Abstract:
A fuel injection system and method for injecting fuel for an internal combustion engine having fuel injection valves arranged on the upstream side and downstream side from the throttle valve respectively which consistently supplies an adequate quantity of fuel into the combustion chamber without fuel adhering to or remaining at the throttle valve, even when the throttle valve is abruptly enclosed. Based on plural parameters including the throttle opening θTH and the engine speed NE, the system includes means for determining the injection quantity of each of the upstream and downstream fuel injection valves, means for detecting a rate of change ΔθTH of the throttle opening in the injection-valve closing direction, means for stopping fuel injection of the upstream fuel injection valve when the rate of change ΔθTH is large, and means for reducing the injection quantity from the downstream fuel injection valve when the fuel injection of the upstream injection valve is stopped.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2002-264559 filed on Sep. 10, 2002, the entire contents thereof is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a fuel injection system and fuel injecting method for an internal combustion engine, and more particularly to a fuel injection system in which injection valves have been provided on the upstream side and on the downstream side respectively with a throttle valve interposed therebetween.  
         [0004]     2. Description of Background Art  
         [0005]     When the fuel injection valve is provided upstream from the throttle valve, the volumetric efficiency is improved because heat is taken from intake air when injection fuel vaporizes. Therefore, the engine output can be increased as compared with when the fuel injection valve is provided downstream from the throttle valve. On the other hand, when the fuel injection valve is provided on the upstream side, a distance between its fuel injection port and the combustion chamber becomes inevitably longer. As a result, when fuel injection is provided on the upstream side a response lag in fuel transport occurs as compared with when the fuel injection valve has been provided downstream from the throttle valve.  
         [0006]     There has been disclosed in, for example, Japanese Patent Laid-Open Nos. 4-183949 and 10-196440, a fuel injection system in which fuel injection valves have been provided upstream from and downstream from the intake pipe respectively with a throttle valve interposed therebetween, in order to improve the engine output and cope with the response lag.  
         [0007]      FIG. 10  is a cross-sectional view showing a major portion of a conventional internal combustion engine in which two fuel injection valves have been arranged, and with a throttle valve  52  of an intake pipe  51  interposed, there are arranged a downstream fuel injection valve  50   a  on the side portion of the downstream side (engine side) and an upstream fuel injection valve  50   b  on the upstream side (air cleaner side). A lower end portion of the intake pipe  51  is connected to an intake passage  52 , and an intake port  53  facing a combustion chamber of this intake passage  52  is opened and closed by an intake valve  54 .  
         [0008]     An injection quantity from each fuel injection valve is determined on the basis of a plurality of parameters including a throttle opening and an engine speed. In a state in which the throttle opening is small, the injection quantity is restricted. According to the above-described conventional technique, however, an injection port of the upstream fuel injection valve  50   b  points to the throttle valve, and in the upstream fuel injection valve  50   b , a response lag occurs because the distance between its fuel injection port and the combustion chamber becomes far.  
         [0009]     Therefore, when the throttle valve  52  is abruptly closed to a totally-enclosed state or is closed with a large rate of change in an injection-valve closing direction although not up to the totally-enclosed state, fuel injected from the upstream fuel injection valve  50   b  adheres to the throttle valve  52  and remains.  
         [0010]     Therefore, when the throttle valve  52  is opened next, at that time, not only fuel injected from each fuel injection valve in response to the throttle opening, but also the fuel which has remained at the throttle valve  52  is fed into the combustion chamber at the same time. Therefore, there was a possibility that the fuel quantity becomes excessive to the intake air quantity.  
       SUMMARY AND OBJECTS OF THE PRESENT INVENTION  
       [0011]     It is an object of the present invention to solve the above-described problems of the conventional technique, and to provide a fuel injection system for an internal combustion engine capable of supplying, in the structure in which fuel injection valves are arranged on the upstream side and on the downstream side from the throttle valve respectively, an adequate quantity of fuel into the combustion chamber all the time without fuel adhering to and remaining at the throttle valve even when the throttle valve is abruptly closed.  
         [0012]     In order to achieve the above-described object, the present invention is characterized in that in a fuel injection system for an internal combustion engine having an intake pipe equipped with a throttle valve, an upstream fuel injection valve provided upstream from the throttle valve, and a downstream fuel injection valve provided downstream from the throttle valve, the following means have been employed.  
         [0013]     On the basis of a plurality of parameters including the throttle opening θTH and the engine speed NE, means for determining each fuel injection quantity of the upstream and downstream fuel injection valves, means for detecting a rate of change of the throttle opening in the injection-valve closing direction, and means for stopping fuel injection of the upstream fuel injection valve when the rate of change is larger than the reference rate of change.  
         [0014]     (2) Means for reducing the injection quantity of the downstream fuel injection valve only for a predetermined time period when the injection of the upstream fuel injection valve is stopped.  
         [0015]     According to the above-described feature (1), since when the throttle valve is abruptly closed, fuel injection from the upstream injection valve is stopped immediately, and fuel adhering to and remaining at the throttle valve is restricted to a minimum.  
         [0016]     According to the above-described feature (2), when fuel injection from the upstream injection valve is stopped in response to abruptly-closed throttle valve, the injection quantity from the downstream fuel injection valve is reduced. As a result, the total supply quantity of fuel can be maintained at an adequate value, even though a small quantity of fuel which may have adhered to and have remained at the throttle valve is supplied into the combustion chamber when the throttle valve is opened again thereafter.  
         [0017]     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:  
         [0019]      FIG. 1  is a general block diagram showing a fuel injection system according to one embodiment of the present invention;  
         [0020]      FIG. 2  is a functional block diagram for a fuel injection control unit  10 ;  
         [0021]      FIG. 3  is a view showing one example of an injection rate table;  
         [0022]      FIG. 4  is a flowchart showing a control procedure of fuel injection;  
         [0023]      FIG. 5  is a flow chart showing “upstream injection stop judgment handling”;  
         [0024]      FIG. 6  is a flowchart showing “downstream lean rendering handling”;  
         [0025]      FIG. 7  is a timing chart showing “downstream lean rendering handling”;  
         [0026]      FIG. 8  is a view showing an example of a lean rendering correction factor (Klean) table;  
         [0027]      FIG. 9  is a view showing an example of a lean rendering duration period (Nlean); and  
         [0028]      FIG. 10  is a cross-sectional view showing a conventional technique in which two fuel injection valves have been arranged. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]      FIG. 1  is a general block diagram showing a fuel injection system according to one embodiment of the present invention, and on a combustion chamber  21  of the engine  20 , there are opened an intake port  22  and an exhaust port  23 . Each port  22  and  23  is provided with an intake valve  24  and an exhaust valve  25  respectively, and an ignition plug  26  is provided.  
         [0030]     On an intake passage  27  leading to the intake port  22 , a throttle valve  28  is provided for adjusting intake air quantity in accordance with its opening θTH, a throttle sensor  5  is provided for detecting the opening θTH, and a vacuum sensor  6  is provided for detecting intake manifold vacuum PB. At a terminal of the intake passage  27  an air cleaner  29  is provided. Within the air cleaner  29 , an air filter  30  is provided, and open air is taken into the intake passage  27  through this air filter  30 .  
         [0031]     In the intake passage  27 , a downstream injection valve  8   b  is provided downstream from the throttle valve  28 , and on the air cleaner  29  upstream from the throttle valve  28 , an upstream injection valve  8   a  is arranged so as to point to the intake passage  27 . Also, an intake temperature sensor  2  for detecting intake (atmospheric) temperature TA is provided on the air cleaner  29 .  
         [0032]     Opposite to a crankshaft  33  coupled to a piston  31  of the engine  20  through a connecting rod  32 , an engine speed sensor  4  is arranged for detecting engine speed NE on the basis of a rotation angle of a crank. Further, opposite to a rotor  34  such as a gear which is coupled to the crankshaft  33  for rotation, a vehicle speed sensor  7  is arranged for detecting vehicle speed V. On a water jacket formed around the engine  20 , a water temperature sensor  3  is provided for detecting cooling water temperature TW representing the engine temperature.  
         [0033]     An ECU (Engine Control Unit)  1  includes a fuel injection control unit  10  and an ignition timing control unit  11 . The fuel injection control unit  10  outputs, on the basis of signals (process values) obtained by detecting by each of the above-described sensors, injection signals Qupper and Qlower to each injection valve  8   a ,  8   b  on the upstream and downstream sides. Each of these injection signals is a pulse signal having pulse width responsive to the injection quantity, and each injection valve  8   a ,  8   b  is opened by time corresponding to this pulse width to inject the fuel. The ignition timing control unit  11  controls ignition timing of an ignition plug  26 .  
         [0034]      FIG. 2  is a functional block diagram for the fuel injection control unit  10 , and the same symbols as in the foregoing represent the same or equal portions.  
         [0035]     A total injection quantity determination unit  101  determines a total quantity Qtotal of fuel to be injected from each fuel injection valve  8   a ,  8   b  on the upstream and downstream sides on the basis of the engine speed NE, the throttle opening θTH and intake pressure PB. An injection rate determination unit  102  refers to an injection rate table on the basis of the engine speed NE and throttle opening θTH to determine an injection rate Rupper of the upstream injection valve  8   a . An injection rate Rlower of the downstream injection valve  8   b  is determined as (1−Rupper).  
         [0036]      FIG. 3  is a view showing an example of the injection rate table. In the present embodiment, an injection rate map is constituted with 15 items (Cne 00  to Cne 14 ) as a reference as the engine speed NE, and with 10 items (Cth 0  to Cth 9 ) as a reference as the throttle opening θTH, and the injection rate Rupper of the upstream injection valve  8   a  is registered in advance at each combination of each engine speed NE and the throttle opening θTH. The injection rate determination unit  102  determines an injection rate Rupper corresponding to the engine speed NE and the throttle opening θTH that have been detected, by means of the four-point interpolation on the injection rate map.  
         [0037]     Reverting to  FIG. 2 , a correction factor calculation unit  103  refers to a data table on the basis of the intake temperature TA and the cooling water temperature TW that have been detected to seek various correction factors including an intake temperature correction factor KTARU and a cooling water temperature correction factor KTWRU. In the injection quantity determination unit  105 , the upstream injection quantity determination unit  1051  seeks a basic injection quantity of the upper injection valve  8   a  on the basis of the injection rate Rupper and the total injection quantity Qtotal, and multiplies this basic injection quantity by various correction factors including the correction factor KTARU, KTWRU to determine the injection quantity Qupper of the upstream injection valve  8   a . A downstream injection quantity determination unit  1052  determines the injection quantity Qlower of the downstream injection valve  8   b  on the basis of the upstream injection quantity Qupper and the total injection quantity Qtotal.  
         [0038]     An injection quantity correction unit  104  corrects the injection quantity of each injection valve  8   a ,  8   b  during acceleration, when abruptly closing the throttle opening θTH and at otherwise time. The injection quantity correction unit  104  further includes an upstream stop unit  104   a  and a downstream lean unit  104   b.    
         [0039]     The upstream stop unit  104   a  stops an operation of the upstream injection valve  8   a  ( 8   a   1  to  8   a   4 ) of each cylinder in order that fuel may not adhere to the throttle valve in high amounts when abruptly closing the throttle valve  28 . In order to prevent an air-fuel mixture from being rendered rich due to a small quantity of fuel adhering to the throttle valve  28  being supplied into the combustion chamber, a downstream lean rendering unit  104   b  reduces the fuel injection quantity of the downstream injection valve  8   b  to render the fuel injection quantity leaner its level prior to when the upstream injection was stopped. As regards a control procedure of the upstream stop unit  104   a  and the downstream lean rendering unit  104   b , with reference to a flowchart, the description will be made in detail later.  
         [0040]     Next, with reference to a flowchart of  FIG. 4 , the description will be made of an operation of the fuel injection control unit  10  in detail. This handling is executed by interruption due to a crank pulse in a predetermined stage.  
         [0041]     In a step S 10 , the engine speed NE, the throttle opening θTH, the manifold air pressure PB, the intake temperature TA and the cooling water temperature TW are detected by each of the above-described sensors. In a step S 11 , in the total injection quantity determination unit  101 , total quantity Qtotal of fuel to be injected from each fuel injection valve  8   a ,  8   b  on the upstream side and on the downstream side is determined on the basis of the engine speed NE, the throttle opening θTH, and the intake pressure PB.  
         [0042]     In a step S 12 , in the injection rate determination unit  102 , an injection rate table is referred to on the basis of the engine speed Ne and the throttle opening θTH, and an injection rate Rupper of the upstream injection valve  8   a is determined. In a step S 13 , the upstream stop unit  104   a  of the injection quantity correction unit  104  determines whether or not the fuel injection of the upstream injection valve  8   a  is stopped.  
         [0043]      FIG. 5  is a flowchart showing a procedure of “upstream injection stop judgment handling” to be executed in the upstream stop unit  104   a , and control in a four-cylinder engine will be exemplified here for description.  
         [0044]     In a step S 21 , the present throttle opening θTH is compared with an upstream injection cut judgment opening θTHref that becomes a judgment criterion as to whether or not the upstream injection will be cut. If θTH. θTHref, in a step S 22 , it is further judged whether or not the throttle opening has been operated in the direction that closes the throttle.  
         [0045]     If under the closing operation, in a step S 23 , a rate of change ΔθTH of the throttle opening θTH is compared with an upstream injection cut judgment rate of change ΔθTHref that becomes a judgment criterion as to whether or not the upstream injection will be cut. If ΔθTH. ΔθTHref and it is judged that the throttle valve  28  is abruptly enclosed, the sequence will proceed to a step S 24  or higher in order to stop the upper injection valve  8   b  which is being operated.  
         [0046]     In a step S 24 , it is judged whether or not the upstream fuel injection valve  8   a   1  of a first cylinder is under injection. If under injection, in a step S 25 , the operation of the fuel injection valve  8   a   1  is stopped, and in a step S 26 , an upstream injection cut flag Fcut is set.  
         [0047]     Similarly, in a step S 27 , it is judged whether or not the upstream fuel injection valve  8   a   2  of a second cylinder is under injection. If under injection, in a step S 28 , the operation of the fuel injection valve  8   a   2  is stopped, and in a step S 29 , the upstream injection cut flag Fcut is set.  
         [0048]     Similarly, in a step S 30 , it is judged whether or not the upstream fuel injection valve  8   a   3  of a third cylinder is under injection. If under injection, in a step S 31 , the operation of the fuel injection valve  8   a   3  is stopped, and in a step S 32 , the upstream injection cut flag Fcut is set.  
         [0049]     Similarly, in a step S 33 , it is judged whether or not the upstream fuel injection valve  8   a   4  of a fourth cylinder is under injection. If under injection, in a step S 34 , the operation of the fuel injection valve  8   a   4  is stopped, and in a step S 35 , the upstream injection cut flag Fcut is set.  
         [0050]     In a step S 36 , the upstream injection cut flag Fcut is referred to, and if this has been set, this rate of change ΔθTH of the throttle opening θTH will be set, in a step S 37 , as a rate of change of the throttle opening θTH when the upstream injection has been stopped, that is, a rate of change ΔθTHcut during injection cut.  
         [0051]     Reverting to  FIG. 4 , in a step S 14 , in the downstream lean rendering unit  104   b , when fuel injection from the upstream injection valve has been stopped in response to the throttle valve being abruptly enclosed, “downstream lean rendering control” is executed, thus lowering the downstream injection to a level lower than its level prior to when injection from the upstream valve was stopped.  
         [0052]      FIG. 6  is a flowchart showing a procedure of the “downstream lean rendering handling” to be executed in the downstream lean rendering unit  104   b , and  FIG. 7  is its timing chart.  
         [0053]     In a step S 51 , it is judged on the basis of flag during lean rendering Flean (to be described later) whether or not the lean rendering handling of the downstream injection valve  8   b  is being continued. Since it is judged that it is not being continued at the beginning, the sequence will proceed to a step S 52 . In the step S 52 , it is judged on the basis of the upstream injection cut flag Fcut whether or not the upstream injection is being stopped, and if it is being stopped, the sequence will proceed to a step S 53 .  
         [0054]     In the step S 53 , the throttle opening θTH is compared with upstream injection stop releasing opening θTHcutcancel, and if θTH. θTHcutcancel, the sequence will proceed to a step S 64  in order to stop the downstream lean rendering, and various variables are initialized to terminate the handling concerned. In contrast to this, if θTH&lt;θTHcutcancel, the sequence will proceed to the step S 54  in order to continue the lean rendering handling. In the step S 54 , the throttle opening θTH is compared with a lean rendering stop opening θTHleanstop, and if θTH. θTHleanstop, the sequence will proceed to a step S 66 . If θTH&lt;θTHleanstop, the sequence will proceed to the step S 55  in order to continue the lean rendering handling.  
         [0055]     In the step S 66 , it is judged whether or not the throttle is open-operated, and if not open-operated, the sequence will proceed to the step S 55  to continue the lean rendering handling. If open-operated, its rate of change ΔθTH is compared with a reference rate of change in a step S 67 . If the rate of change ΔθTH exceeds the reference rate of change, the sequence will proceed to a step S 64  in order to stop the lean rendering handling. If the rate of change ΔθTH is lower than the reference rate of change, the sequence will proceed to the step S 55  in order to continue the lean rendering handling.  
         [0056]     In the step S 55 , it is judged how many times lean rendering handling has been made so far, and since it is judged as the first one at the beginning, the sequence will proceed to a step S 56 . In the step S 56 , a flag during lean rendering Flean is set, and “1” is set, as an initial value, to a lean rendering frequency counter Ncount for counting a lean rendering frequency. In a step S 57 , on the basis of the engine speed NE, there is selected a lean rendering factor table for relieving a lean rendering duration period Nlean for representing time (frequency) for rendering the downstream injection lean, a return opening ΔKlnrtn of the throttle for representing a return speed when returning from the lean rendering and a lean rendering correction factor Klean for reducing the injection quantity by multiplying a fuel injection quantity separately obtained.  
         [0057]      FIG. 8  is a view showing an example of the lean rendering factor table, and the lean rendering correction factor Klean has been registered as a function of a rate of change during the injection cut ΔθTHcut (step S 37  of  FIG. 5 ). A plurality of the lean rendering factor tables have been prepared for each engine speed NE, and a relationship between the lean rendering correction factor Klean and the rate of change during the injection cut ΔθTHcut differs slightly in response to the engine speed NE.  
         [0058]     Reverting to  FIG. 6 , in a step S 58 , this lean rendering correction factor Klean will be retrieved and determined at a time t 1  of  FIG. 7  on the basis of the lean rendering factor table and the rate of change during the injection cut ΔθTHcut. In a step S 59 , the lean rendering duration period table will be retrieved on the basis of the rate of change during the injection cut ΔθTHcut to determine the lean rendering duration period Nlean responsive to the rate of change during the injection cut ΔθTHcut.  
         [0059]      FIG. 9  is a view showing an example of the lean rendering duration period table, and a time period Nlean during which rendering the downstream injection lean is continued has been registered in advance as a function of the rate of change during the injection cut ΔθTHcut. In a step S 61 , the lean rendering frequency counter Ncount is compared with the lean rendering duration period Nlean, and since Ncount. Nlean at the beginning, the handling concerned will be terminated as it is.  
         [0060]     Reverting to  FIG. 4 , in the step S 15 , the injection rate Rupper of the upstream fuel injection valve  8   a  will be corrected on the basis of the following expression (1). 
 
 R upper= R upper× KTWRU×KTARU    (1) 
 
         [0061]     In a step S 16 , the upstream injection cut flag Fcut is referred to, and if this has been set, in a step S 18 , “0” will be set to the injection quantity Qupper. If the flag Fcut has not been set, in a step S 17 , the upstream injection quantity determination unit  1051  will calculate the injection quantity Qupper of the upstream injection valve  8   a  on the basis of the following expression (2). 
 
 Q upper= Q total× R upper   (2) 
 
         [0062]     In a step S 19 , the downstream injection quantity determination unit  1052  will calculate the injection quantity Qlower of the downstream injection valve  8   b  on the basis of the following expression (3). 
 
 Q lower=( Q total− Q upper)× K lean   (3) 
 
         [0063]     In this case, since the lean rendering correction factor Klean is a smaller factor than “1.0” as shown in  FIG. 7 , the injection quantity Qlower of the downstream injection valve  8   b  is to be reduced to a level lower than when injection from the upstream valve is stopped.  
         [0064]     Reverting to  FIG. 6 , since it is judged in the step S 55  that the lean rendering handling has been twice or more times in the next period, the sequence will proceed to a step S 60  to increment the lean rendering frequency counter Ncount by “1”.  
         [0065]     Thereafter, in a step S 61 , since each handling described above will be repeated before it is judged that Ncount&gt;Nlean, the downstream injection will continue to be rendered lean in response to the lean rendering correction factor Klean.  
         [0066]     Thereafter, a relationship of Ncount&gt;Nlean is reached at a time t 2  of  FIG. 7  and this is detected in the step S 61 , the sequence will proceed to a step S 62 . In the step S 62 , an added value (Klean+ΔKlnrtn) of the lean rendering correction factor Klean and a return opening ΔKlnrtn will be renewed and registered as a new lean rendering correction factor Klean. In other words, as shown in  FIG. 7 , at a time t 2  and thereafter, the lean rendering correction factor Klean gradually increases the return opening ΔKlnrtn at a time. Accordingly, the injection quantity Qlower of the downstream injection valve  8   b  to be calculated in a step S 19  of  FIG. 4  also gradually increases.  
         [0067]     In a step S 63 , it is judged whether or not the lean rendering correction factor Klean after renewal exceeds “1.0” of the upper limit value, and if it is not exceeded, the lean rendering correction factor Klean concerned will be adopted as it is. Thereafter, at a time t 3  of  FIG. 7 , the lean rendering correction factor Klean reaches “1.0” and when this is detected in the step S 63 , the sequence will proceed to a step S 64 , where various correction factors will be initialized and the lean rendering correction factor Klean will be regulated at an upper limit value of “1.0”. Accordingly, the injection quantity Qlower of the downstream injection valve  8   b  to be calculated in a step S 19  of the  FIG. 4  also returns to the injection quantity to the level prior to when the injection from the upstream valve was stopped.  
         [0068]     According to the present invention, the following advantages will be achieved.  
         [0069]     (1) Since when the throttle valve is abruptly enclosed, the fuel injection from the upstream injection valve is stopped immediately, and fuel adhering to and remaining at the throttle valve is restricted to a minimum.  
         [0070]     (2) Since when the fuel injection from the upstream injection valve is stopped in response to the throttle valve being abruptly enclosed, the injection quantity from the downstream fuel injection valve is reduced, the total supply quantity of the fuel can be maintained at an appropriate value, even if a small amount of fuel which may have adhered to and have remained at the throttle valve is supplied into the combustion chamber when the throttle valve is opened again thereafter.  
         [0071]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.