US20160018142A1 - Expansion valve with variable opening degree - Google Patents

Abstract

An expansion valve (4) for a vapour compression system (1), and a vapour compression system comprising such an expansion valve (4) are disclosed. The expansion valve (4) comprises a first valve member (7) and a second valve member (8). The first valve member (7) and the second valve member (8) are arranged movably relative to each other, and the relative position of the first valve member (7) and the second valve member (8) determines an opening degree of the expansion valve (4). The first valve member (7) and/or the second valve member (8) is/are automatically movable in response to changes in a differential pressure across the expansion valve (4), the opening degree of the expansion valve (4) thereby being automatically altered in response to changes in the differential pressure across the expansion valve (4). It is ensured that the opening degree of the expansion valve is automatically adjusted to the actual operating conditions, thereby optimising the efficiency of the vapour compression system. Furthermore, this is obtained in a simple manner, without requiring complicated control of the valve.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. patent application Ser. No. 13/990,449, filed on May 30, 2013, which is the National Stage of International Patent Application No. PCT/DK2011/000143 filed on Nov. 30, 2011 and Danish Patent Application No. PA 2010 01086, filed Nov. 30, 2010, the contents of which are incorporated by reference.
TECHNICAL FIELD
• The present invention relates to an expansion valve, in particular an expansion valve for a vapour compression system, such as a refrigeration system, an air condition system or a heat pump. The expansion valve of the invention is capable of defining a variable opening degree. The present invention further relates to a vapour compression system comprising such an expansion valve.
BACKGROUND
• Vapour compression systems, such as refrigeration systems, air condition systems or heat pumps, normally comprise a compressor, a condenser, an expansion device, e.g. in the form of an expansion valve, and an evaporator arranged along a refrigerant path. Refrigerant circulates the refrigerant path and is alternatingly compressed and expanded. Heat exchange takes place in the condenser and the evaporator, and it is thereby possible to provide cooling or heating to a closed volume, e.g. a room or a refrigerated compartment or box.
• In the case that the expansion device is in the form of an expansion valve, the expansion valve expands the refrigerant and controls the supply of refrigerant to the evaporator. The amount of refrigerant supplied to the evaporator is determined by the opening degree of the expansion valve.
• To this end a fixed orifice expansion valve may be used. A fixed orifice expansion valve supplies refrigerant to the evaporator via an orifice with a fixed size. This is very simple, and the valve is easy and cost effective to manufacture. However, it is not possible to adjust the supply of refrigerant to the evaporator, e.g. in response to a measured value of the superheat of refrigerant leaving the evaporator, because it is not possible to adjust the opening degree.
• In vapour compression systems where it is necessary or desirable to be able to control the refrigerant supply to the evaporator, a thermostatic expansion valve may be used. The opening degree of a thermostatic expansion valve is adjustable, and an opening degree which accurately results in a desired superheat value can therefore be selected at any given time. However, thermostatic expansion valves are relatively expensive, and they are therefore normally not applied in low cost vapour compression systems.
SUMMARY
• It is an object of embodiments of the invention to provide an expansion valve which allows an opening degree to be adjusted, without increasing the manufacturing costs significantly.
• It is a further object of embodiments of the invention to provide an expansion valve which is cost effective to manufacture, without significantly compromising the operability and efficiency of the expansion valve.
• According to a first aspect the invention provides an expansion valve for a vapour compression system, the expansion valve comprising a first valve member and a second valve member, the first valve member and the second valve member being arranged movably relative to each other, wherein the relative position of the first valve member and the second valve member determines an opening degree of the expansion valve, and wherein the first valve member and/or the second valve member is/are automatically movable in response to changes in a differential pressure across the expansion valve, the opening degree of the expansion valve thereby being automatically altered in response to changes in the differential pressure across the expansion valve.
• In the present context the term ‘vapour compression system’ should be interpreted to mean any system in which a flow of fluid medium, such as refrigerant, circulates and is alternatingly compressed and expanded, thereby providing either refrigeration or heating of a volume. Thus, the vapour compression system may be a refrigeration system, an air condition system, a heat pump, etc. The vapour compression system, thus, comprises a compressor, a condenser, an expansion device, e.g. in the form of an expansion valve, and an evaporator arranged along a refrigerant path.
• The expansion valve is arranged in the refrigerant path immediately upstream relatively to the evaporator. Thereby the expansion valve expands the refrigerant and controls the supply of expanded refrigerant to the evaporator.
• The expansion valve comprises a first valve member and a second valve member. The first valve member and the second valve member are arranged movably relative to each other. This may be obtained by allowing the first valve member to move while the second valve member is fixed relative to the remaining parts of the expansion valve, by allowing the second valve member to move while the first valve member is fixed relative to the remaining parts of the expansion valve, or by allowing the first valve member as well as the second valve member to move, as long as the movements of the first and second valve members results in a relative movement between the valve members.
• The relative position of the first valve member and the second valve member determines an opening degree of the expansion valve, i.e. the opening degree of the expansion valve is altered when the relative position of the first valve member and the second valve member is changed.
• The first valve member and/or the second valve member is/are automatically movable in response to changes in a differential pressure across the expansion valve. Thus, when the differential pressure across the expansion valve is changed, the first valve member and/or the second valve member is/are automatically moved, thereby changing the relative position of the valve members. Since the opening degree of the expansion valve is determined by the relative position between the valve members, the opening degree is thereby changed. Accordingly, the opening degree of the expansion valve is automatically altered in response to changes in the differential pressure across the expansion valve.
• Thereby the opening degree of the expansion valve is automatically adjusted to correspond to a differential pressure which is presently occurring across the expansion valve. This allows the expansion valve to be operated with one opening degree at low differential pressures and with another opening degree at high differential pressures. This is, e.g., desirable when the expansion valve is arranged in a vapour compression system comprising a compressor being capable of operating a two different capacity levels. The two different compressor capacity levels results in two distinct differential pressure levels across the expansion valve. The opening degree of the expansion valve of the invention is automatically altered when the compressor capacity is changed, thereby allowing the vapour compression system to be operated in an optimal manner at both compressor capacity levels.
• The efficiency of vapour compression systems, such as residential air condition systems, is normally evaluated by means of the so-called ‘Seasonal Energy Efficiency Ratio’ (SEER). SEER rating is a well known standard which permits consumers to compare operating costs of various air condition systems and products. It is calculated as the ratio of the total cooling output over the cooling season and the total electrical energy input over the cooling season. In practice, when an air condition system is rated in accordance with the SEER rating, the efficiency of the system is often evaluated at two selected and weighted operating points, corresponding to expected actual operating conditions, i.e. a low compressor capacity operating point, corresponding to low outdoor temperature, and a high compressor capacity operating point, corresponding to high outdoor temperature. It is therefore an advantage of the expansion valve of the present invention that it allows the vapour compression system to be operated in an optimal manner at such two operating points, because it is thereby possible to obtain a good SEER rating, and an improved efficiency as compared to fixed orifice expansion valves.
• Furthermore, since the opening degree of the expansion valve is altered automatically in response to changes in the differential pressure, the adjustment of the opening degree is obtained without the requirement of complicated control of the expansion device, e.g. of the kind which is used for controlling thermostatic expansion valves. Thereby good energy efficiency and a good SEER rating can be obtained at low costs.
• The first valve member and/or the second valve member may be movable between a first relative position defining a first opening degree at a first differential pressure, and a second relative position defining a second opening degree at a second differential pressure, said second differential pressure being higher than the first differential pressure. The first and/or second valve member may be movable between the two positions in a manner which changes the opening degree discretely, i.e. in such a manner that the opening degree ‘jumps’ directly from the first opening degree to the second opening degree, or vice versa, when the differential pressure reaches a threshold value. As an alternative, the opening degree may change smoothly between the first opening degree and the second opening degree as a function of the differential pressure.
• The first opening degree may be larger than the second opening degree. According to this embodiment, the opening degree of the expansion valve is relatively large at a low differential pressure, corresponding to low compressor capacity, and smaller at a high differential pressure, corresponding to high compressor capacity. At high differential pressures, the fluid flow through an orifice of a given size is higher than at low differential pressures. It is therefore desirable to have a smaller opening degree at high differential pressures, thereby decreasing the fluid flow at high differential pressures and obtaining an optimal refrigerant supply to the evaporator at all differential pressure levels. Furthermore, in the case that a two step compressor is used, a larger opening degree is required at low capacity, and thereby low differential pressure, than at high capacity, and thereby high differential pressure.
• The first valve member may be provided with a fluid passage corresponding to the first opening degree and the second valve member may be provided with a fluid passage corresponding to the second opening degree. According to this embodiment, the fluid flow through the expansion valve is determined by the fluid passage provided in the first valve member when the first valve member and the second valve member are in the first relative position. Correspondingly, the fluid flow through the expansion valve is determined by the fluid passage provided in the second valve member when the first valve member and the second valve member are in the second relative position.
• As an alternative, one of the valve members may be provided with a fluid passage, and the other valve member may be arranged in such a manner that it partly blocks the fluid passage, the unblocked part of the fluid passage defining the opening degree of the expansion valve. The blocking valve member may, e.g., comprise a protruding part having a conical shape and being arranged movably in the fluid passage.
• The first relative position may define a mutual distance between the first valve member and the second valve member, and the first valve member and the second valve member may be arranged substantially in abutment with each other in the second relative position. According to this embodiment, the abutment position may cause one or more fluid passages through the expansion valve to be partly or fully blocked.
• According to an alternative embodiment, the first valve member may be or comprise a hollow conical part, and the second valve member may be arranged in such a manner that relative movements of the first and second valve parts causes the second valve member to squeeze the first valve member, thereby altering the cross sectional size of a fluid passage defined through the hollow conical part.
• The expansion valve may further comprise guiding means arranged for controlling the relative movements of the first valve member and the second valve member in response to changes in the differential pressure across the expansion valve. The guiding means may, e.g., be in the form of mating conical parts formed on the valve members, or in the form of grooves formed on one of the valve members and protruding parts formed on the other valve member. According to this embodiment, the relative movements of the first and second valve members is accurately controlled, due to the guiding means, thereby providing very accurate control of the opening degree of the expansion valve in response to changes in the differential pressure across the expansion valve.
• The expansion valve may further comprise mechanical biasing means arranged to mechanically bias the first valve member and the second valve member in a direction away from each other. The mechanical biasing means may, e.g., comprise a compressible spring arranged between the valve members. Alternatively, the mechanical biasing means may comprise a member made from a resilient material or any other suitable kind of mechanical biasing means. According to this embodiment, the valve members are moved against the biasing force of the mechanical biasing means when they are moved towards each other. The mechanical biasing means may be selected and/or adjusted in such a manner that desired relative movements of the valve members are obtained in response to changes in the differential pressure across the expansion valve during normal operation of the expansion valve, thereby obtaining that the opening degree of the expansion valve is altered in a desired manner.
• The expansion valve may further comprise a reverse flow mechanism for selectively allowing a substantially unrestricted reverse fluid flow through the valve. According to this embodiment, the expansion valve may be applied in a vapour compression system in which the fluid flow is reversible. This is, e.g., desirable in vapour compression systems which are capable of operating in an air condition mode as well as in a heat pump mode. Thereby heating or refrigeration may selectively be provided for a room, depending on the outdoor temperature. In order to allow this, the fluid flow must be reversible, and the condenser must be capable of operating as an evaporator and the evaporator as a condenser. Therefore the expansion valve must also be capable of allowing a substantially unrestricted reverse fluid flow to pass through the expansion valve. This is provided by the reverse flow mechanism.
• The reverse flow mechanism may, e.g., comprise a bypass fluid passage which is opened when the fluid flow is reversed. Alternatively or additionally, a reverse fluid flow may push the first valve member and the second valve member into a relative position, e.g. far from each other, which allows a substantially unrestricted reverse fluid flow to pass through the expansion valve.
• According to a second aspect the invention provides a vapour compression system comprising a compressor, a condenser, an evaporator and an expansion valve according to the first aspect of the invention, the compressor, the condenser, the expansion valve and the evaporator being arranged along a refrigerant path.
• It should be noted that a person skilled in the art would readily recognise that any feature described in combination with the first aspect of the invention could also be combined with the second aspect of the invention, and vice versa.
• The compressor may be a two-step compressor. As described above, the two steps of the compressor defines two distinct differential pressures across the expansion valve. Since the expansion valve is an expansion valve according to the first aspect of the invention, the opening degree of the expansion valve is influenced when the compressor capacity is switched between the two steps, and the differential pressure across the expansion valve is thereby changed, as described above. The expansion valve of the first aspect of the invention is therefore very suitable for use in a vapour compression system comprising a two-step compressor.
• The vapour compression system may be a refrigeration system, such as an air condition system or a refrigeration system of the kind being used in a supermarket. Alternatively, the vapour compression system may be a heat pump, or it may be a vapour compression system which is capable of operating in an air condition mode as well as in a heat pump mode.
BRIEF DESCRIPTION OF THE DRAWINGS
• In the following the invention will be described in further detail with reference to the accompanying drawings in which
• FIG. 1 is a diagrammatic view of a vapour compression system according to an embodiment of the invention,
• FIG. 2ais a side view andFIG. 2bis a cross sectional view of an expansion valve according to a first embodiment of the invention, the expansion valve being in a first position,
• FIG. 3ais a side view andFIG. 3bis a cross sectional view of the expansion valve according to the first embodiment of the invention, the expansion valve being in a second position,
• FIG. 4 is a cross sectional view of the expansion valve according to the first embodiment of the invention, arranged in a refrigerant path of a vapour compression system, the expansion valve being in the first position,
• FIG. 5 is a cross sectional view of the expansion valve according to the first embodiment of the invention, arranged in a refrigerant path of a vapour compression system, the expansion valve being in the second position,
• FIG. 6 is an exploded view of the expansion valve according to the first embodiment of the invention, seen from a first direction,
• FIG. 7 is an exploded view of the expansion valve according to the first embodiment of the invention, seen from a second direction,
• FIG. 8 is a cross sectional view of an expansion valve according to a second embodiment of the invention, the expansion valve being in a first position,
• FIG. 9 is a cross sectional view of the expansion valve according to the second embodiment of the invention, the expansion valve being in a second position,
• FIG. 10 is a cross sectional view of the expansion valve according to the second embodiment of the invention, during a reverse fluid flow through the expansion valve,
• FIG. 11 is an end view of the expansion valve according to the second embodiment of the invention, and
• FIGS. 12 and 13 are graphs illustrating opening degree of an expansion valve according to two embodiments of the invention as a function of differential pressure across the expansion valve.
DETAILED DESCRIPTION
• FIG. 1 is a diagrammatic view of a vapour compression system1 according to an embodiment of the invention. The vapour compression system1 comprises acompressor2, acondenser3, anexpansion valve4 and anevaporator5 arranged along a refrigerant path. During operation, refrigerant flowing in the refrigerant path is compressed in thecompressor2. The compressed refrigerant is supplied to thecondenser3, where it condenses, the refrigerant leaving thecondenser3 thereby being in a substantially liquid state. The refrigerant is then supplied to theexpansion valve4 where it is expanded, thereby forming a mixed state refrigerant, i.e. a mixture of gaseous and liquid refrigerant is supplied from theexpansion valve4 to theevaporator5. In theevaporator5, the liquid part of the refrigerant is evaporated while exchanging heat with a secondary fluid flow, such as an air flow, across theevaporator5, illustrated byarrows6. Finally, the refrigerant is once again supplied to thecompressor2, thereby completing the cycle.
• FIG. 2ais a side view of anexpansion valve4 according to a first embodiment of the invention. Theexpansion valve4 comprises afirst valve member7 and asecond valve member8. Thefirst valve member7 and thesecond valve member8 are arranged in such a manner that they may perform relative movements. This will be described further below with reference toFIGS. 4 and 5. Acompressible spring9 is arranged between thefirst valve member7 and thesecond valve member8, thereby biasing thefirst valve member7 and thesecond valve member8 in a direction away from each other.
• InFIG. 2athefirst valve member7 and thesecond valve member8 are arranged in a first relative position, where a distance is defined between thefirst valve member7 and thesecond valve member8. It is clear fromFIG. 2athat it is possible to compress thecompressible spring9 further, thereby moving thefirst valve member7 and thesecond valve member8 towards each other, against the spring force of thecompressible spring9.
• FIG. 2bis a cross sectional view of the expansion valve ofFIG. 2a. InFIG. 2bit can be seen that thefirst valve member7 is provided with anopening10 defining a fluid passage through thefirst valve member7, theopening10 having a first diameter. When thefirst valve member7 and thesecond valve member8 are in the first relative position shown inFIGS. 2aand2b, the fluid flow through theexpansion valve4 is determined by the diameter of theopening10.
• Thefirst valve member7 is further provided with aconical portion11 extending towards thesecond valve member8. Theconical portion11 of thefirst valve member7 is capable of guiding a matingconical portion12 formed on thesecond valve member8. Thereby it is ensured that theconical portions11,12 are arranged in abutment when thefirst valve member7 and thesecond valve member8 are moved towards each other. This will be described in further detail below with reference toFIGS. 3aand3b.
• Theconical portion11 of thesecond valve member8 is also provided with anopening13. Theopening13 of thesecond valve member8 has a smaller diameter than theopening10 of thefirst valve member7. However, when thefirst valve member7 and thesecond valve member8 are in the first relative position shown inFIGS. 2aand2b, the diameter of theopening13 of thesecond valve member8 is not limiting for the fluid flow through theexpansion valve4, because fluid is allowed to flow past theconical portion11 of thesecond valve member8, since theconical portion11 is attached to the remaining parts of thesecond valve member8 by means of a number ofribs14.
• FIG. 3ais a side view of theexpansion valve4 according to the first embodiment of the invention, shown inFIGS. 2aand2b. InFIG. 3athefirst valve member7 and thesecond valve member8 are arranged in a second relative position, where thevalve members7,8 are as close to each other as possible, actually in abutment with each other. It is clear fromFIG. 3athat thecompressible spring9 is completely compressed in this position.
• FIG. 3bis a cross sectional view of theexpansion valve4 according to the first embodiment of the invention, theexpansion valve4 being in the second position shown inFIG. 3a. FromFIG. 3bit is clear that thefirst valve member7 and thesecond valve member8 are arranged completely in abutment in this relative position. In particular, it is clear that theconical portion12 of thesecond valve member8 is arranged inside theconical portion11 of thefirst valve member7 in such a manner that theopening10 defined by thefirst valve member7 and theopening13 defined by thesecond valve member8 are arranged adjacent to each other. Thereby a fluid flow passing through theexpansion valve4 when thevalve members7,8 are in this relative position, must pass through theopening13 defined by thesecond valve member8. Since the diameter of theopening13 defined by thesecond valve member8 is smaller than the diameter of theopening10 defined by thefirst valve member7, the opening degree of theexpansion valve4 is reduced as compared to the situation illustrated inFIGS. 2aand2b.
• FIG. 4 is a cross sectional view of anexpansion valve4 according to the first embodiment of the invention, theexpansion valve4 being arranged in arefrigerant path15 of a vapour compression system. Theexpansion valve4 is arranged immediately upstream relative to an evaporator (not shown), i.e. it is arranged in the liquid line of the evaporator. InFIG. 4 thefirst valve member7 and thesecond valve member8 of theexpansion valve4 are in the first relative position which is also illustrated inFIGS. 2aand2b.
• Thesecond valve member8 is arranged substantially immovably relatively to therefrigerant path15, and thefirst valve member7 is arranged movably relatively to thesecond valve member8. The position of thefirst valve member7 is determined by the differential pressure across theexpansion valve4 of the refrigerant flowing in therefrigerant path15. Refrigerant flowing in therefrigerant path15 and through theexpansion valve4 flows in a direction from thefirst valve member7 towards thesecond valve member8, i.e. along the direction indicated byarrow16. Thus, when the differential pressure across theexpansion valve4 is increased, thefirst valve member7 will be forced towards thesecond valve member8, against the spring force of thecompressible spring9. As long as thevalve members7,8 are arranged with a mutual distance, the opening degree of theexpansion valve4 will be determined by the diameter of theopening10 defined by thefirst valve member7, as described above with reference toFIG. 2b. Thus, the opening degree of theexpansion valve4 is, in this case, as large as possible. In the situation illustrated inFIG. 4 thefirst valve member7 is arranged far from thesecond valve member8, i.e. the differential pressure across theexpansion valve4 is, in this case, relatively low. Thus,FIG. 4 illustrates that a low differential pressure across theexpansion valve4 results in a large opening degree of theexpansion valve4.
• FIG. 5 is a cross sectional view of theexpansion valve4 according to the first embodiment of the invention, arranged in arefrigerant path15, similarly to the situation shown inFIG. 4. Theexpansion valve4 is arranged immediately upstream relative to an evaporator (not shown), i.e. it is arranged in the liquid line of the evaporator. However, inFIG. 5 thefirst valve member7 and thesecond valve member8 are arranged in the second relative position illustrated inFIGS. 3aand3b, i.e. thefirst valve member7 and thesecond valve member8 are arranged substantially in abutment with each other. As described below with reference toFIG. 3b, the opening degree of the expansion valve is, in this situation, determined by the diameter of theopening13 of thesecond valve member8. Since the diameter of theopening13 of thesecond valve member8 is smaller than the diameter of theopening10 of thefirst valve member7, the opening degree of theexpansion valve4 in the situation illustrated inFIG. 5 is smaller than the opening degree of theexpansion valve4 in the situation illustrated inFIG. 4.
• The position of thefirst valve member7 as close as possible to thesecond valve member8 indicates that the differential pressure across theexpansion valve4 is relatively high. Thus,FIG. 5 illustrates that a high differential pressure across theexpansion valve4 automatically results in a small opening degree of theexpansion valve4.
• FIGS. 6 and 7 are exploded views of theexpansion valve4 according to the first embodiment of the invention, seen from two different angles. Thefirst valve member7, thesecond valve member8 and thecompressible spring9 are clearly seen. Furthermore, details of thefirst valve member7 and thesecond valve member8 can be seen, such as theconical sections11,12 and theopenings10,13.
• FIG. 8 is a cross sectional view of anexpansion valve4 according to a second embodiment of the invention. Theexpansion valve4 is arranged in arefrigerant path15 of a vapour compression system. Theexpansion valve4 comprises afirst valve member7 and asecond valve member8. Thesecond valve member8 is arranged substantially immovable relatively to therefrigerant path15, and thefirst valve member7 is arranged movably relative to thesecond valve member8. Acompressible spring9 is arranged between thefirst valve member7 and thesecond valve member8, biasing thevalve members7,8 in a direction away from each other.
• Thesecond valve member8 is provided with anopening17 defining a fluid passage through theexpansion valve4. Thefirst valve member7 comprises a protrudingelement18 extending in a direction towards thesecond valve member8. The protrudingelement18 has a conical shape, i.e. the diameter of the protrudingelement18 varies along a longitudinal direction of the protrudingelement18.
• During normal operation of the vapour compression system, refrigerant flows in therefrigerant path15 and through theexpansion valve4 along a direction from thefirst valve member7 towards thesecond valve member8, i.e. along the direction indicated byarrow16. Thus, if the differential pressure across theexpansion valve4 increases, thefirst valve member7 will be forced in a direction towards thesecond valve member8, against the spring force of thecompressible spring9. Similarly, if the differential pressure across theexpansion valve4 decreases, thefirst valve member7 will move in the opposite direction, away from thesecond valve member8.
• InFIG. 8 the protrudingelement18 of thefirst valve member7 is arranged in theopening17 of thesecond valve member8, thereby blocking a part of the fluid passage defined by theopening17. Due to the conical shape of the protrudingelement18, the relative position between thefirst valve member7 and thesecond valve member8 determines how large a part of the fluid passage is blocked by the protrudingelement18. Thereby the relative position also determines the size of the remaining passage. Accordingly, the relative position determines the fluid flow through theexpansion valve4, and thereby the opening degree of theexpansion valve4. InFIG. 8 thefirst valve member7 is arranged in a position which defines a relatively large opening degree of theexpansion valve4, indicating that the differential pressure across theexpansion valve4 is relatively low.
• A stoppingmember19 is arranged in therefrigerant path15 upstream relatively to theexpansion valve4. The function of the stoppingmember19 will be described in further detail below with reference toFIG. 10.
• FIG. 9 is a cross sectional view of theexpansion valve4 according to the second embodiment of the invention. InFIG. 9 the differential pressure across theexpansion valve4 is higher than in the situation illustrated inFIG. 8. Accordingly, thefirst valve member7 has been moved towards thesecond valve member8, against the spring force of thecompressible spring9. Thereby the protrudingelement18 has been moved further into theopening17, and a larger part of the fluid passage defined by theopening17 is blocked by the protrudingelement18. Accordingly, the opening degree of theexpansion valve4 is smaller in the situation illustrated inFIG. 9 than in the situation illustrated inFIG. 8.
• Thus,FIGS. 8 and 9 illustrate that the opening degree of theexpansion valve4 automatically decreases when the differential pressure across theexpansion valve4 increases. Similarly, the opening degree of theexpansion valve4 automatically increases when the differential pressure across theexpansion valve4 is decreased.
• FIG. 10 is a cross sectional view of theexpansion valve4 according to the second embodiment of the invention. InFIG. 10 the fluid flow through theexpansion valve4 has been reversed. Thus, refrigerant flowing through theexpansion valve4 flows along a direction from thesecond valve member8 towards thefirst valve member7, i.e. along the direction illustrated byarrow20. This has caused thefirst valve member7 to be pushed away from thesecond valve member8 and into abutment with the stoppingmember19. The stoppingmember19 prevents thefirst valve member7 from being moved further along this direction. When thefirst valve member7 is in this position, the protrudingelement18 is no longer arranged inside theopening17. Thereby theopening17 is not blocked by the protrudingelement18, and the opening degree of theexpansion valve4 is defined by the diameter of theopening17. This is significantly larger than the opening degrees illustrated inFIGS. 8 and 9, and the fluid flow through theexpansion valve4 is in essence unrestricted.
• The reverse flow situation illustrated inFIG. 10 can occur in vapour compression systems which can be selectively operated in an air condition mode or a heat pump mode. In this case the vapour compression system comprises a compressor, two expansion valves and two heat exchangers. The heat exchangers are both capable of operating as an evaporator or as a condenser, depending on the flow direction in the system. Each of the expansion valves is capable of controlling the flow of refrigerant to one of the heat exchangers, when the respective heat exchanger operates as an evaporator. However, when a given heat exchanger operates as a condenser, fluid flow through the corresponding expansion valve should not be restricted. This is obtained by theexpansion valve4 according to the second embodiment of the invention, and theexpansion valve4 illustrated inFIGS. 8-10 is therefore suitable for use in a vapour compression system which is capable of selectively operating in an air condition mode or a heat pump mode.
• FIG. 11 is an end view of theexpansion valve4 according to the second embodiment of the invention. The shape of thefirst valve member7 can be seen, and it is clear that refrigerant is allowed to flow past thefirst valve member7.
• FIG. 12 is a graph illustrating opening degree, OD, of an expansion valve according to the first embodiment of the invention as a function of differential pressure, ΔP, across the expansion valve. In the situation illustrated inFIG. 12, two distinct levels of the opening degree are defined, a high level at low differential pressures, and a low level at high differential pressures. At a threshold value21 of the differential pressure, the opening degree changes abruptly between the two distinct levels. This corresponds to the behaviour of the expansion valve according to the first embodiment of the invention, and described above with reference toFIGS. 2a-7.
• FIG. 13 is a graph illustrating opening degree, OD, of an expansion valve according to the second embodiment of the invention as a function of differential pressure, ΔP, across the expansion valve. In the situation illustrated inFIG. 13, the opening degree decreases substantially linearly as the differential pressure increases. Two illustrative points22,23 on the curve are marked. These could, e.g., illustrate the measurement points used for evaluating the SEER value of the vapour compression system. The graph ofFIG. 13 could, e.g., originate from theexpansion valve4 according to the second embodiment of the invention, described above with reference toFIGS. 8-11.
• Although various embodiments of the present invention have been described and shown, the invention is not restricted thereto, but may also be embodied in other ways within the scope of the subject-matter defined in the following claims.

Claims (20)

What is claimed is:

1. An expansion valve for a vapour compression system, the expansion valve comprising:

a first valve member;

a second valve member, the first valve member and the second valve member being arranged movably relative to each other between a first relative position defining a first opening degree at a first differential pressure and a second relative position defining a second opening degree at a second differential pressure; and

a biasing mechanism arranged to mechanically bias the first valve member and the second valve member in a direction away from each other;

wherein the relative position of the first valve member and the second valve member determines an opening degree of the expansion valve;

wherein the first valve member and/or the second valve member is/are automatically movable in response to changes in a differential pressure across the expansion valve, the opening degree of the expansion valve thereby being automatically altered in response to changes in the differential pressure across the expansion valve;

wherein the first valve member is provided with a fluid passage corresponding to the first opening degree and the second valve member is provided with a fluid passage corresponding to the second opening degree;

wherein the second differential pressure is higher than the first differential pressure; and

wherein the first opening degree is larger than the second opening degree.

2. The expansion valve according toclaim 1, further comprising a guiding mechanism arranged for controlling the relative movements of the first valve member and the second valve member in response to changes in the differential pressure across the expansion valve.

3. A vapour compression system comprising a compressor, a condenser, an evaporator and an expansion valve according toclaim 1, the compressor, the condenser, the expansion valve and the evaporator being arranged along a refrigerant path.

4. The vapour compression system according toclaim 3, wherein the compressor is a two-step compressor.

5. The vapour compression system according toclaim 3, wherein the vapour compression system is a refrigeration system.

6. The expansion valve according toclaim 1, wherein the first relative position defines a mutual distance between the first valve member and the second valve member, and wherein the first valve member and the second valve member are arranged substantially in abutment with each other in the second relative position.

7. An expansion valve for a vapour compression system, the expansion valve comprising:

a first valve member;

a second valve member, the first valve member and the second valve member being arranged movably relative to each other between a first relative position defining a first opening degree at a first differential pressure and a second relative position defining a second opening degree at a second differential pressure; and

a biasing mechanism arranged to mechanically bias the first valve member and the second valve member in a direction away from each other;

wherein the relative position of the first valve member and the second valve member determines an opening degree of the expansion valve;

wherein the first valve member and/or the second valve member is/are automatically movable in response to changes in a differential pressure across the expansion valve, the opening degree of the expansion valve thereby being automatically altered in response to changes in the differential pressure across the expansion valve;

wherein the first valve member is provided with a fluid passage corresponding to the first opening degree and the second valve member is provided with a fluid passage corresponding to the second opening degree;

wherein the first relative position defines a mutual distance between the first valve member and the second valve member; and

wherein the first valve member and the second valve member are arranged substantially in abutment with each other in the second relative position.

8. The expansion valve according toclaim 7, wherein the second differential pressure is higher than the first differential pressure.

9. The expansion valve according toclaim 7, further comprising a guiding mechanism arranged for controlling the relative movements of the first valve member and the second valve member in response to changes in the differential pressure across the expansion valve.

10. A vapour compression system comprising a compressor, a condenser, an evaporator and an expansion valve according toclaim 7, the compressor, the condenser, the expansion valve and the evaporator being arranged along a refrigerant path.

11. The vapour compression system according toclaim 10, wherein the compressor is a two-step compressor.

12. The vapour compression system according toclaim 10, wherein the vapour compression system is a refrigeration system.

13. An expansion valve for a vapour compression system, the expansion valve comprising:

a first valve member;

a second valve member, at least one of the first valve member or the second valve member being arranged movably relative to the other of the first valve member or the second valve; and

a biasing mechanism arranged to mechanically bias the first valve member and the second valve member in a direction away from each other, the first valve member and the second valve member, when biased in a direction away from each other by the mechanical biasing mechanism, allowing a reverse fluid flow to pass through the expansion valve;

wherein the relative position of the first valve member and the second valve member determines an opening degree of the expansion valve;

wherein the first valve member and/or the second valve member is/are automatically movable in response to changes in differential pressure across the expansion valve, the opening degree of the expansion valve thereby being automatically altered in response to changes in the differential pressure across the expansion valve;

wherein the first valve member and/or the second valve member is/are movable between a first relative position defining a first opening degree at a first differential pressure and a second relative position defining a second opening degree at a second differential pressure, said second differential pressure being higher than the first differential pressure; and

wherein the first opening degree is larger than the second opening degree.

14. The expansion valve according toclaim 13, further comprising a guiding mechanism arranged for controlling the relative movements of the first valve member and the second valve member in response to changes in the differential pressure across the expansion valve.

15. A vapour compression system comprising a compressor, a condenser, an evaporator and an expansion valve according toclaim 13, the compressor, the condenser, the expansion valve and the evaporator being arranged along a refrigerant path.

16. The vapour compression system according toclaim 15, further comprising a stopping member arranged in the refrigerant path upstream of the expansion valve.

17. The vapour compression system according toclaim 16, wherein one of the first valve member or second valve member is substantially in abutment with the stopping member when reverse flow passes through the expansion valve.

18. The vapour compression system according toclaim 15, wherein the compressor is a two-step compressor.

19. The vapour compression system according toclaim 15, wherein the vapour compression system is a refrigeration system.

20. The expansion valve according toclaim 13, wherein the first relative position defines a mutual distance between the first valve member and the second valve member, and wherein the first valve member and the second valve member are arranged substantially in abutment with each other in the second relative position.

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