Patent Application
20130000483
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.
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:
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
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
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
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
The inner collar 122 may define a relatively small gap G1 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
The gap G1 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
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 G1 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 104a, as best seen in
Turning now to
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
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
Alternatively, as illustrated in
Turning now to
Turning now to
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 G1 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 G2, G3.
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.
