JP2010096060A - Ignition timing controller for internal combustion engine - Google Patents

Abstract

In an ignition timing control device for an internal combustion engine equipped with an EGR device, there is provided a technique capable of suitably achieving both avoidance of knocking of the internal combustion engine and suppression of misfire.
When the EGR rate at the time of detection of knocking (knock EGR rate Rkcs) exceeds the boundary EGR rate Rbo, the knock avoidance ignition timing STkcs is a misfire that is a retarded limit ignition timing at which the internal combustion engine does not misfire. It is determined that the ignition timing is set to the retard side relative to the limit ignition timing STmf, and the retard request amount COlag is reduced by executing the compression ratio reduction control for reducing the compression ratio on the intake side VVT prior to the knock control ( S205). When the compression ratio reduction control is executed, the knock avoidance ignition timing STkcs related to the knock control is changed to the advance side by the amount by which the retardation required amount COlag is reduced by the reduction of the compression ratio (S206).
[Selection] Figure 7

Description

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

  The knocking of the internal combustion engine means that the normal combustion of the internal combustion engine spreads in the combustion chamber due to the propagation of flame and the combustion pressure gradually increases, whereas the unburned mixture that has not reached the flame propagation in the combustion chamber. It is a phenomenon that causes spontaneous ignition. Knocking causes overheating, melting, etc. of the spark plug electrode and piston, so that knock control is performed to optimize the ignition timing for the air-fuel mixture. As this type of knock control, for example, Patent Document 1 discloses a control that corrects the ignition timing to the retard side when knocking is detected and corrects to the advance side when knocking is not detected. Yes.

  By the way, an EGR (Exaust Gas Recirculation) device that recirculates part of the exhaust discharged from the internal combustion engine to the exhaust passage to the intake passage is known as a technique for improving the fuel efficiency of the internal combustion engine and reducing NOx emission. is there. When the exhaust gas recirculation (hereinafter also referred to as EGR) is performed by the EGR device when the knock control is performed, the combustion temperature in the combustion chamber is lower than that when the EGR is not performed, and the combustion is performed. There is a tendency that the propagation speed of is slow. In relation to this, Patent Document 2 discloses a technique for adjusting an ignition timing related to knock control based on an exhaust gas recirculation amount (hereinafter also referred to as an EGR gas amount). Further, in Patent Document 3, the ignition timing calculated according to the driving state is corrected to the advance side with a required advance value according to the presence or absence of EGR, and the corrected ignition timing is knocked. An ignition timing control device for an internal combustion engine is disclosed that corrects to a retarded angle side with a required retarded angle value until a timing near the limit at which it starts. Further, in this prior art, the retardation value for the knock control is limited within the range of the maximum value calculated according to the driving state, and the retardation value or the maximum value is changed according to the presence or absence of EGR. Yes.

As another related technique, Patent Document 4 discloses a technique for executing a control for retarding the ignition timing to the retard side in accordance with the detection of knocking, and then advancing the ignition timing to the timing before the retard again. ing. In this prior art, an increase amount of the EGR gas amount is calculated so that knocking does not occur when the ignition timing is advanced again, and the EGR gas amount is increased when the ignition timing is advanced. Patent Document 5 discloses a technique for avoiding knocking by controlling a so-called external EGR gas amount and internal EGR gas amount.
JP 2005-127154 A JP 2007-16609 A JP-A-8-151971 JP 2006-291895 A JP 2003-328839 A

  Here, if knocking is detected when a relatively large amount of EGR gas is being introduced into the internal combustion engine by the EGR device, simply retarding the ignition timing will deteriorate the combustion state of the internal combustion engine, The engine may be misfired. The present invention has been made in view of the above circumstances, and an object thereof is to suitably achieve both avoidance of knocking of the internal combustion engine and suppression of misfire in the ignition timing control device of the internal combustion engine provided with the EGR device. Is to provide possible technology.

In order to solve the above problems, the present invention employs the following means.
That is, the ignition timing control device for an internal combustion engine in the present invention is
An ignition device for igniting an air-fuel mixture of an internal combustion engine;
An EGR device for recirculating a part of the exhaust discharged to the exhaust passage of the internal combustion engine to the intake passage;
Compression ratio changing means capable of changing the compression ratio of the internal combustion engine;
Ignition timing control means for controlling the ignition timing of the internal combustion engine to an ignition timing that is advanced with a larger advance correction amount as the EGR rate is higher than the basic ignition timing according to the operating state;
Knock detecting means for detecting knocking of the internal combustion engine;
When knocking is detected by the knock detection means, a predetermined knock that is set as a time when the ignition timing of the internal combustion engine is retarded from the current ignition timing by a retard amount required for avoiding knocking Knock control means for performing knock control to retard the avoidance ignition timing;
When the EGR rate at the time of knocking detection exceeds a predetermined boundary EGR rate, the knock avoidance ignition timing is later than a predetermined misfire limit ignition timing which is a retarded limit ignition timing at which the internal combustion engine does not misfire. Preceding control means for reducing the retardation request amount by determining that the compression ratio is set to the corner side and executing compression ratio reduction control for reducing the compression ratio in the compression ratio changing means prior to the knock control;
When the compression ratio reduction control is executed, setting changing means for changing the knock avoidance ignition timing related to the knock control to the advance side by the amount by which the required retard amount is reduced due to the reduction of the compression ratio;
It is characterized by providing.

  In the present invention, during the control related to the ignition timing for the air-fuel mixture, the basic ignition timing corresponding to the operating state is advanced with the advance correction amount corresponding to the EGR rate. Thereby, even if the combustion temperature of the air-fuel mixture and the propagation speed of combustion change according to the EGR rate, the ignition timing can be made closer to an optimum value (for example, MBT: Minimum spark advance for Best Torque). it can.

  In the internal combustion engine in which the ignition timing is controlled as described above, knocking may occur in the internal combustion engine due to various factors such as a variation in fuel octane number, intake air temperature, and EGR gas amount. In the present invention, when knocking is detected by the knock detection means, the ignition timing of the internal combustion engine is retarded with the required amount of retard required to avoid (suppress) knocking, thereby avoiding knocking. be able to.

  Here, the misfire limit ignition timing is defined as a retarded limit ignition timing at which the internal combustion engine does not misfire, and the misfire limit ignition timing is determined as a value generally correlated with the EGR rate. More specifically, the higher the EGR rate, the greater the proportion of the inert gas component in the air-fuel mixture. Therefore, the higher the EGR rate, the easier the misfire occurs under the same ignition timing conditions. Therefore, the misfire limit ignition timing shifts to the advance side as the EGR rate increases.

  In contrast, the higher the EGR rate, the larger the ignition timing advance correction amount. Therefore, knocking occurs when the internal combustion engine is performing so-called mass EGR, that is, when the EGR rate is maintained relatively high. Then, there is a high possibility that the knock avoidance ignition timing, which is the target value of the ignition timing when performing the knock control, exceeds the misfire limit ignition timing and is set to the retard side.

Therefore, in the above configuration, when the EGR rate at the time of knocking detection (hereinafter referred to as the knock EGR rate) exceeds the boundary EGR rate, the knock avoidance ignition timing is set to be retarded from the misfire limit ignition timing. It was decided to determine. This boundary EGR rate is an EGR rate when the knock avoidance ignition timing is switched from the advance timing to the retard timing as compared to the misfire limit ignition timing as the EGR rate increases. In other words, the boundary EGR rate corresponds to the EGR rate when the set value of the knock avoidance ignition timing coincides with the misfire limit ignition timing. According to this configuration, it is possible to easily determine whether or not the internal combustion engine may misfire if the knock control is executed as it is based on the knock EGR rate.

  If it is determined that the knock avoidance ignition timing is set to be retarded from the misfire limit ignition timing, the compression ratio reduction control is executed prior to the knock control in this configuration, so the combustion in the combustion chamber is slowed down. Can be. As a result, the required amount of retardation can be reduced by reducing the knocking strength.

  Here, the set value of the knock avoidance ignition timing is changed to the advance side by the amount by which the required retard amount is reduced by executing the compression ratio reduction control. For this reason, it is preferable to adjust the reduction amount of the retard required amount so that the knock avoidance ignition timing after the change by the setting changing means is advanced to at least the misfire limit ignition timing. That is, the amount of reduction in the compression ratio related to the compression reduction control is set so that the knock avoidance ignition timing after the change coincides with the misfire limit ignition timing (becomes the same phase) or is advanced relative to the misfire limit ignition timing. Adjust it. Thereby, irrespective of the magnitude of the knock EGR rate, quick avoidance of knocking and suppression of misfire of the internal combustion engine can both be suitably achieved.

An ignition timing control device for an internal combustion engine according to another invention is
An ignition device for igniting an air-fuel mixture of an internal combustion engine;
An EGR device for recirculating a part of the exhaust discharged to the exhaust passage of the internal combustion engine to the intake passage;
Ignition timing control means for controlling the ignition timing of the internal combustion engine to an ignition timing that is advanced with a larger advance correction amount as the EGR rate is higher than the basic ignition timing according to the operating state;
Knock detecting means for detecting knocking of the internal combustion engine;
When knocking is detected by the knock detection means, a predetermined knock that is set as a time when the ignition timing of the internal combustion engine is retarded from the current ignition timing by a retard amount required for avoiding knocking Knock control means for performing knock control to retard the avoidance ignition timing;
When the EGR rate at the time of knocking detection exceeds a predetermined boundary EGR rate, the knock avoidance ignition timing is later than a predetermined misfire limit ignition timing which is a retarded limit ignition timing at which the internal combustion engine does not misfire. Prior control means for determining that the angle is set to the corner side and causing the EGR device to shift the misfire limit ignition timing to the retard side by executing EGR rate reduction control for reducing the EGR rate prior to the knock control. When,
When the EGR rate reduction control is executed, setting change means for changing the set value of the knock avoidance ignition timing related to the knock control to the retard side by the amount by which the advance correction amount is reduced by the reduction of the EGR rate. When,
It is characterized by providing.

  In the present invention, when it is determined that the knock avoidance ignition timing is set to be retarded from the misfire limit ignition timing, the EGR rate reduction control is executed prior to the knock control. Thus, by reducing the EGR rate, the misfire limit ignition timing can be shifted to the retard side according to the amount of reduction in the EGR rate. Further, when the EGR rate is reduced by the EGR rate reduction control, the combustion speed of the air-fuel mixture increases compared to before the EGR rate is reduced. Therefore, the advance correction amount corresponding to the EGR rate after the execution of the EGR rate reduction control Will be less. On the other hand, in this configuration, the set value of the knock avoidance ignition timing is changed to the retard side in accordance with the amount of decrease in the advance correction amount, so that the knock avoidance ignition timing is set to an appropriate value for avoiding knocking. Can be changed.

Here, focusing on the relationship between the amount of decrease in the advance correction amount when the EGR rate reduction control is executed and the amount of shift to the retard side of the misfire limit ignition timing, compared to the amount of decrease in the advance correction amount The shift amount of the misfire limit ignition timing becomes larger. That is, the shift amount of the misfire limit ignition timing is larger than the decrease amount of the advance correction amount per unit reduction amount of the EGR rate.

  Therefore, the relationship between the knock avoidance ignition timing after the change by the setting changing means and the misfire limit ignition timing after the reduction of the EGR rate can be easily adjusted by adjusting the amount of reduction of the EGR rate related to the EGR rate reduction control. Can do. Here, the knock avoidance ignition timing after the change by the setting changing means coincides (becomes the same phase) as the misfire limit ignition timing after the EGR rate is reduced, or the knock avoidance ignition timing after the change is the misfire after the EGR rate is reduced. It is preferable to adjust the amount of EGR rate reduction related to the EGR rate reduction control so that it is on the advance side compared to the limit ignition timing. Thereby, irrespective of the magnitude of the knock EGR rate, quick avoidance of knocking and suppression of misfire of the internal combustion engine can both be suitably achieved.

  In addition, when the advance control means adjusts the amount of reduction in the EGR rate so that the knock avoidance ignition timing after the change by the setting change means matches the misfire limit ignition timing after the EGR rate is reduced (same phase), More preferred. According to this, the EGR is not stopped or the EGR rate is not significantly reduced when the knock control is executed. That is, it is possible to maintain the EGR rate as high as possible while achieving both avoidance of knocking and suppression of misfire. Therefore, the effect relating to the improvement of the fuel consumption of the internal combustion engine by EGR can be enjoyed to the maximum extent.

  Further, the apparatus further comprises compression ratio changing means capable of changing the compression ratio of the internal combustion engine, and the preceding control means executes compression ratio reduction control for reducing the compression ratio by the compression ratio changing means together with the EGR rate reduction control. The setting change means changes the knock avoidance ignition timing to the retard side by the amount by which the advance correction amount is reduced by reducing the EGR rate, and retards by reducing the compression ratio. The advance amount may be changed by an amount corresponding to a reduction in the required amount.

  In such a configuration, when the EGR rate reduction control and the compression ratio reduction control are executed, the preceding control unit matches the knock avoidance ignition timing after the change by the setting change unit with the misfire limit ignition timing after the EGR rate is reduced (same as above). The EGR rate reduction amount and the compression ratio reduction amount are adjusted such that the knock avoidance ignition timing after the change or the changed knock avoidance ignition timing is more advanced than the misfire limit ignition timing after the EGR rate reduction. Thereby, irrespective of the magnitude of the knock EGR rate, quick avoidance of knocking and suppression of misfire of the internal combustion engine can both be suitably achieved. Moreover, according to this structure, the freedom degree at the time of adjusting the reduction amount of an EGR rate and the reduction amount of a compression ratio can be raised.

  Further, the compression ratio changing means has a variable valve operating device capable of changing the closing timing of the intake valve of the internal combustion engine, and the preceding control means is arranged to close the intake valve in the variable valve operating device during the compression ratio reduction control. The effective compression ratio of the internal combustion engine may be reduced by changing the timing. The effective compression ratio is a value obtained by dividing the cylinder volume when the intake valve is closed by the combustion chamber volume (cylinder volume when the piston is at top dead center). In addition, the compression ratio changing means may be a mechanism capable of changing the mechanical compression ratio of the internal combustion engine. The mechanical compression ratio is a value obtained by dividing the cylinder volume when the piston is at the bottom dead center by the combustion chamber volume.

  The means for solving the problems in the present invention can be combined as much as possible.

  According to the present invention, in an ignition timing control device for an internal combustion engine provided with an EGR device, it is possible to suitably achieve both avoidance of knocking of the internal combustion engine and suppression of misfire.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention only to those unless otherwise specified. is not.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a spark ignition internal combustion engine (gasoline engine) for driving a vehicle having four cylinders (cylinders) 2. A piston 3 is slidably provided in the cylinder 2. The piston 3 is connected to a crankshaft 5 via a connecting rod 4, and the crankshaft 5 rotates as the piston 3 reciprocates. An intake port 7 and an exhaust port 8 are connected to the combustion chamber 6 in the upper part of the cylinder 2. The openings of the intake port 7 and the exhaust port 8 to the combustion chamber 6 are opened and closed by an intake valve 9 and an exhaust valve 10, respectively. The opening and closing of the intake valve 9 is controlled by the rotational drive of the intake side cam 11. Opening and closing of the exhaust valve 10 is controlled by rotational driving of the exhaust side cam 12.

  Each cylinder 2 is provided with a spark plug 15 that ignites the air-fuel mixture in the combustion chamber 6. The spark plug 15 has an electrode portion that generates sparks (sparks) facing the combustion chamber 6 and ignites the air-fuel mixture in the combustion chamber 6 by generating sparks. In this embodiment, the spark plug 15 corresponds to the ignition device in the present invention. The voltage applied to the spark plug 15 is supplied by an ignition coil (not shown).

  The intake port 7 is provided with a fuel injection valve 18 that injects fuel into the intake port 7. The intake port 7 is connected to the intake passage 19, and the exhaust port 8 is connected to the exhaust passage 20. The intake passage 19 is provided with an air flow meter 21 that outputs an electric signal corresponding to the mass of fresh air flowing through the intake passage 19. A throttle valve 22 that adjusts the flow rate of fresh air flowing through the intake passage 19 is provided in the intake passage 19 on the downstream side of the air flow meter 21. The exhaust passage 20 is provided with an exhaust purification device (for example, a three-way catalyst) 23.

  In the intake system of the internal combustion engine 1 having the above-described configuration, the flow rate of fresh air flowing through the intake passage 19 is adjusted by the throttle valve 22 and forms an air-fuel mixture together with the fuel injected from the fuel injection valve 18 in the intake port 7. This air-fuel mixture is introduced into each cylinder 2 and combusted by being ignited by the spark plug 16. As a result, when the piston 3 reciprocates, the crankshaft 5 rotates and the driving force of the internal combustion engine 1 is obtained.

  Further, according to the exhaust system of the internal combustion engine 1 having the above configuration, the exhaust valve 10 opens the exhaust port 8 so that the exhaust gas is discharged into the exhaust passage 20. The exhaust gas is discharged into the atmosphere through a muffler (not shown) after the harmful substances contained in the exhaust gas are purified by the exhaust gas purification device 23.

Furthermore, the internal combustion engine 1 includes an exhaust gas recirculation device (EGR device) 25 that recirculates a part of the exhaust gas discharged to the exhaust passage 20 to the intake passage 19. The EGR device 25 includes an EGR passage 26, an EGR valve 27, and an EGR cooler 28. The EGR passage 26 connects the exhaust passage 20 upstream of the exhaust purification device 23 and the intake passage 19 downstream of the throttle valve 22. The EGR valve 27 is provided in the EGR passage 26 and adjusts the flow rate of the recirculation gas (EGR gas) flowing through the EGR passage 26. The EGR cooler 28 is provided in the EGR passage 26 and cools the EGR gas flowing through the EGR passage 26. Here, when the EGR valve 27 is opened, a part of the exhaust gas flowing through the exhaust passage 20 becomes EGR.
The air is recirculated to the intake passage 19 through the passage 26. The EGR gas is introduced into each cylinder 2 while being mixed with fresh air flowing through the intake passage 19. The EGR gas contains an inert gas component that does not burn itself and has a high heat capacity, such as water and carbon dioxide. Therefore, when the EGR gas is contained in the air-fuel mixture, the combustion temperature of the air-fuel mixture is lowered, thereby reducing the amount of nitrogen oxide (NOx) generated. Further, when EGR gas is contained in the air-fuel mixture, an effect of improving the fuel consumption rate can be expected.

  The internal combustion engine 1 is provided with an ECU 30 that is an electronic control unit for controlling the internal combustion engine 1. In addition to the CPU, the ECU 30 includes a ROM, a RAM, and the like that store various programs and maps, and controls the operating condition of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's request. The internal combustion engine 1 is provided with an accelerator opening sensor 32, a crank position sensor 33, and a knock sensor 34. The accelerator opening sensor 32 is a sensor that outputs an electrical signal corresponding to the operation amount (accelerator opening) of the accelerator pedal 31. The crank position sensor 33 is a sensor that detects the rotation angle of the crankshaft 5. The knock sensor 34 is a sensor that detects vibration generated when knocking occurs and outputs a knock signal KCS corresponding to the magnitude of the vibration.

  When knocking occurs in the internal combustion engine 1, high-frequency pressure vibration (for example, 5 to 9 kHz) is generated in the cylinder 2, and this pressure vibration is transmitted to the cylinder block. Knock sensor 34 detects the vibration transmitted to the cylinder block by the piezoelectric element, and converts this vibration into an electric signal. The knocking strength (knocking strength) can be estimated by detecting the amplitude of pressure vibration.

  The air flow meter 21, the accelerator opening sensor 32, the crank position sensor 33, and the knock sensor 34 described above are connected to the ECU 30 via electrical wiring, and output signals from these various sensors are input to the ECU 30. For example, the ECU 30 calculates the engine load LE and the engine speed NE of the internal combustion engine 1 based on the output signals from the accelerator opening sensor 32 and the crank position sensor 33. Further, the spark plug 15, the fuel injection valve 18, the throttle valve 22, and the EGR valve 27 are connected to the ECU 30 through electric wiring, and these various devices are controlled by the ECU 30 according to the operating state of the internal combustion engine 1. .

  In this embodiment, for each operating state of the internal combustion engine 1 (engine load LE and engine speed NE), the EGR gas amount relative to the EGR rate [total intake air amount introduced into the cylinder 2 (new air amount + EGR gas amount)). The target value of [Ratio] is preset. The target value of the EGR rate (hereinafter referred to as the target EGR rate) is obtained in advance through experiments or the like in advance for each operating state of the internal combustion engine 1 from the viewpoint of realizing a reduction in NOx generation and an improvement in the fuel consumption rate. The ECU 30 controls the opening degree of the EGR valve 27 so that the EGR rate matches the target EGR rate.

  The ignition timing (ignition timing for the air-fuel mixture) ST of the internal combustion engine 1 in this embodiment is controlled by the ECU 30. The ignition timing ST is controlled so as to be an MBT (Minimum Advance for Best Torque) that allows the internal combustion engine 1 to obtain a maximum torque in accordance with the operating state of the internal combustion engine 1 and the EGR rate (target EGR rate). Specifically, the ignition timing ST is set such that the basic ignition timing STb, which is set with the operating state of the internal combustion engine 1 (engine load LE, engine speed NE) as a parameter, is set to a larger value as the EGR rate is higher. It is controlled at a time when the advance angle correction amount COad is corrected to the advance angle side. As the basic ignition timing STb, for example, a value of MBT according to the operating state of the internal combustion engine 1 when EGR is not executed can be adopted.

Here, the higher the EGR rate, the lower the combustion temperature of the air-fuel mixture and the lower the combustion speed, so that the air-fuel mixture burns slowly. In the present embodiment, the EGR advance correction amount COad is set to a larger value as the EGR rate is higher. For this reason, even if the combustion propagation of the air-fuel mixture is delayed by introducing a large amount of EGR gas, the ignition timing ST can be suitably brought close to MBT. In this embodiment, the EGR advance angle correction amount COad corresponds to the advance angle correction amount in the present invention. The ECU 30 that controls the ignition timing ST in accordance with the operating state of the internal combustion engine 1 and the EGR rate corresponds to the ignition timing control means in the present invention.

  Here, knocking may occur in the internal combustion engine 1 due to variations in the octane number of fuel (gasoline), intake air temperature, variations in the amount of EGR gas introduced, and the like. This knocking is a phenomenon in which the unburned mixture to which flame propagation does not reach causes spontaneous ignition in the combustion chamber 6 and may cause overheating of the electrode of the spark plug 15 and the piston 3. Therefore, the ECU 30 detects knocking occurring in the internal combustion engine 1 based on the knock signal KCS output from the knock sensor 34. In this embodiment, the knock sensor 34 and the ECU 30 correspond to the knock detection means in the present invention.

  When the ECU 30 detects knocking, knocking control is executed to avoid (suppress) knocking by correcting the ignition timing ST to the retard side. More specifically, the ECU 30 sets the retardation request amount COlag required for avoiding knocking based on the knock signal KCS. Then, the ignition timing ST is retarded to a knock avoidance ignition timing STkcs that is set as a timing that is retarded by the retardation request amount COlag from the current control value. In the present embodiment, the ECU 30 that executes knock control corresponds to the knock control means in the present invention. The set value of the retard required amount COlag can be a constant value, or the retard required amount COlag can be set to a larger value as the knocking strength (degree of knocking strength) is higher.

  FIG. 2 is a map showing the relationship between the EGR rate and each of the ignition timing ST, knock avoidance ignition timing STkcs, and misfire limit ignition timing STmf in the present embodiment. The solid line ST in the figure represents the relationship between the ignition timing ST and the EGR rate. A one-dot chain line STkcs represents the relationship between the knock avoidance ignition timing STkcs and the EGR rate. A two-dot chain line STmf represents the relationship between the misfire limit ignition timing STmf and the EGR rate. The retardation request amount COlag in this figure is substantially constant regardless of the EGR rate. The misfire limit ignition timing STmf is defined as the retarded limit ignition timing at which no misfire occurs in the internal combustion engine 1. Here, knowledge that the relationship between the misfire limit ignition timing STmf and the EGR rate is generally correlated has been obtained by earnest research by the present inventors. The higher the EGR rate, the greater the proportion of the inert gas component in the air-fuel mixture. Therefore, under conditions where the ignition timing ST is equal, the higher the EGR rate, the easier the misfire. That is, as shown in the figure, the misfire limit ignition timing STmf shifts to the advance side as the EGR rate increases.

  Here, focusing on the relationship between the ignition timing ST corresponding to the EGR rate and the misfire limit ignition timing STmf, when the EGR rate is low, the phase difference between the two is relatively large. Then, both phase differences gradually decrease as the EGR rate increases. Therefore, when the knock avoidance ignition timing STkcs obtained by retarding the ignition timing ST with the retardation request amount COlag and the misfire limit ignition timing STmf are compared, the phase relationship between the two is reversed when the EGR rate is low and high. That is, as indicated by the symbol Rbo shown on the horizontal axis in the figure, as the EGR rate increases, the knock avoidance ignition timing STkcs is changed from the advance side timing (region) to the retard side timing (region) with reference to the misfire limit ignition timing STmf ( There is an EGR rate (hereinafter referred to as a boundary EGR rate) when switching to (region). This boundary EGR rate Rbo can be said to be the EGR rate when the knock avoidance ignition timing STkcs and the misfire limit ignition timing STmf coincide.

Focusing on the EGR rate at the time of knock detection (hereinafter referred to as the knock EGR rate Rkcs), when the knock EGR rate Rkcs is equal to or less than the boundary EGR rate Rbo, the knock avoidance ignition timing STkcs advances from the misfire limit ignition timing STmf. It is set as the time on the corner side or the same phase. For example, the symbol R1 shown on the horizontal axis in FIG. 2 is smaller than the boundary EGR rate Rbo. Therefore, when the ignition timing ST, the knock avoidance ignition timing STkcs, and the misfire limit ignition timing STmf corresponding to the knock EGR rate Rkcs being R1 are represented by the symbols ST1, STkcs1, and STmf1, STkcs1 is more advanced than STmf1. Set as time. In this case, there is no possibility that the internal combustion engine 1 will misfire even if the ignition timing ST is retarded from ST1 to STkcs1 when the knock control is executed.

  On the other hand, when knock EGR rate Rkcs is higher than boundary EGR rate Rbo, knock avoidance ignition timing STkcs is set as a timing retarded from misfire limit ignition timing STmf. For example, the symbol R2 shown on the horizontal axis is larger than the boundary EGR rate Rbo. Therefore, when the ignition timing ST, the knock avoidance ignition timing STkcs, and the misfire limit ignition timing STmf corresponding to the knock EGR rate Rkcs being R2 are represented by the symbols ST2, STkcs2, and STmf2, STkcs2 is more retarded than STmf2. Set as time. In this case, if the ignition timing ST is retarded from ST2 to STkcs2 when the knock control is executed, the possibility that the internal combustion engine 1 misfires increases, and it becomes difficult to achieve both avoidance of knocking and suppression of misfire.

  Therefore, in this embodiment, when the knock EGR rate Rkcs exceeds the boundary EGR rate Rbo, it is determined that the knock avoidance ignition timing STkcs is set to be retarded from the misfire limit ignition timing STmf, and the EGR device 25 EGR rate reduction control for reducing the EGR rate is executed prior to knock control. As a result, the misfire limit ignition timing STmf after the reduction of the EGR rate can be shifted to the retard side according to the reduction amount of the EGR rate. That is, the misfire limit ignition timing STmf after the reduction of the EGR rate starts from STmf2 before the reduction of the EGR rate, and shifts on the two-dot chain line STmf to the retard side according to the amount of reduction of the EGR rate.

  When the EGR rate is reduced by the EGR rate reduction control, the combustion speed of the air-fuel mixture increases compared to before the reduction of the EGR rate. Therefore, it is necessary to change the set value of the knock avoidance ignition timing STkcs in consideration of the influence. is there. This is because after the EGR rate is reduced, the EGR advance correction amount COad corresponding to the EGR rate is reduced compared to before the EGR rate is reduced. Therefore, in this embodiment, a process of changing the set value of knock avoidance ignition timing STkcs (hereinafter, this process is referred to as “set value change process”) is performed. In the present embodiment, the setting value changing process is changed to the retard side by the amount that the EGR advance correction amount COad is reduced by the reduction of the EGR rate. Here, the target ignition timing when changing the knock avoidance ignition timing STkcs in the set value changing process is referred to as “target change timing ignition timing STt”. This setting change target ignition timing STt changes from STkcs2 to the retarded side on the one-dot chain line STkcs, and the amount of change is determined according to the reduction amount of the EGR rate.

  In the present embodiment, when executing the EGR rate reduction control, the EGR rate is set so that the target ignition timing STt at the time of setting change matches the misfire limit ignition timing STmf after the EGR rate is reduced (that is, in phase). The amount of reduction ΔRg is adjusted. More specifically, when executing the EGR rate reduction control, the EGR rate reduction amount ΔRg is adjusted so that the EGR rate is reduced from the knock EGR rate Rkcs (R2) to the boundary EGR rate Rbo. This is because the target ignition timing STt at the time of setting change is on the one-dot chain line STkcs, and the misfire limit ignition timing STmf after the reduction of the EGR rate is on the two-dot chain line STmf, and both chain lines intersect at the boundary EGR rate Rbo. Because. That is, when the misfire limit ignition timing STmf when the EGR rate is the boundary EGR rate Rbo is represented by the symbol STbo, if the EGR rate reduction amount ΔRg is determined as described above, the target ignition timing STt at the time of setting change matches STbo. Because it does.

Next, specific processing contents of the control according to the present embodiment will be described with reference to the flowchart of FIG. FIG. 3 is a flowchart showing a control routine in the present embodiment. This control routine is an execution program stored in the ROM of the ECU 30 and is executed by the ECU 30 at regular intervals during the operation of the internal combustion engine 1. When this routine is executed, it is determined in step S101 whether knocking has been detected based on the knock signal KCS. If knocking is detected in this step, the retardation request amount COlag is set based on the knock signal KCS. In this case, the retardation required amount COlag is set to a larger value as the knocking strength of the internal combustion engine 1 is higher. If it is determined that knocking has been detected in this step, the process proceeds to step S102, and if not, this routine is temporarily terminated.

  In step S102, the knock avoidance ignition timing STkcs is set as a timing retarded from the current ignition timing ST by the retard amount COlag. In a succeeding step S103, it is determined whether or not the knock EGR rate Rkcs exceeds the boundary EGR rate Rbo. Here, the knock EGR rate Rkcs can be obtained by reading the set value of the target EGR rate at the time of knock detection. Further, the knock EGR rate Rkcs is calculated from the intake fresh air amount calculated based on the output value of the air flow meter 21, the engine speed NE calculated based on the output value of the crank position sensor 33, the opening degree of the EGR valve 27, and the like. It may be estimated. If a negative determination is made in this step (Rkcs ≦ Rbo) (for example, Rkcs = R1), the process proceeds to step S104. On the other hand, when an affirmative determination is made (Rkcs> Rbo) (for example, Rkcs = R2), it is determined that knock avoidance ignition timing STkcs is set to the retard side with respect to misfire limit ignition timing STmf, and the process proceeds to step S105. .

  In step S104, knock control is executed. That is, the ignition timing ST is changed from the current value (ST1) to the knock avoidance ignition timing STkcs (STkcs1) set in step S102. Thereby, knocking is avoided. Note that STkcs1 is on the more advanced side than STmf1, and the internal combustion engine 1 will not misfire. When the processing of this step is finished, this routine is once finished.

  In step S105, EGR rate reduction control is executed. In this routine, when executing the EGR rate reduction control, the EGR rate reduction amount ΔRg is adjusted so that the target ignition timing STt at the time of setting change matches the misfire limit ignition timing STmf after the EGR rate is reduced. That is, the ECU 30 issues a command signal to the EGR device 25 and decreases the opening degree of the EGR valve 27 so that the EGR rate is reduced from the knock EGR rate Rkcs (R2) to the boundary EGR rate Rbo. As a result, the misfire limit ignition timing STmf after the reduction of the EGR rate shifts to the retard side from STmf2 to STbo. In the present embodiment, the ECU 30 that executes the processing of this step (EGR rate reduction control) corresponds to the preceding control means in the present invention.

  In the subsequent step S106, a set value change process is executed. That is, the target ignition timing STt at the time of setting change is set as a timing delayed from the knock avoidance ignition timing STkcs (STkcs2) set in step S102 by the reduction amount ΔCOad of the EGR advance correction amount. The target ignition timing STt at the time of setting change coincides with STbo. In the present embodiment, the ECU 30 that executes the processing of step S106 (setting value changing processing) corresponds to the setting changing means in the present invention. When the process in this step is completed, the process proceeds to step S107.

  In step S107, knock control is executed. Here, the ignition timing ST is changed from the current value (ST2) to the setting change target ignition timing STt set in step S106. Thereby, knocking is avoided while suppressing misfire of the internal combustion engine 1. When the processing of this step is finished, this routine is once finished.

  As described above, in this embodiment, when the knock EGR rate Rkcs exceeds the boundary EGR rate Rbo, the EGR rate reduction control and the set value change process are executed prior to the knock control, so that the quick knocking is performed. And avoiding misfire can be suitably achieved.

Further, as a modification example related to the EGR rate reduction control, the target ignition timing STt at the time of setting change is EGR.
The reduction amount ΔRg of the EGR rate can be adjusted so as to be set as a timing that is ahead of the misfire limit ignition timing STmf (STbo) after the rate reduction. In this case, the EGR rate is reduced to a value lower than the boundary EGR rate Rbo by the EGR rate reduction control. Thereby, the misfire of the internal combustion engine 1 at the time of knock control execution can be suppressed reliably. However, it is more preferable to improve the fuel efficiency of the internal combustion engine 1 by adjusting the EGR rate reduction amount ΔRg so that the target ignition timing STt at the time of setting change matches the misfire limit ignition timing STmf after the EGR rate is reduced. . This is because the EGR rate can be maintained as high as possible within a range in which knocking can be avoided and misfire can be suppressed. Therefore, according to the control according to the present embodiment, avoidance of knocking and suppression of misfire can be achieved at the same time regardless of the magnitude of the knock EGR rate Rkcs, and the fuel efficiency improvement effect by EGR is maximized. You can enjoy it.

  Next, a second embodiment will be described. FIG. 4 is a diagram showing a schematic configuration of the internal combustion engine and its intake and exhaust system according to the present embodiment. In FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. The internal combustion engine 1 according to the present embodiment includes a variable valve gear (hereinafter referred to as an intake side VVT) 13 that can change the opening / closing timing of the intake valve 9. The intake side VVT 13 is installed on the intake side camshaft to which the intake side cam 11 is attached. Further, the intake side VVT 13 is connected to the ECU 30 via electric wiring and is controlled by the ECU 30. Specifically, the ECU 30 adjusts the opening / closing timing of the intake valve 9 by causing the intake side VVT 13 to change the rotational phase of the intake camshaft with respect to the crankshaft 5 according to the operating state of the internal combustion engine 1.

  FIG. 5 is a map showing the relationship between the EGR rate and each of the ignition timing ST, knock avoidance ignition timing STkcs, and misfire limit ignition timing STmf in the present embodiment. Among the reference numerals in FIG. 5, the same reference numerals as those in FIG. In the present embodiment, when the knock EGR rate Rkcs exceeds the boundary EGR rate Rbo (Rkcs = R2), only the control that is executed prior to the knock control is different from that in the first embodiment. Explained.

  In this embodiment, when the knock EGR rate Rkcs exceeds the boundary EGR rate Rbo (Rkcs = R2), it is determined that the knock avoidance ignition timing STkcs is set to be retarded from the misfire limit ignition timing STmf. Instead of the EGR rate reduction control executed in Example 1, the compression ratio reduction control for reducing the effective compression ratio of the internal combustion engine 1 is executed prior to the knock control. This compression ratio reduction control is also executed by the ECU 30.

  The effective compression ratio is a value obtained by dividing the cylinder volume when the intake valve 9 is closed by the combustion chamber 6 volume (the cylinder volume when the piston 3 is at the top dead center). Therefore, if the effective compression ratio of the internal combustion engine 1 is reduced, the compression end pressure and the compression end temperature of the cylinder 2 are lowered, and knocking is alleviated. Therefore, when the knock EGR rate Rkcs exceeds the boundary EGR rate Rbo, the retardation request amount COlag can be reduced by executing the compression ratio reduction control prior to the knock control.

  Further, in the setting value changing process in the present embodiment, the knock avoidance ignition timing STkcs is changed to the advance side by the amount that the retard required amount COlag is reduced by reducing the effective compression ratio. Here, the amount of reduction in the required retard amount COlag by the compression ratio reduction control is referred to as “retarded angle required reduction amount ΔCOlag”. Then, the target ignition timing STt at the time of setting change in the present embodiment is set as a timing on the advance side by the retard required reduction amount ΔCOlag from the knock avoidance ignition timing STkcs (STkcs2).

In this embodiment, when the compression ratio reduction control is executed, the retardation request reduction amount ΔCOlag is set so that the target ignition timing STt at the time of setting change coincides with the misfire limit ignition timing STmf (STmf2) (so as to be in phase). A target value is set. Then, the effective compression ratio reduction amount Δεe is adjusted so that the retardation required reduction amount ΔCOlag when the compression ratio reduction control is executed becomes the target value.

  Next, a method for reducing the effective compression ratio of the internal combustion engine 1 in the compression ratio reduction control will be described. FIG. 6 is a diagram schematically illustrating a method of reducing the effective compression ratio by operating the intake side VVT 13. The solid line in the figure represents the valve opening period of the intake valve 9 when the compression ratio reduction control is executed, and the alternate long and short dash line represents the valve opening period of the intake valve 9 before execution of the compression ratio reduction control. In addition, the symbols TDC and BDC in the figure represent the piston top dead center (intake top dead center) in the intake stroke and the piston bottom dead center (intake bottom dead center) in the intake stroke. In addition, reference numerals IVO and IVC in the figure represent the opening timing and closing timing of the intake valve 9, respectively.

  Here, the effective compression ratio of the internal combustion engine 1 increases as the IVC approaches the BDC (the smaller the phase difference between both), and the effective compression ratio decreases as the distance from the IVC increases (the larger the phase difference between the two). Therefore, in the compression ratio reduction control in the present embodiment, the IVC is changed to the intake side VVT 13 so that the IVC moves away from the BDC (so that the phase difference between the IVC and the BDC increases) compared to before the execution of the compression ratio reduction control. Thus, the effective compression ratio of the internal combustion engine 1 is reduced. In the example of FIG. 6, IVC (one-dot chain line) before execution of the compression ratio reduction control is set on the retard side with respect to BDC. Therefore, in this case, the effective compression ratio is reduced by further retarding the IVC when the compression ratio reduction control is executed.

  Here, the symbol ΔVTlag is an IVC retardation amount (hereinafter referred to as an IVC retardation amount) at the time of execution of the compression ratio reduction control with reference to before the execution of the compression ratio reduction control. As the IVC retardation amount ΔVTlag is larger, the effective compression ratio reduction amount Δεe for the compression ratio reduction control can be increased. In addition, when IVC (one-dot chain line) before execution of compression ratio reduction control is set to an advance side with respect to BDC, IVC can be advanced in compression ratio reduction control. This is because even if the IVC is changed in this manner, the effective compression ratio of the internal combustion engine 1 is reduced because the phase difference between the IVC and the BDC is increased compared to before the execution of the compression ratio reduction control.

  Next, specific processing contents of the control according to the present embodiment will be described with reference to the flowchart of FIG. FIG. 7 is a flowchart showing a control routine in the present embodiment. This control routine is an execution program stored in the ROM of the ECU 30 and is executed by the ECU 30 at regular intervals during the operation of the internal combustion engine 1. In addition, about the step in which the process similar to the control routine in FIG. 3 is performed, the description is abbreviate | omitted by attaching | subjecting the same step number.

  In this routine, when an affirmative determination is made in step S103 (Rkcs> Rbo) (for example, Rkcs = R2), it is determined that the knock avoidance ignition timing STkcs is set to be retarded from the misfire limit ignition timing STmf. Proceed to step S205. In step S205, compression ratio reduction control is executed. That is, the phase difference between the knock avoidance ignition timing STkcs (STkcs2) and the misfire limit ignition timing STmf (STmf2) is calculated, and this phase difference is set as the target value of the retardation request reduction amount ΔCOlag. Then, the effective compression ratio reduction amount Δεe for the compression ratio reduction control is calculated based on the target value of the retardation request reduction amount ΔCOlag. As the target value of the retardation request reduction amount ΔCOlag is larger, the effective compression ratio reduction amount Δεe is set to a larger value.

Subsequently, the IVC retardation amount ΔVTlag is calculated based on the set value of the effective compression ratio reduction amount Δεe. Then, the ECU 30 causes the intake side VVT 13 to retard the IVC from the current value (phase) by the IVC retardation amount ΔVTlag. As a result, the retardation request amount COlag is decreased by the target value of the retardation request reduction amount ΔCOlag. In this embodiment, the ECU 30 that executes the processing of this step (compression ratio reduction control) corresponds to the preceding control means in the present invention.

  In subsequent step S206, a setting value changing process is executed. That is, the setting change target ignition timing STt is set as a timing advanced from the knock avoidance ignition timing STkcs (STkcs2) by the retard required reduction amount ΔCOlag. That is, the target ignition timing STt at the time of setting change is set to STmf2. In the present embodiment, the ECU 30 that executes the processing of step S206 (setting value changing processing) corresponds to the setting changing means in the present invention. When the process in this step is completed, the process proceeds to step S107.

  As described above, according to the control according to the present embodiment, when the knock EGR rate Rkcs exceeds the boundary EGR rate Rbo, the effective compression ratio of the internal combustion engine 1 is reduced before the knock control. The required corner amount COlag can be reduced. Since the knock control is executed after the set value of the knock avoidance ignition timing STkcs is changed to the advance side by the amount by which the required retard amount COlag is reduced, it is preferable to avoid knocking and suppress misfire of the internal combustion engine 1. Can be compatible.

  As a modified example related to the compression ratio reduction control, the effective compression ratio reduction amount Δεe is set so that the target ignition timing STt at the time of setting change is set as a timing that is ahead of the misfire limit ignition timing STmf (STmf2). Can be adjusted. In this case, the target value of the retard required reduction amount ΔCOlag may be set larger than the phase difference between the knock avoidance ignition timing STkcs (STkcs2) and the misfire limit ignition timing STmf (STmf2).

  In this embodiment, the effective compression ratio of the internal combustion engine 1 is reduced by changing the valve closing timing (IVC) of the intake valve 9 in the intake side VVT 13, but instead, the mechanical compression ratio of the internal combustion engine 1 is increased. Of course, it may be reduced. This mechanical compression ratio is a value obtained by dividing the volume of the cylinder 2 when the piston 3 is at the bottom dead center by the volume of the combustion chamber 6 (the cylinder volume when the piston 3 is at the top dead center). Examples of the mechanism that changes the mechanical compression ratio of the internal combustion engine 1 include a variable compression ratio mechanism that changes the relative position between the crankcase and the cylinder block, and a variable compression ratio mechanism that changes the length of the connecting rod 4. be able to.

  Next, a third embodiment will be described. The schematic configuration of the internal combustion engine 1 according to this embodiment is the same as that shown in FIG. FIG. 8 is a map showing the relationship between the EGR rate and each of the ignition timing ST, knock avoidance ignition timing STkcs, and misfire limit ignition timing STmf in the present embodiment. Of the reference numerals in FIG. 8, the same reference numerals as those in FIGS. 2 and 5 are synonymous and will not be described. In the present embodiment, when the knock EGR rate Rkcs exceeds the boundary EGR rate Rbo (Rkcs = R2), only the control executed prior to the knock control is different from those in the first and second embodiments. The explanation will be focused on.

  Each of STt1 to STt3 in the figure indicates the setting change target ignition timing STt in the first to third embodiments. Here, in the EGR rate reduction control in the first embodiment, the EGR rate is set to the boundary EGR rate in order to make the target ignition timing STt (STt1) at the time of setting change coincide with the misfire limit ignition timing STmf (STbo) after the reduction of the EGR rate. It was necessary to reduce to Rbo. As described above, in order to improve the fuel consumption of the internal combustion engine 1, it is preferable to keep the EGR rate high. Therefore, in this embodiment, as shown in STt3 in the figure, the control is performed so that the target ignition timing STt at the time of setting change matches the misfire limit ignition timing STmf after the EGR rate is reduced without reducing the EGR rate to the boundary EGR rate Rbo. It was decided to do.

FIG. 9 is an explanatory diagram for explaining the control contents according to the present embodiment. Among the reference numerals in FIG. 9, the same reference numerals as those in FIGS. In this embodiment, when the knock EGR rate Rkcs exceeds the boundary EGR rate Rbo, it is determined that the knock avoidance ignition timing STkcs is set to the retard side with respect to the misfire limit ignition timing STmf, and the knock control is preceded. Then, the EGR rate reduction control and the compression ratio reduction control are executed together. “To be executed together” is not limited to executing the EGR rate reduction control and the compression ratio reduction control at the same time. In other words, after performing one of the EGR rate reduction control and the compression ratio reduction control, the other control may be executed.

  Here, the target value when the EGR rate is reduced in the EGR rate reduction control is referred to as a “reduced target EGR rate”. In this figure, the target EGR rate at the time of reduction is R3, and is set as a value higher than the boundary EGR rate Rbo and lower than the knock EGR rate Rkcs (R2). Here, the target EGR rate at the time of reduction is set to a value higher than the boundary EGR rate Rbo. If the target EGR rate at the time of reduction is equal to or less than the boundary EGR rate Rbo, the compression ratio reduction control is not executed and the EGR rate is reduced. This is because only the control needs to be executed (see Example 1). The reduction target EGR rate is set to a value lower than the knock EGR rate Rkcs (R2) because the EGR rate reduction control is not executed when the reduction target EGR rate matches the knock EGR rate Rkcs. This is because only the compression ratio reduction control is executed (see Example 2).

  Here, when the EGR rate is reduced from R2 to R3 by the EGR rate reduction control, the misfire limit ignition timing STmf shifts to the retard side from STmf2 to STmf3. Further, the EGR advance angle correction amount COad decreases by ΔCOlag according to the EGR rate reduction amount ΔRg (R2−R3).

  Further, in the set value changing process in the present embodiment, the set value (STkcs2) of the knock avoidance ignition timing STkcs is changed to the retard side by the amount (ΔCOad) by which the EGR advance correction amount COad is reduced by the reduction of the EGR rate. Further, the target ignition timing STt at the time of setting change is set as a value that is changed to the advance side by the amount (ΔCOlag) by which the retardation required amount COlag is reduced by reducing the effective compression ratio.

  Therefore, in the present embodiment, the target value of the retardation required reduction amount ΔCOlag is set in consideration of the reduction amount ΔCOad of the EGR advance correction amount. Specifically, the EGR advance angle correction amount is reduced to the phase difference (ΔST in FIG. 9) between the set value (STkcs2) of knock avoidance ignition timing STkcs and the misfire limit ignition timing STmf (STmf3) after the EGR rate is reduced. A value obtained by adding the amount ΔCOad is set as a target value of the retardation request reduction amount ΔCOlag. Thereby, the target ignition timing STt (STt3) at the time of setting change can be matched with the misfire limit ignition timing STmf (STmf3) after the EGR rate is reduced.

  FIG. 10 is a flowchart showing a control routine in this embodiment. This control routine is an execution program stored in the ROM of the ECU 30 and is executed by the ECU 30 at regular intervals during the operation of the internal combustion engine 1. In this routine, the same steps as those in FIGS. 3 and 7 are denoted by the same reference numerals, and the description thereof is omitted.

In this routine, if an affirmative determination is made in step S103 (Rkcs> Rbo) (for example, Rkcs = R2), it is determined that the knock avoidance ignition timing STkcs is set to be retarded from the misfire limit ignition timing STmf. Proceed to S301. In step S301, a target EGR rate for reduction (R3) is set. This reduction target EGR rate (R3) can be set according to, for example, the operating state of the internal combustion engine 1 when knocking is detected. In step S302, the map of FIG. 8 is accessed using the knock EGR rate Rkcs (R2) and the target EGR rate during reduction (R3) as parameters, and the misfire limit ignition timing STmf (STmf3) and the EGR advance angle after the reduction of the EGR rate. A correction amount reduction amount ΔCOad is calculated. Further, the reduction target EGR rate (R3) is subtracted from the knock EGR rate Rkcs (R2) to calculate a reduction amount ΔRg of the EGR rate.

  In step S303, the phase difference (ΔST) between the set value (STkcs2) of the knock avoidance ignition timing STkcs and the misfire limit ignition timing STmf (STmf3) after the reduction of the EGR rate is calculated, and the EGR advance angle correction amount is calculated as the phase difference. As a value obtained by adding the reduction amount ΔCOad, the target value of the retardation request reduction amount ΔCOlag is set.

  In step S304, a reduction amount Δεe of the effective compression ratio related to the compression ratio reduction control is calculated based on the target value of the retardation required reduction amount ΔCOlag. Further, the IVC retardation amount ΔVTlag is calculated based on the calculated effective compression ratio reduction amount Δεe.

  In step S305, EGR rate reduction control and compression ratio reduction control are executed. When executing the EGR rate reduction control, the ECU 30 causes the EGR device 25 to reduce the opening of the EGR valve 27 so that the EGR rate is reduced by ΔRg. As a result, the EGR rate decreases from R2 to the target EGR rate during reduction (R3), and the misfire limit ignition timing STmf shifts from STmf2 to STmf3 toward the retard side.

  In executing the compression ratio reduction control, the ECU 30 causes the intake side VVT 13 to retard the IVC by the IVC retardation amount ΔVTlag. As a result, the retardation request amount COlag is reduced by the retardation request reduction amount ΔCOlag. In this embodiment, the ECU 30 that executes the EGR rate reduction control and the compression ratio reduction control in this step corresponds to the preceding control means in the present invention.

  In step S306, a setting value change process is executed. That is, the target ignition timing STt at the time of setting change is set as a value obtained by retarding the set value (STkcs2) of the knock avoidance ignition timing STkcs by the reduction amount ΔCOad of the EGR advance correction amount and by the advance amount by the retardation request reduction amount ΔCOlag. Is set. The target ignition timing STt at the time of setting change at this time coincides with the misfire limit ignition timing STmf (STmf3) after the EGR rate is reduced. In the present embodiment, the ECU 30 that executes the processing of step S306 (setting value changing processing) corresponds to the setting changing means in the present invention. When the process in this step is completed, the process proceeds to step S107.

  As described above, according to the control according to this embodiment, in the EGR rate reduction control, the EGR rate is maintained higher than the boundary EGR rate Rbo, and knocking is avoided and the internal combustion is performed without excessively reducing the effective compression ratio. It is possible to suitably suppress the misfire of the engine 1. Thereby, the fuel consumption and combustion efficiency of the internal combustion engine 1 can be improved.

  Further, in this embodiment, in the adjustment method of the EGR rate reduction amount ΔRg and the effective compression ratio reduction amount Δεe, the EGR rate reduction amount ΔRg is preferentially set, and the target ignition timing STt (STt3) at the time of setting change is set. ) Is set as an amount necessary to match the misfire limit ignition timing STmf (STmf3) after the EGR rate is reduced, but the reduction amount Δεe of the effective compression ratio is set. it can. For example, the effective compression ratio reduction amount Δεe is preferentially set, and the amount necessary for making the setting change target ignition timing STt (STt3) coincide with the misfire limit ignition timing STmf (STmf3) after the EGR rate is reduced. A reduction amount ΔRg of the EGR rate can be set.

Further, according to the control according to the present embodiment, it is possible to reduce the EGR rate reduction amount ΔRg as the effective compression ratio reduction amount Δεe increases, and the EGR rate reduction amount ΔRg as the EGR rate reduction amount ΔRg increases. The amount of reduction Δεe can be reduced. Therefore, the degree of freedom of the combination of the EGR rate reduction amount ΔRg and the effective compression ratio reduction amount Δεe can be suitably increased. For example, the reduction amount of both may be adjusted as appropriate based on the operating state and operating conditions of the internal combustion engine 1 when knocking is detected. Specifically, the EGR rate reduction amount ΔRg is adjusted to be small under the condition where priority is given to the fuel consumption of the internal combustion engine 1, and the effective compression ratio is adjusted under the condition where priority is given to the combustion efficiency of the internal combustion engine 1. The reduction amount Δεe can be adjusted to be small.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an intake / exhaust system thereof according to Embodiment 1. FIG. 3 is a map showing a relationship between an EGR rate and each of an ignition timing ST, a knock avoidance ignition timing STkcs, and a misfire limit ignition timing STmf in the first embodiment. 3 is a flowchart illustrating a control routine in the first embodiment. It is a figure which shows schematic structure of the internal combustion engine which concerns on Example 2, and its intake / exhaust system. 6 is a map showing the relationship between an EGR rate and each of an ignition timing ST, a knock avoidance ignition timing STkcs, and a misfire limit ignition timing STmf in Embodiment 2. It is the figure which modeled the method of operating the intake side VVT and reducing an effective compression ratio. 6 is a flowchart illustrating a control routine in Embodiment 2. 7 is a map showing a relationship between an EGR rate and each of an ignition timing ST, a knock avoidance ignition timing STkcs, and a misfire limit ignition timing STmf in Embodiment 3. FIG. 9 is an explanatory diagram for explaining control contents according to a third embodiment. 10 is a flowchart illustrating a control routine in Embodiment 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Piston 6 ... Combustion chamber 5 ... Intake pipe 9 ... Intake valve 10, ... Exhaust valve 13, ... Variable valve gear (intake side VVT) )
15 .. Spark plug 18 .. Fuel injection valve 19 .. Intake passage 20 .. Exhaust passage 25 .. EGR device 27 .. EGR valve 30 .. ECU
34. ・ Knock sensor

Claims (5)

An ignition device for igniting an air-fuel mixture of an internal combustion engine;
An EGR device for recirculating a part of the exhaust discharged to the exhaust passage of the internal combustion engine to the intake passage;
Compression ratio changing means capable of changing the compression ratio of the internal combustion engine;
Ignition timing control means for controlling the ignition timing of the internal combustion engine to an ignition timing that is advanced with a larger advance correction amount as the EGR rate is higher than the basic ignition timing according to the operating state;
Knock detecting means for detecting knocking of the internal combustion engine;
When knocking is detected by the knock detection means, a predetermined knock that is set as a time when the ignition timing of the internal combustion engine is retarded from the current ignition timing by a retard amount required for avoiding knocking Knock control means for performing knock control to retard the avoidance ignition timing;
When the EGR rate at the time of knocking detection exceeds a predetermined boundary EGR rate, the knock avoidance ignition timing is later than a predetermined misfire limit ignition timing which is a retarded limit ignition timing at which the internal combustion engine does not misfire. Preceding control means for reducing the retardation request amount by determining that the compression ratio is set to the corner side and executing compression ratio reduction control for reducing the compression ratio in the compression ratio changing means prior to the knock control;
When the compression ratio reduction control is executed, setting changing means for changing the knock avoidance ignition timing related to the knock control to the advance side by the amount by which the required retard amount is reduced due to the reduction of the compression ratio;
An ignition timing control device for an internal combustion engine, comprising: An ignition device for igniting an air-fuel mixture of an internal combustion engine;
An EGR device for recirculating a part of the exhaust discharged to the exhaust passage of the internal combustion engine to the intake passage;
Ignition timing control means for controlling the ignition timing of the internal combustion engine to an ignition timing that is advanced with a larger advance correction amount as the EGR rate is higher than the basic ignition timing according to the operating state;
Knock detecting means for detecting knocking of the internal combustion engine;
When knocking is detected by the knock detection means, a predetermined knock that is set as a time when the ignition timing of the internal combustion engine is retarded from the current ignition timing by a retard amount required for avoiding knocking Knock control means for performing knock control to retard the avoidance ignition timing;
When the EGR rate at the time of knocking detection exceeds a predetermined boundary EGR rate, the knock avoidance ignition timing is later than a predetermined misfire limit ignition timing which is a retarded limit ignition timing at which the internal combustion engine does not misfire. Prior control means for determining that the angle is set to the corner side and causing the EGR device to shift the misfire limit ignition timing to the retard side by executing EGR rate reduction control for reducing the EGR rate prior to the knock control. When,
When the EGR rate reduction control is executed, setting change means for changing the set value of the knock avoidance ignition timing related to the knock control to the retard side by the amount by which the advance correction amount is reduced by the reduction of the EGR rate. When,
An ignition timing control device for an internal combustion engine, comprising:   The preceding control means adjusts the amount of reduction in the EGR rate so that the knock avoidance ignition timing after the change by the setting changing means matches the misfire limit ignition timing after the EGR rate is reduced. The ignition timing control device for an internal combustion engine according to claim 2. A compression ratio changing means capable of changing the compression ratio of the internal combustion engine;
In addition to the EGR rate reduction control, the preceding control means reduces the retardation request amount by executing compression ratio reduction control that causes the compression ratio change means to reduce the compression ratio,
The setting changing means changes the knock avoidance ignition timing to the retard side by the amount that the advance correction amount is reduced by reducing the EGR rate, and the retard required amount is reduced by reducing the compression ratio. 3. The ignition timing control apparatus for an internal combustion engine according to claim 2, wherein the ignition timing control apparatus is changed to an advance side by an amount corresponding to the advance angle. The compression ratio changing means has a variable valve gear capable of changing a closing timing of the intake valve of the internal combustion engine,
5. The preceding control means reduces the effective compression ratio of the internal combustion engine by causing the variable valve device to change the closing timing of the intake valve during the compression ratio reduction control. An ignition timing control device for an internal combustion engine according to claim 1.

Images