Spline shaft and manufacturing method thereof

Abstract

To realize a structure capable of suppressing increase in manufacturing cost while securing axial connection strength between the entire metal shaft body and a synthetic resin coating layer.SOLUTION: A radial thickness of a portion of a coating layer 4 that covers an outer peripheral surface of a preliminary shaft part 5 is made thicker than a radial thickness of a portion of the coating layer 4 that covers an outer peripheral surface of a spline shaft part 6. A radial thickness of a portion of the coating layer 4 that covers an outer peripheral surface of an end part on one side of a non-spline shaft part 7 in an axial direction is made thicker than a radial thickness of a portion of the coating layer 4 that covers the outer peripheral surface of the spline shaft part 6.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a spline shaft used as an inner shaft constituting an intermediate shaft of, for example, an automobile steering device, and to a method for manufacturing the same. [Background technology]

[0002] 10 shows an example of a steering device for an automobile. The rotation of a steering wheel 100 is transmitted to an input shaft 102 of a steering gear unit 101, and as the input shaft 102 rotates, a pair of left and right tie rods 103 are pushed and pulled, thereby applying a steering angle to the front wheels. The steering wheel 100 is fixedly supported at the rear end of a steering shaft 104, which is inserted axially through the inside of a steering column 105 and is rotatably supported by the steering column 105. The front end of the steering shaft 104 is connected to the rear end of an intermediate shaft 107 via a universal joint 106, and the front end of the intermediate shaft 107 is connected to the input shaft 102 via another universal joint 108.

[0003] The illustrated steering device is equipped with a telescopic mechanism that allows the fore-aft position of the steering wheel 100 to be adjusted. To achieve this, the steering shaft 104 is configured by combining an inner shaft 109 and an outer tube 110 through spline engagement to enable torque transmission and extension / contraction. Also, the steering column 105 is configured by combining an inner column 111 and an outer column 112 to enable extension / contraction.

[0004] In addition, the intermediate shaft 107 incorporated into the steering device has an expandable structure, for example, to prevent vibrations input from the steering wheels during driving from being transmitted to the steering wheel 100, and / or to allow the intermediate shaft 107 to be incorporated into the vehicle body with its overall length shortened.

[0005] 11 and 12 show a telescopic intermediate shaft (intermediate shaft) 107a described in JP 2020-143766 A. The intermediate shaft 107a includes an inner shaft (inner shaft) 114 having a male spline portion 113 on the outer peripheral surface of one end on one axial side (left side in FIG. 11), and a cylindrical outer tube (outer shaft) 116 having a female spline portion 115 on the inner peripheral surface of the end on the other axial side (right side in FIG. 11). The intermediate shaft 107a is configured by combining the inner shaft 114 and the outer tube 116 so that the entire length can be extended or retracted by spline-engaging the male spline portion 113 with the female spline portion 115.

[0006] The inner shaft 114 includes a metal shaft body (shaft body) 117 and a synthetic resin coating layer (resin layer) 118 that covers one axial end of the shaft body 117.

[0007] The shaft body 117 has, on the outer peripheral surface at one end in the axial direction, a male spline core portion 121 formed by circumferentially arranging a plurality of tooth core portions 119 and groove core portions 120 alternately.

[0008] The male spline core portion 121 has tooth-missing portions 122a, 122b, and 122c at three locations spaced apart in the axial direction. The tooth-missing portions 122a, 122b, and 122c are formed by cutting out the entire circumference of the tooth core portion 119 at each formation position. Therefore, the tooth-missing portions 122a, 122b, and 122c have the same outer diameter as the groove bottom diameter of the male spline core portion 121. Furthermore, of the tooth-missing portions 122a, 122b, and 122c, the axial length of the tooth-missing portion 122b located in the middle is longer than the tooth-missing portions 122a and 122c located on either side.

[0009] The coating layer 118 covers the entire circumference of the male spline core portion 121. The coating layer 118 is joined and fixed to the male spline core portion 121 of the shaft body 117 by injection molding. The portions of the coating layer 118 that cover the multiple tooth core portions 119 and groove core portions 120 form the male spline portion 113 that spline engages with the female spline portion 115 of the outer tube 116.

[0010] In the inner shaft 114 of JP 2020-143766 A, when the coating layer 118 is produced by injection molding, the synthetic resin that constitutes the coating layer 118 is also filled into the toothless portions 122a, 122b, and 122c, forming filled portions 123 in those portions. Therefore, even if a force acts to relatively displace the shaft body 117 and the coating layer 118 in the axial direction, the engagement between the toothless portions 122a, 122b, and 122c and the filled portions 123 can reliably prevent relative axial displacement between the shaft body 117 and the coating layer 118. In other words, in the inner shaft 114 described in JP 2020-143766 A, the toothless portions 122a, 122b, and 122c are provided, thereby ensuring the axial bond strength between the shaft body 117 and the coating layer 118. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2020-143766 Summary of the Invention [Problem to be solved by the invention]

[0012] In the inner shaft 114 described in JP 2020-143766 A, in order to improve the axial bonding strength between the shaft body 117 and the coating layer 118, toothless portions 122a, 122b, and 122c are formed by cutting out the tooth core portion 119 around the entire circumference of the male spline core portion 121. This increases the number of steps required to process the shaft body 117 and reduces the material yield, which may increase the manufacturing cost of the inner shaft 114.

[0013] Furthermore, in the inner shaft 114 described in JP 2020-143766 A, a mold is placed around the male spline core portion 121, and molten synthetic resin is pumped into the mold cavity through a gate located around the central toothless portion 122b, where it is cooled and solidified, forming the coating layer 118. The molten synthetic resin pumped through the gate flows circumferentially around the inside of the toothless portion 122b and merges (collides) with molten synthetic resin pumped through other gates within the toothless portion 122b. This can result in linear marks called weld lines forming on the surface of the synthetic resin filled into the toothless portion 122b, potentially compromising aesthetics and strength.

[0014] In particular, according to a simulation conducted by the inventors, it was found that when a gate for feeding molten synthetic resin is placed around the central toothless portion 122b, the meeting angle between the flow fronts becomes small, which is thought to be why weld lines become more clearly visible.

[0015] In view of the circumstances described above, the present invention aims to realize a spline shaft structure that can reduce manufacturing costs while ensuring the axial bonding strength between the metal shaft body and the synthetic resin coating layer. [Means for solving the problem]

[0016] A spline shaft according to one aspect of the present invention includes a metal shaft body and a synthetic resin coating layer.

[0017] The shaft body includes a spare shaft portion, a splined shaft portion, and a non-splined shaft portion.

[0018] The spare shaft portion is disposed at one end of the shaft body in the axial direction.

[0019] The spline shaft portion has a male spline core portion formed by alternately arranging tooth core portions and groove core portions in the circumferential direction on the outer circumferential surface thereof, and is disposed on the other axial side of the spare shaft portion.

[0020] The non-splined shaft portion is disposed on the other axial side of the splined shaft portion.

[0021] The coating layer covers the outer peripheral surface of the spare shaft portion, the outer peripheral surface of the splined shaft portion, and the outer peripheral surface of one axial end of the non-splined shaft portion.

[0022] In particular, in a spline shaft according to one aspect of the present invention, the outer circumferential surface of the reserve shaft portion and the outer circumferential surface of the spline shaft portion are connected by a first step surface facing one side in the axial direction. Furthermore, the radial thickness of the portion of the coating layer covering the outer peripheral surface of the spare shaft portion is greater than the radial thickness of the portion of the coating layer covering the outer peripheral surface of the splined shaft portion, and the radial thickness of the portion of the coating layer covering the outer peripheral surface of one axial end of the non-splined shaft portion is greater than the radial thickness of the portion of the coating layer covering the outer peripheral surface of the splined shaft portion.

[0023] In the spline shaft according to one aspect of the present invention, the first step surface can be configured by a flat surface that is perpendicular to the central axis of the shaft body. Alternatively, the first step surface may be configured as a truncated cone surface that is inclined in a direction such that the outer diameter increases toward the other side in the axial direction.

[0024] In a spline shaft according to one embodiment of the present invention, the outer peripheral surface of the spline shaft portion and the outer peripheral surface of one axial end of the non-spline shaft portion can be connected by a flat second step surface perpendicular to the central axis of the shaft body.

[0025] A spline shaft according to one aspect of the present invention may have, at a plurality of circumferential positions on the male spline core portion, notched recesses recessed radially inward relative to adjacent portions on the other axial side.

[0026] In the spline shaft according to one aspect of the present invention, it is possible to prevent weld lines from being present in the portion of the coating layer that covers the outer peripheral surface of the spline shaft portion.

[0027] In a spline shaft according to one aspect of the present invention, the coating layer is formed on a portion covering an outer peripheral surface of one end of the non-spline shaft portion in the axial direction, Gate marks can have: In this case, the Gate marks can be made to coincide with the phase in the circumferential direction of any one of the tooth core portions.

[0028] A method for manufacturing a spline shaft according to one aspect of the present invention includes the steps of: arranging a mold around one axial end of the non-splined shaft portion, the splined shaft portion, and the spare shaft portion; and, with a gate arranged around one axial end of the non-splined shaft portion, feeding molten synthetic resin from the gate into a cavity in the mold to form the coating layer, in order to produce the splined shaft according to one aspect of the present invention.

[0029] In the method for manufacturing a spline shaft according to one aspect of the present invention, the shaft body can be set in the mold with the central axis of the shaft body oriented horizontally. In the method for manufacturing a spline shaft according to one aspect of the present invention, the shaft body can be set in the mold with the center axis of the shaft body oriented vertically.

[0030] In a method for manufacturing a spline shaft according to one aspect of the present invention, the outer diameter of one axial end face of the preliminary shank portion can be made smaller than the outer diameter of an ejector pin that presses the one axial end face of the preliminary shank portion when removing the spline shaft from the mold. [Effects of the Invention]

[0031] According to a spline shaft of one aspect of the present invention, it is possible to reduce manufacturing costs while ensuring the axial bonding strength between the metal shaft body and the synthetic resin coating layer. Furthermore, according to a manufacturing method of a spline shaft of one aspect of the present invention, it is possible to industrially efficiently manufacture the spline shaft of one aspect of the present invention. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1(A) is a cross-sectional view showing a spline shaft according to a first example of the embodiment, and FIG. 1(B) is an end view seen from the left side of FIG. 1(A). [Figure 2] FIG. 2 is an enlarged view of the left side portion of FIG. 1(A). [Figure 3] 3A is an enlarged view of the X portion of FIG. 2, and FIG. 3B is an enlarged view of the Y portion of FIG. [Figure 4] FIG. 4 is an enlarged perspective view of a main part of a shaft body according to a first example of the embodiment. [Figure 5] FIG. 5 is a cross-sectional view showing how the coating layer is formed by injection molding. [Figure 6] FIG. 6(A) is an end view of the shaft body as seen from one side in the axial direction, and FIG. 6(B) is an enlarged view of part Z in FIG. 6(A) showing the state after the coating layer has been formed. [Figure 7] FIG. 7 is a diagram corresponding to FIG. 3(B) showing a second example of the embodiment. [Figure 8] FIG. 8 is an enlarged perspective view of a main part of a shaft body according to a second example of the embodiment. [Figure 9] FIG. 9 is a view similar to FIG. 5, showing a third example of the embodiment. [Figure 10] FIG. 10 is a partially cutaway perspective view showing an example of a conventional steering device. [Figure 11] FIG. 11 is a cross-sectional view showing an example of a conventional intermediate shaft. [Figure 12] FIG. 12 is a partially cutaway perspective view showing an example of a conventional inner shaft. DETAILED DESCRIPTION OF THE INVENTION

[0033] [First example of embodiment] A first embodiment of the present invention will be described with reference to Figures 1(A) to 6(B). The spline shaft 1 of this example has a male spline portion 2 on the outer peripheral surface of one axial side portion (the left side portion in Figures 1(A) and 2). The spline shaft 1 can be used in combination with an outer tube 116 (see Figure 11) having a female spline portion 115 on its inner peripheral surface. In other words, the spline shaft (inner shaft) 1 and the outer tube 116 can be combined by spline-engaging the male spline portion 2 with the female spline portion 115 to form a telescopic intermediate shaft 107a.

[0034] The spline shaft 1 comprises a shaft body 3 and a coating layer 4 .

[0035] The shaft body 3 is made of a light alloy such as an aluminum alloy, magnesium alloy, or titanium alloy, and is integrally formed into a hollow cylindrical shape. However, when implementing the present invention, the shaft body may also be made of an iron-based alloy such as carbon steel, and / or may be solid.

[0036] The shaft body 3 includes, in order from one axial end, a spare shaft portion 5, a splined shaft portion 6, and a non-splined shaft portion 7.

[0037] The spare shank 5 is provided at one end in the axial direction of the shaft body 3. The spare shank 5 has a cylindrical outer peripheral surface whose outer diameter does not change in the axial direction, except for a chamfered portion 8a provided on the outer peripheral surface of the end on one side in the axial direction. The spare shank 5 also has a groove bottom diameter (circumscribed circle diameter of the groove core portion 12) d of a male spline core portion 10 provided on the outer peripheral surface of a spline shank 6 (described later). 12 1. In other words, the outer peripheral surface of the spare shank 5 and the outer peripheral surface of the spline shank 6 are connected by a first step surface 9 facing one axial side. In this example, the first step surface 9 is configured as a flat surface perpendicular to the central axis O of the spline shaft 1 (shaft main body 3). However, the first step surface can also be configured as a truncated cone surface inclined in a direction in which the outer diameter increases toward the other axial side. In the example shown, the axial dimension of the spare shank 5 is sufficiently shorter than the axial dimension of the spline shank 6.

[0038] In this example, the outer diameter d5 of the end face on one axial side of the spare shank 5 is the outer diameter D of the ejector pin 30 that presses the end face on one axial side of the spare shank 5 toward the other axial side when the spline shaft 1 is removed from the mold 26 after the coating layer 4 has been injection molded, as will be described later. 30 It is larger than that.

[0039] The spline shank 6 is provided in the shaft body 3 in a range from the axially intermediate portion to the portion adjacent to the other axial side (the right side in Figure 1(A)) of the spare shank 5. The spline shank 6 has a male spline core portion 10 on its outer circumferential surface. The male spline core portion 10 is composed of multiple (18 in the illustrated example) convex tooth core portions 11 extending in the axial direction and multiple concave groove core portions 12 extending in the axial direction, arranged alternately in the circumferential direction.

[0040] In this example, the tooth tip surface of the tooth core portion 11 is composed of a flat surface or a partial cylindrical surface centered on the central axis O, with no axial irregularities, except for both axial end portions, i.e., the end portion on one axial side provided with the chamfered portion 13, and the end portion on the other axial side provided with the convex portion 18 described below. In addition, the bottom surface (the surface facing radially outward) of the groove core portion 12 is composed of a flat surface or a partial cylindrical surface centered on the central axis O, with no axial irregularities.

[0041] The non-splined shaft portion 7 is provided in a portion adjacent to the other axial side of the splined shaft portion 6. The non-splined shaft portion 7 has a connecting portion 14 located at one end in the axial direction, and a small-diameter shaft portion 15 provided in a range from the end on the other axial side to a portion adjacent to the connecting portion 14 on the other axial side.

[0042] The connecting portion 14 has an incomplete male spline core portion 16 on the outer peripheral surface of one axial side portion, and has a first inclined surface portion 17a on the outer peripheral surface of the other axial end portion, which has a truncated conical surface shape that is inclined in a direction in which the outer diameter becomes smaller toward the other axial side. The other axial end portion of the first inclined surface portion 17a is connected to the axial end portion of one axial side of the small diameter shaft portion 15 described below.

[0043] The incomplete male spline core portion 16 is formed by circumferentially arranging a plurality of convex portions 18 (18 of each in the illustrated example) and concave portions 19, each having a right-angled triangular cross section including the central axis O, alternately. The convex portions 18 have, on their outer peripheral surfaces, second inclined surface portions 17b in the shape of a partial truncated cone surface that is inclined in a direction such that the outer diameter decreases toward the other axial side. One axial end of the second inclined surface portion 17b is connected to the other axial end of the tooth tip surface of the tooth core portion 11, and the other axial end of the second inclined surface portion 17b is connected to the outer peripheral surface of the end portion on one axial side of the first inclined surface portion 17a.

[0044] The first inclined surface portion 17a and the second inclined surface portion 17b are present on the same truncated cone surface. That is, in this example, the outer peripheral surface of the other axial end portion of the spline shaft portion 6 and the outer peripheral surface of one axial end portion of the small diameter shaft portion 15 are connected by the inclined surface portion 17 having a truncated cone surface shape and made up of the first inclined surface portion 17a and the second inclined surface portion 17b.

[0045] The small diameter shaft portion 15 is provided in the shaft body 3 in a range from the other axial end to a portion adjacent to the other axial end of the connecting portion 14. The small diameter shaft portion 15 has a cylindrical outer peripheral surface whose outer diameter does not change in the axial direction, except for a chamfered portion 8b provided on the outer peripheral surface of the other axial end. The small diameter shaft portion 15 has a groove bottom diameter (circumscribed circle diameter of the groove core portion 12) d of the male spline core portion 10 provided on the outer peripheral surface of the spline shaft portion 6. 12 outer diameter D 15 In this example, the outer diameter D of the small diameter shaft portion 15 15 is larger than the outer diameter D5 of the spare shaft portion 5 (D 15 >D5).

[0046] The shaft body 3 also has a center hole 21 that passes through the center in the axial direction. The center hole 21 is configured as a stepped hole whose inner diameter increases stepwise toward one axial side, except for the other axial end where the chamfered portion 8c is provided.

[0047] The coating layer 4 is made of a synthetic resin, such as polyamide resin (PA), polyphenylene sulfide resin (PPS), or polyacetal resin (POM), that can reduce sliding resistance against the female spline portion 115 of the outer tube 116 that is combined with the spline shaft 1 of this example. The coating layer 4 covers the entire outer circumferential surface of the spare shaft portion 5, the outer circumferential surface of the spline shaft portion 6, and the outer circumferential surface of one axial side portion of the non-spline shaft portion 7 (the outer circumferential surface of the connecting portion 14 and the outer circumferential surface of one axial side portion of the small diameter shaft portion 15). Note that while FIG. 1(B) shows a circumferential portion of the coating layer 4 omitted, in reality, the coating layer 4 is provided over the entire periphery.

[0048] For this reason, the male spline portion 2 is composed of a male spline core portion 10 provided on the outer peripheral surface of the spline shaft portion 6, and a male spline covering portion 22 of the coating layer 4 that covers the male spline core portion 10. In this example, as shown in FIG. 6(B), the male spline covering portion 22 has cutout recesses 20 at multiple locations (four locations in the illustrated example) in the circumferential direction on the outer peripheral surface of one axial side portion (the range indicated by α in FIG. 1(A)). Each cutout recess 20 has a semicircular cross-sectional shape and opens to the outer peripheral surface of the spline shaft 1 and to one axial side end face. In this example, each cutout recess 20 is provided in a portion of the male spline portion 2 whose phase in the circumferential direction coincides with the spline groove. Note that the cutout recesses 20 are omitted from FIG. 1(B).

[0049] As will be described later, each of the notched recesses 20 is formed by engaging a positioning pin 27 with a spline groove to circumferentially position the shaft body 3 relative to the mold 26 when injection molding the coating layer 4. After the spline shaft 1 is completed, when the spline shaft 1 is combined with the outer tube 116 to form the intermediate shaft 107a, each of the notched recesses 20 can be used as a grease reservoir to hold grease applied to the spline engagement portion between the male spline portion 2 and the female spline portion 115.

[0050] The axial length of each cutout recess 20 is not particularly limited, but may be, for example, 1 / 20 to 1 / 6 of the axial length of the male spline portion 2 .

[0051] The male spline covering portion 22 has a tooth covering portion 23 that covers the tooth core portion 11, and a groove covering portion 24 that covers the groove core portion 12. The radial thickness t of the male spline covering portion 22 is approximately constant in the circumferential and axial directions, except for the portion where the notched recess 20 is provided. The radial thickness t of the male spline covering portion 22 is not particularly limited, but can be, for example, 0.01 mm or more and 0.50 mm or less, and preferably 0.25 mm or more and 0.40 mm or less.

[0052] The radial thickness of the coating layer 4 at the portion where the cutout recess 20 is provided is extremely thin. The radial thickness of the coating layer 4 at the portion where the cutout recess 20 is provided is not particularly limited, but can be, for example, 0.01 mm or more and 0.10 mm or less.

[0053] In this example, the radial thickness T of the first thick portion 25a of the coating layer 4 that covers the outer circumferential surface of the spare shaft portion 5 is A is made thicker than the radial thickness t of the male spline covering portion 22 of the coating layer 4 that covers the male spline core portion 10 provided on the outer circumferential surface of the spline shaft portion 6 (T A >t).

[0054] For this reason, the outer diameter of the portion of the first thick-walled portion 25a that coincides with the tooth core portion 11 in the circumferential direction is set to be the same as the outer diameter of the tooth covering portion 23, and the outer diameter of the portion of the first thick-walled portion 25a that coincides with the groove core portion 12 in the circumferential direction is set to be the same as the outer diameter of the groove covering portion 24. In this example, the outer diameter D5 of the spare shaft portion 5 is set to be 1 / 2 times the groove bottom diameter d of the male spline core portion 10. 12 Since the thickness T A is thicker than the radial thickness t of the male spline covering portion 22 that covers the male spline core portion 10, regardless of the phase in the circumferential direction.

[0055] In this example, the axial length of the radially outer portion of the first thick-walled portion 25a, i.e., the axial length L from the end face on one axial side of the first thick-walled portion 25a to the end of the chamfered portion 13 on the other axial side, is a1 is set to be larger than the radial thickness t of the male spline covering portion 22 (L a1 Furthermore, the axial length of the radially inner portion of the first thick portion 25a, that is, the axial length L from the end face on one side of the axial direction of the first thick portion 25a to the first step surface 9 a2 is set to be larger than the radial thickness t of the male spline covering portion 22 (L a2 >t).

[0056] The radial thickness T of the first thick portion 25a A is not particularly limited, but may be set to, for example, 3 times or more and 7 times or less the radial thickness t of the male spline covering portion 22.

[0057] In addition, the radial thickness (thickest radial thickness) T of the second thick portion 25b of the coating layer 4 that covers the outer peripheral surface of one end of the non-spline shaft portion 7 in the axial direction, i.e., the outer peripheral surface of the connecting portion 14 and the outer peripheral surface of one end of the small diameter shaft portion 15 in the axial direction. B is made thicker than the radial thickness t of the male spline covering portion 22 of the coating layer 4 that covers the male spline core portion 10 provided on the outer circumferential surface of the spline shaft portion 6 (T B >t).

[0058] For this reason, the outer diameter of the portion of the second thick portion 25b that coincides with the tooth core portion 11 in the circumferential direction is set to be the same as the outer diameter of the tooth covering portion 23, and the outer diameter of the portion of the second thick portion 25b that coincides with the groove core portion 12 in the circumferential direction is set to be the same as the outer diameter of the groove covering portion 24. In this example, the groove bottom diameter D of the male spline core portion 10 12 outer diameter D 15 The outer peripheral surface of one end in the axial direction of the small diameter shaft portion 15 having the groove 17 is connected to the outer peripheral surface of the other end in the axial direction of the spline shaft portion 6 by a frustum-shaped inclined surface portion 17. , contact The second thick-walled portion 25b covers the outer peripheral surface of the connecting portion 14 and the outer peripheral surface of the end portion on one axial side of the small diameter shaft portion 15. B is thicker than the radial thickness t of the male spline covering portion 22 that covers the male spline core portion 10, regardless of the phase in the circumferential direction.

[0059] In this example, the axial length of the radially outer portion of the second thick-walled portion 25b, i.e., the axial length L from the end face on the other axial side of the second thick-walled portion 25b to the end of one axial side of the connecting portion 14, is b1 is set to be larger than the radial thickness t of the male spline covering portion 22 (L b1Furthermore, the axial length of the radially inner portion of the second thick-walled portion 25b, i.e., the axial length L from the end face on the other axial side of the second thick-walled portion 25b to the end portion on the other axial side of the connecting portion 14, is b2 is set to be larger than the radial thickness t of the male spline covering portion 22 (L b2 >t).

[0060] The coating layer 4 is formed at one location or at a plurality of locations (not shown) at equal intervals in the circumferential direction on the outer circumferential surface of the thin-walled portion 32 that is located on the other axial side of the second thick-walled portion 25b in the portion covering the small-diameter shaft portion 15. Gate marks Specifically, in this example, the coating layer 4 is formed on the outer peripheral surface of the thin-walled portion 32 at two locations on the opposite sides in the radial direction. Gate marks In this example, Gate marks is formed on the outer peripheral surface of the thin-walled portion 32 at a portion that coincides in phase with the tooth core portion 11 in the circumferential direction. Gate marks As will be described later, after the coating layer 4 is injection molded, a gate 29 is opened. Remove ( Disconnect ) It is formed by scars This refers to...

[0061] The coating layer 4 is formed by injection molding and is simultaneously bonded and fixed to the shaft body 3 .

[0062] Next, a method for manufacturing the spline shaft 1 of this embodiment will be described below.

[0063] First, a metal wire or rod is cut to a predetermined length to obtain a cylindrical material. Next, the cylindrical material is subjected to necessary processes such as forging, cutting, and grinding to obtain the shaft body 3. For example, the male spline core portion 10 can be formed by rolling or cutting.

[0064] In the subsequent step of forming the coating layer 4, first, as shown in Fig. 5, the shaft body 3 is set in a mold 26. In this example, the shaft body 3 is set in the mold 26 with its central axis oriented horizontally. Note that the mold 26 may have, for example, a split mold structure made up of multiple mold parts.

[0065] In this example, with the shaft body 3 set in the mold 26, as shown in FIG. 6(A), positioning pins 27 are engaged (inserted) into some (four in the illustrated example) of the groove core portions 12 that constitute the male spline core portion 10 of the shaft body 3. This positions the shaft body 3 in the circumferential direction relative to the mold 26. In this state, a gate 29 for feeding molten synthetic resin into a cavity 28 present between the inner surface of the mold 26 and the outer circumferential surface of the shaft body 3 is located radially outward of one axial side portion of the small diameter shaft portion 15 (the position indicated by the thick arrow in FIG. 1), and is arranged in a portion that is in phase with the tooth core portion 11 in the circumferential direction. Note that the direction in which the gate 29 is oriented is not limited to a direction perpendicular to the central axis of the shaft body 3, but it may also be arranged in a direction inclined relative to the central axis of the shaft body 3, for example, in a direction that forms an angle of 30° to 60° with the central axis of the shaft body 3 in a cross section including the central axis of the shaft body 3.

[0066] With a mold 26 positioned around one axial end of the shaft body 3, molten synthetic resin is injected under pressure through a gate 29 into a cavity 28, and then the synthetic resin is cooled and solidified within the cavity 28. After the synthetic resin has cooled and solidified, the mold 26 is separated, and an ejector pin 30 is used to press one axial end face of the shaft body 3 (preparatory shaft portion 5) toward the other axial end, thereby removing the spline shaft 1 from the mold 26. The gate 29 is then cut to obtain the completed spline shaft 1. Note that the synthetic resin (male spline covering portion 22) around the male spline core portion 10 in the portion where the positioning pin 27 was located is much thinner than the other portions, and a notched recess 20 is formed in that portion.

[0067] According to the spline shaft 1 of this embodiment, the axial bonding strength between the metal shaft body 3 and the synthetic resin coating layer 4 can be ensured while the manufacturing cost can be reduced.

[0068] That is, in the spline shaft 1 of this example, the radial thickness T A is thicker than the radial thickness t of the male spline covering portion 22 of the coating layer 4 that covers the male spline core portion 10. Also, the radial thickness T B is made thicker than the radial thickness t of the male spline covering portion 22.

[0069] Therefore, because the coating layer 4 is formed by injection molding, the amount of thermal shrinkage (volume reduction) that occurs when the molten synthetic resin is cooled and solidified after filling the cavity 28 is greater in the first thick-walled portion 25a and the second thick-walled portion 25b than in the male spline covering portion 22. As a result, the bonding strength (degree of adhesion) of the first thick-walled portion 25a and the second thick-walled portion 25b, which are located on both axial sides of the male spline core portion 10, to the outer circumferential surface of the shaft body 3 is greater than the bonding strength (degree of adhesion) of the male spline covering portion 22, which covers the male spline core portion 10, to the outer circumferential surface of the shaft body 3. For this reason, the first thick-walled portion 25a and the second thick-walled portion 25b, which have a high bonding strength to the shaft body 3, can be located on both axial sides of the male spline core portion 10 of the shaft body 3. In other words, the male spline core portion 10 can be sandwiched from both axial sides by the first thick-walled portion 25a and the second thick-walled portion 25b, which have a high bonding strength to the shaft body 3. This ensures the bonding strength between the shaft body 3 and the coating layer 4 in the axial direction.

[0070] Furthermore, the spline shaft 1 of this example achieves a structure that ensures the axial bonding strength between the shaft body 3 and the coating layer 4 without forming toothless portions 122a, 122b, and 122c around the entire circumference of the male spline core portion 121 of the shaft body 117, as in the inner shaft 114 described in JP 2020-143766 A. This prevents an unnecessary increase in the number of steps required to process the shaft body 3 and a decrease in material yield, thereby reducing the manufacturing cost of the spline shaft 1.

[0071] In this example, the axial length L of the radially outer portion of the first thick-walled portion 25a a1 and the axial length L of the radially inner part a2 is made larger than the radial thickness t of the male spline covering portion 22, and the axial length L of the radially outer portion of the second thick-walled portion 25b is made b1 and the axial length L of the radially inner part b2 is larger than the radial thickness t of the male spline covering portion 22. This makes it possible to ensure sufficient volumes for the first thick-walled portion 25a and the second thick-walled portion 25b located on both axial sides of the male spline core portion 10. This also makes it possible to ensure the axial bonding strength between the shaft body 3 and the coating layer 4.

[0072] Furthermore, according to the manufacturing method of the spline shaft 1 of this embodiment, the spline shaft 1 can be manufactured industrially efficiently.

[0073] In particular, in this example, when forming the coating layer 4 by injection molding, the shaft body 3 is set in the mold 26 with its central axis oriented horizontally, and a gate 29 for feeding molten synthetic resin into the cavity 28 is positioned radially outward from one axial side of the small diameter shaft portion 15. In this way, because the axial direction of the shaft body 3 is oriented horizontally and the axial position of the gate 29 is regulated, it is possible to prevent weld lines from forming on the surface of the male spline covering portion 22 that constitutes the male spline portion 2. The reason for this will be explained below.

[0074] According to a simulation performed by the inventors, when molten synthetic resin is fed into the cavity 28 from the gate 29, the molten synthetic resin spreads in the circumferential direction and toward one axial side, and then merges (collides) with molten synthetic resin fed from other gates 29 in the circumferential direction around one axial side of the non-splined shaft portion 7 (small-diameter shaft portion 15). After the flow fronts of molten synthetic resin fed from adjacent gates 29 merge around one axial side of the non-splined shaft portion 7, the flow toward one axial side becomes more prevalent. In this example, the molten synthetic resin is made to merge in the circumferential direction around one axial side of the non-splined shaft portion 7 before being fed around the male spline core portion 10. Therefore, the meeting angle between the flow fronts becomes sufficiently large before the molten synthetic resin reaches the outer peripheral surface of the male spline core portion 10. This prevents weld lines from forming in the male spline covered portion 22. That is, it is possible to prevent the aesthetic appearance of the completed spline shaft 1 from being marred and the strength of the male spline covering portion 22 that constitutes the male spline portion 2 from being reduced.

[0075] Although there is a possibility that a weld line may form on the surface of the thin-walled portion 32 of the coating layer 4 that covers the outer peripheral surface of one axial side portion of the non-spline shaft portion 7 (small diameter shaft portion 15), this does not pose a particular problem in terms of ensuring the aesthetic appearance of the completed spline shaft 1 or the strength of the male spline coated portion 22.

[0076] In this example, the phase of the gate 29 in the circumferential direction is made to coincide with the phase of the tooth core portion 11 in the circumferential direction. Therefore, the allowance remaining after cutting the gate 29 can be allowed up to the height of the tooth tip surface of the tooth core portion 11. However, when implementing the present invention, the phase of the gate in the circumferential direction can also be made to coincide with the phase of the groove core portion in the circumferential direction.

[0077] In this example, when forming the coating layer 4 by injection molding, the shaft body 3 is set in the mold 26 with the central axis oriented horizontally. However, when practicing the present invention, the central axis of the shaft body can also be oriented vertically. Alternatively, the shaft body can be set in the mold with the central axis tilted relative to the horizontal.

[0078] Furthermore, the spline shaft of the present invention is not limited to an inner shaft constituting an intermediate shaft for a steering device, but can be applied to various types of spline shafts. For example, the spline shaft of the present invention can be applied to an inner shaft constituting a steering shaft having a rear end to which a steering wheel is supported and fixed.

[0079] [Second example of embodiment] A second embodiment of the present invention will be described with reference to FIGS. 7 and 8. In this embodiment, a shaft body 3a includes, in order from one axial end, a spare shaft portion 5, a splined shaft portion 6, and a non-splined shaft portion 7a. In this embodiment, the non-splined shaft portion 7a consists only of a small-diameter shaft portion 15. That is, unlike the shaft body 3 according to the first embodiment, the shaft body 3a does not include a connecting portion 14 having an incomplete male spline core portion 16 on its outer circumferential surface. The outer circumferential surfaces of the splined shaft portion 6 and the small-diameter shaft portion 15 are connected by a flat second stepped surface 31 perpendicular to the central axis O of the shaft body 3a. The second stepped surface 31 can be formed, for example, by cutting after forging.

[0080] Therefore, the resistance to the assumed displacement of the coating layer 4a relative to the shaft body 3a toward one side in the axial direction can be made larger than that of the spline shaft 1 according to the first example of the embodiment.

[0081] In this example, the volume of the second thick-walled portion 25c of the coating layer 4a that covers one axial end of the non-spline shaft portion 7a is larger than that of the spline shaft 1 according to the first example of the embodiment. However, even in this case, it is possible to prevent weld lines from being formed in the male spline covered portion 22 that constitutes the male spline portion 2.

[0082] Furthermore, according to a simulation conducted by the present inventors, when the outer peripheral surface of the spline shaft portion 6 and the outer peripheral surface of the small diameter shaft portion 15 are connected to each other in a flat plane shape perpendicular to the central axis O of the shaft body 3a, as in this example, Second When the connection is made by the step surface 31, the flow of molten synthetic resin toward the downward side when forming the coating layer 4a by injection molding can be made to be approximately the same speed regardless of the phase in the circumferential direction, compared to when the outer surface of the spline shaft portion 6 and the outer surface of the small diameter shaft portion 15 are connected by a truncated cone-shaped inclined surface portion 17, as in the first example of the embodiment.

[0083] The configuration and effects of other parts are the same as those of the first embodiment.

[0084] [Third example of embodiment] A third embodiment of the present invention will be described with reference to Fig. 9. In this embodiment, the outer diameter d5 of the end face on one axial side of the spare shaft portion 5a of the shaft body 3b is set to be equal to the outer diameter D of the ejector pin 30. 30 The ejector pin 30 is used to press one axial end face of the preliminary shaft portion 5a and one axial end face of the coating layer 4 (one axial end face of the first thick-walled portion 25a) toward the other axial side when the spline shaft 1 is removed from the mold 26 after the coating layer 4 has been injection-molded.

[0085] According to this example, when the spline shaft 1 is removed from the mold 26, the ejector pin 30 can simultaneously press against one axial end face of the preliminary shaft portion 5a and one axial end face of the coating layer 4. This makes it possible to reliably prevent the shaft body 3b and the coating layer 4 from being misaligned in the axial direction when the spline shaft 1 is removed from the mold 26. The configurations and effects of the other parts are the same as those of the first and second examples of the embodiment. [Explanation of symbols]

[0086] 1 spline shaft 2 Male spline part 3, 3a, 3b Shaft body 4, 4a coating layer 5, 5a spare shaft 6 Spline shaft 7, 7a Non-splined shaft 8a, 8b, 8c Chamfered parts 9 First step surface 10 Male spline core 11 Tooth core part 12 Groove core 13 Chamfered part 14 Connection 15 Small diameter shaft 16 Incomplete male spline core 17 Slope section 17a First slope section 17b Second slope section 18 Convex part 19 Recess 20 Notch recess 21 Center hole 22 Male spline coating 23 Tooth covering part 24 Groove covering part 25a First thick section 25b, 25c Second thick section 26 Mold 27 Locating pin 28 Cavity Gate 29 30 Ejector pin 31 Second step surface 32 Thin-walled section 100 steering wheel 101 Steering gear unit 102 Input shaft 103 tie rod 104 Steering shaft 105 steering column 106 Universal joint 107, 107a Intermediate shaft 108 Universal Joint 109 Inner shaft 110 outer tube 111 Innacolumn 112 Outer Column 113 Male spline part 114 Inner shaft 115 Female spline part 116 Outer tube 117 Shaft body 118 Coating Layer 119 Tooth core part 120 Groove core 121 Male spline core 122a, 122b, 122c missing teeth 123 Filling section

Claims

1. a metal shaft body including a spare shank portion disposed at one end in the axial direction, a male spline core portion having tooth core portions and groove core portions alternately disposed on an outer circumferential surface thereof, a spline shank portion disposed on the other axial side of the spare shank portion, and a non-spline shank portion disposed on the other axial side of the spline shank portion; A coating layer made of synthetic resin; Equipped with an outer circumferential surface of the spare shaft portion and an outer circumferential surface of the spline shaft portion are connected by a first step surface facing one side in the axial direction, the coating layer has a first thick portion covering the outer peripheral surface of the spare shaft portion, a male spline covering portion covering the outer peripheral surface of the spline shaft portion, a second thick portion covering the outer peripheral surface of one end portion of the non-spline shaft portion in the axial direction, and a thin portion covering a portion of the outer peripheral surface of the non-spline shaft portion that is offset from the second thick portion to the other side in the axial direction, a radial thickness of the first thick-walled portion is thicker than a radial thickness of the male spline covering portion, and a radial thickness of the second thick-walled portion is thicker than a radial thickness of the male spline covering portion, an outer diameter of the thin-walled portion is smaller than an outer diameter of a portion of the second thick-walled portion that coincides with the tooth core portion in the circumferential direction; the coating layer has a gate mark on the outer peripheral surface of the thin-walled portion; Splined shaft.

2. There are no weld lines on the surface of the male spline covering portion. The spline shaft according to claim 1 .

3. a metal shaft body including a spare shank portion disposed at one end in the axial direction, a male spline core portion having tooth core portions and groove core portions alternately disposed on an outer circumferential surface thereof, a spline shank portion disposed on the other axial side of the spare shank portion, and a non-spline shank portion disposed on the other axial side of the spline shank portion; a synthetic resin coating layer covering an outer peripheral surface of the spare shaft portion, an outer peripheral surface of the splined shaft portion, and an outer peripheral surface of one axial end of the non-splined shaft portion; Equipped with an outer circumferential surface of the spare shaft portion and an outer circumferential surface of the spline shaft portion are connected by a first step surface facing one side in the axial direction, a radial thickness of a portion of the coating layer covering the outer peripheral surface of the spare shaft portion is greater than a radial thickness of a portion of the coating layer covering the outer peripheral surface of the splined shaft portion, and a radial thickness of a portion of the coating layer covering the outer peripheral surface of one axial end of the non-splined shaft portion is greater than a radial thickness of a portion of the coating layer covering the outer peripheral surface of the splined shaft portion, the male spline core portion has, at a plurality of circumferential locations, notched recesses recessed radially inward relative to adjacent portions on the other axial side, Splined shaft.

4. a weld line is not present in the coating layer in a portion that covers the outer peripheral surface of the spline shaft portion; The spline shaft according to claim 3.

5. the coating layer has a gate mark in a portion covering the outer peripheral surface of one end of the non-splined shaft portion in the axial direction; 5. The spline shaft according to claim 4.

6. a phase of the gate mark in the circumferential direction coincides with a phase of any one of the tooth core portions in the circumferential direction; The spline shaft according to claim 5.

7. an outer circumferential surface of the splined shaft portion and an outer circumferential surface of one axial end of the non-splined shaft portion are connected by a flat second stepped surface perpendicular to the central axis of the shaft body; The spline shaft according to claim 1 or 3.

8. A metal shaft body having a spare shaft portion arranged at one end in the axial direction, a male spline core portion having tooth core portions and groove core portions arranged alternately in the circumferential direction on the outer circumferential surface, and including a spline shaft portion arranged on the other axial side of the spare shaft portion, and a non-spline shaft portion arranged on the other axial side of the spline shaft portion; a synthetic resin coating layer covering an outer peripheral surface of the spare shaft portion, an outer peripheral surface of the splined shaft portion, and an outer peripheral surface of one axial end of the non-splined shaft portion; Equipped with an outer circumferential surface of the spare shaft portion and an outer circumferential surface of the spline shaft portion are connected by a first step surface facing one side in the axial direction, a radial thickness of a portion of the coating layer covering the outer peripheral surface of the spare shaft portion is greater than a radial thickness of a portion of the coating layer covering the outer peripheral surface of the splined shaft portion, and a radial thickness of a portion of the coating layer covering the outer peripheral surface of one axial end of the non-splined shaft portion is greater than a radial thickness of a portion of the coating layer covering the outer peripheral surface of the splined shaft portion, a method for manufacturing a spline shaft, the coating layer having a gate mark on a portion covering an outer peripheral surface of one end portion of the non-spline shaft portion in an axial direction, a step of disposing a mold around one axial end of the non-splined shaft portion, the splined shaft portion, and the spare shaft portion, and disposing a gate around one axial end of the non-splined shaft portion, and then feeding molten synthetic resin into a cavity in the mold through the gate, thereby forming the coating layer; an outer diameter of an end surface on one axial side of the spare shaft portion is smaller than an outer diameter of an ejector pin that presses the end surface on one axial side of the spare shaft portion when removing the spline shaft from the mold; A method for manufacturing a spline shaft.

9. The shaft body is set in the mold with the central axis of the shaft body oriented horizontally. The method for manufacturing a spline shaft according to claim 8.

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