Abstract:
A piston assembly includes a piston head having an open bottom cooling gallery and a pair of pin bosses depending from the head and supporting a wrist pin of a connecting rod. A skirt is coupled to the pin bosses for reciprocation with the piston head. A stationary oil spray nozzle extends into the piston skirt from below and cooperates with an oil splash deflector which, at a lowered position of the piston head, directs the flow of oil onto the pin bosses for direct cooling, and at raised position of the piston head, moves out of the way to allow the cooling oil to enter the cooling gallery and cool the piston head.

Description:
The disclosure incorporates the heavy duty piston having oil splash deflector and method of cooling a piston disclosed in provisional application No. 60/192,593, filed Mar. 28, 2000, whose priority date is claimed for this application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates generally to heavy duty pistons for diesel engine applications, and more particularly to the management of cooling oil in articulated pistons. 
     2. Related Art 
     Articulated pistons of conventional construction are often formed with a circumferentially extending cooling gallery in the piston head which is open to the bottom and communicates with one or more oil spray nozzles which extend into the skirt of the piston from below and direct a spray of cooling oil into the cooling gallery as the piston reciprocates in the piston cylinder to provide cooling. Lubrication of the pin bores and wrist pin are usually taken care of by internal oil porting. Any cooling of the pin bores and wrist pin are derived from the lubricating oil. In some applications, the pin bosses, their pin bores, bushings and wrist pin can be heated above desired temperatures which can impair the performance and longevity of the piston. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     A piston assembly constructed according to the invention includes a piston head having an open bottom cooling gallery formed in a bottom surface of the piston head, a pair of pin bosses depending from the piston head and having pin bores for supporting a wrist pin of a connecting rod, a piston skirt coupled to the pin bosses for reciprocal movement with the piston head, and a stationary oil spray nozzle extending into the piston skirt and having an outlet position for directing a flow of cooling oil along a path toward the cooling gallery. An oil deflector shield is carried by the piston skirt in position to substantially obstruct the flow of cooling oil to the cooling gallery and to direct the obstructed flow onto the pin bosses when the piston head is moved to a lowered position. The oil deflector shield is positioned also to move substantially out of the path of the cooling oil to cause the cooling oil to be directed into the cooling gallery when the piston head is moved to a raised position. 
     The invention also contemplates a method of cooling a reciprocating piston which employs the mentioned deflector shield which operates to selectively obstruct the flow of cooling oil to the cooling gallery when the piston is at the bottom of stroke position in order to attain, during a portion of the piston stroke, direct cooling of the pin bore regions of the piston. This invention has the advantage of providing direct cooling to the cooling gallery of the piston head at times during the stroke of the piston when cooling of the head is needed most, namely when the piston is toward the top of stroke position where it sees the most heat and thus requires the most cooling. As the piston travels toward the bottom of stroke position, the piston head is moved away from the heat of combustion so as to lessen the cooling requirements and, according to the invention, the deflector is operative during this time to redirect the cooling oil onto the pin boss regions so that the pin boss regions are directly cooled at a time during the piston cycle when the cooling of the head is less critical. 
     The invention thus has the advantage of providing direct cooling of the pin boss regions without impairing the efficient cooling of the piston head. 
     The invention has the further advantage of achieving cooling of the piston head and pin bores with use of a single oil spray nozzle in conjunction with the deflector. 
    
    
     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 piston assembly constructed according to the invention shown coupled to a fragmentarily illustrated connecting rod; 
     FIG. 2 is a plan view of the piston skirt as viewed generally along lines  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional view taken generally along lines  3 — 3  of FIG. 2; 
     FIG. 4 is a sectional view taken generally along lines  4 — 4  of FIG. 2; and 
     FIG. 5 is a sectional view taken generally along lines  5 — 5  of FIG. 2 showing the piston skirt moved between the upper solid line position and the lower broken line position with the stroke of the piston. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, FIG. 1 shows an articulated piston assembly  10  having a head or crown  12  and a separately formed skirt  14  coupled to the crown  12  in the usual manner by a wrist pin  16 . 
     Referring also to FIGS. 2 and 3, the crown  12  has a central dome portion  18  with a contoured upper surface defining a combustion bowl  20 . Surrounding the dome portion  18  is an annular ring belt portion  22  extending downwardly from an upper face  24  of the crown  12  to a lower face  26 . A plurality of ring grooves  28  are formed in an outer surface  30  of the ring belt portion  22 . Between the ring belt  22  and dome portion  18 , radially spaced walls  32 , 34  define an oil cooling chamber or gallery  36  which, in this particular illustrated embodiment, is open to the bottom for receiving cooling oil L into the gallery  36  from below issuing from one or more oil spray nozzles  38  of an engine (not shown) in which the piston is mounted. 
     Extending downwardly from the dome portion  18  are a pair of laterally spaced pin bosses  40  formed with aligned pin bores  42  for accommodating the wrist pin  16 . In many applications, including the illustrated embodiment, the pin bores  42  are lined with a bushing  44  to serve as a bearing surface for the wrist pin  16 . However, not all applications will require the bushing  44  and the present invention can be practiced with or without the bushing  44 . The wrist pin  16 , of course, couples the piston assembly  10  to the upper end of a connecting rod  45  (schematically shown in FIG. 1) in the usual manner for reciprocating the piston assembly  10  within a cylinder bore (not shown) in typical manner by means of a crank shaft (not shown) with which the other end of a connecting rod  45  is coupled. FIG. 4 illustrates the skirt  14  of the piston assembly  10  near the top of its stroke, whereas FIG. 3 illustrates the piston assembly  10  near a mid stroke and on the way to a bottom of stroke position within the cylinder. FIG. 5 shows the skirt in both positions, with the upper solid line position representing the location of the skirt  14  near top dead center, and the broken chain line position representing the position of the skirt  14  near bottom dead center. The positioned relationship of the skirt relative to the fixed direction flow path of cooling oil L is also illustrated in FIG. 5, as will be discussed further below. The oil spray nozzle  38  is fixed relative to the reciprocating piston in thus the piston assembly  10  moves toward and away from the nozzle  38  in operation. 
     The piston skirt  14  has a pair of partial-cylindrical skirt portions  46  spaced radially outwardly of the pin bosses  40  joined by a pair of end walls  48  extending across the pin bosses  40  in laterally outwardly adjacent relation thereto. The end walls  48  have pin boss openings  50  aligned with the pin bores  42  of the pin bosses  40 . Receipt of the wrist pin  16  in the pin boss openings  50  of the skirt operate to couple the skirt  14  to the crown  12  in articulated fashion, such that the skirt  14  is able to move or rock slightly relative to the crown  12  about the axis of the wrist pin  16 . The skirt  14  has an upper face  52  that is spaced from the lower face  26  of the crown such that the skirt  14  is uncoupled from the crown  12  and joined only through the wrist pin  16 . The crown  12  may be fabricated of steel, whereas the skirt  14  may be fabricated of aluminum or the like. Of course, other material selections are contemplated by the invention, including a steel crown in steel skirt, an aluminum crown and skirt, or variations thereof. 
     As best shown in FIG. 2, the upper end  52  of the skirt  14  is formed with at least one and preferably a plurality of oil reservoirs in the preferred form of cup formations  54  that project radially inwardly of the skirt portions  46  in circumferentially spaced relation to the oil spray nozzle or nozzles  38 , so as to lie outside of the direct spray path of the nozzle, assuring that the cups  54  do not obstruct the direct flow of cooling oil issuing from the nozzle  38  from below into the oil cooling gallery  36 . As the cooling oil runs out of the cooling gallery  36  through its open bottom, some of the oil is captured by the cups  54  so as to provide a “cocktail shaker action” which redirects the captured oil back into the cooling gallery  36  during rapid reciprocating movement of the piston assembly  10  during operation. The cups  54  are partitioned from one another such they form discrete reservoirs. 
     According to the invention, the skirt  14  is further fitted with an oil deflector  56  which operates at least during a portion of the stroke of the piston assembly  10  to direct all or some of the jet of cooling oil issuing from the spray nozzle  38  onto the wrist pin and pin boss portion  40  of the assembly  10  so as to cool the wrist pin  16  and the pin bosses  40 , particularly in the vicinity of the pin bores  42  so as to cool the bearing surface between the pin bosses and wrist pins  16 . In the illustrated example, the pin bores  42  are fitted with bushings  44 , and the deflected oil serves to cool the bushings during operation. 
     The deflector  56  is similar in construction to the oil cooling cups  54 , but is generally wider and oriented on the skirt  14  so as to lie in the path of the jet of cooling oil issuing from the spray nozzle  38  over a portion of the stroke S of the piston (see FIG.  5 ). The deflector  56  presents a deflector wall  58  projecting radially inwardly from the inner wall of the skirt portion  46 , as shown best in FIGS. 2,  3  and  5 . The deflector wall  58  is oriented relative to the oil spray nozzle  38  such that as the piston moves to an upper position toward the top of the stroke of the piston assembly  10  where the crown  12  is exposed to the hot combustion gases, (FIG.  3  and solid line position of FIG. 5) the angle of incidence of the oil spray issuing from the spray nozzle  38  allows a substantial flow of the oil L to pass by the deflector  58  and be directed into the cooling gallery  36  of the crown  12 , for cooling the upper surface  24  and ring belt portion  22 . Circumferentially adjacent the deflector  58  is a recess  59  which is positioned relative to the oil flow L so as to provide passage of the oil L around the deflector  58  and into the gallery  36  when the skirt  14  is moved with the piston to the upper position. As the piston moves downwardly in its stroke to a lowered position toward the bottom of stroke position, the deflector wall  58  enters the path of the oil stream L, as illustrated in FIGS. 2,  3  and  5 , causing obstruction of the flow to the cooling gallery  36  such that a substantial portion of the oil stream L is deflected radially inwardly so as to splash onto the wrist pin  16 , pin bosses  40  and the bushings  44  for cooling these regions of the piston assembly  10  during operation. 
     The nozzle  38  is disposed at an angle relative to the longitudinal axis of the piston skirt  14  (see FIG. 5) such that the oil flow L can bypass the deflector  58  as the piston  10  nears the top of stroke, while entering the path near the bottom of stroke to selectively deflect the oil flow. 
     The upper surface of the oil deflector  56  has a cup-like recess  60  which, like the cups  54 , serves to capture oil running out of the cooling gallery  36  for redirecting such supplemental oil back into the cooling gallery for enhanced cooling. 
     In the preferred embodiment, the oil deflector feature  56  is formed as one piece with the piston skirt  14 , and as such may be cast or forged therewith. Alternatively, the deflector feature  56  could take the form of a welded or bolted on component, although the one-piece structure is preferred. 
     Obviously, many modifications and variation of the present invention are possible in light of the above teachings. 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 invention is defined by the claims.