JP4775320B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a technique for preventing knocking of an internal combustion engine.

  It is known that abnormal combustion called knocking occurs in an internal combustion engine. In general, when knocking occurs, control is performed to retard knocking by retarding the ignition timing of the internal combustion engine. An example of such control is described in Patent Document 1.

  In a gasoline supercharged engine operated at a stoichiometric air-fuel ratio, if the ignition timing is retarded when knocking is detected in the supercharging region, the exhaust gas temperature and the catalyst bed temperature at the turbine inlet rapidly increase. As a measure for preventing such a rapid rise in temperature, a method of controlling the air-fuel ratio to the rich side in conjunction with retarding control of the ignition timing has been proposed (see, for example, Patent Document 2).

  However, when the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, the ignition timing at which the torque becomes maximum (hereinafter referred to as “MBT: Minimum Advance for Best Torque”) shifts to the compression top dead center side, so that the ignition delay is retarded. It becomes necessary to increase the amount, and problems such as deterioration in fuel consumption and generation of smoke occur.

  On the other hand, Patent Document 3 proposes a method of retarding the ignition timing when knocking occurs and correcting the air-fuel ratio to the lean side when a period in which the retard amount exceeds a predetermined value continues for a predetermined time or longer. .

  However, since Patent Document 3 is premised on a compression combustion natural gas (CNG) engine with a lean combustion operation in which the basic ignition timing can be set in the vicinity of MBT, the sensitivity of the exhaust gas temperature, the catalyst bed temperature, etc., to the ignition timing retard amount is increased. Is insensitive. This will be briefly described with reference to FIG. FIG. 7 is a graph showing the relationship between the ignition timing and the exhaust gas temperature or the catalyst bed temperature. When the MBT of the CNG engine as in Patent Document 3 is “MBT1”, the MBT of the gasoline supercharged engine is around “MBT2”. Therefore, when the ignition timing is retarded by the retard amount X for the CNG engine, the temperature rise of the exhaust gas temperature or the catalyst bed temperature is ΔT1, but for the gasoline supercharged engine, the ignition timing is retarded by the same retard amount X. The temperature rise of the exhaust gas temperature or the catalyst bed temperature in the case of cornering becomes ΔT2, and a rapid temperature rise is unavoidable compared to the case of the CNG engine. Therefore, the method of Patent Document 3 cannot be simply applied to a gasoline supercharged engine.

JP 2006-112267 A Japanese Patent Laid-Open No. 10-1765709 JP 2004-346905 A

  The present invention has been made to solve the above-described problems, and is a control device for an internal combustion engine capable of avoiding knocking while suppressing an increase in exhaust gas temperature and catalyst bed temperature when knocking occurs. The purpose is to provide.

In one aspect of the present invention, a control device for an internal combustion engine is supplied to the knocking detection means for detecting knocking in the internal combustion engine, ignition timing control means for controlling the ignition timing of the internal combustion engine, and the internal combustion engine. An air-fuel ratio control means for reducing the fuel to change the air-fuel ratio to the lean side, and a retard amount of the ignition timing by the ignition timing control means based on the load of the internal combustion engine when knocking is detected, and Knocking control means for controlling the amount of fuel decrease by the air-fuel ratio control means , wherein the knocking control means uses the intake air amount of the internal combustion engine as a value indicating the load of the internal combustion engine, When the intake air amount is larger than the first predetermined amount, the knocking control means is configured to reduce the amount of the fuel compared to the case where the intake air amount is smaller than the first predetermined amount. As well as many minor amounts to reduce the retard amount of the ignition timing.

  The control apparatus for an internal combustion engine includes means for detecting knocking, means for retarding the ignition timing, and means for reducing the fuel injection amount to make the air-fuel ratio lean. When knocking is detected, the retard amount of the ignition timing and the fuel decrease amount are controlled based on the load of the internal combustion engine. By retarding the ignition timing, knocking can be avoided, and by making the air-fuel ratio lean, the exhaust gas temperature of the internal combustion engine, the catalyst bed temperature, etc. can be lowered.

Further , the knocking control means increases the amount of decrease in the fuel when the intake air amount is larger than the first predetermined amount as compared with the case where the intake air amount is smaller than the first predetermined amount. In addition, the retard amount of the ignition timing is reduced. In this case, the air-fuel ratio is made lean by increasing the fuel reduction amount, and the MBT shifts to the advance side. Therefore, the knock margin can be ensured even if the ignition retardation amount is decreased accordingly.

In another aspect of the present invention, a control device for an internal combustion engine is supplied to the knocking detection means for detecting knocking in the internal combustion engine, ignition timing control means for controlling the ignition timing of the internal combustion engine, and the internal combustion engine. An air-fuel ratio control means for reducing the fuel to change the air-fuel ratio to the lean side, and a retard amount of the ignition timing by the ignition timing control means based on the load of the internal combustion engine when knocking is detected, and Knocking control means for controlling the amount of fuel decrease by the air-fuel ratio control means, wherein the knocking control means uses the intake air amount of the internal combustion engine as a value indicating the load of the internal combustion engine, The knocking control means supplies the air-fuel ratio control means with an intake air amount that is smaller than an intake air amount when the ignition timing control means starts to decrease the retard amount of the ignition timing. To initiate reduction of that the fuel. Although the exhaust gas temperature changes sensitively with respect to the air-fuel ratio leaning, the sensitivity at which the MBT shifts to the advance side is insensitive, so the air-fuel ratio leaning is executed from a region where the intake air amount is small.

One aspect of the control apparatus for an internal combustion engine includes misfire detection means for detecting occurrence of misfire in the internal combustion engine, wherein the knocking control means has the intake air amount larger than a second predetermined amount, and When misfire is detected, the air-fuel ratio control means is controlled so that the air-fuel ratio becomes a predetermined rich air-fuel ratio. When misfire occurs, the leaning of the air-fuel ratio is stopped and the air-fuel ratio is changed to a rich state. In a preferred embodiment, the rich air-fuel ratio is made richer than the output air-fuel ratio of the internal combustion engine. If the air-fuel ratio is appropriately enriched, there is a possibility that knocking may be promoted. Therefore, the rich state of the output air-fuel ratio or more is changed.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a schematic configuration of a control device for an internal combustion engine according to an embodiment of the present invention. In FIG. 1, solid arrows indicate intake / exhaust flow, and broken arrows indicate signal flow.

  The internal combustion engine control device 1 includes an internal combustion engine (engine) 5, an intake passage 2 and an exhaust passage 6 connected to the engine 5, an ECU 10, and an accelerator opening sensor 11. In the present embodiment, it is assumed that the engine 5 is a gasoline supercharged engine that operates at a stoichiometric air-fuel ratio (hereinafter also referred to as “λ1”).

  The accelerator opening sensor 11 detects an accelerator opening corresponding to the amount of depression of an accelerator pedal (not shown) and supplies a detection signal S11 to the ECU 10.

  An air flow meter 3 and a throttle valve 4 are provided in the intake passage 2. The air flow meter 3 measures the intake air amount Q flowing through the intake passage and supplies a detection signal S3 indicating the intake air amount Q to the ECU 10. The throttle valve 4 is opened / closed according to the accelerator opening degree or the like by a control signal S4 supplied from the ECU 10 to control the intake air amount Q supplied to the engine 5.

  The engine 5 is provided with a turbocharger 13. A compressor 13c of the turbocharger 13 is provided in the intake passage 2, and an intercooler 16 that cools the intake air output from the compressor 13c is provided downstream of the compressor 13c.

  A turbine 13t of the turbocharger 13 is provided in the exhaust passage 6. A catalyst 15 for purifying exhaust gas is provided downstream of the turbine 13t.

  The engine 5 is provided with a fuel injection valve 7, an ignition device 8, a crank angle sensor 9, and a knock sensor 12. The fuel injection valve 7 injects fuel in response to a control signal S7 supplied from the ECU 10, and the ignition device 8 changes to the air-fuel mixture sealed in the cylinder at the ignition timing indicated by the control signal S8 supplied from the ECU 10. Ignite. The crank angle sensor 9 supplies the ECU 10 with a detection signal S9 indicating the engine speed NE and the like by detecting the rotation of the crankshaft.

  Knock sensor 12 detects the occurrence of knocking in engine 5 and supplies detection signal S12 to ECU 10. The ECU 10 determines the presence or absence of knocking based on the detection signal S12. For example, the ECU 10 compares the level of the detection signal output from the knock sensor 12 with a predetermined level, and determines that knocking has occurred when the number exceeding the predetermined level exceeds the predetermined number. For the knocking determination, a known method other than the above may be applied.

  The ECU 10 is an electronic control unit that includes a CPU, a ROM, and a RAM (not shown) and controls the entire operation of the control device 1 for the internal combustion engine. In the above configuration, the knocking detection means in the present invention is constituted by the knock sensor 12 and the ECU 10, and the ignition timing control means is constituted by the ECU 10. The air-fuel ratio control means is constituted by the ECU 10 and the fuel injection valve 7, and the knocking control means is constituted by the ECU 10.

  Next, control at the time of occurrence of knocking according to the present embodiment will be described. In the present embodiment, when knocking occurs, the ignition timing is retarded and the air-fuel ratio is made lean so that the exhaust gas temperature and the catalyst bed temperature (hereinafter collectively referred to as “exhaust temperature”) are increased. While avoiding, knocking is avoided. In order to avoid knocking, it is effective to retard the ignition timing. In addition to this, in the present embodiment, the air-fuel ratio is made lean in order to suppress an increase in the exhaust gas temperature. The reason for this will be briefly described.

  FIG. 2 shows the relationship between the air-fuel ratio of the engine 5 and the exhaust temperature. In order to lower the exhaust temperature by a predetermined temperature C on the basis of the state in which the engine 5 is operated at the stoichiometric air-fuel ratio, a method of changing the air-fuel ratio to the rich side by the change amount A, and a lean side by the change amount B There is a method to change. However, the method of changing the air-fuel ratio to the lean side is advantageous in that the amount of change in the air-fuel ratio is small compared to the method of changing to the rich side. That is, when the air-fuel ratio is changed to the lean side, the exhaust temperature can be lowered with a small change in the air-fuel ratio. For this reason, the present embodiment employs a method of reducing the fuel injection amount and changing the air-fuel ratio to the lean side.

  Next, the knocking control according to the present embodiment will be described. In the present embodiment, when knocking occurs, the exhaust gas temperature is predicted based on the intake air amount indicating the load of the engine 5, the ignition timing is retarded, and the fuel injection amount is decreased. The exhaust temperature can be predicted by using a map having parameters such as the intake air amount, the fuel injection amount, and the ignition retard amount.

  FIG. 3 shows the relationship between the intake air amount, the ignition retardation amount, and the fuel correction amount. Here, the fuel correction amount is a correction amount of the fuel injection amount. Specifically, when the fuel correction amount = 1.0, the fuel injection amount is not corrected, and when the fuel correction amount> 1.0, the fuel injection amount is increased (that is, the air-fuel ratio is enriched) to correct the fuel. When the amount <1.0, the fuel injection amount is decreased (that is, the air-fuel ratio is made lean). Further, the operating region of the engine 5 is classified into the A region to the C region based on the intake air amount.

  First, when knocking occurs in the A region where the intake air amount is small, as shown in the figure, the air-fuel ratio is not made lean (that is, the fuel injection amount is not corrected), and the ignition retard amount is set to a predetermined retard angle Set to quantity D. In area A, since the amount of intake air is small, the exhaust temperature itself is low. Further, the basic ignition timing is on the advance side (MBT side), and no problem occurs due to the rise in the exhaust temperature caused by the ignition delay angle. Therefore, the air-fuel ratio control is not performed, and only the ignition retardation is performed.

  Next, when knocking occurs in the B region where the intake air amount is medium, the fuel correction amount is set to the negative side in order to suppress an increase in the exhaust temperature (that is, fuel correction amount <1.0, fuel injection amount). The air-fuel ratio becomes leaner. The ignition retardation amount is a predetermined retardation amount D as in the A region.

  Next, when knocking occurs in the C region where the intake air amount is large, the fuel correction amount to the negative side is increased to promote leaning of the air-fuel ratio. At the same time, the ignition retard amount is decreased. As described with reference to FIG. 2, the exhaust gas temperature can be lowered by making the air-fuel ratio lean. Further, by making the air-fuel ratio lean, it is possible to reduce the ignition retard amount. This will be described with reference to FIG.

  FIG. 4 schematically shows MBT and knock margin in the stoichiometric air-fuel ratio state and the lean state. In FIG. 4, the horizontal axis indicates the ignition timing. The MBT in the theoretical air-fuel ratio state is “MBT3”, and the MBT in the lean state is “MBT4”. The ignition timing at which knocking occurs is CAk. In the stoichiometric air-fuel ratio state, knocking occurs at the ignition timing CAk, so the ignition timing is retarded by R3 to CA3. The knock margin M in this case is defined by MBT3 and ignition timing CA3.

  On the other hand, in the lean state, when the air-fuel ratio becomes lean, the MBT shifts to the advance side by ΔMBT as compared with the stoichiometric air-fuel ratio state, and becomes the position of MBT4. In this case, if the same knock margin M as in the stoichiometric air-fuel ratio state is secured, the retard amount from the ignition timing CAk at which knocking occurs is R4 (<R3), and the spark retard amount can be reduced. . In other words, the knock margin can be ensured even if the ignition retardation amount at the time of knocking is reduced by the amount that the MBT has shifted to the advance side due to the lean air-fuel ratio. Therefore, in the C region where the intake air amount (high load) is high, the fuel correction amount is increased to the minus side to promote leaning of the air-fuel ratio and reduce the ignition retard amount. Thereby, it is possible to suppress an increase in the exhaust temperature while reliably avoiding knocking. This control also provides the following advantages. First, since the ignition retard amount can be reduced, it is possible to prevent the occurrence of secondary problems such as an increase in the ignition request voltage. Further, since the fuel injection amount is not increased in order to avoid knocking, problems such as deterioration of fuel consumption and occurrence of smoke do not occur.

  In this embodiment, as understood from FIG. 3, the fuel correction for the air-fuel ratio leaning is started in a region on the smaller intake air amount (light load) side than the control for reducing the ignition retard amount. To do. Specifically, the control for reducing the ignition retard amount from the predetermined retard amount starts from the C region, whereas the fuel correction for the air-fuel ratio leaning is performed on the lower intake air amount side B region. Starting from. Since the exhaust temperature reacts sensitively to the air-fuel ratio, the lean control of the air-fuel ratio may be performed after the intake air amount reaches a certain level for the purpose of suppressing the rise in the exhaust temperature. However, since the transition of the MBT due to the lean air-fuel ratio is less sensitive than the change in the exhaust temperature, if the leaning is performed from the lower intake air amount side region and the MBT is not reliably shifted to the advance side, As described above, the ignition retard amount cannot be reduced. For this reason, fuel correction for air-fuel ratio leaning is started in a region on the smaller intake air amount (light load) side than control for reducing the ignition retard amount.

  Next, control when misfire of the engine 5 occurs during the above control will be described. The misfire detection can be performed based on, for example, the HC concentration in the exhaust gas or based on the output of the combustion pressure sensor, but the present invention has no particular limitation on the misfire determination method.

  When a misfire occurs, the above control is basically stopped. FIG. 5 shows the state of control in that case. FIG. 5 shows an example in which the control is stopped in the high intake air amount region where the possibility of misfire is high, that is, the C region. As understood from comparison with the control shown in FIG. 3, when a misfire is detected while the engine is operating in the C region, both the control for leaning the air-fuel ratio and the control for reducing the ignition timing retard amount are performed. Cancel. As a result, the ignition retardation amount is returned to the predetermined retardation amount D.

  On the other hand, the fuel correction amount is changed to the rich side, and the air-fuel ratio is changed to a predetermined rich air-fuel ratio. Here, the predetermined rich air-fuel ratio is an air-fuel ratio in which the MBT position is equal to or advanced from the MBT when the engine 5 is operated in the stoichiometric air-fuel ratio state, and preferably the output air-fuel ratio of the engine 5 The fuel ratio is set. Here, the reason why the air-fuel ratio is made rich to the output air-fuel ratio is as follows. When the air-fuel ratio is in a suitable rich state where the output air-fuel ratio is less than the output air-fuel ratio, the exhaust energy increases, so that the supercharging pressure increases and there is a possibility of increasing knocking. Moreover, since MBT moves to the compression top dead center side, there is a possibility that the avoidance of knocking may be insufficient. Therefore, the air-fuel ratio is enriched to an output air-fuel ratio that is equal to or more advanced than the MBT when operating in the stoichiometric air-fuel ratio state. The example of FIG. 5 shows an example in which the theoretical air fuel ratio is 14.5, the output air fuel ratio is 12.5, and the fuel correction amount is 1.0 to 1.16 (= 14.5 / 12.5). Yes.

  In the example of FIG. 5, an example of a case where misfire occurs in the C region is shown, but also when misfire occurs in the B region, the lean control of the air-fuel ratio is similarly stopped and the air-fuel ratio is set to a predetermined value. What is necessary is just to change to a rich air fuel ratio.

  Next, the knocking control according to the present embodiment will be described with reference to the flowchart of FIG. This control is periodically executed mainly by the ECU 10 that mainly functions as a knocking control means.

  First, the ECU 10 determines whether or not knocking has occurred based on the output of the knock sensor 12 (step S101). When knocking is detected, the ECU 10 first retards the ignition timing by a predetermined retardation amount D (step S102).

  Next, the ECU 10 acquires the intake air amount based on the output of the air flow meter 3 and the like, and determines which region the intake air amount is in (step S103). If the intake air amount is in a low region, for example, in region A in FIG. 3 (step S103; low), the process ends. In this case, as shown in FIG. 3, only the ignition timing retardation control is executed.

  When the intake air amount is in a high region, for example, in the region C in FIG. 3 (step S103; high), the ECU 10 performs control to decrease the ignition retard amount as shown in FIG. Is set to the negative side, and air-fuel ratio leaning control is performed (step S105).

  When the amount of intake air is in a medium region, for example, in region B in FIG. 3 (step S103; medium), the process proceeds to step S105. In this case, the ignition retard amount reduction control is not performed, and only the air-fuel ratio leaning control is performed.

  Thus, in a state where both the ignition retard amount reduction control and the air-fuel ratio leaning control, or only the air-fuel ratio leaning control, are performed, the ECU 10 is based on the HC concentration in the exhaust gas, the combustion pressure, etc. It is determined whether or not misfire has occurred (step S106). When it is determined that misfire has occurred (step S106; Yes), the ECU 10 stops the ignition delay amount reduction control as described with reference to FIG. (Step S107), the air-fuel ratio leaning control is stopped, and the air-fuel ratio is changed to the above-described predetermined rich air-fuel ratio (step S108).

  If it is determined in step S101 that knocking has not occurred and if it is determined in step S106 that no misfire has occurred, the process ends.

  In the above embodiment, the control is performed using the intake air amount as a value indicating the load of the internal combustion engine, but the fuel injection amount may be used instead.

  As described above, in the present embodiment, when knocking occurs, ignition timing retardation control and air-fuel ratio lean control are executed based on the load of the internal combustion engine, specifically, the intake air amount. Therefore, knocking can be avoided while suppressing an increase in exhaust gas temperature.

1 shows a configuration of a control device for an internal combustion engine according to an embodiment of the present invention. It is a graph which shows the relationship between the air fuel ratio of a gasoline supercharged engine, and exhaust temperature. The relationship between the intake air amount by knocking control of embodiment, the fuel correction amount, and the ignition retard amount is shown. The relationship between the MBT position by the air-fuel ratio lean control and the ignition delay amount is shown. The control method at the time of misfire generation | occurrence | production in the knocking control of embodiment is shown. It is a flowchart of knocking control by embodiment. It is a graph which shows the difference in the MBT position and exhaust temperature rise degree in a gasoline supercharged engine and a CNG engine.

Explanation of symbols

3 Air flow meter 4 Throttle valve 5 Engine (internal combustion engine)
7 Fuel Injection Valve 8 Ignition System 9 Crank Angle Sensor 10 ECU
12 Knock sensor 13 Turbocharger 15 Catalyst

Claims (4)

A control device for an internal combustion engine,
Knocking detection means for detecting knocking in the internal combustion engine;
Ignition timing control means for controlling the ignition timing of the internal combustion engine;
Air-fuel ratio control means for reducing the fuel supplied to the internal combustion engine and changing the air-fuel ratio to the lean side;
Knocking control means for controlling the retard amount of the ignition timing by the ignition timing control means and the amount of fuel decrease by the air-fuel ratio control means based on the load of the internal combustion engine when knocking is detected; equipped with a,
The knocking control means uses the intake air amount of the internal combustion engine as a value indicating the load of the internal combustion engine,
The knocking control means increases the amount of decrease in the fuel when the intake air amount is larger than the first predetermined amount, as compared with the case where the intake air amount is smaller than the first predetermined amount. A control device for an internal combustion engine, characterized by reducing a retard amount of the ignition timing . A control device for an internal combustion engine,
Knocking detection means for detecting knocking in the internal combustion engine;
Ignition timing control means for controlling the ignition timing of the internal combustion engine;
Air-fuel ratio control means for reducing the fuel supplied to the internal combustion engine and changing the air-fuel ratio to the lean side;
Knocking control means for controlling the retard amount of the ignition timing by the ignition timing control means and the amount of fuel decrease by the air-fuel ratio control means based on the load of the internal combustion engine when knocking is detected; equipped with a,
The knocking control means uses the intake air amount of the internal combustion engine as a value indicating the load of the internal combustion engine,
The knocking control means starts the reduction of the fuel by the air-fuel ratio control means with an intake air amount smaller than an intake air amount when the ignition timing control means starts to reduce the retard amount of the ignition timing. A control device for an internal combustion engine. Comprising misfire detection means for detecting the occurrence of misfire in the internal combustion engine,
The knocking control means controls the air-fuel ratio control means so that the air-fuel ratio becomes a predetermined rich air-fuel ratio when the intake air amount is larger than a second predetermined amount and the misfire is detected. The control device for an internal combustion engine according to claim 1 , wherein the control device controls the internal combustion engine. The control apparatus for an internal combustion engine according to claim 3 , wherein the rich air-fuel ratio is an air-fuel ratio richer than an output air-fuel ratio of the internal combustion engine.

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