JP2000110552A - Exhaust gas emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas emission control device for internal combustion engine suppressing discharge of H2S. SOLUTION: A second catalyser 32 having an oxygen reserving function is provided on the downstream of a first catalyser 30 free to release a sulfur component occuluded at the time when a high temperature and exhaust gas air-fuel ratio is a rich air-fuel ratio, and air feeding means 40, 42, 44, 45 to feed air to the second catalyser are provided. Thereafter, the aforementioned air feeding means are actuated by an air feeding control means 50 at the time when of an engine driving state when the sulfur component is released from the first catalyser.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly, to a technique for preventing the emission of hydrogen sulfide (H ₂ S) generated by sulfur components in exhaust gas to the atmosphere.

[0002]

2. Description of the Related Art Generally, a fuel contains an S (sulfur) component (sulfur component), and this S component reacts with oxygen to form SOx (sulfur oxide). It is stored as X-SO ₄ in a catalyst (three-way catalyst, NOx catalyst, etc.) (S poisoning). As disclosed in Japanese Patent Application Laid-Open No. 7-217474, the SOx occluded in the catalyst is such that the catalyst has a predetermined high temperature and the exhaust air-fuel ratio is in a rich air-fuel ratio state (a reducing atmosphere in which the oxygen concentration is reduced).
Is known to be reduced to sulfur dioxide (SO ₂ ) and released (S purge).

If the amount of stored SOx is large and the degree of enrichment of the rich air-fuel ratio is large, H ₂ S is generated together with SO ₂ , and the H ₂ S is also discharged into the atmosphere. However, as is well known, H ₂ S has a characteristic of emitting an off-flavor, and it has been a problem to suppress the emission of the H ₂ S. Therefore, Ni (nickel) and Ca
By adding a substance that easily generates sulfide such as (calcium) to the catalyst, SOx is prevented from being occluded in the catalyst body, whereby the temperature of the catalyst becomes a predetermined high temperature and the exhaust air-fuel ratio becomes a rich air-fuel ratio state. A technique for suppressing the generation of H ₂ S in some cases is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-194977.

Further, techniques for example JP-providing H ₂ S trap performing the oxidation and capture of H ₂ S with the catalyst downstream 8-29
No. 4618.

[0005]

However, in the technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 7-194977, the sulfide generated by Ni, Ca or the like continues to remain in the catalyst. Deterioration is accelerated, which is not preferable. Furthermore, there is a limit to the ability to generate sulfides due to Ni, Ca, and the like, and if the limit is exceeded, the above-described conventional problems also occur.

In the technique disclosed in Japanese Patent Application Laid-Open No. 8-294618, when the rich air-fuel ratio operation is continued, the captured H ₂ S is deposited on the H ₂ S trap without being oxidized. When the trapping capacity of the H ₂ S trap is exceeded, H ₂ S may be discharged without being trapped, which is not preferable. The present invention has been made to solve such a problem, and an object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine that suppresses the emission of H ₂ S.

[0007]

In order to achieve the above-mentioned object, according to the first aspect of the present invention, when the exhaust air-fuel ratio is high and the rich air-fuel ratio is a rich air-fuel ratio, the first stored sulfur component can be released. A second catalyst having an oxygen storage function is provided downstream of the catalyst, and air supply means for supplying air to the second catalyst is provided. An air supply control unit is provided for operating the air supply unit when the engine is in an engine operating state in which a sulfur component is released from the first catalyst.

For this reason, when the first catalyst is set to a high temperature and the exhaust air-fuel ratio is set to a rich air-fuel ratio, the stored sulfur component is released and H ₂ S may be generated. When the air supply means is operated by the air supply control means, air is supplied to the second catalyst provided downstream, oxygen in the air is stored in the second catalyst, and H ₂ is generated by the stored oxygen. S is well oxidized. This reliably prevents the exhaust gas from emitting an off-flavor.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to the present invention mounted on a vehicle, and the configuration of the exhaust gas purification device for an internal combustion engine according to the present invention will be described with reference to FIG. explain.

Engine body (hereinafter simply referred to as engine) 1
For example, in-cylinder injection spark ignition capable of performing fuel injection in an intake stroke (intake stroke injection mode) or fuel injection in a compression stroke (compression stroke injection mode) by switching a fuel injection mode (operation mode), for example. It is an inline 4-cylinder gasoline engine. The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric ratio), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio.

As shown in FIG. 1, an electromagnetic fuel injection valve 6 is attached to a cylinder head 2 of an engine 1 together with a spark plug 4 for each cylinder, whereby fuel is injected into a combustion chamber 8. Direct injection is possible. A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, whereby the fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. From the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount depends on the fuel discharge pressure of the high-pressure fuel pump and the valve opening time of the fuel injection valve 6,
That is, it is determined from the fuel injection time.

An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10. The throttle valve 11 is provided with a throttle sensor 11a for detecting a throttle opening θth.

An exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 12 is connected to communicate with each exhaust port. In the figure, reference numeral 13 denotes a crank angle sensor for detecting a crank angle, and the crank angle sensor 13 is capable of detecting an engine rotation speed Ne.

The in-cylinder injection type engine 1 is already known, and the detailed description of its configuration is omitted here. As shown in FIG. 1, an exhaust pipe (exhaust passage) 14 is connected to the exhaust manifold 12. The exhaust pipe 14 has a small proximity three-way catalyst 20 close to the engine 1 and a storage NOx catalyst (first NOx catalyst). A muffler (not shown) is connected through a first catalyst 30 and a three-way catalyst (second catalyst) 32. That is, the exhaust gas purification apparatus of the present invention has the three-way catalyst 32 downstream of the storage NOx catalyst 30. Further, a high temperature sensor 16 for detecting exhaust gas temperature is provided immediately upstream of the storage NOx catalyst 30 in the exhaust pipe 14.

The storage type NOx catalyst 30 has a function of temporarily storing NOx in an oxidizing atmosphere and reducing NOx to N ₂ (nitrogen) or the like in a reducing atmosphere where CO is mainly present. More specifically, the storage type NOx catalyst 3
No. 0 is constituted as a catalyst having platinum (Pt), rhodium (Rh) or the like as a noble metal, and an alkali metal or an alkaline earth metal such as barium (Ba) is adopted as an occlusion material.

The three-way catalyst 32 is a commonly used three-way catalyst and has a function of storing oxygen therein. Also,
A secondary air pipe 40 extends from the atmosphere opening port 46 via a filter 47, and its tip is open to an exhaust passage between the storage NOx catalyst 30 and the three-way catalyst 32.
An air pump 42 and a throttle valve 45 are interposed in the secondary air line 40. By operating the air pump 42 and the solenoid 44 to open the throttle valve 45, air in the atmosphere is released. Can be supplied as secondary air into the three-way catalyst 32 through the exhaust passage (air supply means). Thereby, the oxygen in the secondary air can be sufficiently stored in the three-way catalyst 32.

Further, an input / output device, a storage device (ROM,
RAM, nonvolatile RAM, etc.), central processing unit (CP
U), an ECU (electronic control unit) 50 having a timer counter and the like is installed.
As a result, comprehensive control of the exhaust gas purification device for the internal combustion engine according to the present invention including the engine 1 is performed. Various sensors such as the above-described throttle sensor 11a and high-temperature sensor 16 are connected to the input side of the ECU 50, and detection information from these sensors is input.

On the output side of the ECU 50, the above-described ignition plug 4, fuel injection valve 6, air pump 42, solenoid 44 and the like are connected via an ignition coil. These ignition coil, fuel injection valve 6, air pump Drive signals calculated based on detection information from various sensors are output to the solenoid 42, the solenoid 44, and the like. With respect to the fuel injection valve 6 and the ignition coil, optimum values such as the fuel injection amount and the ignition timing are respectively output, and a proper amount of fuel is injected from the fuel injection valve 6 at a proper timing. Thus, ignition is performed at an appropriate timing.

The ECU 50 determines a target in-cylinder pressure corresponding to the engine load, that is, a target average effective pressure Pe, based on the throttle opening information θth from the throttle sensor 11a and the engine rotation speed information Ne from the crank angle sensor 13. Further, the fuel injection mode is set from a fuel injection mode setting map (not shown) according to the target average effective pressure Pe and the engine rotation speed information Ne. For example, when both the target average effective pressure Pe and the engine speed Ne are small,
The fuel injection mode is a compression stroke injection mode, in which fuel is injected in the compression stroke.On the other hand, when the target average effective pressure Pe increases or the engine speed Ne increases, the fuel injection mode is set to the intake stroke injection mode, and the fuel is injected. It is injected during the intake stroke. The intake stroke injection modes include an intake lean mode that is a lean air-fuel ratio, a stoichiometric feedback mode that is a stoichiometric air-fuel ratio, and an open loop mode (O / L mode) that includes a rich air-fuel ratio.

The target air-fuel ratio (target A / A) is set as a control target based on the target average effective pressure Pe and the engine speed Ne.
F) is set, and the appropriate amount of fuel injection is set to the target A /
It is determined based on F. Further, from the exhaust gas temperature information detected by the high temperature sensor 16, the storage NOx catalyst 3
A temperature of 0, that is, the catalyst temperature Tcat is estimated. More specifically, in order to correct an error that occurs due to the inability to directly install the high-temperature sensor 16 on the storage NOx catalyst 30, the temperature is determined in advance by experiments or the like in accordance with the target average effective pressure Pe and the engine rotation speed information Ne. A difference map (not shown) is set, and the catalyst temperature Tcat is uniquely estimated when the target average effective pressure Pe and the engine speed information Ne are determined.

Hereinafter, the operation of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described. That is, SOx is stored in the storage NOx catalyst 30 in addition to NOx. A procedure for controlling the introduction of secondary air accompanying the release control (S purge control) of the SOx will be described.
Referring to FIG. 2, there is shown a flowchart of a secondary air introduction control routine executed by the ECU 50, which will be described below (air supply control means).

First, at step S10, it is determined whether or not the NOx catalyst has been deteriorated by S (sulfur).
It is determined whether or not the amount of SOx stored in the x catalyst 30 (poisoned S amount Qs) has reached a predetermined amount Qs1. Here, the poisoning S amount Qs is a value obtained by estimation, and a method of estimating the poisoning S amount Qs (detection method) will be briefly described below.

The poisoning S amount Qs is basically set based on the integrated fuel injection amount Qf, and is calculated by the following equation at each execution cycle of a fuel injection control routine (not shown). Qs = Qs (n−1) + ΔQf · K−Rs (1) where Qs (n−1) is the previous value of the poisoning S amount, ΔQf is the fuel injection integrated amount per execution cycle, and K is Correction coefficient, Rs
Indicates the amount of released S per execution cycle, that is, the amount of regeneration.

That is, the current poisoning S amount Qs is integrated by correcting the integrated fuel injection amount ΔQf per execution cycle with the correction coefficient K, and subtracting the released S amount Rs per execution cycle from the integrated value. It is required by that. The correction coefficient K is
For example, as shown in the following equation (2), the S poisoning coefficient K1 according to the air-fuel ratio A / F, the S poisoning coefficient K2 according to the S content in the fuel, and the S poisoning according to the catalyst temperature Tcat. It consists of the product of the three correction coefficients K3.

K = K1, K2, K3 (2) Further, the released S amount Rs per execution cycle is calculated from the following equation (3). Rs = α · R1 · R2 · dT (3) where α is a regeneration rate (set value) per unit time, dT indicates an execution cycle of the fuel injection control routine, and R1 and R2 are respectively A regeneration capacity coefficient according to the catalyst temperature Tcat and a regeneration capacity coefficient according to the air-fuel ratio A / F are shown.

If the result of the determination in step S10 is false (No) and it is determined that the poisoning S amount Qs obtained as described above has not yet reached the predetermined amount Qs1, then step S12 is performed. Proceed to. In step S12, the catalyst temperature Tcat is set to a predetermined high temperature Tcat1 (for example, S purging possible).
(650 ° C.). If the determination result is true (Yes) and the catalyst temperature Tcat is equal to or higher than the predetermined high temperature Tcat1, the process proceeds to step S14.

In step S14, it is determined whether or not the operation state is the rich air-fuel ratio operation based on the above-described fuel injection mode setting map. When the result of the determination is true (Yes), that is, when it is determined that the fuel injection mode is the O / L mode and the vehicle is currently performing the rich air-fuel ratio operation during acceleration or the like, then the process proceeds to step S16. move on. In step S16, secondary air is introduced. Specifically, the air pump 42 is operated and the solenoid 44 is operated to open the throttle valve 45, and the air in the atmosphere is supplied to the three-way catalyst 32 via the exhaust passage.

That is, when the catalyst temperature Tcat is a predetermined high temperature Tcat
When the engine operating state is 1 or more and the operating state is a rich air-fuel ratio operation and the exhaust air-fuel ratio is a rich air-fuel ratio, the S purge of SOx stored in the storage NOx catalyst 30 naturally occurs. This is considered to be a situation in which H ₂ S (hydrogen sulfide) is generated, and in such a case, the storage type N
Air is supplied to the three-way catalyst 32 located downstream of the Ox catalyst 30 to store oxygen. As a result, when the generated H ₂ S passes through the three-way catalyst 32, it is oxidized favorably by the stored oxygen. Therefore, it is possible to reliably prevent the exhaust gas from emitting an odor.

The degree of the rich air-fuel ratio and the poisoning S amount Qs
The generation amount of H ₂ S is considered to change in accordance with the amount of secondary air introduced, that is, by controlling the solenoid 44 in accordance with the degree of the rich air-fuel ratio and the poisoning S amount Qs. The opening of the throttle valve 45 may be variably set. If the determination result of step S12 or step S14 is false (No), H ₂ S is not generated without performing S purge, so step S12 is performed.
At 34, the secondary air is stopped.

On the other hand, if the result of the determination in step S10 is true (Y
In es), when it is determined that the poisoning S amount Qs has reached the predetermined amount Qs1, the process proceeds to step S20, and the control mode is switched to the S purge mode. With this, the storage type NO
The release of SOx stored in the x catalyst 30, that is, the execution of the S purge is permitted. When the S purge is started, it is considered that H ₂ S is generated as described above. Therefore, in the next step S22, the introduction of the secondary air is first started in the same manner as in step S16. Thereby, the three-way catalyst 32
Oxygen is stored enough.

Then, step S24 and step S2
6, the main control of the S purge, that is, the storage type NOx catalyst 3
The temperature is raised to 0 and the air-fuel ratio is made rich air-fuel ratio (referred to as rich spike). Specifically, in step S24, the exhaust gas temperature is increased in order to increase the temperature of the storage NOx catalyst 30.

As the exhaust gas temperature raising process, in addition to a method of slowing down the combustion by retarding the ignition timing, in the in-cylinder injection type engine 1, the fuel injection timing is divided into a plurality of times (for example, two times). There is a method using split injection (for example, two-stage injection). In the two-stage injection, the main injection is performed in the compression stroke or the intake stroke, and the sub-injection is performed in the expansion stroke (particularly, in the middle or later stage of the expansion stroke). And the temperature of the exhaust gas is raised by utilizing the re-combustion.

Actually, in this temperature raising process, temperature feedback control is performed, and the catalyst temperature Tcat is set to a predetermined high temperature Tcat1 suitable for S purge (for example, 650 ° C. to 700 ° C.).
C.), but the detailed description is omitted here. Then, in step S26, the target A / F is set to a predetermined rich air-fuel ratio (for example, value 12) suitable for S purge. When two-stage injection is performed as the temperature raising process, the total A / A including the main injection and the sub-injection
F is set to a predetermined rich air-fuel ratio. At this time, the fuel ratio between the main injection and the sub-injection is variably controlled to perform appropriate air-fuel ratio control, but the description is omitted here.

In the next step S28, SOx is released from the storage type NOx catalyst 30, and the poisoning S amount Qs is calculated by the above equation (1).
It is determined whether or not the predetermined amount is less than the predetermined amount Qs0. The determination result is false (No), and the poisoning S amount Qs is still the predetermined amount Qs0.
If so, step S24 and step S2
6 is repeated, and the S purge is continued. When the S purge is continued in this manner, H ₂ S is generated as described above. However, when the H ₂ S passes through the three-way catalyst 32, the H ₂ S is oxidized favorably by the oxygen stored by the supply of the secondary air to the three-way catalyst 32. Therefore, in this case as well, it is possible to reliably prevent the exhaust gas from emitting an odor in the same manner as described above.

Since the generation amount of H ₂ S is considered to change in accordance with the change in the poisoning S amount Qs, the amount of the secondary air introduced, ie, the secondary air introduction amount in accordance with the change in the poisoning S amount Qs, is considered. The opening of the throttle valve 45 may be variably controlled by controlling the solenoid 44. On the other hand, the determination result of step S28 is true (Yes), and the poisoning S amount Qs is equal to the predetermined amount Qs.
If the value is less than 0, the process proceeds to step S30, and the S purge mode ends. Specifically, the temperature increase process and the rich spike are stopped while the introduction of the secondary air is continued.

In step S32, it is determined whether a predetermined time t1 has elapsed since the end of the S purge mode. If the determination result is true (Yes) and it is determined that the predetermined time t1 has elapsed, step S34 is performed. , The introduction of the secondary air is stopped. The reason why the stop of the secondary air is delayed from the end point of the S purge mode is that a response delay is considered. As a result, H ₂ S generated with a delay after the transmission of the control signal is sufficiently oxidized by oxygen in the continuously supplied secondary air, and it is extremely sure that the exhaust gas emits an odor. Will be prevented.

In the above embodiment, the storage type NOx catalyst 30 is a NOx catalyst capable of realizing both the storage, release and reduction of NOx.
A NOx catalyst having only the function of storing and releasing NOx may be used, and the three-way catalyst 32 on the downstream side may have a function of reducing NOx. In other words, the three-way catalyst 32 may have two functions, that is, the function of oxidizing H ₂ S and the function of reducing NOx.

In the above embodiment, the three-way catalyst 32 is provided downstream of the storage NOx catalyst 30 and the secondary air is introduced into the three-way catalyst 32. However, the present invention is not limited to this.
As long as a catalyst having an oxygen storage capacity is provided downstream of the catalyst capable of storing and releasing Ox, and the secondary air can be supplied to the catalyst having the oxygen storage capacity, the number and types of the catalysts are not limited. You may.

[0039]

As described above in detail, according to the exhaust gas purifying apparatus for an internal combustion engine of the first aspect of the present invention, it is possible to oxidize H ₂ S satisfactorily by the oxygen stored in the second catalyst. It is possible to surely prevent the exhaust gas from emitting an odor.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an exhaust gas purification device for an internal combustion engine according to the present invention.

FIG. 2 is a flowchart showing a secondary air introduction control routine of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine (internal combustion engine) 4 Spark plug 6 Fuel injection valve 11 Throttle valve 11a Throttle sensor 13 Crank angle sensor 16 High temperature sensor 30 Storage type NOx catalyst (first catalyst) 32 Three-way catalyst (second catalyst) 40 Secondary Air line (air supply means) 42 Air pump (air supply means) 44 solenoid (air supply means) 45 Throttle valve (air supply means) 50 Electronic control unit (ECU)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/24 ZAB F01N 3/24 ZABE 3/28 301 3/28 301D (72) Inventor Yasuki Tamura Tokyo 5-33-8 Shiba, Minato-ku Mitsubishi Motors Corporation F-term (reference) 3G091 AA17 AA24 AA28 AB02 AB03 AB06 BA11 BA14 BA15 BA19 BA20 BA33 CA22 CA23 CB02 CB03 CB05 CB08 DA03 DA05 DA07 DA08 DB10 DC01 EA01

Claims (1)

[Claims] 1. A first catalyst provided in an exhaust passage for storing a sulfur component in fuel, and capable of releasing the stored sulfur component when the temperature is high and the exhaust air-fuel ratio is a rich air-fuel ratio; Of which is provided downstream of the first catalyst,
A second catalyst having an oxygen storage function; an air supply unit for supplying air to the second catalyst; and operating the air supply unit in an engine operating state in which a sulfur component is released from the first catalyst. An exhaust gas purifying apparatus for an internal combustion engine, comprising: