Arc-suppressing switching device

BACKGROUND OF THE INVENTION

In conventional bimetallic element containing thermostats for use in electric blankets, electric irons, electric cookers, electric foot warmers, and the like, there are provided capacitors, resistors, semiconductor elements having a nonlinear voltage current characteristic, such as a thermistor or various rectifiers, or combinations thereof connected between the contacts in order to suppress or extinguish the arcs which occur during the opening and closing of the contacts. These conventional thermostats, however, have the drawback that they are complicated and have large terminal structures, making them inconvenient to manufacture and use, because said capacitors, resistors, semiconductor elements, or the combinations thereof must be connected to the switch terminals by being riveted or soldered thereto.

SUMMARY OF THE PRESENT INVENTION

The present invention seeks to overcome the above-mentioned shortcomings of conventional switching devices by interposing one or more arc-suppressing substances, for instance, a high dielectric constant material, resistance material or semiconductor material, between the contact plates, and 25 also mechanically fixing as well as electrically connecting said substance to said contact plates.

Thus, one object of the present invention is to provide a novel switching device which is capable of suppressing or extinguishing arcing during switching, and thereby suppressing the production of radio-wave disturbances, and at the same time, considerably prolonging the life of the contacts by minimizing wear.

Another object of the present invention is to provide a novel switching device which has a simple structure and is small in size despite its arc-suppressing ability, making its manufacture and use easy.

A further object of the present invention is to provide a novel switching device which is capable of suppressing of extinguishing arcs without a substantial change in the conventional construction and size.

shaped element 5 is the fixed end of the moving contact plate 2. Due to such construction, a satisfactory electrical connection is obtained between the impedance element 5 and the fixed contact plate 1, and between the impedance element 5 and the moving contact plate 2. At the same time, a strong mechanical connection is achieved. Fixed contact plate 1 has a pair of mounting pieces 6 thereon for mounting this switching device on an insulated casing or frame. Respective connecting terminals 7 and 8 of the fixed contact plate 1 and the moving contact plate 2 project laterally therefrom.

The impedance element 5 is made of a high dielectric constant material, electric resistance material, semiconductor material having a nonlinear resistance characteristic, such as a thermistor, a rectifier, or the like.

¹³ Said impedance element functions as an arc-suppressing or arc-extinguishing means depending upon the material of the element.

When a high dielectric constant material is employed for 2θ said impedance element 5, the equivalent circuit of the switching device is as shown in FIG. 4α.

In FIG. 4α are shown said fixed contact 3 and moving contact 4, respectively. A capacitance 5α of high dielectric constant and having a high relative permitivity such as 1000— 10,000 corresponds to the impedance element 5. Titanates (for instance, BaTiO₃, PbTiO₃), niobates (for instance, KNbO₃), tantalates (for instance, KTaO₃), etc. can be employed as said high dielectric constant material. Said capacitance 5α is between said fixed contact plate 3 and moving contact plate 4, and thus, the arcs which tend to be produced between the contacts 3 and 4 are extinguished or suppressed by the action of capacitance 5α.

As shown in FIGS. 1 and 3, assuming the width dimension (perpendicular to the plane of the paper in FIG. 3) of said high dielectric constant material to be h·, the thickness to be /, and the length in contact with said moving contact plate 2 to be 21, the capacity c of said capacitor 5α is given by the following equation:

2e<> · e, · Iw c =-------t

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an arc-suppressing switching device according to the present invention;

FIG. 2 is a sectional side elevation view of the embodiment shown in FIG. 1;

FIG. 3 is an enlarged sectional side elevation view indicating one part of the embodiment shown in FIG. 2;

FIGS. 4α, 4b, 4c and 4d are equivalent circuit diagrams of embodiments of the present invention;

FIGS. 5α and 5b are characteristic curves for a semiconductor element employed in the embodiments of the present invention;

FIG. 6 is a sectional side elevation view of another arc-suppressing switching device according to the present invention;

FIG. 7 is a sectional side elevation view of another arc-suppressing switching device according to the present invention; and

FIGS. 8α and 8b are equivalent circuit diagrams of the embodiment of the arc-suppressing switching device shown in FIG. 7.

DETAILED DESCRIPTION OFTHE INVENTION

In FIGS. 1—3, the switching device shown has a fixed contact plate 1 supporting a moving bimetallic contact plate 2. On the free end of said fixed contact plate 1 is mounted a fixed contact 3, while on the free end of said moving contact plate 2 is mounted a moving contact 4 which is opposite fixed contact 3. These contacts 3 and 4 contact and separate from each other due to the action of the bimetallic moving contact plate 2 with changes of temperature. A U-shaped impedance element 5 is mounted on fixed plate 1 and inserted inside the U45 wherein:

e„ is the dielectric constant of a vacuum, and e, is the relative permitivity of the high dielectric constant material.

Therefore, supposing 21 = 20mm., w = 5mm., t = 0.5mm., €„ = 5,000, the capacitor 5a will have a capacity of 0.009 microfarad. This capacity is useful for thermal relays usually employed in electric blankets, electric cushions, electric foot warmers, and the like.

Where electric resistance material is employed for said arcsuppressing impedance element 5, the equivalent circuit of the switching device is as shown in FIG. 4b.

In FIG. 4b are shown said fixed contact 3 and moving contact 4, respectively, A resistance 5b is the equivalent of the impedance element 5. As said resistance 5b is between said fixed contact plate 3 and moving contact plate 4, any arc which tends to occur during the opening motion of the contacts 3 and 4 is effectively extinguished or greatly suppressed due to a suppression of the voltage between said contacts at the moment of their opening.

Assuming by the way of example that the power source voltage is 100 volts, and an electric blanket heater having a total resistance of 100 ohms is connected to said power source through five of these switching devices in series, and the resistance of each of said resistances 5b is 1 kiloohm, the voltages induced between said contacts in each switching device when the contacts are open is very low, resulting in prolonging the life of the contacts ten times the life without such suppressing means.

The resistance material for impedance element 5 can be a metallic resistance material such as ferro-chrome-aluminum alloy, ferro-chromium alloy or ferro-nickel alloy, or a non3,562,584 metallic resistance material such as carbonized ceramic, and the like, depending on the temperature or resistance required.

The equivalent circuit diagram where the impedance 5 is a board-shaped thermistor having a voltage current characteristic curve as shown in FIG. Sa is shown in FIG. 4c.

In FIG. 4c is shown said fixed contact 3 and said moving contact 4, respectively, and the equivalent thermistor Sc is shown connected in shunt thereto.

Due to the connection of the thermistor Sc between the contacts 3 and 4, arcing between them can be greatly suppressed.

The equivalent circuit diagram of the arc-suppressing switching device of this invention in which the impedance element 5 is a board-shaped back-to-back connected composite rectifier element having a voltage current characteristic as shown in FIG. 5b is shown in FIG. 4d.

In FIG. 4d is shown fixed contact 3 and moving contact 4, respectively, with an equivalent back-to-back series-connected composite rectifier element 5d.

Selenium rectifiers, germanium diodes, silicon diodes, or cuprous oxide rectifiers, can be employed for said component rectifier 5.

Due to the Zener effect of the composite rectifier element connected between the contacts 3 and 4, the voltage induced between said contacts is effectively absorbed therein, resulting in effective suppressing of arcing.

In the embodiment of FIG. 6, a fixed contact plate 61 has a fixed contact 63 on its free end. A moving bimetallic contact plate 62 has a moving contact 64 on its free end. Said fixed contact plate 61 and moving contact plate 62 are mechanically connected through insulating piece 66. An impedance element 65 for suppressing or extinguishing the arc is positioned between said pair of contact plates having the opposite end faces connected to the respective contact plates 61 and 62.

High dielectric constant material, electric resistance material, and semiconductor elements having nonlinear resistance, can be used for the impedance element 65. The insulating piece 66 can also be of the same material as said impedance element 65.

The switching device of this embodiment performs as well as those described above.

FIG. 7 shows a fixed contact plate 71 having a contact 73 on its free end. A moving bimetallic contact plate 72 has a fixed contact 74 on its free end. Said fixed contact plate 71 and said moving contact plate 72 are mechanically connected by insulating piece 76. Two different kinds of impedance elements 75 and 77 for suppressing or extinguishing the arc are inserted between said pair of contact plates having their respective terminal faces contacting said contact plates 71 and 72. The two different impedances are selected from materials consisting of high dielectric constant material, electric resistance material and semiconductor elements having a nonlinear resistance characteristic. The insulating piece 76 mechanically connects the two contact plates 71 and 72, while electrically insulating them. This insulating piece can be mica, ceramic or synthetic resin.

FIG. 8α shows the equivalent circuit of this embodiment when impedance element 75 is electric resistance and impedance element 77 is high dielectric constant material. The equivalent resistance is shown at 75α and the equivalent capacitance at 77α. Resistance 75α and capacitance 77α are in parallel with said contacts 73 and 74, so that they satisfactorily absorb the impulsive voltage induced at the moment of switching, and hence, extinguish the arcing.

As described above in connection with the several embodiments, the switching device according to this invention is simple in its construction, small in size, and convenient to use. It performs well in suppressing or extinguishing arcs, and consequently in reducing or eliminating radio-wave disturbances. It also minimizes wear of contacts. All of these features are present and yet the construction is not any different in size and only slightly more complex than conventional switching devices.