JP2778676B2 - Brushless motor drive for electric power steering - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an electric power steering apparatus.

[0002]

2. Description of the Related Art Conventionally, a power steering device for assisting a steering operation of a vehicle is disclosed in, for example, Japanese Patent Laid-Open No.
2. Description of the Related Art An electric power steering device using an electric motor as disclosed in JP-A No. 2576 or JP-A-3-7661 is known. In this conventional example, in order to assist the steering operation, for example, electric power is supplied to a stator on the coil side via a motor output circuit, and a rotor on the permanent magnet side is rotated to assist the movement of the steering shaft. Usually, such a motor output circuit has a characteristic of generating heat, and in particular, a power switch for controlling a motor.
Quenching device, functions by this heating there is a problem that Sun Wei becomes easier. For this reason, Japanese Patent Application Laid-Open No.
For No. 92 576, by measuring the temperature of the power switching device, the temperature has to be decreased controlling the motor current to Osamuru so within a predetermined value, the function is the high temperature of the power switching <br/> element I try not to destroy it.

[0003]

By the way, as in the case of the above-mentioned apparatus, a conventional general brushless motor for power steering has a control unit incorporating a power switching element provided separately from the motor , for example, installed in a vehicle interior. Therefore, a relatively large heat radiation fin has been required to improve the heat radiation. For this reason, an improvement for weight reduction and miniaturization has been desired from the demand of a vehicle-mounted system, but there has been a limit to miniaturization and weight reduction in the past.

[0004]

[Means for Solving the Problems] To solve such problems.
According to a first aspect of the present invention , a nut screw is screwed into a ball screw groove formed in a steering shaft via a ball, a rotor is coupled to the nut screw, and the rotor faces a stator in a housing with a predetermined gap. together allowed to, in the electric power steering drive device so as to connect the stator and the power switching element electrically, to secure the power switching elements adjacent to the stator in the housing, the power scan
A protrusion is formed on the outer surface of the rotor facing the switching element, and the top of the protrusion extends along the axial direction of the steering shaft.
It is characterized by being inclined. Further in claim 2, prior
A check valve for air is provided at a predetermined position between the housing and the rotor.
It is characterized by having been provided .

[0005]

The power switching element is housed inside the housing to reduce the size and weight of the device. However, the heat generated in the power switching element is forcibly air-cooled by the action of the fan of the rotating rotor to maintain the function. Plan. Since the top portion of the projection is inclined, power scan
Air can be blown toward the switching element ,
The blown air is sent in the axial direction of the steering shaft to be convected to enhance the heat radiation effect. If the flow of air is regulated in one direction by a check valve between the housing and the rotor, the cooling effect is enhanced.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a brushless motor driving device according to the present invention will be described with reference to the accompanying drawings. 1 is a longitudinal sectional view showing a main part of the present invention, FIG. 2 is a sectional view taken along line AA of FIG. 1, FIG. 3 is an external view of a radiation fin, and FIGS. 4 and 5 are perspective views showing protrusions of a rotor. is there.

An electric power steering device for a vehicle is configured to rotate a brushless motor based on a signal detected by a torque sensor, and to convert the rotation of the brushless motor into a left-right movement of a steering shaft to supplement a steering wheel operating force. For example, as shown in a conventional system configuration diagram of FIG. 8B, a signal detected by a torque sensor is sent to a CPU for processing, and drive control of a brushless motor is performed via a motor control circuit and a power circuit. I have to.

[0008] Then, such a power circuit, the conventional case where the motor side are those that are built into the control unit side provided to another location, also power switching as used in this power circuit Since the element generates heat, there has been a problem in reliability.

That is, this power switching element
For example, in the case of a MOS-FET of a field effect transistor, the characteristics are linearly deteriorated (decrease in allowable loss value) at 30 ° C. or higher, and almost no function is obtained at 150 ° C., and the power assist function is lost. It has the property of being lost.

Therefore, in the present invention, such a power switch
A switching element is provided in proximity to the brushless motor to reduce the size of the device, and to forcibly cool the power switching element to prevent a reduction in the power assist function.

That is, as shown in FIG. 1, a rack portion formed on a part of the steering shaft 1 (rear side in the figure)
A pinion 2a at the lower end of the handle shaft 2 is meshed with the steering shaft 1. The pinion 2a is configured to convert the rotation of the handle into reciprocating motion of the steering shaft 1, and a ball screw groove 3 is formed in a part of the steering shaft 1. ing.

A nut screw 5 is screwed into the ball screw groove 3 via a plurality of balls 4, and the rotation of the nut screw 5 assists the reciprocation of the steering shaft 1. That is,
The nut screw 5 is connected to an adjacent brushless motor 6.
Of the first housing 1 via a bearing 10 while being connected to the rotor 7
1 supported.

The brushless motor 6 includes a second housing 1
And a cylindrical rotor 7 rotatably inserted into the steering shaft 1.
And a power switching element 15 which is a component of the power circuit unit mounted in the third housing 14.
And a circuit board 9 as another component of the power circuit unit
The stator 13 is configured as a coil winding and controlled by a power switching element 15.
Receive power supply.

The power switching element 15
Are provided along the circumferential direction, as shown in FIG. 2, and are connected to the connection portion 16 in FIG. 2 via the circuit board 9 and the like. The connection source 16 is connected to a power source of the battery 23 shown in FIG.

[0015] In addition, the power switching element 15,
For example, it is a field-effect transistor (MOS-FET) having an oxide film formed on its surface, and has a characteristic that its function is deteriorated by heat generation.

Therefore, the power switching element 15
As shown in FIG. 3, a radiation fin 14 a having a high heat radiation property is provided on the outer side of the third housing 14 for supporting the first housing 14 , and a plurality of projections 17 described later are formed on the outer periphery of the rotor 7 inside the third housing 14. Thus, air can be blown toward the power switching element 15.

The rotor 7 in the second housing 12
As shown in FIG. 1, a permanent magnet 18 is fixed to the outer periphery of the. A slight gap is provided between the permanent magnet 18 and the stator 13.

A plurality of projections 17 are provided on the outer periphery of the rotor 7 in the third housing 14 as described above. On the upper surface of the projections 17, for example, the second housing 12 side is formed along the axial direction. An inclined portion 17a is provided so that the height is low and the height on the opposite side is high, so that the rotation of the rotor 7 allows the protrusion 17 to send air in an oblique direction. That is, directivity can be given to the airflow.

The rotor 7 between the projections 17 is provided with an air passage 20 for communicating the inside and the outside of the cylinder.
Air can be introduced from a gap between the steering shaft 1 and the rotor 7, and a gap is also provided between the third housing 14 and the steering shaft 1 to supply air blown from the projection 17.

The shape of the projection 17 is not only the inclined portion 17a on the upper surface, but also, for example, as shown in FIG. As another configuration example, as shown in FIG. 5, a flange portion 17b may be provided on one end side of the projection 17 so as to further enhance the directivity of air flow.

The projection 17 has the above configuration.
The air blown to the power switching element 15 by the fan action flows toward the nut screw 5 through the gap between the permanent magnet 18 of the rotor 7 and the stator 13.

A check valve 21 is provided at the boundary between the first housing 11 and the second housing 12. The check valve 21 is in the embodiment are to be able to shut off the air passage between the first housing 11 inner surface and the rotor 7 outer surface, for example, as shown in FIG. 6, the power switching element <br/> element Open when the air flows from the 15 side ((b)
(Fig.), Shuts off the flow of air in the opposite direction (Fig. (A)).

The operation of the brushless motor driving device configured as described above will be described.

When the driver operates the steering wheel, the brushless motor 6 operates according to the steering torque and the rotation speed. That is, the electric power transmitted from the battery is supplied to the stator 13 (coil) via the power switching element 15 of the power circuit unit, and the rotor 7 and the nut screw 5 rotate. And steering shaft 1
To assist the steering force.

During this time, when the power switching element 15 functions, heat is generated. However, part of the power switching element 15 is formed by the radiation fins 14a of the third housing 14, and part of the power switching element 1 is formed by the fan action of the projection 17 accompanying the rotation of the rotor 7.
5 is cooled. Since the air used for the cooling has directivity, the stator 13 and the rotor 7
The air flows from the check valve 21 into the first housing 11 through the gap therebetween.

Incidentally, a system configuration diagram of the electric power steering according to the present invention is as shown in FIG. 8 (A). As shown in FIG. 8 (B), the power circuit conventionally incorporated in the control unit is In the present invention, the power circuit can be actively cooled by being integrated into the brushless motor with a fan.

[0027]

As described above, in the brushless motor driving device of the present invention, the power switching element is fixed in the housing, and the protrusion is formed on the rotor facing the power switching element. At the same time, the power switching element functions and the rotor rotates, and at the same time, the cooling air is blown by the fan function of the projection, so that the temperature rise can be prevented. In particular, the inclination of the upper surface of the projection gives directionality to the cooling air, and air blows toward the power switching element.
And sends air in the axial direction of the steering shaft.
As a result, the cooling effect is enhanced because the gas is effectively discharged to the outside. Furthermore, by providing a check valve in the middle of the cooling air to prevent backflow, heat is not stored in the housing, and the cooling effect is further enhanced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a main part of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG. 1;

FIG. 3 is an external view of a radiation fin.

FIG. 4 is a perspective view showing a protrusion of the rotor.

FIG. 5 is a perspective view showing another configuration example of the protrusion of the rotor.

FIG. 6 is an operation diagram showing the operation of a check valve.

FIG. 7 is a schematic view of an electric power steering device.

FIG. 8 shows a system diagram, where (a) is the present model and (b) is a conventional diagram.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steering shaft 4 Ball 5 Nut screw 6 Brushless motor 7 Rotor 11 1st housing 12 2nd housing 13 Stator 14 3rd housing 15 Power switching element 17 Projection 17a Inclined part 18 Permanent magnet 21 Check valve

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B62D 5/04

Claims (2)

(57) [Claims] A nut screw is screwed into a ball screw groove formed on a steering shaft via a ball, a rotor is coupled to the nut screw, and the rotor is opposed to a stator in a housing with a predetermined gap. the electric power steering drive device so as to electrically connect the power switching element and a power switch adjacent to the stator in the housing
Fixing a ring element, the power switching element protrusions on the outer surface of the opposing rotor was formed, the protrusion steering shaft to the top of the
A brushless motor driving device for electric power steering, wherein the brushless motor driving device is inclined along an axial direction of the motor. 2. In a predetermined portion between the housing and the rotor,
Is characterized in that an air check valve is provided.
Brushless motor drive of the described electric power steering
apparatus.