FIELD OF INVENTION The present invention relates to a method for estimating, computing and displaying the remaining program duration in a dishwasher.

BACKGROUND OF THE INVENTION For operating a dishwasher, one sets a washing program for the objects to be washed.

The washing program is chosen according to the condition of the items to be washed.

For informative purposes, the duration of a washing program and the remaining program duration is displayed and continuously modified on the control panel of the dishwasher. But the duration of a washing program is not known a priori. Each washing program may comprise the phases of pre-wash, main-wash, intermediate rinsing, final rinsing and drying. The duration of some of the phases cannot be determined in advance. The duration of heating the washing liquid depends on the temperature of the incoming water, amount and type of items to be washed.

Therefore, while displaying the program duration and remaining program duration, an estimate of the actual program time is displayed. For computing this estimate there are various methods in prior art.

One such method is known from European Patent Application EP 235668. In this application, the temperature of the washing water is measured. After heating the washing water up to a certain temperature, the rate of temperature increase is used for updating the displayed program time.

Another method is described in German Patent Application DE 3715956. In this application, at the beginning of the program an estimate of the program duration is displayed which is a result of the experimental studies and at the end of each heating cycle a correction of the remaining time is achieved. In this method, the initial estimate depends on the experimental values, since the experimental values are obtained in laboratory environment, the differences between the actual and the laboratory conditions can cause major differences between the actual washing time and the estimate.

SUMMARY OF INVENTION The object of this invention is to provide a method for estimating, computing and displaying the remaining program duration in a dishwasher.

DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the dishwasher utilising the method for estimating, computing and displaying the remaining program duration, which is realised in order to attain the said object of the invention is illustrated in the attached drawings, wherein; Figure 1: Schematic view of a dishwasher, Figure 2: A chart showing a program flow.

The components shown in the drawings have been enumerated individually, as follows; 1. Washing tank 2. Sump 3. Spray arm 4. Display means 5. Circulation pump 6. Drain pump 7. Heater 8. Drain pipe 9. Water supply circuit 10. Water inlet valve 11. Door sensor 12. Control unit 13. Memory unit 14. Temperature sensor The dishwasher in which the method is used mainly comprises a washing tank (1) provided on the bottom with a sump (2) for collecting the water. Said washing tank (1) houses one or more rotating spray arms (3) connected to a circulation pump (5) which is adapted to supply water to said rotating spray arms (3) so as to enable them to spray onto the wash load items, the water that then falls by gravity back onto the bottom of the washing tank (1), where it collects in the sump (2).

A heater (7) is housed inside the washing tank (1), below the lower rotating spray arm (3). The heater (7) is used for heating the water and the wash load items.

A drain pump (6) connects the bottom of the sump (2), to a drain pipe (8).

The dishwasher further comprises a water supply circuit (9) adapted to let water from the mains into the washing tank (1) through a water inlet valve (10) controlled by a control unit (12) which includes a memory unit (13) for storing the related data. The control unit (12) is adapted to control the operation of all of the main functional members, such as pumps, motors, heaters etc. of the apparatus. There is further a display means (4) for displaying the related information and a temperature sensor (14) which is integrated within the water inlet valve (10) for measuring the inlet water temperature.

In a known manner, the dishwasher is adapted to carry out certain washing programs.

Each washing program constitutes an operating cycle of the dishwashing machine. An

operating cycle comprises in a sequence, a pre-wash phase (with either cold or hot water mixed with detergent, said phase being anyway excludable from the cycle), a main wash phase with hot water mixed with detergent, at least an intermediate rinse phase with cold water, and a final rinse phase with hot water mixed with some rinse aid or similar product, followed by a wash load drying phase. At the end of each phase of the operating cycle of the machine, the water contained in the sump (2) is sent to the drain pipe (8) by the drain pump (6). The operating cycles are designed by the producer according to the needs of the users and may differ in number of phases included.

For informative purposes, the remaining duration of an operating cycle is displayed by the control unit (12) at the display means (4). Each washing program has different duration. When the user selects a washing program, a total duration (ttot) of the operating cycle is displayed and the total duration (ttot) is decreased by the control unit (12) as time progresses. The total duration (ttot) of an operating cycle can be computed by adding the individual duration of the pre-wash (tpw), the main-wash (tmw), the intermediate rinse (tir), the final rinse (tfr) and the drying (td) phases. For each washing program the duration of the pre-wash (tpw) and the intermediate rinse (tir) phases are determined by the producer and these values are constant and are kept in the memory unit (13) of the control unit (12). Whereas the duration of the main-wash (tmw), the final rinse (tfr) and the drying (td) phases differ from an operating cycle to another. Duration of the main wash (tow), and final rinse (tfr) phases depends on how fast the water is heated, whereas the duration of the drying phase (td) depends on how fast the wash load items cool down. Heating rate of water and cooling rate of wash load items are related to the inlet water temperature, amount and type of items loaded, user preferences and environmental conditions, i. e. temperature and humidity of the kitchen. Therefore, in order to estimate the total duration (ttot) of an operating cycle, estimates for heating up duration in the main-wash phase (tmw-h), heating up duration in the final rinse phase (tfr h) and the drying duration (td) have to be computed.

The method of current invention initially computes the estimates of heating up duration in the main-wash phase (tmw-h), heating up duration in the final rinse phase (tfr-h) and the drying duration (td) using the experimentally determined values by the producer. These values are kept in the memory unit (13). Then, during each operation cycle, values of water inlet temperature (Ti), selected washing program, actual values of the heating up duration in the main-wash phase (tmw-h), the heating up duration in the final rinse phase (tfr h) and the drying duration (td) are kept in the memory unit (13). After a certain number of washing, averages of actual values of heating up duration in the main-wash phase (tmw-h), heating up duration in the final rinse phase (tfr h) and the drying duration (td) replace the experimentally determined values by the producer and used for estimating the total operation cycle duration (ttot).

Details of the method of current invention are described in the following paragraphs: When a washing program is selected by the user, a temperature for the main wash (Tmw set) and a temperature for the final rinse phase (Tfr-set) are set and this information is combined with the inlet water temperature (Twi) that is measured by the temperature sensor (14). For the washing program and the inlet water temperature (Twi) pair, the corresponding values in the memory unit (13) are taken and used as initial estimates of heating up duration in the main-wash phase (tm, _h), heating up

duration in the final rinse phase (tfr h) and the drying duration (td). Then estimates of the main-wash duration (tmw) and the final rinse duration (tfr) are computed using the values for heating up duration in the main-wash phase (tmw-h) and heating up duration in the final rinse phase (tfr-h). Adding the predetermined duration ofpre-wash (tpw) and intermediate rinse (tir) phases that are kept in the memory unit (13) with the estimates of the main-wash duration (tmw), the final rinse duration (tfr) and the drying duration (td) results in a first estimate of the total operation cycle duration f est (ttot). This estimate is displayed at the display means (4). After the completion of the pre-wash phase, at the main-wash phase the heater (7) is turned on and the water is heated up for a constant duration (tcheck). At the end of this duration (teheck) ? water reaches a final temperature (Twf). Then the rate of change of temperature (AT= Tf-Twi/teheck) is computed. Then using the values of the set temperature for the main wash (T, ? the set temperature for the final rinse phase (Tfrset) and the rate of change of temperature (AT), predetermined estimates for heating up duration in the main-wash phase (tmw-h), heating up duration in the final rinse phase (tfr h) and the drying duration (td) that are kept in the memory unit (13) are used. The estimate of the drying duration (td) depends on the set temperature for the final rinse phase (Tfr-set) the rate of change of temperature (AT) and predetermined drying stoppage temperature (Td). Estimates of the main-wash duration (tmW) and the final rinse duration (tfr) are computed using the values for heating up duration in the main-wash phase (tmw-h) and heating up duration in the final rinse phase (tfr-h). Then a second estimate of the total operation cycle duration sest (ttot) is computed by adding the predetermined duration of intermediate rinse (tir) that is kept in the memory unit (13) with the estimates of the main-wash duration (tmw), the final rinse duration (tfr) and the drying duration (td) and displayed by the control unit (12). Then the displayed duration is modified by the control unit (12) as time progresses.

During each operation cycle, values of water inlet temperature (TWi) selected washing program, actual values of the heating up duration in the main-wash phase (tmw-h), the heating up duration in the final rinse phase (tfrh), the rate of change of temperature (AT) and the drying duration (td) are kept in the memory unit (13). Until sufficient data is recorded, experimentally determined values by the producer which are kept in the memory unit (13) are used for computing the first and second estimates of the total operation cycle duration f est (ttot). After a certain number of washing, a moving average of final"n"consecutive values of heating up duration in the main-wash phase (tmw-h), heating up duration in the final rinse phase (tfr h) and the drying duration (td) replace the experimentally determined values which are kept in the memory unit (13) and are used for computing the first and second estimates of the total operation cycle duration f est (ttot). When a washing program is selected by the user, a temperature for the main wash (Tmw set) and a temperature for the final rinse phase (Tfr. set) are set for the dishwasher, this information is combined with the inlet water temperature (Twi) measured by the temperature sensor (14). For the washing program and the inlet water temperature (Twi) pair, the corresponding values in the memory unit (13), i. e. moving averages of final"n"consecutive values, are taken and used as initial estimates of heating up duration in the main-wash phase (tmw-h) : heating up duration in the final rinse phase (tfrh) and the drying duration (td). Then. estimates of the main-wash duration (tmW) and the final rinse duration (tfr) are computed using the values for heating up duration in the main-wash phase (tmw-h) and heating up duration in the final rinse phase (tfr-h). Adding the predetermined duration of pre-wash (tpw) and intermediate rinse (tir) phases that are kept in the memory unit-(13) with the estimates

of the main-wash duration (tmW) the final rinse duration (tfr) and the drying duration (td) results in a first estimate of the total operation cycle duration f est (ttot). This estimate is displayed at the display means (4). After the completion of the pre-wash phase, at the main-wash phase the heater (7) is turned on and the water is heated up for a constant duration (tcheck) At the end of this duration (tchck), water reaches a final temperature (Twf). Then the rate of change of temperature (AT= Twf-TWi/tcheck) is computed. Then, according to the set temperature for the main wash (Tmw set)) the set temperature for the final rinse phase (Tfr-set) and the rate of change of temperature (AT), corresponding values, i. e. moving averages of final"n"consecutive values for heating up duration in the main-wash phase (tmw-h), heating up duration in the final rinse phase (tfr h) and the drying duration (td) that are kept in the memory unit (13) are obtained and used as estimates. Estimates of the main-wash duration (tmW) and the final rinse duration (tfr) are computed using the values for heating up duration in the main-wash phase (tmw-h) and heating up duration in the final rinse phase (tfr-h). Then a second estimate of the total operation cycle duration sest (ttot) is computed by adding the predetermined duration of intermediate rinse (tir) that is kept in the memory unit (13) with the estimates of the main-wash duration (tmW) the final rinse duration (tfr) and the drying duration (td) and displayed by the control unit (12). Then the displayed duration is modified by the control unit (12) as time progresses.

During an operating cycle unexpected interruptions, i. e. the electricity cut off, opening of the door etc., of the washing program may occur. These interruptions, may cause the total program duration ttot to change. If such an interruption occurs, the value of the corresponding total program duration ttot is ignored and is not kept in the memory unit (13). The electricity cut off is realised by the control unit (12). Whereas for realising the opening of the door the dishwasher further comprises a door sensor (11).

When the door of the dishwasher is opened by the user during the washing program, the door sensor (11) sends the door open signal to the control unit (12).

If the dishwasher further comprises a means for detecting the turbidity level of the washing liquid, the control unit (12) may skip or add one or more water intake steps in the main-wash according to the level of turbidity of the washing liquid. In this case, since the duration of the water intake step is known, the total program duration (ttot) is displayed accordingly.

The method of the current invention, by using the first and the second estimates of the total operation cycle duration, minimises the discrepancy that may occur between the displayed and actual program duration at the end of the operation cycle. Also the method of the current invention, with the use of actual values of the heating up duration in the main-wash phase (tmw-h) and the heating up duration in the final rinse phase (te h), gives a more accurate estimate depending on the environmental conditions.