JP2013119810A - Fuel injection control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent excessive fuel injection out of a direct injection injector due to becoming high in pressure of fuel supplied to the direct injection injector, resulting in deterioration of fuel combustion in a cylinder.SOLUTION: In separately jetting injection of a port injection injector 6 and a direct injection injector 7, when high pressure time injection control is performed when direct injection pressure becomes a determining value or more, fuel injected from the direct injection injector 7 is increased as compared with a case where the direct injection pressure is less than the determining value and ordinary injection control is performed. This is achieved by setting the separately injecting ratio K in the separately jetting injection in the high pressure time injection control as a value near to 0% as compared with the separately injecting ratio K in the separately jetting injection in the ordinary injection control. When the fuel injected from the direct injection injector 7 increases, since the fuel in a high pressure fuel pipe 33 connected to the direct injection injector 7 is quickly consumed, the direct injection pressure quickly reduces.

Description

  The present invention relates to a fuel injection control device for an internal combustion engine.

  As shown in Patent Document 1, an internal combustion engine mounted on a vehicle has been put into practical use that includes a port injection injector that injects fuel into an intake port and a direct injection injector that injects fuel into a cylinder. . In the engine, an amount of fuel corresponding to an injection amount command value determined based on the engine operating state is injected from the port injector and the direct injection injector with an injection ratio determined according to the engine operating state. The divided injection is performed in which the injection is performed separately from the injection.

  In this injection-split injection, for example, fuel injection from a port injection injector and fuel injection from a direct injection injector are performed as follows. That is, the injection amount command value is divided into a port injection command value and a direct injection command value based on an injection distribution ratio determined according to the engine operating state, and an amount of fuel corresponding to the port injection command value is supplied from the port injection injector. In addition to injection, an amount of fuel corresponding to the direct injection command value is injected from the direct injection injector.

  The amount of fuel injected from an injector such as a port injection injector or a direct injection injector is determined based on the pressure of the fuel supplied to the injector and the valve opening time (fuel injection time) of the injector. Therefore, in the port injection injector in the divided injection, the port injection injector is configured so that an amount of fuel corresponding to the port injection amount command value is injected under the pressure of the fuel supplied to the injector at that time. The fuel injection time is controlled. Further, in the direct injection injector in the divided injection, the fuel of the direct injection injector is injected so that the fuel corresponding to the direct injection command value is injected under the pressure of the fuel supplied to the injector at that time. The injection time is controlled.

JP 2001-336439 A

  By the way, in the internal combustion engine capable of performing the divided injection, the pressure of the fuel supplied to the direct injection injector is changed to the port injection in order to realize the fuel injection from the direct injection into the cylinder having a high pressure. It is adjusted to a value higher than the pressure of the fuel supplied to the injector. Since the pressure of the fuel supplied to the direct injection injector is thus increased, the fuel injection time tends to be shortened in the direct injection injector. Therefore, if the pressure of the fuel supplied to the direct injection injector becomes too high, when the fuel injection time of the direct injection injector is shortened accordingly, the fuel injection time becomes less than the minimum value due to the structure of the direct injection injector. There is a risk.

  Incidentally, as a situation where the pressure of the fuel supplied to the direct injection injector becomes too high, for example, after fuel injection from only the port injection injector continues, the above-described injection is started and fuel injection from the direct injection injector is started. The situation of being done is given. When fuel injection from only the port injector continues, fuel injection from the direct injection injector is not performed, so that the fuel stagnates in the fuel supply system connected to the direct injection injector. As described above, when the fuel stagnates in the fuel supply system connected to the direct injection injector, the fuel expands by receiving heat from the internal combustion engine or the like, so that the pressure of the fuel supplied to the direct injection injector increases.

  Under these circumstances, when fuel injection from the direct injection injector is performed when the above-described injection divided injection is started, if an amount of fuel corresponding to the direct injection command value is to be injected from the direct injection injector, Since the pressure is high, the fuel injection time must be shortened. If the fuel injection time at this time is less than the minimum value, fuel injection from the direct injector may not be stably performed. For this reason, the fuel injection time in the direct injection injector is guarded at the lower limit with the minimum value. However, if the fuel injection time in the direct injection injector is guarded at the lower limit with the above minimum value, the amount of fuel injected from the direct injection injector becomes excessive, which adversely affects the combustion of fuel in the cylinder. May cause effects.

  Patent Document 1 discloses that the above-described injection division ratio is set so that the fuel injection from the direct injection injector increases as the pressure of the fuel supplied to the direct injection injector decreases. However, even if such a technique is used, when the pressure of the fuel supplied to the direct injection injector becomes high and the fuel injection time from the direct injection injector becomes less than the minimum value, the fuel injection time is the minimum value. Therefore, the problem that the amount of fuel injected from the direct injection injector becomes excessive due to the lower limit guard cannot be avoided.

  The present invention has been made in view of such circumstances, and its purpose is that excessive fuel injection from the direct injection injector is caused by an increase in the pressure of fuel supplied to the direct injection injector. It is an object of the present invention to provide a control device for an internal combustion engine capable of suppressing deterioration of fuel combustion in a cylinder resulting from the above.

In the following, means for achieving the above object and its effects are described.
According to the first aspect of the present invention, the amount of fuel corresponding to the injection amount command value is divided into the injection from the port injection injector and the injection from the direct injection injector with the injection ratio determined according to the engine operating state. Divided jets that are jetted separately are performed. In performing this divided injection, the pressure of the fuel supplied to the direct injection injector becomes high, and the fuel injection time in the direct injection required based on the pressure may be less than the minimum value due to the structure. is there. When the fuel injection amount in the direct injection injector becomes less than the minimum value, the fuel injection amount is forcibly guarded at the lower limit by the minimum value, so that the amount of fuel injected from the direct injection injector is excessive. This may adversely affect the combustion of fuel in the cylinder.

  However, according to the first aspect of the present invention, when performing the divided injection, when the pressure of the fuel supplied to the direct injection injector is equal to or higher than the judgment value, the injection is performed at the injection ratio determined according to the engine operating state. Compared with the case of performing the divided injection, high-pressure injection control is performed in which the divided injection is performed at the injection ratio at which the fuel injection from the direct injection injector increases. When this high-pressure injection control is executed, the amount of fuel injected from the direct injection injector increases and the fuel in the fuel supply system connected to the direct injection injector is quickly consumed, so the pressure of the fuel quickly decreases. To come. Therefore, when the pressure of the fuel supplied to the direct injection injector is high, the fuel injection time of the direct injection injector may be less than the minimum value and may be guarded at the lower limit with the minimum value. Through the execution of the injection control, the pressure of the fuel supplied to the direct injection injector can be quickly reduced. And by the rapid fall of the pressure of the above-mentioned fuel, it can control that the fuel injection time of the direct-injector calculated based on the pressure of the fuel becomes less than the above-mentioned minimum value. Therefore, when the pressure of the fuel supplied to the direct injection injector is high, the amount of fuel injected from the direct injection injector is excessive as the fuel injection time of the direct injection injector is guarded at the lower limit with the above minimum value. It is possible to suppress the deterioration of the combustion of the fuel in the cylinder caused by the excessive amount of the injected fuel.

  Here, during the execution of the high pressure injection control and the engine high load operation, the fuel injection amount to be injected from the direct injection injector increases because of the relationship that the injection amount command value becomes large, and the direct injection injector Even if the pressure of the supplied fuel is high, the fuel injection time of the direct injector does not become less than the minimum value. Under these circumstances, the above-mentioned injection division is performed at an injection division rate at which the fuel injection from the direct injection injector increases compared to when performing injection injection at the injection division rate determined according to the engine operating condition. When the injection is performed, it becomes difficult to obtain the maximum effect by performing the divided injection between the port injection injector and the direct injection injector. This is because, as described above, the injection ratio at the time of performing the divided injection is a value at which the fuel injection from the direct injection injector is larger than the value obtained based on the engine operating state. In this respect, in the first aspect of the present invention, the injection ratio is made equal to the value determined according to the engine operating state during the high-pressure injection control and the engine high load operation. It is possible to obtain the maximum effect by performing the divided injection by the port injection injector and the direct injection injector during the engine high load operation.

  According to the second aspect of the present invention, when fuel is injected from both the direct injection injector and the port injection injector during the high pressure injection control, the injection ratio at that time is determined from the direct injection injector. Guards in the direction of increasing fuel injection. Here, when fuel is injected from both the direct injector and the port injector during the high pressure injection control, if the amount of fuel injected from the port injector is too small, The fuel combustion at the plant gets worse. Specifically, if the amount of fuel injected from the port injector is too small and the fuel injection time in the port injector becomes less than the minimum value due to its structure, fuel injection from the port injector will not be performed stably. The amount of fuel injected from the port injector varies. As a result, it is inevitable that the amount of fuel supplied into the cylinder deviates from an appropriate value, resulting in a problem that fuel combustion in the cylinder deteriorates. However, when high-pressure injection control is being performed and fuel is injected from both the direct injection injector and the port injection injector, the fuel injection from the direct injection injector is large as described above. If the direction is guarded, the fuel injection amount from the port injector will not be excessively reduced. Therefore, it is possible to suppress the fuel injection time at the port injector from becoming less than the above minimum value, and thus to suppress the occurrence of the problem of the deterioration of fuel combustion in the cylinder described above.

1 is a schematic diagram showing an entire internal combustion engine to which a fuel injection control device of the present invention is applied. Explanatory drawing which shows the port injection area | region, the direct injection area | region, and the injection division area | region in an engine operation area | region. Explanatory drawing which shows the relationship between the fuel injection time in an injector, and a fuel pressure. The flowchart which shows the execution procedure of spray injection. The graph which shows the difference of the transition according to the change of the engine load of the injection ratio in the high pressure injection control, and the injection ratio in the normal injection control.

Hereinafter, an embodiment in which the present invention is embodied in a fuel injection control device for an automobile engine will be described with reference to FIGS.
An intake passage 2 of the internal combustion engine 1 shown in FIG. 1 is provided with a throttle valve 4 that opens and closes to adjust the amount of air taken into the combustion chamber 3 (intake air amount). The opening degree of the throttle valve 4 (throttle opening degree) is adjusted according to the operation amount (accelerator operation amount) of the accelerator pedal 5 that is depressed by the driver of the automobile. Further, the internal combustion engine 1 includes a port injection injector 6 that injects fuel from the intake passage 2 toward the intake port 2a of the combustion chamber 3, and a direct injection injector 7 that injects fuel into the combustion chamber 3 (in the cylinder). I have. The fuel stored in the fuel tank 8 is supplied to the injectors 6 and 7.

  That is, the fuel in the fuel tank 8 is pumped up by the feed pump 9 and then supplied to the port injector 6 via the low-pressure fuel pipe 31. The pressure of the fuel in the low-pressure fuel pipe 31 is adjusted to the feed pressure through the drive control of the feed pump 9 and is prevented from excessively rising by the pressure regulator 32 provided in the pipe 31. Further, a part of the fuel in the low-pressure fuel pipe 31 pumped up by the feed pump 9 is pressurized to a pressure higher than the above-mentioned feed pressure (hereinafter referred to as direct injection pressure) by the high-pressure fuel pump 10 and then the high-pressure fuel. It is supplied to the direct injection injector 7 through the pipe 33.

  In the internal combustion engine 1, an air-fuel mixture consisting of fuel injected from the injectors 6 and 7 and air flowing through the intake passage 2 is filled in the combustion chamber 3, and the air-fuel mixture is ignited by the spark plug 12. When the air-fuel mixture after ignition burns, the piston 13 reciprocates due to the combustion energy at that time, and the crankshaft 14 rotates accordingly. On the other hand, the air-fuel mixture after combustion is sent to the exhaust passage 15 as exhaust gas. Note that the combustion chamber 3 and the intake passage 2 are communicated and blocked by an intake valve 26 that opens and closes as the intake camshaft 25 that receives rotation transmission from the crankshaft 14 rotates. Further, the combustion chamber 3 and the exhaust passage 15 are communicated and blocked by an exhaust valve 28 that opens and closes as the exhaust camshaft 27 that receives the rotation transmission from the crankshaft 14 rotates.

Next, the electrical configuration of the fuel injection control device in the internal combustion engine 1 will be described.
The fuel injection control device includes an electronic control device 16 that controls various operations of the internal combustion engine 1. The electronic control unit 16 includes a CPU that executes various arithmetic processes related to the various operation controls, a ROM that stores programs and data necessary for the control, a RAM that temporarily stores CPU calculation results, An input / output port for inputting / outputting a signal is provided.

Various sensors shown below are connected to the input port of the electronic control unit 16.
An accelerator position sensor 17 that detects an accelerator operation amount.
A throttle position sensor 18 that detects the throttle opening.

An air flow meter 19 that detects the amount of air passing through the intake passage 2 (intake air amount of the internal combustion engine 1).
A crank position sensor 20 that outputs a signal corresponding to the rotation of the crankshaft 14.

A cam position sensor 21 that outputs a signal corresponding to the rotational position of the shaft 27 based on the rotation of the intake camshaft 25.
A first pressure sensor 23 that detects the fuel pressure (feed pressure) in the low-pressure fuel pipe 31.

A second pressure sensor 24 that detects the pressure of fuel in the high-pressure fuel pipe 33 (direct injection pressure).
The output port of the electronic control unit 16 is connected to drive circuits of various devices such as the throttle valve 4, the port injection injector 6, the direct injection injector 7, the feed pump 9, the high-pressure fuel pump 10, and the spark plug 12. Yes.

  Then, the electronic control unit 16 grasps the engine operation state such as the engine rotation speed and the engine load based on the signals inputted from the various sensors and the like, and based on the grasped engine operation state, the throttle valve 4, the injectors 6, 7, Command signals are output to drive circuits of various devices such as the feed pump 9 and the spark plug 12. Thus, various operation controls of the internal combustion engine 1, such as throttle opening control of the internal combustion engine 1, fuel injection control, pressure control of the fuel supplied to the injectors 6 and 7, and ignition timing control of the internal combustion engine 1, are electronically controlled. Implemented through device 16. Incidentally, the engine rotation speed is obtained based on a detection signal from the crank position sensor 20. The engine load is calculated from a parameter corresponding to the intake air amount of the internal combustion engine 1 and the engine speed. The parameters corresponding to the intake air amount include an actually measured value of the intake air amount of the internal combustion engine 1 obtained based on the detection signal from the air flow meter 19, a throttle opening degree obtained based on the detection signal from the throttle position sensor 18, And the accelerator depression amount obtained based on the detection signal from the accelerator position sensor 17.

Next, fuel injection control using the port injection injector 6 and the direct injection injector 7 in the internal combustion engine 1 will be described.
In this fuel injection control, an injection amount command value Qfin is obtained based on the engine operating state such as the engine rotation speed and the engine load, and an amount of fuel corresponding to the injection amount command value Qfin is supplied to the port injector 6 and the direct injection injector 7. It is realized by injecting from at least one. By the way, in this internal combustion engine 1, every engine operation area divided according to the engine speed and engine load, that is, every port injection area A1, direct injection area A2, and injection division area A3 shown in FIG. Injectors 6 and 7 used for fuel injection are selected.

  In FIG. 2, the low rotation and low load region of the internal combustion engine 1 is a port injection region A1 in which fuel is injected from the port injection injector 6 for the injection amount command value Qfin. This is because in the low rotation and low load region of the internal combustion engine 1, since the moving speed of the piston 13 becomes slow, it is difficult for the air and fuel to be mixed by the movement of the piston 13 in the combustion chamber 3, and the port injector 6 This is because it is preferable to inject the fuel from only the fuel and to mix the fuel with air in the intake port 2a before sucking it into the combustion chamber 3. Further, in the low rotation and low load region of the internal combustion engine 1, the noise level of the internal combustion engine 1 is low. Therefore, if the fuel injection from the direct injection injector 7 is performed, the noise when the injector 7 is opened becomes a problem. In order to avoid such a problem, the low rotation and low load region of the internal combustion engine 1 is set as the port injection region.

  Further, the high rotation / high load region of the internal combustion engine 1 is a direct injection region A2 in which fuel is injected from the direct injection injector 7 by the injection amount command value Qfin. This is because the piston 13 is cooled by the latent heat of vaporization of the fuel injected from the direct injection injector 7 in the high-rotation and high-load region of the internal combustion engine 1 to increase the intake charging efficiency of the internal combustion engine 1. This is because it is preferable for improving the output of 1. Accordingly, the direct injection region A2 is set to a region in which the output of the internal combustion engine 1 can be expected by direct fuel injection from the direct injection injector 7 into the combustion chamber 3. In FIG. 2, the region between the high load operation region and the low load operation region of the internal combustion engine 1 has characteristics of both the high load region and the low load region. In order to cope with this, it is an injection region A3 in which fuel is injected from both the port injector 6 and the direct injector 7.

  Here, the fuel injection from the port injector 6 and the direct injector 7 (split-split injection) in the spray splitting area A3 will be described in detail. When this divided injection is performed, the injection amount command value Qfin is converted into the port injection command value QP and the direct injection command value QD with an injection distribution ratio K obtained based on the engine operating state such as the engine speed and the engine load. Divided. The total value of the port injection command value QP and the direct injection command value QD thus divided is equal to the injection amount command value Qfin. In addition, the above-mentioned spray division ratio K changes in the range of “0% to 100%”. The direct injection command value QD increases and the port injection command value QP decreases as the injection ratio K becomes closer to “0%”. When the injection division ratio K becomes “0%”, the port injection command value QP becomes “0”, and the direct injection command value QD becomes equal to the injection amount command value Qfin. Further, the direct injection command value QD becomes smaller and the port injection command value QP becomes larger as the injection division ratio K becomes closer to “100%”. When the injection division ratio K becomes “100%”, the direct injection command value QD becomes “0”, and the port injection command value QP becomes equal to the injection amount command value Qfin. As described above, when the port injection command value QP and the direct injection command value QD are determined, the injector 6 is driven so that fuel is injected from the port injector 6 in an amount corresponding to the port injection command value QP. The injector 7 is driven so that fuel injection of an amount corresponding to the direct injection command value QD is performed from the direct injection injector 7.

  In the divided injection, the fuel injection for the port injection command value QP by the port injection injector 6 is realized, for example, as follows. That is, under the feed pressure detected by the first pressure sensor 23, the fuel injection time TAUP of the injector 6 necessary for injecting fuel for the port injection command value QP from the port injector 6 is the feed pressure. Based on. Then, by opening the port injector 6 for the fuel injection time TAUP, fuel injection for the port injection command value QP by the injector 6 is performed. On the other hand, fuel injection for the direct injection command value QD by the direct injection injector 7 is realized as follows, for example. That is, under the direct injection pressure detected by the second pressure sensor 24, the fuel injection time TAUD of the injector 7 necessary for injecting the fuel corresponding to the direct injection command value QD from the direct injection injector 7 is equal to the direct injection pressure. It is determined based on the jet pressure. Then, by opening the direct injection injector 7 for the fuel injection time TAUD, fuel injection for the direct injection command value QD by the injector 7 is performed.

  In a fuel injection valve (injector) such as the port injection injector 6 or the direct injection injector 7, the relationship between the fuel injection amount, the fuel pressure, and the fuel injection time is as shown by a solid line in FIG. This solid line shows the combination of the fuel pressure and the fuel injection time under the condition that the fuel injection amount is constant, and the above right combination in the figure shows the above combination under the condition that the fuel injection amount is increased. . The injector has a minimum fuel injection time due to its structure. This minimum value changes, for example, as shown by a broken line in FIG. If the fuel injection time is shorter than the minimum value, the fuel injection from the injector becomes unstable and the fuel injection amount cannot be adjusted accurately. For this reason, when adjusting the fuel injection time of the injector in fuel injection amount control or the like, the lower limit is guarded so that the fuel injection time does not become less than the minimum value. Incidentally, the minimum value TAUPmin of the fuel injection time in the port injector 6 changes according to the feed pressure, and the minimum value TAUDmin of the fuel injection time in the direct injection injector 7 changes according to the direct injection pressure. The minimum values TAUPmin and TAUDmin in the port injector 6 and the direct injection injector 7 change in different modes with respect to changes in the fuel pressure (feed pressure and direct injection pressure).

  By the way, since the pressure (direct injection pressure) of the fuel supplied to the direct injection injector 7 becomes higher than the pressure (feed pressure) of the fuel supplied to the port injection injector 6, the direct injection injector 7 uses the port injection injector 6. The fuel injection time tends to be shorter than that. Therefore, if the direct injection pressure becomes too high, the fuel injection time TAUD may be less than the minimum value TAUDmin when the fuel injection time TAUD of the direct injection injector 7 is shortened accordingly. The situation in which the direct injection pressure becomes too high is, for example, a situation in which fuel injection from only the port injector 6 is continued, and then the above-described injection is started and fuel injection from the direct injection injector 7 is performed. Can be given. When fuel injection from only the port injector 6 continues, fuel injection from the direct injection injector 7 is not performed, so that the fuel is stagnated in the high-pressure fuel pipe 33 connected to the direct injection injector 7. The stagnant fuel expands by receiving heat from the internal combustion engine 1 or the like, and the pressure of the fuel supplied to the direct injection injector 7 (direct injection pressure) increases.

  Under these circumstances, when fuel injection from the direct injection injector 7 is performed after the above-described divided injection is started, an amount of fuel corresponding to the direct injection command value QD is to be injected from the direct injection injector 7. Since the direct injection pressure is high as described above, the fuel injection time TAUD must be shortened. If the fuel injection time TAUD at this time is less than the minimum value TAUDmin, there is a possibility that fuel injection from the direct injection injector cannot be performed stably. Therefore, the fuel injection time TAUD in the direct injection injector 7 is the minimum value. The lower limit is guarded by TAUDmin. However, if the fuel injection time TAUD in the direct injection injector 7 is guarded at the lower limit with the minimum value TAUDmin as described above, the amount of fuel injected from the direct injection injector 7 becomes excessive, and this is caused in the combustion chamber 3. May adversely affect the combustion of the air-fuel mixture (fuel).

  In order to cope with this, in the present embodiment, when the direct injection pressure is equal to or higher than the determination value, the separate injection is performed at the injection ratio K determined according to the engine operating state. Compared to the time (normal injection control), the high-pressure injection control is performed in which the injection divided injection is performed at the injection dividing ratio K at which the fuel injection from the direct injection injector 7 increases.

  Next, the operation of the fuel injection control device when performing the high-pressure injection control will be described with reference to the flowchart of FIG. This spray injection routine is periodically executed, for example, by a time interruption every predetermined time through the electronic control device 16 when the engine operating state is in the spray distribution area A3 (FIG. 2).

  In the injection control routine of FIG. 4, S101 to S103 are processes for calculating the injection ratio K, S104 and S105 are processes for guarding the lower limit of the injection ratio K, and S106 has the injection ratio K. This is a process for performing the spray-split. In the routine, the high-pressure injection control is realized through the processes of S102 and S106, while the normal injection control is realized through the processes of S103 and S106.

  In this routine, it is first determined whether or not the direct injection pressure is greater than or equal to a determination value (S101). This determination value is determined in advance by experiments or the like so as to be an optimum value for determining whether or not the fuel injection time TAUD of the direct injection injector 7 may be less than the minimum value TAUDmin. A value is used. In the process of S101, if it is determined that the direct injection pressure is less than the determination value and the possibility that the fuel injection time TAUD of the direct injection injector 7 will be less than the minimum value TAUDmin is small, the engine rotational speed and the engine load are normally set. Based on the engine operating state, the injection ratio K is calculated with reference to the normal fuel pressure map set corresponding to the normal direct injection pressure (S103). The injection ratio K calculated in this way changes as shown by a solid line in FIG. 5, for example, as the engine load increases. As can be seen from this solid line, the injection ratio K is 100% in the low load area (less than KL1), while the injection ratio K is 0% in the area where the engine load is higher than the low load area (KL1 or more). And a value between 100%.

  On the other hand, in the process of S101 of FIG. 4, if it is determined that there is a high possibility that the direct injection pressure is greater than or equal to the determination value and the fuel injection time TAUD of the direct injection injector 7 is less than the minimum value TAUDmin, the high-pressure injection is performed. A control injection ratio K is calculated (S102). Specifically, based on the engine operating state such as the engine rotation speed and the engine load, the injection ratio K is calculated with reference to a map for high fuel pressure set corresponding to a state in which the direct injection pressure is equal to or higher than the determination value. (S102). The injection ratio K calculated in this way changes as shown by a broken line in FIG. 5, for example, as the engine load increases. As can be seen from this broken line, in the low load region (less than KL1), the injection ratio K is 100%, while in the medium load region (KL1 to KL2), the injection ratio K is 0%. Furthermore, a first high load region (KL2 to KL3) in which the engine load is higher than the medium load region, and a second high load region in which the engine load is higher than the first high load region. In (KL3 or more), the spray distribution ratio K is greater than 0%. In the second high load region, the injection ratio K is equal to the value (solid line) calculated with reference to the normal fuel pressure map.

  When the injection ratio K is calculated in S102 or S103, the lower limit guard process (S104, S105) for the injection ratio K is performed, and then the injection is performed with the injection ratio K (S106). Specifically, the injection amount command value Qfin is divided into the port injection command value QP and the direct injection command value QD with the above-described injection division ratio K. Then, the injector 6 is driven so that the fuel injection of the amount corresponding to the port injection command value QP is performed from the port injection injector 6, while the fuel injection of the amount corresponding to the direct injection command value QD is performed from the direct injection injector 7. The injector 7 is driven to do so.

  In the injection control routine, when the high-pressure injection control is executed through the processes of S102 and S106, the fuel injected from the direct injection injector 7 is smaller than when the normal injection control is executed through the processes of S103 and S106. Become more. This is because, as shown in FIG. 5, the injection ratio K (broken line) in the high-pressure injection control is closer to 0% than the injection ratio K (solid line) in the normal injection control. is there. When the fuel injected from the direct injection injector 7 increases through the execution of the high pressure injection control, the fuel in the high pressure fuel pipe 33 connected to the direct injection injector 7 is quickly consumed. (Direct injection pressure) starts to drop quickly. Therefore, when the direct injection pressure is a high value such as the determination value or more, the fuel injection time TAUD of the direct injection injector 7 may be longer than the minimum value TAUDmin and may be guarded at the lower limit by the minimum value TAUDmin. The direct injection pressure can be quickly reduced through the execution of the high-pressure injection control. And by the rapid fall of the said direct injection pressure, it can suppress that the fuel injection time TAUD of the direct injection injector 7 calculated | required based on the direct injection pressure becomes less than the said minimum value TAUDmin. Therefore, when the direct injection pressure is high, the fuel injection time TAUD of the direct injection injector 7 is guarded at the lower limit by the minimum value TAUDmin, and therefore the amount of fuel injected from the direct injection injector 7 is prevented from being excessive. It is possible to suppress the deterioration of fuel combustion in the cylinder due to the excessive amount of injected fuel.

  Here, during the execution of the high-pressure injection control and when the internal combustion engine 1 is operated at a high load, the fuel injection amount (direct injection) to be injected from the direct injection injector 7 because the injection amount command value Qfin becomes a large value. The command value QD) also increases. As a result, even if the direct injection pressure becomes a high value equal to or higher than the determination value, the fuel injection time TAUD of the direct injection injector 7 does not become less than the minimum value TAUDmin. Under these circumstances, the injection ratio at which the fuel injection from the direct injection injectors 7 is larger than when the injection is performed at the injection ratio K in the normal injection control, in other words, the above-described injection ratio. If spray injection is performed at a spray distribution rate closer to 0% than K, the following problem occurs. That is, the injection ratio K in the normal injection control is such as the engine speed and the engine load so that the effects of performing the injection divided injection by the port injection injector 6 and the direct injection injector 7 can be maximized. Determined based on engine operating conditions. However, when the divided injection is performed at the injection ratio at which the fuel injection from the direct injection injector 7 is increased as compared with the case where the divided injection is performed at the injection ratio K in the normal injection control, the direct injection from the direct injection injector 7 It is difficult to obtain the effect of performing the divided injection as much as the fuel injection increases.

  Considering this, when the high-pressure injection control is being performed and the engine load is in the second high load region (KL3 or higher in FIG. 5), the injection ratio K (broken line) in the high-pressure injection control is It is made equal to the injection division rate K (solid line) in the normal injection control. Therefore, even when the direct injection pressure is high, the fuel injection time TAUD of the direct injection injector 7 does not become less than the minimum value TAUDmin. Therefore, it can be avoided that the effect of performing the divided injection becomes difficult because the fuel injection from the direct injection injector 7 increases. Accordingly, when the high-pressure injection control is being performed and the engine load is in the second high load region, the effect obtained by performing the divided injection by the port injection injector 6 and the direct injection injector 7 can be maximized. be able to.

  Note that when the high-pressure injection control is being performed and fuel is injected from both the direct injector 7 and the port injector 6, the fuel injection amount (port injection command value QP) from the port injector 6 is small. If it is too long, the combustion of the fuel in the cylinder deteriorates due to this. Specifically, when the port injection command value QP is too small and the fuel injection time TAUP in the port injector 6 becomes less than the minimum value TAUPmin due to the structure, the fuel injection from the port injector 6 is stably performed. The amount of fuel injected from the port injector 6 fluctuates. As a result, it is unavoidable that the amount of fuel supplied into the cylinder deviates from an appropriate value, resulting in a problem that fuel combustion in the cylinder deteriorates.

  Incidentally, as described above, the reason why the fuel injection time TAUP of the port injector 6 becomes less than the minimum value TAUPmin is that the high fuel pressure map is based on the injection ratio K in the high-pressure injection control based on the engine speed and the engine load. When calculating from the above, it is possible to calculate the ejection ratio K corresponding to the grid points of the map by interpolation. For example, if the injection ratio K corresponding to the first high load area (KL2 to KL3) in FIG. 5 is calculated by the above interpolation, the injection ratio K is the injection ratio K (= 0 in the medium load area). %) And the spray distribution rate K (> 0%) in the second high load region, it is calculated by interpolation based on the current engine load. In this case, since the spray distribution rate K in the medium load region is 0%, the spray distribution rate K in the first high load region calculated by the interpolation becomes a value close to 0%. When the divided injection is performed at the injection ratio K close to 0%, the fuel injection amount (port injection command value QP) from the port injector 6 decreases, and accordingly, the fuel injection time TAUP of the port injector 6 is minimized. The value will be less than TAUPmin.

  In order to avoid the above-described problem, in the injection control routine, a process (S104, S105 in FIG. 4) for performing a lower limit guard on the calculated injection ratio K is executed. Specifically, it is determined whether or not the injection ratio K calculated in S102 or S103 is larger than 0% and smaller than 100% (S104). When an affirmative determination is made here, that is, when fuel is injected from both the direct injection injector 7 and the port injection injector 6, the injection division ratio K is guarded at a lower limit with a predetermined guard value (S105). The lower limit of the injection ratio K is thus guarded in the direction in which the fuel injection from the direct injection injector 7 increases, in other words, the fuel injection from the port injector 6. This means guarding in the direction of decreasing As the guard value, a value determined in advance through experiments or the like is used as an optimal value for preventing the fuel injection time TAUP of the port injector 6 from being less than the minimum value TAUPmin.

  The injection ratio K in the first high load region (KL2 to KL3) in FIG. 5 during the high-pressure injection control is guarded at the lower limit through the processing of S104 and S105, so that the engine load changes. It changes in a region closer to 0% than the value at the time of normal injection control (solid line). By this lower limit guard processing (S104, S105) of the injection ratio K, it is possible to suppress the fuel injection time TAUP at the port injector 6 from being less than the minimum value TAUPmin, and thus the above-described fuel combustion deterioration in the cylinder It becomes possible to suppress the occurrence of the problem. When a negative determination is made in S104 and it is determined that the injection ratio K is 0% or 100%, the lower limit guard based on the guard value of the injection ratio K is not performed. This is because the fuel injection from the port injector 6 is not performed when the injection ratio K is 0%, and thus the above-mentioned problem does not occur. When the injection ratio K is 100%, the port injection injector This is because the above-described problem does not occur because many fuel injections are performed at 6.

According to the embodiment described in detail above, the following effects can be obtained.
(1) In the divided injection, when the direct injection pressure becomes equal to or higher than the determination value and the high-pressure injection control is executed, the direct injection pressure is less than the determination value and the normal injection control is executed. Thus, the amount of fuel injected from the direct injection injector 7 increases. This is because the injection division rate K in the high-pressure injection control becomes a value closer to 0% compared to the injection division rate K in the normal injection control. When the fuel injected from the direct injection injector 7 increases through the execution of the high pressure injection control, the fuel in the high pressure fuel pipe 33 connected to the direct injection injector 7 is quickly consumed. (Direct injection pressure) starts to drop quickly. Therefore, when the direct injection pressure is a high value such as the determination value or more, the fuel injection time TAUD of the direct injection injector 7 may be longer than the minimum value TAUDmin and may be guarded at the lower limit by the minimum value TAUDmin. The direct injection pressure can be quickly reduced through the execution of the high-pressure injection control. And by the rapid fall of the said direct injection pressure, it can suppress that the fuel injection time TAUD of the direct injection injector 7 calculated | required based on the direct injection pressure becomes less than the said minimum value TAUDmin. Therefore, when the direct injection pressure is high, the fuel injection time TAUD of the direct injection injector 7 is guarded at the lower limit by the minimum value TAUDmin, and therefore the amount of fuel injected from the direct injection injector 7 is prevented from being excessive. It is possible to suppress the deterioration of fuel combustion in the cylinder due to the excessive amount of injected fuel.

  (2) When the high-pressure injection control is being performed and the engine load is in the second high load region (KL3 or higher in FIG. 5), the injection ratio K (broken line) in the high-pressure injection control is the normal injection control. Is set equal to the spraying ratio K (solid line). Here, during the execution of the high-pressure injection control and when the internal combustion engine 1 is operated at a high load, the fuel injection amount (direct injection) to be injected from the direct injection injector 7 because the injection amount command value Qfin becomes a large value. The command value QD) also increases. As a result, even if the direct injection pressure becomes a high value equal to or higher than the determination value, the fuel injection time TAUD of the direct injection injector 7 does not become less than the minimum value TAUDmin. Under these circumstances, the injection ratio at which the fuel injection from the direct injection injectors 7 is larger than when the injection is performed at the injection ratio K in the normal injection control, in other words, the above-described injection ratio. Assuming that the spray-split injection is performed at a spray split ratio closer to 0% than K, it is difficult to obtain the maximum effect by performing the spray split injection. However, when the high-pressure injection control is being performed and the engine load is in the second high-load region, as described above, the injection ratio K in the high-pressure injection control is equal to the injection ratio K in the normal injection control. Therefore, it is possible to obtain the maximum effect by performing the divided injection by the port injector 6 and the direct injector 7.

  (3) When the high-pressure injection control is being performed and fuel is injected from both the direct injection injector 7 and the port injection injector 6, the port injection command value QP becomes an excessively small value and the port injection injector 6 When the fuel injection time TAUP at the time becomes less than the minimum value TAUPmin, fuel injection from the port injector 6 is not stably performed. As a result, it is unavoidable that the amount of fuel injected from the port injector 6 fluctuates and the amount of fuel supplied into the cylinder deviates from an appropriate value, resulting in combustion of the fuel in the cylinder. The problem of getting worse arises. In order to cope with this problem, when the injection ratio K in the high-pressure injection control is greater than 0%, the injection ratio K is guarded at a lower limit with a predetermined guard value. In other words, the injection ratio K is guarded in the direction in which the fuel injection from the direct injector 7 increases, and is guarded in the direction in which the fuel injection from the port injector 6 decreases. As a result, it is possible to prevent the port injection command value QP from becoming excessively small and the fuel injection time TAUP at the port injector 6 to be less than the minimum value TAUPmin, which leads to the problem of deterioration of fuel combustion in the cylinder described above. Can be suppressed.

In addition, the said embodiment can also be changed as follows, for example.
Instead of switching the map for calculating the injection ratio K between the high-pressure injection control map and the normal injection control map depending on whether the direct injection pressure is equal to or higher than the determination value, the injection distribution ratio As a map for calculating K, a three-dimensional map having the engine speed, the engine load, and the direct injection pressure as parameters may be used.

The lower limit guard process for the spray distribution ratio K can be executed only during the execution of the high pressure injection control.
-It is not always necessary to perform the lower limit guard process of the spray distribution rate K.

  The injection ratio K in the high-pressure injection control may be fixed to a value closer to 0% than the injection ratio K in the normal injection control. In this case, it is preferable to adopt 0% as a fixed value of the injection ratio K in the high-pressure injection control. If the injection ratio K in the high pressure injection control is fixed to 0%, fuel injection is always performed only from the direct injection injector 7 during the execution of the high pressure injection control. The fuel injection can be promoted and the direct injection pressure can be quickly reduced below the judgment value.

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Intake passage, 2a ... Intake port, 3 ... Combustion chamber, 4 ... Throttle valve, 5 ... Accelerator pedal, 6 ... Port injection injector, 7 ... Direct injection injector, 8 ... Fuel tank, 9 ... Feed Pump 10, high pressure fuel pump 12 spark plug 13 piston 14 crankshaft 15 exhaust passage 16 electronic control device 17 accelerator position sensor 18 throttle position sensor 19 air flow meter DESCRIPTION OF SYMBOLS 20 ... Crank position sensor, 21 ... Cam position sensor, 23 ... 1st pressure sensor, 24 ... 2nd pressure sensor, 25 ... Intake camshaft, 26 ... Intake valve, 27 ... Exhaust camshaft, 28 ... Exhaust valve, 31 ... Low pressure fuel piping, 32 ... pressure regulator, 33 ... high pressure fuel piping.

Claims (2)

This is applied to an internal combustion engine having a port injection injector that injects fuel into an intake port and a direct injection injector that injects fuel into a cylinder, and an amount of fuel corresponding to an injection amount command value is obtained according to the engine operating state. In a control device for an internal combustion engine that performs split injection with injection divided into injection from the port injection injector and injection from the direct injection injector,
In performing the divided injection, when the pressure of the fuel supplied to the direct injector is equal to or higher than a determination value, it is compared with the case where the divided injection is performed at the injection ratio determined according to the engine operating state. The high-pressure injection control is performed to perform the injection divided injection at an injection division ratio at which the fuel injection from the direct injection injector increases.
A fuel injection control device for an internal combustion engine, characterized in that the injection ratio is made equal to a value determined according to the engine operating state during execution of the high pressure injection control and during high engine load operation. When fuel is injected from both the direct injector and the port injector during the high pressure injection control, the injection ratio is guarded in the direction in which the fuel injection from the direct injector increases. The fuel injection control device for an internal combustion engine according to claim 1.