Abstract:
A piston system including a body defining a bore and a piston positioned inside the bore and mounted for reciprocation therein. The piston includes a crown and a skirt extending generally away from the crown, the skirt including a pair of opposed panel portions. The piston further includes a transition portion configured to first engage the body during reciprocation of the piston in the bore. The piston is configured such that additional movement of the piston in the bore after the first engagement causes additional contact between the piston and the body, the additional contact increasing or moving in a circumferential direction about the piston. The piston is configured such that maximum side loading forces from the body to the piston are applied to the piston at one of the panel portions.

Description:
[0001]    This application is a divisional of and claims priority to U.S. patent application Ser. No. 12/577,417, filed on Oct. 12, 2009 entitled PISTON WITH IMPROVED SIDE LOADING RESISTANCE, which claims priority to U.S. Provisional Patent Application Ser. No. 61/104,887, filed on Oct. 13, 2008, to which this application also claims priority. The entire contents of both of these applications is incorporated herein by reference. 
         [0002]    The present invention is directed to a piston for use in an internal combustion engine, and more particularly, to such a piston with improved resistance to loading. 
     
    
     BACKGROUND 
       [0003]    Pistons used in internal combustion engines are subjected to high levels of stress during operation. Accordingly, pistons are often designed to have sufficient stiffness and resistance to loads. However, it is also desired to minimize weight of the piston (which improves inertial response), to reduce surface area, particularly on the radially outer surfaces (which reduces dynamic friction), and to account for various other design considerations. 
       SUMMARY 
       [0004]    In one embodiment, the present invention is a piston that is designed to resist loads, particularly side loads, and may also have relatively low weight and relatively low surface area to provide improved performance. More particularly, in one embodiment the invention is a piston system including a body defining a bore and a piston positioned inside the bore and mounted for reciprocation therein. The piston includes a crown and a skirt extending generally away from the crown, the skirt including a pair of opposed panel portions. The piston further includes a transition portion configured to first engage the body during reciprocation of the piston in the bore. The piston is configured such that additional movement of the piston in the bore after the first engagement causes additional contact between the piston and the body, the additional contact increasing or moving in a circumferential direction about the piston. The piston is configured such that maximum side loading forces from the body to the piston are applied to the piston at one of the panel portions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a top perspective view of one embodiment of a piston of the present invention; 
           [0006]      FIG. 2  is a top view of the piston of  FIG. 1 ; 
           [0007]      FIG. 3  is a side view of the piston of  FIG. 1  along the pin axis; 
           [0008]      FIG. 4  is a side view of the piston of  FIG. 1  along an axis that is perpendicular to the pin axis; 
           [0009]      FIG. 5  is a side cross section of the piston of  FIG. 3  inside a bore and attached to a rod; 
           [0010]      FIG. 6  is a side cross section of the piston of  FIG. 4  inside a bore and attached to a rod; and 
           [0011]      FIG. 7  is a top view of another embodiment of the piston. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    As best shown in  FIGS. 1 and 2 , in one embodiment the piston  10  of the present invention includes a crown  12  and a skirt  16  extending generally downwardly and away from the crown  12  (it should be noted that the piston shown in  FIGS. 1 and 2  is inverted from its configuration during use (shown in  FIGS. 5 and 6 ), and therefore the “downwardly” and “upwardly” orientation used herein is opposite from the orientation that shown in  FIGS. 1 and 2 ). The top surface  14  of the crown  12  can have any of a wide variety of configurations, such as dish, flat, domed or others, with various valve reliefs formed therein in the well known manner, but can in many cases be considered to be generally flat. 
         [0013]    Various circumferential grooves  18  may extend around the perimeter of the crown  12 , and are configured to receive various rings and scrapers therein to form a ring pack in a well known manner. The piston  10  may include a pair of pin towers  20  coupled to and/or extending generally downwardly/away from the crown  12 . Each pin tower  20  has a generally circular opening  22  formed therethrough to receive a pin  24  ( FIGS. 5 and 6 ) therethrough. The pin openings  22  define a pin axis A through their centers thereof. The pin axis A may be generally parallel to the crown  12 /top surface of the piston  10 . The piston  10  may also have an offset axis B which is oriented perpendicular to the pin axis A. 
         [0014]    During the power stroke of the piston  10 , the pin towers  20  transmit the combustion forces and downward movement of the piston  10  to the pin  24 , and ultimately to the connecting rod  26  ( FIGS. 5 and 6 ) and crankshaft (not shown). In addition, during the compression and exhaust strokes the pin towers  20  retain the pin  24  and crown  14  from flying upwardly toward the cylinder head. Accordingly, each pin tower  20  is typically a relatively stiff, strong structure, and together the pin towers  20  usually contribute the majority of the mass of the piston  10 . 
         [0015]    The skirt  16  may be generally annular/cylindrical and extend generally circumferentially around the entirety of the perimeter of the piston  10 /crown  12 . The skirt  16  may include a pair of opposed skirt panels/panel portions  32  positioned on about 180° opposite sides of the piston  10 . Each skirt panel  32  is designed to accommodate side loads during operation of the piston  10  and provide alignment of the piston  10  within the cylindrical bore  54 . Accordingly, each skirt panel  32  may be generally continuous, or lack any opening therethrough, and may be an area of increased thickness and/or strength and/or extend radially outwardly from the adjacent/underlying portions of the skirt  16 . In the illustrated embodiment, each skirt panel  32  circumferentially extends for a total angle of about 60° about the outer perimeter of the skirt  16 /piston  10 , although each skirt panel  32  may extend other distances/angles, such as between about 45°and about 75°, or between about 25° and about 75°, to sufficiently resist loading without adding excessive weight and frictional resistance. 
         [0016]    The skirt  16  may include a plurality of openings  34 ,  36  formed therein/therethrough. In particular, in the illustrated embodiment, the skirt  16  has a total of six openings  34 ,  36 , including a pair of opposed pin axis openings  34 , wherein each pin axis opening  34  is positioned on the pin axis A. The skirt  16  may also include two sets (pairs) of intermediate openings  36 , wherein each intermediate opening  36  in a set is positioned on either side of an adjacent skirt panel  32 . The number of openings  34 ,  36  can be varied as desired. 
         [0017]    Each skirt panel  32  may be positioned on the offset axis B. Each skirt panel  32  may be generally “I” shaped (as best shown in  FIG. 4 ), or generally triangular (not shown), in front view, but can also have various other shapes and configurations. In the “I” shaped configuration each skirt panel  32  has a main body portion  32   a,  pair of opposed bottom flanges  32   b  extending outwardly from the main body portion  32   a,  and (optionally) a pair of opposed top flanges  32   c  extending outwardly from the main body portion  32   a.  The main body portion  32   a  may extend generally the full axial height of the skirt  16 . In contrast, each flange portion  32   b / 32   c  may be at least partially positioned below/above an associated or adjacent opening  46 , and thus extend less than the full axial height of the skirt  16 . As shown in, for example,  FIG. 1 , an angled, curved, or chamfered portion  40  may be provided as a transition between the increased thickness of each skirt panel  32  and the reduced-diameter area of the adjacent skirt  16 . 
         [0018]    The piston  10 /skirt  16  may include a generally continuous hoop or band  42  extending circumferentially around the periphery of the piston  10 /skirt  16 . The band  42  may be located at or adjacent to a bottom edge of the piston  10 ; that is, at an axially opposite end of the piston  10  relative to the crown  12 . 
         [0019]    The piston  10  may include a plurality of struts  44 ,  46  that extend from a radially outward end of the piston, positioned at or adjacent to the band  42  and/or skirt panels  32 , radially inwardly to the pin towers  20 . For example, the piston  10  may include a pair of stiffening members or converging strut assemblies, wherein each converging strut assembly includes a pair of struts  44  that converge in the radially outward direction. As shown in  FIG. 2 , each converging strut  44  may form an acute angle C with respect to the offset axis B. The angle C can vary as desired, but in one case is between about 10° and about 35°. 
         [0020]    Each converging strut  44  may terminate (i.e. at its radially outward end) at or adjacent to an associated skirt panel  32  and, more particularly, at or adjacent to the circumferential center of the skirt panel  32 . The converging struts  44  may be configured such that a centerline D drawn through each converging strut  44  intersect at a position E that is positioned outside of but relatively close to the associated skirt panel  32 . In particular, the distance between the intersection point E and the skirt panel  16  (i.e., along the offset axis B) may be less than ½ or ¼ of the average radius of the piston  10 , or more particularly, less than about ⅛ of the average radius of the piston  10 . As will be described in greater detail below, in may be desired to relatively closely position point E relative to the skirt panels  32  so that the struts  44  provide their greatest support at or adjacent to the center of the skirt panel  32 . However, it should be noted that a variety of configuration of struts  44  may be utilized to provide support to the skirt panels  32 , including struts that diverge in a radially outward direction, struts that neither converge or diverge in a radially outward direction, the use of single strut, etc. 
         [0021]    The piston may include two or more sets (or pairs) of supplemental struts  46 . Each supplemental strut  46  may have a radially outward end positioned adjacent to an the end of associated pin axis opening  34 , and extend radially inwardly to an associated pin tower  20 . In the illustrated embodiment each supplemental strut  46  diverges from the associated other supplemental strut in the radially outward direction. However, it should be noted that a variety of configuration of struts  46  may be utilized, including struts  46  that converge in a radially outward direction, struts that neither converge or diverge in a radially outward direction, etc. Each strut  44 ,  46  may extend generally the full axial height of the piston  10 ; i.e. such that each strut  44 ,  46  is not a triangular “buttress-style” strut; although in some cases buttress-style struts may be used. 
         [0022]    The piston  10 , including the crown  12 , skirt  16 , and/or band  42 , may be circular in top view, or may be of a non-circular shape in top view (see  FIG. 7 ), such as oval or elliptical (wherein “oval” as used henceforth shall include ellipses, elliptical shapes, non-elliptical ovals and the like; and wherein “oval” includes circular as a subset thereof). In some cases, the piston  10  may have a uniform outer top-to-bottom shape (i.e. in the axial direction from the crown  12  to the bottom of the skirt  16 /band  42 ). Alternatively, the outer shape of the piston  10  may vary along its the axial height. For example, various portions of the piston  10  may have various shapes and dimensions, such as circular, circles with varying diameters, ovals, ovals having varying diameters (including varying major and minor diameters), etc. 
         [0023]    In one embodiment, the crown  12 , skirt  16  and/or band  42  are of a uniform oval shape having a major axis (i.e., of a greater relative length) oriented generally parallel to the pin axis A, and a minor axis (i.e., of a lesser relative length) oriented generally perpendicular to the pin axis A (i.e., aligned with the offset axis B). Although it may vary, the ratio between the major axis and the minor axis may be between 1.4:1 and 1.05:1, or between 1.4:1 and 1:1 to provide the advantages described below. 
         [0024]    The band  42 , struts  44 ,  46 , and elliptical/oval shape or other configuration provide certain advantages, and together cooperate to improve performance and stiffness of the piston. In particular, as noted above, the piston  10 /skirt  16  may have an oval configuration in which the major axis is oriented parallel to the pin axis A. During operation, the piston  10  is reciprocated up and down but also tends to move laterally (so-called secondary motion or rocking) in the direction of the offset axis B (i.e. as the pin  24  pivots about the pin axis A; see  FIGS. 5 and 6 ). However, since the radially outward end of the chamfer  40  A may protrude outwardly further than any other points on the piston  10  (due to the increased thickness of the skirt panels  32  and the orientation of the oval shape), the chamfer  40  may receive the initial side loads as the piston  10  bears upon the side walls or body  52  of the bore  54  (since the chamfer is positioned closer to the (longer) major axis A than other portions or the protruding skirt panel  32 ). 
         [0025]    Only one side of the skirt  16  may initially engage the wall  52  in a single stroke. Alternately, more than one initial contact point may occur, or additional points of contact between the skirt  16  and wall  52  may arise during continued movement/deformation of the piston  10 . Moreover, it should be noted that the initial contact between the skirt  16  and the wall  52  may not always occur at an chamfer  40 . Depending upon the orientation of the piston  10  and the applied forces, the initial contact may take place at various other positions around the perimeter of the skirt  16 . 
         [0026]    Due to the intermediate openings  36  formed in the skirt  16 , and other designed features along the skirt  16 , the skirt  16 /band  42  may be configured to be relatively easily deformed at the initial point of contact  40 . The relative flexibility of these portions of the skirt  16  thereby causing the skirt  16  to conform to the inner surface  52  of the bore  54 . Accordingly, as increased forces are applied (i.e., the piston  10  is continued to be moved in a stroke) the deformation of the skirt  16  increases/expands/moves circumferentially away from the initial point of contact  40  in the direction as shown by arrow  58  in  FIGS. 1-4 . 
         [0027]    The chamfered/angled edges  40  adjacent to the skirt panels  32  help to guide deformation of the piston  10  such that the skirt panel  32  is smoothly deformed against the bore surface  52 . Thus, each chamfered edge  40  may be considered a guide surface that guides the increasing or greatest stresses toward the center of the skirt panel  32 . The initial area of contact provided by the chamfered edge  40 /flanges  32   b,    32   c  also help to triangulate the piston  10  within the bore  54  and thereby provide several points of contact to guide piston  10  in its reciprocal movement and reduce piston rocking The circumferential extent of each skirt panel  32 , and/or its flanges  32   b ,  32   c,  can be adjusted to provide for desired triangulation characteristics for the piston  10  to reduce secondary motion. 
         [0028]    As the deformation of the skirt  16  expands around its perimeter (i.e., in the direction of arrow  58 ), the leading edge of deformation/contact eventually reaches the main body  32   a  of the skirt panel  32 . Thus, generally all side loading forces applied to the skirt  16 , wherever initially applied, are eventually guided circumferentially toward the main body  32   a  upon the application of sufficient force. Due to the increased stiffness contributed by the main body  32   a,  continued deformation of the skirt  32  is more strongly resisted. However, upon the application of sufficient forces, the center of each skirt panel  32  is pressed into contact with the bore surface  52 , which thereby ensures that the greatest side loads are applied to the circumferential center of the skirt panel  32  (see arrow  56  in  FIG. 6 ). 
         [0029]    As noted above, each converging strut  44  terminates at or adjacent to the center of the associated skirt panel  32 . In this manner, when the greatest loads  56  are applied to the center of the skirt panel  32 , the converging struts  44  provide resistance and transmit side loading stresses to the relatively strong, stiff pin towers  20 . In this manner, the converging struts  44  provide the greatest stiffness at the point at which the greatest loads are typically applied. The skirt panels  32  may also be configured to relatively even spread side loads across their surfaces to minimize high stress/force concentrations. 
         [0030]    In addition, the band  42  extends circumferentially around the lower edge of the skirt  16 , connecting the skirt  16  and all of the struts  44 ,  46  together, thereby providing structural integrity to the piston  10 . The increased stiffness provided by the band  42  and struts  44 ,  46  may enable the thickness of the crown  12  to be reduced, thereby providing cost savings and reduced mass to enable increased inertial response of the piston  10 . The increased stiffness may also reduce stress peaks and stress concentration on the undercrown of the piston  10  (i.e. wherein the pin towers  20  and struts  44 ,  46  are attached to the crown  12 ). 
         [0031]    In addition, since the stiffness provided by the band  42  and struts  44 ,  46  creates a more robust piston  10 , the size of the skirt panels  32  may be able to be correspondingly reduced, thereby further reducing weight and frictional forces during use of the piston  10 . Moreover, reduction of thickness of the crown  12  and the size of the skirt panels  32  helps to ensure that more weight of the piston  10  is positioned closer to the pin axis A, thereby providing a more stable piston assembly. Finally, an improved temperature distribution across the piston  10 , particular across the top surface  14 , may be provided, which reduces thermal stress concentrations within the crown  12 . 
         [0032]    It should be noted that when the piston  10  is oval, the orientation of the oval described herein is opposite to that of typical design. In particular, in many conventional piston designs, the major axis of the oval is perpendicular to the pin axis. This configuration is used since side loading forces are, in that case, initially applied to the ends of the piston that are at positions perpendicular to the pin axis A, which is where the load-resisting side panels are positioned. Thus, such a configuration is designed to resist the initial side loads. 
         [0033]    In contrast, the oval design disclosed herein operates on completely different principles and is designed to resist maximum (and not necessarily initial) side loads. In particular, instead of applying the load initially to the center of skirt panels (which would then be required to deform to distribute the load), the load is initially applied away from the center of the skirt panels (i.e. at the area of initial contact  40 ) at relatively weaker/more deformable areas of the skirt  16 . These areas of the skirt  16  then deform to ultimately distribute the load to the center of the skirt panels  32 , which are designed to be inherently stiff and resist deformation. 
         [0034]    Thus, in sum, side loads are typically relatively low at the beginning of a stroke, and increase to some peak level during a stroke. In this manner, initial contact may begin at the initial contact points  40 , or some other position, or even multiple positions, and move circumferentially around the piston  10  such that the greatest side load forces  56  are applied across the center of a skirt panel  32 . The shape of the piston  10 , and the ratio of the major and minor axes, taking into account the deflection of the skirt  16  and the thickness of the skirt panels  32 , must be carefully selected to ensure that with sufficient deformation the largest side loads are applied to the skirt panels  32 . In this manner, the highest concentration of loading can be resisted by the inherently stiff skirt panels  32  that are not designed or intended to be deflected. Moreover, the converging struts  44  help increase the stiffness at the center of the skirt panels  32 , and the band  42  helps to provide continuity between all the struts  44 ,  46  and pin towers  32  to create a robust piston design. 
         [0035]    Having described the invention in detail and by reference to the various embodiments, it should be understood that modifications and variations thereof are possible without departing from the scope of the invention.