Electric power steering device

Abstract

This electric power steering device comprises: a first housing that accommodates a worm wheel, a worm shaft, and an assist pinion shaft; a second housing that accommodates the worm wheel and the worm shaft; and a sealing member disposed between the first housing and the second housing. An annular raised part that protrudes toward the other side in a first direction is provided on the other side of the first housing in the first direction. A lateral surface part that fits onto the outer circumferential side of the outer circumferential surface of the annular raised part is provided on one side of the second housing in the first direction. A sealing member accommodation groove, which is recessed inward in the radial direction and in which the sealing member is accommodated, is provided on the outer circumferential surface of the annular raised 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, a motor, 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 on 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 the motor.

[0003] The housing includes a first housing that accommodates the rack shaft and the pinion shaft, and a second housing that accommodates the worm wheel, the worm shaft, and the motor. The first housing and the second housing are connected by fastening a flange of the first housing to a flange of the second housing with a bolt.

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

[0005] The pinion shaft is rotatably supported by the first housing via a bearing, and the motor is attached to the second housing. Therefore, in a structure in which the flanges of the first housing and the second housing are fastened together with bolts, the distance between the worm wheel and the worm shaft is likely to change, which can cause abnormal noise when the worm wheel and the worm shaft engage with each other and can easily cause wear on the wheel teeth of the worm wheel and the shaft teeth of the worm shaft.

[0006] Furthermore, a sealing mechanism needs to be provided in the housing to prevent water and the like from entering the housing. In Patent Document 1, because the second housing has a notch at the bottom end of the wall, it is necessary to seal the entire housing by providing, for example, an annular sealing member on the outside of the wall, which may increase the size of the electric power steering device.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide an electric power steering device that is more compact and in which changes in the distance between the worm wheel and the worm shaft during operation of the electric power steering device are more suppressed.

[0008] In order to achieve the above object, an electric power steering device according to one aspect includes an assist pinion shaft that extends in a first direction and has 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 that is attached to the other side in the first direction of the assist pinion shaft and has wheel tooth portions on its outer periphery; a worm shaft that has shaft tooth portions that mesh with the wheel tooth portions, is disposed on one side of the worm wheel in a second direction that intersects the first direction, and is rotated by the driving force of a motor; The assist pinion shaft has a first housing that houses the assist pinion shaft, and a second housing that is arranged adjacent to the other side of the first housing in the first direction and that houses the worm wheel and the worm shaft, and on the other side of the first housing in the first direction, there is provided an annular protrusion that is arranged in a ring shape on the outer periphery of the central axis of the assist pinion shaft and that protrudes toward the other side in the first direction, and on one side of the second housing in the first direction, there is provided a side portion that fits on the outer periphery of the outer surface of the annular protrusion, and a sealing member is provided between the annular protrusion and the side portion.

[0009] As described above, in Patent Document 1, the flange of the first housing and the flange of the second housing are fastened together with bolts, which makes it easy for the distance between the worm wheel and the worm shaft to change. Also, because the wall of the second housing has a notch at the bottom end, it is necessary to seal the entire housing by, for example, providing an annular seal member on the outside of the wall, which may increase the size of the electric power steering device.

[0010] In contrast, in the present disclosure, the first housing has an annular protrusion, and the second housing has a side surface that fits around the outer periphery of the annular protrusion. That is, the first and second housings are positioned by a so-called spigot joint between the side surface and the annular protrusion. This further reduces changes in the distance between the worm wheel and the worm shaft.

[0011] Furthermore, by providing a seal member between the annular convex portion and the side surface portion, the first housing and the second housing are sealed, which makes it possible to make the electric power steering device smaller than the electric power steering device of Patent Document 1. As described above, according to the present disclosure, it is possible to provide an electric power steering device that is smaller in size and in which changes in the distance between the worm wheel and the worm shaft are further suppressed.

[0012] In a preferred embodiment, a seal member accommodating groove that is recessed radially inward and accommodates the seal member is provided along the circumferential direction on either the outer peripheral surface of the annular convex portion or the inner surface of the side surface of the second housing, and the seal member is accommodated in the seal member accommodating groove to seal the gap between the annular convex portion and the side surface. In this way, the seal member is accommodated in the seal member accommodating groove and the side surface of the second housing is fitted to the outer peripheral side of the annular convex portion, thereby sealing the first housing and the second housing, and therefore the electric power steering device can be made smaller than the electric power steering device of Patent Document 1.

[0013] In a preferred embodiment, the annular protrusion includes a first section having a first top surface along a plane perpendicular to the central axis of the assist pinion shaft, and a second section having a second top surface disposed adjacent to the radially outer side of the first section and extending radially outward toward one side in the first direction, the second top surface being disposed opposite the worm shaft. This allows the annular protrusion to be closer to the worm shaft than when the top surface of the second section is along a plane perpendicular to the central axis of the assist pinion shaft. This allows the electric power steering device according to the present disclosure to be more compact.

[0014] In a preferred embodiment, the annular protrusion has a recess that is disposed in at least one of the first portion and the second portion and recessed to one side in the first direction, thereby making it possible to further reduce the weight of the electric power steering device compared to a case in which the annular protrusion has no recess.

[0015] In a preferred embodiment, the annular convex portion includes a first annular portion extending circumferentially around the central axis, a second annular portion disposed on the outer periphery of the first annular portion, and a plurality of support legs extending radially to connect the first annular portion and the second annular portion, wherein the boundary between the first portion and the second portion overlaps with the support legs, and a bearing is provided on the inner periphery of the first annular portion to rotatably support the assist pinion shaft relative to the annular convex portion. Because the support legs extend radially and the bearing is provided on the inner periphery of the first annular portion, the radial support rigidity of the first annular portion is increased. Therefore, radial displacement of the assist pinion shaft during rotation is reduced, resulting in more stable rotation of the assist pinion shaft.

[0016] In a preferred embodiment, a bearing that rotatably supports the assist pinion shaft relative to the annular protrusion is provided on the inner peripheral side of the annular protrusion, and the seal member accommodating groove overlaps with the bearing as viewed in the radial direction of the assist pinion shaft. For example, when the seal member accommodating groove is located on one side or the other side of the bearing in the first direction as viewed in the radial direction of the assist pinion shaft, the height of the first housing or the second housing in the first direction is greater than in the present disclosure. Therefore, the electric power steering device according to the present disclosure can be made more compact.

[0017] According to the present disclosure, the electric power steering device can be made more compact, and the change in the distance between the worm wheel and the worm shaft during operation of the electric power steering device can be further suppressed.

[0018] 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 an enlarged perspective view of a 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 as seen from a different direction. FIG. 7 is a perspective view showing a state in which the second housing has been removed from FIG. 6. FIG. 8 is a schematic view showing a cross-section taken along line VIII-VIII in FIG. 7. FIG. 9 is a perspective view showing the second housing.

[0019] 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 descriptions thereof will be omitted. In this embodiment, the Z direction is the first direction and the Y direction is the second 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.

[0020] 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 an enlarged perspective view of a part of Fig. 2. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 1. Fig. 5 is a schematic diagram enlarging a part of Fig. 4.

[0021] As shown in FIG. 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 300. The housing 300 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. However, the electric power steering device according to the present invention is not limited to the dual-pinion type, and a single-pinion type can also be applied.

[0022] 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.

[0023] 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 FIGS. 2 and 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Next, the housing 300 will be described. As shown in FIGS. 1 and 2, the housing 300 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.

[0028] 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.

[0029] 2 to 4 , the assist-side housing 40 includes a rack shaft accommodating portion 411, the first housing 4, the second housing 400, and a pressing member accommodating portion 412. The rack shaft accommodating portion 411 accommodates the X1-side portion of the rack shaft 15. The pressing member accommodating portion 412 accommodates a portion of the rack shaft 15, the pressing member 153, and the spring 154.

[0030] As shown in FIG. 4 , the rack shaft 15 has rack teeth 152 on its Y1-side side. The Y2-side side of the rack shaft 15 is curved. A pressing member 153, a spring 154, and a sealing member 155 are provided on the Y2 side of the rack shaft 15. Specifically, a cylindrical pressing member accommodating portion 412 protrudes toward the Y2 side from the main body portion 41 of the first housing 4, and the rack shaft 15, pressing member 153, and spring 154 are accommodated inside the pressing member accommodating portion 412. The sealing member 155 is fitted into the Y2-side end of the pressing member accommodating portion 412. Because the spring 154 is accommodated in a compressed state, when the spring 154 presses the pressing member 153 toward the Y1 side, the pressing member 153 is pressed against the assist pinion shaft 21. This maintains the meshing between the rack teeth 152 of the rack shaft 15 and the pinion teeth 22 of the assist pinion shaft 21.

[0031] 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 first housing 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 first housing 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 ).

[0032] As shown in Fig. 4, the first housing 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. A bearing 241 is provided on the Z1 side of the cap 26 of the main body 41. A bearing 242 is provided radially inward of the flange 42.

[0033] As shown in FIG. 4 , the flange 42 has a radially outer portion 421 and an annular protrusion 401. The annular protrusion 401 is provided adjacent to the radially inner side of the radially outer portion 421. The annular protrusion 401 is arranged in an annular shape on the outer circumferential side of the center axis AX3 of the assist pinion shaft 21 and protrudes toward the Z1 side. The annular protrusion 401 is higher in the Z direction than the radially outer portion 421. The lower surfaces of the annular protrusion 401 and the radially outer portion 421 are flush with each other. Therefore, a step is formed between the outer circumferential surface 401 a of the annular protrusion 401 and the upper surface 421 a of the radially outer portion 421.

[0034] As shown in FIGS. 4 and 5 , the annular protrusion 401 includes a first portion 422 and a second portion 423. The first portion 422 has a first top surface portion 422a that is aligned along a plane perpendicular to the center axis AX3 of the assist pinion shaft 21. The second portion 423 is disposed adjacent to the radially outer side of the first portion 422. The boundary between the first portion 422 and the second portion 423 is a boundary 230. The second portion 423 has a second top surface portion 423a. The second top surface portion 423a is an inclined surface that extends toward the Z2 side as it extends radially outward. The second top surface portion 423a is disposed opposite the worm shaft 27. In the embodiment, the second top surface portion 423a has a linear cross-sectional shape. However, for example, the second top surface portion 423a may have a curved shape that is concave in a direction away from the worm shaft 27. An outer peripheral surface 423b of the second portion 423 coincides with the outer peripheral surface 401a of the annular protrusion 401. Furthermore, as shown in Figures 4 and 5, a seal member accommodating groove 514 is provided along the circumferential direction on the outer peripheral surface 423b of the second portion 423 (the outer peripheral surface 401a of the annular protrusion 401). The seal member accommodating groove 514 is recessed radially inward. The seal member S is accommodated in the seal member accommodating groove 514.

[0035] Next, the second housing 400 will be described. As shown in FIGS. 4 and 5 , the second housing 400 includes a worm wheel receiving portion 5 and a worm shaft receiving portion 6. The worm wheel receiving portion 5 receives the worm wheel 23. The worm shaft receiving portion 6 receives 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 second housing 400 receives the worm wheel 23 and the worm shaft 27. The worm wheel receiving portion 5 and the worm shaft receiving portion 6 are integral with each other. The worm wheel receiving portion 5 has a side surface portion 51 and a top surface portion 52. The worm shaft receiving portion 6 has a side surface portion 61 and a top surface portion 62.

[0036] 4 and 5 , the second housing 400 has a side surface portion 402 and a top surface portion 403. The side surface portion 402 of the second housing 400 includes a side surface portion 51 of the worm wheel accommodating portion 5 and a side surface portion 61 of the worm shaft accommodating portion 6. The top surface portion 403 of the second housing 400 includes a top surface portion 52 of the worm wheel accommodating portion 5 and a top surface portion 62 of the worm shaft accommodating portion 6. As shown in FIG. 4 , on the Y2 side of the second housing 400, an inner surface 402a of the side surface portion 402 of the second housing 400 (the inner surface of the side surface portion 51 of the worm wheel accommodating portion 5) abuts against an outer circumferential surface 401a of the annular convex portion 401. Here, the inner surface 402a extends continuously in an annular shape in the circumferential direction around the central axis AX3, which will be described in detail later. 4 and 5 , on the Y1 side of the second housing 400, the inner surface 402a of the side surface portion 402 of the second housing 400 (the inner surface of the side surface portion 61 of the worm shaft accommodating portion 6) abuts against the outer peripheral surface 401a of the annular protrusion 401. In this manner, with the seal member S accommodated in the seal member accommodating groove 514, the gap between the annular protrusion 401 and the side surface portion 402 is sealed.

[0037] Fig. 6 is a perspective view of Fig. 3 as seen from a different direction. Fig. 7 is a perspective view showing a state in which the second housing has been removed from Fig. 6. Fig. 8 is a schematic view showing a cross section taken along line VIII-VIII in Fig. 7. Fig. 9 is a perspective view showing the second housing.

[0038] As shown in Figure 6, the worm wheel accommodating portion 5 in the second housing 400 has a side surface portion 51 and a top surface portion 52. The side surface portion 51 has two protrusions 516 that protrude toward the Y2 side. The protrusions 516 are provided with female threads 517. A circular protrusion 521 is provided in the center of the top surface portion 52.

[0039] 6 and 7 , protrusions 424, 425 are provided on the flange 42 of the first housing 4. Two protrusions 424 are provided and protrude toward the Y2 side. A through hole 424a passes through the protrusions 424. The protrusions 424 overlap with the protrusions 516 of the worm wheel accommodating portion 5. A bolt BL is inserted into the through hole 424a from the lower side (Z2 side) of the protrusions 424 toward the upper side (Z1 side) of the protrusions 424, and the male thread at the tip of the bolt BL is fastened to the female thread 517 of the protrusions 516.

[0040] One protrusion 425 is provided, protruding toward the Y1 side. A through-hole 425a passes through the protrusion 425. A bolt BL is inserted into the through-hole 425a from the lower side (Z2 side) of the protrusion 425 toward the upper side (Z1 side), and the male thread at the tip of the bolt BL is fastened to the female thread of the protrusion of the worm shaft accommodating portion 6.

[0041] As shown in Fig. 7, the annular protrusion 401 is disposed on the inner circumferential side of the radially outer portion 421. The annular protrusion 401 is provided with recesses 43. The recesses 43 are disposed in a first portion 422 and a second portion 423 and recessed toward the Z2 side. The recesses 43 face 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.

[0042] As shown in FIG. 7 , the annular convex portion 401 includes a first annular portion 426 , a second annular portion 427 , and a plurality of (eight in this embodiment) support legs 428 .

[0043] The first annular portion 426 and the second annular portion 427 extend in the circumferential direction around the central axis AX3. The second annular portion 427 is disposed on the outer peripheral side of the first annular portion 426. The support legs 428 extend in the radial direction and connect the first annular portion 426 and the second annular portion 427. The circumferential width of the connection portion of the support legs 428 with the first annular portion 426 is larger than the circumferential width of the radial center portion of the support legs 428. The circumferential width of the connection portion of the support legs 428 with the second annular portion 427 is larger than the circumferential width of the radial center portion of the support legs 428.

[0044] As shown in Figures 4 and 7, the inner circumferential surface of the first annular portion 426 coincides with the inner circumferential surface 42a of the flange 42. A bottom surface 42b is provided adjacent to the inner circumferential side of the inner circumferential surface 42a of the flange 42. A bearing 242 is provided on the inner circumferential side of the inner circumferential surface 42a of the flange 42. The bearing 242 abuts against the inner circumferential surface 42a and the bottom surface 42b. In this manner, the bearing 242 is provided on the inner circumferential side of the first annular portion 426. The bearing 242 supports the assist pinion shaft 21 rotatably with respect to the annular protrusion 401.

[0045] 8 , a boundary 430 between the first portion 422 and the second portion 423 overlaps with the support leg 428. That is, the support leg 428 is disposed across the first portion 422 and the second portion 423. Specifically, the first portion 422 includes the first annular portion 426 and a radially inner portion of the support leg 428. The second portion 423 includes the second annular portion 427 and a radially outer portion of the support leg 428.

[0046] Furthermore, when viewed from the radial direction of the assist pinion shaft 21, the seal member accommodating groove 514 overlaps with the bearing 242. Specifically, the Z direction position of the seal member accommodating groove 514 is between the upper end and the lower end of the bearing 242. Therefore, when viewed from the radial direction of the assist pinion shaft 21, the seal member S also overlaps with the bearing 242.

[0047] As shown in FIG. 9 , a wall portion 513 extending in the Z direction and having a through hole 512 is disposed between the worm wheel receiving portion 5 and the worm shaft receiving portion 6. The wheel teeth 232 and the shaft teeth 271 mesh with each other in the through hole 512. A second edge 512b of the through hole 512 is located on the Z2 side, and a first edge 512a is located on the Z1 side. The second edge 512b is spaced apart from the Z2-side end of the wall portion 513 toward the Z1 side. Thus, the inner surface 402a of the side surface portion 402 of the second housing 400 (the inner surface of the side surface portion 51 of the worm wheel receiving portion 5) extends continuously in an annular shape in the circumferential direction around the central axis AX3. Specifically, the inner surface 402a is annular when viewed in the axial direction of the central axis AX3.

[0048] As described above, the electric power steering device 100 according to this embodiment includes the assist pinion shaft 21 having the pinion teeth 22 that mesh with the rack teeth 152 of the rack shaft 15 on its outer periphery on the Z2 side, the worm wheel 23 that is attached to the Z1 side of the assist pinion shaft 21 and has the wheel tooth portion 232 on its outer periphery, the worm shaft 27 that has the shaft tooth portion 271 that meshes with the wheel tooth portion 232, is arranged on the Y1 side of the worm wheel 23, and is rotated by the driving force of the motor 70, the first housing 4 that accommodates the assist pinion shaft 21, the second housing 400 that is arranged adjacent to the Z1 side of the first housing 4 and accommodates the worm wheel 23 and the worm shaft 27, and a sealing member S that is arranged between the first housing 4 and the second housing 400.

[0049] An annular protrusion 401 is provided on the Z1 side of the first housing 4, arranged in an annular shape on the outer periphery of the center axis AX3 of the assist pinion shaft 21 and protruding toward the Z1 side, while a side surface 51 is provided on the Z2 side of the second housing 400, fitting with the outer periphery of the outer periphery 401a of the annular protrusion 401. A seal member accommodating groove 514 is provided along the circumferential direction on the outer periphery 401a of the annular protrusion 401. The seal member accommodating groove 514 is recessed radially inward and accommodates a seal member S. With the seal member S accommodated in the seal member accommodating groove 514, the gap between the annular protrusion 401 and the side surface 51 is sealed.

[0050] As described above, in Patent Document 1, the flange of the first housing and the flange of the second housing are fastened together with bolts, which makes it easy for the distance between the worm wheel and the worm shaft to change when the electric power steering device is in operation. Also, because the second housing has a notch at the bottom end of the wall, it is necessary to seal the entire housing by, for example, providing an annular seal member on the outside of the wall, which can increase the size of the electric power steering device.

[0051] In contrast, in this embodiment, the first housing 4 is provided with an annular protrusion 401, and the second housing 400 is provided with a side surface 51, which is fitted onto the outer periphery of the annular protrusion 401. In other words, the first housing 4 and the second housing 400 are positioned by a so-called spigot joint between the side surface 51 and the annular protrusion 401. This further suppresses changes in the distance between the worm wheel and the worm shaft.

[0052] Furthermore, a seal member accommodating groove 514 is provided on the outer circumferential surface 401a of the annular protrusion 401, a seal member S is accommodated in the seal member accommodating groove 514, and the side surface portion 51 is fitted to the outer circumferential side of the annular protrusion 401. This seals the first housing 4 and the second housing 400, making it possible to make the electric power steering device smaller than that of Patent Document 1.

[0053] As described above, according to this embodiment, it is possible to provide an electric power steering device 100 that is more compact and in which changes in the distance between the worm wheel and the worm shaft are further suppressed.

[0054] The annular protrusion 401 includes a first portion 422 having a first top surface 422a along a plane perpendicular to the central axis AX3 of the assist pinion shaft 21, and a second portion 423 having a second top surface 423a disposed adjacent to the radially outer side of the first portion 422 and extending radially outward toward the Z2 side. The second top surface 423a is disposed opposite the worm shaft 27.

[0055] Therefore, compared to when the top surface of the second portion 423 is along a plane perpendicular to the center axis AX3 of the assist pinion shaft 21, the annular convex portion 401 can be brought closer to the worm shaft 27. This makes it possible to further miniaturize the electric power steering device 100.

[0056] The annular protrusion 401 is provided with recesses 43 that are disposed in the first portion 422 and the second portion 423 and recessed toward the Z2 side. Therefore, it is possible to further reduce the weight of the electric power steering device 100 compared to when the annular protrusion 401 is not provided with the recesses 43.

[0057] The annular protrusion 401 includes a first annular portion 426 extending in the circumferential direction around the central axis AX3, a second annular portion 427 disposed on the outer circumferential side of the first annular portion 426, and a plurality of support legs 428 extending in the radial direction to connect the first annular portion 426 and the second annular portion 427. A boundary 430 between the first portion 422 and the second portion 423 overlaps with the support legs 428, and a bearing 242 is provided on the inner circumferential side of the first annular portion 426 to rotatably support the assist pinion shaft 21 relative to the annular protrusion 401.

[0058] In this way, the support legs 428 extend in the radial direction and the bearings 242 are provided on the inner peripheral side of the first annular portion 426, thereby increasing the radial support rigidity for the first annular portion 426. Therefore, the radial displacement when the assist pinion shaft 21 rotates relative to the first annular portion 426 via the bearings 242 becomes smaller, and the assist pinion shaft 21 rotates more stably.

[0059] A bearing 242 that rotatably supports the assist pinion shaft 21 relative to the annular protrusion 401 is provided on the inner peripheral side of the annular protrusion 401, and when viewed from the radial direction of the assist pinion shaft 21, the seal member accommodating groove 514 overlaps with the bearing 242.

[0060] When viewed from the radial direction of the assist pinion shaft 21, for example, if the seal member accommodating groove 514 is located on the Z1 side or the Z2 side of the bearing 242, the height in the Z direction of the first housing 4 or the second housing 400 will be greater than in this embodiment. Therefore, in this embodiment, a more compact electric power steering device 100 is provided.

[0061] DESCRIPTION OF SYMBOLS 3 Steering side housing 4 First housing 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 Electric power steering device 111 Universal joint 121 Universal joint 151, 152 Rack teeth 153 Pressing member 154 Spring 155 Sealing member 231 Core metal portion 232 Wheel teeth portion 241 Bearing 242 Bearing 271 Shaft teeth portion 300 Housing 400 Second housing 401 Annular convex portion 401a Outer circumferential surface 402 Side portion 402a Inner circumferential surface 403 Top surface portion 411 Rack shaft accommodating portion 412 Pressing member accommodating portion 413 Vehicle body mounting portion 414 Through hole 421 Radially outer portion 421a Top surface 422 First portion 422a First top surface portion 423 Second portion 423a Second top surface portion 423b Outer circumferential surface 424, 425 Protrusions 424a, 425a Through hole 426 First annular portion 427 Second annular portion 428 Support leg 430 Boundary 514 Sealing member accommodating groove 516 Projection portion 517 Female thread 521 Protruding portion AX1, AX2, AX3 Central axis BL Bolt S Sealing 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 of the worm wheel in a second direction that intersects the first direction, and rotated by the driving force of a motor; a first housing that accommodates the assist pinion shaft; and a second housing that is arranged adjacent to the other side of the first housing in the first direction and accommodates the worm wheel and the worm shaft, wherein the other side of the first housing in the first direction is provided with an annular protrusion that is arranged annularly on the outer periphery of the central axis of the assist pinion shaft and protrudes toward the other side in the first direction, and the one side of the second housing in the first direction is provided with a side portion that fits on the outer periphery of the outer periphery of the annular protrusion. an electric power steering device, wherein a seal member is provided between the annular protrusion and the side surface portion.

2. An electric power steering device according to claim 1, wherein a seal member accommodating groove that is recessed radially inward and accommodates the seal member is provided along the circumferential direction on either the outer peripheral surface of the annular protrusion or the inner surface of the side surface of the second housing, and that seals the gap between the annular protrusion and the side surface when the seal member is accommodated in the seal member accommodating groove.

3. An electric power steering device as described in claim 1 or 2, wherein the annular convex portion comprises: a first portion having a first top surface portion along a plane perpendicular to the central axis of the assist pinion shaft; and a second portion having a second top surface portion disposed adjacent to the radially outer side of the first portion and extending toward one side in the first direction as it goes radially outward, and the second top surface portion is disposed opposite the worm shaft.

4. An electric power steering device according to claim 3, wherein the annular protrusion is provided with a recess that is disposed in at least one of the first portion and the second portion and recessed to one side in the first direction.

5. An electric power steering device according to any one of claims 1 to 4, wherein the annular convex portion comprises: a first annular portion extending circumferentially around the central axis; a second annular portion arranged on the outer periphery of the first annular portion; and a plurality of support legs extending radially to connect the first annular portion and the second annular portion, wherein a boundary between a first portion having a first top surface portion along a plane perpendicular to the central axis of the assist pinion shaft and a second portion having a second top surface portion arranged adjacent to the radially outer side of the first portion and extending towards one side in a first direction as it goes radially outward overlaps with the support legs, and a bearing is provided on the inner periphery of the first annular portion to rotatably support the assist pinion shaft relative to the annular convex portion.

6. An electric power steering device as described in claim 3 or 4, wherein the annular convex portion comprises: a first annular portion extending circumferentially around the central axis; a second annular portion arranged on the outer periphery of the first annular portion; and a plurality of support legs extending radially to connect the first annular portion and the second annular portion, the boundary between the first portion and the second portion overlapping with the support legs, and a bearing is provided on the inner periphery of the first annular portion to rotatably support the assist pinion shaft relative to the annular convex portion.

7. An electric power steering device according to claim 2, wherein a bearing is provided on the inner peripheral side of the annular convex portion to rotatably support the assist pinion shaft relative to the annular convex portion, and when viewed from the radial direction of the assist pinion shaft, the seal member accommodating groove overlaps with the bearing.

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