Patent Publication Number: US-10774781-B2

Title: Piston with anti-coking design features

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates generally to pistons for internal combustion engines, and more particularly to pistons having cooling galleries. 
     2. Related Art 
     Pistons for internal combustion engines oftentimes have a single outer cooling gallery, a central cooling gallery, or two cooling galleries (dual galleries). The dual gallery pistons have an annular, radially outer cooling gallery which is substantially closed and an open central cooling gallery formed between upper and lower crown portions. During operation, cooling oil is contained in or sprayed into the cooling galleries to reduce the temperature of the surround metal body. However, oil deposits oftentimes accumulate on the inner walls bounding the cooling galleries, particularly the closed or substantially closed outer cooling gallery. As the oil deposits accumulate, the cooling effectiveness of the oil circulating therein diminishes. 
     These oil deposits, also referred to as oil coking, in the cooling galleries, is generally associated with high thermally loaded steel pistons. To reduce oil coking, coatings have been applied to the inner surfaces of the cooling galleries. However, the coating solutions and other known solutions to oil coking, are oftentimes expensive or not preferred for other reasons. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention provides a piston with anti-coking design features that are oftentimes preferred over the coatings and other known solutions to oil coking. The piston comprises a piston body including an upper crown portion with an upper combustion wall and a lower crown portion. The upper crown portion and the lower crown portion form an outer cooling gallery therebetween. The lower crown portion presents an outer gallery floor of the outer cooling gallery. The outer gallery floor has an oil inlet allowing oil to flow into the outer cooling gallery and an oil outlet allowing oil to flow out of the outer oil gallery. At least one insert is disposed in the outer cooling gallery, and the at least one insert is sized to prevent escaping of the at least one insert through the oil inlet or through the oil outlet. 
     According to another embodiment, the outer gallery floor of the piston includes a plurality of anti-coking openings, the anti-coking openings are disposed sequentially in decreasing spaced relation from one another. 
     According to yet another embodiment, the outer gallery floor of the piston includes a plurality of anti-coking openings, each of the openings has a length extending circumferentially around the outer cooling gallery, and the lengths of the anti-coking openings vary from one another. 
     Another aspect of the invention provides a method of manufacturing a piston with anti-coking design features. The method comprises the step of providing a piston body including a lower crown portion and an upper crown portion with an upper combustion wall, the upper crown portion and the lower crown portion forming an outer cooling gallery therebetween, the lower crown portion presenting an outer gallery floor of the outer cooling gallery, the outer gallery floor having an oil inlet allowing oil to flow into the outer cooling gallery and an oil outlet allowing oil to flow out of the outer oil gallery. The method also includes disposing at least one insert in the outer cooling gallery, and the at least one insert is sized to prevent the at least one insert from escaping through the oil inlet or the oil outlet. 
     According to another embodiment, the method includes providing a piston body including a lower crown portion and an upper crown portion with an upper combustion wall, the upper crown portion and the lower crown portion forming an outer cooling gallery therebetween, the lower crown portion presenting an outer gallery floor of the outer cooling gallery, the outer gallery floor including a plurality of anti-coking openings, and the anti-coking openings being disposed sequentially in decreasing spaced relation from one another. 
     According to yet another embodiment, the method includes providing a piston body including a lower crown portion and an upper crown portion with an upper combustion wall, the upper crown portion and the lower crown portion forming an outer cooling gallery therebetween, the lower crown portion presenting an outer gallery floor of the outer cooling gallery, the outer gallery floor presenting a plurality of anti-coking openings extending therethrough, each of the openings having a length extending circumferentially around the outer cooling gallery, and the lengths of the anti-coking openings varying from one another. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects, features and advantages of the invention will become more readily appreciated when considered in connection with the following detailed description, appended claims and accompanying drawings, in which: 
         FIG. 1  is a cross-sectional perspective view of a piston with an outer cooling gallery comprising a helical coil for anti-coking according to one embodiment of the invention; 
         FIG. 2  is an unwrapped view of the outer cooling gallery comprising the helical coil of  FIG. 1 ; 
         FIG. 2A  illustrates the outer cooling gallery and helical coil of  FIG. 2  along line A-A; 
         FIG. 3  is an unwrapped view of an outer cooling gallery containing scallops for anti-coking according to another embodiment of the invention; 
         FIG. 4  is an unwrapped view of an outer cooling gallery with anti-coking openings to the outer cooling gallery according to another embodiment of the invention; 
         FIG. 5  is a plan view of an outer cooling gallery with anti-coking openings according to yet another embodiment of the invention; 
         FIG. 6  is a cross-sectional view of a piston with an outer cooling gallery containing examples of anti-coking inserts according to another embodiment of the invention; and 
         FIG. 7  is a plan view of the outer cooling gallery of  FIG. 6  without the anti-coking inserts and showing an oil inlet and oil outlet to the outer cooling gallery. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     One aspect of the invention provides a piston  10  designed with anti-coking features to reduce oil deposits caused by cooling oil during operating of the piston  10  and thus improve piston cooling. As shown in  FIGS. 1 and 6 , the piston  10  has a piston body  12  extending along a central axis  14  along which the piston body reciprocates within a cylinder bore (not shown). The piston body  12  is formed of metal, and preferably steel. The piston body  12  includes an upper crown portion  16  having dome or an upper combustion wall  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. The upper crown portion  16  has at least one, and shown here, by way of example and without limitation, as having a pair of annular upper ribs, referred to hereafter as an upper inner rib  22  and upper outer rib  24 , depending from the upper combustion wall  18  to respective free ends. The piston body  12  further includes a lower crown portion  26  having at least one, and shown here, by way of example and without limitation, as having a pair of annular lower ribs, referred to hereafter as a lower inner rib  28  and lower outer rib  30 , extending to respective free ends 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 region of the piston  10 . The outer cooling gallery  31  presents an oil passage  72  extending circumferentially around the upper crown portion  18 . The outer cooling gallery  31  also surrounds a central cooling gallery  33  located in the central region of the piston  10 . 
     The lower crown portion  26 , by way of example and without limitation, is shown as having an inner gallery floor  32  extending radially inwardly from the lower inner rib  28  toward the central axis  14 . Further, the lower crown portion  26  has an outer gallery floor  48  extending laterally between the lower inner and outer ribs  28 ,  30 . The lower inner rib  28 , the lower outer rib  30 , the upper inner rib  22 , the upper outer rib  24 , the upper combustion wall  18 , and the outer gallery floor  48  present an inner surface  55  defining the outer cooling gallery  31 . The lower inner rib  28 , the upper inner rib  22 , the upper combustion wall  18 , and the inner gallery floor  32  also present an inner surface  57  defining the central cooling gallery  33  therebetween. The inner gallery floor  32  includes a central opening  53  to the central cooling gallery  33  along the central axis  14 . According to another embodiment, the inner gallery floor  32  is not included and thus the central cooling gallery  33  is open. 
     According to certain embodiments, the outer gallery floor  48  has a through opening providing an oil inlet  50  to allow oil to flow into the outer gallery  31  and a through opening providing an oil outlet  52  to allow oil to flow outwardly from the outer gallery  31 . As such, oil from the crankcase is able to flow upwardly into the outer cooling gallery  31  through the oil inlet  50 , whereupon the oil is circulated about the outer cooling gallery  31  and then exits through the oil outlet  52 . To further yet facilitate cooling the piston  10 , the respective inlet and outlet oil flow openings  50 ,  52  extend through the outer gallery floor  48  of the outer cooling gallery  31  in diametrically opposed relation to one another. The openings  50 ,  52  are formed generally 45 degrees offset from the pin axis  44 . 
     According to the example embodiments shown in  FIGS. 1 and 6 , the outer cooling gallery  31  of the upper crown portion  16  has an annular outer oil gallery pocket  56  extending from the inner and outer rib free ends upwardly into an upper ring belt region  58  and an annular inner oil gallery cavity or pocket  60  forming part of the central crown region extending upwardly from the inner free end beneath the combustion bowl  20 . However, the outer cooling gallery  31  could comprise various other shapes. According to these embodiments, the lower crown portion  26  is formed, such as 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 . To further facilitate cooling the piston  10 , one or more oil flow passages can be provided in one or more of the inner ribs  22 ,  28  to allow cooling oil to flow from the outer cooling gallery  31  to the central cooling gallery  33 . For example, as shown in  FIG. 6 , an intermediate oil passage  66  extends through the lower inner rib  28  in ascending relation from a lower most portion of the outer oil gallery  31  to a lower portion of the inner cooling gallery  33 . As such, oil from the crankcase is able to flow upwardly into the outer cooling gallery  31  through the inlet opening  50 , whereupon the oil is circulated about the outer cooling gallery  31  and channeled in part inwardly through the oil flow passage  66  into the central oil gallery  33 . Upon joining or attaching the upper crown portion  16  to the lower crown portion  26 , the central cooling gallery  33  is formed, and the annular outer oil gallery  31  is formed. The outer oil gallery  31  is substantially closed or sealed upon joining the upper crown portion  16  to the lower crown portion  26 , except for the oil inlet  50 , oil outlet  52 , intermediate oil passage  66 , and any other passage or small opening for conveying of cooling oil. 
     A pair of pin bosses  36 ,  38  depend generally from the outer and inner gallery floors  32 ,  48  to provide a pair of wrist pin bores  40 ,  42  aligned along the pin axis  44  for receipt of a wrist pin (not shown) with a space  46  provided between the pin bosses  38 ,  40  for receipt of a small end of a connecting rod (not shown). 
     The piston  10  is designed with at least one anti-coking feature to reduce oil deposits caused by cooling oil contained in the outer cooling gallery  31  during operation of the piston  10  and thus improve cooling of the piston  10 . For example, one aspect of the invention is directed to creating mechanisms inside the outer oil gallery  31  that motivates the oil to move directionally avoiding stagnation and coking, for example by partial drainage and coil approach. Coking in cooling galleries is a problem oftentimes found with highly thermally loaded steel pistons. Coking is a four-variable function, and the variables include cooling media activation energy level (EA), absolute surface temperature (T) of the metal of the piston body  12 , flux of cooling media (M), and residence time (RT) of the cooling media within the reactor, in this case the cooling oil in the outer cooling gallery  31 . The coking process inception is amenable to calculation. An inspection of the Arrhenius equation and extrapolating to real life conditions inside of the engine shows that there are few options for adjusting the activation energy level (EA) and absolute surface temperature (T) of the metal of the piston body  12 . The flux of the cooling media, i.e. lubricant oil, is limited by the expenditure of parasitic power to increase flow and the need to allow sufficient residual volume in the outer cooling gallery  31 , such as to promote an effective cocktail shaker effect. The sufficient residual volume is generally in the range of 50% to 75% of the total volume of the outer cooling gallery  31 . Therefore, the residence time (RT) of the cooling oil within the outer cooling gallery  31  is the remaining variable which can be adjusted to reduce coking. 
     According to one embodiment, at least one anti-coking insert  54  is disposed in the outer cooling gallery  31  to reduce the residence time of the cooling oil in the outer cooling gallery  31  and thus reduce coking. The insert(s)  54  is designed to clean the inner surface  55  of the outer cooling gallery  31  continuously during service and while the engine is running, thus preventing accumulation of oil deposits which could affect the cooling function of the outer cooling gallery  31 . The at least one insert  54 , also referred to as a flux capacitor, can comprise a variety of different sizes and shapes. However, each insert  54  is sized to prevent the insert  54  from escaping through the oil inlet  50 , through the oil outlet  52 , or through any other passage or opening for conveying cooling oil. For example, a minimum thickness t of each insert  54  is greater than a maximum diameter or dimension D 1  of the oil inlet  50 , greater than a maximum diameter or dimension D 2  of the oil outlet  52 , and greater than a maximum diameter or dimension of any other passage or opening to the outer cooling gallery  31  for conveying oil. The insert(s)  54  should also be shaped in a way that allows it to impact the upper combustion wall  18  of the outer cooling gallery  31  where oil deposits are likely. The insert(s)  54  should also be designed to not cause unacceptable noise, vibration, or harshness issues. The insert(s)  54  should also not impede oil flow significantly, and the insert(s)  54  should be durable to provide effective cleaning for the expected service life of the piston  10 . 
     According to one example embodiment, as shown in  FIGS. 1, 2, and 2A , one insert  54  is disposed in the outer cooling gallery  31 , and the insert  54  is a helical coil. The helical coil presents a center coil opening  68  extending circumferentially around the outer cooling gallery  31 . The center coil opening  68  is aligned with the oil passage  72  of the outer cooling gallery  31  for allowing oil to flow therethrough. The helical coil could be provided by forming the inner surface  55  of the outer cooling gallery  31  into the shape of the coil, such that the helical coil is part of the piston body  12 . Alternatively, the helical coil could be a component disposed within the oil passage  72  separate from the piston body  12 . Due to the shape of the helical coil and the ingress of the oil pressure wave during use of the piston  10 , an inherent stabilized unidirectional flow towards the oil outlet  52  is established. An inner diameter d of the helical coil impedes to a degree any backflow, as the cooling fluid is either predominantly near the upper combustion wall  18  of the outer cooling gallery  31  or near the outer gallery floor  48  of the outer cooling gallery  31 . Thus, the helical coil minimizes the residence time (RT) of the cooling oil in the outer cooling gallery  31  and thus reduces oil coking. 
     According to another example embodiment, as shown in  FIG. 3 , the at least one insert  54  includes plurality of scallops spaced from one another circumferentially around the outer cooling gallery  31 . Each scallop has an inner diameter d presenting a scallop center opening  70  aligned with the oil passage  72  of the outer cooling gallery  31  for allowing oil to flow therethrough. The inner diameter d of each scallop decreases in a direction moving from the oil inlet  50  to the oil outlet  52 . For example, the scallops can be venturi-shaped. The scallops are typically fixed to the inner surface  55  of the outer cooling gallery  31 , as shown in  FIG. 3 . Due to the shape of the scallops and the ingress of the oil pressure wave during use of the piston  10 , an inherent directional flow towards the oil outlet  52  is established. The scallops impede to a degree any backflow, as the cooling oil is either predominantly near the upper combustion wall  18  of the outer cooling gallery  31  or near the outer gallery floor  48  of the outer cooling gallery  31 . The scallops speed up the flow of oil along the length of the outer cooling gallery  31 , minimize the residence time (RT) of the cooling oil in the outer cooling gallery  31 , and thus reduce oil coking. Although the anti-coking inserts  54  of  FIG. 3  are shown as symmetrical along the length of the outer cooling gallery  31 , the anti-coking inserts  54  could be staggered along the length of the outer cooling gallery  31  without compromising their function. 
     According to yet another embodiment, the at least one insert  54  is free to move within the outer cooling gallery  31  during reciprocation of the piston body  12  in use. In this case, the outer cooling gallery  31  typically contains a plurality of the inserts  54 . As the inserts  54  move throughout the cooling gallery  31  during reciprocation, they impact the inner surface  55  bounding the outer cooling gallery  31 , thereby preventing or inhibiting the accumulation and build-up of oil deposits on the inner surface  55 . As such, optimal cooling results in the outer cooling gallery  31  without “coking” the oil on the inner surface  55 . 
     The inserts  54  can have various different designs, and example designs are shown in  FIG. 6 . The shape of the at least one insert  54  can be round, polygonal, square, triangular, prismatic, and/or toroidal. For example, the inserts  54  can include balls formed of steel, balls of coarse steel turnings, coil springs, or chips formed of high temperature resistant polymer with abrasive filler. According to one embodiment, the abrasive filler includes at least one of metal fibers and glass fibers. According to another embodiment, the at least one insert  54  includes at least one prismatic rod or prismatic wire having one axis significantly longer than two other axes. 
     According to another example embodiment, the at least one anti-coking feature includes a plurality of anti-coking openings  70  in the outer gallery floor  48 . In this case, the oil inlet  50  and the oil outlet  52  are not required. The anti-coking openings  70  can be the same size or difference sizes. For example, each anti-coking opening  70  can have a circular or oblong shape. The anti-coking openings  70  can be used alone or with the at least one anti-coking insert  54 . 
     In the example embodiment of  FIG. 4 , the anti-coking openings  70  are disposed sequentially in decreasing spaced relation from one another. Preferably, the anti-coking openings  70  are spaced in a way which sequentially minimizes the residence time (RT) of the cooling oil in the outer cooling gallery  31  until it finds the next anti-coking opening  70 . Thus, due to drainage of the superheated cooling oil, the oil coking which would otherwise occur is avoided.  FIG. 4  shows the lengths L 1 , L 2 , LI between the anti-coking openings  70 , wherein L 1 &lt;L 2 &lt;LI. 
     In the example embodiment of  FIG. 5 , each anti-coking opening  70  has a length L extending circumferentially around the outer cooling gallery  31 , and the lengths L of the anti-coking openings  70  vary from one another. For example, the anti-coking openings  70  can be drilled to the desired size, or drilled to form oblong slits as shown in  FIG. 5 . 
     Another aspect of the invention provides a method of manufacturing the piston  10  with the at least one anti-coking feature. The piston body  12  can be formed by forging or casting one piece or multiple pieces of metal. According to one embodiment, the method includes providing the piston body  12  including the lower crown portion  26  and the upper crown portion  16  with an upper combustion wall  18 . The upper crown portion  16  and the lower crown portion  26  form the outer cooling gallery  31  therebetween. The lower crown portion  26  presents an outer gallery floor  48  of the outer cooling gallery  31 , and the outer gallery floor  48  has an oil inlet  50  allowing oil to flow into the outer cooling gallery  31  and an oil outlet  52  allowing oil to flow out of the outer oil gallery  31 . The step of providing the piston body  12  typically includes joining the upper crown portion  16  to the lower crown portion  26 , for example by welding. 
     The method according to this embodiment also includes disposing the at least one insert  54  in the outer cooling gallery  31 , wherein the at least one insert  54  is sized to prevent the at least one insert  54  from escaping through the oil inlet  50  or the oil outlet  52 . The insert(s)  54  is typically disposed in the outer cooling gallery  31  before joining, for by example welding, the upper crown portion  16  to the lower crown portion  26 . After joining, the at least one insert  54  is contained with the resulting outer cooling gallery  31 . The at least one insert  54  can be disposed within one of the pockets  56 ,  62 , as shown in  FIG. 6 . Alternatively, the step of providing the piston body  12  includes joining the upper crown portion  16  to the lower crown portion  26 , and the step of disposing the at least one insert  54  in the outer cooling gallery  31  is conducted after the joining step. In this case, the method can include compressing the least one insert  54 , such as a coil spring, through the oil inlet  50  and/or the oil outlet  52 , and then allowing the at least one insert  54  to expand inside the outer cooling gallery  31  to prevent escaping of the insert  54  back through the openings  50 ,  52  during use. The insert(s)  54  which are in the form of a prismatic ‘rod’ or ‘wire’ with one axis significantly longer than the other two axes could also be inserted into the outer cooling gallery  31  through the oil inlet  50  or oil outlet  52  after joining the upper crown portion  16  to the lower crown portion  26 . 
     According to another example embodiment, the method of manufacturing the piston  10  includes providing the piston body  12  with the lower crown portion  26  and the upper crown portion  16  with the upper combustion wall  18 , wherein the upper crown portion  16  and the lower crown portion  26  form the outer cooling gallery  31  therebetween, the lower crown portion  26  presents the outer gallery floor  48  of the outer cooling gallery  31 , the outer gallery floor  48  includes a plurality of the anti-coking openings  70 , and the anti-coking openings  70  are disposed sequentially in decreasing spaced relation from one another. 
     According to yet another example embodiment, the method of manufacturing the piston  10  includes providing the piston body  12  including the lower crown portion  26  and the upper crown portion  16  with the upper combustion wall  18 , wherein the upper crown portion  16  and the lower crown portion  26  form the outer cooling gallery  31  therebetween, the lower crown portion  26  presents an outer gallery floor  48  of the outer cooling gallery  31 , the outer gallery floor  48  presents a plurality of the anti-coking openings  70  extending therethrough, each of the openings has a length L extending circumferentially around the outer cooling gallery  31 , and the lengths L of the anti-coking openings  70  vary from one another. 
     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 could be constructed as a monolithic piece of material, such as by being formed in a single steel cast process. Further, it is contemplated that the piston, rather than having a “dual gallery” construction, could have a single “outer oil gallery” with a substantially open central crown region. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.