JP2018204517A - Exhaust treatment device for engine - Google Patents

Abstract

To accurately estimate PM accumulation amount in a PM sensor even in a transient state.SOLUTION: An exhaust treatment device for an engine includes: a filter for collecting particulate matters in exhaust gas; a PM sensor provided in a portion downstream of the filter in an exhaust passage; and an ECU. The ECU calculates estimated PM accumulation speed Ve (estimated value of PM accumulation speed to the PM sensor) by using flow speed of the exhaust gas, a soot concentration in the exhaust gas and a temperature difference between the exhaust gas and the PM sensor, and calculates estimated PM accumulation amount (estimated value of PM accumulation amount in the PM sensor) by using the estimated PM accumulation speed Ve. The ECU makes a transient correction for correcting the estimated PM accumulation speed Ve by using change speed ΔVg of the flow speed of the exhaust gas when the change speed ΔVg of the flow speed of the exhaust gas exceeds a reference value Vth.SELECTED DRAWING: Figure 10

Description

  The present disclosure relates to a technique for determining whether there is an abnormality in a filter that collects particulate matter (PM) contained in engine exhaust.

  In general, an exhaust treatment device having a filter (Diesel Particulate Filter) for collecting PM contained in exhaust gas is provided in an exhaust passage of a diesel engine. Some exhaust treatment apparatuses are provided with a PM sensor in order to determine the presence or absence of a filter abnormality (such as cracking or melting). The PM sensor has a sensor element provided in a portion downstream of the filter in the exhaust passage. The sensor element includes a ceramic element that does not conduct electricity and two electrodes that are arranged on the surface of the ceramic element at a predetermined distance. The PM sensor has an electrical resistance between electrodes when the amount of PM deposited on the sensor element (hereinafter also referred to as “PM deposition amount”) exceeds an allowable value and an electrical path is formed between two electrodes. A corresponding current signal is output.

  Japanese Patent Laying-Open No. 2015-135078 (Patent Document 1) discloses an abnormality determination system that performs filter abnormality determination using a PM sensor. This abnormality determination system estimates the amount of PM accumulated on the sensor element, and determines whether there is a filter abnormality based on the output of the PM sensor when the estimated amount of PM accumulation reaches a determination value. Perform filter abnormality determination. Furthermore, this abnormality determination system calculates the change speed (variation amount per unit time) of the exhaust gas flowing through the exhaust passage where the PM sensor is installed, and when the change speed of the exhaust gas flow exceeds the reference value, In view of the fact that PM accumulation on the sensor element may not be performed satisfactorily due to fluctuations in the exhaust flow velocity, the PM accumulation amount estimated so far is reset, and a filter abnormality based on the output of the PM sensor Judgment is not made.

Japanese Patent Laid-Open No. 2015-135078

  However, in the abnormality determination system disclosed in Patent Document 1, the estimated PM accumulation amount is reset in a transient state in which the change rate of the exhaust gas flow rate exceeds the reference value. Therefore, when the engine is driven so as to include many transient states, the estimated PM accumulation amount is frequently reset, and the filter abnormality determination based on the output of the PM sensor cannot be executed at a desired timing. Concerned.

  The present disclosure has been made in order to solve the above-described problem, and an object thereof is to accurately estimate the PM deposition amount in the PM sensor even in a transient state.

  (1) An engine exhaust treatment apparatus according to the present disclosure includes a filter that is provided in an exhaust passage of an engine, collects particulate matter in exhaust gas, and a detection element that is provided in a portion downstream of the filter in the exhaust passage. And a PM sensor that outputs a signal corresponding to the PM deposition amount, which is the amount of particulate matter deposited on the detection element, and a control device. The control device calculates a PM deposition rate indicating the deposition rate of the particulate matter on the detection element using at least one of the flow rate of the exhaust gas in the exhaust passage, the soot concentration in the exhaust gas, and the temperature difference between the exhaust gas and the detection element. The estimated PM deposition amount, which is an estimated value of the particulate matter deposition amount on the detection element, can be calculated using the PM deposition rate. Further, the control device calculates at least one parameter among the change rate of the exhaust gas flow rate, the change rate of the soot concentration, and the change rate of the temperature difference, and the calculated parameter value is a reference value corresponding to the parameter. In the case of exceeding, the correction coefficient corresponding to the parameter exceeding the corresponding reference value is calculated, the transient correction for correcting the PM deposition rate is performed using the calculated correction coefficient, and the PM deposition rate corrected by the transient correction is calculated. And configured to calculate an estimated PM deposition amount.

  According to the above configuration, when at least one of the exhaust gas flow rate change rate, the soot concentration change rate, and the temperature difference change rate exceeds a reference value corresponding to the parameter (that is, in a transient state), the reference Transient correction is performed to correct the PM deposition rate using a parameter exceeding the value. As a result, the PM deposition rate after transient correction is closer to the actual PM deposition rate than when no transient correction is performed. Then, the estimated PM deposition amount is calculated using the PM deposition rate after the transient correction. As a result, the PM accumulation amount in the PM sensor can be accurately estimated even in a transient state.

  (2) In an embodiment, the transient correction is performed when the change rate of the exhaust gas flow rate exceeds a corresponding reference value, and the PM deposition rate than when the change rate of the exhaust gas flow rate does not exceed the corresponding reference value. Includes a process of correcting to a small value.

  Some PM sensors have such characteristics that the larger the change rate of the exhaust gas flow rate is, the more the change rate of the exhaust gas flow rate is, the more the intake of exhaust gas into the PM sensor is inhibited, and the PM deposition rate becomes smaller. In view of this point, in the above configuration, when the change rate of the flow rate of the exhaust gas exceeds the reference value, the PM deposition rate is corrected to a small value by the transient correction. Therefore, when a PM sensor having a characteristic that the PM deposition rate decreases as the change rate of the exhaust gas flow rate increases, the PM deposition rate after transient correction can be made closer to the actual PM deposition rate.

  (3) In one embodiment, the control device calculates two or more parameters of the exhaust gas flow rate change rate, the soot concentration change rate, and the temperature difference change rate when performing the transient correction. Two or more correction coefficients respectively corresponding to two or more parameters are calculated, and the PM deposition rate is corrected using the minimum value or the maximum value of the two or more calculated correction coefficients.

  According to the above configuration, when performing transient correction, it is possible to prevent excessive correction by reflecting all the correction coefficients corresponding to each of the plurality of parameters in the calculation of the PM deposition rate.

  (4) An engine exhaust treatment apparatus according to the present disclosure includes a filter that is provided in an exhaust passage of an engine and collects particulate matter in the exhaust, and a detection element that is provided in a portion downstream of the filter in the exhaust passage. And a PM sensor that outputs a signal corresponding to the PM deposition amount, which is the amount of particulate matter deposited on the detection element, and a control device. The control device is configured to be able to calculate an estimated PM deposition amount, which is an estimated value of the particulate matter deposition amount on the detection element, using at least one of the soot concentration in the exhaust gas and the temperature difference between the exhaust gas and the detection element. The When at least one of the soot concentration change rate and the temperature difference change rate exceeds a reference value corresponding to the parameter, the control device corrects the estimated PM deposition amount using the parameter exceeding the corresponding reference value.

  According to the above configuration, when at least one of the change rate of the soot concentration and the change rate of the temperature difference exceeds a reference value corresponding to the parameter (that is, in a transient state), the parameter exceeding the reference value is used. The estimated PM accumulation amount is corrected. As a result, the PM accumulation amount in the PM sensor can be accurately estimated even in a transient state.

An example of the whole block diagram of an exhaust-gas treatment apparatus is shown. It is a figure which shows the schematic structure of PM sensor, and the installation state to the exhaust passage of PM sensor. It is the figure which expanded a part of sensor element of PM sensor. It is a figure which shows typically an example of the correspondence of PM deposition rate and exhaust flow velocity Vg. It is a figure which shows typically an example of the correspondence of PM deposition rate and soot density | concentration Cs in exhaust_gas | exhaustion. It is a figure which shows typically an example of the correspondence of PM deposition rate and the temperature difference Dt of PM sensor and exhaust_gas | exhaustion. It is the figure which showed the ratio of the deviation | shift amount with respect to the actual PM deposition amount A of the estimated PM deposition amount Ae calculated by the conventional method for every some driving | operation pattern of an engine. It is a figure which shows typically the taking-in state of the exhaust_gas | exhaustion in PM sensor in a steady state. It is a figure which shows typically the taking-in state of the exhaust_gas | exhaustion in PM sensor in a transient state. It is a flowchart (the 1) which shows an example of the process sequence of ECU. FIG. 6 is a diagram (No. 1) showing a correspondence relationship between a change rate ΔVg of an exhaust flow velocity and a transient correction coefficient Kg. It is a figure which shows an example of the change of the engine speed Ne, the exhaust gas flow velocity Vg, the estimated PM deposition speed Ve, the estimated PM deposition amount Ae, and the PM sensor output I in the operation pattern with few sudden accelerations. It is a figure which shows an example of the change of the engine rotational speed Ne, the exhaust gas flow velocity Vg, the estimated PM deposition speed Ve, the estimated PM deposition amount Ae, and the PM sensor output I in the operation pattern with many rapid accelerations. FIG. 6 is a diagram (No. 2) showing a correspondence relationship between the change rate ΔVg of the exhaust flow velocity and the transient correction coefficient Kg. It is a figure which shows an example of the correspondence of the change rate (DELTA) Cs of soot density, and the transient correction coefficient Kc. It is a figure which shows an example of the correspondence of temperature change rate (DELTA) Dt and the transient correction coefficient Kt. It is a flowchart (the 2) which shows an example of the process sequence of ECU.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  FIG. 1 is a diagram schematically showing an example of the overall configuration of an exhaust treatment apparatus according to the present embodiment. This exhaust treatment device is a device that purifies exhaust from the engine 10, and includes an oxidation catalyst 13, a filter 14, a fuel addition valve 30, a PM sensor 80, an electronic control unit (hereinafter referred to as "ECU"). 100).

  The engine 10 is a general diesel engine. The engine 10 may be a gasoline engine. The engine 10 is provided with an engine rotation speed sensor 50. Engine rotation speed sensor 50 detects the rotation speed of engine 10 (hereinafter referred to as “engine rotation speed Ne”), and outputs the detection result to ECU 100.

  Each cylinder of the engine 10 is provided with a fuel injection valve 20. Each fuel injection valve 20 is supplied with fuel from a fuel tank by a fuel pump (not shown). Each fuel injection valve 20 is actuated (opened) by a control signal from the ECU 100 to inject fuel into each cylinder.

  An intake passage 11 and an exhaust passage 12 are connected to the engine 10. An air flow meter 40 is provided in the intake passage 11. The air flow meter 40 detects the intake flow rate Ga flowing through the intake passage 11 and outputs the detection result to the ECU 100.

  The exhaust passage 12 is provided with an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 13 that oxidizes and purifies hydrocarbon (HC) and carbon monoxide (CO) in the exhaust. Further, a filter 14 for collecting PM in the exhaust gas is provided in a portion of the exhaust passage 12 downstream of the oxidation catalyst 13. The filter 14 is composed of a porous ceramic structure, and PM in the exhaust gas is collected when passing through the porous wall.

  A fuel addition valve 30 is provided in the exhaust passage 12 upstream of the oxidation catalyst 13. The fuel addition valve 30 is supplied with fuel from a fuel tank by a fuel pump (not shown). The fuel addition valve 30 is actuated (opened) by a control signal from the ECU 100 and injects fuel into a portion of the exhaust passage 12 upstream of the oxidation catalyst 13.

  Furthermore, three temperature sensors 60, 61, 62 are provided in the exhaust passage 12. The temperature sensor 60 detects the temperature Ta of the exhaust gas flowing near the entrance of the oxidation catalyst 13 and outputs the detection result to the ECU 100. The temperature sensor 61 detects the temperature Tb of the exhaust flowing near the inlet of the filter 14 and outputs the detection result to the ECU 100. The temperature sensor 62 detects the temperature Tc of the exhaust flowing near the outlet of the filter 14 and outputs the detection result to the ECU 100.

  The PM sensor 80 is provided in a portion downstream of the filter 14 in the exhaust passage 12. The structure of the PM sensor 80 will be described later.

  The ECU 100 includes a CPU (Central Processing Unit) and a memory 101 (not shown). The ECU 100 executes various controls related to the engine 10 based on information stored in the memory 101 and information from various sensors.

  In the engine 10 configured as described above, PM contained in the exhaust gas is collected by the filter 14 and the release to the outside is suppressed. However, if cracks or erosion occurs in the base material of the filter 14, the PM trapping function is lowered, and an abnormal state may occur in which sufficient PM trapping cannot be performed.

  Therefore, ECU 100 uses the output of PM sensor 80 disposed on the downstream side of filter 14 to perform processing for determining whether filter 14 is abnormal (hereinafter also referred to as “filter abnormality determination processing”). In describing the filter abnormality determination process, first, the structure of the PM sensor 80 will be described.

  FIG. 2 is a diagram illustrating a schematic configuration of the PM sensor 80 and a state in which the PM sensor 80 is installed in the exhaust passage 12.

  The PM sensor 80 includes a sensor element 81 on which PM in exhaust gas adheres and accumulates, an inner cover 82 that covers the sensor element 81, and an outer cover 83 that covers the inner cover 82. Between the inner cover 82 and the outer cover 83, an exhaust passage 80a through which exhaust flows is formed along the longitudinal direction of both covers (the longitudinal direction of the sensor element 81). The exhaust passage 80 a has one end 80 b communicating with the exhaust passage 12 and the other connected to an exhaust passage 80 e formed in the inner cover 82. An end 80 c of the exhaust passage 80 e on the exhaust passage 12 side is communicated with the exhaust passage 12.

  Therefore, in the PM sensor 80, the exhaust gas is taken into the exhaust flow channel 80a from the end 80b that is the opening of the exhaust flow channel 80a, and further flows into the exhaust flow channel 80e. It returns to the exhaust passage 12 from the end 80c. Since exhaust gas taken into the PM sensor 80 in this way contacts the sensor element 81 when flowing through the exhaust flow path 80e, PM in the exhaust gas adheres to and accumulates on the sensor element 81.

  FIG. 3 is an enlarged view of a part of the sensor element 81 of the PM sensor 80. The sensor element 81 includes a ceramic element C that does not conduct electricity and a pair of electrodes T1 and T2 that are disposed on the surface of the ceramic element C. The pair of electrodes T1 and T2 are arranged at a constant interval from each other without being in contact with each other.

  The ceramic element C has a function of attaching PM. When a voltage from a power supply circuit or the like (not shown) is applied between the electrodes T1 and T2, an electric field is generated between the electrodes T1 and T2, and the charged PM in the exhaust gas is attracted by the electric field, and the electrodes T1 and T2 are attracted. PM accumulates.

  A temperature sensor U and a heater H are embedded in the ceramic element C. The temperature sensor U detects the temperature in the vicinity of the electrodes T1 and T2 as the PM sensor temperature, and outputs the detection result to the ECU 100. The heater H is configured to be energized via a power supply circuit or the like. The heater H generates heat and heats the sensor element 81 by energization from a power supply circuit or the like, and burns and removes PM deposited between the electrodes T1 and T2. Hereinafter, the process of energizing the heater H and removing the PM deposited between the electrodes T1 and T2 is also referred to as “PM sensor regeneration process”.

  PM sensor 80 is electrically connected to ECU 100. PM sensor 80 then outputs to ECU 100 a current I corresponding to the electrical resistance between electrodes T1 and T2. ECU 100 can detect the amount of PM in the exhaust based on current I output from PM sensor 80 (hereinafter also referred to as “PM sensor output I”). Specifically, the PM detection by the PM sensor 80 is started immediately after the PM sensor regeneration process is performed. Immediately after the PM sensor regeneration process, PM is not deposited between the electrodes T1 and T2, so that the electrodes T1 and T2 are insulated, and the PM sensor output I becomes zero.

  And exhaust_gas | exhaustion is taken in in the PM sensor 80, and PM accumulates gradually between electrodes T1, T2. In a state where the amount of PM deposited between the electrodes T1 and T2 of the PM sensor 80 (hereinafter also simply referred to as “PM deposition amount A”) is small, a conduction path due to the PM deposited between the electrodes T1 and T2 is not yet formed. Therefore, the electrodes T1 and T2 are still insulated, and the PM sensor output I remains zero. Thereafter, PM is further deposited between the electrodes T1 and T2, and when the PM deposition amount A reaches a certain amount, a conduction path is formed between the electrodes T1 and T2 by the deposited PM. When such a conduction path is formed, the electrical resistance between the electrodes T1 and T2 decreases, and the PM sensor output I begins to increase. As the PM deposition amount A increases, the conduction path increases and the electrical resistance between the electrodes T1 and T2 further decreases, so the PM sensor output I increases.

  The filter abnormality determination process described above is performed based on whether or not the PM sensor output I is larger than the threshold value Ith. In order to effectively perform the filter abnormality determination process, it is necessary to capture PM for a predetermined period in the PM sensor 80 and reflect the abnormal state of the filter 14 in the PM accumulation amount. Therefore, the ECU 100 assumes that a part of the exhaust discharged from the engine 10 and passed through the filter 14 is taken into the PM sensor 80, and that the PM contained in the taken-out exhaust is deposited on the sensor element 81. An estimated value (hereinafter also referred to as “estimated PM deposition amount Ae”) of the PM deposition amount is calculated. Then, the filter abnormality determination process based on the PM sensor output I is performed at the timing when the estimated PM accumulation amount Ae reaches the “determination value Ath” set as the PM accumulation amount that enables effective abnormality determination. Therefore, in order to perform the filter abnormality determination process with high accuracy, it is important to calculate the estimated PM accumulation amount Ae with high accuracy.

  Here, the amount of PM deposited on the sensor element 81 per unit time (hereinafter also referred to as “PM deposition rate”) is the exhaust flow velocity Vg, the soot concentration Cs in the exhaust, and the exhaust and PM sensor 80 (sensor element 81). It has been conventionally known that there is a characteristic that changes according to the temperature difference Dt.

  FIG. 4 is a diagram schematically showing an example of the correspondence relationship between the PM deposition rate and the exhaust flow velocity Vg. As shown in FIG. 4, the PM deposition rate increases as the exhaust flow velocity Vg increases, because the amount of PM that contacts the sensor element 81 increases.

  FIG. 5 is a diagram schematically showing an example of the correspondence relationship between the PM deposition rate and the soot concentration Cs in the exhaust gas. As shown in FIG. 5, the higher the soot concentration Cs, the greater the amount of PM in the exhaust gas, so the PM deposition rate increases.

  FIG. 6 is a diagram schematically illustrating an example of the correspondence relationship between the PM deposition rate and the temperature difference Dt between the exhaust gas and the PM sensor 80. As shown in FIG. 6, the PM deposition rate increases as the temperature difference Dt increases, because PM is attracted from the high-temperature exhaust to the low-temperature sensor element 81 by thermophoresis.

  Conventionally, based on the characteristics shown in FIGS. 4 to 6, an estimated PM deposition rate Ve is obtained by using the exhaust flow velocity Vg, the soot concentration Cs, and the temperature difference Dt as parameters, and the estimated PM deposition rate Ve is integrated to estimate PM. The mainstream is to determine the deposition amount Ae.

  However, the inventors of the present application have shown that the characteristics shown in FIGS. 4 to 6 are characteristics in a steady state where each parameter is stable, and in the transient state where each parameter fluctuates, the characteristics shown in FIGS. It was found by experiments and the like that the estimated PM deposition amount Ae calculated by the conventional method may deviate from the actual PM deposition amount A.

  FIG. 7 is a diagram showing the ratio of the amount of deviation of the estimated PM accumulation amount Ae calculated by the conventional method with respect to the actually measured PM accumulation amount A for each of a plurality of operation patterns P1 to P8 of the engine 10. is there. Here, the driving patterns P1 to P4 are driving patterns with a relatively large acceleration and a large transient state (less steady running), and the driving patterns P5 to P8 have a relatively small acceleration and a lot of steady running (many transient states). It is a driving pattern. As is clear from FIG. 7, in the operation patterns P1 to P4 including many transient states, the estimated PM deposition amount Ae calculated by the conventional method was actually measured as compared with the operation patterns P5 to P8 including many steady states. It can be understood that there is a considerable deviation from the PM deposition amount A.

  FIG. 8 is a diagram schematically showing the state of intake of exhaust gas into the PM sensor 80 in a steady state where the exhaust gas flow velocity Vg is stable at the predetermined value V1. In a steady state, the intake amount of exhaust is relatively stably ensured.

  FIG. 9 is a diagram schematically showing the state of intake of exhaust gas into the PM sensor 80 in a transient state (accelerated state) that temporarily becomes the predetermined value V1 while the exhaust flow velocity Vg is increasing. In the transient state, the intake of the exhaust gas into the PM sensor 80 is hindered by the fluctuation of the exhaust gas flow velocity Vg, and the intake amount of the exhaust gas tends to be smaller than that in the steady state due to the influence. As a result, in the transient state, the PM deposition on the sensor element 81 is not performed well and the PM deposition rate is lower than in the steady state.

  Therefore, the ECU 100 according to the present embodiment calculates the exhaust flow rate change rate ΔVg, and corrects the estimated PM deposition rate Ve using the exhaust flow rate change rate ΔVg when the exhaust flow rate change rate ΔVg exceeds the reference value Vth. Perform “transient correction”. As a result, the estimated PM deposition rate Ve becomes closer to the actual PM deposition rate than when no transient correction is performed. As a result, the estimated PM accumulation amount Ae can be accurately calculated even in a transient state.

  FIG. 10 is a flowchart illustrating an example of a processing procedure executed when the ECU 100 performs the filter abnormality determination process. This flowchart is started at the start of operation of the engine 10, for example.

  First, the ECU 100 executes the “PM sensor regeneration process” described above (step S10). Thereby, PM deposited between the electrodes T1, T2 of the sensor element 81 of the PM sensor 80 is removed.

  When the PM sensor regeneration process ends, the ECU 100 calculates the exhaust flow velocity Vg, the soot concentration Cs, and the temperature difference Dt, which are parameters for calculating the estimated PM deposition rate Ve (step S11).

  For example, the ECU 100 calculates the exhaust flow velocity Vg using the intake flow rate Ga or the like as a parameter. Further, the ECU 100 calculates the soot concentration Cs using the engine speed Ne, the fuel injection amount from the fuel injection valve 20, and the like as parameters. Further, the ECU 100 calculates a difference between the exhaust temperature estimated from the exhaust temperatures Ta to Tc and the PM sensor temperature detected by the temperature sensor U in the PM sensor 80 as a temperature difference Dt.

  Next, the ECU 100 calculates an estimated PM deposition rate Ve using the exhaust gas flow rate Vg, the soot concentration Cs, and the temperature difference Dt as parameters (step S12). For example, the ECU 100 refers to a map or the like created in consideration of the characteristics shown in FIGS. 4 to 6 described above, and determines the estimated PM deposition rate Ve corresponding to the exhaust gas flow rate Vg, the soot concentration Cs, and the temperature difference Dt. calculate.

  Next, the ECU 100 calculates a change rate ΔVg of the exhaust flow rate (step S14). For example, the ECU 100 calculates the change rate ΔVg of the exhaust flow velocity from the difference between the exhaust flow velocity Vg at the previous calculation and the exhaust flow velocity Vg at the current calculation. Note that the method for calculating the exhaust flow rate change rate ΔVg is not limited to this. For example, in view of the fact that the exhaust flow velocity Vg becomes a transient state due to a change in the engine rotational speed Ne or a change in the fuel injection amount, the exhaust flow velocity change rate ΔVg is calculated from the change in the engine rotational speed Ne and the change in the fuel injection amount. It may be.

  Next, the ECU 100 determines whether or not the exhaust gas flow rate change rate ΔVg exceeds the reference value Vth (step S20). Here, the reference value Vth is determined that the exhaust gas intake failure into the PM sensor 80 is caused by the change rate ΔVe of the exhaust gas flow rate being increased, thereby causing a deviation from the characteristics shown in FIG. For the threshold.

  If the change rate ΔVg of the exhaust flow rate does not exceed the reference value Vth (NO in step S20), there is no exhaust intake failure into the PM sensor 80, and there is no deviation from the characteristics shown in FIG. The ECU 100 skips the transient correction process (steps S22 and S24), and proceeds to S26.

  On the other hand, when the change rate ΔVg of the exhaust flow rate exceeds the reference value Vth (YES in step S20), it is assumed that there is a deviation from the characteristics shown in FIG. 4 due to exhaust intake failure into the PM sensor 80. Therefore, the ECU 100 corrects the estimated PM deposition speed Ve calculated in step S12 using the exhaust flow velocity change speed ΔVg (steps S22 and S24).

  Specifically, the ECU 100 calculates a transient correction coefficient Kg based on the exhaust flow rate change rate ΔVg (step S22). This transient correction coefficient Kg is a coefficient for reflecting the influence of the exhaust flow rate change rate ΔVg on the estimated PM accumulation amount Ae calculated in step S12.

  FIG. 11 is a diagram showing a correspondence relationship between the change rate ΔVg of the exhaust flow rate and the transient correction coefficient Kg. When the exhaust flow rate change rate ΔVg is the reference value Vth, the transient correction coefficient Kg is set to “1.0”, and the transient correction factor Kg is set to be smaller as the exhaust flow rate change rate ΔVg increases. . This reflects the characteristic that, as the change rate ΔVg of the exhaust gas flow rate increases, the intake of the exhaust gas into the PM sensor 80 is hindered and the PM deposition rate decreases. For example, the ECU 100 calculates a transient correction coefficient Kg corresponding to the change rate ΔVg of the exhaust flow velocity with reference to a map or the like created in consideration of the correspondence shown in FIG.

  Returning to FIG. 10, after calculating the transient correction coefficient Kg, the ECU 100 performs “transient correction” for correcting the estimated PM deposition rate Ve calculated in step S12 using the transient correction coefficient Kg (step S24). Specifically, the ECU 100 sets a value obtained by multiplying the estimated PM deposition rate Ve calculated in step S12 by the transient correction coefficient Kg calculated in step S22 as the estimated PM deposition rate Ve after the transient correction.

  Next, the ECU 100 calculates the estimated PM deposition amount Ae using the estimated PM deposition speed Ve calculated in step S22 or step S26 and the following equation (1) (step S26).

Ae (n) = Ae (n−1) + Ve · Δt (1)
In Expression (1), “Ae (n)” is the estimated PM accumulation amount Ae calculated in the current calculation, and “Ae (n−1)” is the estimated PM accumulation amount Ae calculated in the previous calculation. is there. “Δt” is the elapsed time from the previous calculation to the current calculation.

  Next, the ECU 100 determines whether or not the estimated PM accumulation amount Ae (n) calculated in step S26 has reached the determination value Ath (step S30). Here, as described above, the determination value Ath is a value set as a PM accumulation amount that enables effective filter abnormality determination processing.

  If estimated PM accumulation amount Ae (n) has not reached determination value Ath (NO in step S30), ECU 100 returns the process to step S11, and steps until estimated PM accumulation amount Ae (n) reaches determination value Ath. The processes of S11 to S30 are repeated.

  When estimated PM accumulation amount Ae (n) reaches determination value Ath (YES in step S30), ECU 100 performs the above-described filter abnormality determination process (steps S40 to S44).

  Specifically, ECU 100 determines whether PM sensor output I is larger than threshold value Ith (step S40). When PM sensor output I is larger than threshold value Ith (YES in step S40), ECU 100 determines that filter 14 is abnormal (step S42). When PM sensor output I is smaller than threshold value Ith (NO in step S40), ECU 100 determines that filter 14 is normal (step S44).

  In step S40, it is determined whether or not the timing at which the PM sensor output I becomes larger than the threshold value Ith is earlier than the timing at which the estimated PM deposition amount Ae (n) reaches the determination value Ath. May be. In this case, the ECU 100 determines that the filter 14 is abnormal when the timing at which the PM sensor output I becomes larger than the threshold value Ith is earlier than the timing at which the estimated PM accumulation amount Ae (n) reaches the determination value Ath. If not, it can be determined that the filter 14 is normal.

  FIG. 12 is a diagram illustrating an example of changes in the engine rotation speed Ne, the exhaust gas flow velocity Vg, the estimated PM deposition speed Ve, the estimated PM deposition amount Ae, and the PM sensor output I in an operation pattern with little rapid acceleration. When the rapid acceleration is small, the exhaust flow velocity Vg does not change abruptly, and the exhaust flow velocity change speed ΔVg hardly exceeds the reference value Vth. Therefore, the transient correction of the estimated PM deposition rate Ve is hardly performed, and the estimated PM deposition rate Ve is a value calculated using the steady state characteristics as usual.

  In the example shown in FIG. 12, the estimated PM accumulation amount Ae reaches the determination value Ath at time t1, and the PM sensor output I is larger than the threshold value Ith at this timing, so that it is determined that the filter 14 is abnormal. The

  FIG. 13 is a diagram illustrating an example of changes in the engine rotation speed Ne, the exhaust flow velocity Vg, the estimated PM deposition speed Ve, the estimated PM deposition amount Ae, and the PM sensor output I in an operation pattern in which rapid acceleration is frequent. When there is a lot of rapid acceleration, the exhaust flow velocity Vg changes abruptly. Due to this influence, the exhaust gas is not taken into the PM sensor 80, and the actual PM deposition rate decreases.

  Nevertheless, if the estimated PM deposition rate Ve is calculated using only steady-state characteristics as in the past (one-dot chain line), the estimated PM deposition rate Ve becomes larger than the actual PM deposition rate. As a result, the estimated PM accumulation amount Ae reaches the determination value Ath at an early stage, and the filter abnormality determination process is executed at time t11 earlier than the appropriate timing. That is, at time t11, PM deposition on the sensor element 81 is not sufficiently performed. Therefore, if the filter abnormality determination process is performed at time t11, there is a concern that it may be erroneously determined to be normal although the filter 14 is actually abnormal.

  In contrast, the ECU 100 according to the present embodiment performs transient correction of the estimated PM accumulation amount Ae using the exhaust flow velocity change speed ΔVg every time the exhaust flow speed change speed ΔVg exceeds the reference value Vth. As a result, the estimated PM deposition amount Ae is close to the actual PM deposition rate as compared to the conventional value (one-dot chain line) in which the transient correction of the estimated PM deposition amount Ae is not performed. As a result, the estimated PM accumulation amount Ae gradually increases and becomes a value closer to the actual PM accumulation amount. Thereby, the erroneous determination as described above can be avoided.

  In the example shown in FIG. 13, the estimated PM accumulation amount Ae (solid line) after the transient correction reaches the determination value Ath at time t12, and the PM sensor output I is larger than the threshold value Ith at this timing. 14 is determined to be abnormal.

  As described above, the ECU 100 according to the present embodiment uses the exhaust flow velocity change rate ΔVg to calculate the estimated PM deposition amount Ae when the exhaust flow velocity change rate ΔVg is in a transient state exceeding the reference value Vth. The "transient correction" is performed to correct the estimated PM deposition rate Ve. As a result, the estimated PM deposition rate Ve after the transient correction becomes closer to the actual PM deposition rate than when the transient correction is not performed. Then, the ECU 100 calculates the estimated PM deposition amount Ae using the estimated PM deposition speed Ve after the transient correction. As a result, the estimated PM deposition amount Ae can be accurately calculated even in a transient state.

<Modification 1>
In the above-described embodiment, the example in which the transient correction coefficient Kg is decreased as the change rate ΔVg of the exhaust flow rate is increased (see FIG. 11). This is because the PM sensor 80 in the above-described embodiment has a characteristic that the PM deposition rate becomes smaller as the exhaust gas flow rate change rate ΔVg becomes larger, and this characteristic is reflected in the transient correction coefficient Kg. .

  However, depending on the shape of the inner cover 82 and the outer cover 83 of the PM sensor 80, the arrangement of the sensor element 81, and the like, it may be considered that the PM deposition rate increases as the exhaust flow rate change rate ΔVg increases. In such a case, according to the characteristics, the transient correction coefficient Kg may be set to increase as the exhaust flow rate change rate ΔVg increases.

  FIG. 14 is a diagram illustrating a correspondence relationship between the change rate ΔVg of the exhaust flow velocity and the transient correction coefficient Kg in the first modification. In this example, the transient correction coefficient Kg is set to “1.0” when the exhaust flow velocity change speed ΔVg is the reference value Vth, and the transient correction coefficient Kg increases as the exhaust flow speed change speed ΔVg increases. Is set.

<Modification 2>
In the above-described embodiment, when the exhaust flow velocity change rate ΔVg exceeds the reference value Vth, the transient correction coefficient Kg corresponding to the exhaust flow velocity change rate ΔVg is calculated, and the estimated PM accumulation is performed using the transient correction coefficient Kg. An example of correcting the speed Ve has been shown. However, the parameter for correcting the estimated PM deposition rate Ve is not limited to the exhaust flow rate change rate ΔVg.

  For example, the parameter for correcting the estimated PM deposition rate Ve may be the change rate ΔCs of the soot concentration in the exhaust instead of the change rate ΔVg of the exhaust flow rate. That is, when the soot concentration change rate ΔCs exceeds the reference value Cth, a transient correction coefficient Kc corresponding to the soot concentration change rate ΔCs is calculated, and the estimated PM deposition rate Ve is corrected using the transient correction coefficient Kc. It may be.

  FIG. 15 is a diagram illustrating an example of a correspondence relationship between the change rate ΔCs of the soot concentration and the transient correction coefficient Kc. In this example, when the soot concentration change rate ΔCs is the reference value Cth, the transient correction coefficient Kc is set to “1.0”, and as the soot concentration change rate ΔCs increases, the transient correction coefficient Kc is set to a smaller value. Is done.

  Further, the parameter for correcting the estimated PM deposition rate Ve may be the change rate ΔDt of the temperature difference between the exhaust gas and the PM sensor 80 (sensor element 81), instead of the change rate ΔVg of the exhaust gas flow rate. That is, when the temperature difference change rate ΔDt exceeds the reference value Dth, the transient correction coefficient Kt corresponding to the temperature difference change rate ΔDt is calculated, and the estimated PM deposition rate Ve is corrected using the transient correction coefficient Kt. It may be.

  FIG. 16 is a diagram illustrating an example of a correspondence relationship between the temperature difference change rate ΔDt and the transient correction coefficient Kt. In this example, when the temperature difference change rate ΔDt is the reference value Dth, the transient correction coefficient Kt is set to “1.0”, and as the temperature difference change rate ΔDt increases, the transient correction coefficient Kt is set to a smaller value. Is done.

  The parameters for correcting the estimated PM deposition rate Ve may be a soot concentration change rate ΔCs and a temperature difference change rate ΔDt in the exhaust gas instead of the exhaust gas flow rate change rate ΔVg.

<Modification 3>
Further, the transient correction coefficient Kg (see FIG. 11 or FIG. 14) corresponding to the exhaust flow rate change rate ΔVg, the transient correction coefficient Kc (see FIG. 15) corresponding to the soot concentration change rate ΔCs, and the temperature difference change rate ΔDt. A corresponding transient correction coefficient Kt (see FIG. 16) may be calculated, and the estimated PM deposition rate Ve may be corrected using the minimum value or the maximum value of these three transient correction coefficients.

  FIG. 17 is a flowchart illustrating an example of a processing procedure executed when the ECU 100 according to the present modification performs a filter abnormality determination process. In this flowchart, steps S20 to S26 in the flowchart of FIG. 10 are changed to steps S50 to S52. Since the other steps (steps denoted by the same numbers as the steps shown in FIG. 10 described above) have already been described, detailed description thereof will not be repeated here.

  After calculating the estimated PM deposition rate Ve in step S12, the ECU 100 calculates the exhaust flow rate change rate ΔVg, the soot concentration change rate ΔCs, and the temperature difference change rate ΔDt (step S50).

  Next, the ECU 100 calculates transient correction coefficients Kg, Kc, Kt based on the exhaust flow rate change rate ΔVg, the soot concentration change rate ΔCs, and the temperature difference change rate ΔDt, respectively (step S51). ECU 100 calculates transient correction coefficients Kg, Kc, and Kt, respectively, from the correspondence relationships shown in FIG. 11 (or FIG. 14), FIG. 15, and FIG.

  Next, the ECU 100 performs “transient correction” for correcting the estimated PM deposition rate Ve calculated in step S12 using the maximum value max (Kg, Kc, Kt) of the transient correction coefficients Kg, Kc, Kt ( Step S52). Specifically, the ECU 100 multiplies the estimated PM deposition rate Ve calculated in step S12 by the maximum value max (Kg, Kc, Kt) of the transient correction coefficients Kg, Kc, Kt after the correction. The estimated PM deposition rate Ve is used.

  The estimated PM deposition rate Ve may be corrected using the minimum value of the transient correction coefficients Kg, Kc, and Kt.

<Modification 4>
Further, by using the change rate ΔCs of the soot concentration in the exhaust gas and the change rate ΔDt of the temperature difference, the estimated PM deposition amount Ae is directly corrected instead of the estimated PM deposition rate Ve used to calculate the estimated PM deposition amount Ae. You may make it do.

  For example, the ECU 100 determines whether or not at least one parameter of the soot concentration change rate ΔCs and the temperature difference change rate ΔDt in the exhaust gas exceeds a corresponding reference value, and the at least one parameter corresponds to the corresponding reference value. When the value is exceeded, the estimated PM deposition amount Ae may be directly corrected using a parameter exceeding the reference value.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present disclosure is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 10 Engine, 11 Intake passage, 12 Exhaust passage, 13 Oxidation catalyst, 14 Filter, 20 Fuel injection valve, 30 Fuel addition valve, 40 Air flow meter, 50 Engine rotational speed sensor, 60, 61, 62 Temperature sensor, 80 PM sensor, 80a, 80e exhaust flow path, 80b, 80c end, 81 sensor element, 82 inner cover, 83 outer cover, 100 ECU, 101 memory.

Claims (4)

An engine exhaust treatment device,
A filter provided in an exhaust passage of the engine for collecting particulate matter in the exhaust;
A PM sensor having a detection element provided in a portion downstream of the filter in the exhaust passage, and outputting a signal corresponding to a PM deposition amount that is a deposition amount of particulate matter on the detection element;
Using at least one of the flow rate of exhaust in the exhaust passage, the soot concentration in the exhaust, and the temperature difference between the exhaust and the detection element, a PM deposition rate indicating the deposition rate of particulate matter on the detection element is obtained. And a control device configured to calculate an estimated PM deposition amount that is an estimated value of the particulate matter deposition amount on the detection element using the PM deposition rate,
The control device calculates at least one parameter of a change speed of the exhaust gas flow velocity, a change speed of the soot concentration, and a change speed of the temperature difference, and the calculated parameter value corresponds to the parameter. When the reference value is exceeded, a correction coefficient corresponding to the parameter exceeding the corresponding reference value is calculated, and a transient correction for correcting the PM deposition rate is performed using the calculated correction coefficient. An engine exhaust treatment apparatus configured to calculate the estimated PM deposition amount using the corrected PM deposition rate.   In the transient correction, when the change rate of the exhaust gas flow rate exceeds the corresponding reference value, the PM deposition rate is made smaller than when the change rate of the exhaust gas flow rate does not exceed the corresponding reference value. The engine exhaust processing apparatus according to claim 1, comprising a correction process.   When the transient correction is performed, the control device calculates two or more parameters of the exhaust gas flow rate change rate, the soot concentration change rate, and the temperature difference change rate, and the two or more parameters are calculated. 2 or more correction coefficients respectively corresponding to the parameters of the first and second correction coefficients are calculated, and the PM deposition rate is corrected using a minimum value or a maximum value of the calculated two or more correction coefficients. An engine exhaust treatment apparatus according to claim 1. An engine exhaust treatment device,
A filter provided in an exhaust passage of the engine for collecting particulate matter in the exhaust;
A PM sensor having a detection element provided in a portion downstream of the filter in the exhaust passage, and outputting a signal corresponding to a PM deposition amount that is a deposition amount of particulate matter on the detection element;
The estimated PM deposition amount, which is an estimated value of the particulate matter deposition amount on the detection element, is calculated using at least one of the soot concentration in the exhaust gas and the temperature difference between the exhaust gas and the detection element. Control device,
When at least one of the change rate of the soot concentration and the change rate of the temperature difference exceeds a reference value corresponding to the parameter, the control device uses the parameter exceeding the corresponding reference value to deposit the estimated PM An engine exhaust treatment device that corrects the amount.

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