Vehicle air conditioning system and associated control method

Abstract

Vehicle air conditioning system and associated control method. The present invention relates to a method for controlling a refrigerant circuit (2) operating in heat pump mode, the circuit (2) being intended for installation in a vehicle, the circuit (2) comprising at least one refrigerant circulating within the circuit (2), a compression element (20), a gas cooler (22) performing heat exchange between the refrigerant and an airflow sent into a vehicle passenger compartment, the refrigerant entering the gas cooler (22) in a supercritical state, an expansion element (24) and an evaporator (26), the control method being characterized in that it comprises a step of determining a representative value of an equivalent opening diameter (Δeq) of the expansion element (24) as a function of a heating power (Pch) supplied by the gas cooler (22). (Figure 1)

Description

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

[0001] 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.

[0002] Motor vehicles are commonly equipped with a refrigerant circuit used to contribute to the thermal treatment of various areas or components of the vehicle. It is particularly known to use an air conditioning system incorporating a refrigerant circuit to thermally treat an airflow sent into the passenger compartment of a vehicle equipped with such a circuit. This thermal treatment is achieved, in particular, through the circulation of the refrigerant within a ventilation, heating, and / or air conditioning system installed in the vehicle.

[0003] R744 is a natural fluid used as a refrigerant in air conditioning systems. In particular, it improves the coefficient of performance of air conditioning systems operating in heat pump mode. Such heat pump operation is also relevant for heating the passenger compartment of an electric vehicle, in which the absence of an internal combustion engine prevents the use of such an engine as a heat source.

[0004] In air conditioning mode, a refrigerant circuit of such an air conditioning system, in which the refrigerant is in a supercritical state in a high-pressure section of the circuit, includes a gas cooler that supplies heat to the vehicle's outside air. The pressure in the gas cooler is regulated according to the temperature of the refrigerant at the gas cooler outlet, these two parameters being linearly related within the temperature range of the refrigerant at the gas cooler outlet when the latter is in operation. This linear relationship allows for the regulation of the high pressure in the circuit and thus optimizes the system's coefficient of performance.

[0005] The inventors have however found that such regulation is not possible when the air conditioning system is operating in heat pump mode.

[0006] There is therefore 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.

[0007] The present invention aims to remedy at least partially 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 including such a circuit, and a computer program to implement the control process, which optimize the coefficient of performance of the circuit by using a model linking 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.

[0008] 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. ,

[0009] It is understood that in this refrigerant circuit operating in heat pump mode, the first heat exchanger is a heat exchanger operating in certain cases 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.

[0010] The second heat exchanger in the refrigerant circuit, operating in heat pump mode, absorbs 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 of the vehicle. The second heat exchanger can therefore function as a gas evaporator in this heat pump mode.

[0011] The equivalent opening diameter of the expansion member corresponds to the opening diameter of the expansion member when its opening is a circular tube and when the expansion member is passive, that is to say, without active modulation of the fluid passage cross-section in the expansion member, for example an orifice. The The equivalent opening diameter in the determination stage corresponds to an optimized setting of the expansion device in terms of energy consumption of the refrigerant circuit, relative to the heating power supplied.

[0012] In other words, for a given heating power, supplied by the refrigerant circuit, the expansion device is adjusted according to the equivalent opening diameter corresponding to the representative data determined, allows a minimum energy consumption of the refrigerant circuit to supply the required heating power.

[0013] The representative data of 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.

[0014] Thanks to the invention, the energy consumption of the refrigerant circuit is optimized for a given heating power when used in heat pump mode. It is understood that the refrigerant circuit can also operate in air conditioning mode, i.e., cooling the passenger compartment.

[0015] The refrigerant is carbon dioxide (known by the acronym R744)

[0016] A relationship linking the flow rate to the inlet / outlet pressures and inlet temperature is as follows:

[0017] Mrg = Kv. Ro. DiA2 Root(Pi-Po) (eql)

[0018] Ro density of the fluid at its inlet depending on its pressure and temperature.

[0019] In this case Di is said to be the equivalent diameter of the regulator.

[0020] The step of determining the data representative of an equivalent opening diameter includes, 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.

[0021] Alternatively, the step of determining the representative data of an equivalent opening diameter includes at least the calculation of the sum: a1+a2^Pch / Pmax)^ alpha (eq2)°û al is a first predetermined constant, a2 is a second predetermined constant, alpha a third predetermined constant and P is the heating power supplied by the first heat exchanger.

[0022] When the representative data of 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.

[0023] Lasomme al+a2 is the equivalent diameter corresponding to the nominal or maximum heating power.

[0024] 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.

[0025] 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 by means of the characteristic of the ventilation and air conditioning (HVAC) system.

[0026] 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).

[0027] In other words, the determination step is in this case followed by a control step of the electronic expansion device allowing the equivalent opening diameter to be obtained, optimizing the coefficient of performance of the refrigerant circuit.

[0028] More generally, whether the release member is electronic with pulses or not, the determination step is followed by a control step of the release member, to reach the equivalent opening diameter.

[0029] 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 element. This correction step compensates for any imperfections in the expansion valve's characteristic curve.

[0030] The flow rate drawn in by the compressor is estimated either by the compressor characteristic as a function of the inlet / outlet pressures and its rotational speed, or by performing the energy balance

[0031] Pch = Mcpa.(Tair o-Tair i) = MRg.Dhr (eq3)

[0032] 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.

[0033] The step of correcting a setpoint for a refrigerant flow rate is optionally followed by a further step of determining a representative data point 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 new correction step of a setpoint of a refrigerant flow generated by the compression unit as a function of the target outlet temperature of the air sent into the passenger compartment.

[0034] In other words, after the correction step, the control process loops back to the estimation or determination step once the compression unit is activated with the corrected refrigerant flow setpoint. Several loops are performed, for example, until convergence.

[0035] 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 according to 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 outlet of the compressor. In other words, the compressor is controlled so that the refrigerant flow rate it generates respects the mechanical and thermal limits of the compressor.

[0036] 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.

[0037] 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 several processors, these processors are embedded in one or more control units.

[0038] 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.

[0039] Other features and advantages of the invention will become apparent from the following description on the one hand, and from several embodiments given as examples. indicative and not exhaustive, with reference to the attached schematic drawings, on which:

[0040] [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,

[0041] [Fig.2] is an enthalpy diagram on which the refrigerant fluid cycle evolving in the circuit of [Fig. 1] is represented,

[0042] [Fig.3] represents steps of a control method according to the invention, of the circuit of refrigerant fluid of [Fig. 1], in one embodiment of the invention,

[0043] [Fig.4] represents control loops used in the control process of the [Fig.3],

[0044] [Fig.5] represents a first table of data from implementations of the method of controlling [Fig.3], for different heating powers supplied at different ambient temperatures, and

[0045] [Fig.6] represents a second table of data from implementations of the control method of [Fig.3], for different heating powers supplied at different ambient temperatures.

[0046] According to an embodiment of the invention shown in [Fig. 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.

[0047] The gas cooler 22 is a heat exchanger through which the refrigerant circulates and through which air is drawn from outside and / or from the passenger compartment of a vehicle at an inlet temperature Te, and sent warmer into said passenger compartment at an outlet temperature Ts. The inlet temperature Te is therefore the temperature of the air upon entering the gas cooler 22, and the outlet temperature Ts is the temperature of the air upon exiting the gas cooler 22. The heating power released by heating the air in the passenger compartment is referred to as Pch.

[0048] The evaporator 26 is also a heat exchanger through which both the refrigerant fluid and, for example, air from outside the vehicle circulate. This air is initially at a temperature Ti and then expelled from the vehicle at a lower 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.

[0049] The direction of flow of the refrigerant in circuit 2 is represented by arrows on circuit 2. In this embodiment of the invention, the refrigerant is carbon dioxide.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] During this initialization step 102, the refrigerant circuit 2 is therefore activated by controlling the expansion member 24s, this control being carried out by the electronic control means of the expansion member 24. The conversion between the equivalent opening diameter and the control signal is carried out by the conversion module 34.

[0054] 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 it from the passenger compartment.

[0055] The next step, implemented by the calculation module 32, is the determination 106 of an equivalent opening diameter Dide of the expansion device 24 as a function of the previously estimated heating power Pch. This determination step 106 comprises the following calculation 106a:

[0056] Di = a 1+a ^^)~ aI p ha m

[0057] Where:

[0058] - Diest an equivalent opening diameter of the detent member 24, according the equation (eql),

[0059] -

[0060] As an alternative in this determination step 106, the 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.

[0061] 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,

[0062] This conversion uses, for example, a conversion table determined empirically on a test bench. These tests use, for example, relation (2):

[0063] Mgr = k v * 0eqD i 2 *^p2-Pi

[0064] Where:

[0065] - Mgr is the flow rate of refrigerant generated by the expansion valve 24,

[0066] - d is the density of the refrigerant fluid at the inlet of the expansion valve 24,

[0067] - Di is the equivalent opening diameter of the corresponding expansion member a control for opening the trigger mechanism 24,

[0068] - P2 is the pressure of the refrigerant fluid at the inlet of the expansion valve 24, and

[0069] - PI is the pressure of the refrigerant fluid at the outlet of the expansion device 24.

[0070] When a command is applied for the opening of the expansion member 24, relation (2) allows, having calculated Mgr, d and measured the pressures PI and P2, to determine the equivalent opening diameter Di for the command applied.

[0071] The calculation of the density d of refrigerant fluid at the inlet of the expansion member 24 uses for example a measurement of the pressure P2 and the temperature of the refrigerant fluid at the inlet of the expansion member 24.

[0072] The next step is the correction 110 of a setpoint for the flow rate of refrigerant generated by the compressor unit 20 as a function of a target outlet temperature Tse of the air sent into 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 of the compressor unit 20, which corresponds to a setpoint for the flow rate of refrigerant that enables the target temperature to be reached. the target outlet temperature Tse. The computer then sends this setpoint speed Vc to the control means of the compression element 20.

[0073] 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.

[0074] 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.

[0075] 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 the 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.

[0076] Figures 5 and 6 present data tables from the control process 100, implemented for different configurations, each corresponding to a column in one of the tables, the column comprising:

[0077] - the initial temperature Ti of the outside air in degrees Celsius,

[0078] - the heating power Pch supplied to the vehicle's passenger compartment, in kW,

[0079] - the outlet temperature Ts of the air passing through the gas cooler 22, in degrees Celsius,

[0080] - the electrical power Pe expended by the air conditioning system according to the invention in kW,

[0081] - the equivalent opening diameter Di used to adjust the detent member 24, a times the target outlet temperature Tse reached, in mm, and

[0082] - the mass of air Ma in kilograms per unit time that passes through the cooler of gas 22.

[0083] In eight of these twelve configurations, the electrical power Pe expended corresponds to the minimum electrical power achievable for heating power supplied, as empirically estimated on a test bench. In the four other configurations, this minimum electrical power is reached within 3% of a difference.

[0084] 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.

[0085] 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 characteristics 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. A method of controlling (100) 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 as an evaporator, the method of controlling (100) being characterized in that it comprises a step of determining (106) a data representative of an equivalent opening diameter (Di) of the expansion element (24) as a function of a heating power (Pch) supplied by the first heat exchanger (22).

2. Control method (100) according to claim 1, wherein 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 determination step (106) of the representative data of an equivalent opening diameter (Di) uses a function increasing as a function of the heating power supplied by the first heat exchanger (22).

4. 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 rate sent into the passenger compartment, an inlet temperature (Te) and an outlet temperature (Ts) of the air passing through the first heat exchanger (22).

5. A control method (100) according to any one of claims 1 to 4, wherein the data determination step (106) representative of an equivalent opening diameter (Di) is followed by a conversion step (108) of the data representative of an equivalent opening diameter (Di) into a command to be applied to the detent member (24).

6. Control method (100) according to claim 5, comprising a step of estimating a flow rate of refrigerant circulating in the expansion member (24) and comparing the estimated flow rate to a theoretical flow rate obtained from a bijective relationship between the theoretical flow rate and the representative data of the equivalent opening diameter, the bijective relationship depending on the temperature (Ts) and the inlet pressure (P2) of the expansion member (24) as well as the outlet pressure (PI) of the expansion member (24).

7. Control method (100) according to claim 6, wherein when the estimated flow rate differs from the theoretical flow rate, the comparison step is followed by a correction step of the control to be applied to the expansion member (24).

8. Control method (100) according to any one of claims 5 to 7, wherein the conversion step (108) is followed by a correction step (110) of a setpoint for a refrigerant flow rate drawn in 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 8, wherein the correction step (110) of a setpoint for a refrigerant flow rate is followed by a further determination step (106) of a representative data 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 further determination step (106) being followed by a further correction step (110) of a setpoint for a refrigerant flow rate drawn in by the compression member (20) as a function of the target outlet temperature (Tse) of the air sent into the passenger compartment.

10. A control method (100) according to claim 8 or 9, wherein, during the correction step (110) of a setpoint for the flow rate of refrigerant drawn into the compression element (20), the setpoint for the flow rate of refrigerant generated by the compression element (20) is limited according to a low-pressure threshold, a high-pressure threshold, and 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) capable of operating as an evaporator, the air conditioning system further comprising means for controlling the refrigerant circuit (2), the air conditioning system being characterized in that it further comprises means for determining a representative data of an equivalent opening diameter (Di) of the expansion element (24) as a function of a heating power (Pch) supplied by the first heat exchanger (22).

12. Computer program comprising program code instructions for performing the steps of the control method (100) according to any one of claims 1 to 10, when the program is executed by one or more processors.

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