JPH09136652A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict the temperature of an element independently of the environment temperature so as to efficiently radiate the temperature of a case. SOLUTION: This device is provided with an electric motor (m), a front wheel actuator interlocked with this electric motor (m), a board 1 provided with a circuit for controlling the electric motor (m) and a case 5, in which this board 1 is assembled. The case 5, in which the board 1 is assembled, is assembled between a case 3 of the electric motor (m) and a case 6 of the front wheel actuator so as to form an electric power steering device, and the filling material 11 is filled in the case 5, in which the board 1 is assembled, and as the filling material 11, the material, which is solid in the normal temperature and which absorbs the heat for melting when the temperature achieves the melting point thereof, is used.

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 As a conventional electric power steering apparatus, for example, the applicant of the present application has filed Japanese Patent Application No. 7-203888.
Some issues have already been filed. As shown in FIG. 5, a drive circuit 3 that controls switching of the electric motor m and a control circuit 4 that controls the drive circuit 3 are provided on a single metal substrate 1. Then, the metal substrate 1 is incorporated in a case 5 made of aluminum. The case 5 thus constructed is used as a motor case 2 in which an electric motor m is incorporated.
And a gear case 6 incorporating a front wheel actuator (not shown) are mechanically incorporated.

The output shaft 7 of the electric motor m penetrates into the case 5 and is linked to the front wheel actuator, around which the switching element 8 of the drive circuit 3 is arranged. Further, a brush 9 of the electric motor is arranged on the back side of the substrate 1, that is, the surface opposite to the drive circuit 3, and is connected to the switching element 8 by a pigtail line 10. In the electric power steering device described above, the switching element 8
Since the arrangement interval can be reduced and the pigtail line 10 can be shortened, noise radiated from the drive circuit 3 can be suppressed. Further, since the aluminum case 5 is mechanically incorporated between the motor case 2 and the gear case 6, even if the drive circuit 3 generates heat and the temperature inside the case 5 rises, for example, the heat is It can be discharged through the metal substrate 1 → case 5 → motor case 2 and gear case 6.

[0004]

In the conventional electric power steering apparatus described above, for example, when the drive circuit 3 generates heat, the heat is released through the case 5 → the motor case 2 and the gear case 6. At this time, if the environmental temperature is low, the difference between the temperature of the case 5 and the environmental temperature becomes large, and the heat in the case 5 can be released more efficiently. However, for example, if the temperature of the engine room rises, the temperature of case 5 rises accordingly. In addition, if the metal substrate 1 and the case 5 are larger than each other, the temperature of the element is further increased. . An object of the present invention is to provide an electric power steering device configured to suppress the temperature of the element to a low level without being affected by the ambient temperature and to efficiently radiate the heat of the case.

[0005]

The present invention comprises an electric motor, a front wheel actuator that links the electric motor, a board provided with a circuit for controlling the electric motor, and a case that incorporates the board. It is premised on an electric power steering device in which a case incorporating a board is incorporated between an electric motor case and a front wheel actuator case. The first aspect of the present invention encloses a filler in a case in which a substrate is incorporated, and the filler is a substance that is usually solid but melts while absorbing heat when the melting point is reached. It is characterized by The second invention is the first
In the invention of (1), the filler is a substance having a higher thermal conductivity than air in a liquid state, and is characterized in that it is filled in a metal case when completely melted.
A third invention is characterized in that, in the first or second invention, the substrate and circuits and electronic components on the substrate are coated with a liquid-resistant coating material.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment of the present invention shown in FIGS. 1 to 4, in an electric power steering apparatus of the above-mentioned conventional example, a filler 11 is enclosed in an aluminum case 5. The other configurations are similar to those of the conventional example, and detailed description thereof will be omitted. In this embodiment, the metal substrate 1 and the circuits 3 and 4 and electronic parts provided thereon are
It is coated with a coating material 12 having liquid resistance. Then, in the case 5 incorporating the metal substrate 1,
A filling material 11 as described below is enclosed. Here, Ba (OH ₂ ) · 8H ₂ O is used as the filler 11. This Ba (OH ₂ ) / 8H ₂ O is solid at room temperature,
When its melting point reaches 78 degrees, it melts while absorbing heat.
At this time, since the amount of heat absorbed by Ba (OH ₂ ) · 8H ₂ O is used when the phase changes from solid to liquid, the temperature of the substance itself does not rise. Then, in the state in which the phase is changed to a liquid completely, the thermal conductivity of Ba (OH ₂ ) / 8H ₂ O is higher than that of air. The filling material 11 is enclosed in the case 5 in a solid state, and at this time, an appropriate gap 13 is left in the case 5. When the filling material 11 is completely melted, the volume of the filling material 11 changes so that the inside of the case 5 is filled with the filling material 11.

Next, the operation of this electric power steering system will be described. If the amount of heat generated by the drive circuit 3 is small, the filler 11 remains in a solid state as shown in FIG. Therefore, similarly to the conventional example, the heat generated by the drive circuit 3 is radiated through the metal substrate 1 → case 5 → motor case 2 and gear case 6. On the other hand, when the amount of heat generated by the drive circuit 3 increases, the filling material 11 begins to melt from the periphery of the drive circuit 3 as shown in FIG. At this time, since Ba (OH ₂ ) · 8H ₂ O melts while absorbing heat, the temperature of the case 5 is almost constant at the melting point of the filler 11 of 78 degrees until the filler 11 is completely melted. Will be kept. When the amount of heat generated by the drive circuit 3 further increases, the filling material 11 completely changes into a liquid as shown in FIG. Therefore, at this time, the volume of the filler 11 increases and the case 5 is filled with Ba (OH ₂ ) · 8H ₂ O.

The thermal conductivity of liquid Ba (OH ₂ ) / 8H ₂ O is higher than that of air. Therefore, the heat generated by the drive circuit 3 can be dissipated not only to the portion where the metal substrate 1 is in direct contact with the case 5 but also to the entire case 5 through the filling material 11. Moreover, the liquid Ba (OH ₂ ) / 8H ₂ O convects due to the temperature difference in the case 5 and the vibration of the vehicle, so that its heat conduction can be further promoted. When the filler 11 is melted, the gap 13 is also filled with Ba (OH ₂ ) · 8H ₂ O, but the air in the gap 13 dissolves into the liquid as bubbles. Of course, a small hole may be formed in the case 5, or a filter that allows only gas to pass through may be provided in the small hole to positively escape the air in the gap 13.

Here, the relationship between the temperature t of the case 5 and the heat generation amount Q generated by the drive circuit 3 per constant time will be described with reference to FIG. It should be noted that FIG. 4 shows a situation at a time when a certain fixed time has passed since the element began to generate heat. In the following, it is assumed that the temperature of the engine room is maintained at a certain temperature T ₁ . At this time, if the heat generation amount Q of the drive circuit per fixed time is zero, the temperature t of the case is naturally maintained at the temperature T ₁ . Here, it is assumed that the drive circuit 3 generates heat. In a range (range A) in which the heat generation amount Q of the drive circuit 3 per constant time is smaller than the heat generation amount Q ₁ , the filler 11 maintains the above-mentioned solid state. Then, at this time, in this embodiment and the conventional example, the heat generated in the drive circuit 3 is the metal substrate 1 → the case 5 →
Heat is dissipated through the motor case 2 and the gear case 6.
Therefore, in this range, the temperature t of the case 5 gradually rises substantially in proportion to the heat generation amount Q of the drive circuit 3 per certain time (see the solid line X ₁ and the dotted line Y _{1 in} FIG. 4).

In the range (range B) in which the heat generation amount Q of the drive circuit 3 per constant time is larger than the heat generation force Q ₁ ,
The filler 11 of this embodiment melts while absorbing heat.
Therefore, the temperature t of the case 5 is almost constant (filling material 11
The melting point is 78 degrees) (see solid line X _{1 in the} figure). On the other hand, in the conventional example in which the filling material is not enclosed, the temperature t of the case 5 rises almost in proportion to the heat generation amount Q as in the range A (see the dotted line Y _{1 in the} figure). Further, when the amount of heat generation Q per unit time of the drive circuit 3 is larger than the amount of heat generation Q ₂ (range C), the filler 11 of this embodiment is used.
Melts completely. Then, at this time, the thermal conductivity of the filler 11 is higher than that of air, so that the temperature rise of the case 5 can be moderated compared to the conventional example (see the solid line X ₁ and the dotted line Y _{1 in the} figure). .

A case where the temperature of the engine room maintains a certain temperature T ₂ (> T ₁ ) will be described. In this case, the relationship shown by the solid line X ₂ in FIG. 4 is present in this embodiment in which the filler 11 is enclosed, and the relationship is shown in dotted line Y ₂ in the conventional example in which the filler 11 is not enclosed. Since the characteristics of the solid line X ₂ and the dotted line Y ₂ are the same as those of the solid line X ₁ and the dotted line Y _{1 at} the temperature T ₁ , detailed description thereof will be omitted. However, an amount corresponding to the temperature in the engine room becomes higher, when the calorific value Q reaches the calorific value Q ₃ (<Q _1),
The filler 11 will start to melt.

In this embodiment described above, the temperature of the case 5 can be kept constant within the range in which the filler 11 melts even if the amount of heat generated by the drive circuit 3 increases. Even if the amount of heat generated by the drive circuit 3 is further increased, the filler 11 is completely melted and its thermal conductivity is increased, so that the temperature rise of the case 5 can be made more gradual. Further, as can be seen from FIG. 4, even if the environmental temperature is different, the temperature of the case 5 is kept substantially constant at its melting point while the filler 11 is melted. Therefore, the heat in the case 5 can be released without being significantly affected by the environmental temperature. In this embodiment, the filler is used as the control circuit 4
And the drive circuit 3 are used in an electric power steering device provided on the same substrate. However, this filling material 11 is
It may be enclosed in a case in which only one of these circuits is incorporated. In addition to the control circuit and the drive circuit, the filling material may be enclosed in a case in which other circuits are incorporated.

[0013]

According to the first aspect of the present invention, the temperature of the case can be kept substantially constant at a predetermined temperature while the filler is melting, even if the environmental temperature is different while the filler is melting. it can. Therefore, the heat in the case can be dissipated without being much affected by the environmental temperature. According to the second invention, in the first invention, when the filler is completely melted, the thermal conductivity in the case becomes high, so that the heat dissipation can be enhanced. Moreover, since the liquid filler becomes convection in the case due to the temperature difference, the vibration of the vehicle, etc., the heat conduction can be further promoted. According to the third invention, in the first or second invention, since the circuit or the electronic component is coated even when the filling material is completely melted, the liquid may soak into the circuit or the electronic component. There is nothing.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an electric power steering device according to an embodiment of the present invention, showing a filler 11 in a solid state.

FIG. 2 is a diagram showing a state in which a part of a filler 11 in FIG. 1 has begun to melt.

FIG. 3 is a diagram showing a state in which a filler 11 in FIG. 1 is completely melted.

FIG. 4 is a diagram showing a relationship between a temperature t of a case 5 and a heat generation amount Q of heat generated by the drive circuit 3 per constant time.

FIG. 5 is a sectional view of an electric power steering device according to a conventional example of the present invention.

[Explanation of symbols]

 m Electric motor 1 Metal substrate 2 Motor case 3 Drive circuit 4 Control circuit 5 Aluminum case 6 Gear case 11 Filling material 12 Coating material

Claims (3)

[Claims] 1. An electric motor, a front wheel actuator linked with the electric motor, a board provided with a circuit for controlling the electric motor, and a case incorporating the board, wherein the case incorporating the board is electrically driven. In an electric power steering device incorporated between a case of a motor and a case of a front wheel actuator, a filler is enclosed in a case in which a substrate is incorporated, and the filler is usually solid but reaches a melting point. Then, the electric power steering device is characterized by being a substance that melts while absorbing heat. 2. The filler is a substance having a higher thermal conductivity than air in a liquid state, and is filled in a metal case when completely melted. Electric power steering device. 3. The electric power steering apparatus according to claim 1, wherein the substrate and circuits and electronic components on the substrate are coated with a liquid resistant coating material.