JP2008261424A - Telescopic shaft - Google Patents

Abstract

The present invention realizes a structure in which an inner shaft 30 and an outer shaft 31 are easily assembled and has excellent durability.
A buffer material 32 disposed between the shafts 30 and 31 is composed of two kinds of polymer materials having different hardnesses. The first polymer material 35, 35 having a low hardness is between the inner side surfaces 37, 37 constituting the outer peripheral surface of the inner shaft 30 and the outer side surfaces 38, 38 constituting the inner peripheral surface of the outer shaft 31. Are clamped in a state having a tightening allowance. On the other hand, the second polymer materials 36 and 36 having a high hardness are arranged in a state having a gap between the two peripheral surfaces. When a torque of a predetermined magnitude or more acts between the shafts 30 and 31, the second polymer material 36 and 36 comes into contact with the outer side surfaces 38 and 38.
[Selection] Figure 2

Description

  The telescopic shaft according to the present invention is used as a shaft capable of transmitting rotational torque and extending and contracting in the axial direction, such as a steering shaft and an intermediate shaft constituting an automobile steering device. In particular, the present invention realizes a structure in which the assembling property between the inner shaft and the outer shaft is good and the durability is excellent.

  For example, a steering shaft that constitutes a steering device for an automobile and that is provided with a steering wheel at the end, or an intermediate shaft that is located between a pair of universal joints in a part of this steering device is used in the axial direction during a collision. Conventionally known is a technique for reducing the overall length when an impact is applied. Further, a structure having a so-called telescopic function in which the steering shaft can be freely expanded and contracted in the axial direction and the position of the steering wheel is adjusted according to the physique of the driver is also known. As a structure to be applied to such a steering shaft or intermediate shaft, a telescopic shaft that can freely transmit rotational force and can be expanded and contracted in the axial direction has been conventionally used, as described in Patent Documents 1 and 2, for example. Known from.

  In the case of the structures described in these Patent Documents 1 and 2, the inner shaft and the outer shaft constituting the telescopic shaft are smoothly displaced relative to each other in order to expand and contract the telescopic shaft, and the backlash between the two shafts. In order to prevent sticking and to prevent abnormal noise from being generated during rotation transmission, a synthetic resin cushioning material is provided between these two shafts. Among these, the structure described in Patent Document 1 is shown in FIG. The telescopic shaft 1 shown in FIG. 10 covers a part of the outer peripheral surface of the inner shaft 2 with a cushioning material 3 made of nylon. A part of the cushioning material 3 enters the grooves 4 and 4 provided on the outer peripheral surface of the inner shaft 2, and the cushioning material 3 is firmly coupled to the inner shaft 2.

  On the other hand, in the case of the telescopic shaft 1a described in Patent Document 2, as shown in FIG. 11, the buffer material 3a covering a part of the outer peripheral surface of the inner shaft 2a has two layers. That is, the first resin layer 5 made of polyamideimide resin is coated on the outer peripheral surface of the inner shaft 2a, and the second resin layer 6 made of, for example, polyamide resin is coated on the outer peripheral surface of the first resin layer 5. It is covered. The first resin layer 5 ensures adhesion to the inner shaft 2 a and the second resin layer 6 ensures heat resistance.

  As mentioned above, the telescopic shaft that provides a cushioning material between the inner shaft and the outer shaft requires that both the shafts have good assembly properties and that they have excellent durability. Is done. However, it is difficult to satisfy such a demand with a conventional structure as described in Patent Documents 1 and 2 above. That is, it is conceivable to use a synthetic resin having a low hardness as the cushioning material in response to a request for improving the assembling property between the two shafts. When assembling the two shafts, in order to prevent rattling between the two shafts, it is necessary to dispose a cushioning material between the two shafts with a tightening margin. In the case of a synthetic resin having a large hardness (hard), if this tightening margin is increased due to a manufacturing error or the like, the assembling property is not good because a large force is required for assembling. On the other hand, in the case of a synthetic resin with low hardness (soft), it is easy to cope with the change in the tightening allowance, and the assemblability is good, but it is durable by being crushed excessively when transmitting a large torque. It is difficult to secure. For this reason, in terms of ensuring durability, it is better to use a synthetic resin having high strength and excellent strength against compressive force.

  However, in the case of the structure described in Patent Document 1, since only one type of synthetic resin can be used, only one of the two requirements can be satisfied. On the other hand, in the case of the structure described in Patent Document 2, for example, the first resin layer 5 may be a synthetic resin having a low hardness, and the second resin layer 6 may be a synthetic resin having a high hardness. However, when a large torque is transmitted, it is considered that a large compressive stress is generated in the first resin layer 5 which is a synthetic resin having a low hardness. For this reason, it cannot be said that it is excellent in terms of durability.

Japanese Patent Publication No. 2-19325 JP 2003-56588 A

  In view of the circumstances as described above, the present invention has been invented in order to realize a structure in which the inner shaft and the outer shaft can be easily assembled and has excellent durability.

The telescopic shaft of the present invention includes an inner shaft, an outer shaft, and a cushioning material as in the conventional structure described above.
Among these, the inner shaft has a non-circular cross-sectional shape (related to a virtual plane existing in a direction perpendicular to the central axis) on the outer peripheral surface.
The outer shaft has a non-circular cross-sectional shape (with respect to a virtual plane existing in a direction perpendicular to the central axis) on the inner peripheral surface. The diameter of the inscribed circle related to the cross-sectional shape of the inner peripheral surface is smaller than the diameter of the circumscribed circle related to the cross-sectional shape of the outer peripheral surface of the inner shaft, and the inner shaft can be inserted.
Further, the cushioning material exists between the inner shaft and the outer shaft.
And with the inner shaft inserted into the outer shaft, rotation can be transmitted between the two shafts via the cushioning material, and both the shafts can slide in the axial direction. It is.

In particular, in the telescopic shaft of the present invention, the buffer material is composed of two types of polymer materials having different hardnesses such as synthetic resins and elastomers such as rubber.
Among these, a polymer material such as an elastomer such as rubber having a low hardness (low = relatively soft) is an outer peripheral surface of the inner shaft in a no-load state in which no rotation is transmitted between the shafts. Between the inner circumferential surface of the outer shaft and at least a part of the circumferential clearance that exists between the side surfaces facing each other with respect to the rotational direction of both shafts. Yes.
Further, a polymer material having a high hardness (high = relatively hard) such as a synthetic resin or hard rubber is disposed in a state having a gap in the remainder of the circumferential gap in a no-load state.
Further, when transmitting a rotational torque of a predetermined magnitude or more, the high-hardness polymer material deviates from the position where the low-hardness polymer material exists among the side surfaces facing each other in the rotation direction. It touches these two side surfaces at a part of the part.

  As used herein, the term “hardness” refers to the deformation of the surface when a certain load is applied, as is the case with the term “hardness” or “hardness” in general. Point to Kussa. Therefore, the “polymer material having a high hardness” is a polymer material that is not easily deformed, and the “polymer material having a low hardness” is a polymer material that is easily deformed.

As a specific structure for carrying out the above-described invention, for example, as described in claim 2, two types of polymer materials having different hardnesses are alternately present with respect to the rotation direction of both shafts.
Alternatively, as described in claim 3, two types of polymer materials having different hardnesses are alternately present in the axial direction of both shafts.

  Further, when implementing each of the above-described inventions, preferably, as described in claim 4, the boundary portion between two types of polymer materials having different hardnesses is formed between the outer peripheral surface of the inner shaft and the inner periphery of the outer shaft. It arrange | positions in the state which has a clearance gap between some surfaces, irrespective of the load state of rotational torque.

According to the telescopic shaft of the present invention as described above, it is possible to realize a structure in which assembling property between the inner shaft and the outer shaft is good and durability is excellent.
That is, in the no-load state, of the two types of polymer materials constituting the buffer material, only the polymer material having a low hardness exists between the outer peripheral surface of the inner shaft and the inner peripheral surface of the outer shaft. The polymer material which is disposed in a state having a tightening allowance at a part of the circumferential clearance and has a large hardness is disposed in a state having a clearance between both circumferential surfaces. For this reason, when assembling both the shafts, only the polymer material having a low hardness is in a state of having a tightening margin between the both shafts. The power is small. As a result, the assemblability of both shafts is improved.

  On the other hand, when a rotational torque of a predetermined magnitude or more is transmitted, the high-hardness polymer material is at least both of the outer peripheral surface of the inner shaft and the inner peripheral surface of the outer shaft. Abutting side surfaces facing each other in the rotational direction of the shaft. Therefore, torque exceeding the predetermined magnitude can be transmitted mainly through the polymer material having a high hardness. Since the high hardness polymer material has high load resistance, sufficient durability can be ensured even when a large torque is transmitted. The torque less than the predetermined magnitude is transmitted through the polymer material having a low hardness. However, since the torque is small, the polymer material having a low hardness is not damaged early. Further, rattling between the two shafts in an unloaded state is prevented by the polymer material having a low hardness.

In addition, as described in claim 2, if two types of polymer materials having different hardnesses are alternately present in the rotation direction of both shafts, the axial dimension of the cushioning material can be reduced, and the shaft can be used as an expansion / contraction axis. Easy to apply to structures with small directional dimensions.
In addition, as described in claim 3, if two types of polymer materials having different hardnesses are alternately present in the axial direction of both shafts, the axial lengths of these two types of polymer materials are changed. It is easy to obtain a cushioning material with different characteristics.

  Further, the boundary portion between two types of polymer materials having different hardnesses has low strength because the edge portions of these polymer materials exist. For this reason, as described in claim 4, this boundary portion is formed in a state having a gap in a part between the outer peripheral surface of the inner shaft and the inner peripheral surface of the outer shaft regardless of the load state of the rotational torque. By disposing, it is difficult to cause an undesirable phenomenon in which each of the polymer materials is damaged from the respective boundary portions, and the durability of the buffer material composed of these polymer materials can be improved.

[First example of embodiment]
1 to 5 show a first example of an embodiment of the present invention corresponding to claims 1, 2, and 4. FIG. In this example, the present invention is applied to an electric power steering apparatus. First, the electric power steering apparatus will be described with reference to FIG. An electric power steering apparatus 7 shown in FIG. 1 includes a steering shaft 9 having a steering wheel 8 fixed to a rear end portion (right end portion in FIG. 1), a steering column 10 through which the steering shaft 9 can be inserted, and the steering wheel. A steering force assist device (assist device) 11 for applying assist torque to the shaft 9 and a steering gear 13 for displacing (pushing and pulling) the tie rods 12 and 12 based on the rotation of the steering shaft 9 are provided. Among these, the steering shaft 9 is formed by combining an inner shaft 14 and an outer shaft 15 so that rotational force can be transmitted and relative displacement in the axial direction is possible. The inner shaft 14 and the outer shaft 15 are displaced relative to each other in the axial direction at the time of a collision, thereby reducing the overall length of the steering shaft 9.

  Further, the cylindrical steering column 10 inserted through the steering shaft 9 is formed by combining an inner column 16 and an outer column 17 in a telescope shape, and when an axial impact is applied, energy due to the impact is applied. It has a so-called collapsible structure in which the entire length is reduced while absorbing. The front end portion (left end portion in FIG. 1) of the inner column 16 is coupled and fixed to the rear end surface of the gear housing 18 that constitutes the steering force assisting device 11. The inner shaft 14 is inserted into the gear housing 18, and the front end portion of the inner shaft 14 is coupled to the input shaft that constitutes the steering force assisting device 11. Further, a front end portion of the output shaft 19 that is connected to the input shaft via a torsion bar and also constitutes the steering assist device 11 is protruded from the front end surface of the gear housing 18.

  The steering column 10 is supported by a support bracket 20 at a middle portion of the steering column 10 on a part of the vehicle body 21 such as the lower surface of the dashboard. In addition, a locking portion (not shown) is provided between the support bracket 20 and the vehicle body 21, and when an impact in a forward direction is applied to the support bracket 20, the support bracket 20 is separated from the locking portion. I try to come off. Further, by providing a tilt mechanism and a telescopic mechanism, the front / rear position and height position of the steering wheel 8 can be freely adjusted. Such a tilt mechanism and a telescopic mechanism are the same as those conventionally known, and are not related to the gist of the present invention.

  The front end portion of the output shaft 19 constituting the steering force assisting device 11 is connected to the rear end portion of the intermediate shaft 23 via a universal joint 22. Further, the input shaft 25 of the steering gear 13 is connected to the front end portion of the intermediate shaft 23 via another universal joint 24. The intermediate shaft 23 is formed by combining an inner shaft 26 and an outer shaft 27 so that rotational force can be transmitted and relative displacement in the axial direction is possible. The inner shaft 26 and the outer shaft 27 are displaced relative to each other in the axial direction at the time of collision, thereby reducing the overall length of the intermediate shaft 23.

  The steering gear 13 includes a rack and a pinion (not shown), and the input shaft 25 is coupled to the pinion. Further, the rack that meshes with the pinion has the tie rods 12 and 12 connected to both ends. By pushing and pulling the tie rods 12 and 12 on the basis of the displacement of the rack, a desired steering wheel is shown. The rudder angle is given. Further, the steering force assisting device 11 causes the output shaft 19 to generate an assist torque with a predetermined magnitude in a predetermined direction via the worm speed reducer by the electric motor 28.

  In the case of the electric power steering device 7 configured as described above, the torque output from the output shaft 19 of the steering force assisting device 11 can be made larger than the torque applied from the steering wheel 8 to the steering shaft 9. That is, the torque output from the output shaft 19 can be increased by the amount of auxiliary power applied from the electric motor 28 constituting the steering force assisting device 11 via the worm reducer. Therefore, the force required for the driver to operate the steering wheel 8 to give the steering angle to the steered wheels can be reduced by the amount of auxiliary power of the steering force assisting device 11. An electric power steering device may be configured by providing a steering force assisting device around the steering gear 13.

  In the case of this example, the steering shaft 9 or the intermediate shaft 23 incorporated in the electric power steering apparatus 7 configured and acting as described above is configured by the telescopic shaft 29 as shown in FIGS. The telescopic shaft 29 has two types of polymer materials having different hardnesses between the inner shaft 30 (corresponding to the above-described inner shafts 14 and 26) and the outer shaft 31 (corresponding to the above-described outer shafts 15 and 27). The buffer material 32 comprised by these is arrange | positioned. As shown in FIG. 4, the buffer material 32 is formed by coating a part of the outer peripheral surface of the inner shaft 30 with a synthetic resin or rubber, which is a polymer material, by injection molding or vulcanization molding.

Among the polymer materials constituting the buffer material 32, examples of the synthetic resin include polytetrafluoroethylene (PTFE), phenol resin, acetal resin, polyimide resin, polyamideimide resin, polyethersulfone resin, polyphenylene sulfide resin, and the like. Among these synthetic resins, those containing one kind of synthetic resin or plural kinds of synthetic resins can be mentioned. These synthetic resins may contain one or more kinds of solid lubricants such as molybdenum disulfide (MoS ₂ ), graphite, and fluorine compounds. Further, either or both of carbon fiber and carbon beads may be included.

In addition to the synthetic resin material as described above, natural rubber, synthetic rubber, or rubber made of a mixture thereof can be used as the polymer material. Further, one or more kinds of solid lubricants such as molybdenum disulfide (MoS ₂ ), graphite, and fluorine compounds may be included in these rubber materials. In any case, two types having different hardnesses are selected from the above-described polymer materials, and the cushioning material 32 is configured.

  The inner shaft 30 and the outer shaft 31 are made of, for example, carbon steel containing 0.04% by weight or more of carbon in iron, and have a substantially cross-shaped cross section as shown in FIGS. The cross-sectional shape of the outer peripheral surface or inner peripheral surface is non-circular. In order to reduce the weight, one or both of the shafts 30 and 31 (preferably both in consideration of corrosion resistance) may be made of an aluminum alloy. Further, when incorporated in the electric power steering apparatus 7 as in this example, the size of the circumscribed circle of the inner shaft 30 is preferably about 20 to 40 mm.

  The inner shaft 30 of the shafts 30 and 31 has engaging convex portions 33 and 33 protruding radially outward at a plurality of locations (four locations in the illustrated example) on the outer peripheral surface. Further, the outer shaft 31 is formed with engaging concave portions 34 and 34 that are recessed radially outward at positions aligned with the respective engaging convex portions 33 and 33 on the inner peripheral surface. The diameter of the inscribed circle related to the cross-sectional shape of the inner peripheral surface of the outer shaft 31 is smaller than the diameter of the circumscribed circle related to the cross-sectional shape of the outer peripheral surface of the inner shaft 30. Accordingly, when the inner shaft 30 is inserted into the outer shaft 31 and the shafts 30 and 31 are relatively displaced in the rotational direction, the engagement protrusions 33 and 33 and the engagement recesses 34 and 34 Mesh with each other. When the inner shaft 30 and the outer shaft 31 are assembled, the engagement convex portions 33 and 33 are caused to enter the engagement concave portions 34 and 34, respectively. Since the outer peripheral surface of the inner shaft 30 is covered with the cushioning material 32 as described above, after the shafts 30 and 31 are assembled to each other, the engagement convex portions 33 and 33 and the engagement members are connected. The buffer material 32 is present between the joint recesses 34 and 34.

  Since the buffer material 32 is covered on the outer peripheral surface of the inner shaft 30 as described above, the buffer material 32 has a shape that follows the outer peripheral surface of the inner shaft 30. In the case of the illustrated example, the cross section is a substantially cross shape. As described above, such a cushioning material 32 is formed by combining two types of polymer materials having different hardnesses. The first polymer material 35 having a small hardness is formed in a portion existing in the vertical direction in FIG. , 35, the portions existing in the left-right direction in FIG. 2 are respectively constituted by the second high polymer materials 36, 36 (portions indicated by oblique grids in FIGS. 2 and 3) having high hardness. That is, the first and second polymer materials 35 and 36 are alternately present in the rotational direction of the shafts 30 and 31.

  Of these, the first polymer material 35, 35 having a low hardness is in a state where both the shafts 30, 31 are combined, that is, no rotation is transmitted between the shafts 30, 31. In a no-load state, it is arranged in a state having a slight allowance in a part between each of the engaging convex portions 33, 33 and the engaging concave portions 34, 34. That is, the inner side surface 37 on the inner shaft 30 side, which is the side surface facing each other in the rotational direction of the shafts 30, 31 among the surfaces of the respective engagement convex portions 33, 33 and the engagement concave portions 34, 34, 37 and a portion of the first polymeric material 35, 35 are clamped in a circumferential gap that exists between the outer side surfaces 38, 38 on the outer shaft 31 side. In other words, the thickness of the first polymer materials 35 and 35 in the free state is larger than the thickness of the circumferential gap, which is the distance between the side surfaces 37 and 38.

  On the other hand, the second polymer material 36, 36 having a high hardness has a gap with the inner peripheral surface of the outer shaft 31 in an unloaded state in which both the shafts 30, 31 are combined. For this reason, the second polymer material 36, 36 does not contact the outer side surfaces 38, 38 that are part of the inner peripheral surface of the outer shaft 31 in an unloaded state. In other words, the thickness of the second polymer material 36 in the free state is the clearance between the outer circumferential surface of the inner shaft 30 and the inner circumferential surface of the outer shaft 31. It is smaller than the thickness.

  In addition, the space | interval of the front end surface 39 of each said engagement convex part 33, 33 and the back surface 40 of each said engagement recessed part 34, 34 is made into the free state of said 1st, 2nd polymer material 35, 36. It is larger than the thickness. For this reason, between the front end surface 39 and the back surface 40, the first and second polymer materials 35, 36 are arranged with a gap between the back surface 20 and the first and second polymer materials 35 and 36. As will be described later, such a gap exists in order to absorb the deformation when the first polymer material 35, 35 having a low hardness is elastically deformed.

  In the case of this example, the first and second polymer materials 35 and 36 are integrally formed. Then, the boundary portions 41 and 41 between the first and second polymer materials 35 and 36 are placed on a part between the outer peripheral surface of the inner shaft 30 and the inner peripheral surface of the outer shaft 31, and a torque load is applied. It arrange | positions in the state which has the clearance gaps 42 and 42 irrespective of a state. That is, in the state where the boundary portion 41 is opposed to the portions 43 and 43 between the adjacent engaging recesses 34 and 34 on the inner peripheral surface of the outer shaft 31 through the gaps 42 and 42. It is arranged.

  The inter-parts 43, 43 are more curved than the continuous parts of the engaging convex parts 33, 33 constituting the outer peripheral surface of the inner shaft 30 in order to smoothly connect the engaging concave parts 34, 34 to each other. Is made smaller. And the space | interval of the continuous part of each said engagement convex part 33 and 33 and each said part 43 and 43 is made larger than the space | interval of the said inner and outer both side surfaces 37 and 38. FIG. As a result, the gaps 42 and 42 are allowed to exist between the boundary portions 41 and 41 and the inter-interval portions 43 and 43. Even if the second polymer material 36, 36 existing between the inner and outer side surfaces 37, 38 is elastically compressed to some extent, a large torque acts on the gaps 42, 42. The boundary portions 41 and 41 are enlarged so as not to contact a part of the inner peripheral surface of the outer shaft 31.

  In the case of this example configured as described above, when a torque less than a predetermined magnitude acts between the shafts 30, 31, the torque causes the first polymer material 35, 35 having a low hardness to be applied. Is transmitted through. However, since this torque is small, these first polymer materials 35 and 35 are not damaged early. Further, rattling between the shafts 30 and 31 in an unloaded state is prevented by the first polymer materials 35 and 35.

  On the other hand, when transmitting torque of a predetermined magnitude or more, the first polymer material 35, 35 is elastically compressed between the inner and outer side surfaces 37, 38. Then, the inner shaft 30 slightly rotates relative to the outer shaft 31 by the amount compressed. As a result, the second polymeric material 36, 36 having a high hardness comes into contact with the outer side surfaces 38, 38, and the second polymeric material 36, 36 is used to provide a large amount of the large torque. Communicate proportions.

  FIG. 5 shows the relationship between the magnitude of torque transmitted between the shafts 30 and 31 and the relative rotation amount (torsion angle) between the shafts 30 and 31. In the diagram shown in FIG. 5, the straight portions (i) and (b) with a gentle inclination indicate the torque transmission state by only the first polymer materials 35 and 35. On the other hand, straight portions B and B having a steep slope indicate torque transmission states by the first and second synthetic resins 35 and 36. As is clear from FIG. 5 above, in a state before the torsion angle within a predetermined range, in other words, before the second polymeric material 36 abuts against the outer side surfaces 38 a, all of the torque is It can be seen that this is transmitted by the polymer materials 35 and 35. On the other hand, after the second polymer material 36, 36 abuts on the outer side surfaces 38, 38, torque is applied to both the first and second polymer materials above the predetermined range. It can be seen from 35 and 36 that the information is transmitted. Note that the two types of curves drawn on the top and bottom of FIG. 5 are due to hysteresis.

According to the telescopic shaft 29 of this example as described above, it is possible to realize a structure in which the inner shaft 30 and the outer shaft 31 are easily assembled and excellent in durability.
That is, in the no-load state, only the first polymer material 35, 35 having a low hardness among the polymer materials constituting the cushioning material 32 disposed between the shafts 30, 31 is the inner shaft. It arrange | positions in the state between the outer peripheral surface of 30 and the inner peripheral surface of the outer shaft 31 in the state which has a fastening allowance (elastically clamped). On the other hand, the second polymer materials 36 and 36 having a high hardness are disposed with a gap between the two peripheral surfaces. For this reason, when the shafts 30 and 31 are assembled, only the first polymer materials 35 and 35 are in a state of having an interference between the shafts 30 and 31. In the case of the first polymer materials 35 and 35 having a small hardness, it is easy to cope with the change in the tightening allowance. Therefore, even if the tightening allowance is large, the force required for assembling is small. As a result, the assemblability of the shafts 30 and 31 is improved.

  On the other hand, when a torque of a predetermined magnitude or more is transmitted between the shafts 30 and 31, the second polymer material 36 and 36 having a high hardness is formed on the outer circumference of the inner shaft 30. Not only the inner side surfaces 37 and 37 constituting the surface but also the outer side surfaces 38 and 38 constituting the inner peripheral surface of the outer shaft 31 are brought into contact. Accordingly, torque that is greater than or equal to the predetermined magnitude (exceeding the predetermined magnitude) is transmitted through the second polymer materials 36 and 36. These second polymer materials 36, 36 having a high hardness are superior in strength to compressive force (having a large load resistance) as compared with the first polymer materials 35, 35 having a low hardness, and thus a large torque. Even if it is transmitted, it will not be damaged early. As a result, the durability of the telescopic shaft 29 can be ensured.

  In the case of this example, the boundary portion 41 between the first and second polymer materials 35 and 36 is the portion between the engagement recesses 34 and 34 on the inner peripheral surface of the outer shaft 31. 43 with a predetermined gap 42 between them. The boundary portion 41 is not brought into contact with the intermediate portion 43 regardless of the torque load state. Since the boundary portion 41 is a continuous portion of polymer materials having different hardnesses, it is difficult to ensure strength. When a load is applied to the boundary portion 41, damage such as cracks and peeling is likely to occur. In the case of this example, the boundary portion 41 is arranged as described above so that no load is applied to the boundary portion 41, so that the boundary portion 41 is less likely to be damaged, and durability is improved. We are trying to improve.

  In the case of this example, since the first and second polymer materials 35 and 36 are alternately present in the rotational direction of the shafts 30 and 31, the axial dimension of the cushioning material 32 is reduced. it can. That is, even when the cushioning material 32 is composed of two types of polymer materials, it is not necessary to increase the axial dimension of the cushioning material 32. Therefore, it is easy to apply to a structure having a small axial dimension as the telescopic shaft 29. Such a structure of this example can be preferably applied to a structure in which the axial dimension is relatively difficult to increase, for example, like the above-described intermediate shaft 23.

[Second Example of Embodiment]
6 and 7 show a second example of an embodiment of the present invention corresponding to claims 1 and 2. In the case of this example, out of the cushioning material 32 a coated on the outer peripheral surface of the inner shaft 30, the first polymer materials 35 a and 35 a having a low hardness are used as outer side surfaces 38 and 38 constituting the inner peripheral surface of the outer shaft 31. It is arranged in a part of the part opposite to. In addition, second polymer materials 36a and 36a (portions shown by oblique grids in FIGS. 6 and 7) having high hardness are arranged in portions that are out of the first polymer materials 35a and 35a. Therefore, both the first and second synthetic resins 35 a and 36 a face the same outer side surface 38. Further, the intermediate portion of the first polymer material 35a, 35a is expanded, and the thickness of this portion in the free state is set to the thickness of the second polymer material 36a, 36a, It is larger than the interval between the outer side surfaces 37 and 38.

  In the case of the illustrated example, the boundary portions 41 and 41 between the first and second polymer materials 35a and 36a are subjected to a torque of a predetermined magnitude or more between the shafts 30 and 31. There is a possibility that the outer shaft 31 may come into contact with a part of the inner peripheral surface. However, for example, if a groove is provided in a portion of the inner peripheral surface of the outer shaft 31 facing the boundary portions 41 and 41, the boundary portions 41 and 41 and the inner peripheral surface of the outer shaft 31 Contact can be prevented. Other configurations and operations are the same as those of the first example of the above-described embodiment.

[Third example of embodiment]
FIG. 8 shows a third example of the embodiment of the present invention corresponding to claims 1 and 2. The inner shaft 30a assembled to the structure of this example is a spline shaft having a plurality of teeth 44a, 44b on the outer peripheral surface. And the buffer material 32b which consists of 1st, 2nd polymer material 35b, 36b is coat | covered on the outer peripheral surface of such an inner shaft 30a. In the case of this example, of the teeth 44a and 44b provided on the outer peripheral surface of the inner shaft 30a, the teeth covering the second polymer material 36b and 36b (the portion indicated by the oblique lattice in FIG. 8) having a high hardness. The width H of 44a, 44a in the rotational direction of the inner shaft 30a is larger than the width h in the same direction of the teeth 44b, 44b covering the first synthetic resins 35b, 35b having a low hardness.

  Further, the number of the teeth 44a and 44a having a large width is made larger than that of the teeth 44b and 44b having a small width. In the case of the illustrated example, the total number of the teeth 44a and 44b is 10, but 6 of them are the teeth 44a and 44a having a large width, and the remaining 4 are the teeth 44b and 44b having a small width. . In this way, in order to make the number of teeth 44a and 44b different, the teeth 44a and 44a having a large width are made continuous on both sides in the left-right direction in FIG. That is, in this portion, the wide teeth 44a and the narrow teeth 44b are not alternated. As a result, in the outer peripheral surface of the inner shaft 30a, the area covered by the second polymer material 36b, 36b having a high hardness is wider than the area covered by the first polymer material 35b, 35b having a low hardness. Become.

  Further, as described above, if the width of the teeth 44a and 44a covered by the second polymer material 36b and 36b having a high hardness is increased, a large torque is transmitted through the second polymer material 36b and 36b. Even so, the strength of the teeth 44a and 44a can be sufficiently ensured. Further, as described above, if the area covered with the second polymer material 36b, 36b is widened, it becomes easier to transmit a larger torque. In other words, even when a large torque is transmitted, it is easy to ensure the durability of the second polymer material by suppressing the load per unit area applied to the second polymer material 36b, 36b. Although not shown, the shape of the inner peripheral surface of the outer shaft is also a spline having grooves corresponding to the teeth 44a and 44b. Other structures and operations are the same as those of the first example of the above-described embodiment.

[Fourth Example of Embodiment]
FIG. 9 shows a fourth example of an embodiment of the present invention corresponding to claims 1 and 3. In the case of this example, the first and second polymer materials 35c and 36c constituting the buffer material 32c and having different hardnesses are alternately present in the axial direction of the inner shaft 30b and the outer shaft 31a. In the case of this example, the first polymer materials 35c and 35c are arranged on both sides in the axial direction of the second polymer material 36c (portion shown by the oblique lattice in FIG. 9). And the thickness of the part except these axial direction both ends of these 1st polymeric materials 35c and 35c is enlarged, and this part is made into the outer peripheral surface of the said inner shaft 30b, and the inner peripheral surface of the said outer shaft 31a. It arrange | positions in the state which has a slight interference. On the other hand, the second polymer material 36c is disposed with a gap between the second polymeric material 36c and the inner peripheral surface of the outer shaft 31a when torque is not transmitted. The end portions of the first and second polymer materials 35c and 36c are formed by gradually reducing the thicknesses of both end portions of the first polymer materials 35c and 35c toward the ends, Smooth and continuous.

  In the case of this example, the boundary portions 41a and 41a, which are continuous portions of the end portions of the first and second polymer materials 35c and 36c, can transmit the large torque when the outer shaft 31a It contacts a part of the inner peripheral surface. That is, in this example, the portion of the inner peripheral surface facing the boundary portions 41a and 41a moves as the shafts 30b and 31a are relatively displaced in the axial direction. It is not possible to increase only the distance between the boundary portions 41a and 41a. On the other hand, if the thickness of the boundary portions 41a and 41a is made smaller than that of the second polymer material 36c, the boundary portions 41a and 41a can be made to be the inner peripheral surface of the outer shaft 31a regardless of the torque. It can be made not to contact with a part of. However, the strength is reduced by reducing the thickness of the boundary portions 41a and 41a in this way. Therefore, in consideration of the use situation and the thickness that can be secured at the boundary portion, a structure that easily secures the strength is selected.

  Further, the shafts 30b and 31a of this example are either of the structures of the first and second examples (cross-shaped shafts) of the above-described embodiment and the structure of the third example (spline shaft). It may be a structure. In any case, the first and second polymer materials 35c and 36c are alternately arranged in the axial direction on the outer peripheral surface of the inner shaft 30b. According to such a structure of this example, the buffer material 32c having different characteristics can be easily obtained only by changing the axial lengths of the first and second polymer materials 35c and 36c. In the case of this example, since the first polymer materials 35c and 35c are disposed on both sides in the axial direction of the second polymer material 36c, rattling by the first polymer materials 35c and 35c is prevented. The effect can be obtained more stably. That is, these first polymer materials 35c and 35c are sandwiched between the outer peripheral surface of the inner shaft 30b and the inner peripheral surface of the outer shaft 31a at two points separated in the axial direction. , 31a can be effectively prevented from shaking in the direction in which they are inclined to each other. Other structures and operations are the same as those of the first example or the third example of the above-described embodiment.

  In each example of the above-described embodiment, the present invention has been described for the case where the present invention is applied to an electric power steering apparatus. However, the present invention is naturally applicable to a steering shaft and an intermediate shaft constituting a steering apparatus having another structure. Is possible. In addition to such a steering device, the present invention can be applied to any structure that can transmit and receive rotation with each other and that can expand and contract. Further, in each of the above examples, the case where the outer peripheral surface of the inner shaft is coated with the polymer material has been described, but the inner peripheral surface of the outer shaft may be covered. Each embodiment can also be implemented in combination as appropriate.

The figure which shows an example of the electric power steering apparatus incorporating the expansion-contraction shaft of this invention. Sectional drawing which cut | disconnects and shows the 1st example of embodiment of this invention to the radial direction of a shaft. Part A enlarged view of FIG. The perspective view of the inner shaft which coat | covered the shock absorbing material on the outer peripheral surface. The diagram which shows the relationship between a twist angle and the transmission torque at the time of rotating an inner shaft and an outer shaft relatively. The figure similar to FIG. 2 which shows the 2nd example of embodiment of this invention. The B section enlarged view of FIG. The figure similar to FIG. 2 which shows the 3rd example of embodiment of this invention, taking out an inner shaft and a buffer material. Sectional drawing similarly cut | disconnected and shown to the axial direction of a shaft which shows a 4th example. Sectional drawing which cut | disconnects and shows the 1st example of a conventional structure in the axial direction of a shaft. Similarly, the partial expanded sectional view which cuts and shows the 2nd example in the diameter direction of a shaft.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a Telescopic shaft 2, 2a Inner shaft 3, 3a Buffer material 4 Groove 5 First resin layer 6 Second resin layer 7 Electric power steering device 8 Steering wheel 9 Steering shaft 10 Steering column 11 Steering force auxiliary device 12 Tie rod 13 Steering gear 14 Inner shaft 15 Outer shaft 16 Inner column 17 Outer column 18 Gear housing 19 Output shaft 20 Support bracket 21 Car body 22 Universal joint 23 Intermediate shaft 24 Another universal joint 25 Input shaft 26 Inner shaft 27 Outer shaft 28 Electric motor 29 Telescopic shaft 30, 30a, 30b Inner shaft 31, 31a Outer shaft 32, 32a, 32b, 32c Buffer material 33 Engaging protrusion 34 Engaging recess 35, 35a, 35 , 35c first polymeric material 36, 36a, 36b, 36c second polymeric material 37 inner side 38 outer side 39 front end surface 40 inner surface 41,41a boundary portion 42 gap 43 between portions 44a, 44b teeth

Claims (4)

  The inner shaft whose outer peripheral surface has a non-circular cross-sectional shape, and the inner peripheral surface whose cross-sectional shape is non-circular, the diameter of the inscribed circle related to the inner peripheral surface's cross-sectional shape is related to the outer peripheral surface's cross-sectional shape. The outer shaft is smaller than the diameter of the circumscribed circle, and the inner shaft can be inserted freely, and a cushioning material that exists between the inner shaft and the outer shaft. The inner shaft is inserted into the outer shaft. In such a state, in the telescopic shaft in which rotation can be transmitted between the two shafts via the cushioning material and the shafts can slide in the axial direction, the cushioning material is It is composed of two types of polymer materials with different hardness, and the polymer material with small hardness is the rotation transmission between the two shafts In the unloaded state, the circumferential direction that exists between the outer circumferential surfaces of the inner shaft and the inner circumferential surface of the outer shaft, at least between the side surfaces facing each other with respect to the rotational direction of the two shafts. A polymer material having a large allowance is arranged in a part of the gap, and the high-hardness polymer material is arranged in a state having a gap in the remaining part of the circumferential gap in an unloaded state, When transmitting a rotational torque of a magnitude or more, one of the portions where the high-hardness polymer material is out of the locations where the low-hardness polymer material exists among the side surfaces facing each other in the rotation direction. A telescopic shaft characterized in that it abuts on both side surfaces at the part.   The telescopic shaft according to claim 1, wherein two types of polymer materials having different hardnesses are alternately present with respect to the rotation direction of both shafts.   The telescopic shaft according to claim 1, wherein two types of polymer materials having different hardnesses are alternately present in the axial direction of both shafts.   The boundary between two types of polymer materials with different hardnesses is arranged in a part between the outer peripheral surface of the inner shaft and the inner peripheral surface of the outer shaft with a gap regardless of the rotational torque load state. The telescopic shaft according to any one of claims 1 to 3.

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