JP2000313347A - Manufacture of electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an electric power steering device capable of carrying out a measurement of parts further simply and at a high accuracy. SOLUTION: A predetermined dimension relationship is established between an outer diameter surface 103b and a tooth surface 103c by machining the outer diameter surface 103b and the tooth surface 103c of a worm gear 103a using single formed tool T. Accordingly, a tooth surface shape can be presumed at a high accuracy by measuring the outer diameter surface 103b which can be generally measured relatively simply and at a high accuracy without directly measuring the tooth surface 103c of the worm gear which is conventionally difficultly measured. Thereby, a management of a back-lash of the worm gear 103a and a worm wheel, for example, can be severely carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electric power steering apparatus, and more particularly to a method for manufacturing a worm gear of a speed reducer used in an electric power steering apparatus.

[0002]

2. Description of the Related Art As an electric power steering apparatus for a vehicle, the rotational output of an electric motor, which is an auxiliary steering torque, is reduced by a worm gear mechanism and transmitted to an output shaft of the steering mechanism, and a steering force applied to a steering wheel is transmitted. An arrangement for assisting the steering of the wheels is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-309449.

By the way, taking the worm gear mechanism provided in such an electric power steering apparatus as an example, in order to ensure the smooth transmission of the rotational output, a certain value or more is required between the worm gear and the worm wheel. Backlash needs to be set. On the other hand, if the backlash is large, for example, vibrations caused by kickback of the wheels cause repeated contact between the worm gear and the teeth of the worm wheel, thereby generating a continuous fine vibration sound (tooth rattling sound). Might be. Such rattling noises may enter the passenger compartment of the vehicle provided with the electric power steering device, and may cause occupants to feel uncomfortable.
Therefore, the backlash between the worm gear and the worm wheel falls within a relatively narrow tolerance range by accurately measuring the tooth surface shape and dimensions of each part of the worm gear and the worm wheel, and determining the optimal combination of parts. Strict management needs to be performed so that it can be accommodated.

[0004]

However, there is a problem that it is difficult to accurately measure the tooth surface shape of the worm gear. For example, the accuracy of the tooth surface of a worm gear is usually measured by three needles using three inspection pins.
In such a three-needle measurement, there is a problem that the skill of a measurer is required in order to accurately obtain a value down to a micron unit.
On the other hand, in order to ensure the stability of measurement accuracy, there is a thought that a system that can automatically perform three-needle measurement may be constructed, but the whole system becomes large-scale,
The costs are huge.

Further, the variation of the backlash between the worm gear and the worm wheel tends to increase or decrease according to the accuracy (shape, surface roughness, size, etc.) of the tooth surface. However, the accuracy of the outer diameter surface of the worm gear is not particularly related to the variation of the backlash, and therefore, in order to reduce the cost, the outer diameter surface of the worm gear used for the electric power steering device is usually finished. There is the fact that we do not go.

Accordingly, an object of the present invention is to provide a method of manufacturing an electric power steering apparatus capable of measuring components more easily and accurately than in the prior art.

[0007]

In order to achieve the above object, a method of manufacturing an electric power steering apparatus according to the present invention is an electric power steering apparatus for transmitting an output of an electric motor via a speed reducer including a worm gear and a worm wheel. A method of manufacturing a power steering apparatus, wherein an outer diameter surface and a tooth surface of the worm gear are machined using a single tool, so that a predetermined dimension is provided between the outer diameter surface and the tooth surface. The relationship is established.

[0008]

According to the method of manufacturing the electric power steering apparatus of the present invention, the outer diameter surface and the tooth surface of the worm gear are
By processing with a single tool, a predetermined dimensional relationship is established between the outer diameter surface and the tooth surface, so that measurement can be performed relatively easily and accurately in general. By measuring the outer diameter surface, it is possible to accurately estimate the tooth surface shape without directly measuring the tooth surface of the worm gear, which has been conventionally difficult, and thereby, for example, the back surface between the worm gear and the worm wheel can be used. Management such as rush can be performed more strictly. The single tool used here means that it is sufficient to be able to simultaneously machine the outer diameter surface and the tooth surface, so it is not always necessary to be integrated, for example, even if it is a separate body except during processing good.

[0009] When the tool is used as a finishing tool, there is an advantage that only a single tool is required for finishing, and the conventional machining process is not largely changed.

[0010] Further, the tool has a first machining portion for machining an outer diameter surface of the worm gear, and a second machining portion for machining the tooth surface.
If an arc-shaped third machining portion for machining and forming a chamfered portion is provided between the machining portion and the machining portion, the chamfer between the outer diameter surface of the worm gear and the tooth surface can be made into an R-shape. Burrs, sharp edges, and the like can be prevented from being formed at the tip of the tooth.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an electric power steering apparatus 100 according to an embodiment of the present invention.
3 is a partial cross-sectional view in the axial direction of FIG. FIG. 2 shows the configuration of FIG.
It is the figure cut | disconnected by I-II line and seen in the arrow direction.

Referring to FIG. 1, an electric power steering apparatus 100 has a housing 101 and a tube 110 extending therefrom. The housing 101 is fixed to a vehicle body (not shown) by a bracket 114, and the tube 110 is fixed to a vehicle body (not shown) by a bracket 115.
Inside the tube 110 is an input shaft 11 adapted to connect the upper end to a steering wheel (not shown)
1 extends and is rotatably supported with respect to the tube 110. The other end of the input shaft 111 is connected to a torque detecting device (measuring device) 112 which is a detecting means.

The torque detecting device 112 also extends in the housing 101, and is supported by the rotating shaft.
13. The output shaft 113 is engaged with a rack shaft connected to a steering device (not shown) to transmit torque for steering wheels. Torque detector 1
Numeral 12 detects a relative (steering) torque acting between the input shaft 111 and the output shaft 113.

A worm wheel 104 is coaxially mounted on the output shaft 113 near the torque detecting device 112. The worm wheel 104 meshes with a worm gear 103a of the speed reducer input shaft 103 extending in the direction perpendicular to the plane of the drawing of FIG. Reducer input shaft 10
Reference numeral 3 is connected to a rotation shaft (not shown) of the motor 102. The worm wheel 104 and the worm gear 103a form a power transmission mechanism.

In FIG. 2, a speed reducer input shaft 103 is rotatably supported by a housing 101 by bearings 106 and 107.

The operation of the electric power steering apparatus 100 shown in FIG. 1 will be described below. The input shaft 111 rotates in response to the input of a steering torque from a steering wheel (not shown), and the rotation torque is transmitted to the output shaft 113 via the torsion bar 121 of the torque detection device 112. The output shaft 113 is connected to a steering device (not shown) as described above. In this case, the value of the torque detected by the torque detection device 112 is sent to a determination circuit (not shown), where it is compared with a predetermined value. If the torque exceeds a predetermined value, it means that an auxiliary steering force is required, so that a drive command corresponding to the detected torque is issued to drive the motor 102. The motor 102 driven by the drive command causes the reduction gear input shaft 103 to rotate at a predetermined rotational torque.
, And the rotation torque is transmitted to the output shaft 113 via the worm wheel 104.

On the other hand, when the value of the torque detected by the torque detecting device 112 is lower than a predetermined value, the auxiliary steering force is unnecessary, and the motor 102 is not driven.

As shown in FIG. 2, the backlash between the worm wheel 104 and the worm gear 103a is caused by the worm wheel 104 and the worm gear 10a.
3a, the output shaft 113 and the speed reducer input shaft 103
And the distance between the axes. Therefore, in order to manage such backlash, the distance between the shaft between the output shaft 113 and the reducer input shaft 103 and the worm wheel 104
It is necessary to accurately measure the tooth surface shape of the worm gear 103a. Here, the output shaft 113 and the speed reducer input shaft 103
And the tooth flank shape of the worm wheel 104 can be measured relatively easily. However, the tooth surface shape of the worm gear 103a is relatively difficult to measure according to the related art.

Therefore, in the present embodiment, the worm gear 103a is finished using a single forming tool. More specifically, the worm gear 103a is formed through, for example, a cutting process, a grinding process, a barrel process, and the like. In the present embodiment, the worm gear 103a is further formed by a finishing tool using a forming tool.
The outer diameter surface and the tooth surface of 3a are finished simultaneously.

FIG. 3 is a sectional view showing a part of the forming tool T together with the worm gear 103a to be machined.
The forming tool T has a shape substantially corresponding to the contour of the worm gear 103a, and has an outer diameter surface 10 of the worm gear 103a.
3b and a worm gear 103
A second processing portion Tb for processing the tooth surface 103c of FIG. 3A and an R-shaped third processing portion Tc for processing the chamfered portion 103d between the outer diameter surface 103b and the tooth surface 103c.

At the time of finishing, the forming tool T is brought close to the rough-processed worm gear 103a, so that the outer diameter surface 103b, the tooth surface 103c, and the chamfered portion 103d of the worm gear 103a can be finished at one time.

The worm gear 103 is formed by using the forming tool T.
a, the worm gear 103a
Of the tool T (for example, the angle between the first processing part Ta and the second processing part Tb,
The worm gear 1 has a known radius.
When the outer diameter surface 103b of the outer surface 03a is measured,
The shape of c can also be accurately estimated. The measurement of the outer diameter surface 103b is relatively easy.

Furthermore, if the distance between the shaft between the output shaft 113 and the reducer input shaft 103 and the tooth surface shape of the worm wheel 104, which are relatively easy to measure even in the prior art, are determined together, Outer diameter surface 10 of the worm gear 103a
The backlash between the worm wheel 104 and the worm gear 103a can be determined with a certain degree of accuracy, based on the tooth surface shape of the worm gear 103a obtained based on the measured value of 3b. Therefore, such backlash adjustment can be performed relatively easily by changing the combination of parts.

When the outer diameter of the worm gear is measured and the backlash is found to be small,
Perform feedback processing to finish the required amount again, or if it is found that backlash is large, select a worm wheel with a large tooth thickness by the corresponding amount from among the measured values in advance. In addition, it is easy to automate the assembly process of the electric power steering device, and the cost can be reduced.

In addition, the tip of the worm gear is often formed with burrs, sharp edges, and chamfers for improving the meshing property. However, according to this embodiment, it is possible to form up to the chamfer at the same time as finishing. Since there is no step between the rough processing part and the finishing processing part, it is possible to manufacture a worm gear having a highly accurate shape. Further, if the chamfered portion has an R (arc) shape, a sharp edge is not formed at the boundary between the tooth surface of the worm gear and the chamfered portion, and the meshing property is further improved.

As described above, the present invention has been described in detail with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and may be appropriately changed and modified without departing from the spirit of the present invention. Of course, it can be improved.

[0027]

According to the method for manufacturing the electric power steering apparatus of the present invention, the outer diameter surface and the tooth surface are processed by using a single tool to form the outer diameter surface and the tooth surface of the worm gear. Since a predetermined dimensional relationship is established between the worm gear and the surface of the worm gear, it is generally difficult to measure the outer diameter surface, which can be measured relatively easily and with high accuracy. The tooth surface shape can be accurately estimated without directly measuring the worm gear, thereby making it possible to more strictly manage, for example, the backlash between the worm gear and the worm wheel.

[Brief description of the drawings]

FIG. 1 is an axial partial cross-sectional view of an electric power steering apparatus including a rack shaft according to an embodiment.

FIG. 2 is a view of the configuration of FIG. 1 cut along a line II-II and viewed in a direction of an arrow.

FIG. 3 is a cross-sectional view showing a part of a forming tool T together with a worm gear 103a to be machined.

[Explanation of symbols]

 Reference Signs List 101 Housing 103 Reducer input shaft 103a Worm gear 104 Worm wheel 113 Output shaft T Form tool

Claims (3)

[Claims] 1. A method of manufacturing an electric power steering device for transmitting an output of an electric motor through a speed reducer including a worm gear and a worm wheel, wherein the outer diameter surface and the tooth surface of the worm gear are A method for manufacturing an electric power steering device, wherein a predetermined dimensional relationship is established between the outer diameter surface and the tooth surface by machining with a tool. 2. The method according to claim 1, wherein the tool is a finishing tool. 3. The tool according to claim 1, wherein the tool has a circular arc-shaped third processing portion for forming a chamfered portion between a first processing portion for processing an outer diameter surface of the worm gear and a second processing portion for processing the tooth surface. The method for manufacturing an electric power steering device according to claim 1 or 2, further comprising a processing portion.