Abstract:
An improved configuration for internal combustion engine that reduces side forces on pistons during the engine cycle. The improvement is an intermediate and guided bridge element located between pull rods and pistons with articulated connections that allow side forces to be dissipated away from the pistons.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority benefit of provisional application Ser. No. 61/209,904, filed Mar. 12, 2009. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention is related to the field of internal combustion engines and more specifically to improvements in such engines configured with opposing cylinders and opposing pistons in each cylinder (“OPOC engine”). 
       BACKGROUND 
       [0003]    This invention involves improvements to internal combustion engines and in particular OPOC engines of the type described and claimed in earlier U.S. Pat. Nos. 6,170,443, and 7,434,550, which are incorporated herein by reference. Other types of OPOC engines having one or more crankshafts, also can benefit from the present invention. 
         [0004]    As background, the OPOC engine from U.S. Pat. No. 6,170,443 is shown in  FIGS. 1 and 2 . In those figures, the engine configuration is shown to comprise a left cylinder  100  ( 1100   FIG. 2 ), a right cylinder  200  ( 1200 ), and a single central crankshaft  300  ( 1300 ) located between the cylinders. The left cylinder  100  has an outer piston  110  and an inner piston  120 , with combustion faces  111  and  121  respectively, the two pistons forming a combustion chamber  150  between them. The right cylinder  200  similarly has an outer piston  210 , an inner piston  220 , with combustion faces  211  and  221  and combustion chamber  250 . Each of the four pistons  110 ,  120 ,  210 , and  220  are connected to a separate eccentric on the crankshaft  300  ( 1300 ). 
         [0005]    The inner piston  120  of the left cylinder  100  is connected to crankshaft eccentric  312  by means of pushrod  412 ; the inner piston  220  of the right cylinder  200  is similarly connected to crankshaft eccentric  322  by pushrod  422 . During normal engine operation, pushrods  412  and  422  are always under compression. The pushrods have concave ends  413  and  423  which ride on convex cylindrical surfaces  125  and  225  on the rear of the inner pistons. 
         [0006]    The outer piston  110  of the left cylinder  100  ( 1100 ) is connected to crankshaft eccentric  311  by means of pullrod  411  ( 1411 ); the outer piston  210  of the right cylinder  200  ( 1200 ) is similarly connected to crankshaft eccentric  321  by pullrod  421  ( 1421 ). During normal engine operation, pullrod s  411  ( 1411 ) and  421  ( 1421 ) are always under tension. While single pullrods are shown on the near side in  FIGS. 1 and 2 , it should be understood that pairs of pullrods are used, with one pullrod on the near side of each cylinder and one on the far side of each cylinder. The near and far side pullrods connect to separate crankshaft journals having the same angular and offset geometries. The pullrods  411  ( 1411 ) and  421  ( 1421 ) communicate with the outer pistons by means of pins  114  ( 1114 ) and  214  ( 1214 ) that pass through slots ( 1115 ) and ( 1215 ) in the cylinder walls 
         [0007]    The four pistons  110 ,  120 ,  210 , and  220  have a plurality of piston rings  112 ,  122 ,  212 , and  222 , respectively, located behind the combustion faces. Additional piston rings may be added to the piston skirts, as may be required to reduce wear and control lubrication oil distribution. The cylinders  100  and  200  each have intake, exhaust, and fuel injection ports. On the left cylinder  100 , the outer piston  110  opens and closes intake ports  161  (intake piston) and the inner piston  120  opens and closes exhaust ports  163  (exhaust piston). Fuel injection port  162  is located near the center of the cylinder. On the right cylinder  200 , the inner piston  220  opens and closes intake ports  261  and the outer piston opens and closes exhaust ports  263 . Again, fuel injection port  262  is located near the center of the cylinder. The asymmetric arrangement of the exhaust and intake ports on the two cylinders serves to help dynamically balance the engine, as described below. 
         [0008]    Each of the four crankshaft eccentrics  311 ,  312 ,  321 , and  322  are positioned with respect to the crankshaft rotational axis  310 . The eccentrics for the inner pistons  312 ,  322  are further from the crankshaft rotational axis than the eccentrics for the outer pistons  311 ,  321 , resulting in greater travel for the inner pistons than for the outer pistons. The eccentrics for the inner left piston  312  and the outer right piston  321 , the pistons which open and close the exhaust ports in the two cylinders, are angularly advanced, while the eccentrics for the outer left piston  311  and inner right piston  322  are angularly retarded (note that the direction of crankshaft rotation is counterclockwise, as indicated by the arrow in  FIG. 1 ). 
         [0009]    As further shown in  FIGS. 1 and 2 , each cylinder is supercharged. Supercharging improves scavenging, improves engine performance at low rpms and recovers energy from the engine exhaust. 
         [0010]    As mentioned above, the pullrods are always under tension forces F r  that are communicated to and from the piston (via piston pins) as compression forces F p . During the times that the pullrods are at an angle with respect to the reciprocating axis of the outer pistons, there are minor side force components F s  generated at the outer piston pins  114  ( 1114 ) and  214  ( 1214 ). These side forces occur during both the power and compression strokes of the engine cycle and are directed towards the cylinder walls. Several efforts have been made to minimize the effects of such side forces, including increasing the lubrication between the cylinder wall and the piston skirt; providing more piston rings along the piston skirt; and reducing the length of the piston skirt. However, each conventional attempt to reduce the effects of pullrod side forces has resulted in other undesirable effects. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention provides reduction in the side forces attributed to pullrod connections to the outer pistons of an OPOC engine by providing an intermediate bridge member between the pullrods and the outer piston to dissipate the side forces and isolate them from reaching the outer piston. 
         [0012]    The present invention provides reduction in the side forces attributed to pullrod connections to the outer pistons of an OPOC engine by providing an intermediate bridge member with articulated low friction connections to the pullrods and the outer piston. 
         [0013]    The present invention provides reduction in the side forces attributed to pullrod connections to the outer pistons of the OPOC engine by providing an extension to the cylinder housing with a pair of elongated side openings with lubricated guide edge bearing surfaces for allowing an intermediate bridge member between the pullrods and the outer pistons to slide there-along during engine operation to dissipate the side forces and isolate them from reaching the outer piston. 
         [0014]    The present invention provides reduction in the side forces attributed to pullrod connections to the outer pistons of the OPOC engine by providing a low friction and rotatable bearing connection between the pullrods and the intermediate bridge member that is located between the pullrods and the outer piston. 
         [0015]    The present invention provides reduction in the side forces attributed to pullrod connections to the outer pistons of the OPOC engine by providing a ball joint connection between the intermediate bridge member and the outer piston. 
         [0016]    Two embodiments of the intermediate bridge element are shown. In a first embodiment, the bridge element contains a pair of upper and lower wear pads that contact the lubricated guide edge bearing surfaces provided by the extension to the cylinder housing. In a second embodiment, the upper and lower surfaces of the intermediate bridge element are used to directly contact and slide along the lubricated guide edge bearing surfaces provided by the extension to the cylinder housing. 
         [0017]    It is an object of the present invention to provide an improved OPOC engine with reduced friction and increased efficiencies by eliminating side forces on the outer pistons during the engine cycle. 
         [0018]    It is another object of the present invention to provide an improved OPOC engine in which the connections between the outer pistons and their associated pull rods do not allow the communication of off-axis side forces to either element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a cross-sectional concept view depicting the operative elements of a prior art OPOC engine configuration and is discussed above. 
           [0020]      FIG. 2  is a plan view of a physical embodiment of the same prior art OPOC engine shown in  FIG. 1 . 
           [0021]      FIG. 3  is a cut-away perspective view of an OPOC engine containing the improvements of the present invention. 
           [0022]      FIG. 4  is a perspective view of the OPOC engine shown in  FIG. 3  with one end cut-away to illustrate the present invention. 
           [0023]      FIG. 5  is a cross-sectional illustration of an embodiment of the present invention taken along lines  5 - 5  in  FIG. 4 . 
           [0024]      FIG. 6  is an enlarged view of a portion of the OPOC engine shown in  FIG. 4 , containing an embodiment of the present invention. 
           [0025]      FIG. 8  is a partial cross-sectional view taken along section line  8 - 8  in  FIG. 6 . 
           [0026]      FIG. 9  is an enlarged top plan view of the pull rod bridge element of the present invention. 
           [0027]      FIG. 10  is a top plan view of an embodiment of the guided bridge connected between pull rods and the outer piston of an OPOC engine. 
           [0028]      FIG. 11  is a perspective view of the underside of a first embodiment of an OPOC engine outer piston configured to mate with the guided bridge shown in  FIGS. 9 and 10 . 
           [0029]      FIG. 12  is a perspective view of the underside of a second embodiment of an OPOC engine outer piston configured to mate with the guided bridge shown in  FIGS. 9 and 10 . 
           [0030]      FIG. 13  is a perspective partial cross-sectional view of a bridge assembly the present embodiment mated with a second embodiment of the outer piston shown in  FIG. 12 . 
           [0031]      FIGS. 14 and 15  are vector graphs showing the possible effects of conflicting forces on embodiments of the present invention with and without spherical joints between the pull rods and the bridge element. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The present invention is shown in  FIGS. 3-13 , in conjunction with an OPOC engine of the type described above and incorporated herein by reference. In  FIG. 3 , an OPOC engine is shown as having a left cylinder  500 , a right cylinder  600  in a housing  900  and a common crankshaft  700 . Left cylinder  500  has an outer piston  510  and an inner piston  520 . Opposing right cylinder  600  has an outer piston  610  and an inner piston  620 . Outer piston  510  is connected to crankshaft  700  via a pair of pull rods  511   a  and  511   b . Outer piston  610  is connected to the crankshaft  700  via a pair of pull rods  611   a  and  611   b.    
         [0033]    The improvement over the prior art OPOC engine described above results from the use of a guided bridge  800  that is located between the outer piston  510  and the pullrods  511   a  and  511   b . (Although the following discussion is directed to the left cylinder  500 , it should be understood that the right cylinder is identically configured to provide identical improvements to the engine as a whole.) 
         [0034]    Guided bridge  800  is mounted for reciprocating movement in an extension cap  902  that connects to and forms part of engine housing  900 . Guided bridge  800 , in this embodiment, (see  FIGS. 9 and 10 ) has a generally triangular shape with its base  801  being connected to the parallel pullrods  515   a  and  515   b , and the a ball shaped nose  802  extending from the apex of the triangular shape along a projection  805 . Bridge nose  802  is formed as a spherical ball for mating with a like hemispherical ball socket  512  in outer piston  510 . The spherical mating of the bridge to the piston provides for point contact between those elements which in turn provides increased flexibility between the two to significantly reduce side forces being imposed onto the piston. 
         [0035]    The base  801  of the triangular shaped guided bridge  800  has bosses  803   a  and  803   b  that extend outwardly along a horizontal axis “A-A” that is perpendicular to the cylinder axis. Bosses  803   a  and  803   b  fit within the races  507   a  and  507   b  of needle bearings  514   a  and  514   b  ( FIG. 13 ) that are mounted in hubs  515   a  and  515   b  of pullrods  511   a  and  511   b , respectively. The upper and lower surfaces  804 / 806  and  808 / 810  of the guided bridge  800  are ground smooth and serve as the contact points with respect to the lower and upper guide surfaces  904 / 906  and  908 / 910  formed in extension cap  902 . 
         [0036]    Extension cap  902  contains a central aperture  903 ; and two sets of opposing lower and upper guide surfaces  904 / 906  and  908 / 910  that serve as slide bearings. Guide surfaces  904 / 906  and  908 / 910  are parallel to the cylinder axis and the reciprocating directions of travel followed by piston  510  to form a guideway for the guided bridge  800 . The material used for lower and upper guide surfaces  904 / 906  and  908 / 910  can be any low friction polished metal, ceramic or composite that provides long life in a wide range of environmental temperatures and from any caustic elements that may contaminate lubrication fluids. Extension cap  902  contains several intercommunicating passages that allow lubricating oil present in the housing  900  to be circulated to and directed onto the guideway surfaces to further reduce any friction that may otherwise contribute to side forces. 
         [0037]    While the embodiment above is described as having guided bridge face surfaces to guide face surfaces as being smoothly ground or polished metal surfaces, it is because such surfaces can be formed very economically with significantly improved results compared to the prior art. However, it is appreciated that other low friction alloy, ceramic or plastic materials could be implanted into the opposing surfaces to have sliding surface contact if their low friction properties are suitable for improvements in this environment. 
         [0038]    Outer piston  510  ( FIGS. 10 and 11 ) is configured with a hemispherical ball socket  513  to receive the forward part of spherical bridge nose  802  and provide for a spherical contact between guided bridge  800  and outer piston  510 . An expandable wear ring  816  and a snap ring are held in separate circular channels within the under cavity of piston  510  and surround projection  805 , below bridge nose  802 . Expandable wear ring  816  along with snap ring  815  function to keep the spherical socket  512  and bridge nose  802  connected during assembly and during the crank start prior to engine operation. Constant compression during engine operation serves to maintain the connection and no pressure is exerted on those elements during the operation. During the crank start period and prior to ignition, there are periods when the pull rods  511   a  and  511   b  draw the outer piston  510  outwards towards its bottom dead center position. That is when it is necessary for the piston  510  to be retained in contact with the bridge nose  802  on the guided bridge  800 . 
         [0039]    A pin  512  also serves to connect outer piston  510  to bridge nose  802 . The pin is vertically oriented (perpendicular to the horizontal axis extending through bosses  803   a  and  803   b  in piston  510  and a vertically aligned hole  812  in guide bridge nose  802  (aligned perpendicular to the axis of cylinder  500 ). 
         [0040]    When the pistons of left cylinder  500  enter their power stoke of the engine cycle, the expanding gases present on the face of piston  510  force the ball socket  512  against the bridge nose  802 . Due to the interaction of the bosses  803   a  and  803   b  with the bearings  514   a  and  514   b , and the resistance of the angled pull rods  511   a  and  511   b , any side forces that are generated are directed between upper and lower surfaces  804 / 806  and  808 / 810  of guided bridge  800  to the corresponding lower and upper guide surfaces  904 / 906  and  908 / 910  while guided bridge  800  is sliding there along. As a result, almost all pullrod generated side forces are dissipated so as not to be fed back and effect the travel of outer piston  510 . 
         [0041]    When the pistons of left cylinder  500  enter their compression stoke of the engine cycle, pull rods  511   a  and  511   b  are again under tension and being pulled by the crank shaft  700 . Pull rods  511   a  and  511   b  interact with guided bridge  800  through bearings  514   a  and  514   b  and bosses  803   a  and  803   b  to force the bridge nose  802  against socket  512 . This action causes outer piston  510  to be pushed along the cylinder axis towards inner piston  520  against the resistance of air being compressed within the cylinder. Due to the interaction of the angled pull rods  511   a  and  511   b  through bearings  514   a  and  514   b  with bosses  803   a  and  803   b  and the resistance of outer piston  510 , any side forces that are generated are directed between the upper and lower surfaces  804 / 806  and  808 / 810  of the guided bridge  800  to the corresponding lower and upper guide surfaces  904 / 906  and  908 / 910  while guided bridge  800  is sliding there along. Consequently almost all pullrod generated side forces are isolated from outer piston  510 . As stated earlier, the reduction in side forces on the pistons of an internal combustion engine is highly desirable in order to reduce piston chafing or scuffing that may sometimes occur during operating conditions. 
         [0042]      FIGS. 12 and 13  illustrate another piston configuration  310  in which a spherical socket  315  mates with bridge nose  802  on guided bridge  800 . This piston differs from the earlier described piston  510  in the manner in which it is retained to guided bridge  800 , In this case, a pin  312  is fastened to the underside of piston  310  by bolts  314  and  316  (or by other equivalent retaining devices). Pin  312  is fitted through vertical hole  812  in bridge nose  802  and held in place by bolts  314  and  316 . Piston  310  provides for alternative connection means and may offer improvements in durability or assembly costs. 
         [0043]      FIG. 13  also illustrates an improved bearing structure that may be employed in the present invention to further reduce undesired forces to the elements. In this case, the use of a spherical bearing race ring  518   a  and  518   b  inside pull rod hubs  515   a  and  515   b  provides added rotational flexibility. The circular inner surfaces of pull rod hubs  515   a  and  515   b  are spherically curved to accept race rings  518   a  and  518   b  having like outer circular surfaces that are also spherically curved. The mating spherical surfaces provide a spherical bearing that allows for minor rotation to occur between the bosses of guide  800  and the pull rods without creating bending torque on the pull rods. The inner surface of race rings  518   a  and  518   b  are planar to support the rotation of needle bearings  514   a  and  514   b  in a conventional fashion. 
         [0044]    The function of the spherical bearing is illustrated with respect to the vector graphs of  FIGS. 14 and 15 . In  FIG. 14 , the condition without a spherical bearing is illustrated. In  FIG. 15 , the condition with a spherical bearing is illustrated. The vertical dashed line of both  FIGS. 14 and 15  indicates the desired position of the guided bridge, i.e., continuously orthogonal to the cylinder axis. The angle represented in the upper portion of the vector graph illustrates an exaggerated deformation that could be exerted on the guided bridge during unusual operating load conditions. 
         [0045]    In  FIG. 14 , without a spherical bearing, if such angular stress were to occur on the guided bridge and its bosses were thrown off-angle, the result would be a torque angle generated on the rod hobs at “A” that would cause slight bending and stress on the pull rods  511 . 
         [0046]    In contrast,  FIG. 15  illustrates that if the guided bridge were to encounter the same stresses, the bosses would be able to rotate slightly within the rod hubs due the spherical bearing and not induce torque bending on the pull rods  511  at “B” 
         [0047]    The embodiment shown and described herein is merely exemplary of various configurations that may be designed to exhibit the inventive concepts recited in the claims and is not intended to be restrictive.