JPH0757604A - Thermal overload relay - Google Patents

Abstract

PURPOSE:To elongate action time of a thermal overload relay. CONSTITUTION:Plural thin plates 6 of thermal conductor are laminated and held between a bimetal 4 and a heater 5 for composing a heater element of a thermal overload relay. The bimetal 4 is thus heated after the thin plates 6 are heated by the heater 5, so time till the bimetal gets to a specified action temperature delays to elongate action time of the termal relay. This action time can be regulated as desired by changing the number or thickness of the thin plates 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal overload relay (hereinafter referred to as a thermal relay) for opening and closing contacts by utilizing the deformation of a bimetal heated by a heater which generates heat by electric current to protect an electric motor from overload. ,), And in particular to means for delaying its operating time.

[0002]

2. Description of the Related Art A motor to be protected by a thermal relay has various characteristics such as a long starting time and a high and low heat resistant temperature. A thermal relay also has a long operating time or a short operating time according to these characteristics, or Various characteristics such as average one are required. In that case, conventionally, in order to prolong the operating time of the thermal relay, as shown in FIG. 6, the saturable reactor 2 is connected in parallel with the heat element of the thermal relay 1. Reference numeral 3 is an electromagnetic contactor to which the thermal relay 1 is attached.

The saturable reactor 2 does not saturate at the terminal voltage when a rated current flows, and therefore has a large impedance, so that shunting to the reactor hardly occurs, while it saturates when an overcurrent flows. Impedance decreases, and the shunt current to the reactor increases. Therefore, for example, even if a current that is 6 times the rated current flows in the circuit, only about 3 to 4 times the rated current flows in the heater of the thermal relay 1, resulting in a delay in the operating time of the thermal relay 1.

[0004]

However, the conventional structure in which the saturable reactor is provided in parallel with the heat element is as follows.
As can be seen from FIG. 6, since the saturable reactor projects to the outside, the external dimensions are large and the cost is high.
Further, in the conventional configuration, it is difficult to finely set the operation time according to the customer's request. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a thermal relay that has a long external operation time, a small external size, is inexpensive, and can easily and finely set the operating time.

[0005]

The present invention achieves the above object by laminating a plurality of flexible thin plates of a thermal conductor and sandwiching them between a heater and a bimetal. Further, the present invention achieves the above object by laminating and stacking a plurality of flexible thermal conductor thin plates on the surface opposite to the bimetal heater. In the above-mentioned thermal overload relay, if the thin plates or the thin plate and the bimetal are joined by spot welding, there is an advantage that the assembling work becomes easy.

[0006]

The operation time of the thermal relay is determined by the speed at which the temperature of the bimetal rises, but if the heat capacity of the heat element increases, the time required for the bimetal to reach the operation temperature becomes longer as described below. Now, i: current,
R: heater resistance, t: time, θ ₁ : operating temperature of bimetal, θ ₀ : ambient temperature, q: heat capacity of heat element,
H: Assuming the heat dissipation coefficient,

[0007]

## EQU1 ## i ² Rdt = q dθ + H (θ ₁ −θ ₀ ) dt. Note that i ² Rdt in the equation is the amount of heat generated by the heater, q
dθ is the amount of heat accumulated in the heat element, H (θ ₁ −
θ ₀ ) dt means the amount of heat dissipated by the heat element. The solution of Equation 1 above is

[0008]

[Equation 2] θ ₁ −θ ₀ = i ² R / H · (1−e ^{−H / q · t} ). If the heat capacity q is increased by this Equation 2, the operating temperature θ
It can be seen that the time t to reach ₁ increases. Specifically, when the thermal conductor is sandwiched between the heater and the bimetal, the heater heats the thermal conductor and then heats the bimetal, so that the operation time is delayed. Also, if a thermal conductor is placed on the surface of the bimetal opposite to the heater,
The heat of the heater is directly transferred to the bimetal, but the heat is taken away by the thermal conductor, which delays the operation time. When a plurality of thermal conductors are formed into a thin plate and stacked, the operating time can be adjusted arbitrarily and finely by changing the number and thickness of the thin plates. In that case, if the thin plates are joined together, or if the thin plates and the bimetal are joined by spot welding, the thin plates are well organized during assembly and the work is facilitated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. Embodiment 1 FIGS. 1 to 4 show an embodiment in which a thin plate of a thermal conductor is sandwiched between a heater and a bimetal. FIG. 1A is a side view of a heat element, and FIG. 1B is its right side. Front view, Figure 2
1 is an exploded side view of the heat element of FIG. 1, FIG. 3 is a perspective view for explaining the concept of joining the thin plates of the thermal conductor in FIG. 1 by spot welding, and FIG. 4 is the same as the thin plate of the thermal conductor in bimetal by spot welding. It is a perspective view explaining the concept which joins.

In FIGS. 1 and 2, a plurality of thin plates 6 of a thermal conductor are laminated and sandwiched between a bimetal 4 and a heater 5 for heating the bimetal 4, and these are wound with an insulating material 7 interposed therebetween. It is integrally fastened as shown by a stopper plate 8 (FIG. 1). The heater 4 is configured by folding a belt-shaped resistor in a W shape, and terminals 9 and 10 are attached to both ends. A spacing piece 11 made of an insulating material is interposed between the surfaces of the resistors that face each other.

The bimetal 4 is in the form of a strip and has a mounting plate 12 fixed to the upper end thereof. The illustrated heat element is fixed to the case (not shown) with screws via the mounting plate 12. The thin plate 6 of the thermal conductor may be any one as long as it has a required heat capacity and is flexible so as not to hinder the bending of the bimetal 4, and for example, a copper plate or a brass plate can be used. If a plurality of thin plates 6 to be laminated are joined by spot welding at at least one point A as shown in FIG. 3, they are not dispersed during assembly and workability is improved. Also, FIG.
As shown in FIG. 5, even if the plurality of laminated thin plates 6 are joined to the bimetal 4 by spot welding at at least one point B, workability is similarly improved.

As is well known, two or three elements of the heat element are housed in a case, and the tip of the bimetal 4 is connected to an operating portion having a contact switching mechanism via an interlocking plate. When the heater 5 generates heat due to the current flowing through the heating circuit from the terminal 9 through the heater 5 to the terminal 10, and the curvature of the bimetal 4 whose temperature has risen reaches a specified amount, the contacts are switched and electromagnetic contact is made. The exciting current of the device is cut off and an alarm is issued.

In this case, according to the configuration shown in the figure, the heater 5 heats the bimetal 4 through the thin plates 6 of a plurality of thermal conductors having a constant heat capacity, so that the time until the bimetal 4 reaches the operating temperature is delayed. Therefore, the operation time of the thermal relay becomes longer accordingly. As an example, by sandwiching several 0.1 mm-thick copper plates, the operation time was delayed about twice. Therefore, an arbitrary operating time characteristic can be obtained by adjusting the number and thickness of the thin plates 6.

Embodiment 2 FIG. 5 is a side view of a heat element showing an embodiment in which a thin plate of a thermal conductor is superposed on the surface opposite to the bimetal heater. In this embodiment, a plurality of thin plates 6 of a thermal conductor are laminated on the surface of the bimetal 4 on the side opposite to the heater 5 and stacked, and are fastened with a clasp 8 via an insulating material 7.
In such a configuration, the thin plate 6 takes away the heat of the bimetal 4 heated by the heater 5, so that the temperature rise of the bimetal 4 is delayed, and accordingly the operating time of the thermal relay becomes longer. However, since the heat of the heater 5 is directly transferred to the bimetal 4 in this embodiment, the degree of delay of the operation time is smaller than that in the embodiment of FIG. Therefore, the configuration of either the first embodiment or the second embodiment may be selected according to the required operating characteristics. Also in this case, if the thin plates 6 or the thin plate 6 and the bimetal 4 are joined by spot welding, the assembling work becomes easy.

[0015]

According to the present invention, a plurality of thin sheets of a flexible thermal conductor are laminated and sandwiched between the heater and the bimetal, or simply laminated on the surface of the bimetal opposite to the heater. Since the operation time can be delayed, the external dimensions do not increase due to the additional parts protruding to the outside, and the operation can be performed at an extremely low cost. The operating time can be arbitrarily adjusted by changing the number and thickness of the thin plates of the thermal conductor, and it is possible to finely meet any customer request.

[Brief description of drawings]

FIG. 1A is a side view of a heat element showing an embodiment of the present invention, and FIG. 1B is a right front view thereof.

2 is an exploded side view of the heat element of FIG. 1. FIG.

FIG. 3 is a perspective view showing the concept of joining the thin plates of the thermal conductor in FIG. 1 by spot welding.

FIG. 4 is a perspective view showing the concept of joining the thin plate of the thermal conductor in FIG. 1 to a bimetal by spot welding.

FIG. 5 is a side view of a heat element showing another embodiment of the present invention.

FIG. 6 is a front view showing a conventional thermal relay mounted on an electromagnetic contactor.

[Explanation of symbols]

 4 Bimetal 5 Heater 6 Thin plate 7 Insulating material 8 Stopper 9 Terminal 10 Terminal 11 Spacing piece 12 Mounting plate

Claims (3)

[Claims] 1. A thermal dynamic overload relay that opens and closes contacts by utilizing the deformation of a bimetal heated by a heater that generates heat with an electric current by laminating a plurality of flexible thermal conductor thin plates. A thermal overload relay characterized by being sandwiched between a metal and a bimetal. 2. A thermal dynamic overload relay that opens and closes contacts by utilizing the deformation of a bimetal heated by a heater that generates heat with an electric current, wherein a thin plate of a flexible thermal conductor is provided on the opposite side of the bimetal heater. A thermal-type overload relay characterized by stacking multiple layers on the surface of the. 3. The thermal overload relay according to claim 1 or 2, wherein the thin plates or the thin plates and the bimetal are joined by spot welding.