Patent Publication Number: US-8973484-B2

Title: Piston with cooling gallery

Description:
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 typically also have centrally disposed galleries and allow for coolant fluid communication directly between the peripheral and central galleries. Such central galleries may be complex or expensive to form in the piston components. 
     Accordingly, there is a need for a robust, lightweight piston design that reduces frictional losses associated with movement of the piston within the engine bore and also allows adequate cooling, such as by providing a cooling gallery, while simplifying construction of the piston. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the claims are not limited to the illustrated examples, an appreciation of various aspects is best gained through a discussion of various examples thereof. 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  is a perspective view of an exemplary piston assembly; 
         FIG. 2A  illustrates a sectional view of an exemplary piston assembly, taken through the piston pin bore; 
         FIG. 2B  illustrates a sectional view of the exemplary piston assembly of  FIG. 2A , taken perpendicular to the sectional view of  FIG. 2A ; 
         FIG. 3A  illustrates a sectional view of another exemplary piston assembly, taken through the piston pin bore; 
         FIG. 3B  illustrates a sectional view of the exemplary piston assembly of  FIG. 3A , taken perpendicular to the sectional view of  FIG. 3A ; 
         FIG. 4  illustrates a sectional view of an exemplary piston assembly, taken through the piston pin bore; 
         FIG. 5A  illustrates a sectional view of another exemplary piston assembly, taken through the piston pin bore; 
         FIG. 5B  illustrates a sectional view of the exemplary piston assembly of  FIG. 5A , taken perpendicular to the sectional view of  FIG. 5A ; and 
         FIG. 6  is a process flow diagram of an exemplary method of making a piston assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Reference in the specification to “an exemplary illustration”, an “example” or similar language means that a particular feature, structure, or characteristic described in connection with the exemplary approach is included in at least one illustration. The appearances of the phrase “in an illustration” or similar type language in various places in the specification are not necessarily all referring to the same illustration or example. 
     Various exemplary illustrations are provided herein of pistons and methods of making the same. An exemplary piston assembly may include a piston crown and skirt. The crown may include radially inner and outer crown mating surfaces, and the crown may define at least in part a cooling gallery extending about a periphery of the crown. The skirt may include a pair of oppositely disposed pin bosses that each define piston pin bores and cooperate to define a generally open central region configured to receive a connecting rod between the pin bosses. The skirt may further include a radially inner skirt mating surface abutted along a radially inner interface region with the radially inner crown mating surface, and a radially outer skirt mating surface abutted along a radially outer interface region with the radially outer crown mating surface such that the cooling gallery is substantially enclosed. The skirt may further include an inner collar wall disposed radially inwardly of the radially inner interface region and extending upwards to a free end. The free end may be disposed longitudinally above the radially inner mating surface of the skirt with respect to the piston assembly, thereby generally enclosing the radially inner interface region from the central region. In another exemplary illustration, the collar wall cooperates with the radially inner interface region to define an annular gallery having a lateral cross-section that is elongated longitudinally with respect to the piston. 
     An exemplary method of forming a piston may include providing a piston crown including radially inner and outer crown mating surfaces, the crown defining at least in part a cooling gallery extending about a periphery of the crown. The method may further include abutting the inner and outer crown mating surfaces with corresponding inner and outer skirt mating surfaces of a piston skirt. Accordingly, a radially inner interface region is formed between the inner mating surfaces, and a radially outer interface region is formed between the outer mating surfaces. Moreover, a cooling gallery may be disposed between the radially inner and outer interface regions. The skirt may include a pair of oppositely disposed pin bosses defining piston pin bores and cooperating to define a generally open central region configured to receive a connecting rod between the pin bosses. The method may further include forming a collar wall disposed radially inwardly of the radially inner interface region and extending upwards from the skirt to a free end disposed longitudinally above the radially inner mating surface of the skirt with respect to the piston assembly. 
     Turning now to  FIG. 1 , an exemplary piston assembly  100  is illustrated. Piston assembly  100  may include a piston crown  102  and a piston skirt  104 . The piston crown  102  may include a combustion bowl  108  and a ring belt portion  110  that is configured to seal against an engine bore (not shown) receiving the piston assembly  100 . For example, the ring belt portion  110  may define one or more circumferential grooves  111  that receive piston rings (not shown), which in turn seal against engine bore surfaces during reciprocal motion of the piston assembly  100  within the engine bore. 
     The piston skirt  104  generally supports the crown  102  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  104  may have an outer surface 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  104  may generally slide along the bore surfaces as the piston moves reciprocally within the bore. 
     The skirt  104  may also include piston pin bosses  107 . The piston pin bosses  107  may generally be formed with apertures  106  configured to receive a piston pin (not shown). For example, a piston pin may be inserted through the apertures in the piston pin bosses  107 , thereby generally securing the skirt  104  to a connecting rod (not shown). The pin bosses  107  generally define an open area R between the pin bosses  107 , e.g., for receiving the connecting rod (not shown). 
     Turning now to  FIGS. 2A and 2B , an exemplary piston assembly  100   a  is illustrated. The crown  102  and skirt  104  of the piston assembly  100   a  may be secured to each other in any manner that is convenient. For example, the crown  102  may define radially outer and inner mating surfaces  114 ,  116  that are abutted with corresponding radially outer and inner mating surfaces  118 ,  120  of the skirt  104 . The mating surfaces  114 ,  116 ,  118 ,  120  may each extend about at least a portion of a circumference of the crown  102  and skirt  104 , respectively. In the exemplary illustration of  FIGS. 2A and 2B , the radially outer and inner crown mating surfaces  114 ,  116 , respectively, may generally extend substantially about an entire periphery of the crown  102 . Similarly, the radially outer and inner skirt mating surfaces  118 ,  120  also extend about substantially the entire periphery of the piston assembly  100  and/or skirt  104 , and generally correspond to the crown mating surfaces  114 ,  116  as will be described further below. 
     The crown and skirt mating surfaces may cooperate to define a radially inner interface region I between the radially inner mating surfaces  116 ,  120 , and a radially outer interface region O between the radially outer mating surfaces  114 ,  118 . Where the crown  102  and skirt  104  are fixedly secured, the crown  102  and skirt  104  may be secured to each other via one or both of the interface regions I, O. 
     A circumferentially extending cooling gallery  126  may be defined in part by the ring belt portion  110  of the crown  102  and the skirt  104 . For example, the exemplary illustration of  FIGS. 2A and 2B  includes a cooling gallery  126  that generally extends about a perimeter of the piston crown  102 , 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  102  and combustion bowl  108 . 
     The crown  102  and skirt  104  may generally cooperate to define the cooling gallery  108  between the radially inner interface region I and the radially outer interface region O. More specifically, the skirt  104  may form a lower boundary of the cooling gallery  126 , thereby enclosing the cooling gallery  126  within the crown  102 , and preventing coolant from freely entering and escaping the cooling gallery  126 . 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  126  to/from the engine (not shown) in a controlled manner, thereby further reducing and/or stabilizing operating temperatures associated with the piston  100  and components thereof. 
     The crown mating surfaces  114 ,  116  may generally define flat or planar circumferentially extending surfaces that align with the corresponding radially inner and outer mating surfaces  118 ,  120  of the piston skirt  104 . As will be described further below, the skirt mating surfaces  118 ,  120  and crown mating surfaces  114 ,  116  may each be aligned generally parallel to the corresponding mating surface on the other component, thereby facilitating abutment of the crown mating surfaces  114 ,  116  with the skirt mating surfaces  118 ,  120 , respectively. 
     The piston crown  102  and the piston skirt  104  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, soldering, or non-welding methodologies such as adhesive bonding, merely as examples. In one example, the piston crown and skirt are joined in a welding process, e.g., friction welding. In another exemplary illustration, one or both crown mating surfaces  114 ,  116  may be secured to their respective skirt mating surface  118 ,  120  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  102  and skirt  104  together. 
     The radially outer mating surfaces  114 ,  118  of the crown  102  and skirt  104 , respectively, may be in abutment due to the securement of the radially inner mating surfaces  116 ,  120 , and need not be fixedly secured. Alternatively, the radially outer mating surfaces  114 ,  118  may be fixedly secured, e.g., by welding, bonding, or any other manner that is convenient. Fixed securement of both pairs of the radially outer and inner mating surfaces  114 ,  116 ,  118 ,  120  may be desirable, for example, for particularly heavy-duty piston applications where maximum durability is desired. 
     By fixedly joining the piston crown  102  and the piston skirt  104 , the piston assembly  100  is generally formed as a one-piece or “monobloc” assembly where the crown  102  and skirt  104  components are joined at interface regions I, O that include the radially inner mating surfaces  116 ,  120  and radially outer mating surfaces  114 ,  118 , respectively. That is, the piston crown  102  is generally unitized with the piston skirt  104 , such that the piston skirt  104  is immovable relative to the piston crown  102  after securement to the crown, although the crown  102  and skirt  104  are separate components. 
     The piston crown  102  and piston skirt  104  may be constructed from any materials that are convenient. In one exemplary illustration, the crown  102  and skirt  104  are formed of the same material, e.g., steel. In another example, the piston crown  102  may be formed of a different material than the piston skirt  104 . Accordingly, a material used for the piston crown  102  may include different mechanical properties than the piston skirt  104 , e.g., yield point, tensile strength, notch toughness, or thermal conductivity, merely as examples. Any material or combination may be employed for the crown  102  and skirt  104  that is convenient. Merely as examples, the crown  102  and/or skirt  104  may be formed of a steel material, cast iron, aluminum material, composite, or powdered metal material. The crown  102  and skirt  104  may also be formed in different processes, e.g., the crown  102  may be a generally single cast piece, while the skirt  104  may be forged. Any material and/or forming combination may be employed that is convenient. 
     In examples where the crown  102  and skirt  104  are welded together, e.g., by friction welding, one or more weld flashings  115 ,  117 ,  130  may be formed between the crown  102  and skirt  104 . More specifically, weld flashings  117 ,  130  may be formed that extend radially outwardly and inwardly, respectively, from the radially inner interface region I. Additionally, a weld flashing  115  may be formed that extends radially inwardly from the radially outer interface region O. Another weld flashing (not shown) that extends radially outwardly from the radially outer interface region may generally be a further byproduct of a friction welding operation along the radially outer interface region O, and may be removed to form the relatively smooth outer surface of the piston assembly  100 . For example, weld flashing may be removed via a machining operation. 
     As best seen in  FIGS. 2A and 2B , the piston assembly  100  may include a generally circumferentially extending wall or inner “collar”  122  positioned radially inwardly of the radially inner interface region I. The inner collar  122  may generally obstruct or block off the radially inner interface region I and/or weld flashing  130  from a central area of the piston between pin bosses  107   a ,  107   b  of the skirt  104   a . The inner collar thereby generally encloses the radially inner interface region I and/or weld flashing  130 , forming an annular gallery  150   
     The inner collar  122  may define a relatively small gap G 1  that allows fluid communication between the annular gallery  150  and the central area R of the piston. The annular gallery  150  defines a volume V (illustrated in section in  FIGS. 2A and 2B ) that is generally bounded by the inner collar  122  and the radially inner interface region I, including the weld flashing  120 . The inner collar  122  may bound the gallery  150  on a radially inner side and a lower side with a generally vertical wall portion  154  and a lower wall portion  152 , respectively. Further, the radially inner interface region I generally bounds the gallery  150  and volume V on a radially outer side of the gallery  150 , e.g., along the weld flashing  130 . The gallery  150  and/or the annular volume V defined by the collar  122  and radially inner interface region I may extend about a periphery of the piston assembly  100 . As best seen in  FIG. 2A , the gallery  150  and/or volume V may define a lateral cross-section that is elongated with respect to a longitudinal axis L-L of the piston assembly  100   a.    
     The gap G 1  may be sufficiently small that coolant, e.g., oil, does not accumulate within the gallery  150 , which encloses the weld flash  130 . One or more relatively small apertures  160  (see  FIG. 2B ) may be optionally provided in the inner collar  122  to permit draining of any fluids applied to the piston prior to operation, e.g., coatings or other treatments for the piston surfaces. In one exemplary illustration, the aperture  160  is no larger than approximately 5 millimeters (mm) in diameter. 
     In other exemplary approaches fluid retention may be desired within the gallery  150 , e.g., to provide an additional cooling mechanism, so the presence of apertures, e.g., aperture  160 , may be undesirable in such examples. Moreover, the gallery  150 , although illustrated herein as being generally closed off from the cooling gallery  126  by the radially inner interface region I, may alternatively be provided with one or more passages (not shown) extending between the cooling gallery  126  and gallery  150  to promote coolant flow between the gallery  150  and cooling gallery  126 . In any case, a byproduct of the formation of inner collar  122  including its gap G 1  and any aperture(s) is that access to the radially inwardly extending weld flashing  130  is unavailable within this gallery in much the same way as access to weld flashing  115  and  117  is unavailable within cooling gallery  126 , e.g., for removal of the weld flash. 
     The inner collar  122  extends generally upward from the skirt portion  104   a , as best seen in  FIGS. 2A and 2B . The collar  122  extends upward adjacent the radially inner weld flashing  130 , to an upper free end  134  that is positioned above the radially inner mating surface  120  of the skirt  104   a , and/or the weld flashing  130 . For example, in the exemplary illustration of  FIGS. 2A and 2B , the free end  134  defines a height H longitudinally above, with respect to the piston assembly  100   a , the radially inner skirt mating surface  120 . The free end  134  of the lower collar defines a relatively small gap G 1  between a lower surface  136  of the combustion bowl  108 , thereby closing off the radially inner interface region I and/or the weld flashing  130  from a central area R of the piston between the piston pin bosses  107 , within which the connecting rod (not shown) may be received. In one exemplary illustration, the gap G 1  is no greater than approximately 1.5 millimeters (mm). 
     Turning now to  FIGS. 3A and 3B , another exemplary piston assembly  100   b  is illustrated. Piston assembly  100   b  includes a lower collar  122  extending generally vertically upwards from the skirt  104   b . The crown  102   b  also includes an upper collar portion  132  that extends downward from the combustion bowl area to a free end  133  disposed adjacent the free end  134  of the lower collar  122 . The free ends  133 ,  134  of the upper and lower collars  122 ,  132 , respectively, thereby define a relatively small gap G 2 . The upper and lower collars  122 ,  132  cooperate with radially inner interface region I to define an annular gallery  150 . An annular volume V of the gallery  150  may be generally bounded by the radially inner interface region I along the weld flashing  130 , and further by the lower collar  122  and the upper collar  132 . 
     The gallery  150  may generally close off the radially inner weld flashing  130  from a central area R of the piston, e.g., between the pin bosses  107  in a manner similar to that discussed above with respect to  FIGS. 2A and 3B . In one exemplary illustration, the gap G 2  between the free ends  133 ,  134  of the upper and lower collars  122 ,  132  is no greater than approximately 1.5 millimeters. Moreover, the free ends  133 ,  134  of the upper and lower collars  122 ,  132  may be generally aligned longitudinally with respect to the piston assembly  100 , e.g., along axes A-A that are parallel to a longitudinal axis of the piston assembly  100 . The gap G 2  may thereby be generally defined along the axis A-A, between the longitudinally aligned free ends  133 ,  134  of the upper and lower collars  132 ,  122 , respectively. 
     Upper collar  132  may be employed, for example, where an upward vertical extent of the lower collar  122  is less than desired, e.g., for larger compression height piston designs. The upper collar  132  may have a relatively short vertical extent, as illustrated in  FIGS. 3A and 3B . 
     Alternatively, as illustrated in  FIG. 4  an upper collar  132 ′ may have a greater vertical extent. In the exemplary illustration of  FIG. 4 , the piston assembly  100   c  includes a crown  102   c , from which the upper collar portion  132 ′ extends downward. The upper and lower collars  122 ,  132 ′ may define a circumferentially extending gap G 3  therebetween. The upper and lower collars  122 ,  132 ′ cooperate with the radially inner interface region I to define an annular gallery  150  having a volume V. In some cases, e.g., where a compression height H C  of the piston assembly  100   c  (i.e., distance from a piston top surface to centerline of the pin bore  106 ) is relatively large, it may be difficult to form the lower collar  122  with a sufficient upward vertical extent. Accordingly, upper collar portion  132 ′ may be employed to maintain a relatively small gap G 3 . In one exemplary illustration, the gap G 3  is approximately 1.5 millimeters. Moreover, in some approaches, upper collar  132 ′ may be slightly laterally offset from lower collar  122  by a dimension L 1 . In the illustrative example, however, a portion of each free end  133 ,  134  of a respective collar overlap such that only gap G 3  exists. In other words, in the exemplary illustration shown in  FIG. 4 , there is no corresponding lateral gap between the upper and lower collars  122 ,  132 ′ in a direction generally perpendicular to the longitudinal gap G 3 . 
     Turning now to  FIGS. 5A and 5B , another exemplary piston assembly  100   d  is illustrated. The crown  102   d  of the piston assembly  100   d  includes an upper collar  132 ″ and a lower collar  122 . In the exemplary illustration shown in  FIGS. 5A , and  5 B, the upper and lower collars  122 ,  132 ″ overlap vertically, i.e., with respect to a longitudinal axis L-L of the piston. In other words, the free end  133  of the upper collar  132 ″ extends downward past the free end  134  of the lower collar  122 , thereby defining an overlap distance D 1 . The two corresponding mating surfaces defined within overlap distance D 1  are shown either abutting or in very close proximity to one another subject to manufacturing tolerances. Thus, there is no gap between the two mating surfaces. The upper collar  132 ″ cooperates with the lower collar  122  to form an annular gallery  150 . A volume V of the gallery  150  may be generally bounded by the upper and lower collars  132 ″,  122  as well as the radially inner interface region I. 
     Turning now to  FIG. 6 , an exemplary process  600  for making a piston assembly is illustrated. Process  600  may generally begin at block  602 , where a piston crown is provided. For example, as described above a crown  102  may include radially inner and outer crown mating surfaces  114 ,  116 . Additionally, the crown  102  may define at least in part a cooling gallery  126  extending about a periphery of the crown  102 . Process  600  may then proceed to block  604 . 
     At block  604 , inner and outer crown mating surfaces may be abutted with corresponding inner and outer skirt mating surfaces of a piston skirt. For example, as described above a radially inner interface region I may be formed between the inner mating surfaces  116 ,  120 , and a radially outer interface region O may be formed between outer mating surfaces  114 ,  118  of the piston assembly  100 . Moreover, a cooling gallery  126  may be disposed between the radially inner and outer interface regions I, O. Additionally, the skirt  104  may include a pair of oppositely disposed pin bosses  107  defining respective piston pin bores  106 . The pin bosses may cooperate to define a generally open central region R configured to receive a connecting rod between the pin bosses  107 . 
     Proceeding to block  606 , a collar wall may be formed. For example, as described above, various exemplary illustrations of a collar wall  122  may be disposed radially inwardly of the radially inner interface region I, extending upward from the skirt  104  to a free end  134 . In one exemplary illustration, the free end  134  is disposed longitudinally above the radially inner mating surface  120  of the skirt  104  with respect to the piston assembly  100 . Process  600  may then proceed to block  608 . 
     At block  608 , a circumferential gap may be defined between an upper edge of the collar wall and a lower combustion bowl surface of the crown. For example, a gap G 1  may be formed between an upper edge  134  of collar wall  122  and the lower surface  136  of the combustion bowl  108 . 
     Proceeding to block  610 , a radially inner interface region may be generally enclosed from the central region with the inner collar wall. For example, as described above, a radially inner interface region I may be enclosed by the collar wall  122  with respect to a region R defined between the pin bosses  107 . Process  600  may then proceed to block  612 . 
     At block  612 , an upper collar wall portion may be formed. For example, an upper collar wall  132 ,  132 ′,  132 ″ may be formed that extends downward from the crown  102  to an upper free end  133 . The upper free end  133  may cooperate with the lower portion  122  to define a circumferential gap G 2 , G 3 . 
     Proceeding to block  614 , a circumferential volume may be defined in part by the collar wall. For example, as described above the collar wall  122  and the radially inner interface region I may define an annular or circumferential volume V defining a lateral cross-section that is elongated longitudinally with respect to the piston  100 . Process  600  may then proceed to block  616 . 
     At block  616 , the crown and skirt may be fixedly secured together along one or more of the radially inner and outer interface regions. For example, as described above the crown and skirt may be fixedly secured together along the radially inner and/or outer mating surfaces of the crown and skirt by friction welding, adhesive bonding, or any other method that is convenient. In examples where friction welding is employed, welding flash may be formed adjacent the mating surfaces  114 ,  116 ,  118 ,  120 , as illustrated above. In one exemplary illustration, a weld flash  117  extending radially inwardly from the radially inner interface region I is disposed longitudinally with respect to the piston  100  beneath a free end  134  of the collar wall  122 . Accordingly, the weld flashing  117  may be substantially enclosed by the collar wall  122 . 
     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 upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. 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 and is limited only by the following claims. 
     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.