Abstract:
The invention concerns a heat exchanger comprising at least a manifold and a fixing lug attached to the manifold by a mechanical linkage obtained by clinching. The invention also concerns a method for making such a heat exchanger comprising a step for clinching the fixing lug on the manifold before making them definitely integral for furnace soldering. The invention is particularly applicable when the heat exchanger is an air conditioning condenser for a motor vehicle.

Description:
FIELD OF THE INVENTION 
     The invention relates to a heat exchanger, in particular for a motor vehicle, as well as a method for its manufacture. 
     The invention more particularly relates to a heat exchanger comprising at least one manifold and at least one fixing lug for each manifold. The fixing lug comprises a concave contact zone, of a shape adapted to the positioning of the said fixing lug on an outer peripheral surface of the manifold, and an attachment zone that extends radially outward from the manifold. 
     BACKGROUND OF THE INVENTION 
     A heat exchanger may form, for example, a condenser that is capable of forming part of an air conditioning installation for a motor vehicle. 
     A heat exchanger typically is fixed, by means of its fixing lugs, to the environment which surrounds it. In the particular case of an air conditioning condenser, it is habitually fixed either to the structure of the vehicle or to the cooling radiator of the engine of the vehicle. 
     Conventionally, the fixing lugs and the manifold are metallic and joined by welding in an atmosphere of an inert gas. But such a welding operation has a series of drawbacks: it is expensive, it requires a qualified operator, it can only be performed at a low speed that is inadequate on an industrial scale, and moreover the quality of the resultant joint is unsatisfactory. 
     The production of the joint by soldering is also known, which necessitates the provision of means to retain and index the fixing lugs on the heat exchanger before and during the soldering operation, which is performed in a suitable furnace. 
     Known, in particular from document EP-0 440 400, is a heat exchanger of the above-mentioned type, which comprises a heat exchanger body and fixing devices that are fixed to the heat exchanger body. The heat exchanger body comprises flat tubes and fins that are stacked alternately, as well as two hollow manifolds to which the ends of the flat tubes are connected in fluid communication. 
     The fixing devices illustrated in the above mentioned document each comprise a contact portion, of concave shape, fitting to the outer peripheral surface of a manifold and placed in close contact with the manifold, as well as a fixing portion that extends outwardly from one end of the concave portion and forms a bent-back hook. 
     The above-mentioned document discloses that this bent-back hook is inserted between two adjacent tubes so that the fixing devices are welded to the body of the heat exchanger and are made integral with the heat exchanger. 
     In a refinement described in the above-mentioned document, a hole is pierced in the hollow manifold, whereas the fixing lug is punched so as to force back material and form a centring cone in the hole produced in this manner. In another refinement, a hole is pierced in the fixing lug and it is the hollow manifold which is punched. 
     The heat exchanger according to the above-mentioned document has a certain number of drawbacks. The fixing lug is susceptible to undesirable micro-displacements which can cause poor tightness as well as burrs at the moment of welding. Moreover, the presence of perforations either in the manifold or in the fixing lug may result in leaks and/or infiltrations. Furthermore, the necessity for an anchoring hook to limit the displacements in relation to the fixing lug and the manifold before the welding operation complicates the production of the fixing lug and its assembly. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the invention is particularly to overcome the above-mentioned drawbacks. 
     In particular it relates to procuring a heat exchanger in which the or each fixing lug may be pre-fitted and kept in a precise position before and during the permanent assembly operation that is performed by soldering or welding. 
     For this purpose the invention proposes a heat exchanger of the type defined in the introduction, in which the concave contact zone of the fixing lug has a central region of reduced thickness in relation to the normal thickness of the fixing lug, so as to produce a mechanical linkage by clinching, joining the concave contact zone of the fixing lug to the outer peripheral surface of the manifold. 
     Thus, the fixing lug is pre-fitted to the manifold by a so-called clinching operation, performed by drawing and pressing. 
     This clinching produces a mechanical linkage by cooperation between the shapes of the manifold and the fixing lug. It permits perfect retention and indexing before and during the furnace soldering operation. The risk of micro-displacements is thus avoided in a particularly effective manner. 
     Furthermore, this operation may be performed particularly quickly, without requiring a piercing stage as in the prior art. 
     According to yet another characteristic of the invention, the manifold of the heat exchanger has, in the concave contact zone with the fixing lug, a blind recess delimited by an upper base which is connected to a lateral wall of the recess by a concave shoulder over a chosen depth. 
     The fixing lug preferably comprises at least one hole previously made to facilitate the subsequent production of the central region of reduced thickness, thanks to the fact that the material of the lug will partially fill this hole whilst limiting the deformation of the lug. 
     The invention applies in particular to a heat exchanger comprising two manifolds and at least one fixing lug for each manifold. 
     Such a heat exchanger may be produced in particular in the form of a condenser. 
     From another angle, the invention relates to a method for the manufacture of such a heat exchanger comprising, for each fixing lug, the steps comprising positioning the said concave contact zone of the fixing lug on the outer peripheral surface of a manifold, then clinching the fixing lug onto the manifold, and finally permanently joining the assembly, for example by furnace soldering. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the following description, given only by way of example, reference is made to the attached drawings, on which: 
     FIG. 1 is a front view of a heat exchanger, of the condenser type, produced in accordance with the invention; 
     FIG. 2 is a top view of the heat exchanger of FIG. 1; 
     FIG. 3 is a partial sectional view showing a manifold and a fixing lug before assembly; 
     FIG. 4 is a partial top view of a fixing lug, represented flat, in the region of its contact zone; 
     FIG. 5 is a sectional view along line V—V of FIG. 4; 
     FIG. 6 is a similar view to FIG. 3, after joining by clinching; and 
     FIG. 7 is a detail, represented on a larger scale, of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is first made to FIGS. 1 and 2 which represent a heat exchanger  10 , here produced in the form of a condenser capable of forming part of an air conditioning installation for a motor vehicle. The condenser  10  is generally formed by a core  12  formed by an alternate stack of flat tubes  14  and fins  16  having an undulating shape. The flat tubes  14  of the core  12  are connected to two manifolds  18 , into which they open through suitable apertures. The condenser is suitable for a coolant in gaseous form to flow through, which is condensed by heat exchange with a flow of air which sweeps the core, in a manner known in the art of the invention. 
     The condenser  10  comprises four fixing lugs  20  fixed in pairs onto the two manifolds  18 . These lugs are intended to allow the attachment of the condenser  10  to its environment, for example to the structure of a motor vehicle or onto the cooling radiator of the engine of the vehicle. 
     In the example, the tubes  14 , the fins  16 , the manifolds  18  and the fixing lugs  20  are formed from a metal sheet having an aluminium base. 
     The manifolds  18  have a tubular shape and in the example illustrated are delimited by a circular cylindrical wall that has an outer peripheral surface  22  (see FIG.  3 ). Each of the fixing lugs  20  comprises a concave contact zone  24  with a shape adapted to the positioning of the fixing lug on the outer peripheral surface  22  of the manifold. Each of the lugs also comprises an attachment zone  26  that extends radially away from the manifold and is capable of being fixed, in a suitable manner, to the environment of the condenser. 
     A mechanical linkage  28  produced by clinching joins the concave contact zone  24  of the fixing lug  20  to the outer peripheral surface  22  of the manifold. 
     The clinching is a mechanical operation that consists of locally deforming the material of two metallic pieces, for example two sheets that are disposed one against the other to join them mechanically. Such an operation essentially comprises a drawing and a pressing which produce a mechanical linkage between the two pieces by cooperation of shapes. 
     Reference is now made to FIGS. 3 to  7  to describe more particularly the mounting of a fixing lug onto a manifold by a clinching operation. 
     The contact zone  24  of the fixing lug comprises a central region  30 , in the example a rectangular shape, having a reduced thickness E 1  in relation to the normal thickness E 0  of the lug (FIG.  5 ). In fact, the thickness of the fixing lug, in the region which has to be deformed by clinching, must not to be too large, as then the clinching operation would be made difficult. It is therefore desirable to specify a central region  30  of reduced thickness, whilst retaining a greater thickness for the remainder of the fixing lug, so as to bestow good mechanical strength. 
     The central region  30  of reduced thickness is advantageously obtained by a press deformation of the fixing lug. In this respect, it is advantageous to produce beforehand, i.e. before press deformation, at least one hole that passes through the thickness of the lug in the region where the central region  30  has to be formed. 
     The purpose of such a hole is to facilitate the production of the central region of reduced thickness since the material of the lug will partially fill this hole while limiting the deformation of the lug. This filling is performed during the pressing of the material towards the hole. 
     Thus, in the example, two holes  31  (represented in broken lines on FIG. 4) may optionally be provided on either side of the site where the clinching will be performed. 
     As can be seen on FIG. 3, the concave contact zone  24  of the fixing lug  20  is applied against the outer peripheral surface  22  of the manifold  18  in a chosen position. Then a clinching operation is performed by using a punch  32  and a drawing die  34  that are able to be brought closer to one another. In the example, the drawing die  34  is applied against the central region  30 , whereas the punch  32  is moved perpendicularly to the longitudinal axis X-X of the manifold, from the interior of the manifold, and in the direction of the drawing die  34 , as shown by the arrow F on FIG.  3 . The drawing die  34  comprises a hollow portion  36  having a shape adapted to the punch  32  and disposed opposite the said punch. 
     The punch  32  is moved in the direction of the arrow F by a suitable mechanical means which causes a local deformation of the wall of the manifold and of the central region  30  of the concave contact zone of the fixing lug. 
     The displacement of the punch  32  successively causes a drawing and a pressing of the wall of the manifold and the central region  30  of reduced thickness of the fixing lug. 
     As a result the manifold  14  has, in the concave contact zone and the fixing lug, a blind recess  38  (FIGS. 6 and 7) delimited by an upper base  40  of circular shape connected to a lateral wall  42  of the recess by a concave shoulder  44  over a chosen depth P. In the region of the base  40  and the lateral wall  42 , the manifold has a wall of reduced thickness e 1 , whereas the central region  30  of the fixing lug has a reduced thickness e 2  (see detail on an enlarged scale on FIG.  7 ). 
     The fixing lug is thus prefitted to the manifold in a chosen indexed position, this pre-fitting being performed by a simple clinching operation that does not involve any perforation in the manifold or in the fixing lug. Once the fixing lugs have been joined by clinching to the corresponding manifolds, the unit can be soldered in a suitable furnace, without any risk of an even minimal displacement of the fixing lug in relation to the manifold. 
     Thus, the method of the invention ensures the indexing and the retention of the fixing lug of the manifold, whilst guaranteeing perfect temporary immobilisation not only during the transport of the condenser towards the soldering furnace, but also during the soldering operation, and without requiring the normal recourse to retention means. 
     Thanks to the method of the invention, remarkable tightness and mechanical strength are bestowed upon the condenser produced in this manner whilst preventing any micro-displacement in relation to the fixing lugs before and during soldering. 
     Of course, the invention is not limited to the embodiment described above by way of example and it extends to other refinements. 
     Thus, although the invention has been described with particular reference to an air conditioning condenser for a motor vehicle, it may be applied to other types of heat exchangers.