Intermediate shaft and steering device

Abstract

To provide an intermediate shaft capable of improving support rigidity against a bending load.SOLUTION: An intermediate shaft includes a cylindrical outer tube, an inner shaft received in the outer tube, and a plurality of balls. The inner peripheral surface of the outer tube is provided with at least one or more outer ball groove surfaces that are recessed radially outward and extend in an axial direction. The outer peripheral surface of the inner shaft is provided with at least one or more inner ball groove surfaces that are recessed radially inward and extend in the axial direction. The outer ball groove surface is radially opposed to the inner ball groove surface. The intermediate shaft has a partition portion radially extending at a central part in the axial direction of the outer ball groove surface or at a central part in the axial direction of the inner ball groove surface. The balls are disposed between the outer ball groove surface and the inner ball groove surface. The plurality of balls are disposed on one side in the axial direction of the partition portion and on the other side in the axial direction of the partition portion with the partition portion serving as a boundary, respectively.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to an intermediate shaft and a steering device. [Background technology]

[0002] An example of a shaft part used in a steering device for a vehicle is an intermediate shaft. The intermediate shaft is a part for transmitting steering torque transmitted from a steering wheel to a steering shaft to a pinion shaft. The intermediate shaft is expandable and contractible in order to absorb distortions generated in the vehicle body while the vehicle is traveling and to facilitate assembly with other parts.

[0003] Specifically, a conventional intermediate shaft includes a cylindrical outer tube and an inner shaft housed in the outer tube. The inner circumferential surface of the outer tube is provided with a female spline portion. The outer circumferential surface of the inner shaft is provided with a male spline portion that spline-fits with the female spline portion. This connects the outer tube and the outer tube together so that they cannot rotate relative to each other and can slide freely in the axial direction. The intermediate shaft expands and contracts due to sliding between the female spline portion and the male spline portion.

[0004] In the intermediate shaft of Patent Document 1, an outer ball groove surface extending in the axial direction is provided on the inner peripheral surface of the outer tube. An inner ball groove surface facing the outer ball groove surface is provided on the outer peripheral surface of the inner shaft. Balls are provided between the outer ball groove surface and the inner ball groove surface. As a result, when the intermediate shaft expands or contracts, the balls roll, greatly reducing sliding resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4254194 Summary of the Invention [Problem to be solved by the invention]

[0006] When torque is transmitted to the intermediate shaft, a bending load acts on the intermediate shaft. If the outer tube has low support rigidity against the bending load, the inner shaft tilts relative to the outer tube. In other words, the central axis of the outer tube and the central axis of the inner shaft are not aligned concentrically and are bent. If the inner shaft tilts significantly relative to the outer tube, the intermediate shaft may not expand or contract smoothly.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and has an object to provide an intermediate shaft and a steering device that can improve the support rigidity against bending loads. [Means for solving the problem]

[0008] In order to achieve the above object, an intermediate shaft according to one aspect of the present disclosure includes a cylindrical outer tube, an inner shaft extending in an axial direction parallel to the direction in which the outer tube extends and a portion of which is housed in the outer tube, and a plurality of balls disposed between an inner peripheral surface of the outer tube and an outer peripheral surface of the inner shaft. The inner peripheral surface of the outer tube is provided with at least one outer ball groove surface recessed radially outward and extending in the axial direction. The outer peripheral surface of the inner shaft is provided with at least one inner ball groove surface recessed radially inward and extending in the axial direction. The outer ball groove surface and the inner ball groove surface face each other in a radial direction. A partition portion extending in a radial direction is provided in a central portion of the outer ball groove surface in the axial direction or a central portion of the inner ball groove surface in the axial direction. The balls are arranged between the outer ball groove surface and the inner ball groove surface, and are arranged in plurality on one side of the partition in the axial direction and on the other side of the partition in the axial direction, with the partition serving as the boundary.

[0009] In the intermediate shaft described above, the portion supported by the balls is separated into one side and the other side in the axial direction of the partition. In other words, the outer tube has two portions that support the inner shaft via the balls, separated in the axial direction, and has high support rigidity against bending loads. Therefore, even if a bending load acts on the intermediate shaft, the inner shaft does not tilt significantly relative to the outer tube. Therefore, the intermediate shaft expands and contracts smoothly. Also, the portions of the outer tube and the inner shaft that come into contact with the balls are separated in the axial direction. In other words, the load acting on the outer tube and the inner shaft is dispersed in the axial direction. This avoids stress concentration and improves durability.

[0010] In a preferred embodiment of the intermediate shaft, the outer ball groove surfaces and the inner ball groove surfaces are provided in pairs. The two outer ball groove surfaces are arranged at intervals of 180°. The two inner ball groove surfaces are arranged at intervals of 180°.

[0011] Incidentally, the support rigidity is improved in two directions as viewed from the central axis of the inner shaft: the direction in which the ball is arranged and the direction opposite to the direction in which the ball is arranged. In other words, the inner shaft is difficult to tilt in the direction in which the ball is arranged as viewed from the central axis and the direction opposite to the direction in which the ball is arranged as viewed from the central axis. According to the above configuration, the two balls are arranged in opposite directions as viewed from the central axis, and the directions in which the inner shaft is difficult to tilt overlap. Therefore, the support rigidity is very high against bending load in a specific direction (the direction in which the ball is arranged).

[0012] In a preferred embodiment of the intermediate shaft, the outer ball groove surfaces and the inner ball groove surfaces are provided in threes. The three outer ball groove surfaces are arranged at intervals of 120°. The three inner ball groove surfaces are arranged at intervals of 120°.

[0013] According to the above configuration, the directions in which the support rigidity against the bending load is improved (the directions in which the inner shaft is less likely to tilt) are evenly distributed in the circumferential direction, and therefore the bearing has high support rigidity against the bending load in each direction as viewed from the central axis.

[0014] In a preferred embodiment of the intermediate shaft, one end of the inner shaft is inserted into and accommodated in the other end of the outer tube. The other end of the outer tube is provided with an outer fall-out prevention portion that prevents the balls from falling off the outer ball groove surface. One end of the inner shaft is provided with an inner fall-out prevention portion that prevents the balls from falling off the inner ball groove surface.

[0015] According to the above-mentioned configuration, the balls do not fall off from the outer ball groove surface and the inner ball groove surface, so that fasteners for preventing the balls from falling off are not required, and the number of parts is reduced.

[0016] In addition, as a preferred embodiment of the intermediate shaft, the inner peripheral surface of the outer tube is provided with a plurality of concave surfaces that are recessed radially outward and extend in the axial direction. The outer peripheral surface of the inner shaft is provided with a plurality of convex rib portions that protrude radially outward, extend in the axial direction, and enter inside the concave rib surface. The convex rib portions are separated from the concave rib surface, and have gaps on both the radially outer side of the convex rib portions and on both circumferential sides of the convex rib portions. The outer ball groove surface is arc-shaped when viewed from the axial direction. An outer groove bottom portion that is located at the radially outermost side of the outer ball groove surface is provided at the circumferential center of the outer ball groove surface. The radial thickness of the outer tube is the smallest from the outer groove bottom portion to the outer peripheral surface of the outer tube in the entire circumference of the outer tube. The inner ball groove surface is arc-shaped when viewed from the axial direction. An inner groove bottom portion located radially innermost of the inner ball groove surface is provided at the circumferential center of the inner ball groove surface. The radial thickness of the inner shaft is smallest from the inner groove bottom portion to the outer peripheral surface of the inner shaft throughout the entire circumference of the inner shaft. The outer ball groove surface and the inner ball groove surface have a radius of curvature larger than the radius of curvature of the ball. In a neutral state in which the outer tube and the inner shaft are not rotating circumferentially, the ball abuts against the outer groove bottom portion and the inner groove bottom portion with an interference.

[0017] The outer groove bottom and the inner groove bottom, which have the smallest radial thickness, have the lowest rigidity in the circumferential direction of the outer tube and the inner shaft. In addition, the outer ball groove surface and the inner ball groove surface are arc-shaped, and the rigidity of the vicinity of the outer groove bottom and the inner groove bottom (the portion adjacent in the circumferential direction) is also low. From the above, when the ball is abutted against the outer groove bottom and the inner groove bottom in a state with a tightening margin, the outer groove bottom and the inner groove bottom and their vicinity are elastically deformed, and a preload is applied to the ball. Therefore, an elastic member for applying a preload to the ball is not required. In addition, according to the intermediate shaft described above, the concave rib surface and the convex rib portion are separated. Therefore, when the intermediate shaft expands and contracts, the ball rolls on the outer ball groove surface and the inner ball groove surface, and no sliding occurs between the concave rib surface and the convex rib portion. Therefore, the sliding resistance between the outer tube and the inner shaft is small. Furthermore, there is no need to provide a resin layer between the concave rib surface and the convex rib portion to reduce the sliding resistance. According to the intermediate shaft, the outer ball groove surface and the inner ball groove surface have a radius of curvature larger than the radius of curvature of the ball. Therefore, the ball can roll in the circumferential direction between the outer ball groove surface and the inner ball groove surface. However, a preload is applied to the ball. Therefore, the circumferential rattle of the ball is suppressed. Furthermore, since the ball is preloaded, the ball exerts a torsional rigidity that tries to rotate the outer tube and the inner shaft in the same direction. When the torsional torque acting on the intermediate shaft is small, the outer tube and the inner shaft rotate together while the ball is in contact with the outer groove bottom and the inner groove bottom. When the torsional torque becomes larger than the torsional rigidity of the ball, the outer tube or the inner shaft is displaced in the circumferential direction, and the outer groove bottom and the inner groove bottom do not overlap in the radial direction. In other words, the radial width between the outer ball groove surface and the inner ball groove surface becomes smaller, and the preload applied to the ball becomes larger. As a result, the torsional rigidity of the balls increases. Then, with the outer tube or the inner shaft displaced in the circumferential direction, the outer tube and the inner shaft rotate together. Furthermore, when the torsional torque acting on the intermediate shaft increases, the circumferential gap between the concave surface and the convex portion disappears, and the concave surface and the convex portion come into contact with each other.The concave surface and the convex portion provide torsional rigidity instead of the balls, and the outer tube and the inner shaft rotate together. As a result, when the torsional torque acting on the intermediate shaft is large, the concave surface and the convex portion come into contact with each other, restricting the balls, the outer ball groove surface, and the inner ball groove surface from undergoing large elastic deformation. As a result, the balls, the outer ball groove surface, and the inner ball groove surface are less susceptible to fatigue failure and have high durability.

[0018] In addition, as a desirable aspect of the intermediate shaft, the intermediate shaft includes a resin layer that is coated on the outer peripheral surface of the inner shaft and is disposed between the inner peripheral surface of the outer tube and the outer peripheral surface of the inner shaft. The inner peripheral surface of the outer tube is provided with a plurality of grooved surfaces that are recessed radially outward and extend in the axial direction. The grooved surfaces are disposed at equal intervals in the circumferential direction around the entire circumference of the inner peripheral surface of the outer tube. The outer peripheral surface of the inner shaft is provided with a plurality of convex streaks that protrude radially outward, extend in the axial direction, and penetrate into the grooved surface. The inner ball groove surface faces the outer ball groove surface, which is one of the plurality of grooved surfaces, in the radial direction. The ball abuts against the inner ball groove surface and the outer ball groove surface with a tightening margin between them, and the outer tube and the inner shaft cannot rotate relative to each other. The resin layer covers the outer circumferential side of the convex rib portion and has a radial gap and a small circumferential gap with respect to the concave rib surface in a neutral state in which the outer tube and the inner shaft are not rotating in the circumferential direction.

[0019] The ball is assembled between the outer tube and the inner shaft with a tightening margin. Therefore, the circumferential rattle of the ball is suppressed. In addition, although the intermediate shaft has a minute circumferential gap between the resin layer and the concave surface, the outer tube and the inner shaft cannot rotate relative to each other through the ball. Therefore, the contact between the convex portion and the concave surface to generate rattle noise is suppressed. In addition, even if the intermediate shaft is placed in a high-temperature environment, the ball directly contacts the inner ball groove surface and the outer ball groove surface. Therefore, even if the intermediate shaft expands due to heat and then shrinks when it returns to room temperature, no gap is generated between the ball, which is made of the same metal, and the inner ball groove surface and the outer ball groove surface. Therefore, even after being used in a high-temperature environment, the outer tube and the inner shaft are kept unable to rotate relative to each other, and the generation of rattle noise is suppressed. In addition, when the intermediate shaft expands and contracts at room temperature, the ball rolls. On the other hand, there is a radial gap and a circumferential minute gap between the resin layer and the concave streak surface, so that the resin layer and the concave streak surface do not slip. Therefore, the sliding resistance between the outer tube and the inner shaft is small. In addition, when the intermediate shaft is placed in a high-temperature environment, the resin layer thermally expands, and the circumferential minute gap disappears. Therefore, a part of the resin layer abuts against the concave streak surface. When the intermediate shaft expands and contracts, in addition to the rolling of the balls, a part of the resin layer also slips against the concave streak surface. Therefore, the sliding resistance between the outer tube and the inner shaft is larger than at room temperature. However, since the part of the resin layer abutting against the concave streak surface at high temperature has a minute gap against the concave streak surface at room temperature, the surface pressure of the resin layer against the concave streak surface is lower than when the resin layer is already abutting against the concave streak surface from room temperature. In other words, the increase in the sliding resistance between the outer tube and the inner shaft at high temperatures is suppressed to a low level. When torque is transmitted to the intermediate shaft, a bending load acts so that the intermediate shaft bends. As a result, the inner shaft is inclined relative to the outer tube, eliminating minute gaps in the circumferential direction. The convex rib portion and the concave rib surface of the portion come into contact with each other via the resin layer, transmitting torque. In addition, one of the multiple concave rib surfaces is used as the outer ball groove surface. This eliminates the need for processing to form the outer ball groove surface on the inner circumferential surface of the outer tube, making it easier to manufacture the outer tube.In addition, the outer tube has a concave surface around the entire inner circumferential surface, and there is no phase required for assembly to the inner shaft. This makes it easy to assemble the outer tube, and improves the productivity of the intermediate shaft. Furthermore, with the intermediate shaft described above, the resin layer is provided on the outer circumferential surface of the inner shaft, not on the inner circumferential surface of the outer tube. This makes it easy to immerse the inner shaft in a molten resin bath and then mold the resin layer. Furthermore, when molding the resin layer, the resin layer covering the inner ball groove surface can also be removed, making it easy to manufacture the resin layer.

[0020] In addition, as a desirable aspect of the intermediate shaft, the intermediate shaft includes a resin layer that is coated on the inner peripheral surface of the outer tube and is disposed between the inner peripheral surface of the outer tube and the outer peripheral surface of the inner shaft, and the outer peripheral surface of the inner shaft is provided with a plurality of ridges that protrude radially outward and extend in the axial direction. The ridges are disposed at equal intervals in the circumferential direction around the entire circumference of the outer peripheral surface of the inner shaft. The inner peripheral surface of the outer tube is provided with a plurality of recessed surfaces that are recessed radially outward, extend in the axial direction, and into which the ridges are inserted. The outer ball groove surface faces radially opposite an inner ball groove surface that is one of a plurality of recesses provided between the plurality of ridges. The ball abuts against the inner ball groove surface and the outer ball groove surface with a tightening margin between them, and the outer tube and the inner shaft cannot rotate relative to each other. The resin layer covers the inner side of the concave rib surface, and has a radial gap and a small circumferential gap with respect to the convex rib portion in a neutral state in which the outer tube and the inner shaft are not rotating in the circumferential direction.

[0021] In the intermediate shaft described above, the balls are assembled between the outer tube and the inner shaft with a tightening margin, and circumferential rattle is suppressed. The outer tube and the inner shaft cannot rotate relative to each other via the balls. Therefore, the contact between the convex rib portion and the concave rib surface to generate rattle noise is suppressed. In addition, even after use in a high-temperature environment, the outer tube and the inner shaft are kept in a state where they cannot rotate relative to each other, and the generation of rattle noise is suppressed. In addition, since there is no slippage between the resin layer and the convex rib portion, the sliding resistance between the outer tube and the inner shaft is small. In addition, when the intermediate shaft is placed in a high-temperature environment, the resin layer thermally expands, and the minute gap in the circumferential direction disappears. Therefore, a part of the resin layer abuts against the convex rib portion. Then, when the intermediate shaft expands and contracts, in addition to the rolling of the balls, a part of the resin layer also slides against the convex rib portion. Therefore, the sliding resistance between the outer tube and the inner shaft is larger than at room temperature. However, since a part of the resin layer that contacts the convex streak portion at high temperature has a minute gap with respect to the convex streak portion at room temperature, the surface pressure of the resin layer against the convex streak portion is lower than when the resin layer is already in contact with the convex streak portion at room temperature. In other words, the increase in the sliding resistance between the outer tube and the inner shaft at high temperatures is suppressed to be low. In addition, when torque is transmitted to the intermediate shaft, a bending load that bends the intermediate shaft acts. As a result, the inner shaft tilts with respect to the outer tube, and the minute gap in the circumferential direction disappears. The convex streak portion and the concave streak surface contact each other through the resin layer, and the torque is transmitted. In addition, one of the multiple recesses provided between the multiple convex streak portions is used as the inner ball groove surface. Therefore, processing for forming the inner ball groove surface on the inner circumferential surface of the inner shaft is not required, and the inner shaft is easily manufactured. In addition, the inner shaft has a convex streak portion provided around the entire circumference of the inner circumferential surface, and there is no phase for assembling the inner shaft to the outer tube. Therefore, the inner shaft is easily assembled, and the productivity of the intermediate shaft is improved. Furthermore, according to the intermediate shaft described above, the resin layer is manufactured by immersing the outer tube in a molten resin bath and then molding the resin layer. When molding the resin layer, the resin layer covering the outer ball groove surface can be removed at the same time, making the manufacturing of the resin layer easier.

[0022] In order to achieve the above object, a steering device according to one aspect of the present disclosure includes the above-mentioned intermediate shaft.

[0023] According to the above-described configuration, the intermediate shaft has high support rigidity against a bending load. Effect of the Invention

[0024] According to the intermediate shaft and steering device of the present disclosure, the supporting rigidity of the inner shaft in the outer tube is improved. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram of a steering device according to a first embodiment. [Diagram 2] FIG. 2 is a perspective view of the steering device of the first embodiment. [Diagram 3] FIG. 3 is a partially cutaway, enlarged perspective view of the intermediate shaft of the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] FIG. 5 is an enlarged view of the vicinity of the inner ball groove surface and the outer ball groove surface of FIG. [Figure 6] FIG. 6 is a cross-sectional view of the intermediate shaft taken along the axial direction. [Figure 7] FIG. 7 is a cross-sectional view showing a state in which the intermediate shaft is twisted. [Figure 8] FIG. 8 is a cross-sectional view showing a state in which the intermediate shaft is twisted more than in the state shown in FIG. [Figure 9] FIG. 9 is a cross-sectional view of the intermediate shaft of the second embodiment. [Figure 10] FIG. 10 is a cross-sectional view of the intermediate shaft of the third embodiment. [Figure 11] FIG. 11 is an enlarged view of the vicinity of the inner ball groove surface and the outer ball groove surface of FIG. [Figure 12]FIG. 12 is a cross-sectional view of the intermediate shaft of the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] (Embodiment 1) Hereinafter, the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the following modes for carrying out the invention (hereinafter, referred to as embodiments). Furthermore, the components in the following embodiments include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be appropriately combined.

[0027] FIG. 1 is a schematic diagram of a steering device of the first embodiment. FIG. 2 is a perspective view of the steering device of the first embodiment. FIG. 3 is a perspective view of an intermediate shaft of the first embodiment, with a part of the intermediate shaft cut away and enlarged. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3. FIG. 5 is an enlarged view of an inner ball groove surface and an outer ball groove surface in FIG. 4. FIG. 6 is a cross-sectional view of the intermediate shaft cut in the axial direction. FIG. 7 is a cross-sectional view showing a state in which the intermediate shaft is twisted. FIG. 8 is a cross-sectional view showing a state in which the intermediate shaft is twisted more than in the state shown in FIG. 7.

[0028] The basic structure of the steering device 80 will be described with reference to Figures 1 and 2. The steering device 80 includes a steering wheel 81, a steering shaft 82, a steering force assist mechanism 83, a first universal joint 84, an intermediate shaft 85, and a second universal joint 86, in the order in which the force (steering torque) applied by the operator is transmitted.

[0029] The steering force assist mechanism 83 includes an ECU (Electronic Control Unit) 90, a reduction gear device 92, an electric motor 93, a torque sensor 94, and a torsion bar (not shown). When an ignition switch 98 is on, the ECU 90 is supplied with power from a power supply device 99 (for example, an on-vehicle battery). Note that, although an example has been given in which the intermediate shaft 85 of the present embodiment is applied to a steering device 80 (electric power steering device) that includes the steering force assist mechanism 83, the intermediate shaft of the present disclosure may also be applied to a steering device that does not include the steering force assist mechanism 83.

[0030] The steering shaft 82 includes an input shaft 82a and an output shaft 82b. One end of the input shaft 82a is connected to the steering wheel 81. The other end of the input shaft 82a is connected to one end of the output shaft 82b via a torsion bar (not shown) of the steering force assist mechanism 83. When the input shaft 82a rotates due to steering torque, the torsion bar twists, causing an angular difference in rotation between the input shaft 82a and the output shaft 82b.

[0031] The torque sensor 94 detects the angular difference between the input shaft 82a and the output shaft 82b, and transmits the result to the ECU 90. The ECU 90 acquires the traveling speed of the vehicle from a vehicle speed sensor 95 of the vehicle. The ECU 90 drives the electric motor 93 based on the angular difference between the input shaft 82a and the output shaft 82b and the traveling speed of the vehicle. The reduction gear 92 includes a worm (not shown) connected to the output shaft of the electric motor 93, and a worm wheel (not shown) connected to the output shaft 82b. Therefore, when the electric motor 93 is driven, a steering assist torque is applied to the output shaft 82b via the reduction gear 92, and the angular difference in rotation between the input shaft 82a and the output shaft 82b disappears.

[0032] As shown in FIG. 2, the other end of the output shaft 82b is connected to one end of an intermediate shaft 85 via a first universal joint 84. The other end of the intermediate shaft 85 is connected to one end of a pinion shaft 87 via a second universal joint 86. The other end of the pinion shaft 87 is provided with a pinion 88a. The pinion 88a meshes with a rack 88b. The steering gear 88 converts the rotational motion transmitted to the pinion 88a into linear motion by the rack 88b. The rack 88b is connected to a tie rod 89. The angle of the wheels changes as the rack 88b moves.

[0033] Next, the intermediate shaft 85 will be described in detail. In the following description, first, a state in which no torque is applied to the intermediate shaft 85 (neutral state in which the inner shaft 1 and the outer tube 2 are not rotating in the circumferential direction) will be described. Then, the operation of the intermediate shaft 85 will be described.

[0034] As shown in Fig. 3, the intermediate shaft 85 includes an inner shaft 1 joined to a first universal joint 84 (see Fig. 2), an outer tube 2 joined to a second universal joint 86 (see Fig. 2), and a plurality of balls 3 interposed between the outer circumferential surface of the inner shaft 1 and the inner circumferential surface of the outer tube 2. The inner shaft 1, the outer tube 2, and the balls 3 are each made of carbon steel for machine structural use.

[0035] Hereinafter, the direction in which the inner shaft 1 extends is referred to as the axial direction. The direction in which the first universal joint 84 is disposed as viewed from the inner shaft 1 is referred to as the first direction X1. The direction in which the second universal joint 86 is disposed as viewed from the inner shaft 1 is referred to as the second direction X2.

[0036] The inner shaft 1 and the outer tube 2 are each a cylindrical component. A portion of the inner shaft 1 near the end in the second direction X2 forms an inner accommodated portion 10. A portion of the outer tube 2 near the end in the first direction X1 forms an outer accommodating portion 20. The inner accommodated portion 10 is inserted into the end of the outer tube 2 in the first direction X1 and is accommodated in the outer tube 2. The outer accommodating portion 20 is a portion that accommodates the inner accommodated portion 10.

[0037] 4, the inner peripheral surface 11 of the inner accommodated portion 10 is circular about the central axis O1. On the other hand, the outer peripheral surface 12 of the inner accommodated portion 10 is provided with a plurality of convex rib portions 13, a plurality of inner ball groove surfaces 14, and a plurality of standard outer peripheral surfaces 15. Therefore, the radial thickness r1 of the inner accommodated portion 10 is not constant in the circumferential direction.

[0038] The standard outer peripheral surface 15 of the inner accommodated portion 10 is a portion of the outer peripheral surface 12 where the convex rib portion 13 and the inner ball groove surface 14 are not provided. In other words, the standard outer peripheral surface 15 is an arc-shaped surface centered on the central axis O1, which extends between the convex rib portion 13 and the inner ball groove surface 14 or between the inner ball groove surfaces 14.

[0039] The convex rib portion 13 of the inner accommodated portion 10 is a protrusion that protrudes radially outward from the standard outer circumferential surface 15. The convex rib portion 13 has a trapezoidal shape in which the circumferential width narrows toward the radially outward side in a cross-sectional view. The convex rib portion 13 has the same shape and extends in the axial direction (see FIG. 3).

[0040] The inner ball groove surface 14 of the inner accommodated portion 10 is a groove surface that is recessed radially inward from the standard outer circumferential surface 15. The inner ball groove surface 14 has an arc shape in cross section. Therefore, the inner ball groove surface 14 is positioned radially inward from the circumferential end of the inner ball groove surface 14 toward the circumferential center of the inner ball groove surface 14. Hereinafter, the circumferential center of the inner ball groove surface 14 is referred to as the inner groove bottom 14a. The inner ball groove surface 14 has the same shape and extends in the axial direction (see FIG. 3).

[0041] The radius of curvature of the inner ball groove surface 14 is larger than the radius of curvature of the ball 3. Therefore, when the ball 3 is brought into contact with the inner ball groove surface 14, there is one contact point. Note that a preferred range for the radius of curvature of the inner ball groove surface 14 is at least twice the radius of curvature of the ball 3 and is less than the radius of curvature of a circle that is centered on the central axis O1 of the outer tube 2 and passes through the apex of the concave rib surface 23 of the outer tube 2 (the center of the bottom surface 23a).

[0042] The inner groove bottom 14a is located radially inwardly on the outer peripheral surface 12 of the inner accommodated portion 10. In other words, the radial thickness r1 (see FIG. 4) of the inner accommodated portion 10 is smallest in the thickness r2 (see FIG. 5) from the inner groove bottom 14a to the inner peripheral surface 11 of the entire circumference of the inner accommodated portion 10. Therefore, the portion from the inner groove bottom 14a to the inner peripheral surface 11 of the entire circumference of the inner accommodated portion 10 has the lowest rigidity and is most susceptible to elastic deformation.

[0043] In addition, since the inner ball groove surface 14 is arc-shaped, not only the inner groove bottom 14a but also the portions adjacent to the inner groove bottom 14a in the circumferential direction are located radially inward of the imaginary extension line C1 extending from the standard outer circumferential surface 15. Therefore, the portions adjacent to the inner groove bottom 14a in the circumferential direction also have low rigidity and are easily elastically deformed.

[0044] From the above, when a radial load acts on the inner accommodated part 10, the part from the inner groove bottom 14a to the inner peripheral surface 11 and the part adjacent to this part in the circumferential direction are elastically deformed. In addition, in this embodiment, since the inner accommodated part 10 (inner shaft 1) has a cylindrical shape, it is more likely to elastically deform than the solid inner shaft 1.

[0045] 4, the outer circumferential surface 21 of the outer accommodating portion 20 is circular about the central axis O1. On the other hand, the inner circumferential surface 22 of the outer accommodating portion 20 is provided with a plurality of concave rib surfaces 23, a plurality of outer ball groove surfaces 24, and a plurality of standard inner circumferential surfaces 25. Therefore, the radial thickness R1 of the outer accommodating portion 20 is not constant in the circumferential direction.

[0046] The standard inner peripheral surface 25 of the outer accommodating portion 20 is a portion of the inner peripheral surface 22 that does not have the concave rib surface 23 and the outer ball groove surface 24. In other words, the standard inner peripheral surface 25 is an arc-shaped surface centered on the central axis O1, which extends between the concave rib surface 23 and the outer ball groove surface 24 and between the concave rib surfaces 23.

[0047] The concave surface 23 of the outer housing portion 20 is a groove-like surface recessed radially outward from the standard inner peripheral surface 25. The concave surface 23 has a trapezoidal shape in which the circumferential width narrows toward the radially outward side in a cross-sectional view. Thus, the concave surface 23 is similar in shape to the protruding portion 13. The concave surface 23 extends in the axial direction with the same shape (see FIG. 3).

[0048] The outer ball groove surface 24 of the outer accommodating portion 20 is a groove surface that is recessed radially outward from the standard inner peripheral surface 25. The outer ball groove surface 24 has an arc shape in cross section. Therefore, the outer ball groove surface 24 is positioned radially outward from the circumferential end of the outer ball groove surface 24 toward the circumferential center of the outer ball groove surface 24. Hereinafter, the circumferential center of the outer ball groove surface 24 is referred to as the outer groove bottom 24a. The outer ball groove surface 24 has the same shape and extends in the axial direction (see FIG. 3).

[0049] The radius of curvature of the outer ball groove surface 24 is larger than the radius of curvature of the ball. Therefore, when the ball 3 is brought into contact with the outer ball groove surface 24, there is one contact point. The preferred range of the radius of curvature of the outer ball groove surface 24 is at least twice the radius of curvature of the ball 3, and is less than the radius of curvature of a circle that is centered on the central axis O1 of the outer tube 2 and passes through the apex of the concave rib surface 23 of the outer tube 2 (the center of the bottom surface 23a).

[0050] The outer groove bottom 24a is located radially outwardly of the outer peripheral surface 21 of the outer accommodating portion 20. In other words, the radial thickness R1 (see FIG. 4) of the outer accommodating portion 20 is smallest in the thickness R2 (see FIG. 5) from the outer groove bottom 24a to the outer peripheral surface 21 of the entire circumference of the outer accommodating portion 20. Therefore, the portion from the outer groove bottom 24a to the outer peripheral surface 21 of the entire circumference of the outer accommodating portion 20 has the lowest rigidity and is easily elastically deformed.

[0051] In addition, since the outer ball groove surface 24 is arc-shaped, not only the outer groove bottom 24a but also the circumferentially adjacent portions of the outer groove bottom 24a are located radially outward of the imaginary extension line C2 extending from the bottom surface 23a of the concave rib surface 23. Therefore, the circumferentially adjacent portions of the outer groove bottom 24a are also easily elastically deformed.

[0052] From the above, when a radial load acts on the outer accommodating portion 20, the portion from the outer groove bottom 24a to the outer peripheral surface 21 and the portion adjacent to this portion in the circumferential direction are elastically deformed.

[0053] The outer peripheral surface 12 of the inner accommodated portion 10 and the inner peripheral surface 22 of the outer accommodated portion 20 face each other in the radial direction. In detail, the standard inner peripheral surface 25 faces the inner accommodated portion 10 and the standard outer peripheral surface 15 in the radial direction. A gap is provided between the standard outer peripheral surface 15 and the standard inner peripheral surface 25. A plurality of convex rib portions 13 and concave rib surfaces 23 are provided, and face each other in the radial direction. Two each of the inner ball groove surfaces 14 and outer ball groove surfaces 24 are provided, arranged at 180° intervals, and face each other in the radial direction.

[0054] The convex streak portion 13 is embedded inside the concave streak surface 23. The convex streak portion 13 is not in contact with the concave streak surface 23. In detail, as shown in FIG. 5, the top surface 13a of the convex streak portion 13 and the bottom surface 23a of the concave streak surface 23 are separated from each other. A gap S1 is provided between the top surface 13a and the bottom surface 23a. Furthermore, the side surfaces 13b on both sides in the circumferential direction of the convex streak portion 13 are separated from the side surfaces 23b on both sides in the circumferential direction of the concave streak surface 23. A gap S2 is provided on both sides in the circumferential direction of the convex streak portion 13.

[0055] The inner groove bottom 14a and the outer groove bottom 24a are arranged to overlap on an imaginary line L1 extending radially from the central axis O1. Therefore, the radial gap between the inner ball groove surface 14 and the outer ball groove surface 24 is largest on the imaginary line L1 and becomes smaller as it deviates circumferentially from the imaginary line L1. The distance between the inner groove bottom 14a and the outer groove bottom 24a is slightly smaller than the diameter of the ball 3.

[0056] A number of balls 3 are arranged in the axial direction between the inner ball groove surface 14 and the outer ball groove surface 24 (see FIG. 3). The balls 3 are arranged to abut against the inner groove bottom 14a and the outer groove bottom 24a, and the center O2 of the balls overlaps with the imaginary line L1. As described above, the distance between the inner groove bottom 14a and the outer groove bottom 24a is slightly smaller than the diameter of the ball 3. Therefore, when the ball 3 is assembled between the inner ball groove surface 14 and the outer ball groove surface 24, a radial load acts on the inner accommodated portion 10 and the outer accommodated portion 20. As a result, the portion of the inner accommodated portion 10 from the inner groove bottom 14a to the inner peripheral surface 11 and the portion adjacent to this portion in the circumferential direction are elastically deformed. In addition, in the outer accommodating portion 20, a portion from the outer groove bottom portion 24a to the outer peripheral surface 21 and a portion adjacent to this portion in the circumferential direction are elastically deformed. As a result, a pressure is applied to the ball 3.

[0057] From the above, the inner shaft 1 and the outer tube 2 are integrated with the multiple balls 3 sandwiched between them. In other words, the multiple balls 3 to which preload is applied exert axial rigidity that tends to move the inner shaft 1 and the outer tube 2 in the first direction X1 or the second direction X2. Alternatively, the multiple balls 3 exert torsional rigidity that tends to rotate the inner shaft 1 and the outer tube 2 in the same direction.

[0058] In addition, because a preload is applied to the ball 3, the rattle of the ball 3 in the circumferential direction is suppressed. Furthermore, the radial gap between the inner ball groove surface 14 and the outer ball groove surface 24 becomes narrower as it deviates from the imaginary line L1 in the circumferential direction. Therefore, the shape between the inner ball groove surface 14 and the outer ball groove surface 24 makes it difficult for the ball 3 to move in the circumferential direction. For this reason as well, rattle of the ball 3 in the circumferential direction is suppressed.

[0059] As shown in FIG. 5, an inner dropout prevention portion 16 is provided at the end of the inner ball groove surface 14 in the second direction X2 in the axial direction. The inner dropout prevention portion 16 protrudes radially outward from the inner ball groove surface 14. The inner dropout prevention portion 16 is generated by crimping the end face 1a of the inner shaft 1 in the second direction X2. This prevents the ball 3 from dropping out of the end of the inner ball groove surface 14 in the second direction X2 even if the ball 3 moves in the second direction X2. Note that the inner shaft 1 shown in FIG. 3 does not show the inner dropout prevention portion 16 in order to make the inner ball groove surface 14 easier to see.

[0060] Additionally, an outer fall-off prevention portion 26 is provided at an end portion in the first direction X1 of the axial direction of the outer ball groove surface 24. The outer fall-off prevention portion 26 protrudes radially inward from the outer ball groove surface 24. The outer fall-off prevention portion 26 is generated by crimping the end face 2a of the outer tube 2 in the first direction X1. This prevents the ball 3 from falling off from the end portion in the first direction X1 of the outer ball groove surface 24.

[0061] In addition, in this embodiment, the inner fall-off prevention portion 16 and the outer fall-off prevention portion 26 are created by crimping, but in the present disclosure, the inner fall-off prevention portion 16 and the outer fall-off prevention portion 26 may also be created by build-up welding, and are not particularly limited.

[0062] As shown in Fig. 3, a partition portion 17 that protrudes radially outward from inner ball groove surface 14 is provided in the axial center of inner ball groove surface 14. As shown in Fig. 6, the partition portion is a wall portion extending in the radial direction. Thus, inner ball groove surface 14 is divided by partition portion 17 into a first inner ball groove surface 14A that is disposed further in the second direction X2 than partition portion 17 and a second inner ball groove surface 14B that is disposed further in the first direction X1 than partition portion 17.

[0063] As shown in Fig. 3, the balls 3 are evenly arranged, three each, on the first inner ball groove surface 14A and the second inner ball groove surface 14B. As described above, the multiple balls 3 arranged on the first inner ball groove surface 14A and the multiple balls 3 arranged on the second inner ball groove surface 14B are spaced apart in the axial direction. The outer tube 2 supports the inner shaft 1 via the balls 3 to prevent it from tilting, and the support points via the balls 3 are two locations: one on the side of the partition portion 17 in the first direction X1 and one in the second direction X2.

[0064] In addition, according to the partition portion 17, the ball 3 arranged on the first inner ball groove surface 14A cannot roll on the second inner ball groove surface 14B. In other words, the rolling distance of the ball 3 is shorter than that of the inner ball groove surface 14 without the partition portion 17. Therefore, when the intermediate shaft 85 is assembled to the vehicle (when a large amount of expansion and contraction is required for the intermediate shaft 85), the ball 3 slips on the first inner ball groove surface 14A or the second inner ball groove surface 14B. On the other hand, the amount of expansion and contraction of the intermediate shaft 85 during the running of the vehicle (when a small amount of expansion and contraction is required for the intermediate shaft 85) is about 1 mm to 2 mm. Therefore, the first inner ball groove surface 14A and the second inner ball groove surface 14B each have a distance that allows the ball 3 to roll when the intermediate shaft 85 expands and contracts during the running of the vehicle.

[0065] Next, the operation of the intermediate shaft 85 will be described. When the vehicle is traveling, the vehicle body is distorted due to vibrations transmitted from the road surface. As a result, an axial load acts on the intermediate shaft 85 of the steering device 80 (see arrow A1 in FIG. 2). Here, if the load acting on the intermediate shaft 85 is greater than the axial rigidity exerted by the balls 3, the balls 3 roll, and the inner shaft 1 and the outer tube 2 move relatively in the axial direction. As a result, the intermediate shaft 85 expands and contracts in the axial direction, absorbing the distortion of the vehicle body. Note that since the concave streak surface 23 and the convex streak portion 13 are spaced apart, no slippage occurs between the concave streak surface 23 and the convex streak portion 13 when the intermediate shaft 85 expands and contracts.

[0066] Furthermore, when the steering wheel 81 is operated while the vehicle is running, torque (operation torque) is input to the inner shaft 1 connected to the output shaft 82b. As a result, a torsional torque (see arrows A2 and A3 in FIG. 2) acts on the inner shaft 1 and the outer tube 2. Note that the directions of the torsional torque shown in FIG. 2, indicated by the arrows A2 and A3, are merely examples.

[0067] Here, when the torsional torque acting on the intermediate shaft 85 is smaller than the torsional rigidity exerted by the ball 3, the inner shaft 1 and the outer tube 2 rotate together with the ball 3 abutting against the inner groove bottom 14a and the outer groove bottom 24a (see Figures 4 and 5).

[0068] Furthermore, when the torsional torque acting on the intermediate shaft 85 is greater than the torsional rigidity exerted by the balls 3, the inner shaft 1 and the outer tube 2 rotate relative to each other as shown in FIG. 7, and the intermediate shaft 85 is twisted. That is, the inner groove bottom 14a moves in the circumferential direction from the imaginary line L2 passing through the central axis O1 and the outer groove bottom 24a. As a result, the radial width of the inner ball groove surface 14 and the outer ball groove surface 24 becomes smaller, and the preload applied to the balls 3 becomes larger. Then, the torsional rigidity exerted by the balls 3 becomes larger. The balls 3 roll in the rotational direction of the inner shaft 1 to which the operating torque is input.

[0069] The torsional rigidity exerted by the balls 3 gradually increases as the angle of relative rotation between the inner shaft 1 and the outer tube 2 increases (as the radial width of the inner ball groove surface 14 and the outer ball groove surface 24 gradually decreases). When the torsional rigidity exerted by the balls 3 becomes greater than the torsional torque acting on the intermediate shaft 85, the relative rotation between the inner shaft 1 and the outer tube 2 stops, and the inner shaft 1 and the outer tube 2 rotate together with the intermediate shaft 85 in a twisted state (a state in which the inner shaft 1 and the outer tube 2 rotate relative to each other).

[0070] On the other hand, if the torsional rigidity exerted by the balls 3 increases but does not become greater than the torsional torque acting on the intermediate shaft 85, the relative rotation between the inner shaft 1 and the outer tube 2 continues. As a result, as shown in Fig. 8, the circumferential gap S2 (see Fig. 5) between the concave rib surface 23 and the convex rib portion 13 disappears, and the concave rib surface 23 and the convex rib portion 13 come into contact with each other. Then, instead of the balls, the concave rib surface 23 and the convex rib portion 13 exert torsional rigidity, and the outer tube 2 and the inner shaft 1 rotate together.

[0071] Furthermore, when torque (operation torque) is input to the inner shaft 1, a bending load acts on the intermediate shaft 85. As described above, the outer tube 2 supports the inner shaft 1 at two locations: a portion further in the first direction X1 than the partition portion 17, and a portion further in the second direction X2 than the partition portion 17. Therefore, the inner shaft 1 is less likely to incline relative to the outer tube 2 in a direction pointing to the ball 3 as viewed from the central axis O1 (the direction indicated by the arrow B1 when the ball 3 arranged on the upper side of FIG. 4 is used as a reference) and in a direction opposite to the ball 3 as viewed from the central axis O1 (the direction indicated by the arrow B2 when the ball 3 arranged on the upper side of FIG. 4 is used as a reference). In other words, the outer tube 2 has high support rigidity against bending loads.

[0072] Furthermore, in this embodiment, two inner ball groove surfaces 14 and two outer ball groove surfaces 24 are provided, and are arranged in opposite directions as viewed from the central axis. In other words, the directions in which the support rigidity is improved as viewed from the central axis of the inner shaft 1 overlap each other. Therefore, according to the intermediate shaft 85 of the first embodiment, it has a very high support rigidity against a bending load acting in a specific direction (see arrows B1 and B2 in FIG. 4). From the above, even if a bending load acts on the inner shaft 1, the inner shaft 1 does not tilt with respect to the outer tube 2. Therefore, the intermediate shaft 85 also expands and contracts smoothly. In addition, the parts that support the ball while elastically deforming (the outer ball groove surface 24 and the inner ball groove surface 14) are arranged in positions that are point symmetrical with respect to the axis of the outer tube 2. In other words, the positions where stress acts on the outer tube 2 and the inner shaft 1 are dispersed. Therefore, stress concentration is avoided, and durability is high.

[0073] As described above, the steering device 80 of the first embodiment includes an intermediate shaft 85. The intermediate shaft 85 includes a cylindrical outer tube 2, an inner shaft 1 that extends in an axial direction parallel to the direction in which the outer tube 2 extends and is partially housed in the outer tube 2, and a plurality of balls 3 that are disposed between the inner peripheral surface of the outer tube 2 and the outer peripheral surface of the inner shaft 1. The inner peripheral surface of the outer tube 2 is provided with at least one outer ball groove surface 24 that is recessed radially outward and extends in the axial direction. The outer peripheral surface of the inner shaft 1 is provided with at least one inner ball groove surface 14 that is recessed radially inward and extends in the axial direction. The outer ball groove surface 24 and the inner ball groove surface 14 face each other in the radial direction. The axial center of the outer ball groove surface 24 or the axial center of the inner ball groove surface 14 has a partition portion 17 that extends radially. The balls 3 are arranged between the outer ball groove surface 24 and the inner ball groove surface 14, and are arranged in multiple numbers on one side of the partition portion 17 in the axial direction and on the other side of the partition portion 17 in the axial direction, with the partition portion 17 as the boundary.

[0074] According to the first embodiment, the support rigidity of the inner shaft 1 in the outer tube 2 is high. Therefore, the inner shaft 1 is less likely to tilt relative to the outer tube 2, and the intermediate shaft 85 extends and retracts smoothly. Furthermore, the portions of the outer tube 2 and the inner shaft 1 that contact the balls 3 are spaced apart in the axial direction. Therefore, the load acting from the balls 3 on the outer tube 2 and the inner shaft 1 is dispersed in the axial direction. As a result, stress concentration is avoided, and durability is improved.

[0075] In the intermediate shaft 85 of the first embodiment, two outer ball groove surfaces 24 and two inner ball groove surfaces 14 are provided. The two outer ball groove surfaces 24 are disposed at intervals of 180°. The two inner ball groove surfaces 14 are disposed at intervals of 180°.

[0076] The intermediate shaft 85 of the first embodiment has extremely high support rigidity against bending loads in specific directions (arrows B1 and B2 in FIG. 4). Therefore, even if a large bending load acts in the specific directions (arrows B1 and B2 in FIG. 4), the inner shaft 1 is unlikely to tilt with respect to the outer tube 2.

[0077] In the intermediate shaft 85 of the first embodiment, one end of the inner shaft 1 is inserted into and accommodated in the other end of the outer tube 2. The other end of the outer tube 2 is provided with an outer fall-out prevention part 26 that prevents the balls 3 from falling off from the outer ball groove surface 24. One end of the inner shaft 1 is provided with an inner fall-out prevention part 16 that prevents the balls 3 from falling off from the inner ball groove surface 14.

[0078] According to the first embodiment, there is no need for fasteners for preventing the balls 3 from falling off the outer ball groove surface 24 and the inner ball groove surface 14. This makes it possible to further reduce the number of parts.

[0079] In the intermediate shaft 85 of the first embodiment, the inner peripheral surface of the outer tube 2 is provided with a plurality of concave surfaces 23 that are recessed radially outward and extend in the axial direction. The outer peripheral surface of the inner shaft 1 is provided with a plurality of convex streaks 13 that protrude radially outward, extend axially, and enter the inside of the concave streaks 23. The convex streaks 13 are separated from the concave streaks 23, and have gaps S1, S2 on the radial outside of the convex streaks 13 and on both sides of the circumferential direction of the convex streaks 13. The outer ball groove surface 24 is arc-shaped when viewed from the axial direction. The outer ball groove surface 24 is provided at the circumferential center with an outer groove bottom 24a that is located at the radially outermost position of the outer ball groove surface 24. The radial thickness R1 of the outer tube 2 is the smallest in the entire circumference of the outer tube 2, from the outer groove bottom 24a to the outer peripheral surface of the outer tube 2. The inner ball groove surface 14 has an arc shape when viewed from the axial direction. An inner groove bottom 14a is provided at the circumferential center of the inner ball groove surface 14, which is located radially inward among the inner ball groove surfaces 14. The radial thickness r1 of the inner shaft 1 is smallest at a thickness r2 from the inner groove bottom 14a to the outer peripheral surface of the inner shaft 1 over the entire circumference of the inner shaft 1. The outer ball groove surface 24 and the inner ball groove surface 14 have a radius of curvature larger than the radius of curvature of the ball 3. In a neutral state where the outer tube 2 and the inner shaft 1 are not rotating in the circumferential direction, the ball 3 abuts against the outer groove bottom 24a and the inner groove bottom 14a with an interference.

[0080] According to the first embodiment, the outer ball groove surface 24 and the inner ball groove surface 14 are elastically deformed to apply a preload to the ball 3. Therefore, the rattling of the ball 3 in the circumferential direction is suppressed. Therefore, an elastic member for applying a preload to the ball 3 is not required, and the number of parts can be reduced. Furthermore, when the vehicle is running and the intermediate shaft 85 is extended or retracted, the ball 3 rolls, and no slippage occurs between the concave streak surface 23 and the convex streak portion 13. Therefore, the sliding resistance between the outer tube 2 and the inner shaft 1 is small. Furthermore, since no slippage occurs between the concave streak surface 23 and the convex streak portion 13, there is no need to provide a resin layer between the outer tube 2 and the inner shaft 1 to reduce frictional resistance, and the intermediate shaft 85 can be easily manufactured. Furthermore, although the operating torque acting on the inner shaft 1 is generally transmitted to the outer tube 2 via the balls 3, when a large torsional torque acts on the intermediate shaft 85, the concave surface 23 comes into contact with the convex portion 13, restricting large elastic deformation of the balls, the outer ball groove surface 24, and the inner ball groove surface 14. For this reason, the balls, the outer ball groove surface 24, and the inner ball groove surface 14 are less susceptible to fatigue failure and have high durability.

[0081] Next, a description will be given of the intermediate shafts 85A, 85B of embodiments 2 and 3. In the following description, the same components as those described in the above-mentioned embodiment 1 will be given the same reference numerals, and duplicated description will be omitted.

[0082] (Embodiment 2) Fig. 9 is a cross-sectional view of an intermediate shaft of embodiment 2. As shown in Fig. 9, the intermediate shaft 85A of embodiment 2 differs from the intermediate shaft 85 of embodiment 1 in that there are three inner ball groove surfaces 14 provided on the outer peripheral surface 12 of the inner accommodated portion 10 of the inner shaft 1. The intermediate shaft 85A of embodiment 2 also differs from the intermediate shaft 85 of embodiment 1 in that there are three outer ball groove surfaces 24 provided on the inner peripheral surface 22 of the outer accommodating portion 20 of the outer tube 2. The following will focus on the differences.

[0083] The inner ball groove surface 14 and the outer ball groove surface 24 are disposed facing each other in the radial direction. The three outer ball groove surfaces 24 and the three inner ball groove surfaces 14 are disposed at intervals of 120°. Thus, the inner ball groove surfaces 14 and the outer ball groove surfaces 24 are disposed at equal intervals. Although stress acts on the inner ball groove surfaces 14 and the outer ball groove surfaces 24 due to elastic deformation, according to the intermediate shaft 85A of the second embodiment, the stress acting on the inner shaft 1 and the outer tube 2 is evenly distributed in the circumferential direction. Therefore, stress concentration is avoided, and the durability of the inner shaft 1 and the outer tube 2 is improved.

[0084] In addition, each of the inner ball groove surfaces 14 is provided with a partition portion 17 (see FIG. 3 and FIG. 6). Therefore, the multiple balls 3 arranged on the inner ball groove surface 14 are arranged in the first direction X1 and the second direction X2, with the partition portion 17 as a boundary. Therefore, in the intermediate shaft 85A of the second embodiment, the inner shaft 1 is less likely to tilt with respect to the outer tube 2, and the intermediate shaft 85 smoothly expands and contracts. Furthermore, the outer ball groove surface 24 and the three inner ball groove surfaces 14 are arranged at intervals of 120°, and the directions in which the inner shaft 1 is less likely to tilt (directions in which the support rigidity against bending load is improved) are at intervals of 60° (see arrow B3 in FIG. 9). Therefore, according to the intermediate shaft 85A of the second embodiment, the support rigidity is improved against bending loads pointing in each direction as viewed from the central axis O1.

[0085] (Embodiment 3) FIG. 10 is a cross-sectional view of an intermediate shaft of the third embodiment. FIG. 11 is an enlarged view of the vicinity of the inner ball groove surface and the outer ball groove surface of FIG. 10. As shown in FIG. 10, the intermediate shaft 85B of the third embodiment differs from the inner shaft 1 of the first embodiment in the shape of the outer peripheral surface of the inner shaft 101. Also, the intermediate shaft 85B of the third embodiment differs from the outer tube 2 of the first embodiment in the shape of the inner peripheral surface of the outer tube 102. Furthermore, the intermediate shaft 85B of the third embodiment differs from the intermediate shaft 85 of the first embodiment in that it includes a resin layer 104 that covers the outer peripheral side of the inner shaft 101. The following will focus on the differences.

[0086] 10, an inner peripheral surface 111 of an inner accommodated portion 110 of an inner shaft 101 is circular about a central axis O1. On the other hand, an outer peripheral surface 112 of the inner accommodated portion 110 is provided with a plurality of convex streak portions 113, a plurality of inner ball groove surfaces 114, and a plurality of standard outer peripheral surfaces 115. The convex streak portions 113 and the standard outer peripheral surface 115 are the same as the convex streak portions 13 and the standard outer peripheral surface 15 of the first embodiment. Therefore, the points described in the first embodiment will not be described.

[0087] The convex ridges 113 are disposed at equal intervals in the circumferential direction. In other words, when an imaginary line L11 connecting the circumferential central portion 113a of the top surface of the convex ridge 113 to the central axis O1 is drawn on each of the convex ridges 113, the angle formed by adjacent imaginary lines L11 in the circumferential direction is always θ1.

[0088] 11, the inner ball groove surface 114 of the inner accommodated portion 110 is a groove surface recessed radially inward from the standard outer circumferential surface 115. The inner ball groove surface 114 is substantially V-shaped in cross section. Specifically, the inner ball groove surface 114 has an inner groove bottom 114a located at the radially innermost position, and an inner first inclined surface 114b and an inner second inclined surface 114c that are inclined so as to be spaced apart from each other in the circumferential direction as they move radially outward from the inner groove bottom 114a.

[0089] When an imaginary line L12 is drawn connecting the inner groove bottom 114a and the central axis O1, the angle formed by the imaginary line L11 passing through the center 113a of the top surface of the convex rib portion 113 adjacent to the inner ball groove surface 114 in the circumferential direction and the imaginary line L12 is θ2. This angle θ2 is the same as the angle θ1 at which the convex rib portion 113 is arranged. Therefore, on the outer circumferential surface 112 of the inner accommodated portion 110, the convex rib portion 113 and the inner groove bottom 114a are arranged at equal intervals in the circumferential direction.

[0090] The inner first inclined surface 114b and the inner second inclined surface 114c are surfaces that come into contact with the ball 103. Although the inner ball groove surface 114 in this embodiment is substantially V-shaped in cross section, it may be a Gothic arc shape. As shown in Fig. 10, two inner ball groove surfaces 114 are provided, and are arranged at 180° intervals.

[0091] 10, the outer circumferential surface 121 of the outer accommodating portion 120 is circular about the central axis O1. On the other hand, the inner circumferential surface 122 of the outer accommodating portion 120 is provided with a plurality of concave surfaces 123 and a standard inner circumferential surface 125. The standard inner circumferential surface 125 is the same as the standard inner circumferential surface 25 of the first embodiment, and therefore a description thereof will be omitted.

[0092] The concave surface 123 of the outer housing portion 120 is a groove-like surface recessed radially outward from the standard inner peripheral surface 125. The concave surface 123 is similar in shape to the protruding portion 113, and is trapezoidal in cross section with a circumferential width that narrows toward the radially outward side. The concave surface 123 also extends in the axial direction with the same shape.

[0093] The concave rib surfaces 123 are disposed at equal intervals in the circumferential direction around the entire circumference of the inner circumferential surface 122 of the outer accommodating portion 120. In other words, when an imaginary line L13 connecting a circumferential center portion 123a of the bottom surface of the concave rib surface 123 to the central axis O1 is drawn on each of the concave rib surfaces 123, the angle formed by adjacent imaginary lines L13 in the circumferential direction is always θ3.

[0094] The angle θ3 at which the concave surface 123 is disposed is the same as the angles θ1 and θ2 at which the convex portion 113 and the inner ball groove surface 114 are disposed. That is, the imaginary line L13 overlaps with the imaginary lines L11 and L12. Therefore, two of the multiple concave surfaces 123 face the inner ball groove surface 114 in the radial direction. The remaining concave surfaces 123 face the convex portions 113 in the radial direction. The convex portions 113 are inserted into the concave surfaces 123. However, the convex portions 113 are not in contact with the concave surfaces 123. The standard inner peripheral surface 125 faces the standard outer peripheral surface 115 in the radial direction. Hereinafter, the concave surfaces 123 facing the inner ball groove surface 114 in the radial direction will be referred to as the outer ball groove surface 124. As shown in FIG. 11, the outer ball groove surface 124 has a bottom surface 124a extending in the circumferential direction, an outer first inclined surface 124b, and an outer second inclined surface 124c.

[0095] As shown in FIG. 10, the resin layer 104 is a coating layer welded to the outer peripheral surface 112 of the inner accommodated portion 110. In detail, the resin layer 104 covers the multiple convex streak portions 113 and the multiple standard outer peripheral surfaces 115 of the outer peripheral surface 112 of the inner accommodated portion 110. Therefore, the resin layer 104 does not cover the inner ball groove surface 114. In addition, the film thickness of the resin layer 104 is uniform in the circumferential direction. Therefore, the shape of the outer peripheral side of the resin layer 104 is a shape that follows the convex streak portions 113 and the standard outer peripheral surface 115. In addition, the resin layer 104 faces the concave streak surface 123 and the standard inner peripheral surface 125, which are radially opposed to the convex streak portions 113 and the standard outer peripheral surface 115.

[0096] As shown in Fig. 11, the resin layer 104 is separated from the concave streak surface 123 and the standard inner peripheral surface 125. That is, the resin layer 104 has a radial gap S11 with respect to the concave streak surface 123. The resin layer 104 also has minute circumferential gaps S12 and S13 on both sides in the circumferential direction with respect to the convex streak portion 113 as a reference. Furthermore, the resin layer 104 has a radial gap S14 with respect to the standard inner peripheral surface 125. The distance between the gaps S11 and S14 is larger than the distance between the minute gaps S12 and S13. The distance between the minute gaps S12 and S13 is approximately 3 µm or more and less than 15 µm.

[0097] Next, an example of a method for forming the minute gaps S12, S13 of the resin layer 104 will be described. First, the resin layer 104 is provided on the entire circumference of the outer circumferential surface 112 of the inner accommodated portion 110 of the inner shaft 101. The thickness of the portion of the resin layer 104 facing the side of the concave streak surface 123 is adjusted so that it abuts against the side of the concave streak surface 123 and has a minute tightening margin (circumferential tightening margin). In addition, in order to simultaneously form the gaps S11, S14, the thickness of the portion of the resin layer 104 facing the bottom surface of the concave streak surface 123 and the standard inner circumferential surface 125 is adjusted so that it has a radial gap without abutting against the bottom surface of the concave streak surface 123 and the standard inner circumferential surface 125. Next, the inner accommodated portion 110 is inserted into the outer accommodated portion 120, and the inner shaft 101 and the outer tube 102 are fitted together. Next, the fitted inner shaft 101 and outer tube 102 are heated. The heating temperature is the temperature in the high-temperature environment in which the intermediate shaft 85B is placed, and is, for example, 100° C. to 150° C. This heating causes the inner shaft 101, the outer tube 102, and the resin layer 104 to thermally expand.

[0098] Next, the inner shaft 101 and the outer tube 102 are left in the air to cool. This cooling causes the inner shaft 101, the outer tube 102, and the resin layer 104 to shrink. The linear expansion coefficient of the resin layer 104 is greater than that of the metal (the inner shaft 101 and the outer tube 102). That is, the resin layer 104 shrinks more than the outer tube 102. Therefore, between the side of the concave stripe surface 123 of the outer tube 102 and the portion of the resin layer 104 that abuts against the side of the concave stripe surface 123, minute gaps S12 and S13 are generated in the circumferential direction. Note that between the bottom surface of the concave stripe surface 123 and the standard inner peripheral surface 125 and the portion of the resin layer 104 that faces the bottom surface of the concave stripe surface 123 and the standard inner peripheral surface 125, radial gaps S11 and S14 remain unchanged even after the heat treatment. Finally, the portion of the resin layer 104 covering the inner ball groove surface 114 is removed to produce the resin layer 104. Note that the resin layer 104 may be cut in order to make the gaps S11 and S14 larger than the minute gaps S12 and S13.

[0099] The resin layer of the present disclosure is not limited to that manufactured by the above-mentioned manufacturing method. However, the resin layer 104 manufactured by the above-mentioned manufacturing method has been deformed (creeped) once in a high-temperature environment, so that the thermal expansion is gentle when it is next placed in a high-temperature environment.

[0100] A plurality of balls 103 are arranged in the axial direction between the inner ball groove surface 114 and the outer ball groove surface 124. The balls 103 are in contact with the inner first inclined surface 114b and the inner second inclined surface 114c of the inner ball groove surface 114. The balls 103 are in contact with the outer first inclined surface 124b and the outer second inclined surface 124c of the outer ball groove surface 124. That is, the balls 103 are in four-point contact with the inner ball groove surface 114 and the outer ball groove surface 124. Furthermore, the balls 103 are sized to have a tightening margin with respect to the inner ball groove surface 114 and the outer ball groove surface 124. Therefore, the balls 103 are assembled in a state in which a preload is applied.

[0101] The inner shaft 101 of this embodiment is cylindrical and is more easily elastically deformed than a solid one. Therefore, the inner shaft 101 is easily bent in the radial direction in cross section, and the preload applied to the ball 103 can be adjusted to be small. In other words, the rolling resistance of the ball 103 (sliding resistance between the inner shaft 101 and the outer tube 102) can be reduced. In addition, since the rigidity of the inner shaft 101 can be reduced, the ball 103 with a large tightening margin can be used. As a result, even if the ball 103 wears, a gap is less likely to occur between the inner ball groove surface 114 and the outer ball groove surface 124.

[0102] Also, an inner dropout prevention portion 16 (see FIG. 6) is provided at an end portion in the second direction X2 of the axial direction of the inner ball groove surface 114. Also, an outer dropout prevention portion 26 (see FIG. 6) is provided at an end portion in the first direction X1 of the axial direction of the outer ball groove surface 124. This prevents the ball 103 from dropping out of the inner ball groove surface 114 or the outer ball groove surface 124.

[0103] Also, each of the inner ball groove surfaces 14 is provided with a partition portion 17 (see Figs. 3 and 6). That is, the multiple balls 3 arranged on the inner ball groove surface 14 are arranged in the first direction X1 and the second direction X2, separated by the partition portion 17. Therefore, the outer tube 2 supports the inner shaft 1 at two locations: a portion on the first direction X1 beyond the partition portion 17, and a portion on the second direction X2 beyond the partition portion.

[0104] As described above, according to the intermediate shaft 85B, the ball 103 is restrained from moving in the circumferential direction, and the rattling of the ball 103 in the circumferential direction is suppressed. In addition, the inner shaft 101 is restrained from rotating relative to the ball 103 by contacting the ball 103 with the inner first inclined surface 114b and the inner second inclined surface 114c. Similarly, the outer tube 102 is restrained from rotating relative to the ball 103 by contacting the ball 103 with the outer first inclined surface 124b and the outer second inclined surface 124c. Therefore, the inner shaft 101 and the outer tube 102 do not rotate relative to each other. From the above, it is possible to prevent the minute gaps S12 and S13 (see FIG. 11) from disappearing due to the relative rotation of the inner shaft 101 and the outer tube 102, in other words, it is possible to prevent the convex rib portion 113 from contacting the concave rib surface 123 through the resin layer 104, which would cause a rattle noise.

[0105] Furthermore, there is no resin layer 104 between the ball 103 and the inner ball groove surface 114, and between the ball 103 and the outer ball groove surface 124. In other words, the ball 103 is in direct contact with the inner shaft 101 and the outer tube 102. Therefore, even if the intermediate shaft 85B expands due to heat and then contracts when it returns to room temperature, no gaps are generated between the ball 103, the inner ball groove surface 114, and the outer ball groove surface 124, which are all made of the same metal. Therefore, even after use in a high-temperature environment, the inner shaft 101 and the outer tube 102 remain unable to rotate relative to each other, and the generation of rattle noise is suppressed.

[0106] Furthermore, each of the inner ball groove surfaces 14 is provided with a partition portion 17 (not shown), and the outer tube 102 supports the inner shaft 101 at two locations, a portion further in the first direction X1 than the partition portion and a portion further in the second direction X2 than the partition portion. Therefore, even in the intermediate shaft 85B of the third embodiment, the inner shaft 101 is unlikely to tilt relative to the outer tube 102. The inner ball groove surface 114 and the outer ball groove surface 124 are disposed at intervals of 180°. Therefore, the inner ball groove surface 114 and the outer ball groove surface 124 have a very large support rigidity against a bending load in the direction in which the ball 103 is disposed as viewed from the central axis O1 (see arrow B4 in FIG. 10).

[0107] Next, the operation of the intermediate shaft 85B will be described. When the vehicle is traveling, the body of the vehicle is distorted due to vibrations transmitted from the road surface. As a result, an axial load acts on the intermediate shaft 85B of the steering device 80 (see arrow A1 in FIG. 2).

[0108] When the intermediate shaft 85B is placed in an environment at room temperature, the intermediate shaft 85B does not thermally expand. In other words, gaps S11, S14 and minute gaps S12, S13 are provided between the resin layer 104 and the inner circumferential surface 122 of the outer accommodating portion 120, preventing slippage between the resin layer 104 and the outer accommodating portion 120. Therefore, when the intermediate shaft 85B expands or contracts, the balls 103 roll, and the sliding resistance between the inner shaft 101 and the outer tube 102 is small.

[0109] Furthermore, when the environment in which the intermediate shaft 85B is placed is high temperature, each component of the intermediate shaft 85B thermally expands. As a result, the minute gaps S12 and S13, which have a small gap amount, disappear, and a part of the resin layer 104 abuts against the inner circumferential surface 122 of the outer accommodating portion 120. Note that, since the gap amounts of the gaps S11 and S14 are large, the gaps S11 and S14 do not disappear even if the resin layer 104 thermally expands. When the intermediate shaft 85B expands or contracts, the balls 103 roll, and slippage occurs between a part of the resin layer 104 and the inner circumferential surface 122 of the outer accommodating portion 120. Therefore, the sliding resistance between the inner shaft 101 and the outer tube 102 becomes larger than that at room temperature.

[0110] However, a portion of the resin layer 104 that contacts the inner circumferential surface 122 at high temperatures has minute gaps S12, S13 between the resin layer 104 and the inner circumferential surface 122 of the outer accommodating portion 120 at room temperature. Therefore, the surface pressure of the resin layer 104 against the inner circumferential surface 122 of the outer accommodating portion 120 is lower than when the resin layer 104 is already in contact with the inner circumferential surface of the outer accommodating portion 120 at room temperature. For this reason, an increase in the sliding resistance between the inner shaft 101 and the outer tube 102 is kept low in a high-temperature environment.

[0111] In addition, as described above, the resin layer 104 is heat-treated once and thermally expands slowly. Therefore, when the intermediate shaft 85B is placed in a high-temperature environment for a short period of time, the minute gaps S12, S13 are maintained and an increase in the sliding resistance between the inner shaft 101 and the outer tube 102 is avoided.

[0112] In addition, when the steering wheel 81 is operated while the vehicle is running, torque (operation torque) is input to the inner shaft 101 connected to the output shaft 82b (see arrow A2 in FIG. 2). In addition, when the torque is transmitted, a bending load acts on the intermediate shaft 85B. According to this embodiment, the outer tube 2 has high support rigidity against the bending load acting on the inner shaft 1. Therefore, the angle of inclination of the inner shaft 1 with respect to the outer tube 2 becomes small. Therefore, the inner accommodated portion 110 of the inner shaft 101 moves slightly in the radial direction (see arrow D in FIG. 10). As a result, the minute gaps S12 and S13 disappear, and the inner ball groove surface 114 and the outer ball groove surface 124 come into contact with each other via the resin layer 104. As a result, the torque is transmitted from the inner shaft 101 to the outer tube 102. During torque transmission, the torque of the outer tube 102 is transmitted from the inner shaft 101 via the balls 103, but is transmitted mainly by the contact between the inner ball groove surface 114 and the outer ball groove surface 124.

[0113] As described above, the intermediate shaft 85B of the third embodiment includes a resin layer 104 that is coated on the outer peripheral surface of the inner shaft 101 and is disposed between the inner peripheral surface of the outer tube 102 and the outer peripheral surface of the inner shaft 101. The inner peripheral surface of the outer tube 102 is provided with a plurality of grooved surfaces 123 that are recessed radially outward and extend in the axial direction. The grooved surfaces 123 are disposed at equal intervals in the circumferential direction around the entire circumference of the inner peripheral surface of the outer tube 102. The outer peripheral surface of the inner shaft 101 is provided with a plurality of convex streaks 113 that protrude radially outward, extend in the axial direction, and enter the inside of the grooved surfaces 123. The inner ball groove surface 114 faces the outer ball groove surface 124, which is one of the plurality of grooved surfaces 123, in the radial direction. The balls 103 abut against the inner ball groove surface 114 and the outer ball groove surface 124 with an interference therebetween, preventing relative rotation between the outer tube 102 and the inner shaft 101. The resin layer 104 covers the outer circumferential side of the convex rib portion 113, and has radial gaps S11, S14 and minute circumferential gaps S12, S13 with respect to the concave rib surface 123 in a neutral state in which the outer tube 102 and the inner shaft 101 are not rotating in the circumferential direction.

[0114] According to the third embodiment, the circumferential rattle of the ball 103 is suppressed. In addition, the inner shaft 101 and the outer tube 102 are prevented from rotating relative to each other through the ball 103. Therefore, the contact between the convex streak portion 113 and the concave streak surface 123 and the generation of rattle noise is suppressed. In addition, even if the intermediate shaft 85B is placed in a high-temperature environment, no gap is generated between the ball 103 and the inner ball groove surface 114 and the outer ball groove surface 124. Therefore, even after being used in a high-temperature environment, the relative rotation between the inner shaft 101 and the outer tube 102 is maintained, and the generation of rattle noise is suppressed. In addition, when the intermediate shaft 85B expands and contracts at room temperature, the ball 103 rolls, and the sliding resistance is small. In addition, when the intermediate shaft 85B expands and contracts under a high-temperature environment, in addition to the rolling of the balls 103, a part of the resin layer 104 and the concave surface 123 also slide. However, as described above, the surface pressure of the resin layer 104 against the concave surface 123 is low. Therefore, the increase in sliding resistance at high temperatures is suppressed to be low. In addition, one of the multiple concave surfaces 123 is the outer ball groove surface 124. Therefore, processing for forming the outer ball groove surface 124 on the inner peripheral surface of the outer tube 102 is not required, and the outer tube 102 is easily manufactured. In addition, the outer tube 102 is provided with the concave surface 123 over the entire circumference of the inner peripheral surface, and there is no phase for assembling the outer tube 102 to the inner shaft 101. Therefore, the outer tube 102 is easily assembled, and the productivity of the intermediate shaft 85B is improved. In addition, the resin layer 104 is provided on the outer peripheral surface of the inner shaft 101, not on the inner peripheral surface of the outer tube 102. This facilitates the process of immersing the inner shaft 101 in a molten resin bath and then molding the resin layer 104. In addition, when molding the resin layer 104, the resin layer 104 covering the inner ball groove surface 114 can be removed at the same time, making it easier to manufacture the resin layer 104.

[0115] Although each embodiment has been described above, the intermediate shaft and steering device of the present disclosure are not limited to the examples described in the embodiments. For example, the partition portion 17 may be provided on the outer ball groove surface 24, 124 instead of the inner ball groove surface 14, 114. Also, the partition portion 17 may be provided on only one of the multiple inner ball groove surfaces 14, 114. In other words, it is sufficient that the partition portion 17 is provided on at least one of the inner ball groove surfaces 14, 114 or the outer ball groove surface 24, 124.

[0116] Furthermore, the numbers of the inner ball groove surfaces 14, 114 and the outer ball groove surfaces 24, 124 are not limited to two or three as described above, and may be, for example, four or more. Furthermore, in the intermediate shaft and steering device of the present disclosure, the outer ball groove surfaces 24, 124 and the inner ball groove surfaces 14, 114 may not be disposed at equal intervals.

[0117] In the intermediate shafts 85 and 85A of the first and second embodiments, the side surface 23b of the concave streak surface 23 and the side surface 13b of the convex streak portion 13 may be hardened. This makes the intermediate shaft less susceptible to damage even when a large torsional torque acts on the intermediate shaft and the side surface 23b of the concave streak surface 23 and the side surface 13b of the convex streak portion 13 come into contact with each other. This improves the durability of the concave streak surface 23 and the convex streak portion 13. Examples of the hardening treatment include gas soft nitriding and quenching, but are not particularly limited to these.

[0118] In addition, in each embodiment, the inner shaft 1, 101 is the input shaft and the outer tube 2, 102 is the output shaft, but in the intermediate shaft and steering device of the present disclosure, the inner shaft 1, 101 may be the output shaft and the outer tube 2, 102 may be the input shaft. In addition, in the third embodiment, the resin layer 104 is provided on the outer peripheral surface of the inner shaft 101, but in the present disclosure, the resin layer 104 may be provided on the inner peripheral surface of the outer tube 102. This will be described in detail below.

[0119] (Embodiment 4) Fig. 12 is a cross-sectional view of an intermediate shaft of embodiment 4. As shown in Fig. 12, in the inner shaft 101 of embodiment 4, an outer circumferential surface 112 of the inner accommodated portion 110 is provided with a plurality of convex rib portions 113 and a plurality of standard outer circumferential surfaces 115. The convex rib portions 113 are disposed at equal intervals in the circumferential direction over the entire circumference of the outer circumferential surface 112 of the inner accommodated portion 110. In addition, between the plurality of convex rib portions 113, recesses 117 recessed radially inward are formed.

[0120] In the outer tube 102 of the fourth embodiment, the inner peripheral surface 122 of the outer accommodating portion 120 is provided with a plurality of concave rib surfaces 123, an outer ball groove surface 128, and a standard inner peripheral surface 125. The outer ball groove surface 128 is a groove surface that is recessed radially outward from the bottom surface of the concave rib surface 123. The outer ball groove surface 128 is substantially V-shaped in cross section. That is, the outer ball groove surface 128 has an outer groove bottom 128a located at the outermost radial side, and an outer first inclined surface 128b and an outer second inclined surface 128c that are inclined so as to be spaced apart from each other in the circumferential direction as they move radially inward from the outer groove bottom 128a.

[0121] The convex streak portion 113 and the concave streak surface 123 face each other in the radial direction, and the arrangement angles of the convex streak portion 113 and the concave streak surface 123 are the same. The convex streak portion 113 is inserted into the concave streak surface 123. However, the convex streak portion 113 is not in contact with the concave streak surface 123. The outer ball groove surface 128 faces one of the multiple recesses 117 in the radial direction. Hereinafter, the recess 117 facing the outer ball groove surface 128 in the radial direction is referred to as the inner ball groove surface 118. The inner ball groove surface 118 has a bottom surface 118a extending in the circumferential direction, an inner first inclined surface 118b, and an inner second inclined surface 118c.

[0122] The resin layer 104A is welded to the inner peripheral surface 122 of the outer accommodating portion 120. In detail, the resin layer 104A covers the concave streak surfaces 123 and the standard inner peripheral surfaces 125 of the inner peripheral surface 122 of the outer accommodating portion 120. Therefore, the resin layer 104A does not cover the outer ball groove surface 128. In addition, the film thickness of the resin layer 104A is uniform in the circumferential direction. Therefore, the shape of the outer peripheral side of the resin layer 104A is a shape that follows the concave streak surfaces 123 and the standard inner peripheral surface 125.

[0123] The resin layer 104A is separated from the convex streak portion 113 and the standard outer circumferential surface 115. That is, the resin layer 104A has a radial gap S11 with respect to the convex streak portion 113. The resin layer 104A also has minute circumferential gaps S12 and S13 on both sides in the circumferential direction with respect to the convex streak portion 113. Furthermore, the resin layer 104A has a radial gap S14 with respect to the standard outer circumferential surface 115.

[0124] A plurality of balls 103 are arranged in the axial direction between the inner ball groove surface 118 and the outer ball groove surface 128. The balls 103 are in contact with the inner first inclined surface 118b and the inner second inclined surface 118c of the inner ball groove surface 118. The balls 103 are in contact with the outer first inclined surface 128b and the outer second inclined surface 128c of the outer ball groove surface 128. That is, the balls 103 are in four-point contact with the inner ball groove surface 118 and the outer ball groove surface 128. Furthermore, the balls 103 are sized to have a tightening margin with respect to the inner ball groove surface 118 and the outer ball groove surface 128. Therefore, the balls 103 are assembled in a state in which a preload is applied.

[0125] As described above, the intermediate shaft 85C of the fourth embodiment includes a resin layer 104A that is coated on the inner peripheral surface of the outer tube 102 and disposed between the inner peripheral surface of the outer tube 102 and the outer peripheral surface of the inner shaft 101. The outer peripheral surface of the inner shaft 101 is provided with a plurality of convex streaks 113 that protrude radially outward and extend in the axial direction. The convex streaks 113 are disposed at equal intervals in the circumferential direction over the entire circumference of the outer peripheral surface of the inner shaft 101. The inner peripheral surface of the outer tube 102 is provided with a plurality of concave surfaces 123 that are recessed radially outward, extend in the axial direction, and into which the convex streaks 113 are inserted. The outer ball groove surface 128 faces the inner ball groove surface 118, which is one of a plurality of recesses 117 provided between the convex streaks 113, in the radial direction. The balls 103 abut against the inner ball groove surface 118 and the outer ball groove surface 128 with an interference therebetween, preventing relative rotation between the outer tube 102 and the inner shaft 101. The resin layer 104A covers the inner peripheral side of the concave rib surface 123, and has radial gaps S11, S14 and minute circumferential gaps S12, S13 with respect to the convex rib portion 113 in a neutral state in which the outer tube 102 and the inner shaft 101 are not rotating in the circumferential direction.

[0126] The intermediate shaft 85C of the fourth embodiment produces the same effect as the intermediate shaft 85B of the third embodiment. That is, the ball 103 is assembled between the outer tube 102 and the inner shaft 101 with a tightening margin. Therefore, the circumferential rattle of the ball 103 is suppressed. Furthermore, the outer tube 102 and the inner shaft 101 are prevented from rotating relative to each other through the ball 103. Therefore, the convex streak portion 113 and the concave streak surface 123 are prevented from coming into contact with each other to generate rattle noise. Furthermore, even after use in a high-temperature environment, the outer tube 102 and the inner shaft 101 are prevented from rotating relative to each other, and the generation of rattle noise is suppressed. Furthermore, since there is no slippage between the resin layer 104A and the convex streak portion 113, the sliding resistance between the outer tube 102 and the inner shaft 101 is small. Furthermore, when the intermediate shaft 85C is placed in a high-temperature environment, the resin layer 104A thermally expands, and the minute gaps S12 and S13 in the circumferential direction disappear. Thus, a part of the resin layer 104A comes into contact with the ridge portion 113. When the intermediate shaft 85C expands or contracts, in addition to the rolling of the balls 103, a part of the resin layer 104A slides with the ridge portion 113. However, since the part of the resin layer 104A that comes into contact with the ridge portion 113 at high temperatures has the minute gaps S12 and S13 with respect to the ridge portion 113 at room temperature, the surface pressure of the resin layer 104A against the ridge portion 113 is lower than when the resin layer 410A is already in contact with the ridge portion 113 at room temperature. Thus, the increase in the sliding resistance between the outer tube 102 and the inner shaft 101 at high temperatures is suppressed to a low level. Furthermore, when torque is transmitted to the intermediate shaft 85C, a bending load that bends the intermediate shaft 85C acts. As a result, the inner shaft 101 is inclined relative to the outer tube 102, eliminating minute gaps S12, S13 in the circumferential direction. The convex streak portion 113 and the concave streak surface 123 come into contact with each other via the resin layer 104A, and torque is transmitted. Furthermore, the inner shaft 101 has the convex streak portion 113 provided along the entire circumference of the inner circumferential surface, and there is no phase required for assembly to the outer tube 102. This facilitates assembly of the inner shaft 101, improving the productivity of the intermediate shaft 85C. Furthermore, the inner shaft 101 has the same shape along the entire circumference, making it easy to manufacture.The resin layer 104A is manufactured by immersing the outer tube 102 in a molten resin bath, and then performing a process to mold the resin layer 104A. When molding the resin layer 104A, the resin layer covering the outer ball groove surface 128 can be removed at the same time, making it easier to manufacture the resin layer 104A. [Explanation of symbols]

[0127] 1, 101 Inner shaft 2, 102 Outer tube 3. 103 balls 104, 104A resin layer 10, 110 Inner storage part 11, 111 Inner surface 12, 112 Outer surface 13, 113 Convex part 14, 114, 118 Inner ball groove surface 15, 115 Standard outer surface 16 Inner fall prevention part 17 Partition 20, 120 Outer housing 21, 121 Outer surface 22, 122 Inner surface 23, 123 Concave surface 24, 124, 128 Outer ball groove surface 25, 125 Standard inner surface 26 Outer fall prevention part 80 Steering device 85, 85A, 85B, 85C Intermediate shaft 117 Depression

Claims

1. A cylindrical outer tube; an inner shaft extending in an axial direction parallel to a direction in which the outer tube extends and a portion of the inner shaft is accommodated in the outer tube; a plurality of balls disposed between an inner circumferential surface of the outer tube and an outer circumferential surface of the inner shaft; Equipped with The inner circumferential surface of the outer tube is provided with at least one outer ball groove surface that is recessed radially outward and extends in the axial direction, The outer circumferential surface of the inner shaft is provided with at least one inner ball groove surface that is recessed radially inward and extends in the axial direction, the outer ball groove surface and the inner ball groove surface face each other in a radial direction, a partition portion extending in a radial direction is provided at a center portion in the axial direction of the outer ball groove surface or at a center portion in the axial direction of the inner ball groove surface, the ball is disposed between the outer ball groove surface and the inner ball groove surface, the balls are disposed on one side of the partition portion in the axial direction and on the other side of the partition portion in the axial direction, with the partition portion as a boundary; a resin layer that covers an outer peripheral surface of the inner shaft and is disposed between an inner peripheral surface of the outer tube and the outer peripheral surface of the inner shaft, The inner circumferential surface of the outer tube is provided with a plurality of recessed surfaces that are recessed radially outward and extend in the axial direction, The grooved surfaces are disposed at equal intervals in a circumferential direction around the entire circumference of the inner circumferential surface of the outer tube, A plurality of convex ridges are provided on an outer circumferential surface of the inner shaft, the convex ridges protruding radially outward, extending in the axial direction, and extending into the concave ridge surface, the inner ball groove surface is radially opposed to the outer ball groove surface, which is one of the plurality of concave surfaces; The balls are in contact with the inner ball groove surface and the outer ball groove surface with an interference between them, and relative rotation between the outer tube and the inner shaft is disabled. The resin layer covers an outer circumferential side of the protruding portion, and has a radial gap and a small circumferential gap with respect to the recessed surface in a neutral state in which the outer tube and the inner shaft are not rotating in the circumferential direction. Intermediate shaft.

2. A cylindrical outer tube; an inner shaft extending in an axial direction parallel to a direction in which the outer tube extends and a portion of the inner shaft is accommodated in the outer tube; a plurality of balls disposed between an inner circumferential surface of the outer tube and an outer circumferential surface of the inner shaft; Equipped with The inner circumferential surface of the outer tube is provided with at least one outer ball groove surface that is recessed radially outward and extends in the axial direction, The outer circumferential surface of the inner shaft is provided with at least one inner ball groove surface that is recessed radially inward and extends in the axial direction, the outer ball groove surface and the inner ball groove surface face each other in a radial direction, a partition portion extending in a radial direction is provided at a center portion in the axial direction of the outer ball groove surface or at a center portion in the axial direction of the inner ball groove surface, the ball is disposed between the outer ball groove surface and the inner ball groove surface, the balls are disposed on one side of the partition portion in the axial direction and on the other side of the partition portion in the axial direction, with the partition portion as a boundary; a resin layer that covers an inner circumferential surface of the outer tube and is disposed between the inner circumferential surface of the outer tube and an outer circumferential surface of the inner shaft, A plurality of ridges are provided on an outer circumferential surface of the inner shaft, the ridges protruding radially outward and extending in the axial direction, The convex ridges are disposed at equal intervals in a circumferential direction around the entire outer circumferential surface of the inner shaft, an inner circumferential surface of the outer tube is provided with a plurality of recessed surfaces that are recessed radially outward, extend in the axial direction, and receive the protruding portion therein; the outer ball groove surface is radially opposed to an inner ball groove surface which is one of a plurality of recesses provided between the plurality of protruding portions, The balls are in contact with the inner ball groove surface and the outer ball groove surface with an interference between them, and relative rotation between the outer tube and the inner shaft is disabled. The resin layer covers the inner peripheral side of the concave streak surface, and has a radial gap and a small circumferential gap with respect to the convex streak portion in a neutral state in which the outer tube and the inner shaft are not rotating in the circumferential direction. Intermediate shaft.

3. The outer ball groove surface and the inner ball groove surface are provided in two pieces, The two outer ball groove surfaces are arranged at intervals of 180°, The two inner ball groove surfaces are arranged at 180° intervals. The intermediate shaft according to claim 1 or 2.

4. The outer ball groove surfaces and the inner ball groove surfaces are each provided three by three, The three outer ball groove surfaces are arranged at intervals of 120°, The three inner ball groove surfaces are arranged at intervals of 120°. The intermediate shaft according to claim 1 or 2.

5. One end of the inner shaft is inserted into and accommodated in the other end of the outer tube, an outer tube having an outer fall-out prevention portion provided at the other end thereof for preventing the balls from falling out of the outer ball groove surface; An inner dropout prevention portion is provided at one end of the inner shaft to prevent the balls from dropping out from the inner ball groove surface. The intermediate shaft according to any one of claims 1 to 4.

6. A steering device comprising the intermediate shaft according to any one of claims 1 to 5.

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