JP2000310112A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize and simplify an exhaust emission control device by using gel reducing agent. SOLUTION: Gel reducing agent (urea) A is stored within a freely expandable container 17 of a reducing agent storing tank 12 and gel reducing agent A is made a normally pressurizing state by pressure gas B filled into a pressure chamber 18. Gel reducing agent A is supplied within an exhaust pipe 7 from a control valve 14 via a reducing agent supply pipe 13, is heated by a heating part 15 and exhaust gas and is gasified. Gasified reducing agent A, that is, reducing gas flows into selective reducing type NOx catalyst 10 together with exhaust gas and reduces and purifies NOx in exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine for purifying NOx in exhaust gas discharged from an internal combustion engine.

[0002]

2. Description of the Related Art N 2 is used in the presence of a reducing agent in an oxygen-rich atmosphere.
A selective reduction type NOx catalyst for reducing or decomposing Ox (hereinafter, referred to as “NOx catalyst”)
An NOx catalyst is abundantly used as an exhaust gas purifying device for purifying NOx in exhaust gas discharged from an internal combustion engine (for example, a diesel engine or a lean burn gasoline engine) capable of burning at a lean air-fuel ratio.

Conventionally, hydrocarbons have often been used as the reducing agent, but urea has attracted attention as an alternative reducing agent. As a storage form of this urea, three forms of liquid, gas and solid can be considered. Among them, in the case of a liquid such as urea water, the volume and weight increase in order to limit the solubility and avoid freezing, and in the case of a gas such as ammonia gas, an extremely large storage volume is required. In order to incorporate it into an exhaust purification system for a vehicle internal combustion engine,
There is a problem with mountability. Then, utilization of solid urea excellent in vehicle mountability is considered.

[0004] For example, in an exhaust gas purifying apparatus disclosed in Japanese Patent Application Laid-Open No. 5-272331, powder urea contained in a reducing agent tank is led to a heating furnace, and the powder urea is heated in the heating furnace to produce gas. The reduced gas is supplied to an exhaust passage upstream of the selective reduction type NOx catalyst.

[0005]

However, gasification of powdered urea requires a large amount of heat, and there is a problem that the exhaust gas purifying apparatus becomes larger with the increase in the size of the heat source. Further, in the exhaust gas purification device disclosed in the above-mentioned publication, pressurized air is used as means for pumping the reducing gas into the exhaust passage, but an air tank for storing the pressurized air and a pressurized air generating device are used. In addition, equipment such as an air compressor for supplying the air tank to the air tank is required, which results in an increase in the size and complexity of the apparatus and a difficulty in mountability on a vehicle.

Further, in order to control the supply amount of the reducing gas, it is necessary to control the supply amount of the powdered urea supplied to the heating furnace and the flow rate control of the pressurized air. It was complicated and poorly controlled.

Further, heat added when gasifying the powdered urea, heat of exhaust gas, or heat entering from outside the vehicle at a high temperature is transmitted to the reducing agent tank, and the heat is further transferred to the reducing agent tank. The reduced gas is transmitted to the stored solid reducing agent and is generated in the reducing agent tank, and this reducing gas may leak from the reducing agent tank to the atmosphere.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to reduce the size of an exhaust gas purification device by using a gel-like reducing agent. The simplification and controllability are to be improved.

[0009]

The present invention has the following features to attain the object mentioned above. That is, the present invention
NOx provided in the exhaust passage of an internal combustion engine in the presence of a reducing agent
NOx catalyst that reduces or decomposes, a reducing agent storage chamber that stores a reducing agent, and reduction that supplies the reducing agent stored in the reducing agent storage chamber to an exhaust passage upstream of the selective reduction NOx catalyst. And an agent supply means, wherein the reducing agent stored in the reducing agent storage chamber is in a gel state.

The reducing agent in a gel state can be gasified by heating, and the gasified reducing agent, that is, the reducing gas, is supplied to the selective reduction type NOx catalyst together with the exhaust gas. As a result, NOx in the exhaust gas is reduced and purified by the selective reduction type NOx catalyst. The heating source for heating the gel-like reducing agent may be the heat of the exhaust gas or a heating means such as an electric heater. Therefore, it is possible to gasify the gel-like reducing agent only by supplying the gel-like reducing agent to the exhaust passage.

The gelling agent may be gasified at a position just downstream of the reducing agent storage chamber in the reducing agent passage for supplying the reducing agent to the exhaust passage. It is preferable to gasify immediately upstream of the mouth. That is, it is preferable that the reducing agent is transferred in a gel state until it reaches the vicinity of the supply port to the exhaust passage.

[0012] Even when the reducing agent is transferred in a gel state until it reaches the vicinity of the supply port to the exhaust passage, a heating means can be provided near the supply port. In this manner, the gasification of the reducing agent can be promoted, and the auxiliary heating means can be used when the exhaust gas temperature is low. An example of the heating unit is an electric heater.

The reducing agent in the form of a gel requires a smaller storage capacity than the reducing agent in the form of an aqueous solution, and the apparatus can be reduced in size and simplified.

In the present invention, the internal combustion engine can be exemplified by a direct injection type lean burn gasoline engine or a diesel engine. The selective reduction type NOx catalyst includes a catalyst in which a transition metal such as Cu is ion-exchanged and supported on zeolite, and a catalyst in which a noble metal is supported on zeolite or alumina. In the present invention, a reducing agent derived from ammonia can be used as the reducing agent, and urea and ammonium carbamate can be exemplified.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to FIG. This embodiment is an embodiment in which the present invention is applied to a vehicle driving diesel engine as an internal combustion engine.

Air is introduced into the combustion chamber 2 of each cylinder of the vehicle diesel engine 1 from the intake pipe 4 via the air cleaner 3, and fuel is injected from the fuel injection valve 5 into each combustion chamber 2, and burns at a lean air-fuel ratio. Is done. In FIG. 1, reference numeral 6 denotes a piston.

The exhaust gas exhausted from each combustion chamber 2 passes through an exhaust pipe (exhaust passage) 7, a NOx catalytic converter 8, and an exhaust pipe (exhaust passage) 9, and is exhausted to the atmosphere. NOx
The catalytic converter 8 has a zeolite / silica-based selective reduction type NO that reduces or decomposes NOx in the presence of a reducing agent.
An x catalyst (hereinafter sometimes abbreviated as NOx catalyst) 10 is accommodated.

In order to purify NOx in exhaust gas by the selective reduction type NOx catalyst 10, the presence of a reducing agent is necessary. Therefore, this exhaust gas purification apparatus is provided with an exhaust pipe 7 upstream of the NOx catalytic converter 8. A reducing agent supply device 11 for supplying a reducing agent therein is provided.

The reducing agent supply device 11 supplies the reducing agent A in the form of a gel into the exhaust pipe 7, and includes a reducing agent storage tank 12 for storing the reducing agent A in the form of a gel and a reducing agent storage tank 12 A reducing agent supply pipe 13 for guiding the gelling agent A in the exhaust pipe 7, a control valve 14 for controlling the supply amount of the gelling agent A, and a heating unit 15 for heating the gelling agent A Consists of In this embodiment, the gel-like reducing agent A is used.
Gel-like urea is used.

The reducing agent storage tank 12 has a double internal structure, and has a robust outer container 16 and a retractable inner container 17.
And a pressure chamber 18 is provided between them. Inner container 1
The gel 7 contains a reducing agent A in the form of a gel. In this embodiment, the inner container 17 forms a reducing agent storage chamber.
The reducing agent supply pipe 13 is connected to the inner container 17. The pressure chamber 18 contains an inert pressurized gas B
And the pressure of the pressurized gas B is equal to the inner container 17.
Is transmitted to the reducing agent A in the form of a gel through the pressure source, and pressurizes the reducing agent A in the form of a gel.

That is, the inner container 17 contains the gel-like reducing agent A
For separating and sealing the pressurized gas B and the pressurized gas B
Has the function of transmitting the pressure to the reducing agent A in the form of a gel. The inner container 17 can be composed of, for example, a bag made of Teflon resin or a bellows made of stainless steel.

The reducing agent storage tank 12 is of a cartridge type. When the gel-like reducing agent A in the inner container 17 runs out, the reducing agent storage tank 12 is completely replaced. In the case of the reducing agent storage tank 12 of this embodiment, the pressurized gas B is not replenished. Therefore, when the inner container 17 contracts with the decrease of the gel-like reducing agent A, the pressurized gas B Will gradually decrease.

Since the gel-like reducing agent A in the inner container 17 is always pressurized by the pressurized gas B, when the control valve 14 is opened, the gel-like reducing agent A passes through the heating unit 15 and passes through the exhaust pipe 7. Supplied within. The opening and closing time of the control valve 14 is controlled in duty ratio by an electronic control unit (ECU) 19 for engine control.
Supply timing and supply timing are controlled. In this embodiment, the pressure chamber 18, the pressurized gas B sealed therein, the reducing agent supply pipe 13, and the control valve 14 constitute a reducing agent supply unit.

The heating section 15 heats the gel-like reducing agent A flowing out of the control valve 14 to promote gasification of the reducing agent A. The heating section 15 is located near the supply port of the reducing agent A in the exhaust pipe 7. It is provided in. The heating unit 15 is configured by an electric heater, and operates when the temperature of the exhaust gas is equal to or lower than a predetermined temperature T1 and maintains the temperature at about the predetermined temperature T2.
9.

The reducing agent storage tank 12 is provided with a pressure sensor 20 for detecting the pressure of the pressurized gas B. The pressure sensor 20 outputs an output signal proportional to the detected pressure to the ECU.
19 is output. As described above, the pressure of the pressurized gas B decreases with the decrease of the gel-like reducing agent A stored in the inner container 17, and the remaining amount of the reducing agent A is determined from the output value of the pressure sensor 20. The pressure sensor 20 can be estimated.
Also functions as a remaining amount sensor. Therefore, in this embodiment, when the output value of the pressure sensor 20 becomes equal to or less than the predetermined value, the ECU 19 turns on the alarm lamp 31 of the meter panel 30, and the remaining amount of the reducing agent A in the gel state decreases. Let them know.

The exhaust pipe 7 upstream of the NOx catalytic converter 8 is provided with an incoming gas pressure sensor 22 for detecting the pressure of the exhaust gas flowing into the NOx catalytic converter 8, and the incoming gas pressure sensor 22 detects the detected exhaust gas. An output signal proportional to the gas pressure is output to the ECU 19.

The ECU 19 is composed of a digital computer and includes a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processor Unit), an input port, and an output port, which are interconnected by a bidirectional bus. In addition to performing the basic control such as the fuel injection amount control of No. 1, in this embodiment, the supply amount control of the gel-like reducing agent A is performed.

For these controls, an input signal from the accelerator opening sensor 24 is input to an input port of the ECU 19,
An input signal from the crank angle sensor 25 is input. The accelerator opening sensor 24 outputs an output voltage proportional to the accelerator opening to the ECU 19, and the ECU 19 calculates an engine load based on the output signal of the accelerator opening sensor 24. The crank angle sensor 25 outputs an output pulse to the ECU 19 every time the crankshaft of the engine 1 rotates by a certain angle, and the ECU 19 calculates the engine speed based on the output pulse. The operating state of the engine 1 is determined based on the engine load and the engine speed. further,
An input signal from the air flow meter 26 is input to an input port of the ECU 19 via an A / D converter. The air flow meter 26 outputs an output signal proportional to the intake air amount to the ECU.
The ECU 19 calculates the intake air amount based on the output signal of the air flow meter 26.

Further, the relationship between these parameters and the amount of NOx emitted per unit time is determined and mapped by an experiment in advance using the engine load and the engine speed as parameters.
In the ROM.

The ECU 19 calculates the amount of NOx emitted from the engine 1 based on the engine load and the engine speed with reference to the NOx emission amount map. further,
The ECU 19 calculates a target supply amount of the gel-like reducing agent A required for purifying the NOx, calculates a duty ratio of the opening and closing time of the control valve 14 necessary for obtaining the target supply amount, and performs control. The duty ratio of the valve 14 is controlled.

The gel-like reducing agent A flowing through the control valve 14
The flow rate changes when the supply pressure of the gelling agent A and the back pressure at the outlet side of the control valve 14 are different even if the duty ratio of the control valve 14 is the same. At this time, the ECU 19 determines the target based on the pressure of the pressurized gas B detected by the pressure sensor 20 (that is, the supply pressure of the reducing agent A) and the exhaust gas pressure detected by the incoming gas pressure sensor 22. Correct the duty ratio.

Next, the operation of the exhaust gas purifying apparatus for an internal combustion engine will be described. As described above, the ECU 19 controls the duty ratio of the control valve 14 according to the operating state of the engine 1, that is, according to the NOx emission amount, and the gel-like reducing agent A
Control the supply amount of water.

The gel-like reducing agent A flowing out of the control valve 14
Is heated by the heating unit 15 and heated by the heat of the exhaust gas flowing through the exhaust pipe 7 to become a reducing gas (ammonia gas), and flows into the NOx catalytic converter 8 together with the exhaust gas.

This reducing gas reduces or decomposes NOx contained in the exhaust gas in the NOx catalyst 10 to purify the exhaust gas. The purified exhaust gas is discharged to the atmosphere through the exhaust pipe 9.

In the above-described embodiment, a system in which the pressurized gas B is not supplied to the pressure chamber 18 of the reducing agent storage tank 12 has been described as an example. It may be. By doing so, the fluctuation of the supply pressure of the reducing agent A can be reduced, or the supply pressure can be kept constant, and the supply amount control of the reducing agent A becomes easy. As the pressurized gas in this case, a supercharged gas boosted by a turbocharger can be exemplified. Further, instead of the pressurized gas, engine oil pressurized by an oil pump or engine cooling water pressurized by a cooling water pump may be supplied to the pressure chamber 18 to pressurize the reducing agent A in the inner container 17. .

Further, in the above-described embodiment, an example is described in which the fluid pressure in the pressure chamber 18 is used as a means for obtaining the supply pressure of the gelling reducing agent A, but the present invention is not limited to this. For example, a pressurizing pump for increasing the pressure of the gelling reducing agent A may be provided in the middle of the reducing agent supply pipe 13, and the supply pressure of the reducing agent A may be obtained by the pressurizing pump.

In the embodiment described above, the relationship between the operating state of the engine 1 and the NOx emission amount is mapped in advance, and the NOx emission amount in each actual engine operating state is estimated and calculated with reference to this map. However, instead of this, the exhaust pipe 7 on the upstream side of the NOx catalytic converter 8
A NOx sensor for detecting the NOx concentration of the exhaust gas may be provided, and the NOx emission amount may be calculated from the NOx concentration detected by the NOx sensor and the intake air amount detected by the air flow meter 26.

According to the exhaust gas purifying apparatus of this embodiment,
Since the reducing agent A is in the form of a gel, the storage capacity can be reduced, and the reducing agent storage tank 12 can be small. Therefore, the exhaust gas purifying device can be downsized, and the mountability on a vehicle is very excellent. Further, the supply amount of the reducing agent A in a gel state can be easily controlled by the control valve 14.

[0039]

According to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, a selective reduction type NOx catalyst provided in an exhaust passage of an internal combustion engine for reducing or decomposing NOx in the presence of a reducing agent;
A reducing agent storage chamber for storing the reducing agent; and reducing agent supply means for supplying the reducing agent stored in the reducing agent storage chamber to an exhaust passage upstream of the selective reduction type NOx catalyst. Since the reducing agent stored in the chamber is in a gel state, the exhaust gas purifying device can be reduced in size and simplified, and an excellent effect that the supply amount of the reducing agent can be easily controlled can be obtained.

When a heating means is provided near the supply port of the gel-like reducing agent to the exhaust passage, gasification of the gel-like reducing agent supplied to the exhaust passage can be promoted. This has the effect.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 diesel engine (internal combustion engine) 7, 9 exhaust pipe (exhaust passage) 8 NOx catalytic converter 10 selective reduction type NOx catalyst 11 reducing agent supply device 12 reducing agent storage tank 13 reducing agent supply pipe (reducing agent supply means) 14 control valve (Reducing agent supply means) 15 Heating unit 17 Inner vessel (reducing agent storage chamber) 18 Pressure chamber (Reducing agent supply means) 19 ECU A Gel reducing agent B Pressurized gas (Reducing agent supply means)

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tetsu Iguchi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G091 AA12 AA17 AA18 AA24 AB05 BA14 BA39 CA05 CA16 CA17 CB02 DA01 DA02 DA05 DB10 DC05 EA00 EA01 EA03 EA05 EA07 EA31 EA32 EA33 FB10 FC04 GB01W GB01X GB05W GB09W GB10X GB16X HA36 4D048 AA06 AB02 AB03 CC38 CC52 DA01 DA10

Claims (3)

[Claims] 1. A selective reduction type NOx catalyst provided in an exhaust passage of an internal combustion engine for reducing or decomposing NOx in the presence of a reducing agent, a reducing agent storage chamber for storing a reducing agent, and stored in the reducing agent storage chamber And a reducing agent supply means for supplying the reduced agent to the exhaust passage upstream of the selective reduction type NOx catalyst.The reducing agent stored in the reducing agent storage chamber is in a gel state. An exhaust gas purification device for an internal combustion engine, comprising: 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the reducing agent is transferred in a gel state until the reducing agent reaches a vicinity of a supply port to an exhaust passage. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, further comprising a heating means near the supply port.