BIMETAL THERMOSTAT COMBINED WITH POWER RELAY IN RESIN SEALED HOUSING

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The present invention relates to a bimetal thermostat with a power relay. Bimetal thermostats are known which comprise an outer case internally supporting a sensitive thermostatic element connected by means of electric wires to an external power relay adapted to control various external power components.

The presence of two separate devices, the thermostat and the power relay, causes certain inconvenience in installing both devices in equipment to control power components of the same equipment.

Object of the present invention is to provide a thermostat with power relay that is easier to install in equipment for the control of power components. According to the invention, this object is achieved with a bimetal thermostat comprising a power relay and a sensitive thermostatic element electrically connected to said power relay, said power relay comprising electric terminals for the connection with external equipment, said bimetal thermostat comprising a supporting case adapted to housing said sensitive thermostatic element, characterised in that the supporting case internally houses said power relay and a plate provided with a printed circuit adapted to form an electrical connection between the power relay and the sensitive element, said case being filled with an insulating resin.

The characteristics and advantages of the present invention will become more apparent from the following detailed description of an embodiment thereof, illustrated by way of non-limiting example in the enclosed drawings, in which: figure 1 shows a front view of the thermostat according to the present invention; figure 2 shows a vertical sectional view of the thermostat;

figure 3 shows an exploded view of the thermostat of figure 1 ; figure 4 shows the circuitry of the thermostat according to the invention; figures 5 and 6 show the top and bottom parts of the printed circuit of the plate.

Figures 1-6 show a bimetal thermostat according to the present invention. The bimetal thermostat comprises an outer case 1 provided at one end with a part 2 having a male thread 21 for coupling with external equipment. The part 2 is preferably made of brass and has an internal threaded central cavity 22 adapted to receive a sensitive thermostatic element 3. The sensitive element 3 comprises a bulb that is provided with a threaded end 31 to permit a mating connection with the cavity 22 of the part 2 and contains two laminas with a different thermal dilation coefficient (for example, steel and aluminium), rigidly arranged one upon the other, fixed on one side to the bulb and free to move on the other side; the electric contacts or pins 23 are fixed to the ends thereof. As the temperature increases, the more sensitive metal tends to dilate but, being restrained by the other metal, which is more resistant to temperature changes, it bends, thus switching the electric contact.

Present inside the case 1 there is a plate with a printed circuit 10, for example a vetronite plate, which supports a power relay 4. The plate, which may be better seen in figures 5 and 6, comprises a printed circuit 100, which is integral with the plate 10 and adapted to electrically connecting the sensitive element 3 to the power relay 4, as well as means for fixing the power relay 4 to said plate 10. The plate 10 comprises two metal edged holes 5 for the connection with the metal pins 23 of the sensitive element 3; more precisely, the pins 23 of the sensitive element 3 are welded to the holes

5 of the plate 10. The power relay is normally welded to the plate 10 by means of pins disposed over metal edged holes 11 of the plate 10. The

power relay is adapted to work with normal voltages and high levels of current, i.e. with voltages of 12 or 24 Volts and currents on the order of tens of amperes; for example, the relay 4 is capable of working with values of 12

V and 35 A for 10 minutes or 12 V and 25 A for 60 minutes. Connected to the plate 10 there are two electric cables 701, 702, of which the cable 701 is used to supply power to the thermostat (normally 12

V or 24 V) and the cable 702 is used to output the signal originating from the power relay 4 and utilisable by external equipment. As may be better seen in figures 5 and 6, the printed circuit 100 of the plate 10 has metal edged holes 71, 72 for connecting the electric wires of the power cable 701 and metal edged holes 73, 74 for the connection with the electric wires of the output cable 702; the printed circuit 100 comprises metal strips 75 that link the holes 5 with the holes 11 and other metal strips 75 for the connection of the relay to the cable 702 and of said relay 4 and the sensitive element 3 to the cable 701.

The plate 10 serves to avoid interferences between the pins 23 of the sensitive element 3, the electrical path for the power supply and the electrical path for the output signal emitted by the power relay 4, a situation that could cause a short circuit of the relay or in any case prevent the relay 4 itself from functioning correctly, with the result that incorrect output signals would be delivered via the signal output electric cable 702.

This solution permits an easy assembly of the thermostat. An insulating resin 6, e.g. epoxy resin, is applied inside the case 1 to protect the power relay against high temperatures, preferably up to 260°. The reduction in manufacturing times combined with the simplicity of the device justifies a substantial reduction in costs.

The thermostat is of the TCR type, i.e., besides sensing the temperature, upon reaching a predetermined value it causes the switching of an electric contact and the consequent opening or closing of an electric contact. This type of thermostat is used to maintain the temperature within

the fixed limits or in pneumatic and hydraulic equipment, e.g. heat exchangers, the output signal automatically controls the fluid cooling or heating systems.

Figure 4 illustrates the circuitry of the above-described thermostat, where 71 and 72 are the power terminals and 73, 74 are the output terminals in the normally closed contact mode, i.e. when the relay 4 is in an energised state, which is in turn a function of the sensitive element 3.