JP4511265B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine, and more particularly, to an exhaust system provided with a NOx absorption catalyst.

  When the lean burn operation is performed in which the air-fuel ratio of the air-fuel mixture combusted in the combustion chamber of the internal combustion engine is set to be leaner than the stoichiometric air-fuel ratio, the NOx emission tends to increase. Therefore, a technique for providing a NOx absorption catalyst in the exhaust system of the engine to reduce the NOx emission amount has been conventionally known. In an engine having an NOx absorption catalyst in the exhaust system, when only lean burn operation is continued for a long time, the amount of NOx absorbed by the NOx absorption catalyst is saturated. Therefore, in order to reduce the NOx absorbed by the NOx absorption catalyst, it is necessary to reduce the absorbed NOx by setting the exhaust to a reducing atmosphere.

  Patent Document 1 discloses a method of supplying fuel to an engine by dividing the fuel into a main injection and a sub-injection (also referred to as post-injection) as a method of making the exhaust atmosphere a reducing atmosphere. In order to suppress torque fluctuation due to post injection, the apparatus disclosed in Patent Document 1 retards the execution timing of main injection.

  Further, in Patent Document 2, in order to make the exhaust atmosphere into a reducing atmosphere, the amount of intake air is increased by increasing the amount of fuel supplied to the engine without performing post injection and closing the intake control valve of the engine to a certain opening degree. And a method for recirculating exhaust gas to the intake system.

JP 2001-248471 A Japanese Patent No. 2845103

  However, since the post injection is performed in the expansion stroke or the exhaust stroke, there is a problem that the injected fuel leaks from the combustion chamber and the lubricating oil is easily diluted. Therefore, it is desired to reduce the frequency of the post injection for making the exhaust gas into a reducing atmosphere as much as possible.

  Further, in the method disclosed in Patent Document 2, there are cases where the torque fluctuation tends to increase or the particulate matter discharge amount tends to increase in order to ensure combustion stability.

  The present invention has been made paying attention to this point, and appropriately performs post-injection to minimize dilution of lubricating oil and to suppress torque fluctuation or increase in particulate matter discharge. It is an object of the present invention to provide an exhaust emission control device that can perform such a process.

In order to achieve the above object, an invention according to claim 1 is provided in an exhaust system (4) of an internal combustion engine (1), absorbs NOx in the exhaust when the exhaust is in an oxidizing atmosphere, and the exhaust is brought into a reducing atmosphere. In an exhaust gas purification apparatus for an internal combustion engine comprising a NOx absorption catalyst (16) for reducing NOx absorbed at a certain time, NOx or SOx absorbed by the NOx absorption catalyst (16) is reduced to regenerate the NOx absorption catalyst. A regeneration time determining means (S50) for determining the regeneration time to be performed, an operating state detecting means (26, 27) for detecting the operating state of the engine, and an operating state detected by the operating state detecting means at the regeneration time is but when a predetermined low-load operating state or a predetermined high load operating condition, the exhaust by the post injection is changed to a reducing atmosphere, wherein the detected operating condition the predetermined low load luck When the state and a driving state other than the predetermined high load operating condition, the fuel injection quantity control means for controlling not to perform post injection (S72, S75, S76) and provided with, for detecting a combustion variation of the engine combustion Fluctuation detecting means (27, S74), and the fuel injection control means executes the post injection according to the detected combustion fluctuation when the detected operating state is the predetermined low load operating state. It is characterized by that.

According to a second aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, the exhaust system is provided with a particulate matter filter (11) for collecting particulate matter in the exhaust, The fuel injection control means executes the post injection according to a temperature (TDPF) of the particulate matter filter when the detected operation state is the predetermined high load operation state.

According to the first aspect of the present invention, when the engine operation state is the predetermined low load operation state or the predetermined high load operation state at the regeneration time for performing the regeneration treatment of the NOx absorption catalyst, the exhaust gas is reduced by post-injection. When the engine operating state is an operating state other than the predetermined low load operating state and the predetermined high load operating state, the post injection is controlled not to be executed. By executing the post injection in the low load operation state of the engine, the torque fluctuation can be reduced as compared with the case where the post injection is not executed. Further, by executing the post injection in a predetermined high load operation state of the engine, it is possible to reduce the discharge amount of the particulate matter as compared with the case where the post injection is not executed. Furthermore, diluting the lubricating oil can be suppressed by not performing the post-injection except in the predetermined low load operation state and the predetermined high load operation state. Further, when engine combustion fluctuations are detected and the engine operating state is a predetermined low load operating state, post injection is performed in accordance with the detected combustion fluctuations. By increasing the post injection amount, the combustion fluctuation can be effectively suppressed.

According to the second aspect of the present invention, when the engine operating state is the predetermined high load operating state, the post injection is executed according to the temperature of the particulate matter filter provided in the exhaust system. When the temperature of the particulate matter filter is high enough to combust the particulate matter deposited on the particulate matter filter, even if the amount of particulate matter in the exhaust gas increases slightly, the amount of particulate matter deposited Will not increase. Therefore, oil dilution can be more effectively suppressed by decreasing the post-injection amount as the temperature of the particulate matter filter becomes higher in the predetermined high-load operation state.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing an overall configuration of an internal combustion engine (hereinafter referred to as “engine”) and a control device thereof according to an embodiment of the present invention. The engine 1 is a diesel engine that directly injects fuel into a cylinder, and a fuel injection valve 12 is provided in each cylinder. The fuel injection valve 12 is electrically connected to an electronic control unit (hereinafter referred to as “ECU”) 20, and the valve opening timing and valve opening time of the fuel injection valve 12 are controlled by the ECU 20.

  The engine 1 includes an intake pipe 2, an exhaust pipe 4, and a turbocharger 8. The turbocharger 8 includes a turbine 10 driven by exhaust kinetic energy, and a compressor 9 that is rotationally driven by the turbine 10 and compresses intake air.

  The turbine 10 includes a plurality of variable vanes (not shown), and the turbine rotational speed (rotational speed) can be changed by changing the opening of the variable vane (hereinafter referred to as “vane opening”). It is configured. The vane opening degree of the turbine 10 is electromagnetically controlled by the ECU 20. More specifically, the ECU 20 supplies a control signal with a variable duty ratio to the turbine 10 to control the vane opening. Increasing the vane opening improves the efficiency of the turbine 10 and increases the turbine speed. As a result, the supercharging pressure increases.

  A throttle valve 13 for controlling the intake air amount is provided in the intake pipe 2 downstream of the compressor 9. The throttle valve 13 is driven by an actuator 14, and the actuator 14 is connected to the ECU 20. The opening degree TH of the throttle valve 13 is controlled by the ECU 20.

The intake pipe 2 is branched corresponding to each cylinder on the downstream side of the throttle valve 13, and each of the branched intake pipes 2 is branched into two intake ports 2A and 2B. FIG. 1 shows only the configuration corresponding to one cylinder.
Each cylinder of the engine 1 is provided with two intake valves (not shown) and two exhaust valves (not shown). An intake port (not shown) that is opened and closed by two intake valves is connected to each of the intake ports 2A and 2B.

  In addition, a swirl control valve (hereinafter referred to as “SCV”) 15 that generates a swirl in the combustion chamber of the engine 1 by limiting the amount of air sucked through the intake port 2B is provided in the intake port 2B. Yes. SCV15 is a butterfly valve driven by an electric motor (not shown), and the valve opening degree is controlled by ECU20.

  Between the exhaust pipe 4 and the downstream side of the throttle valve 13 of the intake pipe 2, an exhaust recirculation passage 5 for returning the exhaust gas to the intake pipe 2 is provided. The exhaust gas recirculation passage 5 is provided with an exhaust gas recirculation control valve (hereinafter referred to as “EGR valve”) 6 for controlling the exhaust gas recirculation amount. The EGR valve 6 is an electromagnetic valve having a solenoid, and the valve opening degree is controlled by the ECU 20. The EGR valve 6 is provided with a lift sensor 7 for detecting the valve opening degree (valve lift amount) LACT, and the detection signal is supplied to the ECU 20. An exhaust gas recirculation mechanism is configured by the exhaust gas recirculation passage 5 and the EGR valve 6. The EGR valve 6 is controlled by a control signal having a variable duty ratio so that the valve opening degree LACT coincides with the valve opening degree command value LCMD set according to the engine operating state.

  The intake pipe 2 includes an intake air amount sensor 21 that detects an intake air amount GAIR (an amount of air sucked into the engine 1 per unit time), and a supercharging pressure sensor 22 that detects a supercharging pressure BPA downstream of the compressor 9. These detection signals are supplied to the ECU 20.

  A particulate matter filter (hereinafter referred to as “DPF”) 11 and a NOx purification device 16 are provided downstream of the turbine 10 in the exhaust pipe 4. The DPF 11 collects soot, which is a particulate material whose main component is carbon contained in the exhaust gas. The NOx purification device 16 contains a NOx absorbent that absorbs NOx and a catalyst (NOx absorption catalyst) for promoting oxidation and reduction. The DPF 11 is provided with a DPF temperature sensor 25 that detects the temperature TDPF of the DPF 11, and the detection signal is supplied to the ECU 20.

  The NOx purifying device 16 (exhaust gas) in an exhaust lean state in which the fuel injection amount is set to be smaller than the intake air amount, the oxygen concentration in the exhaust gas is relatively high, and the reducing agent (HC and CO) concentration is lower than the oxygen concentration. NOx is absorbed while the fuel injection amount is set to be larger than the intake air amount, the oxygen concentration in the exhaust gas is relatively low, and the reducing agent concentration is higher than the oxygen concentration. In the state (when the exhaust is in a reducing atmosphere), the absorbed NOx is reduced by a reducing agent and discharged as nitrogen gas, water vapor and carbon dioxide.

  NOx is absorbed to the limit of NOx absorption capacity of the NOx absorbent, that is, up to the maximum NOx absorption amount, and no more NOx can be absorbed. ). The enrichment of the air-fuel ratio is performed by increasing the amount of fuel injected from the fuel injection valve 12 and decreasing the intake amount mainly by the throttle valve 13. In this embodiment, the adjustment of the intake air amount when enriching the air-fuel ratio is performed by using not only the throttle valve 13 but also the opening degree of the EGR valve 6, the supercharging pressure control, and the SCV 15 control.

  An upstream side of the DPF 11 is provided with a proportional air-fuel ratio sensor (hereinafter referred to as “LAF sensor”) 23 and an exhaust pressure sensor 24 for detecting the exhaust pressure PEX. The LAF sensor 23 supplies a detection signal to the ECU 20 that is substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas. The exhaust pressure sensor 24 supplies a detection signal indicating the exhaust pressure PEX to the ECU 20.

  Further, an accelerator sensor 26 for detecting an operation amount (hereinafter referred to as “accelerator pedal operation amount”) AP of an accelerator pedal (not shown) of a vehicle driven by the engine 1 and rotation of a crankshaft (not shown) of the engine 1. A crank angle position sensor 27 for detecting the angle is provided. Detection signals from these sensors are supplied to the ECU 20.

  The crank angle position sensor 27 is a cylinder discrimination sensor that outputs a pulse (hereinafter referred to as “CYL pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1, and relates to a top dead center (TDC) at the start of the intake stroke of each cylinder. A TDC sensor that outputs a TDC pulse at a crank angle position before a predetermined crank angle (every crank angle of 180 degrees in a four-cylinder engine), and a CRK that generates a CRK pulse at a constant crank angle period shorter than the TDC pulse (for example, a 30 degree period) It consists of sensors, and a CYL pulse, a TDC pulse, and a CRK pulse are supplied to the ECU 20. These pulses are used for fuel injection control and detection of engine speed (engine speed) NE.

  The ECU 20 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, a central processing unit (hereinafter referred to as “CPU”). A storage circuit for storing various calculation programs executed by the CPU, calculation results, and the like, an output circuit for supplying control signals to the fuel injection valve 12, the EGR valve 6, the turbine 10, the actuator 14, and the like.

The engine 1 is normally operated with the air-fuel ratio set to a leaner side than the stoichiometric air-fuel ratio, and when performing the regeneration processing of the NOx absorption catalyst, the fuel injection amount is increased and the intake air amount is decreased.
Intake control in the regeneration process of the NOx absorption catalyst is performed as follows in accordance with the engine operating state. As shown in FIG. 2, the engine operation region is divided into a first operation region to a fourth operation region in order from the low load side according to the engine speed NE and the engine load, and in the first and second operation regions, SCV15 The opening of the throttle valve 13 is throttled to a medium level, the opening of the EGR valve 6 is relatively increased, and the supercharging pressure is set in the same manner as during normal operation. In the third and fourth operation regions, the opening of the SCV 15 is made relatively small, the opening of the throttle valve 13 is throttled close to the fully closed state, the opening of the EGR valve 6 is almost zero, and the supercharging pressure is compared. Make it bigger.

  The fuel injection control is generally performed as follows. In the second and third operation regions, the pilot injection amount and the main injection amount are increased from those during normal operation, and post injection is not executed. In the first and fourth operation regions, post injection is executed, and a part of the increase in the main injection amount is supplied by post injection.

  FIG. 3A is a diagram showing the relationship between the engine output torque TRQOUT and the particulate matter discharge amount Qsoot when the engine speed NE is relatively high when post injection is not executed. As is apparent from this figure, when the output torque (load) TRQOUT of the engine exceeds the first threshold value TRQ1, the particulate matter discharge amount Qsoot greatly increases. Therefore, in a high load operation region where the output torque TRQOUT exceeds the first threshold value TRQ1, it is desirable to reduce the main injection amount by executing post injection. Therefore, in the present embodiment, post injection is executed in the fourth operating region on the highest load side, and the particulate matter discharge amount Qsoot is reduced.

FIG. 3B is a diagram showing the relationship between the output torque TRQOUT and the Pmi fluctuation rate RDPmi indicating combustion fluctuation (combustion instability) when post injection is not executed. The horizontal axis in this figure is an enlarged view of the low load region LR shown in FIG. In the low load region, when the output torque TRQOUT becomes smaller than the second threshold value TRQ2, the Pmi fluctuation rate RDPmi greatly increases. Therefore, in the low load operation region where the output torque TRQOUT is lower than the second threshold value TRQ2, it is desirable to reduce the main injection amount by executing post injection. Therefore, in the present embodiment, post injection is executed in the first operating region on the lowest load side to suppress combustion fluctuations (instability of combustion).
As described above, by limiting the operation region in which the post injection is performed to the first and fourth operation regions, it is possible to reduce the fuel injection amount by the post injection and suppress the dilution of the lubricating oil.

  4 and 5 are flowcharts of a process for controlling the intake air amount of the engine 1. This process is executed by the CPU of the ECU 20 in synchronization with the TDC pulse.

  Steps S10 to S17 in FIG. 4 correspond to supercharging pressure control (VNT control) for controlling the vane opening of the turbine 10, and steps S21 to S27 are exhaust gas recirculation control (EGR control) for controlling the opening of the EGR valve 6. ), Steps S31 to S38 in FIG. 5 correspond to throttle valve opening control (DBW control) for controlling the opening of the throttle valve 13, and steps S41 to S45 are SCV opening for controlling the opening of the SCV15. This corresponds to control (SCV control).

  In step S10, a deviation ΔBPA (= BPA−BPCMD) between the detected boost pressure BPA and the target boost pressure BPCMD is calculated. The target boost pressure BPCMD is calculated by searching a map set in accordance with the accelerator pedal operation amount AP and the engine speed NE. In step S11, a correction coefficient KBPA is calculated according to the deviation ΔBPA. The correction coefficient KBPA is set to a smaller value as the deviation ΔBPA increases.

  In step S12, it is determined whether or not the enrichment flag FRSP is “1”. The enrichment flag FRSP is a flag set in the process of FIG. 6 described later, and is set to “1” when performing the air-fuel ratio enrichment (regeneration process) for reducing NOx absorbed by the NOx absorption catalyst. The When FRSP = 0 and normal operation is being performed, the first vane opening map value VNTMAP1 is calculated according to the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE (step S13). ), The vane opening basic value VNTMAP is set to the first vane opening map value VNTMAP1 (step S14). Thereafter, the process proceeds to step S17. Thereby, the vane opening basic value VNTMAP is set to a value suitable for normal operation.

  In step S12, when FRSP = 1 and the air-fuel ratio enrichment operation is being performed, the second vane opening map value is determined according to the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE. VNTMAP2 is calculated (step S15), and the vane opening basic value VNTMAP is set to the second vane opening map value VNTMAP2 (step S16). Thereafter, the process proceeds to step S17. The second vane opening degree map value VNTMAP2 is set to a value smaller than the first vane opening degree map value VNTMAP1 (a value for reducing the supercharging pressure) in the same engine operating state. Thereby, the vane opening basic value VNTMAP is set to a value suitable for the air-fuel ratio enrichment operation.

In step S17, the vane opening command value VNTCMD is calculated by multiplying the vane opening basic value VNTMAP by the correction coefficient KBPA.
The vane opening of the turbine 10 is controlled so as to coincide with the vane opening command value VNTCMD.

  In step S21, it is determined whether or not the enrichment flag FRSP is “1” as in step S12. When FRSP = 0, the first control gain GEGR1 of EGR control is calculated according to the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE (step S23), and the control gain GEGR is calculated. The first control gain GEGR1 is set (step S24). Thereafter, the process proceeds to step S27. Thereby, the control gain GEGR for EGR control is set to a value suitable for normal operation.

  If FRSP = 1 in step S21, it is determined whether or not the detected intake air amount GAIR has converged to the target intake air amount GACMD (step S22). Specifically, it is determined whether or not the absolute value of the deviation ΔGAIR between the intake air amount GAIR and the target intake air amount GACMD is equal to or smaller than the convergence determination threshold value ΔGATH. If the answer to step S22 is affirmative (YES), the process proceeds to step S23. If the answer is negative (NO), the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE are selected. Then, the second control gain GEGR2 for EGR control is calculated (step S25), and the control gain GEGR is set to the second control gain GEGR2 (step S26). Thereafter, the process proceeds to step S27. The second control gain GEGR2 is set to a value larger than the first control gain GEGR1 in the same operating state. Thereby, the control gain GEGR of EGR control is set to a value suitable for the air-fuel ratio enrichment operation.

  In step S27, the valve opening command value LCMD of the EGR valve 6 is set according to the intake air amount GAIR, and the EGR valve 6 is controlled so that the actual valve opening LACT coincides with the valve opening command value LCMD. . The control gain GEGR set in steps S23 to S26 is applied as the control gain of this feedback control.

  In step S31 of FIG. 5, it is determined whether or not the enrichment flag FRSP is “1”. When FRSP = 0, the target opening degree THCMD of the throttle valve 13 is set to the full opening degree THMAX (step S32). When FRSP = 1, the target opening degree map value THMAP for the air-fuel ratio enrichment operation is calculated according to the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE. The target opening degree map value THMAP is set to a value smaller than the fully opened opening degree.

  In step S34, as in step S22, it is determined whether or not the intake air amount GAIR has converged to the target intake air amount GACMD. When the answer to step S34 is negative (NO), the difference ΔBPA (= BPA−BPCMD) between the detected boost pressure BPA and the target boost pressure BPCMD is calculated (step S10), similarly to step S10. S35).

In step S36, a correction amount ΔTH1 is calculated according to the deviation ΔBPA. The correction amount ΔTH1 is calculated by searching a ΔTH1 map set in advance according to the deviation ΔBPA and the intake air amount GAIR, or by the following equation (1). That is, the correction amount ΔTH1 is set to a larger value as the deviation ΔBPA increases and the intake air amount GAIR increases.
ΔTH1 = Kth × ΔBPA × GAIR (1)
Here, Kth is a flow rate correction coefficient determined by the shape of the throttle valve 13.

  In step S37, the target opening degree THCMD is calculated by subtracting the correction amount ΔTH1 from the target opening degree map value THMAP. That is, when the air-fuel ratio enrichment operation is performed, the target opening degree THCMD corrects the target opening degree map value THMAP in a decreasing direction by the correction amount ΔTH1 within a period until the intake air amount GAIR converges to the target intake air amount GACMD. Is set to the specified value.

If the answer to step S34 is affirmative (YES) and the intake air amount GAIR converges to the target intake air amount GACMD, the target opening degree THCMD is calculated by the following equation (2) (step S38).
THCMD = (1−α) × THCMD (n−1) + α × THMAP (2)
Here, α is a predetermined coefficient set to a value between 0 and 1, and THCMD (n−1) is a previously calculated value of the target opening.

From equation (2), the target opening THCMD is set so as to gradually approach the target opening map value THMAP.
The opening TH of the throttle valve 13 is controlled so as to coincide with the target opening THCMD.

  In step S41, it is determined whether or not the enrichment flag FRSP is “1”. When FRSP = 0, the first target SCV opening map value SCVMAP1 is calculated according to the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE (step S42), and the target SCV opening is calculated. The degree SCVCMD is set to the first target SCV opening map value SCVMAP1 (step S43). Thereby, the target SCV opening SCVCMD is set to a value suitable for normal operation.

If FRSP = 1 in step S41, a second target SCV opening map value SCVMAP2 is calculated according to the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE (step S44). Then, the target SCV opening SCVCMD is set to the second target SCV opening map value SCVMAP2 (step S45). The second target SCV opening map value SCVMAP2 is set to a value smaller than the first target SCV opening map value SCVMAP1 in the same engine operating state. Thereby, the target SCV opening SCVCMD is set to a value suitable for the air-fuel ratio enrichment operation.
The opening degree of the SCV 15 is controlled so as to coincide with the target SCV opening degree SCVCMD.

  6 and 7 are flowcharts of processing for controlling the fuel injection amount and fuel injection timing by the fuel injection valve 12. This process is executed by the CPU of the ECU 20 in synchronization with the TDC pulse.

  In step S50 of FIG. 6, the timing for performing air-fuel ratio enrichment (NOx absorption catalyst regeneration processing) for reducing NOx absorbed by the NOx purification device 16 is determined. Specifically, first, the NOx emission amount DQNOx per unit time is calculated according to the accelerator pedal operation amount AP and the engine speed NE, and further the integrated value QNOx of the NOx emission amount DQNOx is calculated. When the integrated value QNOx reaches the determination threshold value QNOxTH, the enrichment flag FRSP is set to “1”. The enrichment flag FRSP is returned to “0” when the regeneration process of the NOx absorption catalyst is completed.

Steps S51 to S55 in FIG. 6 correspond to pilot injection control, steps S61 to S65 correspond to main injection control, and FIG. 7 corresponds to post injection control.
In step S51, it is determined whether or not the enrichment flag FRSP is “1”.

  When FRSP = 0 and normal operation is being performed in step S51, the first pilot injection amount Qpilot1 and the first pilot injection are determined according to the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE. Time CApilot1 is calculated (step S52). Next, the pilot injection amount Qpilot is set to the first pilot injection amount Qpilot1, and the pilot injection timing CApilot is set to the first pilot injection timing CApilot1 (step S53). Thereby, the pilot injection amount Qpilot and the pilot injection timing CApilot are set to values suitable for normal operation.

  When FRSP = 1 and the regeneration processing of the NOx absorption catalyst is performed in step S51, the second pilot injection amount Qpilot2 and the second pilot injection amount Qpilot2 are determined according to the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE. 2 Pilot injection timing CApilot2 is calculated (step S54). Next, the pilot injection amount Qpilot is set to the second pilot injection amount Qpilot2, and the pilot injection timing CApilot is set to the second pilot injection timing CApilot2 (step S55). Thereby, pilot injection amount Qpilot and pilot injection timing CApilot are set to values suitable for the regeneration process. When compared in the same engine operating state, during low load operation, the second pilot injection amount Qpilot2 is set to a value larger than the first pilot injection amount Qpilot1, and the second pilot injection timing CApilot2 is set to the first pilot injection timing CApilot1. Set to the more advanced side. Note that pilot injection is not performed during high-load operation.

  In step S61, the same determination as in step S51 is performed. When FRSP = 0 and normal operation is being performed, the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE are One main injection amount Qmain1 and first main injection timing CAmain1 are calculated (step S62). Next, the main injection amount Qmain is set to the first main injection amount Qmain1, and the main injection timing CAmain is set to the first main injection timing CAmain1 (step S63). Thereby, the main injection amount Qmain and the main injection timing CAmain are set to values suitable for normal operation.

  When FRSP = 1 and the regeneration process of the NOx absorption catalyst is performed in step S61, the second main injection amount Qmain2 and the second main injection amount Qmain2 and the engine speed NE according to the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE. 2 The main injection timing CAmain2 is calculated (step S64). Next, the main injection amount Qmain is set to the second main injection amount Qmain2, and the main injection timing CAmain is set to the second main injection timing CAmain2 (step S65). Thereby, the main fuel injection amount Qmain and the main injection timing CAmain are set to values suitable for the regeneration process. When compared in the same engine operating state, the second main injection amount Qmain2 is set to a value larger than the first main injection amount Qmain1, and the second main injection timing CAmain2 is set to an advance side from the first main injection timing CAmain1. Is done.

In step S71 of FIG. 7, the same determination as in step S51 is performed, and when FRSP = 0 and normal operation is being performed, this processing is immediately output. That is, post injection is not performed.
When the regeneration processing of the NOx absorption catalyst is performed with FRSP = 1, the post injection amount Qpost and the post injection timing CApost are calculated according to the engine operating state, specifically, the accelerator pedal operation amount AP and the engine speed NE. (Step S72). In step S73, it is determined whether or not the engine operating state is in a predetermined low load region, that is, the first operating region shown in FIG. If the answer is affirmative (YES), a rotation fluctuation parameter METRM indicating engine rotation fluctuation is calculated (step S74). Specifically, the rotational fluctuation parameter METRM is calculated by calculating the moving average value MSME of the CRK pulse generation time interval CRME output at every crank angle of 30 ° and applying this to the following equation (3). The
METRM = | MSME (n) −MSME (n−1) | / KMSLB
(3)
Here, (n) and (n-1) are given to indicate the current value and the previous value, respectively, and KMSLB is a coefficient set so as to be inversely proportional to the engine speed NE.

  In step S75, the combustion stability correction coefficient αpost is calculated according to the rotation fluctuation parameter METRM calculated in step S74. Specifically, the rotation fluctuation parameter METRM is compared with predetermined threshold values METRMX1 and METRMX2 (<METRMX1), and when METRM> METRMX1, the combustion stability correction coefficient αpost is increased by a predetermined amount Dα, and METRM <METRMX2. At this time, the combustion stability correction coefficient αpost is decreased by a predetermined amount Dα. However, the limit process is performed so that the combustion stability correction coefficient αpost is 0 or more and 1 or less. As a result, the combustion stability correction coefficient αpost is set to a larger value as the engine rotational fluctuation increases, in other words, the combustion becomes unstable.

In step S76, the post injection amount Qpost calculated in step S72 is corrected by the following equation (4), and the main injection amount Qmain is decreased by the post injection amount Qpost by the following equation (5).
Qpost = αpost × Qpost (4)
Qmain = Qmain−Qpost (5)
By correcting the post injection amount Qpost with the combustion stability correction coefficient αpost, the post injection amount Qpost is increased and the main injection amount Qmain is decreased as the combustion becomes unstable. Thereby, instability of combustion can be suppressed in a predetermined low load region.

  If it is determined in step S73 that the engine operating state is not in the predetermined low load region, it is determined whether or not the engine is in the predetermined high load region, that is, the fourth operating region shown in FIG. 2 (step S77). If this answer is affirmative (YES), the βpost table shown in FIG. 8 is searched according to the detected DPF temperature TDPF to calculate the DPF continuous regeneration coefficient βpost (step S78). The βpost table is set so that the DPF continuous regeneration coefficient βpost decreases as the DPF temperature TDPF increases. However, when the DPF temperature TDPF is equal to or lower than the first predetermined temperature T1 (for example, 250 ° C.), the DPF continuous regeneration coefficient βpost is set to “1.0” and is equal to or higher than the second predetermined temperature T2 (for example, 400 ° C.). If there is, it is set to a predetermined value close to “0”. When the DPF temperature TDPF is equal to or higher than the second predetermined temperature T2, the particulate matter deposited on the DPF 11 burns continuously, so there is no need to consider an increase in the amount of particulate matter deposited, and the post injection amount is minimum. The limit is enough. When the DPF temperature TDPF is lower than the second predetermined temperature, the particulate matter does not burn continuously, so the DPF continuous regeneration coefficient βpost is set to increase as the DPF temperature TDPF decreases. Thereby, the discharge | emission amount of the particulate matter in a predetermined high load area | region can be suppressed effectively.

In step S79, the post injection amount Qpost is corrected by the following equation (6), and the main injection amount Qmain is corrected by the equation (5).
Qpost = βpost × Qpost (6)
When the engine operating state is not in the predetermined high load region in step S77, the post injection amount Qpost is set to “0” (step S80), and this process is terminated. Therefore, when the engine operating state is not in either the predetermined low load region or the predetermined high load region, that is, in the second and third operating regions of FIG. 2, post injection is not executed.

  As described above, in the present embodiment, the operating region in which the post injection is performed is limited to the minimum range, so that dilution of the lubricating oil due to the post injection can be suppressed. Further, by performing post injection in the first operation region, combustion fluctuations (instability of combustion) can be suppressed, and by performing post injection in the fourth operation region, particulate matter emission is suppressed. can do.

  In the present embodiment, the accelerator sensor 26 and the crank angle position sensor 27 correspond to the operating state detection means, and the crank angle position sensor 27 constitutes a part of the combustion fluctuation detection means. Further, the ECU 20 constitutes a part of a regeneration timing determination unit, a fuel injection amount control unit, and a combustion fluctuation detection unit. Specifically, step S50 in FIG. 6 corresponds to the regeneration timing determination means, steps S72, S73, S75 to S80 in FIG. 7 correspond to the fuel injection amount control means, and step S74 in FIG. Corresponds to a part of

  The present invention is not limited to the embodiment described above, and various modifications can be made. For example, in the above-described embodiment, the combustion stability correction coefficient αpost is calculated according to the rotational fluctuation parameter METRM indicating the rotational fluctuation of the engine 1, but the in-cylinder pressure for detecting the pressure (in-cylinder pressure) PCYL in the combustion chamber. A sensor may be provided in at least one cylinder, the indicated mean effective pressure Pmi and its fluctuation rate RDPmi may be calculated from the detected in-cylinder pressure PCYL, and the combustion stability correction coefficient αpost may be set according to the Pmi fluctuation rate RDPmi. . In this case, the combustion stability correction coefficient αpost is set so as to increase as the Pmi fluctuation rate RDPmi increases. The Pmi fluctuation rate RDPmi is calculated by dividing the standard deviation of the indicated mean effective pressure detection data of a predetermined number of samples by the average value.

  In the above-described embodiment, the example in which the present invention is applied in the case of performing the air-fuel ratio enrichment operation to reduce the NOx absorbed by the NOx absorption catalyst has been shown. For example, the NOx absorption catalyst is so-called sulfur poisoned. In some cases, the present invention may be applied when performing an air-fuel ratio enrichment operation (a regeneration process of the NOx absorption catalyst) in order to remove SOx. In this case, the execution time of the reproduction process is determined as follows, for example. The accumulated value TOPACC of the operation time of the engine 1 (reset to “0” when the regeneration process is executed) reaches the predetermined accumulated operation time TOPACTH, or the travel distance DRACC of the vehicle driven by the engine 1 (regeneration process) Is reset to “0” when the operation has been executed) reaches the predetermined travel distance DRACTH as the execution timing of the regeneration process.

In the above-described embodiment, the post injection is executed in both the first operation region and the fourth operation region shown in FIG. 2, but the post injection may be executed only in one of them.
The present invention can also be applied as an exhaust purification device for a marine vessel propulsion engine such as an outboard motor having a vertical crankshaft.

It is a figure which shows the structure of the internal combustion engine and its control apparatus concerning one Embodiment of this invention. It is a figure which shows the engine operation area | region according to engine speed (NE) and engine load. It is a figure which shows the relationship between engine output torque (TRQOUT), particulate matter discharge | emission amount (Qsoot), and Pmi fluctuation rate (RDPmi). It is a flowchart of an intake control process. It is a flowchart of an intake control process. It is a flowchart of a fuel injection control process. It is a flowchart of a fuel injection control process. It is a figure which shows the table referred by the process of FIG.

Explanation of symbols

1 Internal combustion engine 12 Fuel injection valve 20 Electronic control unit (regeneration timing determination means, combustion fluctuation detection means, fuel injection amount control means)
26 Accelerator sensor (operating state detection means)
27 Crank angle position sensor (operating state detecting means, combustion fluctuation detecting means)

Claims (2)

In an exhaust gas purification apparatus for an internal combustion engine, which is provided in an exhaust system of an internal combustion engine and includes a NOx absorption catalyst that absorbs NOx in the exhaust when the exhaust is in an oxidizing atmosphere and reduces the absorbed NOx when the exhaust is in a reducing atmosphere.
Regeneration timing determining means for determining the regeneration timing for performing the regeneration treatment of the NOx absorption catalyst by reducing NOx or SOx absorbed by the NOx absorption catalyst;
Operating state detecting means for detecting the operating state of the engine;
When the operation state detected by the operation state detection means is a predetermined low load operation state or a predetermined high load operation state at the regeneration time, the exhaust is changed to a reducing atmosphere by post injection, and the detected operation state Is a fuel injection amount control means for controlling so as not to perform post-injection when the operation state is other than the predetermined low load operation state and the predetermined high load operation state ,
Combustion fluctuation detecting means for detecting combustion fluctuation of the engine,
It said fuel injection control means, wherein when the detected operating state is the predetermined low-load operating condition, the exhaust gas purifying apparatus for an internal combustion engine, characterized that you perform the post injection in accordance with the detected combustion variation . The exhaust system is provided with a particulate matter filter that collects particulate matter in the exhaust, and the fuel injection control means is configured such that when the detected operating state is the predetermined high-load operating state, The exhaust purification device for an internal combustion engine according to claim 1, wherein the post-injection is executed in accordance with a temperature of the particulate matter filter.

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