JP3062710B2 - Catalyst deterioration detection 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 catalyst deterioration detecting apparatus for an engine having a so-called lean NOx catalyst in an exhaust system.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Application Laid-Open No. 3-25013, a transition metal is used as a catalyst for purifying NOx in engine exhaust gas in a lean air-fuel ratio region in which the air-fuel ratio is larger than a stoichiometric air-fuel ratio. Alternatively, an engine having a so-called lean NOx catalyst in an exhaust system, which is made of zeolite carrying a noble metal and reduces NOx in exhaust gas in an oxidizing atmosphere in the presence of HC, is known.

Further, as described in Japanese Patent Application Laid-Open No. 63-97852, for example, in an engine provided with a catalyst in an exhaust system, deterioration of the catalyst is detected based on an output of a gas concentration sensor downstream of the catalyst. Some are provided with a device. Apart from this, there is also known one that detects deterioration based on a difference in exhaust gas temperature between the upstream side and the downstream side of the catalyst.

[0004]

The lean NOx catalyst adsorbs HC and NOx in the exhaust gas components to reduce and purify NOx. However, when adsorbing oxygen, the catalyst deteriorates and remarkably deteriorates the purification performance. However, the deterioration due to oxygen adsorption is only temporary deterioration, and can be recovered by heating the catalyst or sending a rich mixture. On the other hand, when the catalyst has deteriorated due to aging, it is necessary to replace the catalyst itself. Therefore, in the detection of the deterioration of the lean NOx catalyst, it is necessary to distinguish and detect whether the deterioration is temporary deterioration due to oxygen adsorption as described above or deterioration with time of the catalyst itself. However, it is impossible for a conventional catalyst deterioration detecting device to detect a lean NOx catalyst by distinguishing between temporary deterioration and temporal deterioration.

The present invention has been made in view of the above problems, and provides a catalyst deterioration detecting device capable of determining whether the deterioration of a lean NOx catalyst is temporal or temporary. The purpose is to do.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an apparatus for detecting deterioration of a catalyst, and comprises at least a lean N-fuel ratio in a lean air-fuel ratio region where the air-fuel ratio is larger than a stoichiometric air-fuel ratio.
In an engine in which NOx in exhaust gas is reduced by an Ox catalyst by reduction and purification or the like, first and second exhaust temperature sensors for detecting exhaust temperatures upstream and downstream of a lean NOx catalyst, and the first and second exhaust temperature sensors Exhaust temperature difference calculating means for calculating the exhaust temperature difference between the upstream side and the downstream side of the lean NOx catalyst by receiving the output of the exhaust
A temperature state detecting means for detecting a temperature state of the Ox catalyst, and first and second oxygen concentration sensors for detecting oxygen concentrations on the upstream side and the downstream side of the lean NOx catalyst. For detecting oxygen in exhaust gas
And second exhaust gas component detection sensors,
A lean NOx catalyst, such as an oxygen concentration difference integrated value calculating means for receiving an output of an exhaust gas component detection sensor such as a second oxygen concentration sensor and calculating an integrated value of an oxygen concentration difference between an upstream side and a downstream side of the lean NOx catalyst. Temperature, such as an adsorbed state calculating means for calculating an adsorbed state of oxygen , an exhaust temperature difference calculating means for receiving outputs of the first and second exhaust temperature sensors and calculating an exhaust temperature difference between an upstream side and a downstream side of the lean NOx catalyst. Based on the output of the state detection means and the output of the adsorption state calculation means such as the oxygen concentration difference integrated value calculation means, it is determined that the lean NOx catalyst has deteriorated based on the temperature state, such as when the exhaust gas temperature difference is equal to or less than a predetermined temperature difference. When the degree of oxygen adsorption is equal to or higher than a predetermined value, such as when the integrated value of the oxygen concentration difference is equal to or higher than a predetermined value, lean NOx
It is characterized by comprising catalyst deterioration determining means for determining that the catalyst is in a state of temporary deterioration.

[0007] The deterioration detecting device may include a threshold value reducing means, and may reduce a predetermined value of the oxygen concentration difference integrated value for the temporary deterioration determination in accordance with the aging of the lean NOx catalyst. .

Further, the deterioration detecting device may include a judgment interval changing means for shortening an interval of execution of the deterioration judgment by the catalyst deterioration judging means as the engine speed and the load become higher.

Further, the deterioration detecting device is provided with oxygen releasing means for releasing oxygen adsorbed on the lean NOx catalyst when the deterioration determining means determines that the lean NOx catalyst is in a temporarily deteriorated state. be able to.

FIG. 1 is an overall configuration diagram showing the above configuration of the present invention.

[0011]

When NOx is being purified by the lean NOx catalyst, the exhaust gas temperature rises due to heat generated by a chemical reaction inside the catalyst, causing a difference in exhaust gas temperature between the upstream side and the downstream side of the lean NOx catalyst. As a result, the oxygen concentration in the exhaust gas is reduced, and the oxygen concentration is also reduced by the adsorption of oxygen on the catalyst surface, so that an oxygen concentration difference occurs between the upstream side and the downstream side of the lean NOx catalyst. The difference between the exhaust gas temperature and the difference in oxygen concentration gradually decreases with the lapse of time from the start of the lean operation due to the temporary deterioration due to oxygen adsorption, and the values decrease as the deterioration with time progresses. Further, the value obtained by integrating the oxygen concentration difference at a predetermined interval sharply increases immediately after the start of the lean operation, and thereafter gradually decreases as temporary deterioration proceeds, and the value decreases as the deterioration with time progresses as a whole. I do.

According to the present invention, when the exhaust gas temperature difference becomes equal to or less than a predetermined value, the lean N
If it is determined that the Ox catalyst is deteriorated, and if the degree of oxygen adsorption is equal to or greater than a predetermined value, such as the integrated value of the oxygen concentration difference at that time is equal to or greater than a predetermined value, it is determined that the lean NOx catalyst is temporarily deteriorated. Is smaller than the predetermined value, it is determined that the battery has deteriorated with time.

Further, the threshold value of the integrated value of the oxygen concentration difference is reduced in accordance with the aging of the lean NOx catalyst, so that when the purification rate of the catalyst itself is reduced due to the aging, the detection of the temporary deterioration is performed early. Will be Therefore, it is possible to perform a recovery operation for temporary deterioration early.
It is easier to cope with a decrease in the purification rate due to aging.

[0014] Further, since the interval of the execution of the deterioration determination is shortened as the engine speed and the load become higher, even when the engine speed becomes higher or the load becomes larger and the NOx emission amount becomes larger. By detecting catalyst deterioration early, a high purification rate can be maintained.

By providing a means for releasing oxygen from the lean NOx catalyst when it is determined that the fuel is temporarily deteriorated, the purification performance at the time of the temporary deterioration can be recovered.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a system diagram of one embodiment of the present invention. 1, a surge tank 3 is formed in an intake passage 2 of the engine 1. A throttle valve 4 is provided upstream of the surge tank 3, and a fuel injection valve 5 is provided downstream thereof.
Is provided. An inlet of the intake passage 2 is connected to an air cleaner 6, and an air flow meter 7 is provided immediately downstream of the air cleaner 6.

On the other hand, the exhaust passage 8 of the engine 1 is provided with a lean NOx catalyst 9 for reducing and purifying NOx during lean operation in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. And
A first oxygen concentration sensor 10a and a first exhaust gas temperature sensor 11a are provided on the upstream side of the lean NOx catalyst 9, and a second oxygen concentration sensor 10a is provided on the downstream side of the lean NOx catalyst 9.
b and a second exhaust gas temperature sensor 11b.

The control of the fuel injection valve 5 is performed by a control unit 12 constituted by a microcomputer. Therefore, an engine speed signal is input to the control unit 12 from a rotation sensor attached to the distributor 13, an intake air amount signal is input from the air flow meter 7, and an engine water temperature signal is input from a water temperature sensor (not shown). Further, the respective oxygen concentration signals are input to the control unit 12 from the first and second oxygen concentration sensors provided on the upstream side and the downstream side of the lean NOx catalyst 9, and are sent to the upstream side and the downstream side of the lean NOx catalyst 9. Each exhaust temperature signal is input from the installed first and second exhaust temperature sensors 11a and 11b.

When the operating state of the engine 1 is a predetermined lean F /
When in zone B, the basic injection amount of fuel is set based on the engine speed and the intake air amount, and various corrections based on the water temperature and the like are added thereto. An injection amount is calculated. Then, a control pulse corresponding to the final injection amount is applied to the fuel injection valve 5, whereby the air-fuel ratio of the engine 1 is controlled to a target value for lean setting.

When the engine 1 enters the lean steady operation, the first and second engine operation are started at a predetermined interval immediately after the start of the lean steady operation to detect the deterioration of the lean NOx catalyst 9.
The detection signals of the two oxygen concentration sensors 10a, 10b and the first and second exhaust temperature sensors 11a, 11b are read into the control unit 12, and the difference between the exhaust gas temperature and the oxygen concentration on the upstream side and the downstream side of the lean NOx catalyst 9 is detected. A difference integrated value is calculated. Then, based on the relationship between the exhaust gas temperature difference ΔT (horizontal axis) and the purification rate η (vertical axis) of the lean NOx catalyst 9 shown in FIG. 3, the exhaust gas temperature difference ΔT corresponding to the required minimum purification rate η _limit is obtained. A threshold ΔT _limit is set, then
From the time change of the exhaust gas temperature difference ΔT shown in FIG.
T is determined whether or not equal to or less than the threshold ΔT _limit, lean NOx Once you become less than or equal to the threshold value ΔT _limit
It is determined that the catalyst 9 has deteriorated. In FIG. 4, a broken line with respect to a solid line indicates a state in which the deterioration of the catalyst 9 with time has advanced.

The exhaust gas temperature difference ΔT is equal to the threshold value ΔT
_limit below, when it is determined that the deterioration of the lean NOx catalyst 9, the elapsed time _{t l} imit when equal to or less than the threshold [Delta] T _limit is determined from FIG. 4, then, the oxygen concentration difference shown in FIG. 5 | delta O.D. ₂ | integrated value ∫ | ΔO ₂ | from time variation of dt, the oxygen concentration difference in the elapsed time t _limit | delta
It is determined whether or not the integrated value Ｏ | ΔO ₂ | dt of O ₂ | is equal to or greater than a predetermined threshold value O _2limit (corresponding to the dashed line in the upper part of the figure), and the oxygen concentration difference | ΔO ₂ | If the integrated value ∫ | ΔO ₂ | dt is equal to or _larger than the threshold value O _2limit , it is determined that the deterioration of the lean NOx catalyst 9 is temporary deterioration, and the integrated value 酸 素 | ΔO ₂ | of the oxygen concentration difference | ΔO ₂ | If dt is smaller than the threshold value O _2limit, it is determined that deterioration with time has _occurred . In FIG. 5, the broken line with respect to the solid line also shows a state in which the deterioration of the catalyst 9 with time has advanced. Further, in such a state where the deterioration with time has advanced, the threshold value O _2limit is lowered to a level corresponding to the dashed line on the lower side of the figure.

The interval for detecting deterioration is changed according to the air-fuel ratio, the exhaust temperature, the engine speed and the load. That is, the oxygen concentration difference | ΔO ₂ |
The time-dependent characteristic of the integrated value changes depending on the air-fuel ratio and the exhaust gas temperature. The higher the air-fuel ratio and the lower the exhaust gas temperature, the faster the rise of the characteristic curve. FIG. 6 shows a change in the integrated value time change characteristic depending on the air-fuel ratio and the exhaust temperature. The solid line indicates a large air-fuel ratio or a low exhaust temperature, and the dashed line indicates a small air-fuel ratio or a high exhaust temperature. Corresponds to the case. When the air-fuel ratio increases or the exhaust gas temperature decreases, the characteristic curve moves in the direction indicated by the arrow in the figure. Therefore, in this embodiment, as shown in FIG. 7, as the air-fuel ratio is larger or the exhaust gas temperature is lower, the above interval is reduced and the lean NOx catalyst 9 is reduced.
The deterioration of can be detected early. Also, when the engine speed increases or the load increases,
Since the emission amount of NOx increases, it is necessary to detect catalyst deterioration early and maintain a high purification rate. Therefore, in this embodiment, as shown in FIG. 7, as the engine speed is higher or the load is larger, the interval is made smaller.

FIG. 8 is a flowchart for executing the above-described process of detecting deterioration in this embodiment. S1 to S13 indicate the respective steps.

In the flowchart of FIG. 8, the process is started, and in S1, it is determined whether or not the lean steady operation is started. If the lean steady operation is not started, the routine returns as it is. If the lean steady operation is started, the air-fuel ratio, the exhaust gas temperature, the engine speed and the load are read in S2 for the detection interval calculation. At S3, a detection interval is calculated based on the temperature, the engine speed, and the load.

After calculating the interval in S3, the timer is started in S4, and the exhaust gas temperature sensors 11a and 11b and the oxygen concentration sensors 10a and 10b in S5.
The detected value of b is read, and an exhaust gas temperature difference ΔT and an oxygen concentration difference integrated value ∫ | ΔO ₂ | dt are calculated in S6.

Next, in S7, it is determined whether or not the exhaust gas temperature difference ΔT is larger than a threshold value ΔT _limit (see FIG. 4). If it is determined that the exhaust gas temperature difference ΔT is larger than the threshold value ΔT _limit , it is determined whether the lean steady operation is continuing in S8. If so, the process returns to S4 and returns to S4.
The routine from S8 to S8 is repeated, and the routine returns if the lean steady operation is not continued.

If it is determined in step S7 that the exhaust gas temperature difference ΔT is equal to or smaller than the threshold value ΔT _limi , the process proceeds to step S9, where the oxygen concentration difference integrated value ∫ | ΔO ₂ | dt is set to the threshold value O _2limit (see FIG. 5).
Determining whether more, the oxygen concentration difference integrated value ∫ | ΔO ₂ |
If dt is equal to or _larger than the threshold value O _2limit, it is determined in S10 that the lean NOx catalyst 9 is temporarily deteriorated due to oxygen adsorption, and S1 is determined.
Proceed to Step 1 to recover the catalyst purification performance (catalyst heating,
Supply of a rich mixture). And it returns.

The oxygen concentration difference integrated value ∫ | ΔO ₂ | dt
Is smaller than the threshold value O _2limit , it is determined in S12 that the lean NOx catalyst 9 has deteriorated with time, and the _routine proceeds to S13, in which the lean operation is stopped, and the operation at λ (excess air ratio) = 1 is performed.
And it returns.

[0030]

Since the present invention is configured as described above, it is possible to determine whether the lean NOx catalyst has deteriorated over time or temporarily, and to take appropriate measures according to the type of deterioration. Becomes possible.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of the present invention.

FIG. 2 is a system diagram of an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between an exhaust gas temperature difference and a purification rate in one embodiment of the present invention.

FIG. 4 is a characteristic diagram showing a time change of an exhaust gas temperature difference in one embodiment of the present invention.

FIG. 5 is a characteristic diagram showing a time change of an oxygen concentration difference integrated value in one embodiment of the present invention.

FIG. 6 is a characteristic diagram showing a change of an oxygen concentration difference integrated value change characteristic by various parameters in one embodiment of the present invention.

FIG. 7 is a characteristic diagram showing a change in a detection interval according to various parameters in one embodiment of the present invention.

FIG. 8 is a flowchart for executing a process of detecting deterioration according to an embodiment of the present invention;

[Explanation of symbols]

 Reference Signs List 1 engine 8 exhaust passage 9 lean NOx catalyst 10a, 10b oxygen concentration sensor 11a, 11b exhaust temperature sensor 12 control unit

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tadataka Nakakaku 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Former Moto Suetsugu 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Matsu (56) References JP-A-64-45913 (JP, A) JP-A-3-50315 (JP, A) JP-A 62-61919 (JP, U) JP-A 63-128221 (JP, A) , U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08-3/38 F01N 9/00-11/00 F02D 41/00-41/40 F02D 43/00-45 / 00

Claims (5)

(57) [Claims] In an engine that reduces and purifies NOx in exhaust gas with a lean NOx catalyst at least in a lean air-fuel ratio region in which an air-fuel ratio is greater than a stoichiometric air-fuel ratio, exhaust gas temperatures upstream and downstream of the lean NOx catalyst are detected. Receiving the outputs of the first and second exhaust gas temperature sensors and the first and second exhaust gas temperature sensors.
exhaust temperature difference calculating means for calculating an exhaust gas temperature difference between the upstream side and the downstream side of the x catalyst; first and second oxygen concentration sensors for detecting oxygen concentrations on the upstream side and the downstream side of the lean NOx catalyst; Oxygen concentration difference integrated value calculation means for receiving the outputs of the first and second oxygen concentration sensors and calculating the integrated value of the oxygen concentration difference between the upstream side and the downstream side of the lean NOx catalyst;
When the output of the exhaust gas temperature difference calculating means and the output of the oxygen concentration difference integrated value calculating means are received, and the exhaust gas temperature difference is equal to or less than a predetermined temperature difference, and the integrated value of the oxygen concentration difference is equal to or more than a predetermined value, An apparatus for detecting deterioration of a catalyst, comprising: catalyst deterioration determining means for determining that the lean NOx catalyst is in a state of temporary deterioration. 2. A catalyst deterioration detecting device according to claim 1, further comprising a threshold value reducing means for reducing a predetermined value of said oxygen concentration difference integrated value for temporary deterioration determination in accordance with a temporal change of the lean NOx catalyst. . 3. The engine according to claim 1, further comprising a determination interval changing unit that shortens an interval of the deterioration determination executed by the catalyst deterioration determining unit as the engine speed and the load increase.
A catalyst deterioration detection device according to the above. 4. When the lean NOx catalyst is determined to be in a state of temporary deterioration by the deterioration determining means, the lean
2. The catalyst deterioration detecting device according to claim 1, further comprising oxygen desorbing means for desorbing oxygen adsorbed on the Ox catalyst. 5. An engine in which NOx in exhaust gas is reduced by a lean NOx catalyst at least in a lean air-fuel ratio region in which the air-fuel ratio is greater than a stoichiometric air-fuel ratio.
Temperature state detecting means for detecting the temperature state of the Ox catalyst; and acid in exhaust gas on the upstream and downstream sides of the lean NOx catalyst.
The first and second and the exhaust gas component detection sensor, the first and second exhaust gas component receives the output of the detection sensor adsorption state calculating means for calculating the adsorption state of oxygen by the lean NOx catalyst for detecting a hydrogen Receiving the output of the temperature state detection means and the output of the adsorption state calculation means, it is determined that the lean NOx catalyst is deteriorated based on the temperature state, and the degree of adsorption of oxygen is equal to or more than a predetermined value. A catalyst deterioration detection device, comprising: catalyst deterioration determination means for determining that the lean NOx catalyst is in a state of temporary deterioration at any time.