JPH05190276A - Noise preventing device - Google Patents

Abstract

PURPOSE:To reduce a noise due to a low pressure loss by preventing unnecessary radiation of the noise. CONSTITUTION:A case 4, formed of conductive material having suction and exhaust ports 9, 10 and storing noise generating sources 1, 2, is arranged in a forced cooling passage 7, and a collective unit of pillar-shaped elements 11, 12, formed of conductive material to provide an internal passage, is provided in any of at least the suction and exhaust ports 9, 10. By high numerical aperture of the collective unit and further by an impedance characteristic against a noise, suppression of unnecessary radiating noise to the outside of a case 6 of the noise generating sources 1, 2, stored in the case, and cooling performance are simultaneously obtained, to contrive lowness of the noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter application device such as a microwave oven and a switching power supply, and more particularly to prevention of generation of radiation noise such as microwaves in a cooling structure of a heating element.

[0002]

2. Description of the Related Art Conventionally, this type of radiation noise prevention apparatus has a heating chamber 31 for housing and heating an object to be heated such as food in a main body 30 like a microwave oven shown in FIG.
A magnetron 33 for supplying microwaves into the heating chamber 31 via a waveguide 32, a high voltage transformer arranged on a printed board 34 for applying a high voltage to the magnetron 33, a high voltage capacitor, a diode, a semiconductor switching element, etc. The inverter power supply 35, which is a power supply component, and the magnetron 33, a cooling fan 36 that cools the inverter power supply 35, and the like, are enclosed by an outer box 37. The outer box 37 is provided with an intake port 38 and an exhaust port 39 that serve as inlets and outlets for air (indicated by a solid arrow) sucked by the cooling fan 36. These are TV band noise of several hundred MHz leaking from the magnetron 33, 2450 MHz, and Microwave radiation noise of its harmonics or inverter power supply 35
In order to prevent the switching noise of several tens of KHz to several tens of MHz radiated from the outside from being radiated to the outside of the outer box 37, the aperture ratio is relatively low. In particular, the suction port 38 and the exhaust port 39 are composed of a perforated plate having a relatively small hole diameter having a diameter or pitch determined by the wavelength thereof in order to prevent the radiation noise in the microwave band from leaking.

[0003]

However, in the above-mentioned conventional structure, unnecessary radiation noise leaking from the noise source such as magnetron or inverter power source through the outer box is
The hole diameter of the air inlet / outlet provided for cooling is made as small as possible in order not to affect the TV, radio and HA system. Therefore, the means for suppressing the radiation noise causes a large pressure loss in the cooling passage of the cooling fan, so that the device itself must be upsized to satisfy the cooling, or the cooling fan must be upsized and speeded up. There was a problem that the noise of the car became very loud.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and provides a noise prevention device capable of suppressing unnecessary radiation of noise and reducing pressure loss of a cooling passage to achieve low noise. It has one purpose.

A second object is to prevent noise radiation from the motor itself which drives the cooling fan and improve the cooling efficiency.

[0006]

In order to achieve this first object, the noise prevention device of the present invention comprises a forced cooling passage,
A case made of a conductive material having a suction port and an exhaust port and accommodating a noise generation source is arranged, and at least one of the suction port and the exhaust port is provided with an assembly of columnar elements having an internal passage made of a conductive material. It is a thing.

In order to achieve the second object, the cooling fan is also housed in the case.

[0008]

[Operation] By driving the noise source, noise such as microwaves is generated in the case and propagates to each part of the case. However, except for the suction port and the exhaust port, it is almost sealed with a conductive material. It is reflected and does not leak outside. Especially in the case of a non-magnetic material, the effect is even greater. Also,
The suction port and the exhaust port are composed of an assembly of columnar elements, and the columnar elements are composed of a thin-walled conductive material to realize a high aperture ratio and at the same time have an assembly structure with a large depth dimension. There is. On the other hand, the amount of attenuation of electromagnetic waves (radiation noise) passing through the conductive porous plate is theoretically expressed by the following approximate expression (1).

TdB = A × log ₁₀ (B × λ ÷ d ³ ) + C × t ÷ d From the equation (1), it is a function of the hole diameter d of the perforated plate and the plate thickness t (hole depth). Attenuation TdB of electromagnetic wave passing through the plate
It can be seen that is larger as d is smaller and is larger as t is larger. Here, TdB shown in the approximate expression (1) is the attenuation amount of the electromagnetic wave (radiation noise) that passes through, λ is the wavelength of the electromagnetic wave, d is the diameter of the hole, t is the depth dimension of the hole, A, B, and C.
Is a constant. Therefore, the electromagnetic waves (radiation noise) propagating to the suction port and the exhaust port composed of the above-described assembly can obtain the same attenuation amount by increasing the depth t even if the hole diameter d is increased. This means that a sufficient shielding effect of electromagnetic waves (radiation noise) can be obtained, and at the same time, a high aperture ratio can be achieved, and cooling air rectified in the thickness direction with almost no pressure loss can be supplied to the noise source. It realizes the configuration.

Further, when the cooling fan is housed in the case, all the air supplied from the cooling fan passes through the case, the cooling efficiency to the noise generating source is improved, and at the same time, the radiation noise from the cooling fan itself is also outside the case. Radiation is prevented.

[0011]

Embodiments of the present invention will be described below with reference to the drawings, taking a microwave oven as an example.

FIG. 1 shows an example of an inverter microwave oven. Reference numeral 1 is a magnetron for generating microwaves, 2 is an inverter power source for driving the magnetron, and these noise sources are a case of a non-magnetic material having conductivity together with a printed circuit board 3 on which power source components constituting the inverter power source 2 are arranged. The printed circuit board 3 is housed in the housing 4, and the printed circuit board 3 is fixed via a support component 5. The case 4 is arranged in a cooling passage 7 surrounded by an outer casing 6 of the main body, and cooling air is forcibly supplied by a cooling fan 8 provided on the upstream side of the case 4. The case 4 has a suction port 9 and an exhaust port 10 on the upstream side and the downstream side of the magnetron 1 and the inverter power supply 2, respectively. In this embodiment, the honeycomb structure 1 is an aggregate.
1 and 12 show the case where this honeycomb structure 1 is used.
Like the case 4, the reference numerals 1 and 12 are conductive and made of a non-magnetic material.

In the above structure, when the cooling fan 8 is operated, cooling air (indicated by a solid arrow in the figure) is partially guided into the main body through the inlet portion 13 provided in the outer casing 6 of the main body, and the cooling passage 7 is formed.
Inside the case 4, the honeycomb structure 11 at the suction port 9 of the case 4 enters the case 4 and is discharged to the outside of the case 4 through the honeycomb structure 12 provided on the downstream side of the magnetron 1 while cooling the magnetron 1 and the inverter power supply 2. From the outlet portion 14 provided in the outer casing 6 of the main body, it is guided to the outside of the main body. For example, by setting the side of the honeycomb lattice of the honeycomb structures 11 and 12 to be about 2 mm and the depth thereof to be about 5 mm, it is possible to provide a sufficient blocking effect against noise in the microwave band (2450 MHz and its harmonics). Therefore, unnecessary radiation in the microwave band can be completely shielded, and interference electromagnetic noise to other electronic devices can be suppressed to improve reliability. Further, since the pressure loss generated at the intake port 9 and the exhaust port 10 can be significantly reduced, even if the case 4 is arranged in the cooling passage 7, most of the cooling air can be guided into the case 4 and the cooling fan 8 can be operated at a low rotational speed. Further, the flow of the cooling air when entering the case 4 through the suction port 9 and the exhaust port 10 is rectified and the disturbance is suppressed, so that the noise emitted from the case 4 is hardly generated and the noise from the main body is reduced. To be done. Further, since the magnetron 1 and the inverter power supply 2 are integrated in the case 4 to forcibly form the cooling passage, the cooling air is efficiently blown to the heat-generating components such as the magnetron 1 and the inverter power supply 2 with a small air volume to be sufficiently cooled. It

Next, FIG. 2 shows a second embodiment, which is an inverter power supply block for a microwave oven. Case 15
A centrifugal cooling fan 16 is housed inside together with the magnetron 1 and the inverter power supply 2. The cooling fan 16 is provided with a printed circuit board 3 on which power supply components constituting the inverter power supply 2 are arranged and a case 15 via a support component 5. It is fixed to. In addition, a suction port 17 and an exhaust port 18 are provided near the cooling fan 16 and on the downstream side of the magnetron 1,
Honeycomb structures 19 and 20 made of a conductive and non-magnetic material are attached to each of the cases in the same manner as the case 15.
In addition, a partition plate 23 is provided in the case 15 to block the intake port 21 and the discharge port 22 of the cooling fan 16. The cooling fan 16 includes an impeller 24 and a scroll-shaped casing 2.
5 and the DC motor 26, and the printed circuit board 3 also serves as the bottom plate of the casing 25.

In the above structure, the partition plate 23 blocks the negative pressure region corresponding to the upstream side of the cooling fan 16 and the positive pressure region corresponding to the downstream side of the cooling fan 16 in the case 15, so that the case 1
When the cooling fan 16 is operated in the cooling fan 5, cooling air (indicated by a solid arrow in the figure) passes from the suction port 17 through a passage formed by a large number of honeycomb lattices of the honeycomb structure 19, and the cooling fan 1
6 is introduced into the casing 25, enters the casing 25, is pressurized, and is discharged again into the case 15 through the discharge port 22 located near the center of the case 15. While cooling the inverter power supply 2 and the magnetron 1, the honeycomb structure 20 is removed. It is discharged to the outside of the case 15. As a result, the cooling fan 16, the magnetron 1, and the inverter power supply 2 are integrated in the case 15 in addition to the effect of reducing unnecessary radiation noise and noise, so that useless cooling air is not generated and all cooling air is generated. It is supplied to the magnetron 1 and the inverter power supply 2 for highly efficient cooling. Further, even if a motor such as the DC motor 26 with a brush that easily generates radiation noise is used as the driving motor, the generation of noise does not have to be a problem. Furthermore, by unitizing the power supply block, the arrangement of parts is simplified and the size of the microwave oven can be reduced. At the same time, automatic assembly is facilitated even when the microwave oven is attached to the main body, and cost can be reduced by reducing the number of assembly steps.

Next, another embodiment of the present invention will be described with reference to FIG. 3 is different from the above embodiment in that the suction port 17 is provided in the case 15 opposed to the suction port 21 of the cooling fan 16 and the outside of the case 15 is communicated with the suction port 21 by the honeycomb structure 19. As a result, the recirculation of the cooling air generated when the cooling fan 16 is arranged in the case 15 is
This is prevented by the honeycomb structure 19 and can be dealt with regardless of the seal with each surface of the case 15 and the complicated shape inside the case 15 which are necessary when the partition plate 23 is provided, and the assemblability can be further improved. Further, since the passage of the honeycomb structure 19 is directly opened to the intake port 21 of the cooling fan 16, an air guide is formed, and the conventional bell mouth-shaped intake port 21 provided for the lateral flow is required. Instead, the shape of the intake port 21 can be simplified.

In the embodiment shown in FIG. 4, the case 15 is provided with a holding portion A27 for holding a part of the honeycomb structure 19, the honeycomb structure 19 is inserted, and the honeycomb structure 19 is sandwiched between the holding portions B28 holding the other side. This is the case of the configuration. The holding portions A27 and B28 are made of a conductive material and are in electrical contact with the periphery of the honeycomb structure 19. As a result,
There is no electrical gap between the honeycomb structure 19 and the holding portions 27, 28, and noise is prevented from leaking to the outside.

Further, in the embodiment shown in FIG. 5, the honeycomb structure 19 is housed in a frame 29 that holds the periphery of the honeycomb structure 19 in advance, and the periphery of the frame 29 and the case 15 are attached so as to make electrical contact with each other. With such a configuration, it is possible to prevent noise leakage at the mounting portion of the honeycomb structure 19 and solve the processing of the weak surroundings during assembly, which simplifies the assembly.
Workability is improved.

In the above embodiments, the case where the honeycomb structure is used has been described, but the structure is not limited to this, and a structure equivalent to this, that is, a columnar body having a large number of through holes, may be used.

[0020]

As described above, according to the noise prevention device of the present invention, the following effects can be obtained. (1) A noise source such as an inverter power supply is housed in a case made of a conductive material, the case is arranged in a cooling passage, and an internal passage made of a conductive material is provided at an inlet and an outlet of the case for taking in cooling air. Since the aggregate of the columnar elements is provided, the aperture ratio can be increased and the leakage of noise to the outside can be suppressed. As a result, the pressure loss generated at the intake port and the exhaust port is significantly reduced, cooling air can be taken into the case, and the rotation speed of the cooling fan can be reduced. Further, since the flow of the cooling air at the intake port and the exhaust port is also rectified, there is no turbulence, and the noise emitted from the case is greatly reduced. (2) A cooling fan that cools the noise source together with the noise source is housed in a unit, so the cooling passage configuration is simplified and all the cooling air passes through the case and is efficiently blown to the heating element. To be cooled. Also, noise of the motor itself that drives the cooling fan is prevented from leaking to the outside of the case. As a result, a device having a unit can be downsized, and even when the device is mounted on the device, automatic assembly can be performed because the main components are unitized, and the cost can be reduced by reducing the number of assembly steps. (3) Since the suction port is provided on the case surface facing the cooling fan intake port and the assembly communicates the outside of the case with the intake port, recirculation between the cooling fan intake port and the discharge port inside the case is prevented. It is not necessary to provide a partition plate for the partition plate, and when the partition plate is provided, it is possible to deal with the seal with each surface of the case and the complicated partition shape in the case, and the assemblability can be further improved. Further, since the assembly serves as an air guide and guides the flow in the axial direction of the cooling fan, a bell mouth shape is not required for the intake port of the cooling fan, which can be simplified. (4) Since the holding portion holding the assembly and the case are in electrical contact with the entire circumference, noise leakage is completely prevented. (5) Since the periphery of the assembly is housed in a frame that holds it in advance, and the periphery of the frame and the case are attached so as to make electrical contact, noise is prevented from leaking at the assembly mounting portion, and it is also attached to the case. It will be easier and workability will be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a microwave oven according to an embodiment of the present invention.

FIG. 2 is a sectional view of an essential part of an inverter power supply block according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a main part of an inverter power supply block according to another embodiment.

FIG. 4 is a sectional view of a main part of a noise prevention device according to another embodiment.

FIG. 5 is a cross-sectional view of a main part of a noise prevention device according to another embodiment.

FIG. 6 is a perspective view of a noise prevention device in a conventional microwave oven.

[Explanation of symbols]

1, 2 Noise source 4, 15 Case 7 Cooling passage 9, 17 Suction port 10, 18 Exhaust port 11, 12, 19, 20 Column assembly (honeycomb structure) 16 Cooling fan 21 Inlet 27 Holding part A 28 Holding part B 29 Frame body

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Nakabayashi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Makoto Shibuya, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A forced cooling passage is provided with a case made of a conductive material having a suction port and an exhaust port and containing a noise source, and at least one of the suction port and the exhaust port is made of a conductive material. A noise prevention device provided with an assembly of columnar elements having a round internal passage. 2. A noise generating source, a case for containing a cooling fan, made of a conductive material having an inlet and an outlet, and an interior made of an electrically conductive material for at least one of the inlet and the outlet. A noise prevention device provided with an assembly of columnar elements having passages. 3. The noise according to claim 2, wherein a suction port is provided at a position facing the suction port of the cooling fan, and an assembly of columnar elements having an internal passage is provided so that the suction port and the suction port communicate with each other. Prevention device. 4. A case is provided with a holding portion A and a holding portion B for fixing an aggregate of columnar elements having internal passages, and at least one of the holding portion A and the holding portion B is made of a conductive material. The noise prevention device according to claim 1 or 2, wherein the noise prevention device has an electrical contact with the periphery of the assembly. 5. The structure according to claim 1, wherein a frame body for holding the aggregate is provided around the aggregate of columnar elements having an internal passage, and the frame is attached to the case while making electrical contact. Item 2. The noise prevention device according to item 2.