Patent Publication Number: US-2022228517-A1

Title: Small air-cooled engine assembly with dry sump lubrication system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/775,704, filed on May 11, 2018, which claims priority to PCT Application No. PCT/US2016/058,909, filed on Oct. 26, 2016, which claims the benefit U.S. Provisional Patent Application No. 62/335,500, filed May 12, 2016, and U.S. Provisional Patent Application No. 62/255,227, filed Nov. 13, 2015, and is a continuation of U.S. patent application Ser. No. 15/295,294, filed Oct. 17, 2016, all of which are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The present invention relates generally to the fields of small internal combustion engines and outdoor power equipment, and in particular, engine assemblies including small internal combustion engines and dry sump lubrication systems, external oil reservoirs for use with dry sump lubrication systems, oil filters for use with dry sump lubrication systems, and outdoor power equipment including dry sump lubrication systems. 
     SUMMARY 
     One embodiment of the invention relates to an engine assembly including a small air-cooled engine and a dry sump lubrication system including an external oil reservoir, wherein the dry sump lubrication system has an overall oil capacity that provides at least five hundred hours of engine oil life. 
     In some embodiments, the external oil reservoir has an oil fill capacity of at least five quarts. 
     In some embodiments, the dry sump lubrication system includes a crankcase chamber; wherein an intended oil fill level of the crankcase chamber is between 2.5 quarts to 3 quarts. 
     In some embodiments, the small air-cooled engine includes a crankshaft including a counterweight positioned in a crankcase chamber. In some embodiments, a recommended oil level of the crankcase chamber during normal operation of the engine is below a lowermost portion of the counterweight. 
     In some embodiments, an intended oil fill level of the crankcase chamber is between 2.5 quarts to 3 quarts. 
     In some embodiments, the small air-cooled engine includes an engine block, an oil gallery configured to distribute oil, a crankcase cover, and a crankcase chamber defined by the engine block and the crankcase cover. The dry sump lubrication system includes the external oil reservoir, a supply pump, and a return pump. The external oil reservoir includes an oil tank defining an oil chamber and an oil filter assembly. The oil filter assembly includes a housing and a filter. The housing at least partially defines a filter chamber. The filter chamber is in fluid communication with the oil chamber. The filter is positioned within the filter chamber. The supply pump is in fluid communication with the oil chamber and the oil gallery. The supply pump is configured to draw oil from the oil chamber and provide pressurized oil to the oil gallery. The return pump is in fluid communication with the crankcase chamber and the filter chamber. The return pump is configured to draw oil from the crankcase chamber and provide pressurized oil to the filter chamber. The filter is configured to filter the pressurized oil provided to the filter chamber. 
     In some embodiments, the return pump is configured to pressurize oil to less than ten pounds per square inch. 
     In some embodiments, the crankcase chamber and the oil chamber have an overall oil capacity that provides at least five hundred hours of engine oil life between routine oil changes. 
     In some embodiments, the crankcase chamber has a crankcase volume and the oil chamber has a reservoir volume greater than the crankcase volume. 
     In some embodiments, the reservoir volume is at least five quarts. 
     In some embodiments, an intended oil fill level of the crankcase chamber is between 2.5 quarts to 3 quarts. 
     In some embodiments, the reservoir volume is greater than five quarts and a recommended oil fill capacity of the oil chamber is five quarts. 
     In some embodiments, the engine assembly includes a crankshaft including a counterweight positioned in the crankcase chamber. In some embodiments, a recommended oil level of the crankcase chamber during normal operation of the engine is below a lowermost portion of the counterweight. 
     In some embodiments, an intended oil fill level of the crankcase chamber is between 2.5 quarts to 3 quarts. 
     In some embodiments, the oil filter assembly includes a fill inlet so that oil can be added to the oil chamber through the oil filter. 
     In some embodiments, wherein the filter includes filter media and an oil fill conduit extending through the filter media so that oil can be added to the oil chamber through the oil fill conduit without being filtered by the filter media. 
     In some embodiments, the oil filter assembly includes a vent assembly in fluid communication with the oil chamber, the filter chamber, and the internal combustion engine. In some embodiments, the vent assembly is configured to allow air to flow from the filter chamber and the oil chamber to the internal combustion engine. 
     In some embodiments, the engine assembly includes a second oil filter assembly including a second housing and a second filter. The second housing at least partially defines a second filter chamber. The second filter chamber is fluidly coupled to the supply pump and the oil gallery. The second filter is positioned within the second filter chamber. The second filter chamber is configured to filter the pressurized oil provided to the oil gallery. 
     In some embodiments, the small air-cooled engine includes an engine block, an oil gallery configured to distribute oil, a crankcase cover, and a crankcase chamber defined by the engine block and the crankcase cover. In some embodiments, the dry sump lubrication system includes the external oil reservoir, a supply pump, and a return pump. The oil filter assembly includes a housing at least partially defining a filter chamber and a filter positioned within the filter chamber. The supply pump is in fluid communication with the oil chamber and is configured to provide pressurized oil to the oil gallery. The return pump is in fluid communication with the crankcase chamber and the filter chamber. The return pump is configured to draw oil from the crankcase chamber and provide pressurized oil to the filter chamber. The filter chamber is fluidly coupled to the supply pump and the oil gallery. The filter is configured to filter the pressurized oil provided to the oil gallery. 
     In some embodiments, the small air-cooled engine includes an engine block, a blower housing, and a blower fan. The blower housing extends over a portion of the engine block and is configured to direct cooling air over the engine block. The blower fan is configured to pull air into the blower housing through an air inlet. 
     Another embodiment of the invention relates to an engine assembly including an engine, an external oil reservoir, a supply pump, and a return pump. The engine includes an engine block, an oil gallery configured to distribute oil, a crankcase cover, and a crankcase chamber defined by the engine block and the crankcase cover. The external oil reservoir includes an oil tank defining an oil chamber and an oil filter assembly including a housing at least partially defining a filter chamber, wherein the filter chamber is in fluid communication with the oil chamber, and a filter positioned within the filter chamber. The supply pump is in fluid communication with the oil chamber and the crankcase chamber and the supply pump is configured to draw oil from the oil chamber and provide pressurized oil to the oil gallery. The return pump in fluid communication with the crankcase chamber and the filter chamber and the return pump is configured to draw oil from the crankcase chamber and provide pressurized oil to the filter chamber. The filter is configured to filter the pressurized oil provided to the filter chamber. In some embodiments, the engine assembly is a component of a lawn mower. In different embodiments, the lawn mower is a riding lawn mower, a wide-area walk-behind lawn mower, a zero-turn radius lawn mower, or a standing lawn mower. 
     Another embodiment of the invention relates to an engine assembly including a small air-cooled engine and an external oil reservoir. The small air-cooled engine includes an engine block, a crankcase cover, and a crankcase chamber defined by the engine block and the crankcase cover. The external oil reservoir includes an oil tank defining an oil chamber. The crankcase chamber and the oil chamber are sized to provide at least five hundred hours of engine oil life. 
     Another embodiment of the invention relates to an engine assembly including a small air-cooled engine and a dry sump lubrication system. In some embodiments, the dry sump lubrication system includes an external oil reservoir and has an overall oil capacity that provides at least five hundred hours of engine oil life. In some embodiments, the engine assembly is a component of a lawn mower. In different embodiments, the lawn mower is a riding lawn mower, a wide-area walk-behind lawn mower, a zero-turn radius lawn mower, or a standing lawn mower. 
     Another embodiment of the invention relates to an engine assembly including a small air-cooled engine and an external oil reservoir. The small air-cooled engine includes an engine block, a crankcase cover, and a crankcase chamber defined by the engine block and the crankcase cover, the crankcase chamber having a crankcase volume. The external oil reservoir includes an oil tank defining an oil chamber, the oil chamber having a reservoir volume. The reservoir volume is greater than the crankcase volume. In some embodiments, the crankcase volume and the reservoir volume have an overall oil capacity that provides at least 500 hours of engine oil life. In some embodiments, the reservoir volume is at least five quarts. In some embodiments, the reservoir volume is greater than five quarts and a recommended oil fill capacity of the oil chamber is five quarts. In some embodiments, the engine assembly is a component of a lawn mower. In different embodiments, the lawn mower is a riding lawn mower, a wide-area walk-behind lawn mower, a zero-turn radius lawn mower, or a standing lawn mower. 
     Another embodiment of the invention relates to an external oil reservoir for use with an internal combustion engine including an oil tank defining an oil chamber and an oil filter assembly. The oil filter assembly includes a housing at least partially defining a filter chamber, wherein the filter chamber is in fluid communication with the oil chamber, a filter positioned within the filter chamber, and a return inlet in fluid communication with the filter chamber to provide oil returned from the internal combustion engine to the filter chamber to be filtered by the filter. In some embodiments, the external oil reservoir is a component of a lawn mower. In different embodiments, the lawn mower is a riding lawn mower, a wide-area walk-behind lawn mower, a zero-turn radius lawn mower, or a standing lawn mower. 
     Another embodiment of the invention relates to an external oil reservoir for use with an internal combustion engine including an oil tank defining an oil chamber and an oil filter assembly including a filter and a return inlet configured to provide oil returned from the internal combustion engine to the filter for filtration. In some embodiments, the external oil reservoir is a component of a lawn mower. In different embodiments, the lawn mower is a riding lawn mower, a wide-area walk-behind lawn mower, a zero-turn radius lawn mower, or a standing lawn mower. 
     Another embodiment of the invention relates to an engine assembly including an internal combustion engine and an oil tank. The engine includes at least one cylinder, a crankcase chamber, a vertical crankshaft extending through the crankcase chamber, the crankshaft configured to rotate about a vertical crankshaft axis, a supply pump including a supply inlet and a supply outlet, an oil gallery in fluid communication with the supply outlet, the oil gallery configured to distribute oil within the engine, and a return pump including an return inlet and a return outlet, wherein the return inlet is in fluid communication with a front portion of the crankcase chamber and wherein the return pump is configured to draw oil from the front portion of the crankcase chamber through the return inlet into the return pump. The oil tank defines an oil chamber and includes a filter positioned within a filter chamber. The return outlet is in fluid communication with the filter chamber and the return pump is configured to pump oil from the front portion of the crankcase chamber to the filter chamber to be filtered by the filter. The filter chamber is in fluid communication with the oil chamber so that filtered oil passes from the filter to the oil chamber. The supply inlet is in fluid communication with the oil chamber and the supply pump is configured to pump oil from the oil chamber to the oil gallery. In some embodiments, the return pump is configured to pump oil to the filter chamber under a first pressure and pressurize the oil chamber and the supply pump is configured to draw oil from the oil chamber under a vacuum and provide oil to the oil gallery under a second pressure. In some embodiments, the first pressure is less than 15 pounds per square inch (1.034e+005 newtons/square meter). In some embodiments, the second pressure is greater than 30 pounds per square inch (2.068e+005 newtons/square meter). In some embodiments, the return pump pumps oil at a lower output pressure than the supply pump. In some embodiments, the engine assembly is a component of a lawn mower. In different embodiments, the lawn mower is a riding lawn mower, a wide-area walk-behind lawn mower, a zero-turn radius lawn mower, or a standing lawn mower. 
     Another embodiment of the invention relates to an internal combustion engine for use with an external oil reservoir. The engine includes at least one cylinder, a crankcase chamber, a vertical crankshaft extending through the crankcase chamber, the crankshaft configured to rotate about a vertical crankshaft axis, a supply pump including a supply inlet and a supply outlet, the supply pump configured to receive oil from the external oil reservoir via the supply inlet, an oil gallery in fluid communication with the supply outlet to receive oil from the supply pump, the oil gallery configured to distribute oil within the engine, and a return pump including an return inlet and a return outlet, wherein the return inlet is in fluid communication with a front portion of the crankcase chamber and wherein the return pump is configured to draw oil from the front portion of the crankcase chamber through the return inlet into the return pump. In some embodiments, the engine is a component of a lawn mower. In different embodiments, the lawn mower is a riding lawn mower, a wide-area walk-behind lawn mower, a zero-turn radius lawn mower, or a standing lawn mower. 
     Another embodiment of the invention relates to an oil filter for use with an oil reservoir. The oil filter includes a top including a fill inlet comprising a screen having a plurality of openings, a bottom including a filter outlet, an oil fill conduit extending between the top and the bottom and in fluid communication with the fill inlet and the filter outlet, and filter media surrounding the oil fill conduit and positioned between the top and the bottom. The filter is configured so that oil passes through the openings of the screen of the fill inlet, the oil fill conduit, and the filter outlet without being filtered by the filter media. In some embodiments, the top includes a quick connect fitting configured to secure the oil filter to the oil reservoir. 
     Another embodiment of the invention relates to riding outdoor power equipment including an internal combustion engine and an oil reservoir. The engine includes an engine block including a first cylinder and a second cylinder arranged in a V-twin configuration, a first cylinder head for the first cylinder, and a second cylinder head for the second cylinder, wherein the first cylinder head and the second cylinder head are located at a front of the engine opposite a rear of the engine. The oil reservoir is configured for storing oil and at least a portion of the oil reservoir is located between the rear of the engine and the first cylinder head. In some embodiments, at least a second portion of the oil reservoir is located between the rear of the engine and the second cylinder head. In some embodiments, the riding outdoor power equipment also includes an operator seat and the top of the oil reservoir is located below the top of the seat. In some embodiments, at least a portion of the oil reservoir is positioned between the seat and the internal combustion engine. In some embodiments, the entire oil reservoir is positioned between the seat and the internal combustion engine. In some embodiments, the outdoor power equipment also includes a roll bar including two upwardly extending legs, wherein the oil reservoir is positioned between the two legs of the roll bar. 
     Another embodiment of the invention relates to outdoor power equipment including an internal combustion engine and an oil reservoir. The engine includes an engine block including a first cylinder and a second cylinder arranged in a V-twin configuration, a first cylinder head for the first cylinder, and a second cylinder head for the second cylinder, wherein the first cylinder head and the second cylinder head are located at a front of the engine opposite a rear of the engine. The oil reservoir is configured for storing oil and at least a portion of the oil reservoir is located between the rear of the engine and the first cylinder head. In some embodiments, at least a second portion of the oil reservoir is located between the rear of the engine and the second cylinder head. In some embodiments, the outdoor power equipment is a lawn mower. In different embodiments, the lawn mower is a riding lawn mower, a wide-area walk-behind lawn mower, a zero-turn radius lawn mower, or a standing lawn mower. 
     Alternative exemplary embodiments relate to other features and combinations of features as may be generally recited in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings. 
         FIG. 1  is a top view of an engine assembly including an engine and an external oil reservoir, according to an exemplary embodiment. 
         FIG. 2  is a side view of the engine assembly of  FIG. 1 . 
         FIG. 3  is an exploded view of the crankcase cover of the engine of  FIG. 1 . 
         FIG. 4  is a top view of the crankcase cover of  FIG. 3 . 
         FIG. 5  is a perspective view of the oil reservoir of  FIG. 1 . 
         FIG. 6  is an exploded view of a portion of the oil reservoir of  FIG. 5 . 
         FIG. 6A  is a front view of an upper portion of a filter housing of the oil reservoir of  FIG. 5 . 
         FIG. 7  is a section view of the oil reservoir of  FIG. 5 . 
         FIG. 8  is a section view of an oil filter assembly, according to an exemplary embodiment. 
         FIG. 8A  is a perspective view of the filter of the oil filter assembly of  FIG. 8 . 
         FIG. 8B  is another perspective view of the filter of the oil filter assembly of  FIG. 8 . 
         FIG. 8C  is a top view of the filter of the oil filter assembly of  FIG. 8 . 
         FIG. 8D  is a perspective view from above of a portion of the oil filter assembly of  FIG. 8 . 
         FIG. 8E  is a perspective view from below of the upper portion of the filter housing of the oil reservoir of  FIG. 5   
         FIG. 9  is a perspective view of an external oil reservoir, according to an exemplary embodiment. 
         FIG. 10  is an exploded view of a portion of the oil reservoir of  FIG. 9 . 
         FIG. 11  is a perspective view of a portion of the engine of  FIG. 1 . 
         FIG. 12  is a section view of a check valve, according to an exemplary embodiment. 
         FIG. 13  is a perspective view of a portion of a lawn mower including the engine assembly of  FIG. 1 . 
         FIG. 14  is a top view of a portion of the lawn mower of  FIG. 13 . 
         FIG. 15A  is a schematic illustration of the engine assembly of  FIG. 1 . 
         FIG. 15B  is a schematic illustration of an engine assembly, according to an exemplary embodiment. 
         FIG. 15C  is a schematic illustration of an engine assembly, according to an exemplary embodiment. 
         FIG. 16  is a top view of an engine assembly including an engine and an external oil reservoir, according to an exemplary embodiment. 
         FIG. 17  is a perspective view of the engine assembly of  FIG. 16 . 
         FIG. 18  is an exploded view of the crankcase cover of the engine of  FIG. 16 . 
         FIG. 19  is a top view of the crankcase cover of  FIG. 18 . 
         FIG. 20  is a perspective view of the oil reservoir of  FIG. 16 . 
         FIG. 21  is a perspective view of a portion of a lawn mower including the engine assembly of  FIG. 16 . 
         FIG. 22  is a top view of a portion of the lawn mower of  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION 
     Before turning to the figures, which illustrate the exemplary embodiments in detail, it should be understood that the application is not limited to the details or methodology set forth in the description or illustrated in the figures. It should also be understood that the terminology is for the purpose of description only and should not be regarded as limiting. 
     Referring to  FIGS. 1-2 , an engine assembly including an internal combustion engine  100  and an external oil tank or reservoir  112  is illustrated according to an exemplary embodiment. The internal combustion engine  100  includes an engine block  101  having two cylinders  102  and  103 , two cylinder heads  137  and  139 , two pistons, and a crankshaft  104 . Each piston reciprocates in a cylinder along a cylinder axis to drive the crankshaft  104 . The crankshaft  104  rotates about a crankshaft axis  105 . The crankshaft  104  is positioned in part within a crankcase chamber  130  defined by the engine block  101  and a sump or crankcase cover  106 . The engine  100  also includes a fuel system for supplying an air-fuel mixture to the cylinder (e.g., a carburetor, an electronic fuel injection system, a fuel direct injection system, etc.), an air filter assembly  107 , a camshaft  119  for actuating intake and exhaust valves in the cylinder heads, a muffler  108 , a flywheel, and a blower fan. The engine  100  includes a blower housing  110  configured to direct cooling air over the engine block  101  and other components of the engine. The blower fan pulls air into the blower housing  110  through an air inlet. The crankshaft  104  may be oriented horizontally (i.e., a horizontal engine) or vertically (i.e., a vertical engine). The engine may include one cylinder or two or more cylinders. The illustrated engine  100  is a vertically-shafted two cylinder engine arranged in a V-twin configuration. 
     The engine assembly may be used in outdoor power equipment, standby generators, portable jobsite equipment, or other appropriate uses. Outdoor power equipment includes lawn mowers, riding tractors, snow throwers, pressure washers, portable generators, tillers, log splitters, zero-turn radius mowers, walk-behind mowers, wide-area walk-behind mowers, riding mowers, standing mowers, industrial vehicles such as forklifts, utility vehicles, etc. Outdoor power equipment may, for example, use an internal combustion engine to drive an implement, such as a rotary blade of a lawn mower, a pump of a pressure washer, an auger of a snow thrower, the alternator of a generator, and/or a drivetrain of the outdoor power equipment. Portable jobsite equipment includes portable light towers, mobile industrial heaters, and portable light stands. 
     Referring to  FIGS. 2-4 , the engine  100  includes a dry sump lubrication system that includes the external oil tank  112  ( FIG. 2 ), a supply pump  113  ( FIG. 3 ) for supplying oil (lubricant) from the tank  112  to the engine via oil galleries for distribution to various locations within the engine  100 , a return or scavenge pump  114  ( FIG. 4 ) for returning (scavenging) oil from the crankcase chamber  130  to the tank  112 , and the conduits (hoses, tubes, other plumbing) for fluidly connecting the tank  112 , the pumps  113 ,  114 , the oil galleries  124 , and the crankcase chamber  130  to one another. 
     The oil tank  112  is sized to hold oil sufficient to extend the engine oil life for a commercial lawn mower (e.g., a zero-turn lawn mower, standing mowers, etc.) to 500 plus hours. Typical commercial lawn mower best practice is to assume 100 hours of engine oil life for a conventional engine without an external oil tank and routinely change the engine oil after 100 hours of engine operation. Providing at least 500 hours of engine oil life with the dry sump system described herein enables operation of the lawn mower (e.g., operated by a commercial lawn services provider) for an entire summer mowing season without having to change the oil, thereby reducing downtime and maintenance during the season in which the mower will be operated. The dry sump lubrication system described herein can reduce oil change labor and replacement filter costs by at least 60%. In exemplary embodiments of the dry sump system described herein about 5-6 quarts (about 4.732-5.678 liters) of oil is sufficient to provide at least 500 hours of engine oil life. In other embodiments, more or less oil may be sufficient to provide at least 500 hours of engine oil life depending on the particular arrangement of the engine used with the dry sump system. The dry sump system extends engine oil life as compared to an engine that does not include an external oil tank. 
     Engine oil life is a measure of the operation time of an engine between recommended oil changes. During operation of an engine, the oil used to lubricate and cool the engine breaks down. Engine oil break down is due in part to heat and mechanical shearing of the hydrocarbons that make up the oil. Also, the oil may accumulate particles (e.g., metal particles worn off engine components) that negatively impact the oil&#39;s viscosity. Finally, oil contains a number of additives called an additive package, including for example anti-foaming, detergent, viscosity modifiers, and anti-corrosion additives, that help the oil perform to manufacturer and industry standards (e.g., American Petroleum Institute or Society of Automotive Engineer (“SAE”) standards). These additives are basic in nature and can be identified by the total base number (“TBN”). TBN is used as a measure of reserve alkalinity in the oil. As the engine operates the total acid number (“TAN”) increases from a value of zero and the TBN decreases. TAN is used as a measure of acid concentration in the oil. As the engine operates, the additive package loses effectiveness. 
     As the engine oil breaks down, its viscosity increases so that the oil may appear thick, sludgy, or dirty in comparison to new oil. Manufacturers (e.g., engine manufacturers and equipment manufacturers) determine the engine oil life or recommended oil change intervals for particular lubrication systems. Signs that engine oil life for a particular lubrication system has been exceeded and an oil change should occur are when the TBN and TAN begin to approach one another (e.g., within 5%-10% of the same value) or when the TAN is greater than the TBN. Oxidation of the oil can also be measured as a way of determining engine oil life for a particular lubrication system. The viscosity of oil in a test engine can be measured as a way of determining engine oil life for a particular lubrication engine. For example, new oil measured at a rated viscosity of SAE  20  may be measured at a rated viscosity of SAE  50  after a period of operation in a test engine. This change in viscosity can be used to establish the engine oil life. Visual inspection of a test engine can also be used as a way of determining engine oil life for a particular lubrication system by evaluating the components of a test engine for signs of wear (e.g., worn bearings), by evaluating the appearance of the oil itself (e.g., dirty or dark oil), measuring the presence of wear metals in the oil (e.g., aluminum, iron, nickel, silicon, etc). 
       FIGS. 3-4  illustrate the sump or crankcase cover  106  according to an exemplary embodiment. The pumps  113  and  114  are incorporated into the crankcase cover  106 . As illustrated, the pumps  113  and  114  are gerotor pumps. The crankcase cover  106  includes a crankshaft opening or aperture  115  through which the crankshaft  104  extends to drive one or more components of a lawn mower or other piece of equipment. A transmission  116  including one or more gears  117  or other reduction mechanism (e.g., belts) connects the crankshaft  104  to a drive shaft  118  for the supply pump  113  so the supply pump  113  is driven by the crankshaft  104  at a lower rotational speed than that of the crankshaft  104 . The supply pump  113  and the drive shaft  118  rotate about an axis of rotation  133 . The camshaft  119  is directly connected to a drive shaft  120  for the return pump  114  so the return pump  114  is directly driven by the camshaft  119  at the same rotational speed as the camshaft  119 . The return pump  114  and the drive shaft  120  rotate about an axis of rotation  134 . A transmission connects the camshaft  119  to the crankshaft  104  so that the camshaft  119  is driven at a rotational speed less than that that of the crankshaft  104 . 
     The supply pump  113  and the return pump  114  are located near opposite sides of the crankcase cover  106 . The supply pump  113  is located near the rear  136  of the crankcase cover  106  and the engine  100  and the return pump  114  is located near the front  138  of the crankcase cover  106  and the engine  100 . 
     The supply pump  113  is positioned in a supply pump housing  121  formed in the exterior of the crankcase cover  106 . The supply pump  113  is in fluid communication with a supply inlet  122  for receiving oil (e.g., supply oil) from the external oil tank  112  and a supply outlet  123  for providing oil for distribution within the engine  100  by one or more oil galleries  124 . As illustrated, the supply inlet  122  includes a fitting for connecting a hose or other conduit to the supply pump  113 . The supply pump  113  pumps oil to the oil gallery  124  to distribute oil within the engine. A cover plate  125  is secured to the crankcase cover  106  (e.g., by threaded fasteners) to close the pump housing  121 . A gasket  126  is provided between the cover plate  125  and the crankcase cover  106  to form a seal. 
     The return pump  114  is positioned in a return pump housing  127  formed in the exterior of the crankcase cover  106 . The return pump  114  is in fluid communication with a return inlet  128  for receiving oil (e.g., return oil, scavenged oil) from the crankcase chamber  130  and a return outlet  129  for providing oil to the external oil tank  112 . As illustrated, the return outlet  129  includes a fitting for connecting a hose or other conduit to the return pump  114 . A cover plate  144  is secured to the crankcase cover  106  (e.g., by threaded fasteners) to close the pump housing  127 . A gasket  146  is provided between the cover plate  144  and the crankcase cover  106  to form a seal. 
     As shown in  FIG. 4 , the return inlet  128  is formed through the crankcase cover  106  to place the return pump  114  in fluid communication with the crankcase chamber  130 . The return inlet  128  is formed in a front portion  131  of the crankcase cover  106  to be in fluid communication with the front portion of the crankcase chamber  130 . The front portion  131  is located forward of a vertical plane  132  including the vertical crankshaft axis  105 . The plane  132  is perpendicular to a second vertical plane  142  including the crankshaft axis  105  and the axis of rotation  134  of the return pump  114 . The cylinders  102  and  103  and cylinder heads are also located forward of the vertical plane  132 . The return pump  114  draws oil from the front portion  131  of the crankcase chamber  130  into the return pump  114 . The return pump  114  pumps the oil to the external oil tank  112 . 
     Locating the return inlet  128  near the front  138  of the engine  100  helps to ensure that sufficient oil is returned from the crankcase chamber  130  to the external oil tank  112  by the return pump  114  to prevent the engine  100  (i.e., crankcase chamber, cylinders, cylinder heads, oil galleries, etc.) from overfilling with oil supplied by the supply pump  113  from the external oil tank  112 . When the lawn mower is tilted or tipped forward toward the front  138  (e.g., when traveling up or down a hill or incline), the oil in the crankcase chamber  130  moves toward the front portion  131  and the return inlet  128 , which will reduces possible occurrences of the return pump  114  being starved for oil. If the return inlet  128  were located near the rear of the engine, this orientation would cause the oil to move away from the return inlet and possibly starve the return pump. When the return pump  114  has an insufficient or otherwise unavailable oil supply (is starved for oil), the engine  100  could overfill with oil as the supply of oil from the supply pump  113  outpaces the removal of oil by the return pump  114 , potentially negatively impacting operation of the engine. Overfilling is a concern in part because the maximum volume of oil intended to be present in the engine  100  during normal operating conditions in the crankcase chamber (e.g., about 2.5 quarts-3 quarts (about 2.366 liters-2.839 liters)) is less than the volume of the external oil tank  112  (e.g., more than 5 quarts (4.732 liters)). When oil in excess of the intended maximum oil volume is present in the engine, the excess oil can impair operation of the engine (e.g., burning excess oil during combustion) and cause damage (e.g., damaging seals, gaskets, bearings, etc.). The crankshaft  104  includes one or more counterweights  109 . As shown in  FIGS. 15A-15B , it is preferred to keep the recommended oil level  111  in the crankcase chamber  130  below the level of the lowermost portion of the counterweights  109  of the crankshaft  104 . When the oil level is at or above the level of the lowermost portion of the counterweights  109 , this excess oil can be transferred to the combustion chamber of the cylinders  102 ,  103 , where it is combusted and causes unwanted smoke during operation of the engine  100 . Also the location of the return inlet  128  near the front  138  of the engine  100  helps the engine&#39;s performance when operated at an angle from the normal operating position shown in  FIGS. 1 and 2 . Angled operation of an engine is dependent on the engine&#39;s ability to handle excessive amounts of oil in particular locations (e.g., in the cylinders) and to prevent starving the return inlet  128  of the return pump  114  for oil. During tests performed by the Applicant, the engine  100  was able to operate when positioned at an angle of 45 degrees forward, 45 degrees rearward, 45 degrees to the left, or 45 degrees to the right relative to the normal operating illustrated in  FIGS. 1-2  for a period of two minutes to simulate expected angled operation by a user and for a period of one hour to simulate an extreme example of angled operation by a user. 
       FIGS. 5-10  illustrate the external oil tank  112  of the engine  100  according an exemplary embodiment. The oil tank  112  includes a tank body  135  that defines an oil reservoir, volume, or chamber  148  for storing oil. The tank  112  may be formed from metal (e.g. aluminum) to provide advantageous heat transfer properties and/or contoured to maximize the surface area exposed to air to aid in cooling the oil stored in the chamber  148 . In some embodiments, an oil cooler is provided to further cool the oil. 
     The external oil tank  112  includes an integrated oil filter assembly  150 .  FIG. 6  illustrates the oil filter assembly  150  according to an exemplary embodiment. The oil filter assembly  150  includes an oil filter housing  152 , a cover or cap  154 , and a filter  156 . The filter  156  is a cylindrical cartridge including a cylinder of filter media or material  158  and two end caps  160  and  162 . 
     The housing  152  includes an upper portion  164  and a lower portion  166 . The upper portion  164  includes a mount or flange  168  for securing the housing  152  to the top  170  of the oil tank  112 . The upper portion  164  also includes a substantially cylindrical filter body  172  extending upward from the flange  168 . The lower portion  166  is substantially cup-shaped with a bottom  174  and a cylindrical sidewall  176 . An opening or aperture  178  is formed through the bottom  174 . A cylindrical neck or collar  180  extends downward from the bottom  174  around the opening  178 . The lower portion  166  is attached to the upper portion  164  (e.g., by a threaded fastener, glue, adhesive, etc.) to form a filter chamber  181  for receiving the filter  156 . 
     In some embodiments, as illustrated in  FIGS. 5-7 , the flange  168  includes a dipstick opening or aperture  182  and a neck or support  184  surrounding the aperture  182 . A corresponding dipstick opening  186  is formed in the top  170  of the oil tank  112 . A dipstick  188  is guided by the neck  184  through the apertures  182  and  186  into the chamber  148  to measure the oil level therein. In other embodiments, as illustrated in  FIGS. 8-10 , the flange  168  does not include components related to the dipstick  188  and instead the neck  184  extends upward from the top  170  of the oil tank  112  around a single aperture, the aperture  186  through the top  170 . 
     The top  170  of the oil tank  112  includes an aperture or opening  190  for receiving the lower portion  166  of the housing  152 . The flange  168  is attached to the top  170  of the oil tank  112  (e.g., by threaded connection, welding, or other appropriate fastening technique) with a gasket  192  positioned between the flange  168  and the top  170 . The lower portion  166  of the housing  152  extends into the aperture  190  in the top  170  of the oil tank  112 . 
     The lower end cap or bottom  162  of the filter  156  includes a flange  194  and a cylindrical neck or collar  196  extending downward from the flange  194 . A filter outlet, aperture, or opening  198  is formed through the flange  194  and the collar  196  to allow filtered oil to exit the filter  156 . An O-ring or gasket  200  is positioned within a circumferential groove  201  in the collar  196  to provide a seal between the lower end cap  162  and the bottom  174  of the lower portion  166  of the housing  152  when the filter  156  is attached to the housing  152 . 
     A cylindrical support or conduit  202  extends between and is coupled to the lower end cap  162  and the upper end cap  160 . The support  202  includes multiple openings  204  to allow oil filtered by the filter media  158  to pass through the support  202  to the filter outlet  198 . The filter media  158  (e.g., pleated filter paper or other appropriate filter material) also extends between and is coupled to the lower end cap  162  and the upper end cap  160 . The lower end of the filter media  158  contacts the flange  194  of the lower end cap  162  and a base  206  of the upper end cap  160 . 
     As shown in  FIGS. 8-8D , the upper end cap or top  160  includes the base  206  and a sidewall  208  extending upward from the periphery of the base  206 . An O-ring or gasket  210  is positioned within a circumferential groove  211  in the sidewall  208  to provide a seal between the upper end cap  160  and the upper portion  164  of the housing  152 . Above the gasket  210 , quick-connect tabs, lugs, or protrusion  212  extends outward from the sidewall  208 . The protrusion  212  includes one or more recesses  209  to allow a corresponding protrusion  228  of the housing  152  to pass through the protrusion  212  of the end cap  160 . A fill inlet, screen, or grill  214  including one or more openings or apertures  216  functions as an oil inlet, allowing oil to flow through the upper end cap  160 , the support  202 , and the lower end cap  162  to the chamber  148  and as an air vent, allowing air to flow from the chamber  148  through the lower end cap  162 , the support  202 , and the upper end cap  160 . In some embodiments, as illustrated, the screen  214  is a frustoconical in shape with a series of circular walls  213  or members surrounding a central aperture  216  and separated from each other by apertures  216  decreasing in diameter as the screen  214  extends axially away from the base  206 . A series of ribs  215  connect the walls  213  to each other and the base  206 . A handle  217  extends through a midpoint of the screen  214  and includes a grasping portion located above the screen  214  to provide a grasping point for the user to manipulate the filter  156  as needed to attach and remove the filter  156  from the housing  152 . 
     The filter body  172  of the upper portion  164  of the housing  152  includes an upper sidewall  218 . Two quick connect protrusions or tabs  220  extends outward from the upper sidewall  218 . A platform or shelf  224  extends inward from the upper sidewall  218  to a neck or collar  226 . The inner diameter of the upper sidewall  218  is greater than the inner diameter of the collar  226 , with the shelf  224  taking up the distance in between. The collar  226  extends downward from the shelf  224  and is spaced apart from a lower sidewall  232  to form an annular volume between the collar  226  and the lower sidewall  232 . Two quick-connect protrusions  228  are located above the shelf  224  and extend outward from the upper sidewall  218  to form a groove  230  between the protrusions  228  and the shelf  224  for receiving the protrusions  212  of the upper end cap  160  of the filter  156 . The shelf  224 , the protrusions  228 , the groove  230 , and the protrusions  212  interact to form a quarter-turn quick-connect connection between the upper end cap  160  of the filter  156  and the upper portion  164  of the housing  152  so that a user can quickly and easily attach the filter  156  to the housing  152  and quickly and easily un-attach the filter  156  from the housing  152 . Alternatively, other quick-connect arrangements or other types of attachments (e.g. a threaded attached) may be used to attach the filter  156  to the housing  152 . With the filter  156  attached to the housing  152 , the gasket  210  forms a seal between the upper end cap  160  of the filter  156  and the upper sidewall  218  of the filter body  172  of the upper portion  164  of the housing  152 . 
     The cover  154  closes the upper end of the filter chamber  181  when attached to the upper portion  164  of the housing  152 . The cover  154  includes a groove  234  formed between an outer wall  236  and an inner wall  238 . An O-ring or gasket  239  is positioned in a groove in the inner wall  238  and forms a seal with the upper sidewall  218  of the upper portion  164  of the housing  152  when the cover  154  is attached to the housing  152 . The cover  154  and the protrusions  220  of the upper portion  164  of the housing  152  interact to form a quarter-turn quick-connect connection between the cover  154  and the upper portion  164  of the housing  152  so that a user can quickly and easily attach the cover  154  to the housing  152  and quickly and easily un-attach the cover  154  from the housing  152 . Alternatively, other quick-connect arrangements or other types of attachments (e.g. a threaded attached) may be used to attach the cover  154  to the housing  152 . 
     The cover  154  also includes a protrusion  240  that extends downward from the top of the cover  154  into the interior of the cover  154 . If the filter  156  is not properly attached to the housing  152 , the filter  156  will sit up higher within the filter chamber  181  than when properly attached and the protrusion  240  will contact the handle  217  of the filter  156 , preventing the cover  154  from being attached to the housing  152 . This provides a physical indication (the impact between the protrusion  240  and the handle  217 ) and a visual indication (the cover  154  not seated properly on the housing  152 ) to the user that the oil filter  156  has not been properly attached to the housing  152 . As shown in  FIG. 8 , when the filter  156  is properly attached to the housing  152 , the protrusion  240  does not contact the handle  217  and the cover  154  can be properly seated and attached to the housing  152 . In some embodiments, the cover  154  is attached to the upper end cap  160  of the filter  156  so that the cover  154  and filter  156  may be separated from the housing  152  as a single integral unit. 
     The upper portion  164  of the housing  152  also includes a return conduit  242  that receives return oil from the return pump  114 . A return inlet  244  is in fluid communication with the return outlet  129  of the return pump  114  (e.g., by a hose or other conduit). As illustrated, the return inlet  244  includes a fitting for connecting a hose or other conduit to the oil filter assembly  150 . The return conduit  242  is in fluid communication with the filter chamber  181  through a return outlet  246  to deliver return oil to the outside (dirty) side of the filter  156 . The return outlet  246  is located below the upper end cap  160  and the shelf  224  to deliver oil to the filter chamber  181  below the seal formed by the gasket  210  between the upper end cap  160  and the upper portion  164  of the housing  152 . The return outlet  246  is located between the seal formed by the gasket  210  between the upper end cap  160  and the upper portion  164  of the housing  152  and the seal formed by the gasket  200  between the lower end cap  162  and the lower portion  166  of the housing  152 . As shown in  FIG. 8E , the return outlet  246  is formed in the lower sidewall  232  so that return oil enters the annular volume between the lower sidewall  232  and the collar  226 . The direction of return oil flow is substantially tangential to the collar  226  to induce circular flow of the return oil through the annular volume between the lower sidewall  232  and the collar  226  to distribute the return oil around the circumference of the filter media  158 . 
     The upper portion  164  of the housing  152  also includes a vent assembly  248  that provides a flow path for air from the external oil tank  112  to the engine  100 . The vent assembly  248  includes a filter conduit  250  in fluid communication with the filter chamber  181 , a tank conduit  252  in fluid communication with the oil chamber  148  through an opening or aperture  254  formed through the top  170  of the oil tank  112 , and an engine conduit  256  including a vent outlet  258 . As illustrated, the vent outlet  258  includes a fitting for connecting a hose or other conduit to the vent assembly  248 . 
     All three conduits  250 ,  252 , and  256  are in fluid communication with each other at a joint or manifold  259 . The conduit  250  includes an inlet aperture  251  in fluid communication with the filter chamber  181  above the upper end cap  160  ( FIG. 8D ) so that the conduit  250  provides a flow path for air to exit the filter chamber  181 . The conduit  252  includes an inlet aperture  253  in fluid communication with oil the chamber  148  and positioned in the oil chamber  148  to provide a flow path for air to exit the oil chamber  148 . The conduit  256  includes an inlet aperture  257  in fluid communication with the manifold  249  to provide a flow path for air to travel from the oil tank  112  to the engine  100 . 
       FIG. 11  illustrates a portion of the engine  100  including a vent inlet  260  for receiving air from the vent assembly  248  of the oil filter assembly  150 . As illustrated, the vent inlet  260  is includes a fitting for connecting a hose or other conduit to the engine  100 . The vent inlet  260  is in fluid communication with the crankcase chamber  130  via a vent conduit  262  to vent air from the oil tank  112  to the engine  100 . 
     The upper portion  164  of the housing  152  also includes a bypass conduit  264 , a bypass valve  266  and a bypass passage  268 . The bypass conduit  264  is fluid communication with the filter chamber  181  and the bypass passage  268 . A bypass inlet  265  is formed in the lower sidewall  232  of the upper portion  164  of the housing  152 . The bypass passage  268  is a volume in fluid communication with the chamber  148  of the oil tank  112  via the opening  254  formed through the top  170  of the oil tank  112  ( FIG. 8 ) and in fluid communication with the filter chamber  181  below the upper end cap  160  via the bypass inlet  265  ( FIG. 8E ). The bypass valve  266  is positioned in the bypass conduit  264  and selectively opens and closes to allow fluid flow from the filter chamber  181  to the chamber  148  via the bypass passage  268 . The bypass valve  266  is normally-closed and pressure actuated so that when the pressure in the filter chamber  181  reaches a threshold pressure, the valve  266  opens and allows pressurized oil from the filter chamber  181  flow to the chamber  148  of the oil tank  112  without passing through the filter  156 . This may occur when the filter  156  is clogged or dirty and not able to filter the volume of oil attempting to pass through the filter  156  or during cold engine starting conditions, in which relatively high viscosity of the oil slows the rate at which oil passes through the filter  156 , causing the filter chamber  181  to fill with oil and exceed the threshold pressure of the bypass valve  266 . The tank conduit  252  of the vent assembly  248  extends downward from the manifold  259  through the bypass passage  268  and the opening  254  through the top  170  of the oil tank  112  into the chamber  148  of the oil tank  112 . 
     As shown in  FIG. 7 , the oil tank  112  includes a supply outlet  270 . As illustrated, the supply outlet  270  includes a fitting for connecting a hose or other conduit to the oil tank  112 . The supply outlet  270  is in fluid communication with a supply conduit  272  that extends into the chamber  148  of the oil tank  112 . The supply conduit  272  includes a supply inlet  274  located near a front  276  of the oil tank  112 . When a lawn mower or other equipment including the engine  100  an the oil tank  112  is tilted or tipped forward toward the front  276  (e.g., when traveling down a hill or incline), the oil in the chamber  148  moves toward the front  276  and the supply inlet  274 , which will reduces possible occurrences of the supply pump  113  being starved for oil from the oil tank  112  due to an insufficient or otherwise unavailable oil supply. A screen may be provided in the supply conduit  272  to filter large particulates and prevent them from reaching the engine  100 . A drain  278  is provided for draining oil from the chamber  148 . 
     The recommended fill level  279  of the chamber  148  of the oil tank  112  is located below the level  281  of filter outlet  198  the oil filter  156 . This arrangement prevents the filter outlet  198  from being submerged in a volume of standing oil within the chamber  148 , which creates an unwanted backpressure on the oil filter  156  that prevents incoming oil from properly flowing through the filter. This arrangement also positions the bottom of the filter media  158  above the recommended fill level  279  which prevents the filter media  158  from being submerged in standing oil. In a preferred embodiment, the recommended fill level or recommended oil fill capacity  279  provides five quarts of oil for use by the engine  100  and the oil chamber  148  has six quarts of capacity below the level  281  of the filter outlet  198 . 
     The tank body  135  of the oil tank  112  includes the top  170 , a bottom  280 , the front  276 , a rear  282 , a left side  284 , and a right side  286  that in combination define the volume of the oil chamber  148 . The oil tank  112  is relatively tall with its height (top to bottom) exceeding its width (left side to right side) and depth (front to rear). A recess  288  is formed in the rear  282  near the left side  284  to allow the oil tank  112  to be positioned closely to the engine  100 . The recess  288  allows the oil tank  112  to be positioned near the rear  136  of the engine  100  and next to the cylinder  103 . As shown in  FIG. 1 , a volume  290  having a triangular cross-section is formed by a plane  292  extending along the rear  136  of the engine  100  (horizontal as illustrated), a plane  294  extending forward from the front outer corner of the blower housing  110  covering the cylinder  103  (vertical as illustrated and parallel to the right side  280  of the oil tank  112 ), and a plane  296  extending along the outer edge of the blower housing  110  covering the cylinder  103  (angled and intersecting the planes  292  and  294  as illustrated). At least a portion of the oil tank  112  is located within the triangular cross-section of the volume  290  and is considered to be located at least in part between the rear  136  of the engine  100  and the cylinder head  139  of the cylinder  103 . In alternative embodiments, the oil tank  112  could be similarly configured but be located between the rear  136  of the engine  100  and the cylinder head  137  of the cylinder  102 . 
     As shown in  FIG. 12 , a check valve  298  is positioned downstream of the supply inlet  122 . The check valve  298  is normally closed to prevent oil from the oil tank  112  draining to the crankcase chamber  130  through the supply conduit (e.g., when the engine  100  is not running). The check valve  298  opens and allows oil to flow from the oil tank  112  to the engine  100  when the supply pump  113  produces a vacuum in the supply port  122  sufficient to overcome the threshold of the check valve  298 . 
       FIGS. 13 and 14  illustrate the engine  100  and the external oil tank  112  in use on a zero-turn lawn mower  300 . In other embodiments, the engine  100  and the external oil tank  112  are used with other types of outdoor power equipment, including riding lawn tractors or other riding outdoor power equipment. The engine  100  and the external oil tank  112  are located on a mounting platform  302  located between the two rear wheels  304  and  306  and behind the operator location  308 , illustrated as a seat. The engine  100  and the external oil tank  112  are also located between the vertical legs  310  and  312  of a roll bar for protecting the operator. The uppermost point of the oil tank  112  (i.e., the cover  154 ) is located well below the top of the back  314  of the operator seat  308 . A portion of the oil tank  112  is located between the seat  308  and the engine  100 . Locating the tank  112  near the operator location  308 , within the vertical legs  310  and  312  of the roll bar, near the center of the mower (i.e., between the wheels  304  and  306 ), and relatively low (i.e., the uppermost point below the top of the back  314  of the operator seat  308 ) helps to protect the oil tank  112  from collisions (e.g., from branches or other overhanging obstacles) because the tank is close to the operator and reduces the likelihood the oil tank  112  will interfere with baggers or other accessories that may be mounted to the mower  300 . 
     To install the oil filter  156 , the user grasps the handle  217  and inserts the oil filter  156  into the filter chamber  181  of the filter housing  152 . The collar  196  of the lower end cap  162  is inserted into the aperture  178  in the bottom  174  of the lower portion  166  of the housing  152  so that the gasket  200  forms a seal between the collar  196  of the lower end cap  162  and the collar  180  of the housing  152 . The user then rotates the filter  156  a quarter turn (i.e., 90 degrees) so that the shelf  224 , the protrusions  228 , the groove  230 , and the protrusions  212  interact to form a quarter-turn quick-connect connection between the upper end cap  160  of the filter  156  and the upper portion  164  of the housing  152  to attach the filter  156  to the housing  152 . The user may add oil to the oil tank  112  through the screen  214 . This process requires about two and a half minutes to fill the oil chamber  148  to the recommended oil tank fill level of five quarts. In some embodiments, the entire lubrication system consisting of the engine  100 , the oil tank  112 , and the conduits connecting the two has an overall recommended oil capacity or fill level of six quarts of oil. Alternatively, the user may add oil to the oil tank  112  prior to installing the filter  156  by pouring oil through the aperture  178  in the bottom  174  of the lower portion  166  of the housing  152 . This process requires less than one minute to fill the oil chamber  148  to the recommended oil tank fill level of five quarts. Filling through the screen  214  allows the user to add oil to the oil tank  112  without unseating or un-attaching the oil filter  156  from the filter housing  152 . For example, a user can top off the amount of oil in the oil tank  112  as needed after checking the fill level with the dipstick  188 , without having to remove or unseat the oil filter  156 . This reduces the chances of operating the engine  100  with the oil filter  156  not being properly attached by reducing the number of times a user needs to remove or adjust the oil filter  156 . The screen  214  prevents large debris (e.g., twigs, grass clippings, etc.) from entering the oil chamber  148  through the oil filter  156 . 
     The cover  154  is attached by the user grasping the cover  154 , positioning the cover  154  over the protrusions  220  of the upper portion  164  of the housing  152  and rotates the cover  154  a quarter turn (i.e., 90 degrees) so that cover  154  and the protrusions  220  interact to form a quarter-turn quick-connect connection between the cover  154  and the upper portion  164  of the housing  152  to attach the cover  154  to the housing  152 . To change the oil filter  156 , the user removes the cover  154  from the housing  152 . The filter  156  is lifted upward away from the housing  152  so that excess oil will tend to drain down off of the filter  156  into the filter chamber  181  of the housing  152  and from the filter chamber  181  to the oil tank  112 . This arrangement helps to reduce the mess of dirty oil that is common when changing the oil filter of a conventional oil filter assembly. 
       FIG. 15A  provides a schematic illustration of an engine assembly including the engine  100  and the external oil tank  112 . In operation, the return pump  114  creates a vacuum to draw in oil from the crankcase chamber  130  through the return inlet  128 . The return pump  114  pressurizes the oil (e.g., to about 5 psi (about 3.447e+004 newtons/square meter)) and distributes the pressurized return oil via the return outlet  129  to the return inlet  244  of the oil filter assembly  150  through a return oil conduit  314 . The return oil is transported via a low pressure hose, line, or conduit  314  that fluidly couples the return outlet  129  with the return inlet  244 . The return oil tends to be hot and aerated (frothy). A pressure relief valve or other device may be provided to limit pressure of the return oil provided to the oil filter assembly  150  to be below a threshold pressure. In some embodiments, the return pump  114  generates between 4 and 5 pounds per square inch (2.758e+004 and 3.447e+004 newtons/square meter) (psi) in a ⅜ inch (0.9525 centimeter) diameter return oil conduit  314  during normal operation. In some embodiments, the return pump generates less than 10 pounds per square inch (6.895e+004 newtons/square meter). This pressure provides sufficient flow of return oil to the oil tank  112  during operation of the engine  100 . 
     As shown in  FIG. 8 , the return oil enters the oil filter housing  152  through the return inlet  244  and passes through the return conduit  242  to the filter chamber  181  between the seals formed by the gasket  210  of the upper end cap  160  and the gasket  200  of the lower end cap  162 . This sealed portion of the filter chamber  181  is pressurized by the incoming return oil. The pressure forces the oil through the filter media  158 , thereby filtering particulates from the return oil and also separating air from the aerated return oil. [0085] The separated air is returned to the engine  100  via the vent assembly  248 . The air travels upward through the support  202 , passes through the screen  214  and is drawn into the filter conduit  250  of the vent assembly  248  and travels to the manifold  259 . The vent assembly  248  also allows air from the oil chamber  148  of the oil tank  112  to vent to the engine  100 . Air from the oil chamber  148  enters tank conduit  252 , mixes with air from the filter conduit  250  at the manifold  249 , and the mixture passes through the manifold  259  to the engine conduit  256 . The air leaves the engine conduit  256  through the vent outlet  258  into a vent hose, line, or conduit  316  that fluidly couples the vent outlet of the vent assembly  248  with the vent inlet  260  of the engine  100 . The vent inlet  260  is in fluid communication with the crankcase chamber  130  so that the air passes from the vent inlet  260  to the crankcase chamber. Differences in pressure between the filter chamber  181 , the oil chamber  148 , and the crankcase chamber  130  cause the air to flow as described. 
     The filtered oil passes downward through the support  202  of the oil filter  156  and exits the filter  156  through the filter outlet  198 . From the filter outlet  198 , the filtered oil enters the chamber  148  of the oil tank  112 . There, the oil collects until being drawn back to the engine  100  by the supply pump  113 . The supply pump  113  creates a vacuum to draw oil into the supply conduit  272  through the supply inlet  274 . The oil exits the supply conduit  272  through the supply outlet  270 , which is fluidly coupled to the supply inlet  122  of the supply pump  113  by a supply oil hose, line, or conduit  318 . The oil enters the engine  100  through the supply inlet  122  and the supply pump  113  pressurizes the oil (e.g., greater than 30 psi (2.068e+005 newtons/square meter)) and supplies the oil via one or more oil galleries  124  to various locations within the engine, which may include the cylinder heads, the crankshaft, the camshaft, the crankcase chamber, various bearings, and other parts of the engine that require lubrication. In some embodiments, the oil is pressurized by the supply pump  113  to about 40-60 psi (4.137e+005 newtons/square meter). 
     Conventional automotive dry sump lubrication systems provide the oil filter on the supply side of the system and filter the oil at high pressure, not the return side with filtering done at low pressure (e.g., less than 15 psi (1.034e+005 newtons/square meter)) as in the systems described herein. In a conventional automotive dry sump lubrication system, oil is pumped at high pressure from the crankcase chamber through a first high pressure oil conduit to an oil filter and back from the oil filter at high pressure through a second high pressure oil conduit. By positioning the oil filter assembly  150  on the return side of the dry sump system and filtering at low pressure, the need for high pressure conduits is eliminated, resulting in cost savings and eliminating a location for a possible leak, blow-off, or other malfunction. 
     In alternative embodiments, as shown in  FIG. 15B , a dry sump lubrication system has the oil filter assembly  150  positioned on the supply side of the dry sump system (fluidly coupled between the supply pump  113  and the oil gallery  124 ) and not the return side (fluidly coupled between the return pump  114  and the oil tank  112 ), as shown in  FIG. 15A . For example, as shown in  FIG. 15B , the oil filter assembly  150  is positioned downstream of the supply pump  113  to receive pressurized oil from the supply pump  113 . After the return pump  114  sends oil from the crankcase chamber  130  to the oil tank  112 , the oil is drawn by the supply pump  113  from the oil tank  112  and is sent from the supply pump  113  to the oil filter assembly  150 . After the pressurized oil is filtered by the oil filter  156 , the filtered pressurized oil exits the oil filter assembly  150  through an outlet  245  fluidly coupled to the oil gallery  124  for distribution in the engine  100 . The oil filter assembly  150  and the oil filter  156  used in this arrangement may be a conventional high pressure oil filter assembly and oil filter. 
     In alternative embodiments, as shown in  FIG. 15C , a dry sump lubrication system includes two oil filter assemblies  150  with the first oil filter assembly  150  positioned on the supply side of the dry sump system (fluidly coupled between the supply pump  113  and the oil gallery  124 ) and the second oil filter assembly  150  positioned on the return side (fluidly coupled between the return pump  114  and the oil tank  112 ). This arrangement provides extra filtering capabilities as compared to the arrangements illustrated in  FIGS. 15A and 15B . 
     Referring to  FIGS. 16-20 , an engine assembly including an internal combustion engine  400  and external oil tank or reservoir  412  is illustrated according to an exemplary embodiment. The engine  400  and the oil tank  412  are similar in many respects to the engine  100  and the oil tank  112  described above, with differences described in more detail below. 
     As shown in  FIGS. 16-17 , the internal combustion engine  400  is structurally similar to the engine  100 . The engine  400  includes an engine block  401  having two cylinders  402  and  403 , two cylinder heads ( 439  shown in  FIG. 17 ), two pistons, and a crankshaft  404 . A crankcase chamber  430  is defined by the engine block  401  and a sump or crankcase cover  406 . The engine  400  also includes a fuel system for supplying an air-fuel mixture to the cylinder (e.g., a carburetor, an electronic fuel injection system, a fuel direct injection system, etc.), an air filter assembly  407 , a camshaft  419  for actuating intake and exhaust valves in the cylinder heads, a muffler  408 , a flywheel, and a blower fan. The engine  400  includes a blower housing  410  configured to direct cooling air over the engine block  401  and other components of the engine. The blower fan pulls air into the blower housing  410  through one or more air inlets  411 . The illustrated engine  400  is a vertically-shafted two cylinder engine arranged in a V-twin configuration. 
     As shown in  FIGS. 18-19 , the crankcase cover  406  is structurally similar to the crankcase cover  106 . The crankcase cover  406  includes a supply pump  413  and a return pump  414  that are incorporated into the crankcase cover  406 . The crankcase cover  406  includes a crankshaft opening or aperture  415  through which the crankshaft  404  extends to drive one or more components of a lawn mower or other piece of equipment. The crankshaft  404  rotates about a crankshaft axis  405 . A transmission  416  including one or more gears  417  or other reduction mechanism (e.g., belts) connects the crankshaft  404  to a drive shaft  418  for the supply pump  413  so the supply pump  413  is driven by the crankshaft  404  at a lower rotational speed than that of the crankshaft  404 . The supply pump  413  and the drive shaft  418  rotate about an axis of rotation  433 . The camshaft  419  is directly connected to a drive shaft  420  for the return pump  414  so the return pump  414  is directly driven by the camshaft  419  at the same rotational speed as the camshaft  419 . The return pump  414  and the drive shaft  420  rotate about an axis of rotation  434 . A transmission connects the camshaft  419  to the crankshaft  404  so that the camshaft  419  is driven at a rotational speed less than that that of the crankshaft  404 . The supply pump  413  is located near the rear  426  of the crankcase cover  406  and the engine  400  and the return pump  414  is located near the front  438  of the crankcase cover  406  and the engine  400 . 
     The supply pump  413  is positioned in a supply pump housing  421  formed in the exterior of the crankcase cover  406 . The supply pump  413  is in fluid communication with a supply inlet  422  for receiving oil (e.g., supply oil) from the external oil tank  412  and a supply outlet  423  for providing oil for distribution within the engine  400 . A cover plate  425  is secured to the crankcase cover  406  (e.g., by threaded fasteners) to close the pump housing  421 . A gasket  426  is provided between the cover plate  425  and the crankcase cover  406  to form a seal. 
     The return pump  414  is positioned in a return pump housing  427  formed in the exterior of the crankcase cover  406 . The return pump  414  is in fluid communication with a return inlet  428  for receiving oil (e.g., return oil, scavenged oil) from the crankcase chamber  430  and a return outlet  429  for providing oil to the external oil tank  412 . The return inlet  428  is formed through the crankcase cover  406  to place the return pump  414  in fluid communication with the crankcase chamber  430 . The return inlet  428  is formed in a front portion  431  of the crankcase cover  406  to be in fluid communication with the front portion of the crankcase chamber  430 . The front portion  431  is located forward of a vertical plane  432  including the vertical crankshaft axis  405 . The plane  432  is perpendicular to a second vertical plane  442  including the crankshaft axis  405  and the axis of rotation  434  of the return pump  414 . The cylinders  402  and  403  and cylinder heads are also located forward of the vertical plane  432 . The supply pump axis of rotation  433  is located to the side of the plane  442 . The return pump  414  draws oil from the front portion  431  of the crankcase chamber  430  into the return pump  414 . A cover plate  444  is secured to the crankcase cover  406  (e.g., by threaded fasteners) to close the pump housing  427 . A gasket  446  is provided between the cover plate  444  and the crankcase cover  406  to form a seal. 
     As shown in  FIG. 20 , the oil tank  412  is structurally similar to oil tank  112 . The oil tank  412  includes a tank body  435  that defines an oil reservoir, volume, or chamber for storing oil. The tank body  435  of the oil tank  412  includes a top  470 , a bottom  580 , a front  576 , a rear  582 , a left side  584 , and a right side  586  that in combination define the volume of the oil chamber. In contrast to the oil tank  112 , which is relatively tall, the tank  412  is relatively wide with its width (left side to right side)) exceeding its height (top to bottom) and depth (front to rear). A recess  588  is formed in the rear  582  to allow the oil tank  412  to be positioned closely to the engine  400 . The recess  588  allows the oil tank  412  to be positioned near the rear  436  of the engine  100 . As shown in  FIG. 16 , a volume  590  having a triangular cross-section is formed by a plane  592  extending along the rear  436  of the engine  400  (horizontal as illustrated), a plane  594  extending forward from the front outer corner of the blower housing  410  covering the cylinder  403  (vertical as illustrated), and a plane  596  extending along the outer edge of the blower housing  410  covering the cylinder  403  (angled and intersecting the planes  592  and  594  as illustrated). A volume  591  having a triangular cross-section is formed by the plane  592  extending along the rear  436  of the engine  400  (horizontal as illustrated), a plane  593  extending forward from the front outer corner of the blower housing  410  covering the cylinder  402  (vertical as illustrated), and a plane  597  extending along the outer edge of the blower housing  410  covering the cylinder  402  (angled and intersecting the planes  592  and  593  as illustrated). The oil tank  412  is located at least in part within the cross-sections of the two volumes  590  and  591  and is considered to be located at least in part between the rear  436  of the engine  400  and the cylinder head of the cylinder  103  located at least in part between the rear  436  of the engine  400  and the cylinder head of the cylinder  102 . Like the oil tank  112 , the oil tank  412  includes a supply outlet  570  and a drain  578 . 
     The external oil tank  412  includes an integrated oil filter assembly  450  substantially the same as the oil filter assembly  150 , except for a shorter dipstick  488  to account for the shorter height of the oil tank  412 . The oil filter assembly  450  includes an oil filter housing  452 , an oil filter (not shown), and a cover  454 . 
       FIGS. 21-22  illustrate the engine  400  and the external oil tank  412  in use on a zero-turn lawn mower  600 . In other embodiments, the engine  400  and the external oil tank  412  are used with other types of outdoor power equipment, including riding lawn tractors or other riding outdoor power equipment. The engine  400  and the external oil tank  412  are located on a mounting platform  602  located between the two rear wheels  604  and  606  and behind the operator location  608 , illustrated as a seat. The engine  400  and the external oil tank  412  are also located between the vertical legs  610  and  612  of a roll bar for protecting the operator. The uppermost point of the oil tank  412  (i.e., the cover  454 ) is located well below the top of the back  614  of the operator seat  608 . A portion of the oil tank  412  is located between the seat  608  and the engine  400 . Locating the tank  412  near the operator location  608 , within the vertical legs  610  and  612  of the roll bar, near the center of the mower (i.e., between the wheels  604  and  606 ), and relatively low (i.e., the uppermost point below the top of the back  614  of the operator seat  608 ) helps to protect the oil tank  412  from collisions (e.g., from branches or other overhanging obstacles) because the tank is close to the operator and reduces the likelihood the oil tank  412  will interfere with baggers or other accessories that may be mounted to the mower  600 . The engines ( 100  and  400 ) and external oil tanks ( 112  and  412 ) described herein can be used on different types of lawn mowers than the zero-turn lawn mowers ( 300  and  600 ) described herein. For example, the engines and external oil tank can be used on a riding mower that includes a mowing deck, a seat for the operator to sit in, and one or more blades or a drivetrain for one or more wheels (e.g., a transmission) driven by the engine. As another example, the engines and external oil tanks can be used on a wide-area walk-behind walk mower that includes a mowing deck, one or more blades or a drivetrain for one or more wheels (e.g., a transmission), and a handle that allows the user to direct and control the mower while walking behind the mower. As another example, the engines an external oil tanks can be used on a standing lawn mower that includes a mowing deck, a standing platform for the operator to stand on, and one or more blades or a drivetrain for one or more wheels (e.g., a transmission) driven by the engine. 
     The construction and arrangement of the apparatus, systems and methods as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, some elements shown as integrally formed may be constructed from multiple parts or elements, the position of elements may be reversed or otherwise varied and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present disclosure.