JPH11291923A - Steering shaft of shock absorbing type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent rattling at normal times, stabilize the collapse load, and facilitate coordination of the relation between the collapse amount and collapse load. SOLUTION: A male serration 25 formed at one end of an inner shaft 20 is fitted to a female serration 23 formed at one end of an outer shaft 21. A projection 27 is provided on the inner shaft 20 in its part exposed at normal times from the outer shaft 21. At collision, the overall length of this steering shaft 19 of shock absorbing type is shrunk while the projection 27 bites into the inside surface of the outer shaft 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a shock-absorbing steering shaft which is incorporated in a steering apparatus of an automobile and is used for transmitting the movement of a steering wheel to a steering gear.

[0002]

2. Description of the Related Art In a vehicle steering system, a transmission mechanism as shown in FIG. 9 is used to transmit the movement of a steering wheel to a steering gear. As shown in FIG. 9, at the upper end of the first steering shaft 1,
The steering wheel 2 is fixed. The steering column 3 is fixed to the vehicle body on the lower surface of the instrument panel 6 by upper and lower brackets 4 and 5. The first steering shaft 1
Is rotatably inserted through the inside of the steering column 3. A portion of the lower end of the first steering shaft 1 protruding from the lower end opening of the steering column 3 is connected to an upper end of a second steering shaft 8 via a first universal joint 7. . Further, the lower end of the second steering shaft 8 is connected via a second universal joint 9 to a third steering shaft 10 communicating with a steering gear (not shown).

[0003] Since the transmission mechanism of the vehicle steering system is constructed as described above, the movement of the steering wheel 2 is as follows.
The power is transmitted to the steering gear via the first steering shaft 1, the first universal joint 7, the second steering shaft 8, the second universal joint 9, and the third steering shaft 10 through which the steering column 3 is inserted. . Then, the steering gear gives a steering angle corresponding to the movement of the steering wheel 2 to the wheels.

[0004] In the steering apparatus for an automobile constructed as described above, the steering column 3 and each of the steering shafts 1 and 8 are provided to protect the driver in the event of a collision.
It is common practice to use a shock-absorbing type in which the overall length shrinks with the impact. Conventionally, such a shock-absorbing steering shaft is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 8-91231 and 9-267753,
JP-A-9-267754, JP-A-9-27247, JP-B-47-46092, and JP-A-1-583.
No. 73, No. 5-35542, No. 5-3764
No. 2, No. 6-8150, Japanese Utility Model Publication No. 57-167.
Nos. 73, 58-51096 and the like are known.

[0005] Figs.
1 shows a shock absorbing steering shaft 11 described in Japanese Patent No. 16773. The shock-absorbing steering shaft 11 allows the inner shaft 12 and the outer shaft 13 to freely transmit a rotational force, and between the inner shaft 12 and the outer shaft 13.
When a large axial load is applied, the axial dimension is contractably combined. For this purpose, the cross-sectional shape of one end of the inner shaft 12 (the left end in FIG. 10) and one end of the outer shaft 13 (the right end in FIG. 10) is formed into an oval shape. Are combined in a telescope shape. or,
At two positions on the outer peripheral surface of one end of the inner shaft 12, the concave grooves 14, 14 are provided. Each is formed. Then, the synthetic resin 16, 16 is provided inside each of the concave grooves 14, 14 and the through holes 15, 15, and the synthetic resin 16, 16 and the through holes 15, 1,
5 and filled.

Further, a hard ball 17 is supported and fixed to a portion exposed from one end edge (right end edge in FIG. 10) of the outer shaft 13 in a middle portion of the inner shaft 12 in a normal state (before occurrence of a collision accident). I have. That is, the steel ball 17 is internally fitted and fixed in a locking concave portion 18 formed in an intermediate portion of the inner shaft 12. In this state, this steel ball 17
A part of the outer shaft 13 protrudes from the outer peripheral surface of the intermediate portion of the inner shaft 12 and is allowed to collide with the inner peripheral surface of the outer shaft 13 as the shock absorbing steering shaft 11 contracts.

The operation of the shock-absorbing steering shaft 11 configured as described above is as follows. First, in a normal state, the rotational force is transmitted between the outer shaft 13 and the outer shaft 13 based on a non-circular fit between the outer circumferential surface of the one end and the inner circumferential surface of the one end of the outer shaft 13. In such a normal state, the synthetic resin 1 is used.
6 and 16 prevent the two shafts 12 and 13 from being displaced from each other based on the engagement between the recesses 14 and 14 and the through holes 15 and 15, and
Prevents the overall length from accidentally shrinking.

Further, when an impact load is applied in the axial direction at the time of a collision (at the time of a primary collision or a secondary collision), the synthetic resin 1
6 and 16 are torn at a continuous portion between the recesses 14 and 14 and the through holes 15 and 15, and the relative displacement of the two shafts 12 and 13 is started, so that the total length of the shock absorbing steering shaft 11 is reduced. Shrink. After the steel ball 17 reaches one edge of the outer shaft 13, when the overall length of the shock absorbing steering shaft 11 is further reduced, the steel ball 17 bites into the inner peripheral surface of the outer shaft 13. . For this reason, the shock absorbing steering shaft 11
The load required for shortening the overall length of the vehicle increases. FIG.
Shows the relationship between the so-called collapse load required to shorten the overall length of the shock absorbing steering shaft 11 and the contraction amount (collapse amount) of the shock absorbing steering shaft 11. The initial peak load shown in FIG. 12 corresponds to the moment when the synthetic resins 16 and 16 are torn, and the reason that the load is large at the end is
The steel ball 17 corresponds to a portion that bites into the inner peripheral surface of the outer shaft 13.

[0009]

In the case of a conventional shock absorbing steering shaft 11 as shown in FIGS.
There is room for improvement in the following points: It is difficult to stabilize the collapse load. With the increase of the collapse amount, the collapse load cannot be gradually increased. For this reason, when the collapse load is small, the shock absorbing steering shaft 11 contracts completely (full collapse L), and the contraction is completed. On the other hand, when the collapse load is large, a large resistance is generated at the moment when the steel ball 17 starts to bite into the inner peripheral surface of the outer shaft 13, and it is difficult to enhance the protection of the driver.

First, the above-mentioned problem is caused by one end of the inner shaft 12 and the outer shaft 13
This is caused by forming the cross-sectional shape of one end of the Oval shape into an oval shape. That is, in order to prevent the fitting portion of the two shafts 12 and 13 from rattling when the rotational force is transmitted between the two shafts 12 and 13, it is necessary to prevent a gap from being generated in the fitting portion. . On the other hand, it is difficult to control the dimensions and the shape in order to prevent rattling in the fitting portion having an oval cross section, and when the steel ball 17 bites into the inner surface of the outer shaft 13, a substantially flat plastic surface is formed. Due to the deformation, even a slight change in interference results in a variation in fitting resistance, and the collapse load greatly fluctuates.

Next, the above problem is caused by the fact that the plastic deformation state of the inner peripheral surface of the outer shaft 13 by the steel ball 17 and the frictional engagement state of the two shafts 12 and 13 are increased irrespective of the increase of the collapse amount. It happens based on things that don't change. On the other hand, in order to effectively absorb the impact energy in the event of a collision and to effectively protect the driver, it is preferable that the collapse load increases as the collapse amount increases. In the case of the conventional shock-absorbing steering shaft 11 as shown in FIGS. 10 to 11, such a demand cannot be met, and it is difficult to design a steering apparatus for an automobile that can sufficiently enhance protection of the driver. The shock absorbing steering shafts described in the other publications mentioned above have almost the same problem. The shock absorbing steering shaft of the present invention is
The present invention has been made in view of such circumstances.

[0012]

The shock absorbing steering shaft according to the present invention, like the conventional shock absorbing steering shaft described above, has at least one inner shaft formed with a male serration on the outer peripheral surface at one end and at least one inner shaft. And an outer shaft having a female serration formed on an inner peripheral surface at one end. By engaging the male serration and the female serration, the inner shaft and the outer shaft are combined so that rotational force can be transmitted freely, and a large axial load is applied between the inner shaft and the outer shaft. The shock absorbing portion is provided so that the axial dimension can be contracted only when the shock absorber is used. In addition, the serration referred to in this specification includes a spline-shaped one having a large pitch between a peak and a valley.

[0013] In particular, in the shock absorbing steering shaft according to the first aspect of the present invention, the shock absorbing portion includes at least one of the male serration and the female serration. Of the valley portion of the serration, which does not normally engage with the opposing serration, but includes a convex portion fixed to a portion that engages with the opposing serration when the steering shaft contracts due to a collision accident. The convex portion is deformed by engagement with the mountain portion of the other serration in accordance with the contraction of the shock absorbing steering shaft. In addition, such a convex portion is formed integrally with the shaft on which the serration is formed by making a part of the valley portion of the one serration shallower than the other portion. It can also be constituted by another hard member such as a steel ball fitted and fixed to a part of.

Further, in the shock absorbing steering shaft according to the second aspect, the shock absorbing portion is a part of at least one of the male serration and the female serration, and is normally a counterpart serration. The shape of the part that does not engage with the other serration when the steering shaft contracts due to a collision accident,
It has a shape that does not smoothly engage with the opposing serration, and includes an incomplete engagement portion.

[0015]

In the shock absorbing steering shaft of the present invention having the structure described above, the collapse load can be stabilized and the collapse load can be gradually increased as the amount of collapse increases. That is, one end portion of the inner shaft and one end portion of the outer shaft are combined so as to be able to transmit a rotational force by fitting the male serration and the female serration. The fitting strength between these male serrations and female serrations does not change significantly if the dimensional accuracy and shape accuracy are slightly shifted. Therefore, it is possible to stabilize the collapse load while preventing rattling of the fitting portion.

When the projection or the incompletely engaged portion engages with the other serration when the shock-absorbing steering shaft is contracted due to the occurrence of a collision accident, the other serration becomes plastically deformed, scuffed, galling, etc. Deformation such as scraping. As the shock absorbing steering shaft further contracts, the deformed portion of the mating serration frictionally engages with one of the serrations forming the convex portion or the incompletely engaging portion. Such a load required for displacement at the frictional engagement portion including the deformed portion is large based on an increase in the contact pressure or a bite of a small piece caused by a tear or the like,
Moreover, the friction engagement portion becomes gradually longer as the amount of collapse increases. As a result, the collapse load increases as the amount of collapse increases. The magnitude of the collapse load can be freely set regardless of the fitting strength between the male serration and the female serration. Therefore, the collapse load increases with an increase in the amount of collapse, which facilitates design for enhancing protection of a driver in the event of a collision.

[0017]

1 to 3 show a first embodiment of the present invention corresponding to claim 1. FIG. In the shock absorbing steering shaft 19 of the present invention, the inner shaft 20 and the outer shaft 21 are arranged in the axial direction (FIG. 1).
(Left and right directions) so that the overall length is reduced when an impact force is applied in the axial direction. Outer shaft 21 of these
Has a tubular shape as a whole, and has one end (the left end in FIG. 1).
The small diameter portion 22 is formed at one end by drawing. A female serration 23 is formed on the inner peripheral surface of the small diameter portion 22. One inner shaft 20 also has a circular tubular shape, and is also subjected to drawing at one end (the right end in FIG. 1) to form a small-diameter portion 2.
4 are formed. A male serration 25 is formed on the outer peripheral surface of the small diameter portion 24 to engage with the female serration 23 formed on the inner peripheral surface of the outer shaft 21.

The female serrations 23 and the male serrations 25 do not allow the tops of the respective ridges to reach the bottoms of the respective valleys, as in the general serrations. When the serration 25 is engaged, a gap between the top and the bottom is formed as shown in FIG.
As shown in the figure, a gap 2 having a height dimension h in the diametrical direction is h.
8, 28 are formed.

In particular, in the shock absorbing steering shaft 19 of the present invention, as shown in FIGS. 1 and 2, one of the bottoms of one or a plurality of valleys 26 constituting the male serration 25 in the axial direction. The protrusion 27 is formed in the portion. The axial position of the projection 27 does not normally engage with the female serration 23 but engages with the female serration 23 when the shock absorbing steering shaft 19 contracts due to a collision accident. The convex part 27
Is larger than the height h of the gaps 28 (H> h). As described above, the male serration 25 in which the convex portion 27 is provided in a part of the valley portion 26,
Since the inner shaft 20 is formed by rolling, the manufacturing cost of the inner shaft 20 does not increase. In the illustrated example, both axial end surfaces of the convex portion 27 are gently inclined so that the axial dimension of the convex portion 27 becomes larger toward the bottom surface of the valley portion 26 of the male serration 25. ing.

Each of the female serrations 23 as described above
Inner shaft 20 having a male serration 25
In order to configure the shock absorbing steering shaft 19 of the present invention by combining the shaft 21 and the outer shaft 21, the first half of the male serration 25 (the right half of FIG. 1)
Into the female serrations 23. In the state where the serrations 23 and 25 are engaged with each other in this manner,
In order to prevent the engagement portion between the serrations 23 and 25 from rattling, an appropriate rattling preventing means is provided. As the rattling preventing means, for example, after deforming one or both of the inner shaft 20 and the outer shaft 21 into an elliptical cross section, the first half of the male serration 25 is pushed into the female serration 23. And so on. For example, as described in Japanese Utility Model Laid-Open Publication No. 6-8150, the tip of the outer shaft 21 existing at one axial end (left end in FIG. 1) of the fitting portion between the female serration 23 and the male serration 25 is described. After the cross-sectional shape of the end portion of the inner shaft 20 existing at the axial end (the right end in FIG. 1) of the portion and the fitting portion is changed to an elliptical shape, the shafts 21 and 20 are fitted together. If they are combined, preferable characteristics can be obtained such that the load required to shift the fitting portion in the axial direction can be reduced and the bending rigidity can be secured.

In the case of the shock absorbing steering shaft 19 of the present invention configured as described above, it is possible to stabilize the collapse load and to gradually increase the collapse load as the amount of collapse increases. That is, one end of the inner shaft 20 and one end of the outer shaft 21 are combined so as to be able to transmit a rotational force by fitting the male serration 25 and the female serration 23.
The fitting strength between the male serrations 25 and the female serrations 23 does not change significantly if the dimensional accuracy and the shape accuracy are slightly shifted. In other words, even if the fitting strength is somewhat weak, it is difficult to cause large rattling, and the allowable value of the fitting strength is wide. Therefore, it is possible to stabilize the collapse load while preventing rattling of the fitting portion between the male serration 25 and the female serration 23. In particular, as described above, a structure is employed in which one or both of the inner shaft 20 and the outer shaft 21 are deformed into an elliptical cross section, and then the first half of the male serration 25 is pressed into the female serration 23. In this case, the rattling prevention and the collapse load stabilization can be more effectively achieved.

In the event of a collision, the shock absorbing steering shaft 19 is connected to the inner shaft 20.
Starts contraction against a frictional force acting on a fitting portion between one end of the outer shaft 21 and one end of the outer shaft 21. The shock absorbing steering shaft 19 is moved by a predetermined amount (FIG. 1).
(L) of the female serrations 23 engages with the ridges of the female serrations 23 to plastically deform the ridges of the female serrations 23. In the case of the example shown in the figure, since the both end surfaces in the axial direction of the convex portion 27 are inclined, the plastic deformation of the crest of the female serration 23 by the convex portion 27 is performed smoothly, and the plastic deformation starts. Sometimes an undesired peak value does not occur in the collapse load. In order to prevent the occurrence of the peak value, the end face on the side (the right side in FIG. 1) of the both end faces of the projection 27 which engages with the top of the crest of the female serration 23 is inclined. Is enough. The axial length of the plastically deformed portion at the top of the hill formed as described above increases as the amount of contraction of the shock absorbing steering shaft 19 increases. And
The plastically deformed portion is provided with the male serration 25 as the shock absorbing steering shaft 19 contracts.
And frictional engagement.

That is, the width of the top of the peak of the female serration 23, whose top is crushed by the projection 27, in the circumferential direction is widened. For this reason, the frictional force acting on the frictional engagement portion between the top and the inner surface of the valley of the male serration 25 is considerably larger than before the top of the peak is plastically deformed. As described above, the load required for displacement at the frictional engagement portion including the plastically deformed portion at the top of the peak is large, and the frictional engagement portion gradually becomes longer as the amount of collapse increases. As a result, the collapse load increases as the amount of collapse increases. FIG. 4 shows the relationship between the collapse load required to reduce the overall length of the shock absorbing steering shaft 19 of the present invention and the contraction amount (collapse amount) of the shock absorbing steering shaft 19. As is apparent from a comparison between FIG. 4 and the relationship between the collapse load and the amount of collapse in the case of the conventional structure shown in FIG. 12 described above, according to the structure of the present invention, the amount of collapse is increased. The collapse load is said to increase accordingly,
Preferred characteristics can be obtained from the viewpoint of driver protection. For this reason, even if the amount of collapse is small, it is possible to realize a structure capable of effectively absorbing the impact energy applied to the impact absorbing steering shaft 19 in the event of a collision.

Moreover, in the case of the shock absorbing steering shaft 19 of the present invention, the magnitude of the collapse load is determined by the fitting strength of the fitting portion between one end of the male serration 25 and one end of the female serration 23. Can be set freely regardless of The effect of the fitting strength of the fitting portion on the collapse load depends on the impact absorbing steering shaft 19.
Is only the initial value immediately after the start of contraction. Therefore, as described above, the collapse load increases with an increase in the collapse amount, and the design for enhancing the protection of the driver in the event of a collision becomes easy. This leads to simplification of the design for enhancing the protection of the driver, particularly in the steering device of a small car. In order to further stabilize the collapse load, if at least one surface of the male serration 25 and the female serration 23 is subjected to a surface treatment such as a metallic soap, the peak of the female serration 23 by the convex portion 27 is formed. At the time of plastic deformation of the top, or at the time of frictional engagement between the resulting plastically deformed portion and the inner surface of the valley of the male serration 25, a phenomenon such as galling that significantly increases the load required for deformation or displacement occurs. Can be prevented.

Next, FIG. 5 shows a second embodiment of the present invention, corresponding to claim 1, in a state where a collision accident has occurred and the shock absorbing steering shaft 19 has already contracted. . In the case of this example, valley 2 of male serration 25
6 shows an example in which convex portions 27, 27 are formed at two positions in the axial direction, so that the relationship between the collapse amount and the collapse load can be more freely adjusted. Also in the case of this example, each of the convex portions 2
Each of the projections 2 is inclined by inclining both axial end surfaces of the projections 7 and 27.
7, so that the plastic deformation of the top of the female serration 23 by the top 7 can be smoothly performed. In the example shown in the figure, an example is shown in which each of the convex portions 27 is formed in the same valley portion 26. However, in order to more arbitrarily adjust the relationship between the collapse amount and the collapse load, the convex portions 27, 27 may be formed at different valleys with their axial positions shifted from each other. Other configurations and operations are the same as those of the above-described first example.

FIG. 6 shows a third embodiment of the present invention corresponding to claim 1. In the case of this example, the convex portion 2 formed at a part of the valley portion of the male serration 25
7 a is constituted by a steel ball 29. That is, a concave hole 30 is formed in a part of the valley portion 26 of the male serration 25, and the steel ball 29 is fitted and fixed in the concave hole 30 in a state where a part thereof projects from the concave hole 30. I have. For this purpose, the inner diameter of the concave hole 30 is made slightly smaller than the outer diameter of the steel ball 29, and the steel ball 29 is pressed into the concave hole 30 or the steel ball 29 is inserted into the concave hole 30. After that, the opening of the concave hole 30 is swaged. In the case of such a structure of the present example, in the event of a collision accident, a portion of the steel ball 29 protruding from the concave hole 30 plastically deforms the crest of the female serration 23. The configuration and operation of the other parts
This is the same as the case of the first example described above.

Next, FIG. 7 shows a fourth embodiment of the present invention corresponding to claim 1. In the case of the present example, the recesses 30, 30 are respectively formed in a part of the valleys 26, 26 at a plurality of places (three places in the illustrated example) of the male serration 25.
Are formed, and steel balls 2 are respectively inserted into these concave holes 30 and 30.
9 and 29 are internally fitted and fixed to form convex portions 27a and 27a. Except for the increase in the number of steel balls 29, 29, the configuration and operation are the same as in the above-described third example. In this embodiment, if the axial positions of the projections 27a are different from each other, the relationship between the collapse amount and the collapse load can be adjusted more arbitrarily.

Next, FIG. 8 shows a fifth embodiment of the present invention corresponding to claim 2. In the case of this example, a part of the male serration 25 formed on the outer peripheral surface of one end of the inner shaft 20, that is, a part of the male serration 25 in the first example of the above-described embodiment of FIG. The shape of the portion that does not engage with the female serration 23 formed on the inner peripheral surface at one end of the outer shaft 21 and engages with the female serration 23 when the shock absorbing steering shaft 19 contracts due to a collision accident is determined by the female serration 23. The shape is such that it does not engage smoothly with the incomplete engagement portion. For this reason, in the case of this example, the shape of the above-mentioned part is made elliptical.

The shock absorbing steering shaft 19 contracts with the collision accident, and the outer shaft 21
Reaches the incompletely engaged portion having the elliptical cross section, the frictional force acting between the female serration 23 and the male serration 25 increases, and the shock absorbing steering shaft 19 is contracted. At the same time as the required collapse load increases, the outer shaft 21
Undergo plastic deformation. As a result, the frictional engagement portion that increases the load required for the relative displacement gradually increases with an increase in the amount of collapse, and the collapse load increases with an increase in the amount of collapse. Other configurations and operations are the same as in the case of the above-described first example.

As the incompletely engaged portion, in addition to the hollow inner shaft 20 having an elliptical cross section as shown in the figure, the solid inner shaft is crushed to push the cross section into an elliptical shape. A crushed one, or a part of the valley of at least one of the male serration and the female serration, or a middle part of at least one crest of the male serration and the female serration is deformed in the circumferential direction. Can be considered.

[0031]

The shock-absorbing steering shaft of the present invention is constructed and operated as described above, so that the collapse load is stabilized while sufficiently preventing rattling during normal operation, and further, the collapse amount is improved. It becomes easy to design the relationship between the collapse amount and the collapse load as desired, such as increasing the collapse load with an increase in the load.

[Brief description of the drawings]

FIG. 1 is an essential part cross-sectional view showing a first example of an embodiment of the present invention.

FIG. 2 is a partially enlarged perspective view of an inner shaft.

FIG. 3 is a sectional view taken along line AA of FIG. 1;

FIG. 4 is a diagram showing a relationship between a collapse amount and a collapse load in the structure of the first example.

FIG. 5 is a sectional view of an essential part showing a second example of the embodiment of the present invention in a state after a collision accident has occurred.

FIG. 6 is a view similar to FIG. 3, showing the third example.

FIG. 7 is a view similar to FIG. 3, showing the fourth example.

FIG. 8 is a view showing the fifth example and corresponding to a BB section in FIG. 1;

FIG. 9 is a side view showing an example of a steering mechanism incorporating a shock absorbing steering shaft to which the present invention is applied.

FIG. 10 is a sectional view of a main part showing an example of a conventional structure.

FIG. 11 is an enlarged sectional view taken along the line CC of FIG. 10;

FIG. 12 is a diagram showing a relationship between a collapse amount and a collapse load in a conventional structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First steering shaft 2 Steering wheel 3 Steering column 4 Upper bracket 5 Lower bracket 6 Instrument panel 7 First universal joint 8 Second steering shaft 9 Second universal joint 10 Third steering shaft 11 Shock absorption Type Steering Shaft 12 Inner Shaft 13 Outer Shaft 14 Concave Groove 15 Through Hole 16 Synthetic Resin 17 Steel Ball 18 Locking Concave 19 Shock Absorbing Steering Shaft 20 Inner Shaft 21 Outer Shaft 22 Small Diameter 23 Female Serration 24 Small Diameter 25 Male Serration 26 Valley 27, 27a Convex 28 Gap 29 Steel ball 30 Concave hole

Claims (2)

[Claims] An inner shaft having at least one end formed with a male serration on an outer peripheral surface, and an outer shaft having at least one end formed with a female serration on an inner peripheral surface, wherein the male serration and the female serration are engaged with each other. An impact absorbing portion that combines the inner shaft and the outer shaft so that rotational force can be freely transmitted, and allows the axial dimension to contract only when a large axial load is applied between the inner shaft and the outer shaft. In the shock absorbing steering shaft provided with, the shock absorbing portion is a part of the valley of at least one of the male serration and the female serration, and does not normally engage with the opposing serration, Serration when the steering shaft contracts due to a collision And a convex portion fixed to a portion engaging with the serration. The convex portion is engaged with a peak portion of a mating serration as the shock absorbing steering shaft contracts. A shock-absorbing steering shaft characterized by deforming the steering shaft. 2. An inner shaft having at least one end formed with a male serration on an outer peripheral surface thereof, and an outer shaft having at least one end formed with a female serration on an inner peripheral surface formed by engaging the male serration and the female serration. An impact absorbing portion that combines the inner shaft and the outer shaft so that rotational force can be freely transmitted, and allows the axial dimension to contract only when a large axial load is applied between the inner shaft and the outer shaft. In the shock-absorbing steering shaft provided with the above, the shock-absorbing portion is a part of at least one of the above-mentioned male serration and female serration, and does not normally engage with the opposing serration, resulting in a collision accident. Engage with other serrations when steering shaft shrinks An impact-absorbing steering shaft, characterized in that the shape of the portion to be engaged is formed so as not to smoothly engage with the mating serration and includes an incompletely engaging portion.