JP2000170526A - Exhaust gas purification device for diesel engine - Google Patents

Abstract

(57) Abstract: In an exhaust gas purifying apparatus for a diesel engine, emission of particulates and NO _X can be constantly suppressed while avoiding deterioration of fuel efficiency as much as possible. In the middle of the exhaust passage 1 A diesel engine, from the upstream side to the flow of the exhaust gas, NO _X catalyst 2,
An oxidation catalyst 3 and a particulate filter 4 for collecting fine particles in exhaust gas are provided in series in this order.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine exhaust gas purifying apparatus suitable for use in an automobile.

[0002]

2. Description of the Related Art Conventionally, in diesel engines mounted on automobiles and the like, particulate matter (PM: Particulate Matte) in exhaust gas discharged to the atmosphere through an exhaust passage of the diesel engine is known.
er) and various technologies for reducing NO _x (nitrogen oxide) have been developed. For example, Japanese Patent Application Laid-Open No. Hei 1-318715 discloses that, as shown in FIG. 3, a regeneration oxidation catalyst (hereinafter simply referred to as an oxidation catalyst) 3A is provided in an exhaust pipe 1, and PM is collected downstream of the exhaust gas flow. diesel particulate filter use (DPF: diesel particulate filter) 4 and by arranging a technique capable of carrying out the reduction of PM and NO _X at the same time is disclosed (hereinafter, sometimes this system called DPF system) .

[0003] The main component of PM is soot, that is, C (carbon) and HC (hydrocarbon). However, as the load on the engine increases, the PM is exposed to high-temperature exhaust gas and HC is vaporized. C comes to occupy most of the components of PM. Therefore, hereinafter, when referring to PM, it indicates C (carbon). Now, with the structure shown in FIG. 3, in the oxidation catalyst 3A, NO (nitrogen monoxide) in the exhaust gas is oxidized to generate NO ₂ (nitrogen dioxide) (2NO + O ₂ →).
2NO ₂ ) On the other hand, in the downstream DPF 4, PM in the exhaust gas is collected.

In the DPF 4, NO ₂ generated by the oxidation catalyst 3A reacts with PM collected by the DPF 4, NO ₂ is decomposed into N ₂ , and PM is oxidized to CO _2. (2NO ₂ + 2C → N ₂ + 2C
O ₂ ), PM and NO _x are reduced (toxification) at the same time. Here, NO ₂ has a higher function as an oxidizing agent than NO, and can oxidize PM with low activation energy (ie, burn PM at a relatively low temperature). For this reason, the oxidation catalyst 3A is installed on the upstream side with respect to the exhaust gas flow of the DPF 4, and NO ₂ is generated by the oxidation catalyst 3A. Thus, by utilizing the temperature of the exhaust gas itself, NO ₂ and PM react with each other to reduce PM and NO _X.

Further, in addition to the above publication of the DPF system, as shown in FIG. 4, the exhaust pipe 1, DE-NO _X catalyst (hereinafter, simply NO: _X catalyst) and 2, the exhaust gas flows downstream interposed an oxidation catalyst 3B on the side, the exhaust pipe 1 further light oil addition device 5 to the exhaust gas stream upstream of the NO _X catalyst 2
And attached to, NO _X a technique for reducing it has been proposed in the exhaust gas (hereinafter, sometimes the system of NO _X catalyst system).

[0006] This NO_XThe catalyst 2 reacts with NO in the exhaust gas.
Promote the reaction with HC to reduce NO to N_TwoDecompose into
(NO + HC → N_Two+ CO_Two+ H_TwoO). Only
In diesel engines, most of the exhaust gas (for example,
80% to 90%) is occupied by NO, while exhaust gas
HC is very small. Therefore, simply NO _X
Simply installing the catalyst 2 in the exhaust pipe 1 will cause a shortage of HC.
The reduction of NO cannot be achieved sufficiently. So, NO_XTouch
A gas oil addition device 5 is installed on the upstream side of the exhaust gas flow of the medium 2,
An electronic control unit (ECU) 10 controls the light oil adding device.
Control unit 5 to control a predetermined amount of light oil mainly composed of HC (eg,
For example, 2-5% of main fuel)
It is structured as follows. This allows the exhaust gas
NO to compensate for HC shortage_XUse catalyst 2 to reduce NO
I am trying to do it.

Further, among the light oil injected into the exhaust gas by the light oil addition device 5 (HC), the HC became surplus not react with NO in NO _X catalyst 2, the oxidation catalyst 3
It is oxidized by B and discharged as H ₂ O or CO ₂ (detoxified and discharged) (HC + O
₂ → H ₂ O + CO ₂ ). In the reaction formula used in the description of the NO _X catalyst system, for the sake of convenience, C ₁₆ H ₃₄ , C ₁₆ H _35, etc., which are the main components of light oil, are collectively referred to as HC [unspecified number of H
(Hydrogen) and C (carbon). Therefore, these reaction formulas simply indicate what is the substance that causes the reaction and the substance that is generated by the reaction. In these reaction formulas, the numbers of the elements do not match on the left side and the right side.

[0008]

However, such a conventional technique has the following problems. First,
In the DPF system shown in FIG. 3, by reacting PM deposited in the DPF 4 with NO _{2 in} exhaust gas,
Although these PM and NO ₂ are reduced, the amount of PM contained in the exhaust gas changes depending on the combustion state of the engine. Therefore, depending on the combustion state of the engine, D
The amount of PM flowing into the PF4 is reduced, the NO ₂ is also a trace amount is reduced to N ₂ by reaction with PM accordingly. Therefore, depending on the combustion state of the engine, the effect of reducing NO _x (NO ₂ ) in exhaust gas may be reduced.

On the other hand, in the above-mentioned NO _X catalyst system, it is necessary to add light oil to the exhaust gas in order to reduce NO _X in the exhaust gas. Problem. Further, in this NO _X catalyst systems, there is a problem that can not be removed PM in the exhaust gas.

Further, light oil (H
Among C), since the oxidation catalyst 3B for oxidizing the one which does not react with NO in NO _X catalyst 2 in H ₂ O and CO ₂ are required, there is also a problem that the equipment becomes large. The present invention has been in view conceived of the above problems, which make it possible to significantly reduce emissions of PM and NO _X, and an object thereof is to provide an exhaust gas purifying device for a diesel engine.

[0011]

A solution for the] Therefore, in the exhaust gas purification device for a diesel engine of the present invention according to claim 1, in the exhaust passage, NO _X catalyst, a particulate (PM) of the oxidation catalyst and the exhaust gas A particulate filter for trapping is provided in series in this order from the upstream side with respect to the flow of the exhaust gas.

[0012] Thus, the PM in the exhaust gas in the particulate filter are collected, the oxidized the NO _X (e.g. NO ₂₎ and the PM reacts with the oxidation catalyst, N
O ₂ is decomposed into N ₂ and C (carbon), which is the main component of PM,
Is oxidized to CO ₂ , thus suppressing the emission of NO _X and PM. When the amount of PM trapped by the particulate filter is small, that is, when PM sufficient for NO ₂ is not present in the particulate filter, HC (hydrocarbon) and NO _{X are} converted by the NO _X catalyst. Reacts with NO to decompose NO _X into N ₂ . The above N
O _X catalyst HC became surplus in is oxidized by the oxidation catalyst provided downstream of the NO _X catalyst is discharged as H ₂ O and CO _2. Therefore, the emission of PM and NO _X is always suppressed.

A conventional DPF system (a system in which a particulate filter and an oxidation catalyst are arranged in series) and a conventional NO _X catalyst system (a system in which a NO _X catalyst and an oxidation catalyst are arranged in series) are simply connected in series. When arranged, each system requires an oxidation catalyst, and a total of two oxidation catalysts are required. On the other hand, in the exhaust gas purifying apparatus for a diesel engine of the present invention, a system is efficiently constructed. cage, only equipped with a single oxidation catalyst, it is possible to combine the functions of such a conventional DPF systems and NO _X catalyst system.

Further, removal of PM deposited on the particulate filter (regeneration process of the particulate filter)
Includes the PM, because it is carried out by oxidation with enhanced NO _X in oxidation function is oxidized by the oxidation catalyst, it is possible to combust the particulates at relatively low temperatures. Further, in the exhaust gas purifying apparatus for a diesel engine according to the present invention, an additive for reducing NO _X in the exhaust gas is injected into the exhaust passage upstream of the flow of the exhaust gas from the NO _X catalyst. And a deposition amount detection device for detecting the amount of PM deposited on the particulate filter is provided, based on detection information from the deposition amount detection device, when the PM deposition amount is equal to or less than a predetermined value. , The additive is sprayed from the addition device.

[0015] Thus, it is possible in accordance with the amount of deposition of PM in the particulate filter, are additive from the additive devices injection, effectively reduces the NO _X.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an exhaust gas purifying apparatus for a diesel engine as an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. As shown in FIG. 1, the exhaust gas purifying apparatus for a diesel engine according to the present embodiment is interposed in an exhaust pipe (exhaust passage) 1, and particulates (PM: Particulate) in exhaust gas flowing through the exhaust pipe 1.
It is intended to reduce the Matter) and NO _X.

[0017] Then, the exhaust gas purifying device, the NO _X catalyst 2, and the oxidation catalyst 3, a diesel particulate filter for PM trapping (DPF: Diesel Pariculate Filt
er) 4 are provided in series in this order from the upstream side with respect to the flow of the exhaust gas. Further, on the upstream side of the NO _X catalyst 2, the light oil addition device (dosing device) 5 is provided between the oxidation catalyst 3 DPF 4, PM accumulation amount detecting device (accumulation amount detecting device) 6, is attached respectively ing.

The diesel engine of the present embodiment
In the exhaust gas purifying device of the present invention, a sufficient amount of PM is contained in the DPF 4.
Is present, the oxidation catalyst 3 removes NO in the exhaust gas.
NO _TwoAnd this NO in the DPF 4_TwoAnd PM
(C: carbon) to react with NO_TwoTo N_TwoBroken down into
PM to CO_TwoIt is designed to oxidize. In other words, this
When there is a sufficient amount of PM in DPF4 as shown in
Exhaust gas is mainly purified by the oxidation catalyst 3 and the DPF 4
It has become so.

On the other hand, if it is determined that the amount of PM present in the DPF 4 has decreased to a predetermined amount (predetermined value) or less based on the detection information from the PM accumulation amount detection device 6, the ECU 10
By operating the light oil addition device 5, the light oil (HC) is supplied to the exhaust gas. This gives N
O _X catalyst 2 in the NO and HC in the exhaust gas reacts, N
O is decomposed into N ₂ , and the excess HC
Is oxidized by the oxidation catalyst 3 to be discharged as H ₂ O or CO ₂ . That is, in this case, NO
_The exhaust gas is purified by the _X catalyst 2 and the oxidation catalyst 3.

During this time, when it is detected that more PM than the predetermined amount has accumulated in the DPF 4 again, E
The supply of light oil (HC) by the light oil addition device 5 is stopped by the CU 10, and the exhaust gas is purified again by the oxidation catalyst 3 and the DPF 4. Here, the oxidation catalyst 3
Is alumina Al ₂ O ₃ was coated on a honeycomb-shaped substrate as a catalyst supporting layer are those of carrying platinum Pt or palladium Pd or the like to the catalyst supporting layer, a coating of alumina Al ₂ O ₃ is an exhaust This is for roughening the surface so as to increase the contact area with the gas.

[0021] Then, to the oxidation catalyst 3, the exhaust gas mainly composed of NO flows through the NO _X catalyst 2, the reaction is mainly promoted as the oxidation catalyst 3, the following reaction formula (1) It is supposed to be. 2NO + O ₂ → 2NO ₂ (1) That is, NO ₂ has a higher function as an oxidizing agent than NO, and can oxidize PM with low activation energy. Therefore, NO in the exhaust gas by the oxidation catalyst 3 is oxidized into NO _2, this NO _2, which is the PM collected on DPF4 the downstream side of the oxidation catalyst 3 so as to oxidize (burn) It is.

The DPF 4 is a ceramic honeycomb filter. In the DPF 4, exhaust gas passages whose upstream ends are closed and exhaust gas passages whose downstream ends are closed are alternately arranged. I have. For this reason, the exhaust gas flowing into the DPF 4 first flows into the exhaust gas passage whose upstream end is opened, and the downstream end is opened from the porous wall provided between the exhaust gas passage and the adjacent exhaust gas passage. The exhaust gas flows into the exhaust gas passage and flows downstream, and in this process, the PM in the exhaust gas collides with or adsorbs to the wall surface and is collected.

Here, when a relatively large amount of PM is deposited on the DPF 4, light oil is not injected by the light oil addition device 5, so NO in the exhaust gas is reduced to N by the NO _X catalyst 2. It is not decomposed into ₂ (the function of the NO _X catalyst 2 will be described later). Therefore, in the oxidation catalyst 3, the reaction of the above-mentioned reaction formula (1) is promoted, and the exhaust gas containing a relatively large amount of NO ₂ flows into the DPF 4. Thus, the DPF 4 promotes an oxidation reaction represented by the following reaction formula (2).

2NO ₂ + 2C → N ₂ + 2CO ₂ (2) That is, the PM deposited on the DPF ₄ is oxidized (combusted) by NO ₂ to convert the PM into CO ₂ and convert the PM into CO _2.
And NO _x (NO ₂ ) in exhaust gas
Is decomposed into N ₂ , so that the exhaust gas can be purified (the PM and NO _X emissions are reduced).

It should be noted that PM deposited on such a DPF 4
The removal of DPF4 also has a DPF4 regeneration processing function of preventing the PM from being excessively deposited on the DPF4 and making it impossible to collect PM, and maintaining the performance of the DPF4. For this reason, N necessary for PM removal (DPF4 regeneration processing)
The oxidation catalyst 3 that generates O ₂ is also referred to as a regeneration oxidation catalyst.

By the way, the effect of reducing NO _X by the reaction shown in the reaction formula (2) is due to the P deposited on the DPF 4.
It varies depending on the amount of M. If a certain amount of PM is not deposited on the DPF 4, NO _X
Almost no reduction effect. Therefore, in the exhaust gas purifying apparatus according to the present embodiment, P is set between the oxidation catalyst 3 and the DPF 4.
An M deposition amount detection device 6 is provided.
PM accumulated in DPF 4 based on detection information from
If it is determined that the amount of
According to the control command 10, light oil is injected from the light oil addition device 5 into the exhaust gas.

As a result, the PM less than a predetermined amount is stored in the DPF 4.
If you have not only deposited only sentence of reduced reduction of the NO _X in the DPF 4, it has become to compensate for the reduction of the NO _X by NO _X catalyst 2. Where N
O _X catalyst 2 is the same as that described in the prior art. That is, it promotes the reaction between NO and HC in the exhaust gas to decompose NO into N ₂ . However, as described above, in a diesel engine, most of the exhaust gas is occupied by NO, whereas the amount of H contained in the exhaust gas is high.
C is trace. Therefore, the amount of H required for the decomposition of NO
The light oil addition device 5 converts light oil (additive) mainly composed of HC such as C ₁₆ H ₃₄ or C ₁₆ H ₃₅ into the exhaust gas flow upstream of the NO _X catalyst 2 so that C is contained in the exhaust gas. Injects into exhaust gas.

[0028] At this time, the reaction occurring in the NO _X catalyst 2,
For example, the following reaction formulas (3) and (4) are obtained. _{98NO + 2C 16 H 34 → 49N} 2 + 32CO 2 + 34H 2 O ··· (3) 198NO + 4C 16 H 35 → 99N 2 + 64CO 2 + 70H 2 O ·· (4) Thus, in the case where no sufficient PM is deposited DPF4 even, NO by the action of the NO _X catalyst 2,
Converted to harmless substances of N ₂ , CO ₂ and H ₂ O, NO
_X can be reduced.

Further, the light oil addition device 5 converts the exhaust gas into exhaust gas.
NO in the injected light oil (HC)_XWith NO at catalyst 2
The excess HC that did not react was NO_Xcatalyst
Oxidation catalyst 3 installed downstream of exhaust gas flow 2
It is oxidized and made harmless. That is,
In this case, [light oil (C
₁₆H₃₄, C ₁₆H₃₅) Is injected), the oxidation catalyst
In No. 3, NO in the injected light oil _XNO with catalyst 2
Those which do not respond are, for example, the following reaction formulas (5) and (6)
Oxidation reactions such as
You.

2C₁₆H₃₄+ 49O_Two→ 32CO_Two+ 34H_TwoO ... (5) 4C₁₆H₃₅+ 99O_Two→ 64CO_Two+ 70H_TwoO (6) NO_XN generated by decomposition of NO in the catalyst 2_Two
Is oxidized by the oxidation catalyst 3 to form NO or NO_TwoNO such as
_XThere is no such thing as becoming. This is N_TwoIs O
NO by reacting with (oxygen)_XTo be a big activity
Energy is required, and diesel engines
Exhaust gas temperature (for example, about 250 ° C on average,
However, at about 600 ° C.), the action of the oxidation catalyst 3 causes N
_TwoIs NO _XDoes not change. Furthermore, N_TwoIs NO
_XThe reaction rate (chemical reaction rate) that changes to
Therefore, in a short time when the exhaust gas flows through the oxidation catalyst 3,
Such a reaction hardly occurs.

[0031] Then, while this way is injected from the light oil addition device 5 light petroleum (HC), thereby reducing the NO _X, D
When the PM accumulation amount detection device 6 detects that a predetermined amount of PM has been accumulated again on the PF 4, the supply of light oil from the light oil addition device 5 is stopped, and the action of the oxidation catalyst 3 and the DPF 4 again causes By reacting NO _X and PM, these harmful substances are decomposed.

Here, the light oil adding device 5 is an injector whose opening and closing is controlled by an ECU (control means) 10. The injection amount of the light oil of the light oil adding device 5 is determined by the ECU 10 based on the engine speed Ne and the effective pressure Pe. It is to be decided. Incidentally, effective pressure Pe is calculated from the information of the engine rotational speed Ne and the accelerator opening theta _A.
Here, the engine speed Ne and the accelerator opening θ _A are:
Input is made to the ECU 10 from a crank angle sensor and an accelerator position sensor (not shown).

Further, each of the PM accumulation amount detecting devices 6
Exhaust gas temperature sensor and exhaust gas pressure sensor not shown
And the exhaust gas temperature T_GAnd exhaust gas pressure
Force P _GIs detected and output to the ECU 10.
You. That is, as the PM accumulates in the DPF 4, the DP
The exhaust resistance of F4 increases, and accordingly, the exhaust pipe 1
The exhaust gas upstream of the DPF 4, that is, in the vicinity of the PM accumulation amount detection device 6
Gas pressure P_GWill also be higher. Therefore, the exhaust gas pressure P
_GIs the predetermined pressure (threshold) P₀Higher or lower
When the amount of PM deposited on the DPF 4 is_X
ECU 10 determines whether or not it is larger than a predetermined amount that can reduce
Can be determined.

The ECU 10 sets the predetermined pressure P ₀ to:
Exhaust gas temperature T _G input from the PM accumulation amount detection device 6
And an intake air flow input from a flow meter (not shown). This exhaust gas pressure P _G is other amount of PM deposited in DPF 4, to change in accordance with the exhaust gas amount and exhaust gas temperature, the exhaust gas temperature and the exhaust gas amount for a given pressure P ₀ The correction is made. Accordingly, in comparison with a predetermined pressure P ₀ and the exhaust gas pressure P _G, it is offset the influence of other factors PM accumulation amount, whether the amount of PM deposited on DPF4 more than a predetermined amount, exactly That is, it can be determined.

In this exhaust gas purifying apparatus, the exhaust gas
Pressure P₀Instead of compensating for
Intake air input from the flow meter installed in the
Approximate by correction by amount. The predetermined pressure P₀Complement
Instead of correcting, the exhaust gas pressure P_GIs the exhaust gas temperature T _G
And the intake air flow.

Since the exhaust gas purifying apparatus according to one embodiment of the present invention is configured as described above, the operation mode is switched according to, for example, a flowchart shown in FIG. First, in step S10, a predetermined pressure (threshold) P ₀ of the exhaust gas is determined according to the exhaust gas temperature _TG detected by the PM accumulation amount detection device 6 and the intake air amount input from a flow meter (not shown). Correction is made,
Proceed to step S20.

[0037] Then, in step S20, the PM deposition amount of DPF 4, whether it exceeds a predetermined amount of DPF 4 is capable of exhibiting NO _x reduction function is determined by the exhaust gas pressure P _G. In other words, the exhaust gas pressure P _G is a predetermined pressure P ₀
If it is equal to or less than the predetermined value, it is determined that the DPF 4 cannot exert the NO _x reduction function because the PM accumulation amount of the DPF 4 is equal to or less than the predetermined amount, and the process proceeds to step S30. Then, step S30
Then, the light oil addition device 5 performs the light oil addition. In this case, reduction of the NO _x is promoted by the reaction and the gas oil (HC) NO in NO _X catalyst 2.

On the other hand, if the exhaust gas pressure P _G is higher than the predetermined pressure P ₀ , it is determined that the DPF 4 can exhibit the NO _x reduction function because the PM deposition amount of the DPF 4 exceeds the predetermined amount. If light oil addition has been performed according to 5, the light oil addition is stopped in step S40. In this case, NO ₂ and PM react in the DPF 4 to decompose and oxidize these substances, thereby purifying the exhaust gas.

With the above operation, the exhaust gas purifying apparatus for a diesel engine according to the present invention has the following advantages. In other words, if the deposition number of PM than the predetermined amount in DPF 4, reduction of the NO _x is performed by the DPF 4. In addition, only when the DPF 4 cannot exhibit the NO _x reduction function because only the PM equal to or less than the predetermined amount is deposited on the DPF 4, the diesel fuel is added to the exhaust gas by the diesel oil adding device 5 and the NO _X catalyst is removed. 2 reduces NO _x . On the other hand, PM is always collected by the DPF 4.

Therefore, light oil is added to the exhaust gas.
While avoiding deterioration in fuel efficiency as much as possible
And NO_XHas the advantage that the emission of
You. And, by this, NO_XAnd total emissions of PM
Can be greatly reduced. Ma
In addition, the oxidation catalyst 3 contains HC originally contained in the exhaust gas.
And CO are oxidized and exhausted by gas oil addition device 5
NO in HC (light oil) injected into gas _XWith catalyst 2
HC that has not reacted with NO is oxidized. Therefore, HC
And also has the advantage of reducing CO emissions.
You.

To perform the DPF regeneration process, D
It is necessary to burn PM deposited on the PF. However, to burn PM, a considerably high temperature (for example, about 600 ° C.) is required, and a normal exhaust gas temperature (for a diesel engine, for example, 250 ° C.) ), PM cannot be burned. Therefore, a heater, a burner, and the like are generally required as a heating device. In contrast, according to the exhaust gas purification device for a diesel engine of the present invention, NO in the exhaust gas is oxidized to generate NO ₂ by the oxidation catalyst 3, a high NO ₂ of this oxidation function, DPF
By reacting the PM on the surface 4, the PM can be burned at the temperature of the exhaust gas itself.

Accordingly, there is an advantage that a heater or a burner as a heating device is not required, and a thermal load due to the regeneration process is reduced, and the life of the DPF 4 is extended. Further, when arranging the prior art DPF system (see FIG. 3) and the NO _X catalyst system (see FIG. 4) just in series, it becomes necessary one oxidation catalyst in the system, must have two oxidation catalysts become. In contrast, in the present exhaust gas purifying apparatus, efficiently and system is constructed, only equipped with a single oxidation catalyst 3, it is possible to combine the functions of such a conventional DPF systems and NO _X catalyst system . Therefore, there is also an advantage that the space for installing the exhaust gas purifying device can be reduced to save space.

The exhaust of the diesel engine of the present invention
The gas purification device is not limited to the above-described embodiment.
However, various modifications can be made. For example, on
In the above-described embodiment, the exhaust gas is detected by the PM deposition amount detection device 6.
The amount of PM deposited on the DPF 4 is
Although it is determined whether the amount is equal to or greater than the
No. 6_XYou may comprise by a sensor. in this case,
NO _XA sensor is provided downstream of the exhaust pipe 1 on the DPF 4 side.
NO_XNO from sensor_XDetection value and predetermined value C₁And the ratio
The operation of the light oil addition device 5 is controlled based on the comparison.

That is, when the detected NO _X value is higher than the predetermined value C _1, it is determined that the DPF 4 does not exhibit the NO _X reduction function because a sufficient amount of PM has not been deposited on the DPF 4, and light oil addition is performed. Light oil injection is performed by the device 5, and NO _x is reduced by the NO _x catalyst 2. Further, when the NO _X detection value is equal to or less than the predetermined value C _1, since the number of PM than the predetermined amount is accumulated in DPF 4 DPF
4 is judged to be exhibiting a sufficient NO _X reduction effect,
The injection of the light oil by the light oil adding device 5 is stopped.

The predetermined value C ₁ is corrected by subtracting the correction value α from the reference value C ₀ (predetermined value C ₁ = reference value C ₀ −correction value α). Here, the reference value C ₀ is a constant, and the correction value α is a reduction in NO _X due to light oil injection. The correction value α is determined by the ECU 10 based on, for example, a light oil injection amount or the like. That, NO _X detection value, other amount of PM deposited on the DPF 4,
Light oil is injected by the light oil adding device 5 (N
O _X by the catalyst 2 is reduced of the NO _X being performed) or not largely affected. Therefore, by correcting by subtracting the amount of decrease of the NO _X by diesel injection (correction value alpha) from the reference value C _0, to eliminate the influence of light oil injection, thereby, on the basis of the NO _X detection value, Thus, it is possible to accurately determine whether the amount of PM deposited on the DPF 4 is larger than a predetermined amount.

[0046]

As described in detail above, the book according to claim 1
According to the diesel engine exhaust gas purification apparatus of the invention
For example, the action of the particulate filter and the oxidation catalyst
No _XAnd fine particles (PM)
The emission of harmful substances can be suppressed, and
NO with sufficient filter and oxidation catalyst_XReduction effect
If no result is obtained, the oxidation catalyst and NO_XN with catalyst
O_XTo decompose NO_XEmissions can be reduced.

Therefore, the disadvantages of the conventional DPF system (a system in which a particulate filter and an oxidation catalyst are arranged in series) and the conventional NO _X catalyst system (a system in which a NO _X catalyst and an oxidation catalyst are arranged in series) are considered. They can complement each other and always maintain PM and NO _X
There is an advantage that the amount of emission of methane can be reduced. Thus, there is also an advantage that each total emission amount of NO _X and PM can be reduced.

Also, the conventional DPF system and the conventional NPF
O _X catalyst Arranging a system simply in series, become necessary one oxidation catalyst in the system, it will need two oxidation catalysts. In contrast, in the exhaust gas purification device for a diesel engine of the present invention, efficient system has been constructed, only equipped with a single oxidation catalyst, the function of such a conventional DPF systems and NO _X catalyst system You can have both. Therefore, there is an advantage that the space for installing the exhaust gas purifying device is reduced by the installation space of the oxidation catalyst, and the space can be saved.

According to the exhaust gas purifying apparatus for a diesel engine according to the second aspect of the present invention, there are the following advantages. In other words, if you have deposited many PM than the predetermined amount in the particulate filter, after having improved oxidation function it is oxidized by the oxidation catalyst the NO _x in the exhaust gas, the NO
It is possible to reduce NO _x by reacting _x and PM deposited on the particulate filter. The accelerator, if not deposited only a predetermined amount below the PM in the particulate filter is to inject the additive from the additive devices, the reaction of the NO _x in the exhaust gas with the additive, the NO _X catalyst Thus, NO _X can be reduced efficiently.
On the other hand, PM is always reduced by a particulate filter.

Therefore, there is an advantage that the emission of PM and NO _X can always be efficiently suppressed. As a result, there is an advantage that the total emission amount of NO _X and PM can be significantly reduced. Further, for example, in the case where diesel oil, which is the fuel of a diesel engine, is used as an additive, injection of diesel oil into exhaust gas is limited to when only a predetermined amount or less of PM is accumulated on a particulate filter. PM and NO while minimizing deterioration of fuel efficiency due to light oil injection.
There is an advantage that emission of _X can be suppressed.

The oxidation catalyst oxidizes HC and CO originally contained in the exhaust gas, and oxidizes additives that are not reacted by the NO _X catalyst among the additives injected into the exhaust gas by the addition device. Become Therefore, there is an advantage that discharge of HC, CO, and additives to the outside can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an exhaust gas purifying apparatus for a diesel engine as one embodiment of the present invention.

FIG. 2 is a flowchart showing switching control of an operation mode in the exhaust gas purifying apparatus for a diesel engine as one embodiment of the present invention.

FIG. 3 is a schematic diagram showing a configuration of a conventional DPF system.

FIG. 4 is a schematic diagram showing a configuration of a conventional NO _X catalyst system.

[Explanation of symbols]

First exhaust pipe (exhaust passage) 2 DE-NO _X catalyst (NO _X catalyst) 3 Play oxidation catalyst (oxidation catalyst) 4 DPF (diesel particulate filter) 5 light oil addition device (dosing device) 6 PM accumulation amount detecting device ( Deposition amount detection device) 10 ECU

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G090 AA02 AA06 BA01 CA01 DA03 DA12 DA18 DA20 EA02 3G091 AA02 AA18 AB02 AB05 AB13 BA07 BA14 BA15 BA19 BA31 CA18 DB10 DB13 EA00 EA01 EA03 EA05 EA07 EA17 EA31 GB01 FC01 GB01 GB10X GB16X HA07 HA09 HA15 HA36 HA37 HA38 HA47

Claims (2)

[Claims] To 1. A middle of the exhaust passage of a diesel engine, from the upstream side to the flow of the exhaust gas, NO _X catalyst, in series with the particulate filter above sequence for trapping oxidation catalyst and particulates in the exhaust gas An exhaust gas purification device for a diesel engine, which is provided. 2. An addition device capable of injecting an additive for reducing NO _X in the exhaust gas is provided upstream of the NO _X catalyst, and detects an amount of the fine particles deposited on the particulate filter. A deposit amount detection device that is configured to eject the additive from the addition device when the deposition amount of the fine particles is equal to or less than a predetermined value based on detection information from the deposition amount detection device. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein: