JP2000168583A - Motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make small the overall structure of a power assist part and reduce the weight of the whole device. SOLUTION: A power assist part is composed of an electric motor 4, a worm shaft 1 receiving power from the motor 4, a wheel gear 2 to be mounted on a steering shaft 5 and engaged with a worm teeth part 11 constituting a major part of the worm shaft 1, ball bearings 3 and 3' to support the worm shaft 1 at its ends, a housing 6 to accommodate the ball bearings 3 and 3' and a worm-and-wheel mechanism consisting of the work teeth part 11 and wheel gear 2, and a preloading nut 8 to give a preload to the ball bearings 3 and 3'. The outer rings of the bearings are arranged not approaching each other while the inner rings can approach each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus, and more particularly to a mounting structure of a worm shaft forming a power assist portion.

[0002]

2. Description of the Related Art In general, a worm wheel mechanism is used in an electric power steering apparatus having a power assist unit mainly composed of an electric motor. By employing such a worm wheel mechanism, the power from the electric motor can be transmitted to the steering device in a greatly amplified state, and the road surface reaction force (kickback force) from the steered wheels can be transmitted to the steering device. Transmission to the wheel side can be prevented. By the way, in the worm wheel mechanism of the electric power steering apparatus having such a configuration, the backlash between the worm shaft and the wheel gear is set to a predetermined value in order to secure a predetermined steering feeling during power assist. It is necessary to keep it below. For this reason, a predetermined preload is applied between the two ball bearings supporting the ends of the worm shaft on which the worm is provided, thereby eliminating the backlash of each ball bearing and the axis of the worm shaft. It keeps in the state where play in the direction is lost.

[0003]

As an example of a method of applying a preload to the worm shaft supporting ball bearing in the worm wheel mechanism of the electric power steering apparatus, Utility Model Registration No. 2566 is used.
No. 355 is already known. However, in this known device, a preload is applied to the outer ring side of a ball bearing that supports both ends of a worm shaft. Therefore, in this device, the stepped portion for positioning (fixing) the inner rings of the ball bearings supporting the worm shaft in the axial direction is provided outside the worm tooth portion having a predetermined length. To be provided. As a result, the mounting span of the ball bearing that supports the worm shaft must be longer overall,
There is a problem that the entire structure of the power assist unit having such a worm wheel mechanism must be enlarged. Further, in this case, in order to apply a preload, a spacer for pressing the outer ring, a male screw bolt for pressing the spacer, a lock nut for fixing the male screw bolt, and the like are required, and the number of parts as a whole is not increased. Not get. Therefore, the cost of the entire apparatus increases. In order to solve such a problem, an electric power steering system in which a preload for adjusting the backlash in the worm wheel mechanism is applied to the inner ring side of both ball bearings for supporting the worm shaft. It is an object of the present invention to provide a device.

[0004]

Means for Solving the Problems In order to solve the above problems, the present invention takes the following measures. That is, in the invention according to claim 1, an electric type having a power assist unit including a wheel gear connected to the steering shaft, a worm shaft meshingly engaged with the wheel gear, an electric motor driving the worm shaft, and the like. With respect to the power steering device, both ends of the worm shaft forming the power assist portion are supported by ball bearings, and respective outer rings forming these ball bearings are accommodated in the worm shaft and the wheel gear. Inside the housing
These two outer rings are installed so that they do not approach each other in the axial direction.In addition, the inner ring of the ball bearing is installed on the worm shaft, and a predetermined preload is set based on the operation of the preload applying means. A configuration is adopted in which the unit is installed so that it can approach each other in the axial direction while holding it.

[0005] By adopting such a configuration, the present invention has the following effects. That is, in a state where the wheel gear and the worm shaft are installed in a predetermined housing, by operating the preload applying means (see FIG. 1), a predetermined preload is applied to both ball bearings,
In such a state, the relative positional relationship between the worm shaft and the wheel gear is fixed. As a result, the worm shaft and the wheel gear are assembled while maintaining a predetermined backlash.

According to the present invention, the ball bearing for supporting the worm shaft is fixed in the axial direction by the outer ring shoulder. The inner ring mounted on the worm shaft is adapted to relatively move on the worm shaft. That is, the worm shaft to which the inner ring is attached is not provided with a step for fixing the inner ring. As a result, the attachment span of the inner race is set to a value excluding the step portion, that is, a value as close as possible to the length of the portion forming the worm tooth portion. Therefore,
The mounting span of the ball bearing supporting the worm shaft can be shortened as compared with the conventional one. By shortening the mounting span of the ball bearing, it is possible to reduce the size and weight of the entire structure of the power assist section, including the housing for housing the worm wheel mechanism.

Next, the invention according to claim 2 will be described. This is also basically the same as the first aspect. The feature is the claim 1
In the electric power steering apparatus described above, the outer rings of the two ball bearings supporting the worm shaft are engaged with the steps provided in the housing, whereby the outer rings approach each other in the axial direction. That is, the configuration is such that there is no problem. By adopting such a configuration, also in the present invention, it is possible to reduce the size and weight of the entire structure as in the case of the first aspect.

Next, the invention according to claim 3 will be described. This is also basically the same as the first aspect. The feature is the claim 1
In the electric power steering apparatus described above, a spacer is provided between the outer rings of the ball bearings, thereby adopting a configuration in which the outer rings do not approach each other in the axial direction. . By adopting such a configuration, the device of the present invention basically exhibits the same operation as that of the first aspect. That is, the mounting span of the ball bearing that supports the worm shaft is shortened, and the size and weight of the entire device can be reduced.
In addition to the above, according to the present invention, the machining of the mounting holes for holding the outer race of the ball bearing is simplified. That is, in the present invention,
The step provided for fixing the shoulder of the outer ring is eliminated, and a spacer is provided between the outer rings instead. By adopting such a configuration, it has been necessary to drill mounting holes from both sides with the center position adjusted in the past, but it is now necessary to drill straight holes only from one direction. ,
This makes it possible to simplify the processing steps and reduce the manufacturing cost.

Next, the invention according to claim 4 will be described. In this case, the preload applying means is screwed to an end of the worm shaft, and the preload applying means is connected to one of the two ball bearings. However, it has a configuration in which it is constituted by a preload nut that operates to press the inner ring. By adopting such a configuration, in the present invention, adjustment of the preload and the like can be performed by appropriately tightening the preload nut, and adjustment of the preload by a simple operation, and further, The backlash adjustment and the like are performed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. Although it relates to the present embodiment, as shown in FIG. 1, the configuration is such that a worm shaft 1 receiving power from an electric motor 4 and a portion of a worm tooth portion 11 forming a main part of the worm shaft 1 are meshed and engaged. A wheel gear 2 attached to a steering shaft 5, ball bearings 3 and 3 'for supporting both ends of the worm shaft 1, and ball bearings 3 and 3' and worm teeth. A housing 6 for accommodating a worm / wheel mechanism comprising a portion 11 and a wheel gear 2;
And a preload nut 8 which is a preload applying means for applying a preload to the nut. The power assist unit 99 having such a configuration is incorporated in a part of the steering device as shown in FIG. Specifically, the steering wheel 5
The wheel gear 2 is attached to a part of the steering shaft 5 connected to the worm shaft 5, and a worm shaft 1 having a worm tooth portion 11 that meshes with and engages with the wheel gear 2 is provided. The electric motor 4 is connected. By providing such a power assist unit 99 in a part of the steering device, an electric power steering device is formed.

As shown in FIGS. 1 and 2, the worm shaft 1 has the worm teeth 11 interposed therebetween and has ball bearings 3 and 3 at both ends. 'Is to be supported. The ball bearings 3 and 3 'have inner rings 31, 31' and outer rings 32, 32 '.
And balls 33, 33 'installed between these inner and outer rings. Further, the ball bearings 3, 3 'having such a configuration are further provided.
As shown in FIG. 1, the outer races 32, 32 'forming shoulders engage the shoulders 62, 62' of the stepped holes formed in the housing 6 at their shoulders, so that they can approach each other in the axial direction. Is to be prevented. Also, balls 33, 33 'are interposed between the outer rings 32, 32'.
Inner ring 31, 31 'forming a bearing through the
Are arranged at both ends of the worm shaft 1 with the worm teeth 11 interposed therebetween. As shown in FIG. 1 and FIG. 2, one of the inner races 31 has a circlip 17 at the shoulder thereof.
At the same time, the movement in the axial direction (the direction moving away from the other inner ring 31 ′) is restricted.
The other inner ring 31 'is provided with a preload nut 8 serving as a preload applying means.
Is mounted so as to be able to slide on the worm shaft 1 and move in the axial direction (the direction approaching the one inner ring 31) by the tightening operation described above. That is,
By such a tightening operation of the preload nut 8, a predetermined preload is applied between the two ball bearings 3, 3 '.

Incidentally, such a ball bearing 3,
When the outer ring 3 ′ is mounted in the housing 6 of the outer ring 3 ′,
As for the fixing method of 2, 32 ', another method as shown in FIG. 2 is also conceivable. In this case, as shown in FIG. 2, a straight hole having no step is provided in the housing 6 for housing the worm shaft 1, and one of the ball bearings 3 is provided in the innermost portion. A groove for installing the circlip 67 for fixing the outer ring 32 is provided. That is, the steps 62, 6 in FIG.
2 'is eliminated to simplify the hole drilling process. The outer rings 32, 32 'of the two ball bearings 3, 3' are installed at the processing holes for storing the worm shaft 1 having such a configuration.
2 and 32 ', a distance piece 7 as a spacer having a C-shaped cross section (see FIG. 3) as shown in FIGS. 2 and 3 is provided. A circlip 67 is provided for fixing the shoulder of the outer ring 32 to be formed, thereby positioning the outer rings 32 and 32 '. This is the same as that shown in FIG. 1 in other respects. In FIG. 2, by tightening the preload nut 8, the inner races 31 and 31 'come close to each other, thereby A predetermined preload is applied between 3 ′. In this state, the positions of the ball bearings 3 and 3 ′, that is, the relative positional relationship of the worm teeth 11 forming the worm shaft 1 with respect to the wheel gear 2 are also restricted.

Next, the operation and the like of the embodiment having the above-described configuration will be described. That is, in a state where the wheel gear 2, the worm shaft 1, the ball bearings 3, 3 'and the like are installed in the housing 6 by a predetermined procedure, the preload nut 8 provided at the tip of the worm shaft 1 is tightened. Then,
First, the inner ring 31 'of the ball bearing 3' on the other side (adjacent to the preload nut 8) moves on the worm shaft 1 in the direction of the inner ring 31 of the ball bearing 3 on the other side (adjacent to the circlip 17). Slide. As a result, the outer ring 32 'is pressed via the ball 33', and as a result, the play of the ball bearing 3 'is removed. When the preload nut 8 is further tightened in this state, the inner ring 31 'and the worm shaft 1 slide, and the worm shaft 1 is pulled rightward in FIGS. As a result, the inner ring 31 of the ball bearing 3 moves together with the worm shaft 1 and the circlip 17 so as to relatively approach the inner ring 31 '. As a result, the outer ring 32 is pressed via the ball 33, and the play of the ball bearing 3 is removed. By these series of operations, a predetermined preload is applied to both the ball bearings 3 and 3 'shown in FIGS. Further, in such a state, the relative positional relationship of the worm tooth portion 11 provided on the worm shaft 1 with respect to the wheel gear 2 is also fixed. As a result, the worm shaft 1 and the worm teeth 11 and the wheel gear 2 are fixed in a state where a predetermined backlash is maintained.

In this embodiment having such a mounting structure, in the present embodiment, the ball bearings 3, 3 'supporting the worm shaft 1 are fixed in the axial direction by the outer races 32, 32'. Inner rings 31 and 3 attached to the worm shaft 1 are formed by shoulders.
Numeral 1 'is adapted to relatively move on the worm shaft 1. That is, in the place of the worm shaft 1 to which the inner rings 31, 31 'are attached, the inner rings 31, 31'
There is no step provided for fixing. as a result,
The attachment span of the inner rings 31, 31 'has a length excluding the step, that is, a value as close as possible to the length of the portion forming the worm teeth 11. Thus, the mounting span of the ball bearings 3, 3 'supporting the worm shaft 1 is formed shorter than that of the conventional one. By shortening the mounting span of the ball bearings 3 and 3 ′, the entire structure of the power assist unit 99 including the housing 6 that houses the worm wheel mechanism can be downsized. The weight of the entire device can be reduced.

Further, in the arrangement in which the distance piece 7 is provided between the two ball bearings 3 and 3 ', the steps 62 and 62' provided for fixing the shoulders of the outer races 32 and 32 'are eliminated. Instead, a collar-shaped distance piece 7 is provided between the outer rings 32 and 32 ', and one end of the distance piece 7 is connected to the housing 6 by a circlip 67 via the outer ring 32 of a ball bearing. It is fixed. Therefore, in this case, it is not necessary to machine the stepped holes from both sides with the center position aligned,
The processing steps can be simplified. As a result, manufacturing costs can be reduced. In addition, since processing from one direction is sufficient, concentricity of the two ball bearings 3 and 3 'can be easily ensured.

[0016]

According to the present invention, as a means for applying a predetermined preload between the two ball bearings supporting the worm shaft, the arrangement is such that the inner rings of the respective ball bearings are brought closer to each other. Therefore, the mounting span between the ball bearings supporting the worm shaft is shortened, and the entire structure of the power assist unit including the housing for housing the worm wheel mechanism can be downsized. It became so.
As a result, the weight of the entire device can be reduced.

Further, in the case where a spacer is provided between the two ball bearings, there is no stepped hole provided for fixing the shoulder portion of the outer ring, so that the manufacturing cost can be reduced. Now you can. That is, instead of processing the stepped holes from both sides with the center position aligned, it is only necessary to perform straight hole processing from only one direction, and the processing steps can be simplified. Was. Furthermore, since a configuration is adopted in which the preload is applied only by tightening the preload nut, the number of parts is reduced and the structure is simplified. As a result, it has become possible to reduce the manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing the overall configuration of the present invention.

FIG. 2 is a vertical cross-sectional view showing an entire configuration of a device provided with a distance piece according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a cross-sectional shape of a distance piece that is a spacer.

FIG. 4 is a diagram showing a configuration of an entire steering device having a power assist unit according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 worm shaft 11 worm tooth part 17 circlip 2 wheel gear 3 ball bearing 3 'ball bearing 31 inner ring 31' inner ring 32 outer ring 32 'outer ring 33 ball 33' ball 4 electric motor 5 steering shaft 55 steering wheel 6 housing 62 step 62 '' Step 67 circlip 7 distance piece (spacer) 8 preload nut (preload applying means) 99 power assist

Claims (4)

[Claims] 1. An electric power steering apparatus comprising a wheel gear connected to a steering shaft, a worm shaft meshingly engaged with the wheel gear, an electric motor for driving the worm shaft, and the like. Both ends of the worm shaft forming the power assist portion are supported by ball bearings, and respective outer rings forming these ball bearings are placed in a housing in which the worm shaft and the wheel gear are housed. The two outer rings were installed so as not to approach each other in the axial direction, the inner ring of the ball bearing was installed on the worm shaft, and a predetermined preload was maintained based on the operation of the preload applying means. It was decided to install so that it could approach each other in the axial direction in the state An electric power steering device having a configuration. 2. The electric power steering apparatus according to claim 1, wherein the two outer rings of the ball bearing engage with step portions formed in the housing, respectively, and the two outer rings approach each other in the axial direction. An electric power steering apparatus characterized by having a configuration in which no problem is caused. 3. The electric power steering apparatus according to claim 1, wherein a spacer is provided between both outer rings of the ball bearing so that the outer rings do not approach each other in the axial direction. An electric power steering device having a configuration. 4. The electric power steering apparatus according to claim 1, wherein the preload applying means comprises:
An electric power steering device, which is screw-connected to an end of the worm shaft, and comprises a preload nut for pressing an inner ring of one of the ball bearings.