JP2000120483A - Lean-burn internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the thermal degradation of an exhaust emission control catalyst by setting a reducing atmosphere while preventing output from increasing more than output of an engine operation state causing an oxidizing atmosphere when detecting an engine state where a catalyst temperature is higher than a prescribed temperature and the periphery of the exhaust emission control catalyst becomes the oxidizing atmosphere. SOLUTION: When a mode becomes a lean operation mode of a fuel cut, a low load and a low rotation area from a rich operation mode of stoichiometric or a high load and a high rotation area (S10), a judgment is made on whether or not a catalyst temperature is above a lean heat resistant temperature (S20). When the catalyst temperature is not less than the lean heat resistant temperature, a fuel injection valve is actuated on and after the middle period of an expansion stroke to perform additional fuel injection control as reducing atmosphere forming control by a reducing atmosphere forming control means separately from main fuel injection (S30). Next, a judgment is made on whether or not the catalyst temperature is not less than a rich heat resistant temperature in additional fuel injection (S40), and when the catalyst temperature is not less than a rich catalyst temperature, the additional fuel injection is stopped, and a throttle valve is controlled to the valve closing side to increase an exhaust gas flow rate (S50, S60).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the harmful components in the exhaust gas, in particular, comprises an exhaust gas purifying catalyst for purifying NO _X, relates lean burn internal combustion engine.

[0002]

2. Description of the Related Art Generally, an exhaust passage of an internal combustion engine for a vehicle is used.
Harmful components (HC, CONO)_XEtc.)
A catalyst is provided. As this catalyst,
Internal combustion engine that performs only stoichiometric operation or rich operation
The conventional three-way catalyst is applied for stoichiometric operation or
For internal combustion engines that perform lean operation in addition to
In a three-way catalyst, the NO_XTen
Because the air-fuel ratio is lean
NO in exhaust gas _XCan purify NO_XCatalyst applied
It is.

[0003] Here, NO _X catalyst, a selective reduction to selectively reduce NO _X in the lean atmosphere roughly divided into the NO _X adsorbed on the catalyst in a lean atmosphere, on the catalyst in stoichiometric ratio or rich atmosphere the adsorbed NO _X emission can be classified into the occlusion-type reducing.

[0004]

[SUMMARY OF THE INVENTION Incidentally, the heat resistance temperature of the three-way catalyst and NO _X catalyst is generally the case when the catalyst around a reducing atmosphere (exhaust gas air-fuel ratio is for rich) in an oxidizing atmosphere than (exhaust gas air-fuel ratio Is leaner). Therefore, when the surroundings of the catalyst are in a reducing atmosphere, the catalyst temperature is adjusted so as to be lower than or equal to the heat resistance temperature (rich heat resistant temperature) in the case of the reducing atmosphere. (Lean heat resistance temperature) The catalyst temperature must be adjusted to be below.

However, for example, a three-way catalyst and NO _X
In a lean-burn internal combustion engine equipped with a catalyst, even if the catalyst temperature is adjusted so as to be lower than the rich heat resistance temperature in the case of a reducing atmosphere, the temperature of the catalyst is equal to or higher than a predetermined temperature, that is, the lean heat resistance temperature in the case of an oxidizing atmosphere. During high-temperature rich operation (during high-load / high-speed operation), for example, when the fuel system shifts to a fuel-cut operation state or is switched to lean operation (operation at low-load / low-speed operation), the exhaust system Becomes an oxidizing atmosphere in which O _{2 is} excessive. In this case, since the temperature of the catalyst does not immediately decrease, a state in which the temperature exceeds the lean heat-resistant temperature occurs in an oxidizing atmosphere, and the catalyst is thermally degraded.

[0006] Generally, the heat resistance temperature of the NO _X catalyst,
Since lower than the heat resistant temperature of the three-way catalyst, problems of thermal degradation in the NO _X catalyst is particularly remarkable. In addition, storage type NO _X
For lean-burn internal combustion engine having a catalyst, this means that the sulfur component contained in the exhaust gas will be trapped by the occluding type NO _X catalyst, purifying ability of the NO _X by the occlusion-type NO _X catalyst is reduced (which Is called S poisoning), for example,
As disclosed in Japanese Patent Laid-Open No. 7-217474, a catalyst and a reducing atmosphere, and, the occlusion-type NO _X catalyst predetermined high temperature; requires catalyst regeneration control according to (catalyst regeneration temperature, for example about 600 ° C.) is there.

However, when the catalyst regeneration control is being performed, if a predetermined operation state such as deceleration is performed and the fuel supply is stopped (fuel cut) or suppressed so as not to deteriorate drivability, the occlusion is performed. it may type NO _X catalyst resulting in thermal degradation, also sometimes to perform the catalyst regeneration control becomes difficult. In other words, when the catalyst regeneration control is performed and the catalyst temperature is equal to or higher than the lean heat-resistant temperature, a predetermined operation state such as deceleration is performed, and the fuel supply is stopped (fuel cut) or the drivability is not deteriorated. Once suppressed, since the catalyst around the state of oxidizing atmosphere at a lean heat-resistant temperature higher, so that the occlusion-type NO _X catalyst resulting in thermally deteriorated in this case.

When the catalyst regeneration control is performed and the catalyst temperature is equal to or higher than the catalyst regeneration temperature but is equal to or lower than the lean heat-resistant temperature, a predetermined operation state such as deceleration is performed, and the fuel supply is stopped (fuel cut). Or the drivability is suppressed to such an extent that the drivability is not deteriorated, the surroundings of the catalyst become an oxidizing atmosphere and the catalyst temperature also decreases, so that it is possible to reliably release SO _X from the storage NO _X catalyst. It is difficult to maintain the catalyst temperature at a temperature equal to or higher than the possible catalyst regeneration temperature, and in practice, it becomes difficult to execute the catalyst regeneration control.

Therefore, as a measure against thermal degradation of the catalyst at the time of fuel cut, for example, Japanese Patent Application Laid-Open No. 8-144814 proposes prohibiting the fuel cut operation when the catalyst temperature is higher than a predetermined temperature. However, in this technology, it is possible to prevent the catalyst from exceeding the allowable temperature limit during the fuel cut operation by certainly not setting the surroundings of the catalyst to an oxidizing atmosphere, but despite the fact that the fuel cut operation is required, Since the fuel cut is prohibited, the drivability deteriorates.

[0010] The present invention has been made in view of the above problems, and even if the catalyst temperature is higher than a predetermined temperature and becomes an oxidizing atmosphere, drivability and fuel efficiency are not deteriorated. sulfur and to reliably suppress thermal deterioration of the catalyst for exhaust gas purification, a first object to provide a lean-burn internal combustion engine, also in the case of using the occlusion-type NO _X catalyst, which is stored in the catalyst It is a second object of the present invention to provide a lean-burn internal combustion engine capable of efficiently removing components.

[0011]

Therefore, in the lean-burn internal combustion engine according to the present invention, the reducing atmosphere control means determines that the catalyst temperature detected or estimated by the temperature detecting means is equal to or higher than a predetermined temperature. When the operating state detecting means detects or estimates an engine operating state in which the surroundings of the exhaust gas purifying catalyst are in an oxidizing atmosphere, the output of the exhaust gas purifying catalyst is prevented from increasing more than the output in the engine operating state in an oxidizing atmosphere. The surrounding area is set as a reducing atmosphere.

As a result, the drivability is deteriorated.
If the catalyst temperature is higher than the predetermined temperature,
Exhaust gas purification because the surrounding area of the catalyst
Thermal degradation of the catalyst for use can be suppressed. Claim 2
In the lean burn internal combustion engine of the present invention, the exhaust gas purifying catalyst
But NO in exhaust gas under oxygen-excess atmosphere_xOccludes and acid
NO occluded in an atmosphere with reduced elemental concentration _xRelease type
NO_xIt is a catalyst. And the exhaust gas is detected by the poison detection means.
Poisoning of exhaust gas purifying catalyst by sulfur component in
Is estimated and fuel supply is suppressed during regeneration control by the regeneration means.
The fuel supply for main combustion is stopped or
A place where you want to curb your livelihood
In this case, the reducing atmosphere control means
The surrounding area is set as a reducing atmosphere.

Thus, even if the throttle valve is fully or substantially fully closed and the fuel supply for main combustion is stopped or suppressed to such an extent that drivability is not deteriorated, the reducing atmosphere control means is used. The area around the exhaust gas purifying catalyst is a reducing atmosphere, so that a decrease in catalyst temperature can be suppressed, and sulfur components can be efficiently desorbed from the exhaust gas purifying catalyst.

According to a third aspect of the present invention, the lean burn internal combustion engine includes a fuel injection valve for directly injecting fuel into the combustion chamber. Then, the reducing atmosphere control means operates the fuel injection valve during the expansion stroke or the exhaust stroke separately from the fuel injection for the main combustion to inject additional fuel. This allows the surroundings of the exhaust gas purifying catalyst to be in a reducing atmosphere without deteriorating the drivability while performing the operation according to the driver's request in a predetermined operation state such as at the time of deceleration.

According to a fourth aspect of the present invention, there is provided a lean-burn internal combustion engine including a fuel injection valve for injecting fuel into a combustion chamber or an intake passage, and an ignition plug disposed to face the combustion chamber. Then, the reducing atmosphere control means executes the operation of the fuel supply suppressing means and the inhibition of the operation of the ignition plug in a predetermined operation state in which the throttle valve is fully or substantially fully closed. As a result, in accordance with the driver's request in a predetermined operation state such as deceleration, the fuel supply for main combustion does not contribute to the output, and the area around the exhaust gas purifying catalyst is reliably reduced. It can be.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. First, a lean-burn internal combustion engine according to a first embodiment will be described with reference to FIGS. The lean-burn internal combustion engine according to the present embodiment is configured as shown in FIG. 1, and is a four-stroke engine lean-burn internal combustion engine that performs each of the intake, compression, expansion, and exhaust strokes in one operation cycle. The engine is configured as a direct injection type internal combustion engine (direct injection engine) which is of a spark ignition type and directly injects fuel into a combustion chamber.

An intake passage 2 and an exhaust passage 3 are connected to the combustion chamber 1 so that the intake passage 2 and the exhaust passage 3 can communicate with each other.
The opening and closing of the exhaust passage 3 and the combustion chamber 1 is controlled by an exhaust valve 5. The intake passage 2 is provided with an air cleaner and a throttle valve 12 (not shown), and the exhaust passage 3 is provided with an exhaust gas purifying catalyst 6 and a muffler (muffler) (not shown).

Here, as shown in FIG. 1, the exhaust gas purifying catalyst 6 includes a lean NO _x catalyst (hereinafter, referred to as NO _x catalyst) 6F and a three-way catalyst 6B. Done That, CO in the exhaust gas under the stoichiometric air-fuel ratio, the three-way catalyst 6B having a can purify ternary function HC and NO _x is provided with further savings operating the engine while the air-fuel ratio to the lean that because of the engine, so that it can fully purify NO _x in the exhaust gas generated during lean operation, NO _x catalyst 6F upstream of the three-way catalyst 6B is provided.

Here, the NO _x catalyst 6F of the present embodiment is
In a type which purifies NO _X in the exhaust gas by selectively reducing NO _X in lean atmosphere (selective reduction type lean NO _X catalyst), for example, alumina Al ₂ O ₃ as a carrier, on the carrier , Iridium and the like are supported. Further, the throttle valve 12 is electrically driven by a motor 13 based on a signal of the depression amount of an accelerator pedal (not shown) to change its opening degree.
The amount of air introduced into the inside is adjusted.

The injector (fuel injection valve) 8
In order to inject fuel directly into the combustion chamber 1 in the cylinder, the opening is arranged to face the combustion chamber 1. Naturally, the injectors 8 are provided for each cylinder. For example, if the engine of the present embodiment is an in-line four-cylinder engine, four injectors 8 are provided.

With such a configuration, the air sucked through the air cleaner (not shown) in accordance with the opening of the throttle valve 12 which is electrically controlled is drawn into the combustion chamber 1 by opening the intake valve 4, and the combustion chamber 1 Inside, the intake air and fuel directly injected from the injector 8 based on a signal from an electronic control unit (ECU) 20 as a control means are mixed, and an ignition plug (ignition plug) is formed in the combustion chamber 1.
After the engine 7 is ignited at an appropriate timing and burned to generate engine torque, exhaust gas is discharged from the combustion chamber 1 to the exhaust passage 3 and the exhaust gas purification device 6
In CO in the exhaust gas, HC, since the purifying three harmful components NO _x, are muted in the muffler so as to be discharged to the atmosphere side.

The engine is provided with various sensors, and detection signals from the sensors are sent to the ECU 20. For example, the upstream portion of the exhaust passage 3 and O ₂ sensor 11 is provided, the O ₂ sensor 11 detects the atmosphere around the exhaust gas purifying catalyst 6, the detection signal is adapted to be sent to the ECU20 ing.

Further, on the downstream side of the O ₂ sensor 11,
A high temperature sensor (exhaust gas temperature sensor, temperature detecting means) 9 is provided at an upstream portion of the exhaust gas purifying catalyst 6 in the exhaust passage 3, and a detection signal from the high temperature sensor 9 is sent to the ECU 20. As described later, the catalyst temperature is estimated based on detection information from the high temperature sensor 9 and the like. If a sensor capable of directly detecting the temperature of the exhaust gas purifying catalyst 6 can be provided, this sensor may be used as a temperature detecting means instead of the high temperature sensor 9.

Here, the operation mode of the present engine will be described.
The intake air flow flowing into the inside is formed so as to form a vertical vortex (reverse tumble flow), and in the combustion chamber 1, the intake air flow forms such a vertical vortex. A small amount of fuel can be collected only in the vicinity of the spark plug 7 disposed in the center of the top of the chamber 1 and an extremely lean air-fuel ratio can be obtained in a portion separated from the spark plug 7. To a stoichiometric air-fuel ratio or a rich air-fuel ratio to achieve stable stratified combustion (stratified super-lean combustion)
While suppressing fuel consumption. The optimum fuel injection timing in this case is the latter stage of the compression stroke in which the air flow is weak and fuel is not excessively diffused by the time of ignition.

When a high output is obtained from the engine, the fuel from the injector 8 is homogenized in the entire combustion chamber 1 to bring the entire combustion chamber 1 into a mixture state of a stoichiometric air-fuel ratio or a lean air-fuel ratio. The stoichiometric air-fuel ratio can provide a higher output than the lean air-fuel ratio. Of course, the timing at which the fuel is sufficiently atomized and vaporized is also used. By performing the fuel injection, a high output can be obtained efficiently. In such a case, the optimal fuel injection timing is set so as to end the fuel injection during the intake stroke so that atomization and vaporization of the fuel can be promoted using the intake air flow.

For this reason, in the present engine, as a mode of fuel injection, operation (super lean) in a very lean state of the fuel (that is, the air-fuel ratio is much larger than the stoichiometric air-fuel ratio) due to the stratified combustion by the compression stroke fuel injection. (Combustion operation), a compression lean operation mode, an intake lean operation mode in which the operation is performed in a fuel-lean state (that is, the air-fuel ratio is larger than the stoichiometric air-fuel ratio) although not as much as the compression lean operation mode, and an air-fuel ratio A stoichiometric operation mode (stoichiometric feedback operation mode) in which feedback control is performed based on O ₂ sensor information or the like so as to achieve a stoichiometric air-fuel ratio, and a state in which fuel is rich (that is, the air-fuel ratio is smaller than the stoichiometric air-fuel ratio) And an enriched operation mode (open loop mode) for performing the operation in the above.

Then, based on the engine speed Ne and the effective pressure Pe indicating the load state, the engine speed N
When e is low and the load Pe is small, the compression lean operation mode is selected, and as the engine speed Ne and the load Pe become larger, the intake lean operation mode, the stoichiometric feedback operation mode, and the open loop Mode is selected.

In addition, a fuel cut mode is provided. In the fuel cut mode, when the throttle valve 12 is fully closed or substantially fully closed during deceleration or the like, since the driver does not request an output, the fuel is cut for the purpose of preventing wasteful fuel consumption and the like. This is a mode in which the supply is stopped or suppressed to such an extent that the drivability is not deteriorated. By the way, as shown in FIG. 2, the heat-resistant temperature of the exhaust gas purifying catalyst 6 is generally lower in the oxidizing atmosphere (in the case where the exhaust gas air-fuel ratio is rich) than in the case where the atmosphere around the catalyst is the reducing atmosphere (when the exhaust gas air-fuel ratio is rich). Case) is lower. For this reason, when the surroundings of the catalyst are in a reducing atmosphere, the catalyst temperature is adjusted so as to be lower than the heat resistance temperature (rich heat resistant temperature; for example, 800 ° C.) of the reducing atmosphere. The catalyst temperature is adjusted so as to be lower than the heat-resistant temperature (lean heat-resistant temperature; for example, 700 ° C.) in this case.

However, for example, if the fuel cut is performed during normal operation, the exhaust system becomes an oxidizing atmosphere with an excess of O ₂ (lean atmosphere in which the exhaust gas air-fuel ratio is lean). In this case, the temperature around the catalyst becomes high and the atmosphere becomes lean, and the temperature of the catalyst may exceed its heat-resistant temperature, which may cause the exhaust gas purifying catalyst 6 to be thermally degraded.

For example, in a state where the catalyst temperature is constantly adjusted to be equal to or lower than the rich heat resistance temperature in the case of the rich operation, in order to improve fuel efficiency and prevent damage to the engine, etc.
In a predetermined operation state, control for stopping the fuel supply to the internal combustion engine (this is called fuel cut) is performed, and FIG.
As shown in Fig. 2, when the operation mode is switched from rich to fuel cut (the exhaust gas air-fuel ratio becomes lean), the catalyst temperature becomes lean heat resistant, for example, for several seconds to several hundred seconds after switching, as shown by the solid line A in Fig. 2. In some cases, the temperature of the exhaust gas purifying catalyst 6 is deteriorated by heat.

Also, when the operation mode is switched from the stoichiometric operation mode or the enrichment operation mode (operation mode in a high load / high rotation range) to the lean operation mode (operation mode in a low load / low rotation range), the fuel As in the case of cutting, when the catalyst temperature exceeds its heat-resistant temperature, the surroundings of the catalyst may become an oxidizing atmosphere, and the exhaust gas purifying catalyst 6 is thermally degraded.

For this reason, in the case where the operating mode is switched to the fuel cut mode or the lean operating mode in a state where the catalyst temperature exceeds the lean heat-resistant temperature, for example, when the catalyst periphery becomes an oxidizing atmosphere, A reduction atmosphere control is performed so that the atmosphere around the catalyst is a reduction atmosphere. That is, the ECU 20 determines whether the operation mode is the lean operation mode or the fuel cut mode, that is, whether the engine is in the engine operation state in which the surroundings of the catalyst are in an oxidizing atmosphere, by determining the throttle valve position, the vehicle speed, the operation mode, the engine load, the engine load, and the like. Detection or estimation is performed based on the rotation speed or the like. Then, the engine operating state in which the catalyst temperature detected based on the detection information from the high temperature sensor 9 is equal to or higher than the lean heat-resistant temperature (predetermined temperature) and the surroundings of the catalyst become an oxidizing atmosphere is detected or estimated by the operating state detecting means. In this case, the periphery of the catalyst is set to a reducing atmosphere while the output is not increased more than the output in the engine operating state.

Among the functions in the ECU 20, a function of detecting or estimating whether or not the engine is in an oxidizing atmosphere around the catalyst is called an operating state detecting means, and is controlled so that the area around the catalyst becomes a reducing atmosphere. The function is called a reducing atmosphere control means. Therefore, in the lean burn internal combustion engine according to the first embodiment of the present invention, the control for reducing the atmosphere around the catalyst to the reducing atmosphere is performed as follows.

That is, as shown in the flowchart of FIG. 3, first, in step S10, it is determined whether or not the fuel cut mode or the lean operation mode has been switched from the stoichiometric operation mode or the rich operation mode. If the result of this determination is that the fuel cut mode or the lean operation mode has not been switched from the stoichiometric operation mode or the rich operation mode, the routine returns. On the other hand, when the mode is changed from the stoichiometric operation mode or the rich operation mode to the fuel cut mode or the lean operation mode, the process proceeds to step S20, and whether or not the catalyst temperature (the output of the high temperature sensor 9) is equal to or higher than the lean heat resistance temperature (for example, 700 ° C.). Is determined.

If the result of this determination is that the catalyst temperature is equal to or higher than the lean heat-resistant temperature, the routine proceeds to step S30, in which the fuel injection valve 8 is operated after the middle stage of the expansion stroke to separate the main fuel injection for obtaining the output torque. Additional fuel injection control is performed as reducing atmosphere control by reducing atmosphere control means for performing additional fuel injection. On the other hand, if it is determined in step S20 that the catalyst temperature is lower than the lean heat-resistant temperature, the process returns.

Then, the process proceeds to a step S40, wherein it is determined whether or not the catalyst temperature becomes equal to or higher than the rich heat-resistant temperature (for example, 800 ° C.) by the additional fuel injection control. If the result of this determination is that the catalyst temperature is equal to or higher than the rich heat-resistant temperature, the catalyst temperature becomes excessively high, and thermal deterioration of the catalyst occurs. Therefore, the process proceeds to step S50, and the additional fuel injection control is stopped. Proceeding to S60, in order to lower the catalyst temperature, the throttle valve 12 is controlled to the valve opening side to increase the exhaust gas flow rate, and the routine returns.

Therefore, according to the lean burn internal combustion engine of this embodiment, when the catalyst temperature is higher than the lean heat-resistant temperature,
In order to perform additional fuel injection after the middle stage of the expansion stroke as reduction atmosphere control, in the fuel cut mode such as at the time of deceleration due to the throttle fully closed or substantially fully closed, or in the predetermined operation state where the stoichiometric or enriched operation mode becomes the lean operation mode, without affecting the output torque (i.e., without deteriorating the drivability), NO _X catalyst 6
The periphery of F can be a reducing atmosphere, and the heat resistant temperature becomes a rich heat resistant temperature higher than the lean heat resistant temperature. Thereby, there is an advantage that thermal deterioration of the exhaust gas purifying catalyst 6 due to the catalyst temperature exceeding the heat resistant temperature can be reliably suppressed.

In the reducing atmosphere control according to the present embodiment, the additional fuel is injected into the combustion chamber to reduce the atmosphere around the catalyst. However, for example, in the predetermined operation state of the fuel cut mode, the additional fuel is not injected. The main fuel injection is performed by operating the fuel injection valve 8 without stopping, and
The operation of the ignition plug 7 may be prohibited, and the atmosphere around the catalyst may be set as a reducing atmosphere.

[0039] In this technique, performed operation in response to a request of the driver in the predetermined operating condition, without affecting the output torque, there is an advantage that the periphery of the NO _X catalyst 6F may be a reducing atmosphere. This method is particularly effective in an intake pipe injection type internal combustion engine. In the present embodiment, the NO _X catalyst 6F is a selective reduction type NO _X catalyst. However, the NO _X catalyst is not limited to this, and may be a storage type NO _X catalyst. The effect can be obtained.

In this embodiment, a lean-burn internal combustion engine is described. However, a conventional internal combustion engine that performs only a rich operation or a stoichiometric operation may be used. In this case, a three-way catalyst is provided. The reduction atmosphere control may be performed based on the heat resistance temperature of the three-way catalyst to control the thermal degradation of the catalyst. In this embodiment, the opening of the throttle valve 12 is adjusted to increase the flow rate of exhaust gas flowing into the exhaust gas purifying catalyst 6. However, in the case of an internal combustion engine having a bypass passage that bypasses the throttle valve 12, Alternatively, an ABV (air bypass valve) or an ISC (idle speed control) valve provided in the bypass passage may be fully opened to increase the amount of intake air and increase the flow rate of exhaust gas flowing into the exhaust gas purifying catalyst 6. Alternatively, a separate air pump may be provided to introduce the air in the atmosphere into the exhaust passage 3 as secondary air, thereby increasing the flow rate of exhaust gas flowing into the exhaust gas purifying catalyst 6.

Next, a lean-burn internal combustion engine according to a second embodiment will be described with reference to FIGS. The lean-burn internal combustion engine according to the present embodiment, as shown in FIG. 4, although NO _X catalyst 6A is provided upstream of the three-way catalyst 6B, the NO _X catalyst 6A is different from the first embodiment, NO By storing _X on the catalyst, N
Of the type which purifies O _X (occlusion-type lean NO _X catalyst, trap type lean NO _X catalyst) A, the NO
Front catalyst (light-off catalyst) upstream of _X catalyst 6A
6C is added.

The front catalyst 6C is used to remove C from the exhaust gas.
O, composed of a three-way catalyst that functions to purify HC and NO _x. The light-off catalyst 6D is disposed in the exhaust passage 3 immediately downstream of the combustion chamber 1 of the engine such that the light-off catalyst 6D is immediately activated by the high-temperature exhaust gas from a cold start of the engine. During the cold start, HC in the exhaust gas is reduced.

The NO constituting the exhaust gas purifying catalyst 6
_XNO at the downstream side of the catalyst 6A _XSensor 10 is provided
NO_XDetecting decrease in purification efficiency of catalyst 6A
I have. NO_XThe information detected by the sensor 10 is ECU
20 and the ECU 20 determines NO_XDetection of sensor 10
Based on the output information etc., reduce the atmosphere around the catalyst to a reducing atmosphere.
A revival system that controls the air-fuel ratio of the engine to stoichiometric or rich
You (rich spikes) are performed.

[0044] In addition, NO _X catalyst 6A is an oxidizing atmosphere N
Sulfur component in the exhaust gas with O _X also will be occluded S
Poisoned. For this reason, the ECU 20 calculates the integrated value of the fuel pulse width, which is considered to be a parameter corresponding to the SO _X adsorption amount adsorbed on the NO _X catalyst 6A, and determines whether or not the integrated value is equal to or larger than a predetermined amount. NO _X catalyst 6A is adapted to estimate whether the poisoned by sulfur components in the. Incidentally, the function of estimating the poisoning of the NO _X catalyst 6A of the ECU20 as poisoning detecting means. Further, the poisoning detecting means may directly detect the SO _X adsorption amount.

Further, ECU 20, when the poisoning of the NO _X catalyst 6A is detected by the poisoning detecting means, NO _X catalyst 6
It raised the temperature of A and a high temperature state of the catalyst temperature, for example 650 ° C. or higher, the sulfur component is adapted to perform reproduction control to be released from the catalyst the periphery of the NO _X catalyst 6A as the reducing atmosphere. The function of the ECU 20 is referred to as a reproducing unit.

In the lean-burn internal combustion engine, as in the case of the first embodiment, when the throttle valve 12 is closed in a predetermined operation state such as during deceleration, the driver requests an output. For this purpose, a fuel cut mode is provided as an operation mode in which fuel supply is stopped or the drivability is suppressed to such an extent that drivability is not deteriorated.

The operation mode is switched by the ECU 20.
The function of the ECU 20 is that the operation mode is changed to the fuel cut mode by the ECU 20, and the function of stopping the fuel supply from the injector 8 for the main combustion or suppressing the drivability to such an extent that the drivability is not deteriorated is referred to as fuel supply suppression means. Further, the ECU 20, when the operation mode is the fuel cut mode when running regeneration control for regenerating the NO _X catalyst 6A to improve the NO _X purification efficiency of the NO _X catalyst 6A, NO _X catalyst 6A is adapted to not to thermal degradation, or efficiently perform a reducing atmosphere of control that a reducing atmosphere surrounding the catalyst to play nO _X catalyst 6A. The function of the ECU 20 is referred to as a reducing atmosphere control means.

Next, the control for reducing atmosphere performed in the lean burn internal combustion engine according to the second embodiment of the present invention will be described.
This will be described with reference to the flowchart of FIG. First, in step A10, SO to poisoning detecting means NO _X catalyst 6A
It is determined whether the _X adsorption amount is equal to or more than a predetermined amount. That is, it is determined whether the SO _X adsorption amount calculated as the integrated value of the fuel pulse width is equal to or more than a predetermined amount. As a result of this determination, if it is determined that the SO _X adsorption amount is not equal to or more than the predetermined amount, the process returns because the regeneration control is not required yet.

On the other hand, if it is determined in step A10 that the SO _X adsorption amount is equal to or more than the predetermined amount, the NO _X catalyst 6A
Since NO _X purification efficiency is reduced by the adsorption of SO _X on the surface, the process proceeds to step A20, and the regeneration control is executed. In this regeneration control, by injecting additional fuel in the expansion stroke after the middle period in addition to main injection for main combustion, NO _X catalyst 6
A is heated to a desired high temperature state (for example, 650 ° C .; this is referred to as catalyst regeneration temperature). Thereafter, the additional fuel injection is stopped and only the main injection is performed. At this time, the air-fuel ratio is set to, for example, a rich air-fuel ratio of about 12 so that the area around the catalyst becomes a reducing atmosphere.

[0050] Since the catalyst temperature by performing reproduction control in order to release the sulfur component from the NO _X catalyst 6A is set to be above the catalyst regeneration temperature, the catalyst temperature is lean heat temperature (e.g. 700 ° C.) or higher May be. Therefore, the difference in catalyst temperature when entering the fuel cut mode, that is, when the catalyst temperature is equal to or higher than the catalyst regeneration temperature, the catalyst temperature is different between the case where the catalyst temperature is equal to or higher than the lean heat-resistant temperature and the case where the catalyst temperature is lower than the lean heat-resistant temperature. Problems arise.

[0051] That is, when the catalyst temperature entering the fuel cut mode when it is lean heat resistance temperature or higher, the catalyst peripheral becomes oxidizing atmosphere, NO _X catalyst 6A is that resulting in thermal degradation. On the other hand, it enters the fuel cut mode, with a catalyst around the oxidizing atmosphere, since the catalyst temperature is lowered, when the catalyst temperature is less than the lean heat temperature, NO _X catalyst 6A immediately catalyst regeneration temperature becomes below, can not be sufficiently release the sulfur component from the NO _X catalyst 6A, it is to regenerate the NO _X catalyst 6A efficiently difficult.

Therefore, in step A30, the ECU 2
From the signal of 0, it is determined whether or not the operation mode is the fuel cut mode. When the fuel cut mode is set, the process proceeds to step A40, and additional fuel injection is performed as reducing atmosphere control by the reducing atmosphere control means.
In this case, the reducing atmosphere of control, when the catalyst temperature is lean heat resistance temperature or higher is for NO _X catalyst 6A is prevented from thermal deterioration, when the catalyst temperature is less than the lean heat temperature NO _X catalyst 6A by regeneration control
As the sulfur component is fully released from, NO _X
This is for efficiently regenerating the catalyst 6A. On the other hand, if the fuel cut mode is not set, the routine returns.

[0053] NO _X by such a reducing atmosphere of control
Since the vicinity of the catalyst 6A is a reducing atmosphere (rich atmosphere), it is possible to prevent the surroundings of the catalyst from becoming an oxidizing atmosphere when the catalyst temperature is equal to or higher than the lean heat-resistant temperature. In addition, when the temperature is lower than the lean heat resistance temperature, the catalyst temperature can be prevented from lowering, whereby the reducing atmosphere state can be maintained at a predetermined temperature (for example, about 650 ° C.) or higher suitable for desorbing the sulfur component. That is, the SO _X adsorbed on the NO _X catalyst 6A is efficiently released even during the fuel cut mode, and the NO _X purification efficiency by the NO _X catalyst 6A is restored at an early stage.

Therefore, according to the lean burn internal combustion engine of this embodiment, even in the case of a predetermined operation state such as deceleration during the regeneration control, the surroundings of the catalyst can be brought into the reducing atmosphere without deteriorating the drivability. can, thereby it is possible to prevent thermal deterioration of the NO _X catalyst 6A, without lowering the catalyst temperature even in the predetermined operating state, N =
There is an advantage that SO _X can be efficiently desorbed from the O _X catalyst 6A.

In the present embodiment, the surrounding area of the catalyst is brought into a reducing atmosphere by injecting additional fuel. However, in a predetermined operating state, the fuel injection valve 8 is operated to perform main fuel injection, and the ignition plug 7 is operated. so as to prohibit the periphery of the nO _X catalyst 6A so as not to affect the output torque may be a reducing atmosphere. Further, in each of the above-described embodiments, as the reducing atmosphere control means, the additional fuel injection is performed after the middle stage of the expansion stroke.
If the ignition plug 7 is smoldering easily, that is, if fuel easily adheres to the ignition plug 7, the additional fuel injection in the exhaust stroke is actively performed as the regeneration control so that the additional fuel injected fuel is exhausted. The fuel stay time around the spark plug 7 may be shortened as much as possible to improve the smoldering resistance.

In each of the above embodiments, the internal combustion engine is described as a direct injection internal combustion engine, but the internal combustion engine is not limited to this. Further, the internal combustion engine according to each of the above embodiments has been described as a lean burn engine. However, since the fuel cut operation is performed not only for the lean burn engine, the control according to the first embodiment is different from the conventional rich operation. Alternatively, the present invention can be applied to an internal combustion engine that performs only the stoichiometric operation. That is, even if the engine is not a lean burn engine, if the fuel cut is performed, the exhaust gas air-fuel ratio becomes lean. In this case, if the exhaust gas purifying catalyst 6 is at or above a predetermined temperature, it will be thermally degraded. To suppress this, the present invention can be applied.

[0057]

As described in detail above, claims 1, 3, 4
According to the lean-burn internal combustion engine of the present invention described above, there is an advantage that the thermal deterioration of the exhaust gas purifying catalyst due to the catalyst temperature exceeding the allowable temperature can be reliably suppressed without deteriorating drivability. According to the lean-burn internal combustion engine of the present invention, there is an advantage that thermal deterioration of the exhaust gas purifying catalyst can be prevented and SO _X can be efficiently released from the exhaust gas purifying catalyst. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an overall configuration of a lean burn internal combustion engine according to a first embodiment of the present invention.

FIG. 2 is a view showing a heat resistant temperature of an exhaust gas purifying catalyst provided in the lean burn internal combustion engine according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing a reducing atmosphere control of the lean burn internal combustion engine according to the first embodiment of the present invention.

FIG. 4 is a schematic diagram showing an overall configuration of a lean burn internal combustion engine according to a second embodiment of the present invention.

FIG. 5 is a flowchart showing a control of regeneration of an exhaust gas purifying catalyst by a reducing atmosphere control means of a lean burn internal combustion engine according to a second embodiment of the present invention.

[Explanation of symbols]

6 exhaust gas purifying catalyst 6A, 6F NO _X catalyst 6B three way catalyst 6C front catalyst 7 spark plug (ignition plug) 8 fuel injection valve 9 hot sensor (temperature detecting means) 10 NO _X sensor 11 O ₂ sensor 12 throttle valve 20 ECU (Operating state detection means, fuel supply suppression means,
Temperature detecting means, poisoning detecting means, regeneration means, reducing atmosphere control means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) F01N 3/28 301 F01N 3/28 301D F02D 41/02 301 F02D 41/02 301A 41/04 330 41/04 330Z 43/00 301 43/00 301A 301H 301K 45/00 312 45/00 312J 314 314R (72) Inventor Kazuhito Kawashima F33-term, 33-3, Shiba 5-chome, Minato-ku, Tokyo F-term (reference 3G084 AA04 BA13 BA15 BA16 BA24 CA06 DA02 DA10 DA22 EB24 EC02 EC03 FA10 FA18 FA27 FA28 FA38 3G091 AA02 AA12 AA17 AA24 AB03 AB05 AB06 BA07 BA13 BA14 CB02 CB03 CB05 DA01 DA02 DA06 DA08 DA10 DB03 EA01 EA03 EA03 EA01 EA03 JA03 JA15 JA21 JA25 JA33 KA01 KA08 KA09 KA11 KA16 KA24 KA25 LA00 LA01 LA04 LB02 LB04 MA01 MA11 MA19 MA24

Claims (4)

[Claims] 1. An exhaust gas purifying catalyst provided in an exhaust passage of an internal combustion engine for purifying harmful components in exhaust gas, and an operating state for detecting or estimating an engine operating state in which an area around the exhaust gas purifying catalyst becomes an oxidizing atmosphere. Detecting means; temperature detecting means for detecting or estimating the temperature of the exhaust gas purifying catalyst; catalyst temperature detected or estimated by the temperature detecting means being equal to or higher than a predetermined temperature; and the exhaust gas purifying catalyst being detected by the operating state detecting means. If the engine operating state in which the periphery of the exhaust gas is in an oxidizing atmosphere is detected or estimated, the reducing atmosphere control means for reducing the output around the exhaust gas purifying catalyst to a reducing atmosphere while preventing the output from increasing more than the output in the engine operating state. And a lean-burn internal combustion engine. 2. The method according to claim 1, wherein the exhaust gas purifying catalyst is in an oxygen-excess atmosphere.
NO in exhaust gas below _xOccluded in an atmosphere with low oxygen concentration
NO absorbed_x-Type NO that releases nitrogen_xIf it is a catalyst
Both poisoning of the exhaust gas purification catalyst by sulfur components in the exhaust gas
Detecting means for detecting or estimating the poisoning of the exhaust gas purifying catalyst by the poisoning detecting means.
Or, if estimated, raise the temperature of the exhaust gas purifying catalyst.
And a reducing atmosphere around the exhaust gas purifying catalyst.
Release sulfur component from the exhaust gas purifying catalyst
The throttle valve is fully closed or substantially full by the regeneration means and the operation state detection means.
The main fuel is shut off when a predetermined operating state to close is detected or estimated.
Turn off fuel supply for baking or driveability
Fuel supply suppression means to prevent fuel from deteriorating
The reducing atmosphere control means includes a regeneration control by the regeneration means.
The fuel supply is stopped or suppressed by the fuel supply suppression means during
The exhaust gas purifying catalyst and the surrounding area
The lean-burn internal combustion engine according to claim 1, wherein
Seki. 3. A fuel injection valve for directly injecting fuel into a combustion chamber, wherein the reducing atmosphere control means operates the fuel injection valve in an expansion stroke or an exhaust stroke separately from injection for main combustion. The lean-burn internal combustion engine according to claim 1, wherein a surrounding area of the exhaust gas purifying catalyst is reduced by injecting additional fuel. 4. A fuel injection valve for injecting fuel into a combustion chamber or an intake passage; a spark plug disposed so as to face the combustion chamber; and a throttle valve fully or substantially fully closed by the operating state detecting means. Fuel supply suppression means for stopping fuel supply for main combustion or suppressing drivability to the extent that drivability is not deteriorated when the predetermined operating state is detected or estimated, and the reduction atmosphere conversion control means comprises: 2. The lean-burn internal combustion engine according to claim 1, wherein the operation of the fuel supply suppressing means and the operation of the ignition plug are prohibited in the predetermined operation state, thereby reducing the atmosphere around the exhaust gas purifying catalyst to a reducing atmosphere. .