JP2000220437A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply an NOX reducing agent with a simple structure. SOLUTION: A solid urea lump 24 is placed in a bypass tube 22 returning to an exhaust pipe 18 diverged from the exhaust pipe 18 in an upper stream of exhaust catalyst 19. And a bypass control valve 26 is arranged at the entrance part 22a of the bypass tube 22. A generated material including a reducing agent generated from the solid urea lump 24 when the solid urea lump 24 is heated by exhaust gas circulating in the bypass tube 22 is separated from the solid urea lump 24 and supplied to exhaust emission catalyst 19. The opening of a bypass control valve 26 is controlled in accordance with NOX amount discharged from an engine to control the amount of generated material supplied to the exhaust emission catalyst 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

2. Description of the Related Art Powdered solid urea is supplied to an electric heater to heat the solid urea, thereby generating a reducing gas, and supplying the reducing gas into an exhaust passage upstream of an exhaust purification catalyst. A known exhaust gas purifying apparatus for an internal combustion engine is known (see JP-A-5-272331). When the solid urea is heated, a reducing gas containing, for example, ammonia NH ₃ is generated, and this reducing gas can reduce NO _X. Therefore, in this exhaust gas purification device, solid urea is heated to generate a reducing gas, and NO
_X is reduced.

[0003]

However, in this exhaust gas purification apparatus, a supply device for supplying solid urea to the electric heater, an electric heater for heating the solid urea, and a supply device for supplying the reducing gas to the engine exhaust passage. Therefore, there is a problem that not only the configuration of the exhaust gas purification device is complicated but also the cost is increased.

[0004]

According to a first aspect of the present invention, a solid urea is disposed in an engine exhaust passage upstream of an exhaust purification catalyst so that the solid urea is heated by the exhaust gas. The substance generated from the solid urea is separated from the solid urea and supplied to the exhaust purification catalyst.
That is, in the first aspect, since the solid urea is heated by the exhaust gas and the generated substance is directly supplied to the exhaust gas purification catalyst, the reducing agent is supplied with a simple configuration.

According to a second aspect, in the first aspect, means for controlling the temperature of the solid urea is provided. That is, in the second invention, since the amount of generated substance depends on the temperature of solid urea, the amount of generated substance is controlled by controlling the temperature of solid urea. Also, 3
According to the first invention, in the first invention, a branch passage is provided for connecting the exhaust passage upstream of the solid urea bypassing the solid urea and the exhaust passage between the solid urea and the exhaust gas purification catalyst to each other. Means for controlling the ratio of the flow rate of the exhaust gas flowing through the exhaust passage to the flow rate of the exhaust gas.
That is, in the third aspect, the amount of the generated substance supplied to the exhaust gas purification catalyst depends on the flow rate of the exhaust gas flowing through the exhaust passage. Therefore, the amount of the generated substance supplied to the exhaust gas purification catalyst is controlled by controlling the flow rate of the exhaust gas flowing through the exhaust passage. The amount of generated substances is controlled.

According to a fourth aspect of the present invention, in the first aspect, there is provided means for controlling an amount of a supplied substance which is a substance supplied from the solid urea to the exhaust purification catalyst,
So as to control the supply generating material amount depending on the required generation substance amount seeking necessary generating substance amount is generating substance amount required to reduce the NO _X exhausted from the engine. That is, in the fourth invention, the amount of the supplied and generated substances is controlled in accordance with the amount of NO _X discharged from the engine.

[0007]

FIG. 1 shows a case where the present invention is applied to a diesel engine. However, the present invention can be applied to a spark ignition type engine. Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber, 3 is an intake port, 4 is an intake valve, 5 is an exhaust port, 6 is an exhaust valve, and 7 is an electromagnetic type for directly injecting fuel into the combustion chamber 2. Are shown, respectively. Each fuel injection valve 7 is connected to a fuel pump 9 via a common fuel pressure accumulating chamber 8. In this way, one cylinder
A plurality of fuel injections can be performed in a combustion cycle. The intake port 3 of each cylinder is connected to a common surge tank 11 via a corresponding intake branch pipe 10, and the surge tank 11 is connected to an air cleaner 1 via an intake duct 12.
3 is connected. On the other hand, the exhaust port 5 of each cylinder is connected via a common exhaust manifold 14 and an exhaust pipe 15 to a casing 17 containing an oxidation catalyst 16. The casing 17 is connected to a casing 20 containing an exhaust purification catalyst 19 via an exhaust pipe 18, and the casing 20 is connected to an exhaust pipe 21.

[0008] A casing 23 is formed at the bottom of the bypass pipe 22 which branches downward from the exhaust pipe 18 and returns to the exhaust pipe 18 again. The casing 23 accommodates a solid urea lump 24. A bypass control valve 26 driven by, for example, a negative-pressure-driven actuator 25 is disposed at the inlet 22 a of the bypass pipe 22. When the opening degree of the bypass control valve 26 increases, the proportion of the exhaust flow rate flowing through the bypass pipe 22 among the exhaust flow rate discharged from the engine body 1 increases, and the proportion of the exhaust flow rate flowing through the exhaust pipe 18 decreases. When the opening degree of the bypass control valve 26 decreases, the ratio of the flow rate of exhaust gas flowing through the bypass pipe 22 decreases, and the ratio of the flow rate of exhaust gas flowing through the exhaust pipe 18 increases.

An electronic control unit (ECU) 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, R
AM (random access memory) 33, CPU (microprocessor) 34, BR constantly connected to power supply
An AM (backup RAM) 35, an input port 36, and an output port 37 are provided. An intake air amount sensor 38 that generates an output voltage proportional to the intake air mass flow rate is disposed in the intake duct 12. A temperature sensor 39 for generating an output voltage proportional to the temperature of the exhaust gas flowing into the bypass pipe 22 is mounted in the bypass pipe 22 upstream of the solid urea mass 24. The temperature of this exhaust represents the temperature TUB of the solid urea mass 24. Also, the outlet 22 of the bypass pipe 22
A temperature sensor 40 for generating an output voltage proportional to the temperature of the exhaust gas flowing into the exhaust purification catalyst 19 is attached to the exhaust pipe 18 between the exhaust gas purification catalyst 19 and the exhaust pipe 18. The temperature of this exhaust represents the catalyst temperature TCAT. The depression amount sensor 41 is a depression amount D of an accelerator pedal (not shown).
Generates an output voltage proportional to EP. These sensors 3
The output voltages of 8, 39, 40 and 41 correspond to the corresponding A
The data is input to the input port 36 via the D converter 42. The input port 36 is connected to a rotation speed sensor 43 that generates an output pulse indicating the engine rotation speed N. On the other hand, the output ports 37 are connected to the respective fuel injection valves 7 and the actuators 25 via the corresponding drive circuits 44, respectively.

In this embodiment, the exhaust purification catalyst 19 comprises platinum Pt, palladium Pd, rhodium Rh supported on a porous carrier such as zeolite, ferrierite, mordenite, alumina Al ₂ O ₃ , titania TiO ₂ .
Noble metals such as iridium Ir, copper Cu, iron Fe, cobalt Co, nickel Ni, chromium Cr, vanadium V,
It comprises a transition metal such as titanium Ti or an oxide of these transition metals. Zeolite such as ZSM-5
High silica containing zeolites such as molds can be used. The exhaust purification catalyst 19 selectively reacts NO _X with a reducing agent in an oxygen atmosphere containing a reducing agent such as hydrocarbon HC, carbon monoxide CO, and ammonia NH ₃ , thereby converting NO _X to nitrogen N ₂ . Can be reduced. That is, the exhaust purification catalyst 19 in the exhaust gas flowing is as containing a reducing agent, even if an oxygen atmosphere to reduce the NO _X in the inflowing exhaust gas.

On the other hand, in the diesel engine shown in FIG. 1, oxygen excess combustion is always performed in order to reduce smoke and particulates discharged from the engine. Has been maintained. In this case, unburned HC and CO exhausted from the engine acts as a reducing agent for NO _X, NO _X is reduced so that in the exhaust purification catalyst 19. However, the amount of NO _X to be purified is overwhelmingly larger than the amount of unburned HC discharged from the diesel engine,
There is a shortage of reducing agent for purifying _X well. Therefore, it is necessary to supply the reducing agent to the exhaust purification catalyst 19 secondarily.

On the other hand, when the solid urea is heated, for example, NH ₃
A generating substance containing a reducing agent such as It is not clear what kind of substance is contained in the substance generated when the solid urea is heated by exhaust gas. However, the generated substances include NH ₃ , biuret, cyanuric acid, cyanic acid and the like, and furthermore, NH ₃ or NH ₃ from these biuret, cyanuric acid and cyanic acid.
It is believed that _three precursors are formed. Therefore, in the present embodiment, the solid urea mass 24 is disposed as a reducing agent source in the engine exhaust passage upstream of the exhaust purification catalyst 19, and the solid urea mass 2
A substance generated from the solid urea lump 24 when the fuel cell 4 is heated by the exhaust gas is separated from the solid urea lump 24 and supplied to the exhaust purification catalyst 19.

That is, when the bypass control valve 26 is opened, the exhaust gas flowing through the bypass pipe 22 comes into direct contact with the solid urea mass 24, and as a result, the solid urea mass 24 is heated and A generated substance containing is generated.
The generation material is transferred is separated from the solid urea mass 24 by the exhaust to the exhaust purification catalyst 19, then reducing the NO _X. In this case, since NH ₃ has a stronger reducing power than HC, CO, and hydrogen, it can surely reduce NO _X.

However, N to be reduced by the exhaust purification catalyst 19
O _X amount varies according to the engine operating conditions, therefore it is necessary to control the amount of reducing agent supplied to the exhaust purification catalyst 19. On the other hand, the amount of the reducing agent supplied to the exhaust gas purification catalyst 19 depends on the amount of the generated substance supplied to the exhaust gas purification catalyst 19, and the amount of the supplied substance depends on the temperature of the solid urea mass 24. Further, the temperature of the solid urea lump 24 depends on the flow rate of exhaust gas flowing through the bypass pipe 22. Therefore, in the present embodiment, the opening of the bypass control valve 26 is changed according to the amount of NO _X flowing into the exhaust purification catalyst 19.
Next, a method of controlling the opening of the bypass control valve 26 will be described with reference to the routine of FIG. The routine in FIG. 2 is executed by interruption every predetermined set time.

Referring to FIG. 2, first, at step 50, the inflow NO _X which is the amount of NO _X flowing into the exhaust purification catalyst 19 is set.
The quantity QN is calculated. The inflow NO _X amount QN is stored in advance in the ROM 32 as a function of the accelerator pedal depression amount DEP representing the engine load and the engine speed N, for example. In a succeeding step 51, a required generated substance amount RGM which is a required substance amount for reducing NO _X by the inflowing NO _X amount QN is calculated. The required generated substance amount RGM is, for example, an inflow NO _X amount QN and a catalyst temperature TC representing the NO _X reduction efficiency.
It is stored in the ROM 32 in advance as a function with the AT. In the following step 52, the generated substance is determined as the required generated substance amount R.
A required exhaust flow rate REG, which is an exhaust flow rate flowing through the bypass pipe 22 and required to obtain only GM, is calculated. The required exhaust gas flow rate REG is stored in the ROM 32 in advance as a function of, for example, the required generated substance amount RGM and the solid urea mass temperature TUB. In the following step 53, the opening degree DBV of the bypass control valve 26 is calculated. The opening degree DBV is stored in advance in the ROM 32 as a function of the required exhaust gas flow rate REG and the intake air mass flow rate Ga, for example. In the following step 54, the bypass control valve 2 is controlled so that the opening becomes DBV.
6 is driven.

[0016] Incidentally, the exhaust purification catalyst 19 in the exhaust passage downstream of the NO _X sensor for detecting the amount of NO _X discharged from the exhaust purifying catalyst 19 disposed, _the amount of NO _X discharged from the exhaust purifying catalyst 19 Can be controlled so that is maintained below a certain amount. Meanwhile, the unburned HC flowing into the exhaust purification catalyst 19 in order to satisfactorily reacting NO _X and NH ₃ in the exhaust purification catalyst 19, it is preferable to reduce as much as possible CO, NO _X
It is preferable in the form of NO ₂ than the NO. Therefore, in the present embodiment, an oxidation catalyst 16 is provided upstream of the exhaust purification catalyst 19 to oxidize and remove unburned HC and CO discharged from the combustion chamber ₂ and convert NO to NO ₂ .

As described above, in this embodiment, since the solid urea lump 24 is disposed in the exhaust passage, an electric heater for heating the solid urea lump 24 and the generated substance are discharged from the exhaust purification catalyst 19.
Does not require any equipment to supply to FIG. 3 shows another embodiment. Referring to FIG. 3, the exhaust pipe 18
Pipe 2 which branches upward from the pipe and returns to the exhaust pipe 18 again
A casing 23 containing a solid urea lump 24 is arranged at the top of the second. The supply port 2 is provided on the bottom surface 23a of the casing 23.
3b is formed. On the other hand, the upper space 2 of the casing 23
A three-way valve 60 for selectively connecting the upper space 23c to the atmosphere or the outlet of the air pump 61 is connected to 3c. The upper space 23c is normally connected to the atmosphere. further,
A level sensor 45 that generates an output voltage proportional to the height position of the solid urea block 24 is attached to the casing 23, and the output voltage of the level sensor 45 is supplied to an input port of the electronic control unit 30 via a corresponding AD converter. Is entered. The height position of the solid urea mass 24 indicates the remaining amount of the solid urea mass 24. The three-way valve 60 and the air pump 61 are connected to the electronic control unit 30 via corresponding drive circuits.
Output port. Furthermore, a warning device 62, for example, consisting of a lamp or a buzzer,
Connected to the output port.

When the exhaust gas flows into the bypass pipe 22, the solid urea mass 24 is heated through the casing bottom surface 23a acting as a heat receiving surface. As a result, for example, a generated substance in a liquid phase is generated and a generated substance pool 24a is formed in the casing 23 below the solid urea lump 24, and the generated substance falls into the bypass pipe 22 through the supply port 23b, and then falls. The exhaust gas is transferred to the exhaust purification catalyst 19.

Also in this embodiment, the bypass control valve opening DBV is controlled in accordance with the inflow NO _X amount. However, for example, when the required amount of generated substances sharply and largely increases due to the engine rapid acceleration operation, even if the bypass control valve opening DBV sharply and largely increases, the amount of supply generated substances does not sharply increase. Therefore, in the present embodiment, when the amount of the necessary substance suddenly increases significantly, the three-way valve 60 is controlled to temporarily connect the casing upper space 23c to the air pump 61, and to temporarily operate the air pump 61. Upper space 2
By supplying high-pressure air to 3c, the solid urea mass 24 is moved downward, whereby the generated substance in the generated substance pool 24a is pushed out into the bypass pipe 22. As a result, shortage of the reducing agent for reducing NO _X is prevented.

By the way, when the solid urea lump 24 is almost consumed and the generated substance is hardly generated, N
It can not be satisfactorily reduced the O _X. Therefore, in the present embodiment, when the remaining amount of the solid urea lump 24 becomes smaller than a predetermined set amount, the warning device 62 is activated,
The fact that the solid urea mass 24 should be refilled is notified.

When the remaining amount of the solid urea lump 24 becomes smaller than the set amount, the fuel is injected secondary from the fuel injection valve 7 to the engine expansion stroke or the exhaust stroke, that is, the secondary fuel is injected. Thereby, HC as a reducing agent is supplied to the exhaust purification catalyst 19. As a result, the amount of NO _X discharged from the exhaust purification catalyst 19 can be kept low. The secondary fuel injection is different from the main fuel injection performed around the compression top dead center, for example, and the fuel by the secondary fuel injection hardly contributes to the engine output. Other configurations and operations of the exhaust gas purifying apparatus are the same as those in the embodiment of FIG.

FIG. 4 shows still another embodiment.
Referring to FIG. 4, the casing 23 is provided at the top of the exhaust pipe 18.
Is arranged. The casing 23 is provided with the annular refrigerant passage 7.
0, the outlet of the refrigerant passage 70 is connected to the suction side of a refrigerant pump 72 whose discharge amount can be controlled via a cooling device 71, and the discharge side of the refrigerant pump 72 is connected to the inlet of the refrigerant passage 70. Connected.

In this embodiment, when the amount of the supply-generating substance is to be increased, the amount of the refrigerant flowing through the refrigerant passage 70 is reduced, so that the solid urea mass temperature TUB is increased, and the amount of the supply-generating substance is reduced. When to be, refrigerant passage 70
The amount of the refrigerant flowing through the inside is increased, so that the solid urea mass temperature TUB is lowered. Further, the upper space 23c of the casing 23 is connected to the exhaust pipe 2 upstream of the casing 23.
3 is connected to a pressure port 73 provided in the apparatus 3. Therefore, when the pressure in the exhaust pipe 18 increases, the solid urea mass 24
Is pushed downward, the amount of the supplied material increases, and when the pressure in the exhaust pipe 18 decreases, the amount of the supplied material decreases. On the other hand, when the pressure in the exhaust pipe 18 is high, the inflow NO _X amount of the exhaust purification catalyst 19 is large, and when the pressure in the exhaust pipe 18 is low, the inflow NO _X amount is small. Therefore, when the inflow NO _X amount increases, the supply generation material amount increases, and the inflow N
Supply generating material amount and O _X amount decreases is reduced. As a result, shortage of the reducing agent for reducing NO _X is prevented.

[0024]

It is possible to supply the reducing agent for NO _X reduction with in according to the present invention a simple structure.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a flowchart for controlling an opening degree of a bypass control valve.

FIG. 3 is a diagram showing another embodiment.

FIG. 4 is a diagram showing another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine main body 7 ... Fuel injection valve 18 ... Exhaust pipe 19 ... Exhaust purification catalyst 22 ... Bypass pipe 24 ... Solid urea lump 26 ... Bypass control valve

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Claims (4)

[Claims] A solid urea is disposed in an engine exhaust passage upstream of an exhaust purification catalyst, and a substance generated from the solid urea when the solid urea is heated by exhaust gas is separated from the solid urea to purify exhaust gas. An exhaust purification device for an internal combustion engine adapted to supply to a catalyst. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising means for controlling a temperature of the solid urea. 3. An exhaust passage which bypasses solid urea and connects an exhaust passage upstream of solid urea and an exhaust passage between the solid urea and the exhaust purification catalyst to each other. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising means for controlling a ratio of an exhaust flow rate flowing through the inside. 4. A means for controlling the amount of generated substances supplied from the solid urea to the exhaust gas purification catalyst, the amount of generated substances being required to reduce NO _X discharged from the engine. 2. The method according to claim 1, wherein the amount of the required generated substance is obtained and the supplied generated substance amount is controlled in accordance with the required generated substance amount.
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1.