Method For Detecting A Load-related Change In Thermal Capacity Of A Water-bearing Domestic Appliance

Abstract

A water-bearing appliance, such as a dishwasher, and a method for detecting the load-related change in thermal capacity of the water-bearing domestic appliance, in order to optimize the drying process. In an exemplary embodiment, the method includes detecting a temperature gradient during the cooling of the items to be cleaned.

Description

[0001] The invention relates to a method as claimed in the preamble of claim 1.

[0002] In water-bearing domestic appliances such as dishwashers, the thermal behavior of said appliances varies as a function of the amount and type of wash items, i.e. the items loaded cause a change in thermal capacity, with the result that, for example, the duration of cooling or drying processes is extended or reduced.

[0003] WO 2004/047608 A1 discloses a method for detecting the amount of items in the washing compartment (tub) of a dishwasher, wherein both motor operating data of a circulating pump and the so-called heating gradient in the dishwasher are recorded at least in a pre-wash phase and in a heating phase. The actual values captured are compared with the stored setpoint values and the amount of items in the washing compartment is inferred therefrom. The wash program can then be adapted to suit the amount of items ascertained. This method requires a high degree of open- and closed-loop control complexity, as a large number of curve or measurement data scenarios must be stored in a program control unit and compared with the captured values for the setpoint/actual comparison. In addition, the heating power of a dishwasher depends on the locally available electricity supply voltage, with the result that variations in the locally available supply voltage can falsify the measurement result.

[0004] The object of the invention is therefore to provide an improved method.

[0005] The object of the invention is achieved by a method for detecting the load-related change in thermal capacity of a water-bearing domestic appliance, in particular a dishwasher, to optimize a drying process.

[0006] It is provided according to the invention that a temperature trend during cooling of the wash items is captured. For example, during the main cleaning cycle, the temperature of the cooling wash liquor, which is in temperature equilibrium with the wash items, is measured. Because a large load cools down more slowly than a small one, the captured temperature trend of the wash liquor can be used as a measure for the load. It can be captured in a technically simple manner via a temperature sensor, because the sensor can be incorporated in the circulation path without great technical complexity. Alternatively or in addition, the temperature trend can be captured on a condensation surface, e.g. on the inside of a door or on the outside of a water tank used as a container for temporarily storing water and/or wash liquor. Advantageously, in both variants for determining the temperature trend, pairs of temperature values are captured at two different locations in the appliance. A first value can be determined in an area upstream of the wash items, and a second downstream thereof. A temperature difference e.g. of the wash liquor can therefore be obtained from values before and after contact with the wash items. The change in thermal capacity due to the wash items can be determined from the change in the difference. Similarly, the correlation between temperature trend and thermal capacity also applies to measuring a temperature on the condensation surface.

[0007] In another embodiment of the invention it is provided that the temperature trend is captured after mixing of wash liquor with fresh water, i.e. the change in thermal capacity due to the load is determined calorimetrically by measuring a mixing temperature from one of the two temperature values in the event of a change or at least partial change in the wash liquor. This can take place, for example, during the cleaning cycle or an intermediate wash cycle. On completion of a first cleaning cycle with warm water, it can be wholly or partially pumped off and cold fresh water supplied to the wash tub. The fresh water is heated by contact with the warm wash items and possibly by mixing with warm water remaining from the cleaning cycle. Disregarding the temperature of the wash items prior to the supply of fresh water, the thermal capacity can be derived by means of a calorimetric calculation from the temperature and amount of fresh water supplied, possibly the quantity and temperature of the fresh water remaining from the cleaning cycle, and the mixing temperature. This data can also be obtained in a technically simple manner--in some cases using means already present, i.e. with a low degree of technical complexity.

[0008] Such a procedure would not be convenient. In an advantageous embodiment of the invention, a time dependence of a temperature indicative of the temperature of the wash items themselves and/or the time dependence of a temperature indicative of the temperature of a condensation surface are captured. The time dependence of the temperature of the wash items or condensation surface is to be understood as meaning the temperature trend. The humidity in the wash tub during cooling as part of a drying process is formed on the condensation surface. In particular, determining the temperature on the condensation surface provides a capturing possibility that is both simple and independent of the wash liquor and circulating pump or rather its performance data. The invention therefore makes use of the recognition that the trend of the wash item temperature, i.e. its change over a particular time period, is directly correlated to the thermal capacity and temperature of the wash items. This provides a technically simple calculation method for indirectly determining, or rather estimating within tight limits, the per se difficult to detect size of the thermal capacity.

[0009] In the above mentioned embodiments, a fit function describing the time dependence of the temperature during cooling or mixing can be matched to the time dependence during cooling or mixing, said fit function having the thermal capacity of the wash items as a fit parameter. The thermal capacity of the wash items can also be determined in a simple manner as a measure for the load in this way.

[0010] In addition to measuring the temperature trend during a cool-down phase and/or of a mixing temperature, it can preferably also be provided to capture the temperature trend during a wash liquor heat-up phase, particularly of re-circulated wash liquor, in order thus to increase the accuracy by combining these measurements.

[0011] The invention also relates to a water-bearing domestic appliance, in particular a dishwasher, at least having means for detecting the load-related ability to store thermal energy. According to the invention, the water-bearing domestic appliance has means for measuring a temperature trend during cooling of the wash items. The current load is determined automatically, i.e. without operator input, thereby considerably simplifying the operation of the dishwasher.

[0012] According to the invention, the load can be detected indirectly by determining the thermal capacity of the wash items. To determine the thermal capacity, the dishwasher can incorporate a temperature sensor for capturing a temperature indicative of the wash items, and means for evaluating the captured temperature and/or its time dependence. The temperature sensor can be disposed in the washing compartment or in the circulation path and comes into contact with water circulated during a cleaning cycle, said water in turn being in heat-exchanging contact with the wash items. It must therefore be disposed such that it can at least indirectly capture the temperature of the wash items. A second temperature sensor with associated evaluation means for measuring the temperature of freshly supplied, not yet heated fresh water can also be provided. In the case of dishwashers of the type incorporating a heat store, the second temperature sensor can be in heat-exchanging contact with the heat store. The second temperature sensor and the evaluation means enable the thermal capacity of the load to be determined according the method last described above.

[0013] The dishwasher can incorporate a control unit which is designed to process the data of the temperature sensor(s), i.e. carry out the above described method or sections thereof and their variants.

[0014] The principle of the invention will now be explained in greater detail using examples and with reference to the accompanying drawings in which:

[0015] FIG. 1: shows a temperature trend in the tub of a dishwasher,

[0016] FIG. 2: shows a segment of such a temperature trend for different loads,

[0017] FIG. 3: shows a schematic sectional view of a first dishwasher, and

[0018] FIG. 4: shows a schematic sectional view of another dishwasher.

[0019] FIG. 1 shows the known cycles in a dishwasher with residual heat drying. These comprise a pre-wash 2, a heat-up phase 4, a cleaning cycle 6, an intermediate wash cycle 8, a rinse 10, and a drying cycle 12 completing this sequence of operations. In the pre-wash 2, cold fresh water (approx. 3.4-3.9 l) is supplied and circulated through the wash tub 14 (see FIGS. 3 and 4) for a predetermined time of approx. 15 min by a circulating pump 20. A heater 56 (see FIGS. 3 and 4) in the hydraulic circuit heats up the fresh water of the pre-wash 2 in approx. 13 to 14 min to an initial cleaning temperature of approx. 51.degree. C. This also heats up the wash items 28 in the tub 14. In the subsequent cleaning cycle 6, the heated wash liquor provided with detergent is circulated, thereby essentially cleaning the wash items 28.

[0020] Between the cleaning cycle 6 and the intermediate wash cycle 8, the wash liquor is pumped out of the tub 14 and clean, cold fresh water is supplied. During the intermediate wash cycle 8, the fresh water is circulated for a period of approx. 5 min, heating up as it does so primarily due to contact with or rather heat transfer from the wash items 28 still warm from the cleaning cycle 6 and possibly a heat exchanger 38 (FIG. 4). For the change from the intermediate wash cycle 8 to the subsequent rinse 10, the intermediate wash water is pumped out of the tub 14 and cold fresh water is re-supplied.

[0021] In conventional dishwashers with residual heat drying, the cold fresh water supplied is circulated in the rinse cycle 10 for a predetermined, fixed time of e.g. approximately 15 min during which it is heated to the initial temperature T.sub.o for the final drying cycle 12, e.g. to approx. 65.degree. C., using a predetermined, fixed heating power.

[0022] FIG. 2 illustrates the trend over time of the characteristic temperature, i.e. the time dependence of the temperature in the tub for different loads during the rinse 10 and drying cycle 12. The middle curve in FIG. 2 shows the temperature trend in the tub for a defined standard load B.sub.standard. The upper and lower curves in FIG. 2 represent the temperature trend in the tub for a (compared to the standard load B.sub.standard) higher load B+:=B.sub.standard+AB and lower load B-:=B.sub.standard-.DELTA.B respectively. Due to the supply of heat energy, the temperature in the tub 14, and therefore also the temperature of the wash items 28, increases essentially proportionally to the time t during the rinse 10. The less than proportional temperature rise shown in FIG. 2 is the result of heat transfer losses through the walls of the tub 14 and the loading door 16, among other things.

[0023] For the standard load B.sub.standard, the temperature during the heat-up phase in the rinse 10 is adjusted to an initial temperature T.sub.0,standard according to the middle curve in FIG. 2. Immediately thereafter there commences the residual heat drying cycle 12, i.e. the complete evaporation of the water film on the wash items. If a higher or lower load was detected, a correspondingly larger or smaller heat energy input is required for residual heat drying. Accordingly, the temperature during the heat-up phase is set to a higher or lower initial temperature T.sub.o-FAT or T.sub.o-AT for the residual heat drying cycle 12.

[0024] With the removal of the heating power supplied to the circulated wash liquor during the rinse 10, the drying cycle 12 begins. The temperature in the tub essentially follows a falling exponential function during which a film of moisture present on the wash items 28 evaporates and condenses on a condensation surface. At a time t.sub.12, as a characteristic feature, a temperature T.sub.12 is reached which then changes only insignificantly and marks the attainment of an essentially asymptotic state. The film of moisture on the wash items 28 is then completely evaporated and the drying process 12 can be terminated. As the reaching of time t.sub.12 is dependent on the load, its detection is critically important for controlling the drying process in respect of energy input and time trend.

[0025] According to the invention, the time dependence T1(t) of an actual temperature T1 in the tub during the cool-down phase of the cleaning cycle 6, i.e. the temperature trend over time t, is captured. From this is obtained the thermal capacity of the load as a measure for the actual load B.sub.act. The time dependence T1(t) of the temperature during the cool-down phase essentially follows an exponential function in time t

T1(t).apprxeq.e.sup.-c.sup.tot.sup.(t-t.sup.0.sup.) (1)

where C.sub.tot=C(B.sub.act)+C(water) is the total thermal capacity which is understood as being the sum of the thermal capacity C(B.sub.act) of the current load B.sub.act and the thermal capacity C(water) of the circulated water. t.sub.0 is the time at which the cool-down phase begins. The thermal capacity C(water) of the circulated wash liquor depends on the admitted amount of water which is measured when the tub is filled with fresh water. The total thermal capacity C.sub.tot is determined by matching a fit function to the cool-down curve T1(t) with C.sub.tot as the fit parameter. Finally, the change in thermal capacity C(B.sub.act) due to the current load B.sub.act is calculated by subtracting the measured thermal capacity C(water) from the thermal capacity C.sub.tot derived from the cool-down curve T1(t).

[0026] According to an alternative embodiment of the invention for determining the change in thermal capacity due to the load, the mixing temperature obtaining in the intermediate wash cycle 8 is measured. For this purpose, a function is matched by fitting to the time dependence of the temperature measured in the intermediate wash cycle 8, and the mixing temperature obtaining after the supply of the cold fresh water at the start of the intermediate wash cycle 8 due to temperature equalization with the wash items 28 still warm from the cleaning cycle 6 is determined as an asymptotic approximation to the temperature-time dependence in the intermediate wash cycle 8 using known mathematic equations or models for calorimetric temperature mixing.

[0027] The dishwasher shown in FIG. 3 comprises a tub 14 in which the wash items 28 are placed in a dish rack 30, a loading door 16 attached to the tub 14, a rotary water spray arm 24 pivotally disposed in the tub 14, a circulating pump 20 disposed below a base wall 19 of the tub 14 for circulating the wash liquor, a feed 22a connecting the circulating pump 20 to the spray arm 24, a drain 22b in the base wall 19 of the tub 14 which is connected to the suction side of the circulating pump 20, a heater 56 on the feed 22a for heating up the circulated water, a first temperature sensor 32 and a second temperature sensor 34, a control unit 58 for controlling the cycles and devices of the dishwasher and for reading and evaluating the measurement signals of the temperature sensors 32, 34, a supply pipe 48 for supplying fresh water, a drain pipe 52 for removing used wash liquor, and a heating device 56 on the feed 22a with a control line 56s to the control unit 58.

[0028] The first temperature sensor 32 is disposed in the circulating pump 20 and is used to capture the temperature T1 of the water or rather wash liquor in the circulation path. However, it can also be disposed in other positions in the circulation path, such as in the feed 22a, in the drain 22b or in a recess in the base wall of the tub 14 near the opening of the drain 22b. The second temperature sensor 34 is disposed in contact with the inside wall, i.e. the wall of the loading door 16 facing the tub 14, and is used for measuring a reference temperature T2 indicative of the temperature of a cold surface in the tub 14. It can also be disposed, for example, in a control panel 18 in the loading temperature 16 (sic).

[0029] The temperature sensor 32 in the circulating pump 20 captures a temperature trend of the wash liquor over time and forwards the data to the control device 58. The temperature of the wash liquor is determined, on the one hand, by the output temperature of the fresh water from the domestic supply pipe. As the fresh water first passes into the circulating pump 20 before it is pumped further, the sensor 32 is able to capture its temperature. The heating power subsequently supplied to the fresh water is likewise known. Largely constant or of at least only relatively slight effect are the energy losses via the line 22a and the walls of the tub 14. The control device 58 can therefore determine the temperature of the wash liquor when it enters the tub 14 before it comes into contact with the wash items 28.

[0030] Also affecting the temperature of the wash liquor is the temperature of the wash items 28 on which the wash liquor can be heated or cooled. When the wash liquor is repeatedly circulated e.g. during the heat-up phase 4 (cf. FIG. 1), after each discharge from the tub 14 the liquor acquires a lower temperature than it had in the feed pipe 22a because it is cooled on the wash items 28. The control device 58 can infer the degree of loading of the tub 14 both from the captured temperature difference between the wash liquor flowing into and out of the tub 14 and from the change in said temperature difference over time. For a smaller amount of wash items 28, a lower thermal capacity is present in the tub 14, which means that the wash liquor is cooled less. The wash items 28 therefore heat up more quickly, thereby enabling the heat-up phase 4 to be shortened or the power of the heater 56 to be reduced. Conversely, for a larger load it is necessary to extend the heat-up phase 4 or increase the heating power.

[0031] Alternatively or additionally, namely to improve the data set of the control unit 58 for determining the load, a second temperature sensor 34 can be mounted in or on the loading door 16. The loading door 16 constitutes a relatively cool condensation surface in the residual heat drying cycle 12. The wash items 28 heated up in the preceding rinse 10 evaporate the moisture adhering thereto which forms on the loading door 16 as a cool condensation surface. The trend of the temperature of the condensation surface is also an indication of the degree of loading of the tub 14, as a larger amount of wash items 28 can bind a correspondingly larger amount of moisture on their surface. The subsequent condensation delivers more heat to the condensation surface of the loading door 16 than a smaller load can.

[0032] The second embodiment of the dishwasher shown in FIG. 4 differs from the first embodiment shown in FIG. 3 in that it has a water reservoir 38 used as a heat store. Identical elements of the first and second embodiment are denoted by the same reference characters.

[0033] The dishwasher shown in FIG. 4 comprises the supply pipe 48 provided with the controllable valve 50 for filling the heat exchanger 38 with fresh water and a connecting pipe 40 between the heat exchanger 38 and the circulating pump 20, and also a third temperature sensor 36 disposed in the reservoir 38 for recording the temperature T3 of the water in the reservoir 38. The connecting pipe 40 is opened and closed by the controllable connecting valve 42. The valve 42 can be controlled via a line 42s to the control unit 58. If the valve 42 is closed and the valve 50 is open, the reservoir 38 is filled with cold fresh water. If the valve settings are reversed, it is filled with water from the circulation path which can be heated if necessary.

[0034] The reservoir 38 is implemented in the form of a container disposed parallel to the sidewall of the tub 14 and abutting said sidewall. The third temperature sensor 36 is disposed in contact with the wall of the reservoir 38 facing the tub 14. To improve the heat drying efficiency, the reservoir 38 is filled with cold fresh water during the drying cycle 12, which means that the sidewall of the tub 14 facing the reservoir 38 becomes a cooled condensation surface. On the one hand, therefore, the temperature sensor 36 fulfills the same purpose as the sensor 34 in the last described example. However, as it is only in the fresh water flow of the circulating pump 20, it can capture the output temperature of the fresh water more precisely than the temperature sensor 32. Consequently, it provides a better data set for load determination by the control unit 58.

LIST OF REFERENCE CHARACTERS

[0035] 2 pre-wash [0036] 4 heat-up phase/heat up [0037] 6 cleaning cycle/clean [0038] 8 intermediate wash cycle/intermediate wash [0039] 10 rinse [0040] 12 drying cycle/drying [0041] 14 tub [0042] 16 loading door [0043] 18 control panel [0044] 19 base plate [0045] 20 circulating pump [0046] 20s control line for circulating pump [0047] 22a feed [0048] 22b drain [0049] 24 rotary spray arm [0050] 28 wash items [0051] 30 dish rack [0052] 32 first temperature sensor (circulation path) [0053] 34 second temperature sensor condensation surface (e.g. loading door) [0054] 36 third temperature sensor (heat exchanger) [0055] 38 heat exchanger [0056] 40 connecting pipe [0057] 42 connecting valve [0058] 42s control line for connecting valve [0059] 44 supply [0060] 48 supply pipe [0061] 52 drain pipe [0062] 56 heater [0063] 56s control line for heater [0064] 58 control unit

Claims

1-11. (canceled)

12. A method for detecting a load-related change in thermal capacity of a water-bearing domestic appliance for optimizing a drying process, comprising: measuring a temperature trend during cooling of wash items in the appliance.

13. The method as claimed in claim 12, wherein the temperature trend is a temperature trend of wash liquor in a circulation path of the appliance.

14. The method as claimed in claim 12, wherein the temperature trend is a temperature trend of a condensation surface of the appliance.

15. The method as claimed in claim 12, wherein the temperature trend is a temperature trend of a water reservoir of the appliance.

16. The method as claimed in claim 15, wherein the temperature trend is a temperature trend of wash liquor mixed with fresh water measured in at least one of the circulation path and the condensation surface.

17. The method as claimed in claim 12, wherein the temperature trend is measured over a predefined period of time.

18. The method as claimed in claim 12, wherein the temperature trend is measured within a predefined time interval.

19. The method as claimed in claim 12, wherein the temperature trend is measured at least one of continuously and at predefined intervals.

20. The method as claimed in claim 12, wherein the temperature trend is a temperature trend of wash liquor measured during a wash liquor heat-up phase.

21. A water-bearing domestic appliance, comprising: a sensor structured to detect a load-related capacity for storing thermal energy, and to measure a temperature trend during cooling of wash items disposed in the appliance.