Biddau, Costantino (Via Bachelet 13, ARDARA, Province of Sassari, I-07010, IT)
| 1. | Thermostat comprising: a temperature controller (6) provided with a bimetallic strip (1) and a trip switch (5) operated by the said bimetallic strip (1); a moveable electric contact (14) acting on a fixed electric contact (15) connected to a metal supporting element (8); and temperaturelimiting means (20,21, 22,23, 25,27) supported by the said supporting element (8); which thermostat is characterized in that the said temperaturelimiting means comprise a first flexible metal strip (20) which at one end has a first electric contact (21) and at the other end is connected to the said supporting element (8), and a second flexible metal strip (23) which at one end has a second electric contact (22) and acts on the said first electric contact (21), and at the other end is connected to the said supporting element (8), the said second metal strip (23) being flexed elastically towards the said first metal strip (20), in such a way as to close the said electric contacts (21,22), by an element (27) made of a fusible material sensitive to overheating of the thermostat and supported by a rigid metal plate (25) connected at one end to the said supporting element (8). |
| 2. | Thermostat according to Claim 1, characterized in that the said element (27) made of fusible material is in direct contact with the said second metal strip (23) and the said rigid metal plate (25). |
| 3. | Thermostat according to Claim 1, characterized in that the said rigid metal plate (25) is separated from the said bimetallic strip (1) by at least one spacer (28) made of a material that insulates from the electric current but conducts the heat. |
| 4. | Thermostat according to Claim 1, characterized in that the said second flexible metal strip (23) is positioned, at the end connected to the said supporting element (8), between the said rigid metal plate (25) and a connector (32) for the electrical supply to the thermostat. |
| 5. | Thermostat according to Claim 1, characterized in that, between the said first flexible metal strip (20) and the said second flexible strip (23) there is positioned on the said supporting element (8) at least one spacer (24) made of insulating material, the said first flexible strip (20) being in contact with a rigid metal plate (17) of the said fixed electric contact. |
| 6. | Thermostat according to Claim 1, characterized in that the said element made of fusible material is essentially a ball (27) lying in a concavity (26) formed in the top of the said rigid metal plate (25). |
| 7. | Thermostat according to Claim 6, characterized in that the flow of the current through the said second flexible strip (23), the said rigid metal plate (25) and the said element (27) made of fusible material causes it, by the heating effect of a current, to melt early, approaching as far as possible the temperature of the heating metal plate. |
DESCRIPTION The present invention relates to thermostats provided with temperature controlling and limiting means.
As is known, these thermostats or thermally controlled electric switches, can be used to control and limit the desired temperature of electrically heated metal plates, such as the metal plates of clothes irons.
The temperature controlling means used in such thermostats generally comprise a bimetallic strip and a trip switch operated by this bimetallic strip and provided with a movable electric contact acting on a fixed electric contact positioned on a supporting element of the thermostat.
The means for limiting the maximum temperature of these thermostats may take the form for example of a lower plate supporting a suitably shaped fusible element, the plate being in contact with the bimetallic strip. This plate supports an insulating pin acting on the said fusible element and in contact, during normal operation of the thermostat, with the underside of a moveable contact connected to the thermostat supporting element and separated from the said plate by an insulating spacer. The top surface of the moveable contact meanwhile is in contact with the underside of this fixed electric contact provided in the temperature control means.
This type of temperature limiter has differences including the presence of an insulating body acting on the fusible element, which limits the efficiency of the temperature limiter, and the direct contact between the plate supporting the fusible element and the lower bimetallic strip of the thermostat, which requires among other things a special shaping of the said plate to lift it off the said bimetallic strip in the area where the fusible element is supported, in order to bring the fusible element towards the moveable contact which must be open and therefore separated from the fixed contact of the temperature controller in the event of excessive overheating of the thermostat.
The object of the present invention is therefore to improve thermostats provided with the said temperature limiting means described above by means of a thermostat comprising: a temperature controller provided with a bimetallic strip and a trip switch operated by this bimetallic strip; a moveable electric contact acting on a fixed electric contact connected to a metal supporting element ; and temperature-limiting means supported by this supporting element ; which thermostat is characterized in that these temperature-limiting means comprise a first flexible metal strip which at one end has a first electric contact and at the other end is connected to this supporting element, and a second flexible metal strip which at one end has a second electric contact and acts on this first electric contact, and at the other end is connected to this supporting element ; this second metal strip is being flexed elastically towards this first metal strip, in such a way as to close these electric contacts, by an element made of a fusible material sensitive to overheating of the thermostat and supported by a rigid metal plate connected at one end to this supporting element.
In accordance with other aspects of the present invention, this element made of fusible material is in direct contact with this second metal strip and this rigid metal plate. In addition this rigid metal plate is separated from this bimetallic strip by at least one spacer made of a material that insulates from the electric current but conducts heat.
In this thermostat, therefore, the fusible element is advantageously free, carrying current, like the plate which supports it, and does not interact with any pin or insulating body as in the known thermostats described above. Also, the heat is transmitted to this supporting plate of the fusible element by the spacer or washer which insulates from the current but conducts the heat and not by the bimetallic strip of the thermostat.
Other objects and advantages of the present invention will be understood more clearly from the following description, considered as a nonlimiting example referring to the attached drawings, in which:
Fig. 1 is a side elevation of a thermostat with temperature controlling and limiting means according to the present invention in a situation of normal operation; and Fig. 2 is a side elevation of the thermostat of Fig. 1 with the temperature limiter operating due to excessive overheating.
Referring to the attached drawings and particularly to Fig. 1 thereof, reference number 1 denotes a bimetallic strip, fixed to the forward end of which, that is on the right when viewing the figure, is the lower end of a pin 2 that can move up and down, as indicated by the double arrow V. The upper end of the said pin 2 is fixed to the front part 4 of a suitably shaped activating plate 16 of a quick-tripping switch 5. This switch 5 has a dead point or tripping point which is set by a temperature controller 6 positioned above the said switch 5 and comprising a supporting arm 7 fixed to a hollow metal rivet 8. At the front of this supporting arm 7 is a threaded cylindrical guide 9 in which a corresponding threaded screw 10 is engaged, its head being mounted internally at the lower end of a rotatable knob 11. An-essentially conical pin 12 is formed at the lower end of this screw 10 and acts on one of the strips 3 and 13 of a known spring system used in the quick-tripping switch 5 to adjust its dead point or tripping point. Behind the actuating plate 4 of this switch 5 is a first moveable contact 14 that acts on a second, fixed contact 15 essentially parallel to the bimetallic strip 1. Both the actuating plate 16 of the switch 5 and the fixed contact 15 are fixed to the hollow rivet 8, for which purpose the said fixed contact 15 is supported by a metal plate 17 mounted on the said rivet 8. The rotatable knob 11 supports a wheel 18 with a mark 19 to indicate the temperature the thermostat is to reach before the switch 5 automatically trips. The limit positions of this mark 19 are defined by its contact with a post 33 at the front end of the arm 7.
Below this plate 17 on which the fixed contact 15 is supported is a first flexible metal strip 20, on the end of which is a moveable contact 21 that closes the electric circuit of the thermostat by acting on another moveable contact 22 supported by a second flexible metal strip 23 mounted at the rear in the rivet 8 and separated from the first flexible strip 20 by an insulating spacer 24. The rear part of this flexible strip
23 rests on a rigid metal plate 25, formed in the free surface of which is a concavity 26 accommodating a ball 27 made of a material that melts at a certain overheating temperature of the thermostat. As can be seen, this ball 27 pushes, causing it to flex elastically, the second strip 23 and hence the moveable contact 22 against the moveable contact 21 supported by the first flexible strip 20, and it too is slightly deformed elastically. This rigid plate 25 on which the ball 27 of fusible material is supported is advantageously separated from the bimetallic strip 1 by another spacer 28 made of a material that insulates from the electric current but conducts the heat.
Naturally, this ball 27 made of fusible material could be replaced by an element of any other shape capable of sitting stably on the rigid plate 25 and keeping the moveable contact 22 of the second flexible strip 23 pressed against the moveable contact 21 of the first flexible strip 20. Completing the description of the present thermostat are two more insulating spacers 29 and 30 mounted on the rivet 8, and between these is inserted a first connector 31 for the incoming electric current, while the second connector 32 for the outgoing electric current is mounted between the spacer 24 and the second flexible strip 23.
The operation of the present thermostat, see Figures 1 and 2, is as follows : by turning the rotatable knob 11 of the temperature controller 6 and with the aid of the mark 19 it is possible to define the temperature at which the two contacts 14 and 15 are separated from the quick-tripping switch 5. They are normally closed as shown in the situation of Fig. 1. When electric current is supplied to the thermostat through the two connectors 31 and 32, the lower bimetallic strip 1 begins to heat up and deform, causing an upward movement, in the direction of arrow V, of the pin 2 which acts on the activating plate 4, which then itself rises upwards, separating the moveable contact 14 from the fixed contact 15. The upward movement of this pin 2 will be greater the higher the pin 12 is set by the rotation of the knob 11, and hence the higher the temperature desired in the bimetallic strip 1. When this bimetallic strip 1 cools down the spring system comprising the two strips 3 and 13 allows the switch 5 to close the contact 14 against the contact 15 again, after the pin 2 has descended.
Let us assume that, due to some malfunction of the thermostat, the moveable contact
14 of the controller 6 does not come away from the fixed contact 15 when the desired temperature is reached. Under normal conditions the electric contacts 21 and 22 on the two flexible metal strips 20 and 23 close the functioning circuit of the thermostat and are pushed together by the ball 27 of fusible material, which presses on the flexible strip 23: if the overheating of the bimetallic strip 1 becomes excessive and the temperature exceeds a certain threshold value, the ball 27 of fusible material dissolves, causing, see Fig. 2, the second flexible strip 23 to return elastically downwards to its rest position and interrupting the electrical supply to the entire thermostat. This stops the overheating of the bimetallic strip 1. The first flexible strip 20 also relaxes, flexing downwards slightly, but not as far as the second flexible strip 23.
As will have been realized from the above description, the advantages consequent upon the use of a thermostat provided with temperature controlling and limiting means according to the invention are numerous, as are the embodiments that may be adopted to achieve these advantages without departing from the scope of the appended claims.