Air-conditioning system for vehicle and associated control method

Abstract

The present invention relates to a method for controlling a refrigerant circuit (2) operating in heat pump mode, the circuit (2) being intended to be installed in a vehicle, the circuit (2) comprising at least one refrigerant circulating within the circuit (2), a compression member (20), a gas cooler (22) performing heat exchange between the refrigerant and an air flow sent into a passenger compartment of the vehicle, the refrigerant arriving in the gas cooler (22) in the supercritical state, an expansion member (24) and an evaporator (26), the control method being characterized in that it comprises a step of determining a data item representative of an equivalent opening diameter (∅eq) of the expansion member (24) as a function of the heating power (Pch) supplied by the gas cooler (22). (Figure 1)

Description

[0001] DESCRIPTION

[0002] Title of the invention: Vehicle air conditioning system and associated control method

[0003] The present invention relates to the field of heat treatment systems for motor vehicles, and more specifically concerns an air conditioning system for a vehicle passenger compartment.

[0004] Motor vehicles are commonly equipped with a refrigerant circuit used to contribute to the thermal treatment of various areas or components within the vehicle. It is particularly well known that an air conditioning system with a refrigerant circuit is used to thermally treat the airflow sent into the passenger compartment of a vehicle equipped with such a circuit. This thermal treatment is achieved primarily through the circulation of the refrigerant within a ventilation, heating, and / or air conditioning system installed in the vehicle.

[0005] R744 is a natural fluid used as a refrigerant in air conditioning systems. It notably improves the coefficient of performance (COP) of air conditioning systems operating in heat pump mode. This type of heat pump operation is also relevant for heating the passenger compartment of electric vehicles, where the absence of an internal combustion engine prevents its use as a heat source.

[0006] In air conditioning mode, a refrigerant circuit in such an air conditioning system, where the refrigerant is in a supercritical state in a high-pressure section of the circuit, includes a gas cooler that transfers heat to the vehicle's outside air. The pressure in the gas cooler is regulated based on the temperature of the refrigerant at its outlet; these two parameters are linearly related within the temperature range of the refrigerant at the gas cooler's outlet when it is operating. This linear relationship allows for precise regulation of the high pressure in the circuit, thus optimizing the system's coefficient of performance.

[0007] The inventors have found, however, that such regulation is not possible when the air conditioning system is operating in heat pump mode.

[0008] Therefore, there is a need to control a refrigerant circuit operating in heat pump mode for R744, and which allows the coefficient of performance of the refrigerant circuit to be optimized in this operating mode.

[0009] The present invention aims to remedy at least in part the aforementioned drawbacks by providing a method for controlling a refrigerant circuit operating in heat pump mode, in which the refrigerant is in a supercritical state in a high-pressure part of the circuit, as well as a vehicle air conditioning system comprising such a circuit, and a computer program for implementing the control method, which optimize the coefficient of performance of the circuit by using a model relating an equivalent opening diameter of an expansion device of the refrigerant circuit to a heating power supplied by a gas cooler of the refrigerant circuit.

[0010] To this end, the invention proposes a method for controlling a refrigerant circuit operating in heat pump mode, the circuit being intended to be installed in a vehicle, the circuit comprising at least one refrigerant circulating within the circuit, a compression element, a first heat exchanger operating a heat exchange between the refrigerant and an airflow sent into a passenger compartment of the vehicle, an expansion element and a second heat exchanger operating a heat exchange between the refrigerant and a heat transfer fluid such as, for example, an airflow from outside the vehicle, the control method being characterized in that it uses a relationship between a flow rate circulating in the expansion element and an equivalent opening diameter of the expansion element as a function of the upstream and downstream temperature conditions of the expansion element,a determination step (106) of a representative data of an equivalent opening diameter Di (Æeq) of the expansion member (24) as a function of a heating power (Pch) supplied by the first heat exchanger (22), control of the opening of the expansion member (24) from the equivalent opening diameter determined for the required heating power.

[0011] It is understood that in this refrigerant circuit operating in heat pump mode, the first heat exchanger is a heat exchanger which in some cases operates as a gas cooler and in which both the refrigerant and an airflow circulate, which is sent into the passenger compartment, after having taken heat from the refrigerant in the first heat exchanger.

[0012] The second heat exchanger in the refrigerant circuit, operating in heat pump mode, extracts heat from a heat transfer fluid, such as an airflow passing through it. This airflow originates from outside the vehicle and is returned cooled to the outside. Therefore, the second heat exchanger can function as a gas evaporator in this heat pump mode.

[0013] The equivalent opening diameter of the expansion valve corresponds to the opening diameter of the expansion valve when its opening is a circular tube and when the expansion valve is passive, i.e., without active modulation of the fluid passage cross-section, such as an orifice. The equivalent opening diameter in the determination stage corresponds to an optimized expansion valve setting in terms of the refrigerant circuit's energy consumption relative to the heating output.

[0014] In other words, for a given heating power, supplied by the refrigerant circuit, the expansion device is set according to the equivalent opening diameter corresponding to the determined representative data, allowing a minimum energy consumption of the refrigerant circuit to supply the required heating power.

[0015] The representative data for this equivalent opening diameter is the variable relating the flow rate of the expanded refrigerant under the operating conditions of the expansion valve, i.e.: its inlet and outlet pressure, its inlet temperature.

[0016] Thanks to this invention, the energy consumption of the refrigerant circuit is optimized for a given heating output when used in heat pump mode. It is understood that the refrigerant circuit can also operate in air conditioning mode, i.e., to cool the passenger compartment.

[0017] The refrigerant is carbon dioxide (known by the acronym R744)

[0018] A relationship linking flow rate to inlet / outlet pressures and inlet temperature is as follows:

[0019] Mrg = Kv. Ro. Di A 2. Root(Pi-Po) (eq1)

[0020] The density of the fluid at its inlet depends on its pressure and temperature.

[0021] In this case, Di is said to be the equivalent diameter of the regulator.

[0022] The step of determining the data representative of an equivalent opening diameter involves, for example, reading from a data table containing several data representative of equivalent opening diameters Di and several heating powers Pch, said table associating each of the heating powers with one of the data representative of equivalent opening diameters.

[0023] Alternatively, the step of determining the representative data for an equivalent opening diameter includes at least the calculation of the sum: a + a2* (Pcl'i / Pmax) 1 '- alpha (eq2) where a is a first predetermined constant, a2 is a second predetermined constant, alpha is a third predetermined constant and P ch is the heating power supplied by the first heat exchanger.

[0024] When the data representing an equivalent opening diameter is an equivalent opening diameter or radius, the first predetermined constant corresponds, for example, to the minimum equivalent opening diameter or radius achievable by the expansion member.

[0025] The sum a1+a2 is the equivalent diameter corresponding to the nominal or maximum heating power.

[0026] In one embodiment of the invention, the step of determining the data representative of an equivalent opening diameter is preceded by a step of estimating the heating power supplied by the first heat exchanger, as a function of an air flow sent into the passenger compartment, an inlet temperature and an outlet temperature of the air passing through the first heat exchanger.

[0027] The inlet and outlet temperatures of air passing through the first heat exchanger are estimated or measured, and the airflow sent into the passenger compartment is estimated, for example, using information on the voltage of the fan sending air into the first heat exchanger, then into the passenger compartment using the characteristic of the ventilation and air conditioning (HVAC) system.

[0028] Furthermore, when the expansion member is an electronic expansion member, the step of determining the representative data of an equivalent opening diameter is followed by a step of converting the representative data of a determined equivalent opening diameter into an input signal for controlling the expansion valve following its characteristic curve Di = function (signal).

[0029] In other words, the determination step is in this case followed by a control step of the electronic expansion device allowing to obtain the equivalent opening diameter optimizing the coefficient of performance of the refrigerant circuit.

[0030] More generally, whether the expansion device is electronic with pulses or not, the determination step is followed by a control step of the expansion device, to achieve the equivalent opening diameter.

[0031] The conversion step, or more generally the adjustment step, is potentially followed by a verification or correction step depending on the refrigerant flow rate drawn into the compression device. This correction step compensates for any imperfections in the expansion valve's characteristic curve.

[0032] The flow rate drawn in by the compressor is estimated either by the compressor's characteristics as a function of the inlet / outlet pressures and its rotational speed, or by performing an energy balance.

[0033] Pch = Mcpa.(Tair o-Tair i) = MRg.Dhr (eq3)

[0034] Dhr: difference in enthlapy of the R744 fluid between the inlet / outlet of the first exchanger, determined according to the estimated and / or measured pressures and temperatures.

[0035] The step of correcting a setpoint for a refrigerant flow rate is possibly followed by a further step of determining a representative data for an equivalent opening diameter of the expansion device as a function of a new heating power supplied by the first heat exchanger, the new determination step being followed by a further step of correcting a setpoint for a refrigerant flow rate generated by the compression device as a function of the target outlet temperature of the air sent into the passenger compartment.

[0036] In other words, after the correction step, the control process loops back to the estimation or determination step once the compressor unit is activated with the corrected refrigerant flow setpoint. Several loops are performed, for example, until convergence.

[0037] During the step of correcting a setpoint for the refrigerant flow rate generated by the compressor, the setpoint for the refrigerant flow rate generated by the compressor may be limited based on a low-pressure threshold (thus limiting the heating power achieved), a high-pressure threshold, a maximum compression ratio, and a maximum temperature threshold at the compressor outlet. In other words, the compressor is controlled so that the refrigerant flow rate it generates respects the mechanical and thermal limits of the compressor.

[0038] The invention also relates to a vehicle air conditioning system, comprising a refrigerant circuit capable of operating in heat pump mode, the circuit comprising a compression element, a first heat exchanger capable of carrying out a heat exchange between the refrigerant and an airflow sent into a passenger compartment of the vehicle, an expansion element and a second heat exchanger carrying out a heat exchange between the refrigerant and a heat transfer fluid such as an airflow from outside the vehicle, the air conditioning system further comprising means for controlling the refrigerant circuit, the air conditioning system being characterized in that it further comprises, when the refrigerant is capable of circulating in the supercritical state, R744.

[0039] The invention also relates to a computer program comprising program code instructions for executing the steps of the control method according to the invention, when the program is executed by one or more processors. When there are multiple processors, these processors are embedded in one or more control units.

[0040] The air conditioning system according to the invention, and the computer program according to the invention, have advantages similar to those of the control method according to the invention.

[0041] Other features and advantages of the invention will become apparent from the following description on the one hand, and from several illustrative and non-limiting examples of embodiments given with reference to the attached schematic drawings on the other hand, in which:

[0042] [Fig. 1] represents a refrigerant fluid circuit of an air conditioning system according to the invention, operating in heat pump mode, in one embodiment of the invention.

[0043] [fig 2] is an enthalpy diagram on which the cycle of the refrigerant fluid evolving in the circuit of figure 1 is represented,

[0044] [Fig. 3] represents steps of a control method according to the invention, of the refrigerant circuit of Figure 1, in an embodiment of the invention; [Fig. 4] represents control loops used in the control method of Figure 3.

[0045] [Fig. 5] represents a first table of data from implementations of the control process of Figure 3, for different heating powers supplied at different ambient temperatures, and

[0046] [fig 6] represents a second table of data from implementations of the control process of figure 3, for different heating powers supplied at different ambient temperatures.

[0047] According to an embodiment of the invention shown in Figure 1, an air conditioning system according to the invention comprises a refrigerant circuit 2 operating here in heat pump mode. The refrigerant circuit 2 comprises a compression element 20, a gas cooler 22, an expansion element 24, and an evaporator 26.

[0048] The gas cooler 22 is a heat exchanger through which the refrigerant circulates. Air is drawn in from outside and / or from the passenger compartment of a vehicle at an inlet temperature Te and then sent into the passenger compartment at a higher temperature Ts. The inlet temperature Te is therefore the temperature of the air entering the gas cooler 22, and the outlet temperature Ts is the temperature of the air exiting the gas cooler 22. The heating power generated by heating the passenger compartment air is denoted Pch.

[0049] The evaporator 26 is also a heat exchanger through which both the refrigerant and, for example, air from outside the vehicle circulate. This air, initially at a temperature Ti, is then expelled from the vehicle at a lower temperature, reaching a final temperature To. The initial temperature Ti is therefore the temperature of the air entering the evaporator 26, and the final temperature To is the temperature of the air exiting the evaporator 26.

[0050] The direction of refrigerant flow in circuit 2 is indicated by arrows on circuit 2. In this embodiment of the invention, the refrigerant is carbon dioxide.

[0051] The air conditioning system further comprises means for controlling the refrigerant circuit, capable of implementing a control method 100 according to the invention, described now with reference to Figures 3 and 4. The control means comprise, in this embodiment of the invention, at least electronic control means for the expansion member 24, temperature sensors, a speed sensor, a computer implementing an estimation module 30, a calculation module 32, a conversion module 34 and a speed regulator 36.

[0052] The computer is capable of receiving data from the sensors and sending instructions to the electronic control means of the expansion member 24 as well as to control means of the compression member 20. The computer executes a computer program according to the invention, enabling the implementation of the control method 100 according to the invention by means of the control means.

[0053] During an initialization step 102 of the control process 100, a heating power Pch, for example of 4kW, is entered into the calculation module 32 to obtain an initial equivalent opening diameter of the expansion member 24. The operation of the calculation module 32 is detailed later in relation to a subsequent step of determining an equivalent opening diameter.

[0054] During this initialization step 102, the refrigerant circuit 2 is therefore activated by controlling the expansion device 24s, this control being carried out by the electronic control means of the expansion device 24. The conversion between the equivalent opening diameter and the control signal is carried out by the conversion module 34.

[0055] The next step, implemented by the estimation module 30, is the estimation 104 of the heating power Pch supplied by the gas cooler 22, as a function of the airflow rate sent into the passenger compartment, the inlet temperature Te and the outlet temperature Ts of the air passing through the gas cooler 22. The inlet temperature Te and the outlet temperature Ts of the air are measured or estimated by the temperature sensors located respectively at the inlet and outlet of the gas cooler 22. The airflow rate sent into the passenger compartment is estimated using the control of the fan located at the inlet or outlet of the gas cooler 22, which sends air into the passenger compartment after having previously drawn air from it.

[0056] The next step, implemented by calculation module 32, is the determination 106 of an equivalent opening diameter Dide of the expansion valve 24 as a function of the previously estimated heating power Pch. This determination step 106 includes the following calculation 106a:

[0057] OR :

[0058] - Diest an equivalent opening diameter of the expansion member 24, according to equation (eq1),

[0059] As an alternative in this determination step 106, calculation 106a is replaced by a reading of the equivalent opening diameter Di in a data table, providing for a given heating power, a corresponding equivalent opening diameter.

[0060] The next step is the conversion 108, by the conversion module 34, of the equivalent opening diameter Di determined previously, into a command, and the control of the expansion member 24, by the electronic control means of the expansion member 24,

[0061] This conversion uses, for example, a conversion table determined empirically on a test bench. These tests use, for example, relation (2):

[0062] Mgr = kv.* 0eqDi 2 * 2 — PI (eq2)

[0063] OR :

[0064] - Mgr is the flow rate of refrigerant generated by the expansion valve 24,

[0065] - d is the density of the refrigerant fluid at the inlet of the expansion valve 24,

[0066] - Di is the equivalent opening diameter of the release member corresponding to a command to open the release member 24,

[0067] - P2 is the pressure of the refrigerant fluid at the inlet of the expansion valve 24, and

[0068] - P1 is the pressure of the refrigerant fluid at the outlet of the expansion valve 24.

[0069] When a command is applied to open the expansion valve 24, equation (2), after calculating Mgr, d, and measuring the pressures P1 and P2, allows the equivalent opening diameter Di for the applied command to be determined. The calculation of the refrigerant density d at the inlet of the expansion valve 24 uses, for example, a measurement of the pressure P2 and the temperature of the refrigerant at the inlet of the expansion valve 24.

[0070] The next step is the correction 110 of a setpoint for the flow rate of refrigerant generated by the compressor unit 20, based on a target outlet temperature Tse of the air supplied to the passenger compartment. This correction step 110 is implemented by the speed controller 36, which receives a difference E between, on the one hand, the outlet air temperature Ts, measured at the outlet of the gas cooler 22, and, on the other hand, the target outlet temperature Tse. From this difference E, the speed controller 36 calculates a setpoint speed Vc for the compressor unit 20, which corresponds to a setpoint for the flow rate of refrigerant required to reach the target outlet temperature Tse. The control unit then sends this setpoint speed Vc to the control means of the compressor unit 20.

[0071] The setpoint speed Vc thus calculated corresponds to a refrigerant flow setpoint corrected with respect to the previous refrigerant flow setpoint, provided that the target outlet temperature Tse is not reached.

[0072] Furthermore, during this correction step 110, the setpoint for the flow rate of refrigerant generated by the compression unit 20 is limited according to a low pressure threshold, set for example at 9 bars, a high pressure threshold, set for example at 130 bar, a maximum compression ratio, set for example at 6 bars and a maximum temperature threshold of the refrigerant at the outlet of the compression unit 20, set for example at 130°C. These limitations related to the mechanical and thermal constraints of the compression unit 20, have an impact on the speed Vc calculated at the outlet of the speed regulator 36.

[0073] At the end of the correction step 110, when the air outlet temperature Ts of the gas cooler 22 is stabilized, the control process 100 loops back to step 104 of estimating the heating power Pch supplied by the gas cooler 22, so as to redetermine 106 an equivalent opening diameter Di allowing to optimize the coefficient of performance of the air conditioning system according to the invention, then to convert 108 this equivalent opening diameter Di into a new electronic control of the expansion member 24. These new steps are then followed, as long as the target outlet temperature Tse is not reached, by a new correction step 110 of a setpoint for the flow rate of refrigerant generated by the compression member 20, and so on.

[0074] Figures 5 and 6 present data tables from control process 100, implemented for different configurations, each corresponding to a column in one of the tables, the column containing:

[0075] - the initial temperature Ti of the outside air in degrees Celsius,

[0076] - the heating power Pch supplied to the vehicle's passenger compartment, in kW,

[0077] - the outlet temperature Ts of the air passing through the gas cooler 22, in degrees Celsius,

[0078] - the electrical power Pe consumed by the air conditioning system according to the invention in kW,

[0079] - the equivalent opening diameter Di used to adjust the expansion valve 24, once the target outlet temperature Tse is reached, in mm, and

[0080] - the mass of air Ma in kilograms per unit time that passes through the gas cooler 22.

[0081] In eight of these twelve configurations, the electrical power Pe consumed corresponds to the minimum electrical power achievable for the heating power supplied, as empirically estimated on a test bench. In the other four configurations, this minimum electrical power is reached within 3% of the target.

[0082] The invention therefore provides a control method minimizing the electrical consumption of a refrigerant circuit operating in heat pump mode, the refrigerant being in a supercritical state at the inlet of the gas cooler, while achieving the required heating power.

[0083] Of course, the invention is not limited to the examples just described, and many modifications can be made to these examples without departing from the scope of the invention. In particular, the features of the different embodiments of the invention envisaged in this application can be combined to carry out the invention, provided that these embodiments are not incompatible with each other.

Claims

DEMANDS 1- Control method (100) of a refrigerant circuit (2) operating in heat pump mode, the circuit (2) being intended to be installed in a vehicle, the circuit (2) comprising at least one refrigerant circulating within the circuit (2), a compression element (20), a first heat exchanger (22) operating a heat exchange between the refrigerant and an airflow sent into a passenger compartment of the vehicle, an expansion element (24) and a second heat exchanger (26) operating a heat exchange functioning as an evaporator, the control method (100) being characterized in that it uses a relationship between a flow rate circulating in the expansion element and an equivalent opening diameter of the expansion element as a function of the upstream and downstream temperature conditions of the expansion element,a determination step (106) of a representative data of an equivalent opening diameter Di (Æeq) of the expansion member (24) as a function of a heating power (Pch) supplied by the first heat exchanger (22), control of the opening of the expansion member (24) from the equivalent opening diameter determined for the required heating power. 2- Control method (100) according to claim 1, in which the determination step (106) of the data representative of an equivalent opening diameter Di comprises a reading in a data table comprising several data representative of equivalent opening diameters and several heating powers, said table associating each of the heating powers with one of the data representative of equivalent opening diameters. 3- Control method (100) according to claim 1, wherein the step of determining (106) the representative data of an equivalent opening diameter (0eq) comprises at least the calculation (106a) of the sum: where a is a first predetermined constant, a2 is a second predetermined constant, alpha a third predetermined constant and Pch is the heating power supplied by the first heat exchanger (22). 4- The equivalent diameter Di connecting the relaxed flow is given by the equation Mgr = kv.* d * Di 2 * 2 — PI Mgr refrigerant flow rate, kv a predetermined constant, d: fluid density at the inlet of the expansion valve, P2, P1: upstream / downstream pressure of the expansion valve 5- Control method (100) according to any one of claims 1 to 3, wherein the determination step (106) of the representative data of an equivalent opening diameter Di is preceded by an estimation step (104) of the heating power (Pch) supplied by the first heat exchanger (22), as a function of an air flow sent into the passenger compartment, an inlet temperature (Te) and an outlet temperature (Ts) of the air passing through the first heat exchanger (22). 6- The refrigerant flow rate Mrg is estimated through the energy balance of the first exchanger or by the compressor characteristic, this flow rate allows verification of the applied value of the equivalent diameter for a possible correction. 7- Control method (100) according to any one of claims 1 to 4, wherein, where the detent member (24) is an electronic detent member, the determination step (106) of the representative data of an equivalent opening diameter Di is followed by a conversion step (108) of the representative data of an equivalent opening diameter Di determined into a command, to be applied to the electronic detent member. 8- Control method (100) according to claim 5, wherein the conversion step (108) is followed by a correction step (110) of a setpoint of a refrigerant flow generated by the compression member (20) as a function of a target outlet temperature (Tse) of the air sent into the passenger compartment. 9- Control method (100) according to claim 6, wherein the correction step (110) of a setpoint for a refrigerant flow rate is followed by a further determination step (106) of a data representative of an equivalent opening diameter of the expansion member as a function of a new heating power (Pch) supplied by the first heat exchanger (22), the new determination step (106) being followed by a further correction step (110) of a setpoint for a refrigerant flow rate generated by the compression member (20) as a function of the target outlet temperature (Tse) of the air sent into the passenger compartment. 10- Control method (100) according to claim 6 or 7, wherein during the correction step (110) of a setpoint of a refrigerant flow generated by the compression unit (20), the setpoint for the flow rate of refrigerant generated by the compression unit (20) is limited according to a low pressure threshold, a high pressure threshold, a maximum compression ratio and a maximum temperature threshold at the outlet of the compression unit (20). 11- Vehicle air conditioning system, comprising a refrigerant circuit (2) capable of operating in heat pump mode, the circuit (2) comprising a compression element (20), a first heat exchanger (22) capable of carrying out heat exchange between the refrigerant and an airflow sent into a passenger compartment of the vehicle, an expansion element (24) and a second heat exchanger (26) carrying out heat exchange between the refrigerant and an airflow from outside the vehicle, the air conditioning system further comprising means for controlling the refrigerant circuit (2), the air conditioning system being characterized in that it further comprises, when the refrigerant is capable of circulating in a supercritical state in the first heat exchanger (22),means of determining a representative data for an equivalent opening diameter (0eq) of the expansion device (24) as a function of a heating power (Pch) supplied by the first heat exchanger (22). 12- Computer program comprising program code instructions for the execution of the steps of the control process (100) according to any one of claims 1 to 8, when the program is executed by one or more processors.

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