JP2001059417A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) [PROBLEMS] To improve an NOx purification rate in an exhaust gas purification device in which two NOx catalysts having different activation temperature ranges are provided in series. SOLUTION: A high temperature active NOx catalyst 6 and a low temperature active NOx catalyst 7 are provided in series in an exhaust pipe 5 in that order. A reducing agent (light oil) is supplied to these NOx catalysts 6 and 7 by a reducing agent supply device 10. As the supply pump 11 of the reducing agent supply device 10, a pump capable of controlling the supply pressure by controlling the magnitude of the driving voltage of the supply pump 11 is used, and the injection nozzle 12 A nozzle capable of changing the injection pressure according to the pressure is used.
When the incoming gas temperature detected by the incoming gas temperature sensor 8 is lower than a predetermined temperature, the injection pressure is increased so that a required amount of reducing agent can be supplied to the low-temperature active NOx catalyst 7.

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 purifying exhaust gas discharged from an internal combustion engine capable of lean combustion.

[0002]

2. Description of the Related Art As an exhaust gas purifying apparatus for purifying exhaust gas discharged from an internal combustion engine capable of lean combustion such as a diesel engine or a lean burn gasoline engine, there are NOx catalysts such as a selective reduction type NOx catalyst and a storage reduction type NOx catalyst. .

[0003] A selective reduction type NOx catalyst is a catalyst that reduces or decomposes NOx in the presence of hydrocarbons (HC) in an oxygen-excess atmosphere. To purify NOx with this selective reduction type NOx catalyst, an appropriate amount of NOx catalyst is used. An HC component is required. When this selective reduction type NOx catalyst is used for purifying the exhaust gas of the internal combustion engine, the amount of the HC component in the exhaust gas during the normal operation of the internal combustion engine is extremely small. It is necessary to supply the HC component to the type NOx catalyst.

On the other hand, the NOx storage reduction catalyst, the air-fuel ratio of the inflowing exhaust gas when the lean absorb NOx, the oxygen concentration of the inflowing exhaust gas releases NOx absorbed and reduced, is reduced to N ₂ It is a catalyst.

When this storage-reduction type NOx catalyst is used for purifying the exhaust gas of the internal combustion engine, the air-fuel ratio of the exhaust gas during normal operation of the internal combustion engine is lean.
Ox is absorbed by the NOx catalyst. However, if the exhaust gas having the lean air-fuel ratio is continuously supplied to the NOx catalyst, the NOx absorption capacity of the NOx catalyst reaches saturation, and it becomes impossible to absorb NOx any more, thereby causing NOx to leak. Therefore, in the NOx storage reduction catalyst, the oxygen concentration is extremely reduced by enriching the air-fuel ratio of the inflowing exhaust gas at a predetermined timing before the NOx absorption capacity is saturated, thereby reducing the NOx absorbed by the NOx catalyst. release was then reduced to N _2, it is necessary to recover the NOx absorbing capacity of the NOx catalyst.

[0006] These NOx catalysts have their own temperature characteristics. In other words, each NOx catalyst has its own active temperature range, and the NOx purification rate varies depending on the temperature even within the active temperature range.

When a NOx catalyst having such a temperature characteristic is installed in the exhaust passage of an internal combustion engine and used, the exhaust gas temperature of the internal combustion engine greatly changes according to the operating state of the internal combustion engine. It changes according to the gas temperature. Therefore, there is a problem that the NOx purification rate is reduced due to the exhaust gas temperature.

[0008]

The first problem is that since the variation range of the exhaust gas temperature of the internal combustion engine is extremely wide, one N
The problem is that it is difficult to maintain a high NOx purification rate over the entire operating temperature range using only the Ox catalyst.

In order to solve this problem, a technique has been developed in which a plurality of catalysts having different NOx purification temperature characteristics are arranged in series in an exhaust passage of an internal combustion engine so that a high NOx purification rate can be obtained in a wide temperature range. Was.

For example, a low-temperature NOx catalyst capable of obtaining a high NOx purification rate in a relatively low temperature region is disposed downstream of a high-temperature NOx catalyst capable of obtaining a high NOx purification ratio in a relatively high temperature region. An exhaust gas purification device for supplying a certain HC from the upstream side of the high-temperature NOx catalyst has been devised. With this configuration, when high-temperature exhaust gas is discharged from the internal combustion engine, NOx in the exhaust gas is purified by the high-temperature NOx catalyst, and when low-temperature exhaust gas is discharged, low-temperature NOx is discharged.
Since NOx in exhaust gas is purified by the catalyst, it was expected that a high NOx purification rate could be obtained in a wide range from low to high temperatures.

However, in the exhaust gas purifying apparatus in which a plurality of NOx catalysts are arranged in series, the N
The effect of improving the Ox purification rate was not obtained. The cause was insufficient supply of HC to the low-temperature NOx catalyst. As described above, both the selective reduction type NOx catalyst and the storage reduction type NOx catalyst require an appropriate amount of HC in order to purify NOx. Should be supplied to the high-temperature NOx catalyst, but since the supply of HC is performed from the upstream side of the high-temperature NOx catalyst, much of the supplied HC is consumed by the high-temperature NOx catalyst, and the low-temperature NOx catalyst It is estimated that the required amount of HC was not supplied.

To solve this problem, Japanese Patent Laid-Open No.
As disclosed in JP-A-288030, HC can be supplied to both the upstream of the high-temperature NOx catalyst and the upstream of the low-temperature NOx catalyst, and when exhaust gas in the low-temperature region is discharged, the upstream of the low-temperature NOx catalyst is discharged. From the high temperature NOx catalyst when exhaust gas in a high temperature range is exhausted.

However, in such a case,
There is a disadvantage that two HC supply routes are required and the apparatus becomes complicated. Further, according to the technology described in the above publication, when the exhaust gas temperature is low, the exhaust gas is
When the temperature of the exhaust gas is high, the exhaust gas that has passed through the high-temperature NOx catalyst is guided to a cooling device to be cooled, and then flows to the low-temperature NOx catalyst. Is designed to increase the NOx purification rate when the exhaust gas temperature is high. However, such a configuration causes a problem that the apparatus becomes complicated and the cost increases.

Another problem is that a temperature difference occurs in the NOx catalyst even when the exhaust gas temperature is not changing, and the NOx purification rate is reduced due to the temperature difference. When the NOx catalyst is installed in the exhaust passage of the internal combustion engine, as shown in FIG.
The catalyst has a higher catalyst temperature than the NOx catalyst arranged on the outer peripheral portion of the exhaust passage. One of the reasons why the temperature distribution occurs in the NOx catalyst is that the influence of heat radiation is greater at the outer peripheral portion of the exhaust passage than at the central portion. Also,
As another reason, generally, the passage area of the portion where the NOx catalyst is provided (that is, the cross-sectional area of the casing containing the NOx catalyst) is larger than the passage area of the NOx catalyst upstream (that is, the cross-sectional area of the exhaust pipe upstream of the NOx catalyst). Therefore, a large amount of exhaust gas flows through the central portion of the NOx catalyst.

If the temperature distribution occurs in the NOx catalyst as described above, the NOx purification rate is greatly reduced in the following cases, which causes a problem. First, when the temperature of the exhaust gas becomes close to the lower limit value of the active temperature range of the NOx catalyst, the temperature of the outer peripheral portion of the NOx catalyst becomes lower than the lower limit value of the active temperature and becomes NO.
x There is a possibility that the purification rate may drop significantly,
The Ox purification rate may decrease. Further, when the temperature of the exhaust gas becomes close to the upper limit value of the active temperature range of the NOx catalyst, the temperature of the central portion of the NOx catalyst further rises due to the catalytic action, so that the temperature of the central portion becomes the upper limit value of the active temperature range. Therefore, there is a possibility that the NOx purification rate becomes higher and the NOx purification rate drops significantly, and the overall NOx purification rate may decrease.

The present invention has been made in view of such problems of the conventional technology, and the problem to be solved by the present invention is that it has a simple structure but covers a wide temperature range from a low temperature to a high temperature. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can obtain a high NOx purification rate. Another problem to be solved by the present invention is to suppress the deterioration of the NOx purification rate due to the temperature distribution in the NOx catalyst,
As a result, it is intended to improve the NOx purification rate.

[0017]

The present invention has the following features to attain the object mentioned above. (1) A first invention according to the present application relates to a high-temperature activated NOx catalyst and a low-temperature activated NOx catalyst provided in series in an exhaust passage of an internal combustion engine capable of lean combustion, and provided on an upstream side of the NOx catalyst. Reducing agent injection means for injecting a reducing agent into the exhaust passage from an upstream side of the NOx catalyst to the NOx catalyst, and an exhaust gas temperature of the internal combustion engine or the NO.
reducing agent pressure control means for controlling the pressure of the reducing agent injected into the exhaust passage from the reducing agent injection means in accordance with the catalyst temperature of any one of the x catalysts. It is an exhaust gas purification device for an internal combustion engine.

When a high-temperature activated NOx catalyst and a low-temperature activated NOx catalyst are arranged in series in an exhaust passage and a reducing agent is injected from a reducing agent injection device, the reducing agent is consumed in the NOx catalyst arranged on the upstream side. Therefore, NO arranged on the downstream side
x It is difficult to supply the required amount of reducing agent to the catalyst. In the exhaust gas purifying apparatus of the first invention, the NO arranged on the downstream side
When it is desired to supply a large amount of the reducing agent to the x catalyst, by increasing the injection pressure of the reducing agent by the reducing agent pressure control means, it is possible to increase the amount of the reducing agent that is passed without being consumed by the upstream NOx catalyst, and The required amount of reducing agent can be supplied to the NOx catalyst on the side. Thereby, a high NOx purification rate can be obtained in a wide temperature range from a low temperature to a high temperature.

The first aspect of the present invention can be realized by arranging either the high-temperature activated NOx catalyst or the low-temperature activated NOx catalyst on the upstream side. However, it is preferable that the high-temperature activated NOx catalyst be replaced with the low-temperature activated NOx catalyst. Should also be provided upstream. The high-temperature activated NOx catalyst exhibits a high NOx purification rate when the catalyst temperature (exhaust gas temperature) is high. However, when the internal combustion engine emits high-temperature exhaust gas, the amount of NOx emission increases, so that NOx Requires a large amount of reducing agent. If the high-temperature activated NOx catalyst is arranged on the downstream side, if the injection pressure is increased in order to allow the low-temperature activated NOx catalyst arranged on the upstream side to pass without reducing the reducing agent, the injection amount of the reducing agent is increased. Is further increased, leading to deterioration of fuel efficiency. Therefore, in consideration of fuel efficiency, it is preferable to provide the high-temperature activated NOx catalyst upstream of the low-temperature activated NOx catalyst.

In the exhaust gas purifying apparatus of the first invention,
As described above, the high-temperature activated NOx catalyst is replaced with the low-temperature activated Nx catalyst.
When provided upstream of the Ox catalyst, the reducing agent pressure control means controls the exhaust gas temperature of the internal combustion engine or the NO.
Control is performed so that the pressure of the reducing agent is higher when the catalyst temperature of the x catalyst is lower than when it is higher.

(2) A second invention according to the present application is directed to a NOx catalyst provided in an exhaust passage of an internal combustion engine capable of lean combustion, wherein the NOx catalyst is provided in the exhaust passage from upstream of the NOx catalyst toward the NOx catalyst. Reducing agent injection means for injecting a reducing agent, and an injection angle for controlling an injection angle of the reducing agent injected into the exhaust passage from the reducing agent injection means according to the exhaust gas temperature of the internal combustion engine or the catalyst temperature of the NOx catalyst. And a control unit.

The catalyst temperature of the NOx catalyst provided in the exhaust passage generally has a higher temperature distribution at the center than at the outer periphery. Further, the NOx catalyst has an active temperature range, and even within the active temperature range, the NOx purification rate varies depending on the temperature. Therefore, even when the exhaust gas having the same temperature is flowing, the NOx purification rate differs between the central portion and the outer peripheral portion of the NOx catalyst. In the exhaust gas purifying apparatus of the second invention,
As the reducing agent is injected into the part with high NOx purification rate,
The injection angle control means controls the injection angle of the reducing agent according to the exhaust gas temperature or the catalyst temperature.

In the exhaust gas control apparatus according to a second aspect of the present invention, the injection angle control means controls the injection angle to be small when the exhaust gas temperature of the internal combustion engine or the catalyst temperature of the NOx catalyst is lower than a predetermined temperature. When the exhaust gas temperature or the catalyst temperature of the NOx catalyst is higher than a predetermined temperature, it is preferable to control the injection angle to be large.
As described above, since the temperature distribution of the NOx catalyst is higher in the central portion than in the outer peripheral portion, in the high temperature region in the active temperature range, even if the outer peripheral portion is in the active temperature range, the central portion is the upper limit of the active temperature range. In this case, the reducing agent should be injected into the outer peripheral portion. On the other hand, in the low temperature region in the active temperature range, the outer peripheral portion is in the active temperature range even if the central portion is in the active temperature range. In some cases, the reducing agent should be injected into the central part.

In the exhaust gas purifying apparatus of the second invention, when the injection angle is controlled to be small by the injection angle control means, the reducing agent is solidly injected from the reducing agent injection means and the injection angle is controlled to be large. Sometimes it is preferred that the reducing agent is injected in the form of a hollow cone. A swirl nozzle can be exemplified as an injection unit capable of controlling the injection mode as described above.

In the exhaust gas purifying apparatus according to the first and second aspects of the present invention, the in-cylinder direct-injection lean-burn gasoline engine and the diesel engine are exemplified as the lean-burn internal combustion engine. Can be.

The high-temperature active NOx catalyst and the low-temperature active NOx in the exhaust gas purifying apparatus of the first invention according to the present application.
As the catalyst or the NOx catalyst in the exhaust gas purification apparatus of the second invention, a storage reduction type NOx catalyst or a selective reduction type NOx catalyst can be exemplified.

The NOx storage reduction catalyst absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases to reduce it to N ₂ . It is a catalyst. This storage reduction type NOx
The catalyst uses, for example, alumina as a carrier, and on this carrier, for example, alkali metals such as potassium K, sodium Na, lithium Li, and cesium Cs, alkaline earths such as barium Ba and calcium Ca, lanthanum La, and yttrium Y. At least one selected from rare earths,
A noble metal such as platinum Pt is carried.

The selective reduction type NOx catalyst refers to a catalyst which reduces or decomposes NOx in the presence of hydrocarbons in an oxygen-excess atmosphere. A catalyst in which a transition metal such as Cu is ion-exchanged on zeolite, zeolite or alumina is used. And a catalyst supporting a noble metal.

In the exhaust gas purifying apparatus according to the first and second aspects of the present invention, the reducing agent injection means may include:
It can be constituted by a reducing agent supply pump, a reducing agent injection nozzle and the like.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to FIGS. The embodiment described below is an aspect in which the exhaust emission control device according to the present invention is applied to a vehicle driving diesel engine as an internal combustion engine.

[First Embodiment] First, a first embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS. As shown in FIG. 1, intake air that has been boosted by the compressor 2 a of the turbocharger 2 and cooled by the intercooler 3 is introduced into the combustion chamber of each cylinder of the diesel engine 1 through the intake pipe 4.

Fuel is injected into the combustion chamber from a fuel injection valve (not shown), and the amount of injection is determined by an engine control electronic control unit (E) according to the operating state of the engine 1.
CU) 100.

Exhaust gas generated by burning fuel in the combustion chamber is exhausted to an exhaust pipe (exhaust passage) 5 where the exhaust gas is discharged.
After passing through the turbine 2b, the high-temperature activated NOx catalyst 6,
The gas passes through the low-temperature activated NOx catalyst 7 and is discharged to the atmosphere via a muffler (not shown). The high-temperature activated NOx catalyst 6 and the low-temperature activated NOx catalyst 7 are coaxially arranged in series.

In the exhaust pipe 5, between the turbine 2b and the high-temperature active NOx catalyst 6, an output signal corresponding to the temperature of the exhaust gas flowing into the high-temperature active NOx catalyst 6 (hereinafter referred to as "input gas") is output to the ECU 100. The incoming gas temperature sensor 8 is attached.

Further, in the exhaust pipe 5, downstream of the inlet gas temperature sensor 8 and immediately upstream of the high-temperature active NOx catalyst 6, when the high-temperature active NOx catalyst 6 and the low-temperature active NOx catalyst 7 reduce NOx, Is provided with a reducing agent supply device (reducing agent injection means) 10 for supplying a necessary reducing agent.
In this embodiment, light oil which is the fuel of the diesel engine 1 is used as the reducing agent.

The reducing agent supply device 10 includes a supply pump 11
, An injection nozzle 12 and an electromagnetic valve 13 as main components. The supply pump 11 pumps up light oil stored in the fuel tank 14 of the diesel engine 1 and sends it to the injection nozzle 12 through the fuel pipe 15. The supply pump 11 includes a drive circuit section 16 that varies a drive voltage of a drive motor (not shown) of the supply pump 11. The drive circuit section 16 changes the magnitude of the drive voltage to change the supply pump 11. It is possible to change the magnitude of the pressure of the light oil pumped from.

The drive circuit section 16 is controlled by the ECU 100, whereby the operation and stop of the supply pump 11 and the control of the light oil pressure by the drive voltage are performed.
Basically, the supply pump 11 is constantly operated.

The solenoid valve 13 is controlled to open and close by the ECU 100. When the solenoid valve 13 is open, light oil pressurized by the supply pump 11 is supplied to the injection nozzle 12, and when the solenoid valve 13 is closed, fuel oil is supplied. Since the pipe 15 is shut off, light oil is not supplied to the injection nozzle 12.

The injection nozzle 12 has its injection center arranged on the extension of the central axis of the high-temperature active NOx catalyst 6 and the low-temperature active NOx catalyst 7, and the light oil pressurized by the supply pump 11 is supplied to the solenoid valve 13. When the valve is opened, the fuel is injected from the injection nozzle 12 toward the high-temperature activated NOx catalyst 6. The injection nozzle 12 has a pressure of light oil (hereinafter, referred to as “injection pressure”) that is injected from the injection nozzle 12 according to a pressure of light oil supplied to the injection nozzle 12 (hereinafter, referred to as “supply pressure”). Adopt a type of nozzle that changes. In the injection nozzle 12, the injection pressure increases as the supply pressure increases.

Thus, in the reducing agent supply device 10, by changing the drive voltage in the drive circuit section 16, the magnitude of the pressure of the light oil pumped from the supply pump 11 (that is, the pressure of the light oil supplied to the injection nozzle 12) is reduced. ) Can be changed, and therefore, the injection pressure of light oil injected from the injection nozzle 12 can be changed.

The ECU 100 comprises 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 basic control such as fuel injection amount control of the engine 1, in this embodiment, control of the reducing agent supply device 10 and the like are performed.

For these controls, an input signal from the accelerator opening sensor 21 and an input signal from the crank angle sensor 22 are input to the input ports of the ECU 100. The accelerator opening sensor 21 outputs an output voltage proportional to the accelerator opening to the ECU 100, and the ECU 100 calculates an engine load based on the output signal of the accelerator opening sensor 21. The crank angle sensor 22 outputs an output pulse to the ECU 100 every time the crankshaft rotates by a certain angle, and the ECU 100 calculates the engine speed based on the output pulse. The operating state of the engine is determined based on the engine load and the engine speed.

Each of the high-temperature activated NOx catalyst 6 and the low-temperature activated NOx catalyst 7 is composed of a storage-reduction NOx catalyst. The storage reduction type NOx catalyst (hereinafter simply referred to as NOx catalyst) uses, for example, alumina (Al ₂ O ₃ ) as a carrier,
On this carrier, for example, potassium K, sodium Na, lithium Li, alkali metal such as cesium Cs, barium Ba, at least one selected from alkaline earths such as calcium Ca, lanthanum La, and rare earths such as yttrium Y , And a noble metal such as platinum Pt.

This NOx catalyst absorbs NOx when the air-fuel ratio of the inflowing exhaust gas (hereinafter referred to as exhaust air-fuel ratio) is lean, and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases. Performs the absorption and release action. Here, the exhaust air-fuel ratio means the ratio of the sum of the amount of air supplied to the exhaust passage, the engine combustion chamber, the intake passage and the like upstream of the NOx catalyst to the sum of the fuel (hydrocarbon). I do. Therefore, when no fuel, reducing agent, or air is supplied into the exhaust passage upstream of the NOx catalyst, the exhaust air-fuel ratio matches the air-fuel ratio of the air-fuel mixture in the engine combustion chamber.

It is considered that the absorption and release of the NOx catalyst is performed by a mechanism as shown in FIG. Hereinafter, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier,
The same mechanism is obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.

First, when the air-fuel ratio of the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases,
As shown in FIG. 2A, oxygen O ₂ adheres to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ . On the other hand, NO contained in the inflowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of the platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ).

[0047] Then, NO ₂ generated while being oxidized on the platinum Pt and is absorbed in the NOx catalyst bonding with the barium oxide BaO, 2 nitrate as shown in (A) ions NO ₃ ^- in And diffuses into the NOx catalyst in the form. In this way, NOx is absorbed in the NOx catalyst.

As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NOx absorption capacity of the NOx catalyst is not saturated, NO ₂ is absorbed in the NOx catalyst and nitrate ions NO ₃ ⁻ Is generated.

On the other hand, when the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, the oxygen concentration in the inflowing exhaust gas decreases, so that the amount of generated NO ₂ decreases and the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and nitrate ions N in the NOx catalyst
O ₃ ^- is released from the NOx catalyst in the form of NO ₂ or NO. That is, when the oxygen concentration in the inflowing exhaust gas decreases, the N
NOx will be released from the Ox catalyst.

On the other hand, at this time, HC, CO
Is oxidized by reacting with oxygen O ₂ ^- or O ^2- on platinum Pt. In addition, NO ₂ or NO released from the NOx catalyst due to a decrease in the oxygen concentration in the inflowing exhaust gas is shown in FIG.
As shown in (B), it reacts with unburned HC and CO to be reduced to N ₂ .

[0051] That is, HC in the inflowing exhaust gas, CO, first oxygen O ₂ on the platinum Pt ^- or O ^2- immediately be reacted with oxidized, then the platinum Pt on the oxygen O ₂ ^- or O ^2- If HC and CO still remain after consumption, this H
C, NOx discharged from the released NOx, the engine from the NOx catalyst by CO is made to reduction to N _2.

In this way, NO _{2 is} deposited on the surface of platinum Pt.
Alternatively, when NO is no longer present, NO ₂ or NO is released one after another from the NOx catalyst, and is further reduced to N ₂ . Thus, NOx from the NOx catalyst is released and reduced to N ₂ within a short period of time when the exhaust air-fuel ratio to the stoichiometric air-fuel ratio or rich air-fuel ratio.

As described above, when the exhaust air-fuel ratio becomes lean, NOx is absorbed by the NOx catalyst, and when the exhaust air-fuel ratio is set to the stoichiometric air-fuel ratio or rich air-fuel ratio, NOx is released from the NOx catalyst in a short time, and N ₂ Is reduced to Therefore, emission of NOx into the atmosphere can be prevented.

By the way, in the case of a diesel engine,
Since combustion is performed in a much leaner region than the stoichiometric ratio (the stoichiometric air-fuel ratio, A / F = 13 to 14), the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is very lean under a normal engine operating condition. NOx in the exhaust gas is absorbed by the NOx catalyst, and the amount of NOx released from the NOx catalyst is extremely small.

In the case of a gasoline engine, the air-fuel ratio of the exhaust gas is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio by changing the mixture supplied to the combustion chamber to a stoichiometric or rich air-fuel ratio, and the oxygen concentration in the exhaust gas is increased. And N
Although NOx absorbed by the Ox catalyst can be released, in the case of a diesel engine, if the air-fuel mixture supplied to the combustion chamber is made stoichiometric or rich air-fuel ratio, soot is generated during combustion. Yes, cannot be adopted.

Therefore, in a diesel engine, N
At a predetermined timing before the NOx absorption capacity of the Ox catalyst is saturated, it is necessary to supply a reducing agent into the exhaust gas to reduce the oxygen concentration in the exhaust gas, and release and reduce the NOx absorbed by the NOx catalyst. is there.

For this reason, in this embodiment, the ECU 1
00, the supply condition of the reducing agent is calculated from the history of the operating state of the diesel engine 1, and the operation of the reducing agent supply device 10 is basically controlled based on the supply condition to supply the reducing agent into the exhaust gas. Then, the oxygen concentration in the exhaust gas flowing into the high-temperature activated NOx catalyst 6 and the low-temperature activated NOx catalyst 7 is reduced, and the N2 absorbed by these NOx catalysts 6 and 7 is reduced.
Ox is the release, so that reduced to N _2. Here, the supply conditions of the reducing agent refer to the supply pressure (and, consequently, the injection pressure), the supply period, and the supply interval of the reducing agent (light oil in this embodiment), in other words, the supply of the reducing agent. It is nothing but quantity.

In the following description, the supply condition of the reducing agent obtained by calculating from the history of the operating state of the diesel engine 1 as described above is referred to as a basic supply condition. The supply pressure, the injection pressure, the supply period, and the supply interval are referred to as a basic supply pressure, a basic injection pressure, a basic supply period, and a basic supply interval, respectively.

Therefore, in this embodiment, when the electromagnetic valve 13 is closed and light oil is not being injected from the injection nozzle 12, NOx in the exhaust gas is high-temperature activated N
Absorbed by the Ox catalyst 6 or the low-temperature activated NOx catalyst 7,
The solenoid valve 13 is open and the exhaust pipe 5
When light oil is being injected into the inside, the NOx catalysts 6, 7
Absorbed NOx is released, it will be reduced to N ₂ in.

By the way, in this exhaust gas purifying apparatus, a high-temperature activated NOx catalyst 6 and a low-temperature activated NOx catalyst 7
Are arranged in series in order to obtain a high NOx purification rate in a wide temperature range.

FIG. 3 shows the NOx purification temperature characteristics when the high-temperature active NOx catalyst 6 or the low-temperature active NOx catalyst 7 is used alone. N of high temperature activated NOx catalyst 6
As shown by the square mark (□) in FIG. 3, the Ox purification temperature characteristic shows a substantially constant extremely high NOx purification rate when the input gas temperature is equal to or higher than T1, and the NOx purification rate when the input gas temperature is lower than T1. Decreases rapidly.

The NOx purification temperature characteristic of the low-temperature activation type NOx catalyst 7 shows the maximum NOx purification rate near the gas inlet temperature T1, as shown by the black circle mark (●) in FIG. No matter whether it is high or high, the NOx purification rate decreases.

More specifically, when the incoming gas temperature is lower than T1, the NOx purification rate of the low-temperature activated NOx catalyst 7 is larger than the NOx purification rate of the high-temperature activated NOx catalyst 6, and Is higher than T1, the NOx purification rate of the high-temperature activated NOx catalyst 6 is larger than the NOx purification rate of the low-temperature activated NOx catalyst 7.

When the high-temperature active type NOx catalyst 6 and the low-temperature active type NOx catalyst 7 are arranged in series and the supply of the reducing agent is performed in accordance with the basic supply conditions in the entire active temperature range, the NOx purification temperature characteristics at that time As shown by a white circle (浄化) in FIG. 3, the NOx purification rate when the input gas temperature is lower than T1 becomes smaller than the NOx purification rate when the low-temperature active NOx catalyst 7 is used alone. . The reason is that a part of the supplied reducing agent is consumed by the high-temperature activated NOx catalyst 6 disposed on the upstream side, and the required amount of the reducing agent is supplied to the low-temperature activated NOx catalyst 7 disposed on the downstream side. This is because supply cannot be performed as described above.

Therefore, in the exhaust gas purifying apparatus of this embodiment, in order to supply a required amount of reducing agent to the low-temperature activated NOx catalyst 7 in order to improve the NOx purification rate when the input gas temperature is lower than T1, Only when the incoming gas temperature is lower than T1, the supply pressure is increased from the basic supply pressure, and the injection pressure of light oil injected from the injection nozzle 12 is increased from the basic injection pressure. When the injection pressure is increased from the basic injection pressure, the penetration force of the light oil injected from the injection nozzle 12 increases, so that the amount of the light oil consumed by the high-temperature activated NOx catalyst 6 can be reduced, and as a result, Furthermore, the amount of light oil supplied to the low-temperature activated NOx catalyst 7 can be increased.

It should be noted that how much the supply pressure when the incoming gas temperature is lower than T1 is increased with respect to the basic supply pressure is as follows.
An experiment is performed in advance, and a supply pressure or an increase rate optimal for improving the NOx purification rate is set based on the experiment result.

At that time, it is preferable to set in consideration of the relationship with the exhaust gas flow rate of the diesel engine 1. That is, the light oil injected from the injection nozzle 12 is less likely to slip through the high-temperature active NOx catalyst 6 when the flow rate of the exhaust gas is low (in other words, when the engine speed is low).
When the exhaust gas flow rate is high (in other words, when the engine speed is high), it is easier to slip through the high-temperature activated NOx catalyst 6, and therefore, when the engine speed is low, the increase in the supply pressure with respect to the basic supply pressure is large. However, when the engine speed is high, it is preferable to set the degree of increase of the supply pressure to the basic supply pressure to be small.

Therefore, in this embodiment, an experiment is conducted in advance, and the supply pressure increase rate β most effective for improving the low-temperature NOx purification rate is determined in relation to the exhaust gas flow rate (engine speed N). (Hereinafter, this map is referred to as an “engine speed / supply pressure increase rate map”) and stored in the ROM of the ECU 100 in advance. FIG. 4 is an example of an engine speed / supply pressure increase rate map.

When the supply pressure of light oil to the injection nozzle 12 is controlled to be increased and the injection pressure is controlled to be increased when the incoming gas temperature is lower than T1, the NOx purification temperature characteristic becomes as shown in FIG.
Is improved as shown by a triangle mark (△). That is, when the input gas temperature is lower than T1, the NOx purification rate of this exhaust gas purification device is slightly higher than the NOx purification rate when the low-temperature active NOx catalyst 7 is used alone, and when the input gas temperature becomes T1 or higher. The NOx purification rate of this exhaust gas purification device is the same as the NOx purification rate when the high-temperature activation type NOx catalyst 6 is used alone.
It is almost equal to the purification rate. That is, in this exhaust gas purification apparatus, high NO in a wide temperature range from a low temperature to a high temperature.
x Purification rate can be obtained.

The reason why the high-temperature activated NOx catalyst 6 is arranged upstream of the low-temperature activated NOx catalyst 7 in the exhaust gas purifying apparatus according to the first embodiment is as follows. The amount of NOx emitted from the diesel engine 1 is low when the exhaust gas temperature is low such as low engine speed and low load when the engine operation state is low, and high when the exhaust gas temperature is high such as when the engine operation state is high rotation and high load. Sometimes more. This is also true for a diesel engine having an exhaust gas recirculation device (hereinafter abbreviated as EGR). That is, in a low-rotation, low-load operation state, the exhaust gas recirculation amount (EGR amount) can be increased to reduce the NOx emission amount. However, in a high-rotation, high-load operation state, increasing the EGR amount causes smoke. Such as EG
The NOx emission cannot be reduced by increasing the R amount. Therefore, the amount of the reducing agent required to reduce NOx is required to be higher at high exhaust gas temperatures where NOx emissions increase.

Here, suppose that the low-temperature activated NOx catalyst 7 is disposed upstream of the high-temperature activated NOx catalyst 6 when the exhaust gas is at a high temperature. In order to reduce NOx, not only a high supply pressure for injecting a large amount of reducing agent is required, but also an increase in the supply pressure for slipping through the low-temperature active NOx catalyst 7 is required. In addition, the amount of increase in the supply pressure at a high temperature must be extremely increased. As a result, the amount of reducing agent injected at high temperature increases,
Fuel economy will deteriorate. By arranging the high-temperature activated NOx catalyst 6 upstream of the low-temperature activated NOx catalyst 7, such a problem can be avoided.

This means that the low-temperature active NOx catalyst 7 can be arranged upstream of the high-temperature active NOx catalyst 6 when it is not necessary to consider the deterioration of fuel efficiency and thermal deterioration. .

Next, an injection pressure control routine in this embodiment will be described with reference to FIG. The flowchart comprising the steps constituting this routine is described in ECU1.
00 is stored in the ROM of the CPU 100, and all the processes in each step of the flowchart are executed by the CPU of the ECU 100.

<Step 101> First, the ECU 100
In step 101, the high-temperature activated NOx catalyst 6
Alternatively, it is determined whether or not a condition for supplying the reducing agent to the low-temperature active NOx catalyst 7 (hereinafter, referred to as an exhaust system fuel supply condition) is satisfied. The exhaust system fuel supply condition is that the catalyst temperature of the high-temperature active NOx catalyst 6 or the low-temperature active NOx catalyst 7 falls within the active temperature range. If the catalyst temperature is not within the activation temperature range, NOx cannot be purified even if the reducing agent is supplied, so that there is no need to supply the reducing agent. Therefore, the ECU 100 executes Step 1
If a negative determination is made in 01, this routine ends.
In this embodiment, the incoming gas temperature detected by the incoming gas temperature sensor 8 is used as the catalyst temperature.

<Step 102> If it is determined in step 101 that the exhaust system fuel supply condition is satisfied (that is, if the determination is affirmative), the ECU 100 proceeds to step 102, in which the operation state of the diesel engine 1 is determined. From the history, basic supply conditions (basic supply pressure P0, basic supply period t, basic supply interval S) of light oil by the reducing agent supply device 10 are calculated.

<Step 103> Next, the ECU 100
Proceeds to step 103, and determines whether or not the incoming gas temperature T detected by the incoming gas temperature sensor 8 is higher than a threshold value T1.

<Step 104> If an affirmative determination is made in step 103, the ECU 100 proceeds to step 104 and sets the supply pressure P of light oil to the injection nozzle 12 to the basic supply pressure P0 obtained in step 102 (P = P0). That is, when the incoming gas temperature T is higher than T1, the supply condition of the light oil to the exhaust system remains the basic supply condition.

<Step 105> Next, the ECU 100
Proceeds to step 105, executes injection of light oil into the exhaust pipe 5 by the reducing agent supply device 10 according to the basic supply condition, and ends the routine. When executing the supply of light oil to the exhaust system, the ECU 100 calculates the drive voltage of the supply pump 11 corresponding to the basic supply pressure P0, controls the operation of the supply pump 11 based on the drive voltage, and controls the basic supply pressure. The opening / closing control of the electromagnetic valve 13 according to the period t and the basic supply interval S is executed.

<Step 106> On the other hand, step 103
If a negative determination is made in step 1, the ECU 100 proceeds to step 1
In step 06, the engine speed is read, and the supply pressure increase rate β according to the engine speed is calculated with reference to the engine speed / supply pressure increase rate map.

<Step 107> Next, the ECU 100
Proceeds to step 107, and multiplies the basic supply pressure P0 by the supply pressure increase rate β obtained in step 106,
Let the supply pressure P of light oil to the injection nozzle 12 be (P = P0
× β). That is, when the incoming gas temperature T is equal to or lower than T1, the supply condition of the light oil to the exhaust system is defined as the supply pressure P = P0 × β,
A basic supply period t and a basic supply interval S are set.

Next, the ECU 100 proceeds from step 107 to step 105 and executes injection of light oil into the exhaust pipe 5 by the reducing agent supply device 10 according to the supply conditions. At this time, the supply pressure P = P0 ×
A drive voltage of the supply pump 11 corresponding to β is calculated, and operation control of the supply pump 11 is executed based on the drive voltage,
In addition, opening / closing control of the electromagnetic valve 13 according to the basic supply period t and the basic supply interval S is executed.

In this embodiment, when the incoming gas temperature T is equal to or lower than T1, the supply conditions of the light oil to the exhaust system are as follows: supply pressure P = P0 × β, basic supply period t, basic supply interval S
Therefore, as the injection pressure of the light oil injected from the injection nozzle 12 increases, the total supply amount of the light oil increases as compared with the basic supply condition, but the increase corresponds to the high-temperature active NOx catalyst 6. Thus, an appropriate amount of light oil with almost no excess or deficiency is supplied to the low-temperature NOx catalyst 7.

However, when it is necessary to finely control the supply amount of the reducing agent when the incoming gas temperature T is equal to or lower than T1, not only the supply pressure is increased but also the supply pressure is increased. It is also possible to correct for the period and the supply interval.

In the first embodiment, the supply pump 11 (including the drive circuit section 16), the injection nozzle 12, and step 103 in the injection pressure control routine
The ECU 100 executes steps 107 through 107 to implement the reducing agent pressure control means in the present invention.

[Second Embodiment] Next, FIGS.
A second embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to FIG. In the exhaust gas purifying apparatus of the first embodiment described above, two NOx storage reduction catalysts are arranged in series in the exhaust pipe 5. However, in the exhaust gas purifying apparatus of the second embodiment, FIG. As shown in
There is only one NOx storage reduction catalyst provided in the exhaust pipe 5. Storage reduction type NO in the second embodiment
As the x catalyst, a high-temperature activated NOx catalyst 6, a low-temperature activated Nx catalyst
Although any of the Ox catalysts 7 can be employed, the following description will be given by taking as an example a case where the low-temperature activation type NOx catalyst 7 is employed.

In the exhaust gas purifying apparatus according to the second embodiment, a nozzle called a swirl nozzle is used as the injection nozzle 12 of the reducing agent supply device (reducing agent injection means) 10. The swirl nozzle is a nozzle that can change the injection angle and the injection mode of the fuel injected from the nozzle according to the magnitude of the supply pressure.

The schematic configuration of the swirl nozzle will be described with reference to FIG. 7. A fuel reservoir chamber 12b is formed inside the nozzle body 12a, and the fuel reservoir chamber 12b
Is fixed to the nozzle core 12c. On the base side of the nozzle body 12a, there is provided a valve chamber 12d connected to the fuel storage chamber 12b, and a fuel pipe 15 is connected to the valve chamber 12d. The valve chamber 12d is provided with a check valve 12e that allows fuel to flow from the fuel pipe 15 to the valve chamber 12d and prevents fuel from flowing in the opposite direction. The check valve 12e is urged in the valve closing direction by a spring 12f, and is set to open when the fuel pressure supplied from the fuel pipe 15 becomes equal to or higher than a predetermined valve opening pressure.

A fuel passage 12g is provided between the inner peripheral surface of the nozzle body 12a and the outer peripheral surface of the nozzle core 12c, and the fuel flowing from the fuel pipe 15 into the fuel storage chamber 12b passes through the fuel passage 12g to the nozzle core 12c. Flows forward. Further, a plurality of slits 12h for forming swirl are provided on the tapered surface at the tip portion of the nozzle core 12c, and a swirl flow is generated by the slit 12h when the fuel flows out of the fuel passage 12 to the front of the nozzle core 12c. The fuel delivered to the front of the nozzle core 12c is supplied to the injection hole 1 provided at the tip of the nozzle body 12a.
Injected from 2i.

In the injection nozzle 12 composed of the swirl nozzle configured as described above, when the supply pressure of the light oil supplied through the fuel pipe 15 becomes higher than the valve opening pressure, the light oil is injected from the injection hole 12i. However, there is an injection characteristic in which the injection angle and the injection form change depending on the magnitude of the supply pressure. More specifically, when the supply pressure is low, the intensity of the swirl flow is weak, so that the injection angle of the light oil injected from the injection hole is small and solid, as shown in FIG. 8A. On the other hand, when the supply pressure becomes very large, the intensity of the swirl flow becomes very strong.
As shown in (B), the injection angle of the light oil injected from the injection hole 12i increases, and the light oil is injected in a hollow cone shape.

In the exhaust gas purifying apparatus for an internal combustion engine according to the second embodiment, since the configuration of the apparatus other than the above-described configuration is completely the same as that of the above-described first embodiment, the same reference numerals are given to the same aspects. And the description is omitted.

In the second embodiment, by utilizing the injection characteristics of the swirl nozzle constituting the injection nozzle 12 and changing the injection angle and the injection mode in accordance with the exhaust gas temperature, the low-temperature active NOx catalyst 7 The NOx purification rate is improved. Hereinafter, this will be described in detail.

As described above, the low-temperature activation type NOx catalyst 7 has an active temperature range, and when the temperature falls outside the active temperature range, the NOx purification rate is greatly reduced even if the temperature is low or high. On the other hand, the low-temperature activated NOx catalyst 7
Is provided, the catalyst temperature is highest at the center of the flow and decreases as approaching the outer periphery as shown in FIG. 9, as described above.

Therefore, when the temperature of the exhaust gas flowing into the low-temperature active type NOx catalyst 7 (the incoming gas temperature in this embodiment) is a temperature corresponding to the lower limit region in the active temperature region as shown in FIG. In the vicinity of the central portion of the low-temperature active NOx catalyst 7, the catalyst temperature falls within the active temperature range and a predetermined NOx purification rate is exhibited. Below this value, the NOx purification rate may drop extremely, and the NOx purification rate of the low-temperature activated NOx catalyst 7 as a whole may decrease.

Therefore, when the incoming gas temperature is in the lower limit region, the supply pressure to the injection nozzle 12 is lower than usual in order to concentrate and supply the reducing agent (light oil) near the center of the low-temperature active type NOx catalyst 7. Set to a predetermined lower limit pressure Pmin,
The injection angle of the injection nozzle 12 is reduced so as to perform solid injection.

When light oil is injected in this way, NOx reduction and purification are efficiently performed in the vicinity of the central portion of the low-temperature active type NOx catalyst 7 which is within the active temperature range. At this time, since light oil is not supplied to the vicinity of the outer peripheral portion of the low-temperature activated NOx catalyst 7 which may be out of the activation temperature range, the release of NOx absorbed in the vicinity of the outer peripheral portion is suppressed. can do. In addition, it is possible to suppress HC deterioration near the outer peripheral portion.

On the other hand, when the temperature of the incoming gas is a temperature corresponding to the upper limit of the active temperature range of the low-temperature active NOx catalyst 7 as shown in FIG.
Although the catalyst temperature falls within the active temperature range near the outer peripheral portion and exhibits a predetermined NOx purification rate, the catalyst temperature further rises near the central portion of the low-temperature active type NOx catalyst 7 due to the catalytic action. The NOx purification rate may exceed the upper limit and decrease extremely, and the NOx purification rate of the low-temperature active NOx catalyst 7 as a whole may decrease.

Therefore, when the incoming gas temperature is in the upper limit region, the supply pressure to the injection nozzle 12 is set higher than usual so that the reducing agent (light oil) is concentrated and supplied to the vicinity of the outer periphery of the low-temperature active NOx catalyst 7. A high predetermined upper limit pressure Pmax is set, the injection angle of the injection nozzle 12 is increased, and the injection is performed in a hollow cone shape.

When light oil is injected in this manner, NOx reduction and purification are efficiently performed in the vicinity of the outer peripheral portion within the active temperature range in the low-temperature active type NOx catalyst 7. At this time, since light oil is not supplied to the vicinity of the central portion of the low-temperature activated NOx catalyst 7 where there is a possibility of deviating from the activation temperature range, thermal degradation in the vicinity of the central portion due to catalytic reaction can be suppressed.

Next, an injection pressure control routine according to the second embodiment will be described with reference to FIG. The flowchart consisting of the steps constituting this routine is EC
The processing in each step of the flowchart is stored in the ROM of U100, and is entirely executed by the CPU of ECU100.

<Step 201> First, the ECU 100
In step 201, the low-temperature activated NOx catalyst 7
It is determined whether or not a condition for supplying a reducing agent to the fuel cell (hereinafter referred to as an exhaust system fuel supply condition) is satisfied. The exhaust system fuel supply condition is that the catalyst temperature of the low-temperature activation type NOx catalyst 7 is within the activation temperature range. If the catalyst temperature is not within the activation temperature range, NOx cannot be purified even if the reducing agent is supplied, so that there is no need to supply the reducing agent. Therefore, if a negative determination is made in step 201, the ECU 100 ends this routine. In this embodiment, the incoming gas temperature detected by the incoming gas temperature sensor 8 is used as the catalyst temperature.

<Step 202> If it is determined in step 201 that the exhaust system fuel supply condition is satisfied (that is, if an affirmative determination is made), the ECU 100 proceeds to step 202 where the operation state of the diesel engine 1 is determined. From the history, basic supply conditions (basic supply pressure P0, basic supply period t, basic supply interval S) of light oil by the reducing agent supply device 10 are calculated.

<Step 203> Next, the ECU 100
Goes to step 203, and the incoming gas temperature T detected by the incoming gas temperature sensor 8 is changed to a lower limit region (T ≦ Tmin), an upper limit region (T ≧ Tmax), and an intermediate temperature region (Tmin <T <T).
max)).

<Step 204> If it is determined in step 203 that the incoming gas temperature T belongs to the lower limit region (T ≦ Tmin), the ECU 100 proceeds to step 204 and increases the supply pressure P of the light oil to the injection nozzle 12. Lower limit pressure P
min (P = Pmin). That is, if the incoming gas temperature T is Tmin
The supply conditions of the light oil to the exhaust system when the pressure is lower than the above are the supply pressure Pmin, the basic supply period t, and the basic supply interval S.
Note that the lower limit pressure Pmin is an optimum value obtained by an experiment in advance, and is a value lower than the basic supply pressure P0. This lower limit pressure Pmin is stored in the ROM of the ECU 100 in advance.

<Step 205> Next, the ECU 100
Proceeds to step 205, executes injection of light oil into the exhaust pipe 5 by the reducing agent supply device 10 according to the supply conditions, and ends the routine. When executing the supply of light oil to the exhaust system, the ECU 100 determines that the supply pressure P = Pmin
, And controls the operation of the supply pump 11 based on the drive voltage. The solenoid valve 13 according to the basic supply period t and the basic supply interval S
The opening / closing control is performed.

<Step 206> On the other hand, step 203
In the case where the incoming gas temperature T is in an intermediate temperature range (Tmin <T <
Tmax), the ECU 100
Goes to step 206, where the supply pressure P of the light oil to the injection nozzle 12 is set to the basic supply pressure P0 obtained in step 202.
(P = P0). That is, when the incoming gas temperature T is in the intermediate temperature range (Tmin <T <Tmax), the supply condition of light oil to the exhaust system remains the basic supply condition.

Next, the ECU 100 proceeds from step 206 to step 205, executes injection of light oil into the exhaust pipe 5 by the reducing agent supply device 10 in accordance with the supply conditions, and ends this routine. When executing the supply of light oil to the exhaust system, the ECU 100 calculates the drive voltage of the supply pump 11 corresponding to the basic supply pressure P0, controls the operation of the supply pump 11 based on the drive voltage, and controls the basic supply pressure. The opening / closing control of the electromagnetic valve 13 according to the period t and the basic supply interval S is executed.

<Step 207> Step 203
If it is determined that the incoming gas temperature T belongs to the upper limit region (T ≧ Tmax) in
Proceeding to 7, the supply pressure P of light oil to the injection nozzle 12 is set to the upper limit pressure Pmax (P = Pmax). That is, when the incoming gas temperature T is higher than Tmax, the conditions for supplying light oil to the exhaust system are as follows:
The supply pressure Pmax, the basic supply period t, and the basic supply interval S are obtained. Note that the upper limit pressure Pmax is an optimum value obtained by an experiment in advance, and is a value higher than the basic supply pressure P0. This upper limit pressure Pmax is stored in the ROM of the ECU 100 in advance.

Next, the ECU 100 proceeds to step 205, executes injection of light oil into the exhaust pipe 5 by the reducing agent supply device 10 in accordance with the supply conditions, and ends this routine. Note that when supplying light oil to the exhaust system,
U100 calculates the drive voltage of the supply pump 11 corresponding to the supply pressure P = Pmax, controls the operation of the supply pump 11 based on the drive voltage, and controls the electromagnetic force corresponding to the basic supply period t and the basic supply interval S. The opening and closing control of the valve 13 is executed.

In the second embodiment, the supply pump 11 (including the drive circuit 16), the injection nozzle 12, and the step 203 in the injection pressure control routine are executed.
The injection angle control means of the present invention is realized by the ECU 100 executing the steps from 207 to 207.

[Third Embodiment] Next, a third embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS. The exhaust gas purification apparatus according to the third embodiment can be said to be a combination of the first embodiment and the second embodiment.

As shown in FIG. 12, the device configuration of the exhaust gas purification device according to the third embodiment is basically the same as the device configuration of the exhaust gas purification device according to the first embodiment. The same reference numerals in the drawings denote the same parts as in the exhaust gas purification apparatus of the embodiment, and a description thereof will be omitted.

The exhaust gas purifying apparatus according to the third embodiment is different from the first embodiment only in the structure of the exhaust gas purifying apparatus, except that the injection nozzle 12 according to the third embodiment is different from the second embodiment. It is configured of a swirl nozzle similarly to the injection nozzle 12 in the embodiment.

As described above, the swirl nozzle can change the injection angle and the injection form of the fuel injected from the nozzle in accordance with the magnitude of the supply pressure. But not
The injection pressure of light oil injected from the nozzle changes according to the magnitude of the supply pressure.

That is, when the supply pressure is small, the injection pressure is small, the injection angle is small, and the injection is solid. However, as the supply pressure increases, the injection pressure gradually increases, and the injection angle gradually increases. The injection mode gradually changes from a solid state to a hollow cone state.

The exhaust gas purifying apparatus according to the third embodiment utilizes the injection characteristics of the swirl nozzle constituting the injection nozzle 12 and changes the injection pressure, the injection angle, and the injection mode in accordance with the exhaust gas temperature. By maximizing the NOx purifying ability of the high-temperature activated NOx catalyst 6 and the low-temperature activated NOx catalyst 7, the NOx purification rate of the exhaust purification device is improved. Hereinafter, this will be described with reference to the input gas temperature / supply pressure increase rate map shown in FIG. 13 and the flowchart shown in FIG.

The map shown in FIG. 13 shows the temperature (inlet gas temperature) of the exhaust gas flowing into the high-temperature active NOx catalyst 6 and the temperature of the injection nozzle 1 in the exhaust gas purifying apparatus of the third embodiment.
2 is an inlet gas temperature / supply pressure increase rate map showing a relationship of an increase rate (supply pressure increase rate) of supply pressure of light oil supplied to No. 2;

In the input gas temperature / supply pressure increase rate map, the magnitude relation between the input gas temperatures T3, T4, T5 and the supply pressure increase rates β1, β2, β3, β4 are as follows. Inlet gas temperature: T3 <T4 <T5 Supply pressure increase rate: β1 <1 <β2 <β3 <β4

The supply condition of the exhaust system fuel injection in the third embodiment will be described with reference to the input gas temperature / supply pressure increase rate map. Note that the input gas temperature / supply pressure increase rate map is stored in the ROM of the ECU 100 in advance.

(1) When the incoming gas temperature T is lower than the threshold value T3 (T <T3) When the incoming gas temperature T is lower than the threshold value T3 in the third embodiment, the input is performed in the first embodiment. Gas temperature T
Is lower than the threshold value T1. That is, when the incoming gas temperature T is lower than the threshold value T3, a necessary amount of the reducing agent is supplied to the low-temperature active NOx catalyst 7 so that the low-temperature active NOx catalyst 7 disposed on the downstream side can efficiently purify NOx. Is supplied, the injection pressure of the light oil injected from the injection nozzle 12 is increased from the basic injection pressure. For this purpose, the supply pressure of light oil to the injection nozzle 12 is increased from the basic supply pressure. At that time, the supply pressure increase rate is set in the range of β3 to β4 according to the engine speed.

(2) When the incoming gas temperature T is equal to or higher than the threshold value T3 (T ≧ T3) In the third embodiment, when the incoming gas temperature T is equal to or higher than the threshold value T3, the input gas temperature in the second embodiment is changed. Is in the activation temperature range. However, in the second embodiment, the light oil supply condition is controlled in order to improve the NOx purification rate of the low-temperature activation type NOx catalyst 7. However, in the third embodiment, the high-temperature activation catalyst disposed on the upstream side is controlled. The supply condition of light oil is controlled to improve the NOx purification rate of the type NOx catalyst 6.

(2-1) When the incoming gas temperature T is T3 ≦ T ≦ T4 When the incoming gas temperature T is T3 ≦ T ≦ T4, in the second embodiment, the incoming gas temperature T is not more than Tmin (T ≤ Tmin). At this time, the high-temperature activated NOx catalyst 6
The supply pressure to the injection nozzle 12 is reduced from the basic supply pressure in order to concentrate the supply of light oil near the center of the nozzle.
In the third embodiment, to set the supply pressure at this time, a supply pressure increase rate β1 smaller than 1 is adopted,
The product obtained by multiplying the basic supply pressure by the supply pressure increase rate β1 was defined as the supply pressure.

(2-2) When the incoming gas temperature T is T ≧ T5 When the incoming gas temperature T is T ≧ T5, in the second embodiment, the incoming gas temperature T is higher than Tmax (T ≧ Tmax). Corresponds to the case. At this time, the supply pressure to the injection nozzle 12 is increased from the basic supply pressure in order to concentrate and supply light oil to the vicinity of the outer periphery of the high-temperature active NOx catalyst 6. Third
In the embodiment of the present invention, the supply pressure at this time is set by using a supply pressure increase rate β2 greater than 1 and less than β3, and obtained by multiplying the basic supply pressure by the supply pressure increase rate β2. The product was the supply pressure.

(2-3) When the incoming gas temperature T is T4 <T <T5 When the incoming gas temperature T is T4 <T <T5, in the second embodiment, the incoming gas temperature T is Tmin <T < This corresponds to the case of Tmax. At this time, the supply pressure to the injection nozzle 12 is set as the basic supply pressure.

Next, an injection pressure control routine according to the third embodiment will be described with reference to FIG. The flowchart consisting of the steps constituting this routine is EC
The processing in each step of the flowchart is stored in the ROM of U100, and is entirely executed by the CPU of ECU100.

<Step 301> First, the ECU 100
In step 301, the high-temperature activated NOx catalyst 6
Alternatively, it is determined whether or not a condition for supplying the reducing agent to the low-temperature active NOx catalyst 7 (hereinafter, referred to as an exhaust system fuel supply condition) is satisfied. The exhaust system fuel supply condition is that the catalyst temperature of the high-temperature active NOx catalyst 6 or the low-temperature active NOx catalyst 7 falls within the active temperature range. Step 30
If a negative determination is made in step 1, the ECU 100 ends this routine. In this embodiment, the incoming gas temperature detected by the incoming gas temperature sensor 8 is used as the catalyst temperature.

<Step 302> If an affirmative determination is made in step 301, the ECU 100 proceeds to step 3
In step 02, the basic supply conditions (basic supply pressure P0, basic supply period t, basic supply interval S) of light oil by the reducing agent supply device 10 are calculated from the history of the operating state of the diesel engine 1.

<Step 303> Next, the ECU 100
Proceeds to step 303, and determines whether or not the incoming gas temperature T detected by the incoming gas temperature sensor 8 is lower than a threshold value T3.

<Step 304> If an affirmative determination is made in step 303, the ECU 100 proceeds to step 304, reads the engine speed, and calculates the supply pressure increase rate β corresponding to the engine speed by the ratio of engine speed / supply. The calculation is performed with reference to the pressure increase rate map. In the engine speed / supply pressure increase rate map according to the third embodiment, it is assumed that the supply pressure increase rate β changes between β3 and β4.

<Step 305> Next, the ECU 100
Goes to step 305, and multiplies the product obtained by multiplying the basic supply pressure P0 by the supply pressure increase rate β obtained in step 304,
Let the supply pressure P of light oil to the injection nozzle 12 be (P = P0
× β). That is, when the incoming gas temperature T is lower than T3, the supply condition of light oil to the exhaust system is determined as follows: supply pressure P = P0 × β,
A basic supply period t and a basic supply interval S are set. However, the supply pressure increase rate β is a value in the range of β3 to β4.

<Step 306> Next, the ECU 100
Proceeds to step 306 to execute injection of light oil into the exhaust pipe 5 by the reducing agent supply device 10 according to the supply conditions. At this time, the ECU 100 determines that the supply pressure P = P0
A drive voltage of the supply pump 11 corresponding to × β is calculated, operation control of the supply pump 11 is executed based on the drive voltage, and opening and closing of the solenoid valve 13 according to the basic supply period t and the basic supply interval S. Execute control.

<Step 307> If a negative determination is made in step 303, the ECU 100 proceeds to step 307, in which the incoming gas temperature T detected by the incoming gas temperature sensor 8 becomes
It is determined to which of T3 ≦ T ≦ T4, T4 <T <T5, and T ≧ T5 the region belongs.

<Step 308> If it is determined in step 307 that the incoming gas temperature T belongs to the temperature range (T3 ≦ T ≦ T4), the ECU 100 proceeds to step 308 and sets the supply pressure increase rate to β1. The product obtained by multiplying the basic supply pressure P0 by the supply pressure increase rate β1 is defined as the supply pressure P of light oil to the injection nozzle 12 (P = P0 × β
1). That is, the supply condition of the light oil to the exhaust system when the incoming gas temperature T belongs to the above-mentioned temperature range is defined as supply pressure P = P
0 × β1, a basic supply period t, and a basic supply interval S. still,
This supply pressure increase rate β1 is smaller than 1 and therefore
The supply pressure P becomes smaller than the basic supply pressure P0.

Next, the ECU 100 proceeds to step 306, executes injection of light oil into the exhaust pipe 5 by the reducing agent supply device 10 in accordance with the supply conditions, and ends the present routine. Note that when supplying light oil to the exhaust system,
U100 calculates the drive voltage of the supply pump 11 corresponding to the supply pressure P = P0 × β1, controls the operation of the supply pump 11 based on the drive voltage, and responds to the basic supply period t and the basic supply interval S. The opening / closing control of the solenoid valve 13 is executed.

<Step 309> On the other hand, step 307
In this case, the incoming gas temperature T falls within the aforementioned temperature range (T4 <T <
If it is determined that the time belongs to T5), the ECU 100
Proceeding to step 309, the supply pressure P of light oil to the injection nozzle 12 is set to the basic supply pressure P0 determined in step 302 (P = P0). That is, the supply condition of the light oil to the exhaust system when the incoming gas temperature T belongs to the above temperature range remains the basic supply condition.

Next, the ECU 100 proceeds to step 306, executes injection of light oil into the exhaust pipe 5 by the reducing agent supply device 10 in accordance with the basic supply conditions, and ends this routine. Note that when supplying light oil to the exhaust system,
U100 is a supply pump 1 corresponding to the basic supply pressure P0.
1 is calculated, the operation of the supply pump 11 is controlled based on the drive voltage, and the opening / closing control of the solenoid valve 13 according to the basic supply period t and the basic supply interval S is executed.

<Step 310> Step 307
In the above, the input gas temperature T is within the above-mentioned temperature range (T ≧ T5).
If the ECU 100 determines that the oil pressure belongs to the fuel oil injection rate, the ECU 100 proceeds to step 310, sets the supply pressure increase rate to β2, and multiplies the basic supply pressure P0 by the supply pressure increase rate β2 to calculate the product (P = P0 ×
β2). In other words, the supply condition of light oil to the exhaust system when the incoming gas temperature T belongs to the above temperature range is determined by the supply pressure P =
P0 × β2, basic supply period t, and basic supply interval S.
Note that the supply pressure increase rate β2 is larger than 1, and therefore, the supply pressure P becomes larger than the basic supply pressure P0.

Next, the ECU 100 proceeds to step 306, executes injection of light oil into the exhaust pipe 5 by the reducing agent supply device 10 according to the supply conditions, and ends the present routine. Note that when supplying light oil to the exhaust system,
U100 calculates the drive voltage of the supply pump 11 corresponding to the supply pressure P = P × β2, controls the operation of the supply pump 11 based on the drive voltage, and responds to the basic supply period t and the basic supply interval S. The opening / closing control of the solenoid valve 13 is executed.

[Other Embodiments] In the above-described embodiment, the present invention is applied to a diesel engine. However, the present invention can be applied to a lean-burn gasoline engine.

In each of the above embodiments, the high-temperature active N
Ox catalyst 6 and low-temperature activated NOx catalyst 7
Although these catalysts were composed of Ox catalysts, these catalysts were selectively reduced NOx
It can also be composed of a catalyst. When the NOx catalyst is a selective reduction type NOx catalyst, the same operation and effect as in the case of the storage reduction type NOx catalyst are exerted.

[0140]

According to the exhaust gas purifying apparatus for an internal combustion engine according to the first invention of the present application, a high-temperature activated NOx catalyst and a low-temperature activated NOx catalyst provided in series in an exhaust passage of an internal combustion engine capable of lean combustion. A reducing agent injection means for injecting a reducing agent into the exhaust passage from the upstream of the NOx catalyst provided on the upstream side of the NOx catalyst toward the NOx catalyst; and an exhaust gas temperature of the internal combustion engine or the NOx Reducing agent pressure control means for controlling the pressure of the reducing agent injected into the exhaust passage from the reducing agent injection means according to the catalyst temperature of one of the catalyst NOx catalyst,
An excellent effect that a high NOx purification rate can be obtained in a wide temperature range because a required amount of reducing agent can be supplied to the NOx catalyst when purifying NOx with the NOx catalyst arranged on the downstream side. Is played.

Further, according to the exhaust gas purifying apparatus for an internal combustion engine according to the second invention of the present application, a NOx catalyst provided in an exhaust passage of an internal combustion engine capable of performing lean combustion, and a NOx catalyst disposed upstream of the NOx catalyst. Reducing agent injection means for injecting a reducing agent into the exhaust passage toward the exhaust gas, and reducing agent injected from the reducing agent injection device into the exhaust passage according to the exhaust gas temperature of the internal combustion engine or the catalyst temperature of the NOx catalyst. Injection angle control means for controlling the injection angle of the
The reducing agent can be injected into a portion having a high NOx purification rate according to the exhaust gas temperature or the catalyst temperature, and as a result, an excellent effect that NOx can be efficiently purified can be obtained.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
It is a schematic structure figure of an embodiment.

FIG. 2 is a diagram for explaining the NOx absorbing / releasing action of a NOx storage reduction catalyst.

FIG. 3 is a diagram showing NOx purification temperature characteristics of a NOx catalyst.

FIG. 4 is an engine speed / supply pressure increase rate map used in the exhaust gas purification apparatus of the first embodiment.

FIG. 5 is an injection pressure control routine in the exhaust gas purification apparatus according to the first embodiment.

FIG. 6 shows a second embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention.
It is a schematic structure figure of an embodiment.

FIG. 7 is a diagram showing a schematic configuration of a swirl nozzle used in the exhaust gas purification apparatus of the second embodiment.

FIG. 8 is a view showing an injection mode of the swirl nozzle.

FIG. 9 is a diagram showing a temperature distribution in a NOx catalyst.

FIG. 10 is a view showing a NOx purification temperature characteristic of a NOx catalyst in the exhaust purification device of the second embodiment.

FIG. 11 is an injection pressure control routine in the exhaust gas purification apparatus according to the second embodiment.

FIG. 12 is a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to a third embodiment of the present invention.

FIG. 13 is an inlet gas temperature / supply pressure increase rate map used in the exhaust gas purification apparatus of the third embodiment.

FIG. 14 is an injection pressure control routine in the exhaust gas purification apparatus according to the third embodiment.

[Explanation of symbols]

Reference Signs List 1 diesel engine (internal combustion engine) 5 exhaust pipe (exhaust passage) 6 high-temperature activated NOx catalyst 7 low-temperature activated NOx catalyst 10 reducing agent supply device (reducing agent injection means) 11 supply pump (reducing agent pressure control means, injection angle control) Means) 12 injection nozzle (reducing agent pressure control means, injection angle control means) 100 ECU (reducing agent pressure control means, injection angle control means)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G091 AA10 AA12 AA17 AA18 AA28 AB06 CA18 EA07 EA17 EA18 FB10 GB02W GB03W GB04W GB05W GB06W GB10X HA08

Claims (6)

[Claims] 1. A high-temperature activated NOx catalyst and a low-temperature activated NOx catalyst provided in series in an exhaust passage of an internal combustion engine capable of lean burn, and a NOx catalyst provided upstream of a NOx catalyst provided on an upstream side of the NOx catalyst. Reducing agent injection means for injecting a reducing agent into the exhaust passage toward the NOx catalyst; and the reducing agent according to the exhaust gas temperature of the internal combustion engine or the catalyst temperature of one of the NOx catalysts. An exhaust gas purification device for an internal combustion engine, comprising: a reducing agent pressure control unit that controls a pressure of a reducing agent injected from an injection unit into an exhaust passage. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the high-temperature activated NOx catalyst is provided upstream of the low-temperature activated NOx catalyst. 3. The reducing agent pressure control means controls the pressure of the reducing agent to be higher when the exhaust gas temperature of the internal combustion engine or the catalyst temperature of the NOx catalyst is lower than when it is high. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, characterized in that: 4. A NOx catalyst provided in an exhaust passage of an internal combustion engine capable of lean combustion, a reducing agent injection means for injecting a reducing agent into the exhaust passage from upstream of the NOx catalyst toward the NOx catalyst, Injection angle control means for controlling an injection angle of a reducing agent injected from the reducing agent injection means into an exhaust passage according to an exhaust gas temperature of the internal combustion engine or a catalyst temperature of the NOx catalyst. An exhaust gas purification device for an internal combustion engine. 5. The injection angle control means controls the injection angle to be small when the temperature of the exhaust gas of the internal combustion engine or the catalyst temperature of the NOx catalyst is lower than a predetermined temperature, and controls the temperature of the exhaust gas of the internal combustion engine or the NOx. The exhaust gas purifying apparatus for an internal combustion engine according to claim 4, wherein the injection angle is controlled to be large when the catalyst temperature of the catalyst is higher than a predetermined temperature. 6. When the injection angle is controlled to be small by the injection angle control means, the reducing agent is solidly injected from the reducing agent injection means, and when the injection angle is controlled to be large, the reducing agent is injected in a hollow cone shape. The exhaust gas purifying apparatus for an internal combustion engine according to claim 5, wherein: