Patent Publication Number: US-6904879-B2

Title: Lubrication system for two-cycle engine

Description:
PRIORITY INFORMATION 
   This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2002-214474, filed on Jul. 23, 2002, the entire contents of which is hereby expressly incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present application relates to a lubrication system for a two-cycle engine and, more particularly, to a lubrication system that incorporates a lubrication pump that pressurizes and delivers lubricant to a portion of a two-cycle engine. 
   2. Description of Related Art 
   In all fields of engine design, there is an increasing emphasis on obtaining more effective emission control. Recent two-cycle engines, therefore, incorporate a lubricant pump to deliver a desired amount of lubricant to lubricate internal portions of the engines. Mechanically operated pumps can be used as the lubricant pump. Such mechanical pumps, however, are not easily controlled to provide highly precise amounts of lubricant in response to engine operations. Electrically operable pumps tend to replace the mechanical pumps because higher precision controls are more widely available with such electrical pumps. 
   The electrical pumps can periodically pressurize lubricant under the control of a control device, such as, for example, an electronic control unit (ECU). The ECU can control a frequency of the periodic pressurization with, for example, an electronic control signal configured to operate the pump in accordance with a desired duty cycle. The higher the frequency, the greater the amount of the lubricant. 
   An electromagnetic solenoid pump is one type of such electrical pump. Japanese Laid Open Patent Publication 10-37730 discloses a lubrication system incorporating such an electromagnetic solenoid pump. The solenoid pump has a pumping piston reciprocally disposed in a pump housing. A plunger is coupled with the pumping piston. An electromagnetic solenoid can actuate the plunger. A control device controls the solenoid to selectively actuate or release the plunger such that the pumping piston periodically pressurizes the lubricant. 
   The control device disclosed in Japanese Laid Open Patent Publication 10-37730 has a control map that provides an amount of lubricant required by the engine versus an engine speed and determines a frequency of energization of the solenoid using the control map. The solenoid pump thus can pressurize a proper amount of lubricant in response to the engine speed of the engine. 
   SUMMARY OF THE INVENTION 
   One aspect of at least one of the inventions disclosed herein includes the realization that where a solenoid is operated under a duty cycle to provide lubricant to an engine based on engine speed, the amount of lubricant delivered can be inadequate under certain operating conditions. For example, when the engine speed is constant, engine load can still vary. For instance, if the engine powers a land vehicle, the engine load can increase when the vehicle ascends a slope, i.e., goes up a hill). Also, if the engine powers a watercraft, the engine load can increase when the watercraft proceeds against wind. Under such circumstances, the engine requires a more appropriate amount of lubricant. 
   In accordance with another aspect of at least one of the inventions disclosed herein, an internal combustion engine comprises a lubrication system arranged to lubricate at least a portion of the engine with lubricant. The lubrication system has a lubrication pump that pressurizes the lubricant toward the portion of the engine. A first sensor is configured to sense an engine speed of the engine. A second sensor is configured to sense an engine load of the engine. A control device is configured to control the lubrication pump. The control device determines an amount of lubricant that is pressurized by the lubrication pump based upon outputs from the first and second sensors to control the lubrication pump. 
   In accordance with another aspect of at least one of the inventions disclosed herein, an internal combustion engine comprises a lubrication system arranged to lubricate at least a portion of the engine with lubricant. The lubrication system has a lubrication pump that periodically pressurizes the lubricant toward the portion of the engine. A first sensor is configured to sense an engine speed of the engine. A second sensor is configured to sense an engine load of the engine. A control device is configured to control the lubrication pump. The control device determines a frequency of periodic pressurization by the lubrication pump based upon outputs from the first and second sensors to control the lubrication pump. 
   In accordance with a further aspect of at least one of the inventions disclosed herein, an internal combustion engine comprises a lubrication system arranged to lubricate at least a portion of the engine with lubricant. The lubrication system has a lubrication pump that periodically pressurizes the lubricant toward the portion of the engine. A first sensor is configured to sense an engine speed of the engine. A second sensor is configured to sense an engine load of the engine. A control device is configured to control the lubrication pump. The control device determines a pressurization time of the lubrication pump based upon at least one of outputs from the first and second sensors to control the lubrication pump. 
   In accordance with a further aspect of at least one of the inventions disclosed herein, an internal combustion engine comprises a lubrication system arranged to lubricate at least a portion of the engine with lubricant. The lubrication system has a lubrication pump that periodically pressurizes the lubricant toward the portion of the engine. A first sensor is configured to sense an engine speed of the engine. A second sensor is configured to sense an engine load of the engine. A third sensor is configured to sense a temperature of the lubricant or the engine. A control device is configured to control the lubrication pump. The control device determines a pressurization time of the lubrication pump based upon at least one of outputs from first, second and third sensors. 
   In accordance with a further aspect of at least one of the inventions disclosed herein, an internal combustion engine comprises a lubrication system arranged to lubricate at least a portion of the engine with lubricant. The lubrication system has a lubrication pump that periodically pressurizes the lubricant toward the portion of the engine. A first sensor is configured to sense an engine speed of the engine. A second sensor is configured to sense an engine load of the engine. A third sensor is configured to sense a temperature of the lubricant or the engine. A control device is configured to control the lubrication pump. The control device determines a frequency of periodic pressurization by the lubrication pump based upon outputs from the first and second sensors. The control device determines a pressurization time of the lubrication pump based upon at least one of the outputs from the first and second sensors and an output from the third sensor. 
   In accordance with a further aspect of at least one of the inventions disclosed herein, a control method is provided for a lubrication system that lubricates at least a portion of an engine. The method comprises sensing an engine speed of the engine, sensing an engine load of the engine, determining an amount of lubricant that is pressurized by a lubrication pump based upon the sensed engine speed and the sensed engine load, aid actuating the lubrication pump to pressurize the determined amount of lubricant. 
   In accordance with a further aspect of at least one of the inventions disclosed herein, a control method is provided for a lubrication system that lubricates at least a portion of an engine. The lubrication system has a lubrication pump periodically pressurizes lubricant. The method comprises sensing an engine speed of the engine, sensing an engine load of the engine, determining a frequency of periodic pressurization by the lubrication pump based upon the sensed engine speed and the sensed engine load, and actuating the lubrication pump to pressurize the lubricant with the determined frequency. 
   In accordance with a further aspect of at least one of the inventions disclosed herein, a control method is provided for a lubrication system that lubricates at least a portion of an engine. The lubrication system has a lubrication pump periodically pressurizes lubricant. The method comprises sensing an engine speed of the engine, sensing an engine load of the engine, determining a pressurization time of the lubrication pump based upon at least the sensed engine speed or the sensed engine load, and actuating the lubrication pump to pressurize the lubricant with the determined pressurization time. 
   In accordance with a further aspect of at least one of the inventions disclosed herein, a control method is provided for a lubrication system that lubricates at least a portion of an engine. The lubrication system has a lubrication pump periodically pressurizes lubricant. The method comprises sensing an engine speed of the engine, sensing an engine load of the engine, sensing a temperature of the lubricant or the engine, determining a pressurization time of the lubrication pump based upon at least the sensed engine speed, the sensed engine load or the sensed temperature of the lubricant or the engine, and actuating the lubrication pump to pressurize the lubricant with the determined pressurization time. 
   In accordance with a further aspect of at least one of the inventions disclosed herein, a control method is provided for a lubrication system that lubricates at least a portion of an engine. The lubrication system has a lubrication pump periodically pressurizes lubricant. The method comprises sensing an engine speed of the engine, sensing an engine load of the engine, sensing a temperature of the lubricant or the engine, determining a frequency of periodic pressurization by the lubrication pump based upon the sensed engine speed and the sensed engine load, determining a pressurization time of the lubrication pump based upon at least the sensed engine speed, the sensed engine load or the sensed temperature of the lubricant or the engine, and actuating the lubrication pump to pressurize the lubricant with the determined frequency and the determined pressurization time. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the inventions disclosed herein are described below with reference to the drawings of a preferred embodiment, which is intended to illustrate and not to limit the inventions. The drawings comprise eight figures in which: 
       FIG. 1  illustrates a schematic diagram of portions of an outboard motor that has an engine incorporating a lubrication system that is configured in accordance with preferred embodiments of the at least one of the inventions disclosed herein, wherein an upper part of the outboard motor is broken away, and the engine and an air intake system for the engine are shown in a top plan view; 
       FIG. 2  illustrates a schematic view of a lubrication pump applied in the lubrication system of  FIG. 1 ; 
       FIG. 3  illustrates a timing chart in accordance with which the lubrication pump of  FIGS. 1 and 2  can operate; 
       FIG. 4  illustrates a lubricant amount control map that provides an amount of lubricant corresponding to an engine speed and an engine load; 
       FIG. 5  illustrates a lubricant amount adjustment calculation map that provides an adjustment coefficient corresponding to an engine temperature or a lubricant temperature; 
       FIG. 6  illustrates a flow chart of a preferred control routine with which a control device of the lubrication system can controls the lubrication pump of  FIGS. 1 and 2 ; 
       FIG. 7  illustrates a duration calculation map for the lubrication pump of  FIGS. 1 and 2  that can provide a duration of ON signal of a solenoid actuator of the lubrication pump corresponding to an engine speed and an engine load, wherein the duration calculation map is used for a control of the lubrication pump delivering the lubricant into the air intake passage of  FIG. 1 ; 
       FIG. 8  illustrates another duration calculation map for the lubrication pump of  FIGS. 1 and 2  that can provide a duration of ON signal of the solenoid actuator of the lubrication pump corresponding to an engine speed and an engine load, wherein the duration calculation map is used for a control of the lubrication pump delivering the lubricant into a crankcase chamber of the engine of FIG.  1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present lubrication system described below has particular utility in the context of a two-cycle engine for an outboard motor, and thus, is described in the context of such an outboard motor. The lubrication system, however, can be used with other types of two-cycle engines employed by any machines whatsoever using engine power such as, for example, watercrafts (e.g., personal watercrafts), land vehicles (e.g., motorcycles) and utility machines (e.g., lawn mowers). 
   With reference to  FIG. 1 , an outboard motor  30  has a bracket assembly comprising a swivel bracket and a clamping bracket which are typically associated with a housing unit  32 . The outboard motor  30  can be mounted on an associated watercraft by the bracket assembly. The outboard motor  30  includes a power head that is positioned above the housing unit  32 . The power head comprises a protective cowling assembly and an internal combustion engine  34 . An engine support is unitarily or separately formed atop the housing unit  32  and forms a tray together with the cowling assembly. The tray holds a bottom of the engine  34  and the engine  34  is affixed to the engine support. 
   The engine  34  comprises an engine body  38  and a crankshaft  40  that is rotatably journaled relative to the engine body  38 . The crankshaft  40  rotates about a generally vertically extending axis. This facilitates the connection of the crankshaft  40  to a driveshaft  42  which depends into the housing unit  32 . 
   A propulsion device is mounted on a lower portion of the housing unit  32  and the driveshaft  42  drives the propulsion device. The illustrated propulsion device is a propeller  44 . The driveshaft  42  drives the propeller  44  through a transmission (not shown). The transmission includes a changeover mechanism that can change a rotational direction of the propeller  44  among forward, neutral and reverse. 
   The engine  34  operates on a two-cycle, crankcase compression principle. The illustrated engine  34  is generally configured in a V-shape, with a pair of cylinder bank  48  extending generally rearwardly. Each bank  48  defines one or more cylinder bores. In the illustrated embodiment, each bank  48  defines three cylinder bores. The cylinder bores extend generally horizontally and are vertically spaced apart from each other in the bank  48 . As used in this description, the term “horizontally” means that the subject portions, members or components extend generally in parallel to the water line where the associated watercraft is resting when the outboard motor  30  is not tilted. The term “vertically” in turn means that portions, members or components extend generally normal to those that extend horizontally when the associated watercraft is resting when the outboard motor  30  is not tilted. Although the inventions are described in conjunction with the engine  34 , the inventions disclosed herein can be utilized with an engine having other cylinder numbers and other cylinder configurations. 
   The crankshaft  40  is journaled for rotation within a crankcase chamber defined in part by a crankcase member  50  that is affixed to the cylinder banks  48 . Pistons are reciprocally disposed within the cylinder bores. The pistons are coupled with the crankshaft  40  through connecting rods. The crankshaft  40  thus rotates with the reciprocal movement of the pistons. 
   Cylinder head assemblies  52  are affixed to each cylinder bank  48  to close open ends of the respective cylinder bores. Each cylinder head assembly  52  defines a plurality of recesses on its inner surface corresponding to the cylinder bores. Each of these recesses defines a combustion chamber together with the cylinder bore and the piston. 
   The engine  34  preferably is provided with an air intake system  56  that guides air to each section of the crankcase chamber associated with each cylinder bore. The air finally is supplied to the combustion chambers through a route described below. The intake system  56  comprises a plurality of air intake conduits  58 . The air is drawn into the respective intake conduits  58  through an air inlet device as indicated by the arrow  59 . The air intake device preferably defines a plenum chamber. Each air intake conduit  58  defines an air intake passage  60  connecting the plenum chamber and each section of the crankcase chamber associated with each combustion chamber. The air drawn into the plenum chamber thus is delivered to the sections of the crankcase chamber through the intake conduits  58 . 
   Each intake conduit  58  preferably incorporates a reed valve  62  configured to allow air to flow into the section of the crankcase chamber and to prevent the air in the section of the crankcase chamber from flowing back to the plenum chamber. Each intake conduit  58  also incorporates a throttle valve  66  between the plenum chamber and the reed valve  62 . Each throttle valve  66  preferably is a butterfly type and is pivotally journaled on each intake conduit  58  to regulate an amount of air flowing therethrough. The operator can change the pivotal position, i.e., a throttle valve position or throttle valve open degree, through a suitable control mechanism (not shown). 
   The air drawn into the respective sections of the crankcase chamber is preliminarily compressed by the pistons, during their movement toward the crankshaft  40 . The air, then, moves into the combustion chambers through a scavenge system. The scavenge system preferably is formed as a Schnurle-type system that comprises a pair of main scavenge passages connected to each cylinder bore and positioned on diametrically opposite sides. These main scavenge passages terminate in main scavenge ports so as to direct scavenge air flows into the combustion chamber. 
   In addition, an auxiliary scavenging passage is formed between the main scavenge passages and terminates in an auxiliary scavenging port which also provides a scavenge air flow. Thus, at the scavenge stroke, the air in the crankcase chamber is transferred to the combustion chambers to be further compressed by the pistons during their movement toward the cylinder head assemblies  52 . The scavenge ports are selectively opened and closed as the piston reciprocates. 
   The engine  34  preferably is provided with a fuel supply system  70  that supplies fuel  72  to the combustion chambers. The illustrated fuel supply system  70  is configured to operate under a direct fuel injection principle in which the fuel is directly sprayed into the combustion chambers. The fuel supply system  70  comprises fuel injectors  74  allotted to the respective combustion chambers. The fuel injectors  74  preferably are mounted on the cylinder head assemblies  52 . 
   A control device controls the fuel injectors  74  to inject fuel. In the illustrated embodiment, the control device preferably is an electronic control unit (ECU)  76 . The ECU  76  preferably controls an injection timing and a duration of each injection. The ECU  76  comprises at least a central processing unit (CPU) and at least one storage or memory device. The ECU  76  preferably controls engine related components other than the fuel injectors  74 , which will be described shortly. The storage devices store control programs and reference maps for controlling the components including the fuel injectors  74 . The CPU preferably conducts the control programs to control the engine related components in referring to the maps based upon output signals from sensors. 
   The fuel supply system  70  additionally comprises a fuel supply tank  78  that contains the fuel  72 . The fuel supply tank  78  preferably is placed in the hull of the watercraft. A fuel delivery unit  82  is provided between the fuel supply tank  78  and the fuel injectors  74  and particularly on the outboard motor  30  to deliver the fuel  72  to the fuel injectors  74 . The fuel delivery unit  82  preferably comprises a vapor separator tank  84  and a plurality of fuel pumps  86 , although  FIG. 1  schematically illustrates the fuel delivery unit  82 . The vapor separator tank  84  temporarily contains the fuel  72  and also can separate vapor from the fuel  72  to prevent vapor lock from occurring in the fuel supply system  70 . 
   The fuel pumps  86  preferably include low pressure fuel pumps and high pressure fuel pumps to develop an extremely high pressure step by step. At least one of the fuel pumps operates under control of the ECU  76 . The fuel delivery unit  82  also comprises high pressure regulators to regulate the developed high pressure at a fixed or constant pressure level. Excessive fuel preferably returns back to the vapor separator  84 . 
   With continued reference to  FIG. 1 , the engine  34  preferably is provided with an ignition or firing system. Spark plugs  90  are affixed to the cylinder head assemblies  52  so as to expose an electrode thereof into the combustion chambers. The spark plugs  90  ignite air/fuel charges in the combustion chambers under control of the ECU  76 . 
   The engine  34  preferably is provided with an exhaust system (not shown) that guides burned charges, i.e., exhaust gases, to an external location from the combustion chambers. The exhaust system has one or more exhaust ports that are formed in the cylinder banks  48  to communicate with each combustion chamber. The exhaust ports are selectively opened or closed with the reciprocal movement of each piston. The exhaust system can discharge the exhaust gases to the body of water, which surrounds the outboard motor  30 , through a hub of the propeller  44  above idle operation. At idle, the exhaust gasses can be discharged to the atmosphere through an above-water outlet. 
   Each fuel injector  74  sprays fuel directly into the associated combustion chamber. The sprayed fuel is mixed with the air delivered through the scavenge passages to an air/fuel charge. The injection timing and the duration of the fuel injection and the firing timing are under control of the ECU  76 . The spark plug  90  fires the air/fuel charge. Once the air/fuel charge burns in each combustion chamber, each piston is moved by the pressure produced in the combustion chamber. At this time, exhaust ports are uncovered. The burnt charge or exhaust gases thus are discharged through the exhaust system. 
   With reference to  FIGS. 1 and 2 , the engine  34  is provided with the foregoing lubrication system, which is identified generally by the reference numeral  94 . The lubrication system  94  preferably comprises a lubricant tank  96  and a lubrication pump  98 . The lubricant tank  96  contains lubricant oil  100 . A lubricant supply passage  102  couples the lubrication tank  96  with the lubrication pump  98 . Preferably but not necessarily, the lubricant tank  96  is mounted on the engine body  38 . 
   An auxiliary lubricant tank (not shown), which preferably has a larger capacity than the lubricant tank  96 , preferably is placed in the watercraft to store a sufficient amount of the lubricant  100  to provide a desired range of operation of the associated watercraft. Preferably, the auxiliary lubricant tank is connected to the lubricant tank  96  through a proper lubricant passage and a pump pressurizes the lubricant in the auxiliary lubricant tank to the lubricant tank  96 . 
   Preferably, the lubrication pump  98  periodically pressurizes lubricant toward portions of the engine  34  that benefit from lubrication. In the illustrated arrangement, the lubrication pump  98  has one inlet port and six outlet ports. The inlet port is connected to the lubricant tank  96  through the lubricant supply passage  102 . The outlet ports preferably are connected to the respective intake passages  60  upstream of the reed valves  62  to inject the lubricant  100  into the intake passages  60 . The lubricant is drawn into the crankcase chamber together with the air and is delivered to the engine portions such as, for example, connecting portions of the connecting rods with the pistons and also with the crankshaft  40 . 
   In one variation, the outlet ports can be positioned downstream of the reed valves  62 . In another variation, the outlet ports can be connected directly to the crankcase chamber within the crankcase member  50  as indicated by the phantom line of FIG.  1 . 
   In the illustrated arrangement, some forms of direct lubrication can be additionally employed for delivering lubricant directly to certain engine portions. For example, an extra outlet port can be formed on the lubrication pump  98  to deliver part of the lubricant  100  to the vapor separator tank  84  through a lubricant delivery passage  106 . Alternatively, the lubricant delivery passage  106  can be branched off from the lubricant supply passage  102 , one branch passage directed to the lubrication pump  98  and another branch passage directed to the vapor separator tank  84 . In this alternative, a lubricant delivery pump is additionally necessary in the lubricant delivery passage  106  to pressurize the part of the lubricant  100  to the vapor separator tank  84 . 
   The lubrication pump  98  preferably comprises an electromagnetic solenoid actuator  108  that is controlled by the ECU  76 . The lubrication pump  98  and the solenoid actuator  108  are described in greater detail below with reference to FIG.  2 . 
   The outboard motor  30  can have other systems, devices and components which are not described above. For instance, a water cooling system can be provided to cool the engine  34  and the exhaust system with the water. The cooling system can be an open-loop type that takes water into the system from the body of water and discharges the water thereto after the water has traveled around water jackets in the engine body  38  and portions of the exhaust system. 
   With reference to  FIG. 1 , as described above, the ECU  76  controls at least the fuel injectors  74 , the spark plugs  90 , one of the fuel pumps  86  and the lubrication pump  98 . In order to control these components, the outboard motor  30  is provided with a number of sensors that sense either engine running conditions, ambient conditions or conditions of the outboard motor  30  that can affect engine performance. 
   There is provided a crankshaft angle position sensor  112  that senses a crankshaft angle position and outputs a crankshaft angle position signal to the ECU  76 . The ECU  76  can calculate an engine speed N (r.p.m.) using the crankshaft angle position signal versus time. In this regard, the crankshaft angle position sensor  112  and part of the ECU  76  form an engine speed sensor. The crankshaft angle position sensor  112 , or another sensor, can also be used to provide reference position data to the ECU  76  for timing purposes, such as for the timing of fuel injection and/or ignition timing. 
   Operator&#39;s demand or engine load, as indicated by an angular position Th? of the throttle valve  66 , is sensed by a throttle valve position sensor  196  which outputs a throttle valve position or load signal to the ECU  76 . Alternatively or additionally, an intake pressure sensor can be provided downstream of the throttle valve  66  in the intake passage  60  to sense the intake pressure that can also represent the engine load. The intake pressure sensed by the intake pressure sensor is negative pressure unless the reed valve  62  closes. Further, an air amount sensor such as, for example, an air flow meter can alternatively or additionally be provided to sense an amount of the air in the intake passage  60  that can also represent the engine load. 
   A lubricant temperature sensor  116  is provided at the lubrication pump  98  to sense a temperature T L  of the lubricant  100  that is injected to the intake passages  60  and outputs a lubricant temperature signal to the ECU  76 . In one variation, the lubricant temperature sensor  116  can be positioned at the lubricant tank  96 . 
   An engine temperature sensor  118  is provided at a portion of the engine body  38  to sense a temperature T E  of the engine body  38  and outputs an engine temperature signal to the ECU  76 . In one variation, the engine temperature sensor  118  can sense a temperature of the cooling water in the water jackets instead of directly sensing the temperature of the engine body  38 . 
   Preferably, other than those sensors described above, a number of sensors can be provided. For example, a lubricant level sensor can be placed at the lubricant tank  96  to sense a lubricant level in the lubricant tank  96  and outputs a lubricant level signal to the ECU  76  such that the ECU  76  can control the lubricant delivery pump to pressurize the lubricant in the auxiliary lubricant tank to the lubricant tank  96  when the lubricant level is lower than a preset level. 
   With reference to  FIG. 2 , a structure and an operation of the lubrication pump  98  is described below. It should be noted that the actual lubrication pump  98  has at least six outlet ports connected to the respective intake passages  60  of the intake conduits  58  as described above, although  FIG. 2  schematically illustrates only one outlet port. If necessary, an extra outlet port is added to deliver the lubricant  100  to the fuel supply system  70 . 
   The lubrication pump  98  preferably comprises a pump unit  122  and a solenoid unit  124 . The pump unit  122  has a pump housing  126 , while the solenoid unit  124  has a solenoid housing  128 . Both housings  126 ,  128  are coupled with each other by fastening members such as, for example, screws. In one variation, the housings  126 ,  128  can be unitarily formed as a single housing. 
   The pump housing  126  defines a cavity  130  in which a piston  134  is reciprocally disposed. The piston  134  occupies a certain volume of the cavity  130  and a distal end of the piston  134  can move in a full stroke range or distance FS. The full stroke range FS substantially determines a full displacement of the lubrication pump  98 . In other words, the maximum amount of the lubricant injected every stroke of the piston  134  is determined depending on the full stroke range FS. 
   The pump housing  126  defines an opening communicating with an inside of the solenoid housing  128 . A piston rod  136  extends from the piston  134  through the opening and enters the inside of the solenoid housing  128  beyond a distal end of the pump housing  126 . The opening is widened toward the inside of the solenoid housing  128  to form a step. The piston rod  136  has a retainer at a portion in close proximity to its end. A coil spring  138  is placed between the step and the retainer to bias the piston rod  136  toward the solenoid unit  124 . Thus, the piston  134  normally is biased toward an initial position as indicated by the solid line of FIG.  2 . 
   The cavity  130  also communicates outside through an inlet port  140  and outlet ports  142  generally located on a side opposite to the solenoid unit  124 . In the illustrated arrangement, the inlet port  140  is connected to the lubricant tank  96  through the lubricant supply passage  102  and the outlet ports  142  are connected to the respective intake passages  60  as described above. 
   The inlet port  140  is narrowed toward the outside from a mid portion of the inlet port  140  to form a step. A ball valve  146  is positioned at the step so as to be movable toward the cavity  130 . A coil spring  148  is placed between the ball  146  and a retainer disposed at an inner surface of the inlet port  140  to bias the ball  146  onto the step. The inlet port  140  is closed when the ball  146  is seated at the step. Thus, the ball  146  normally is seated at the step. The ball  146  and the spring  148  together form a check valve  150  that allows the lubricant  100  to flow into the cavity  130  and prevents the lubricant  100  from flowing out of the cavity  130  through the inlet port  140 . 
   Similarly, each outlet port  142  is narrowed toward the cavity  130  from a mid portion of the outlet port  142  to form a step. A ball valve  152  is positioned at the step so as to be movable toward the outside. A coil spring  154  is placed between the ball  152  and a retainer formed at an inner surface of the outlet port  142  to bias the ball  152  onto the step. The outlet port  142  is closed when the ball  152  is seated at the step. The ball  152  normally is seated at the step. The ball  152  and the spring  154  together form a check valve  156  that allows the lubricant to flow outside and prevents the lubricant from flowing back to the cavity  130  from the outlet port  142 . 
   The solenoid unit  124  incorporates the electromagnetic solenoid actuator  108 , a plunger  160  and a stopper  162  in the solenoid housing  128 . The solenoid  108  surrounds the plunger  160  so as to allow the plunger  160  to move axially therein. An end of the plunger  160  abuts the piston rod  136  and pushes the piston rod  136  toward the check valves  150 ,  156  when the plunger  160  is actuated. The stopper  162  limits a stroke of the plunger  160 . The stroke limit of the plunger  160  preferably is equal to or slightly larger than the stroke limit of the piston  134 . The piston  134  thus moves fully in the full stroke range FS when the plunger  160  moves to the stopper  162 . The fully extended position of the piston  134  is indicated by the phantom line of FIG.  2 . 
   With reference to  FIGS. 2 and 3 , the solenoid  108  is energized when an ON signal is provided from the ECU  76  and is de-energized when an OFF signal is provided or when the ON signal is not provided. An electric power supply device such as, for example, a battery, preferably is provided to supply electric power at least to the ECU  76  and the solenoid  108 . The solenoid  108  actuates the plunger  160  while energized and releases the plunger  160  while de-energized. 
   Preferably, the ECU  76  provides the solenoid  108  with a sequential control command in which a high voltage part and a low voltage part alternately and repeatedly appear, which is also known as a “duty cycle”. The high voltage part corresponds to the ON signal and the low voltage part corresponds to the OFF signal. 
   In the preferred embodiment, the lubrication pump  98  periodically pressurizes the lubricant  100  under control of the ECU  76 . Preferably, the ECU  76  determines a frequency of periodic pressurization for the lubrication pump  98  and also determines a pressurization time of the lubrication pump  98 , described in greater detail below. 
   With continued reference to  FIGS. 2 and 3 , in an initial state, the piston  134  stays at the initial position as indicated by the solid line of FIG.  2  and the lubricant  100  fills the remainder space in the cavity  130 . The inlet and outlet ports  140 ,  142  are closed and the lubricant  100  is not sucked into the cavity  130  nor supplied to the intake passages  60  as indicated by the phrase “STOP” of FIG.  3 . 
   The piston  134  moves toward the inlet and outlet ports  140 ,  142  from the initial position as indicated by the arrow A of  FIG. 2  when the solenoid  108  is energized and the plunger  160  pushes the piston  134 . The piston  134  in this state is indicated by the arrow of  FIG. 3  having the phrase “EXTENDING.” The piston  134  pressurizes the lubricant  100  in the cavity  130 . The lubricant  100  in the cavity  130  thus moves out through each outlet port  142  toward the intake passage  60  because each check valve  156  opens. That is, the lubricant  100  is supplied to the intake passages  60  as indicated by the phrase “SUPPLY” of FIG.  3 . The check valve  150  still closes at this moment. 
   The piston  134  comes to a standstill despite the solenoid  108  is still energized because the piston  134  has moved to the fully extended position in the stroke range FS indicated by the phantom line of FIG.  2 . The phrase “STANDSTILL” of  FIG. 3  indicates this state of the piston  134  when in the fully extended position. The lubricant  100  thus is no longer supplied to the intake passages  60  as indicated by the phrase “NO SUPPLY” of FIG.  3 . 
   Then, the piston  134  returns back to the initial position under the force of the spring  138 , as indicated by the arrow B of  FIG. 2  when the solenoid  108  is de-energized to release the plunger  160 . The phrase “RETRACTING” of  FIG. 3  indicates the movement of the piston  134  under the force of the spring  138 . The check valve  150  opens due to the reduced pressure caused by the retracting movement of the piston  134 . The retracting movement of the piston  134  also draws lubricant  100  is into the cavity  130  through the lubricant supply passage  102 , as indicated by the phrase “SUCK” of FIG.  3 . Additionally, the reduced pressure in the chamber  130  causes the check valves  152  to close. 
   The solenoid  108  is remains de-energized for period of time, after the piston  134  has been retracted to the fully retracted position After this period of time, the solenoid  108  again is energized when the ON signal is provided by the ECU  76  as shown in FIG.  3 . The ECU  76  causes the pump  98  to repeat these movements during operation of the engine  34 . 
   As thus described, during an ON signal, the time corresponding to the state identified as “EXTENDING” (i.e., the time over which the piston  134  moves from the fully retracted position to the fully extended position is the foregoing pressurization time of the lubrication pump  98 . In general, the pressurization time can vary. In other words, the piston  134  can reach the fully moved position faster under a certain condition, while the piston  134  can reach the fully moved position slower under a certain condition. The dotted arrow H of the state of the phrase “EXTENDING” of  FIG. 3  indicates the faster movement. The one dot chain arrow J of the state of the phrase “EXTENDING” of  FIG. 3  indicates the slower movement. 
   The speed of the piston  134  depends on, for example, the viscosity of the lubricant  100  or the internal pressure of the component to which the lubricant pump  98  injects the lubricant  100 . The component can the intake passage  60  or the crankcase chamber in this embodiment. Thus, a higher viscosity of the lubricant  100  inhibits the piston  134  from moving faster. Similarly, a higher internal pressure inhibits the piston  134  from moving faster. If, however, the internal pressure is negative pressure, the pressure assists the piston  134  rather than inhibiting it. If the piston  134  reaches the fully extended position more quickly, the time corresponding to the “STANDSTILL” state can be longer. If the piston  134  reaches the fully moved position more slowly, the time corresponding to the state “STANDSTILL” can be shorter. 
     FIG. 3  also illustrates a range of unit time UT that varies depending on a frequency or cycle of the sequential control command that includes the ON signal and the OFF signal alternating with another. An amount Q of the lubricant  100  injected by the lubrication pump  98  per unit time UT is in proportion to the frequency of the sequential control command. The frequency can vary. The frequency preferably is determined by the ECU  76  such that the lubricant amount Q is generally optimum to lubricate engine portions at every moment. 
   The lubricant amount Q per unit time UT can be calculated by multiplying an amount of the lubricant  100  moved out from the cavity  130  for each stroke of the piston  134  by a frequency of the sequential control command (i.e., the number of times the piston  134  completes a “SUPPLY” movement within the time UT). That is, if the amount of the lubricant  100  moved out from the cavity  130  per one stroke of the piston  134  is given by the reference Qa and the frequency of the sequential control command is given by the reference F, the lubricant amount Q is calculated by the following equation:
 
Q=Qa×F
 
   In this preferred embodiment, the ECU  76  can calculate a desired lubricant amount Q using a lubricant amount calculation map  166  shown in FIG.  4 . That is, the lubricant amount Q can be determined based upon the engine speed N and the engine load. In this embodiment, the engine load is the throttle valve position Th?. As described above, the engine speed N is calculated by the ECU  76  using the crankshaft angle position sensed by the crankshaft angle position sensor  112 . The engine load or throttle valve position Th? is provided by the throttle valve position sensor  114 . The intake pressure or the air amount sensed by the intake pressure sensor or the air amount sensor, respectively, can be used instead of the throttle valve position to represent the engine load. 
   With reference to  FIG. 4 , the lubricant amount calculation map  166  provides various lubricant amounts Q ranging from extremely small, small, medium, large and extremely large amounts in accordance with the engine speed N and the engine load Th?. In general, the lubricant amount Q is extremely small when both the engine speed N and the engine load Th? are low. On the other hand, the lubricant amount Q is extremely large generally when both the engine speed N and the engine load Th? are high. 
   The phantom line C shows a typical change of the lubricant amount Q regarding the engine  34  of the outboard motor  30 . The area under the line C generally represents a low load area relative to the engine speed N, while the area above the line C generally represents a high load area relative to the engine speed N. 
   The ECU  76  can also be configured to calculate a desired frequency F. For example, the ECU  76  can be configured to calculate the frequency F using an equation F=Q/Qa derived from the equation set forth above, Q=Qa×F. In a preferred embodiment, the ECU  76  uses a frequency control map (not shown) in which a specific frequency F is given if a particular lubricant amount Q is specified. 
   The lubricant amount Q in the lubricant amount calculation map  166  is an amount of the lubricant  100  that is desired under a normal temperature condition. For example, the normal temperature is approximately 17° C. During operation, the lubricant amount Q varies in accordance with the temperature T L  of the lubricant  100  because the viscosity of the lubricant  100  changes in accordance with the temperature T L  of the lubricant  100 . For example, if the temperature T E  of the engine  34  is low and accordingly the lubricant temperature T L  also is low, it is desirable that the amount of the lubricant  100  is greater than the lubricant amount Q because the viscosity of the lubricant  100  is greater. 
   In general, the lower the lubricant temperature T L , the higher the viscosity, although the viscosity does not vary linearly relative to the lubricant temperature T L . If the viscosity is high, the lubricant  100  is difficult to pump and thus more difficult to move toward the engine  34  because the lubricant  100  can behave like a lump or mass that prevents smooth flow of the lubricant  100 . Thus, the lubrication system  94  requires a larger amount of lubricant when the lubricant temperature T L  is low rather than when the lubricant temperature T L  is high. The ECU  76  thus adjusts the frequency F in accordance with the lubricant temperature T L . Preferably, the ECU  76  calculates an adjusted frequency F A  using an adjustment coefficient. 
     FIG. 5  illustrates an adjustment coefficient calculation map  168  that is used by the ECU  76  in this embodiment. The lubricant temperature T L  varies generally in accordance with the engine temperature T E . The ECU  76  thus can use an adjustment coefficient K E  in connection with the engine temperature T E  instead of an adjustment coefficient K L  in connection with the lubricant temperature T L . 
   The adjustment coefficient calculation map  168  provides a specific adjustment coefficient K E  corresponding to a specific engine temperature T E . Generally, the coefficient K E  becomes smaller when the engine temperature T E  becomes higher as shown in FIG.  5 . The coefficient K E  is “1” generally at the engine temperature T E  is 17° C. The engine temperature T E  is sensed by the engine temperature sensor  118 . The ECU  76  calculates the adjusted frequency F A  by multiplying the frequency F by the adjustment coefficient K E . That is, the adjustment equation is indicated as follows:
 
 F   A   =F×K   E 
 
   The ECU  76  can, of course, use an adjustment coefficient K L  in connection with the lubricant temperature T L . The adjustment coefficient calculation map  168  of  FIG. 5  also shows the relationship between the adjustment coefficient K L  and the lubricant temperature T L  because the relationship therebetween is quite similar to the relationship between the adjustment coefficient K E  and the engine temperature T E . In this alternative, the adjustment coefficient calculation map  168  provides a specific adjustment coefficient K L  corresponding to a specific lubricant temperature T L . The lubricant temperature T L  can be sensed by he lubricant temperature sensor  116 . Also, the ECU  76  calculates the adjusted frequency F A  by multiplying the frequency F by the adjustment coefficient K L . That is, the adjustment equation is indicated as follows:
 
 F   A   =F×K   L 
 
   In one variation, the ECU  76  can calculate an adjusted lubricant amount using the adjustment coefficient K E  or K L . That is, the adjusted lubricant amount can be obtained by multiplying the lubricant amount Q by the adjustment coefficient K E  or K L  as follows:
 
 Q   A   =Q×K   E  or  K   L  ( Q   A : adjusted lubricant amount)
 
Then, the ECU  76  can calculate the adjusted frequency F A  based upon the adjusted lubricant amount.
 
   With the frequency F A  desired frequency determined, the ECU  76  can be configured to further calculate the duration T ON  of the ON signal to vary the duration T ON  in accordance with the environmental conditions. 
   Preferably, the duration T ON  of the ON signal is precisely equal to the pressurization time, which corresponds to the state “EXTENDING” of the pumping piston  34  (FIG.  3 ), and the time of “STANDSTILL” is eliminated, because the solenoid  108  merely wastes the electric power during the time of “STANDSTILL.” As described above, the pressurization time varies in response to, for example, the viscosity of the lubricant  100  or the pressure inside of the intake passages  60  or the crankcase chamber. Accordingly, the ECU  76  further calculates the duration T ON  of the ON signal. Thus, at least some of the “STANDSTILL” can be eliminated, thereby saving electric power and reducing the total energization time of the solenoid  108 . 
     FIG. 6  illustrates a method that can be used to control the pump  98 . In the illustrated embodiment, the method is represented by a flow chart, which is used to represent decisions and operations of a control routine  172 . It is to be noted that the various portions of the method described below, including decisions and operations, can be performed in orders different from that described below. Generally, the control routine  172  can be used to operate the ECU  72  to determine the lubricant amount Q and the frequency F, to adjust the frequency F, to determines the duration T ON  of the ON signal, and to command the lubrication pump  134  to operate in accordance with the determinations. 
   The routine  172  starts and proceeds to a step S 1 . In the step S 1 , the ECU  76  reads a reference duration of the ON signal at the step S 1  and stores the duration of the ON signal in a proper storage area of the storage. For example, the reference ON duration can be a predetermined duration that will provide satisfactory operation of the pump  98  under all operating conditions. The reference duration corresponds to the solid line arrow identified as “ENERGIZED” and “Ton” in the solenoid control signal in FIG.  3 . This reference duration can be constant. After the step S 1 , the routine  172  then proceeds to a step S 2 . 
   At the step S 2 , the engine speed and the engine load is determined. For example, the ECU  76  can calculate the engine speed N based upon the output of the crankshaft angle position sensor  112 . Additionally, the ECU  76  can determine the engine load based on the throttle vale position Th? from the output of the throttle valve position sensor  114 . The ECU  76  stores the engine speed N and the engine load Th? in a proper storage area of the storage device of the ECU  72 . The routine  172  then proceeds to a step S 3 . 
   At the step S 3 , the engine temperature is determined. For example, the ECU  76  can read the engine temperature T E  from the engine temperature sensor  118 . Preferably, the ECU  76  stores the engine temperature T L  in a proper storage area of the storage device. The routine  172  then proceeds to a step S 4 . 
   At the step S 4 , the lubricant temperature T L  is determined. For example, the ECU  76  can read the lubricant temperature T L  from the lubricant temperature sensor  116 . Preferably, the ECU  76  and stores the lubricant temperature T L  in a proper storage area of the storage device. The routine  172  then proceeds to a step S 5 . 
   At the step S 5 , a desired lubricant amount Q is determined. For example, The ECU  76 , can calculate the desired lubricant amount Q using the lubricant amount calculation map  166  of FIG.  4  and based upon the engine speed N and the engine load Th? stored in the storage area of the storage device. Preferably, the ECU  76  stores the lubricant amount Q in a proper storage area of the storage device. The routine  172  then proceeds to a step S 6 . 
   At the step S 6 , a desired frequency F of operation of the pump  98  is determined. For example, the ECU  76  can calculate the frequency F using the frequency calculation map (not shown) and based upon the lubricant amount Q stored in the storage area of the storage. Additionally, ECU  76  preferably stores the frequency F in a proper storage area of the storage device. The routine  172  then proceeds to a step S 7 . 
   At the step S 7 , the adjustment coefficient K E  or the adjustment coefficient K L  is determined. For example, the ECU  76  can calculate the adjustment coefficient K E  or the adjustment coefficient K L  based upon the engine temperature T E  or the lubricant temperature T L , respectively, using the adjustment coefficient calculation map  168  of FIG.  5 . In this embodiment, the ECU  76  calculates the adjustment coefficient K E . Then, the ECU  76  calculates the adjusted frequency F A  using the adjustment coefficient K E  and replaces the stored frequency F by the adjusted frequency F A . The routine  172  then proceeds to a step S 8 . 
   At the step S 8 , a reduced duration time T ON  is determined. For example, the ECU  76  can calculate the adjusted duration T ON  of the ON signal. In a preferred embodiment, the ECU  76  can calculate the adjusted duration T ON  using a duration calculation map  176  of  FIG. 7  or a duration calculation map  178  of FIG.  8 . If the lubrication pump  98  delivers the lubricant  100  to the intake passages  60 , the ECU  76  uses the duration calculation map  176  of FIG.  7 . If the lubrication pump  98  delivers the lubricant  100  to the crankcase chamber, the ECU  76  uses the duration calculation map  178  of FIG.  8 . 
   Both the duration calculation maps  176 ,  178  are based upon two parameters which are the engine speed and the engine load Th?. That is, the duration calculation maps  176 ,  178  provide various adjusted durations T ON  ranging between extremely short, short, medium, long and extremely long in accordance with the engine speed N and the engine load Th?. In the maps  176 ,  178 , the adjusted duration T ON  generally increases with the engine speed N and/or the engine load Th?. 
   The phantom line D of FIG.  7  and the phantom line G of  FIG. 8  show a typical change of the adjusted duration T ON  of each map  176 ,  178  during operation of the engine  34  of the outboard motor  30 . The adjusted duration T ON  of the ON signal preferably is given in the duration calculation maps  176 ,  178  such that the duration T ON  is equal to or slightly longer than a time in which the piston  134  moves from the initial position to the fully moved position under any conditions of the engine speed N and the engine load Th? (i.e., a time for one stroke of the piston  134 ). 
   The initial reference duration T ON  read in the step S 1  can correspond to the largest area in the maps  176 ,  178 . For example, the area of the medium period in each map  76 ,  78  can be suitable as the reference duration. If the adjusted duration T ON  determined in step S 8  is equal to the reference duration, the ECU  76  keeps the reference duration in the storage device. If the adjusted duration T ON  is different from the reference duration, the ECU  76  replaces the reference duration with the adjusted duration T ON . The routine  172  then proceeds to a step S 9 . 
   In one variation of the routine  172 , the step S 1  can be omitted such that the initial reference duration is not used. In this variation, the adjusted duration T ON  from the duration calculation map  176 ,  178  is stored into the proper storage area of the storage at the step S 8 . 
   In another variation, the duration T ON  can be calculated based upon either the engine speed N or the engine load Th? rather than based upon both of them. Also, in a further variation, the duration T ON  can be calculated based upon either the engine temperature T E  or the lubricant temperature T L , or both of the engine temperature T E  and the lubricant temperature T L , because the viscosity of the lubricant  100  can affect the pressurization time (i.e., the time corresponding to the state “EXTENDING” of FIG.  3  and the time for one stroke of the piston  134 ) as described above. In general, the higher the viscosity of the lubricant  100 , the longer the duration T ON  can be used. Thus, the adjusted duration T ON  can be determined based upon at least one of the engine speed N, the engine load Th?, the engine temperature T E  or the lubricant temperature T L . 
   In such performing such determinations, the ECU  76  can use any maps, equations and other measures for calculation other than the duration calculation map  176 ,  178 . For example, the adjustment coefficient calculation map  168  of  FIG. 5  (either in connection with the engine temperature T E  or the lubricant temperature T L ) is applicable. The adjusted duration T ON  can be calculated by multiplying the reference duration of the ON signal read at the step S 1  by the adjustment coefficient K E  or K L . 
   As described above, the ECU  76  can adjust the frequency F based upon the engine temperature T E  at the step S 7  in this embodiment. Because the viscosity of the lubricant  100  at temperatures under approximately 0° C. can particularly affect the amount of the lubricant  100 , the ECU  76  in this embodiment further adjusts the adjusted frequency F A  referring to the lubricant temperature T L . For instance, the further adjustment can used immediately after the engine  34  is started in a cold atmospheric temperature which is lower than 0° C. 
   Thus, at the step S 9 , it is determined whether the lubricant temperature T L  is equal to or less than 0° C. For example, the ECU  76  can determine whether the lubricant temperature T L  is equal to or less than 0° C. If the determination at the step S 9  is negative, the ECU  76  recognizes that the further adjustment to the frequency is not necessary and the routine  172  proceeds to a step S 10 . The ECU  76  executes the adjusted frequency F A  (or the frequency F if under the normal temperature condition) and the adjusted duration T ON  to control the solenoid actuator  108 . The routine  172  then returns back to the step S 1  to repeat the routine of the routine  172 . 
   If the determination at the step S 9  is positive, the routine  172  proceeds to a step S 11 . At the step S 11 , the adjustment coefficient K L  is determined. For example, the ECU  76  can calculate the adjustment coefficient K L  based upon the lubricant temperature T L  using the adjustment coefficient calculation map  168  of  FIG. 5  that is related to the lubricant temperature T L . Then, the ECU  76  calculates a further adjusted frequency F AA  using the adjustment coefficient K L  and replaces the stored frequency F or the stored adjusted frequency F A  by the further adjusted frequency F AA . Then, the routine  172  proceeds to the step S 10  to execute the further adjusted frequency F AA  and the adjusted duration T ON  to control the solenoid actuator  108 . The routine  172  returns back to the step S 1  to repeat the routine of the routine  172 . 
   In one variation, the ECU  76  calculates, at the step S 7 , the adjustment coefficient K L  based upon the lubricant temperature T L  using the adjustment coefficient calculation map  168  of  FIG. 5  that is related to the lubricant temperature T L . The steps S 9  and S 11  can be omitted in this variation. 
   It should be noted that the adjusted duration T ON  executed at the step S 10  is not a fixed value and varies as calculated at the step S 8  in this embodiment. 
   Also, in this embodiment, the same amount of the lubricant  100  is delivered to the fuel delivery unit  82  from the additional outlet ports  142  of the lubrication pump  98  through the lubricant delivery passage  106 . This lubricant  100  is mixed with the fuel  72  and will be injected into the combustion chambers with the fuel  72  by the fuel injectors  74 . Alternatively, if the lubricant  100  to the fuel delivery unit  82  is pressurized by another pump, the amount of lubricant  100  to the fuel delivery unit  82  can be different from the lubricant amount injected into the intake passages  60 . 
   In preferred embodiment described above, the duration T ON  of the ON signal varies in accordance with at least one of the engine speed N, the engine load Th?, the engine temperature T E  or the lubricant temperature T L . This is advantageous because the time of “STANDSTILL” of  FIG. 3  can be shortened as short as possible or be completely eliminated. Thus, the electric power will not be wasted to uselessly keep the solenoid actuator  108  in the activated state. 
   Generally, the duration T ON  in the arrangement that the lubricant  100  is delivered to the intake passage  60  (shown in actual line of  FIG. 1 ) can be shorter than the arrangement that the lubricant  100  is delivered to the crankcase chamber (shown in phantom line of  FIG. 1 ) because the negative pressure in the intake passage  60  is greater than the negative pressure in the crankcase chamber. That is, the negative pressure can assist the injection of the lubricant  100  rather than inhibit the injection thereof. Accordingly, the duration T ON  in the duration calculation map  176  is shorter than the duration T ON  in the duration calculation map  178 . For a similar reason, the duration T ON  when the throttle valve open degree is small can be shorter than the duration T ON  when the throttle valve open degree is large under the same engine speed condition because the negative pressure when the throttle valve open degree is small is larger than the negative pressure when the throttle valve open degree is large. 
   As thus described, the lubrication system  94  in the preferred embodiment can provide an appropriate amount of lubricant to the engine portions in every engine operation. Additionally, because of the appropriate amount of lubricant, white smoke can be reduced the discharged exhaust gases. 
   A similar lubrication system for a two-cycle engine is disclosed in, for example, a co-pending U.S. application filed May 15, 2003, titled LUBRICATION SYSTEM FOR TWO-CYCLE ENGINE, which serial number is 10/439,049, the entire contents of which is hereby expressly incorporated by reference. 
   Although this invention has been disclosed in the context of a certain preferred embodiment and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiment to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while several variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combination or sub-combinations of the specific features and aspects of the embodiments or variations may be made and still fall within the scope of the invention. It should be understood that various features and aspects of the disclosed embodiment can be combined with or substituted for one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein-disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.