JPS60232630A - Bimetal protection switch - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a bimetallic protection switch of the type defined in the preamble of claim 1.

(Prior art) The above-mentioned protection switch is disclosed in West German Patent No. 3231.
It is described in the specification of No. 136. In this known bimetallic protection switch, two electrical connection pieces are embedded in a flat support of electrical insulation, one of which is connected to a stationary switch contact element fixed to the upper surface of the support, and The other end is electrically conductively connected to an end fixed to the upper surface of the contact spring support. The contact spring is adapted with a movable end to cooperate with a fixed switch contact member. A bimetallic snap plate is loosely held on the upper surface of the contact spring between the front and rear pawls of the contact spring and the side joint plates of the contact spring.

A thick-film resistor is placed on the bottom surface of the support, which consists of 2
conductively coupled to one connecting piece.

The insulating support of the bimetal protection switch has a cutout passing through it from bottom to top, through which the ohmic heat generated in the resistor can reach the contact spring and the snap plate. This known switch is used as an overtemperature switch. That is, when the bimetallic snap plate is heated to a temperature above its switch temperature due to an increase in the surrounding temperature, the snap plate changes its curvature significantly, thus opening the switch, after which the current only flows through the resistor and the resistor is heated and releases an amount of heat to the bimetallic element such that the bimetallic element remains at a temperature above the switch temperature as long as current flows through the resistance. SUMMARY OF THE INVENTION It is an object of the invention to improve a bimetallic protection switch of the above type in such a way that it can be used not only as an overtemperature switch, but also as an overcurrent switch.

Such a dual use is known from DE 32 31 136 A1, in which the contact spring is at the same time a bimetallic element of a protection switch. However, not only does the contact spring exert the required closing force (for which it must have certain spring properties), but it must also have a given value of electrical resistance and a sufficient opening behavior. In some cases, it is difficult to guarantee optimal and above all reliable switch behavior.

Means for solving the problem The above-mentioned problem is solved according to the invention by the features of patent claim 1.

Accordingly, in the invention, the opening of the bimetallic protection switch,
Care has been taken to keep the opening keeping and closing functions separate from each other. West German Patent Application Publication No. 323113
As in the case of the bimetallic protection switch of No. 6, the contact spring only has the role of closing the switch and allowing current to flow in the closed switch, although it does not have to limit the current. The opening of the switch when a predetermined ambient temperature or a predetermined value of current intensity is exceeded is carried out by a bimetallic element, in particular a bimetallic snap plate, which is separate from the contact spring; This is because the snap plate has a particularly well-defined switch temperature and causes a particularly large lifting of the contact parts when they are separated, which also has a negative impact on the reliability of the switch and the ability to keep the protective switch open. This also has an advantageous effect on reliability.

The transfer of heat from the environment or from the preresistance provided according to the invention to the current limit takes place by heat transfer and heat dissipation.

After the bimetal protection switch is opened by the bimetal element, the current only flows through the resistor bridging the switch, the current heats the resistor and heats the bimetal element, so that the protection switch is opened. remain in the same state.

The resistance value of the resistor that bridges the bimetal protection switch and holds the switch open after a fault occurs is adapted to the respective switching tasks and monitoring tasks of the protection switch.
In a closed protection switch (when the equipment being monitored is operating without faults), a very large part of the current flowing through the bimetallic protection switch takes a path through the contact splash and the closed switch contact member, and Only a small fraction of the current flows through the resistor in parallel with the switch contact member, so that the ohmic heat generated in the resistor is not sufficient to heat the bimetallic element of the protection switch to the switch temperature. selected as follows.

On the other hand, the resistance value is sufficient so that the ohmic heating generated as a result of the relatively high current passing through the resistor in an open switch keeps the bimetallic element above the switch temperature and keeps the switch open. must be selected as such.

The heating power required for this purpose is typically on the order of a few watts. At a supply voltage of 220 V, a suitable resistance value of the resistor is on the order of IOKΩ, for example between 5Ω and 25Ω.

Restoration of a bimetal protection switch is accomplished by cutting off the current supply to the resistor holding the switch open. In the simplest case, this can be done by pulling out the power plug or, in any case, opening the power switch. However, the reservoir may also be provided with a separate disconnect switch. Such a switch can in principle be installed at any point on the equipment, so that no special integration problems arise for the case of a recoverable bimetallic protection switch. Bimetal protection switches are particularly suitable as protection switches for small electric appliances, built-in thermostats, small motors, small transformers, cooking and household appliances, and the like.

A thick-film resistor is preferably used as the heating resistor for holding the bimetal protection switch open.

Because of their plate-like construction, thick-film resistors can distribute heat over a large area and dissipate heat, which can lead to deformation or damage to the switch (especially if the insulating support or casing is made of plastic). localized overheating is not a possibility when using thick film resistors.

Another advantage of thick film resistors is that the resistance can be adjusted very precisely to the nominal value of the resistance by trimming with laser radiation. Therefore, the deviation of the resistor series from its nominal value is small and there is no need to include in the design a heating power reserve for safety reasons, as is the case with known thermal switches.

Another advantage of thick-film resistors is that it is possible to adapt the reference area of the resistor to the given geometrical conditions of the switch, so that in each switch there is an optimal heat transfer from the thick-film resistor to the bimetallic element. You get movement.

In the bimetallic protection switch according to the invention, the stationary switch contact element and the contact spring with the movable contact element are located on one side of an electrically insulating support, and the ohmic resistance is on the opposite side of the support. and a recess is provided in the support between the resistor and the bimetallic element or contact spring on the opposite side of the support, so that a good heat transfer from the resistor to the bimetallic element is achieved between both. This is achieved despite the fact that electrically insulating supports are located between them.

In order to enable as unhindered a heat transfer as possible between the preresistor provided according to the invention and the bimetallic element, the preresistor is arranged in a recess in the insulating support. The cutout allows good heat transfer between the contact spring and the resistor of the spring holding the switch open, which is parallel to the protection switch. Of course, if the bimetallic element is arranged below the contact fin and is not therefore shielded against the two electrical resistances by the contact fin, then
Heat transfer is particularly advantageous. It is furthermore advantageous to use a resistance wire as the preresistor, 9 from which a loop-shaped section is located in a recess in the insulating support. Such resistance wires make it possible to carry out current limiting in a very simple and inexpensive manner, with current strengths that are not too large, such as are typical in domestic appliances, and which also allow the resistance wire to be cut in its support. Not only is the loop located in the recess very well positioned with respect to the desired heat transfer to the bimetallic element, but also the loop is located on the underside of the support from the resistance of the reservoir holding the switch open. It is not acceptable to prevent heat transfer to the bimetallic element.

When unacceptably high current strengths occur, the switch of the invention provides a very quick response and reliable holding of the switch open after the response.

These two characteristics are highly desirable in protection switches.

The arrangement according to the invention of the preresistor in an insulating recess has the advantage that the preresistor can be arranged in a protected manner in the recess and does not require additional space.

Embodiments The illustrated protection switch is an oven switch (of course the invention is also applicable to encapsulated switches).

On the underside 6 of the flat, electrically insulating support 1, two electrical contact pieces 2.3 facing in opposite directions are mounted with holes 4, 5 for soldering. There is.

A contact spring 10 is fastened with one end by a rivet to the upper side 9 of the carrier 1 and is at the same time electrically conductively connected to the contact piece 3. The rivet passes through the insulating support 1 (only the head 8 is shown). Contact splash 1
0 holds a switch contact member 11 at its movable end, and the switch contact member 11 is connected to a stationary switch contact member 12.
K to cooperate with the connecting piece 2, and is riveted to the connecting piece 2. An opening 14 is provided in the contact spring 10 near the switch contact member 11;
A centering pin 15, which is fixed in the support 1 and projects perpendicularly from the upper surface 9 of the support 1, passes through it.

Between the contact spring 10 and the upper surface 9 of the support 1, a bimetal snap plate 16 is arranged loosely but not separated.The bimetal snap plate 16 has a recess at one end. This recess partially surrounds the centering pin, while the opposite end engages with a notch 17 in the upper surface of the support 1 formed between the side plates 13 of the support 1. Because of this, they are inseparable.

A thick film resistor 18 is arranged on the lower surface of the support 1 . Thick film resistor 18 is typically in the form of a coated flat ceramic plate.

Thick-film resistor 180 Two rigid connecting pieces 20 , 21 are guided from the thick-film resistor 18 in mutually opposite directions and are soldered to the connecting pieces 2 and 3 of the protection switch.

The support 1 has a notch 19 passing through it, through which the resistance heat generated in the thick film resistor 18 is transmitted to the contact spring 10 and the bimetal snap plate 16. .

Furthermore, an electrical pre-resistance 30 composed of a piece of resistance wire
is provided. The loop-shaped part of the pre-resistance is located in the cutout 19 of the support 1 and one end 32 of the pre-resistance
It is fixed to the connection piece 3 of the Fi protection switch, and the other end is guided laterally through the gap between the support 1 and the thick film resistor 18, and is connected to the hole 31 for soldering. has been done.

In the built-in, closed switch, the current flows from the hole 31 through the pre-resistor 30 to the connecting piece 3 and from there on the one hand through the contact spring 10 and on the other hand through the (very small) thickness. It passes through the membrane resistor 18 and reaches the connection piece 2 . However, the switch opens in response when a preselected ambient temperature is exceeded, or when a preselected current intensity is exceeded, i.e., the bimetallic snap plate 16.
significantly changes its curvature and raises the recess 10a of the contact spring 10, so that the switch contact members 11 and 12 are separated from each other and the current therefore only flows through the thick-film resistor 18. The thick film resistor 18 heats up and the thick film resistor 18 releases enough heat to the bimetallic snap plate 16 to remain above the switch temperature unless the current from the thick film resistor 18 is disconnected.

By arranging the thick film resistor 18 in the notch 19 and by arranging the front resistor 30 in the notch 19 of the support 1, the heat generated in these two resistors can be easily transferred to the bimetal snap plate 16. guaranteed to have a safe passageway,
This ensures a quick response of the protection switch in the event of a fault and a reliable holding of the switch in the open state after the fault.

This new switch features an extremely simple configuration,
Therefore, it can be produced at a very low cost, which is important for mass-produced products. The switch is also versatile and easily adaptable to different switch tasks.

Next, a measurement example regarding the illustrated protection switch will be described.

Normally operated at a current strength of 2 amps and with a current strength of 6
When using a protection switch to protect equipment that is designed to shut off when the amperage is reached,
As a pre-resistance, a resistance wire material having a resistance value not exceeding 100 mΩ, a thick film resistor having a resistance value of 10 to 20 Ω, and a bimetal snap plate having a switch temperature of about 80° C. are used. As long as the electrical equipment is receiving a set current intensity of about 2 amps, the preresistor will only be slightly heated. However, if a malfunction occurs, for example when the electric motor stops working,
Alternatively, if a short circuit occurs in the heating spiral wire of a heating device, the current intensity increases rapidly.

As a result, the temperature of the resistor also rises very rapidly, heating up the bimetallic snap plate and causing the protection switch to open within a few seconds, and after that, current flows only through the thick film resistor, and this current causes the switch to open. maintain the condition.

[Brief explanation of drawings]

FIG. 1 is a plan view of one embodiment of the bimetal protection switch of the present invention, and FIG. 2 is a side view showing the bimetal protection switch of FIG. 1 partially in section. DESCRIPTION OF SYMBOLS 1...Support, 2.3...Connection piece, 4.5...Hole, 6...Bottom surface, 8...Head, 9...Top surface, 1o...Contact spring, 10a... Recess, 11. 12. Switch contact member, 13. Side plate, 14. Opening, 15. Centering pin, 16.・Bimetal snap plate, 17...
・Notch, 18... Thick film resistor, 19... Notch, 20
, 21... Connection piece, 3o... Front resistance, 31... Hole, 32... End. 1 other person

Claims (3)

[Claims] (1) A bimetallic protection switch, which is opened by a bimetallic element when a preselected temperature is exceeded and is held open by an ohmic resistor, especially a thick film resistor, bridging the switch. and the bimetallic element simultaneously constitutes a contact spring, the contact spring comprising a movable switch contact member and a stationary switch contact member of a bimetallic protective switch and arranged on one side of an electrically insulating support. and the resistor is arranged on the opposite side of the support, and the support has a notch between the resistor and the contact spring, in which a pre-resistance (30) is provided. Bimetallic protection switch, characterized in that it is arranged in a recess (19) of an insulating support (1). (2) The pre-resistance (30) is constituted by a resistance wire, and the loop-shaped portion of the resistance wire is located within the notch (19) of the support (1). bimetal protection switch. (3) A bimetal element (16), preferably a bimetal snap plate, connects the contact spring (10) and the insulating support (1).
The bimetal protection switch according to claim 1 or 2, which is disposed between.