Abstract:
A motor vehicle heat exchanger has a bundle ( 10 ) formed solely from flexible tubes ( 12 ) made of plastics, as well as two end blocks ( 22, 24 ) joining these tubes. The heat exchanger further has at least one spacer ( 50 ) arranged at a chosen location between the end blocks ( 22, 24 ) and including apertures for the tubes to pass in order to provide support for the tubes ( 12 ) with a chosen spacing or pitch.

Description:
FIELD OF THE INVENTION 
     The invention relates to heat exchangers, for a motor vehicle in particular. 
     It relates more particularly to a heat exchanger of the type comprising a bundle formed solely from flexible tubes made of plastics, as well as two end blocks joining these tubes. 
     BACKGROUND OF THE INVENTION 
     Heat exchangers of this type are already known; they are also called “finless exchangers” given that the bundle is formed solely from flexible tubes, also called capillary tubes. These may be of small diameter, typically of the order of 1 or 2 millimeters, and are usually produced by extrusion of a thermoplastic material, for example a polyamide. 
     Such heat exchangers can be used in the automobile industry, for example, to constitute a radiator for cooling the engine, a radiator for heating the passenger compartment, a cooler for the supercharger air or even a condenser of an air-conditioning circuit. 
     The advantage of these flexible tubes is that they make it possible to produce heat exchangers the tube bundle of which may exhibit particular shapes, including curved or arched shapes, so as to be able to be housed in an appropriate site in the motor vehicle. Moreover, they have the advantage of being lighter than the conventional heat exchangers with metal tubes, and they are moreover more resistant to impacts, because of their capability for deformation. 
     However, the production of such flexible-tube heat exchangers poses certain problems, given that it is not always possible to apply the usual techniques used in the manufacture of traditional heat exchangers with metal fins and tubes. 
     In the known heat exchangers with flexible tubes, the end blocks each comprise a manifold in the form of a plate provided with apertures individually accommodating the tubes of the bundle. This solution requires intricate assembly operations having regard to the fineness of the tubes and the large numbers of them. 
     Another problem relating to these known heat exchangers is due to the flexibility of the tubes. In fact, they have a tendency to move closer to one another thus forming an obstacle to the passage of the airflow that should sweep over the bundle. It is therefore necessary to provide means for holding the tubes spaced apart. The design of such spacer means poses numerous problems having regard to the fineness of the tubes and to the high number of them. 
     Another problem posed by these known heat exchangers lies in the supporting of the tubes which not only are flexible, but may also be of non-linear shapes. 
     The object of the invention is at least to partially mitigate the abovementioned drawbacks. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a heat exchanger, for a motor vehicle in particular, comprising a bundle formed solely from flexible tubes made of plastics, as well as two end blocks joining these tubes, characterized in that it comprises at least one spacer arranged at a chosen location between the end blocks and including apertures for the tubes to pass in order to provide support for the tubes with a chosen spacing or pitch. 
     It results therefrom that the tubes of the bundle are held spaced apart from one another, in such a way that the bundle can be correctly swept by a flow of air. 
     In one embodiment of the invention, each spacer is produced in the form of a generally flat plate provided with a plurality of individual holes spaced apart from one another and each suitable for being traversed by one tube of the tube bundle. 
     In another embodiment, each spacer is produced in the form of a generally flat plate provided with a plurality of oblong apertures spaced apart from one another and each suitable for being traversed by an aligned series of tubes of the bundle. 
     In this latter embodiment, the exchanger advantageously comprises at least one first spacer having first oblong apertures each suitable for being traversed by a row of tubes and at least one second spacer having second oblong apertures each suitable for being traversed by a column of tubes, the first oblong apertures and the second oblong apertures extending in orthogonal directions. 
     This second embodiment allows easier assembly than the preceding one, given that the tubes are introduced in aligned series and not individually. 
     According to another characteristic of the invention, each spacer is fixed between two crosspieces (also called cheeks) framing the tube bundle. These crosspieces contribute to supporting the bundle and to the rigidity of the assembly. 
     Advantageously, each spacer and the crosspieces are formed from a plastics material, particularly a thermoplastic material such as a polyamide. 
     Each spacer can be fixed to the crosspieces either by mechanical means, in particular by clipping, or else by bonding or by welding. 
     According to yet another characteristic of the invention, each spacer is placed in an orientation chosen in order to channel a flow of air sweeping the bundle of tubes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the description which follows, given solely by way of example, reference will be made to the attached drawings, in which: 
     FIG. 1 is a perspective view of a heat exchanger with flexible tubes according to a first embodiment of the invention; 
     FIG. 2 is a partial plan view taken in the direction of the arrow II of FIG. 1; 
     FIG. 3 is a plan view, in the direction of the arrow III of FIG. 1, with partial cutaway; 
     FIG. 4 is a plan view of a spacer in one embodiment of the invention; 
     FIGS. 5 and 6 are perspective views of two spacers in another embodiment of the invention; 
     FIG. 7 is a view similar to FIG. 3 in a second embodiment of the invention; and 
     FIG. 8 is a perspective view of a heat exchanger according to this second embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the various figures, like reference numerals refer to like parts. 
     Referring first of all to FIG. 1, a heat exchanger is represented which, in this example, is suitable for constituting a cooler of the supercharging air for a motor-vehicle engine. 
     This exchanger comprises a bundle  10  formed solely from flexible tubes  12 , also called capillary tubes, the diameter of which is generally of the order of a millimeter. These tubes are produced by extrusion of a thermoplastic material, in particular a polyamide. As can be seen in FIG. 1, these tubes are not linear, but in contrast have a particular arched shape which, in this example, makes it possible to incorporate the heat exchanger into a housing defined behind the front bumper (not represented) of the vehicle. 
     The tubes  12  have respective extremities  14  and  16  configured in such a way that the extremities  14  are grouped together against one another so as to form a packet inserted into a pipe  18 . In a corresponding way, the extremities  16  of the tubes are grouped together against one another so as to form a packet which is inserted into another pipe  20 . 
     These pipes  18  and  20  form part respectively of two end blocks  22  and  24 . The structure of the end block  22  will now be described more particularly, with reference to FIGS. 2 and 3. The pipe  18 , in this example, takes up a generally circular cylindrical shape delimiting an internal passage  26  of generally circular cylindrical shape into which the extremities  14  of the tubes are pushed. In the coursing part of the bundle, lying between the extremities  14  and  16 , the tubes are spaced apart from one another by means which will be described later. 
     In contrast, in the pipes  18  and  20 , the extremities of the tubes are grouped together to form a packet which is inserted into the pipe. 
     The pipe  18  includes a conical entry  28  (FIG. 3) to facilitate the insertion of the extremities of the tubes, which have previously been grouped together into a packet. At its other end, the pipe includes an external retaining bead  30  (FIGS. 2 and 3) which may serve for connecting to a flexible hose or duct (not represented) held by an appropriate collar. 
     Each of the pipes  18  and  20  is produced by molding from plastics, advantageously a thermoplastic material such as a polyamide. In this example, each of these pipes is molded integrally with a support plate  32 ,  34  respectively, which extends in a direction generally perpendicular to the respective axes XX and YY of the pipes  18  and  20 . In order to hold the tubes and preserve leaktightness between the tubes and the inside of the corresponding pipe, an adhesive  35  is applied, some of which can be perceived in FIG. 3, in the annular area lying between the conical entry  28  and the tubes of the bundle. 
     This adhesive, which is of the silicone type, for example, can be applied in different ways. One of the solutions which can be envisaged is to inject it, after insertion of the extremities of the tubes into the corresponding pipe. Another solution consists in depositing the adhesive in advance around the tubes, before engaging the extremities of the tubes into the corresponding pipes. 
     As can be seen in FIG. 1, the end blocks  22  and  24  are fixed between two crosspieces  36  and  38 , also called “cheeks” or “flanks”. These crosspieces frame the bundle  10 . They are produced in the form of two generally flat plates extending parallel to each other. In this example, these plates have a particular shape which makes it possible to shape the bundle  10  to the desired form. These crosspieces  36  and  38  are advantageously produced by molding from a plastics material, in particular a polyamide. 
     The crosspieces  36  and  38  are of matched shapes. Thus, the crosspiece  36  includes a central web  14  of arched shape connected to two end parts  42  and  44  which are substantially parallel to each other and which serve as a support respectively for the end blocks  22  and  24 , in such a way as to give these blocks a chosen orientation. In this example, the respective axes XX and YY of the pipes  18  and  20  are substantially parallel. 
     As can be seen in FIG. 1, the support plate  32  of the end block  22  includes two opposite lugs  46  taking the form of hooks turned towards one another, which allow mechanical fixing of the support plate  32  onto the end  42  of the crosspiece  36 . This support plate is fixed by similar means to the crosspiece  38 . The same goes for the support plate  34  of the end block  24 . 
     Furthermore, the heat exchanger comprises a plurality of spacers  50  each arranged at chosen locations between the end blocks  22  and  24 . Each spacer  50  is produced in the form of a plate which extends perpendicularly between the crosspieces  36  and  38  and which is fixed to them by appropriate means. Furthermore, these spacers are each traversed by the tubes  12  of the bundle  10 . 
     In the embodiment of FIG. 4, the spacer  50  includes individual apertures  52  for the tubes of the bundle to pass through. These apertures, of circular shape, correspond in number to that of the tubes of the bundle (several hundreds in the example represented). These apertures  52  are aligned in columns and in rows and they define, by their envelope, a generally elliptical or oval overall shape. In this embodiment, it is therefore necessary to thread each of the tubes  12  into the respective holes  52  of each of the spacers  50 , the latter then being placed at appropriate locations between the crosspieces  36  and  38 . 
     In this example, each of the spacers  50  includes, on one side, a pair of lugs  54  in the form of opposed teeth and, on the other side, another pair of lugs  56 , also in the form of opposed teeth. These pairs of lugs allow mechanical fixing of the spacers  50  between the crosspieces  36  and  38  by clipping or the like. 
     In the embodiment of FIGS. 5 and 6, at least one first spacer  58  and one second spacer  60  are used, having substantially the same shape. The spacer  58  has oblong apertures  62  each suitable for being traversed by an aligned series of tubes of the bundle, in this example a row of tubes. In contrast, the second spacer  60  has oblong apertures  64  each suitable for being traversed by an aligned series of tubes, in this example a column of tubes. 
     As can be seen in FIGS. 5 and 6, the oblong apertures  62  and the oblong apertures  64  extend in orthogonal directions. The embodiment of FIGS. 5 and 6 facilitates the fitting of the tubes, given that they can be inserted in aligned series (rows or columns) through the spacers  58  and  60 , instead of being inserted individually into apertures  52  in the case of the spacer  50 . 
     The spacers  58  and  60  are fixed to the crosspieces  36  and  38  by lugs  54  and  56  similar to those of the spacer  50  described above. 
     In a variant, the spacers  50 ,  58  and  60  can be fixed to the crosspieces by other means, in particular by bonding or by welding. 
     As can be seen in FIG. 1, the spacers  50  are not only placed at chosen locations, but also with chosen orientations, which makes it possible to channel a flow of air F passing through the bundle. 
     It is also advantageous, for channeling the flow of air, to give the crosspieces  36  and  38  a particular shape. Hence, as can be seen more particularly in FIG. 7, these crosspieces have profiles shaped to promote the guidance of the flow of air F. In particular, the crosspieces  36  and  38  have respective leading edges  66  and  68  of rounded shape turned to face into the air flow. This facilitates the guiding of the air flow F which can then appropriately sweep over the tubes of the bundle, which are held with a regular spacing by virtue of the spacers  50  or else  58  and  60 . 
     In the embodiment of FIG. 8, a general structure similar to that of FIG. 1 is again found. 
     The principal differences lie in the way in which the spacers  50  are fixed to the crosspieces  36  and  38 . In this example, these spacers have lugs  70  for clipping with the crosspiece  36  and lugs  72  for clipping with the crosspiece  38 . 
     Moreover, the crosspiece  36  includes two fixing lugs  74  and  76  molded integrally with it. These lugs are intended either for fixing the crosspiece onto the structure of the vehicle, or for fixing accessories onto the heat exchanger. The other crosspiece  38  may include at least one similar fixing lug, as the case may be. 
     Obviously, the invention is not limited to the embodiments described above by way of example and extends to other variants. 
     It will be understood that the heat exchanger can be produced according to a multitude of possible configurations.