Abstract:
A multi-part piston for an internal combustion engine has an upper piston part having a piston crown, and a lower piston part having pin boss supports and pin bosses connected with them. The upper piston part and lower piston part each have an inner and an outer support element, which delimit an outer circumferential cooling channel. The inner support elements delimit a cavity that is open toward the pin bosses, and the cavity is provided with a separate cooling oil collector that has at least one cooling oil opening. In a method for producing a piston, the upper and lower piston parts are manufactured, the cooling oil collector is inserted into one of the upper and lower piston parts in a region of the cavity, and the upper and lower piston parts are connected together at their support elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part of U.S. patent application Ser. No. 12/381,841, filed on Mar. 17, 2009, which claims priority from German Patent Application No. DE 10 2008 055 912.1, filed on Nov. 5, 2008, for which priority is also claimed under 35 U.S.C. §119. Applicants also claims priority under 35 U.S.C. §119 of German Patent Application No. DE 10 2009 032 916.1, 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 that has 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 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 European Patent Application No. 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 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 achieved by a multi-part piston for an internal combustion engine that has an upper piston part having a piston crown, and a lower piston part having pin boss supports and pin bosses connected with them. The upper piston part and lower piston part each have an inner and an outer support element, which delimit an outer circumferential cooling channel. According to the invention, the inner support elements delimit a cavity that is open toward the pin bosses, and the cavity is provided with a separate cooling oil collector that has at least one cooling oil opening. 
         [0008]    The method according to the invention has 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; connecting the upper piston part and the lower piston part in such a manner that the inner and outer support elements, in each instance, delimit an outer circumferential cooling channel and a cavity that is open toward the pin bosses and provided with the cooling oil collector. 
         [0009]    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 therefore have 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 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. 
         [0010]    In a preferred embodiment of the piston according to the invention, the cooling oil collector is held on or rests on the lower piston part in the region of the inner support element. In this position, the cooling oil collector can rest on the pin boss supports, if applicable, and is thereby additionally fixed in place. 
         [0011]    In a preferred embodiment, a holding element that extends vertically in the direction of the lower piston part, from the underside of the piston crown, is provided in the cavity; the cooling oil collector supports itself, with force fit and/or shape fit, against this element, in the axial direction. With this measure, as well, additional fixation of the holding element in the direction of the piston axis is achieved. 
         [0012]    For this purpose, the cooling oil collector can have a hat-shaped elevation that interacts with the holding element. This elevation imparts additional stability to the cooling oil collector. 
         [0013]    The holding element can be formed onto the underside of the piston crown, in one piece with it. However, it can also be configured as a separate element, and held on the underside of the piston crown with force fit and/or shape fit. The selection is at the discretion of a person skilled in the art, and allows flexible adaptation of the piston properties to the requirements in operation, in each instance. 
         [0014]    If the holding element is configured as a separate component, it can be pressed onto the underside of the piston crown after assembly of the piston according to the invention, for example, or it can be connected with the underside of the piston crown using a pin connection or screw connection. These methods of construction are particularly easy to implement. 
         [0015]    Independent of how the holding element is connected with the underside of the piston crown, the end of the holding element that faces the lower piston part, for example, can have a circumferential contact shoulder that surrounds a projection, for example, which shoulder rests on the cooling oil collector. The projection engages into a bore provided in the cooling oil collector. The projection can be configured as a journal, and the holding element can be riveted to the cooling oil collector by means of this journal. In this embodiment, the shape-fit connection between holding element and cooling oil collector offers a particularly reliable, stable hold. 
         [0016]    It is practical if the length of the holding element is dimensioned in such a manner that the cooling oil collector is firmly supported on the inner support element and/or on the pin boss connection, and thus no longer has any lateral play. In this way, the cooling oil collector is positioned particularly firmly on the lower piston part. 
         [0017]    For the purpose of further stabilization of the cooling oil collector, the cooling oil collector can have a flange that runs at least partially on the circumference, or tongues disposed at least on the outer edge, which lie against the inner support element and bring about additional friction fit. 
         [0018]    The lower piston part and the upper piston part can be connected with one another, at least by way of their inner support elements, for example, by means of a method that produces friction weld beads. Preferably, the flange or the tongues are bent axially upward, and either 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. 
         [0019]    Additional securing of the position of the cooling oil collector can be achieved, by a resilient support element on a side of the cooling oil collector facing the piston crown, which element supports itself on the underside of the piston crown. 
         [0020]    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. 
         [0021]    The cooling oil collector and the support element can be configured in one piece or in multiple pieces. If multiple pieces are used, 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. 
         [0022]    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 this case, the length of the holding element should be dimensioned accordingly. 
         [0023]    In the simplest case, the cooling oil collector has an essentially round shape and can be provided with a slight curvature. 
         [0024]    The at least one cooling oil opening in the cooling oil collector can be configured as a usual, round opening, or, for example, 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. The cooling oil collector preferably has two or more cooling oil openings, so that a very precisely metered amount of cooling oil can flow out of the cavity in the direction of the piston pin. 
         [0025]    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 forged steel. The connection between the upper piston part and lower piston part can be produced in any desired manner. Welding, particularly friction welding, is a particularly suitable joining method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    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. 
           [0027]    In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
           [0028]      FIG. 1  shows a section through a first embodiment of a piston according to the invention; 
           [0029]      FIG. 2  shows a section through another embodiment of a piston according to the invention; 
           [0030]      FIG. 3  shows a section through another embodiment of a piston according to the invention; 
           [0031]      FIG. 4  shows a section through another embodiment of a piston according to the invention; 
           [0032]      FIG. 5  shows a perspective representation of the cooling oil collector according to  FIGS. 3 and 4 ; and 
           [0033]      FIG. 6  shows an enlarged representation of a detail from FIG.  3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0034]    Referring now in detail to the drawings,  FIG. 1  shows a first 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 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). 
         [0035]    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 , in the exemplary embodiment, and has a joining surface  24 . 
         [0036]    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 , and has a joining surface  28 . Pin boss supports  32  for connecting pin bosses  18  are provided below inner support element  25  of lower piston part  12 . 
         [0037]    Upper piston part  11  and lower piston part  12  can be joined in any desired manner, whereby joining surfaces  23  and  27 , and  24  and  28 , respectively, are connected with one another. In the embodiment shown, upper piston part  11  and lower piston part  12  were welded together. 
         [0038]    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 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 upper piston part  11  and inner support element  25  of lower piston part  12  delimit 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  furthermore delimit a cavity  31  that is open toward pin bosses  18 , which cavity is disposed essentially below piston crown  13 . 
         [0039]    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, the cooling oil channels can also be disposed exclusively or additionally in 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 . 
         [0040]    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, 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. Furthermore, cooling oil collector  35  is disposed in such a manner that its curvature is directed toward upper piston part  11 . 
         [0041]    A holding element  41 , which is configured as a separate component and consists of a metallic material, projects into the cavity  31  vertically in the direction of lower piston part  12 , proceeding from the underside of piston crown  13 , in the center axis M of piston  10 . At its free end that projects into cavity  31 , holding element  41  has a projection  44  that is surrounded by a circumferential contact shoulder. Projection  44  passes through a center bore  43  provided in cooling oil collector  35 , whereby the contact shoulder lies on the top of cooling oil collector  35 . Projection  44  is configured as a journal, and holding element  41  is riveted to cooling oil collector  35  by means of this journal. At its free end facing piston crown  13 , holding element  41  rests firmly against the underside of piston crown  13 . The length of holding element  41  is dimensioned in such a way that cooling oil collector  35  supports itself on inner support element  25  or on pin boss supports  32 , under spring bias, whereby flange  26  lies against inner support element  25  and brings about an additional friction fit between cooling oil collector  35  lower piston part  12 . Cooling oil collector  35  is therefore held in a particularly secure and play-free manner. 
         [0042]    Cooling oil collector  35  collects the cooling oil that passes through cooling oil channels  33 , out of outer cooling channel  29 , into cavity  31 , and guides it in the direction of the underside of 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  37 ,  38  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. 
         [0043]    For assembly of piston  10  according to the invention, first upper piston part  11 , lower piston part  12 , cooling oil collector  35 , and holding element  41  are produced as separate components. Then, holding element  41  is riveted to the cooling oil collector. Cooling oil collector  35  is inserted into lower piston part  12 , in the region of 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 any joining method that is selected, by way of joining surfaces  23 ,  27  and  24 ,  28 , respectively, in such a manner that cooling oil collector  35  is accommodated in cavity  31  in the finished piston, and that holding element  41  is pressed against the underside of piston crown  13 , so that it is held with force fit there. For stabilization, a recess in the shape of a flattened dome or cone, for example, can be provided on the underside of piston crown  13 , into which holding element  41  engages. 
         [0044]      FIG. 2  shows another embodiment of a piston  110  according to the invention. Piston  110  is identical in construction, in essential parts, with piston  10  according to  FIG. 1 , so that the same structures are provided with the same reference numbers, and reference is made to the description of  FIG. 1  with regard to these reference numbers. 
         [0045]    A significant difference as compared with piston  10  according to  FIG. 1  is that with piston  110 , holding element  141  is formed on, in one piece, on the underside of piston crown  13 , on lower piston part  111 . Furthermore, cooling oil collector  135  has a hat-shaped elevation  142 , which interacts with the free end of holding element  141 . The length of holding element  141  is dimensioned in such a way that cooling oil collector  135  supports itself on inner support element  25  or on pin boss supports  32 , under spring bias. Flange  26  lies against inner support element  25  and brings about an additional friction fit between cooling oil collector  135  and lower piston part  12 . Thus, cooling oil collector  135  is held in particularly secure and play-free manner. 
         [0046]    Of course, the cooling oil collector in both embodiments can also consist of a non-resilient, preferably metallic material, and be held in lower piston part  12  with force fit. 
         [0047]    For assembly of piston  110  according to the invention, first upper piston part  111  with holding element  141  formed onto it in one piece, lower piston part  12 , and cooling oil collector  135  are produced as separate components. In the embodiment shown, cooling oil collector  135  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  111  and lower piston part  12  are connected with one another, by any joining method that is selected, by way of joining surfaces  23 ,  27  and  24 ,  28 , respectively, so that cooling oil collector  135  is accommodated in cavity  31  in the finished piston, and that holding element  141  is pressed against hat-shaped elevation  142  of cooling oil collector  135 . 
         [0048]      FIGS. 3 ,  5  and  6  shows another embodiment of a piston  210  according to the invention. Piston  210  essentially corresponds to piston  10  according to  FIG. 1 , so that structural elements that agree with one another are provided with the same reference numbers. 
         [0049]    The significant difference consists in the cooling oil collector  235  of the piston  210  according to  FIG. 3  disposed in cavity  31 . cooling oil collector  235  and its placement in cavity  31  are also shown enlarged in  FIGS. 5 and 6 . 
         [0050]    In this embodiment, cooling oil collector  235  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 shallow dome, and has a thickness of about 0.8 mm. In contrast to cooling oil collector  35  according to  FIG. 1 , cooling oil collector  235  has a circumferential, spring-elastic edge  236  that is bent axially upward. Furthermore, cooling oil openings  237  and slits  238  are provided, which both increase the elasticity of edge  236  in the radial direction, and serve as additional cooling oil openings. 
         [0051]    Holding element  41 , as described for the piston  10  according to  FIG. 1 , ensures that cooling oil collector  235  supports itself on inner support element  25  or on pin boss supports  32 , under spring bias. In contrast to piston  10  according to  FIG. 1 , in the embodiment shown here, edge  236  touches the friction-weld bead  34  and supports itself on it, if necessary. 
         [0052]    In the embodiment shown here, cooling oil collector  235  is furthermore provided with a support element  251 . Support element  251  is configured as a separate component. However, it can also be configured in one piece with cooling oil collector  235 , and can be produced by punching it out from cooling oil collector  235 , for example. It is practical if support element  251  is also produced from a spring steel sheet, and it has three spring arms  252  that support themselves on the underside of the piston crown  13  of the piston  210  in the assembled state. Spring arms  252  go from a center hub  253 , which is attached to cooling oil collector  235  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  251  is connected with cooling oil collector  235  so that it can rotate. Support element  251  brings about additional spring-elastic securing of the position of cooling oil collector  235  in cavity  31 , which is therefore flexibly able to withstand stress during operation. 
         [0053]    The function and the assembly of cooling oil collector  235  are the same as described for the cooling oil collector  35 . 
         [0054]      FIG. 4  shows another embodiment of a piston  310  according to the invention. Piston  310  has the same construction, in essential parts, as piston  210  according to  FIG. 3 , so that the same structures are provided with the same reference numbers, and reference is made to the description of  FIG. 3  with regard to these reference numbers. 
         [0055]    The significant difference as compared with the piston  210  according to  FIG. 3  is that in the case of the piston  310  of  FIG. 4 , holding element  141  is formed on, in one piece, onto the underside of piston crown  13 , as is also the case in piston  110  according to  FIG. 2 . In the embodiment of  FIG. 4 , the length of holding element  141  is dimensioned in such a way that cooling oil collector  235  supports itself on inner support element  25  or on pin boss supports  32  under spring bias. Thus, the cooling oil collector  235  is held in particularly secure and play-free manner. 
         [0056]    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 in all the embodiments. 
         [0057]    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.