JP2001088717A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent separation of a magnet of a motor. SOLUTION: A motor shaft 15 is covered with an electromagnetic stainless made cylindrical member 23 one end 23a of which is pressure inserted into the motor shaft 15. Namely, only the one end 23a thereof is fixed to the motor shaft 15 while the other end thereof is free, not fixed. A ring magnet 22 is magnetically attached to an outer circumferential surface of the member 23. Accordingly, even if the motor shaft 15 is extended or contracted axially by a shock, the member 23 just moves in the axial direction of the motor shaft 15, and thereby there is less possibility that the ring magnet 22 magnetically attached to the cylindrical member 23 is separated therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention assists the axial movement of a rack shaft inserted through the center of rotation of a motor shaft by rotating a hollow motor shaft inserted through the rotation shaft of the motor. The present invention relates to a so-called rack assist type electric power steering device.

[0002]

2. Description of the Related Art Conventionally, as the electric power steering device,
For example, those shown in FIGS. 3 and 4 are known. FIG. 3 is a partial cross-sectional explanatory view in the axial direction of the electric power steering device, and FIG. 4 is an enlarged view of a portion where a brushless DC motor is mounted in FIG. As shown in FIG. 3, the electric power steering device 40 includes a rack housing 11
A tube yoke housing 13 coaxially attached to an end of the rack housing 11; and an end housing 14 coaxially attached to an end of the tube yoke housing 13. Each of these three housings is formed in a hollow and substantially cylindrical shape, and a rack shaft 12 is inserted therein. The bearing 1 is provided in the tube yoke housing 13.
A hollow iron motor shaft 15 is rotatably inserted through the inner and outer shafts 7 and 30, and the rack shaft 12 is inserted into the motor shaft 15 through a ball screw nut 16.
Are movably connected in the axial direction. Tie rods 19 connected to the steered wheels via ball joints 18 are connected to both ends of the rack shaft 12, respectively.

As shown in FIG. 4, a brushless DC motor 20 is mounted inside a tube yoke housing 13, and a motor shaft 15 as a rotation shaft is inserted through the brushless DC motor 20. . The brushless DC motor 20 includes an armature core 21 fixed to the inner peripheral surface of the tube yoke housing 13, and a ring magnet 22 bonded to the outer peripheral surface of the motor shaft 15.
And That is, the motor shaft 15 forms a magnetic path. Although not entirely shown, the armature core 21 is divided into a plurality of pieces in the circumferential direction, and an armature winding is wound around each. When a drive current flows from the motor controller (not shown) to each armature winding via the lead wires 31 and 32 (FIG. 3), the motor shaft 15 rotates, and the rotation torque is applied to the ball screw nut 16.
Is converted into a force for moving the rack shaft in the axial direction.

[0004]

However, when the steered wheels receive a reaction force from the road surface, the motor shaft 15 is applied to the motor shaft 15 via the rack shaft 12 in the axial direction (the direction indicated by the arrow F1 or F2 in FIG. 4). For example, since an impact force of about 8 ton is applied, the motor shaft 15 expands and contracts due to stress. Therefore, when an impact force more than expected is applied, the adhesive surface between the motor shaft 15 and the ring magnet 22 may be separated. . Also, due to the difference in the linear expansion coefficient between the motor shaft 15 and the ring magnet 22, the above-mentioned separation may occur when the temperature rises. That is, in the conventional electric power steering device 40, the performance of the brushless DC motor 20 may be deteriorated due to the separation of the ring magnet 22.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to realize an electric power steering apparatus capable of preventing a magnet of a motor from peeling off.

[0006]

Means for Solving the Problems, Functions and Effects of the Invention
In order to achieve the above object, according to the present invention, a motor housing, a motor provided inside the motor housing, and a hollow motor serving as a rotating shaft of the motor are provided. A shaft, a rack shaft inserted through the center of rotation of the motor shaft,
An electric power steering device that rotates the motor shaft by driving the motor and assists the rack shaft in moving in the axial direction by the rotation of the motor shaft.
The motor shaft is covered with a cylindrical member made of electromagnetic stainless steel, and one end of the cylindrical member is fixed to the motor shaft, and the other end is adapted to expand and contract in the axial direction of the motor shaft. A technical means is used in which the magnet of the motor is mounted on the outer peripheral surface of the cylindrical member.

The cylindrical member covered on the motor shaft is
One end is fixed to the motor shaft, and the other end can be displaced in accordance with the expansion and contraction of the motor shaft in the axial direction. Even if the shaft expands and contracts, the cylindrical member only displaces in the direction of expansion and contraction of the motor shaft, so the magnet attached to the cylindrical member only moves together with the cylindrical member, so that the magnet can be separated from the cylindrical member. Absent. Further, since the linear expansion coefficient of the electromagnetic stainless steel is closer to the linear expansion coefficient of the magnet than iron, the possibility that the magnet is peeled off from the cylindrical member due to thermal expansion is small. Further, electromagnetic stainless steel is desirable as a magnetic path because it has excellent magnetic properties such as magnetic permeability, magnetic flux density, and coercive force.

According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, a technical means is provided in which one end of the cylindrical member is fixed by press-fitting the motor shaft. Used.

That is, by press-fitting one end of the cylindrical member into the motor shaft, one end of the cylindrical member is fixed to the motor shaft, and the other end moves freely in accordance with the expansion and contraction of the motor shaft in the axial direction. Can be at the end.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electric power steering apparatus according to an embodiment of the present invention will be described below with reference to the drawings. In this embodiment, an electric power steering apparatus equipped with a brushless DC motor will be described as an example. In addition, the same reference numerals are used for components common to the conventional electric power steering device 40 shown in FIGS. 3 and 4, and the description of the common parts is simplified. FIG. 1 is an explanatory cross-sectional view of a portion where a brushless DC motor is mounted in the electric power steering apparatus according to this embodiment. FIG. 2 (A)
FIG. 2 is an explanatory view showing a structure of a ring magnet, a cylindrical member, and a motor shaft in the electric power steering apparatus shown in FIG. 1, and FIG. 2B is an enlarged explanatory view showing a press-fit portion of the cylindrical member. is there. Note that FIG. 2B is exaggerated from the actual structure in order to make the structure easy to understand.

As shown in FIG. 1, a cylindrical member 23 made of electromagnetic stainless steel is put on the motor shaft 15, and one end 23 a of the cylindrical member 23 is pressed into the motor shaft 15. That is, one end 2 of the cylindrical member 23
Only 3a is fixed to the motor shaft 15, and the other end 23b is free and is not fixed. And
The ring magnet 22 is adhered to the outer peripheral surface of the cylindrical member 23. As shown in FIG. 2, one end 23 a of the cylindrical member 23 has an inner peripheral surface in a range indicated by L <b> 1
5 is pressed into the outer peripheral surface. Further, as shown in FIG. 2B, a clearance D2 is formed between the inner peripheral surface other than the press-fitted inner peripheral surface of the cylindrical member 23 and the outer peripheral surface of the motor shaft 15.

In this embodiment, the cylindrical member 23
The cylindrical member 23 has a linear expansion coefficient smaller than that of iron and larger than that of the ring magnet 22. The thickness D1 of the cylindrical member 23 is, for example, 2.0 to 3.0 mm, and the clearance D2 is 0.1 mm or less. Further, the thickness of the ring magnet 22 is 2.0 to 3.0 mm.
And bonded to the cylindrical member 23 with an epoxy resin adhesive. Furthermore, the inner diameter of the motor shaft 15 is 30 to 50 mm, and as described above, if the electric power steering device 10 according to this embodiment is used, the cylindrical member 23 covered on the motor shaft 15 is One end 2
3a is fixed to the motor shaft 15 and the other end 23a
Since b can be displaced in accordance with the expansion and contraction of the motor shaft 15 in the axial direction, an impact force is applied to the motor shaft 15 in the axial direction (the direction indicated by the arrow F1 or F2 in FIG. 1). Even when the motor shaft 15 expands and contracts in the axial direction, the cylindrical member 23 is only displaced in the axial direction of the motor shaft 15. Therefore, the ring magnet 2 attached to the cylindrical member 23
2 also moves only together with the cylindrical member 23, so that the possibility that the ring magnet 22 is separated from the cylindrical member 23 is small.

The linear expansion coefficient of the electromagnetic stainless steel forming the cylindrical member 23 is smaller than that of iron.
Since the linear expansion coefficient is close to 2, the possibility that the ring magnet 22 is separated from the cylindrical member 23 due to the difference in thermal expansion between the two even when the temperature changes is small. Further, electromagnetic stainless steel is desirable as a magnetic path because it has excellent magnetic properties such as magnetic permeability, magnetic flux density, and coercive force. Further, since the electromagnetic stainless steel has excellent corrosion resistance, the durability of the electric power steering device 10 can be enhanced. Further, one end 23a of the cylindrical member 23 is connected to the motor shaft 15
, The one end 23a of the cylindrical member 23 can be fixed to the outer peripheral surface of the motor shaft 15, and the other end 23b can be a free end.

In the above-described embodiment, the method of press-fitting one end 23a of the cylindrical member 23 into the motor shaft 15 is used.
Can be used. Further, the cylindrical member 23 may be formed of an iron-nickel alloy having a small linear expansion coefficient and a high magnetic permeability. Further, the cylindrical member 2
3, a ring magnet 22 is adhered to the inner peripheral surface of the non-press-fitted area, and a clearance D2 is provided between the adhered ring magnet 22 and the outer peripheral surface of the motor shaft 15.
May be formed. Furthermore, the electric power steering apparatus according to the present invention has been described by taking a brushless DC motor as an example, but the present invention can be applied to an electric power steering apparatus equipped with another motor. Of course. Incidentally, the tube housing 13 corresponds to the motor housing of the present invention.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of a portion where a brushless DC motor is mounted in an electric power steering apparatus according to an embodiment of the present invention.

FIG. 2A is an explanatory view showing a structure of a ring magnet, a cylindrical member, and a motor shaft in the electric power steering apparatus shown in FIG. 1, and FIG. 2B is a press-fitting of a stainless steel cylinder. It is explanatory drawing which expands and shows a part.

FIG. 3 is a partial cross-sectional view in the axial direction of a conventional electric power steering device.

FIG. 4 is an enlarged view of a portion in FIG. 3 where a brushless DC motor is mounted.

[Explanation of symbols]

Reference Signs List 10 electric power steering device 12 rack shaft 13 tube yoke housing (motor housing) 15 motor shaft 16 ball screw nut 20 brushless DC motor 21 armature iron core 22 ring magnet 23 cylindrical member 23a one end of cylindrical member 23b the other end of cylindrical member L1 Press-fit range

Claims (2)

[Claims] A motor housing, a motor provided inside the motor housing, a hollow motor shaft that is a rotation shaft of the motor, and a rack shaft inserted through the rotation center of the motor shaft. Rotating the motor shaft by driving the motor,
In the electric power steering device that assists the axial movement of the rack shaft by its rotation, the motor shaft is covered with a cylindrical member made of electromagnetic stainless steel, and one end of the cylindrical member is While being fixed to the motor shaft, the other end is displaceable in accordance with expansion and contraction of the motor shaft in the axial direction, and a magnet of the motor is attached to an outer peripheral surface of the cylindrical member. Electric power steering device. 2. The electric power steering apparatus according to claim 1, wherein one end of the cylindrical member is fixed by press-fitting the motor shaft.