JP4597876B2 - 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 apparatus equipped with a DPF (diesel particulate filter) that captures soot (particulate matter) in exhaust gas and a NOx trap that collects NOx.

  Patent Document 1 discloses an exhaust emission control device including a DPF and a NOx trap provided in an exhaust system of an internal combustion engine. In this apparatus, when the regeneration process for burning the soot accumulated in the DPF is necessary, when the NOx amount captured by the NOx trap reaches a predetermined amount, the NOx reduction process is performed. When the trapped NOx amount does not reach the predetermined amount, the DPF regeneration process is executed if the engine operating state is in a reproducible region where the DPF regeneration process is possible.

JP 2005-48747 A

  In the above-described conventional apparatus, when the DPF regeneration process is started, it is not determined whether or not the engine operating state is in the reproducible region, and the DPF regeneration process is performed continuously for a predetermined time. For this reason, the NOx amount trapped in the NOx trap during the DPF regeneration process may exceed a predetermined amount and the NOx emission amount may increase.

  The present invention has been made paying attention to this point, and appropriately executes the regeneration process of the DPF and the NOx reduction process of the NOx trap, maintains both the DPF and the NOx trap in a good state, and discharges soot and NOx. An object of the present invention is to provide an exhaust emission control device that can prevent the amount from increasing.

  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), and a particulate filter (17) for collecting soot in the exhaust, and the exhaust system ( 4) Exhaust gas of an internal combustion engine provided with a NOx trap (18) for collecting NOx in the exhaust, and filter regeneration means for performing filter regeneration for burning soot accumulated on the particulate filter (17) In the purifying device, an operation state determination unit that determines whether or not the operation state of the engine is in a filter regeneration difficulty region (R3) during filter regeneration by the filter regeneration unit, and an operation state of the engine is the filter regeneration difficulty. And NOx trap regeneration means for controlling the exhaust gas flowing into the NOx trap (18) to a reducing atmosphere when it is determined that the region (R3) is present. And features.

  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 post-injection in which the filter regeneration means supplies fuel into the cylinder of the engine in an expansion stroke or an exhaust stroke of the cylinder. The NOx trap regeneration means controls the exhaust gas to a reducing atmosphere by the post injection.

  According to the first aspect of the present invention, when it is determined that the engine operating state is in the filter regeneration difficult region during regeneration of the particulate filter, the exhaust gas flowing into the NOx trap is controlled to the reducing atmosphere. The NOx trapped in the NOx trap can be reduced, and the amount of NOx trapped in the NOx trap can be prevented from exceeding the trapping ability of the NOx trap and the NOx emission amount increasing. In addition, since the particulate filter regeneration process cannot be executed in the filter regeneration difficult region, the NOx reduction process does not delay the particulate filter regeneration process. When the engine operating state returns to the filter regeneration possible region, the filter regeneration process is executed again. Therefore, the filter regeneration process and the NOx reduction process can be efficiently executed, and both the particulate filter and the NOx trap can be maintained in a good state.

  According to the second aspect of the present invention, when the filter regeneration process is executed by the post injection, when the engine operating state shifts to the filter regeneration difficult region, the exhaust is controlled to the reducing atmosphere by the post injection. . Therefore, changes in the engine operating parameters are reduced, and the engine regeneration state can be smoothly shifted to the NOx reduction process while maintaining the engine operating state stably.

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 fuel injection valve 12 is connected to a high pressure pump (not shown) via a common rail 11, and the fuel in the fuel tank (not shown) is boosted by the high pressure pump and then fueled via the common rail 11. It is supplied to the injection valve 12. The common rail 11 is provided with a fuel pressure sensor 24 that detects the fuel pressure PF in the common rail 11.

  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 rotation speed (rotational speed) can be changed by changing the opening of the variable vanes (hereinafter referred to as “vane opening”) VO. It is configured as follows. The vane opening VO of the turbine 10 is electromagnetically controlled by the ECU 20. More specifically, the ECU 20 supplies a control signal having a variable duty ratio to the turbine 10, thereby controlling the vane opening VO. When the vane opening VO is increased, the efficiency of the turbine 10 is improved and the turbine rotational speed is increased. As a result, the supercharging pressure increases.

  A throttle valve 13 for controlling the amount of intake air 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 is provided with an intake air amount sensor 21 for detecting an intake air amount GAIR (an amount of air taken into the engine 1 per unit time), and these detection signals are supplied to the ECU 20.
A catalytic converter 16, a particulate filter (hereinafter referred to as “DPF”) 17, and a NOx trap 18 are provided in this order from the upstream side of the exhaust pipe 4 on the downstream side of the turbine 10. The catalytic converter 16 incorporates an oxidation catalyst for promoting the oxidation of hydrocarbons and carbon monoxide contained in the exhaust gas. The DPF 17 collects soot, which is a particulate material whose main component is carbon contained in the exhaust gas.

  Since there is a limit to the soot collecting ability of the DPF 17, a DPF regeneration process for burning soot is executed at appropriate times. The DPF regeneration process mainly includes post-injection in which fuel is injected in the expansion stroke or exhaust stroke of the cylinder, or air-fuel ratio enrichment in which post-injection is not performed (for example, the opening of the throttle valve 13 is reduced and the boost pressure is increased). It is executed by air-fuel ratio enrichment by lowering.

  The NOx trap 18 contains a NOx adsorbent that adsorbs NOx and a catalyst for promoting oxidation and reduction. The NOx trap 18 is an exhaust lean state in which the air-fuel ratio of the air-fuel mixture in the combustion chamber is set to be leaner than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is relatively high, and the reducing agent (HC and CO) concentration is lower than the oxygen concentration. In contrast, while the NOx is adsorbed, the air-fuel ratio of the air-fuel mixture in the combustion chamber is set to a richer side than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is relatively low, and the reducing agent concentration is higher than the oxygen concentration. In the state, the adsorbed NOx is reduced by a reducing agent and discharged as nitrogen gas, water vapor and carbon dioxide.

  The NOx adsorption capacity of the NOx adsorbent, that is, when NOx is adsorbed up to the maximum NOx adsorption amount, no more NOx can be adsorbed. Therefore, the NOx reduction process for supplying the reducing agent to the NOx trap 18 to reduce NOx in a timely manner. Is executed. This NOx reduction process is performed by enriching the air-fuel ratio by increasing the amount of fuel injected from the fuel injection valve 12 and mainly decreasing the amount of intake air 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 control of the SCV 15. . Due to the enrichment of the air-fuel ratio, the reducing agent is supplied to the exhaust pipe 4.

A proportional air-fuel ratio sensor (hereinafter referred to as “LAF sensor”) 23 is provided upstream of the catalytic converter 16. The LAF sensor 23 supplies the ECU 20 with a detection signal that is substantially proportional to the oxygen concentration (air-fuel ratio) OC in the exhaust gas.
Further, an accelerator sensor 25 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 a crankshaft (not shown) of the engine 1. A crank angle position sensor 26 for detecting the rotation angle is provided. Detection signals from these sensors are supplied to the ECU 20.

  The crank angle position sensor 26 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 DPF regeneration process or the NOx reduction process, the air-fuel ratio is set to a richer side than the stoichiometric air-fuel ratio.

  FIG. 2 is a flowchart of a main part of an engine control process executed by the CPU of the ECU 20. This process is executed every predetermined time (for example, 10 milliseconds). FIG. 3 is a diagram showing an operation region of the engine 1 defined by the engine speed NE and the required torque TRQ. Regions R1 and R2 shown in FIG. 3 are operation regions in which the regeneration temperature for burning the soot accumulated on the DPF 17 can be maintained, and regions R3 shown with hatching are operation regions in which it is difficult to maintain the regeneration temperature. is there. In the following description, the region R1 is referred to as a “high load high rotation region”, the region R2 is referred to as a “medium load medium rotation region”, and the region R3 is referred to as a “DPF regeneration difficult region”. The predetermined rotational speeds NE1 and NE2 shown in FIG. 3 are, for example, 1000 rpm and 4000 rpm, respectively, and the predetermined torques TRQ1 to TRQ4 are, for example, 20 Nm, 100 Nm, 200 Nm, and 350 Nm, respectively. The required torque TRQ of the engine 1 is calculated according to the accelerator pedal operation amount AP. Hereinafter, FIG. 2 and FIG. 3 will be referred to together.

  In step S11, it is determined whether or not a DPF regeneration request flag FDPFRR requesting regeneration processing of the DPF 17 is “1”. The DPF regeneration request flag FDPFRR is set to “1” when the estimated value of the soot accumulation amount in the DPF 17 reaches a predetermined amount in a process (not shown). When FDPFRR = 0, this process is immediately terminated.

  When FDPFRR = 1 and DPF regeneration processing is requested, it is determined whether or not the operating state of the engine 1 is in the DPF regeneration difficult region R3. If this answer is negative (NO), that is, if the engine operating state is in the high load / high rotation region R1 or the medium load intermediate rotation region R2, DPF regeneration processing is executed according to the engine operating state (step S13). Specifically, in the high-load high-rotation region R1, the first regeneration process is executed to reduce the opening degree of the throttle valve 13 (and SCV15) and reduce the vane opening degree VO so as to reduce the supercharging pressure. In the middle load mid-rotation region R2, the second regeneration process for performing the post injection is executed.

  In step S14, it is determined whether or not the DPF regeneration process has been executed for a predetermined time TDPFRR. If the answer to step S14 is negative (NO), the process immediately ends. When the DPF regeneration process is executed for a predetermined time TDPFRR, the DPF regeneration request flag FDPFRR is returned to “0” (step S15), and the DPF regeneration process is terminated. Note that the execution time of the DPF regeneration process is calculated by integrating the execution times of step S13.

  If the answer to step S12 is affirmative (YES), that is, if the engine operating state is in the DPF regeneration difficult region R3, it is determined whether or not a rich control end flag FREND is “1” (step S16). The rich control end flag FREND is set to “1” when the rich control for reducing the NOx trapped in the NOx trap 18 is ended (see step S21).

  Initially, the answer to step S16 is negative (NO), so the process proceeds to step S17 to determine whether post injection has been executed immediately before. If the answer is negative (NO) and post-injection has not been executed, the routine proceeds to step S18, where the first rich control is executed, and NOx trapped in the NOx trap 18 is reduced. In the first rich control, the air-fuel ratio is enriched by reducing the opening of the throttle valve 13 (and the SCV 15) and increasing the opening of the EGR valve 6 without performing post injection. At this time, it is desirable to advance the fuel injection timing and simultaneously execute the control to increase the fuel pressure PF to reduce the soot discharge amount and the combustion noise.

  If the answer to step S17 is affirmative (YES), that is, if post injection has been executed, the process proceeds to step S19, where the second rich control is executed, and NOx trapped in the NOx trap 18 is reduced. In the second rich control, post-injection is executed, and the air-fuel ratio enrichment is performed by reducing the opening degree and supercharging pressure of the throttle valve 13 (and SCV15), and stopping the exhaust gas recirculation (the EGR valve 6 is fully closed). I do. At this time, it is desirable to further retard the fuel injection timing and simultaneously increase the fuel pressure PF to further increase the exhaust gas temperature.

  After execution of step S18 or S19, it is determined whether or not the rich control is executed for a predetermined time TREDR (step S20). If this answer is negative (NO), this process is immediately terminated. If the answer is affirmative (YES), the rich control end flag FREND is set to “1” (step S21). When the rich control end flag FREND is set to “1”, the rich control for NOx reduction is not executed even if the answer to step S12 is affirmative (YES).

  According to the process of FIG. 2, when it is determined that the engine operating state is in the DPF regeneration difficult region R3 during the regeneration process of the DPF 17, the first rich control or the second rich control is performed, and the NOx trap 18 Since the inflowing exhaust gas is controlled in a reducing atmosphere, the NOx trapped in the NOx trap 18 can be reduced, and the amount of NOx trapped in the NOx trap 18 exceeds the trapping capacity of the NOx trap 18 and the NOx. Can be prevented from increasing. Since the regeneration process of the DPF 17 cannot be performed in the DPF regeneration difficult region R3, the NOx reduction process does not delay the regeneration process of the DPF 17. If the engine operating state returns to the region R1 or R2 where the DPF regeneration process is possible, the DPF regeneration process is executed again (step S13). Therefore, the DPF regeneration process and the NOx reduction process can be efficiently executed, and both the DPF 17 and the NOx trap 18 can be maintained in a good state.

  Further, when the DPF regeneration process with post-injection is executed, that is, when the engine operating state shifts from the middle load mid-rotation region R2 to the DPF regeneration difficult region R3, the first rich control with post-injection is performed. Exhaust is controlled to a reducing atmosphere. Therefore, changes in the engine operating parameters are reduced, and the engine operation state can be maintained stably, and the DPF regeneration process can be smoothly shifted to the rich control for NOx reduction.

  In this embodiment, the throttle valve 13, SCV15, turbocharger 8, fuel injection valve 12, and ECU 20 constitute filter regeneration means. The throttle valve 13, SCV15, EGR valve 6, turbocharger 8, fuel injection valve 12, and The ECU 20 constitutes a NOx trap regeneration means, and the ECU 20 constitutes an operating state determination means. More specifically, step S13 in FIG. 2 corresponds to part of the filter regeneration means, steps S16 to S21 correspond to part of the NOx trap regeneration means, and step S12 corresponds to the operating state determination means.

The present invention is not limited to the embodiment described above, and various modifications can be made. For example, as shown in FIG. 4, the catalytic converter 16, the DPF 17, and the NOx track 18 may be arranged in the order of the NOx trap 18, the catalytic converter 16, and the DPF 17 from the upstream side.
The throttle valve 13 may be disposed on the upstream side of the compressor 9.

  In the above-described embodiment, the rich control executed in step S18 or S19 in FIG. 2 is ended after a predetermined time TREDR from the start time, but an oxygen concentration sensor is provided on the downstream side of the NOx trap 18, The end time of rich control may be determined according to the output of the oxygen concentration sensor.

  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 flowchart of the principal part of the process which controls the internal combustion engine shown in FIG. It is a figure which shows the operation area | region of an internal combustion engine. It is a figure which shows the modification of arrangement | positioning of the apparatus provided in an exhaust system.

Explanation of symbols

1 Internal combustion engine 6 Exhaust gas recirculation control valve (trap regeneration means)
8 Turbocharger (filter regeneration means, NOx trap regeneration means)
12 Fuel injection valve (filter regeneration means, NOx trap regeneration means)
13 Throttle valve (filter regeneration means, NOx trap regeneration means)
15 Swirl control valve (filter regeneration means, NOx trap regeneration means)
17 Diesel particulate filter 18 NOx trap 20 Electronic control unit (filter regeneration means, operation state determination means, NOx trap regeneration means)

Claims (2)

A particulate filter provided in the exhaust system of the internal combustion engine for collecting soot in the exhaust, a NOx trap provided in the exhaust system for collecting NOx in the exhaust, and soot accumulated on the particulate filter. In an exhaust gas purification apparatus for an internal combustion engine comprising filter regeneration means for performing filter regeneration for combustion,
An operation state determination unit that determines whether or not the operation state of the engine is in a filter regeneration difficult region during filter regeneration by the filter regeneration unit;
An exhaust gas purification apparatus for an internal combustion engine, comprising: NOx trap regeneration means for controlling the exhaust gas flowing into the NOx trap to a reducing atmosphere when it is determined that the operating state of the engine is in the filter regeneration difficulty region. .   When the filter regeneration means is performing post injection for supplying fuel into the cylinder of the engine during the expansion stroke or exhaust stroke of the cylinder, the NOx trap regeneration means is configured to bring the exhaust into a reducing atmosphere by the post injection. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is controlled.

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