Patent Publication Number: US-9404439-B2

Title: Piston with cooling gallery and cooling gallery fins

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional patent application 61/713,042, filed on Oct. 12, 2012, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     A power cylinder assembly of an internal combustion engine generally comprises a reciprocating piston disposed within a cylindrical cavity of an engine block. One end of the cylindrical cavity may be closed while another end of the cylindrical cavity may be open. The closed end of the cylindrical cavity and an upper portion or crown of the piston defines a combustion chamber. The open end of the cylindrical cavity permits oscillatory movement of a connecting rod, which joins a lower portion of the piston to a crankshaft, which is partially submersed in an oil sump. The crankshaft converts linear motion of the piston (resulting from combustion of fuel in the combustion chamber) into rotational motion. 
     Engines, and in particular the pistons, are under increased stress as a result of constant efforts to increase overall efficiency, e.g., by reducing piston weight and/or increasing pressures and temperatures associated with engine operation. Piston cooling is therefore increasingly important for withstanding the increased stress of such operational conditions over the life of the engine. To reduce the operating temperatures of piston components, a cooling gallery may be provided about a perimeter of the piston, into which crankcase oil may be introduced to reduce the operating temperature of the piston. 
     Known piston designs having peripheral cooling galleries may not provide adequate cooling. Additional cooling features may be difficult to form or otherwise assemble with existing cooling gallery and piston designs. Accordingly, there is a need for a robust, lightweight piston design that provides enhanced cooling, such as by providing a cooling gallery, while also allowing reliable and cost-efficient production of the piston in a mass manufacturing environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings, exemplary illustrations are shown in detail. Although the drawings represent representative examples, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an illustrative example. Further, the exemplary illustrations described herein are not intended to be exhaustive or otherwise limiting or restricting to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary illustrations are described in detail by referring to the drawings as follows: 
         FIG. 1  illustrates an exemplary piston having an annular cooling gallery, where the piston includes a joint between the upper and lower parts that is positioned below the combustion bowl, and cooling fins that extend upward from a lower surface of the cooling gallery; 
         FIG. 2  illustrates an exemplary piston having an annular cooling gallery, where the piston includes a joint between the upper and lower parts that is positioned within the combustion bowl, and cooling fins that extend downward from an upper surface of the cooling gallery; 
         FIG. 3  shows an enlarged view of an exemplary cooling gallery of a piston, where a plurality of cooling fins are provided, with at least one cooling fin that extends downward from an upper surface of the cooling gallery, and at least one cooling fin that extends upward from a lower surface of the cooling gallery; 
         FIG. 4A  shows an enlarged view of an exemplary cooling gallery block that includes angled radially outer and inner surfaces, e.g., as may result from an exemplary forging or casting process; 
         FIG. 4B  shows an enlarged view of exemplary cooling gallery fins formed from the cooling gallery block shown in  FIG. 4A , and including a radially outermost cooling gallery fin having an angled radially outer surface, and a radially innermost cooling gallery fin having an angled radially inner surface; and 
         FIG. 5  is a flow chart illustrating a method of assembling the piston of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-3, 4A, and 4B  illustrate exemplary piston assemblies. A piston assembly  100  may include a piston crown  101  and a piston skirt  102  that may be joined together, e.g., by a welding process, such as friction welding or laser welding, or by a brazing process, merely as examples. As shown, piston ring grooves  103  may be provided about the perimeter or periphery  104  of the crown  101  adjacent an annular cooling gallery  105 . Additionally, a combustion bowl  106  may also be formed in an upper surface  107  of the crown  101 . 
     With reference to  FIG. 1 , the piston skirt  102  generally supports the crown  101  during engine operation, e.g., by interfacing with surfaces of an engine bore (not shown) to stabilize the piston assembly  100  during reciprocal motion within the bore. For example, the skirt  102  may have an outer surface  108  that generally defines a circular outer shape about at least a portion of a perimeter of the piston assembly  100 . The outer shape may correspond to the engine bore surfaces, which may be generally cylindrical. The skirt  102  may generally slide along the bore surfaces as the piston moves reciprocally within the bore (not shown). 
     The skirt  102  may also include piston pin bosses  110  extending downward from the skirt  102 . The piston pin bosses  110  may generally be formed with apertures  109  configured to receive a piston pin (not shown). For example, a piston pin may be inserted through the apertures  109  in the piston pin bosses  110 , thereby generally securing the skirt  102  to a connecting rod (not shown). The pin bosses  110  may generally define an open area between the pin bosses  110 , e.g., for receiving the connecting rod (not shown). 
     An exemplary piston assembly  100  may include a crown  101  defining radially outer and inner mating surfaces  111 ,  112  that are abutted with corresponding radially outer and inner mating surfaces  113 ,  114  of the skirt  102 . The mating surfaces may each extend about at least a portion of a circumference of the crown  101  and skirt  102 , respectively. The radially outer and inner crown mating surfaces  111 ,  112 , respectively, may generally extend substantially about an entire periphery of the crown  101 . Similarly, the radially outer and inner skirt mating surfaces  113 ,  114  also extend about substantially the entire periphery of the piston assembly  100  and/or skirt  102 , and generally correspond to the crown mating surfaces  111 ,  112 . 
     The crown  101  and skirt  102  mating surfaces may cooperate to define a radially inner interface region  115  between the radially inner mating surfaces  112 ,  114  and a radially outer interface region  116  between the radially outer mating surfaces  111 ,  113 . Where the crown  101  and skirt  102  are fixedly secured, the crown and skirt  102  may be secured to each other via one or both of the interface regions  115 ,  116 . 
     A circumferentially extending cooling gallery  105  may be defined in part by the ring belt portion  117  of the crown  101  and the skirt  102 . For example, the crown  101  and skirt  102  cooperate to define a cooling gallery  105  that generally extends about a perimeter of the piston crown  101 , and may circulate a coolant during operation, e.g., engine oil, thereby reducing an operating temperature of the piston. Additionally, the circulation of the coolant may facilitate the maintaining of a more stable or uniform temperature about the piston assembly  100 , and especially in the upper portion of the piston assembly  100 , e.g., the crown  101  and combustion bowl  106 . 
     The crown  101  and skirt  102  may generally cooperate to define the cooling gallery  105  between the radially inner interface region  115  and the radially outer interface region  116 . More specifically, the skirt  102  may form a lower boundary  119  of the cooling gallery  105 , thereby enclosing the cooling gallery  105  within the crown  101 , which may form at least part of an upper boundary  120  of the cooling gallery  105 , and preventing coolant from freely entering and escaping the cooling gallery  105 . At the same time, one or more apertures (not shown) may also be provided to allow oil or other coolants to exit and enter the cooling gallery  105  to/from the engine (not shown) in a controlled manner, thereby further reducing and/or stabilizing operating temperatures associated with the piston and components thereof. 
     The crown mating surfaces  111 ,  112  may, prior to joining to the skirt mating surfaces  113 ,  114 , generally define flat or planar circumferentially extending surfaces that align with the corresponding radially inner and outer mating surfaces  115 ,  116  of the piston skirt  102 . The skirt mating surfaces  113 ,  114  and crown mating surfaces  111 ,  112  may each be aligned generally parallel to the corresponding mating surface on the other component, thereby facilitating abutment of the crown mating surfaces  111 ,  112  with the skirt mating surfaces  113 ,  114 , respectively. 
     The piston crown  101  and the piston skirt  102  illustrated in  FIG. 1  may be secured or fixedly joined to one another in any manner that is convenient including, but not limited to, welding methodologies such as friction welding, beam welding, laser welding, or non-welding methodologies such as soldering, brazing, or adhesive bonding, merely as examples. In one example, the piston crown  101  and skirt  102  are joined in a welding process, e.g., friction welding or laser welding. In another exemplary illustration, one or both crown mating surfaces  111 ,  112  may be secured to their respective skirt mating surface  113 ,  114  in any manner that is convenient, e.g., by way of a welding operation such as friction welding or adhesive bonding, merely as examples, thereby securing the crown  101  and skirt  102  together. 
     The radially outer mating surfaces of the crown and skirt illustrated in  FIG. 1 , respectively, may be in abutment due to the securement of the radially inner mating surfaces  112 ,  114 , and need not be fixedly secured. Alternatively, the radially outer mating surfaces  111 ,  113  may be fixedly secured, e.g., by a friction welding process. Welding, bonding, or any other manner that is convenient may be employed to join the mating surfaces. Fixed securement of both pairs of the radially outer and inner mating surfaces, e.g., by welding, may be desirable, for example, for particularly heavy-duty piston applications where maximum durability is desired. 
     By fixedly joining the piston crown  101  and the piston skirt  102 , the piston assembly  100  is generally formed as a one-piece or “monobloc” assembly where the crown  101  and skirt  102  components are joined at interface regions that include the radially inner mating surfaces  112 ,  114  and radially outer mating surfaces  111 ,  113  respectively. That is, the piston crown  101  is generally unitized with the piston skirt  102 , such that the piston skirt  102  is immovable relative to the piston crown  101  after securement to the crown, although the crown  101  and skirt  102  are separate components. 
     The piston crown  101  and piston skirt  102  may be constructed from any materials that are convenient. In one exemplary illustration, the crown  101  and skirt  102  are formed of the same material, e.g., steel. In another example, the piston crown  101  may be formed of a different material than the piston skirt  102 . 
     In examples where the crown  101  and skirt  102  are welded together, e.g., by friction welding, one or more weld flashings (not shown) may be formed between the crown  101  and skirt  102 . More specifically, weld flashings may be formed that extend radially outwardly and inwardly, respectively, from the radially inner interface region  115 . Additionally, a weld flashing may be formed that extends radially inwardly from the radially outer interface region  116 . Another weld flashing may extend radially outwardly from the radially outer interface region  116  and may generally be a further byproduct of a friction welding operation along the radially outer interface region  116 . The weld flashing extending radially outwardly from the radially outer interface region  116  may be subsequently removed, e.g., by machining, to form the relatively smooth outer surface of the piston assembly  100  and/or piston ring grooves  103  therein. 
     As shown in  FIG. 1 , one or more cooling fins  121  may be provided in the cooling gallery  105 . The cooling fins  121  may be formed integrally with the cooling gallery  105 , e.g., by forging or casting the fin  121  integrally with the crown  101  or skirt  102  parts. Integrally forming the cooling fins  121  with the crown  101  or skirt  102  may enhance the cooling fins&#39;  121  structural stability as no coupling mechanism is required to attach cooling fin  121  to the cooling gallery surface. Likewise, integrally forming the cooling fin  121  with the cooling gallery block, e.g., by machining, may reduce production or manufacturing time as the cooling fin  121  may be formed in conjunction with forming the crown  101  or skirt  102 . In an alternative exemplary approach, the cooling fins  121  may be formed as a separate component which connects to the cooling gallery surface, e.g., by welding or by brazing/soldering. The cooling fins  121  may extend substantially about the entire circumference or perimeter of the piston. The fins  121  may thereby provide increased surface area in the interior of the gallery  105 , thereby enhancing a cooling effect of coolant (e.g., engine oil) circulated within the gallery  105 . 
     The cooling gallery fins  121  may be formed in any manner that is convenient. In one example, a relatively wide fin or block  121  is provided in the upper or lower piston part, e.g., by a forging, casting, or machining process. A plurality of fins  121  may be subsequently formed in the fin/block  121 , e.g., by machining, thereby forming a plurality of relatively thin fins  121  that generally increase surface area of the gallery while minimizing any weight added by the fins  121 . Thus, the cooling fins  121  may be configured in order to optimize the cooling performance and to adjust the cooling performance to meet the requirements of each individual case. The presence of the fins  121  may provide particular cooling advantages for upper regions of the piston closest to the combustion chamber, e.g., the bowl rim and top ring groove areas. 
     While the cooling gallery fins  121  illustrated in  FIGS. 1, 2, and 3  may generally appear extending away from their respective cooling gallery surfaces in a vertically or substantially vertically manner, exemplary forming processes such as forging or casting may result in slightly angled surface(s) of the cooling gallery fins. As shown in  FIG. 4B , for example, a radially outer surface  123  of a radially outermost cooling gallery fin  124  may be angled slightly radially inwardly, due to tolerances for a forging or casting process. Additionally, a radially inner surface  125  of a radially innermost cooling gallery fin  126  may similarly be angled slightly radially outwardly. Thus, the cooling fins  121  may include sloping sides that extend from a base (e.g., the interior surface of the cooling gallery  105 ) and converge at an apex, the apex of which may be generally centered with respect to the cooling fin  121 . 
     As shown in  FIG. 4A , for example, an initial cast or forged cooling fin block  121  may have a radially outermost surface  127  that is angled radially inwardly in a direction moving away from the associated cooling gallery surface, thereby defining an angle α with vertical. A radially innermost surface  128  of the fin block  121  may similarly have an innermost surface that is angled radially outwardly in a direction moving away from the associated cooling gallery surface, thereby defining an angle β with vertical. As noted above, these angled surfaces may result from tolerances that may be necessary to allow removal of a cast or forged part from an associated die. The angled surfaces of the cooling fins  121  may promote flow of coolant away from the apex of the cooling fin  121 . Additionally, the angled surfaces of the cooling fins  121  may enhance cooling fin  121  structural stability and improve overall weight. That is, for example, a base with greater surface area (e.g., wider or thicker relative to the apex) may act as a stronger support thereby reducing undesired separation of the cooling fin  121  from the interior surface of the cooling gallery  105 . Likewise, a cooling fin  121  base with a greater surface area may promote heat transfer from the cooling fluid to the cooling gallery surface. Additionally, employing a cooling fin  121  which gradually decreases in width as the height increases with respect to the interior cooling gallery surface may minimize cooling fin  121  weight due to requiring less material as the angled surfaces converge towards the apex. 
     As shown in  FIG. 4B , after the cooling fin block  121  is initially cast or forged, a machining operation may be employed to remove material from a portion of the cooling fin block  121  to form multiple cooling gallery fins  121 . More specifically, in the example shown in  FIG. 4B , two fins  121  are formed. The radially outermost fin  124  may have a radially inner surface  133  that is substantially vertical, while the radially innermost fin  126  may have a radially outer surface  134  that is also substantially vertical. The substantially vertical surfaces may result from the exemplary machining process, which in contrast may more easily form a vertically extending surface relative to the piston assembly  100 , as compared with forged or cast outer surfaces of the cooling gallery fins  121 . 
     As best seen in  FIG. 4A , a base of each cooling gallery fin  121  on both the radially inward and radially outward sides thereof, may define a radius R with respect to an associated cooling gallery surface. The radius R may generally result from tolerances from a forming operation associated with the cooling gallery fin block, e.g., a forging or casting operation as described above. Alternatively or additionally, with reference to  FIG. 4A , a radius R extending between a cooling gallery fin  121  and an adjacent cooling gallery surface may be necessitated by tolerances or limitations of a machining operation associated with forming the cooling gallery fins  121  in the cooling gallery fin block. The radius R may provide additional surface area thereby enhancing the exchange of heat from the cooling gallery surface and cooling fluid. 
     The cooling gallery fins  121  may be positioned anywhere within the cooling gallery  105  that is convenient. The piston  100  shown in  FIG. 1  includes a joint between the upper piston part (i.e., crown  101 ) and lower piston part (i.e., skirt  102 ). A joint may be formed by interfacing the crown  101  and skirt  102  mating surfaces. For example, a radial inner joint  131  may be formed from fixing the radially inner crown and skirt mating surfaces  112 ,  114 . Additionally, a radially outer joint  132  may be formed by fixing the radially outer crown and skirt mating surfaces  111 ,  113 . The joint may be included beneath the combustion bowl, as shown in  FIG. 1 . In such examples, it may be more difficult to form cooling fins  121  in the upper surface of the cooling gallery  105  where access is restricted by the width of the upper portion of the cooling gallery  105 . It may be comparatively easier to provide fins  121  in a lower or bottom surface of the gallery  105  as a result. 
     Turning now to  FIG. 2 , another exemplary piston assembly  100  having cooling fins  121  is shown. The radially inner joint  131  of the piston is provided in the combustion bowl  106 . The joint between the upper and lower piston parts, i.e., the crown  101  and skirt  102 , respectively, may be welded, e.g., in a friction welding or laser welding process. The example shown in  FIG. 2  includes cooling fins  121  provided in an upper surface  129  of the cooling gallery  105 . In examples where a radially inner joint  131  between the upper and lower piston parts is located in the combustion bowl  106 , as in  FIG. 2 , providing cooling fins  121  in an upper portion of the cooling gallery  105  may be more convenient since the upper part may be relatively easier to form. By comparison, access to lower portions of the cooling gallery  105  may be more restricted. 
     While the above examples in  FIGS. 1 and 2  illustrate fins extending from only one of the upper and lower gallery surfaces  119 ,  120 , cooling fins may be provided that extend from any interior surface of the cooling gallery  105 . For example, as shown in  FIG. 3 , an exemplary cooling gallery  105  is illustrated having cooling fins  121  extending from both lower and upper surfaces  129 ,  130  of the cooling gallery  105 . For example, the upper cooling gallery fin  121  may bifurcate two lower cooling gallery fins  121  extending upwards, or vice versa. As such, the surface area of the interior cooling gallery  105  is increased as a result of including more cooling fins  121 , thereby improving the degree of heat transfer between the cooling surface and cooling fluid. Moreover, a radially inner joint  131  between the upper piston part and lower piston part may be provided either in or below the combustion bowl  106 . 
     Still referring to  FIG. 3 , an exemplary piston may include cooling fins  121  made of a different material than the piston crown or skirt  101 ,  102 . For example, the cooling fins  121  may be made of aluminum, stainless steel, or a similar material. Additionally or alternatively, the cooling fins  121  may be insertable and/or removable from the cooling gallery interior surface. For instance, cooling fins  121  may be added or removed in order to effectuate a desired degree of heat transfer from the cooling fluid and the interior surface of the cooling gallery  105 . Further, the cooling fins  121  may vary in height relative to the cooling gallery surface and the cooling fins may vary in width. Consequently, the cooling fin  121  may be lighter overall as compared to integrally formed cooling fins  121  and may likewise be insertable and/or removable if damaged or to increase/decrease the surface area of the interior surface of the cooling gallery  105 . 
     Accordingly, cooling gallery fins  121  may be provided that extend from interior surface(s)  119 ,  120  of a piston cooling gallery  105  that increase overall cooling effect of a coolant circulated within the cooling gallery  105  by increasing surface area of the cooling gallery  105 . The increase in cooling effect may allow correspondingly increased tolerance of high temperatures and pressures, allowing greater power requirements to be met with the piston. 
       FIG. 5  illustrates a method  500  of configuring the piston assembly  100 . At block  505 , the upper part or piston crown  101  having radially inner and outer crown mating surfaces  111 ,  112  may be provided. The crown  101  may define at least in part the upper portion of the cooling gallery  105  extending in the periphery of the crown  101 . The piston assembly  100  may include a corresponding lower part or piston skirt  102  having radially inner and outer skirt mating surfaces  113 ,  114 . The skirt  102  may define at least in part the lower portion of the cooling gallery  105  extending in the periphery of the skirt  102 . The skirt  102  may include a pair of oppositely disposed pin bosses  110  defining piston pin bores  109 . 
     At block  510 , the method  500  may proceed by disposing at least one cooling gallery fin  121  extending from an interior surface of the cooling gallery  105 . For example, the cooling gallery fins  121  may be integrally formed in the crown  101  or skirt  102  by forging, casting, or machine processing. Alternatively, the cooling fin(s)  121  may be insertable and securely fixed onto the cooling gallery interior surface. The cooling gallery  105  may include a single fin  121 , or a plurality of fins  121 . The cooling gallery fin(s)  121  may extend from the lower boundary or surface of the cooling gallery  105  (e.g., extending substantially vertically from the skirt  102 ) or from the upper boundary of the cooling gallery  105  (e.g., extending substantially vertical from the piston crown  101 ). Additionally or alternatively, multiple cooling fins  121  may extend from the upper or lower cooling gallery surface. 
     At block  515 , the method  500  may include abutting the inner and outer crown mating surfaces  111 ,  112  with the corresponding inner and outer skirt mating surfaces  113 ,  114  to form a radially inner interface region  115  between the inner mating surfaces  112 ,  114 , and a radially outer interface region  116  between the outer mating surfaces  111 ,  113 . The cooling gallery  105  may be disposed between the radially inner and outer interface regions  115 ,  116 . Interfacing the inner crown and skirt mating surfaces  111 ,  113  along the radially inner interface region  115  may form a radially inner joint  131 , which may be positioned located in or below the combustion bowl area  106 . The radially inner and outer crown mating surfaces  111 ,  112  may be fixed to the radially inner and outer skirt mating surfaces  113 ,  114  by friction welding, laser welding, brazing, or soldering. In one example, the radially outer crown and skirt mating surfaces  111 ,  113  may be in abutment due to the securement of the radially inner crown and skirt mating surfaces  112 ,  114 , and need not be fixedly secured. Alternatively, the radially inner crown and skirt mating surface  112 ,  114  may be in abutment due to the securement of the radially outer crown and skirt mating surface  111 ,  113 . Additionally, both the crown and skirt radially inner and outer mating surfaces  111 ,  112 ,  113 ,  114  may be fixedly secured. The radially inner mating surfaces of the crown and skirt  112 ,  114  (e.g., the radially inner interface region  115  or radially inner joint  131 ) may be formed below the combustion bowl area  106 . Alternatively, the radially inner mating surfaces of the crown and skirt  112 ,  114  may be formed in the combustion bowl area  106 . 
     With regard to the processes, systems, methods, heuristics, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claimed invention. 
     Accordingly, it is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent upon reading the above description. It is anticipated and intended that future developments will occur in the arts discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the invention is capable of modification and variation. 
     All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those skilled in the art unless an explicit indication to the contrary in made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.