JPH1186703A - Thermal protector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the response speed, without increasing thickness by arranging a film-like resistor connected to a conductive to a conductive plate of a spring plate having a moving contact contacted to or separated from a fixed contact with a bimetal plate and an external between the bimetal plate and the conductive plate, so that main heating region generating a specific ratio of the heating value faces to the inversion region of a bimetal plate. SOLUTION: A bimetal plate 3 located on a side opposite to a fixed plate 1 having a fixed contact 1b across a conductive plate 2 of an elastic body having a moving contact 2b and a hook section 2c at the tip is inverter at a prescribed temperature or above, and it lifts up the hooked hook section 2c to make it nonconductive. A film-like resistor 5 of a metal foil connected in series with the conductive plate 2 and an external circuit is arranged between the conductive plate 2 fixed to a columnar member 6 through a fixing member 4 and the bimetal plate 3. A main heating region 5M, made of the meandering metal foil and generating 50% or more of the calorific value is provided between the bimetal plate 3 which is partially kept in contact with the film-like resistor 5 and the conductive plate 2, and heat transferred effectively through heat conduction and heat radiation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a thermal protector using a bimetal plate as a thermal element. The thermal protector is disposed in a power supply unit of the electric appliance, and cuts off the electric appliance from the power supply when an excessive current flows. Thus, when a failure occurs in the electric appliance, the power supply is cut off.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. Hei 6-20571 discloses that in order to increase the response speed of a thermal protector, a heating element is connected in series to the thermal protector and the thermal protector is heated by the heat generated by the heating element. ing.
In this thermal protector, since the heat generating portion is separated from the bimetal plate, the speed of heat transfer is low, and there has been a problem that the inside may be locally overheated before the bimetal plate operates.

[0003] JP-T-63-501833 describes that a heating element is arranged near a bimetal. In this invention, there remains a problem that the thermal protector cannot be made thin.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to increase the response speed without increasing the thickness of the thermal protector.

[0005]

The above object has been attained by forming the heating element with a film-shaped resistor and arranging the main heating area near the bimetal.

[0006]

1 to 5 show a first embodiment of the present invention. As shown in FIGS. 1 and 2, the fixed plate 1 is connected at one end to a first terminal A for connection to an external circuit, and has a fixed contact 1b at the other end.

The conductive plate 2 is made of an elastic electric conductor and has a movable contact 2b at one end. The movable contact 2b is arranged at a position facing the fixed contact 1b.

[0008] A bimetal plate 3 is provided on the opposite side of the fixed plate 1 of the conductive plate 2. One end of the bimetal plate 3 is loosely locked by a hook 2c formed at the tip of the conductive plate, and the other end is fixed by a fixing member 4 for fixing the conductive plate.

The bimetal plate 3 is a so-called snap-action type bimetal, in which, when the temperature exceeds a predetermined temperature, the sign of the curvature of the shape is suddenly reversed and the direction in which the plate recurs is reversed. In this example, the bimetal plate 3 is inverted at a portion not in contact with the fixing member 4. This part is called an inversion area.

When the temperature exceeds a predetermined temperature, the direction in which the bimetal is warped is reversed, the hook 2c of the conductive plate 2 is lifted, and the movable contact 2b is separated from the fixed contact 1b. As a result, the first terminal A and the second terminal B become non-conductive, and the electric appliance is cut off from the power supply.

In this embodiment, a film-like resistor 5 shown in FIGS. 3 and 4 is arranged between the conductive plate 2 and the bimetal plate 3.

The film-shaped resistor 5 is made of a metal foil (for example, a stainless steel foil having a thickness of 50 μm) 5b having a relatively large resistance.
Both surfaces are covered with flexible electric insulating thin films (for example, polyimide resin) 5a and 5c. Both ends 5d and 5e of the metal foil are exposed, and one end 5d is a conductive plate 2
The other end 5e is connected to a terminal B for connection to an external circuit or directly to the external circuit.

The conductive plate 2, the bimetal plate 3, and the film-shaped resistor 5 are fixed to a columnar member 6 by a fixing member 4. However, the main heat generating region that generates 50% or more of the heat generated by the film-shaped resistor 5 is outside this fixed portion, and the main heat generating region 5M is arranged in the space between the conductive plate 2 and the bimetal plate 3. Note that this can be attached to the conductive plate 2 and fixed.

The main heating area 5M is formed by meandering a metal foil. The electrical resistance can be adjusted by changing the thickness and width of the metal foil 5b.

As shown in FIG. 5, a fixed plate 1, a conductive plate 2,
The film resistors 5 are connected in series. Terminal A,
When a current flows between B, the film-shaped resistor 5 generates heat.
Since a part of the bimetal plate 3 serving as the temperature sensing part is in contact with the film-shaped resistor 5 and the main heat generating region 5M is arranged in the vicinity, heat is effectively transferred by heat conduction and heat radiation. Conveyed to.

When the electric appliance is normal, the heat generated by the electric current supplied to the electric appliance and the heat dissipation from the surface of the housing 7 of the thermal protector are balanced, and the temperature of the bimetal plate at that time is equal to that of the bimetal plate. The direction of the warping does not reverse.

When an abnormality such as an electrical short circuit occurs in the electric appliance, the current flowing through the film-shaped resistor 5 rapidly increases, the amount of heat generation increases, and the temperature of the bimetal plate 3 becomes higher than a predetermined temperature. The direction of the warping of the plate is reversed, the bimetal plate 3 lifts the hook 2c, and the movable contact 2b
Is separated from the fixed contact 1b, and the power supply from the power supply to the electric appliance is stopped. It is desirable that this operation be performed as quickly as possible.

In this embodiment, the metal foil as the resistor is formed of a stainless steel foil. Stainless steel has a relatively large temperature coefficient of electric resistance of about 1000 ppm / ° C. (a Ni foil can be used as a metal foil, in which case the temperature coefficient of electric resistance is about 6800 ppm / ° C.).
As a result, when self-heating occurs, the heat increases the resistance of the resistor itself. Thereby, the temperature rises at an accelerated rate.
That is, the time from the occurrence of an abnormality in the electric appliance to the interruption of the power supply is short. In general, when a metal foil having a substantially linear and positive temperature characteristic is used, this accelerated temperature rise phenomenon can be caused.

If a larger current is applied, the melting point of the metal foil resistor may be exceeded and the resistor may be blown before the thermal protector operates. That is, the film-shaped resistor can function as a fuse.

The conditions such as the current to be operated as a fuse are determined by locally adjusting the thickness and width of the metal foil.
It can be adjusted in the range of 1/5 to 1 time of the standard value.

Since the metal foil of the film-shaped resistor is covered on both sides with an insulating thin film, the fusing portion does not come into contact with another conductive portion. The thickness of the insulating thin film can be locally increased at a position corresponding to the portion to be blown off of the metal foil.

FIGS. 6 to 10 show a second embodiment of the present invention. In this embodiment, a bimetal plate is used as a conductive plate. That is, the conductive plate 8 made of a bimetal plate has the functions of the conductive plate 2 and the bimetal plate 3 in the first embodiment.

As shown in FIGS. 6 and 7, the fixed plate 1 is provided at one end with a first terminal A for connection to an external circuit, and at the other end with a fixed contact 1b.

The conductive plate 8 is made of a bimetal plate and has a movable contact 8b at one end. The movable contact 2b is arranged at a position facing the fixed contact.

The conductive plate 8 made of the bimetal plate is formed as a snap action type bimetal.

A film resistor 9 is connected to the other end of the conductive plate 8. The film resistor 9 has almost the same structure as the film resistor 5 in the first embodiment. That is, a metal foil 9b of stainless steel or the like is covered on both sides with flexible electric insulating thin films 9a and 9c.

Both ends 9d and 9e of the metal foil 9b are exposed, one end is fixed to the conductive plate 8 by welding or the like, and the other end is connected to a terminal B connected to an external circuit or directly to the external circuit. I have.

The main heating region 9M of the film-shaped resistor 9 is arranged near the conductive plate 8 made of a bimetal plate.
It can also be attached to a conductive plate.

The effect of the film resistor 9 is almost the same as the effect of the film resistor 5 in the first embodiment. In other words, the temperature rise is accelerated by the positive temperature coefficient of the resistance, and the fuse can be made to function as a fuse by fusing due to the temperature rise.

In the first embodiment, since the bimetal plate 3 and the conductive plate 2 are formed of different members, there is a wide choice of materials for the conductive plate 2, whereas in the second embodiment, the bimetal plate 3 and the conductive plate 2 are different. Since the plate and the conductive plate are formed integrally, there is little room for selecting a material. Therefore, in the second embodiment, the fact that the electric resistance can be adjusted by changing the thickness and width of the metal foil 9b of the film-shaped resistor is very advantageous in that the degree of freedom in design is increased. Characteristics.

[0031]

According to the present invention, the amount of generated heat increases at an accelerated rate with respect to the overcurrent, and the temperature of the bimetal plate immediately rises because the heat generating portion is disposed near the temperature-sensitive portion, so that the bimetal operates. This is equivalent to an increase in the current sensitivity of the thermal protector.

The effects of the present invention are summarized as follows. 1) It is possible to attach a series resistor with a minimal design change to a conventional component while keeping the conventional size. 2) Since the resistor is mounted near the bimetal, it is possible to realize high responsiveness with a minimum resistance value and stability that is hardly influenced by ambient conditions. 3) Since it is a film-shaped resistor, the shape can follow the operation of the conductive plate and the bimetal. For this reason, even if it is mounted near the bimetal, there is no problem in operation. 4) Since the temperature characteristic of the resistor has a positive value and the resistance is increased in accordance with the heat generated by energization, the response is higher. 5) The resistor is insulated on both sides, so that even if the resistor blows due to the flow of an excessive current, the blown portion does not come into contact with another energized portion.

[Brief description of the drawings]

FIG. 1 is a sectional plan view of a thermal protector according to a first embodiment of the present invention.

FIG. 2 is a sectional elevation view of the thermal protector of FIG.

FIG. 3 is a perspective view of a film-shaped resistor of the thermal protector of FIG.

FIG. 4 is an exploded perspective view of the film-shaped resistor of FIG.

FIG. 5 is a view showing an electrical connection relationship of the film-shaped resistor of FIG. 1;

FIG. 6 is a sectional plan view of a thermal protector according to a second embodiment of the present invention.

7 is a sectional elevation view of the thermal protector of FIG.

FIG. 8 is a perspective view of a film-shaped resistor of the thermal protector of FIG.

FIG. 9 is an exploded perspective view of the film-shaped resistor of FIG.

FIG. 10 is a diagram showing an electrical connection relationship of the film-shaped resistor of FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixed plate 1b Fixed contact 2 Conductive plate 2b Movable contact 2c Hook 3 Bimetal plate 4 Fixed member 5 Film-shaped resistor 5a, 5c Electrically insulating thin film 5b Metal foil 5d, 5e End 5M Main heating area 6 Columnar member 7 Housing Reference Signs List 8 conductive plate 8b movable contact 9 film-like resistor 9M main heating area 9a, 9c electrically insulating thin film 9b metal foil 9d, 9e end A terminal B terminal

Claims (6)

[Claims] 1. A bimetal plate whose reversing direction is reversed when a set temperature is exceeded, a fixed plate having one end connected to an external circuit and having a fixed contact at the other end, and a movable contact at a position facing the fixed contact. A conductive plate made of a spring plate, the movable contact of which is in contact with and separated from the fixed contact by the bimetal plate; and a resistor made of a film-shaped resistor connected in series to the conductive plate and having one end connected to an external circuit. In the thermal protector, the heating value of the resistor is 50
A thermal protector, wherein the resistor is arranged between the bimetal plate and the conductive plate such that a main heat generating region in which the% or more is generated faces an inversion region of the bimetal plate. 2. A fixed plate having one end connected to an external circuit and having a fixed contact at the other end, and a bimetal plate whose reversing direction is reversed when a set temperature is exceeded, and having a movable contact at a position facing the fixed contact. A thermal protector including a conductive plate, comprising: a resistor formed of a film-shaped resistor having one end connected to an external circuit and the other end connected in series to the conductive plate;
A thermal protector, wherein the resistor is arranged such that a main heat generating region where 50% or more of the heat generation of the resistor is generated faces the bimetal plate. 3. The thermal protector according to claim 1, wherein a part of the resistor is blown by an excessive current, and the blown part does not contact another conductive part. 4. The thermal protector according to claim 1, wherein said resistor has a substantially linear positive temperature coefficient. 5. The thermal protector according to claim 1, wherein a main heating region of the resistor is attached to the conductive plate. 6. The thermal protector according to claim 1, wherein said resistor has a stainless steel foil coated on both sides with an insulating polyimide resin.