JP2011241752A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

The present invention relates to an exhaust gas purification system for an internal combustion engine that controls a low pressure EGR device so that combustion fluctuation does not occur when a reducing agent is supplied from a reducing agent supply device to an exhaust gas purification device. It is an object to provide a technique capable of suppressing combustion fluctuation.
An internal combustion engine that performs an adjustment process for adjusting an EGR rate so that an oxygen concentration of a gas sucked into a cylinder does not change before and after the supply of the reducing agent when the reducing agent is supplied from a supply device. In the engine exhaust gas purification system, when combustion fluctuation occurs due to the execution of the adjustment process, the cause of the combustion fluctuation is at the execution timing of the adjustment process based on the history of the combustion state, or the control of the EGR rate in the adjustment process It is determined whether the amount is within the amount, and the control timing of the adjustment processing or the control amount of the EGR rate in the adjustment processing is corrected according to the determination result.
[Selection] Figure 7

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine, and more particularly to an exhaust gas purification system including a mechanism for supplying a reducing agent into an exhaust passage and an EGR mechanism.

  2. Description of the Related Art An internal combustion engine equipped with a turbocharger is known that includes a low-pressure EGR device that returns exhaust gas (EGR gas) from an exhaust passage downstream of a turbocharger turbine to an intake passage upstream of a turbocharger compressor.

Furthermore, upstream of the exhaust passage from the extraction portion of the downstream and the EGR gas from the turbine is also known an exhaust purification system disposed with a reducing agent supply device of the exhaust purification device (NO _X catalyst and the particulate filter, etc.). In such an exhaust purification system, there is a possibility that the reducing agent supplied from the reducing agent supply device is guided to the intake passage by the low pressure EGR device, and combustion fluctuations of the internal combustion engine are induced.

  With respect to such a problem, there is a technique for controlling the low pressure EGR device so that the oxygen concentration of the gas sucked into the cylinder does not change before and after the supply of the reducing agent when the reducing agent is supplied from the reducing agent supply device. It has been proposed (see, for example, Patent Document 1).

JP 2008-208723 A JP 05-215044 A

  The present invention suppresses combustion fluctuations more reliably in an exhaust gas purification system for an internal combustion engine that controls a low-pressure EGR device so that combustion fluctuations do not occur when reducing agent is supplied from the reducing agent supply device to the exhaust gas purification device. It is an issue to provide technology that can be used.

The present invention employs the following means in order to solve the above-described problems. That is, the exhaust gas purification system for an internal combustion engine according to the present invention is:
An EGR mechanism including an EGR passage for leading a part of the exhaust gas from the exhaust passage of the internal combustion engine to the intake passage as EGR gas, and an EGR valve for changing a passage cross-sectional area of the EGR passage;
An exhaust purification device disposed in the exhaust passage upstream of the connection portion of the EGR passage;
A supply device for supplying a reducing agent to the exhaust purification device;
Control means for performing adjustment processing for adjusting the EGR rate so that the oxygen concentration of the gas sucked into the cylinder does not change before and after the supply of the reducing agent when the reducing agent is supplied from the supply device;
Detecting means for detecting a combustion state in the cylinder when the adjustment process is being performed;
Determination means for determining the occurrence of combustion fluctuations from the detection value of the detection means;
Based on the combustion state history detected by the detection means when the determination means determines that combustion fluctuation has occurred, the cause of the combustion fluctuation is at the execution timing of the adjustment process or the EGR rate in the adjustment process Determining means for determining whether the amount is within the control amount;
Correction means for correcting the execution timing of the adjustment process or the control amount of the EGR rate in the adjustment process according to the determination result of the determination means;
I was prepared to.

  As a result of the inventor's earnest experiment and verification, a case where combustion fluctuation occurs due to the execution timing of the adjustment process and a case where combustion fluctuation occurs due to the control amount of the EGR rate in the adjustment process Then, it discovered that a combustion state showed a different behavior.

  Therefore, the exhaust gas purification system for an internal combustion engine according to the present invention is based on the combustion state history detected by the detecting means when the combustion fluctuation occurs, or whether the cause of the combustion fluctuation is at the execution timing of the adjustment process or the adjustment. It is determined whether or not the control amount of the EGR rate in the process is present, and the combustion fluctuation can be eliminated by correcting the execution timing of the adjustment process or the control amount of the EGR rate in the adjustment process according to the determination result. did.

  When combustion fluctuations are eliminated by the present invention, it is possible to suppress torque fluctuations in the internal combustion engine, an increase in exhaust emissions, and an increase in fuel consumption rate.

  As the detection means according to the present invention, an in-cylinder pressure sensor for detecting the pressure in the cylinder can be used. According to the knowledge of the present inventor, when the execution timing of the adjustment process deviates from an appropriate value, a phenomenon in which the peak value of the in-cylinder pressure is higher than the normal value and a phenomenon in which the peak value is lower than the normal value occur alternately. On the other hand, when the control amount (for example, target EGR rate) of the EGR rate in the adjustment process deviates from an appropriate value, a phenomenon in which the peak value is higher or lower than the normal value occurs once.

  Therefore, if the phenomenon in which the peak value of the in-cylinder pressure detected by the detection means alternately occurs and the phenomenon in which the peak value of the in-cylinder pressure is lower than the normal value occur alternately, the cause of combustion fluctuation is the timing of execution of the adjustment process. If the phenomenon that the peak value of the in-cylinder pressure detected by the detection means is higher or lower than the normal value occurs once, the cause of the combustion fluctuation is the control amount of the EGR rate in the adjustment process. You may judge.

  According to such a determination method, it is possible to determine whether the cause of the combustion fluctuation is the execution timing of the adjustment process or the control amount of the EGR rate in the adjustment process. As a result, the correction unit can correct (correct) the adjustment processing execution timing or the control amount of the EGR rate to an appropriate value.

  In addition, according to the results of intensive experiments and verifications by the inventor of the present application, a phenomenon in which the peak value of the in-cylinder pressure becomes higher than the normal value occurs when the execution timing of the adjustment process is too early with respect to the appropriate timing. When the adjustment timing is too late with respect to the proper timing, the peak value of the in-cylinder pressure becomes higher than the normal value after the phenomenon that the peak value is lower than the normal value occurs. It was found that the phenomenon occurred.

  Therefore, when the phenomenon that the peak value of the in-cylinder pressure detected by the detection means becomes higher than the normal value and the phenomenon that becomes lower than the normal value occurs after the occurrence of the phenomenon that the peak value of the in-cylinder pressure is detected by the detection means, If the phenomenon that the peak value of the in-cylinder pressure detected by the detection means becomes lower than the normal value after the phenomenon that becomes higher than the normal value occurs, the adjustment processing execution timing is set to an appropriate timing. On the other hand, it may be determined that it is too late. In this case, the correction unit can correct the execution timing of the adjustment process to an appropriate timing. As a result, combustion fluctuation can be more reliably suppressed.

  In addition, according to the results of intensive experiments and verifications by the inventor of the present application, the peak value of the in-cylinder pressure becomes lower than the normal value when the control amount of the EGR rate in the adjustment process is excessive with respect to the appropriate value. It has also been found that when the control amount of the EGR rate in the adjustment process is too small relative to the appropriate value, a phenomenon that the peak value of the in-cylinder pressure becomes higher than the normal value occurs once.

  Therefore, when the phenomenon in which the peak value of the in-cylinder pressure detected by the detection unit is lower than the normal value occurs once, the determination unit determines that the control amount of the EGR rate in the adjustment process is excessive with respect to the appropriate value. When the phenomenon in which the peak value of the in-cylinder pressure detected by the detecting means is once higher than the normal value occurs, it is determined that the control amount of the EGR rate in the adjustment process is too small relative to the appropriate value. Also good. In this case, the correction unit can correct (correct) the control amount of the EGR rate in the adjustment process to an appropriate value. As a result, combustion fluctuation can be more reliably suppressed.

  As a method of correcting (correcting) the control amount of the EGR rate in the adjustment process, a method of correcting (correcting) the opening degree of the EGR valve can be used. For example, when a phenomenon occurs in which the peak value of the in-cylinder pressure detected by the detection unit is lower than the normal value, the control amount (target opening degree) of the EGR valve is decreased and the in-cylinder pressure detected by the detection unit is reduced. When the phenomenon that the peak value of the valve becomes higher than the normal value occurs once, the control amount (target opening degree) of the EGR valve may be increased.

  According to the present invention, when the reducing agent is supplied from the reducing agent supply device, the internal combustion engine that controls the low pressure EGR device so that the oxygen concentration of the gas sucked into the cylinder does not change before and after the supply of the reducing agent. In the exhaust purification system, combustion fluctuations can be more reliably suppressed.

1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied and its intake and exhaust system. It is a timing chart which shows the execution procedure of adjustment processing. It is a figure which shows the time-dependent change of in-cylinder pressure in case a transport delay time is shorter than an appropriate value. It is a figure which shows the time-dependent change of the in-cylinder pressure when a transport delay time is longer than an appropriate value. It is a figure which shows the time-dependent change of in-cylinder pressure when the target opening for adjustment is larger than an appropriate value. It is a figure which shows the time-dependent change of in-cylinder pressure when the target opening for adjustment is smaller than an appropriate value. It is a flowchart which shows the control routine which ECU performs at the time of execution of adjustment processing.

  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.

  An internal combustion engine 1 shown in FIG. 1 is a compression ignition internal combustion engine (diesel engine) for driving a vehicle having four cylinders 2. Each cylinder 2 of the internal combustion engine 1 is provided with a fuel injection valve 3 that directly injects fuel into the cylinder 2.

  An intake manifold 5 and an exhaust manifold 7 are connected to the internal combustion engine 1. An intake passage 4 is connected to the intake manifold 5. An exhaust passage 6 is connected to the exhaust manifold 7. A compressor 8 a of a centrifugal supercharger (turbocharger) 8 is installed in the intake passage 4. A turbine 8 b of a turbocharger 8 is installed in the exhaust passage 6.

A first throttle valve 9 is provided in the intake passage 4 downstream of the compressor 8a. A second throttle valve 19 is provided upstream of the compressor 8 a in the intake passage 4. An intercooler 40 is provided in the intake passage 4 downstream of the compressor 8 a and upstream of the first throttle valve 9.

  On the downstream side of the turbine 8b in the exhaust passage 6, an oxidation catalyst 23 and a particulate filter 24 are arranged in order from the upstream side along the exhaust flow direction. The oxidation catalyst 23 and the particulate filter 24 are one embodiment of the exhaust purification device according to the present invention. The exhaust manifold 7 is provided with an addition valve 25 for adding fuel as a reducing agent into the exhaust gas. The addition valve 25 is an embodiment of the supply device according to the present invention.

  The intake / exhaust system of the internal combustion engine 1 is provided with a high pressure EGR device 11 and a low pressure EGR device 15. The high pressure EGR device 11 includes a high pressure EGR passage 12, a high pressure EGR valve 13, and a high pressure EGR cooler 14. One end of the high-pressure EGR passage 12 is connected to the exhaust manifold 7, and the other end is connected to a portion of the intake passage 4 downstream of the first throttle valve 9 (or the intake manifold 5).

  The high pressure EGR valve 13 and the high pressure EGR cooler 14 are provided in the high pressure EGR passage 12. The high-pressure EGR valve 13 is a valve mechanism that changes the passage sectional area of the high-pressure EGR passage 12, and is introduced from the exhaust manifold 7 into the intake passage 4 by changing the passage sectional area of the high-pressure EGR passage 12 by the high-pressure EGR valve 13. The flow rate of the high pressure EGR gas to be changed is changed.

  The low pressure EGR device 15 includes a low pressure EGR passage 16, a low pressure EGR valve 17, and a low pressure EGR cooler 18. One end of the low pressure EGR passage 16 is connected to a portion of the exhaust passage 6 downstream of the particulate filter 24, and the other end of the low pressure EGR passage 16 is downstream of the second throttle valve 19 and upstream of the compressor 8a. It is connected.

  The low pressure EGR valve 17 and the low pressure EGR cooler 18 are provided in the low pressure EGR passage 16. The low-pressure EGR valve 17 is a valve mechanism that changes the passage sectional area of the low-pressure EGR passage 16, and is introduced from the exhaust passage 6 into the intake passage 4 by changing the passage sectional area of the low-pressure EGR passage 16 by the low-pressure EGR valve 17. The flow rate of the low pressure EGR gas is controlled.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 20. Various sensors such as a crank position sensor 21, an accelerator position sensor 22, an oxygen concentration sensor 26, and an in-cylinder pressure sensor 27 are electrically connected to the ECU 20.

The crank position sensor 21 is a sensor that outputs an electrical signal correlated with the rotational position of the output shaft (crankshaft) of the internal combustion engine 1. The accelerator position sensor 22 is a sensor that outputs an electrical signal correlated with the amount of operation of the accelerator pedal (accelerator opening). The oxygen concentration sensor 26 is a sensor that outputs an electrical signal correlated to the concentration of oxygen in the exhaust passage 6 (O ₂₎ (concentration of oxygen (O ₂₎ contained in the exhaust gas). In the example shown in FIG. 1, the oxygen concentration sensor 26 is disposed in the exhaust passage 6 in the vicinity of the connection portion of the low pressure EGR passage 16. The in-cylinder pressure sensor 27 is a sensor that outputs an electrical signal correlated with the pressure in the cylinder 2. In the example shown in FIG. 1, the in-cylinder pressure sensor 27 is attached to all the cylinders 2, but the in-cylinder pressure sensor 27 may be attached to only some of the cylinders 2.

  The ECU 20 is electrically connected to various devices such as the fuel injection valve 3, the first throttle valve 9, the second throttle valve 19, the addition valve 25, the high pressure EGR valve 13, and the low pressure EGR valve 17. The ECU 20 controls various devices based on the detection signals of the various sensors described above.

  For example, the ECU 20 supplies fuel from the addition valve 25 when it is necessary to raise the exhaust gas temperature, such as when it is necessary to oxidize and remove particulate matter (PM) collected by the particulate filter 24. By performing the supply, an addition process for oxidizing the added fuel in the oxidation catalyst 23 is executed.

By the way, when the addition process is executed when the low-pressure EGR valve 17 is opened, the added fuel is oxidized by the oxidation catalyst 23 or the particulate filter 24 oxidizes PM, whereby carbon dioxide (CO ₂ ) increases. Accordingly, carbon dioxide (CO ₂ ) contained in the low pressure EGR gas also increases.

Therefore, when the intake air amount and the EGR rate are kept constant before and after the execution of the addition process, the gas sucked into the cylinder 2 (a mixed gas of air and low pressure EGR gas, or air and low pressure EGR gas and high pressure) As the amount of carbon dioxide (CO ₂ ) in the mixed gas with EGR gas increases, the amount of oxygen (O ₂ ) decreases. Thus, when the amount of carbon dioxide (CO ₂ ) and oxygen (O ₂ ) changes, the combustion state of the fuel changes (combustion fluctuation). As a result, torque fluctuation, an increase in exhaust emission, or an increase in fuel consumption rate may be induced. The “EGR rate” here is the ratio of the amount of low-pressure EGR gas to the amount of mixed gas.

In response to such a problem, the ECU _{20 determines} the amount of oxygen (O ₂ ) contained in the mixed gas (the amount of carbon dioxide (CO ₂ )) when the addition process is performed while the low pressure EGR valve 17 is opened. Is performed (adjustment process) to reduce the EGR rate (decrease the amount of low-pressure EGR gas) so that it becomes substantially constant before and after the execution of the addition process.

In the adjustment process, the ECU ₂₀ acquires the change amount ΔO ₂ of the oxygen concentration in the exhaust gas from the output signal of the oxygen concentration sensor 26. The ECU 20 changes the target EGR rate according to the change amount ΔO ₂ of the oxygen concentration, and calculates the target opening degree of the low pressure EGR valve 17 corresponding to the changed target EGR rate. Note that the ECU ₂₀ may directly calculate the target opening degree (or the correction amount of the target opening degree) of the low pressure EGR valve 17 from the change amount ΔO ₂ of the oxygen concentration. At that time, the relationship between the change amount ΔO ₂ of the oxygen concentration and the target opening degree (or the correction amount of the target opening degree) of the low-pressure EGR valve 17 may be obtained in advance by an adaptation process using an experiment or the like. Hereinafter, the target opening obtained in this way is referred to as “adjustment target opening”.

  Further, a gas transport delay occurs until the gas containing fuel added from the addition valve 25 (hereinafter referred to as “control target gas”) reaches the low-pressure EGR valve 17. Therefore, the ECU 20 calculates the time (hereinafter, referred to as “transport delay time”) Δt required for the control target gas to reach the low pressure EGR valve 17. The transport delay time Δt is calculated using as parameters the volume V of the path from the addition valve 25 to the low pressure EGR valve 17, the gas amount Gex discharged from the internal combustion engine 1 per cycle, and the engine speed Ne. be able to.

When the target opening for adjustment and the transport delay time Δt are obtained, the ECU 20 adjusts the opening of the low pressure EGR valve 17 when the transport delay time Δt has elapsed from the execution start timing of the addition process, as shown in FIG. Change to target opening. In that case, changes in the amount of carbon dioxide (CO ₂ ) and oxygen (O ₂ ) sucked into the cylinder 2 before and after execution of the addition process are suppressed. As a result, it is possible to avoid combustion fluctuations resulting from the execution of the addition process, thereby suppressing the occurrence of torque fluctuations, an increase in exhaust emission, and an increase in fuel consumption rate.

The oxygen concentration detected by the oxygen concentration sensor 26 and the oxygen concentration in the low-pressure EGR gas are different, the oxygen concentration in the air or the carbon dioxide concentration varies, the calculated value of the transport delay time and the actual transport delay There may be a case where an error occurs with respect to time. In such a case, the target opening for adjustment or the transport delay time will deviate from the appropriate value. As a result, although the combustion fluctuation is reduced as compared with the case where the adjustment process is not performed, a slight combustion fluctuation may occur.

  Therefore, in the present embodiment, when combustion fluctuation occurs during the adjustment process, it is determined whether the cause is a shift in the transport delay time Δt or a shift in the target opening for adjustment. The transport delay time Δt or the target opening for adjustment is corrected according to the result.

  Here, as a result of diligent experimentation and verification by the present inventor, combustion fluctuation occurs due to a shift in transport delay time Δt and combustion fluctuation occurs due to a shift in adjustment target opening. We found that the behavior of the state was different.

  FIG. 3 is a diagram illustrating a change in the in-cylinder pressure when the transport delay time Δt is shorter than the appropriate value (when the execution timing of the adjustment process is too early with respect to the appropriate timing). (A), (b), and (c) in FIG. 3 show changes over time in the in-cylinder pressure. For example, FIG. 3A shows the in-cylinder pressure of the cylinder that first reaches the combustion timing after the start of the adjustment process, and FIG. 3B shows the in-cylinder pressure of the cylinder that reaches the second combustion time after the adjustment process starts. 3 (c) shows the in-cylinder pressure of the cylinder that reaches the third combustion timing after the start of the adjustment process. When the in-cylinder pressure sensor 27 is provided in only one cylinder, (a) in FIG. 3 shows the in-cylinder pressure in the first cycle after the start of the adjustment process, and (b) in FIG. The in-cylinder pressure in the second cycle is shown, and (c) in FIG. 3 may be considered to indicate the in-cylinder pressure in the third cycle after the start of the adjustment process. 3 indicates the in-cylinder pressure when the transport delay time Δt is shorter than the appropriate value, and the broken line in FIG. 3 indicates the in-cylinder pressure when the transport delay time Δt is the appropriate value (in-cylinder pressure at normal time). Is shown.

  In FIG. 3, when the transport delay time Δt becomes shorter than the appropriate value, the peak value of the in-cylinder pressure first becomes higher than that at the normal time (see (a) in FIG. 3). Subsequently, the peak value of the in-cylinder pressure becomes lower than that in the normal state (see (b) in FIG. 3). After such a phenomenon occurs alternately, the peak value of the in-cylinder pressure converges to a value equivalent to that during normal operation (see (c) in FIG. 3).

  FIG. 4 is a diagram illustrating a change in the in-cylinder pressure when the transport delay time Δt is longer than the appropriate value (when the execution timing of the adjustment process is too late with respect to the appropriate timing). (A), (b), and (c) in FIG. 4 show changes over time in the in-cylinder pressure as in FIG. 3 described above. 4 indicates the in-cylinder pressure when the transport delay time Δt is longer than the appropriate value, and the broken line in FIG. 4 indicates the in-cylinder pressure when the transport delay time Δt is the appropriate value (in-cylinder pressure at normal time). Is shown.

  In FIG. 4, when the transport delay time Δt becomes longer than the appropriate value, the peak value of the in-cylinder pressure first becomes lower than that at the normal time (see (a) in FIG. 4). Subsequently, the peak value of the in-cylinder pressure becomes higher than that at the normal time (see (b) in FIG. 4). After such a phenomenon occurs alternately, the peak value of the in-cylinder pressure converges to a value equivalent to that during normal operation (see (c) in FIG. 4).

  FIG. 5 is a diagram illustrating a change in the in-cylinder pressure when the adjustment target opening is larger than the appropriate value (when the control amount of the EGR rate is excessive with respect to the appropriate value). (A) and (b) in FIG. 5 show changes over time in the in-cylinder pressure. For example, (a) in FIG. 5 shows the in-cylinder pressure of the cylinder that reaches the combustion timing first after the start of the adjustment process, and (b) in FIG. 5 shows the in-cylinder pressure of the cylinder that reaches the combustion time second after the start of the adjustment process. . When the in-cylinder pressure sensor 27 is provided in only one cylinder, (a) in FIG. 5 shows the in-cylinder pressure in the first cycle after the start of the adjustment process, and (b) in FIG. It may be considered that the in-cylinder pressure in the second cycle is shown. 5 indicates the in-cylinder pressure when the adjustment target opening is larger than the appropriate value, and the broken line in FIG. 5 indicates the in-cylinder pressure when the adjustment target opening is the appropriate value (cylinder at normal time). (Internal pressure).

  In FIG. 5, when the adjustment target opening becomes larger than the appropriate value, the peak value of the in-cylinder pressure becomes lower than normal (see (a) in FIG. 5), and then converges to a value equivalent to that in normal ( (See (b) in FIG. 5).

  FIG. 6 is a diagram illustrating a change in the in-cylinder pressure when the adjustment target opening is smaller than the appropriate value (when the control amount of the EGR rate is too small with respect to the appropriate value). 6 (a) and 6 (b) show changes over time in the in-cylinder pressure as in FIG. 5 described above. 6 indicates the in-cylinder pressure when the adjustment target opening is smaller than the appropriate value, and the broken line in FIG. 6 indicates the in-cylinder pressure when the adjustment target opening is the appropriate value (cylinder at normal time). (Internal pressure).

  In FIG. 6, when the adjustment target opening becomes smaller than the appropriate value, the peak value of the in-cylinder pressure becomes higher than normal (see (a) in FIG. 6), and then converges to a value equivalent to that in normal ( (See (b) in FIG. 6).

  As described above, when the transport delay time Δt deviates from an appropriate value, a phenomenon in which the peak value of the in-cylinder pressure is higher than normal and lower than normal is alternately generated as shown in FIGS. On the other hand, when the target opening for adjustment deviates from the appropriate value, a phenomenon in which the peak value of the in-cylinder pressure is higher than normal or lower than normal as shown in FIGS. appear.

  Therefore, by monitoring the detection signal of the in-cylinder pressure sensor 27, the ECU 20 can determine whether the cause of the combustion fluctuation is a shift in the transport delay time Δt or a shift in the adjustment target opening. Furthermore, when the cause of combustion fluctuation is a shift in the transport delay time Δt, it is possible to determine whether the transport delay time Δt is longer or shorter than an appropriate value. In addition, when the cause of the combustion fluctuation is the deviation of the adjustment target opening, it is possible to determine whether the adjustment target opening is larger or smaller than the appropriate value.

  When the cause of the combustion fluctuation is determined by such a method, the ECU 20 corrects the transport delay time Δt or the adjustment target opening according to the determined factor. The correction amount at that time may be a predetermined fixed value. It is desirable that the fixed value described above is determined such that the corrected peak value does not overshoot or undershoot the normal peak value. Further, the correction amount described above may be a variable value that is increased or decreased in accordance with the difference between the peak value detected by the in-cylinder pressure sensor 27 and the peak value at the normal time. For example, the correction amount may be increased when the difference between the peak value detected by the in-cylinder pressure sensor 27 and the peak value at normal time is large compared to when the difference is small.

  When the transport delay time Δt or the adjustment target opening is corrected by the method described above, it is possible to more reliably suppress the occurrence of combustion fluctuations due to the execution of the addition process. As a result, it is possible to suppress the occurrence of torque fluctuations, an increase in exhaust emission, and an increase in fuel consumption rate.

  Hereinafter, the execution procedure of the adjustment process in the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart showing a control routine executed by the ECU 20 when the adjustment process is performed. This control routine is stored in advance in the ROM or the like of the ECU 20, and is periodically executed by the ECU 20.

  In the control routine of FIG. 7, the ECU 20 first reads various data in S101. For example, the ECU 20 reads the PM collection amount of the particulate filter 24 in addition to the detection signals of the various sensors described above. The amount of collected PM is calculated by a separate routine.

  In S102, the ECU 20 determines whether an execution condition for the addition process is satisfied. For example, the ECU 20 determines that the addition process execution condition is satisfied when the amount of PM trapped by the particulate filter 24 is equal to or greater than a predetermined upper limit value. If a negative determination is made in S102, the ECU 20 once ends the execution of this routine. On the other hand, if a positive determination is made in S102, the ECU 20 proceeds to S103.

  In S103, the ECU 20 determines whether or not the low pressure EGR process is being executed. That is, the ECU 20 determines whether or not the low pressure EGR valve 17 is in an open state. If a negative determination is made in S103, the ECU 20 once ends the execution of this routine. On the other hand, when a positive determination is made in S103, the ECU 20 proceeds to S104.

  In S104, the ECU 20 starts executing the adjustment process. That is, as described in the description of FIG. 2 described above, the ECU 20 calculates the transport delay time Δt and the adjustment target opening, and when the transport delay time Δt has elapsed from the start of the addition process, the low pressure EGR valve 17 The low-pressure EGR valve 17 is controlled so that the opening degree is changed to the adjustment target opening degree. In addition, the control means concerning this invention is implement | achieved when ECU20 performs the process of S104.

  In S105, the ECU 20 starts reading the detection signal of the in-cylinder pressure sensor 27. That is, the ECU 20 starts monitoring the combustion state.

  In S106, the ECU 20 determines whether or not a combustion fluctuation has occurred. For example, the ECU 20 may determine whether or not combustion fluctuation has occurred based on the rotational angular velocity of the crankshaft calculated from the detection signal of the crank position sensor 21, or the in-cylinder pressure from the detection value of the in-cylinder pressure sensor 27. It is also possible to determine whether or not combustion fluctuation has occurred by specifying the peak value of and comparing the specified peak value with the peak value in the previous cycle. Note that the ECU 20 executes the processing of S106, thereby realizing the determination means according to the present invention.

  If a negative determination is made in S106, the ECU 20 once ends the execution of this routine. On the other hand, if a positive determination is made in S106, the ECU 20 proceeds to S107. In S107, the ECU 20 refers to the detection signal of the in-cylinder pressure sensor 27 and determines whether or not the cause of the combustion fluctuation is a shift (timing abnormality) in the transport delay time Δt. As a determination method at that time, the method described in the description of FIGS. 3 to 6 is used. The ECU 20 executes the processing of S107, thereby realizing the determination means according to the present invention.

  If an affirmative determination is made in S107, the ECU 20 proceeds to S108. On the other hand, when a negative determination is made in S107 (when the cause of combustion fluctuation is the deviation of the adjustment target opening), the ECU 20 proceeds to S109.

  In S108, the ECU 20 corrects the transport delay time Δt. At this time, if the detection signal of the in-cylinder pressure sensor 27 shows the behavior as shown in FIG. 3, the ECU 20 corrects the transport delay time Δt by an increased amount. On the other hand, if the detection signal of the in-cylinder pressure sensor 27 shows the behavior as shown in FIG. 4 described above, the ECU 20 corrects the transport delay time Δt by a reduced amount. When the transport delay time Δt is corrected in this way, the combustion fluctuation due to the shift of the transport delay time Δt is eliminated.

In S109, the ECU 20 corrects the adjustment target opening. At that time, if the detection signal of the in-cylinder pressure sensor 27 shows the behavior as shown in FIG.
Correct the target opening for adjustment by decreasing. On the other hand, if the detection signal of the in-cylinder pressure sensor 27 shows the behavior as shown in FIG. 6 described above, the ECU 20 corrects the adjustment target opening by an increase. When the adjustment target opening is corrected in this way, the combustion fluctuation due to the deviation of the adjustment target opening is eliminated.

  It should be noted that the correction means according to the present invention is realized by the ECU 20 executing the processing of S108 or S109.

  As described above, when the ECU 20 executes the control routine of FIG. 7 and the combustion fluctuation caused by the addition process occurs, the cause of the fluctuation is the deviation of the transport delay time Δt or the adjustment target opening degree. It is possible to determine whether or not there is a deviation. Therefore, it becomes possible to correct | amend appropriately the transport delay time (DELTA) t or the adjustment target opening degree, and can suppress a combustion fluctuation | variation more reliably. As a result, occurrence of torque fluctuations, increase in exhaust emission, and increase in fuel consumption rate are avoided.

In the present embodiment, the configuration in which the oxidation catalyst 23 and the particulate filter 24 are disposed in the exhaust passage 6 is described as an example. However, instead of the oxidation catalyst 23 and the particulate filter 24, an occlusion reduction type NO _X catalyst is disposed. May be. In this case, ECU 20 can be determined that the added processing execution conditions when _the NO _X storage amount of storage reduction NO _X catalyst in S102 in the control routine described above is predetermined upper limit amount or more is satisfied Good.

  Further, in the present invention, a method for determining whether the cause of combustion fluctuation is a deviation in the transportation delay time or a deviation in the target opening for adjustment based on the history (behavior) of the detection signal of the in-cylinder pressure sensor 27. As an example, an oxygen concentration sensor is attached to the intake passage 4 or the intake manifold 5 downstream from the connection portion of the low pressure EGR passage 16, and a deviation in transport delay time from the detection signal of the oxygen concentration sensor or a target opening for adjustment The deviation may be determined.

1 Internal combustion engine 2 Cylinder 3 Fuel injection valve 4 Intake passage 5 Intake manifold 6 Exhaust passage 7 Exhaust manifold 8 Turbocharger 8a Compressor 8b Turbine 9 First throttle valve 11 High pressure EGR device 12 High pressure EGR passage 13 High pressure EGR valve 14 High pressure EGR cooler 15 Low pressure EGR device 16 Low pressure EGR passage 17 Low pressure EGR valve 18 Low pressure EGR cooler 19 Second throttle valve 20 ECU
21 Crank position sensor 22 Accelerator position sensor 23 Oxidation catalyst 24 Particulate filter 25 Addition valve 26 Oxygen concentration sensor 27 In-cylinder pressure sensor 40 Intercooler

Claims (4)

An EGR mechanism including an EGR passage for leading a part of the exhaust from the exhaust passage of the internal combustion engine to the intake passage as EGR gas, and an EGR valve for changing a passage cross-sectional area of the EGR passage;
An exhaust purification device disposed in an exhaust passage upstream of a connection portion of the EGR passage;
A supply device for supplying a reducing agent to the exhaust gas purification device;
Control means for performing adjustment processing for adjusting the EGR rate so that the oxygen concentration of the gas sucked into the cylinder does not change before and after the supply of the reducing agent when the reducing agent is supplied from the supply device;
Detecting means for detecting a combustion state in the cylinder when the adjustment process is being performed;
Determination means for determining the occurrence of combustion fluctuations from the detection value of the detection means;
Based on the combustion state history detected by the detection means when the determination means determines that a combustion fluctuation has occurred, the cause of the combustion fluctuation is at the execution timing of the adjustment process or the EGR in the adjustment process A discriminating means for discriminating whether the rate is within a control amount;
Correction means for correcting the execution timing of the adjustment process or the control amount of the EGR rate in the adjustment process according to the determination result of the determination means;
An exhaust purification system for an internal combustion engine comprising: In Claim 1, the said detection means is a cylinder pressure sensor which detects the pressure in a cylinder,
When the phenomenon in which the peak value of the in-cylinder pressure detected by the detecting means repeatedly exceeds the normal value and the phenomenon in which the peak value of the in-cylinder pressure is lower than the normal value repeatedly occurs, the determining means determines that the factor of combustion fluctuation is the execution timing of the adjustment process If the phenomenon that the peak value of the in-cylinder pressure detected by the detecting means is higher or lower than the normal value occurs once, the cause of the combustion fluctuation is in the control amount of the EGR valve in the adjustment process. An exhaust gas purification system for an internal combustion engine that judges   3. The execution timing of the adjustment process according to claim 2, wherein when the phenomenon that the peak value of the in-cylinder pressure detected by the detection means becomes higher than a normal value and the phenomenon that the peak value becomes lower than the normal value occurs is determined, If the phenomenon that the peak value of the in-cylinder pressure detected by the detection means becomes lower than the normal value after the phenomenon that becomes higher than the normal value occurs, the execution timing of the adjustment process is An exhaust purification system for an internal combustion engine that is determined to be too late.   The determination unit according to claim 2, wherein the control amount of the EGR rate in the adjustment process is excessive when a phenomenon in which the peak value of the in-cylinder pressure detected by the detection unit is lower than a normal value occurs once. When the phenomenon that the peak value of the in-cylinder pressure detected by the detecting means is higher than the normal value occurs once, it is determined that the control amount of the EGR rate in the adjustment process is too small. Engine exhaust purification system.

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