JP2009262777A - Worm supporting structure of steering auxiliary device, and bush used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a worm supporting structure of a steering auxiliary device favorable for reducing the cost while suppressing generation of the rattling noise of gears. <P>SOLUTION: An inner bush 22 is fitted to a shaft part 1006 of a worm 10, and the inner bush 22 is turnably supported by a bush fitting part of a housing 14 via a bearing 24 and an outer bush 26. The outer bush 26 is formed of an elastic material, and has an outer circumferential cylindrical surface and an inner circumferential cylindrical surface which are in the coaxial relationship. A groove 30 is formed in the outer circumferential cylindrical surface. Due to the groove 30, the outer bush 26 has a high rigid portion 26A which is a substantially half circumferential portion without any groove 30, and a low rigid portion 26B which is a substantially half circumferential portion with the groove 30. In the outer bush 26, the low rigid portion 26B is directed to the side of a worm wheel 12, and fitted to a bush fitting cylindrical surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a steering assist device for an automobile, and more particularly to a worm support structure for a steering assist device and a bush used therein.

As an automobile steering assist device, for example, an electric power steering device has been conventionally provided.
In this type of electric power steering apparatus, the output of the electric motor is decelerated via a worm and a worm wheel and transmitted to a steering mechanism to assist the steering operation with torque.
On the other hand, a backlash is required for meshing between the worm and the worm wheel, but a rattling sound (rattle sound) due to the backlash is generated during traveling.

Therefore, conventionally, a bearing that rotatably supports the worm is supported by a housing via a leaf spring, and the worm is urged toward the worm wheel by the leaf spring to suppress generation of rattling noise (patent) References 1-4).
JP 2006-175891 Patent No. 3788576 Patent No. 39951913 JP2002-96749

However, in such a configuration, a bearing with high accuracy is required, and a special material is required for the leaf spring, which is disadvantageous in reducing the cost of a steering assist device for an automobile.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a worm support structure for a steering assist device and a bush used therefor that are advantageous in reducing the cost while suppressing the occurrence of rattling noise. There is to do.

In order to achieve the above object, according to the present invention, there is provided a worm support structure for a steering assist device in which shaft portions at both ends of a worm meshing with a worm wheel are supported in a housing. Is supported via a first bush mounted on a bush mounting portion formed in the housing, and a bearing interposed between the first bush and the one shaft portion, 1 bush is formed of an elastic material, the bush mounting portion has a bush mounting cylindrical surface, the first bush includes an outer peripheral cylindrical surface fitted to the bush mounting cylindrical surface, and the bearing. An inner peripheral cylindrical surface for supporting, the outer peripheral cylindrical surface and the inner peripheral cylindrical surface are in a concentric relationship, and the first bush has a groove extending substantially over a half circumference of the outer peripheral cylindrical surface. Formed Thus, the first bush has a high-rigidity portion that is a substantially semicircular portion where the groove is not formed and a low-rigidity portion that is a substantially semicircular portion where the groove is formed. The low-rigidity portion is directed to the worm wheel side and fitted to the bush mounting cylindrical surface.
The bush of the present invention is formed of an elastic material, and has an outer peripheral cylindrical surface and an inner peripheral cylindrical surface that are concentric with each other, and a groove is formed to extend substantially over the outer peripheral cylindrical surface. Thus, it has a high-rigidity portion that is a substantially semicircular portion where the groove is not formed and a low-rigidity portion that is a substantially semicircular portion where the groove is formed.

According to the worm support structure and the bush of the steering assist device of the present invention, the worm shaft center can be minutely moved by utilizing the elastic deformation of the bush interposed between the bearing supporting the one end of the worm and the housing. ing.
This bushing is mounted so as to fill the space between the bearing and the housing, so that it is possible to reliably prevent the generation of noise caused by moving the worm shaft relative to the worm wheel. Is done.
Further, since the impact force acting on the worm tooth surface from the worm wheel tooth surface during operation of the steering assist device is buffered by the deformation of the outer bush, the tooth caused by the collision between the tooth surface of the worm wheel and the tooth surface of the worm. The bearing noise is suppressed to a low level, and the bearing that supports the worm is preloaded in the axial direction of the worm, so that the backlash of the bearing can be eliminated and the generation of abnormal noise due to the backlash can be prevented. .
In addition, the bush mounting part formed in the housing is a cylindrical hole, and the bush has concentric cylindrical outer peripheral surface and inner peripheral surface, so that more accurate components can be manufactured at lower cost. Therefore, high-precision assembly can be performed at low cost.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view of a main part of a steering assist device, FIG. 2 is an explanatory view of a support structure for one end of a worm on the side where motor power is input, and FIG. 3 is a support structure for the other end of the worm to which the present invention is applied. FIG. 4 is an explanatory view of the inner bush, the bearing, and the outer bush, and FIG. 5 is a side view of the outer bush.
In the electric power steering device that is the steering assist device 8 of the automobile, the power of the steering assist motor is decelerated via the worm 10 and the worm wheel 12 and transmitted to the steering mechanism.
The steering assist device 8 includes a housing 14 that rotatably supports the worm 10.
The worm 10 includes a tooth portion 1002 and shaft portions 1004 and 1006 at both ends of the tooth portion 1002.
As shown in FIG. 2, the shaft portion 1004 of the worm 10 on the side where the power of the motor is input has an inner bush made of a synthetic resin such as polyacetal resin or polyamide resin as a third bush on the outer peripheral surface thereof. 16 is fitted, and the worm 10 is press-fitted to the outer peripheral surface of the inner bush 16 and is rotatably supported by a bearing 18 fixed to the bearing portion 20 of the housing 14.
The inner bush 16 includes a cylindrical portion 1602 and a flange portion 1604 formed at one end portion of the cylindrical portion 1602 so as to expand radially outward, and the flange portion 1604 includes the inner bushing 1604. When 16 is fitted to the outer peripheral surface of the shaft portion 1004, it is disposed in contact with a flange 1010 provided on the shaft portion 1004.
The inner race of the bearing 18 is press-fitted and fitted to the outer peripheral surface of the cylindrical portion 1602 of the inner bush 16, and the outer race of the bearing 18 is fitted and fixed to the bearing portion 20 of the housing 14.

As shown in FIGS. 3 and 4, the other shaft portion 1006 of the worm 10 is made of a synthetic resin such as polyacetal resin or polyamide resin or natural rubber as a second bush fitted and fixed to the outer peripheral surface thereof. An inner bush 22 made of an elastic material such as synthetic rubber, polyurethane rubber, acrylic rubber, polyester elastomer, a bearing 24 fitted to the outer peripheral surface of the inner bush 22, and a housing surrounding the outer peripheral surface of the bearing 24 The outer bush 26 made of an elastic material such as natural rubber, synthetic rubber, polyurethane rubber, acrylic rubber, polyester elastomer or the like is disposed as a first bush fixed to the 14 bush mounting portion 28, and the worm 10 is between the inner bush 22 and the outer bush 26. It is rotatably supported by a bearing 24 engaged.
The inner bush 22 includes a cylindrical portion 2202 and a flange portion 2204 formed at one end portion of the cylindrical portion 2202 so as to expand radially outwardly, and the flange portion 2204 includes the inner bushing 22204. When the bush 22 is fitted to the outer peripheral surface of the shaft portion 1006, the bush 22 is disposed in contact with a flange 1012 provided on the shaft portion 1006.
When the worm 10 is assembled to the housing 14, the flange portions 1604 and 2204 of the inner bushes 16 and 22 that are fitted and fixed to the outer peripheral surfaces of the shaft portions 1004 and 1006 at both ends of the worm 10 are respectively in the axial direction of the worm 10. Due to the tightening allowance, the bearings 18 and 24 can be preloaded between the flanges 1604 and 2204 and the flanges 1010 and 1012. As a result, the backlash of the bearings 18 and 24 can be eliminated. The generation of abnormal noise can be prevented.
In the present embodiment, the example in which the flange portion 1604 of the inner bush 16 has the tightening allowance in the axial direction of the worm 10 has been described. However, as shown in FIG. And the flange 1604 can be formed separately, and a spring member such as a wave washer, a spring washer, or a disc spring can be used for the flange 1604.

The bush mounting portion 28 has a bush mounting cylindrical surface 2802 and an annular end surface 2804.
A rotation-preventing engagement portion (engagement recess) 2806 for preventing the outer bush 26 from rotating in the circumferential direction is provided at a location of the bush mounting cylindrical surface 2802 located opposite to the worm wheel 12.

The outer bush 26 has an outer peripheral cylindrical surface 2602 that fits into the bush mounting cylindrical surface 2802 and an inner peripheral cylindrical surface 2604 that supports the bearing 24. The outer peripheral cylindrical surface 2602 and the inner peripheral cylindrical surface 2604 are concentric. In a relationship.
More specifically, the inner race of the bearing 24 is fitted to the cylindrical portion 2202 of the inner bush 22, and the outer race of the bearing 24 is fitted to the inner peripheral cylindrical surface 2604 of the outer bush 26.

A groove 30 is formed on the outer peripheral cylindrical surface 2602 of the outer bush 26 so as to extend almost half of its circumference.
Due to the groove 30, the outer bush 26 has a high-rigidity portion 26A that is a substantially semicircular portion where the groove 30 is not formed, and a low-rigidity portion 26B that is a substantially semicircular portion where the groove 30 is formed. Yes.
In the present embodiment, the outer bush 26 has a uniform thickness (the thickness here is a dimension in the axial direction of the worm), and the outer cylindrical surface 2602 is the thickness of the outer bush 26. The outer circumferential cylindrical surface 2602 has a width along the axial direction of the outer bush 26, and the groove 30 extends in the circumferential direction at the center of the outer circumferential cylindrical surface 2602 in the width direction. Being formed.

Further, the outer bush 26 engages with a rotation prevention engagement portion (engagement recess) 2806 of the bush mounting portion 28 and engages with the rotation prevention engagement portion 2806 to prevent the outer bush 26 from rotating in the circumferential direction. A joint portion (engagement convex portion) 2606 is provided.
The rotation prevention engaging portion (engagement convex portion) 2606 is formed on the outer peripheral cylindrical surface 2602 in the present embodiment.

Further, end faces are located at both ends in the thickness direction of the outer bush 26, and the outer bush 26 protrudes radially inward at the end of the inner peripheral cylindrical surface 2604 on the end face side located near the end of the shaft portion 1006. A first flange 2610 extending in the direction is provided.
Further, the end portion of the inner circumferential cylindrical surface 2604 on the end surface side opposite to the place where the first flange portion 2610 is provided protrudes radially inwardly with a smaller protrusion size than the first flange portion 2610 in the circumferential direction. An extended second collar portion 2612 is provided.
Furthermore, an inclined surface 2614 that is displaced toward the first flange portion 2610 toward the inner side in the radial direction is provided on the inner peripheral portion of the end surface located at the location where the second flange portion 2612 is provided. The mounting on the circumferential cylindrical surface 2604 is facilitated.

  The outer bush 26 is disposed with the low-rigidity portion 26 </ b> B facing the worm wheel 12 and fitted to the bush mounting cylindrical surface 2802.

According to the present embodiment, the following effects are exhibited.
(1) The structure for supporting the worm 10 so that the shaft center of the worm 10 can move minutely in the direction approaching and separating from the worm wheel 12 has a sliding part and a gap securing part like the conventional structure. Rather, the shaft center of the worm 10 can be moved minutely by utilizing the elastic deformation of the outer bush 26 interposed between the bearing 24 supporting the one end 1006 of the worm 10 and the housing 14.
Since the outer bush 26 is mounted so as to fill a space between the bearing 24 and the housing 14, the noise generated by moving the shaft center of the worm 10 relative to the worm wheel 12. Occurrence is reliably prevented.
Further, since the impact force acting on the tooth surface of the worm 10 from the tooth surface of the worm wheel 12 during operation of the steering assist device 8 is buffered by the deformation of the outer bush 26, the tooth surface of the worm wheel 12 and the tooth of the worm 10 The rattling noise caused by the collision with the surface is also suppressed.
(2) The bush mounting portion 28 formed in the housing 14 is a cylindrical hole portion, and the outer bush 26 has a concentric cylindrical outer peripheral surface 2602 and an inner peripheral surface 2604. Thus, compared with the case where a non-cylindrical mounting part and a non-cylindrical part are used, a more accurate component can be manufactured at lower cost.
In the assembly, the outer race of the cylindrical bearing 24 is fitted to the cylindrical inner peripheral surface 2604 of the outer bush 26, and the cylindrical outer peripheral surface 2602 of the outer bush 26 is attached to the cylindrical bush of the housing 14. This is done by fitting to the portion 28. However, when such cylindrical surfaces are fitted to each other, since high-precision centering is automatically achieved, high-precision assembly can be performed at low cost. .
(3) The outer bush 26 to be used has a high-rigidity portion 26A having a substantially half circumference and a low-rigidity portion 26B having a substantially half circumference.
Therefore, when the shaft center of the worm 10 is about to move away from the worm wheel 12, the movement is reliably suppressed by the high-rigidity portion 26A of the outer bush 26.
Therefore, the movement of the worm 10 axis in the undesired direction is reliably suppressed, while the minute movement of the worm 10 axis toward the worm wheel 12 is smoothly performed.
(4) The low-rigidity portion 26B is formed by providing the outer circumferential surface 2602 with the grooves 30 in the circumferential direction. According to this configuration, the low-rigidity portion 26B has high dimensional accuracy and high rigidity. The outer bush 26 which can be set to the design value can be manufactured at a low cost.
(5) Since preload is applied to the bearings 18 and 24 supporting the worm 10 in the axial direction of the worm 10, the backlash of the bearings 18 and 24 can be eliminated, and the generation of abnormal noise due to backlash can be prevented. be able to.

  As described above, according to the worm support structure of the steering assist device 8 according to the present embodiment and the outer bush 26 according to the present embodiment, the center adjustment function between the worm 10 and the worm wheel 12 is provided. It is possible to manufacture a high-precision worm support structure at a low cost, and the worm support structure has a high degree of accuracy to prevent abnormal noise due to its high precision, and the tooth can be reduced while reducing costs. It is possible to suppress the occurrence of a beating sound (rattle sound).

It is principal part sectional drawing of a steering assistance device. It is explanatory drawing of the support structure of the end of the worm | warm at the side into which the motive power of a motor is input. It is explanatory drawing of the support structure of the other end of the worm to which this invention was applied. It is explanatory drawing of an inner bush, a bearing, and an outer bush. It is a side view of an outer bush. It is principal part sectional drawing of the modification of a steering assistance device.

Explanation of symbols

  8 ... Steering assist device, 10 ... Worm, 1004, 1006 ... Shaft, 12 ... Worm wheel, 14 ... Housing, 16 ... Inner bush, 18 ... Bearing, 22 ... Inner bush, 24 ... ... bearings, 26 ... outer bushings, 26A ... high rigidity parts, 26B ... low rigidity parts, 28 ... bush mounting parts, 30 ... grooves.

Claims (9)

In the worm support structure of the steering assist device in which the shaft portions at both ends of the worm meshing with the worm wheel are supported in the housing,
One shaft portion of the shaft portions at both ends is interposed between a first bush mounted on a bush mounting portion formed on the housing, and between the first bush and the one shaft portion. Supported through bearings,
The first bush is formed of an elastic material;
The bush mounting portion has a bush mounting cylindrical surface,
The first bush has an outer peripheral cylindrical surface that fits into the bush mounting cylindrical surface and an inner peripheral cylindrical surface that supports the bearing, and the outer peripheral cylindrical surface and the inner peripheral cylindrical surface are concentric. Relationship
The first bush includes a high-rigidity portion, which is a substantially semicircular portion where the groove is not formed, and a groove formed so as to extend substantially over the semicircular circumference of the outer peripheral cylindrical surface. A low-rigidity portion that is substantially a half-circular portion,
The first bush is fitted to the bush mounting cylindrical surface with the low rigidity portion directed toward the worm wheel.
A worm support structure for a steering assist device. The outer peripheral cylindrical surface has a width along the axial direction of the first bush,
The groove is formed in the center in the width direction of the outer peripheral cylindrical surface and extends in the circumferential direction.
The worm support structure for a steering assist device according to claim 1. The first bushing and the bush mounting portion are provided with a rotation-preventing engagement portion that prevents the first bushing from rotating in the circumferential direction by being engageable with each other.
The worm support structure for a steering assist device according to claim 1. End faces are respectively located at both axial ends of the first bush,
At the end portion of the inner cylindrical surface on the end surface side located near the end portion of the one shaft portion, a collar portion that extends in the circumferential direction while protruding radially inward is provided.
The worm support structure for a steering assist device according to claim 1. End faces are respectively located at both axial ends of the first bush,
A first flange portion extending in the circumferential direction while protruding radially inward is provided at an end portion of the inner peripheral cylindrical surface on the end surface side located near the end portion of the one shaft portion,
Extending in the circumferential direction while projecting radially inwardly at the end of the inner circumferential cylindrical surface on the end surface side opposite to the location where the first collar is provided, with a projecting dimension smaller than the first collar. A second collar part is provided,
The worm support structure for a steering assist device according to claim 1. An inclined surface that is displaced toward the first flange portion as it goes radially inward is provided on the inner peripheral portion of the end surface located at the location where the second flange portion is provided.
The worm support structure for a steering assist device according to claim 5. The worm has a tooth portion between the shaft portions at both ends,
A second bush and a third bush are respectively fitted to the shaft portions at both ends of the worm,
The second bush is supported by the bearing;
The third bush is supported by a bearing different from the bearing,
A flange portion that is annularly extended radially outward is formed at a location near the tooth portion of the second bush and the third bush,
When the worm is assembled, the flanges of the second bush and the third bush are tightened in the axial direction of the worm via the housing and the bearing.
The worm support structure for a steering assist device according to any one of claims 1 to 6. The worm has a tooth portion between the shaft portions at both ends,
A second bush and a third bush are respectively fitted to the shaft portions at both ends of the worm,
The second bush is supported by the bearing;
The third bush is supported by a bearing different from the bearing,
A flange portion that is annularly expanded radially outward is formed at a location near the tooth portion of the second bush,
The third bush has a cylindrical shape, and is formed of a member different from the third bush that extends in an annular shape on the outer side in the radial direction of the third bush at a location near the tooth portion of the third bush. An annular plate-shaped spring member arranged,
When the worm is assembled, the flange portion and the spring member of the second bush are tightened in the axial direction of the worm via the housing and the bearing.
The worm support structure for a steering assist device according to any one of claims 1 to 6. Formed of elastic material,
An outer peripheral cylindrical surface and an inner peripheral cylindrical surface that are concentric with each other;
A groove is formed so as to extend substantially half a circumference of the outer peripheral cylindrical surface, so that a high-rigidity part that is a substantially half-circumferential part in which the groove is not formed and a substantially half-circumferential part in which the groove is formed. Having a low rigidity part,
Bush characterized by that.

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