Stub shaft and power transmission shaft

Abstract

To provide a stub shaft and a power transmission shaft capable of improving strength and durability of a spline part or a serration part.SOLUTION: The power transmission shaft PS1 is provided with the extension portion 28 adjacent to the spline shaft portion 27, so that heat applied to the spline shaft portion 27 can be released to the extension portion 28. Accordingly, the generation of the excessive heat input in the front end portion of the spline shaft portion 27 is suppressed, and there is no concern that the decarburization is caused in the front end portion of the spline shaft portion 27. As a result, in the spline shaft portion 27, the thermosetting treatment portion 29 can be formed over the entire region in the direction of the rotation axis Z (axial direction), and the strength and durability of the spline shaft portion 27 can be improved.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a stub shaft and a power transmission shaft. [Background technology]

[0002] A known conventional power transmission shaft is, for example, that described in Patent Document 1 below.

[0003] That is, this power transmission shaft has a spline portion at the tip of the shaft portion, and the surface of this spline portion is hardened to form a heat-hardened portion, which is formed only in a predetermined range on the base end side of the spline portion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-275878 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional power transmission shaft, the tip of the spline portion is not formed with a heat-hardened treatment. On the other hand, if the tip of the spline portion of the conventional power transmission shaft is hardened, there is a risk of decarburization due to excessive heat input during the hardening. This may result in a decrease in the strength and durability of the spline portion, and there is still room for improvement.

[0006] Therefore, the present invention was devised in consideration of the technical problems with the conventional power transmission shafts, and aims to provide a stub shaft and a power transmission shaft that can improve the strength and durability of the spline portion or serration portion. [Means for solving the problem]

[0007] In one aspect of the present invention, an extension portion is provided adjacent to the tip side of the spline portion or serration portion, and a heat-hardened treatment portion is formed on each surface of the spline portion or serration portion and the extension portion. [Effects of the Invention]

[0008] According to the present invention, the strength and durability of the spline portion or serration portion can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a half vertical cross-sectional view showing the entire power transmission shaft according to a first embodiment of the present invention. [Figure 2] 2 is a half-longitudinal cross-sectional view of the stub shaft shown in FIG. 1, showing an enlarged view of the vicinity of the tip end of the stub shaft. FIG. [Figure 3] FIG. 2 is a half-longitudinal cross-sectional view of a stub shaft showing a hardening mode of the shaft portion shown in FIG. [Figure 4] 10 is a half vertical cross-sectional view of the stub shaft illustrating a connecting operation when connecting the power transmission shaft to the vehicle side. FIG. [Figure 5] FIG. 10 is a half-longitudinal cross-sectional view of a stub shaft showing an enlarged view of the vicinity of the tip end of a stub shaft according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiments of a stub shaft and a power transmission shaft according to the present invention will be described in detail below with reference to the drawings. Note that in the following embodiments, the stub shaft and the power transmission shaft will be described as being applied to a propeller shaft for an automobile. Furthermore, the stub shaft and the power transmission shaft according to the present invention can be applied to other power transmission shafts, such as a drive shaft for an automobile, in addition to the propeller shaft exemplified in this embodiment.

[0011] [First embodiment] 1 to 5 show a first embodiment of a power transmission shaft according to the present invention. In the description of this embodiment, for convenience, the left side of Fig. 1 will be referred to as the "front" and the right side as the "rear." In addition, the direction along the rotation axis Z in Fig. 1 will be referred to as the "axial direction," the direction perpendicular to the rotation axis Z as the "radial direction," and the direction around the rotation axis Z as the "circumferential direction."

[0012] (Propeller shaft configuration) FIG. 1 is a diagram showing the overall configuration of a propeller shaft PS1 according to a first embodiment of the present invention, and shows a half cross-sectional view of the propeller shaft PS1 cut along the rotation axis Z of the propeller shaft PS1.

[0013] 1, the propeller shaft PS1 according to this embodiment is disposed between a first shaft (not shown) disposed in the front of the vehicle and a second shaft (not shown) disposed in the rear of the vehicle. Here, the first shaft corresponds to, for example, the output shaft of a transmission disposed in the front of the vehicle, and the second shaft corresponds to, for example, the input shaft of a differential disposed in the rear of the vehicle.

[0014] The propeller shaft PS1 according to this embodiment is a so-called one-piece propeller shaft, and its front end is connected to the first shaft portion (not shown) and its rear end is connected to the second shaft portion (not shown) via a joint member 4. That is, the propeller shaft PS1 has a cylindrical tube 1 that corresponds to the tubular member of the present invention, a first shaft member 2 that is a stub shaft of the present invention that is inserted into a first end portion 11 that is the front end portion of the tube 1, and a second shaft member 3 that is inserted into a second end portion 12 that is the rear end portion of the tube 1.

[0015] The tube 1 is integrally formed by laminating, for example, carbon fiber reinforced plastic material (so-called CFRP) in the radial direction, and is formed into a cylindrical shape with a constant inner diameter in the axial direction. Furthermore, the outer diameters of the first end 11 and the second end 12 of the tube 1 are each formed to be enlarged, and the wall thickness (radial width) of the first end 11 and the second end 12 is formed to be thicker than the wall thickness of a general portion of the intermediate portion excluding the first end 11 and the second end 12. In other words, the first end 11 and the second end 12 of the tube 1 are each formed with at least two layers, an inner layer and an outer layer.

[0016] The first shaft member 2 is integrally formed from a metal material and has a first main body portion 21 that is exposed from the first end 11 of the tube 1 and is connected to the first shaft portion (not shown) of the vehicle, and a first insertion portion 22 that extends axially from the rear end of the first main body portion 21 and is inserted into the inner side of the first end 11 of the tube 1.

[0017] The first main body portion 21 has a bottomed tubular portion 23 that is formed with a stepped diameter narrowing from the front end of the first insertion portion 22, and has a front end closed by a bottom 230 and an open rear end, and a generally solid shaft portion 24 that is formed with a narrowed diameter relative to the bottomed tubular portion 23 and extends axially from the bottom 230 forward (in the direction away from the bottomed tubular portion 23).

[0018] The first insertion portion 22 has a first serration portion 25 on its outer periphery that is serrated and coupled to the inner periphery of the first end 11 of the tube 1. The outer diameter of the tooth tips 250 of the first serration portion 25 is set to be slightly larger than the inner diameter of the tube 1. In other words, when the first insertion portion 22 is inserted into the inner periphery of the tube 1, the tooth tips 250 of the first serration portion 25 bite into the inner periphery of the tube 1, thereby engaging the first insertion portion 22 and the tube 1 so that they can rotate together.

[0019] The second shaft member 3 is integrally formed from a metal material and has a second main body portion 31 that is exposed from the second end portion 12 of the tube 1 and connected to the coupling member 4, and a second insertion portion 32 that extends axially from the rear end portion of the second main body portion 31 and is inserted into the inner peripheral side of the second end portion 12 of the tube 1.

[0020] The second main body portion 31 integrally includes a generally cylindrical tubular portion 33 whose diameter tapers in a step-like manner from the rear end of the second insertion portion 32, and a joint connecting portion 34 whose diameter expands in a trifurcated manner from the rear end of the tubular portion 33 and is connected to the joint member 4. The tubular portion 33 and the joint connecting portion 34 are connected by well-known friction stir welding so as to be integrally rotatable.

[0021] The second insertion portion 32 has a second serration portion 35 on its outer periphery that is serrated and coupled to the inner periphery of the second end 12 of the tube 1. The outer diameter of the tooth tips 350 of the second serration portion 35 is set to be slightly larger than the inner diameter of the tube 1. In other words, when the second insertion portion 32 is inserted into the inner periphery of the tube 1, the tooth tips 350 of the second serration portion 35 bite into the inner periphery of the tube 1, thereby engaging the second insertion portion 32 and the tube 1 so that they can rotate together.

[0022] The coupling member 4 is a so-called rubber joint, and is provided on the axially opposite side of the tube 1 with respect to the second shaft member 3. That is, the coupling member 4 is substantially annular, and has three first bolt through holes 41 arranged at equal intervals in the circumferential direction and used for connection to the joint connecting portion 34, and three second bolt through holes 52 arranged at approximately equal intervals between the first bolt through holes 41 in the circumferential direction and used for connection to the second axle portion (not shown) of the vehicle.

[0023] Specifically, the joint connection part 34 and the joint member 4 are connected via a first bolt B1 inserted into the first bolt through-hole 41, thereby fixing the joint connection part 34 and the joint member 4 so as to be rotatable together. On the other hand, the second axle part (not shown) of the vehicle, which has a trifurcated shape similar to the joint connection part 34, is connected to the joint member 4 via a second bolt (not shown) inserted into the second bolt through-hole 42, thereby fixing the second axle part (not shown) of the vehicle and the joint member 4 so as to be rotatable together.

[0024] Fig. 2 shows an enlarged view of the main part of Fig. 1, enlarging the tip of the shaft part 24 shown as part A in Fig. 1. Fig. 3 shows an enlarged view of the main part of the first shaft member 2, illustrating the construction mode of the heat hardening treatment part of the stub shaft (first shaft member 2) shown in Fig. 2.

[0025] For example, as shown in Figure 2, the shaft portion 24 integrally includes a base portion 26 connected to the bottomed tubular portion 23 and extending along the axial direction, a splined shaft portion 27 extending from the tip portion (front end) of the base portion 26 in the axially opposite direction from the bottomed tubular portion 23, and an extension portion 28 extending from the tip portion (front end) of the splined shaft portion 27 in the axially opposite direction from the base portion 26.

[0026] The spline shaft portion 27 has a plurality of spline teeth 271 that are arranged at approximately equal intervals in the circumferential direction and have an outer diameter D2 that is larger than the outer diameter D1 of the base portion 26, and spline grooves 272 that are arranged between the spline teeth 271 in the circumferential direction and have an outer diameter D3 that is slightly smaller than the outer diameter D1 of the base portion 26. Note that, in the present embodiment, the spline teeth 271 are formed by a well-known hobbing process, but the spline teeth 271 may be formed by other processing methods, such as rolling, in addition to the hobbing process exemplified in this embodiment. Furthermore, although not specifically shown in the drawings, the spline shaft portion 27 may be formed as a well-known serrated shaft portion in which the spline teeth 271 are formed by serration teeth.

[0027] The extension portion 28 has a generally constant outer diameter D4 that is smaller than the outer diameter D3 of the spline groove 272 and an axial length L2 that is shorter than the axial length L1 of the spline shaft portion 27. The extension portion 28 can have any outer diameter as long as it is equal to or smaller than the outer diameter D3 of the spline groove 272 and larger than the outer diameter of an opening of a recess 282 (tapered portion 282a) described later. The extension portion 28 also has a chamfered portion 281 that is generally conically tapered and chamfered to a predetermined width along the circumferential direction on the outer peripheral edge of the tip end face 280. The extension portion 28 also has a recess 282 at the center of the tip end face 280 that is recessed toward the spline shaft portion 27. The recess 282 has a tapered portion 282a whose inner diameter gradually decreases from the tip end face 280 toward the spline shaft portion 27, and a small-diameter hole portion 282b formed at the end of the tapered portion 282a on the axially opposite side from the tip end face 280. Here, the recess 282 functions as a support hole that supports the shaft portion 24 when the spline teeth 271 of the spline shaft portion 27 are machined.

[0028] The surface of the shaft portion 24 is formed with a heat-hardened portion 29, which has been subjected to a predetermined heat-hardening treatment such as induction hardening. The heat-hardened portion 29 is formed over a predetermined axial region (the region shown by hatching in FIGS. 1 and 2 ) from the rear end of the base portion 26 (the end on the bottomed tubular portion 23 side) to the middle of the extension portion 28. More specifically, the heat-hardened portion 29 is formed over the entire axial region of the base portion 26 and the splined shaft portion 27, and over a partial axial region of the extension portion 28 adjacent to the splined shaft portion 27. The heat-hardened portion 29 is formed in the axial region facing the heating coil CL by passing a high-frequency induction current through the heating coil CL, which is disposed in close proximity to the outer circumferential surface of the shaft portion 24, as shown in FIG. 3 , for example.

[0029] The thermosetting treatment portion 29 is formed in the base portion 26 to a generally constant depth over the entire axial area from the surface of the base portion 26 to a first predetermined depth T1. In other words, the thermosetting treatment portion 29 in the base portion 26 is formed so that the radial distance from the rotation axis Z to the boundary with the thermosetting treatment portion 29 is a generally constant first predetermined distance X1. Note that the depth of the thermosetting treatment portion 29 in the base portion 26 does not necessarily have to be constant as long as it is formed to be equal to or greater than the predetermined depth (first predetermined depth T1) necessary to ensure strength.

[0030] Furthermore, the thermally hardened portions 29 are formed over the entire axial length of the spline shaft portion 27, from the tips of the spline teeth 271 to a second predetermined depth T2 radially inward of the spline grooves 272. That is, the thermally hardened portions 29 of the spline shaft portion 27 are formed over the entire tooth depth of the spline teeth 271, and are formed to a depth from the surface of the spline grooves 272 that is approximately the same as the first predetermined depth T1. In other words, the thermally hardened portions 29 of the spline shaft portion 27 are formed so that the radial distance from the rotation axis Z to the boundary of the thermally hardened portions 29 is a substantially constant second predetermined distance X2. The spline grooves 272 are slightly recessed radially inward with respect to the surface of the base portion 26, and the second predetermined distance X2 is slightly smaller than the first predetermined distance X1.

[0031] Furthermore, the depth of the heat-hardened portion 29 in the spline shaft portion 27 does not necessarily have to be constant as long as it is formed to be equal to or greater than a predetermined depth (second predetermined depth T2) necessary to ensure strength. In this embodiment, the extension portion 28 is provided adjacent to the spline shaft portion 27, so that the depth of the heat-hardened portion 29 in the spline shaft portion 27 does not decrease as it approaches the extension portion 28 adjacent to the spline shaft portion 27. In other words, the radial distance (second predetermined distance X2) of the heat-hardened portion 29 in the spline shaft portion 27 from the rotation axis Z does not increase as it approaches the extension portion 28 adjacent to the spline shaft portion 27.

[0032] Furthermore, the thermally hardened portion 29 is formed in the extended portion 28 over a predetermined axial region Lx from the surface of the extended portion 28 to a third predetermined depth T3, from the rear end of the extended portion 28 (the end on the spline shaft portion 27 side) to an intermediate portion of the extended portion 28 (specifically, a position closer to the spline shaft portion 27 than the chamfered portion 281). In other words, the thermally hardened portion 29 is formed so that the radial distance from the rotation axis Z to the boundary of the thermally hardened portion 29 is a third predetermined distance X3. The diameter of the extended portion 28 tapers radially inward relative to the surface of the spline groove 272, and the third predetermined distance X3 is smaller than the first predetermined distance X1.

[0033] Furthermore, since the extension portion 28 does not contribute to torque transmission of the propeller shaft PS1 and does not require great strength, it is sufficient that the heat-hardened portion 29 of the extension portion 28 is formed in a part adjacent to the spline shaft portion 27 so that the heat-hardened portion 29 has a predetermined depth (second predetermined depth T2) at the tip of the spline shaft portion 27 adjacent to the extension portion 28. Furthermore, the depth (third predetermined depth T3) of the heat-hardened portion 29 in the extension portion 28 is formed so as to gradually decrease toward the front end, that is, so that the radial distance (third predetermined distance X3) from the rotation axis Z to the boundary of the heat-hardened portion 29 gradually increases toward the front end.

[0034] (Method of connecting the power transmission shaft to the vehicle) FIG. 4 is a semi-vertical cross-sectional view of the first shaft member 2 illustrating the connecting operation when connecting the propeller shaft PS1 to the first shaft portion 6 on the vehicle side (not shown).

[0035] When spline-connecting the propeller shaft PS1 to the first shaft portion 6 extending from the transmission side of the vehicle (not shown), first, as shown in Figure 4(a), the tip end of the extension portion 28 of the shaft portion 24 is inserted into a spline hole 60 formed along the axial direction in the center of the first shaft portion 6. By inserting the extension portion 28 into the spline hole 60 of the first shaft portion 6 in this way, it is possible to axially align the shaft portion 24 of the propeller shaft PS1 with the first shaft portion 6 of the vehicle (not shown).

[0036] In view of the fact that the extension portion 28 is used for axial alignment with the first shaft portion 6 of the vehicle (not shown), it is desirable that the extension portion 28 be set to be slightly smaller than the outer diameter D3 (see FIG. 2) of the spline grooves 272 of the spline shaft portion 27, that is, slightly smaller than the inner diameter D6 between the spline teeth 61 of the first shaft portion 6. In this way, by setting the extension portion 28 to be slightly smaller than the inner diameter D6 between the spline teeth 61 of the first shaft portion 6, the extension portion 28 can more accurately align the shaft portion 24 of the propeller shaft PS1 with the first shaft portion 6 of the vehicle (not shown).

[0037] Next, as shown in Figure 4(b), the extension portion 28 inserted into the spline hole 60 of the first shaft portion 6 is inserted all the way to the base, and the circumferential position (phase) of the spline teeth 271 of the shaft portion 24 and the spline teeth 61 of the first shaft portion 6 is adjusted, and the spline teeth 271 of the shaft portion 24 and the spline teeth 61 of the first shaft portion 6 are meshed with each other.

[0038] Thereafter, as shown in FIG. 4(c), with the spline teeth 271 of the shaft portion 24 and the spline teeth 61 of the first shaft portion 6 meshed together, the spline shaft portion 27 (spline teeth 271) of the shaft portion 24 is inserted into the spline hole 60 (spline groove 62) of the first shaft portion 6, thereby forming a spline connection between the shaft portion 24 and the first shaft portion 6, and completing the work of connecting the propeller shaft PS1 to the first shaft portion 6.

[0039] (Effects of this embodiment) As mentioned above, conventional power transmission shafts have a problem in that the tip end of the spline shaft portion 27 is not hardened. Furthermore, if the tip end of the spline shaft portion 27 of the conventional power transmission shaft were hardened, there is a possibility that decarburization would occur due to excessive heat input. This could result in a decrease in the strength and durability of the spline shaft portion 27, and there is still room for improvement.

[0040] In contrast, the propeller shaft PS1 according to this embodiment can solve the problems of the conventional power transmission shafts by providing the following effects.

[0041] The propeller shaft PS1 has the extension portion 28 provided adjacent to the spline shaft portion 27, which allows heat applied to the spline shaft portion 27 to escape to the extension portion 28. This prevents excessive heat input to the tip portion of the spline shaft portion 27, eliminating the risk of decarburization at the tip portion of the spline shaft portion 27, and makes it possible to form the heat-hardened treated portion 29 over the entire area of ​​the spline shaft portion 27 in the direction of the rotation axis Z (axial direction). As a result, the strength and durability of the spline shaft portion 27 can be improved.

[0042] Furthermore, because the extension portion 28 is provided at the tip end of the splined shaft portion 27, when engaging the splined shaft portion 27 of the propeller shaft PS1 with the splined hole 60 of the first shaft portion 6 (see FIG. 4) of the vehicle (not shown), the extension portion 28 is first inserted into the splined hole 60, and the axes of the propeller shaft PS1 and the first shaft portion 6 of the vehicle (not shown) are aligned, and the phases of the splined shaft portion 27 and the splined hole 60 are aligned, and then the splined shaft portion 27 can be inserted into the splined hole 60. This makes it relatively easy to connect the splined shaft portion 27 of the propeller shaft PS1 to the first shaft portion 6 of the vehicle (not shown), compared to when the splined shaft portion 27 of the propeller shaft PS1 is directly inserted into the splined hole 60 of the first shaft portion 6 of the vehicle (not shown) for connection.

[0043] Furthermore, in this embodiment, the depth (second predetermined depth T2) of the heat-hardened portion 29 at the tip end of the spline shaft portion 27 does not decrease in the axial direction as it approaches the extended portion 28. In other words, in the heat-hardened portion 29 of the spline shaft portion 27, the radial distance (second predetermined distance X2) from the rotation axis Z does not increase in the axial direction as it approaches the extended portion 28. This ensures sufficient strength at the tip end of the spline shaft portion 27, and effectively improves the durability of the spline shaft portion 27.

[0044] In this embodiment, the depth (second predetermined depth T2) of the heat-hardened portion is set to be approximately the same in the axial direction of the spline shaft portion 27. This makes it possible to improve the strength of the spline shaft portion 27 in a generally uniform manner, and ensures good durability of the spline shaft portion 27.

[0045] Furthermore, in this embodiment, the recess 282 is provided in the tip surface 280 of the extension portion 28 of the shaft portion 24, and therefore the recess 282 can be used as a support hole for supporting the shaft portion 24 when machining the splined shaft portion 27. This allows the splined shaft portion 27 to be machined appropriately, improving the manufacturing efficiency of the first shaft member 2, which is a stub shaft.

[0046] Second Embodiment Figure 5 shows a second embodiment of a stub shaft and a power transmission shaft according to the present invention, and illustrates the configuration of the extension portion 28 of the propeller shaft PS1 according to the first embodiment. The basic configuration other than the above changes is the same as that of the first embodiment, and therefore the same components as those in the first embodiment are denoted by the same reference numerals and will not be described again. For convenience, the left side of Figure 5 will be referred to as the "front" and the right side as the "rear" in the description of this embodiment. The direction along the rotation axis Z in Figure 5 will be referred to as the "axial direction," the direction perpendicular to the rotation axis Z as the "radial direction," and the direction around the rotation axis Z as the "circumferential direction."

[0047] 5, for example, in a propeller shaft PS2 according to this embodiment, the extension portion 28 is not solid as in the first embodiment, but is formed as a hollow cylinder having a through hole 283 penetrating along the axial direction on the inner peripheral side. The through hole 283 has an inner diameter larger than the outer diameter of the opening of a recess 282, which will be described later. In this embodiment, since the extension portion 28 is formed as a hollow cylinder, a recess 282 is formed in the tip surface 270 of the spline shaft portion 27, which faces the through hole 283 on the inner peripheral side of the extension portion 28. The configuration of the recess 282 is the same as in the first embodiment, and therefore a detailed description thereof will be omitted.

[0048] In this embodiment, the depth (third predetermined depth T3) of the thermally hardened portion 29 in the extension portion 28 is set smaller than the radial width Tx of the extension portion 28. In other words, the radial distance (third predetermined distance X3) from the rotation axis Z to the boundary of the thermally hardened portion 29 in the extension portion 28 is set larger than the inner diameter D5 of the through hole 283.

[0049] (Effects of this embodiment) As described above, in the propeller shaft PS2 according to this embodiment, the extension 28 is formed in a generally hollow shape having a through hole 283 on the inner peripheral side. This makes it possible to reduce the weight of the first shaft member 2 of the propeller shaft PS2, and suppress an increase in the weight of the propeller shaft PS2 that would be caused by providing the extension 28.

[0050] In this embodiment, the depth (second predetermined depth T2) of the heat-hardened portion 29 of the shaft portion 24 is set smaller than the radial width Tx of the hollow cylindrical extension portion 28. Therefore, there is no risk of the heat-hardened portion 29 being burned through in the extension portion 28. This effectively improves the strength and durability of the heat-hardened portion 29.

[0051] The present invention is not limited to the configurations and aspects exemplified in the above-described embodiments, and can be freely modified depending on the specifications and costs of the target application as long as the configuration can achieve the above-described effects of the present invention.

[0052] For example, in the above embodiment, the first shaft portion (not shown) is the output shaft of the vehicle's transmission and the second shaft portion (not shown) is the input shaft of the vehicle's differential device, but the reverse may also be true.

[0053] Furthermore, in the case of a vehicle in which the transmission is provided on the drive wheel (rear wheel) side, the first shaft portion (not shown) may be the output shaft of the engine and the second shaft portion (not shown) may be the input shaft of the transmission, or vice versa.

[0054] The present invention can also be applied to a vehicle that uses an electric motor as a continuously variable reducer instead of the transmission. [Explanation of symbols]

[0055] PS1, PS2... propeller shaft (power transmission shaft), 1... tube (cylindrical member), 2... first shaft member (stub shaft), 26... bottomed cylindrical portion, 27... spline shaft portion (shaft portion), 271... spline teeth (spline portion), 28... extension portion, 282... recess, 29... heat-hardened processed portion, Z... rotation axis,

Claims

1. A stub shaft used in a power transmission shaft, a bottomed tubular portion having an open end in the rotational axis direction of the stub shaft and a closed bottom end in the other direction; a shaft portion extending from the bottom portion in the direction of the rotation axis and having a spline portion or a serration portion formed on an outer periphery thereof; an extension portion provided adjacent to a tip end of the shaft portion in the rotation axis direction and extending in a direction away from the bottom; the spline portion or the serration portion in the rotation axis direction; a heat-hardened treatment portion formed on the surface of the shaft portion and the extension portion; A stub shaft comprising:

2. 2. The stub shaft of claim 1, a depth of the heat-hardened portion formed on the surface of the spline portion or the serration portion does not decrease toward the extension portion in the direction of the rotation axis; A stub shaft characterized by:

3. 3. The stub shaft according to claim 2, the depth of the heat-hardened portion formed on the surface of the spline portion or the serration portion is substantially the same in the direction of the rotation axis; A stub shaft characterized by:

4. 2. The stub shaft according to claim 1, the extension portion is formed hollow in the direction of the rotation axis and has an inner circumferential surface facing an inner space, In a radial direction perpendicular to the rotation axis, a distance from the rotation axis to the heat-hardened treatment portion is greater than a distance from the rotation axis to the inner circumferential surface. A stub shaft characterized by:

5. 2. The stub shaft according to claim 1, the extension portion has a recess recessed from a tip end surface of the extension portion toward the spline portion or the serration portion in the direction of the rotation axis, A stub shaft characterized by:

6. a cylindrical member connected to a rotary shaft that transmits driving force of a vehicle; a stub shaft connected to the tubular member, a bottomed tubular portion having an open end in the rotational axis direction of the stub shaft connected to the tubular member and a closed bottom end in the rotational axis direction; a shaft portion extending from the bottom portion in the direction of the rotation axis and having a spline portion or a serration portion formed on an outer periphery thereof; an extension portion provided adjacent to a tip end of the shaft portion in the rotation axis direction and extending in a direction away from the bottom; the spline portion or the serration portion in the rotation axis direction; a heat-hardened treatment portion formed on the surface of the shaft portion and the extension portion; the stub shaft having A power transmission shaft comprising:

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