JP2000064827A - Exhaust emission control device for combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent catalyst poisoning by sulfur compound even when sulfur is contained in fuel and to effectively purify NOx. SOLUTION: In an exhaust gap purifying system of a diesel engine 1, NO in exhaust gas is oxidized into NO2 by an Ag-based catalyst within a first catalytic converter 15, and NO2 is reduced to N2 by a Pt-based catalyst within a second catalytic converter 16 to be purified. When a catalyst temperature within the first catalytic converter 15 enters a temperature range in which the Ag-based catalyst is easily poisoned by sulfur compound such as SO2 or SO3, CO is formed by expansion stroke fuel injection, an increase in EGR ratio and reduction of opening of a swirl valve. By this CO, the Ag-based catalyst within the first catalytic converter 15 is prevented from combining with sulfur compounds, catalyst poisoning is prevented and NOx is effectively purified.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas purifying apparatus for a combustion engine such as an engine.

[0002]

2. Description of the Related Art Generally, in a combustion engine, for example, an automobile engine, HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide) is contained in exhaust gas (combustion gas) generated by combustion of fuel. Etc. Air pollutants are included. Therefore, in order to purify the air pollutants in the exhaust gas, the exhaust passage that discharges the exhaust gas to the atmosphere is
A catalytic converter using an exhaust gas purifying catalyst is provided.
A three-way catalyst that can collectively purify C, CO, and NOx is widely used. This three-way catalyst oxidizes HC and CO to convert them into harmless H ₂ O (water) or CO ₂ (carbon dioxide), and also uses a part of HC as a reducing agent to reduce NOx and harmless. Change to N ₂ (nitrogen). Here, in order to effectively purify NOx with a three-way catalyst, it is necessary to make the O ₂ (oxygen) concentration in the exhaust gas relatively low in order to promote the reduction reaction.

By the way, in recent years, because of its high fuel efficiency, diesel engines are becoming popular as engines for small automobiles. However, in the case of diesel engines, fuel is normally burned in an O ₂ excess atmosphere. O ₂ concentration in exhaust gas becomes relatively high (eg 10%
that's all). Also in the gasoline engine for automobiles,
In recent years, in order to improve fuel efficiency, the air-fuel ratio of the air-fuel mixture is set to be considerably leaner than the theoretical air-fuel ratio (for example, the air-fuel ratio A / F is 22 or more) (lean burn is performed) at low load. Although a burn engine is widely used, even when lean burn is performed in such a lean burn engine, the O ₂ concentration in the exhaust gas becomes relatively high (for example, 4% or more). Therefore, in a diesel engine or a lean burn engine, if a three-way catalyst is used as an exhaust gas purifying catalyst, NOx cannot be sufficiently purified.

Therefore, in recent years, an exhaust gas purifying apparatus has been proposed in which, in a diesel engine or a lean burn engine, in addition to a catalytic converter for purifying HC and CO, a catalytic converter excellent in NOx purifying performance is provided. For example, the applicant of the present application filed Japanese Patent Application No. 10-8
No. 4,820, in particular, as a catalytic converter for purifying NOx, NO (nitrogen monoxide) in exhaust gas is first oxidized by an Ag-based catalyst (silver-based catalyst) to generate NO.
₂ is changed to (nitrogen dioxide), a further catalytic converter 2 step process structures such the NO ₂ or originally the NO ₂ present in the exhaust gas is reduced with Pt catalyst (platinum catalyst) is changed to N ₂ is suggesting.

[0005]

By the way, in general, the fuel, especially diesel oil which is a fuel for diesel engines, may contain a sulfur content, and in such a case, the sulfur content is oxidized to produce SO ₂ (dioxide). Sulfur) or SO ₃ (sulfur trioxide), which will be contained in the exhaust gas. On the other hand, the above-mentioned Ag-based catalyst used in a catalytic converter for purifying NOx has a problem that it is poisoned by a sulfur compound (sulfur component) such as SO ₂ or SO ₃ and its catalytic activity is lowered. That is, when a sulfur compound is contained in the exhaust gas, Ag in the catalyst is combined with the sulfur compound to form Ag ₂ SO ₄ , but Ag ₂ SO ₄ is NO.
This is because the catalytic activity for oxidizing NO to NO ₂ is extremely low.

Therefore, NO is converted to NO by using an Ag-based catalyst.
_It is difficult to use a catalytic converter that oxidizes to ₂ and reduces NO ₂ to N ₂ with a Pt-based catalyst when a fuel containing sulfur is likely to be used, for example, in a diesel engine. There's a problem. The present invention is
The present invention has been made in order to solve the above-mentioned conventional problems, and even when the fuel contains a sulfur content, it is possible to prevent catalyst poisoning due to a sulfur compound such as SO ₂ or SO ₃ , and to use NOx effectively. It is an object to be solved to provide an exhaust gas purifying apparatus for a combustion engine that can purify the exhaust gas.

[0007]

An exhaust gas purifying apparatus for a combustion engine according to the present invention, which has been made to solve the above problems, includes (a) a predetermined air pollutant (for example, NOx) contained in exhaust gas. In an exhaust gas purifying apparatus for a combustion engine in which a catalytic converter using an exhaust gas purifying catalyst that oxidizes or reduces is provided in an exhaust passage, (b) the catalytic converter is combined with a sulfur component (sulfur compound) in the exhaust gas. Whether the combustion engine contains a catalyst metal having a higher degree of binding with carbon monoxide than the degree of binding, and (c) the combustion engine is in a state where the degree of binding between the catalyst metal and the sulfur component in the exhaust gas is high. If the degree of bond between the catalyst metal and the sulfur component in the exhaust gas is detected by the sulfur bond degree detector for detecting whether or not (d) the sulfur bond degree detector is high, the catalytic converter It is characterized in that the carbon monoxide increasing means for increasing the presence degree of carbon monoxide in the exhaust gas on the upstream side (an amount which is in contact with the catalyst per unit time) is provided.

Here, examples of the combustion engine include a gasoline engine and a diesel engine. Examples of the catalyst metal include those containing one or more of Ag, Co (cobalt), alkali metal, alkaline earth metal and rare earth metal. In addition,
When the air pollutant is NOx, Ag is particularly effective as the catalyst metal.

In this exhaust gas purifying apparatus, when the combustion engine is in an operating state in which the degree of coupling between the catalytic metal and the sulfur component in the exhaust gas is high, the exhaust gas in the exhaust gas upstream of the catalytic converter is The presence of carbon monoxide is increased. Since the catalytic metal has a higher degree of bonding with carbon monoxide than the degree of bonding with the sulfur component in the exhaust gas, the catalytic metal bonds with or combines with carbon monoxide, and the catalytic metal is a sulfur component. Does not bind or react with. Therefore, even if the exhaust gas contains SO ₂
Even if a sulfur component such as SO ₃ or a sulfur compound is contained, the catalyst metal is not poisoned by these.

In the above exhaust gas purifying apparatus, the sulfur bond degree detecting means is arranged so that when the temperature of the catalytic converter is within a predetermined temperature range (for example, 300 to 450 ° C.),
It is preferable to determine that the degree of bonding between the catalyst metal and the sulfur component in the exhaust gas is high. Generally, the poisoning by the sulfur component of the catalyst metal becomes strong within a certain temperature range, for example, 300 to 450 ° C, while the poisoning becomes weak outside this temperature range. Thus, poisoning by the sulfur component of the catalyst metal can be effectively prevented.

In the above exhaust gas purifying apparatus, the sulfur bond degree detecting means determines the temperature of the catalytic converter based on at least one of the combustion engine temperature, the intake air amount, the engine load, and the elapsed time after the engine is started. It is preferable that it is designed to be estimated. With this configuration, the temperature of the catalytic converter can be grasped without providing a special sensor for detecting the temperature of the catalytic converter.

In the above exhaust gas purifying apparatus, when the combustion engine is an engine, the carbon monoxide increasing means supplies the fuel into the combustion chamber during the expansion stroke so that the exhaust gas in the exhaust gas upstream of the catalytic converter is It is preferably adapted to increase the presence of carbon monoxide.
In this way, the existing fuel injection mechanism can be used to control the degree of carbon monoxide present in the exhaust gas on the upstream side of the catalytic converter without providing a mechanism for generating or increasing extraordinary carbon monoxide. Can be increased.

In the above exhaust gas purifying apparatus, when the combustion engine is an engine, the carbon monoxide increasing means includes at least one of increasing the EGR rate, reducing the swirl intensity, and reducing the fuel injection pressure. Thus, the degree of presence of carbon monoxide in the exhaust gas on the upstream side of the catalytic converter may be increased. Also in this case,
The existing degree of EGR mechanism, swirl valve drive mechanism, or fuel injection mechanism can be used to increase the degree of carbon monoxide existing in the exhaust gas on the upstream side of the catalytic converter.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below. First, an overall configuration of a diesel engine (combustion engine) including an exhaust gas purification system (exhaust gas purification device) according to the present invention will be described with reference to FIG. The present invention can be applied to various types of combustion engines and is not limited to diesel engines or engines. Figure 1
As shown in FIG. 4, in the engine body 2 of the diesel engine 1 (hereinafter, simply referred to as “engine 1”), four fuel combustion airs are supplied from the surge tank 3 through the independent intake passages 4, respectively. The cylinders 5 are arranged in series. Then, each cylinder 5 is provided with an injector 7 (fuel injection valve) for injecting the fuel supplied from the common rail 6 containing the high-pressure fuel into the cylinder.

The common rail 6 is connected to a fuel pressure pump 9 via a fuel passage 8. The fuel pressure pump 9 is connected to a fuel tank (not shown), sucks the fuel in the fuel tank, and discharges the fuel into the fuel passage 8 at high pressure. Here, a pressure regulating valve 10 is provided in the fuel passage 8, and the pressure regulating valve 10 regulates the injection pressure of the injector 7 by regulating the pressure of the fuel sent to the common rail 6. . The fuel pressure in the common rail 6 is measured by the fuel pressure sensor 11
So that the fuel pressure detected by the fuel pressure sensor 11 is maintained at a set value.
0 is controlled by the ECU 36 (engine control unit). Thus, the fuel discharged from the fuel pressure pump 9 to the fuel passage 8 is supplied to each injector 7 via the common rail 6 and injected into the cylinder at a predetermined injection pressure.

The fuel injected from the injector 7 into the cylinder 5 comes into contact with the hot air in the cylinder 5 and ignites and burns. Then, the exhaust gas (combustion gas) generated by the combustion of the fuel is discharged into the atmosphere through the exhaust manifold 12 and the exhaust passage 13 (exhaust pipe) connected to the exhaust manifold 12. In the exhaust passage 13, the turbine 14 of the exhaust turbocharger and the first to third catalytic converters 15 to 1 are arranged in this order from the upstream side in the exhaust gas flow direction.
And 7 are provided. Here, the first catalytic converter 1
5 is filled with an Ag-based catalyst (exhaust gas purifying catalyst) in which Ag is supported on γ-alumina for mainly oxidizing NO in exhaust gas to NO ₂ . In the second catalytic converter 16, platinum for mainly reducing NO ₂ in the exhaust gas to N ₂ is used as MFI or ZSM.
A Pt-based catalyst (exhaust gas purification catalyst) which is ion-exchanged and supported on a zeolite such as −5 is filled. Further, the third catalytic converter 17 mainly contains HC and CO in H ₂
It is filled with an ordinary oxidation catalyst (exhaust gas purification catalyst) that oxidizes and purifies O or CO ₂ .

Further, the engine 1 includes a turbine 1
4 is provided with an EGR passage 19 for recirculating a part of the exhaust gas in the exhaust passage 13 to the common intake passage 18 that supplies air to the surge tank 3, and the EGR passage 19 has an EGR flow rate ( E for controlling EGR rate)
The GR valve 20 is interposed. The EGR valve 20 is controlled by the ECU 36 as described later. The EGR may be returned to the surge tank 3.

Next, a specific structure of the engine 1 will be described. As shown in FIGS. 2 and 3, in each cylinder 5,
A piston 23 is fitted in a cylinder bore 22 formed in the cylinder block 21 so as to be capable of reciprocating in the cylinder bore axial direction (vertical direction). A combustion chamber 25 is defined by the lower surface of the cylinder head 24 arranged on the upper side of the cylinder block 21, the inner peripheral surface of the cylinder bore 22, and the upper surface of the piston 23.

The cylinder head 24 is provided with two intake ports 26 and two exhaust ports 27 which communicate with the combustion chamber 25, respectively. The upstream ends of both intake ports 26 are connected to the independent intake passage 4. Further, the downstream ends of both the exhaust ports 27 are connected to the exhaust manifold 12.
It is connected to the. Here, the opening 26a of each intake port 26 to the combustion chamber 25 is opened and closed by the intake valve 28 at a predetermined timing. On the other hand, the opening 27a of each exhaust port 27 to the combustion chamber 25
Are opened and closed by exhaust valves 29 at predetermined timings. In addition, the valve shaft 2 of the intake valve 28
8a and the valve shaft 29a of the exhaust valve 29 penetrate the cylinder head 24 and project upward. Also,
The umbrella portion 28b of the intake valve 28 corresponds to the opening 2 of the intake port 26.
The valve seat 30 fitted to the valve seat 3 fitted in the valve seat 6a is attached to or separated from the valve seat 30 fitted to the valve seat 3a, and the umbrella portion 29b of the exhaust valve 29 is fitted in the opening 27a of the exhaust port 27.
It comes in close contact with and separates from 0.

Further, the cylinder head 24 is provided with an injector insertion hole 31 opening at a central position on the ceiling surface of the combustion chamber 25. Then, the injector 7 is inserted into the injector insertion hole 31, and the fuel injection portion 7 at the tip thereof is inserted.
It is fitted so that a is exposed in the combustion chamber 25. The injector 7 is fixed by screwing the mounting bolt 32 into the cylinder head 24 through the fixing plate 33 disposed above the flange portion 7b.

As described above, each cylinder 5 has two
Although one intake port 26 is provided, a swirl valve 35 is provided at one of the intake ports 26. This swirl valve 35
The opening degree (hereinafter referred to as "swirl valve opening degree") is
It is controlled by the ECU 36. Here, the smaller the opening degree of the swirl valve, the larger the flow velocity of the air flowing into the combustion chamber 25 from the intake port 26 provided with the swirl valve 35, and the stronger swirl (vortex flow) is formed in the combustion chamber 25. Thus, the mixing property of the fuel and the air, that is, the combustibility of the fuel is improved.

The control mechanism of the engine 1 will be described below.
Again, as shown in FIG. 1, an ECU 36 including a computer is provided to perform various controls of the engine 1. In the ECU 36, in addition to the fuel pressure in the common rail 6 detected by the fuel pressure sensor 11, the crank angle detected by the crank angle sensor 37 and the engine water temperature (combustion engine temperature) detected by the water temperature sensor 38 are detected. , The intake air temperature detected by the intake air temperature sensor 39, the exhaust gas temperature in the exhaust manifold 12 detected by the first exhaust gas temperature sensor 40 (hereinafter referred to as “first exhaust gas temperature”), the second exhaust gas temperature sensor 41. Exhaust gas temperature immediately upstream of the first catalytic converter 15 (hereinafter referred to as "second exhaust temperature") detected by the exhaust gas, and exhaust gas immediately downstream of the first catalytic converter 15 detected by the third exhaust temperature sensor 42. Gas temperature (hereinafter referred to as "third exhaust temperature"), engine load detected by the engine load sensor 43, and accelerator opening An accelerator opening detected by the sensor 44, the intake air amount and the like are input as control information detected by the intake air amount sensor 45 (air flow sensor). The ECU 3
Reference numeral 6 is a comprehensive control device for the engine 1 including the "sulfur bond degree detection means" described in the claims.

Thus, the ECU 36 is adapted to perform various controls of the engine 1 on the basis of these control information, but a general engine control control method is well known, and such a general control method is also well known. Since the engine control is not the gist of the present invention, its description is omitted. In the following, according to the gist of the present invention, control for preventing poisoning by the sulfur component or the sulfur compound of the exhaust gas purification catalyst (hereinafter, This will be described only as "sulfur poisoning prevention control").

First, the basic structure of the exhaust gas purification system of the engine 1 which is the target of this sulfur poisoning prevention control will be described. The exhaust gas of this engine 1 contains HC, CO and NO.
However, since the engine 1 is a diesel engine, the O ₂ concentration in the exhaust gas is relatively high, and therefore it is difficult to reduce (purify) NOx using an ordinary three-way catalyst. Below. Therefore, in the exhaust gas purification system of the engine 1, the first catalytic converter 1
5 in the Ag-based catalyst and Pt in the second catalytic converter 16
NOx is treated in two stages by a system catalyst, and harmless N ₂
I am trying to change it.

Specifically, the first catalytic converter 15 has an Ag (catalyst metal) A supported on γ-alumina.
It is filled with a g-based catalyst. NO contained in exhaust gas
Most of x (generally 90% or more) is NO and the rest is NO ₂ , but this Ag-based catalyst is
Has a function of almost completely oxidizing NO ₂ into NO ₂ . On the other hand, the second catalytic converter 16 is filled with a Pt-based catalyst in which Pt (catalytic metal) is ion-exchanged and supported on zeolite such as MFI or ZMS-5. This Pt-based catalyst has a function of almost completely reducing NO _{2 in} exhaust gas to N ₂ . Thus, NOx (NO and NO ₂ ) is changed to N ₂ by the first catalytic converter 15 and the second catalytic converter 16.

By the way, as described above, the Ag-based catalyst in the first catalytic converter 15 is poisoned by sulfur compounds such as SO ₂ or SO ₃ in the exhaust gas, and oxidizes NO into NO ₂ . The catalytic activity is lost.
This is approximately the chemical reaction shown by the following formula 1-3 is a catalyst metal Ag is varied Ag ₂ SO _4, Ag ₂
This is because SO ₄ does not have the function of oxidizing NO to NO ₂ .

[Equation 1] SO ₂ + (1/2) O ₂ → SO ₃ …………………………………… Equation 1

[Formula 2] 2Ag + (1/2) O ₂ → Ag ₂ O ……………………………… Formula 2

## EQU3 ## Ag ₂ O + SO ₃ → Ag ₂ SO ₄ …………………………………………………………………….
It has a feature that it easily occurs at ° C.

Therefore, in the exhaust gas purifying system for the engine 1, basically, the upstream side of the first catalytic converter 15 has a higher degree of coupling with Ag than SO ₂ or SO ₃ (that is, the coupling is easy). ) CO is supplied to the exhaust gas to prevent the formation of Ag ₂ SO ₄ and prevent the reduction or loss of the catalytic activity. That is, Ag
Coupling degree between the CO (degree of binding) is higher than the degree of coupling between SO ₂ or SO _3, in the exhaust gas, when the CO and SO ₂ or SO ₃ coexist, Ag is the following The chemical reaction shown in Formula 4 preferentially binds to CO to form Ag ₂ CO ₃ , and thus Ag ₂ SO ₄
Is not generated.

## EQU4 ## Ag ₂ O + CO + (1/2) O ₂ → Ag ₂ CO ₃・ ・ ・ Equation 4 Note that Ag ₂ CO ₃ differs from Ag ₂ SO _{4 in} that NO is changed to N.
It has a catalytic function of oxidizing to O ₂ .

Here, in the chemical reaction of Equation 3, the temperature of the Ag-based catalyst (exhaust gas purifying catalyst) in the first catalytic converter 15 (hereinafter, simply referred to as "catalyst temperature") is roughly 3
When the catalyst temperature is outside this range, poisoning of the Ag-based catalyst hardly occurs. Therefore, in the exhaust gas purification system of the engine 1, basically, CO is supplied to the exhaust gas on the upstream side of the first catalytic converter 15 only when the catalyst temperature is within the range of 300 to 450 ° C. I am trying. The range of the catalyst temperature may be set according to the concentration of the sulfur content in the fuel. For example, the low concentration of sulfur in the fuel, indirectly determined by the operating state, or detected by a sulfur sensor placed in the fuel or exhaust,
In such a case, CO may be supplied when the catalyst temperature is within the range of 350 to 450 ° C.

Although the poisoning of the Ag-based catalyst by SO ₂ or SO ₃ is prevented in this way, the operating temperature of the engine 1 is such that the catalyst temperature is less likely to cause poisoning of the Ag-based catalyst.
More preferably, it is controlled to be maintained within the range of 300 ° C. In addition, when starting the supply of CO to the exhaust gas, the exhaust gas bypasses the first catalytic converter 15 and the second catalytic converter 16 during a transition, and the first catalytic converter 15 and the second catalytic converter 1
Smoke (particulates) may be prevented from being introduced into 6.

The catalyst temperature is determined by the first catalytic converter 1
The detection value of the third exhaust gas temperature sensor 42 immediately downstream of 5 can be used as a substitute, but a temperature sensor may be arranged directly in the first catalytic converter 15 for detection. Alternatively, the estimation may be performed based on at least one of the engine water temperature, the intake air amount, the engine load, and the elapsed time after the engine is started by a well-known estimation method.

As described above, in the exhaust gas purification system of the engine 1, CO is easily supplied to the exhaust gas on the upstream side of the first catalytic converter 15 under the condition that SO ₂ or SO ₃ is easily generated. However, the poisoning of the Ag-based catalyst by SO ₂ or SO ₃ is prevented. Specific methods for producing CO include, for example, expansion stroke fuel injection, increase in EGR rate, reduction in swirl strength,
Alternatively, a technique such as reducing the fuel injection pressure can be used.

Here, the CO generation method by the expansion stroke fuel injection is a method of injecting fuel from the injector 7 into the cylinder in the expansion stroke and incompletely burning this fuel to generate CO. The regular fuel injection for generating the output energy of the engine 1 is performed at the end of the compression stroke.

The CO generation method by increasing the EGR rate increases the EGR rate by increasing the opening degree of the EGR valve 20 as compared with the normal time, thereby reducing the intake air amount and increasing the ratio of fuel to air ( Enriching) and slightly reducing O ₂ to generate CO. Since the amount of smoke (or particulates) generated increases when the EGR rate is increased in this way, when CO is generated by the increase of the EGR rate, the fuel injection timing is slightly advanced or the fuel injection pressure is slightly increased. Alternatively, it is preferable to enhance the combustibility of the fuel by suppressing the generation of smoke by slightly strengthening the swirl strength.

In the CO production method by reducing the swirl strength, the opening degree of the swirl valve 35 is made larger than usual to weaken the swirl strength to lower the degree of mixing of fuel and air and cause incomplete combustion. It is a method of generating CO. Note that, if the swirl strength is reduced in this way, the amount of smoke generated increases. Therefore, when CO is generated by reducing the swirl strength, the fuel injection timing may be slightly advanced, the fuel injection pressure may be slightly increased, or EG
It is preferable to increase the combustibility of the fuel by slightly reducing the R ratio and suppress the generation of smoke.

In the method of producing CO by reducing the fuel injection pressure, the fuel injection pressure, that is, the pressure of the fuel in the common rail 6 is made lower than that in the normal time, so that the degree of mixing of the fuel and the air is lowered to cause incomplete combustion. It is a method of inducing CO to generate CO.

Hereinafter, referring to the flow chart shown in FIG. 4, when CO is generated by the expansion stroke fuel injection,
A specific control method of sulfur poisoning prevention control will be described. The control routine shown in FIG. 4 is executed each time the crank angle in each cylinder 5 reaches a predetermined value. As shown in FIG. 4, in the sulfur poisoning prevention control, first, in step S1, the third exhaust temperature sensor 42 detects the third exhaust temperature sensor 42.
Exhaust temperature, that is, the catalyst temperature of the first catalytic converter 15, the accelerator opening detected by the accelerator opening sensor 44, the crank angle detected by the crank angle sensor 37, the engine load detected by the engine load sensor 43, and other controls. Data is entered.

Next, at step S2, the operating state of the engine 1 is judged mainly based on the accelerator opening degree, and then at step S3, the basic injection amount T _{p of the} cylinder 5 is calculated according to the operating state of the engine 1. To be done. Here, the basic injection amount T _p is the injection amount of fuel that should be injected from the injector 7 into the cylinder 5 at the end of the compression stroke in order to generate the output energy of the engine 1.

Subsequently, in step S4, it is compared and determined whether or not the cylinder has reached the basic injection timing. If the basic injection timing has not been reached (NO), step S4 is repeatedly executed. That is, it waits until the basic injection timing comes. When it is determined in step S4 that the cylinder 5 has reached the basic injection timing (YES), step S5
Then, the injector 7 of the cylinder 5 is opened for the time corresponding to the basic injection amount T _p , and the basic injection is performed.

Next, at step S6, it is judged if the catalyst temperature of the first catalytic converter 15 is within a predetermined temperature range. Here, in the above-mentioned predetermined temperature range, normally, poisoning by a sulfur compound such as SO ₂ or SO ₃ of the Ag-based catalyst in the first catalytic converter 15 is likely to occur 300 to 4
Set to 50 ° C. As described above, when the sulfur content in the fuel is small, the temperature may be set to 350 to 450 ° C, for example. When it is determined in step S6 that the catalyst temperature is not within the predetermined temperature range (NO), it is considered that the Ag-based catalyst in the first catalytic converter 15 is not substantially poisoned by the sulfur compound. Therefore, it is not necessary to supply CO to the upstream side of the first catalytic converter 15. Therefore, the following steps S7 to S9 are skipped and the control routine of this time is ended.

On the other hand, when it is determined in step S6 that the catalyst temperature is within the predetermined temperature range (YES), the Ag catalyst in the first catalytic converter 15 is poisoned by the sulfur compound in the exhaust gas. CO is produced by the expansion stroke fuel injection as it is more likely. That is, first, in step S7, the expansion stroke injection amount is set. Here, as the expansion stroke injection amount increases, the CO production amount increases, but when the injection amount increases too much, the smoke generation amount increases. Therefore, it is preferable to set this expansion stroke injection amount to a value as large as possible within the range where smoke does not increase.

Next, in step S8, it is determined whether or not the crank angle of the cylinder 5 is a predetermined crank angle in the expansion stroke, that is, the timing at which the expansion stroke fuel injection should be performed. If not (N
O), this step S8 is repeatedly executed. That is, the process waits until the timing for performing the expansion stroke fuel injection. Then, when it is determined in step S8 that the crank angle has reached the predetermined crank angle (YES), in step S9, the injector 7 of the cylinder 5 is opened for the time corresponding to the expansion stroke injection amount, and the expansion stroke is expanded. Fuel injection is performed.

Thus, the expansion stroke fuel injection supplies CO to the exhaust gas, and this CO prevents the Ag-based catalyst in the first catalytic converter 15 from being poisoned by sulfur compounds such as SO ₂ or SO ₃ .

A specific control method of the sulfur poisoning prevention control when CO is generated by increasing the EGR rate will be described below with reference to the flowchart shown in FIG. In addition,
The control routine shown in FIG. 5 is executed every time a fixed time elapses. As shown in FIG. 5, in the sulfur poisoning prevention control, first in step S11, the third exhaust temperature detected by the third exhaust temperature sensor 42, that is, the catalyst temperature of the first catalytic converter 15, the accelerator opening sensor 44. Accelerator opening detected by, crank angle detected by crank angle sensor 37, engine load sensor 43
Various control data such as engine load detected by is input.

Next, at step S12, the operating state of the engine 1 is determined mainly based on the accelerator opening degree, and then at step S13, the basic EGR rate EGR _BASE is calculated according to the operating state of the engine 1. Where the basic EG
The R rate EGR _BASE is the EGR rate during normal operation of the engine 1.

Succeedingly, in a step S14, it is determined whether or not the catalyst temperature of the first catalytic converter 15 is within a predetermined temperature range. Here, the predetermined temperature range is 300 to 300 as in the case of the sulfur poisoning prevention control by the expansion stroke fuel injection.
It is set to 450 ° C or 350 to 450 ° C. When it is determined in step S14 that the catalyst temperature is not within the predetermined temperature range (NO), it is considered that the Ag-based catalyst in the first catalytic converter 15 is not substantially poisoned by the sulfur compound. Because it will be EGR
It is not necessary to increase the rate and supply CO to the upstream side of the first catalytic converter 15. Therefore, the EGR rate increment EGR _C is set to 0 in step S16. It should be noted that the EGR rate increment EGR _C means EG for generating CO in the exhaust gas.
The total EGR rate EGR _T , which is the increase in EGR rate for increasing R and is the final EGR rate, is the basic E
The GR rate EGR _BASE is added to this EGR rate increment EGR _C. After this, step S17 is executed.

On the other hand, if it is determined in step S14 that the catalyst temperature is within the predetermined temperature range (YES), the first
Since the Ag-based catalyst in the catalytic converter 15 is highly likely to be poisoned by the sulfur compound in the exhaust gas,
In order to generate CO by increasing the rate, step S15
A predetermined value A is set in the EGR rate increment EGR _C. Here, the larger the EGR rate increment EGR _{C, the} more C
Although the amount of O produced increases, if the EGR rate becomes too large, the generation of smoke increases. Therefore, it is preferable to set the EGR rate increment EGR _C to a value as large as possible within a range where smoke does not increase. Then, step S17 is executed.

In step S17, the total EGR rate EGR _T is calculated by the following equation 5.

[Equation 5] EGR _T = EGR _BASE + EGR _C ……………………………… Equation 5 However, EGR _T : Total EGR rate EGR _BASE : Basic EGR rate EGR _C : EGR rate increment Then, In step S18, the EGR valve 20 is driven,
With the total EGR rate EGR _T , part of the exhaust gas in the exhaust passage 13 is recirculated to the common intake passage 18 as EGR.

Thus, due to the increase in the EGR rate, CO is supplied to the exhaust gas, and this CO prevents the Ag-based catalyst in the first catalytic converter 15 from being poisoned by sulfur compounds such as SO ₂ or SO ₃ .

A specific control method of sulfur poisoning prevention control when CO is generated by reducing the swirl strength will be described below with reference to the flowchart shown in FIG.
It should be noted that the control routine shown in FIG. 6 is executed every time a certain period of time elapses. As shown in FIG. 6, in the sulfur poisoning prevention control, first, in step S21, the third exhaust temperature detected by the third exhaust temperature sensor 42, that is, the first exhaust temperature is detected.
Catalyst temperature of the catalytic converter 15, accelerator opening sensor 4
Various control data such as the accelerator opening detected by 4, the crank angle detected by the crank angle sensor 37, the engine load detected by the engine load sensor 43, and the like are input.

Next, at step S22, the operating state of the engine 1 is determined mainly based on the accelerator opening degree, and then at step S23, the basic swirl valve opening SRC _BASE is calculated according to the operating state of the engine 1. . Here, the basic swirl valve opening SRC _BASE is the swirl valve opening during normal operation of the engine 1.

Succeedingly, in a step S24, it is determined whether or not the catalyst temperature of the first catalytic converter 15 is within a predetermined temperature range. Here, the predetermined temperature range is 300 to 450 ° C. or 350 to 45 ° C. as in the case of the sulfur poisoning prevention control by the expansion stroke fuel injection or the increase of the EGR rate.
Set to 0 ° C. If it is determined in step S24 that the catalyst temperature is not within the predetermined temperature range (N
O), since it is considered that the Ag-based catalyst in the first catalytic converter 15 is not substantially poisoned by the sulfur compound, the swirl strength is particularly reduced and CO is supplied to the upstream side of the first catalytic converter 15. do not have to. Therefore, in step S26, the swirl valve opening increment SRC _{C is set} to 0.
Is set. In addition, the swirl valve opening increment SRC _C is an increment of the swirl valve opening for reducing the swirl strength to generate CO in the exhaust gas, and is the final swirl valve opening. Swirl valve opening SRC
_T is the sum of the basic swirl valve opening SRC _BASE and the swirl valve opening increment SRC _C. After that, step S27 is executed.

On the other hand, if it is determined in step S24 that the catalyst temperature is within the predetermined temperature range (YES), the first
Since the Ag-based catalyst in the catalytic converter 15 is highly likely to be poisoned by the sulfur compound in the exhaust gas, in order to generate CO by reducing the swirl strength, step S
At 25, the predetermined value B is set to the swirl valve opening increment SRC _C. Here, the larger the swirl valve opening increment SRC _C , the larger the CO production amount, but if the swirl valve opening becomes too large, the smoke generation increases. Therefore, it is preferable to set the swirl valve opening increment SRC _C to a value as large as possible within a range where smoke does not increase. Then, step S27 is executed.

In step S27, the total swirl valve opening SRC _T is calculated by the following equation 6.

[6] However _{SRC T = SRC BASE + SRC C} .......................................... formula 6, SRC _T: total swirl valve opening SRC _BASE: basic swirl valve opening SRC _C: swirl valve Next, in step S28, the swirl valve 35 is driven so that the swirl valve opening becomes the total swirl valve opening SRC _T.

Thus, due to the decrease in swirl strength, CO is supplied to the exhaust gas, and this CO prevents the Ag-based catalyst in the first catalytic converter 15 from being poisoned by sulfur compounds such as SO ₂ or SO ₃ .

Any two of the sulfur poisoning prevention control by the expansion stroke fuel injection, the sulfur poisoning prevention control by increasing the EGR rate, and the sulfur poisoning prevention control by reducing the swirl strength are used together or in combination. Alternatively, all of them may be used in combination or in combination. In the present embodiment, the sulfur poisoning prevention control as described above is performed when the temperature is within the predetermined temperature range. However, when the temperature is within this range, CO is temporarily (every predetermined time) supplied. As a result, it is possible to reduce the influence of such control, such as output reduction, on the operating state of the engine.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of a diesel engine equipped with an exhaust gas purification device according to the present invention.

FIG. 2 is an elevational sectional view around an injector of the diesel engine shown in FIG.

FIG. 3 is a cross-sectional view taken along the line AA of the diesel engine shown in FIG.

FIG. 4 is a flowchart showing a control method of sulfur poisoning prevention control by injection of expansion stroke fuel.

FIG. 5 is a flowchart showing a control method of sulfur poisoning prevention control by increasing the EGR rate.

FIG. 6 is a flowchart showing a control method of sulfur poisoning prevention control by reducing swirl strength.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine (diesel engine), 2 ... Engine main body part, 3 ... Surge tank, 4 ... Independent intake passage, 5 ... Cylinder, 6 ... Common rail, 7 ... Injector, 7a ... Fuel injection part, 7b ... Flange part, 8 ... Fuel passage, 9 ... Fuel pressure pump, 10 ... Pressure regulating valve, 11 ... Fuel pressure sensor, 1
2 ... Exhaust manifold, 13 ... Exhaust passage, 14 ... Turbine, 15 ... First catalytic converter, 16 ... Second catalytic converter, 17 ... Third catalytic converter, 18 ... Common intake passage, 19 ... EGR passage, 20 ... EGR valve , 21 ... Cylinder block, 22 ... Cylinder bore, 23 ... Piston, 2
4 ... Cylinder head, 25 ... Combustion chamber, 26 ... Intake port, 26a ... Opening part, 27 ... Exhaust port, 27a ... Opening part, 28 ... Intake valve, 28a ... Valve shaft, 28b ... Umbrella part, 29
... Exhaust valve, 29a ... Valve shaft, 29b ... Umbrella part, 30 ... Valve seat, 31 ... Injector insertion hole, 32 ... Mounting bolt, 33 ... Fixing plate, 35 ... Swirl valve, 36 ... ECU
(Engine control unit), 37 ... crank angle sensor, 38 ... water temperature sensor, 39 ... intake air temperature sensor, 40
... 1st exhaust temperature sensor, 41 ... 2nd exhaust temperature sensor, 42 ...
Third exhaust temperature sensor, 43 ... Engine load sensor, 44 ...
Accelerator position sensor, 45 ... Intake air amount sensor.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02M 25/07 570 F02M 25/07 570J (72) Inventor Tomoaki Saito 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture No. Mazda Co., Ltd. (72) Inventor Mitsunori Kondo No. 3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) No. 3 Toshitsugu Ueoka Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture F, Mazda Corporation term (reference) 3G062 AA01 AA03 AA05 AA06 BA04 BA05 DA01 EA10 FA04 GA01 GA04 GA06 GA08 GA09 3G091 AA02 AA10 AA11 AA18 AA28 AB02 AB05 BA11 BA33 CA18 CB02 CB03 CB07 CB08 DA02 DB06 DB10 DB13 EA00 EA01 EA03 EA05 EA07 EA16 EA17 EA30 FB10 FB11 FB12 GA06 GB01W GB06W GB09W GB10X GB16X HA08 HA09 HA10 HA12 HA36 HA37 HA42 HB05 HB06 3G301 HA02 HA04 HA06 HA09 HA10 HA13 HA15 HA17 JA25 JA26 LB11 MA11 MA18 MA23 MA26 NE13 NE14 NE15 PA01A PA11A PA17A PD11A PE01A PE03A PE04A PE08A PF03A

Claims (9)

[Claims] 1. An exhaust gas purifying apparatus for a combustion engine, wherein a catalytic converter using an exhaust gas purifying catalyst for oxidizing or reducing a predetermined air pollutant in exhaust gas is provided in an exhaust passage, wherein the catalytic converter comprises: The combustion engine contains a catalyst metal having a higher degree of bonding with carbon monoxide than the degree of bonding with the sulfur component in the exhaust gas, and the combustion engine has a degree of bonding between the catalyst metal and the sulfur component in the exhaust gas. When the degree of bond between the catalyst metal and the sulfur component in the exhaust gas is detected to be high by the sulfur bond degree detection means for detecting whether or not it is in a high state, and the sulfur bond degree detection means, Exhaust of a combustion engine, characterized in that carbon monoxide increasing means for increasing the degree of presence of carbon monoxide in the exhaust gas on the upstream side of the catalytic converter is provided. Gas purification device. 2. The sulfur bond degree detecting means determines that the bond degree between the catalyst metal and the sulfur component in the exhaust gas is high when the temperature of the catalytic converter is within a predetermined temperature range. The exhaust gas purifying device for a combustion engine according to claim 1, wherein 3. The predetermined temperature range is 300 to 450 °
The exhaust gas purifying apparatus for a combustion engine according to claim 2, wherein the exhaust gas purifying apparatus is C. 4. The sulfur bond degree detecting means estimates the temperature of the catalytic converter based on at least one of a combustion engine temperature, an intake air amount, an engine load, and an elapsed time after engine start. The exhaust gas purifying apparatus for a combustion engine according to claim 2 or 3, characterized in that. 5. The combustion engine is an engine, and the carbon monoxide increasing means supplies fuel into the combustion chamber during an expansion stroke, whereby carbon monoxide in exhaust gas upstream of the catalytic converter is increased. The exhaust gas purifying apparatus for a combustion engine according to any one of claims 1 to 4, wherein the degree of existence is increased. 6. The fuel engine is an engine, and the carbon monoxide increasing means is upstream of the catalytic converter by at least one of an increase in EGR rate, a reduction in swirl intensity, and a reduction in fuel injection pressure. The exhaust gas purifying apparatus for a combustion engine according to any one of claims 1 to 4, wherein the degree of presence of carbon monoxide in the exhaust gas on the side is increased. 7. The exhaust gas purifying apparatus for a combustion engine according to claim 5, wherein the engine is a diesel engine. 8. The catalyst according to claim 1, wherein the catalyst metal contains at least one of silver, cobalt, an alkali metal, an alkaline earth metal and a rare earth metal. Exhaust gas purification device for combustion engine. 9. The exhaust gas purifying apparatus for a combustion engine according to claim 1, wherein the air pollutant is nitrogen oxide.