EP1332325B1 - Refrigerating device with an automatic defrosting system - Google Patents

Abstract

The invention relates to a refrigerating device comprising a refrigeratory (3) arranged on a refrigerating chamber (2), a first sensor (5) for detecting the temperature of the refrigerating chamber (3), a second sensor (6) for detecting the temperature(Tv) of the refrigerating agent, a third sensor (7) for detecting the external temperature (Te), a heating device (9) for the refrigeratory (3) and a control device (8) for operating the heating device (9) according to the temperatures (Ti, Tv) measured by the first and second sensors (5,6). The control device (8) activates the heating device (9) if the temperature (Tv) measured by the second sensor (5,6) falls below a threshold value (Tlim) which is set according to the temperatures (Ti, Te) measured by the first and third sensors (5, 7).

Description

The present invention relates to a refrigerator according to the preamble of claim 1. Such refrigerators, also referred to as a no-frost refrigeration appliance, are e.g. used as household refrigerators or freezers. The evaporators of such refrigerators are equipped with heaters, which are operated from time to time to heat the evaporator to a temperature above 0 ° C and thus to bring Reif to melt, which is reflected in the course of operation on the evaporator and its Cooling performance impaired.

In order to operate such a refrigeration device economically, a compromise between conflicting requirements must be found. On the one hand, it is favorable for a high cooling capacity of the evaporator when there is as little frost on it as possible, on the other hand, considerable energy is needed for the defrost cycle to heat the evaporator above the freezing point, defrost the frost and then the evaporator back to his Cool operating temperature. In addition, during defrosting, the evaporator can not cool.

It is difficult to directly measure the thickness of a frost layer on an evaporator to use as a criterion for the need for defrosting, and has not yet found any practical application. Therefore, in most practical applications, the operating time of the refrigerator is measured to control the automatic defrost, and a defrost is initiated when a predetermined period of time has elapsed. A purely on the operating time oriented control can of course not take into account different conditions of use of a refrigerator. Thus, the amount of rime that accumulates in a given time in a household refrigerator, can vary greatly, depending on how often and how long the door of the refrigerator is opened and how high the moisture content of the case entering the refrigerator outside air. It has therefore been proposed in US-A-4,251,988 an adaptive method for defrost control, in which a control of the duration of a defrost back to the amount of frost or layer thickness, which must have been present at the beginning of the defrost on the evaporator, and the shortened the time between two defrosts, if this amount has been greater than a limit, and the extends the period if this amount has been less than a limit, so as to achieve that the defrost always takes place at a predetermined layer thickness. The disadvantage of such control is that it necessarily lags behind long-term changes in the operating conditions of a refrigeration appliance. Thus, for example, gets in the summer, at relatively high outdoor temperatures and when in an apartment in which such a refrigerator is placed, generally not heated, with each opening a relatively large amount of moisture in the device. The known automatic adaptive defrosting system thus adjusts itself over time to relatively short time intervals between two defrosting operations. When the apartments are heated again in the winter and the ambient temperature of such a refrigeration appliance is typically lower and the humidity lower, the humidity input is also lower and the automatic transmission gradually proceeds to longer time intervals between two defrosting operations. In the transitional periods, however, optimal control is not given.

From US 6,032,471 a method for defrosting the evaporator of a refrigeration device is known, in which the defrosting operation starts due to the measured temperature of the evaporator. For the defrosting a heater of the refrigerator is turned on. Depending on the measured during the defrosting temperatures inside and outside of the refrigerator, and the number of openings of the door of the refrigerator, a fan of the refrigerator is additionally turned on.

For larger refrigeration systems, a temperature-dependent automatic defrost control is also used. So it is e.g. It is known to measure the evaporation temperature and the air temperature at the evaporator inlet or outlet of an air-flowed evaporator and to initiate a defrosting process whenever the difference between these two temperatures exceeds an initial value measured immediately after a defrosting operation by a predetermined percentage.

While this technique avoids mismatching in the case when the amount of moisture introduced into the refrigerator over time changes, it has the disadvantage that it is unable to accommodate a change in the ambient temperature and hence the cooling demand. If the temperature rises in the environment of a controlled in this way refrigerator, so does the heat input in the refrigerator and thus increases the difference between the evaporation temperature and air temperature. In In such a case, the automatic triggers a defrost before it is actually necessary. When the ambient temperature drops, the defrosting process is delayed beyond the economically reasonable extent.

A similar problem arises with a change in the controller position. If this is set to a lower target temperature in the refrigerator of the refrigerator, this also leads to an increase in the temperature difference, with the result that a defrosting and thus a warming of the refrigerator is just brought about when the user actually wanted to achieve a stronger cooling.

Object of the present invention is to provide a refrigeration device with defrosting automatic, which maintains a favorable time interval of defrosting even with changes in the outside temperature or set by a user target temperature of the refrigerator.

This object is achieved in a refrigeration device having the features of claim 1.

The control circuit can be implemented in a simple manner with a memory which receives values of the limit value for different pairs of outdoor and cold room temperature. In order to be able to keep the size of this memory small and still achieve a sensitive control of the defrosting time, the control circuit may further comprise an interpolation unit for calculating the threshold for pairs of temperatures measured by the first and third sensor based on the values recorded in the memory.

The limits are preferably selected for all pairs of outdoor and refrigerator temperature, that they correspond to a predetermined frost layer thickness on the evaporator. These values can be measured, for example, on a prototype of the refrigeration appliance under standardized conditions of use, and the limit values thus obtained are stored in the control devices of the refrigeration appliances supplied by the manufacturer.

It is also conceivable to design the control device in such a way that it is able to change these limit values.

Preferably, the controller is capable of measuring the time required by the heater to defrost the evaporator, and thus inferring the amount of frost or film thickness actually present on the evaporator. When the time required for defrost differs from a set value corresponding to the optimum amount of frost, the control means changes the threshold values of the second sensor so that the time required for the downtime converges to the set value. That is, if the defrost lasts too long, the limit of the temperature difference is lowered, if it does not last long enough, it will be increased.

Preferably, such an adjustment of the limits is selectively made only at those limits associated with pairs of outdoor and cold room temperatures only a small distance from the outdoor temperature cold room temperature pair at which the defrost time measurement was taken. As a result of this selective readjustment, a refrigerator according to the invention acquires a set of limit values of the second temperature sensor in the course of its operation which is adapted in an absolutely flexible manner to the specific operating conditions of the refrigeration appliance.

• Fig. 1 eine stark schematisierte Darstellung eines erfindungsgemäßen Kältegeräts; und
• Fig. 2 ein Flußdiagramm eines von der Steuereinrichtung des Kältegeräts ausgeführten Steuerverfahrens.

Further features and advantages of the invention will become apparent from the following description of an embodiment with reference to the accompanying figures. Show it:

• Fig. 1 is a highly schematic representation of a refrigeration device according to the invention; and
• Fig. 2 is a flowchart of a running of the control device of the refrigeration control method.

1 shows a highly schematic representation of a refrigeration device with an insulating housing 1, which encloses a cooling space 2. From a refrigerant circuit of the refrigerator, an evaporator 3 in the interior of the refrigerator and a compressor 4 are shown in the figure, which supplies the evaporator 3 with liquefied refrigerant and evacuated vaporized refrigerant therefrom. A first sensor 5 is in the refrigerator for detecting of its temperature Ti arranged. A second temperature sensor 6 is located on the evaporator 3 in the vicinity of the refrigerant inlet to measure the evaporation temperature T _{v of} the refrigerant. A third sensor 7 for measuring the outside temperature T _e is arranged outside the housing 1. All three sensors are connected to a control device, here a microprocessor 8. The microprocessor 8 controls the operation of the compressor 4 on the basis of the temperature T _i measured by the first sensor 5 and controls the operation of a heating element 9 arranged on the evaporator 3 on the basis of the temperatures measured by all three sensors 5, 6, 7 and a set of limit values stored in another microprocessor 8 memory 10 is stored.

The process performed by the microprocessor 8 to control the operation of the heater 9 will be described with reference to the flowchart of FIG.

In a first step S1, the microprocessor 8 detects the temperatures T _{i of} the interior measured by the sensors 5, 6, 7, T _{e of} the surroundings and T _{v of} the evaporator. In step S2, it determines a threshold T _{lim of} the evaporator temperature associated with the measured values of T _i , T _e . This determination may be made, for example, by storing the microprocessor 8 among the pairs of indoor and outdoor temperature to which a threshold in the memory 10 which is closest to the measured pair of indoor and outdoor temperature and whose threshold value is taken as the associated threshold. It is also conceivable to round the measured temperature values in each case to the next higher or next lower temperature value to which a limit value is present in the memory 10.

An alternative is that the microprocessor 8 for a pair (T _i , T _e ) of measured indoor and outdoor temperatures those four pairs (T _i- , T _e- ), (T _i- , T _{e +} ), (T _{i +} , T _e- ) and (T _{i +} , T _{e +} ) determined, for the T _i- (T _e- ) each to T _i (T _e ) next smaller and T _{i +} (T _{e +} ) of the to T _i (T _e ) next larger temperature value to which a limit is stored in the memory 10, and that the microprocessor the limit for (T _i , T _e ) by interpolation of the limits to (T _i- , T _e- ), (T _i- , T _{e +} ), (T _{i +} , T _e- ) and (T _{i +} , T _{e +} ).

In step S3, the found limit value T _{lim is} compared with the evaporator temperature T _v . If the evaporator temperature is higher than the threshold, it is concluded that defrosting is not yet necessary, and the process returns to the beginning. If the evaporator temperature T _{v is} lower than the threshold, it is considered that a frost layer has formed on the evaporator, which must be defrosted. As a result, the microprocessor 8 sets a timer to 0 in step S4 and starts energizing the heater 9 to defrost the evaporator 3. As soon as the temperature T _v measured by the second sensor rises above 0 ° C., it is assumed that the evaporator has defrosted, the power supply of the heating device 9 is interrupted and the microprocessor 8 reads the timer to determine the duration t of the defrosting operation (step S5). In step S6, the duration t is compared with a first limit value. If the duration t is greater than this limit lim1, the limit read from the memory 10 in step S2 is reduced in step S7. All other limits in memory remain unchanged. If t is smaller than the setpoint value lim1, a comparison of the time duration t with a smaller setpoint valuelim2 follows in step S8. If the time duration t falls below this setpoint value, the limit value T _lim determined in step _{S 2 is increased} in the memory 8 in step S 9.

If t is between the two limit values lim1 and lim2, this means that the defrost time period is within the desired, predetermined frame, and T _lim remains unchanged. The reduction or increase of T _lim in steps S7 and S9 can be done by subtracting or adding a fixed, small positive value or by subtracting or adding a value proportional to the difference between t and the set value lim1 or lim2. Also a reduction or enlargement by multiplying or dividing with a predetermined fixed or proportional to the factor factor comes into consideration. Alternatively, it is also possible to use a single setpoint value instead of the two setpoint values lim1 and lim2, and to carry out step S7 if t exceeds the setpoint value and to carry out step S9 if t exceeds the setpoint value.

If the limit value T _{lim has} been determined by interpolation as indicated above, all the limit values in the memory 10 which have entered the interpolation are adapted in the manner described above. The extent of the adaptation of a limit value is usefully proportional to the weight with which the limit value was included in the interpolation.

With the method described above, a limit value T _lim for the evaporator temperature, which is exactly one predetermined set thickness of a frost layer, is obtained over time for each use condition of the refrigerator defined by a pair (from an outside temperature T _e and an interior or refrigerator temperature T _i ) on the evaporator 3 corresponds. Changes in the conditions of use, whether by fluctuations in the outside temperature T _e or because a user sets a different refrigerator temperature T _i between two defrosts, can no longer lead to disturbances in the rhythm of the defrosting operations, since for all combinations of these temperatures the appropriate evaporator temperature limit T _v is stored as a limit in the memory 10. The defrost control is thus completely time-independent. It performs no unnecessary defrosting when, for example due to a temporary absence of the user, the door of the refrigerator is not opened and no moisture can penetrate into its interior and form frost on the evaporator. If the door remains open for a long time and accordingly more moisture than usual enters the device, is defrosted accordingly more often. A change in the behavior of the controller, which could result in subsequent normal operation to an unadjusted control, is not connected.

Claims (7)

1. Refrigerating appliance with a cooling chamber (2), an evaporator (3), which is arranged at the cooling chamber (2), for a refrigerant, a first sensor (5) for detecting a temperature (T_i) of the cooling chamber (2), a second sensor (6) for detecting a temperature (T_v) of the refrigerant, a third sensor (7) for detecting an external temperature (T_e), a heating device (9) for the evaporator (3) and a control device (9) for operating the heating device (9) in dependence on the temperatures (T_i, T_v, T_e) measured by the first sensor (5), the second sensor (6) and the third sensor (7), which device is equipped for activating the heating device (9) when the temperature (T_v) measured by the second sensor (6) falls below a limit value (T_lim), characterised in that the refrigerating appliance is equipped in such a manner that the limit value (T_lim) is fixed in dependence on the temperatures (T_i, T_e) measured by the first sensor (5) and the third sensor (7).
2. Refrigerating appliance according to claim 1, characterised in that the control device (8) comprises a memory (10) which records values of the limit value (T_lim) for different pairs of external and cooling space temperatures.
3. Refrigerating appliance according to claim 2, characterised in that the control device (8) comprises an interpolation unit for calculating the limit value for pairs of temperatures (T_i, T_e), which are measured by the first sensor (5) and the third sensor (7), on the basis of the values recorded in the memory (10).
4. Refrigerating appliance according to one of the preceding claims, characterised in that the limit values (T_lim) for all pairs of external and cooling chamber temperatures (T_i, T_e) are so selected that they correspond with a predetermined frost thickness at the evaporator (3).
5. Refrigerating appliance according to one of claims 1 to 4, characterised in that the limit values (T_lim) of the second temperature sensor (6) are variable by the control device (8).
6. Refrigerating appliance according to claim 5, characterised in that the control device (8) is in a position of measuring the time (t) required by the heating device (9) for thawing the evaporator (3) and in the case of deviation of this temperature from a target value (lim1, lim2) so changing the limit values (T_lim) of the sensor (6) that the time (t) required for thawing converges towards the target value.
7. Refrigerating appliance according to claim 6, characterised in that if in the case of a given pair of external and cooling chamber temperatures (T_i, T_e) the time (t) required for the thawing deviates from the target value (lim1, lim2) the control device (8) changes the limit values of temperature pairs, which are adjacent to the given pair, more strongly than those more remote.

Images