Gear housing and electric assist device

Abstract

To provide a gear housing capable of suppressing vibration of an electric motor and a power-assisted device provided with the gear housing.SOLUTION: A gear housing 16 is provided with: a wheel receiving part 25; a worm receiving part 26; a motor support flange 27 extending radially outward from one axial end of the worm receiving part 26 and having engaging holes 33 to engage an electric motor only at two places opposite to each other relating to a radial direction of the worm receiving part 26; and an inner side lib 28 connected with an inner peripheral surface of one axial end of the worm receiving part 26 and extending in a direction substantially orthogonal to a straight line connecting centers of the engaging holes 33 at the two places viewing from the axial direction of the worm receiving part 26.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a gear housing that constitutes an electric assist device and an electric assist device.

Background Art

[0002] In the field of steering devices, electric power steering devices equipped with an electric assist device that applies an assist driving force to a steering force transmission path are widespread in order to reduce the force required for the rotational operation of a steering wheel.

[0003] The form of an electric power steering device is roughly classified according to the position where the assist driving force by the electric assist device is applied. For example, a column assist type that applies an assist driving force to a steering shaft rotatably supported inside a steering column, a pinion assist type that applies an assist driving force to a pinion shaft that is an input shaft of a steering gear unit, and a dual pinion type in which a steering gear unit is provided with a pinion shaft different from the pinion shaft that is the input shaft and an assist driving force is applied to the different pinion shaft are known.

[0004] As described in, for example, Japanese Patent Application Laid-Open No. 2010-100105, an electric assist device includes a gear housing, an electric motor supported by the gear housing, and a worm reducer that is housed inside the gear housing and increases the assist driving force of the electric motor.

[0005] The gear housing comprises a wheel housing, a worm housing, and a motor support flange. The wheel housing is the part that houses the worm wheel on the inside and is configured in an annular shape. The worm housing is the part that houses the worm on the inside and is configured in a cylindrical shape with one end on the axial side open, and its own central axis is positioned at a twist relative to the central axis of the wheel housing, and is connected to a portion of the circumferential direction of the radially outer end of the wheel housing. The motor support flange extends radially outward from one end on the axial side of the worm housing and has coupling holes at multiple locations in the circumferential direction (for example, three or four locations) for coupling an electric motor. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2010-100105 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In recent years, in order to meet the demand for space-saving in electric assist devices, it has been proposed to reduce the size of the motor support flange and to arrange the coupling holes of the motor support flange in only two locations that are on opposite sides of the worm housing in the radial direction, that is, to fix the electric motor to the gear housing at only these two locations.

[0008] However, when this configuration is adopted, the rigidity of one axial end of the worm housing is reduced in the direction perpendicular to the line connecting the centers of the two coupling holes when viewed from the axial direction of the worm housing. As a result, when assist driving force is applied, the electric motor is more likely to vibrate in the direction perpendicular to the line, which may increase the operating noise of the electric motor. Therefore, there is room for improvement in terms of suppressing this operating noise.

[0009] The present invention aims to provide a gear housing capable of suppressing vibration of an electric motor, and an electric assist device equipped with the gear housing. [Means for solving the problem]

[0010] A gear housing according to one aspect of the present invention comprises a wheel housing, a worm housing, a motor support flange, and an inner rib.

[0011] The wheel housing section is configured in an annular shape and houses a worm wheel inside.

[0012] The worm housing is configured as a cylindrical shape with one end on the axial side open, its central axis is positioned at a twisted position relative to the central axis of the wheel housing, and is connected to a portion of the circumferential direction of the radially outer end of the wheel housing, housing a worm inside.

[0013] The motor support flange extends radially outward from one axial end of the worm housing and has coupling holes for connecting an electric motor at only two locations on opposite sides of the worm housing in the radial direction.

[0014] The inner rib is connected to the inner circumferential surface of one axial end of the worm housing and extends in a direction substantially perpendicular to the straight line connecting the centers of the two coupling holes when viewed from the axial direction of the worm housing.

[0015] A gear housing according to one aspect of the present invention includes a cylindrical inner cylinder portion arranged coaxially with the worm housing portion, radially inward from one axial end of the worm housing portion, and the inner rib is connected to the outer circumferential surface of the inner cylinder portion.

[0016] In one embodiment of the present invention, the gear housing has a cylindrical shape.

[0017] In the gear housing according to one aspect of the present invention, the inner peripheral surface of the inner cylindrical portion is inclined in a direction in which the inner diameter of the inscribed circle decreases as it goes toward the other side in the axial direction.

[0018] The gear housing according to one aspect of the present invention includes an outer rib that is connected to the outer peripheral surface of one end portion on the axial direction one side of the worm housing portion and extends in a direction substantially perpendicular to the straight line connecting the centers of the two coupling holes when viewed from the axial direction of the worm housing portion.

[0019] An electric assist device according to one aspect of the present invention includes a worm wheel having wheel teeth, a worm having worm teeth that mesh with the wheel teeth, a gear housing that houses the worm wheel and the worm inside, and an electric motor that is supported by the gear housing and rotationally drives the worm. The gear housing is constituted by the gear housing according to one aspect of the present invention.

Advantages of the Invention

[0020] According to one aspect of the present invention, it is possible to provide a gear housing that suppresses the vibration of an electric motor, and an electric assist device provided with the gear housing.

Brief Description of the Drawings

[0021] [Figure 1] FIG. 1 is a side view of an electric power steering device according to a first example of an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view of the rear side portion of the electric power steering device according to the first example as viewed from the front side. [Figure 3] FIG. 3 is a perspective view of the rear side portion of the electric power steering device according to the first example as viewed from the rear side. [Figure 4] FIG. 4 is a side view of the rear side portion of the electric power steering device according to the first example. [Figure 5] FIG. 5 is a cross-sectional view taken along the line A-A of FIG. 4. [Figure 6] FIG. 6 is a cross-sectional view taken along the line B-B of FIG. 5. ​Figure 7 is a cross-sectional view taken along the line C-C of Figure 4. [Figure 8] Figure 8 is a cross-sectional view taken along the line D-D of Figure 7. [Figure 9] Figure 9 is a perspective view of the gear housing of the first example as seen from the front side. [Figure 10] Figure 10 is a perspective view of the gear housing of the first example as seen from the rear side. [Figure 11] Figure 11 is a side view of the gear housing of the first example. [Figure 12] Figure 12 is a side view of the gear housing of the first example as seen from the back side of Figure 11. [Figure 13] Figure 13 is a view of the gear housing of the first example as seen from the front side. [Figure 14] Figure 14 is a view of the gear housing of the first example as seen from the rear side. [Figure 15] Figure 15 is a view of the gear housing of the first example as seen from the upper side. [Figure 16] Figure 16 is a view of the gear housing of the first example as seen from the lower side. [Figure 17] Figure 17(a) is a view of the gear housing of the first example as seen from one axial side of the worm housing, and Figure 17(b) is a view similar to Figure 17(a) showing the state where an electric motor is attached to the gear housing of the first example. [Figure 18] Figure 18 is a cross-sectional view taken along the line E-E of Figure 14. [Figure 19] Figure 19 is a view corresponding to a part of Figure 17(a), showing a modified example of the first example.

Mode for Carrying Out the Invention

[0022] [First Example] The first example of the embodiment of the present invention will be described with reference to FIGS. 1 to 18.

[0023] As shown in Figure 1, the electric power steering system 1 in this example comprises a steering wheel 2, a steering shaft 3, a steering column 4, a pair of universal joints 5a and 5b, an intermediate shaft 6, a steering gear unit 7, and an electric assist device 8.

[0024] In the following description of the electric power steering system 1, the front-rear direction refers to the front-rear direction of the vehicle, the left-right direction refers to the width direction of the vehicle, and the up-down direction refers to the up-down direction of the vehicle. The front side is the left side in Figures 1, 4, 6, 11, and 15 to 17(b), and the rear side is the right side in these figures.

[0025] The steering wheel 2 is supported and fixed to the rear end of the steering shaft 3. The steering shaft 3 is rotatably supported inside the steering column 4, which is supported by the vehicle body. The front end of the steering shaft 3 is connected to the pinion shaft 9 of the steering gear unit 7 via a rear universal joint 5a, an intermediate shaft 6, and a front universal joint 5b. Therefore, when the driver rotates the steering wheel 2, the rotation of the steering wheel 2 is transmitted to the pinion shaft 9 via the steering shaft 3, a pair of universal joints 5a and 5b, and the intermediate shaft 6. The rotation of the pinion shaft 9 is converted into linear motion of a rack shaft (not shown) of the steering gear unit 7, which is meshed with the pinion shaft 9. As a result, a pair of tie rods 10 are pushed and pulled, and a steering angle corresponding to the amount of rotation of the steering wheel 2 is applied to the left and right steering wheels.

[0026] The electric power steering system 1 in this example includes a tilt mechanism for adjusting the vertical position of the steering wheel 2 according to the driver's physique and driving posture. For this purpose, an electric assist device 8 fixed to the front end of the steering column 4 is supported relative to the vehicle body via a front support bracket 39, allowing for oscillating displacement around a tilt axis 11 in the left-right direction. The vertical position of the steering wheel 2 is adjusted by oscillating the steering shaft 3, steering column 4, and electric assist device 8 in the vertical direction around the tilt axis 11.

[0027] As shown in Figures 6 and 7, the electric assist device 8 in this example comprises a worm wheel 12 having wheel teeth 13 on its outer circumference, a worm 14 having worm teeth 15 that mesh with the wheel teeth 13 on its outer circumference, a gear housing 16 that houses the worm wheel 12 and the worm 14 inside, and an electric motor 17 supported by the gear housing 16 that rotates the worm 14. The worm wheel 12 and the worm 14, when combined with each other, constitute a worm gear reducer.

[0028] As shown in Figure 6, the electric assist device 8 in this example further includes a cover 18 fixed to the front end of the gear housing 16. In this example, the housing 19 is formed by combining the gear housing 16 and the cover 18.

[0029] The electric assist device 8 in this example further comprises a torsion bar 20 and an output shaft 21. In this example, the front end of the steering shaft 3 is inserted inside the housing 19 and connected to the output shaft 21 via the torsion bar 20. The front end of the output shaft 21 protrudes forward from inside the housing 19 and is connected to the intermediate shaft 6 via a universal joint 5a at the rear (see Figure 1). The output shaft 21 is rotatably supported at two axially separated points relative to the housing 19 by ball bearings 22 and 23.

[0030] The electric assist device 8 in this example further includes a torque sensor 24 housed inside the housing 19 and positioned around the rear end of the output shaft 21. The torque sensor 24 detects the direction and magnitude of the torque applied from the steering wheel 2 to the steering shaft 3. The electric motor 17 rotates a worm 14 based on the detection signal from the torque sensor 24, the vehicle speed signal output from a vehicle speed sensor incorporated in the transmission, and other factors, thereby providing assist driving force to the output shaft 21 via the worm wheel 12. As a result, the force required for the driver to rotate the steering wheel 2 is reduced.

[0031] As shown in Figures 6 to 17(b), the gear housing 16 in this example comprises a wheel housing 25, a worm housing 26, a motor support flange 27, and an inner rib 28. In this example, the gear housing 16 is integrally constructed from a light alloy such as an aluminum alloy, or from a thermoplastic resin. That is, in the following description of the structure of this example, the connections between the various parts constituting the gear housing 16 refer to integral connections. The gear housing 16 can be manufactured, for example, by die-casting a light alloy such as an aluminum alloy, or by injection molding a thermoplastic resin.

[0032] The wheel housing section 25 is the part that houses the worm wheel 12 on its inside and is configured in an annular shape. In this example, the wheel housing section 25 has a cylindrical wheel section 29 arranged around the worm wheel 12 and an annular wheel bottom section 30 extending radially inward from the axial rear end of the wheel section 29.

[0033] The worm housing section 26 is the part that houses the worm 14 inside. In this example, the worm housing section 26 is configured as a bottomed cylindrical shape with one end on the axial side (left side in Figures 7 and 8) open and the other end on the axial side (right side in Figures 7 and 8) closed. However, when implementing the present invention, the worm housing section can also be configured as a cylindrical shape with both the axial end and the axial end open, and the opening at the axial end closed with a closing member.

[0034] The worm housing 26 is connected to a circumferential portion of the radially outer end of the wheel housing 25. In this example, the worm housing 26 is connected to the lower end of the wheel housing 25. The central axis of the worm housing 26 is positioned at a twist relative to the central axis of the wheel housing 25. In this example, the central axis of the worm housing 26 is slightly inclined with respect to the left-right direction; specifically, as viewed from the front of the wheel housing 25, it is inclined upwards as it moves to the right, as shown in Figure 13. The internal space of the worm housing 26 communicates with the internal space of the wheel housing 25.

[0035] In this example, the axial end of the worm housing 26 (the portion indicated by range X1 in Figures 7 and 8) has a larger inner diameter than the axial middle portion and the axial end of the worm housing 26. That is, the axial end of the worm housing 26 consists of a conical cylindrical portion 31 whose inner diameter increases towards the axial side, and a cylindrical portion 32 extending axially from the axial end of the conical cylindrical portion 31. The axial end of the conical cylindrical portion 31 is connected to the axial middle portion of the worm housing 26.

[0036] The motor support flange 27 extends radially outward from one axial end of the worm housing 26. More specifically, in this example, the motor support flange 27 extends radially outward from the cylindrical portion 32. The motor support flange 27 has coupling holes 33 for coupling the electric motor 17 at only two locations on opposite sides of the worm housing 26 in the radial direction. In this example, the two coupling holes 33 are configured as female threaded holes for screwing in bolts 34. However, when implementing the present invention, the two coupling holes can also be configured as through holes for inserting bolts.

[0037] In this example, the motor support flange 27 has a substantially square contour shape (outer circumference shape) centered on the central axis of the worm housing 26, as shown in Figure 17(a), when viewed from the axial direction of the worm housing 26. In this example, one diagonal Ld of the contour shape is perpendicular to the central axis O of the wheel housing 25.

[0038] In this example, the centers of the two coupling holes 33 are located on a diagonal line Ld, as shown in Figure 17(a), when viewed from the axial direction of the worm housing 26. That is, in this example, when viewed from the axial direction of the worm housing 26, the straight line connecting the central axis O of the worm housing 26 and the center of one coupling hole 33 and the straight line connecting the central axis O of the worm housing 26 and the center of the other coupling hole 33 are located on the same straight line (diagonal line Ld). However, when implementing the present invention, when viewed from the axial direction of the worm housing, the straight line connecting the central axis of the worm housing and the center of one coupling hole may be inclined by an angle range of, for example, ±5°.

[0039] In this example, the front end of the motor support flange 27 has a notch 35. The notch 35 is provided to facilitate the laying of a cable (not shown) connected to the electric motor 17. However, when implementing the present invention, the notch 35 may be omitted, and the contour shape of the front end of the motor support flange 27 may be made into a roughly triangular shape as shown by the dashed line Lv in Figure 17(a), that is, the overall contour shape of the motor support flange 27 may be made into a shape closer to a square. When implementing the present invention, the contour shape of the motor support flange can be any shape as long as two connection holes can be provided.

[0040] In this example, when viewed from the axial direction of the worm housing 26, the straight line (diagonal line Ld) connecting the centers of the two coupling holes 33 is positioned perpendicular to the central axis of the wheel housing 25 (= central axis of the steering column 4). By adopting this arrangement in this example, it is easier to suppress the electric motor 17 coupled to the motor support flange 27 from tilting downward due to its own weight or vibrating vertically during vehicle operation. However, when implementing the present invention, the direction of the straight line (diagonal line Ld) relative to the central axis of the wheel housing 25 can be set to any direction different from that in this example, according to the vehicle layout.

[0041] In this example, there are multiple inner ribs 28 (six in the illustrated example), as shown in Figure 17(a). Each of the six inner ribs 28 is connected to the inner circumferential surface of one axial end of the worm housing 26 and extends in a direction perpendicular to the straight line (diagonal Ld) connecting the centers of the two coupling holes 33 (left-right direction in Figure 17(a)) when viewed from the axial direction of the worm housing 26.

[0042] In this example, the six inner ribs 28 are arranged at approximately equal intervals with respect to the circumferential direction of the worm housing 26. More specifically, in this example, three inner ribs 28 are arranged on each side of a straight line (diagonal line Ld) connecting the centers of the two coupling holes 33. The phase of the arrangement of the inner ribs 28 with respect to the direction of this straight line (diagonal line Ld) (the vertical direction in Figure 17(a)) coincides with each other on both the front and rear sides of the straight line (diagonal line Ld). However, the phase can also be made to differ from each other on the front and rear sides.

[0043] In this example, each of the six inner ribs 28 is positioned in the axial middle portion (the portion indicated by range X2 in Figure 8) of one axial end (the portion indicated by range X1 in Figure 8) of the worm housing 26, as shown in Figure 8. In this example, each of the six inner ribs 28 is connected to the inner circumferential surface of one axial half of the conical cylindrical portion 31 and to the inner circumferential surface of the other axial half of the cylindrical portion 32.

[0044] When implementing the present invention, the number of inner ribs can be set to any number of one or more. When implementing the present invention, the inner ribs only need to extend in a direction approximately perpendicular to the straight line connecting the centers of the two coupling holes when viewed from the axial direction of the worm housing. Here, the approximately perpendicular direction includes not only the perfectly perpendicular direction as in this example, but also directions that are inclined within an angular range of, for example, ±5 degrees relative to the perfectly perpendicular direction. When implementing the present invention, from the viewpoint of ensuring the rigidity in the perpendicular direction (left-right direction in Figure 17(a)) of the rigidity of one end of the worm housing 26 in the axial direction, it is preferable to make the length of the inner ribs of the worm housing 26 in the axial direction as large as possible, while keeping the inner ribs from interfering with the electric motor 17.

[0045] In this example, the gear housing 16 further includes an inner cylindrical portion 36.

[0046] The inner cylindrical portion 36 is arranged coaxially with the worm housing portion 26, radially inward from one axial end of the worm housing portion 26. In this example, the inner cylindrical portion 36 has a cylindrical shape overall. When carrying out the present invention, the shape of the inner cylindrical portion 36a can be any number of polygonal cylindrical shapes (hexagonal cylindrical shape in the illustrated example), as shown in the modified structure in Figure 19.

[0047] In this example, as shown in Figures 7 and 8, the other axial end of the inner cylindrical portion 36 is connected to the inner circumferential surface of the other axial half of the conical cylindrical portion 31.

[0048] Six inner ribs 28 are connected to the outer circumferential surface of the inner cylindrical portion 36. In other words, in this example, the inner circumferential surface of one axial end of the worm housing portion 26 and the outer circumferential surface of the inner cylindrical portion 36 are connected via the six inner ribs 28.

[0049] In this example, the axial end faces of the six inner ribs 28 and the axial end face of the inner cylindrical portion 36 are arranged on the same virtual plane perpendicular to the central axis of the worm housing 26. When implementing the present invention, from the viewpoint of ensuring the rigidity in the perpendicular direction (left-right direction in Figure 17(a)) of the axial end of the worm housing 26, it is preferable to make the axial length of the inner cylindrical portion as large as possible, within the range in which the inner cylindrical portion does not interfere with the electric motor 17.

[0050] In this example, the inner circumferential surface of the inner cylinder portion 36 is inclined in a direction such that the diameter of the inscribed circle decreases as it is directed toward the other axial direction. The end of the inner circumferential surface of the inner cylinder portion 36 toward the other axial direction is connected to the inner circumferential surface of the axial intermediate portion of the worm housing portion 26. In addition, the inner cylinder portion can be omitted when implementing the present invention. If the inner cylinder portion is omitted, the configuration of the inner ribs can be any configuration as long as they extend in a direction approximately perpendicular to the straight line connecting the centers of the two coupling holes when viewed from the axial direction of the worm housing portion.

[0051] In this example, the gear housing 16 further comprises a pair of hinge portions 37.

[0052] Each hinge portion 37 constituting a pair of hinge portions 37 extends forward from the upper left and right sides of the outer circumferential surface of the wheel cylinder portion 29. Each hinge portion 37 constituting a pair of hinge portions 37 has an insertion hole 38 at its front end for inserting the tilt shaft 11 (see Figures 1 to 4 and Figure 6).

[0053] In this example, the gear housing 16 further includes a shaft insertion portion 40.

[0054] The shaft insertion section 40 is the part through which the shaft that rotates with the worm wheel 12 is inserted. The shaft insertion section 40 is constructed in a cylindrical shape and extends from the radially inner end of the wheel bottom section 30 toward the rear, as shown in Figure 6. In this example, the front end of the steering shaft 3 and the rear end of the output shaft 21 are inserted inside the shaft insertion section 40. The torque sensor 24 is located inside the front end of the shaft insertion section 40.

[0055] In this example, the gear housing 16 further includes a clamped portion 41.

[0056] The clamped portion 41 is the part that is supported by the vehicle body via the rear support bracket 42. The clamped portion 41 has a roughly rectangular block shape and is connected to the lower part of the rear end of the shaft insertion portion 40. The clamped portion 41 is clamped from both the left and right sides by each of the support plate portions 43 that constitute a pair of support plate portions 43 provided on the rear support bracket 42. The clamped portion 41 has a through hole 44 that penetrates in the left-right direction. A switching rod 45 for switching whether or not the vertical position of the steering wheel 2 can be adjusted is inserted through the through hole 44.

[0057] In this example, the gear housing 16 further includes an outer rib 46.

[0058] In this example, there are multiple outer ribs 46 (two in the illustrated example), as shown in Figures 10, 14-16, and 18. In this example, each of the two outer ribs 46 is connected to the outer circumferential surface of the axial portion of the worm housing 26 (the portion located axially to one side of the shaft insertion portion 40), including the axial end of the worm housing 26, and extends in a direction perpendicular to the straight line (diagonal Ld) connecting the centers of the two coupling holes 33 (left-right direction in Figure 17(a)) when viewed from the axial direction of the worm housing 26.

[0059] Specifically, in this example, the two outer ribs 46 each have a flat plate shape and are spaced apart in the vertical direction and arranged parallel to each other. Furthermore, the two outer ribs 46 extend in the direction perpendicular to the axial direction of the worm housing 26 (the left-right direction in Figure 17(a)), but as shown in Figures 10 and 14, they are not arranged parallel to the central axis of the worm housing 26, but are arranged slightly inclined with respect to the central axis of the worm housing 26. Specifically, the two outer ribs 46 are arranged to extend in the axial and left-right directions of the wheel housing 25 and the shaft insertion portion 40.

[0060] In this example, the two outer ribs 46 are connected to the outer circumferential surface of the worm housing 26, the other axial side of the motor support flange 27, and the left-right side (= motor support flange 27 side) of the front part of the shaft insertion portion 40. In this example, the upper of the two outer ribs 46 is also connected to the rear end of the outer circumferential surface of the motor support flange 27, as shown in Figure 10.

[0061] In this example, the two outer ribs 46 are positioned so as to be slightly inclined with respect to the central axis of the worm housing 26 in order to connect them to the side surface of the shaft insertion portion 40. When implementing the present invention, the outer ribs can also be positioned parallel to the central axis of the worm housing 26. When the two outer ribs 46 are positioned so as to be slightly inclined with respect to the central axis of the worm housing 26, as in this example, it is preferable to keep the angle of inclination to, for example, 30° or less.

[0062] When implementing the present invention, the number of outer ribs can be set to any number of one or more. When implementing the present invention, the outer ribs only need to extend in a direction approximately perpendicular to the straight line connecting the centers of the two coupling holes when viewed from the axial direction of the worm housing. Here, the approximately perpendicular direction includes a perfectly perpendicular direction as in this example, as well as a direction that is inclined with respect to the perfectly perpendicular direction within an angular range of, for example, ±5 degrees. When implementing the present invention, the outer ribs can also be omitted.

[0063] In this example, the gear housing 16 is further equipped with additional ribs 47.

[0064] The additional rib 47 has a flat plate shape and, as shown in Figures 7 and 14, is connected to the outer circumferential surface of the worm housing 26, the other axial side of the motor support flange 27, and the outer circumferential surface of the wheel housing 25, on the upper side of the portion near one axial end of the worm housing 26. The additional rib can be omitted when implementing the present invention.

[0065] In this example, the cover 18 is configured in a roughly circular shape. With the gear housing 16 and the cover 18 combined to form the housing 19, the rear portion of the cover 18 is fitted into the front end of the wheel cylinder portion 29, and the rear end surface of the radially outer end of the cover 18 abuts against the front end surface of the wheel cylinder portion 29.

[0066] In this example, as shown in Figures 7 and 8, the worm 14 has worm teeth 15 on the outer circumferential surface of its axial intermediate portion, and a male spline 48 on the outer circumferential surface of one end on the axial side. The worm 14 is rotatably supported inside the worm housing 26 by ball bearings 49 and 50.

[0067] As shown in Figures 6 and 7, the worm wheel 12 has wheel teeth 13 on its outer circumference and is rotatably supported inside the wheel housing 25. For this reason, in this example, the worm wheel 12 is externally fitted and fixed to the portion of the output shaft 21 located between the two ball bearings 22 and 23. The ball bearing 22 is internally fitted to the cover 18 and externally fitted to the portion of the output shaft 21 adjacent to the front side of the worm wheel 12. The ball bearing 23 is internally fitted to the wheel bottom 30 and externally fitted to the portion of the output shaft 21 adjacent to the rear side of the worm wheel 12.

[0068] In this example, the electric motor 17 is coupled to the gear housing 16, as shown in Figures 7, 8, and 17(b). Specifically, the electric motor 17 comprises an insertion portion 51 that is inserted into the cylindrical portion 32 of the gear housing 16 without radial play, and a motor-side flange 52 that is superimposed on one axial side of the motor support flange 27 of the gear housing 16. As shown in Figures 17(a) and 17(b), the motor-side flange 52 has a contour shape substantially similar to that of the motor support flange 27. The motor-side flange 52 has two motor-side coupling holes 53 that align with the coupling holes 33 of the motor support flange 27. In this example, the two motor-side coupling holes 53 are composed of through holes for inserting bolts 34. The electric motor 17 is coupled to the gear housing 16 by screwing bolts 34, which are inserted through the two motor-side coupling holes 53, into the two coupling holes 33.

[0069] When implementing the present invention, the two coupling holes of the motor support flange can be configured as through holes, and the two motor-side coupling holes of the motor-side flange can be configured as female threaded holes. That is, the electric motor can be coupled to the gear housing by screwing bolts inserted through the two coupling holes of the motor support flange into the two motor-side coupling holes of the motor-side flange.

[0070] In this example, with the electric motor 17 coupled to the gear housing 16, the motor output shaft 54 ​​and the worm 14 are connected in a torque-transmitting manner by engaging the female spline 55 provided on the inner circumferential surface of the tip of the motor output shaft 54 ​​of the electric motor 17 with the male spline 48 of the worm 14. In this example, the connection portion between the motor output shaft 54 ​​and the worm 14 is located radially inward of the inner cylindrical portion 36 of the gear housing 16. When carrying out the present invention, the method of connecting the motor output shaft and the worm in a torque-transmitting manner is not particularly limited. For example, the motor output shaft and the worm can also be connected in a torque-transmitting manner via a coupling that can absorb (allow) misalignment of their axes.

[0071] In the electric assist device 8 of this example, the gear housing 16 is provided with an inner rib 28 connected to the inner circumferential surface of one axial end of the worm housing 26. The inner rib 28 extends perpendicular to the straight line (diagonal Ld) connecting the centers of the two coupling holes 33 when viewed from the axial direction of the worm housing 26. Therefore, the inner rib 28 can effectively improve the rigidity of the axial end of the worm housing 26 in the aforementioned perpendicular direction. Consequently, when assist driving force is applied, the oscillation of the electric motor 17 in the aforementioned perpendicular direction can be suppressed, and the operating noise of the electric motor 17 can be reduced. Such effects can also be obtained when the direction of the straight line (diagonal Ld) with respect to the central axis of the wheel housing 25 is set to any direction different from that of this example.

[0072] In particular, in this example, the inner ribs 28 are provided at multiple locations spaced apart in the circumferential direction of the worm housing 26. Therefore, the rigidity in the perpendicular direction of one end of the worm housing 26 on the axial side can be improved more effectively.

[0073] In this example, the gear housing 16 further includes an inner cylindrical portion 36 arranged coaxially with the worm housing 26, radially inward from one axial end of the worm housing 26, and an inner rib 28 is connected to the outer circumferential surface of the inner cylindrical portion 36. As a result, the inner rib 28 functions as a reinforcing core material, which more effectively improves the rigidity of the axial end of the worm housing 26 in the perpendicular direction.

[0074] In this example, the gear housing 16 further includes an outer rib 46 connected to the outer circumferential surface of one axial end of the worm housing 26. The outer rib 46 extends perpendicular to the line connecting the centers of the two coupling holes 33 when viewed from the axial direction of the worm housing 26. Therefore, the outer rib 46 can more effectively improve the rigidity of the axial end of the worm housing 26 in the direction perpendicular to the line.

[0075] In particular, in this example, the outer ribs 46 are provided at two locations separated vertically, perpendicular to the line connecting the centers of the two coupling holes 33. This makes it possible to more effectively improve the rigidity of the axial end of the worm housing 26 in the direction perpendicular to the line. Furthermore, in the structure of this example, since there is a gap between the two outer ribs 46, the gear housing 16 can be made lighter compared to a structure in which the gap is filled with material.

[0076] In this example, the additional ribs 47 provided on the gear housing 16 can also improve the rigidity of the axial end of the worm housing 26 in the perpendicular direction.

[0077] In this example, the inner circumferential surface of the inner cylinder portion 36 is inclined in a direction such that the diameter of the inscribed circle decreases as it is directed toward the other axial side. Therefore, when inserting the worm 14 and ball bearings 49 and 50 into the worm housing portion 26 from the opening on one axial side of the worm housing portion 26, the inner circumferential surface of the inner cylinder portion 36 can be used as a guide surface, making the insertion process easier.

[0078] In the embodiments described above, the present invention is applied to a column-assist type electric power steering system, but the present invention can also be applied to other types of electric power steering systems, such as pinion-assist type and dual-pinion type. [Explanation of Symbols]

[0079] 1. Electric power steering system 2 Steering Wheel 3. Steering shaft 4. Steering column 5a, 5b Flexible joint 6 Intermediate shaft 7. Steering Gear Unit 8. Electric assist device 9 Pinion shaft 10 Tie Rods 11 Tilt axis 12 worm wheel 13 Wheel Teeth 14 Warm 15 Warm teeth 16 Gear Housing 17 Electric motor 18 Lid 19 Housing 20 Torsion Bar 21 Output shaft 22 Ball bearing 23 Ball bearings 24 Torque Sensor 25 Wheel housing 26 Worm containment section 27 Motor support flange 28 Inner Rib 29 Wheel cylinder section 30 Wheel base 31. Conical cylindrical section 32 Cylindrical part 33 Binding hole 34 volts 35 Notches 36 Inner cylinder part 37 Hinge section 38 Through hole 39 Front support bracket 40 Shaft insertion section 41 Clamped part 42 Rear support bracket 43 Support plate part 44 Through hole 45 Switching rod 46 Outer rib 47 Additional Ribs 48 Male splines 49 Ball bearing 50 ball bearings 51 Insertion part 52 Motor-side flange 53 Motor-side coupling hole 54 Motor output shaft 55 Female splines

Claims

1. It is configured in a ring shape, with a wheel housing section that houses the worm wheel on the inside, A worm housing is configured in a cylindrical shape with one end on the axial side open, and its own central axis is positioned at a twisted position with respect to the central axis of the wheel housing, and is connected to a circumferential portion of the radially outer end of the wheel housing, and houses a worm inside. A motor support flange extending radially outward from one axial end of the worm housing and having coupling holes for connecting an electric motor at only two locations on opposite sides of the worm housing in the radial direction, An inner rib connected to the inner circumferential surface of one axial end of the worm housing and extending in a direction substantially perpendicular to the straight line connecting the centers of the two coupling holes when viewed from the axial direction of the worm housing, A cylindrical inner cylinder portion is provided, which is arranged coaxially with the worm housing portion, radially inward from one axial end of the worm housing portion, Equipped with, The inner rib is connected to the outer circumferential surface of the inner cylindrical portion. Gear housing.

2. The gear housing according to claim 1, wherein the inner cylindrical portion has a cylindrical shape.

3. The gear housing according to claim 1 or 2, wherein the inner circumferential surface of the inner cylinder portion is inclined in a direction such that the diameter of the inscribed circle decreases as it is directed toward the other axial direction.

4. The gear housing according to any one of claims 1 to 3, wherein the gear housing is provided with an outer rib connected to the outer circumferential surface of one axial end of the worm housing and extending in a direction substantially perpendicular to the straight line connecting the centers of the two coupling holes when viewed from the axial direction of the worm housing.

5. A worm wheel having wheel teeth, A worm having worm teeth that mesh with the wheel teeth, A gear housing that houses the worm wheel and the worm on the inside, An electric motor supported by the gear housing rotates the worm, Equipped with, The gear housing is composed of the gear housing described in any one of claims 1 to 4. Electric assist device.

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