Method of operating a dishwasher

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of copending International Application No. PCT/EP01/03486, filed Mar. 27, 2001, which designated the United States.

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0002] The invention lies in the field of appliances. The invention relates to a method of operating a dishwasher in which items that are to be cleaned are subjected to the action of a cleaning liquid.

[0003] In all prior art dishwashers, including household dishwashers in particular, the items that are to be cleaned are continuously subjected to the action of the cleaning liquid, which normally is water, possibly with the admixture of cleaning or rinsing agents.

[0004] The cleaning liquid may usually be delivered by a circulating pump (which may be configured, for example, as a centrifugal pump) from a constantly refilling supply tank, through liquid feed lines, to spray devices. The spray devices apply the liquid to the items to be cleaned.

[0005] With the items that are to be cleaned subjected to such action, a sufficient cleaning result is achieved by the quantity of the chemical additives that may be admixed to the cleaning liquid, but mainly by the items that are to be cleaned being subjected to such action for a sufficient duration and by items that are to be cleaned having dirt removed from them mechanically over this period of time. In addition to the high outlay in terms of energy that is necessary for delivering the cleaning liquid, the cleaning requires a long cleaning-program duration.

[0006] If use is made of centrifugal pumps, the centrifugal action causes gases and solid particles to separate. As a result, the delivery quantity and the efficiency of the pump are adversely affected.

[0007] In the case of conventional pumping processes, e.g., using customary pumps, the liquids have to flow into the pump from a charge tank under a dedicated hydrostatic pressure. The active, moving part of the pump (in the case of the centrifugal pump, the impeller) produces a negative pressure and takes the liquid into the pump. The negative pressure is limited by the inflow of the liquid. If there is insufficient hydrostatic pressure on the suction side to force a sufficient quantity of liquid into the pump and to limit the abovementioned negative pressure, it is possible for the absolute pressure that is being established at the suction connection to drop below the steam pressure of the liquid, which results in the liquid being evaporated and, then, in steam, instead of the liquid, passing into the pump. As a result, the delivery capacity drops to a fraction of the envisaged delivery quantity. Furthermore, excessive noise development caused by condensation of the steam bubbles is produced during the operation, otherwise referred to as cavitation.

[0008] Because, at relatively high temperatures and with the presence of solid particles (so-called germs) the steam pressure increases, i.e., approaches the atmospheric pressure. Such occurrences are particularly pronounced and frequent during pumping of hot and contaminated liquids, as is the case, in particular, in dishwashers, which may result in the above-described grave disruption to operation, and cause the above-described excessive noise development, or may go as far as destroying the pump.

[0009] To avoid these disadvantages, attempts have been made, as has already been described above, to allow the liquid to flow into the pump under a dedicated, sufficient hydrostatic pressure, e.g., from a charge tank. For such a purpose, it is necessary to maintain a minimum height for the liquid, the Net Positive Suction Head (“NPSH”) on the suction side of the pump, e.g., in the above-mentioned charge tank. As a result, the necessary hydrostatic pressure can be produced. The minimum height for the liquid—usually referred to as inflow height—cannot always be ensured, however, because this is not spatially possible, for example, in a dishwasher and renders the construction of the dishwasher complicated and high in outlay or because a requisite charge of an additional mass of liquid that is basically not used for operation is undesirable.

SUMMARY OF THE INVENTION

[0010] It is accordingly an object of the invention to provide a method of operating a dishwasher that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that saves energy and water and makes it not necessary to comply with any specific inflow requirements in order to use the dishwasher.

[0011] With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of operating a dishwasher including the step of cleaning items with a cleaning liquid delivered by a pressurized, gaseous delivery medium.

[0012] Because the cleaning liquid is delivered by a pressurized, gaseous delivery medium, no specific inflow and intake conditions are necessary. Such a process allows for a more straightforward construction of the dishwasher. Because no pump is used for delivering the cleaning liquid, there is no need for any minimum introduction quantities of cleaning liquid. As a result, the water consumption can be reduced in relation to the prior art. Thus, less energy is required for delivering the cleaning liquid than for the continuous use of an electrically operated circulating pump according to the prior art. The invention makes it possible to provide a method of operating a dishwasher of the type mentioned in the introduction in which energy and water can be saved and it is not necessary to comply with any specific inflow requirements in order to use the same.

[0013] In accordance with another mode of the invention, the cleaning liquid is delivered at time intervals by the pressurized, gaseous delivery medium. When the items that are to be cleaned are subjected to the action of the cleaning liquid at time intervals, at the beginning of each action there is an increase in pressure in the cleaning liquid acting on the items, and, at the end of each action, there is a drop in the pressure in the cleaning liquid acting on the items. It has been found, in practice, that the alternating increase and drop in the pressure of the cleaning liquid, and the resulting alternating increase and drop in the mechanical forces acting on the soiling on the items that are to be cleaned, achieves a sufficient cleaning result with the duration of the cleaning-liquid action being shorter in comparison with the above-described prior art. As a result, the cleaning-program duration is shortened.

[0014] In accordance with a further mode of the invention, the cleaning liquid is delivered in a pulsed manner. As a result, the alternating increase and drop in the pressure of the cleaning liquid, and the resulting alternating increase and drop in the mechanical forces acting on the soiling on the items that are to be cleaned, take place in a very short period of time. It has been found, in practice, that, as a result, it is possible to achieve a further significant improvement in the cleaning with the items that are to be cleaned being subjected to the cleaning-liquid action for a shorter duration.

[0015] In accordance with an added mode of the invention, the ratio of the duration of the time interval between the operations for delivering the cleaning liquid and the duration of the delivery of the cleaning liquid is approximately 3:1. Preferably, the duration of the delivery is approximately 0.5 seconds. Such a short pulse duration optimizes the cleaning action of the cleaning liquid applied under pressure to the items that are to be cleaned.

[0016] In order for the items that are to be cleaned to be subjected straightforwardly to the cleaning-liquid action, in accordance with an additional mode of the invention, a cyclic pumping process delivers the gaseous delivery medium. In accordance with yet another mode of the invention, the cyclic pumping process is achieved in that the gaseous delivery medium is delivered by a cyclically operating pump, e.g., a reciprocating or diaphragm pump, etc.

[0017] Alternatively, in accordance with yet a further mode of the invention, the gaseous delivery medium is to be introduced cyclically from a supply source for acting on the cleaning liquid.

[0018] According to a preferred embodiment, the cleaning liquid is delivered by a cyclic plug flow process in which the cleaning liquid is subjected, by the gaseous delivery medium, to a pressure that is changed alternately between two pressure levels such that at a low pressure level, at which a negative pressure prevails, liquid is taken in and, when the higher pressure level is applied, at which a positive pressure prevails, the cleaning liquid is delivered in the desired delivery direction. By virtue of the application of low pressure, a sufficient quantity of the cleaning liquid can be taken in despite a low inflow height. By virtue of then being subjected to higher pressure, the delivery of the cleaning liquid is forced to take place by displacement. Because the gaseous delivery medium can also be taken in for compression purposes, the measure means that the negative pressure present anyway is also used for delivering the cleaning liquid, in particular, for accelerating the follow-up flow of a new quantity of cleaning liquid that is to be delivered.

[0019] In accordance with yet an additional mode of the invention, the gaseous delivery medium is air. As a result, the most frequently occurring gas is used for delivering the cleaning liquid.

[0020] In accordance with again another mode of the invention, the gaseous delivery medium is directed into a treatment chamber of the dishwasher during a “drying” sub-program step. As a result, the gaseous delivery medium (air) already present improves the drying result during the drying operation by blowing off the liquid remaining on the items that are to be cleaned. Thus, the duration of the “drying” sub-program step is considerably shortened.

[0021] With the objects of the invention in view, there is also provided a method of operating a dishwasher including the steps of pressurizing a gaseous delivery medium and cleaning items with a cleaning liquid delivered by the pressurized medium.

[0022] Other features that are considered as characteristic for the invention are set forth in the appended claims.

[0023] Although the invention is illustrated and described herein as embodied in a method of operating a dishwasher, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

[0024] The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]
FIG. 1 is a cross-sectional view of a household dishwasher with an apparatus for implementing the method according to the invention;

[0026]
FIG. 2 is a block and schematic circuit diagram of the apparatus for implementing the method according to the invention; and

[0027]
FIG. 3 is a time profile graph of a spray pulse in the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a household dishwasher 25, in which an apparatus 1 for implementing the method according to the invention is installed. In the household dishwasher 25 described, the cleaning liquid that acts on the non-illustrated items that are to be cleaned is water that is mixed, if appropriate, with cleaning or rinsing agent and may also possibly be contaminated with detached residues of food.

[0029] The household dishwasher 25 has a dishwashing compartment 26 in which non-illustrated items that are to be cleaned are disposed and washed. The compartment 26 can be closed by a non-illustrated door (also not described any more specifically) that, in the case of household dishwashers, can be pivoted about a horizontal axis. Provided in the dishwashing compartment 26 are dish racks 27, 28 in which the items that are to be cleaned, e.g. cutlery, plates, cups, glasses, etc., are disposed. The items are subjected to the action of the cleaning liquid by spray devices, e.g., so-called spray arms 29, 30, by the method according to the invention. The cleaning liquid running back off from the items, in the dish racks, that are to be cleaned accumulates in the lowermost section of the dishwashing compartment 26, which is usually referred to as the sump 9 or drainage pan.

[0030] According to the exemplary embodiment of the invention, the cleaning liquid is delivered at time intervals and in a pulsed manner by a pressurized, gaseous delivery medium. In the exemplary embodiment described, the gaseous delivery medium is air. The method according to the invention is implemented by a cyclic pumping process, in particular, a cyclic plug flow process, in an apparatus 1 described below and best seen in FIG. 2.

[0031] The apparatus 1 for delivering the cleaning liquid in the exemplary embodiments shown has a configuration 10 in which the gaseous delivery medium is pressurized by a compressor 2. Connected downstream of the compressor 2, as seen in the flow direction of the gaseous delivery medium, at a pressure outlet 3 of the compressor, is a pressure vessel 4 into which the gaseous delivery medium is introduced and stored therein.

[0032] In the exemplary embodiment, the configuration 10 has a pressure chamber 11 that is connected for liquid-channeling action to the sump 9. The gaseous delivery medium, controlled by a valve 5, is introduced into the pressure chamber 11. The valve 5, for controlling the introduction of the gaseous delivery medium into the delivery chamber 11, is disposed in a connecting line 21 between the pressure vessel 4 and an inlet 20 of the gaseous delivery medium into the delivery chamber 11.

[0033] A liquid-discharge line 12 is connected for liquid-channeling action to the pressure chamber 11 and the sump 9. A liquid line 13 continues from the sump 9 to the liquid-discharge line 12 and has a branched-off portion 14 to the pressure chamber 11. Disposed between the sump 9 and the pressure chamber 11 is a valve 15 that is intended for opening and closing the connection between the sump 9 and the pressure chamber 11 and, preferably, is a non-return valve that has a spherical closure body and closes a liquid outlet from the sump 9 if flow directed toward the sump 9 takes place. Disposed between the pressure chamber 11 and the liquid-discharge line 12 is a valve 16 that is intended for opening and closing the liquid-discharge line 12 and, preferably, is a non-return valve that has a spherical closure body and closes the liquid-discharge line 12 if flow directed toward the sump 9 or toward the liquid-discharge line 12 takes place. The pressure chamber 11 has a further inlet 18, which is controlled by a valve 17 and to which a venting line 19 is connected.

[0034] In the use position, i.e., for a front view of FIGS. 1 and 2, the inlet 20 for the gaseous delivery medium into the pressure chamber 11 is disposed at the top and the inlet of the liquid line 13, i.e., the branched-off portion 14, is disposed at the bottom. The configuration also has a connection 22 between the liquid-discharge line 12 and the compressor 2 for the gaseous delivery medium between the liquid-discharge line 12 and the pressure vessel 4. A further valve 6 for controlling the introduction of the gaseous delivery medium into the liquid-discharge line 12 is disposed in the connection 22. Furthermore, the configuration described has a connection 23 between the pressure chamber 11 and a suction line 7 of the compressor 2. The suction line 7 of the compressor 2 has a further valve 8, for opening or closing the suction line 7 in relation to the surroundings, upstream, as seen in the flow direction of the gaseous delivery medium, of the branched-off portion for the connection 23 to the valve 17 of the further inlet 20, controlled by a valve 17, of the pressure chamber

[0035] The method according to the invention of operating a dishwasher 25 and the pulsed delivery of the cleaning liquid executed therein, in which the cleaning liquid in the configuration is alternately subjected, by the gaseous delivery medium, to a negative pressure and, at a time interval to a positive pressure, are executed by the above-explained apparatus 1 according to the following text.

[0036] The valves 5, 6, 8, and 16 are initially closed, and the valves 15 and 17 are open. The liquid extends, in the sump 9, to the liquid level N1 and, in the pressure chamber 11, due to the suction function of the negative pressure described hereinbelow, to the considerably higher liquid level N1′. B y virtue of the valve 17 being closed and the valve 5 being simultaneously opened, the gaseous delivery medium under positive pressure is introduced into the pressure chamber 11. As a result, the liquid is displaced to a lower liquid level N2. In such a case, the valve 15 is closed and the valve 16 is opened, with the result that the liquid penetrates further into the liquid-discharge line 12, an identical quantity of liquid being moved from the liquid-discharge line 12 to the spray arms 29, 30. Approximately at the same time as the valve 5 opens, the valve 8 is also opened, so that the compressor 2 can take in gas and the gas is equalized in terms of pressure and quantity. The valve 5 is then closed and the further valve 6, for controlling the introduction of the gaseous delivery medium into the liquid-discharge line 12, is opened—or it is possible, conversely, first of all for the further valve 6, for controlling the introduction of the gaseous delivery medium to the liquid-discharge line 12, to be opened and then for the valve 5 to be closed—as a result of which, in both alternative method steps, the gaseous delivery medium is directed into the liquid-discharge line 12 and the second application of the higher pressure level for subjecting the liquid to a positive pressure takes place. As a result, the liquid located in the liquid-discharge line 12 is replenished, so that liquid is again moved to the spray arms 29, 30. The valve 16 is closed. The valve 6 and the valve 8 are then also closed and the valve 17 is opened. As a result, the gaseous delivery medium located in the pressure chamber 11 is directed, through the venting line 19 and the suction line 7, to the compressor 2 and a negative pressure is produced in the pressure chamber 11. By virtue of the negative pressure, or, for the case where the valve 15 is not a non-return valve, by virtue of external control, the valve 15 then opens, resulting in liquid being drawn into the pressure chamber 11 from the sump 9 as a result of the negative pressure prevailing in the pressure chamber 11. The valve 16 is kept in a closed position. The valve 17 is then closed and, at the same time, the valve 8 is opened again. The operation is then repeated as long as liquid delivery is required. Before the valve 5 is opened again, for introduction of the pressurized gaseous delivery medium into the pressure chamber 11, there is a pause of approximately half a second in the above-described exemplary embodiment of the method according to the invention.

[0037] The profile over time of a spray pulse produced by the method explained above is shown in FIG. 3, which shows the time taken and the water pressure produced from the point in time at which the valve 17 is opened for taking the cleaning liquid into the pressure chamber 11. The period of time for taking in liquid is designated Ts in FIG. 3 and is approximately one second. In the exemplary embodiment, there is, then, a pause over a period of time Tp of approximately half a second. The pause period is followed by the pulse-like delivery of the cleaning liquid, by virtue of the valve 5 being opened, with a pulse height If of approximately 310 millibars together with the replenishing, by virtue of the valve 6 being opened, with a pulse height In of approximately 90 millibars in addition over a period of time Ti of half a second. In the exemplary embodiment described, the ratio of the duration of the time intervals (Ts+Tp) between the deliveries of the cleaning liquid to the duration of the delivery of the cleaning liquid Ti is approximately 3:1. The very short pulse duration Ti optimizes the cleaning action of the cleaning liquid applied under pressure to the items that are to be cleaned.

[0038] When the items that are to be cleaned are subjected to the action of the cleaning liquid at time intervals, at the beginning of each action there is a rise in pressure in the cleaning liquid acting on the items, and at the end of each action there is a drop in the pressure in the cleaning liquid acting on the items. It has been found, in practice, that the alternating increase and drop in the pressure of the cleaning liquid, and the resulting alternating increase and drop in the mechanical forces acting on the soiling on the items that are to be cleaned, achieves a sufficient cleaning result with the duration of the cleaning-liquid action being shorter in comparison with the above-described prior art. Such is true, in particular, if the cleaning liquid is delivered in a pulsed manner, the alternating increase and drop in the pressure of the cleaning liquid, and the resulting alternating increase and drop in the mechanical forces acting on the soiling on the items that are to be cleaned, taking place in a very short period of time and, thus, very intensively.

[0039] Furthermore, in the case of the exemplary embodiment of the invention, during a “drying” sub-program step, the gaseous delivery medium is directed into the dishwashing compartment 26 of the household dishwasher 25. As a result, the gaseous delivery medium that is present anyway—the air—improves the drying result during the drying operation as a result of blowing off the liquid remaining on the items that are to be cleaned, and considerably shortens the duration of the “drying” sub-program step.

[0040] As the cleaning liquid is delivered by a pressurized, gaseous delivery medium, no specific inflow and intake conditions are necessary, which allows a more straightforward construction of the dishwasher. Because no pump is used for conveying the cleaning liquid, there is no need for any minimum introduction quantities of cleaning liquid. As a result, the water consumption can be reduced in relation to the prior art. It is, thus, also the case that less energy is required for delivering the cleaning liquid than for the continuous use of an electrically operated circulating pump according to the prior art. The invention has made it possible to provide a method of operating a dishwasher of the type mentioned in the introduction in which energy and water can be saved and it is not necessary to comply with any specific inflow requirements in order to use the same.

	Number	Date	Country
Parent	PCT/EP01/03486	Mar 2001	US
Child	10008333	Dec 2001	US

Method of operating a dishwasher

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