JP2007145062A - 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: Stress at both ends of the bellows portion 16 is reduced to improve the durability by making pitches PR, PL at both ends of the bellows portion larger than a pitch PC at the center portion in an axial direction of the bellows portion 16 of the bellows tube 13 to obtain the original shock absorption function of the bellows portion 16. Besides, the stress generated at the bellows portion 16 is made roughly constant by gradually increasing the pitches of the bellows portion 16 from the center portion to both the ends in the axial direction, thus improving the durability over the total length of the bellows portion 16. <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 impact is collapsible, that is, deforms to absorb the impact, 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, it is necessary to reduce the bending load on the entire bellows part for absorbing the impact, and it is necessary to reduce the stress generated in the bellows part for durability. 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 pitch at both ends of the bellows portion is larger than the pitch of the bellows at the central portion in the axial direction.

The pitch of the bellows indicates a distance between adjacent mountain portions (portions protruding outside the bellows portion) of the bellows portions, or a distance between adjacent valley portions (portions recessed inside the bellows portion). . The steering shaft according to the first aspect of the present invention is characterized in that both ends are larger than the pitch of the bellows in the central portion in the axial direction of the bellows.
According to a second aspect of the present invention, the steering shaft according to the first aspect is characterized in that, in the first aspect, the pitch of the bellows is gradually increased from the axial center to both ends.

Thus, according to the steering shaft according to claim 1 of the present invention, the pitch of both ends of the bellows portion is made larger than the pitch of the bellows at the central portion in the axial direction, so The stress at both ends of the bellows part where the reaction force acts more can be reduced, and in addition to the original shock absorbing function of the bellows part, both the shock absorbing function and durability can be achieved.
Further, according to the steering shaft of the present invention, the pitch of the bellows is gradually increased from the axial center to both ends, so that the stress can be reduced in the entire bellows.

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 a circular cross section of a crest portion (portion protruding outside the bellows portion 16) 14 and a valley portion (portion retracted inside the bellows portion 16) 15 of the bellows portion 16. Both were connected by the linear cross section (conical surface as a whole shape) diagonal to the radial direction and the axial direction of the bellows tube 13. The outer diameter D of the peak portion 14 of the bellows portion 16 is 44 mm, and the outer diameter d of the valley portion 15 of the bellows portion 16 and the outer diameter 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 pitches PL and PR at both ends of the bellows portion 16 are made larger than the bellows pitch PC at the axially central portion and gradually increased from the axially central portion to both ends. Specifically, the pitch PC at the center is 10 mm, the adjacent pitches PCR and PCL are 10.4 mm, and the pitches PR and PL at both ends are 10.8 mm. FIG. 3 is prepared as a comparative example of the bellows tube 13 of FIG. 2, and the pitch P of the bellows portion 16 is fixed to 10 mm. For example, assuming that the right end of the bellows tube 13 is connected to the steering wheel 2 side and the left end is connected to the steering gear 3 side, the right end portion of the bellows tube 13 and the axis perpendicular direction are loaded to the right end portion. As a result of analyzing the tensile stress when the moment is applied by the finite element method, the stress σL of the valley 15 at the left end of the bellows portion 16, the stress σCL of the valley 15 adjacent to the right, the stress of the valley 15 at the center The ratio to σC was 1.10: 1.05: 1.00. On the other hand, in FIG. 2, the pitch PC at the center of the bellows portion 16 is 10 mm, the pitch PCR and PCL on both sides thereof are 10.4 mm, and the pitches PR and PL at both ends are 10.8 mm. The ratio of the stress σL of the portion 15, the stress σCL of the valley portion 15 adjacent to the right side thereof, and the stress σC of the valley portion 15 at the center portion was 1.00: 1.00: 1.00. As a result, the durability of the bellows pipe 13 can be improved over the entire length in the axial direction, and both the impact absorbing function of the bellows part 16 can be achieved.

In this embodiment, the pitch PC at the center of the bellows portion 16 is 10 mm, the pitch PCR and PCL on both sides thereof are 10.4 mm, and the pitches PR and PL at both ends are 10.8 mm. The corners R of the portion 14 and the valley portion 15 can be increased, thereby further reducing the stress.
As shown in FIG. 2, when one end of the bellows tube 13 is supported and a right-angle load and moment are applied only to the other end, only the pitch of the bellows on the support side is increased. Although it is good in such a case, there exists a possibility that the direction of the bellows pipe | tube 13 may be assembled | attached accidentally. In the present embodiment, the bellows pipe 13 is not mistakenly assembled by making the bellows pitch at both ends of the bellows part 16 larger than the central part.

FIG. 4 shows another embodiment of the bellows tube 13 used in the steering shaft of the present invention. In this embodiment, only the pitch PC at the central portion in the axial direction of the bellows portion 16 is smaller than the bellows tube 13 in FIG. 2, and the pitches PCR and PCL on both sides and the pitches PR and PL on both ends are made equal and larger. According to this embodiment, the durability cannot be improved over the entire axial length as in the embodiment of FIG. 2, but at least the stress at both ends of the bellows portion 16 can be reduced, so the durability is also improved.
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.

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)
18 is a cylindrical part

Claims (2)

  In a steering shaft disposed in a steering force transmission path from a steering wheel to a steering gear and formed with a bellows portion composed of a plurality of large diameter portions and small diameter portions, of the bellows portions, the bellows of the central portion in the axial direction. A steering shaft characterized in that the pitch at both ends is larger than the pitch.   2. The steering shaft according to claim 1, wherein the pitch of the bellows is gradually increased from the axial center to both ends.

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