JP7476611B2 - Electric motor - Google Patents

Description

The present invention relates to an electric motor with a built-in fuse.

For example, as described in Patent Document 1, a molded motor is known in which a glass tube fuse that protects the motor from overcurrent is integrally molded inside the motor casing.

A fuse is a current interruption device that melts when a current greater than its rated current flows, protecting the circuit from overcurrent. Fuses generally have a rated derating and a temperature derating. When selecting a fuse, it is necessary to determine the design conditions taking these deratings into consideration. The rated derating is determined by the fuse specifications, and is, for example, about 0.75. On the other hand, the temperature derating is determined by the resistance temperature coefficient of the fuse, and is determined so that the higher the temperature, the lower the rated current. Therefore, when selecting a fuse, the steady-state current of the fuse must be less than or equal to the rated current multiplied by the rated derating and temperature derating.

Patent No. 3697589

In recent years, as electric motors have become smaller and more sophisticated, the difference between steady-state current and abnormal current is becoming smaller. Fuses used in such motors are required to pass a steady-state current while melting quickly when an abnormal current flows.

However, there is a limit to the rated current of fuses available on the market. Furthermore, the fuse's rated derating and temperature derating must be taken into consideration when selecting a fuse. This makes it difficult to select a fuse with a rated current suitable for a circuit where the difference between the steady-state current and abnormal current is small.

In addition, when the operating environment temperature is relatively high, it may be necessary to select a fuse with a relatively high capacity (high rated current) so that the required steady-state current can flow stably. However, the higher the capacity of the fuse, the longer the fuse's melting time for the current, which creates the problem that when an abnormal current flows, the current cannot be cut off within the desired melting time.

In view of the above circumstances, the object of the present invention is to provide an electric motor that can operate a fuse stably even when the difference between the steady-state current and the abnormal current is small.

In order to achieve the above object, an electric motor according to one embodiment of the present invention includes a motor body, a casing, a circuit board, and an insulating heat-conducting part.
The motor body includes a stator and a rotor.
The casing has at least a portion thereof made of metal as a heat dissipating portion and houses the motor body.
The circuit board is housed in the casing and includes a fuse that protects the motor body from overcurrent.
The insulating heat-conducting portion is disposed between the fuse and the heat dissipation portion.

The casing may have a case body that houses the motor body and the circuit board, and a lid that has the heat dissipation section, is attached to the case body, and faces the circuit board.

The insulating heat conductive part may be an elastically deformable insulating heat conductive resin.

The insulating thermally conductive resin may be a silicone resin.

According to the present invention, the fuse can be operated stably even when the difference between the steady-state current and the abnormal current is small.

1 is a cross-sectional view of an electric motor according to an embodiment of the present invention. FIG. 2 is an exploded perspective view of the electric motor. FIG. 2 is a side cross-sectional view of a main part of the electric motor. 1A and 1B are diagrams showing an example of fuse characteristics, in which (A) shows temperature derating and (B) shows melting characteristics. 10A and 10B are diagrams showing a modified configuration of the cover portion of the electric motor, in which (A) is an outer perspective view and (B) is an inner perspective view.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Fig. 1 is a cross-sectional view of an electric motor 1 according to a first embodiment, and Fig. 2 is an exploded perspective view thereof. In this embodiment, an axial air-gap type electric motor will be described as an example of the electric motor 1.

The electric motor 1 comprises a cylindrical stator 2 and a pair of disk-shaped rotors 3a, 3b arranged to face each other with a predetermined gap between them on both the left and right sides of the stator 2 in FIG. 1. Each rotor 3a, 3b is fixed to an output shaft 4 that passes through the stator 2 and outputs a rotational driving force, and each rotor 3a, 3b and the stator 2 are arranged coaxially with the output shaft 4 as the central axis. The stator 2 and each rotor 3a, 3b constitute the motor body M of the electric motor 1.

The electric motor 1 further includes a circuit board 5 for driving the electric motor. The circuit board 5 has a disk-shaped board body on which components such as a power IC chip 51, a control IC chip 52, and a fuse 53, which will be described later, are mounted. The circuit board 5 is disposed between one rotor 3a (the rotor 3a on the left side in FIG. 1) and the cover 6. The circuit board 5 may also be disposed on the other rotor 3b side.

The stator 2 is housed in a case body 10 made of synthetic resin. As shown in FIG. 2, the stator 2 includes a plurality of pole members 21 arranged in a ring shape along the circumferential direction centered on the output shaft 4. Referring also to FIG. 1, the pole members 21 are formed by winding a coil 24 around a stator core having a pair of flange-shaped teeth surfaces 22 on the left and right, and the stator core is formed by stacking a plurality of electromagnetic steel plates formed into an H-shape along the radial direction.

Each pole member 21 is entirely covered with an insulator made of insulating resin, leaving only the teeth surface 22. The insulator is provided with connecting means (not shown) for connecting each pole member to another. Note that the configuration of the stator 2 is optional in the present invention.

Next, the pair of rotors 3a and 3b will be described. However, since the pair of rotors 3a and 3b have the same configuration, in this example, the rotors 3a and 3b will be described together. As shown in FIG. 2, the rotors 3a and 3b are equipped with a disk-shaped yoke 31 and a plurality of magnets 32 arranged in a ring shape around the output shaft 4 on the yoke 31. Note that in the present invention, the specific configuration of the rotors 3a and 3b is also optional.

In this example, each rotor 3a, 3b shares the same output shaft 4, but it may be a two-output shaft type in which each rotor 3a, 3b has an output shaft 4.

After each pole member 21 is connected in an annular shape via this connecting means, it is molded integrally with the bearings 23a and 23b using resin by insert molding. As a result, the case body 10 is integrally formed on the outer periphery of the stator 2. The bearings 23a and 23b have a pair of radial ball bearings and rotatably support the output shaft 4.

As shown in FIG. 1, the case body 10 is made of engineering plastic such as BMC resin, and has storage recesses 11a, 11b formed at both ends for storing the rotors 3a, 3b. At one end of the case body 10 (the left end in FIG. 1), a guide groove 12z (see FIG. 2) into which the bushing 7 fits is cut out in a U-shape along the axial direction. The bushing 7 clamps the power cable 54 that connects the circuit board 5 to a power source (not shown).

The storage recesses 11a and 11b are formed between the inner circumferential surface of the case body 10 and both side surfaces of the stator 2. The storage recesses 11a and 11b have a size (depth) that allows the rotor 3 to be rotatably stored therein, and in this example, one of the storage recesses 11a (the left side in FIG. 1) has a depth that allows the circuit board 5 to be further stored therein.

The open ends of the storage recesses 11a and 11b are provided with locking surfaces 111 to which the lids 6a and 6b are fixed. The locking surfaces 111 are stepped surfaces formed between the inner peripheral surface of the storage recess 11 and a side surface having an inner diameter one size larger than the inner diameter of the storage recess 11, and the flanges 61 of the lids 6a and 6b abut against the locking surfaces 111, thereby fixing the lids 6a and 6b to the case body 10. The case body 10 and the lids 6a and 6b form the casing C that houses the motor body M and the circuit board 5.

The lids 6a and 6b are formed of a metal material such as stainless steel or an aluminum alloy. The lids 6a and 6b are formed in a disk shape that can be pressed into the open end of the case body 10, and a flange portion 61 that engages with the engaging surface 111 of the case body 10 is provided on the outer periphery. A pull-out portion 62 for pulling out the output shaft 4 to the outside is provided in the center of the lids 6a and 6b. The pull-out portion 62 protrudes toward the surface side of the lids 6a and 6b.

The circuit board 5 is housed in the housing recess 11a with the mounting surface on which components such as the power supply IC 51, control IC 52, and fuse 53 are mounted facing the lid 6a. The power supply IC 51 converts the power input via the power cable 54 into a predetermined power. The control IC 52 generates a coil current for exciting the coil 24 based on the power generated by the power supply IC 51.

The fuse 53 is an element that cuts off the current when an abnormal current flows through the circuit board 5 due to a short circuit in the coil 24, etc., and protects the circuit board 5 and the coil 24 from burning. The fuse 53 has a rated current equal to or greater than the maximum value of the drive current (coil current) of the motor 1, and has a current-cutting characteristic that melts when a preset abnormal current flows.

The power supply power IC 51 and the control IC 52 are electrically insulated from the lid portion 6a by forming a predetermined gap between them. On the other hand, the fuse 53 faces the lid portion 6a with the insulating heat conductive portion 63 in between.

Figure 3 is a side cross-sectional view of the main parts showing the relationship between the fuse 53 and the cover 6a. The fuse 53 is a surface-mounted chip fuse having a body 53a that houses a fuse element (conductor) and a pair of electrodes 53b provided at both ends of the body 53a, and the pair of electrodes 53b are soldered to the circuit board 5. The body 53a includes a tube such as a ceramic tube or a glass tube. The fuse 53 is not limited to being directly soldered to the circuit board 5, but may be inserted into a terminal block (socket) previously mounted on the circuit board 5.

The insulating heat conductive portion 63 is sandwiched between the upper surface of the fuse 53 and the inner surface of the lid portion 6a (the lower surface of the lid portion 6a in FIG. 3). Since the lid portion 6a is made of a metal material, it functions as a heat dissipation portion that dissipates heat generated in the fuse 53 via the insulating heat conductive portion 63.

In this embodiment, the insulating heat conductive part 63 is a heat conductive sheet made of an electrically insulating material, and may typically be a silicone-based/non-silicone-based heat conductive resin, or a heat conductive ceramic. When the insulating heat conductive part 63 is made of a heat conductive resin, the insulating heat conductive part 63 is elastically deformable, and therefore has a buffering effect against external forces applied to the lid part 6a. This prevents stress applied to the lid part 6a from acting directly on the fuse 53.

The thickness T of the insulating heat conductive portion 63 is not particularly limited as long as electrical insulation between the fuse 53 and the lid portion 6a can be ensured, and can be set appropriately depending on the elasticity and heat conduction characteristics of the heat conductive sheet that constitutes the insulating heat conductive portion 63. The thermal conductivity of the insulating heat conductive portion 63 is not particularly limited as long as it has a higher thermal conductivity than air, and is preferably 0.1 W/m·K or more.

The insulating heat conductive part 63 may be an adhesive sheet. In this case, the insulating heat conductive part 63 is attached to the fuse 53 or the lid part 6a in advance, and when the lid part 6a is attached to the case body 10 (when pressed in in this embodiment), the insulating heat conductive part 63 is sandwiched between the fuse 53 and the lid part 6a.

The insulating heat conductive portion 63 is not limited to a sheet-like one, and may be a hardened paste material. In this case, the fuse 53 is molded on the circuit board 5 with the paste material. After the paste material is hardened, the cover portion 6a is brought into contact with the hardened paste material when the cover portion 6a is attached to the case body 10 (when the cover portion 6a is pressed into the case body 10 in this embodiment).

In the electric motor 1 of this embodiment configured as described above, the circuit board 5 inputs a drive current to the coil 24 of the stator 2, causing the stator 2 to generate a rotating magnetic field. This causes the rotors 3a and 3b to rotate relative to the stator 2, and the rotational drive force is transmitted to an external device via the output shaft 4. An example of the external device is a fan device (indoor fan or outdoor fan) in an air conditioner.

When the electric motor 1 is driven, heat is generated due to heat generation from the coil 24, etc., and the inside of the casing C rises to a predetermined temperature (for example, 100°C). Since the electric motor 1 has an insulating heat conductive part 63 between the fuse 53 and the lid part 6a, heat acting on the fuse 53 is transferred through the insulating heat conductive part 63 to the lid part 6a, which serves as a heat dissipation part. This improves the heat dissipation properties of the fuse 53, so that the fuse 53 is maintained at a lower temperature than the temperature of its surroundings.

As described above, the fuse 53 cuts off the current when an abnormal current flows through the circuit board 5 due to a short circuit in the coil 24, etc., and protects the circuit board 5 and the coil 24 from burning. The fuse 53 has a rated current equal to or greater than the drive current of the motor 1, and has a current-cutting characteristic that causes it to melt when a preset abnormal current flows. The rated current of the fuse 53 is explained below.

Generally, fuses have a rated derating and a temperature derating, so the steady-state current of the fuse must be less than or equal to the rated current multiplied by the rated derating and temperature derating, as shown in the following formula.
Steady-state current ≦ rated current × steady-state derating × temperature derating … (1)

Temperature derating is determined by the resistance temperature coefficient of the fuse, and the higher the temperature, the higher the resistance value. Figure 4(A) shows an example of the temperature derating characteristics of a fuse. In the figure, the horizontal axis is the ambient temperature, and the vertical axis is the rate of change (%) of the rated current. Typically, there is a tendency for the rated current to decrease at temperatures higher than room temperature, and for the rated current to increase at temperatures lower than room temperature.
Moreover, Fig. 4(B) shows an example of the It characteristic of a fuse. In this figure, the horizontal axis indicates the current value, and the vertical axis indicates the melting time. In other words, the It characteristic corresponds to the melting characteristic of a fuse, which indicates the relationship between the magnitude of the current flowing through the fuse and the melting time. As shown in this figure, the general melting characteristic is that the greater the current value, the shorter the melting time, and even if the current value is the same, the greater the rated current of the fuse, the longer the melting time.

As an example, a method for selecting a fuse to be used under conditions of a steady-state current of 0.825 A (voltage of AC 250 V) and an ambient temperature of 100° C. will be described. In the case of a fuse with a steady-state derating of 0.8 and a temperature derating of 0.8, the rated current is calculated from formula (1) above as follows:
0.825 [A] / (0.8 × 0.8) = 1.289 [A] ... (2)
Therefore, a fuse used under the above conditions must have a capacity of 1.289 A or more, that is, a rated current.
However, when fuses available on the market only come in eight types of rated current, from smallest to largest, as shown in Figure 4(B), namely 1 A, 1.25 A, 1.6 A, 2 A, 2.5 A, 3.15 A, 4 A, and 5 A, one has no choice but to choose the 1.6 A fuse. In this case, if the abnormal current is 3 A, it will take more than 20 seconds for the fuse to melt, which raises safety concerns from the standpoint of circuit protection.

In contrast, in the electric motor 1 of this embodiment, the fuse 53 is connected to the metal cover portion 6a via the insulating heat conductive portion 63, and therefore the heat dissipation properties of the fuse 53 are improved compared to when the insulating heat conductive portion 63 is not present.
For example, if it is possible to reduce the temperature of fuse 53 by 20° C. (corresponding to an ambient temperature of 80° C.) by dissipating heat to lid portion 6 a, in the case of a fuse having the temperature derating characteristics shown in FIG. 4(A), the temperature derating will be 0.85 or more, and the rated current will be expressed by the following equation.
0.825 [A] / (0.8 × 0.85) = 1.213 [A] ... (2) '
In this case, in the above example, a rated current of 1.25 A can be selected for fuse 53. In this case, when the abnormal current is 3 A, the melting time can be set to 0.3 seconds or less, so that the fuse can melt more quickly when an abnormal current flows, thereby protecting the circuit from overcurrent, compared to when a fuse with a rated current of 1.6 A is selected.

As described above, according to this embodiment, since the insulating heat conductive portion 63 is disposed between the fuse 53 on the circuit board 5 and the lid portion 6a serving as a heat dissipation portion, the fuse 53 can be maintained at a temperature lower than the ambient temperature. This suppresses the decrease in rated current caused by temperature derating of the fuse, and therefore allows for a wider range of fuses to be selected from the limited lineup of fuses with rated currents.

As a result, by improving the heat dissipation of the fuse, it becomes possible to select a rated current that could not be selected due to the fuse's derating characteristics. Furthermore, it is possible to prevent the melting time from becoming longer even for fuses used under harsh conditions such as high ambient temperatures. This allows fuse 53 to operate stably even when the difference between the steady-state current and the abnormal current is small.

The above describes an embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in the above embodiment, an axial air gap type motor in which a rotor faces a stator with a gap in the axial direction has been described as an example of the motor, but the present invention is not limited to this, and can also be applied to a radial gap type motor in which a rotor faces a stator with a gap in the radial direction.

In the above embodiment, the entire lid 6a serving as a heat dissipation portion is made of a metal material, but this is not limited thereto, and only the portion facing the fuse 53 may be made of a metal material.
For example, FIGS. 5A and 5B are an outer perspective view and an inner perspective view of a lid portion 60 according to a modified example.
As shown in the figure, the entire cover 60 is made of a synthetic resin material, and a metal heat dissipation section 64 is provided only in the area facing the fuse 53. Examples of synthetic resin materials include ABS (achloronitrile-butadiene-styrene) and PPS (polyphenylene sulfide).
The heat dissipation portion 64 is a rectangular metal plate, the front and back surfaces of which form part of the outer and inner surfaces of the lid portion 60 .
With this configuration as well, it is possible to obtain the same effects as those of the above-described embodiment.
In this example, the heat dissipation section 64 is integrated into the lid section 60 by insert molding. Alternatively, an opening may be provided in a pre-molded lid section 60, and the heat dissipation section 64 may be fixed to the opening by adhesive or other methods.

REFERENCE SIGNS LIST 1...motor 2...stator 3a, 3b...rotor 4...output shaft 5...circuit board 6a...lid (heat dissipation section)
10: Case body 53: Fuse 63: Insulating heat conductive part 64: Heat dissipation part C: Housing M: Motor body

Claims (4)

a motor body having a stator and a rotor;
a casing that has at least a metal heat dissipation portion in at least a portion thereof and that houses the motor body;
a circuit board that is housed in the casing and has a fuse mounted thereon that melts when an overcurrent flows to protect the motor body from the overcurrent;
an insulating heat conductive portion disposed between the fuse and the heat dissipation portion. 2. The electric motor according to claim 1,
The casing comprises:
a case body that houses the motor body and the circuit board;
a cover portion having the heat dissipation portion, attached to the case body, and facing the circuit board;
An electric motor having 3. The electric motor according to claim 1 or 2,
The electric motor, wherein the insulating and heat-conducting portion is made of an elastically deformable insulating and heat-conducting resin. 4. The electric motor according to claim 3 ,
The electric motor, wherein the insulating thermally conductive resin is a silicone resin.

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