Abstract:
An oil pressure control warning system for an outboard motor which uses timers dependent on various predetermined oil pressures to correctly determine actual harmful lubrication deficiencies and warn the operator of such lubrication deficiencies. The alarm warning can include an audible and visual operation and is turned off as soon as the correct oil pressure is resumed.

Description:
PRIORITY INFORMATION 
     This application is based on and claims priority to Japanese Patent Application No. 2001-132607, filed Apr. 27, 2001 and to the Provisional Application No. 60/322,239, filed Sep. 13, 2001, the entire contents of which is hereby expressly incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to an oil pressure system for an engine, and more particularly to an oil pressure monitoring system to warn the operator of an inadequate lubrication pressure in a watercraft engine. 
     DESCRIPTION OF THE RELATED ART 
     Watercraft engines typically incorporate lubrication systems. The lubrication system embodies an oil pump driven by the engine and provides lubricant under pressure to vital moving parts throughout the engine. The lubricant acts to lubricate as well as help cool these vital moving parts of the engine. 
     Watercraft may operate in rough water environments. The oil pump in the lubrication system may suck up air instead of the intended lubricant because the oil is being pushed away from the oil pump suction passage during rough operation. The importance of the lubrication system is essential and therefore many lubrication systems incorporate a monitoring system with an alarm in order to warn the operator if the oil pressure is inadequate to safely lubricate the engine. 
     SUMMARY OF THE INVENTION 
     Certain reductions in oil pressure are more essential to the correct engine operation than others. For example, a small drop or short reduction in oil pressure at low engine speed is less vital to the engine than if there is a lack of lubrication pressure for prolonged periods of time at higher engine speeds. 
     One aspect of the invention is a lubrication control system wherein the oil pressure is accurately monitored for the higher engine speeds and operational environments in order to provide the operator with a precise condition of the lubrication system. Such an advanced lubrication control system allows for a long, maintenance free engine life. 
     Another aspect of the present invention is to accurately monitor the engine lubrication pressure and compare the measured pressure with a calculated pressure dependent on engine speed, engine temperature, and oil temperature. A further aspect of the present invention further sets oil pressure limits each corresponding to a timer. The operator is given warning if the oil pressure falls below a set limit for an extended period of time as set by a corresponding limit timer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features, aspects, and advantages of the present invention will now be described with reference to the drawings of a preferred embodiment that is intended to illustrate and not to limit the invention. The drawings comprise eleven figures in which: 
     FIG. 1 is a side elevational view of an outboard motor configured in accordance with a preferred embodiment of the present invention, with an associated watercraft partially shown in section; 
     FIG. 2 is a side elevational view of an upper section of an outboard motor configured in accordance with a preferred embodiment of the present invention, with various parts shown in phantom; 
     FIG. 3 is a top view of an outboard motor configured in accordance with a preferred embodiment of the present invention, with various parts shown in phantom; 
     FIG. 4 is a schematic diagram of the electronic control unit and its control parameters; 
     FIG. 5 is a top view of an outboard motor configured in accordance with a preferred embodiment of the present invention, with various electronically controlled parameters shown; 
     FIG. 6 is a graphical view showing engine oil pressure with reference to engine speed; 
     FIG. 7 is a graphical view showing the relationship between the oil pressure sending unit output voltage and the engine oil pressure; 
     FIG. 8 is a graphical view showing the relationship between timer values and engine oil pressure; 
     FIG. 9 is a graphical view showing various engine oil pressures with reference to time; 
     FIG. 10 is a flowchart representing a control routine arranged and configured in accordance with certain features, aspects, and advantages of the present invention; and 
     FIG. 11 is a flowchart representing another control routine arranged and configured in accordance with certain features, aspects, and advantages of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The Overall Construction 
     With reference to FIGS. 1-5, an outboard motor  10  includes a drive unit  12  and a bracket assembly  14 . The bracket assembly  14  attaches the drive unit  12  to a transom  16  of an associated watercraft  18  and supports a marine propulsion device such as propeller  57  in a submerged position relative to a surface of a body of water. 
     As used to this description, the terms “forward,” “forwardly,” and “front” mean at or to the side where the bracket assembly  14  is located, unless indicated otherwise or otherwise readily apparent from the context use. The terms “rear,” “reverse,” “backwardly,” and “rearwardly” mean at or to the opposite side of the front side. 
     The illustrated drive unit  12  includes a power head  20  and the housing unit  22 . Unit  22  includes a drive shaft housing  24  and the lower unit  26 . The power head  20  is disposed atop the housing unit  22  and includes an internal combustion engine  28  within a protective cowling assembly  30 , which advantageously is made of plastic. The protective cowling assembly  30  typically defines a generally closed cavity  32  in which the engine  28  is disposed. The engine  28  is thereby is generally protected by the cowling assembly  30  from environmental elements. 
     The protective cowling assembly  30  includes a top cowling member  34  and a bottom cowling member  36 . The top cowling member  34  is advantageously detachably affixed to the bottom cowling member  36  by a suitable coupling mechanism to facilitate access to the engine and other related components. 
     The top cowling member  34  includes a rear intake opening (not shown) defined from an upper end portion. This rear intake member with one or more air ducts can, for example, be formed with, or affixed to, the top cowling member  34 . The rear intake member, together with the upper rear portion of the top cowling member  34 , generally defines a rear air intake space. Ambient air is drawn into the closed cavity  32  near the rear intake opening and the air ducts of the rear intake member. Typically, the top cowling member  34  tapers in girth toward its top surface, which is in the general proximity of the air intake opening. This taper reduces the lateral dimension of the outboard motor, which helps to reduce the air drag on the watercraft  18  during movement. 
     The bottom cowling member  36  has an opening for which an upper portion of an exhaust guide member  38  extends. The exhaust guide member  38  advantageously is made of aluminum alloy and is affixed to the top of the driveshaft housing  24 . The bottom cowling member  36  and the exhaust guide member  38  together generally form a tray. The engine  28  is placed on to this tray and can be connected to the exhaust guide member  38 . The exhaust guide member  38  also defines an exhaust discharge passage through which burnt charges (e.g., exhaust gases) from the engine  28  pass. 
     The engine  28  in the illustrated embodiment preferably operates on a four-cycle combustion principle. With reference now to FIGS. 2 and 3, the engine embodiment illustrated is a DOHC six-cylinder engine having a V-shaped cylinder block  40 . The cylinder block  40  thus defines two cylinder banks, which extend generally side by side with each other. In the illustrated arrangement, each cylinder bank has three cylinder bores such that the cylinder block  40  has six cylinder bores in total. The cylinder bores of each bank extend generally horizontally and are generally vertically spaced from one another. This type of engine, however, merely exemplifies one type of engine. Engines having other numbers of cylinders, having other cylinder arrangements (in line, opposing, etc.), and operating on other combustion principles (e.g., crankcase compression, two-stroke or rotary) can be used in other embodiments. 
     As used in this description, the term “horizontally” means that members or components extend generally and parallel to the water surface (i.e., generally normal to the direction of gravity) when the associated watercraft  18  is substantially stationary with respect to the water surface and when the drive unit  12  is not tilted (i.e., as shown in FIG.  1 ). The term “vertically” in turn means that proportions, members or components extend generally normal to those that extend horizontally. 
     A movable member, such as a reciprocating piston, moves relative to the cylinder block  40  in a suitable manner. In the illustrated arrangement, a piston (not shown) reciprocates within each cylinder bore. Because the cylinder block  40  is split into the two cylinder banks, each cylinder bank extends outward at an angle to an independent first end in the illustrated arrangement. A pair of cylinder head members  42  are fixed to the respective first ends of the cylinder banks to close those ends of the cylinder bores. The cylinder head members  42  together with the associated pistons and cylinder bores provide six combustion chambers (not shown). Of course, the number of combustion chambers can vary, as indicated above. Each of the cylinder head member  42  is covered with the cylinder head cover member  44 . 
     A crankcase member  46  is coupled with the cylinder block  40  and a crankcase cover member  48  is further coupled with a crankcase member  46 . The crankcase member  46  and a crankcase cover member  48  close the other end of the cylinder bores and, together with the cylinder block  40 , define the crankcase chamber. Crankshaft  50  extends generally vertically through the crankcase chamber and journaled for rotation about a rotational axis by several bearing blocks. Connecting rods couple the crankshaft  50  with the respective pistons in any suitable manner. Thus, a reciprocal movement of the pistons rotates the crankshaft  50 . 
     With reference again to FIG. 1, the driveshaft housing  24  depends from the power head  20  to support a drive shaft  52 , which is coupled with crankshaft  50  and which extends generally vertically through driveshaft housing  24 . A driveshaft  52  is journaled for rotation and is driven by the crankshaft  50 . 
     The lower unit  26  depends from the driveshaft housing  24  and supports a propulsion shaft  54  that is driven by the driveshaft  52  through a transmission unit  56 . A propulsion device is attached to the propulsion shaft  54 . In the illustrated arrangement, the propulsion device is the propeller  57  that is fixed to the transmission unit  56 . The propulsion device, however, can take the form of a dual counter-rotating system, a hydrodynamic jet, or any of a number of other suitable propulsion devices. 
     Preferably, at least three major engine portions  40 ,  42 ,  44 ,  46 , and  48  are made of aluminum alloy. In some arrangements, the cylinder head cover members  44  can be unitarily formed with the respective cylinder members  42 . Also, the crankcase cover member  48  can be unitarily formed with the crankcase member  46 . 
     The engine  28  also comprises an air intake system  58 . The air intake system  58  draws air from within the cavity  32  to the combustion chambers. The air intake system  58  shown comprises six intake passages  60  and a pair of plenum chambers  62 . In the illustrated arrangement, each cylinder bank communicates with three intake passages  60  and one plenum chamber  62 . 
     The most downstream portions of the intake passages  60  are defined within the cylinder head member  42  as inner intake passages. The inner intake passages communicate with the combustion chambers through intake ports, which are formed at inner surfaces of the cylinder head members  42 . Typically, each of the combustion chambers has one or more intake ports. Intake valves are slidably disposed at each cylinder head member  42  to move between an open position and a closed position. As such, the valves act to open and close the ports to control the flow of air into the combustion chamber. Biasing members, such as springs, are used to urge the intake valves toward their respective closed positions by acting between a mounting boss formed on each cylinder head member  42  and a corresponding retainer that is affixed to each of the valves. When each intake valve is in the open position, the inner intake passage thus associated with the intake port communicates with the associated combustion chamber. 
     Other portions of the intake passages  60 , which are disposed outside of the cylinder head members  42 , preferably are defined with intake conduits  64 . In the illustrated arrangement, each intake conduit  64  is formed with two pieces. One piece is a throttle body  66 , in which a throttle valve assembly  68  is positioned. Throttle valve assemblies  68  are schematically illustrated in FIG.  2 . The throttle bodies  66  are connected to the inner intake passages. Another piece is an intake runner  70  disposed upstream of the throttle body  66 . The respective intake conduit  64  extend forwardly alongside surfaces of the engine  28  on both the port side and the starboard side from the respective cylinder head members  42  to the front of the crankcase cover member  48 . The intake conduits  64  on the same side extend generally and parallel to each other and are vertically spaced apart from one another. 
     Each throttle valve assembly  68  preferably includes a throttle valve. Preferably, the throttle valves are butterfly valves that have valve shafts journaled for pivotal movement about generally vertical axis. In some arrangements, the valve shafts are linked together and are connected to a control linkage. The control linkage is connected to an operational member, such as a throttle lever, that is provided on the watercraft or otherwise proximate the operator of the watercraft  18 . The operator can control the opening degree of the throttle valves in accordance with operator request through the control linkage. That is, the throttle valve assembly  68  can measure or regulate amounts of air that flow through intake passages  60  through the combustion chambers in response to the operation of the operational member by the operator. Normally, the greater the opening degree, the higher the rate of air flow and the higher the engine speed. 
     The respective plenum chambers  62  are connected with each other through one or more connecting pipes  72  (FIG. 3) to substantially equalize the internal pressures within each chamber  62 . The plenum chambers  62  coordinate or smooth air delivered to each intake passage  60  and also act as silencers to reduce intake noise. 
     The air within the closed cavity  32  is drawn into the plenum chamber  62 . The air expands within the plenum chamber  62  to reduce pulsations and then enters the outer intake passages  60 . The air passes through the outer intake passage  60  and flows into the inner intake passages. The throttle valve assembly  68  measures the level of airflow before the air enters into the inner intake passages. 
     The engine  28  further includes an exhaust system that routes burnt charges, i.e., exhaust gases, to a location outside of the outboard motor  10 . Each cylinder head member  42  defines a set of inner exhaust passages that communicate with the combustion chambers to one or more exhaust ports which may be defined at the inner surfaces of the respective cylinder head members  42 . The exhaust ports can be selectively opened and closed by exhaust valves. The construction of each exhaust valve and the arrangement of the exhaust valves are substantially the same as the intake valve and the arrangement thereof, respectively. Thus, further description of these components is deemed unnecessary. 
     Exhaust manifolds preferably are defined generally vertically with the cylinder block  40  between the cylinder bores of both the cylinder banks. The exhaust manifolds communicate with the combustion chambers through the inner exhaust passages and the exhaust ports to collect the exhaust gas therefrom. The exhaust manifolds are coupled with the exhaust discharge passage of the exhaust guide member  38 . When the exhaust ports are opened, the combustion chambers communicate with the exhaust discharge passage through the exhaust manifolds. A valve cam mechanism preferably is provided for actuating the intake and exhaust valves in each cylinder bank. In the embodiment shown, the valve cam mechanism includes second rotatable members such as a pair of camshafts  74  per cylinder bank. The camshafts  74  typically comprise intake and exhaust camshafts that extend generally vertically and are journaled for rotation between the cylinder head members  42  and the cylinder head cover members  44 . The camshafts  74  have cam lobes (not shown) to push valve lifters that are fixed to the respective ends of the intake and exhaust valves in any suitable manner. Cam lobes repeatedly push the valve lifters in a timely manner, which is in proportion to the engine speed. The movement of the lifters generally is timed by rotation of the camshaft  74  to appropriately actuate the intake and exhaust valves. 
     The camshaft drive mechanism  76  preferably is provided for driving the valve cam mechanism. The camshaft drive mechanism  76  in the illustrated arrangement is formed above a top surface  78  (see FIG. 2) of the engine  28  and includes driven sprockets  80  positioned atop at least one of each pair of camshafts  74 , a drive sprocket  82  positioned atop the crankshaft  50  and the flexible transmitter, such as a timing belt or chain  84 , for instance, wound around the driven sprockets  80  and the drive sprocket  82 . The crankshaft  50  thus drives the respective crankshaft  74  through the time belt  84  in the timed relationship. 
     The illustrated engine  28  further includes indirect, port or intake passage fuel injection. In one arrangement, the engine  28  comprises fuel injection and, in another arrangement, the engine  28  is carburated. The illustrated fuel injection system shown includes six fuel injectors  86  with one fuel injector allotted to each one of the respective combustion chambers. The fuel injectors  86  preferably are mounted on the throttle body  66  of the respective banks. 
     Each fuel injector  86  has advantageously an injection nozzle directed downstream within the associated intake passage  60 . The injection nozzle preferably is disposed downstream of the throttle valve assembly  60 . The fuel injectors  86  spray fuel into the intake passages  60  under control of an electronic control unit (ECU)  88  (FIG.  4 ). The ECU  88  controls both the initiation, timing and the duration of the fuel injection cycle of the fuel injector  86  so that the nozzle spray a desired amount of fuel for each combustion cycle. 
     A vapor separator  90  preferably is in full communication with the tank and the fuel rails, and can be disposed along the conduits in one arrangement. The vapor separator  90  separates vapor from the fuel and can be mounted on the engine  28  at the side service of the port side. 
     The fuel injection system preferably employs at least two fuel pumps to deliver the fuel to the vapor separator  90  and to send out the fuel therefrom. More specifically, in the illustrated arrangement, a lower pressure pump  92 , which is affixed to the vapor separator  90 , pressurizes the fuel toward the vapor separator  90  and the high pressure pump (not shown), which is disposed within the vapor separator  90 , pressurizes the fuel passing out of the fuel separator  90 . 
     A vapor delivery conduit  94  couples the vapor separator  90  with at least one of the plenum chambers  62 . The vapor removed from the fuel supply by the vapor separator  90  thus can be delivered to the plenum chambers  62  for delivery to the combustion chambers with the combustion air. In other applications, the engine  28  can be provided with a ventilation system arranged to send lubricant vapor to the plenum chamber(s). In such applications, the fuel vapor also can be sent to the plenum chambers via the ventilation system. 
     The engine  28  further includes an ignition system. Each combustion chamber is provided with a spark plug  96  (see FIG.  4 ), advantageously disposed between the intake and exhaust valves. Each spark plug  96  has electrodes that are exposed in the associated combustion chamber. The electrodes are spaced apart from each other by a small gap. The spark plugs  96  are connected to the ECU  88  through ignition coils  98 . One or more ignition triggering sensors  100  are positioned around a flywheel assembly  102  to trigger the ignition coils, which in return trigger the spark plugs  96 . The spark plugs  96  generate a spark between the electrodes to ignite an air/fuel charge in the combustion chamber according to desired ignition timing maps or other forms of controls. 
     Generally, during an intake stroke, air is drawn into the combustion chambers through the air intake passages  60  and fuel is mixed with the air by the fuel injectors  86 . The mixed air/fuel charge is introduced to the combustion chambers. The mixture is then compressed during the compression stroke. Just prior to a power stroke, the respective spark plugs ignite the compressed air/fuel charge in the respective combustion chambers. The air/fuel charge thus rapidly burns during the power stroke to move the pistons. The burnt charge, i.e., exhaust gases, then is discharged from the combustion chambers during an exhaust stroke. 
     The flywheel assembly  102 , which is schematically illustrated with phantom line in FIG. 3, preferably is positioned atop the crankshaft  50  and is positioned for rotation with the crankshaft  50 . The flywheel assembly  102  advantageously includes a flywheel magneto for AC generator that supplies electric power directly or indirectly via a battery to various electrical components such as the fuel injection system, the ignition system and the ECU  88 . An engine cover  104  preferably extends over almost all of the engine  28 , including the flywheel assembly  102 . 
     In the embodiment of FIG. 1, the driveshaft housing  24  defines an internal section of the exhaust system that leaves the majority of the exhaust gases to the lower unit  26 . The internal section includes an idle discharge portion that extends from a main portion of the internal section to discharge idle exhaust gases directly to the atmosphere through a discharge port that is formed on a rear surface of the driveshaft housing  24 . 
     Lower unit  26  also defines an internal section of the exhaust system that is connected with the internal exhaust section of the driveshaft housing  24 . At engine speeds above idle, the exhaust gases are generally discharged to the body of water surrounding the outboard motor  10  through the internal sections and then a discharge section defined within the hub of the propeller  57 . 
     The engine  28  may include other systems, mechanisms, devices, accessories, and components other than those described above such as, for example, a cooling system. The crankshaft  50  through a flexible transmitter, such as timing belt  84  can directly or indirectly drive those systems, mechanisms, devices, accessories, and components. 
     The Oil Pressure Control System 
     The illustrated engine includes a lubrication system to lubricate the moving parts within the engine  28 . The lubrication system is a pressure fed system for lubricating the bearings and other rotating surfaces. The oil pressure control system described informs the operator of the status of the lubrication pressure in the engine and sounds an alarm if there is inadequate lubrication pressure. 
     Referring to FIG. 5, the lubrication oil is collected from an oil pan  106  within the engine  28  by an oil pump  108  and is delivered under pressure through an oil filter  110 . Referring to FIG. 4, an oil pressure sensor  112  measures the pressure of the lubrication system, which relays the information to the ECU  88 . The lubricating oil may also travel through an oil thermostat and oil cooler in order to maintain a proper lubricating temperature. The oil is then dispersed throughout the engine to lubricate the internal moving parts. The oil pump  108  may be directly driven from the crankshaft  50 . The oil pump  108  may also be driven by, for example, the camshafts  74 , an intermediate shaft, or an auxiliary shaft. 
     As illustrated in FIG. 6, the oil pressure advantageously rises as a function of engine speed. The engine speed is calculated by the ECU using the ignition triggering sensors  100  coupled to ECU  88 . Thus, when the engine  28  is operating at idle or a low speed the corresponding oil pressure is less than when the engine is operating at a higher speed. At increasing engine speeds lubrication pressure becomes more important and vital to long engine life and proper engine operation. 
     The graph of FIG. 7 illustrates the relationship of the oil pressure sensor voltage and the actual pressure of the lubricating system. As the oil pressure rises, the oil pressure sensor voltage rises linearly. This oil pressure sensor voltage accurately represents the actual engine lubrication pressure for constant monitoring by the ECU  88 . 
     The viscosity, or degree of resistance of a substance to oppose displacement forces, of the oil in the engine is higher at cold engine temperatures and decreases as the engine temperature rises. Therefore, the oil pressure will be higher in a cold engine at a particular engine speed than in a warm engine operating at the same speed. In a preferred embodiment the oil pressure control system incorporates an engine temperature sensor  116  located in the engine block  40  as well as oil temperature switches  118 ,  120  in each cylinder head member  42  to properly translate the engine and individual cylinder head temperatures to the ECU  88 . The ECU  88  is programmed to use these temperature value inputs to accurately evaluate proper lubrication pressures for the engine  28 . 
     In one embodiment of the present invention the predetermined oil pressure values are dependent on the engine speed. For example, at higher engine speeds the predetermined oil pressure threshold value is higher because a increased oil pressure is necessary to effectively lubricate and protect the rotating engine components. At a lower engine speed a lower oil pressure threshold is adequate to effectively lubricate and protect the rotating engine components. Therefore, the operator will be correctly warned at every engine speed if an inadequate oil pressure is present. As described above, ECU  88  is coupled to the ignition triggering sensors  108  and is programmed to initiate different oil pressure alarm timed sequences depending upon engine speed. 
     A significant feature of the engine embodiment illustrated is that oil pressure alarm limits are also a function of predetermined time intervals. FIG. 8 illustrates a graph showing how different pressure threshold values, Po, P 1 , and P 2  correspond to different timers To, T 1 , and T 2 . When a particular pressure is detected, the corresponding timer is activated. As the detected oil pressure becomes lower and passes a lower oil pressure threshold, a shorter timer is activated. 
     FIG. 9 illustrates examples of various changing oil pressure values, how the oil pressure control system monitors the oil pressure, and at which point the system triggers an alarm to warn the operator of a lapse of lubrication pressure. At a point  122  when an oil pressure value drops below an initial pressure threshold Po, a corresponding timer To is initiated. By way of specific example, the pressure Po may represent a pressure of 350 kilopascals (kpa) and To sets a predetermined time internal of one second. If the oil pressure remains below the initial pressure Po for the predetermined amount of time designated by the timer To, for example at point  124  one second later than point  122 , an alarm system will be activated to warn the operator of inadequate oil pressure. The warning alarm system may include, but is not limited to, an audible alarm  123  and/or a visual alarm  125 . If, however, during this time internal To, the oil pressure rises above the pressure threshold Po, for example at point  126  on a pressure trace depicted by a dashed line  128 , the timer To is automatically reset and no alarm is activated. 
     In another example shown in FIG. 9, the oil pressure value drops below a second pressure threshold P 1  and a corresponding timer T 1  is initiated. By way of specific example, P 1  may represent a pressure of 300 kpa and T 1  is set to a time corresponding to 0.5 seconds. If during this time internal T 1 , the oil pressure remains below the second pressure P 1  for the predetermined amount of time designated by the timer T 1 , for example at point  132  0.5 seconds later than point  130 , an alarm will be activated to warn the operator of inadequate oil pressure. If, however, during the time interval T 1 , the oil pressure rises above the pressure threshold P 1 , for example at points  134  on pressure traces depicted by dashed lines  128  or  136 , the timer T 1  is reset and no alarm is activated. 
     At yet another point  138  when an oil pressure value drops below a third pressure threshold P 2 , a corresponding timer T 2  is initiated. T 2  can be set to a time corresponding to 0.2 seconds. P 2  may represent a pressure of 250 kpa. If the oil pressure remains below the third pressure P 2  for the predetermined amount of time designated by the timer T 2 , for example at point  140 , an alarm will be activated to properly warn the operator of inadequate oil pressure. If, however the oil pressure at any time after the timer T 2  begins rises above the pressure threshold P 2 , for example at point  142  on the pressure trace depicted by a dashed line  136 , the timer T 2  is reset and no alarm is activated. 
     The flow charts in FIGS. 10 and 11 further illustrate the function of the control system. The first flow chart in FIG. 10 corresponds to the oil pressure system using one pressure threshold to activate an alarm and properly warn the operator of an inadequate lubrication pressure. FIG. 11 shows another flow chart corresponding to the oil pressure system using three pressure thresholds to activate an alarm and properly warn the operator of an inadequate lubrication pressure. 
     FIG. 10 shows a control routine  144  of ECU  88  that is arranged and configured in accordance with certain features, aspects, and advantages of the present invention. The control routine  144  begins and moves to a first operation block P 10  in which the engine oil pressure Pa is measured and stored. Advantageously, the ECU  88  is programmed to perform the oil pressure determination method. The control routine  144  then moves to decision block P 11 . 
     In decision block P 11  it is determined if the measured pressure Pa is less than a threshold pressure Po. If the measured oil pressure Pa is not less than the threshold pressure Po, the control routine returns to the input of block P 10 . If, however, the measured pressure Pa is less than the threshold pressure Po, the control routine  144  moves to operation block P 12 . 
     In operation block P 12 , the timer To is started. The control routine  144  moves to operation block P 13   
     In operation block P 13  a second oil pressure Pb is detected. The control routine  144  moves to a decision block P 14   
     In decision block P 14  the second measured oil pressure Pb is compared to the threshold pressure Po. If the second measured pressure Pb is greater than the threshold pressure Po, the control routine  144  moves to operation block P 15 . If, however the second measured oil pressure Pb is not greater than the threshold pressure Po, the control routine  144  moves to decision block P 16 . 
     In operation block P 15  the timer To is reset and the control routine  144  returns. 
     In decision block P 16  it is determined if timer To has elapsed. If the timer To has not elapsed, the control routine  144  moves to the operation block P 13 . If, however, in decision block P 16  the timer To has elapsed, the control routine  144  moves to operation block P 17 . 
     In operation block P 17  a drop in oil pressure is determined. The control routine  144  moves to operation block P 18 . 
     In operation block P 18  a warning system is initiated. The warning system may contain, but is not limited to, an audible alarm system and/or a visual alarm system. The control routine  144  moves to operation block P 19 . 
     In operation block P 19  the timer To is reset and the control routine  144  returns. 
     FIG. 11 shows a control routine  148  of ECU  88  that is arranged and configured in accordance with certain features, aspects, and advantages of the present invention. The control routine  148  begins and moves to operation block P 20  where an oil pressure Pa is measured and stored. The control routine  148  moves to decision block P 21 . 
     In decision block P 21  it is determined if the measured oil pressure Pa is less than Po. If the measured pressure Pa is not less than the pressure threshold Po, the control routine  148  returns. If, however, the measured oil pressure Pa is less than the threshold pressure Po, the control routine  148  moves to operation block P 22 . 
     In operation block P 22  a timer To is started. The timer To corresponds to the threshold pressure Po. The control routine  148  moves to operation block P 23 . 
     In operation block P 23  a second oil pressure Pb is detected. The operation block  148  moves to decision block P 24 . 
     In decision block P 24  it is determined if the second measured oil pressure Pb is greater than the threshold pressure Po. If the measured oil pressure Pb is greater than threshold pressure Po, the control routine  148  moves to operation block P 25 . If, however, in decision block P 24  it is determined that the measured oil pressure Pb is not greater than the threshold pressure Po, the control routine  148  moves to decision block P 26 . 
     In operation block P 25  the timer To is reset and the control routine  148  returns. 
     In decision block P 26  it is determined if the second measured oil pressure Pb is less than a second threshold pressure P 1 . If the second measured oil pressure Pb is not less than the second oil pressure threshold P 1 , the control routine  148  moves to decision block P 38 . If, however in decision block P 26  the second measured oil pressure Pb is less than the second threshold oil pressure P 1 , the control routine  148  moves to operation block P 27 . 
     In operation block P 27  a timer T 1  is started and the control routine  148  moves to operation block P 28 . 
     In operation block P 28  a third oil pressure Pc is measured. The control routine  148  moves to decision block P 29 . 
     In decision block P 29  it is determined if the third measured oil pressure Pc is greater than the second threshold pressure P 1 . If the third measured oil pressure Pc is greater than the second threshold oil pressure P 1 , the control routine  148  moves to operation block P 30 . If in decision block P 29 , it is determined that the third measured oil pressure PC is not greater than the second threshold pressure P 1 , the operation block P 48  moves to decision block P 31 . 
     In operation block P 30  the timer T 1  is reset and the control routine  148  moves to the decision block P 26 . 
     In decision block P 31  it is determined if the third measured oil pressure Pc is less than the third oil pressure threshold P 2 . If the third measured oil pressure Pc is not less than the third oil pressure threshold P 2 , the control routine  148  moves to decision block P 32 . If the second measured oil pressure Pc is less than the third oil pressure threshold P 2 , the control routine  148  moves to operation block P 33 . 
     In decision block P 32  it is determined if the timer T 1  has elapsed. If the timer T 1  has elapsed, the control routine  148  moves to operation block P 39 . If the timer T 1  has not elapsed, the control routine  148  returns to operation block P 28 . 
     In operation block P 33  a timer T 2  is started and the control routine  148  moves to operation block P 35 . 
     In operation block P 35  a fourth oil pressure Pd is detected and the control routine  148  moves to decision block P 36 . 
     In decision block P 36  it is determined if the fourth measured oil pressure Pd is greater than the third oil pressure threshold P 2 . If the fourth measured oil pressure Pd is greater than the third oil pressure threshold P 2 , the control routine  148  moves to operation block P 34 . If the fourth measured oil pressure Pd is not greater than the third pressure threshold P 2 , the control routine  148  moves to decision block P 37 . 
     In operation block P 34  the timer T 2  is reset and the control routine  148  moves to decision block P 31 . 
     In decision block P 37 , it is determined if the timer T 2  has elapsed. If the timer T 2  has not elapsed, the control routine  148  moves to operation block P 35 . If, however, the timer T 2  has elapsed, the control routine  148  moves to operation block P 39 . 
     In operation block P 39  a drop in oil pressure is determined and the control routine  148  moves to operation block P 40 . 
     In operation block P 40  a warning system is initiated. The warning system may contain, but is not limited to, an audible alarm system and/or a visual alarm system. The control routine  148  moves to operation block P 41 . 
     In operation block P 41  the timers T 0 , T 1 , and T 2  are reset and the control routine  148  returns. 
     It is to be noted that embodiments of the control systems described above may be in the form of a hard-wired feedback control circuits. Alternatively, the control systems may be constructed of a dedicated processor and memory for storing a computer program configured to perform the steps described above in the context of the flowcharts. Additionally, the control systems may be constructed of a general-purpose computer having a general-purpose processor and memory for storing the computer program for performing the routines. Preferably, however, the control systems are incorporated into the ECU  88 , in any of the above-mentioned forms. 
     Although the present invention has been described in terms of a certain preferred embodiments, other embodiments apparent to those of ordinary skill in the art also are within the scope of this invention. Thus, various changes and modifications may be made without departing from the spirit and scope of the invention. For instance, various steps within the routines may be combined, separated, or reordered. In addition, some of the indicators sensed (e.g., engine speed and throttle position) to determine certain operating conditions (e.g., rapid deceleration) can be replaced by other indicators of the same or similar operating conditions. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present invention. Accordingly, the scope of the present invention is intended to be defined only by the claims that follow.