Intermediate shaft for steering system

Abstract

To provide an intermediate shaft for a steering device which can prevent removal of a yoke of a universal joint and a shaft while reducing manufacturing costs.SOLUTION: An intermediate shaft for a steering device includes: a yoke 31 of a universal joint 30 formed with a coupling hole 33 having a hole side serration 34 on an inner peripheral surface; and a shaft 11 in which a shaft side serration 14 to be fitted with the hole side serration 34 is formed on an outer peripheral surface and which is fitted in the coupling hole 33. The yoke 31 has: a base 32 in which the coupling hole 33 is formed; and a yoke arm 37 extending from the base 32. The shaft 11 which is fitted in the coupling hole 33 has a first swage part 21 and a second swage part 22 protruding to the radial outer side of the shaft 11 in a portion at the side where the yoke arm 37 is located. The second swage part 22 is disposed having a straight part 16 at the shaft side serration 14 between itself and the base 32. The first swage part 21 is disposed without having the straight part 16 of the shaft side serration 14 between itself and the base 32.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to an intermediate shaft for a steering device used in an automotive steering device.

Background Art

[0002] An intermediate shaft that constitutes a steering shaft of a steering device mounted on an automobile is structurally composed of a plurality of shafts connected by a universal joint. In the intermediate shaft of the steering device, for example, a cardan joint is used as the universal joint. The cardan joint is configured by rotatably attaching each shaft of a cross shaft that intersects two shafts called a cross spider to a shaft. The shafts connected by the universal joint are provided with yokes, which are bifurcated members that rotatably support each shaft of the cross shaft, at the ends of the shafts, and any one of the shafts of the cross shaft is rotatably attached to each yoke, whereby the shafts are connected to each other via the universal joint.

[0003] Since the intermediate shaft of the steering device transmits the rotational torque input to the steering wheel to the steering gear unit side, the rotational torque is also transmitted between the universal joint that connects the shafts and the shafts. Therefore, the yoke of the universal joint and the shaft are connected so as to enable the transmission of rotational torque.

[0004] For example, in Patent Documents 1 to 4, serrations that mesh with each other are formed on each of the hole in the yoke of the universal joint that fits onto the shaft and the portion of the shaft that fits into the yoke, and the yoke and the shaft are connected by serration coupling. Further, in Patent Documents 2 to 4, the yoke and the shaft that are serration-coupled are fixed by welding. In Patent Documents 1 to 4, a caulking portion is formed at the end of the shaft as a retaining means in the axial direction between the yoke of the universal joint and the shaft.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2007-40420 [Patent Document 2] Japanese Patent Publication No. 2012-112509 [Patent Document 3] Japanese Patent Publication No. 2013-32795 [Patent Document 4] Japanese Patent Publication No. 2013-43516 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In conventional steering devices, the relative axial movement between the yoke and shaft of a universal joint is fixed by forming a crimped portion on the shaft, as in Patent Document 1, or by welding the yoke and shaft together, as in Patent Documents 2-4. However, when the axial fixation between the yoke and shaft of a universal joint is performed by a crimped portion on the shaft, if the crimped portion breaks, there is a possibility that the yoke and shaft will move relative to each other in the axial direction and become detached.

[0007] Furthermore, when fixing the yoke and shaft of a universal joint in the axial direction by welding, and when a crimped joint is formed in addition to the welding to prevent both from coming apart, the crimped joint can prevent the joint from coming apart if the weld fails. However, welding tends to increase manufacturing costs. In other words, welding the yoke and shaft is time-consuming, and furthermore, the work must be done with high precision to ensure the quality of the weld. Therefore, welding is time-consuming in this respect as well, and welding joints tend to increase manufacturing costs.

[0008] Therefore, it is difficult to achieve both a mechanism to prevent the yoke and shaft from coming apart when the mechanism that fixes the relative axial movement between the yoke and shaft of the universal joint breaks, and to keep manufacturing costs down.

[0009] This disclosure has been made in view of the above, and aims to provide an intermediate shaft for a steering device that can prevent the yoke and shaft of a universal joint from coming loose while keeping manufacturing costs down. [Means for solving the problem]

[0010] The intermediate shaft for a steering device according to this disclosure comprises a yoke of a universal joint having a coupling hole with a hole-side protrusion on its inner circumferential surface, and a shaft having a shaft-side protrusion formed on its outer circumferential surface that is press-fitted into the hole-side protrusion, and a shaft that fits into the coupling hole, wherein the yoke has a base in which the coupling hole is formed, and a yoke arm extending from the base into which the cross shaft of the universal joint is fitted, and the shaft that fits into the coupling hole extends from the base on the opposite side of the side where the yoke arm is positioned, and the coupling The shaft that fits into the hole has a first crimping portion and a second crimping portion that protrude radially outward from the shaft on the side where the yoke arm is located in the axial direction of the shaft relative to the coupling hole. The cross section of the axial-side uneven portion between the second crimping portion and the base portion has a straight portion which is a part that extends in the axial direction of the shaft, and the cross section of the axial-side uneven portion between the first crimping portion and the base portion has a straight portion which is a part that extends in the axial direction of the shaft, and the cross section of the axial-side uneven portion between the first crimping portion and the base portion does not have the straight portion which is the first crimping portion.

[0011] With this configuration, the relative movement between the yoke and shaft is restricted by the first crimped section without welding the yoke and shaft, and if the first crimped section is damaged, the relative movement between the yoke and shaft can be restricted by the second crimped section. Therefore, the welding process can be eliminated, reducing welding costs, and even if the steering device is subjected to a load greater than normal and a part of the steering device is damaged, the yoke can be prevented from coming off the shaft. As a result, the yoke and shaft of the universal joint can be prevented from coming off while keeping manufacturing costs down.

[0012] In a desirable configuration, the hole-side protrusions and the shaft-side protrusions are provided with a first meshing portion in which the hole-side protrusions and the shaft-side protrusions contact each other without any gap in the circumferential direction of the shaft between them, and a second meshing portion in which there is a gap in the circumferential direction of the shaft between the hole-side protrusions and the shaft-side protrusions.

[0013] This configuration allows the shaft and yoke to be integrated at the first engagement point, thereby transmitting rotational torque between the shaft and the yoke. Furthermore, since a second engagement point is provided in addition to the first engagement point on the bore-side and shaft-side protrusions, even if the first engagement point is damaged, rotational torque can still be transmitted by the second engagement point, and the driver can be alerted to the damage by a delay in response to the driver's input or by a striking sound. Therefore, it is possible to ensure the controllability of the vehicle when the steering system is damaged while allowing the driver to recognize the damage to the steering system.

[0014] In a desirable configuration, the second meshing portion has a width in the circumferential direction of the shaft of the protrusions of the shaft-side protrusions that is greater than the width of the protrusions of the shaft-side protrusions in the first meshing portion.

[0015] This configuration ensures the strength of the protrusion in the second meshing portion. This prevents damage to the second protrusion of the second meshing portion by the rotational torque when the first meshing portion is damaged and rotational torque is transmitted by the second meshing portion, thus ensuring a reliable transmission path for rotational torque through the second meshing portion. Therefore, it is possible to maintain vehicle controllability even when the steering system is damaged.

[0016] In a desirable configuration, the first meshing portion is located in the range in the circumferential direction of the shaft where the yoke arm is positioned, and the second meshing portion is located in a position different from the position in the circumferential direction of the shaft where the yoke arm is positioned.

[0017] In this configuration, the first meshing section is located in a roughly rectangular area formed by the two yoke arms, the cross shaft supported by the two yoke arms, and the portion connecting the bases of the two yoke arms. This ensures the rigidity of the section that transmits rotational torque via the universal joint. Furthermore, because the first meshing section is located near the bases of the yoke arms, the bending stress on the protrusions of the shaft-side protrusions when force is transmitted between the yoke arms and the shaft via the base of the yoke can be reduced. This suppresses damage to the protrusions caused by large bending stresses on the shaft-side protrusions, thereby suppressing damage to the first meshing section. Consequently, the steering system is less likely to be damaged even when subjected to a large load, ensuring the controllability of the vehicle.

[0018] In a desirable configuration, the first crimping portion is located in the circumferential direction of the shaft at a position where the first engaging portion is positioned, and the second crimping portion is located in the circumferential direction of the shaft at a position where the second engaging portion is positioned.

[0019] With this configuration, the first crimping portion is located in the circumferential direction of the shaft where the first meshing portion is positioned, thus suppressing damage to the first meshing portion. In other words, the first crimping portion restricts the relative movement between the shaft and the yoke in the axial direction, so even when small relative movements occur between the shaft and the yoke during vehicle operation, the first crimping portion can suppress the small axial movements between the shaft and the yoke. This suppresses wear due to small movements between the shaft-side protrusions and hole-side protrusions that mesh at the first meshing portion, thereby suppressing damage to the first meshing portion caused by wear. Furthermore, since the second crimping portion is located in the circumferential direction of the shaft where the second meshing portion is positioned, even if the first meshing portion is damaged, the second crimping portion can be prevented from being affected by the damage to the first meshing portion. This prevents damage to the second crimping portion even if the first meshing portion is damaged, and the relative movement between the shaft and the yoke in the axial direction can be restricted by the second crimping portion. As a result, vehicle controllability can be ensured.

[0020] In a desirable configuration, the first meshing portion is located in the range where the yoke arm is positioned in the circumferential direction of the shaft, the second meshing portion is located at a position different from the position where the yoke arm is positioned in the circumferential direction of the shaft, the first crimping portion is located at the position where the first meshing portion is positioned in the circumferential direction of the shaft, and the second crimping portion is located at the position where the second meshing portion is positioned in the circumferential direction of the shaft.

[0021] According to this configuration, since the first engaging portion is disposed near the base of the yoke arm, the bending stress of the convex portion of the shaft-side concavo-convex portion when force is transmitted between the yoke arm and the shaft can be reduced. Therefore, damage to the convex portion of the shaft-side concavo-convex portion can be suppressed, and damage to the first engaging portion can be suppressed. Further, since the first caulking portion is positioned at the position where the first engaging portion is disposed in the circumferential direction of the shaft, minute movement in the axial direction between the shaft and the yoke can be suppressed by the first caulking portion, and damage to the first engaging portion caused by wear due to the minute movement can be suppressed. Accordingly, it is possible to suppress damage to the steering device caused by a large load acting on the steering device and wear due to minute movement, and to ensure the controllability of the vehicle.

Advantages of the Invention

[0022] The intermediate shaft for a steering device according to the present disclosure has an effect that it is possible to prevent the yoke of the universal joint and the shaft from coming off while suppressing the manufacturing cost.

Brief Description of the Drawings

[0023] [Figure 1] FIG. 1 is a schematic view of a steering device according to an embodiment. [Figure 2] FIG. 2 is a perspective view of a steering device according to an embodiment. [Figure 3] FIG. 3 is a detailed view of the universal joint. [Figure 4] FIG. 4 is a perspective view of the yoke of the universal joint shown in FIG. 3, and is a cross-sectional view of the main part of the yoke. [Figure 5] FIG. 5 is a front view of the yoke shown in FIG. 4 as viewed in the direction along the central axis of the coupling hole. [Figure 6] FIG. 6 is a cross-sectional view taken along line A-A of FIG. 5. [Figure 7] FIG. 7 is a detailed view of the main part of the shaft that fits into the coupling hole of the yoke. [Figure 8] FIG. 8 is a view taken in the direction of arrow B-B of FIG. 7. [Figure 9]Figure 9 is an explanatory diagram showing the shaft fitted into the connecting hole of the yoke. [Figure 10] Figure 10 is a view from the CC arrow in Figure 9. [Figure 11] Figure 11 is an explanatory diagram showing the state in which the shaft end is fitted into the connecting hole of the yoke. [Figure 12] Figure 12 is a cross-sectional view of Figure 10. [Figure 13] Figure 13 is a detailed view of section F in Figure 12. [Figure 14] Figure 14 is a cross-sectional view of EE in Figure 10. [Figure 15] Figure 15 is a detailed view of section G in Figure 14. [Figure 16] Figure 16 is a view from the direction of arrow HH in Figure 13. [Figure 17] Figure 17 is a view from the JJ arrow in Figure 15. [Figure 18] Figure 18 is a modified example of the intermediate shaft according to the embodiment, illustrating the case where a groove is formed on the base side of the shaft end. [Modes for carrying out the invention]

[0024] The present disclosure will be described in detail below with reference to the drawings. However, the present disclosure is not limited to the embodiments described below. Furthermore, the components in the embodiments below include those easily conceivable by those skilled in the art, those substantially identical, and those within the scope of equivalents. Moreover, the components disclosed in the embodiments below can be combined as appropriate.

[0025] [Embodiment] Figure 1 is a schematic diagram of the steering device 80 according to the embodiment. Figure 2 is a perspective view of the steering device 80 according to the embodiment. As shown in Figure 1, the steering device 80 is connected to a stub shaft 87 and includes a steering wheel 81, a steering shaft 82, a steering force assist mechanism 83, a universal joint 30, an intermediate shaft 10, and another universal joint 30, in the order in which the force applied by the operator is transmitted. In the steering device 80 according to the embodiment, the steering force assist mechanism 83 is located closer to the steering wheel 81 and is positioned inside the vehicle cabin, separated from the outside.

[0026] In this embodiment, the steering shaft 82, intermediate shaft 10, stub shaft 87, and universal joint 30 are described as different components for convenience. However, the steering shaft 82, intermediate shaft 10, and stub shaft 87 each include yokes 31 and 50 (see Figure 3) that are part of the universal joint 30 and fit onto each shaft. In other words, the universal joint 30 positioned between the steering shaft 82 and the intermediate shaft 10 is composed of the yokes 31 and 50 of the steering shaft 82 and the intermediate shaft 10, and a cross shaft 55 (see Figure 3) that connects these yokes 31 and 50. Similarly, the universal joint 30 positioned between the intermediate shaft 10 and the stub shaft 87 is composed of the yokes 31 and 50 of the intermediate shaft 10 and the stub shaft 87, and a cross shaft 55 that connects these yokes 31 and 50.

[0027] A steering wheel 81 is attached to one end of the steering shaft 82, and an intermediate shaft 10 is connected to the other end of the steering shaft 82 via a universal joint 30. The steering shaft 82 rotates due to the torque input from the steering wheel 81. The steering shaft 82 includes an input shaft 82a, an output shaft 82b, and a torsion bar (not shown). The torsion bar is connected to both the input shaft 82a and the output shaft 82b, and the input shaft 82a and the output shaft 82b are connected via the torsion bar. The steering wheel 81 is attached to the steering shaft 82 by being connected to one end of the input shaft 82a, and a torsion bar extends from the other end of the input shaft 82a. A torsion bar extends from one end of the output shaft 82b, and the other end is connected to the intermediate shaft 10 via a universal joint 30. Rotational torque is transmitted between the input shaft 82a and the output shaft 82b via the torsion bar connected to both.

[0028] As shown in Figure 1, the intermediate shaft 10 has universal joints 30 at both ends in the extending direction. Of the universal joints 30 at both ends of the intermediate shaft 10, the universal joint 30a at one end connects the intermediate shaft 10 to the steering shaft 82. Of the universal joints 30 at both ends of the intermediate shaft 10, the universal joint 30b at the other end connects the intermediate shaft 10 to the stub shaft 87. As a result, the intermediate shaft 10 is connected to the steering shaft 82 at one end and to the stub shaft 87 at the other end via the universal joints 30. The universal joints 30 are, for example, cardan joints. The end of the stub shaft 87 opposite to the side connected to universal joint 30b is connected to the steering gear 88. The rotation of the steering shaft 82 is transmitted to the stub shaft 87 via the intermediate shaft 10. That is, the intermediate shaft 10 rotates in conjunction with the steering shaft 82.

[0029] As shown in Figure 1, the steering gear 88 includes a pinion gear 88a and a rack 88b. The pinion gear 88a is connected to a stub shaft 87. The rack 88b meshes with the pinion gear 88a. The steering gear 88 converts the rotational motion transmitted to the pinion gear 88a into linear motion using the rack 88b. The rack 88b is connected to a tie rod 89. The movement of the rack 88b changes the angle of the wheels.

[0030] As shown in Figure 1, the steering force assist mechanism 83 includes a reduction gear 92 and an electric motor 94. The reduction gear 92 is, for example, a worm gear reduction gear. The reduction gear 92 increases the torque generated by the electric motor 94 and transmits it to the output shaft 82b. In this way, the reduction gear 92 provides auxiliary steering torque to the output shaft 82b. The steering device 80 is a column-assist type electric power steering device. A column-assist type electric power steering device refers to a power steering device that applies assist torque generated by the electric motor 94 to the steering shaft 82 connected to the steering wheel 81.

[0031] As shown in Figure 1, the steering device 80 includes an ECU (Electronic Control Unit) 90, a torque sensor 91, and a vehicle speed sensor 95. The electric motor 94, torque sensor 91, and vehicle speed sensor 95 are electrically connected to the ECU 90. The torque sensor 91 outputs the steering torque transmitted to the input shaft 82a to the ECU 90 as an analog signal. The vehicle speed sensor 95 detects the driving speed (vehicle speed) of the vehicle on which the steering device 80 is mounted. The vehicle speed sensor 95 is mounted on the vehicle body and outputs the vehicle speed to the ECU 90 via CAN communication.

[0032] The ECU 90 controls the operation of the electric motor 94. The ECU 90 acquires signals from the torque sensor 91 and the vehicle speed sensor 95. When the ignition switch 98 is ON, the ECU 90 is supplied with power from the power supply unit 99 (e.g., the vehicle's battery). The ECU 90 calculates an auxiliary steering command value based on the steering torque and vehicle speed. The ECU 90 adjusts the power value supplied to the electric motor 94 based on the auxiliary steering command value. The ECU 90 acquires information on the induced voltage of the electric motor 94 or information output from a resolver or the like provided on the electric motor 94. By controlling the electric motor 94, the force required to operate the steering wheel 81 is reduced.

[0033] Figure 3 is a detailed view of the universal joint 30. Although Figure 3 shows a universal joint 30b connecting the intermediate shaft 10 and the stub shaft 87 for illustrative purposes, a universal joint 30a connecting the intermediate shaft 10 and the steering shaft 82 is configured similarly.

[0034] The universal joint 30 has a yoke 31 on the intermediate shaft 10, a yoke 50 on the shaft member connected to the intermediate shaft 10 via the universal joint 30, and a cross shaft 55. In the universal joint 30b shown in Figure 3, the shaft member connected to the intermediate shaft 10 via the universal joint 30 is a stub shaft 87, and the yoke 50 shown in Figure 3 is attached to the stub shaft 87.

[0035] The cross shaft 55 is a component formed by combining two orthogonal shafts. The yoke 31 attached to the intermediate shaft 10 and the yoke 50 attached to the stub shaft 87 are each formed with a bifurcated shape on the opposite side of the side attached to the intermediate shaft 10 or stub shaft 87. One of the two orthogonal shafts of the cross shaft 55 is rotatably attached at both ends to the bifurcated portion of the yoke 31 attached to the intermediate shaft 10. The other of the two orthogonal shafts of the cross shaft 55 is rotatably attached at both ends to the bifurcated portion of the yoke 50 attached to the stub shaft 87.

[0036] As described above, the universal joint 30 allows for the connection of two shaft members while varying the relative angle between them, by connecting the yokes 31 and 50, which are attached to the two shaft members connected by the universal joint 30, via the cross shaft 55.

[0037] Figure 4 is a perspective view of the yoke 31 of the universal joint 30 shown in Figure 3, and is a cross-sectional view of the main part of the yoke 31. Figure 5 is a front view of the yoke 31 shown in Figure 4, viewed in the direction along the central axis of the coupling hole 33. Figure 6 is a cross-sectional view of AA in Figure 5. The yoke 31 of the universal joint 30 is attached to the intermediate shaft 10 by fitting the end of the shaft 11 used as the intermediate shaft 10 into the coupling hole 33 formed in the yoke 31. The intermediate shaft 10 has a shaft 11 used as the intermediate shaft 10 and the yoke 31 of the universal joint 30. The yoke 31 of the universal joint 30 has a base 32 in which the coupling hole 33 is formed, and a yoke arm 37 extending from the base 32 into which the cross shaft 55 (see Figure 3) of the universal joint 30 is fitted.

[0038] The base portion 32 is a substantially circular plate-shaped member, and the connecting hole 33 formed in the base portion 32 is a substantially circular hole that penetrates the base portion 32 in the thickness direction. More specifically, the base portion 32 has a recessed hole 36, which is a substantially circular bottomed hole, formed on one surface in the thickness direction, and the connecting hole 33 is formed by penetrating the base portion 32 in the thickness direction, from the bottom surface 36a of the recessed hole 36 to the surface of the base portion 32 opposite to the surface in the thickness direction of the base portion 32 where the recessed hole 36 is formed. A chamfer 33a is formed on the end of the connecting hole 33 opposite to the side where the recessed hole 36 is located.

[0039] The connecting hole 33 formed in the base portion 32 has a hole-side serration 34 on its inner circumferential surface, which is a hole-side uneven surface. The hole-side serration 34 is formed by a plurality of recesses 35 that are recessed toward the outward direction in the radial direction of the connecting hole 33 and extend in a direction along the central axis of the connecting hole 33, and are arranged in a line in the circumferential direction of the connecting hole 33. In other words, the hole-side serration 34 is formed by a plurality of protrusions that are convex toward the inward direction in the radial direction of the connecting hole 33 and extend in a direction along the central axis of the connecting hole 33, and are arranged in a line in the circumferential direction of the connecting hole 33. That is, the hole-side serration 34 is formed by the alternating arrangement of recesses 35 and protrusions that extend in a direction along the central axis of the connecting hole 33 in a repeated manner in the circumferential direction of the connecting hole 33.

[0040] In this embodiment, the hole-side irregularities are formed by hole-side serrations 34, but the hole-side irregularities may be formed by means other than serrations. For example, the hole-side irregularities may be formed by a so-called spline in which recesses and protrusions extending in a direction along the central axis of the connecting hole 33 are alternately and repeatedly arranged in the circumferential direction of the connecting hole 33.

[0041] The yoke arm 37 is positioned on the side of the base 32 where the recessed hole 36 is formed in the thickness direction, and is located radially outward of the recessed hole 36 in the base 32, i.e., radially outward of the coupling hole 33. The yoke arm 37 protrudes from the radially outward position of the recessed hole 36 in the thickness direction of the base 32 and is formed to extend in a direction parallel to the thickness direction of the base 32. Two yoke arms 37 are arranged on one yoke 31. The two yoke arms 37 are positioned on both sides of the coupling hole 33. That is, the two yoke arms 37 are positioned approximately 180° apart from each other in the circumferential direction of the coupling hole 33.

[0042] Each of the two yoke arms 37 has a support hole 38 formed in it, into which the cross shaft 55 is fitted and supported. The support holes 38 formed in the two yoke arms 37 are positioned and oriented such that their central axes coincide. That is, the two support holes 38 are positioned on each other's extension lines. As a result, the two yoke arms 37 can rotatably support the cross shaft 55 by inserting both ends of one of the two orthogonal shafts into the support holes 38 formed in each of the two yoke arms 37. Thus, when the yoke 31 is viewed along the central axis of the connecting hole 33, the central axes of the two support holes 38 are positioned on the central axis of the connecting hole 33.

[0043] The hole-side serrations 34 formed on the inner circumferential surface of the connecting hole 33 have recesses 35 that are recessed outward in the radial direction of the connecting hole 33, with multiple widths in the circumferential direction of the connecting hole 33. Specifically, the hole-side serrations 34 have a first recess 35a with a relatively small width in the circumferential direction of the connecting hole 33, and a second recess 35b with a larger width in the circumferential direction of the connecting hole 33 than the first recess 35a. The first recess 35a of the hole-side serrations 34 is located in the circumferential direction of the connecting hole 33 within the range where the yoke arm 37 is positioned. The second recess 35b of the hole-side serrations 34 is located in a position different from the position where the yoke arm 37 is positioned in the circumferential direction of the connecting hole 33.

[0044] In this embodiment, the first recess 35a is positioned in a predetermined range on both sides of the circumferential direction of the coupling hole 33, centered on the position through which the central axes of the two support holes 38 formed in the two yoke arms 37 pass when the yoke 31 is viewed in a direction along the central axis of the coupling hole 33. In other words, the first recess 35a is positioned in a predetermined range on both sides of the circumferential direction of the coupling hole 33, centered on the line connecting the respective center positions in the width direction (left-right direction in Figure 5) of the two yoke arms 37 when the yoke 31 is viewed in a direction along the central axis of the coupling hole 33.

[0045] The second recess 35b is located in a predetermined range on both sides of the circumferential direction of the connecting hole 33, with respect to a hypothetical line that is inclined 90° with respect to the center of the connecting hole 33 relative to the central axis of the two support holes 38 formed in the two yoke arms 37, when the yoke 31 is viewed in a direction along the central axis of the connecting hole 33. In other words, the second recess 35b is located in a predetermined range on both sides of the circumferential direction of the connecting hole 33, with respect to a hypothetical line that is inclined 90° with respect to the center of the connecting hole 33 relative to the line connecting the center positions in the width direction (left-right direction in Figure 5) of the two yoke arms 37, when the yoke 31 is viewed in a direction along the central axis of the connecting hole 33.

[0046] In other words, as shown in Figure 5, when the two yoke arms 37 are positioned vertically and the yoke 31 is viewed along the central axis of the connecting hole 33, the first recess 35a is located within a predetermined range in the vertical direction, and the second recess 35b is located within a predetermined range in the horizontal direction.

[0047] Figure 7 is a detailed view of the main part of the shaft 11 that fits into the coupling hole 33 of the yoke 31. Figure 8 is a view taken along arrow BB in Figure 7. The shaft 11, which is used as an intermediate shaft 10 and fits into the coupling hole 33 of the yoke 31, has shaft-side serrations 14 formed on the outer circumferential surface near its end. The shaft-side serrations 14 are provided as shaft-side protrusions that are press-fitted into the hole-side serrations 34 formed in the coupling hole 33 of the yoke 31, and are formed on the shaft end 12 formed at the end of the shaft 11. The shaft end 12 has a smaller diameter than the main part of the shaft 11, and a chamfered portion 13 is formed between the main part of the shaft 11 and the shaft end 12, inclined with respect to the axis of the shaft 11 in a direction in which the diameter decreases from the main part of the shaft 11 toward the shaft end 12.

[0048] The shaft-side serrations 14 are formed on the outer circumferential surface of the shaft end portion 12, which has a smaller diameter than the main portion of the shaft 11. Specifically, the shaft end portion 12 is approximately the same size as the diameter of the coupling hole 33 formed in the yoke 31. Therefore, the shaft 11 can be fitted into the coupling hole 33 by fitting the shaft end portion 12 into the coupling hole 33.

[0049] The shaft-side serrations 14 are formed by multiple convex portions 15 extending in a direction along the axis of the shaft 11, which are convex outward in the radial direction of the shaft end 12 of the shaft 11, and are arranged in a line around the circumferential direction of the shaft end 12. In other words, the shaft-side serrations 14 are formed by multiple concave portions extending in a direction along the axis of the shaft 11, which are concave inward in the radial direction of the shaft end 12 of the shaft 11, and are arranged in a line around the circumferential direction of the shaft end 12. That is, the shaft-side serrations 14 are formed by the alternating arrangement of convex portions 15 and concave portions extending in a direction along the axis of the shaft 11, in a line around the circumferential direction of the shaft end 12.

[0050] In this embodiment, the shaft-side uneven portion is formed by shaft-side serrations 14, but the shaft-side uneven portion may be formed by means other than serrations. For example, the shaft-side uneven portion may be formed by a so-called spline in which protrusions and recesses extending in a direction along the axis of the shaft 11 are alternately and repeatedly arranged in the circumferential direction of the shaft end portion 12.

[0051] The shaft-side serrations 14 formed on the outer circumferential surface of the shaft end portion 12 of the shaft 11 have convex portions 15 that protrude outward in the radial direction of the shaft end portion 12, and these convex portions have multiple widths in the circumferential direction of the shaft end portion 12. Specifically, the shaft-side serrations 14 have a first convex portion 15a with a relatively small width in the circumferential direction of the shaft end portion 12, and a second convex portion 15b with a larger width in the circumferential direction of the shaft end portion 12 than the first convex portion 15a.

[0052] Of these, the first protrusion 15a has a circumferential width at the shaft end 12 of the shaft 11 that is approximately the same size as the circumferential width of the first recess 35a of the hole-side serration 34 formed in the coupling hole 33 of the yoke 31, and is substantially the same size. In contrast, the second protrusion 15b has a circumferential width at the shaft end 12 of the shaft 11 that is smaller than the circumferential width of the second recess 35b of the hole-side serration 34 formed in the coupling hole 33 of the yoke 31.

[0053] As described above, the first protrusion 15a and the second protrusion 15b of the axial-side serration 14 formed on the axial end 12 of the shaft 11 are positioned in a range in the circumferential direction of the axial end 12 that corresponds to the range in the circumferential direction of the hole-side serration 34 formed on the coupling hole 33 of the yoke 31, where the first recess 35a and the second recess 35b are positioned. In other words, when viewing the shaft 11 in the axial direction, the first protrusion 15a and the second protrusion 15b of the axial-side serration 14 are positioned such that a straight line passing through the center of the range in the circumferential direction of the axial end 12 and the axis of the axial end 12 intersects at a 90° angle with a straight line passing through the center of the range in the circumferential direction of the axial end 12 and the axis of the axial end 12.

[0054] Therefore, as shown in Figure 8, when the shaft end 12 is viewed in the direction along the axial direction of the shaft 11 with the position of the first protrusion 15a of the shaft-side serration 14 positioned in the vertical direction, the second protrusion 15b is positioned within a predetermined range in the left-right direction.

[0055] Figure 9 is an explanatory diagram showing the state in which the shaft 11 is fitted into the coupling hole 33 of the yoke 31. Figure 10 is a view from arrow CC in Figure 9. When fitting the shaft 11 into the coupling hole 33 of the yoke 31, the shaft end 12 of the shaft 11 is inserted into the coupling hole 33 of the yoke 31 and fitted into the coupling hole 33. The shaft 11 to be fitted into the coupling hole 33 of the yoke 31 is fitted by inserting the shaft end 12 into the coupling hole 33 from the opposite side of the yoke 31 from the side where the yoke arm 37 is located. Therefore, when the shaft end 12 of the shaft 11 is fitted into the coupling hole 33 of the yoke 31, the shaft 11 that fits into the coupling hole 33 extends to the opposite side of the base 32 from the side where the yoke arm 37 is located.

[0056] When fitting the shaft 11 into the coupling hole 33 of the yoke 31, the shaft 11 is fitted in such a orientation that the first protrusion 15a of the shaft-side serration 14 formed on the shaft end 12 is positioned at the location of the first recess 35a of the hole-side serration 34 formed in the coupling hole 33, and the second protrusion 15b of the shaft-side serration 14 is positioned at the location of the second recess 35b of the hole-side serration 34.

[0057] Figure 11 is an explanatory diagram showing the state in which the shaft end 12 of the shaft 11 is fitted into the coupling hole 33 of the yoke 31. The first protrusion 15a of the shaft-side serration 14 formed on the shaft end 12 of the shaft 11 has a width in the circumferential direction of the shaft end 12 that is approximately the same as the width in the circumferential direction of the first recess 35a of the hole-side serration 34 formed in the coupling hole 33 of the yoke 31. Therefore, when fitting the shaft end 12 of the shaft 11 into the coupling hole 33 of the yoke 31, the shaft-side serration 14 formed on the shaft end 12 is press-fitted into the hole-side serration 34 formed in the coupling hole 33. In other words, the first protrusion 15a of the shaft-side serration 14 formed on the shaft end 12 is press-fitted into the first recess 35a of the hole-side serration 34 formed in the coupling hole 33.

[0058] On the other hand, the second protrusion 15b of the shaft-side serration 14 formed on the shaft end 12 of the shaft 11 has a width in the circumferential direction of the shaft end 12 that is smaller than the width in the circumferential direction of the second recess 35b of the hole-side serration 34 formed in the coupling hole 33 of the yoke 31. Therefore, when the first protrusion 15a of the shaft-side serration 14 formed on the shaft end 12 is press-fitted into the first recess 35a of the hole-side serration 34 formed in the coupling hole 33, the second protrusion 15b of the shaft-side serration 14 will have gaps on both sides in the circumferential direction relative to the second recess 35b of the hole-side serration 34.

[0059] In other words, when the shaft-side serration 14 is press-fitted into the hole-side serration 34, the second protrusion 15b of the shaft-side serration 14 is positioned inside the second recess 35b of the hole-side serration 34, with a gap between it and the second recess 35b of the hole-side serration 34 on both sides in the circumferential direction. Preferably, the circumferential gap between the second protrusion 15b of the shaft-side serration 14 and the second recess 35b of the hole-side serration 34 is within the range of 1° to 5°.

[0060] As described above, when the shaft-side serration 14 is press-fitted into the hole-side serration 34, the meshing state between the first protrusion 15a and the first recess 35a is different from the meshing state between the second protrusion 15b and the second recess 35b. When the shaft-side serration 14 is press-fitted into the hole-side serration 34, among the parts where the meshing states are different as described above, the part where the first protrusion 15a and the first recess 35a mesh becomes the first meshing part 41, and the part where the second protrusion 15b and the second recess 35b mesh becomes the second meshing part 42.

[0061] The first meshing portion 41 is the portion that presses the first protrusion 15a into the first recess 35a, so the first meshing portion 41 is the portion where the hole-side serration 34 and the shaft-side serration 14 are in contact without any gap in the circumferential direction of the shaft 11 between them. The second meshing portion 42 is the portion where the second protrusion 15b is positioned inside the second recess 35b with a gap between it and the second recess 35b, so the second meshing portion 42 is the portion where there is a gap in the circumferential direction of the shaft 11 between the hole-side serration 34 and the shaft-side serration 14.

[0062] Furthermore, the width of the second meshing portion 42 in the circumferential direction of the shaft 11 is smaller than that of the first meshing portion 41. As a result, the width of the protrusions 15 of the shaft-side serrations 14 in the second meshing portion 42 in the circumferential direction of the shaft 11 is smaller than the width of the protrusions 15 of the shaft-side serrations 14 in the first meshing portion 41.

[0063] Furthermore, since the first meshing portion 41 is the portion where the first protrusion 15a formed on the shaft 11 and the first recess 35a formed on the yoke 31 mesh, the first meshing portion 41 is located in the area where the yoke arm 37 (see Figure 10) is positioned in the circumferential direction of the coupling hole 33 of the yoke 31 or the shaft 11. In this embodiment, the first meshing portion 41 is positioned in a predetermined area on both sides in the circumferential direction of the shaft 11 or the coupling hole 33, with the line connecting the center positions in the width direction of the two yoke arms 37 of the yoke 31 as the center.

[0064] Furthermore, since the second meshing portion 42 is the portion where the second protrusion 15b formed on the shaft 11 and the second recess 35b formed on the yoke 31 mesh, the second meshing portion 42 is located in a position different from the position where the yoke arm 37 is arranged in the circumferential direction of the shaft 11. In this embodiment, the second meshing portion 42 is located in a predetermined range on both sides in the circumferential direction of the shaft 11 or the coupling hole 33, with respect to a virtual line that is inclined 90° with respect to the axis of the shaft 11 relative to the line connecting the center positions in the width direction of the two yoke arms 37 when viewed in the direction along the axial direction of the shaft 11.

[0065] The hole-side serrations 34 and shaft-side serrations 14, which have a first meshing portion 41 and a second meshing portion 42 at these positions, mesh with the first convex portion 15a and the first concave portion 35a in a press-fit state at the first meshing portion 41, and mesh with the second convex portion 15b and the second concave portion 35b in a circumferential gap at the second meshing portion 42.

[0066] Furthermore, the shaft 11, which is fitted into the coupling hole 33 by press-fitting the shaft-side serrations 14 into the hole-side serrations 34, has a first crimping portion 21 and a second crimping portion 22 that protrude radially outward from the shaft 11 on the side where the yoke arm 37 is located in the axial direction of the shaft 11 relative to the coupling hole 33.

[0067] The first crimping portion 21 is located in the circumferential direction of the shaft 11 at the position where the first engagement portion 41 is positioned. In this embodiment, the first crimping portion 21 is positioned so as to coincide with the line connecting the center positions in the width direction of the two yoke arms 37 of the yoke 31 when viewed in the direction along the axial direction of the shaft 11.

[0068] Furthermore, the second crimping portion 22 is located in the circumferential direction of the shaft 11 at the position where the second engagement portion 42 is positioned. In this embodiment, the second crimping portion 22 is positioned so as to coincide with a virtual line that is inclined 90° around the axis of the shaft 11 with respect to the line connecting the center positions in the width direction of the two yoke arms 37, when viewed in the direction along the axial direction of the shaft 11.

[0069] Figure 12 is a cross-sectional view of section DD of Figure 10. Figure 13 is a detailed view of section F of Figure 12. The shaft end 12 of the shaft 11 is inserted into the coupling hole 33 from the opposite side of the base 32 of the yoke 31 where the yoke arm 37 is positioned. When fitting the shaft end 12 into the coupling hole 33, the shaft end 12 is inserted to a position where the relative movement of the shaft 11 with respect to the yoke 31 toward the side where the yoke arm 37 is located is restricted. In this embodiment, the shaft end 12 of the shaft 11 is inserted into the coupling hole 33 to a position where the chamfered portion 13 formed on the shaft 11 abuts against the chamfer 33a formed in the coupling hole 33 of the yoke 31.

[0070] The shaft 11, inserted into the coupling hole 33 from the opposite side of the yoke 31 where the yoke arm 37 is positioned, has its relative movement restricted toward the side where the yoke arm 37 is located, as the chamfered portion 13 of the shaft 11 abuts against the chamfer 33a formed in the coupling hole 33 of the yoke 31. The chamfered portion 13 formed on the shaft 11 is provided as a movement restricting portion that restricts the relative movement between the shaft 11 and the yoke 31 by abutting against the yoke 31 in this way.

[0071] The first crimping portion 21 is positioned between the position of the axial end 17 of the shaft 11 at the shaft end 12 and the bottom surface 36a of the recessed hole 36 formed in the base 32 of the yoke 31, when the shaft end 12 of the shaft 11 is fitted into the coupling hole 33 of the yoke 31. Thus, the first crimping portion 21 is formed to protrude radially outward from the shaft 11 at the position between the position of the end 17 at the shaft end 12 and the bottom surface 36a of the recessed hole 36 formed in the base 32 of the yoke 31.

[0072] Furthermore, the first crimping portion 21 is positioned between the base portion 32 of the yoke 31 and the straight portion 16 of the axial serration 14. In this case, the straight portion 16 of the axial serration 14 is the part of the axial serration 14 that extends in the axial direction of the shaft 11. More specifically, the straight portion 16 of the axial serration 14 passes through the axis of the shaft 11 and is the part of the cross-section of the axial serration 14 in the cross-section of the shaft 11 along the axis of the shaft 11 that extends in the axial direction of the shaft 11. The straight portion 16 of the axial serration 14 is, for example, the part of each convex portion 15 of the axial serration 14 that extends parallel to the axial direction of the shaft 11 at the radially outer end of the shaft 11, or the part that extends parallel to the axial direction of the shaft 11 between adjacent convex portions 15.

[0073] The first crimping portion 21 is positioned between the bottom surface 36a of the recessed hole 36 formed in the base portion 32 of the yoke 31 and the end portion 17 of the shaft end portion 12 of the shaft 11, without having a straight portion 16 of the shaft-side serration 14 between the bottom surface 36a of the recessed hole 36 and the shaft end portion 17 of the shaft end portion 12. Therefore, the first crimping portion 21 formed on the shaft end portion 12 of the shaft 11 has no gap with the bottom surface 36a of the recessed hole 36 and is positioned in substantially contact with the bottom surface 36a of the recessed hole 36.

[0074] As a result, the relative movement of the shaft 11 to the side opposite to the side where the yoke arm 37 is positioned relative to the yoke 31 is restricted by the first crimping portion 21 that contacts the bottom surface 36a of the recessed hole 36. The relative movement of the shaft 11 to the side where the yoke arm 37 is positioned relative to the yoke 31 is restricted by the contact between the chamfered portion 13 of the shaft 11 and the chamfer 33a of the coupling hole 33. Therefore, the relative movement of the shaft 11 in the axial direction relative to the yoke 31, when fitted into the coupling hole 33 of the yoke 31, is restricted in any direction.

[0075] Figure 14 is a cross-sectional view of section EE in Figure 10. Figure 15 is a detailed view of section G in Figure 14. The second crimping section 22 is positioned similarly to the first crimping section 21, between the position of the axial end 17 of the shaft 11 at the shaft end 12 and the bottom surface 36a of the recessed hole 36 formed in the base 32 of the yoke 31, when the shaft end 12 of the shaft 11 is fitted into the coupling hole 33 of the yoke 31. Thus, the second crimping section 22 is formed to protrude radially outward from the shaft 11 at a position between the position of the end 17 at the shaft end 12 and the bottom surface 36a of the recessed hole 36 formed in the base 32 of the yoke 31.

[0076] Furthermore, the second crimping portion 22 is located closer to the end 17 of the shaft 11 than the first crimping portion 21 in the axial direction of the shaft 11. As a result, the second crimping portion 22 is positioned between itself and the base 32 of the yoke 31, with a straight portion 16 of the axial serration 14. In other words, the second crimping portion 22 is positioned between itself and the bottom surface 36a of the recessed hole 36 formed in the base 32 of the yoke 31, with, for example, a convex portion 15 of the axial serration 14 or a portion between adjacent convex portions 15 that extends parallel to the axial direction of the shaft 11. Therefore, the second crimping portion 22 has a gap between itself and the bottom surface 36a of the recessed hole 36 formed in the base 32 of the yoke 31, and is positioned away from the bottom surface 36a of the recessed hole 36.

[0077] The first crimped portion 21 and the second crimped portion 22, which are formed on the shaft end 12 of the shaft 11 in this manner, are formed using a crimping jig or device while the shaft end 12 of the shaft 11 is fitted into the coupling hole 33 of the yoke 31.

[0078] Figure 16 is a view taken along the HH arrow in Figure 13. Figure 17 is a view taken along the JJ arrow in Figure 15. The first crimping portion 21 and the second crimping portion 22 have approximately the same width in the circumferential direction of the shaft 11. The first crimping portion 21 is formed in the area where the first protrusions 15a of the shaft-side serration 14 are located, and extends across multiple first protrusions 15a. For example, the first crimping portion 21 is formed across four first protrusions 15a.

[0079] In contrast, the second crimping portion 22 is formed in the area where the second protrusion 15b is located on the axial side serration 14, but the width of the second protrusion 15b is greater than the width of the first protrusion 15a. For this reason, the number of second crimping portions 22 formed on the second protrusion 15b is fewer than the number of first crimping portions 21 formed on the first protrusion 15a. The second crimping portion 22 may be formed in the area where one second protrusion 15b is located, or it may be formed over three second protrusions 15b, one second protrusion 15b and the two second protrusions 15b on either side of it.

[0080] Furthermore, since the first crimping portion 21 and the second crimping portion 22 are formed at the positions where the shaft-side serrations 14 are formed, the shape of the convex portion 15 of the shaft-side serrations 14 is more likely to appear at the radially outer ends of the shaft 11 in the first crimping portion 21 and the second crimping portion 22. In this case, the first crimping portion 21 is formed at the position of the first convex portion 15a, which has a smaller width and pitch in the circumferential direction compared to the second convex portion 15b where the second crimping portion 22 is formed. For this reason, the shape of the convex portion 15 of the shaft-side serrations 14 is more likely to appear at the radially outer end of the first crimping portion 21 than at the second crimping portion 22, that is, the radially outer end of the first crimping portion 21 is more likely to have an uneven shape than the second crimping portion 22.

[0081] Furthermore, since the distance of the second crimping portion 22 from the end 17 of the shaft 11 is smaller than that of the first crimping portion 21, the size of the base material member for the second crimping portion 22 in the axial direction of the shaft 11 is smaller than that of the first crimping portion 21. However, the second crimping portion 22 is formed on a second protrusion 15b, which has a width in the circumferential direction of the shaft 11 that is larger than that of the first protrusion 15a. Therefore, since the size of the base material member for the second crimping portion 22 is larger than that of the base material member for the first crimping portion 21, the strength of the second crimping portion 22 can be ensured even though the distance of the second crimping portion 22 from the end 17 of the shaft 11 is smaller than that of the first crimping portion 21.

[0082] Next, the operation of the steering device 80 according to this embodiment will be described. When the steering wheel 81 is operated while driving a vehicle equipped with the steering device 80, the steering force applied to the steering wheel 81 is transmitted from the steering wheel 81 to the steering shaft 82.

[0083] The steering force transmitted to the steering shaft 82 is transmitted as steering torque from the steering shaft 82 to the intermediate shaft 10 via the universal joint 30a, and from the intermediate shaft 10 to the pinion gear 88a via the universal joint 30b and the stub shaft 87. As a result, the steering gear 88, which has the pinion gear 88a, converts the rotational motion transmitted from the pinion gear 88a into linear motion of the rack 88b, and operates the tie rod 89.

[0084] Furthermore, the steering device 80 according to this embodiment has an electric motor 94 that generates auxiliary steering torque to assist the driver's steering. The electric motor 94 generates auxiliary steering torque based on the steering torque detected by a torque sensor 91 arranged along the steering shaft 82.

[0085] The torque sensor 91 detects the steering torque applied to the steering shaft 82 based on the angle of relative rotation when the input shaft 82a and output shaft 82b of the steering shaft 82 rotate slightly relative to each other due to the twisting of the torsion bar connecting them. The torque sensor 91 outputs the detected steering torque as an electrical signal to the ECU 90.

[0086] The ECU 90 operates the electric motor 94 based on the electrical signal transmitted from the torque sensor 91, generating auxiliary steering torque in the electric motor 94. In other words, the electrical signal transmitted from the torque sensor 91 to the ECU 90 changes based on the steering torque acting between the input shaft 82a and the output shaft 82b of the steering shaft 82. Therefore, the ECU 90 uses the electrical signal transmitted from the torque sensor 91 as information that changes according to the steering torque acting on the steering shaft 82, and adjusts the power value supplied to the electric motor 94 based on the electrical signal transmitted from the torque sensor 91, thereby generating auxiliary steering torque in the electric motor 94.

[0087] Specifically, the ECU 90 acquires a steering torque signal from the torque sensor 91, a vehicle speed signal from the vehicle speed sensor 95, and operational information of the electric motor 94 from a rotation detection device provided on the electric motor 94. Based on this operational information, the steering torque, and the vehicle speed signal, the ECU 90 generates auxiliary steering torque in the electric motor 94. The auxiliary steering torque generated by the electric motor 94 is transmitted to the output shaft 82b of the steering shaft 82 via the reduction gear 92. As a result, the steering force applied by the driver to the steering wheel 81 is assisted by the auxiliary steering torque generated by the electric motor 94, and steering assist control is implemented.

[0088] When the steering wheel 81 is operated, the steering torque is transmitted between the steering shaft 82 and the intermediate shaft 10, and between the intermediate shaft 10 and the stub shaft 87, via the universal joint 30 having the yoke 31. Next, the transmission of torque by the universal joint 30 will be described.

[0089] Between the intermediate shaft 10 and the universal joint 30, steering torque is transmitted by the transmission of rotational torque between the shaft 11 used as the intermediate shaft 10 and the yoke 31 of the universal joint 30. The shaft 11 and the yoke 31 are connected by a serration connection between the shaft-side serrations 14 formed on the shaft end 12 of the shaft 11 and the hole-side serrations 34 formed in the coupling hole 33 of the yoke 31. Therefore, rotational torque is transmitted between the shaft 11 and the yoke 31 by the shaft-side serrations 14 and the hole-side serrations 34.

[0090] Specifically, the shaft-side serration 14 and the hole-side serration 34 have a first meshing portion 41 where they contact each other without any gap in the circumferential direction, and a second meshing portion 42 where there is a gap in the circumferential direction between them. Therefore, the rotational torque between the shaft 11 and the yoke 31 is transmitted by the first meshing portion 41 between the shaft-side serration 14 and the hole-side serration 34. In other words, the rotational torque between the shaft 11 and the yoke 31 is transmitted by the transmission of circumferential force between the first recess 35a of the hole-side serration 34 and the first protrusion 15a of the shaft-side serration 14 that is press-fitted into the first recess 35a.

[0091] In this way, the rotational torque transmitted between the shaft 11 and the yoke 31 is transmitted to the other yoke 50 of the universal joint 30 via the cross shaft 55 fitted into the yoke arm 37 of the yoke 31, and then to the steering shaft 82 or stub shaft 87 to which the yoke 50 is attached. As a result, rotational torque is transmitted between the steering shaft 82 or stub shaft 87 and the intermediate shaft 10 via the universal joint 30.

[0092] Furthermore, the shaft 11 used as the intermediate shaft 10 is fitted into the coupling hole 33 of the yoke 31 such that the chamfered portion 13 of the shaft 11 abuts against the chamfer 33a of the coupling hole 33 of the yoke 31, and the first crimped portion 21 is formed without having a straight portion 16 of the axial serration 14 between the base portion 32 of the yoke 31 and the first crimped portion 21.

[0093] Therefore, the relative movement of the shaft 11 in the axial direction between the yoke 31 of the universal joint 30 and the shaft 11 is restricted in any direction in the axial direction. As a result, when rotational torque is transmitted between the shaft 11 of the intermediate shaft 10 and the universal joint 30, the rotational torque is transmitted without relative movement between the intermediate shaft 10 and the universal joint 30 in the axial direction.

[0094] Here, it is conceivable that the steering device 80 may be subjected to a load greater than the load normally acting on it when the vehicle is in operation. For example, if the vehicle drives onto a curb at high speed, a large load will be applied to the steering device 80. The large load applied to the steering device 80 will become a large force that also acts on the shaft, including the intermediate shaft 10, and if the force acting on the shaft exceeds a predetermined threshold, it may be partially damaged. The steering device 80 according to this embodiment is configured to allow the vehicle to continue operating even if it is partially damaged by such a large force acting on the shaft.

[0095] For example, if a large rotational torque acts between the shaft 11 of the intermediate shaft 10 and the universal joint 30, and the first meshing portion 41 between the hole-side serrations 34 formed in the coupling hole 33 of the yoke 31 and the shaft-side serrations 14 of the shaft 11 is damaged, the first meshing portion 41 will no longer be able to transmit rotational torque.

[0096] In other words, if a large rotational torque acts between the shaft 11 and the yoke 31, and the first convex portion 15a of the shaft-side serration 14 or the first concave portion 35a of the hole-side serration 34 that constitute the first meshing portion 41 is damaged, the rotational torque will no longer be transmitted at the first meshing portion 41 between the shaft-side serration 14 and the hole-side serration 34. In this case, the shaft 11 and the yoke 31 will rotate relative to each other, but the shaft-side serration 14 and the hole-side serration 34 have a second meshing portion 42 in addition to the first meshing portion 41.

[0097] The second meshing portion 42 has a circumferential gap between the second protrusion 15b of the shaft-side serration 14 and the second recess 35b of the hole-side serration 34, with the second protrusion 15b fitting inside the second recess 35b. Therefore, if the first meshing portion 41 is damaged, the shaft 11 and the yoke 31 will rotate relative to each other by the amount of the gap between the second protrusion 15b and the second recess 35b, and when the second protrusion 15b and the second recess 35b of the second meshing portion 42 come into contact due to the relative rotation, rotational torque can be transmitted by the second protrusion 15b and the second recess 35b.

[0098] As a result, even if the first meshing portion 41 is damaged due to a large rotational torque acting between the shaft 11 and the yoke 31, and the rotational torque can no longer be transmitted through the first meshing portion 41, the rotational torque can still be transmitted through the second meshing portion 42.

[0099] At that time, since there is a gap between the second protrusion 15b and the second recess 35b in the second meshing portion 42, the shaft 11 and the yoke 31 rotate relative to each other by the amount of the gap between the second protrusion 15b and the second recess 35b, and after the second protrusion 15b and the second recess 35b come into contact, rotational torque is transmitted. For this reason, when rotational torque is transmitted by the second meshing portion 42, there is a delay between the upstream and downstream sides in the direction of rotational torque transmission. As a result, the driver operating the steering device 80 will feel a delay in the vehicle's movement in response to the operation of the steering wheel 81, making it easy for the driver to feel uncomfortable while operating the vehicle.

[0100] Furthermore, when rotational torque is transmitted by the second meshing portion 42, the rotational torque is transmitted after the second protrusion 15b of the shaft-side serration 14 and the second recess 35b of the hole-side serration 34 come into contact. Therefore, when rotational torque is transmitted by the second meshing portion 42, the rotational torque is transmitted while generating a striking sound that occurs when the second protrusion 15b and the second recess 35b come into contact.

[0101] When the first meshing portion 41 is damaged and the rotational torque is transmitted by the second meshing portion 42, a delay occurs in response to the operation of the steering wheel 81, and a knocking sound is produced. The driver can perceive these effects and recognize the damage to the first meshing portion 41. As a result, the driver can continue driving the vehicle while being aware of the damage to the steering device 80.

[0102] Furthermore, the second protrusion 15b of the shaft-side serration 14 that engages with the hole-side serration 34 at the second engagement portion 42 is wider than the first protrusion 15a, so the strength of the second protrusion 15b is higher than that of the first protrusion 15a. Therefore, even if the first engagement portion 41 is damaged and the rotational torque is transmitted by the second engagement portion 42, the second engagement portion 42 is less likely to be damaged, and the rotational torque can be continuously transmitted by the second engagement portion 42. As a result, the driver can continue to operate the vehicle by operating the steering device 80.

[0103] Furthermore, if the first meshing portion 41 is damaged due to a larger-than-usual load acting on the steering device 80, the shaft 11 and the yoke 31 become more susceptible to relative movement in the axial direction. In other words, while the relative movement of the shaft 11 and the yoke 31 in the axial direction is restricted by the first crimping portion 21, in the first meshing portion 41, the first protrusion 15a of the shaft-side serration 14 is press-fitted into the first recess 35a of the hole-side serration 34. Therefore, the relative movement of the shaft 11 and the yoke 31 in the axial direction is restricted not only by the first crimping portion 21 but also by the fitting force caused by the press-fitting of the first protrusion 15a of the shaft-side serration 14 into the first recess 35a of the hole-side serration 34 in the first meshing portion 41.

[0104] However, if the first engagement portion 41 is damaged, the fitting force between the shaft-side serrations 14 and the hole-side serrations 34 is lost, and the relative movement of the shaft 11 and the yoke 31 in the axial direction is restricted by the first crimping portion 21. For this reason, if a larger-than-usual load is applied to the steering device 80, and a large force is applied that causes the shaft 11 and the yoke 31 to move relative to each other in the axial direction, the first crimping portion 21 may be damaged by this large force. If the first crimping portion 21 is damaged, the first crimping portion 21 will no longer be able to restrict the relative movement of the yoke 31 relative to the shaft 11 towards the side where the yoke arm 37 is located.

[0105] In this case, the yoke 31 moves relative to the shaft 11 on the side where the yoke arm 37 is located due to a force that moves the shaft 11 and the yoke 31 relative to each other in the axial direction. However, in addition to the first crimped portion 21, the shaft 11 also has a second crimped portion 22. The second crimped portion 22 is located closer to the end 17 of the shaft 11 than the first crimped portion 21 in the axial direction of the shaft 11, and is positioned between the second crimped portion 22 and the base 32 of the yoke 31, with a straight portion 16 of the axial serration 14.

[0106] Therefore, if the first crimping portion 21 is damaged and the yoke 31 moves relative to the shaft 11 towards the side where the yoke arm 37 is located, i.e., towards the end 17 of the shaft 11, the yoke 31 will come into contact with the second crimping portion 22 and its movement will be restricted by the second crimping portion 22. Specifically, the bottom surface 36a of the recessed hole 36 formed in the base portion 32 of the yoke 31 comes into contact with the second crimping portion 22, thereby restricting the relative movement of the yoke 31 in the direction in which the end 17 of the shaft 11 is located.

[0107] In this case, although the yoke 31 does not come off the shaft 11, it becomes possible for it to move relative to the shaft in the axial direction between the position where the bottom surface 36a of the recessed hole 36 contacts the second crimping portion 22 and the position where the chamfer 33a of the coupling hole 33 contacts the chamfered portion 13 of the shaft 11. As a result, axial play occurs between the shaft 11 of the intermediate shaft 10 and the universal joint 30, and this play is transmitted to the driver as vibration.

[0108] The driver can recognize damage to the first engagement portion 41 by sensing vibrations transmitted from the steering device 80, in addition to delays in response to the operation of the steering wheel 81 and impact noises. This allows the driver to continue driving the vehicle while recognizing the damage to the steering device 80, and prompts the driver to have the vehicle repaired at a repair shop.

[0109] As described above, the intermediate shaft 10 for the steering device 80 according to this embodiment has a first crimping portion 21 which is positioned between the yoke 31 and the base 32 without having a straight portion 16 of the shaft-side serration 14, and a second crimping portion 22 which is positioned between the yoke 31 and the base 32 with a straight portion 16 of the shaft-side serration 14. Therefore, without welding the yoke 31 and the shaft 11, the relative movement between the yoke 31 and the shaft 11 can be restricted by the first crimping portion 21, and if the first crimping portion 21 is damaged, the relative movement between the yoke 31 and the shaft 11 can be restricted by the second crimping portion 22. Accordingly, the welding process can be omitted, thus reducing welding costs, and even if a part of the steering device 80 is damaged due to a load greater than normal acting on the steering device 80, it is possible to prevent the yoke 31 from coming off the shaft 11. As a result, it is possible to prevent the yoke 31 and the shaft 11 of the universal joint 30 from coming off while keeping manufacturing costs down.

[0110] Furthermore, the bore-side serration 34 and the shaft-side serration 14 are provided with a first meshing portion 41 in which the bore-side serration 34 and the shaft-side serration 14 come into contact without any circumferential gap between them. This allows the shaft 11 and the yoke 31 to be integrated at the first meshing portion 41, thereby transmitting rotational torque between the shaft 11 and the yoke 31. In addition to the first meshing portion 41, the bore-side serration 34 and the shaft-side serration 14 are also provided with a second meshing portion 42 in which there is a circumferential gap between the bore-side serration 34 and the shaft-side serration 14. Therefore, even if the first meshing portion 41 is damaged, rotational torque can still be transmitted by the second meshing portion 42, and the driver can become aware of the damage through a delay in response to the driver's operation or a striking sound. As a result, the controllability of the vehicle when the steering device 80 is damaged can be ensured while allowing the driver to recognize the damage to the steering device 80.

[0111] Furthermore, in the second meshing portion 42, the width of the second protrusion 15b of the shaft-side serration 14 is greater than the width of the first protrusion 15a of the shaft-side serration 14 in the first meshing portion 41, thus ensuring the strength of the protrusion 15 in the second meshing portion 42. As a result, when the first meshing portion 41 is damaged and rotational torque is transmitted by the second meshing portion 42, damage to the second protrusion 15b of the second meshing portion 42 due to rotational torque can be suppressed, and the transmission path of rotational torque by the second meshing portion 42 can be ensured. Consequently, the controllability of the vehicle can be ensured even if the steering device 80 is damaged.

[0112] Furthermore, since the first meshing portion 41 is located in the area where the yoke arm 37 is positioned in the circumferential direction of the shaft 11, loosening of the part that receives a large force when rotational torque is transmitted by the universal joint 30 can be suppressed, and rigidity can be ensured. In other words, when rotational torque is transmitted by the universal joint 30, the torque is transmitted between the two yokes 31 and 50 of the universal joint 30 via the cross shaft 55 supported by the yoke arm 37. For this reason, when rotational torque is transmitted by the universal joint 30, the torque is transmitted mainly in the portion that receives a large force, which is formed in a roughly rectangular shape by the two yoke arms 37, the cross shaft 55 supported by the two yoke arms 37, and the portion connecting the bases of the two yoke arms 37.

[0113] The first meshing portion 41, located in the area where the yoke arm 37 is positioned in the circumferential direction of the shaft 11, and in which the first convex portion 15a is press-fitted into the first recess 35a, is positioned in a substantially rectangular area that receives a large force when transmitting rotational torque. Therefore, the rigidity of the portion that transmits rotational torque by the universal joint 30 can be ensured. In other words, by positioning the first meshing portion 41 in the area where the yoke arm 37 is positioned in the circumferential direction of the shaft 11, loosening of the portion that receives a large force when transmitting rotational torque by the universal joint 30 at the fitting portion between the shaft 11 and the yoke 31 can be suppressed, and rigidity can be ensured.

[0114] Furthermore, since the first meshing portion 41 is located near the base of the yoke arm 37, the bending stress on the protrusion 15 of the axial serration 14 can be reduced when force is transmitted between the yoke arm 37 and the shaft 11 via the base 32 of the yoke 31. In other words, when the first meshing portion 41 is not damaged, torque is transmitted between the shaft 11 and the yoke 31 by the first meshing portion 41, where the first protrusion 15a is press-fitted into the first recess 35a. However, if the first meshing portion 41 is located far from the base of the yoke arm 37, the bending stress generated at the first protrusion 15a during torque transmission tends to be large. In contrast, in this embodiment, the first meshing portion 41 is located within the range in the circumferential direction of the shaft 11 where the yoke arm 37 is positioned, thus being located close to the base of the yoke arm 37, and the bending stress generated at the first protrusion 15a during torque transmission can be reduced.

[0115] This suppresses damage to the first protrusion 15a caused by large bending stress, and thus suppresses damage to the first meshing portion 41. As a result, the steering device 80 is less likely to be damaged even when a large load is applied to it, and the controllability of the vehicle can be ensured.

[0116] Furthermore, although the second meshing portion 42 is located at a different position from the position where the yoke arm 37 is positioned in the circumferential direction of the shaft 11, the second protrusion 15b of the second meshing portion 42 has a greater circumferential width than the first protrusion 15a, thus increasing the strength of the protrusion 15 in the second meshing portion 42. Therefore, even if the first meshing portion 41 is damaged and rotational torque is transmitted by the second meshing portion 42, it is possible to suppress the generation of large stresses at the second protrusion 15b, which is located at a position far from the base of the yoke arm 37. As a result, the controllability of the vehicle can be ensured.

[0117] Furthermore, since the first crimping portion 21 is located in the circumferential direction of the shaft 11 at the position where the first meshing portion 41 is positioned, damage to the first meshing portion 41 can be suppressed. In other words, since the first crimping portion 21 is positioned between the base portion 32 of the yoke 31 and the first crimping portion 21 without having a straight portion 16 of the axial side serration 14, it is positioned without a gap between it and the yoke 31, and relative movement between the shaft 11 and the yoke 31 in the axial direction can be restricted. For this reason, even when a small relative movement occurs between the shaft 11 and the yoke 31 during vehicle operation, the small axial movement between the shaft 11 and the yoke 31 can be suppressed by the first crimping portion 21. As a result, wear due to small movements between the first convex portion 15a and the first concave portion 35a that mesh at the first meshing portion 41 can be suppressed, and damage to the first meshing portion 41 caused by wear can be suppressed.

[0118] Furthermore, since the second crimping portion 22 is located in the circumferential direction of the shaft 11 where the second engagement portion 42 is positioned, even if the first engagement portion 41 is damaged, the second crimping portion 22 can be prevented from being affected by the damage to the first engagement portion 41. As a result, even if the first engagement portion 41 is damaged, damage to the second crimping portion 22 can be prevented, and the relative movement between the shaft 11 and the yoke 31 in the axial direction can be restricted by the second crimping portion 22. As a result, the controllability of the vehicle can be ensured.

[0119] Furthermore, because the first meshing portion 41 is positioned near the base of the yoke arm 37, the bending stress on the protrusions 15 of the shaft-side serrations 14 when force is transmitted between the yoke arm 37 and the shaft 11 can be reduced, thereby suppressing damage to the protrusions 15 of the shaft-side serrations 14 and thus suppressing damage to the first meshing portion 41. In addition, because the first crimping portion 21 is positioned in the circumferential direction of the shaft 11 where the first meshing portion 41 is located, the first crimping portion 21 can suppress minute movements in the axial direction between the shaft 11 and the yoke 31, thereby suppressing damage to the first meshing portion 41 caused by wear due to minute movements. Consequently, damage to the steering device 80 due to large loads acting on it and wear due to minute movements can be suppressed, and as a result, the controllability of the vehicle can be ensured.

[0120] [Differentiation] In the above-described embodiment, a chamfered portion 13 is formed on the shaft 11 as a movement restricting portion that restricts the relative movement between the shaft 11 and the yoke 31 together with the first crimping portion 21. However, the movement restricting portion may be formed by something other than the chamfered portion 13. Figure 18 is a modified example of the intermediate shaft 10 according to the embodiment, and is an explanatory diagram showing the case in which a groove portion 18 is formed on the base side of the shaft end portion 12 of the shaft 11. The portion of the shaft end portion 12 of the shaft 11 opposite to the end portion 17, that is, the portion on the base side of the shaft end portion 12, may be formed in a shape other than the chamfered portion 13 as in the above-described embodiment. For example, as shown in Figure 18, a groove portion 18 may be formed. In this case, the groove portion 18 is a groove formed around the circumference of the shaft 11 on the base side of the shaft end portion 12. Also, since the shaft end portion 12 has a smaller diameter than the main portion of the shaft 11, the outer diameter of the groove wall of the groove portion 18 is larger on the main portion side of the shaft 11 than on the groove wall on the shaft end portion 12 side. In other words, of the groove walls of the groove portion 18, the end face 18a, which is the groove wall located on the side of the main part of the shaft 11, has an outer diameter that is larger than the outer diameter of the shaft end portion 12.

[0121] When the shaft end 12 of the shaft 11, in which the groove 18 is formed, is fitted into the coupling hole 33 of the yoke 31, the end of the base 32 of the yoke 31 opposite to the side where the yoke arm 37 is positioned comes into contact with the end face 18a of the groove 18. This restricts the relative movement of the shaft 11 toward the side where the yoke arm 37 is located. The end face 18a of the groove 18 formed on the shaft 11 is provided as a movement restricting part that restricts the relative movement between the shaft 11 and the yoke 31 by coming into contact with the yoke 31 in this way. That is, the movement restricting part may be formed by creating a groove 18 on the shaft 11 and using the end face 18a of the groove 18 as the movement restricting part. The form of the movement restricting part is not limited as long as it can restrict the relative movement of the shaft 11 and the yoke 31 in the axial direction.

[0122] While preferred embodiments of this disclosure have been described above, this disclosure is not limited to those described in the embodiments described above. The configurations described as embodiments and modifications may be combined as appropriate. [Explanation of symbols]

[0123] 10 Intermediate shaft 11 shafts 12 Shaft end 13 Chamfered section 14. Axial serrations 15 Convex part 15a First protrusion 15b Second protrusion 16. Straight section 17 End 18 grooves 18a End face 21 First crimping section 22 Second crimping section 30 Universal joint 31 York 32 Base 33 Binding hole 33a Chamfer 34 Hole-side serrations 35 recess 35a First recess 35b Second recess 36 recessed holes 36a Bottom 37 Yoke Arm 41 First interlocking section 42 Second interlocking section 50 York 55 Cross axis 80 Steering system 81 Steering Wheel 82 Steering shaft 83 Steering force assist mechanism 87 Stub Shaft 88 Steering gear 89 Tie Rod 90 ECU 91 Torque sensor 92 Reducer 94 Electric motor

Claims

1. A yoke of a universal joint having a coupling hole with a hole-side uneven surface formed on its inner circumferential surface, A shaft is formed on its outer surface, which is press-fitted into the hole-side protrusions, and the shaft fits into the coupling hole. Equipped with, The yoke has a base portion in which the coupling hole is formed, and a yoke arm extending from the base portion into which the cross shaft of the universal joint is fitted. The shaft that fits into the coupling hole extends to the side opposite to the side of the base where the yoke arm is positioned, The shaft that fits into the coupling hole has a first crimping portion and a second crimping portion that protrude radially outward from the shaft on the side where the yoke arm is located in the axial direction of the shaft relative to the coupling hole, The cross-section of the shaft-side irregularities between the second crimping portion and the base portion has a straight portion that extends in the axial direction of the shaft, and the second crimping portion is positioned therein. An intermediate shaft for a steering device, wherein the cross-section of the shaft-side uneven portion between the first crimping portion and the base portion has the first crimping portion arranged without having the straight portion.

2. The intermediate shaft for a steering device according to claim 1, wherein the hole-side uneven portion and the shaft-side uneven portion are provided with a first meshing portion in which the hole-side uneven portion and the shaft-side uneven portion contact each other without a gap in the circumferential direction of the shaft between them, and a second meshing portion in which there is a gap in the circumferential direction of the shaft between the hole-side uneven portion and the shaft-side uneven portion.

3. The intermediate shaft for a steering device according to claim 2, wherein the width of the protrusions of the shaft-side uneven portion in the circumferential direction of the shaft is greater than the width of the protrusions of the shaft-side uneven portion in the first meshing portion.

4. The first meshing portion is located in the area where the yoke arm is positioned in the circumferential direction of the shaft, The intermediate shaft for a steering device according to claim 2 or 3, wherein the second meshing portion is located at a position different from the position where the yoke arm is positioned in the circumferential direction of the shaft.

5. The first crimping portion is located in the circumferential direction of the shaft at the position where the first engagement portion is arranged. The intermediate shaft for a steering device according to claim 2 or 3, wherein the second crimping portion is located in the circumferential direction of the shaft at a position where the second meshing portion is arranged.

6. The first meshing portion is located in the area where the yoke arm is positioned in the circumferential direction of the shaft, The second meshing portion is located in a position different from the position where the yoke arm is positioned in the circumferential direction of the shaft. The first crimping portion is located in the circumferential direction of the shaft at the position where the first engagement portion is arranged. The intermediate shaft for a steering device according to claim 2 or 3, wherein the second crimping portion is located in the circumferential direction of the shaft at a position where the second meshing portion is arranged.

Images