JP2868815B2 - Magnetron for microwave oven - Google Patents

Description

The present invention relates to a magnetron for a microwave oven, and more particularly to an improvement in a high-frequency output unit thereof.

(Prior Art) The main part of a magnetron for a microwave oven is generally a third type.
The configuration is as shown in the figure. In the figure, reference numeral 11 denotes an oscillation part main body, 12 denotes an anode cylinder, 13 denotes a plurality of anode vanes constituting a part of a cavity resonator, 14 denotes a strap ring, 15 denotes a filament cathode, 16 denotes an end shield thereof, 17, 18
Is a pole piece fixed to the open end of the anode cylinder 12, 19
Is a cylindrical metal container, 20 is a high-frequency output part, 21 is a ceramic cylinder of the output part, 22 is a sealing ring at the output tip, 23 is a metal exhaust pipe hermetically bonded thereto, 24 is a metal cap of the output part, and 25 is an output antenna One end 25 a is electrically connected to one of the vanes 13, passes through the through hole 17 a of the pole piece 17, penetrates the metal container 19, and the ceramic cylinder 21, and has a tip 25 b connected to the metal exhaust pipe 23. And hermetically sealed off.

Further, reference numeral 26 denotes a ring-shaped permanent magnet coaxially arranged on the outer periphery of the metal container 19, 27 denotes a yoke made of a ferromagnetic material, 28 denotes a ferromagnetic thin plate, and 29 denotes a reticulated conductive gasket.

A small diameter first harmonic choke metal cylinder 30 is hermetically soldered to the lower end of the ceramic cylinder 21, and a second harmonic choke metal cylinder 31 is positioned on the outer periphery thereof. Touched. The second harmonic choke metal cylinder 31 is hermetically soldered to the tip of the metal container 19, and the tip 31 a holds the inner periphery of the gasket 29.

With this structure, the quarter-wave choke groove C _{2 for the second} harmonic, the choke groove C ₄ for the fourth harmonic, and the metal container 19 and its inner space 2 are formed in the metal exhaust pipe 23.
5th harmonic choke groove C ₅ by three metal cylinders 30 and 31
Third harmonic choke groove C ₃ are formed.

In addition, the metal container 19 and the metal cylinders 30 and 31 for both chokes are formed of thin ferromagnetic cylinders made of iron or an iron alloy.

The first harmonic choking metal cylinder 30, the necessary and sufficient for obtaining a choke effect, small and fifth harmonic wavelengths that the inner diameter D ₁ is than the inner diameter D ₂ of the ceramic cylinder 21 1 /
It is set to a dimension smaller than 2.

In such a magnetron, a fundamental wave of, for example, 2450 MHz is efficiently radiated from the output unit during operation, while external radiation of each harmonic component is suppressed by the choke effect of the choke groove.

(Problems to be Solved by the Invention) As described above, in order to obtain a reliable choke effect on a higher harmonic component such as the fifth harmonic, the inner diameter of the first harmonic choke metal cylinder 30 is increased. Needs to be reduced to some extent. With such a small diameter, of course, this choke metal cylinder 30 and the anode passing inside it
The distance S from the distance 25 becomes shorter. A high high-frequency voltage is applied between them, and high-frequency discharge may occur due to a relationship with a reflected wave from a harmonic load such as a microwave oven.

Assuming an extreme case, during use of the microwave oven, if for some reason the rotation of the stellar fan stops and there is little or no heated object that is a high-frequency load, the high-frequency reflection to the magnetron is stationary Wave ratio (VSWR) can be over 30.

In such a case, a discharge occurs between the antenna lead 25 and the metal cylinder 30 for harmonic choke, and in an extreme case, a part of the antenna lead 25 or the metal cylinder 30 for harmonic choke generates heat due to high-frequency discharge and melts. It is also possible to do.
If any part is melted, a gas discharge is caused locally by the generated gas, and furthermore, the high-frequency electric field is disturbed and reflected by them, causing a chain discharge in the output part area and a fatal part of each part. It is conceivable that excessive melting and breakage may occur.

Such high frequency discharge can be presumed to be a multipactor discharge phenomenon in many cases. That is, the leaked DC magnetic flux from the permanent magnet 26 extends substantially parallel to the tube axis in the space between the antenna lead 25 and the harmonic choke metal cylinder 30. The magnetic flux in this space has a substantially axially symmetric distribution. These metal parts usually have a secondary electron emission ratio of 1
Since the electrons are larger, when floating electrons or the like collide with the antenna lead 25 or the inner surface of the metal cylinder 30 for harmonic choke, secondary electrons are generated.

The electrons are accelerated or decelerated by a high-frequency electric field between the antenna lead 25 and the harmonic choke metal cylinder 30. If an electron emitted from one of the two conductors encounters a high-frequency accelerating electric field, it is accelerated and collides with the other conductor, emitting many secondary electrons. If this high-frequency electric field reverses and becomes an electric field that accelerates these secondary electrons in the direction of the original conductor, these secondary electrons are also accelerated and collide with the original conductor, releasing many secondary electrons again. I do.

When the electrons and the high frequency electric field synchronize in this way, the secondary electrons will increase exponentially and increase in energy, so that both conductors will heat up and eventually cause melting. Such a phenomenon is a discharge called a double side multipactor.

On the other hand, the electrons make a swirling motion due to the DC magnetic field existing in this region. If the cycle of the high-frequency electric field and the cycle of the circling motion of the electrons are synchronized, it is presumed that secondary electrons are cumulatively generated, and the metal cylinder material rapidly generates heat due to its collision energy and finally melts. Such a phenomenon is called one-sided multipactor discharge.

The present invention more reliably suppresses the occurrence of multipactor discharge in the high-frequency output section even when operated under the above-mentioned severe conditions, and prevents the metal cylinder for harmonic choke and the antenna lead from being blown. It is an object of the present invention to provide a magnetron for a microwave oven.

[Constitution of the Invention] (Means for Solving the Problems) The present invention relates to a portion of a flange portion of a metal cylinder for harmonic choke from a brazing portion to another adjacent member to an inner peripheral surface of the metal cylinder. This is a magnetron for a microwave oven in which a circumferential recess is formed.

According to the present invention, the brazing filler metal is stored in the concave portion provided in the flange portion of the metal cylinder for harmonic choke and does not flow to the inner peripheral surface of the metal cylinder. Is suppressed. As a result, it is possible to prevent the metal cylinder for harmonic choke and the antenna lead from fusing.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

A magnetron for a microwave oven that generates a fundamental wave in the 2450 MHz band to which the present invention is applied is configured as shown in FIGS. 1 and 2, wherein FIG. 1 shows the whole and FIG. 2 shows the first harmonic. 3 shows a metal cylinder for chalk.

That is, a plurality of vanes 13 are radially arranged inside the anode cylinder 12 constituting the oscillating portion main body 11 to constitute a cavity resonator. Upper and lower ends of each vane 13 are connected to every other by a pair of large and small strap rings 14, respectively. In the electron working space surrounded by the free ends of the plurality of vanes 13, a helical filament cathode 15 is disposed along the axis of the anode cylinder 12, and each end is an end shield.
Fixed to 16.

Furthermore, a substantially funnel-shaped pole piece 17, 18 is fixed to each end of the anode cylinder 12, and a cylindrical metal container 19 is also fixed to one pole piece 17 in contact with one end of the anode cylinder 12. I have.

At the upper opening end of the metal container 19, a second harmonic choke metal cylinder 31 having a large-diameter portion and a small-diameter portion is hermetically bonded. In this case, the step portion between the large-diameter portion and the small-diameter portion is air-tightly joined to the opening end of the metal container 19, the large-diameter portion is approximately the same diameter as the metal container 19, and the output portion is a ceramic cylinder 21.
Is in contact with the gasket ring 29.
The small-diameter portion is disposed coaxially inside the metal container 19 so as to extend in the vane direction. And the metal container 19 and the second
Of the metal cylinder 31 for harmonic choke
1-wavelength choke C ₃ quarters for harmonic suppression is configured.

Inside this second harmonic choke metal cylinder 31,
A small diameter first harmonic choke metal cylinder 30 is coaxially disposed on the second harmonic choke metal cylinder 31 and the metal container 19. In this case, the first harmonic choke metal cylinder 30 is shorter in length than the second harmonic choke metal cylinder 31 and has a flange portion 30a at one end. The peripheral portion of the flange portion 30a is hermetically joined to the step between the large-diameter portion and the small-diameter portion of the cylinder 31, and the vicinity of the center of the flange portion 30a is brazed to the lower end portion of the ceramic cylinder 21. . By the small diameter portion and the first harmonic choking metal cylinder 30 of the second harmonic choking metal cylinder 31, 1-wavelength choke C ₅ quarters for the fifth harmonic suppression is configured I have.

As is clear from FIG. 2, the first harmonic choke metal cylinder 30 has a flange portion 30a extending from the brazed portion of the ceramic cylinder 21 to the inner peripheral surface thereof in the circumferential direction. Are formed, which is a feature of the present invention.

As described above, the lower end face of the ceramic cylinder 21 constituting the output section is air-tightly joined to the flange portion 30a of the first harmonic choke metal cylinder 30 by brazing. , A holding ring 22 is hermetically joined. An output portion metal cap 24 is fixed to a side surface of the holding ring 22, and a metal exhaust pipe 23 is hermetically joined and held at an inner bent portion of the holding ring 22. or,
One end 25a of an antenna lead 25 is electrically connected to one of the vanes 13, and this antenna lead 25 is
Extends through the output portion 20 along the tube axis through the through hole 17a,
The other end 25b is fixedly held by the exhaust pipe 23.

The fourth 1-wavelength choke C ₄ quarters for harmonic suppression is formed by a retaining ring 22 and the exhaust pipe 23, an exhaust pipe
1-wavelength choke C ₂ quarters for the second harmonic suppression is comprised of the 23 and the antenna lead 25.

A permanent magnet 26 having a tapered lower portion on the inner surface is provided on the outer periphery of the metal container 19. These permanent magnets
A frame yoke 27 is provided so as to surround the anode cylinder 12, the cooling fins (not shown) attached to the outer periphery of the anode cylinder 12, and the like. The center hole of the frame-shaped yoke 27
A gasket ring 29 is provided between the large-diameter portion of the metal cylinder 31 for harmonic choke. One surface of the permanent magnet 26 is in contact with the frame yoke 27 and the gasket ring 29 via the magnetic guide plate 28, and the other surface is in contact with the projection of the metal container 19.

Now, in the case of a magnetron for a microwave oven with a high frequency output of about 500 W at a fundamental wave oscillation frequency of the 2450 MHz band, between the antenna lead 25 and the first harmonic choke metal cylinder 30 when there is no high frequency reflection from the load side. The high frequency voltage of about 45
It is estimated to be around 0V. However, when the high-frequency reflection from the load side is large, it is estimated to exceed 1000V.

By the way, Ag and Au contained in the brazing filler metal have a high secondary electron generation ratio in a very wide collision energy range.
Conversely, if Ag adheres to the surface of the first harmonic choke metal cylinder 30 facing the antenna lead 25, the above-described multipactor discharge phenomenon is extremely likely to occur.

However, in the present invention, as described above, the circumferential concave portion 3a is formed in the flange portion 30a of the first harmonic choke metal cylinder 30.
2 is formed, and the Ag-containing brazing material that has flowed out from the brazing portion with the ceramic cylinder 21 accumulates in the concave portion 32 and is closed, and the first harmonic choke metal cylinder 30 facing the antenna lead 25 is formed. It does not flow on the inner peripheral surface. Therefore, generation and continuation of the multipactor discharge can be prevented.

[Effects of the Invention] As described above, according to the present invention, of the flange portion of the metal cylinder for harmonic choke, the circumferential portion extends from the brazing portion with the other adjacent member to the inner peripheral surface of the metal cylinder. A recess in the direction is formed, and the brazing material is stored in the recess and does not flow on the inner peripheral surface of the metal cylinder for harmonic choke. Therefore, it is difficult to generate and maintain the multipactor discharge in the space between the antenna lead.

As a result, heat generation and fusing of the metal cylinder for harmonic choke and the antenna lead can be prevented beforehand, and stable operation with high reliability can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a magnetron for a microwave oven according to an embodiment of the present invention, and FIG. 2 is a front view including a partial cross-section showing a metal cylinder for a first harmonic choke in the magnetron for a microwave oven according to the present invention. FIG. 3 is a sectional view showing a conventional magnetron for a microwave oven. 12 ... Anode cylinder, 13 ... Vane, 17, 18 ... Pole piece, 19 ... Metal container, 21 ... Ceramic cylinder, 25 ... Antenna lead, 30 ... Metal cylinder for first harmonic choke, 32 ... recess.

Claims (1)

(57) [Claims] 1. A cavity resonator is formed by fixing a plurality of anode vanes inside an anode cylinder. A pole piece is fixed to an open end of the anode cylinder, and a cylindrical metal container is joined. An output ceramic cylinder is joined to the open end of the container, and an antenna lead, one end of which is electrically connected to the cavity resonator, extends through the inside of the metal container and the ceramic cylinder. A metal cylinder for harmonic choke having a smaller diameter than the antenna lead and having a flange portion brazed to another surrounding member surrounding the antenna lead is provided, and a ring-shaped permanent magnet is provided on the outer periphery of the metal container. In the magnetron for a microwave oven arranged, a flange portion of the metal cylinder for harmonic choke, from a brazing portion with the other adjacent member, is connected to the inner periphery of the metal cylinder. A magnetron for a microwave oven, wherein a concave portion in a circumferential direction is formed in a portion reaching a surface.