DESCRIPTION

Field of the Invention

This invention relates to an electric control device whose operation is tied to the prevailing pressure within a boiler of a domestic steam generator, and to a method of generating an electric control signal as a function of the boiler pressure of a domestic steam generator.

Background Art

Steam generators often require a number of actions and/or indications tied to a pressure level attained by the steam in a boiler.

A simple design and reliable operation are features of primary importance to domestic appliances, such as smoothing irons and cleaning appliances, both in view of the need to keep their manufacturing costs and retail prices as low as possible, and of their prerequisite for long term safety. Domestic appliances are very seldom given regular maintenance, and are often expected to operate properly in severe conditions, e.g. on hard water which readily results in the formation of scale deposits. Thus, it is of extreme importance that these appliances be least prone to failure.

Boiler pressure is usually detected by means of specific sensors which tend, however, to be complicated and critical. As a result, these sensors are liable to frequent problems or malfunction, especially when used with hard waters that are apt to grow heavy scale deposits.

Summary of the Invention

The underlying problem of this invention is to provide an electric control device whose operation is tied to pressure, specifically intended for appliances for household use .

Thus, the invention provides, according to a first aspect thereof, an electric control device tied operatively to the pressure prevailing in a boiler of a domestic steam generator, characterized in that it comprises: a body having an annular structure with a through- going cavity; an elastically deformable reed plate mounted on the body to seal the through-going cavity and define a forward chamber and rearward chamber within the body; an electric switch mounted in the rearward chamber of the body, the electric switch having a movable driving member in driving engagement with the reed plate; the device body being adapted to fit tightly within a window provided in the boiler, with the forward chamber facing the boiler interior.

By having the electric switch operated by deformation of the reed plate, the desired electric control can be implemented in an extremely simple manner. Thus, the device is quite suitable for use in household appliances, by reason of its low cost and of the high degree of reliability brought about by its simple construction.

Preferably, the device comprises: a frame, for installation on the boiler; a cylindrical sleeve attached to the frame and forming said body in cooperation therewith; and an axial ledge formed inside the sleeve, with the reed plate being held securely against the ledge by the

f rame .

Thus, the reed plate can be held in place in a most practical and simple manner.

Preferably, the device comprises a holding plate for the electric switch, which plate is mounted adjustably on the body and has the electric switch secured thereon. Preferably, at least one screw for fastening the plate to the body, and at least one spring biasing the plate away from the body, are provided. In this way, the electric switch can be adjusted in position relative to the reed plate, while the device trip pressure can be set in an easy and effective manner.

According to a second aspect, the invention relates to a boiler for a domestic steam generator, which comprises: a sealed water storage tank; a heater means for the water in the boiler; a window provided in the boiler; and an electric control device tied operatively to the pressure level, and comprising: an annular body structure having a cavity therethrough and fitting tightly within the boiler window; an elastically deformable reed plate mounted on the body to seal the through-going cavity defining, within the body, a forward chamber facing into the boiler and a rearward chamber; and an electric switch mounted in the rearward chamber of the body, the electric switch having a movable driving member in driving engagement with the reed plate .

According to a third aspect, the invention relates to a method of generating an electric control signal as a function of the boiler pressure of a domestic steam

generator, characterized in that it comprises the following steps: providing a window in the boiler; closing the window with an elastically deformable reed plate; mounting an electric switch on the boiler exterior, in close proximity to the reed plate and at such a location that, with the boiler pressure below a predetermined value, the electric switch is in a first operational position, and with the boiler pressure above the predetermined value, the electric switch is in a second operational position.

Preferably, the reed plate and electric switch are mounted on a body, in turn mounted on the boiler.

Further features and advantages of this invention can be more clearly appreciated by having reference to the following detailed description of a preferred embodiment thereof, to be read in conjunction with the accompanying drawings.

List of the Drawing Figures

Figure 1 is a sectional view of a steam generating boiler in a household appliance, incorporating a pressure- operated electric control device.

Figure 2 is a sectional view of a detail of the electric control device shown in Figure 1, taken along line II-II.

Figures 3 and 4 are sectional views of the electric control device of Figure 1, in two different conditions of its operation.

Figure 5 is an exploded part-sectional view showing a detail of the boiler of Figure 1 including the electric

control device.

Detailed Description of a Pre err Embodiment of the

Invention

Depicted in Figure 1 is a steam generating boiler 1 in a household appliance (not shown) , such as a smoothing iron, a cleaning appliance, or the like.

The boiler 1 includes a water storage tank 2 which is sealed at the top by a cover 3, with a sealing gasket 4 interposed which may be of the 0-ring type. The boiler also includes a heater means, such as an electric resistance heater 5 housed within the tank 2 and being submerged in use by the water therein.

The boiler 1 is provided with a window or opening 6 which is circular in shape and cut either through the cover 3 or in some other region above the water fill level. A seat 7 is formed around the window 6 in the boiler 1.

Mounted on the boiler 1 at the location of the window 1 is a pressure-operated electric control device, generally denoted by the numeral 10 and being accommodated inside the seat 7.

The device 10 comprises a main body 11 having approximately annular structure, with an inner cavity 12 which extends vertically through the body 11. The body 11 is divided into an upper frame 13 and a lower cylindrical sleeve 14 which are releasably fastened to each other. The cavity 12 is divided into two sealed chambers 15 and 16 by an elastically deformable circular reed plate 17 accommodated inside a respective axial seating ledge 18 formed in the sleeve 14, with a sealing gasket 19, such as an O-Ring, interposed therebetween; the reed plate 17 is held in place immovably between the

frame 13 and the sleeve 14. With respect to its installed position on the boiler 1, chamber 15 will be referred to hereinafter as the forward chamber, and chamber 16 as the rearward chamber.

The frame 13 has two drilled brackets 20 for attaching the device 10 to the boiler 1 by means of screws or the like fasteners (not shown) . A sealing gasket 21, such as an O-Ring, is interposed between the sleeve 14 of the device 10 and the seat 7. Thus, the device 10 will be facing into the boiler 1 through the window 6, and particularly the reed plate 17 will be facing the boiler 1 interior.

The device 10 also comprises an electric switch 22, known per se and described and illustrated in no greater detail herein. The electric switch is provided with clamp terminals for electric connection, e.g. three clamp terminals 23, 24 and 25, and a movable driving member or pushbutton 26. For example, the electric switch 22 may be of a type wherein the pulled-up position of the movable member 26 corresponds to an electric contact being made across the terminals 23 and 24 and an electric contact broken across the terminals 24 and 25, whereas a sufficiently pushed-down position thereof corresponds to the electric contact across the terminals 23 and 24 being broken and the electric contact across the terminals 24 and 25 being made, or vice versa. A spring-biased means (not shown) in the electric switch 22 holds the movable member 26 in its normally pulled-up position.

The electric switch 22 accommodated within the rearward chamber 16 is mounted adjustably on the frame 13 of the body 11 by means of a plate 27, to which the electric switch 22 is secured with two pins 28. The plate 27, with the electric switch 22 thereon, is guided for

movement in the vertical direction on the frame 13. Two springs 29 bias the plate 27 upwards, away from the frame 13, and two screws 30 secure the plate 27 on the frame 13, adjustably in position.

The elastically deformable reed plate 17 is formed from a suitable material having good elastic and heat-resisting properties, for example a metal material such as stainless steel. The reed plate dimensions will be dictated by the elastic deformability of the material used, as well as by the travel distance of the movable driving member 26 of the electric switch 22; it has been ascertained that the amount of deformation required for proper operation of a commercially available electric switch 22 can be obtained by using a stainless steel reed plate 17 having a thickness of about 0.2 mm and a diameter of about 20 mm.

During operation of the boiler 1, the reed plate 17 is exposed to the pressure from the steam generated by heating the water with the electric resistance heater 5. Specifically, the reed plate 17 will be exposed to ambient pressure on one side (rearward chamber 16) , and the internal pressure of the boiler 1 on the other side (forward chamber 15, facing into the boiler) .

When the boiler 1 is cold, the reed plate 17 will be in a substantial planar condition, as shown in Figures 1, 2 and 3. In this condition, the movable driving member 26 of the electric switch 22 is in its pulled-up position, close to or in substantial contact with the reed plate 17.

With the boiler 1 in operation (Figure 4), steam pressure is applied to the reed plate 17, which will accordingly undergo a deflection toward the rearward chamber 16.

This deformation of the reed plate 17 results in a thrust force being exerted on the movable driving member 26 of the electric switch 22; the movable driving member 26 will then be moved to its pushed-down position as dictated by the steam pressure prevailing in the boiler 1 and the position of the plate 27 relative to the frame 13. Briefly, by adjusting the plate 27 position relative to the frame 13 with the screws 30, a pressure value can be selected at which the electric switch 22 will be operated.

The switch operation may either result in an electric connection being engaged or disengaged, depending on the electric switch type. For example, the power supply to the electric resistance heater 5 could be cut off upon a predetermined maximum pressure value being reached; alternatively, a steam delivery solenoid valve could be opened only upon a predetermined minimum pressure value being reached; or alternatively, light and/or sound indicators could be turned on upon predetermined pressure values being overtaken.

By using an electric switch 22 of conventional design, provided with a movable driving member 26 having two operational positions, a device 10 according to the invention can handle two or more actions simultaneously, but always at a single predetermined tripping pressure . Where plural actions at different pressures are envisaged, it will be possible to use two or more devices 10, each set for a different pressure, or some special electric switches having a movable driving member through three or more sequential positions.

As apparent from the foregoing description, a device according to this invention can be particularly beneficial to household appliances, for most of which

cutting off the power supply upon reaching a predetermined pressure is a primary consideration. Furthermore, the very simplicity of the device construction and its adjustment are particularly appreciated with household appliances, in that they keep down the device cost and enhance its reliability.

It should be further noted that the device of this invention is unaffected by scale deposits. In fact, the continual deformations undergone by the reed plate will inhibit scale formations in its middle region; as soon as film scale happens to form, this is ruptured and removed upon the next deformation of the reed plate, given the substantial inflexible and crumbling-prone nature of scale deposits. Scale deposits might indeed form over the peripheral regions of the reed plate, as well as over the other stationary parts facing the boiler interior; however, such deposits can hardly interfere with proper operation of the reed plate. Finally, by removing the device from the boiler, any parts that may have grown scale deposits, either on the device or the boiler, can be readily accessed through the fairly large window provided.