EP2138086A1

EP2138086A1 - A dishwasher and a method for reducing noise generated in a dishwasher

Info

Publication number: EP2138086A1
Application number: EP08011652A
Authority: EP
Inventors: Alf Johansson
Original assignee: Electrolux Home Products Corp NV
Current assignee: Electrolux Home Products Corp NV
Priority date: 2008-06-27
Filing date: 2008-06-27
Publication date: 2009-12-30

Abstract

The system for controlling a multi-compartment dishwasher (1), which dishwasher (1) comprises a first washing compartment (10), having a first circulation pump (16) for circulating water in the washing compartment (10) during a washing operation, a second washing compartment (20), having a second circulation pump (26) for circulating water in the washing compartment (20) during a washing operation. The system comprising a control unit (30), operatively associated with the first and second washing compartments (10, 20), which control unit is arranged to control the first circulation pump (16) to alternate between a first target rotational frequency (f1 h) and a second target rotational frequency (f1l), the first target rotational frequency (f1 h) being higher than the second target rotational frequency (f1l), and to control the second circulation pump (26) to alternate between a first target rotational frequency (f2h) and a second target rotational frequency (f2l), the first target rotational frequency (f2h) being higher than the second target rotational frequency (f2l). The control unit (30) further is arranged for controlling the first and second circulation pumps (16, 26) such that at any given instant, at the most one circulation pump (16, 26) is running at the first target rotational frequency (f1 h, f2h).

Description

Technical field

The present invention relates to dishwashers and, more particularly, to a system for controlling a multi-compartment dishwasher, and to a dishwasher comprising such a system.

Background

In general, multi-compartment dishwashers are well-known. Typically, a multi-compartment dishwasher includes several pull-out drawers, slidably mounted in a cabinet.
A multi-compartment dishwasher is generally arranged such that a washing operation can be performed in only one of the compartments at a time, or in several compartments simultaneously.
In most multi-compartment dishwashers, each compartment comprises a washing tub that is arranged to receive the dishes to be washed, a circulation pump for establishing a flow of water in the washing compartment during a washing operation, a motor driving the circulation pump, and a rotating spray arm from which water jets are ejected onto the dishes during the washing operation.
During a washing operation in a washing compartment, acoustic noise is primarily generated when water from the rotating spray arm hits the walls of the washing tub and the dishes arranged within the washing tub.
For obtaining the best washing result possible it is common to let the motor and thereby the impeller of the circulation pump alternate between different rotational frequencies. The strength of the water jets ejected from the rotating spray arm depends on the rotational frequency of the circulation pump. At a high rotational frequency of the circulation pump, a stronger force is exerted by the water jets as they hit the dirty dishes and the walls of the washing tub than at a low rotational frequency of the circulation pump. A stronger force improves the ability of the water jets to remove soil from the dishes, but it also causes generation of more acoustic noise than what is generated at a low rotational frequency of the circulation pump.
It is desirable to reduce the acoustic noise generated in a dishwasher as much as possible. In particular, there is a need for a multi-compartment dishwasher combining good washing results in all washing compartments with a low sound level.

Summary

An object of the present invention is to provide system for controlling a multi-compartment dishwasher in which a minimum of acoustic noise is generated.
Another object of invention is to provide a multi-compartment dishwasher in which a minimum of acoustic noise is generated.
A third object of the invention is to provide a method for controlling a multi-compartment dishwasher, in which dishwasher a minimum of acoustic noise is generated.
According to a first aspect of the invention, a system is provided, for controlling a multi-compartment dishwasher, which dishwasher comprises a first washing compartment, having a first circulation pump for circulating water in the washing compartment during a washing operation, and a second washing compartment, having a second circulation pump for circulating water in the washing compartment during a washing operation. The system comprises a control unit which is operatively associated with the first and second washing compartments, and is arranged to control the first circulation pump to alternate between a first target rotational frequency and a second target rotational frequency, the first target rotational frequency being higher than the second target rotational frequency, and to control the second circulation pump to alternate between a first target rotational frequency and a second target rotational frequency, the first target rotational frequency being higher than the second target rotational frequency. The system is characterized in that the control unit further is arranged for controlling the first and second circulation pumps such that at any given instant, at the most one circulation pump is running at its first target rotational frequency.
By providing a system ensuring that, at any given instant, at the most one circulation pump is running at its first target rotational frequency, a multi-compartment dishwasher is obtained for which the acoustic noise is reduced compared to a multi-compartment dishwasher having several circulation pumps that may be running at their first target rotational frequencies at the same time.
According to an embodiment of the invention, the control unit comprises a first sub control unit for controlling the first circulation pump, a second sub control unit for controlling the second circulation pump, and a communication link between the sub control units for enabling communication between the sub control units. By providing a sub control unit for each washing compartment, each washing compartment becomes capable of independent operation such that a user may operate one or both washing compartments depending on a particular need. The communication link between the sub control units enables mutual communication between the sub control units.
According to another embodiment of the invention, the control unit generates a square wave signal for controlling the circulation pumps. A square wave signal, alternating between two different levels, constitutes a simple control signal for controlling the rotational frequency of a circulation pump to switch between two values. The square wave signal is also easy to produce, e.g. using a pulse generator.
According to yet another embodiment of the invention, the system further comprises an arrangement for measuring a rotational frequency of each circulation pump, wherein the control unit is arranged to use the measured frequencies for controlling the circulation pumps. The arrangement for measuring a rotational frequency of each circulation pump enables feedback control of the circulation pumps, such that for each instant, the nominal value of the rotational frequency can be adjusted depending on the actual rotational frequency of the circulation pump.
According to another embodiment of the invention, the system comprises means for switching the rotational frequency of the first circulation pump from the first target rotational frequency to the second target rotational frequency, means for comparing a measured frequency of the first circulation pump with a predetermined threshold value, and means for setting a rotational frequency of the second circulation pump to the first target rotational frequency when the measured rotational frequency of the first circulation pump is lower than the predetermined threshold value.
According to another embodiment of the invention, the control unit is arranged to control a pulse generator, which pulse generator is arranged to supply the first circulation pump with a first control signal and to supply the second circulation pump with a second control signal, such that at any given instant, at the most one circulation pump is running at its first target rotational frequency. The use of a pulse generator is an easy way to supply the circulation pumps of different washing compartments with control signals having predetermined characteristics. As a result of the predetermined characteristics of the control signals, a predictable control procedure is achieved. Furthermore, even if there are several compartments in a dishwasher, only one pulse generator is needed, since the pulse generator can generate several different control signals.
According to a second aspect of the invention, a dishwasher comprising a system according to the first aspect of the invention is provided.
According to a third aspect of the invention, a method for controlling a dishwasher is provided, wherein the dishwasher comprises a first washing compartment, having a first circulation pump for circulating water in the washing compartment during a washing operation, and a second washing compartment, having a second circulation pump for circulating water in the washing compartment during a washing operation. The method comprises the following steps:
Controlling the first circulation pump to alternate between a first target rotational frequency and a second target rotational frequency, the first target rotational frequency being higher than the second target rotational frequency;
Controlling the second circulation pump to alternate between a first target rotational frequency and a second target rotational frequency, the first target rotational frequency being higher than the second target rotational frequency;
Controlling the first and second circulation pumps such that at any given instant, at the most one circulation pump is running at its first target rotational frequency.
By letting the method comprise the step of controlling the first and second circulation pumps such that, at any given instant, at the most one circulation pump is running at its first target rotational frequency, the total generation of acoustic noise in the washing machine will be low, even if washing operations are performed in several washing-compartments at the same time.
According to an embodiment of the third aspect of the invention, the method further comprises the steps of:
Measuring a rotational frequency of the circulation pump, and using the measured frequency for controlling the circulation pumps.
By letting the method comprise the steps of measuring a rotational frequency of a circulation pump and using the measured frequency for controlling the circulation pumps, feedback control of the circulation pumps is enabled, such that a better and more flexible adaptation of the rotational frequencies is achieved.
According to another embodiment of the third aspect of the invention, the method further comprises the following steps:
Switching the rotational frequency of the first circulation pump from the first target rotational frequency to the second target rotational frequency;
Comparing a measured rotational frequency of the first circulation pump with a predetermined threshold value;
Setting the rotational frequency of the second circulation pump to the first target rotational frequency when the measured rotational frequency of the first circulation pump is lower than the predetermined threshold value.
By letting the method comprise the step of comparing the measured rotational frequency of the first circulation pump with a predetermined threshold value, it becomes possible to regulate the rotational frequency of the second circulation pump quickly, and still without causing several circulation pumps to run at a high rotational frequency at the same time.

Brief description of the drawings

Embodiments of the present invention will be described in more detail hereinafter, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic side view of a cross section of a multi-compartment dishwasher according to the invention;
Fig. 2 is a schematic block diagram of a system according to the invention;
Fig. 3 is a flow chart showing a method for controlling a dishwasher according to the present invention.

Description

The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The invention deals with a multi-compartment dishwasher, such as a drawer-type dishwasher. For the sake of simplicity, a dishwasher having two washing compartments is described in this disclosure, but the number of washing compartments may also be three or more.
Each washing compartment is capable of independent operation such that a user may operate one or both washing compartments depending on a particular need.
Fig. 1 shows in cross-section a schematic side view of a multi-compartment dishwasher 1, having two washing compartments 10, 20. A washing compartment 10, 20 may be configured as a pull-out drawer which is slidably mounted in a cabinet (not shown). Dishwashers in which the washing compartments 10, 20 are configured as drawers are generally known as drawer-type dishwashers.
Each washing compartment 10, 20 has a washing tub 13, 23 for receiving dirty dishes or other objects that are to be washed.
A washing operation is performed in a washing compartment 10, 20, in order to clean the dishes in the washing tub 13, 23. A washing operation comprises several procedures. The dishes are cleaned during a washing procedure, preceded by a water intake procedure which is performed for admitting an adequate quantity of water into the washing compartment 10, 20 for use during the washing procedure. Other procedures that can be included in a washing operation are e.g. a heating procedure for heating water that is used to wash the dishes, a drain procedure for discharging water from the washing compartment 10, 20, and a drying procedure for drying the cleaned dishes.
Each washing compartment 10, 20 has a circulation pump 16, 26, for establishing a flow of water in the washing compartment. The circulation pump is driven by a motor 16a, 26a. The upstream side of each circulation pump 16, 26 is fluidly connected to a sump 13c, 23c, formed in a lower part of the washing tub, whereas the downstream side of each circulation pump 16, 26 is connected to a conduit 17, 27, which is in communication with a rotatable spray arm or sprinkler 18, 28 positioned in the washing tub 13, 23.
During a washing procedure in either of the washing compartments 10, 20, the circulation pump 16, 26 sucks water from the sump 13c, 23c and propels it into the conduit 17, 27 by means of an impeller 16b, 26b in the circulation pump 16, 26. Water in the conduit 17, 27 is further guided into the sprinkler 18, 28 in the washing tub 13, 23. The spray arm 18, 28 has an array of jet orifices, from which water fed from the conduit 17, 27 is sprayed onto the dishes in an upper part 13a, 23a of the washing tub 13, 23. Water then returns to the sump 13c, 23c through a filter portion 13b, 23b, to be recirculated back to the washing tub 13, 23 by the circulation pump 16, 26.
During a washing operation in a washing compartment 10, 20, acoustic noise is primarily generated when water ejected from the jet orifices of the rotating spray arm 18, 28 hits the walls of the washing tub 13, 23 and the dishes arranged within the washing tub 13, 23.
The strength of the water jets ejected from the rotating spray arm 18, 28 depends on the rotational frequency of the circulation pump impeller 16b, 26b. At a high rotational frequency of the circulation pump impeller 16b, 26b, a stronger force is exerted by the water jets as they hit the dirty dishes and the walls of the washing tub 13, 23 than at a low rotational frequency of the circulation pump impeller 16b, 26b. A stronger force improves the ability of the water jets to remove soil from the dishes, but it also causes generation of more acoustic noise than what is generated at a low rotational frequency of the circulation pump.
The rotational speed of the circulation pump impeller 16b, 26b is equal to the rotational speed of the motor 16a, 26a driving the impeller 16b, 26b, since thee impeller is mounted on the drive shaft of the motor 16a, 26a.
In order to provide a washing machine that combines good washing results and a low sound level, it is common to let control unit 30 control the motor 16a, 26a, and thereby the circulation pump impeller 16b, 26b, to alternate between different rotational frequencies. The dishwasher according to the invention has control unit 30, arranged for controlling the rotational frequencies of the motors 16a, 26a of the different washing compartments 10, 20.
According to an embodiment of the invention, the control unit 30 comprises a first sub control unit 31 for controlling the first circulation pump 16, a second sub control unit 32 for controlling the second circulation pump 26. There is also a communication link 33 between the sub control units, for enabling communication between the sub control units 31, 32.
The present invention is based on the insight that the sound level in a multi-compartment dishwasher is particularly crucial since noise generated in the different compartments 10, 20 is added, resulting in a dishwasher that might be conceived as disturbingly noisy.
According to the invention, a multi-compartment dishwasher 1 is provided in which the circulation pump impeller 16b of the first washing compartment 10 is controlled to alternate between a first target rotational frequency f1h and a second target rotational frequency f1l, and the circulation pump impeller 26b of the second washing compartment 20 is controlled to alternate between a first target rotational frequency f2h and a second target rotational frequency f2l.
The first target rotational frequencies f1 h, f2h are higher than the second target rotational frequencies f1l, f2l. In the disclosed embodiment of the invention, the circulation pump impellers 16b, 26b run at their second rotational frequencies f1l, f2l most of the time, and are controlled to switch to their first rotational frequencies f1h, f2h for shorter time periods at specified time intervals, in a pulsed manner. The intervals for which a circulation pump impeller 16b, 26b is controlled to rotate at its first target rotational frequency might e.g. last for 1 second each, whereas the intervals for which the circulation pump impeller 16b, 26b is controlled to rotate at its second target rotational frequency might last for e.g. 3-4 seconds each.
In order to enable feedback control of the motors 16a, 26a thereby the circulation pump impellers 16b, 26b, the system for controlling the dishwasher according to an embodiment of the invention comprises an arrangement 13, for measuring the actual rotational frequency f1 of the first motor 16a and the first circulation pump impeller 16b and/or an arrangement 23 for measuring the actual rotational frequency f2 of the second motor 26a and the second circulation pump impeller 26b. These arrangements might be tachometers 13, 23, which generally indicate instantaneous values of rotational frequency in revolutions per minute. When the rotational frequency f1, f2 of a circulation pump impeller16b, 26b or a motor 16a, 26a has been measured, the detected value can be used to know when if it is possible or not to switch the rotational frequency of another circulation pump impeller16b, 26b or a motor 16a, 26a to a higher value than the actual rotational frequency f1, f2 of that circulation pump impeller16b, 26b or a motor 16a, 26a.
A possible scenario: At a certain instant, the first circulation pump impeller 16b is controlled to rotate at its first rotational frequency f1 h, whereas the second circulation pump impeller 26b is controlled to rotate at its second rotational frequency f21. Then the first circulation pump impeller 16b is controlled to switch from its first rotational frequency f1 h to its second rotational frequency f1l. A tachometer 13 measures the actual rotational frequency f1 of the impeller 16b and as long as the detected value f1 is higher than a predetermined threshold value f1, the second circulation pump impeller is controlled to remain at its second rotational frequency f2l. When the tachometer detects a value f1 that is lower than the threshold value ft, the second circulation pump impeller 26b can be controlled to switch to its first rotational frequency f2h.
For changing the rotational frequency of a circulation pump impeller 16b, 26b, some kind of switching means can be used. If a pulse generator, generating square wave pulses is used for controlling the circulation pump impellers 16b, 26b, no separate switching means is needed since all the information about when to switch between the different target frequencies is present in the pulse signals.
In the drawings and specification, there have been disclosed preferred embodiments and examples of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being set forth in the following claims.

Claims

A system for controlling a multi-compartment dishwasher (1), which dishwasher (1) comprises:
a first washing compartment (10), having a first circulation pump (16) for circulating water in the washing compartment (10) during a washing operation;

a second washing compartment (20), having a second circulation pump (26) for circulating water in the washing compartment (20) during a washing operation,

the system comprising:

a control unit (30), operatively associated with the first and second washing compartments (10, 20),

which control unit is arranged to

control the first circulation pump (16) to alternate between a first target rotational frequency (f1h) and a second target rotational frequency (f1l), the first target rotational frequency (f1h) being higher than the second target rotational frequency (f1l), and to

control the second circulation pump (26) to alternate between a first target rotational frequency (f2h) and a second target rotational frequency (f2l), the first target rotational frequency (f2h) being higher than the second target rotational frequency (f2l),

characterized in that the control unit (30) further is arranged for controlling the first and second circulation pumps (16, 26) such that at any given instant, at the most one circulation pump (16, 26) is running at the first target rotational frequency (f1h, f2h).
The system as claimed in claim 1, wherein the control unit (30) comprises a first sub control unit (31) for controlling the first circulation pump (16), a second sub control unit (32) for controlling the second circulation pump (26), and a communication link (33) between the sub control units (31, 32) for enabling communication between the sub control units (31, 32).
The system as claimed in claim 1 or 2, wherein the control unit generates a square wave signal for controlling the circulation pumps (16, 26).
The system as claimed in claim 1 or 2, wherein the system further comprises an arrangement (13, 23) for measuring a rotational frequency (f1, f2) of each circulation pump (16, 26), wherein the control unit (30) is arranged to use the measured frequencies (f1, f2) for controlling the circulation pumps (16, 26).
The system as claimed in claim 4, the system having:
means for switching the rotational frequency of the first circulation pump (16) from the first target rotational frequency (f1 h) to the second target rotational frequency (f1l);

means for comparing a measured frequency (f1) of the first circulation pump (16) with a predetermined threshold value (ft);

means for setting a rotational frequency (f2) of the second circulation pump (26) to the first target rotational frequency (f2h) when the measured rotational frequency (f1) of the first circulation pump (16) is lower than the predetermined threshold value (ft).
The system as claimed in claims 1-3, wherein the control unit (30) is arranged to control a pulse generator (34), which pulse generator is arranged to supply the first circulation pump (16) with a first control signal and to supply the second circulation pump (26) with a second control signal, such that at any given instant, at the most one circulation pump (16, 26) is running at its first target rotational frequency (f1 h, f2h).
A multi-compartment dishwasher comprising a system according to any of claims 1-6.
Method (100) for controlling a multi-compartment dishwasher (1), which dishwasher has
a first washing compartment (10), having a first circulation pump (16) for circulating water in the washing compartment (10) during a washing operation;
a second washing compartment (20), having a second circulation pump (26) for circulating water in the washing compartment (20) during a washing operation,
the method (100) comprising:
controlling (101) the first circulation pump (16) to alternate between a first target rotational frequency (f1h) and a second target rotational frequency (f1l), the first target rotational frequency (f1h) being higher than the second target rotational frequency (f1l);

controlling (102) the second circulation pump (26) to alternate between a first target rotational frequency (f2h) and a second target rotational frequency (f2l), the first target rotational frequency (f2h) being higher than the second target rotational frequency (f2l),

controlling (103) the first and second circulation pumps (16, 26) such that at any given instant, at the most one circulation pump (16, 26) is running at its first target rotational frequency (f1h, f2h).
The method as claimed in claim 8, the method further comprising the steps of:
measuring (104) a rotational frequency (f1, f2) of the circulation pump (16, 26); and

using (105) the measured frequency (f1, f2) for controlling the circulation pumps (16, 26).
The method as claimed in claim 9, the method further comprising the steps of
switching (106) the rotational frequency of the first circulation pump (16) from the first target rotational frequency (f1h) to the second target rotational frequency (f1l);
comparing (107) a measured rotational frequency (f1) of the first circulation pump (16) with a predetermined threshold value (ft);
setting (108) the rotational frequency of the second circulation pump (26) to the first target rotational frequency (f2h) when the measured rotational frequency (f1) of the first circulation pump (16) is lower than the predetermined threshold value (ft).