Abstract:
An apparatus for controlling the speed of a direct fuel injected, scavenged, two-stroke engine comprises a first sensor for sensing the degree to which the throttle is open, means for sensing whether the intake air amount is in the air-excess range, means for sensing whether the degree to whcih the throttle is open has been substantially constant for a predetermined amount of time, a sensor for sensing the engine revolution speed, means for producing a desired engine revolution speed based on the degree to which the throttle is open, and means for producing a signal coresponding to the difference between the engine revolution speed and the desired engine speed, when the degree to which the throttle is open has been substantially constant for the predetermined amount of time. A control device adjusts an engine running parameter based on this difference, to reduce this difference.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to fuel control systems, particularly to fuel injection systems for 2-cycle, internal combustion engines. 
     Waves and water level fluctuations cause the load on the propulsion system of a boat to vary. This variation may be significant when the boat is trolling or even while the boat is idling. This in turn causes the engine speed to rise in fall. This variation in engine speed causes irregular combustion, fuel wastage, and may cause the engine to stall. 
     Japanese Unexamined Patent Publication Heil-294936 discloses a fuel injection control system for the 2-cycle engine in which air is supplied to the combustion chamber through an intake passage while fuel is injected directly into the combustion chamber mixed with air. 
     As the engine load is varied by waves or water level fluctuations while the boat is running with the throttle opening kept fixed, the engine revolution speed also varies and the passengers may feel unpleasant. To stabilize the engine revolution speed of a crank case scavenged, two stroke engine, prior fuel injection control systems have adjusted the intake air amount by adjusting the throttle opening, and the intake passage cross-sectional area. 
     However, this requires the installation of actuators for adjusting the throttle opening, and the intake passage cross-sectional area, to stabilize the engine revolution speed by adjusting the intake air amount. The performance of these systems may deteriorate over time due to salt damage to the actuators. 
     Thus there was felt a need for an engine speed regulating system which would effectively reduce engine speed variation without requiring the installation of additional actuators. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an apparatus for controlling the speed of revolution of a direct fuel injected, scavenged, two-stroke engine, comprising a first sensor for sensing the degree to which the throttle is open, means for sensing whether the intake air amount is in the air-excess range and means coupled to the first means for sensing whether the degree to which the throttle is open has been substantially constant for a predetermined amount of time. The apparatus further includes a second sensor for sensing the engine revolution speed and means for producing a desired engine revolution speed based on the degree to which the throttle is open. When the degree to which the throttle is open has been substantially constant for the predetermined time the engine revolution speed is compared to the desired engine revolution speed means and a signal corresponding to the difference between the engine revolution speed and said desired engine speed is produced. A control device adjusts at least one engine running parameter based on this difference in order to reduce this difference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an outboard motor according to a first embodiment of the present invention. 
     FIG. 2 shows a top view of an engine according to the present invention. 
     FIG. 3 shows a fuel injector and spark plug arranged in a cylinder of an engine according to the present invention. 
     FIG. 4 is a graphic representation of the relative timing of the feeding of fuel to a metering device charged with high pressure air and the subsequent injection of this fuel-air mixture to the cylinder. 
     FIG. 5 is a graphic representation of the pressure in a cylinder and the fuel-air mixture injection pressure over time as the piston moves from bottom dead center to top dead center. 
     FIG. 6 shows an outboard motor according to a second embodiment of the present invention. 
     FIGS. 7A and 7B are a flow chart illustrating the operation of the first embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 and 2 show an engine 10 for an outboard motor according to a first embodiment of the invention. The engine 10 is a 2-cycle engine mounted on the top of the propulsion unit (not shown) and having a cylinder block 11, a crankcase 12, a cylinder head 13, pistons 14, and a crankshaft 15 the lower end portion of which is connected the drive shaft 16 of the propulsion unit. 
     In the engine 10, air is taken into the combustion chamber 22 through an intake passage constituted of a throttle valve 18 installed in the intake pipe 17 connected with the crankcase 12, a reed valve 19, crank chamber 20 and a scavenging passage 21, while fuel-air mixture is directly injected into the combustion chamber 22 portion around the ignition plug 24 by an injecting device 23 mounted on the cylinder head 13 (FIG. 3). 
     The injection device 23 meters fuel fed by a fuel pump (not shown) through a pressure regulator with its metering device 25, and supplies the metered fuel to the metering chamber 26 at the supply starting timing A shown in FIG. 4. The metering chamber 26 is kept supplied with compressed air from an air compressor at a pressure regulated by a pressure regulator, and the fuel supplied in the metering chamber 26 is injected, as fuel-air mixture, into the combustion chamber 22 when the injection valve 28 is opened at the injection starting timing B shown in FIG. 4. The engine 10 is also provided with an exhaust passage 29. 
     The engine 10 has a fuel injection control system 30 for controlling the injection device 23 composed of an air-excess range judging unit 31, an engine output recognizing unit 32, an engine control parameter computer 33 and an injection signal generator 34 as shown in FIG. 1. 
     The air-excess range judging unit 31 judges whether or not the amount of air taken in the combustion chamber 22 is in the air-excess range on the basis of the engine revolution speed as represented by the detection signal of a pulser coil 31A installed on the engine 10 around the upper end portion of the crankshaft 15 and the air intake amount based on the opening of throttle valve 18 as represented by the detection signal of the throttle opening detector 31B, or as represented by the detection signal of a crank chamber pressure sensor installed in the crank chamber. 
     The engine output recognizing unit 32 is incidentally provided with a load uniformity detector 32A which judges that the engine is in the fixed throttle opening state on the basis of the detection signal of the throttle opening detector 31B. The load uniformity detector 32A generates a signal indicating a fixed throttle state whenever the throttle opening is kept fixed for more than a predetermined time. 
     A load detector 32B detects the engine revolution speed on the basis of the detection signal of the pulser coil 31A while the engine is in the fixed throttle opening state. When the engine is in the fixed throttle opening state, a desired revolution speed is calculated based on the degree to which the throttle is open as represented by the signal from the throttle opening detector 31B. 
     When the air-excess range judging unit judges that the intake air amount is in the air-excess range, the engine control parameter computer 33 adjusts the fuel injection amount and the injection starting timing so that the desired output recognized by the output recognizing unit may be realized. 
     More specifically, the memory integrated in the air-excess range judging unit 31 stores a three-dimensional map of data for the air-excess ratios that are optimized in response to the throttle opening angle and the engine speeds detected. Based on this map, the air-excess range judging unit 31 judges, immediately upon receiving the signals for the throttle opening angle and the engine speed, whether the air amount detected is in the excess range. In this particular engine, the air-excess ratios over 1 are applied only for relatively small throttle opening angles at low engine speed operation. The ratios 1 and less are applied for all other conditions. 
     The injection signal generator 34 delivers an injection valve opening signal with the injection amount and injection starting timing based on the computing results of the engine control parameter computer 33. More specifically, the air intake amount data, which is experimentally determined to correspond to certain throttle openings and engine speeds, is stored in the engine control parameter computer 33. The engine control parameter computer 33 operates on this data, in light the air-excess ratios, to calculate the fuel injection amount. The fuel injection timing, on the other hand, is predetermined in correspondence with the engine speeds. The engine control parameter computer 33 may be such that it adjusts the ignition timing. 
     The output of engine 10 may be increased by increasing the fuel injection amount increment, or through higher injection speed achieved by the increased pressure difference corresponding to the advanced injection starting timing, or through the more complete combustion associated with the advanced ignition timing. 
     In the fuel-air mixture injection type engine 10 according to this invention, the larger the pressure difference between the fuel-air mixture and the combustion chamber interior, the better the fuel atomization and fuel combustion. This, consequently, increases the engine revolution speed. Assuming that the fuel-air mixture pressure is fixed, the lower the combustion chamber pressure, that is, the nearer the injection starting timing is to bottom dead center (the more is advanced the injection starting timing), the larger the pressure difference (see FIG. 5). That is, the output of the engine 10 is increased by advancing the injection starting timing. 
     In the engine 10, since appropriate fuel-air mixture is fed into the combustion chamber 22 portion around the ignition plug 24 while sufficient excessive air is taken into the combustion chamber 22 to improve fuel consumption and exhaust gas purification, especially under the condition of small throttle opening angle and low engine speed, the combustion chamber 22 interior is in an air-excess state and excessive air remains there even after the completion of fuel combustion. 
     FIGS. 7A and 7B are a flow chart illustrating the operation of an engine control system according to the first embodiment of the invention. The degree to which the throttle valve is open is detected in step 1, and the engine speed of revolution is detected in step 2. In step 3 these values are used to determine whether the amount of intake air is in the air-excess range. If the intake air is not in the air-excess range the engine is controlled by predetermined parameters in step 4. If the intake air is in the air-excess range, the system determines whether or not the degree to which the throttle is open has been constant for a predetermined amount of time in step 5. If the throttle has not been in a constant position for a predetermined amount of time, the engine is controlled by the predetermined parameters in step 4. If the degree to which the throttle is open has been constant for a predetermined time, the system compares the engine speed of revolution with a desired engine speed of revolution based on the degree to which the throttle is open in step 6. When the detected engine speed is greater than the desired engine speed various engine running parameters are modified and the amount of fuel injection is reduced and the injection starting timing and spark timing are retarded in step 7. If the detected engine speed is equal to the desired engine speed, the engine is controlled based on predetermined parameters in step 8. Finally, when the detected engine speed is less than the desired engine speed the amount of fuel injected is increased and the injection starting timing and the spark timing are advanced in step 9. 
     Therefore, the control system 30 adjusts the engine output by adjusting the fuel injection amount and injection starting timing without adjusting the intake air amount by adjusting the throttle opening or the like, and realizes the fixed throttle opening running at a desired engine output while preventing fluctuation of the engine revolution speed. 
     That is, the control system 30 stabilizes the engine revolution speed without using actuators for the throttle opening adjustment or the like to realize the desired fixed throttle opening running, as (especially under conditions of small throttle opening angle and low engine speed) the stable running of the engine is not affected by external disturbances such as waves and water level fluctuations. 
     A second embodiment of the invention has a control system 40 as described hereafter for controlling the injection device 23 in the engine 10 which is the same as the engine in the first embodiment. 
     The control system 40 is different from the control system 30 of the first embodiment in that the output recognizing unit 32 is provided with an output setting switch 32C in place of the load uniformity detector 32A and the load detector 32B as shown in FIG. 6. The output setting switch 32C recognizes the driver&#39;s desired output in response to the driver&#39;s manual operation of the output setting switch 32C, and actuates the engine control parameter computer 33 according to this desired output. 
     The engine output of the engine according to the second embodiment is adjust toward the driver&#39;s desired output and the engine revolution speed is stabilized by changing the engine control parameters in the air-excess range without using actuators for adjusting the intake air amount. 
     The descriptions of the preferred embodiments of the invention are for the purpose of illustrating the invention, and are not to be considered as limiting or restricting the scope of the invention. Many modifications may be made by those skilled in the art without departing from the teachings of the present invention which is intended to be limited only by the appended claims.