Abstract:
Provided is a control device for an in-cylinder injection engine which reduces an amount of fuel attaching and remaining on a piston crown surface so as to bring the first injection as advanced as possible and suppress an increase in the number of exhaust particles of PM, when fuel injection is performed a plurality of times in one cycle in the in-cylinder injection engine. At least the first fuel injection of the respective injections dividedly performed the plurality of times is performed in an intake stroke. At least the first injection start timing of the respective injections dividedly performed the plurality of times is set in accordance with an EGR amount. The first injection start timing is more advanced when the EGR amount is large than when the EGR amount is small.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a control device for an in-cylinder fuel injection type internal combustion engine. 
         [0003]    2. Background Art 
         [0004]    An in-cylinder injection type internal combustion engine which injects fuel directly into a cylinder is widely known. The in-cylinder injection type internal combustion engine performs direct fuel injection into a combustion chamber by means of a fuel injection valve, and is intended to achieve a reduction in exhaust gas substance and fuel consumption, enhancement in output, and the like. 
         [0005]    In the in-cylinder injection type internal combustion engine, the injected fuel may attach to a piston crown surface or a cylinder bore wall surface depending on a fuel injection start timing. 
         [0006]    If an amount of fuel attaching and remaining on the cylinder bore wall surface is large, such fuel cannot be vaporized completely until ignition in some cases, so that unburned gas is apt to increase. Therefore, for example, JP Patent Publication (Kokai) No. 2009-102997 and JP Patent Publication (Kokai) No. 2009-102998 each disclose a technology of changing, when a temperature on the cylinder bore wall surface is low, the fuel injection start timing from an injector in an intake stroke so that the fuel spreads over the piston crown surface to be easily vaporized. 
         [0007]    In addition, JP Patent Publication (Kokai) No. 2002-161790 discloses a technology in which: fuel injection is performed a plurality of times in one cycle, and the fuel injection amount for each time is accordingly made smaller, to thereby reduce the fuel attachment to the cylinder bore wall surface; and an interval between one injection and the next injection is kept constant at a rough crank angle with respect to a change in operation conditions of an engine, that is, the injection interval is set to be longer as the rotation becomes lower and is set to be shorter as the rotation becomes higher, to thereby decentrally spray the fuel. 
         [0008]    On the other hand, if an amount of fuel attaching and remaining on the piston crown surface and the cylinder bore wall surface is large, the number of exhaust particles of particulate matters (hereinafter, referred to as PM) is apt to increase. In particular, if the amount of fuel attaching on the piston crown surface is large, the number of exhaust particles of PM is apt to increase. In recent years, there is an increasing need for the in-cylinder injection type internal combustion engine to reduce the number of exhaust particles of PM. 
       SUMMARY OF THE INVENTION 
       [0009]    In the in-cylinder injection type internal combustion engine, when the injection start timing is advanced in order to reduce the amount of fuel attaching and remaining on the cylinder bore wall surface, the amount of fuel attaching and remaining on the piston crown surface increases, and the number of exhaust particles of PM is apt to increase. On the other hand, when the injection start timing is retarded in order to suppress the increase in the number of exhaust particles of PM, the amount of fuel attaching and remaining on the cylinder bore wall surface increases, and unburned gas is apt to increase. 
         [0010]    Such a problem similarly arises in the case of divided injection in which the fuel injection is performed a plurality of times in one cycle. In addition, the interval between one injection and the next injection is required in the divided injection, and hence an end timing of the injection is closer to the retard side than the case of injecting the fuel only once in one cycle. If an end timing of the last divided injection is closer to the retard side than a predetermined crank angle, the fuel cannot be vaporized completely until ignition in some cases, so that the homogeneity of a mixture gas inside of the cylinder is apt to decrease. 
         [0011]    The present invention has an object to provide a control device for an in-cylinder injection type internal combustion engine which reduces an amount of fuel attaching and remaining on a piston crown surface so as to bring the first injection as advanced as possible and suppress an increase in the number of exhaust particles of PM, when fuel injection is performed a plurality of times in one cycle in the in-cylinder injection type internal combustion engine. 
         [0012]    In order to achieve the above-mentioned object, the present invention provides a control device for an in-cylinder fuel injection type internal combustion engine, in which a fuel injection valve which injects fuel directly into a combustion chamber is provided, the control device including: divided multi-stage injection means for performing fuel injection a plurality of times in one cycle; an EGR device which allows exhaust gas emitted from the combustion chamber to flow back into the combustion chamber; and means for detecting or calculating an EGR amount allowed to flow back into the combustion chamber, in which: at least a first fuel injection of the respective injections dividedly performed the plurality of times is performed in an intake stroke; at least a first injection start timing of the respective injections dividedly performed the plurality of times is set in accordance with an EGR amount; and the first injection start timing is more advanced when the EGR amount is large than when the EGR amount is small. 
         [0013]    According to the present invention, in divided multi-stage injection in which the fuel to be injected in one cycle is dividedly injected a plurality of times, the first injection start timing of the respective injections dividedly performed the plurality of times is set in accordance with the EGR amount. Accordingly, the divided multi-stage injection can be performed at such an injection timing that an amount of fuel attaching and remaining on a piston crown surface can be reduced, and an increase in the number of exhaust particles of PM can be suppressed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a configuration schematic view of an overall control system of an in-cylinder injection engine according to an embodiment of the present invention. 
           [0015]      FIG. 2  is a block diagram illustrating an input/output signal relation of an engine control unit, which is used in the system configuration describing an embodiment of a control device for the in-cylinder injection engine according to the embodiment of the present invention. 
           [0016]      FIG. 3  is a graph showing relations of a fuel attachment amount and a PM exhaust amount with a fuel injection timing. 
           [0017]      FIG. 4  is a graph showing relations of the PM exhaust amount, a fuel consumption rate, and an oil dilution ratio with the fuel injection timing. 
           [0018]      FIG. 5  is a graph showing a relation between the number of times of divided injections and the PM exhaust amount. 
           [0019]      FIG. 6  is a graph showing a relation between a divided injection interval and the PM exhaust amount. 
           [0020]      FIG. 7  is a graph showing a relation between an EGR amount and the PM exhaust amount. 
           [0021]      FIG. 8  is a flow chart showing control contents of divided multi-stage injection control of the in-cylinder injection engine according to the embodiment of the present invention. 
           [0022]      FIG. 9  is a flow chart showing processing contents of divided injection timing setting shown in  FIG. 8 . 
           [0023]      FIG. 10  is a graph showing a map function for calculating a basic injection timing shown in  FIG. 9 . 
           [0024]      FIG. 11  is a graph showing a map function for calculating a final injection timing shown in  FIG. 9 . 
           [0025]      FIG. 12  is a diagram illustrating a first control example of the divided multi-stage injection control according to the embodiment of the present invention. 
           [0026]      FIG. 13  is a diagram illustrating a second control example of the divided multi-stage injection control according to the embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]    Hereinafter, an embodiment of the present invention is described in detail with reference to the drawings. 
         [0028]      FIG. 1  is a configuration schematic view of an overall control system of an in-cylinder injection type internal combustion engine  1  constituting the embodiment of the present invention. Intake air taken in from an entrance part of an air cleaner  102  passes through an intake air flowmeter (airflow sensor)  103 , passes through an electronically-controlled throttle valve  104  which controls an intake air flow rate, is distributed to each intake pipe  105  connected to each cylinder, and then is introduced into a combustion chamber  106  of each cylinder. In addition, a signal representing the intake air flow rate is outputted from the intake air flowmeter  103  to an engine control unit  101 . A throttle opening degree sensor  107  which detects the opening degree of the electronically-controlled throttle valve  104  is attached, and a signal thereof is also outputted to the engine control unit  101 . 
         [0029]    Fuel is primarily pressurized by a low-pressure fuel pump (not shown), then is secondarily pressurized into a higher pressure by a high-pressure fuel pump  108 , passes through a common rail  117 , and is injected into the combustion chamber  106  from a fuel injection valve  109  provided to each cylinder. The fuel injected into the combustion chamber is used to generate a mixture gas with the intake air, is ignited at a spark plug  111  by ignition energy from an ignition coil  110 , and burns inside of the combustion chamber  106 . 
         [0030]    Exhaust gas emitted from the combustion chamber  106  is emitted to an exhaust pipe, and an EGR inlet is formed in the middle of the exhaust pipe. Part of the exhaust gas flowing through the exhaust pipe (EGR gas) enters an EGR pipe  112  from the EGR inlet, flows to an EGR control valve  113 , and flows back into the intake pipe  105  from an EGR outlet. 
         [0031]    A flow rate of the EGR gas is adjusted by the EGR control valve  113 . An EGR flow rate sensor  114  for sensing the flow rate of the EGR gas is attached to the inside of the EGR pipe. A flow rate detection signal of the EGR flow rate sensor is outputted to the engine control unit  101 . 
         [0032]    A crank angle sensor  116  attached to a crankshaft  115  of the engine outputs a signal representing a rotation position of the crankshaft to the engine control unit  101 . 
         [0033]      FIG. 2  illustrates an input/output relation of the engine control unit. The engine control unit  101  includes an I/O LSI  101   a  including an A/D converter, a CPU  101   b , and the like. The engine control unit  101  is configured to: take in, as inputs, signals from various sensors including the airflow sensor  103 , the throttle opening degree sensor  107 , the crank angle sensor  116 , a water temperature sensor  202 , an air-fuel ratio sensor  203 , a fuel pressure sensor  204 , an oil temperature sensor  205 , and the EGR flow rate sensor  114 ; execute predetermined arithmetic processing; output various control signals calculated as arithmetic processing results; and supply predetermined control signals to the electronically-controlled throttle valve  104 , a high-pressure pump solenoid  206 , the ignition coil  110 , and each fuel injection valve  109  which are actuators, to thereby perform control of fuel pressure inside of the common rail, fuel injection amount control, ignition timing control, and the like. The I/O LSI is provided with a drive circuit which drives each injector, causes a step-up circuit (not shown) to raise and supply a voltage supplied from a battery, and causes an IC (not shown) to control a current, to thereby drive each injector. 
         [0034]    With reference to  FIG. 3 , a relation between a fuel injection timing (a fuel injection start timing) and a PM exhaust amount is described. 
         [0035]      FIG. 3  shows relations of an amount of fuel attachment to a piston crown surface, an amount of fuel attachment to a cylinder bore, and the PM exhaust amount with the injection timing when the fuel is injected once. In the case where the fuel injection timing is excessively early (near TDC), the amount of fuel attachment to the piston crown surface increases, and the PM generation amount is apt to increase. On the other hand, in the case where the fuel injection timing is excessively late (near BDC), the amount of fuel attachment to the cylinder bore increases, and similarly, the PM generation amount is apt to increase. In addition, an influence of the PM generation amount on the fuel attachment to the cylinder bore is relatively smaller than that on the fuel attachment to the piston crown surface. 
         [0036]    In order to minimize the PM generation amount when the fuel is injected once, it is desirable to inject the fuel during the intake stroke middle period during which the sum of the amount of fuel attachment to the piston crown surface and the amount of fuel attachment to the cylinder bore becomes smallest. 
         [0037]    With reference to  FIG. 4 , relations of the PM exhaust amount, a fuel consumption rate, and an oil dilution ratio are described. 
         [0038]      FIG. 4  shows the PM exhaust amount, the fuel consumption rate, and the oil dilution ratio when the fuel injection timing is changed. The fuel injection timing at which the PM exhaust amount becomes smallest falls within the intake stroke middle period, whereas the fuel injection timings at which the fuel consumption rate and the oil dilution ratio become smallest fall within the intake stroke initial period. In order to make all the parameters the best, it is desirable to reduce PM at an early fuel injection timing. 
         [0039]    With reference to  FIG. 5 , a relation between the number of times of divided injections and the PM exhaust amount is described. 
         [0040]      FIG. 5  shows the PM exhaust amount with respect to the number of times of division when a fuel amount necessary for one cycle is divided and the fuel is injected a plurality of times. Each time the number of times of division is increased, the fuel injection amount for each time decreases. As a result, the fuel attachment to the piston crown surface decreases, and the PM exhaust amount decreases. 
         [0041]    With reference to  FIG. 6 , a relation between a divided injection interval and the PM exhaust amount is described. 
         [0042]    If the divided injection interval is excessively short, an effect of the divided injection cannot be obtained sufficiently, and hence a reduction in PM exhaust amount cannot be achieved. This means that it is necessary to set an interval between one injection and the next injection to a predetermined interval or longer in order to reduce the PM exhaust amount. 
         [0043]    With reference to  FIG. 7 , a relation between an EGR amount and the PM exhaust amount is described. 
         [0044]      FIG. 7  shows the PM exhaust amount when the EGR amount increases in order of (I)→(II)→(III)→(IV) during divided injection with a given number of times of division. As the EGR amount increases, the PM exhaust amount decreases. This is because a temperature of air taken into the combustion chamber is raised by the EGR gas, vaporization of the fuel injected into the cylinder is promoted, and the amount of fuel attachment to the piston crown surface is accordingly decreased. 
         [0045]    In the case of comparison using a given PM generation amount level, with reference to a fuel injection timing (A) at which the given PM exhaust amount can be achieved at the time of the EGR amount (I), as the EGR amount increases in order of (II)→(III)→(IV), the fuel injection timing (fuel injection start timing) at which the given PM generation amount can be achieved can be made earlier in order of (B)→(C)→(D). 
         [0046]    Next, with reference to  FIG. 8  to  FIG. 11 , specific control contents of divided multi-stage injection control of the internal combustion engine according to the present embodiment are described. 
         [0047]      FIG. 8  is a flow chart showing the control contents of the divided multi-stage injection control according to the embodiment of the present invention. 
         [0048]    The contents of  FIG. 8  are programmed in the CPU of the engine control unit  101 , and are repeatedly executed in a predetermined cycle. On the basis of an injection pulse width and an injection timing which are calculated according to the processing contents of  FIG. 8 , the engine control unit  101  supplies a predetermined control signal to each fuel injection valve  109 , and executes a plurality of fuel injections in one cycle. 
         [0049]    In Step  801 , a total injection pulse width TI_TOTAL, which is a total fuel amount injected in one cycle from each fuel injection valve  109 , is set. The total injection pulse width TI_TOTAL is set in accordance with an intake air amount sensed by the airflow sensor  103 , an air-fuel ratio set according to an operation state and the like, a fuel pressure calculated using a signal of the fuel pressure sensor  204 , and the like. 
         [0050]    In Step  802 , a minimum injection pulse width TI_MIN is calculated. Here, the minimum injection pulse width is set in accordance with various characteristics such as a fuel pressure characteristic, an electrical characteristic, and a mechanical characteristic of the fuel injection valve  109  and a drive current waveform of the injector. 
         [0051]    In Step  803 , the injection interval, which is an injection interval between divided injections, is calculated. The injection interval is set to a predetermined interval or longer in terms of fuel attachment and homogeneity of the mixture gas and in terms of securement of an injector drive current. If the injection interval is excessively short, a fuel spray state becomes substantially the same as that of one-time injection. As a result, an effect of the divided injection cannot be obtained, and the fuel attachment to the piston crown surface and the cylinder bore cannot be decreased. In addition, each time the injector drive circuit drives the injector, a voltage in the step-up circuit drops. Therefore, a period of time until a return to its original voltage is required, and it is necessary to stand by without performing the next fuel injection during this step-up return period. 
         [0052]    In Step  804 , a division count N is set. A division expression of TI_TOTAL÷TI_MIN is calculated by using the total injection pulse width TI_TOTAL set in Step  801  and the minimum injection pulse width TI_MIN set in Step  802 , and the resultant quotient is set as the division count N. 
         [0053]    In Step  805 , a counter n is initialized. 
         [0054]    In Step  806 , it is determined whether or not the counter n is larger than the division count N. If yes (settings of n=1 to N are completed), the processing is finished. If the counter n is equal to or smaller than the division count N, processing in Step  807  and the subsequent steps is performed. 
         [0055]    In Step  807 , an injection pulse width TI_n (n=1 to N) of each injection is calculated. A division expression of TI_TOTAL÷N is calculated by using the total injection pulse width TI_TOTAL calculated in Step  801  and the division count N calculated in Step  804 . 
         [0056]    In Step  808 , an EGR rate is calculated. The EGR rate REGR is obtained by calculating a division expression of QEGR÷(QA+QEGR) by using an EGR gas amount QEGR sensed by the EGR flow rate sensor  114  and an intake air amount QA sensed by the airflow sensor  103 . 
         [0057]    In Step  809 , an injection timing (an injection start timing) of each injection in the divided multi-stage injection is set. The detail of Step  809  is shown in  FIG. 9 . 
         [0058]    In Step  810 , an increment process of the counter n is performed, and the processing returns to Step  805 . In this way, processing of n=1 to N is repeated, and each injection pulse width and each injection timing are set. 
         [0059]    With reference to  FIG. 9 , the detail of Step  809  (injection timing setting) of  FIG. 8  is described. 
         [0060]    In Step  901 , a basic injection timing is calculated. The basic injection timing ITB is calculated by using, as inputs, the divided injection pulse width TI_n calculated in Step  807  of  FIG. 8  and the EGR rate REGR calculated in Step  808  of  FIG. 8  to thereby refer to a map MITB as shown in  FIG. 10 . The map MITB sets thereon a basic fuel injection timing (a basic fuel injection start timing) in consideration of a fuel attachment amount based on the divided fuel injection amount and a vaporization rate increase amount based on EGR. 
         [0061]    In Step  902 , a final injection timing (a final fuel injection start timing) ITF, to which correction of a piston crown surface temperature TPI is added, is calculated. 
         [0062]    The final injection timing ITF is calculated by using, as inputs, the basic injection timing ITB calculated in Step  901  and the piston crown surface temperature TPI to thereby refer to a map MITF as shown in  FIG. 11 . The map MITF is set in consideration of an influence of the piston crown surface temperature TPI on a fuel attachment amount and a vaporization rate. In addition, it is desirable to estimate the crown surface temperature TPI according to a method of using an air amount, an air-fuel ratio, ignition timing, and the like to thereby configure a thermal model. From a point of view of simplification in control, the crown surface temperature TPI may be estimated by using, as input values, a water temperature and an oil temperature sensed by the water temperature sensor  202  and the oil temperature sensor  205  to thereby search the map MITF. 
         [0063]    In Step  903 , it is determined whether or not the first injection timing (the first injection start timing) of the divided injections in one cycle is to be set. If n=1, the processing proceeds to Step  905 , and is finished by making such setting that the first injection timing IT 1 =ITF. If n≠1 (in the case of the second or subsequent injection timing), the processing proceeds to Step  904 , and an n-th injection start possible angle IT_n is calculated. The n-th injection start possible angle IT_n is calculated by adding the divided injection pulse width TI_(n−1) and the injection interval TI_INT calculated in Step  803  of  FIG. 8  to previous IT_(n−1). 
         [0064]    With reference to  FIG. 12  and  FIG. 13 , specific control examples obtained by configuring as shown in  FIG. 8  to  FIG. 11  are described. 
         [0065]      FIG. 12  is a diagram illustrating an injection timing when fuel injection is dividedly performed three times in I cycle in the state where the piston crown surface temperature is high, for example, in the case where the engine is completely warmed up. The lower part corresponds to when the EGR amount has a small flow rate, the middle part corresponds to when the EGR amount has a middle flow rate, and the upper part corresponds to when the EGR amount has a large flow rate. The first injection timing is advanced in accordance with the EGR amount. The second and subsequent injections are also changed to the advance side in accordance with the first injection timing advance amount, while the injection interval is maintained. 
         [0066]      FIG. 13  is a diagram illustrating an injection timing when fuel injection is dividedly performed three times in I cycle in the state where the piston crown surface temperature is lower than the piston crown surface temperature (ordinary temperature) in the complete warming up of the engine, for example, in the middle of a warm-up operation after start of the engine. The lower part corresponds to when the EGR amount has a small flow rate, the middle part corresponds to when the EGR amount has a middle flow rate, and the upper part corresponds to when the EGR amount has a large flow rate. Although the first injection timing is advanced in accordance with the EGR amount similarly to the case illustrated in  FIG. 12  where the piston crown surface temperature is high, the first injection timing is closer to the retard side than the case where the temperature is high. In the same manner, the second and subsequent injections are changed to the advance side in accordance with the first injection timing advance amount, while the injection interval is maintained.