JP2006257880A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of accurately detecting failure of a DPF, particularly, very small leakage, with a relatively simple constitution. <P>SOLUTION: When an engine 1 stops, a secondary air pump 14 is operated, and air of a very small flow rate is sent to the DPF 13 (S104). At this time, differential pressure DPDPF between upstream side pressure PEUP and downstream side pressure PEDOWN of the DPF 13 is measured (S105), and differential pressure DPNORDPF of a reference state except for influence of soot and ash generated by combustion of the soot, is calculated by correcting its differential pressure DPDPF (S106). The collection ratio CE of the DPF 13 is calculated in response to reference state differential pressure DPNORDPF (S107), and when the collecting ratio CE is a determined threshold value CETH or less, it is determined that the DPF 13 is in failure (S108, and S109). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine, and more particularly to a device having a filter (DPF: Diesel Particulate Filter) for collecting particulates (particulate matter) in exhaust gas from an internal combustion engine.

  2. Description of the Related Art Conventionally, a technique for reducing a particulate discharge amount by providing a DPF for collecting particulates in exhaust gas in an exhaust system of a diesel internal combustion engine has been widely used. When a failure such as a crack or a hole occurs in the filter element constituting the DPF, the filter function of the DPF is lowered, and the particulate discharge amount is increased. Therefore, such a failure needs to be detected quickly.

In Patent Document 1, a pressure sensor is provided on the downstream side of the DPF, and the difference between the maximum value and the minimum value of the detected pressure during engine operation, that is, the pulsation amplitude is obtained. A technique for determining occurrence has been shown.
JP 2004-308454 A

  However, since the pulsation amplitude of the exhaust pressure monitored in the method disclosed in Patent Document 1 fluctuates irregularly depending on the engine operating state, a minute amount of particulate leakage (hereinafter referred to as “small leakage”) is detected. It is difficult to do. Further, the method disclosed in Patent Document 1 requires a complicated calculation in order to monitor and analyze the pulsation amplitude of the exhaust pressure.

  On the other hand, it is considered effective to provide a particulate sensor that directly detects the leaked particulate on the downstream side of the DPF, but such a sensor has not yet been developed.

  The present invention has been made in consideration of the above-described points, and an object of the present invention is to provide an exhaust emission control device capable of accurately detecting a DPF failure, particularly a minute leak, with a relatively simple configuration.

  In order to achieve the above object, an invention according to claim 1 is directed to an exhaust gas purification apparatus for an internal combustion engine comprising a filter means (13) for collecting particulates in the exhaust gas of the internal combustion engine (1). Gas supply means (14, 15) for supplying gas to the filter means (13) at times, and pressure change detection means for detecting pressure changes due to the resistance of the filter means (13) to the flow of the supplied gas (21, 22) and a failure detection means for detecting a failure of the filter means (13) based on the output (DPDPF) of the pressure change detection means at the time of gas supply by the gas supply means (14, 15). It is characterized by providing.

  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 gas supply means supplies the gas by a supercharger (8) or a secondary air pump (14). It is characterized by that.

  According to the first aspect of the present invention, the gas is supplied to the filter means when the engine is stopped, and the failure of the filter means is detected based on the pressure change caused by the resistance of the filter means detected at that time. When the filter means is cracked or perforated and particulate leakage occurs, the resistance when the gas passes through the filter means becomes small, so the value of the pressure change becomes small. Therefore, when the value of the pressure change is below the normal value range, it can be determined that a failure due to cracking or perforation has occurred in the filter means. In addition, since the pressure change is detected in a state where the internal combustion engine is stopped, that is, in a state where the piston is stopped, there is no influence of exhaust pulsation. As a result, it is possible to accurately detect the minute leakage of the particulates, which has been difficult to detect conventionally.

  According to invention of Claim 2, supply of the gas to a filter means is performed by a supercharger or a secondary air pump. In this way, the configuration can be simplified by using the device originally provided in the internal combustion engine. Since the internal combustion engine is stopped, there is no fluctuation in the output of the supercharger or the secondary air pump due to the operation of the internal combustion engine, and the pressure pulsation of the gas supplied by the supercharger or the secondary air pump Since it is extremely small compared with the exhaust pulsation due to the operation of, it can be ignored.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing the configuration of an internal combustion engine equipped with an exhaust emission control device according to an embodiment of the present invention and its control device. An internal combustion engine (hereinafter simply referred to as “engine”) 1 is a diesel engine that directly injects fuel into a cylinder, and a fuel injection valve 16 is provided in each cylinder. The fuel injection valve 16 is electrically connected to an electronic control unit (hereinafter referred to as “ECU”) 20, and the valve opening time and valve opening timing of the fuel injection valve 16 are controlled by the ECU 20.

  The engine 1 includes an intake pipe 2, an exhaust pipe 4, and a supercharger 8. The supercharger 8 includes a turbine 10 driven by kinetic energy of exhaust, a compressor 9 that is rotationally driven by the turbine 10 and compresses intake air, and an electric actuator 11 that assists in driving the compressor 9. It is an assist turbocharger.

  The turbine 10 includes a plurality of variable vanes (not shown), and is configured to change the turbine rotational speed (rotational speed) by changing the opening degree of the variable vanes. The vane opening degree of the turbine 10 is electromagnetically controlled by the ECU 20. The electric actuator 11 operates according to a control signal supplied from the ECU 20 when supercharging is performed when the kinetic energy of the exhaust is insufficient.

  An intercooler 5 for cooling the pressurized air and an intake shutter (throttle valve) 3 for controlling the intake air amount are provided in the intake pipe 2 downstream of the compressor 9. The intake shutter 3 is controlled to be opened and closed by the ECU 20 via an actuator (not shown).

  Between the upstream side of the turbine 10 in the exhaust pipe 4 and the downstream side of the intake shutter 5 in the intake pipe 2, an exhaust gas recirculation passage 6 for returning the exhaust gas to the intake pipe 2 is provided. The exhaust gas recirculation passage 6 is provided with an exhaust gas recirculation control valve (hereinafter referred to as “EGR valve”) 7 for controlling the exhaust gas recirculation amount. The EGR valve 7 is an electromagnetic valve having a solenoid, and the valve opening degree is controlled by the ECU 20.

  On the downstream side of the turbine 10 in the exhaust pipe 4, a catalytic converter 12 for purifying exhaust and a DPF 13 are provided in this order from the upstream side. Further, a secondary air pump 14 for supplying air via a passage 15 is provided on the upstream side of the catalytic converter 12. The secondary air pump 14 is driven by a motor supplied with electric power from a battery, and its operation is controlled by the ECU 20. The secondary air pump 14 is normally driven when accelerating the combustion of unburned fuel in the catalytic converter 12, but in the present embodiment, it is also driven when performing a failure diagnosis of the DPF 13 as will be described later.

  The catalytic converter 12 contains a NOx absorbent that absorbs NOx and a catalyst for promoting oxidation and reduction. The NOx absorbent absorbs NOx in an exhaust lean state in which the air-fuel ratio of the air-fuel mixture in the combustion chamber of the engine 1 is set to be leaner than the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust is relatively high (NOx is high). On the other hand, when the air-fuel ratio of the air-fuel mixture is set near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, the exhaust gas has a characteristic of releasing the absorbed NOx in an exhaust rich state where the oxygen concentration in the exhaust gas is relatively low. .

  The catalytic converter 12 is configured so that NOx released from the NOx absorbent in the exhaust rich state is reduced by HC and CO and discharged as nitrogen gas, and HC and CO are oxidized and discharged as water vapor and carbon dioxide. It is configured.

  When the exhaust gas passes through the fine holes in the filter wall, the DPF 13 deposits soot, which is a particulate mainly composed of carbon (C) in the exhaust gas, on the surface of the filter wall and the holes in the filter wall. Collect by letting. As a constituent material of the filter wall, for example, ceramics such as silicon carbide (SiC) or a porous metal body is used.

  If soot is collected up to the limit of the soot collecting ability of the DPF 13, that is, the accumulation limit, the exhaust pressure is increased, so that it is necessary to perform a regeneration process for burning the soot in a timely manner. In this regeneration process, post-injection control is executed in order to raise the exhaust temperature to the soot combustion temperature. In the post injection control, the fuel injection valve 16 performs not only normal injection in the compression stroke, but also post injection (post injection) in the subsequent explosion stroke and exhaust stroke. The fuel injected by the post injection may be burned in the combustion chamber of the engine 1 or burned by the catalytic converter 12 depending on the injection timing.

Pressure sensors 21 and 22 for detecting the upstream pressure PEUP and the downstream pressure PEDDOWN are provided on the upstream side and the downstream side of the DPF 13. Detection signals from these sensors are supplied to the ECU 20.
Furthermore, a crank angle position sensor that detects the rotation angle of the crankshaft of the engine 1, an intake air flow rate sensor that detects the intake air amount flow rate of the engine 1, and a cooling water temperature sensor that detects the cooling water temperature of the engine 1 (all not shown) The detection signals of these sensors are supplied to the ECU 20. The rotational speed of the engine 1 is calculated from the output of the crank angle position sensor.

  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 that stores various calculation programs executed by the CPU, calculation results, and the like, and an output circuit that supplies control signals to the fuel injection valve 16, the EGR valve 7, and the like.

FIG. 2 is a flowchart showing a procedure of processing for diagnosing a failure of the DPF 13, specifically, a deterioration of the filter function due to cracking or perforation of the filter wall. This failure diagnosis process is executed by the CPU of the ECU 20.
In step S101, a soot accumulation amount GSOOT in the DPF 13 is calculated. This soot accumulation amount GSOOT is calculated in advance according to an existing method, for example, the operating state of the engine 1 (engine speed and engine load) and the differential pressure DDPPF between the upstream pressure PEUP and the downstream pressure PEDOWN of the DPF 13. This is done by calculating the deposition amount at regular intervals based on the stored algorithm and map.

  When the soot accumulation amount GSOOT exceeds the regeneration control threshold value GPTH, regeneration control for burning the deposited soot is performed. The regeneration control is performed by raising the exhaust gas temperature by post injection as described above. When the complete regeneration in which all the soot is burned by the regeneration control is performed, the soot accumulation amount GSOOT is reset to “0”. Further, when incomplete regeneration is performed in which a part of the deposited soot is burned, the soot accumulation amount GSOOT is updated by subtracting the burned soot amount GSCMB.

  In step S102, the ash deposition amount GASH, which is the ash deposition amount after the soot burns in the DPF 13, is calculated. This ash deposition amount GASH is calculated by the same method as the method of calculating the soot deposition amount GSOOT in step S101 when complete regeneration by regeneration control is performed. However, the algorithm and map in this case are for calculating the ash deposition amount.

  In step S103, it is determined whether or not the engine 1 is stopped. When the engine 1 is stopped, the secondary air pump 14 is operated to send air to the DPF 13 (step S104). The air flow rate at this time is preferably a very small flow rate.

  As a factor of the pressure loss of the DPF 13, there are a resistance (passage resistance) when passing through the passage provided in the DPF 13 and a resistance (filter resistance) when passing through the filter wall, The passage resistance becomes small and can be ignored. As a result, the influence of slight cracks or the like generated in the DPF 13 appears remarkably as a pressure loss of the DPF 13, and a minor failure can be detected. The preferable air flow rate varies depending on the capacity of the DPF 13 and the like, but is about 50 [kg / h] in the case of a 2.2 liter engine, for example.

In step S105, the differential pressure DDPPF between the upstream pressure PEUP detected by the pressure sensors 21 and 22 and the downstream pressure PEDDOWN is measured while air is being sent. Then, the differential pressure DDPPF is applied to the following equation (1) to calculate the reference state differential pressure DPNORDPF (step S106).
DPNORDPF = DPDPF− (DPASH + DPSOOT) (1)

  Here, DPASH is a pressure loss (hereinafter referred to as “ash loss”) corresponding to the ash accumulation amount GASH of the DPF 13, and DPSOOT is a pressure loss (hereinafter referred to as “soot loss”) corresponding to the soot accumulation amount GSOOT. . The reference state differential pressure DPNORDDPF calculated by the equation (1) corresponds to the differential pressure in the reference state excluding the influence of ash (ash) and soot accumulated on the DPF 13.

  The ash loss DPASH is calculated by searching the DASH table shown in FIG. 3A according to the ash accumulation amount GASH. The soot loss DPSOOT is calculated by searching the DPSOOT table shown in FIG. 3B according to the soot accumulation amount GSOOT. Here, the DPASH table and the DPSOOT table are experimentally obtained in advance corresponding to the air flow rate supplied to the DPF 13 and stored in the storage circuit of the ECU 20.

  In step S107, the particulate collection rate CE by the DPF 13 is calculated according to the flow rate QGAS of the air sent to the DPF 13 and the reference state differential pressure DPNORDPF calculated in step S106. FIG. 3 (C) shows the relationship between the air flow rate QGAS and the reference state differential pressure DPNORDDPF, where the solid line corresponds to the case where the collection rate CE is 99%, and the broken line is the collection rate CE is 60%. This corresponds to the case.

If the flow rate of air supplied to the DPF 13 is QG1, the differential pressure corresponding to a collection rate of 99% and the differential pressure corresponding to a collection rate of 60% are DP99 and DP60, respectively. Therefore, the collection rate CE (%) is calculated by performing the interpolation calculation by applying the reference state differential pressure DPNORDDPF calculated in step S106 to the following equation (2).

  In step S108, it is determined whether or not the collection rate CE is equal to or less than a determination threshold value CETH (for example, 80%). As a result, when the collection rate CE is equal to or less than the determination threshold value CETH, it is determined that the DPF 13 has failed, that is, the filter function has been degraded due to cracking or perforation (step S109), and the collection rate CE is When it is larger than the determination threshold value CETH, it is determined that the DPF 13 is normal (step S110).

  As described above, in the present embodiment, when the engine 1 is stopped, the secondary air pump 14 sends a minute flow of air to the DPF 13, and the differential pressure DDPPF due to the resistance of the DPF 13 to this air flow is detected. By correcting the differential pressure DDPPF so as to eliminate the effects of ash and soot accumulated in the DPF 13, the reference state differential pressure DPNORDDPF is calculated. Then, the collection rate CE of the DPF 13 is calculated based on the reference state differential pressure DPNORDDPF and the air flow rate QGAS. When the collection rate CE is equal to or less than the determination threshold value CETH, it is determined that the DPF 13 has failed. Here, since the detection of the differential pressure DDPPF is performed when the engine 1 is stopped, there is no influence of exhaust pulsation. As a result, it is possible to accurately detect the minute leakage of the particulates, which has been difficult to detect conventionally.

  Further, since the engine 1 is stopped, there is no fluctuation in the output of the secondary air pump 14 due to the operation of the engine 1, and the pressure pulsation of the air supplied by the secondary air pump 14 is caused by the exhaust of the piston. Since it is extremely small compared to pulsation, it can be ignored. Therefore, an accurate determination can be made.

  In the present embodiment, the DPF 13 corresponds to the filter means, the secondary air pump 14 and the passage 15 correspond to the gas supply means, and the pressure sensors 21 and 22 correspond to the pressure change detection means. Moreover, ECU20 comprises a failure detection means. Specifically, the process of FIG. 2 corresponds to a failure detection unit.

(Modification)
The present invention is not limited to the embodiment described above, and various modifications can be made. For example, in the above-described embodiment, air is sent to the DPF 13 by the secondary air pump 14 and the passage 15, but instead, the compressor 9 of the supercharger 8 is driven by the actuator 11 to send air to the DPF 13. You may make it send. In the case of a multi-cylinder engine, since the intake / exhaust valve of any cylinder is open even when the engine is stopped, an air flow path from the intake pipe 2 to the exhaust pipe 4 is ensured. Accordingly, the exhaust gas recirculation passage 6 may be used as a flow path for air sent by the compressor 9. Further, the gas supply means is not limited to the secondary air pump 14 or the supercharger (electrically assisted turbocharger) 8 described above, but an electric assist supercharger or an electric supercharger that does not use engine exhaust or rotational driving force. You may make it comprise by these.

  In the above-described embodiment, the differential pressure DDPPF between the upstream pressure PEUP and the downstream pressure PEDOWN of the DPF 13 is measured, but the pressure on one of the upstream side or the downstream side of the DPF 13 is compared with the reference pressure. Thus, a pressure change for failure detection may be detected. For example, the pressure loss of the DPF 13 may be detected by measuring the upstream pressure PEUP and comparing it with the atmospheric pressure PA. In that case, it is not necessary to provide the downstream pressure sensor 22.

  The flow rate of the air sent by the DPF 13 when the engine is stopped need not be constant, and the air flow rate may be changed periodically by giving the output of the secondary air pump 14 periodicity. In this case, since the engine 1 is stopped, the change period of the air flow rate can be set regardless of the operation of the engine 1. When the DPF 13 is cracked or the like, the pressure waveform differs between the upstream side and the downstream side of the DPF 13, so that the behavior of the differential pressure between the upstream pressure PEUP and the downstream pressure PEDOWN is also normal. It will be clearly different. Therefore, a failure of the DPF 13 can be accurately detected by capturing this difference.

  In the above-described embodiment, as the calculation method for calculating the collection rate CE, primary interpolation (linear interpolation) using two points of differential pressures DP99 and DP60 as sample points is performed. However, the sample points may be three points or more. In addition, the function passing through the sample points is not limited to a linear function but may be a curve interpolation as a quadratic or higher function, or the collection rate CE is calculated from the sample points obtained in advance by the extrapolation method. May be.

In the above-described embodiment, a very small amount of air is sent to the DPF 13. However, the gas sent to the DPF 13 is not limited to air, and may be other gases (for example, carbon dioxide, oxygen, etc.).
The exhaust emission control device of the present invention can also be applied to a marine vessel propulsion engine such as an outboard motor having a crankshaft in a vertical direction.

It is a figure showing composition of an internal combustion engine provided with an exhaust-air-purification device concerning one embodiment of the present invention, and its control device. It is a flowchart which shows the procedure of the failure diagnosis of DPF shown by FIG. It is a figure which shows the table used for the failure diagnosis of DPF.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 4 Exhaust pipe 13 DPF (filter means)
14 Secondary air pump (gas supply means)
15 passage (gas supply means)
20 Electronic control unit (failure detection means)
21 Pressure sensor (pressure change detection means)
22 Pressure sensor (pressure change detection means)

Claims (2)

In an exhaust gas purification apparatus for an internal combustion engine comprising filter means for collecting particulates in the exhaust gas of the internal combustion engine,
Gas supply means for supplying gas to the filter means when the engine is stopped;
Pressure change detecting means for detecting a pressure change caused by resistance of the filter means with respect to the flow of the supplied gas;
An exhaust emission control device for an internal combustion engine, comprising: a failure detection unit that detects a failure of the filter unit based on an output of the pressure change detection unit during gas supply by the gas supply unit.   The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the gas supply means supplies the gas by a supercharger or a secondary air pump.

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