Electric power steering device

Abstract

This electric power steering device comprises an assist pinion shaft, a worm wheel, a worm shaft, a first housing that includes an assist pinion shaft accommodation part for accommodating the assist pinion shaft, and a second housing that includes a worm wheel accommodation part for accommodating the worm wheel and a worm shaft accommodation part for accommodating the worm shaft. A first attachment part is provided to one side of the first housing in a first direction, and a second attachment part is provided to the other side of the second housing in the first direction, the second attachment part having a seal surface extending in an annular form.

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 pinion shaft, a worm wheel, a worm shaft, and a housing. Specifically, a worm wheel is attached to the axial end of the pinion shaft and meshes with the worm shaft. The housing includes a worm wheel receiving portion that receives the worm wheel, and a worm shaft receiving portion that is integral with the worm wheel receiving portion and receives the worm shaft. A wall portion is disposed between the worm wheel receiving portion and the worm shaft receiving portion, and a notch is provided at the lower end of the wall portion to avoid interference with the worm shaft. That is, the notch is recessed upward and is disposed adjacent to the upper side of the worm shaft. This allows the vertical height of the housing to be kept low.

[0003] Japanese Patent Application Laid-Open No. 2001-271913

[0004] Here, 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 wall has a notch at the lower end, it is necessary to provide, for example, an annular sealing wall separate from the wall on the outside, and use the sealing surface of the sealing wall to seal the entire housing, which may increase the size of the electric power steering device.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and has an object to provide a more compact electric power steering device.

[0006] 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 that intersects the first direction, and rotated by a driving force of a motor; a first housing including an assist pinion shaft accommodating portion that accommodates the assist pinion shaft; a worm wheel accommodating portion that accommodates the worm wheel; and a worm shaft accommodating portion that is disposed adjacent to the one side in the second direction of the worm wheel accommodating portion and that accommodates the worm shaft. a second housing including a housing portion and arranged on the other side of the first housing in the first direction, wherein a wall portion extending in the first direction and having a through hole is arranged between the worm wheel accommodating portion and the worm shaft accommodating portion, and the wheel tooth portion and the shaft tooth portion mesh with each other in the through hole, and a first mounting portion located on the other side of the first housing in the first direction and a second mounting portion located on one side of the second housing in the first direction and attached to the first mounting portion are provided, an end face on one side of the second mounting portion in the first direction has a sealing surface abutting against the first mounting portion, and when viewed from the first direction, the sealing surface of the second mounting portion has an annular shape that partially overlaps with the worm shaft and the worm shaft accommodating portion and extends circumferentially on the outer periphery of the assist pinion shaft.

[0007] As described above, it is necessary to provide a sealing mechanism in the housing to prevent water and the like from entering the housing. In Patent Document 1, because there is a notch at the lower end of the wall, it is necessary to seal the entire housing by providing, for example, an annular sealing surface on the outside of the wall, which may increase the size of the electric power steering device.

[0008] In contrast, in the present disclosure, a wall portion having a through hole is disposed between the worm wheel housing portion and the worm shaft housing portion, and a sealing surface is provided on the annular second mounting portion, and the sealing surface abuts against the first mounting portion. As a result, according to the present disclosure, the circumferential length of the sealing surface can be made smaller than in Patent Document 1, and ultimately the housing and the electric power steering device can be made smaller.

[0009] In a preferred aspect, the sealing surface of the second mounting portion extends obliquely toward the other side of the first direction as it approaches the other side of the second direction, as viewed from a third direction intersecting the first and second directions. This allows the position of the through hole to be set closer to the other side of the first direction in the wall portion, thereby making it possible to further reduce the height of the housing and make the housing and the electric power steering device more compact.

[0010] In a preferred aspect, the first mounting portion and the second mounting portion are sealed via a seal member that extends annularly along the circumferential direction on the outer circumferential side of the assist pinion shaft. According to the present disclosure, the circumferential length of the seal member can be made smaller than that of Patent Document 1, and therefore the housing and the electric power steering device can be made smaller.

[0011] In a preferred embodiment, the seal member has an elliptical or circular shape when viewed from the first direction, and therefore, compared to a rectangular seal member, the seal member according to the present disclosure has a smaller circumferential length, which in turn allows the electric power steering device to be made smaller.

[0012] In a preferred aspect, the worm wheel accommodating portion includes a cylindrical side portion that includes the wall portion and is arranged on the outer circumferential side of the wheel tooth portion, and a lid portion that seals an opening of the side portion on the other side in the first direction, wherein an end face of the side portion on the other side in the first direction is the sealing surface, and a first edge on the other side in the first direction of the edge of the through hole in the wall portion is located at the boundary between the side portion and the lid portion, and a second edge on one side in the first direction is spaced apart from the end of the wall portion on the one side in the first direction to the other side in the first direction. This allows the position of the through hole to be set closer to the other side in the first direction in the wall portion, thereby making it possible to reduce the height of the housing and further reduce the size of the housing and the electric power steering device.

[0013] In a preferred aspect, the first housing includes a pressing member accommodating portion that protrudes from the other side of the assist pinion shaft accommodating portion in the first direction toward the other side of the second direction and accommodates the rack shaft and a pressing member that presses the rack shaft toward the assist pinion shaft, and when viewed from the third direction, a gap is provided along the first direction between the pressing member accommodating portion and the end of the worm wheel accommodating portion on the other side in the second direction, and the gap becomes larger as it goes toward the other side in the second direction.

[0014] The worm wheel housing generates abnormal noises such as interference noises when the wheel teeth and the shaft teeth mesh together, motor vibration noises, etc. If there is no gap between the worm wheel housing and the pressing member housing and the worm wheel housing and the pressing member housing are integrated, the abnormal noises may increase.

[0015] However, if a gap is provided between the worm wheel accommodating portion and the pressing member accommodating portion, and the gap becomes larger as it goes toward the other side in the second direction, the transmission of abnormal noise to the pressing member accommodating portion is blocked, making it possible to further reduce abnormal noise.

[0016] According to the present disclosure, a more compact electric power steering device is provided.

[0017] 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 schematic diagram of Fig. 2 as viewed from the X1 side. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 1. Fig. 5 is a schematic diagram of an enlarged part of Fig. 2. Fig. 6 is a schematic diagram of Fig. 5 as viewed from the axial direction of an assist pinion shaft.

[0018] Modes (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments. Furthermore, the components described below include those that can be easily imagined by a person skilled in the art and those that are substantially the same. Furthermore, the components described below can be combined as appropriate. Furthermore, parts with the same structure are given the same reference numerals, and descriptions thereof will be omitted.

[0019] In this embodiment, the Z direction is defined as the first direction, the Y direction is defined as the second direction, and the X direction is defined as the third direction. The Z direction intersects with the Y direction. The X direction intersects with the Y and Z directions.

[0020] An electric power steering device according to an embodiment will be described below. 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.

[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, tie rods 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 electric power steering device 100 according to this embodiment 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 Figures 1 and 2, the housing 300 includes a steering-side housing 3 and an assist-side housing 40. The steering-side housing 3 is disposed on the X2 side, and the assist-side housing 40 is disposed on the X1 side. A flange 30 is provided at the X1-side end of the steering-side housing 3, and a flange 43 is provided at the X2-side end of the assist-side housing 40. The flange 30 and the flange 43 are fastened together via bolts BL, thereby connecting the steering-side housing 3 and the assist-side housing 40.

[0028] 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. A through hole 32 is provided in the vehicle body mounting portion 31, and a fastening member (e.g., a bolt) is inserted into the through hole 32. A through hole 414 is provided in the vehicle body mounting portion 413, and a fastening member (e.g., a bolt) is inserted into the through hole 414. 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 it 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. The assist-side housing 40 will be described in detail later.

[0030] Fig. 3 is a schematic diagram of Fig. 2 as viewed from the X1 side. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 1. Fig. 5 is a schematic diagram of an enlarged portion of Fig. 2. Fig. 6 is a schematic diagram of Fig. 5 as viewed from the axial direction of the assist pinion shaft.

[0031] As shown in Figures 2 and 4, the assist-side housing 40 includes a rack shaft accommodating portion 411, a first housing 1, and a second housing 2. The first housing 1 includes an assist pinion shaft accommodating portion 4 and a pressing member accommodating portion 412. The second housing 2 includes a worm wheel accommodating portion 5 and a worm shaft accommodating portion 6. The rack shaft accommodating portion 411 accommodates a portion of the rack shaft 15 on the X1 side. The assist pinion shaft accommodating portion 4 accommodates the assist pinion shaft 21. The worm wheel accommodating portion 5 accommodates the worm wheel 23. The worm shaft accommodating portion 6 accommodates the worm shaft 27. The pressing member accommodating portion 412 accommodates the pressing member 153 and the spring 154.

[0032] The assist pinion shaft accommodating portion 4 includes a main body 41 and a flange (first mounting portion) 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. In addition, 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] The flange (first mounting portion) 42 has a radially outer portion 421 and a radially inner portion (convex portion) 422. The radially inner portion (convex portion) 422 is higher in the Z direction than the radially outer portion 421. In other words, the lower surface 422b of the radially inner portion 422 is at the same height as the lower surface 421b of the radially outer portion 421, and the upper surface 422a of the radially inner portion 422 is located closer to the Z1 side than the upper surface 421a of the radially outer portion 421. Therefore, a step is formed between the side surface 422c of the radially inner portion 422 and the upper surface 421a of the radially outer portion 421.

[0034] 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 assist pinion shaft accommodating portion 4, and the pressing member 153 and the spring 154 are accommodated inside the pressing member accommodating portion 412. A 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.

[0035] The assist pinion shaft 21 is accommodated inside the assist pinion shaft accommodating portion 4. The center axis of the assist pinion shaft 21 is a center axis AX3. The center axis AX3 extends in the Z direction. A nut 25 is fastened to the Z2 side end of the assist pinion shaft 21. A bearing 241 is disposed on the Z1 side of the nut 25. The Z2 side end of the assist pinion shaft 21 is rotatably supported by the main body portion 41 via the bearing 241. The Z1 side portion of the pinion teeth 22 of the assist pinion shaft 21 is rotatably supported by the flange 42 via a bearing 242.

[0036] A worm wheel 23 is attached to the Z1 side end of the assist pinion shaft 21. The worm wheel 23 is housed in the worm wheel housing 5. The worm wheel 23 includes a core metal portion 231 on the radially inner side and a wheel tooth portion 232 on the radially outer side of the core metal portion 231. The core metal portion 231 is fitted onto the assist pinion shaft 21.

[0037] The worm shaft 27 is accommodated in the worm shaft accommodating portion 6. The worm shaft 27 rotates in the circumferential direction around a central axis AX1. The central axis AX1 extends in the X direction. The worm shaft 27 has shaft teeth 271 on its outer periphery. The shaft teeth 271 mesh with the wheel teeth 232. As shown in FIG. 2 , the worm shaft accommodating portion 6 is cylindrical and has an open end on the X1 side, which is sealed with a disk-shaped cap 26. A motor mounting portion 7 is provided at the X2 side end of the worm shaft accommodating portion 6. The motor mounting portion 7 has a protrusion 72, and a motor 70 is fastened to the protrusion 72 via a bolt BL.

[0038] 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.

[0039] 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 via the worm wheel 23 and the worm shaft 27. This generates an assist force that moves the rack shaft 15 connected to the assist pinion shaft 21 in the X direction.

[0040] As shown in FIG. 5 , the worm wheel receiving portion 5 and the worm shaft receiving portion 6 included in the second housing 2 are integrally formed. The worm wheel receiving portion 5 includes a side portion 51, a cover portion 52, and a flange (second mounting portion) 515. The flange 515, also referred to as the second mounting portion, is attached to the flange (first mounting portion) 42 shown in FIG. 4 . A seal material receiving groove 514 extending annularly along the circumferential direction is provided at the lower end of the inner circumferential surface 511 of the side portion 51. As shown in FIG. 4 , the radially inner portion (convex portion) 422 of the flange (first mounting portion) 42 is fitted into the inner circumferential side of the lower portion of the side portion 51. The seal material receiving groove 514 has an L-shaped cross section, and a seal member S is received in the seal material receiving groove 514. That is, a gap having a rectangular cross section is formed between the seal material accommodating groove 514, the side surface 422c of the radially inner portion 422, and the upper surface 421a of the radially outer portion 421. The seal member S is accommodated in this gap. As a result, the radially inner portion (convex portion) 422 of the flange (first mounting portion) 42 and the lower portion of the inner circumferential surface 511 of the side surface portion 51 are sealed via the seal member S.

[0041] As shown in FIG. 5 , the inner peripheral surface 511 of the side portion 51 is a cylindrical surface extending in the circumferential direction around the central axis AX3. The lid portion 52 has a disk shape. A convex portion 521 protruding toward the Z1 side is provided at the radial center of the lid portion 52. The lid portion 52 seals the Z1-side opening of the side portion 51. The flange 515 protrudes radially outward from the side portion 51. The flange 515 is provided with three protrusions 516 spaced apart in the circumferential direction. A through hole 517 passes through the protrusions 516. The Z2-side end face of the flange 515 forms a sealing surface 518. In other words, the Z2-side end face of the flange (second mounting portion) 515 has the sealing surface 518 that abuts against the flange (first mounting portion) 42. 4, when viewed from the Z direction, the sealing surface 518 partially overlaps with the worm shaft 27 and the worm shaft accommodating portion 6. The sealing surface 518 has an annular shape extending circumferentially on the outer circumferential side of the assist pinion shaft 21.

[0042] The worm shaft accommodating portion 6 has a cylindrical shape extending along the central axis AX1. An inner circumferential surface 61 is provided inside the worm shaft accommodating portion 6. The inner circumferential surface 61 is a cylindrical surface extending in the circumferential direction about the central axis AX1. The worm shaft accommodating portion 6 also has a motor mounting portion 7. A motor 70 (see FIG. 2 ) is mounted to the motor mounting portion 7. The motor mounting portion 7 extends in the circumferential direction about the central axis AX1. The motor mounting portion 7 has an annular flange 71. Three protrusions 72 are provided on the flange 71 at intervals in the circumferential direction. A through hole 73 passes through the protrusions 72.

[0043] As shown in FIG. 5 , a wall portion 513 extending in the Z direction and having a through hole 512 is disposed between the worm wheel accommodating portion 5 and the worm shaft accommodating portion 6. The wheel teeth 232 and the shaft teeth 271 mesh with each other in the through hole 512. When viewed from the Y direction, the through hole 512 has a generally elliptical shape that is elongated in the X direction. A second edge 512b is located on the Z2 side of the through hole 512, and a first edge 512a is located on the Z1 side. The second edge 512b has a curved shape that is convex toward the Z2 side. The second edge 512b is spaced from the Z2-side end (sealing material accommodating groove 514) of the wall portion 513 toward the Z1 side. The first edge 512a is a boundary line between the cover portion 52 and the side surface portion 51. The first edge 512a is a straight line extending along the central axis AX1. That is, the through hole 512 is located on the wall portion 513 closest to the Z1 side.

[0044] 3 and 4, an upper surface 421a of the radially outer portion 421 is a sealing surface 417, which abuts against a sealing surface 518 of the flange 515. As shown in Fig. 3, when viewed from the X direction, the sealing surfaces 417, 518 are inclined toward the Z1 side as they approach the Y2 side. In other words, the sealing surfaces 417, 518 are obliquely disposed at an inclination angle θ with respect to a straight line L (dotted line) perpendicular to the central axis AX3.

[0045] Therefore, as shown in FIG. 4 , a gap G is provided between the pressing member accommodating portion 412 and the worm wheel accommodating portion 5 along the Z direction, and the gap G becomes larger toward the Y2 side. Also, as shown in FIG. 6 , when the sealing material accommodating groove 514 is viewed in the axial direction of the central axis AX3, it has an elliptical shape that is elongated in the X direction. However, when viewed in the normal direction to a plane including the sealing material accommodating groove 514, the sealing material accommodating groove 514 has an annular shape. In the present invention, the shape of the sealing material accommodating groove 514 may be either an elliptical or circular shape. That is, the sealing material accommodating groove 514 may have an annular shape when viewed in the axial direction of the central axis AX3. In this case, the sealing material accommodating groove 514 has an elliptical shape when viewed in the normal direction to a plane including the sealing material accommodating groove 514.

[0046] Furthermore, the sealing member S that fits into the sealing material accommodating groove 514 is elliptical when viewed from the axial direction of the center axis AX3, but it may also be annular when viewed from the axial direction of the center axis AX3 (elliptical when viewed from the normal direction of the plane including the sealing material accommodating groove 514).

[0047] As described above, the electric power steering device 100 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 Z2-side outer periphery, the worm wheel 23 that is attached to the Z1 side of the assist pinion shaft 21 and has wheel tooth portions 232 on its outer periphery, the worm shaft 27 that has shaft tooth portions 271 that mesh with the wheel tooth portions 232, is disposed on the Y1 side of the worm wheel 23, and is rotated by the driving force of the motor 70, and the assist-side housing 40 in the housing 300. The assist-side housing 40 includes a first housing 1 and a second housing 2. The first housing 1 includes an assist pinion shaft accommodating portion 4 that accommodates the assist pinion shaft 21. The second housing 2 includes a worm wheel accommodating portion 5 that accommodates the worm wheel 23 , and a worm shaft accommodating portion 6 that is arranged adjacent to the worm wheel accommodating portion 5 on the Y1 side and that accommodates the worm shaft 27 .

[0048] A wall portion 513 extending in the Z direction and having a through hole 512 is disposed between the worm wheel accommodation portion 5 and the worm shaft accommodation portion 6, and the wheel teeth portion 232 and the shaft teeth portion 271 mesh with each other in the through hole 512. A flange (first mounting portion) 42 located on the Z1 side of the assist pinion shaft accommodation portion 4 is attached to a flange (second mounting portion) 515 located on the Z2 side of the worm wheel accommodation portion 5. An end face of the flange (second mounting portion) 515 has a sealing surface 518 that abuts against the flange (first mounting portion) 42. When viewed from the Z direction, the sealing surface 518 partially overlaps with the worm shaft 27 and the worm shaft accommodation portion 6. The sealing surface 518 has an annular shape extending circumferentially on the outer circumferential side of the assist pinion shaft 21.

[0049] As described above, it is necessary to provide a sealing mechanism in the housing to prevent water and the like from entering the housing. In Patent Document 1, because there is a notch at the lower end of the wall, it is necessary to seal the entire housing by providing, for example, an annular sealing surface on the outside of the wall, which may increase the size of the electric power steering device.

[0050] In contrast to this, in the present embodiment, the flange (second mounting portion) 515 is provided with a sealing surface 518, and the sealing surface 518 abuts against the flange (first mounting portion) 42. As a result, according to the present embodiment, the circumferential length of the sealing surface 518 can be made smaller than that of Patent Document 1, and as a result, the housing 300 and the electric power steering device 100 can be made smaller.

[0051] In this embodiment, a wall portion 513 having a through hole 512 is disposed between the worm wheel housing portion 5 and the worm shaft housing portion 6. The flange (second mounting portion) 515 and the flange (first mounting portion) 42 are sealed via an annular seal member S. Therefore, according to this embodiment, the housing 300 and the electric power steering device 100 can be made even more compact.

[0052] The seal member S has an elliptical or circular shape when viewed from the Z direction (first direction). Therefore, compared to a rectangular seal member, for example, the circumferential length of the seal member S according to this embodiment can be made smaller, which in turn allows the housing 300 and the electric power steering device 100 to be made smaller.

[0053] When viewed from the X direction (third direction), the flange (first mounting portion) 42 and the flange (second mounting portion) 515 extend obliquely toward the Z1 side as they approach the Y2 side. This allows the position of the through hole 512 to be set closer to the Z1 side in the wall portion 513, thereby making it possible to further reduce the height of the housing 300 and make the housing 300 and the electric power steering device 100 more compact.

[0054] The seal member S is sandwiched between the radially inner portion (convex portion) 422 and the side surface portion 51. That is, the first mounting portion and the second mounting portion are connected by a so-called spigot joint, so that the worm wheel accommodating portion 5 can be easily positioned relative to the assist pinion shaft accommodating portion 4.

[0055] The worm wheel accommodating portion 5 includes a cylindrical side surface portion 51 that includes a wall portion 513 and is disposed on the outer circumferential side of the wheel tooth portion 232, and a lid portion 52 that seals an opening on the Z1 side of the side surface portion 51. Of the edges of the through hole 512 in the wall portion 513, a first edge 512a on the Z1 side is located at the boundary between the side surface portion 51 and the lid portion 52, and a second edge 512b on the Z2 side is spaced apart from the Z2-side end of the wall portion 513 toward the Z1 side. This allows the position of the through hole 512 to be set closer to the Z1 side in the wall portion 513, thereby making it possible to further reduce the height of the housing 300 and further reduce the size of the housing 300 and the electric power steering device 100.

[0056] A pressing member accommodating portion 412 is provided on the Z1 side of the assist pinion shaft accommodating portion 4, and extends toward the Y2 side to accommodate the rack shaft 15 and the pressing member 153 that presses the rack shaft 15 toward the assist pinion shaft 21. When viewed from the X direction (third direction), a gap G is provided along the Z direction between the pressing member accommodating portion 412 and the Y2-side end of the worm wheel accommodating portion 5, and the gap G becomes larger toward the Y2 side.

[0057] Abnormal noises such as interference noise when the wheel teeth 232 and the shaft teeth 271 mesh with each other and vibration noise from the motor are transmitted to the worm wheel accommodating portion 5. If there is no gap G between the worm wheel accommodating portion 5 and the pressing member accommodating portion 412 and the worm wheel accommodating portion 5 and the pressing member accommodating portion 412 are integrated, the abnormal noises may increase.

[0058] However, if a gap G is provided between the worm wheel accommodating portion 5 and the pressing member accommodating portion 412 and the gap G becomes larger as it moves toward the Y2 side, the transmission of abnormal noise to the pressing member accommodating portion 412 is blocked, making it possible to further reduce the abnormal noise.

[0059] REFERENCE SIGNS LIST 1 First housing 2 Second housing 3 Steering side housing 4 Assist pinion shaft accommodating portion (first housing) 5 Worm wheel accommodating portion (second housing) 6 Worm shaft accommodating portion (second housing) 7 Motor mounting portion 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 25 Nut 26 Cap 27 Worm shaft 30 Flange 31 Vehicle body mounting portion 32 Through hole 33 Steering pinion shaft accommodating portion 40 Assist side housing 41 Main body portion 42 Flange (first mounting portion) 43 Flange 51 Side portion 52 Lid portion 61 Inner peripheral surface 70 Motor 71 DESCRIPTION OF SYMBOLS Flange 72 Projection 73 Through hole 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 411 Rack shaft accommodating portion 412 Pressing member accommodating portion (first housing) 413 Vehicle body mounting portion 414 Through hole 417 Sealing surface 421 Radially outer portion 422 Radially inner portion (convex portion) 511 Inner circumferential surface 512 Through hole 512a First edge 512b Second edge 513 Wall portion 514 Sealing material accommodating groove 515 Flange (second mounting portion) 516 Projection 517 Through hole 518 Sealing surface 521 Convex portion AX1, AX2, AX3 Central axis BL Bolt G Gap L Straight line S Sealing member

Claims

1. 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 that has shaft tooth portions that mesh with the wheel tooth portions, is arranged 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; a first housing including an assist pinion shaft accommodating portion that accommodates the assist pinion shaft; and a second housing arranged on the other side in the first direction of the first housing, the second housing including: a worm wheel accommodating portion that accommodates the worm wheel; and a worm shaft accommodating portion that is arranged adjacent to the worm wheel accommodating portion on one side in the second direction and that accommodates the worm shaft, an electric power steering device in which a wall portion extending in a first direction and having a through hole is arranged between the worm wheel accommodating portion and the worm shaft accommodating portion, the wall portion extending in a first direction and having a through hole, the wheel tooth portion and the shaft tooth portion meshing in the through hole; a first mounting portion located on the other side of the first direction in the first housing, and a second mounting portion located on one side of the second housing in the first direction and mounted to the first mounting portion are provided; an end face on the one side in the first direction of the second mounting portion has a sealing surface abutting against the first mounting portion; and when viewed from the first direction, the sealing surface of the second mounting portion has an annular shape that partially overlaps with the worm shaft and the worm shaft accommodating portion and extends circumferentially on the outer periphery of the assist pinion shaft.

2. An electric power steering device as set forth in claim 1, wherein the sealing surface of the second mounting portion extends obliquely toward the other side of the first direction as it approaches the other side of the second direction, when viewed from a third direction intersecting the first and second directions.

3. An electric power steering device according to claim 1 or 2, wherein the first mounting portion and the second mounting portion are sealed via a seal member that extends annularly along the circumferential direction on the outer periphery of the assist pinion shaft.

4. The electric power steering device according to claim 3, wherein the sealing member is elliptical or circular when viewed from the first direction.

5. An electric power steering device as claimed in any one of claims 1 to 4, wherein the worm wheel accommodating section comprises a cylindrical side portion that includes the wall portion and is arranged on the outer circumferential side of the wheel tooth portion, and a lid portion that seals an opening on the other side of the side portion in the first direction, the end face of the side portion on the other side in the first direction being the sealing surface, and a first edge on the other side of the first direction of the edge of the through hole in the wall portion is located at the boundary between the side portion and the lid portion, and a second edge on one side in the first direction is spaced apart from the end of the wall portion on one side in the first direction to the other side in the first direction.

6. An electric power steering device according to any one of claims 1 to 5, wherein the first housing includes a pressing member accommodating portion that protrudes from the other side of the assist pinion shaft accommodating portion in the first direction toward the other side of the second direction and accommodates the rack shaft and a pressing member that presses the rack shaft toward the assist pinion shaft, and when viewed from the third direction, a gap is provided along the first direction between the pressing member accommodating portion and the end of the worm wheel accommodating portion on the other side in the second direction, and the gap becomes larger as it goes toward the other side in the second direction.

Images