Field of the Invention

The present invention refers to a thermal load compensating system that automatically adjusts the operational temperature in a refrigeration appliance of the type which comprises a compressor, optionally at least one fan, and a control means for activating and deactivating the compressor and/or the fan (if existing) as a function of the variations of the temperature reigning inside a refrigeration compartment which can be defined in a cabinet of a refrigerator or freezer or in a room of any building or construction. The present invention refers to a system that changes the behavior of the appliance in order to obtain a better performance/recovery of the adequate operational temperature for the loads to be refrigerated, according to the operational conditions to which the appliance is submitted (thermal loads, opening of the refrigeration compartment door) . The operation of the appliance is implemented in an electronic control means to be mounted in the refrigerator, freezer, air conditioner or other similar refrigeration appliance. Prior Art

The present invention is designed to be applied to domestic refrigeration appliances provided with a single speed compressor and in the form of a refrigerator, a freezer, or even an air conditioner, in which the refrigeration compartment, as generically denominated hereinafter, presents a respective adjusting device, generally in the form of a knob operatively associated with a control means, which allows the user to modify the operational conditions

of the appliance, altering the activation and deactivation temperatures of the compressor and/or the fans to cooler or less cool values from a nominal medium operational value. In these known temperature adjusting systems, when the user wishes to select an operational temperature (for example a lower temperature for food preservation) , he/she manually operates the adjusting device so that the control means detects said temperature alteration and varies, correspondingly, the deactivation temperature of the compressor (and/or of the existing fans) . It should be understood that the variation of the compressor activation temperature can be also altered or maintained constant in the case of the refrigeration compartments with a freezer function. Hereinafter, the expression "activation or deactivation temperature of the compressor" is to be understood as being also applicable to the fan or fans when the latter are provided in the refrigeration appliance.

In these known systems, besides the user being able to adjust the temperature operational range within which the refrigeration appliance will operate, adjusting this range to cooler or less cool conditions, the control means is operatively associated with means to detect the current temperature in the refrigeration compartment and to check whether said temperature is in the same level or above the activation temperature of the compressor so as to activate the latter. When the temperature of the refrigeration compartment informed to the control means is equal to or lower than the deactivation temperature of the compressor, the control means provides the deactivation of the latter. This operational system makes the temperature inside the refrigeration compartment oscillate between

the activation and deactivation temperatures of the compressor.

However, it is known from the prior art that the temperature of the load being refrigerated does not present the same characteristics of variation of the temperature reigning inside the refrigeration compartment, since the thermal inertia of the load delays its temperature fluctuations. Aspects to be considered as detrimental to the maintenance of an adequate temperature for a load stored in the interior of a refrigeration compartment are related to events, such as the addition of a large thermal load (food products, for example) into the refrigeration compartment, and the opening of a door for an excessively long period sufficient to allow the occurrence of an undesirable rise of the load temperature. In such situations, even if the temperature measured by a temperature sensor installed in the refrigeration compartment rapidly returns to its nominal value, due to adjustments in the compressor operation, the temperature of the stored load, usually food products in the case of refrigerators and freezers, will take a longer time to reach the desired value. The recovery of the load (food) temperature is thus more important than the recovery of the air temperature inside the refrigeration compartment. However, the known temperature adjusting systems do not permit a rapid recovery of the temperature of the load stored in the refrigeration compartment.

In the known systems, the control means is constructed so as to detect when the temperature reigning inside the refrigeration compartment, measured by the temperature sensor, surpasses the activation temperature of the compressor due to an event that

provokes said temperature rise, and the control means is designed to adjust, to lower values, the deactivation temperature of the compressor and also, optionally and if necessary, the activation temperature of the compressor, in order to minimize the temperature variations to which the load is submitted. In these solutions, the control means verifies the occurrence of the anomalous temperature rise in the refrigeration compartment and instructs a corresponding adjustment to be effected in the deactivation temperature of the compressor, the adjustment of the deactivation temperature of the compressor being achieved as a function of the value of the anomalous temperature, allowing the refrigeration system to respond, taking into account only the deviation of the temperature detected by the temperature sensor, i.e., the deviation of the temperature reigning inside the refrigeration compartment . While minimizing the temperature oscillations inside the refrigeration compartment, the control system of the type mentioned above does not adjust the deactivation temperature of the compressor as a function of the periods of time in which the temperature varies between predetermined values, failing to consider the inertia of the thermal load imposed to the refrigeration compartment, thereby preventing the compressor from operating to provide a more rapid recovery of the temperature of the load stored in the refrigeration compartment.

Other temperature control systems of a refrigeration compartment allow processing different operational parameters, usually guaranteeing an adequate -cooling of the load. However, said control systems that control multiple parameters are very complex,

requiring the provision of sensors and other high cost implementation means which increase the cost of the end product .

Summary of the Invention As a function of the disadvantages mentioned above, it is a general object of the present invention to provide a system for automatically adjusting the deactivation temperature of the compressor of a refrigeration appliance, such as a freezer, refrigerator, or air conditioner, as a function of anomalous temperature rises inside a refrigeration compartment, containing a thermal load, for example food products, in order to promote a rapid recovery of the desired operational temperature of said load. It is a further object of the present invention to provide a system as described above, which can be applied to a refrigeration appliance without requiring any additional components, such as a sensor or an electronic component, i.e., without increasing the cost of the appliance.

These and other objects and advantages of the invention are attained by the provision of a thermal load compensating system for a refrigeration appliance of the type which comprises a compressor associated with a refrigeration circuit, a temperature sensor provided inside a refrigeration compartment, and a control means operatively associated with both the compressor and the temperature sensor and which is provided with a timer and constructed to activate and deactivate the compressor when the interior of the refrigeration compartment reaches activation and deactivation temperatures, respectively. The refrigeration appliance can further contain one or more fans for distributing cool air to different and respective refrigeration compartments. In this case,

the control means may actuate in the operation of both the compressor and the fans .

According to the invention, the control means is constructed in such a way as to alter the deactivation temperature of the compressor and/or the fan, whenever in an operational cycle of the compressor the temperature decrease rate between the activation and deactivation values deviates, by a certain predetermined value, from a reference temperature decrease rate of the refrigeration compartment, obtained in at least one previous operational cycle of the compressor and stored in the control means, the alteration in the deactivation temperature of the compressor being directly proportional to the variation, detected by the control means, of the temperature decrease rate in relation to the reference temperature decrease rate.

The construction mentioned above allows the control means to automatically adjust the deactivation temperature of the compressor when both the temperature sensor of the refrigeration compartment and the timer (measuring the time elapsed between the limits of the activation and deactivation temperatures of the compressor) detect, in relation to at least one previous operational cycle, a reduction of the temperature decrease rate between the limits of the temperature range being used by the refrigeration appliance . Brief Description of the Drawings The invention will be described below, with reference being made to the enclosed drawings given by way of example of an embodiment of the invention, and in which:

Figure 1 is a schematic median vertical sectional view of a refrigerator -presenting a refrigeration

compartment and provided with the present thermal load compensating system;

Figure 2 is a schematic diagram showing how the temperatures of the food (thermal load) and of the refrigeration compartment (detected by the sensor) vary in relation to time in a conventional refrigeration appliance;

Figure 3 is a schematic diagram showing how the temperatures of the food (thermal load) and of the refrigeration compartment (detected by the sensor) vary in relation to time in a refrigeration appliance provided with the system of the present invention; and Figure 4 is a block diagram showing the characteristics of the actuation of the control means of a refrigeration appliance provided with the present thermal load compensating system. Detailed Description of the Invention

As illustrated in figure 1, the invention is related to a system for adjusting the operational temperature in a refrigeration appliance of the type which comprises a cabinet 10 defining at least one refrigeration compartment RC closed by a front door 11. The refrigeration appliance further comprises a refrigeration circuit, which is not illustrated, except the part defined by the compressor 20 operatively associated with a control means 30 provided with a timer 31 and which is constructed in any known adequate manner to activate and deactivate the compressor 20 when the interior of the refrigeration compartment RC reaches activation and deactivation temperatures, respectively, detected by a temperature sensor 40 positioned inside the refrigeration compartment RC to sense the air temperature reigning inside the latter. The temperature sensor 40 is also operatively associated

with the control means 30 to indicate to the latter when the air temperature inside the refrigeration compartment RC reaches any of the activation and deactivation values of the compressor 20, said activation and deactivation temperatures, specific in different operational temperature ranges, being associated with different operational conditions of the refrigeration appliance. It should be understood herein that the refrigeration appliance can be of the type that comprises two or more refrigeration compartments RC, one of them defining, for example, a refrigeration compartment and another one defining a freezing compartment, which compartments are designed to be operated through independent controls operatively associated with air temperature sensors inside the compartment . The refrigeration appliance can also be of the forced ventilation type provided with only one fan 50 operatively associated with an evaporator 55, or with two fans, one associated with a refrigeration compartment and the other with a freezing compartment, in the case of a combined refrigerator-freezer appliance. Figure 2 schematically illustrates the temperature variation standards of the thermal load and of the refrigeration compartment RC detected by the temperature sensor 40. As it can be noted, in a first period of time A of the temperature versus time diagram, the temperature of the refrigeration compartment (or the temperature in the temperature sensor 40) oscillates between the upper and lower limits adjusted for the compressor operation, while the load temperature oscillates between upper and lower values contained within the temperature variation range of the refrigeration compartment. The

diagram presented herein refers to an operational condition particularly associated with a freezing compartment of a refrigeration appliance. At a determined instant B, there occurs a special event, such as for example the opening of the door 11 for an excessively long time, or the introduction of a relevant load (food) in the interior of the refrigeration compartment, said load being at a temperature substantially higher than that reigning inside the refrigeration compartment RC. In the first situation cited above, the temperature of the refrigeration compartment rises abruptly, which does not occur with the previously stored load already presenting its temperature within the desired range. However, when a new "hot" load is introduced at the instant B, the temperature of the refrigeration compartment rises rapidly, accompanying the high temperature of the load and indicating the need of occurring an alteration in the operation of the refrigeration system, since more heat must be removed from the refrigeration compartment RC to compensate for the additional thermal load.

In the period of time C of figure 2 diagram, the recovery of the load temperature is illustrated. Due to the thermal inertia of the load in changing its temperature, the cooling of the load to the desired operational range takes much more time than that necessary to recover' the temperature of the refrigeration compartment RC, as shown in figure 2. In the conventional systems, the recovery of the operational temperature of the refrigeration compartment RC occurs more rapidly, whereas the load (of food products, for example) takes a much longer time C to reach the ' desired adequate operational temperature.

Thus, it is the object of present invention to provide a thermal load compensating system which, by means of a simple and low cost arrangement, allows for a more rapid recovery of the temperature of a "hot" thermal load positioned inside the refrigeration compartment RC of the refrigeration appliance.

Figure 3 illustrates a diagram similar to that of figure 2, but illustrating the temperature variation standards of the thermal load and of the refrigeration compartment sensed by the temperature sensor 40, when the refrigeration appliance is provided with the compensating system of the present invention. The period of time A of the diagram is identical to that showed in figure 2 diagram, but with a special event occurring at the instant B, as described above in relation to the introduction of a "hot" load in the refrigeration compartment RC, the temperature of the refrigeration compartment rises rapidly, accompanying the temperature of the added thermal load and providing the activation of the compressor 20.

According to the present invention, upon detecting a rapid and intense temperature rise inside the refrigeration compartment RC, the control means 30 promotes a corresponding decrease in the deactivation temperature of the compressor 20, as illustrated in figure 3, accelerating the refrigeration of the load, so that the latter reaches the desired operational range in a time D substantially shorter than the time C required in the conventional systems . The difference between the two recovery times of the load temperature is defined by the period of time E (figure 3) which can be of several minutes or several hours . Still according to the invention, the control means 30 is designed to reduce (alter) the deactivation temperature of the compressor 20 when the temperature

decrease rate in an operational cycle of the compressor 20 deviates, by a certain predetermined value, for example of the order of 25%, from a basic temperature decrease rate obtained in at least one previous operational cycle of the compressor 20.

It should be understood that the alteration of the deactivation temperature could be made both downwardly and upwardly, since the temperature decrease rate in a determined operational cycle of the compressor 20 can be higher than the reference temperature decrease rate preferably obtained as an average of the temperature decrease rates occurred in the previous operational cycles of the compressor 20 recorded in the control means 30. Thus, the present system measures the temperature decrease rate (ratio of the difference between the activation and deactivation temperatures to the elapsed time for said decrease) , by comparing the temperature decrease rate with a reference rate, generally representative of the average of the temperature decrease rates of the previous operational cycles of the compressor 20 and which is calculated and stored in the control means 30.

According to the constructive form of the invention, when the door of the refrigeration compartment is opened for the introduction of a thermal load, the temperature sensor 40 detects the air temperature of the refrigeration compartment RC, indicating an increase in its measured temperature. A priori, when the door of the refrigeration compartment RC is closed with the compressor 20 activated (under operation) , the temperature lowers again, according to a new decrease rate, determined by the total thermal load in the interior of the refrigeration compartment RC defined after the introduction of the additional load

and which takes into account the time during which the doors remains open and the quantity/temperature of the load introduced.

The control means 30 measures the temperature decrease rate. If this rate is lower than the reference rate, it means that a loading occurred and that a corrective action is needed. There is also a relationship between the quantity of the thermal load introduced and how much the temperature decrease rate changes. That is to say, the more thermal load, the lower will be the rate .

The present system is designed, through the fixation of two known temperature intervals, to measure the time between both intervals (indirectly measuring the temperature decrease rate) and to compare with the average of the decrease rates. If this value that is read is close to the previous average value, it means that no loading occurred in the system. In case the decrease rate is lower than the average of the previous values (reference rate) , the control means 30 considers that it is a case of extra cooling and changes the deactivation temperature of the compressor, which is altered to a lower temperature, thus keeping the compressor switched on for a longer time. This action may or may not be proportional to the loading and, consequently, may or may not offer a visual indication to the user that the deactivation temperature has been reduced as a function of the thermal load imposed to the refrigeration compartment . The decrease of the .deactivation temperature of the compressor 20 modifies the value of said temperature, corresponding to the value of the activation and deactivation temperature operational range being used in the moment of adjustment, to a value corresponding to that of a lower range in a scale of activation and

deactivation temperature ranges of the compressor 20. It is also possible a situation in which the intensity of the decrease of the temperature operational range, defined in a determined operational cycle of the compressor, corresponds to activation and deactivation temperatures lower than those of the lowest temperature range in the scale of the activation and deactivation temperature operational ranges of the compressor 20. When this occurs, the control means 30 instructs to repeat the decrease of the activation and deactivation temperature operational range during a subsequent operational cycle of the compressor, aiming at bringing the temperature of the stored product, and consequently of the interior of the refrigeration compartment, to desired values.

Figure 3 illustrates the actuation procedures or steps of the control means 30 during the operation of the refrigeration appliance, and as a function of the parameters received from both the temperature sensor 40 and the timer 31, in order to effect, when necessary, an adjustment in the deactivation temperature of the compressor 20 and/or the fan 50 (when existing) , considering the application of the system for adjusting the temperature of a refrigeration compartment or a freezing compartment generically denominated herein as refrigeration compartments .

In the block diagram of figure 3 , the references in alphabetical characters are reproduced below with the respective meanings:

T _0n = activation temperature of the compressor 20 and/or the fan 50;

T _of f = deactivation temperature of the compressor 20 and/or the fan 50; T _d = temperature decrease rate,-

T _x = reference rate, which corresponds to the temperature decrease rate in each operational cycle of the compressor 20; and

T _dev = percent deviation value of the temperature decrease rate (in the example, of the order of 25%) . As illustrated, the present compensating system starts the operation with the activation of the compressor 20 at temperature T _0n previously defined in the project of the refrigeration appliance and detected by the temperature sensor 40 located inside the refrigeration compartment RC. The compressor 20 is maintained activated by the control means until the temperature inside the refrigeration compartment RC and measured by the temperature sensor 40 reaches a temperature value T _O ff . When this occurs, the control means 30 compares the temperature decrease rate T _d , measured until the event cited above, with the previous temperature decrease rate or reference rate T _x . In case the temperature decrease rate T _d is higher (with a deviation T _de v of the order of 25%) than the reference rate T _x , corresponding to the previous temperature decrease rate T _x , it is considered that no loading has occurred, thus allowing the appliance to adopt a previous new temperature decrease rate or reference rate T _x by calculating the arithmetical average of the measured temperature decrease rates T _d , whereby the control means 30 deactivates the compressor 20. On the other hand, in case the temperature decrease rate Td is lower (with a deviation T _dev of the order of 25%) than the previous temperature decrease rate or reference rate T _x , the control means 30 assumes a new temperature deactivation value T _off , to only then switch off the compressor 20. The control means 30 further calculates and records a reference temperature

decrease rate T _x in said operational cycle of the compressor 20, said rate being equal to the ratio of the difference between the activation temperature T _0n and the deactivation temperature T _O ff to the elapsed time.

Upon start of the operation of the refrigeration appliance, the control system has the parameter of the previous temperature decrease rate or reference rate T _x erased. At each operational cycle of the compressor 20, the temperature decrease rate T _d is compared with the previous reference temperature decrease rate T _x obtained in the previous cycle (s), said previous reference temperature decrease rate T _x being obtained as an average of the temperature decrease rates T _d obtained and recorded in the previous cycles.