The present invention relates to an improved thermostat without connections to the electrical mains.

Thermostats are known devices able to measure and control the tem peratu re of a body or environment and to maintain it within a predetermined variation range. In the particular case of temperature control of an environment, the operating principle of the thermostat is to cause heat to be administered to (subtracted from) the environment in which it is positioned when the temperature falls (rises) below (above) a predetermined lower (upper) limiting value, and to interrupt heat administration (subtraction) when the temperature reaches the predetermined upper (lower) value.

As h eat is g en era l ly ad ministered or subtracted by electrical appliances, i.e. by electrically powered or controlled appliances, a traditional thermostat is inserted into the electrical feed or control circuit of said electrical appliance. This requires an electrical connection between the thermostat and the appliance power circuit, and as the thermostat position must generally satisfy certain criteria which ensure control reliability and must hence be able to be distant from said power circuit, connections dedicated to this function are required.

An object of the invention is to eliminate these connections by proposing a thermostat which does not require electrical connection to the power circuit of the electrical appliance controlled by it.

In this respect, thermostats have already been proposed associated with a transmitter apparatus tuned to a receiver apparatus installed in the electrical appliance or in its power circuit. This enables the thermostat to be installed distant from the electrical circuit, but requires a radio transmitter which has to be powered by a self-contained electrical energy source. In addition, whereas a thermostat installed in proximity to the distribution mains can withdraw therefrom the energy required to power it, a thermostat installed distant from the mains must be equipped with batteries, which discharge with time and have to be replaced . In some cases this is simple and merely requires period ic checks, whereas in other cases a poorly accessible thermostat position can result in considerable difficulty.

A further object of the invention is to provide a self-powered thermostat free of all the drawbacks presented by known thermostats.

These and other objects which will be apparent from the ensuing description are attained , according to the invention, by an improved thermostat as described in claim 1.

The present invention is further clarified hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a schematic longitudinal section through a thermostat according to the invention with the inductive electrical generator shown in its rest condition,

Figure 2 shows it in the same view as Figure 1 with the inductive electrical generator in its switched-over condition, and

Figure 3 shows a variant thereof in the same view as Figure 1.

As can be seen from the figures, the thermostat according to the invention comprises a snap-action electrical generator 2, of inductive type, a discoidal ampoule 4 with undulated surfaces containing a heat expandable gas and forming the thermodeformable element, and a radio transmitter 6 powered by the electrical generator 2. The thermodeformable element 4 can also consist of a curved or bimetallic metal strip or any other element able to deform as the temperature varies. If the thermodeformable element 4 is an ampoule containing the heat expandable gas, and if the thermostat cannot be positioned directly in contact with the body the temperature of which is to be measured, said ampoule is connected, via a capillary, to a probe or other heat conducting element to be positioned in contact with said body.

The electrical generator 2 is for example of the type described in Ital ian patent appl ication M I2008A002028 of 14 Novem ber 2008 and essentially comprises, within a cylindrical casing 8, a cylindrical pushbutton 10 movable axially between two separate positions, namely a rest position (Figure 1 ) and a switched-over position (Figure 2). When in its rest position th e pu sh button 1 0 i s reta i n ed with i n th e cyl i n d rica l cas i ng 8 by a circumferential step 12 provided therein.

The electrical generator 2 also comprises a ferromagnetic core 14 in which a winding 16 is positioned, and a magnetic bar 18 which in the absence of external stresses adheres to the ferromagnetic core 14 but can be spaced therefrom by the thrust of two arms 20 rigid with the pushbutton 10.

The thermodeformable element 4 preferably consists of a discoidal ampoule but, as stated, it could be a different thermodeformable element able to undergo heat deformation of such an extent as to mechanically operate the pushbutton 10.

It rests on the external base of the pushbutton 10 via a spring 22 advantageously applied to it to cause the pushbutton to undergo snap-like movement, as will be apparent hereinafter, including the movement from its working position to its rest position. Also associated with the thermodeformable element 4 there is an adjustment member 24 operable from the outside via a knob 26 and acting on the thermodeformable element in the sense of predefining its rest position, to which the desired thermostat setting temperature corresponds.

The two terminals of the wind ing 16 are connected to the radio transmitter 6 for its powering. It is tuned to the same frequency as a radio receiver, operationally connected to the power circuit of the appliance, not shown, which is to be controlled by the thermostat.

The thermostat of the invention operates in the following manner:

when in its rest condition the thermodeformable element 4 is inactive and maintains the pushbutton 10 of the electrical generator 2 at rest, with the magnet 18 resting on the ferromagnetic core 14.

In this state the appliance controlled by the thermostat, for example an air conditioner, is not yet powered.

If, in the environment containing the thermostat, the temperature rises above the predetermined value, which corresponds to the thermostat set value, the thermodeformable element deforms and acts on the pushbutton 10 of the electrical generator 2. During the initial stage of deformation of the thermodeformable element 4, this deformation is absorbed by the spring 24, which becomes loaded. However when its reaction exceeds the force with which the magnetic bar 18 adheres to the ferromagnetic core 14, it begins to separate, to suddenly reduce this attraction force and cause the bar 10 to move snap-like as far as the end-of-travel position of the pushbutton 10.

The sudden flux variation in the magnetic circuit formed by the core 14 and the magnetic bar 18 induces within the winding 16 an electromotive force pulse, which powers the radio transmitter 6. This then generates a signal which can be received by the radio receiver, which is tuned to it, and be used, after possible processing, to connect the controlled air conditioner to the electrical mains.

As the air conditioner operates, it progressively cools the environment, with the temperature reduction acting on the thermodeformable element 4 in the opposite sense to the preceding. Again in this case the spring 22, aided by the attracting effect between the bar 18 and the core 14, transforms the continuous deformation movement of the thermodeformable element into a snap-like movement of the pushbutton 10, and hence of the magnetic bar 18, towards the rest configuration, with the generation in the winding 16 of a new induced electromotive force pulse of opposite sign to the preceding.

The voltage pu lse generated in th is man ner powers the rad io transmitter 6, which sends a new signal to the radio receiver to cause it to interrupt electrical power to the air conditioner.

From the aforegoing it is apparent that the thermostat of the invention fully attains the stated objects, in that it is able to control an electrical appliance on the basis of the temperature measured by the thermodeformable element 4, this being achieved without any cable connection with said appliance, and without the need for external electrical power or batteries.

In the embodiment shown in Figure 3, which uses the same principle as in the preceding embodiment, the mechanical connection between the thermodeformable element 4 and the pushbutton 10 of the electrical generator is not direct, but instead is obtained by a lever system 28, which amplifies the deformations of the thermodeformable element 4 and hence makes them independent of the operative travel of the pushbutton.