TECHNICAL FIELD

The present disclosure relates to a refrigerator and to a refrigerator employing a control method.

BACKGROUND

Refrigerators are used to keep goods such as food and the like at a cooled temperature in a cooled compartment. If the refrigerator is used to keep the goods at a temperature below the freezing point the refrigerator is sometimes called a freezer. However, the term refrigerator will be used for any apparatus used to store goods at a cooled temperature such that the temperature inside the refrigerator can be lower than the ambient air outside the refrigerator.

In a refrigerator, the temperature is typically kept at a narrow band around a set temperature. Thus, it is typically desired to not let the temperature become much lower than the set temperature because there will then be a loss of energy. Other negative effects may also occur. On the other hand, it is also desired to not let the temperature become higher than the set temperature. For example, if the goods stored in the refrigerator is food, the food may have a shortened storing time.

In order to control the temperature inside the refrigerator a temperature sensor is typically used. The temperature sensor is typically located outside the cooled compartment such that the temperature sensor can obtain a correct reding of the temperature inside the cooled compartment. For example, the temperature sensor can be located directly behind and in contact with the inner liner so as to obtain a correct reading of the temperature inside the cooled compartment.

There is a constant desire to improve the operation of refrigerators and to reduce the cost for operating refrigerator. Hence, there exists a need for an improved control of a refrigerator. SUMMARY

It is an object of the present invention to provide an improved method of controlling a refrigerator.

This object and/or others are obtained by the method and refrigerator as set out in the appended claims.

As has been realized by the inventors, when placing warm goods such as food in the cooled compartment of a refrigerator, there is a risk that the temperature sensor will give a wrong output if the warm goods are placed very close to the temperature sensor. For example, if the temperature sensor is placed directly behind the inner liner and warm goods are placed in contact with the inner lining of the cooled compartment, the temperature sensor will give a reading close to the temperature of the warm goods instead of the temperature of the cooled compartment. This will lead to a high demand for cooling and the compressor will be run for an unnecessary long time or with an unnecessary high speed in case of a variable-speed compressor, resulting in a waste of energy and a too low temperature inside the cooled compartment.

To prevent such a problem from occurring, a space can be formed in front of the temperature sensor inside the cooled compartment where no goods can be placed. For example, a shelf in front of the temperature sensor can be designed to not extend all the way to the inner lining whereby a short distance is formed between the inner liner and the shelf where no goods can be placed.

Another way to address the problem could be to utilize multiple temperature sensors. Only the reading from the sensor with the lowest temperature is then used to control the temperature inside the cooled compartment.

However, the above methods for solving the problem when warm goods are placed in the cooled compartment of a refrigerator have drawbacks. For example, using a distance to the inner liner will reduce the amount of space that can be utilized inside the cooled compartment. The use of multiple temperature sensors will increase the cost and it can be difficult to determine which temperature sensor (if any) that gives the correct reading. For example, if frozen goods are placed to thaw in the cooled compartment, the temperature sensor giving the lowest reading can give a too low temperature.

It is an object of the invention to provide a refrigerator that can detect that warm (or cold) goods have been placed close to the temperature sensor, and controls the cooled compartment based on such a detection. Thus, when a condition is met that goods having deviating temperature is in the cooled compartment leading to an incorrect reading of the temperature inside the cooled compartment the refrigerator is configured to enter a different control mode that takes into account such an incorrect reading.

In accordance with the invention a refrigerator comprising a cooled compartment for storing goods to be cooled is provided. A door is provided for accessing the cooled compartment, and a cooling arrangement comprising a compressor for cooling the cooled compartment is also provided. The refrigerator further comprises a liner delimiting the cooled compartment from a space of the refrigerator outside of the cooled compartment, and a temperature sensor is provided in the space outside the cooled compartment and in direct contact with the liner. A controller is used for controlling the cooling arrangement based on an output from the temperature sensor. The cooled compartment is configured to store goods in direct contact with the liner at a location directly opposite to the location of the temperature sensor, and the controller is adapted to detect that goods are located in the cooled compartment at a location contacting the liner where the temperature sensor is located. The controller controls the cooling arrangement based on detection of such goods in contact with the liner. Hereby an efficient cooling of the cooled compartment can be achieved without reducing the space used for storing goods and with sensor arrangement that has low complexity.

In accordance with one embodiment, the liner is a rear wall liner of the cooled compartment. Hereby a refrigerator configuration that is easy to assemble and that make good use of the space in the refrigerator is obtained. In accordance with one embodiment, the cooled compartment comprises a shelf for storing goods, the shelf extending all the way to the liner such that goods when placed on the shelf can contact the liner at a location corresponding to the location of the temperature sensor at the opposite side of the liner. Hereby the cooled compartment can be fully utilized for storing goods.

In accordance with one embodiment, the controller is adapted to detect that goods are located in the cooled compartment at a location contacting the liner where the temperature sensor is located based on a temperature derivative of a temperature sensor output signal. The controller can then enter a special detection mode. Hereby an efficient algorithm that is robust can be provided.

In accordance with one embodiment, the controller is adapted to detect that goods are located in the cooled compartment at a location contacting the liner where the temperature sensor is located based on a comparison between the temperature derivative of a temperature sensor output signal with a pre- stored value or values of a temperature derivative.

In accordance with one embodiment the controller is in the detection mode adapted to command the compressor to switch between an on state and an off state for a number of cycles. Hereby an efficient method for detecting goods close to the sensor can be obtained.

In accordance with one embodiment the controller is adapted to obtain temperature derivatives for both the compressor on state and the compressor off state and detect that goods are located in the cooled compartment at a location contacting the liner where the temperature sensor based on both the temperature derivative during the compressor-on state and the temperature derivative during the compressor-off state. Hereby an improved detection of goods can be obtained.

In accordance with one embodiment the controller is adapted to enter a mode where the compressor is switched between the compressor on state and the compressor off state based on a pre-determined condition. Hereby a suitable start condition can be programmed to the controller. For example, the pre-determined condition can be the opening or closing of the door; and/or based on a determined temperature derivative obtained from the temperature sensor.

In accordance with one embodiment, multiple cooled compartments are provided and an arrangement (28) is provided to control a refrigerant to circulate to different cooled compartments. Hereby the detection of goods can be applied to a refrigerator with multiple cooled compartments.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way of non-limiting examples and with reference to the accompanying drawings, in which:

- Fig. 1 is a view of a refrigerator,

- Fig. 2 is a partial cross-sectional view of the refrigerator of Fig. 1 .

- Fig. 3 is a view illustrating a cooling arrangement,

- Fig. 4 is a flow chart illustrating steps performed when detecting goods in a cooled compartment of a refrigerator,

- Fig. 5 illustrates a controller used for controlling the temperature in a cooled compartment of a refrigerator, and

- Fig. 6 illustrates an exemplary speed pattern for a variable speed compressor.

DETAILED DESCRIPTION

In Fig. 1 a refrigerator 10 is depicted. The refrigerator 10 can be any type of appliance designed to keep goods at a cooled temperature and can typically be a household refrigerator or a household freezer. The term refrigerator is used herein to refer to any apparatus used for keeping goods at a temperature cooler than the ambient air. The refrigerator 10 is delimited by outer walls 12. The refrigerator 10 has a cooled compartment 14. The cooled compartment 14 can be accessed via a door 16. The door 16 can be any type of opening used for accessing the cooled compartment such as a drawer or so-called French doors. The door can have a sensor associated therewith so that it can be determined when the door is opened and or closed. The cooled compartment 14 is cooled by a cooling arrangement 18 as will be described in more detail below. The cooled compartment 14 can further have a shelf 20 whereon goods to be cooled can be placed. In Fig. 2 a partial cross-sectional view from above along the line A- A of Fig. 1 is shown. In Fig 2 a liner 40 is located inside the refrigerator. The liner 40 separates the cooled compartment 14 from a space 30. The space 30 is located between the liner 40 and an outer wall 12. In the example of Fig. 2, the outer wall is a rear wall 44 such that the liner 40 forms a rear wall liner. In the space 30 electronics and other parts such as ducts and the like that are hidden from the user can be placed. In Fig. 2, a temperature sensor 34 is located in the space 30 directly behind the liner 40 and in particular in contact with the liner 40. In some embodiments the temperature sensor 34 can even be located in the liner 40. However, such an implementation is also considered to be behind the liner 40 in this disclosure. Hereby a good reading of the temperature inside the cooled compartment can be obtained. Other devices such as in particular a controller 32 can also be located in the space 30. The cooled compartment 14 can comprise a shelf 20. The shelf 20 can extend all the way to the liner 40 without any hinder preventing goods to be placed against the liner 40. In particular goods can be placed in direct contact with the liner 40 at a location directly opposite to the location of the temperature sensor 34. Hence, goods can be placed very close to the temperature sensor 34. In in accordance with some embodiments only the liner 40 or a fraction of the liner 40 separate the goods from the temperature sensor 34.

It is to be noted that the exemplary configuration of the refrigerator in the example of Figs 1 and 2 only illustrates one of many possible configurations. For example, multiple cooled compartments can be provided. The cooled compartments can in some embodiments comprise one or multiple freezer compartments. Also, the temperature sensor can be located behind a laterally arranged liner or in some other way that makes it possible for goods stored in the cooled compartment to influence the output from the temperature sensor used to determine the temperature in the cooled compartment.

In Fig 3 an exemplary a cooling arrangement 18 is depicted. The cooling arrangement 18 can comprise a compressor 52, a condenser 54 and an evaporator 56. The cooling arrangement 18 also comprises an expansion valve 26. The expansion valve 26 can typically be a capillary tube or a similar device. The cooling arrangement 18 is controlled by the controller 32. Typically, the controller 32 can be configured to determine when and for how long to run the compressor 52 or at what speed to run the compressor. This in turn provides cooling capacity that the cooling arrangement 18 can deliver. The temperature that the controller strives to keep can be set by a user as a target temperature and the controller 32 can be fed with an input signal indicative of a temperature of a cooled compartment to be kept at the cooled temperature from a temperature sensor 34. The cooling arrangement 18 can also comprise additional components such a closable a valve 28. Further, the cooling arrangement 18 can comprise additional compartments to be cooled. The cooling arrangement can then comprise additional evaporators 56. In accordance with some embodiments the valve 28 is used to divert the coolant to such additional compartments having corresponding evaporators (not shown).

In a refrigerator configuration such as the one exemplified above in conjunction with Fig. 2, it is advantageous to enable detection of when goods, such a food package, is put in contact with the air temperature sensor. This can for example be the case when goods are placed in direct contact with the liner 40 close to where the temperature sensor 34 is located. When this happens, the temperature sensor will be influenced by the temperature of the goods and temperature reading can deviate from the air temperature inside the cooled compartment. The undesired effect caused by such a contact is twofold. The desired reading of the temperature sensor may be corrupted, since the measured temperature can become that of the goods and not that of the air. Also, the dynamics of the cooling system are modified, since the goods increases the thermal inertia as perceived by the controller 32 and the controller cannot regulate efficiently anymore. This is because the control loop employed by the controller 32 is not calibrated for the changed inertia. As a matter of fact, the thermal capacity of the air is orders of magnitude smaller than that of most goods such as food or food container that may come in contact with the temperature sensor.

In order to provide an efficient control of the cooling arrangement when the reading of the air temperature inside the cooled compartment from the temperature is impaired by goods placed close to the temperature sensor, such a condition need to be detected. Then the control of the cooling arrangement can be adjusted to take into account the detected condition.

Thus, first when goods with a temperature deviating from the air temperature inside the cooled compartment is placed close to the temperature sensor, this condition is detected. This can be performed in various ways. If, for example, the temperature difference is relatively large such as in the order of several degrees Celsius for example at least three or five degrees Celsius, this can be detected by detected a quick change in the read temperature. This can be done for instance by monitoring the derivative (slope) of the temperature after a door-opening or some other predefined condition. If the derivative becomes larger than a positive threshold parameter, then the contact of warm goods can be detected. On the other hand, if the temperature derivative becomes smaller than a negative threshold parameter, then the contact of cold goods, like frozen food, is detected.

However, when the temperature of the goods placed in contact with, or close to, the temperature sensor is close to the air temperature inside the cooled compartment, the measured derivative cannot always be used to correctly detect this condition.

This can for example occur when a user shifts some goods already present in the cooled compartment, and places for example a package in contact with the temperature sensor.

Although the temperature of the goods in contact with the sensor is similar to that of the compartment, this case is not less harmful than that of warm or cold goods in contact. Indeed, the thermal inertia of the goods in contact with the sensor can lead the control loop to instability, since it is calibrated for a smaller inertia.

In order to detect such a condition, when the temperature of the goods is near the temperature of the cooled compartment such as within three or within one degree Celsius from the temperature of the cooled compartment another method can be more efficient. In accordance with one embodiment the detection of contact of goods with the temperature sensor can be based on a direct or indirect measure or an estimate of the thermal inertia as seen by the cooling arrangement 18. In accordance with one embodiment the thermal inertia is measured by comparing the derivative of the temperature during cooling-ON phase, i.e., when refrigerator fluid flows inside the evaporator of the cooling arrangement used for cooling the cooled compartment with the derivative of the temperature measured or estimated during cooling-OFF phase, i.e., when refrigerator fluid does not flow inside the evaporator of the cooled compartment.

The derivatives of the air temperature can advantageously be computed with a technique which is robust to quantization, such that even small ripples, due to the switching of the compressor ON-/OFF can be identified. The change of the thermal inertia is detected by computing a detection signal, i.e., a function of the derivative(s), that indicates the level of similarity of the measured pattern of derivative(s) with a nominal pattern, i.e., a pattern expected to occur if there is no contact with the temperature sensor. The detection signal is thus compared to a reference threshold value to determine if the temperature sensor is in contact with goods with a temperature deviating from the air temperature inside the cooled compartment.

When a contact is detected based on the comparison of the detection signal with the reference threshold, the control system is slowed down, in order to adapt the dynamics of the controller loop to the increased thermal inertia, and to keep the control loop in a stable condition.

In Fig. 4 an exemplary control method in accordance with the above is depicted. First a start (entry) condition is determined in a step 300. For example, the opening of the door to the cooled compartment 18 can be used to start the control method set out in Fig. 4. When such a condition is detected, the controller can switch to a detection mode in step 301 that is designed to facilitate detection if goods is placed close to or in contact with the temperature sensor. In the detection mode the compressor is run in an ON-OFF operating mode for a predetermined number of cycles (if this was not already the operation mode for the compressor before entering the detection mode). In other words, the compressor can in the detection mode be forced to switch on and off for a period of time (or a number N cycles) in a step 303. In accordance with some embodiments, the minimum speed can be increased during the on phase of the compressor or set to a minimum value in order to better excite the system. Hereby detection of goods close to the temperature sensor can be improved. However, the cooling capacity can be kept unchanged by running the compressor at higher speed but during shorter time intervals.

Next, in a step 305, the temperature derivatives are determined during cooling-ON phases and or cooling-OFF phases. In the case of appliances having a singlecompartment and single-evaporator, the cooling-on and cooling-off phases of the cooling compartment typically match the compressor-on and compressor-off states of the compressor. In the case of multi-compartment appliances having multiple evaporators (and typically also multiple temperature sensors) and a function such as a valve used to either to stop or to divert the refrigerant on one of the evaporators, the cooling on-phase can correspond to the simultaneous occurrence of compressor- on and a state, for example a valve setting, that permits the refrigerant to feed the evaporator of the cooled compartment. If the compressor is off or if the valve takes any other position, then the state of the cooled compartment corresponds to cooling- off.

The derivative of the air temperature can advantageously be computed with a technique which is robust to quantization such that even small ripples, due to the ON- OFF of the compressor (or cooling ON/OFF), can be identified. The determined values of the derivatives are compared with a stored value or set of values that corresponds to the inertia when the temperature sensor is in contact with air (normal mode of operation) in a step 307. Based on the determination in step 307 the controller can determine that the temperature sensor is in contact with goods having a temperature deviating from the air temperature inside the cooled compartment in a step 309. If such goods are detected the controller enters a contact mode in a step 311 where the control loop is changed to take into account the higher inertia resulting from the goods in the cooled compartment. Typically, the control loop can in the contact mode be set to run the compressor less than the temperature sensor would indicate in a normal control loop. In other words, the control loop is slowed down in order to adapt the dynamics of the controller to the increased thermal inertia, and to keep the control loop stable. If, however, there is no indication that goods with deviating temperature from the air in the cooled compartment has been placed near the temperature sensor, the detection mode can be exit and the control can return to normal operation of the compressor in a step 315. Thus, if in step 309 it is determined that no goods are in contact with the temperature sensor based on the determined values of the derivatives, the controller exits the detection mode and returns to normal mode of operation.

The controller can exit the contact mode based on some predetermined condition in a step 313. For example, the detection mode can be run again to determine if goods are still in contact with the liner 40. In another embodiment the controller always exits the contact mode when the door is opened in which case the detection mode can be re-entered in step 300.

Fig. 6 illustrates an exemplary speed pattern for a variable speed compressor if such a compressor is used in the cooling arrangement 18. In Fig.6 the compressor speed is shown as a function of time (upper Figure) The sensed temperature at the corresponding time is also shown (lower Figure). Thus, when the entry condition is met in step 300 above, the variable speed compressor starts to switch between low speed and high speed. The variable speed compressor can then be run this way until no contact is determined as in step 309.

In order to constantly monitor the system, the derivative computation and pattern check is as described above in conjunction with Fig. 4 can also be performed also in normal mode of operation, but in this case the compressor speed is unaffected. In such an implementation if a change of the thermal inertia is detected the controller can enter the detection mode as described in conjunction with Fig. 3. In other words, the detection of a pattern indicating that goods are stored in contact with the temperature sensor during normal mode of operation can trigger the start of the detection mode in step 300 as described above.

The controller 32 as described herein can be implemented using suitable hardware and or software. An exemplary controller 32 is depicted in Fig. 5. The hardware can comprise one or many processors 401 that can be arranged to execute software stored in a readable storage media 402. The processor(s) can be implemented by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared or distributed. Moreover, a processor or may include, without limitation, digital signal processor (DSP) hardware, ASIC hardware, read only memory (ROM), random access memory (RAM), and/or other storage media. The processor 32 is adapted to send and receive signals from other entities using an interface 403. Such signals can be an input signal from a temperature sensor and a control signal emitted to control the run of the compressor.

Using the invention can enable detection of frosting or warming of goods when a warm or cold package is put in contact with the temperature sensor (directly or indirectly). With a warm package, the controller reads a temperature warmer than that of the air, so it will provide excessive cooling capacity to the cavity, bringing the air temperature far below the target. With a cold package, the controller reads a temperature colder than that of the air, so it will provide insufficient cooling capacity to the cavity, bringing the air temperature far above the target temperature. Also, instability of the cooling system when a package with temperature close to the target temperature placed in contact with the temperature sensor can be avoided or the effects reduced. Although in this case the measured temperature is close to that of the air, the increased thermal inertial can lead the control loop to instability, since it is calibrated for a smaller inertia.