Telescopic shaft and method of manufacturing the same

Abstract

To provide a telescopic shaft which can be efficiently manufactured.SOLUTION: A telescopic shaft 10 includes an inner shaft 30, an outer shaft 20, and a sliding member 50. An outer tooth portion 31 is formed on an outer peripheral surface 30a of the inner shaft 30. The outer tooth portion 31 has a plurality of outer teeth 32 arranged in a circumferential direction Cd of the telescopic shaft 10. An inner tooth portion 21 is formed on an inner peripheral surface 20a of the outer shaft 20. The inner tooth portion 21 has a plurality of inner teeth 22 arranged at a position where it is engaged with the outer tooth portion 31. The sliding member 50 is fixed to one of the outer tooth portion 31 and the inner tooth portion 21, and is arranged slidably in an axial direction Ad with respect to the other of the outer tooth portion 31 and the inner tooth portion 21. The sliding member 50 has a holding groove 55 which extends in the axial direction Ad and holds a lubricant 90.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a telescopic shaft and a manufacturing method thereof. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a steering device mounted on a vehicle is provided with a shaft member that transmits rotational torque for steering steered wheels, and the shaft member includes a telescopic shaft that is freely extendable and retractable in the axial direction.

[0003] For example, Patent Document 1 discloses a splined telescopic shaft including an inner shaft and a cylindrical outer shaft fitted together so as to be axially movably, an external spline provided on the outer periphery of the inner shaft, an internal spline provided on the inner periphery of the outer shaft, a resin coating provided on at least one of the external spline and the internal spline, and a lubricant retaining groove formed in the resin coating using either a laser, a water jet, or compressed air and extending in a direction intersecting the axial direction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-174498 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a telescopic shaft composed of an inner shaft and an outer shaft, as in the above-mentioned conventional telescopic shaft, the resin coating provided on at least one of the outer circumference of the inner shaft and the inner circumference of the outer shaft is provided with a lubricant-retaining groove, which is useful for improving telescopic properties (ease of telescopic movement). However, in the above-mentioned conventional telescopic shaft, after removing unnecessary parts of the synthetic resin that covers part of the inner shaft, it is necessary to form a lubricant-retaining groove that extends in a direction intersecting the axial direction in the synthetic resin using a laser or the like. This is disadvantageous from the viewpoint of efficiently manufacturing a telescopic shaft.

[0006] The present invention was made by the inventors of the present application by newly focusing on the above-mentioned problems, and an object of the present invention is to provide a telescopic shaft that can be efficiently manufactured and a manufacturing method thereof. [Means for solving the problem]

[0007] In order to achieve the above object, a telescopic shaft according to one aspect of the present invention is a telescopic shaft that can be extended and contracted in an axial direction, and includes an inner shaft having an external tooth portion formed on its outer peripheral surface, the external tooth portion having a plurality of external teeth arranged in a circumferential direction of the telescopic shaft, an outer shaft having an internal tooth portion formed on its inner peripheral surface, the internal tooth portion having a plurality of internal teeth arranged in a position to mesh with the external tooth portion, and a sliding member fixed to one of the external tooth portion and the internal tooth portion and arranged to be slidable in the axial direction relative to the other of the external tooth portion and the internal tooth portion, and the sliding member has a retaining groove extending in the axial direction that retains a lubricant.

[0008] A method for manufacturing a telescopic shaft according to one aspect of the present invention is a method for manufacturing a telescopic shaft that can be extended and contracted in an axial direction, the telescopic shaft comprising an inner shaft having an external tooth portion formed on an outer circumferential surface thereof, the external tooth portion having a plurality of external teeth arranged in a circumferential direction of the telescopic shaft, an outer shaft having an internal tooth portion formed on an inner circumferential surface thereof, the internal tooth portion having a plurality of internal teeth arranged at a position to mesh with the external tooth portion, and a sliding member fixed to one of the external tooth portion and the internal tooth portion and arranged to be slidable in the axial direction relative to the other of the external tooth portion and the internal tooth portion, the manufacturing method including: a molding step of molding a resin coating that serves as a base material of the sliding member on one of the external tooth portion and the internal tooth portion; and a processing step of forming a retaining groove that extends in the axial direction in the resin coating and is capable of retaining a lubricant, by moving the die relative to the resin coating in the axial direction while pressing a convex portion formed on the die against the resin coating. Effect of the Invention

[0009] According to the present invention, it is possible to provide a telescopic shaft that can be efficiently manufactured and a manufacturing method thereof. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram showing an outline of a configuration of a steering device according to an embodiment; [Diagram 2] FIG. 2 is an external perspective view of the telescopic shaft according to the embodiment. [Diagram 3] FIG. 2 is an exploded perspective view of the telescopic shaft according to the embodiment. [Figure 4] FIG. 2 is a first enlarged perspective view showing an external tooth portion of an inner shaft in the embodiment. [Diagram 5] FIG. 4 is a second enlarged perspective view showing the external teeth portion of the inner shaft in the embodiment. [Figure 6] FIG. 2 is an enlarged perspective view showing an internal teeth portion of an outer shaft in the embodiment. [Figure 7] FIG. 2 is a cross-sectional view of a telescopic shaft according to an embodiment. [Figure 8] FIG. 2 is a cross-sectional view showing the configuration of the external teeth and their surroundings according to the embodiment. [Figure 9] 4 is a cross-sectional view of the external teeth and their surroundings in the external teeth portion according to the embodiment. FIG. [Figure 10] 4 is a cross-sectional view showing a state in which a resin coating is formed on an external tooth portion according to an embodiment. FIG. [Figure 11] 11 is a partial cross-sectional view of a mold for removing a part of the resin coating shown in FIG. 10. [Figure 12] FIG. 13 is a schematic diagram illustrating a process of removing a part of the resin coating using a mold. [Figure 13] 13 is a cross-sectional view showing the resin coating after a portion of the resin coating has been removed by the step shown in FIG. 12. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments and modifications will be described in detail with reference to the drawings. Note that the embodiments and modifications described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement and connection forms of the components, and the order of the manufacturing process shown in the following embodiments and modifications are merely examples and are not intended to limit the present invention. In addition, among the components in the following embodiments and modifications, components that are not described in the independent claims showing the highest concept will be described as optional components.

[0012] In addition, the drawings are schematic diagrams in which emphasis, omission, or ratio adjustment is appropriately performed to illustrate the present invention, and may differ from the actual shape, positional relationship, and ratio. Furthermore, in the following embodiments and claims, expressions indicating relative directions or attitudes, such as parallel and perpendicular, may be used, but these expressions may not strictly mean the direction or attitude. For example, two directions being parallel not only means that the two directions are completely parallel, but also means that the two directions are substantially parallel, that is, that there is a difference of, for example, about several percent.

[0013] (Embodiment) [1. Overview of the configuration of the steering device 100] First, an outline of the configuration of a steering device 100 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing the outline of the configuration of the steering device 100 according to an embodiment. As shown in Fig. 1, the steering device 100 according to this embodiment is a device that steers steered wheels 210 based on a rotational torque generated by a driver operating an operating member 200 such as a steering wheel.

[0014] The steering device 100 includes a steering column shaft 190 having an operating member 200 connected to one end thereof, a telescopic shaft 10, a belt transmission device 101, a shaft body 110, a ball nut 120, and a housing 140. The belt transmission device 101 includes an assist motor 150, a driving pulley 153, a driven pulley 130, and a belt 160.

[0015] The steering column shaft 190 is a member that mechanically transmits the rotational torque of the operating member 200 operated by the driver to the shaft body 110 via the telescopic shaft 10. The shaft body 110 is a rod-shaped member having a screw groove 111 on a part of the outer circumferential surface in the axial direction. The shaft body 110 is connected to the steered wheels 210 via a tie rod 211, and functions as a steering shaft that steers the steered wheels 210. In addition, a rack 112 is provided on the shaft body 110, and a rack-and-pinion mechanism is formed in which the pinion gear of the pinion shaft 191 and the rack 112 mesh with each other. The steering device 100 is a so-called electric power steering device in which the rotational torque transmitted via the steering column shaft 190 is converted into linear motion of the shaft body 110, and the assist torque by the assist motor 150 is converted into linear motion of the shaft body 110. 1 illustrates that the assist torque from the assist motor 150 is transmitted to the shaft body 110 via the drive pulley 153, the belt 160, the driven pulley 130, and the ball nut 120, but there is no particular limitation on the method of transmitting the assist torque to the shaft body 110. For example, the assist torque from the assist motor 150 may be transmitted to the shaft body 110 via a pinion gear. In addition, the steering device 100 does not need to be an electric power steering device. The steering device 100 may have a structure that steers the steered wheels 210 only by the rotational torque transmitted via the steering column shaft 190.

[0016] The housing 140 is a member that houses the shaft body 110. In this embodiment, the housing 140 is fixed to the vehicle body using an integrally molded bracket, holds the shaft body 110 housed inside, and guides the movement of the shaft body 110. The housing 140 is formed, for example, from an aluminum alloy. Corrugated tubular boots 142 made of rubber or the like are attached to both ends of the housing 140. The boots 142 seal the openings at both longitudinal ends of the housing 140, thereby preventing water, mud, and the like from entering the inside of the housing 140.

[0017] In this embodiment, the telescopic shaft 10 is a telescopic shaft member, for example, called an intermediate shaft. The telescopic shaft 10 mechanically connects a steering column shaft 190 and a pinion shaft 191. The telescopic shaft 10 includes a cylindrical outer shaft 20 and an inner shaft 30, which is a solid shaft body. In this embodiment, each of the outer shaft 20 and the inner shaft 30 is made of a metal such as iron. Each of the outer shaft 20 and the inner shaft 30 may be made of a material having a predetermined rigidity and durability, and for example, a non-metallic material such as resin may be used as a part or all of the material.

[0018] The inner shaft 30 is attached to the outer shaft 20 with its end inserted inside the outer shaft 20. More specifically, the outer shaft 20 and the inner shaft 30 are fitted together in a state in which one can move relative to the other in the axial direction of the telescopic shaft 10 and one cannot rotate relative to the other in the circumferential direction of the telescopic shaft 10. That is, in the telescopic shaft 10, the outer shaft 20 and the inner shaft 30 have a structure in which they slide relative to each other in the axial direction and engage with each other in the circumferential direction. Furthermore, the telescopic shaft 10 is connected to the steering column shaft 190 via a universal joint 29 and to the pinion shaft 191 via a universal joint 39. This mechanically connects the steering column shaft 190 and the pinion shaft 191, which have different axial directions, and allows the rotational torque received from the steering column shaft 190 to be transmitted to the pinion shaft 191. The steering column shaft 190 and the telescopic shaft 10 may be collectively referred to as the "steering shaft". In this case, the telescopic shaft 10 is a part of the steering shaft. The telescopic shaft 10 according to this embodiment will be described in more detail below.

[0019] [2. Configuration of telescopic shaft 10] FIG. 2 is an external perspective view of the telescopic shaft 10 according to the embodiment. FIG. 2 illustrates a state in which universal joints 29 and 39 are attached to both ends of the telescopic shaft 10 in the axial direction. In FIG. 2, the dashed line with the reference symbol A indicates the rotation axis A (virtual axis) of the telescopic shaft 10. The "axial direction Ad" means a direction parallel to the rotation axis A, and in this embodiment, it is made to coincide with the X-axis direction. The "circumferential direction Cd" means a direction around the rotation axis A with the rotation axis A as the center. FIG. 3 is an exploded perspective view of the telescopic shaft 10 according to the embodiment. FIG. 4 is a first enlarged perspective view showing the external teeth portion 31 of the inner shaft 30 according to the embodiment. In FIG. 4, the external teeth portion 31 is shown in a state in which the sliding member 50 is not arranged. FIG. 5 is a second enlarged perspective view showing the external teeth portion 31 of the inner shaft 30 according to the embodiment. In FIG. 5, the external teeth portion 31 is shown in a state in which the sliding member 50 is arranged. FIG. 6 is an enlarged perspective view showing the internal teeth portion 21 of the outer shaft 20 according to the embodiment. Fig. 7 is a cross-sectional view of the telescopic shaft 10 according to the embodiment. Fig. 7 shows a schematic cross-section of the telescopic shaft 10 in the YZ plane passing through the line VII-VII in Fig. 2. Fig. 8 is a cross-sectional view showing the configuration of the external teeth 32 and its surroundings according to the embodiment. Fig. 8 shows an enlarged cross-section of a dotted rectangular area marked with the symbol VIII in Fig. 7.

[0020] As shown in FIG. 2, the telescopic shaft 10 includes an inner shaft 30 and an outer shaft 20. On the outer peripheral surface 30a of the inner shaft 30, an external tooth portion 31 having a plurality of external teeth 32 arranged in the circumferential direction Cd is formed as shown in FIGS. 3 to 5. In this embodiment, the external tooth portion 31 is formed by 18 external teeth 32 arranged at equal intervals in the circumferential direction Cd. On the inner peripheral surface 20a of the outer shaft 20, an internal tooth portion 21 is formed as shown in FIGS. 6 and 7. The internal tooth portion 21 has a plurality of (18 in this embodiment) internal teeth 22 arranged at positions meshing with the external tooth portion 31 of the inner shaft 30. Each of the multiple external teeth 32 of the external tooth portion 31 extends in the axial direction Ad on the inner shaft 30, and each of the multiple internal teeth 22 of the internal tooth portion 21 extends in the axial direction Ad on the outer shaft 20. The external tooth portion 31 is also called, for example, an "external spline", and the internal tooth portion 21 is also called, for example, an "internal spline".

[0021] In this way, the telescopic shaft 10 according to this embodiment has a structure in which the external teeth portion 31 having a plurality of external teeth 32 protruding radially outward and provided on the inner shaft 30 and the internal teeth portion 21 having a plurality of internal teeth 22 protruding radially inward and provided on the outer shaft 20 mesh (engage) with each other in the circumferential direction Cd of the telescopic shaft 10. As a result, a rotational torque applied to one of the inner shaft 30 and the outer shaft 20 is transmitted to the other. Furthermore, since the external teeth portion 31 and the internal teeth portion 21 extend in the axial direction Ad, the telescopic shaft 10 can change its overall length in the axial direction Ad while maintaining the function of transmitting rotational torque from one end to the other end in the axial direction Ad.

[0022] In this embodiment, when the telescopic shaft 10 extends and retracts, the outer shaft 20 and the inner shaft 30 do not slide while being in direct contact with each other, but are configured to slide via a sliding member 50 arranged between the outer shaft 20 and the inner shaft 30 in the radial direction.

[0023] Specifically, the telescopic shaft 10 includes a sliding member 50 disposed between the external teeth portion 31 and the internal teeth portion 21, as shown in FIG. 3. In this embodiment, the sliding member 50 is fixed to the external teeth portion 31 of the inner shaft 30. More specifically, in this embodiment, the heated external teeth portion 31 is placed in a container (fluidized immersion tank) in which powder paint is flowing, so that the powder paint is melted and adhered to the external teeth portion 31. As a result, a resin coating that becomes the base material of the sliding member 50 (the sliding member 50 before completion) is formed on the external teeth portion 31. This method is called, for example, a fluidized immersion method. A part of the resin coating formed on the external teeth portion 31 is scraped off using a mold, and thus the sliding member 50 having the holding groove 55 described later is formed. Details of the method of forming the sliding member 50 will be described later with reference to FIGS. 9 to 13. The method of fixing the sliding member 50 to the external teeth portion 31 or the internal teeth portion 21 is not particularly limited. The sliding member 50, which has been formed in advance to a predetermined size and shape, may be fixed to the external teeth portion 31 or the internal teeth portion 21 of the inner shaft 30 by adhesive, welding, screwing, crimping, or the placement of a stopper, or a combination of these.

[0024] The sliding member 50 is a member formed of, for example, a resin, and has a relatively small sliding friction on the surface. This improves the slidability (ease of sliding) of one of the inner shaft 30 and the outer shaft 20 relative to the other. Examples of resins forming the sliding member 50 include polyethylene and polytetrafluoroethylene (PTFE). In addition, the sliding member 50 is designed so that a gap exists between the radial outer side and the internal teeth portion 21, which also improves the ease of sliding.

[0025] Specifically, as shown in Figs. 7 and 8, the sliding member 50 fixed to the external tooth portion 31 of the inner shaft 30 is disposed so as to be in close contact with the outer surface of the external tooth portion 31 (multiple external teeth 32). Meanwhile, a gap is formed between the sliding member 50 and the internal tooth portion 21 (multiple internal teeth 22) of the outer shaft 20. More specifically, a relatively wide gap is formed between the tooth tip portion 22a (see Fig. 8) of the internal tooth 22 of the internal tooth portion 21 and the sliding member 50, and between the tooth bottom portion 23 formed between two adjacent internal teeth 22 of the internal tooth portion 21 and the sliding member 50. The tooth bottom portion 23 is a part of the inner peripheral surface 20a of the internal tooth 22 (see Figs. 6 and 8). Furthermore, a relatively narrow gap is formed between the internal tooth 22 and the external tooth 32 in the circumferential direction Cd of the telescopic shaft 10. A lubricant 90 can be contained in the gaps between these sliding members 50 and the internal teeth portion 21. In Fig. 8, the areas where the lubricant 90 can be contained are represented by dotted areas. This lubricant 90 allows one of the inner shaft 30 and the outer shaft 20 to move more smoothly relative to the other.

[0026] Furthermore, the sliding member 50 according to this embodiment is provided with a retaining groove 55 extending in the axial direction Ad, which retains the lubricant 90. For example, when the telescopic shaft 10 is assembled, when the telescopic shaft 10 extends and retracts, and / or when the telescopic shaft 10 rotates, a part of the lubricant 90 retained in the retaining groove 55 is supplied between the sliding member 50 and the internal teeth portion 21. This suppresses deterioration or damage of the sliding member 50 and the generation of abnormal noise due to the stick-lip phenomenon caused by a lack of the lubricant 90 between the sliding member 50 and the internal teeth portion 21.

[0027] More specifically, in the telescopic shaft 10, the internal teeth portion 21 and the external teeth portion 31 engage with each other in the circumferential direction Cd to transmit the rotational torque from one end to the other end in the axial direction Ad. Therefore, if the gap between the sliding member 50 and the internal teeth portion 21 in the circumferential direction Cd is large, the sliding member 50 and the internal teeth portion 21 collide in the circumferential direction Cd, or one of the outer shaft 20 and the inner shaft 30 is tilted with respect to the axial direction Ad, which tends to cause rattling. Such rattling can cause problems such as deterioration of the telescopic shaft 10 and a decrease in the operability of the steering device 100. In this regard, in the telescopic shaft 10 according to the present embodiment, a small gap is provided between the sliding member 50 and the internal teeth portion 21 in the circumferential direction Cd, thereby suppressing rattling of the telescopic shaft 10 while ensuring ease of movement of one of the inner shaft 30 and the outer shaft 20 in the axial direction Ad relative to the other. In addition, the presence of the lubricant 90 in the gap improves the ease of sliding of the sliding member 50 relative to the internal teeth portion 21.

[0028] Furthermore, the opposing portions of the sliding member 50 and the internal teeth portion 21 in the circumferential direction Cd are in a relationship in which they can come into contact with each other when the outer shaft 20 rotates based on the operation of the operating member 200 by the driver. In other words, the portion that can be a factor of an increase in frictional resistance when the telescopic shaft 10 extends and retracts extends in the axial direction Ad. In contrast, the sliding member 50 according to this embodiment is provided with a retaining groove 55 that extends in the axial direction Ad. This allows the lubricant 90 to be efficiently supplied to the portion of the telescopic shaft 10 that can be a factor of an increase in frictional resistance.

[0029] Furthermore, in this embodiment, in the circumferential direction Cd, a retaining groove 55 is provided on each of both sides of one external tooth 32 of the external tooth portion 31. This allows the lubricant 90 to be efficiently supplied to a narrow gap between the sliding member 50 and the internal tooth portion 21 in the circumferential direction Cd, to which the lubricant 90 is difficult to be supplied.

[0030] 8, the lubricant 90 may be disposed in the entire gap between the sliding member 50 and the internal teeth portion 21, but it is not necessary that the lubricant 90 be disposed in the entire gap. From the viewpoint of smooth extension and contraction of the telescopic shaft 10, it is preferable that the lubricant 90 be disposed at least in the portion where there is a high probability of contact between the sliding member 50 and the internal teeth portion 21 in the circumferential direction Cd.

[0031] [3. Manufacturing method of telescopic shaft 10] Next, an example of a manufacturing method of the telescopic shaft 10 configured as described above will be described with reference to Figs. 9 to 13. Fig. 9 is a cross-sectional view of the external teeth 32 and its periphery in the external teeth portion 31 according to the embodiment. Fig. 9 shows the external teeth portion 31 in a state where the sliding member 50 is not arranged. Fig. 10 is a cross-sectional view showing a state where the resin coating 50a is formed on the external teeth portion 31 according to the embodiment. Fig. 11 is a partial cross-sectional view of a die 500 for removing a part of the resin coating 50a shown in Fig. 10. Fig. 12 is a schematic diagram showing a process of removing a part of the resin coating 50a using the die 500. Fig. 13 is a cross-sectional view showing the resin coating 50a after a part is removed by the process shown in Fig. 12. That is, in Fig. 13, a cross section of the sliding member 50 having the holding groove 55 is shown together with a cross section of the external teeth portion 31. In Fig. 13, the removed part (unnecessary part) of the resin coating 50a is shown by a dotted area on the outside of the sliding member 50.

[0032] When manufacturing the telescopic shaft 10 shown in Figs. 1 to 8, a sliding member 50 is disposed on one of the inner shaft 30 and the outer shaft 20 before inserting the inner shaft 30 into the outer shaft 20. In this embodiment, the sliding member 50 is disposed on the external teeth portion 31 of the inner shaft 30. Specifically, a resin coating 50a is formed on the inner shaft 30 (see Fig. 9) on which the sliding member 50 is not disposed. In this embodiment, the resin coating 50a is formed on the external teeth portion 31 of the inner shaft 30 by a fluidized bed method using a powder paint (see Fig. 10). There is no particular limitation on the method for forming the resin coating 50a, and for example, the resin coating 50a may be formed on the external teeth portion 31 by spraying liquid resin onto the external teeth portion 31 and solidifying it.

[0033] The resin coating 50a thus formed is not uniform in thickness and has a relatively rough surface. Therefore, a step of adjusting the thickness of the resin coating 50a is carried out using, for example, a mold 500 shown in Fig. 11. As a result, the slide member 50 having the shape shown in Figs. 7 and 8 is obtained.

[0034] Specifically, as shown in Fig. 11, the mold 500 has a recess 501 for forming a portion of the sliding member 50 that covers the external teeth 32, and a pair of protrusions 505 for forming the holding groove 55, which are disposed inside the recess 501. Note that Fig. 11 shows only one recess 501 and its periphery in the mold 500, but the mold 500 has a plurality of recesses 501 that correspond one-to-one to the plurality of external teeth 32 of the external teeth portion 31. Each of the plurality of recesses 501 has a pair of protrusions 505. That is, the overall shape of the mold 500 has, for example, a through hole 502 in the center through which the resin coating 50a passes, and a plurality of recesses 501 are arranged on the inner peripheral surface of the through hole 502.

[0035] The inner shaft 30 is inserted into the through hole 502 of the mold 500 thus configured (see FIG. 12). That is, one of the mold 500 and the inner shaft 30 is moved in the axial direction Ad relative to the other. For example, the inner shaft 30 is moved in the axial direction Ad relative to the fixed mold 500. As a result, at least the portion of the inner shaft 30 on which the resin coating 50a is formed (including the external teeth portion 31) is inserted into the through hole 502 of the mold 500 and passes through the through hole 502. As a result, the unnecessary portion of the resin coating 50a is scraped off by the mold 500, and the sliding member 50 having the shape shown in FIG. 13 is formed. In addition, the sliding member 50 is formed with a retaining groove 55 extending from one end to the other end in the axial direction Ad. Specifically, a pair of retaining grooves 55 (see FIGS. 7, 8, and 13) is arranged on each of the multiple external teeth 32 in the external teeth portion 31 of the inner shaft 30.

[0036] After the sliding member 50 is obtained through such steps, the lubricant 90 (for example, grease) is applied to the sliding member 50. As a result, the lubricant 90 is disposed on the surface of the sliding member 50 other than the multiple holding grooves 55, and the lubricant 90 is held in each of the multiple holding grooves 55. In this state, the end of the inner shaft 30 to which the sliding member 50 is fixed (the end provided with the external teeth portion 31) is inserted into the inside of the internal teeth portion 21 of the outer shaft 20, thereby assembling the telescopic shaft 10. At this time, a part of the lubricant 90 applied to the sliding member 50 is pushed outward, but at least the lubricant 90 inside the multiple holding grooves 55 is maintained almost as it is. Thereafter, for example, when the telescopic shaft 10 expands and contracts or rotates, a part of the lubricant 90 held in each of the one or more holding grooves 55 is supplied between the sliding member 50 and the internal teeth portion 21.

[0037] In this manner, in the sliding member 50 according to the present embodiment, the inner shaft 30 on which the resin coating 50a is formed is moved relative to the die 500 in the axial direction Ad. As a result, the size and shape of the resin coating 50a are adjusted to a size and shape that can suppress rattling during rotation of the telescopic shaft 10 and improve ease of telescopic movement, and further, a retaining groove 55 extending in the axial direction Ad is formed in the resin coating 50a. In other words, the sliding member 50 having the retaining groove 55 is formed by a single relative movement of the inner shaft 30 with respect to the die 500.

[0038] [4. Summary of the embodiment] The technical features of the telescopic shaft 10 and the manufacturing method thereof according to the present embodiment described above can be explained as follows, for example, in items (1) to (6).

[0039] (1) The telescopic shaft 10 according to this embodiment is telescopic in the axial direction Ad of the telescopic shaft 10. The telescopic shaft 10 includes an inner shaft 30, an outer shaft 20, and a sliding member 50. An external toothed portion 31 is formed on the outer peripheral surface 30a of the inner shaft 30. The external toothed portion 31 has a plurality of external teeth 32 arranged in the circumferential direction Cd of the telescopic shaft 10. An internal toothed portion 21 is formed on the inner peripheral surface 20a of the outer shaft 20. The internal toothed portion 21 has a plurality of internal teeth 22 arranged at positions meshing with the external toothed portion 31. The sliding member 50 is fixed to one of the external toothed portion 31 and the internal toothed portion 21, and is arranged to be slidable in the axial direction Ad relative to the other of the external toothed portion 31 and the internal toothed portion 21. The sliding member 50 has a retaining groove 55 extending in the axial direction Ad, which retains a lubricant 90.

[0040] According to this configuration, the holding groove 55 extends in the axial direction Ad in the sliding member 50. Therefore, for example, the holding groove 55 can be formed in the base material by a process of bringing the die 500 into contact with the base material (the resin coating 50a in this embodiment) of the sliding member 50 fixed to one of the external teeth portion 31 and the internal teeth portion 21 and moving the die 500 in the axial direction Ad. Therefore, the holding groove 55 extending in the axial direction Ad can be formed easily and accurately. In other words, the sliding member 50 having the holding groove 55 can be efficiently manufactured, and as a result, the telescopic shaft 10 can be efficiently manufactured.

[0041] In this embodiment, the portion where the sliding member 50 and the other of the external toothed portion 31 and the internal toothed portion 21 can come into contact with each other extends in the axial direction Ad. Therefore, the lubricant 90 is efficiently supplied to the portion from the retaining groove 55 extending along the portion. In other words, the lubricant 90 can be efficiently supplied to the portion of the telescopic shaft 10 that can be a factor in increasing frictional resistance. This more reliably obtains the effect of improving the telescopic property of the telescopic shaft 10 by the lubricant 90. For example, even if the amount of movement of one of the inner shaft 30 and the outer shaft 20 in the axial direction Ad relative to the other (the amount of expansion and contraction of the telescopic shaft 10) is relatively small, the lubricant 90 can be supplied from the retaining groove 55 to a range wider than the amount of movement because the retaining groove 55 extends in the axial direction Ad.

[0042] In the present embodiment, the sliding member 50 is fixed to the external teeth portion 31, and is disposed so as to be slidable in the axial direction Ad relative to the internal teeth portion 21. Therefore, processing (see FIGS. 11 to 13) for forming the holding grooves 55 can be easily performed on the base material (resin coating 50a) disposed on the external teeth portion 31.

[0043] The sliding member 50 may be fixed to the internal teeth portion 21 and disposed so as to be slidable in the axial direction Ad relative to the external teeth portion 31. Even in this case, it is possible to form one or more holding grooves 55 in the resin coating 50a formed on the surface of the internal teeth portion 21, for example, by inserting a die having one or more protrusions protruding radially outward into an internal space (see FIG. 6) located inside the internal teeth portion 21 of the outer shaft 20. In addition, even when the sliding member 50 is fixed to the internal teeth portion 21, the lubricant 90 is supplied between the sliding member 50 and the external teeth portion 31 from the holding grooves 55 formed in the sliding member 50.

[0044] (2) In the telescopic shaft 10 described in (1) above, the retaining groove 55 is formed over the entire area of ​​the sliding member 50 in the axial direction Ad. Therefore, the lubricant 90 can easily reach the entire area of ​​the sliding member 50 in the axial direction Ad. This further improves the telescopic property of the telescopic shaft 10.

[0045] (3) In the telescopic shaft 10 described in (1) or (2) above, the retaining groove 55 is formed between the external teeth 32 and the internal teeth 22 adjacent to each other in the circumferential direction Cd among the multiple external teeth 32 and the multiple internal teeth 22 (see Figures 7 and 8).

[0046] Here, in terms of suppressing wobbling of the telescopic shaft 10, it is advantageous for the gap between the sliding member 50 fixed to one of the external teeth portion 31 and the internal teeth portion 21 in the circumferential direction Cd and the other of the external teeth portion 31 and the internal teeth portion 21 to be narrow. However, if the gap is narrow, a problem of increased friction resistance between the sliding member 50 and the other is likely to occur. In this regard, in this embodiment, a retaining groove 55 is disposed at a position between the external teeth 32 and the internal teeth 22 of the sliding member 50 in the circumferential direction Cd. This makes it possible to improve the telescopic property of the telescopic shaft 10 while suppressing wobbling of the telescopic shaft 10.

[0047] (4) In the telescopic shaft 10 described in (3) above, the retaining grooves 55 are formed on both sides of the external teeth 32 in the circumferential direction Cd in the sliding member 50 (see FIG. 8). Therefore, when the outer shaft 20 rotates based on the operation of the operating member 200 by the driver, for example, the lubricant 90 is efficiently supplied from the retaining grooves 55 to both sides of the sliding member 50 in the circumferential direction Cd.

[0048] For example, in FIG. 8, it is assumed that the outer shaft 20 rotates clockwise based on the operation of the operating member 200 by the driver. In this case, the sliding member 50 and the inner teeth 22 are in a state of pressing against each other on the left side (Y-axis minus direction) of the outer teeth 32 of the inner shaft 30, and the gap between the sliding member 50 and the inner teeth 22 on the right side (Y-axis plus direction) of the outer teeth 32 becomes large. This makes it easier for the lubricant 90 to be supplied to the gap from the holding groove 55 located on the right side of the outer teeth 32. Thereafter, it is assumed that the outer shaft 20 rotates counterclockwise based on the operation of the operating member 200 by the driver. In this case, the lubricant 90 supplied to the gap from the holding groove 55 on the right side of the outer teeth 32 is spread so as to fill the gap as the gap narrows. On the other hand, the gap between the sliding member 50 and the inner teeth 22 on the left side of the outer teeth 32 becomes large, and this makes it easier for the lubricant 90 to be supplied to the gap from the holding groove 55 on the left side of the outer teeth 32. Further, thereafter, as the outer shaft 20 rotates clockwise, the lubricant 90 supplied to the gap on the left side of the external tooth 32 narrows, and spreads to fill the gap. In this manner, by arranging a pair of retaining grooves 55 sandwiching the external tooth 32 in the circumferential direction Cd, the lubricant 90 is efficiently supplied to the narrow gap between the sliding member 50 and the internal tooth portion 21 in the circumferential direction Cd, into which the lubricant 90 is difficult to be supplied.

[0049] (5) The manufacturing method of the telescopic shaft 10 according to this embodiment is described, for example, as follows. The manufacturing method of the telescopic shaft 10 includes a molding step of molding a resin coating 50a, which serves as a base material of the sliding member 50, on one of the external teeth portion 31 and the internal teeth portion 21, and a processing step of processing the resin coating 50a. In the processing step, the die 500 is moved relative to the resin coating 50a in the axial direction Ad while a protrusion 505 formed on the die 500 is pressed against the resin coating 50a, thereby forming a retaining groove 55 in the resin coating 50a that extends in the axial direction Ad and is capable of retaining the lubricant 90.

[0050] In this manner, in this embodiment, the retaining groove 55 extending in the axial direction Ad is formed by moving the convex portion 505 formed on the die 500 relative to the resin coating 50a. Therefore, it is possible to obtain the sliding member 50 arranged on one of the external teeth portion 31 and the internal teeth portion 21, the sliding member 50 having the retaining groove 55 extending over a relatively wide range in the axial direction Ad. In other words, according to the manufacturing method for the telescopic shaft 10 of this embodiment, it is possible to efficiently manufacture the sliding member 50 having the retaining groove 55 capable of supplying the lubricant 90 over a relatively wide range in the axial direction Ad. As a result, it is possible to efficiently manufacture the telescopic shaft 10.

[0051] (6) In the manufacturing method of the telescopic shaft 10 described in (5) above, in the processing step, the mold 500 is moved relative to the resin coating 50a in the axial direction Ad to form the retaining groove 55 in the resin coating 50a and remove at least a portion of the resin coating 50a other than the retaining groove 55.

[0052] That is, in the manufacturing method for the telescopic shaft 10 according to the present embodiment, the mold 500 can be used to adjust the size and / or shape of the portion of the resin coating 50a other than the retaining groove 55, and the retaining groove 55 can be formed in the resin coating 50a. Therefore, for example, the thickness of the resin coating 50a can be made uniform and the retaining groove 55 can be formed in the resin coating 50a at the same time. Therefore, the sliding member 50 that can structurally guide the smooth movement of the telescopic shaft 10 and further retain the lubricant 90 can be efficiently manufactured.

[0053] The processing step in the manufacturing method of the telescopic shaft 10 may include at least the formation of the retaining groove 55. In other words, the processing step does not have to include removing at least a part of the resin coating 50a other than the retaining groove 55. For example, a film member formed to a substantially uniform thickness is arranged along the surface of the external teeth portion 31 of the inner shaft 30, and then, in a state in which the convex portion 505 formed on the die 500 is pressed against the film member, the die 500 is moved relative to the film member in the axial direction Ad. In this way, a sliding member 50 using the film member as a base material and having a retaining groove 55 extending in the axial direction Ad may be produced.

[0054] (Other embodiments) The telescopic shaft according to the present invention has been described above based on the embodiment. However, the present invention is not limited to the above embodiment. As long as it does not deviate from the spirit of the present invention, various modifications conceivable by a person skilled in the art to the above embodiment, or forms constructed by combining multiple components described above, are also included within the scope of the present invention.

[0055] For example, the number of external teeth 32 of the external toothed portion 31 and the number of internal teeth 22 of the internal toothed portion 21 may be other than 18. The external toothed portion 31 and the internal toothed portion 21 may have a plurality of teeth that engage with each other in the circumferential direction Cd.

[0056] The number of retaining grooves 55 in the sliding member 50 may be one or more. By forming at least one retaining groove 55 in the sliding member 50, the lubricant 90 can be supplied from the at least one retaining groove 55 to a relatively wide range in the axial direction Ad between the sliding member 50 and the internal tooth portion 21 or the external tooth portion 31.

[0057] The telescopic shaft 10 according to the embodiment is disposed between the steering column shaft 190 and the pinion shaft 191, but the telescopic shaft 10 may be used as all or part of the steering column shaft 190. The steering column shaft 190 may have an axial telescopic function for adjusting the position of the operating member 200, etc. Therefore, by using the telescopic shaft 10 as all or part of the steering column shaft 190, the rotational torque caused by operating the operating member 200 can be transmitted to the downstream pinion shaft 191, etc., and the operating member 200 can be moved smoothly when adjusting the position.

[0058] The telescopic shaft 10 may be incorporated into a steer-by-wire system in which the operating member 200 and the steered wheels are not mechanically connected. For example, even in a steer-by-wire system, a function for moving the operating member 200 in the axial direction may be required for reasons such as storing the operating member 200 in a predetermined storage area in front of the driver's seat. In this case, therefore, by employing the telescopic shaft 10 as a shaft member to one end of which the operating member 200 is connected, it is possible to appropriately perform a steering operation based on a rotational torque generated by the operation of the operating member 200, and to smoothly move the operating member 200.

[0059] The retaining groove 55 for retaining the lubricant 90 does not need to be formed over the entire area in the axial direction Ad of the sliding member 50. For example, if a portion of the sliding member 50 (i.e., the resin coating 50a) in the axial direction Ad before the retaining groove 55 is formed is thinner than the other portions, the retaining groove 55 may be formed only in the other portions of the resin coating 50a. In other words, the retaining groove 55 may be formed only in a portion of the sliding member 50 in the axial direction Ad.

[0060] The sliding member 50 having the retaining groove 55 may be produced by a process different from the process described with reference to Figs. 9 to 13. For example, the sliding member 50 having the retaining groove 55 may be produced by injection molding of a resin. In this case, the sliding member 50 and one of the inner shaft 30 and the outer shaft 20 may be fixed by bonding with an adhesive, welding, or the like. The sliding member 50 having the retaining groove 55 and integrated with one of the inner shaft 30 and the outer shaft 20 may be produced by insert molding. [Industrial Applicability]

[0061] The telescopic shaft according to the present invention is useful as a telescopic shaft used in a steering device provided in a vehicle such as an automobile. [Explanation of symbols]

[0062] 10: telescopic shaft, 20: outer shaft, 20a: inner peripheral surface, 21: internal teeth, 22: internal teeth, 22a: tooth tip, 23: tooth bottom, 29, 39: universal joint, 30: inner shaft, 30a: outer peripheral surface, 31: external teeth, 32: external teeth, 50: sliding member, 50a: resin coating, 55: retaining groove, 90: lubricant, 100: steering device, 101: belt transmission device, 110: shaft, 111: screw groove, 112: rack, 12 0: ball nut, 130: driven pulley, 140: housing, 142: boot, 150: assist motor, 153: driving pulley, 160: belt, 190: steering column shaft, 191: pinion shaft, 200: operating member, 210: steered wheel, 211: tie rod, 500: mold, 501: recess, 502: through hole, 505: protrusion, Ad: axial direction, Cd: circumferential direction

Claims

1. An extendable shaft that is extendable in the axial direction, an inner shaft having an outer circumferential surface formed with an external tooth portion having a plurality of external teeth arranged in a circumferential direction of the telescopic shaft; an outer shaft having an internal tooth portion formed on an inner peripheral surface thereof, the internal tooth portion having a plurality of internal teeth arranged at positions that mesh with the external tooth portion; a sliding member fixed to one of the external tooth portion and the internal tooth portion, the sliding member being arranged to be slidable in the axial direction relative to the other of the external tooth portion and the internal tooth portion, The sliding member has a retaining groove extending in the axial direction and configured to retain a lubricant. Telescopic axis.

2. The retaining groove is formed over the entire area of ​​the sliding member in the axial direction. The telescopic shaft according to claim 1.

3. The retaining groove is formed between the external teeth and the internal teeth that are adjacent to each other in the circumferential direction among the plurality of external teeth and the plurality of internal teeth. The telescopic shaft according to claim 1 or 2.

4. The retaining grooves are formed on the sliding member on both sides of the external teeth in the circumferential direction. The telescopic shaft according to claim 3.

5. A method for manufacturing a telescopic shaft that is extendable and contractible in an axial direction, comprising the steps of: The telescopic shaft is an inner shaft having an outer circumferential surface formed with an external tooth portion having a plurality of external teeth arranged in a circumferential direction of the telescopic shaft; an outer shaft having an internal tooth portion formed on an inner peripheral surface thereof, the internal tooth portion having a plurality of internal teeth arranged at positions that mesh with the external tooth portion; a sliding member fixed to one of the external tooth portion and the internal tooth portion, the sliding member being arranged to be slidable in the axial direction relative to the other of the external tooth portion and the internal tooth portion, The manufacturing method includes: a molding step of molding a resin coating that serves as a base material of the sliding member on one of the external tooth portion and the internal tooth portion; and a processing step of moving the die relative to the resin film in the axial direction while pressing a convex portion formed on the die against the resin film, thereby forming a retaining groove in the resin film that extends in the axial direction and is capable of retaining a lubricant. Manufacturing method of telescopic shaft.

6. In the processing step, the mold is moved relative to the resin film in the axial direction to form the retaining groove in the resin film and remove at least a part of the resin film other than the retaining groove. A method for manufacturing the telescopic shaft according to claim 5.

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