[0001]    The present invention relates to a heat exchanger suitable for use in particular in a fuel circuit. The invention also concerns a cooling circuit, a fuel circuit and a vehicle comprising such a heat exchanger. 
       BACKGROUND OF THE INVENTION 
       [0002]    A fuel circuit, more particularly a diesel circuit, includes a return circuit connecting a member for delivering fuel to the injectors (e.g. a distributor rail) back to the tank for the purpose of returning diesel that has not been injected. The return circuit generally includes a heat exchanger that is arranged to lower the temperature of the diesel from about 125° C. at the distributor member to about 85° C., in particular for the purpose of making it possible to use a tank that is made of polyethylene, which is lighter than a tank made of metal and less expensive than a tank made of polyamide that is better at withstanding high temperatures. 
         [0003]    The heat exchanger comprises a fuel transport tube that is shaped to form a coil that is positioned under the vehicle in order to be subjected to a flow of air of the kind generated by the vehicle moving. The tube used at present is a smooth metal tube. The cooling that is obtained is effective, but the use of metal makes the heat exchanger relatively heavy. 
         [0004]    To obviate that drawback, proposals have been made to replace the metal constituting the tube that is shaped into a coil with a plastics material, and more particularly a polyamide. 
         [0005]    The heat exchanger is thus indeed lighter in weight, but a drop in its cooling performance is observed. 
       OBJECT OF THE INVENTION 
       [0006]    It would therefore be advantageous to have a heat exchanger combining the advantages of metal tube coolers with the advantages of thermoplastic material tube coolers. 
       SUMMARY OF THE INVENTION 
       [0007]    To this end, the invention provides a heat exchanger comprising a fluid transport tube of thermoplastic material shaped to form a coil, the tube being made of a thermoplastic material and comprising at least one corrugated segment. 
         [0008]    The presence of corrugations makes it possible to increase the heat exchange area between the tube and the surrounding air, and the corrugations disturb the flow of air by creating turbulence therein. These two phenomena encourage heat exchange between the fluid transported by the tube and the air surrounding the tube. 
         [0009]    Preferably, the tube has at least one bend portion extending in a corrugated segment. 
         [0010]    The disposition of the corrugated segment in the bend portion of the tube makes it possible to omit a stage of bending as is necessary with metal tubes or of high temperature forming as is necessary with smooth tubes made of thermoplastic material. The shape of the bend portion is maintained by means of members for fastening the tube to its support. 
         [0011]    The invention also concerns a cooling circuit and a fuel circuit comprising a heat exchanger having at least one of the previous features. 
         [0012]    Besides, the invention concerns a vehicle comprising a body and such a heat exchanger, wherein the heat exchanger is fixed on the outside of the bodywork. 
         [0013]    Thus, the heat exchanger is submitted to the flow of air resulting from the vehicle movement. The corrugations disturb the flow of air encouraging feat exchange between the transported fluid and the air surrounding the heat exchanger. 
         [0014]    Other characteristics and advantages of the invention appear on reading the following description of a particular and non-limiting embodiment of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Reference is made to the accompanying drawings, in which: 
           [0016]      FIG. 1  is a fragmentary view of a heat exchanger in accordance with the invention; 
           [0017]      FIG. 2  is a detail view of a tube used in making up the heat exchanger; and 
           [0018]      FIG. 3  is a fragmentary longitudinal section view of the tube; 
           [0019]      FIG. 4  is a schematic view of a vehicle fitted with a heat exchanger in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The heat exchanger of the invention is for installing in a diesel return circuit, of which pipes are represented in chain-dotted lines and given reference  1  in  FIG. 1 , and for being secured under the bodywork  2  of a motor vehicle. 
         [0021]    The heat exchanger in accordance with the invention comprises a tube given overall reference  10 , made up of a succession of smooth segments  11  and of corrugated segments  12 . The tube  10  is made of a thermoplastic material, in this case a polyamide, and more particularly a polyamide  12 . Nevertheless, the tube could be made of other thermoplastic materials, in the form of single layers or of multiple layers. 
         [0022]    The tube  10  is connected to the return circuit  1  by means of endpieces in the form of teats or Christmas-tree serrations; other connection techniques could naturally be envisaged. 
         [0023]    The tube  10  is shaped to constitute a coil, so as to present bend portions  13 . These bend portions are shaped in the corrugated portions  12 . Fastener members  14 , themselves known and for example of the type commonly referred to as clips, connect the smooth segments  11  to the bodywork  2  of the vehicle. The fastener members  14  serve firstly to hold the tube  10  to the bodywork  2 , and secondly to keep the bend portions  13  in shape. 
         [0024]    The length of the tube  10  and its coil shape (number of bend portions), and also its disposition on the vehicle, serve to adapt the heat exchange produced by the heat exchanger to the requirements of the application. 
         [0025]    The corrugations could be of a shape other than that shown in the figures, for example they could be helical in shape or they could have a section that is substantially sinusoidal, triangular, squarewave-shaped, 
         [0026]    Naturally, the invention is not limited to the embodiment described and variant embodiments could be applied thereto without going beyond the ambit of the invention as defined by the claims. 
         [0027]    Optionally, it is possible for the tube that is shaped into coils to be fastened to a plate that serves simultaneously to perform the function of protecting the tube and of performing a deflector function for directing a flow of air against the tube, the tube then extending between the bodywork and the plate. 
         [0028]    By way of example, the heat exchanger is for fastening under the body of a vehicle or to any other location in which the heat exchanger will be subjected to a flow of air. 
         [0029]    It is also possible to envisage other applications, and in particular static applications, for heating or cooling purposes,. 
         [0030]    The tube may be made up of one or more parts. 
         [0031]    The invention is not limited to the fuel circuit but also concerns for example cooling circuit mounted on vehicles or other devices. The described circuit can thus be used as a cooling circuit for an other application.
A heat exchanger comprising a fluid transport tube shaped to form a coil, the tube being made of a thermoplastic material and comprising at least one corrugated segment. Cooling circuit, fuel circuit and vehicle comprising such a heat exchanger.