The present invention relates to a thermostat for gas cooking appliances.

Thermostats are known for application to gas cooking appliances, and in particular to gas ovens.

Their purpose is to regulate the flow of gas to the burner installed in the oven, such as to ensure that the temperature inside the oven is maintained around a desired value preset by an adjustment knob. Their operating principle is such that they comprise a thermostatic bulb installed inside the oven and a temperature-sensitive fluid contained in the bulb and operationally connected to a valve disposed inside the thermostat body.

Thermostats with two exits are also known for feeding two different burners of the oven, namely the main burner and a secondary burner for the grill or the pilot flame of the main burner.

The characteristic of these known two-exit thermostats is the fact that one of these exits is controlled, hence the flow rate of the delivered gas is variable on the basis of the temperature measured by a suitable sensor, while the other exit has a flow rate which is not temperature-controlled.

An object of the invention is to provide a two-exit thermostat which enables the gas delivery from both exits to be controlled by a single thermostatic bulb and by a single temperature-sensitive fluid, on the basis of the temperature measured inside the oven.

Another object of the invention is to be able to make this adjustment in a precise and reliable manner. Another object of the invention is to provide a thermostat of simple form at low cost.

Another object of the invention is to provide a thermostat which, in the specific application to an oven with a double flame ring burner, enables a minimum temperature to be reached which is less than that reachable in ovens in which the burner is controlled by a traditional thermostat.

All these and other objects which will be apparent from the ensuing description are attained according to the invention by a two-exit thermostat for gas cooking appliances in accordance with claim 1 .

The present invention is further clarified hereinafter in terms of a preferred embodiment thereof provided by way of non-limiting example with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a thermostat according to the invention, Figures 2a and 2b are plan views thereof without the cap,

Figure 3 is a section therethrough on the line Ill-I ll of Figure 2a,

Figure 4 is a section therethrough on the line IV-IV of Figure 2a,

Figure 5 is a section therethrough on the line V-V of Figure 2a,

Figure 6 is a section therethrough on the line VI-VI of Figure 2a,

Figure 7 is a section therethrough on the line VII-VII of Figure 2b,

Figure 8 is a section therethrough on the line VIM-VIM of Figure 2b,

Figure 9 is a schematic view thereof shown applied to two different burners of an oven,

Figure 10 is a schematic view thereof shown applied to the inner flame ring and to the outer flame ring of a gas oven burner, Figure 1 1 shows a graph representing the variation in the temperature inside an oven cavity, with which a thermostat according to the invention is associated, as a function of the angular rotation of the thermostat knob.

As can be seen from the figures, the thermostat 1 according to the invention comprises a body 2 shaped externally as an approximately irregular parallelepiped, overlaid by an approximately cylindrical cap 4, and provided with a plurality of chambers and passages which will be referred to during the course of the ensuing description.

More particularly, inside the body 2 there are provided three main chambers, substantially defined by cylindrical cavities which are preferably parallel, and more precisely a pre-chamber 6, housing a safety valve 8 and its control rod 10, a first chamber 14, housing a slider valve 16 (i.e. a valve in which the slider acts as the valving element), and a second chamber 18 housing a distributor 20 comprising a control rod 22.

Preferably, the first chamber 14 and the second chamber 18 are provided mutually side by side within the body 2, i.e. they are not concentric, with one chamber inside the other; in particular, this is particularly advantageous as it makes their mechanical construction extremely simple.

As will be more apparent hereinafter, the purpose of the distributor 20 is to deviate, depending on its state, i.e. on the axial position of its control rod 22, the main gas stream, controlled by the slider valve 16, towards two different exits of the thermostat.

In this respect , the body 2 is provided with two exits 24 and 26, of which the exit 24 is substantially positioned on the prolongation of the second chamber 18 of the distributor 20 and can be connected outside the thermostat to one of the two burners of a gas oven and, if the oven is provided with a burner with two flame rings, in particular with an inner flame ring 28 and an outer flame ring 30, it is connected to its inner flame ring 28 (see Figure 10). The exit 26 is instead connectable to its outer flame ring 30 (see Figure 10) or to a second burner 30' which could for example be a burner which integrates the burner 28' which heats the oven inner cavity (see Figure 9) or the grill burner.

The upper end of the control rod 10 of the safety valve 8 and the upper end of the control rod 22 of the distributor 20 emerge from the upper base of the parallelepiped body 2, i.e. from the base opposite that in which the two exits 24 and 26 are present, and are housed within the cylindrical cavity 32 defined by the cap 4. They cooperate with different tracks of a control cam 34 which is also housed within the cylindrical cavity 32 and is rigid with a pin 36 which emerges from the base of the cap 4 and is intended to be inserted into a control and adjustment knob 38.

The pin 36 is rotationally rigid, but free in its axial movements, with respect to a pin 40 which rests on an expandable element 42 provided with an internal cavity communicating, via a capillary, with a bulb intended to be inserted in the oven cavity 44 and generally into that compartment, of which the inner temperature is to be controlled.

The expanding element 42, the capillary and the bulb contain in their interior a thermally expandable fluid, for example a diathermic oil, as described for example in WO2014/064605, the content of which is to be considered as entirely incorporated herein for reference. In greater detail, the pin 40, which is rotationally rigid with the pin 36, is provided with a cylindrical axial cavity , in which there engages the cylindrical end of another pin 48, rigid with the expanding element 42. The pin 40 has a threaded outer portion which engages in a thread provided in a sleeve 45, fixed with respect to the thermostat body 2. In this manner, the rotations of the knob 38 and of the pin 40 rigid with it, not only cause the control cam 34 to rotate, but also cause the pin 48 to undergo axial movements.

The expanding element 42 is also connected to the slider 16 by way of an interposed elastic element 50, as described in the said WO2014/064605. In particular, the arrangement of the various parts is such that by rotating the knob 38, the rest position of the expanding element 42 is set, as is the rest position of the slider 16, whereas during operation, the expansions of said expanding element 42 enable the gas flow rate towards the burner to be modified by means of the movement of the slider 16, to control the temperature inside the compartment heated by this.

The thermostat body 2 is provided, on a lateral wall thereof, with a gas inlet 52 which, by way of a conduit 54 provided inside the body itself, opens into the bottom of the pre-chamber 6, upstream of the valving element 56 of the safety valve 8.

Within the body 2 a further conduit 58 is also provided which connects that region of the pre-chamber 6 downstream of the valving element 56 to the first chamber 14 housing the slider valve 16.

This first chamber 14 also has a main outlet 60, which is closable by the slider 16 and communicates via a conduit 62 with the second chamber 18 of the distributor 20, in a region which can be intercepted by this latter. The first chamber 14 is also provided on its lateral surface with another outlet 63, which cannot be closed by the slider 16 and which communicates, via a screw 65 with a sized hole and a conduit 64, with a region of the second chamber 18 of the distributor 20, which lies downstream of the distributor itself and therefore cannot be intercepted by this (see Figures 5 and 6). In particular, the outlet 63, the holed screw 65 and the conduit 64 define a first bypass circuit.

The second chamber 18 is provided with two apertures and, depending on the axial position of the distributor 20, it communicates with either the first exit 24 of the thermostat body (see Figure 6) or, by way of a region 66, with the second exit 26 (see Figure 8).

Finally, the first chamber 14 is provided on its lateral surface with a third outlet 68, which cannot be closed by the slider 16 and which communicates, in sequence, with a conduit 70, with a screw 72 provided with a sized hole, and with a conduit 67. Moreover, in that portion of the body 2 which upperly bounds the second chamber 18, passages 69 are provided which communicate with the conduit 67 and which, depending on the axial position of the control rod 22 of the distributor 20, can either be in fluidic communication or not be in fluidic communication with the region 66, which is directly connected to the second exit 26. In particular, the outlet 68, the conduit 70, the holed screw 72, the portion 67, the passages 69 and the region 66 define a second bypass circuit, which is controlled by the axial position of the control rod 22 of the distributor 20.

In consideration of the fact that the flow/path of the gas which enters the body 2 through the inlet 54 and leaves from said body through the exit conduits 24 and 26, it is apparent that the second chamber 18 is positioned downstream of the first chamber 14, which in its turn is positioned downstream of the pre-chamber 6.

The purpose of the cam 34 is to operate the control rod 10 of the safety valve 8 and the control rod 22 of the distributor 20. More particularly, the cam 34, when rotated, causes the rod 22 to undergo axial movements by virtue of the fact that its upper end rests on a first circumferential track 76, and, when moved axially, causes the rod 1 0 to undergo axial movements by virtue of the fact that its upper end rests on a second track 74, provided on the lower surface of the cam 34. It should be noted that the first track 76 is concentric with the second track 74.

The fact that the control rod 22 is axially movable means that a particularly precise and flexible distributor 20 is achieved, in that in order to modify the angular position of the control knob 38, at which the distributor deviates the gas flow from the exit 24 to the exit 26, as apparent hereinafter, it is sufficient to suitably modify merely the track 76.

In the thermostat according to the present invention, the means 40, 45 for modifying the position of the slider 16 and the means 34, 76 for shifting the distributor 20 are implemented by the same control member, i.e. by the knob 38.

The thermostat according to the invention operates in the following manner:

When at rest, the knob is maintained in the 0° position, and the safety valve 8 is maintained with its valving element 56 in the closed position by a spring 80, and in this manner prevents the gas, which is present in the conduit 54, from passing through the pre-chamber 6, and reaching the first chamber 14 of the slider valve 16.

To light the burner 28' (see Figure 9), or its inner flame ring 28 (see Figure 10), the user axially presses the knob 38 while at the same time rotates it to bring it to an angle between 52° and X°. In this manner, the rod 10 acts on the safety valve 8 to open it and cause the gas to pass towards the first chamber 14 of the slider valve 16 and from there, via the first bypass circuit (i.e. through the aperture 63, the holed screw 65 and the conduit 64), to the first exit 24. At the same time, a traditional ignition spark plug (not represented), positioned in proximity to the inner flame ring 28 of the burner, causes the spark to strike and generate the inner flame ring, which hits the thermocouple, also positioned in proximity to the burner inner flame ring 28, and in traditional manner maintains the safety valve 8 open even after releasing the knob 38.

By virtue of the particular configuration of its track 76, the rotation of the knob 38 enables a spring 82, associated with the rod 22, to maintain the distributor 20, for the entire time of the angular excursion of the knob from 0° to the value X°, in a position such as to maintain the second chamber 18 closed towards the region 66, and hence towards the second exit 26, but open towards the first exit 24.

Moreover, in this situation, the second bypass circuit is closed, in that the distributor 20 lies in a position such as to interrupt the fluidic connection between the passages 69, provided in the upper portion with respect to the second chamber 18, and the region 66 connected to the second exit 26.

In this situation, the angular position of the knob between 0° and X° determines the rest position of the slider valve 16 in its seat 14 relative to the main outlet aperture 60 of the seat itself, to hence ensure the outflow from the first thermostat aperture 24, of both the gas stream which passes through the main aperture 60 and the conduit 62, and the gas stream which passes through the first bypass circuit (i.e. through the aperture 63, the holed screw 65 and the conduit 64). The result is that both a main stream controlled by the thermostat and a bypass stream not controlled by the thermostat reach the burner inner flame ring 28 or the burner 28'.

When the angular value X° of the knob 38 has been exceeded and until the limit value of Y°, the track 76 maintains the rod 22 of the distributor 20 axially pushed such that it maintains the second chamber 18 open towards the region 66 and towards the second exit 26, and closes it towards the first exit 24. Consequently, in this condition, only the first bypass stream passing through the conduit 64 passes through the exit 24 connected to the burner inner flame ring 28 or to the burner 28', whereas the gas originating from the first chamber 14 passes through the second exit 26 and is controlled by the slider 16.

In this condition, the gas stream also passes through the second bypass circuit, given that the axial position of the distributor 20 is such as to enable the fluid connection between the passages 69 and the region 66 connected to the second exit 26. In greater detail, the gas emerging from the first chamber 14 through the aperture 68 passes in sequence through the conduit 70, the holed screw 72, the portion 67 and the passages 69, it reaches the region 66 and finally leaves from the exit 26 to equally feed the burner outer flame ring 30 or the burner 30'.

Essentially, during the angular excursion X°-Y°, only the first bypass stream, which is not controlled by the temperature sensitive element 42, passes through the first exit 24, and feeds the inner flame ring 28 or the burner 28', while through the second exit 26 which feeds the outer flame ring 30 or the burner 30', there pass both the main gas stream, controlled by the slider valve 16 and hence by the temperature sensitive element 42, and the second bypass stream, which is not controlled by the temperature sensitive element, but is activated via the distributor 20.

To also represent graphically the temperature adjustment obtainable by the thermostat according to the invention, reference can be made to the graph of Figure 1 1 , in which the horizontal axis shows the values of the angular excursion of the adjustment knob 38 from the value 0° to the value Y°, while the vertical axis shows the corresponding temperature values inside the oven cavity 44. It can be seen that at the angular excursion value of the knob 38, generally equal to 52° and corresponding to the burner ignition position, there is minimum temperature inside the oven because only the inner flame ring 28 (or only the burner 28') is fed, namely by only the first bypass circuit defined by the path 63, 65 and 64. In the portion from 52° to the value X°, the temperature inside the oven continually increases by virtue of the flow of a gas stream controlled by the slider valve 16 which, together with the gas stream which passes through the first bypass circuit 64, feeds the burner inner flame ring 28. As soon as the position X° has been exceeded, the distributor 20 switches over to cause interruption of the feed to the burner inner flame ring 28 (or to the burner 28') by the gas stream controlled by the slide valve 16, while the feed by the first bypass circuit continues, and at the same time this causes opening of the second bypass circuit (defined by the path 68, 72, 70, 67, 69 and 66), which feeds the burner outer flame ring 30 via the second aperture 26. In the portion from X° to the value Y°, the temperature inside the oven increases continuously by virtue of the flow of a gas stream, controlled by the slider valve 16, which feeds the outer burner flame ring 30 (or the burner 30'), together with the gas stream which passes through the second bypass circuit. Advantageously, during the portion from X° to the value Y°, the inner flame ring 28 (or the burner 28') is in any event fed via the first bypass circuit, this enabling particularly high temperatures to be reached inside the oven cavity 44.

From the aforegoing it is apparent that the thermostat according to the invention is particularly advantageous in that:

- it enables both exits to be temperature regulated; in particular, this enables a considerable energy saving to be achieved, hence improving the energy rating of the oven in which the thermostat according to the invention is installed,

- it enables a gas flow to be controlled such as to provide a particularly high maximum power, related to the facility for activating one of the two main temperature regulated exits and both the bypass circuits,

- it enables the gas flow to be controlled in such a manner as to provide a particularly low minimum power, related to the facility for activating only the bypass circuit associated with the smaller burner (in the thermostat application to two separate burners) or to the inner flame ring of a burner having multiple flame rings (when applying the thermostat to the flame rings of one and the same burner).