DE102013113221A1 - Inner heat exchanger with variable heat transfer - Google Patents

Abstract

The present invention relates to an internal heat exchanger (13, 16) for the refrigerant circuit (10) of an air-conditioning device, in particular in a motor vehicle. The inner heat exchanger (13, 16) comprises a first line section (13, 18B) for guiding the refrigerant on the high-pressure side of the refrigerant circuit (10), a second line section (16, 19C) for guiding the refrigerant on the low-pressure side of the refrigerant circuit (10). and a heat exchange path in which the first and second line sections (13, 18B, 16, 19C) extend at least partially adjacent to each other in heat-conductive contact. The inner heat exchanger (13, 16) is characterized by a bypass (18C), which is guided past a partial section (20) of the first line section (13, 18B) lying at least partially in the region of the heat exchange path, and whose mass flow is controlled by means of a shut-off device (17A ; 17B) is controllable, which is automatically controlled depending on the thermo-fluid dynamic state of the refrigerant circuit, so that the heat exchange over the heat exchange path is variable.

Description

The present invention relates to an internal heat exchanger, in particular for a refrigerant circuit of an air conditioning device in a motor vehicle. Generic internal heat exchangers include a first conduit section for guiding the refrigerant on the high-pressure side of the refrigerant circuit and a second conduit section for guiding the refrigerant on the low-pressure side of the refrigerant circuit. They furthermore comprise a heat exchange path, in which the first and the second line sections extend at least partially in heat-conducting contact next to one another. The invention further relates to a refrigerant circuit with such an inner heat exchanger.

In a refrigerant circuit, refrigerant is compressed in a compressor, flows through a condenser, in which heat is discharged to the outside and the refrigerant thereby at least partially condenses. The refrigerant is expanded when passing through an expansion element and subsequently flows through an evaporator, in which the refrigerant absorbs heat to be sucked from there as a so-called suction gas from the compressor. Because the refrigerant in the first line section between the compressor and the expansion device is guided at a higher pressure level than in the second line section between the expansion element and the compressor, the first line section is also referred to as the high-pressure side and the second line section as the low-pressure side. The temperature level is on the high pressure side above the low pressure side.

Internal heat exchangers for refrigerant circuits are known in principle from the prior art. Along the heat exchange path, the line sections are typically coaxial to each other, wherein the suction gas leading low pressure side is then advantageously guided inside. But there are also other arrangements possible, such as side by side guided flat tubes. The inner heat exchanger removes heat on the high-pressure side from the compressed refrigerant coming from the condenser and supplies this heat to the refrigerant flowing from the evaporator to the compressor on the low-pressure side. This can increase energy efficiency.

The DE 10 2008 046 590 A1 discloses, for example, an internal heat exchanger for a vehicle air conditioning system with a variable heat exchange path. If it comes at high load conditions to overheat the compressor, by means of an electronically controlled solenoid valve, a bypass in the heat exchange path can be released, so that by partial or complete bypassing the heat exchange path of the heat exchange is adjustable.

Internal heat exchangers must be adapted to each development project depending on the system design. It often happens that an internal heat exchanger adapted to high load conditions or optimized with a fixed heat exchange path at low load conditions leads to unstable behavior in the refrigerant circuit. The unstable behavior leads to a phase change of the refrigerant at the evaporator outlet. Due to the control characteristics of the expansion element, this mass flow change of the refrigerant is amplified, which leads to an increase in the probability of occurrence of sound development.

It is the object of the present invention to provide an internal heat exchanger for a refrigerant circuit, which allows for low load conditions operational stability, in particular with respect to the phase state of the refrigerant to reduce the occurrence of flow noise.

This object is achieved by an internal heat exchanger having the features of claim 1 and a refrigerant circuit having the features of claim 10. Advantageous training and further developments emerge from the dependent claims.

The internal heat exchanger according to the invention is characterized by a bypass, which is guided past a partial section of the first line section lying at least partially in the region of the heat exchange section, and whose mass flow is controllable by means of a shut-off device which is automatically adjustable as a function of the thermo-fluid dynamic state of the refrigerant circuit. so that the heat exchange through the heat exchange path is variable. The thermo-fluid dynamic state of the refrigerant circuit (ie mass flow, pressure and temperature distribution) varies depending on the load condition. Depending on the flow rate of the refrigerant results in a spatially and device technology firmly predetermined circuit a certain temperature setting. The inventors have realized that these state parameters can be used to provide a self-regulating circuit without an externally controlled valve. Depending on the state thus automatically results in a setting of the shut-off valve. The bypass is typically guided in parallel and spaced from the first line section, so that the refrigerant flowing therethrough is not in heat-conducting contact with the low-pressure side. This reduces the heat transfer and it can be specific Points in the refrigerant circuit, in particular at the evaporator output, set the temperature point and thus a shift in the phase diagram (proportion of liquid / gaseous refrigerant) can be achieved.

According to one embodiment of the invention, the shut-off device is a 3-way valve which keeps constant the sum of the flow rates through the bypass and through the partial section of the first line section. The 3-way valve opens the bypass as the section is closed.

The shut-off device is expediently independently controllable in dependence on a detected, relatively elevated temperature such that the mass flow through the bypass is lowered. In other words, that at an elevated temperature condition, the heat exchange distance and thus the heat transfer can be increased. As a result, the refrigerant on the high-pressure side downstream of the inner heat exchanger is comparatively more cooled (as compared to a further open bypass). This comparatively strong cooling also influences the refrigerant-side outlet state at the evaporator with constant energy exchange at the evaporator. This can lead to incomplete evaporation of the refrigerant up to the entry into the inner heat exchanger. At an elevated temperature condition, this temperature reduction at the evaporator is acceptable as long as the refrigerant is supplied with sufficient energy as it flows through the evaporator. In the opposite case, in the line sections, in particular at the evaporator outlet, the presence of the refrigerant in the mixing phase may result in disturbing structure-borne noise.

It should be noted here that the elevated temperature condition is due to the thermodynamic behavior of the refrigerant circuit to be explained later, typically at an increased load condition and / or increased ambient temperature or outside temperature. Therefore, an ambient temperature and / or a temperature in the refrigerant circuit is advantageously used for the regulation of the shut-off device. To detect the ambient temperature, in particular the outside temperature sensor present in motor vehicles can be used.

For the automatic control of the shut-off device, it can be advantageously provided that the shut-off device is coupled to a thermo-mechanical element and can be actuated by it. In this case, the thermo-mechanical element is then thermally coupled to a measuring point in the refrigerant circuit, preferably the condenser outlet and / or the evaporator outlet. For correct actuation, the thermo-mechanical element is then adapted to respond to a temperature change at the measurement point with a mechanical change such that the shut-off device is changed to the desired setting. As a thermo-mechanical elements this example, cost-effective and proven for vehicle expansion elements or bimetallic strips can be used.

According to an advantageous embodiment of the invention, the shut-off device is a thermostatic valve. In this case, it is possible, as an alternative or in addition to the aforementioned regulation, to adjust independently as a function of the temperature condition.

According to one embodiment of the invention, the shut-off device can be coupled to the expansion element of the refrigerant circuit, so that the shut-off device can be regulated automatically as a function of the regulation of the expansion element. Regardless of how the expansion element is controlled itself, this specifies a thermo-fluid dynamic state of the refrigerant circuit, depending on which then the bypass is automatically controlled. The expansion element of the refrigerant circuit is preferably a valve which can be regulated automatically as a function of the pressure and / or the temperature of the refrigerant guided on the low-pressure side.

According to an advantageous embodiment of the invention, it is provided that the shut-off device is integrated into the expansion device such that the setting of the shut-off device is changed by a mechanical adjusting movement of the expansion element. In particular, it may be provided that the expansion valve, e.g. a known from the prior art thermostatically controlled expansion valve, a pin in a bore raises and lowers. In the bore, a passage can be closed or released by a tapering of the pin by the raising and lowering movement. This passage can then be used as a shut-off device for the bypass of the internal heat exchanger.

The expansion element of the refrigerant circuit can advantageously still be integrated into the inner heat exchanger, resulting in a compact, weight-reduced design of the inner heat exchanger. It may have a flange with two outputs for the lines of the low pressure side. This also allows easy handling during assembly or maintenance.

According to the invention, a refrigerant circuit with a compressor, a condenser, an expansion element and an evaporator with equipped with a previously mentioned internal heat exchanger.

The invention will now be explained in more detail with reference to embodiments and with reference to the figures.

The 1 12 schematically shows a phase diagram with states of the refrigerant, as it typically passes through the refrigerant circuit in the context of the invention,

the 2 shows schematically the structure of a refrigerant circuit with an internal heat exchanger according to a first embodiment of the invention,

the 3 shows schematically the construction of a refrigerant circuit with an internal heat exchanger according to a second embodiment of the invention,

the 4 schematically shows a detail view of the inner heat exchanger according to an embodiment of the invention and

the 5 shows a schematic representation of the bypass check valve, which is integrated according to a preferred embodiment in the expansion valve of the refrigerant circuit.

The refrigerant circuits described below 10 are particularly, but not exclusively, suitable for the cooling operation of an air conditioning system in motor vehicles.

1 schematically shows a phase diagram with conditions of the refrigerant, as in the context of the invention typically the refrigerant circuit 10 according to the 2 and 3 passes. The phase diagram is a so-called Mollier diagram showing the enthalpy on the x-axis and the representation of the pressure on the y-axis. The refrigerant is a refrigerant known per se in the art for use in automotive air conditioning systems, such as, but not limited to, R134a or R1234yf. The refrigerant has three phases below a critical pressure, namely a liquid phase I, a wet steam phase II and a superheated steam phase III. In the wet steam phase II, vaporous and boiling refrigerant coexist, whereas in the superheated steam phase III only gaseous, superheated refrigerant occurs.

In the 2 and 3 are schematic refrigerant circuits 10 with inner heat exchanger 13 . 16 illustrated according to various embodiments of the invention. The similarities will be described below, while the differences of the two embodiments will be discussed below. In this case, the states of the refrigerant when passing through the refrigerant circuit 10 with reference to the 1 briefly described. There are a state curve 1 the refrigerant at high load (with maximum heat exchange of the internal heat exchanger 13 ) and two state curves 2A and 2 B of the refrigerant at low load. The state curves are indicated in each case with the sections w-z. Regarding the state curve 2A is the inner heat exchanger 13 . 16 fixed in relation to the state curve 2 B however adjustable with variable heat exchange.

First of all, a fixed internal heat exchanger 13 assumed, which is optimized for high load operation. The refrigerant is supplied by a compressor 11 compressed and over the line section 18A a capacitor 12 fed. In this compression, the state of the refrigerant changes according to the load according to the curve sections 1w (high load) or 2AW (low load). When passing through the capacitor 12 The compressed refrigerant cools down and passes through the curve section in the phase diagram 1x or 2ax until cutting the curve 3 , which represents a capacitor characteristic, ie the cooling capacity, which is predetermined by the design of the capacitor.

The refrigerant passes downstream via the line section 18B to the high pressure side of the inner heat exchanger 13 through which the still relatively hot refrigerant is cooled further compared to the low pressure side. This corresponds to the curve section 1x respectively. 2ax between the intersections with the curves 3 and 4A , The curve 4A sets the characteristics of the internal heat exchanger 13 represents, ie the heat transfer performance, the design due to the design of the inner heat exchanger 13 is predetermined. The state 5 is the largest possible subcooling point of the refrigerant at a given maximum temperature at the compressor outlet. After leaving the high pressure side of the inner heat exchanger 13 the refrigerant is at the expansion valve 14 relaxed and over the line section 19A the evaporator 15 fed. This corresponds to the curve section 1y or 2ay , When passing through the evaporator 15 If the refrigerant absorbs heat, it is vaporized successively, passing through the curve section in the phase diagram 1z or 2Az ,

The refrigerant continues downstream over the line section 19B to the low pressure side of the inner heat exchanger 16 , through which the still relatively cool refrigerant is still warmed up compared to the high pressure side and finally over the line section 19C as suction gas from the compressor 11 is sucked, which closes the circuit.

The refrigerant circuit 10 must be stable in operation over a defined operating range. In order to increase the energy efficiency, therefore, the largest possible heat transfer at high ambient temperatures is required, for example above 25 ° C. At these temperatures, the refrigerant circuit typically runs in high load operation. At relatively low ambient temperatures, typically between 5 and 25 ° C, there is the problem that, although there may be a desired operating with respect to the air conditioning system, in this temperature range, on the one hand only a weak cooling performance, ie a low energy exchange is required, on the other hand caused by the lower ambient temperature incomplete evaporation of the refrigerant becomes. At low load conditions according to the state curve 2A It can happen then that the state 8th of the refrigerant at the evaporator outlet 15A is still clearly in the wet steam phase II of the phase diagram. This leads to unstable operating conditions in which by inhomogeneities increased structure-borne noise in the corresponding line section 19B arises.

Due to the variable heat exchange distance can now be achieved according to the invention that at low load, the subcooling in the inner heat exchanger 13 is controlled so that the state point 6 when leaving the inner heat exchanger 13 according to the intersection with the curve 4B (the characteristic of the variable internal heat exchanger 13 ) to the state point 7 is moved. The refrigerant then no longer runs according to the state curve 2A but according to the dashed state curve 2 B so also the state point 8th at the evaporator outlet 15A is shifted so that the new state point 9 now moved into the superheated steam phase III.

The variable heat exchange path is through a bypass 18C reached, which at a heat exchange additional route 20 of the internal heat exchanger 13 is passed, and its mass flow by means of a shut-off device described below 17A . 17B is controllable, which is automatically regulated depending on the thermo-fluid dynamic state of the refrigerant circuit, so that the heat exchange over the heat exchange path is variable.

The shut-off device 17A . 17B In this case, it is configured in such a way that it is automatically controllable automatically at a relatively elevated temperature in such a way that the mass flow through the bypass 18C is lowered and through the heat exchange auxiliary path 20 increased (to increase energy efficiency). In the opposite case, the mass flow through the bypass 18C is increased to overcooling too much, especially at the evaporator outlet 15A to avoid for the reasons mentioned above.

In the first embodiment with reference to the 2 the shut-off device is a 3-way valve 17A , The 3-way valve 17A divides the mass flow of the refrigerant to the bypass 18C and the heat exchange auxiliary section 20 depending on the outlet temperature of the refrigerant at the condenser outlet 12A on. The sum of the flow rates through the bypass 18C and through the heat exchange auxiliary section 20 remains constant and both mass flows are only between the high pressure side of the inner heat exchanger 13 and the expansion valve 14 merged again. Alternatively or additionally, the ambient temperature can be taken into account as a controlled variable. Incidentally, at a very low load, this temperature almost corresponds to the temperature of the refrigerant before reaching the expansion valve 14 and is therefore a good indicator, whether at the evaporator outlet 15A a state in the superheated steam phase is achievable or not.

The 3-way valve 17A is coupled to a thermo-mechanical element, eg a per se known expansion element (not shown), and actuated by this. The thermo-mechanical element detects the temperature at the capacitor output 12A or at another suitable measuring point representative of the required cooling capacity of the refrigerant circuit 10 is. The thermo-mechanical element is then configured to respond to a temperature change at the measurement point with a mechanical change such that the adjustment of the 3-way valve 17A and thus the distribution of the mass flow to the bypass 18C and the heat exchange auxiliary section 20 is changed. When using a Dehnstoffelements a change in length, for example, used in such a way that in the 3-way valve successively one of the two outputs is opened to the extent that the other output is closed. In this way, a gradual adjustment of the internal heat exchanger with variable heat exchange can be achieved.

In the second embodiment with reference to the 3 the shut-off device is a shut-off valve 17B which can be coupled to the expansion element of the refrigerant circuit, so that the shut-off device automatically in response to the control of the expansion valve 14 is controllable.

In the 4 schematically is a detail view of the inner heat exchanger 13 . 16 represented according to an embodiment of the invention. The Low pressure side 16 the inner heat exchanger is guided as an inner tube, while the high pressure side 13 surround it appropriately. The pipeline of the high pressure side 13 surrounds, for example, the inner tube of the low pressure side 16 coaxial or spirally or helically wound around this. The heat exchange auxiliary section 20 can through the bypass 18C throttled or completely bypassed when the shut-off valve 17B partially or completely closed. Instead of the shut-off valve 17B In this embodiment, other shut-off devices can be used, for example, a 3-way valve 17A according to the 2 by placing it at the front branch point (not shown).

In the embodiment according to the 4 is also the expansion valve 14 in the inner heat exchanger 13 . 16 integrated. On the connection side shown on the left are the inlets and outlets 19A . 19B the low pressure side indicated. The expansion valve 14 is controlled as a thermostatic valve automatically depending on the temperature of the guided on the low pressure side refrigerant. Depending on the temperature level in the low pressure range, the valve needle is changed in a known manner, for example by raising and lowering in the position in the valve seat, so that the flow rate of the expansion valve 14 and thus the pressure drop can be adjusted to the low pressure side.

In the 5 is a further embodiment shown schematically, in which the shut-off valve 17B in the expansion valve 14 is integrated in such a way that by a mechanical adjusting movement of the expansion valve 14 the setting of the shut-off valve 17B is changed. At the expansion valve 14 In this embodiment, it may in particular, but not necessarily, be a thermostatically controlled valve, which is described with reference to FIGS 4 has been described. The valve body comprises a bore 21 in which a pen 22 is movable up and down. The pencil 22 has a rejuvenation in the middle 23 , For example, a hollow cylindrical recess. The hole 21 also has a side of a supply and discharge. Between supply line and discharge there is a passage 24 , which depends on the position of the pen 22 can be opened and closed. In one possible configuration, the supply line is the end piece of the heat exchange auxiliary section 20 and the derivative is a connector 25 at which the mass flow of the heat exchange additional section 20 and the bypass 25 be merged again. But there are other configurations possible.

In the first position shown on the left is the taper 23 with the passage 24 brought to cover. This will cause the maximum mass flow through the passage 24 and thus through the heat exchange additional route 20 Approved. In the second position shown on the right is the taper 23 moved up so the pen 22 the passage 24 completely closes. This will cause a mass flow through the passage 24 and thus through the heat exchange additional route 20 prevented. Depending on the intermediate positions, the flow rate through the passage 24 be controlled gradually.

It will be apparent to those skilled in the art that, with regard to the mentioned embodiments, the arrangement and selection of the shut-off device of the bypass 18C as well as to the concrete designs of the valves 14 . 17A . 17B There are numerous combinations and variations. In particular, it should be noted that a specific characteristic for controlling the mass flow can be generated by a concrete choice of the coupling properties. For example, depending on the cross-sectional profile of the supply and discharge lines in a linear lifting or lowering of the pen 22 a non-linear opening characteristic can be achieved. Depending on the specific configuration of the internal heat exchanger and the refrigerant circuit, the mechanical adjusting movement can then be adjusted in simple tests such that the operating point 9 according to 1 is moved into the wet steam region III.

LIST OF REFERENCE NUMBERS

I

liquid phase

II

Wet steam phase

III

Superheated steam phase

1 (wz)

Condition curve of the refrigerant at high load

2A-2B

 (w-z) Condition curve of the refrigerant at low load

3

Capacitor characteristic

4A-4B

Characteristic of the internal heat exchanger

5-9

Condition points of the refrigerant

10

Refrigerant circulation

11

compressor

12

capacitor

12A

condenser outlet

13

inner heat exchanger / high pressure side

14

expansion valve

15

Evaporator

15A

evaporator outlet

16

inner heat exchanger / low pressure side

17A

3-way valve

17B

shut-off valve

18A-18C

Line sections high pressure side

18C

bypass

19A-19C

Line sections low-pressure side

20

Additional heat exchange path

21

drilling

22

pen

23

rejuvenation

24

passage

25

joint

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008046590 A1 [0004]

Claims (10)

Inner heat exchanger ( 13 . 16 ) for the refrigerant circuit ( 10 ) an air conditioning device, in particular in a motor vehicle, comprising - a first line section ( 13 . 18B ) for guiding the refrigerant on the high-pressure side of the refrigerant circuit ( 10 ), - a second line section ( 16 . 19C ) for guiding the refrigerant on the low pressure side of the refrigerant circuit ( 10 ) - a heat exchange path, wherein the first and the second line section ( 13 . 18B . 16 . 19C ) run at least partially in heat-conducting contact next to each other, characterized by a bypass ( 18C ), - which at an at least partially lying in the region of the heat exchange section ( 20 ) of the first line section ( 13 . 18B ), and - its mass flow by means of a shut-off device ( 17A ; 17B ) is regulated, which is automatically controlled depending on the thermo-fluid dynamic state of the refrigerant circuit, so that the heat exchange over the heat exchange path is variable. Inner heat exchanger according to claim 1, characterized in that the shut-off device is a 3-way valve ( 17A ), which is the sum of the flow rates through the bypass ( 18C ) and through the leg ( 20 ) of the first line section keeps constant. Inner heat exchanger according to one of claims 1 or 2, characterized in that the shut-off device ( 17A . 17B ) is independently controllable in dependence on a detected, relatively elevated temperature such that the mass flow through the bypass ( 18C ) is lowered. Inner heat exchanger according to claim 3, characterized in that an ambient temperature and / or a temperature in the refrigerant circuit ( 10 ) for the regulation of the shut-off device ( 17A . 17B ) is used. Inner heat exchanger according to claim 4, characterized in that - the shut-off device ( 17A . 17B ) is coupled to a thermo-mechanical element and actuated by this, - wherein the thermo-mechanical element thermally with a measuring point in the refrigerant circuit ( 10 ), preferably the capacitor output and / or the evaporator output, and - wherein the thermo-mechanical element reacts to a temperature change at the measuring point with a mechanical change such that the setting of the shut-off device ( 17A . 17B ) is changed. Inner heat exchanger according to one of the preceding claims, characterized in that the shut-off device ( 17A . 17B ) is a thermostatic valve. Inner heat exchanger according to one of the preceding claims, characterized in that the shut-off device ( 17A . 17B ) with the expansion organ ( 14 ) of the refrigerant circuit ( 10 ) is coupled, so that the shut-off ( 17A . 17B ) automatically depending on the regulation of the expansion organ ( 14 ) is controllable. Inner heat exchanger according to claim 7, characterized in that the expansion element ( 14 ) of the refrigerant circuit ( 10 ) is a valve which is automatically controlled in dependence on the mass flow and / or the temperature of the guided on the low pressure side refrigerant. Inner heat exchanger according to one of claims 7 or 8, characterized in that the shut-off device ( 17A . 17B ) into the expansion organ ( 14 ) is integrated in such a way that by a mechanical adjusting movement of the expansion organ ( 14 ) the setting of the shut-off device ( 17A . 17B ) is changed. Refrigerant circuit with a compressor ( 11 ), a capacitor ( 12 ), an expansion organ ( 14 ), an evaporator ( 15 ) and an internal heat exchanger ( 13 . 16 ) according to one of claims 1 to 9.

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