JP2593125Y2 - Diesel engine exhaust purification system - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an exhaust gas purification device for a diesel engine.

[0002]

2. Description of the Related Art An apparatus for purifying nitrogen oxides discharged from a diesel engine is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-149.
No. 317 and JP-A-63-100919, a reduction catalyst is provided in the middle of the exhaust passage.
In some cases, a reducing agent is added upstream of the reduction catalyst.

Conventionally, as shown in FIG. 6, for example, as shown in FIG. 6, a reduction catalyst 3 is interposed in an exhaust passage 2 of a diesel engine 1 and a part of light oil stored in a fuel tank 4 is removed. Some include an addition device 5 that adds a reducing agent upstream of the reduction catalyst 3 in the exhaust passage 2.
The reduction catalyst 3 is designed to decompose nitrogen oxides in the exhaust gas into nitrogen and oxygen by contacting the exhaust gas containing the nitrogen oxides in an oxidizing atmosphere or in the presence of a hydrocarbon (Japanese Unexamined Patent Publication (Kokai) No. Heisei 9 (1994) -207). 1-11-1809 reference).

[0004]

However, in such a conventional exhaust gas purifying apparatus for a diesel engine, when a reducing agent is supplied during a warm-up period in which the temperature of the exhaust gas rises to a temperature at which the reduction catalyst is activated, the following problems occur. As shown in FIG. 7, there is a problem that the reducing agent is discharged without reacting.

The present invention focuses on the above-mentioned problems, and has as its object to suppress the discharge of the reducing agent without being reacted during the warm-up of the reduction catalyst.

[0006]

According to the present invention, as shown in FIG. 1, an exhaust passage 2 of a diesel engine 1 is provided .
A reduction catalyst 3 interposed in the middle, and addition device 5 for adding a reducing agent to the upstream side of the reduction catalyst 3, and sensors 7 and 8 for detecting the inlet temperature T ₂ and the outlet temperature T ₃ of the reduction catalyst 3 , Reduction
And determining means 11 a first operating condition the inlet temperature T ₂ of the catalyst 3 is increased beyond a predetermined value _{T 1,} the difference _T 3 -T ₂ of the outlet temperature _{T 3} and the inlet temperature _{T 2} of the reduction catalyst 3 Is a predetermined value T ₀
It comprises means 12 for determining the second operating condition as described above, and reducing agent addition control means 13 for starting addition of the reducing agent when both the first and second operating conditions are satisfied.

According to a second aspect of the present invention, as shown in FIG. 4, a reduction catalyst 3 provided in the middle of an exhaust passage 2 of a diesel engine 1 and an additive for adding a reducing agent upstream of the reduction catalyst 3 are provided. a device 5, the sensors 7 and 8 for detecting the inlet temperature T ₂ and the outlet temperature T ₃ of the reduction catalyst 3, a means 20 for detecting the engine speed and the engine load, from the detected value of the engine speed and the engine load reduction Means 21 for determining a third operating condition for starting the addition of the agent, and determining a second operating condition in which a difference T ₃ −T ₂ between the outlet temperature T ₃ and the inlet temperature T ₂ becomes equal to or more than a predetermined value T _0. And a reducing agent addition control unit 22 that starts adding the reducing agent when both the second and third operating conditions are satisfied.

[0008]

[Action] When the inlet temperature T ₂ of the reduction catalyst 3 rises above a predetermined temperature T ₁ of the given catalyst activity is obtained, the reduction catalyst 3
The temperature of the outlet temperature T ₃ of the reduction catalyst 3 by the reaction carried out through
There gradually becomes higher than the inlet temperature T _2. Therefore, the inlet temperature T ₂ is increased beyond a predetermined temperature T _1, and the temperature difference T ₃ -
When T ₂ is equal to or greater than a predetermined value T _0, the catalyst can be determined to be in the fully activated temperature state.

Therefore, according to the first aspect of the present invention, when the first and second operating conditions are both satisfied, the reducing agent is added to reduce the catalyst at a sufficiently activated temperature state. As a result, the reducing agent is prevented from being discharged to the outside through the exhaust passage 2 without being reacted.

In the invention according to the second aspect, the third operating condition for starting the addition of the reducing agent is determined from the detected value of the engine speed and the engine load, so that the inlet temperature T is determined.
₂ is determined to be a driving condition rises above the predetermined temperature T ₁ of the given catalyst activity.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, a diesel engine 1
The reduction catalyst 3 is interposed in the middle of the exhaust passage 2. The reduction catalyst 3 has a structure in which a base material such as alumina, silica, zeolite and the like and a catalyst material composed of a metal such as copper are supported on a honeycomb-shaped carrier, and in a oxidizing atmosphere or in the presence of a hydrocarbon, a nitrogen oxide is used. By contacting an exhaust gas containing (NOx), nitrogen oxides in the exhaust gas are decomposed into nitrogen and oxygen.

As a means for adding the reducing agent upstream of the reduction catalyst 3, an addition device 5 for adding a part of the light oil stored in the fuel tank 4 to the exhaust passage 2 upstream of the reduction catalyst 3 is provided.

As means for detecting the inlet temperature and the outlet temperature of the reduction catalyst 3, a temperature sensor 7 disposed immediately upstream of the reduction catalyst 3 and a temperature sensor 8 disposed immediately downstream of the reduction catalyst 3 are provided. Is provided.

In the figure, reference numeral 6 denotes a control device for controlling the amount of the reducing agent added from the adding device 5. The control device 6 controls the reduction catalyst 3
Inlet temperature T ₂ becomes ₁ or more predetermined value T, and the reduction catalyst 3
The difference T ₃ -T ₂ is a predetermined value T between the outlet temperature T ₃ and the inlet temperature T ₂ of
When it becomes ₀ or more, the addition device 5 is instructed to start adding the reducing agent.

FIG. 2 is a flowchart showing a control program executed by the control device 6 for adding a reducing agent, which is performed at regular intervals.

To explain this, first, in step 1
Then, the detected temperatures T ₂ and T ₃ of the temperature sensors 7 and 8 are read, and in step 2 it is determined whether or not the catalyst inlet temperature T ₂ is equal to or higher than a predetermined value T ₁ . Catalyst inlet temperature T ₂ stops addition of the reducing agent proceeds to step 5 is lower than a predetermined value T _1.

[0018] proceeds when the catalyst inlet temperature T ₂ is higher than the predetermined value T ₁ in Step 3, the difference T ₃ -T ₂ is a predetermined value T ₀ or more and outlet temperature T ₃ and the inlet temperature T ₂ of the reduction catalyst 3 It is determined whether or not the temperature difference T ₃ −T ₂ is equal to or more than the predetermined value T _0, and proceeds to step 4 to add the reducing agent. If the temperature difference T ₃ −T ₂ is lower than the predetermined value T ₀ , Proceeding to step 5, the addition of the reducing agent is stopped.

Next, the operation will be described.

As shown in FIG. 3, the operating conditions of the inlet temperature T ₂ is equal to or less than the predetermined value T ₁ reduction catalyst 3, because the catalytic activity is little, the inlet temperature T ₂ and the outlet temperature T ₃ of the reduction catalyst 3
Rise at substantially the same temperature in response to the rise in the temperature of the exhaust gas. When the inlet temperature T ₂ of the reduction catalyst 3 is increased beyond a predetermined value T ₁ which predetermined catalytic activity is obtained, the outlet temperature T ₃ of the reduction catalyst 3 by reactions carried out through the reduction catalyst 3 than the inlet temperature T ₂ It gets higher gradually. Therefore, the temperature difference T ₃ −T
_{When 2} becomes equal to or more than the predetermined value T ₀ , it can be determined that the catalyst is in a sufficiently activated temperature state.

[0021] Thus, the inlet temperature T ₂ of the reduction catalyst 3 rises beyond a predetermined value T _1, and from the temperature difference T ₃ -T ₂ is equal to or greater than a predetermined value T _0, starts the addition of the reducing agent As a result, the reducing agent is added in a temperature state in which the catalyst is sufficiently activated, and the total hydrocarbon (TH
The discharge amount of C) can be promptly reduced, and the discharge of the reducing agent to the outside through the exhaust passage 2 without reacting can be suppressed.

Next, in another embodiment shown in FIG. 4, means 20 for detecting the engine speed N and the engine load Q, and the addition of the reducing agent is started from the detected values of the engine speed N and the engine load Q. Means 21 for determining a third operating condition to be performed;
Outlet temperature T ₃ and the difference T ₃ -T ₂ is a predetermined value T ₀ of the inlet temperature T ₂
It comprises means 22 for determining the second operating condition as described above, and reducing agent addition control means 23 for starting addition of the reducing agent when both the second and third operating conditions are satisfied.

FIG. 5 is a flowchart showing a control program for adding a reducing agent, which is executed in the control device 6, and is executed at regular intervals.

To explain this, first, in step 1
In step 1, the detected temperatures T ₂ and T ₃ of the temperature sensors 7 and 8 are read, and the engine speed N and the engine load Q are read.
In step 12, a third operating condition for starting the addition of the reducing agent is determined. The control performed in step 12 corresponds to the control performed in step 2 of FIG.
₂ it is determined that an operating condition rises above the predetermined temperature T ₁ of the given catalyst activity.

If it is determined that the third operating condition is satisfied, the process proceeds to step 13, where it is determined whether the difference T ₃ -T ₂ between the outlet temperature T ₃ and the inlet temperature T ₂ of the reduction catalyst 3 is equal to or greater than a predetermined value T _0. Judge,
If the temperature difference T ₃ −T ₂ is equal to or greater than the predetermined value T ₀ , step 14
Then, the process proceeds to step 15 to add the reducing agent. If the temperature difference T ₃ −T ₂ is lower than the predetermined value T ₀ , the process proceeds to step 15 to stop the addition of the reducing agent.

[0026]

As described above, according to the first aspect of the present invention, in the exhaust gas purifying apparatus for a diesel engine, a reducing catalyst interposed in an exhaust passage and a reducing agent are added upstream of the reducing catalyst. Means, means for detecting an inlet temperature and an outlet temperature of the reduction catalyst, means for determining a first operating condition in which the inlet temperature of the reduction catalyst rises above a predetermined value, and an outlet temperature and an inlet temperature of the reduction catalyst. And a reducing agent addition control unit that starts adding a reducing agent when both of the first and second operating conditions are satisfied. By adding the reducing agent after the catalyst has been sufficiently activated, it is possible to suppress the time required for warming up the catalyst and the discharge of the unreacted reducing agent due to a response delay.

According to a second aspect of the present invention, there is provided a reduction catalyst disposed in the middle of an exhaust passage, a means for adding a reducing agent upstream of the reduction catalyst, and a means for detecting an inlet temperature and an outlet temperature of the reduction catalyst. Means for detecting the engine speed and the engine load, means for determining a third operating condition to start adding the reducing agent from the detected value of the engine speed and the engine load,
Means for determining a second operating condition in which the difference between the outlet temperature and the inlet temperature of the reduction catalyst is equal to or greater than a predetermined value, and starting addition of the reducing agent when both the second and third operating conditions are satisfied. Since the catalyst is provided with the reducing agent addition control means, the catalyst is sufficiently activated before the reducing agent is added, so that it takes time for the catalyst to warm up and the unreacted reducing agent due to a response delay. It can be suppressed that it is discharged as it is.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing control contents.

FIG. 3 is a diagram showing the same operation.

FIG. 4 is a diagram showing another embodiment.

FIG. 5 is a flowchart showing control contents.

FIG. 6 is a configuration diagram showing a conventional example.

FIG. 7 is a diagram showing the same operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Exhaust passage 3 Reduction catalyst 5 Addition device (addition means) 6 Control device 11 First operation condition determination means 12 Second operation condition determination means 13 Reducing agent addition control means 21 Third operation condition determination means 22 Reducing agent addition control means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-231615 (JP, A) JP-A-63-302120 (JP, A) JP-A-4-79920 (JP, U) JP-A-2-231 101010 (JP, U) Japanese Utility Model 63-146116 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F01N 3/08 F01N 3/24

Claims (1)

(57) [Scope of request for utility model registration] A reduction catalyst interposed in the exhaust passage;
Means for adding a reducing agent upstream of the reduction catalyst, means for detecting the inlet and outlet temperatures of the reduction catalyst,
Means for determining a first operating condition in which the mouth temperature rises above a predetermined value; means for determining a second operating condition in which the difference between the outlet temperature and the inlet temperature of the reduction catalyst is equal to or more than a predetermined value; An exhaust gas purification device for a diesel engine, comprising: a reducing agent addition control unit that starts adding a reducing agent when both the first and second operating conditions are satisfied.