function and durability when the shock absorption function is added by forming a bellows portion at a part of a steering shaft. <P>SOLUTION: The durability of a bellows tube 13 can be improved by making a curvature radius R of roots 17 of both ends of the bellows portion 16 of the bellows tube 13 larger than a curvature radius r of a valley portion 15 of one of the bellows portion 16 to obtain the original shock absorption function of the bellows portion 16. Besides, stress of the valley portions 15 of the bellow portion 16 can be reduced by making an outer diameter d of the valley portions 15 of the bellows portion 16 larger than a diameter D of cylindrical portions 18 at both the ends of the bellows portion 16, thus further improving the durability of the bellows tube 13. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a steering shaft that is used by being incorporated in a steering device of an automobile and transmits a movement of a steering wheel to a steering gear.

  The steering shaft needs torsional strength to transmit the steering torque. On the other hand, the steering shaft is also required to have a function of absorbing an impact from the front, for example. The shock absorbing function required for the steering device is mainly divided into two, and one of them is a function for absorbing the shock when the driver collides with the steering device. It is greatly improved by the combined use. The other is a function of absorbing the impact of the steering device pushing up the driver as a result of the body or engine being pushed back by the force of the collision and the steering shaft being pushed down in the same manner.

In order to give an impact absorbing function to such a steering shaft itself, for example, a hollow steering shaft is partially bellows to form a so-called bellows portion (bellows portion). For example, Patent Document 1 listed below discloses a technique related to an impact absorbing function in the bellows portion.
JP-A-9-150747

However, the bellows part formed to absorb the shock is collapsible, that is, deforms to absorb the shock, and on the other hand, it has sufficient durability to transmit the steering wheel movement (rotational torque) to the steering gear. Sex is also required. Specifically, in order to absorb the impact, it is necessary to reduce the bending load on the entire bellows portion, and in order to have durability, it is necessary to reduce the stress generated in the bellows portion. This is a seemingly contradictory requirement in terms of mechanical strength. In the above-mentioned patent document, there is no description regarding the compatibility between the impact absorbing function and the durability of the bellows part.
The present invention has been made paying attention to the above-described problems, and an object of the present invention is to provide a steering shaft capable of achieving both an impact absorbing function and durability.

  In order to solve the above-mentioned problems, a steering shaft according to claim 1 of the present invention is disposed in a steering force transmission path from a steering wheel to a steering gear, and is a bellows portion comprising a plurality of large-diameter portions and small-diameter portions. In the steering shaft in which is formed, the radius of curvature of the roots at both ends of the bellows part is larger than any of the curvature radii of the valleys excluding both ends of the bellows part.

The roots at both ends of the bellows portion indicate a connecting portion between the bellows portion and a portion that is not. Usually, so-called corners R are provided in the bellows peaks (portions protruding outside the bellows portions) and valleys (portions retracted inside the bellows portions) in order to suppress stress concentration. Similarly, a corner R is also provided at the connecting portion between the bellows portion and the other portion. The steering shaft according to claim 1 of the present invention is characterized in that the radius of curvature of the corner R provided at the root of both ends of the bellows portion is larger than the radius of curvature of the corner R of the valley portion of the bellows portion.
According to a second aspect of the present invention, the steering shaft according to the first aspect is characterized in that, in the invention according to the first aspect, an outer diameter of the valley portion of the bellows portion is larger than an outer diameter of both ends of the bellows portion. .

Thus, according to the steering shaft according to claim 1 of the present invention, the radius of curvature at the base of both ends of the bellows part is made larger than any of the curvature radii of the valleys excluding both ends of the bellows part. It is possible to reduce the stress at the base of both ends of the bellows part where the steering input or the reaction force against the steering input acts more, and to combine the shock absorbing function and durability together with the original shock absorbing function of the bellows part. Can do.
In the steering shaft according to claim 2 of the present invention, the root outer diameter of the bellows portion is made larger than the outer diameter of the bellows portion at both ends, thereby further reducing the stress at the root of the bellows portion. be able to.

Next, an embodiment of the steering shaft of the present invention will be described with reference to the drawings.
FIG. 1A is a schematic configuration diagram showing a normal state of a column type electric steering apparatus in which a bellows structure and a steering shaft of this embodiment are assembled, and FIG. 1B is a schematic configuration diagram showing a state at the time of deformation. is there. The column-type electric power steering apparatus 1 is configured to change the rotational motion of the steering shaft 4 to linear motion by the steering gear 3 and transmit the steering force of the steering wheel 2 to the steered wheels via a tie rod (not shown). Yes. The steering shaft 4 (which is actually divided in the steering column 5) is rotatably supported in the steering column 5, and the steering column 5 includes two lower side mounting portions 6 and an upper side mounting portion 7. It is attached to the vehicle body side member at the place.

 In this column type electric power steering apparatus 1, a steering assist mechanism is provided on the steering shaft 4, and the steering assist of the steering shaft 4 is performed via the speed reduction mechanism 9 by driving the motor 8. The output torque assisted by the motor 8 is transmitted to the intermediate shaft 11 via the first universal joint 10 provided at the lower end (left side in the figure) of the steering shaft 4, and the output torque provided at the lower end of the intermediate shaft 11. It is transmitted to the steering gear 3 through the two universal joints 12. At this time, since the torque assisted by the motor 8 is transmitted to the intermediate shaft 11, a larger torque is applied than the other steering devices. Therefore, as the collapsible shaft, it is desirable to use a metal bellows tube 13 that can freely determine expansion / contraction / bending characteristics and has excellent rotation transmission characteristics as the intermediate shaft 11. With this configuration, when a load is applied in the direction of the arrow in FIG. 1b due to a collision, the steering gear 3 moves backward so as to move to the right in the figure, and the bellows tube 13 is deformed accordingly. Thus, the impact is absorbed and the influence on the steering column 5 is prevented. On the other hand, if a heavy object such as the motor 8 or the speed reduction mechanism 9 is moved, the shock absorbing function may become unstable, so the lower side mounting portion 6 has a structure that does not separate at the time of a secondary collision. .

 FIG. 2 shows details of the bellows tube 13 of the column type electric power steering apparatus 1 of FIG. The bellows tube 13 is formed by, for example, bulging a metal cylindrical tube having a thickness of about 0.1 mm to 10 mm. Further, the bellows tube 13 of the present embodiment has the same curvature at the crest portion (portion protruding outside the bellows portion 16) 14 and the trough portion (portion retracted inside the bellows portion 16) 15 of the bellows portion 16. An arc cross section having a radius r was used, and the two were connected by a linear cross section (conical surface as an overall shape) oblique to the radial direction and the axial direction of the bellows tube 13. The pitch P of the bellows portion 16 is constant at 10 mm. In the present embodiment, the outer diameter d of the valley portion 15 of the bellows portion 16 and the outer diameter D of the cylindrical portion 18 connected to both ends of the bellows portion 16 are set equal to 34 mm.

 In the present embodiment, the base 17 at both ends of the bellows portion 16, that is, the curvature radius R of the connection portion between the bellows portion 16 and the cylindrical portion 18 at both ends thereof is calculated from the curvature radius r of the valley portion 15 of the bellows portion 16 described above. It is enlarged. FIG. 3 is prepared as a comparative example of the bellows tube 13 of FIG. 2, in which the curvature radius r of the root 17 at both ends of the bellows portion 16 is the same as the curvature radius r of the valley portion 15. For example, assuming that the right end of the bellows pipe 13 is connected to the steering wheel 2 side and the left end is connected to the steering gear 3 side (or vice versa), the right end of the bellows pipe 13 is perpendicular to the axis. As a result of analyzing the tensile stress when the load and the torque around the axis are applied by the finite element method, the stress σ17 of the root 17 at the left end of the bellows portion 16 to which the steering torque is inputted is the valley of the bellows portion 16 adjacent to the right. It was 1.05 times the stress σ15 of the portion 15. Therefore, in FIG. 2, the curvature radius R (specifically, 2.5 mm) of the root 17 at both ends of the bellows portion 16 is 1.25 times the curvature radius r (specifically, 2.0 mm) of the valley portion 15. As a result, the stress σ 17 of the root 17 at the left end of the bellows portion 16 to which the steering torque is input can be made substantially equal to the stress σ 15 of the valley portion 15 of the bellows portion 16 adjacent to the right. As a result, the durability of the bellows tube 13 can be improved, and both the bellows portion 16 and the original shock absorbing function can be achieved. The numerical values of the curvature radii R and r are not limited to the above, and the effect of the present invention can be obtained if R> r.

 Further, in order to make the stress with respect to the steering torque equal at the root 17 and the valley 15 of the bellows portion 16, the left end root 17 of the bellows portion 16 to which the steering torque is inputted (the root of one end portion of the bellows portion). It is sufficient to increase only the radius of curvature R of this, but if so, there is a risk that the orientation of the bellows tube 13 will be wrongly assembled. In the present embodiment, since the curvature radius R of the root 17 at both ends of the bellows portion 16 is made larger than the curvature radius r of the valley portion 15, the orientation of the bellows tube 13 is not erroneously assembled.

 FIG. 4 shows another embodiment of the bellows tube 13 used in the steering shaft of the present invention. In this embodiment, the outer diameter d of the valley portion 15 of the bellows portion 16 is as large as 36 mm with respect to the bellows tube 13 of FIG. The pitch P = 10 mm of the bellows portion 16 and the outer diameter D = 34 mm of the cylindrical portion 18 at both ends of the bellows portion 16 are the same. In this embodiment, the stress σ17 of the root 17 at the left end of the bellows portion 16 to which the steering torque when the radius of curvature R at the both ends of the bellows portion 16 is the same as the curvature radius r of the valley portion 15 is The stress σ15 of the valley portion 15 of the bellows portion 16 on the right side was 1.1 times. Therefore, in the present embodiment, the radius of curvature R (specifically, 2.8 mm) of the root 17 at both ends of the bellows portion 16 is 1.4 times the radius of curvature r (specifically, 2.0 mm) of the valley portion 15. As a result, the stress σ 17 of the root 17 at the left end of the bellows portion 16 to which the steering torque is input can be made equal to the stress σ 15 of the valley portion 15 of the bellows portion 16 adjacent to the right. The numerical values of the curvature radii R and r are not limited to the above, and the effect of the present invention can be obtained if R> r.

 That is, as compared with the embodiment of FIG. 2, the base of the left end of the bellows portion 16 to which the steering torque is inputted when the radius of curvature R of both ends of the bellows portion 16 is the same as the radius of curvature r of the valley portion 15 is input. The ratio of the stress σ17 of 17 to the stress σ15 of the valley portion 15 of the bellows portion 16 adjacent to the right is increased because the outer diameter d of the valley portion 15 of the bellows portion 16 is increased. This is because the stress σ 15 of 15 is reduced. Therefore, the curvature radius R of the root 17 at both ends of the bellows portion 16 is set to 1.4 times the curvature radius r of the valley portion 15, and the stress σ17 of the root 17 at the left end of the bellows portion 16 to which the steering torque is input is If the stress σ15 of the valley portion 15 of the bellows portion 16 adjacent to the right is made equal, the stress σ17 of the root 17 can also be made smaller than that of the embodiment of FIG. As a result, the durability of the bellows tube 13 can be further improved, and both the bellows portion 16 and the original shock absorbing function can be achieved.

 FIG. 5 shows still another embodiment of the bellows pipe 13 used in the steering shaft of the present invention. In this embodiment, the outer diameter D of the cylindrical portion 18 at both ends of the bellows portion 16 is made equal to the outer diameter of the peak portion 14 of the bellows portion 16 with respect to the bellows tube 13 of FIG. FIG. 6 shows still another embodiment of the bellows pipe 13 used in the steering shaft of the present invention. In this embodiment, the outer diameter D of the cylindrical portion 18 at both ends of the bellows portion 16 is larger than the outer diameter of the peak portion 14 of the bellows portion 16 with respect to the bellows tube 13 of FIG. In any case, the outer diameter D of the cylindrical portion 18 is larger than the outer diameter d of the valley portion 15 of the bellows portion 16. And also in these embodiments, durability of the bellows pipe 13 is improved by making the radius of curvature R of the root 17 at both ends of the bellows portion 16 larger than the radius of curvature r of any valley portion 15 of the bellows portion 16. It was possible to achieve both the bellows part 16 and the original shock absorbing function.

In all the embodiments, the pitch of the bellows portion does not need to be constant, and may be a pitch of unequal intervals.
In the above embodiment, only the example of the column type electric power steering apparatus has been described in detail. However, the present invention can be applied to a hydraulic power steering apparatus or a steering apparatus without an assist mechanism.

It is a schematic block diagram which shows one Embodiment of the column type electric power steering apparatus using the bellows structure and steering shaft of this invention, (a) is normal, (b) shows the state at the time of a collision. It is a longitudinal cross-sectional view which shows one Embodiment of the bellows pipe | tube used for the column type electric power steering apparatus of FIG. It is a longitudinal cross-sectional view which shows the comparative example of the bellows pipe | tube of FIG. It is a longitudinal cross-sectional view which shows other embodiment of the bellows pipe | tube used for the column type electric power steering apparatus of FIG. It is a longitudinal cross-sectional view which shows further another embodiment of the bellows pipe | tube used for the column type electric power steering apparatus of FIG. It is a longitudinal cross-sectional view which shows further another embodiment of the bellows pipe | tube used for the column type electric power steering apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 is a column type electric power steering device 2 is a steering wheel 3 is a steering gear 4 is a steering shaft 5 is a steering column 6 is a lower side mounting portion 7 is an upper side mounting portion 8 is a motor 9 is a speed reduction mechanism 10 is a first universal joint 11 is an intermediate shaft 12 is a second universal joint 13 is a bellows tube 14 is a peak 15 is a valley 16 is a bellows (bellows)
17 is the base 18 is the cylindrical part

Claims (2)

  In a steering shaft disposed in a steering force transmission path from a steering wheel to a steering gear and having a bellows portion formed of a plurality of large-diameter portions and small-diameter portions, the radius of curvature of the base at both ends of the bellows portion is the bellows A steering shaft characterized by being larger than any curvature radius of a trough excluding both ends of the portion.  The steering shaft according to claim 1, wherein an outer diameter of a valley portion of the bellows portion is larger than an outer diameter of both ends of the bellows portion.

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