Steering shaft and manufacturing method thereof

Abstract

A steering shaft includes an inner shaft having a first tooth portion, an outer shaft having a second tooth portion, and a resin layer. The resin layer has a plurality of thick film portions and at least four thin film portions. The thick film portions are arranged with gaps with respect to the second tooth portion, and the thin film portions are in contact with both the first tooth portion and the second tooth portion. In a cross section orthogonal with respect to a center axis of the inner shaft, the thickness of the thin film portions is smaller than the thickness of the thick film portions.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a steering shaft and a manufacturing method of a steering shaft. BACKGROUND

[0002] A vehicle is provided with a steering device as a device for transmitting an operation of an operator (a driver) on a steering wheel to a wheel (for example, refer to Patent Literature 1). The steering device includes a steering shaft that transmits a rotational torque. The steering shaft includes an inner shaft having a plurality of first tooth portions on an outer periphery, an outer shaft having a plurality of second tooth portions on an inner periphery, and a resin layer provided to an outer peripheral surface of the first tooth portions. The resin layer portion provided to the tooth surface (side surface) of the first tooth portions is substantially the same in thickness along the circumferential direction in whichever of the first tooth portions.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2017-145945 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] Resin has a higher linear expansion coefficient than metal. Therefore, the steering shaft described in Patent Literature 1, when it becomes high temperature, the resin layer portion provided to the tooth surface of the first tooth portions expands to contact both the tooth surface of the first tooth portions and the tooth surface of the second tooth portions. Thereafter, when the steering shaft returns to normal temperature, the resin layer portion contracts. Thus, a gap is generated between the resin layer portion provided to the tooth surface of all the first tooth portions and the tooth surface of the second tooth portions, and therefore, there is a possibility that the backlash becomes large and a gap noise is generated when the vehicle travels.

[0008] The present disclosure was achieved in view of the above-described problems, and aims to provide a steering shaft and a manufacturing method of a steering shaft that can further reduce a gap noise generated when a vehicle travels.

[0009] MEANS FOR SOLVING THE PROBLEMS

[0010] To achieve the object, a turning shaft according to the present disclosure includes: an inner shaft having a plurality of first tooth portions arranged along a circumferential direction on an outer peripheral surface; an outer shaft having a plurality of second tooth portions arranged along the circumferential direction on an inner peripheral surface, and arranged on an outer peripheral side of the first tooth portions; and a resin layer arranged between the first tooth portions and the second tooth portions, the resin layer having a plurality of thick film portions arranged between tooth surfaces of the first tooth portions and tooth surfaces of the second tooth portions, and arranged with a gap with respect to one of the first tooth portions and the second tooth portions, and at least four thin film portions arranged between the tooth surfaces of the first tooth portions and the tooth surfaces of the second tooth portions, and in contact with both the first tooth portions and the second tooth portions, in a cross section orthogonal to a center axis of the inner shaft, a thickness of the thin film portions along a third imaginary line extending along a radial direction between a first imaginary line passing through an outer peripheral end of the first tooth portions and extending in the circumferential direction and a second imaginary line passing through an inner peripheral end of the second tooth portions and extending in the circumferential direction is smaller than a thickness of the thick film portions along the third imaginary line. In addition, the inner shaft and the outer shaft according to the present disclosure can be applied to either one of spline engagement and saw-tooth engagement.

[0011] Thus, the thin film portions are arranged between the tooth surfaces of the first tooth portions and the tooth surfaces of the second tooth portions, and in contact with both the first tooth portions and the second tooth portions. That is, the tooth surfaces of the first tooth portions and the tooth surfaces of the second tooth portions adjacent in the circumferential direction are in contact with the thin film portions provided with at least four therebetween without a gap. In a high temperature environment, the resin layer expands in the circumferential direction to be in contact with the tooth surfaces of the first tooth portions and the tooth surfaces of the second tooth portions without a gap. At this time, sometimes the resin layer pushes the tooth surfaces of the first tooth portions and the tooth surfaces of the second tooth portions in the circumferential direction. In this regard, since the thickness of the thin film portions in the circumferential direction is smaller than that of the thick film portions, the expansion amount of the thin film portions is smaller than that of the thick film portions, and the resin of the thin film portions is less likely to move to the outside in the radial direction than the thick film portions. Therefore, even after returning from the high temperature environment to a normal temperature environment, a gap is less likely to occur around the thin film portions. Thus, the turning shaft according to the present disclosure has a smaller backlash after returning from the high temperature environment to the normal temperature environment than the turning shaft of Patent Document 1, and can further reduce a gap rattle generated when a vehicle travels.

[0012] As a preferable mode of the turning shaft, a plurality of sets of the thin film portions are arranged with a gap in the circumferential direction. Thus, the turning shaft according to the present disclosure has a smaller backlash than the turning shaft of Patent Document 1, and can further reduce a gap rattle generated when a vehicle travels.

[0013] As a preferable mode of the steering shaft, a plurality of the film portions are arranged at equal intervals along the circumferential direction. That is, since a plurality of the film portions are arranged at equal intervals along the circumferential direction, the steering shaft of the present disclosure can further reduce the backlash and further reduce the backlash noise generated when the vehicle travels, as compared with the steering shaft of Patent Document 1. In addition, one group of film portions refers to a set of film portions arranged adjacent to each other in the circumferential direction.

[0014] As a preferable mode of the steering shaft, the number of groups of the plurality of the film portions is two, and thus the number of groups of the film portions can be reduced, the backlash of the steering shaft can be reduced, and the backlash noise generated when the vehicle travels can be further reduced.

[0015] As a preferable mode of the steering shaft, one group of the film portions includes four of the film portions, and thus the backlash of the steering shaft can be further reduced, and the backlash noise generated when the vehicle travels can be further reduced, as compared with two of the film portions.

[0016] As a preferable mode of the steering shaft, the inner shaft is a hollow member, and thus the weight of the steering shaft can be reduced.

[0017] As a preferable mode of the steering shaft, the plurality of the first teeth include thick-walled teeth and thin-walled teeth having a width along the circumferential direction smaller than that of the thick-walled teeth, and the film portion is in contact with both the thick-walled teeth and the second teeth. In this way, the film portion can be easily formed by changing a part of the plurality of the first teeth to the thick-walled teeth.

[0018] As a preferable mode of the steering shaft, the plurality of the second teeth include thick-walled teeth and thin-walled teeth having a width along the circumferential direction smaller than that of the thick-walled teeth, and the film portion is in contact with both the thick-walled teeth and the first teeth. In this way, the film portion can be easily formed by changing a part of the plurality of the second teeth to the thick-walled teeth.

[0019] A manufacturing method of a steering shaft according to a technical solution of the present disclosure includes: a resin layer forming step of forming a resin layer on an inner shaft or an outer shaft, the inner shaft having a plurality of first teeth arranged along a circumferential direction on an outer peripheral surface, the outer shaft having a plurality of second teeth arranged along the circumferential direction on an inner peripheral surface, and the outer shaft being arranged on an outer peripheral side of the first teeth of the inner shaft; a heating step of heating the inner shaft, the outer shaft, and the resin layer while the resin layer is in contact with tooth surfaces of all of the first teeth and tooth surfaces of all of the second teeth; and a cooling step of cooling the inner shaft, the outer shaft, and the resin layer after the heating step, the plurality of the first teeth including thick-walled teeth and thin-walled teeth having a width along the circumferential direction smaller than that of the thick-walled teeth.

[0020] The gap in the circumferential direction between the tooth surface of the thick-walled tooth of the first tooth portion and the tooth surface of the second tooth portion is smaller than the gap in the circumferential direction between the tooth surface of the thin-walled tooth of the first tooth portion and the tooth surface of the second tooth portion. Therefore, the resin layer arranged in the gap between the thick-walled tooth and the second tooth portion becomes a thin film portion, and the resin layer arranged in the gap between the thin-walled tooth and the second tooth portion becomes a thick film portion. In the heating process, a part of the resin of the thick film portion moves in the circumferential direction, and is solidified as it is in the cooling process, and thus a gap is generated between the solidified thick film portion and the tooth surface of the second tooth portion. However, the thin film portion is in contact with the thick-walled tooth and the second tooth portion in either of the heating process and the cooling process, and thus no gap is generated. In this way, the thin film portion and the thick film portion of the resin layer can be formed by a relatively easy work.

[0021] The manufacturing method of the steering shaft according to the present disclosure includes: a resin layer forming process of forming a resin layer on an inner shaft or an outer shaft, the inner shaft having a plurality of first tooth portions arranged on an outer circumferential surface in a circumferential direction, the outer shaft having a plurality of second tooth portions arranged on an inner circumferential surface in the circumferential direction, and the outer shaft being arranged on an outer circumferential side of the first tooth portions of the inner shaft; a heating process of heating the inner shaft, the outer shaft, and the resin layer while the resin layer is in contact with tooth surfaces of all of the first tooth portions and tooth surfaces of all of the second tooth portions; and a cooling process of cooling the inner shaft, the outer shaft, and the resin layer after the heating process, the plurality of second tooth portions including a thick-walled tooth and a thin-walled tooth, the thin-walled tooth having a width in the circumferential direction that is smaller than a width in the circumferential direction of the thick-walled tooth.

[0022] The gap in the circumferential direction between the tooth surface of the thick-walled tooth of the second tooth portion and the tooth surface of the first tooth portion is smaller than the gap in the circumferential direction between the tooth surface of the thin-walled tooth of the second tooth portion and the tooth surface of the first tooth portion. Therefore, the resin layer arranged in the gap between the thick-walled tooth and the first tooth portion becomes a thin film portion, and the resin layer arranged in the gap between the thin-walled tooth and the first tooth portion becomes a thick film portion. In the heating process, a part of the resin of the thick film portion moves in the circumferential direction, and is solidified as it is in the cooling process, and thus a gap is generated between the solidified thick film portion and the tooth surface of the first tooth portion. However, the thin film portion is in contact with the thick-walled tooth and the first tooth portion in either of the heating process and the cooling process, and thus no gap is generated. In this way, the thin film portion and the thick film portion of the resin layer can be formed by a relatively easy work.

[0023] Effects of the Invention

[0024] According to the present disclosure, it is possible to provide a steering shaft and a manufacturing method of a steering shaft that can further reduce a gap rattle generated when a vehicle travels. Attached Figure Description

[0025] Figure 1 This is a schematic diagram showing a general outline of the steering device according to the first embodiment.

[0026] Figure 2 This is a schematic perspective view showing the steering device of the first embodiment.

[0027] Figure 3 It means Figure 2 Side view of the lower shaft and universal joint.

[0028] Figure 4 It means in Figure 3 A schematic diagram of the cross section at line IV-IV.

[0029] Figure 5 It means Figure 4 A schematic diagram of the inner shaft and the cross-section of the resin layer.

[0030] Figure 6 It's enlarged. Figure 5 A partial schematic diagram.

[0031] Figure 7 It's enlarged. Figure 5 A partial schematic diagram.

[0032] Figure 8 It's enlarged. Figure 5 A partial schematic diagram.

[0033] Figure 9 This is a schematic diagram illustrating the manufacturing method of the lower shaft according to the first embodiment, and it shows the state in which the lower shaft is housed inside a heating furnace after the resin layer formation process is completed.

[0034] Figure 10 This is a schematic diagram illustrating the manufacturing method of the lower shaft according to the first embodiment, and a diagram showing the cooling process.

[0035] Figure 11 This is a schematic diagram showing the deformation state of the inner and outer shafts when the lower shaft of the first embodiment is exposed to a high-temperature environment.

[0036] Figure 12 This is a schematic diagram showing the cross-section of the lower shaft in the second embodiment.

[0037] Figure 13 It means Figure 12 A schematic diagram of the cross-section of the outer shaft.

[0038] Figure 14 It's enlarged. Figure 12 A partial schematic diagram.

[0039] Figure 15 is a partial view of Figure 12 enlarged.

[0040] Figure 16 is a view showing a cross section of the lower shaft of the third embodiment.

[0041] Figure 17 is a partial view of Figure 16 enlarged. DETAILED DESCRIPTION

[0042] Embodiments for carrying out the present application will be explained in detail with reference to the drawings. The present application is not limited to the contents described in the following embodiments. Furthermore, the constituent elements described below include those which can be easily conceived by those skilled in the art, substantially the same elements. Moreover, the constituent elements described below can be appropriately combined.

[0043] [First Embodiment]

[0044] Figure 1 is a schematic view showing an outline of the steering device of the first embodiment. Figure 2 is a perspective view showing an outline of the steering device of the first embodiment.

[0045] As shown in Figure 1 and Figure 2 , the steering device 80 is provided with a steering wheel 81, an upper shaft 82, a steering force assisting mechanism 83, a universal joint 84, a lower shaft (steering shaft) 1, and a universal joint 86 in the order of force transmission from a force applied by an operator, and the steering device 80 is engaged with a pinion shaft 87. Furthermore, the steering device 80 is provided with an ECU (Electronic Control Unit) 90 and a torque sensor 94. A vehicle speed sensor 95 is provided to a vehicle body, and a vehicle speed signal V is output to the ECU 90 through CAN (Controller Area Network) communication.

[0046] The upper shaft 82 includes an input shaft 82a and an output shaft 82b. One end portion of the input shaft 82a is connected to the steering wheel 81, and the other end portion of the input shaft 82a is connected to the output shaft 82b. Furthermore, one end portion of the output shaft 82b is connected to the input shaft 82a, and the other end portion of the output shaft 82b is connected to the universal joint 84. In the present embodiment, the input shaft 82a and the output shaft 82b are formed of a general steel material such as a mechanical structural carbon steel (SC material (Carbon Steel for Machine Structural Use)) or a mechanical structural carbon steel steel tube (so-called STKM material (Carbon Steel Tubes for Machine Structural Purposes)).

[0047] The lower shaft (steering shaft) 1 is a member that is coupled to the output shaft 82b via the universal joint 84. One end portion of the lower shaft 1 is coupled to the universal joint 84, and the other end portion is coupled to the universal joint 86. One end portion of the pinion shaft 87 is coupled to the universal joint 86, and the other end portion is coupled to the steering gear 88.

[0048] The steering gear 88 includes a pinion 88a and a rack 88b. The pinion 88a is coupled to the pinion shaft 87. The rack 88b is engaged with the pinion 88a. The steering gear 88 converts rotational motion transmitted to the pinion 88a into straight motion by the rack 88b. The rack 88b is coupled to the tie rod 89. That is, the steering device 80 is a rack-and-pinion type.

[0049] The steering force assisting mechanism 83 includes a reduction device 92 and an electric motor 93. The electric motor 93 is, for example, a brushless motor, but can also be a motor including a brush (slider) and a commutator (reverser). The reduction device 92 is, for example, a worm reduction device. Torque generated by the electric motor 93 is transmitted to a worm wheel via a worm inside the reduction device 92, causing the worm wheel to rotate. The reduction device 92 increases the torque generated by the electric motor 93 using the worm and the worm wheel. Then, the reduction device 92 applies an assisting steering torque to the output shaft 82b. That is, the steering device 80 is a column-assist type.

[0050] The torque sensor 94 detects the steering force exerted by the operator via the steering wheel 81 to the input shaft 82a as the steering torque. The vehicle speed sensor 95 detects the vehicle speed (vehicle speed) of the vehicle body equipped with the steering device 80. The electric motor 93, torque sensor 94, and vehicle speed sensor 95 are electrically connected to the ECU 90. The ECU 90 controls the operation of the electric motor 93. Furthermore, the ECU 90 obtains signals from both the torque sensor 94 and the vehicle speed sensor 95. That is, the ECU 90 obtains the steering torque T from the torque sensor 94 and the vehicle speed signal V from the vehicle speed sensor 95. The ECU 90 is powered by a power source (e.g., the vehicle's battery) 99 when the ignition switch 98 is on. The ECU 90 calculates the auxiliary steering command value based on the steering torque T and the vehicle speed signal V. Then, the ECU 90 adjusts the power value X supplied to the electric motor 93 based on the calculated auxiliary steering command value. The ECU 90 acquires information about the induced voltage from the electric motor 93 or information output from a rotary transformer located in the electric motor 93 as action information Y. The steering force input by the operator (driver) to the steering wheel 81 is transmitted via the input shaft 82a to the reduction gear 92 of the steering assist mechanism 83. At this time, the ECU 90 acquires the steering torque T input to the input shaft 82a from the torque sensor 94 and the vehicle speed signal V from the vehicle speed sensor 95. Then, the ECU 90 controls the operation of the electric motor 93. The auxiliary steering torque generated by the electric motor 93 is transmitted to the reduction gear 92. The steering torque (including the auxiliary steering torque) output via the output shaft 82b is transmitted to the lower shaft (steering shaft) 1 via the universal joint 84, and then to the pinion shaft 87 via the universal joint 86. The steering force transmitted to the pinion shaft 87 is transmitted to the steering tie rod 89 via the steering gear 88, causing wheel displacement.

[0051] Figure 3 It means Figure 2 A 3D view of the lower shaft and universal joint. (See attached image.) Figure 3 As shown, the lower shaft (steering shaft) 1 includes an inner shaft 2, an outer shaft 3, and a resin layer 4 (see reference). Figure 4 The lower shaft 1 is connected to universal joints 84 and 86. The end of the lower shaft 1 is connected to universal joints 84 and 86. The inner shaft 2 and the outer shaft 3 extend axially along the central axis Ax.

[0052] The universal joint 84 is engaged with the end of the inner shaft 2. The universal joint 84 includes a base 841 and a yoke 842. The yoke 842 branches into two, each with a through hole. The yoke 21 of the inner shaft 2 also has a through hole. The universal joint 84 is engaged with the inner shaft 2 by fitting the cross shaft 843 into these through holes.

[0053] The universal joint 86 is coupled to the end portion of the outer shaft 3. The universal joint 86 includes a base portion 861 and a yoke portion 862. The yoke portion 862 is branched into two, each of which is provided with a through hole. The yoke portion 31 of the outer shaft 3 is also provided with a through hole. The universal joint 86 is coupled to the outer shaft 3 by fitting a cross shaft 863 into these through holes.

[0054] Figure 4 is a schematic view showing a cross section at the IV-IV line of Figure 3 Figure 5 is a schematic view showing a cross section of the inner shaft and the resin layer of Figure 4 Figure 6 is a schematic view showing a part of Figure 5 Figure 4 and Figure 5 The inner shaft 2 includes a cylindrical portion 22 and a first tooth portion 23. The inner shaft 2 can be made of, for example, a metal such as carbon steel.

[0055] The cylindrical portion 22 is hollow inside and extends in a cylindrical shape along the circumferential direction around the central axis Ax. Thus, the inner shaft 2 is a hollow member. The first tooth portion 23 protrudes toward the radial outer side on the outer peripheral surface of the inner shaft 2. The first tooth portion 23 is provided with a plurality of teeth at equal intervals along the circumferential direction on the outer peripheral surface of the cylindrical portion 22. The first tooth portion 23 has a tooth top 231, a tooth surface (side surface) 232, and a tooth bottom 233. The first tooth portion 23 has thick-walled teeth 24 and thin-walled teeth 25. The thick-walled teeth 24 are provided at both ends on the Yl side as shown in Figure 4

[0056] The resin layer 4 is provided on the outer peripheral surface of the first tooth portion 23 as shown in Figure 4 Figure 5 Figure 4 The resin layer 4 is provided on the outer peripheral surface of the first tooth portion 23 as shown in Figure 4 ​​​​​​The end portion on the Y1 side is provided with a pair of end portions adjacent in the circumferential direction, and the end portion on the Y2 side is provided with a pair of end portions adjacent in the circumferential direction. In the present embodiment, the portions of the resin layer 4 other than the thin film portions 41 and facing the tooth surfaces 232 are all thick film portions 42. In this way, the thin film portions 41 are provided in total four at symmetrical positions across the center axis Ax. In the present disclosure, the number of the thin film portions 41 is not limited to this, and the number of the thin film portions 41 can be four or more, and one group of the thin film portions 41 can be provided three or more in the circumferential direction. In addition, the plurality of groups of the thin film portions 41 can be provided at equal intervals in the circumferential direction, but the present disclosure is not limited to this, and the plurality of groups of the thin film portions 41 can be provided at positions that are not equal intervals. Details will be described later.

[0057] As shown in Figure 4 and Figure 6 , the outer shaft 3 includes a cylindrical portion 32 and a second tooth portion 33. The outer shaft 3 can be widely used, for example, a metal such as carbon steel.

[0058] The inside of the cylindrical portion 32 is hollow and extends in a cylindrical shape along the circumferential direction around the center axis Ax. The second tooth portion 33 protrudes toward the radially inner side on the inner periphery of the cylindrical portion 32. The second tooth portion 33 is provided with a plurality of teeth at equal intervals in the circumferential direction on the inner peripheral surface of the outer shaft 3. The second tooth portion 33 has a tooth top 331, a tooth surface 332, and a tooth bottom 333. The widths of the second tooth portion 33 in the circumferential direction are all the same.

[0059] Figure 7 is a schematic view of a portion enlarged Figure 5 . Figure 8 is a schematic view of a portion enlarged Figure 5 . As shown in Figure 6 to Figure 8 , in a cross section of the inner shaft 2 orthogonal to the center axis Ax, a first imaginary line 110, a second imaginary line 120, and a third imaginary line 130 are set. The first imaginary line 110 extends along the circumferential direction with the center axis Ax as the center and passes through the tooth top (outer peripheral end) 231 of the first tooth portion 23. The second imaginary line 120 extends along the circumferential direction with the center axis Ax as the center and passes through the tooth top (inner peripheral end) 331 of the second tooth portion 33. The third imaginary line 130 passes through the middle in the radial direction between the first imaginary line 110 and the second imaginary line 120 and extends in the circumferential direction.

[0060] Here, as shown in Figure 6 , the width of the thick wall tooth 24 in the first tooth portion 23 along the third imaginary line 130 is a width T1. In addition, the width of the thin wall tooth 25 along the third imaginary line 130 is a width T2. The width T2 of the thin wall tooth 25 is smaller than the width T1 of the thick wall tooth 24. The thick wall tooth 24 has a tooth top 241 and a tooth surface (side surface) 242. The thin wall tooth 25 has a tooth top 251 and a tooth surface (side surface) 252.

[0061] Moreover, as shown in Figure 7 , the thin film portion 41 of the resin layer 4 is provided between the thick-walled tooth 24 of the first tooth portion 23 and the second tooth portion 33. Specifically, the thin film portion 41 contacts both the tooth surface 242 of the thick-walled tooth 24 and the tooth surface 332 of the second tooth portion 33. Further, the number of the second tooth portions 33 arranged between a set of circumferentially adjacent thin film portions 41 is one. The thickness of the thin film portion 41 along the third imaginary line 130 is thickness tl. A plurality of sets of thin film portions 41 are arranged at intervals along the circumferential direction. In addition, a set of thin film portions refers to a set of thin film portions arranged adjacent to each other in the circumferential direction. Further, it is preferable that the thickness tl of the thin film portion 41 be, for example, 0.2 mm or less.

[0062] Moreover, as shown in Figure 8 , in the present embodiment, the thick film portion 42 is a portion of the resin layer 4 arranged between the tooth surface 232 (refer to Figure 6 ) and the tooth surface 332, that is, a portion other than the thin film portion 41. Specifically, the thick film portion 42 of the resin layer 4 is provided between the thin-walled tooth 25 of the first tooth portion 23 and the second tooth portion 33. More specifically, the thick film portion 42 is provided between the tooth surface 252 of the thin-walled tooth 25 and the tooth surface 332 of the second tooth portion 33. The thickness of the thick film portion 42 along the third imaginary line 130 is thickness t2. The thickness tl of the thin film portion 41 is smaller than the thickness t2 of the thick film portion 42. In addition, as shown in Figure 8 , the side surface 421 of the thick film portion 42 is separated from the tooth surface 332 of the second tooth portion 33. In other words, a gap G is provided between the side surface 421 of the thick film portion 42 and the tooth surface 332 of the second tooth portion 33. This gap G is provided, for example, in the case where the temperature is 80 degrees or less.

[0063] Next, the manufacturing method of the lower shaft (steering shaft) 1 will be described. Figure 9 is a schematic view that explains the manufacturing method of the lower shaft of the first embodiment, and is a view that shows a state in which the lower shaft 1 after the resin layer forming step is housed inside a heating furnace. Figure 10 is a schematic view that explains the manufacturing method of the lower shaft of the first embodiment, and is a view that shows a state in which the lower shaft 1 after the resin layer forming step is housed inside a heating furnace.

[0064] First, the resin layer 4 is formed on the outer peripheral side of the inner shaft 2, and the outer shaft 3 is fitted to the outer peripheral side of the inner shaft 2 with the resin layer 4 interposed therebetween, thereby assembling the lower shaft 1. In a state in which the inner shaft 2 and the outer shaft 3 are fitted to each other, a radial gap is provided between the resin layer 4 and the tooth bottom 333 (refer to Figure 8 ) of the second tooth portion 33. Further, no gap G (refer to Figure 8 ) is provided between the tooth surface 332 of the second tooth portion 33 and the entire resin layer 4. That is, the resin layer 4 contacts both the tooth surface 232 of the entire first tooth portion 23 and the tooth surface 332 of the entire second tooth portion 33. Thus, for the resin layer 4, the tooth surface 232 of the first tooth portion 23 and the tooth surface 332 of the second tooth portion 33 are in contact with each other. Figure 9The end portion on the Y1 side and the end portion on the Y2 side are each provided with a group of thin film portions 41. In this state, as shown in Figure 9 the inside of the heating furnace 140.

[0065] The inside of the heating furnace 140 is warmed to, for example, 130 degrees. Since the linear expansion coefficient of the resin is higher than that of metal, the resin layer 4 expands more than the metal-made inner shaft 2 and outer shaft 3. Here, as described above, the end portion on the Y1 side and the end portion on the Y2 side are each provided with a group of thin film portions 41. Thus, when the resin layer 4 thermally expands, the thick film portions 42 of the end portion on the X1 side and the end portion on the X2 side expand more in the circumferential direction than the thin film portions 41 of the end portion on the Y1 side and the end portion on the Y2 side. Further, a part of the resin of the thick film portions 42 moves to the outside in the radial direction. On the other hand, since the thin film portions 41 are smaller in thickness in the circumferential direction than the thick film portions 42, the amount of thermal expansion of the thin film portions 41 at the time of heating is smaller than that of the thick film portions 42. Therefore, in the heating process, the resin of the thin film portions 41 is difficult to move to the outside in the radial direction. Next, as shown in Figure 10 the inner shaft 2 and the outer shaft 3 are taken out of the heating furnace 140 and cooled. Thereby, a part of the resin of the thick film portions 42 is solidified in a state where it has moved to the outside in the radial direction. On the other hand, the thin film portions 41 are solidified in a state where they hardly move to the outside in the radial direction.

[0066] Thereby, as shown in Figure 10 the thin film portions 41 of the end portion on the Y1 side and the end portion on the Y2 side come into contact with both the tooth surface 242 of the thick-walled tooth 24 and the tooth surface 332 of the second tooth portion 33. On the other hand, in the thick film portions 42, as explained in Figure 8 , a gap G is formed between the tooth surface 332 of the second tooth portion 33 and the resin layer 4.

[0067] Next, the deformed state of the lower shaft when it is exposed to a high-temperature environment will be described with reference to Figure 11 . Figure 11 is a schematic view showing the deformed state of the inner shaft and the outer shaft of the lower shaft of the first embodiment when it is exposed to a high-temperature environment. Hereinafter, the case where the rigidity of the inner shaft 2 is higher than that of the outer shaft 3 and the case where the rigidity of the inner shaft 2 is lower than that of the outer shaft 3 will be described.

[0068] [Case where rigidity of inner shaft 2 is higher than that of outer shaft 3]

[0069] In the case where the radial thicknesses of the outer shaft 3 and the inner shaft 2 are the same degree, the radial rigidity of the outer shaft 3 becomes smaller than that of the inner shaft 2. Also, in the case where the lower shaft 1 is exposed to a high temperature, the amount of expansion (amount of elastic deformation) of the inner shaft 2 is extremely small, and the outer shaft 3 expands (elastically deforms) more than the inner shaft 2.

[0070] Further, in a high temperature environment, the side surface 421 of the thick film portion 42 (refer to FIG. 4) comes into contact with the tooth surface 332 of the second tooth portion 33, and the thick film portion 42 pushes and expands the tooth surface 332 of the second tooth portion 33 in the circumferential direction. Further, the thin film portion 41 also comes into contact with the tooth surface 232 of the first tooth portion 23 and the tooth surface 332 of the second tooth portion 33 in a normal temperature environment. However, since the thick film portion 42 is thicker than the thin film portion 41, the force with which the thick film portion 42 pushes and expands the second tooth portion 33 in the circumferential direction is greater than the force with which the thin film portion 41 pushes and expands the second tooth portion 33 in the circumferential direction at the time of thermal expansion in a high temperature environment. Here, as described above, the thin film portion 41 is located at the end portion on the Yl side and the end portion on the Y2 side of the inner shaft 2. Thus, the portions on the XI side and the X2 side of the outer shaft 3 are greater in the amount of deformation in the circumferential direction than the portions on the Yl side and the Y2 side, and the outer shaft 3 on the outer circumferential side is elastically deformed to be longer in the lateral direction by extending in the X direction. Further, since the inner shaft 2 is extremely small in the amount of deformation, the amount of deformation is smaller than that of the outer shaft 3, and thus the inner shaft 2 exposed to a high temperature maintains a substantially circular shape. As described above, as shown in FIG. 4, the outer shaft 3 is elastically deformed to be longer in the lateral direction by expanding in the X direction, and the resin layer 4 hardly moves to the outside in the radial direction. Thereafter, when the temperature returns to a normal temperature environment, the resin layer 4 shrinks, and the outer shaft 3 also returns to the original shape. Thus, in a normal temperature environment, the thin film portion 41 again comes into contact with the tooth surfaces of the first tooth portion 23 and the second tooth portion 33, and a gap G (refer to FIG. 4) is again generated between the thick film portion 42 and the tooth surface 332. Figure 8 Figure 11 Figure 8

[0071] [Case in which the rigidity of the inner shaft 2 is lower than the rigidity of the outer shaft 3]

[0072] ​​​In the case where the radial thickness of the inner shaft 2 is smaller than that of the outer shaft 3 and the radial rigidity of the inner shaft 2 is smaller than that of the outer shaft 3, the inner shaft 2 elastically deforms more than the outer shaft 3 in a high-temperature environment. In the high-temperature environment, the thin film portion 41 comes into contact with the tooth surfaces 232 of the first tooth portions 23 and the tooth surfaces 332 of the second tooth portions 33 due to the expansion of the resin layer 4, and the thick film portion 42 acts to push and expand the second tooth portions 33. The force with which the thick film portion 42 pushes and expands the second tooth portions 33 is greater than the force with which the thin film portion 41 pushes and expands the second tooth portions 33. Also, since the radial rigidity of the inner shaft 2 is smaller than that of the outer shaft 3, the inner shaft 2 elastically deforms on the inner peripheral side to extend in the Y direction, and the outer shaft 3 elastically deforms only slightly to maintain a substantially circular shape. Thus, since the inner shaft 2 expands in the Y direction, the inner shaft 2 elastically deforms into an oblong shape that is longer in the longitudinal direction, and the resin layer 4 hardly moves to the radial outer side. Thereafter, when the temperature returns to the normal temperature environment, the resin layer 4 contracts, and the inner shaft 2 also returns to the original shape. Thus, in the normal temperature environment, the thin film portion 41 again comes into contact with the tooth surfaces of the first tooth portions 23 and the second tooth portions 33, and a gap G is again generated between the thick film portion 42 and the tooth surfaces 332 (see FIG. 6). Figure 8 ).

[0073] As described above, the lower shaft (steering shaft) 1 of the first embodiment includes the inner shaft 2 having a plurality of first tooth portions 23 arranged along the circumferential direction on the outer peripheral surface, the outer shaft 3 having a plurality of second tooth portions 33 arranged along the circumferential direction on the inner peripheral surface and arranged on the outer peripheral side of the first tooth portions 23, and the resin layer 4 arranged between the first tooth portions 23 and the second tooth portions 33. The resin layer 4 has a plurality of thick film portions 42 arranged with a gap with respect to the second tooth portions 33 between the tooth surfaces 232 of the first tooth portions 23 and the tooth surfaces of the second tooth portions 33, and at least four thin film portions 41 arranged between the tooth surfaces 232 of the first tooth portions 23 and the tooth surfaces 332 of the second tooth portions 33 and in contact with both the first tooth portions 23 and the second tooth portions 33. In a cross section orthogonal to the central axis Ax of the inner shaft 2, the thickness tl of the thin film portion 41 along a third imaginary line 130 extending along the radial direction between the first imaginary line 110 passing through the outer peripheral end of the first tooth portion 23 and extending in the circumferential direction and the second imaginary line 120 passing through the inner peripheral end of the second tooth portion 33 and extending in the circumferential direction is smaller than the thickness t2 of the thick film portion 42 along the third imaginary line 130.

[0074] Thus, the thin film portions 41 are arranged between the tooth surfaces 232 of the first tooth portions 23 and the tooth surfaces 332 of the second tooth portions 33, and are in contact with both the first tooth portions 23 and the second tooth portions 33. That is, the tooth surfaces 232 of the first tooth portions 23 and the tooth surfaces 332 of the second tooth portions 33, which are adjacent in the circumferential direction, are in contact with the thin film portions 41, which are arranged therebetween, without a gap. The number of the thin film portions 41 is at least four. In a high-temperature environment, the resin layer 4 expands in the circumferential direction and comes into contact with the tooth surfaces 232 of the first tooth portions 23 and the tooth surfaces 332 of the second tooth portions 33 without a gap. Since the thin film portions 41 have a smaller thickness in the circumferential direction than the thick film portions 42, the amount of thermal expansion of the thin film portions 41 in the circumferential direction in a high-temperature environment is smaller than the amount of thermal expansion of the thick film portions 42 in the circumferential direction. Thus, in a high-temperature environment, the resin of the thin film portions 41 is less likely to move to the outside in the radial direction than the resin of the thick film portions 42. Therefore, even after returning from a high-temperature environment to a normal-temperature environment, it is difficult to create a gap in the periphery of the thin film portions 41. Thus, the steering shaft 1 of the first embodiment has a smaller backlash after returning from a high-temperature environment to a normal-temperature environment than the steering shaft of Patent Document 1, and can further reduce the gap noise generated when the vehicle is running. Furthermore, the number of the second tooth portions 33 arranged between the groups of the thin film portions 41 is one, and the groups of the thin film portions 41 are arranged at equal intervals in the circumferential direction. Thus, the steering shaft 1 of the first embodiment has a further smaller backlash than the steering shaft of Patent Document 1, and can further reduce the gap noise generated when the vehicle is running. Moreover, the inner shaft 2 is a hollow member. Thus, the radial rigidity of the inner shaft 2 is low. Thus, the steering shaft 1 of the first embodiment can further reduce the backlash and can transmit a large torque. Furthermore, the weight of the steering shaft 1 can be reduced.

[0075] Furthermore, the plurality of first tooth portions 23 include thick wall teeth 24 and thin wall teeth 25 having a smaller width in the circumferential direction than the thick wall teeth 24, and the thin film portions 41 are in contact with both the thick wall teeth 24 and the second tooth portions 33. Thus, by changing a part of the plurality of first tooth portions 23 to the thick wall teeth 24, the thin film portions 41 of the resin layer 4 can be easily formed.

[0076] Furthermore, since the number of groups of the thin film portions 41 is two, the number of groups of the thin film portions 41 can be reduced, the backlash of the steering shaft can be reduced, and the gap noise generated when the vehicle is running can be further reduced.

[0077] The manufacturing method of the lower shaft (steering shaft) 1 of the first embodiment includes: a resin layer forming step of forming a resin layer 4 on the inner shaft 2 having a plurality of first tooth portions 23 arranged along the circumferential direction on the outer circumferential surface; a heating step of heating the inner shaft 2, the outer shaft 3, and the resin layer 4 in a state where the resin layer 4 is in contact with the tooth surfaces 232 of all of the first tooth portions 23 and the tooth surfaces 332 of all of the second tooth portions 33; and a cooling step of cooling the inner shaft 2, the outer shaft 3, and the resin layer 4 after the heating step. The plurality of first tooth portions 23 include thick tooth portions 24 and thin tooth portions 25 having a smaller width along the circumferential direction than the thick tooth portions 24.

[0078] The gap along the circumferential direction between the tooth surface 242 of the thick tooth portion 24 of the first tooth portion 23 and the tooth surface 332 of the second tooth portion 33 is smaller than the gap along the circumferential direction between the tooth surface 252 of the thin tooth portion 25 of the first tooth portion 23 and the tooth surface 332 of the second tooth portion 33. Therefore, the resin layer 4 arranged in the gap between the thick tooth portion 24 and the second tooth portion 33 becomes a thin film portion 41, and the resin layer 4 arranged in the gap between the thin tooth portion 25 and the second tooth portion 33 becomes a thick film portion 42. In the heating step, a part of the resin of the thick film portion 42 moves to the outside in the radial direction, and is solidified as it is in the cooling step, so a gap is generated between the solidified thick film portion 42 and the tooth surface 332 of the second tooth portion 33. However, the thin film portion 41 does not move to the outside in the radial direction as the thick film portion 42 does in the heating step. Therefore, no gap is generated around the thin film portion 41 in the cooling step. In this way, the thin film portion 41 and the thick film portion 42 of the resin layer 4 can be formed by an easy work. In addition, in the steering shaft of Patent Document 1, when the steering shaft is exposed to a high-temperature environment, all of the resin layer portions of the first tooth portions expand, and there is a possibility that the sliding resistance between all of the resin layer portions and all of the tooth surfaces of the second tooth portions becomes high. In contrast, in the steering shaft of the present disclosure, when exposed to a high-temperature environment (for example, 80 degrees or 100 degrees), the thin film portion 41 is in contact with the tooth surfaces of the first tooth portion 23 and the second tooth portion 33, but in the thick film portion 42 other than the thin film portion 41, a gap is present between the tooth surfaces of the tooth portions in an environment at normal temperature (for example, 80 degrees or less), so the force of contact with the tooth surfaces of the tooth portions in a high-temperature environment becomes weak, and the sliding resistance between the resin layer 4 and the tooth surfaces of the tooth portions is made lower in the steering shaft of the present disclosure than in Patent Document 1.

[0079] [Second Embodiment]

[0080] Next, the steering shaft of the second embodiment will be described. The same components as those of the steering shaft of the first embodiment described above are denoted by the same reference numerals, and the description thereof will be omitted.

[0081] Figure 12 is a schematic view showing a cross section of the lower shaft of the second embodiment.Figure 13 It means Figure 12 A schematic diagram of the cross-section of the outer shaft. Figure 14 It's enlarged. Figure 12 A partial schematic diagram. Figure 15 It's enlarged. Figure 12 A partial schematic diagram.

[0082] like Figure 12 As shown, the lower shaft (steering shaft) 1A includes an inner shaft 2A, an outer shaft 3A, and a resin layer 4A. In the first embodiment, the widths of all second teeth 33 are the same, but in the second embodiment, the second tooth 33A includes a thick-walled tooth 34 and a thin-walled tooth 35, the circumferential width of the thin-walled tooth 35 being smaller than the circumferential width of the thick-walled tooth 34. The thick-walled tooth 34 has a tooth tip 341 and a tooth surface (side surface) 342. The thin-walled tooth 35 has a tooth tip 351 and a tooth surface (side surface) 352. Furthermore, in the first embodiment, the first tooth 23 includes a thick-walled tooth 24 and a thin-walled tooth 25, but in the second embodiment, the widths of all first tooth 23A are the same. The thin film portion 41A of the resin layer 4A contacts both the thick-walled tooth 34 and the first tooth 23A.

[0083] like Figure 12 As shown, the inner shaft 2A includes a cylindrical portion 22A and a first toothed portion 23A. The inner shaft 2A can be made of metals such as carbon steel, for example.

[0084] The inner shaft 2A is a hollow component. Multiple first teeth 23A are arranged at equal intervals along the circumferential direction on the outer circumferential surface of the inner shaft 2A. For example... Figure 15 As shown, the first tooth portion 23A has a tooth tip 231A, a tooth surface (side surface) 232A, and a tooth root 233A. All teeth of the first tooth portion 23A have the same width.

[0085] like Figure 12 As shown, the resin layer 4 has a thin film portion 41A and a thick film portion 42A. The thin film portion 41A is in... Figure 12 One set is provided at the end on the Y1 side, and another set is provided at the end on the Y2 side, for a total of four sets. In other words, the thin film portion 41A has... Figure 12The ends on the Y1 side are arranged in a pair adjacent to each other in the circumferential direction, and the ends on the Y2 side are also arranged in a pair adjacent to each other in the circumferential direction. The thick film portion 42A is the portion of the resin layer 4A disposed between the tooth surface 232A and the tooth surface 332A, i.e., the portion excluding the thin film portion 41A. Thus, a total of four thin film portions 41A are provided symmetrically across the central axis Ax. However, in this disclosure, it is not limited to this; there may be four or more thin film portions 41A, or a group of three or more thin film portions 41A may be arranged in the circumferential direction. Furthermore, multiple groups of thin film portions 41A may be arranged at equal intervals in the circumferential direction, but this is not a limitation; the positions of the multiple groups of thin film portions 41A may not be equally spaced.

[0086] like Figure 12 and Figure 13 As shown, the outer shaft 3A includes a cylindrical portion 32A and a second toothed portion 33A. The outer shaft 3A can be made of metals such as carbon steel, for example.

[0087] like Figure 14 and Figure 15 As shown, the second tooth 33A has multiple teeth arranged at equal intervals along the circumferential direction on the inner circumferential surface of the outer shaft 3A. Figure 15 As shown, the second tooth 33A has a tooth tip 331A, a tooth surface (side surface) 332A, and a tooth root 333A. Furthermore, as... Figure 12 and Figure 13 As shown, the second tooth portion 33A includes a thick-walled tooth 34 and a thin-walled tooth 35, wherein the circumferential width of the thin-walled tooth 35 is smaller than the circumferential width of the thick-walled tooth 34. The thick-walled tooth 34... Figure 12 Two teeth are provided at the end on the Y1 side, and two teeth are provided at the end on the Y2 side, for a total of four teeth. In this embodiment, all teeth except the thick-walled teeth 34 are thin-walled teeth 35.

[0088] Moreover, such as Figure 14 As shown, the thin film portion 41A of the resin layer 4A is disposed between the thick-walled tooth 34 of the second tooth portion 33A and the first tooth portion 23A. Specifically, the thin film portion 41A is in contact with both the tooth surface 342 of the thick-walled tooth 34 and the tooth surface 232A of the first tooth portion 23A. The number of first teeth 23A disposed between a group of adjacent thin film portions 41A in the circumferential direction is one. The thickness of the thin film portion 41A along the third imaginary line 130 is thickness t3.

[0089] Moreover, such as Figure 15As shown, the thick film portion 42A is the resin layer 4A at a portion other than the thin film portion 41A. Specifically, the thick film portion 42A is provided between the tooth surface 232A of the first tooth portion 23A and the tooth surface 332A of the second tooth portion 33A. The thickness of the thick film portion 42A along the third imaginary line 130 is thickness t4. The thickness t3 of the thin film portion 41A is smaller than the thickness t4 of the thick film portion 42A. In addition, a gap G is provided between the side surface 421A of the thick film portion 42A and the tooth surface 332A of the second tooth portion 33A.

[0090] In addition, the manufacturing method of the lower shaft (steering shaft) 1A of the second embodiment is substantially the same as the manufacturing method of the lower shaft (steering shaft) 1 of the first embodiment. Specifically, the manufacturing method of the lower shaft 1A includes: a resin layer forming step of forming the resin layer 4A on the inner shaft 2A having the plurality of first tooth portions 23A; a heating step of heating the inner shaft 2A, the outer shaft 3A, and the resin layer 4A inside the heating furnace 140 (see FIG. 2) in a state where the resin layer 4A is in contact with the tooth surface 232A of the entire first tooth portion 23A and the tooth surface 332A of the entire second tooth portion 33A; and a cooling step of cooling the inner shaft 2A, the outer shaft 3A, and the resin layer 4A after the heating step, the plurality of second tooth portions 33A including the thick wall tooth 34 and the thin wall tooth 35 having a width along the circumferential direction that is smaller than the width along the circumferential direction of the thick wall tooth 34. Figure 9 ) of the heating furnace 140 (see FIG. 2) in a state where the resin layer 4A is in contact with the tooth surface 232A of the entire first tooth portion 23A and the tooth surface 332A of the entire second tooth portion 33A; and a cooling step of cooling the inner shaft 2A, the outer shaft 3A, and the resin layer 4A after the heating step, the plurality of second tooth portions 33A including the thick wall tooth 34 and the thin wall tooth 35 having a width along the circumferential direction that is smaller than the width along the circumferential direction of the thick wall tooth 34.

[0091] In the heating step, when the resin layer 4A thermally expands, Figure 12 The thick film portion 42A of the end portion on the X1 side and the end portion on the X2 side expands more in the circumferential direction than the thin film portion 41A of the end portion on the Y1 side and the end portion on the Y2 side. In addition, a part of the resin of the thick film portion 42A moves to the outside in the radial direction. On the other hand, since the thin film portion 41A has a smaller thickness in the circumferential direction than the thick film portion 42A, the amount of thermal expansion of the thin film portion 41A at the time of heating is smaller than the amount of thermal expansion of the thick film portion 42A. Therefore, in the heating step, it is difficult for the resin of the thin film portion 41A to move to the outside in the radial direction. Thus, in the cooling step, a part of the resin of the thick film portion 42A is solidified in a state where it has moved to the outside in the radial direction. On the other hand, the thin film portion 41A is solidified in a state where it has hardly moved to the outside in the radial direction.

[0092] As explained above, in the second embodiment, the plurality of second teeth 33A include thick teeth 34 and thin teeth 35 having a width in the circumferential direction smaller than that of the thick teeth 34, and the thin film portion 41A is in contact with both the thick teeth 34 and the first teeth 23A. Thus, by changing a part of the plurality of second teeth 33A to the thick teeth 34, the thin film portion 41A can be easily formed. Further, the inner shaft 2A and the outer shaft 3A of the present embodiment can also be applied to either of the spline fitting and the saw-tooth fitting.

[0093] Further, the manufacturing method of the lower shaft (steering shaft) 1A of the second embodiment includes a resin layer forming step of forming the resin layer 4A on the inner shaft 2A having the plurality of first teeth 23A arranged in the circumferential direction on the outer circumferential surface, a heating step of heating the inner shaft 2A, the outer shaft 3A, and the resin layer 4A in a state where the resin layer 4A is in contact with the tooth surfaces 232A of all of the first teeth 23A and the tooth surfaces 332A of all of the second teeth 33A, and a cooling step of cooling the inner shaft 2A, the outer shaft 3A, and the resin layer 4A after the heating step, and the plurality of second teeth 33A include thick teeth 34 and thin teeth 35 having a width in the circumferential direction smaller than that of the thick teeth 34.

[0094] The gap in the circumferential direction between the tooth surface 342 of the thick tooth 34 of the second teeth 33A and the tooth surface 232A of the first teeth 23A is smaller than the gap in the circumferential direction between the tooth surface 352 of the thin tooth 35 of the second teeth 33A and the tooth surface 232A of the first teeth 23A. Therefore, the resin layer 4A arranged in the gap between the thick tooth 34 and the first teeth 23A becomes the thin film portion 41A, and the resin layer 4A arranged in the gap between the thin tooth 35 and the first teeth 23A becomes the thick film portion 42A. In the heating step, a part of the resin of the thick film portion 42A moves in the radial direction, and is solidified as it is in the cooling step, and therefore, a gap is generated between the solidified thick film portion 42A and the tooth surface 332A of the second teeth 33A. However, the thin film portion 41A is in contact with both the thick tooth 34 and the first teeth 23A even in either of the heating step and the cooling step, and therefore, no gap is generated. Thus, the thin film portion 41A and the thick film portion 42A of the resin layer 4A can be formed by an easy work.

[0095] [Third Embodiment]

[0096] Next, the steering shaft of the third embodiment will be described, and the same reference numerals are attached to the parts having the same configuration as the steering shaft of the above-described first embodiment, and the description thereof will be omitted.

[0097] Figure 16 is a schematic view showing a cross section of the lower shaft of the third embodiment. Figure 17 is an enlarged view ofFigure 16 A partial view of the schematic view. As Figure 16 indicated, the lower shaft (steering shaft) 1B of the third embodiment includes an inner shaft 2B, an outer shaft 3, and a resin layer 4B. The inner shaft 2B includes a cylindrical portion 22B and a first tooth portion 23B. The inner shaft 2B can be widely applied to, for example, a metal such as carbon steel.

[0098] The inside of the cylindrical portion 22B is formed hollow and extends in a cylindrical shape along the circumferential direction around the center axis Ax. Thus, the inner shaft 2B is a hollow member. The first tooth portion 23B protrudes toward the radial outside on the outer peripheral surface of the inner shaft 2B. The first tooth portion 23B is provided with a plurality of teeth at equal intervals along the circumferential direction on the outer peripheral surface of the cylindrical portion 22B. The first tooth portion 23B has a first thick-walled tooth 24B, a second thick-walled tooth 24C, and a thin-walled tooth 25. Two first thick-walled teeth 24B and one second thick-walled tooth 24C are adjacent in the circumferential direction. That is, as Figure 16 indicated, the first thick-walled tooth 24B, the second thick-walled tooth 24C, and the first thick-walled tooth 24B are arranged in this order when viewed from the clockwise direction.

[0099] As Figure 17 indicated, the first thick-walled tooth 24B has a tooth top 241B and a tooth surface (side surface) 242B. The second thick-walled tooth 24C has a tooth top 241C and a tooth surface (side surface) 242C. The width of the second thick-walled tooth 24C along the third imaginary line 130 is a width T3. The width of the first thick-walled tooth 24B along the third imaginary line 130 is a width T4. In addition, the width of the thin-walled tooth 25 along the third imaginary line 130 is a width T2. The width T4 of the first thick-walled tooth 24B is greater than the width T2 of the thin-walled tooth 25. The width T3 of the second thick-walled tooth 24C is greater than the width T4 of the first thick-walled tooth 24B.

[0100] Furthermore, as Figure 16 and Figure 17 indicated, the resin layer 4B has a thin film portion 41B and a thick film portion 42B. The thin film portion 41B is provided with one set of ends on the Y1 side as Figure 16 indicated and one set of ends on the Y2 side, for a total of two sets. One set of thin film portions 41B is provided with four adjacent in the circumferential direction. That is, the thin film portion 41B is provided with a total of eight.

[0101] As Figure 17 indicated, the thin film portion 41B of the resin layer 4B is provided between the first thick-walled tooth 24B and the second tooth portion 33 and between the second thick-walled tooth 24C and the second tooth portion 33. Specifically, the thin film portion 41B is in contact with both the tooth surface 242B of the first thick-walled tooth 24B and the tooth surface 332 of the second tooth portion 33. In addition, the thin film portion 41B is in contact with both the tooth surface 242C of the second thick-walled tooth 24C and the tooth surface 332 of the second tooth portion 33.

[0102] Further, the thickness of the film portions 41B along the third imaginary line 130 is thickness t1. In the present embodiment, one group of the film portions is four film portions 41B adjacent in the circumferential direction. Further, four film portions 41B are provided at the end portion on the Y1 side. The four film portions 41B are one group of the film portions adjacent in the circumferential direction. One group of the film portions at the end portion on the Y2 side and one group of the film portions at the end portion on the Y1 side are disposed at symmetrical positions across the center axis Ax.

[0103] Thus, the film portions 41B are provided in total eight at symmetrical positions across the center axis Ax. In addition, in the present disclosure, it is not limited thereto, and the film portions 41B can be provided more than eight, and one group of the film portions 41B can be disposed more than four in the circumferential direction. Further, a plurality of groups of the film portions 41B can be disposed at equal intervals in the circumferential direction, but it is not limited thereto, and the disposed positions of the plurality of groups of the film portions 41B can not be at equal intervals.

[0104] As described above, in the lower shaft 1B of the third embodiment, two groups of the film portions 41B are included, and one group is four film portions 41B adjacent in the circumferential direction. Thus, in the present embodiment, since one group of the film portions 41B includes four film portions 41B, the backlash of the steering shaft can be made smaller compared to two film portions 41, and the gap noise generated when the vehicle travels can be further reduced.

[0105] In addition, the present disclosure is not limited to the above-described embodiments, and can be applied to a wide range of technical fields. For example, in the above-described embodiments, the resin layers 4, 4A, 4B are formed in the first tooth portions 23, 23A, 23B of the inner shafts 2, 2A, 2B, but can be formed in the second tooth portions 33, 33A of the outer shafts 3, 3A. Further, in the embodiments, an example in which the number of the first tooth portions 23, 23A, 23B of the inner shafts 2, 2A, 2B is 18 teeth is shown, but it is not limited thereto, and various numbers of teeth such as 19 teeth and 23 teeth can be adopted. Moreover, in the embodiments, an example in which a plurality of groups of the film portions 41 are disposed at equal intervals in the circumferential direction is shown, but it is not limited thereto, and the disposed positions of the plurality of groups of the film portions 41 can not be at equal intervals.

[0106] Explanation of Reference Numerals 1, 1A, 1B, lower shaft (steering shaft); 2, 2A, 2B, inner shaft; 21, yoke portion; 22, 22A, cylindrical portion; 23, 23A, 23B, first tooth portion; 231, 231A, tooth tip (outer peripheral end); 232, 232A, tooth surface (side surface); 233, 233A, tooth root; 24, thick-walled tooth; 24B, first thick-walled tooth; 24C, second thick-walled tooth; 241, 241B, 241C, tooth tip; 242, 242B, 242C, tooth surface; 25, thin-walled tooth; 251, tooth tip; 252, tooth surface; 3, 3A, outer shaft; 31, yoke portion; 32, 32A, cylindrical portion; 33, 33A, second tooth portion; 331, 331A, tooth tip (inner peripheral end); 332, 332A, tooth surface (side surface); 333, 333A, tooth root; 34, thick-walled tooth; 341, tooth tip; 342, tooth surface; 35, thin-walled tooth; 351, tooth tip; 352, tooth surface; 4, 4A, 4B, resin layer; 41, 41A, 41B, thin film portion; 42, 42A, 42B, thick film portion; 80, steering device; 81, steering wheel; 82, upper shaft; 82a, input shaft; 82b, output shaft; 83, steering force assisting mechanism; 87, pinion shaft; 88, steering gear; 88a, pinion; 88b, rack; 89, tie rod; 90, ECU; 92, speed reduction device; 93, electric motor; 94, torque sensor; 95, vehicle speed sensor; 98, ignition switch; 99, power supply device; 110, first imaginary line; 120, second imaginary line; 130, third imaginary line; 140, heating furnace; Ax, center axis; T1, T2, width; t1, t2, t3, thickness.

Claims

1. A steering shaft, wherein, The steering shaft includes: An inner shaft having a plurality of first teeth arranged circumferentially on its outer peripheral surface; An outer shaft having a plurality of second teeth arranged circumferentially on its inner circumferential surface, and the outer shaft being disposed on the outer circumferential side of the first teeth; and A resin layer disposed between the first tooth and the second tooth. The resin layer has multiple thick film portions and at least four thin film portions. The thick film portion is disposed between the tooth surfaces of the first tooth and the second tooth, with a gap relative to one of the first tooth and the second tooth. The thin film portion is disposed between the tooth surfaces of the first tooth and the second tooth, and is in contact with both the first tooth and the second tooth. In a cross section orthogonal to the central axis of the inner shaft, the thickness of the thin film portion along a third imaginary line that passes through the middle of the radial direction between the first and second imaginary lines and extends circumferentially is less than the thickness of the thick film portion along the third imaginary line. The first imaginary line passes through the outer peripheral end of the first tooth and extends circumferentially, and the second imaginary line passes through the inner peripheral end of the second tooth and extends circumferentially.

2. The steering shaft according to claim 1, wherein, Multiple sets of the thin film portions are arranged at open intervals along the circumferential direction.

3. The steering shaft according to claim 1 or 2, wherein, Multiple sets of the thin film portions are arranged at equal intervals along the circumferential direction.

4. The steering shaft according to claim 2, wherein, The number of groups of the thin film portion is two.

5. The steering shaft according to claim 1 or 2, wherein, A set of the film portions comprises four of the film portions.

6. The steering shaft according to claim 1 or 2, wherein, The inner shaft is a hollow component.

7. The steering shaft according to claim 1 or 2, wherein, The plurality of first teeth include thick-walled teeth and thin-walled teeth, wherein the circumferential width of the thin-walled teeth is smaller than the circumferential width of the thick-walled teeth. The thin film portion comes into contact with both the thick-walled tooth and the second tooth portion.

8. The steering shaft according to claim 1 or 2, wherein, The plurality of said second teeth include thick-walled teeth and thin-walled teeth, wherein the circumferential width of the thin-walled teeth is smaller than the circumferential width of the thick-walled teeth. The thin film portion comes into contact with both the thick-walled tooth and the first tooth portion.

9. A method for manufacturing a steering shaft, wherein, The manufacturing method of this steering shaft includes: In the resin layer forming process, a resin layer is formed on an inner shaft or an outer shaft, wherein the inner shaft has a plurality of first teeth arranged circumferentially on its outer peripheral surface, and the outer shaft has a plurality of second teeth arranged circumferentially on its inner peripheral surface, and the outer shaft is disposed on the outer peripheral side of the first teeth of the inner shaft. In the heating process, the inner shaft, the outer shaft, and the resin layer are heated while the resin layer is in contact with the tooth surfaces of all the first teeth and all the tooth surfaces of the second teeth; and A cooling process is performed after the heating process to cool the inner shaft, the outer shaft, and the resin layer. The plurality of first teeth include thick-walled teeth and thin-walled teeth, wherein the circumferential width of the thin-walled teeth is smaller than the circumferential width of the thick-walled teeth. The second tooth has the same width along the circumferential direction.

10. A method for manufacturing a steering shaft, wherein, The manufacturing method of this steering shaft includes: In the resin layer forming process, a resin layer is formed on an inner shaft or an outer shaft, wherein the inner shaft has a plurality of first teeth arranged circumferentially on its outer peripheral surface, and the outer shaft has a plurality of second teeth arranged circumferentially on its inner peripheral surface, and the outer shaft is disposed on the outer peripheral side of the first teeth of the inner shaft. In the heating process, the inner shaft, the outer shaft, and the resin layer are heated while the resin layer is in contact with the tooth surfaces of all the first teeth and all the tooth surfaces of the second teeth; and A cooling process is performed after the heating process to cool the inner shaft, the outer shaft, and the resin layer. The plurality of said second teeth include thick-walled teeth and thin-walled teeth, wherein the circumferential width of the thin-walled teeth is smaller than the circumferential width of the thick-walled teeth. The width of the first tooth is the same along the circumferential direction.

Images