Patent Publication Number: US-2020291844-A1

Title: Two-Cycle Diesel Engine Configured for Operation with High Temperature Combustion Chamber Surfaces

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/577,728, filed on Sep. 20, 2019, which is a continuation of U.S. patent application Ser. No. 16/224,281, filed on Dec. 18, 2018, now U.S. Pat. No. 10,458,307, which is a continuation of International Application No. PCT/US2016/039853, filed on Jun. 28, 2016, which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to a two-cycle, diesel engine. In particular, the invention relates to a novel, diesel engine configuration permitting operation of the engine with combustion chamber surface temperatures which allow the engine to properly function while using diesel fuels having a range of cetane (also referred to as hexadecane) levels. The engine configuration also permits restarting of the engine at low atmospheric pressures of the type experience when using the engine for aviation applications. 
     SUMMARY OF THE INVENTION 
     One embodiment of the invention relates to a two-cycle diesel engine for operating with high combustion chamber surface temperatures. The engine includes an aluminum engine block including at least one cylinder including a first intake port and a first exhaust port. The engine block including a first fluid flow channel for cooling the engine block and a second fluid flow channel located at the exhaust port to cool the portion of the cylinder proximate the exhaust port. The engine also includes a cylinder sleeve having a top end and a bottom end, and fabricated from a metal composite to include a second intake port and a second exhaust port proximate the bottom end. The sleeve being fastened to the interior of the cylinder with the intake ports being in fluid communication and the exhaust ports being in fluid communication. The engine also includes a head assembly engaged with the engine block, the head assembly including a third cooling fluid flow channel. The engine also includes a fuel injector assembly including an injector tip. The assembly is supported by the head assembly. The injector assembly including a fuel flow channel between a fuel source and the injector tip, a return fuel channel between the injector tip and the fuel source and a cooling fuel channel between the injector tip and the fuel source. The engine also includes a stainless steel fire plate resiliently supported between the top end of the cylinder sleeve and the head assembly to cooperate with the fuel injector assembly to close the top end of the cylinder sleeve. The engine also includes a crank shaft coupled to a connecting rod. The engine also includes an aluminum piston having a titanium alloy crown, the piston being located within the sleeve. The piston connected to the connecting rod to move the crown between the top of the cylinder sleeve, and below the second intake and exhaust ports. The engine also includes a turbocharger including a turbine coupled to the exhaust ports and a compressor. The compressor including an input coupled to an air filter and an output. The engine also includes a supercharger including a compressor coupled to the compressor output and the intake ports. 
     Another embodiment of the Invention relates to a two-cycle diesel engine for operating with high combustion chamber surface temperatures. The engine includes an aluminum engine block including at least four cylinders each including a first intake port and a first exhaust port. The engine block including a first fluid flow channel for cooling the engine block and a second fluid flow channel located at the exhaust ports to cool the portions of the cylinders proximate the exhaust ports. The engine also includes at least four cylinder sleeves each having a top end and a bottom end. The cylinder sleeves fabricated from a metal composite to each include a second intake port and a second exhaust port proximate the bottom ends. The sleeves being fastened to the interior of a respective cylinder with the intake ports being in fluid communication and the exhaust ports being in fluid communication. The engine also includes at least four head assemblies engaged with the engine block, the head assemblies each including a third cooling fluid flow channel. The engine also includes at least four fuel injector assemblies each including an injector tip. The assemblies are each supported by a respective head assembly. The injector assemblies each including a fuel flow channel between a fuel source and the injector tip, a return fuel channel between the injector tip and the fuel source and a cooling fuel channel between the injector tip and the fuel source. The engine also includes at least four stainless steel fire plates. Each of the fire plates is resiliently supported between the top end of respective cylinder sleeves and the head assemblies to cooperate with the fuel injector assembly to close the top end of a respective cylinder sleeve. The engine also includes a crank shaft coupled to at least four connecting rods. The engine also includes at least four aluminum pistons each having a titanium alloy crown. The pistons are located within a respective sleeve and connected to a respective connecting rod to move the crown between the top of the cylinder sleeve, and below the second intake and exhaust ports. The engine also includes a turbocharger including a turbine coupled to at least one of the exhaust ports. The turbocharger also includes a compressor including an input coupled to an air filter and an output. The engine also includes a supercharger including a compressor coupled to the output and at least one of the intake ports. 
     Another embodiment of the invention relates to an engine unit. The engine unit includes an engine block including at least one cylinder. The at least one cylinder includes a first intake port and a first exhaust port. The engine block includes a first fluid flow channel for cooling the engine block and a second fluid flow channel located at the exhaust port to cool the portion of the cylinder proximate the exhaust port. The second fluid flow channel includes a first branch passing over the top portion of the first exhaust port and a second branch passing under the bottom portion of the first exhaust port. The engine unit also includes a cylinder sleeve having a top end and a bottom end. The top and bottom end fabricated from a metal composite to include a second intake port and a second exhaust port proximate the bottom end. The sleeve is fastened to the interior of the cylinder with the intake ports being in fluid communication and the exhaust ports being in fluid communication. The engine unit also includes a head assembly engaged with the engine block. The head assembly includes threads for engaging the head to the engine block and including a third cooling fluid flow channel. The engine unit also includes a fuel injector assembly including an injector tip. The assembly is supported by the head assembly. The injector assembly includes a fuel flow channel between a fuel source and the injector tip, a return fuel channel between the injector tip and the fuel source and a cooling fuel channel between the injector tip and the fuel source. The engine unit also includes a stainless steel fire plate. The engine unit also includes a deflected belleville washer. The belleville washer is located between the head assembly and the stainless steel fire plate. The engine unit also includes a sealing washer. The sealing washer is located between the stainless steel fire plate and the top end of the cylinder sleeve. The sealing washer, fire plate and fuel injector assembly are arranged to close the top end of the cylinder sleeve. The engine unit also includes a crank shaft coupled to a connecting rod. The engine unit also includes an aluminum piston having a titanium alloy crown. The piston is located within the sleeve and connected to the connecting rod to move the crown between the top of the cylinder sleeve, and below the second intake and exhaust ports. The engine unit also includes a wrist pin supported at its ends and center by the piston. The end of the connecting rod includes a saddle which surrounds less than 180 degrees of the wrist pin and is fastened to the wrist pin. The engine unit also includes a turbocharger including a turbine coupled to the exhaust ports and a compressor including an input coupled to an air filter and an output. The engine unit also includes a supercharger including a compressor coupled to the compressor output and the intake ports. 
     Alternative example embodiments relate to other features and combinations of features as may be generally recited in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This application will become more fully understood from the following detailed description, taken in conjunction with the accompanying figures, wherein like reference numerals refer to like elements in which: 
         FIG. 1  is an elevational view of an internal combustion engine in which the present invention is employed. 
         FIG. 2  is a sectional view taken along line II-II illustrating a cylinder head, a cylinder, a piston and a connecting rod of the engine of  FIG. 1 . 
         FIG. 3 a    is a cross-sectional view taken along line III-III of  FIG. 2 . 
         FIG. 3 b    is a top perspective view of a crown the piston of  FIG. 2   
         FIG. 3 c    is a perspective cross-sectional view of the piston and crown of  FIG. 2   
         FIG. 4  is a schematic of a fuel injection system for the engine of  FIG. 1 . 
         FIG. 5  is a cross-sectional view taken along line VII-VII of  FIG. 8 .  FIG. 5  is also an enlarged view of a portion of  FIG. 2  illustrating in greater detail the cylinder, the cylinder head, the fuel injector and the cooling cap. 
         FIG. 6  is a perspective view of a fuel injector body of the engine of  FIG. 1 . 
         FIG. 7  is a cross-sectional view taken along line V-V of  FIG. 6 . 
         FIG. 8  is a top-view of  FIG. 5 . 
         FIG. 9  is an elevational view of another internal combustion engine in which the present invention is employed. 
         FIG. 10  is a partial sectional view of a portion of the engine shown in  FIG. 9 . 
         FIG. 11  is an exploded perspective view of certain components of the engine of  FIG. 9  and as further shown in  FIG. 10 . 
         FIG. 12  is an enlarged view of a portion of  FIG. 10 . 
         FIG. 13  is a top view of a cylinder head and cooling cap according to another embodiment of the invention. 
         FIG. 14  is a cross-sectional view taken along line XV-XV of  FIG. 13 . 
         FIG. 15  is a top down view of the engine block having the cylinder heads removed and cut to see the flow path of the exhaust pipe cooling system. 
         FIG. 16  is a cross-sectional view taken along line XVI-XVI of  FIG. 15 . 
         FIG. 17  is a perspective view of a crankcase pressure regulator of the engine of  FIG. 1 . 
         FIG. 18  is a partial cross-sectional side view of the crankcase pressure regulator of 
         FIG. 17  taken along line III-III of  FIG. 17 . 
         FIG. 19  is an oil flow diagram of the engine of  FIG. 1 . 
         FIG. 20  is an air flow diagram of the engine of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The engine configuration discussed in detail below uses various combinations of engine component configurations and materials which permit operation of an engine using combustion temperatures which allow the engine to properly function while using diesel fuels of varying cetane content. Of particular concern are diesel fuels with low cetane levels. For example, the ASTM D1655 standard for Jet A type fuel does not control for cetane levels, which results in high cetane variation amongst different sources of the same Jet A fuel type. The cetane number is an indicator of the combustion speed of diesel fuel as typically measured by the time period between the start of injection and the first identifiable pressure increase during combustion of the diesel fuel. Higher cetane fuels will have shorter ignition delay periods than lower cetane fuels. By way of reference, the characteristic diesel “knock” occurs when fuel that has been injected into the cylinder ignites after a delay causing a late shock wave. Minimizing this delay results in less unburned fuel in the cylinder and less intense knock. Therefore higher-cetane fuel usually causes an engine to run more smoothly and quietly. 
     Generally, diesel engines operate well using diesel fuel having a cetane number between 40 to 55. In Europe, diesel cetane numbers were set at a minimum of 38 in 1994 and 40 in 2000. The current minimum in the EU is a cetane number of 51. In North America, most states have adopted a minimum cetane number for diesel fuel of 40, with typical values in the 42-45 range. By way of further example, California requires that diesel fuel have a minimum cetane of 53. 
     One embodiment of the engine is configured for use as an aircraft engine. When used in aircraft, the diesel fuels available at various airports will vary and may have cetane levels which are low enough to produce poor engine performance. However, the ignition delays caused by low cetane levels can, within a range, be compensated for by increasing the combustion temperatures of a diesel engine. However, increasing the combustion surface temperature to a level effective to produce such compensation is not merely a matter of just allowing an engine to run hotter. Rather, the increased temperature requires an engine which is configured to provide proper heat removal from the engine while permitting increased localized temperatures in a combustion chamber configured to operate at higher temperatures and configured to cause mixing and movement/flow of a fuel-air mixture to improve ignition at a given temperature. The novel engine configuration disclosed herein provides for a two-cycle diesel engine which can properly function at cetane levels as low as 28. 
     Illustrated in  FIG. 1  is an internal combustion engine  10 . The engine  10  is a two-stroke, diesel engine having four cylinders  22  in a V-type arrangement operable to drive a propeller  411  (see  FIG. 20 ). Engine  10  (and version  310  discussed further below) generally is a four cylinder engine wherein diesel fuel is direct injected directly at the top and center of each cylinder. One structural feature of engine  10 , which permits this direct injection, is that engine  10  does not include either exhaust or intake valves. Rather, intake and exhaust ports are located in the cylinder and sleeve walls so that engine  10  exhausts and intakes fresh combustion air when the piston  26 ,  330  is at or near the bottom of its stroke. To improve performance and efficiency of engine  10 , a supercharger  1 , an intercooler  2  and a turbocharger  3  are used (shown schematically in  FIGS. 1 and 9 ). In particular, the turbocharger  3  is coupled to the exhaust ports and powered by the exhaust energy from the cylinders. The supercharger  1  is located between the cylinders  22  and is coupled between the input ports of engine  10  to further pressurize the fresh air entering the cylinders of engine  10  during operation. Intercooler  2  is coupled to the output of turbocharger  3  and the input of supercharger  1 . In addition to improving engine performance, the addition of supercharger  1  in combination with turbocharger  3  and intercooler  2  reduces the time for engine starting and restarting. In one embodiment, the supercharger  1  starts the flow of gas in engine  10  and spools up turbocharger  3 , which lessens the amount of work required of supercharger  1 . By way of specific example, for aircraft applications, engines may need to be restarted during flight. In this situation, short restart times are desirable. Ideally, restart times are shorter than the time it takes for a plane to make an unintended landing. 
     Referring to  FIG. 2 , engine block  14  at least partially defines a crankcase  18  and two sets of two cylinders (only two of the cylinders  22  are shown in  FIG. 1  and are labeled  22 a and  22 b. Unless a description requires specific reference to a particular cylinder, the cylinders will be referred to only with reference numeral “ 22 ”). The four cylinders  22  are generally identical, and only one cylinder will be described in detail. A crankshaft (not shown) is rotatably supported within the crankcase  18  by pressure lubricated bearings. A piston  26  reciprocates in the cylinder  22  and is connected to the crankshaft via connecting rod  30 . As the piston  26  reciprocates within the cylinder  22 , the crankshaft rotates. 
     The connecting rod  30  includes a first end  34  which is connected to the crankshaft. The connecting rod  30  further includes a second end  38  which includes an arcuate portion  42  that does not completely encircle a wrist pin  46 . Preferably, the arcuate portion  42  of the connecting rod  30  has an arcuate extent that is about or slightly less than 180 degrees. The wrist pin  46  has an annular wall  50  including a cylindrical inner surface  54  ( FIG. 3 a   ) and a cylindrical outer surface  58 , which engages the arcuate portion  42  of the connecting rod  30 , and is pivotally connected to the piston  26 . A plurality of fasteners  62  extend through the annular wall  50  of the wrist pin  46  and into a wrist pin insert  66  (see also,  FIG. 3 a   ) to secure the wrist pin  46  to the arcuate portion  42  of the connecting rod  30 . Preferably, the wrist pin insert  66  is cylindrical or trunnion type wrist pin. Using a trunnion type wrist pin increases the available bearing area. Preferably, the fasteners  62  are screws and thread into the wrist pin insert. This connecting rod arrangement permits the top portion of the piston to have more uniformity than a connecting rod arrangement wherein end  38  surrounds the wrist pin  46 . In the arrangement where end  38  surrounds the associated wrist pin  46 , material is removed from the top portion of the piston  26 . The removed material changes the deformation characteristics of the piston  26  when it is heated and cooled during engine operation either during transient periods or as the engine cycles through its diesel combustion cycle. 
     Additionally, as shown in  FIG. 3 a   , where the upper or second end  38  of the connecting rod  30  does not encircle the wrist pin  46 , the piston  26  bears against the wrist pin  46  along the entire top of the wrist pin  46 , thereby more evenly distributing the load on the wrist pin  46 . The use of the wrist pin insert  66  further increases the strength and stability of the wrist pin  46 . The forced rocking of the wrist pin  46  as the connecting rod  30  pivots and the increased bearing surface area of the wrist pin  46  minimizes uneven wear on the bearing surface of wrist pin  46  during operation of the engine  10 . 
     Referring now more specifically to the top of piston  26 ,  FIG. 3 b    is a top perspective view of a crown  27  of piston  26  and  FIG. 3 c    is a perspective cross-sectional view of the piston showing the configuration of crown  27 . In particular, crown  27  includes the arcuate grooves  29 . Grooves  29  cause improved mixing of the fuel air mixture during the initial combustion of the mixture which increases the combustion speed for fuel having a given cetane level. When combined with the other structural features of engine  10 , grooves  29  improve the performance of engine  10  when burning low cetane diesel fuels. 
     As generally discussed above, engine performance for fuels having a given cetane level is also improved if the surface temperatures of the surfaces defining the interior combustion chamber (generally referenced as  74  in  FIGS. 2, 5, 12 and 14 , and as  350  in  FIG. 10 ) are maintained sufficiently high. Accordingly, these surfaces must be fabricated or formed from materials which are suitable for use in an engine at high operating temperatures. The first of these surfaces is the top surface of crown  27 . A suitable material for use in fabricating crown  27  is a titanium metal. By way of specific example, for the engine  10  as disclosed herein it is desirable to use a titanium compound such as Ti 6Al-4V. This example alloy by weight percentage includes Carbon (maximum 0.10%), Aluminum (5.50 to 6.75%), Vanadium (3.50 to 4.50%), Nitrogen (approximately 0.05%), Iron (maximum 0.40%), Oxygen (maximum 0.020%), Hydrogen (maximum 0.015%), Other (maximum 0.40%), and balance Titanium. 
     The grooves  29  are formed into the top of crown  27 . In one embodiment, a ball end mill is used to cut out grooves  29 . The crown  27  is joined to skirt  31  of piston  26 . In one embodiment, threads are formed on the interior of crown  27  that are configured to mate with threads formed on skirt  31 . Crown  27  is further staked at three different locations. Accordingly, the shape of and material used for crown  27  provide one of the surfaces which define the interior of combustion chamber  74 . This surface is designed to both improve fuel air mixing and be useable at a surface temperature which is suitable for burning lower cetane fuels. 
     Referring to  FIG. 4 , engine  10  includes four fuel injectors  70   a ,  70   b ,  70   c  and  70   d , one for each cylinder  22 . (Unless a description requires specific reference to a particular fuel injector, fuel injectors will be referred to only with reference numeral “ 70 .”) Fuel injectors  70  are substantially identical to each other, and only one will be described in detail. Referring generally to  FIG. 5 , fuel injector  70 , is located to inject fuel into a combustion chamber  74  which has an internal surface defined by the surfaces of piston crown  27 , a cylinder sleeve  322 , and fireplate  338 . The fuel injector  70  includes a fuel injector nut  86  which is received by an appropriately sized tapered bore in a cylinder head  78 . Inside the injector nut  86  is a fuel injector tip  90  housing a pressure responsive, movable pintle (not shown). The nut  86  and the tip  90  define a main fuel outlet  92  communicating with the combustion chamber  74 . A fuel injector body  82  is threaded into the upper end of the nut  86 . 
     Referring to  FIGS. 6 and 7 , the fuel injector body  82  includes a main fuel inlet port  98  which communicates with and transitions into fuel passage  106 . A fuel inlet cooling port  110  communicates with and transitions into a cooling port  118 . An injector overflow fuel outlet port  114  communicates with and transitions into outlet port  120 . Although not shown, the fuel injector further includes a flow straightener, a check valve, a check valve receiver, a spring mechanism and a spring guide, all of which are positioned within a hollow space  94  of the fuel injector nut  86  between the body  82  and the tip  90 . The addition of the inlet cooling port  110  and the cooling port  118  allows cooling of the fuel injector as described below. 
       FIG. 4  illustrates a fuel flow schematic for a fuel injection system  122 . Shown is fuel supply tank  126 , fuel line  128 , fuel filter  130 , fuel pump  132  which includes delivery pump  134  and high pressure pump  138 , and fuel lines  142  connected to the fuel inlet ports  98  of the injector bodies  82  of the injectors  70 . Fuel line  146  is connected to the cooling port  110  of injector  70 d. Ports  114  and  110  of injectors  70 d and  70 c are in fluid communication, ports  114  and  110  of injectors  70 c and  70 b are in fluid communication and ports  114  and  110  of injectors  70 b and  70 a are in fluid communication. Port  114  of injector  70 a is connected to return fuel line  148 . The fuel flowing through ports  98 ,  110 , and  114  mixes in space  94  and provides for a fuel flow through at least three locations in injector body  82  to maintain the injector body at a temperature which is approximately the average temperature of the fuel in space  94 . 
     Referring to  FIGS. 2, 5 and 10 , it can be seen that the injectors are engaged and in thermal contact with the cylinder head  78 ,  342  and in thermal contact with fireplate  338  (if used). As a consequence, the additional cooling provided by cooling ports  110  and  118  allow engine  10  to operate with relatively high surface temperatures on the surfaces of chamber  74 . Without these ports, the surface temperatures would need to be lower to prevent over heating of body  82  and the fuel which flows through body  82 . By providing an injector with additional cooling, combustion chamber  74  temperatures for burning lower cetane fuels are more readily achieved. In addition, the warmed overflow fuel will warm all of the fuel in the system which serves to limit jelling of the fuel at cold temperatures of the type experienced in cold weather or at high altitudes. 
       FIGS. 5 and 8  illustrate a cooling cap  154  mounted on the cylinder head  78  to cool the cylinder head  78 . The cooling cap  154  has an annular coolant groove  158  which mates with an annular coolant groove  162  of the cylinder head  78  to define an annular cooling passageway  166  when the cooling cap  154  is mounted on the cylinder head  78 . In other embodiments, such as the embodiment which is illustrated in  FIGS. 9-12 , only one of the cooling cap  154  and the cylinder head  78  includes a groove such that the combination of the cooling cap  154  and the cylinder head  78  define the annular cooling passageway  166 . The cooling cap  154  includes inlet port  170  and outlet port  174  which communicate with the annular cooling passageway  166 , so that cooling fluid can flow into the inlet port  170 , through the annular cooling passageway  166  and out the outlet port  174 , thereby cooling the cylinder head  78 . As used within the claims, “substantially annular” includes an enclosed loop similar to that illustrated in  FIGS. 5 and 8 , and a partial loop similar to that illustrated in  FIGS. 9-12  (e.g., an annular groove that is separated by a divider pin, or projection  406 ). 
     The engine block  14  includes a cooling jacket  178  with an outlet  182  and an inlet (not shown). The cooling cap  154  is placed on the cylinder head  78  with the inlet port  170  in alignment with the outlet port  182  of the cooling jacket  178  and the outlet port  174  in alignment with the inlet port of the cooling jacket  178 . A first transfer tube  186  communicates between the inlet port  170  of the cooling cap  154  and the outlet port  182  of the cooling jacket  178 , and a second transfer tube (not shown) communicates between the outlet port  174  of the cooling cap  154  and the inlet port of the cooling jacket  178 . 
     As shown in  FIG. 8 , the inlet port  170  and the outlet port  174  of the cooling cap  154  are not diametrically opposed around the annular cooling passageway  166 . Thus, a first portion of the annular cooling passageway  166  extends in one direction from the inlet port  170  to the outlet port  174  (representatively shown as arrow  190  in  FIG. 8 ) and a second portion of the annular cooling passageway  166  extends in an opposite direction from the inlet port  170  to the outlet port  174  (representatively shown as arrow  194  in  FIG. 8 ). The first portion of the annular cooling passageway  166  is shorter in length than the second portion of the annular cooling passageway  166 . The flow rate through the annular cooling passageway  166  in either direction is proportional to the distance traveled. The first portion of the annular cooling passageway  166  is restricted. In this way, cooling fluid travels in both directions through the annular cooling passageway  166  to cool the cylinder head  78 . 
     The cooling cap  154  is adjustably positionable around the cylinder head  78 , so that the inlet port  170  and the outlet port  174  are properly alignable with the associated inlet and outlet ports of the cooling jacket  178 . This accommodates the cylinder head  78  which threads into the cylinder block or engine block  14 . Engine block  14  includes female threads concentric with the cylinder  22 , and the cylinder head  78  includes male threads which engage the female threads of the engine block  14 . Because the cylinder head  78  threads into the engine block  14 , it is not exactly known where the cylinder head  78  will be located with respect to the engine body. Once the adjustable cooling cap  154  is properly located on the cylinder head  78 , a plurality of clamping members  198 , preferably equally spaced apart, span across the top of the cooling cap  154  to secure the cooling cap  154  to the cylinder head  78 . Each of the clamping members  198  has opposite ends  202  and  206 , and is secured to the cylinder head  78  by a pair of fasteners  210 . One fastener  210  is located adjacent end  202  and the other fastener  210  is located adjacent end  206 . Preferably, the fasteners  210  thread into the top of the cylinder head  78 . Preferably, the cylinder head  78  includes a plurality of sets of pre-drilled, threaded holes such that each fastener  210  can be located in a plurality of positions relative to the cylinder head  78 . Preferably, end  202  of each clamping member  198  is received by an annular groove  214  in the fuel injector nut  86 , thereby also securing the fuel injector  70  to the cylinder head  78 . 
     In the embodiment illustrated in  FIGS. 5 and 8 , the coolant initially flows from a pump (not shown) into the cooling jacket  178 . From the cooling jacket  178 , the coolant flows through the outlet port  182  of the cooling jacket  178  into the first transfer tube  186 , and then into the inlet port  170  of the cooling cap  154 . From the inlet port  170 , the coolant travels through the cooling passageway  166  to the outlet port  174  of the cooling cap  154  removing heat from the cylinder head  78 . The coolant then flows from the outlet  174  of the cooling cap  154  through the second transfer tube and inlet port of the cooling jacket  178  to return to the cooling jacket  178 . From the cooling jacket  178 , the heated coolant is returned to the pump of the coolant system to be cooled and returned to the cooling jacket  178 . 
     Another embodiment of the cooling cap  154  is illustrated in  FIGS. 13 and 14 . This embodiment is substantially similar to the embodiment shown in  FIGS. 5 and 8  except that the embodiment illustrated in  FIGS. 13 and 14  includes a different coolant flow path. Reference numbers used with respect to the embodiment illustrated in  FIGS. 5 and 8  are also used in  FIGS. 13 and 14  to indicate like components. 
     With reference to  FIGS. 13 and 14 , the coolant initially flows from a pump (not shown), through a supply conduit  172 , and into the cooling jacket  178 . From the cooling jacket  178 , the coolant flows into and through the outlet port  182  of the cooling jacket  178 , through the first transfer tube  186 , through the inlet port  170  of the cooling cap  154 , and into the annular cooling passageway  166 . From the inlet port  170 , the coolant travels through the cooling passageway  166  in the direction of arrow  194  to the outlet port  174  of the cooling cap  154  removing heat from the cylinder head  78 . In this embodiment, the coolant is blocked from flowing toward the outlet  174  in a direction opposite to the arrow  194 . The coolant then flows from the outlet  174  of the cooling cap  154  through a second transfer tube  184  and into a return port  188 . From the return port  188 , the coolant is directed back to the pump through the return line  192  to be cooled and returned to the cooling jacket  178  through the supply conduit  172 . As just described, the coolant flows into the cooling jacket  178 , then flows into the cooling cap  154 , and then returns to the pump. In contrast, the coolant used with the embodiment illustrated in  FIGS. 5 and 8  flows into the cooling jacket  178 , then flows into the cooling cap  154 , then flows back into the cooling jacket  178 , and then finally returns to the pump. 
     In one embodiment of engine  10 , a cross-feed cooling passageway extends between the respective cooling jackets for the engine cylinders providing cooling fluid flow between the cooling jackets. The cross-feed cooling passageway may be drilled through the portion of the engine block  14  supporting the main bearing support for the crankshaft. If a thermostat communicating with the one of the cooling jackets  178  fails, the cross-feed cooling passageway enables cooling fluid to continue to flow to minimize or prevent damage to the respective cylinder head. The cross-feed cooling passageway also reduces the thermal gradient between the cylinder heads and the lower crankcase of the engine to reduce distortion of the aluminum block due to unacceptable temperature gradients and, thereby increase engine life. 
     Illustrated in  FIG. 9  is another embodiment of the engine, referenced as engine  310 . In this embodiment, a cylindrical sleeve  322  is positioned within the cylinder  318 . The sleeve  322  may be an aluminum sleeve that is shrink fitted into the cylinder  318  and bonded to the engine block  314  with an epoxy resin having an aluminum filler. The sleeve  322  includes a shoulder  326 . A piston  330  reciprocates within the sleeve  322 . Preferably, the sleeve would be fabricated from a metal matrix to provide a wear resistant internal surface at surface temperatures which permit efficient combustion of relatively low cetane diesel fuels. One example of such a matrix is a 10S4G Aluminum Composite. Application-10S4G uses a silicon carbide (SiC) particulate and a nickel (Ni) coated graphite for improved wear resistance, continuous lubricity and good high temperature strength. The base alloy of the matrix by weight percent is composed of Silicon (8.5-9.5%), Iron (0.20% maximum), Copper (0.20% maximum), Manganese (0.10% maximum), Magnesium (0.45-0.65%), Zinc (0.10% maximum), Titanium (0.20% maximum), Other matter (0.05% maximum each and 0.15 maximum total), Aluminum (remainder %). To form the fmal composite SiC and Ni coated graphite are added to the base alloy. In one embodiment, the SiC is 10% by volume and is nominally 30 microns in diameter, and the Ni coated graphite (e.g. Novamet 60% NCG) is 4% by volume. Then, the combined composite is solution and precipitation heat treated. The fmal composite following treatment has specific tensile and yield properties. When measured at room temperature, the fmal composite has a minimum tensile strength of 33 KiloPounds per square inch (KSI) and a minimum yield of 27 KSI. When measured at approximately 300 degrees Fahrenheit, the final composite has a minimum tensile strength of 23 KSI and a minimum yield of 20 KSI. 
     As another suitable alternative, sleeve  322  would be fabricated from aluminum with a steel coated internal surface. These embodiments provide for another portion of the internal surface of combustion chamber  74  which can be maintained at relatively high temperatures during engine operation to provide improved engine performance with relatively low cetane diesel fuels. By way of example, the steel coating of sleeve  322  is preferably accomplished with steel wire used in a plasma-transferred wire arc process. After the appropriate amount of steel is applied to the internal surface of the sleeve  322 , the surface is honed for use with an appropriate piston and ring set. 
     Referring to  FIGS. 10-12 , a gasket  334  is positioned on the shoulder  326  of the sleeve  322 . In one embodiment, the gasket  334  is a copper gasket. As will be further explained below, the, gasket  334  acts as both a sealing mechanism and a shimming device. 
     The fireplate  338  is positioned between a cylinder head  342  and the gasket  334 . A bottom side  346  of the fireplate  338  cooperates with the crown  27  of piston  330  and the sleeve  322  to define a combustion chamber  350 . An annular ledge  354  on the fireplate  338  receives an  0 -ring  358  to provide a seal between the side wall  356  of the fireplate  338  and the cylinder  318 . In one design, the cylinder head  342  is made of aluminum and the fireplate  338  is made of stainless steel which provides a surface for chamber  350  which is suitable for use at a relatively high temperature during engine operation. 
     A head spring  362  is positioned between the cylinder head  342  and the fireplate  338 . A bottom side  366  of the cylinder head  342  has an annular groove  370  which receives the head spring  362 , and a top side  374  of the fireplate  338  has a recess  378  which also receives the head spring  362 . The head spring  362  is preferably a belleville spring. The head spring  362  is also preferably made of stainless steel. Belleville springs take the form of a shallow, conical disk with a hole through the center thereof. A very high spring rate or spring force can be developed in a very small axial space with these types of springs. Predetermined load-deflection characteristics can be obtained by varying the height of the cone to the thickness of the disk. 
     As can be observed with reference to  FIGS. 10-12 , the cylinder head  342  threads into a portion of the engine block  314 . When the cylinder head  342  is threaded into the engine block  314 , the cylinder head  342  compresses the head spring  362  against the fireplate  338  to provide a downward force against the top side  374  of the fireplate  338  to offset an upward force created by combustion within the combustion chamber  350 . The downward force provided by the deflection or deformation of spring  362  generates a spring force which resiliently forces fireplate  338  into contact with the gasket  334 , which is forced against shoulder  326  of the sleeve  322  to provide an appropriate combustion seal during operation of the engine  310 . 
     The head spring  362  also acts to allow for the expansion and contraction of the relevant mating engine components during changing loading and thermal conditions of the engine  310  without adversely affecting the combustion seal, much like traditional head bolts act. As noted above, head bolts can be used to provide a clamping force that seals a cylinder head to an engine block. Because the head bolts are allowed to expand and contract with the associated engine components as the loading and temperature of the engine varies, the head bolts are capable of maintaining the clamping force during operation of the engine. However, the threaded cylinder head  342  does not generally have the stretching capabilities of typical head bolts because of its relatively large diameter and short thread length. 
     As suggested above, the load provided by the head spring  362  can be calculated based on the deflection of the spring  362 . A specific amount of deflection translates into a consistent amount of downward force, which ensures a proper combustion seal. In one embodiment, the desired deflection for the head spring  362 , the cylinder head  342  and associated components are obtained by assembling the components as shown in  FIG. 11 . The threads which hold cylinder head  342  in place can be preloaded. By preloading these threads or head bolts (if a bolted head configuration is used) the range of varying force applied to the threads or bolts is reduced, thus increasing the fatigue life of these components. 
     The use of gasket  334  allows for the effective control of the location of piston  330  relative to fireplate  338  to accurately set the top dead center of piston  330  relative to fireplate  338 . In particular, gasket  334  accommodates the accumulation of a deviation from ideal dimensions resulting from the combination of the tolerances associated with the engine block  314 , the cylinder head  342 , the sleeve  322 , and the piston  330 . After the fireplate  338  is positioned on the gasket  334 , the cylinder head  342  is threaded into the engine block  314  until such time as the bottom side  366  of the cylinder head  342  contacts the top side  374  of the fireplate  338 . Once contact is made between the cylinder head  342  and the fireplate  338 , the final assembly position of the cylinder head  342  with respect to the engine block  314  is known. The final assembly position of the cylinder head  342  is then marked or otherwise recorded for future reference so that a gasket  334  of appropriate thickness can be selected for final assembly. 
     Providing a cooling system for the cylinder head  342  allows the combustion chamber surfaces to operate at sufficiently high temperatures to accommodate low cetane fuels. A cooling cap  382  is mounted on the cylinder head  342 . The cooling cap  382  cooperates with an annular groove  390  of the cylinder head  342  to define a cooling passageway  394 . The cooling cap  382  includes an inlet port  398  and an outlet port  402 . The inlet port  398  is adapted to receive a cooling fluid flowing through the engine  310 , and the outlet port  402  is adapted to send the cooling fluid on through the engine  310  after the cooling fluid has been used to cool the cylinder head  342 . As best shown in  FIG. 10 , the inlet port  398  and the outlet port  402  are adjacent to one another. A divider pin  406 , or projection extends from the cooling cap  382  into the cooling passageway  394  (see  FIG. 12 ) to substantially close the short passageway between the inlet port  398  and the outlet port  402 . In this way, the cooling fluid is only allowed to flow around the cooling passageway  394  in a single direction to cool the cylinder head  342 . Although allowing the cooling fluid to flow in both directions around the cooling passageway  394  between the inlet port  398  and an outlet port  402  would cool the cylinder head  342 , it has been determined that causing the cooling fluid to flow in one direction around substantially the entire cooling passageway  394  also provides effective cooling. In other embodiments, the divider pin  406  is eliminated and only a partial annular groove is formed in the cylinder head  342  and/or the cooling cap  382  such that the combination of the cylinder head  342  and the cooling cap  382  define a unidirectional cooling passage without the need for a divider pin  406 . In a further embodiment, divider pin  406  is configured to allow some portion of cooling fluid to flow into the short passageway between the inlet port  398  and the outlet port  402 . Allowing cooling fluid to flow into the short passageway maintains a substantially uniform cooling around the cylinder head  342 . 
     The manner of attaching the cooling cap  382  to the cylinder head  342  is substantially described above in relation to engine  10 . Reference is also made to the description above in relation to engine  10  for the description and manner of operating the fuel injector  410 . In one embodiment engine  310  includes nine sets of holes  414  for the associated clamping members  418 , as compared to the six sets of holes as shown for engine  10 . It was determined that nine sets of holes enables easier positioning of the cooling cap  382  with respect to the cylinder head  342 . In an alternative embodiment, cooling cap  382  is fastened to cylinder head  342  with 3 clamping members  418 . In this embodiment, the external most holes from the set of holes  414  are omitted and only the interior nine holes are needed to position cooling cap  382  with respect to the cylinder head  342 . 
     Referring now to  FIG. 15 , a top down view of one side of the engine block  14  having the cylinder heads removed and cut perpendicularly across is shown. Each cylinder head  22  includes a corresponding exhaust pipe a first exhaust pipe  600  in communication with one of the cylinders  22  and a second exhaust pipe  602  in communication with a different one of the cylinders  22  are shown in  FIG. 15 . Engine block  14  includes a water jacket  604  surrounding two of the cylinders  22 . A similar setup is used for the two cylinders on the opposite side of the engine  10  (not shown). Water jacket  604  includes a channel  606  in which cooling fluid flows around the first and second exhaust pipes  600  and  602  and the cylinders  22  in the manner described below to remove heat from the system. Cooling fluid enters water jacket  604  from a pump (not shown) at cooling intake port  608 . The cooling fluid flows at a constant rate in the directions indicated by arrows A 1  and A 2  through channel  606  around both cylinders  22  as indicated by arrows B 1  and B 2  and C 1  and C 2 . The cooling fluid flows into cooling outtake port  610  as show by arrows D 1  and D 2 . From cooling outtake port  610 , the cooling fluid is returned to the pump where it is cooled and pumped back into cooling intake port  608 . In one embodiment, water jacket  604  and cooling jacket  178  described above are integrated and the coolant flows around both the cylinders  22 , the first and second exhaust pipes  600  and  602 , and the cylinder heads as described above before returning to the pump. 
     Referring now to  FIG. 16 , a cross-sectional view of engine  10  and water jacket  604  taken along line XVI-XVI of  FIG. 15  is shown. First exhaust pipe  600  includes a top portion  612  and a bottom portion  614 . Similarly, second exhaust pipe  602  includes a top portion  616  and a bottom portion  618 . In one embodiment, channel  606  includes a first branch  620  passing over the top portions  612  and  616  and a second branch  622  passing under the bottom portions  614  and  618 . The first and second branches merge together on the opposite sides of exhaust pipes  600  and  602  to reform uniform channel  606 . In this embodiment, the cooling fluid flows into water jacket  604  and begins to flow around cylinders  22  as indicated by arrows A 1  and A 2  in figure  15 . As the cooling fluid approaches the first and second exhaust pipes  600  and  602 , one portion of the cooling fluid flows over the top portions  612  and  616  as indicated by arrows E 1  and E 2  while another portion of the cooling fluid is diverted to flow under the bottom portions  614  and  618  as indicated by arrows F 1  and F 2  and G 1  and G 2 . After the cooling fluid passes separately over the top and bottom portions of exhaust pipes  600  and  602 , the two fluid flows merge to continue flowing around cylinders  22  as described above. Having cooling fluid flow over the top and bottom portions of the exhaust pipes  600  and  602  allows for bidirectional cooling and prevents the bottom portions  614  and  618  from overheating that can occur when the exhaust pipes are only cooled from the top. 
     Referring to  FIG. 19 , a schematic illustration of an embodiment of engine  10  as a dry sump engine that includes an oil sump pump or scavenge pump  420  to remove oil and air from within the crankcase  18 . Referring to  FIG. 19 , the engine  10  also includes an oil tank  422  and a scavenge discharge line  424  that provides fluid communication between the crankcase  18 , the scavenge pump  420 , and the oil tank  422 . Engine  10  further includes a supply oil pump  426 , an oil pressure regulator  428 , and an oil cooler or heat exchanger  430 . The oil supply pump  426  supplies oil to the engine block  14  and crankcase  18  from the oil tank  422  during operation of the engine  10 . The oil pressure regulator  428  bleeds or allows a portion of oil to travel back to the oil tank  422  if the discharge pressure of the supply pump  426  exceeds a predetermined value. For example, in one construction, the oil pressure regulator  428  is set such that the oil pressure within the heat exchanger  430  does not exceed about 150 psi. An oil filter  432  is disposed between the oil tank  422  and the engine block  14  to filter oil supplied to the engine block  14  from the tank  422 . 
     Referring to  FIGS. 19 and 20 , a schematic view of an embodiment of engine  10  wherein turbocharger  3  includes a compressor  435  and a turbine  436  that drives the compressor  435  using exhaust gas from the engine  10 . An oil supply line  438  ( FIG. 19 ) fluidly couples the turbocharger  3  and the oil tank  422  to supply oil to the turbocharger  3 . An oil return line  440  fluidly couples the turbocharger  3  and the oil tank  422  to return oil from the turbocharger  3  back to the oil tank  422 . A pressure sensor  442  and a temperature sensor  444  are in fluid communication with a main oil supply line  446  to sense the pressure and temperature, respectively, of oil being supplied to the engine block  14 , the crankcase  18 , and the turbocharger  3 . 
     Referring to  FIG. 20 , an air inlet  450  and an air filter  452  are arranged in series in an air inlet line  454  of the engine  10 . Referring to  FIG. 19 , an air vent line  462  fluidly couples the oil tank  422  with the air inlet  450  to vent the oil tank  422  to the air inlet line  454 . 
     The engine  10  further includes a crankcase pressure regulator  466  that is in fluid communication with the oil tank  422  and the crankcase  18  via a crankcase breather line  468 . The crankcase breather line  468  includes a first portion  470  that extends between the crankcase pressure regulator  466  and the crankcase  18  to provide fluid communication between the crankcase  18  and the crankcase pressure regulator  466 . A second portion  472  of the breather line  468  extends between the pressure regulator  466  and the oil tank  422  to provide fluid communication between the pressure regulator  466  and the oil tank  422 . 
     Referring to  FIGS. 17 and 18 , the crankcase pressure regulator  466  includes a body  476 . In one embodiment, the body  476  is formed to define a first internal passageway  478  and a second internal passageway  480  that both extend through the body  476  of the pressure regulator  466 . The body  476  further includes a first aperture  482  and a second aperture  484 . The first passageway  478  is defined as a flow path through the first aperture  482  and the second aperture  484 . The second passageway  480  is defined as a flow path through the first aperture  482  and the second aperture  484  such that the second passageway  480  is in a parallel arrangement to the first passageway  478 . A first connector  486  is partially located within the first aperture  482  in order to fluidly couple the first aperture  482  with the crankcase  18  of the engine  10  via the first portion  470  of the breather line  468 . A second connector  488  is partially located within the second aperture  484  to fluidly couple the second aperture  484  with the oil tank  422  via the second portion  472  of the breather line  468 . While the first and second connectors  486  and  488 , respectively, are threaded nipples or bushings, in other constructions, any suitable connector can be utilized. 
     Furthermore, while  FIG. 20  schematically illustrates the crankcase pressure regulator  466  connected to the crankcase breather line  468  at both the connectors  486  and  488 , the connectors  486  and  488  can be utilized to directly couple the pressure regulator  466  to either the crankcase  18  or the oil tank  422 . For example, in one construction the pressure regulator  466  can be mounted on the oil tank  422  using an aperture  490  of the body  476  and the second connector  488  can be connected to the oil tank  422 . Of course, in other constructions, other suitable arrangements of the pressure regulator  466  within the flow path of the crankcase  18 , crankcase breather line  468 , and the oil tank  422  can be utilized. 
     The body  476  of the pressure regulator  466  further includes a first auxiliary aperture  494  and a second auxiliary aperture  496 . The first and second auxiliary apertures  494  and  496  are utilized while manufacturing the pressure regulator  466  to access the passageways  478  and  480  and other components within the pressure regulator  466 . In one embodiment, threaded plugs  498  and  500  are utilized to block or close the apertures  494  and  496 , respectively, after the requisite manufacturing and assembling processes are completed within the body  476 . 
     The pressure regulator  466  further includes a first check valve  504  and a second check valve  506 . The first check valve  504  includes a seat  508 , which is integrally formed in the body  476 . The first check valve  504  further includes a valve member  510 , and a biasing member  512 . In one embodiment, valve member  510  is a ball and biasing member  512  is a coil spring. The biasing member  512  contacts the first connector  486  to bias the valve member  510  against the seat  508  or into a closed position of the valve  504 . As will be discussed in more detail below, the first check valve  504  regulates flow through the first passageway  478 , and the first check valve  504  is arranged to allow fluid flow through the first passageway  478  in the direction of the arrows of  FIG. 18  along the first passageway  478  while preventing fluid flow in the opposite direction. 
     The second check valve  506  includes a seat  514 , which is integrally formed in the body  476 . The second check valve  506  further includes a valve member  516 , and a biasing member  520 . In one embodiment, valve member  516  is a ball and biasing member  520  is a coil spring. The biasing member  520  of the second check valve  506  contacts the threaded plug  498  of the first auxiliary aperture  494  such that the valve member  516  is biased against the seat  514  or into a closed position of the valve  506 . As will be discussed in more detail below, the second check valve  506  regulates flow through the second passageway  480 , and the second check valve  506  is arranged to allow fluid flow through the second passageway  480  in the direction of the arrows of  FIG. 18  along the second passageway  480  while preventing fluid flow in the opposite direction. While the check valves  504  and  506  in the illustrated construction are ball-type check valves, it should be understood that other types of valves and check valves can be utilized. 
     In one embodiment, the crankcase pressure regulator  466  includes a pressure sensor  524 . The pressure sensor  524  is in fluid communication with the first and second passageways  478  and  480 , respectively, such that pressure sensor  524  is operable to measure the pressure within the crankcase  18  regardless of the position (i.e., open or closed) of the first and second check valves  504  and  506 , respectively. 
     Referring to  FIG. 20 , during operation of the engine  10 , ambient air for combustion is drawn through the air inlet  450 , then through the air filter  452  by the compressor  435  of the turbocharger  3 . The compressor  435  is driven by the turbine  436  to compress the combustion air. The turbine  436  is driven by exhaust gases from the engine  10  that are delivered to the turbine  436  by an exhaust line  530 . The compressed combustion air then travels through the intercooler  2  and supercharger  1  before entering the combustion chamber of the engine  10 . 
     Concurrently, referring now to  FIG. 19 , the scavenge pump  420  removes air and oil from within the crankcase  18  through the scavenge discharge line  424 , which generally reduces the pressure within the crankcase  18  below the ambient pressure. The air and oil removed by the scavenge pump  420  can include air and oil from the combustion chamber that bypasses the piston rings. 
     The first check valve  504 , which is biased into the closed position, inhibits make-up air from entering the crankcase  18  through the crankcase breather line  468  until the pressure within the crankcase  18  reaches a predetermined average lower level. Thus, the average pressure within the crankcase  18  is reduced and maintained below ambient pressure, particularly during low power operation of the engine  10 . The first check valve  504  remains closed until the average crankcase pressure is less than the predetermined average lower level. When the crankcase pressure is less than the predetermined lower level, the pressure within the oil tank  422  (about ambient pressure) acting against the valve member  510  overcomes the force of the biasing member  512  to lift the valve member  510  from the seat  508  to open the first valve  504  to allow make-up air to flow into the crankcase  18  in order to maintain the air pressure within the crankcase  18  above the predetermined average lower level. 
     The pistons  26 ,  330  being alternatively drawn into the crankcase  18  and the pistons  26 ,  330  being pushed into the cylinders during the normal compression and combustion strokes of the engine  10  generate a pressure wave in the crankcase  18 . In one construction of the engine  10 , this pressure wave is about +/−4 psi. In such a construction, the biasing member  512  of the first check valve  504  can be chosen such that the first check valve  504  opens when the average pressure within the crankcase  18  is about −6 psi. Alternatively stated, the first check valve  504  opens to allow make-up air to pass through the first passageway  478  when the pressure within the crankcase  18  is 6 psi less than the pressure within the oil tank  422 , which is about ambient pressure. Therefore, if the pressure wave is about +/−4 psi, the instantaneous pressure within the crankcase  18  will oscillate between about −10 psi and −2 psi and the peak of the pressure wave will not exceed ambient pressure (e.g., 0 psi). In the illustrated construction, the make-up air is drawn from the oil tank  422  through the breather line  468 . While in the construction of the pressure regulator  466  discussed above, the first check valve  504  opens at −6 psi, in other constructions the first check valve  504  can open at an average pressure greater than or less than −6 psi. For example, the engine seals and/or the amplitude of the pressure wave generated by piston oscillation may make a different opening average pressure for the check valve  504  more desirable. 
     During operation of the engine  10 , particularly during low power operation of the engine  10 , the pressure within the intake manifold is relatively low or near atmospheric pressure. Thus, in the construction described above, the instantaneous pressure within the crankcase  18  does not exceed about −2 psi or remains lower than the intake manifold pressure. As a result, the amount of oil that is forced by pressure from the crankcase  18  toward the intake manifold is greatly reduced. 
     During high power operation of the engine  10 , the pressure within the intake manifold can be relatively high. Furthermore, as discussed above, the pressure regulator  466  lowers the average pressure within the crankcase  18 . As a result, there can be an excessive amount of air that leaks past the piston rings and into the crankcase  18 . While the scavenge pump  420  removes air from the crankcase  18 , the leakage may be at such a rate that the pump  420  is unable to remove a sufficient amount of air to maintain a negative (i.e., less than ambient) pressure within the crankcase  18 . If the pressure within the crankcase  18  exceeds a predetermined average level, the second check valve  506  opens to allow air to pass through the second passageway  480  and to the oil tank  242  and vent  462  thereby venting the crankcase  18  to the air inlet line  454  ( FIG. 20 ). The second check valve  506  remains closed until the average crankcase pressure is greater than the predetermined level. When the crankcase pressure is greater than the predetermined level, the pressure within the crankcase  18  acting against the valve member  516  overcomes the force of the biasing member  520  to lift the valve member  516  from the seat  514  to open the second valve  506 . 
     In one construction, the biasing member  520  of the second check valve  506  is chosen such that the second check valve  506  opens when the average pressure within the crankcase is about 0.2 psi above ambient pressure. Of course in other constructions, the second check valve  506  can be designed to open at more or less than 0.2 psi. 
     The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention in the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings in skill or knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain the best modes known for practicing the invention and to enable others skilled in the art to utilize the invention as such, or other embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims are to be construed to include alternative embodiments to the extent permitted by the prior art. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. 
     For purposes of this disclosure, the term “coupled” means the joining of two components directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional member being attached to one another. Such joining may be permanent in nature or alternatively may be removable or releasable in nature. 
     While the current application recites particular combinations of features in the claims appended hereto, various embodiments of the invention relate to any combination of any of the features described herein whether or not such combination is currently claimed, and any such combination of features may be claimed in this or future applications. Any of the features, elements, or components of any of the exemplary embodiments discussed above may be used alone or in combination with any of the features, elements, or components of any of the other embodiments discussed above.