WO2006048977A1

WO2006048977A1 - Exhaust gas purifying device

Info

Publication number: WO2006048977A1
Application number: PCT/JP2005/017128
Authority: WO
Inventors: Nobuhiko Masaki; Tomoyasu Harada
Original assignee: Nissan Diesel Motor Co., Ltd.
Priority date: 2004-11-04
Filing date: 2005-09-16
Publication date: 2006-05-11
Also published as: JP4290110B2; JP2006132384A

Abstract

While an engine runs, the pressure in upper space of a reducing agent container having a sealed structure is increased up to a predetermined pressure p1 by a pressure regulator that is capable of arbitrarily regulating the pressure in closed space. On the other hand, while the engine is stopped, the pressure in the upper space of the reducing agent container is reduced by the pressure regulator to a predetermined pressure p2 that is at least equal to or below atmospheric pressure. While the engine runs, a liquid reducing agent is pressed by air present in the upper space of the reducing agent container and sent by pressure to a reducing agent supply system. Further, while the engine is stopped, the liquid reducing agent in the reducing agent supply system is reliably recovered to the reducing agent container. As a result, even if slight clogging occurs in the reducing agent supply system, the clogging is forcibly eliminated by the reducing agent sent by pressure, and only a solvent evaporates from the liquid reducing agent during the stop of the engine to suppress the solute of the agent from separating.

Description

Specification

Exhaust purification equipment

Technical field

TECHNICAL FIELD [0001] The present invention relates to a technique that makes it difficult for clogging to occur in a reducing agent supply system in an exhaust purification device that reduces and purifies nitrogen oxides (NOx) in exhaust using a liquid reducing agent.

Background art

As a catalyst purification system for removing NOx contained in engine exhaust, an exhaust purification device disclosed in Japanese Patent Application Laid-Open No. 2000-27627 (Patent Document 1) has been proposed. Such an exhaust purification device performs catalytic reduction of NOx and liquid reducing agent in the exhaust gas by injecting and supplying a liquid reducing agent according to the engine operating state upstream of the reduction catalyst disposed in the engine exhaust system. It reacts to purify NOx into harmless components. Here, as the liquid reducing agent, an aqueous urea solution that generates ammonia by hydrolysis using exhaust heat and water vapor in the exhaust is used.

Patent Document 1: JP 2000-27627 A

Disclosure of the invention

Problems to be solved by the invention

[0003] However, in the conventional exhaust purification device, as a result of heating the reducing agent supply system by exhaust heat, when the temperature of the liquid reducing agent becomes equal to or higher than the boiling point of the solvent, only the solvent evaporates and a solute precipitates, There is a risk of clogging in the agent supply system. When clogging occurs in the reducing agent supply system, the liquid reducing agent is not supplied to the reducing catalyst, so that the reduction reaction of NOx in the reducing catalyst does not proceed and the required exhaust purification performance cannot be exhibited.

[0004] Therefore, in view of the conventional problems as described above, the present invention supplies the liquid reducing agent by pressurizing the upper space of the closed reducing agent container for storing the liquid reducing agent to a predetermined pressure or higher. It is an object of the present invention to provide an exhaust purification device that assists in reducing the clogging of the reducing agent supply system.

Means for solving the problem

[0005] Therefore, the exhaust emission control device according to the first embodiment of the present invention stores a liquid reducing agent. A reducing agent container having a sealed structure; a reduction catalyst disposed in an engine exhaust passage for reducing and purifying nitrogen oxides in the exhaust gas using a liquid reducing agent supplied from the reducing agent container; and an upper portion of the reducing agent container A pressure regulator capable of adjusting the space to an arbitrary pressure, an operation state detection device that detects the engine operation state, and a control that controls the pressure regulator by inputting the engine operation state detected by the operation state detection device. And the control unit determines whether or not the engine is operating based on the engine operating state, and when determining that the engine is operating, the reducing agent container The pressure regulator is controlled so that the upper space of the chamber becomes equal to or higher than a predetermined pressure.

[0006] In addition, the exhaust gas purification apparatus according to the second embodiment of the present invention is provided in a sealed reducing agent container for storing a liquid reducing agent and an engine exhaust passage, and is supplied from the reducing agent container. A reduction catalyst for reducing and purifying nitrogen oxides in the exhaust gas using a liquid reducing agent, an air reservoir for storing air, a pressure reducing valve for reducing the air stored in the air reservoir to a predetermined pressure, and the pressure reducing valve An air supply control valve that controls the supply of the decompressed air into the reducing agent container, an operation state detection device that detects the engine operation state, and an engine operation state detected by the operation state detection device are input. A control unit that controls opening and closing of the air supply control valve, and the control unit determines whether or not the engine is operating based on the engine operating state. The air supply control valve is opened when it is determined that the engine is operating. The invention's effect

[0007] According to the exhaust emission control device of the present invention, when the engine is operating, the upper space of the reducing agent container is pressurized to at least a predetermined pressure, so that the liquid reduction stored in the reducing agent container is performed. The agent is pressed by the air present in the upper space and is pumped to the reducing agent supply system. For this reason, even if a slight clogging occurs in the reducing agent supply system, it is forcibly discharged by the liquid reducing agent that is pumped, so that the clogging in the reducing agent supply system can be made difficult to occur. In addition, since the liquid reducing agent is pumped to the reducing agent supply system, the degree of freedom in equipment layout can be improved.

Brief Description of Drawings

FIG. 1 is an overall configuration diagram of an exhaust emission control device to which the present invention is applied. 2] FIG. 2 is an enlarged view of a main part of the exhaust gas purification apparatus according to the first embodiment.

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

[Fig. 4] Fig. 4 is an enlarged view of a main part of an exhaust purification apparatus according to a second embodiment.

FIG. 5 is a flowchart showing the control content of the above.

Explanation of symbols

10 engine

14 Exhaust pipe

20 NOx reduction catalyst

24 Reducing agent container

32 Reducing agent added ECU

34 Engine ECU

38 Pressure regulator

40 Pressure sensor

42 Air release control valve

44 Air supply control valve

46 Airizano

48 Pressure reducing valve

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Figure 1 shows the overall configuration of an exhaust purification system that uses urea aqueous solution as a liquid reducing agent to purify NOx in engine exhaust by a catalytic reduction reaction.

An exhaust pipe 14 connected to the exhaust manifold 12 of the engine 10 includes a nitrogen oxidation catalyst 16 that oxidizes monoxide-nitrogen (NO) to diacid-nitrogen (NO) along the exhaust flow direction.

2

An injection nozzle 18 for supplying an aqueous urea solution, an NOx reduction catalyst 20 that reduces and purifies NOx with ammonia obtained by hydrolyzing the aqueous urea solution, and an ammonia that passes through the NOx reduction catalyst 20 A soot ammonia acid catalyst 22 is provided. The aqueous urea solution stored in the reducing agent container 24 having a sealed structure is supplied to the reducing agent addition device 28 through a supply pipe 26 having a suction opening at the bottom thereof, while the reducing agent-added calorie is supplied. Excess urea aqueous solution that does not contribute to the injection in the apparatus 28 is returned to the upper space of the reducing agent container 24 through the return pipe 30.

[0011] The reducing agent addition device 28 is controlled by a reducing agent addition control unit (hereinafter referred to as "reducing agent addition ECU") 32 having a built-in computer, and mixes an aqueous urea solution according to the engine operating state with air. While being supplied to the injection nozzle 18. Here, the engine operation state including the engine operation information is read from an engine control unit (hereinafter referred to as “engine ECU”!) 34 connected via CAN (Controller Area Network). In the present embodiment, the engine ECU 34 corresponds to the driving state detection device, but the driving state detection device may be configured by various sensors (the same applies hereinafter).

Note that reference numeral 36 in the figure denotes a concentration sensor that detects the concentration of the urea aqueous solution stored in the reducing agent container 24 that ensures the function as an exhaust gas purification device.

The urea aqueous solution injected and supplied from the injection nozzle 18 through the powerful exhaust purifier is hydrolyzed by the exhaust heat and the water vapor in the exhaust, and converted into ammonia. It is known that the converted ammonia reacts with NOx in the exhaust gas in the NOx reduction catalyst 20 and is purified into water and harmless gas. At this time, NO is reduced by NOx reduction catalyst 20 to improve NO X purification efficiency.

It is oxidized to 2, and the ratio of NO to NO in the exhaust is improved to be suitable for catalytic reduction reaction. NOx return

2

The ammonia that has passed through the original catalyst 20 is oxidized by the ammonia acid catalyst 22 disposed downstream of the exhaust gas, so that it is possible to prevent ammonia that emits a strange odor from being released into the atmosphere as it is.

On the other hand, as shown in FIG. 2, the reducing agent container 24 includes a pressure regulator 38 that can adjust the upper space to an arbitrary pressure, and a pressure detection device that detects the pressure p of the upper space. A pressure sensor 40 is attached respectively. The reducing agent addition ECU 32 controls the pressure regulator 38 according to signals from the engine ECU 34 and the pressure sensor 40 by executing a control program stored in the ROM (Read Only Memory).

FIG. 3 shows specific contents of a control program that is repeatedly executed at predetermined time intervals in the reducing agent addition ECU 32.

In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the pressure sensor 40 starts the reducing agent. Read the pressure p in the upper space of container 24.

In step 2, it is determined whether or not the engine 10 is operating based on the engine operation information read from the engine ECU 34 via CAN. Then, if the engine 10 is operating, the process proceeds to step 3 (Yes), while if the engine 10 is stopped! / Speaks, the process proceeds to step 5 (No).

[0015] In step 3, whether the pressure p in the upper space of the reducing agent container 24 is less than a first predetermined value p.

1

Determine whether or not. Here, the first predetermined value p is a value for pressurizing the upper space of the reducing agent container 24.

1

This is a threshold value for determining whether or not the pressure is sufficient, and is set to a value that allows the urea aqueous solution to be pumped to the supply pipe 26. If the pressure p is less than the first predetermined value p, proceed to step 4.

1

(Yes), pressurization control of the pressure regulator 38 is performed. On the other hand, if the pressure p is greater than or equal to the first predetermined value p

1

Since no pressurization is required, the process is terminated (No).

[0016] In step 5, whether the pressure p in the upper space of the reducing agent container 24 is greater than a second predetermined value p.

2

Determine whether or not. Here, the second predetermined value p is a value for depressurizing the upper space of the reducing agent container 24.

2

This is a threshold value for determining whether or not there is a leakage, and is a value that allows the urea aqueous solution to be sucked from the reducing agent supply system including the reducing agent addition device 28, specifically, a negative pressure below atmospheric pressure. Set to pressure. Then, if the pressure p is larger than the second predetermined value p, proceed to Step 6 (Yes),

2

The pressure regulator 38 is pressure-reduced. On the other hand, if the pressure p is less than or equal to the second predetermined value p, the pressure is reduced.

2

Since it is unnecessary, the process is terminated (No).

[0017] According to the exhaust gas purification device, when the engine 10 is operating, the upper space of the reducing agent container 24 is pressurized to a pressure equal to or higher than the first predetermined value p by the pressure regulator 38. Is done. This

1

Therefore, the urea aqueous solution stored in the reducing agent container 24 is pressed by the air existing in the upper space and is pumped to the supply pipe 26. Therefore, even if a slight clogging occurs in the reducing agent supply system, it is forcibly discharged from the injection nozzle 18 by the urea aqueous solution that is pumped, so that the reducing agent supply system is hardly clogged. In addition, since the urea aqueous solution is pumped to the reducing agent supply system, the reducing agent addition device 28 can be positioned above the reducing agent container 24, and the degree of freedom in equipment layout can be improved.

On the other hand, when the engine 10 is stopped, the upper space of the reducing agent container 24 is reduced to a negative pressure equal to or less than the second predetermined value p by the pressure regulator 38. For this reason, the reducing agent supply system The existing urea aqueous solution is sucked into the reducing agent container 24 by a negative pressure, and can be reliably collected in the reducing agent container 24 in a short time. Therefore, when the engine 10 is stopped, the solute (urea) is hardly precipitated from the urea aqueous solution present in the reducing agent supply system, and clogging is less likely to occur in the reducing agent supply system.

[0019] In order to pressurize and depressurize the upper space of the reducing agent container 24, the following configuration may be employed. That is, as shown in FIG. 4, the reducing agent container 24 is controlled to control the supply of air that has been regulated to a predetermined pressure and the atmospheric release control valve 42 that is an electromagnetic on-off valve that arbitrarily opens the upper space to the atmosphere. An air supply control valve 44 composed of an electromagnetic on-off valve is attached. The air stored in the air reservoir 46 is supplied to the air supply control valve 44 after being reduced to a predetermined pressure by the pressure reducing valve 48. Then, the reducing agent addition ECU 32 executes the control program stored in the ROM, thereby controlling the opening / closing of the air release control valve 42 and the air supply control valve 44 according to the signal from the engine ECU 34.

FIG. 5 shows specific contents of a control program that is repeatedly executed at predetermined time intervals in the reducing agent addition ECU 32.

In step 11, it is determined whether or not the engine 10 is operating based on the engine operation information read from the engine ECU 34 via CAN. If the engine 10 is operating, the process proceeds to step 12 (Yes), while if the engine 10 is stopped, the process proceeds to step 13 (No).

[0021] In step 12, the air release control valve 42 is closed while the air supply control valve 44 is opened.

In step 13, the air release control valve 42 is opened while the air supply control valve 44 is closed.

According to a powerful exhaust purification system, when the engine 10 is in operation, the upper space of the reducing agent container 24 can be secured by the air release control valve 42 being closed. In addition, the air supply control valve 44 is opened, so that the air reduced to a predetermined pressure is supplied from the air reservoir 46. For this reason, the urea aqueous solution stored in the reducing agent container 24 is pressed by the air supplied to the upper space and is pumped to the supply pipe 26. At this time, when the pressure force in the upper space of the reducing agent container 24 becomes equal to the pressure of the air reduced by the pressure reducing valve 48, Since the air supply to the reducing agent container 24 is stopped, the air stored in the air reservoir 46 is not wasted even if the air supply control valve 44 is kept open.

On the other hand, when the engine 10 is stopped, the upper space of the reducing agent container 24 is depressurized to atmospheric pressure by opening the air release control valve 42 and the air supply control valve 44 is closed. The air supply from Air Lisano 6 is shut off by valve. For this reason, it is possible to recover the aqueous urea solution present in the reducing agent supply system to the reducing agent container 24 without any trouble while suppressing unnecessary consumption of the air stored in the air reservoir 6.

[0023] The other actions and effects are the same as those of the exhaust gas purification apparatus shown in Figs. 2 and 3, so refer to them.

The present invention is not limited to an exhaust gas purification device that uses an aqueous urea solution as a reducing agent, but can also be applied to an ammonia aqueous solution, light oil mainly composed of hydrocarbons, gasoline, kerosene, or the like as a reducing agent. That's ugly! /

Claims

The scope of the claims

[1] a closed reducing agent container for storing a liquid reducing agent;

A reduction catalyst disposed in the engine exhaust passage and reducing and purifying nitrogen oxides in the exhaust gas using a liquid reducing agent supplied from the reducing agent container;

A pressure regulator capable of adjusting the upper space of the reducing agent container to an arbitrary pressure, an operation state detection device for detecting an engine operation state,

A control unit for inputting the engine operating state detected by the operating state detecting device and controlling the pressure regulator;

Comprising

The control unit determines whether or not the engine is operating based on the engine operating state, and when determining that the engine is operating, the upper space of the reducing agent container becomes equal to or higher than a predetermined pressure. An exhaust purification device characterized by controlling a pressure regulator.

[2] A pressure detection device that detects the pressure in the upper space of the reducing agent container,

2. The exhaust emission control device according to claim 1, wherein the control unit controls the pressurization of the pressure regulator when the pressure detected by the pressure detection device is less than a first predetermined value.

[3] The control unit further determines whether or not the engine is stopped based on the engine operating state. When determining that the engine is stopped, the upper space of the reducing agent container is large. The exhaust emission control device according to claim 1, wherein the pressure regulator is controlled so as to be equal to or lower than the atmospheric pressure.

[4] A pressure detection device that detects the pressure in the upper space of the reducing agent container,

4. The exhaust emission control device according to claim 3, wherein the control unit controls the pressure regulator to be depressurized when the pressure detected by the pressure detection device is greater than a second predetermined value.

[5] a closed reducing agent container for storing the liquid reducing agent;

A reduction catalyst that is disposed in the engine exhaust passage and that reduces and purifies nitrogen oxides in the exhaust gas using a liquid reducing agent supplied from the reducing agent container; An air reservoir for storing air;

A pressure reducing valve for reducing the air stored in the air reservoir to a predetermined pressure;

An air supply control valve for controlling the supply of air decompressed by the pressure reducing valve into the reducing agent container;

An operation state detection device for detecting an engine operation state;

A control unit that inputs an engine operation state detected by the operation state detection device and controls opening and closing of the air supply control valve;

Comprising

The control unit determines whether or not the engine is operating based on an engine operating state, and when determining that the engine is operating, opens the air supply control valve. Exhaust purification equipment.

An air release control valve for arbitrarily opening the upper space of the reducing agent container to the atmosphere is provided, and the control unit further determines whether or not the engine is stopped based on the engine operating state, and the engine is stopped. 6. The exhaust emission control device according to claim 5, wherein when it is determined that the air supply control valve is closed, the air supply control valve is closed and the atmosphere release control valve is opened.