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  Air conditioning systems for vehiclesUSPTO Application #: 20070028633Title: Air conditioning systems for vehicles Abstract: An air conditioning system for a vehicle includes a compressor, a gas cooler, an expansion means, and a cooler. The system also includes an elevated pressure density detector for detecting or estimating one or more physical values having a correlation with a density of an elevated pressure refrigerant in a refrigeration cycle. An elevated pressure density controller controls the density of the elevated pressure refrigerant. This control is achieved at least in part by using at least one of the one or more physical values. (end of abstract) Agent: Baker Botts LLP C/o Intellectual Property Department - Washington, DC, US Inventors: Kenichi Suzuki, Masato Tsuboi, Yuuichi Matsumoto USPTO Applicaton #: 20070028633 - Class: 062190000 (USPTO) Related Patent Categories: Refrigeration, Automatic Control, Refrigeration Producer The Patent Description & Claims data below is from USPTO Patent Application 20070028633. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates generally to air conditioning systems for vehicles. More specifically, the present invention is directed towards vehicle air conditioning systems having a vapor compression refrigeration cycle which may use a natural-system refrigerant, such as carbon dioxide. [0003] 2. Description of Related Art [0004] Vehicle air conditioning systems using carbon dioxide gas as a refrigerant in a vapor compression refrigeration cycle operate at an elevated pressure. The pressure of the refrigerant in an elevated pressure-side line is adjusted by controlling with an external control signal an opening degree of a valve of an electric expansion mechanism (for example, Japanese Published Patent Application No. HO-7-294033A). An objective of such a system is the optimization of a coefficient of performance of the refrigeration cycle through control of the pressure in the elevated pressure-side line. The pressure in the elevated pressure-side line is calculated using the temperature of the elevated pressure-side refrigerant in the elevated pressure-side line. The opening degree of the valve of the expansion mechanism then is controlled so that the pressure of the elevated pressure-side refrigerant moves towards an optimum value. [0005] In the known systems described above, the displacement of a variable displacement compressor externally is controlled in order to adjust an exit-side air temperature of an evaporator. The signal for controlling the displacement is calculated from information of thermal load. [0006] In this known system and control method, it is difficult to achieve stable control using the elevated pressure-side refrigerant temperature alone, because the temperature is measured during a transient state of the refrigeration cycle and a target pressure of the elevated pressure-side line changes continuously with the temperature. More specifically, because the temperature is measured during a transient state of the refrigeration cycle, the system may search for the optimization point without achieving stable control. SUMMARY OF THE INVENTION [0007] Accordingly, a need has arisen for vehicle air conditioning systems that overcome these and other inconveniences of the related art. A technical advantage of the present invention is the ability to achieve stable control of the system. Another technical advantage of the present invention is the simplification of the control of the system. Yet another technical advantage of the present invention is an improved coefficient of performance of the refrigeration cycle. [0008] According to an embodiment of the present invention, an air conditioning system for a vehicle comprises a compressor, a gas cooler, an expansion means, and a cooler. The system also comprises an elevated pressure density detecting means for detecting or estimating one or more physical values having a correlation with the density of an elevated pressure refrigerant in a refrigeration cycle. An elevated pressure density control means controls the density of the elevated pressure refrigerant. This control is achieved at least in part by using at least one of the one or more physical values. [0009] According to another embodiment of the present invention, a method is provided for controlling an air conditioning system for a vehicle during a refrigeration cycle. The method comprises the steps of detecting or estimating one or more physical values and calculating a value of the density of the elevated pressure refrigerant. The method further comprises the steps of determining whether a second at least one of said one or more physical values is greater than or equal to a predetermined threshold value, and setting a density target value based on the result of the determination. In addition, the method comprises the steps of calculating the value of a control signal using a deviation between the calculated density value and the density target value. The method further comprises the steps of controlling an expansion means with the control signal. [0010] Other objects, features, and advantages of the present invention will be apparent to persons of ordinary skill in the art in view of the following detailed description of the invention and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0011] For a more complete understanding of the present invention, the needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following description taken in connection with the accompanying drawings. [0012] FIG. 1 is a schematic diagram of an air conditioning system for vehicles according to an embodiment of the present invention. [0013] FIG. 2 is a block diagram of a control method according to an embodiment of the present invention. [0014] FIG. 3 is a flowchart of a control method according to an embodiment of the present invention. [0015] FIG. 4 is a pressure-enthalpy-diagram of carbon dioxide refrigerant for illustrating that an elevated pressure-side refrigerant density may be determined from a refrigerant pressure and a refrigerant temperature according to embodiments of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0016] Embodiments of the present invention and their features and technical advantages may be understood by referring to FIGS. 1-4. These embodiments are presented by way of example only and are not intended to limit the present invention. [0017] FIG. 1 depicts an air conditioning system for vehicles according to an embodiment of the present invention. FIG. 1 shows the mechanical arrangement of components and the control means of an air conditioning system using carbon dioxide gas as the natural-system refrigerant. The mechanical arrangement of components may include an air circuit and a refrigeration circuit. In the refrigeration circuit, a compressor 1, a gas cooler 4 (e.g., a radiator), an expansion means 8 (e.g. an electronic expansion valve), a cooler 9 (e.g., an evaporator), and a liquid/gas separator 13 (e.g., an accumulator) may be provided. Further, in this embodiment, an inside heat exchanger 7 may be provided in the refrigeration circuit for performing heat exchange between the elevated pressure-side refrigerant and the lower-pressure side refrigerant. Gas cooler 4 may reduce the temperature of the elevated pressure-side refrigerant using outside air sent by a fan 5 for heat radiation. Cooler 9 may be disposed in an air duct 12 of an air conditioning unit. The temperature of air sent from a blower 11 may be reduced by cooler 9, and the cooled air may be sent toward the vehicle interior. [0018] A fixed displacement compressor, a variable displacement compressor, or the equivalent may be used as compressor 1. An engine of a vehicle may be used as a drive source, but other non-engine drive sources also may be used. The cooling effect of cooler 9 may be controlled via a displacement control signal of compressor 1, which controls a displacement control valve 2, or via ON/OFF control of a clutch (not shown) of compressor 1. Feedback for the temperature control loop may be obtained from the temperature of air exiting cooler 9, which may be detected by an air temperature sensor 10. Liquid/gas separator 13 may separate the refrigerant sent from cooler 9 into liquid and gas, may store the liquid refrigerant, and may flow out the gas refrigerant towards compressor 1. [0019] As shown in FIG. 1, a first PT sensor 3 (P: pressure; T: temperature) may be provided at a discharge side of compressor 1 for detecting a pressure and a temperature of the elevated pressure-side refrigerant discharged by compressor 1. A second PT sensor 6 may be provided at an exit-side of gas cooler 4 for detecting a pressure and a temperature of the elevated pressure-side refrigerant after being cooled by gas cooler 4. Detection signals Pd and Td from first PT sensor 3, detection signals Pgout (refrigerant pressure at the exit-side of the gas cooler) and Tgout (refrigerant temperature at the exit-side of the gas cooler 4), and the detection signal from air temperature sensor 10 may be sent to a controller 14, which may control the air conditioning system. Further, a compressor rotational speed signal Nc, a voltage (rotational speed) signal BLV of blower 11, a vehicle running speed signal VS, an outside air temperature signal Tamb, and other signals may be input to controller 14. The displacement control signal for compressor 1 may be output from controller 14 to displacement control valve 2. Another control signal may be output from controller 14 to expansion means 8 for controlling the density of the elevated pressure-side refrigerant. A value of the control signal may be calculated using a density value, which is detected or estimated according to a predetermined characteristic (e.g. FIG. 4), and a density target value, which may be a predetermined constant value. The value of the control signal may determine an opening degree of a valve or an expansion ratio (i.e., a ratio between pressures at an entrance and an exit of the expansion means), which in turn may change the density of the elevated pressure refrigerant to become the density target value. [0020] A density detecting means may also be constructed substantially integrally with expansion means 8. In this embodiment, second PT sensor 6 may be located downstream of inside heat exchanger 7 with expansion means 8. Continue reading... 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