Abstract:
A heat exchanger for a motor vehicle, particularly a motorcycle in which a bent cooling element is disposed between a first and second collector tank. The bent cooling element is provided with a longer and a shorter side as well as lateral connecting planes for joining the cooling element to the collector tanks. The collector tanks are made of a material that has substantially lower strength than the material of the cooling element.

Description:
[0001]     This application is a Continuation of PCT/EP2005/003351, filed Mar. 31, 2005, and claims the priority of DE 10 2004 019 769.5, filed Apr. 23, 2004, the disclosures of which are expressly incorporated by reference herein. 
     
    
     BACKGROUND AND SUMMARY OF THE INVENTION  
       [0002]     The invention relates to a heat exchanger for a motor vehicle, in particular for a motorcycle, having a first and a second collecting tank and a curved heat sink arranged between the collecting tanks, so that flow can pass through it, also having lateral connecting planes for attachment to the collecting tanks and having a longer side and a shorter side between the collecting tanks.  
         [0003]     Cooling of efficient internal combustion engines in motor vehicles is usually accomplished by using a coolant which absorbs heat in areas of the internal combustion engine that are to be cooled and releases this heat elsewhere via a heat exchanger through which air can flow. The evolution of heat and thus the requirement for dissipation of heat via the heat exchanger depend on the power of the internal combustion engine. Very powerful internal combustion engines require especially effective heat exchangers having the largest possible surface area exposed to oncoming flow.  
         [0004]     Especially in the motorcycle area, however, the available surface area is limited. With very powerful internal combustion engines, in particular and/or when very little space is available because of design factors, very complex measures must sometimes be taken to ensure an adequate cooling capacity.  
         [0005]     An efficient heat exchanger for a motorcycle is known from the Honda company Fireblade brochure of February, 2004; in the installed position, this heat exchanger has an oncoming flow surface that is inclined at the side and bent about the vertical axis. The known heat exchanger having lateral collecting tanks comprises a heat sink through which coolant can flow transversely and which has a longer side at the top and a shorter side at the bottom between the collecting tanks and is formed from a plurality of individual cross tubes. The heat sink as well as the collecting tanks that are fixedly attached to the heat sink with the known heat exchanger are made of metal with the individual components being welded together.  
         [0006]     The curved heat sink of the heat exchanger has a smaller bending radius on its upper longer side than the lower shorter side, with the result that the lateral collecting tanks experience torsion, which leads to stresses. These stresses are dissipated via areas of lower strength, often over a very long period of time.  
         [0007]     The invention is based on the object of further improving upon a heat exchanger as defined in the introduction and especially facilitating the dissipation of stresses in the case of twisted collecting tanks. Furthermore, an especially economical method of manufacturing such a heat exchanger is to be made available.  
         [0008]     This object is achieved with a heat exchanger, whereby according to the basic idea, the collecting tanks are made of a material having much lower strength values than the material of the heat sink.  
         [0009]     It is especially preferable if the material of the heat sink has at least 1.5 times, especially approximately 2.5 to 20 times the strength of the material of the collecting tanks. The heat sink is expediently made of metal and the collecting tanks are made of plastic. It is possible for the heat sink to be made of a lightweight metal or a lightweight metal alloy such as an aluminum alloy and for the collecting tanks to be made of a thermoplastic material such as polyamide.  
         [0010]     According to a very advantageous exemplary embodiment, the heat sink in the installed position has an oncoming flow surface at the bottom that is chamfered or rounded at the side and has flangeable straps on its lateral connecting planes for attachment to the collecting tanks, these straps being tightly attached to the heat sink with the inclusion of a gasket.  
         [0011]     It has proven advantageous for one of the collecting tanks for holding a thermostatic valve that controls the heat exchanger flow as a function of temperature to be integrally connected to a housing. It is likewise regarded as expedient if the collecting tanks are provided with fastening points for mounting on the vehicle and/or attaching other elements.  
         [0012]     An especially preferred method for manufacturing such a heat exchanger is characterized in that the collecting tanks are connected to the planar heat sink on its lateral connecting planes and bending of the heat sink is performed subsequently; after this bending, the longer side of the heat sink has a smaller bending radius than the shorter side, so that with the bending of the heat sink, the collecting tanks connected to its lateral connecting planes are twisted.  
         [0013]     The stresses that occur in bending the heat sink and the associated twisting of the collecting tanks are advantageously absorbed essentially by the collecting tanks and can be dissipated into the collecting tanks due to the material.  
         [0014]     It is highly expedient if the dissipation of stresses into the collecting tanks is supported by means of heat and/or substances that reduce the strength of the material of the collecting tanks. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The invention is explained in greater detail below on the basis of an exemplary embodiment with reference to the figures which show schematic diagrams as examples.  
         [0016]      FIG. 1  shows a motorcycle having a heat exchanger.  
         [0017]      FIG. 2   a  shows a heat exchanger for a motorcycle in accordance with an embodiment of the present invention having a curved heat sink arranged between two collecting tanks in an isometric view.  
         [0018]      FIG. 2   b  shows a heat exchanger for a motorcycle of  FIG. 2   a  having a curved heat sink arranged between two collecting tanks in a side view.  
         [0019]      FIG. 2   c  shows a heat exchanger for a motorcycle of  FIG. 2   a  having a curved heat sink arranged between two collecting tanks as seen from above.  
         [0020]      FIG. 3  shows a heat exchanger for a motorcycle in accordance with another embodiment of the present invention having a curved heat sink arranged between two collecting tanks with the connecting plane of the collecting tanks twisted. 
     
    
     DETAILED DESCRIPTION  
       [0021]      FIG. 1  shows a motorcycle  100 . A reciprocating piston internal combustion engine  102  is provided to drive the motorcycle  100 , transmitting the driving forces via a cardan shaft  106 , for example, a driving belt or a drive chain to the driven wheel  108  with a transmission  104  in between. The cooling of the internal combustion engine  102  is accomplished by means of a circulating coolant which absorbs heat in areas of the internal combustion engine that are to be cooled and releases this heat elsewhere via a heat exchanger  110  through which air can flow.  
         [0022]     A heat exchanger  200  for cooling the internal combustion engine of a motorcycle, having a collecting tank  204  on the radiator forward flow end and a collecting tank  206  on the radiator return flow end with a curved heat sink  202  arranged between them, as shown in an ISO view in  FIG. 2   a ;  FIG. 2   b  shows a side view of the collecting tank  204  on the radiator forward flow end and  FIG. 2   c  shows the curved heat exchanger  200  as seen from above.  
         [0023]     In the installed position, the heat sink  202  has a laterally inclined oncoming flow surface at the bottom in the installed position. In the present case, the oncoming flow surface of the heat sink  202  is formed geometrically by an upper rectangular area  208  and a lower trapezoidal area  210 , but it may also be expedient if the heat sink  202  has a different surface, e.g., a V-shaped surface adapted to the available space. It shall be emphasized that the heat sink  202  has a longer side  212  and a shorter side  214  between the collecting tanks  204 ,  206 .  
         [0024]     The heat sink  202  has a plurality of cross tubes through which flow passes from the collecting tank  204  on the radiator forward flow end to the collecting tank  206  on the radiator return flow end, these cross tubes each being fixedly connected with lateral connecting planes  216 ,  218  for connecting to the collecting tanks  204 ,  206 . The cross tubes and the lateral connecting planes  216 ,  218  are made of metal, in particular lightweight metal or a lightweight metal alloy such as aluminum, and are soldered, welded or glued together.  
         [0025]     For connecting the collecting tanks  204 ,  206  to the lateral connecting planes  216 ,  218 , the connecting planes  216 ,  218  have straps that can be flanged on the peripheral edges and engage behind a peripheral edge of the collecting tanks  204 ,  206  in the installed state. Gaskets (not visible here) are provided for a tight connection of the collecting tanks  204 ,  206  to the lateral connecting planes  216 ,  218 . The collecting tanks  204 ,  206  are made of a thermoplastic material such as fiberglass-reinforced nylon, e.g., nylon 6.6 containing 30% glass fibers. A housing  228  to hold a thermostatic valve that controls the flow through the heat exchanger as a function of temperature is integrally connected to the collecting tank  206  on the return flow end of the radiator.  
         [0026]     Fabrication of the heat exchanger  200  begins with a flat, uncurved heat sink  202  having lateral connecting planes  216 ,  218 . The collecting tanks  204 ,  206  are mounted with a gasket and secured by flanging the straps. The heat sink  202 ,  302  is subsequently bent, as illustrated on an exaggerated scale in  FIG. 3 , whereby the longer side  212 ,  312  undergoes a greater bending than the shorter side  214 ,  314  owing to the difference in bending resistance torques, with the result that the collecting tanks  204 ,  206 ,  304 ,  306  together with the connecting planes  216 ,  218 ,  316 ,  318  are twisted.  
         [0027]     The collecting tanks  204 ,  206 ,  304 ,  306 , which are made of plastic, have lower strength values in comparison with the metallic material of the heat sink  202 ,  302  and the connecting planes  216 ,  218 ,  316 ,  318  and accordingly they absorb a significant portion of the stresses occurring in deformation, so that the area of the connection of the individual radiator cross tubes with the connecting planes  216 ,  218 ,  316 ,  318  is relieved in particular. The plastic of the collecting tanks  204 ,  206 ,  304 ,  306  in the present case has a strength value R m  of 30 to 80 N/mm 2 , while the cooling bodies  202 ,  302  and the connecting planes  216 ,  218 ,  316 ,  318  made of an aluminum alloy have a strength value R m  of 200 to 600 N/mm 2 , so the material of the heat sink  202 ,  302  and the connecting planes  216 ,  218 ,  316 ,  318  is 2.5 to 20 times stronger than the material of the collecting tanks  204 ,  206 ,  304 ,  306 .  
         [0028]     The stresses occurring in deformation of the heat sink  202 ,  302 , the connecting planes  216 ,  218 ,  316 ,  318  and the collecting tanks  204 ,  206 ,  304 ,  306  are dissipated, in particular in the collecting tanks due to the material by yielding of the material. The dissipation of stress in the collecting tanks is supported by heat and/or substances that reduce the strength of the material of the collecting tanks; for example the coolant of the internal combustion engine has a strength-reducing effect as a function of operating temperature and/or due to the glycol contained therein. In the present case, the strength of the material of the collecting tanks  204 ,  206 ,  304 ,  306  is reduced by 30 to 40%. The dissipation of internal stresses is accomplished comparatively rapidly and has a very positive effect on the long-term functionality of the heat exchanger and rejects in production can be reduced.  
         [0029]     The collecting tanks  204 ,  206  are equipped with fastening points for securing them on the motor vehicle  220  and/or for attaching additional elements  222 ,  224 ,  226  such as fans, paneling parts, air ducts and/or protective grids. In the production of the collecting tanks  204 ,  206 , the torsion-induced displacement in the assembly state is performed so that all the fastenings and connection points assume their intended positions after the deformation.  
         [0030]     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.