WO2007006632A1 - Cooling system, in particular, motor vehicle air conditioning system - Google Patents

Abstract

The invention relates to a cooling system, in particular, a motor vehicle air conditioning system (4), comprising a coolant circuit (2) which can be cross-flown by CO<SUB>2</SUB> which acts as a coolant, said coolant circuit comprising a compressor (6), a capacitor and/or a gas cooler (10), an expansion element (18) comprising a controllable throttle cross-section and a vaporiser (20). According to the invention, the maximum control area of the throttle cross-section is approximately 1 mm<SUP>2</SUP>.

Description

 Refrigeration system, in particular motor vehicle air conditioning

The invention relates to a refrigeration system, in particular a motor vehicle air conditioning system, with a refrigerant circuit through which a refrigerant flows as a refrigerant, which comprises a compressor, a condenser or gas cooler, an expansion valve with a controllable throttle cross section and an evaporator.

State of the art

Refrigeration systems, and in particular motor vehicle air conditioning systems with a refrigerant circuit through which CO2 flows, will become increasingly important in the future, since CO2 can be disposed of without any problem unlike conventional refrigerants, such as fluorinated hydrocarbons. When operating a motor vehicle air conditioning system with CO2, however, in contrast to an operation with conventional refrigerants, at least under certain environmental conditions, a supercritical operation is required. The CO2 is not condensed in the condenser serving as a heat exchanger, but only cooled in a supercritical state, which is why the condenser is also referred to as a gas cooler.

In refrigeration systems, which are operated with a refrigerant which, like CO ₂ , can release heat in the supercritical range due to its thermodynamic properties, unlike refrigerants with heat release in the wet steam range, the pressure of the refrigerant during heat release can be set independently of the ambient temperature. In order to make use of this additional degree of freedom for achieving optimum efficiencies or cooling allow the refrigeration systems to be equipped with an adjustable expansion valve. This expansion valve is used to control the pressure prevailing in the refrigerant circuit high pressure to adjust under the respective operating conditions, such as ambient temperature and temperature in the evaporator, to a value at which the efficiency or the cooling capacity of the refrigeration system is optimal, whereby in a motor vehicle air conditioning Fuel consumption for the operation of the air conditioning can be significantly reduced.

In order to allow a desired high-pressure setting, the throttle section of the expansion valve must be adjusted as a function of the respective operating conditions and depending on the selected operating strategy, that is, either optimizing the refrigerating capacity or optimizing the coefficient of performance (COP) to let. If the selected operating strategy is established, there is a dependency between the high pressure prevailing in the refrigerant circuit and a throttle cross section required for optimum operation of the system. This required throttle cross-section is shown in FIG. 2 of the drawing for various representative operating points for a maximum cooling capacity by black squares and for maximum efficiency by black diamonds, wherein in the former case at least one adjustment or control range from 0.6 to 2 mm ² and in the latter case, at least one adjustment or control range of 0.1 to 1, 7 mm ^{2 is} required if optimum cooling capacity and optimum efficiency should be achieved under all operating conditions occurring. The control task then consists in adjusting the throttle cross-section of the expansion valve pressure-dependent and thereby regulate that he on the points with optimum cooling capacity or optimum efficiency, corresponding to the black squares or black diamonds shown in FIG. 2, for which the curve A shown in FIG. 2 represents a first approximation. However, expansion valves whose throttle cross section can be adjusted over a range of 0 to 2 mm ² and are suitable for a CO _2- operated refrigeration system have the disadvantage that they are structurally relatively complex and require a control corresponding to the control, whereby they are relatively high are expensive.

In order to reduce these costs and simplify the refrigeration system, it has already been considered to use a fixed orifice instead of a variable expansion valve, which has a constant, i.e. from the prevailing in the refrigerant circuit high pressure independent throttle cross-section, as shown in Fig. 2 by the horizontal straight line B. However, the use of a fixed throttle does not make it possible to operate the refrigeration system with optimum refrigeration capacity or optimum efficiency. In addition, the compressor in refrigeration systems must be regulated with a fixed throttle in order to prevent an increase in the high pressure above the permissible operating pressure of the system.

Advantages of the invention

The refrigeration system according to the invention with the features mentioned in claim 1 offers the advantage that can be used by the limitation of the adjustment or control range simply constructed, manufactured in high volumes for brake systems of motor vehicles valves, compared to conventional controllable expansion valves for operated with CO ₂ - A -

Refrigeration systems are significantly cheaper. Although these expansion valves only have a maximum throttle cross-section of about 1 mm ² or an adjustment or control range between 0 and about 1 mm ² , this is sufficient under moderate ambient conditions to ensure optimum efficiency and optimum cooling capacity of the refrigeration system to care. Since moderate ambient conditions predominate during most of the annual operating hours of a motor vehicle air conditioning system, a substantial reduction in the fuel consumption of the air conditioning system is made possible and an overall cost-effective mode of operation is ensured. In contrast, higher ambient temperatures, which would require larger throttle cross sections for optimum operation of the air conditioning system, are only of secondary importance with respect to their duration and thus with regard to fuel consumption and can therefore be neglected. In addition to the advantages mentioned above, the valves produced for brake systems of motor vehicles, such as a valve available under the name MV1.80 from Robert Bosch GmbH, also have a lower drive power, a lower weight and a smaller installation space than conventional controllable expansion valves for refrigeration systems and, moreover, due to their small throttle cross-section, allow cycling without the production of audible sounds.

According to a preferred embodiment of the invention, a fixed throttle having a constant throttle cross section may be connected in parallel with the controllable expansion valve, wherein the total throttle cross section of the fixed throttle and the controllable expansion valve is at most about 1 mm ² and wherein the throttle cross section Section of the fixed throttle (Orifice) is suitably smaller than the throttle cross-section of the expansion valve.

The fixed throttle may be a separate component, but is suitably designed in the form of a bypass bore in a valve block of the variable expansion valve.

Instead of a fixed throttle, a parallel to the expansion valve switched overflow valve may be provided which also serves as a pressure limiter and opens when a first predetermined high pressure in the refrigerant circuit is exceeded, for example at 120 bar, and at a second predetermined high pressure, for example at 130 bar , is fully opened with an opening cross section exceeding the throttle cross-section of the expansion valve. The opening pressure of the overflow valve expediently corresponds to the high pressure, in which, with a maximum throttle cross-section of the expansion valve, an optimum efficiency or an optimal cooling capacity is achieved.

Of course, it is also possible to connect both an overflow valve and a fixed throttle in parallel to the expansion valve, whereby the advantages of the overflow valve can be combined with those of the fixed throttle.

The expansion valve may have any suitable design, for example as a cone or ball valve with a conical or ball seat for a corresponding valve member, needle valve or as a sliding sleeve valve and be operated as needed as a proportional valve or as a clocked valve, wherein it each of these two modes is electrically controlled. To increase the performance, the refrigeration system may expediently comprise an internal heat exchanger, in which the compressed refrigerant flowing out of the condenser or gas cooler to the expansion valve is cooled by heat exchange with the refrigerant flowing from the evaporator to the compressor.

In refrigeration systems and in particular motor vehicle air conditioning systems of the aforementioned type, which in addition to the evaporator still comprise a second evaporator, the controllable expansion valve with a maximum throttle cross section of less than 1 mm ^{2 can} also be used to advantage for controlling a refrigerant mass flow of the second evaporator.

drawing

The invention will be explained in more detail in some embodiments with reference to the accompanying drawings. Show it:

Figure 1 is a schematic representation of a flowed through by CO2 refrigerant circuit of a motor vehicle air conditioning system with an expansion element and an internal heat exchanger;

2 shows a representation of the throttle cross sections of an expansion element of a refrigeration system for maximum efficiency (black squares) or for maximum refrigeration conduction (black diamonds) as a function of high pressure, as well as with approximation curves for the control of a known controllable expansion valve with an adjustment range of the throttle cross section from 0 to 2 mm ² , a known fixed throttle (orifice) with a throttle cross section of 0.32 mm ² and an expansion valve according to the invention with a control range from 0 to 1 mm ² ;

Figure 3 is a schematic representation of a first embodiment of the expansion device of Fig. 1;

Figure 4 is a schematic representation of a second embodiment of the expansion device of Fig. 1;

Figure 5 is a partially sectioned view of a valve block of the embodiment of Figure 4;

Figure 6 is a schematic representation of a third embodiment of the expansion device of Fig. 1;

FIG. 7 shows a schematic representation of a fourth embodiment of the expansion element from FIG. 1.

Description of the embodiments

The illustrated in Figure 1 refrigerant circuit 2 operated with CO2 as a refrigerant motor vehicle air conditioning system 4 consists in a known manner substantially from a compressor 6, an oil separator 8, a gas cooler 10 and a first part 12 of an inner heat exchanger 14, in a high pressure section 16 of the refrigerant circuit 2 are arranged behind the compressor 6 and are flowed through by the compressed refrigerant, an expansion sion member 18 for relaxing and cooling the compressed refrigerant, and designed as a heat exchanger evaporator 20 and a collector 22, which together with a second part 24 of the inner heat exchanger 12 in a low pressure section 26 of the refrigerant circuit 2 between the expansion member 18 and the suction side of the compressor. 6 are arranged.

In the compressor 6 driven by the internal combustion engine or an electric motor (not shown) of the motor vehicle, the gaseous refrigerant is compressed to increase its internal energy. Subsequently, the refrigerant is passed through the oil separator 8 to deposit oil residues contained in the refrigerant and to return to the lubrication of the compressor 6 through a return line 28 to this. Thereafter, the compressed refrigerant is cooled in the gas cooler 10 serving as a heat exchanger with supplied ambient air 30, wherein the refrigerant releases a part of its internal heat energy and assumes a supercritical gaseous state. From the gas cooler 10, the compressed refrigerant flows countercurrently to the refrigerant flowing through the low-pressure portion 26 through the inner heat exchanger 12, and its temperature is further lowered. In the expansion element 18, the refrigerant is subsequently expanded and cooled down a further time before it subsequently flows through the evaporator 20, which is designed as a heat exchanger, and evaporates therein at least partially. By the evaporator 20, a medium to be cooled is blown, for example, for cooling purposes in the passenger compartment of the motor vehicle supplied air 32nd The expansion element 18 comprises an electrically controllable expansion valve 34, as shown in FIGS. 1 and 3, whose throttle cross-section is changed as a function of the high pressure prevailing in the high-pressure section 16 and measured by a sensor (not shown). The expansion valve 34 has a control range of 0 to 1 mm ² and is formed for example by a valve produced in large numbers for brake systems of motor vehicles with anti-lock braking system (ABS) or electronic stability program (ESP) valve, the company Robert Bosch GmbH the designation MV1.80 is available. This valve has at moderate environmental conditions, good control characteristics, and makes it possible to operate the air conditioner ciency below an ambient temperature of about 25 ⁰ C in response to the high pressure at an optimum cooling capacity or optimum WIR, as indicated by the approximate curve C for the control of of the expansion valve 34 shown in Fig. 2. In contrast to the approximation curve A for the control of known controllable expansion valves, the curve C runs at inlet pressures of more than 118 bar at the entrance of the expansion device 18 horizontally, ie parallel to the straight line B, so that exceeding the allowable operating pressure of the air conditioner 4 must be prevented.

FIGS. 4 to 7 show further possible embodiments of the expansion element 18, wherein the expansion element 18 shown in FIGS. 4 and 5 comprises, in addition to the controllable expansion valve 34, a fixed throttle (orifice) 36 connected in parallel thereto. As shown in FIG. 5, the fixed throttle 36 is an oblique bypass bore 38 between a radial valve inlet bore 40 and an axial valve outlet bore 42 in a valve block 44 formed of the expansion member 18, wherein the cross section of the bypass bore 38, for example, 0.2 mm ² , while the throttle cross-section of the variable expansion valve 34, depending on the high pressure between 0 and 0.5 mm ² or between 0 and 0.8 mm ^{2 is} adjustable and because of the small cross-sections is particularly well suited for a clock operation. The controllable expansion valve 34 is an electrically controlled valve, which may be formed as a ball, conical, needle or sliding sleeve valve depending on the selected mode, ie clock or proportional operation, and the existing installation conditions.

The expansion element 18 shown in FIG. 6 contains, in addition to the controllable expansion valve 34, an overflow valve 46 which opens, for example, at a pressure of 120 bar and is fully opened at 130 bar, so that in this way the permissible operating pressure of the air conditioning system is exceeded 4 in the horizontal part of the curve C can be prevented. When using the expansion valve 34 shown in Figures 3 and 4, this could be achieved by de-excitation of the compressor 6. The expansion element 18 shown in FIG. 7 contains, in addition to the expansion valve 34, a fixed throttle 36 and an overflow valve 46, which are both connected in parallel to the expansion valve 34.

Referring again to Figure 1, the collector 22 downstream of the evaporator 20 serves to collect and store the liquid, that is to say non-vaporized, refrigerant after it has passed through the evaporator 20, in order, if necessary, for example, to reduce the temperature Speed of the compressor 6, back from the collector 22 in the evaporator 20 due. The vaporized in the evaporator 20 gaseous refrigerant is from the compressor 6, wherein it flows through the low pressure section 26 and the second part 24 of the inner heat exchanger 14 and heats up with simultaneous cooling of the refrigerant in the high pressure section 16.

Claims

claims 1. refrigeration system, in particular motor vehicle air-conditioning system, with a refrigerant circuit through which flows as a refrigerant comprising a compressor, a condenser or gas cooler, an expansion valve with a controllable throttle cross section and an evaporator, characterized in that a control range of the throttle cross section is at most about 1 mm ² . 2. Refrigeration system according to claim 1, characterized in that the control range of the throttle cross-section is between 0 and about 1 mm ² . 3. Refrigeration system according to claim 1 or 2, characterized by a parallel to the expansion valve (34) connected fixed throttle (36) with a constant throttle area. 4. refrigeration system according to claim 3, characterized in that the fixed throttle (36) in a valve block (44) of the expansion valve (34) is integrated. 5. Refrigeration system according to claim 4, characterized in that the fixed throttle (36) as a bypass bore (38) in the valve block (44) of the expansion valve (34) is formed. 6. Refrigeration system according to one of the preceding claims, characterized by a parallel to the expansion valve (34) switched overflow valve (46). 7. Refrigeration system according to one of claims 1 to 6, characterized in that the expansion valve has a conical or ball seat for a valve member. 8. Refrigeration system according to one of claims 1 to 6, characterized in that the expansion valve is a needle valve. 9. refrigeration system according to one of claims 1 to 6, characterized in that the expansion valve is a sliding sleeve valve. 10. Refrigeration system according to one of the preceding claims, characterized by an internal heat exchanger (14). 11. refrigeration system, in particular motor vehicle air-conditioning system, with a refrigerant circuit through which refrigerant flows as a refrigerant, comprising a first and a second evaporator, a compressor, a gas cooler and an expansion element, characterized by a controllable expansion valve with a maximum throttle cross-section of less than 1 mm ² for controlling a refrigerant flow of the second evaporator.