JP2007308057A - Expansion/contraction shaft for vehicle steering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an expansion/contraction shaft for a steering effectively preventing damage by increase of slide resistance by an indentation and friction by preventing the indentation from being generated on a portion slide-contacted with a torque transmission part. <P>SOLUTION: In the expansion/contraction shaft for the vehicle steering, a male shaft 11 and a female shaft 12 are fitted so as to be transmitting torque and be relatively movable in an axial direction. A lithium-iron composite oxide layer 30 is provided on a front surface of axial grooves 21a-21c for transmitting torque formed on an outer peripheral surface of the male shaft 11, and a surface modification layer 32 in which a nitrogen element as a surface modification diffusion element is bonded to the other element in a matrix material of the male shaft 11 is provided just below the lithium-iron composite oxide layer 30 and heating treatment is applied. Thereby, generation of indentation by slide contact of the torque transmission part 14 is prevented. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a telescopic shaft for vehicle steering that is incorporated in a steering shaft of a vehicle and has a male shaft and a female shaft that are non-rotatably and slidably fitted.

  The telescopic shaft of the steering mechanism portion of the automobile is required to absorb the axial displacement generated when the automobile travels and to transmit the displacement and vibration on the steering wheel. Further, in order to obtain an optimum position for the driver to drive the automobile, a function of moving the position of the steering wheel in the axial direction and adjusting the position is required. In any of these cases, the telescopic shaft is required to reduce the rattling noise, reduce the rattling on the steering wheel, and reduce the sliding resistance during the sliding operation in the axial direction. .

For this reason, in Patent Document 1, a cylindrical body composed of needle rollers as a plurality of sets of torque transmission members between a plurality of sets of axial grooves formed on the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft. Is fitted. As a result, when the steering torque transmitted from the steering wheel is small, it is possible to prevent rattling between the male shaft and the female shaft. Thus, torque can be transmitted in a highly rigid state. Furthermore, in order to prevent rattling of the needle roller in the rotational direction (circumferential direction), a plastic cage shape is provided. Therefore, the position of the needle roller in the rotational direction can be adjusted with the plastic member, and the accuracy error between the male shaft and the female shaft can be absorbed by the elastic deformation of the plastic.
European Patent Application No. 1078843

However, in the conventional example described in Patent Document 1, a plurality of needles as torque transmission members are provided between a plurality of sets of axial grooves formed on the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft. Since a cylindrical body made of a roller is fitted, there is a risk that this cylindrical body may come into sliding contact with the raceway surface of the axial groove to generate an indentation, and the raceway surface due to an increase in sliding resistance or friction due to the indentation produced. There is an unresolved problem that damage occurs.
Therefore, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, and prevents the occurrence of indentation due to the sliding contact of the torque transmitting portion, and due to an increase in sliding resistance or friction due to the indentation. An object of the present invention is to provide a telescopic shaft for vehicle steering that can effectively prevent damage.

  In order to achieve the above object, a telescopic shaft for vehicle steering according to claim 1 is incorporated in a steering shaft of a vehicle, and a vehicle steering device in which a male shaft and a female shaft are fitted so as to be able to transmit torque and move relative to each other in the axial direction. In the telescopic shaft for rolling, when the two shafts move relative to each other in the axial direction between the axial grooves formed on the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft, The rolling element is interposed, the axial movement is possible between the male shaft and the female shaft at a circumferential position different from the position where the elastic body is arranged, and the movement in the rotational direction is restricted. A torque transmission portion is provided, and at least one of the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft is provided with a lithium / iron composite oxide layer on the outermost surface, immediately below the lithium / iron composite oxide layer, Nitrogen as a surface modifying diffusion element The formation of indentation due to sliding contact of the torque transmitting portion is prevented by performing a heat treatment provided with a surface modification layer bonded to another element in at least one base material of the female shaft. The telescopic shaft for vehicle steering.

According to a second aspect of the present invention, in the telescopic shaft for vehicle steering according to the first aspect, the elastic body exerts a preload action when the transmitted steering torque is less than a predetermined value and exhibits a low rigidity characteristic. The torque transmission unit is configured to exhibit a high rigidity characteristic and to obtain a two-stage torsional rigidity characteristic when the steering torque is equal to or greater than a predetermined value.
According to a third aspect of the present invention, in the telescopic shaft for vehicle steering according to the first or second aspect, the torque transmission portion includes serrations formed on the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft. Either one of the splines is configured.

According to a fourth aspect of the present invention, in the telescopic shaft for vehicle steering according to the first or second aspect, the torque transmitting portion is an axial direction formed on the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft. It is comprised by the cylindrical body arrange | positioned between the groove | channels.
According to a fifth aspect of the present invention, in the telescopic shaft for vehicle steering according to any one of the first to fourth aspects, the heat treatment is such that at least the hardness of the portion in sliding contact with the torque transmitting portion is HV400 or higher. .

According to a sixth aspect of the present invention, in the telescopic shaft for vehicle steering according to any one of the first to fifth aspects, a yoke assembly in which the male shaft and a yoke used for a universal joint are joined by welding. The heat treatment was performed.
Furthermore, the invention according to claim 7 is a vehicle steering telescopic shaft according to any one of claims 1 to 5, wherein the female shaft and a yoke used for a universal joint are joined by welding. The heat treatment was performed.

  According to the present invention, the lithium / iron composite oxide layer is provided on the outermost surface of the axial groove on at least one of the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft, and immediately below the lithium / iron composite oxide layer. In addition, a heat treatment is performed by providing a surface modification layer in which nitrogen element as a surface modification diffusion element is combined with other elements in at least one of the base material of the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft. At least one of the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft has increased surface hardness and increased mechanical strength while improving corrosion resistance. As a result, it is possible to prevent the occurrence of indentation due to the sliding contact of the torque transmitting portion, effectively prevent the torque transmitting portion from being damaged due to an increase in sliding resistance or friction due to the indentation, and the elastic body in the rotational direction. It is possible to prevent backlash and transmit torque in a highly rigid state.

Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described in detail with reference to the drawings.
(Overall configuration of vehicle steering shaft)
FIG. 1 is a side view showing an embodiment in which a vehicle steering telescopic shaft according to the present invention is applied to a steering mechanism of an automobile.
The steering mechanism shown in FIG. 1 includes an upper steering shaft 120 (steering column 103 and steering that is rotatably held by the steering column 103) attached to a member 100 on the vehicle body via an upper bracket 101 and a lower bracket 102. A steering wheel 105 attached to the upper end of the steering shaft 104, a lower steering shaft portion 107 connected to the lower end of the steering shaft 104 via a universal joint 106, and steering to the lower steering shaft portion 107 A pinion shaft 109 connected via a shaft coupling 108, a steering rack shaft 112 connected to the pinion shaft 109, and another frame 110 of the vehicle body supporting the steering rack shaft 112. It is composed of a steering rack support member 113 fixed through an elastic member 111.

  Here, the upper steering shaft portion 120 and the lower steering shaft portion 107 use the vehicle steering telescopic shaft (hereinafter simply referred to as the telescopic shaft) according to the present invention. The lower steering shaft portion 107 is formed by fitting a male shaft and a female shaft. The lower steering shaft portion 107 absorbs axial displacement that occurs when the vehicle travels, and a steering wheel. The performance which does not transmit the displacement and vibration on 105 is required.

In such performance, the vehicle body has a sub-frame structure, and the member 100 for fixing the upper part of the steering mechanism and the frame 110 to which the steering rack supporting member 113 is fixed are separated, and the steering rack supporting member 113 is This is required in the case of a structure that is fastened and fixed to the frame 110 via an elastic body 111 such as rubber.
As another case, when the steering shaft joint 108 is fastened to the pinion shaft 109, the operator may need to have a telescopic function to temporarily retract the telescopic shaft and then engage the pinion shaft 109 for fastening. is there.

  In addition, the upper steering shaft portion 120 at the upper part of the steering mechanism is also fitted with a male shaft and a female shaft, and such an upper steering shaft portion 120 is optimal for a driver to drive an automobile. In order to obtain a correct position, the function of moving the position of the steering wheel 105 in the axial direction and adjusting the position is required. Therefore, the function of expanding and contracting in the axial direction is required. In all the cases described above, it is possible to reduce the rattling noise of the fitting portion on the telescopic shaft, to reduce the backlash on the steering wheel 105, and to reduce the sliding resistance when sliding in the axial direction. Required.

(First embodiment)
FIG. 2 is a longitudinal sectional view of the telescopic shaft for vehicle steering with a cardan shaft joint according to the first embodiment of the present invention. FIG. 3 is an enlarged view of the telescopic shaft for vehicle steering shown in FIG. FIG. 4 is an enlarged cross-sectional view taken along line AA in FIG.
As shown in FIG. 2, a telescopic shaft for vehicle steering (hereinafter simply referred to as a telescopic shaft) 10 (a lower steering shaft portion 107 in FIG. 1) is a male shaft 11 that is non-rotatable and slidably fitted. And the female shaft 12.

The male shaft 11 is joined by welding to a yoke 51 of a cardan shaft joint 50 (universal joint 106 in FIG. 1) on the steering wheel side, and the female shaft 12 made of carbon steel for mechanical structure such as S25C is used for steering. The gear-side cardan shaft joint 53 (steering shaft joint 108 in FIG. 1) is joined to the yoke 54 by welding. Reference numerals 52 and 55 in FIG. 2 indicate welds on the male shaft 11 side and the female shaft 12 side.
Between the outer peripheral surface of the male shaft 11 and the inner peripheral surface of the female shaft 12, as shown in FIG. Similarly, a torque transmission portion 14 is provided at the central portion in the circumferential direction and equally distributed at intervals of 120 degrees in the circumferential direction.

The preload portion 13 is formed on the outer peripheral surface of the male shaft 11 by extending three axial grooves 15a to 15c for rolling elements having a substantially inverted trapezoidal cross section equally distributed in the circumferential direction at intervals of 120 degrees. Yes. Correspondingly, on the inner peripheral surface of the female shaft 12, the rolling element axial direction that forms a pair with the rolling element axial grooves 15 a to 15 c in which the cross section equally distributed at intervals of 120 degrees in the circumferential direction has a Gothic arc shape. Grooves 16a to 16c are formed extending in the axial direction. Here, the axial grooves 15a to 15c for the rolling elements of the male shaft 11 are formed in an inverted C-shaped tapered side surface portion 15d that becomes narrower in the radial direction from the outer peripheral surface, and these tapered side surface portions 15d. Are formed in an inverted trapezoidal shape with a bottom surface portion 15e connecting the inner peripheral sides of the two.
Then, leaf springs 17 a to 17 c are interposed in the rolling element axial grooves 15 a to 15 c of the male shaft 11, and between the leaf springs 17 a to 17 c and the rolling element axial grooves 16 a to 16 c of the female shaft 12. Ball rows 18a to 18c in which a plurality of balls are connected in series are inserted.

  As shown in FIG. 3, the leaf springs 17 a to 17 c are formed at the rear end portions of the rolling element axial grooves 15 a to 15 c of the male shaft 11 and project outwardly, and the distal end of the male shaft 11. It is held in a state of being sandwiched between an annular elastic body 19b disposed in the section. That is, after the elastic body 19b is disposed on the outer periphery of the reduced diameter portion formed at the distal end portion of the male shaft 11, the metal annular stopper plate 19a is placed in the outer peripheral groove formed in the reduced diameter portion of the male shaft 11. Fixed in the caulking state. The elastic body 19b pressed against the annular stopper plate 19a elastically biases toward the stepped portion 20 side while abutting against one end of the plate springs 17a to 17c, thereby restricting axial movement of the plate springs 17a to 17c. And hold.

  Here, as shown in FIGS. 4 and 5, each of the leaf springs 17a to 17c is in contact with the balls of the ball rows 18a to 18c at two points, and the ball side contact portion 17d. A groove surface side contact portion 17e that is spaced apart at a predetermined interval in the circumferential direction and contacts the tapered side surface portion 15d of the axial grooves 15a to 15c of the male shaft 1, and the ball side contact portion 17d and the groove surface side. It has a biasing portion 17f that elastically biases the contact portion 17e in a direction away from each other, and a bottom portion 17g that contacts the bottom surface portion 15e of the axial grooves 15a to 15c. The urging portion 17f has a substantially U shape and is bent in a substantially arc shape. The urging portion 17f having the bent shape causes the ball side contact portion 17d and the groove surface side contact portion 17e to be mutually connected. Can be elastically biased so as to be separated from each other.

  The torque transmission portion 14 includes axially transmitting torque transmission grooves 21 a to 21 c each having an arcuate cross section extending in the axial direction and formed in the circumferential center between the rolling element axial grooves 15 a to 15 c of the male shaft 11. Torque transmitting axial grooves 22a to 22c that are paired with torque transmitting axial grooves 21a to 21c formed in the circumferential center between the rolling element axial grooves 16a to 16c of the female shaft 12, respectively. And have.

The needle rollers 23 a to 23 c are slidably fitted to the female shaft 12 between the axial grooves 21 a to 21 c of the male shaft 11 and the axial grooves 22 a to 22 c of the female shaft 12. These needle rollers 23 a to 23 c are also formed by a step portion 20 formed at the rear end portion of the rolling element axial grooves 15 a to 15 c of the male shaft 11 and an annular elastic body 19 b disposed at the front end portion of the male shaft 11. It is held in a state of being sandwiched between them.
Then, the male shaft 11 and the yoke 51 of the cardan shaft joint 50 described above are joined by welding to form a yoke assembly, and the yoke assembly is at least in contact with the needle rollers 23a to 23c by heat treatment to be described later. While being hardened so that the hardness of the slidable contact surfaces of the grooves 21a to 21c is HV400 or more, the corrosion resistance is improved.

  In the heat treatment of this embodiment, as shown in FIG. 6, a lithium / iron composite oxide layer 30 is formed on the outermost surface of the male shaft 11 that is a material to be heat treated. A soft nitride layer 32 is formed between the surface of the shaft 11. The surface of the soft nitride layer 32 is formed in a porous state, and the lithium / iron composite oxide is mixed in the porous holes, so that the lithium / iron composite oxide layer 30 and the soft nitride layer 32 In between, the mixed layer 34 of the lithium / iron composite oxide and the soft nitride layer 32 is formed.

The male shaft 11 is preferably made of carbon steel for mechanical structure such as S25C.
A lithium / iron composite oxide layer 30 and a soft nitride layer 32 are formed on the surface of the male shaft 11 by a salt bath nitriding method. That is, the male shaft 11 is immersed in a nitride bath containing Li ⁺ , Na ⁺ and K ⁺ as cation components and CNO ⁻ and CO 3 ⁻ as anion components, and a soft nitriding layer 32 is formed on the surface thereof. At this time, an oxidizing power enhancing substance selected from the group consisting of alkali hydroxide, bonded water, free water and wet air is added to the nitride bath to enhance the oxidizing power of the nitride bath, At the same time as the soft nitriding layer 32 is formed, the lithium / iron composite oxide layer 30 is formed on the outermost surface thereof.

The adhesion amount of the lithium / iron composite oxide layer 30 is preferably 10 to 1,500 mg / m ² as lithium atoms.
The soft nitriding layer 32 has a porous structure, and a mixed layer 34 is formed by mixing lithium / iron composite oxide in the porous portion of the upper layer of the soft nitriding layer 32. Thereby, even when the outermost lithium / iron composite oxide layer 30 is removed, the mixed layer 34 in which the lithium / iron composite oxide is mixed remains in the upper layer, so that the corrosion resistance is maintained.

In this way, by performing heat treatment on the male shaft 11, the lithium / iron composite oxide layer 30 is formed on the outermost surface, and a soft nitride layer is formed between the lithium / iron composite oxide layer 30 and the surface of the male shaft 11. 32 and a mixed layer 34 of the lithium / iron composite oxide layer 30 and the soft nitrided layer 32 is formed between the lithium / iron composite oxide layer 30 and the soft nitrided layer 32. Becomes HV400 or more, and the corrosion resistance is improved.
Here, the needle rollers 23a to 23c are made of high carbon chrome bearing steel such as SUJ2, and the surface hardness of the needle rollers 23a to 23c is based on the surface hardness of the torque transmission axial grooves 21a to 21c. It is set large.

By setting the surface hardness of the torque transmission axial grooves 21a to 21c of the male shaft 11 to HV400 or more, the needle rollers 23a to 23c transmit torque of the male shaft 11 when the male shaft 11 and the female shaft 12 are moved relative to each other. When the axial grooves 21a to 21c are slid, it is possible to prevent generation of indentation, and the generation of the indentation increases the sliding resistance of the needle rollers 23a to 23c, or the needle rollers 23a to 23c. Can be prevented from being damaged by friction or the like due to indentations. Incidentally, if the surface hardness of the torque transmission axial grooves 21a to 21c of the male shaft 11 is less than HV400, when the needle rollers 23a to 23c are brought into sliding contact with each other, the torque transmission axial grooves 21a to 21c are brought into contact with the torque transmission axial grooves 21a to 21c. Indentation is generated, and the sliding resistance of the needle rollers 23a to 23c is increased by the generated indentation, and the needle rollers 23a to 23c are damaged by friction due to the indentation, and the male shaft 11 and the female shaft 12 The sliding resistance becomes unstable.
Here, the elastic body according to the claims corresponds to the leaf springs 17a to 17c, the rolling elements according to the claims correspond to the ball rows 18a to 18c, the torque transmission portions according to the claims correspond to the needle rollers 23a to 23c, The surface modified layer of the term corresponds to the soft nitrided layer 32.

Next, the operation of the first embodiment will be described.
In the telescopic shaft 10 having the above-described configuration, the ball trains 18a to 18c are moved by the leaf springs 17a to 17c when the steering torque is not applied to the steering wheel 105 described above and when the steering torque is not transmitted or when the torque is below a predetermined value. Is preloaded to the extent that there is no backlash, so that backlash between the male shaft 11 and the female shaft 12 can be prevented, and the male shaft 11 and the female shaft 12 are stable without backlash. It can slide in the axial direction with a sliding load. At this time, as shown in FIG. 4, there are gaps between the torque transmission axial grooves 21 a to 21 c of the male shaft 11 and the torque transmission axial grooves 22 a to 22 c of the female shaft 12 and the needle rollers 23 a to 23 c. The male shaft 11 and the female shaft 12 can be slightly rotated in the circumferential direction when no torque is input. The needle rollers 23 a to 23 c are fixed to the male shaft 11 in the axial direction by the stopper plate 19 a, the elastic body 19 b and the step portion 20, so that the needle rollers 23 a to 23 c are torque transmission axial grooves 21 a of the male shaft 11. To 21c or the axial grooves 22a to 22c for torque transmission of the female shaft 12 or a part of both, and slides.

  On the other hand, at the time of steering torque transmission in which a steering torque greater than or equal to a predetermined value is applied from the driver to the steering wheel 105, the needle rollers 23a to 23b interposed between the male shaft 11 and the female shaft 12 as shown in FIG. 23c plays a role of torque transmission. For example, when torque is input from the male shaft 11, in the initial stage, preload is applied to the ball rows 18a to 18c by the leaf springs 17a to 17c, thereby preventing rattling.

  As the torque further increases, the needle rollers 23a to 23c of the torque transmitting portion 14 are placed on the side surfaces of the torque transmitting axial grooves 21a to 21c of the male shaft 11 and the torque transmitting axial grooves 22a to 22c of the female shaft 12. The needle rollers 23a to 23c receive a stronger reaction force than the ball rows 18a to 18c, and the torque transmission unit 14 mainly transmits torque. Therefore, it is possible to prevent backlash in the rotational direction between the male shaft 11 and the female shaft 12, and to transmit torque in a highly rigid state. At this time, the needle rollers 23a to 23c and the torque transmission axial grooves 21a to 21c and 22a to 22c mainly receive the load by being continuously contacted in the axial direction, and therefore the ball trains 18a to 18c receiving the load by point contact. There is an advantage that the contact pressure can be kept lower than that.

Further, when the steering torque is less than a predetermined value, the leaf springs 17a to 17c can buffer and reduce unpleasant sounds and vibrations transmitted from the engine room by the preload action.
Therefore, the telescopic shaft 10 of the present embodiment has a two-stage torsional rigidity while effectively utilizing space, reducing the number of parts, and reducing the manufacturing cost because the torque transmission and sliding mechanism also serve as a buffer mechanism. The telescopic shaft 10 having the characteristics can be provided.

  Further, by performing heat treatment on the male shaft 11, a lithium / iron composite oxide layer 30 is formed on the outermost surface, and a soft nitride layer 32 is formed between the lithium / iron composite oxide layer 30 and the surface of the male shaft 11. A male shaft in which a mixed layer 34 of lithium / iron composite oxide and soft nitriding is formed between the lithium / iron composite oxide layer 30 and the soft nitride layer 32 and the needle rollers 23a to 23c are in sliding contact with each other. 11, the surface hardness of the torque transmission axial grooves 21a to 21c is HV400 or more, and the corrosion resistance is improved. Therefore, when the needle rollers 23a to 23c are in sliding contact, the inclination of the male shaft 11 and the female shaft 12 is different. The stick rollers of the needle rollers 23a to 23c prevent indentation from being generated in the torque transmission axial grooves 21a to 21c, and the needle rollers 23a to 23c are slid by the occurrence of the indentation. Damage of the needle roller 23a~23c due to friction resistance increases and indentations can be prevented.

In addition, since the surface hardness of the needle rollers 23a to 23c is set to be larger than the surface hardness of the torque transmitting axial grooves 21a to 21c, durability due to wear of the needle rollers 23a to 23c can be improved.
Here, it is conceivable to heat treat only the male shaft 11 before joining the yoke 54 and the male shaft 11 of the cardan shaft joint 53. In this case, however, masking or the like covering the welding position with the yoke 54 may be used. There is a problem in terms of high cost and mass production. In contrast, in the present embodiment, heat treatment is performed on the yoke assembly in which the male shaft 11 and the yoke 51 of the cardan shaft joint 50 are joined together by welding, thereby eliminating the need for masking and the like and simultaneously with the male shaft 11. Since the yoke 51 is also heat-treated, the cost can be reduced and mass production can be realized. Moreover, if heat treatment is performed on the yoke assembly in which the male shaft 11 and the yoke 51 are joined by welding, the residual stress at the time of welding of the welded portion 52 shown in FIG. Since the base material structure becomes uniform, the mechanical strength of the welded portion 52 can be prevented from being lowered.

In addition, although the said embodiment demonstrated the case where the leaf | plate springs 17a-17c were arrange | positioned in the axial grooves 15a-15c for rolling elements of the male shaft 11, it is not limited to this, The rolling body of the female shaft 12 You may make it arrange | position the leaf | plate springs 17a-17c in the axial grooves 16a-16c for use.
In the above embodiment, the case where the ball rows 18a to 18c and the needle rollers 23a to 23c are held in the rolling element axial grooves 15a to 15c and the torque transmitting axial grooves 21a to 21c of the male shaft 11 has been described. However, the present invention is not limited to this, and the ball rows 18 a to 18 c and the needle rollers 23 a to 23 c are held in the rolling element axial grooves 16 a to 16 c and the torque transmitting axial grooves 22 a to 22 c of the female shaft 12. It may be.

When the needle rollers 23 a to 23 c are held in the torque transmission axial grooves 22 a to 22 c of the female shaft 12, the composite oxide layer 30 is formed on the outermost surface of the female shaft 12 that the needle rollers 23 a to 23 c are in sliding contact with. A soft nitride layer 32 is formed between the composite oxide layer 30 and the surface of the male shaft 11, and the composite oxide layer 30 and the soft nitride layer are provided between the composite oxide layer 30 and the soft nitride layer 32. Heat treatment for forming 32 mixed layers 34 may be performed. In this case, heat treatment is performed on the yoke assembly in which the female shaft 12 and the yoke 55 are joined by welding.
Further, the entire outer peripheral surface of the male shaft 11 or the entire inner peripheral surface of the female shaft 12 may be heat-treated, and further, both the male shaft 11 and the female shaft 12 may be heat-treated.

(Second Embodiment)
7 is a longitudinal sectional view of a telescopic shaft for vehicle steering according to a second embodiment of the present invention, FIG. 8 is a sectional view taken along line BB in FIG. 7, and FIG. 9 is a perspective view showing a leaf spring. is there.
In the second embodiment, the needle rollers 23a to 23c of the first embodiment described above and the torque transmission axial grooves 21a to 21c of the male shaft 11 and the torque transmission axial grooves 22a to 22c of the female shaft 12 are accommodated. 22c is omitted, and serrations 35a to 35c as torque transmitting portions are formed instead of them, and are interposed between the ball rows 18a to 18c and the axial grooves 16a to 16c for the rolling elements of the female shaft 12. The leaf springs 17a to 17c are omitted, and the leaf springs 36a to 36c are interposed between the rolling element axial grooves 37a to 37c of the male shaft 11 and the ball rows 18a to 18c instead. The configuration is the same as that of the first embodiment.

  Here, as shown in FIGS. 7 and 8, the male shaft 11 is formed in a hollow pipe shape and formed with rolling element axial grooves 37a to 37c for accommodating the ball rows 18a to 18c. Serration shaft portions 38a to 38c are respectively formed in the circumferential center portions between adjacent grooves of the rolling element axial grooves 37a to 37c. Each of the serration shaft portions 38a to 38c has two strip-shaped trapezoidal protrusions formed at a predetermined distance in the circumferential direction, as is apparent from FIG. Here, each of the axial grooves 37a to 37c for the rolling elements includes an inverted C-shaped tapered side plate portion 37d that becomes narrower in order from the outer peripheral surface to the inside, and an inner side of these tapered side plate portions 37d. It is comprised by the bottom face board part 37e which connects the circumference side.

On the other hand, the female shaft 12 is formed with Gothic arc-shaped rolling element axial grooves 16a to 16c which are opposed to the rolling element axial grooves 37a to 37c of the male shaft 11 and are paired with these. Serration groove portions 39a to 39c that engage with the serration shaft portions 38a to 38c are formed at the circumferential center between adjacent grooves of the axial grooves 16a to 16c. The serration shaft portions 38a to 38c and the serration groove portions 39a to 39c constitute serrations 35a to 35c serving as torque transmission members. Here, although not shown, the serration shaft portions 38a to 38c and the serration groove portions 39a to 39c are opposed to each other in the circumferential direction with a small gap therebetween.
Further, leaf springs 36 a to 36 c as elastic bodies are interposed between the ball rows 18 a to 18 c and the rolling element axial grooves 37 a to 37 c of the male shaft 11.

  As shown in FIG. 9, each of the leaf springs 36a to 36c has a ball side contact portion 36d that makes contact with the balls of the ball rows 18a to 18c at two points, and a predetermined circumferential direction with respect to the ball side contact portion 36d. A groove surface side contact portion 36e that contacts the tapered side surface plate portion 37d of the axial grooves 37a to 37c of the rolling shaft of the male shaft 11, and the ball side contact portion 36d and the groove surface side contact portion. A biasing portion 36f that resiliently biases 36e in a direction away from each other, a bottom portion 36g that contacts the bottom plate portion 36e of the axial grooves 37a to 37c for the rolling elements, and one end in the longitudinal direction of the bottom portion 36g. It has an engagement piece 36h bent at a substantially right angle to the bottom 36g in the direction opposite to the direction in which the urging portion 36f extends. Here, the urging portion 36f has a bent shape that is substantially U-shaped and bent in a substantially arc shape, and the ball-side contact portion 36d and the groove surface-side contact portion 36e are formed by the bent urging portion 36f. Can be elastically biased so as to be separated from each other.

As shown in FIG. 7, a stopper 40 is fitted to the end of the male shaft 11 having a hollow pipe shape. The stopper 40 is a member that includes a convex fitting portion 40 a that fits into the shaft hole of the male shaft 11, and a flange portion 40 b that has a diameter capable of contacting the end surface of the male shaft 11.
Each of the leaf springs 36a to 36c described above is disposed in a state where the engaging piece 36h bent from one end of the bottom portion 36g is sandwiched between the end surface of the male shaft 11 and the flange portion 40b of the stopper 40. Has been. In this manner, the leaf springs 36a to 36c in which the engagement piece 36h is sandwiched between the flange portion 40b of the stopper 40 are held in a state in which the axial movement is restricted.
Further, the hardness of the sliding contact surfaces of the serration shaft portions 38a to 38c contacting the serration groove portions 39a to 39c on the male shaft 11 after being joined to the yoke 54 of the cardan shaft joint 53 by welding becomes HV400 or more, and corrosion resistance. Heat treatment is performed so that

Also in the heat treatment of this embodiment, as shown in FIG. 6, the lithium / iron composite oxide layer 30 is formed on the outermost surface of the male shaft 11 that is the material to be heat treated. A soft nitrided layer 32 is formed between the surface of the male shaft 11 and the male shaft 11. The soft nitriding layer 32 is formed in a surface porous state, and the lithium / iron composite oxide is mixed in the pores in the porous state, so that the lithium / iron composite oxide layer 30 and the soft nitriding layer 32 A mixed layer 34 of the lithium / iron composite oxide and the soft nitride layer 32 is formed therebetween.
Here, the elastic body of a claim corresponds to the leaf springs 36a to 36c, and the torque transmitting portion of the claim corresponds to the serrations 35a to 35c.

  Also in this embodiment, the serration shaft portions 38a to 38c are heat-treated to have a surface hardness of HV400 or higher, and the corrosion resistance is improved. Therefore, the male shaft 11 and the female shaft 12 are moved relative to the male shaft 11 and the female shaft 12. And the serration shaft portions 38a to 38c and the serration groove portions 39a to 39c can prevent stick indentation from being generated, and serrations 35a to 35c due to the generation of the indentation can be prevented. It is possible to prevent damage to the serration shaft portions 38a to 38c or the serration groove portions 39a to 39c due to an increase in sliding resistance or friction due to indentation.

Further, in the present embodiment, by performing heat treatment on the yoke assembly in which the male shaft 11 and the yoke 51 are joined by welding, work such as masking becomes unnecessary, and the yoke 51 is also heat treated simultaneously with the male shaft 11. Since this is done, the cost can be reduced and mass production can be realized.
On the other hand, the leaf springs 36a to 36c can sufficiently bend the ball side contact portion 36d via the biasing portion 36f, and can ensure a sufficient amount of bending.

  In addition to the ball rows 18a to 18c, the serration shaft portions 38a to 38c and the serration groove portions 39a to 39c are provided with serrations 35a to 35c. Therefore, when transmitting the steering torque, the serration shaft portions 38a to 38c and the serration groove portion are provided. 39a to 39c come into contact with the plate springs 36a to 36c before an excessive load (stress) is applied, and the serrations 35a to 35c mainly transmit torque, so the ball trains 18a to 18c and the plate spring 36a The excessive load (stress) is not applied to .about.36c.

  As described above, the leaf springs 36a to 36c can secure a sufficient amount of bending, and an excessive load (stress) is not applied to the balls of the ball rows 18a to 18c and the leaf springs 36a to 36c. Therefore, the stress generated in the ball trains 18a to 18c and the leaf springs 36a to 36c at the time of transmitting the steering torque can be relieved, so that no high stress is generated and “sag” is caused by permanent deformation. And can maintain preload performance over a long period of time.

  In the present embodiment, the rolling element axial grooves 37a to 37c of the male shaft 11 are configured such that both the tapered side plate portion 37d and the bottom plate portion 36e are flat. The center line of the rolling element axial grooves 37a to 37c is directed toward the center point of the male shaft 11, and the tapered side plate portion 37d has a wedge shape that is a right and left object from the center of the rolling element axial grooves 37a to 37c. ing. The wedge angle (contact angle) is preferably 40 to 70 degrees with respect to the center of the rolling element axial grooves 37a to 37c. As a result, the leaf springs 36a to 36c are firmly fixed to the wedge surfaces of the axial grooves 37a to 37c for the rolling elements, so that when the steering torque is applied, the entire leaf springs 36a to 36c are unlikely to slip. Therefore, the transmission torque is not reduced, and excessive hysteresis can be prevented.

In the present embodiment, the case where the leaf springs 36a to 36c are provided on the male shaft 11 side has been described. However, the present invention is not limited to this and can be provided on the female shaft 12 side.
In the present embodiment, the case where the heat treatment is performed so that the hardness of the sliding contact surface of the serration shaft portions 38a to 38c of the male shaft 11 contacting the serration groove portions 39a to 39c is HV400 or more and the corrosion resistance is improved is described. However, the present invention is not limited to this, and at least only the serration shaft portions 38a to 38c or the serration groove portions 39a to 39c or their peripheral portions may be partially heat-treated, and further, the ball rows 18a to 18c. Only the rolling element axial grooves 16a to 16c of the female shaft 12 in contact with the rolling contact 18c or a peripheral portion including the rolling element axial grooves 16a to 16c may be partially subjected to heat treatment. Further, the entire outer peripheral surface of the male shaft 11 or the entire inner peripheral surface of the female shaft 12 may be heat-treated, or both the male shaft 11 and the female shaft 12 may be heat-treated.

Further, in the present embodiment, the case where the serration portions 35a to 35c are applied as the torque transmission members has been described. However, the present invention is not limited to this, and the spline groove portion and the spline shaft portion are replaced with the serration portions 35a to 35c. You may make it provide the spline part comprised by these.
Furthermore, in the present embodiment, the case where three sets of rolling elements constituted by the ball rows 18a to 18c and three torque transmission members constituted by the serration portions 35a to 35c are provided, respectively, but the present invention is not limited thereto. The number of rolling elements and the number of torque transmission members can be arbitrarily set.

Furthermore, in the present embodiment, the case where the ball rows 18a to 18c are applied as rolling elements has been described. However, the present invention is not limited to this, and a plurality of rolling elements in the axial direction of the male shaft 11 and the female shaft 12 are described. It is also possible to apply a roller row in which the rollers are arranged.
Further, the telescopic shaft for vehicle steering shown in the first embodiment and the second embodiment is not applied to the steering mechanism portion of the automobile shown in FIG. 1, but for example, as shown in FIG. Even when applied to a power steering apparatus including a power assist mechanism 121 incorporating a motor, the same effects can be obtained.

1 is a schematic side view of a steering mechanism part of an automobile to which a telescopic shaft for vehicle steering according to an embodiment of the present invention is applied. It is a longitudinal cross-sectional view of the expansion-contraction shaft for vehicle steering with a cardan shaft coupling which concerns on 1st Embodiment of this invention. FIG. 3 is an enlarged view of a main part of a telescopic shaft for vehicle steering shown in FIG. 2. It is a cross-sectional view along the AA line of FIG. It is a perspective view which shows the leaf | plate spring used in 1st Embodiment of this invention. It is the figure which showed typically the structure | tissue of the surface vicinity of the male shaft which heat-processed in 1st Embodiment of this invention. It is a longitudinal cross-sectional view of the telescopic shaft for vehicle steering which concerns on 2nd Embodiment of this invention. FIG. 8 is a cross-sectional view taken along line BB in FIG. 7. It is a perspective view which shows the leaf | plate spring used in 2nd Embodiment of this invention. It is a figure which shows the steering mechanism part of the motor vehicle which applied the telescopic shaft for vehicle steering which concerns on embodiment of this invention different from FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Telescopic shaft, 11 ... Male shaft, 12 ... Female shaft, 13 ... Preload part, 14 ... Torque transmission part, 15a-15c ... Rolling body axial groove, 16a-16c ... Rolling body axial groove, 17a- 17c ... leaf spring, 18a-18c ... ball train, 21a-21c ... axial groove for torque transmission, 22a-22c ... axial groove for torque transmission, 23a-23c ... needle roller, 30 ... lithium / iron composite oxide layer 32 ... soft nitrided layer, 34 ... mixed layer, 35a-35c ... serration, 36a-36c ... leaf spring, 37a-37c ... axial groove for rolling elements, 38a-38c ... serration shaft, 39a-39c ... serration groove 50 ... Cardan shaft coupling, 51 ... Yoke, 53 ... Cardan shaft coupling, 54 ... Yoke, 100 ... Member, 101 ... Upper bracket, 102 ... Lower bracket, 103 ... Steel Ring column, 104 ... steering shaft, 105 ... steering wheel, 106 ... universal joint, 107 ... lower steering shaft, 108 ... steering shaft joint, 109 ... pinion shaft, 110 ... frame, 111 ... elastic body, 112 ... steering rack shaft 113 ... Steering rack support part, 120 ... Upper steering shaft part

Claims (7)

In a telescopic shaft for vehicle steering that is incorporated in a steering shaft of a vehicle and fitted so that a male shaft and a female shaft can transmit torque and can move relative to each other in the axial direction.
Between the axial grooves formed in the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft, via a rolling element that rolls in the axial relative movement of the two shafts via an elastic body for preload. Dress
A torque transmission part that enables relative movement in the axial direction between the male shaft and the female shaft and restricts movement in the rotational direction at a circumferential position different from the position where the elastic body is disposed,
On at least one of the outer peripheral surface of the male shaft and the inner peripheral surface of the female shaft, a lithium / iron composite oxide layer is provided on the outermost surface, and a surface modifying diffusion element is provided directly below the lithium / iron composite oxide layer. Generation of indentation due to sliding contact of the torque transmitting portion by performing a heat treatment provided with a surface modification layer in which the nitrogen element is bonded to another element in at least one of the base material of the male shaft and the female shaft. A telescopic shaft for vehicle steering, characterized in that it is prevented.   The elastic body exerts a preload action when the transmitted steering torque is less than a predetermined value and exhibits a low rigidity characteristic, and the torque transmitting portion exhibits a high rigidity characteristic when the steering torque is equal to or greater than a predetermined value. The telescopic shaft for vehicle steering according to claim 1, wherein two-stage torsional rigidity characteristics are obtained.   3. The vehicle steering according to claim 1, wherein the torque transmission portion is configured by one of a serration and a spline formed on an outer peripheral surface of the male shaft and an inner peripheral surface of the female shaft. Telescopic shaft.   The said torque transmission part is comprised by the cylindrical body arrange | positioned between the axial direction grooves formed in the outer peripheral surface of the said male axis | shaft, and the inner peripheral surface of the said female axis | shaft. Telescopic shaft for vehicle steering.   The telescopic shaft for vehicle steering according to any one of claims 1 to 4, wherein the heat treatment is performed so that at least a portion in sliding contact with the torque transmission portion has a hardness of HV400 or more.   The telescopic shaft for vehicle steering according to any one of claims 1 to 5, wherein the heat treatment is performed on a yoke assembly in which the male shaft and a yoke used for a universal joint are joined by welding.   The telescopic shaft for vehicle steering according to any one of claims 1 to 5, wherein the heat treatment is performed on a yoke assembly in which the female shaft and a yoke used for a universal joint are joined by welding.

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