FR3066584A1 - INDIRECT INDIRECT AIR CONDITIONING CIRCUIT FOR A MOTOR VEHICLE AND METHOD FOR MANAGING HEAT PUMP MODE - Google Patents

Abstract

The present invention relates to an indirect reversible air conditioning circuit (1) comprising: a first refrigerant fluid loop (A) comprising: a compressor (3), an electronic expansion valve (7), a first heat exchanger (7), heat (9), ° a tube orifice (11), ° a second heat exchanger (13), and ° a bypass line (30) of the second heat exchanger (13), • a second heat transfer fluid loop (B) ), and • a bifluid heat exchanger (5) arranged jointly on the first refrigerant loop (A) and on the second heat transfer fluid loop (B), the indirect reversible air conditioning circuit comprising: • a pressure sensor and or temperature (41) of the high pressure refrigerant, said sensor (41) being disposed downstream of the two-fluid heat exchanger (5), • a central control unit (40) connected to said pressure sensor and / or temperature (41) at height pressure, said central control unit being also connected to the electronic expansion valve (7).

Description

The invention relates to the field of motor vehicles and more particularly to a motor vehicle air conditioning circuit and its management method in heat pump mode.

Today's motor vehicles increasingly include an air conditioning circuit. Generally, in a “conventional” air conditioning circuit, a refrigerant passes successively through a compressor, a first heat exchanger, called a condenser, placed in contact with an air flow outside the motor vehicle to release heat, a device expansion valve and a second heat exchanger, called an evaporator, placed in contact with an air flow inside the motor vehicle to cool it.

There are also more complex air conditioning circuit architectures which make it possible to obtain an invertible air conditioning circuit, that is to say that it can use a heat pump operating mode in which it is able to absorb energy. calorific in the outside air at the level of the first heat exchanger, then called evapo-condenser, and restore it in the passenger compartment in particular by means of a third dedicated heat exchanger.

This is possible in particular by using an indirect air conditioning circuit. Indirect here means that the air conditioning circuit has two circulation loops of two separate fluids (such as a refrigerant and glycol water) in order to carry out the various heat exchanges.

The air conditioning circuit thus comprises a first coolant loop in which a coolant circulates, a second coolant loop in which a coolant circulates, and a two-fluid heat exchanger arranged jointly on the first coolant loop and on the second loop of heat transfer fluid, so as to allow heat exchanges between said loops.

Such an air conditioning circuit allows use according to different operating modes but struggles to provide an operating mode whose performance is satisfactory to allow a rapid rise in temperature of the indoor air flow regardless of the external conditions and in particular the temperature. outside air flow. This is particularly the case in heat pump mode where the coefficient of performance of the air conditioning circuit is not always optimal.

One of the aims of the present invention is therefore to at least partially remedy the drawbacks of the prior art and to propose an improved air conditioning circuit as well as its management method in heat pump mode.

The present invention therefore relates to an indirect reversible air conditioning circuit for a motor vehicle comprising:

A first coolant loop in which a coolant circulates, said first coolant loop comprising in the direction of circulation of the coolant:

° a compressor, ° an electronic expansion valve, ° a first heat exchanger being intended to be traversed by a flow of air inside the motor vehicle, ° a tube orifice, ° a second heat exchanger being intended to be traversed by a flow of air outside the motor vehicle, and ° a bypass pipe of the second heat exchanger, • a second loop of heat transfer fluid in which a heat transfer fluid circulates, and • a two-fluid heat exchanger arranged jointly on the first loop of coolant downstream of the compressor, between said compressor and the electronic expansion valve, and on the second loop of coolant, so as to allow heat exchanges between the first loop of coolant and the second loop of coolant , the indirect reversible air conditioning circuit comprising:

• a pressure and / or temperature sensor of the high-pressure refrigerant, said sensor being arranged downstream of the dual-fluid heat exchanger, between said dual-fluid heat exchanger and the electronic expansion valve, • a central processing unit control connected to said pressure and / or temperature sensor of the high pressure refrigerant, said central control unit also being connected to the electronic expansion valve so as to control the opening of said electronic expansion valve.

According to one aspect of the invention, the first refrigerant loop comprises a first internal heat exchanger allowing a heat exchange between the high pressure refrigerant leaving the dual-fluid heat exchanger and the refrigerant leaving the first heat exchanger or the second heat exchanger.

According to another aspect of the invention, the first refrigerant loop includes a second internal heat exchanger allowing a heat exchange between the high pressure refrigerant leaving the first internal heat exchanger and the circulating low pressure refrigerant. in the bypass line.

According to another aspect of the invention, the temperature and pressure sensor of the high-pressure refrigerant is disposed between the dual-fluid heat exchanger and the first internal heat exchanger.

According to another aspect of the invention, the second loop of heat transfer fluid comprises:

° the two-fluid heat exchanger, ° a first heat transfer fluid circulation pipe comprising a third heat exchanger intended to be traversed by a flow of air inside the motor vehicle, and connecting a first junction point arranged downstream of the 'two-fluid heat exchanger and a second junction point arranged upstream of said two-fluid heat exchanger, ° a second heat-transfer fluid circulation pipe comprising a fourth heat exchanger intended to be traversed by a flow of air outside the motor vehicle, and connecting the first junction point arranged downstream of the two-fluid heat exchanger and the second junction point arranged upstream of said two-fluid heat exchanger, and ° a pump arranged downstream or upstream of the two-fluid heat exchanger, between the first junction point and the second junction point.

The present invention also relates to a method for managing an indirect reversible air conditioning circuit according to a heat pump mode in which:

° the refrigerant circulates in the compressor where said refrigerant passes at high pressure and successively circulates in the two-fluid heat exchanger and the electronic expansion valve where said refrigerant passes at an intermediate pressure, said refrigerant then successively circulates in the first heat exchanger, the tube orifice where said refrigerant passes at low pressure, the second heat exchanger before returning to the compressor, ° the heat transfer fluid at the outlet of the dual-fluid heat exchanger circulates only in the third heat exchanger heat of the first circulation line, ° the central control unit calculates the sub-cooling of the refrigerant at the outlet of the dual-fluid heat exchanger according to the following formula:

ΔΤ = T _p -T _m where ΔΤ is the subcooling, T _p is the liquid saturation temperature of the refrigerant at the high pressure value and T _m is the temperature measured by the high pressure refrigerant temperature sensor , Centrale central control unit controlling the opening of the electronic expansion valve so that said subcooling is between 2 and 12 ° K.

According to one aspect of the method according to the invention, the central control unit controls the opening of the electronic expansion valve so that said subcooling is between 6 and 10 ° K.

Other characteristics and advantages of the invention will appear more clearly on reading the following description, given by way of illustrative and nonlimiting example, and of the appended drawings among which:

Figure 1 shows a schematic representation of an indirect reversible air conditioning circuit according to a first embodiment, Figure 2 shows a schematic representation of an indirect reversible air conditioning circuit according to a second embodiment, Figure 3 shows a representation schematic of an indirect reversible air conditioning circuit according to a third embodiment, FIGS. 4a and 4b show schematic representations of expansion devices according to different embodiments, FIG. 5 shows a schematic representation of the second loop of heat transfer fluid of the indirect reversible air conditioning circuit of Figures 1 to 3, according to an alternative embodiment, Figure 6a shows the indirect invertible air conditioning circuit of Figure 1 according to a cooling mode, Figure 6b shows a pressure / enthalpy diagram of the mode of cooling illustrated in Figure 6a, the fig re 7a shows the indirect reversible air conditioning circuit of figure 1 according to a heat pump mode, figure 7b shows a pressure / enthalpy diagram of the heat pump mode illustrated in figure 7a, figures 8a and 8b show graphs of the evolution of the coefficient of performance and of various parameters of the indirect reversible air conditioning circuit of FIG. 1 as a function of the pressure of the refrigerant fluid at the outlet of the first heat exchanger.

In the various figures, identical elements have the same reference numbers.

The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the characteristics apply only to a single embodiment. Simple features of different embodiments can also be combined and / or interchanged to provide other embodiments.

In the present description, it is possible to index certain elements or parameters, such as for example first element or second element as well as first parameter and second parameter or even first criterion and second criterion etc. In this case, it is a simple indexing to differentiate and name elements or parameters or criteria that are similar but not identical. This indexing does not imply a priority of an element, parameter or criterion over another and one can easily interchange such names without departing from the scope of this description. This indexing does not imply an order in time for example to assess this or that criterion.

In the present description, the term "placed upstream" means that one element is placed before another with respect to the direction of circulation of a fluid. Conversely, by "placed downstream" is meant that one element is placed after another with respect to the direction of circulation of the fluid.

Figure 1 shows an indirect air conditioning circuit 1 for a motor vehicle. This indirect air conditioning circuit 1 includes in particular:

• a first coolant loop A in which a coolant circulates, • a second coolant loop B in which a coolant circulates, and • a two-fluid heat exchanger 5 arranged jointly on the first coolant loop A and on the second loop of heat transfer fluid B, so as to allow heat exchange between said first loop of coolant A and said second loop of heat transfer fluid B.

The first coolant loop A, shown in solid lines in the various figures, more particularly comprises in the direction of circulation of the coolant:

° a compressor 3, ° the two-fluid heat exchanger 5, arranged downstream of said compressor 3, ° a first expansion device, more precisely an electronic expansion valve 7, ° a first heat exchanger 9 being intended to be traversed by an internal air flow 100 to the motor vehicle, ° a second expansion device, more precisely a tube orifice 11, ° a second heat exchanger 13 being intended to be traversed by an external air flow 200 to the motor vehicle, and ° a bypass line 30 of the second heat exchanger 13.

The bypass pipe 30 can more specifically connect a first connection point 31 and a second connection point 32.

The first connection point 31 is preferably arranged, in the direction of circulation of the coolant, downstream of the first heat exchanger 9, between said first heat exchanger 9 and the second heat exchanger 13. More particularly, and as illustrated in FIG. 1, the first connection point 31 is disposed between the first heat exchanger 9 and the tube orifice 11. It is however quite possible to imagine that the first connection point 31 is disposed between the orifice tube 11 and the second heat exchanger 13 as long as the refrigerant has the possibility of bypassing said tube orifice 11 or crossing it without undergoing pressure loss.

The second connection point 32 is preferably arranged downstream of the second heat exchanger 13, between said heat exchanger 13 and the compressor 3.

As illustrated in FIG. 2, the first loop of refrigerant A can also include a first internal heat exchanger 19 (IHX for "internai heat exchanger") allowing a heat exchange between the refrigerant at the outlet of the heat exchanger dual fluid 5 and the refrigerant at the outlet of the second heat exchanger 13 or the bypass pipe 30. This first IHX 19 notably has an inlet and an outlet for coolant coming from the second connection point 32, as well as an inlet and a coolant outlet from the dual fluid heat exchanger 5.

As illustrated in FIG. 3, the first refrigerant loop A may comprise, in addition to the first IHX 19, a second IHX 19 'allowing heat exchange between the high pressure refrigerant leaving the first IHX 19 and the fluid low pressure refrigerant circulating in the bypass pipe 30, that is to say coming from the first connection point 31. By high pressure refrigerant is meant by this a refrigerant having undergone a pressure increase at the compressor 3 and that it has not yet suffered a pressure loss due to the electronic expansion valve 7 or the tube orifice 11. This second IHX 19 ′ notably has an inlet and an outlet for coolant coming from the first connection point 31, as well as an inlet and an outlet for high-pressure refrigerant coming from the first IHX 19.

At least one of the first 19 or second 19 ′ IHX can be a coaxial heat exchanger, that is to say comprising two coaxial tubes and between which the heat exchanges take place.

Preferably, the first IHX 19 can be a coaxial IHX with a length between 50 and 120mm while the second IHX 19 'can be a coaxial IHX with a length between 200 and 700mm.

As shown in Figures 1 and 2, the first coolant loop may also include an accumulator 15 disposed upstream of the compressor 3, more precisely between the second connection point 32 and said compressor 3. In the case where a first IHX 19 is present, said accumulator 15 is disposed upstream of said first IHX 19, between the second connection point 32 and said first IHX 19. This accumulator 15 makes it possible in particular to carry out a phase separation of the refrigerant fluid so that the refrigerant fluid arriving at the compressor 3 or in the first IHX 19 is in the gas phase.

According to a variant illustrated in FIG. 3, the first cooling fluid loop A can comprise, instead of an accumulator 15, a desiccant bottle 15 ′ disposed downstream of the dual-fluid heat exchanger 5, more precisely between said heat exchanger two-fluid heat 5 and the first IHX 19. Such a desiccant bottle 15 ′ disposed on the high pressure side of the air conditioning circuit, that is to say downstream of the compressor 3 and upstream of an expansion device, has a smaller footprint as well as a reduced cost compared to other phase separation solutions such as an accumulator which would be disposed on the low pressure side of the air conditioning circuit, that is to say upstream of the compressor 3, in particular upstream of the first IHX 19 .

The indirect reversible air conditioning circuit 1 also includes a device for redirecting the refrigerant coming from the first heat exchanger 9 to the second heat exchanger 13 or to the bypass pipe 30.

This device for redirecting the refrigerant coming from the first heat exchanger 9 may in particular comprise:

• a first stop valve 22 disposed downstream of the first connection point 31, between said first connection point 31 and the second expansion device 11. An alternative to this first stop valve 22 may be that the second expansion valve 11 has a stop function so as to be able to block the coolant and prevent it from circulating, • a second stop valve 33 disposed on the bypass pipe 30, and • a non-return valve 23 disposed downstream of the second heat exchanger 13, between said second heat exchanger 13 and the second connection point 32.

Another alternative (not shown) may also be to have a three-way valve at the first connection point 31.

By stop valve, non-return valve, three-way valve or expansion device with stop function, is meant here mechanical or electromechanical elements which can be controlled by a central control unit on board the motor vehicle.

As shown in more detail in FIGS. 4a and 4b, the electronic expansion valve 7 and the tube orifice 11 can be bypassed by a bypass line A ', notably comprising a stop valve 25, 25 ’. This bypass line A 'allows the refrigerant to bypass the electronic expansion valve 7 and / or the tube orifice 11 without undergoing a pressure loss. An alternative for the coolant to pass through the electronic expansion valve 7 without pressure loss is that the latter has a maximum opening function in which the coolant passes through it without loss of pressure.

The second heat transfer fluid loop B, shown in a line comprising three dashes and two points in the different figures, may in turn include:

° the dual-fluid heat exchanger 5, ° a first circulation pipe 50 of heat-transfer fluid comprising a third heat exchanger 54 intended to be traversed by an interior air flow 100 to the motor vehicle, and connecting a first junction point 61 disposed downstream of the dual-fluid heat exchanger 5 and a second junction point 62 disposed upstream of said dual-fluid heat exchanger 5, ° a second circulation pipe 60 of coolant comprising a fourth heat exchanger 64 intended to be traversed by an outside air flow 200 to the motor vehicle, and connecting the first junction point 61 disposed downstream of the dual-fluid heat exchanger 5 and the second junction point 62 disposed upstream of said dual-fluid heat exchanger 5, and ° a pump 17 arranged downstream or upstream of the two-fluid heat exchanger 5, between the first junction point 61 and the second junction point 62.

The indirect reversible air conditioning circuit 1 includes, within the second heat transfer fluid loop B, a device for redirecting the heat transfer fluid from the two-fluid heat exchanger 5 to the first circulation line 50 and / or to the second heat line traffic 60.

As illustrated in FIGS. 1 to 3, said device for redirection of the heat-transfer fluid coming from the dual-fluid heat exchanger 5 can in particular comprise a fourth stop valve 63 disposed on the second circulation pipe 60 in order to block or not block the heat transfer fluid and prevent it from circulating in said second circulation pipe 60.

The indirect reversible air conditioning circuit 1 may also include a shutter 310 for blocking the interior air flow 100 passing through the third heat exchanger 54.

This embodiment notably makes it possible to limit the number of valves on the second heat transfer fluid loop B and thus makes it possible to limit the production costs.

According to an alternative embodiment illustrated in FIG. 5, the device for redirection of the heat-transfer fluid coming from the dual-fluid heat exchanger 5 may in particular comprise • a fourth stop valve 63 disposed on the second circulation pipe in order to block or not the heat transfer fluid and prevent it from flowing in said second circulation pipe 60, and • a fifth stop valve 53 disposed on the first circulation pipe in order to block or not the heat transfer fluid and prevent it from circulate in said first circulation pipe 50.

The second heat transfer fluid loop B can also include an electric heating element 55 of the heat transfer fluid. Said electric heating element 55 is notably arranged, in the direction of circulation of the heat-transfer fluid, downstream of the dual-fluid heat exchanger 5, between said dual-fluid heat exchanger 5 and the first junction point 61.

As shown in Figures 1 to 3, the indirect reversible air conditioning circuit further comprises a central control unit 40 controlling and controlling various elements in order to allow the passage from one operating mode to another as well as to control the different modes of operations.

In order to control in particular the transition from an operating mode to another central control unit 40 can in particular be connected to the device for redirecting the refrigerant coming from the first heat exchanger 9 and more particularly to the first shut-off valve 22 and the second stop valve 33 in order to control their opening or closing. The central control unit 40 can also be connected to the stop valves 25 and 25 ′ of the bypass lines A ′ enabling the electronic expansion valve 7 and the tube orifice 11 to be bypassed. These various connections are not is not shown in the figures. The central control unit 40 can also be connected to the heat transfer fluid redirection device in order to control the circulation of the heat transfer fluid in the second heat transfer fluid loop B.

The central control unit 40 can be connected to the electronic expansion valve 7 in order to control its opening and to define the pressure of the refrigerant fluid at the outlet of said electronic expansion valve.

The central control unit 40 can also be connected to the compressor 3 in order to control it and define its speed and thus define the pressure of the refrigerant fluid leaving said compressor 3.

The indirect reversible air conditioning circuit 1 may include a pressure and / or temperature sensor 41 of the high pressure refrigerant. This sensor 41 is arranged downstream of the two-fluid heat exchanger 5, between said two-fluid heat exchanger 5 and the electronic expansion valve 7. When the indirect reversible circuit 1 comprises a first IHX 19, the pressure sensor and / or temperature 41 of the high pressure refrigerant is disposed between the two-fluid heat exchanger 5 and the first internal heat exchanger 19 so that the pressure and temperature measurements are not affected by said first IHX 19. This sensor pressure and / or temperature 41 of the high pressure refrigerant is connected to the central control unit 40 and allows the latter to know the pressure as well as the temperature of the refrigerant leaving the dual-fluid heat exchanger 5.

The indirect reversible air conditioning circuit 1 may include a temperature sensor 42 for the outside temperature as well as a pressure sensor 43 for the refrigerant at intermediate pressure. This pressure sensor 43 is arranged downstream of the electronic expansion valve 7, between said electronic expansion valve 7 and the tube orifice 11. More particularly, the pressure sensor 43 of the refrigerant at intermediate pressure is arranged in downstream of the first heat exchanger 9, between said first heat exchanger 9 and the first connection point, as illustrated in FIGS. 1, 2 and 3. It is nevertheless quite possible to have this pressure sensor 43 upstream of the heat exchanger, between the electronic expansion valve 7 and said first heat exchanger 9.

The temperature sensor 42 of the outside temperature as well as the pressure sensor 43 of the refrigerant at intermediate pressure are both connected to the central control unit 40 and allow the latter to know the temperature of the air outside the vehicle. automotive as well as the coolant pressure at the outlet of the electronic expansion valve 7.

The indirect reversible air conditioning circuit 1 can also include a pressure sensor 44 of the low pressure refrigerant. This pressure sensor 44 is disposed downstream of the bypass pipe 30, more precisely between the second connection point 32 and the compressor 3. When the indirect reversible circuit 1 comprises a first IHX 19, the pressure sensor 44 of the refrigerant to low pressure is arranged between the second connection point 32 and the first internal heat exchanger 19 so that the pressure measurement is not affected by said first IHX 19.

In FIGS. 6a to 7b are illustrated operating methods of the indirect reversible air conditioning circuit 1 according to different operating modes. In FIGS. 6a and 7a, only the elements in which the coolant and / or the coolant circulate are shown. The direction of circulation of the refrigerant and / or the coolant is represented by arrows.

FIG. 6a shows more particularly an operating method according to a cooling mode in which:

• the refrigerant passes successively through the compressor 3, the two-fluid heat exchanger 5, the electronic expansion valve 7 and the first heat exchanger 9 before returning to the compressor 3, • a portion of the heat transfer fluid leaving the bifluid heat exchanger 5 circulates in the third heat exchanger 54 of the first circulation line 50 and another portion of the heat transfer fluid at the outlet of the bifluid heat exchanger 5 circulates in the fourth heat exchanger 64 of the second pipe circulation 50, • the shutter 310 is closed so as to prevent the interior air flow

100 to circulate in the third heat exchanger 54.

The pressure and enthalpy variations undergone by the refrigerant during this cooling mode are illustrated on the pressure / enthalpy diagram in FIG. 6b. Curve X represents the saturation curve of the refrigerant.

The refrigerant at the inlet of compressor 3 is in the gas phase. The refrigerant undergoes compression, illustrated by arrow 300, passing through the compressor 3. This is called high-pressure refrigerant.

The high-pressure refrigerant passes through the dual-fluid heat exchanger 5 and undergoes a loss of enthalpy, illustrated by arrow 500, due to the passage in the liquid phase of the refrigerant and the transfer of enthalpy to the heat transfer fluid of the second heat transfer fluid loop B. The refrigerant fluid then loses enthalpy while remaining at a constant pressure.

The refrigerant then passes through the electronic expansion valve 7. The refrigerant undergoes an isenthalpic pressure loss, illustrated by arrow 700 and crosses the saturation curve X, which puts it in a state of liquid mixture plus gas . This is called low pressure refrigerant.

The low pressure refrigerant then passes into the first heat exchanger 9 where it gains enthalpy as illustrated by the arrow 900 by cooling the interior air flow 100. The low pressure refrigerant thus joins the saturation curve X and returns to the gaseous state.

At the outlet of the first heat exchanger 9, the low-pressure refrigerant is redirected to the bypass pipe 30 before re-entering the compressor 3.

This cooling mode is useful for cooling the interior air flow 100.

In this cooling mode, the coolant redirection device is configured so that the coolant does not circulate in the second heat exchanger 13.

This is in particular possible by closing the first stop valve 22 and by opening the second stop valve 33 so that the low-pressure refrigerant leaving the first heat exchanger 9 does not circulate in the second heat exchanger 13 and passes through bypass 30.

The non-return valve 23 makes it possible to prevent low-pressure refrigerant fluid leaving the bypass pipe 30 from flowing back to the second heat exchanger 13.

According to a first variant not shown, the cooling mode can operate when the indirect reversible air conditioning circuit 1 comprises a first IHX 19. This first variant of the cooling mode comprises the same steps as the cooling mode illustrated in FIG. 6a, the difference that:

• before arriving in the electronic expansion valve 7, the high pressure refrigerant passes through the first IHX 19, and • before arriving in the compressor 3, the low pressure refrigerant coming from the bypass 30 also goes through the first IHX 19.

The first IHX 19 allows a reduction in the enthalpy of the high pressure refrigerant before entering the first heat exchanger 9 by transferring part of its enthalpy to the low pressure refrigerant upstream of the compressor 3. The first IHX 19 allows an increase in cooling power and improves the coefficient of performance (or COP for “coefficient of performance”) by reducing the enthalpy of the high pressure refrigerant leaving the dual-fluid heat exchanger 5 and transferring it to the low pressure refrigerant before entering the compressor 3.

According to a second variant not shown, the cooling mode can operate when the indirect reversible air conditioning circuit 1 comprises a first 19 and a second 19 ’IHX. This second variant of the cooling mode comprises the same steps as the cooling mode illustrated in FIG. 6a, with the difference that:

• before arriving in the electronic expansion valve 7, the high-pressure refrigerant passes successively through the first IHX 19 and the second IHX 19 ', and • before arriving in the compressor 3, the low-pressure refrigerant pressure from the first heat exchanger 9 passes into the second IHX 19 'by passing through the bypass pipe 30 and then passes through the first IHX 19.

In this second variant of the cooling mode, the two IHX 19 and 19 ′ are active and their effects add up. The use of IHX 19 and 19 'one after the other makes it possible to reduce the halenthalpy of the high pressure refrigerant entering the electronic expansion valve 7. The high pressure refrigerant in the liquid state at the outlet of the dual-fluid heat exchanger 5 is cooled by the refrigerant in the gaseous state and at low pressure leaving the first heat exchanger 9. The difference in enthalpy at the terminals of the first heat exchanger 9 significantly increases which allows both an increase in the cooling capacity available at said first heat exchanger 9 which cools the air flow 100 and this therefore results in an improvement in the performance coefficient.

In addition, the addition of enthalpy to the low pressure refrigerant at the level of the first 19 and second 19 'IHX makes it possible to limit the proportion of refrigerant in the liquid phase before entering the compressor 3, in particular when the air conditioning circuit 1 comprises a desiccant bottle 15 disposed downstream of the two-fluid heat exchanger 5.

At the second heat transfer fluid loop B, the heat transfer fluid gains enthalpy from the coolant at the two-fluid heat exchanger 5.

As illustrated in FIG. 6a, a portion of the heat transfer fluid circulates in the first circulation pipe 50 and passes through the third heat exchanger 54. The heat transfer fluid does not, however, lose any enthalpy because the obstruction flap 310 is closed and blocked the interior air flow 100 so that it does not pass through the third heat exchanger 54.

Another portion of the heat transfer fluid circulates in the second circulation line 60 and passes through the fourth heat exchanger 64. The heat transfer fluid loses enthalpy at said heat exchanger 64 by releasing it into the external air flow 200. The fourth stop valve 63 is open to allow the passage of the heat transfer fluid.

An alternative solution (not shown) so that the heat transfer fluid does not exchange with the interior air flow 100 at the third heat exchanger 54, is to provide, as in FIG. 4, the first circulation pipe 50 of the fifth shut-off valve 53 and to close it so as to prevent the coolant from flowing in said first circulation pipe 50.

FIG. 7a more particularly shows an operating method according to a heat pump mode in which:

• the refrigerant passes successively through the compressor 3, the two-fluid heat exchanger 5, the electronic expansion valve 7, the first heat exchanger 9, the tube orifice 11 and the second heat exchanger 13 before returning to the compressor 3, • the heat transfer fluid leaving the dual-fluid heat exchanger 5 circulates only in the third heat exchanger 54 of the first circulation pipe 50, • the obstruction flap 310, when it is present, is open so as to allow the interior air flow 100 to circulate in the third heat exchanger 54.

The pressure and enthalpy variations undergone by the refrigerant during this heat pump mode are illustrated on the pressure / enthalpy diagram in FIG. 7b. Curve X represents the saturation curve of the refrigerant.

The refrigerant at the inlet of compressor 3 is in the gas phase. The refrigerant undergoes compression, illustrated by the arrow 300, passing through the compressor 3. Here we speak of high pressure refrigerant.

The high-pressure refrigerant passes through the dual-fluid heat exchanger 5 and undergoes a loss of enthalpy, illustrated by arrow 500, due to the passage in the liquid phase of the refrigerant and the transfer of enthalpy to the heat transfer fluid of the second heat transfer fluid loop B. The high pressure refrigerant then loses enthalpy while remaining at a constant pressure.

The high-pressure refrigerant then passes through the electronic expansion valve 7. The refrigerant undergoes a first isenthalpic pressure loss, illustrated by arrow 700 and crosses the saturation curve X, which puts it in a state of liquid mixture plus gas. We are talking here about medium pressure fluid.

The refrigerant at intermediate pressure then passes through the first heat exchanger 9 where it continues to lose enthalpy as illustrated by arrow 900 by heating the internal air flow 100.

At the outlet of the first heat exchanger 9, the refrigerant at intermediate pressure is redirected to the second heat exchanger 13. Before arriving at the second heat exchanger 13, the refrigerant at intermediate pressure passes into the orifice tubell where it undergoes a second isenthalpic pressure loss illustrated by arrow 110. This is called low pressure fluid.

The low pressure refrigerant then passes through the second heat exchanger 13 where it gains enthalpy, as illustrated by arrow 130, by absorbing enthalpy from the outside air flow 200. The low pressure refrigerant joins thus the saturation curve X and returns to the gaseous state.

The low pressure refrigerant then joins the compressor 3.

In this heat pump mode, the coolant redirection device is configured so that the coolant at intermediate pressure does not circulate in the bypass line 30.

This is in particular possible by opening the first stop valve 22 and closing the second stop valve 33 so that the refrigerant at intermediate pressure at the outlet of the first heat exchanger 9 does not circulate in the bypass pipe 30 and passes in the tube orifice 11 and the second heat exchanger 13.

According to a first variant not shown, the heat pump mode can operate when the indirect invertible air conditioning circuit 1 comprises a first IHX 19. This variant of the heat pump mode comprises the same steps as the dehumidification mode illustrated in FIG. 7a, with the difference that:

• before arriving in the electronic expansion valve 7, the high pressure refrigerant passes through the first IHX 19, and • before arriving in the compressor 3, the low pressure refrigerant coming from the second heat exchanger Heat 13 also goes through the first IHX 19.

According to a second variant not shown, the heat pump mode can operate when the indirect reversible air conditioning circuit 1 includes a first 19 and a second 19 ’IHX. This second variant of the heat pump mode comprises the same steps as the pump mode illustrated in FIG. 7a, with the difference that before arriving in the electronic expansion valve 7, the high-pressure refrigerant passes successively through the first IHX 19 and the second IHX 19 '.

However, the second IHX 19 ’has no influence because the refrigerant does not pass through the bypass loop 30.

The first IHX 19 allows a reduction in the enthalpy of the high pressure refrigerant before entering the first heat exchanger 9 by transferring part of its enthalpy to the low pressure refrigerant upstream of the compressor 3. The addition of enthalpy with the low pressure refrigerant at the first IHX 19 makes it possible to limit the proportion of low pressure refrigerant in the liquid phase before it enters the compressor 3, in particular when the air conditioning circuit 1 comprises a desiccant bottle 15 arranged in downstream of the two-fluid heat exchanger 5.

The effect of the first IHX 19 can be limited when the latter is short, for example with a length between 50 and 120mm. This size limits the heat exchange between the high pressure refrigerant and the low pressure refrigerant so that the exchanged enthalpy limits the proportion of refrigerant in liquid phase before entering the compressor 3 without as much to penalize the efficiency of the heat pump mode. Indeed, the purpose of this heat pump mode is to release as much enthalpy as possible into the interior air flow 100 in order to heat it up at the level of the first heat exchanger 9.

At the second heat transfer fluid loop B, the heat transfer fluid gains enthalpy from the coolant at the two-fluid heat exchanger 5.

As illustrated in FIG. 7a, the heat transfer fluid circulates in the first circulation pipe 50 and passes through the third heat exchanger 54. The heat transfer fluid loses enthalpy by heating the interior air flow 100. For this, the shutter obstruction 310 is open or the fifth stop valve 53 is open. The fourth stop valve 63 is closed in order to prevent the passage of the heat transfer fluid in the second circulation pipe 60.

This heat pump mode is useful for heating the interior air flow 100 both at the level of the first heat exchanger 9 and of the third heat exchanger 54 by absorbing enthalpy of the exterior air flow 200 at the level of the second heat exchanger 13.

In addition, the electric heating element 55 can be in operation in order to provide an additional supply of heat energy to the heat transfer fluid to heat the interior air flow 100.

According to a management method, when the indirect reversible air conditioning circuit 1 is in the heat pump operating mode, the central control unit 40 calculates the sub-cooling of the refrigerant fluid at the outlet of the dual-fluid heat exchanger 5. The subcooling is calculated according to the following formula:

ΔΤ = T _p -T _m where ΔΤ is the subcooling, T _p is the liquid saturation temperature of the refrigerant at the high pressure value and T _m is the temperature measured by the high pressure refrigerant temperature sensor . This subcooling is illustrated in FIG. 7b by the interval Y.

The liquid saturation temperature of the refrigerant at the high pressure value T _p is a defined value and varies according to the types of refrigerant. The pressure of the coolant as well as its temperature at the outlet of the two-fluid heat exchanger 5 are known to the central control unit 40 due to the pressure and / or temperature sensor 41 of the high pressure coolant.

Depending on the result of sub-cooling, the central control unit 40 controls the electronic expansion valve 7 so that said sub-cooling is between 2 and 12 ° K, preferably between 6 and 10 ° K. For this, the central control unit 40 varies the opening of said electronic expansion valve 7 in order to vary the pressure loss at its level and thus modulate the sub-cooling.

This sub-cooling control makes it possible to maintain an optimal coefficient of performance of the indirect reversible air conditioning circuit 1 in heat pump mode.

This management process is particularly suitable for a refrigerant which can be, among other things, R1234yf or R134a.

FIGS. 8a and 8b show graphs describing the evolution of the coefficient of performance (COP) illustrated by the curve 200, as a function of the pressure of the refrigerant fluid at the outlet of the first heat exchanger 9.

On the same graph is also shown the change in heating power (expressed in power / lOOW), illustrated by curve 300, as a function of the pressure of the refrigerant leaving the first heat exchanger 9.

The curve 400 shows the evolution of the sub-cooling at the outlet of the two-fluid heat exchanger 5 as a function of the pressure of the refrigerant fluid at the outlet of the first heat exchanger 9.

The curve 500 shows the evolution of the temperature of the internal air flow 100 at the outlet of the first heat exchanger 9 as a function of the pressure of the refrigerant fluid at the outlet of the first heat exchanger 9.

Figure 8a more specifically shows these curves for an outdoor temperature in the range of -18 ° C and Figure 8b for an outdoor temperature in the range of 0 ° C.

In these Figures 8a and 8b and in particular in Figure 8a, it is thus visible that when the subcooling (curve 400) is between 2 and 12 ° K, the coefficient of performance (curve 200) is the most important while having a high heating power (curve 300). More precisely, when the sub-cooling is between 6 and 10 ° K, the coefficient of performance is optimal, whatever the outside temperature.

Outside this sub-cooling range of 2 to 12 ° K, the coefficient of performance (curve 200) tends to decline.

Other operating modes such as dehumidification, defrosting or heating modes can also be envisaged with such an architecture of the indirect reversible air conditioning circuit 1.

Thus, it is clear that due to its architecture and its operating process, the indirect invertible air conditioning circuit 1, allows a mode of operation in heat pump with an optimal performance coefficient.

Claims (7)

1. Indirect reversible air conditioning circuit (1) for a motor vehicle comprising: A first coolant loop (A) in which a coolant circulates, said first coolant loop (A) comprising in the direction of circulation of the coolant: ° a compressor (3), ° an electronic expansion valve (7), ° a first heat exchanger (9) being intended to be traversed by an interior air flow (100) to the motor vehicle, ° a tube orifice (11), ° a second heat exchanger (13) being intended to be traversed by a flow of air outside (200) to the motor vehicle, and ° a bypass line (30) of the second heat exchanger (13), • a second heat transfer fluid loop (B) in which a heat transfer fluid circulates, and • a two-fluid heat exchanger (5) arranged jointly on the first coolant loop (A) downstream of the compressor (3), between said compressor (3) and the electronic expansion valve (7), and on the second coolant loop (B), so as to allow heat exchanges between the first coolant loop (A) and the second fluid loop coolant (B), characterized in that it c omorts: A pressure and / or temperature sensor (41) of the high-pressure refrigerant, said sensor (41) being arranged downstream of the dual-fluid heat exchanger (5), between said dual-fluid heat exchanger (5) and the electronic expansion valve (7), • a central control unit (40) connected to said pressure and / or temperature sensor (41) at high pressure, said central control unit (40) also being connected to the valve electronic expansion valve (7) so as to control the opening of said electronic expansion valve (7). 2. Indirect reversible air conditioning circuit (1) according to the preceding claim, characterized in that the first coolant loop (A) comprises a first internal heat exchanger (19) allowing a heat exchange between the high pressure coolant at the outlet of the two-fluid heat exchanger (5) and the refrigerant fluid at the outlet of the first heat exchanger (9) or the second heat exchanger (13). 3. Indirect reversible air conditioning circuit (1) according to one of the preceding claims, characterized in that the first coolant loop (A) comprises a second internal heat exchanger (19 ') allowing heat exchange between the fluid high pressure refrigerant at the outlet of the first internal heat exchanger (19) and the low pressure refrigerant circulating in the bypass line (30). 4. Indirect reversible air conditioning circuit (1) according to one of claims 2 or 3, characterized in that the temperature and pressure sensor of the high-pressure refrigerant is disposed between the dual-fluid heat exchanger (5) and the first internal heat exchanger (19). 5. Indirect reversible air conditioning circuit (1) according to one of the preceding claims, characterized in that the second heat transfer fluid loop (B) comprises: ° the two-fluid heat exchanger (5), ° a first circulation pipe (50) for heat transfer fluid comprising a third heat exchanger (54) intended to be traversed by an internal air flow (100) in the motor vehicle, and connecting a first junction point (61) disposed downstream of the dual-fluid heat exchanger (5) and a second junction point (62) disposed upstream of said dual-fluid heat exchanger (5), ° a second circulation pipe (60) of heat transfer fluid comprising a fourth heat exchanger (64) intended to be traversed by an external air flow (200) to the motor vehicle, and connecting the first junction point (61) disposed downstream of the exchanger dual fluid heat (5) and the second junction point (62) disposed upstream of said dual fluid heat exchanger (5), and ° a pump (17) disposed downstream or upstream of the dual fluid heat exchanger (5) , between the first junction point (61) and the two x junction point (62). 6. Method for managing an indirect invertible air conditioning circuit (1) according to claim 5, according to a heat pump mode in which: ° the refrigerant circulates in the compressor (3) where said refrigerant passes at high pressure and successively circulates in the two-fluid heat exchanger (5) and the electronic expansion valve (7) where said refrigerant passes at a pressure intermediate, said refrigerant then circulates successively in the first heat exchanger (9), the tube orifice (11) where said refrigerant passes at low pressure, the second heat exchanger (13) before returning to the compressor (3) , ° the heat transfer fluid at the outlet of the dual-fluid heat exchanger (5) circulates only in the third heat exchanger (54) of the first circulation pipe (50), ° the central control unit (40) calculates the sub-cooling of the refrigerant at the outlet of the two-fluid heat exchanger (5) according to the following formula: ΔΤ = T _p -T _m 5 where ΔΤ is the subcooling, T _p is the liquid saturation temperature of the refrigerant at the high pressure value and T _m is the temperature measured by the temperature sensor of the high pressure refrigerant, the central unit of control (40) controlling the opening of the electronic expansion valve (7) so that said subcooling is between 2 and 10 12 ° K. 7. A method of managing an indirect reversible air conditioning circuit (1) according to the preceding claim, characterized in that the central control unit (40) controls the opening of the electronic expansion valve (7) so of said sub-cooling is between 6 and 10 ° K.