FR2853859A1 - AIR CONDITIONING SYSTEM OF MOTOR VEHICLE WITH CO2 COOLING AGENT - Google Patents

Abstract

The invention relates to a compression refrigerant system of an air conditioning system of a motor vehicle in which is carried out, via refrigerant conduits (6), a continuous circulation of a CO2 refrigerant which leaves of a compressor (1), passes through a gas cooler (2), a regulator (4) and an evaporator (5) before returning to said compressor (1). There is, between the compressor (1) and the gas cooler (2), a switching valve (9) making it possible to switch with said compressor (1) in a second refrigerant circuit intended for a "heating" mode a throttling element (7) and a heating heat exchanger (8). In "heating" mode, the system operates in a mode called "hot gas". In order to be able to regulate it stably, a volume of coolant of at least 50 cm3 is provided between the compressor (1) and the throttling element (7).

Description

I

  The invention relates to a compression refrigerant system of an air-conditioned system of a motor vehicle, in which, via refrigerant conduits, a continuous circulation of a CO 2 refrigerant agent from a compressor, passes through a gas cooler, a pressure reducer and an evaporator 5 before returning to said compressor. Such a compression refrigeration system is known from DE 199 25 744 AI.

  Motor vehicle air conditioning systems using carbon dioxide as a refrigerant are increasingly seen as a more environmentally friendly alternative than conventional air conditioning systems using a fluorinated hydrocarbon refrigerant. Carbon dioxide is also inexpensive, available everywhere, non-toxic and has the added benefit of not being flammable. It therefore also meets the high safety requirements to which the motor vehicle sector is subject. Owing to the high pressures, up to 140 bar, existing in the carbon dioxide cooling circuit, it is however not possible to carry out a simple exchange of refrigerant while preserving the existing systems. On the contrary, the design of such systems must be largely revised.

  As for carbon dioxide air conditioning systems, it has already been proposed to use them also for heating. To do this, there is provided a second refrigerant circuit having a heat exchanger for the "heating" mode. The switching between the two refrigerant circuits is carried out by means of a suitable switching valve. In "heating" mode, the system operates in so-called "hot gas" mode (triangle process). Initial tests 25 have shown that, in the case of air conditioning systems of this type intended for passenger cars, the hot gas process exhibits a high dynamic, that is to say that high pressure variations appear in the refrigerant lines. Therefore, the hot gas process is not stably adjustable in these passenger car air conditioning systems.

  The problem which is the basis of the invention is therefore to improve the compression refrigeration system so that the hot gas process can be adjusted stably in "heating" mode.

  The problem is solved by means of a compression refrigerant of an air-conditioned system of a motor vehicle in which, via refrigerant conduits, a continuous circulation of a CO 2 refrigerant starts from a compressor. , passes through a gas cooler, an expansion valve and an evaporator before returning to said compressor, a switching valve being installed between the compressor and the gas cooler, which makes it possible to switch with said compressor in a second refrigerant circuit intended for in a "heating" mode, a throttling element and a heating heat exchanger, and the volume of refrigerant present between the compressor and the throttling element being at least 50 cm3.

  The compression refrigeration system according to the invention may also include one or more of the following advantageous characteristics: the volume of refrigerant present between the compressor and the throttling element is at least 100 cm 3, preferably between 100 cm3 and 10,200 cm3; - There is between the compressor and the choke element a coolant reservoir, produced in particular in the form of a coolant connection duct; - the refrigerant line between the compressor and the switching valve and / or between the switching valve and the throttle has a cross section greater than that of the refrigerant lines between the other components ; - the refrigerant line between the switching valve and the throttle is longer than the refrigerant line between the switching valve and the gas cooler.

  The compression refrigeration system usually has a first refrigerant circuit allowing a continuous circulation of a CO 2 refrigerant which starts from a compressor, passes through a gas cooler, an expansion valve and an evaporator before returning to said audit. compressor. In a second refrigerant circuit intended for the "heating" mode, the circulation of the refrigerant to CO 2 takes place from the compressor through a throttling element and a heating heat exchanger. Switching between the first and second refrigerant circuits is accomplished using a switching valve located between the compressor and the gas cooler. Due to the limited space reserved for an air conditioning system of a motor vehicle, this must be of very compact construction. The refrigerant conduits are therefore very short and have a small volume. It has now been realized that the difficulties in adjusting, in "heating" mode, the hot gas process were due to the small volume of refrigerant present upstream of the throttling element. The invention therefore proposes to increase the volume of refrigerant between the compressor and the throttling element to at least 50 cm3, preferably at least 100 cm3. This volume of refrigerant present upstream of the throttling element makes it possible to generate a reserve of sufficient pressure so as to be able to largely prevent the appearance of pressure variations. It is now possible to regulate the hot gas process stably. An increase in the volume of coolant upstream of the throttle element to more than 200 cc generally does not provide any additional benefit. The optimal volume should however be determined on a case-by-case basis.

  There are different ways to increase the volume of coolant present upstream of the throttle. On the one hand, it is possible to have a reservoir of refrigerant, in particular in the form of a connection conduit, between the compressor and the throttling element. On the other hand, it is also possible to obtain the volume of refrigerant required by increasing the cross section of the refrigerant conduits used. Thus, the refrigerant conduit can have, between the compressor and the switching valve and / or between the switching valve and the throttling element, a cross section greater than that of the refrigerant conduits located between the others. components. Another possibility of obtaining the necessary volume consists in adapting the length of the coolant conduit without modifying the section thereof. Thus, the refrigerant conduit located between the switching valve and the throttling element can in particular be made so as to be longer than the refrigerant conduit located between the switching valve and the gas cooler .

  The invention will be described below in more detail using an embodiment and the single figure.

  Figure 1 shows for this purpose a compression refrigeration system comprising two refrigerant circuits.

  The compression refrigeration system shown in FIG. 1 has a compressor 1. The compressor 1 can be actuated both by an electric motor and by the motor of the motor vehicle. The refrigerant used is carbon dioxide. The refrigerant system also has a gas cooler 2, a heat exchanger (internal heat exchanger) 3 which is not essential for the basic operation of the refrigerant system, a pressure reducer 4 and an evaporator 5. The compressor 1 , the gas cooler 2, the pressure reducer 4 and the evaporator 5 are connected, in the manner shown, by refrigerant conduits 6, so as to obtain a continuous circulation of the refrigerant to C02 which leaves from compressor 1, passes through the gas cooler 2, the regulator 4 and the evaporator 5 before returning to said compressor 1. The refrigerant system according to FIG. 1 also has an accumulator 11 in the refrigerant circuit.

  In the compressor 1, the refrigerant is compressed, then brought to the gas cooler 2. In the gas cooler 2, heat is transmitted to an external fluid. In the pressure reducer 4, the refrigerant relaxes and thus reduces the pressure. The refrigerant then exists as a wet vapor. The part between the compressor 1 and the regulator 4 passing through the gas cooler 2 forms the high pressure side of the refrigerant system. The refrigerant expanded by the expansion valve 4 enters the evaporator 5 where it absorbs heat from an external fluid, this fluid being in this case air which must be brought into the passenger compartment of the vehicle. automobile. The gaseous refrigerant is finally sucked up by the compressor 1 and the whole process resumes from the start. The part between the expansion valve 4 and the inlet of the compressor 1 passing through the evaporator 5 forms the low pressure side of the refrigerant system. This at the same time constitutes the part comprising a low temperature level compared to the temperature level on the high pressure side. Thanks to the additional heat exchanger 3 which allows a heat exchange between the high pressure side and the suction duct leading to the compressor 1, it is possible to improve the cooling power of the entire system.

  The compression refrigeration system has, for the "heating" mode, a second refrigerant circuit. This starts from the compressor 1, passes through a pressure reducer called here throttle element 7 and a heating heat exchanger 8 before returning to said compressor 1. The switching between the first and the second refrigerant circuit is carried out by means a switching valve 9 installed between the compressor 1 and the gas cooler 2 or the throttle element 7.

  The electrical adjustment of such a refrigerating system is carried out, in a manner known per se, by means of a regulator not shown.

  Due to the compact construction of a compression refrigeration system for a private car, the refrigerant lines 6 are very short. A stable "heating" mode passing through the second refrigerant circuit cannot be achieved with such short refrigerant conduits. The invention therefore provides for an increase in the volume of refrigerant between the compressor 1 and the throttling element 7. To do this, there are several possibilities indicated in FIG. 1. On the one hand, it is possible to provide a coolant reservoir, in particular in the form of a coolant connection conduit, between the compressor 1 and the throttle element 7. In FIG. 1 are shown, for this purpose, a reservoir of refrigerant 10a located between the compressor 1 and the switching valve 9 and a tank of refrigerant 1Ob located between the switching valve 9 and the throttling element 7. It goes without saying that a single tank d refrigerant 10 is sufficient insofar as this makes it possible to obtain the minimum necessary volume of refrigerant. Alternatively or in addition to the coolant reservoir 5, it is possible to increase the volume of coolant by increasing the section of the coolant duct 6a located between the compressor 1 and the switching valve 9 and / or that of the coolant conduit 6b located between the switching valve 9 and the throttle element 7. This is shown schematically in FIG. 1. As a general rule, the cross section of the coolant conduit 10 6a will, for this purpose, be constant over the entire length between the compressor 1 and the switching valve 9, as well as over the section of the assembly of the coolant conduit 6b between the switching valve 9 and the throttle element 7. An increase in the volume of coolant upstream of the throttle element 7 can also be obtained by an appropriate arrangement of the throttle element 7 and the refr gas cooler 2. To do this, it is for example possible to arrange the throttle element 7 so that the throttle element 7 is farther from the switching valve 9 than from the gas cooler 2 This results, by the simple elongation of the coolant conduit 6b between the switching valve 9 and the throttle element 7 relative to the coolant conduit 6c between the switching valve 9 and the gas cooler 2, a corresponding increase in the volume of coolant present upstream of the throttle element 7. Likewise, by skillfully combining the above-mentioned construction possibilities to increase the volume of coolant between the compressor 1 and the throttling element 7, it is possible, despite the compact dimensions of a passenger car air conditioning system, to obtain the minimum refrigerant volume required area with a stable hot gas process in "heating" mode.

  In the motor vehicle, air is transported in a known manner by the heat exchanger 5 or by the heating heat exchanger 8 and brought, once cooled or warmed, into the passenger compartment of the motor vehicle.

Claims (6)

  1. Compression refrigerant system of an air conditioning system of a motor vehicle in which, via refrigerant conduits, a continuous circulation of a CO 2 refrigerant starts from a compressor (1), passes through a gas cooler (2), a pressure reducer (4) and an evaporator (5) before returning to said compressor (1), a switching valve (9) being installed between the compressor (1) and the gas cooler (2), which makes it possible to switch with said compressor (1) in a second refrigerant circuit intended for a 1i0 "heating" mode, a throttling element (7) and a heating heat exchanger (8), and the volume of refrigerant present between the compressor (1) and the throttling element (7) being at least 50 cm3.   2. Compression refrigeration system according to claim 1, characterized in that the volume of refrigerant present between the compressor (1) and the throttling element (7) is at least 100 cm3.   3. Compression refrigerant system according to claim 1 or 2, characterized in that the volume of refrigerant present between the compressor (1) and the throttling element (7) is between 100 cm3 and 200 cm3.   4. Compression refrigerant system according to one of the preceding claims, characterized in that there is between the compressor (1) and the arrangement element (7) a reservoir of refrigerant (10), produced in particular in the form of a coolant connection pipe.   5. Compression refrigerant system according to one of the preceding claims, characterized in that the coolant conduit (6a, 6b) between the compressor (1) and the switching valve (9) and / or between the switching valve (9) and the throttling element (7) has a cross section greater than that of the refrigerant conduits included between the other components.   6. Compression refrigerant system according to one of the preceding claims, characterized in that the coolant conduit (6b) between the switching valve (9) and the throttle element (7) is longer as the coolant conduit (6c) between the switch valve (9) and the gas cooler (2).