JP3575370B2 - Fuel injection device for internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel injection device for an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art A fuel injection device for an internal combustion engine having a plurality of cylinders and performing a sub-injection at a time interval from a main injection within one combustion cycle of each cylinder, that is, a pilot injection, for example, is known (Japanese Patent Application Laid-Open No. Hei 6 (1994)). 129296).
[0003]
[Problems to be solved by the invention]
However, in this case, the fuel injection timing of the main injection of one cylinder and the fuel injection timing of the sub injection of another cylinder may overlap each other. A plurality of fuel injection valves provided in the engine are usually connected to a common power supply, and power is supplied only during a period in which fuel is to be injected, that is, a period in which the fuel injection valve is to be opened. Therefore, if the fuel injection timings of a plurality of fuel injections overlap with each other, it becomes impossible to supply sufficient electric power to the fuel injection valve to perform regular fuel injection, so that the actual fuel injection amount becomes less than the required fuel injection amount. There is a problem that the amount may deviate.
[0004]
Such a problem may also occur when a plurality of sub-injections are performed at a time interval from the main injection in one combustion cycle of each cylinder.
An object of the present invention is to provide a fuel injection device for an internal combustion engine that can maintain an actual fuel injection amount at a required fuel amount.
[0005]
[Means for Solving the Problems]
According to the present invention, a plurality of cylinders are provided, and a first sub-injection is performed at a first timing interval from a main injection within one combustion cycle of each cylinder. In the fuel injection device for an internal combustion engine, which performs the second sub-injection at a second timing interval shorter than the first timing interval from the injection, the first and second sub-injections of each cylinder are provided. When the fuel injection timing of the first sub-injection of one cylinder and the fuel injection timing of the second sub-injection of another cylinder overlap each other, the fuel injection timing of the second sub-injection is calculated. The fuel injection timing of the first sub-injection is changed without changing the fuel injection timing so that these fuel injection timings do not overlap each other.
[0006]
Immediate Chi, since one of the fuel injection timing is changed when the fuel injection timing of the two fuel injection overlap with each other, the fuel injection amount of the fuel injection is maintained at a required fuel amount. Further, since the fuel injection timing of the second sub-injection whose timing interval from the main injection is smaller is not changed, the influence on the engine output or the exhaust is reduced.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a case where the present invention is applied to a diesel engine. However, the present invention can be applied to a spark ignition type engine.
Referring to FIG. 1, the engine body 1 includes, for example, four cylinders # 1, # 2, # 3, and # 4. Each cylinder is connected to a common surge tank 3 via a corresponding intake branch pipe 2, and the surge tank 3 is connected via an intake duct 4 and an intercooler 5 to an outlet of a supercharger, for example, a compressor 6 c of an exhaust turbocharger 6. Connected to the unit. The inlet of the compressor 6c is connected to an air cleaner 8 via an air suction pipe 7. A throttle valve 10 driven by an actuator 9 is arranged in the intake duct 4 between the surge tank 3 and the intercooler 5. A variable nozzle mechanism 6v whose opening area can be changed is attached to the exhaust gas inlet of the exhaust turbine 6t. If the area of the exhaust gas inlet of the exhaust turbine 6t is reduced by the variable nozzle mechanism 6v, the supercharging pressure can be increased even during low engine speed operation where the exhaust pressure is low.
[0008]
Each cylinder is connected to an inlet of the exhaust turbine 6t of the exhaust turbocharger 6 through an exhaust manifold 11 and an exhaust pipe 12, the outlet portion of the exhaust turbine 6t is an NO _X reduction catalyst 14 via the exhaust pipe 13 houses An exhaust throttle valve 18 driven by an actuator 17 is disposed in an exhaust pipe 13 connected to an exhaust pipe 16. The NO _X reduction catalyst 14 includes, for example, a zeolite supporting copper. This NO _X reduction catalyst 14 can reduce NO _X even in an oxidizing atmosphere if the inflowing exhaust gas contains a reducing agent such as HC or CO. The combustion order of the engine 1 is # 1- # 3- # 4- # 2.
[0009]
Each cylinder has a fuel injection valve 20 for directly injecting fuel into the cylinder. Each fuel injection valve 20 is connected to a fuel pump 22 whose discharge amount can be controlled via a common fuel pressure accumulation chamber or a common rail 21. The fuel pump 22 is connected to a fuel tank (not shown) via a low-pressure pump (not shown). Fuel discharged from the fuel pump 22 is supplied to the common rail 21 and then to each fuel injection valve 20. . The discharge amount of the fuel pump 22 is controlled so that the fuel pressure in the common rail 21 becomes a predetermined target fuel pressure. The target fuel pressure can be determined, for example, according to the engine operating state.
[0010]
Each fuel injection valve 20 includes, for example, an electromagnetic actuator. When the electromagnetic actuator is energized, the fuel injection valve 20 opens to start fuel injection, and when deactivated, the fuel injection valve 20 closes. Fuel injection is stopped. Therefore, roughly speaking, fuel injection is performed only while power is being supplied to the fuel injection valve 20. Each fuel injection valve 20 is connected to a common power source (not shown).
[0011]
Still referring to FIG. 1, the exhaust manifold 11 and the intake duct 4 downstream of the throttle valve 10 are connected to each other via an exhaust gas recirculation (hereinafter, referred to as EGR) passage 23, and are driven by an actuator 24 in the EGR passage 23. EGR control valve 25 is arranged.
An electronic control unit (ECU) 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, and always connected via a bidirectional bus 31. It has a B-RAM (backup RAM) 35, an input port 36, and an output port 37 connected to a power supply. A water temperature sensor 38 that generates an output voltage proportional to the engine cooling water temperature is attached to the engine body 1. An intake pressure sensor 39 that generates an output voltage proportional to the pressure in the intake duct 4 and an intake temperature sensor that generates an output voltage proportional to the intake air temperature in the intake duct 4 are provided in the intake duct 4 downstream of the throttle valve 10. 40 are arranged. An exhaust temperature sensor 41 that generates an output voltage proportional to the temperature of exhaust gas flowing out of the NO _X reduction catalyst 14 is disposed in the exhaust pipe 16. A fuel pressure sensor 42 that generates an output voltage proportional to the fuel pressure in the common rail 21 is attached to the common rail 21. The depression amount sensor 43 generates an output voltage proportional to the depression amount of an accelerator pedal (not shown). The output voltages of these sensors 38, 39, 40, 41, 42, 43 are input to the input port 36 via the corresponding AD converters 44, respectively. The input port 36 is connected to a crank angle sensor 45 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. The CPU 34 calculates the engine speed N based on the output pulse of the crank angle sensor 45, and calculates the intake air amount Ga based on the output voltage of the intake pressure sensor 39.
[0012]
On the other hand, the output port 37 is connected to the variable nozzle mechanism 6v, the actuators 9, 17, 24, the fuel injection valves 20, and the fuel pump 22 via the corresponding drive circuits 46, respectively.
By the way, when the common rail 21 is provided, it becomes possible to inject fuel a plurality of times in one combustion cycle of each cylinder. Therefore, in this embodiment, apart from the main injection that is performed around the compression top dead center to generate the engine output torque, the sub-injection is performed at a timing interval from the main injection to the advance side or the retard side at a time interval. I have to. The sub-injection includes pilot injection, post-injection, and HC supply injection.
[0013]
The pilot injection is to inject a small amount of fuel prior to the main injection. The pilot injection is performed, for example, in a compression stroke before the main injection, that is, for example, at about 0 ° crank angle (hereinafter, referred to as CA) from 70 before compression top dead center (hereinafter, referred to as BTDC). When it is large, it forms a premixed gas, and when it is small, it forms an ignition source for igniting and burning fuel by main injection. It is also possible to perform a plurality of pilot injections, so that both pilot injection for forming a premixed gas and pilot injection for forming an ignition source can be performed. Multiple injections can be performed. In this embodiment, it is possible to perform two pilot injections, that is, a pilot injection for forming a premixed gas mixture and a pilot injection for forming an ignition source.
[0014]
The post-injection is performed after the main injection is completed in order to completely combust HC in the combustion gas or exhaust gas and reduce soot discharged from the engine. This post-injection is preferably performed while the combustion flame remains in the combustion chamber. For example, the post-injection is performed at about -30 ° CA from BTDC0 after completion of the main injection (0 to 30 ° CA after compression top dead center). .
[0015]
The HC supply injection is for supplying HC (hydrocarbon) as a reducing agent to the NO _X reduction catalyst 14. This HC supply injection is performed, for example, from BTDC-150 after the completion of the main injection or the post-injection to about −210 ° CA. Fuel by HC supply injection Italian the NO _X reduction catalyst 14 without complete combustion, reducing the NO _X flowing.
[0016]
FIG. 2A schematically shows the fuel injection timing of each fuel injection operation in the form of a valve opening period of the fuel injection valve 20. Here, j indicates the order or type of fuel injection that can be performed in one combustion cycle of each cylinder, that is, j = 1 indicates pilot injection for forming a premixed gas mixture, and j = 2 indicates pilot injection for forming an ignition source. , J = 3 indicates main injection, j = 4 indicates post-injection, and j = 5 indicates HC supply injection.
[0017]
While the main injection is always performed in one combustion cycle of each cylinder, whether or not the pilot injection, the post-injection, and the HC supply injection are performed is determined depending on the engine operating state. Therefore, the number of fuel injections performed in one combustion cycle of each cylinder can be changed between one and five. For example, in the example shown in FIG. 2B, fuel injection is performed only four times in one combustion cycle of each cylinder, and in the example shown in FIG. 2C, it is performed only three times.
[0018]
The fuel injection timing of each fuel injection is calculated as the optimal fuel injection timing for each purpose. More specifically, the fuel injection timing of the premixed air formation pilot injection and the ignition source formation pilot injection is the fuel injection timing required to form a good premixed air and ignition source, respectively. For example, they are stored in the ROM 32 in advance as functions of the engine speed N and the accelerator pedal depression amount DEP, respectively. The fuel injection timing of the main injection is the optimum fuel injection timing for making the engine output torque equal to the required torque, and is stored in advance in the ROM 32 as a function of the engine speed N and the accelerator pedal depression amount DEP. The post-injection fuel injection timing is a fuel injection timing required to reduce HC discharged from the cylinder, and is stored in advance in the ROM 32 as a function of the engine speed N and the accelerator pedal depression amount DEP. . Fuel injection timing of the HC supply injection is a fuel injection timing needed to reduce the amount of NO _X discharged from the NO _X reduction catalyst 14, the amount of NO _X flowing per NO _X reducing catalyst 14 per unit time It is stored in advance in the ROM 32 as a function of the intake air amount Ga and the engine speed N.
[0019]
Although each fuel injection timing calculated in this way is common to each cylinder in terms of the crank angle of the corresponding cylinder, for example, with respect to the exhaust top dead center, all of these fuel injection timings are calculated from the exhaust top dead center of the first cylinder. In this sense, a different value is taken for each cylinder. That is, for example, when the main injection of each cylinder is to be performed at the compression top dead center of each cylinder, it becomes 360 ° CA for the first cylinder and 540 ° CA for the third cylinder.
[0020]
FIG. 3 shows the fuel injection timing of each fuel injection calculated as described above for four cylinders. In FIG. 3, TDC indicates the top dead center of the exhaust of each cylinder.
Referring to FIG. 3, in this example, the fuel injection timing of the HC supply injection of the first cylinder # 1 and the fuel injection of the main injection of the third cylinder # 3 in which combustion is performed following the combustion of the first cylinder # 1. The times overlap with each other. Further, depending on the setting of the fuel injection timing of each fuel injection or the number of cylinders, the fuel injection timing of the HC supply injection of the first cylinder # 1 and the pilot injection for forming the premixed gas of the third cylinder # 3 and the ignition source formation There is a possibility that the fuel injection timing of the pilot injection or the post-injection may overlap each other. Alternatively, the pilot injection for forming the ignition source of the first cylinder # 1 in which the fuel injection timing of the pilot injection for forming the premixed air mixture of the third cylinder # 3 is performed prior to the combustion of the third cylinder # 3, There is a possibility that the fuel injection timing of the injection or the post-injection may overlap with each other.
[0021]
However, when the fuel injection timings overlap each other, the following problems occur. That is, since the plurality of fuel injection valves 20 provided in the engine are connected to a common power supply, when the fuel injection timings overlap each other, it is necessary to supply sufficient power to the fuel injection valves 20 to perform regular fuel injection. Therefore, the actual fuel injection amount may deviate from the required fuel amount. Further, when the fuel injection timings overlap each other, a plurality of fuel injections are performed simultaneously. In this case, the fuel pressure in the common rail 21 fluctuates rapidly, so that the actual fuel injection pressure deviates from the target fuel injection pressure. There is a possibility that large pressure pulsation may occur in the common rail 21.
[0022]
Therefore, when the calculated fuel injection timings overlap each other, it is necessary to change the fuel injection timings so that the fuel injection timings do not overlap each other. However, since the fuel injection timing calculated as described above is an optimum timing for combustion or exhaust performance, it is preferable that the fuel injection timing is not changed as much as possible.
Therefore, in the present embodiment, the fuel injection is prioritized, and the fuel injection timing of the lower priority fuel injection is changed without changing the fuel injection timing of the higher priority fuel injection. The timings do not overlap each other.
[0023]
The priority of the fuel injection is higher as the degree of deterioration of the combustion or exhaust performance when the fuel injection timing is changed is higher. Specifically, the main injection is the highest. This is because the fuel injection timing of the main injection has the greatest effect on combustion or exhaust performance. Further, the fuel injection timing of the main injection should not be changed from the viewpoint of generating the engine output torque.
[0024]
Next, post injection is performed. This is because the post-injection is for completely combusting HC as described above, and the fuel injection timing has a large effect on combustion or exhaust performance. Next, the ignition source forming pilot injection is performed. This is because the ignition timing of the premixed gas largely depends on the fuel injection timing of the pilot injection for forming the ignition source, and the combustion or exhaust performance largely depends on the ignition timing of the premixed gas. Next, pilot injection for forming a premixed gas mixture is performed. This is because the time required for the fuel to be diffused by the premixed gas forming pilot injection until it is ignited depends on the fuel injection timing of the premixed gas forming pilot injection. The lowest order is the HC supply injection. This is because the HC supply injection is performed after the combustion is completed.
[0025]
On the other hand, a fuel injection having a smaller time interval from the fuel injection timing of the main injection may have a greater effect on combustion or exhaust performance. Therefore, it can be seen that the priority is higher for a fuel injection having a smaller timing interval from the main injection.
Although not shown in FIGS. 2 and 3, it is also possible to perform the premixed gas mixture forming pilot injection a plurality of times at a time interval. In this case, when the premixed gas forming pilot injections overlap each other, that is, when the fuel injection timing of the premixed gas forming pilot injection of one cylinder and the fuel injection timing of the premixed gas forming pilot injection of another cylinder overlap each other. The pilot injection for forming a premixed gas having a smaller timing interval from the corresponding main injection is prioritized, that is, the fuel injection timing is not changed, and the premixed gas formation having a larger timing interval from the main injection is given. The fuel injection timing of the pilot injection is changed. The same applies to the pilot injection for forming the ignition source, so the description is omitted.
[0026]
Such a calculation operation of the fuel injection timing is performed at a predetermined calculation timing, for example, at each compression top dead center of the third cylinder. This calculation timing is indicated by an arrow in FIG. That is, the fuel injection timing of the fuel injection performed in, for example, the m-th combustion cycle of each cylinder is calculated at the (m-1) th compression top dead center of the third cylinder. At this time, the fuel injections performed in the m-th combustion cycle of each cylinder do not overlap in fuel injection timing.
[0027]
Still referring to FIG. 3, even when the m-th combustion cycle of the first cylinder starts, the (m-1) -th combustion cycle of the remaining cylinders has not been completed. Accordingly, the period from the start of the m-th combustion cycle of the first cylinder to the completion of the (m-1) -th combustion cycle of the second cylinder is referred to as an overlap period. This means that the cycle and the (m-1) th combustion cycle overlap each other.
[0028]
In this overlap period, the fuel injection timing of the fuel injection performed in the preceding m-th combustion cycle and the fuel injection timing of the fuel injection performed in the subsequent (m-1) -th combustion cycle may overlap each other. There is. Therefore, when these fuel injection timings overlap each other, one of the fuel injection timings is changed in accordance with the above-described priority order.
[0029]
In this case, if the priority of the fuel injection performed in the m-th combustion cycle is lower, the fuel injection timing of this fuel injection may be changed. At this time, the fuel injection timing of the fuel injection performed in the m-th combustion cycle is calculated.
However, if the priority of the fuel injection performed in the (m-1) -th combustion cycle is lower, the calculation of the fuel injection timing of this fuel injection has already been completed. Therefore, in this case, at the calculation timing for the fuel injection timing of the fuel injection performed in the m-th combustion cycle, the fuel injection timing of the fuel injection performed in the (m-1) -th combustion cycle should be changed. Is recalculated.
[0030]
Accordingly, the fuel injection timing of the fuel injection performed from the time when the m-th combustion cycle of the first cylinder starts to the time when the m-th combustion cycle of the second cylinder is completed is the (m-1) th fuel injection of the third cylinder. Is calculated at the compression top dead center, and the fuel injection timings of the fuel injections performed within this calculation range do not overlap each other.
As described above, when the calculated fuel injection timings overlap each other, the fuel injection timing of the lower priority fuel injection is changed. When the changed fuel injection timing overlaps with the fuel injection timing of another fuel injection, the fuel injection timing is further changed according to the priority between them.
[0031]
The fuel injection timing may be changed in any way as long as the fuel injection timing does not overlap. However, as described above, if the fuel injection timing is changed, the combustion or exhaust performance may decrease. Therefore, the fuel injection timing should be changed so that the influence on the combustion or exhaust performance is minimized.
Therefore, in the present embodiment, when the fuel injection timing is to be changed, the fuel injection timing is changed so that the time interval from the fuel injection timing of the corresponding main injection becomes large. That is, the fuel injection timing is advanced for the pilot injection for forming the premixed gas mixture or the ignition source which is performed prior to the main injection, and the fuel injection is performed for the post injection or the HC supply injection performed subsequent to the main injection. Timing is retarded.
[0032]
From the above, when the calculated fuel injection timings overlap each other, the final fuel injection timing is obtained by changing the calculated fuel injection timing for the lower priority fuel injection, and the higher priority is higher. As for the fuel injection, the calculated fuel injection timing is directly used as the final fuel injection timing. Even when the calculated fuel injection timings do not overlap each other, the calculated fuel injection timing is used as the final fuel injection timing.
[0033]
FIG. 4 shows a routine for calculating the fuel injection timing. This routine is executed by interruption every predetermined set time.
Referring to FIG. 4, first, at step 100, it is determined whether or not the current fuel injection timing is calculated, for example, whether it is the compression top dead center of the third cylinder. If it is not the current fuel injection timing calculation timing, the processing cycle is ended, and if it is the current fuel injection timing calculation timing, the routine proceeds to step 101, where the fuel injection timing of each fuel injection is calculated based on the above-described map. In the following step 102, it is determined whether or not there is any fuel injection whose calculated fuel injection timing overlaps with the fuel injection timing of the main injection. If there is no fuel injection whose calculated fuel injection timing overlaps with the fuel injection timing of the main injection, the process proceeds to step 104. If there is, the process proceeds to step 103 and then to step 104. In step 103, the fuel injection timing of the fuel injection overlapping with the fuel injection timing of the main injection is changed without changing the fuel injection timing of the main injection. In this case, the fuel injection timing is changed so as not to overlap with the fuel injection timing of the main injection.
[0034]
In step 104, it is determined whether or not there is a fuel injection whose calculated fuel injection timing overlaps with the fuel injection timing of the sub-injection. If there is no fuel injection whose calculated fuel injection timing overlaps the fuel injection timing of the sub-injection, the process proceeds to step 106. If there is, the process proceeds to step 105 and then to step 106. In step 105, the fuel injection timing of the fuel injection overlapping with the fuel injection timing of the sub-injection is changed without changing the fuel injection timing of the sub-injection. In this case, the fuel injection timing of the main injection and the sub injection is changed so as not to overlap.
[0035]
In step 106, it is determined whether or not there is any fuel injection whose calculated fuel injection timing overlaps with the fuel injection timing of the ignition source forming pilot injection. If there is no fuel injection whose calculated fuel injection timing overlaps the fuel injection timing of the ignition source forming pilot injection, the process proceeds to step 108. If there is, the process proceeds to step 107 and then to step 108. move on. In step 107, the fuel injection timing of the fuel injection overlapping with the fuel injection timing of the ignition source forming pilot injection is changed without changing the fuel injection timing of the ignition source forming pilot injection. In this case, the fuel injection timing is changed so as not to overlap with the fuel injection timing of the main injection, the sub-injection, and the pilot injection for forming the ignition source.
[0036]
In step 108, it is determined whether or not there is any fuel injection whose calculated fuel injection timing overlaps with the fuel injection timing of the premixed-air mixture forming pilot injection. If there is no fuel injection in which the calculated fuel injection timing overlaps with the fuel injection timing of the premixed gas forming pilot injection, the process proceeds to step 108. If there is, the process proceeds to step 109 and then to step 108. move on. In step 109, the fuel injection timing of the fuel injection overlapping with the fuel injection timing of the premixed air formation pilot injection is changed without changing the fuel injection timing of the premixed air formation pilot injection. In this case, the fuel injection timing is changed so as not to overlap with the fuel injection timing of the main injection, the sub-injection, the pilot injection for forming the ignition source, and the pilot injection for forming the premixed mixture.
[0037]
【The invention's effect】
The actual fuel injection amount can be maintained at the required fuel amount.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is a diagram for explaining a fuel injection timing and the number of fuel injections performed in one cylinder combustion cycle.
FIG. 3 is a diagram showing fuel injection timings of four cylinders.
FIG. 4 is a flowchart showing a routine for calculating a fuel injection timing.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine body 20 ... Fuel injection valve 21 ... Common rail

Claims (1)

A plurality of cylinders, a first sub-injection is performed at a first timing interval from the main injection within one combustion cycle of each cylinder, and a second sub-injection is shorter than the first timing interval from the main injection. In the fuel injection device of the internal combustion engine, which performs the second sub-injection at a time interval, the fuel injection timings of the first and second sub-injections of each cylinder are calculated, and the When the fuel injection timing of the first sub-injection and the fuel injection timing of the second sub-injection of another cylinder overlap each other, the fuel of the first sub-injection is changed without changing the fuel injection timing of the second sub-injection. A fuel injection device for an internal combustion engine in which the injection timing is changed so that these fuel injection timings do not overlap each other.

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