JP3316066B2 - Failure diagnosis device for exhaust gas purification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure diagnosis device for an exhaust gas purification device mounted on a lean burn engine for a vehicle.

[0002]

2. Description of the Related Art In general, an exhaust gas purifying apparatus for a vehicle engine includes an exhaust system, which includes HC, CO, and harmful components in exhaust gas.
A three-way catalyst capable of simultaneously purifying three components of NOx is installed. However, to most efficiently purifying process in the three-way catalyst, it should always be set to the vicinity of the stoichiometric air-fuel ratio of the mixture and thus to detect the oxygen concentration in the exhaust gas by the O ₂ sensor, the oxygen concentration Thus, the air-fuel ratio is feedback-controlled.

[0003] On the other hand, as a new generation of fuel-saving engine, for example, a swirl or turbulent flow such as swirl is generated in a combustion chamber at the time of intake, and combustion is performed with a mixture having a leaner air-fuel ratio than the stoichiometric air-fuel ratio. Research and development of a lean burn engine that is capable of operating is under active development. In the case of this lean-burn engine, the oxygen concentration in the exhaust gas is high and the oxidation reaction is prioritized in the conventional three-way catalyst, so that it becomes difficult to purify NOx. However, the lean-burn engine is typified by the copper ion exchange ZSM5 zeolite catalyst. NO in the presence of HC even in such an oxidizing atmosphere.
A lean NOx catalyst capable of reducing and purifying x has been proposed. Therefore, when a lean NOx catalyst is used, it is required to appropriately diagnose a failure, a change with time, and deterioration of the lean NOx catalytic converter.

[0004] Conventionally, there is a first prior art of Japanese Patent Application Laid-Open No. 63-97852 regarding failure diagnosis of the above-mentioned catalytic converter.
Calculate the number of reversals of the output of the air-fuel ratio sensor downstream of the catalyst,
This shows that when the number of reversals is equal to or more than a predetermined value, it is determined that the catalyst has deteriorated.

In the second prior art of Japanese Patent Application Laid-Open No. Hei 3-74540, a linear O ₂ sensor is provided downstream of the catalyst, and whether the catalyst is normal or abnormal is determined based on whether the sensor output is within a predetermined range. It is shown to be.

In the third prior art disclosed in Japanese Patent Application Laid-Open No. Sho 62-153546, when the air-fuel ratio is controlled by an O ₂ sensor upstream of the catalyst during steady operation, a NOx sensor downstream of the catalyst, C
It is shown that the NOx concentration and the CO concentration in the exhaust gas are measured by an O sensor, and the abnormality of the catalyst is determined by comparing with the determination level.

[0007]

By the way, in the first, second and third prior arts, all of them are O _2.
Since it is assumed that the air-fuel ratio is feedback-controlled near the stoichiometric air-fuel ratio by the output of the sensor, it is difficult to apply the lean-burn engine to which the present invention is applied. In the third prior art, a NOx sensor is used and its NOx sensor is used.
The presence or absence of an abnormality is determined based on the x concentration and the determination level. The determination level is a map of a preset engine speed and a basic injection time. Therefore, the determination of the abnormality is limited during the steady operation in relation to the determination level of the map.

SUMMARY OF THE INVENTION In view of the foregoing, an object of the present invention is to always and accurately diagnose a failure of a lean NOx catalytic converter of an exhaust gas purifying device in a lean burn engine.

[0009]

SUMMARY OF THE INVENTION In order to achieve this object, the present invention relates to an exhaust gas purifying apparatus in which a lean NOx catalytic converter for purifying NOx is attached to an exhaust system of a lean-burn engine body. Lean NO
an NOx concentration sensor mounted at the most downstream position downstream of the x catalytic converter and not affected by the outside air from the tail, integrating means for integrating the NOx emission by the actual NOx concentration of the NOx concentration sensor for a predetermined time; And a failure determination means for diagnosing the presence or absence of a failure in the lean NOx catalytic converter based on the integrated value calculated from the above.

[0010]

According to the present invention having the above-described structure, of the harmful components of the exhaust gas from the lean-burn engine body, mainly NOx is effectively purified by the lean NOx catalytic converter. In this case, since the NOx concentration sensor is mounted at the most downstream position downstream of the lean NOx catalytic converter and not affected by outside air from the tail, the NOx concentration after passing through the converter is detected with high accuracy. By calculating an integrated value obtained by integrating the NOx emission amount based on the NOx concentration for a predetermined time, and comparing the integrated value with a reference for failure diagnosis, the failure of the lean NOx catalytic converter in the operating region including the steady operation and the transient state is performed. Is appropriately diagnosed.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 illustrates the overall configuration of the lean burn engine. Reference numeral 1 denotes a lean-burn engine body. In an intake system of the engine body 1, an air cleaner 2 has a duct 3, a throttle body 5 having a throttle valve 4,
Injector 7 that communicates with the combustion chamber via intake manifold 6 and injects fuel into each cylinder of intake manifold 6
Is installed. The intake manifold 6 of the engine body 1 is provided with a swirl or tumble generating means (not shown), which generates a vortex or a turbulent flow in the combustion chamber upon intake.
It is configured to be able to burn with a mixture having a leaner air-fuel ratio than the stoichiometric air-fuel ratio.

In the lean burn engine, the oxygen concentration in the exhaust gas is high, and the reduction and purification of NOx is difficult. For this reason, the exhaust manifold 8 of the engine body 1 has a lean NOx catalytic converter 1 as an exhaust gas purification device.
0, and mainly NOx of the exhaust gas, lean N
The Ox catalyst is configured to perform a purification reaction by performing a reduction reaction in the presence of HC. Then, the lean NOx catalytic converter 10 is further connected to the muffler 9 via the exhaust pipe 11.

Next, the control system will be described. First,
Explaining the control principle, the lean NOx catalyst mainly purifies NOx, so by monitoring NOx after passing through the converter under each engine operating condition,
The presence or absence of a failure can be diagnosed together with the purification state of the lean NOx catalytic converter 10. Therefore, the signals of the air flow meter 12 for detecting the intake air amount Q and the crank angle sensor 13 for detecting the engine speed N are input to the control unit 20. A NOx concentration sensor 14 for detecting the NOx concentration in the gas after passing through the converter is attached downstream of the lean NOx catalytic converter 10 at a position not affected by the outside air from the tail immediately before the muffler 9. Input to the unit 20.

The control unit 20 has an operating condition determining means 21 to which the engine speed N and the intake air amount Q are inputted, and determines the engine operating condition based on both parameters. The signal of the operating condition is input to the NOx standard amount calculating means 22, and the NOx standard amount Sg, which is a reference for failure diagnosis, is determined for each operating condition. That is, the NOx standard concentration SNOxconc, which is a reference for failure diagnosis, for each operating condition is experimentally determined in advance and set in a table, and the NOx standard concentration SNOxconc is searched from this table to calculate the NOx standard amount Sg. The NOx concentration sensor 14 also has NOx emission amount calculating means 23 to which a signal of the actual NOx concentration NOxconc and a signal of the operating condition are inputted. Based on the NOx concentration NOxconc, the actual NOx emission amount g after passing through the lean NOx catalytic converter 10 is calculated. calculate.

Both the standard amount Sg and the emission amount g of NOx are input to integrating means 24 and 25 and integrated for a predetermined time to obtain integrated values SG and G. These integrated values SG and G are input to the failure determination means 26, and the two are compared to determine the failure of the lean NOx catalytic converter 10 when G> SG. In the event of a failure, a warning is displayed by the warning display means 27 or the engine output is limited by the engine output limiting means 28 depending on the degree of the failure.

The control unit 20 determines an appropriate fuel injection condition according to the operating state based on various input information, and outputs this injection signal to the injector 7. The ignition timing is determined, and the ignition signal is output to the igniter.

Next, the operation of this embodiment will be described. First, during operation of the engine, air is drawn into the engine body 1 in accordance with the opening of the throttle valve 4, and at this time, swirl or the like is generated in the combustion chamber by the swirl generating means of the intake manifold 6. The intake air amount Q and the engine speed N
The fuel injection amount is calculated based on the basic fuel injection amount based on the above and various correction coefficients such as a reduction correction coefficient, and this fuel is injected by the injector 7 at a predetermined injection timing. Therefore, the mixture of air and fuel in the combustion chamber is ignited by the ignition plug as the vortex is generated, and the mixture is stratified so that the vicinity of the ignition plug is thick and the surrounding area is thin.
The air-fuel mixture having a lean air-fuel ratio burns well, and good fuel efficiency and operability are obtained.

On the other hand, the exhaust gas from the lean combustion is discharged from the engine body 1 to the exhaust manifold 8. In this case, the oxygen concentration in the exhaust gas is high due to the lean air-fuel ratio, and N
Since the action of reducing and purifying Ox becomes difficult, it is particularly necessary to reduce NOx. The exhaust gas containing NOx is lean N
The NOx is introduced into the Ox catalytic converter 10, and the NOx is reduced by a lean NOx catalyst in the presence of HC to be purified. Then, the gas purified by the lean NOx catalytic converter 10 is discharged through the muffler 9 further downstream.

In this case, the lean NOx catalytic converter 1
Immediately after zero, the exhaust gas is still in an unstable state due to the reduction reaction of NOx, and is stabilized as the distance from the converter 10 increases. Here, the NOx concentration sensor 14 is the converter 1
The NOx concentration NOxconc in the exhaust gas after passing through the converter is detected in a stable state with high accuracy by being mounted at a position away from 0 and not affected by the outside air from the tail immediately before the muffler 9.

Next, the failure diagnosis control of the lean NOx catalytic converter 10 during the operation of the lean burn engine will be described with reference to FIG.
This will be described with reference to the flowchart of FIG. First, step S
In step S1, a timer reset is performed at predetermined time intervals. In step S2, the operating conditions are determined based on the engine speed N and the intake air amount Q. Standard concentration SNOxco
nc. Then, the process proceeds to step S4, where NOx
Based on the standard concentration SNOxconc, the intake air amount Q and the specific gravity γ of NOx, the NOx standard amount Sg is calculated by the following equation: Then, in step S5, the NOx standard amount S
g is integrated, and the integrated value SG is calculated. Step S
6 checks whether or not a predetermined time has elapsed, and returns to step S2 again within the predetermined time. Therefore, when the operating conditions change, the same operation is repeated again, and thus an integrated value SG obtained by integrating the NOx standard amount Sg for a predetermined time is obtained.

On the other hand, in step S7, the actual NOx concentration NOx after passing through the converter by the NOx concentration sensor 14 is used.
conc, the NOx concentration NOxc is read in step S8.
onc, intake air amount Q and specific gravity γ of NOx, NO
The x emission amount g is calculated by g = Q · NOxconc · γ. Then, in step S9, the NOx emission amount g
To calculate the integrated value G. Thereafter, it is similarly checked in step S6 whether a predetermined time has elapsed, and within the predetermined time, the flow returns to step S2 again. If the operating conditions change, the same operation is repeated again. An integrated value G obtained by integrating the quantity g is similarly obtained.

After obtaining the integrated values SG and G of the standard amount of NOx and the emission amount for a predetermined time, the process proceeds to step S10 to compare the two. And NOx emission is small, G
If ≦ SG is satisfied, it is determined that the lean NOx catalytic converter 10 is normal, and the process returns to the original state. If the amount of NOx emission increases and G> SG, it is determined that the lean NOx catalytic converter 10 has failed, changed over time, deteriorated, or the like. In this case, the process proceeds to step S11 to display a warning. Thus, when the lean NOx catalytic converter 10 of the exhaust gas purifying device mainly performs NOx purification processing in the lean burn engine, the integrated value G of the NOx emission amount under the actual operating conditions is calculated for a predetermined time downstream of the converter. Thus, the presence / absence of the failure of the lean NOx catalytic converter 10 in the transient state as well as the steady operation is properly diagnosed.

Although the embodiment of the present invention has been described above, the present invention is not limited to this.

[0024]

As described above, according to the present invention,
NOx is mainly used in the exhaust system of the lean-burn engine body.
In an exhaust gas purification apparatus equipped with a lean NOx catalytic converter for purifying NOx, a NOx concentration sensor is attached at the most downstream position downstream of the lean NOx catalytic converter and not affected by outside air from the tail. The actual NOx concentration in the exhaust gas can be accurately detected. N based on the actual NOx concentration of the NOx concentration sensor
Since the Ox emission amount is integrated for a predetermined time and the integrated value is used to diagnose the presence or absence of a failure in the lean NOx catalytic converter, the converter can be directly diagnosed in all operation regions including the transient state. Since the integrated value of the standard NOx amount is used as a reference for the failure diagnosis, the accuracy of the diagnosis is high.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment suitable for a failure diagnosis device for an exhaust gas purification device according to the present invention.

FIG. 2 is a flowchart of a failure diagnosis control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 10 Lean NOx catalytic converter 14 NOx concentration sensor 20 Control unit

Claims (2)

(57) [Claims] 1. An exhaust system of a lean-burn engine body,
In an exhaust gas purification apparatus equipped with a lean NOx catalytic converter that mainly purifies NOx, a NOx concentration sensor is mounted at the most downstream position downstream of the lean NOx catalytic converter and not affected by outside air from the tail. Integral means for integrating the NOx emission amount based on the actual NOx concentration of the sensor for a predetermined time, and failure determining means for diagnosing the presence or absence of a failure in the lean NOx catalytic converter based on the integrated value calculated from the integral means. Diagnosis device of exhaust gas purification device to be used. 2. An NOx standard amount calculating means for calculating a NOx standard amount serving as a reference for failure diagnosis under actual operating conditions, and an integrating means for integrating a NOx standard amount calculated from the NOx standard amount calculating means for a predetermined time. 2. A failure diagnosis device for an exhaust gas purifying device according to claim 1, wherein a failure diagnosis is performed by comparing an integral value calculated by said integration means with an integral value of said NOx emission amount.