JP7283444B2 - engine system - Google Patents

Description

The present invention relates to engine systems.

BACKGROUND ART As a conventional engine system, for example, the technique described in Patent Document 1 is known. The engine system described in Patent Document 1 includes a NOx storage reduction catalyst disposed in an exhaust gas passage of a diesel engine, and an excess air ratio sensor and a first NOx sensor disposed upstream of the NOx storage reduction catalyst. , a second NOx sensor disposed downstream of the NOx storage reduction catalyst, and a regeneration control device. The regeneration control device estimates the NOx storage amount of the NOx storage reduction type catalyst using the detection values of the first NOx sensor and the second NOx sensor, and when the NOx storage amount exceeds a predetermined determination amount, it is detected by the excess air ratio sensor. NOx regeneration control is performed by reducing and removing NOx stored in the NOx storage reduction catalyst when the obtained oxygen concentration is within a predetermined determination range.

JP 2008-291715 A

By the way, when the NOx stored in the NOx storage reduction catalyst (NOx purification catalyst) is periodically reduced and removed, a large amount of PM and unburned HC are generated from the engine. When the end face of the NOx storage reduction catalyst is clogged with PM and unburned HC contained in the exhaust gas, the NOx purification performance of the NOx storage reduction catalyst deteriorates, and output decreases due to worsening of emissions and lower back pressure. Therefore, in addition to measures to prevent the end face clogging of the NOx storage reduction type catalyst, the fact that the end face clogging of the NOx storage reduction type catalyst has occurred or is about to occur is detected with high accuracy, and the end face clogging of the NOx storage reduction type catalyst is detected. It is necessary to take measures to suppress or eliminate them.

SUMMARY OF THE INVENTION An object of the present invention is to provide an engine system capable of improving detection accuracy of end face clogging of a NOx purification catalyst.

An engine system according to an aspect of the present invention includes an engine, an exhaust passage connected to the engine through which exhaust gas generated in the engine flows, and a NOx purification system disposed in the exhaust passage to purify NOx contained in the exhaust gas. A first purification rate calculation for calculating an estimated NOx purification rate of the NOx purification catalyst based on the catalyst, a NOx detection unit that detects NOx existing at least downstream of the NOx purification catalyst, and a current state of the NOx purification catalyst. a second purification rate calculation unit that calculates the NOx purification rate detection value of the NOx purification catalyst based on the detected value of the NOx detection unit; an estimated NOx purification rate calculated by the first purification rate calculation unit; 2 Calculate the difference from the NOx purification rate detection value calculated by the purification rate calculation unit, and when the difference between the NOx purification rate estimated value and the NOx purification rate detection value becomes equal to or greater than the specified value within a specified time, the NOx a clogging determination unit that determines that there is a possibility that an end face of the purification catalyst is clogged.

In such an engine system, an estimated NOx purification rate of the NOx purification catalyst is calculated based on the current state of the NOx purification catalyst, and NOx detection is performed to detect NOx existing at least downstream of the NOx purification catalyst. A NOx purification rate detection value of the NOx purification catalyst is calculated based on the detection value of the part. Then, the difference between the NOx purification rate estimated value and the NOx purification rate detected value is calculated, and when the difference becomes equal to or larger than the specified value within the specified time, there is a possibility that the end face of the NOx purification catalyst is clogged. It is determined that there is Therefore, when the difference between the NOx purification rate estimated value and the NOx purification rate detected value increases in a shorter period of time than expected, there is a possibility that the end face of the NOx purification catalyst is clogged rather than deteriorated. It is determined that there is This improves the detection accuracy of the end face clogging of the NOx purification catalyst.

The engine system further includes an exhaust temperature raising section that raises the temperature of the exhaust gas flowing into the NOx purification catalyst when the clogging judgment section judges that the end face of the NOx purification catalyst may be clogged. may In such a configuration, when it is determined that the end face of the NOx purification catalyst may be clogged, the temperature of the exhaust gas flowing into the NOx purification catalyst rises. Material is burned off. Therefore, the end face clogging of the NOx purification catalyst is suppressed or eliminated.

The first purification rate calculation unit calculates the NOx purification rate of the NOx purification catalyst based on the temperature and flow rate of the exhaust gas flowing into the NOx purification catalyst, the deterioration degree of the NOx purification catalyst, the NOx storage amount, and the sulfur poisoning amount. An estimate may be calculated. With such a configuration, the current state of the NOx purification catalyst can be appropriately obtained, so the NOx purification rate estimated value of the NOx purification catalyst can be calculated with high accuracy.

The engine system may further include a decision propriety determining section that determines whether the exhaust gas is in a stable state and permits execution of the determination processing by the clogging determining section when the exhaust gas is in a stable state. In such a configuration, execution of the determination process by the clogging determination unit is permitted when exhaust gas with conditions suitable for the end face clogging determination process of the NOx purification catalyst is obtained. Therefore, the detection accuracy of end face clogging of the NOx purification catalyst is further improved.

The determination propriety determination unit may allow the clogging determination unit to perform the determination process when the stable state of the exhaust gas continues for a certain period of time. With such a configuration, the influence of variations in the NOx purification rate estimated value and the NOx purification rate detected value during one judgment processing period by the clogging judgment section is reduced. Therefore, the detection accuracy of end face clogging of the NOx purification catalyst is further improved.

The number of NOx detection units may be two, and the NOx detection units may detect NOx existing upstream and downstream of the NOx purification catalyst. With such a configuration, a highly accurate NOx purification rate detection value can be obtained, so that the detection accuracy of end face clogging of the NOx purification catalyst is further improved.

According to the present invention, it is possible to improve the detection accuracy of the end face clogging of the NOx purification catalyst.

1 is a configuration diagram schematically showing an engine system according to one embodiment of the present invention; FIG. 2 is a configuration diagram of a control system of the engine system shown in FIG. 1; FIG. FIG. 3 is a flow chart showing details of a procedure of calculation processing executed by a first purification rate calculation unit shown in FIG. 2; FIG. FIG. 3 is a flow chart showing details of a procedure of calculation processing executed by a second purification rate calculation unit shown in FIG. 2; FIG. FIG. 3 is a flow chart showing the details of the procedure of determination processing executed by the clogging determination unit shown in FIG. 2; FIG. FIG. 3 is a flow chart showing the details of the procedure of judgment processing executed by a judgment propriety judging unit shown in FIG. 2; FIG. FIG. 4 is a timing chart showing an example of detection of end face clogging of an NSR catalyst;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram schematically showing an engine system according to one embodiment of the present invention. In FIG. 1, an engine system 1 of this embodiment is mounted on a vehicle. The engine system 1 includes an engine 2, an intake passage 3, an exhaust passage 4, a throttle valve 5, an injector 6, and an NSR catalyst 7 (NOx Storage-Reduction catalyst).

Engine 2 is a diesel engine. Although not shown, the engine 2 has cylinders forming combustion chambers. The intake passage 3 and the exhaust passage 4 are connected to the engine 2 . The intake passage 3 is a passage through which intake air flows. The exhaust passage 4 is a flow path through which exhaust gas generated in the combustion chamber of the engine 2 flows.

A throttle valve 5 is arranged in the intake passage 3 . The throttle valve 5 is a flow control valve that adjusts the flow rate of intake air supplied to the engine 2 . The injector 6 is a fuel injection valve that injects fuel toward the combustion chamber of the engine 2 .

The NSR catalyst 7 is arranged in the exhaust passage 4 . The NSR catalyst 7 is a NOx purification catalyst that purifies NOx contained in the exhaust gas. The NSR catalyst 7 has a structure in which a catalyst noble metal and a NOx storage material are supported on a carrier.

The engine system 1 also includes an accelerator sensor 8, a rotation speed sensor 9, an air flow meter 10, an exhaust temperature sensor 11, an upstream NOx sensor 12, a downstream NOx sensor 13, and an ECU 14 (engine control unit). I have.

An accelerator sensor 8 detects the opening of an accelerator pedal (not shown) as an engine load. A rotation speed sensor 9 detects the rotation speed of the engine 2 (engine speed). The airflow meter 10 detects the intake air amount to the engine 2 . The exhaust temperature sensor 11 detects the temperature of the exhaust gas (exhaust temperature).

The upstream NOx sensor 12 constitutes a NOx detector that detects NOx present upstream of the NSR catalyst 7 . The downstream NOx sensor 13 constitutes a NOx detector that detects NOx existing downstream of the NSR catalyst 7 . The upstream NOx sensor 12 and the downstream NOx sensor 13 detect, for example, NOx concentration or NOx amount as NOx state quantities.

The ECU 14 includes a CPU, RAM, ROM, input/output interfaces, and the like. The ECU 14 acquires the detected values of the accelerator sensor 8, the rotation speed sensor 9, the air flow meter 10, the exhaust temperature sensor 11, the upstream NOx sensor 12, and the downstream NOx sensor 13, executes predetermined processing, and controls the throttle valve 5 and Control injector 6.

As shown in FIG. 2 , the ECU 14 has a first purification rate calculator 15 , a second purification rate calculator 16 , a clogging determination section 17 , an exhaust temperature raising section 18 , and a determination propriety determination section 19 . are doing.

The first purification rate calculator 15 calculates an estimated NOx purification rate of the NSR catalyst 7 based on the current state of the NSR catalyst 7 . The current state of the NSR catalyst 7 is determined by the engine load detected by the accelerator sensor 8, the engine speed detected by the speed sensor 9, the intake air amount detected by the air flow meter 10, and the exhaust temperature sensor 11. is estimated based on the exhaust temperature.

FIG. 3 is a flowchart showing the details of the procedure of calculation processing executed by the first purification rate calculator 15. As shown in FIG. This processing is executed, for example, when an ignition switch is turned on. In FIG. 3, the first purification rate calculator 15 first acquires detection values of the accelerator sensor 8, the rotation speed sensor 9, the airflow meter 10, and the exhaust temperature sensor 11 (step S101).

Subsequently, the first purification rate calculation unit 15 determines the amount of exhaust gas flowing into the NSR catalyst 7, the NSR catalyst 7 , the NOx storage amount, and the sulfur poisoning amount (S poisoning amount) are estimated (step S102).

Specifically, the fuel injection amount and fuel injection timing from the injector 6 to the engine 2 are determined based on the engine load and the engine speed. The amount of exhaust gas flowing into the NSR catalyst 7 is calculated based on the amount of intake air to the engine 2 and the amount of fuel injection. The degree of deterioration, NOx storage amount and sulfur poisoning amount of the NSR catalyst 7 are calculated based on the engine load, engine speed and exhaust temperature. The amount of exhaust gas, the degree of deterioration of the NSR catalyst 7, the amount of NOx storage, and the amount of sulfur poisoning are calculated by map calculation, for example.

Subsequently, the first purification rate calculation unit 15 calculates the NOx amount upstream and downstream of the NSR catalyst 7 based on the exhaust temperature, exhaust gas amount, deterioration degree of the NSR catalyst 7, NOx storage amount, and sulfur poisoning amount. is estimated (step S103). As a result, estimated NOx values upstream and downstream of the NSR catalyst 7 are obtained (see FIG. 7(b)).

The NOx estimated value on the upstream side of the NSR catalyst 7 (see solid line P1 in FIG. 7(b)) is calculated based on the exhaust temperature and the amount of exhaust gas. The NOx estimated value on the downstream side of the NSR catalyst 7 (see solid line P2 in FIG. 7(b)) is calculated based on the exhaust temperature, the amount of exhaust gas, the degree of deterioration of the NSR catalyst 7, the NOx storage amount, and the sulfur poisoning amount. be done. The estimated NOx values upstream and downstream of the NSR catalyst 7 are calculated by map calculation, for example.

Subsequently, the first purification rate calculation unit 15 calculates the estimated NOx purification rate of the NSR catalyst 7 (see solid line P in FIG. 7(d)) based on the estimated NOx values on the upstream and downstream sides of the NSR catalyst 7. is calculated (step S104). When the NOx amount on the upstream side of the NSR catalyst 7 is A1 and the NOx amount on the downstream side of the NSR catalyst 7 is A2, the NOx purification rate of the NSR catalyst 7 is calculated from (A1-A2)/A1.

The second purification rate calculator 16 calculates the NOx purification rate detection value of the NSR catalyst 7 based on the NOx state quantity detected by the upstream NOx sensor 12 and the downstream NOx sensor 13 .

FIG. 4 is a flowchart showing the details of the procedure of calculation processing executed by the second purification rate calculator 16. As shown in FIG. This processing is executed, for example, when an ignition switch is turned on. In FIG. 4, the second purification rate calculator 16 first acquires the detection values of the upstream NOx sensor 12 and the downstream NOx sensor 13 as NOx detection values (step S111).

Subsequently, the second purification rate calculation unit 16 calculates the upstream NOx detection value of the NSR catalyst 7 acquired by the upstream NOx sensor 12 (see solid line Q1 in FIG. 7(c)) and the downstream NOx sensor 13. Based on the acquired NOx detection value downstream of the NSR catalyst 7 (see the solid line Q2 in FIG. 7(c)), the NOx purification rate detection value of the NSR catalyst 7 (see the solid line Q in FIG. 7(d)) ) is calculated (step S112). The formula for calculating the NOx purification rate detection value of the NSR catalyst 7 is the same as in step S104 in FIG.

The clogging determination unit 17 calculates the difference between the NOx purification rate estimated value calculated by the first purification rate calculation unit 15 and the NOx purification rate detection value calculated by the second purification rate calculation unit 16, and estimates the NOx purification rate. It is determined that there is a possibility that the front end surface 7a of the NSR catalyst 7 is clogged when the difference between the value and the NOx purification rate detection value becomes equal to or greater than a specified value within a specified time.

FIG. 5 is a flow chart showing the details of the procedure of determination processing executed by the clogging determination unit 17. As shown in FIG. This process is executed when a determination permission flag, which will be described later, is set to 1.

In FIG. 5, the clogging determination unit 17 first acquires the NOx purification rate estimated value calculated by the first purification rate calculation unit 15 and the NOx purification rate detection value calculated by the second purification rate calculation unit 16 (procedure S121). Subsequently, the clogging determination unit 17 calculates the difference between the NOx purification rate estimated value and the NOx purification rate detected value as the NOx purification rate difference (step S122).

Subsequently, the clogging determination unit 17 determines whether or not the NOx purification rate difference is equal to or greater than a predetermined specified value (step S123). When the clogging determination unit 17 determines that the NOx purification rate difference is equal to or greater than the specified value, it determines whether or not the elapsed time since the previous determination process was performed is within a predetermined specified time ( step S124). Degradation of the NSR catalyst 7 over time may also cause the NOx purification rate difference to exceed the specified value. The prescribed time here is a judgment value for excluding a case where the NOx purification rate difference exceeds a prescribed value simply due to aged deterioration of the NSR catalyst 7 .

The clogging judging section 17 judges that there is a possibility that the front end surface 7a of the NSR catalyst 7 is clogged when judging that the elapsed time since the previous judging process is within the specified time. (Step S125).

When the clogging determination unit 17 determines in step S123 that the NOx purification rate difference is smaller than the specified value, it determines that the front end surface 7a of the NSR catalyst 7 is not clogged (step S126). The clogging judging section 17 judges that the front end surface 7a of the NSR catalyst 7 is not clogged even when it judges that the elapsed time since the previous judging process was performed in step S124 exceeds the specified time. (Step S126).

The exhaust temperature raising unit 18 raises the temperature of the exhaust gas flowing into the NSR catalyst 7 when the clogging determination unit 17 determines that the front end surface 7a of the NSR catalyst 7 may be clogged. to control the injector 6 or the throttle valve 5.

The exhaust temperature raising unit 18 raises the temperature of the exhaust gas by changing the combustion state of the engine 2 . Specifically, the exhaust temperature raising unit 18 raises the temperature of the exhaust gas by controlling the injector 6 to retard the fuel injection timing determined based on the engine load and the engine speed. Further, the exhaust temperature raising unit 18 may raise the temperature of the exhaust gas by controlling the throttle valve 5 so as to reduce the intake air amount to the engine 2 .

The determination propriety determination unit 19 determines whether the exhaust gas discharged from the engine 2 is in a stable state, and permits the clogging determination unit 17 to perform determination processing when the exhaust gas is in a stable state. A stable state of the exhaust gas is a state in which the exhaust amount and the exhaust temperature are stable. Here, the determination propriety determination unit 19 determines whether or not the engine 2 is in a steady operating state based on the engine load detected by the accelerator sensor 8 and the engine speed detected by the speed sensor 9. to determine whether the exhaust gas is in a stable state.

FIG. 6 is a flow chart showing the details of the procedure of the judgment processing executed by the judgment propriety judging section 19. As shown in FIG. This processing is executed, for example, when an ignition switch is turned on. In FIG. 6, the determination propriety determination unit 19 first acquires the detection values of the accelerator sensor 8 and the rotation speed sensor 9 (step S131).

Subsequently, the judgment propriety judging section 19 judges whether or not the engine 2 is in a steady operating state based on the engine load and the engine speed (step S132). The steady operating state of the engine 2 is a state in which the vehicle is running at a constant speed as the accelerator pedal is depressed at a constant opening. In this case, the exhaust gas discharged from the engine 2 contains an appropriate amount of NOx, and is in a stable state suitable for the clogging determination unit 17 to determine whether the end face of the NSR catalyst 7 is clogged.

When the determination unit 19 determines that the engine 2 is in the steady operation state, it determines whether the duration of the steady operation state of the engine 2 has reached the duration threshold value t (see FIG. 7A). (step S133). The duration threshold t is a time sufficiently shorter than the specified time in step S124 of FIG. In other words, the determination propriety determination unit 19 determines whether the stable state of the exhaust gas continues for a certain period of time.

When determining that the duration of the steady operation state of the engine 2 has reached the duration threshold value t, the determination propriety determination unit 19 sets the determination permission flag to 1 (step S134). The judgment permission flag is a flag for permitting the judgment processing of end face clogging of the NSR catalyst 7 by the clogging judging section 17 (see FIG. 7(e)). The determination permission flag is set to 1 when the determination process is permitted. The determination permission flag is set to 0 when the determination process is not permitted.

When determining in step S132 that the engine 2 is not in the steady operating state, the determination propriety determination unit 19 sets the determination permission flag to 0 (step S135). The determination propriety determination unit 19 also sets the determination permission flag to 0 when determining in step S133 that the duration of the steady operation state of the engine 2 has not reached the duration threshold t (step S135).

In the engine system 1 configured as described above, as shown in FIG. A NOx estimated value (see solid line P2) on the downstream side of the NSR catalyst 7 is calculated. Then, as shown in FIG. 7(d), the estimated NOx purification rate of the NSR catalyst 7 (see solid line P) is calculated. In FIG. 7(d), only the NOx purification rate estimated value when the engine 2 continues to be in steady state is shown as the NOx purification rate estimated value for end face clogging determination.

Further, as shown in FIGS. 7(c) and 7(d), the upstream NOx detection value (see solid line Q1) of the NSR catalyst 7 acquired by the upstream NOx sensor 12 and the downstream NOx sensor 13 Based on the acquired NOx detection value downstream of the NSR catalyst 7 (see solid line Q2), the NOx purification rate detection value of the NSR catalyst 7 (see solid line Q) is calculated. In FIG. 7(d), only the NOx purification rate detection value when the engine 2 continues to be in steady operation is shown as the end face clogging determination NOx purification rate detection value.

Here, as shown in FIGS. 7A and 7E, in the period T1, the duration of the steady operation state of the engine 2 reaches the duration threshold t, so that the determination permission flag is set to 1. . Therefore, since the end face clogging determination process of the NSR catalyst 7 is permitted, the NOx purification rate difference, which is the difference between the NOx purification rate estimated value and the NOx purification rate detected value, is calculated. At this time, since the NOx purification rate difference is smaller than the specified value, it is determined that the front end surface 7a of the NSR catalyst 7 is not clogged.

After that, in the period T2, the engine 2 enters a steady operating state, but the duration of the steady operating state of the engine 2 does not reach the duration threshold value t, so the determination permission flag is set to 0. Therefore, the end face clogging determination process of the NSR catalyst 7 is not performed.

After that, in the period T3, the determination permission flag is set to 1 because the duration of the steady operation state of the engine 2 reaches the duration threshold t. Therefore, since the end face clogging determination process of the NSR catalyst 7 is permitted, the NOx purification rate difference is calculated. At this time, the NOx purification rate difference is equal to or greater than the specified value, and the elapsed time since the previous determination process was performed is within the specified time. Therefore, it is determined that the front end surface 7a of the NSR catalyst 7 may be clogged.

In this case, the temperature of the exhaust gas flowing into the NSR catalyst 7 is increased by controlling the injector 6 or the throttle valve 5 . Therefore, the exhaust gas burns and removes the clogging material on the front end face 7a of the NSR catalyst 7. As shown in FIG.

By the way, as a method for detecting the end face clogging of the NSR catalyst 7, for example, the integrated inflow amount of clogging substances to the front end face 7a of the NSR catalyst 7 is detected, and the end face clogging is estimated from the integrated inflow amount. There is a method of detecting the pressure difference between the upstream side and the downstream side of the NSR catalyst 7 and estimating the end face clogging from the pressure difference.

However, in the method of detecting the accumulated inflow amount of the product clogging the front end face 7a of the NSR catalyst 7, there is a possibility of erroneous estimation depending on the detection accuracy of the accumulated inflow amount of the product material. Even if the pressure does not rise, the purification performance of the NSR catalyst 7 deteriorates. Therefore, the method of detecting the pressure difference between the front and rear sides of the NSR catalyst 7 may not be able to estimate the end face clogging. Therefore, in order to eliminate the end face clogging of the NSR catalyst 7 before the purification performance of the NSR catalyst 7 deteriorates due to the end face clogging of the NSR catalyst 7, the end face clogging is detected with a margin and the temperature of the exhaust gas is raised. There is a need. In this case, the frequency of detection of end face clogging of the NSR catalyst 7 increases. As a result, when the frequency of raising the temperature of the exhaust gas increases, the fuel efficiency deteriorates.

In response to such a problem, in the present embodiment, the NOx purification rate estimated value of the NSR catalyst 7 is calculated based on the current state of the NSR catalyst 7, and The NOx purification rate detection value of the NSR catalyst 7 is calculated based on the detection values of the upstream NOx sensor 12 and the downstream NOx sensor 13 that detect NOx. Then, the difference between the NOx purification rate estimated value and the NOx purification rate detected value is calculated, and when the difference becomes equal to or larger than the specified value within the specified time, it is possible that the front end surface 7a of the NSR catalyst 7 is clogged. determined to be viable. Therefore, when the difference between the NOx purification rate estimated value and the NOx purification rate detected value becomes larger in a shorter period of time than expected, the NSR catalyst 7 is not deteriorated, but the front end surface 7a of the NSR catalyst 7 is clogged. It is judged to be possible. As a result, the detection accuracy of end face clogging of the NSR catalyst 7 is improved. As a result, frequent detection of end face clogging of the NSR catalyst 7 in order to suppress clogging of the front end face 7a of the NSR catalyst 7 before the purification performance of the NSR catalyst 7 deteriorates is eliminated. In other words, the frequency of detection of end face clogging of the NSR catalyst 7 can be reduced.

Further, in this embodiment, when it is determined that the front end surface 7a of the NSR catalyst 7 may be clogged, the temperature of the exhaust gas flowing into the NSR catalyst 7 rises. Substances clogging the front end face 7a are burned and removed. Therefore, clogging of the end faces of the NSR catalyst 7 is suppressed. At this time, as described above, the frequency of detection of end face clogging of the NSR catalyst 7 is reduced, so the frequency of raising the temperature of the exhaust gas is also reduced. Therefore, deterioration of fuel efficiency can be prevented.

Further, in the present embodiment, the NOx purification rate of the NSR catalyst 7 is estimated based on the temperature and flow rate of the exhaust gas flowing into the NSR catalyst 7, the degree of deterioration of the NSR catalyst 7, the NOx storage amount, and the sulfur poisoning amount. value is calculated. Therefore, since the current state of the NSR catalyst 7 can be obtained appropriately, the NOx purification rate estimated value of the NSR catalyst 7 can be calculated with high accuracy.

Further, in the present embodiment, execution of the determination process by the clogging determination unit 17 is permitted when the exhaust gas is in a stable state. For this reason, the clogging determination unit 17 is permitted to perform the determination process when the exhaust gas under conditions suitable for the end face clogging determination process of the NSR catalyst 7 is obtained. Therefore, the detection accuracy of end face clogging of the NSR catalyst 7 is further improved.

Further, in the present embodiment, execution of the determination process by the clogging determination unit 17 is permitted when the stable state of the exhaust gas continues for a certain period of time. Therefore, the influence of variations in the NOx purification rate estimated value and the NOx purification rate detected value during one determination processing period by the clogging determination unit 17 is reduced. Therefore, the detection accuracy of end face clogging of the NSR catalyst 7 is further improved.

In addition, in the present embodiment, by using the upstream NOx sensor 12 and the downstream NOx sensor 13, a highly accurate NOx purification rate detection value can be obtained, so the end face clogging detection accuracy of the NSR catalyst 7 is further improved. .

In addition, this invention is not limited to the said embodiment. For example, in the above-described embodiment, when the exhaust gas is in a stable state for a certain period of time, execution of the determination process by the clogging determination unit 17 is permitted. Instead, execution of the determination process by the clogging determination unit 17 may be permitted periodically.

Further, in the above embodiment, the upstream NOx sensor 12 that detects NOx existing upstream of the NSR catalyst 7 and the downstream NOx sensor 13 that detects NOx existing downstream of the NSR catalyst 7 are provided. However, the present invention is not particularly limited to that form, and the upstream NOx sensor 12 may be omitted. In this case, for example, based on the NOx estimated value on the upstream side of the NSR catalyst 7 calculated by the first purification rate calculator 15 and the NOx detection value on the downstream side of the NSR catalyst 7 obtained by the downstream NOx sensor 13 , the NOx purification rate detection value of the NSR catalyst 7 may be calculated. Also, based on the downstream NOx detection value of the NSR catalyst 7 acquired by the downstream NOx sensor 13, the amount of NOx passing through the NSR catalyst 7 is calculated, thereby calculating the NOx purification rate detection value of the NSR catalyst 7. You may

Further, although the NSR catalyst 7 is arranged in the exhaust passage 4 in the above embodiment, the present invention can also be applied to an engine system in which an SCR (Selective Catalytic Reduction) catalyst is arranged in the exhaust passage 4. The SCR catalyst is a NOx purification catalyst that purifies NOx by injecting urea water into the exhaust gas.

DESCRIPTION OF SYMBOLS 1... Engine system, 2... Engine, 4... Exhaust passage, 7... NSR catalyst (NOx purification catalyst), 7a... Front end face (end face), 12... Upstream NOx sensor (NOx detector), 13... Downstream NOx sensor (NOx detection unit) 15 First purification rate calculation unit 16 Second purification rate calculation unit 17 Clogging determination unit 18 Exhaust gas temperature raising unit 19 Judgment propriety determination unit.

Claims (6)

engine and
an exhaust passage connected to the engine through which exhaust gas generated in the engine flows;
a NOx purification catalyst disposed in the exhaust passage to purify NOx contained in the exhaust gas;
a NOx detector that detects NOx existing at least downstream of the NOx purification catalyst;
a first purification rate calculation unit that calculates an estimated NOx purification rate of the NOx purification catalyst based on the current state of the NOx purification catalyst;
a second purification rate calculation unit that calculates the NOx purification rate detection value of the NOx purification catalyst based on the detection value of the NOx detection unit;
calculating a difference between the NOx purification rate estimated value calculated by the first purification rate calculation section and the NOx purification rate detected value calculated by the second purification rate calculation section; an engine system comprising: a clogging determination unit that determines that there is a possibility that an end face of the NOx purification catalyst is clogged when a difference from the NOx purification rate detection value becomes equal to or greater than a prescribed value within a prescribed time. The exhaust temperature raising unit further comprises an exhaust temperature raising unit for raising the temperature of the exhaust gas flowing into the NOx purification catalyst when the clogging judgment unit judges that there is a possibility that the end face of the NOx purification catalyst is clogged. The engine system according to claim 1. The first purification rate calculation unit calculates the NOx purification based on the temperature and flow rate of the exhaust gas flowing into the NOx purification catalyst, the deterioration degree of the NOx purification catalyst, the NOx storage amount, and the sulfur poisoning amount. 3. The engine system according to claim 1, wherein an estimated NOx purification rate of the catalyst is calculated. 4. The apparatus according to any one of claims 1 to 3, further comprising a determination propriety determination unit that determines whether the exhaust gas is in a stable state and permits execution of determination processing by the clogging determination unit when the exhaust gas is in a stable state. An engine system according to any preceding claim. 5. The engine system according to claim 4, wherein the determination propriety determination section permits execution of determination processing by the clogging determination section when the stable state of the exhaust gas continues for a certain period of time. The number of the NOx detection units is two,
The engine system according to any one of claims 1 to 5, wherein the NOx detector detects NOx existing upstream and downstream of the NOx purification catalyst.

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