JP5626431B2 - Method for manufacturing shock absorbing steering shaft - Google Patents

Description

The present invention relates to an improvement in a manufacturing method of an impact absorption type steering shaft constituting an automobile steering device. Specifically, when manufacturing this steering shaft, the occurrence of galling between the inner edge of the inner shaft and the outer peripheral surface of the outer shaft is prevented, thereby suppressing an increase in the manufacturing cost of the steering shaft. On the other hand, a manufacturing method capable of stabilizing the shock absorbing performance is realized. Note that the steering shaft that is an object of the present invention includes not only a shaft supported on the inside of the steering column but also an intermediate shaft disposed on the front side of the steering column.

For example, a structure as shown in FIG. 5 is widely known as a steering device for giving a steering angle to a steered wheel (usually a front wheel except for a special vehicle such as a forklift). In this steering device, a steering shaft 3 is rotatably supported on the inner diameter side of a cylindrical steering column 2 supported by a vehicle body 1. A steering wheel 4 is fixed to the rear end portion of the steering shaft 3 protruding rearward from the rear end opening of the steering column 2. When the steering wheel 4 is rotated, this rotation is transmitted to the input shaft 8 of the steering gear unit 7 via the steering shaft 3, the universal joint 5a, the intermediate shaft 6, and the universal joint 5b. When the input shaft 8 rotates, a pair of tie rods 9, 9 arranged on both sides of the steering gear unit 7 are pushed and pulled, and a steering wheel according to the operation amount of the steering wheel 4 is turned to a pair of left and right steering wheels. Give a corner. In the case of the structure shown in FIG. 5 , the steering column 2 and the steering shaft 3 are extendable so that the front and rear positions of the steering wheel 4 can be adjusted. In addition, in recent years, an electric power steering apparatus in which the electric motor 10 is incorporated as an auxiliary power source in the steering apparatus as described above has also become widespread.

The steering column 2 and the steering shaft 3 are configured to displace the steering wheel 4 while absorbing impact energy in the event of a collision. That is, in the event of a collision accident, a secondary collision in which the driver's body collides with the steering wheel 4 occurs following a primary collision in which the automobile collides with another automobile or the like. In order to alleviate the impact applied to the driver's body during the secondary collision and to protect the driver, the steering shaft 3 supporting the steering wheel 4 is subjected to the secondary collision with respect to the vehicle body 1. It is necessary to support it so that it can be displaced forward by a forward impact load. For this reason, the steering column 2 is contracted by the impact load of the secondary collision, the outer column 11 is shortened by the entire length of the steering column 2, and the steering shaft 3 is contracted by the outer shaft 12 by the total length of the steering shaft 3. However, a large impact is prevented from being applied to the driver's body colliding with the steering wheel 4 by being displaced forward.
The outer column and the inner column that constitute the telescopic steering column as described above, and the front and rear positions of the outer shaft and the inner shaft that constitute the steering shaft may be opposite to the illustrated structure. As a technique for manufacturing the telescopic steering shaft as described above, there are techniques described in Patent Documents 1 and 2, for example.

6 to 9 show a conventional example of an impact absorbing steering shaft and a manufacturing method thereof described in Patent Document 1 among them. The steering shaft 3a is configured such that the outer shaft 12a and the inner shaft 13 are engaged with each other so as to be relatively displaceable in the axial direction, and the total length is shortened by an impact load applied in the axial direction at the time of a secondary collision.
The outer shaft 12a is formed into a tubular shape as a whole, and a small diameter portion 14 is formed at one end portion by drawing one end portion (left end portion in FIGS. 6 to 7 ). A female serration 15 is formed on the inner peripheral surface of the small diameter portion 14. Further, the inner shaft 13 is also formed in a circular tube shape as a whole, and a large-diameter portion 16 is formed at one end portion by expanding one end portion (the right end portion in FIGS. 6 to 7 ). A male serration 17 that engages with the female serration 15 is formed on the outer peripheral surface of the large diameter portion 16.

When the steering shaft 3a as shown in FIG. 6 is manufactured by combining the outer shaft 12a and the inner shaft 13 as described above, first, as shown in FIG. 7 , the female serration 15 and the male serration 17 Are engaged with each other at the distal end portion (left end portion in FIG. 7 ) of the small diameter portion 14 and the distal end portion (right end portion in FIG. 7 ) of the large diameter portion 16.
And the outer peripheral surface of the front-end | tip part of the said small diameter part 14 is pressed to radial direction inward with the said both serrations 15 and 17 being mutually engaged. That is, a pair of pressing pieces 18, 18 are arranged around the distal end portion of the small diameter portion 14 and the distal end portion of the large diameter portion 16, and the two small pressing portions 18, 18 are brought close to each other, whereby the small diameter portion 14 strongly presses the outer peripheral surface of the tip portion. On the inner side surfaces of these pressing pieces 18, 18 are formed recesses 19, 19 in which the cross-sectional shape of the portion contacting the outer peripheral surface is arcuate in the portion contacting the outer peripheral surface of the tip of the small diameter portion 14 doing.

As shown in FIG. 8 , in a state where both the concave portions 19 and 19 are lightly brought into contact with the outer peripheral surface of the distal end portion of the small diameter portion 14, the thickness is between the end surfaces of the both pressing pieces 18 and 18. T gaps 20 and 20 are formed. From this state, both the pressing pieces 18, 18 are strongly pressed in a direction approaching each other by a pressing device (not shown). Then, as shown in FIG. 9 , the pressing pieces 18, 18 are brought close to each other until the thickness of the gaps 20, 20 becomes 0, and the cross-sectional shape of the distal end portion of the small diameter portion 14 is shown in FIG. 9. It is plastically deformed into an oval shape as shown in. At the same time, the distal end portion of the large diameter portion 16 inserted into the distal end portion of the small diameter portion 14 is also pressed through the both serrations 15 and 17, and the sectional shape of the distal end portion of the large diameter portion 16 is also shown in FIG. Plastically deform into an elliptical shape as shown.

In this way, if the distal end portion of the small diameter portion 14 and the distal end portion of the large diameter portion 16 are pressed radially inward, and the cross-sectional shape of both the distal end portions is plastically deformed into an elliptical shape, then, The outer shaft 12a and the inner shaft 13 are relatively displaced in the axial direction so as to approach each other. That is, after the outer shaft 12a and the inner shaft 13 are taken out from the pressing pieces 18, 18, the outer shaft 12a is moved to the left in FIG. The relative displacement is made. Then, as shown in FIG. 6 , the distal end portion of the small diameter portion 14 is press-fitted into the proximal end portion of the large diameter portion 16, and the distal end portion of the large diameter portion 16 is replaced with the proximal end portion of the small diameter portion 14. Press-fit into. The intermediate portion of the small diameter portion 14 and the intermediate portion of the large diameter portion 16 that are not plastically deformed by the two pressing pieces 18 and 18 are loosely engaged with each other.
Since the inner shaft 13 constituting the shock absorbing steering shaft as described above has a smaller outer diameter than the outer shaft 12a, it is often formed of carbon steel having a high hardness such as S35C in order to ensure strength. Alternatively, it can be formed of a carbon steel pipe such as STKM12B. In this case, the radial thickness is increased in order to ensure strength.

Although the above description has been given with respect to the steering shaft 3 that fixes the steering wheel 4 (see FIG. 5 ) to the rear end portion, the intermediate shaft 6 disposed in the front side portion of the steering device is similarly axially arranged. It may be configured to be shrinkable. Such a contraction type (shock absorption type) intermediate shaft 6 reduces the total length of the steering wheel 4 from the impact load associated with the primary collision at the time of the primary collision when the automobile collides with another automobile or the like. The driver is prevented from being pushed up to protect the driver. The intermediate shaft 6 transmits the output torque of the electric motor 10 as an auxiliary power source in addition to the torque applied from the steering wheel 4 to the steering shaft 3 by the operation of the driver. For this reason, when the shock absorbing steering shaft as described above is applied to the intermediate shaft 6, the holding force (fitting strength) of the engaging portion between the outer shaft 12a and the inner shaft 13 is increased, and the durability is improved. Need to be high. As a result, the contact pressure between the outer peripheral edge (sharp edge) of the distal end portion of the large-diameter portion 16 and the inner peripheral surface of the small-diameter portion 14 increases, and the method for manufacturing the shock absorbing steering shaft as described above When the outer shaft 12a and the inner shaft 13 are relatively displaced in the axial direction in the direction approaching each other, galling is likely to occur at the outer peripheral edge of the distal end portion of the large diameter portion 16. That is, at the time of this relative displacement, the long diameter portion of the outer peripheral edge of the distal end portion of the large diameter portion 16 having an elliptical cross-sectional shape and the inner peripheral surface of the small diameter portion 14 having a circular cross sectional shape are strongly rubbed. The outer peripheral edge of the tip portion bites into the inner peripheral surface of the small diameter portion 14. If the galling generated in this way is left unattended, the energy absorption performance in the event of a collision may become unstable. Therefore, in order to stabilize the energy absorption performance, it is necessary to remove a surplus portion (peeling portion) generated by galling by cutting or the like. Also, depending on the degree of galling, the completed shock absorbing steering shaft must be discarded as a defective product, which increases manufacturing costs due to increased processing effort and yield, and improvements are desired. . In particular, in the case of the intermediate shaft 6, as described above, there is a great need for improvement in order to increase the contact pressure of the fitting portion in order to secure the holding force.

Japanese Patent No. 3168841 Japanese Patent No. 3716590

In view of the circumstances as described above, the present invention is an impact-absorbing steering system in which an outer shaft and an inner shaft are coupled to each other so as to be capable of relative displacement in the axial direction in accordance with an impact load applied during a secondary collision. When manufacturing the shaft, it prevents the occurrence of galling between the outer peripheral edge of the tip of the inner shaft and the inner peripheral surface of the outer shaft, while suppressing the increase in processing and the occurrence of defective products, The invention was invented to realize a manufacturing method capable of suppressing an increase in manufacturing cost so as to obtain an impact absorbing steering shaft having stable energy absorbing performance.

In the manufacturing method of the shock absorbing steering shaft of the present invention, the outer peripheral surface of the outer shaft front end is engaged with a pair of pressing pieces while the outer shaft front end and the inner shaft front end are engaged. The inner shaft is pressed inward (in the direction in which the opposite positions in the radial direction approach each other), and the distal end portion of the outer shaft and the distal end portion of the inner shaft are in the radial direction (the pressing direction is the short diameter and the perpendicular direction is the long diameter). Plastic deformation). Next, the shafts are relatively displaced in the axial direction so as to approach each other. And the front-end | tip part of the said outer shaft is press-fitted and fitted to the intermediate part of the said inner shaft, and the front-end | tip part of this inner shaft is each press-fitted to the intermediate part of this outer shaft. A portion between the front end portion and the intermediate portion of the outer shaft and a portion between the front end portion and the intermediate portion of the inner shaft are loosely engaged with each other.
In particular, in the manufacturing method of the shock absorbing type steering shaft of the present invention, the inner shaft has a circular tubular shape, and the tip edge portion of the inner shaft is formed by drawing the tip edge portion of the inner shaft. A part provided with a throttle part that gradually decreases as the outer diameter and inner diameter approach the tip edge and has a constant thickness dimension in the radial direction is used. When the distal end portion of the outer shaft and the distal end portion of the inner shaft are plastically deformed in the radial direction, the proximal end portion of the throttle portion is positioned radially inward of the axial intermediate portion of the two pressing pieces. .

When the shock absorbing steering shaft manufacturing method of the present invention as described above is carried out, for example, as in the invention described in claim 2 , at least one small diameter portion having a small inner diameter is provided at one end portion as the outer shaft. As the inner shaft, at least one large-diameter portion having a large outer diameter is provided at one end portion, and at least the outer diameter of the portion close to the tip edge of the tip portion of the large-diameter portion is small toward the tip edge. Use each one. Then, with the tip portion of the small diameter portion and the tip portion of the large diameter portion engaged, the outer peripheral surface of the tip portion of the small diameter portion is directed radially inward (in the direction in which the opposite radial positions approach each other). ) Press and plastically deform the tip of the small-diameter portion and the tip of the large-diameter portion in the radial direction (in a cross-sectional ellipse in which the pressing direction is the short diameter and the direction perpendicular thereto is the long diameter). Next, the shafts are relatively displaced in the axial direction so as to approach each other, the distal end portion of the small diameter portion is the proximal end portion of the large diameter portion, and the distal end portion of the large diameter portion is the proximal end portion of the small diameter portion The intermediate portion of the small diameter portion and the intermediate portion of the large diameter portion are loosely engaged with each other.

According to the shock absorbing steering shaft manufacturing method of the present invention configured as described above, galling occurs between the tip edge of the inner shaft and the inner peripheral surface of the outer shaft when the steering shaft is manufactured. It is possible to assemble an impact-absorbing steering shaft that can exhibit excellent impact energy absorption performance while suppressing the increase in processing effort and the occurrence of defective products, and suppressing the increase in the manufacturing cost of the steering shaft Thus , the shock absorbing steering shaft can be manufactured industrially efficiently . This is because the inner shaft has a narrowed portion that decreases as the outer diameter of the inner shaft approaches the leading edge, so that when the shock absorbing steering shaft is manufactured, the inner edge of the inner shaft This is because it is possible to prevent galling between the inner peripheral surface of the outer shaft. In other words, since the outer diameter of the inner edge of the inner shaft (throttle portion) decreases toward the distal edge, the outer peripheral edge (sharp edge) of the inner shaft and the inner peripheral surface of the outer shaft are in contact with each other. Do not touch (do not rub). Of the tip edge portion of the inner shaft, the portion of the inner shaft that contacts the inner peripheral surface of the outer shaft has a large cross-sectional radius of curvature (or a small inclination angle with respect to the inner peripheral surface of the outer shaft). The abutting pressure between the tip edge portion and the inner peripheral surface of the outer shaft can be reduced. For this reason, when these two shafts are relatively displaced in the axial direction in the direction of approaching each other, the friction acting between the tip edge portion of the inner shaft and the inner peripheral surface of the outer shaft can be reduced. The tip edge portion can be prevented from biting into the inner peripheral surface, and the occurrence of the galling can be prevented. In particular, in the case of the present invention, when the distal end portion of the outer shaft and the distal end portion of the inner shaft are plastically deformed in the radial direction, the base end portion of the throttle portion is the diameter of the axial intermediate portion of the two pressing pieces. It is located inward. For this reason, it is possible to appropriately control the force that presses the throttle portion provided at the tip edge portion of the inner shaft inward in the radial direction (prevents becoming larger than the intermediate portion).

Sectional drawing of a steering shaft which shows the 1st example of the reference example regarding this invention. Similarly, the same figure as FIG. Sectional drawing which takes out and shows the inner shaft which shows the 2nd example of the reference example regarding this invention. The figure similar to FIG. 2 which shows an example of embodiment of this invention . The side view which shows one example of the steering device conventionally known in the state which cut | disconnected a part. Sectional drawing which shows one example of the conventional structure of the shock absorption type steering shaft used as the object of this invention. Sectional drawing which shows the state which engaged the front-end | tip part of the inner shaft, and the front-end | tip part of the outer shaft at the time of manufacture of a conventional structure. XX sectional drawing of FIG. FIG. 9 is a view similar to FIG. 8, showing a state where both the tip portions are plastically deformed radially inward by a pair of pressing pieces.

[First example of reference example ]
1 and 2 show a first example of a reference example related to the present invention . In addition, including the present reference example , the shock absorbing type steering shaft manufacturing method according to the present invention is characterized in that galling is prevented between the tip edge of the inner shaft 13a and the inner peripheral surface of the outer shaft 12a. In order to realize a manufacturing method that can suppress an increase in manufacturing cost by assembling an impact absorbing steering shaft that can exhibit excellent impact energy absorption performance while suppressing an increase in processing time and occurrence of defective products is there. Construction and operation of the other parts, including the structure and the manufacturing method thereof illustrated in Figures 6-9 described above, because it is similar to the shock absorbing type steering shaft, and a manufacturing method thereof is known in the art, relates to similar parts The illustration and description will be omitted or simplified, and the following description will focus on the features of this reference example .

In the case of the structure of this reference example , the rear end portion (right side in FIGS. 1 and 2) constituting the steering shaft 3b has a larger outer diameter than the front end portion (left side in FIGS. 1 and 2). A diameter portion 16a is provided. Such a large diameter portion 16a is formed by cutting the outer peripheral surface of the front end portion of the inner shaft 13a. Alternatively, if the inner shaft 13a is circular, it may be formed by expanding the rear end portion of the inner shaft 13a as in the case of the conventional structure described above. Alternatively, if the inner shaft 13a can be inserted into the inner diameter side of the outer shaft 12a, the outer diameter of the inner shaft 13a may be the same over the entire axial length without providing the large diameter portion 16a. it can. However, in this case, male serrations 17 are formed on the outer peripheral surface of the inner shaft 13a over the entire length in the axial direction in order to prevent the shrinkage load of the steering shaft 3b from becoming excessive.
A small-diameter portion 14 having an inner diameter smaller than that of the rear end portion (right side in FIGS. 1 and 2) is provided at the front end portion (left side in FIGS. 1 and 2) of the outer shaft 12a. Such a small-diameter portion 14 is formed by drawing the front end portion of the outer shaft 12a which is tubular like the conventional structure described above, or by cutting the inner peripheral surface of the rear end portion. To do. Alternatively, if the inner shaft 13a can be inserted into the inner diameter side of the outer shaft 12a, the inner diameter of the outer shaft 12a can be made the same over the entire length in the axial direction without providing the small diameter portion 14. However, in this case, in order to prevent the shrinkage load of the steering shaft 3b from becoming excessive, a female serration that engages with the male serration 17 over the entire length in the axial direction on the inner peripheral surface of the outer shaft 12a. 15 is formed.
In the case of the structure of this reference example shown in FIGS. 1 and 2, by cutting the outer peripheral surface of the front end portion of the inner shaft 13a, the large-diameter portion 16a is drawn at the rear end portion, and the front end portion of the outer shaft 12a is narrowed down. Each of the small diameter portions 14 is provided by processing.

Furthermore, by providing a chamfered portion 21 having a partial arc shape (R shape) in cross-section at the outer peripheral edge (right side in FIGS. 1 and 2) of the distal end portion of the large diameter portion 16a, the distal end portion of the large diameter portion 16a is provided. The outer diameter is made smaller (decrease gradually) toward the tip edge (right side in FIGS. 1 and 2) of the large-diameter portion 16a. In the case of this reference example , a concave hole 22 is provided at the tip end portion (the right end portion in FIGS. 1 and 2) of the large diameter portion 16a of the inner shaft 13a, and as will be described later, When the distal end portion of the small-diameter portion 14 and the distal end portion of the large-diameter portion 16a are plastically deformed in the radial direction, the required pressing force is not excessively increased.

In order to manufacture the shock absorbing steering shaft of this reference example configured as described above, first, as shown in FIG. 2, the tip of the large diameter portion 16 a is engaged with the tip of the small diameter portion 14. . Then, the outer peripheral surface of the distal end portion of the small diameter portion 14 is pressed radially inward by the two pressing pieces 18 and 18, as in the case of FIG. 8 → 9 showing an example of the conventional structure described above, the The distal end portion of the small-diameter portion 14 and the distal end portion of the large-diameter portion 16a are plastically deformed in the radial direction so that a cross-sectional shape related to a virtual plane orthogonal to the central axis of the steering shaft 3b is an ellipse. At this time, the pressing force for pressing both the pressing pieces 18, 18 may be adjusted. That is, the thicknesses of the gaps 20 and 20 (see FIG. 8 ) between the end faces of both the pressing pieces 18 and 18 are set to positive values in the state where both the tip portions are plastically deformed (the gaps 20 and 20 are set to be the same). The amount of deformation of both the tip portions can be adjusted. Further, the shape of the outer peripheral surface abutting portion of the tip portion of the small diameter portion 14 at the inner surfaces of the both pressing pieces 18 and 18, such cross-section shown in FIG. 8-9 arcuate recesses 19 and 19 described above Not limited to this, as long as the radially opposite positions of the outer peripheral surface of the distal end portion of the small-diameter portion 14 can be pressed toward each other, the plane or the cross-sectional shape can be a V-shaped surface or the like. Furthermore, even when the cross-sectional arc shape is used, the magnitude relationship with the curvature radius of the outer peripheral surface of the tip end portion of the small diameter portion 14 may be any. The base end portion (large-diameter side end portion) of the chamfered portion 21 is formed by the pressing pieces 18 and 18 when the outer shaft 12a and the inner shaft 13a are pressed by the pressing pieces 18 and 18. It is located inward in the radial direction of the axially intermediate portion (within the thickness range of both the pressing pieces 18, 18). If the engaging portion between the two tip portions is plastically deformed, then the outer shaft 12a and the inner shaft 13a are relatively displaced in the axial direction, and the tip portion of the small diameter portion 14 is moved to the large diameter portion 16a. The base end portion of the small-diameter portion 14 is press-fitted into the base end portion of the large-diameter portion 16a. Further, the intermediate portion of the small diameter portion 14 and the intermediate portion of the large diameter portion 16a are loosely fitted to each other.

According to the shock absorbing steering shaft and the manufacturing method thereof of the present embodiment configured as described above, when manufacturing the steering shaft 3b, the leading edge of the large-diameter portion 16a of the inner shaft 13a and the outer shaft 12a Assembling an impact-absorbing steering shaft that prevents the occurrence of galling with the inner peripheral surface of the small-diameter portion 14 and suppresses an increase in the manufacturing cost of the steering shaft 3b and exhibits excellent impact energy absorption performance. I can do things. The reason for this is that by providing a chamfered portion 21 having a partial arc shape (R shape) in the outer peripheral edge of the distal end portion of the large-diameter portion 16a, out of the distal end edge portion of the distal end portion of the large-diameter portion 16a. This is because the diameter is made smaller toward the leading edge of the large diameter portion 16a. Since such a configuration is adopted, when the steering shaft 3b is manufactured, when the outer shaft 12a and the inner shaft 13a are relatively displaced in the axial direction in a direction approaching each other, the large-diameter portion 16a. The tip edge of the small diameter portion and the inner peripheral surface of the small diameter portion 14 do not rub against each other. That is, since the outer diameter of the tip edge portion of the large diameter portion 16a is small, the outer peripheral edge (sharp edge) of the large diameter portion 16a and the inner peripheral surface of the small diameter portion 14 are not matched. Do not touch. Of the leading edge portion of the large-diameter portion 16a, an R-shaped chamfered portion 21 is provided at a portion that contacts the inner peripheral surface of the small-diameter portion 14, and the curvature radius of the cross-sectional shape is increased. The contact pressure between the edge portion and the inner peripheral surface of the small diameter portion 14 is low. Therefore, when the shafts 12a and 13a are relatively displaced, the frictional force acting between the tip edge portion of the large-diameter portion 16a and the inner peripheral surface of the small-diameter portion 14 can be reduced. The leading edge portion can be prevented from biting into the inner peripheral surface, and the occurrence of a surplus portion due to galling on the inner peripheral surface can be prevented.

  The base end portion (large-diameter side end portion) of the chamfered portion 21 is radially inward of the intermediate portion in the axial direction of the pressing pieces 18 and 18 when the shafts 12a and 13a are plastically deformed. Therefore, the force of pressing the portion whose outer diameter is small at the tip edge portion of the large diameter portion 16a inward in the radial direction is appropriately controlled (preventing becoming larger than the intermediate portion) it can. As a result, it is possible to more stably prevent galling at the rubbing portion between the tip edge of the large diameter portion 16a and the inner peripheral surface of the small diameter portion 14.

[Second example of reference example ]
FIG. 3 shows a second example of a reference example relating to the present invention . In the case of this reference example , the outer diameter of the tip edge portion becomes smaller toward the tip edge portion (right side in FIG. 3) of the large diameter portion 16b of the inner shaft 13b toward the tip edge of the large diameter portion 16b. In addition, a tapered surface portion 23 having a straight line shape (partial conical surface shape) is provided. The taper angle θ of the taper surface portion 23 is 60 degrees or less in order to reduce the contact pressure between the taper surface portion 23 and the inner peripheral surface of the small diameter portion 14 (see FIGS. 1-2 and 6-9 ) of the outer shaft 12a. It is desirable that When the taper angle θ is larger than 60 degrees, the angle of the continuous portion between the proximal end portion of the tapered surface portion 23 and the intermediate portion of the large diameter portion 16b becomes small (less than 150 degrees). The contact pressure with the inner peripheral surface of the small diameter portion 14 may increase. As a result, it may not be possible to prevent galling at the rubbing portion between the continuous portion and the inner peripheral surface of the small diameter portion 14.

Further, in the case of the present reference example , a chamfered portion 21 a having a partial arc shape (R shape) in cross section is formed on the continuous portion, which is the base end portion (large diameter side end portion) of the tapered surface portion 23. Provided. In the case of this reference example , the angle of the continuous part is increased (150 degrees or more) and the chamfered part 21a is provided in the continuous part, so that the continuous part and the inner circumference of the small diameter part 14 are provided. The surface pressure of the contact portion with the surface is suppressed to be lower, and the occurrence of galling at the contact portion can be suppressed more effectively. The base end portion (large-diameter side end portion) of the chamfered portion 21a is an intermediate portion in the axial direction of the pair of pressing pieces 18, 18 when the shafts 12a, 13b are plastically deformed. It is positioned radially inwardly within the thickness range of the pieces 18, 18.
Since the configuration and operation of the other parts are the same as those in the first example of the reference example described above, the same parts are denoted by the same reference numerals, and redundant description is omitted.

[Example of Embodiment]
FIG. 4 shows an example of an embodiment of the present invention. In the case of this example, the inner shaft 13c is formed in a circular tube shape, and a large-diameter portion 16c is provided at one end portion (the right end portion in FIG. 4) of the inner shaft 13c. Then, by drawing the tip edge portion of the large diameter portion 16c, the outer diameter and inner diameter of the tip edge portion of the large diameter portion 16c gradually decrease toward the tip edge (right side in FIG. 4). In addition, an aperture 24 is provided. When the outer shaft 12a and the inner shaft 13c are plastically deformed, the base end portion (large diameter side end portion) of the narrowed portion 24 is an axially intermediate portion of the pair of pressing pieces 18, 18 (both of these pressing portions). It is positioned radially inwardly within the thickness range of the pieces 18, 18.
Since the configuration and operation of the other parts are the same as those of the first example of the reference example described above, the same parts are denoted by the same reference numerals, and redundant description is omitted.

DESCRIPTION OF SYMBOLS 1 Car body 2 Steering column 3, 3a-3b Steering shaft 4 Steering wheel 5a, 5b Universal joint 6 Intermediate shaft 7 Steering gear unit 8 Input shaft 9 Tie rod 10 Electric motor 11 Outer column 12, 12a Outer shaft 13, 13a-13c Inner shaft 14 Small diameter portion 15 Female serration 16, 16a to 16c Large diameter portion 17 Male serration
18 pressing pieces 19 recessed portions 20 clearances 21 and 21a chamfered portions 22 recessed holes 23 tapered surface portions 24 throttle portions

Claims (2)

A tubular outer shaft in which female serrations are formed on the inner peripheral surface of at least a portion extending from the leading edge to the intermediate portion, and a male that engages with the female serrations on the outer peripheral surface of at least the portion extending from the leading edge to the intermediate portion. The outer shaft of the outer shaft is pressed radially inward by a pair of pressing pieces with the inner shaft having the serration engaged with the tip of the outer shaft and the tip of the inner shaft. As a result, the outer shaft and the inner shaft are plastically deformed in the radial direction, and then the outer shaft and the inner shaft are relatively displaced in the axial direction so as to approach each other. The front end of the shaft is press-fitted into the intermediate portion of the inner shaft, and the front end of the inner shaft is inserted into the outer shaft. Manufacture of an impact-absorbing steering shaft that is press-fitted into an intermediate portion, and loosely engages a portion between the tip portion and the intermediate portion of the outer shaft and a portion between the tip portion and the intermediate portion of the inner shaft. In the method, the inner shaft is tubular, and the tip end portion of the inner shaft is subjected to a drawing process so that the outer diameter and inner diameter of the inner shaft are directed toward the tip edge. When the diameter of the outer shaft and the inner shaft are plastically deformed in a radial direction by using a throttle portion that is gradually reduced in size and has a constant thickness in the radial direction. A method of manufacturing an impact-absorbing steering shaft, wherein a base end portion of the throttle portion is positioned radially inward of an axially intermediate portion between the pressing pieces. The outer shaft is provided with a small-diameter portion having at least a small inner diameter at one end portion, and a female serration is formed on the inner peripheral surface of the small-diameter portion. The inner shaft has at least a large outer diameter at one end portion. And a male serration that engages with the female serration is formed on the outer peripheral surface of the large diameter portion, and the outer diameter of the distal end portion of the large diameter portion is the tip edge. By pressing the outer peripheral surface of the small diameter portion inward in the radial direction in a state where the tip portion of the small diameter portion and the tip portion of the large diameter portion are engaged. Then, after plastically deforming the distal end portion of the small diameter portion and the distal end portion of the large diameter portion in the radial direction, the outer shaft and the inner shaft are relatively displaced in the axial direction so as to approach each other, and the small diameter portion The tip part is the base of the large diameter part. While press-fitted into parts, the tip portion of the large-diameter portion is fitted pressed into the proximal end of the small diameter portion, thereby an intermediate portion of the intermediate portion and the large diameter portion of the small-diameter portion engaged loosely engaged with each other, The manufacturing method of the impact-absorbing type steering shaft according to claim 1 .

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