Electricity: electrothermally or thermally actuated switches – Thermally actuated switches – With bimetallic element
Reexamination Certificate
2000-04-21
2004-04-20
Vortman, Anatoly (Department: 2835)
Electricity: electrothermally or thermally actuated switches
Thermally actuated switches
With bimetallic element
C337S380000, C337S381000
Reexamination Certificate
active
06724293
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device having an electrical load and a cavity for receiving a temperature-dependent switching mechanism for protecting the load from overtemperature, and/or overcurrent, there being provided in the cavity a first countercontact for the switching mechanism which is electrically connected to the load, and a second countercontact which is electrically connected to an external terminal for supplying electricity to the load.
2. Related Prior Art
A device of this kind is known from DE 195 06 342 C1.
The known device has a cavity into which project two electrodes which grip between them an encapsulated temperature monitor. The first electrode is connected to an external terminal, and the second electrode to an electrical load of the device.
The temperature monitor has a two-part, electrically conductive housing made up of an upper part and lower part that are electrically insulated from one another and receive the gripping forces of the two electrodes. At the same time, the upper part and lower part create the electrical connection to the electrodes.
Arranged in the housing of the temperature monitor is a temperature-dependent switching mechanism that creates, as a function of its temperature, an electrically conductive connection between the upper part and the lower part. As long as the temperature monitor remains below its response temperature, it thus creates an electrically conductive connection between the two electrodes, so that by way of the external terminal, current can flow to the electrical load, which of course is connected to a further external terminal. In the event of an impermissible rise in the ambient temperature and/or an excessive operating current, the temperature-dependent switching mechanism heats up to the point that it interrupts the connection, and the load experiences no current.
A temperature-dependent switching mechanism such as the one used in the temperature monitor utilized in the known device is known, for example, from DE 29 17 482 C2. The temperature-dependent switching mechanism comprises a spring disk that centeredly carries a movable contact on which a bimetallic snap disk is centeredly arranged. The temperature-dependent switching mechanism constitutes a lossproof unit.
Below the response temperature, the spring disk is braced at the bottom on its rim against the lower part of the temperature monitor, and pushes the movable contact element against the interior of the upper part so that a current can flow from the upper part, via the contact element and the spring disk, into the lower part. In this switch position, the bimetallic snap disk exerts no force. If the temperature then rises, the bimetallic snap disk snaps over from its convex shape into a concave shape, thereby bracing itself against the interior of the upper part and pushing the movable contact element away from the upper part against the force of the spring disk, so that the switch constituted by the temperature monitor is opened. Also to be mentioned in this context is an insulating layer, on the interior of the upper part, which prevents the bimetallic snap disk from coming into electrical contact with the upper part.
The temperature monitor known from DE 29 17 482 C2 is highly pressure-resistant, so that it can be used with the device as described in DE 195 06 342 C1. A pressure-resistant housing of this kind is necessary so that the gripping forces for retaining the temperature monitor can be designed to be sufficiently great such that mechanical and electrical contact can reliably be made to the temperature monitor even in the presence of severe vibrations, for example when used in a drain pump of a washing machine.
An advantage of the known device is that the temperature monitor used is not one that is usually equipped with soldered or crimped terminals, but rather the also known temperature monitor having the two-part metal housing, so that very easy installation and contacting of the temperature monitor in the known device can be achieved. Because of its insensitivity to pressure, the known temperature monitor can be stocked as a bulk item, and during final assembly of the known device simply needs to be inserted—optionally by way of an automatic production machine—between the two resilient electrodes, where it is simultaneously held in place mechanically and electrically contacted.
Although the known device is very satisfactory in terms of assembly engineering, and although secure retention of the temperature monitor is also achieved, it nevertheless has the disadvantage that a more expensive temperature monitor needs to be used because of the need for a pressure-resistant housing.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to improve the device mentioned at the outset in such a way that it can be equipped in economical fashion with a temperature-dependent switching function that moreover can easily be installed and contacted.
According to the present invention, this object is achieved, in the case of the device mentioned at the outset, in that the cavity is configured for receiving a housingless switching mechanism that, below its response temperature, is in direct contact with the two countercontacts.
The object underlying the invention is completely achieved in this fashion.
Specifically, the inventor of the present application has recognized that it is possible to insert, so to speak, “naked” switching mechanisms directly into a cavity provided on a device, this switching mechanism then being clamped between the two countercontacts. As a result, on the one hand it is no longer necessary for the countercontacts to be of resilient configuration, and on the other hand it is additionally possible to dispense with a housing for the temperature-dependent switching mechanism. It is thus possible to use economical switching mechanisms, and lesser demands are also made on the countercontacts in the cavity, which can now be rigid electrodes or contact points. What is exploited in this context is the fact that each temperature-dependent switching mechanism is in any case already designed so that it is clamped in its housing between the two countercontacts in such a way that it remains securely positioned and contacted even when used in a severely vibration-affected environment. The spring forces of the bimetallic element and/or of the spring element of the temperature-dependent switching mechanism necessary for this purpose are relatively small, since the mass of the “naked” switching mechanism is already kept as low as possible simply in order to achieve short switching times.
This means, however, that the forces necessary for secure retention of a switching mechanism are much lower than the forces needed, in the case of the device mentioned at the outset, to securely retain the temperature monitor, with its metal housing that is very heavy by comparison with the switching mechanism.
The use of a housingless switching mechanism thus yields cost advantages not only in terms of the device, in which resilient countercontacts are no longer necessary, but also because the housing of the temperature monitor can be dispensed with.
Of course the new device offers all the advantages that were already present in the context of final assembly of the known device: no soldering or crimping operations are necessary in order to make contact to the switching mechanism, and the switching mechanism merely needs to be placed into the cavity. It is true that housingless switching mechanisms cannot readily be stocked as bulk goods, since any mechanical stress, in particular bending of the bimetallic elements, must be avoided so that their functional reliability is not negatively affected.
The inventor of the present application has recognized, however, that it is easily possible for switching mechanisms such as those known from the aforementioned DE 29 17 482 C2, i.e. those which constitute a lossproof unit, to be stocked like tablets in blister packs. The switching m
Harness & Dickey & Pierce P.L.C.
Vortman Anatoly
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