EP1778068B1

EP1778068B1 - Dishwasher with pulse width modulation control

Info

Publication number: EP1778068B1
Application number: EP05805021A
Authority: EP
Inventors: Orhan Arcelik Anonim Sirketi DIRIL; Kerem Arcelik Anonim Sirketi ERENAY; Alper Arcelik Anonim Sirketi BAYKUT
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2004-07-21
Filing date: 2005-07-11
Publication date: 2009-08-19
Anticipated expiration: 2025-07-11
Also published as: EP1778068A1; WO2006033027A1; ES2330029T3; TR200700213T1; ATE439795T1; DE602005016124D1

Abstract

This invention relates to a dishwasher (1) where the signals generated by the speed controller (7) of the variable speed motor (5) that drives the circulation pump (4) are observed by the control card (8) and the motor (5) input voltage is adjusted and where elements that adversely affect washing performance such as filter clogging, foaming, increase in viscocity or inappropriate amount of water in washing chamber (3) are detected. Pulse width modulation signals (PWM" constitute the output signals of the speed controller (7).

Description

This invention relates to a dishwasher wherein the washing performance is improved.
The washing performance of dishwashers can be adversely affected according to conditions of use like the amount of water taken into the washing chamber, the amount of load, soil level of load and viscosity change of water in relation to the kind of soil, clogging of filters by the high density of soil, increase of foaming or misuse. It is attempted to improve the washing performance by the use of optimum amounts of water and electrical energy through appropriate washing algorithms obtained by data compiled by detecting the afore mentioned adverse conditions. Basically, the washing operation in a dishwasher is determined by the way the circulation pump operates. The washing performance is improved by the circulation pump functioning at variable r.p.m.'s and by the continuity of circulation with relative speeds conforming to conditions. The water circulation and the spraying system in the dishwasher can lead to excess water intake and high speed circulation depending on the amount of load, the distribution of load, the amount of water intake and the rotation speed of pump, thus resulting in high water consumption together with more use of electric energy both for the heating and the circulation of water. In order to provide uninterrupted circulation, the pump needs sufficient amount of water with respect to the speed employed. When uninterrupted circulation is applied with sufficient amount of water, the difference in the input-output pressure of the pump, the power required for constant pump drive, the output power of the motor that drives the pump and the current drawn from the network by the pump motor remains constant. Lack of sufficient amount of water for the continuity of circulation results in a pressure difference between pump input-output thus leading to change in the power that should be drawn from the drive motor. The current drawn from the power supply network by the drive motor demonstrates a likewise change. This operation conditions can be detected by measuring the operation conditions, motor current, number of revolutions or pump pressure, however, the need arises for an additional device, sensor or electronic evaluation equipment for the afore mentioned measurements, thus leading to a rise in the cost of the commodity.
In the European Patent No. EP0118719 , a transducer is described which generates an output signal proportional to the outlet pressure of the circulation pump. When output signal amplitude of the transducer decreases below a preset value, the control unit responsive to variations of said output signals causes the water inlet valve to be closed stopping the water entrance into the dishwashing machine.
In the European Patent application No. EP0326893 , a dishwasher is described
wherein the water inlet valve is controlled with the help of the data obtained from the measurements of the capacitor voltage , rotation speed of the electric motor, pump pressure, flow rate in the spraying system, the noise level and the vibrations of the machine in order to provide a constant measuring value of uniform water levels thereafter water reaches a level above the minimum in the water chamber.
In the German Patent application No. DE 4418721 , in a dishwashing machine wherein the washing water can not maintain a uniform circulation, the revolutions of the pomp motor and the current fluctuations are recorded and the changes in the phase angles of the motor are assessed, thus keeping the pump motor at a preset constant speed.
In the German Patent No. DE2013716 , a description is given wherein a pressure detector placed at the pump outlet detects the clogged filter and when necessary solves the problem with repeated intake and discharge of water.
The German Patent No. DE2646383 describes the case wherein water is taken in up to a maximum level following the pressure measurement by a pressure detector placed at pump outlet and with repeated inlet and discharge of water it is attempted to remove the foam and soil.
In the German Patent No. DE4435096 , the pressure detectors and the fluid consistency measuring devices are used concurrently to observe the condition of the washing water and, parametric washing programs are employed according to the results obtained in the observations. This document forms the basis for the preamble of the independent claim.
In the German Patent No. DE4400877 , the water levels in the washing chamber and in front of the pump suction are compared to observe the clogging condition of the filter.
The aim of the present invention is to realize a dishwasher wherein the washing performance is improved without the need for extra measuring devices or sensors by detecting the adverse elements affecting the washing performance through the observations carried out on the continuous circulation of water.
The dishwasher realized in order to attain above mentioned aim of the present invention is illustrated in the attached figures, where:
Figure 1 -A schematic view of a dishwasher
Figure 2 - A voltage - time graph showing the adjustment of the input voltage to supply the motor in a dishwasher.
Figure 3 to 6 - The PWM - time graphs illustrating the state of the dishwasher when the amount of water in the washing tank increases in consecutive phases.
Figure 7 - The PWM - time graphs illustrating the state of the dishwasher when washing water does not return as the consequence of being held on the load or when the load is increased in a dishwasher.
Figure 8 - The PWM - time graph illustrating the state of the dishwasher when there is foaming of washing water.
Figure 9 - The PWM - time graph illustrating the state when there is clogging of the filter in a dishwaher.
Figure 10- The PWM - time graph illustrating the state when the viscosity of the washing water in a dishwasher increases.
Elements shown in the figures are numbered individually as follows:

1. Dishwasher
2. Washing tank
3. Washing chamber
4. Circulation pump
5. Motor
6. Discharge pump
7. Speed controller
8. Control card

The said dishwasher(1) comprises of a washing tank (2) wherein dishware is placed, a washing chamber (3) positioned below the washing tank (2) to collect water in the washing tank (2) during the washing process, a circulation pump (4) which transfers water in the washing chamber (3) onto the dishware in the washing tank (2) thus attaining circulation, a variable speed DC (direct current) motor (5), preferably brushless, that drives the circulation pump (4), a drain pump (6) that discharges the water collected in the washing tub (3) to the outside of the dishwasher (1) upon completion of the washing process, preferably PI (proportional integral) or PID (proportional integral derivative) type speed controller (7) which maintains the motor speed at a determined speed by comparing the real speed of the motor with a preset reference speed , a control card (8) which observes the modulations of PWM dutycycle rate determined by the PWM (pulse width modulation) drives of the output signals of speed controller (7) in relation to time and a control card (8) that adjusts motor (5) input voltage using standard deviation and mean average information to determine which of the elements is adversely affecting the washing process like water holding of the load, increase in load, clogging of the filter, increase in viscocity, foaming or inappropriate amount of water in the washing chamber (3).
In cases where the circulation pump (4) is confronted with varying loads and the motor (5) that drives the circulation pump (4) is forced to operate in a different speed other than the preset one, the speed controller (7) constantly compares the real speed of the motor (5) with the reference speed and tries to adjust the motor speed to the reference level. In accomplishing this task, the motor (5) chops the input voltage (V_dc), applies V₁ and V₀ voltages in T₁ and T₀ periods relatively, reaching the phase control switch with square waving, wherein the transformed voltage (V_app) reaches the desired value and reaches the motor (5) via the motor (5) phase control switch. While the input voltage (V_dc) is transformed in the speed controller (7) in the above mentioned manner, and the output voltage (V_app) is applied to the motor (5), the output signal of speed controller (7) is generated as PWM (pulse width modulation) control signals. The control card (8) starting out with PWM signals reaches the variation data of T₁/(T₁ +T₀) ratio with respect to time. T₁/(T₁+T₀) ratio is denoted as PWM (pulse width modulation) dutycycle. The PWM dutycycle is perceived as a graphic that changes with time according to the varying power requirement of the motor (5), the PWM dutycycle generates different profiles that express different operating conditions of the motor (5) confronted with various load conditions.
When the input voltage (V_dc) is applied in the dishwasher(1) of the present invention, the rpm of motor (5) can be maintained at a constant speed, wherein the change of PWM dutycycle means a change in the desired power of the motor (5), the voltage applied to the motor (V_app.) changes in direct proportion with PWM dutycycle that increases or decreases according to the required power (V_app. =PWM dutycycle*V _dc). For example, when the input voltage (V_dc) is controlled by a low value PWM dutycycle, the applied voltage (V_app) to the motor (5) is low, whereas if controlled by a high value PWM dutycycle, the applied voltage (V_app) to the motor (5) is high.
Since the voltage applied (V_app) to the motor (5) controlled by PWM dutycycle is in direct proportion with the input current (I) that the motor uses, the PWM dutycycle also increases or decreases in direct proportion to current (I), when an information on current (I) is needed to detect a problem, there is no need to measure the input current. The motor's winding resistance (R) and the induced voltage (E) kept constant, for the applied voltage (V_app) to the motor we can write :
From equation V_app =R*I+E
V_dc *PWM dutycycle = R * I + E where it can be seen that the PWM dutycycle is directly proportional to current (I) .
Furthermore, since rotational moment (M) of the motor shaft and the pressure (P) of the circulation pump (4) are directly proportional to the input current (I), PWM dutycycle is also directly proportional to moment (M) and pressure (P). So with only the measurement of PWM dutycycle, it is possible to gather information on rotational moment (M) and pressure (P) without the need for measurement devices thereof.
Even if the network voltage is above or under normal values, the averages and standard deviations of PWM dutycycle are evaluated in accordance to changing network voltage, consequently nonuniform network voltage is compensated, the elements adversely affecting the washing performance are detected.
At the start, a minimum amount of water is taken into the washing chamber (3) by way of the control card (8) and the PWM dutycycle is being observed, then gradually increasing amounts of water is taken in, and observation of the PWM dutycycle goes on with each amount until reaching the amount (of water) where circulation pump (4) can operate without pumping air. Since there is no need for water intake in excess of the amount needed for satisfactory washing, water consumption is economized.
For example while circulation is conducted with 3 liters of water, the average and standard deviation is low in the PWM dutycycle-time graph, and oscilations with long and uniform intervals are observed. In this case it is inferred that the amount of water intake in the washing chamber (3) is very low and it takes a long time for the water pumped by the circulation pump (4) to return and accumulate in the washing chamber (3) (Figure 3).
When for example 3,7 liters is reached by continuing water intake into the washing chamber (3), both the average and standard deviation increases in the PWM dutycycle-time graph and oscilations are observed with short intervals. In this case, it is inferred that the amount of water intake into the washing chamber (3) is above minimum, nevertheless not enough. (Figure 4)
When for example 3,85 liters is reached by continuing water intake into the washing chamber (3), the average increases and standard deviation decreases in the PWM dutycycle-time graph, and it is inferred that almost the ideal amount of water level has been reached (Figure 5).
When, for example, an amount of 4 liters is reached by continuing water intake into the washing chamber (3), the average comes to normal and standard deviation nears to minimum in the PWM dutycycle-time graph, and it is inferred that the required amount of water level for washing has been reached (Figure 6).
Even if there is enough water at the start, when PWM dutycycle oscilates with non-uniform intervals, and increase in standard deviation and decrease in average is observed, and some of the water pumped by the circulation pump (4) does not return to the washing chamber (3), the control card (8) detects the problem called "inverted bowl" with water collecting in the dishware or load size is increased during the washing process (Figure 7).
When PWM dutycycle is normal in the beginning and then starts to oscilate with an increase in standard deviation and a decrease in average, which after a short while returns to normal upon intake of water to the washing chamber (3) and again starts to oscilate, the control card (8) detects that there is foaming in washing water and circulation pump (4) is pumping water mixed with air (Figure 8). When foaming is detected, the rotation speed of the circulation pump is decreased until standard deviation of PWM dutycycle comes down to a preset level, consequently the circulation pump (4) in the washing chamber (3) stays above suction level, and the circulation pump (4) can make enough water suction thus enabling the continuity of washing.
When PWM dutycycle is normal in the beginning and then starts to oscilate with an increase in standard deviation and a decrease in average, then oscilation ends and standard deviation decreases again and continues with low average, the control card (8) detects that the filter is clogged and will not let water to return to the washing chamber (3) (Figure 9). When clogging of the filter is detected, some water is taken into the dishwasher(1) and the rotation speed of the circulation pump (4) is decreased resuming normal washing process. If no improvement is noticed while observing the changes in PWM dutycycle, then it is decided that filter is not cleaned within normal circulation and the water is drained completely, clean water is taken in, the filter is washed by clean water and the water is discharged.
When PWM dutycycle proceeds normally in the beginning, then starts to oscilate, with increasing standard deviation and average and after a while oscilation ends, standard deviation decreases again, and proceeds with high average, the control card (8) detects that there is viscosity increase of washing water and the circulation pump (4) gradually needs more power to pump the water (Figure 10). For eliminating the problem after detection of viscosity increase in washing water, the circulation pump (4) is operated at a low rotation speed, if no improvement is observed in PWM dutycycle, then it is decided that washing water is not suitable and washing water is drained and clean water is taken in.
In the dishwasher which is the object of the present invention, the average and standard deviations of PWM dutycycle are observed by the control card (8) for detecting and solving problems like the amount of water required for continuity of circulation, correct amount of water intake relative to load, foaming, increase in viscosity, clogging of filter, and due to precise measurements obtained and easy interpretation of observed data, there is no need for extra measurement devices for detecting the input current (I) drawn by the motor (5), the rotation moment (M) executed by the motor shaft and the pressure (P) of the circulation pump (4).

Claims

A dishwasher (1), comprising a washing chamber (3) where water is collected during the washing process, a circulation pump (4) which executes circulation by transferring water onto the dishware in a washing tank (2), a variable speed motor (5) that drives the circulation pump (4), a speed controller (7) that keeps the motor speed at the preset level by comparing the real speed of the motor and a preset reference speed, and characterized by a control card (8) that determines which of elements, such as water holding of load, increase in load, clogging of the filter, increase in viscocity, foaming or inappropriate amount of water in a washing chamber (3), is adversely affecting washing performance by observing pulse width modulation (PWM) dutycycle changes with respect to time, wherein, the PWM dutycycle is perceived as a graphic that changes with time according to the varying power requirement of the motor (5), the PWM dutycycle generating different profiles that express different operating conditions of the motor (5) confronted with various load conditions and using the standard deviation and (mean) average of PWM dutycycle signals that constitute the output signals of the speed controller (7) for detecting and solving problem.
A dishwasher (1) as in Claim 1, characterized by the control card (8) enabling the taking of a minimum amount of water into washing chamber (3) at the start and beginning to observe PWM dutycycle, later enabling the continuation of water intake by incremental amounts and while observing PWM dutycycle for each incremental level until the water amount where the circulation pump (4) will operate without pumping air is reached, wherein the average comes to normal and standard deviation nears to minimum in the PWM dutycycle-time graph, and it is inferred that the required amount of water level for washing has been reached.
A dishwasher (1) as in Claim 1, characterized by the control card (8) detecting that an "inverted bowl" condition with water collecting in the dishware or load size is increased during the washing process, when the PWM dutycycle oscilates with non-uniform intervals and there is an increase in standard deviation and a decrease in mean average in the case of having sufficient water in the washing chamber (3), some of the water pumped by the circulation pump (4) collects in the dishware and does not return to the washing chamber, (3) or the load is increased during washing.
A dishwasher (1) as in Claim 1, characterized by the control card (8) detecting foaming in washing water, when PWM dutycycle is normal at the beginning and then starts to oscilate and repetitive increases in standard deviation and decreases in averages are observed.
A dishwasher (1) as in Claim 1, characterized by the control card (8) detecting that the filter is clogged if PWM dutycycle is observed normal at the beginning and then starts to oscilate with an increase in standard deviation and a decrease in average, then oscilation stops, standard deviation decreases again and continues with low average.
A dishwasher (1) as in Claim 1, characterized by the control card (8) detecting viscosity increase of washing water when PWM dutycycle is observed normal at the beginning and then starts to oscilate with an increase in both standard deviation and average and then oscilation ends, standard deviation decreases again and continues with high average.