JP2017155648A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make compatible both the stability of combustion and the suppression of NOx which is generated by the combustion, in an internal combustion engine which performs the combustion of a homogeneous air-fuel mixture.SOLUTION: A control device of an internal combustion engine having an ignition plug and an in-cylinder injection valve for directly injecting fuel into a cylinder performs first fuel injection for forming a homogeneous air-fuel mixture in the cylinder, and second fuel injection for forming a prescribed air-fuel mixture in the vicinity of an ignition region of the ignition plug. Then, when a combustion variation exceeds a variation threshold, and a prescribed interval between the start timing of the second fuel injection and ignition timing is longer than prescribed minimum timing, the control device correctively shortens a prescribed interval at a succeeding combustion cycle by at least either of the retardation of the start timing of the second fuel injection and the retardation of the ignition timing.SELECTED DRAWING: Figure 5

Description

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

  In an internal combustion engine that burns by spark ignition, a homogeneous mixture is formed in the cylinder, and then a dense mixture is formed around the spark plug and ignited to ensure stable ignitability and a relatively low concentration homogeneous A technique for stably burning an air-fuel mixture is widely known (see, for example, Patent Document 1). In this technology, the spray angle in the fuel injection into the cylinder for forming the rich air-fuel mixture is made smaller than the spray angle in the fuel injection into the cylinder for forming the homogeneous air-fuel mixture. A rich mixture is formed around the spark plug.

  Further, in an internal combustion engine that forms a homogeneous mixture as described above and then forms a rich mixture around the spark plug, the amount of fuel for forming the rich mixture is reduced in order to suppress knocking during combustion. The technique to adjust is disclosed by patent document 2, for example. In this technique, the lower the engine speed of the internal combustion engine, the lower the amount of fuel for forming the rich mixture. Patent Document 3 discloses a technique for controlling the fuel injection timing for forming the rich mixture and the ignition timing by the spark plug for stable combustion of the homogeneous mixture.

JP 2003-049651 A JP 2003-013784 A JP-A-2005-337104

  In order to stabilize the combustion of the homogeneous mixture, a rich mixture having a relatively low air-fuel ratio is formed around the spark plug, and the rich mixture is ignited by the spark plug. However, when a rich mixture is formed in this way, the amount of NOx produced can be relatively large depending on the fuel concentration distribution. However, in the prior art, many contrivances have been made with respect to stabilizing the combustion of a homogeneous mixture, but it is difficult to say that sufficient measures have been taken with respect to the suppression of the NOx generation amount.

  The present invention has been made in view of the above-described problems, and provides a technique that suitably balances the stability of combustion and the suppression of NOx caused by combustion in an internal combustion engine that performs combustion of a homogeneous mixture. With the goal.

  In order to solve the above-mentioned problems, the present applicant, in an internal combustion engine that performs combustion of a homogeneous air-fuel mixture, starts combustion fluctuation and NOx generation and fuel injection for a predetermined air-fuel mixture formed around a spark plug. We focused on the correlation between the predetermined interval from the timing to the ignition timing by the spark plug and the fuel injection amount for the predetermined mixture. When considering both combustion stability and NOx suppression, the inventor of the present application states that it is more preferable to correct the predetermined interval than to correct the fuel injection amount. It is what I found.

More specifically, the present invention relates to a control device for an internal combustion engine having an ignition plug and an in-cylinder injection valve that directly injects fuel into a cylinder, and the control device is configured to form a homogeneous mixture in the cylinder. A first injection means for injecting fuel with an in-cylinder injection valve; and a second injection for injecting a predetermined minute amount of fuel with the in-cylinder injection valve to form a predetermined air-fuel mixture in the vicinity of an ignition part of the ignition plug Ignition means for igniting the homogeneous mixture and the predetermined mixture by the spark plug at a timing when a predetermined time has elapsed from the start timing of fuel injection by the second injection means, and ignition by the ignition execution means Detection means for detecting combustion fluctuations in the internal combustion engine when the engine is executed, and on the basis of the combustion fluctuations detected by the detection means, the combustion cycle next to the combustion cycle in which the detection is performed. A predetermined interval defined as a period from the start timing of fuel injection by the second injection means to the ignition timing of the spark plug, or a control means for controlling the fuel injection amount by the second injection means. Prepare. When the combustion fluctuation exceeds a predetermined fluctuation threshold and the predetermined interval is longer than a predetermined minimum period, the control means delays the start timing of fuel injection by the second injection means. And at least one of advancement of the ignition timing of the spark plug, the predetermined interval in the next combustion cycle is corrected to be shortened, the combustion fluctuation exceeds the predetermined fluctuation threshold, and the predetermined interval is When it is the predetermined minimum period, the fuel injection amount by the second injection means in the next combustion cycle is increased and corrected.

  According to the present invention, in an internal combustion engine that performs combustion of a homogeneous air-fuel mixture, it is possible to suitably achieve both the stability of combustion and the suppression of NOx generated by the combustion.

1 is a diagram showing a schematic configuration of an internal combustion engine to which a control device according to the present invention is applied. It is a figure which shows the fuel-injection characteristic of the fuel injection valve with which the internal combustion engine shown in FIG. 1 is provided. It is a figure which shows each transition of the fuel injection in one combustion cycle, and an ignition timing in the control apparatus which concerns on this invention. In the fuel injection processing by the control device according to the present invention, the correlation between the initial combustion period and the NOx generation amount when the length of the predetermined interval between the pre-ignition injection timing and the ignition timing is changed, and the pre-ignition injection It is a figure which shows the said correlation when changing quantity. It is a flowchart of the fuel-injection process performed with the control apparatus which concerns on this invention. FIG. 6 is a view showing a control map in which the reference values of the homogeneous mixture, the pre-ignition injection amount, and the predetermined interval when the pre-ignition injection is performed by the fuel injection processing shown in FIG. 5 are associated with the operating state of the internal combustion engine. is there.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram illustrating a schematic configuration of an internal combustion engine 1 to which a control device according to the present embodiment is applied. The internal combustion engine 1 is a cylinder ignition type spark ignition internal combustion engine for driving a vehicle. In the internal combustion engine 1, an intake port 2 and an exhaust port 3 are connected to the cylinder 8. The intake port 2 sends intake air into the cylinder 8 through opening and closing of the intake valve 4, and the exhaust port 3 sends combustion gas and the like as exhaust to the exhaust passage 10 through opening and closing of the exhaust valve 5. The exhaust passage 10 is provided with a three-way catalyst 11 which is a catalyst for exhaust purification. A piston 9 is arranged in the cylinder 8.

In the internal combustion engine 1, a fuel injection valve 7 is provided at the top of the cylinder 8 that faces the piston 9. The fuel injection valve 7 is a solenoid-driven fuel injection valve. A passage through which fuel flows is formed in the body, and fuel is supplied from a delivery pipe (not shown) to the passage, and the supplied fuel is fuel injection. Gasoline fuel can be directly injected into the cylinder 8 in accordance with the operation of the needle valve that is electromagnetically driven in the valve 7. A spark plug 6 is arranged at a position where the fuel spray injected from the fuel injection valve 7 can be ignited.

  Here, the internal combustion engine 1 is equipped with an ECU 20 that is an electronic control device, and various controls in the internal combustion engine 1 are executed. Further, an accelerator opening sensor 21 is electrically connected to the ECU 20 in the internal combustion engine 1, and the ECU 20 receives a signal corresponding to the accelerator opening, and calculates torque required for the internal combustion engine 1 from the signal. . Further, the crank position sensor 22 is electrically connected to the ECU 20, and the ECU 20 receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 1 and calculates the engine rotational speed and the like of the internal combustion engine 1. Further, the ECU 20 is also electrically connected to an air flow meter 23 installed in an intake passage (not shown) connected to the intake port 2 so that the intake flow rate flowing through the intake passage can be detected. The ECU 20 is also electrically connected to various sensors provided in the internal combustion engine 1 other than the above, and the ECU 20 controls the fuel injection amount and fuel injection timing from the fuel injection valve 7 and the spark plug 6. The control of the ignition timing and other various controls in the internal combustion engine 1 are executed.

  Here, in the internal combustion engine 1, in order to realize stable combustion of the homogeneous mixture, an extremely small amount of fuel is injected before ignition of the ignition plug 6, and a predetermined concentration that is higher than the homogeneous mixture near the ignition part of the ignition plug 6. The fuel is injected to form the air-fuel mixture. This very small amount of fuel injection is referred to as “pre-ignition injection” in the present application. The dense predetermined air-fuel mixture is ignited by the spark plug 6. Here, the pre-ignition injection will be described with reference to FIG. FIG. 2 shows the fuel injection characteristics of the fuel injection valve 7, and the horizontal axis represents the injection instruction period instructed from the ECU 20 to the fuel injection valve 7. This injection instruction period corresponds to a period during which a drive current is applied to the electromagnetic drive mechanism in order to drive the needle valve of the fuel injection valve 7. The vertical axis in FIG. 2 represents the fuel injection amount actually injected in response to the injection instruction. As shown in FIG. 2, when the injection instruction period is shorter than t1, the fuel is not actually injected from the fuel injection valve 7. This is because if the injection instruction period is short, even if a drive current is applied, an electromagnetic driving force sufficient to displace the needle valve within the fuel injection valve 7 cannot be generated. Further, when the injection instruction period is longer than t2 (t2> t1), a sufficient electromagnetic driving force can be generated, so that the fuel injection amount can be adjusted linearly with respect to the length of the injection instruction period. . Thus, when the injection instruction period is longer than t2, a relatively large amount of fuel can be injected from the fuel injection valve 7.

  On the other hand, in the pre-ignition injection of the present application, an extremely small amount of fuel that can be injected in the injection instruction period in the range from t1 to t2 is injected. Specifically, an injection instruction in a range in which fuel can be substantially injected due to mechanical factors of the fuel injection valve 7 and the injection instruction period t1 ′ closest to the t1 is a lower limit value and the t2 is an upper limit value. The fuel injection according to the period is executed by the pre-ignition injection. In this way, in the pre-ignition injection, a very small amount of fuel is injected, so that a relatively rich mixture can be formed in the homogeneous mixture in the vicinity of the ignition part of the ignition plug 6 so that it does not spread unnecessarily. It is possible to achieve both stable combustion and suppression of the amount of NOx produced during combustion.

  FIG. 3 shows the transition of the fuel injection state by the fuel injection valve 7 and the ignition timing by the spark plug 6 in one combustion cycle when pre-ignition injection is performed in the internal combustion engine 1. As shown in FIG. 3, the fuel injection from the fuel injection valve 7 in one combustion cycle can be distinguished into a main injection m1 performed during the intake stroke and a pre-ignition injection m2 performed immediately before ignition of the spark plug 6. The main injection m1 is a fuel injection that is performed relatively early in order to form a homogeneous air-fuel mixture in the cylinder 8. On the other hand, as described above, the pre-ignition injection m2 is a predetermined air-fuel mixture in the vicinity of the ignition part of the spark plug 6 in order to achieve both stable combustion of the homogeneous air-fuel mixture and suppression of the amount of NOx generated during combustion. It is a fuel injection that forms (a rich mixture having a higher fuel concentration than a homogeneous mixture). A predetermined interval that is a period between the fuel injection start timing of the pre-ignition injection m2 and the ignition timing of the spark plug 6 is represented by Δt.

  Here, when the inventor of the invention of the present application intensively burns a homogeneous air-fuel mixture in the internal combustion engine 1, the combustion stability and the NOx generation amount are the fuel injection in the internal combustion engine 1 accompanied by the pre-ignition injection. It was found that it depends greatly on the conditions. When combustion of a homogeneous mixture is performed in the internal combustion engine 1, the amount of NOx generated can be suppressed by setting the mixture air-fuel ratio to the lean air-fuel ratio. However, if the air-fuel ratio shifts excessively to the lean side, the combustion becomes unstable and the combustion fluctuation of the internal combustion engine 1 becomes remarkable. The combustion fluctuations of the internal combustion engine 1 are reflected as fluctuations in the engine rotational speed of the internal combustion engine 1 and fluctuations in its output torque.

  The combustion fluctuation of the internal combustion engine 1 is largely related to the initial combustion period that reflects the combustion speed of the air-fuel mixture immediately after ignition of the spark plug 6. The initial combustion period can be defined as, for example, the length of the period that 10% of the injected fuel required for combustion. The longer the initial combustion period, the greater the combustion fluctuation. Therefore, in order to suppress such combustion fluctuations, it is effective to form an air-fuel mixture having a relatively high fuel concentration in the vicinity of the ignition part of the spark plug 6 by injection before ignition. Is as important as possible from the viewpoint of suppressing combustion fluctuations. On the other hand, in order to suppress NOx, a homogeneous mixture is burned, but since a relatively rich mixture is formed by performing the pre-ignition injection, a situation in which NOx is likely to occur at that portion is formed. For this reason, when performing the pre-ignition injection, it is also important to determine the injection conditions from the viewpoint of NOx suppression.

  Based on the above, the present invention focuses on the length of the predetermined interval Δt and the pre-ignition injection amount among the injection conditions related to the pre-ignition injection. FIG. 4 shows the correlation between the initial combustion period and the amount of NOx generated when the length of the predetermined interval Δt is changed by a line L1, and further shows the initial combustion period when the pre-ignition injection amount is changed. The correlation with the NOx generation amount is represented by a line L2. The correlation shown in FIG. 4 is obtained when the operation state of the internal combustion engine 1 is a predetermined operation state in which the pre-ignition injection is performed.

  The white arrow regarding the line L1 shown in FIG. 4 represents the transition of the correlation between the initial combustion period and the NOx generation amount when the predetermined interval Δt is shortened with the pre-ignition injection amount fixed at a certain amount. ing. Further, the black arrow regarding the line L2 represents the transition of the correlation between the initial combustion period and the NOx generation amount when the pre-ignition injection amount is increased while the predetermined interval Δt is fixed to a certain length. Yes. As can be seen from FIG. 4, regarding the initial combustion period related to the combustion fluctuation, the length of the predetermined interval Δt has a greater influence than the pre-ignition injection amount. That is, in order to suppress the combustion fluctuation, shortening the predetermined interval Δt can shorten the initial combustion period and suppress the combustion fluctuation more effectively than adjusting the pre-ignition injection amount. On the other hand, when the pre-ignition injection amount is increased, the initial combustion speed is somewhat shortened, but a tendency for the NOx generation amount to become remarkable can be found. On the other hand, it can be found that the increase amount of the NOx generation amount when the predetermined interval Δt is shortened is relatively small.

  From the above, when performing combustion of a homogeneous mixture in the internal combustion engine 1, from the viewpoint of coexistence of suppression of combustion fluctuations and suppression of NOx generation amount, the fuel injection condition when executing the pre-ignition injection m2 is predetermined. It can be seen that it is preferable to shorten the interval Δt preferentially. Note that if the predetermined interval Δt is excessively shortened, the initial combustion period tends to become longer again. Therefore, in the example shown in FIG. 4, it is preferable to adjust the predetermined interval Δt until the initial combustion period indicated by the point P1 on the line L1 is achieved. That is, the predetermined interval Δt corresponding to the initial combustion period indicated by the point P1 represents an example of the minimum value of the predetermined interval Δt when the internal combustion engine 1 is in a predetermined operation state.

When adjusting the pre-ignition injection amount as the fuel injection condition when executing the pre-ignition injection m2, it is preferable to increase the pre-ignition injection amount after the predetermined interval Δt is set to the minimum value. . Increasing the pre-ignition injection amount facilitates ignition of the homogeneous mixture, so that combustion stability is obtained. However, when the pre-ignition injection amount is increased as shown by line L2 in FIG. This is because the tendency to increase can be found. A point P2 on the line L2 represents the initial combustion period and the NOx generation amount when the pre-ignition injection amount is the minimum value, that is, when the injection instruction period shown in FIG. 2 is t1 ′.

  Here, the flow of the fuel injection process in the internal combustion engine 1 will be described with reference to FIG. Note that the fuel injection process is repeatedly realized for each combustion cycle by executing a predetermined control program by the ECU 20 during operation of the internal combustion engine 1 that performs combustion of the homogeneous mixture. First, in S101, it is determined whether or not the operating state specified by the engine speed and the engine load of the internal combustion engine 1 belongs to a predetermined region in which the pre-ignition injection is executed. In the internal combustion engine 1, combustion of the homogeneous air-fuel mixture occurs in a region where the engine load is within a predetermined load range and the engine rotational speed is within the predetermined speed range (hereinafter referred to as “pre-ignition injection execution region”). Executed. FIG. 6 shows a control map in which the reference values of the homogeneous mixture air-fuel ratio, the pre-ignition injection amount, and the predetermined interval when the pre-ignition injection is performed are associated with the operating state of the internal combustion engine. In each control map, the pre-ignition injection execution region is represented by R1. In the upper part (a) of FIG. 6, the reference value of the air-fuel ratio of the homogeneous mixture (the air-fuel ratio of the mixture formed by the main injection m1 shown in FIG. 3) in the pre-ignition injection execution region R1 is shown. In the middle stage (b), the distribution of reference values of the pre-ignition injection amount (the injection amount by the pre-ignition injection m2 shown in FIG. 3) in the pre-ignition injection execution region R1 is shown. In the lower part (c), the distribution of reference values for the length of the predetermined interval Δt in the pre-ignition injection execution region R1 is shown.

Each of these reference values is derived from a prior experiment or the like in a reference internal combustion engine, and is capable of achieving both suppression of combustion fluctuations and suppression of NOx generation amount, a homogeneous air-fuel ratio, a pre-ignition injection amount, and a predetermined interval. This is a reference value for the length of Δt. For example, in the pre-ignition injection execution region R1, when the operating state of the internal combustion engine 1 belongs to a sub region where the homogeneous air-fuel ratio is 28.0, the pre-ignition injection amount is 1.2 mm ³ , and The length of the predetermined interval Δt is 8 degrees in crank angle. As an example of the distribution tendency of each reference value, as the engine load increases or the engine speed increases, the homogeneous air-fuel ratio becomes the leaner air-fuel ratio, the pre-ignition injection amount increases, The length of the predetermined interval Δt is shortened. Although not shown, the injection start timing of the main injection m1 and the ignition timing of the spark plug 6 are also set to specific times according to the operating state of the internal combustion engine 1. Based on these conditions, the injection amount of the main injection m1 and the injection start timing of the pre-ignition injection m2 are also specified.

  If a positive determination is made in S101, the process proceeds to S102, and if a negative determination is made, the process proceeds to S110. In S102, fuel injection with pre-ignition injection m2, that is, fuel injection in the form shown in FIG. 3 is performed. As described above, the injection conditions of the fuel injection performed in S102 include the homogeneous mixture air-fuel ratio derived from the control map shown in FIG. 6, the injection amount before ignition, each reference value of the predetermined interval Δt, etc. Is determined based on the injection condition correction coefficient set in S105, S106, S108, and S109, which will be described later. Details thereof will be described in each of S105, S106, S108, and S109. When the process of S102 ends, the process proceeds to S103.

In S103, it is determined whether or not the combustion fluctuation in the internal combustion engine 1 has exceeded a predetermined threshold as a result of the combustion of the fuel by the fuel injection in S102. The combustion fluctuation of the internal combustion engine 1 can be detected based on the fluctuation of the engine speed of the internal combustion engine 1 calculated based on the detection value of the crank position sensor 22. As another method, it is possible to detect a variation in output torque of the internal combustion engine 1 calculated based on a detected value of a strain gauge (not shown) provided on the output shaft of the internal combustion engine 1 and a combustion pressure in the cylinder 8. The combustion fluctuation of the internal combustion engine 1 can also be detected based on the fluctuation of the detection value of a pressure sensor (not shown). It should be noted that the predetermined threshold value that is a comparison target of the combustion fluctuation can be determined based on a combustion state that can be permitted as stable combustion in the internal combustion engine 1. If a positive determination is made in S103, the process proceeds to S104, and if a negative determination is made, the process proceeds to S107.

  In S104, the length of the predetermined interval Δt under the fuel injection condition when it is determined that the combustion fluctuation has exceeded a predetermined threshold is the predetermined interval at which the initial combustion period becomes the minimum value with respect to the current operating state of the internal combustion engine 1. It is determined whether or not the length is greater than Δtmin. This Δtmin is the length of a predetermined interval corresponding to the point P1 if the operation state of the internal combustion engine 1 is the operation state of the internal combustion engine 1 in FIG. If a positive determination is made in S104, the process proceeds to S105, and if a negative determination is made, the process proceeds to S106.

  In S105, a correction coefficient for shortening and correcting the length of the predetermined interval Δt is set. When an affirmative determination is made in S104, there is a margin for shortening the predetermined interval Δt, which is an effective fuel injection condition for suppressing combustion fluctuations, as described with reference to FIG. Therefore, when an affirmative determination is made in S103 and it is determined that the combustion fluctuation in the internal combustion engine 1 exceeds a predetermined threshold, the predetermined interval Δt calculated based on the operating state of the internal combustion engine 1 for the predetermined interval Δt. A correction coefficient for shortening and correcting the reference value (see FIG. 6C) is set. Note that the correction coefficient for shortening correction set here is reflected at the time of fuel injection accompanying pre-ignition injection performed in the next combustion cycle (see the description of S102 above). In addition, regarding the execution of the shortening correction of the predetermined interval Δt, the start timing of the pre-ignition injection may be retarded, or the ignition timing of the spark plug 6 may be advanced. The start timing of the pre-injection may be retarded and the ignition timing of the spark plug 6 may be advanced. After the process of S105, the fuel injection process ends, and the fuel injection process for the next combustion cycle is started again.

  On the other hand, in S106, a correction coefficient for increasing the pre-ignition injection amount is set. When a negative determination is made in S104, there is no room for further shortening the predetermined interval Δt, which is an effective fuel injection condition for suppressing combustion fluctuations, as described with reference to FIG. Therefore, when an affirmative determination is made in S103 and it is determined that the combustion fluctuation in the internal combustion engine 1 exceeds a predetermined threshold, the pre-ignition injection amount is calculated based on the operating state of the internal combustion engine 1 before ignition. A correction coefficient for correcting the increase in the reference value of the injection amount (see FIG. 6B) is set. It should be noted that the correction coefficient for increasing correction set here is reflected at the time of fuel injection accompanying pre-ignition injection performed in the next combustion cycle (see the description of S102 above). After the process of S106, the fuel injection process ends, and the fuel injection process for the next combustion cycle is started again.

  Next, when a negative determination is made in S103 and the process proceeds to S107, the pre-ignition injection amount under the fuel injection condition when it is determined that the combustion fluctuation does not exceed the predetermined threshold is the current operating state of the internal combustion engine 1. On the other hand, it is determined whether or not the pre-ignition injection amount is larger than a predetermined pre-ignition injection amount Qm1min that is the minimum value. This Qm1min is the pre-ignition injection amount corresponding to the point P2 if the operating state of the internal combustion engine 1 is the operating state of the internal combustion engine 1 in FIG. If a positive determination is made in S107, the process proceeds to S108, and if a negative determination is made, the process proceeds to S109.

In S108, a correction coefficient for reducing the pre-ignition injection amount is set. When an affirmative determination is made in S107, there is a margin for further reducing the pre-ignition injection amount, which is a fuel injection condition, which is easily reflected in the increase in the NOx generation amount as described with reference to FIG. Therefore, a negative determination is made in S103, and based on the fact that the combustion fluctuation does not exceed a predetermined threshold in the internal combustion engine 1, that is, there is some margin to maintain stable combustion in the internal combustion engine 1, in S108, before ignition. With respect to the injection amount, a correction coefficient is set for correcting the decrease in the reference value (see FIG. 6B) of the pre-ignition injection amount calculated based on the operating state of the internal combustion engine 1. The correction coefficient for the reduction correction set here is reflected in the fuel injection accompanying the pre-ignition injection performed in the next combustion cycle (see the description of S102 above). Although the combustion fluctuation of the internal combustion engine 1 may increase due to the reduction correction of the injection amount before ignition, if the predetermined threshold is not exceeded, the combustion fluctuation is permissible. It becomes possible to suppress the NOx generation amount by the correction. After the process of S108, the fuel injection process ends, and the fuel injection process for the next combustion cycle is started again.

  In S109, a correction coefficient for extending and correcting the length of the predetermined interval Δt is set. When the negative determination is made in S107, there is no room for further reducing the pre-ignition injection amount, which is the fuel injection condition, which is easily reflected in the increase in the NOx generation amount as described with reference to FIG. This means that there is no room for suppressing the amount of NOx produced by reducing the amount of pre-ignition injection. Therefore, a negative determination is made in S103, and based on the fact that the combustion fluctuation does not exceed a predetermined threshold in the internal combustion engine 1, that is, there is some margin for maintaining stable combustion in the internal combustion engine 1, a predetermined interval is set in S109. For the length of Δt, a correction coefficient for extending and correcting the reference value (see FIG. 6C) of the length of the predetermined interval Δt calculated based on the operating state of the internal combustion engine 1 is set. Note that the correction coefficient for extension correction set here is reflected at the time of fuel injection accompanying pre-ignition injection performed in the next combustion cycle (see the description of S102 above). Although the combustion fluctuation of the internal combustion engine 1 may increase due to the extension correction of the length of the predetermined interval Δt, the combustion fluctuation is allowed if it does not exceed the predetermined threshold value. Even if the combustion fluctuation becomes unacceptable after that, the length of the predetermined interval Δt can be corrected by shortening and a margin for quickly suppressing the combustion fluctuation can be secured by the extension correction. As for execution of extension correction of the predetermined interval Δt, the start timing of the pre-ignition injection may be advanced, or the ignition timing of the spark plug 6 may be retarded. The start timing of the pre-injection may be advanced and the ignition timing of the spark plug 6 may be retarded. After the process of S109, the fuel injection process ends, and the fuel injection process for the next combustion cycle is started again.

  When a negative determination is made in S101 and the process proceeds to S110, in S110, normal fuel injection that is fuel injection without pre-ignition injection m2 is performed. In this normal fuel injection, a homogeneous mixture is formed in the cylinder 8 by the fuel of the main injection m1 in the intake stroke shown in FIG. 3, and the homogeneous mixture is ignited and burned by the spark plug 6. The injection conditions for the normal fuel injection are determined based on the operating state of the internal combustion engine 1. However, since the injection conditions are determined according to the prior art, detailed description thereof is omitted.

  As described above, in the present fuel injection process, when fuel injection with pre-ignition injection is performed in the internal combustion engine 1, if the combustion fluctuation exceeds a predetermined threshold, the length of the predetermined interval Δt included in the fuel injection condition, and the ignition By preferentially shortening and correcting the length of the predetermined interval Δt of the pre-injection amount, it is possible to suppress the increase in the NOx generation amount relatively small while effectively suppressing the combustion fluctuation. . That is, in the internal combustion engine 1, it is possible to suitably achieve both the stability of combustion and the suppression of NOx generated by the combustion.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 4 ... Intake valve 5 ... Exhaust valve 6 ... Spark plug 7 ... Fuel injection valve 8 ... Cylinder 20 ... ECU
21 ... Crank position sensor 22 ... Accelerator opening sensor 23 ... Air flow meter

Claims (1)

A control device for an internal combustion engine having an ignition plug and an in-cylinder injection valve that directly injects fuel into the cylinder,
First injection means for injecting fuel with the in-cylinder injection valve to form a homogeneous mixture in the cylinder;
Second injection means for injecting a predetermined minute amount of fuel by the in-cylinder injection valve in order to form a predetermined air-fuel mixture in the vicinity of an ignition part of the spark plug;
Ignition executing means for igniting the homogeneous mixture and the predetermined mixture by the spark plug at a timing when a predetermined time has elapsed from the start timing of fuel injection by the second injection means;
Detecting means for detecting combustion fluctuations in the internal combustion engine when ignition is executed by the ignition executing means;
Based on the combustion fluctuation detected by the detection means, a period from the start timing of fuel injection by the second injection means to the ignition timing of the spark plug in the combustion cycle subsequent to the combustion cycle in which the detection is performed A control unit for controlling a predetermined interval defined as: or a fuel injection amount by the second injection unit;
With
The control means includes
When the combustion fluctuation exceeds a predetermined fluctuation threshold and the predetermined interval is longer than a predetermined minimum period, the start timing of fuel injection by the second injection means is retarded and the ignition timing of the spark plug The predetermined interval in the next combustion cycle is shortened and corrected by at least one of the advancement of
If the combustion fluctuation exceeds the predetermined fluctuation threshold and the predetermined interval is the predetermined minimum period, the fuel injection amount by the second injection means in the next combustion cycle is increased and corrected.
Control device for internal combustion engine.

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