JPH08260947A - Emission control device of diesel engine - Google Patents

Abstract

PURPOSE: To reduce the discharge of a non-reacted reducing agent by operating the amount of the reducing agent to be added by the engine load, the engine speed, and the specific gravity of the reducing agent to determine the appropriate amount of the reducing agent to be added to the catalyst. CONSTITUTION: The load, the engine speed, and the temperature of the catalyst are read by sensors 7, 8, 9 of the load, the engine speed, and the temperature, no reducing agent is added until the temperature of the catalyst rises to the value where the catalyst is activated, and a measurement is made whether or not the condition is in the range to add the reducing agent according to the load and the engine speed. If in the range to add the reducing agent, the specific gravity of the reducing agent is read by a specific gravity sensor 10, and the weight of the reducing agent to be added in read by a reducing agent added flow rate calculating means 11b from the reducing agent adding weight table according to the engine load and the engine speed, and the flow rate of the reducing agent to be added is calculated based on the read specific gravity. A pressurizing pump 6 is turned on by a reducing agent addition control means 11c, and the condition is returned to the original after the reducing agent of the obtained flow rate of the reducing agent is added. on the other hand, if a judgment is made that the condition is not in the range to add the reducing agent, the pressurizing pump 6 is turned off, and the condition is returned to the original after addition of the reducing agent is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device for a diesel engine, and more particularly to a technique for adding a reducing agent to a catalyst for removing nitrogen oxides in exhaust gas.

[0002]

Exhaust gas recirculation (EGR) is known as an effective means for reducing the concentration of nitrogen oxides (hereinafter referred to as NOx) contained in the exhaust gas of an engine.
As another means, a catalyst is provided in the exhaust passage of the engine,
A method of reducing NOx with this catalyst is also conceivable.

In this case, in order to efficiently reduce NOx, it is known that a diesel engine is provided with a device for adding light oil as a reducing agent to the exhaust passage on the upstream side of the catalyst (actual exploitation 5). -87218).

[0004]

By the way, a light oil (hereinafter, referred to as a reducing agent) as a reducing agent used in an exhaust emission control device of a diesel engine has a change in the property of the reducing agent or a temperature of the reducing agent. The specific gravity changes due to changes or the like. However, in the reducing agent addition device used in the conventional reducing agent addition device, for example, the pressure pump,
The control was performed based on the flow rate. Therefore, when the specific gravity of the reducing agent changes, the weight at a constant flow rate changes, so the NOx purification rate and the discharge amount of the unreacted reducing agent that depended on the weight of the reducing agent change, and the NOx purification rate changes. In addition, it is difficult to maintain the discharge amount of the unreacted reducing agent at a predetermined target value, and the discharge amount of the unreacted reducing agent may exceed the allowable value.

In view of the conventional problems as described above, the present invention optimizes the amount of reducing agent added to the catalyst to reduce the emission of unreacted reducing agent and to achieve the optimum NOx purification rate. The purpose is to maintain the fuel consumption and improve the deterioration of fuel consumption when using light oil as the reducing agent.

[0006]

Therefore, the invention according to claim 1 is, in an exhaust emission control device for removing nitrogen oxides contained in exhaust gas of an engine by a catalyst interposed in an exhaust passage, the catalyst of the catalyst. A reducing agent addition means for adding a reducing agent to the upstream side by flow control, an engine load detecting means for detecting an engine load, an engine speed detecting means for detecting an engine speed, and a reducing agent for detecting a specific gravity of the reducing agent. Specific gravity detecting means, reducing agent addition flow rate calculating means for calculating reducing agent addition flow rate based on the detected engine load, engine speed and reducing agent specific gravity, and reducing agent calculated by the reducing agent addition flow rate calculating means The exhaust gas purification device for a diesel engine is configured to include a reducing agent addition control unit that controls the reducing agent addition unit so that the addition flow rate is achieved.

[0007]

According to the present invention, the amount of the reducing agent added to the catalyst is optimized to reduce the emission of unreacted reducing agent, maintain an optimum NOx purification rate, and reduce the amount of the reducing agent used as a reducing agent. It is possible to improve the deterioration of fuel efficiency when using the above diesel oil.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows the overall system configuration of an embodiment of an exhaust emission control device for a diesel engine of the present invention. The exhaust pipe 2 of the diesel engine 1 is provided with a catalyst 3 for purifying NOx, and the exhaust pipe 2 upstream of the catalyst 3 is provided with a nozzle 4 for adding light oil as a reducing agent. It is set up. The nozzle 4 communicates with the light oil tank 5 via a light oil supply pipe 5a. The light oil supply pipe 5a is provided with a pressurizing pump 6 as a reducing agent adding means controlled by a flow rate.

On the other hand, the diesel engine 1 has a load sensor 7 as an engine load detecting means for detecting an engine load (for example, a control rack position of a fuel injection pump) and an engine speed detecting means for detecting an engine speed. And a temperature sensor 9 as catalyst temperature detecting means for detecting the catalyst inlet temperature as the catalyst temperature is provided on the upstream side of the catalyst 3. A temperature sensor that directly detects the temperature of the catalyst 3 may be provided. In addition, a specific gravity sensor 10 as a reducing agent specific gravity detecting means is provided on the light oil supply pipe 5a upstream of the pressurizing pump 6.
Is provided.

Outputs from the respective sensors are input to a control device 11 for controlling addition of a reducing agent, and the control device 11
Controls the pressurizing pump 6 based on the detected signals from the respective sensors. FIG. 2 shows a control block diagram of the reducing agent addition control according to the present invention. Control device 1
Reference numeral 1 denotes input means 11a for inputting signals from sensors as various detection means, reducing agent addition flow rate calculation means 11b for calculating addition flow rate of reducing agent based on signals from various sensors, and addition control of reducing agent. The reducing agent addition control means 11c for performing the above, and the output means 11d for outputting the signal of the reducing agent addition control means 11c.

A load sensor 7 and a rotation speed sensor 8 are also provided.
And the output of the specific gravity sensor 10 calculates the reducing agent addition flow rate calculating means 1 for calculating the reducing agent addition flow rate via the input means 11a.
The reducing agent addition flow rate obtained as a result of being input to 1b and being calculated by the reducing agent addition flow rate calculating means 11b is input to the reducing agent addition control means 11c that controls the addition of the reducing agent.
In addition to this, the reducing agent addition control means 11c outputs the outputs of the load sensor 7, the rotation speed sensor 8 and the temperature sensor 9,
It is input through the input means 11a. On the other hand, the output of the reducing agent addition control means 11c is input to the pressurizing pump 6 via the output means 11d.

The flowchart shown in FIG.
The content of the reducing agent addition control executed in 1 will be described. In step 1 (abbreviated as S1 in the figure, the same applies hereinafter),
The engine load Q, the engine speed N, and the catalyst temperature T are read from the load sensor 7, the rotation speed sensor 8, and the temperature sensor 9.

In step 2, the reducing agent is not added until the catalyst temperature T rises to a temperature at which the catalyst is activated, and it is judged by the engine speed N and the engine load Q whether or not it is in the reducing agent addition region. If it is the addition region, the process proceeds to step 3, and if it is not the addition region, the process proceeds to step 7. In step 3, the specific gravity γ of the light oil is measured by the specific gravity sensor 10.
Read.

In step 4, the reducing agent addition weight M is read from the reducing agent addition weight table in which the reducing agent addition weight is set based on the engine speed N and the engine load Q. Further, in step 5, the reducing agent addition flow rate S is calculated from the specific gravity γ and the reducing agent addition weight M obtained in steps 3 and 4. The processes of steps 4 to 5 described above correspond to the reducing agent addition flow rate calculating means according to claim 1 of the present invention.

In the processing in steps 4 to 5, the reducing agent addition flow rate was calculated by using the weight-based reducing agent addition weight table when determining the reducing agent addition flow rate. Alternatively, a flow rate-based reducing agent addition flow rate table may be used, and the reducing agent addition flow rate may be corrected by the specific gravity γ. In step 6, the pressurizing pump 6 is turned on to add the reducing agent at the calculated reducing agent addition flow rate, and then the process returns to step 1.

On the other hand, when it is determined in step 2 that the region is not the reducing agent addition region, in step 7, the pressure pump 6
After turning off and stopping the addition of the reducing agent, the process returns to step 1. By performing the control as described above, the reducing agent addition amount can be kept optimum even when the specific gravity of the reducing agent changes.
Further, FIG. 4 shows various exhaust characteristics showing the effect of the present invention, and FIG. 5 shows various exhaust characteristics in the prior art. The effects of the present invention and the problems of the prior art will be described in detail with reference to these drawings.

In the prior art, the amount of reducing agent added was controlled by the flow rate. Therefore, a phenomenon occurs in which the added weight of the reducing agent increases and decreases at a constant flow rate as the specific gravity of the reducing agent changes, and the NOx purification rate and the amount of unreacted reducing agent discharged increase and decrease under the conditions of a constant flow rate (Fig. 5). That is, at a predetermined appropriate control flow rate, a certain range (change amount) occurs in the NOx purification rate and the unreacted reducing agent discharge amount, and the predetermined target values of the NOx purification rate and the unreacted reducing agent discharge amount are maintained. However, there is a problem in that the amount of unreacted reducing agent discharged may exceed the allowable value.

Therefore, in the present invention, the addition amount of the reducing agent is controlled by weight, the flow rate is calculated from the weight using the specific gravity of the reducing agent, and then the addition amount of the reducing agent is controlled by the flow rate. Therefore, the flow rate increases and decreases with the change in the specific gravity of the reducing agent (see FIG. 4), but since the weight is constant, it is easy to maintain the NOx purification rate and the amount of unreacted reducing agent discharged at a predetermined constant value. . The effect can be obtained by correcting the flow rate by the specific gravity instead of limiting the addition amount of the reducing agent by weight.

[0019]

As described above, according to the invention of claim 1, the addition amount of the reducing agent is calculated by the engine load, the engine speed and the reducing agent specific gravity. The amount of reducing agent added is optimized, the emission of unreacted reducing agent is reduced, the optimum NOx purification rate is maintained, and the deterioration of fuel efficiency when using light oil as the reducing agent is improved. it can.

[Brief description of drawings]

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

FIG. 2 is a control block diagram of the same as above.

FIG. 3 is a flowchart showing the control contents of the above.

[Fig. 4] Various exhaust characteristic diagrams showing the same effect.

FIG. 5: Various exhaust characteristic diagrams in the prior art

[Explanation of symbols]

 3 Catalyst 6 Pressurizing Pump 7 Load Sensor 8 Rotation Speed Sensor 10 Specific Gravity Sensor 11 Controller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisashi Akagawa 1-chome, Ichome, Ageo City, Saitama Prefecture Nissan Diesel Industry Co., Ltd.

Claims (1)

[Claims] 1. An exhaust gas purification device for removing nitrogen oxides contained in exhaust gas of an engine with a catalyst interposed in an exhaust passage, and a reducing agent adding means for adding a reducing agent to a upstream side of the catalyst by controlling a flow rate. An engine load detecting means for detecting an engine load, an engine speed detecting means for detecting an engine speed, a reducing agent specific gravity detecting means for detecting a specific gravity of a reducing agent, an engine load and an engine speed detected. A reducing agent addition flow rate calculation means for calculating the reducing agent addition flow rate based on the reducing agent specific gravity, and a reduction for controlling the reducing agent addition flow rate so that the reducing agent addition flow rate is calculated by the reducing agent addition flow rate calculation means. An exhaust emission control device for a diesel engine, comprising: a chemical agent addition control means.