EP0563724A1 - Method and device for evaluating frost formation on an evaporator in a refrigerator, in particular of the forced-air circulation type - Google Patents
Method and device for evaluating frost formation on an evaporator in a refrigerator, in particular of the forced-air circulation type Download PDFInfo
- Publication number
- EP0563724A1 EP0563724A1 EP93104634A EP93104634A EP0563724A1 EP 0563724 A1 EP0563724 A1 EP 0563724A1 EP 93104634 A EP93104634 A EP 93104634A EP 93104634 A EP93104634 A EP 93104634A EP 0563724 A1 EP0563724 A1 EP 0563724A1
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- European Patent Office
- Prior art keywords
- evaporator
- motor
- air
- fan
- flow rate
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
- F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
- F25D21/02—Detecting the presence of frost or condensate
Definitions
- This invention relates to a method for evaluating frost formation on an evaporator in a refrigerator, in particular of the forced-air circulation type and comprising a cabinet containing one or more temperature-controlled compartments provided with their own access doors and arranged to contain food during its preservation, there being provided on the wall of the compartment in which the evaporator is located at least one heating element which when activated defrosts the evaporator, and a fan driven by a usual electric motor connected to an electrical power line for circulating air through the evaporator and for ventilating the compartment or compartments via usual ducts provided within said cabinet, said fan, to achieve said circulation, cooperating with a usual conveying member to direct the air circulating within said compartment or compartments onto the evaporator so that the air is again cooled.
- Said defrosting is effected in various ways.
- the evaporator may be defrosted automatically after a fixed period of operation of the usual refrigeration circuit of the refrigerator (or of the known compressor of this circuit).
- this method of defrosting does not take account of whether it is really necessary to remove frost from the evaporator at that time, hence defrosting may take place when there is no real need for it (with obvious disadvantages in terms of refrigerator operation).
- An object of the present invention is to provide a method for sensing the presence of frost on the evaporator by which this latter is defrosted only if it is covered with a layer of frost to the extent of changing its heat transfer characteristics.
- a further object is to provide a method of the aforesaid type which is of low implementation cost and which enables the evaporator defrosting process to be optimized.
- a further object of the invention is to provide a device for evaluating the thickness of frost on an evaporator which is of simple construction, of reliable use and operation, and is able to activate the heating element associated with the evaporator only when on the surface of this latter there is a quantity of frost present such as to change its heat transfer characteristics.
- Said method is implemented by a device applied to a refrigerator of the aforesaid type, characterised by comprising switch means connected into the fan power line, and sensor means for sensing an intrinsic characteristic of the fan and generating a signal relative to the fan operating condition, said signal being fed to comparison and control means which compare it with a reference signal and on the basis of this comparison act on the switch means to change the fan operating conditions, and on the heating element to activate it and hence defrost the evaporator.
- Said method is also implemented by a device applied to a refrigerator of the aforesaid type, characterised by comprising means for measuring the flow rate of the air circulated through the compartment by the fan and cooled by the evaporator, said means generating an electrical signal based on the measured flow rate, said means, on the basis of this comparison, acting on switch means connected into the fan power line to alter the fan operating conditions, and activating the heating element to defrost the evaporator.
- a refrigerator for example a domestic refrigerator
- a refrigerator for example a domestic refrigerator
- a known control member 5 such as a static switch controlled by a usual control unit, not shown, connected to a known timer which controls the operation of the refrigerator.
- the fan 3 is contained in a compartment 100 provided in the cabinet 1A of the refrigerator, in correspondence with an evaporator 102, and can also feed air through a duct 103 if the refrigerator is of the type comprising several superposed compartments, said duct terminating in at least one of these compartments.
- the fan also feeds air directly into the compartment 100 via an aperture 105 provided in correspondence with the evaporator 102.
- a usual air conveying member 106 through which air can be drawn from the compartment 100 and onto the evaporator via an aperture 107.
- the evaporator comprised a body 110 provided with fins 111 in known manner.
- the motor 2 of the fan 3 is connected to the control member 5 by a return line 4A, said control member being powered in known manner by mains voltage V R .
- a feedback branch 6 connects the member 5 to an integrator member or circuit 8 connected by electrical branches 9 and 10 to the ends 11 and 12 of the motor 3.
- the integrator member or circuit measures the feed voltage across the ends 11 and 12 of the motor 3 and generates in the feedback branch a control signal V A which enables the member 5 to maintain the feed voltage of the motor 3 constant in known manner.
- a tachometer dynamo 15 (or a control circuit comprising such a dynamo) measures the r.p.m. of the motor 3.
- the dynamo 15 is connected to a digital/analog converter 16 connected to a non-inverting input 17 of any known comparator circuit or member 18.
- the inverting input 19 of the circuit or member 18 receives a reference signal V E corresponding to a very thin layer of frost on the evaporator, ie unable to significantly impede the air flow traversing the evaporator 102.
- the output 20 of said circuit 18 is connected to a usual heating element 21 located in correspondence with the evaporator 102.
- Said comparator circuit or member 18 also controls the opening of a switch 23 in the line 4, for example via a usual bistable element (not shown) or an analogous relay 28 connected to its output 20.
- the switch 4 is normally closed during normal operation of the refrigerator.
- the member 5 controls the operation of the motor 2 in any known manner. As stated, via the integrator circuit 8 the member 5 controls the power supply to the motor 2 such that it is operated at constant voltage.
- This member is also connected by an electrical branch 29 to a usual relay 30 arranged to control a switch 31 in the output 20 of the circuit 18 towards the heating element 21 (as shown in Figure 3).
- frost forms on the evaporator and with the passage of time reaches a significant thickness such as to reduce the normal flow of air along the evaporator fins 111. This changes the fan r.p.m., which tends to "rotate idly". This increase is sensed by the tachometer 15.
- the tachometer During normal refrigerator operation with no frost on the evaporator 102, the tachometer generates a signal V B (digital) of a value only slightly different from or lower than the signal V E .
- V C analog or digital
- the member 5 senses the opening of the switch 23 in known manner and acts (directly or indirectly) on the usual compressor (not shown) of the refrigeration circuit of which the evaporator 102 forms part, and halts it. The operation of the refrigerator consequently ceases.
- the member 5 acts on the relay 30, which opens tile switch 31 (normally closed). This interrupts the operation of the heating element 21.
- the relay 28 closes the switch 23 in known manner.
- the member 5 can therefore again control the operation of the fan 3 and reactivate the compressor to return the refrigerator to operation.
- frost sensor senses that there is no longer frost on the evaporator.
- Modifications are however possible, such as the tachometer not generating a digital signal but instead directly generating an analog signal which is compared continuously by the circuit or member 18 with the reference signal (also analog in this case).
- This latter can be fixed or variable, and be set by usual electrical members such as a trimmer or other known member.
- the member 5 can also be a usual microprocessor circuit and effect the comparison between the signals V B and V E . This can be done either continuously during the entire period of operation of the refrigerator 1 or cyclically at particular times.
- FIG 4 in which parts corresponding to those of Figure 3 are indicated by the same reference numerals, shows a further embodiment of the invention.
- the feedback branch (by which the member 5 controls the operation of the motor 2 at a constant r.p.m.) is connected directly to the digital/analog converter 16 or to the tachometer 15 if this generates an analog signal V B or if the member 5 is able to operate directly on a digital signal.
- a shunt resistor 40 is connected into the return branch 4A from the motor 2 to the member 5 in series with this motor, and has its ends 41, 42 connected to electrical branches 43, 44 leading to the integrator circuit 8, and to branches 45, 56 leading to a known current member or sensor 47.
- the circuit 8 and the sensor 47 are connected by electrical branches 48, 49 respectively, to a usual multiplier 50. These branches carry signals corresponding to the voltage and to the current absorbed by the motor 2 respectively.
- the multiplier 50 generates in its output branch 51 a signal V D proportional to the power absorbed from the mains by the motor 2 during its operation.
- the branch 51 terminates at the non-inverting input of the circuit or member 18.
- the signal V C is substantially close to or less than the signal V E (in value).
- FIG. 5 shows a further embodiment of the invention.
- parts corresponding to those of the previously described figures are indicated by the same reference numerals.
- the operation of the motor 2 is again controlled at constant r.p.m. by the tachometer dynamo 15.
- Frost formation is however evaluated via the integrator circuit 8 or via the variation in the feed voltage of the motor 2 as measured by the circuit 8.
- circuit 18 acts in the described manner, to halt the motor 2 and activate the heating element 21.
- the motor 2 is again operated and the heating element 21 switched off (as already described).
- FIG. 6 shows a further embodiment of the invention.
- parts corresponding to those of the previously described figures are indicated by the same reference numerals.
- the current sensor 47 During refrigerator operation, if the frost thickness on the evaporator is unable to substantially hinder the flow of air grazing the evaporator, the current sensor 47 generates a signal V H substantially close to or less than the threshold signal V E .
- the motor is again operated in the described manner and the element 21 switched off.
- the method of the invention can be implemented by direct measurement of the flow rate of the air leaving the aperture 105 (arrow F) or returning to the evaporator 102 through the aperture 106 (arrow G).
- FIGS 7 and 8 show a flow rate measurement member 90 positioned in correspondence with the aperture 105.
- This member is a usual anemometer 91 connected to a control circuit 92.
- This latter receives a signal V M generated by the anemometer (a function of the air flow rate through the aperture 105) and compares this with a reference signal V RIF corresponding to a minimum acceptable air flow rate (corresponding to a maximum acceptable frost quantity on tile evaporator 102). If V M is less than V RIF (ie the frost has reduced the air flow leaving the aperture 105 to too low a value), the circuit 92 operates the switch 23 to halt the motor 2, and operates the heating element 21. The evaporator is therefore defrosted and the member 5 simultaneously halts the operation of the refrigerator 1, in the described manner.
- the member When defrosting is complete the member senses that the frost has been removed from the evaporator and causes the circuit 92, via an electrical branch 93, to halt the operation of the element 92 and close the switch 23. The member 5 hence reactivates the refrigerator.
- two pressure sensors 94 and 95 are positioned in correspondence with the apertures 105 and 106 to determine the flow rate of the air which has already grazed the evaporator and that of the air which returns to it.
- the circuit 92 senses a pressure difference between the apertures 105 and 106.
- the circuit 92 measures this (for example by making a usual comparison between the signals V O and V P from the sensors, this latter being considered the reference signal) and acting on the heating element 21 and switch 23 as already described in relation to Figures 7 and 8.
- the anemometer 91 can be replaced by a heated wire grazed by the air leaving the aperture 105.
- This wire involves a current and generates across its ends a potential difference which is proportional to the cooling which it undergoes as a result of the air striking it, so changing its resistance. As the flow rate of the air striking it changes, so does the potential difference across its ends.
- the control circuit associated with the wire acts to halt the motor and activate the heating element.
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
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- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Defrosting Systems (AREA)
Abstract
Description
- This invention relates to a method for evaluating frost formation on an evaporator in a refrigerator, in particular of the forced-air circulation type and comprising a cabinet containing one or more temperature-controlled compartments provided with their own access doors and arranged to contain food during its preservation, there being provided on the wall of the compartment in which the evaporator is located at least one heating element which when activated defrosts the evaporator, and a fan driven by a usual electric motor connected to an electrical power line for circulating air through the evaporator and for ventilating the compartment or compartments via usual ducts provided within said cabinet, said fan, to achieve said circulation, cooperating with a usual conveying member to direct the air circulating within said compartment or compartments onto the evaporator so that the air is again cooled.
- As is well known, during the use of such a refrigerator frost forms (for known reasons) on the evaporator surface, resulting in a reduction in heat transfer between this surface and the air which grazes it. The evaporator performance is consequently reduced, with obvious drawbacks.
- To free the evaporator of the layer of frost which forms on it, there is associated with it a usual electrical resistance element (or other equivalent heating element) which when current flows through it heats the frost and converts it into water.
- This is then removed from the evaporator via a suitable channel.
- Said defrosting is effected in various ways. For example, the evaporator may be defrosted automatically after a fixed period of operation of the usual refrigeration circuit of the refrigerator (or of the known compressor of this circuit). However this method of defrosting does not take account of whether it is really necessary to remove frost from the evaporator at that time, hence defrosting may take place when there is no real need for it (with obvious disadvantages in terms of refrigerator operation).
- Methods and devices for sensing the presence of frost on the evaporator are known (such as those using optical sensing means), these then, on the basis of this, either activating or not activating the heating element associated with the evaporator (while at the same time interrupting the operation of the refrigeration circuit of which this latter forms part). These methods and devices however have a level of implementation and/or construction cost which negatively affects the overall cost of the refrigerator. In addition, said methods and devices do not allow accurate measurement of the frost thickness on the evaporator, and are able only to sense whether a layer is present on a given portion of it. Consequently, operation of the heating element associated with the evaporator, based on the sensing of frost on it, may sometimes be unnecessary, so negatively affecting the refrigerator performance.
- An object of the present invention is to provide a method for sensing the presence of frost on the evaporator by which this latter is defrosted only if it is covered with a layer of frost to the extent of changing its heat transfer characteristics.
- A further object is to provide a method of the aforesaid type which is of low implementation cost and which enables the evaporator defrosting process to be optimized.
- A further object of the invention is to provide a device for evaluating the thickness of frost on an evaporator which is of simple construction, of reliable use and operation, and is able to activate the heating element associated with the evaporator only when on the surface of this latter there is a quantity of frost present such as to change its heat transfer characteristics.
- These and further objects which will be apparent to the expert of the art are attained by a method of the aforesaid type, characterised by evaluating the variation in the flow rate of the air grazing the evaporator with respect to a flow rate reference value, determining the quantity of frost present on the evaporator surface on the basis of this evaluation, and then if necessary activating the heating element associated with the evaporator.
- Said method is implemented by a device applied to a refrigerator of the aforesaid type, characterised by comprising switch means connected into the fan power line, and sensor means for sensing an intrinsic characteristic of the fan and generating a signal relative to the fan operating condition, said signal being fed to comparison and control means which compare it with a reference signal and on the basis of this comparison act on the switch means to change the fan operating conditions, and on the heating element to activate it and hence defrost the evaporator.
- Said method is also implemented by a device applied to a refrigerator of the aforesaid type, characterised by comprising means for measuring the flow rate of the air circulated through the compartment by the fan and cooled by the evaporator, said means generating an electrical signal based on the measured flow rate, said means, on the basis of this comparison, acting on switch means connected into the fan power line to alter the fan operating conditions, and activating the heating element to defrost the evaporator.
- The present invention will be more apparent from the accompanying drawing, which is provided by way of non-limiting example and in which:
- Figure 1 is a schematic view of a refrigerator constructed in accordance with the invention;
- Figure 2 is a section on the line 2-2 of Figure 1;
- Figure 3 is a block diagram of a first embodiment of a device according to the invention;
- Figure 4 is a block diagram of a second embodiment of a device according to the invention;
- Figure 5 is a block diagram of a third embodiment of a device according to the invention;
- Figure 6 is a block diagram of a fourth embodiment of a device according to the invention;
- Figure 7 is a schematic section on the line 2-2 of a refrigerator provided with a fifth embodiment of a device according to the invention;
- Figure 8 is a block diagram of the embodiment of Figure 7; and
- Figure 9 is a simplified block diagram of a sixth embodiment of the invention.
- With reference to Figures 1 and 2, a refrigerator (for example a domestic refrigerator) is indicated overall by 1 and comprises a
fan 3 driven by amotor 2 powered via anelectrical line 4 by a known control member 5 (such as a static switch controlled by a usual control unit, not shown, connected to a known timer which controls the operation of the refrigerator). Thefan 3 is contained in acompartment 100 provided in thecabinet 1A of the refrigerator, in correspondence with anevaporator 102, and can also feed air through aduct 103 if the refrigerator is of the type comprising several superposed compartments, said duct terminating in at least one of these compartments. The fan also feeds air directly into thecompartment 100 via anaperture 105 provided in correspondence with theevaporator 102. In proximity to this later there is also a usualair conveying member 106 through which air can be drawn from thecompartment 100 and onto the evaporator via an aperture 107. The evaporator comprised abody 110 provided withfins 111 in known manner. - Specifically (see Figure 3), the
motor 2 of thefan 3 is connected to thecontrol member 5 by areturn line 4A, said control member being powered in known manner by mains voltage VR. Afeedback branch 6 connects themember 5 to an integrator member orcircuit 8 connected byelectrical branches 9 and 10 to theends motor 3. The integrator member or circuit (of any known type) measures the feed voltage across theends motor 3 and generates in the feedback branch a control signal VA which enables themember 5 to maintain the feed voltage of themotor 3 constant in known manner. - A tachometer dynamo 15 (or a control circuit comprising such a dynamo) measures the r.p.m. of the
motor 3. Thedynamo 15 is connected to a digital/analog converter 16 connected to anon-inverting input 17 of any known comparator circuit ormember 18. - The inverting
input 19 of the circuit ormember 18 receives a reference signal VE corresponding to a very thin layer of frost on the evaporator, ie unable to significantly impede the air flow traversing theevaporator 102. Theoutput 20 ofsaid circuit 18 is connected to ausual heating element 21 located in correspondence with theevaporator 102. Said comparator circuit ormember 18 also controls the opening of aswitch 23 in theline 4, for example via a usual bistable element (not shown) or ananalogous relay 28 connected to itsoutput 20. - The
switch 4 is normally closed during normal operation of the refrigerator. - The implementation of the method according to the invention will now be described in relation to the control of the
fan motor 2 connected to thecircuit 25 shown in Figure 3. - During normal refrigerator operation, the
member 5 controls the operation of themotor 2 in any known manner. As stated, via theintegrator circuit 8 themember 5 controls the power supply to themotor 2 such that it is operated at constant voltage. - This member is also connected by an
electrical branch 29 to ausual relay 30 arranged to control aswitch 31 in theoutput 20 of thecircuit 18 towards the heating element 21 (as shown in Figure 3). - For known reasons, during the refrigerator operation frost forms on the evaporator and with the passage of time reaches a significant thickness such as to reduce the normal flow of air along the
evaporator fins 111. This changes the fan r.p.m., which tends to "rotate idly". This increase is sensed by thetachometer 15. - During normal refrigerator operation with no frost on the
evaporator 102, the tachometer generates a signal VB (digital) of a value only slightly different from or lower than the signal VE. - Consequently when the signal VB, made analog, reaches the comparator member or
circuit 18, this latter generates no output signal. - When frost forms on the evaporator, the signal VB increases possibly considerably with respect to the signal VE.
- The comparison between these two by the
member 18 consequently results in this latter generating a signal VC (analog or digital) which both causes theswitch 23 to open and theheating element 21 to operate. In this manner thefan 3 stops and the evaporator defrosting proceeds. - Advantageously the
member 5 senses the opening of theswitch 23 in known manner and acts (directly or indirectly) on the usual compressor (not shown) of the refrigeration circuit of which theevaporator 102 forms part, and halts it. The operation of the refrigerator consequently ceases. - After a predetermined time period sufficiently long to enable the evaporator to defrost, the
member 5 acts on therelay 30, which opens tile switch 31 (normally closed). This interrupts the operation of theheating element 21. - At substantially the same time (or possibly sooner), the
relay 28 closes theswitch 23 in known manner. Themember 5 can therefore again control the operation of thefan 3 and reactivate the compressor to return the refrigerator to operation. - Alternatively the frost sensor (not shown) senses that there is no longer frost on the evaporator.
- One particular embodiment of the invention has been described.
- Modifications are however possible, such as the tachometer not generating a digital signal but instead directly generating an analog signal which is compared continuously by the circuit or
member 18 with the reference signal (also analog in this case). - This latter can be fixed or variable, and be set by usual electrical members such as a trimmer or other known member.
- The
member 5 can also be a usual microprocessor circuit and effect the comparison between the signals VB and VE. This can be done either continuously during the entire period of operation of the refrigerator 1 or cyclically at particular times. - Figure 4, in which parts corresponding to those of Figure 3 are indicated by the same reference numerals, shows a further embodiment of the invention.
- In this figure the feedback branch (by which the
member 5 controls the operation of themotor 2 at a constant r.p.m.) is connected directly to the digital/analog converter 16 or to thetachometer 15 if this generates an analog signal VB or if themember 5 is able to operate directly on a digital signal. - A
shunt resistor 40 is connected into thereturn branch 4A from themotor 2 to themember 5 in series with this motor, and has itsends electrical branches 43, 44 leading to theintegrator circuit 8, and tobranches 45, 56 leading to a known current member orsensor 47. Thecircuit 8 and thesensor 47 are connected byelectrical branches usual multiplier 50. These branches carry signals corresponding to the voltage and to the current absorbed by themotor 2 respectively. - Consequently the
multiplier 50 generates in its output branch 51 a signal VD proportional to the power absorbed from the mains by themotor 2 during its operation. Thebranch 51 terminates at the non-inverting input of the circuit ormember 18. - During the operation of the refrigerator 1, the signal VC is substantially close to or less than the signal VE (in value).
- Consequently the comparison between the two signals does not cause the
circuit 18 to generate any output signal VC. - When an excessive quantity of frost forms on the
evaporator 102, this changes the voltage and current absorption by themotor 2. - Consequently the absorbed power of this latter changes. The signal VD therefore changes to a value which can be considerably different from VE. This, as already described, leads to generation of the signal VC, stoppage of the
motor 2 and defrosting of the evaporator. After a suitable time the system returns to the initial conditions, as already described in relation to Figure 3. - Figure 5 shows a further embodiment of the invention. In this figure, parts corresponding to those of the previously described figures are indicated by the same reference numerals.
- In this case, the the operation of the
motor 2 is again controlled at constant r.p.m. by thetachometer dynamo 15. Frost formation is however evaluated via theintegrator circuit 8 or via the variation in the feed voltage of themotor 2 as measured by thecircuit 8. - In the case of Figure 5, the creation of an excessive frost layer leads to an increase in the voltage absorbed from the mains by the motor 2 (operating at constant r.p.m.). The
circuit 8 consequently generates towards the circuit 18 a signal VG which is considerably different from the signal VE (which it approaches or falls below during normal operation of the refrigerator 1 with a frost layer on the evaporator which is less than that which would considerably hinder the air flow traversing the evaporator or reduce the cross-section of the passage at the evaporator through which said air flows). - In this case the
circuit 18 acts in the described manner, to halt themotor 2 and activate theheating element 21. - Following defrosting of the evaporator, the
motor 2 is again operated and theheating element 21 switched off (as already described). - Figure 6 shows a further embodiment of the invention. In this figure, parts corresponding to those of the previously described figures are indicated by the same reference numerals.
- In Figure 6 there is no control feedback to the fan motor because in this case the motor used is a known high-efficiency motor with a very constant torque-r.p.m. characteristic. This motor, indicated by 2A in the figure, operates at constant voltage and known r.p.m. It is "current" controlled, ie the
resistor 40 is connected into thebranch 4A and itsends branches current sensor 47. - During refrigerator operation, if the frost thickness on the evaporator is unable to substantially hinder the flow of air grazing the evaporator, the
current sensor 47 generates a signal VH substantially close to or less than the threshold signal VE. - When a considerable frost layer forms on the
evaporator 102 the signal VH becomes considerably greater than the signal VE. Thecircuit 18 therefore generates the signal VC, which results in stoppage of themotor 2 and operation of theheating element 21. - After the evaporator has been defrosted, the motor is again operated in the described manner and the
element 21 switched off. - With reference to Figures 3 to 6, devices for implementing the method of the invention have been described in which the frost on the evaporator is evaluated indirectly by measuring the variation in a characteristic of the
motor 2 of the fan 3 (r.p.m., absorbed power, absorbed voltage or current). - However the method of the invention can be implemented by direct measurement of the flow rate of the air leaving the aperture 105 (arrow F) or returning to the
evaporator 102 through the aperture 106 (arrow G). - Embodiments of devices which enable the method to be implemented in this form are shown in Figures 7 to 9. In these figures, parts corresponding to those of the previously described figures are indicated by the same reference numerals.
- Figures 7 and 8 show a flow rate measurement member 90 positioned in correspondence with the
aperture 105. This member is ausual anemometer 91 connected to acontrol circuit 92. This latter receives a signal VM generated by the anemometer (a function of the air flow rate through the aperture 105) and compares this with a reference signal VRIF corresponding to a minimum acceptable air flow rate (corresponding to a maximum acceptable frost quantity on tile evaporator 102). If VM is less than VRIF (ie the frost has reduced the air flow leaving theaperture 105 to too low a value), thecircuit 92 operates theswitch 23 to halt themotor 2, and operates theheating element 21. The evaporator is therefore defrosted and themember 5 simultaneously halts the operation of the refrigerator 1, in the described manner. - When defrosting is complete the member senses that the frost has been removed from the evaporator and causes the
circuit 92, via anelectrical branch 93, to halt the operation of theelement 92 and close theswitch 23. Themember 5 hence reactivates the refrigerator. - In Figure 9, two
pressure sensors apertures circuit 92 senses a pressure difference between theapertures - If the frost reduces the air flow this pressure difference decreases. The
circuit 92 measures this (for example by making a usual comparison between the signals VO and VP from the sensors, this latter being considered the reference signal) and acting on theheating element 21 and switch 23 as already described in relation to Figures 7 and 8. - When defrosting is complete, the motor is returned to operation and the
element 21 switched off in the previously described manner. - Various embodiments of the invention have been described. However further embodiments are possible, to be considered as falling within the scope of the present document.
- For example, the
anemometer 91 can be replaced by a heated wire grazed by the air leaving theaperture 105. This wire involves a current and generates across its ends a potential difference which is proportional to the cooling which it undergoes as a result of the air striking it, so changing its resistance. As the flow rate of the air striking it changes, so does the potential difference across its ends. By measuring this (in any known manner, for example by a circuit analogous to thecircuit 92 of Figure 8), when the potential difference reaches a predetermined value the control circuit associated with the wire acts to halt the motor and activate the heating element.
Claims (26)
- A method for evaluating frost formation on an evaporator in a refrigerator, in particular of the forced-air circulation type and comprising a cabinet containing one or more temperature-controlled compartments provided with their own access doors and arranged to contain food during its preservation, there being provided on the wall of the compartment in which the evaporator is located at least one heating element which when activated defrosts the evaporator, and a fan driven by a usual electric motor connected to an electrical power line for circulating air through the evaporator and for ventilating the compartment or compartments via usual ducts provided within said cabinet, said fan, to achieve said circulation, cooperating with a usual conveying member to direct the air circulating within said compartment or compartments onto the evaporator so that the air is again cooled, said method being characterised by evaluating the variation in the flow rate of the air grazing the evaporator (102) with respect to a flow rate reference value, determining the quantity of frost present on the surface of the evaporator (102) on the basis of this evaluation, and then if necessary activating the heating element (21) associated with the evaporator.
- A method as claimed in claim 1, characterised in that the variation in the air flow rate is measured directly.
- A method as claimed in claim 2, characterised in that the direct measurement of the air flow rate is made as the air enters the compartment (100) of the refrigerator (1).
- A method as claimed in claim 2, characterised in that the direct measurement of the air flow rate is made by comparing the difference between the pressure of the air fed into the refrigerator compartment (100) and that of the air returning from said compartment to the evaporator (102).
- A method as claimed in claim 1, characterised in that the flow rate variation is evaluated indirectly by measuring the variation in an intrinsic characteristic of the motor (2) operating the fan (3).
- A method as claimed in claim 5, characterised in that the measured characteristic is the voltage absorbed from the mains by the motor (2) when operating at a constant r.p.m.
- A method as claimed in claim 5, characterised in that the measured characteristic is the current absorbed from the mains by the motor (2) when operating at a constant r.p.m.
- A method as claimed in claim 5, characterised in that the measured characteristic is the power absorbed from the mains by the motor (2) when operating at a constant r.p.m.
- A method as claimed in claim 5, characterised in that the measured characteristic is the r.p.m. of the motor (2) when operating at constant voltage, and hence of the fan (3).
- A device for implementing the method claimed in claim 1, characterised by comprising switch means (23) connected into the line (4) powering the motor (2) of the fan (3), sensor means (15, 8, 47, 50) for sensing an intrinsic characteristic of the fan (3) or of its motor (2) and generating a signal (VB, VD , VG, VH) relative to the fan operating condition, said signal being fed to comparison and control means (18) which compare it with a reference signal (VE) and on the basis of this comparison act on the switch means (23) to change the operating conditions of the fan (3), and on the heating element (21) to activate it to achieve defrosting of the evaporator (102).
- A device as claimed in claim 10, characterised in that the fan motor (2) operates at constant voltage and the sensor means are a tachometer dynamo (15).
- A device as claimed in claim 10, characterised in that the fan motor (2) operates at constant r.p.m. and the sensor means are a known integrator circuit (8).
- A device as claimed in claim 10, characterised in that the fan motor (2) operates at constant r.p.m., said motor being preferably of high-efficiency type, and the sensor means are a known current measurement member (47) connected to the ends (41, 42) of a resistor (40) connected in series with said motor (2).
- A device as claimed in claim 10, characterised in that the fan motor (2) operates at constant r.p.m. and the sensor means are a multiplier member (50) connected to an integrator circuit (8) measuring the voltage absorbed from the mains by the motor (2), and to a current measurement member (47) measuring the current absorbed from the mains by the motor (2), said multiplier member (50) generating a signal (VD) fed to the comparison means (18) and corresponding to the power absorbed from the mains by said motor (2).
- A device as claimed in claim 10, characterised in that the comparison means are a comparator circuit (18) or an equivalent member.
- A device as claimed in claim 15, characterised in that the comparison means are connected to an actuator member (28) for opening or closing the switch means (23).
- A device as claimed in claim 10, characterised in that the operation of the fan motor (2) is controlled by a control member (5) which preferably controls the operation of the refrigerator.
- A device as claimed in claim 17, characterised in that the control member (5) is operationally connected to switch means (31) in an electrical line (20) connecting the comparison means (18) to the heating element (21).
- A device as claimed in claim 17, characterised in that the control member is a microprocessor circuit.
- A device for implementing the method claimed in claim 1, characterised by comprising means (91; 105; 106) for measuring the flow rate of the air circulated by the fan (3) through the compartment (100) and cooled by the evaporator (102), said means (91; 105; 106) generating an electrical signal based on the measured flow rate, said signal being fed to comparison and control means (92) which compare it with a reference signal, said means (92), on the basis of this comparison, acting on switch means (23) connected into power line (4) to the fan motor (2) to change the fan operating conditions, and activating the heating element (21) to defrost the evaporator.
- A device as claimed in claim 20, characterised in that the flow rate measurement means are an anemometer (91) located in correspondence with the region (105) in which the cold air is fed into the refrigerator compartment (100).
- A device as claimed in claim 20, characterised in that the flow rate measurement means are a conductor of wire form maintained at relatively high temperature and involving current, said wire being positioned in correspondence with the region (105) in which air is fed into the refrigerator compartment (100).
- A device as claimed in claim 20, characterised in that the measurement means are pressure sensors (94, 94) positioned in correspondence with the passages (105, 106) through which the air passes to the compartment (100) and from this latter to the evaporator (102).
- A device as claimed in claims 20 and 23, characterised in that the reference signal is the signal (VP) generated by the pressure sensor (95) positioned in correspondence with the passage (106) though which the air passes towards the evaporator (102).
- A device as claimed in claim 20, characterised in that a circuit (5) for controlling the operation of the fan motor (2A) is connected to and operates on the comparison means (92).
- A device as claimed in claim 20, characterised in that the reference signal corresponds to the flow rate of the air grazing the evaporator (102) when this is substantially free of frost.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
ITMI920755 | 1992-03-30 | ||
ITMI920755A IT1254854B (en) | 1992-03-30 | 1992-03-30 | METHOD AND DEVICE FOR DETECTING THE FORMATION OF RAIN ON AN EVAPORATOR OF A REFRIGERATOR, IN PARTICULAR OF THE FORCED AIR CIRCULATION TYPE |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0563724A1 true EP0563724A1 (en) | 1993-10-06 |
EP0563724B1 EP0563724B1 (en) | 1996-09-18 |
Family
ID=11362693
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP93104634A Expired - Lifetime EP0563724B1 (en) | 1992-03-30 | 1993-03-22 | Method and device for evaluating frost formation on an evaporator in a refrigerator, in particular of the forced-air circulation type |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0563724B1 (en) |
DE (1) | DE69304761T2 (en) |
IT (1) | IT1254854B (en) |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE19533957A1 (en) * | 1994-09-15 | 1996-03-21 | Lg Electronics Inc | Defrosting appts. for refrigerator |
DE10019905A1 (en) * | 2000-04-20 | 2001-10-31 | Bosch Gmbh Robert | Method and device for detecting the risk of icing in pumps used for tank leak diagnosis in motor vehicles |
DE10057006C1 (en) * | 2000-11-17 | 2002-05-23 | Friedhelm Meyer | Operating method, for climate control and cooling plant, uses ionization of air to be cooled before passing over cooler for preventing moisture deposition |
DE10116693A1 (en) * | 2001-04-04 | 2002-10-17 | Bosch Gmbh Robert | Heated tank leak diagnosis unit, in particular for motor vehicles |
WO2004088221A1 (en) * | 2003-04-04 | 2004-10-14 | BSH Bosch und Siemens Hausgeräte GmbH | Refrigeration device with adaptive automatic defrosting and corresponding defrosting method |
CN113237684A (en) * | 2021-05-20 | 2021-08-10 | 长虹美菱股份有限公司 | Test method for evaluating frosting degree of freezing chamber of refrigerator |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE102021201380A1 (en) | 2021-02-15 | 2022-08-18 | Volkswagen Aktiengesellschaft | Method for initiating a defrosting process of a heat exchanger of a heat pump of a motor vehicle |
DE102021201377A1 (en) | 2021-02-15 | 2022-08-18 | Volkswagen Aktiengesellschaft | Method for initiating a defrosting process of a heat exchanger of a heat pump of a motor vehicle |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3728867A (en) * | 1971-04-29 | 1973-04-24 | Ranco Inc | Defrost control system |
GB2033582A (en) * | 1978-10-31 | 1980-05-21 | Dart Ausschank Rat Tech | Liquid metering method and device |
US4806833A (en) * | 1986-09-22 | 1989-02-21 | General Electric Company | System for conditioning air, method of operating such, and circuit |
-
1992
- 1992-03-30 IT ITMI920755A patent/IT1254854B/en active IP Right Grant
-
1993
- 1993-03-22 DE DE69304761T patent/DE69304761T2/en not_active Expired - Fee Related
- 1993-03-22 EP EP93104634A patent/EP0563724B1/en not_active Expired - Lifetime
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3728867A (en) * | 1971-04-29 | 1973-04-24 | Ranco Inc | Defrost control system |
GB2033582A (en) * | 1978-10-31 | 1980-05-21 | Dart Ausschank Rat Tech | Liquid metering method and device |
US4806833A (en) * | 1986-09-22 | 1989-02-21 | General Electric Company | System for conditioning air, method of operating such, and circuit |
Non-Patent Citations (1)
Title |
---|
PATENT ABSTRACTS OF JAPAN vol. 010, no. 356 (E-459)29 November 1986 & JP-A-61 154 496 ( MITSUBISHI ELECTRIC ) * |
Cited By (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE19533957A1 (en) * | 1994-09-15 | 1996-03-21 | Lg Electronics Inc | Defrosting appts. for refrigerator |
DE10019905A1 (en) * | 2000-04-20 | 2001-10-31 | Bosch Gmbh Robert | Method and device for detecting the risk of icing in pumps used for tank leak diagnosis in motor vehicles |
DE10019905C2 (en) * | 2000-04-20 | 2002-04-25 | Bosch Gmbh Robert | Method and device for detecting the risk of icing in pumps used for tank leak diagnosis in motor vehicles |
US6446615B2 (en) | 2000-04-20 | 2002-09-10 | Robert Bosch Gmbh | Method and arrangement for detecting icing in pumps utilized in the diagnosis of tank leakage in motor vehicles |
DE10057006C1 (en) * | 2000-11-17 | 2002-05-23 | Friedhelm Meyer | Operating method, for climate control and cooling plant, uses ionization of air to be cooled before passing over cooler for preventing moisture deposition |
DE10116693A1 (en) * | 2001-04-04 | 2002-10-17 | Bosch Gmbh Robert | Heated tank leak diagnosis unit, in particular for motor vehicles |
US6959587B2 (en) | 2001-04-04 | 2005-11-01 | Robert Bosch Gmbh | Heatable tank leakage diagnosis unit, particularly for motor vehicles |
WO2004088221A1 (en) * | 2003-04-04 | 2004-10-14 | BSH Bosch und Siemens Hausgeräte GmbH | Refrigeration device with adaptive automatic defrosting and corresponding defrosting method |
CN113237684A (en) * | 2021-05-20 | 2021-08-10 | 长虹美菱股份有限公司 | Test method for evaluating frosting degree of freezing chamber of refrigerator |
CN113237684B (en) * | 2021-05-20 | 2022-05-10 | 长虹美菱股份有限公司 | Test method for evaluating frosting degree of freezing chamber of refrigerator |
Also Published As
Publication number | Publication date |
---|---|
DE69304761D1 (en) | 1996-10-24 |
IT1254854B (en) | 1995-10-11 |
EP0563724B1 (en) | 1996-09-18 |
ITMI920755A0 (en) | 1992-03-30 |
ITMI920755A1 (en) | 1993-09-30 |
DE69304761T2 (en) | 1997-03-20 |
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