JP2020143631A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

To provide an exhaust emission control device for an internal combustion engine capable of accurately detecting deterioration of a selective reduction type catalyst.SOLUTION: An exhaust emission control device includes: a selective reduction type catalyst 44 provided in an exhaust passage of an internal combustion engine; acquisition sections 11, 62 acquiring an ammonia concentration in exhaust gas on the upstream side and downstream side of the selective reduction type catalyst 44; and a determination section 11 determining whether the selective reduction type catalyst 44 has deteriorated. The determination section 11 determines whether the selective reduction type catalyst 44 has deteriorated on the basis of an ammonia concentration on the upstream side and an ammonia concentration on the downstream side when a temperature of the selective reduction type catalyst 44 is a first temperature and an ammonia concentration on the upstream side and an ammonia concentration on the downstream side when the temperature of the selective reduction type catalyst 44 is a second temperature higher than the first temperature.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas purification device for an internal combustion engine.

In order to purify nitrogen oxides (NOx) in the exhaust generated from the internal combustion engine, for example, a catalyst such as a selective reduction catalyst (SCR catalyst: Selective Catalytic Reduction) is used. An addition valve for adding an additive (urea water) and an SCR catalyst located downstream of the addition valve are provided in the exhaust passage of the internal combustion engine. Urea water is added to the exhaust gas from the addition valve, and ammonia (NH ₃ ) is generated from the urea water. The SCR catalyst adsorbs NOx and decomposes it into nitrogen and water by reducing it with ammonia to purify NOx. Part of the ammonia flows downstream from the SCR catalyst. A technique for determining deterioration of an SCR catalyst from the amount of ammonia and NOx flowing out of the SCR catalyst is known (Patent Document 1).

Japanese Unexamined Patent Publication No. 2015-97086

However, there is a risk that an erroneous judgment will occur in the deterioration judgment of the catalyst. Therefore, it is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine capable of detecting deterioration of a selective reduction catalyst with high accuracy.

The purpose of the above is to provide a selective reduction catalyst provided in the exhaust passage of the internal combustion engine, an acquisition unit for acquiring the concentration of ammonia in the exhaust on the upstream side and the downstream side of the selective reduction catalyst, and the selective reduction catalyst. A determination unit for determining whether or not the catalyst has deteriorated is provided, and the determination unit includes the concentration of ammonia on the upstream side and the ammonia on the downstream side when the temperature of the selective reduction catalyst is the first temperature. And the selective reduction catalyst based on the concentration of ammonia on the upstream side and the concentration of ammonia on the downstream side when the temperature of the selective reduction catalyst is a second temperature higher than the first temperature. This can be achieved by an exhaust purification device of an internal combustion engine that determines whether or not the catalyst is deteriorated.

It is possible to provide an exhaust gas purification device for an internal combustion engine capable of detecting deterioration of a selective reduction catalyst with high accuracy.

FIG. 1 is a schematic diagram illustrating an exhaust gas purification device. 2 (a) and 2 (b) are diagrams showing the ammonia slip ratio. FIG. 3A is a diagram showing the relationship between the ammonia slip ratio and the catalyst temperature. FIG. 3B is a diagram showing the relationship between the NOx slip ratio and the catalyst temperature. 4 (a) and 4 (b) are flowcharts illustrating the control executed by the ECU. FIG. 5 is a flowchart illustrating the control executed by the ECU.

Hereinafter, the exhaust gas purification device for the internal combustion engine of the present embodiment will be described with reference to the drawings. FIG. 1 is a schematic view illustrating the exhaust gas purification device 100. FIG. 1 is a schematic view illustrating the exhaust gas purification device 100. As shown in FIG. 1, the exhaust gas purification device 100 is applied to an engine 10 (internal combustion engine), and includes an ECU 11, an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 40 and 48, a filter (DPF: Diesel Particulate Filter) 42, and an SCR catalyst 44. , Addition valve 50, dispersion plate 54, temperature sensor 60, and gas sensor 62.

The engine 10 is, for example, a four-cylinder diesel engine having four cylinders # 1 to # 4, and is mounted on a vehicle. Cylinders # 1 to # 4 of the engine 10 are connected to the intake manifold 22 and the exhaust manifold 24. An intake passage 20 is connected to the upstream side of the intake manifold 22. The exhaust passage 26 is connected to the downstream side of the exhaust manifold 24.

The intake passage 20 is provided with an air flow meter 21, a turbocharger 36 compressor 36a, an intercooler 25, and a throttle valve 30 in this order from the upstream side. The air flow meter 21 measures the amount of air taken in. The intake air is supercharged by the rotation of the compressor 36a. The intercooler 25 cools the intake air. The flow rate of intake air is adjusted by the opening degree of the throttle valve 30. The intake air is introduced into cylinders # 1 to # 4 through the intake manifold 22.

Each cylinder is provided with a fuel injection valve 12 and a glow plug 14. The fuel injection valve 12 is connected to the common rail 18. High-pressure fuel is supplied from the pump 16 to the common rail 18, and when the fuel injection valve 12 is opened, the fuel is injected into the cylinder. The air-fuel mixture compressed in the cylinder ignites. The exhaust generated by combustion is discharged through the exhaust manifold 24 and the exhaust passage 26. The turbine 36b and the compressor 36a rotate as the exhaust gas flows.

The intake manifold 22 and the exhaust manifold 24 are connected by an EGR passage 28. A part of the exhaust gas passes through the EGR passage 28 and joins the intake air in the intake manifold 22. The EGR passage 28 is provided with an EGR valve 32 and an EGR cooler 34. By adjusting the opening degree of the EGR valve 32, the circulation amount of the exhaust gas in the EGR passage 28 is adjusted. The EGR cooler 34 lowers the temperature of the exhaust gas in the EGR passage 28.

In the exhaust passage 26, the turbine 36b of the turbocharger 36, the air-fuel ratio sensor 51, the oxidation catalyst 40, the filter 42, the addition valve 50, the temperature sensor 60, the dispersion plate 54, the SCR catalyst 44, the gas sensor 62, and the oxidation catalyst are arranged in this order from the upstream side. 48 is provided.

The oxidation catalyst 40 oxidizes HC in the exhaust gas. The filter 42 collects PM (fine particle substances) in the exhaust with, for example, a porous ceramic. The filter 42 may carry a catalyst that promotes the oxidation of PM. By raising the temperature of the exhaust gas, the filter 42 can be regenerated.

The SCR catalyst 44 and the oxidation catalyst 48 are provided on the downstream side of the filter 42. The SCR catalyst 44 is, for example, a copper zeolite catalyst, and uses ammonia as a reducing agent to reduce and purify NOx in the exhaust gas.

An add-on valve 50 is used to supply the reducing agent to the SCR catalyst 44. Urea water is supplied to the addition valve 50 from the tank 52. The addition valve 50 injects urea water upstream of the SCR catalyst 44 in the exhaust passage 26. Urea water collides with the dispersion plate 54 and is dispersed. Ammonia is generated by hydrolyzing urea water by the heat of the exhaust gas. Ammonia is adsorbed on the SCR catalyst 44 on the downstream side. NOx is reduced and purified using ammonia as a reducing agent, and decomposed into nitrogen (N ₂ ) and water (H ₂ O). Since ammonia is atomized by the dispersion plate 54, the purification efficiency of the SCR catalyst 44 is improved. The oxidation catalyst 48 oxidizes the ammonia in the exhaust gas. Therefore, the release of ammonia into the atmosphere is suppressed.

The air-fuel ratio sensor 51 detects the air-fuel ratio and also detects the NOx concentration in the exhaust gas. The temperature sensor 60 measures the temperature of the exhaust gas. The gas sensor 62 detects the ammonia concentration and the NOx concentration in the exhaust gas on the downstream side of the SCR catalyst 44.

The ECU (Electronic Control Unit) 11 includes a storage device such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), and various controls are performed by executing a program stored in the storage device. I do. The ECU 11 controls fuel injection, urea water injection from the addition valve 50, and opening degrees of the throttle valve 30 and the EGR valve 32.

The ECU 11 acquires the flow rate of the intake air from the air flow meter 21, acquires the exhaust temperature from the temperature sensor 60, and estimates the temperature of the SCR catalyst 44 based on the exhaust temperature. The ECU 11 acquires the ammonia concentration and the NOx concentration in the exhaust gas downstream from the SCR catalyst 44 from the gas sensor 62. The ECU 11 acquires the flow rate of the exhaust gas based on the amount of air detected by the air flow meter 21, and acquires the ammonia concentration on the upstream side of the SCR catalyst 44 based on the flow rate of the exhaust gas and the amount of urea water added.

As described above, in the SCR catalyst 44, ammonia reacts with NOx in the exhaust gas, but a part of the ammonia flows out to the downstream side of the SCR catalyst 44, and another part is oxidized to NOx and flows out to the downstream side. To do. The ECU 11 acquires the ammonia concentration and the NOx concentration from the gas sensor 62, calculates the ammonia slip ratio using the following formula (1) based on them, and calculates the NOx slip ratio using the formula (2).
Ammonia slip ratio = (ammonia concentration on the downstream side of the SCR catalyst 44) / (ammonia concentration on the upstream side of the SCR catalyst 44) × 100 (1)
NOx slip ratio = (NOx concentration on the downstream side of the SCR catalyst 44) / (Ammonia concentration on the upstream side of the SCR catalyst 44) × 100 (2)

Ammonia slip ratio and NOx slip ratio vary depending on the temperature and the state of the SCR catalyst 44. The ECU 11 functions as a determination unit for determining whether or not the SCR catalyst 44 has deteriorated based on the ammonia slip ratio.

2 (a) and 2 (b) are diagrams showing the ammonia slip ratio, FIG. 2 (a) is an example in which the catalyst temperature is T1, and FIG. 2 (b) is a diagram in which the catalyst temperature is, for example, 100 ° C. than T1. This is an example of high T2. In each figure, the ammonia slip ratio in the new SCR catalyst 44, the normal SCR catalyst 44, and the deteriorated SCR catalyst 44 is shown in order from the left. The normal SCR catalyst 44 is capable of purifying the exhaust gas. The deteriorated SCR catalyst 44 is an abnormal catalyst (NG product) that has deteriorated to the extent that it is difficult to purify the exhaust gas.

As shown in FIG. 2A, at the temperature T1, the new ammonia slip ratio is X1, and the ammonia slip ratio of the normal SCR catalyst 44 is X2, which is higher than X1. The ammonia slip ratio of the deteriorated SCR catalyst 44 is X3, which is higher than that of X2. X2 and X3 are, for example, five times or more of X1.

As shown in FIG. 2B, at the temperature T2, the new ammonia slip ratio is X4, which is about the same as X1 in FIG. 2A, for example. The ammonia slip ratio of the normal SCR catalyst 44 is X5, which is higher than X4 and lower than X2 in FIG. 2 (a). The ammonia slip ratio of the deteriorated SCR catalyst 44 is X6, which is slightly higher than that of X4, and is about 1/5 of that of X5.

FIG. 3A is a diagram showing the relationship between the ammonia slip ratio and the catalyst temperature. The horizontal axis represents the catalyst temperature, and the temperature rises from T0 to T3. The vertical axis represents the ammonia slip ratio. The circles indicate the new SCR catalyst 44, the squares indicate the normal SCR catalyst 44, and the triangles indicate the deteriorated SCR catalyst 44, respectively.

As shown in FIG. 3A, the ammonia slip ratio of any SCR catalyst decreases as the temperature increases. The ammonia slip ratio of the deteriorated SCR catalyst 44 decreases significantly with increasing temperature as compared with the normal SCR catalyst 44, and particularly sharply decreases from the temperature T1 to T2.

FIG. 3B is a diagram showing the relationship between the NOx slip ratio and the catalyst temperature. The horizontal axis represents the catalyst temperature, and the vertical axis represents the NOx slip ratio. The circles indicate the new SCR catalyst 44, the squares indicate the normal SCR catalyst 44, and the triangles indicate the deteriorated SCR catalyst 44, respectively, indicating the NOx slip ratio. As shown in FIG. 3B, the NOx slip ratio of the new SCR catalyst 44 is about the same at any temperature. The NOx slip ratio of the normal SCR catalyst 44 and the deteriorated SCR catalyst 44 increases with temperature. The NOx slip ratio of the deteriorated SCR catalyst 44 increases significantly with increasing temperature as compared with the normal SCR catalyst 44. It is considered that in the deteriorated SCR catalyst 44, a large amount of ammonia is oxidized to NOx at a high temperature as compared with the normal SCR catalyst 44, and such NOx flows out from the SCR catalyst 44. Therefore, the ammonia slip rate decreases and the NOx slip rate increases.

4 (a) and 4 (b) are flowcharts illustrating the control executed by the ECU 11, FIG. 4 (a) is the control for calculating the ammonia slip ratio, and FIG. 4 (b) is for determining the deterioration of the SCR catalyst 44. It is control. The ECU 11 calculates the ammonia slip ratio by controlling FIG. 4A at a plurality of temperatures, for example, T0 to T3 in FIG. 3A, and then determines deterioration by controlling FIG. 4B. I do.

As shown in FIG. 4A, the ECU 11 acquires the temperature of the SCR catalyst 44 based on the exhaust temperature detected by the temperature sensor 60 (step S10). The ECU 11 injects urea water from the addition valve 50, acquires the ammonia concentration on the upstream side of the SCR catalyst 44 based on the flow rate of the exhaust gas and the amount of urea water added, and further, the ammonia on the downstream side of the SCR catalyst 44 from the gas sensor 62. Acquire the concentration (step S12). The ECU 11 calculates the ammonia slip ratio using the above equation (1) (step S14), and stores it in association with the temperature. This completes the control.

As shown in FIG. 4B, the ECU 11 calculates the amount of change ΔX in the ammonia slip ratio as the difference in the ammonia slip ratio at different temperatures (step S20). The ECU 11 determines whether or not the amount of change ΔX is equal to or greater than a predetermined value Xth (step S22). In the case of a negative determination (No), the ECU 11 determines that the SCR catalyst 44 is normal (step S24). In the case of affirmative determination (Yes), the ECU 11 determines that the SCR catalyst 44 has deteriorated (step S26).

For example, the ECU 11 acquires the ammonia slip ratio at the temperatures T1 and T2, and calculates the difference (change amount ΔX) between them. If the amount of change ΔX between temperatures is small as shown by the square in FIG. 3A, the ECU 11 determines that the SCR catalyst 44 is normal. If the amount of change ΔX is large as shown by the triangle in FIG. 3A, the ECU 11 determines that the SCR catalyst 44 has deteriorated.

According to the present embodiment, the ECU 11 determines whether or not the SCR catalyst 44 has deteriorated based on the ammonia concentrations on the upstream side and the downstream side of the SCR catalyst 44 at a plurality of temperatures. Specifically, the ECU 11 determines that the SCR catalyst 44 has deteriorated if the amount of change between the ratio of the ammonia concentration on the upstream side and the downstream side at low temperature (ammonia slip ratio) and the ammonia slip ratio at high temperature is large. To do. By using the change in the ammonia slip ratio with the temperature change, it is possible to detect the deterioration of the SCR catalyst 44 with high accuracy.

(Modification example)
FIG. 5 is a flowchart illustrating the control executed by the ECU 11, and shows the control for calculating the ammonia slip ratio in the modified example. As shown in FIG. 5, the ECU 11 performs a fuel cut and stops the fuel injection from the fuel injection valve 12 (step S9). The ECU 11 calculates the ammonia slip ratio in the fuel cut state. The control of the deterioration determination in FIG. 4B is also implemented in the modified example.

According to the modified example, since the ammonia slip ratio is calculated at the time of fuel cut, the influence of NOx, CO, HC and the like in the exhaust gas on the ammonia slip ratio can be suppressed. Therefore, the accuracy of deterioration determination is improved.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment, and various modifications and modifications are made within the scope of the gist of the present invention described in the claims. It can be changed.

10 engine 11 ECU
12 Fuel injection valve 14 Glow plug 16 Pump 18 Common rail 20 Intake passage 22 Intake manifold 24 Exhaust manifold 25 Intercooler 26 Exhaust passage 30 Throttle valve 32 EGR valve 34 EGR cooler 36 Turbocharger 36a Compressor 36b Turbine 40, 48 Oxidation catalyst 42 SCR catalyst 50 Add-on valve 51, 60 Temperature sensor 52 Tank 54 Dispersion plate 62 Gas sensor 100 Exhaust gas recirculation device

Claims (1)

A selective reduction catalyst provided in the exhaust passage of an internal combustion engine and
An acquisition unit for acquiring the concentration of ammonia in the exhaust gas on the upstream side and the downstream side of the selective reduction catalyst, and an acquisition unit.
A determination unit for determining whether or not the selective reduction catalyst has deteriorated is provided.
In the determination unit, when the temperature of the selective reduction catalyst is the first temperature, the concentration of ammonia on the upstream side and the concentration of ammonia on the downstream side, and the temperature of the selective reduction catalyst are the first. An exhaust purification device for an internal combustion engine that determines whether or not the selective reduction catalyst has deteriorated based on the concentration of ammonia on the upstream side and the concentration of ammonia on the downstream side when the second temperature is higher than the temperature.

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