Abstract:
A fuel supply system for an outboard motor regulates the fuel pressure to a vapor separator in a fuel injection system by using a pressure relief valve that returns excess fuel to the intake of the fuel pump. In order to permit excess fuel flow without substantial excess at low speeds, the fuel pump speed is regulated depending upon engine speed, fuel temperature, and fuel pressure.

Description:
PRIORITY INFORMATION 
     This application is based on and claims priority to Japanese Patent Application No. 2000-348863, filed Nov. 15, 2000 and to the Provisional Application No. 60/322,352, filed Sep. 13, 2001, (Attorney Docket No. FS.17314US0PR) the entire contents of which is hereby expressly incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a fuel supply control arrangement for an engine, and more particularly to an improved fuel supply control arrangement for a split-bank, multicylinder engine. 
     DESCRIPTION OF THE RELATED ART 
     It has been the practice in conjunction with fuel injection systems for engines to provide a pressure relief system so that the fuel pressure at the injector is maintained stable. This is important to ensure that the injection strategy results in the injection of the appropriate amount of fuel for proper engine operation. Normally, the fuel pressure is regulated by a pressure relief valve that returns excess fuel supplied to the injectors, their associated fuel rail, or both back to some place in the supply circuit. The excess fuel may be returned directly to the fuel tank or to other locations in the fuel supply system upstream of the injector. 
     In order to have excess fuel for pressure regulation, the amount of fuel supplied to the injectors must be somewhat greater than the total amount of fuel which will be consumed by the engine under all running conditions for which pressure regulation is desired. This supply of excess fuel has certain advantages. 
     If excess fuel is supplied, then it is possible to use the fuel flow to cool certain components of the engine, particularly the fuel injector. Furthermore, by continuously recycling a portion of the fuel, the fuel vapor separator can do a better job of separating vapors from the fuel to ensure that the fuel supplied to the engine is vapor free. Vapors in the fuel will result in the injection of less fuel than desired if the vapors are not separated before delivery to the injectors. 
     It is also known that the fuel pump must supply adequate amounts of fuel for all operating conditions, particularly under high speed and high load conditions. Thus, if a constantly operated pump is employed, large excesses of fuel will be pumped under low speed and low load conditions. The pumping of large excesses of fuel has certain disadvantages. 
     Although circulating excess fuel has the advantage of providing cooling for the fuel, the circulation of to much fuel can heat the fuel such that the desired cooling effect is not achieved. Also, if there are gross differences in the amount of fuel supplied, then the pressure regulator may not be capable of providing the desired regulation at all engine speeds and load ranges. 
     SUMMARY OF THE INVENTION 
     A principal object of the embodiments of the present invention is to provide an improved fuel supply system for an engine. 
     A further object of the embodiments of the present invention is to provide an improved fuel supply system for an internal combustion engine that will provide appropriate slight excesses of fuel supply under all running conditions. 
     The embodiments of the present invention are adapted to be embodied in a fuel supply system for an engine. The fuel supply system includes a tank that stores fuel, a fuel injector that injects the fuel to the engine, and an electrically driven pump that pumps fuel from the tank to the fuel injector through a conduit. A bypass system is provided for returning excess fuel pumped by the fuel pump to the injectors back to a supply side of the system. Means are provided for monitoring engine conditions to detect the amount of fuel being consumed. When the fuel consumption is determined to be lower than a predetermined value, then the electrically driven pump is driven at a lower rate. 
     One aspect of the present invention is a fuel supply system for an internal combustion engine. The fuel supply system provides fuel to the internal combustion engine. The fuel supply system comprises at least one fuel pump driven by an electric motor, and an electronic control unit that controls the electric motor to control the fuel flow through the fuel pump in response to engine speed, fuel temperature and fuel pressure. 
     Preferably, the fuel pump is a low pressure pump supplying the fuel to a vapor separator, wherein the speed of the low pressure fuel pump is controlled by the electronic control unit dependent on engine speed, fuel pressure, and fuel temperature. The engine speed is determined using an engine speed sensor, the fuel temperature is determined using a fuel temperature sensor, and the fuel pressure is determined using a fuel pressure sensor. A fuel pressure relief valve relieves fuel pressure from the pressure side of the low pressure fuel pump and delivers the fuel to the scavenge side of the low pressure fuel pump. Preferably, the fuel pressure sensors and the fuel temperature sensor are located on the pressure side of the low pressure fuel pump and before the pressure relief valve circuit. 
     Within the internal combustion engine, a plurality of fuel injectors are in communication with a high pressure fuel pump being supplied by the vapor separator. The fuel injectors deliver vaporless fuel to at least one intake port or directly into at least one combustion chamber. 
     The internal combustion engine is advantageously a marine engine. For example, the marine engine provides power to a watercraft. In preferred embodiments, the marine engine is an outboard motor. 
    
    
     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 two 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 schematic drawing illustrating the fuel supply control system; and 
     FIG. 3 is a flow chart showing a control routine arranged and configured in accordance with certain features, aspects, and advantages of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates an overall construction of an outboard motor  30  that employs an internal combustion engine  32  configured in accordance with certain features, aspects and advantages of the present invention. The engine  32  has particular utility in the context of a marine drive, such as, for example the outboard motor  30 , and thus is described in the context of an outboard motor. The engine  32 , however, can be used with other types of marine drives (i.e., inboard motors, inboard/outboard motors, etc.) and also with certain land vehicles, which include lawnmowers, motorcycles, go carts, all terrain vehicles, and the like. Furthermore, the engine  32  can be used as a stationary engine for some applications that will become apparent to those of ordinary skill in the art. 
     In the illustrated arrangement, the outboard motor  30  generally comprises a drive unit  34  and a bracket assembly  36 . The bracket assembly  36  supports the drive unit  34  on a transom  38  of an associated watercraft  40  and places a marine propulsion device (e.g., a propeller) in a submerged position with the watercraft  40  resting relative to a surface  42  of a body of water. 
     The illustrated drive unit  34  comprises a power head  58  and a housing unit  60 , which includes a driveshaft housing  62  and a lower unit  64 . The power head  58  is disposed atop the housing unit  60  and includes an internal combustion engine  32  that is positioned within a protective cowling assembly  66 , which preferably is made of plastic. In most arrangements, the protective cowling assembly  66  defines a generally closed cavity  68  in which the engine  32  is disposed. 
     A top cowling member  70  preferably has a rear intake opening  76  defined through an upper rear portion. A rear intake member with one or more air ducts is unitarily formed with or is affixed to the top cowling member  70 . The rear intake member, together with the upper rear portion of the top cowling member  70 , generally defines a rear air intake space. Ambient air is drawn into the closed cavity  68  via the rear intake opening  76  and the air ducts of the rear intake member as indicated by an arrow  78  of FIG.  1 . 
     A bottom cowling member  72  has an opening through which an upper portion of an exhaust guide member or support member  80  extends. The exhaust guide member  80  preferably is made of aluminum alloy and is affixed atop the driveshaft housing  62 . The bottom cowling member  72  and the exhaust guide member  80  together generally form a tray. The engine  32  is placed onto this tray and can be affixed to the exhaust guide member  80 . The exhaust guide member  80  also defines an exhaust discharge passage through which burnt charges (e.g., exhaust gases) from the engine  32  pass. 
     The engine  32  in the illustrated embodiment operates on a four-cycle combustion principle. This type of engine, however, merely exemplifies one type of engine on which various aspects and features of the present invention can be suitably used. Preferably, the engine has at least two cylinder banks, which extend separately of each other. For instance, an engine having an opposing cylinder arrangement can use certain features of the present invention. Nevertheless, 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) also can employ various features, aspects and advantages of the present invention. In addition, the engine can be formed with separate cylinder bodies rather than a number of cylinder bores formed in a cylinder block. Regardless of the particular construction, the engine preferably comprises an engine body that includes at least one cylinder bore. 
     A crankshaft  82  extends generally vertically through a cylinder block  84  and can be journaled for rotation about a rotational axis  86  by several bearing blocks. Connecting rods (not shown) couple the crankshaft  82  with the respective pistons (not shown) in any suitable manner. Thus, the reciprocal movement of the pistons (not shown) rotates the crankshaft  82 . 
     Watercraft engines typically incorporate electrical generators. The crankshaft  82  rotates a magneto generator  87  (FIG. 2) and the electricity produced is used to recharge a battery  89  or to directly power the ignition system used to ignite the fuel/air mixture inside the cylinder of the engine  32 . The magneto generator includes a pulsar coil  91  to trigger an ignition device (not shown) for igniting the air/fuel mixture. 
     As shown in FIG. 1, the cylinder block  84  is preferably located at the forwardmost position of the engine  32 . A cylinder head assembly  88  is disposed rearward from the cylinder block  84 . Generally, the cylinder block  84  (or individual cylinder bodies) and the cylinder head assembly  88  together define the engine  32 . 
     The engine  32  preferably has an intake system  90  comprising an intake silencer  92  and indirect, port or intake passage fuel injection. The fuel injection system preferably comprises six fuel injectors  94  with one fuel injector allotted for each one of the respective cylinders. The fuel injectors  94  preferably are mounted on throttle bodies  96 . Fuel rails  98  also define portions of the fuel conduits to deliver fuel to the injectors  94 . 
     Each fuel injector  94  preferably has an injection nozzle directed downstream within associated intake passages  100 , which are downstream of the throttle bodies  96 . The fuel injectors  94  spray fuel into the intake passages  100  under control of an electronic control unit (ECU)  102  (FIG.  2 ). The ECU  102  controls both the initiation timing and the duration of the fuel injection cycle of the fuel injectors  94  so that the nozzles spray a proper amount of fuel each combustion cycle. 
     The engine  32  typically includes a cooling system, a lubrication system and other systems, mechanisms or devices other than the systems described above. 
     As shown in FIG. 1, the driveshaft housing  62  depends from the power head  58  to support a driveshaft  104  which is coupled with the crankshaft  82  and which extends generally vertically through the driveshaft housing  62 . The driveshaft  104  is journaled for rotation and is driven by the crankshaft  82 . The driveshaft housing  62  defines an internal section  106  of the exhaust system that leads the majority of exhaust gases to the lower unit  64 . The internal section  106  includes an idle discharge portion that is branched off from a main portion of the internal section  106  to discharge idle exhaust gases directly out to the atmosphere through a discharge port that is formed on a rear surface of the driveshaft housing  62  in idle speed of the engine  32 . 
     The lower unit  64  depends from the driveshaft housing  62  and supports a propulsion shaft  108  that is driven by the driveshaft  104 . The propulsion shaft  108  extends generally horizontally through the lower unit  64  and is journaled for rotation. A propulsion device is attached to the propulsion shaft  108 . In the illustrated arrangement, the propulsion device is a propeller  110  that is affixed to an outer end of the propulsion shaft  108 . 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. 
     As shown in FIG. 2, the engine  32  includes a fuel supply system  112 . The fuel supply system  112  includes a remotely positioned fuel tank  114  that is disposed in the hull of a watercraft  40  (FIG.  1 ). A fuel scavenge conduit  116  extends from the fuel tank  114  to the scavenge side of a low pressure fuel pump  118 . By positioning the main fuel tank  114  remotely, the fuel tank can have a much larger volume and can store more fuel  120  than if the fuel tank were located on the motor  30 . 
     A motor  121  drives the low pressure fuel pump  118 . In accordance with the invention, the motor  121  is controlled by the ECU  102  so as to regulate the speed of the low pressure fuel pump  118 . The ECU  102  regulates the speed of the low pressure pump  118  in response to parameters provided by various sensors including an engine speed sensor  122 , a fuel pressure sensor  124 , and a fuel temperature sensor  126 . The low pressure fuel pump  118  pumps the fuel  120  through a pressured fuel conduit  127  through a fuel filter  128  and then to a fuel vapor separator  130 . An in-tank, high-pressure fuel pump  132  is mounted within the vapor separator  130 . The high pressure fuel pump  132  picks up the fuel  120  and delivers the fuel to the various fuel injectors  94 . The high-pressure fuel pump  132  and the ECU  102  are powered through the battery  89  as seen in the schematic of FIG.  2 . The high pressure fuel pump  132  is controlled by the ECU  102  through a relay  136 . 
     To assure that the fuel in the pressure fuel conduit  127  and the fuel supplied to the vapor separator  130  are at a constant pressure, a pressure regulator valve  138  is mounted between the pressure fuel conduit  127  and the scavenge fuel conduit  116 . The pressure regulator valve  138  regulates pressure by dumping excess fuel back to the scavenge fuel conduit  116 . In a preferred arrangement, the fuel is returned directly to the low pressure fuel pump  118  through the scavenge fuel conduit  116 . 
     As noted above, it is desirable to provide some excess fuel flow under substantially all running conditions. However, this means that the low pressure fuel pump  118  delivers substantially more fuel than is required for operating at low speeds if the fuel pump  118  is capable of supplying excess fuel at high speeds. Therefore, the embodiments of the present invention provide an arrangement for operating the low pressure fuel pump  118  at varying speeds through multiple stages or steps. 
     In the illustrated embodiment, the varying speed control for operating the low-pressure fuel pump  118  operates in response to engine speed, fuel temperature, and fuel pressure. Hence, the ECU  102 , specifically the control phase thereof, receives signals from the engine speed sensor  122 , the fuel temperature sensor  126 , and the fuel pressure sensor  124 . 
     As shown in FIG. 3, a flowchart showing an exemplary control routine for the ECU  102  is arranged and configured in accordance with certain features, aspects, and advantages of the present invention. The control routine begins and moves to a first decision block P 10  in which the engine speed is compared to a predetermined engine speed “X” (e.g., X can be about 1000 RPM some applications). 
     If the speed is greater than “X”, the routine moves to operation block P 16  where the fuel pump speed is decreased. After the fuel pump speed is reduced, the routine repeats. 
     Returning to decision block P 10 , if the engine speed is not below a predetermined speed “X”, then the routine moves to decision block P 12  where the fuel temperature is compared to a predetermined value “Y”. If the fuel temperature is greater than “Y”, then the routine moves to operation bock P 16  where the fuel pump speed is decreased. After the fuel pump speed is reduced, the routine repeats. 
     If in decision block P 12  the fuel temperature is less than the predetermined value “Y”, the routine moves to decision block P 14 . In the decision block P 14  the fuel pressure is compared to a predetermined value “Z”. If the fuel pressure is greater than a predetermined value “Z”, then the routine moves to operation block P 16 , where the fuel pump speed is decreased. If in the decision block P 14  the fuel pressure is less than a predetermined value “Z”, than the routine returns. Preferably, the routine repeats substantially continuously during engine operation. 
     Although the flowchart of FIG. 3 illustrates the decision steps P 10 , P 12 , P 14  being executed in a particular sequence, one skilled in the art will appreciate that the steps can be executed in any order. Furthermore, in particular embodiments, the steps may be executed concurrently such that the ECU  102  continuously monitors the three sensors  122 ,  124 ,  126  and responds when one or more of the sensors outputs a signal outside an acceptable range. 
     Circulating excess fuel has the advantage of cooling the fuel, however if the fuel is circulated too much then the circulation of the fuel can itself heat the fuel and the desired optimal fuel temperature range is not achieved. The fuel can also be heated through a high fuel pressure, which can also contribute to not achieving an optimal fuel temperature range. 
     In the preferred embodiment, the fuel temperature, the fuel pressure and the engine speed are closely monitored by the fuel temperature sensor  126 , the fuel pressure sensor  124  and the engine speed sensor  122 . The monitored parameters enable the fuel system to provide the fuel injectors with vaporless fuel, which increases engine performance, improves exhaust emissions, and provides accurate engine response and efficiency. 
     Thus, from the foregoing description it should be readily apparent that the described construction is very effective in providing good fuel flow to the engine and yet ensuring against excess fuel flow. Of course, the foregoing description is that of a preferred embodiment of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.