Abstract:
A multi-part piston for an internal combustion engine has an upper piston part having a piston crown, and a lower piston part. The lower piston part has pin boss supports and pin bosses connected with them and the upper piston part and the lower piston part each have an inner and an outer support element, which elements delimit an outer circumferential cooling channel. The inner support elements delimit a cavity that is open toward the pin bosses. The cavity has a separate cooling oil collector that has at least one cooling oil opening. The piston is produced by manufacturing the upper piston part and lower piston part, inserting the cooling oil collector into the upper piston part or lower piston part, and joining the upper and lower piston parts together by friction welding.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part of U.S. patent application Ser. No. 12/381,842 filed on Mar. 17, 2009, which claims priority from DE 10 2008 055 910.5 filed on Nov. 5, 2008. Applicants also claim priority under 35 U.S.C. 119 of German Application No. 10 2009 032 865.3 filed on Jul. 14, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a multi-part piston for an internal combustion engine, having an upper piston part that has a piston crown, and a lower piston part. The lower piston part has pin boss supports and pin bosses connected with them, and the upper piston part and the lower piston part each have an inner and an outer support element, which elements delimit an outer circumferential cooling channel. The present invention furthermore relates to a method for the production of such a piston. 
         [0004]    2. The Prior Art 
         [0005]    A multi-part piston is disclosed, for example, in EP 1 222 364 B1. This piston has an outer circumferential cooling channel and an inner cooling chamber whose cooling chamber bottom is provided with an opening. This opening allows cooling oil to flow away out of the inner cooling chamber in the direction of the piston pin, in order to lubricate the piston pin and to intensify the cooling effect by means of effective cooling oil circulation. In order to achieve this goal, the opening in the cooling chamber bottom cannot be too large, because then, the cooling oil would no longer flow away in a metered manner, and effective cooling oil circulation would thereby be impaired. This means that the cooling chamber bottom is configured essentially as a relatively wide and thin circumferential ring land that extends approximately in the radial direction, in the upper region of the lower piston part. However, such a structure is difficult to produce. In the case of a forged lower piston part, in particular, there is the additional problem that when using a forging method, only a very thick and heavy cooling chamber bottom can be produced, due to forging tolerances and production restrictions. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an object of the present invention to provide a multi-part piston as well as a method for its production, which guarantees a good cooling effect of the cooling oil as well as effective lubrication of the piston pin, and, at the same time, is as simple as possible to produce as a light piston, also in the form of a forged piston. 
         [0007]    This object is accomplished by a piston having a piston crown, and a lower piston part with pin boss supports and pin bosses connected with them. The upper piston part and the lower piston part each have an inner and an outer support element, which elements delimit an outer circumferential cooling channel. The inner support elements delimit a cavity that is open toward the pin bosses. The cavity is provided with a separate cooling oil collector that has at least one cooling oil opening. The method according to the invention is characterized by the following method steps: producing an upper piston part having a piston crown as well as an inner and an outer support element, producing a lower piston part having pin boss supports and pin bosses connected with them, as well as having an inner and an outer support element; inserting a separate cooling oil collector, having at least one cooling oil opening, into the upper piston part or the lower piston part, in the region of each of their inner support elements; connecting the upper piston part and the lower piston part in such a manner that each of the inner and outer support elements delimit an outer circumferential cooling channel and a cavity that is open toward the pin bosses and provided with the cooling oil collector. 
         [0008]    According to the invention, an inner cooling chamber and thus a cooling chamber bottom in the piston are therefore eliminated. The problem of producing a circumferential ring land that extends approximately in the radial direction, as a relatively wide and thin region, is therefore completely eliminated. The upper piston part and the lower piston part of the piston according to the invention can therefore also be produced as forged parts, in a relatively simple manner, and as comparatively light components. The piston according to the invention and the production method according to the invention are thus also characterized by clearly improved economic efficiency. In this connection, the cooling oil collector serves to optimize the cooling effect of the cooling oil, particularly below the piston crown. The at least one cooling oil opening in the cooling oil collector provided according to the invention also allows significantly better and more precise metering of the cooling oil that flows away in the direction of the piston pin, so that the lubrication of the piston pin is also improved, as compared with the pistons known in the state of the art. Since the cooling oil collector can be produced and installed as a very simply structured and light component, the economic efficiency of the piston according to the invention, and of the production method according to the invention, remains unimpaired. 
         [0009]    In a preferred embodiment of the piston according to the invention, the upper piston part and the lower piston part are connected with one another by a friction welding method that produces a friction weld bead, at least by way of their inner support elements, and the cooling oil collector is held between the friction weld beads and pin boss supports. As an alternative, the cooling oil collector can also be held between the friction weld beads and the underside of the piston crown. Positioning of the cooling oil collector in the cavity can thus be selected as desired, and can take place both above and below the friction weld beads, depending on the requirements of an individual case. The friction weld beads furthermore ensure particularly secure axial support of the cooling oil collector. 
         [0010]    A possible embodiment of such a cooling oil collector consists in that the cooling oil collector has a flange, or edge with at least two elastic spring tongues disposed on the outer edge. In the latter case, the slits that delimit the spring tongues can serve as cooling oil openings, at the same time. 
         [0011]    If the cooling oil collector is held between the friction weld beads and the pin boss supports, the edge or the tongues are preferably bent axially upward, and either touch the friction weld bead or rest against it or engage behind it. In the case that the cooling oil collector is held between the friction weld beads and the underside of the piston crown, the edge or the tongues are bent axially downward, and touch the friction weld bead or rest against it or engage behind it. In this manner, particularly reliable securing of the position of the cooling oil collector in the cavity, able to withstand stress, is achieved. 
         [0012]    Additional securing of the position of the cooling oil collector can be achieved by a resilient support element on the side of the cooling oil collector facing the piston crown, which element supports itself on the underside of the piston crown. 
         [0013]    In a preferred embodiment, the support element can have at least two, preferably three, but also more than three spring arms that support themselves on the underside of the piston crown. The cooling oil collector and the support element can be configured in one piece or in multiple pieces. In the latter case, the support element can be attached to the cooling oil collector in any desired manner, for example by means of screwing, riveting, pressing, welding, soldering and the like. 
         [0014]    The cooling oil collector can be made from any desired material, but it is practical if the collector is configured as an at least partially spring-elastic component. In this case, it can be held in one of the two components before the upper piston part and the lower piston part are connected, under spring bias. A suitable material is, for example, a spring steel sheet. In the simplest case, the cooling oil collector has an essentially round shape and can be provided with a slight curvature. 
         [0015]    The cooling oil collector preferably has two or more cooling oil openings, so that a very precisely metered amount of cooling oil can flow away out of the cavity, in the direction of the piston pin. 
         [0016]    The at least one cooling oil opening in the cooling oil collector can be configured as a usual, round opening, or, for example, also as a slit that is disposed at the edge of the cooling oil collector or extends inward from the edge of the cooling oil collector. 
         [0017]    The upper piston part and/or the lower piston part can be cast parts or forged parts, and can be produced, for example, from a steel material, particularly a forged steel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention. 
           [0019]    In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
           [0020]      FIG. 1  shows a section through a first embodiment of a piston according to the invention; 
           [0021]      FIG. 2  shows the piston according to  FIG. 1  in section, rotated 90° as compared with  FIG. 1 ; 
           [0022]      FIG. 3  shows a section through a second embodiment of a piston according to the invention; 
           [0023]      FIG. 4  shows the piston according to  FIG. 3  in section, rotated 90° as compared with  FIG. 3 ; 
           [0024]      FIG. 5  shows a perspective representation of the cooling oil collector according to  FIGS. 3 and 4 ; and 
           [0025]      FIG. 6  shows an enlarged representation of a detail from  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    Referring now in detail to the drawings,  FIGS. 1 and 2  show a first exemplary embodiment of a piston  10  according to the invention. Piston  10  is composed of an upper piston part  11  and a lower piston part  12 , which, in the exemplary embodiment, are forged from a steel material. Upper piston part  11  has a piston crown  13  having a combustion bowl  14 , as well as a circumferential top land  15  and a circumferential ring belt  16 . Lower piston part  12  has a piston skirt  17  and pin bosses  18  having pin bores  19 , for accommodating a piston pin (not shown). 
         [0027]    Upper piston part  11  has an inner support element  21  and an outer support element  22 . Inner support element  21  is disposed on the underside of piston crown  13 , circumferentially, in ring shape, and has a joining surface  23 . Outer support element  22  of upper piston part  11  is formed below ring belt  16 , and has a joining surface  24 . 
         [0028]    Lower piston part  12  also has an inner support element  25  and an outer support element  26 . Inner support element  25  is disposed on the top of lower piston part  12 , circumferentially, and has a joining surface  27 . Outer support element  26  is formed as an extension of piston skirt  17  in the embodiment shown, and has a joining surface  28 . Pin boss supports  32  for connecting the pin bosses  18  are provided below inner support element  25  of lower piston part  12 . 
         [0029]    Upper piston part  11  and lower piston part  12  are joined in known manner, by means of a friction welding method, whereby joining surfaces  23  and  27 , and  24  and  28 , respectively, are connected with one another. 
         [0030]    Upper piston part  11  and lower piston part  12  form an outer circumferential cooling oil channel  29 . In this connection, ring belt  16  and outer support element  22  of the upper piston part  11  as well as outer support element  26  of lower piston part  12  delimit outer cooling channel  29  toward the outside. Inner support element  21  of the upper piston part and the inner support element  25  of the lower piston part delimit the outer cooling channel  29  toward the piston interior. Inner support element  21  of upper piston part  11  and inner support element  25  of lower piston part  12  delimit a cavity  31  that is open toward pin bosses  18 , which cavity is disposed essentially below piston crown  13 . 
         [0031]    In the embodiment shown, cooling oil channels  33  are provided in inner support element  21  of upper piston part  11 , which connect outer cooling channel  29  with cavity  31 . Cooling oil channels  33  run at an angle downward, in the direction of cavity  31 , proceeding from outer cooling channel  29 . Of course, cooling oil channels  33  can also be disposed in the inner support element  25  of lower piston part  12 , and/or can run at an angle upward, in the direction of cavity  31 , proceeding from outer cooling channel  29 . 
         [0032]    As a result of the friction welding process for connecting upper piston part  11  and lower piston part  12 , friction weld beads  34  project both into cavity  31  and into outer cooling channel  29 . 
         [0033]    Cavity  31  is provided with a cooling oil collector  35 . Cooling oil collector  35  is produced from a spring steel sheet, has an essentially round shape, is provided with a slight curvature, approximately in the shape of a flattened dome, and has a thickness of approximately 0.8 mm. It has a circumferential spring-elastic flange  36  and cooling oil openings  37 . Flange  36  is provided with slits  38 , which both increase the elasticity of flange  36  in the radial direction and serve as additional cooling oil openings. Cooling oil collector  35  is held between pin boss supports  32  and friction weld bead  34 , in the region of lower piston part  12 , and supports itself on pin boss supports  32  in the direction of pin bosses  18 , and on friction weld beads  34  in the direction of upper piston part  11 . Cooling oil collector  35  is disposed in such a manner that its curvature is directed toward upper piston part  11 . Depending on the placement of the cooling oil collector  35  in cavity  31 , the curvature can also be directed toward pin bosses  18 . 
         [0034]    Of course, cooling oil collector  35  can also be disposed in the region of upper piston part  11 , so that it supports itself both on friction weld beads  34  and in the region of the underside of the piston crown  13 . In this case, it is practical to dispose cooling oil channels  33  in the inner support element  25  of lower piston part  12 . 
         [0035]    Cooling oil collector  35  serves to collect cooling oil that passes through cooling oil channels  33 , out of outer cooling channel  29 , into cavity  31 , and to guide it in the direction of the underside of the piston crown  13 , particularly by means of the shaker effect that occurs during operation, in order to increase the cooling effect in this region. Cooling oil openings  33  make it possible to guide a defined amount of cooling oil in the direction of the piston pin (not shown) accommodated in pin bores  19 , in order to improve its lubrication. 
         [0036]    For assembly of piston  10  according to the invention, first upper piston part  11 , lower piston part  12 , and cooling oil collector  35  are produced as separate components. In the exemplary embodiment, cooling oil collector  35  is inserted into lower piston part  12 , in the region of the inner circumferential support element  25 , and held there under spring bias, with force fit. Subsequently, upper piston part  11  and lower piston part  12  are connected with one another, by a friction welding method, by way of joining surfaces  23 ,  27  and  24 ,  28 , respectively, in such a manner that cooling oil collector  35  supports itself and is held both on friction weld bead  34  that has formed and on pin boss supports  32 . 
         [0037]    The inner cooling chamber having a cooling chamber bottom in the form of a wide, radially circumferential ring land, which is required in the state of the art, has therefore been eliminated. 
         [0038]      FIGS. 3 and 4  show another exemplary embodiment of a piston  110  according to the invention. Piston  110  essentially corresponds to piston  10  according to  FIGS. 1 and 2 , so that structural elements that agree with one another are provided with the same reference numbers. 
         [0039]    The significant difference consists in cooling oil collector  135  of the piston  110  according to  FIGS. 3 and 4  disposed in cavity  31 . Cooling oil collector  135  and its placement in cavity  31  are also shown enlarged in  FIGS. 5 and 6 . 
         [0040]    Cooling oil collector  135  is also produced from a spring steel sheet, has an essentially round shape, is provided with a slight curvature, approximately in the shape of a flattened dome, and has a thickness of about 0.8 mm. In contrast to cooling oil collector  35  according to  FIGS. 1 and 2 , cooling oil collector  135  has a circumferential, spring-elastic edge  136  that is bent axially upward. Furthermore, cooling oil openings  137  and slits  138  are provided, which both increase the elasticity of edge  136  in the radial direction, and serve as additional cooling oil openings. In the exemplary embodiment, cooling oil collector  135  is held between pin boss supports  32  and friction weld bead  34 , in the region of lower piston part  12 . Cooling oil collector  135  supports itself on pin boss supports  32  in the direction of pin bosses  18 . In the direction of upper piston part  11 , in the exemplary embodiment shown here, edge  136  touches friction weld bead  34  and supports itself on it, if necessary. Cooling oil collector  135  is disposed in such a manner that its curvature is directed toward upper piston part  11 . Depending on the placement of cooling oil collector  135  in cavity  31 , the curvature can also be directed toward pin bosses  18 . 
         [0041]    Of course, cooling oil collector  135  can also be disposed in the region of upper piston part  11 , so that it supports itself on or touches the region of the underside of piston crown  13  and friction weld beads  34 . In this case, edge  136  is bent axially downward. It is practical if cooling oil channels  33  are disposed in inner support element  25  of lower piston part  12 . 
         [0042]    In the embodiment shown here, cooling oil collector  135  is furthermore provided with a support element  151 . Support element  151  is configured as a separate component. However, it can also be configured in one piece with cooling oil collector  135 , and can be produced by punching it out from cooling oil collector  135 , for example. It is practical if support element  151  is also produced from a spring steel sheet. Support element  151  has three spring arms  152  that support themselves on the underside of the piston crown  13  of piston  110  in the assembled state. In the exemplary embodiment, spring arms  152  go from a center hub  153 , which is attached to cooling oil collector  135  in the longitudinal piston axis. Attachment can take place in any desired manner, for example by means of screwing, riveting, welding, or soldering it on, and the like. It is advantageous if support element  151  is connected with cooling oil collector  135  so that it can rotate. Support element  151  brings about additional spring-elastic securing of the position of cooling oil collector  135  in cavity  31 , which is therefore flexibly able to withstand stress during operation. 
         [0043]    The function and the assembly of cooling oil collector  135  are the same as described for cooling oil collector  35 . 
         [0044]    Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.