Steering shaft

Abstract

A steering shaft (10) comprises an input shaft (11), an output shaft (12), and a torsion bar (13). The input shaft has a first end part to which torque is applied and a second end part provided with a contact part (11B). The output shaft has an input shaft insertion part (12D, 12E) into which the second end part of the input shaft is inserted. The input shaft insertion part opens onto a first end part of the output shaft. The axial inner end face of the input shaft insertion part has a recessed part (12G). A portion of the input shaft that is exposed to the outside of the input shaft insertion part has sensor components (16, 17) that face the first end part of the output shaft in the axial direction. A gap in the axial direction between the leading end face of the contact part and the inner end face of the recessed part facing the leading end face is narrower than a gap in the axial direction between the sensor components and the first end part of the output shaft.

Description

steering shaft

[0001] The present disclosure relates to a steering shaft.

[0002] For example, the steering shaft disclosed in Patent Document 1 includes an upper shaft and a lower shaft. A first end of the upper shaft is connected to a steering wheel. The lower shaft includes 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 coupled to the second end of the upper shaft via a spline fit. The input shaft has a fixing hole. The fixing hole opens to the second end of the input shaft. The output shaft is a stepped cylindrical body with a circular cross-sectional shape. The second end of the input shaft is rotatably inserted into an insertion portion provided at the first end of the output shaft.

[0004] A first end of the torsion bar is fitted into a fixing hole in the input shaft, and the first end of the torsion bar is rotatable integrally with the input shaft. A second end of the torsion bar is fitted onto the inner periphery of the second end of the output shaft, and the second end of the torsion bar is rotatable integrally with the output shaft.

[0005] Japanese Patent Application Laid-Open No. 2023-132532

[0006] The steering shaft of Patent Document 1 has the following concerns. Specifically, if the output shaft is a stepped cylindrical body, there is a risk that the wall thickness of the output shaft may be thin in some places depending on the inner diameter or depth of the insertion portion. The depth is the axial length of the insertion portion. As a result, there is a concern that the strength of the output shaft may be reduced.

[0007] The steering shaft includes an input shaft, an output shaft, and a torsion bar. The input shaft includes an input shaft body having a first end to which torque is applied by operating the steering wheel and a second end into which a non-through fixing hole extending axially opens, and an abutment portion provided at the second end of the input shaft body and having a diameter smaller than that of the input shaft body. The output shaft is a cylindrical body having a circular cross-sectional shape with both ends open in the axial direction, and includes 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 by being press-fitted into the fixing hole, and a second end fixed to the output shaft by being press-fitted inside the output shaft. The large-diameter portion has an input shaft insertion portion opening 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 small-diameter portion has a torsion bar insertion portion opening at the second end of the output shaft. The torsion bar insertion portion has a diameter smaller than the inner diameter of the input shaft insertion portion, and the second end of the torsion bar is press-fitted into the torsion bar insertion portion and fixed to the small diameter portion. The axial inner end surface of the input shaft insertion portion has a recess recessed in a direction from the first end to the second end of the output shaft, the recess having an inner diameter smaller than the inner diameter of the input shaft insertion portion and larger than the inner diameter of the torsion bar insertion portion. A portion of the input shaft exposed to the outside of the input shaft insertion portion has a sensor component constituting a sensor device that detects torque, and the sensor component axially faces the first end of the output shaft. The abutting portion has a tip surface facing the inner end surface of the recess in the axial direction of the input shaft, and an axial gap between the tip surface of the abutting portion and the inner end surface of the recess is narrower than the axial gap between the sensor component and the first end of the output shaft.

[0008] Fig. 1 is a cross-sectional view of a main part of a steering shaft according to one embodiment, and Fig. 2 is a cross-sectional view of a main part of a steering shaft according to a comparative example.

[0009] A steering shaft according to one embodiment will be described. As shown in Fig. 1, a steering shaft 10 is used, for example, in an electric power steering device 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.

[0010] The input shaft 11 is a solid cylindrical body with a circular cross-sectional shape and includes an input shaft main body 11A and an abutment portion 11B. Torque is applied to a first end of the input shaft main body 11A by operating the steering wheel 14. The abutment portion 11B is a protrusion provided on a second end of the input shaft main 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 main body 11A. The input shaft 11 has a fixing hole 11C. The fixing hole 11C is provided on the axial end surface of the abutment portion 11B. The fixing hole 11C is a blind hole with a circular cross-sectional shape. The fixing hole 11C extends in a direction from the axial end surface of the abutment portion 11B toward the first end of the input shaft 11.

[0011] The output shaft 12 is a hollow cylindrical body having a circular cross section and both axial ends are open. The second end of the input shaft 11 is rotatably inserted into the first end of the output shaft 12.

[0012] The output shaft 12 is a stepped cylindrical body having a large diameter portion 12A and a small diameter portion 12B. The large diameter portion 12A is a portion that includes a first end of the output shaft 12. The small diameter portion 12B is a portion that includes a 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 step surface 12C is formed at the boundary between the large diameter portion 12A and the small diameter portion 12B. The step surface 12C is a surface located on an imaginary plane that extends in a direction perpendicular to the axial direction of the output shaft 12. The step surface 12C is formed around the entire circumference of the steering shaft 10.

[0013] A bearing 18 is attached to 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, which are held rollably between the inner ring and the outer ring. The bearing 18 is positioned in the axial direction by the stepped surface 12C. That is, the inner ring of the bearing 18 abuts against the stepped surface 12C in the axial direction, thereby restricting the movement of the bearing 18 in the direction from the second end to the first end of the output shaft 12. The inner ring of the bearing 18 is maintained in contact with the stepped surface 12C.

[0014] 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 connected to one another. The first to third insertion portions 12D, 12E, and 12F are arranged in order from the first end to the second end of the output shaft 12. The first insertion portion 12D and the second insertion portion 12E are provided in the large diameter portion 12A. The third insertion portion 12F is provided in the small diameter portion 12B. The stepped surface 12C is located radially outward of the inner circumferential surfaces of the first insertion portion 12D and the second insertion portion 12E. In other words, when viewed in the axial direction of the output shaft 12, the stepped surface 12C does not overlap with the first insertion portion 12D or the second insertion portion 12E.

[0015] The first insertion portion 12D opens to a first end surface 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 to a second end surface of the output shaft 12. The inner diameters of the first to third insertion portions 12D, 12E, and 12F decrease in this order. 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 main body 11A.

[0016] A recess 12G is provided on the axial inner end surface of the second insertion portion 12E. The recess 12G is a countersunk hole having a circular cross section and extends in a direction from the first end to the second end of the output shaft 12. In the axial direction of the output shaft 12, the position of the inner end surface of the recess 12G coincides with the position of the step 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.

[0017] 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 interposed between the outer peripheral surface of the input shaft main body 11A and the inner peripheral surface of the first insertion portion 12D. The bearing 15 is, for example, a needle bearing. The input shaft 11 is rotatably supported by 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.

[0018] In the axial direction of the input shaft 11, the second end of the input shaft body 11 faces the inner end surface of the second insertion portion 12E. The abutting 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 tip surface of the abutting portion 11B and the inner end surface of the recess 12G. The tip surface is the end surface of the abutting portion 11B 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 surface of the input shaft body 11 and the inner end surface of the second insertion portion 12E. The first gap δ1 is narrower than the second gap δ2.

[0019] The torsion bar 13 is a rod-shaped body having a circular cross section and has a first end and a second end. The outer diameters of the first end and the second end are larger than the outer diameter of the portion of the torsion bar 13 between the first end and the second end. The first end of the torsion bar 13 is fixed to the input shaft 11 by being press-fitted into a fixing hole 11A of the input shaft 11. The first end of the torsion bar can rotate integrally with the input shaft 11. The second end of the torsion bar 13 is inserted into a third insertion portion 12F and exposed 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 portion 12F by being press-fitted into the inner circumferential surface of the third insertion portion 12F. The second end of the torsion bar 13 can rotate integrally with the output shaft 12. The third insertion portion 12F corresponds to a torsion bar insertion portion.

[0020] A sensor magnet 17 is fixed via a magnet holder 16 to the outer peripheral surface of the portion of the input shaft 11 that is exposed from the output shaft 12. The magnet holder 16 and the sensor magnet 17 are cylindrical bodies with circular cross-sectional shapes. The sensor magnet 16 is a source of magnetic flux. 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 that are located opposite each other in the axial direction of the input shaft 11. The first end face is the end face of the holder 16 that is farther from the output shaft 12 in the axial direction of the input shaft 11. The second end face is the end face of the holder 16 that is closer to the output shaft 12 in the axial direction of the input shaft 11.

[0021] A third gap δ3 is formed between the second end face of the magnet holder 16 and the first end face of the output shaft 12 in the axial direction of the input shaft 11. The third gap δ3 is wider than the second gap δ2. That is, of the first to third gaps δ1, δ2, and δ3, the first gap δ1 is the narrowest and the third gap δ3 is the widest.

[0022] The magnet holder 15 and the sensor magnet 16 are sensor components that constitute a sensor device. The sensor device is, for example, a torque sensor that detects steering torque applied to a 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 in response to the steering torque, causing 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 magnetic flux that corresponds to the amount of twist of the torsion bar 13. The steering torque is used, for example, to control an electric power steering device.

[0023] <Operation of the Present Embodiment> Next, the operation of the present embodiment will be described. During a vehicle collision, a primary collision occurs in which the vehicle collides with another vehicle or a building, etc., followed by a secondary collision in which the driver collides with the steering wheel 14 due to inertia caused by a sudden decrease in vehicle speed. An impact force F1 during this secondary collision acts on the steering shaft 10 in a pushing direction D1, which is a direction in which the input shaft 11 is pushed into the output shaft 12. The impact force F1 is transmitted in the order of the input shaft 11, the torsion bar 13, and the output shaft 12. When the impact force F1 exceeds the holding force caused by the press-fitting 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 together in the pushing direction D1.

[0024] Movement of the input shaft 11 and the torsion bar 13 in the pushing direction D1 is restricted by the tip surface of the abutment portion 11B abutting in the axial direction against the inner end surface of the recess 12G. However, because the first gap δ1 is narrower than the second gap δ2, the tip surface of the abutment portion 11B abuts against the inner end surface of the recess 12G before the second end surface of the input shaft main body 11 abuts against the inner end surface of the second insertion portion 12E. Furthermore, because the first gap δ1 is narrower than the third gap δ3, the tip surface of the abutment portion 11B abuts against the inner end surface of the recess 12G before the second end surface of the magnet holder 16 abuts against the first end surface of the output shaft 12. Contact between the magnet holder 16 and the output shaft 12 is avoided, thereby suppressing damage to the sensor magnet 17.

[0025] The input shaft 11 has the abutment portion 11B, and the output shaft 12 has the recess 12G, thereby ensuring a wall thickness W1 of the output shaft 12. The thickness W1 is the length between a first corner where the outer circumferential surface of the small diameter portion 12B intersects with the step surface 12C, and a second corner where the inner circumferential surface of the first insertion portion 12E intersects with the inner end face in the axial direction. 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.

[0026] As a comparative example, consider a configuration in which the abutment portion 11 is omitted from the input shaft 11 and the recess 12 is omitted from the output shaft 12. As shown in FIG. 2 , when the abutment portion 11 is omitted from the input shaft 11, the input shaft main body 12A becomes the input shaft 12 itself. Furthermore, when the recess 12 is omitted from the output shaft 12, for example, the axial length of the second insertion portion 12E is extended in the pushing direction D1 by the axial length of the recess 12. In this case, the axial position of the inner end face of the second insertion portion 12E coincides with the axial position of the step surface 12C, for example. Therefore, the wall thickness W1 of the output shaft 12 in the comparative example shown in FIG. 2 is thinner than the thickness W1 of the present embodiment shown in FIG. 1 .

[0027] However, the second gap δ2 is narrower than the third gap δ3. The second gap δ2 is an axial gap between the second end face of the input shaft body 11 and the inner end face of the second insertion portion 12E. The third gap δ3 is an 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 pushing direction D1 is restricted by the second end face of the input shaft body 12A abutting axially against the inner end face of the second insertion portion 12E.

[0028] In the present embodiment, the axial position of the inner end face of the second insertion portion 12E is located on the opposite side of the pushing-in direction D1 from the axial position of the inner end face of the second insertion portion 12E of the comparative example by the axial length of the recess 12. That is, the inner end face of the second insertion portion 12E of the present embodiment is farther away from the step surface 12C in the direction opposite to the pushing-in direction D1 than the inner end face of the second insertion portion 12E of the comparative example. Therefore, according to the present embodiment, it is possible to ensure a larger wall thickness W1 of the output shaft 12 than in the comparative example.

[0029] Therefore, it is possible to avoid contact between the output shaft 12 and the magnet holder while suppressing a decrease in the strength of the entire output shaft 12. Furthermore, the strength of the entire output shaft 12 is ensured. Therefore, in the event of a secondary collision, deformation or breakage of a portion of the output shaft 12 due to the impact when the tip surface of the abutment portion 11B abuts on the inner end surface of the recess 12G in the axial direction is suppressed. An example of a portion of the output shaft 12 that is prone to deformation or breakage is a portion having a thickness W1 between the first corner and the second corner of the output shaft 12.

[0030] <Effects of this embodiment> This embodiment has the following effects. (1) The input shaft 11 has an input shaft main body 11A and an abutment portion 11B. The second end of the input shaft main body 11A has a fixing hole 11C into which the first end of the torsion bar 13 is press-fitted. The output shaft 12 has a large diameter portion 12A and a small diameter portion 11B. The large diameter portion 11A has a first insertion portion 12D and a second insertion portion 12E, and the small diameter portion 11B has a third insertion portion 12F. The first insertion portion 12D and the second insertion portion 12E constitute an input shaft insertion portion. The third insertion portion 12F corresponds to a torsion bar insertion portion.

[0031] The axial inner end surface of the input shaft insertion portion has a recess 12G recessed in a direction from the first end to the second end of the output shaft 12. 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 abutting portion 11B has a tip surface that faces the inner end surface of the recess 12G in the axial direction of the input shaft 11. A first gap δ1, which is the axial gap between the tip surface of the abutting portion 11B and the inner end surface of the recess 12G, is narrower than a third gap δ3, which is the axial gap between the sensor component and the first end of the output shaft 12. The sensor component includes a magnet holder 16 and a sensor magnet 17.

[0032] In the event of a secondary collision in which the driver collides with the steering wheel 14, the input shaft 11 may move in the pushing direction D1 together with the torsion bar 13. The pushing direction D1 is a direction in which the input shaft 11 is pushed into the output shaft 12. In this case, the tip surface of the abutting portion 11B abuts against the inner end surface of the recess 12G in the axial direction before the sensor component abuts against the first end of the output shaft 12 in the axial direction. This allows the sensor component to be protected.

[0033] The inner end surface of the input shaft insertion portion also has a recess 12G. Therefore, the axial position of the inner end surface of the input shaft insertion portion is located on the opposite side of the axial position of the stepped surface 12C in the pushing direction D1 by the axial length of the recess 12G. Therefore, compared to a case where the axial length of the input shaft insertion portion is extended in the pushing direction D1 by the axial length of the recess 12G instead of providing the recess 12G, the wall thickness W1 of the output shaft 12 can be ensured. Furthermore, the strength of the output shaft 13 can be ensured. The thickness W1 is the length between a first corner where the outer circumferential surface of the small diameter portion 12B and the stepped surface 12C intersect and a second corner where the inner circumferential surface of the first insertion portion 12E intersects with the axial inner end face.

[0034] (2) A step surface 12C that extends in a direction perpendicular 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 surface of the recess 12G coincides with the axial position of the step surface 12C. Therefore, the wall thickness W1 of the output shaft 12 can be ensured more reliably than if, instead of providing the recess 12G, the axial length of the input shaft insertion portion were extended so that the axial position of the inner end surface of the input shaft insertion portion coincides with the axial position of the step surface 12C.

[0035] (3) The stepped surface 12C is located radially outward of the inner circumferential surface of the input shaft insertion portion. In a steering shaft 10 having this configuration, depending on the inner diameter or depth of the input shaft insertion portion, portions where the wall thickness W1 of the output shaft 12 is thin are likely to occur. The depth is the axial length of the input shaft insertion portion. For this reason, this embodiment is suitable for a steering shaft 10 having an output shaft 12 that is a stepped cylindrical body.

[0036] (4) The gap between the tip surface of the abutment portion 11B and the inner end surface of the recess 12G is a first gap δ1. The axial gap between the second end of the input shaft body 11A and the inner end surface of the input shaft insertion portion is a second gap δ2. The axial gap between the sensor component and the first end of the output shaft 12 is a third gap δ3. The first gap δ1 is narrower than the second gap δ2. The second gap δ2 is narrower than the third gap δ3. With this configuration, when a secondary collision occurs, the tip surface of the abutment portion 11B can be first brought into axial contact with the inner end surface of the recess 12G.

[0037] Other Embodiments This embodiment may be modified as follows: The axial position of the inner end surface of the recess 12G does not have to coincide with the axial position of the step surface 12C. For example, the axial position of the inner end surface of the recess 12G may be located on the opposite side of the axial position of the step surface 12C in the pushing direction D1.

[0038] The stepped surface 12C may be located radially outward from the inner circumferential surface of the second insertion portion 12E. For example, at least a portion of the stepped surface 12C may overlap the first insertion portion 12D when viewed in the axial direction of the output shaft 12. The expression "at least a portion of A" used in this specification means "a portion of A or all of A."

Claims

1. A steering shaft comprising an input shaft, an output shaft, and a torsion bar, wherein: The input shaft has an input shaft body having a first end to which torque is applied by an operation of a steering wheel and a second end at which a non-penetrating fixing hole extending in the axial direction opens, and a contact portion provided at the second end of the input shaft body and having a smaller diameter than the input shaft body; The output shaft is a cylindrical body having a circular cross-sectional shape with both ends open in the axial direction, 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 in a state of being press-fitted into the fixing hole and a second end fixed to the output shaft in a state of being press-fitted into the output shaft; The large-diameter portion has an input shaft insertion portion opening 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 small-diameter portion has a torsion bar insertion portion opening at the second end of the output shaft, the torsion bar insertion portion has a smaller diameter than the inner diameter of the input shaft insertion portion, and the second end of the torsion bar is fixed to the small-diameter portion in a state of being press-fitted into the torsion bar insertion portion; The inner end face in the axial direction of the input shaft insertion portion has a recess recessed in the direction from the first end to the second end of the output shaft, the recess has an inner diameter smaller than the inner diameter of the input shaft insertion portion and larger than the inner diameter of the torsion bar insertion portion; A portion of the input shaft exposed 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 contact portion has a tip face opposed to the inner end face of the recess in the axial direction of the input shaft, and the axial gap between the tip face of the contact portion and the inner end face of the recess is narrower than the axial gap between the sensor component and the first end of the output shaft. A steering shaft.

2. The steering shaft according to claim 1, wherein a step surface extending in a direction perpendicular to the axial direction of the output shaft is formed at a boundary between the large-diameter portion and the small-diameter portion, and an axial position of the inner end face of the recess coincides with an axial position of the step surface.

3. A stepped surface that extends 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, and the stepped surface is located radially outside the inner peripheral surface of the input shaft insertion portion. The steering shaft according to claim 1 or 2.

4. The axial gap between the tip end surface of the contact portion and the inner end surface of the concave portion is a first gap, the axial gap between the second end portion of the input shaft main body and the inner end surface of the input shaft insertion portion is a second gap, and the axial gap between the sensor component and the first end portion of the output shaft is a third gap. The first gap is narrower than the second gap, and the second gap is narrower than the third gap. The steering shaft according to claim 1 or 2.

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