Abstract:
A piston ( 10, 10′ ) includes a piston body ( 12, 12′ ) having an upper crown portion ( 16, 16′ ) with an upper combustion dome ( 18, 18′ ) against which combustion forces act. The underside of the upper combustion dome ( 18, 18′ ) comprises an under-crown region ( 60, 60′ ). The piston body ( 12, 12′ ) also includes a lower crown portion ( 26, 26′ ) with a pair of pin bosses ( 36, 38 ) spaced apart for pivotally adjoining a connecting rod. An outer oil gallery ( 31, 31′ ) is formed as an inclusion between the upper ( 16, 16′ ) and lower ( 26, 26′ ) crown portions. The outer oil gallery ( 31, 31′ ) has an oil inlet ( 50, 50′ ) and an oil outlet ( 52, 52′ ). A tubular cooling nozzle ( 54, 54′ ) is affixed in fluid communication with the oil outlet ( 52, 52′ ) and extends toward the under-crown region ( 60, 60′ ) where oil is discharged during reciprocation of the piston ( 16, 16′ ). Cooling oil from the outer oil gallery ( 33 ) is channeled by the cooling nozzle ( 54, 54′ ) to the under-crown region ( 60, 60′ ) providing supplemental cooling in a passively actuated system.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Provisional Patent Application No. 61/168,291 filed Apr. 10, 2009, the entire disclosure of which is hereby incorporated by reference and relied upon. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to pistons for internal combustion engines, and more particularly to diesel pistons having internal oil cooling features. 
     2. Related Art 
     Hollow piston constructions for diesel engines are known for providing enhanced cooling capabilities, which in turn often yield improvements in exhaust emissions and extended service life. In these applications, the normal engine lubricating oil is used to help cool (convectively) the hot head, or specifically the under-crown region, as well as the outer ring belt region of the piston. In some hollow piston configurations, a single outer cooling gallery near the ring belt region may be used, or a central oil gallery under the crown region, or two galleries paired (dual galleries) in various combinations of open and closed geometries. Dual gallery pistons typically have an annular, radially outer cooling gallery and an open central cooling gallery formed between upper and lower crown portions. The outer and central galleries can either be isolated from one another or arranged in relatively open fluid communication with one another via multiple oil passages extending through intervening ribs. In addition, it is known to provide pin lubrication passages extending from one or both of the galleries to a wrist pin. The lubrication passages can, for example, extend into a wrist pin bore of a pin boss and/or between laterally spaced pin bosses. The outer gallery, whether formed as a single or dual gallery construction, is particularly suited for cooling a ring belt region of the piston, while the central gallery, if present, is particularly suited for cooling a central crown region formed in part by a combustion bowl wall or dome, which is directly exposed to hot combustion gasses. 
     The combustion dome and underlying central crown region (i.e., under-crown) are exposed to extreme heat in use. Without proper management of heat in this under-crown region, several problems can result. For example, it is possible that carbon build-up on the under-crown will form over time. This carbon build up will further reduce the heat transfer from the combustion bowl leading to higher temperatures on that region. This carbon build up can eventually flake off. Loose carbon flakes can be caught between moving components and cause scratches. Another problem associated with excessive heat build-up in the under-crown region relates to exhaust emissions. If combustion temperatures are not tightly controlled in diesel engines, the combustion process can not be optimally regulated for efficiency and emissions concerns. And further, if the piston temperatures are allowed to rise too high, the lubricating oil can become over-heated and begin to chemically break down prematurely, thus reducing its service life. 
     Over the years, engine designers have sought to provide sufficient oil flow in the central crown region while at the same time avoiding deterioration of the oil due to over-heating to avoid the aforementioned problems. If an insufficient supply of oil is directed to the under-crown region, or if the oil is allowed to remain in the region for too long, the oil over-heats and its cooling and lubrication functions are diminished. As such, an ample flow of cooling oil must be provided in order to properly regulate the temperature of the under-crown region. 
     There is therefore a need in the art for improved temperature management strategies in piston design, and in particular for the design of diesel pistons, that optimally cools the under-crown region with lubricating oil during use. 
     SUMMARY OF THE INVENTION 
     The invention contemplates a piston for an internal combustion engine having an upper crown portion and a lower crown portion. The upper crown portion includes an upper combustion wall against which combustion forces act, along with an under-crown surface formed on the undersurface of the upper combustion wall. The lower crown portion includes at least one pin boss for coupling to a connecting rod. An outer cooling gallery is formed between the upper crown portion and the lower crown portion. An oil inlet communicates directly with the cooling gallery for conducting oil into the outer cooling gallery. An oil outlet is spaced from the inlet and communicates directly with the outer cooling gallery for conducting oil out of the outer cooling gallery. A cooling nozzle is provided communicating directly with the outlet for conducting at least a portion of oil exiting the outer cooling gallery through the outlet toward the under-crown. The cooling nozzle enables oil to be routed or channeled from the outer cooling gallery and sprayed generally toward the under-crown in response to reciprocating motion of the piston when in operation. In addition to enhanced cooling properties, the cooling nozzle is well-suited to provide a sufficient supply of oil to the under-crown so that the oil will not over-heat. 
     According to another aspect of this invention, a method is provided for cooling a reciprocating piston with oil in an internal combustion engine. The method includes the steps of providing a piston having an upper combustion wall against which combustion forces act, an internal outer oil gallery and an under-crown region directly below the upper combustion wall and generally concentrically disposed relative to the outer cooling gallery. The piston is reciprocated in an internal combustion engine generally along a central reciprocating axis. Simultaneously with the reciprocating step, a flow of cooling oil is directed into the outer oil gallery. Cooling oil inside the outer oil gallery drains from through an outlet. The method further includes the step of channeling the cooling oil drained from the outer oil gallery to the under-crown through a cooling nozzle. 
    
    
     
       BRIEF DESCRIPTION OF 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 cross-sectional view of a dual gallery piston taken generally through the pin bore axis and constructed in accordance with one embodiment of the invention; 
         FIG. 2  is a cross-sectional view taken generally along lines  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of an alternative single gallery piston embodiment taken generally perpendicular to the pin bore axis; and 
         FIG. 4  is a cross-sectional view taken generally along lines  4 - 4  in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the figures wherein like numerals indicate like or corresponding parts throughout the several views,  FIG. 1  illustrates a dual gallery type diesel piston  10  constructed in accordance with one embodiment of the invention. The piston  10  has a piston body  12  extending along a central axis  14  that generally coincides with the reciprocating path of the piston  10  within a cylinder bore (not shown). The piston body  12  includes an upper crown portion  16  having an upper combustion wall or dome  18 , represented here, by way of example and without limitation, as having a recessed combustion bowl  20 , against which combustion forces directly act in the cylinder bore, thereby providing a location for extreme heat generation. An under-crown  60  is formed on the opposite side of the upper combustion wall  18  beneath the combustion bowl  20 . The upper crown portion  16  is preferably formed as a separate, or loose, piece and then subsequently assembled as part of the piston  10 . In its initial, loose-piece state, the upper crown portion  16  has at least one, and shown here a pair, of annular upper ribs  22 ,  24 . These ribs are referred to hereafter as an upper inner rib  22  and upper outer rib  24 , and they each depend from the upper combustion wall  18  to respective free ends (in the pre-assembled condition). 
     The piston body  12  further includes a lower crown portion  26  that is also preferably pre-formed as a component and then subsequently assembled to the upper crown portion  16 . The lower crown portion  26  has at least one, and shown here a pair, of annular lower ribs  28 ,  30 . These ribs are referred to hereafter as a lower inner rib  28  and lower outer rib  30 , and extends to respective free ends (in the pre-assembled condition) arranged in alignment for fixed abutment with the respective free ends of the upper inner and outer ribs  22 ,  24  to form and separate an outer cooling gallery  31  from a central crown region, also referred to as a central cooling gallery  33 . These opposing ribs can be joined by any suitable means including, for example, friction welding, resistance welding, stir welding, bonding, mechanical interlock, and the like. 
     The lower crown portion  26 , in this example, has an inner gallery floor  32  provided by an annular flange  34  extending radially inwardly from the lower inner rib  28  toward the central reciprocating axis  14 . The lower crown portion  26  has an outer gallery floor  48  extending laterally between the lower inner and outer ribs  28 ,  30 . At least one, but normally a pair of pin bosses  36 ,  38  depend generally from the outer and central galleries  31 ,  33  to provide wrist pin bores  40 ,  42  aligned along a pin axis  44  for pivotally connecting a wrist or gudgeon pin (not shown). A space  46  provided between the pin bosses  38 ,  40  accommodates the small end of a connecting rod (not shown) in the usual manner. 
     As shown in  FIG. 2 , the outer gallery floor  48  has a through opening providing an oil inlet  50  to allow oil to admit oil into the outer gallery  31  by any of the traditional methods. Another through opening provides an oil outlet  52  to allow oil to exit from the outer gallery  31 . A cooling nozzle  54  extends from the oil outlet  52  and is routed radially inwardly toward the under-crown  60 . The cooling nozzle  54  passively channels oil flowing outwardly from the outer oil gallery  31  to the under-crown  60 . More specifically, during upward movement of the piston  10 , inertial forces act on the oil contained within the outer gallery  31  which have the effect of pushing the oil toward the floor  48  and out through the oil outlet  52 . Naturally, the oil will move freely through the outlet  52  and into the cooling nozzle  54 . The forces of a reciprocating piston are sufficiently large enough that the oil will be pushed though the cooling nozzle  54  with relatively high velocity, resulting in a forceful squirt of oil onto the under-crown surface  60  with each upward stroke of the piston  10 . Although preferably tubular in shape, the cooling nozzle  54  may be shaped by any suitable device or method, including integral formations in the piston body  12 . As such, an improved oil flow is provided beneath the combustion bowl  20  to provide enhanced cooling to the under-crown region  60  without over-heating the oil. 
     The upper crown portion  16  is represented as having an annular outer oil gallery pocket  56  extending from the inner and outer rib free ends upwardly into an upper ring belt region  58  in this example. However, these particular design details are subject to revision depending upon the particular application or other parameters. 
     The lower crown portion  26  may be formed in a casting or forging process from steel or other metal, having an annular outer oil gallery pocket  62  extending from the inner and outer rib free ends downwardly into a lower ring belt region  64 . Upon attaching the upper crown portion  16  to the lower crown portion  26 , the annular outer oil gallery, represented here as a substantially closed outer oil gallery  31 , and the open inner or central cooling gallery  33  are formed. The outer oil gallery  31  is bounded by the outer ribs  24 ,  30  and inner ribs  22 ,  28  while the central oil gallery  33  is bounded at its outer periphery by the inner ribs  22 ,  28  and at its upper surface by the dome  18 . 
     In appropriate circumstances, it may be desirable to provide one or more supplemental oil flow passages in the lower ribs  32 ,  34  and/or through the annular inner ribs  22 ,  28 . For example, as shown in  FIGS. 1 and 2 , a supplemental oil passage  66  may be formed through the lower inner rib  28  in preferably ascending relation from a lower most portion of the outer oil gallery  31  to a floor of the central oil gallery pocket  33  formed by the flange  34 . As the piston reciprocates, the ascending passage(s)  66  allows additional cooling oil to be shaken through from the outer gallery  31  into the central gallery region  33 . Through a sloshing effect, oil in the central gallery region  33  will be splashed against the under-crown  60  before it falls though the central opening inside the flange  34  and eventually rejoins the general reserve of lubricating oil in the engine. 
     To facilitate cooling the piston  10 , the respective inlet and outlet oil flow openings  50 ,  52  may be oriented with respect to one another in any suitable arrangements.  FIG. 2  shows these features passing through the floor  48  of the outer oil gallery  31  in diametrically opposed relation to one another, and formed generally 45 degrees offset from the wrist pin axis  44 . This is but one example, and it is contemplated that other geometric relationships may provide acceptable performance. In any event, oil from the engine crankcase will flow upwardly into the outer oil gallery  31  through the inlet opening  50 , whereupon the oil is circulated about the outer oil gallery  31  and channeled downwardly out of the outer oil gallery  31  through the outlet opening  52  and through the cooling nozzle  54  where it is forcefully squirted against the under-crown  60 . If the piston  10  is fitted with the optional oil flow passage  66  or other supplemental outlet feature, oil within the outer gallery  31  that is not channeled through the cooling nozzle  54  will exit through the oil passage  66 . 
     The cooling nozzle  54  preferably has one end  68  attached to the outer gallery floor  48  with a coupling  69 . The coupling  69  is in fluid communication with the outlet opening  52 . An opposite end  70  of the cooling nozzle  54  extends in somewhat cantilevered fashion toward and/or into the central oil gallery  33 . The coupling  69  of the cooling nozzle  54  can be attached using any suitable technique, e.g., snap in, force fit, interlock, threaded attachment, bonding or welding, to name a few. Supplemental attachment of the cooling nozzle  54  along its length to the lower crown portion  26  may be accomplished, if desired, such as by a bracket or clip (not shown). Installation of the cooling nozzle  54  can be accomplished prior to joining the lower crown portion  26  to the upper crown portion  16  or after joining. The cooling nozzle  54  can be constructed from any suitable type of metal or from a high-temperature rated polymeric, plastic material. Lighter weight materials would be favored to reduce the effects of inertia on the cooling nozzle  54 , coupling  69  and any bracketry during operation. 
     The cooling nozzle  54  can be configured as may desired to suit a particular installation or application. The cooling nozzle  54  is shown in  FIGS. 1 and 2  bent in a generally U-shape, and having a generally uniform inner diameter. Of course, the length and passage configuration of the cooling nozzle  54  may be re-configured as needed to more effectively spray oil from the outer gallery  31  upwardly onto the under-crown region  60 . As such, the oil flowing from the outer gallery  31  is re-circulated to help manage the temperature of the under-crown region  60  without over-heating the oil. 
       FIG. 3  is a cross-sectional view of an alternative single gallery piston embodiment  10 ′ taken generally perpendicular to the pin bore axis  44 ′. For convenience, in this alternative embodiment, like or corresponding reference numerals are re-used but with prime designations throughout both  FIGS. 3 and 4 . The reader is directed to the preceding text for a complete description of the components referenced in  FIGS. 3 and 4 . 
     In this alternative embodiment, the piston  10 ′ does not have a central oil gallery. Therefore, in this application, the cooling nozzle  54 ′ enables an intentional, meaningful and reliable application of cooling oil to the under-crown region  60 ′ which would not otherwise be possible. As in the preceding example, the cooling nozzle  54 ′ is attached at one end  68 ′ to the floor  48 ′ of the outer oil gallery  31 ′ via a coupling  69 ′. The opposite end  70 ′ of the cooling nozzle  54 ′ is routed inwardly and upwardly toward the under-crown region  60 ′.  FIG. 4  illustrates the manner in which the location of the cooling nozzle  54 ′ is selected to avoid interference with the pin bosses, similar to the first described embodiment. Discharge from the end  70 ′ of the cooling nozzle  54 ′ is preferably along a vector that intersects the central reciprocating axis  14 ′. 
     As with the first described example, the cooling nozzle  54 ′ operates as a passive system, automatically channeling oil in direct response to the reciprocating motion of the piston  10 ′. This results due to inertial forces generated by a reciprocating piston  10 ′ acting on the oil in the outer gallery  31 ′, with inertia fluctuations that result from changes in engine RPM. The faster the piston  10 ′ reciprocates (i.e., at higher RPM), the more oil will be circulated and greater heat transfer is possible. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, it is contemplated that the piston  10 ,  10 ′ could be constructed as a closed gallery articulated design. In addition, it is contemplated that a plurality of cooling nozzles  54 ,  54 ′ could be incorporated, as desired. Other configurations are likewise possible. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 
     The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention.