JP2009156153A - Fuel injection control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control system for a compression ignition type internal combustion engine where pilot injection is performed prior to main injection, for converging the generation amount of smoke and/or the degree of combustion noise into an allowable range. <P>SOLUTION: The fuel injection control system for the internal combustion engine corrects other fuel injection parameters without changing an injection interval when an actual ignition interval is predicted to deviate from a target ignition interval. Thereby, the system makes the actual ignition interval approximate the target ignition interval while avoiding a departure resulting from a change of the injection interval. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel injection control technique for a compression ignition type internal combustion engine.

Conventionally, in a compression ignition type internal combustion engine, a technique of performing pilot injection prior to main fuel injection (main injection) is known. In such a technique, a method of controlling pilot injection timing so that the ignition delay time of pilot-injected fuel (pilot injection fuel) coincides with a desired ignition delay time has been proposed (for example, Patent Document 1). See).
JP 2000-64891 A JP 2002-47975 A Japanese Patent Laid-Open No. 10-274088 JP 2001-254645 A

  By the way, according to the inventor's diligent experiment and verification, the amount of smoke generated and the magnitude of combustion noise are determined by the timing at which pilot injected fuel ignites and the main injected fuel ignited rather than the ignition delay time of pilot injected fuel. It was found that there is a correlation with an interval (hereinafter referred to as an “ignition interval”) with the timing to perform.

  An object of the present invention is to converge the amount of smoke generated and / or the magnitude of combustion noise within an allowable range using the above-described correlation.

  In order to solve the above-described problem, a fuel injection control system for an internal combustion engine according to the present invention fixes another fuel injection while fixing the injection interval when the actual ignition interval is predicted to be far from the target ignition interval. The actual ignition interval was approximated to the target ignition interval by correcting the parameters.

  Specifically, the present invention relates to a fuel injection control system for a compression ignition type internal combustion engine in which pilot injection is performed prior to main injection, and includes a plurality of injection intervals between pilot injection and main injection based on operating conditions of the internal combustion engine. Determining means for determining the fuel injection parameter, first acquisition means for acquiring the actual state quantity that is the actual state quantity in the cylinder, and acquiring the target state quantity that is the state in the cylinder that matches the operating conditions of the internal combustion engine And a timing at which pilot-injected fuel is ignited when the fuel injection is performed in accordance with the fuel injection parameter determined by the determining unit under the actual state quantity acquired by the first acquiring unit, and the main injection Predicting means for predicting an ignition interval that is an interval from the timing at which fuel is ignited, and the target acquired by the second acquiring means Setting means for predicting an ignition interval when fuel injection is performed in accordance with the fuel injection parameter determined by the determination means under the state quantity, and setting the predicted ignition interval as a target ignition interval; and the prediction means If the difference between the ignition interval predicted by the setting means and the target ignition interval set by the setting means exceeds an allowable value, other fuel injection parameters are corrected without changing the injection interval determined by the determination means. Correction means for approximating the ignition interval to the target ignition interval.

The fuel injection parameters determined by the determining means (hereinafter referred to as “basic fuel injection parameters”) are determined so that the magnitude of combustion noise and the amount of smoke generated fall within an allowable range. By the way, the basic fuel injection parameters described above are determined on the assumption that the actual state quantity in the cylinder matches the target state quantity assumed in advance. However, when the internal combustion engine is in a transient operation state, the actual state quantity in the cylinder may be far from the target state quantity.

  If fuel injection is performed according to the basic fuel injection parameter when the actual state quantity in the cylinder is far from the target state quantity, the magnitude of combustion noise and the amount of smoke generated may deviate from the allowable range.

  According to the inventor's diligent experiment and verification, it has been found that the cause of the above problem is mainly the ignition interval. For example, if the ignition interval is shortened, the amount of smoke generated increases because the mixing time of the main injected fuel and the intake air is shortened. On the other hand, when the ignition interval becomes long, the combustion noise is generated twice, so that the noise increases.

  Therefore, the internal combustion engine fuel injection control system according to the present invention is configured such that when the actual state quantity in the cylinder is different from the target state quantity, the ignition interval realized under the actual state quantity approximates the target ignition interval. The basic fuel injection parameters were corrected.

  Specifically, an ignition interval (hereinafter referred to as “actual ignition interval predicted value”) when fuel injection is performed in accordance with basic fuel injection parameters under actual state quantities, and basic fuel injection under target state quantities. An ignition interval (target ignition interval) when fuel injection is performed according to the parameters is predicted.

  When the difference between the actual ignition interval predicted value and the target ignition interval is larger than the allowable value, the basic fuel injection parameter is corrected so that the difference between the two is less than the allowable value. At this time, the injection interval between the pilot injection timing and the main injection timing is not corrected, and other fuel injection parameters are corrected.

  Pilot-injected fuel burns (or oxidizes) when the pressure and temperature in the cylinder exceed a certain value (pressure and temperature at which the fuel can be oxidized). For this reason, under conditions where the pressure and temperature in the cylinder are below a certain value, the ignition timing of the pilot injected fuel hardly changes even if the pilot injection timing is changed.

  On the other hand, if the injection interval is changed, an unexpected pulsation occurs in the fuel pressure in the fuel supply system (for example, a fuel supply pipe or a common rail), so the pilot injection amount and the main injection amount deviate from the target injection amount. There is a possibility.

  Therefore, when the other fuel injection parameters are corrected while maintaining the injection interval determined by the determining means, the actual ignition interval can be approximated to the target ignition interval while avoiding the above-described problem. As a result, it is possible to keep the amount of smoke generated and / or the magnitude of combustion noise within an allowable range.

  In the fuel injection control system for an internal combustion engine according to the present invention, examples of the fuel injection parameter corrected by the correcting means include at least one of pilot injection amount, main injection timing (and pilot injection timing), and injection pressure. it can.

  When the pilot injection amount increases, the ignition timing of the pilot injected fuel becomes earlier. Conversely, when the pilot injection amount decreases, the ignition timing of the pilot injected fuel is delayed. Therefore, the actual ignition interval can be approximated to the target ignition interval by correcting the pilot injection amount.

  If the main injection timing is changed while the injection interval is fixed, the ignition timing of the main injected fuel can be changed without changing the ignition timing of the pilot injected fuel. Therefore, the actual ignition interval can be approximated to the target ignition interval by correcting the main injection timing.

  When the injection pressure is changed, the ignition timing changes. For example, when the fuel injection amount is relatively small, the ignition timing can be advanced by lowering the injection pressure. Further, when the fuel injection amount is relatively large, the ignition timing can be advanced by increasing the injection pressure. Therefore, the actual ignition interval can be approximated to the target ignition interval by correcting the injection pressure.

  In the present invention, examples of the state quantity acquired by the first acquisition unit and the second acquisition unit include in-cylinder oxygen concentration, in-cylinder pressure, or in-cylinder temperature.

  According to the present invention, since the ignition interval between the pilot injected fuel and the main injected fuel can be optimized, the amount of smoke generated and / or the magnitude of combustion noise can be converged within an allowable range. .

  Hereinafter, specific embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of a fuel injection control system for an internal combustion engine according to the present invention.

  An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) having a plurality of cylinders 2. The internal combustion engine 1 includes a fuel injection valve 3 that directly injects fuel into the cylinder 2. The fuel injection valve 3 communicates with the common rail 30. The fuel injection valve 3 injects high-pressure fuel supplied from the common rail 30 into the cylinder 2.

  The interior (combustion chamber) of the cylinder 2 communicates with the intake passage 4. A compressor housing 50 and an intercooler 6 of the turbocharger 5 are disposed in the intake passage 4.

  The intake air that has flowed into the intake passage 4 is compressed by the compressor housing 50. The intake air compressed by the compressor housing 50 is guided to the cylinder 2 after being cooled by the intercooler 6. The intake air introduced into the cylinder 2 is ignited and burned in the cylinder 2 together with the fuel injected from the fuel injection valve 3.

  Each cylinder 2 communicates with the exhaust passage 7. In the middle of the exhaust passage 7, a turbine housing 51 and an exhaust purification device 8 are arranged. Gas burned in each cylinder 2 (burned gas) is discharged to the exhaust passage 7. The exhaust discharged into the exhaust passage 7 is discharged into the atmosphere via the turbine housing 51 and the exhaust purification device 8 in order.

  The exhaust purification device 8 includes, for example, an NOx storage reduction catalyst and / or a particulate filter, and purifies harmful gas components in the exhaust.

A portion of the intake passage 4 downstream of the intercooler 6 and a portion of the exhaust passage 7 upstream of the turbine housing 51 are connected to each other by an EGR passage 9. In the middle of the EGR passage 9, an EGR valve 10 that adjusts the flow rate of exhaust gas (hereinafter referred to as “EGR gas”) flowing through the EGR passage 9 and an EGR cooler for cooling the EGR gas flowing through the EGR passage 9. 11 is arranged. In the intake passage 4, downstream of the intercooler 6 and the EGR passage 9
An intake throttle valve 12 is disposed at a location upstream of the connecting portion.

  The internal combustion engine 1 configured as described above is provided with an ECU 13. The ECU 13 is an electronic control unit that includes a CPU, ROM, RAM, backup RAM, and the like. The ECU 13 is electrically connected to various sensors such as an air flow meter 14, a crank position sensor 15, a water temperature sensor 16, an air-fuel ratio sensor 17, an accelerator position sensor 18, and a pressure sensor 31.

  The air flow meter 14 is attached to the intake passage 4 upstream of the compressor housing 50 and measures the amount of air flowing into the intake passage 4. The crank position sensor 15 is attached to the internal combustion engine 1 and measures the rotational position of an unillustrated engine output shaft (crankshaft). The water temperature sensor 16 is attached to the internal combustion engine 1 and measures the temperature of the cooling water circulating through the internal combustion engine 1. The air-fuel ratio sensor 17 is attached to the exhaust passage 7 and measures the air-fuel ratio of the exhaust flowing through the exhaust passage 7. The accelerator position sensor 18 is attached to an accelerator pedal (not shown) and measures the amount of operation of the accelerator pedal (accelerator opening). The pressure sensor 31 is attached to the common rail 30 and measures the fuel pressure in the common rail 30.

  The ECU 13 electrically controls the fuel injection valve 3, the EGR valve 10, and the intake throttle valve 12 based on the measurement values of various sensors as described above. For example, the ECU 13 performs fuel injection control that is the gist of the present invention. Hereinafter, fuel injection control in the present embodiment will be described.

  The ECU 13 determines a fuel injection parameter (basic fuel injection parameter) according to the operating conditions (for example, the engine speed Ne and the accelerator opening degree Accp) of the internal combustion engine 1. The fuel injection parameters here include a pilot injection amount, a main injection amount, a pilot interval (an interval between pilot injections and / or an interval between pilot injection and main injection), main injection timing, injection pressure, and the like.

  By the way, the basic fuel injection parameters are determined on the assumption that the state quantity (cylinder oxygen concentration, cylinder pressure, cylinder temperature, etc.) in the cylinder 2 matches a desired target state quantity. However, during transient operation, such as during acceleration operation or when returning from fuel cut operation, the actual state quantity (actual state quantity) may be far from the target state quantity.

  If the fuel injection control is performed according to the basic fuel injection parameters when the actual state quantity is far from the target state quantity, the magnitude of combustion noise and the amount of smoke generated may deviate from the allowable range.

  According to the earnest knowledge of the inventor of the present application, it has been found that the cause of the above problem is mainly in the ignition interval. For example, as shown in FIGS. 2 and 3, when the ignition interval is shortened, the main injected fuel and the pilot injected fuel are burned substantially simultaneously, so the noise is reduced, but the mixing time of the main injected fuel and the intake air is shortened. The amount of smoke generated tends to increase. On the other hand, if the ignition interval is lengthened, the mixing time of the main injected fuel and the intake air becomes longer, so that the amount of smoke generated decreases, but the noise increases because the combustion timing of the pilot injected fuel and the combustion timing of the main injected fuel are different. Tend.

  Therefore, if the fuel injection control is performed according to the basic fuel injection parameter when the actual state quantity is far from the target state quantity, the ignition interval becomes inappropriate with respect to the state quantity in the cylinder 2. It is considered that the magnitude of combustion noise deviates from the allowable range.

Therefore, in the fuel injection control of the present embodiment, the basic fuel injection parameter is corrected so that the ignition interval during transient operation approximates the target ignition interval. Hereinafter, a case where the in-cylinder oxygen concentration is used as the state quantity in the cylinder 2 will be described as an example.

  The ECU 13 predicts an ignition interval realized by an actual in-cylinder oxygen concentration (hereinafter referred to as “actual in-cylinder oxygen concentration”) (hereinafter referred to as “actual ignition interval predicted value”) and also sets a target in-cylinder oxygen. The ignition interval (target ignition interval) realized under the concentration is predicted, and the basic fuel injection parameter is corrected when the difference exceeds the allowable value.

  First, the actual ignition interval prediction value and the target ignition interval prediction method will be described. When pilot injection is performed a plurality of times, the interval between the timing at which the final pilot injected fuel ignites and the timing at which the main injected fuel ignites is regarded as the ignition interval.

  The ECU 13 predicts the actual ignition interval predicted value based on the basic fuel injection parameter and the actual in-cylinder oxygen concentration. At that time, the relationship among the basic fuel injection parameter, the actual in-cylinder oxygen concentration, and the actual ignition interval predicted value may be obtained experimentally in advance and the relationship may be mapped.

  The ECU 13 predicts a target ignition interval based on the basic fuel injection parameter and the target in-cylinder oxygen concentration. In that case, ECU13 may utilize the map used when predicting an actual ignition interval prediction value.

  The actual in-cylinder oxygen concentration may be estimated from the intake air amount, the supercharging pressure, the intake air temperature, the EGR gas transport delay, or the like, or directly measured by an oxygen concentration sensor attached to the intake manifold or the intake port. May be. The target in-cylinder oxygen concentration may be specified from the target EGR rate, the target intake air amount, the target fuel injection amount, and the like.

  When the actual ignition interval predicted value and the target ignition interval are predicted by the method as described above, the ECU 13 determines whether or not the difference between the two exceeds an allowable value.

  When the difference between the actual ignition interval predicted value and the target ignition interval is equal to or less than the allowable value, the ECU 13 operates the fuel injection valve 3 according to the basic fuel injection parameter. On the other hand, when the difference between the actual ignition interval predicted value and the target ignition interval exceeds the allowable value, the ECU 13 corrects the basic fuel injection parameter so that the difference between the two is less than the allowable value, and the corrected fuel The fuel injection valve 3 is operated according to the injection parameters.

  Here, a fuel injection parameter correction method will be described. Here, an example in which the main injection timing is used as the fuel injection parameter will be described. Hereinafter, the main injection timing corresponding to the basic fuel injection parameter is referred to as basic main injection timing.

  The ignition timing of the main injection fuel becomes earlier as the main injection timing becomes earlier, and becomes later as the main injection timing becomes later. Therefore, the basic main injection timing may be advanced when the actual ignition interval predicted value is longer than the target ignition interval, and the basic main injection timing may be delayed when the actual ignition interval predicted value is shorter than the target ignition interval.

When the basic main injection timing is corrected in this way, the ECU 13 performs fuel injection control according to the corrected basic main injection timing (hereinafter referred to as “adapted main injection timing”). Note that the ECU 13 may specify a main injection timing that satisfies the actual in-cylinder oxygen concentration and the target ignition interval in the above-described map, and may use the specified main injection timing as the adapted main injection timing.

  By the way, when the main injection timing is corrected, the injection interval between the pilot injection timing and the main injection timing changes. When the injection interval changes, fuel pressure pulsation may occur in the fuel supply system including the common rail 30, or the pulsation cycle that originally occurred may change.

  In this case, there is a possibility that the fuel injection amount varies for each cylinder 2 or the fuel injection amount of each cylinder 2 is different from the target fuel injection amount.

  On the other hand, when correcting the basic main injection timing, the ECU 13 changes the pilot injection timing at the same time so that the injection interval does not change.

  When the pilot injection timing is changed, there is a concern that the ignition timing of the pilot injected fuel also changes. However, the pilot injected fuel does not oxidize or burn unless the temperature in the cylinder 2 reaches the oxidizable temperature range of the fuel. Therefore, even if the pilot injection timing is changed simultaneously with the correction of the basic main injection timing, the ignition timing of the pilot injected fuel hardly changes.

  However, when the pilot injection is performed after the timing at which the temperature in the cylinder 2 reaches the oxidizable temperature range of the fuel (hereinafter referred to as “predetermined timing”) (the pilot injection timing before and after correction is divided before and after the predetermined timing). In other cases, such as when the pilot injection timing before and after the correction is after a predetermined timing), the ECU 13 preferably changes the injection interval. For example, the ECU 13 may correct only the main injection timing without changing the pilot injection timing.

  As described above, when the fuel injection parameter is corrected, the actual ignition interval can be approximated to the target ignition interval while avoiding the contradiction caused by the pulsation of the fuel pressure as much as possible.

  Hereinafter, the execution procedure of the fuel injection control in the present embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing a fuel injection control routine in the present embodiment. This fuel injection control routine is a routine stored in advance in the ROM of the ECU 13 and is periodically executed by the ECU 13.

  In the fuel injection control routine, first, in S101, the ECU 13 obtains the operating conditions (the engine speed Ne, the accelerator opening degree Accp) of the internal combustion engine 1.

  In S102, the ECU 13 calculates basic fuel injection parameters based on the operating conditions acquired in S101.

  In S103, the ECU 13 acquires the actual in-cylinder oxygen concentration roxc.

  In S104, the ECU 13 predicts the actual ignition interval predicted value aintig based on the basic fuel injection parameter calculated in S102 and the actual in-cylinder oxygen concentration roxc acquired in S103.

  In S105, the ECU 13 acquires the target in-cylinder oxygen concentration roxctrg.

In S106, the ECU 13 predicts the target ignition interval aintigtrg based on the basic fuel injection parameter calculated in S102 and the target in-cylinder oxygen concentration roxctrg acquired in S105.

  In S107, the ECU 13 determines whether or not the difference between the actual ignition interval predicted value aintig predicted in S104 and the target ignition interval aintigtrg predicted in S106 (= | aintigtrg-aintig |) is greater than the allowable value a. To do.

  If a negative determination is made in S107 (| aintigtrg-aintig | ≦ a), the ECU 13 proceeds to S110. In S110, the ECU 13 operates the fuel injection valve 3 in accordance with the basic fuel injection parameter obtained in S102.

  On the other hand, when an affirmative determination is made in S107 (| aintigtrg-aintig |> a), the ECU 13 proceeds to S108. In S108, the ECU 13 corrects the basic injection parameter calculated in S102 in order to make the actual ignition interval coincide with the target ignition interval.

  Specifically, the ECU 13 specifies the main injection timing that satisfies the actual in-cylinder oxygen concentration and the target ignition interval in the map described above, and sets the specified main injection timing as the adapted main injection timing. Further, the ECU 13 calculates the difference between the basic main injection timing and the compatible main injection timing, and corrects the pilot injection timing by the difference.

  In S109, the ECU 13 operates the fuel injection valve 3 in accordance with the main injection timing and the pilot injection timing corrected in S108.

  As described above, when the ECU 13 executes the fuel injection control routine of FIG. 4, the determination means, the first acquisition means, the second acquisition means, the prediction means, the setting means, and the correction means according to the present invention are realized. .

  Therefore, according to the fuel injection control system for an internal combustion engine of the present embodiment, in the fuel injection control system for a compression ignition internal combustion engine in which pilot injection is performed prior to main injection, the actual ignition interval is not changed without changing the injection interval. Can be approximated to the target ignition interval. As a result, the amount of smoke generated during transient operation and the magnitude of the combustion noise can be kept within an allowable range while avoiding the contradiction caused by the change in the injection interval.

  In this embodiment, the main injection timing is taken as an example of the fuel injection parameter to be corrected. However, the present invention is not limited to this, and the pilot injection amount and the injection pressure (fuel pressure in the common rail 30) It may be. In short, any parameter may be used as long as it can change the ignition timing of the main injection fuel or the ignition timing of the pilot injection fuel.

It is a figure which shows schematic structure of the fuel-injection control system of an internal combustion engine. It is a figure which shows the relationship between an ignition interval and the generation amount of smoke. It is a figure which shows the relationship between an ignition interval and the magnitude | size of a combustion noise. It is a flowchart which shows a fuel-injection control routine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve 4 ... Intake passage 5 ... Turbocharger 6 ... Intercooler 7.・ ・ ・ ・ Exhaust passage 8 ・ Exhaust gas purification device 9 ・ EGR passage 10 ・ ・ ・ ・ EGR valve 11 ・ ・ ・ ・ EGR cooler 12 ・ ・ ・ ・ Intake throttle valve 13 ・ ・ ・ ・ECU
14 .... Air flow meter 15 .... Crank position sensor 16 .... Water temperature sensor 17 .... Air-fuel ratio sensor 18 .... Accelerator position sensor 30 ... Common rail 31 ... Pressure Sensor 50 ... Compressor housing 51 ... Turbine housing

Claims (4)

In a fuel injection control system for a compression ignition internal combustion engine in which pilot injection is performed prior to main injection,
Determining means for determining a plurality of fuel injection parameters including an injection interval between the pilot injection and the main injection based on an operating condition of the internal combustion engine;
First acquisition means for acquiring an actual state quantity that is an actual state quantity in the cylinder;
A second acquisition means for acquiring a target state quantity that is a state in the cylinder corresponding to an operating condition of the internal combustion engine;
The timing at which pilot-injected fuel ignites and the timing at which main-injected fuel ignites when fuel injection is performed according to the fuel injection parameter determined by the determining means under the actual state quantity acquired by the first acquiring means. A prediction means for predicting an ignition interval that is an interval;
The ignition interval when fuel injection is performed according to the fuel injection parameter determined by the determination unit under the target state quantity acquired by the second acquisition unit is predicted, and the predicted ignition interval is set as the target ignition interval. Setting means to set to,
When the difference between the ignition interval predicted by the prediction means and the target ignition interval set by the setting means exceeds an allowable value, another fuel injection parameter is not changed without changing the injection interval determined by the determination means. And correcting means for approximating the ignition interval to the target ignition interval;
A fuel injection control system for an internal combustion engine.   2. The fuel injection control system for an internal combustion engine according to claim 1, wherein the fuel injection parameter corrected by the correcting means is at least one of a pilot injection amount, a main injection timing, and an injection pressure.   3. The correction unit according to claim 2, wherein the correction unit retards the main injection timing when the ignition interval predicted by the prediction unit is shorter than the target ignition interval, and the ignition interval predicted by the prediction unit is the target ignition interval. A fuel injection control system for an internal combustion engine, wherein the main injection timing is advanced when longer.   4. The fuel injection control system for an internal combustion engine according to claim 1, wherein the state quantity in the cylinder is at least one of in-cylinder oxygen concentration, in-cylinder pressure, or in-cylinder temperature.

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