Abstract:
A heavy duty diesel piston includes upper and lower portions joined across a friction weld and internally contoured to provide a dual gallery structure including an outer annular gallery and a central gallery joined by passages for communicating cooling oil therebetween. The dual-gallery structure allows oil to enter from the outer gallery, which is formed by the circumferential annular recess in the crown and crown bottom, into the central gallery to cool the piston and particularly the central crown region exposed to hot combustion gases. The friction weld provides high structural integrity and minimizes the number of manufacturing steps need to attach the crown to the crown bottom.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/158,510, filed Oct. 8, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention is directed to pistons for heavy duty diesel engine applications, and more particularly to the formation of such pistons having internal galleries for cooling oil. 
     2. Related Art 
     Piston structures having two closed galleries are known, for example, in U.S. Pat. Nos. 3,613,521; 4,581,983; 4,662,319; and 4,532,686. 
     In each of the patents, upper and lower crown parts are separately formed and then joined across mating surfaces to define an inner and outer chamber within the piston body. In U.S. Pat. No. 3,613,521, the crown parts are joined by brazing through provision of a gap at the bottom of annular grooves machined in the lower crown part in which annular ribs of the upper crown part are received. U.S. Pat. No. 4,581,983 joins the upper crown part to the lower crown part by means of charge carrier rays. U.S. Pat. No. 4,662,319 presents a complex arrangement of internal chambers and passages which would be extremely costly to produce. U.S. Pat. No. 4,532,686 provides dual chambers but which are not in fluid communication with one another for the flow of cooling oil from one chamber to the other. 
     It is an object of the present invention to improve upon dual gallery pistons to provide an efficient, robust piston structure. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, an articulated piston assembly for heavy duty diesel engine applications is provided comprising a piston body including a one piece upper crown part and a one piece lower crown part in conjunction with an articulated piston skirt provided as a separate structure from the piston body. The upper crown part has a lower connecting portion formed with inner and outer annular ribs which are spaced from one another and extend axially to free ends each presenting a planar joining surface of the ribs. The lower crown part has an upper connecting portion from which a pair of pin boss portions depend having a space between them to receive a connecting rod. The upper connecting portion has inner and outer annular ribs extending axially to free ends thereof each presenting a planar joining surface of the lower crown part ribs. The lower crown part further has an inner gallery floor arranged above the space between the rib bosses and surrounded by the inner annular rib of the lower crown part. According to the invention, the inner and outer ribs of the upper and lower crown parts are joined across their respective joining surfaces by friction weld joints to define an inner and outer oil gallery within the joined crown parts separated by the inner ribs. The inner rib of the lower crown part is formed with at least one fluid transfer port spaced axially from the joining surface thereof and extending between the outer oil gallery and the inner oil gallery to establish fluid communication therebetween. 
     The inner gallery floor includes an opening establishing fluid communication between the inner gallery and the space between the pin bosses. 
     According to a further aspect of the invention, a monobloc piston assembly for heavy duty diesel engine applications is provided having one piece upper and lower crown parts sharing the same features as the articulated piston above, except that in place of the articulated piston skirt, the monobloc piston has a skirt which is formed as one piece with the pin bosses as an integral structure of the lower crown part. 
     The invention has the advantages of providing upper and lower crown parts joined by friction welding to define dual galleries within the piston structure to provide a high integrity connection between the upper and lower crown parts which is superior to brazing or charged carrier rays of the known prior art pistons above having communicating dual oil galleries. 
     The invention further provides a simple dual gallery structure which is highly effective at cooling the upper region of the piston with cooling oil that circulates within and between the chambers to extract heat from the piston. 
     Another advantage of the friction welding process employed in joining the upper and lower crown parts is that the inner and outer ribs can be friction welded simultaneously in a single operation. 
    
    
     THE DRAWINGS 
     These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein: 
     FIG. 1 is a schematic exploded perspective view of an articulated piston body constructed according to a first embodiment of the present invention; 
     FIG. 2 is a schematic section view of the piston body of FIG. 1; 
     FIG. 3 is a perspective elevational view, shown partly in section, of the completed piston assembly; and 
     FIG. 4 is a perspective elevational view of a piston constructed according to an alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring initially to FIGS. 1-3, a piston sub-assembly or body  100  according to the invention has an upper crown part  102  and a lower crown part  104  to be connected together and thereafter coupled to an articulated skirt  103  (FIG. 3) to provide a piston assembly  105  of FIG.  3 . 
     To form a preferred dual-gallery structure, the upper crown part  102  is provided with a circumferential annular recess  101  and a central recess  106 . The recess  101  is defined by an inner annular rib  107  and an outer annular rib  109  which is spaced radially outwardly of the inner rib  107 . The ribs  107 ,  109  depend from a connecting portion  111  of the upper crown part  102  and extend axially in substantially parallel relation to a longitudinal axis A of the piston body  100  including their wall surfaces adjacent the free ends. A first joining or welding surface  108  is provided at a free end of the outer rib  109  and is disposed around the circumferential annular recess  101  and is preferably flat or planar for mating with a corresponding joining or welding surface  116  provided on the free end of an outer annular rib  115  projecting axially from a connecting portion  117  of the lower crown part  104 . 
     Similarly, a second welding surface  110  is provided on the free end of the inner rib  107  of the upper crown part  102  and borders the recess  101  and is also preferably flat or planar for mating with a corresponding joining surface  118  provided on the free end of an inner rib  113  projecting axially from the connecting portion  117  of the lower crown part  104 . The rib  113  extends preferably in generally parallel relation to the axis A of the piston  100 . The upper crown part  102  and lower crown part  104  can be made of any known material appropriate to piston structures and suitable for friction welding, such as steel of identical or different compositions. The upper and lower crown parts  102 ,  104  can be made of a different material than that employed for the piston skirt  105  which may be made of aluminum, for example. 
     The lower crown part  104  includes pin boss portions  121  depending from the connecting portion  117  and separated by a space  127  formed with pin bores  121   a  in which bushings (not shown) may be disposed for receiving a wrist pin  119  in conventional manner to couple the piston  107  to a connecting rod (not shown) and to couple the articulated skirt  103  to the piston body  100 . The lower crown part  104  may also have a circumferential annular recess  112  and a central recess  114 , which correspond to the circumferential annular recess  101  and the central recess  106  in the upper crown part  102 . The lower crown part  104  may have other recess configurations than that shown as long as the lower crown part  104  has a shape appropriate for friction welding to the upper crown part  102 . 
     To accommodate friction welding of the crown parts  102 ,  104 , the lower crown part  104  has a third welding surface  116  and a fourth welding surface  118 . The third welding surface  116  is shaped to mate with the first welding surface  108  on the upper crown  102 , and the fourth welding surface  118  is shaped to mate with the second welding surface  110  on the upper crown. Preferably, all of the welding surfaces  108 ,  110 ,  116 ,  118  are flat and planar. The third welding surface  116  is preferably disposed around the central recess  114 . 
     To form the piston sub-assembly  100 , the crown  102  and the crown bottom  104  are positioned to align the first and third welding surfaces  108 ,  116   310  together and the second and fourth welding surfaces  110 ,  118  together. The welding surfaces  108 ,  110 ,  116 ,  118  then bonded together via friction-welding. For example, the crown  102  and crown bottom  104  can be pressed together and spun about the axis A against each other to generate friction necessary to bond the upper crown part  102  and lower crown part  104  together. Preferably, all of the corresponding welding surfaces  108 ,  110 ,  116 ,  118  are welded together in a single manufacturing step, which can be achieved if all of the welding surfaces  108 ,  110 ,  116 ,  118  mate with each other simultaneously. Because the joining surfaces of the upper crown  102  and lower crown  104  do not have slots, which are often used in other welding processes, the flat surfaces greatly simplify the friction welding process, reducing the manufacturing time. 
     Once the upper crown part  102  and the lower crown part  104  are friction-welded together to provide friction weld joints  106   b,    106   g  at the interfaces, the resulting piston sub-assembly  100  has an inner oil gallery  120  and an outer annular gallery  122 . The inner gallery  120  is formed by the combined central recesses  106 ,  114  of the upper crown part  102  and the lower crown part  104 , respectively. Similarly, the outer gallery  122  is formed by the combined circumferential recesses  105 ,  112  of the upper crown part  102  and the lower crown part  104 , respectively. 
     Referring to FIG. 3, a series of transfer holes  123  are provided in the inner rib  113  and extend between and establish fluid communication of the outer gallery  122  and inner gallery  120 . Oil inlet holes  125  extend from the pin boss opening  121   a  into the outer gallery  122 . The transfer holes  123  are spaced axially below the friction weld joints  106   b,    106   g.    
     The inner gallery  120  has a generally dome-shaped configuration and includes a lower cylindrical section  106   a  extending across the friction weld joint  106   b  for ease of alignment and welding. A concave upper section  106   c  extends across and closes the upper end of the gallery  120 . A relatively thin annular floor portion  106   d  extends from the lower extremity of the cylindrical section  106   a  and serves to close the bottom portion of the gallery  120 . The floor portion  106   d  is formed with a central opening  106   e  communicating externally of the chamber  120  with the space  127  between the pin bosses  101 . The opening  106   e  is surrounded by an upstanding annular rim or dam  106   f.  It will be seen from the drawing FIGS. 1-3 that all corners of the chamber  120  are rounded (i.e., where the various wall portions transition into one another and change angle), to prevent the entrapment or accumulation of oil in the corners. 
     The floor  106   d  is spaced axially below the joining surface  118  of the inner rib  113 . The outer gallery  122  has a floor  124  spaced axially below the joining surfaces  116 ,  118  and preferably below the inner gallery floor  106   d.  The transfer holes  123  extend upwardly at an angle from the outer gallery  122  to the inner gallery  120 . The transfer holes  123  are preferably spaced above the floor  124  of the outer gallery  122  in order to retain an amount of cooling oil in the outer gallery  122 . The transfer holes  123  preferably enter the inner gallery  120  at floor level. 
     In operation, cooling oil is pumped through the oil inlet holes  125  under pressure into the outer chamber  122  where it cools the outer oil ring section of the crown  102 . From there, the oil flows into the inner gallery  120  through transfer holes  123 . As illustrated in the referenced drawings, the holes  123  enter the gallery  120  at or near the floor portion  106   d,  and preferably in the corner transition region between the floor  106   d  and the cylindrical portion  106   a.  The holes  123  are thus formed in the lower crown portion  104  below the weld joint  106   b.  The upward angle of the transfer holes  123  helps move the oil from the outer gallery  122  to the inner gallery  120 . As the piston  105  reciprocates, the oil on the downstroke of the piston  105  is launched relatively upwardly where some of the oil enters and passes with considerable velocity and turbulence through the transfer holes  123  and into the inner gallery  120 . 
     An outer surface  126  of the crown section  106   c  is contoured to provide a bowl configuration exposed to hot combustion gases in operation. During the up and down reciprocating movement of the piston  105 , the oil in the inner  120  and outer  122  galleries is splashed about with a “cocktail” shaker action to cool the walls of the chambers  120 ,  122  to extract heat therefrom. The rim  106   f  contains a certain volume of the oil within the inner chamber  120  when at rest and allows oil above the level of the dam  106   f  to drain from the chamber  120  through the drain hole  106   e  where it falls back to the crank case (not shown). 
     The friction-welded joint  106   b,    106   g  between the upper crown part  102  and the lower crown part  104  ensures maximum structural integrity of the piston sub-assembly  100 . The friction weld also prevents potential loosening between the upper crown part  102  and the lower crown part  104  due to the different expansion rates of the different materials. 
     FIG. 4 illustrates an alternative embodiment of the invention wherein like reference numerals are used to represent like features but are offset by  100  (i.e., in the 200 series). The piston  205  is of a monobloc construction, wherein the skirt  203  is fabricated as one unitary piece with the lower pin boss portion  221 , such as casting or forging to provide a unitary lower crown/skirt portion CS. The unitized portion CS and upper crown section  202  are joined across the same type of co-planar mating surface  208 ,  210 ,  216 ,  218  at friction weld joints  206   b,    206   g , to provide similar inner  220  and outer  222  chambers having similar wall portions, passages, holes, etc., with the flow of oil through the chambers  220 ,  222  being the same. It will be seen from FIG. 4 that the floor portion  206   d  of the central chamber is convex dome-shaped, such that the oil runs radially outwardly toward the lower peripheral corner regions  206   g,  which resides below the level of the central drain hole  223 . As such, the rim  206   f  is not needed for containing a certain volume in the chamber  220 . The convex geometry of the floor portion  206   d  achieves this. 
     The floor  224  of the outer gallery  222  preferably extends into the skirt  203  and preferably below the apex or upper margin (i.e., highest point) of the pin bores  221   a,  as shown in FIG.  4 . The port  223  is well above the floor  224  yet is still set at the upward angle. 
     Accordingly, the present invention provides a dual gallery piston and manufacturing method wherein upper and lower sections are joined by welding and internally configured to provide inner and outer oil cooling chambers that are in flow communication with one another. The friction joint allows increases flexibility in distributing mechanical loads and selecting the size and location of the dual oil galleries. Because the piston sub-assembly  100  and skirt are separate in an articulated piston (FIGS.  1 - 3 ), they can be made from different materials to create the articulated piston (e.g., an aluminum skirt with a steel sub-assembly  100 ). 
     The disclosed embodiments are representative of presently preferred forms of the invention, but are intended to be illustrative rather than definitive thereof The invention is defined in the claims.