JP2589592Y2 - 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. 4, for example, as shown in FIG. 4, 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 rises to a temperature at which the catalyst is activated, FIG. As described above, 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, there is provided a reduction catalyst provided in the middle of an exhaust passage, a means for adding a reducing agent upstream of the reduction catalyst, a means for detecting a temperature of the reduction catalyst,
Means for determining at the start of addition of the detection from the temperature and the temperature of the reduction catalyst becomes equal to or higher than a predetermined value <br/> reducing agent, a means for detecting the engine speed and the engine load, the detection of the engine speed and engine load Means for calculating the addition amount of the reducing agent from the value, and adding the reducing agent by multiplying the calculated amount by a constant α of 1 or less.
The means for determining the amount and the amount of reducing agent added to this determined amount
Control means, and return when the temperature of the reduction catalyst is equal to or higher than a predetermined value.
The constant α is initially set according to the elapsed time from the start of the addition of the base agent.
Means for gradually increasing the period value to 1 .

[0007]

According to the first aspect of the present invention, the reduction catalyst is used.
The temperature is higher than a predetermined value (the temperature at which catalytic activity can be obtained)
It is determined that the addition of the reducing agent has started. Amount of reducing agent added
Is calculated from the detected value of the engine speed and the engine load.
Is calculated by multiplying the calculated amount by a constant α.
The constant α depends on the elapsed time from the start of the addition of the reducing agent.
Then, it gradually increases from the initial value to 1. As a result, the addition of a reducing agent
The amount gradually increases to the calculated value according to the degree of activation of the catalyst
Control so that the temperature of the reduction catalyst
However, the activation of the catalyst is not yet enough and some of the reducing agent
It is possible to suppress the discharge without being reacted
You .

[0008]

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 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 temperature of the reduction catalyst 3,
A temperature sensor 7 for detecting the temperature of exhaust gas is disposed immediately upstream of the reduction catalyst 3. Note that a sensor that directly detects the temperature of the reduction catalyst 3 may be provided as a unit that detects the temperature of the reduction catalyst 3.

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 includes a temperature sensor 7
From the detected value of, the inlet temperature of the reduction catalyst 3 starts activation of the catalyst.
Determining at the start of addition of the reducing agent and circle a predetermined value above T ₁
(Addition start determination means 11) and the engine speed
And the detection signal from the engine load detection means 12
Means for calculating the addition amount M of the reducing agent (addition amount calculation means 1)
3) and a method of controlling a command (control signal) to the adding device 5
(Addition amount control means 14). Addition amount control
The stage 14 is not shown, but the calculated amount M of the reducing agent is set to a value of 1 or less.
Means for determining the addition amount (M × α) of the reducing agent by multiplying by a number α
And outputs a control signal corresponding to the determined amount (M × α).
Means for reducing the reducing agent when the temperature of the reducing catalyst is equal to or higher than a predetermined value.
Initial value of constant α according to the elapsed time from the start of
means for gradually increasing from α ₁ to 1.

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, step 1
Then, the engine speed N and the engine load Q are read, and in step 2, the addition amount M of the reducing agent according to these operating conditions is searched based on a predetermined map.

Subsequently, in step 3, the detected temperature T of the temperature sensor 7 is read, and in step 4, the catalyst inlet temperature T is set to a predetermined value T.
Determine if it is ₁ or more. When the catalyst inlet temperature T reaches a predetermined value T ₁
If it is lower, the process proceeds to step 13, and the addition of the reducing agent is stopped.

If the catalyst inlet temperature T is equal to or higher than the predetermined value T ₁ , the routine proceeds to step 5 where the elapsed time t after the catalyst inlet temperature T exceeds the predetermined value T ₁ is measured.

If it is determined in step 6 that the elapsed time t is shorter than the predetermined time t ₁ , the flow advances to step 7 to calculate the addition amount as M × α ₁ (α ₁ <1).

If it is determined in step 8 that the elapsed time t is equal to or longer than the predetermined time t ₁ and shorter than the predetermined time t ₂ , the process proceeds to step 9 and the added amount is set to M × α ₂ (1> α ₂ > α ₁ ). calculate.

Similarly, the program proceeds to steps 10, 11, and 12, and as the elapsed time t increases, the addition amount of the reducing agent is gradually increased to a predetermined addition amount M.

Next, the operation will be described.

As shown in FIG. 3, as the time t elapses after the inlet temperature T of the reduction catalyst 3 exceeds a predetermined value T _{1 at} which a predetermined catalyst activity can be obtained, the activation of the catalyst is started. move on.

Therefore, after the inlet temperature T of the reduction catalyst 3 rises above the predetermined temperature T ₁ , the amount of addition is increased stepwise according to the elapsed time, whereby the catalyst is reduced according to the activated state. As a result, the reduction efficiency of nitrogen oxides can be promptly increased, and the emission amount of total hydrocarbons (THC) can be rapidly reduced. It can be suppressed from being discharged outside.

[0023] Incidentally, as means for determining the operating condition detecting temperature of the reduction catalyst rises above a predetermined value, instead of determining the detected temperature T of the temperature sensor 7 whether a predetermined value above T _1, the engine speed The start of the addition of the reducing agent may be determined based on the detected values of N and the engine load Q.

[0024]

As described above, according to the present invention, the reduction catalyst interposed in the exhaust passage of the diesel engine, the means for adding the reducing agent upstream of the reduction catalyst, and the detection of the temperature of the reduction catalyst means for, touch reduced from this detected temperature
Means for determining when to start adding the reducing agent when the temperature of the medium becomes equal to or higher than a predetermined value ; means for detecting the engine speed and the engine load; and calculating the amount of the reducing agent added from the detected values of the engine speed and the engine load. Means and the calculated amount is 1 or less
Means for determining the amount of reducing agent to be added by multiplying by the constant α of
Means for controlling the addition amount of the reducing agent to the determined amount, and the reduction catalyst
From the time when the addition of the reducing agent starts when the temperature of the
Gradually increases the constant α from the initial value to 1 according to the elapsed time of
Means , the reducing agent is added in accordance with the degree of activation of the catalyst, so that the warming-up of the catalyst takes time and the reducing agent is discharged unreacted due to a response delay. Can be suppressed.

[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 configuration diagram showing a conventional example.

FIG. 5 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 Addition start determination means 12 Engine speed and load detection means 13 Reducing agent addition amount calculation means 14 Reducing agent addition control means

Claims (1)

(57) [Scope of request for utility model registration] A reduction catalyst interposed in the exhaust passage;
Means for adding a reducing agent to the upstream side of the reduction catalyst, and means for detecting the temperature of the reduction catalyst, the reduction catalyst from the detected temperature
Means for determining when to start adding the reducing agent when the temperature is equal to or higher than a predetermined value ; means for detecting the engine speed and the engine load; and means for calculating the amount of the reducing agent added from the detected values of the engine speed and the engine load. And the calculated amount is less than 1
A means for determining the amount of reducing agent to be added by multiplying by a number α;
Means for controlling the amount of the reducing agent added for the determination, and the temperature of the reduction catalyst
When the degree is equal to or higher than the predetermined value,
Means for gradually increasing the constant α from the initial value to 1 according to the elapsed time
And an exhaust purification device for a diesel engine.