JP2017137835A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine the abnormality of a filter utilizing a before-and-behind-filter differential pressure while reducing erroneous determination resulting from an atmospheric pressure when acquiring the before-and-behind-filter differential pressure.SOLUTION: An exhaust emission control device for an internal combustion engine includes a filter provided in an exhaust passage of the internal combustion engine for trapping particulate matters from exhaust gas, a differential pressure detection part for detecting a before-and-behind-filter differential pressure as a difference in pressure between the exhaust upstream side and the exhaust downstream side of the filter, an atmospheric pressure detection part for detecting an atmospheric pressure around the internal combustion engine, a correction part for correcting the before-and-behind-filter differential pressure into a corrected before-and-behind-filter differential pressure as a before-and-behind-filter differential pressure under a predetermined atmospheric pressure, on the basis of the atmospheric pressure detected by the atmospheric pressure detection part at a time when detecting the before-and-behind-filter differential pressure, an average calculation part for calculating an average before-and-behind-filter differential pressure as the average of a plurality of corrected before-and-behind-filter differential pressures, and a determination part for determining whether there is the abnormality of the filter or not on the basis of whether the average before-and-behind-filter differential pressure is at a threshold value or higher, or not.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  An exhaust gas purification device for purifying exhaust gas is provided in the exhaust passage of the internal combustion engine. In such an exhaust purification device, a filter for collecting particulate matter (PM) in the exhaust is provided in the exhaust passage, and the amount of PM discharged to the outside by the filter is reduced. doing.

  When there is a failure such as cracking in the filter, the exhaust pressure upstream of the filter, that is, the back pressure, decreases, and the differential pressure between the upstream pressure of the filter and the downstream pressure of the filter (hereinafter referred to as the front and rear of the filter). Called differential pressure). A method for determining an abnormality of a filter using this phenomenon has been conventionally known. For example, in Patent Document 1, the amount of PM accumulated on the filter is estimated based on the operating state of the internal combustion engine, and the differential pressure before and after the filter when the estimated amount of PM accumulation is a predetermined value or more is predetermined. When the value is below the threshold, it is determined that an abnormality has occurred in the filter.

JP 2009-103043 A

  When judging the abnormality of the filter using the differential pressure before and after the filter, the average differential pressure before and after the filter is calculated by averaging the differential pressure before and after the filter acquired at a plurality of times (for example, 25), taking into account the running variation and the like. It is common to determine the abnormality of the filter based on whether or not the average differential pressure before and after the filter is below a threshold value.

  By the way, when the operating state of the internal combustion engine does not change, the differential pressure before and after the filter is affected by the air density and decreases as the air density decreases. Since the air density decreases as the altitude increases and the atmospheric pressure decreases, the differential pressure across the filter decreases as the altitude increases when the operating state of the internal combustion engine does not change. Therefore, as the data of the differential pressure across the filter acquired at high altitude increases, the average differential pressure across the filter decreases. When a filter abnormality is determined using such an average differential pressure before and after the filter, it may be erroneously determined that the filter is abnormal even though the filter is normal.

  In view of this, the exhaust gas purification apparatus for an internal combustion engine disclosed in the present specification can reduce misjudgment caused by atmospheric pressure at the time of obtaining the filter front-rear differential pressure in the filter abnormality determination using the filter front-rear differential pressure. Let it be an issue.

  In order to solve such a problem, an exhaust emission control device for an internal combustion engine disclosed in the present specification is provided in an exhaust passage of the internal combustion engine, and includes a filter that collects particulate matter in the exhaust, and an exhaust upstream of the filter. A differential pressure detection unit that detects a differential pressure across the filter that is a difference between a pressure on the exhaust side and a pressure on the exhaust downstream side of the filter, an atmospheric pressure detection unit that detects an atmospheric pressure around the internal combustion engine, and the filter Based on the atmospheric pressure detected by the atmospheric pressure detection unit at the time when the pressure difference between the front and the back is detected, the detected pressure difference between the front and rear of the filter is a difference between the front and rear of the correction filter that is the pressure difference before and after the filter under a predetermined atmospheric pressure. A correction unit that corrects pressure, an average calculation unit that calculates an average filter front-rear differential pressure that is an average of the plurality of correction filter front-rear differential pressures, and whether the average filter front-rear differential pressure is greater than or equal to a threshold value The above And a determination unit for determining whether or not there is an abnormality in the filter.

  According to the exhaust gas purification apparatus for an internal combustion engine disclosed in the present specification, it is possible to reduce misjudgment due to atmospheric pressure at the time when the filter front-rear differential pressure is acquired in the filter abnormality determination using the filter front-rear differential pressure. it can.

FIG. 1 is a schematic diagram illustrating a configuration of an engine system to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment is applied. FIG. 2A is a diagram showing an example of the relationship between the altitude and the travel distance when the vehicle travels, and FIG. 2B shows the differential pressure before and after the filter acquired in the environment shown in FIG. It is a figure which shows an example. FIG. 3 is a flowchart illustrating an example of the acquisition / correction processing of the differential pressure across the filter. FIG. 4 is an example of a map in which the relationship between the atmospheric pressure and the correction coefficient is plotted. FIG. 5 is a flowchart illustrating an example of a filter abnormality determination process. 6A is a diagram showing the differential pressure before and after the filter with respect to the exhaust gas flow rate, and FIG. 6B is a diagram showing the differential pressure before and after the correction filter with respect to the exhaust gas flow rate.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, and the like of each part may not be shown so as to completely match the actual ones. In some cases, details are omitted in some drawings.

  First, an engine system to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment is applied will be described with reference to FIG. FIG. 1 is a schematic diagram showing a configuration of an engine system 100 to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment is applied. Note that “upstream” and “downstream” described in this specification are based on the flow direction of the exhaust gas in the exhaust system.

  As shown in FIG. 1, the engine system 100 includes an intake passage 10, an internal combustion engine 20, an exhaust passage 30, a correction unit, an average calculation unit, and an ECU (Electronic Control Unit) 50 as a determination unit. .

  The internal combustion engine 20 is, for example, a diesel engine, and includes a plurality of cylinders #N (N = 1 to 4), and a plurality of cylinders for injecting and supplying high-pressure fuel to the combustion chambers 21 of the respective cylinders #N. The fuel injection valve 22 is attached. These cylinders #N are connected to an intake port 11 for introducing outside air into each combustion chamber 21 and an exhaust port 31 for discharging combustion gas generated in each combustion chamber 21.

  The intake port 11 is provided with an intake valve 12 for opening and closing the intake port 11. An intake passage 10 is connected to the intake port 11 via an intake manifold. The intake passage 10 is provided with a throttle valve 14 for metering intake air. The throttle valve 14 is driven to open and close by a motor 15.

  The exhaust port 31 is provided with an exhaust valve 32 for opening and closing the exhaust port 31. An exhaust passage 30 is connected to the exhaust port 31 via an exhaust manifold.

  The exhaust passage 30 is provided with an oxidation catalyst 41 that oxidizes and purifies hydrocarbons (HC) and carbon monoxide (CO) in the exhaust, and a filter 42 that collects PM in the exhaust.

  An electromagnetic fuel addition valve 33 that can add fuel (reducing agent) to the exhaust gas flowing into the oxidation catalyst 41 is provided on the upstream side of the oxidation catalyst 41 in the exhaust passage 30.

  The ECU 50 includes a central processing unit (CPU), a ROM (Read Only Memory) that stores various programs and maps in advance, a RAM (Random Access Memory) that temporarily stores CPU calculation results, a storage device, And an input / output interface. The ECU 50 performs various controls by executing programs stored in the ROM.

  In order to control the engine system 100, the ECU 50 receives signals from an air flow meter 61, differential pressure sensors 63 and 66, temperature sensors 64, 65 and 67, an atmospheric pressure sensor 68, and the like.

  The air flow meter 61 is provided upstream of the throttle valve 14 in the intake passage 10 and detects the mass flow rate of air flowing into the combustion chamber 21 (hereinafter referred to as intake air amount).

  The differential pressure sensor 63 is provided in the exhaust passage 30 and detects a catalyst differential pressure ΔPc that is a difference between the upstream pressure of the oxidation catalyst 41 and the downstream pressure of the oxidation catalyst 41. In the following description, the differential pressure sensor 63 is referred to as a catalyst differential pressure sensor 63.

  The differential pressure sensor 66 is provided in the exhaust passage 30 and detects a filter front-rear differential pressure ΔPf that is a difference between the upstream pressure of the filter 42 and the downstream pressure of the filter 42. In the following description, the differential pressure sensor 66 is referred to as a filter differential pressure sensor 66. The filter differential pressure sensor 66 is an example of a differential pressure detection unit. In addition, a pressure sensor may be provided before and after the filter 42, and the ECU 50 may obtain an output difference between the two sensors and calculate the differential pressure based on the difference.

  The temperature sensor 64 is provided in the oxidation catalyst 41 and detects the catalyst bed temperature Tc. Hereinafter, the temperature sensor 64 is referred to as a catalyst temperature sensor 64.

  The temperature sensor 65 is provided between the oxidation catalyst 41 and the filter 42 and detects the temperature of the exhaust gas flowing into the filter 42 (filter inflowing exhaust gas temperature) Tin. Hereinafter, the temperature sensor 65 is referred to as a filter upstream temperature sensor 65.

  The temperature sensor 67 is provided on the downstream side of the filter 42 in the exhaust passage 30 and detects the temperature of exhaust gas flowing out from the filter 42 (filter outflow exhaust temperature) Tout. Hereinafter, the temperature sensor 67 is referred to as a filter downstream side temperature sensor 67.

  The atmospheric pressure sensor 68 detects the atmospheric pressure around the internal combustion engine 20. The atmospheric pressure sensor 68 is an example of an atmospheric pressure detection unit.

  The ECU 50 also includes a throttle opening sensor that detects the opening of the throttle valve 14, a crank angle sensor that detects the crank angle of the internal combustion engine 20, an accelerator sensor that detects the amount of depression of the accelerator pedal, and an external air temperature that is detected. Various information and signals relating to the operating state and operating conditions of the engine are input from various sensors such as an air temperature sensor and a vehicle speed sensor that detects the rotational speed of the output shaft of the automatic transmission proportional to the vehicle speed.

  In addition to the motor 15, the fuel injection valve 22, and the fuel addition valve 33, various actuators such as a spark plug (not shown) are connected to the output side of the ECU 50. The ECU 50 controls the fuel injection amount and fuel injection timing of the fuel injection valve 22, the opening degree of the throttle valve 14, and the fuel injection amount and fuel of the fuel addition valve 33 based on the information and signals described above. Control the injection timing. Further, the ECU 50 executes a filter front-rear differential pressure acquisition / correction process and a filter abnormality determination process necessary for the filter abnormality determination process for determining whether or not the filter 42 is abnormal.

  Next, a situation in which the filter is erroneously determined to be abnormal although it is normal will be described with reference to FIGS. 2 (a) and 2 (b). FIG. 2A is a diagram illustrating an example of the relationship between the altitude and the travel distance during vehicle travel, and FIG. 2B is a filter acquired in a vehicle traveling in the environment illustrated in FIG. It is a figure which shows an example of front-back differential pressure.

  As described above, when determining the filter abnormality using the filter front-rear differential pressure, the average filter front-rear difference obtained by averaging the filter front-rear differential pressures obtained at a plurality of times (for example, 25) in consideration of running variation and the like. Generally, it is determined whether the filter is abnormal based on whether the pressure is equal to or lower than a threshold value.

  Here, for example, as shown in FIG. 2A, 24 points of differential pressure before and after the filter are acquired in the section L1 (high altitude (environment where the atmospheric pressure is low)), and data of the differential pressure before and after the filter is acquired in the section L2. Suppose that the differential pressure before and after the filter at the 25th point is acquired at the position P (flat ground (environment where the atmospheric pressure is higher than the highland)). In this case, the threshold value used for the filter abnormality determination is corrected based on the atmospheric pressure (atmospheric pressure on the flat ground) at the time of obtaining the 25th filter differential pressure before and after the filter. For example, FIG. The value is indicated by a one-dot chain line. The reason why the differential pressure before and after the filter is not acquired in the section L2 is that there is a possibility that the appropriate differential pressure before and after the filter cannot be acquired for the abnormality determination process because the load is low on the downhill.

  On the other hand, the average differential pressure before and after the filter obtained by averaging the data of 25 differential pressures before and after the filter is affected by the 24 low differential data before and after the filter obtained in an environment where the atmospheric pressure is low. As indicated by the dotted line, the value is lower than the threshold value. As a result, the filter may be erroneously determined to be abnormal although it is normal.

  Therefore, in the engine system 100 according to the present embodiment, the ECU 50 performs all of the acquired differential pressure across the filter before and after the filter under a predetermined atmospheric pressure based on the atmospheric pressure at the time when the differential pressure across the filter is acquired. A filter abnormality determination process is performed by correcting each of the differential pressures, and erroneous determination as described above is reduced.

  First, acquisition / correction processing of the differential pressure across the filter executed by the ECU 50 will be described with reference to FIG. FIG. 3 is a flowchart illustrating an example of the filter front-rear differential pressure data acquisition / correction process executed by the ECU 50.

  The processing in FIG. 3 is repeatedly executed at a predetermined calculation cycle (for example, 0.1 to 0.2 ms (milliseconds)).

The EUC 50 first determines whether or not a differential pressure acquisition permission flag for permitting acquisition of the differential pressure across the filter is ON (step S11). For example, the differential pressure acquisition permission flag is turned on when all of the following conditions are satisfied.
PM deposition amount <W _PM
T1 <filter inflow exhaust gas temperature Tin <T2
T3 <filter outflow exhaust temperature Tout <T4
V1 <Fluctuation amount of catalyst differential pressure ΔPc <V2
T5 <catalyst bed temperature Tc <T6
Note that W _PM , T1 to T6, V1, and V2 are predetermined threshold values. The PM accumulation amount is calculated by the ECU 50 using a known method. For example, the ECU 50 may calculate the PM accumulation amount based on the differential pressure ΔPf before and after the filter, or may calculate it based on the operating condition of the internal combustion engine 20. T1, T3, and T5 may be different from each other, or at least two of them may be the same. T2, T4 and T6 may be different from each other, or at least two of them may be the same.

  When the differential pressure acquisition permission flag is not ON (S11 / NO), the ECU 50 ends the process of FIG.

When the differential pressure acquisition permission flag is ON (S11 / YES), the ECU 50 calculates a volume flow rate (exhaust gas flow rate) V [m ³ / s] of exhaust gas passing through the filter 42 (step S13). For example, the ECU 50 calculates the exhaust gas flow rate V using the following equation of state.
V = (Ga + Gf + Gad) × gas constant × (Tin + 273.15) /
(Atmospheric pressure + downstream pressure of filter 42 + ΔPc)
Ga represents the intake air amount, Gf represents the fuel injection amount of the fuel injection valve 22, and Gad represents the fuel injection amount of the fuel addition valve 33. Tin is the filter inflow exhaust gas temperature detected by the filter upstream temperature sensor 65, and ΔPc is the catalyst differential pressure detected by the catalyst differential pressure sensor 63. Further, the downstream pressure of the filter 42 is a value estimated by the ECU 50 based on the intake air amount.

Next, the ECU 50 determines whether a condition for acquiring the differential pressure across the filter is satisfied (step S15). For example, the ECU 50 determines that the condition for acquiring the differential pressure across the filter is satisfied when all of the following conditions are satisfied.
Number of times the filter 42 is played> N
V3 <Fluctuation amount of exhaust gas flow rate V <V4
V5 <exhaust gas flow rate V <V6
N and V3 to V6 are predetermined threshold values.

  If the condition for acquiring the differential pressure across the filter is not satisfied (S15 / NO), the ECU 50 ends the process of FIG.

  On the other hand, when the condition for acquiring the differential pressure across the filter is satisfied (S15 / YES), the ECU 50 acquires the differential pressure across the filter from the filter differential pressure sensor 66 (step S17).

  Next, the ECU 50 calculates a corrected filter front-rear differential pressure obtained by correcting the acquired filter front-rear differential pressure (step S19). In the present embodiment, the ECU 50 acquires the correction coefficient from the map shown in FIG. 4 based on the atmospheric pressure acquired from the atmospheric pressure sensor 68 when the differential pressure across the filter is acquired in step S17. In the present embodiment, the correction coefficient is a coefficient determined as “1” when atmospheric pressure = 101.325 kPa, and the correction coefficient decreases as the atmospheric pressure decreases. The ECU 50 calculates the corrected differential pressure before and after the filter by correcting the differential pressure before and after the filter to the differential pressure before and after the atmospheric pressure = 101.325 kPa by dividing the differential pressure before and after the filter by the correction coefficient. By this step, all the acquired differential pressure before and after the filter is corrected to the differential pressure before and after the filter under atmospheric pressure = 101.325 kPa based on the atmospheric pressure at the time when the respective differential pressure before and after the filter is acquired. Note that 101.325 kPa is an example of a predetermined atmospheric pressure, and the predetermined atmospheric pressure may not be 101.325 kPa and can take any value.

  Next, the ECU 50 stores the exhaust gas flow rate acquired in step S13 and the correction filter front-rear differential pressure calculated in step S19 (step S20).

  Next, the ECU 50 determines whether or not the number of data of differential pressure before and after the correction filter has reached n (step S21). n is the number of data necessary for determining the abnormality of the filter, and can be 25, for example.

  When the number of data of the differential pressure before and after the correction filter is not n (S21 / NO), the ECU 50 ends the process of FIG.

  On the other hand, when the number of data of the differential pressure before and after the correction filter is n (S21 / YES), the ECU 50 calculates and stores an average filter differential pressure before and after averaging the n correction filter differential pressures before and after (step 21). S23).

  Next, the ECU 50 calculates and stores an average exhaust gas flow rate obtained by averaging the n stored exhaust gas flow rate data (step S25), and ends the processing of FIG. In addition, the process of step S23 and step S25 may be performed in parallel, and the order may be changed.

  Next, filter abnormality determination processing executed by the ECU 50 will be described. FIG. 5 is a flowchart illustrating an example of a filter abnormality determination process executed by the ECU 50.

  When the processing of FIG. 5 is started, the ECU 50 first determines whether or not the ignition switch (IGSW) has been turned “OFF” (step S51). When the ignition switch is not set to “OFF” (S51 / NO), the ECU 50 ends the process of FIG.

  On the other hand, when the ignition switch is turned “OFF” (S51 / YES), the ECU 50 determines whether or not the average differential pressure before and after the filter is stored (step S53). If the average differential pressure before and after the filter is not stored (S53 / NO), the ECU 50 ends the process of FIG.

  On the other hand, when the average differential pressure before and after the filter is stored (S53 / YES), the ECU 50 calculates a threshold value used for determining the abnormality of the filter (step S55). For example, the ECU 50 uses the average exhaust gas flow rate calculated in step S25 of FIG. 3 to calculate the threshold value from a map in which the relationship between the exhaust gas flow rate and the threshold value under atmospheric pressure = 101.325 kPa is plotted.

  Next, the ECU 50 determines whether or not the average differential pressure before and after the filter is greater than or equal to a threshold value (step S59).

  If the average differential pressure before and after the filter is less than the threshold value (S59 / NO), the ECU 50 turns on a normal flag indicating that the filter 42 is normal (step S61), and ends the process of FIG.

  On the other hand, if the average differential pressure before and after the filter is equal to or greater than the threshold value (S59 / YES), the ECU 50 turns on an abnormality flag indicating that the filter 42 is abnormal (step S63), and ends the process of FIG.

  6A is a diagram showing the relationship between the differential pressure across the filter acquired by the filter differential pressure sensor 66 and the exhaust gas flow rate, and FIG. 6B is the relationship between the corrected differential pressure across the filter and the exhaust gas flow rate. FIG. In FIGS. 6A and 6B, the solid line represents a threshold value for determining that the filter is abnormal, and the filter abnormality determination process is an area where the exhaust gas flow rate is equal to or greater than a predetermined value indicated by a one-point difference line. (Abnormality determination target area).

  As shown in FIG. 6A, when the differential pressure before and after the filter is not corrected, there are many values below the threshold indicated by the straight line L1 in the abnormality determination target region, and there is no abnormality even though the filter 42 is not abnormal. There is a possibility that it is misjudged that this has occurred. On the other hand, as shown in FIG. 6B, when the differential pressure before and after the filter is corrected to the differential pressure before and after the filter under atmospheric pressure = 101.325 kPa, the value below the threshold value is decreased and an abnormality occurs. It is possible to determine that the filter 42 (normal product) that is not normal is normal.

  As is clear from the above description, the engine system 100 according to the present embodiment is provided in the exhaust passage 30 and collects the particulate matter in the exhaust, the pressure upstream of the filter 42 on the exhaust side, A filter differential pressure sensor 66 that detects a differential pressure ΔPf before and after the filter that is a difference from the pressure on the exhaust downstream side of the filter 42, an atmospheric pressure sensor 68 that detects an atmospheric pressure around the internal combustion engine 20, and a differential pressure ΔPf before and after the filter Based on the atmospheric pressure detected by the atmospheric pressure sensor 68 at the time when is detected, the detected filter front-rear differential pressure ΔPf is changed to a corrected filter front-rear differential pressure that is a differential pressure across the filter under atmospheric pressure = 101.325 kPa. Correcting, calculating an average filter front-rear differential pressure that is an average of a plurality of correction filter front-rear differential pressures, and based on whether the average filter front-rear differential pressure is greater than or equal to a threshold, Determines whether there is an abnormality in filter 42 comprises a ECU 50, the. Since all the differential pressure ΔPf before and after the filter detected by the filter differential pressure sensor 66 is corrected to the differential pressure before and after the filter under the atmospheric pressure = 101.325 kPa based on the atmospheric pressure at the time of obtaining the differential pressure ΔPf before and after the filter, The influence of the atmospheric pressure at the time when the differential pressure is acquired on the differential pressure before and after the filter can be eliminated. As a result, the data of the differential pressure before and after the filter acquired in an environment where the atmospheric pressure is low reduces the average differential pressure before and after the filter, and erroneously determines that the filter 42 is normal but is abnormal. Can be reduced.

  The above-described embodiments are merely examples for carrying out the present invention, and the present invention is not limited to these. Various modifications of these embodiments are within the scope of the present invention, and It is apparent from the above description that various other embodiments are possible within the scope.

20 Internal combustion engine 30 Exhaust passage 42 Filter 50 ECU
66 Differential pressure sensor 68 Atmospheric pressure sensor 100 Engine system (exhaust gas purification device for internal combustion engine)

Claims (1)

A filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
A differential pressure detector for detecting a differential pressure across the filter, which is a difference between the pressure on the exhaust upstream side of the filter and the pressure on the exhaust downstream side of the filter;
An atmospheric pressure detector for detecting atmospheric pressure around the internal combustion engine;
Based on the atmospheric pressure detected by the atmospheric pressure detector when the differential pressure across the filter is detected, the detected differential pressure across the filter is a correction filter that is the differential pressure across the filter under a predetermined atmospheric pressure. A correction unit that corrects the differential pressure across the front and back;
An average calculating unit that calculates an average filter front-rear differential pressure that is an average of the plurality of correction filter front-rear differential pressures;
A determination unit that determines whether or not the filter has an abnormality based on whether or not the average differential pressure before and after the filter is greater than or equal to a threshold;
An exhaust gas purification apparatus for an internal combustion engine.

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