Steering device

Abstract

To reduce a dimension of a steering device along an axial direction of a steering shaft while mounting an electric motor and a reduction gear at a driver's seat side.SOLUTION: A steering device includes: a steering shaft 1; an electric motor 4 that is provided at an end-1a side where a steering wheel is provided in both ends 1a and 1b of the steering shaft 1; a reduction gear 5 that decelerates the rotation force by the electric motor 4; a ball screw mechanism 2 that is provided at the steering shaft 1; a sector gear 3 that has teeth 3a to be meshed with rack teeth 20c provided on an outer circumferential surface of a nut 20; and a four-point contact ball bearing 21 that is arranged at a fifth shaft portion 12e located at the end 1b side that is an opposite side of the side where the electric motor 4 is provided in both ends 1a and 1b of the steering shaft 1. The four-point contact ball bearing 21 receives thrust force and radial force both applied to the steering shaft 1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a steering device.

Background Art

[0002] As a steering device, for example, the steering device described in Patent Document 1 below is known.

[0003] In the steering device of Patent Document 1, it is configured as an integral type steering device used for large vehicles and the like. In this steering device, an electric motor that applies a steering assist force to the steering shaft and a speed reducer that decelerates the rotational force of the electric motor are arranged on the ground side.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the electric motor and the speed reducer are arranged on the ground side as in the steering device of Patent Document 1, there is a risk that the electric motor and the speed reducer interfere with vehicle peripheral devices, and there is a problem of poor mountability.

[0006] Therefore, in order to solve this problem, it is conceivable to arrange the electric motor and the speed reducer on the driver's seat side. However, in this case, the axial dimension on the driver's seat side becomes long, and for example, there is a risk that a part of the housing interferes with the floor panel.

[0007] The present invention has been devised in view of the above technical problems, and an object of the present invention is to provide a steering device capable of shortening the dimension of the steering device along the axial direction of the steering shaft while mounting the electric motor and the speed reducer on the driver's seat side.

Means for Solving the Problem

[0008] The steering apparatus of the present invention includes a steering shaft to which rotation from a steering wheel is input, an electric motor that is disposed on the end side where the steering wheel is provided among both end portions of the steering shaft and applies a steering assist force to the steering shaft, a speed reducer that decelerates the rotational force of the electric motor, a ball screw mechanism provided on the steering shaft, the first ball screw groove which is a spiral groove formed on the outer peripheral surface of the steering shaft, the second ball screw groove which is a spiral groove formed on the inner peripheral surface of a nut provided around the steering shaft, and a ball screw mechanism having a plurality of balls disposed between the first ball screw groove and the second ball screw groove, a sector gear having a second tooth portion that meshes with a first tooth portion provided on the outer peripheral surface of the nut, and a four-point contact bearing that is disposed at the end portion on the side opposite to the side where the electric motor is provided among both end portions of the steering shaft and rotatably supports the steering shaft.

Effect of the Invention

[0009] According to the present invention, while mounting the electric motor and the speed reducer on the driver's seat side, the dimensions of the steering apparatus along the axial direction of the steering shaft can be shortened.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the steering apparatus of the present invention will be described with reference to the drawings. In the following embodiments, an example in which this steering apparatus is applied as an integral type steering apparatus used for large vehicles or the like is shown.

[0012] [First Embodiment] FIG. 1 is a longitudinal sectional view of a steering apparatus according to a first embodiment. In FIG. 1, for convenience of explanation, the side linked to the steering wheel in the direction of the rotation axis Z of the steering shaft 1 (the upper side in the figure) is referred to as a “first end portion 1a”, and the side to which the four-point contact ball bearing 21 is attached (the lower side in the figure) is referred to as a “second end portion 1b”. In FIG. 1, for convenience of explanation, the internal structures of the detection unit 16 and the signal processing unit 23 of the torque sensor 14 are not shown. Also, regarding the detection unit 16 and the signal processing unit 23, the shape of the housing that houses them will be mainly described.

[0013] This steering apparatus mainly includes a steering shaft 1 linked to a steering wheel (not shown), a sector gear 3 connected to the steering shaft 1 via a ball screw mechanism 2 and used for steering of a steered wheel, an electric motor 4 that applies a steering assist force to the steering shaft 1, and a speed reducer 5 that decelerates the rotation of the electric motor 4.

[0014] The steering shaft 1 passes through a cylindrical first housing 6, a cylindrical second housing (reduction gear side housing) 7 to which the first housing 6 is attached, and a cylindrical connecting member 8 provided on the end face 7a on the second end portion 1b side of the second housing 7, and extends into a cylindrical third housing (nut side housing) 9 provided on the second end portion 1b side of the connecting member 8. The steering shaft 1 includes an input shaft 10 to which a rotational force from a steering wheel (not shown) is transmitted, and an output shaft 12 connected to the input shaft 10 via a torsion bar 11.

[0015] The input shaft 10 has a one - end - side shaft portion 10a located on the first end portion 1a side, an intermediate shaft portion 10b formed integrally with the one - end - side shaft portion 10a and having a larger diameter than the one - end - side shaft portion 10a, and the other - end - side shaft portion 10c formed integrally with the intermediate shaft portion 10b and having a smaller diameter than the intermediate shaft portion 10b. An annular dust seal 13 for preventing the intrusion of dust and dirt from the outside into the interior of the first housing 6 etc. is provided at a position on the outer peripheral surface of the intermediate shaft portion 10b closer to the one - end - side shaft portion 10a. Also, a cylindrical magnet portion 15, at which a change in magnetism is detected by a torque sensor 14 (to be described later), is caulked and fixed at a position on the outer peripheral surface of the intermediate shaft portion 10b axially adjacent to the other - end - side shaft portion 10c.

[0016] The output shaft 12 has a cylindrical first shaft portion 12a located on the first end portion 1a side, a cylindrical second shaft portion 12b formed integrally with the first shaft portion 12a and having a larger diameter than the first shaft portion 12a, a cylindrical third shaft portion 12c formed integrally with the second shaft portion 12b and having a larger diameter than the second shaft portion 12b, a cylindrical fourth shaft portion 12d formed integrally with the third shaft portion 12c and having a smaller diameter than the third shaft portion 12c, a fifth shaft portion 12e formed integrally with the fourth shaft portion 12d and having a smaller diameter than the fourth shaft portion 12d, and a sixth shaft portion 12f formed integrally with the fifth shaft portion 12e and having a smaller diameter than the fifth shaft portion 12e.

[0017] On the outer peripheral surface of the first shaft portion 12a, a reduced-diameter portion 16b of a detection portion 16 (described later) of the torque sensor 14 is press-fitted and fixed. Further, on the outer peripheral surface of the second shaft portion 12b, a core metal portion 18 of a worm wheel 17 (described later) of the speed reducer 5 is press-fitted and fixed. Further, on the outer peripheral surface of the third shaft portion 12c, a deep groove ball bearing 19 that rotatably supports the third shaft portion 12c is provided. Further, around the fourth shaft portion 12d, a nut 20 that constitutes a part of the ball screw mechanism 2 is provided. Further, on the outer peripheral surface of the fifth shaft portion 12e, a four-point contact ball bearing 21 that rotatably supports the fifth shaft portion 12e is provided. Further, around the sixth shaft portion 12f, a fixing member 22 that fixes the four-point contact ball bearing 21 to the fifth shaft portion 12e is provided.

[0018] The first housing 6 is generally formed in a cylindrical shape from a metal material and mainly houses the torque sensor 14 provided around the input shaft 10.

[0019] The second housing 7 is generally formed in a cylindrical shape from a metal material and mainly houses the speed reducer 5 disposed around the second shaft portion 12b of the output shaft 12.

[0020] The connecting member 8 is generally formed in a cylindrical shape from a metal material. The connecting member 8 connects the end face 7a on the second end portion 1b side of the second housing 7 and the end face 9a on the first end portion 1a side of the third housing 9, and holds a shielded or rubber-sealed deep groove ball bearing 19 between the outer peripheral surface of the third shaft portion 12c of the output shaft 12.

[0021] The third housing 9 is generally formed in a cylindrical shape from a metal material. The third housing 9 has a nut housing portion 9b that mainly houses the nut 20 provided around the output shaft 12, and a sector gear housing portion 9c that communicates with the nut housing portion 9b and houses the sector gear 3.

[0022] The torque sensor 14 is configured as a well-known magnetic torque sensor that uses a magnet portion 15 caulked and fixed to the outer peripheral surface of the input shaft 10. The torque sensor 14 includes a detection unit 16 that detects a signal corresponding to a change in magnetism of the magnet portion 15 that rotates with the input shaft 10, and a signal processing unit 23 that is disposed around the detection unit 16, processes the signal detected by the detection unit 16, and calculates the steering torque. Note that the signal processing unit 23 may be configured to calculate the steering angle instead of or in addition to the steering torque.

[0023] The detection unit 16 (housing of the detection unit) is formed in an annular shape from a synthetic resin material and is disposed around the magnet portion 15. An annular protrusion 16a that protrudes toward the first end portion 1a along the direction of the rotation axis Z of the steering shaft 1 is formed at a position adjacent to the inner peripheral surface of the detection unit 16 on the axial end surface on the first end portion 1a side of the detection unit 16. Further, an annular reduced-diameter portion 16b that protrudes in a stepped reduced-diameter shape toward the second end portion 1b is formed at a position adjacent to the inner peripheral surface of the detection unit 16 on the axial end surface on the second end portion 1b side of the detection unit 16. This reduced-diameter portion 16b is press-fitted and fixed to the outer peripheral surface of the first shaft portion 12a of the output shaft 12 and rotates with the output shaft 12.

[0024] The signal processing unit 23 (housing of the signal processing unit) is formed in an annular shape by a synthetic resin material and is disposed around the detection unit 16. At a position adjacent to the outer peripheral surface of the signal processing unit 23 on the axial end surface on the second end portion 1b side of the signal processing unit 23, two columnar rotation restricting portions 23a are formed to restrict the rotation of the signal detection unit 16 being dragged by the rotation of the detection unit 16. As shown in FIG. 1, the two rotation restricting portions 23a are arranged to be radially symmetric with the output shaft 12 interposed therebetween. Each rotation restricting portion 23a has an extended portion 23b in a columnar shape that protrudes with a constant diameter toward the second end portion 1b side along the direction of the rotation axis Z of the steering shaft 1 and then tapers in a conical shape, and a columnar rotation restricting cylinder portion 23c that protrudes toward the second end portion 1b side along the direction of the rotation axis Z of the steering shaft 1 from the tip of the extended portion 23b. The rotation restricting cylinder portion 23c is formed to be elastically deformable and has an engaging portion (provided on the back side in FIG. 1) not shown on the tip side. This engaging portion is elastically engaged with a cylindrical portion 7d integrally formed on an overhanging portion 7c that protrudes radially inward from the inner peripheral portion on the first end portion 1a side of the peripheral wall portion 7b of the second housing 7. More specifically, it is elastically engaged with an edge portion 7g on the second end portion 1b side of the circular hole portion 7f of the cylindrical portion 7d. By this elastic engagement, the signal detection unit 16 is held by the second housing 7.

[0025] The speed reducer 5 includes a worm shaft 24 and a worm wheel 17 that meshes with the worm shaft 24. The worm shaft 24 is connected to an output shaft (not shown) of the electric motor 4. The worm wheel 17 is formed by insert molding a metallic core portion 18 having a cylindrical shape into a gear forming portion 25 made of synthetic resin. By press-fitting this core portion 18 onto the outer peripheral surface of the second shaft portion 12b of the output shaft 12, the core portion 18 abuts against the axial end surface on the first end portion 1a side of the third shaft portion 12c. An annular recess 26 continuous in the circumferential direction of the steering shaft 1 is provided between the gear forming portion 25 and the core portion 18. As shown in FIG. 1, the axial end surface 25a on the first end portion 1a side of the gear forming portion 25 is located on the first end portion 1a side with respect to the axial end surface 18a on the first end portion 1a side of the core portion 18.

[0026] The axial end of the second end 2a side of the cylindrical portion 7d of the second housing 7 extends into the annular recess 26 along the direction of the rotation axis Z of the steering shaft 1. For this reason, the axial end face 7h of the second end 1b side of the cylindrical portion 7d is located on the second end 1b side with respect to the axial end face 18a of the first end 1a side of the core metal portion 18. As described above, since the engaging portion of the rotation restricting cylindrical portion 23c is elastically engaged with the edge portion 7g of the circular hole portion 7f of the cylindrical portion 7d, the portion on the second end 1b side of the rotation restricting cylindrical portion 23c also extends into the annular recess 26. That is, the portion on the second end 1b side of the rotation restricting cylindrical portion 23c is inserted into the annular recess 26 up to about half of the depth of the annular recess 26 with reference to the axial end face 18a of the core metal portion 18. In other words, the portion on the second end 1b side of the rotation restricting cylindrical portion 23c overlaps the internal space of the annular recess 26 by an axial length of about half of the depth of the annular recess 26 in the radial direction of the steering shaft 1.

[0027] Also, an annular support portion 7i that protrudes toward the first end 1a side is formed at a position radially outside the cylindrical portion 7d in the protruding portion 7c of the second housing 7. In the state where the first housing 6 is assembled to the second housing 7 as shown in FIG. 1, the tip of the annular support portion 7i is in contact with the annular portion 6a that protrudes radially outward from the outer peripheral surface of the first housing 6.

[0028] Also, a flange portion 7j that protrudes radially outward is formed at the axial end of the circumferential wall portion 7b of the second housing 7 on the second end 1b side. A first hole portion 7k into which a fixing member, for example, a bolt 27 is inserted is formed through the flange portion 7j along the direction of the rotation axis Z of the steering shaft 1.

[0029] The electric motor 4 is driven and controlled based on the steering torque detected by the torque sensor 14 or the like. The electric motor 4 is disposed on the side of the first end portion 1a where the steering wheel is provided among both end portions 1a and 1b of the steering shaft 1. More specifically, the electric motor 4 is disposed at a position adjacent to the first housing 6, the second housing 7, and the connecting member 8, relatively close to the steering wheel provided in the driver's seat (not shown), on the side opposite to the sector gear 3 with the steering shaft 1 interposed therebetween.

[0030] The deep groove ball bearing 19 is a bearing disposed between the third shaft portion 12c of the output shaft 12 and the connecting member 8, and receives a radial force which is a radial force acting on the output shaft 12. The deep groove ball bearing 19 is disposed on the side opposite to the four-point contact ball bearing 21 with the ball screw mechanism 2 interposed therebetween in the axial direction of the steering shaft 1.

[0031] Also, an annular groove into which an O-ring 28, which is an annular seal member formed of, for example, rubber, is fitted is formed at the axial center position of the outer peripheral surface of the third shaft portion 12c. The O-ring 28 seals the space between the outer peripheral surface of the third shaft portion 12c and the inner peripheral surface of the deep groove ball bearing 19 in a liquid-tight manner, whereby lubricant is stored in the vicinity of the speed reducer 5 in the third housing 9, and the lubrication of the meshing portion between the worm shaft 24 and the worm wheel 17 can be improved.

[0032] The connecting member 8 has a cylindrical tubular main body portion 8a, an annular protrusion portion 8b protruding radially outward from the axial center position of the outer peripheral surface of the tubular main body portion 8a, an annular protrusion portion 8c protruding radially inward from the position on the inner peripheral surface of the tubular main body portion 8a closest to the first end portion 1a side, a cylindrical extension portion 8d extending in the direction of the rotation axis Z of the steering shaft 1 from the axial end portion on the first end portion 1a side of the annular protrusion portion 8c toward the first end portion 1a side, and an annular ceiling wall portion 8e extending radially inward from the position on the inner peripheral surface of the extension portion 8d closest to the first end portion 1a side.

[0033] Of the annular protrusion 8b, the portion 8f that faces the sector gear 3 across the third housing 9 in the direction of the rotation axis Z of the steering shaft 1 is expanded radially outward compared to the remaining portions. A second hole portion 8g into which the bolt 27 is inserted is formed to penetrate along the direction of the rotation axis Z of the steering shaft 1 in this portion 8f. By screwing the bolt 27 into the second hole portion 8g of the portion 8f, the first hole portion 7k of the flange portion 7j of the second housing 7, and the screw hole 9d provided in the sector gear housing portion 9c of the portion 8f and the third housing 9, the second housing 7 and the connection member 8 are jointly fastened and fixed to the third housing 9.

[0034] The inner peripheral surfaces of the annular protrusion 8c and the extension portion 8d hold the deep groove ball bearing 19 between them and the outer peripheral surface of the third shaft portion 12c.

[0035] The ceiling wall portion 8e has a radial length that covers the deep groove ball bearing 19 from the first end portion 1a side.

[0036] The ball screw mechanism 2 is composed of a steering shaft side ball screw groove 12g which is a spiral groove provided on the outer peripheral surface of the fourth shaft portion 12d of the output shaft 12, a nut side ball screw groove 20a which is a spiral groove provided on the inner peripheral surface of the nut 20, and a plurality of balls 29 arranged between the ball screw grooves 12g and 20a. The balls 29 support the nut 20 so as to be relatively rotatable with respect to the fourth shaft portion 12d. As shown in FIG. 1, the back surface 20b on the opposite side of the outer peripheral surface of the nut 20 from the sector gear 3 is separated from the inner peripheral surface of the nut housing portion 9b of the third housing 9 that houses the nut 20.

[0037] Further, a plurality of rack teeth 20c are formed on the outer peripheral portion of the nut 20 on the sector gear housing portion 9c side. These rack teeth (tooth portions) 20c mesh with the tooth portion 3a of the sector gear 3. As shown in FIG. 1, the surface 20e on the second end portion 1b side of the outer peripheral surface of the nut 20 from the rack teeth 20c is separated from the inner peripheral surface of the third housing 9.

[0038] The four-point contact ball bearing 21 is arranged at the second end portion 1b on the side opposite to the side where the electric motor 4 is provided (the ground side) among both end portions 1a and 1b of the steering shaft 1. More specifically, the four-point contact ball bearing 21 is arranged around the fifth shaft portion 12e of the output shaft 12. The four-point contact ball bearing 21 has an axial dimension and a radial dimension larger than those of the deep groove ball bearing 19. The four-point contact ball bearing 21 receives both a thrust force, which is a force acting in the axial direction of the output shaft 12, i.e., the direction of the rotation axis Z, and a radial force, which is a force acting in the radial direction of the output shaft 12. More specifically, regarding the force acting on one contact point P among the four contact points of the four-point contact ball bearing 21, for example, the force F acting on the second end portion 1b side of the outer race 30 of the four-point contact ball bearing 21 as shown in FIG. 1, this force F is decomposed into a thrust force F1, which is a force along the direction of the rotation axis Z of the steering shaft 1, and a radial force F2, which is a force directed outward in the radial direction of the steering shaft 1. Therefore, the four-point contact ball bearing 21 receives a thrust force F1 acting through the contact point P and also a radial force F2 acting through the same contact point P and smaller than the thrust force F1. In one example, the thrust force F1 is about 1.5 to 2 times the magnitude of the radial force F2. Therefore, the four-point contact ball bearing 21 is configured such that the contribution rate when receiving the thrust force F1 is much larger than the contribution rate when receiving the radial force F2. In a large vehicle having a sector gear 3 as in the present embodiment, compared with a vehicle of a general size, the thrust force acting on the steering shaft 1 is very large. Therefore, it is advantageous to use the four-point contact ball bearing 21 to receive such a large thrust force and radial force simultaneously.

[0039] Furthermore, the four-point contact ball bearing 21 includes an inner race 31 disposed on the outer peripheral side of the fifth shaft portion 12e, an outer race 30 disposed on the outer peripheral side of the inner race 31, and a plurality of balls 32 disposed between the inner race 31 and the outer race 30. The four-point contact ball bearing 21 is press-fitted into the inner peripheral surface of the third housing 9. Of the corner portions 31a and 31b on the inner peripheral side of the inner race 31, the corner portion 31a on the first end portion 1a side abuts against a stepped portion 12h formed between the fourth shaft portion 12d and the fifth shaft portion 12e of the output shaft 12. On the other hand, of the corner portions 30a and 30b on the outer peripheral side of the outer race 30, the corner portion 30a on the first end portion 1a side abuts against a stepped portion 9e provided on the inner peripheral surface of the third housing 9.

[0040] The fixing member 22 is configured as a nut member and has a female thread portion 22a formed on the inner peripheral surface. The female thread portion 22a on the fixing member side is screwed with a male thread portion 12i on the steering shaft side formed on the outer peripheral surface of the sixth shaft portion 12f of the output shaft 12. By this screwing, the corner portion 31b of the inner race 31 is pressed, and the corner portion 31a of the inner race 31 is pressed against the stepped portion 12h provided on the output shaft 12, so that the inner race 31 is fixed to the output shaft 12.

[0041] A disk-shaped closing member 33 is provided at a position on the second end portion 1b side of the four-point contact ball bearing 21 in the direction of the rotation axis Z of the steering shaft 1. The closing member 33 closes the opening of the third housing 9 from the four-point contact ball bearing 21 side and fixes the outer race 30 of the four-point contact ball bearing 21 to the third housing 9. The closing member 33 is formed of metal or synthetic resin. The closing member 33 has a circular plate-shaped bottom wall portion 33a, a cylindrical inner peripheral wall portion 33b rising from the outer edge portion of the bottom wall portion 33a toward the first end portion 1a side, an annular projecting portion 33c projecting radially outward from the end portion of the inner peripheral wall portion 33b on the first end portion 1a side, and a cylindrical outer peripheral wall portion 33d extending from the outer edge portion of the annular projecting portion 33c toward the second end portion 1b side.

[0042] The space surrounded by the bottom wall portion 33a and the inner peripheral wall portion 33b serves as a fixed member accommodating portion 34 for accommodating the fixed member 22. Also, the length of the outer peripheral wall portion 33d along the direction of the rotation axis Z of the steering shaft 1 is greater than the length of the inner peripheral wall portion 33b along the direction of the rotation axis Z of the steering shaft 1. The axial end face 33e on the first end portion 1a side of the outer peripheral wall portion 33d is located closer to the first end portion 1a side than the axial end face 33f on the first end portion 1a side of the annular projecting portion 33c. For this reason, the axial end face 33e is in contact with the axial end face 30c on the second end portion 1b side of the outer race 30 of the four-point contact ball bearing 21, while the axial end face 33f is spaced apart from the axial end face 31c on the second end portion 1b side of the inner race 31 of the four-point contact ball bearing 21.

[0043] Also, an annular seal groove into which an O-ring 35, which is a seal member, is fitted is formed at a position on the outer peripheral surface of the outer peripheral wall portion 33d closer to the axial end face 33e. The O-ring 35 seals the space between the inner peripheral surface of the third housing 9 and the outer peripheral surface of the outer peripheral wall portion 33d airtightly.

[0044] Also, a male screw portion 33g on the closing member side is formed at a position on the outer peripheral surface of the outer peripheral wall portion 33d on the second end portion 1b side of the O-ring 35, and this male screw portion 33g on the closing member side is screwed into a female screw portion 9f formed on the inner peripheral surface of the end portion on the second end portion 1b side of the third housing 9. By this screwing, the axial end face 33e of the outer race 30 is pressed, and by pressing the corner portion 30a of the outer race 30 against the stepped portion 9e of the third housing 9, the outer race 30 is fixed to the third housing 9.

[0045] The sector gear 3 is provided swingably within a sector gear accommodating portion 9c provided in the third housing 9. One axial end side of the sector gear 3 is connected to the nut 20 via the tooth portion 3a, and the other end side is linked to a steering wheel (not shown) via a pitman arm (not shown).

[0046] In such a steering apparatus, when a driver rotates the steering wheel, the input shaft 10 rotates to twist the torsion bar 11, and the output shaft 12 rotates by the elastic force of the torsion bar 11 generated thereby. As the output shaft 12 rotates, the nut 20 moves in the direction of the rotation axis Z of the steering shaft 1, causing the sector gear 3 to rotate. As a result, the pitman arm is pulled in the vehicle width direction, changing the direction of the steered wheels.

[0047] FIG. 2 is an explanatory diagram showing various steps of the assembly method of the steering apparatus according to the first embodiment. FIG. 2(a) shows the press-fitting step of the worm wheel 17, FIG. 2(b) shows the arrangement step of the connecting member 8 and the arrangement step of the second housing 7, and FIG. 2(c) shows the press-fitting step of the detection portion 16 of the torque sensor 14 and the caulking step of the magnet portion 15. FIG. 3 is an explanatory diagram showing various steps of the assembly method of the steering apparatus according to the first embodiment. FIG. 3(a) shows the assembly step of the first housing 6 and the assembly step of the nut 20, which are subsequent steps to FIG. 2(c), FIG. 3(b) shows the assembly step of the assembly including the steering shaft 1, and FIG. 3(c) shows the assembly step of the sector gear 3, the fixing member 22, the closing member 33, and the electric motor 4.

[0048] First, in the press-fitting step of the worm wheel 17 in FIG. 2(a), the core metal portion 18 having the gear forming portion 25 is press-fitted onto the outer peripheral surface of the second shaft portion 12b of the output shaft 12.

[0049] Next, in the arrangement step of the connecting member 8 in which the outer race of the deep groove ball bearing 19 shown in FIG. 2(b) is press-fitted and fixed, the connecting member 8 is arranged from the second end portion 1b side of the steering shaft 1 so as to be adjacent to the worm wheel 17. Then, in the arrangement step of the second housing 7, the second housing 7 is arranged on the annular protrusion 8b of the connecting member 8 from the first end portion 1a side of the steering shaft 1.

[0050] After the step of arranging the second housing 7, in the step of assembling the torque sensor 14 shown in FIG. 2(c), the reduced-diameter portion 16b of the detection portion 16 is press-fitted onto the outer peripheral surface of the first shaft portion 12a of the output shaft 12. After this press-fitting, the signal processing unit 23 is attached to the cylindrical portion 7d of the second housing 7 by engaging the engaging portion of the rotation restricting cylindrical portion 23c of the signal processing unit 23 with the edge portion 7g of the circular hole portion 7f of the cylindrical portion 7d.

[0051] Then, in the caulking step of the magnet portion 15 shown in FIG. 2(c), the magnet portion 15 is caulked onto the outer peripheral surface of the intermediate shaft portion 10b of the input shaft 10.

[0052] Next, in the step of assembling the first housing 6 shown in FIG. 3(a), the annular portion 6a of the first housing 6 is assembled onto the annular support portion 7i of the second housing 7.

[0053] Also, in the step of assembling the nut 20 shown in FIG. 3(a), the nut 20 is assembled around the fourth shaft portion 12d of the output shaft 12 of the steering shaft 1.

[0054] After the step of assembling the nut 20, the four-point contact ball bearing 21 is press-fitted onto the inner peripheral surface of the third housing 9.

[0055] Next, in the step of assembling the assembly including the steering shaft 1 shown in FIG. 3(b), the assembly assembled as shown in FIG. 3(a) is inserted into the third housing 9 equipped with the four-point contact ball bearing 21. In the state where the assembly is inserted, the fifth shaft portion 12e of the output shaft 12 is inserted into the inner race 31 of the four-point contact ball bearing 21. Further, in this state, the end face 9a on the first end portion 1a side of the third housing 9 is in contact with the annular protrusion 8b of the connecting member 8.

[0056] Then, in the step of assembling the sector gear 3 shown in FIG. 3(c), the sector gear 3 is assembled so that the tooth portion 3a of the sector gear 3 meshes with the rack teeth 20c of the nut 20.

[0057] Also, in the step of assembling the fixing member 22 shown in FIG. 3(c), the fixing member 22 is assembled to the sixth shaft portion 12f by screwing the female screw portion 22a on the fixing member side of the fixing member 22 onto the male screw portion 12i on the steering shaft side of the sixth shaft portion 12f of the output shaft 12. Thereby, the inner race 31 of the four-point contact ball bearing 21 is fixed to the stepped portion 12h provided on the output shaft 12.

[0058] Also, after the step of assembling the fixing member 22, the closing member 33 is assembled to the third housing 9 by screwing the male screw portion 33g on the closing member side of the outer peripheral wall portion 33d of the closing member 33 onto the female screw portion 9f on the housing side of the third housing 9. Thereby, the outer race 30 of the four-point contact ball bearing 21 is fixed to the stepped portion 9e of the third housing 9.

[0059] Also, in the step of assembling the electric motor 4 shown in FIG. 3(c), the electric motor 4 is assembled to the second housing 7 such that the worm shaft 24 meshes with the gear forming portion 25 of the worm wheel 17.

[0060] [Effects of the First Embodiment] As described above, in the first embodiment, the electric motor 4 is arranged on the first end portion 1a side of the both end portions 1a and 1b of the steering shaft 1 where the steering wheel is provided, that is, on the first end portion 1a side on the driver's seat side. In this configuration, the four-point contact ball bearing 21 is arranged around the fifth shaft portion 12e on the second end portion 1b side which is the side opposite to the side where the electric motor 4 is provided among the both end portions 1a and 1b of the steering shaft 1. When the electric motor 4 and the speed reducer 5 associated with the electric motor 4 are arranged on the driver's seat side, the structure on the driver's seat side of the steering device becomes complicated. When further adding components on the driver's seat side, the axial dimension on the driver's seat side of the steering device becomes large, and for example, there is a possibility of causing interference between the first housing 6 and a floor panel (not shown). Therefore, in the present embodiment, by arranging the four-point contact ball bearing 21 on the second end portion 1b side of the steering shaft 1 where there is relatively more space, most of the force applied to the steering shaft 1 of the steering device used for large vehicles is received. Thereby, the axial dimension of the steering device can be shortened. In particular, the axial dimension on the driver's seat side of the steering device can be shortened, and thus, interference between the first housing 6 and a floor panel (not shown) can be suppressed.

[0061] Also, in the present embodiment, the deep groove ball bearing 19 is arranged on the side opposite to the four-point contact ball bearing 21 with the ball screw mechanism 2 interposed therebetween in the axial direction of the steering shaft 1. In other words, the deep groove ball bearing 19 is arranged on the driver's seat side adjacent to the electric motor 4 and the speed reducer 5. Since the four-point contact ball bearing 21 provided on the second end portion 1b side of the steering shaft 1 receives both the thrust force and the radial force, particularly the thrust force having a large ratio acting in large vehicles, a deep groove ball bearing 19 smaller than the four-point contact ball bearing 21 is provided on the driver's seat side, and it is sufficient to receive a relatively small radial force. Therefore, compared with the case where four-point contact ball bearings 21 are provided on both the driver's seat side and the ground side, the axial space on the driver's seat side of the steering device can be efficiently secured.

[0062] Note that the four-point contact ball bearing 21 receives both thrust force and radial force, and is larger than ball bearings and deep groove ball bearings 19. Therefore, since the four-point contact ball bearing 21 needs to be firmly fixed, the fixing means becomes relatively large. Accordingly, if the four-point contact ball bearing 21 is arranged on the driver's seat side, the axial space on the driver's seat side of the steering device will be narrowed.

[0063] Furthermore, in the present embodiment, the connecting member 8 connects the end face 7a on the second end portion 1b side of the peripheral wall portion 7b of the second housing 7 and the end face 9a on the first end portion 1a side of the third housing 9, and holds the deep groove ball bearing 19 between the outer peripheral surface of the third shaft portion 12c of the output shaft 12. For this reason, after aggregating the first housing 6, the second housing 7, the torque sensor 14, the worm wheel 17, etc. above the connecting member 8 to form an assembly in which the nut 20 is assembled to the steering shaft 1, the steering device can be assembled relatively easily only by inserting this assembly into the third housing 9. In addition, since the connecting member 8 has a holding function of the deep groove ball bearing 19 in addition to the aggregating function of the first housing 6 and the like and the connecting function between the second housing 7 and the third housing 9, there is no need to separately provide a component for holding the deep groove ball bearing 19.

[0064] Also, if there is no separate connecting member 8, since the second housing 7, the connecting member 8, and the third housing 9 are configured as one elongated housing integrally molded, it becomes impossible to press-fit the core metal portion 18 of the speed reducer 5 onto the steering shaft 1 inserted into such a housing.

[0065] In addition, in the present embodiment, the steering device further includes a disk-shaped closing member 33 that fixes the outer race 30 of the four-point contact ball bearing 21 to the third housing 9. The closing member 33 fixes the outer race 30 of the four-point contact ball bearing 21 to the stepped portion 9e provided in the third housing 9 by screwing the housing-side female thread portion 9f of the third housing 9 and the closing member-side male thread portion 33g of the closing member 33. Therefore, the four-point contact ball bearing 21, which is larger than the deep groove ball bearing 19 or the like and receives a large force, can be firmly fixed to the third housing 9 side.

[0066] Furthermore, in the present embodiment, the steering device further includes an annular fixing member 22 that fixes the inner race 31 of the four-point contact ball bearing 21 to the steering shaft 1. The fixing member 22 fixes the inner race 31 of the four-point contact ball bearing 21 to the stepped portion 12h provided on the steering shaft 1 by screwing the steering shaft-side male thread portion 12i of the output shaft 12 of the steering shaft 1 and the fixing member-side female thread portion 22a. Therefore, the four-point contact ball bearing 21 that receives a large force can be firmly fixed to the steering shaft 1 side.

[0067] Also, in the present embodiment, the torque sensor 14 has a detection unit 16 that detects a change in magnetism of the magnet unit 15 fixed to the steering shaft 1, and a signal processing unit 23 that processes a signal corresponding to the change in magnetism of the magnet unit 15. The signal processing unit 23 has a rotation restricting portion 23a that extends in the axial direction of the steering shaft 1, and the rotation restricting portion 23a restricts the rotation of the signal processing unit 23 accompanying the rotation of the detection unit 16. The tip of the rotation restricting portion 23a is inserted into an annular recess 26 provided between the core metal portion 18 and the gear forming portion 25 of the speed reducer 5. That is, in the radial direction of the steering shaft 1, the tip side of the rotation restricting portion 23a overlaps the internal space of the annular recess 26. Therefore, the axial dimension of the steering device can be shortened compared to the case where the tip side of the rotation restricting portion 23a does not overlap the internal space of the annular recess 26 in the radial direction of the steering shaft 1.

[0068] [Second Embodiment] FIG. 4 is a longitudinal sectional view of the steering apparatus according to the second embodiment. In FIG. 4, for convenience of explanation, the internal structures of the detection unit 16 and the signal processing unit 23 of the torque sensor 14 are not shown.

[0069] In the steering apparatus according to the second embodiment, the deep groove ball bearing 19 of the first embodiment is eliminated, and further, the back surface 20b of the nut 20 is configured to be slidably in contact with the inner peripheral surface of the third housing 9. Also, in the second embodiment, with the elimination of the deep groove ball bearing 19, the dimension of the third shaft portion 12c along the direction of the rotation axis Z of the steering shaft 1 is shorter than that of the first embodiment. Along with this, the dimension of the connecting member 8 along the direction of the rotation axis Z of the steering shaft 1 is also shorter.

[0070] The connecting member 8 includes a cylindrical main body portion 8a having a cylindrical shape, an annular protruding portion 8b protruding radially outward from the axial center position of the outer peripheral surface of the cylindrical main body portion 8a, and an annular protruding wall portion 8h protruding radially inward from a position on the inner peripheral surface of the cylindrical main body portion 8a closest to the first end portion 1a side and extending to the vicinity of the outer peripheral surface of the third shaft portion 12c of the output shaft 12. The inner peripheral surface of the annular protruding wall portion 8h has a gap that maintains the airtightness between the second housing 7 and the third housing 9, that is, seals the second housing 7 and the third housing 9 but does not support the third shaft portion 12c.

[0071] The back surface 20b on the side of the nut 20 opposite to the sector gear 3 has a recessed portion 20d formed at the axial center position. In the present embodiment, the length of the recessed portion 20d along the direction of the rotation axis Z of the steering shaft 1 is set to be smaller than one-third of the length of the nut 20 along the direction of the rotation axis Z of the steering shaft 1. As shown in FIG. 4, the portion of the back surface 20b excluding the recessed portion 20d is slidably in contact with the inner peripheral surface of the third housing 9. By this contact, the radial force acting on the output shaft 12 is transmitted to the third housing 9 via the nut 20. Also, as shown in FIG. 4, the surface 20e on the side of the second end portion 1b of the outer peripheral surface of the nut 20 with respect to the rack teeth 20c is slidably in contact with the inner peripheral surface of the third housing 9.

[0072] [Effects of the Second Embodiment] In the second embodiment, the steering device does not have the deep groove ball bearing 19, and the rear surface 20b of the nut 20 slides on the inner peripheral surface of the third housing 9. In this embodiment, the radial force that was received by the deep groove ball bearing 19 in the first embodiment is received by the third housing 9 via the rear surface 20b of the nut 20. Therefore, by eliminating the deep groove ball bearing 19 and shortening the axial dimension of the connecting member 8, the axial dimension of the steering device can be shortened.

Explanation of Reference Numerals

[0073] 1 ··· Steering shaft, 2 ··· Ball screw mechanism, 3 ··· Sector gear, 4 ··· Electric motor, 5 ··· Reducer, 6 ··· First housing, 7 ··· Second housing, 8 ··· Connecting member, 9 ··· Third housing, 14 ··· Torque sensor, 16 ··· Detection unit, 19 ··· Deep groove ball bearing, 21 ··· Four-point contact ball bearing, 22 ··· Fixing member, 23 ··· Signal processing unit, 23a ··· Rotation restricting unit, 33 ··· Blocking member

Claims

1. a steering shaft to which rotation from a steering wheel is input; an electric motor that is disposed on the end side where the steering wheel is provided among both end portions of the steering shaft and applies a steering assist force to the steering shaft; a speed reducer that decelerates the rotational force of the electric motor; a ball screw mechanism provided on the steering shaft, the ball screw mechanism including a first ball screw groove that is a spiral groove formed on an outer peripheral surface of the steering shaft, a second ball screw groove that is a spiral groove formed on an inner peripheral surface of a nut provided around the steering shaft, and a plurality of balls disposed between the first ball screw groove and the second ball screw groove; a sector gear having a second tooth portion that meshes with a first tooth portion provided on an outer peripheral surface of the nut; a four-point contact ball bearing that is disposed on an end portion opposite to the side where the electric motor is provided among both end portions of the steering shaft and rotatably supports the steering shaft; A steering apparatus comprising the above.

2. The steering apparatus according to claim 1, further comprising a deep groove ball bearing that rotatably supports the steering shaft, wherein the deep groove ball bearing is disposed on a side opposite to the four-point contact ball bearing with the ball screw mechanism interposed therebetween in an axial direction of the steering shaft. The steering apparatus according to claim 1, further comprising a deep groove ball bearing that rotatably supports the steering shaft, wherein the deep groove ball bearing is disposed on a side opposite to the four-point contact ball bearing with the ball screw mechanism interposed therebetween in an axial direction of the steering shaft. The steering apparatus according to claim 2, further comprising a cylindrical speed reducer side housing that houses the speed reducer, a cylindrical nut side housing that houses the nut, and a cylindrical connecting member that connects the speed reducer side housing and the nut side housing, wherein the connecting member has an annular protrusion that protrudes radially inward from an inner peripheral surface of the connecting member and holds the deep groove ball bearing.

3. The steering apparatus according to claim 2, further comprising a cylindrical speed reducer side housing that houses the speed reducer, a cylindrical nut side housing that houses the nut, and a cylindrical connecting member that connects the speed reducer side housing and the nut side housing, wherein the connecting member has an annular protrusion that protrudes radially inward from an inner peripheral surface of the connecting member and holds the deep groove ball bearing. The steering apparatus according to claim 3, further comprising a cylindrical speed reducer side housing that houses the speed reducer, a cylindrical nut side housing that houses the nut, and a cylindrical connecting member that connects the speed reducer side housing and the nut side housing, wherein the connecting member has an annular protrusion that protrudes radially inward from an inner peripheral surface of the connecting member and holds the deep groove ball bearing. The steering apparatus according to claim 4, further comprising a cylindrical nut side housing that houses the nut, wherein the nut has a back surface that is located on a side opposite to the sector gear with the steering shaft interposed therebetween on an outer peripheral surface of the nut, and the back surface of the nut slides with respect to an inner peripheral surface of the nut side housing.

4. The steering apparatus according to claim 1, further comprising a cylindrical nut side housing that houses the nut, wherein the nut has a back surface that is located on a side opposite to the sector gear with the steering shaft interposed therebetween on an outer peripheral surface of the nut, and the back surface of the nut slides with respect to an inner peripheral surface of the nut side housing. The steering apparatus according to claim 4, further comprising a cylindrical speed reducer side housing that houses the speed reducer and a cylindrical connecting member that connects the speed reducer side housing and the nut side housing. The steering apparatus according to claim 4, further comprising a cylindrical speed reducer side housing that houses the speed reducer and a cylindrical connecting member that connects the speed reducer side housing and the nut side housing. The steering apparatus according to claim 4, further comprising a cylindrical speed reducer side housing that houses the speed reducer and a cylindrical connecting member that connects the speed reducer side housing and the nut side housing.

5. The steering apparatus according to claim 4, further comprising a cylindrical speed reducer side housing that houses the speed reducer and a cylindrical connecting member that connects the speed reducer side housing and the nut side housing. The steering apparatus according to claim 5, further comprising a cylindrical speed reducer side housing that houses the speed reducer and a cylindrical connecting member that connects the speed reducer side housing and the nut side housing. The steering device is characterized in that the connecting member seals the speed reducer side housing and the nut side housing.

6. The steering device according to claim 1, further comprising a cylindrical nut side housing that houses the nut, and a disk-shaped closing member that closes the nut side housing from the four-point contact ball bearing side and fixes the outer race of the four-point contact ball bearing to the nut side housing, wherein an outer peripheral surface of the closing member has a closing member side male thread portion that engages with a housing side female thread portion formed on an inner peripheral surface of the nut side housing, and the closing member fixes the outer race of the four-point contact ball bearing to a stepped portion provided on the nut side housing by screwing the housing side female thread portion and the closing member side male thread portion. The steering device is characterized by this.

7. The steering device according to claim 6, further comprising an annular fixing member that fixes an inner race of the four-point contact ball bearing to the steering shaft, wherein an inner peripheral surface of the fixing member has a fixing member side female thread portion that engages with a steering shaft side male thread portion formed on an outer peripheral surface of the steering shaft, and the fixing member fixes the inner race of the four-point contact ball bearing to a stepped portion provided on the steering shaft by screwing the steering shaft side male thread portion and the fixing member side female thread portion. The steering device is characterized by this.

8. The steering device according to claim 1, wherein the speed reducer has a worm wheel, and the worm wheel has a mandrel portion fixed to the steering shaft and a gear forming portion fixed to the mandrel portion, further comprising a torque sensor that is adjacent to the speed reducer in the axial direction of the steering shaft and detects a steering torque of the steering shaft, wherein the torque sensor has a detection portion that is fixed to the steering shaft and detects a change in magnetism of a magnet fixed to the steering shaft, and a signal processing portion that is disposed around the detection portion and processes a signal corresponding to the change in magnetism, wherein the signal processing portion extends in the axial direction of the steering shaft and has a rotation restricting portion that restricts rotation of the signal processing portion accompanying rotation of the detection portion, and a tip side of the rotation restricting portion is inserted into an annular recess provided between the mandrel portion and the gear forming portion of the speed reducer. The steering device is characterized by this.

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