Electric power steering device

Abstract

This electric power steering device comprises an assist pinion shaft, a worm wheel, a worm shaft, a bolt, an assist pinion shaft housing part, a worm shaft housing part, a first attachment part provided in the assist pinion shaft housing part, and a third attachment part provided in the worm shaft housing part. The third attachment part is attached to the first attachment part via the bolt in a state in which a large diameter portion of the bolt is in contact with the first attachment part and a male screw portion of the bolt is engaged with a female screw portion of the third attachment part. When viewed from a first direction, at least a part of the large diameter portion of the bolt overlaps the worm shaft housing part.

Description

Electric power steering device

[0001] The present disclosure relates to an electric power steering device.

[0002] The electric power steering device of Patent Document 1 includes a rack shaft, a pinion shaft, a worm wheel, a worm shaft, and a housing. Specifically, pinion teeth are provided at one axial end of the central axis of the pinion shaft, and the pinion teeth mesh with rack teeth of the rack shaft. A worm wheel is attached to the other axial end of the pinion shaft, and the worm wheel meshes with the worm shaft. The worm shaft is rotatably attached to the output shaft of a motor.

[0003] The housing includes a pinion shaft accommodating portion that accommodates the pinion shaft, a worm wheel accommodating portion that accommodates the worm wheel, and a worm shaft accommodating portion that accommodates the worm shaft. The worm wheel accommodating portion and the worm shaft accommodating portion are arranged above the pinion shaft accommodating portion. A flange of the worm shaft accommodating portion and a flange of the pinion shaft accommodating portion are fastened together via bolts. Specifically, a through hole is formed in the flange of the worm shaft accommodating portion, and a female thread portion is formed in the flange of the pinion shaft accommodating portion. The bolts are arranged with their heads on the upper side and their male threads on the lower side, and the male threads of the bolts engage with the female threads of the flange of the pinion shaft accommodating portion, with the bolt heads abutting the upper surface of the flange of the worm shaft accommodating portion.

[0004] Japanese Patent Application Laid-Open No. 2001-271913

[0005] The flange of the worm shaft accommodating portion protrudes laterally from the lower end of the side surface of the worm shaft accommodating portion. To avoid interference between the head of the bolt and the side surface of the worm shaft accommodating portion, for example, it is necessary to position the bolt away from the side surface of the worm shaft accommodating portion or to increase the height of the flange of the worm shaft accommodating portion to a position where the head of the bolt does not interfere with the side surface of the worm shaft accommodating portion. Specifically, in Patent Document 1, as shown in FIG. 3 , a bolt 53 is inserted into a through-hole of a mounting boss 32 f, which corresponds to the flange of the worm shaft accommodating portion, and the male thread portion of the bolt 53 engages with the female thread portion of the flange of the pinion shaft accommodating portion, thereby fixing the worm shaft accommodating portion to the pinion shaft accommodating portion. By positioning the mounting boss 32 f at a height higher than the height of the worm shaft, the head of the bolt 53 does not interfere with the side surface of the worm shaft accommodating portion. As described above in Patent Document 1, when a bolt is inserted into a through hole formed in the flange of the worm shaft accommodating portion and the male thread portion of the bolt is tightened into the female thread of the flange of the pinion shaft accommodating portion to fix the worm shaft accommodating portion to the pinion shaft accommodating portion, the flange becomes large, which may result in an increase in the size of the electric power steering device.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and has an object to provide an electric power steering device that is more compact.

[0007] In order to achieve the above object, an electric power steering device according to one aspect includes an assist pinion shaft extending in a first direction and having pinion teeth that mesh with rack teeth of a rack shaft on its outer periphery on one side in the first direction; a worm wheel attached to the other side in the first direction of the assist pinion shaft and having wheel tooth portions on its outer periphery; a worm shaft having shaft tooth portions that mesh with the wheel tooth portions, disposed on one side of the worm wheel in a second direction intersecting the first direction, and rotated by a driving force of a motor; a plurality of bolts that have a large diameter portion including a head and a male thread portion whose diameter is smaller than the maximum diameter of the large diameter portion, the large diameter portion being disposed on one side in the first direction and the male thread portion being disposed on the other side in the first direction; an assist pinion shaft accommodating portion that accommodates the assist pinion shaft and has a first attachment portion and a second attachment portion on the other side in the first direction; the housing includes a worm wheel accommodating portion arranged on the other side of the worm shaft accommodating portion in the first direction, a worm shaft accommodating portion arranged on one side of the worm wheel accommodating portion in the second direction and accommodating the worm shaft, a third mounting portion provided in the worm shaft accommodating portion and attached to the first mounting portion via the bolt, and a fourth mounting portion provided in the worm wheel accommodating portion and attached to the second mounting portion via the bolt, wherein the first mounting portion has a through hole through which the male threaded portion of the bolt can pass, and the third mounting portion has a female threaded portion with which the male threaded portion of the bolt engages, and the third mounting portion is attached to the first mounting portion via the bolt with the large diameter portion of the bolt abutting on the first mounting portion and the male threaded portion of the bolt engaging with the female threaded portion of the third mounting portion, and at least a portion of the large diameter portion of the bolt overlaps with the worm shaft accommodating portion when viewed from the first direction. In a similar aspect, the third mounting portion includes a first flange protruding to one side in the second direction, the first flange is provided with the female thread portion, and when viewed from the first direction, a portion of the large diameter portion of the bolt overlaps with the worm shaft accommodating portion.

[0008] As described above, in Patent Document 1, the flange of the worm shaft housing and the flange of the pinion shaft housing are fastened together with the bolt head positioned on the upper side and the male thread portion positioned on the lower side. To avoid interference between the bolt head and the side surface of the worm shaft housing, the bolt needs to be positioned away from the side surface of the worm shaft housing. This requires a larger flange, which may result in an increased size of the electric power steering device.

[0009] In contrast, in the present disclosure, the bolt is arranged upside down opposite to that of Cited Document 1. That is, the third attachment portion provided in the worm shaft accommodating portion and the first attachment portion provided in the assist pinion shaft accommodating portion are fastened together with the large diameter portion of the bolt positioned on the lower side (one side in the first direction) and the male thread portion positioned on the upper side (the other side in the first direction). Furthermore, at least a portion of the large diameter portion of the bolt overlaps with the worm shaft accommodating portion when viewed from the first direction.

[0010] Therefore, while making the third mounting portion and the first mounting portion smaller than the flanges of Patent Document 1, it is possible to prevent interference between the head of the bolt and the wall surface of the worm shaft accommodating portion, and ultimately it is possible to provide an electric power steering device that is more compact.

[0011] In a preferred embodiment, the female threaded portion penetrates the first flange in the first direction, which increases the axial engagement length between the bolt and the female threaded portion compared to when the female threaded portion is a blind hole, thereby increasing the fastening force between the third mounting portion and the first mounting portion.

[0012] In a preferred embodiment, the entire large diameter portion of the bolt overlaps the worm shaft housing when viewed from the first direction, which allows the third mounting portion and the first mounting portion to be made even smaller, thereby making it possible to provide an even more compact electric power steering device.

[0013] In a preferred embodiment, the fourth mounting portion includes a second flange, the second flange having a female threaded portion with which the male threaded portion of the bolt engages, the second mounting portion including a third flange arranged opposite the second flange on the other side in the first direction, the third flange having a through hole through which the male threaded portion of the bolt can pass, and the second flange is mounted to the third flange via the bolt with the large diameter portion of the bolt abutting against the third flange and the male threaded portion of the bolt engaging with the female threaded portion of the second flange.

[0014] In this way, when fastening the fourth mounting portion provided in the worm wheel housing portion to the second mounting portion provided in the assist pinion shaft housing portion, the vertical positions of the bolts are reversed compared to Patent Document 1, and the bolts are mounted with the large diameter portions on the bottom and the male thread portions on the top. This ensures that the large diameter portions and male thread portions of all bolts are in the same vertical position. Therefore, all bolt fastening work can be done from below, making the fastening work easier.

[0015] In a desirable aspect, the rack shaft is provided on the other side in the second direction relative to the assist pinion shaft, a rack guide is provided on the other side in the second direction relative to the rack shaft for pushing the rack shaft toward the assist pinion shaft, the rack shaft extends in a third direction intersecting the first direction and the second direction, the rack guide protrudes toward the other side in the second direction, the housing includes a rack shaft accommodating portion that extends in the third direction and accommodates the rack shaft, and a rack guide accommodating portion that protrudes from the rack shaft accommodating portion toward the other side in the second direction and accommodates the rack guide, and the second flange and the third flange are located at a corner where the rack shaft accommodating portion and the rack guide accommodating portion intersect, as viewed from the first direction.

[0016] The corner where the rack shaft housing and the rack guide housing intersect is dead space, so by locating the second flange and the third flange at the corner, it is possible to effectively utilize the dead space.

[0017] In a preferred embodiment, the large diameter portion of the bolt includes the head and a washer having a diameter larger than that of the head, so that even in a bolt provided with a washer, the third mounting portion and the first mounting portion can be made smaller.

[0018] According to the present disclosure, the electric power steering device can be made smaller.

[0019] FIG. 1 is a schematic diagram of an electric power steering device according to an embodiment. FIG. 2 is a perspective view showing a portion of FIG. 1. FIG. 3 is an enlarged perspective view of a portion of FIG. 2. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 1. FIG. 5 is a schematic view showing an enlarged portion of FIG. 4. FIG. 6 is a perspective view of FIG. 3 seen from a different direction. FIG. 7 is a perspective view of FIG. 6 seen from the axial direction of the assist pinion shaft. FIG. 8 is a perspective view showing a state in which bolts have been removed from FIG. 7. FIG. 9 is a perspective view showing a state in which a worm wheel receiving portion and a worm shaft receiving portion have been removed from FIG. 7. FIG. 10 is a perspective view of FIG. 7 seen from below. FIG. 11 is a cross-sectional view showing a modified example, and corresponds to FIG. 5.

[0020] 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 identical. Furthermore, the components described below can be combined as appropriate. Furthermore, parts with the same structure are given the same reference numerals and their description will be omitted. In this embodiment, the Z direction is the first direction, the Y direction is the second direction, and the X direction is the third direction. The Z direction intersects with the Y direction. The X direction intersects with the Y and Z directions. The Z2 side is one side of the first direction, and the Z1 side is the other side of the first direction. The Y1 side is one side of the second direction, and the Y2 side is the other side of the second direction.

[0021] [Embodiment] An electric power steering device according to an embodiment will be described. FIG. 1 is a schematic diagram of an electric power steering device according to an embodiment. FIG. 2 is a perspective view showing a part of FIG. 1. FIG. 3 is a perspective view showing an enlarged part of FIG. 2. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 1. FIG. 5 is a schematic view showing an enlarged part of FIG. 4. FIG. 6 is a perspective view of FIG. 3 seen from a different direction. FIG. 7 is a perspective view of FIG. 6 seen from the axial direction of the assist pinion shaft. FIG. 8 is a perspective view showing a state in which bolts have been removed from FIG. 7. FIG. 9 is a perspective view showing a state in which a worm wheel receiving portion and a worm shaft receiving portion have been removed from FIG. 7. FIG. 10 is a perspective view showing FIG. 7 seen from below.

[0022] 1, the electric power steering device 100 includes a steering wheel 10, a first steering shaft 11, a second steering shaft 12, a steering pinion shaft 13, a rack shaft 15, a tie rod 16, an assist pinion shaft 21, a worm wheel 23, a worm shaft 27, a motor 70, and a housing 400. The housing 400 includes a steering-side housing 3 and an assist-side housing 40. The steering-side housing 3 and the assist-side housing 40 are connected to form an integrated structure. The electric power steering device 100 is, for example, a so-called dual-pinion type steering device.

[0023] 1, a steering wheel 10 is connected to a first steering shaft 11, which is connected to a second steering shaft 12 via a universal joint 111. The second steering shaft 12 is connected to a steering pinion shaft 13 via a universal joint 121. Pinion teeth 14 are provided on the outer periphery of the lower end of the steering pinion shaft 13.

[0024] As shown in FIG. 1 , the rack shaft 15 extends in the X direction. Here, if the central axis of the rack shaft 15 is defined as a central axis AX2 (see FIG. 3 ), the axial direction of the central axis AX2 is aligned with the X direction. That is, the rack shaft 15 extends in the axial direction of the central axis AX2. The X direction is, for example, the vehicle width direction. As shown in FIG. 1 , rack teeth 151 are provided on the outer periphery of the X2 side of the rack shaft 15. The rack teeth 151 mesh with the pinion teeth 14 of the steering pinion shaft 13. Rack teeth 152 are provided on the outer periphery of the X1 side of the rack shaft 15. The rack teeth 152 mesh with the pinion teeth 22 of the assist pinion shaft 21. Both ends of the rack shaft 15 on the X1 side and the X2 side are connected to wheels 17 via tie rods 16.

[0025] As described above, the steering wheel 10 is connected to the steering pinion shaft 13 via the first steering shaft 11 and the second steering shaft 12. Therefore, when the driver applies steering torque to the steering wheel 10 in the left or right direction, the steering torque is transmitted to the steering pinion shaft 13 via the first steering shaft 11 and the second steering shaft 12. Then, because the pinion teeth 14 of the steering pinion shaft 13 mesh with the rack teeth 151, the steering torque is converted into a force that moves the rack shaft 15 in the X direction.

[0026] In addition, a steering torque sensor (not shown) detects the steering torque applied to the steering wheel 10, and a controller (not shown) supplies current to the motor 70 in accordance with the detected steering torque. When current is supplied to the motor 70, the assist torque generated by the motor 70 is transmitted to the assist pinion shaft 21 connected to the motor 70 via the worm wheel 23 and the worm shaft 27, and an assist force is generated that moves the rack shaft 15 connected to the assist pinion shaft 21 in the X direction.

[0027] That is, by driving the motor 70 in accordance with the steering torque generated by steering the steering wheel 10, it is possible to assist the rack shaft 15 in moving in the X direction.

[0028] Next, the housing 400 will be described. As shown in FIGS. 1 and 2, the housing 400 includes a steering-side housing 3 on the X2 side and an assist-side housing 40 on the X1 side. As shown in FIG. 2, vehicle body mounting portions 31, 413 are attached to the X2-side end of the steering-side housing 3 and the X1-side end of the assist-side housing 40, respectively. The vehicle body mounting portion 31 is provided with a through-hole 32, into which a fastening member (e.g., a bolt) is inserted. The vehicle body mounting portion 413 is provided with a through-hole 414, into which a fastening member (e.g., a bolt) is inserted. In other words, the steering-side housing 3 and the assist-side housing 40 are mounted to the vehicle body by passing a fastening member through the through-holes 32, 414 and then fastening the fastening member to the vehicle body.

[0029] The steering-side housing 3 accommodates the steering pinion shaft 13 and the X2 side portions of the rack shaft 15. Specifically, the tip end of the steering pinion shaft 13 is accommodated inside the steering pinion shaft accommodating portion 33. The assist-side housing 40 accommodates the assist pinion shaft 21, the worm wheel 23, the worm shaft 27, and the X2 side portion of the rack shaft 15.

[0030] 2 to 4 , the assist-side housing 40 includes a rack shaft accommodating portion 411, an assist pinion shaft accommodating portion 4, a worm wheel accommodating portion 5, a worm shaft accommodating portion 6, and a rack guide accommodating portion 412. The rack shaft accommodating portion 411 accommodates the rack shaft 15. The rack guide accommodating portion 412 accommodates the rack guide 153 and the spring 154.

[0031] As shown in FIG. 4 , the rack shaft 15 has rack teeth 152 on its Y1-side side surface. The Y2-side side surface of the rack shaft 15 is curved. A rack guide 153, a spring 154, and a sealing member 155 are provided on the Y2 side of the rack shaft 15. Specifically, a cylindrical rack guide housing 412 protrudes toward the Y2 side from the main body 41 of the assist pinion shaft housing 4. The rack guide 153 and the spring 154 are housed inside the rack guide housing 412. The sealing member 155 is fitted into the Y2-side end of the rack guide housing 412. Because the rack guide 153 and the spring 154 are housed together when the spring 154 is compressed, when the spring 154 presses the rack guide 153 toward the Y1 side, the rack guide 153 is pressed against the assist pinion shaft 21. This maintains meshing between the rack teeth 152 of the rack shaft 15 and the pinion teeth 22 of the assist pinion shaft 21. The assist pinion shaft 21 has a center axis AX3. The axial direction of the center axis AX3 is along the Z direction (first direction).

[0032] As shown in FIG. 4 , the worm wheel 23 is fitted onto the Z1-side end of the assist pinion shaft 21. A portion of the assist pinion shaft 21 on the Z1 side is rotatably supported by the main body 41 of the assist pinion shaft accommodating portion 4 via a bearing 241. A portion of the assist pinion shaft 21 on the Z2 side is rotatably supported by the flange 42 of the assist pinion shaft accommodating portion 4 via a bearing 242. The worm wheel 23 includes a core metal portion 231 and a wheel tooth portion 232. The wheel tooth portion 232 meshes with a shaft tooth portion 271 of the worm shaft 27. The worm shaft 27 has a central axis AX1. The worm shaft 27 is rotatably attached to the output shaft of the motor 70 (see FIG. 2 ).

[0033] As shown in Fig. 4, the assist pinion shaft accommodating portion 4 includes a main body 41 and a flange 42. The main body 41 is a cylindrical member extending in the Z direction. The flange 42 is provided at the end of the main body 41 on the Z1 side and extends radially outward from the main body 41. The end of the main body 41 on the Z2 side is open, and this opening is sealed with a cap 26.

[0034] 4 and 5 , the flange 42 has an annular protrusion 401 on its radially inner side. A seal member accommodating groove 514 is provided along the circumferential direction on the outer peripheral surface 401 a of the annular protrusion 401. The seal member accommodating groove 514 is recessed radially inward. A seal member S is accommodated in the seal member accommodating groove 514.

[0035] As shown in FIG. 9 , the flange 42 includes a protruding portion (first mounting portion) 425 located on the Y1 side and a third flange (second mounting portion) 424 located on the Y2 side. That is, the protruding portion 425 is the Y1-side portion of the flange 42 and is also referred to as the first mounting portion. A through-hole 425a is provided in the protruding portion 425. The male thread portion 212 of the bolt 200 passes through the through-hole 425a. The third flange 424 is the Y2-side portion of the flange 42 and is also referred to as the second mounting portion. Two third flanges 424 are provided. The third flanges 424 are each provided with a through-hole 424a. The male thread portion 212 of the bolt 200 passes through the through-hole 424a.

[0036] As shown in FIG. 9 , the annular protrusion 401 is provided with a recess 43. The recess 43 faces a bottom surface 43a and a side surface 43b. A plurality of recesses 43 (eight in this embodiment) are provided along the circumferential direction of the annular protrusion 401. The annular protrusion 401 also includes a first annular portion 426, a second annular portion 427, and a plurality of support legs 428 (eight in this embodiment). A bottom surface 42b is provided adjacent to the inner peripheral side of the inner peripheral surface 42a of the flange 42. A bearing 242 is provided on the inner peripheral side of the inner peripheral surface 42a of the flange 42.

[0037] Next, the worm wheel accommodating portion 5 and the worm shaft accommodating portion 6 will be described. As shown in FIGS. 4 and 5 , the worm wheel accommodating portion 5 is disposed on the Z1 side of the assist pinion shaft accommodating portion 4. The worm shaft accommodating portion 6 is disposed on the Y1 side of the worm wheel accommodating portion 5. The worm wheel accommodating portion 5 accommodates the worm wheel 23. The worm shaft accommodating portion 6 accommodates the worm shaft 27. The worm shaft 27 is attached to the output shaft of the motor 70, and as shown in FIG. 2 , the motor 70 is attached to the motor mounting plate 7. The worm wheel accommodating portion 5 and the worm shaft accommodating portion 6 are integral with each other. The worm wheel accommodating portion 5 has a side surface portion 51 and a top surface portion 52. The worm shaft accommodating portion 6 has a side surface portion 61 and a top surface portion 62.

[0038] As shown in FIG. 5 , the bolt 200 has a large-diameter portion 211 including a head portion 210 and a male thread portion 212. The bolt 200 has a central axis AX4 and extends in the axial direction of the central axis AX4. The large-diameter portion 211 is the portion of the bolt 200 with the largest diameter. For example, the large-diameter portion 211 is the head portion 210 of the bolt 200. Furthermore, if a washer 213 (see FIG. 11 described later) having a diameter larger than that of the head portion 210 is provided, the large-diameter portion 211 is the washer 213. The large-diameter portion 211 has a maximum diameter 211A. The male thread portion 212 has a diameter smaller than the maximum diameter 211A of the large-diameter portion 211. The bolt 200 extends along the Z direction with the large-diameter portion 211 disposed on the Z2 side and the male thread portion 212 disposed on the Z1 side. That is, the bolt 200 is fastened with the axial direction of the central axis AX4 substantially aligned with the Z direction.

[0039] Next, the first mounting portion 310 and the third mounting portion 330 will be described with reference to FIG. 5 . The first mounting portion 310 and the third mounting portion 330 are included in the housing 400. The third mounting portion 330 is provided in the worm shaft housing 6 and attached to the first mounting portion 310 via the bolt 200. A specific description will be given below. As described above, the first mounting portion 310 is the protruding portion 425 of the flange 42. The protruding portion 425 is provided with a through-hole 425a. In this embodiment, the third mounting portion 330 is the first flange 331. The first flange 331 protrudes from the side surface portion 61 of the worm shaft housing 6 toward the Y1 side. The first flange 331 is provided with a female thread portion 332. The female thread portion 332 penetrates the first flange 331 in the Z direction.

[0040] Next, a procedure for fastening the bolt 200 to the first mounting portion 310 and the third mounting portion 330 will be briefly described. First, the bolt 200 is positioned along the Z direction, with the large diameter portion 211 on the Z2 side (lower side) and the male threaded portion 212 on the Z1 side (upper side), and then the bolt 200 is positioned on the Z2 side of the protruding portion 425. Then, the bolt 200 is moved toward the Z1 side (upper side) until the male threaded portion 212 passes through the through-hole 425a, engages with the female threaded portion 332, and the large diameter portion 211 abuts against the underside of the protruding portion 425. This allows the bolt 200 to be fastened to the first mounting portion 310 and the third mounting portion 330.

[0041] 5, dashed two-dot lines L1 and L2 are lines that pass through the outer peripheral edge of the large diameter portion 211 of the bolt 200 and are parallel to the central axis AX4. Line L1 passes through the portion of the outer peripheral edge of the large diameter portion 211 that is closest to the Y2 side, and line L2 passes through the portion of the outer peripheral edge of the large diameter portion 211 that is closest to the Y1 side. Line L1 passes through the side surface portion 61 of the worm shaft housing 6. In other words, when viewed from the Z direction, a portion of the large diameter portion 211 of the bolt 200 overlaps with the worm shaft housing 6.

[0042] Next, the second mounting portion 320 and the fourth mounting portion 340 will be described with reference to FIGS. 6 to 9 . As shown in FIGS. 6 to 9 , the second mounting portion 320 and the fourth mounting portion 340 are included in the housing 400. The fourth mounting portion 340 is provided in the worm wheel accommodating portion 5 and attached to the second mounting portion 320 via the bolt 200. A detailed description will be given below. As described above, the second mounting portion 320 is the third flange 424. Two third flanges 424 are provided, one on the X2 side and one on the X1 side. Specifically, as shown in FIG. 9 , when viewed from the Z direction, one third flange 424 is provided on the X1 side and one on the X2 side of the rack guide accommodating portion 412. The fourth mounting portion 340 is the second flange 516. Two second flanges 516 are provided, and are arranged opposite the third flange 424 on the Z1 side. The second flange 516 is provided with a female thread portion 517. When viewed from the Z direction, one second flange 516 is disposed on the X1 side and one on the X2 side of the rack guide accommodating portion 412. The second flange 516 is attached to the third flange 424 via the bolt 200 in a state in which the large diameter portion 211 of the bolt 200 abuts against the third flange 424 and the male thread portion 212 of the bolt 200 engages with the female thread portion 517 of the second flange 516. Note that the procedure for fastening the bolt 200 to the second flange 516 and the third flange 424 is the same as the procedure for fastening the bolt 200 to the first mounting portion 310 and the third mounting portion 330, as described above.

[0043] 4, the rack shaft 15 is provided on the Y2 side of the assist pinion shaft 21, and the rack guide 153 is provided on the Y2 side of the rack shaft 15. The rack guide 153 pushes the rack shaft 15 toward the assist pinion shaft 21.

[0044] As shown in FIG. 10 , the rack shaft 15 extends in the X direction, and the rack guide 153 protrudes toward the Y2 side. The rack guide housing 412 protrudes toward the Y2 side from the rack shaft housing 411. Corners 350, 351, indicated by thick dashed lines, are provided on the X1 and X2 sides of the rack guide housing 412. The contours of the corners 350, 351 are, for example, rectangular when viewed from the Z direction. In other words, the rack shaft housing 411 extending in the X direction and the rack guide housing 412 extending in the Y direction intersect, and the corners 350, 351 are formed at the intersection. The corner 350 is located on the X1 side of the rack guide housing 412, and the corner 351 is located on the X1 side of the rack guide housing 412. When viewed from the Z direction, a second flange 516 and a third flange 424 are located at the corners 350, 351.

[0045] As described above, the electric power steering device 100 according to this embodiment includes the assist pinion shaft 21 that extends in the Z direction (first direction) and has pinion teeth 22 that mesh with the rack teeth 152 of the rack shaft 15 on its outer periphery on the Z2 side (one side in the first direction), the worm wheel 23 that is attached to the Z1 side (the other side in the first direction) of the assist pinion shaft 21 and has wheel tooth portions 232 on its outer periphery, and the worm shaft 27 that has a shaft tooth portion 271 that meshes with the wheel tooth portion 232, is positioned on the Y1 side of the worm wheel 23, and rotates by the driving force of the motor 70. The housing 400 includes an assist pinion shaft accommodating portion 4 that accommodates the assist pinion shaft 21 and has a first mounting portion 310 and a second mounting portion 320 provided on the Z1 side, a worm wheel accommodating portion 5 that accommodates the worm wheel 23 and is arranged on the Z1 side of the assist pinion shaft accommodating portion 4, and a worm shaft accommodating portion 6 that is arranged on the Y1 side (one side in the second direction) of the worm wheel accommodating portion 5 and accommodates the worm shaft 27. The electric power steering device 100 also includes a third mounting portion 330 that is provided in the worm shaft accommodating portion 6 and attached to the first mounting portion 310 via a bolt 200, and a fourth mounting portion 340 that is provided in the worm wheel accommodating portion 5 and attached to the second mounting portion 320 via the bolt 200. The bolt 200 has a large diameter portion 211 including a head 210 and a male thread portion 212 having a diameter smaller than the maximum diameter 211A of the large diameter portion 211, and extends along the Z direction with the large diameter portion 211 positioned on the Z2 side and the male thread portion 212 positioned on the Z1 side.

[0046] The first mounting portion 310 is provided with a through-hole 425a through which the male threaded portion 212 of the bolt 200 can pass, and the third mounting portion 330 is provided with a female threaded portion 332 with which the male threaded portion 212 of the bolt 200 meshes. The third mounting portion 330 is attached to the first mounting portion via the bolt 200 in a state in which the large diameter portion 211 of the bolt 200 abuts against the first mounting portion 310 and the male threaded portion 212 of the bolt 200 meshes with the female threaded portion 332 of the third mounting portion 330. The third mounting portion 330 includes a first flange 331 protruding toward the Y1 side, and the female threaded portion 332 is provided on the first flange 331. When viewed from the Z direction, a portion of the large diameter portion 211 of the bolt 200 overlaps with the worm shaft accommodating portion 6.

[0047] As described above, in Patent Document 1, the flange of the worm shaft housing and the flange of the pinion shaft housing are fastened together with the bolt head positioned on the upper side and the male thread portion positioned on the lower side. To avoid interference between the bolt head and the side surface of the worm shaft housing, the bolt needs to be positioned away from the side surface of the worm shaft housing. This requires a larger flange, which may result in an increased size of the electric power steering device.

[0048] In contrast to this, in this embodiment, with the large diameter portion 211 of the bolt 200 positioned on the lower side (Z2 side) and the male thread portion 212 positioned on the upper side (Z1 side), the first flange 331 (third mounting portion 330) provided on the worm shaft accommodating portion 6 and the protrusion 425 (first mounting portion 310) provided on the assist pinion shaft accommodating portion 4 are fastened together. Furthermore, when viewed from the Z direction, a portion of the large diameter portion 211 of the bolt 200 overlaps with the worm shaft accommodating portion 6.

[0049] Therefore, the first flange 331 (third mounting portion 330) and the protrusion 425 (first mounting portion 310) can be made smaller than the flanges of Patent Document 1, which in turn makes it possible to provide an electric power steering device 100 that is smaller in size.

[0050] The female thread portion 332 penetrates the first flange 331 in the Z direction. Therefore, the axial engagement length between the bolt 200 and the female thread portion 332 is longer than when the female thread portion 332 is a blind hole. Therefore, the fastening force between the first flange 331 and the protrusion 425 is greater.

[0051] The fourth mounting portion 340 includes a second flange 516, which is provided with a female thread portion 517 that engages with the male thread portion 212 of the bolt 200. The second mounting portion 320 includes a third flange 424 that is disposed opposite the second flange 516 on the Z2 side, and which is provided with a through hole 424a that allows the male thread portion 212 of the bolt 200 to pass through. The second flange 516 is mounted to the third flange 424 via the bolt 200 in a state in which the large diameter portion 211 of the bolt 200 abuts against the third flange 424 and the male thread portion 212 of the bolt 200 engages with the female thread portion 517 of the second flange 516.

[0052] In this way, when the fourth mounting portion 340 provided in the worm wheel housing 5 and the second mounting portion 320 provided in the assist pinion shaft housing 4 are fastened together, the bolts 200 are mounted with the large diameter portions 211 positioned on the lower side (Z2 side) and the male thread portions 212 positioned on the upper side (Z1 side). In this way, the large diameter portions 211 and male thread portions 212 of all of the bolts 200 are positioned in the same vertical position. Therefore, all of the bolts 200 can be fastened from the lower side (Z2 side), making the fastening work easier.

[0053] The rack shaft 15 is provided on the Y2 side (the other side in the second direction) of the assist pinion shaft 21, and a rack guide 153 that presses the rack shaft 15 toward the assist pinion shaft 21 is provided on the Y2 side of the rack shaft 15. The rack shaft 15 extends in the X direction (the third direction), and the rack guide 153 protrudes toward the Y2 side. When viewed from the Z direction, the housing 400 includes a rack shaft accommodating portion 411 that extends in the third direction and accommodates the rack shaft 15, and a rack guide accommodating portion 412 that protrudes from the rack shaft accommodating portion 411 toward the Y2 side and accommodates the rack guide 153. When viewed from the Z direction, the second flange 516 and the third flange 424 are located at corners 350, 351 where the rack shaft accommodating portion 411 and the rack guide accommodating portion 412 intersect.

[0054] The corners 350 and 351 where the rack shaft accommodating portion 411 and the rack guide accommodating portion 412 intersect are dead spaces. Therefore, by arranging the second flange 516 and the third flange 424 at the corners 350 and 351, the dead spaces can be effectively utilized.

[0055] [Modification] Next, an electric power steering device 100A according to a modification will be described. Fig. 11 is a cross-sectional view showing the modification, and is a view corresponding to Fig. 5. In the modification, the entire large diameter portion 211 of the bolt 200 overlaps with the worm shaft housing portion 6 when viewed from the Z direction. This will be described in detail below.

[0056] As shown in FIG. 11 , in the electric power steering device 100A according to the modified example, the boundary between the third mounting portion 330A and the worm shaft accommodating portion 6 is a boundary 360 indicated by a thick dashed line. The portion on the Y1 side of the boundary 360 is the third mounting portion 330A. The boundary 360 includes a first portion 360A, a second portion 360B, and a third portion 360C. The first portion 360A extends from a first end P1 in the Z direction to a second end P2. The second portion 360B is an arc extending in the circumferential direction around the center axis AX1. The second portion 360B extends from the second end P2 to a third end P3. The third portion 360C extends from the third end P3 in the Z direction to a fourth end P4.

[0057] A female thread portion 332 is provided in the third mounting portion 330A. In a modified example, the female thread portion 332 is a blind hole. Therefore, if the boundary 360 is too close to the inner surface of the worm shaft accommodating portion 6, the thickness at which the female thread portion 332 is provided will be reduced. Therefore, it is desirable to set the boundary 360 so that a constant thickness is maintained relative to the inner surface of the worm shaft accommodating portion 6. In addition, the first mounting portion 310A is a flange 42. Since a washer 213 is provided on the bolt 200, in a modified example, the washer 213 serves as the large diameter portion 211. The maximum diameter 211A of the washer 213 is larger than that of the male thread portion 212.

[0058] 11 , the lines that pass through the outer peripheral edge of the washer 213 and are parallel to the central axis AX4 are designated by dashed two-dot lines L1 and L2. Line L1 passes through the portion of the outer peripheral edge of the washer 213 that is closest to the Y2 side, and line L2 passes through the portion of the outer peripheral edge of the washer 213 that is closest to the Y1 side. Both line L1 and line L2 pass through the side surface portion 61 of the worm shaft housing 6. In other words, the entire large diameter portion 211 of the bolt 200 overlaps with the worm shaft housing 6 when viewed from the Z direction.

[0059] As described above, in the electric power steering device 100A according to the modified example, when viewed from the Z direction, the entire large diameter portion 211 of the bolt 200 overlaps with the worm shaft housing 6. Therefore, the third mounting portion 330A and the flange 42 (first mounting portion 310A) can be made smaller than in the embodiment, and it is therefore possible to provide an electric power steering device 100A that is more compact.

[0060] Furthermore, the large diameter portion 211 of the bolt 200 includes the head 210 of the bolt 200 and a washer 213 having a diameter larger than that of the head 210. Therefore, even in the case of the bolt 200 provided with the washer 213, the third mounting portion 330A and the flange 42 (first mounting portion 310A) can be made smaller.

[0061] DESCRIPTION OF SYMBOLS 3 Steering side housing 4 Assist pinion shaft accommodating portion 5 Worm wheel accommodating portion 6 Worm shaft accommodating portion 7 Motor mounting plate 10 Steering wheel 11 First steering shaft 12 Second steering shaft 13 Steering pinion shaft 14 Pinion teeth 15 Rack shaft 16 Tie rod 17 Wheel 21 Assist pinion shaft 22 Pinion teeth 23 Worm wheel 26 Cap 27 Worm shaft 31 Vehicle body mounting portion 32 Through hole 33 Steering pinion shaft accommodating portion 40 Assist side housing 41 Main body portion 42 Flange 42a Inner peripheral surface 42b Bottom surface 43 Recess 43a Bottom surface 43b Side surface 51 Side portion 52 Top surface portion 61 Side portion 62 Top surface portion 70 Motor 100, 100A REFERENCE SIGNS LIST 111 Universal joint 121 Universal joint 151, 152 Rack teeth 153 Rack guide 154 Spring 155 Sealing member 200 Bolt 210 Head 211 Large diameter portion 211A Maximum diameter 212 Male thread portion 213 Washer 231 Core portion 232 Wheel tooth portion 241 Bearing 242 Bearing 271 Shaft tooth portion 310, 310A First mounting portion 320 Second mounting portion 330, 330A Third mounting portion 331 First flange 332 Female thread portion 340 Fourth mounting portion 350, 351 Corner portion 360 Boundary 360A First portion 360B Second portion 360C Third portion 400 Housing 401 Annular convex portion 401a Outer circumferential surface 411 Rack shaft accommodating portion 412 Rack guide accommodating portion 413 Vehicle body mounting portion 414 Through hole 424 Third flange (second mounting portion) 425 Projecting portion (first mounting portion) 424a, 425a Through hole 426 First annular portion 427 Second annular portion 428 Support leg 514 Seal member accommodating groove 516 Second flange (fourth mounting portion) 517 Female thread portion AX1, AX2, AX3, AX4 Central axis S Seal member

Claims

1. An assist pinion shaft extending in a first direction and having pinion teeth on its outer periphery on one side in the first direction that mesh with rack teeth of a rack shaft; a worm wheel attached to the other side in the first direction of the assist pinion shaft and having wheel tooth portions on its outer periphery; a worm shaft having shaft tooth portions that mesh with the wheel tooth portions, arranged on one side in a second direction intersecting the first direction with respect to the worm wheel, and rotated by the driving force of a motor; a plurality of bolts each having a large diameter portion including a head and a male thread portion whose diameter is smaller than the maximum diameter of the large diameter portion, the large diameter portion being arranged on one side in the first direction and the male thread portion being arranged on the other side in the first direction, and extending along the first direction; a housing including: an assist pinion shaft accommodating portion that accommodates the assist pinion shaft and has a first attachment portion and a second attachment portion provided on the other side in the first direction; a worm wheel accommodating portion that accommodates the worm wheel and is arranged on the other side in the first direction of the assist pinion shaft accommodating portion; a worm shaft accommodating portion that is arranged on one side in the second direction of the worm wheel accommodating portion and accommodates the worm shaft; a third attachment portion that is provided in the worm shaft accommodating portion and attached to the first attachment portion via the bolt; and a fourth attachment portion that is provided in the worm wheel accommodating portion and attached to the second attachment portion via the bolt; wherein the first attachment portion has a through hole that allows the male thread portion of the bolt to pass therethrough, and the third attachment portion has a female thread portion that engages with the male thread portion of the bolt, and the third attachment portion is attached to the first attachment portion via the bolt with the large diameter portion of the bolt abutting on the first attachment portion and the male thread portion of the bolt engaging with the female thread portion of the third attachment portion, an electric power steering device, wherein, when viewed from a first direction, at least a portion of the large diameter portion of the bolt overlaps with the worm shaft accommodating portion.

2. An electric power steering device as set forth in claim 1, wherein the third mounting portion includes a first flange protruding to one side in the second direction, the first flange is provided with the female thread portion, and when viewed from the first direction, a portion of the large diameter portion of the bolt overlaps with the worm shaft accommodating portion.

3. The electric power steering device according to claim 2, wherein the female thread portion penetrates the first flange in a first direction.

4. An electric power steering device according to any one of claims 1 to 3, wherein, when viewed from a first direction, the large diameter portion of the bolt entirely overlaps with the worm shaft accommodating portion.

5. An electric power steering device as claimed in any one of claims 1 to 4, wherein the fourth mounting portion includes a second flange, the second flange having a female threaded portion with which the male threaded portion of the bolt engages, the second mounting portion includes a third flange arranged opposite the other side of the second flange in the first direction, the third flange having a through hole through which the male threaded portion of the bolt can pass, and the second flange is mounted to the third flange via the bolt with the large diameter portion of the bolt abutting against the third flange and the male threaded portion of the bolt engaging with the female threaded portion of the second flange.

6. An electric power steering device according to claim 5, wherein the rack shaft is provided on the other side in the second direction relative to the assist pinion shaft, and a rack guide is provided on the other side in the second direction relative to the rack shaft for pushing the rack shaft toward the assist pinion shaft, the rack shaft extends in a third direction intersecting the first direction and the second direction, and the rack guide protrudes toward the other side in the second direction, the housing includes, when viewed from the first direction, a rack shaft accommodating portion that extends in the third direction and accommodates the rack shaft, and a rack guide accommodating portion that protrudes from the rack shaft accommodating portion toward the other side in the second direction and accommodates the rack guide, and the second flange and the third flange are located at a corner where the rack shaft accommodating portion and the rack guide accommodating portion intersect when viewed from the first direction.

7. An electric power steering device according to any one of claims 1 to 6, wherein the large diameter portion of the bolt includes the head and a washer having a diameter larger than that of the head.

Images