JP2007155277A - Refrigerating cycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a refrigerating cycle capable of obtaining good cooling efficiency even in a condition of a comparatively low thermal load and maintaining an optimal cooling efficiency even when the load fluctuates, in the case a refrigerating cycle using an internal heat exchanger and an expansion machine is used for securing refrigerant capacity at a time of high load. <P>SOLUTION: The refrigerating cycle is equipped with a compressor 2 for giving pressure rise to the refrigerant, a radiator 3 for radiating heat of the pressure-raised refrigerant by the compressor 2, the expansion machine 4 arranged further on the downstream side than the condenser 3 for taking out power by decompressing and expanding the refrigerant, an evaporator 5 for vaporizing the refrigerant decompressed and expanded in the expansion machine 4, and the internal heat exchanger 8 for heat exchanging a high pressure refrigerant introduced from the condenser 3 to the expansion machine 4, and the low pressure refrigerant introduced from the evaporator 5 to the compressor 2. The heat changing amount of the high pressure refrigerant and the low pressure refrigerant by the internal heat exchanger 8 can be adjusted. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a refrigeration cycle used for vehicles and the like.

  A refrigeration cycle including a compressor that boosts the refrigerant, a radiator that cools the boosted refrigerant, an expansion valve that decompresses the cooled refrigerant, and an evaporator that evaporates the decompressed refrigerant has a known cycle configuration. However, in such a configuration, since the energy when the refrigerant is decompressed and expanded by the expansion valve is discarded without being recovered, there is a disadvantage that the efficiency of the cycle is poor.

Therefore, conventionally, a compressor that boosts the refrigerant, a radiator that cools the refrigerant that has been boosted by the compressor, and a refrigerant that is disposed downstream of the radiator and that is cooled is decompressed and expanded. And an evaporator that is arranged downstream of the refrigerant of the expander and evaporates the refrigerant. The expander decompresses and expands the refrigerant to recover energy, and the recovered energy is used as the refrigerant. The method of using for compression of this is considered (refer patent document 1, 2).
In such a configuration, the effect of improving the cooling efficiency is particularly great when carbon dioxide is used as the refrigerant.

Japanese Patent Laid-Open No. 11-63707 JP 2002-22298 A

  However, in the refrigeration cycle using the expander described above, an internal heat exchanger that exchanges heat between the high-pressure refrigerant guided from the radiator to the expander and the low-pressure refrigerant guided from the evaporator to the compressor must be used in combination. At high load, the cooling capacity is inferior compared to the refrigeration cycle using only the internal heat exchanger, and the condition that the heat load is relatively low by simply using the expander and the internal heat exchanger together As a result of the research, it became clear that the cooling efficiency decreased.

  That is, looking at the cooling capacity (Q) and cooling efficiency (COP) when the heat load is high, as shown in FIG. 4, a refrigeration cycle using an internal heat exchanger and an expander together (hereinafter referred to as a combined cycle). ) Also has a cooling capacity (Q) as compared to a refrigeration cycle using only an internal heat exchanger (hereinafter referred to as an internal heat exchanger cycle) or a refrigeration cycle using only an expander (hereinafter referred to as an expander cycle). Although both cooling efficiency (COP) is improved, when the heat load is relatively low, the combined cycle efficiency is inferior to the expander cycle efficiency as shown in FIG.

  In addition, when the heat load is high, the cooling capacity increases as the high-pressure side pressure increases in any cycle. Therefore, the high-pressure side set pressure corresponding to the required cooling capacity is set within a range that does not exceed the upper limit for safety. However, when the heat load is relatively low, there is an optimum high-pressure side pressure that maximizes the cooling efficiency (see FIG. 5). It is preferable to operate the refrigeration cycle so that a characteristic line as shown in FIG.

  The present invention has been made in view of the above circumstances, and in the case of adopting a refrigeration cycle in which an internal heat exchanger and an expander are used together in order to ensure cooling capacity at high loads, a comparison is made. It is a main object to provide a refrigeration cycle that can obtain good cooling efficiency even under low thermal heat load conditions and can optimally control the cooling efficiency even when the load fluctuates.

  In order to achieve the above object, a refrigeration cycle according to the present invention is provided with a compressor that boosts the refrigerant, a radiator that cools the refrigerant that has been pressurized by the compressor, and a refrigerant downstream side of the radiator. An expander that decompresses and expands the refrigerant to extract power; an evaporator that evaporates the refrigerant decompressed and expanded by the expander; a high-pressure refrigerant that is led from the radiator to the expander; and the compressor from the evaporator An internal heat exchanger for exchanging heat with the low-pressure refrigerant led to the heat exchanger, and the amount of heat exchange between the high-pressure refrigerant and the low-pressure refrigerant by the internal heat exchanger can be adjusted. 1).

  As described above, under the conditions other than the high load, the efficiency of the expander cycle becomes better than the efficiency of the combined cycle. Under such conditions, it can be said that the cooling efficiency is improved by reducing the heat exchange capacity of the internal heat exchanger. For this reason, by adjusting the amount of heat exchange between the high-pressure refrigerant and the low-pressure refrigerant by the internal heat exchanger, it becomes possible to improve the cooling efficiency so as to approach the cooling efficiency of the expansion cycle, which is favorable at high loads. It is possible to obtain a good cooling efficiency even under conditions other than a high load while ensuring the cooling capacity.

In the above configuration, the amount of refrigerant flowing through the expander may be adjustable. In such a configuration, when the power extracted by the expander is used for boosting the refrigerant, the high-pressure side pressure can be adjusted by adjusting the power extracted by the expander. The efficiency can be adjusted to an optimum value.
Here, since the high pressure side pressure at which the maximum cooling efficiency is obtained is determined in relation to the heat load, the power that can be recovered by the expander, that is, the refrigerant flow rate that flows through the expander is adjusted according to the heat load. It is preferable to adjust to the intended high pressure.

  As a method of using the power extracted by the expander, an auxiliary compressor for boosting the refrigerant is provided between the evaporator and the compressor, and this auxiliary compressor is operated by the power extracted by the expander. The refrigerant sent to the compressor may be preloaded by the auxiliary compressor (Claim 3), or the power extracted by the expander may be used directly for the power of the compressor (Claim). 4).

  Furthermore, the configuration for adjusting the amount of heat exchange between the high-pressure refrigerant and the low-pressure refrigerant by the internal heat exchanger is as follows: at least one of the high-pressure path from the radiator to the expander and the low-pressure path from the evaporator to the compressor A bypass passage that bypasses the heat exchanger and a bypass valve that adjusts the flow rate of refrigerant flowing through the bypass passage are provided, and the amount of heat exchange by the internal heat exchanger is adjusted by adjusting the flow rate of refrigerant flowing through the bypass passage by the bypass valve. (Claim 5). As a configuration for adjusting the amount of refrigerant flowing through the expander, a bypass passage that bypasses the expander and a pressure reducing valve that adjusts the flow rate of refrigerant flowing through the bypass passage are provided, and the flow rate of refrigerant flowing through the bypass passage by the pressure reducing valve is adjusted. By adjusting, the amount of refrigerant flowing through the expander may be adjusted (claim 6).

  The above configuration is particularly effective when a supercritical fluid such as carbon dioxide is used as the refrigerant (claim 7).

As described above, according to the present invention, in the refrigeration cycle in which the expander and the internal heat exchanger are used together, the amount of heat exchange between the high-pressure refrigerant and the low-pressure refrigerant by the internal heat exchanger can be adjusted. It is possible to ensure the cooling capacity at the time of load, and to obtain a good cooling efficiency even under a relatively low heat load condition, so that the efficiency can be optimally maintained regardless of the load fluctuation.
In addition, by adjusting the flow rate of the refrigerant flowing through the expander, the high-pressure side pressure of the refrigeration cycle can be adjusted, and the cooling efficiency can be adjusted to the optimum value.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, the best embodiment of the invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a configuration example of a refrigeration cycle 1 according to the present invention mounted on a vehicle. The refrigeration cycle 1 uses a carbon dioxide representing a supercritical fluid as a refrigerant, and a compressor 2 that compresses the refrigerant. A radiator 3 that cools the refrigerant compressed by the compressor 2, an expander 4 that is disposed downstream of the refrigerant in the radiator 3, and an evaporator 5 that evaporates the refrigerant decompressed by the expander 4 An auxiliary compressor 6 disposed on the refrigerant downstream side of the evaporator 5, an accumulator 7 disposed between the evaporator 5 and the auxiliary compressor 6, and a high-pressure refrigerant guided from the radiator 3 to the expander 4. An internal heat exchanger 8 that exchanges heat with the low-pressure refrigerant guided from the evaporator 5 to the compressor 2 is connected by piping.

  The compressor 2 is driven by using an engine or a motor as a drive source, and the expander 4 and the auxiliary compressor 6 each have an impeller (not shown) stored therein, and these impellers are connected to the same shaft. 10 so that it can rotate at the same time.

  Furthermore, in this refrigeration cycle 1, at least one of the high pressure path 11 from the radiator 3 to the expander 4 and the low pressure path 12 from the evaporator 5 to the compressor 2, in this example, compression from the auxiliary compressor 6 is performed. The low-pressure path 12 leading to the machine 2 is provided with a bypass passage 13 that bypasses the internal heat exchanger 8 and a bypass valve 14 that adjusts the flow rate of refrigerant flowing through the bypass passage 13, and the amount of heat exchange in the internal heat exchanger 8. Is adjusted by controlling the opening degree of the bypass valve 14.

  A bypass passage 15 that bypasses the expander 4 and a pressure reducing valve 16 that adjusts the flow rate of the refrigerant flowing through the bypass passage 15 are provided, and the refrigerant flow rate that flows through the expander 4 by controlling the opening degree of the pressure reducing valve 16. That is, the power that can be taken out by the expander 4 is adjusted.

  In the above-described configuration, the refrigerant compressed by the compressor 2 enters the radiator 3 as a high-temperature and high-pressure gaseous refrigerant, and is cooled by exchanging heat with the air passing through the radiator 3. This cooled refrigerant is further cooled by exchanging heat with the low-pressure side refrigerant in the internal heat exchanger 8 and then sent to the expander 4 where it adiabatically expands into a low-temperature and low-pressure wet steam. The impeller of the expander 4 is rotated by the energy generated in. Thereby, an expander takes out the energy at the time of adiabatic expansion of a refrigerant | coolant as motive power which rotates an impeller. The refrigerant sent to the evaporator 5 via the expander 4 exchanges heat with the air passing through the evaporator 5 to absorb heat, and is sent to the auxiliary compressor 6 via the accumulator 7 as a gaseous refrigerant. Since the impeller of the auxiliary compressor 6 is arranged coaxially with the impeller of the expander 4 and is rotated by the power obtained by the expander 4, the power extracted by the expander 4 is used as the auxiliary compressor. 6 is converted into work for pre-pressurizing the refrigerant, and the refrigerant is sent to the internal heat exchanger 8 in a state where the pressure is somewhat increased. Then, the internal heat exchanger 8 exchanges heat with the high-pressure side refrigerant, further absorbs heat, is returned to the compressor 2 as a complete gaseous refrigerant, and is compressed again.

  In such a refrigeration cycle 1, in order to adjust the flow rate of refrigerant flowing through the bypass passage 13 bypassing the internal heat exchanger 8 and the pressure reducing valve 16 for adjusting the flow rate of refrigerant flowing through the bypass passage 15 bypassing the expander 4. The bypass valve 14 is controlled in opening degree based on a control signal from the control unit 20.

  The control unit 20 includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), an input / output port, and the like, and a drive circuit that drives and controls the pressure reducing valve 16 and the bypass valve 14. A high pressure sensor 21 for detecting the high pressure side pressure, a low pressure sensor 22 for detecting the low pressure side pressure, a radiator outlet temperature sensor 23 for detecting the radiator outlet refrigerant temperature, and an outside temperature sensor 24 for detecting the outside temperature. A signal from a discharge temperature sensor 25 or the like for detecting the discharge refrigerant temperature of the compressor is input, the input signal is processed according to a predetermined program given to the ROM or RAM, and the decompression valve 16 or the bypass valve 14 is opened. The degree is controlled.

  In FIG. 2, an example of the control operation of the refrigeration cycle 1 by the control unit 20 is shown as a flowchart, which will be described below based on this flowchart.

  The control unit 20 executes this control routine after a predetermined initial setting process or the like. In step 50, the outside air temperature, the high pressure side pressure, the low pressure side pressure, the radiator outlet refrigerant temperature detected by various sensors. Then, a detection signal such as the discharge refrigerant temperature is input, and in step 52, the required cooling capacity is calculated based on these signals.

  Thereafter, it is determined whether or not the calculated required cooling capacity is the maximum value. If it is determined that the required cooling capacity is the maximum value, the target high pressure side pressure Pd is set to a preset maximum value (for example, , 13 MPa), and when it is determined that the required cooling capacity is not the maximum value, it is a factor representative of the heat load, for example, as shown in FIG. The target high-pressure side pressure Pd at which such maximum cooling efficiency is obtained is calculated.

  Then, the target opening degree of the pressure reducing valve 16 is calculated so as to be the target high pressure side pressure Pd calculated in step 56 or step 58 (step 60), and the opening degree of the pressure reducing valve 16 is obtained so as to obtain the target opening degree. Is controlled (step 62).

  Thereafter, the required heat exchange capacity of the internal heat exchanger corresponding to the heat load is calculated based on the input signal (step 64), and the target opening degree of the bypass valve 14 is calculated so as to obtain the heat exchange capacity ( Step 66).

  At this time, if the discharge refrigerant temperature of the compressor 2 is within the allowable temperature range (for example, 150 ° C.), the opening degree of the bypass valve 14 is controlled so as to become the target opening degree (step 70), and the discharge refrigerant. If it is determined that the temperature exceeds the allowable refrigerant temperature, the target opening of the bypass valve calculated in step 66 is corrected so that the discharged refrigerant temperature is within the allowable refrigerant temperature range (step 72). Then, the opening degree of the bypass valve 14 is controlled so as to be the corrected target opening degree (step 70).

  Therefore, according to the control described above, it is possible to control the high-pressure side pressure so as to obtain the maximum cooling efficiency by adjusting the flow rate of the refrigerant flowing through the expander 4 by adjusting the opening degree of the pressure reducing valve 16, and the bypass valve. By adjusting the opening degree of 14 and adjusting the amount of heat exchange between the high-pressure side refrigerant and the low-pressure side refrigerant by the internal heat exchanger 8, it becomes possible to maintain good cooling efficiency regardless of the heat load.

  Specifically, when the heat load is high, the high pressure side pressure is increased and, as is clear from the characteristics of FIG. 4, the internal heat exchanger 8 actively exchanges heat between the high pressure side refrigerant and the low pressure side refrigerant. Since it is preferable to increase the cooling capacity and cooling efficiency, the opening of the pressure reducing valve 16 is minimized to maximize the power extracted by the expander 4 (power contributing to the pressure increase of the refrigerant) and the bypass valve 14. The amount of heat exchange between the high-pressure side refrigerant and the low-pressure side refrigerant in the internal heat exchanger 8 is set to the maximum.

  On the other hand, it is better not to perform heat exchange between the high-pressure side refrigerant and the low-pressure side refrigerant by the internal heat exchanger 8 under the condition that the heat load is relatively low, as is clear from the characteristics of FIG. From the viewpoint of power saving, it is preferable to select the high pressure side pressure that maximizes the cooling efficiency even in order to obtain the capacity. Therefore, the opening degree of the pressure reducing valve 16 is controlled so as to obtain the high pressure side pressure that maximizes the cooling efficiency. Then, the opening degree of the bypass valve 14 is maximized to minimize the amount of heat exchange between the high-pressure side refrigerant and the low-pressure side refrigerant in the internal heat exchanger 8.

  Therefore, in the refrigeration cycle in which the internal heat exchanger 8 and the expander 4 are used in combination, by performing the above-described control, sufficient cooling capacity at a high load can be ensured and good even under relatively low heat load conditions. Cooling efficiency can be obtained, and the efficiency can be optimally maintained even when the load fluctuates.

  In the above-described configuration, the accumulator 7 is arranged upstream of the auxiliary compressor 6 and the internal heat exchanger 8 is arranged downstream, but the accumulator 7 is arranged downstream of the auxiliary compressor 6. Alternatively, the internal heat exchanger 8 may be arranged on the upstream side of the auxiliary compressor 6. Furthermore, in the above description, the expander and the auxiliary compressor have been described as the impeller type, but the present invention is not limited to this. Further, the high pressure control may use a valve whose opening degree can be adjusted in series on the upstream side of the expander.

  Further, in the above-described configuration, as a method of using the power extracted by the expander 4, the auxiliary compressor 6 disposed between the evaporator 5 and the compressor 2 is driven and used to preload the refrigerant. However, as shown in FIG. 3, the auxiliary compressor is not provided, the expander 4 and the compressor 2 are connected, and the power extracted by the expander 4 is used as auxiliary power for the compressor 2. It may be. Since other configurations and control operation examples are the same as those in the above-described configuration example, the same portions are denoted by the same reference numerals and description thereof is omitted.

FIG. 1 is a diagram showing a configuration example of a refrigeration cycle according to the present invention. FIG. 2 is a flowchart showing an example of a control operation of the refrigeration cycle by the control unit. FIG. 3 is a diagram showing another configuration example of the refrigeration cycle according to the present invention. FIG. 4 is a characteristic diagram showing the relationship between the cooling capacity (Q) and the cooling efficiency (COP) with respect to a change in the high-pressure side pressure when the heat load is high. FIG. 5 is a characteristic diagram showing the relationship between the cooling capacity (Q) and the cooling efficiency (COP) with respect to a change in the high-pressure side pressure when the heat load is relatively low. FIG. 6 is a characteristic diagram showing the relationship between the refrigerant temperature (heat radiator outlet refrigerant temperature) that maximizes the cooling efficiency and the high-pressure side pressure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Refrigeration cycle 2 Compressor 3 Radiator 4 Expander 5 Evaporator 6 Auxiliary compressor 8 Internal heat exchanger 11 High pressure path 12 Low pressure path 13, 15 Bypass path 14 Bypass valve 16 Pressure reducing valve

Claims (7)

A compressor that pressurizes the refrigerant, a radiator that cools the refrigerant that has been pressurized by the compressor, an expander that is disposed downstream of the radiator and that expands the refrigerant under reduced pressure to extract power, and the expansion An evaporator that evaporates the refrigerant decompressed and expanded by the machine, and an internal heat exchanger that exchanges heat between the high-pressure refrigerant led from the radiator to the expander and the low-pressure refrigerant led from the evaporator to the compressor In the refrigeration cycle provided,
A refrigeration cycle characterized in that the amount of heat exchange between the high-pressure refrigerant and the low-pressure refrigerant by the internal heat exchanger can be adjusted. The refrigeration cycle according to claim 1, wherein the flow rate of the refrigerant flowing through the expander is adjustable. 2. The refrigeration according to claim 1, wherein an auxiliary compressor for increasing the pressure of the refrigerant is provided between the evaporator and the compressor, and the auxiliary compressor is driven by power extracted by the expander. cycle. The refrigeration cycle according to claim 1, wherein power extracted by the expander is used as power for the compressor. A bypass passage that bypasses the internal heat exchanger in at least one of a high-pressure path from the radiator to the expander and a low-pressure path from the evaporator to the compressor, and a flow rate of refrigerant flowing through the bypass passage is adjusted. The refrigeration cycle according to claim 1, further comprising: a bypass valve that controls the amount of heat exchange by the internal heat exchanger by controlling the bypass valve. The bypass flow path for bypassing the expander and a pressure reducing valve for adjusting the flow rate of refrigerant flowing through the bypass path are provided, and the flow rate of the refrigerant flowing through the expander is adjusted by controlling the pressure decrease valve. 2. The refrigeration cycle according to 2. The refrigeration cycle according to claim 1, wherein carbon dioxide is used as the refrigerant.

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