JP2011099417A - Ignition control system for internal combustion engine - Google Patents

Abstract

An ignition control system for a spark ignition type internal combustion engine having an EGR mechanism suppresses occurrence of knocking and a decrease in combustion stability even when the amount of EGR gas introduced is different for each cylinder. The issue is to provide technology that can be used.
The present invention relates to an ignition control system for a spark ignition type internal combustion engine having an EGR mechanism, and when a retard control of a target ignition timing due to the occurrence of knocking is performed in an operation region of the EGR mechanism. The inter-cylinder variation in the EGR rate is specified according to the retard amount, and the subsequent target ignition timing is determined based on the inter-cylinder variation in the EGR rate.
[Selection] Figure 7

Description

  The present invention relates to an ignition control system for a spark ignition type internal combustion engine, and more particularly to an ignition control system for a spark ignition type internal combustion engine provided with an EGR mechanism.

  As a spark ignition type internal combustion engine, one having an EGR mechanism for introducing exhaust gas taken out from an exhaust passage into an intake port is known. In such an internal combustion engine, when knocking occurs during the introduction of EGR gas, a technique has been proposed in which the opening degree of the EGR valve is gradually increased to learn the opening degree at which knocking does not occur (for example, Patent Documents). 1).

JP 2009-108759 A JP 2004-11619 A JP-A-8-151971

  By the way, in an internal combustion engine equipped with an EGR mechanism, the amount of EGR gas introduced into a cylinder may be different for each cylinder. In particular, when EGR gas is introduced into the intake port of each cylinder, the amount of EGR gas introduced into the cylinder tends to be different for each cylinder.

  When the amount of EGR gas introduced into the cylinder is different for each cylinder, there is a possibility that a cylinder whose ignition timing becomes inappropriate with respect to the amount of EGR gas introduced may occur. For example, there is a possibility that the ignition timing is too early in a cylinder where the introduction amount of EGR gas is too small, or the ignition timing is too late in a cylinder where the introduction amount of EGR gas is excessive.

  The present invention has been made in view of various circumstances as described above, and an object thereof is to provide an EGR gas introduction amount different for each cylinder in an ignition control system of a spark ignition type internal combustion engine equipped with an EGR mechanism. Even if it is a case, it exists in provision of the technique which can suppress generation | occurrence | production of knocking or a fall of combustion stability.

  The present invention employs the following means in order to solve the above-described problems. That is, according to the present invention, in the ignition control system of a spark ignition type internal combustion engine equipped with an EGR mechanism, when the retard control of the target ignition timing with respect to knocking is performed in the operation region of the EGR mechanism, the present invention responds to the retard amount. Thus, the variation in the EGR rate between the cylinders is specified, and the subsequent target ignition timing is determined based on the variation in the EGR rate between the cylinders.

Specifically, the present invention is an ignition control system for a spark ignition internal combustion engine having a plurality of cylinders,
An EGR mechanism comprising an EGR passage for leading a part of the exhaust gas flowing through the exhaust passage to the intake passage as EGR gas, and an EGR valve for changing a passage sectional area of the EGR passage;
Detecting means for detecting knocking of the internal combustion engine;
Retarding means for retarding the target ignition timing until an ignition timing at which knocking does not occur when knocking is detected by the detection means;
Obtaining means for obtaining a retard amount of the target ignition timing when the retard of the target ignition timing is performed by the retard means in the operation region of the EGR mechanism;
Conversion means for converting the retardation amount acquired by the acquisition means into a deficiency of the actual EGR rate with respect to the target EGR rate;
Based on a plurality of EGR rate deficiencies obtained under the same engine operating conditions and different EGR valve opening degrees, the correlation between the target EGR rate, the EGR rate deficiency, and the engine operating status is calculated. Identification means to identify;
Estimating means for estimating an EGR rate deficiency that matches the current engine operating state and the target EGR rate from the correlation specified by the specifying means;
Determining means for determining a target ignition timing using the EGR rate deficiency estimated by the estimating means as a parameter;
I was prepared to.

  When knocking occurs in the operation region of the EGR mechanism, the target ignition timing is delayed to an ignition timing at which knocking does not occur. The retardation amount at that time correlates with an amount in which the actual EGR rate is insufficient with respect to the target EGR rate (an insufficient amount of EGR rate). When the EGR rate is different among the cylinders, the retardation amount correlates with the EGR rate deficiency of the cylinder having the lowest EGR rate (hereinafter referred to as “the lowest cylinder”). Therefore, the retard amount of the target ignition timing can be converted into an EGR rate deficient amount.

  A plurality of such EGR rate deficiency data is obtained in a situation where the engine operating state is equivalent to that at the time of occurrence of knocking and the opening of the EGR valve (hereinafter referred to as “EGR opening”) is different. . Next, the correlation among the target EGR rate, the engine operating state, and the EGR rate deficiency is specified using the plurality of EGR rate deficiencies.

  After the above-described correlation is specified, an EGR rate deficiency (current EGR rate deficiency) that matches the current engine operating state and the target EGR rate is estimated based on the correlation. Then, the target ignition timing is determined using the current EGR rate deficiency as a parameter. That is, the EGR rate used as a parameter when calculating the target ignition timing is corrected by the current EGR rate shortage (for example, the EGR rate shortage is subtracted from the target EGR rate), and the corrected EGR rate (= (target The target ignition timing is determined using EGR rate) − (EGR rate deficiency)) as a parameter.

  When the target ignition timing is determined in this way, even if the EGR rate varies among cylinders, the target ignition timing is determined in accordance with the EGR rate of the lowest cylinder, so that the occurrence of knocking is suppressed in all cylinders. can do. Furthermore, after the above correlation is specified, the occurrence of knocking can be prevented even in the operation region where the retard amount of the target ignition timing due to the occurrence of knocking is not learned.

  The ignition control system for an internal combustion engine of the present invention is in an engine operating state equivalent to the case where a plurality of EGR rate deficiencies described above is required, and when knocking occurs in a situation where the EGR opening becomes zero, You may make it further provide a memory | storage means to memorize | store the retard amount of the target ignition timing by a retard means as a basic retard amount. In that case, the conversion means converts the value obtained by subtracting the basic retardation amount from the retardation amount acquired by the acquisition means into an EGR rate deficiency amount.

  Here, knocking of the internal combustion engine may occur due to a change in environmental conditions in addition to a shortage of EGR rate and variations between cylinders. For example, knocking may occur due to factors such as a change in fuel properties (change in octane number), a change in intake air temperature, a change in humidity, or a change in combustion chamber volume due to deposit accumulation. Knocking due to these factors also occurs when the EGR mechanism is not operating (when the EGR opening is zero).

  Therefore, the ignition control system for an internal combustion engine according to the present invention is in an engine operating state equivalent to that obtained when the plurality of EGR rate deficiencies are obtained, and knocking is performed under a situation where the EGR opening is zero (closed valve). If it occurs, the retard amount obtained by the obtaining means is corrected using the retard amount (basic retard amount) of the target ignition timing with respect to the knocking.

  When the retardation amount acquired by the acquisition means is corrected by the basic retardation amount, the retardation amount corresponding to insufficient EGR rate or variation between cylinders can be obtained. As a result, a more accurate EGR rate deficiency can be obtained.

  Next, the ignition control system for an internal combustion engine according to the present invention calculates the difference between the EGR rate at the target opening and the EGR rate at the actual opening when the actual opening of the EGR valve is smaller than the target opening. You may make it further provide a calculating means. In this case, the specifying unit may specify the correlation based on a value obtained by subtracting the difference calculated by the calculation unit from the EGR rate deficiency calculated by the conversion unit.

  When the actual EGR rate (hereinafter referred to as “actual EGR rate”) is insufficient with respect to the target EGR rate, in addition to the case where the actual EGR rate varies among cylinders, the actual opening of the EGR valve is not performed. The degree (hereinafter referred to as “actual EGR opening”) may differ from the target value (hereinafter referred to as “target EGR opening”).

  On the other hand, the EGR rate deficiency corresponding to the variation between the cylinders can be obtained by subtracting the deficiency in the EGR rate due to the deviation of the EGR opening from the EGR rate deficiency calculated by the conversion means. As a result, the accuracy of the correlation between the engine operating state, the target EGR rate, and the EGR rate deficiency can be improved.

  By the way, when the EGR rate deficiency is calculated (in other words, when the acquisition unit acquires the retard amount of the target ignition timing), if the EGR opening is not linearly related to the EGR rate, the actual EGR opening and the target An insufficient amount of the EGR rate due to the deviation from the EGR opening cannot be obtained accurately.

  On the other hand, when the EGR rate deficiency amount (retard amount of the target ignition timing) is acquired when the relationship between the EGR opening amount and the EGR rate has linearity, the actual EGR opening amount and the target EGR opening amount An insufficient amount of EGR rate due to the deviation can be accurately obtained.

  The ignition control system for an internal combustion engine of the present invention keeps the engine operating state of the internal combustion engine constant when obtaining a plurality of EGR rate deficiencies (in other words, when the acquisition means acquires the retard amount of the target ignition timing). You may make it further provide the mechanism to keep. In that case, it becomes possible to quickly acquire a plurality of EGR rate deficiencies, in other words, a plurality of ignition timing retardation amounts.

  Examples of the mechanism for keeping the engine operating state constant include a hybrid system including a prime mover (for example, an electric motor) in addition to the internal combustion engine, and a continuously variable transmission (CVT) capable of continuously changing a gear ratio. can do.

Next, according to the present invention, when the EGR rate deficiency of the lowest cylinder exceeds a predetermined threshold value, processing for reducing the variation in the EGR rate between the cylinders may be performed. Specifically, the ignition control system for an internal combustion engine of the present invention is:
An EGR mechanism comprising an EGR passage for leading a part of the exhaust gas flowing through the exhaust passage to the intake passage as EGR gas, and an EGR valve for changing a passage sectional area of the EGR passage;
A variable mechanism for changing the closing timing of the intake valve;
Detecting means for detecting knocking of the internal combustion engine;
Retarding means for retarding the target ignition timing until an ignition timing at which knocking does not occur when knocking is detected by the detection means;
Acquisition means for acquiring a retard amount of the ignition timing when the ignition timing is retarded by the retard means in the operation region of the EGR mechanism;
Conversion means for converting the retardation amount acquired by the acquisition means into a deficiency of the actual EGR rate with respect to the target EGR rate;
Based on a plurality of EGR rate deficiencies obtained under the same engine operating conditions and different EGR valve opening degrees, the correlation between the target EGR rate, the EGR rate deficiency, and the engine operating status is calculated. Identification means to identify;
Estimating means for estimating an EGR rate deficiency that matches the current engine operating state and the target EGR rate from the correlation specified by the specifying means;
Determining means for determining a target ignition timing using the EGR rate deficiency estimated by the estimating means as a parameter;
Control means for controlling the variable mechanism to retard the closing timing of the intake valve when the EGR rate deficiency estimated by the estimation means exceeds a predetermined threshold;
You may make it provide.

  If the ignition timing of all cylinders is determined in accordance with the EGR rate of the lowest cylinder, the ignition timing may be inappropriate in cylinders other than the lowest cylinder. For example, when the EGR rate deficiency of the lowest cylinder increases, the retard amount of the target ignition timing also increases. Therefore, in a cylinder having a relatively high EGR rate, the ignition timing is excessively retarded with respect to the EGR rate, and combustion stability may be reduced.

  According to the knowledge of the present inventor, the variation in the EGR rate between cylinders becomes more prominent as the pressure difference between the upstream end (exhaust passage) and the downstream end (intake passage) of the EGR passage increases. Therefore, when the EGR rate shortage amount of the lowest cylinder exceeds the threshold value, the pressure in the intake passage increases when the intake valve closing timing is retarded. When the pressure in the intake passage (intake pressure) increases, the EGR rate variation between the cylinders can be reduced while maintaining the EGR rate of the entire internal combustion engine substantially equal.

  Therefore, according to the above-described invention, when the EGR rate deficiency exceeds the threshold value, it is possible to suppress a decrease in combustion stability in the other cylinders while suppressing the occurrence of knocking in the lowest cylinder.

  Note that when the intake valve closing timing is retarded, the effective compression ratio decreases, and the torque fluctuation may exceed the allowable range. On the other hand, a method for reducing the EGR opening when the valve closing timing of the intake valve is retarded is conceivable. When the EGR opening degree is decreased, the EGR rate is reduced, so that the torque fluctuation is reduced. Therefore, the EGR opening degree may be decreased to an opening degree where the torque fluctuation falls within the allowable range.

  According to the present invention, in a spark ignition internal combustion engine equipped with an EGR mechanism, it is possible to suppress the occurrence of knocking and the deterioration of combustion stability even when the amount of EGR gas introduced is different for each cylinder.

It is a figure which shows schematic structure of the ignition control system of the internal combustion engine in a 1st Example. It is a figure which shows typically the generation | occurrence | production mechanism of knocking resulting from the variation between cylinders of an EGR rate. It is a figure which shows the map which prescribed | regulated the relationship between knock retardation amount (DELTA) It and EGR rate deficiency amount. It is a figure which shows typically the procedure which specifies the relationship between an EGR rate deficiency amount, an average EGR rate, and an engine operating state. It is a figure which shows typically the procedure which specifies the EGR rate insufficient quantity resulting from the error of an EGR opening degree. It is a figure which shows the relationship between a target EGR opening degree and an average EGR rate. It is a flowchart which shows the control routine for calculating | requiring the correlation with an EGR rate deficiency amount, an average EGR rate, and an engine operating state. It is a flowchart which shows the control routine for determining the target ignition timing in an EGR operation area | region. It is a figure which shows schematic structure of the ignition control system of the internal combustion engine in a 2nd Example. It is a figure which shows typically the execution procedure of the variation variation process between cylinders of an EGR rate.

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

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine ignition control system according to the present invention.

  An internal combustion engine 1 shown in FIG. 1 is a spark ignition type internal combustion engine (gasoline engine) having four cylinders 2. Each cylinder 2 of the internal combustion engine 1 is provided with a spark plug 3. Each cylinder 2 communicates with each branch pipe 40 of the intake manifold 4 via an intake port.

  The collecting portion 41 of the intake manifold 4 is connected to an intake pipe (intake pipe) 5. Air sucked from the open end of the intake pipe 5 is guided to the collecting portion 41 of the intake manifold 4 by the intake pipe 5 and then distributed from the collecting portion 41 to each cylinder 2 through the branch pipes 40.

  An air cleaner 6 for collecting dust and dirt in the air is disposed in the middle of the intake pipe 5. A throttle valve 8 that adjusts the amount of air flowing in the intake pipe 5 is disposed in the intake pipe 5 downstream of the air cleaner 6.

  Each cylinder 2 of the internal combustion engine 1 communicates with the exhaust manifold 9 through an exhaust port. Connected to the exhaust manifold 9 is an EGR passage 10 for taking out part of the exhaust gas flowing through the exhaust manifold 9.

  The EGR passage 10 is branched into four from the middle thereof and connected to the four branch pipes 40 of the intake manifold 4. In the EGR passage 10, an EGR valve 11 that changes the passage cross-sectional area of the EGR passage 10 is disposed upstream of the branch portion (exhaust manifold 9 side). The EGR passage 10 and the EGR valve 11 correspond to the EGR mechanism according to the present invention.

The internal combustion engine 1 configured as described above is provided with an ECU 12. The ECU 12 is an electronic control unit that includes a CPU, ROM, RAM, backup RAM, and the like. Various sensors such as an air flow meter 7, a crank position sensor 13, an accelerator position sensor 14, a knock sensor 15, and an intake pressure sensor 16 are electrically connected to the ECU 12.

  The air flow meter 7 is a sensor that is disposed in the intake pipe 5 between the air cleaner 6 and the throttle valve 8 and outputs an electrical signal corresponding to the amount of intake air flowing through the intake pipe 5. The crank position sensor 13 is a sensor that outputs an electrical signal corresponding to the rotational speed (rotational speed) of the output shaft (crankshaft) of the internal combustion engine 1. The accelerator position sensor 14 is a sensor that outputs an electrical signal corresponding to the operation amount (accelerator opening) of the accelerator pedal. Knock sensor 15 is an acceleration sensor for detecting the occurrence of knocking. The intake pressure sensor 16 is a pressure sensor that is attached to the intake manifold 4 and detects the intake pressure downstream of the throttle valve 8.

  In addition, the ECU 12 is electrically connected to devices such as the spark plug 3, the throttle valve 8, and the EGR valve 11. The ECU 12 controls the various devices according to signals input from the various sensors.

  For example, the ECU 12 determines an EGR operating region (an operating region where the EGR valve 11 is opened) in which an engine operating state specified by an engine speed, an engine load, an intake air amount, an engine temperature (cooling water temperature), and the like is predetermined. ) Or not.

  When the engine operating state belongs to the EGR operating region, the ECU 12 opens the EGR valve 11. The target opening degree of the EGR valve 11 at that time is determined according to the engine operating state. Note that the relationship between the target opening degree of the EGR valve 11 and the engine operating state may be mapped in advance by an adaptation process using an experiment or the like.

  When the engine operating state belongs to the EGR operating region, the ECU 12 is in addition to the above-described control, the actual EGR rate (= (EGR gas amount) / (intake air amount + EGR gas amount)) is suitable for the engine operating state. The feedback control is also performed to adjust the opening degree of the EGR valve 11 so as to converge to the target EGR rate. For example, the ECU 12 feedback-controls the opening degree of the EGR valve 11 so that the output signal (intake air amount) of the air flow meter 7 converges within the range of the target intake air amount.

  Thus, when the opening degree of the EGR valve 11 is controlled, the temperature at which the fuel burns in each cylinder 2 can be lowered. As a result, nitrogen oxides (NOx) discharged from the internal combustion engine 1 are reduced.

  The ECU 12 controls the operation timing (ignition timing) of the spark plug 3 according to the engine operating state. For example, the ECU 12 determines the target ignition timing by correcting the ignition timing (basic ignition timing) determined according to the engine speed and the engine load according to the coolant temperature and the like. Further, when knocking is detected by the knock sensor 15, the ECU 12 also performs knock control for correcting the basic ignition timing by retarding.

  When the spark plug 3 is controlled in this way, the maximum torque can be generated in the internal combustion engine 1 within a range in which knocking can be avoided.

  By the way, even when the amount of EGR gas introduced into the internal combustion engine 1 (total amount of EGR gas introduced into all cylinders 2) converges within the target range, the amount of EGR gas introduced into each cylinder 2 May not be even. That is, as shown in FIG. 2, the amount of EGR gas introduced into each cylinder 2 (circle mark in FIG. 2) may differ for each cylinder 2.

In particular, as illustrated in the present embodiment, in the configuration in which the EGR gas is distributed to each branch pipe 40 of the intake manifold 4, the EGR gas amount varies depending on the shape and installation angle of the EGR passage 10 or deposit accumulation. There may be a difference between the two. At that time, in the cylinder 2 in which the amount of EGR gas is insufficient, the ignition timing becomes too early with respect to the actual amount of EGR gas introduced, and knocking may occur.

  On the other hand, in this embodiment, the ignition timing is determined according to the variation in the EGR gas amount between the cylinders.

  First, a retard amount of ignition timing (hereinafter referred to as “knock retard amount”) ΔIt by knock control is converted into an EGR rate deficiency amount. Here, when knocking occurs due to variation in the EGR gas rate between cylinders, the target ignition timing is retarded until knocking does not occur in the cylinder (lowest cylinder) having the lowest EGR gas rate. Therefore, the knock retard amount ΔIt correlates with the EGR rate deficiency amount of the lowest cylinder.

  The EGR rate deficiency mentioned here corresponds to a value obtained by subtracting the EGR rate of the lowest cylinder from the average EGR rate of the four cylinders 2. Note that when the actual EGR rate has converged to the target EGR rate (specifically, when the difference between the actual EGR rate and the target EGR rate is within an allowable range), the EGR rate deficiency is determined by the target EGR rate. This is equal to the value obtained by subtracting the EGR rate of the lowest cylinder from the value divided by the number of cylinders.

  The relationship between the knock retardation amount ΔIt and the EGR rate deficiency amount may be obtained experimentally in advance, and the relationship may be stored in the ROM of the ECU 12 as a map as shown in FIG. However, the relationship between the knock retardation amount ΔIt and the EGR rate deficiency varies depending on the engine speed NE and the engine load KL. This is because the flow rate of EGR gas and the pulsation level of intake and exhaust gas change according to the engine speed NE and the engine load KL.

  Therefore, the line L in FIG. 3 is preferably defined by a function (f (NE, KL, ΔIt)) having the engine speed NE, the engine load KL, and the knock retardation amount ΔIt as parameters. It is assumed that the function f is obtained in advance by an adaptation process using an experiment or the like.

  Incidentally, knocking of the internal combustion engine 1 may occur due to changes in environmental conditions in addition to the variation between cylinders. For example, knocking may occur due to factors such as a change in fuel properties (change in octane number), a change in intake air temperature, a change in humidity, or a change in combustion chamber volume due to deposit accumulation.

  For this reason, the knock retardation amount ΔIt described above may include a part caused by an insufficient EGR rate and a part caused by environmental conditions. Therefore, in order to obtain an accurate EGR rate deficiency, it is necessary to specify a knock retardation amount (basic retardation amount) ΔItbase caused by environmental conditions.

  Knocking due to environmental conditions also occurs when the EGR mechanism is not operating. Therefore, when knocking occurs in the EGR operation region, the ECU 12 closes the EGR valve 11 under the same operating conditions, and stores the knock retardation amount at that time in the RAM or the backup RAM as the basic retardation amount ΔItbase. .

  When the basic retardation amount ΔItbase is acquired as described above, the ECU 12 subtracts the basic retardation amount ΔItbase from the knock retardation amount ΔIt acquired in the EGR operation region, and the calculation result (hereinafter, “net knock delay amount”). (Referred to as “angle amount ΔIts”) is converted into an insufficient amount of EGR rate. As a result, a more accurate EGR rate deficiency can be obtained.

The EGR rate deficiency obtained in accordance with the above procedure is obtained under a plurality of situations in which the engine speed NE and the engine load KL are equal and the opening degree (average EGR rate) of the EGR valve 11 is different. . That is, the ECU 12 obtains a plurality of coordinates determined from the average EGR rate and the EGR rate deficiency in a situation where the engine speed NE and the engine load KL are equal.

  The ECU 12 specifies the correlation between the EGR rate deficiency, the average EGR rate (or target EGR rate), and the engine operating state based on the plurality of coordinates described above. The EGR rate deficiency tends to increase as the average EGR rate decreases, and tends to approach zero as the average EGR rate increases.

  Therefore, the ECU 12 obtains an asymptotic line M as indicated by a broken line in FIG. 4 by linearly interpolating the plurality of coordinates. Subsequently, the ECU 12 calculates an approximate function (solid line in FIG. 4) of the above asymptotic line M. The approximate function is a function (g (average EGR rate, NE, KL)) having the average EGR rate, the engine speed NE, and the engine load KL as parameters.

  The function g obtained in this way is stored in the RAM or backup RAM of the ECU 12. Then, the ECU 12 determines the target ignition timing using the function g when determining the subsequent target ignition timing.

  When the actual opening degree (actual EGR opening degree) of the EGR valve 11 is different from the target EGR opening degree, particularly when the actual EGR opening degree is smaller than the target EGR opening degree, the average EGR rate becomes large. However, the EGR rate deficiency does not gradually approach zero.

  For this reason, as shown by the solid line in FIG. 5, the asymptotic line M is offset toward the increase side of the EGR rate deficiency when the actual EGR opening is equal to the target EGR opening (broken line in FIG. 5). It becomes the shape made.

  The above-described offset amount Δd corresponds to an insufficient amount of EGR due to a deviation of the actual EGR opening (= (target EGR opening) − (actual EGR opening)). Therefore, the EGR rate deficiency due to the variation between the cylinders can be obtained by subtracting the offset amount Δd from the plurality of EGR rate deficiencies obtained based on the map of FIG.

  As a method for obtaining the above-described offset amount Δd, a method of acquiring the EGR rate deficiency when the change in the asymptote M converges (when the EGR rate deficiency becomes substantially constant with respect to the increase in the average EGR rate). Can be illustrated.

  However, the above-described offset amount Δd needs to be obtained under conditions that are constant regardless of the average EGR rate. That is, the offset amount Δd needs to be obtained under the condition that the relationship between the target EGR opening degree and the EGR rate is linear.

  FIG. 6 is a diagram illustrating a relationship between the target EGR opening degree and the EGR rate (average EGR rate). The solid line in FIG. 6 shows the relationship when the actual EGR opening is smaller than the target EGR opening, and the broken line shows the relationship when the actual EGR opening is equal to the target EGR opening.

  In FIG. 6, in the region where the target EGR opening is equal to or smaller than the predetermined opening θ1, the EGR rate when the actual EGR opening is equal to the target EGR opening and the EGR rate when the actual EGR opening is smaller than the target EGR opening. Is constant regardless of the target EGR opening. Therefore, a plurality of EGR rate deficiencies (knock retardation amounts ΔIt) may be acquired within a range where the target EGR opening is equal to or less than the predetermined opening θ1.

Since the relationship between the target EGR opening and the actual EGR opening varies depending on the engine speed NE and the engine load KL, the predetermined opening θ1 is a map using the engine speed NE and the engine load KL as parameters. Alternatively, it may be obtained by a function. The map and function at that time are obtained in advance by an adaptation process using experiments or the like.

  Next, a method for determining the target ignition timing using the function g will be described. This method is performed when the engine operating state is in the EGR operating region, and is not performed when the engine operating state is not in the EGR operating region.

  The ECU 12 acquires the current engine speed NE, the engine load KL, and the average EGR rate, and substitutes these values into the function g to obtain the current EGR rate deficiency (the current EGR rate deficiency of the lowest cylinder). calculate.

  Subsequently, the ECU 12 obtains the EGR rate of the lowest cylinder by subtracting the EGR rate deficiency from the current average EGR rate. Then, the ECU 12 determines the target ignition timing according to the EGR rate of the lowest cylinder.

  In this case, the target ignition timing for all cylinders is determined according to the EGR rate of the lowest cylinder. As a result, it is possible to avoid the occurrence of knocking due to the variation in the EGR rate between the cylinders. Furthermore, after the above function g is obtained, it is possible to prevent the occurrence of knocking even in an operation region where the knock retardation amount is not learned.

  Hereinafter, a method for determining the ignition timing in the EGR operating region will be described with reference to FIGS. FIG. 7 is a flowchart showing a control routine for obtaining a correlation (function g) among the EGR rate deficiency, the average EGR rate, and the engine operating state. FIG. 8 is a flowchart showing a control routine for determining the target ignition timing in the EGR operation region.

  In the control routine of FIG. 7, the ECU 12 first determines in S101 whether or not a learning condition for variation between cylinders in the EGR rate is satisfied. This condition is satisfied when conditions such as the engine operating state is in the EGR operating region, knocking has occurred, or the function g has not yet been obtained.

  When a negative determination is made in S101, the ECU 12 once ends the execution of this routine. On the other hand, if an affirmative determination is made in S101, the ECU 12 proceeds to S102, and acquires the retard amount of the ignition timing (knock retard amount ΔIt) with respect to the occurrence of knocking.

  Specifically, the ECU 12 first calculates the predetermined opening θ1 using the engine speed NE, the engine load KL, and the target EGR opening when knocking occurs as parameters. Subsequently, the ECU 12 changes the target EGR opening within a range in which the engine speed NE and the engine load KL are equal to those at the time of occurrence of knocking and the target EGR opening is equal to or less than the predetermined opening θ1, and each target EGR Knock control is executed at the opening. The ECU 12 includes a plurality of knock retardation amounts (including a plurality of knock retardation amounts ΔIt and basic retardation amounts ΔItbase) calculated by knock control with respect to each target EGR opening, and an average EGR corresponding to each target EGR opening. Get rates and,

  In S103, the ECU 12 calculates a plurality of net knock retardation amounts ΔIts by subtracting the basic knock retardation amount ΔIt from each knock retardation amount ΔIt.

  In S104, based on the engine speed NE and the engine load KL when the knock retardation amount ΔIt is acquired, the net knock retardation amount ΔIts obtained in S103, and the map of FIG. 3 described above. , EGR rate deficiency is calculated.

  In S105, the ECU 12 is based on the engine speed NE and engine load KL at the time of occurrence of knocking, the plurality of EGR rate deficiencies calculated in S104, and the average EGR rate corresponding to each EGR rate deficiency. The function g as described in the description of FIG. 5 is specified.

  Specifically, the ECU 12 first displays an asymptote M as shown in FIG. 4 based on the plurality of EGR rate deficiencies calculated in S104 and the average EGR rate corresponding to each EGR rate deficiency. get. Subsequently, the ECU 12 acquires the offset amount Δd of the asymptotic line M, and corrects the coordinates of the asymptotic line M based on the offset amount Δd. The ECU 12 specifies the approximate function g based on the corrected asymptote M. The offset amount Δd and the function g obtained in S105 are stored in the RAM or backup RAM of the ECU 12.

  In S106, the ECU 12 rewrites the value of the inter-cylinder variation learning flag to “1”. The inter-cylinder variation learning flag stores “0” as an initial value, and “1” is stored when the function g is specified in S105.

  As described above, the ECU 12 executes the control routine of FIG. 7 to realize the detecting means, the retarding means, the acquiring means, the converting means, the storing means, the calculating means, and the specifying means according to the present invention.

  Next, in the control routine of FIG. 8, the ECU 12 determines whether or not the engine operating state of the internal combustion engine 1 is in the EGR operating region in S201. If a negative determination is made in S201, the ECU 12 once ends the execution of this routine. On the other hand, if an affirmative determination is made in S201, the ECU 12 proceeds to S202.

  In S202, the ECU 12 determines whether or not the value of the inter-cylinder variation learning flag is “1”. If a negative determination is made in S202 (inter-cylinder variation learning flag = 0), the ECU 12 proceeds to S206 and determines the target ignition timing as usual. That is, the ECU 12 calculates the target ignition timing using the average EGR rate of the four cylinders as a parameter.

  If an affirmative determination is made in S202 (inter-cylinder variation learning flag = 1), the ECU 12 proceeds to S203. In S203, the ECU 12 calculates the EGR rate deficiency of the lowest cylinder by substituting the current engine speed NE, engine load KL, and average EGR rate into the function g.

  In S204, the ECU 12 determines the current EGR rate of the lowest cylinder based on the offset amount Δd obtained in the control routine of FIG. 7, the EGR rate deficiency calculated in S203, and the current average EGR rate. (Hereinafter referred to as “minimum EGR rate”) is calculated (estimated). That is, the ECU 12 calculates the minimum EGR rate by subtracting the EGR rate shortage amount and the offset amount Δd from the average EGR rate.

  In S205, the ECU 12 calculates the target ignition timing. More specifically, the ECU 12 first calculates the target ignition timing by replacing the value of the average EGR rate used as a parameter when calculating the target ignition timing with the minimum EGR rate. Further, the ECU 12 calculates the final target ignition timing by adding the basic retardation amount ΔItbase obtained in the control routine of FIG. 7 to the target ignition timing.

  Thus, when the ECU 12 executes the control routine of FIG. 8, the estimation means and the determination means according to the present invention are realized.

  According to the embodiment described above, when the EGR rate varies between cylinders, the target ignition timing is determined in accordance with the EGR rate (minimum EGR rate) of the lowest cylinder, so that the occurrence of knocking is avoided. It becomes possible to do. Furthermore, after the above-described function g is specified, the occurrence of knocking can be prevented even in the operation region where the retard amount of the target ignition timing due to the occurrence of knocking is not learned.

  In addition, when a prime mover (for example, an electric motor) other than the internal combustion engine 1 is mounted on a vehicle to which the present invention is applied, a continuously variable transmission (CVT) capable of continuously changing a gear ratio is mounted as a transmission. In this case, the electric motor or the continuously variable transmission may be controlled so that the operating point (the engine speed NE and the engine load KL) of the internal combustion engine 1 does not change when acquiring a plurality of knock retardation amounts ΔIt. In this case, a plurality of knock retardation amounts ΔIt can be acquired quickly.

  In the present embodiment, an example in which a plurality of knock retardation amounts ΔIt are acquired under the condition where the engine speed NE and the engine load KL are equal is described. However, the engine speed NE and the engine load KL are different. A plurality of knock retardation amounts ΔIt may be acquired. In such a case, the engine load KL and the change amount of the knock retardation amount due to the change of the engine load KL are obtained in advance by an adaptation process using experiments or the like, and the function g is obtained by subtracting the change amount. Good.

<Example 2>
Next, a second embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  The difference between the first embodiment described above and the present embodiment is that a process for reducing the EGR rate variation between cylinders when the EGR rate deficiency of the lowest cylinder is excessive (hereinafter referred to as “inter-cylinder variation relaxation process”). ”) Is executed.

  If the EGR rate deficiency of the lowest cylinder is excessively large, EGR gas corresponding to the EGR rate deficiency may be introduced into the other cylinders 2. In such a case, if the target ignition timing is determined in accordance with the EGR rate (minimum EGR rate) of the lowest cylinder, the combustion stability of the other cylinders 2 described above is impaired, the fuel consumption deteriorates, and the torque fluctuations May cause problems such as an increase in

  In contrast, in this embodiment, when the EGR rate deficiency of the lowest cylinder exceeds a predetermined threshold value, the knocking suppression and the combustion stability are maintained by executing the inter-cylinder variation mitigation process. I tried to figure it out.

  As a method of reducing the variation in the EGR rate between the cylinders, a method of reducing the pressure difference between the upstream end (exhaust manifold 9) and the downstream end (intake pipe 5) of the EGR passage 10 is effective. This is based on the knowledge of the present inventor that the variation in the EGR rate between the cylinders increases as the flow rate of the EGR gas flowing in the EGR passage 10 increases.

  Therefore, in this embodiment, when the EGR rate deficiency of the lowest cylinder exceeds the threshold value, the pressure difference is reduced by increasing the pressure (intake pipe pressure) at the downstream end of the EGR passage 10. Examples of the method for increasing the intake pipe pressure include a method for increasing the opening of the throttle valve 8 and a method for retarding the closing timing of the intake valve.

  Hereinafter, an example in which the inter-cylinder variation mitigation process is executed by a method of delaying the closing timing of the intake valve will be described.

  FIG. 9 is a diagram showing a schematic configuration of an ignition control system for an internal combustion engine in the present embodiment. In FIG. 9, the same components as those in the first embodiment are denoted by the same reference numerals. The internal combustion engine 1 shown in FIG. 9 includes a phase variable mechanism 17 that changes the phase of an intake camshaft (not shown) (the phase of the intake camshaft with respect to the crankshaft). The phase variable mechanism 17 is electrically controlled by the ECU 12. Other configurations are the same as those of the first embodiment described above.

  In the ignition control system for the internal combustion engine configured as described above, the ECU 12 performs the closing timing of the intake valve when the EGR rate deficiency of the lowest cylinder obtained by the control routine of FIG. The phase variable mechanism 17 is controlled so that is delayed. The retardation amount at that time is determined so that the fuel consumption is minimized within a range where the torque fluctuation of the internal combustion engine 1 falls within the allowable range.

  Here, FIG. 10 shows changes in fuel consumption, torque fluctuation, knock retardation amount ΔIt, EGR rate deficiency, and EGR opening according to changes in the intake valve closing timing IVC. The solid line in FIG. 10 shows changes in the respective data when there is no variation in the EGR rate between the cylinders, and the broken line indicates when the variation in the EGR rate between the cylinders exceeds the allowable range (the EGR rate deficiency is below the threshold). It shows the change of each data.

  In FIG. 10, when the closing timing of the intake valve is retarded from IVC0 to IVC1, the intake pipe pressure increases. When the intake pipe pressure increases, the amount of EGR gas decreases, so the EGR opening is increased by feedback control of the EGR valve 11. When the intake pipe pressure increases and the EGR opening increases, the flow rate of the EGR gas decreases due to their synergistic effect. When the flow rate of EGR gas decreases, the EGR rate deficiency decreases (the variation in the EGR rate between cylinders is reduced).

  As described above, when the EGR rate deficiency decreases, the knock retardation amount decreases accordingly. As a result, the torque fluctuation is reduced and the fuel efficiency is improved due to the synergistic effect of the decrease in the EGR rate deficiency and the knock retardation amount.

  The above IVC1 is the valve closing timing at which the fuel consumption becomes the best within the range where the torque fluctuation falls within the allowable range (range α in FIG. 10), and the engine speed NE, the engine load KL, the EGR opening, and the EGR rate are insufficient. You may make it calculate from the map which uses quantity etc. as an argument. The map at that time is obtained in advance by an adaptation process using an experiment or the like.

  Note that if the intake valve closing timing IVC is retarded, the effective compression ratio of the internal combustion engine 1 is reduced, which may reduce combustion resistance. As a result, depending on the operating conditions of the internal combustion engine 1, even if the intake valve closing timing IVC is retarded, the torque fluctuation may not fall within the allowable range.

  Therefore, the ECU 12 may reduce the opening degree of the EGR valve 11 when the torque fluctuation after delaying the closing timing IVC of the intake valve deviates from the allowable range α. In this case, the EGR rate becomes lower than the target EGR rate, but the combustion resistance can be increased by increasing the intake air amount.

When the inter-cylinder variation alleviation process is executed according to the procedure described above, the control means according to the present invention is realized. As a result, it is possible to reduce the variation between the cylinders with almost no change in the engine load KL and the EGR rate. Therefore, it is possible to suppress the occurrence of knocking due to the variation between the cylinders and the deterioration of the combustion stability due to the excessive retardation of the target ignition timing.

  In the present embodiment, the example in which the inter-cylinder variation mitigation process is executed when the EGR rate deficiency of the minimum cylinder obtained by the control routine of FIG. 8 described above exceeds the threshold value has been described. Inter-cylinder variation alleviation processing may be executed when the retardation amount of the target ignition timing (knock retardation amount ΔIt) exceeds a threshold value.

  According to such a method, the correlation (function g) between the EGR rate deficiency, the average EGR rate, and the engine operating state is not specified (the cause of knocking is not specified in the EGR operating region). ), It is possible to suppress knocking and maintain combustion stability.

  In the present embodiment, the example in which the phase closing mechanism 17 is used to retard the closing timing of the intake valve has been described. However, the internal combustion engine 1 changes the operating angle of the intake valve in addition to the phase varying mechanism 17. When the operating angle variable mechanism is provided, the phase closing mechanism 17 and the operating angle variable mechanism may be used together to retard the closing timing of the intake valve. In this case, it is possible to retard the valve closing timing without changing the valve opening timing of the intake valve.

1 Internal combustion engine 2 Cylinder 3 Spark plug 4 Intake manifold 5 Intake pipe 6 Air cleaner 7 Air flow meter 8 Throttle valve 9 Exhaust manifold 10 EGR passage 11 EGR valve 12 ECU
13 Crank position sensor 14 Accelerator position sensor 15 Knock sensor 16 Intake pressure sensor 17 Phase variable mechanism 40 Branch pipe 41 Collecting portion

Claims (7)

An ignition control system for a spark ignition internal combustion engine having a plurality of cylinders,
An EGR mechanism comprising an EGR passage for leading a part of the exhaust gas flowing through the exhaust passage to the intake passage as EGR gas, and an EGR valve for changing a passage sectional area of the EGR passage;
Detecting means for detecting knocking of the internal combustion engine;
Retarding means for retarding the target ignition timing until an ignition timing at which knocking does not occur when knocking is detected by the detection means;
Obtaining means for obtaining a retard amount of the target ignition timing when the retard of the target ignition timing is performed by the retard means in the operation region of the EGR mechanism;
Conversion means for converting the retardation amount acquired by the acquisition means into a deficiency of the actual EGR rate with respect to the target EGR rate;
Based on a plurality of EGR rate deficiencies obtained under the same engine operating conditions and different EGR valve opening degrees, the correlation between the target EGR rate, the EGR rate deficiency, and the engine operating status is calculated. Identification means to identify;
Estimating means for estimating an EGR rate deficiency that matches the current engine operating state and the target EGR rate from the correlation specified by the specifying means;
An ignition control system for an internal combustion engine, comprising: a determining unit that determines a target ignition timing using the insufficient amount of EGR estimated by the estimating unit as a parameter. 2. The retarding means according to claim 1, wherein when the engine is in an engine operating state equivalent to when the plurality of EGR rate deficiencies are obtained and knocking occurs in a situation where the opening degree of the EGR valve becomes zero. Storage means for storing the retard amount of the ignition timing by the basic retard amount;
The internal combustion engine ignition control system, wherein the conversion means converts a value obtained by subtracting the basic retardation amount from the retardation amount acquired by the acquisition means into an EGR rate deficiency amount. In Claim 1 or 2, when the actual opening of the EGR valve is smaller than the target opening, it further comprises calculation means for calculating the difference between the EGR rate at the target opening and the EGR rate at the actual opening.
The internal combustion engine ignition control system characterized in that the specifying means specifies the correlation based on a value obtained by subtracting the difference from an EGR rate deficiency calculated by the conversion means.   4. The internal combustion engine ignition control system according to claim 3, wherein the plurality of EGR rate deficiencies are obtained when the opening degree of the EGR valve is linearly related to the EGR rate.   5. The ignition control system for an internal combustion engine according to claim 1, further comprising a mechanism that keeps the engine operating state of the internal combustion engine constant when the plurality of EGR rate deficiencies are obtained. 6. An ignition control system for a spark ignition internal combustion engine having a plurality of cylinders,
An EGR mechanism comprising an EGR passage for leading a part of the exhaust gas flowing through the exhaust passage to the intake passage as EGR gas, and an EGR valve for changing a passage sectional area of the EGR passage;
A variable mechanism for changing the closing timing of the intake valve;
Detecting means for detecting knocking of the internal combustion engine;
Retarding means for retarding the target ignition timing until an ignition timing at which knocking does not occur when knocking is detected by the detection means;
Obtaining means for obtaining a retard amount of the target ignition timing when the retard of the target ignition timing is performed by the retard means in the operation region of the EGR mechanism;
Conversion means for converting the retardation amount acquired by the acquisition means into a deficiency of the actual EGR rate with respect to the target EGR rate;
Based on a plurality of EGR rate deficiencies obtained under the same engine operating conditions and different EGR valve opening degrees, the correlation between the target EGR rate, the EGR rate deficiency, and the engine operating status is calculated. Identification means to identify;
Estimating means for estimating an EGR rate deficiency that matches the current engine operating state and the target EGR rate from the correlation specified by the specifying means;
Determining means for determining a target ignition timing using the EGR rate deficiency estimated by the estimating means as a parameter;
Control means for controlling the variable mechanism to retard the closing timing of the intake valve when the EGR rate deficiency estimated by the estimation means exceeds a predetermined threshold;
An ignition control system for an internal combustion engine, comprising:   7. The internal combustion engine ignition control system according to claim 6, wherein the control means reduces the opening of the EGR valve when retarding the closing timing of the intake valve.

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