steering shaft

Abstract

A steering shaft (10) has an input shaft (11), an output shaft (12), and a torsion bar (13). The input shaft has a first end portion to which a torque is applied, and a second end portion provided with an abutting portion (11B). The output shaft has an input shaft insertion portion (12D, 12E) into which the second end portion of the input shaft is inserted. The input shaft insertion portion is open at a first end portion of the output shaft. An inner end surface of the input shaft insertion portion in the axial direction has a recess (12G). A portion of the input shaft that is exposed to the outside of the input shaft insertion portion has a sensor member (16, 17) that opposes the first end portion of the output shaft in the axial direction. A gap in the axial direction between a front end surface of the abutting portion and an inner end surface of the recess that opposes the front end surface is smaller than a gap in the axial direction between the sensor member and the first end portion of the output shaft.

Description

Technical Field

[0001] This disclosure relates to steering shafts. Background Technology

[0002] For example, the steering shaft in Patent Document 1 has an upper shaft and a lower shaft. The first end of the upper shaft is connected to the steering wheel. The lower shaft has an input shaft, an output shaft, and a torsion bar. The torsion bar connects the input shaft and the output shaft to each other.

[0003] The first end of the input shaft is joined to the second end of the upper shaft via a spline engagement. The input shaft has a fixing hole. The fixing hole opens at the second end of the input shaft. The output shaft is a stepped cylindrical body with a circular cross-section. The second end of the input shaft is rotatably inserted into an insertion portion located at the first end of the output shaft.

[0004] The first end of the torsion bar is fitted into the fixing hole of the input shaft. The first end of the torsion bar can rotate integrally with the input shaft. The second end of the torsion bar is fitted into the inner circumference of the second end of the output shaft. The second end of the torsion bar can rotate integrally with the output shaft.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2023-132532

[0006] In the steering shaft of Patent Document 1, there is a concern that, when the output shaft is a stepped cylindrical body, the wall thickness of the output shaft may become thinner depending on the inner diameter or depth of the insertion part. Depth refers to the axial length of the insertion part. Therefore, there is a concern about a reduction in the strength of the output shaft. Summary of the Invention

[0007] A steering shaft includes an input shaft, an output shaft, and a torsion bar. The input shaft has: an input shaft body having a first end to which torque is applied via steering wheel operation, and a second end for an axially extending, non-through-hole opening in a fixing hole; and an abutment portion disposed at the second end of the input shaft body, having a diameter smaller than the input shaft body. The output shaft is a cylindrical body with a circular cross-sectional shape, open at both ends axially, and has a large-diameter portion including the first end of the output shaft and a small-diameter portion including the second end of the output shaft. The torsion bar has: a first end fixed to the input shaft when pressed into the fixing hole; and a second end fixed to the output shaft when pressed into its interior. The large-diameter portion has an input shaft insertion portion open at the first end of the output shaft, and the second end of the input shaft is rotatably inserted into the input shaft insertion portion. The aforementioned small-diameter portion has a torsion bar insertion portion that opens at the second end of the aforementioned output shaft. The inner diameter of the torsion bar insertion portion is smaller than the inner diameter of the aforementioned input shaft insertion portion. The second end of the aforementioned torsion bar is fixed to the aforementioned small-diameter portion when pressed into the aforementioned torsion bar insertion portion. The axial inner end face of the aforementioned input shaft insertion portion has a recess that is recessed in a direction from the first end of the aforementioned output shaft toward the second end. The recess has an inner diameter smaller than the inner diameter of the aforementioned input shaft insertion portion and larger than the inner diameter of the aforementioned torsion bar insertion portion. The portion of the aforementioned input shaft that protrudes outside the aforementioned input shaft insertion portion has a sensor component constituting a sensor device for detecting the aforementioned torque. The sensor component is axially opposed to the first end of the aforementioned output shaft. The aforementioned abutment portion has a front end face that faces the inner end face of the aforementioned recess in the axial direction of the aforementioned input shaft. The axial gap between the front end face of the aforementioned abutment portion and the inner end face of the aforementioned recess is smaller than the axial gap between the aforementioned sensor component and the first end of the aforementioned output shaft. Attached Figure Description

[0008] Figure 1 This is a cross-sectional view of the main part of the steering shaft involved in one embodiment.

[0009] Figure 2 This is a sectional view of the main part of the steering shaft involved in the comparative example. Detailed Implementation

[0010] A steering shaft according to one embodiment will be described.

[0011] like Figure 1 As shown, the steering shaft 10 is used, for example, in an electric power steering system of a vehicle. The steering shaft 10 has an input shaft 11, an output shaft 12, and a torsion bar 13. The torsion bar 13 connects the input shaft 11 and the output shaft 12.

[0012] The input shaft 11 is a solid cylindrical body with a circular cross-sectional shape, and includes an input shaft body 11A and an abutment portion 11B. Torque is applied to the first end of the input shaft body 11A by operating the steering wheel 14. The abutment portion 11B is a protrusion located at the second end of the input shaft body 11A, and is a cylindrical body with a circular cross-sectional shape. The outer diameter of the abutment portion 11B is smaller than the outer diameter of the input shaft body 11A. The input shaft 11 has a fixing hole 11C. The fixing hole 11C is located on the axial end face of the abutment portion 11B. The fixing hole 11C is a non-through hole with a circular cross-sectional shape. The fixing hole 11C extends from the axial end face of the abutment portion 11B toward the first end of the input shaft 11.

[0013] The output shaft 12 is a hollow cylindrical body with a circular cross-sectional shape and open at both ends in the axial direction. The second end of the input shaft 11 is rotatably inserted into the first end of the output shaft 12.

[0014] The output shaft 12 is a stepped cylindrical body with a large-diameter portion 12A and a small-diameter portion 12B. The large-diameter portion 12A is the part containing the first end of the output shaft 12. The small-diameter portion 12B is the part containing the second end of the output shaft 12. The outer diameter of the large-diameter portion 12A is larger than the outer diameter of the small-diameter portion 12B. A stepped surface 12C is formed at the boundary between the large-diameter portion 12A and the small-diameter portion 12B. The stepped surface 12C is a surface located on an imaginary plane extending in a direction orthogonal to the axial direction of the output shaft 12. The stepped surface 12C is formed over the entire circumference of the steering shaft 10.

[0015] A bearing 18 is mounted on the outer peripheral surface of the small diameter portion 12B. The bearing 18 is, for example, a rolling bearing. The bearing 18 has an inner ring, an outer ring, and a plurality of rolling elements. The rolling elements are, for example, balls, and are held between the inner and outer rings in a rolling manner. The bearing 18 is axially positioned by a stepped surface 12C. That is, the inner ring of the bearing 18 abuts against the stepped surface 12C axially, thereby restricting the movement of the bearing 18 from the second end of the output shaft 12 toward the first end. The inner ring of the bearing 18 remains in contact with the stepped surface 12C.

[0016] The output shaft 12 has a first insertion portion 12D, a second insertion portion 12E, and a third insertion portion 12F. The first to third insertion portions 12D, 12E, and 12F constitute the inner circumferential surface of the output shaft 12 and are interconnected. The first to third insertion portions 12D, 12E, and 12F are arranged sequentially from the first end of the output shaft 12 toward the second end. The first insertion portion 12D and the second insertion portion 12E are located in the large-diameter portion 12A. The third insertion portion 12F is located in the small-diameter portion 12B. The stepped surface 12C is located radially outward from the inner circumferential surfaces of the first insertion portion 12D and the second insertion portion 12E. That is, when viewed axially from the output shaft 12, the stepped surface 12C does not overlap with the first insertion portion 12D and the second insertion portion 12E.

[0017] The first insertion portion 12D opens at the first end face of the output shaft 12. The second insertion portion 12E is disposed between the first insertion portion 12D and the third insertion portion 12F. The third insertion portion 12F opens at the second end face of the output shaft 12. The inner diameters of the first to third insertion portions 12D, 12E, and 12F decrease sequentially. The inner diameters of the first insertion portion 12D and the second insertion portion 12E are larger than the outer diameter of the input shaft body 11A.

[0018] A recess 12G is provided on the inner end face of the second insertion portion 12E in the axial direction. The recess 12G is a countersunk hole with a circular cross-sectional shape and extends in the direction from the first end of the output shaft 12 toward the second end. In the axial direction of the output shaft 12, the position of the inner end face of the recess 12G coincides with the position of the stepped surface 12C. The inner diameter of the recess 12G is larger than the inner diameter of the third insertion portion 12F and smaller than the inner diameter of the second insertion portion 12E.

[0019] The second end of the input shaft 11 is inserted into the second insertion portion 12E in a non-contact state via the first insertion portion 12D. A bearing 15 is sandwiched between the outer peripheral surface of the input shaft body 11A and the inner peripheral surface of the first insertion portion 12D. The bearing 15 is, for example, a needle roller bearing. The input shaft 11 is rotatably supported on the output shaft 12 via the bearing 15. The first insertion portion 12D and the second insertion portion 12E constitute the input shaft insertion portion.

[0020] In the axial direction of the input shaft 11, the second end face of the input shaft body 11 faces the inner end face of the second insertion portion 12E. The abutment portion 11B is located inside the second insertion portion 12E. In the axial direction of the input shaft 11, a first gap δ1 is formed between the front end face of the abutment portion 11B and the inner end face of the recess 12G. The front end face is the end face of the abutment portion 11B on the side opposite to the input shaft body 11A. In the axial direction of the input shaft 11, a second gap δ2 is formed between the second end face of the input shaft body 11 and the inner end face of the second insertion portion 12E. The first gap δ1 is smaller than the second gap δ2.

[0021] The torsion bar 13 is a rod-shaped body with a circular cross-section and has a first end and a second end. The outer diameters of the first and second ends are larger than the outer diameter of the portion between the first and second ends of the torsion bar 13. The first end of the torsion bar 13 is fixed to the input shaft 11 in a state where it is pressed into the fixing hole 11A of the input shaft 11. The first end of the torsion bar is rotatable integrally with the input shaft 11. The second end of the torsion bar 13 is inserted into the third insertion part 12F and protrudes to the outside from the second end of the output shaft 12. The second end of the torsion bar 13 is fixed to the third insertion part 12F in a state where it is pressed into the inner circumferential surface of the third insertion part 12F. The second end of the torsion bar 13 is rotatable integrally with the output shaft 12. The third insertion part 12F is equivalent to the torsion bar insertion part.

[0022] A sensor magnet 17 is fixed to the outer peripheral surface of the portion of the input shaft 11 exposed from the output shaft 12 via a magnet holder 16. Both the magnet holder 16 and the sensor magnet 17 are cylindrical bodies with a circular cross-sectional shape. The sensor magnet 16 is the source of magnetic flux generation. The magnet holder 16 has a first end face and a second end face. The first end face and the second end face are end faces of the magnet holder 16 located on opposite sides of each other in the axial direction of the input shaft 11. The first end face is the end face of the magnet holder 16 on the side away from the output shaft 12 in the axial direction of the input shaft 11. The second end face is the end face of the magnet holder 16 on the side closer to the output shaft 12 in the axial direction of the input shaft 11.

[0023] A third gap δ3 is formed in the axial direction of the input shaft 11 between the second end face of the magnet holder 16 and the first end face of the output shaft 12. The third gap δ3 is larger than the second gap δ2. That is, among the first to third gaps δ1, δ2, and δ3, the first gap δ1 is the smallest and the third gap δ3 is the largest.

[0024] The magnet holder 16 and the sensor magnet 17 are sensor components constituting a sensor device. The sensor device is, for example, a torque sensor that detects the steering torque applied to the steering wheel 14. The steering torque applied to the steering wheel 14 is transmitted to the output shaft 12 via the input shaft 11 and the torsion bar 13. When the steering wheel is operated, the torsion bar 13 twists according to the steering torque, generating relative rotation between the input shaft 11 and the output shaft 12. The sensor device detects the steering torque applied to the steering shaft 10 based on the magnetic flux corresponding to the amount of torsion of the torsion bar 13. The steering torque is used, for example, for the control of an electric power steering system.

[0025] <The function of this implementation method>

[0026] Next, the function of this embodiment will be explained.

[0027] In a vehicle collision, following the initial collision with other vehicles or buildings, a secondary collision occurs due to inertia caused by the rapid decrease in vehicle speed, resulting in the driver colliding with the steering wheel 14. The impact force F1 of this secondary collision acts in the direction D1, which presses the input shaft 11 towards the output shaft 12 relative to the steering shaft 10. The impact force F1 is transmitted sequentially through the input shaft 11, the torsion bar 13, and the output shaft 12. When the impact force F1 exceeds the holding force generated by the pressing of the second end of the torsion bar 13 into the third insertion portion 12F, the input shaft 11 and the torsion bar 13 move integrally in the pressing direction D1.

[0028] The movement of the input shaft 11 and the torsion bar 13 in the pressing direction D1 is restricted by the axial contact between the front end face of the abutment portion 11B and the inner end face of the recess 12G. However, the first gap δ1 is smaller than the second gap δ2, so the front end face of the abutment portion 11B contacts the inner end face of the recess 12G before the second end face of the input shaft body 11 contacts the inner end face of the second insertion portion 12E. Furthermore, the first gap δ1 is smaller than the third gap δ3, so the front end face of the abutment portion 11B contacts the inner end face of the recess 12G before the second end face of the magnet holder 16 contacts the first end face of the output shaft 12. Contact between the magnet holder 16 and the output shaft 12 is avoided, thus suppressing damage to the sensor magnet 17.

[0029] Furthermore, since the input shaft 11 has an abutment portion 11B and the output shaft 12 has a recess 12G, the thickness W1 of the wall of the output shaft 12 is ensured. The thickness W1 is the length between the first corner where the outer peripheral surface of the small-diameter portion 12B intersects the stepped surface 12C, and the second corner where the inner peripheral surface of the first insertion portion 12E intersects the axial inner end face. More specifically, the thickness W1 is the length of the wall of the output shaft 12 in the direction connecting the first corner and the second corner.

[0030] As a comparative example, we will discuss the case in which the abutment portion 11B of the input shaft 11 is omitted and the recess portion 12G of the output shaft 12 is omitted.

[0031] like Figure 2 As shown, when the abutment portion 11B of the input shaft 11 is omitted, the input shaft body 11A becomes the input shaft 11 itself. Furthermore, when the recess 12G of the output shaft 12 is omitted, for example, the axial length of the second insertion portion 12E extends in the pressing direction D1 by the amount of the axial length of the recess 12G. In this case, the axial position of the inner end face of the second insertion portion 12E coincides, for example, with the axial position of the stepped surface 12C. Therefore, Figure 2 The thickness W1 of the wall of the output shaft 12 in the comparative example shown is greater than that of the output shaft 12. Figure 1 The thickness W1 of the embodiment shown is thin.

[0032] However, the second gap δ2 is smaller than the third gap δ3. The second gap δ2 is the axial gap between the second end face of the input shaft body 11A and the inner end face of the second insertion part 12E. The third gap δ3 is the axial gap between the second end face of the magnet holder 16 and the first end face of the output shaft 12. When a secondary collision occurs, the movement of the input shaft 11 and the torsion bar 13 in the pressing direction D1 is restricted by the axial contact between the second end face of the input shaft body 11A and the inner end face of the second insertion part 12E.

[0033] In this embodiment, the axial position of the inner end face of the second insertion portion 12E is located at a position offset by the axial length of the recess 12G on the side opposite to the pressing direction D1, compared to the axial position of the inner end face of the second insertion portion 12E in the comparative example. That is, the inner end face of the second insertion portion 12E in this embodiment is located further away from the step surface 12C in a direction opposite to the pressing direction D1 compared to the inner end face of the second insertion portion 12E in the comparative example. Therefore, according to this embodiment, the wall thickness W1 of the output shaft 12 can be ensured compared to the comparative example.

[0034] Therefore, it is possible to suppress the reduction in the overall strength of the output shaft 12 while preventing contact between the output shaft 12 and the magnet holder. Furthermore, the overall strength of the output shaft 12 is ensured. Therefore, in the event of a secondary collision, it is possible to suppress the deformation or breakage of a portion of the output shaft 12 caused by the impact of the front end face of the abutment portion 11B abutting against the inner end face of the recess 12G in the axial direction. A portion of the output shaft 12 that is prone to deformation or breakage is, for example, the portion of the output shaft 12 having a thickness W1 between the first corner and the second corner.

[0035] <Effects of this implementation method>

[0036] This implementation method has the following effects.

[0037] (1) The input shaft 11 has an input shaft body 11A and an abutment portion 11B. The second end of the input shaft body 11A has a fixing hole 11C for pressing the first end of the torsion bar 13 into. The output shaft 12 has a large-diameter portion 12A and a small-diameter portion 12B. The large-diameter portion 12A has a first insertion portion 12D and a second insertion portion 12E, and the small-diameter portion 12B has a third insertion portion 12F. The first insertion portion 12D and the second insertion portion 12E constitute the input shaft insertion portion. The third insertion portion 12F corresponds to the torsion bar insertion portion.

[0038] The axial inner end face of the input shaft insertion portion has a recess 12G that is recessed in the direction from the first end of the output shaft 12 toward the second end. The inner diameter of the recess 12G is smaller than the inner diameter of the input shaft insertion portion and larger than the inner diameter of the torsion bar insertion portion. The abutment portion 11B has a front end face that faces the inner end face of the recess 12G in the axial direction of the input shaft 11. The axial gap between the front end face of the abutment portion 11B and the inner end face of the recess 12G, i.e., the first gap δ1, is smaller than the axial gap between the sensor component and the first end of the output shaft 12, i.e., the third gap δ3. The sensor component includes a magnet holder 16 and a sensor magnet 17.

[0039] In the event of a secondary collision involving the driver and steering wheel 14, the input shaft 11 may move together with the torsion bar 13 in the pressing direction D1. The pressing direction D1 is the direction in which the input shaft 11 is pressed into the output shaft 12. In this case, before the sensor component and the first end of the output shaft 12 abut in the axial direction, the front end face of the abutment portion 11B abuts in the axial direction with the inner end face of the recess 12G. Therefore, the sensor component can be protected.

[0040] Furthermore, the inner end face of the input shaft insertion portion has a recess 12G. Therefore, the axial position of the inner end face of the input shaft insertion portion, relative to the axial position of the stepped surface 12C, is located at a position offset by the axial length of the recess 12G to the side opposite to the pressing direction D1. Therefore, compared to the case where the axial length of the input shaft insertion portion is extended in the pressing direction D1 by the amount of the recess 12G instead of providing the recess 12G, the wall thickness W1 of the output shaft 12 can be ensured. Additionally, the strength of the output shaft 12 can be ensured. The thickness W1 is the length between the first corner where the outer peripheral surface of the small-diameter portion 12B intersects the stepped surface 12C, and the second corner where the inner peripheral surface of the first insertion portion 12E intersects the axial inner end face.

[0041] (2) A stepped surface 12C extending in a direction orthogonal to the axial direction of the output shaft 12 is formed at the boundary between the large-diameter portion 12A and the small-diameter portion 12B. The axial position of the inner end face of the recess 12G coincides with the axial position of the stepped surface 12C. Therefore, compared to the case where the axial length of the input shaft insertion portion is extended instead of the recess 12G so that the axial position of the inner end face of the input shaft insertion portion coincides with the axial position of the stepped surface 12C, the wall thickness W1 of the output shaft 12 can be ensured.

[0042] (3) The stepped surface 12C is located radially outward from the inner circumferential surface of the input shaft insertion portion. In a steering shaft 10 with this structure, depending on the inner diameter or depth of the input shaft insertion portion, a portion of the wall thickness W1 of the output shaft 12 is easily produced to be thinner. Depth refers to the axial length of the input shaft insertion portion. Therefore, this embodiment is suitable for a steering shaft 10 having a stepped cylindrical body, i.e., an output shaft 12.

[0043] (4) The gap between the front end face of the abutment portion 11B and the inner end face of the recess 12G is the first gap δ1. The axial gap between the second end of the input shaft body 11A and the inner end face of the input shaft insertion portion is the second gap δ2. The axial gap between the sensor component and the first end of the output shaft 12 is the third gap δ3. The first gap δ1 is smaller than the second gap δ2. The second gap δ2 is smaller than the third gap δ3. According to this structure, in the event of a secondary collision, the front end face of the abutment portion 11B can first abut against the inner end face of the recess 12G in the axial direction.

[0044] <Other Implementation Methods>

[0045] This implementation method can also be modified as follows.

[0046] The axial position of the inner end face of the recess 12G may not coincide with the axial position of the step surface 12C. For example, the axial position of the inner end face of the recess 12G may be located on the side opposite to the pressing direction D1 relative to the axial position of the step surface 12C.

[0047] The stepped surface 12C only needs to be located radially outward from the inner circumferential surface of the second insertion portion 12E. For example, when viewed axially from the output shaft 12, at least a portion of the stepped surface 12C may overlap with the first insertion portion 12D. As used in this specification, the expression "at least a portion of A" means "a part of A or all of A".

Claims

1. A steering shaft, characterized in that, It has an input shaft, an output shaft, and a torsion bar. The input shaft has: an input shaft body having a first end to which torque is applied by operation of a steering wheel, and a second end for a non-through fixed hole opening extending axially; and an abutment portion disposed at the second end of the input shaft body, having a diameter smaller than that of the input shaft body. The output shaft is a cylindrical body with a circular cross-section, open at both ends in the axial direction, and has a large-diameter portion including a first end of the output shaft and a small-diameter portion including a second end of the output shaft. The torsion bar has: a first end, which is fixed to the input shaft when pressed into the fixing hole; and a second end, which is fixed to the output shaft when pressed into the interior of the output shaft. The large-diameter portion has an input shaft insertion portion that opens at a first end of the output shaft, and the second end of the input shaft is rotatably inserted into the input shaft insertion portion. The small-diameter portion has a torsion bar insertion portion that opens at the second end of the output shaft. The inner diameter of the torsion bar insertion portion is smaller than the inner diameter of the input shaft insertion portion. The second end of the torsion bar is fixed to the small-diameter portion when pressed into the torsion bar insertion portion. The axial inner end face of the input shaft insertion portion has a recess that is recessed in the direction from the first end of the output shaft toward the second end. The recess has an inner diameter that is smaller than the inner diameter of the input shaft insertion portion and larger than the inner diameter of the torsion bar insertion portion. The portion of the input shaft that protrudes outside the input shaft insertion portion has a sensor component constituting a sensor device for detecting the torque, the sensor component being axially opposed to the first end of the output shaft. The abutment portion has a front end face facing the inner end face of the recess in the axial direction of the input shaft, and the axial gap between the front end face of the abutment portion and the inner end face of the recess is smaller than the axial gap between the sensor component and the first end of the output shaft.

2. The steering shaft according to claim 1, characterized in that, A stepped surface extending in a direction orthogonal to the axial direction of the output shaft is formed at the boundary between the large-diameter portion and the small-diameter portion. The axial position of the inner end face of the recess is consistent with the axial position of the stepped surface.

3. The steering shaft according to claim 1 or 2, characterized in that, A stepped surface extending in a direction orthogonal to the axial direction of the output shaft is formed at the boundary between the large-diameter portion and the small-diameter portion. The stepped surface is located radially outward from the inner circumferential surface of the input shaft insertion part.

4. The steering shaft according to claim 1 or 2, characterized in that, The axial gap between the front end face of the abutment portion and the inner end face of the recess is the first gap. The axial gap between the second end of the input shaft body and the inner end face of the input shaft insertion part is the second gap. The axial gap between the sensor component and the first end of the output shaft is the third gap. The first gap is smaller than the second gap, and the second gap is smaller than the third gap.

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