FR3091562A1 - Control method of an electric air conditioning compressor and air conditioning system implementing such a control method - Google Patents

Abstract

Method for controlling an electric air conditioning compressor and air conditioning system implementing such a control method The present invention relates to a method (8) for controlling an electric air conditioning compressor (2) for a motor vehicle, comprising : a step (E3) for calculating the compression ratio TC, a step (E4) for calculating a setpoint value VC as a function of a suction pressure PA of said compressor, a step (E5) for comparing the rate compression TC with the setpoint VC, if the compression ratio TC is equal to the setpoint VC, the method (8) further comprises: a step (E6) of modulating the speed of rotation of said compressor (2 ) and / or the opening of an electronic expansion valve. Figure for the abstract: Figure 4

Description

Description

Title of the invention: Method for controlling an electric air conditioning compressor and air conditioning system implementing such a control method

The invention relates to the automotive field and more particularly to methods of controlling electric air conditioning compressors for electric or hybrid motor vehicles. The invention also relates to air conditioning systems implementing such processes.

Motor vehicles are generally provided with an air conditioning system, the main objective of which is to supply fresh or hot air in the passenger compartment.

The air conditioning systems of motor vehicles include in their simplified form an air conditioning circuit provided with an air conditioning compressor which allows to compress and circulate a refrigerant in the circuit, a pressure reducer to lower the fluid pressure refrigerant, and two heat exchangers respectively a condenser and an evaporator, the latter being located in the passenger compartment.

The air conditioning compressor is an element of the air conditioning system which tends to heat depending on the demand for cold. It is necessary to cool it.

In electric or hybrid vehicles, the outside air cools the air conditioning compressor. However, the outside air may not be able to cool the air conditioning compressor effectively. This is for example the case when the outside air is hot or when the vehicle is traveling at low speed while the air conditioning is on at high level.

When the air conditioning compressor reaches a mechanical torque or a compression rate that is too high, it can malfunction. Among the possible malfunctions, temporary or permanent shutdown of the compressor, or even demagnetization of the electric motor of said air conditioning compressor are possible. Automobile manufacturers want to overcome these malfunctions in order to improve the reliability of air conditioning systems in electric and hybrid vehicles.

The objective of the invention is to remedy at least one of the above-mentioned drawbacks.

Thus, firstly, a method is provided for controlling an electric air conditioning compressor for a motor vehicle, comprising: a. a step of calculating the compression ratio,

b. a step of calculating a set value as a function of a suction pressure of said compressor,

vs. a step of comparing the compression ratio with the set value,

d. if the compression ratio is greater than or equal to the set value, the method further comprises:

e. a step of modulating the speed of rotation of said compressor and / or the opening of an electronic expansion valve, this in particular to protect the air conditioning compressor.

Such a control method effectively protects the air conditioning compressor. More specifically, it avoids malfunctions such as the temporary or permanent shutdown of the compressor or the demagnetization of the electric motor of said compressor.

Various additional characteristics can be provided alone or in combination:

at. the control process includes:

i. a step of measuring the suction pressure carried out directly upstream of said compressor, and

ü. a step of measuring a discharge pressure carried out directly downstream of the compressor, according to the direction of flow of the fluid;

b. the compression ratio is calculated according to the following formula:

i. [Math 1]

ü. [Math.l] t _PjL ^T C ~ P _A iii. where P _R is the discharge pressure and P _A is the suction pressure;

vs. the control process includes:

i. a step of measuring the suction pressure carried out directly upstream of said compressor, and

ü. a step of measuring a condensation pressure P _c carried downstream of a heat exchanger, according to the direction of flow of the fluid;

d. the compression ratio is calculated according to the following formula:

i. [Math 2]

ü. [Math.2]

iii. where P _c is the condensing pressure, P _A is the suction pressure and f is the pressure drop between an outlet from the compressor and an outlet from the heat exchanger;

e. the set value V _c is equal to a maximum compression ratio T _Cmax minus a safety coefficient C _s , in other words V _c = T _cmax - C _s , the safety coefficient C _s corresponds to a maximum margin on the discharge pressure P _R.

f. The safety factor C _s is defined such that C _s = max (P _{R Max} - P _R ), with P R_Max being the maximum authorized or possible delivery pressure.

g. the coefficient Cs is between 0.5 bar and 2.5 bar, in particular equal to 1.5 bar.

Secondly, an air conditioning system for a motor vehicle is provided, comprising:

at. an air conditioning compressor,

b. means capable of measuring the compression ratio of the air conditioning compressor, and

vs. a programmable computer unit capable of implementing a method for controlling said air conditioning compressor as described above.

Various additional characteristics can be provided alone or in combination:

at. this comprises at least one pressure sensor capable of measuring a suction pressure directly upstream of the air conditioning compressor and at least one pressure sensor capable of measuring a discharge pressure directly downstream of the air conditioning compressor in the direction d 'fluid flow;

b. this comprises at least one pressure sensor capable of measuring a suction pressure directly upstream of the air conditioning compressor and at least one pressure sensor capable of measuring a discharge pressure downstream of a heat exchanger, according to the direction of fluid flow.

Finally, there is provided a motor vehicle comprising an air conditioning system as previously described.

Other features and advantages of the invention will appear in the following description in connection with the accompanying drawings, given by way of non-limiting examples:

at. [Figure 1] is a schematic representation of an air conditioning system according to a first embodiment of the invention;

b. [Figure 2] is a schematic representation of an air conditioning system according to a second embodiment of the invention;

vs. [Figure 3] is a graphical representation of the evolution of a compression ratio as a function of the suction pressure,

d. [Figure 4] is a schematic representation of a method of controlling an air conditioning compressor of the air conditioning system of Figures 1 and 2.

In Figure 1 is shown an air conditioning system 1. The air conditioning system 1 comprises an electric air conditioning compressor 2, an evaporator 3, a condenser 4, and a pressure reducer (not shown). The air conditioning compressor 2 comprises an electric motor (not shown) whose speed of rotation varies as a function of an electric current applied to it.

The air conditioning system 1 comprises means capable of measuring the compression ratio T _c of the air conditioning compressor 2. These means for measuring the compression ratio T _c comprise an upstream sensor 5, located directly upstream of the air conditioning compressor 2 and capable of measuring a suction pressure P _A , and a downstream sensor 6 located directly downstream of the compressor 2 of air conditioning and able to measure a discharge pressure P _R , according to the direction of circulation of a refrigerant.

The term "directly" used in the present application means that the pressure sensors 5, 6 are arranged at the inlet and the outlet of the air conditioning compressor 2 so that no element, for example a heat exchanger , is not interposed between the air conditioning compressor 2 and the pressure sensor 5, 6.

The air conditioning system 1 includes a computer unit 7. The computer unit 7 is programmable and can implement a process 8 for controlling the air conditioning compressor 2.

The method 8 for controlling the air conditioning compressor 2 comprises: a. a step E3 of calculating the compression ratio T _c ,

b. a step E4 of calculating a set value V _c as a function of a suction pressure P _{A of} said compressor 2,

vs. a step E5 of comparing the compression ratio T _c with the reference value V _c previously calculated.

When the compression ratio T _c is greater than or equal to the set value V _c , the method further comprises a step E5 of modulating the speed of rotation of the air conditioning compressor 2. The modulation consists in reducing the speed of rotation of the air conditioning compressor 2 in order to protect it against a possible excessively high torque or even possible overheating. This modulation step E5 can also correspond to a modulation of the opening of the electronic expansion valve. More precisely, this modulation step makes it possible to increase the opening of the regulator. This modulation step E5 can also reduce the compressor rotation speed and increase the opening of the regulator at the same time.

In order to carry out the step of calculating the compression ratio T _c , the control method comprises:

at. a step E 1 for measuring the suction pressure P _A carried out by means of the upstream sensor 5, and

b. a step E2 of measuring the discharge pressure P _R carried out by means of the downstream sensor 6.

The reliability of the measurement of the suction pressure P _A is of particular importance. Indeed, on this measurement depends in particular the determination of the set value V _c . It is therefore particularly useful to measure the suction pressure P _A directly upstream of the air conditioning compressor 2 in order to obtain a reliable set value V _c .

The compression ratio is calculated according to the following formula:

[MATH 1]

„_ P _R ^{1 C} ~ PA

P _R and P _A correspond respectively to the discharge pressure P _R and to the suction pressure P _A measured

The setpoint V _c is calculated as a function of the suction pressure P _A measured. With reference to FIG. 3, the set value V _c is determined, for a given suction pressure P _A (abscissa axis) by calculating the difference between a maximum compression rate T _Cma x and a safety coefficient C _s . In other words :

[MATH 3]

(P -Q) t / _ t ^R _Max f

D- PI

The safety factor C _s , fixed, improves protection and guarantees better longevity of the air conditioning compressor 2. In the absence of a safety coefficient C _s, the set value V _c would be equal to the maximum compression rate T _Cmax for a given suction pressure P _A. Thus, the control process could potentially approach the maximum compression ratio T _Cmax several times during the use of the air conditioning system 1, which would reduce the longevity of the air conditioning compressor 2.

As can be seen in Figure 3, the maximum compression ratio T _Cmax varies depending on the suction pressure P _A. In the embodiment shown in FIG. 3, the safety coefficient C _s is constant.

Advantageously, the safety coefficient C _s is between 0.5 and 2.5 bar. A safety coefficient C _s between these values makes it possible to effectively reduce the risks of malfunctions of the air conditioning compressor 2.

Preferably, the safety coefficient C _s is substantially equal to 1.5 bar. It has been determined that such a safety coefficient C _s allows safe use of the air conditioning compressor 2.

According to a second embodiment shown in Figure 2, the downstream pressure sensor 6 is located downstream of the condenser 4. Thus the downstream pressure sensor 6 is able to measure a discharge pressure P _R downstream of the condenser 4.

The control method comprises a step of measuring the suction pressure P _A performed directly upstream of the air conditioning compressor 2 and a step of measuring a discharge pressure P _R performed downstream of the condenser 4. The difference with the control method of the first embodiment lies in the fact that the measurement of the discharge pressure P _R is not carried out directly downstream of the air conditioning compressor 2, but downstream of the condenser 4.

The compression ratio T _c is then calculated differently in order to take account of the pressure drop induced by the condenser 4. In the second embodiment, the compression ratio T _c is calculated according to the following formula:

[MATH 2]

P _c + f ¹ C ~ p J

P _c , P _A and f correspond respectively to the condensation pressure P _c , the suction pressure P _A and the pressure drop between the outlet of the compressor 2 and the outlet of the condenser 4.

Claims (1)

[Claim 1] Method (8) for controlling an electric air conditioning compressor (2) for a motor vehicle, comprising: at. a step (E3) of calculating the compression ratio T _c , b. a step (E4) of calculating a set value V _c as a function of a suction pressure P _{A of} said compressor, vs. a step (E5) of comparing the compression ratio T _c with the set value V _c , d. if the compression ratio T _c is equal to the set value V c, the method (8) further comprises: e. a step (E6) of modulating the speed of rotation of said compressor (2) and / or of the opening of an electronic expansion valve. [Claim 2] Control method (8) according to claim 1 in which it comprises: at. a step (E1) for measuring the suction pressure P _A carried out directly upstream of said compressor (2), and b. a step (E2) of measuring a discharge pressure P _R carried out directly downstream of the compressor (2), according to the direction of flow of the fluid. [Claim 3] Control method (8) according to claim 2 in which the compression ratio T _c is calculated according to the following formula: a- _T P _R ^{1 C} ~ PA b. where P _R is the discharge pressure and P _A is the suction pressure. [Claim 4] Control method (8) according to claim 1 comprising: at. a step (E1) for measuring the suction pressure P _A carried out directly upstream of said compressor (2), and b. a step (E2) of measuring a discharge pressure P _R carried out downstream of a heat exchanger (3), according to the direction of flow of the fluid. [Claim 5] Control method (8) according to claim 4 in which the compression ratio T _c is calculated according to the following formula: a. Pç + f ^{1 c} ~ Pa b. where P _c is the condensing pressure measured, P _A is the suction pressure and f is the pressure drop between an outlet from the compressor (2) and an outlet from the heat exchanger (3). [Claim 6] Control method (8) according to any one of the preceding claims, in which the set value V _c is equal to a maximum compression ratio T _Cm ax minus a safety coefficient C _s . [Claim 7] Control method (8) according to claim 6, in which the safety factor C _s is between 0.5 and 2.5 bar. [Claim 8] Motor vehicle air conditioning system (1) comprising: a. an air conditioning compressor (2), b. means (5, 6) capable of measuring the compression ratio T _c of the air conditioning compressor (2), and c. a programmable computer unit (7) capable of implementing a method (8) for controlling said air conditioning compressor (2) according to any one of the preceding claims. [Claim 9] Air conditioning system (1) according to claim 8 wherein it comprises at least one pressure sensor (5) capable of measuring a suction pressure directly upstream of the air conditioning compressor (2) and at least one sensor (6) pressure capable of measuring a discharge pressure directly downstream of the air conditioning compressor (2) according to the direction of flow of the fluid. [Claim 10] Air conditioning system (1) according to claim 8 wherein it comprises at least one pressure sensor (5) capable of measuring a suction pressure directly upstream of the air conditioning compressor (2) and at least one sensor (6) pressure capable of measuring a discharge pressure downstream of a heat exchanger (3), according to the direction of flow of the fluid. 1/2