Electric power steering system

Abstract

To provide an electric power steering device which achieves further downsizing and inhibits change in a distance between a worm wheel and a worm shaft.SOLUTION: An electric power steering device includes: a first housing which houses a worm wheel, a worm shaft, and an assist pinion shaft; a second housing which houses the worm wheel and the worm shaft; and a seal member disposed between the first housing and the second housing. An annular protruding part protruding to the other side in a first direction is provided at the other side in the first direction at the first housing. A side surface part configured to fit in the outer periphery side of an outer peripheral surface of the annular protruding part is provided at one side in the first direction at the second housing. The outer peripheral surface of the annular protruding part is provided with a seal member housing groove which is recessed to the radial inner side and houses the seal member.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[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 end in the axial direction of the central axis of the pinion shaft, and the pinion teeth mesh with the rack teeth of the rack shaft. A worm wheel is attached to the other end in the axial direction 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 houses the rack shaft and the pinion shaft, and a second housing that houses the worm wheel, the worm shaft, and the motor. The first housing and the second housing are connected by fastening the flange of the first housing and the flange of the second housing via bolts.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The pinion shaft is rotatably supported in the first housing via a bearing, and the motor is mounted in the second housing. Therefore, in a structure where the flange of the first housing and the flange of the second housing are fastened together via bolts, the distance between the worm wheel and the worm shaft tends to change, which can lead to abnormal noise when the worm wheel and worm shaft mesh, and can also cause wear on the wheel teeth of the worm wheel and the shaft teeth of the worm shaft.

[0006] Furthermore, a sealing mechanism is necessary in the housing to prevent water and other substances from entering the housing. In Patent Document 1, there is a notch at the lower end of the wall of the second housing, so for example, an annular sealing member must be provided on the outside of the wall to seal the entire housing, which may result in a larger electric power steering device.

[0007] This disclosure has been made in view of the aforementioned problems and aims to provide an electric power steering system 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 system are further suppressed. [Means for solving the problem]

[0008] To achieve the above objective, an electric power steering device according to one embodiment includes: an assist pinion shaft extending in a first direction and having pinion teeth on its outer circumference on one side in the first direction that mesh with the rack teeth of a rack shaft; a worm wheel attached to the other side of the assist pinion shaft in the first direction and having wheel teeth on its outer circumference; a worm shaft having shaft teeth that mesh with the wheel teeth, positioned on one side in a second direction intersecting the first direction with respect to the worm wheel, and rotating by the driving force of a motor; and the assist pinion shaft. The assist pinion shaft comprises a first housing for housing a pinion shaft, and a second housing adjacent to the other side of the first housing in the first direction for housing the worm wheel and the worm shaft. The other side of the first housing in the first direction is provided with an annular projection that is arranged in a ring on the outer circumference of the central axis of the assist pinion shaft and protrudes toward the other side of the first direction. The one side of the second housing in the first direction is provided with a side portion that fits onto the outer circumference of the outer surface of the annular projection, and a sealing member is provided between the annular projection and the side portion.

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

[0010] In contrast, the present disclosure provides an annular projection on the first housing and a side portion on the second housing, with the side portion fitted to the outer circumference of the annular projection. That is, the positioning of the first housing and the second housing is achieved by a so-called spigot joint between the side portion and the annular projection. Consequently, changes in the distance between the worm wheel and the worm shaft are further suppressed.

[0011] Furthermore, by providing a sealing member between the annular protrusion and the side portion, the first housing and the second housing are sealed, making it possible to miniaturize the electric power steering device compared to the electric power steering device of Patent Document 1. Therefore, according to the present disclosure, it is possible 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 are further suppressed.

[0012] In a preferred embodiment, a seal member housing groove is provided along the circumferential direction on either the outer circumferential surface of the annular projection or the inner surface of the side portion of the second housing, which is recessed radially inward and accommodates the seal member, thereby sealing the space between the annular projection and the side portion when the seal member is housed in the seal member housing groove. In this way, by housing the seal member in the seal member housing groove and fitting the side portion of the second housing to the outer circumferential side of the annular projection, the first housing and the second housing are sealed, making it possible to miniaturize the electric power steering device compared to that described in Patent Document 1.

[0013] In a preferred embodiment, the annular protrusion comprises a first portion having a first top surface that aligns with a plane perpendicular to the central axis of the assist pinion shaft, and a second portion having a second top surface that is positioned adjacent to the radially outer side of the first portion and extends toward one side in the first direction as it extends radially outward, wherein the second top surface is positioned opposite the worm shaft. Therefore, compared to the case where the top surface of the second portion aligns with a plane perpendicular to the central axis of the assist pinion shaft, the annular protrusion can be brought closer to the worm shaft. Thus, the electric power steering device according to this disclosure can be made more compact.

[0014] In a preferred embodiment, the annular projection is provided with a recess located in at least one of the first and second portions, which is recessed on one side in the first direction. Therefore, the weight of the electric power steering device can be further reduced compared to the case where the annular projection does not have a recess.

[0015] In a preferred embodiment, the annular projection comprises a first annular portion extending circumferentially around the axis of the central shaft, a second annular portion positioned on the outer circumference side of the first annular portion, and a plurality of support legs extending radially and connecting 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 circumference side of the first annular portion to rotatably support the assist pinion shaft relative to the annular projection. In this way, since the support legs extend radially and a bearing is provided on the inner circumference side of the first annular portion, the radial support rigidity relative to the first annular portion is increased. Consequently, the radial displacement of the assist pinion shaft during rotation is reduced, and the assist pinion shaft rotates more stably.

[0016] In a preferred embodiment, a bearing is provided on the inner circumference of the annular projection to rotatably support the assist pinion shaft relative to the annular projection, and the seal member housing groove overlaps with the bearing when viewed from the radial direction of the assist pinion shaft. When viewed from the radial direction of the assist pinion shaft, for example, if the seal member housing groove is located on one or the other side of the bearing in the first direction, the height of the first housing or the second housing in the first direction will be greater than in the present disclosure. Therefore, the electric power steering device according to the present disclosure can be made more compact. [Effects of the Invention]

[0017] According to this disclosure, the electric power steering system can be made more compact. In addition, the change in the distance between the worm wheel and the worm shaft during operation of the electric power steering system can be further suppressed. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a schematic diagram of an electric power steering system according to an embodiment. [Figure 2] Figure 2 is a perspective view showing a portion of Figure 1. [Figure 3] Figure 3 is a perspective view that is an enlarged portion of Figure 2. [Figure 4]FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 1. [Figure 5] FIG. 5 is a schematic view enlarging a part of FIG. 4. [Figure 6] FIG. 6 is a perspective view of FIG. 3 viewed from another direction. [Figure 7] FIG. 7 is a perspective view showing a state where the second housing is removed from FIG. 6. [Figure 8] FIG. 8 is a schematic view showing a cross-section taken along line VIII-VIII of FIG. 7. [Figure 9] FIG. 9 is a perspective view showing the second housing.

Mode for Carrying Out the Invention

[0019] A mode (embodiment) for carrying out the present invention will be described in detail while referring to the drawings. The present invention is not limited by the content described in the following embodiments. Further, the constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be combined as appropriate. Furthermore, the same reference numerals are given to the parts having the same structure, and the description thereof is omitted. In the present embodiment, the Z direction is taken as the first direction, and the Y direction is taken as the second direction. The Z direction intersects the Y direction. The X direction intersects the Y direction and the Z direction. 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] The electric power steering device according to the embodiment will be described. FIG. 1 is a schematic view 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 of FIG. 1. FIG. 5 is a schematic view enlarging a part of FIG. 4.

[0021] As shown in Figure 1, the electric power steering system 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 and form an integrated structure. The electric power steering system 100 is, for example, a so-called dual-pinion type steering system. However, the electric power steering system according to the present invention is not limited to the dual-pinion type, and a single-pinion type can also be applied.

[0022] As shown in Figure 1, the steering wheel 10 is connected to a first steering shaft 11, and the first steering shaft 11 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 circumference of the lower end of the steering pinion shaft 13.

[0023] As shown in Figure 1, the rack shaft 15 extends in the X direction. Here, if the central axis of the rack shaft 15 is the central axis AX2 (see Figures 2 and 3), then the axial direction of the central axis AX2 is along 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 width direction of the vehicle. As shown in Figure 1, rack teeth 151 are provided on the outer circumference of the part of the rack shaft 15 on the X2 side. The rack teeth 151 mesh with the pinion teeth 14 of the steering pinion shaft 13. Rack teeth 152 are provided on the outer circumference of the part of the rack shaft 15 on the X1 side. 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 the wheels 17 via tie rods 16.

[0024] As explained 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. The pinion teeth 14 of the steering pinion shaft 13 mesh with the rack teeth 151, so the steering torque is converted into a force that moves the rack shaft 15 in the X direction.

[0025] Furthermore, 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 according to 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, which is connected to the motor 70 via the worm wheel 23 and the worm shaft 27, generating an assist force that moves the rack shaft 15 connected to the assist pinion shaft 21 in the X direction.

[0026] In other words, by driving the motor 70 in accordance with the steering torque generated by steering the steering wheel 10, it is possible to assist in the movement of the rack shaft 15 in the X direction.

[0027] Next, the housing 300 will be described. As shown in Figures 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 Figure 2, vehicle body mounting portions 31 and 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. That is, the steering-side housing 3 and the assist-side housing 40 are attached to the vehicle body by fastening the fastening members through the through holes 32 and 414 and then fastening them to the vehicle body.

[0028] The steering side housing 3 houses the steering pinion shaft 13 and the X2 side portion of the rack shaft 15. Specifically, the tip of the steering pinion shaft 13 is housed inside the steering pinion shaft housing 33. The assist side housing 40 houses the assist pinion shaft 21, worm wheel 23, worm shaft 27, and the X2 side portion of the rack shaft 15.

[0029] As shown in Figures 2 to 4, the assist-side housing 40 comprises a rack shaft housing section 411, a first housing 4, a second housing 400, and a pressing member housing section 412. The rack shaft housing section 411 houses the X1 side portion of the rack shaft 15. The pressing member housing section 412 houses a part of the rack shaft 15, a pressing member 153, and a spring 154.

[0030] As shown in Figure 4, the rack shaft 15 has rack teeth 152 on its Y1 side. The Y2 side of the rack shaft 15 is a curved surface. 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 housing protrudes from the main body 41 of the first housing 4 toward the Y2 side, and the rack shaft 15, the pressing member 153, and the spring 154 are housed inside the pressing member housing 412. The sealing member 155 is fitted to the Y2 end of the pressing member housing 412. Since the spring 154 is housed in a compressed state, when the spring 154 pushes 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 Figure 4, the worm wheel 23 is fitted to the Z1-side end of the assist pinion shaft 21. The Z1-side portion of the assist pinion shaft 21 is rotatably supported on the main body portion 41 of the first housing 4 via a bearing 241. The Z2-side portion of the assist pinion shaft 21 is rotatably supported on the flange 42 of the first housing 4 via a bearing 242. The worm wheel 23 comprises a core portion 231 and a wheel tooth portion 232. The wheel tooth portion 232 meshes with the shaft tooth portion 271 of the worm shaft 27. The worm shaft 27 has a central axis AX1. The worm shaft 27 is rotatably mounted on the output shaft of the motor 70 (see Figure 2).

[0032] As shown in Figure 4, the first housing 4 comprises a main body portion 41 and a flange 42. The main body portion 41 is a cylindrical member extending in the Z direction. The flange 42 is provided at the Z1 end of the main body portion 41 and widens radially outward from the main body portion 41. The Z2 end of the main body portion 41 is open, and this opening is sealed by a cap 26. A bearing 241 is provided on the Z1 side of the cap 26 on the main body portion 41. A bearing 242 is provided on the radially inward side of the flange 42.

[0033] As shown in Figure 4, the flange 42 has a radially outer portion 421 and an annular projection 401. The annular projection 401 is provided adjacent to the radially outer portion 421 on the radially inner side. The annular projection 401 is arranged in a ring on the outer circumference of the central axis AX3 of the assist pinion shaft 21 and protrudes toward the Z1 side. The annular projection 401 is taller in the Z direction than the radially outer portion 421. The lower surface of the annular projection 401 and the lower surface of the radially outer portion 421 are at the same height. Therefore, a step is formed between the outer circumferential surface 401a of the annular projection 401 and the upper surface 421a of the radially outer portion 421.

[0034] As shown in Figures 4 and 5, the annular protrusion 401 comprises a first portion 422 and a second portion 423. The first portion 422 has a first top surface portion 422a that aligns with a plane perpendicular to the central axis AX3 of the assist pinion shaft 21. The second portion 423 is positioned adjacent to the first portion 422 on its radially outer side. The boundary between the first portion 422 and the second portion 423 is 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 positioned opposite the worm shaft 27. In this embodiment, the cross-sectional shape of the second top surface portion 423a is linear, but for example, the second top surface portion 423a may have a curved shape that is recessed away from the worm shaft 27. The outer circumferential surface 423b of the second portion 423 coincides with the outer circumferential surface 401a of the annular projection 401. Furthermore, as shown in Figures 4 and 5, a seal member housing groove 514 is provided along the circumferential direction on the outer circumferential surface 423b of the second portion 423 (the outer circumferential surface 401a of the annular projection 401). The seal member housing groove 514 is recessed radially inward. The seal member S is housed in the seal member housing groove 514.

[0035] Next, the second housing 400 will be described. As shown in Figures 4 and 5, the second housing 400 includes a worm wheel housing 5 and a worm shaft housing 6. The worm wheel housing 5 houses the worm wheel 23. The worm shaft housing 6 houses the worm shaft 27. The worm shaft 27 is attached to the output shaft of the motor 70, and as shown in Figure 2, the motor 70 is attached to the motor mounting plate 7. The second housing 400 houses the worm wheel 23 and the worm shaft 27. The worm wheel housing 5 and the worm shaft housing 6 are integrated. The worm wheel housing 5 has a side surface 51 and a top surface 52. The worm shaft housing 6 has a side surface 61 and a top surface 62.

[0036] Here, as shown in Figures 4 and 5, the second housing 400 has a side portion 402 and a top portion 403. The side portion 402 of the second housing 400 includes the side portion 51 of the worm wheel housing 5 and the side portion 61 of the worm shaft housing 6. The top portion 403 of the second housing 400 includes the top portion 52 of the worm wheel housing 5 and the top portion 62 of the worm shaft housing 6. As shown in Figure 4, on the Y2 side of the second housing 400, the inner surface 402a of the side portion 402 of the second housing 400 (the inner surface of the side portion 51 of the worm wheel housing 5) abuts against the outer circumferential surface 401a of the annular projection 401. Here, the inner surface 402a extends continuously in an annular shape along the circumferential direction about the axis of the central axis AX3, which will be described in detail later. Furthermore, as shown in Figures 4 and 5, on the Y1 side of the second housing 400, the outer circumferential surface 401a of the annular projection 401 abuts against the inner surface 402a of the side portion 402 of the second housing 400 (the inner surface of the side portion 61 of the worm shaft housing portion 6). In this way, the space between the annular projection 401 and the side portion 402 is sealed when the seal member S is housed in the seal member housing groove 514.

[0037] Figure 6 is a perspective view of Figure 3 from a different direction. Figure 7 is a perspective view of Figure 6 with the second housing removed. Figure 8 is a schematic diagram showing a cross-section along line VIII-VIII in Figure 7. Figure 9 is a perspective view showing the second housing.

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

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

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

[0041] As shown in Figure 7, the annular projection 401 is positioned on the inner circumference side of the radially outer portion 421. The annular projection 401 is provided with recesses 43. The recesses 43 are positioned in the first portion 422 and the second portion 423 and are recessed toward the Z2 side. The recesses 43 face the bottom surface 43a and the side surface 43b. Multiple recesses 43 (eight in this embodiment) are provided along the circumferential direction of the annular projection 401.

[0042] Furthermore, as shown in Figure 7, the annular projection 401 comprises a first annular portion 426, a second annular portion 427, and a plurality (eight in this embodiment) of support legs 428.

[0043] The first annular section 426 and the second annular section 427 extend circumferentially around the axis of the central axis AX3. The second annular section 427 is positioned on the outer circumference side of the first annular section 426. The support leg 428 extends radially and connects the first annular section 426 and the second annular section 427. The circumferential width of the connection portion of the support leg 428 with the first annular section 426 is greater than the circumferential width of the radial center of the support leg 428. The circumferential width of the connection portion of the support leg 428 with the second annular section 427 is greater than the circumferential width of the radial center of the support leg 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 is in contact with the inner circumferential surface 42a and the bottom surface 42b. Thus, a bearing 242 is provided on the inner circumferential side of the first annular portion 426. The bearing 242 rotatably supports the assist pinion shaft 21 with respect to the annular protrusion 401.

[0045] As shown in Figure 8, the boundary 430 between the first part 422 and the second part 423 overlaps with the support leg 428. That is, the support leg 428 is positioned across the first part 422 and the second part 423. Specifically, the first part 422 includes the first annular part 426 and the radially inner portion of the support leg 428. The second part 423 includes the second annular part 427 and the 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 housing groove 514 overlaps with the bearing 242. Specifically, the Z-direction position of the seal member housing groove 514 is between the upper and lower ends of the bearing 242. Therefore, the seal member S also overlaps with the bearing 242 when viewed from the radial direction of the assist pinion shaft 21.

[0047] As shown in Figure 9, a wall portion 513 extending in the Z direction and having a through hole 512 is positioned between the worm wheel housing portion 5 and the worm shaft housing portion 6. The wheel teeth 232 and the shaft teeth 271 mesh in the through hole 512. Of the edges of the through hole 512, the second edge 512b is located on the Z2 side and the first edge 512a is located on the Z1 side. The second edge 512b is spaced away from the Z2 end of the wall portion 513 toward the Z1 side. In this way, the inner surface 402a of the side portion 402 of the second housing 400 (the inner surface of the side portion 51 of the worm wheel housing portion 5) extends continuously in an annular shape along the circumferential direction around the axis of the central axis AX3. Specifically, when viewed from the axial direction of the central axis AX3, the inner surface 402a is annular.

[0048] As described above, the electric power steering device 100 according to this embodiment includes an assist pinion shaft 21 on which pinion teeth 22 that mesh with the rack teeth 152 of the rack shaft 15 are provided on the outer circumference on the Z2 side; a worm wheel 23 attached to the Z1 side of the assist pinion shaft 21 and provided with wheel teeth 232 on the outer circumference; a worm shaft 27 having shaft teeth 271 that mesh with the wheel teeth 232, positioned on the Y1 side relative to the worm wheel 23 and rotated by the driving force of the motor 70; a first housing 4 that houses the assist pinion shaft 21; a second housing 400 positioned adjacent to the Z1 side of the first housing 4 and housing the worm wheel 23 and the worm shaft 27; and a sealing member S positioned between the first housing 4 and the second housing 400.

[0049] On the Z1 side of the first housing 4, an annular projection 401 is provided, which is arranged in a ring on the outer circumference of the central axis AX3 of the assist pinion shaft 21 and protrudes toward the Z1 side. On the Z2 side of the second housing 400, a side portion 51 is provided that fits onto the outer circumference of the outer surface 401a of the annular projection 401. A seal member housing groove 514 is provided on the outer surface 401a of the annular projection 401 along the circumferential direction. The seal member housing groove 514 is recessed radially inward and accommodates the seal member S. With the seal member S housed in the seal member housing groove 514, the space between the annular projection 401 and the side portion 51 is sealed.

[0050] As mentioned above, in Patent Document 1, the flange of the first housing and the flange of the second housing are fastened together via 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 there is a notch at the lower end of the wall of the second housing, it is necessary to seal the entire housing by, for example, providing an annular sealing member on the outside of the wall, which may increase the size of the electric power steering device.

[0051] In contrast, in this embodiment, the first housing 4 is provided with an annular projection 401, and the second housing 400 is provided with a side portion 51, which is fitted to the outer circumference of the annular projection 401. That is, the first housing 4 and the second housing 400 are positioned by a so-called spigot joint between the side portion 51 and the annular projection 401. Therefore, changes in the distance between the worm wheel and the worm shaft are further suppressed.

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

[0053] Based on the above, this embodiment makes it 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 comprises a first portion 422 having a first top surface portion 422a that aligns with a plane perpendicular to the central axis AX3 of the assist pinion shaft 21, and a second portion 423 having a second top surface portion 423a that is positioned adjacent to the radially outer side of the first portion 422 and extends toward the Z2 side as it extends radially outward. The second top surface portion 423a is positioned opposite the worm shaft 27.

[0055] Therefore, when the top surface of the second part 423 is aligned with a plane perpendicular to the central axis AX3 of the assist pinion shaft 21, the annular protrusion 401 can be brought closer to the worm shaft 27. Thus, the electric power steering device 100 can be made more compact.

[0056] The annular projection 401 is provided with recesses 43 located at the first portion 422 and the second portion 423, which are recessed toward the Z2 side. Therefore, compared to the case where the annular projection 401 is not provided with recesses 43, the weight of the electric power steering device 100 can be further reduced.

[0057] The annular projection 401 comprises a first annular portion 426 extending circumferentially around the axis of the central axis AX3, a second annular portion 427 positioned on the outer circumference side of the first annular portion 426, and a plurality of support legs 428 extending radially and connecting the first annular portion 426 and the second annular portion 427. The 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 circumference side of the first annular portion 426 to rotatably support the assist pinion shaft 21 relative to the annular projection 401.

[0058] As described above, the support legs 428 extend radially, and the bearing 242 is provided on the inner circumference side of the first annular portion 426, thus increasing the radial support rigidity of the first annular portion 426. Consequently, the radial displacement when the assist pinion shaft 21 rotates relative to the first annular portion 426 via the bearing 242 becomes smaller, and the assist pinion shaft 21 rotates more stably.

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

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

[0061] 3. Steering side housing 4. Housing 1 5. Worm wheel housing 6. Worm shaft housing 7 Motor mounting plate 10 Steering Wheel 11. First steering shaft 12. Second steering shaft 13 Steering pinion shaft 14 pinion teeth 15 rack axis 16 Tie Rods 17 wheels 21 Assist pinion shaft 22 pinion teeth 23 Worm Wheel 26 caps 27 Worm shaft 31 Body mounting section 32 Through holes 33 Steering pinion shaft housing 40 Assist side housing 41 Main body 42 Flange 42a Inner surface 42b Base 43 Recess 43a Bottom 43b side 51 Side part 52 Top section 61 Side part 62 Top section 70 Motor 100 Electric power steering system 111 Universal Joint 121 Universal Joint 151, 152 Rack teeth 153 Pressing member 154 Spring 155 Sealing member 231 Core metal section 232 Wheel teeth 241 Bearing 242 Bearings 271 Shaft teeth 300 Housing 400 Second Housing 401 Annular protrusion 401a Outer surface 402 Side part 402a Inside surface 403 Top section 411 Rack shaft housing 412 Pressing member housing section 413 Body mounting section 414 Through hole 421 Radial outer portion 421a top side 422 Part 1 422a 1st top section 423 Part 2 423a 2nd top section 423b Outer surface 424, 425 Protrusion 424a, 425a through hole 426 First Ring Section 427 Second Ring Section 428 Support leg 430 Boundary 514 Seal member housing groove 516 Protrusion 517 Female thread 521 Protruding section AX1, AX2, AX3 center axis BL Bolt S sealing member

Claims

1. An assist pinion shaft extending in a first direction, and having pinion teeth on one outer circumference in the first direction that mesh with the rack teeth of the rack shaft, A worm wheel is attached to the other side of the assist pinion shaft in the first direction, and has wheel teeth on its outer circumference, A worm shaft having shaft teeth that mesh with the wheel teeth, positioned on one side of a second direction intersecting the worm wheel in a first direction, and rotated by the driving force of a motor, A first housing that accommodates the assist pinion shaft, A second housing is arranged adjacent to the other side of the first housing in the first direction and houses the worm wheel and the worm shaft, Equipped with, On the other side of the first direction in the first housing, an annular projection is provided which is arranged in a ring in the circumferential direction about the axis of the central axis of the assist pinion shaft and which protrudes toward the other side in the first direction. On one side of the second housing in the first direction, a side portion is provided that fits onto the outer circumferential surface of the annular projection. A sealing member is provided between the annular projection and the side portion. The annular protrusion, in a cross-section including the central axis, A first portion having a first top surface that extends in a second direction along a plane perpendicular to the central axis and to a first end which is one end in the second direction, The first part comprises a second part which is arranged adjacent to one side in the second direction with respect to the first part, The second part is, It has a second top surface portion that extends toward one side in the first direction as you go from the first end toward one side in the second direction, and an outer peripheral surface that extends toward one side in the first direction from the second end, which is the end of the second top surface portion toward one side in the second direction, The second top surface is positioned opposite the worm shaft, The aforementioned side portion, in a cross-section including the central axis, The second portion has an inner circumferential surface that abuts the outer circumferential surface, and a third top surface portion that extends from the third end, which is the other end of the inner circumferential surface in the first direction, to one side in the second direction, The third end is located on one side in the first direction relative to the first end. Electric power steering system.

2. Either the outer circumferential surface of the annular projection or the inner circumferential surface of the side surface of the second housing is provided with a seal member housing groove that is recessed in the radial direction of the assist pinion shaft and accommodates the seal member, thereby sealing the space between the annular projection and the side surface when the seal member is housed in the seal member housing groove. The electric power steering device according to claim 1.

3. The aforementioned annular protrusion includes, A recess is provided in at least one of the first portion and the second portion, which is recessed on one side in the first direction. The electric power steering device according to claim 1.

4. The aforementioned annular protrusion is, A first annular portion extending in the circumferential direction around the axis of the central axis, A second annular portion is arranged on the outer circumference of the first annular portion, The assist pinion shaft is provided with a plurality of support legs that extend radially and connect the first annular portion and the second annular portion, The boundary between the first part and the second part overlaps with the support leg when viewed from the circumferential direction of the assist pinion shaft. A bearing is provided on the inner circumference side of the first annular portion to rotatably support the assist pinion shaft relative to the annular protrusion. The electric power steering device according to claim 1 or 2.

5. A bearing is provided on the inner circumference side of the annular projection, which rotatably supports the assist pinion shaft relative to the annular projection. Viewed radially from the assist pinion shaft, the seal member housing groove overlaps with the bearing. The electric power steering device according to claim 2.

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