Patent Publication Number: US-8122736-B2

Title: Condenser for a motor vehicle air conditioning circuit, and circuit comprising same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation of U.S. patent application No. 10/532,513, filed on Apr. 25, 2005, which is now U.S. Pat. No. 7,469,554, which claims priority to and all the advantages of International Patent Application PCT/FR2003/003055, filed on Oct. 31, 2003, which claims priority to and all the advantages of French Patent Application FR 02/13671, filed Oct. 31, 2002. 
    
    
     The invention relates to motor vehicle air-conditioning circuits. 
     Modern motor vehicles are often equipped with a circuit for air-conditioning their cabin. These circuits particularly comprise a condenser, through which an air-conditioning fluid in the gaseous state is cooled in order to condense it. 
     In this field it is also known practice to use air-conditioning fluids, such as CO 2 , on which the circuit can operate without the fluid changing phase. The circuit is then equipped with a heat exchanger able to lower their temperature, without, however, going so far as to condense them. 
     The invention is as applicable to an actual condenser proper as it is to such exchangers. In order not to make the remainder of the text overly unwieldy, only the term condenser will be used. Nonetheless, it is to be understood that this term covers both a heat exchanger intended to allow a fluid to be condensed and a heat exchanger intended simply to allow the fluid of a motor vehicle air conditioning circuit to be cooled. 
     Currently known condensers generally consist of a bundle of tubes, the tubes being connected at each of their ends to header boxes. The tubes are equipped with heat-exchange surfaces such as pins or corrugated inserts. They are cooled by exchanging heat with the atmospheric air and, for this purpose, are placed at the front of the motor vehicle, generally in front of the engine cooling circuit radiator. 
     These known condensers exhibit several disadvantages. They are not able to exchange heat with the water in the engine cooling circuit. Their side-to-side area, and therefore their size, are great. Furthermore, they have a necessity to be placed along the front face of the motor vehicle so that they can be cooled effectively. 
     It is also known practice to produce condensers consisting of a multitude of stacked main-section plates assembled to delimit first flow channels for a refrigerating fluid which alternate with second flow channels for a cooling fluid. A condenser of this type is described in document WO 01/88454. 
     Thanks to these features, a condenser such as this can be cooled by a liquid, particularly by the liquid in the engine cooling circuit. It is therefore more compact than an air-cooled condenser. There is no need to site it along the front face of the vehicle. It can therefore be placed near the evaporator, making it possible to shorten the length of pipework in the air-conditioning circuit. However, a condenser of this type also exhibits disadvantages, particularly the fact that it is unable to perform sufficient exchange of heat. 
     The subject of the invention is a condenser, particularly for a motor vehicle cabin air-conditioning circuit, which overcomes these disadvantages. This condenser needs to allow improved cooling of the air-conditioning circuit air-conditioning fluid by the water in the engine cooling circuit. 
     To this end, the invention proposes a condenser of the type defined hereinabove which comprises at least two passes over the refrigerating fluid. 
     The term “pass” is to be understood to mean a group or sub-group of plates between which the fluid follows one and the same direction in one and the same sense. In plates of one and the same pass, the inlet and outlet orifices are situated, in particular, at two opposite edges of said plates. On moving on from one pass to another, the sense in which the fluid circulates is reversed. It is thus possible to lengthen the path of the fluid through the exchanger. By virtue of these features, the condenser according to the invention exhibits improved performance. 
     The condenser is made up of a stack of main-section plates. One end plate is arranged at each of the ends of the stack of main-section plates. 
     The plates comprise communication passages to allow the refrigerating fluid and the cooling fluid to pass from one flow channel to the other, annular ducts are provided alternately facing the communication passages so as to prevent fluids from mixing. 
     As a preference, the main-section plates are equipped with two communication passages intended for the passage of the air-conditioning fluid and with two communication passages intended for the passage of the cooling fluid. Thus, each main-section plate has, in total, four communication passages. 
     In one particular embodiment, the plates are equipped with turned-up peripheral edges which are joined together in a sealed manner so as to delimit the first flow channels and the second flow channels. 
     In another particular embodiment, the condenser comprises at least two passes over the cooling fluid. 
     Advantageously, the condenser comprises at least one inlet and one outlet for refrigerating fluid and at least one pass over the refrigerating fluid communicating with said inlet, known as the inlet pass, and another pass communicating with said outlet, known as the outlet pass, the cross section of the passes diminishing from the inlet pass towards the outlet pass. 
     In exchangers of a known type, the passes are produced either by separating partitions arranged in the header boxes in the case of tube-type exchangers, or by spacer pieces arranged between the plates of stacked-plate heat exchangers. By contrast, in the condenser of the invention, circulation passes for the fluids can be achieved without adding additional components. To achieve this, all that is required is the omission of certain communication passages made in the main-section plates. For this, one refrigerating fluid communication passage or, as appropriate, one cooling fluid communication passage, is omitted in some of the main-section plates so as to determine passes for the circulation of the refrigerating fluid or, as appropriate, for the circulation of the cooling fluid. 
     As already stated, in one embodiment of the invention, the cross section of the passes diminishes from the pass communicating with the inlet of the condenser, known as the inlet pass, towards the pass communicating with the outlet of said condenser, known as the outlet pass. 
     The condenser according to the invention may comprise at least three passes, the number of channels allocated to the inlet pass to the number of channels allocated to the outlet pass lying, for example, between 2 and 5, the cross section of the channels being designed to be constant from one channel to the other. 
     Advantageously, the plates of the condenser are arranged in a first series for cooling the refrigerating fluid until it condenses, and a second series for cooling the refrigerating fluid below the temperature at which it condenses (to supercool it). 
     Advantageously too, the condenser of the invention comprises a bottle built in between the first and second series of plates. 
     In order to improve the exchange of heat between the fluids, elements which disrupt the flow, known as turbulence generators, may be provided. In one alternative form, the turbulence generators are arranged between the plates. In another alternative form, the plates themselves have reliefs which constitute turbulence generators. 
     As a preference, the hydraulic diameter of the circulation channels is between 0.1 mm and 3 mm. It may in particular be from 0.1 to 0.5 mm in the case of fluids intended not to change phase, except under exceptional circumstances, and from 0.5 to 3 mm in the case of fluids which are intended to be condensed. It will, for example, range from 1 to 2.6 mm for the cooling fluid, which may be water, particularly that of the cooling circuit. 
     Finally, the annular ducts advantageously consist of bowls formed in the plates. Manifolds are thus defined without the need to provide any additional components. 
     As a preference, the cooling fluid consists of the water from the motor vehicle engine cooling circuit. 
     Furthermore, the invention relates to an air-conditioning circuit, particularly for the cabin of a motor vehicle, comprising an evaporator, a compressor, a condenser, an expansion valve in which a refrigerating fluid circulates, in which the condenser is in accordance with the present invention. 
    
    
     
       Other features and advantages of the invention will become further apparent from reading the description which follows of some embodiments which are given by way of illustration with reference to the attached figures. In these figures: 
         FIG. 1  is a view in section of a condenser according to the invention; 
         FIG. 2  is a view in section of a condenser according to the invention, comprising two passes with the refrigerating fluid; 
         FIG. 3  is a schematic perspective view of a condenser according to the invention, comprising three passes with the refrigerating fluid and one pass with the cooling liquid; 
         FIG. 4  is a schematic perspective view of a condenser according to the invention comprising two passes with the refrigerating fluid and two passes with the cooling liquid; 
         FIG. 5  is an exploded perspective view of an exchanger with two passes with the refrigerating fluid and two passes with the cooling fluid and which illustrates the circulation of these two fluids; 
         FIG. 6  is an external perspective view of the condenser according to the invention, comprising a built-in bottle; 
         FIG. 7  is a view from the left of the condenser depicted in  FIG. 6 ; 
         FIG. 8  is a view in cross section of the condenser depicted in  FIGS. 6 and 7 ; 
         FIG. 9  is a view in section on a plane passing through the longitudinal axis of the bottle of the condenser of  FIGS. 6 to 8 ; 
         FIG. 10  depicts a first embodiment of a turbulence generator inserted between the plates; 
         FIG. 11  depicts another embodiment of a turbulence generator inserted between the plates; 
         FIG. 12  depicts straight corrugated turbulence generators formed from reliefs formed in the plates; 
         FIG. 13  depicts turbulence generators in the form of V-shaped baffles formed from reliefs formed in the plates; and 
         FIG. 14  depicts a three-pass condenser according to the invention. 
     
    
    
       FIG. 1  depicts a cross section of a condenser according to the present invention. It comprises a multiplicity of main-section plates  2  stacked one upon the other and each equipped with a peripheral rim  3 . The peripheral edges are assembled in a sealed manner so as to delimit between the plates  2  first flow channels for a refrigerating fluid F 1  which alternate with second flow channels for a cooling fluid F 2 . The stack of main-section plates has an end plate  6  at each of its ends. 
     In order to enhance the pressure withstand of the condenser, the main-section plates  2  are sandwiched between a lower reinforcing plate  8  and an upper reinforcing plate  10 . The refrigerating or air-conditioning fluid F 1  enters the condenser via an inlet pipe (not depicted in  FIG. 5 ) and emerges therefrom via an outlet pipe  14 . The cooling fluid F 2  enters the condenser via an inlet pipe  20  and emerges therefrom via an outlet pipe (not depicted). Refrigerating fluid F 1  enters in the gaseous state. It circulates through the first channels, exchanging heat with the cooling fluid F 2 , which causes it to condense. The fluid F 1  therefore leaves the condenser in the liquid state. 
     The refrigerating or air-conditioning fluid is, for example, the fluid R134a or R744 (CO 2 ), while the cooling fluid F 2  consists of the water from the engine cooling circuit. It may also involve an independent water loop. 
     The condenser depicted in  FIG. 2  comprises two circulation passes for the air-conditioning or refrigerating fluid. This fluid enters the pipe  12  as depicted schematically by the arrow F 1 , it enters an annular duct  24  acting as an inlet header box and, from there, enters the first circulation channels provided between the plates  2 , as depicted schematically by the arrow  26 . Having covered the entire heat-exchange surface, the air-conditioning fluid reaches an annular duct  28  and, from there, enters the first circulation channels provided between the plates  2  situated below the dividing partition  30 , as depicted schematically by the arrow  32 . It passes through the exchanger a second time, from right to left, in a second pass, to reach the lower part  34  of the annular duct which acts as an outlet header box, as depicted schematically by the arrow  36 , and leaves the condenser via the outlet pipe  14 , as depicted schematically by the arrow  38 . 
     As can be seen in  FIG. 3  which depicts a perspective view of a condenser according to the invention, the refrigerating fluid F 1  and the cooling fluid F 2  do not necessarily travel through the condenser with the same number of passes. In the example depicted, the condenser has three passes depicted schematically by the arrows  40 ,  42  and  44 , for the refrigerating fluid, and just one pass, depicted schematically by the arrow  48 , for the cooling fluid F 2 . The fluid F 1  moves on from the first pass to the second having crossed the passage orifice  50 , then from the second pass  42  to the third pass  44  once it has crossed the communication passage  52 . It reemerges from the exchanger via the outlet pipe  14 . The cooling fluid F 2  enters via the inlet pipe  20 , and passes through the exchanger in a single pass  48  and reemerges from the condenser via the outlet pipe  22 . 
     In  FIG. 4 , the condenser has two circulation passes for the refrigerating fluid and two passes also for the cooling fluid. The refrigerating fluid F 1  enters the condenser via the inlet pipe  12 , runs along the plates in its first pass  54 , crosses the communication passage  56  and travels through the second pass  58  before reemerging via the outlet pipe  14 . The cooling fluid F 2  enters the condenser via the inlet pipe  20 , runs through the first pass, as depicted schematically by the arrow  60 , crosses the communication passage  62  before covering the second pass  64 . It then reemerges from the exchanger via the outlet pipe  24 . 
       FIG. 5  schematically depicts an exploded perspective view which illustrates the circulation of the fluids in a condenser according to the invention comprising two circulation passes for the air-conditioning fluid F 1  and two passes for the cooling fluid F 2 . The fluid F 1  enters the upper part of the exchanger via the inlet pipe  12  into the volume delimited by the end plate  6  and the adjacent plate  2 . Some of the fluid flows through this space from left to right according to  FIG. 5 , as depicted schematically by the arrow  66 . The rest of the fluid enters an annular duct  68  arranged between the plates  2   a  and  2   b , as depicted schematically by the arrow  70 . On leaving the annular duct, it enters the space that lies between the plates  2   b  and  2   c . The proportion of the fluid which passed through the space lying between the end plate  6  and the first main-section plate  2   a  reemerges from this space via a tubular duct  72  arranged between the plates  2   a  and  2   b.    
     The flat space between the plates  2   b  and  2   c  has just one communication passage  74  allowing the fluid F 2  out. This fluid passes through the annular passage  76  to arrive between the plates  2   d  and  2   e  having undergone a change in the sense in which it circulates. What actually happens is that it crosses this space from right to left, whereas previously it was circulating from left to right. 
     Likewise, the cooling fluid F 2  which enters the condenser via an inlet pipe (not depicted) situated at the lower part of the exchanger, circulates from left to right in the flat spaces lying between two successive plates. It passes from a space lying between two plates to the next space, these spaces alternating with spaces provided for the fluid F 1  via annular ducts similar to the ducts  70  or  76  mentioned earlier. Having arrived in the space between the plates  2   e  and  2   f , as depicted schematically by the arrow  80 , the fluid F 2  enters the annular duct  82 , as depicted schematically by the arrow  84 , and changes the sense in which it circulates. In the upper part of the condenser, it circulates from right to left, whereas it was circulating from left to right in the lower part. This then produces a second circulating pass for the fluid F 2  also. 
     It is noted thus that the condenser of the invention has three types of plate which differ as far as the number of communication passages are concerned. The end plates, such as the plate  6 , have just two communication passages, the first for letting one of the fluids in, the second for letting the other fluid out. The main-section plates, such as the plate  2   f , have four communication passages. Two of these passages are devoted to the first fluid F 1 , while the other two passages are devoted to the fluid F 2 . The plates situated just before the end plate  6 , such as the plate  2   a , have three communication passages instead of four in the case of the main-section plate. The plate  2   d , which allows the circulation passes of the two fluids to be achieved, has just two communication passages. This is because by omitting two of the four communication passages, dividing partitions are produced which allow the sense in which the fluid circulates to be changed. The plates  2   c  and  2   e , adjacent to the plate  2   d , have three communication passages, instead of four in the case of the main-section plates. There are thus three types of plate. The two end plates and the plate  2   d  have just two passages. The plates adjacent to the end plates and to the plate  2   d  have three passages, while the main-section plates of the condenser have four. 
     In  FIG. 14  it can be seen that the condenser according to the invention may have at least three passes “a”, “b” and “c”. The number of channels allocated to the inlet pass “a”, that is to say the pass communicating with the inlet via which the refrigerating fluid enters the condenser, to the number of channels allocated to the outlet pass “c”, that is to say the pass communicating with the outlet of the refrigerating fluid from the condenser, is between 2 and 5, the cross section of the channels being constant from one pass to the other. 
     In the case of a three-pass condenser one might have, by way of illustrative example, 15 to 20 channels in the inlet pass “a”, 8 to 10 channels in the intermediate pass “b”, and 4 to 7 channels in the outlet pass “c”. In the example of  FIG. 14 , the numbers of the channels are, respectively, N 1 =17 for pass “a”, N 2 =10 for pass “b”, and N 3 =6 for pass “c”, hence a ratio N 1 /N 3 =17/6=2.83. 
       FIGS. 6 and 7  respectively depict a sectioned view and a view from the left of a second embodiment of a condenser according to the present invention. Its distinguishing feature is that its plates are arranged in a first series  94  and a second series  96  which series are separated from one another by a frame  98  in which a bottle  100  is housed. The first series of plates  94  is relatively larger than the second series  96 . It is preferably sited at the upper part of the exchanger, while the second series is sited at the lower part. 
     The plates of the first series constitute a section for cooling the refrigerating fluid, and the plates of the second series constitute a section for supercooling this fluid. The bottle  100 , also known as the intermediate reservoir, allows the refrigerating fluid to be filtered and water removed. It also allows variations in its volume to be compensated for and allows the liquid and gaseous phases to be separated. Its insertion between an upstream part and a downstream part  96  of the condenser makes it possible for only fluid in the liquid state to be circulated through the supercooling section. The refrigerating fluid is thus cooled below its liquid-gas equilibrium temperature, thus improving the performance of the condenser and making it relatively independent of the amount of fluid contained within the air-conditioning circuit. 
     The refrigerating fluid and the cooling fluid may be circulated in one or more passes through the cooling section  94 , and through the supercooling section  16 . The refrigerating fluid F 1  enters the cooling section  94  via the inlet pipe  12  situated in the upper part of the condenser. It passes through the cooling section, in one or more passes, then passes into the bottle  100 , in which it is filtered and dehydrated, then it returns to the supercooling section  96  before leaving the exchanger via the outlet pipe  14 . 
     The cooling fluid F 2  flows countercurrent with respect to the refrigerating fluid. It enters the lower part of the condenser, into the supercooling section  96 , via the inlet pipe  20  (see  FIG. 7 ). It passes through the supercooling section  96  then enters the cooling section  94  directly before reemerging from the condenser via the outlet pipe  22 . As can be seen more particularly in  FIG. 7 , the frame  98  has two sole plates  102  and a central part  103  in which there are formed three cylindrical bores  104  which constitute the bottle. One of these bores, the right-hand one in  FIG. 7 , houses a filter and desiccating salts. The plates in the first series  94  and in the second series  96  rest against the sole plates  102  of the frame  98 . It will also be noted that, in this example, their concave faces face in opposite directions. 
       FIGS. 8 and 9  respectively depict a view of the condenser in longitudinal section passing through the longitudinal axis of the part of the bottle  100  that contains the filter and the desiccating salts, and a cross section through this same exchanger. The corresponding cylindrical bore  104  is extended by a cylindrical part  106  projecting from the condenser. This cylindrical part houses a stopper  108  with a hexagonal head  110  which plugs the bottle. The stopper  108  is fitted with an O-ring seal  112 . An elongate cylindrical cartridge  114  is housed inside the cylindrical bore  104 . It contains the desiccant  116  that dehydrates and filters the refrigerating fluid F 1 . 
       FIG. 9  provides an appreciation of the special shape of the plates  2  of the condenser. Each plate has a flat-bottomed half-bowl  122  through which a passage orifice  124  passes. When the plates of the exchanger are stacked up, the flat bottoms of the bowls come into contact with one another. During the exchanger brazing operation, they are assembled together in a sealed manner. This then advantageously produces annular ducts that allow the refrigerating fluid F 1  and the cooling fluid F 2  to circulate from one passage channel to another without having to use additional components situated between the plates. Of course, as an alternative form of embodiment, one plate in every two could be flat, the bowl formed in the adjacent plate having a depth corresponding to the full separation between two successive plates. 
     Furthermore, according to the invention, turbulence generators (also known as turbulators) intended to improve the exchange of heat may be arranged between the plates.  FIG. 10  depicts a first alternative form of embodiment of a turbulence generator  132 . It consists of pressed sheet metal shaped to exhibit straight corrugations  134  arranged, for example, in the lengthwise direction of the plates. In this case, the plates  2  have a generally flat bottom. 
       FIG. 11  depicts another embodiment of a turbulence generator  136 . It comprises pressings  138  exhibiting the overall shape of a square tooth wave form. This square tooth wave form is arranged as two series of teeth offset from one another. Such a turbulence generator  136  is located between plates  2  which also have a generally flat bottom. 
     The turbulence generators  132  and  136  depicted in  FIGS. 10 and 11  entail the manufacture of an additional component and its interposition between the plates. It is possible to omit this additional component by making the turbulence generators in the form of reliefs formed on the plates themselves and obtained by a pressing operation. 
     Thus, in  FIG. 12 , the condenser comprises first plates  140  each having a bottom  142  with corrugations  144  defined by generatrices running in a first direction D 1  and second plates  146  arranged in alternation with the first plates  140  and each exhibiting a bottom  148  having corrugations  150  defined by generatrices running in a second direction D 2  which is more or less at right angles to the first direction D 1 . The respective corrugations in the plate allow the channels to be given a special three-dimensional structure which encourages turbulent flow of the fluid F 1  and of the fluid F 2  and, as a result, good heat exchange between the two. This also makes it possible to dispense with turbulence generators inserted between the plates. 
       FIG. 13  depicts an alternative form of embodiment of the turbulence generators of  FIG. 12 . The exchanger comprises a first series of plates  154  and a second series of plates  156 , these respectively comprising corrugations  158  and  160  in the form of V-shaped baffles. These corrugations also define a three-dimensional structure for the fluid flow channels and this encourages turbulent flow and good exchange of heat between the two.