Switching arrangement with thermal and magnetic functions

Abstract

 A switch combining magnetic control and thermal control. A movable contact is urged by a magnet into contact with a fixed contact. A bimetallic strip is capable of urging the movable contact out of contact with the fixed contact upon exposure to a thermal overload. For a switch responsive to both burglary and fire detection, a permanent magnet urges the movable and fixed contact into a normally closed position. When the magnet's influence is no longer felt, such as when a burglary occurs, the movable and fixed contacts will separate. A bimetallic strip, when sensing a thermal overload, will also move the movable contact out of contact with the fixed contact even in the absence of a burglary. The switch responsive to both magnetic and thermal energy is also used to protect a relay controlled circuit from thermal overload.

Description

Background of the Invention

[0001] Known thermal switches are activated by a bimetallic strip that undergoes a temperature change. The bimetallic strip controls an electrical contact as it undergoes temperature changes. Thermal switches based upon bimetallic strips have a wide range of applications including current overload protection, temperature control, fire detection, etc..

[0002] Known magnetic switches are controlled either by a permanent magnet, as in the case of a magnetic reed switch, or controlled by an electromagnet. Magnetic reed switches are used in burglary detection, and electromagnetic controlled switches are used in relays.

[0003] It would be desirable to provide a simple and inexpensive switch that would be responsive to both thermal energy and magnetic energy.

Summary of the Invention

[0004] 

[0005] Accordingly, it is a primary object of the invention to provide a switch arrangement which is responsive to both thermal energy and magnetic energy.

[0006] To achieve the foregoing and other objects an electrical switch is provided which includes a housing, a fixed wire supported by the housing, a fixed electrical contact supported by the fixed wire, a movable spring wire supported by the housing, and a movable electrical contact supported by the movable spring wire. The movable electrical contact is capable of contacting the fixed electrical contact and is movable by magnetic force urging the movable contact towards the fixed contact. At the same time tha the movable contact is under the influence of the magnetic force, the movable wire is also movable by thermal energy to move it away from the fixed wire thereby permitting the movable electrical contact to be moved by thermal energy out of contact with the fixed electrical contact. The movable wire is comprised of a bimetallic strip having magnetic properties. Such a movable wire is responsive to both magnetic energy using it in one direction and thermal energy urging it in the opposite direction at the same time.

[0007] One example of use of the switching arrangement of the invention is for a combined burglary detection and fire detection switch. For such an application, the movable contact resides on a movable thermally responsive bimetallic strip that is also responsive to magnetic control. The movable contact will be urged towards the fixed contact by a permanent magnet such as used in a conventional magnetic reed switch. Such a permanent magnet is normally present in a location such as a door or window, and magnet influence is felt as long as there is no burglary; that is as long as the permanent magnet is in the proximity of the switch contacts. When a burglary occurs, the magnet is no longer in the vicinity of the switch contacts, and the switch contacts will open.

[0008] At the same time that the magnet is urging the movable bimetallic strip to be in the normally closed position with the fixed contact, the bimetallic strip is responsive to thermal energy and will cause the movable contact to move in the opposite direction when sufficient thermal energy is sensed. That is, when sufficient thermal energy is sensed, such as from a fire, the bimetallic strip will cause the movable contact to move away from the fixed contact.

[0009] The thermally responsive bimetallic strip can respond to both extraneous thermal energy, such as in detecting a fire, and can also respond to thermal energy generated by excessive electrical current running through the circuit and across the movable and fixed electrical contacts. In this way, the switch of the invention can be used as a protective device for a circuit overload. The switch of the invention can be used for overload protection for both a burglary/fire detection switch and a relay switch.

[0010] Although the examples discussed above describe the magnetic energy as urging the electrical contacts into the closed position and the thermal energy urging the contacts into the open position, the opposite situation can also be utilized; that is, the magnetic energy can be used to urge the switch contacts into the open position, and the thermal energy can urge the switch contacts into the closed position. The key feature is that the magnetic energy and the thermal energy urge the switch contacts into the opposite positions.

Brief Description of the Drawings

[0011] 

Fig. 1 is a view of a magnetic and thermal reed switch in the absence of a magnet to influence the switch.

Fig. 1-1 is a view of the switch in Fig. 1 when a permanent magnet is influencing the switch in the absence of a temperature overload.

Fig. 1-2 is a view of the switch in Fig. 1-1 when a temperature overload is present.

Fig. 2 is a view of a relay having a switching arrangement responsive to both magnetic and thermal energies.

Fig. 3 is a view an electromagnet operated switch that is also responsive to thermal energy.

Detailed Description of the Preferred Embodiment

[0012] With reference to Fig. 1, housing 105 supports fixed wire 102 on insulated part 104 and also supports movable wire 101. Movable wire 101 has bimetallic strip 103 which supports movable contact 106. The fixed wire 102 supports fixed contact 107. Switch contacts 106 and 107 are normally open in the absence of magnetic energy as shown in Fig. 1.

[0013] In Fig. 1-1, a permanent magnet 110 is present and causes switch contacts 106 and 107 to be normally closed. In Fig. 1-1, there is no thermal overload.

[0014] In Fig. 1-2, the permanent magnet 110 is still exerting its influence to urge the switch contacts closed. However, a thermal overload is present as depicted by the candle flame 111, and the bimetallic strip 103 causes the switch contacts 106 and 107 to open.

[0015] It is understood that if the thermal overload would be removed, then the switch contacts would resume their closed position shown in Fig. 1-1. It is also understood that the source of thermal overload can be a circuit overload in the circuit including the switch contacts 106 and 107.

[0016] As shown in Figs. 1-1 and 1-2, the bimetallic strip 103 is connected at one of its ends to the movable wire 101. At the other end of the bimetallic strip, the movable contact 106 is supported. With this arrangement, the movement of the switch contacts 106 and 107 apart during thermal overload is at a maximum level.

[0017] In Fig. 2, the switch arrangement of the invention is shown in an electric relay. Here, electromagnet coil 201 surrounds iron core 202 which is connected to support 203. In Fig. 2, the coil 201 is deenergized, and the switch contacts 106 and 107 are open.

[0018] However, when the coil 201 is energized, magnetically responsive structure 204 is pulled toward the coil 201 and the switch contacts 106 and 107 will close (as shown in the circled region at the end of the arrow in Fig. 2). As all times, spring 205 biases the element 204 to remain away from the coil 201 and keep switch contacts 106 and 107 open. Only when the coil 201 is energized, will the spring 205 be overcome and the switch contacts 106 and 107 close.

[0019] The bimetallic strip 103 protects the relay controlled circuit from overload. When the relay controlled circuit is overloaded, the bimetallic strip 103 will overheat and will open the switch contacts 106 and 107 even though the coil 201 is energized.

[0020] In Fig. 3 another electromagnetic controlled switch is shown. The bimetallic strip 103 is present on one or more of multiple movable contacts 106. The operation of the switch in Fig. 3 is similar to the operation of the relay shown in Fig. 2.

Claims

1. An electrical switch, comprising:
a housing,
a fixed wire supported by said housing,
a fixed electrical contact supported by said fixed wire,
a movable spring wire supported by said housing,
a movable electrical contact supported by said movable spring wire, said movable electrical contact capable of contacting said fixed electrical contact,
said movable wire being movable by magnetic force towards said fixed wire thereby permitting said movable electrical contact to by moved by magnetic force into contact with said fixed electrical contact, and
said movable wire being movable by thermal energy away from said fixed wire thereby permitting said movable electrical contact to be moved by thermal energy out of contact with said fixed electrical contact.

2. The electrical switch described in Claim 1 wherein said movable wire is a bimetallic strip.

3. The electrical switch described in Claim 2 wherein said bimetallic strip is located on said movable wire on the side of said movable wire that is opposite to the side of said movable wire which supports said movable contact.

4. The electrical switch described in Claim 1 wherein said movable contact is urged away from said fixed contact by a spring bias, and wherein said movable contact is urged toward said fixed contact by magnetic force.

5. An electrical switch according to anyone of Claims 1 to 3 characterised in that the movable wire is movable by a permanent magnet towards said fixed wire thereby permitting said movable electrical contact to be moved by magnetic force into contact with said fixed electrical contact, and in that the movable wire is movable by extraneous thermal energy away from said fixed wire thereby permitting said movable electrical contact to be moved by extraneous thermal energy out of contact with said fixed electrical contact.

6. An electrical switch, according to anyone of Claims 1 to 3 characterised in that the movable wire is movable by a permanent magnet towards said fixed wire thereby permitting said movable electrical contact to be moved by magnetic force into contact with said fixed electrical contact, and in that the movable wire is movable away from said fixed wire by thermal energy from an electric current running through said movable wire thereby permitting said movable electric contact to be moved out of contact with said fixed electrical contact by thermal energy generated within said housing.

7. An electrical switch according to anyone of Claims 1 to 3 characterised in that the movable wire is movable by an electromagnet towards said fixed wire thereby permitting said movable electrical contact to be moved by magnetic force into contact with said fixed electrical contact, and in that the movable wire is movable by extraneous thermal energy away from said fixed wire thereby permitting said movable electrical contact to be moved by extraneous thermal energy out of contact with said fixed electrical contact.

8. An electrical switch according to anyone of Claims 1 to 3 characterised in that the movable wire is movable by an electromagnet towards said fixed wire thereby permitting said movable electrical contact to be moved by magnetic force into contact with said fixed electrical contact, and in that the movable wire is movable away from said fixed wire by thermal energy generated by an electric current running through said movable wire thereby permitting said movable electrical contact to be moved out of contact with said fixed electrical contact by thermal energy generated within said housing.

9. An electrical switch according to Claim 5 or Claim 6 characterised in that the permanent magnet is disposed outside the housing.

10. An electrical switch according to Claim 5 or Claim 6 characterised in that the permanent magnet is disposed inside the housing.

Drawing