Electric power steering device and manufacturing method thereof

Abstract

To provide a further miniaturized electric power steering device and a manufacturing method for the same.SOLUTION: An electric power steering device includes: a pinion shaft provided with a pinion tooth; a housing; a first bearing rotatably supporting the pinion shaft with respect to the housing; a worm wheel having a core metal portion and a wheel tooth portion; an annular fixing member in contact with an end face, on the other side in an axial direction, of an inner ring of the first bearing; and a worm shaft rotated by a driving force of an electric motor. The first bearing has the inner ring, an outer ring, and a rolling element. The core metal portion has an annular, radially inside portion. As viewed from the axial direction, the inner ring and the radially inside portion overlap. The inner ring and the radially inside portion are located apart from each other in the axial direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electric power steering device and a manufacturing method thereof. [Background technology]

[0002] The electric power steering device of Patent Document 1 includes a pinion shaft, a worm wheel, a bearing, a fixing member, and a casing. The pinion shaft extends in the axial direction of a central axis. One axial end of the pinion shaft is connected to a steering wheel via a steering shaft. A worm wheel is fixed to the other axial end of the pinion shaft, and pinion teeth are formed on the outer periphery of an axially intermediate portion of the pinion shaft.

[0003] The bearing and fixed member are provided between the pinion teeth and the worm wheel, and are each formed into annular shapes extending in a direction around the central axis. Specifically, on the outer periphery of the pinion shaft, the inner ring of the bearing is fitted onto the other axial side of the pinion teeth, and the fixed member is fitted onto the other axial side of the inner ring. The fixed member abuts against the end face of the other axial side of the inner ring, positioning the inner ring in the axial direction. The outer ring of the bearing is attached to the casing, and the inner ring rotates relative to the outer ring, so that the pinion shaft is rotatably supported by the casing via the bearing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-126464 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, a cylindrical flange is provided on the radially inner side of the worm wheel, extending toward the bearing. One axial end of the cylindrical flange is provided on the outer periphery of the fixed member, and the end face of the end abuts against the other axial end face of the inner ring.

[0006] Here, if the contact area between the end face of the cylindrical flange and the end face of the inner ring is increased to ensure more reliable axial positioning of the bearing by the worm wheel, the diameter of the bearing will become larger, which could result in the electric power steering device becoming larger.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and has an object to provide a more compact electric power steering device and a manufacturing method thereof. [Means for solving the problem]

[0008] In order to achieve the above object, an electric power steering device according to one aspect includes: a pinion shaft extending in an axial direction of a central axis, one side of which in the axial direction is connected to a steering shaft, and having pinion teeth provided on an outer periphery thereof; a housing that accommodates at least a part of the pinion shaft; an inner ring attached to an outer periphery of a first portion of the pinion shaft that is located on the other side of the pinion teeth in the axial direction; an outer ring attached to the housing; and rolling elements provided between the inner ring and the outer ring, and the first bearing rotatably supports the pinion shaft with respect to the housing; the worm wheel having an annular core portion extending in a radial direction intersecting the axial direction and wheel teeth provided on the outer periphery of the core portion; and an annular fixing member provided on the outer periphery of the pinion shaft between the first portion and the second portion and abutting the end face of the inner ring on the other side in the axial direction, wherein the pinion teeth are capable of meshing with rack teeth of a rack shaft extending in the vehicle width direction, the core portion is attached to the outer periphery of the second portion and has an annular radially inner portion extending in a direction around the central axis, and when viewed from the axial direction, the inner ring and the radially inner portion overlap, and the inner ring and the radially inner portion are positioned apart in the axial direction.

[0009] In this way, the inner ring of the first bearing and the radially inner portion of the worm wheel are positioned apart in the axial direction. Therefore, the diameter of the first bearing can be made smaller than when the inner ring of the first bearing and the radially inner portion of the worm wheel abut in the axial direction, and as a result, the entire electric power steering device 80 can be made smaller. This is briefly explained below.

[0010] As mentioned above, in Patent Document 1, to more reliably position the bearing in the axial direction by the worm wheel, the end face of the cylindrical flange on the radially inner side of the worm wheel is brought into contact with the end face of the inner ring. In order to increase the contact area between the end face of the cylindrical flange and the end face of the inner ring, the radial thickness of the inner ring of the bearing needs to be increased. In particular, because the annular fixing member is located on the inner periphery of the end of the cylindrical flange on the radially inner side of the worm wheel, the radial thickness of the inner ring of the bearing needs to be increased.

[0011] Here, it is possible to consider reducing the radial thickness of the inner ring of the bearing and the radial thickness of the cylindrical flange of the worm wheel, but in that case, the strength of the cylindrical flange will decrease, and there is a possibility that the cylindrical flange will be damaged when assembling the bearing and worm wheel to the pinion shaft.

[0012] As described above, according to the present disclosure, because the inner ring of the first bearing and the radially inner portion of the worm wheel are spaced apart in the axial direction, it is not necessary to match the radial thickness of the radially inner portion of the worm wheel with the radial thickness of the inner ring of the bearing. In other words, it is not necessary to provide a surface on the end face of the inner ring of the first bearing for the cylindrical flange to abut. Therefore, the diameter of the first bearing can be made smaller, allowing the overall size of the electric power steering device to be reduced.

[0013] In a preferred embodiment, one axial end of the radially inner portion of the worm wheel is located on the other axial side of the fixed member in the axial direction. This allows the diameter of the first bearing to be made even smaller than when the radially inner portion is positioned so as to overlap the fixed member in the axial direction, thereby further reducing the overall size of the electric power steering device.

[0014] In a preferred aspect, a convex portion that protrudes radially outward is provided in a portion of the pinion shaft between the axial end of the radially inner portion and the fixed member, and the convex portion and the axial end of the radially inner portion are arranged at a distance in the axial direction.

[0015] This makes it difficult for the axial end face of the radially inner part of the worm wheel to come into contact with the convex part even if the axial position of the worm wheel varies slightly when press-fitting the worm wheel onto the outer peripheral surface of the output shaft. In other words, if the axial end face of the radially inner part were to come into contact with the convex part, the fixing member housed in the concave part could become dislodged.

[0016] On the other hand, according to the present disclosure, the axial end face of the radially inner portion is less likely to come into contact with the convex portion, thereby preventing the fixing member from coming off.

[0017] In a desirable aspect, the pinion teeth include a first tooth portion and a second tooth portion adjacent to the first tooth portion on the other side in the axial direction, the radial distance between a tooth bottom of the first tooth portion and the central axis is a first distance, the radial distance between a tooth bottom of an end of the second tooth portion on the other side in the axial direction and the central axis is a second distance greater than the first distance, and the end of the second tooth portion on the other side in the axial direction abuts against an end face of the inner ring on one side in the axial direction.

[0018] The pinion shaft is assembled to the rack shaft by rotating the pinion shaft with its pinion teeth meshing with the rack teeth of the rack shaft. Because the other axial ends of the pinion teeth abut against one axial end face of the inner ring of the bearing, it is desirable to increase the strength of the other axial ends of the pinion teeth to prevent damage to the pinion teeth. In the present disclosure, the second distance, which is the radial distance between the tooth bottom of the second tooth portion at the other axial end and the central axis, is greater than the first distance, which is the radial distance between the tooth bottom of the first tooth portion and the central axis. Therefore, the area of ​​the second tooth portion in contact with the inner ring of the first bearing is smaller than when the second distance is smaller than the first distance, and the support rigidity of the inner ring of the first bearing is increased. As described above, the present disclosure makes it possible to assemble the rack shaft while further increasing the support rigidity of the inner ring of the first bearing provided by the pinion teeth.

[0019] In a preferred aspect, at the other axial end of the second tooth portion, the radial distance between the tooth bottom and the tooth tip is a third distance, and the radial distance between the inner peripheral surface of the inner ring and the tooth bottom is a fourth distance that is greater than the third distance. This reduces the area of ​​the second tooth portion that contacts the inner ring of the first bearing compared to when the fourth distance is smaller than the third distance, further increasing the support rigidity of the inner ring of the first bearing.

[0020] In a desirable aspect, the inner circumferential surface of the housing is disposed radially outside the pinion teeth so as to face each other, the radial distance between the tip of the pinion tooth and the inner circumferential surface of the housing is a fifth distance, the radial distance between the bottom of the pinion tooth and the tip of the pinion tooth is a sixth distance, and the fifth distance is smaller than the sixth distance. Therefore, a housing having an inner circumferential surface with a small gap between it and the pinion teeth can be used, thereby making it possible to reduce the size of the electric power steering device.

[0021] In a preferred embodiment, a second bearing for rotatably supporting the pinion shaft relative to the housing is provided at a third portion of the pinion shaft on one side of the pinion teeth in the axial direction, and the second bearing has an inner ring attached to the outer periphery of the third portion, an outer ring attached to the housing, and rolling elements provided between the inner ring and the outer ring. This makes it possible to support the pinion shaft relative to the housing more stably.

[0022] A method of manufacturing an electric power steering device according to one aspect includes a first step of installing a rack shaft having rack teeth on an outer periphery thereof in a housing; a second step of, after the first step, inserting the pinion shaft into the housing toward the other side in the axial direction while meshing the pinion teeth with a second bearing disposed between the pinion teeth and a large diameter portion of the pinion shaft, the large diameter portion having a diameter larger than that of the pinion teeth, and the pinion shaft; a third step of, after the second step, inserting a first bearing onto an outer periphery of a first portion of the pinion shaft that is located on the other side in the axial direction of the pinion teeth; and a third step of, after the third step, inserting a first bearing onto an outer periphery of a first portion of the pinion shaft that is located on the other side in the axial direction of the pinion teeth. a fourth step of inserting an annular fixing member into an outer periphery of a portion of the pinion shaft on the other axial side of the first bearing, a fifth step of plastically deforming the fixing member radially inward after the fourth step to bring the fixing member into contact with an end face of the first bearing on the other axial side, thereby fixing the first bearing with the fixing member in a state in which the end face of the first bearing on one side in the axial direction and the end of the pinion tooth on the other axial side are in contact, and a sixth step of press-fitting a worm wheel into a second portion of the pinion shaft on the other axial side of the fixing member while providing an axial gap between the worm wheel and the first bearing. The fifth step includes a movement preventing step of preventing axial movement of the pinion shaft, and a diameter reducing step of reducing a diameter of the other axial side of the fixing member so that the other axial side of the fixing member is brought into contact with the outer periphery of the pinion shaft after the movement preventing step.

[0023] As described above, in Patent Document 1, the output shaft includes a pinion portion and a lower bearing fitting portion adjacent to the lower side (the other axial side) of the pinion portion, and a bearing is fitted onto the outer periphery of the lower bearing fitting portion. The pinion portion has pinion teeth formed only in the axial middle portion, and no pinion teeth are formed below the pinion teeth on the pinion portion. Therefore, with the output shaft structure of Patent Document 1, it is not possible to insert the output shaft into the housing while rotating the output shaft to mesh the pinion teeth with the rack teeth, as in the second step of this embodiment. That is, in Patent Document 1, a structure is required to prevent the pinion shaft 1 from interfering with the rack teeth 21 formed on the rack shaft 2 when inserting the pinion shaft 1. Specifically, as shown in FIG. 6 of Patent Document 1, the rack teeth are provided with recesses 21b to prevent interference with the pinion shaft. Furthermore, as shown in FIG. 5 of Patent Document 1, when inserting the pinion shaft, the pinion shaft is inserted after being shifted in a direction perpendicular to the axis, which results in a large diameter hole for inserting the pinion shaft.

[0024] In the present disclosure, because the pinion teeth are formed all the way to the other axial end, the output shaft of the pinion shaft can be inserted into the housing while rotating the pinion shaft to engage the pinion teeth with the rack teeth. Therefore, there is no need to provide a recess in the rack shaft to prevent interference, simplifying the rack shaft structure. Furthermore, because there is no need to shift the pinion shaft radially when inserting it, the hole through which the pinion shaft is inserted can be made smaller, allowing the overall housing to be made more compact.

[0025] In a preferred aspect, a convex portion that protrudes radially outward is provided in a portion of the pinion shaft between the axial end of the radially inner portion and the fixed member, and the convex portion and the axial end of the radially inner portion are arranged at a distance in the axial direction.

[0026] When the worm wheel is press-fitted onto the outer peripheral surface of the output shaft, even if the axial position of the worm wheel varies slightly, the axial end face of the radially inner portion of the worm wheel is less likely to abut against the convex portion. In other words, if the axial end face of the radially inner portion abuts against the convex portion, the fixing member housed in the concave portion may become dislodged. Therefore, according to the present disclosure, the axial end face of the radially inner portion is less likely to abut against the convex portion, thereby preventing the fixing member from becoming dislodged.

[0027] In a desirable aspect, the inner circumferential surface of the housing is disposed radially outward of the pinion teeth, the radial distance between the tips of the pinion teeth and the inner circumferential surface of the housing is a fifth distance, the radial distance between the bottoms and tips of the pinion teeth is a sixth distance, and the fifth distance is smaller than the sixth distance. This makes it easy to insert the rack shaft into a housing having an inner circumferential surface with a small gap between it and the pinion teeth. [Effects of the Invention]

[0028] According to the present disclosure, a more compact electric power steering device and a manufacturing method thereof are provided. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic diagram of an electric power steering device according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing a part of FIG. [Figure 3] 3 is a perspective view showing a part of FIG. 1 as seen from a different viewpoint than that of FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV in FIG. [Figure 5] FIG. 5 is an enlarged cross-sectional view of a part of FIG. [Figure 6] FIG. 6 is a schematic enlarged cross-sectional view of a portion of FIG. [Figure 7] FIG. 7 is a cross-sectional view showing a state in which the fixing member mounting jig is attached to a part of the electric power steering device. [Figure 8] FIG. 8 is an enlarged cross-sectional view of a part of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0030] Modes (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments. Furthermore, the components described below include those that can be easily imagined by a person skilled in the art and those that are substantially the same. Furthermore, the components described below can be combined as appropriate. Furthermore, parts with the same structure are given the same reference numerals, and descriptions thereof will be omitted.

[0031] An electric power steering device according to an embodiment will be described. Fig. 1 is a schematic diagram of the electric power steering device according to the embodiment. Fig. 2 is a perspective view showing a part of Fig. 1. Fig. 3 is a perspective view showing a part of Fig. 1.

[0032] As shown in FIG. 1, the electric power steering device 80 includes a steering wheel 81, a first steering shaft 82, a second steering shaft 83, a pinion shaft 1, a worm reduction mechanism 400, a rack shaft 2, a tie rod 84, an ECU 89, and a power supply device 90.

[0033] The first steering shaft 82 is connected to the steering wheel 81. The first steering shaft 82 is rotatably supported. The first steering shaft 82 rotates due to the torque that steers the steering wheel 81. Specifically, when the driver grips and rotates the steering wheel 81, the rotational torque (steering torque) is transmitted to the first steering shaft 82, causing the first steering shaft 82 to rotate.

[0034] The second steering shaft 83 is connected to the first steering shaft 82 via a first universal joint 85. The second steering shaft 83 is rotatably supported. The rotational torque of the first steering shaft 82 is transmitted to the second steering shaft 83 via the first universal joint 85, causing the second steering shaft 83 to rotate.

[0035] As shown in FIG. 1 , the pinion shaft 1 is connected to the second steering shaft 83 via the second universal joint 86. The rotational torque of the second steering shaft 83 is transmitted to the pinion shaft 1 via the second universal joint 86, causing the pinion shaft 1 to rotate. The pinion shaft 1 is provided with pinion teeth 120. The pinion shaft 1 is rotatably supported by the housing 87 via a second bearing 91 and a first bearing 3. The second bearing 91 supports an upper portion of the pinion shaft 1. The first bearing 3 supports a lower portion of the pinion shaft 1. Specifically, the second bearing 91, which rotatably supports the pinion shaft 1 relative to the housing 87, is provided on a cylindrical surface 128 (third portion) above the pinion teeth 120 (one axial side).

[0036] The worm reduction mechanism 400 includes a worm shaft 51 and a worm wheel 4. The worm shaft 51 is provided on the output shaft of an electric motor 52. The worm shaft 51 meshes with the worm wheel 4. The worm wheel 4 is fixed to the lower end of the pinion shaft 1. Therefore, when the electric motor 52 is operated, the worm shaft 51 rotates, and the worm wheel 4 meshing with the worm shaft 51 rotates together with the pinion shaft 1. This reduces the force required to steer the steering wheel 81.

[0037] The rack shaft 2 extends in the vehicle width direction (left-right direction). Rack teeth 21 are provided on the side of the rack shaft 2. The rack teeth 21 mesh with pinion teeth 120 of the pinion shaft 1. A pair of tie rods 84 are provided on both the left and right sides of the rack teeth 21. The tie rods 84 are connected to wheels 88. Therefore, when the pinion shaft 1 rotates, a force in the vehicle width direction is transmitted to the rack teeth 21 meshing with the pinion teeth 120, causing the rack shaft 2 to move left and right. This causes the tie rods 84 to move left and right, tilting the wheels 88 and changing the direction of travel of the vehicle.

[0038] The ECU 89 is connected to a power supply device 90 (for example, an on-board battery), and power is supplied from the power supply device 90 to the ECU 89. The ECU 89 controls the operation of the electric motor 52. The ECU 89 acquires signals from a torque sensor and a vehicle speed sensor (not shown). The ECU 89 calculates an auxiliary steering command value based on the steering torque and the vehicle speed. The ECU 89 adjusts the value of power supplied to the electric motor 52 based on the auxiliary steering command value. The ECU 89 acquires information on the induced voltage from the electric motor 52 or information output from a resolver or the like provided in the electric motor 52. By the ECU 89 controlling the operation of the electric motor 52, the force required to steer the steering wheel 81 is reduced, as described above.

[0039] Fig. 2 is a perspective view showing a part of Fig. 1. Fig. 3 is a perspective view showing a part of Fig. 1 seen from a different viewpoint than Fig. 2. Fig. 4 is a cross-sectional view taken along line IV in Fig. 3. Fig. 5 is an enlarged cross-sectional view of a part of Fig. 4. Fig. 6 is a schematic enlarged cross-sectional view of a part of Fig. 4.

[0040] 2 and 3, the pinion shaft 1 extends in the axial direction of the central axis AX. The pinion shaft 1 rotates in the direction around the central axis AX. The housing 87 has a first housing 871, a second housing 872, and a third housing 873.

[0041] 2 and 3, the second housing 872 is located below the first housing 871, and the third housing 873 is located below the second housing 872. That is, the first housing 871 is located in the upper part of the housing 87, the second housing 872 is located in the middle part of the housing 87, and the third housing 873 is located in the lower part of the housing 87. Boots 874 are provided on both the left and right sides of the second housing 872. The rack shaft 2 is housed inside the second housing 872 and the boots 874.

[0042] As shown in FIG. 4, the pinion shaft 1 has an input shaft 11 and an output shaft 12. The input shaft 11 is located above the output shaft 12. The input shaft 11 may be a torsion bar that is a component of a torque sensor (not shown). The pinion shaft 1 does not necessarily have to include the input shaft 11. In detail, in the assembly process described below, the axial movement of the pinion shaft 1 may be restricted by a crimping jig when the torsion bar is not assembled to the output shaft 12.

[0043] As shown in FIGS. 2 and 3, a portion of the input shaft 11 protrudes upward from the first housing 871. As shown in FIG. 4, the input shaft 11 and the output shaft 12 extend in the axial direction of the center axis AX. Specifically, a fitting recess 125 is provided at the upper end of the output shaft 12. The lower end of the input shaft 11 is fitted into the fitting recess 125. This assembles the input shaft 11 and the output shaft 12, and prevents relative rotation between the input shaft 11 and the output shaft 12. Note that although FIG. 4 illustrates the second bearing 91 as a needle bearing having a plurality of needles 91a, it may also be a normal deep groove ball bearing.

[0044] As shown in FIG. 4, rack teeth 21 are provided on the side surface of the rack shaft 2 facing the output shaft 12. A plurality of rack teeth 21 are provided along the front-to-rear direction of the paper on which FIG. 4 is drawn. Pinion teeth 120 are provided on the outer periphery of the output shaft 12. The pinion teeth 120 extend spirally in the axial direction of the central axis AX. The pinion teeth 120 mesh with the rack teeth 21. In other words, when the pinion shaft 1 and the pinion teeth 120 rotate in the direction around the central axis AX, the rack teeth 21 meshed with the pinion teeth 120 and the rack shaft 2 move in the vehicle width direction.

[0045] 4 and 5, a cylindrical surface 126 (first portion) is provided on the lower side (the other axial side) of the pinion teeth 120 of the pinion shaft 1, and a cylindrical surface 127 (second portion) is provided on the lower side (the other axial side) of the cylindrical surface 126 (first portion). A first bearing 3 is attached to the cylindrical surface 126 (first portion). The first bearing 3 will be described in detail later.

[0046] As shown in Figures 4 and 5, the worm wheel 4 is attached to the cylindrical surface 127 (second portion). The worm wheel 4 includes a core metal portion 41 and a wheel tooth portion 42. The core metal portion 41 is made of, for example, metal. The core metal portion 41 has a radially inner portion 412, a connecting portion 413, and a radially outer portion 411.

[0047] As shown in FIG. 5 , the radially inner portion 412 is a cylindrical body attached to the outer periphery of the lower end of the output shaft 12. The radially inner portion 412 has an axial end face 412a located on one axial side (upper side) and an axial end face 412b located on the other axial side (lower side). The axial end face 412a and the axial end face 412b extend in a radial direction perpendicular to the axial direction. The axial end face 412a and the axial end face 412b have an annular shape extending in a direction around the central axis AX. The connecting portion 413 extends radially outward from the radially inner portion 412 to the radially outer portion 411. The radially outer portion 411 is provided with a wheel tooth portion 42. The wheel tooth portion 42 is made of, for example, resin. Specifically, the wheel tooth portion 42 can be provided on the radially outer portion 411 by, for example, insert-molding resin onto the outside of the radially outer portion 411. The wheel teeth portion 42 meshes with the shaft teeth portion 511 of the worm shaft 51. As described with reference to FIG. 1, the worm shaft 51 is driven to rotate by the electric motor 52. The wheel teeth portion 42 and the first bearing 3 are housed inside the third housing 873.

[0048] 5, the first bearing 3 is provided on the cylindrical surface 126 (first portion) of the output shaft 12. The first bearing 3 has an inner ring 31, an outer ring 32, and rolling elements 33. Specifically, the inner ring 31 is attached to the outer periphery of the cylindrical surface 126 (first portion). The third housing 873 is provided with a bearing accommodating portion 873d. The bearing accommodating portion 873d is a recess, and the outer ring 32 of the first bearing 3 is accommodated in the bearing accommodating portion 873d.

[0049] As shown in FIG. 6 , the inner ring 31 has an end face 31a on one axial side (upper side) and an end face 31b on the other axial side (lower side). The end face 31b is in contact with the fixed member 6. The fixed member 6 is formed in an annular shape along the axial direction about the central axis AX. The diameter of the fixed member 6 increases toward the axial side (upper side). The end face 31b is positioned in the axial direction by the fixed member 6. Specifically, a recess 124 recessed radially inward is formed on the outer periphery of the output shaft 12. A protrusion 123 protruding radially outward is formed below the recess 124. The recess 124 and the protrusion 123 are formed in an annular shape along the axial direction about the central axis AX. The fixed member 6 fits into the recess 124, and the protrusion 123 prevents the lower end of the fixed member 6 from moving downward. 6, the lower end 123a (the other axial end) of the protrusion 123 and the axial end face 412a of the worm wheel 4 are spaced apart by a distance D50 in the axial direction. The end face 31b comes into contact with the fixing member 6, so that the end face 31b is positioned in the axial direction by the fixing member 6. The end face 31b of the inner ring 31 and the axial end face 412a of the worm wheel 4 are spaced apart by a distance D1 in the axial direction. In other words, a gap 100 is provided in the axial direction between the end face 31b of the inner ring 31 and the axial end face 412a of the worm wheel 4, and the distance of the gap 100 in the axial direction is distance D1.

[0050] As shown in FIG. 5 , the third housing 873 has a protruding portion 873a that protrudes downward. The support member 60 is fastened to the inner periphery of the protruding portion 873a. Specifically, a female thread is formed on the inner periphery of the protruding portion 873a, and a male thread is formed on the outer periphery of the support member 60. The female thread on the inner periphery of the protruding portion 873a meshes with the male thread on the outer periphery of the support member 60. An end face 60a on one axial side (upper side) of the protruding portion 873a contacts an end face 32b on the other axial side (lower side) of the outer ring 32 of the first bearing 3. An end face 32a on one axial side (upper side) of the outer ring 32 of the first bearing 3 contacts a bent portion 873c of the third housing 873. In this way, the outer ring 32 of the first bearing 3 is sandwiched in the axial direction between the bent portion 873c of the third housing 873 and the support member 60.

[0051] 5, the third housing 873 is open at its lower end. That is, an opening is provided in a lower end 873b of the third housing 873. A cover 875 is fitted inside the lower end 873b. A groove is formed in an outer peripheral flange 875a of the cover 875, and an O-ring 101 is housed in the groove. The cover 875 is disposed at an angle relative to the radial direction.

[0052] As shown in FIG. 6, the pinion teeth 120 of the output shaft 12 have a first tooth portion 121 provided in the first region P1 and a second tooth portion 122 provided in the second region P2.

[0053] As shown by the dashed line in Fig. 6, the tooth bottom 121a of the first tooth portion 121 has a constant radial distance from the central axis AX. That is, in the first region P1, a first distance D10, which is the radial distance between the central axis AX and the tooth bottom 121a, is constant in the axial direction. In other words, in the first tooth portion 121, the radial distance between the tooth bottom 121a and the tooth tip 121b is a sixth distance D11. The sixth distance D11 is the tooth height of the first tooth portion 121. In the first region P1, the sixth distance D11 is constant.

[0054] As shown by the dashed line in FIG. 6 , the radial distance of the tooth bottom 122a of the second tooth portion 122 from the central axis AX increases toward the first bearing 3. That is, in the second region P2, at one axial end (upper side), the radial distance between the central axis AX and the tooth bottom 122a is a first distance D10, and at the other axial end (lower side), the radial distance between the central axis AX and the tooth bottom 122a is a second distance D20. The second distance D20 is greater than the first distance D10. In other words, at one axial end (upper side) of the second tooth portion 122, the radial distance between the tooth bottom 122a and the tooth tip 122b is a sixth distance D11, and at the other axial end (lower side), the radial distance between the tooth bottom 122a and the tooth tip 122b is a third distance D21. The third distance D21 is the tooth height of the second tooth portion 122. The third distance D21 is smaller than the sixth distance D11.

[0055] Here, the support of the inner ring 31 of the first bearing 3 will be described. As shown in FIG. 6, on the outer periphery of the output shaft 12, a cylindrical surface 126 (first portion) is adjacent to the other axial side (lower side) of the second tooth portion 122 in the axial direction. The cylindrical surface 126 (first portion) is formed in an annular shape along the direction around the central axis AX. The cylindrical surface 126 (first portion) extends to an end 126a on one axial side (upper side). The diameter of the cylindrical surface 126 (first portion) is a distance D30. That is, the radial distance between the central axis AX and the cylindrical surface 126 (first portion) is the distance D30. The distance D30 is shorter than the second distance D20.

[0056] As shown in FIG. 6, the other axial end (lower end) of the second tooth portion 122 has a first end face 122c on the radially inner side and a second end face 122d on the radially outer side. The first end face 122c and the second end face 122d extend radially. The first end face 122c and the second end face 122d are disposed adjacent to each other in the radial direction. The first end face 122c extends radially outward from the end 126a. The radial distance of the first end face 122c is a fourth distance D40. The second end face 122d extends radially outward from the radially outer end of the first end face 122c. The radial distance of the second end face 122d is a third distance D21. The fourth distance D40 is greater than the third distance D21.

[0057] The inner ring 31 of the first bearing 3 has axial end faces 31a and 31b, an inner circumferential face 31c, and an outer circumferential face 31d. The inner circumferential face 31c contacts the cylindrical surface 126. The outer circumferential face 31d is located radially outward of the tooth tips 122b of the second toothed portion 122. The end face 31a contacts the first end face 122c and the second end face 122d of the second toothed portion 122. Thus, the inner ring 31 of the first bearing 3 has the end face 31b contacting the fixed member 6 and the end face 31a contacting the first end face 122c and the second end face 122d of the second toothed portion 122. That is, the inner ring 31 is sandwiched in the axial direction between the fixed member 6 and the first end face 122c and the second end face 122d.

[0058] 4, the inner peripheral surface 872a of the second housing 872 is disposed radially outward of the first tooth portion 121 of the pinion teeth 120 so as to face the inner peripheral surface 872a. The radial distance between the tooth tip 121b of the first tooth portion 121 and the inner peripheral surface 872a is a fifth distance D60. The radial distance between the tooth bottom and the tooth tip of the first tooth portion 121 is a sixth distance D11. The fifth distance D60 is smaller than the sixth distance D11.

[0059] Next, a manufacturing method for an electric power steering device will be described with reference to Fig. 7 and Fig. 8. Fig. 7 is a cross-sectional view showing a state in which a fixing member mounting jig is attached to a part of the electric power steering device. Fig. 8 is a cross-sectional view showing an enlarged portion of Fig. 7. First, as a premise, the structure of a fixing member mounting jig 200 that mounts a fixing member 6 to the outer periphery of the output shaft 12 of the pinion shaft 1 will be described.

[0060] As shown in FIG. 7, the fixing member attaching jig 200 includes a pressing jig 210 and a crimping jig 220, and the crimping jig 220 moves up and down by an actuator (not shown). Holding jig 210 is a plate-shaped member having a through-hole 211 formed in its radial center. A flange 871a is provided on first housing 871, and holding jig 210 can hold pinion shaft 1 from above. In other words, holding jig 210 can prevent pinion shaft 1 from moving in the axial direction.

[0061] As shown in FIGS. 7 and 8 , the crimping jig 220 is a cylindrical member having a through hole 221 extending therethrough along the axial direction. The axial end portion of the output shaft 12, including the cylindrical surface 127, is inserted into the through hole 221. The crimping jig 220 has an upper surface 222, a lower surface 223, an inner circumferential surface 224, an outer circumferential surface 225, and a tapered surface 226. The inner circumferential surface 224 and the outer circumferential surface 225 are cylindrical surfaces that extend in the circumferential direction about the central axis AX. The upper surface 222 and the lower surface 223 are flat surfaces that extend in the radial direction perpendicular to the central axis AX. The tapered surface 226 is provided at an intersection (corner) between the upper surface 222 and the inner circumferential surface 224. The tapered surface 226 is a flat surface that extends downward (to the other axial side) as it extends radially inward. The tapered surface 226 may be continuous over the entire circumference in the circumferential direction, or may have a shape in which a portion in the circumferential direction is missing.

[0062] Next, a method for manufacturing the electric power steering device will be briefly described. [Step 1] 1, in the first step, the rack shaft 2 is installed in the second housing 872 of the housing 87. The rack shaft 2 has rack teeth 21 provided on its outer periphery.

[0063] [Second Step] 7, in the second step, the output shaft 12 of the pinion shaft 1 is inserted into the first housing 871 and the second housing 872. This will be explained in detail below.

[0064] 7, pinion teeth 120 are formed on the outer periphery of the output shaft 12 of the pinion shaft 1, and a large diameter portion 12a having a diameter larger than that of the pinion teeth 120 is provided above the pinion teeth 120 (on one axial side). In a second step, with a second bearing 91 disposed between the pinion teeth 120 and the large diameter portion 12a, the pinion shaft 1 is rotated to bring the pinion teeth 120 into mesh with the rack teeth 21 of the rack shaft 2. This allows the output shaft 12 to be inserted downward (to the other axial side) into the first housing 871 and the second housing 872.

[0065] [Third Step] In the third step, as shown in Fig. 7, the first bearing 3 is inserted onto the outer periphery of the cylindrical surface 126 (first portion) of the pinion shaft 1. Specifically, as shown in Fig. 7, the first bearing 3 is accommodated between the bearing accommodating portion 873d of the third housing 873 and the outer periphery of the cylindrical surface 126 (first portion).

[0066] [Fourth Step] In a fourth step, an annular fixing member 6 is inserted onto the outer periphery of a portion of the pinion shaft 1 below the first bearing 3 (the other axial side). As shown in Fig. 8, the fixing member 6 before deformation is a cylinder that extends circumferentially around the central axis AX. Before deformation, an upper end 6a of the fixing member 6 abuts against a lower end face 31b of the inner ring 31 of the first bearing 3, and a lower end 6b of the fixing member 6 abuts against a tapered surface 226 of the crimping jig 220.

[0067] [5th ​​step] In the fifth step, the fixing member 6 is plastically deformed radially inward to bring the fixing member 6 into contact with the end surface 31b of the first bearing 3. That is, as shown in Fig. 7, when the pinion shaft 1 is held down from above by the holding jig 210 and the crimping jig 220 is moved upward as indicated by the arrow 110 as shown in Fig. 8, the lower end 6b of the fixing member 6 is deformed radially inward relative to the upper end 6a. That is, as indicated by the arrow 111 in Fig. 8, the lower end 6b of the fixing member 6 slides along the upper surface of the protrusion 123 as indicated by the two-dot chain line while maintaining the position of the upper end 6a, and the fixing member 6 is accommodated in the recess 124. In this way, as shown in Figure 8, the first bearing 3 is fixed by the fixing member 6 in a state in which the end face 31a of the first bearing 3 abuts against the other axial end 120a of the pinion tooth 120 (the first end face 122c and the second end face 122d shown in Figure 6).

[0068] In other words, the fifth step can be said to include a movement preventing step and a diameter reducing step. The movement preventing step is a process in which pinion shaft 1 is pressed from above by pressing jig 210, as shown in Fig. 7, and pressing jig 210 can prevent movement of pinion shaft 1 in the axial direction. The diameter reducing step is a process in which crimping jig 220 is moved upward as shown by arrow 110, as shown in Fig. 8, to reduce the diameter of fixing member 6 radially inward, thereby bringing lower end 6b of fixing member 6 into contact with the outer periphery of pinion shaft 1.

[0069] [Step 6] In the sixth step, as shown in Fig. 6, the worm wheel 4 is press-fitted into a cylindrical surface 127 (second portion) of the pinion shaft 1 that is below the fixed member 6 (the other axial side) with an axial gap provided between the worm wheel 4 and the first bearing 3. Specifically, using a jig (not shown), the worm wheel 4 is press-fitted into the cylindrical surface 127 (second portion) of the pinion shaft 1. In the press-fitting step, the distance from the worm wheel 4 to the end of the pinion shaft 1 is determined, thereby enabling the worm wheel 4 to be positioned.

[0070] As described above, electric power steering device 80 of this embodiment includes pinion shaft 1 that extends in the axial direction of center axis AX, has an upper side (one axial side) connected to second steering shaft 83 (steering shaft), and has pinion teeth 120 provided on its outer periphery, housing 87 that accommodates at least a portion of pinion shaft 1, and cylindrical surface 126 (first portion) of pinion shaft 1 that is located below pinion teeth 120 (the other axial side) and is connected to housing 87. The pinion shaft 1 includes a first bearing 3 rotatably supported relative to the pinion shaft 1, a worm wheel 4 attached to a cylindrical surface 127 (second portion) located below the cylindrical surface 126 (first portion) (the other axial side) of the pinion shaft 1 and having a radially extending core metal portion 41 and wheel teeth portion 42 provided on the outer periphery of the core metal portion 41, and a worm shaft 51 having shaft teeth portion 511 meshing with the wheel teeth portion 42 and rotated by the driving force of an electric motor 52. The first bearing (bearing) includes an inner ring 31 attached to the outer periphery of the cylindrical surface 126 (first portion), an outer ring 32 attached to the housing 87, and rolling elements 33 provided between the inner ring 31 and the outer ring 32. The core metal portion 41 has an annular radially inner portion 412 attached to the outer periphery of the cylindrical surface 127 (second portion), and the inner ring 31 and the radially inner portion 412 overlap when viewed in the axial direction. The inner ring 31 and the radially inner portion 412 are positioned apart from each other in the axial direction.

[0071] In this way, the inner ring 31 of the first bearing 3 and the radially inner portion 412 of the worm wheel 4 are positioned apart in the axial direction. Therefore, the diameter of the first bearing 3 is smaller than when the inner ring 31 of the first bearing 3 and the radially inner portion 412 of the worm wheel 4 abut against each other in the axial direction, which in turn reduces the size of the entire electric power steering device 80. This will be briefly explained below.

[0072] As mentioned above, in Patent Document 1, to more reliably position the bearing in the axial direction by the worm wheel, the end face of the cylindrical flange on the radially inner side of the worm wheel is brought into contact with the end face of the inner ring. In order to increase the contact area between the end face of the cylindrical flange and the end face of the inner ring, the radial thickness of the inner ring of the bearing needs to be increased. In particular, because the annular fixing member is located on the inner periphery of the end face of the cylindrical flange on the radially inner side of the worm wheel, the radial thickness of the inner ring of the bearing needs to be further increased.

[0073] Here, it is possible to consider reducing the radial thickness of the inner ring of the bearing and the radial thickness of the cylindrical flange of the worm wheel, but in that case, the strength of the cylindrical flange will decrease, and there is a possibility that the cylindrical flange will be damaged when assembling the bearing and worm wheel to the pinion shaft. As described above, according to this embodiment, the inner ring 31 of the first bearing 3 and the radially inner portion 412 of the worm wheel 4 are spaced apart in the axial direction, so there is no need to match the radial thickness of the radially inner portion 412 of the worm wheel 4 with the radial thickness of the inner ring of the bearing. Therefore, the diameter of the first bearing 3 can be made smaller, and the entire electric power steering device 80 can be made smaller.

[0074] Moreover, the radially inner portion 412 is located below (on the other axial side of) the fixed member 6. This allows the diameter of the first bearing 3 to be made even smaller than when the radially inner portion 412 overlaps with the fixed member 6 in the axial direction, and ultimately allows the entire electric power steering device 80 to be made even more compact.

[0075] The pinion teeth 120 include a first tooth portion 121 and a second tooth portion 122 adjacent to the lower side (the other axial side) of the first tooth portion 121. The radial distance between a tooth bottom 121a of the first tooth portion 121 and the central axis AX is a first distance D10. The radial distance between a tooth bottom 122a at the lower end (the other axial side) of the second tooth portion 122 and the central axis AX is a second distance D20 that is larger than the first distance D10. A first end face 122c and a second end face 122d, which are the lower end (the other axial side) of the second tooth portion 122, contact the inner ring 31 of the first bearing 3.

[0076] The pinion shaft 1 is assembled to the rack shaft 2 by rotating the pinion shaft 1 with the pinion teeth 120 of the pinion shaft 1 meshed with the rack teeth 21 of the rack shaft 2. The lower (other axial) ends of the pinion teeth 120 abut against the upper (one axial side) end face 31a of the inner ring 31 of the first bearing 3. Therefore, it is desirable to increase the strength of the lower (other axial) ends of the pinion teeth 120 to prevent damage to the pinion teeth 120. Here, in this embodiment, a second distance D20, which is the radial distance between the tooth bottom 122a of the lower (other axial side) end of the second tooth portion 122 and the central axis AX, is greater than a first distance D10, which is the radial distance between the tooth bottom 121a of the first tooth portion 121 and the central axis AX. Therefore, the area of ​​the second tooth portion 122 in contact with the inner ring 31 of the first bearing 3 is smaller than when the second distance D20 is equal to or shorter than the first distance D10, and the support rigidity of the inner ring 31 of the first bearing 3 is increased. As described above, according to this embodiment, the support rigidity of the inner ring 31 of the first bearing 3 by the pinion teeth 120 can be increased while enabling the rack shaft 2 to be assembled.

[0077] Furthermore, at the lower end (the other axial end) of the second tooth portion 122, the radial distance between the tooth bottom 122a and the tooth tip 122b is a third distance D21. The radial distance between the inner circumferential surface 31c of the inner ring 31 and the tooth bottom 122a is a fourth distance D40 that is greater than the third distance D21.

[0078] 6, at the position where the inner ring 31 and pinion teeth 120 abut, the area of ​​the region where the pinion teeth 120 are not formed and where a solid member exists (the ring-shaped region with inner diameter D30 and outer diameter D30+D40) can be made larger than the area of ​​the region where the pinion teeth 120 are formed and where no member exists (the ring-shaped region with inner diameter D30+D40 and outer diameter D30+D40+D21). Compared to the region where no member exists, the region where a solid member exists has higher rigidity, and therefore the support rigidity for supporting the inner ring 31 can be improved.

[0079] Further, a second bearing 91 that rotatably supports the pinion shaft 1 relative to the housing 87 is provided on a cylindrical surface 128 (third portion) on the upper side (one axial side) of the pinion teeth 120. This allows the pinion shaft 1 to be supported more stably relative to the housing 87.

[0080] The manufacturing method of the electric power steering device includes a first step of installing the rack shaft 2 in the housing, a second step of inserting the output shaft 12 of the pinion shaft 1 into the first housing 871 and the second housing 872 while rotating the pinion shaft 1 to mesh the pinion teeth 120 with the rack teeth 21, a third step of inserting the first bearing 3 between the bearing accommodating portion 873d of the third housing 873 and the outer periphery of the cylindrical surface 126 (first portion), and a third step of inserting the first bearing 3 into the portion of the pinion shaft 1. a fourth step of inserting an annular fixed member 6 into the outer periphery of the pinion shaft 1 below the first bearing 3 (the other axial side); a fifth step of reducing the diameter of the fixed member 6 radially inward to bring the fixed member 6 into contact with the end face 31 b of the inner ring 31 of the first bearing 3; and a sixth step of press-fitting the worm wheel 4 into a cylindrical surface 127 (second portion) of the pinion shaft 1 below the fixed member 6 (the other axial side) with an axial gap provided between the worm wheel 4 and the first bearing 3. The fifth step includes a movement preventing step of preventing axial movement of the pinion shaft 1, and a diameter reducing step of reducing the diameter of a lower end 6 b (the other axial side) of the fixed member 6 to bring the lower end 6 b into contact with the outer periphery of the pinion shaft 1 after the movement preventing step.

[0081] As described above, in Patent Document 1, the output shaft includes a pinion portion and a lower bearing fitting portion adjacent to the lower side (the other axial side) of the pinion portion, and a bearing is fitted onto the outer periphery of the lower bearing fitting portion. The pinion portion has pinion teeth formed only in the axial middle portion, and no pinion teeth are formed below the pinion teeth on the pinion portion. Therefore, with the output shaft structure of Patent Document 1, it is not possible to insert the output shaft into the housing while rotating the output shaft to mesh the pinion teeth with the rack teeth, as in the second step of this embodiment. That is, in Patent Document 1, a structure is required to prevent the pinion shaft 1 from interfering with the rack teeth 21 formed on the rack shaft 2 when inserting the pinion shaft 1. Specifically, as shown in FIG. 6 of Patent Document 1, the rack teeth are provided with recesses 21b to prevent interference with the pinion shaft. Furthermore, as shown in FIG. 5 of Patent Document 1, when inserting the pinion shaft, the pinion shaft is inserted after being shifted in a direction perpendicular to the axis, which results in a large diameter hole for inserting the pinion shaft.

[0082] In this embodiment, the pinion teeth 120 are formed up to the other axial end 120a shown in Figure 8 (the first end face 122c and the second end face 122d shown in Figure 6), so that the output shaft 12 of the pinion shaft 1 can be inserted into the first housing 871 and the second housing 872 while rotating the pinion shaft 1 to engage the pinion teeth 120 with the rack teeth 21.

[0083] Furthermore, in this embodiment, the first bearing 3 is fixed to the pinion shaft 1 by reducing the diameter of the fixing member 6 radially inward, so that the first bearing 3 can be attached to the pinion shaft 1 with a simple operation. Note that, as shown in Fig. 8 , when the crimping jig 220 is raised to its upper end position and the tapered surface 226 of the crimping jig 220 is brought close to the protrusion 123, the lower end 6b of the fixing member 6 slides on the tapered surface 226, and then the lower end 6b moves onto the upper surface of the protrusion 123 and is then housed in the recess 124.

[0084] 6, the end 123a on the lower side (the other axial side) of the protrusion 123 and the axial end face 412a of the worm wheel 4 are separated by a distance D50 along the axial direction. In the sixth step, the worm wheel 4 is press-fitted onto the outer peripheral surface of the output shaft 12. Even if the axial position of the worm wheel 4 varies slightly, the axial end face 412a of the radially inner portion 412 of the worm wheel 4 is unlikely to come into contact with the protrusion 123. In other words, if the axial end face 412a of the radially inner portion 412 hits the protrusion 123, the fixing member 6 housed in the recess 124 may become dislodged. Therefore, by separating the end 123a and the axial end face 412a by the distance D50 as in this embodiment, the axial end face 412a of the radially inner portion 412 is unlikely to come into contact with the protrusion 123, and therefore, the fixing member 6 is prevented from becoming dislodged.

[0085] Furthermore, the radial distance between the tooth tip 121b of the first tooth portion 121 and the inner circumferential surface 872a is a fifth distance D60. The radial distance between the tooth bottom and the tooth tip of the first tooth portion 121 is a sixth distance D11. The fifth distance D60 is smaller than the sixth distance D11. Therefore, it becomes easy to insert the rack shaft 2 into the housing 87, which has an inner circumferential surface 872a with a small gap between it and the pinion teeth 120. [Explanation of symbols]

[0086] 1 Pinion shaft 2 rack shaft 3 First bearing 4 worm wheels 6 Fixing member 6a Upper end 6b Bottom end 11 Input shaft 12 Output shaft 12a Large diameter section 21 rack teeth 31 Inner circle 31a, 31b end face 31c Inner surface 31d Outer surface 32 outer ring 32a, 32b end face 33 Rolling elements 41 Core metal part 42 Wheel tooth 51 Worm shaft 511 Shaft tooth 52 Electric motor 60 Support member 80 Electric power steering device 81 Steering wheel 82 First steering shaft 83 Second steering shaft (steering shaft) 84 tie rod 85 First universal joint 86 Second universal joint 87 Housing 88 wheels 89 ECU 90 Power supply 91 Second bearing 91a Needle 120 pinion teeth 120a edge 121 1st tooth part 121a Root of tooth 121b Tooth tip 122 2nd tooth part 122a Root 122b Tooth tip 122c 1st end face 122d 2nd end face 123 Convex 124 recess 125 mating recess 126 Cylindrical surface (first part) 127 Cylindrical surface (second part) 128 Cylindrical surface (third section) 200 Fixture mounting jig 210 Holding jig 220 Crimping jig 221 Through hole 400 Worm reduction mechanism (worm gear) 411 radial outer part 412 radially inner part 412a Axial end face 412b Axial end face 413 Connection section 871 1st Housing 871a flange 872 Second Housing 872a Inner surface 873 Third Housing 873a Protrusion 873b Bottom end 873c Bend section 873d Bearing housing 874 Boots 875 cover D10 1st distance D11 6th distance D20 2nd distance D21 3rd distance D40 4th distance D60 5th distance D30 Distance P1 1st area P2 2nd area

Claims

1. a pinion shaft extending in an axial direction of the central axis, one side of which in the axial direction is connected to the steering shaft, and having pinion teeth on an outer periphery thereof; a housing that accommodates at least a portion of the pinion shaft; a first bearing including: an inner ring attached to an outer periphery of a first portion of the pinion shaft that is located on the other side of the pinion teeth in the axial direction; an outer ring attached to the housing; and rolling elements provided between the inner ring and the outer ring, the first bearing rotatably supporting the pinion shaft with respect to the housing; a worm wheel including: an annular core portion extending in a radial direction intersecting the axial direction from an outer periphery of a second portion of the pinion shaft that is located on the other side of the first portion in the axial direction; and a wheel tooth portion provided on an outer periphery of the core portion; an annular fixing member provided on an outer periphery of a portion of the pinion shaft between the first portion and the second portion and abutting against an end surface of the inner ring on the other side in the axial direction; Equipped with the pinion teeth are capable of meshing with rack teeth of a rack shaft extending in the vehicle width direction, the core metal portion is attached to an outer periphery of the second portion and has an annular radially inner portion extending in a direction around the central axis, When viewed from the axial direction, the inner ring and the radially inner portion overlap, The inner ring and the radially inner portion are spaced apart from each other in the axial direction, an axial end of the radially inner portion on one side in the axial direction is located on the other side in the axial direction relative to the fixing member; Electric power steering device.

2. a protrusion protruding radially outward is provided in a portion of the pinion shaft between the axial end of the radially inner portion and the fixed member, and the protrusion and the axial end of the radially inner portion are disposed apart from each other in the axial direction.

2. The electric power steering device according to claim 1.

3. A pinion shaft extending in an axial direction of a central axis, one side of which in the axial direction is connected to a steering shaft, and pinion teeth are provided on an outer periphery thereof; a housing that accommodates at least a portion of the pinion shaft; a first bearing including: an inner ring attached to an outer periphery of a first portion of the pinion shaft that is located on the other side of the pinion teeth in the axial direction; an outer ring attached to the housing; and rolling elements provided between the inner ring and the outer ring, the first bearing rotatably supporting the pinion shaft with respect to the housing; a worm wheel including: an annular core portion extending in a radial direction intersecting the axial direction from an outer periphery of a second portion of the pinion shaft that is located on the other side of the first portion in the axial direction; and a wheel tooth portion provided on an outer periphery of the core portion; an annular fixing member provided on an outer periphery of a portion of the pinion shaft between the first portion and the second portion and abutting against an end surface of the inner ring on the other side in the axial direction; Equipped with the pinion teeth are capable of meshing with rack teeth of a rack shaft extending in the vehicle width direction, the core metal portion is attached to an outer periphery of the second portion and has an annular radially inner portion extending in a direction around the central axis, When viewed from the axial direction, the inner ring and the radially inner portion overlap, The inner ring and the radially inner portion are spaced apart from each other in the axial direction, the pinion teeth include a first tooth portion and a second tooth portion adjacent to the first tooth portion on the other side in the axial direction, a radial distance between a tooth bottom of the first tooth portion and the central axis is a first distance, a radial distance between a tooth bottom at an end of the second tooth portion on the other side in the axial direction and the central axis is a second distance that is greater than the first distance, an end of the second tooth portion on the other side in the axial direction abuts against an end surface of the inner ring on one side in the axial direction; Electric power steering device.

4. an axial end of the radially inner portion on one side in the axial direction is located on the other side in the axial direction relative to the fixing member; 4. The electric power steering device according to claim 3.

5. a protrusion protruding radially outward is provided in a portion of the pinion shaft between the axial end of the radially inner portion and the fixed member, and the protrusion and the axial end of the radially inner portion are disposed apart from each other in the axial direction.

5. The electric power steering device according to claim 4.

6. At the other end of the second tooth portion in the axial direction, a radial distance between the tooth bottom and the tooth tip is a third distance, a radial distance between an inner peripheral surface of the inner ring and the tooth bottom is a fourth distance that is greater than the third distance; 6. An electric power steering device according to claim 3, 4 or 5.

7. The inner circumferential surface of the housing is disposed radially outward of the first tooth portion, and a radial distance between a tooth tip of the first tooth portion and the inner circumferential surface of the housing is a fifth distance, a radial distance between the tooth bottom and the tooth tip in the first tooth portion is a sixth distance, the fifth distance is smaller than the sixth distance; 7. The electric power steering device according to claim 3.

8. a second bearing that rotatably supports the pinion shaft relative to the housing is provided at a third portion of the pinion shaft on one side of the pinion teeth in the axial direction, The second bearing includes an inner ring attached to an outer periphery of the third portion, an outer ring attached to the housing, and a rolling element provided between the inner ring and the outer ring. The electric power steering device according to any one of claims 1 to 7.

9. a first step of installing a rack shaft having rack teeth on its outer periphery in a housing; a second step, after the first step, of inserting a pinion shaft into the housing toward the other side in the axial direction while meshing the pinion teeth with the rack teeth, in a state in which a second bearing is disposed between the pinion teeth and the large diameter portion of the pinion shaft, the pinion teeth being formed on an outer periphery thereof and the large diameter portion being provided on one side in the axial direction of the pinion teeth; a third step, after the second step, of inserting a first bearing onto an outer periphery of a first portion of the pinion shaft that is located on the other side of the pinion teeth in the axial direction; a fourth step, after the third step, of inserting an annular fixing member onto an outer periphery of a portion of the pinion shaft that is on the other side in the axial direction than the first bearing; a fifth step, after the fourth step, plastically deforming the fixing member radially inward to bring the fixing member into contact with an end face of the first bearing on the other side in the axial direction, thereby fixing the first bearing with the fixing member in a state in which the end face of the first bearing on one side in the axial direction and an end of the pinion tooth on the other side in the axial direction are in contact with each other; a sixth step, after the fifth step, of press-fitting a worm wheel into a second portion of the pinion shaft that is on the other side of the fixed member in the axial direction, with a gap along the axial direction provided between the worm wheel and the first bearing, the worm wheel has an annular radially inner portion that fits onto the pinion shaft, a protrusion protruding radially outward is provided between one axial end of the radially inner portion of the pinion shaft in the axial direction and the fixed member, and the protrusion and the axial end of the radially inner portion are disposed apart from each other in the axial direction. A manufacturing method for an electric power steering device.

10. A first step of installing a rack shaft having rack teeth on its outer periphery in a housing; a second step, after the first step, of inserting a pinion shaft into the housing toward the other side in the axial direction while meshing the pinion teeth with the rack teeth, in a state in which a second bearing is disposed between the pinion teeth and the large diameter portion of the pinion shaft, the pinion teeth being formed on an outer periphery thereof and the large diameter portion being provided on one side in the axial direction of the pinion teeth; a third step, after the second step, of inserting a first bearing onto an outer periphery of a first portion of the pinion shaft that is located on the other side of the pinion teeth in the axial direction; a fourth step, after the third step, of inserting an annular fixing member onto an outer periphery of a portion of the pinion shaft that is on the other side in the axial direction than the first bearing; a fifth step, after the fourth step, plastically deforming the fixing member radially inward to bring the fixing member into contact with an end face of the first bearing on the other side in the axial direction, thereby fixing the first bearing with the fixing member in a state in which the end face of the first bearing on one side in the axial direction and an end of the pinion tooth on the other side in the axial direction are in contact with each other; a sixth step, after the fifth step, of press-fitting a worm wheel into a second portion of the pinion shaft that is on the other side of the fixed member in the axial direction, with a gap along the axial direction provided between the worm wheel and the first bearing, The inner circumferential surface of the housing is disposed radially outward of the pinion teeth so as to face the outer circumferential surface of the housing. a radial distance between a tip of the pinion tooth and the inner circumferential surface of the housing is a fifth distance, a radial distance between a tooth bottom and a tooth tip of the pinion tooth is a sixth distance, the fifth distance is smaller than the sixth distance; A manufacturing method for an electric power steering device.

11. The fifth step is a movement preventing step of preventing axial movement of the pinion shaft; a diameter reducing step of reducing a diameter of the other side of the fixing member in the axial direction and bringing an end of the other side into contact with an outer periphery of the pinion shaft after the movement preventing step, A method for manufacturing an electric power steering device according to claim 9 or 10.

12. the worm wheel has an annular radially inner portion that fits onto the pinion shaft, a protrusion protruding radially outward is provided between one axial end of the radially inner portion of the pinion shaft in the axial direction and the fixed member, and the protrusion and the axial end of the radially inner portion are disposed apart from each other in the axial direction. A method for manufacturing the electric power steering device according to any one of claims 9 to 11.

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