Steering shaft

Abstract

To provide a steering shaft which has a larger impact energy absorption amount.SOLUTION: A steering shaft comprises: a first shaft part having an outer circumference formed with a spline or a serration; and a solid second shaft part. The first shaft part is provided with a blind hole extending from a first end to a second end in an axial direction. An axial direction distance between a boundary and the second end is 24% or more to 47% or less relative to the small diameter of the spline or the serration of the first shaft part.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a shaft for a steering device. [Background technology]

[0002] A steering device for an automobile or the like includes a steering device shaft for transmitting steering torque input from a steering wheel to the wheel side. The steering device shaft includes, for example, a torque sensor shaft, a steering shaft, and an intermediate shaft. Patent Document 1 discloses a torque sensor shaft. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6737399 Summary of the Invention [Problem to be solved by the invention]

[0004] When a vehicle is subjected to an impact load during a collision or the like, the steering shaft may be twisted about its central axis, in which case the impact energy is absorbed by the steering shaft being twisted and plastically deformed. However, in recent years, there has been a demand for steering shafts that are able to absorb a greater amount of impact energy.

[0005] An object of the present disclosure is to provide a shaft for a steering device that absorbs a greater amount of impact energy. [Means for solving the problem]

[0006] A shaft for a steering device according to one embodiment of the present disclosure comprises a first shaft portion having splines or serrations formed on its outer circumference, extending in the axial direction, and receiving input of a rotational steering force of a steering wheel, and a solid second shaft portion adjacent to the first shaft portion on one side of the axial direction, wherein the diameter of the second shaft portion is smaller than the minor diameter of the splines or serrations of the first shaft portion, the first shaft portion is provided with a blind hole extending in the axial direction from a first end that coincides in the axial direction with the end of the first shaft portion on the other side of the axial direction to a second end that is located on the other side of the axial direction of the boundary between the first shaft portion and the second shaft portion, and the axial distance between the boundary and the second end is 24% or more and 47% or less of the minor diameter of the splines or serrations of the first shaft portion.

[0007] Thus, in the present disclosure, the axial distance between the boundary and the second end is 24% to 47% of the minor diameter of the spline or serration of the first shaft portion, which distributes stress over a wide area when the steering device shaft is twisted circumferentially around the central axis, thereby suppressing breakage, and thus increasing the amount of impact energy absorbed.

[0008] Here, when a steering shaft is twisted, in a graph with the horizontal axis (X-axis) representing the torsion angle and the vertical axis (Y-axis) representing the torque, the area enclosed by the measured torque value and the X-axis represents the amount of impact energy absorbed. If the steering shaft breaks before reaching the target torsion angle, the torsion angle on the horizontal axis will become smaller, and the area enclosed by the measured torque value and the X-axis will also become smaller, resulting in a decrease in the amount of impact energy absorbed.

[0009] From the above, by setting the axial distance between the boundary and the second end to be 24% or more and 47% or less of the minor diameter of the spline or serration of the first shaft portion, it is possible to provide a steering device shaft that absorbs a greater amount of impact energy.

[0010] In a preferred embodiment of the present disclosure, the axial distance between the boundary and the second end is 35% to 47% of the minor diameter of the spline or serration of the first shaft portion, which further reduces breakage when the steering device shaft is twisted in the circumferential direction around the central axis and distributes stress over a wider area, thereby further increasing the amount of impact energy absorbed. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a steering device shaft that absorbs a larger amount of impact energy. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a configuration diagram showing an example of an electric power steering device according to a first embodiment. [Diagram 2] FIG. 2 is a schematic perspective view showing an example of the electric power steering device according to the first embodiment. [Diagram 3] FIG. 3 is a cross-sectional view of the electric power steering device including the steering shaft according to the first embodiment. [Figure 4] FIG. 4 is a side view of the torque sensor shaft according to the first embodiment. [Diagram 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a view of FIG. 4 as seen from the X2 side. [Figure 7] FIG. 7 is a view of FIG. 4 as seen from the X1 side. [Figure 8] FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. [Figure 9A] FIG. 9A is a schematic diagram showing stresses generated when a torque sensor shaft is twisted around a central axis. [Figure 9B] FIG. 9B is a schematic diagram showing stresses generated when the torque sensor shaft is twisted around the central axis. [Figure 9C] FIG. 9C is a schematic diagram showing stresses generated when the torque sensor shaft is twisted around the central axis. [Figure 10] FIG. 10 is a cross-sectional view of a torque sensor shaft according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A mode (embodiment) for carrying out the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited to the contents described in the following embodiment. The components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the components described below can be appropriately combined. In the following figures, the axial direction is the X direction. One side of the axial direction is the X1 side, and the other side of the axial direction is the X2 side.

[0014] [First embodiment] Fig. 1 is a configuration diagram showing an example of an electric power steering device according to the first embodiment. Fig. 2 is a schematic perspective view showing an example of an electric power steering device according to the first embodiment. The outline of the electric power steering device will be described with reference to Figs. 1 and 2.

[0015] 1 and 2, the electric power steering device 100 includes, in the order of transmission of force applied by a driver (operator), a steering wheel 21, a steering shaft 22, a torque sensor 24, an electric assist device 25, a universal joint 26, an intermediate shaft 27, a universal joint 28, a steering gear mechanism 29, and a tie rod 30. The electric power steering device 100 is of a column assist type in which at least a portion of the electric assist device 25 is supported by a steering column 41 described later, and an assist force is applied to the steering shaft 22.

[0016] The steering shaft 22 includes an input shaft 22A, an output shaft 22B, and a torque sensor shaft (shaft for steering device) 23. The torque sensor shaft 23 is disposed between the input shaft 22A and the output shaft 22B. One end of the input shaft 22A is coupled to the steering wheel 21, and the other end is connected to the torque sensor shaft 23. The torque sensor shaft 23 is connected to one end of the output shaft 22B via a torque sensor 24. The steering shaft 22 rotates due to the steering force applied to the steering wheel 21.

[0017] The torque sensor 24 detects the steering torque T of the steering shaft 22. The torque sensor 24 is connected to an ECU (Electronic Control Unit) 10, and outputs information on the detected steering torque T to the ECU 10.

[0018] The electric assist device 25 has an electric motor 31 and a reduction gear 32. The electric motor 31 is an electric motor that generates an auxiliary steering torque to assist the driver's steering. The electric motor 31 may be a brushless motor or a motor having a brush and a commutator. The electric motor 31 is connected to the reduction gear 32, and the auxiliary steering torque is output to the reduction gear 32. The reduction gear 32 is rotated by the auxiliary steering torque input from the electric motor 31, and the torque is transmitted to the output shaft 22B.

[0019] The intermediate shaft 27 includes an upper shaft 27A and a lower shaft 27B. The upper shaft 27A is connected to the output shaft 22B via a universal joint 26. The lower shaft 27B is connected to a pinion shaft 29A of a steering gear mechanism 29 via a universal joint 28. The upper shaft 27A and the lower shaft 27B are spline-coupled to transmit the torque of the output shaft 22B and are capable of relative movement in a direction parallel to the central axis. This relative movement causes the intermediate shaft 27 to expand and contract in the axial direction.

[0020] The steering gear mechanism 29 includes a rack-and-pinion mechanism. The steering gear mechanism 29 has a pinion shaft 29A, a pinion 29B, and a rack 29C. One end of the pinion shaft 29A is connected to the intermediate shaft 27 via a universal joint 28, and the other end is connected to the pinion 29B. The rack 29C meshes with the pinion 29B. The rotational motion of the steering shaft 22 is transmitted to the steering gear mechanism 29 via the intermediate shaft 27. This rotational motion is converted into linear motion by the rack 29C. A tie rod 30 is connected to the rack 29C.

[0021] A vehicle (not shown) on which the electric power steering device 100 is mounted includes an ECU 10, a vehicle speed sensor 12, a power supply device 13, an ignition switch 14, etc., all of which are shown in FIG. 1. The electric power steering device 100 is controlled by the ECU 10 provided in the vehicle. The power supply device 13 is, for example, an on-board battery device, and is connected to the ECU 10. When the ignition switch 14 is turned on, power is supplied from the power supply device 13 to the ECU 10.

[0022] The steering force of the driver input to the steering wheel 21 is transmitted to the reduction gear 32 of the electric assist device 25 via the input shaft 22A. At this time, the ECU 10 acquires the steering torque T input to the input shaft 22A from the torque sensor 24. The ECU 10 acquires a vehicle speed signal V from the vehicle speed sensor 12. Then, the ECU 10 calculates an auxiliary steering command value of an assist command based on the steering torque T and the vehicle speed signal V. The ECU 10 outputs a control signal X according to the auxiliary steering command value to control the operation of the electric motor 31.

[0023] The auxiliary steering torque generated by the electric motor 31 is transmitted to the reduction gear 32. Furthermore, the ECU 10 acquires information on induced voltage or rotation information of the rotor from the electric motor 31 as operation information Y. The reduction gear 32 then applies the auxiliary steering torque to the output shaft 22B. The output shaft 22B outputs a torque obtained by adding the auxiliary steering torque transmitted from the electric motor 31 to the steering torque T of the steering wheel 21. In this manner, the electric power steering device 100 assists the steering of the steering wheel 21 by the driver.

[0024] Next, the configuration of the steering shaft 22 will be described with reference to Fig. 3. Fig. 3 is a cross-sectional view of an electric power steering device including the steering shaft according to the first embodiment.

[0025] 3, the electric power steering device 100 includes a steering shaft 22, a steering column 41, a vehicle body mounting bracket 48, and a housing 45. As described above, the steering shaft 22 includes the input shaft 22A, the output shaft 22B, the torque sensor shaft (steering device shaft) 23, and the torsion bar 22C. The input shaft 22A includes a first portion 22A1 on the X2 side and a second portion 22A2 on the X1 side. A spline groove 42 extending in the X direction is formed on the inner periphery of the second portion 22A2.

[0026] The steering column 41 is a cylindrical member. The steering column 41 is fixed to a vehicle body mounting bracket 48 by a clamp mechanism, and is attached to the vehicle body via the vehicle body mounting bracket 48. The housing 45 is disposed on the X1 side of the steering column 41.

[0027] At least a portion of the steering shaft 22 is disposed inside the steering column 41. In this embodiment, the input shaft 22A and a portion of the torque sensor shaft 23 are disposed inside the steering column 41. The X1 side portion of the torque sensor shaft 23 and the output shaft 22B are located on the X1 side of the steering column 41. A bearing 40A is provided on the inner circumferential surface of the steering column 41. The bearing 40A rotatably supports the input shaft 22A. The bearing 40A can be a rolling bearing capable of supporting a radial load and a thrust load.

[0028] The torque sensor shaft 23 has a first shaft portion 23A, a second shaft portion 23B, and a third shaft portion 23C. The first shaft portion 23A has a spline 43 on its outer periphery. The spline 43 meshes with a spline groove 42 provided on the inner periphery of the second portion 22A2 of the input shaft 22A, and the rotational torque applied to the input shaft 22A is transmitted to the first shaft portion 23A. The first shaft portion 23A is movable in the axial direction relative to the input shaft 22A. The third shaft portion 23C is coupled to the output shaft 22B.

[0029] The third shaft portion 23C extends in a direction along the central axis AX coaxially with the first shaft portion 23A and the second shaft portion 23B. The third shaft portion 23C has an outer diameter larger than that of the second shaft portion 23B. With this configuration, the torque applied to the input shaft 22A is transmitted to the output shaft 22B via the torque sensor shaft 23. Here, the torque sensor shaft 23 is an example of a "steering device shaft" in the present disclosure. A detailed configuration of the torque sensor shaft 23 will be described later.

[0030] One end of the torsion bar 22C is fitted into a hole 62 (see Figs. 3 and 7) provided in the third shaft portion 23C, and is fixed to the third shaft portion 23C by, for example, a pin or the like via a through hole H provided in the third shaft portion 23C. The other end of the torsion bar 22C is fixed to the output shaft 22B. As a result, the torsion bar 22C connects the output shaft 22B and the torque sensor shaft 23. A torsion moment is generated in the torsion bar 22C according to the magnitude of the steering torque input to the torque sensor shaft 23, and the output shaft 22B rotates in a state displaced in the rotational direction relative to the torque sensor shaft 23. The torque sensor 24 detects the steering torque based on the amount of relative rotational displacement between the torque sensor shaft 23 and the output shaft 22B.

[0031] The housing 45 is disposed on the X1 side of the steering column 41 and on the outer periphery side of the output shaft 22B and the third shaft portion 23C. The housing 45 is formed of a material having high thermal conductivity. The housing 45 is formed of at least one of aluminum, an aluminum alloy, magnesium, and a magnesium alloy, for example. The housing 45 is manufactured by, for example, die casting.

[0032] The housing 45 includes a first housing 45A, a second housing 45B, and a third housing 45C. The first housing 45A, the second housing 45B, and the third housing 45C are arranged in this order from the X2 direction side toward the X1 direction. The first housing 45A is a cylindrical member. The second shaft portion 23B is arranged inside the first housing 45A. The end of the first housing 45A on the X2 side is fixed to the steering column 41. The first housing 45A is fixed to the second housing 45B and the third housing 45C via a fixing member 46A. The first housing 45A may be provided integrally with the steering column 41. The first housing 45A, the second housing 45B, and the third housing 45C may be provided integrally.

[0033] The second housing 45B is provided on the outer periphery of the second shaft portion 23B and the output shaft 22B. The torque sensor 24 described above is disposed in the internal space surrounded by the first housing 45A and the second housing 45B. The third housing 45C is provided on the outer periphery of the output shaft 22B. The worm wheel 32A of the reduction gear 32 described above is provided in the internal space surrounded by the second housing 45B and the third housing 45C. The worm wheel 32A is connected to the output shaft of the electric motor 31 (see FIG. 1) via a worm (not shown), and transmits the auxiliary steering torque of the electric motor 31 to the output shaft 22B.

[0034] A bearing 40B is provided on the inner circumference of the second housing 45B, and a bearing 40C is provided on the inner circumference surface of the third housing 45C. The bearings 40B and 40C rotatably hold the output shaft 22B. The housing 45 may be connected to a tilt mechanism (not shown) or the like and be rotatable around the tilt axis BX. This allows the angle of the central axis AX of the steering shaft 22 to be changed, and the vertical position of the steering wheel 21 to be adjusted by the clamp mechanism.

[0035] Next, the configuration of the torque sensor shaft 23 will be described with reference to Fig. 4 to Fig. 8. Fig. 4 is a side view of the torque sensor shaft according to the first embodiment. Fig. 5 is a cross-sectional view taken along line VV in Fig. 4. Fig. 6 is a view of Fig. 4 as seen from the X2 side. Fig. 7 is a view of Fig. 4 as seen from the X1 side. Fig. 8 is a cross-sectional view taken along line VIII-VIII in Fig. 5.

[0036] As shown in FIG. 4, the torque sensor shaft 23 has a first shaft portion 23A, a second shaft portion 23B, and a third shaft portion 23C. In this embodiment, the torque sensor shaft 23 is made of carbon steel for mechanical construction (for example, JIS standard S35C). The torque sensor shaft 23 is not limited to this, and may be made of copper, aluminum, brass, or the like. The second shaft portion 23B is adjacent to the first shaft portion 23A on the X1 side, and the third shaft portion 23C is adjacent to the second shaft portion 23B on the X1 side. As shown in FIG. 5, the first shaft portion 23A includes a spline shaft portion 23A1 and a cylindrical surface portion 23A2. A spline 43 is formed on the outer periphery of the spline shaft portion 23A1. The cylindrical surface portion 23A2 is a cylindrical surface whose outer periphery extends in the circumferential direction around the central axis AX. The spline 43 extends in the X direction (axial direction).

[0037] As shown in FIG. 6 and FIG. 8, the spline 43 has a plurality of convex portions 43a arranged along the circumferential direction around the central axis AX. That is, the spline 43 has valley bottoms 43b and convex portions 43a arranged alternately along the circumferential direction. The tops of the convex portions 43a are arranged radially outward from the valley bottoms 43b. Here, the diameters (diameters) of the spline 43 include a large diameter Db, which is the diameter of the convex portions 43a, and a small diameter Da, which is the diameter of the valley bottoms 43b. In other words, the large diameter Db is the length of a line segment that connects the tops of the convex portions 43a among the line segments that pass through the central axis AX in a cross section perpendicular to the central axis AX, and the small diameter Da is the length of a line segment that connects the valley bottoms 43b among the line segments that pass through the central axis AX. As shown in FIG. 8, the second portion 22A2 of the input shaft 22A is arranged on the outer circumferential side of the spline shaft portion 23A1 of the first shaft portion 23A. A spline groove 42 is formed on the inner circumference of the second portion 22A2. Teeth of the spline groove 42 mesh between the protrusions 43a. Note that D shown in Fig. 8 is the diameter of the pitch circle. Furthermore, since the small diameter Da is the diameter of the valley bottom 43b, when the torque sensor shaft 23 moves axially relative to the input shaft 22A, the spline groove 42 and the torque sensor shaft 23 do not interfere with each other, and the relative movement between the second portion 22A2 of the input shaft 22A and the torque sensor shaft 23 in the X direction (axial direction) is not affected.

[0038] In the present invention, serrations may be formed on the outer periphery of the first shaft portion 23 A. The diameter of the serrations may be large or small.

[0039] The third shaft portion 23C is disposed on the X1 side, which is the output shaft 22B side. The third shaft portion 23C has a large diameter portion 53, a stopper portion 54, and a cylindrical portion 55. The cylindrical portion 55 is fitted into the second cylindrical portion 22Bb of the output shaft 22B.

[0040] As shown in FIG. 7, a spline portion including a plurality of projections and recesses is formed on the outer peripheral surface of the stopper portion 54. The plurality of projections and recesses are alternately arranged along the circumferential direction. As shown in FIG. 4, the plurality of projections and recesses are provided along the axial direction. The output shaft 22B is provided with a first cylindrical portion 22Ba (see FIG. 3) on the X2 side of the second cylindrical portion 22Bb. The inner peripheral surface of the first cylindrical portion 22Ba is formed with a plurality of projections and recesses along the circumferential direction. The projections and recesses of the stopper portion 54 and the projections and recesses of the first cylindrical portion 22Ba are coupled with a gap in the circumferential direction. As shown in FIG. 3, the output shaft 22B and the torque sensor shaft 23 are coupled by a torsion bar 22C. When a large torque is input to the torque sensor shaft 23, the projections and recesses of the stopper portion 54 come into contact with the projections and recesses of the first cylindrical portion 22Ba, making it possible to transmit the large torque. As shown in FIG. 7, the large diameter portion 53 has an outer diameter larger than the stopper portion 54 and the cylindrical portion 55.

[0041] 4, the second shaft portion 23B is an intermediate shaft portion provided between the first shaft portion 23A and the third shaft portion 23C, and connects the first shaft portion 23A and the third shaft portion 23C. In this embodiment, the first shaft portion 23A, the second shaft portion 23B, and the third shaft portion 23C are integral. That is, the torque sensor shaft 23 is an integrally molded product, and the third shaft portion 23C is connected to the output shaft 22B.

[0042] The second shaft portion 23B is cylindrical. As shown in FIG. 5, the second shaft portion 23B includes a cylindrical portion 23B1 and a curved portion 23B2. The cylindrical portion 23B1 has a constant outer diameter Dc in the X direction. The curved portion 23B2 is adjacent to the cylindrical portion 23B1 on the X2 side. The outer diameter of the curved portion 23B2 increases toward the X2 side. The curved portion 23B2 has an R-surface (curved surface) that is connected to the outer diameter of the cylindrical portion 23B1. That is, the curved portion 23B2 connects the outer diameter of the cylindrical portion 23B1 and the outer diameter of the cylindrical surface portion 23A2. By making the outer diameter of the curved portion 23B2 an R-surface (curved surface), stress when the cylindrical portion 23B1 is twisted is prevented from concentrating on the curved portion 23B2. The end 23B2a of the curved portion 23B2 on the X2 side has a small diameter Da. The small diameter Da is greater than the outer diameter Dc. Note that an end 23B2a on the X2 side of the curved portion 23B2 coincides with a boundary 200 in the X direction between the first shaft portion 23A and the second shaft portion 23B.

[0043] As shown in FIG. 5, the first shaft portion 23A is provided with a blind hole 61. The blind hole 61 extends along the X direction. The blind hole 61 has an open end on the X2 side. The blind hole 61 faces a bottom surface 61b on the X1 side and a cylindrical inner wall surface 61a extending in the X direction. The end on the X2 side of the inner wall surface 61a is open. The blind hole 61 extends along the X direction from a first end 611 to a second end 612. The first end 611 coincides with the end surface 23Aa on the X2 side of the first shaft portion 23A in the X direction. The second end 612 coincides with the bottom surface 61b in the X direction. The length of the blind hole 61 in the X direction is a distance L1. The blind hole 61 has an inner diameter Dd. In addition, in a cross section including the central axis AX, the distance in the X direction between the boundary 200 between the first shaft portion 23A and the second shaft portion 23B and the second end 612 (bottom surface 61b) of the blind hole 61 is distance L2. The area between the boundary 200 and the second end 612 is solid. The inner diameter Dd is a diameter at which, when the first shaft portion 23A is twisted, the first shaft portion 23A does not twist before the second shaft portion 23B is twisted.

[0044] Next, the relationship between the distance L2 between the boundary 200 and the second end 612 and the minor diameter Da of the spline 43 will be briefly described.

[0045] The axial distance (distance L2) between the boundary 200 and the second end 612 is 24% or more and 47% or less of the minor diameter Da of the spline 43 of the first shaft portion 23A. Preferably, the distance L2 is 35% or more and 47% or less of the minor diameter Da.

[0046] The same can be applied to serrations instead of the splines 43. That is, the distance L2 is 24% or more and 47% or less of the minor diameter Da of the serrations of the first shaft portion 23A, and preferably, the distance L2 is 35% or more and 47% or less of the minor diameter Da of the serrations.

[0047] As described above, the torque sensor shaft 23 (steering device shaft) according to this embodiment includes the first shaft portion 23A having the splines 43 or serrations formed on its outer periphery, extending in the X direction, and receiving the rotational steering force of the steering wheel 21, and the solid second shaft portion 23B adjacent to the first shaft portion 23A on the X1 side. The first shaft portion 23A is provided with a blind hole 61 (blind hole) extending in the X direction from a first end 611 to a second end 612. The X direction distance (axial distance) between the boundary 200 and the second end 612 is 24% or more and 47% or less of the small diameter Da of the splines 43 or serrations of the first shaft portion 23A.

[0048] Thus, in this embodiment, the X-direction distance (axial distance) between the boundary 200 and the second end 612 is 24% to 47% of the minor diameter Da of the spline 43 or serration of the first shaft portion 23A. This prevents stress from being distributed over a wide area and breakage from occurring when the torque sensor shaft 23 is twisted in the circumferential direction around the central axis AX, thereby increasing the amount of impact energy absorbed.

[0049] When the torque sensor shaft 23 is twisted, in a graph with the torsion angle on the horizontal axis (X-axis) and the torque on the vertical axis (Y-axis), the area enclosed by the measured torque value and the X-axis represents the amount of absorbed impact energy. If the torque sensor shaft 23 breaks before reaching a target torsion angle, the torsion angle on the horizontal axis will become smaller, and the area enclosed by the measured torque value and the X-axis will also become smaller, resulting in a decrease in the amount of absorbed impact energy.

[0050] From the above, as described above, by setting the X-direction distance (axial distance) between the boundary 200 and the second end 612 to be 24% or more and 47% or less of the small diameter Da of the spline 43 or serration of the first shaft portion 23A, it is possible to provide a steering device shaft that absorbs a larger amount of impact energy.

[0051] Furthermore, it is more desirable that the X-direction distance (axial distance) between the boundary 200 and the second end 612 is 35% to 47% of the small diameter Da of the spline 43 or serration of the first shaft portion 23A. This further reduces the risk of breakage when the torque sensor shaft 23 is twisted in the circumferential direction about the central axis AX, and distributes stress over a wider area, thereby further increasing the amount of impact energy absorbed.

[0052] The background to the invention will be described below. First, as a premise, the second shaft portion 23B shown in FIG. 4 absorbs the impact energy of torsion. Then, the diameter and length of the cylindrical portion 23B1 are set so that the torsional torque and torsional angle are set to target values. Also, in order to reduce the weight of the torque sensor shaft 23, a hollow blind hole 61 is provided in the first shaft portion 23A. The blind hole 61 is intended to be a hole that will make the torque sensor shaft 23 the lightest.

[0053] The diameter of the blind hole 61 is set so that when the first shaft portion 23A is twisted, the first shaft portion 23A does not twist before the second shaft portion 23B twists. Here, it is desirable to ensure that the axial length of the blind hole 61 is as long as possible to reduce weight while the influence of the twisting of the blind hole 61 on the second shaft portion 23B is small.

[0054] [Example] Next, the first embodiment will be specifically verified through examples. Figures 9A, 9B, and 9C are CAE analysis data when the torque sensor shaft is twisted. Specifically, Figures 9A, 9B, and 9C are schematic diagrams showing stresses generated when the torque sensor shaft is twisted around the central axis, and show a part of the torque sensor shaft. The torque sensor shaft used in this example is the torque sensor shaft 23 shown in Figure 5. The stress values ​​appearing in the torque sensor shaft 23 when the torque sensor shaft 23 is twisted in the direction around the central axis AX were confirmed. Figure 9A shows sample numbers 23-0 and 23-1. Figure 9B shows sample numbers 23-2 and 23-3. Figure 9C shows sample numbers 23-4 and 23-5.

[0055] Sample number 23-0 shows a state before being twisted in the axial direction. Sample number 23-1 shows that the distance L2 (the distance in the X direction between the boundary 200 and the second end 612 of the blind hole 61) described in FIG. 5 is 0 mm. That is, the second end 612 of the blind hole 61 and the boundary 200 coincide in the X direction. Sample number 23-2 shows that the distance L2 is 2 mm. Sample number 23-3 shows that the distance L2 is 4 mm. Sample number 23-4 shows that the distance L2 is 6 mm. Sample number 23-5 shows that the distance L2 is 8 mm. In addition, in sample numbers 23-0 to 23-5, the minor diameter Da of the spline 43 shown in FIG. 5 is 17 mm.

[0056] The stress values ​​are divided into a first stress value 110A to an eighth stress value 110H. The first stress value 110A is equal to or greater than 0 and less than 0.025. The second stress value 110B is equal to or greater than 0.025 and less than 0.05. The third stress value 110C is equal to or greater than 0.05 and less than 0.075. The fourth stress value 110D is equal to or greater than 0.075 and less than 0.1. The fifth stress value 110E is equal to or greater than 0.1 and less than 0.125. The sixth stress value 110F is equal to or greater than 0.125 and less than 0.15. The seventh stress value 110G is equal to or greater than 0.15 and less than 0.175. The eighth stress value 110H is equal to or greater than 0.175 and less than 0.2. As shown in FIG. 9A to FIG. 9C, the type and density of hatching are changed to distinguish the first stress value 110A to the eighth stress value 110H. The evaluation was made with the following scale: ◯, Δ, and ×. Δ is better than ×, and ◯ is better than Δ. × is outside the scope of the present invention, Δ and ◯ are within the scope of the present invention, and ◯ is the most excellent.

[0057] In sample number 23-1, a fracture site 101 extending from the bottom surface 61b of the blind hole 61 toward the X1 side is formed. In addition, the eighth stress value 110H, which is the largest stress value, is widely concentrated at the boundary 200. Therefore, among all the samples, sample number 23-1 is most affected by the blind hole 61 in the cylindrical portion 23B1, and is evaluated as ×, being outside the scope of the present invention.

[0058] In sample number 23-2 as well, the eighth stress value 110H is widely concentrated at boundary 200. Therefore, sample number 23-2 was rated as × and was evaluated as being outside the scope of the present invention.

[0059] In sample number 23-3, the region of the eighth stress value 110H is significantly smaller than that of sample number 23-2. Therefore, sample number 23-3 was evaluated as Δ, and was evaluated as being within the range of the present invention.

[0060] In sample number 23-4, the region of the eighth stress value 110H is significantly smaller than that of sample number 23-3. Also, the region of the fifth stress value 110E is smaller than that of sample number 23-3. Therefore, sample number 23-4 was evaluated as △ and was recognized as being within the scope of the present invention.

[0061] In sample number 23-5, there is no region of the eighth stress value 110H, which is the highest stress value. In addition, there is no region of the seventh stress value 110G, which is the next highest stress value after the eighth stress value 110H, in the vicinity of the boundary 200. Therefore, sample number 23-5 was evaluated as ◯ and was evaluated to be within the scope of the present invention.

[0062] Here, the distance L2 (the distance in the X direction between the boundary 200 and the second end 612 of the blind hole 61) is divided by the minor diameter Da (17 mm) of the spline 43, and the result is rounded off to the first decimal place to obtain the following percentage:

[0063] Sample No. 23-1: 0%, Sample No. 23-2: 12%, Sample No. 23-3: 24%, Sample No. 23-4: 35%, Sample No. 23-5: 47%

[0064] From the above, the ratio of the distance L2 to the small diameter Da is 24% or more and 47% or less for sample number 23-3 (L2 is 4 mm) to sample number 23-5 (L2 is 8 mm). Also, the ratio of the distance L2 to the small diameter Da is 35% or more and 47% or less for sample number 23-4 (L2 is 6 mm) to sample number 23-5 (L2 is 8 mm), which is more preferable.

[0065] [Second embodiment] Next, a torque sensor shaft according to a second embodiment will be described. Fig. 10 is a cross-sectional view of the torque sensor shaft according to the second embodiment.

[0066] A torque sensor shaft 230 according to the second embodiment is different from the torque sensor shaft 23 according to the first embodiment in the shape of the first shaft portion 23A. This will be specifically described below.

[0067] In the first embodiment, the first shaft portion 23A includes a splined shaft portion 23A1 and a cylindrical surface portion 23A2, and splines 43 are formed on the outer periphery of the splined shaft portion 23A1.

[0068] In contrast to this, in the second embodiment, the first shaft portion 23A has the splines 43 formed over the entire area in the X direction. That is, the entire area of ​​the first shaft portion 23A in the X direction is a splined shaft portion 23A1.

[0069] As described above, in the torque sensor shaft 230 (steering device shaft) according to this embodiment, the X-direction distance (axial distance) between the boundary 200 and the second end 612 is 24% to 47% of the small diameter Da of the spline 43 or serration of the first shaft portion 23A. As a result, similar to the first embodiment, when the torque sensor shaft 23 is twisted in the circumferential direction about the central axis AX, breakage is suppressed and stress is evenly distributed in the axial direction of the cylindrical portion 23B1, so that the amount of impact energy absorbed is increased. [Explanation of symbols]

[0070] 21 Steering Wheel 22 Steering shaft 22A Input Shaft 22B Output shaft 22C torsion bar 23 Torque sensor shaft (steering device shaft) 23A First shaft section 23B Second shaft section 23C 3rd shaft section 24 Torque Sensor 26, 28 Universal joint 27 Intermediate Shaft 27A Upper Shaft 27B Lower shaft 29 Steering gear mechanism 42 Spline groove 43 Spline 43a Convex 43b Valley bottom 45 Housing 53 Large diameter section 54 Stopper part 55 Cylindrical part 61 Blind Hole Da Small diameter Db Large diameter 100 Electric power steering device 200 boundaries

Claims

1. a first shaft portion having a spline or serration formed on an outer periphery thereof, extending in an axial direction, and receiving a rotational steering force of a steering wheel; and a second shaft portion adjacent to the first shaft portion on one side in the axial direction and solid, a diameter of the second shaft portion is smaller than a minor diameter of the splines or serrations of the first shaft portion; The first shaft portion is provided with a blind hole extending in the axial direction from a first end that coincides with an end of the first shaft portion on the other side in the axial direction to a second end that is located on the other side in the axial direction relative to a boundary between the first shaft portion and the second shaft portion, an axial distance between the boundary and the second end is 24% or more and 47% or less of the small diameter of the spline or serration of the first shaft portion; Steering gear shaft.

2. The axial distance between the boundary and the second end is 35% or more and 47% or less of a minor diameter of the spline or serration of the first shaft portion.

2. The steering shaft according to claim 1.

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