JP4715768B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to a fuel injection control device for an internal combustion engine that controls split fuel injection.

  2. Description of the Related Art Conventionally, a technique for dividing fuel in an internal combustion engine is known. When split injection is performed, intake or a thin air-fuel mixture can be sandwiched between split injected fuels, and as a result, fuel and intake air are more easily mixed. Qi homogeneity can be increased. For example, Patent Documents 1 to 8 propose such techniques for split injection.

Japanese Patent Laid-Open No. 10-212988 JP 2001-98971 A Japanese Patent No. 2879993 JP 3617310 A JP 2002-115593 A JP 2001-349292 A JP-A-11-82029 JP 2001-90592 A

  Incidentally, it is generally known that a fuel injection valve that injects fuel has a phenomenon (hereinafter referred to as needle bounce) in which the valve is closed again by an inertial force remaining in the fuel and then opened again. FIG. 5 is a diagram showing the fuel injection rate when the fuel is divided and injected, and the waveform data shown in FIG. 5A is obtained when the fuel is divided and injected twice. Note that FIG. 5B further schematically shows the waveform data shown in FIG.

  From FIG. 5, it can be seen that the fuel is also injected after the first fuel injection is performed until the second fuel injection is performed (hereinafter, this fuel injection is referred to as a secondary injection). Called). Although this is due to the needle bounce described above, it can be seen from FIG. 5 that this secondary injection is generated after the second fuel injection as well as after the first fuel injection. That is, it can be seen from FIG. 5 that when divided injection is performed, secondary injection is generated for the number of divisions. For this reason, when the divided injection is performed, the influence of the secondary injection on the air-fuel ratio becomes larger than when the divided injection is not performed, and as a result, the air-fuel ratio is largely deviated.

  Accordingly, the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a fuel injection control device for an internal combustion engine that can prevent the air-fuel ratio from shifting due to the influence of secondary injection during split injection. .

  In order to solve the above-described problems, the present invention is a fuel injection control device for an internal combustion engine for controlling fuel injection of the internal combustion engine. In performing split fuel injection, after the fuel is injected, the secondary injection is performed. It is characterized by comprising specific split injection control means for performing new fuel injection before the occurrence. According to the present invention, it is possible to prevent the occurrence of secondary injection between fuel injections, and therefore it is possible to suppress the deviation of the air-fuel ratio due to the effect of secondary injection during split injection. In other words, according to the present invention, the air-fuel ratio can be made equal to that obtained when fuel is injected once without split injection.

  In the present invention, the specific divided injection control means may perform new fuel injection based on a predetermined injection interval after injecting fuel. Here, for example, even if the fuel injection pressure is the same, the generation characteristic of the secondary injection differs depending on the fuel injection valve. For this reason, in performing the second and subsequent new fuel injections, specifically, for example, it is preferable to use an injection interval that is predetermined by experiment or the like as in the present invention.

  In the present invention, when the divided injection is performed, the specific fuel injection unit may perform the fuel injection when the fuel injection period per injection is equal to or less than a predetermined value. Here, when the fuel injection period per injection is equal to or less than a predetermined value, for example, when the internal combustion engine is rotating at a high speed, or among the divided injections, the first fuel injection is set to the compression stroke. This means a case where the time until the fuel is vaporized before the time when combustion is performed is shorter and disadvantageous. In this case, for example, as described in Patent Document 8 described above, if the fuel injection period is long (for example, 3 ms or more), there is a possibility that the divided injection cannot be performed.

  In addition, the present invention is not limited to this, and the homogeneity of the air-fuel mixture when the operation state of the internal combustion engine is in a predetermined operation region such as a light load (for example, a load factor of 20% or less) operation region among the operation regions in which split injection is performed. In order to increase the fuel injection period, the fuel injection period per injection may be equal to or less than a predetermined value, or divided injection may be performed multiple times or may be desired. On the other hand, when performing divided injection to prevent the occurrence of secondary injection, the case where the divided injection is performed in a short injection interval is preferable.

  In the present invention, when the split injection is performed, the specific split injection control means may perform the fuel injection when the air-fuel ratio further deviates from a target air-fuel ratio by a predetermined value or more. Here, the case where the air-fuel ratio deviates from the target air-fuel ratio by a predetermined value or more occurs when the fuel injection amount becomes no longer appropriate due to deposit adhesion. Can be determined, for example, based on whether or not the air-fuel ratio learning mode is entered in which the correction value of the air-fuel ratio exceeds a specified value (eg, 3%). In this case, the air-fuel ratio has already shifted, and if it is further affected by the secondary injection, there is a high possibility that the air-fuel ratio will be significantly shifted. For this reason, in performing divided injection to prevent the occurrence of secondary injection, such a case is also suitable.

  In the present invention, when the divided injection is performed, and the fuel injection amount per injection is further minimum, the specific fuel injection unit performs the fuel injection in accordance with the generation timing of the secondary injection. Also good. Here, the case where the fuel injection amount per injection is the minimum is that the fuel injection amount cannot be stably performed due to the decrease in the fuel injection amount, whereas the fuel injection amount is the minimum at which the fuel injection can be performed stably. This means that the fuel injection amount is reached. In this case, the total fuel injection amount decreases, and the ratio of the secondary injection amount to the total fuel injection amount relatively increases. Therefore, the secondary injection is larger than the air-fuel ratio. Will have an impact. Further, in this case, the behavior of the needle of the fuel injection valve becomes unstable, so that variations in the fuel injection amount easily occur due to this.

  On the other hand, according to the present invention, it is possible to prevent the air-fuel ratio from deviating due to the influence of the secondary injection during the divided injection, and further, the behavior of the needle is achieved by performing the fuel injection in accordance with the generation timing of the secondary injection. Therefore, in addition to stabilizing the fuel injection when the fuel injection amount is the minimum, the variation can be reduced, and the limit of the minimum fuel injection amount can be expanded.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel-injection control apparatus of the internal combustion engine which can suppress that an air fuel ratio shifts | deviates by the influence of secondary injection at the time of split injection can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram schematically showing an internal combustion engine start control device according to the present embodiment realized by an ECU (Electronic Control Unit) 1 together with an internal combustion engine system 100. The internal combustion engine system 100 includes an intake system 10, an exhaust system 20, a fuel injection system 30, and an internal combustion engine 50. The intake system 10 is configured to introduce air into the internal combustion engine 50, and includes an air cleaner 11 for filtering the intake air, an air flow meter 12 for measuring the intake air amount, a throttle valve 13 for adjusting the intake air amount, A surge tank 14 for temporary storage, an intake manifold 15 for distributing intake air to each cylinder of the internal combustion engine 50, and an intake pipe appropriately disposed between them are configured. The intake system 10 is provided with a throttle opening sensor (not shown) for detecting the opening of the throttle valve 13. Based on the output of the throttle opening sensor, in addition to the opening of the throttle valve 13, an internal combustion engine is also provided. The load on the engine 50 can also be detected.

  The exhaust system 20 includes an exhaust manifold 21, a three-way catalyst 22, a silencer (not shown), and an intake pipe appropriately disposed between these components. The exhaust manifold 21 is configured to merge exhaust from the cylinders. The three-way catalyst 22 is configured to purify exhaust gas, and performs oxidation of hydrocarbons HC and carbon monoxide CO and reduction of nitrogen oxides NOx. In the exhaust system 20, an A / F sensor 23 for linearly detecting the air-fuel ratio based on the oxygen concentration in the exhaust is upstream of the three-way catalyst 22, and the air-fuel ratio is based on the oxygen concentration in the exhaust from the stoichiometric air-fuel ratio. Also, oxygen sensors 24 for detecting whether the gas is rich or lean are arranged downstream of the three-way catalyst 22 as air-fuel ratio sensors.

  The fuel injection system 30 is configured to supply and inject fuel, and includes a fuel injection valve 31, a fuel injection pump 32, a fuel tank 33, and the like. The fuel injection valve 31 is configured to inject fuel, and is opened at an appropriate injection timing and injects fuel under the control of the ECU 1. The fuel injection amount is adjusted by the length of the fuel injection period until the fuel injection valve 31 is closed under the control of the ECU 1. The fuel injection pump 32 is configured to pressurize the fuel to generate an injection pressure, and adjusts the injection pressure to an appropriate injection pressure under the control of the ECU 1. Although the fuel injection valve 31 is not particularly limited, the fuel injection valve 31 has high control responsiveness due to the nature of the control of performing new fuel injection to prevent the occurrence of secondary injection when performing split injection. A piezo valve or the like is preferably applied.

  The internal combustion engine 50 includes a cylinder block 51, a cylinder head 52, a piston 53, a spark plug 54, an intake valve 55, and an exhaust valve 56. The internal combustion engine 50 shown in the present embodiment is a gasoline engine comprising in-cylinder direct fuel injection type in-line four cylinders. However, the internal combustion engine 50 is not particularly limited as long as it is an internal combustion engine capable of implementing the present invention, and may have other appropriate cylinder arrangement structure and number of cylinders. In FIG. 1, the main part of the internal combustion engine 50 is shown with respect to the cylinder 51a as a representative of each cylinder. However, in this embodiment, the other cylinders have the same structure. The cylinder block 51 is formed with a substantially cylindrical cylinder 51a. A piston 53 is accommodated in the cylinder 51a. A cylinder head 52 is fixed to the upper surface of the cylinder block 51. The combustion chamber 57 is formed as a space surrounded by the cylinder block 51, the cylinder head 52 and the piston 53.

  In addition to an intake port 52a for guiding intake air to the combustion chamber 57, the cylinder head 52 is formed with an exhaust port 52b for exhausting the combusted gas from the combustion chamber 57, and opens and closes the intake and exhaust ports 52a and 52b. For this purpose, intake and exhaust valves 55 and 56 are provided. The spark plug 54 is disposed in the cylinder head 52 with an electrode protruding substantially in the center above the combustion chamber 57. The fuel injection valve 31 is disposed in the cylinder head 52 with a fuel injection hole protruding from directly above into the combustion chamber 57 so that fuel can be directly injected into the cylinder. However, the arrangement of the fuel injection valve 31 is not limited to this and may be arranged at other appropriate positions. In addition, the internal combustion engine 50 is provided with various sensors such as a crank angle sensor 71 that generates an output pulse proportional to the rotational speed NE and a water temperature sensor 72 for detecting the water temperature of the internal combustion engine 50.

  The ECU 1 is a microcomputer (hereinafter simply referred to as a microcomputer) that includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory) (not shown). And an input / output circuit and the like. The ECU 1 is mainly configured to control the internal combustion engine 50. In this embodiment, the ECU 1 controls the fuel injection valve 31, the fuel injection pump 32, the ignition plug 54 (more specifically, an igniter not shown), and the like. In addition to the fuel injection valve 31 and the like, various control objects are connected to the ECU 1 via a drive circuit (not shown). The ECU 1 is connected to various sensors such as an air flow meter 12, a throttle opening sensor, a crank angle sensor 71, and a water temperature sensor 72.

  The ROM is configured to store a program in which various processes executed by the CPU and map data are stored. In this embodiment, in addition to a program for controlling the internal combustion engine 50, a fuel injection control for controlling fuel injection. Stores programs. The fuel injection control program may be configured as a part of the internal combustion engine 50 control program. The fuel injection control program is configured to have a split injection control program for split injection of fuel, and this split injection control program is used for the operating state (for example, the rotational speed NE and the load) of the internal combustion engine 50. In order to perform divided injection accordingly, it is determined whether or not the operating state of the internal combustion engine 50 is in the operation region in which divided injection is performed, and when the determination is affirmative, the divided injection is performed. .

  On the other hand, the ROM also stores injection map data (not shown) in which an operation region in which divided injection is performed according to the operating state of the internal combustion engine 50 is defined. The above-described divided injection control program is more specific. Specifically, the operation state of the internal combustion engine 50 is detected and the injection map data is referred to so as to determine whether or not the operation region is in the divided injection region. Note that the first fuel injection performed in the split injection may be performed at an appropriate timing. For example, the fuel injection may be performed in the intake stroke, from the intake stroke to the compression stroke, or in the compression stroke. In this regard, the first fuel injection is generally advantageous for the improvement of the homogeneity of the air-fuel mixture and the fuel vaporization in the intake stroke that can ensure a long period from when the fuel is injected until when the combustion is performed. Become.

  Further, the split injection control program has a specific split injection control program for performing new fuel injection after the fuel is injected until the secondary injection occurs when performing split injection of fuel. Has been. Specifically, the specific division injection control program is created so as to perform new fuel injection based on a predetermined injection interval after fuel is injected. As this injection interval, a value determined in advance by experiment according to the characteristics of the fuel injection valve 31 is stored in the ROM.

  The fuel injection based on the specific split injection control program is performed when the split injection is performed and the fuel injection period per injection is a predetermined value (for example, 1 ms) or less. On the other hand, in the above-described injection map data, an operation region corresponding to a case where the fuel injection period per injection is equal to or less than a predetermined value is also set. Specifically, this operating region is an operating region in which split injection is performed. Further, when the rotational speed of the internal combustion engine 50 is high, or when the first fuel injection is set to the compression stroke, or the internal combustion engine 50 This is a predetermined operation region corresponding to when the load is light. In response to this, the aforementioned program for divided injection control detects whether or not the operating state of the internal combustion engine 50 is within a predetermined operating region by detecting the operating state of the internal combustion engine 50 and referring to the injection map data. If the determination is affirmative, the fuel injection based on the specific split injection control program is performed.

  The fuel injection based on the specific split injection control program is also performed when the split injection is performed and when the air-fuel ratio further deviates from the target air-fuel ratio by a predetermined value or more. On the other hand, if the above-described split injection control program determines whether or not it is in the operation region in which split injection is performed, if the determination is affirmative, the air-fuel ratio feedback correction value is further set to a specified value (for example, 3%), it is determined whether or not the air-fuel ratio learning mode has been entered. If the determination is affirmative, the fuel injection based on the specific split injection control program is performed.

  Further, the fuel injection based on the specific split injection control program is performed when the split injection is performed and when the fuel injection amount per injection is the minimum. At this time, the fuel injection for the specific split injection control is performed. The program is created so as to perform new fuel injection in accordance with the generation timing of the secondary injection. The fuel injection amount when the fuel injection amount per injection is the minimum (hereinafter referred to as the minimum fuel injection amount qmin) and the timing of occurrence of the secondary injection are previously determined by experiments according to the characteristics of the fuel injection valve 31. The determined value is stored in the ROM.

  On the other hand, if the above-described split injection control program determines whether or not it is in the operation region in which split injection is performed, if the determination is affirmative, the fuel injection amount is further the minimum fuel injection amount qmin. If the determination is affirmative, the fuel injection based on the specific split injection control program is performed. Further, in this case, new fuel injection is performed in accordance with the generation timing of the secondary injection based on the specific divided injection control program. In this embodiment, the microcomputer, the internal combustion engine 50 control program, the divided injection control program, and the like realize various detection means, determination means, control means, and the like. Thus, the specific split injection control means is realized.

  Next, the process performed by ECU1 is explained in full detail using the flowchart shown in FIG. The ECU 1 controls the divided injection so that the secondary injection is prevented by executing the processing shown in the flowchart based on various programs such as the above-described specific divided injection control program stored in the ROM. The CPU executes a process of detecting the operating state of the internal combustion engine 50 and also executes a process of determining whether or not the operating state of the internal combustion engine 50 is in an operating region where split injection is performed (step S11). If the determination is negative, processing that does not require special processing is terminated in this flowchart. On the other hand, if the determination is affirmative, the CPU further executes a process of determining whether or not the operating state of the internal combustion engine 50 is in a predetermined operating region (step S12).

  If an affirmative determination is made in step S12, the CPU executes a process for controlling the divided injection so that a new fuel injection is performed based on a predetermined injection interval after the fuel is injected (step S13). As a result, the occurrence of secondary injection during fuel injection can be prevented and the deviation of the air-fuel ratio can be suppressed, and a plurality of times can be taken when the internal combustion engine 50 is rotating at a high speed or to improve the homogeneity of the air-fuel mixture. The divided injection can be suitably performed also when the divided injection is performed. An example of the new fuel injection timing T1 at this time is schematically shown in FIG. On the other hand, if a negative determination is made in step S12, the CPU executes a process of determining whether or not the air-fuel ratio learning mode in which the air-fuel ratio feedback correction value exceeds a specified value (eg, 3%) has been entered (step S14). . If it is affirmation determination, it will progress to step S13. Thereby, it is possible to prevent the occurrence of secondary injection during fuel injection and prevent the air-fuel ratio from deviating significantly.

  On the other hand, if a negative determination is made in step S14, the CPU executes a process of determining whether or not the fuel injection amount is the minimum fuel injection amount qmin (step S15). If the determination is negative, no particular processing is required, and the processing shown in this flowchart is terminated. On the other hand, if it is affirmation determination, after injecting fuel, CPU will perform the process for controlling split injection so that a new fuel may be injected according to the generation timing of secondary injection (step S16). As a result, it is possible to prevent the occurrence of secondary injection between fuel injections to suppress the deviation of the air-fuel ratio, stabilize fuel injection when the fuel injection amount is minimum, reduce variations, and reduce the minimum fuel injection amount. The limit of qmin can be expanded. An example of the new fuel injection timing T2 at this time is shown in FIG. As described above, it is possible to realize the ECU 1 that can suppress the deviation of the air-fuel ratio due to the influence of the secondary injection during the divided injection.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

1 is a diagram schematically showing an ECU 1 together with an internal combustion engine system 100. FIG. It is a figure which shows the process performed by ECU1 with a flowchart. It is a figure which shows typically an example of timing T1 of new fuel injection. It is a figure which shows typically an example of the timing T2 of new fuel injection. It is a figure which shows a mode when fuel is divided and injected with a fuel injection rate.

Explanation of symbols

1 ECU
DESCRIPTION OF SYMBOLS 10 Intake system 20 Exhaust system 30 Fuel injection system 31 Fuel injection valve 50 Internal combustion engine 100 Internal combustion engine system

Claims (5)

A fuel injection control device for an internal combustion engine for controlling fuel injection of the internal combustion engine,
A fuel injection control device for an internal combustion engine, comprising: specific split injection control means for performing a new fuel injection after the fuel is injected until the secondary injection occurs when performing the fuel split injection . 2. The fuel injection control device according to claim 1, wherein the specific divided injection control means performs new fuel injection based on a predetermined injection interval after injecting fuel. 3. The internal combustion engine according to claim 1, wherein when the split injection is performed, the specific split injection control unit performs fuel injection when a fuel injection period per injection is equal to or less than a predetermined value. Engine fuel injection control device. 3. The internal combustion engine according to claim 1, wherein when the split injection is performed, the specific split injection control means performs fuel injection when the air-fuel ratio further deviates from a target air-fuel ratio by a predetermined value or more. Engine fuel injection control device. When the split injection is performed and the fuel injection amount per injection is further minimum, the specific split injection control means performs a new fuel injection in accordance with the generation timing of the secondary injection. 3. The fuel injection control device for an internal combustion engine according to claim 1, wherein the fuel injection control device is an internal combustion engine.

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