Abstract:
A fuel injection control apparatus is capable of supplying a proper amount of fuel by improving response when the throttle position is abruptly changed. The fuel injection control apparatus includes an electronic control unit for determining a fuel injection time period for a fuel injection system, based on the engine speed and the throttle position. The electronic control unit is operable to determine a base fuel injection time period based on engine speed and throttle position to start fuel injection, and adjusts the initial fuel injection time period thereafter, based on changes in the engine speed and the throttle position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2004-039613, filed on Feb. 17, 2004. The subject matter of the above-identified priority document is incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a fuel injection control system, to a fuel injection control method, and to a fuel injection control apparatus for determining a fuel injection time period in a fuel injection system.  
         [0004]     2. Description of the Background Art  
         [0005]     Generally speaking, fuel injection systems have been substituted for carburetors in many internal combustion engines, for reasons of improved fuel control precision, cleaner exhaust emissions, better fuel economy and the like. In recent years, fuel injection systems have been adopted in place of carburetors in many motorcycle engines.  
         [0006]     A fuel-injected engine generally includes a control device for determining a fuel injection time period in a fuel injection system. The time period is determined based on the engine speed and the throttle position. A fuel-injected engine of this general type is disclosed in Japanese published patent document JP-A 323187/1994.  
         [0007]     This conventional control device adjusts fuel injection flow volume in response to engine speed, and specifically, controls an energizing time period to be applied to the fuel injection system, depending on the result of a comparison between the engine speed and a predetermined speed.  
         [0008]     In the conventional fuel injection system described above, the fuel injection time period is generally determined by an electronic control unit ECU. However, after the fuel injection time period is determined, a lag time may be required before fuel injection is actually started. Also, although the fuel injection time period is generally determined in response to throttle position, after the fuel injection time period has been determined, the conventional control device has difficulty responding quickly to changing operating conditions.  
         [0009]     For example, when the throttle is abruptly opened, the need for fuel rapidly increases, and when the throttle is abruptly closed, the need for fuel rapidly decreases, and conventional systems experience a lag in responding to such changing conditions. This difficulty is particularly acute at low speeds, because when the throttle position is frequently opened and closed, the frequent adjustments occur during an injection interval.  
         [0010]     A fuel control system is needed which could respond quickly to changing fuel needs of an engine, under changing operating conditions.  
       SUMMARY OF THE INVENTION  
       [0011]     It is an object of the present invention to solve the above-described problems of conventional fuel injection systems, and to provide a fuel injection control apparatus capable of quickly adjusting and supplying the proper amount of fuel under changing operating conditions of a vehicle. The fuel control system hereof provides improved fuel response when the throttle is abruptly opened and the like, as well as improved response to a decrease in a required amount of fuel when the throttle is abruptly closed.  
         [0012]     According to a first embodiment of the present invention, a fuel injection control apparatus is provided for determining a base fuel injection time period, based on engine speed and throttle position, in a fuel injection system. The control apparatus determines a base fuel injection time period to start fuel injection operation, based on the engine speed and throttle position.  
         [0013]     The control device according to the first embodiment is also operable to adjust the base fuel injection time period, based on changes in engine speed and throttle position within a predetermined time period.  
         [0014]     According to the present invention, the response of the fuel injection system to an abrupt change in throttle position is improved. Specifically, after the base fuel injection time period is determined to start fuel injection, if it is necessary to inject more fuel due to the throttle having been abruptly opened and the like, the required fuel can be supplied immediately. Similarly, after the base fuel injection time period is determined to start the fuel injection, if the fuel injection volume required decreases, due to the throttle being abruptly closed or the like, the fuel injection time period is quickly reduced by an appropriate amount, whereby the proper amount of the fuel is supplied to the engine.  
         [0015]     When the engine is operating at low speed, it is possible for the control mechanism to determine a second, adjusted fuel injection time period, and based on this determination, to adjust the base fuel injection time period and derive an adjusted fuel injection time period.  
         [0016]     When the engine is operating at low speed, the amount of interruption of a pulser or the like is small in an electronic control unit (ECU). Thus, even if the ECU is required to provide an adjusted injection time period after the base injection time period has been determined, a load on the CPU is light, and the control can be executed without placing any excessive load on the ECU.  
         [0017]     When the engine is not operating at low speed, the control device does not determine a second, adjusted fuel injection time period, but instead injects fuel based on the base fuel injection time period.  
         [0018]     When the engine is operating at a high speed, the amount of interruption of the pulser or the like increases in the electronic control unit ECU. In this case, since the second, adjusted injection time period is not determined, such that the fuel injection is executed in accordance with the base injection time period, the control is still executed without placing any excessive load on the electronic control unit.  
         [0019]     Further, when the base fuel injection time period is equal to or less than a predetermined threshold value, the control device only injects the fuel after waiting a predetermined delay period.  
         [0020]     Generally, in order to optimize the fuel supply, it is preferable to inject fuel, for example, immediately before an inlet valve for supplying required fuel is opened, using substantially the same timing as intake timing into the engine cylinder.  
         [0021]     In the practice of the present invention, since when the first determined, base injection time period is equal to or less than a predetermined value, the injection start timing for injecting the fuel is delayed, it is possible to supply the required fuel at substantially the same timing as intake timing into the engine cylinder.  
         [0022]     According to the present invention, it is possible to improve the fuel system response for supplying the proper amount of fuel. Improved fuel system response is required, for example, when the throttle is abruptly opened, or when the throttle is abruptly closed.  
         [0023]     For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  is a side plan view of a motorcycle including a fuel injection system according to the present invention;  
         [0025]      FIG. 2  is a top plan view of an isolated motorcycle body frame showing the engine in phantom, with the fuel injection device mounted thereon supported by the body frame;  
         [0026]      FIG. 3  is an enlarged side detail view of the motorcycle of  FIG. 1 , partially cut away, and showing the engine with the fuel injection device mounted thereon supported by the body frame;  
         [0027]      FIG. 4  is a cross-sectional view of the motorcycle engine of  FIG. 3 , taken along a medial vertical plane, and showing the fuel injection system mounted thereon;  
         [0028]      FIG. 5  is a cross-sectional view of the motorcycle engine of  FIG. 3 , viewed in a direction transverse to that of  FIG. 3 , and showing the fuel injection system mounted thereon;  
         [0029]      FIG. 6  is a schematic block diagram of the electronic control unit (ECU) showing sensor inputs into the ECU as well as connections to the regulator, fuel injector, and ignition;  
         [0030]      FIG. 7  is a flow chart showing a process for determination of a base injection time period, and for determination of an adjusted injection time period at low engine speeds;  
         [0031]      FIG. 8A  is a chart showing injector output over time for a case where the engine is operating at a low speed and the base injection time period is less than the adjusted injection time period;  
         [0032]      FIG. 8B  is a chart showing injector output over time for the case wherein the engine is operating at a low speed and the first determined injection time period is greater than the adjusted injection time period;  
         [0033]      FIG. 9  is a chart showing injector output over time for the case wherein the engine is operating at a high speed;  
         [0034]      FIG. 10  is a flow chart showing a process for determination of an injection time period for a second embodiment of the invention;  
         [0035]      FIG. 11  is a chart showing injector output over time for the second embodiment of the invention; and  
         [0036]      FIG. 12  is a flow chart showing a process for determination of an injection time period for a third embodiment of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0037]     Hereinafter, a number of selected illustrative embodiments of the present invention will be described, with reference to the accompanying drawings.  
         [0038]      FIGS. 1 and 2  show a trail-type motorcycle M intended for off-road operation. This motorcycle M is provided with a body frame  1 , including a head pipe  2  arranged at the front-end portion thereof. The body frame  1  also includes a pair of main frame sections  3  extending from the head pipe  2  toward the rear of the vehicle body, and extending obliquely downwardly toward the rear, with a space left between the main frame sections  3  in the widthwise direction of the vehicle body. A pair of down tubes  4  extend obliquely downwardly below the main frame sections  3  toward the rear, with a space left therebetween in the widthwise direction of the vehicle body, in a manner similar to, but at a larger angle than, the main frame sections  3 . A coupling portion  5  is provided for coupling the main frame sections  3  to the down tubes  4 .  
         [0039]     A front fork  7  is pivotally attached to the head pipe  2 , for supporting a front wheel  6  in a manner so as to enable steering of the motorcycle M. A swing arm or rear fork  10 , for supporting a rear wheel  9 , is pivotally attached to the lower end portions of the main frame sections  3 , so as to allow a reciprocal swinging motion in the up-and-down direction. A rear shock absorber  11  is interposed between the rear fork  10  and the body frame  1 .  
         [0040]     A fuel tank  41  is placed between the upper half portions of the main frame sections  3 . A fuel pump  45  is mounted to the fuel tank  41 .  
         [0041]     Also, a body cover  43  is provided extending substantially continuously from the fuel tank  41 , and above the lower half portion of the main frame sections  3 . The body cover  43  is formed to have a central portion  43 A which is positioned lower then the respective ends of the body cover  43 , as shown in  FIG. 1 .  
         [0042]     A single-cylinder four-cycle engine  13  is installed between the main frame sections  3  and the down tubes  4 , so as to be positioned close to an inclined portion of the body frame  1 . The engine  13  is secured to the main frame sections  3  via a plurality of brackets as shown in  FIG. 3 , and the underside of the engine  13  is covered with an engine guard  14 . The above-described engine  13  includes a cylinder block  16 , a cylinder  17  and a cylinder head  18 .  
         [0043]     Power produced by the engine  13  is transmitted to the rear wheel  9  via a chain transmission system  15  ( FIG. 1 ). An exhaust pipe  19  is connected on the front side of the cylinder head  18 , and the exhaust pipe  19  passes through on the left side of the engine  13 , extends toward the rear of the vehicle body, and is coupled to a muffler  19 A.  
         [0044]     A piston  20  is provided in the cylinder  17  in such a manner as to be freely reciprocally slidable therein. As shown in  FIGS. 4 and 5 , the piston  20  is coupled to a crankshaft  21  via a connecting rod  23 , and the crankshaft  21  is axially supported on a crankcase  22 .  
         [0045]     Also, as shown in  FIG. 4 , a throttle body  24  is operatively attached to the backside of the cylinder head  18 . The throttle body  24  has a central axis L 2  oriented so as to intersect an axis L of the cylinder  17  substantially at a right angle. Clean air for combustion is supplied to this throttle body  24  via an air cleaner (not shown).  
         [0046]     The throttle body  24  has an idling adjustment screw  25  and a throttle valve  26 . When, for example, the screw  25  is turned to the right during idling adjustment, the throttle valve  26  is incrementally opened, and the amount of air supplied increases to increase the engine speed. When the screw  25  is turned to the left, the throttle valve  26  is incrementally closed, and the amount of air supplied decreases to decrease the engine speed.  
         [0047]     The downstream portion of the throttle valve  26  intersects an intake passage  28  of the cylinder head  18 , and an injector (fuel injection system)  31  intersects this intake passage  28 .  
         [0048]     The injector  31  is directly installed to the cylinder head  18  such that an axis L 1  of the injector  31  is oriented at a predetermined angle (acute angle) θ, with respect to the central axis L 2  of the throttle body  24 . Also, as seen best in  FIG. 1 , the injector  31  is arranged such that the body portion  31 A thereof is substantially completely overlapped by the main frame sections  3  of the motorcycle body  1 , and yet a cap portion  31 B of the injector protrudes above the main frame sections  3  so as to be adjacent to the underside surface of the body cover  43 .  
         [0049]     Further, the injector  31  has a connection port  31 C for a fuel tube, and a fuel pump  45  is fluidly connected to this connection port  31 C (See  FIG. 1 ). The fuel pump  45  is also attached to the fuel tank  41 , and fuel is supplied via this fuel pump  45 .  
         [0050]     The electronic control unit ECU is integrally mounted to the throttle body  24 , and the electronic control unit ECU is also connected to a coupler  31 D of the injector  31 , via a signal cable (not shown).  
         [0051]     The crankshaft  21  is mounted on the crankcase  22 , as shown in  FIGS. 4 and 5 . The crankshaft  21  is supported on both a roller bearing  114  and a radial ball bearing  115 . In addition to the crankshaft  21 , the crankcase  22  supports a main shaft  33 , a countershaft  34 , a shift drum  35 , a shift spindle  36  and a shift fork  37 . These components constitute a constant-mesh type gear speed change unit (transmission). In this case, a rotating force of the crankshaft  21  is transmitted to the main shaft  33 , or is cut off via a multiple-disc friction clutch  101  shown in  FIG. 5 .  
         [0052]     The multiple disc clutch  101  is arranged coaxially with the main shaft  33 , and is constructed by having: a clutch outer  102  having clutch disks  102 A; a clutch center  103  having clutch plates  103 A; a pressure plate  104  movable in the axial direction for engaging the clutch by pressing the clutch plates  103 A against the clutch disks  102 A; a plurality of clutch springs  105  for biasing this pressure plate  104  in a clutch engaging direction; and a clutch disengaging mechanism  106  for moving the pressure plate  104  in a clutch disengaging direction.  
         [0053]     The clutch disengaging mechanism  106  has a release cylinder  107 . The release cylinder includes a space portion  107 A filled with oil that is connected to the oil cylinder connected to the clutch lever (not shown).  
         [0054]     Other related components include a kick shaft  110 ; a cam chain  111 ; a camshaft  112 ; and a rocker shaft  113 .  
         [0055]     A gear  108  is affixed to the end of the crankshaft  21 , on the clutch  101  side of the engine. Another gear  109  is affixed to the clutch outer disc  102  of the multiple-disc clutch  101 , and engages this gear  108 . Therefore, when the crankshaft  21  rotates, the clutch outer  102  always rotates via these gears  108 ,  109 .  
         [0056]     During clutch engagement, the pressure of the oil, with which the space portion  107 A of the release cylinder  107  has been filled, presses the pressure plate  104  in the direction of the left side of the drawing, and a biasing force of the clutch spring  105  presses the clutch center  103  in the direction of the left side of the drawing, whereby the clutch plate  103 A is pressed against the clutch disk  102 A. In this state, a rotating force of the crankshaft  21 , transmitted to the clutch outer  102  via the above-described gears  108 ,  109 , is further transmitted to the clutch center  103  via the clutch disk  102 A and the clutch plate  103 A, and is transmitted to the main shaft  33  via this clutch center  103 .  
         [0057]     When the clutch has been disengaged by operating the clutch lever (not shown), the oil, with which the space portion  107 A has been filled, escapes on the oil cylinder side connected to the clutch lever. Thereby, the pressure plate  104  moves in the direction of the right side of the drawing, the biasing force of the clutch spring  105  becomes weaker, and a press contact state between the clutch disk  102 A and the clutch plate  103 A is released. When press contact state is released, the clutch center  103  idles to cut off the transmission of power to the main shaft  33 .  
         [0058]     The rotating force is transmitted from the crankshaft  21  to the main shaft  33  is transmitted to the counter shaft  34  after its speed is changed into, for example, first speed, second speed or third speed via the gear speed change unit. The rotating force is transmitted to an output shaft (not shown) coupled to the counter shaft  34  via a gear, and is transmitted to the rear wheel  9  from the output shaft via the chain transmission system  15  as power of the engine  13 .  
         [0059]     A change pedal (not shown) fitted to the crankcase of the motorcycle is operated to the speed into, for example, first speed, second speed or third speed. Prior to operation of the change pedal, the clutch lever (not shown) is operated to disconnect the crankshaft  21  and the main shaft  33  via the multiple disc clutch  101 . Next, while in the disconnected state, the change pedal is operated. This change pedal is coupled to the shift spindle  36  shown in  FIG. 4 . When the change pedal is operated, the shift spindle  36  rotates, and in synchronization therewith, the shift drum  35  rotates via a gear mechanism (not shown). This rotation slides either of the shift forks  37  in the axial direction via a shift pin  37 A engaged with a groove (not shown) of the shift drum  35 . The operated shift fork  37  moves either gear  34 A ( FIG. 5 ) on the counter shaft  34  in the axial direction to engage either gear  33 A ( FIG. 5 ) on the main shaft  33 .  
         [0060]     A gear ratio is determined by gears to be engaged each other. The rotating force, transmitted from the crankshaft  21  to the main shaft  33 , is transmitted to the counter shaft  34  after its speed is changed into first speed, second speed or third speed in accordance with its gear ratio via the gear speed change unit. The rotating force is transmitted to an output shaft (not shown) coupled to the counter shaft  34  via a gear; and is transmitted to the rear wheel  9  from the output shaft via the chain transmission system  15  as power of the engine  13 .  
         [0061]     The above-described engine is a water-cooled engine. Referring to  FIG. 1 , one end of a pair of hoses  51  is connected to a water jacket of the cylinder head  18 . The other end of each hose  51  is connected to a radiator  53  supported between the down tubes  4 . The cooling system includes a radiator fan  55 . Driven by the engine, a water pump (not shown) circulates cooling water, that has cooled the engine via the water jacket, to the radiator  53 . Water cooled within the radiator is then re-circulated to the water jacket.  
         [0062]     An alternator  117  ( FIG. 5 ) is coupled to the above-described engine. Two capacitors  62 ,  63  are connected to this alternator  117  via a regulator  61 . Each respective capacitor  62 ,  63  has a different use. Specifically, one capacitor  62  is connected to a spark plug  118  ( FIG. 5 ) of the engine  13  via an ignition coil  64 . A voltage boosted by an ignition coil  64  is applied to the spark plug  118 . The other capacitor  63  is connected to the above-described injector  31  and fuel pump  45 , and is used for a fuel injection system.  
         [0063]     Both capacitors  62 ,  63  are provided at the lower end portion of the main frame sections  3 , such that one part overlaps or is flush with the underside of the lower end portion, whereby the layout efficiency is improved. By dividing the capacitor function into two separate capacitors  62 ,  63 , the fuel injection system hereof is able to perform control that is substantially unaffected by noise from the ignition coil  64 .  
         [0064]     The above-described electronic control unit ECU, as shown in  FIG. 6 , is connected to a plurality of sensors, including a negative pressure sensor  41 , a throttle position sensor  42 , an intake temperature sensor  43 , an engine cooling water temperature sensor  44 , and an engine speed sensor (crank angle sensor)  45 . The ECU is also connected with the alternator  117  and a regulator  61 . Further, the above-described injector  31  is connected to the ECU via a signal cable, and the ignition coil  64  and the spark plug  118  are also connected to the ECU.  
         [0065]     The above-described engine  13  is a single-cylinder four-cycle engine, and in this case, the electronic control unit ECU determines fuel injection volume every two revolutions (720°) of the crankshaft  21 , transmits the result to the injector  31 , and injects the fuel into the intake passage  28  of the cylinder head  18  only for a time period corresponding to a selected fuel injection volume.  
         [0066]      FIG. 7  is a flow chart describing a process for determining a fuel injection time period.  
         [0067]     In first step (S 1 ) of this process, the electronic control unit ECU calculates engine speed Ne based on information from the engine speed sensor  45 . In the second step (S 2 ), the ECU reads the throttle position θ from the throttle position sensor  42 . The ECU further reads various other sensor information (for example, information based on the negative pressure sensor  41 , the intake temperature sensor  43 , the engine cooling water temperature sensor  44  and the like) in step (S 3 ).  
         [0068]     Thus, based on the engine speed Ne, the throttle position θ, and various additional sensor information, the electronic control unit ECU calculates the fuel injection time period (hereinafter, referred to as the base injection time period) corresponding to the first fuel injection volume to start fuel injection, in accordance with step (S 4 ).  
         [0069]     Next, at step (S 5 ), the electronic control unit ECU judges whether or not the engine speed Ne is within a low speed region NC. If the engine speed is within the low speed region NC, at step (S 6 ) the electronic control unit ECU calculates the engine speed Ne again at a predetermined time within a predetermined time period. Note that during this calculation, fuel injection proceeds in accordance with the base injection time period. Then, at step (S 7 ), the ECU reads the throttle position θ. Subsequently, at step (S 8 ), the ECU reads various sensor information. Thus, at step (S 9 ), based on the engine speed Ne, throttle position θ and various sensor information, the electronic control unit ECU calculates a second fuel injection time period (hereinafter referred to as the adjusted injection time period).  
         [0070]     The fuel injection time period is generally determined based on the engine speed Ne and the throttle position θ. Since, however, intake air volume of the engine, responsive to the throttle position θ, varies with engine operating conditions, the intake air volume is, in the present structure, determined after the information of the throttle position θ is adjusted based on various sensor information.  
         [0071]     Next, based on the adjusted injection time period determined in step (S 9 ), the base injection time period is modified, step (S 10 ). In this adjustment process, the base injection time period determined may be renewed as the adjusted injection time period.  
         [0072]      FIG. 8  is a time chart showing adjustment of injector output over time.  FIG. 8A  shows injector output for a case where the engine is operating at a low speed and the first determined, base injection time period is less than the adjusted injection time period. In this case, at time T 1 , the base injection time period is determined; at time T 2 , a first injection timer is set; and at time T 3 , slightly delayed from setting of the first injection timer, fuel injection by the injector  31  is started. In this case, the base injection time period is from time T 3  to time T 7 .  
         [0073]     Next, at a predetermined time, that is, at time T 4 , the adjusted injection time period is determined. At time T 5 , a second injection timer is set. If the adjusted injection time period at this time is from time T 3  to time T 8 , in step (S 10 ) in  FIG. 7 , the base injection time period is extended by a time period α. Time period α corresponds to the difference in time of injection periods between the basic and adjusted time periods. In this case, the predetermined time can be set by linking with the crank angle of the crankshaft  21 . Time T 9  is a limit for completion of injection.  
         [0074]     Accordingly, even if after the base injection time period is determined and fuel injection is started, it becomes necessary to inject more fuel (for example, due to the throttle position being abruptly opened or for any other reason), it is possible to supply the shortage immediately, and thus it is possible to improve response to rapid changes in fuel supply requirements.  
         [0075]      FIG. 8B  shows injector output for a case where the engine is operating at a low speed and the first determined, base injection time period is greater than the adjusted injection time period. In this case, at time T 1 , the base injection time period is determined; at time T 2 , a first injection timer is set; and at time T 3 , slightly delayed from time of setting the first injection timer, fuel injection by the injector  31  is started. The base injection time period in this case is from time T 3  to time T 7 .  
         [0076]     Next, at a predetermined time, that is, at time T 4 , the adjusted injection time period is determined, and at time T 5 , a second injection timer is set. If the adjusted injection time period at this time is from time T 3  to time T 6 , in step (S 10 ) in  FIG. 7 , the base injection time period is shortened by a time period β. The time period β corresponds to the difference in time of injection periods between the base and adjusted time periods. Time T 9  is the limit for completion of injection.  
         [0077]     Accordingly, even after the base injection time period is determined and fuel injection is started, if the required fuel injection volume is reduced due to the throttle position being abruptly closed or the like, the system hereof is able to supply the proper amount of fuel, by shortening the injection time period.  
         [0078]     The above-described motorcycle is a trail vehicle for a competition, and in this case, particularly when the engine speed is within a low speed region, the throttle position is frequently opened and closed by a rider. In the present embodiment, even for such trail motorcycle, the fuel injection control apparatus sufficiently responds to the rider&#39;s operating request.  
         [0079]     On the other hand, if at step (S 5 ) in  FIG. 7 , it is determined that the engine speed is not within a low speed region NC, that is, when the engine is operating at a high speed, the fuel injection is executed based on the first determined, base injection time period, and such determination and of the adjusted injection time period, as shown in steps S 6  to S 9 , will not be executed.  
         [0080]      FIG. 9  is a time chart showing injector output over time for a case where the engine is operating at a high speed. At time T 11 , the base injection time period is determined; at time T 12 , the first injection timer is set; and at time T 13 , which is slightly delayed from time of setting the first injection timer, the fuel injection by the injector  31  is started. The base injection time period is from time T 13  to time T 14 . When the engine speed is within a high speed region, the second, adjusted injection time period is not determined, but instead at time T 14 , the fuel injection by the injector  31  is ended. Time T 15  is the limit for completion of injection.  
         [0081]     Accordingly, when the engine speed is operating within a high speed region, the second adjusted injection time period is not determined, and thus a load on the electronic control unit ECU, which is operating under high speed conditions in which an amount of interruption of pulser or the like increases, can be restricted.  
         [0082]      FIG. 10  is a flow chart describing a process for determining a fuel injection time period according to a second embodiment of the present invention.  
         [0083]     In this case, when the first determined, base fuel injection time period is equal to or less than a predetermined value, the second adjusted injection time period is not determined, and the fuel injection will be executed based on first determined, base fuel injection time period after being delayed by a predetermined time period.  
         [0084]     In other words, in  FIG. 10  and at step (S 11 ), the electronic control unit ECU calculates engine speed Ne. At step S 12 , the ECU reads throttle position θ, and further at step (S 13 ) reads various sensor information. Thus, at step (S 14 ), based on the engine speed Ne, the throttle position θ and various sensor information, the electronic control unit ECU determines the first base injection time period.  
         [0085]     Next, at step (S 15 ), the electronic control unit ECU judges whether or not the first base injection time period is equal to or less than a predetermined value. When the first base injection time period is equal to the predetermined value or less, the process proceeds to step (S 16 ). At step (S 16 ), the start of fuel injection is delayed by a predetermined time period that has been set in advance. Next, at step (S 17 ), fuel injection is started in compliance with the base injection time period, and the injection is executed in accordance with the base injection time period.  
         [0086]     However, if at step (S 15 ) the first base injection time period exceeds the predetermined value, the process proceeds to step (S 18 ). At step (Si 8 ), the fuel injection is started in accordance with the first base injection time period. Then, at step (S 19 ), as in the case of the above-described embodiment, the electronic control unit ECU calculates the engine speed Ne, again at a predetermined time within a predetermined time period during fuel injection in compliance with the base injection time period. At step (S 20 ), the ECU reads the throttle position θ, and at step (S 21 ), the ECU reads various sensor information. Further, at step (S 22 ), based on the engine speed Ne, throttle position θ and various sensor information, the electronic control unit ECU determines a second adjusted fuel injection time period. At step (S 23 ), the ECU adjusts the base injection time period determined at step (S 14 ) based on the adjusted injection time period determined in step (S 22 ), in accordance with similar processing to the above-described adjustment processing. In this adjustment processing, the first determined, base injection time period may be renewed by the adjusted injection time period.  
         [0087]      FIG. 11  is a chart showing injector output over time for the second embodiment of the invention as illustrated in  FIG. 10 . At time T 21 , the base injection time period is determined, and it is judged whether or not the base injection time period is a predetermined value or less.  
         [0088]     When the base injection time period is the predetermined value or less, the adjusted injection time period is not determined. Thus, after being delayed for a predetermined time period, at time T 24 , injection in compliance with the base injection time period is started, and at time T 25 , the injection is completed. Time T 26  is the limit for completion of injection. Delay time periods from time T 21  to time T 24  in this case substantially correspond to a total amount of a time period T 22  corresponding to determination of the adjusted injection time period, a time period T 23  corresponding to setting of the injection timer, and a slightly delayed time period T 24  in the above-described embodiment.  
         [0089]     In the second embodiment hereof, since when the base injection time period is the predetermined value or less, the fuel injection start is delayed until at least after a time at which the adjusted injection time period should be primarily determined, the fuel can be supplied into the cylinder of the engine  13  at the substantially same timing as intake timing. Therefore, immediately before the inlet valve of the cylinder head  18  is opened, the fuel injection is executed, thereby optimizing the fuel supply.  
         [0090]      FIG. 12  is a flow chart showing a process for determination of an injection time period according to a third embodiment of the invention. In the third embodiment, at step (S 25 ), the electronic control unit ECU calculates engine speed Ne. At step (S 26 ), the electronic control unit ECU reads throttle position θ, and further at step (S 27 ), reads various sensor information. Thus, as step (S 28 ), based on the engine speed Ne, the throttle position θ and various sensor information, the electronic control unit ECU determines the first base injection time period.  
         [0091]     Next, at step (S 29 ), the electronic control unit ECU judges whether or not the first base injection time period is equal to a predetermined value or less. When the base injection time period is equal to the predetermined value or less, the process is transferred to step (S 30 ). At step (S 30 ) the start of fuel injection is delayed for a predetermined time period that has been set in advance, and then at step (S 31 ) fuel injection in compliance with the base injection time period is started, and the injection is executed in accordance with the base injection time period. Delay time periods in this case can be set to substantially correspond to a total amount of a time period T 22  corresponding to determination of the adjusted injection time period, a time period T 23  corresponding to setting of the injection timer, and a slightly delayed time period T 24  in the above-described embodiment.  
         [0092]     When in step (S 29 ), the first base injection time period exceeds the predetermined value, the process is transferred to step (S 31 ). At step (S 31 ), the fuel injection is started in accordance with the first base injection time period without delaying the injection start time.  
         [0093]     Accordingly, since when the base injection time period is the predetermined value or less, the injection start is delayed by the predetermined time period, the fuel can be supplied into the cylinder of the engine  13  at the substantially same timing as intake timing. Therefore, immediately before the inlet valve of the cylinder head  18  is opened, the fuel injection is executed, thus optimizing the fuel supply.  
         [0094]     Although the description of the present invention has been made herein based on a number of selected illustrative embodiments, the present invention is not limited to the described embodiments. In the adjustment of the base injection time period of the above-described embodiment, the adjusted injection time period is determined, and the base injection time period is adjusted by comparing with the adjusted injection time period. However, the base injection time period may be adjusted by directly comparing, for example, the first and second engine speeds Ne and throttle positions θ without determining the adjusted injection time period. Also, in the above-described embodiments, when completion of the fuel injection exceeds the limit for completion of injection, control for completing this fuel injection is executed before the limit for completion of injection.  
         [0095]     While a number of illustrative examples of the present invention have been described above, the present invention is not limited to the working examples described above, but various design alterations may be carried out without departing from the present invention as set forth in the claims.