WO2010109946A1

WO2010109946A1 - Rationality diagnostic apparatus and rationality diagnostic method for nox sensor

Info

Publication number: WO2010109946A1
Application number: PCT/JP2010/051322
Authority: WO
Inventors: 弘之笠原
Original assignee: ボッシュ株式会社
Priority date: 2009-03-23
Filing date: 2010-02-01
Publication date: 2010-09-30
Also published as: JPWO2010109946A1

Abstract

Provided is a rationality diagnostic apparatus and a rationality diagnostic method for an NO_X sensor wherein the reliability is improved in rationality diagnosis of an NO_X sensor utilizing the peak of the amount of NO_X. The rationality diagnostic apparatus for an NO_X sensor which diagnoses the rationality of an NO_X sensor provided on the downstream side of a reduction catalyst in an exhaust gas purifier which purifies NO_X in exhaust gas discharged from an internal combustion engine by using a reduction catalyst comprises an operation unit for upstream-side NO_X amount which calculates the amount of NO_Xon the upstream side of the reduction catalyst, an NO_X sensor value operation unit which detects the sensor value of the NO_X sensor, a rationality diagnostic unit which diagnoses rationality of the NO_X sensor by determining whether or not the NO_X sensor responds to a peak appearing in the transition of the amount of NO_Xon the upstream side, a catalyst temperature operation unit which detects the temperature of the reduction catalyst, and a diagnosis execution determination unit which determines execution of rationality diagnosis of the NO_X sensor when the temperature of the reduction catalyst is lower than a predetermined threshold.

Description

NOx sensor rationality diagnostic device and rationality diagnostic method

The present invention relates to a rationality diagnostic device and a rationality diagnostic method for a NO _x sensor. In particular, NO performing rationality diagnosis of the NO _X sensor whether NO _X sensor provided on the downstream side of the reduction catalyst with respect to the peak appearing in the transition of the upstream side of the NO _X amount of the reduction catalyst is responding _{The present} invention relates to a rationality diagnostic device and a rationality diagnostic method for an _X sensor.

Conventionally, exhaust gas discharged from an internal combustion engine such as a diesel engine contains NO _x (nitrogen oxide) that may affect the environment. As an exhaust gas purification apparatus used to purify the NO _X, there is an exhaust gas purification apparatus using the disposed in an exhaust passage reduction catalyst.
In this exhaust purification device, for example, a catalyst that selectively reduces NO _{x in} exhaust gas is used, and a reducing agent such as urea aqueous solution or unburned fuel (HC) is supplied into the exhaust gas upstream of the reduction catalyst. Thus, NO _x is reduced in the catalyst by the generated reducing component, and the exhaust gas is purified.

In such an exhaust purification device, an NO _x sensor may be provided in the exhaust passage downstream of the reduction catalyst. This NO _X sensor is used, for example, for calculating the injection amount of the reducing agent and for failure diagnosis of the exhaust purification device, etc., but the injection amount of the reducing agent and the failure diagnosis result of the exhaust purification device are the components of NO _X or the reducing agent. Has a major impact on whether or not is released into the atmosphere. For this reason, high reliability is required for the output of the NO _X sensor, and the control device of the exhaust purification device is required to be able to diagnose the rationality of the NO _X sensor.

Here, as a method of diagnosing the rationality of the NO _X sensor provided in the exhaust purification device, whether or not the NO _X sensor is responding to the peak appearing in the NO _X amount upstream of the reduction catalyst. There is a method of diagnosing the rationality of the NO _X sensor by determining the above.

For example, it sets the reference pattern as a reference for temporal changes of the exhaust NO _X flow discharged from an internal combustion engine, the tracking pattern as a reference for temporal change detection NO _X concentration detected by the NO _X sensor, in advance, when discharged NO _X flow rate remained with a predetermined relationship with a reference pattern, by determining whether the trend with a predetermined relationship to the detection NO _X concentration following pattern, responsiveness of the NO _X sensor Is disclosed (see Patent Document 1).

JP 2008-190383 A (full text, full diagram)

By the way, the above-described reduction catalyst has a property that the NO _x purification efficiency is increased at a temperature equal to or higher than the catalyst activation temperature, and the NO _x concentration on the downstream side of the reduction catalyst greatly depends on the active state of the reduction catalyst. . That is, in a situation where the reduction catalyst is in an activated state, even if a peak appears in the transition of the NO _x amount upstream of the reduction catalyst, most of the NO _x is reduced in the reduction catalyst as long as the reducing component is present. As a result, almost no outflow of NO _x to the downstream side of the reduction catalyst occurs.

Therefore, when the NO _x sensor rationality diagnosis method using the peak appearing in the transition of the NO _x amount as described in Patent Document 1 or the like is performed in a situation where the reduction catalyst is in the activated state, the NO _x sensor There to show no response will be determined that there is no rationality of the nO _X sensor or without rationality of the nO _X sensor.

Accordingly, the inventors of the present invention have made diligent efforts to execute the rational diagnosis of the NO _X sensor using the peak appearing in the transition of the NO _X amount. When the catalyst temperature is less than a predetermined threshold, the rationality of the NO _X sensor is obtained. The present inventors have found that such a problem can be solved by executing sex diagnosis, and have completed the present invention. That is, the present invention is to provide a rationality diagnosis apparatus and rationality diagnosis method of the NO _X sensor improved reliability is achieved rationality diagnosis of the NO _X sensor using a peak appearing in the amount of NO _X Trends With the goal.

According to the present invention, the NO _x for diagnosing the rationality of the NO _x sensor provided on the downstream side of the reduction catalyst in the exhaust purification device that purifies NO _x in the exhaust gas discharged from the internal combustion engine using the reduction catalyst. in rationality diagnosis apparatus _X sensor, the upstream amount of NO _X calculation unit for calculating the amount of NO _X at the upstream side of the reduction catalyst, a NO _X sensor value detector for detecting a sensor value of the NO _X sensor, upstream and rationality diagnosis unit for diagnosing the rationality of the NO _X sensor by NO _X sensor to determine whether or not the response to the peak appearing on the amount of NO _X transition in, detects the temperature of the reduction catalyst catalyst temperature detecting unit and, rationality diagnosis apparatus of the NO _X sensor temperature of the reduction catalyst, characterized in that it comprises a diagnosis execution judging unit to execute the rationality diagnosis of the NO _X sensor when less than a predetermined threshold value to Provided the above-mentioned issues It is possible to attain.

In constituting the rationality diagnosis apparatus of the NO _X sensor of the present invention, rationality diagnosis apparatus of the NO _X sensor, the exhaust gas upstream of the reduction catalyst in accordance with the amount of NO _X at the upstream side of the reduction catalyst It is preferably used for rational diagnosis of the NO _x sensor provided in the exhaust gas purification device that purifies NO _x by the mixed reducing component.

Further, in configuring the NO _x sensor rationality diagnosis device according to the present invention, the rationality diagnosis unit performs the reference pattern as the basis for the transition of the NO _x amount on the upstream side and the transition of the sensor value of the NO _x sensor. and follow pattern as a reference, is stored, changes _the amount of NO _X at the upstream side when the transition with a predetermined relationship with a reference pattern, the sensor value of the NO _X sensor with a predetermined relationship to follow the pattern It is preferable to diagnose the rationality of the NO _x sensor by determining whether or not it has been done.

Another aspect of the present invention is the rationality of the NO _X sensor provided on the downstream side of the reduction catalyst in the exhaust purification apparatus that purifies NO _X in the exhaust gas discharged from the internal combustion engine using the reduction catalyst. in rationality diagnosis method of the NO _X sensor to diagnose, when the temperature of the reduction catalyst is less than the predetermined threshold value, it detects the transition of the sensor values of transition and NO _X sensor of the NO _X amount in the upstream side of the reduction catalyst while, NO _X sensor, characterized in that diagnosing the rationality of the NO _X sensor by NO _X sensor with respect to the peak appearing in the NO _X amount of transition of the upstream side to determine whether it is responding This is a rational diagnostic method.

The NO _X rationality diagnosis apparatus and rationality diagnosis method of sensor of the present invention, the catalyst temperature only when less than a predetermined threshold value, rationality diagnosis of the NO _X sensor using a peak appearing in the NO _X amount of transition row Is called. Therefore, when the peak appears in the NO _X amount of transition of the upstream side of the reduction catalyst, since the NO _X most in reducing catalyst flows out to the downstream side of the reduction catalyst without being reduced, upstream of the reduction catalyst It is accurately determined whether or not the downstream NO _x sensor is responding to the peak appearing in the transition of the NO _x amount on the side. Therefore, the reliability of the rational diagnosis of the NO _X sensor is improved.

It is a figure which shows the structural example of an exhaust gas purification apparatus. It is a block diagram for explaining a configuration example of a rationality diagnosis apparatus of the NO _X sensor according to the embodiment of the present invention. It is a timing chart for explaining the rationality diagnosis method of the NO _X sensor according to an embodiment of the present invention. It is a flow diagram illustrating an example of a rationality diagnosis method of the NO _X sensor according to the embodiment of the present invention. It is a flow diagram illustrating an example of a rationality diagnosis method of the NO _X sensor according to the embodiment of the present invention. It is a flow diagram illustrating an example of a rationality diagnosis method of the NO _X sensor according to the embodiment of the present invention. It is a flow diagram illustrating an example of a rationality diagnosis method of the NO _X sensor according to the embodiment of the present invention.

Embodiments relating to a rationality diagnostic apparatus and rationality diagnostic method for a NO _x sensor according to the present invention will be specifically described below with reference to the drawings. However, this embodiment shows one aspect of the present invention and does not limit the present invention, and can be arbitrarily changed within the scope of the present invention. In addition, in each figure, what has attached | subjected the same code | symbol has shown the same member, and description is abbreviate | omitted suitably.

1. NO _X Sensor Rationality Diagnosis Device (1) Exhaust Gas Purification Device First, a configuration example of an exhaust gas purification device provided with an NO _X sensor rationality diagnostic device according to an embodiment of the present invention will be described with reference to FIG. .
Exhaust purifying apparatus 10 shown in Figure 1, using urea aqueous solution as the reducing agent, an exhaust purifying apparatus 10 for the exhaust gas flowed into the reduction catalyst 13 with the reducing agent to selectively reduce NO _X to. The exhaust purification device 10 is disposed in an exhaust passage 11 of an internal combustion engine, and a reduction catalyst 13 for selectively reducing NO _x contained in exhaust gas, and an exhaust passage 11 upstream of the reduction catalyst 13. And a reducing agent supply device 20 including a reducing agent injection valve 31 for injecting the reducing agent therein.

Further,

temperature sensors

15 and 16 are provided on the upstream side and the downstream side of the reduction catalyst 13 in the exhaust passage 11 respectively, and the NO _x concentration in the exhaust gas is detected on the downstream side of the reduction catalyst 13. NO _x sensor 17 is provided. As the NO _x sensor 17 and the

temperature sensors

15 and 16, known ones are used.

The reduction catalyst 13 is a selective reduction catalyst that adsorbs ammonia generated by hydrolysis of an aqueous urea solution injected into the exhaust passage 11 at an upstream side thereof, and selectively reduces NO _x in the inflowing exhaust gas. It is used.
The saturated adsorption amount of ammonia in the reduction catalyst 13 decreases as the catalyst temperature increases. On the other hand, the NO _x purification efficiency of the reduction catalyst 13 is increased at the catalyst activation temperature or higher.

The reducing agent supply device 20 includes a reducing agent injection valve 31, a reducing agent storage tank 50, and a pump 41 that pumps the reducing agent in the storage tank 50 toward the reducing agent injection valve 31. Further, the storage tank 50 and the pump 41 are connected by a first supply path 57, the pump 41 and the reducing agent injection valve 31 are connected by a second supply path 58, and further, the reducing agent injection valve 31 and the storage tank. 50 is also connected by a circulation path 59. The reducing agent injection valve 31 and the pump 41 are controlled by a control device 60 described later.

Although not shown, the storage tank 50 includes a temperature sensor for detecting the temperature of the reducing agent in the storage tank 50, a level sensor for detecting the remaining amount of the reducing agent, and a concentration for detecting the concentration of the reducing agent. A sensor is provided. The values detected by these sensors are output to the control device 60. As these sensors, known ones are appropriately used.
In this embodiment, an aqueous urea solution is used as the reducing agent. However, an aqueous ammonia solution or unburned fuel (HC) can also be used.

The pump 41 is an electric pump, for example, and is driven by the control device 60. A pressure sensor 43 is provided in the second supply path 58 on the downstream side of the pump 41, and the sensor value of the pressure sensor 43 is output to the control device 60. A known pressure sensor 43 is appropriately used.

The reducing agent injection valve 31 is, for example, an on / off valve that controls opening and closing of the valve by switching between energization and non-energization. The reducing agent injection valve 31 is controlled to be opened and closed by the control device 60, and when the reducing agent injection valve 31 is opened, the reducing agent is injected into the exhaust passage 11.

A circulation path 59 disposed between the reducing agent injection valve 31 and the storage tank 50 is provided in the second supply path 58 when the pressure of the reducing agent pumped by the pump 41 exceeds a predetermined value. This is a passage for returning a part of the reducing agent to the storage tank 50. By controlling the pressure of the reducing agent supplied to the reducing agent injection valve 31 at a predetermined value, it becomes easy to control the injection amount of the reducing agent.

(2) Control device (rationality diagnosis device)
The control device 60 mainly performs drive control of the pump 41 and the reducing agent injection valve 31 of the reducing agent supply device 20 so that an appropriate amount of the reducing agent is injected into the exhaust passage 11. In addition, the control device 60 of the present embodiment further has a function as a rationality diagnostic device for the NO _X sensor 17.

The control device 60 is configured around a microcomputer having a known configuration, and includes a portion for controlling the operation of the reducing agent injection valve 31, a portion for controlling the drive of the pump 41, and the rationality of the exhaust purification device 10. It has a diagnostic part. Specifically, each of these units is realized by executing a program by a microcomputer (not shown).

Among these, the pump drive control unit continuously reads the sensor value of the pressure sensor 43 provided in the second supply path 58 and keeps the pressure in the second supply path 58 at a predetermined value. 41 feedback control is performed.

The reducing agent injection valve operation control unit reads the temperature of the exhaust gas, the catalyst temperature, the NO _x concentration downstream of the reduction catalyst 13 and further information on the operating state of the internal combustion engine 5 to reduce NO _x in the exhaust gas. The amount of reducing agent injection necessary for this is calculated, and a control signal for the reducing agent injection valve 31 is output to the actuator of the reducing agent injection valve 31.

The diagnosis unit performs rational diagnosis of the NO _X sensor 17 provided on the downstream side of the reduction catalyst 13. FIG. 2 shows a configuration example in which a portion related to rationality diagnosis in the control device 60 of the present embodiment is represented by functional blocks. Rationality diagnosis of the control device 60, the upstream-side amount of NO _X calculation unit 61, an NO _X sensor value detector 63, a rationality diagnosis portion 65, a catalyst temperature detection unit 67, and a diagnosis execution judging section 69 I have. Specifically, each of these units is realized by executing a program by a microcomputer. The control device 60 is provided with a RAM (Random Access Memory) 71 and a timer 73. The RAM 71 stores values calculated or detected by each unit.

Among these, the upstream NO _x flow rate calculation unit 61 of the control device 60 of the present embodiment is configured to be able to calculate the mass flow rate Nfu of NO _x per unit time discharged from the internal combustion engine. Specifically, the upstream NO _x amount calculation unit 61 reads information relating to the operating state of the internal combustion engine 5, calculates the NO _x concentration Nu discharged from the internal combustion engine 5, and the exhaust gas mass flow rate Gf. Based on the calculated value, the mass flow rate Nfu of NO _x discharged from the internal combustion engine 5 per unit time is calculated. The calculated values of the NO _x concentration Nu, the exhaust gas mass flow rate Gf, and the NO _x mass flow rate Nfu are stored in the RAM 71.

Information on the operating state of the internal combustion engine 5 includes the fuel injection amount, the rotational speed, the status of the exhaust circulation device, the exhaust circulation amount, the air intake amount, the cooling water temperature, and the like of the internal combustion engine 5. Based on such information, the calculation of the exhaust gas mass flow rate Gf and the NO _x concentration Nu is performed by a known method.

_The amount of NO _X to be calculated on the upstream side _the amount of NO _X calculation unit 61, in addition of the NO _X in the mass flow rate (g · L) as in the present embodiment in NO _X concentration (ppm) and NO _X flow rate (L), etc. There may be. Further, when the NO _x sensor is provided on the upstream side of the reduction catalyst 13, it is possible to calculate the NO _x amount not based on the operating state of the internal combustion engine 5, but based on the sensor value of the NO _x sensor. is there.

The NO _X sensor value detection unit 63 is configured to be able to read the sensor value of the NO _X sensor 17 and calculate the NO _X concentration Nd based on this sensor value. The calculated value of the NO _x concentration Nd is stored in the RAM 71.

The catalyst temperature detector 67 is configured to be able to estimate the catalyst temperature Tscr by reading the sensor values of the

temperature sensors

15 and 16 provided on the upstream side and the downstream side of the reduction catalyst 13. The estimated catalyst temperature Tscr is output to the diagnosis execution determination unit 69.

The catalyst temperature Tscr to be detected is detected by a temperature sensor provided in the exhaust passage 11 in the vicinity of the reduction catalyst 13 in addition to the estimated catalyst temperature estimated based on the sensor values of the

temperature sensors

15 and 16 as in the present embodiment. If the measured value of the exhaust gas temperature to be measured or direct measurement is possible, the measured temperature of the reduction catalyst 13 may be used. That is, the detected catalyst temperature may be a temperature that is linked to the actual temperature of the reduction catalyst 13.

The diagnosis execution determination unit 69 compares the catalyst temperature Tscr estimated by the catalyst temperature detection unit 67 with a predetermined threshold value T0. When the catalyst temperature Tscr is less than the threshold value T0, the diagnosis execution signal is sent to the rationality diagnosis unit 65. Is output. The threshold value T0 is typically the catalyst activation temperature of the reduction catalyst 13, but may not be completely coincident.

Rationality diagnosis portion 65, the catalyst temperature Tscr is less than the threshold value T0 state, based on the values of the NO _X concentration Nd detected based on the mass flow rate Nfu and NO _X sensor 17 of the NO _X stored in the RAM71 to, by using a predetermined reference pattern and follow the pattern, by NO _X mass flow Nfu transition appeared NO _X concentration Nd corresponding to the peak of determining whether to remain, of the NO _X sensor 17 It is configured to make a rational diagnosis.

Rationality diagnosis portion 65 of the present embodiment, by NO _X mass flow Nfu undergoes a transition so as to satisfy a predetermined condition with respect to the reference pattern, is recognized peak appeared in the course of the mass flow rate Nfu of the NO _X shifts to the diagnostic mode when the stack checks NO _X sensor 17 to determine whether the response to changes of the NO _X concentration sensor value of the NO _X sensor 17 accurately responds in accordance with the change of the NO _X concentration And a peak check to determine whether or not

Specifically, stack checking, by transitioning to satisfy a predetermined condition with respect to the mass flow rate Nfu reference pattern on the upstream side of the NO _X of the reduction catalyst 13, a peak in the course of the mass flow rate Nfu of the NO _X Is recognized by determining whether or not the NO _X concentration Nd detected by the NO _X sensor 17 changes by more than a specified value ABS.
In addition, the peak check indicates that a peak appears in the transition of the NO _x mass flow rate Nfu as the NO _x mass flow rate Nfu on the upstream side of the reduction catalyst 13 changes so as to satisfy a predetermined condition with respect to the reference pattern. When it is recognized, it is performed by determining whether or not the NO _X concentration Nd detected by the NO _X sensor 17 exceeds the follow-up pattern.

However, the method of rationality diagnosis of the NO _X sensor 17 confirms that the peak appeared in the course of the upstream-side amount of NO _X, determine the sensor value of the NO _X sensor 17 is responding to this peak If it does, it is not limited to the diagnostic method mentioned above. For example, the occurrence of a peak in the upstream NO _x amount can be detected based on the transition of the NO _x concentration Nu or the NO _x flow rate, and the occurrence of the peak is determined based on the transition of a plurality of these values. You can also

2. NO _x sensor rationality diagnosis method (1) Rationality diagnosis timing chart Next, when the catalyst temperature Tscr is less than the catalyst temperature threshold value T0 by the control device (rationality diagnostic device) 60 of the present embodiment, the NO _x sensor. A method for diagnosing the rationality of 17 will be described in detail with reference to the timing chart shown in FIG.

In the timing chart of FIG. 3, the reference pattern of the transition of the NO _x mass flow rate Nfu upstream of the reduction catalyst 13 includes a front-stage steady region, an inclined region, and a back-stage steady region. The reference pattern includes a delay area in which the start point of the inclined area is delayed by the timer 3. Further, the tracking pattern of the transition of the NO _X concentration Nd detected by the NO _X sensor 17 includes a tracking slope area and a tracking steady area.

First, the estimation of the catalyst temperature Tscr, continuously performs calculation of the NO _X concentration Nd based on the sensor value of the calculated mass flow rate Nfu at the upstream side of the NO _X of the reduction catalyst 13 and the NO _X sensor 17, catalyst temperature Tscr threshold At the time t1 when the mass flow rate Nfu of the upstream NO _x becomes equal to or less than the reference value MINnfu in the upstream stationary region of the reference pattern, the timer 1 is activated. The reason for operating the timer 1 is to execute a rational diagnosis of the NO _X sensor 17 in a state where the diagnosis conditions are all stable. In the time chart of FIG. 3, the timer 1 is activated when both the upstream NO _x mass flow rate Nfu and the catalyst temperature Tscr satisfy a predetermined condition, but each value satisfies a predetermined condition. In addition, each timer may be operated.

With the catalyst temperature Tscr has remained below the threshold T0, from the time of the mass flow rate Nfu at the upstream side of the NO _X set time of the timer 1 remains less than the reference value MINnfu elapses t2, the upstream side of the NO _X mass The standby state is entered until the flow rate Nfu exceeds the reference value MINnfu. During this time, whether the catalyst temperature Tscr is lower than the threshold value T0 is continuously monitored.
At this time, the timer is separately activated simultaneously with the end of the timer 1 to set the maximum waiting time, and the diagnosis is terminated when the NO _x mass flow rate Nfu does not exceed the reference value MINnfu before the set time elapses. It can also be. In this way, it is possible to avoid an unstable state where the diagnostic program does not operate for a long time.

Thereafter, at time t3 when the upstream NO _x mass flow rate Nfu exceeds the reference value MINnfu, the timer 2, timer 3, timer 5 and timer 6 are activated and detected by the NO _x sensor 17 at time t3. storing NO _X concentration Nd is as the starting value Nd0. At the time t3, the mode is shifted to the rationality diagnosis mode, and the start value Nd0 of the follow-up gradient area of the follow-up pattern is set. The start value Nd0, in peak check and stack checking of the NO _X sensor 17 is performed in this embodiment, is detected by the NO _X sensor 17 corresponding to the peak appearing on the mass flow rate Nfu at the upstream side of the NO _X NO _This is a reference for determining whether or not the _X concentration Nd is accurately responding.

From the time point t3 to the time point t4 when the set time of the timer 3 elapses, the transition of the upstream NO _x mass flow rate Nfu and the reference pattern are not compared, and the time point t4 is the slope of the reference pattern It is the start time of the region. In this way, by providing the delay region between the time point t3 when the upstream NO _x mass flow rate Nfu exceeds the reference value MINnfu and the start point t4 of the inclined region, Even if the increase rate of the upstream NO _x mass flow rate Nfu decreases after the time point, the risk that the NO _x mass flow rate Nfu falls below the reference pattern is reduced, and the rationality diagnosis continues without interruption. It becomes easy to be done.

For the upstream NO _x mass flow rate Nfu after time t4, it is determined whether the NO _x mass flow rate Nfu is equal to or greater than the slope region value SLOPE until t5 when the set time of timer 2 elapses. Further, it is determined whether the mass flow rate Nfu of NO _x is equal to or greater than the value MAXnfu of the subsequent stage steady region until the set time of the timer 4 elapses after the time point t5. After this time t3, if the upstream NO _x mass flow rate Nfu falls below the values SLOPE and MAXnfu of each region of the reference pattern at any time, the rational diagnosis of the NO _x sensor 17 can be accurately determined. It is determined that no peak has occurred, and the value stored in the RAM 71 is reset. During this time, the catalyst temperature Tscr even when below the threshold T0, since there may not be determined accurately rationality diagnosis of the NO _X sensor 17, the value stored in the RAM71 is reset.

On the other hand, the NO _X concentration Nd detected by the NO _X sensor 17, after the timing t3, the peak check is made by being compared with the follow pattern. That is, the follow-up pattern is set based on the time point t6 when the set time of the timer 5 activated at the time point t3 elapses. After the time point t6, the mass flow rate Nfu of the upstream NO _x becomes the value MAXnfu of the subsequent steady region. It is determined whether or not the NO _x concentration Nd remains higher than the value Ramp of the follow-up gradient region and the value max of the follow-up steady-state region until the set time of the timer 4 changing as described above elapses.

after the timing t6, until the set time of timer 4 has elapsed, if it be NO _X concentration Nd is remained remains above value max value Ramp and follow later stage constant region of the follow-up slope region, NO _X sensor 17 it is determined that the responding accurately to follow the peak appearing in the course of the mass flow rate Nfu of the upstream NO _X. On the other hand, after the timing t6, until the set time of timer 4 has elapsed, when the NO _X concentration Nd is less than the value max value Ramp and follows subsequent constant regions in the follow-up slope region, NO _X sensor 17 upstream because to follow the peak appearing in the transition of a mass flow rate Nfu side of the nO _X not responding, it is determined that rationality of the nO _X sensor 17 is lost.

Further, in the rationality diagnosis of the NO _x sensor 17 of the present embodiment, the stack check is performed simultaneously with the peak check as described above. That is, the timer 6 is actuated at the time of t3, NO _X NO _X concentration Nd detected by the sensor 17, by the time of t7 the set time of the timer 6 has passed, the specified value ABS or more starting values Nd0 basis It is determined whether or not it changes. When the NO _X concentration Nd does not change more than the specified value ABS with respect to the start value Nd0, the NO _X sensor 17 does not react to the peak appearing in the transition of the upstream NO _X mass flow rate Nfu. It is determined that the rationality of the NO _X sensor 17 is lost.

(2) Flow of Rationality Diagnosis Method Next, an example of a specific routine of the rationality diagnosis method of the NO _X sensor 17 performed by the control device 60 shown in FIG. 2 will be described with reference to the flowcharts of FIGS. explain. This routine may be executed constantly during operation of the internal combustion engine, or may be executed by interruption every predetermined time.

First, after the start, the catalyst temperature Tscr is detected in step S10, and it is determined whether or not the detected catalyst temperature Tscr is less than a threshold value T0. If the catalyst temperature Tscr is equal to or higher than the threshold value T0, the rational diagnosis of the NO _x sensor 17 may not be performed accurately. Therefore, the detection of the catalyst temperature Tscr is repeated without proceeding to the next step S11. If the catalyst temperature Tscr is less than the threshold value T0, the process proceeds to step S11.

Next, in step S11, it is determined whether or not the mass flow rate Gf of the exhaust gas discharged from the internal combustion engine 5 is less than the reference value MINgas. If the exhaust gas mass flow rate Gf is greater than or equal to the reference value MINgas, the rational diagnosis of the NO _X sensor 17 may not be performed accurately, so the routine ends without proceeding to the next step S12. On the other hand, if the exhaust gas mass flow rate Gf is less than the reference value MINgas, the process proceeds to step S12.

Then, based on the mass flow rate Gf and NO _X concentration Nu of exhaust gas discharged from the internal combustion engine 5 in the step S12, with the mass flow rate Nfu of the NO _X in the upstream side is calculated of the reduction catalyst 13, it is calculated It is determined whether or not the NO _x mass flow rate Nfu is less than the reference value MINnfu in the preceding stationary region of the reference pattern and the NO _x concentration Nu is less than the reference value MINnu. If the condition of step S12 is not satisfied, this routine is terminated. If the condition of step S12 is satisfied, the process proceeds to step S13, and the timer 1 is activated.

Next, in step S14, the catalyst temperature Tscr is detected again, and it is determined whether or not the catalyst temperature Tscr is lower than the threshold value T0. Further, in step S15, the mass flow rate Gf of the exhaust gas discharged from the internal combustion engine 5 is determined. Is less than the reference value MINgas. If either of the conditions of step S14 or step S15 is not satisfied, the rational diagnosis of the NO _X sensor 17 may not be performed accurately. Therefore, after resetting the timer 1 in step S16, this routine is executed. On the other hand, if both conditions are satisfied, the process proceeds to step S17.

In step S17, again based on the mass flow rate Gf and NO _X concentration Nu exhaust gas, together with the mass flow rate Nfu of the NO _X in the upstream side is calculated of the reduction catalyst 13, the mass flow rate Nfu of the calculated NO _X a reference value of less than MINnfu of the preceding constant region of the reference pattern, and, NO _X concentration Nu whether is less than the reference value MINnu is determined. Does not satisfy these conditions, since the mass flow rate Nfu at the upstream side of the NO _X is unstable, the routine ends after resetting the timer 1 at step S16. On the other hand, if these conditions are satisfied, the process proceeds to step S18 to determine whether or not the set time of the timer 1 has elapsed. If the set time of timer 1 has not elapsed, the process returns to step S14. If the set time of timer 1 has elapsed, the process proceeds to step S19.

In step S19, the catalyst temperature Tscr is detected again, and it is determined whether the catalyst temperature Tscr is less than the threshold value T0. Further, in step S20, based on the exhaust gas mass flow rate Gf and the NO _x concentration Nu, with the mass flow rate Nfu of the NO _X in the upstream side is calculated of the reduction catalyst 13, the mass flow rate Nfu of the calculated NO _X is not less than the reference value MINnfu of the preceding constant region of the reference pattern, and, NO _X concentration Nu Is greater than or equal to the reference value MINnu, and it is determined whether or not the mass flow rate Gf of the exhaust gas is greater than or equal to the reference value MINgas. If these conditions are not satisfied, the process returns to step S19. If these conditions are satisfied, the process proceeds to step S21, and the NO _X concentration Nd detected by the NO _X sensor 17 at this time is the start value. While being stored as Nd0,

timers

2, 3, 5, and 6 are activated in step S22.

Next, in step S23, calculation of the absolute value D of the difference between the NO _X concentration Nd detected by the NO _X sensor 17 and the stored start value Nd0 is started. Further, in step S24, the catalyst temperature Tscr is detected again, and it is determined whether or not the catalyst temperature Tscr is lower than the threshold value T0. In step S25, the exhaust gas mass flow rate Gf becomes equal to or higher than the reference value MINgas. It is determined whether or not. Since the rationality diagnosis of the NO _X sensor 17 when not meeting any of these criteria in step S24 or step S25 is may not accurately performed, the

timer

2, 3, 5, 6 in step S26 While the routine ends after resetting, if both conditions are satisfied, the process proceeds to step S27.

In step S27, it is determined whether or not the absolute value D started to be calculated in step S23 is greater than or equal to the specified value ABS. If the absolute value D is less than the specified value ABS, the process proceeds to step S29. On the other hand, if the absolute value D is equal to or greater than the specified value ABS, the NO _X sensor 17 appears in the transition of the upstream NO _X mass flow rate Nfu. Since the timer 6 is stopped in step S28 and the stack check OK flag is set in step S28, the process proceeds to step S29.

In step S29, it is determined whether or not the set time of the timer 3 has elapsed. If the set time of the timer 3 has not elapsed, the process returns to step S24, whereas if the set time of the timer 3 has elapsed, the process proceeds to step S30. . In step S30, the catalyst temperature Tscr is detected again, and it is determined whether or not the catalyst temperature Tscr is lower than the threshold value T0. Further, in step S31, whether the exhaust gas mass flow rate Gf is equal to or higher than the reference value MINgas. It is determined whether or not. Since the rationality diagnosis of the NO _X sensor 17 when not meeting any of these criteria in step S30 or step S31 may not be performed accurately, and resets the

timer

2, 5, 6 in step S32 After the routine is finished, if both conditions are satisfied, the process proceeds to step S33.

In step S33, the mass flow rate Nfu of NO _x on the upstream side of the reduction catalyst 13 is calculated, and whether the calculated mass flow rate Nfu of NO _x is equal to or greater than the value SLOPE of the slope region of the reference pattern. Determined. When the mass flow rate Nfu of NO _X is less than the slope region value SLOPE, no peak appears in the transition of the mass flow rate Nfu of NO _X , so the process proceeds to step S32 and the

timers

2, 5, 6 are reset. This routine ends.

On the other hand, if the calculated NO _X mass flow rate Nfu is equal to or greater than the slope region value SLOPE in step S33, the process proceeds to step S34, where the NO _X concentration Nd detected by the NO _X sensor 17 and the start value are determined. It is determined whether or not the absolute value D of the difference from Nd0 is greater than or equal to the specified value ABS. If the absolute value D is less than the specified value ABS, the process proceeds to step S37 as it is. If the absolute value D is greater than or equal to the specified value ABS, it is confirmed in step S35 whether the stack check OK flag is set. If the stack check OK flag is set, the process proceeds to step S37 as it is. If the stack check OK flag is not set, the timer 6 is stopped and the stack check OK flag is set in step S36. Proceed to S37.

In step S37, it is determined whether or not the set time of the timer 2 has elapsed. If the set time of the timer 2 has not elapsed, the process returns to step S30, whereas if the set time of the timer 2 has elapsed, step S38. The timer 4 is started.

Next, in step S39, the catalyst temperature Tscr is detected again, and it is determined whether or not the catalyst temperature Tscr is less than the threshold value T0. Further, in step S40, the exhaust gas mass flow rate Gf becomes equal to or higher than the reference value MINgas. It is determined whether or not. If any of the conditions of step S39 or step S40 is not satisfied, the rational diagnosis of the NO _X sensor 17 may not be performed accurately, so the timers 4, 5, and 6 are reset in step S41. After the routine is finished, if both conditions are satisfied, the process proceeds to step S42.

In step S42, the mass flow rate Nfu of NO _x on the upstream side of the reduction catalyst 13 is calculated, and whether the calculated mass flow rate Nfu of NO _x is equal to or greater than the value MAXnfu in the subsequent steady region of the reference pattern. Is determined. _If the mass flow rate Nfu of NO _X is less than the value MAXnfu in the subsequent stage steady region, the peak is not sufficiently generated, so that the routine proceeds to step S41 and the timers 4, 5, and 6 are reset, and then this routine is terminated. On the other hand, if the mass flow rate Nfu of NO _X is equal to or greater than the value MAXnfu in the subsequent steady region, the process proceeds to step S43, and it is determined whether or not the set time of the timer 5 has elapsed. If the set time of the timer 5 has not elapsed, the process proceeds to step S44, and it is determined whether or not the absolute value D is greater than or equal to the specified value ABS.

In step S44, if the absolute value D is less than the specified value ABS, the process directly returns to step S39. On the other hand, if the absolute value D is greater than or equal to the specified value ABS, it is determined in step S45 whether or not the stack check OK flag is set. If the stack check OK flag is set, the process directly returns to step S39. If the stack check OK flag is not set, the timer 6 is stopped in step S46, the stack check OK flag is set, and the process returns to step S39.

On the other hand, when the set time of the timer 5 has elapsed in step S43, the process proceeds to step S47, where the NO _X concentration Nd detected by the NO _X sensor 17 is the value Ramp of the tracking pattern tracking slope region or the post-tracking steady region. It is determined whether or not the value is greater than or equal to max. If NO _X concentration Nd is equal to or greater than the value max value Ramp or follow later stage constant region of the follow-up slope region, the process proceeds to step S48, the conjunction is detected again catalyst temperature Tscr, catalyst temperature Tscr is less than the threshold value T0 In step S49, it is determined whether or not the exhaust gas mass flow rate Gf is greater than or equal to the reference value MINgas. If either of these conditions of step S48 or step S49 is not satisfied, the rational diagnosis of the NO _X sensor 17 may not be performed accurately. Therefore, after resetting the timers 4 and 6 in step S50, While the routine is ended, if both conditions are satisfied, the process proceeds to step S51.

In step S51, it is determined whether or not the set time of the timer 4 has elapsed. If the set time of the timer 4 has not elapsed, the process returns to step S47. If the set time of the timer 4 has elapsed, the NO _x sensor 17 changes the mass flow rate Nfu of the upstream NO _x. Since it responds to the peak that appears and responds appropriately following the peak, it is determined that the NO _x sensor 17 is reasonable, and the diagnosis result of TestOK is output in step S52. Then, this routine ends.

In step S47, the when NO _X concentration Nd detected by the NO _X sensor 17 is less than the value max value Ramp or follow later stage constant region of the follow-up slope region, the process proceeds to step S53, the absolute value D is stipulated value ABS It is determined whether or not this is the case. When the absolute value D is equal to or greater than the specified value ABS, the NO _X sensor 17 responds to the peak appearing in the transition of the upstream NO _X mass flow rate Nfu, but corresponds to the peak. Therefore, in step S54, the diagnosis result of responsiveness Error is output, and this routine is terminated.

On the other hand, when the absolute value D is less than the stipulated value ABS, the processing proceeds to step S55, whether stack checking OK flag is set is determined, if the stack checking OK flag is set, also NO _X Although the sensor 17 shows a response to the peak appearing in the transition of the upstream NO _x mass flow rate Nfu, it is determined that the sensor 17 does not respond appropriately following the peak, In step S54, the diagnosis result of responsiveness Error is output, and this routine ends.

If the stack check OK flag is not set in step S55, it is determined in step S56 whether the set time of the timer 6 has elapsed. Since the set time of the timer 6 in the case where the elapse is determined not to have little response to peak NO _X sensor 17 appears in changes in the mass flow rate Nfu at the upstream side of the NO _X even after the lapse of a predetermined time, In step S57, the diagnostic result of the reactive error is output, and this routine ends.

On the other hand, if the set time of the timer 6 has not elapsed, the process proceeds to step S58, the catalyst temperature Tscr is detected again, and it is determined whether or not the catalyst temperature Tscr is lower than the threshold value T0. In S59, it is determined whether or not the exhaust gas mass flow rate Gf is greater than or equal to a reference value MINgas. If any of these conditions of step S58 or step S59 is satisfied, the process returns to step S53. On the other hand, if any of the conditions is not satisfied, the NO _X sensor 17 detects the mass flow rate of NO _X on the upstream side. In response to the peak appearing in the transition of Nfu, it is determined that it is not responding properly, but the test environment condition is not determined to determine whether or not it has responded to the peak. Since it is no longer satisfied, the diagnosis result of responsiveness Error is output in step S60, and the routine is terminated.

In the NO _x sensor rationality diagnosis method of the present embodiment described above, the peak appearing in the transition of the NO _x mass flow rate Nfu upstream of the reduction catalyst 13 only when the catalyst temperature Tscr is less than the threshold value T0. responsiveness and diagnosis of reactive of the NO _X sensor utilizing are performed. Therefore, whether the downstream NO _X sensor corresponding to a peak appearing in the NO _X amount of transition of the upstream side of the reduction catalyst is responding is determined accurately, the possibility of misdiagnosis is greatly reduced The

Claims

In the exhaust purification apparatus that purifies with NO X reduction catalyst in the exhaust gas discharged from an internal combustion engine, rationality of the NO X sensor for diagnosing the rationality of the NO X sensor provided on the downstream side of the reduction catalyst In the diagnostic device,
An upstream NO x amount calculation unit for calculating the NO x amount on the upstream side of the reduction catalyst;
And NO X sensor value detector for detecting a sensor value of the NO X sensor,
And rationality diagnosis unit for diagnosing the reasonableness of the NO X sensor by determining whether the NO X sensor with respect to the peak appearing in the transition of the amount of NO X at the upstream side is responding,
A catalyst temperature detector for detecting the temperature of the reduction catalyst;
A diagnosis execution determination unit for executing a rational diagnosis of the NO X sensor when the temperature of the reduction catalyst is lower than a predetermined threshold;
An NO x sensor rationality diagnostic device comprising:
The NO x sensor rationality diagnostic device purifies the NO x by reducing components mixed with the exhaust gas upstream of the reduction catalyst according to the amount of NO x upstream of the reduction catalyst. rationality diagnosis apparatus of the NO X sensor according to claim 1, characterized in that used in the rationality diagnosis of the NO X sensor provided in the apparatus.
The rationality diagnosis unit stores a reference pattern as a reference for the transition of the NO x amount on the upstream side and a follow-up pattern as a reference for the transition of the sensor value of the NO x sensor. By determining whether or not the sensor value of the NO X sensor has changed with a predetermined relationship with respect to the tracking pattern when the amount of NO X has changed with a predetermined relationship with respect to the reference pattern, rationality diagnosis apparatus of the NO X sensor according to claim 1 or 2, characterized in that diagnosing the rationality of the NO X sensor.
In the exhaust purification apparatus that purifies with NO X reduction catalyst in the exhaust gas discharged from an internal combustion engine, rationality of the NO X sensor for diagnosing the rationality of the NO X sensor provided on the downstream side of the reduction catalyst In the diagnostic method,
When the temperature of the reduction catalyst is below a predetermined threshold,
While detecting the transition of sensor values of the NO X amount changes and the NO X sensor on the upstream side of the reduction catalyst, said NO X sensor with respect to the peak appearing on the amount of NO X transition in the upstream rationality diagnosis method of the NO X sensor, wherein diagnosing the reasonableness of the NO X sensor by determining whether or not the response.