Patent Publication Number: US-8539918-B2

Title: Multi-cylinder opposed piston engines

Description:
PRIORITY 
     This patent application claims priority to U.S. Provisional application for patent 61/208,136, filed Feb. 20, 2009, and to U.S. Provisional application for patent 61/209,911, filed Mar. 11, 2009, both commonly assigned herewith. 
    
    
     RELATED APPLICATIONS 
     This application contains subject matter related to the subject matter of the following patent applications 
     U.S. patent application Ser. No. 10/865,707, filed Jun. 10, 2004 for “Two Cycle, Opposed Piston Internal Combustion Engine”, published as US/2005/0274332 on Dec. 15, 2005, now U.S. Pat. No. 7,156,056, issued Jan. 2, 2007; 
     PCT application US2005/020553, filed Jun. 10, 2005 for “Improved Two Cycle, Opposed Piston Internal Combustion Engine”, published as WO/2005/124124 on Dec. 29, 2005; 
     U.S. patent application Ser. No. 11/095,250, filed Mar. 31, 2005 for “Opposed Piston, Homogeneous Charge Pilot Ignition Engine”, published as US/2006/0219213 on Oct. 5, 2006, now U.S. Pat. No. 7,270,108, issued Sep. 18, 2007; 
     PCT application US/2006/011886, filed Mar. 30, 2006 for “Opposed Piston, Homogeneous Charge, Pilot Ignition Engine”, published as WO/2006/105390 on Oct. 5, 2006; 
     U.S. patent application Ser. No. 11/097,909, filed Apr. 1, 2005 for “Common Rail Fuel Injection System With Accumulator Injectors”, published as US/2006/0219220 on Oct. 5, 2006, now U.S. Pat. No. 7,334,570, issued Feb. 26, 2008; 
     PCT application US/2006/012353, filed Mar. 30, 2006 “Common Rail Fuel Injection System With Accumulator Injectors”, published as WO/2006/107892 on Oct. 12, 2006; 
     U.S. patent application Ser. No. 11/378,959, filed Mar. 17, 2006 for “Opposed Piston Engine”, published as US/2006/0157003 on Jul. 20, 2006, now U.S. Pat. No. 7,360,511, issued Apr. 22, 2008; 
     PCT application PCT/US2007/006618, filed Mar. 16, 2007 for “Opposed Piston Engine”, published as WO 2007/109122 on Sep. 27, 2007; 
     U.S. patent application Ser. No. 11/512,942, filed Aug. 29, 2006, for “Two Stroke, Opposed-Piston Internal Combustion Engine”, published as US/2007/0039572 on Feb. 22, 2007; 
     U.S. patent application Ser. No. 11/629,136, filed Jun. 10, 2005, for “Two-Cycle, Opposed-Piston Internal Combustion Engine”, published as US/2007/0245892 on Oct. 25, 2007; 
     U.S. patent application Ser. No. 11/642,140, filed Dec. 20, 2006, for “Two Cycle, Opposed Piston Internal Combustion Engine”; 
     U.S. patent application Ser. No. 11/725,014, filed Mar. 16, 2007, for “Opposed Piston Internal Combustion Engine With Hypocycloidal Drive and Generator Apparatus”; 
     U.S. patent application Ser. No. 12/075,374, filed Mar. 11, 2008, for “Opposed Piston Engine With Piston Compliance”, published as US/2008/0163848 on Jul. 10, 2008; and, 
     U.S. patent application Ser. No. 12/075,557, filed Mar. 12, 2008, for “Internal Combustion Engine With Provision for Lubricating Pistons”. 
     BACKGROUND 
     The field includes internal combustion engines. More particularly, the field includes opposed piston engines. More particularly still, the field includes opposed piston engines with a plurality of cylinders, or multi-cylinder opposed piston engines. 
     In an opposed piston engine, each cylinder has two ends and two pistons, with a piston disposed in each end. An inlet port is machined or formed in one end (“the inlet end”) of the cylinder, and an exhaust port in the other end (“the exhaust end”). An opposed piston engine may have one or more crankshafts and/or other outputs and may use a variety of fuels. In a typical opposed piston engine, an air-fuel mixture is compressed in the cylinder bore between the crowns of the pistons as they move toward each other. The heat resulting from compression causes combustion of the air-fuel mixture as the pistons near respective top dead center (TDC) positions in the middle of the cylinder. Expansion of gases produced by combustion drives the opposed pistons apart, toward respective bottom dead center (BDC) positions near the ports. Movements of the pistons are phased in order to control operations of the inlet and exhaust ports during compression and power strokes. Advantages of opposed piston engines include efficient scavenging, high thermal and mechanical efficiencies, simplified construction, and smooth operation. See  The Doxford Seahorse Engine , J F Butler, et al., Trans. I. Mar. Eng., 1972, Vol. 84. 
     Recent technology designs described in the cross-referenced patent applications have improved many aspects of opposed piston engine construction and operation. For example, novel cooling designs focus on the thermal profiles exhibited by engine power components during engine operation. In this regard, tailored cooling effectively compensates for the longitudinally asymmetrical thermal signatures exhibited by cylinders during engine operation, while the opposed pistons are cooled by radially symmetrical application of coolant to the backs of their crowns. Cylinder construction is simplified by limiting cylinder liner length, which allows pistons to be substantially withdrawn and their skirts to be lubricated during engine operation. This design reduces welding and increases the power-to-weight ration of the engine. In order to reduce side forces on the pistons, no linkage pins (also called wristpins and gudgeon pins) are mounted within or upon the pistons. 
     Nevertheless, there is a need to integrate recent technological advances with additional improvements in multi-cylinder opposed piston engine constructions in order to further enhance the power-to-weight ratio, durability, adaptability, and compactness, and thereby increase the range of use, of such engines. 
     SUMMARY 
     Accordingly, the engine constructions described in this specification include certain improvements in an integrated, multi-cylinder opposed piston engine design including a unitary engine support structure to which cylinder liners are removeably mounted secured, and sealed, and on which crankshafts are rotatably supported. Cylinder liners are decoupled from exhaust, air intake, and cooling components, and pressurized air is provided to all cylinders in a single input plenum. 
     An opposed piston engine construction is constituted of an elongate member with a lengthwise dimension, a plurality of through bores extending through the member transversely to the lengthwise direction, and cylinder liners supported in the through bores. The cylinder liners are disposed in the through bores with exhaust ends extending out of the through bores along one side of the elongate member, and with inlet ends extending out of the through bores along an opposite side of the elongate member. The inlet ends of the cylinder liners extend through an elongate inlet plenum chamber on the elongate member with inlet ports of the liners all positioned within the plenum chamber. Scavenging air is provided through the plenum chamber to all of the inlet ports at a substantially uniform pressure to ensure substantially uniform combustion and scavenging in the cylinder liners throughout engine operation. The plenum chamber is supported entirely on the elongate member so as to be mechanically and thermally decoupled from the cylinder liners. This arrangement substantially reduces or eliminates transmission of mechanical and thermal stresses between engine structures and the cylinder liners, which might otherwise cause non-uniform distortion during engine operation of the cylinder liners and pistons disposed therein. 
     An opposed piston engine construction is constituted of a spar with a lengthwise dimension and a plurality of through bores transverse to the lengthwise dimension. A cylinder liner is supported in each through bore, with a pair of opposed pistons disposed in the internal bore of each liner. Top and bottom main bearings are mounted and aligned lengthwise with each other on the top and bottom of the spar, spaced from respective sides of the through bores. First and second crankshafts are supported in the top and bottom main bearings in a spaced parallel relationship in which the longitudinal axes of the crankshafts lie in a plane that intersects the cylinder liners and is perpendicular to the axes of their bores. A first lubricant distribution gallery extends generally lengthwise in the top of the spar with lubricant feed passages extending through the spar to the top main bearings. A second lubricant distribution gallery extends generally lengthwise in the bottom of the spar with coolant feed passages extending through the spar to coolant channels between the through bores and the cylinder liners and lubricant feed passages extending through the spar to the bottom main bearings. A pumped lubricant source is connected to provide a flow of lubricant to the first and second lubricant distribution galleries. 
     Further, the engine constructions described in this specification include certain improvements in the construction of cooled pistons with flexible skirts and compression seals, and in the construction of cylinders with control structures mounted in the bores to manage lubricant in the cylindrical interstice between the cylinder bore and the piston skirts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a multi-cylinder opposed piston engine constructed according to this specification. 
         FIG. 1B  is a perspective cross section of the engine of  FIG. 1A  taken transversely and perpendicularly to a longitudinal axis of the engine. 
         FIG. 1C  is a perspective vertical cross section of the engine of  FIG. 1A  taken along the longitudinal axis of the engine of  FIG. 1A . 
         FIG. 1D  is a perspective horizontal cross section of the engine of  FIG. 1A  taken along the longitudinal axis of the engine of  FIG. 1A . 
         FIG. 2A  is a perspective view of a longitudinal member, or spar, of the engine of  FIG. 1A  looking toward a first side of a drive train support structure. 
         FIG. 2B  is an exploded perspective view of elements of the engine positioned with respect to one side of the spar of  FIG. 2A . 
         FIG. 2C  is the exploded perspective view of the elements shown in  FIG. 2B  positioned with respect to another side of the spar of  FIG. 2A . 
         FIG. 2D  is a view of the spar from the same perspective as  FIG. 2C , with the elements seen in  FIGS. 2B and 2C  assembled thereto. 
         FIG. 2E  is a perspective view of a partially rotated cross section of the spar, with elements assembled thereto. 
         FIG. 2F  is a perspective vertical cross section of the spar of  FIG. 2A  taken along a longitudinal axis of the spar. 
         FIG. 2G  is a perspective view of a vertical cross section of the spar of  FIG. 2A , with certain elements assembled thereto. 
         FIG. 3A  is an exploded perspective view of a cylinder liner which may be assembled to the spar of  FIG. 2A . 
         FIG. 3B  is a side sectional view of the cylinder liner of  FIG. 3A . 
         FIG. 3C  is a side sectional view of a through bore of the spar of  FIG. 2A  which receives a cylinder liner such as the cylinder liner of  FIG. 3A . 
         FIG. 3D  is a frontal vertical cross sectional view of the spar of  FIG. 2A  with the elements of  FIGS. 2B and 2C  assembled thereto. 
         FIG. 3E  is a perspective view of the cylinder liner of  FIG. 3A , with an alternate 
         FIG. 4  is a perspective view of the engine of  FIG. 1A , with covers removed from one side thereof. 
         FIG. 5A  is a side sectional view of a piston with a moveable skirt which may be received in the cylinder liner of  FIG. 3A . 
         FIG. 5B  is a perspective exploded view of the piston of  FIG. 5A  showing elements of the piston. 
         FIG. 5C  is a side sectional view of the piston of  FIG. 5A  rotated by 90° from its position in  FIG. 5A . 
         FIG. 5D  is a perspective view showing each of a plurality of pistons according to  FIG. 5A  coupled by connecting rods to two crankshafts seen in  FIG. 1B . 
         FIG. 6  is an exploded view of a main bearing assembly of the engine of  FIG. 1A . 
         FIG. 7A  is an enlarged cross sectional view of a wiper for seating in the inner bore of the cylinder liner of  FIG. 3A .  FIG. 7B  is a side sectional view of the exhaust side of a cylinder liner showing the position of a wiper with respect to a piston at TDC in the cylinder liner.  FIG. 7C  is a side sectional view of the exhaust side of the cylinder liner showing the position of the wiper with respect to the piston at BDC in the cylinder liner. 
         FIG. 8A  is a perspective view of a first vertical section of the spar with elements mounted thereto, looking toward a second side of a drive train support structure. 
         FIG. 8B  is a perspective view of the spar with elements mounted thereto, looking toward the first side of the drive train support structure, with certain features cut away. 
         FIG. 8C  is a perspective sectional view of the spar, with elements mounted thereto, taken along lines C-C of  FIG. 8A . 
         FIG. 9  is a schematic drawing showing a control mechanization that regulates and manages the provision of lubricant for lubrication and cooling in the engine of  FIG. 1A . 
         FIG. 10  is a block diagram of an air charge system for use in the engine of  FIG. 1A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Constructions of a multi-cylinder, opposed piston engine are described and illustrated. Although the engine constructions include four cylinders, this configuration is intended to illustrate a representative embodiment, and should not limit the principles presented in this specification only to four-cylinder opposed piston engines. 
       FIG. 1A , is a perspective view, looking toward a first end of a multi-cylinder opposed piston engine  10 . The engine includes an air inlet adapter  12  and two crankshafts  14 ,  16  with dampers  18 ,  20  mounted to their respective corresponding ends. Engine exhaust is collected along a first side  31  of the engine  10 , and pressurized inlet air is distributed along a second side  32 . 
     As seen in  FIGS. 1B and 1C , the housing of the engine  10  includes an upper cover  35  and a lower cover  36 . The engine  10  has a generally lengthwise dimension along a longitudinal axis A l  ( FIG. 1B ), and includes an elongate longitudinal member, or spar,  50  that supports components of the engine, including the crankshafts  14 ,  16 , an output drive train  40 , a flywheel  41 , various auxiliary equipment (including a fuel pump  42 ), and cylinder liners (also referred to as “sleeves”)  70 . The cylinder liners  70  are disposed side by side, in a spaced parallel relationship oriented generally transversely to the longitudinal axis A l . Two opposed pistons  80  are supported for reciprocal movement in the bore of each cylinder liner  70 , toward and away from each other. Each piston  80  has a piston rod  82  fixed at one end to the back surface of the piston&#39;s crown, and coupled at the other end by a linking pin  84  to connecting rods  100 ,  110 . Each piston is coupled or linked by two connecting rods  100  to one crankshaft and by one connecting rod  110  to the other crankshaft. The connecting rods  100 ,  110  are cabined by the engine housing for reciprocal movement therein. The crankshafts  14 ,  16  are rotatably disposed in a spaced, parallel relationship by main bearings  60  mounted in longitudinal alignment along opposing top and bottom surfaces of the spar  50 . With the crankshafts  14 ,  16  mounted in this fashion, their longitudinal axes lie in a plane that intersects the cylinder liners  70  and is perpendicular to the axes of the bores in the cylinder liners  70 . The covers  35  and  36  form an engine enclosure within which lubricant is thrown and splashed by moving parts of the engine. A sump  129  on the bottom of the engine  10  collects oil for recirculation to the engine. In this description, the crankshaft  14  is referred to as the upper crankshaft, and the crankshaft  16  is the lower crankshaft. 
     Refer now to  FIG. 1C . The four cylinder liners  70  are supported in the spar  50 , as are four fuel injectors  130 , each mounted in a downwardly angled injector bore  131  through the top surface of the spar to a respective through bore  54 . An injection port  71  through the side of each cylinder liner  70  receives the nozzle tip of a fuel injector  130 . Preferably, the injection port  71  is positioned substantially at the longitudinal midpoint of the cylinder liner  70 , so as to provide fuel under pressure into the combustion space in the bore of the cylinder liner when the pistons are at or near top dead center during engine operation. As per  FIG. 1D , piston coolant manifolds  150  are supported on the insides of the engine covers, with one manifold extending along the engine within the first side  31  and the other manifold extending along the engine within the second side  32 . Each piston coolant manifold  150  includes four piston coolant jets  152 , each of which extends laterally from the manifold through sliding couplings in a respective linking pin  84  to deliver coolant into the bore of an associated piston rod  82  for cooling the associated piston  80 . In order not to interfere with piston movement, each jet  152  is fixed only to the piston coolant manifold  150  from which it extends, but is not fixed to the piston to which it provides coolant. 
     The spar  50 , best seen in  FIG. 2A , is the principal support element of the engine  10 . Preferably, the spar is cast from a high strength, lightweight aluminum alloy. Certain preformed elements such as tubes may be incorporated into the spar structure during casting to provide passages and galleys. Once cast, the spar may then be machined to fill out and complete its basic structure. The cast and machined spar preferably comprises through bores to support cylinder liners, an intake plenum, main bearing pedestals, a drive train support structure, and various galleries, passageways, and bores. 
     Referring now to  FIGS. 2A ,  2 B and  2 C, the spar  50  has first and second sides  51  and  52 , a lengthwise dimension  53 , and through bores  54  transverse to the lengthwise direction. The through bores  54  are disposed side by side in a spaced, parallel relationship, with their axes extending between the first and second sides of the engine. The air inlet adapter  12  is mounted to the spar  50  in fluid communication with an air intake (“inlet”) plenum  56  along the second side  52 . The inlet plenum  56  is constituted of an elongate trench formed in the second side  52  of the spar  50  into which inlet ends of the through bores  54  protrude. Two sets of main bearing assemblies  60  are mounted along the lengthwise dimension on opposing top and bottom surfaces of the spar  50 , which correspond respectively to the top and bottom of the engine. The main bearings  60  of each set are aligned lengthwise with each other on their respective surface. Each main bearing assembly has a pedestal  61  preferably formed as a part of the spar casting, and a removable outer bearing piece  62  attached by threaded screws or bolts to each main bearing pedestal  61 . 
     As per  FIG. 2B , a cylinder liner  70  is supported in each through bore  54 . of the spar  50 . The cylinder liners  70  are preferably removable from the through bores, although in some constructions, they may be press fit thereinto. Preferably, each cylinder liner  70  is mounted in a respective through bore  54  so as to be sealed therewith against fluid movement along its external surface, yet also so as to be removable therefrom. Each cylinder liner  70  includes an exhaust end  72  with an exhaust port  73  constituted of a circumferential ring of openings, an inlet end  74  with an inlet port  75  also constituted of a circumferential ring of openings, an external circumferential peripheral surface  76 , and an internal bore  77  with a longitudinal axis  78 . The cylinder liners  70  are disposed in the through bores  54  with the exhaust ends  72  extending out of the through bores along the first side  51  of the spar  50 , and with the inlet ends  74  extending out of the through bores  54  along the second side  52  of the spar  50 . As best seen in  FIG. 2C , an elongate intake cover  57  is attached by threaded screws or bolts to the spar  50 , over the inlet plenum  56 , to cover and seal the inlet plenum and to form a single plenum chamber wherein air at a positive pressure is provided for all of the cylinder inlet ports  75 . The cylinder liners  70  are disposed with the longitudinal axes  78  of their internal bores  77  parallel to each other and lying in a common plane that intersects the inlet plenum chamber. Further, the inlet ports  75  are all positioned within the plenum chamber. A plurality of cones  58  is formed on the inside of the intake cover  57 , such that all cones face the inlet plenum  56  when the cover is mounted. Each inlet cone  58  includes an opening  58   o  through the intake cover  57 . Each opening  58   o  has a circumferential seal seating groove  58   g . A seen in  FIG. 2D , the inlet end  74  of each cylinder liner  70  extends through the opening  58   o  of a respective inlet cone  58 . Each inlet cone  58  includes at least one, and preferably a plurality of vanes  58   v  situated in a circular array in the plenum chamber, around the inlet port  75  of the cylinder liner that extends through the opening  58   o . The vanes  58   v  of each inlet cone deflect pressurized air from the plenum chamber into the openings of an inlet port  75 . Advantageously, this plenum arrangement replaces prior art constructions in which multiple ducts and/or manifolds are attached to the outside of an engine block to feed air to each inlet port individually. Instead, this construction includes a single plenum chamber integrated into the structure of the spar to distribute pressurized air to all of the inlet ports. Further, the vanes  58   v  disposed in the plenum chamber induce swirl into the pressurized air entering the cylinder liners  70  through the inlet ports  75 . 
     Referring to  FIG. 2E , lubricant distribution galleries  180  and  190  extend generally lengthwise in the upper and lower portions of the spar  50 , respectively, or opposed sides of the through bores  54 . Feed passages extend in the spar  50  from the lubricant distribution gallery  180  to the upper main bearing pedestals  61  along the top of the spar; one such feed passage  182  is seen in  FIG. 2G . As seen in  FIGS. 2E and 2G , each lubricant feed passage  182  opens into a circumferential lubricant feed groove  64  in the cylindrical inner surface of a respective upper main bearing pedestal  61 . 
     Referring to  FIGS. 2F and 2G , lubricant feed passages, one indicated by  192 , extend downwardly in the spar  50  from the lubricant distribution gallery  190  to the lower main bearing pedestals  61  along the bottom of the engine. Preferably, each lubricant feed passage  192  opens into a circumferential lubricant feed groove  64  in the cylindrical inner surface of a respective lower main bearing pedestal  61 . Coolant feed passages  194  extend in the lower portion of the spar  50 , upwardly ramped from the lubricant distribution gallery  190  to the through bores  54 . Each coolant feed passage  194  opens into a circumferential coolant feed groove  195  on the inside surface of a respective through bore  54  at a location that is diametrically aligned with the axis of a fuel injector bore  131 . Upon insertion of the cylinder liners  70  as discussed below, each coolant feed groove  195  forms a coolant passage between the associated through bore  54  and the exterior surface of the cylinder liner  70 . As per  FIG. 3D , a coolant drain passage  196  extends in the upper portion of the spar  50  upwardly from each through bore  54 . Preferably, each through bore  54  is served by at least one, and preferably two, such drain passages. As per  FIGS. 3C and 3D , each drain passage  196  opens at one end into respective circumferential collector groove of a through bore  54 , and at the other end (as seen in  FIG. 2F ) through the top of the spar  50 , preferably through the upper surface of the spar, where the upper main bearing assemblies  60  are mounted. 
     All of the cylinder liners  70  may be constructed and assembled as shown in  FIGS. 3A and 3B , where the cylinder liner  70  includes a liner tube  300  with the exhaust and inlet ports  73 ,  75  formed near its end rims  302 ,  304 . A circumferential flange  305  is formed on the external surface of the liner tube, abutting the inside edge of the exhaust port  73  such that the exhaust port  73  is located between the flange  305  and the exhaust end  72 . An alignment notch  306  is provided in the flange  305 . The exhaust end  72  is constituted of an end cap  307  that is aligned with the rim  304  by pin  308 /hole  309  and is attached to the rim  304  by threaded screws or bolts. At the exhaust end  72 , the internal bore of the liner tube  300  has an increased internal diameter, forming a raised shoulder  310  displaced longitudinally into the liner from the exhaust end  72 . The outer diameter of the end cap  307  is reduced around its inner end  311 , and the rim of the inner end  311  is received through the rim  302  of the liner tube. When the end cap  307  is attached to the rim  302 , the inner end  311  is positioned just short of the raised shoulder  310 , forming an annular wiper groove  312  ( FIG. 3B ) wherein an annular wiper  313  is received and retained. With reference to  FIG. 3B , the groove  312  and wiper  313  are located in the internal bore  77 , between the exhaust end  72  and exhaust port  73  of the liner. The displacement between the groove  312  and the port  73  defines an annular area where compression rings (described below), mounted to the crown of the piston, are located when the piston is at BDC during engine operation. In some aspects of the constructions described herein, longitudinal oil discharge grooves  314  may be formed on the inside surface of the end cap&#39;s bore. If provided, the grooves preferably extend from the oil discharge groove  314  to the outside rim of the end cap  307 . The inlet end  74  may be similarly constructed, and an annular wiper groove  312  and wiper  313  are located in the internal bore of the cylinder liner  70 , between the inlet port and the inlet end of the liner  70 . In some aspects, the discharge grooves can be replaced with discharge passages bored through the end cap to the wiper groove  312 . In alternative embodiments, the end cap bore may have no discharge grooves or discharge passages, as seen in  FIG. 3E . 
     As best seen in  FIG. 3A , a shallow, preferably flat, circumferential trench  315  is formed in the central portion of the external surface  76  of the cylinder liner  70 . The circumferential trench  315  is interrupted or split to provide a support area through which the injection port  71  is bored. A narrow circumferential central groove  317  is formed generally in the center of the trench  315 . Longitudinal grooves  318 ,  319 , extending from the central groove  317  toward the ends  72  and  74 , are formed in the external surface  76 . The grooves  318  extending toward the exhaust end  72  are of uniform length so that their ends  320  align circumferentially on the external surface  76 . The grooves  319  extending toward the inlet end  74  are of uniform length so that their ends  321  align circumferentially on the external surface  76 . Per  FIG. 3A , the length of the grooves  318  may be greater than the length of the grooves  319  in order to provide asymmetrical cooling of the cylinder liner as described in the referenced publication US 2007/0245892, wherein greater cooling capacity is afforded to the exhaust side of the cylinder liner  70  than to the inlet side. As seen in  FIG. 3B , a split collar or flattened ring  327  fits into, and covers, the trench  315  and groove  317 , but leaves the longitudinal grooves  318  and  319  uncovered. A sequence of holes  328  runs along each half circumference of the collar  327 , from a respective edge of the split to with a non-apertured portion  330  opposite the split  329  in the ring. Around each half circumference, the diameters of the holes  328  increase incrementally from the portion  330  to the split  329 . 
     Per  FIG. 3E , the asymmetrical cooling configuration of the cylinder liner  70  may include bores drilled longitudinally in the cylinder liner, as is taught in the reference publication US2007/0245892. In this regard, grooves  318   a  of the plurality of longitudinal grooves  318  that align with bridges  73   b  of the exhaust port  73  and that are longer than the other grooves  318 . The grooves  318   e  may extend toward, if not up to, the flange  305 . The end of each groove  318   e  is in fluid communication with a longitudinal passage  318   b  bored through an exhaust port bridge  73   b  and to the exhaust end  72  of the cylinder liner  70 . In addition, the ends  320  of the grooves  318  on either side of the injection port  71  may be brought together into a common groove in fluid communication with a longitudinal passage  318   b . Each of the bored longitudinal passages  318   b  opens to a hole  318   h  in an end cap  307 . Fluid communication between an elongated groove  318   e  and an associated longitudinal bore  318   b  may be provided by a bore drilled radially to the cylinder liner between the end of the groove  318   e  and the bore  318   b . This configuration permits coolant to flow through the elongated grooves  318   e  and the exhaust port bridges  73   b , and then out of the exhaust end  72  of the cylinder liner. 
     All of the through bores  54  in the spar  50  may have the construction shown in  FIG. 3C . The through bore  54  has exhaust and inlet ends  54   e  and  54   i , an inner bore surface  340  with coolant collector grooves  342  and  344 , a coolant feed groove  195  between the collector grooves, a seating groove  346  in the inlet end  54 , and a seating groove  347  in the exhaust end  54   e . With reference to  FIGS. 3C and 3D , when a cylinder liner  70  is assembled to the through bore  54 , an annular seal  349 , such as an elastomeric O-ring, is seated in the groove  346  in the bore surface  340 . Then the cylinder liner  70  is inserted through the exhaust end  54   e  of the through bore  54 , inlet end  74  first, with the notch  306  ( FIG. 3A ) aligned with a through bore pin  348  in order to orient the injection port  71  of the cylinder liner  70  with an injector bore (not seen) in the spar  50 . With the cylinder liner  70  thus oriented, it is pushed home until the flange  305  contacts and is seated against the edge of the seating groove  347 . As per  FIG. 3D , with the cylinder liner  70  oriented and seated in the through bore  54 , the coolant collector groove  342  is aligned with the ends  320  of the longitudinal grooves  318 , the coolant feed groove  195  is aligned with the holes  328  in the collar  327 , the coolant collector groove  344  is aligned with the ends  321  of the longitudinal grooves  319 , and the injection port  71  is aligned with an injector bore. The cylinder liner  70  is secured in place on the spar  50  at its inlet end  74  by the intake cover  57  and, at its exhaust end  72  by an exhaust collector  400  secured to the exhaust end  54   e  of the through bore  54 . An annular seal  351 , such as an elastomeric O-ring, is seated in the groove  58   g  in the cone opening  58   o  of the intake cover. An annular seal  353 , such as an elastomeric O-ring, is seated in a groove of exhaust collector  400 . 
     As per  FIG. 3D , with the cylinder liner  70  oriented and seated in the through bore  54 , the seal  349  seats against the external surface of the cylinder liner  70 , between the ends  321  and the inlet port  75 , forming a fluid seal that blocks leakage of liquid along the external surface from the ends  321  into the inlet plenum chamber and the inlet port  75 . The seal  351  seats against the external surface of the cylinder liner  70 , between the inlet end  74  and the inlet port  75 , forming a fluid seal that blocks the leakage of fluid in either direction. That is to say, the seal  351  blocks the passage of liquid lubricant along the external surface of liner  70  from the inlet end  74  into the plenum chamber and inlet port  75 . The seal  351  also blocks the leakage of air into and out of the inlet plenum chamber. The seal  353  seats against the external surface of the cylinder liner  70 , between the exhaust port  73  and the exhaust end  72 , forming a fluid seal that blocks the leakage of fluid in either direction. That is to say, the seal  353  blocks the passage of liquid lubricant along the external surface of the cylinder liner  70  from the exhaust end  72  into the exhaust collector  400  and exhaust port  75 . The seal  353  also blocks the leakage of air into and exhaust gasses out of the exhaust collector  400 . The flange  305  blocks the leakage of liquid along the external surface from the ends  320  into the exhaust collector  400  and the exhaust port  73 . 
     Thus, while a cylinder liner  70  is supported in a through bore  54 , it is stabilized and secured against movement in the spar  50  by retaining the liner&#39;s flange in the seating groove at the exhaust end of a through bore when an exhaust collector  400  is secured thereto. No part of the cylinder liner is formed integrally with any other component of the engine. Each cylinder liner is therefore isolated from the introduction of thermal and mechanical distortions from those quarters. In the preferred embodiment, the cylinder liner  70  can be removed from the engine, which facilitates repair and maintenance. Further, when seated in a through bore, the cylinder liner  70  is sealed against passage of fluid between its external surface and the through bore in which it is seated. During engine operation, the cylinder liner  70  is seated, secured, and sealed more firmly in the through bore  54  when it expands in response to the heat of combustion. Of course, while it is preferred that the cylinder liners  70  be removable from the through bores  54 , there may be instances where the cylinder liners would be press fit into the through bores so as to be permanently seated therein. 
     As seen in  FIG. 4 , an arrangement of exhaust collectors  400  extends lengthwise on the spar  50  along the first side. Each exhaust collector  400  is mounted to the exhaust end  54   e  of a through bore  54 . As seen in  FIGS. 3C and 3D , an exhaust collector is in fluid communication with the exhaust port  73  of a respective cylinder liner  70 . All of the exhaust collectors may be constructed and assembled as shown in  FIGS. 2B and 3D , where the exhaust collector  400  forms a generally toroidal chamber  401  that surrounds the exhaust port  73  of a cylinder liner  70 . As best seen in  FIG. 4 , each exhaust collector  400  includes a duct  403 . Each duct  403  is offset from the vertical midline of the exhaust end  72  of the cylinder liner  70  to which it is mounted, which is reserved for reciprocal movement of connecting rods. Each duct transitions to an exhaust pipe  405  leading through the engine casing to an exhaust manifold (not seen). Per  FIG. 3D , a toroidal potion of each exhaust collector  400  includes an inner collector  410  and an outer collector  420 . The inner and outer collectors have the general shape of a torus cut in half around its outside perimeter with flattened front and rear surfaces. As best seen in  FIG. 3C , the inner collector  410  is secured to the exhaust end  54   e  of the through bore  54  by way of threaded screws or bolts received in threaded bores (seen in  FIG. 2B ), which are spaced around the exhaust end  54   e . As per  FIG. 3C , the inner and outer collectors  410  and  420  are joined at a flange  424  with threaded openings through which screws or bolts are received to secure the two parts together. As per  FIG. 3D , the inner edge of the inner collector&#39;s rear surface abuts the outer edge of the flange  305 . The outer collector  420  includes an annular groove  425  in its inner bore facing the exhaust end of the cylinder liner, in which the annular seal  353  is seated. 
     All of the pistons  80  may be constructed and assembled as shown in  FIGS. 5A and 5B , where the piston  80  includes a crown  510 , a skirt  520 , and the piston rod  82 , which has a tubular construction. The piston is assembled to a pin  84 . As per  FIG. 5C , the rear of the crown  510  is formed with wedge-shaped radial walls  511  with inner and outer rings of threaded bores. The thin ends of the radial walls converge on a central dome  512  that slopes toward wedge-shaped notches  513  between the walls. The skirt  520  has a tubular shape with a flange  521  formed on the inner surface  522  of the skirt, near the end of the skirt that joins the crown  510 . As per  FIG. 5A , the crown  510  is received on and closes the one end of the skirt  520 . A flexible ring  523  (such as an O-ring) grips a lower inset rim of the back of the crown  510  and is held between a circumferential ridge formed in the back of the crown and one side of the flange  521 . Another flexible ring  524  (such as an O-ring) is held between the other side of the flange and the outer edge of a retaining ring  525  that is mounted to the back of the crown. The flexible rings and the flange form an annular, resiliently deformable joint coupling the crown  510  and skirt  520  that permits the skirt  520  to swing slightly on the crown  510  with respect to the piston rod  82 , within a truncated cone centered on the axis of the rod and widening from the flange  521  toward the open end of the piston skirt. 
     As per  FIGS. 5A and 5B , the piston rod  82  includes flanges  531  and  532  on its external surface. The flange  531  is set back from one end of the rod, and the flange  532  is set back from a threaded end of the rod, and has a smaller diameter than that of the flange  531 . The construction of the piston  80  further includes an insert  550  attached to the back of the crown  510  by threaded screws or bolts received in the inner ring of threaded bores, with wedge-shaped notches  551  aligned with the corresponding notches in the crown  510 . As per  FIG. 5C , the flexible ring  524  grips the outer perimeter of the insert  550 . The piston rod  82  is secured to the insert  550  with one end of the piston rod  82  centered in the central opening  552  of the insert and the circumferential flange  531  sandwiched between the insert  550  and a rod retainer  560  passed over the flange  532 . Threaded screws or bolts secure the retainer  560  to the insert  550 . The retaining ring  525  mounts on the back of the insert  550 , around the insert, and is secured to the crown  510  by threaded screws or bolts that extend through the insert and are received in the outer ring of threaded bores in the back of the crown  510 . With reference to the side sectional views of  FIGS. 5A and 5C , the wedge-shaped spaces in the back of the crown  510  and the insert  550  are mutually aligned and are centered on, and radially symmetrical with respect to, the tubular piston rod  82 . Further, as seen in  FIG. 5A , the outer end of the piston rod  82  is press fit to the lower half of a split collar  565  attached to a pin  84 . As further described in U.S. Pat. No. 7,360,511, a piston coolant jet  152  extends through the pin  84  into the bore of the tubular piston rod  82 . During engine operation, the pin  84  slides back and forth along the piston coolant jet, which is fixed to a piston coolant manifold. 
     As best seen in  FIG. 5D , each connecting rod  100  and  110  is a bent beam having an elongate open work configuration framed by an outside perimeter frame  120 . At least one strut  121 , extending between the opposing long sides of the perimeter frame, is provided near the end of each connecting rod that is coupled to the pin  84 , and at least one other strut  122  extending between the opposing long sides of the perimeter frame is provided near the end that is coupled to a crankshaft. In the manner described in referenced U.S. Pat. No. 7,360,511, three connecting rods that swing on the pin  84  couple each piston  80  to both crankshafts  14  and  16 . In this regard, a single, connecting rod  110  with a split end  110   e  received on the pin  84 , around the split collar  565 , links the piston to one crankshaft, and two connecting rods  100  with single ends  100   e  received on the pin  84  on respective outer sides of the split end  110   e  link the piston to the other crankshaft. 
     With reference to  FIG. 5A , one or more circumferential grooves  515  may be formed in the upper portion of the perimeter of the crown  510 . For example, two grooves may be formed therein with one or more split, annular, compression rings  516  mounted therein. Preferably, one steel compression ring is mounted in each of the two grooves, with their gaps offset by, for example, 180°. The compression seals are provided to seal the narrow annular space between the crown  510  and the bore of a cylinder against the passage of combustion gasses (also referred to as “blowby”) during engine operation. Preferably, the compression rings  516  are conventional steel rings with nominal diameters greater than that of the inner bore of the cylinder liner such that the seals are loaded against the bore of the cylinder liner. 
     Alternatively, low friction compression seals may be used in place of the compression rings. During engine operation, combustion gas pressures produced by combustion near top dead center of each piston&#39;s stroke act against on the inside edge of a compression seal. The pressurized gas enters the groove or grooves where the compression seals are mounted and exert an outward force against the inner surfaces of the seals, which urges the outside edge into sealing engagement with the bore. As the piston moves away from top dead center following combustion, the combustion pressure declines to ambient, and the compression seals relax into the grooves so as again to be only lightly loaded against the bore as they transit an inlet or exhaust port. Preferably, a compression seal may be fabricated to yield a circular perimeter when compressed into the cylinder with, for example, about a 0.015″ circumferential gap. The as-machined nominal outside diameter of the seal may be, for example, about 0.010″ larger than the liner bore diameter to ensure a light load against the port region. The thickness of the seal may be, for example, 0.040″ to keep the forces exerted by gas pressure to a low level. Two such seals may be mounted in a single groove having a nominal width of 0.080″, with their gaps being spaced 180° apart. The seal may be fabricated by machining steel that is later plated with a layer of nitride. 
     Each of the main bearings  60  may be constructed and assembled as shown in  FIG. 6 , where the main bearing  60  includes a pedestal  61 , an outer piece  62 , and a tubular bearing sleeve  63 . When the outer piece  62  is secured to the pedestal  61 , a circumferential lubricant feed groove  64  is defined in the cylindrical inner surface formed by the main bearing pedestal  61  and the outer piece  62 . A lubricant feed passage  192  extends through the spar  50  from the lubricant distribution gallery  190  to the portion of the lubricant feed groove  64  in the main bearing pedestal. An opening  65  in the bearing sleeve  63  is positioned over the groove  64 , opposite the upper surface of the spar  50 , when the sleeve  63  is received and held between the pedestal  61  and the outer piece  62 . Each main bearing  60  rotatably supports a main journal of a crankshaft. Although not seen, drilled lubricant feed passages in each crankshaft extend between main journals and adjacent crank journals, and each crank journal, includes one or more bores from which lubricant flows to hydro-dynamically lubricated journal rod bearings by which connecting rods are coupled to the journal. Thus, during engine operation, lubricant flows into the main bearings  60 , and through the openings  65  to lubricate the bearing interface between the main bearing sleeves  63  and the main journals of the crankshafts  14 ,  16 . As the crankshafts rotate, lubricant is also injected from the bearing sleeve openings  65  into the drilled feed passages in the main bearing journals, and flows through those passages to the hydro-dynamically lubricated journal bearings. 
     All of the annular wipers of the engine may be constructed and assembled as shown in  FIG. 7A , where the annular wiper  313  includes an elastomeric annulus  702  with walls forming a circumferential groove  703 . The inside wall of the wiper  313  includes a ramped surface terminating in a circumferential notch  705 . The outside wall has a wavy surface including at least one projection  707 . During assembly, the inner and outer walls are spread apart and an annular ring  709 , such as a steel spring or an elastomeric an O-ring is seated in the groove  703 . When the walls are subsequently released, they move against the annular ring  709 , squeezing it into an oblong shape and maintaining a spreading force between the walls. With reference to  FIGS. 3B and 7A , the outer diameter of the annulus  702  is nominally equal to the inner diameter of the annular wiper grooves  312  in the bore of a cylinder liner  70  near the inlet and exhaust ends. When an end cap  307  is secured to the end of the liner tube  300 , the annulus is lodged in the wiper groove between the inner end  311  of the end cap  307  and the raised shoulder  310 . The flattened ring  709  exerts a spring force against the inner wall, thereby urging the lower edge of the notch  705  against the outside surface of a piston skirt  520 . The projection  707  contacts the floor of the wiper groove  312 , thereby resisting displacement of the annulus  702  in a longitudinal direction in the bore of the cylinder liner. Thus seated, the wiper ring  313  grips the outer surface of a piston skirt  520 , wiping excess lubricant from the skirt as the piston reciprocates during engine operation. For example, with reference to  FIGS. 3B and 7A , during splash lubrication occurring when a piston skirt is withdrawn from a cylinder bore as the piston transits through its bottom dead center position, excess lubricant can be skived from the skirt  520  by the lower edge of the notch  705  and transported over the ring  709  to the end cap  307 . The excess lubricant flows over the inner bore of the end cap and out of the exhaust end of the cylinder liner  70 , from where it transits to be collected in the sump  129  ( FIG. 1B ). 
     With reference to  FIGS. 7B and 7C , the wipers  313  are located in the bore of a cylinder liner  70  so as to avoid damage by contact with the compression rings  516  while preventing the transport of lubricant on the outside surface of a piston skirt  520  into an exhaust or inlet port. Preferably, each wiper is located between an exhaust or inlet port and the corresponding end of a cylinder liner. This relationship is illustrated in  FIG. 7B , where the wiper  313  is seated in the bore of the cylinder liner between the exhaust port  73  and the exhaust end  72 . As the exhaust side piston  80  moves through TDC, the exhaust port  73  is located between the compression rings  516  and the wiper  313 . In  FIG. 7C , when the piston  80  moves through BDC, the compression rings  516  are located between the exhaust port  73  and the wiper  313 . Thus, while the compression rings transit the exhaust port  73  twice each cycle, they do not transit the wiper groove  312  at all. 
     The engine constructions thus far described provide lubricant delivery structures in which a liquid lubricant, such as oil, provided under pressure by a pumped source, can be distributed throughout a multi-cylinder, opposed piston engine for lubricating bearings, for cooling cylinders, and for lubricating and cooling pistons. Preferably, the pumped source includes two pumps mounted on the spar  50 . As per  FIG. 2A , the spar  50  includes, at an output end, a drive train support structure  800  with provision for mounting the engine drive train and certain auxiliary components. For example, as seen in  FIG. 8A  two pumps  802  are integrated into opposing sides of the support structure  800 . Now, with reference to  FIGS. 8A and 8B , a liquid lubricant is delivered, under pressure, to the upper and lower lubricant distribution galleries  180  and  190 , and to the piston coolant manifolds  150  by the two pumps. As best seen in  FIG. 8B  the pumps  802  are driven by drive train gears  803 ,  804 , and each pumps lubricant collected in the sump from the sump, into a control mechanism  805 . From a control mechanism, pumped lubricant flows through a coupling  806 , into a piston coolant manifold  150 . Each control mechanism  805  also provides pumped lubricant through a coupling  808  into a delivery passage  811  bored in the spar  50  that is transverse to the spar&#39;s longitudinal direction. The lower lubricant distribution gallery  190  opens into the transverse passage  811  as does a riser passage  813  bored in the spar which extends to the upper lubricant distribution gallery  180 . 
     As best seen in  FIGS. 8B and 5C , the pumped lubricant flows through the piston coolant manifolds  150 , out through the piston coolant jets  152 , and into the piston rods  82 . In each piston the lubricant is distributed in turbulent streams, with radial symmetry, through the wedge-shaped notches  551  that impinge on and cool the back of the crown  510 . As taught in U.S. Pat. No. 7,360,511, rotationally symmetrical delivery of streams of liquid coolant directed at the back surface of the crown  510  assures uniform cooling of the crown during engine operation and eliminates, or substantially reduces, swelling of the crown and the portion of the skirt immediately adjacent the crown during engine operation. The lubricant flows from the notches  551  along the inner surface  522  of the piston skirt  520 , and out the open end of the skirt. Exiting the skirt, the lubricant is thrown about and scattered by the movement of the piston  80 , the pin  84  attached to the piston, and the connecting rods  100 ,  110  coupled to the pin  84 . The scattered lubricant is splashed onto the outside surface of the piston skirt  520  and onto the bearings with which the connecting rods  100 ,  110  are coupled to the pin  84 . With reference to  FIG. 3B , excess lubricant transported on the outside surface of the skirt  520  is skived off the outside surface by wipers  313  and channeled out of the ends of the cylinder liner  70  by discharge grooves  314 , whence it is thrown into the mist of splashed oil. Thus, lubricant that is pumped to the pistons is employed for both cooling the piston crowns and splash lubrication of the piston skirt outer surfaces and connecting rod bearings. The engine covers  35 ,  36  confine the scattered and splashed lubricant in the engine space occupied by the crankshafts (the engine crank space). 
     With reference to  FIG. 2E , lubricant that is provided under pressure by the pumps  802  flows through the upper and lower lubricant distribution galleries  180  and  190 . As seen in  FIG. 2F , from the upper gallery  180 , the lubricant flows into the lubricant feed passages  182  to feed grooves  64  of the upper main bearings  60 . As illustrated in  FIG. 6 , in each main bearing  60 , the lubricant enters the lubricant feed groove  64  from a lubricant feed passage at the portion of the bearing where the maximum pressure is brought to bear by the crankshaft in response to the tensile forces exerted by the crankshafts. That portion is centered on the midpoint of the semicircle supported by the pedestal  61 . From that portion, the lubricant travels in opposite directions in the feed groove  64 , until it reaches the portion of the main bearing  60  where the minimum pressure is brought to bear by the crankshaft. The minimal pressure portion is spaced circumferentially 180° around the bearing from the maximum pressure portion. The maximum pressure portion is centered on the midpoint of the semicircle defined by the outer piece  62 . From there, the lubricant passes through the opening  65  in the bearing sleeve. Some of the lubricant exiting the feed groove is transported throughout, and lubricates the interface between, the crankshaft main journal and the inner surface of the bearing sleeve; some is received into the drilled passages in the crankshaft and transported thereby to the hydro-dynamically lubricated bearing interfaces between the crank throws and ends of the connecting rods  100 ,  110 . Lubricant flows continually from those interfaces to be thrown into the mist of splashed lubricant in the engine crankcase. 
     As seen in  FIGS. 2F and 2G , from the lower gallery  190 , the lubricant also flows into the lubricant feed passages  192  to feed grooves  64  of the lower main bearings  60  from where lubrication of the lower crankshaft  16  and bearings coupled thereto is accomplished in the manner described in connection with the upper main bearings. In addition, the lubricant flows from the lower gallery  190  into the coolant feed passages  194  and then, as seen in  FIGS. 3C and 3D , into the circumferential coolant feed grooves  195  of the through bores  54 . Lubricant enters a through bore feed groove  195  ( FIG. 2F ), against the non-apertured portion  330  of a split collar  327  ( FIG. 3A ). With reference to  FIG. 3A , the flow of lubricant splits into two streams that flow clockwise and counterclockwise along one face of the split collar  327  in the direction of the split  329 . The uniform increase in the size of the holes  328  from  330  to  329  in both directions equalizes the rate at which lubricant flows through the split collar  327  into the trench  315  and then the circumferential groove  317 . From the circumferential groove  317  lubricant flows into the longitudinal grooves  318  toward the exhaust end  72  and also into the longitudinal grooves  319  toward the inlet end  74 . The flow of lubricant in the longitudinal grooves  318  and  319  cools the cylinder liner asymmetrically, delivering more cooling capacity from the center toward the exhaust side of the liner than toward the inlet side. As taught in U.S. Pat. No. 7,360,511, the end portion of the cylinder liner  70  with the exhaust port  73  experiences a greater heat load than the end portion with the inlet port  75 , and thus minimizes non-uniformities in the temperature of the cylinder liner and resulting cylindrical non-uniformity of the liner bore. However, the construction of the coolant delivery elements  315 ,  317 ,  318 ,  319 , and  327  yields a cylinder liner that is much easier and less expensive to construct than the corresponding arrangement taught in U.S. Pat. No. 7,360,511. Further, the combination of tailored asymmetrical cooling of the cylinder liner  70  and radially symmetrical cooling of the pistons  80  that it contains eliminates non-uniform distortion of the cylinder liner and expansion of the piston crowns, and thereby maintains a substantially constant and circularly symmetrical mechanical clearance between the bore of the cylinder and the pistons during engine operation. 
     Continuing with the description of the cylinder coolant flow with reference to  FIGS. 3A and 3D , lubricant flows out the ends  320  of the longitudinal grooves  318 , into the through bore coolant collector groove  342  (seen in  FIG. 3C ), and out of the spar  50  through one coolant drain passage  196 . Lubricant flows out the ends  321  of the longitudinal grooves  319  into the through bore coolant collector groove  344  (seen in  FIG. 3C ), and out of the spar  50  through another coolant drain passage  196 . Lubricant flows continually from the coolant drain passages along the top of the spar  50 , whence it is thrown into the mist of splashed oil in the engine. 
     Lubricant splashed about the engine crank space continually rains to the bottom of the engine and flows into the sump  129 , from which it is pumped and delivered as described above for lubrication and cooling. The described engine constructions preferably include a control mechanization to manage the delivery of pumped lubricant for lubrication and cooling through the lubricant distribution galleries and the piston coolant manifolds described above and represented in schematic form in  FIG. 9 . 
     As per  FIG. 9 , delivery of the lubricant outputs of the pumps  802  is controlled by integrated control subsystems. Each control subsystem may be self-actuating, or may be actuated by way of an electronic control unit. For example, the self-actuating control subsystems  910  illustrated in  FIG. 9  include a thermostat valve  911 , a piston cooling regulator valve  912 , and a pressure relief valve  914 . The outputs of the pumps  802  are connected, in series, to a cooling line  916  wherein the lubricant is cooled. Preferably, the cooling line  916  includes a filter  918  and a heat exchanger  920  connected in series, although other cooling elements may be used. The cooling line  916  is connected through one pump  802  to the passage bore  811  in the spar  50 , in common with the valves  912  and  914 . The passage bore  811  is connected to the other pump assembly  802 , in common with the valves  912  and  914  of that assembly. When open, a thermostat valve  911  shunts the output of a hydraulic pump  802  over the cooling line  916  to the passage bore  811 . 
     In the control mechanization of  FIG. 9 , the thermostat valves  911  respond to the temperature of the lubricant, and the valves  912  and  914  respond to the fluid pressure of the lubricant. When the lubricant temperature T is less than a first predetermined level T L  (a minimum temperature, in other words), the thermostat valves  911  open and shunt lubricant across the cooling line  916  to the passage bore  811 . When the temperature of the lubricant attains a second predetermined level T H , a maximum temperature which is greater than T L , the thermostat valves  911  shut and force lubricant to flow through the cooling line  916 , the filter  918 , and the heat exchanger  920 . From the heat exchanger  920 , filtered, cooled lubricant flows back through the cooling line  916  and into the passage bore  811 . The valves  912  and  914  remain closed for so long as a fluid pressure P has not attained a first predetermined (minimum) level, P L . When the first predetermined level P L  is attained, the piston cooling regulator valves  912  open while the pressure relief valves  914  remain shut. When fluid pressure reaches a predetermined relief level P H , the pressure relief valves open. Finally, the thermostat valves  911  may also respond to fluid pressure and open when fluid pressure reaches a maximum allowable pressure level P HH  which exceeds P H . Thus, per Table I, 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 P &lt; P L   
                 P H  &gt; P &gt; P L   
                 P &gt; P H   
                 P = P HH   
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 T &lt; T L   
                 S 
                 SJ 
                 SJB 
                 SJB 
               
               
                   
                 T &gt; T H   
                 SH 
                 SJH 
                 SJBH 
                 SJB 
               
               
                   
                   
               
               
                   
                 where P is lubricant fluid pressure, T is lubricant temperature, S = spar 50, J = piston cooling Jets 152, B = Bypass via valves 914, and H = transport of lubricant through the cooling line 916, the Heat exchanger 920, and the filter 918. 
               
            
           
         
       
     
     According to Table I, under engine start up and operation when the lubricant is relatively cool (T&lt;T L ), and the pressure is low (P&lt;P L ), the thermostat valves  911  are open, shunting the lubricant across the cooling line, directly to the passage bore  811  in the spar  50 . However, when the engine starts, the pumps  910  might not be fully primed, and lubricant flow may be insufficient to ensure adequate flow to the main bearings, which require immediate lubrication, and to the cylinder liners, which require immediate cooling, as well as to the pistons. Thus, in order to ensure viability of the main bearings and cylinder liners before fluid pressure builds to a level adequate to ensure that all lubrication and cooling needs are served, the piston cooling valves  912  remain closed, preventing lubricant from flowing to the piston cooling manifolds  150 . Once the pumps and lubricant passages are primed and fluid pressure reaches P L , the piston cooling regulator valves  912  open, permitting lubricant to flow to the piston coolant manifolds  150 . The fluid pressure level range P L &lt;P&lt;P H  which establishes precise magnitudes for P L  and P H  will depend upon a number of factors related to a specific engine designs and constructions. For example, such factors may include lubricant flow requirement to control temperature across the main bearings, pressure required to avoid cavity formation in the crankshaft passages feeding lubricant from the main bearings, lubrication requirements of auxiliary equipment such as turbochargers, sufficiency of piston coolant flow for varying levels of power loading and piston acceleration, sufficiency of cylinder coolant flow for varying levels of power loading, avoidance and/or mitigation of cavity formation at the pump inlets, and the fluid properties of the selected lubricant. As the fluid level reaches P H  the pressure relief valves  914  open, shunting lubricant out of ports into the covered engine space until the fluid pressure drops below P H . 
     According to Table I, under engine start up and operational conditions when the lubricant is relatively hot (T&gt;T H ) the thermostat valves  911  are closed, directing the lubricant through the cooling line  916 , the filter  918 , and the heat exchanger  920  and then to the passage bore  811  in the spar  50 ; otherwise, the control mechanization causes the lubricant to be distributed in response to fluid pressure P as disclosed above. 
     There may be certain failure modes and hazards that can be anticipated and provided for in the control mechanization of  FIG. 9 . For example, any one or more of the cooling line  916 , the filter  918 , and the heat exchanger  920  may become obstructed or fail under high temperature conditions, causing pressure to rise. In such a case, as is evident in Table I, when T H  is exceeded and P reaches P HH , the thermostat valves  911  again close and shunt the pumped lubricant past the cooling line  916 , directly to the passage  811  and the pressure regulator valves  916 , thereby avoiding obstruction in the cooling line circuit. 
     The control mechanization illustrated in  FIG. 9  and Table I may be adjusted or adapted to account for non-uniform heating effects on the pistons during engine operation. An adaptation described above is the tailored cooling of the cylinder liners to account for non-uniform heating in which exhaust ends of the liners typically run hotter than intake ends. Correlative adaptations may be made in the control mechanization just described to account for differential heating of the pistons during engine operation. In this regard, the pistons in the exhaust sides of the cylinder liners heat more quickly and typically run hotter than the intake side pistons. Thus, with reference to  FIG. 9 , the piston coolant regulator valves  912  may be selected to have offset operating points so as to provide lubricant to the piston coolant manifold serving the exhaust side pistons before lubricant is provided to cool the intake side pistons. Thus, the valve  912  controlling the coolant manifold serving the exhaust side pistons would open at a lower fluid pressure than the valve controlling the intake side manifold. Further, the piston coolant regulator valves  912  may be selected to have offset fluid flow limits in order to provide lubricant at a higher flow rate to the exhaust side pistons than to the intake side pistons. 
     A control mechanization that regulates and manages the distribution of a liquid lubricant for lubricating and cooling the opposed-piston engine constructions taught herein under a range of engine operating conditions is not limited to a self-actuating construction such as is illustrated in  FIG. 9 . For example a control mechanization may be constituted of an electronic engine control unit (ECU), electronic sensors, and electronically-controlled valves. In this regard, the sensors could be deployed to report lubricant temperature and pressure to the ECU. As temperature and pressure change, the ECU would determine the required lubricant delivery settings and would regulate the flow of pumped lubricant to the distribution galleries and piston cooling manifolds by issuing control signals to the electronically actuated valves. 
     A representative embodiment of a self-actuating control mechanization such as is illustrated in  FIG. 9  may be understood with reference to the figures. Although the embodiment includes two pumps, and two physically separate control entities, this is merely to illustrate underlying principles, but is not meant to so limit the principles. It is expected that control mechanizations that manage the provision of pumped lubricant for lubrication and cooling may be practiced with fewer, and more, than two pumps, and with fewer, and more, than two control entities as determined by specific circumstances. 
     Referring now to an example understood with reference to certain figures, a pumped source that provides pumped lubricant may include two pumps, each mounted in a respective one of the in recesses  815  ( FIG. 2A ) in a lower corner of the support structure  800 . As illustrated in  FIG. 8A , a mechanization that controls the provision of the pumped lubricant for lubricating and cooling elements of an opposed piston engine may include two control mechanisms  805 , each control mechanism being constructed to control the output of a respective one of the pumps  802 . A pump and an associated control mechanism may be constructed and assembled as shown in  FIGS. 8A-8B , where  FIG. 8B  shows a drive train gear  803  that drives a pump  802  (seen in  FIG. 8C ) during engine operation. As indicated by the sequence of arrows, the lubricant is pumped from the sump, through an intake pipe  817 , to and through the pump  802 . As seen in  FIG. 8C , the pump  802  delivers pumped lubricant into an intake chamber  819 . When the thermostat valve  911  is open, the pumped lubricant flows through the valve  911  into an outlet chamber  820 . When the thermostat valve  911  is closed, the pumped lubricant flows out of the intake chamber  817  via a cooling input pipe  821 , into the cooling line  916 , where it is filtered and cooled at  918  and  920 . After filtration and cooling, the pumped lubricant flows from the cooling line  916  into a cooling output pipe  823  into the output chamber  820 . From the output chamber  820 , the flow of pumped lubricant flows into the passage bore  811  for distribution to lubricate bearings and cool cylinder liners. With reference to  FIG. 8A , as the fluid pressure of the lubricant in the output chamber  820  rises, provision of the lubricant to the piston cooling manifolds from the output chamber  820  is controlled, or gated, by the valve  912 . As fluid pressure in the output chamber  820  rises above the level specified for bypass, venting the lubricant from the output chamber  820  through a bypass aperture (indicated by reference numeral  825  in  FIG. 8A ) is controlled, or gated, by the valve  914 . 
     Selection of a liquid lubricant suitable for the engine constructions described and illustrated in this specification should depend upon many factors, including the lubrication requirements for bearings and the cooling requirements of the cylinder liners and pistons. In some aspects, SAE 10W20, SAE15W40, or other lubricating oils may be used. 
       FIG. 10  illustrates an air charge system which may be used with the engine constructions described above. In the figure, the air charge system includes a turbocharger  1000  with a compressor  1010  and a variable nozzle turbine  1012 . Intake air is drawn into the compressor  1010  and compressed. The hot, compressed air is cooled in a first intercooler  1013  after which it passes through a bypass valve  1014  controlled by a controller  1015 . The air is then further compressed by a supercharger  1016  and the resulting hot, compressed air is cooled by a second intercooler  1018 . Pressurized air is passed from the second intercooler  1018  through the air inlet adapter  12  into the plenum chamber  56 ,  57 , wherein the inlet port  75  of each cylinder liner  70  is positioned. The pressurized air in the plenum chamber  56 ,  57  is provided to the inlet ports  75  of all of the cylinder liners  70  at a substantially uniform pressure to ensure substantially uniform combustion and scavenging in the among the cylinder liners  70  throughout engine operation. Preferably, exhaust gasses from each individual cylinder liner  70  are fed through an exhaust collector  400  into a manifold  1019 . The exhaust gasses then pass through the variable nozzle turbine  1012  of the turbocharger  1000  in response to signals from the controller  1015 . 
     Although opposed piston engine constructions have been described in detail with reference to specific embodiments, it should be understood that various modifications can be made without departing from the principals underlying those embodiments. Accordingly, an invention embracing those principals should be limited only by the following claims. Further, the scope of the novel engine constructions described and illustrated herein may suitably comprise, consist of, or consist essentially of more or fewer elements than those described. Further, the novel engine constructions disclosed and illustrated herein may also be practiced in the absence of any element which is not specifically disclosed in the specification, illustrated in the drawings, and/or exemplified in the embodiments of this application.