JP2010156295A - Diagnosis device and control device of multi-cylinder internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily detect EGR distribution degradation between cylinders and address the degradation. <P>SOLUTION: When an EGR device is operated, a knocking frequency is obtained by a knock sensor for every cylinder, and a knocking frequency ratio between the cylinders is calculated. Then, a difference between the knocking frequency ratio for every cylinder and a pre-stored initial knocking frequency ratio for every cylinder is calculated, and an EGR distribution degrading state is diagnosed. Then, an ignition timing of a cylinder where the difference from the initial ratio exceeds a determination value 1 (EGR reduced cylinder) is corrected to a retarding side, and a fuel injection amount is corrected to an increasing side. Further, if there is a cylinder where the difference from the initial ratio exceeds a determination value 2, an alert is issued as a failure being occurred. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  In a multi-cylinder internal combustion engine having an EGR (Exhaust Gas Recirculation) device that recirculates a part of exhaust gas from an exhaust system to an intake system, the EGR distribution deterioration state (deterioration state of EGR gas distribution to each cylinder) The present invention relates to a technique for diagnosing and dealing with the problem.

In Patent Document 1, an ignition timing knock control system (which includes a knock detection means and calculates a retard amount with respect to the basic ignition timing when knock is detected) is used depending on whether or not it is in the EGR operation region. Based on the assumption that the basic ignition timing is set near the knock limit, the retard amount when in the EGR operation region is compared with the retard amount when not in the EGR operation region, and an abnormality of the EGR device is judged. I am doing so.
Japanese Patent Laid-Open No. 6-200833

  In recent years, EGR technology has been in the spotlight again due to the ever-increasing social demands for improving fuel efficiency and the tightening of exhaust regulations, and its role is increasing. Accordingly, a decrease in the amount of EGR gas due to clogging of the EGR pipe and a deterioration in distribution to each cylinder immediately cause deterioration in fuel consumption and exhaust performance.

  For example, with the tightening of exhaust gas regulations, a slight deterioration in exhaust gas due to slight variations in air-fuel ratio between cylinders has become a problem. It causes variation.

  Accordingly, there is an increasing number of cases where variations in the EGR amount between the cylinders become a problem, and further, as legal regulations, the deterioration of the variation is detected as a failure by an OBD (On Board Diagnosis). It has become an era that requires that.

  Conventionally, as a method of detecting an abnormality of the EGR device such as a decrease in the amount of EGR gas, there is a method as disclosed in Patent Document 1 described above.

  However, no simple method has been found to detect the variation (loss of uniformity) in the EGR amount variation between cylinders, and the variation has been limited to measures such as suppressing the deterioration by devising the hardware of the EGR system. .

  Even if a detection system or control is assumed in order to detect variation, a considerable additional setting such as addition of a dedicated sensor is required.

  In view of such a situation, it is a main object of the present invention to provide a diagnostic device for a multi-cylinder internal combustion engine that can easily diagnose deterioration of EGR distribution between cylinders.

  Therefore, in the present invention, paying attention to the fact that the knock frequency increases in the EGR decreasing cylinder, when the EGR device is operated, the knock frequency is obtained for each cylinder, and the ratio of the knock frequency between the cylinders is calculated. Based on this, it was set as the structure which diagnoses an EGR distribution deterioration state.

  According to the present invention, it is possible to easily diagnose an EGR distribution deterioration state based on a knock frequency ratio between cylinders. Further, since the knock frequency can be detected by using a knock control system (its sensor) generally employed in an internal combustion engine, this can also be easily implemented. Furthermore, if the ignition timing of the internal combustion engine and the fuel injection amount are controlled (corrected) for each cylinder by using the diagnosis result, knocking and air-fuel ratio error in the cylinder with poor distribution can be prevented.

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

  FIG. 1 is a system diagram of a vehicle engine (spark ignition type multi-cylinder internal combustion engine) showing an embodiment of the present invention.

  In the engine, a combustion chamber 4 of each cylinder defined by a cylinder head 1, a cylinder block 2 and a piston 3 is connected to an intake passage 6 through an intake valve 5 and is connected to an exhaust passage 8 through an exhaust valve 7. It is connected.

  A throttle valve 9 is provided in the intake passage 6 of the engine on the upstream side of the intake manifold 6a. The throttle valve 9 is controlled in opening degree by a step motor or the like that is operated by a signal from an electronic control unit (hereinafter referred to as ECU) 20 to control the amount of intake air.

  In the combustion chamber 4 of the engine, an injector (fuel injection valve) 10 and a spark plug 11 are installed.

  The injector 10 is energized to the solenoid by an injection pulse signal output from the ECU 20 in synchronization with the engine rotation, and opens the fuel, and the fuel adjusted to a predetermined pressure supplied from the fuel gallery 12 is injected. Yes. Thereby, an air-fuel mixture is formed in the combustion chamber 4.

  The spark plug 11 ignites and burns the air-fuel mixture at a timing based on an ignition signal from the ECU 20.

  The combustion modes in this direct injection engine include a homogeneous combustion mode and a stratified combustion mode. In the homogeneous combustion mode, fuel is injected during the intake stroke, and a homogeneous air-fuel mixture is formed in the entire combustion chamber 4 to perform homogeneous combustion at a stoichiometric or lean air-fuel ratio. On the other hand, in the stratified combustion mode, fuel injection is performed in the latter half of the compression stroke, and a stratified air-fuel mixture is formed around the spark plug 11 in the combustion chamber 4, so that an extremely lean air space as a whole. Perform stratified combustion at the fuel ratio. However, the engine may be of a type in which an injector is provided for each cylinder in the intake system, and the combustion type is not limited.

  The exhaust after combustion is discharged to the exhaust passage 8 via the exhaust valve 7. An exhaust purification catalyst 13 is provided in the exhaust passage 8 on the downstream side of the exhaust manifold 8a.

  Further, an EGR passage 14 and an EGR valve 15 interposed in the middle thereof are provided as an EGR device that extracts a part of the exhaust from the exhaust passage 8 and recirculates it to the intake passage 6. The opening degree of the EGR valve 15 is controlled by a signal from the ECU 20 to control the EGR amount (EGR rate).

  In particular, in the EGR device of the present embodiment, the EGR passage 14 forms one passage from the EGR gas outlet of the exhaust manifold 8a, but branches on the downstream side of the EGR valve 15 and is independent for each cylinder. The branch end is connected to the intake port of each cylinder. That is, the gallery portion 14a on the downstream side of the EGR valve 15 forms a branch passage 14b that is independent for each cylinder, and each branch passage 14b opens to the intake port of the cylinder head 1.

  According to such an EGR device, the EGR passage 14 branches on the downstream side of the EGR valve 15 and independently for each cylinder as compared with the case where the EGR gas is introduced into the collecting portion (surge tank) of the intake manifold. Thus, uniform distribution of EGR gas to each cylinder is facilitated. Further, the branch end portion of the EGR passage 14 can be connected to the intake port of each cylinder (that is, a position close to the combustion chamber 4), and introduction / stop of EGR gas into the cylinder by turning the EGR valve 15 ON / OFF. Responsiveness can be improved.

  The ECU 20 is composed of a microcomputer and includes a CPU, a ROM, a RAM, an input / output interface, and the like. In addition, some RAMs retain their stored contents by a backup power supply even after the engine key is turned off.

  The ECU 20 receives signals from the crank angle sensor 21 and the cylinder discrimination sensor 22 and can detect the engine speed NE together with the crank angle position (including cylinder discrimination) from these signals. Further, the accelerator opening Acc detected by the accelerator opening sensor 23, the intake air amount Qa detected by the hot-wire air flow meter 24, the exhaust air-fuel ratio λ detected by the air-fuel ratio sensor 25, and the like are input. Further, a signal is also input from a knock sensor 26 as a knock detection means.

  The knock sensor 26 detects knocking from mechanical vibrations of the engine. The knock sensor 26 includes a piezoelectric element having a resonance frequency of 6 to 8 kHz generated by knocking, and is attached to the wall of the cylinder block 2. ing.

  The ECU 20 detects engine operating conditions based on these input signals, and according to this, the opening of the throttle valve 9, the fuel injection timing and fuel injection amount of the injector 10, the ignition timing of the spark plug 11, the EGR valve 15 Control the opening of the.

  As another input / output device, there is an odometer 27 for measuring an accumulated travel distance, and the measurement information can be input to the ECU 20. Further, there is a warning lamp 28 for notifying the driver of a failure when a failure is diagnosed by OBD (self-fault diagnosis), and can be turned on by the output of the ECU 20.

  Next, an outline of the diagnosis (detection) of the deterioration of EGR distribution and the processing when the deterioration is detected will be described.

  As a method for detecting the change in the EGR rate for each cylinder, it is conceivable to obtain it by measuring the air-fuel ratio and the exhaust temperature for each cylinder, but this is not very realistic. On the other hand, if the fact that the knocking ignition timing (knock limit) changes greatly when the EGR rate changes is used, a part of the existing knock control system can be used without adding a new sensor. Thus, it becomes possible to detect a change in the EGR rate for each cylinder.

  For this reason, as part of the knock control system, there is a cylinder-specific knock counter that counts the number of knock detections for each cylinder, and the count-up speed (count-up value within a certain period of time) of this counter is measured. Find the frequency.

  Also, the clogging of the EGR pipe that causes the structural deterioration is a structural deterioration such as a reduction in the cross-sectional area of the EGR passage, and the same deterioration is caused regardless of the engine operating state. Therefore, detection of the clogging is sufficient if it can be detected under a specific operating condition. If it is found that the EGR distribution is deteriorated under the specific operating condition, an adverse effect occurs in all the operating conditions in which the EGR device is operated. Can be estimated with high accuracy.

  For this reason, specific operating conditions are determined, and the knock frequency for each cylinder under the conditions is obtained. Then, the knock frequency ratio between cylinders under that condition (inter-cylinder ratio of the count-up speed of the cylinder specific knock counter) is calculated and learned as the knock frequency ratio.

  For this purpose, the specific operating condition is an operating region in which the EGR rate is set to a large value, and is a rotational load region in which the ignition timing setting is aimed at the knock limit. However, if the load is too high, the EGR rate is small, so it is desirable that the region is not too high.

  On the other hand, when the vehicle is in a new vehicle state (initial state), the knock frequency ratio learned at that time is stored as the initial knock frequency ratio. Compared with the initial knock frequency ratio, the change from the initial stage (difference from the initial stage) is monitored, and the EGR distribution deterioration is diagnosed based on the change from the initial stage.

  However, it is possible to diagnose the EGR distribution deterioration from the knock frequency ratio itself without considering the change from the initial level of the knock frequency ratio, assuming that the EGR distribution in the initial state is uniform. Even if it depends on the change from the initial stage, the initial knock frequency ratio may be regarded as constant.

When the knock frequency ratio or the change thereof exceeds a predetermined first level, the following control is performed.
(1) The ignition timing setting for each cylinder that applies a difference to the ignition timing for each cylinder is applied, and the ignition timing is retarded in order to suppress knocking of a cylinder having a large knock frequency ratio (cylinder having deteriorated EGR distribution).
(2) Applying an injection amount setting for each cylinder that makes a difference in the fuel injection amount for each cylinder, the fuel injection amount is set to suppress an air-fuel ratio error in a cylinder having a large knock frequency ratio (a cylinder in which EGR distribution has deteriorated). Increase the amount.
(3) When the knock frequency ratio or the change further exceeds the predetermined second level, it is determined that the EGR distribution deterioration has exceeded the allowable limit, and failure detection processing (warning or the like) based on OBD is performed.

  As a further improvement, in order to prevent the change in the knock frequency ratio caused by causes other than the deterioration in EGR from being mistakenly regarded as the deterioration in EGR distribution, the above knock frequency ratio learning is performed in the EGR-OFF area separately from the EGR-ON area. By providing a set and matching both the data in the EGR-ON area and the data in the EGR-OFF area, it is possible to reliably determine that the EGR distribution is deteriorated.

  Next, diagnosis (detection) of deterioration of EGR distribution and processing at the time of detection of deterioration will be described in detail with reference to the flowcharts of FIGS.

  FIG. 2 is a flowchart of knock control, which is executed at a timing synchronized with ignition (ignition synchronization interrupt). This flow is a simplified description of the knock control system.

  In S1, based on the signal from the knock sensor 26, it is determined whether or not a knock has occurred during the current ignition.

  If knocking occurs, the process proceeds to S2 to retard the ignition timing. That is, the retard correction amount θk for knock control is updated to a predetermined amount (or an amount corresponding to the knock level) Δθ1 increasing side (θk = θk + Δθ1), and from a map or the like based on operating conditions (engine speed and load) The ignition timing θ = θB−θk is set by subtracting the updated retardation correction amount θk from the set basic ignition timing θB (advance value).

  Further, the process proceeds to S3, where the current ignition cylinder (n) is determined based on the signals from the crank angle sensor 21 and the cylinder determination sensor 22. Then, the process proceeds to S4, the knock counter cknk (n) of the determined ignition cylinder (n) is counted up, and this routine is finished.

  If knocking has not occurred, the process proceeds to S5 to advance the ignition timing. That is, the retard correction amount θk for knock control is updated to a small amount Δθ2 decreasing side (θk = θk−Δθ2), and the basic ignition timing θB (set from a map or the like based on the operating conditions (engine speed and load) is set. The ignition timing θ = θB−θk is set by subtracting the updated retardation correction amount θk from the advance angle value). Thus, the ignition timing is controlled to the knock limit. If knocking has not occurred, the routine ends here.

  FIG. 3 is a flowchart for calculating the knock frequency ratio, which is executed in the main routine of the program.

  In S11, it is determined whether or not the vehicle is in a learning operation region (operation region in which knock frequency ratio learning is performed). This learning operation region is a region in which a predetermined region is set by rotation and load in a region where the EGR rate is set large and the ignition timing setting is aimed at the knock limit.

  If it is not the learning operation region, the process proceeds to S16 to clear the knock counter cknk (n) of all the cylinders, clear the timer ctime, and end this routine.

  When it is in the learning operation region, the process proceeds to S12, and it is determined whether or not a predetermined time has elapsed since entering the learning operation region. This predetermined time is a stable waiting time for eliminating the transient effects of the EGR rate and the knock occurrence state.

  Before the predetermined time has elapsed after entering the region (before stabilization), the process proceeds to S16, where the knock counters cknk (n) of all the cylinders are cleared, the timer ctime is cleared, and this routine is terminated.

  After a predetermined time has elapsed after entering the region (after stabilization), the process proceeds to S13, and it is determined based on the value of the timer ctime whether or not the required measurement time Cexam has elapsed. That is, it is determined whether ctime> Cexam.

  Before the time required for measurement elapses, this routine is finished as it is. During this time, in the routine of FIG. 2, the knock counter cknk (n) of the knocking cylinder is counted up by the occurrence of knocking.

  After the measurement required time has elapsed, at that time, the process proceeds to S14, and the knock frequency ratio is calculated. That is, the knock counter cknk (n) of each cylinder is normalized (normalized) to the relative ratio, and the knock frequency ratio FR (n) is calculated.

  For example, the ratio of the number of knock occurrences (cylinder knock counter value) of each cylinder to the total number of knock occurrences within the required measurement time is obtained for each cylinder, and this is set as the knock frequency ratio FR (n). In this case, the sum of the knock frequency ratios of all cylinders is 100%.

  Further, the process proceeds to S15, and the knock frequency ratio learning value LFR (n) on the backup RAM is updated by, for example, the following equation using the current knock frequency ratio FR (n) for each cylinder.

LFR (n) = LFR (n) × (1-w) + FR × w
w is a weighting constant, and 0 <w <1.

  After the learning update, the process proceeds to S16 to clear the knock counter cknk (n) for all the cylinders, clear the timer ctime, and end this routine.

  FIG. 4 is a flowchart of the initial knock frequency ratio storage, for storing and holding the knock frequency ratio learning value at that time as an initial value when the vehicle is new, that is, before the EGR piping system is clogged. It is a routine.

  Even if the frequency of knocking cylinders is already different in the initial state where the EGR distribution has not deteriorated due to individual differences among the engines, only the effect of the EGR distribution deterioration is separated and detected by comparing with the initial state. Because it can.

  In S21, it is determined whether or not the vehicle is in a new vehicle state based on whether or not the integrated travel distance of the odometer 27 is less than a predetermined distance.

  Only in the case of the new vehicle state, the process proceeds to S22, and the knock frequency ratio learning value LFR (n) at that time (in the new vehicle) is stored and retained in the backup RAM as the initial knock frequency ratio storage value LFRINT (n) for each cylinder. .

  In the above-described calculation method of the knock frequency ratio FR (n) described above, assuming that the EGR distribution in the new vehicle state (initial state) is uniform, the initial knock frequency ratio of each cylinder is constant and 100 / The number of cylinders (%), and therefore 25% for 4 cylinders.

  FIG. 5 is a flowchart of the EGR distribution deterioration diagnosis and the deterioration process, and is executed as a sequential process.

  In S31, for each cylinder, the current knock frequency ratio learning value LFR (n) is compared with the initial knock frequency ratio stored value LFRINT (n), and a difference between these values (a difference from the initial value) is calculated.

  In S32, for each cylinder, it is determined whether or not the difference from the initial value (knock frequency ratio learned value−initial knock frequency ratio stored value) is greater than a determination value 1 corresponding to the first level (correction request level). If it is small (small in all cylinders), this routine is terminated.

  When the difference from the initial value is larger than the determination value 1 (when there is a cylinder whose difference from the initial value is larger than the determination value 1), the process proceeds to S33, and the difference from the initial value corresponds to the second level (failure warning level). It is determined whether or not it is greater than a determination value 2 (> determination value 1).

  When the difference from the initial value is larger than the determination value 2 (when there is a cylinder whose difference from the initial value is larger than the determination value 2), the process proceeds to S34, and the failure detection process by OBD is executed. That is, by turning on the warning lamp 28, the driver is informed of the failure, and a failure code representing the failure content is recorded. By recording the failure code, a mechanic or the like can read out the failure code using a dedicated machine and immediately identify the failure location.

  When the difference from the initial value is larger than the determination value 1, but smaller than the determination value 2, the process proceeds to S35 without going through S34, and the difference from the initial value is larger than the determination value 1 and further larger than the determination value 2. Goes to S35 via S34. Therefore, when the difference from the initial value is larger than the determination value 1 (when there is a cylinder whose difference from the initial value is larger than the determination value 1), the process proceeds to S35.

  In S35, a command is issued to execute the cylinder specific ignition timing correction and the cylinder specific injection amount correction.

  In the ignition timing correction for each cylinder, the ignition timing is corrected to the retarded side in order to suppress knocking for a cylinder whose difference from the initial value is larger than the determination value 1, that is, an EGR distribution deterioration cylinder (EGR decreasing cylinder).

  Specifically, the ignition timing θ is obtained by subtracting the retard correction amount θk (common to all cylinders) set by the knock control from the basic ignition timing θB set from a map or the like based on the engine operating conditions (engine speed and load). Is calculated, the cylinder specific correction amount θc (n) is set, and the cylinder specific ignition timing θ (n) is calculated by the following equation.

θ (n) = θB−θk−θc (n)
Then, by setting the cylinder specific correction amount θc (n) larger than the initial value 0 for a cylinder whose difference from the initial value is larger than the determination value 1, that is, the EGR distribution worsening cylinder (EGR decreasing cylinder). Is corrected to the retarded angle side.

  As described above, an increase in the overall (equal to all cylinders) knock frequency due to deterioration over time can be dealt with by increasing the retardation correction amount θk by the normal knock control, and therefore, EGR distribution due to clogging of the EGR pipe or the like. An increase in knock frequency due to a decrease in EGR in some cylinders due to deterioration is detected by a change in the knock frequency ratio between cylinders, and is dealt with by correction for each cylinder.

  In addition, when the cylinder-specific correction of the ignition timing is performed on the EGR distribution deterioration cylinder, the cylinder-specific correction of the ignition timing according to the deterioration level may be performed on the other cylinders. Further, when cylinders other than the EGR distribution worsening cylinder are retarded too much by average knock control, correction for each cylinder in the ignition timing advance direction may be performed for these cylinders.

  In the cylinder-by-cylinder injection amount correction, in order to suppress the air-fuel ratio error (lean error) for the cylinder whose difference from the initial value is larger than the determination value 1, that is, the EGR distribution deterioration cylinder (EGR decrease cylinder), the fuel injection amount is increased to the increase side. to correct. In the EGR distribution worsening cylinder (EGR decreasing cylinder), the intake air amount increases as the EGR gas amount in the cylinder decreases, so the air-fuel ratio becomes lean. Note that the intake air amount detected by the air flow meter increases due to the increase in the total intake air amount, and the total fuel injection amount slightly increases due to the air-fuel ratio control. A leaner fuel ratio will occur. Therefore, the fuel injection amount is corrected to the increase side in order to suppress this leaning (lean error).

  Specifically, the basic fuel injection amount TAU0 is calculated from the intake air amount Qa and the engine speed NE, and this is corrected with various correction coefficients K including an air-fuel ratio feedback correction coefficient (and a learning correction coefficient) to obtain the fuel injection amount. If TAU is calculated, a cylinder specific correction coefficient KEGR (n) is set, and a cylinder specific fuel injection amount TAU (n) is calculated by the following equation.

TAU (n) = TAU0 × K × KEGR (n)
Then, by setting a cylinder specific correction coefficient KEGR (n) larger than the initial value 1 for a cylinder whose difference from the initial value is larger than the determination value 1, that is, an EGR distribution worsening cylinder (EGR decreasing cylinder). The fuel injection amount TAU (n) is corrected to the increase side.

  As described above, a general (equal to all cylinders) air-fuel ratio error due to deterioration over time can be dealt with by correction by normal air-fuel ratio feedback control (and learning control), so EGR distribution due to clogging of EGR piping or the like. Leaning of the air-fuel ratio due to EGR reduction in some cylinders due to deterioration is detected by a change in the knock frequency ratio between the cylinders, and is dealt with by correction for each cylinder.

  When the cylinder-specific correction of the fuel injection amount is performed for the EGR distribution deterioration cylinder, the cylinder-specific correction of the fuel injection amount according to the deterioration level may be performed for the other cylinders. Further, when cylinders other than the EGR distribution deterioration cylinder are enriched by average air-fuel ratio feedback control, the cylinder-by-cylinder correction in the decreasing direction may be performed on these cylinders.

  According to the present embodiment, when the EGR device is operated, the knock frequency ratio calculating means for calculating the knock frequency ratio between the cylinders by calculating the knock frequency for each cylinder, and the EGR based on the knock frequency ratio between the cylinders. EGR distribution deterioration state diagnosing means for diagnosing the distribution deterioration state, thereby increasing the knock frequency in the EGR decreasing cylinder (especially in the case of an engine that performs a large amount of EGR, in order to ensure combustion performance, the basic ignition timing Therefore, the EGR distribution worsening state based on the ratio of knock frequency between cylinders is considered based on the fact that knocking is unavoidable in the EGR decreasing cylinder due to the worsening of EGR distribution. A simple diagnosis can be made. Further, since the knock frequency and the like can be detected by using a knock control system, this point can be easily implemented.

  Further, according to the present embodiment, the EGR distribution worsening state diagnosing unit further includes an initial knock frequency ratio storage unit that stores a knock frequency ratio between cylinders in an initial state as an initial knock frequency ratio. Even if there is a variation in the EGR distribution in the initial state (new vehicle state) by obtaining a change from the initial knock frequency ratio for the knock frequency ratio for each cylinder and diagnosing the EGR distribution deterioration state based on this change, Changes from the initial stage, that is, EGR distribution deterioration due to clogging of the EGR pipe can be detected and diagnosed separately.

  Further, according to the present embodiment, the EGR distribution is provided by providing a correction unit that corrects at least one of the ignition timing and the fuel injection amount for each cylinder according to the EGR distribution deterioration state diagnosed by the diagnosis unit. It becomes possible to avoid the deterioration of driving performance and exhaust performance due to deterioration.

  Further, according to the present embodiment, the correction means corrects at least one of the ignition timing and the fuel injection amount for the cylinder in which the ratio of the knock frequency or the change thereof exceeds the first level (correction request level). By doing so, it is possible to cope with the occurrence of knocking in the EGR distribution worsening cylinder and the air-fuel ratio error.

  Further, according to the present embodiment, the correction means corrects the ignition timing to the retard side for the cylinder whose knock frequency ratio or its change has exceeded the first level, so that the EGR distribution deterioration cylinder Can be reliably avoided.

  Further, according to the present embodiment, the correction means corrects the fuel injection amount to the increase side for the cylinder in which the ratio of the knock frequency or the change thereof exceeds the first level, so that the EGR distribution deterioration cylinder It is possible to reliably avoid the air-fuel ratio error (lean error).

  Further, according to the present embodiment, when there is a cylinder in which the ratio of the knock frequency or the change thereof exceeds the second level (failure warning level) set to be larger than the first level, warning means for warning as a failure , The driver can be urged for early repairs, etc., and it will be possible to meet future legal regulations.

  Next, another embodiment of the present invention will be described.

  The present embodiment further includes an EGR non-operational knock frequency ratio calculating means for calculating a knock frequency ratio between the cylinders by calculating a knock frequency for each cylinder when the EGR device is not in operation, and the EGR distribution deterioration After the state diagnosis means confirms the deterioration of EGR distribution by comparing the ratio of the knock frequency when the EGR device is operated and the ratio of the knock frequency when the EGR device is not operated, the knock frequency between the cylinders when the EGR is operated The EGR distribution deterioration state is diagnosed on the basis of the ratio.

  For this reason, in the present embodiment, as in the above-described one embodiment, the knock control is performed by the flow of FIG. 2, the knock frequency ratio is calculated by the flow of FIG. 3, and the initial operation is performed by the flow of FIG. Although the knock frequency ratio is stored, the knock frequency ratio is calculated when the EGR is not operated by a flow (not shown) in parallel with the calculation of the knock frequency ratio (the calculation of the knock frequency when the EGR is operated) in FIG.

  In other words, the flow of FIG. 3 shows that the determination as to whether or not the learning operation region (learning operation region during EGR operation) in S11 is replaced by the determination as to whether or not the learning operation region is during EGR non-operation. Learn knock frequency ratio during operation.

  Then, instead of the flow of FIG. 5, the EGR distribution deterioration diagnosis and the deterioration process are executed according to the flow of FIG. 6.

  FIG. 6 is a flowchart of the EGR distribution deterioration diagnosis and the process at the time of deterioration in another embodiment, and the determination of S30 is added to the beginning of the flow of FIG.

  In S30, the knock frequency ratio learning value at the time of EGR operation is compared with the knock frequency ratio learning value at the time of EGR non-operation, and whether or not the EGR distribution is deteriorated (that is, whether the change of the knock frequency ratio is due to the influence of EGR). Only when it is confirmed that there is an EGR distribution deterioration, the EGR distribution deterioration diagnosis and the process at the time of deterioration after S31 are performed.

  Specifically, for example, when there is almost no variation in knock frequency ratio between cylinders when EGR is not operating, and there is a variation in knock frequency ratio between cylinders during EGR operation, there is a deterioration in EGR distribution (the effect of EGR) ), And EGR distribution deterioration diagnosis and processing at the time of deterioration after S31 are performed.

  Thus, after confirming EGR distribution deterioration (variation in knock frequency ratio among cylinders due to EGR) by comparing the knock frequency ratio during operation of the EGR device with the knock frequency ratio during non-operation of the EGR device. By diagnosing the EGR distribution deterioration state based on the knock frequency ratio at the time of EGR operation, it is possible to greatly improve the reliability of the EGR distribution deterioration diagnosis and subsequent deterioration processing.

  In the above embodiment, the case where an EGR device in which the EGR passage 14 branches on the downstream side of the EGR valve 15 and is independent for each cylinder is described, and in this case, the branch passage for each cylinder is used. Although it is remarkable that the EGR distribution deteriorates due to clogging of 14b, even when an EGR device in which the EGR passage is not independent for each cylinder is employed, depending on the clogging state of the EGR passage, for example, an EGR gas ejection portion When the ejection direction of the EGR gas changes due to the uneven clogging of EGR, the EGR distribution deteriorates. Therefore, the present invention is applied even when such a non-independent EGR device is adopted. Can do.

Engine system diagram showing an embodiment of the present invention Knock control flowchart Knock frequency ratio calculation flowchart Flow chart of initial knock frequency ratio storage Flow chart of EGR distribution deterioration diagnosis and processing at the time of deterioration Flowchart of EGR distribution deterioration determination and deterioration processing in another embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder head 2 Cylinder block 3 Piston 4 Combustion chamber 5 Intake valve 6 Intake passage 6a Intake manifold 7 Exhaust valve 8 Exhaust passage 8a Exhaust manifold 9 Throttle valve 10 Injector 11 Spark plug 12 Fuel gallery 13 Exhaust purification catalyst 14 EGR passage 14a Gallery part 14b Branch passage 15 EGR valve 20 ECU
21 Crank angle sensor 22 Cylinder discrimination sensor 23 Accelerator opening sensor 24 Air flow meter 25 Air-fuel ratio sensor 26 Knock sensor 27 Odometer 28 Warning light

Claims (10)

In a multi-cylinder internal combustion engine equipped with an EGR device that recirculates part of the exhaust from the exhaust system to the intake system,
Knock frequency ratio calculating means for calculating a knock frequency ratio between cylinders by calculating a knock frequency for each cylinder when the EGR device is in operation;
EGR distribution deterioration state diagnosis means for diagnosing an EGR distribution deterioration state based on a ratio of knock frequencies between cylinders;
A diagnostic apparatus for a multi-cylinder internal combustion engine, comprising: And an initial knock frequency ratio storage means for storing a knock frequency ratio between the cylinders in an initial state as an initial knock frequency ratio.
2. The EGR distribution deterioration state diagnosing means obtains a change from the initial knock frequency ratio with respect to the knock frequency ratio for each cylinder, and diagnoses an EGR distribution deterioration state based on the change. A diagnostic device for a multi-cylinder internal combustion engine. Further, the EGR device includes a knock frequency ratio calculation means for non-operation of EGR that calculates a knock frequency ratio between the cylinders by calculating a knock frequency for each cylinder when the EGR device is not operated.
The EGR distribution deterioration state diagnosing means confirms the deterioration of EGR distribution by comparing the ratio of the knock frequency when the EGR device is in operation with the ratio of the knock frequency when the EGR device is not operated. 3. The diagnostic apparatus for a multi-cylinder internal combustion engine according to claim 1, wherein the deterioration state of EGR distribution is diagnosed based on a ratio of knock frequency between cylinders at the time.   4. The multi-cylinder internal combustion engine according to claim 1, wherein the EGR device has an EGR passage branched downstream of an EGR valve and independent for each cylinder. 5. Diagnostic device.   The diagnostic device for a multi-cylinder internal combustion engine according to claim 4, wherein a branch end portion of the EGR passage is connected to an intake port of each cylinder. The diagnostic device according to any one of claims 1 to 5,
Correction means for correcting at least one of the ignition timing and the fuel injection amount for each cylinder according to the EGR distribution deterioration state diagnosed by the diagnostic device;
A control apparatus for a multi-cylinder internal combustion engine, comprising:   The multi-cylinder internal combustion engine according to claim 6, wherein the correction unit corrects at least one of an ignition timing and a fuel injection amount for a cylinder in which the knock frequency ratio or a change thereof exceeds a first level. Engine control device.   8. The control apparatus for a multi-cylinder internal combustion engine according to claim 7, wherein the correction means corrects the ignition timing to the retard side for a cylinder whose knock frequency ratio or change exceeds a first level. .   8. The control apparatus for a multi-cylinder internal combustion engine according to claim 7, wherein the correction means corrects the fuel injection amount to an increase side for a cylinder in which the ratio of the knock frequency or the change thereof exceeds a first level. .   And a warning means for warning that a failure occurs when there is a cylinder whose knock frequency ratio or change exceeds a second level set larger than the first level. The control device for a multi-cylinder internal combustion engine according to any one of claims 7 to 9.

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