BACKGROUND OF THE INVENTION
The present invention relates to steam pressing irons, and similar appliances such as steam wrinkle removers. In such appliances, water is conveyed slowly from a reservoir to a steam chamber in which water is converted into steam. More particularly, the invention concerns means for conveying the water into the steam chamber.
The most well known devices for this purpose are drip devices functioning by gravity, but they have the drawback that they cease to function when the pressure of steam in the steam chamber becomes higher than that of the column of water available above the drip device.
One solution to this problem consists in adapting an electromagnetic piston or membrane pump actuated by an electromagnet or an electric motor. Such devices are described, for example, in French patents numbers FR2368862 and FR2690932. Also known are rotary pumps such as centrifugal pumps as described in French patent number FR2688013 as well as peristaltic pumps, an example of which is disclosed in French patent number FR2691210, less commonly used.
These types of pumps have proven satisfactory with regard to flow rate and pressure. However, they also generate noise and vibrations, their flow rate is not easily variable, which leads them to operate in bursts, and they are relatively costly.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a household electric appliance containing a water reservoir that may be filled with tap water and that is equipped with a pump that is silent, economical and durable to transfer water from the reservoir toward the steam chamber, with a continuous flow rate that is easily adjustable with precision and is interruptible, as well as having a sufficient pressure to overcome the counter pressure generated in the steam chamber during ironing.
Primarily, the invention is embodied in an ironing appliance having a water reservoir and a pump for transferring water from the reservoir toward the steam chamber, wherein the pump is an electro-osmotic pump.
An electro-osmotic pump, as contemplated by the present invention, is a device having a first compartment that is normally connected to the water reservoir or that forms a part of this reservoir, and a second compartment connected to the steam chamber in which water transferred by the pump is converted into steam, the two compartments being separated by a porous solid body. Each compartment is furnished with an electrode in proximity to the porous body, the electrodes allowing water to flow therepast.
Thus, when a voltage is applied between the electrodes, a flow of water is created from the first compartment toward the second compartment and supplies the steam chamber. The principle of an electro-osmotic pump is described for example in U.S. Pat. No. 3,143,691. This document cites the pressures obtained with water, which reach the equivalent of a height of water of 11 mm per volt applied between the electrodes. However, the device described only transfers water from one chamber to another without flowing in a circuit, or serves to detect a pressure or flow rate.
Uses are known in fields that are radically different from that of the present invention. For example, French patent FR1446109 describes numerous devices using a pump of this nature, but with non-aqueous liquids. Several patents also describe medical uses for distributing medications in very small quantities, uses in chromatography to cause an electrolyte to circulate in a column, and uses in fluidics with low flow rates as in U.S. Pat. No. 6,012,902.
All of these uses concern movements of electrolytes or diverse solutions having characteristics far removed from running water, generally in fields that are very sophisticated and that involve low flow rates.
French patent FR2467178 describes a water purifier using electro-osmotic pumps, but the pumps used only operate if the water is purified, by resin devices that demineralize the water.
None of the above-cited documents envisions or suggests the utilization of such a pump in a household electric appliance, or even less in a pressing iron. However, an iron provided with an electro-osmotic pump performs particularly well and is particularly quiet.
The pump is placed between the reservoir and the steam chamber. Its water inlet communicates with the reservoir or is located within the reservoir, while its outlet is connected to the steam chamber.
According to one embodiment, the pump is constituted by an enclosure made of electrically non-conductive plastic, containing a porous body composed of grains of fritted glass, in the form of a disc occupying the entire cross-section of the enclosure. The fluid inlet and outlet are arranged at respective opposite sides of the porous disc. Two electrodes are placed to one side and the other of the disc, in contact with the fritted glass and in the path of the fluid. The pump is actuated by application of a direct voltage between the electrodes, of the order of 10-200 volts. Water is displaced, in this case of a siliceous covering of the disc, from the anode toward the cathode, the flow/pressure characteristic being linear and being directly dependant on the applied voltage.
Preferably, the cross-section of the porous body corresponding to the water passage has dimensions greater than the thickness of the porous body.
Specifically, the diameter of the disc is greater than its thickness. This thus avoids having a localized bubble in the porous body interrupt the passage of the electric current and the operation of the pump. In effect, a possible gas bubble, generated by the electrodes and trapped in the porous body, cannot have a diameter greater than the thickness of the porous body and thus cannot obstruct the entire passage cross-section for the water and the electric current.
In a preferred embodiment, the porous body is constituted by a bed of grains of very fine alluvial sand having a grain size of 0.2 mm or less.
Thus, fritted glass is replaced by the sand. This provides an economical form of construction of the medium in which the electro-osmosis is produced. Preferably, the porous body is of a siliceous nature, such as a quartz sand.
The bed of grains is maintained in an enclosure made of plastic by the electrodes, which are preferably made of stainless steel and provided with holes, the electrodes being placed on two flat faces of the bed.
Preferably, the electrodes are made of sheets of stainless steel that are perforated and expanded.
The electrodes do not significantly interfere with the passage of water in the pump.
Preferably, the electrodes are separated from the bed of grains, which they retain, by porous membranes.
The membranes aid retention of the sand so that the perforations in the electrodes do not have to be particularly small.
The electric supply of the pump, for reasons of safety, includes a transformer or a switch mode power supply including a galvanic isolation.
The invention also permits a linear variation of the flow rate by modification of the direct voltage applied between the electrodes.