Patent Publication Number: US-8122935-B2

Title: Casting core for forming a cooling channel in a piston produced by casting

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of PCT/DE2008/000770 filed on Apr. 25, 2008, which claims priority under 35 U.S.C. §119 of German Application No. 10 2007 019 930.0 filed on Apr. 27, 2007 and German Application No. 10 2007 044 105.5 filed on Sep. 15, 2007. The international application under PCT article 21(2) was not published in English. 
     The invention relates to a casting core for forming a cooling channel in a piston produced by casting, in accordance with the preamble of claim  1 . 
     A water-soluble salt casting core for forming a cooling channel in a cast piston for an internal combustion engine is known from the Japanese patent application having the publication number 2006090159 A, which core is configured to be ring-shaped and has a region that lies parallel to the piston axis, which forms the oil run-off of the cooling channel and makes a transition into the ring-shaped part of the cooling channel by way of a quarter-circle core bend. Furthermore, the salt core has a region disposed parallel to the piston axis, which forms the oil run-in of the cooling channel, whereby the salt core has a notch on the side that lies opposite this region, to form a jet splitter that narrows conically in the direction of the injected oil jet. The jet splitter has the function of dividing the oil jet up into the halves of the cooling channel that lie on both sides of it, whereby the division of the cooling oil into the two cooling channel halves depends both on the position of the piston relative to an oil nozzle that issues the oil jet, and on crosswise accelerations that the oil jet experiences due to movements of the engine equipped with the piston. From this, the disadvantage results that the amount of cooling oil that is introduced into the halves of the cooling channel that lie on both sides of the jet splitter is subject to great variations, which can result in temperature problems for the piston that can lead to damage to the engine equipped with the piston. 
     It is the task of the invention to avoid this disadvantage of the state of the art. This task is accomplished with the characteristics standing in the characterizing part of the main claim. Practical embodiments of the invention are the object of the dependent claims. 
    
    
     
       An exemplary embodiment of the invention will be described in the following, using the drawings. These show: 
         FIG. 1  a perspective representation of a piston produced using the casting process, half in section, using the soluble casting core according to the invention to form a cooling channel, 
         FIG. 2  the soluble casting core according to the invention in a perspective representation, before it is laid into a casting mold for the piston, 
         FIG. 3  an embodiment of the casting core, having two oil run-off openings and a cross-section that increases in the direction of the main run-off opening, and 
         FIG. 4  another embodiment of the casting core, having an oval run-in opening. 
     
    
    
       FIG. 1  shows, in a perspective representation, a piston  1  for an internal combustion engine, half in section, which piston is produced using the casting method, whereby a casting core  2  produced from a material that can be dissolved out is also cast in. In  FIG. 1 , the casting core  2  is shown completely; it is configured in ring shape and is disposed close to the piston crown  3 , in the radially outer region of the piston  1 . The piston  1  can be produced from aluminum or from cast iron, while the soluble casting core  2  can consist of salt or of sand, so that after the piston  1  has been cast, the casting core  2  can be washed out of the piston  1  with water or with another suitable liquid. 
     The piston  1  is provided with a combustion bowl  4  formed into the piston crown  3 , and with a ring belt  5 , radially on the outside, in the vicinity of the piston crown, whereby the groove  6  that lies closest to the piston crown  3  has a ring insert  20 , for example consisting of Niresist, for a compression ring not shown in the drawing. The piston  1  furthermore has two pin bosses  7 ,  8  that lie opposite one another, on the side of the piston  1  that faces away from the piston crown  3 , each having a pin bore  9 ,  10 , and furthermore skirt elements that connect the pin bosses  7 ,  8  with one another and are formed onto the piston crown  3 , of which only the skirt element  11  is visible in the representation of the piston  1  according to  FIG. 1 . 
     The piston  1  shown in  FIG. 1  is cut open in such a way that the run-in opening  12  and main run-off openings  13  of the cooling channel, formed by the casting core  2 , can be seen.  FIG. 2  shows that the casting core  2  has short regions  14 ,  15  both in the region of the run-in opening  12  and in the region of the main run-off opening  13 , which regions have at least approximately the same cross-section diameter, and which make a transition into the ring-shaped part of the casting core  2  by way of a core bend  17 ,  18  in the shape of a quarter circle, in each instance. In this connection, the region  14 , which forms the run-in opening  12 , lies at least approximately parallel to the piston axis  16 . The two regions  14  and  15  of the casting core  2  are disposed at a slight distance from one another, which approximately corresponds, in the present exemplary embodiment, to the cross-section diameter of the region  14  or  15 , but maximally to twice the cross-section diameter of the region  14  or  15 . In this connection, the second region  14  runs into that end of the casting core  2  that forms the run-in opening  12  of the cooling channel. 
     In the region of the main run-off opening  13  of the cooling channel, the casting core  2  can have another core bend  19 , by way of which the first region  15  of the casting core  2  that lies parallel to the piston axis  16  makes a transition into the part of the casting core  2  that forms the main run-off opening  13 , which is oriented in such a way, in this connection, that the cooling oil that exits from it, as can be seen in  FIG. 1 , spurts in the direction of a piston pin not shown in  FIG. 1 . In this way, the cooling oil can be used, after cooling the piston  1 , to cool the pin of the piston  1 , and to lubricate the small connecting rod end of a connecting rod that is connected with the piston. 
     In this connection, the shape of the casting core  2  in the region of the run-in opening  12  and in the region of the main run-off opening  13 , with the regions  14  and  15  that lie parallel to the piston axis  16 , and with the core bends  17  and  19 , has the advantage that cooling oil can be injected into the oil run-in opening  12  formed by the casting core  2  under high pressure, independent of the position of the piston  1  in an oil injection nozzle disposed in the region of the crankshaft, for example, whereby the oil injection nozzle is disposed in such a manner that it sprays out the cooling oil parallel to the piston axis  16  and, in doing so, injects it into the run-in opening  12 . The oil then gets into the ring-shaped part of the oil channel by way of the part of the cooling channel formed by the core bend  17 , with only slight flow resistance, passes through this part quickly, and gets to the main run-off opening  13  by way of the parts of the cooling channel formed by the core bends  18  and  19 , with little flow resistance, so that in this way, a large oil throughput is guaranteed, which leads to improved cooling of the piston  1  as compared with the state of the art. 
     Furthermore, the slight distance between the parts of the cooling channel that are formed by the regions  14  and  15  of the casting core  2  that lie parallel to the piston axis  16  has the advantage that only a very slight part of the piston  1  remains uncooled by the cooling oil. 
     The exemplary embodiment of a casting core  21  shown in  FIG. 3 , in comparison with the casting core  2  according to  FIG. 2 , has a center region  26  that faces away from the piston crown  3 , which forms a central run-off opening  22 , and which is disposed on the side of the casting core  21  that lies opposite the regions  14  and  15 ′ for the run-in opening  12  and for the main run-off opening  13 . Furthermore, the cross-section of the casting core  21  increases, proceeding from its center region  26 , to its first region  15 ′ that forms the run-off opening  13 . In this connection, the cross-section of the entire casting core  21  has an oval shape, the ovality of which lies in the direction of the piston axis  16 . The cooling channel formed by the casting core  21  has the advantage that because of the additional, central run-off opening  22  and because of the cross-section that increases in the direction of the first region  15 ′, it offers very little flow resistance to the cooling oil introduced into the run-in opening  12 , so that as a result, the amount of the cooling oil passed through the cooling channel increases further, and cooling of the piston  1  is improved. 
       FIG. 4  shows an embodiment of a casting core  23  whose run-in opening  24  is configured in oval shape, whereby its ovality lies perpendicular to the piston radius  25 . This brings with it the advantage that the oil injection nozzle, which is disposed in the region of the crankshaft, and by the aid of which the cooling oil is passed to the cooling channel piston, does not have to be oriented in such a way that it sprays oil exclusively parallel to the piston axis  16 . The cooling oil can be sprayed at a slant, in other words at an acute angle to the piston axis  16 , in the direction of the run-in opening  24 , as a function of the location where the oil injection nozzle is installed, whereby the oil injection nozzle must be oriented in such a manner that the oil jet hits the run-in opening  24  independent of the position of the piston  1  between the upper and lower dead-center position. 
     REFERENCE SYMBOL LIST 
     
         
           1  piston 
           2  casting core 
           2  casting core 
           3  piston crown 
           4  combustion bowl 
           5  ring belt 
           6  groove 
           7 ,  8  pin boss 
           9 ,  10  pin bore 
           11  skirt element 
           12  run-in opening 
           13  main run-off opening 
           14  second region of the casting core  2   
           15  first region of the casting core  2   
           15 ′ first region of the casting core  23   
           16  piston axis 
           17 ,  18 ,  19  core bend 
           20  ring insert 
           21  casting core 
           22  central run-off opening 
           23  casting core 
           24  run-in opening 
           25  piston radius 
           26  center region of the casting core  23