JP2002193119A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of precisely measuring a characteristic of a motor unit and reducing an opening end of a rack housing in diameter. SOLUTION: One end side (pinion shaft 17 side) of a motor shaft 18 is supported by a first bearing 21 provided between a motor housing 14 and the first rack housing 12. The other end side is constituted to be supported by the motor housing 14 by the second bearing 20.

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 device.

[0002]

2. Description of the Related Art Various types of steering devices for automobiles have been put into practical use.
There is a pinion type steering device. In this method, a rack shaft having rack teeth formed along a predetermined length in the axial direction is extended in the left-right direction of the vehicle body, and both ends of the rack shaft are steered through tie rods (front wheels). ). Further, a pinion shaft meshing with the rack shaft is connected to a steering wheel via a column shaft. Then, the rotation of the pinion shaft according to the steering operation is transmitted to the rack shaft, and the rack shaft moves in the axial direction within the range of the formation length of the rack teeth to change the direction of the steering wheel. In this case, the steering is changed.

When such a rack-and-pinion type steering device is configured as an electric power steering device, the rotation of a steering assist motor is directly transmitted to the rack shaft, and the rack shaft is moved in the axial direction. It is reasonable to adopt a configuration that allows for this. For this purpose, a mechanism for converting the rotation of the motor into a linear motion for moving the rack shaft is necessary.In this motion conversion mechanism, the output of the motor may be accompanied by a predetermined deceleration in the process of motion conversion. desirable. As a motion conversion mechanism that can meet such demands, for example, an electric power steering device using a ball screw structure has been conventionally proposed.

In this electric power steering apparatus, a helical ball screw groove is formed in a part of an outer periphery of a rack shaft (a part different from a formation area of a rack tooth), and a hollow cylindrical housing for supporting the rack shaft is formed. Inside,
A ball screw nut is supported rotatably coaxially with the rack shaft. A large number of balls are interposed between the ball screw nut and the ball screw groove to form a ball screw structure. Then, the electric power steering apparatus drives the ball screw nut to rotate by transmission from a steering assist motor, and
The rack shaft is transmitted via a number of balls rolling along the ball screw groove, the rack shaft is moved in the axial direction, and the above-described steering is assisted in accordance with a steering operation. At this time, the rotation of the steering assist motor is greatly reduced according to the lead angle of the ball screw groove, and is converted into the movement of the rack shaft.

In the above electric power steering apparatus, the outer diameter of the ball screw nut is larger than the outer diameter of the rack shaft. In addition, since the rack housing has a structure in which the axial displacement of the rack shaft is restricted and sealed at the opening end of the rack housing, the inner diameter of the rack housing opening end is smaller than the outer diameter of the ball screw nut. I have. Measurement of motor characteristics in this configuration
Since measurement cannot be performed by the motor alone, a measuring device is connected to a rack shaft, which is an output shaft of the completed electric power steering device, and the thrust in the axial direction is measured.

[0006]

However, in the above-described measuring method, the measurement is performed using the rack shaft via the ball screw structure, and the characteristics of the ball screw structure and the processing error of the rack shaft are included. .

To measure the characteristics of the motor alone,
Measure the characteristics of the ball screw structure and the rack shaft in advance, or measure by assembling a temporary rack housing (measurement jig) with the ball screw structure incorporated before the housing is assembled. The measurement jig had to be removed after the measurement.

In any case, there is a concern that the characteristics of the motor alone cannot be measured accurately. It is an object of the present invention to provide an electric power steering device capable of accurately measuring the characteristics of a single motor in view of the above circumstances.

[0009]

According to one aspect of the present invention, there is provided an electric power steering apparatus.
In the invention described in the above, a rack shaft having a ball screw groove of a ball screw structure is inserted and arranged along the axial direction of the motor shaft of the motor formed in a hollow cylindrical shape,
A motor housing that covers the motor shaft with a ball screw nut having a ball screw structure interposed between the motor shaft and the rack shaft; and a plurality of rack housings that are coaxially coupled to both ends of the motor housing and cover the rack shaft. , Wherein both ends of the motor shaft are supported by bearings provided at both ends of the motor housing.

[0010] Further, the invention of claim 2 of the present application is the above-described claim 1.
In the invention described in (1), the bearing that supports one end of the motor shaft is fitted inside the motor housing and also fitted inside the rack housing.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment in which the present invention is embodied in an electric power steering apparatus will be described in detail with reference to FIGS.

FIG. 1 shows an electric power steering device 11. A hollow cylindrical first rack housing 12, a hollow cylindrical second rack housing 13, and a hollow cylindrical motor housing 14 coaxially coupled to the two rack housings are attached to a body of a vehicle body (not shown). It is screwed and supported via a mounting portion 15 formed in one rack housing 12.

A rack shaft 16 is built in a cylindrical body composed of the first rack housing 12, the second rack housing 13, and the motor housing 14 so as to be non-rotatable and movable in the axial direction.
The left and right front wheels are connected via tie rods (not shown) connected to both ends of the front wheel. The rack shaft 16 is connected to a steering wheel (not shown) via a pinion shaft 17 provided in the first rack housing 12. Rack shaft 16 and pinion shaft 17
A meshing portion (not shown) of the rack-and-pinion mechanism is formed between them. Note that the motor housing 14 also functions as a rack housing of the electric power steering device.

Next, a description will be given with reference to FIG. A stator 19 on which a winding is applied is fitted on the inner periphery of the motor housing 14, and a motor shaft 18 is coaxially disposed outside the rack shaft 16 in a hollow cylindrical shape at an intermediate portion of the rack shaft 16 in the axial direction. It is fitted.

The motor shaft 18 has a fitting step 18c formed at one end side (pinion shaft 17 side), and the fitting step 18c is connected to the motor housing 14 via a first bearing 21 as a bearing. 1 rack housing 1
2 supported. The first bearing 21
Are fitted and fixed to a first fitting step 14a and a fitting step 12a formed so as to go around the inner peripheral surface of the end of the motor housing 14 and the inner peripheral surface of the end of the first rack housing 12, respectively. ing.

The first bearing 21 is fixed to the motor shaft 18 by being pressed in the axial direction by being tightened by a first lock nut 22 screwed to the end of the motor shaft 18. A permanent magnet 27 is externally fixed to the motor shaft 18.

The motor housing 14 is connected to a first rack housing 1 by a first contact portion 14c provided at an end.
2 are in contact with each other at a contact portion 12b provided at the end, and a fixing screw 24 inserted through the contact portion 12b
By screwing to the contact portion 14c, both are fixed to the fixing screw 2
4, they are fastened and connected to each other. A thin packing 23 is interposed on the mating surface between the first contact portion 14c and the contact portion 12b. The packing 23 allows the motor housing 14 and the first rack housing 1
Intrusion of liquids such as water and oil from the fitting portion with the inside 2 is prevented. With this configuration, the motor housing 14 and the first
The rack housing 12 and the first bearing 21 are fitted at one place. Further, a first bearing 21 fitted inside the motor housing 14 and the first rack housing 12 is provided.
, The movement of the motor shaft 18 in the axial direction is restricted.

The other end of the motor shaft 18 (opposite to the pinion shaft 17) is integrally formed with a hollow cylindrical nut holding portion 18a having a diameter larger than that of an intermediate portion. Further, on the inner peripheral surface on the other end side of the motor housing 14,
The orbiting second fitting step 14b is formed. The motor shaft 18 has a nut holding portion 18a
It is rotatably supported around its own axis by being internally fitted to a second bearing 20 as a bearing internally fitted and fixed to the fitting step portion 14b. The second bearing 20 is configured to be movable in the axial direction between the second fitting step 14b of the motor housing 14 and the end 13a of the second rack housing 13.

The end 13a of the second rack housing 13
The abutment portion 13 is fitted inside the motor housing 14 and extended from the outer peripheral surface of the end portion 13a.
b is in contact with the end surface of the second contact portion 14d of the motor housing 14. Then, the motor housing 14 and the second rack housing 13 are fastened and connected to each other by the fixing screw 25 by screwing the fixing screw 25 into which the contact portion 13b is inserted to the second contact portion 14d.

End 1 Internally Fitted in Motor Housing 14
A peripheral groove 13d is formed on the outer peripheral surface of the peripheral groove 3a.
An O-ring 29 is fitted in 3d. And
The O-ring 29 prevents liquid such as water or oil from entering the inside from the fitting portion between the motor housing 14 and the second rack housing 13.

The motor housing 14 and the motor shaft 18 are connected to the first bearing 21 and the second bearing 2.
With 0, the coaxiality is configured with high accuracy. With the above configuration, both ends of the motor shaft 18 are supported by the first bearing 21 and the second bearing 20 provided at both ends of the motor housing 14.

The nut holding portion 18a of the motor shaft 18
A ball screw nut 26 is coaxially fitted therein. The ball screw nut 26 has a nut holding portion 18a.
The second lock nut 28 is screwed into the inside in a state of being fitted inside, so that the second lock nut 28 is locked and secured.

The outer peripheral surface of the rack shaft 16 is provided with a helical ball screw groove 16a in a predetermined range in the axial direction. A helical ball screw groove 26 a is provided on the inner peripheral surface of the ball screw nut 26, and the ball screw groove 16 a
A number of balls (not shown) are rollably received between the ball screw groove 26a and the ball screw groove 26a. As described above, the ball screw groove 16 a of the rack shaft 16 and the ball screw nut 26 form a ball screw mechanism having a ball screw structure. Then, by this ball screw mechanism, the rotational torque of the forward / reverse rotation of the motor shaft 18 is converted into the assisting force of the reciprocating motion of the rack shaft 16 in the axial direction,
The steering force of a steering wheel (not shown) connected to the pinion shaft 17 is reduced.

Next, a method for assembling the electric power steering apparatus and a method for measuring the characteristics of the motor alone according to the present embodiment will be described. The stator 19 on which the winding is applied is fitted on the inner peripheral surface of the motor housing 14, and the second bearing 20 is press-fitted into the second fitting step 14 b of the motor housing 14.

The first bearing 21 is pressed into the fitting step 18c of the motor shaft 18, and the first lock nut 22 is screwed into the fitting step 18c.
To prevent it from falling off.

Next, the stator 19 and the second bearing 20
The motor shaft 18 having the first bearing 21 externally fitted therein is fitted into the motor housing 14 in which the first bearing 21 is internally fitted along the axial direction from the end opening on the first rack housing 12 side.

Then, the first bearing 21 externally fitted to the motor shaft 18 is fitted into the first fitting step portion 14a of the motor housing 14, and positioning of the motor shaft 18 in the axial direction and the radial direction is performed. Also, on the nut holding portion 18a side, the outer peripheral surface 18b of the nut holding portion 18a and the inner peripheral surface of the second bearing 20 are press-fitted and supported by fitting.

Since the motor is configured to obtain the driving force through the above steps, the characteristics of the motor alone can be measured. Measurement of the characteristics of the motor alone
Is fixed by a jig, the motor shaft 18 is connected to the measuring instrument via the jig, and the winding provided on the stator 19 is energized.

After measuring the characteristics of the motor alone, the jig and the measuring device are removed, and the following assembly is performed. The rack shaft 16 has a ball screw mechanism (ball nut 26) in advance.
And the balls) are assembled, and the rack shaft 16 to which the ball screw mechanism is assembled is inserted and arranged in the motor shaft 18 from the nut holding portion 18a side. Then, the ball screw nut 26 of the ball screw mechanism is fixed in the nut holding portion 18a by the second lock nut 28.

After that, the first rack housing 12 is fitted to the side surface and a part of the outer peripheral surface of the first bearing 21 at the fitting step 12a, and the fixing screw 24 is fitted to the first contact portion 14.
c, the motor housing 14
Connect with

Next, an O-ring 29 is fitted in the circumferential groove 13d of the second rack housing 13. Then, the second rack housing 13 is connected to the motor housing 14 at its end.
After that, the fixing screw 25 is screwed into the second contact portion 14d to be connected to the motor housing 14.

With the above, the assembly of the electric power steering apparatus and the measurement of the characteristics of the motor alone according to the first embodiment of the present invention are completed. In the first embodiment, the following effects can be obtained by configuring the electric power steering apparatus as described above. (1) In the present embodiment, the motor is configured to obtain a driving force without assembling the first rack housing 12, the second rack housing 13, and the ball screw mechanism. Therefore, the characteristics of the motor alone can be accurately measured without including the characteristics of the ball screw mechanism and the processing error of the rack shaft 16, and the two rack housings 12 and 13 can be accurately measured.
Since it is not necessary to assemble the motor, the weight of the motor alone is reduced, and the characteristic measurement can be efficiently and easily performed.

Further, it is not necessary to measure the characteristics of the ball screw mechanism and the rack shaft 16 in advance.
First rack housing 12 and second rack housing 13
Before assembling, a temporary motor housing (measurement jig) corresponding to the motor housing 14 is attached to the stator 1.
It is no longer necessary to attach it to the outer periphery of 9 and measure it. Further, after the measurement, it is not necessary to go through a complicated process of having to remove the measuring jig.

Furthermore, unlike the related art, there is no need to insert a measuring jig from the open end of the rack housing.
Since the opening end can be made small and the position of the motor is not affected by the axial length of the jig, the motor can be freely arranged in the motor housing 14.

Here, the conventional configuration will be described, and points different from the effect (1) will be described. For example, conventionally, a method disclosed in Japanese Patent Application Laid-Open No. 10-24852 has been known. The contents of the publication will be described using an electric power steering device 101 shown in FIG.

In the electric power steering apparatus 101, a motor shaft 102 of a motor is formed in a hollow cylindrical shape.
A rack shaft 103 is coaxially inserted into the motor shaft 102 so as to reciprocate in the axial direction. A ball screw groove 104 having a ball screw structure is formed in the rack shaft 103, and a ball screw nut 105 having the ball screw structure is coaxially provided at one axial end of the motor shaft 102. The motor shaft 10 of the motor housing 106
The inner diameter A of the portion extending from the portion surrounding the one end in the axial direction to the open end is larger than the outer diameter D of the ball screw nut 105.

In the electric power steering apparatus 101 configured as described above, a jig for measurement is inserted from the open end of the motor housing 106 when measuring the characteristics of the motor alone, so that the inner diameter of the open end of the motor housing 106 is measured. There is a restriction that A has a large diameter.

Further, when measuring the characteristics of the motor alone, it is necessary to assemble a rack housing 107 (corresponding to the first rack housing 12 in the first embodiment). Had been longer. Therefore, it is necessary to increase the measurement space when measuring, and furthermore, the rack housing 107
Because of this, there is a concern that the weight required for obtaining the motor characteristics becomes heavy, which makes the operation inconvenient, and that the efficiency of the characteristic measurement is deteriorated. (2) In the present embodiment, one end side (pinion shaft 17 side) of the motor shaft 18 is connected to the motor housing 14.
And the first rack housing 12 is supported by a first bearing 21 provided so as to fit inside. For this reason, the support accuracy and coaxiality of the motor shaft 18 by the motor housing 14 are improved, and the mounting accuracy and coaxiality between the motor housing 14 and the first rack housing 12 are improved, and cogging torque is reduced.

Here, the conventional configuration will be described, and points different from the effect (2) will be described. Conventionally, as shown in an electric power steering apparatus 101 in FIG. 4, one end of a motor shaft 102 has a bearing 108 externally fitted to the motor shaft 102, and the bearing 108 is mounted on a rack housing (in the first embodiment). (It corresponds to the first rack housing 12). The other end of the motor shaft 102 is supported by a motor housing 106 via a bearing 110.

The rack housing 107 is a rack housing 10 that abuts against an end face of the motor housing 106.
7 is connected to the motor housing 106 by screwing a fixing screw 109 to the contact portion 107a.

That is, conventionally, the motor shaft 102
Was supported by the rack housing 107 and the other end was supported by the motor housing 106. However, in the first embodiment, both ends of the motor shaft 18 are
It is directly supported on the motor housing 14. That is, another housing (first rack housing 12)
Single housing (motor housing 1
4), the stator 19 and the motor shaft 18 of the motor are mounted on a single housing, so that the mounting accuracy and coaxiality are improved.

(3) In the present embodiment, the first bearing 21 is the first fitting step 14a at the end of the motor housing 14.
And a fitting step 12 a at the end of the first rack housing 12. For this reason, the coaxial accuracy between the motor housing 14 and the first rack housing 12 is also ensured via the first bearing 21.

By ensuring the coaxial accuracy, the pinion shaft 17 provided in the first rack housing 12 is provided.
And the first and second bearings 2 on the motor housing 14.
1, 20, motor shaft 18 and ball screw nut 2
A proper positional relationship with the rack shaft 16 supported via the support 6, that is, a proper meshing state at a meshing portion (not shown) of the rack and pinion mechanism is ensured. For this reason, the operation of the rack and pinion mechanism becomes smooth, and a good steering feeling is obtained.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. In the first embodiment, one end of the motor shaft 18 (the pinion shaft 1
7) is supported by a first bearing 21 which is fitted between the motor housing 14 and the first rack housing 12. Instead of this configuration, the second embodiment differs from the first embodiment in that one end side (pinion shaft 17 side) of the motor shaft 18 is supported by a first bearing 52 fitted only to the motor housing 14.

Hereinafter, only the components different from those of the first embodiment will be described, and the same components as those of the first embodiment will be denoted by the same reference symbols in the drawings, without redundant description.

FIG. 3 shows an electric power steering apparatus 51 according to the second embodiment. One end side (pinion shaft 17 side) of the motor shaft 18 is formed with a fitting step 18d, and the fitting step 18d is used as a bearing internally fitted and fixed to the first fitting step 14f of the motor housing 14. The first bearing 52 is supported by fitting and fixing.
The first bearing 52 is attached by being pressed in the axial direction by a first lock nut 53 screwed to the outer peripheral surface of the motor shaft 18. Further, the first bearing 52
Is press-fitted with the third lock nut 54 fitted inside the motor housing 14 and pressed in the axial direction.

The fitting portion 12c at one end of the first rack housing 12 is externally fitted to a third fitting portion 14g at one end of the motor housing 14 (pinion shaft 17 side). In addition, the first contact portion 14e protruding outward from one end of the motor housing 14 and the contact portion 12d provided at the end of the first rack housing 12 are in contact with each other. The motor housing 14 is connected and fixed to the first rack housing 12 by screwing the fixing screw 55 inserted into the contact portion 12d to the first contact portion 14e. This fitted motor housing 1
In the outer peripheral surface of the third fitting portion 14g of FIG. 4, an orbiting groove is provided, and an O-ring 56 is fitted in the groove. Prevents liquids such as water and oil from entering.

Next, a method for assembling the electric power steering apparatus and a method for measuring the characteristics of the motor alone according to the present embodiment will be described. The stator 19 on which the winding is applied is fitted on the inner peripheral surface of the motor housing 14, and the second bearing 20 is press-fitted into the second fitting step 14 b of the motor housing 14.

The first bearing 52 is press-fitted into the fitting step 18d of the motor shaft 18 in an outer fitting state.
The first lock nut 53 is screwed into the fitting step 18d, and the inner race side of the first bearing 52 is pressed to be attached.

Next, the stator 19 and the second bearing 20
The motor shaft 18 in which the first bearing 52 is externally fitted is axially fitted into the motor housing 14 in which is fitted.

Then, the motor shaft 18 is fitted into the first fitting step portion 14 f projecting inward from the inner peripheral surface of the motor housing 14 by the first bearing 52 fitted outside the motor shaft 18. The positioning in the axial direction and the radial direction of 18 is performed. In addition, the nut holding portion 18a side is the outer peripheral surface 18 of the nut holding portion 18a.
b and the inner peripheral surface of the second bearing 20 are press-fitted and fitted and supported.

Thereafter, the third lock nut 54 is screwed into the motor housing 14 in a state of being fitted inside, so that the first bearing 52
Is pressed in the axial direction. The first bearing 52 is prevented from coming off by the first lock nut 53 and the third lock nut 54.

Since the motor is configured to obtain the driving force through the above steps, the characteristics of the motor alone can be measured. To measure the characteristics of a single motor, use the motor housing 1
4 is fixed with a jig, the motor shaft 18 is connected to the measuring instrument via the jig, and the winding provided on the stator 19 is energized.

After measuring the characteristics of the motor alone, the jig and the measuring instrument are removed, and the following assembly is performed. A ball screw mechanism is assembled on the rack shaft 16 in advance, and the rack shaft 16 with the ball screw mechanism is inserted and arranged in the motor shaft 18. Then, the second lock nut 28 abuts on the ball screw nut 26 of the ball screw mechanism, and is fixed by being pressed into the nut holding portion 18a.

Next, the O-ring 56 is fitted into the concave groove of the third fitting portion 14 g of the motor housing 14, and the fitting portion 12 c of the first rack housing 12 is screwed with the fixing screw 55.

Thereafter, an O-ring 29 is fitted into the peripheral groove 13d of the second rack housing 13. Then, the second rack housing 13 is screwed with the fixing screw 25 inserted into the contact portion 13b with the second contact portion 14d,
It connects with the motor housing 14.

Thus, the assembly of the electric power steering apparatus and the measurement of the characteristics of the motor alone according to the second embodiment of the present invention are completed. In the second embodiment, the following effects can be obtained in addition to the effect (1) of the first embodiment by configuring the electric power steering apparatus as described above.

(1) In this embodiment, one end (pinion shaft 17 side) of the motor shaft 18 is supported by the first bearing 52 provided at one end of the motor housing 14. The support accuracy of 18 is improved, and the cogging torque is reduced.

Each of the above embodiments can be modified and embodied as follows. In the present embodiment, the winding is applied to the stator 19, but the winding may be applied to the motor shaft 18 side. In this case, the motor shaft 18 side on which the winding is applied rotates, so that a means for supplying electricity to the winding is required. For example, electricity is supplied using a slip ring or the like.

Next, technical ideas that can be grasped from the above embodiments will be described below. (1) The electric power steering device according to claim 1, wherein the rack housing includes a first rack housing and a second rack housing connected to the motor housing. (2) In the method of assembling the electric power steering apparatus according to the technical idea (1), a step of assembling the motor, a step of measuring characteristics of the motor alone, a step of assembling the first rack housing to the motor, and Assembling a rack housing with the motor.

[0061]

The present invention is configured as described above, and has the following effects. According to the electric power steering device of the present invention, the characteristics of the motor alone can be accurately measured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an entire electric power steering device according to a first embodiment.

FIG. 2 is an enlarged view of a main part of the electric power steering device according to the first embodiment.

FIG. 3 is an enlarged view of a main part of an electric power steering device according to a second embodiment.

FIG. 4 is an enlarged view of a main part of a conventional electric power steering device.

[Explanation of symbols]

12 first rack housing, 13 second rack housing, 14 motor housing, 16 rack shaft, 18 motor shaft, 20 second bearing (bearing), 21 first bearing (bearing), 26 ball Screw nut.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takuji Ishikawa 1-1-1 Asahi-cho, Kariya-shi, Aichi F-term in Toyota Koki Co., Ltd. 3D033 CA02 CA04

Claims (2)

[Claims] 1. A rack shaft having a ball screw groove having a ball screw structure is inserted and arranged along the axial direction of a motor shaft of a motor formed in a hollow cylindrical shape, and a ball screw nut having a ball screw structure is connected to the motor shaft. An electric power steering apparatus, comprising: a motor housing interposed between a shaft and a rack shaft to cover the motor shaft; and a plurality of rack housings coaxially coupled to both ends of the motor housing to cover the rack shaft. An electric power steering apparatus wherein both ends of a motor shaft are supported by bearings provided at both ends of a motor housing. 2. The electric power steering apparatus according to claim 1, wherein the bearing that supports one end of the motor shaft fits inside the motor housing and also fits inside the rack housing.