DESCRIPTION The present invention refers to an improved thermostat, in particular a thermostat of the type adapted for use in conjunction with refrigeration appliances.

Thermostats of the above cited kind are generally known to usually comprise a load-bearing casing that is closed by means of a metal cover on whose inner surface there is attached a bellows-like member communicating with an open end of a capillary tube made of copper or similar material, the opposite end of which is on the contrary sealed. Said bellows element and the capillary tube form a sealed variable-volume chamber that is filled with a working fluid featuring a high coefficient of thermal expansion.

In response to the temperature being detected by said capillary tube, the working fluid in said chamber expands or contracts, thereby causing the bellows element to expand or to shrink, accordingly. In correspondence of a pre-determined expansion/contraction position, the bellows element is adapted to actuate at least an electric or similar switch to open or close the respective circuit.

Near its open end, the capillary tube is attached to the cover by means of a soldered joint that may for instance be carried out with the use of a tin-lead alloy.

For the thermostat to operate in an adequate manner, the variable-volume chamber should of course be perfectly sealed, ie. fully tight against any possible leakage of working fluid contained therein. This has been hitherto achieved by using, as a working fluid, some CFC-based medium, such as Freon or the like, ie.

a substance that does not give rise to any substantial problem in connection with possible leakages through microcrackings and/or micropores as they may be present for instance in correspondence of the soldered joint of the capillary tube, ie. a particular point of the thermostat commonly known for its relative criticalness and fragility.

The current need for all CFC-containing media and substances to be phased out and eliminated has led to Freons being replaced with propane gas, which, however, is generally known to be such as to easily give rise to problems of related working fluid leaking in correspondence of said soldered joint, thereby making the entire thermostat substantially unreliable.

Such a problem is particularly aggravated in the case of thermostats intended for use, for instance, in refrigeration appliances, owing not only to the low working temperatures prevailing in such applications, but also, and mainly, to the fact that no use of lead is allowed in soldering alloys for use in applications involving handling and/or storage of foodstuffs. In these cases, therefore, tin-lead alloys are replaced with a different alloy, such as for instance a tin-silver alloy, which is generally known to be less amalgamating and therefore favours the formation of porosity (with resulting osmosis processes) in correspondence of the soldered joint. Furthermore, said soldered joint turns out to be undesirably fragile, so that propane, which is an inflammable substance, can easily percolate, ie. escape from the variable-volume chamber, thereby giving rise not only to situations of unreliablity of the entire thermostat, but also to dangerous situations for the user of the related appliance.

It therefore is a purpose of the present invention to provide a simple improved thermostat in which, while doing in any case away with the use of CFC-containing or anyway polluting media, all such drawbacks connecte with prior-art solutions are effectively removed.

In a more precise manner, it is a purpose of the present invention to provide a thermostat of the above cited kind which is particularly reliable and substantially free from problems arising from working fluid leaking therefrom.

Yet another purpose of the present invention is to provide a thermostat of the above cited kind which is capable of being manufactured in a simple, quick and economic manner in a large-scale industrial production system.

According to the present invention, such aims are reached in an improved thermostat embodying the features and characteristics as substantially recited in the appended claims.

The features and advantages of the present invention will anyway be more readily and clearly understood from the description that is given below by way of non-limiting example with reference to the accompanying drawing, in which the sole Figure appearing there is a schematical, partially cross-sectional view of a preferred embodiment of the thermostat according to the present invention.

With reference to the above cited Figure, the thermostat may for instance be of the type adapted for use in refrigeration appliances and mainly comprises a box-like load-bearing casing 1 with a closure element or covering cap 2 that is preferably made of tinned iron.

The cap 2 is provided with an opening that is preferably made in correspondence of a recess 3 in the same cap.

The thermostat further includes at least an expansible member 4, preferably in the form of a bellows-like member and made for instance of such a material as bronze, which is attached in an air-tight manner to the inner surface of the cap 2 by means of at least a soldered joint 5. An appropriate soldering alloy for said soldered joint 5 is preferably constituted by a tin-silver alloy, but it may also be a tin-lead alloy or the like.

The thermostat also comprises at least a tubular temperature sensor 6, or the like, which may for example be constituted by a capillary tube of soft tinned copper. Said sensor 6 has a sealed end 7 and an open end 8, wherein the latter is inserted in the opening provided in the cap 2. To this purpose, near the end 8 of the capillary tube there is provided a bulge 9 adapted to abut against the outer surface of the cap 2. The capillary tube 6 is attached in an air-tight manner to the cap 2, in correspondence of its open end 8, by means of at least a soldered joint 10. Even in this case, an appropriate soldering alloy for said soldered joint 10 is preferably a tin-silver alloy, but it may also be a tin-lead or similar alloy.

The bellows 4 communicate with the capillary tube 6, with which it so forms a sealed variable-volume chamber 15 containing a working fluid that has a high coefficient of thermal expansion. This working fluid may for example be a Freon medium, but it preferably comprises propane or a similar CFC-free medium.

In a per se known manner, said working fluid expands or contracts in accordance with the temperature being detected by the above cited temperature sensor 6, thereby causing the bellows 4 to expand or contract, accordingly. In correspondence of a predetermined expansion/contraction position, the bellows 4 are therefore adapted to actuate at least an electric switch 11, or the like, so as to cause it to open or close the associated electric circuit, wherein said switch is housed in the afore cited box-like casing and is associated to appropriate electric terminals 12,13 protruding in an air-tight manner from the same box-like casing.

According to the present invention, at least the soldered joint 10 of the capillary tube 6 is substantially covered by a mass 14 of hardened resin, which preferably includes Loctite 662 (registered trademark).

Said Loctite 662 resin is largely known to be usually employed in such simple applications as bonding and sealing of electronic component so as to protect them against water, moisture and dust. Conversely, in the improved thermostat according to the present invention such a resin may be deposited onto the soldered joint 10 and be for example hardened in a quick and affective manner by

means of the application of W rays. In this manner the surprising, experimentally verified result is obtained that the so hardened resin not only is effective in preventing any propane gas from leaking from said sealed chamber 15 in the case of microcracks or porosity coming to exist in the soldering alloy used for said soldered joint 10, but also substantially improves the mechanical strength in correspondence of the same joint.

As a result, although said soldered joint 10 is carried out with the use of a soldering alloy that does not contain lead (and therefore is compatible with foodstuffs, but less amalgamating than usual alloys), and although propane (or similar medium nt containing any CFC, but exibiting a marked tendency to leaking through microcracks or pores) is used as a working fluid, any leakage of working fluid from the sealed chamber 15 is effectively and advantageously prevented.

The hardened resin mass 14 may of course be of any other type adapted to answer the particular purpose. In particular, it may be any other type of resin (ie. a substance that is normally in a semisolid, ie. viscous state with a good wetting property) featuring an adequate sealing power, mechanical strength, an adequate resistance to working temperatures, further to the capability of being used in a simple, convenient manner in industrial manufacturing environments. In a preferred manner, such a resin should of course be free from emissions that might affect the final testing of the thermostat.

As it has also been found experimentally, an alternative resin 14 capable to meet the above stated requirements may for instance include the Loctite 151869 (registered trademark) or Loctite 3501 (registered trademark) materials which find usually application as sealant for electronic components and adhesive for simple bonding applications, respectively.

Anyway, in view of an easier and more reliable application on an industrial scale, the mass 14 of hardened resin is preferably applied to cover the soldered joint 10 in correspondence of the outer surface of the cap 2 and can be most conveniently deposited into the recess 3 of the same cap.

It will be appreciated that the above described thermostat may be the subject of any of a number of variants and modifications without departing from the scope of the present invention. For instance, in order to further eliminate any possibility for the working fluid to leak from the chamber 15, even the soldered joint 5 may be substantially covered with a mass of hardened resin 16 similar to the mass of resin 14.