WO2004005059A1 - Air-conditioning unit equipped with an electronic control device - Google Patents

Abstract

The invention concerns a motor vehicle air-conditioning unit, equipped with an injection calculator, and an electronic control device. The unit comprises a first metering member for estimating high pressure (P1) and a second metering member for estimating low pressure (P2). It further comprises storage means forming tables with three inputs. Said table is filled on the basis of prior data on the relationships between coefficients (a, b, c) and three measurable quantities related to the operating conditions of the air-conditioning circuit (N, Text, Vp), and instantly supplies the value of said coefficients to the electronic control device. The electronic control device uses the solution of an equation relating the power absorbed by the compressor to the values measured by the first and second metering members, said equation being obtained from the coefficients supplied by the table. The unit uses said equation to regulate the air-conditioning circuit.

Description

Air conditioning system fitted with an electronic control device

The invention relates to air conditioning circuits of motor vehicles.

In conventional motor vehicles, the air conditioning system compressor is driven by the engine and therefore consumes part of the engine power. Although the power absorbed by the compressor, when it is running, is not significant, it still influences the performance of the engine. By reducing the efficiency of the engine, the power actually absorbed by the compressor increases fuel consumption and the pollution generated by the vehicle's exhaust gases.

One way to optimize engine efficiency is to estimate the instantaneous power actually absorbed by the compressor. Knowledge of this information makes it possible, in fact, to adapt the engine injection parameters to real needs. In the absence of this information, the injection computer chooses, by default, injection parameters corresponding to the maximum value of the power absorbed, a value which is rarely reached in practice.

This drawback can relate to mechanical compressors with internal control which operate by means of the clutch interposed between the engine and the compressor. In regulated mode, the compressors with internal control adapt their displacement according to a linear law connecting the value of the pressure at the inlet of the compressor, called low pressure to the output value of the compressor, called high pressure. However, it sometimes happens that the power actually absorbed by the compressor is less than its nominal power.

Such compressors absorb a power which depends on the operating conditions and which cannot therefore be reduced, even if the power actually absorbed by the compressor is known. On the other hand, it is possible to regulate the operation of the air conditioning by disengaging the compressor when the power is not acceptable. This drawback is even more troublesome for compressors with external control, the use of which is becoming widespread.

In fact, in mechanical compressors with external control, the power actually absorbed by the compressor is often less than its nominal power. Consequently, the injection of the engine must compensate for the difference between the nominal mechanical power and the mechanical power actually absorbed, which reduces the efficiency of the engine.

In known embodiments, the estimate of the instantaneous power absorbed by the compressor is obtained from a mapping of the most used operating states. This mapping includes reference states, each reference state being associated with a value of the power absorbed by the compressor, provided by prior tests. The estimate of the power absorbed by the compressor is obtained by comparing the operating state of the air conditioning circuit with a reference state forming part of the map.

More precisely, this reference state is determined by using the instantaneous value of the high pressure measured by a first sensor and information relating to the operation of the vehicle measured by a second sensor. The methods based on such a mapping require significant development times and are based on exclusively empirical data. They have the disadvantage of not taking into account all the possible cases of operation and consequently of providing approximate results.

French patent application No. 01 16568 proposes an air conditioning system capable of providing an estimate of the instantaneous power absorbed from the estimate of the flow rate of refrigerant in the air conditioning circuit. This installation has the drawback of providing an estimate of the refrigerant flow rate from information relating to the speed of the vehicle and from information relating to the voltage of the motor-fan assembly, these two information being not available. on all vehicles.

It is an object of the invention to provide an air conditioning installation allowing the setting implementation of a relation linking the power absorbed by the compressor to the instantaneous values of the high pressure and the low pressure, and to pre-calculated values.

It is another object of the invention to provide such an installation capable of controlling the consumption of the engine.

To this end, the invention provides an air conditioning installation for a motor vehicle equipped with an injection computer and a refrigerant circuit comprising a compressor, a condenser, an expansion device and an evaporator, as well as a electronic control device intended to interact with the refrigerant circuit and the injection computer. Advantageously, the installation comprises: a first measurement member capable of supplying a value relating to the pressure of the fluid leaving the compressor, known as high pressure,

a second measurement member for supplying a value relating to the pressure of the fluid entering the compressor, known as the low pressure,

memory means forming a table with three inputs, this table being filled as a function of prior data on relationships between coefficients and three quantities linked to the operation of the air conditioning circuit, and instantaneously supplying the value of said coefficients to the electronic control device, the electronic control device being able to implement the resolution of an equation relating the power absorbed by the compressor to the high pressure and to the low pressure in order to calculate an estimate of a quantity relating to the refrigerant, said equation being obtained from the coefficients provided by the table.

According to a characteristic of the invention, the three quantities linked to the operation of the air conditioning circuit relate to the speed of rotation of the compressor, the temperature of the outside air arriving in the evaporator and the voltage of the blower.

The inputs of the table are connected to the injection computer to receive the instantaneous value of the three quantities linked to the operation of the air conditioning circuit.

According to another characteristic of the invention, the air conditioning installation comprises an air conditioning computer connected to the injection computer and to the fluid circuit refrigerant, while the memory means and the electronic control device are arranged in the air conditioning computer.

In a first embodiment according to the invention, the quantity relating to the refrigerant is the power absorbed by the compressor, and the electronic control device is able to solve said equation from instantaneous values of high pressure and low pressure.

In a second embodiment according to the invention, the quantity relating to the refrigerant is the maximum value of the compression ratio of the compressor and the electronic control device is capable of solving said equation from the maximum value of the power absorbed by the compressor, supplied by the injection computer and the high pressure value.

According to the second embodiment, the electronic control device is able to calculate an estimate of the instantaneous value of the compression ratio of the compressor from the values of high pressure and of low pressure, and to compare this value with the value maximum compression ratio.

In particular, the electronic control device is able to react to the fact that the value of the compression ratio is greater than the maximum value of the compression ratio by adjusting the operation of the compressor.

In a third embodiment according to the invention, the quantity relating to the refrigerant is the minimum value of the low pressure and the electronic control device is capable of solving said equation from the maximum value of the power absorbed by the compressor , provided by the injection and high pressure value calculation.

According to the third embodiment, the electronic control device is able to compare the minimum value of the low pressure with the instantaneous value of the low pressure. In particular, the electronic control device is able to react to the fact that the value of the low pressure is less than the minimum value of the low pressure by adjusting the operation of the compressor.

According to another characteristic of the invention, the first measurement member is a probe placed at the inlet of the condenser directly within the liquid part of the refrigerant, capable of providing a measurement of the value of the condensation temperature.

The electronic control device is capable of calculating the value of the high pressure from the value of the condensation temperature supplied by the first measuring member.

As a variant, the first measurement member is a sensor, placed between the outlet of the compressor and the inlet of the condenser, suitable for measuring the instantaneous value of the high pressure.

As a variant, the first measuring member is a sensor, placed between the outlet of the condenser and the inlet of the expansion member, suitable for measuring the instantaneous value of the high pressure.

According to an advantageous embodiment, the compressor is an externally controlled compressor provided with a control valve, while the second measurement member is a sensor linked to the injection computer, suitable for measuring the instantaneous value of the intensity of the control valve.

The electronic control device is able to determine the value of the intensity of the maximum displacement control valve and to compare said value with the value of the intensity of the measured control valve.

In particular, the value of the intensity of the control valve measured is less than the intensity of the control valve in maximum displacement while the electronic control device is able to calculate the value of the low pressure from l intensity of the control valve measured. As a variant, the value of the intensity of the control valve measured is greater than the intensity of the control valve in maximum displacement while the electronic control device is capable of calculating the value of the low pressure, and from the intensity of the maximum displacement control valve.

Advantageously, the value of the intensity of the maximum displacement control valve is determined from the instantaneous value of the outside air temperature, the instantaneous value of the compressor speed and the value supplied by the first measuring device.

According to another embodiment according to the invention, the second measurement member is a probe, placed in the fins of the evaporator, capable of providing the instantaneous value of the evaporation temperature.

As a variant, the second measurement member is a probe, placed within the refrigerant, capable of providing the instantaneous value of the evaporation temperature. The electronic control device is capable of calculating the value of the low pressure from the instantaneous value of the evaporation temperature supplied by the second measuring member.

As a variant, the second measurement member is a sensor, placed between the evaporator and the compressor, capable of providing the instantaneous value of the low pressure.

The invention also covers a product program, which can be defined as comprising the functions for solving said equation in order to estimate the power absorbed by the air conditioner.

Other characteristics and advantages of the invention will appear on examining the detailed description below, and the appended drawings in which: - Figure 1 shows an overview of an air conditioning device installed on board 'a vehicle,

FIG. 2 is a diagram of an installation of a motor motor vehicle, fitted with the control device according to a first embodiment of the invention, FIG. 3 is a view similar to FIG. 2 in an alternative embodiment,

FIG. 4 is a flow diagram illustrating the various steps implemented by an installation provided with an externally controlled compressor, according to the invention,

FIG. 5 is a diagram illustrating the regulation curve of an externally controlled compressor, and

- Figures 6a to 6d illustrate the precision of the estimation of the power absorbed by the compressor according to the invention.

Annex A contains the main mathematical equations used in the installation.

The drawings essentially contain elements of a certain character. They can therefore not only serve to better understand the description, but also contribute to the definition of the invention, if necessary.

We first refer to Figure 1 which shows an example of an overview of an air conditioning unit integrated into a vehicle. The air conditioning unit includes a closed refrigerant circuit. The air conditioning apparatus also comprises a compressor 14, a condenser 11, an expansion member 12 and an evaporator 13, traversed in this order by the refrigerant. The circuit may further include an accumulator 17 placed between the outlet of the evaporator and the inlet of the compressor to avoid liquid blows.

The condenser 11 receives an external air flow 16 to evacuate the heat taken from the passenger compartment, which under certain operating conditions is set in motion by a motor-fan unit 15.

The evaporator 13 receives an air flow from a blower 20 supplied by an external air flow 18 and produces a flow of conditioned air 21 which is sent to the passenger compartment of the vehicle.

FIG. 2 represents the installation, according to the present invention, installed in a motor vehicle. The motor vehicle is driven by an engine 43, controlled by an injection computer 42. The computer receives information from various sensors which it interprets to adjust the parameters. In general, it is able to provide information on the interior or exterior conditions of the vehicle (information provided by a solar collector, number of occupants, etc.). In particular, it is capable of providing information 33 on instantaneous values relating to the operation of the vehicle, and in particular the voltage of the blower N, the temperature of the outside air T _ext entering the air conditioning unit and the speed of rotation. compressor Ν.

The vehicle is also equipped with the air conditioning unit 10 described above, shown diagrammatically in FIG. 2. In addition, the installation is provided with an air conditioning computer 40, comprising a cabin regulator 41 and a regulator air conditioning loop 402. The cabin regulator 41 is intended to set the temperature setpoint for the outside air 18 blown at the inlet of the evaporator 11.

The engine injection computer can act on the air conditioning device using the air conditioning loop regulator 402, via link 33. This link only allows the air conditioning device to be started or stopped according to conditions related to engine operation or external controls. For example, it makes it possible to prohibit switching on the air conditioning unit when the engine is under heavy load.

This link 33 is limited to this "all or nothing" operation. In the absence of a device for instantly estimating the power absorbed by the compressor, the air conditioning loop regulator 402 cannot adjust the operation of the air conditioning loop.

The Applicant has set up such a device making it possible to improve this operation, by using a relationship linking the power absorbed by the compressor Pa to the pressure of the refrigerant entering the compressor, known as low pressure P ₂ and to the pressure of the refrigerant leaving the compressor, called the high pressure P ,, obtained in a table as a function of the operating conditions of the air conditioning circuit.

For this, the cabin regulator 41, the engine injection computer 42 and the air conditioning unit 10 are connected to an electronic card 401 for a bidirectional exchange of information. The electronic card is programmed to implement the resolution of an equation connecting the power absorbed by the compressor to the high pressure P, and to the low pressure P ₂ . In addition, it is programmed to solve the equations for estimating the high pressure P, and the low pressure P ₂ from measurements supplied by the installation. It can transmit information resulting from this estimate to the injection computer, via link 32.

The electronic card 401 can be considered as an integral part of the air conditioning computer 40 of the vehicle.

It is in connection with the air conditioning loop regulator 402 which has the role in particular of adapting the amount of heat taken from the passenger compartment, called cooling capacity, to reach the set point of blown air at the inlet of the evaporator. or the interior sensor setpoint. This instruction is previously indicated to the air conditioning regulator 402 by the passenger compartment regulator (link 35).

The electronic card is connected to memory means forming a table with three inputs and three outputs. The table contains pre-calculated values of three coefficients a, b and c. Each of these three values is pre-calculated from a relation linking the value to information related to the operation of the air conditioning loop, in particular, to the voltage of the blower V, to the temperature of the outdoor air T _ext arriving in the air conditioning circuit and at the speed of rotation of compressor N.

The electronic card uses the instantaneous values of these three pieces of information at the input of the table, which provides according to the data it contains, an estimate of three coefficients, a, b and c which fully determine the equation connecting the power absorbed by the compressor at high pressure Pi and at low pressure P ₂ .

The memory means are provided by the air conditioning computer 40 and constitute a kind of mapping which makes it possible to define the coefficients of the equation as a function of selected ranges of values of the voltage of the blower V _p , of the air temperature outside T _ext and the compressor rotation speed N. The instantaneous values of the blower voltage N _p , the outside air temperature T _ext are supplied by the regulator of cabin 41 (link 35) and the speed of rotation N of the compressor is supplied by the injection computer 42.

Furthermore, the electronic card 401 receives information from sensors installed on the air conditioning apparatus by the link 30 to determine the instantaneous values of the high pressure P, and of the low pressure P ₂ .

The installation shown in FIG. 2 is capable of providing an estimate of the equation connecting the power absorbed by the compressor to the high pressure of the compressor P, and to the low pressure of the compressor P ₂ , and of providing the instantaneous values of high pressure P, and low pressure P ₂ .

The formula in Annex A 1 represents a linear equation relating the value of the power absorbed by the compressor P _a to the compression ratio τ (ratio between high pressure and low pressure). The coefficients of this equation a and b depend on the following parameters:

- the voltage of the blower V _p ,

- the outside air temperature T _ext

- the rotational speed N of the compressor, and - the relative humidity RH of the air upstream of the evaporator.

The Applicant has established a simplified equation between the power consumed by the compressor P _a and the compression ratio, in which the coefficients depend only on the following parameters: - the voltage of the blower V _p ,

- the outside air temperature T _ex „and

- the speed of rotation N of the compressor.

Appendix A2 represents this equation. More precisely, this equation links the power consumed by the compressor P _a to the high pressure P, and to the low pressure P ₂ , the parameters a, b and c depending only on the voltage of the blower V _p , the temperature of the outside air T _ext , and the speed of rotation N of the compressor. This equation was obtained by determining the coefficients a and b, as well as the high pressure P, under the conditions of dry air, according to the relation of appendix Al. The high pressure under the conditions of dry air, said reference pressure, corresponds to the coefficient c and depends on the compression ratio τ.

The relationships between the coefficients a, b, c and N, T _ext and V _p result from preliminary tests carried out on a vehicle or on a test bench, after having set parameters for the air conditioning loop.

The following test configurations are given by way of example for different ranges of values of the outside air temperature T _ext , the relative humidity RH, the voltage of the blower, and the speed of rotation N of the compressor. :

- T _ext = 25 ° C, HR = 40%, V _p = {55 to 69 g / s; 83 g / s; 111 to 138 g / s}, N = {1000 rpm; 2000tr / min; 3000rpm}, - T _ext = 30 ° C, HR = 40%, V _p = {55 to 69 g / s; 83 g / s; 111 to 138 g / s}, N = {1000 rpm; 2000tr / min; 3000tr / min},

- T _ext = 35'C, HR = 40%, V _p = {55 to 69 g / s; 83 g / s; 111 to 138 g / s}, N = {1000 rpm; 2000tr / min; 3000tr / min},

- T _ext = 45 ° C, HR = 40%, V _p = {55 to 69 g / s; 83 g / s; 111 to 138 g / s}, N = {1000 rpm; 2000tr / min; 3000tr / min}.

With a relative humidity of 40%, the conditions of the dry air are checked, which makes it possible to use the relation of appendix Al to calculate the coefficients a, b and c. For example, when the compressor is externally controlled, the compressor control is varied during the tests in steps of 5%, from the maximum displacement to the minimum displacement. The values of the high pressure P ,, of the low pressure P ₂ and of the power P _a absorbed by the compressor are recorded at each level.

The coefficients a, b and c are determined according to the formula for calculating the power absorbed by the compressor under dry air conditions, according to Annex A1. The coefficient c corresponds to the high pressure P, under the conditions of dry air.

From the coefficients a, b and c obtained by these tests carried out for a relative humidity by 40%, the values of these coefficients are obtained and the estimate of the power absorbed by the compressor under the other conditions is deduced therefrom.

The parameters on which the equation of Annex A2 depends are therefore less numerous than those of the equation of Annex A1. Consequently, the determination of the coefficients of the equation is simplified.

In an advantageous embodiment, the equation in appendix A2 is used by the installation to calculate an estimate of the power absorbed by the compressor P _a .

Figure 4 is a flowchart showing the steps performed by the installation to provide this estimate, in particular for an externally controlled compressor.

In the initial step 100, the electronic card 401 receives the instantaneous values of the temperature of the outside air T _ext blown at the input of the motor-fan unit, and of the voltage of the blower V _p , supplied by the cabin regulator. 41 (link 35) and the instantaneous value of the speed of rotation of the compressor supplied by the injection computer 42 (link 33). This information is transmitted to the input of the memory means table, which supplies the corresponding values of the coefficients a, b and c in step 102.

The values of a, b and c obtained in step 102 provide the relationship which links the power absorbed by the compressor to the high pressure P, and to the low pressure P ₂ . The estimate of the power absorbed by the compressor can then be obtained by determining the instantaneous values of these pressures.

In step 106, the installation provides an estimate of the pressure at the outlet of the compressor P ₁₅ called low pressure.

In a particular embodiment, the device comprises a first measuring member capable of supplying a value relating to the high pressure P i.

In a particular embodiment, shown in Figure 2, the high pressure can be estimated from the measurement of the instantaneous value of the condensing temperature. This value can be measured by a probe 23 placed in the condenser, in the liquid part of the refrigerant. Indeed, this location is chosen such that the refrigerant is in a state of liquid / vapor mixture, for example at the end of the first pass of the condenser if the latter contains 4 passes. The electronic card 401 then calculates an estimate of the high pressure using the law of saturation of the fluids and the value of the measured condensation temperature.

As a variant, the high pressure can be measured directly, with reference to FIG. 3. For this, the installation includes the sensor 123 of FIG. 3 which measures the instantaneous value of the pressure of the refrigerant leaving the compressor and therefore the high pressure P ,. This value is transmitted to the electronic card 401.

In addition, the installation according to the invention comprises a second measuring member capable of providing a value relating to the low pressure P ₂ .

In a particular embodiment, the compressor of the air conditioning circuit is an externally controlled compressor provided with a control valve. The low pressure of an externally controlled compressor can be estimated from the value of the intensity Iv of the compressor control valve.

FIG. 5 represents the curve connecting the low pressure of an externally controlled compressor to the intensity I _v . The equation corresponding to part I of the curve is provided in appendix A3.1. However, when the compressor is at maximum displacement (part II of the curve), the low pressure of the compressor no longer varies and the equation in appendix A3.1 is no longer valid. The low pressure is then estimated by the equation in Appendix A3.2.

According to this embodiment, the second measurement member is able to determine the instantaneous value of the intensity Iv of the compressor control valve and to transmit this value to the electronic card. The electronic card 401 then estimates the value of the low pressure P ₂ from the value of the intensity I _v thus obtained.

The low pressure P ₂ of the compressor is estimated in steps 108, 110, 112, 113, and 114, according to this embodiment. In step 108, the instantaneous value of the intensity Iv of the control valve is measured by the second measuring member. This measurement member is a sensor linked to the injection computer 42.

In step 110, the electronic card calculates an estimate of the intensity Iv_max of the control valve in maximum displacement, from instantaneous values of the speed of rotation N and the temperature of the outside air T _ext of l step 100, and from the value of the high pressure P, established in step 106.

In step 112, the electronic card compares the value of the intensity Iv of the control valve measured with the value of the intensity Iv_max of the control valve in maximum displacement.

If the measured intensity Iv is less than the intensity Iv_max in maximum displacement, the electronic card calculates the low pressure P ₂ according to the equation of appendix A3.1, in step 113. Otherwise, the electronic card calculates the low pressure P ₂ according to the equation in appendix A3.2, in step 114.

Other alternative embodiments make it possible to estimate the low pressure P ₂ , for any type of compressor.

In a first alternative embodiment, with reference to FIG. 2, the second measurement member is a sensor 22, placed between the evaporator and the compressor, which measures the instantaneous value of the low pressure P ₂ of the compressor. This measurement is transmitted to the electronic card 401, via the link 30.

In a second variant, the second measurement member is a probe, designated by the reference 122 in FIG. 3, which measures the evaporation temperature. This probe may be a thermistor probe, of conventional structure, placed in the fins of the evaporator. The probe can also be placed within the refrigerant itself, in a duct or in the expansion member 12, for example.

In this alternative embodiment, the measured value of the evaporation temperature is transmitted to the electronic card (link 30) which applies the law of saturation of fluids to deduce therefrom the value of low pressure P ₂ .

The electronic card then uses the values of low pressure P ₂ and high pressure P, estimated to solve the equation determined in step 102 and provide an estimate of the power absorbed by the compressor P _a in step 1044 .

FIGS. 6a to 6d illustrate the precision of the measurement of the mechanical power according to this embodiment, during tests carried out for different ranges of values of the temperature of the outside air T _ext , the relative humidity RH, the voltage of the blower N _p , and of the speed of rotation Ν of the compressor:

- Figure 6a corresponds to T _ext = 35 ° C, V _p = {55 to 69 g / s; 111 to 139 g / s}, Ν = {1000 rpm; 3000tr / min; 5000 rpm}, RH = 0%

- Figure 6b corresponds to T _ext = 25 ° C, V _p = 111 to 139 g / s, N = {1000 rpm; 3000tr / min; 5000 rpm}, RH = 0%

- Figure 6c corresponds to T _ext = 35 ° C, V _p = {55 to 69 g / s, 111 to 139 g / s}, N- {1000 rpm; 3000tr / min; 5000 rpm}, RH = 80%

- Figure 6d corresponds to T _ext = 25 ° C, V _p = 111 to 139 g / s, N = {1000 rpm; 3000tr / min; 5000 rpm}, RH = 80%.

Graphs 6a to 6d show the difference between the calculated values of the power absorbed by the compressor (P _a calculated), represented on the ordinate, and the measured values of the power absorbed by the compressor (P _a measured), represented on the abscissa . These graphs indicate that the estimation error is less than or equal to 300 watts and therefore satisfactory accuracy.

The computer then sends the engine injection module the estimated value of the mechanical power absorbed by the compressor. The computer then adapts the nominal mechanical power absorbed by the compressor, if this exceeds a maximum value defined by the computer from this estimated value. As a result, fuel consumption is reduced and excessive increases in the power absorbed by the compressor are better controlled. In the case of compressors with internal control, the installation according to the present invention is also used to estimate the mechanical power absorbed by the compressor. However, for this type of compressor, this estimated power is used to disengage the compressor in order to reduce the mass flow rate of refrigerant absorbed by the compressor.

In addition, the Applicant has developed an optimization of the strategy for controlling the air conditioning circuit based on the equation obtained in step 102. In this embodiment, the regulation of the air conditioning circuit 10 is carried out from 'an estimate of the value of the maximum compression ratio τ_max or the minimum low pressure P ^ min.

Referring to Figure 4, the installation calculates the maximum compression ratio τ_max to regulate the air conditioning circuit. In this variant, the value of the maximum compression ratio τ_max is estimated from the equation obtained in step 102 and the value of the high pressure P, obtained in step 106, in accordance with the equation of l Annex A4. The relationship of Annex A4 is deduced from Annex A2. The equation of appendix A4 is solved by the electronic card, in step 1040, using the maximum value of the power of the compressor P ^ max, defined by the injection computer 42.

Steps 108, 110, 112, 113, 114 provide in parallel the value of the low pressure P ₂ , which makes it possible to calculate in step 116 an estimate of the instantaneous value of the compression ratio τ.

In step 120, the electronic card compares the compression rate τ estimated with the maximum compression rate τ_max. The air conditioning system must operate with a compression ratio lower than τ_max. Thus, if the compression rate τ is greater than the rate τ_, the electronic card adjusts the operation of the compressor, for example by correcting the intensity of the compressor control valve in step 122.

In another variant, the installation calculates the value of the minimum low pressure P ^ min, in step 1042, to regulate the air conditioning circuit. In this variant, the value of the pressure P ^ min is estimated from the equation obtained in step 102 and the value of the low pressure obtained in step 106, in accordance with the equation in appendix A5.

Steps 108, 110, 112, 113 and 114 simultaneously provide an estimate of the instantaneous value of the low pressure P ₂ .

In step 118, the electronic card compares the estimated low pressure P ₂ with the minimum low pressure P ^ min. The air conditioning circuit must operate with a low pressure greater than or equal to P ^ min. Thus, if the low pressure P ₂ is lower than the pressure P ^ nin, the electronic card performs a correction of the intensity of the control valve Iv in step 124.

The present invention also relates to the software code which it involves, particularly when it is made available on any medium readable on a computer. The term "computer-readable medium" covers a storage medium, for example magnetic or optical, as well as a means of transmission, such as a digital or analog signal.

Annex A

Al. Estimation of the mechanical power absorbed by the air conditioning according to the prior art P _a = [a.τ + b] a = A (N, T _ext N _p , HR) b = B (Ν, T _ext N _p , HR) τ = PP ₂

A2. Estimation of the mechanical power absorbed by the air conditioning according to the invention P _a = [a.τ + b] .P, / ca = A (Ν, T _ext N _p ) b = B (Ν, T _ext N _p ) c = C (Ν, T _ext N _p ) t = P, / P ₂

A3. Estimation of the low pressure of an externally controlled compressor A3.1- Iv <Iv max: P ₂ = kl. Iv ² + k2.Iv + k3

A3.2- Iv> Iv max:

P ₂ = kl. Ivjnax ² + k2.Iv_max + k3

A4. Estimated maximum compression ratio τ max of an externally controlled compressor τ_max = [c.P ^ max / P, - b] / a

AT 5. Estimation of the minimum low pressure Pτ_min of an externally controlled compressor P ^ min ≈ a.P, / [c.P ^ max / P, - b]

Claims

claims 1. Air conditioning installation for a motor vehicle, provided with an injection computer (42) and with a refrigerant circuit comprising a compressor (14), a condenser (11), an expansion device (12) and an evaporator (13), as well as an electronic control device (401) intended to interact with the refrigerant circuit (10) and the injection computer (42), characterized in that it comprises: a first measuring member capable of supplying a value relating to the pressure of the fluid leaving the compressor (P,), called high pressure, a second measuring member capable of providing a value relating to the pressure of the fluid entering the compressor (P ₂ ), called low pressure, - memory means forming a table with three inputs, this table being filled as a function of preliminary data on relationships between coefficients (a, b, c) and three quantities linked to the operation of the air conditioning circuit (N, T _ext , V _p ), and instantaneously supplying the value of said coefficients to the electronic control device (401), the electronic control device (401) being capable of implementing the resolution of an equation linking the power absorbed by the compressor (P to the high pressure (P,) and low pressure (P ₂ ) to calculate an estimate of a quantity relating to the refrigerant, said equation being obtained from the coefficients provided by the table. 2. Air conditioning installation according to claim 1, characterized in that the three quantities linked to the operation of the air conditioning circuit relate to the speed of rotation of the compressor (N), to the temperature of the outside air arriving in the evaporator (T _ext ) and at the pulser voltage (V _p ). 3. Air conditioning installation according to claim 2, characterized in that the inputs of the table are connected to the injection computer (42) to receive the instantaneous value of the three quantities linked to the operation of the air conditioning circuit. 4. Air conditioning installation according to one of the preceding claims, characterized in that it comprises an air conditioning computer (40) connected to the injection computer (42) and to the refrigerant circuit (10), and in that the memory means and the electronic control device (401) are arranged in the air conditioning computer (40). 5. Air conditioning installation according to one of the preceding claims, characterized in that the quantity relating to the refrigerant is the power absorbed by the compressor (PJ, and in that the electronic control device is capable of solving said equation from high pressure (P,) and low pressure (P ₂ ) values. 6. Air conditioning installation according to one of claims 1 to 4, characterized in that the quantity relating to the refrigerant is the maximum value of the compression ratio (τ_max) of the compressor and in that the electronic control device is capable of solve said equation from the maximum value of the power absorbed (P ^ max) by the compressor supplied by the injection computer (42) and the value of the high pressure (P,). 7. Air conditioning installation according to claim 6, characterized in that the electronic control device is capable of calculating an estimate of the instantaneous value of the compression ratio (τ) of the compressor from the values of the high pressure (P,) and low pressure (P ₂ ), and to compare this value with the maximum value of the compression ratio (τ_max). 8. Air conditioning installation according to claim 7, characterized in that the electronic control device is able to react to the fact that the instantaneous value of the compression ratio (τ) is greater than the maximum value of the compression ratio (τ_max) in adjusting the operation of the compressor. 9. Air conditioning installation according to one of claims 1 to 4, characterized in that the quantity relating to the refrigerant is the minimum value of the low pressure (P ^ min) and in that the electronic control device is capable of solve said equation from the maximum value of the power absorbed (P _L max) by the compressor, provided by the injection calculation (42) and from the value of high pressure (P,). 10. Air conditioning installation according to claim 9, characterized in that the electronic control device is able to compare the minimum value of the low pressure (P ^ min) to the instantaneous value of the low pressure (P ₂ ). 11. Air conditioning installation according to claim 10, characterized in that the electronic control device is capable of reacting to the fact that the instantaneous value of the low pressure (P ₂ ) is less than the minimum value of the low pressure (P ^ min) by adjusting the compressor operation. 12. Air conditioning installation according to one of the preceding claims, characterized in that the first measuring member is a probe (23) placed at the inlet of the condenser (11) directly within the liquid part of the refrigerant, clean to provide a measure of the value of the condensing temperature. 13. Air conditioning installation according to claim 12, characterized in that the electronic control device (401) is capable of calculating the high pressure (Pj) from the value of the condensation temperature supplied by the first measuring member. 14. Air conditioning installation according to one of the preceding claims, characterized in that the first measurement member is a sensor (123), placed between the outlet of the compressor (14) and the inlet of the condenser (11), suitable for measure the instantaneous value of the high pressure (P,). 15. Air conditioning installation according to one of the preceding claims, characterized in that the first measurement member is a sensor (123), placed between the outlet of the condenser (11) and the inlet of the expansion member (12 ), suitable for measuring the instantaneous value of the high pressure (P,). 16. Air conditioning installation according to one of the preceding claims, characterized in that the compressor is an externally controlled compressor provided with a valve. control, and in that the second measurement member is a sensor linked to the injection computer, suitable for measuring the instantaneous value of the intensity of the control valve (I _v ). 17. Air conditioning installation according to claim 16, characterized in that the electronic control device is able to determine the value of the intensity of the control valve in maximum displacement (I _v _max) and to compare said value with the value of the intensity of the control valve measured (I _v ). 18. Air conditioning installation according to one of claims 16 or 17, characterized in that the value of the intensity of the control valve measured is less than the intensity of the control valve in maximum displacement and in that the electronic control device is able to calculate the low pressure value (P ₂ ) from the intensity of the measured control valve (I _v ). 19. Air conditioning installation according to one of claims 16 or 17, characterized in that the value of the intensity of the control valve measured is greater than the value of the intensity of the control valve in maximum displacement and in what the electronic control device is able to calculate the value of the low pressure (P ₂ ) from the intensity of the control valve in maximum displacement (I _v _max). 20. Air conditioning installation according to one of claims 17 to 19, characterized in that the value of the intensity of the maximum displacement control valve (I _v _max) is determined from the instantaneous value of the temperature of the outside air (T _e χ _t ) _" of the instantaneous value of the speed of rotation of the compressor (N) and of the value (P,) supplied by the first measuring member. 21. Air conditioning installation according to one of claims 1 to 15, characterized in that the second measurement member is a probe (122), placed in the fins of the evaporator (P), capable of providing the instantaneous value of the evaporation temperature. 22. Air conditioning installation according to one of claims 1 to 15, characterized in that the second measuring member is a probe (122), placed within the refrigerant, capable of providing the instantaneous value of the evaporation temperature. 23. Air conditioning installation according to one of claims 21 or 22, characterized in that the electronic control device is capable of calculating the value of the low pressure (P ₂ ) from the instantaneous value of the evaporation temperature supplied by the second measuring device. 24. Air conditioning installation according to one of claims 1 to 15, characterized in that the second measurement member is a sensor (22), placed between the evaporator (13) and the compressor (14), suitable for providing the instantaneous low pressure value (P ₂ ).