JP3684968B2 - Fuel injection device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND 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 a diesel engine in which a fuel injection valve is provided in each of a plurality of cylinders, and these fuel injection valves are connected to a common fuel pressure accumulating chamber or a common rail so that fuel is supplied from the common rail to each fuel injection valve. (See JP-A-6-129296). In this way, it is possible to inject fuel multiple times from each fuel injection valve within one combustion cycle of each cylinder.
[0003]
Thus, conventionally, a fuel injection device for a diesel engine is known in which post-injection is performed after main injection within one combustion cycle of each cylinder. By burning the fuel by the post-injection in the combustion chamber, the soot contained in the combustion gas or the burned gas is burned, and thus the amount of soot discharged from the engine can be reduced.
[0004]
[Problems to be solved by the invention]
However, there is a possibility that the amount of soot discharged from the engine cannot be sufficiently reduced even if the post injection is simply performed. That is, generally speaking, if the fuel injection amount of the post-injection is too small, the soot cannot be sufficiently combusted, and if it is too large, the amount of soot discharged from the engine may increase.
[0005]
Therefore, an object of the present invention is to provide a fuel injection device for an internal combustion engine that can reduce the amount of soot discharged from the engine.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problem, according to the first invention, an internal combustion engine that performs post-injection in order to reduce the amount of soot discharged from the engine following main injection in one combustion cycle. In the fuel injection device of the engine, the fuel injection amount of the post-injection is smaller than the fuel injection amount of the main injection. and to determine a fuel injection amount and fuel injection timing of the post injection based. That is, according to the present inventor, it is confirmed that the optimal fuel injection amount and fuel injection timing of the post-injection for reducing the amount of soot discharged from the engine depend on the air-fuel ratio at the time when the main injection is completed. Has been. Therefore, in the first invention, the fuel injection amount and the fuel injection timing of the post-injection are obtained based on this air-fuel ratio or the air-fuel ratio representing this.
[0007]
Further, according to the second invention, in the first invention, the fuel injection amount of the post-injection is increased when the air-fuel ratio at the time when the main injection is completed or when the air-fuel ratio representing the main injection is large compared to when the air-fuel ratio is small. ing. That is, according to the present inventor, if the air-fuel ratio at the time when the post-injection is completed is too large, that is, if it is excessively lean, the soot in the combustion gas cannot be burned sufficiently, and if it is too small, that is, excessively It has been confirmed that the amount of soot discharged from the engine increases when it is rich. Therefore, in the second aspect of the invention, when the air-fuel ratio at the time when the main injection is completed or the air-fuel ratio indicating this is small, the fuel injection amount of the post-injection is decreased, and when it is large, the fuel injection amount is increased, and when the post-injection is completed. The air-fuel ratio is maintained optimally.
[0008]
Further, according to the third invention, in the second invention, after the main injection is completed, the post-injection is performed after the main injection is completed, as compared with the case where the air-fuel ratio at the time when the main injection is completed or the air-fuel ratio representing this is small. The time interval until the start is extended. That is, in order to sufficiently burn soot, it is preferable to start the post-injection as soon as possible after the main injection is completed. However, if a large amount of fuel is injected in the post-injection, soot discharged from the engine may increase. Therefore, in the third aspect of the invention, when the air-fuel ratio at the time when the main injection is completed or the air-fuel ratio representing it is large and the amount of fuel injection of the post-injection is large, the main injection is completed and then a long time interval is passed. The injection is started.
[0009]
In order to solve the above-mentioned problem, according to the fourth aspect of the invention, after the main injection in one combustion cycle , the post-injection is performed in order to reduce the amount of soot discharged from the engine. In the fuel injection device for an internal combustion engine, the air-fuel ratio at the time when the main injection is completed or the air-fuel ratio representing the air-fuel ratio is obtained, and the post-injection is prohibited when the air-fuel ratio is larger than a predetermined threshold value. ing. That is, when the air-fuel ratio at the time when the main injection is completed is excessively large, the amount of fuel injection necessary to optimize the air-fuel ratio at the time when the post-injection is completed becomes excessive, and as a result, the fuel is discharged from the engine. The amount of soot may increase. Therefore, in the fourth aspect of the invention, the post-injection is prohibited when the air-fuel ratio at the time when the main injection is completed or the air-fuel ratio indicating this is larger than the threshold value.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a case where the present invention is applied to a diesel engine. However, the present invention can also be applied to a spark ignition 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 to an outlet of a compressor 6 c of a supercharger, for example, an exhaust turbocharger 6, via an intake duct 4 and an intercooler 5. Connected to the part. An inlet portion of the compressor 6 c is connected to an air cleaner 8 through an air suction pipe 7. A throttle valve 10 driven by an actuator 9 is disposed 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 inlet of the exhaust turbine 6t. If the exhaust nozzle area 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.
[0011]
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 the exhaust pipe 13 connected to the exhaust pipe 16. The NO _x reduction catalyst 14 comprises, for example, a zeolite supporting copper. The NO _x reduction catalyst 14 can reduce NO _x even in an oxidizing atmosphere if the reducing exhaust gas such as HC and CO is contained in the inflowing exhaust gas. The combustion order of the engine 1 is # 1- # 3- # 4- # 2.
[0012]
Each cylinder includes a fuel injection valve 20 that directly injects fuel into the cylinder. Each fuel injection valve 20 is connected to a fuel pump 22 through which a discharge amount can be controlled via a common fuel accumulator chamber or common rail 21. The fuel pump 22 is connected to a fuel tank (not shown) via a low pressure pump (not shown), and the fuel discharged from the fuel pump 22 is supplied to the common rail 21 and then supplied 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 according to, for example, the engine operating state.
[0013]
Further, 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 recirculation (hereinafter referred to as EGR) passage 23, and are driven by an actuator 24 in the EGR passage 23. An EGR control valve 25 is disposed.
The electronic control unit (ECU) 30 is a digital computer, and is connected to each other via a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, and a constant time. A B-RAM (backup RAM) 35 connected to a power source, an input port 36, and an output port 37 are provided. 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 for generating an output voltage proportional to the pressure in the intake duct 4 in the intake duct 4 downstream of the throttle valve 10 and an intake temperature sensor for generating an output voltage proportional to the intake air temperature in the intake duct 4 40 is arranged. An air-fuel ratio sensor 41 that generates an output voltage representing the air-fuel ratio 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. Further, 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 and 43 are input to the input port 36 via the corresponding AD converters 44. The input port 36 is connected to a crank angle sensor 45 that generates an output pulse every time the crankshaft rotates, for example, 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.
[0014]
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 within one combustion cycle of each cylinder. Therefore, in this embodiment, so-called pilot injection is performed. That is, pre-injection or pilot injection for injecting a small amount of fuel is performed prior to main injection, which is generally performed around the compression top dead center in order to generate engine output torque. The pilot injection is performed, for example, at a compression stroke before the main injection, that is, for example, at a compression top dead center (hereinafter referred to as BTDC) 70 to 0 ° crank angle (hereinafter referred to as CA), and a time interval with respect to the main injection. When the value is large, a premixed gas is formed, and when the value is small, an ignition source for igniting and burning fuel by main injection is formed. It is also possible to perform a plurality of pilot injections. Therefore, it is possible to perform both pilot injection for premixed gas formation and pilot injection for forming an ignition source, and pilot for premixed gas formation. It is also possible to perform the injection multiple times. In this embodiment, two pilot injections can be performed. The pilot injection performed first is referred to as a first pilot injection, and the pilot injection performed later is referred to as a second pilot injection.
[0015]
Further, post-injection is performed after main injection is completed in order to completely burn HC in the combustion gas or exhaust gas. This post-injection is performed, for example, from about BTDC0 after completion of main injection to about -30 ° CA (0 to 30 ° CA after compression top dead center). Further, HC supply injection for supplying HC (hydrocarbon) as a reducing agent to the NO _x reduction catalyst 14 is also performed. This HC supply injection is performed, for example, from about BTDC-150 after completion of main injection or post-injection to about -210 ° CA. The fuel from the HC supply injection reaches the NO _x reduction catalyst 14 without complete combustion, and reduces the inflow NO _x .
[0016]
FIG. 2A schematically shows the fuel injection timing of each fuel injection action with arrows. Here, j represents the order or type of fuel injection that can be performed in one combustion cycle of each cylinder, that is, j = 1 is the first pilot injection, j = 2 is the second pilot injection, and j = 3 represents main injection, j = 4 represents post-injection, and j = 5 represents HC supply injection.
[0017]
While main injection is always performed in one combustion cycle of each cylinder, whether or not pilot injection, post-injection, and HC supply injection are performed is determined by the engine operating state. Therefore, the number of fuel injections performed in one combustion cycle of each cylinder can be changed between 1 and 5. 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]
By the way, the post-injection is for completely burning the HC in the combustion gas or the exhaust gas as described above. More specifically, the fuel from the post-injection is burned by the combustion flame in the combustion chamber, so that the soot contained in the combustion gas or burned gas is burned. As a result, the amount of soot discharged from the engine is reduced. Therefore, it is necessary to perform post-injection while the combustion flame remains in the combustion chamber. On the other hand, since the fuel by the HC supply injection needs to reach the NO _x reduction catalyst 14 without complete combustion, the HC supply injection should be performed after the combustion flame in the combustion chamber disappears. It differs from post-injection in nature.
[0019]
Next, a method of calculating the post-injection fuel injection time TAUPO and the fuel injection start timing ISTPO will be described with reference to FIG. In this embodiment, the post-injection fuel injection start timing ISTPO is obtained by adding a timing interval or time interval INTPO to the main injection fuel injection end timing IETM. Accordingly, the post-injection is started when the time interval INTPO has elapsed after the main injection has ended.
[0020]
In the present embodiment, as shown in FIG. 3, the engine operation determined by the engine speed N and the air-fuel ratio AF before the post-injection is performed after the main injection is completed, that is, after the main injection is completed. The state is divided into three regions, and a fuel injection time TAUPO and a time interval INTPO for post-injection are determined for each region. That is, in the region I, the fuel injection time TAUPO is set to the allowable minimum time TAUMIN, and the timing interval INTPO is set to the allowable minimum interval INTMIN. In region II, the fuel injection time TAUPO is set to TAUMIN + a obtained by adding a constant value a (> 0) to the allowable minimum time TAUMIN, and the timing interval INTPO is set to INTMIN + b where a fixed value b (> 0) is added to the allowable minimum interval INTMIN. It is said. In region III, the fuel injection time TAUPO and the time interval INTPO are both zero, that is, no post-injection is performed.
[0021]
Comparing the region I and the region II, it means that the fuel injection amount of the post-injection is increased when the air-fuel ratio at the time when the main injection is completed is large compared with when it is small. This is due to the following reason. That is, if the air-fuel ratio at the time when the post-injection is completed is too large, the fuel in the post-injection diffuses, and soot in the combustion gas cannot be burned sufficiently. On the other hand, if the air-fuel ratio at the time when the post-injection is completed is too small, an excessive fuel spray is formed in the combustion chamber, which may increase the amount of soot discharged from the engine. If the air-fuel ratio at the time when the main injection is completed is small, the fuel injection amount of the post-injection is decreased, and if it is increased when the air-fuel ratio is large, the air-fuel ratio at the time when the post-injection is completed is for soot combustion. Can be optimally maintained.
[0022]
Further, when comparing the region I and the region II, the fuel injection amount of the post-injection is increased when the engine speed N is high compared to when the engine speed N is low. This is because when the engine speed N is high, the intake air amount Ga is larger than when the engine speed N is low, and it is necessary to increase the amount of fuel commensurate with it.
Further, when comparing the region I and the region II, the time interval INTPO is made longer when the fuel injection time TAUPO of the post-injection is longer than when it is shorter. In order to sufficiently burn soot, it is preferable to start the post-injection as soon as possible after the main injection is completed. However, immediately after the main injection is completed, the combustion flame in the combustion chamber is large, and when a large amount of fuel is injected into this large combustion flame, a rich fuel spray is formed in the combustion chamber, so There is a risk that soot discharged will increase. Therefore, the timing interval INTPO is lengthened when the fuel injection amount of the post injection is large, and the timing interval INTPO is shortened when the fuel injection amount of the post injection is small.
[0023]
In view of this point, it can be said that the timing interval INTPO is made longer when the air-fuel ratio at the time of completion of the main injection is larger than when it is small or when it is low when the engine speed N is high.
On the other hand, when comparing the region I and the region II with the region III, it means that the post-injection is prohibited when the air-fuel ratio at the time when the main injection is completed is larger than a predetermined threshold value. . That is, when the air-fuel ratio at the time when the main injection is completed is excessively large, a very large amount of fuel is required to optimize the air-fuel ratio at the time when the post-injection is completed, and as a result, the soot discharged from the engine. The amount may increase. Therefore, the post-injection is prohibited when the air-fuel ratio at the time when the main injection is completed is larger than the threshold value. Note that the threshold value in this case is represented by a boundary line between the region I and the region II and the region III (see FIG. 3).
[0024]
In this regard, it can be considered that the post-injection is prohibited when the engine speed N is higher than a predetermined threshold value.
By the way, it is difficult to directly obtain the air-fuel ratio AF when the main injection is completed. Therefore, in this embodiment, the air-fuel ratio detected by the air-fuel ratio sensor 41 is the air-fuel ratio at the time when the main injection is completed. Strictly speaking, the air-fuel ratio detected by the air-fuel ratio sensor 41 may not match the air-fuel ratio at the time when the main injection is completed. However, the difference between them is based on the fuel injection amount of the post-injection and the HC supply injection, and the fuel injection amount of the post-injection and the HC supply injection is considerably smaller than the fuel injection amount of the main injection. That is, it can be said that the air-fuel ratio detected by the air-fuel ratio sensor 41 represents the air-fuel ratio at the time when the main injection is completed. Therefore, the air-fuel ratio detected by the air-fuel ratio sensor 41 is used.
[0025]
On the other hand, the air-fuel ratio at the time when the main injection is completed is calculated from the intake air amount Ga detected by the intake pressure sensor 39 and the calculated fuel injection times of the first and second pilot injections and the main injection. Is also possible. However, particularly when the fuel injection valve 20 has changed over time, the actual fuel injection time may not match the calculated fuel injection time, and the calculated air-fuel ratio does not match the actual air-fuel ratio. . On the other hand, the air-fuel ratio sensor 41 detects the actual air-fuel ratio, and this is more advantageous than a method for obtaining the air-fuel ratio by calculation.
[0026]
FIG. 4 shows a routine for calculating the post-injection fuel injection time TAUPO and the fuel injection start timing ISTPO. This routine is executed by interruption every predetermined time.
Referring to FIG. 4, first, at step 100, the current region is determined from the map of FIG. In the subsequent step 101, the fuel injection time TAUPO and the timing interval INTPO of the post-injection are calculated according to the current region. In the subsequent step 102, the fuel injection completion timing IETM of the main injection calculated by a routine not shown is read. In the subsequent step 103, the fuel injection start timing ISTPO for post-injection is calculated (ISTPO = IETM + INTPO). Accordingly, at the fuel injection start timing ISTPO, fuel is injected as post-injection from each fuel injection valve 20 by TAUPO.
[0027]
Comparing region I and region II in FIG. 3 again, the post-injection fuel injection time TAUPO and the time interval INTPO are changed in steps. However, the operating region can be subdivided so that these TAUPO and INTPO change continuously. In this way, TAUPO and INTPO can be accurately optimized. However, precise control of TAUPO and INTPO is difficult and not practical. Therefore, in this embodiment, the operation region is divided into three.
[0028]
【The invention's effect】
The amount of soot discharged from the engine can be reduced.
[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 combustion cycle of a cylinder.
FIG. 3 is a diagram representing a region.
FIG. 4 is a flowchart showing a calculation routine for a post-injection fuel injection time TAUPO and a fuel injection start timing ISTPO.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine main body 20 ... Fuel injection valve 41 ... Air-fuel ratio sensor

Claims (4)

In a fuel injection device for an internal combustion engine in which post-injection is performed so that the amount of soot discharged from the engine is reduced following main injection in one combustion cycle, the fuel injection amount of post-injection is the main injection amount. fuel injection quantity of the injection has become less than, so as to obtain a fuel injection amount and fuel injection timing after based on the air-fuel ratio injection seeking air-fuel ratio or an air-fuel ratio which represents this at the time of main injection is completed A fuel injection device for an internal combustion engine.   2. The fuel injection device for an internal combustion engine according to claim 1, wherein when the air-fuel ratio at the time when the main injection is completed or the air-fuel ratio representing the air-fuel ratio is large, the fuel injection amount of post-injection is increased compared to when it is small.   Claims in which the time interval from the completion of main injection to the start of post-injection is longer than when the air-fuel ratio at the time of completion of main injection or the air-fuel ratio that represents it is small Item 6. A fuel injection device for an internal combustion engine according to Item 1. In a fuel injection device for an internal combustion engine in which post-injection is performed in order to reduce the amount of soot discharged from the engine following main injection in one combustion cycle, at the time when main injection is completed A fuel injection apparatus for an internal combustion engine, which obtains an air-fuel ratio or an air-fuel ratio representing the air-fuel ratio and prohibits post-injection when the air-fuel ratio is larger than a predetermined threshold value.

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