Method For Controlling The Operation Of An Air-Conditioning Loop In A Vehicle

Abstract

The present invention relates to a method for controlling the outlet temperature (TRCPO) of a compressor (CP) built into the air-conditioning loop of a vehicle in which a subcritical refrigerant fluid flows and including a condenser (CD), an expansion valve (EXV), and an evaporator (EV). The monitoring method comprises the steps of calculating a limit temperature at the compressor inlet (TRCPI_L), estimating a temperature at the compressor inlet (TRCPI_E), and modifying a control signal of the compressor (PWMCP) or a setpoint value of the evaporation temperature (SP_TEV).

Description

The present invention relates to the general field of methods for controlling the operation of an air-conditioning loop in a vehicle in which a subcritical refrigerant fluid flows, and comprising, in the flow direction of the refrigerant fluid, particularly a compressor, a condenser, and an expansion valve, and an evaporator.

In such air-conditioning loops, the compressor is generally externally controlled according to a principle relating the pressure at the compressor inlet to the amperage for controlling a control valve of the compressor.

The invention also relates to the air-conditioning loops comprising an internal exchanger for carrying out heat transfers between the fluid flowing between the condenser and the expansion valve and the fluid flowing between the evaporator and the compressor.

Such an architecture allows for the consumption of the air-conditioning loop to be reduced. Such a consumption reduction advantageously causes a reduction of the pollution due to the operation of the air- conditioning loop. In addition, having an internal exchanger increases the cooling power of the air-conditioning loop.

However, it has been observed that such an arrangement can cause excessive overheating of the refrigerant fluid flowing in the air-conditioning loop at the compressor outlet. This phenomenon occurs when the efficiency of the internal exchanger is high in some operating conditions of the air-conditioning loop. Therefore, in such a case, it is necessary for the temperature at the condenser inlet or at the compressor outlet to be controlled.

To this end, there are currently two solutions to control the discharge temperature of the compressor or the temperature at the condenser inlet.

According to a first method, an opening of the expansion valve is defined so that substantially no overheating is carried out at the evaporator outlet. This solution is simple but presents several risks since it is based on the hypothesis that the discharge temperature of the compressor is satisfactory without having to undergo any control.

The second method consists in using a temperature sensor at the compressor outlet and in carrying out a control method using the value measured by the temperature sensor to limit the discharge temperature of the compressor. The drawback of this solution is that it requires the air-conditioning loop to be equipped with an additional sensor, at a non-negligible cost.

The main object of the present invention is thus to overcome the drawbacks of the known solutions by providing a method for controlling the outlet temperature of a compressor built into an air-conditioning loop in a vehicle in which a subcritical refrigerant fluid flows, and comprising at least a compressor, a condenser, an expansion valve, and an evaporator.

According to an alternative embodiment, the air-conditioning loop comprises an internal exchanger to carry out heat transfers between the fluid flowing between the condenser and the expansion valve and the fluid flowing between the evaporator and the compressor.

The control method comprises, successively, simultaneously, or alternatively:

• • a step of calculating a limit temperature at the compressor inlet;
  • a step of estimating a temperature at the compressor inlet;
  • a step of acquiring a speed of the vehicle, an external temperature and the pressure measured at the condenser outlet;
  • a step of acquiring a voltage of a motor-fan system generating an air flow through the condenser;
  • a step of acquiring a pressure at the condenser outlet, an estimated pressure at the compressor inlet, a speed of the compressor, and a predetermined limit temperature at the condenser inlet or at the compressor outlet;
  • a step of acquiring an amperage for controlling the control valve of the compressor, a step of estimating the pressure at the compressor inlet being carried out as a function of an amperage for controlling the control valve of the compressor;
  • a step of determining an efficiency parameter of the internal exchanger, preferably carried out as a function of a mass flow of the refrigerant fluid;
  • a step of determining a mass flow as a function of the speed of the vehicle, of the external temperature, and of the pressure measured at the condenser outlet.
  • a step of estimating a pressure estimated at the evaporator outlet from the pressure estimated at the compressor inlet and from the mass flow of the refrigerant fluid;
  • a step of estimating a pressure drop between the evaporator outlet and the compressor inlet from the mass flow of the refrigerant fluid;
  • a step of determining overheating characteristics as a function of the pressure estimated at the evaporator outlet;
  • a step of estimating the temperature at the evaporator outlet from overheating characteristics and from the pressure estimated at the evaporator outlet, and
  • a step of modifying a signal for controlling the compressor or a setpoint value of the evaporation temperature.

According to the present invention, the step of calculating the limit temperature at the compressor inlet is carried out as a function of the pressure estimated at the compressor inlet, the compressor speed, and the predetermined limit temperature at the condenser inlet or at the compressor outlet.

In addition, the control method provides for the step of estimating the pressure at the evaporator outlet to be carried out as a function of the pressure drop and of the estimated pressure at the compressor inlet.

According to a first embodiment, the present invention further provides for the control method to comprise:

• • a step of estimating the temperature at the evaporator outlet from an estimated pressure saturation temperature at the evaporator outlet and from overheating characteristics;
  • a step of estimating a limit temperature at the compressor inlet from an efficiency parameter of the exchanger, from the saturation temperature corresponding to the pressure at the condenser inlet or at the compressor outlet and from the estimated temperature at the evaporator outlet, and
  • a step of estimating a limit pressure at the condenser outlet from the limit temperature at the condenser outlet.

According to this first embodiment, the modification step is such that the signal for controlling the compressor or the setpoint value of the evaporation temperature is modified when the estimated temperature at the compressor inlet is greater than or equal to the calculated limit temperature at the compressor inlet.

According to a second embodiment, the control method further comprises:

• • a step of calculating a limit temperature at the evaporator outlet from the efficiency parameter of the exchanger, from the limit temperature at the compressor inlet, and from the pressure saturation temperature at the condenser inlet or at the compressor outlet;
  • a step of calculating a limit pressure at the evaporator outlet from the limit temperature at the evaporator outlet and from overheating characteristics;
  • a step of calculating a limit pressure at the compressor inlet from the limit pressure at the evaporator outlet and from the estimated pressure drop, and
  • a step of calculating a limit value of the amperage for controlling the control valve of the compressor as a function of the limit pressure at the compressor inlet.

The modification step is such that the control signal for the control valve of the compressor is modified for the amperage for controlling the control valve of the compressor to always be less than the limit value of the amperage for controlling the control valve of the compressor. If the measured amperage is greater than the limit value of the voltage of the amperage for controlling the control valve of the compressor, the control method reduces the control signal for the control valve of the compressor so the amperage measured is less than the limit value of the amperage for controlling the control valve of the compressor.

According to a third embodiment, the present invention further provides for the control method to comprise:

• • a step of estimating the temperature at the evaporator inlet from an estimated pressure saturation temperature at the evaporator outlet and from overheating characteristics;
  • a step of estimating a limit temperature at the condenser outlet from an efficiency parameter, from the estimated temperature at the evaporator outlet and from the limit temperature at the compressor inlet, and
  • a step of estimating a limit pressure at the condenser outlet from the limit temperature at the condenser outlet.

According to this third embodiment, the modification step is such that the control signal of the compressor or the setpoint value of the evaporation temperature is modified when the pressure at the condenser outlet is greater than or equal to the limit pressure at the condenser outlet.

In addition, the control method according to the present invention can further provide for:

• • a step of acquiring pressure at the condenser inlet or at the compressor outlet and an air temperature in the evaporator, and
  • a step of calculating a limit temperature at the compressor inlet as a function of the predetermined limit value of the temperature at the condenser inlet or at the compressor outlet, of the pressure at the condenser outlet, of the pressure estimated at the compressor inlet, and of the speed of the compressor.

The invention thus provides for controlling the discharge temperature of the compressor independent of the use of a temperature sensor at the condenser inlet or at the compressor outlet. This allows for the air-conditioning loop comprising an internal exchanger to be controlled with exactly the same sensors as an air-conditioning loop not comprising such an internal exchanger. Therefore, the sensors used are thus a pressure sensor at the condenser outlet, an air temperature measurement in the evaporator, and the value of the control voltage of the control valve of the compressor.

The present invention thus provides for a step of modifying the control signal of the compressor or the setpoint value of the evaporation temperature, independent of the presence, or lack thereof, of a temperature sensor at the condenser inlet, by decrementation, when a value connected to the temperature at the compressor inlet calculated as a function of the acquired data is greater than the limit value calculated as a function of the acquired data.

According to the principle of the invention, the control signal of the compressor or the setpoint value of the evaporation temperature is modified as a function of a comparison between an estimated value, representative of the temperature at the compressor outlet or at the condenser inlet and a limit value.

According to the present invention, the step of determining a mass flow of fluid is carried out from a model of condenser using, in particular, a measurement of the speed of the vehicle, a measurement of the external temperature, a measurement of the voltage of a motor-fan system generating an air flow flowing through the condenser and the pressure at the compressor inlet for determining the mass flow. This characteristic makes it easy to determine the mass flow from parameters known from a microprocessor for centralizing operational data of the vehicle and air-conditioning loop.

Other characteristics and advantages of the present invention will become apparent from the description that follows, with reference to the annexed drawings, given by way of non-limiting examples, which can serve to better understand the present invention and how it is made but also, if necessary, contribute to its definition, wherein:

FIG. 1 presents an air-conditioning loop according to the present invention ;

FIG. 2 presents a flowchart of the method for controlling the compressor built into an air-conditioning loop according to FIG. 1 according to the present invention ;

FIG. 3 shows a curve showing the change of an efficiency parameter of the internal exchanger as a function of the mass flow according to the present invention, and

FIG. 4 shows a chart grouping together the data resulting from the application of the method according to the present invention.

FIG. 1 is a schematic representation of an air-conditioning loop in which the present invention can be controlled. A refrigerant fluid subjected to a thermodynamic cycle defined by means of various components integrated into the air-conditioning loop flows through the air-conditioning loop. In FIG. 1, the air-conditioning loop comprises, in the flow direction of the refrigerant fluid, a compressor CP, a condenser CD, an expansion valve EXV, and an evaporator EV.

The air-conditioning loop can further comprise, optionally, an internal exchanger IHX. The internal exchanger IHX enables a heat transfer between, on the one hand, the refrigerant fluid flowing between the evaporator EV and the compressor CP and, on the other hand, the refrigerant fluid flowing between the condenser CD and the expansion valve EXV. The internal exchanger IHX makes it possible to improve the performance coefficient of the air-conditioning loop.

The air-conditioning loop is associated with a motor-fan system (not shown) which makes it possible to generate an air flow flowing through the condenser CD in order to proceed with a heat transfer between the refrigerant fluid flowing in the condenser CD and the air flow flowing through the condenser to evacuate the heat which has been produced.

FIG. 2 shows a flow chart of a method for controlling the inlet temperature of the compressor CP of the air-conditioning loop according to a first embodiment of the invention.

According to the present invention, the control method comprises the acquisition of several parameters, particularly:

• • an amperage for controlling a control valve of the compressor I_V—M,
  • a speed of the compressor N_CP—M,
  • a pressure measured at the outlet of the condenser PRCDO_M, or at the outlet of the compressor PRCPO_M.

In addition, the control method can also comprise a step of acquiring pressure at the inlet of the condenser PRCDI_M.

In addition, a limit temperature at the outlet of the compressor TRCDO_L is predetermined. Preferably, the limit temperature at the outlet of the compressor TRCDO_L is set at 130° C.

The control method comprises a step E0 for estimating the pressure at the inlet of the compressor PRCPI_E as a function of:

• • the amperage for controlling the control valve of the compressor I_V—M,

according to the control characteristic of the compressor CP.

The method subsequently comprises a step E1 for calculating a limit temperature at the inlet of the compressor TRCPI_L as a function of a predetermined limit temperature at the inlet of the condenser TRCDI_L, of the pressure measured at the outlet of the condenser PRCDO_M, of the estimated pressure at the inlet of the compressor PRCPI_E obtained at step E0, and the speed of the compressor N_CP—M.

The calculation of the limit temperature at the inlet of the compressor TRCPI_L is advantageously in the form:

$\mathrm{TRCPI\_L}=\frac{\mathrm{TRCDI\_L}}{{\left(\frac{\mathrm{PRCDO\_M}}{\mathrm{PRCPI\_M}}\right)}^{\frac{\lambda -1}{\lambda }}}+f1$

whereby PRCPI_M is a pressure measured at the inlet of the compressor,

• • and
  • λ is a constant ;
  • f1 is a function dependent upon:
    • the speed of the compressor N_CP—M,
    • a pressure measured at the outlet of the condenser PRCDO_M, and
    • the pressure estimated at the inlet of the compressor PRCPI_E.

In particular, the pressure measured at the outlet of the condenser PRCDO_M is equal to the pressure measured at the inlet of the condenser PRCDI_M.

The method according to the invention further comprises a step E2 for determining a mass flow MF of the refrigerant fluid from a model of operation of the condenser CD. The step E2 can be carried before, simultaneously, or after steps E0 and/or E1.

Advantageously, and as shown in FIG. 2, the model of operation of the condenser CD makes it possible to estimate the mass flow MF of the refrigerant fluid from a speed of the vehicle V_V, from an external temperature T_E and from the pressure measured at the outlet of the condenser PRCDO_M. In addition to the parameters listed hereinabove, the model of operation of the condenser CD makes it possible to estimate the mass flow MF of the refrigerant fluid also from a voltage U_GMV of the motor-fan system generating the air flow flowing through the condenser CD.

Subsequent to step E2, the invention provides for a step E3 for estimating a pressure estimated at the outlet of the evaporator PREVO_E from the pressure estimated at the inlet of the compressor PRCPI_E obtained at step E0 and from a pressure drop ΔP_EV—CP between the outlet of the evaporator EV and the inlet of the compressor CP.

The pressure drop ΔP_EV—CP is estimated from the mass flow determined at step E2. Therefore, the pressure estimated at the outlet of the evaporator PREVO_E is given by the relation:

PREVO_E=PRCPI_E+ΔP_EV—CP

The pressure estimated at the outlet of the evaporator PREVO_E is used with the characteristics of the operating point of the expansion valve EXV in a step E4 to determine characteristics of static overheating SH_E. The characteristics of static overheating SH_E comprise a static overheating SH and an offset of the overheating ΔSH, for example comprised between 0 and 10° K. Therefore, the static overheating SH_E is given by the relation:

SH _— E=SH+ΔSH.

The mass flow MF obtained at step E2 is also used in a step E5 for determining an efficiency parameter EF_IHX of the internal exchanger IHX. The determination of the efficiency parameter EF_IHX of the internal exchanger IHX is shown in FIG. 3 by a curve showing the change of efficiency of the internal exchanger IHX EF_IHX as a function of the mass flow MF.

Before, simultaneously, or after step E5, the invention comprises a step E6 for estimating a temperature at the outlet of the evaporator TREVO_E from characteristics of the overheating SH_E defined at step E4 and from the pressure estimated at the outlet of the evaporator PREVO_E estimated at step E3.

The pressure estimated at the outlet of the evaporator PREVO_E makes it possible to define the saturation temperature Tsat corresponding to the pressure estimated at the outlet of the evaporator PREVO_E. Advantageously, the temperature estimated at the outlet of the evaporator TREVO_E is given by the relation:

TREVO_E=Tsat(PREVO_E)+SH+ΔSH.

Subsequently, the method comprises a step E7 for estimating a temperature at the inlet of the compressor TRCPI_E from the efficiency parameter EF_IHX of the internal exchanger IHX, the estimated temperature at the outlet of the evaporator TREVO_E estimated at step E6 and the saturation temperature Tsat corresponding to the pressure measured at the outlet of the condenser PRCDO_M.

In a step E8, the temperature estimated at the inlet of the compressor TRCPI_E estimated at step E7 is compared to the limit temperature at the inlet of the compressor TRCPI_L calculated at step E1.

Step E8 determines whether the temperature at the inlet of the compressor TRCPI_E is greater than or equal to the limit temperature at the inlet of compressor TRCPI_L.

If this is not the case, that is, if the temperature at the inlet of the compressor TRCPI_E is not greater than or equal to the limit temperature at the inlet of the compressor TRCPI_L (case N of step E8 of FIG. 2), the method comprises, by default, a step E9 for controlling the compressor CP. Step E9 is carried out as a function of a temperature of the air after going through the evaporator T_EV. Following step E9, a control signal of the compressor PWM_CP(k) is set to control the compressor CP, particularly to control the capacity of the compressor CP. More particularly, the control signal of the compressor PWM_CP(k) depends upon the temperature of the air after having gone through the evaporator T_EV. Therefore,

PWM_Cp(k)=PWM_CP(T_EV).

If this is the case, that is, if the temperature at the inlet of the compressor TRCPI_E is greater than or equal to the limit temperature at the inlet of the compressor TRCPI_L (case ◯ of step E8 of FIG. 2), the method comprises a step E10 for controlling the compressor CP.

At step E10, if the temperature at the inlet of the compressor TRCPI_E is equal to the limit temperature at the inlet of the compressor TRCPI_L, the control signal of the compressor is kept constant. We thus have the following relation:

PWM_CP(k)=PWM_CP(k−1).

In the case where the temperature at the inlet of the compressor TRCPI_E is greater than the limit temperature at the at the inlet of the compressor TRCPI_L, the method according to the present invention provides two solutions based on a same principle to carry out the control of the compressor CP.

The first solution consists of a direct control of a control signal of the compressor PWM_CP decremented by a value corresponding to the difference between the estimated temperature at the inlet of the compressor TRCPI_E and the limit temperature at the inlet of the compressor TRCPI_L. One therefore has the following relation:

PWM_CP(k)=PWM_CP(k−1)−K1*(TRCPI_E−TRCPI_L)

whereby K1 is a coefficient.

The second solution consists of a direct control of a setpoint value of the evaporation temperature SP _T_EV by using the difference between the estimated temperature at the inlet of the compressor TRCPI_E and the limit temperature at the inlet of the compressor TRCPI_L which is thus negative. One thus has the following relation:

SP _— T _EV(k)=SP_—T_EV(k−1)+K2*(TRCPI_E−TRCPI_L).

whereby K2 is a coefficient.

The implementation of the present invention has thus made it possible to obtain, in particular, the results identified in the chart shown in FIG. 4, wherein:

• • PRCDO_M is the pressure measured at the outlet of the condenser,
  • TRCDI_M is the temperature measured at the inlet of the condenser,
  • PRCPI_M is the pressure measured at the inlet of the compressor, and
  • TRCPI_M is the temperature measured at the inlet of the compressor.

The chart of FIG. 4 presents a series of measures consisting in controlling the temperature at the inlet of the condenser TRCDI or at the outlet of the compressor TRCPO, at the limit value of 130° C. It is observed that the estimated value of the temperature consists of a direct control and is very similar to the real measured value. In any event, it is observed that the temperature at the inlet of the compressor TRCPI_E is very close to the measured value and remains less than the limit temperature at the inlet of the compressor TRCPI_L. Therefore, it can be known if the value of the temperature at the inlet of the condenser TRCDI is less than the limit value 130° C.

In a second embodiment of the invention, the method comprises a step of calculating a limit temperature at the outlet of the evaporator TREVO_L from the efficiency parameter of the exchanger EF_IHX, from the limit temperature at the inlet of the compressor TRCPI_L, and from the pressure saturation temperature at the inlet of the condenser, in a manner similar to the calculation of step 6. The following relation is thus obtained:

TREVO_L=Tsat(PREVO_L)+SH+ΔSH

Subsequently, on the basis of the equation obtained previously, a step of calculating a limit pressure at the inlet of the compressor PRCPI_L is carried out from a limit pressure at the outlet of the evaporator PREVO_L and estimated pressure drop:

PRCPI_L=PREVO_L−ΔP_EV—CP.

Finally, a step of calculating the limit amperage for controlling the control valve of the compressor I_V—L is carried out as a function of the calculated limit pressure at the inlet of the compressor PRCPI_L:

I _{V —} L=f(PRCPI_L).

In this embodiment, the control of the air-conditioning loop modifies the control signal of the compressor valve so that the measured amperage for controlling the control valve of the compressor CP is less than the limit amperage for controlling the control valve of the compressor CP.

A third embodiment is such that the method comprises a step of estimating the temperature at the outlet of the evaporator TREVO_E from the pressure saturation temperature estimated at the outlet of the evaporator Tsat(PREVO_E) and from characteristics of the overheating:

TREVO_E=Tsat(PREVO_E)+SH+ΔSH.

Subsequently, a step of estimating a limit temperature at the outlet of the condenser TRCDO_L is carried out from the efficiency parameter EF_IHX of the internal exchanger IHX, from the estimated temperature at the outlet of the evaporator TREVO_E and from the limit temperature at the inlet of the compressor TRCPI_L.

Then follows a step of estimating a limit pressure at the outlet of the condenser PRCDO_L from the limit temperature of the outlet of the condenser TRCDO_L.

The step of modifying the operation of the compressor is such that the control signal of the compressor or the setpoint value of the evaporation temperature is modified by decrementation when the pressure measured at the outlet of the condenser PRCDO_M is greater than the limit pressure at the outlet of the condenser PRCDO_L.

The modification of the operation of the compressor can thus be in the form:

PWM_CP(k)=PWM_CP(k−1)−K3*(PRCDO_M−PRCDO_L)

or

SP _— T _EV(k)=SP_—T_EV(k−1)+K4*(PRCDO_M−PRCDO_L)

whereby K3 et K4 are coefficients.

In the opposite case, by default, the conventional control as a function of the evaporation temperature is active.

Naturally, the invention is not limited to the embodiments described above and given only by way of examples. Various embodiments can be carried out according to the principles of the invention. It encompasses various modifications, alternative forms and other alternatives which can be envisioned by one having ordinary skill in the art in the context of the present invention and particularly any combination of the different embodiments described above.

Claims

1. A method for controlling the outlet temperature (TRCPO) of a compressor (CP) built into an air-conditioning loop of a vehicle in which flows a subcritical refrigerant fluid and comprising at least a condenser (CD), an expansion valve (EXV), and an evaporator (EV), the control method comprising: a step of calculating a limit temperature at the inlet of the compressor (TRCPI_L),step of estimating a temperature at the inlet of the compressor (TRCPI_E), anda step of modifying a control signal of the compressor (PWMCP) or a setpoint value of the evaporation temperature (SP_TEV).

2. A control method according to claim 1, wherein the air-conditioning loop comprises an internal exchanger (IHX) for carrying out heat transfers between the fluid flowing between the condenser (CD) and the expansion valve (EXV) and the fluid flowing between the evaporator (EV) and the compressor (CP).

3. A control method according to claim 1, further comprising: a step of acquiring a speed of the vehicle (VV), an external temperature (TE), and a pressure measured at the outlet of the condenser (PRCDO_M).

4. A control method according to claim 1, further comprising: a step of acquiring a pressure at the outlet of the condenser (PRCDO_M), a pressure estimated at the inlet of the compressor (PRCPI_E), a speed of the compressor (NCP—M) and a predetermined limit temperature at the inlet of the condenser (TRCDI_L).

5. A control method according to claim 4, characterized in that further comprising: a step of acquiring an amperage for controlling the control valve of the compressor (IV—M),and wherein the step of estimating the pressure at the inlet of the compressor (PRCPI_E) is carried out as a function of an amperage for controlling the control valve of the compressor (Iv—M).

6. A control method according to claim 4, wherein the step of calculating the limit temperature at the inlet of the compressor (TRCPI_L) is carried out as a function of the estimated pressure at the inlet of the compressor (PRCPI_E), of the speed of the compressor (NCP—M), and of the predetermined limit temperature at the inlet of the condenser (TRCDI_L).

7. A control method according to claim 6, further comprising: a step of determining an efficiency parameter (EF_IHX) of the internal exchanger (IHX).

8. A control method according to claim 7, wherein the step of determining the efficiency parameter (EF_IHX) is carried out as a function of a mass flow (MF) of the refrigerant fluid.

9. A control method according to claim 8, further comprising: a step of determining the mass flow (MF) carried out as a function of the speed of the vehicle (VV), of the external temperature (TE), and of the pressure measured at the outlet of the condenser (PRCDO_M).

10. A control method according to claim 8, further comprising: a step of determining a pressure estimated at the outlet of the evaporator (PREVO_E) from the estimated pressure at the inlet of the compressor (PRCPI_E) and of the mass flow (MF) of the refrigerant fluid.

11. A control method according to claim 7, further comprising: a step of estimating a pressure drop (ΔPEV—CP) between the outlet of the evaporator (EV) and the inlet of the compressor (CP) from the mass flow (MF) of the refrigerant fluid.

12. A control method according to claim 11, wherein the step of estimating the pressure at the outlet of the evaporator (PREVO_E) is carried out as a function of the pressure drop (ΔPEV—CP) and of the estimated pressure at the inlet of the compressor (PRCPI_E).

13. A control method according to claim 10, further comprising: a step of determining characteristics of overheating (SH_E) as a function of the estimated pressure at the outlet of the evaporator (PREVO_E).

14. A control method according to claim 13, further comprising: a step of estimating the temperature at the outlet of the evaporator (TREVO_E) from characteristics of overheating (SH_E) and from the estimated pressure at the outlet of the evaporator (PREVO_E).

15. A control method according to claim 20, comprising: a step of calculating a limit temperature at the outlet of the evaporator (TREVO_L) from the efficiency parameter of the exchanger (EF_IHX), from the limit temperature at the compressor inlet (TRCPI_L) and from the pressure saturation temperature at the condenser inlet (Tsat(PRCDI_M)),a step of calculating a limit pressure at the evaporator outlet (PREVO_L) from the limit temperature at the evaporator outlet (TREVO_L) and from characteristics of overheating (SH_E),a step of calculating a limit pressure at the compressor inlet (PRCPI_L) from the limit pressure at the evaporator outlet (PREVO_L), and from the estimated pressure drop (ΔPEV—CP), anda step of calculating a limit value of the amperage for controlling the control valve of the compressor (IV—L) as a function of the limit pressure at the compressor inlet (PRCPI_L).

16. A control method according to claim 13, further comprising: a step of calculating the temperature at the evaporator outlet (TREVO_E) from an estimated pressure saturation temperature at the outlet of the evaporator (Tsat(PREVI_E)) and from characteristics of the overheating (SH_E),a step of estimating a limit temperature at the condenser outlet (TRCDO_L) from the efficiency parameter (EF_IHX), from the estimated temperature at the evaporator outlet (TREVO_E) and from the limit temperature at the compressor inlet (TRCPI_L), anda step of estimating a limit pressure at the condenser outlet (PRCDO_L) from the limit temperature at the condenser outlet (TRCDO_L).

17. A control method according to claim 1, wherein the modification step is such that the control signal of the compressor (PWMCP) or the setpoint value of the evaporation temperature (SP_TEV) is modified when the estimated temperature at the inlet of the compressor (TRCPI_E) is greater than or equal to the calculated limit temperature at the compressor inlet (TRCPI_L).

18. A control method according to claim 15, wherein the modification step is such that the control signal for the control valve of the compressor is modified for the amperage for controlling the control valve of the compressor (IV—M) to always be less than the limit value of the amperage for controlling the control valve of the compressor (IV—L).

19. A control method according to claim 16, wherein the modification step is such that the control signal of the compressor (PWMCP) or the setpoint value of the evaporation temperature (SP_TEV) is modified when the pressure at the condenser outlet (PRCDO_M) is greater than or equal to the limit pressure at the condenser outlet (PRCDO_L).

20. A control method according to claim 12, further comprising: a step of determining characteristics of overheating (SH_E) as a function of the estimated pressure at the outlet of the evaporator (PREVO_E).