JPH1047042A - Emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently purify NOX in the wide operation region (in particular, an operation region by extra lean combustion) of a cylinder infection type internal combustion engine, in a emission control system to perform emission control of a cylinder injection type internal combustion engine to inject fuel directly in a combustion chamber. SOLUTION: A lean NOX catalyst 9 to purify mainly NOX is provided in a cylinder injection type internal combustion engine to inject fuel directly in a combustion chamber 1 and switching premixture lean combustion and layer- from lean combustion, and disposed in the exhaust passage 3 of an engine. The lean NOX catalyst 9 comprises a high temperature type lean NOX mainly bringing NOX under emission control and catalyst 9A having a high catalyst activation temperature area; and a low temperature type lean NOX catalyst 9B having a catalyst activation temperature area being lower than that of the catalyst 9A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to an exhaust gas purification system for exhaust gas purification in-cylinder injection type internal combustion engine which directly injects fuel into a combustion chamber, in particular, suitable for use in the NO _X purification during lean combustion, The present invention relates to an exhaust gas purification system.

[0002]

2. Description of the Related Art At present, the air-fuel ratio range is wider than that of a conventional lean burn internal combustion engine that switches between operation in a stoichiometric range near the stoichiometric air-fuel ratio and operation in a lean range leaner than the stoichiometric air-fuel ratio. As an engine capable of operating in an ultra-lean region to further improve fuel efficiency, an in-cylinder spark ignition internal combustion engine that directly injects fuel into a combustion chamber has been developed.

[0003] The exhaust gas temperature during operation in the stoichiometric region of this in-cylinder injection type internal combustion engine becomes as high as the exhaust gas temperature during operation in the stoichiometric region of the conventional lean burn internal combustion engine. The exhaust gas temperature during operation in the ultra-lean region of the engine (during super-lean combustion operation) is the same as the conventional lean-burn internal combustion engine (lean burn engine).
Therefore, the temperature range of the exhaust gas temperature of the in-cylinder injection type internal combustion engine becomes wider than that of the conventional lean burn internal combustion engine because the exhaust gas temperature during operation in the lean region is further lowered.

[0004] As described above, the in-cylinder injection type internal combustion engine sometimes sets a wide operating range in a lean region in order to further improve fuel efficiency. In general, in a cylinder injection type internal combustion engine, when performing stoichiometric operation, fuel injection is performed during the intake stroke to perform premixed combustion, and when performing super-lean operation, stratified combustion is performed. Fuel injection. When the stratified combustion is performed by the late compression injection, the stratified combustion region cannot be expanded to a very high load from the viewpoint of smoke generation due to fuel concentration around the spark plug. Therefore, in order to further improve the fuel efficiency as described above, it is required to set the air-fuel ratio to a leaner side than the stoichiometric ratio in the premixed combustion in which the intake stroke injection is performed. That is, in the in-cylinder injection type internal combustion engine, in order to promote the improvement of fuel efficiency, the air-fuel ratio in at least a part of the premixed combustion region is made leaner than stoichiometric, and the premixed lean combustion operation and the stratified lean are performed according to the operation state. The switching and the lean operation area are expanded. By the way, during premixed lean combustion, the air-fuel ratio is generally set smaller on the higher load side than in stratified lean combustion, so that there is a characteristic that the exhaust gas temperature is higher than during stratified lean combustion. Then, when performing the lean combustion, how to remove the generated NO _X has been a conventional problem. As a technique for reducing NO _X during lean combustion, it is known in Japanese Patent Application Laid-Open No. H03-111636 to use a lean NO _X catalyst.

[0005]

However, this lean NO _X catalyst has a catalytically active temperature range (temperature range in which exhaust gas can be purified) of the catalyst itself which is supported by each noble metal (active noble metal Pt, Ir, etc.). All of the catalysts have a narrow catalyst activation temperature range under the influence of the activation temperature of the internal combustion engine, and there is a problem that it is not possible to sufficiently cover a wide exhaust gas temperature range in a direct injection internal combustion engine.

In other words, in the cylinder injection type internal combustion engine with further improved fuel efficiency, the premixing in which the combustion energy is large and the exhaust gas temperature is high is changed from the ultra-lean combustion operation (that is, the stratified lean operation) in which the combustion energy is small and the exhaust gas temperature is low. Until the lean combustion operation, there is a wide lean air-fuel ratio region. When the above-described lean NO _X catalyst is applied to an engine that operates in such a wide exhaust gas temperature atmosphere, this wide air-fuel ratio region whole (especially, super lean region) there is a problem that can not be purified sufficiently nO _X in.

The present invention has been made in view of such a problem, and has a sufficient N in a wide operating range of a direct injection internal combustion engine (particularly, an operating range by ultra-lean combustion).
The O _X was set to be clean, and to provide an exhaust gas purification system.

[0008]

According to the present invention, there is provided an exhaust gas purification system according to the present invention, in which a fuel is directly injected into a combustion chamber to switch between premixed lean combustion and stratified lean combustion. provided to the engine, is disposed in the exhaust passage of the engine, mainly lean purifying NO _x NO _x
Comprises a catalyst, the lean NO _x catalyst, the catalytic activity and high-temperature type lean NO _x catalyst temperature range is high, the catalyst activity temperature range the high-temperature lean NO _x low low-temperature lean NO _x of the catalyst
And a catalyst.

[0009] Considering the exhaust temperature characteristics of a direct injection type internal combustion engine, to do NO _X purification in a wide operating range, the catalyst activation temperature range of the high-temperature lean NO _X catalyst is from about 300 to 550
℃ about, the catalyst activation temperature range of the low temperature lean NO _X catalyst 1
It is preferable that the temperature be about 50 to 300 ° C. In addition, the lean NO _X catalyst has a NO _X storage that oxidizes NO _X to a base adsorbent in the catalyst in an excess oxygen region and adsorbs the NO _X on the catalyst to remove NO _X adsorbed at a stoichiometric or rich air-fuel ratio. and reduction, the oxygen has a NO _X catalytic reduction type to selectively reduce NO _X in excess region of the HC coexistence of the catalyst, in view of durability and heat resistance of the surface, N is the a lean NO _X catalyst
O _X catalytic reduction type is preferable. In this case, the high-temperature lean N
O _X catalyst is iridium as the active metal, copper, cobalt, the catalyst having one of silver, low temperature lean NO
_{The X} contact is preferably a catalyst in which the noble metal is one or more selected from platinum, rhodium, and palladium.

The exhaust gas purification system according to the present invention is provided in an in-cylinder injection type internal combustion engine which directly injects fuel into a combustion chamber and switches between premixed lean combustion and stratified lean combustion. A lean NO _x catalyst that is disposed in the passage and mainly purifies NO _x during at least the premixed lean combustion; and an exhaust gas recirculation unit that recirculates exhaust gas into the intake passage of the engine during the stratified lean combustion. It is characterized by:

According to a third aspect of the present invention, there is provided an exhaust gas purifying system provided in an in-cylinder injection type internal combustion engine which directly injects fuel into a combustion chamber and switches between premixed lean combustion and stratified lean combustion. disposed in the passage includes a lean NO _x catalyst for purifying mainly NO _x at least the premixed lean combustion, and exhaust gas recirculation means for recirculating exhaust gases during the stratified lean combustion into the intake passage of the engine,
It said lean NO _x catalyst, and a catalyst activation temperature range is higher high-temperature lean NO _x catalyst, lower low temperature than the catalyst activation temperature range is provided downstream of the high-temperature lean NO _x catalyst is the high-temperature type lean NO _x catalyst It is characterized in that it is composed of a lean NO _x catalyst.

According to a fourth aspect of the present invention, there is provided an exhaust gas purifying system according to any one of the first to third aspects.
Characterized by comprising detecting means for detecting or estimating the temperature of the lean NO _x catalyst, and a Atsushi Nobori means for raising the temperature of the lean NO _x catalyst when the catalyst temperature decrease is detected or estimated by said detection means And According to a fifth aspect of the present invention, there is provided the exhaust gas purifying system according to any one of the first to fourth aspects, wherein a heat retaining means is provided on an outer periphery of the exhaust passage upstream of the lean NO _x catalyst. .

As the heat retaining means, it is preferable that the structure for attaching the heat retaining member and the exhaust passage have a double pipe structure.
According to a sixth aspect of the present invention, in the exhaust gas purifying system according to the fifth aspect, the heat retaining means is provided except for the vicinity of the exhaust manifold near the combustion chamber.

[0014] exhaust gas purifying system of the present invention of claim 7, wherein, in the structure of any of claims 1,3～6, the high-temperature type lean NO _x catalyst is iridium catalyst, the low temperature lean It is characterized in that the NO _x catalyst is a platinum-based catalyst.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an exhaust gas purifying system according to an embodiment of the present invention; FIG.
This will be described with reference to FIG. The present exhaust gas purification system has a configuration in which a catalyst is configured to sufficiently purify NO _X in the entire operation region by lean burn (lean burn), and has such a configuration in order to efficiently purify NO _X in exhaust gas. that combines catalyst and the exhaust gas recirculation means, a point in which a heating means for catalyst warm to activation temperature to ensure the NO _X purification in exhaust gas, improving the purification efficiency of the catalyst further suppressing a decrease in exhaust gas temperature It is characterized in that a heat retaining means is provided for the purpose.

FIG. 1 shows the configuration of a direct injection type internal combustion engine provided with such an exhaust gas purifying system. The internal combustion engine performs intake, compression, expansion and exhaust strokes in one operation cycle. The engine, that is, a four-cycle engine, is a spark ignition type, and is configured as a direct injection engine (direct injection internal combustion engine) that 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 they can communicate with each other. The communication between the intake passage 2 and the combustion chamber 1 is controlled by an intake valve 4.
The communication between 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 6 and a throttle valve 7 in order from the upstream side, and the exhaust passage 3 is provided with an exhaust gas purifying catalytic converter 9 as an exhaust gas purifying catalyst in order from the upstream side.
A muffler (muffler) not shown is provided.
Note that a surge tank 2a is provided in the intake passage 2.

Further, an exhaust gas recirculation device (hereinafter, referred to as an EGR device) 10 as an exhaust gas recirculation means is provided. That is, the exhaust gas recirculation passage 10 is connected to connect the surge tank 2 a of the intake passage 2 and the upstream side of the exhaust passage 3.
b in the exhaust gas recirculation passage 10b.
An R valve 10a is attached. And this E
The GR valve 10a allows the exhaust passage 3 to move from the intake passage 2 to the intake passage 2.
It is possible to control the flow rate of exhaust gas (also referred to as exhaust gas, exhaust gas or exhaust gas). The control of the EGR valve 10a is performed according to the operating state of the engine.

The EGR device is controlled so that the exhaust gas is recirculated into the intake passage 2 in a later-described injection mode (lean operation by stratified combustion) described later. It should be noted that the recirculation amount is reduced during premixed combustion, and the exhaust gas recirculation amount is set to 0 or extremely small during premixed lean combustion.
The opening of the throttle valve 7 changes in accordance with the amount of depression of an accelerator pedal (not shown), whereby the amount of air introduced into the combustion chamber 1 is adjusted. Further, 16 is an idle speed control valve (I
SC valve), which is provided in a bypass passage 16A that bypasses a throttle valve installation portion of the intake passage 2 and is driven to open and close by a stepper motor (not shown), and mainly controls the idle speed when the throttle valve 7 is fully closed or substantially fully closed. Fine tune.

Reference numeral 50 denotes an air bypass valve (ABV) which is connected to a bypass passage 50A which connects the intake passage 2 upstream of the throttle valve 7 and the surge tank 2a so as to bypass a portion of the intake passage 2 where the throttle valve 7 is provided. Provided,
The air-fuel ratio can be adjusted by adjusting the intake air amount separately from the throttle valve 7. The injector (fuel injection valve) 8 is arranged so that its opening faces the combustion chamber 1 so as to directly inject fuel toward the combustion chamber 1 in the cylinder. 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 this configuration, the air sucked through the air cleaner 6 in accordance with the opening of the throttle valve 7 is sucked into the combustion chamber 1 by opening the intake valve 4, and the air sucked inside the combustion chamber 1 And the fuel directly injected from the injector 8 are mixed, and the ignition plug 35
Is ignited at an appropriate timing to cause combustion and generate engine torque.
The exhaust gas is exhausted from the inside to the exhaust passage 3, and a catalytic converter (hereinafter, also simply referred to as a catalyst) 9 emits C in the exhaust gas.
O, HC, since the purifying three harmful components NO _x,
The sound is muted by the muffler and released to the atmosphere.

The engine will be further described. In this engine, the intake air flowing into the combustion chamber 1 from the intake passage 2 forms a vertical vortex (reverse tumble flow). Since the flow forms such a vertical vortex, the fuel is collected only in the vicinity of the spark plug 35 disposed at the center of the top of the combustion chamber 1 while utilizing the vertical vortex, and the fuel is collected at a portion separated from the spark plug 35. In this case, an extremely lean air-fuel ratio state (for example, an air-fuel ratio of 30 or more) can be obtained, and only the vicinity of the ignition plug 35 is set to the stoichiometric air-fuel ratio, thereby realizing stable stratified lean combustion and suppressing fuel consumption. be able to. The optimal fuel injection timing in this case is the latter half of the compression stroke in which the air flow is weak.

When a high output is obtained from the engine, the entire combustion chamber 1 is stoichiometrically or leanly air-fuel ratio (for example, air-fuel ratio 18 to 24) having a smaller air-fuel ratio than that in the stratified combustion.
The premixed combustion may be performed with a uniform mixture state of about 1). Of course, a higher output can be obtained by setting the stoichiometric air-fuel ratio in the combustion chamber 1 to a stoichiometric air-fuel ratio than by setting the air-fuel ratio to a lean air-fuel ratio. , According to the operating state (for example, load or rotation speed). Also in the case of these premixed combustions, a high output can be obtained efficiently by performing the fuel injection at a timing such that the fuel is sufficiently atomized and vaporized. In such a case, the optimal fuel injection timing is set so as to end the fuel injection early or in the first half of the intake stroke so that atomization and vaporization of the fuel can be promoted using the intake air flow. . Note that a case in which the premixed combustion is performed by setting the entire inside of the combustion chamber 1 to a mixture state having a lean air-fuel ratio is referred to as premixed lean combustion.

In the present engine, as shown in FIG. 5, the late injection mode, the injection mode, the stoichiometric mode, and the open loop mode are set according to the operating state (load and rotation speed) as the operation mode of the engine. And
As will be described in more detail later, in each mode, a case where the EGR is operated and a case where the EGR is stopped are set, and one of these modes is selected according to the operating state of the engine or the running state of the vehicle, and the engine control is performed. It is supposed to be.

Of these, in the latter-stage injection mode, in the present embodiment, the total air-fuel ratio is set to a range of about 24 or more.
The leanest combustion can be achieved, but in this mode, fuel injection is performed at a stage very close to the ignition timing, such as the latter stage of the compression process, and the fuel is collected very close to the ignition plug to make it partially rich and overall The lean operation is performed while saving ignitability and combustion stability.

In the first-stage injection mode, lean combustion can also be realized. In this mode, fuel injection is performed before the second-stage injection mode, and the fuel is premixed to make the overall mixture leaner than the stoichiometric air-fuel ratio. Saving operation is performed while obtaining a certain output while ensuring ignitability and combustion stability. Here, the region of the first injection mode is set to a region where the total air-fuel ratio is about 24 or less and is equal to or more than the stoichiometric air-fuel ratio.

In the stoichiometric mode, a sufficient engine output can be efficiently obtained based on the output of the O ₂ sensor while maintaining the air-fuel ratio in the stoichiometric state. In the open loop mode, combustion is performed at the stoichiometric or reach air-fuel ratio by the open loop mode control so that a sufficient output can be obtained at the time of acceleration, starting, and the like. In these modes, premix combustion based on fuel injection in the intake process is performed.

As described above, since the present engine is an engine that can perform economizing operation while keeping the air-fuel ratio lean,
In all operating ranges, the lean operating range (early injection mode,
(Late injection mode) is set widely. For this reason, in the entire operation range of the lean operation, the exhaust gas temperature fluctuates in a wide temperature range (for example, while the exhaust gas temperature is about 150 degrees in the lean operation by the stratified lean combustion, the lean operation by the premixed lean combustion is performed). In this exhaust gas purification system, the exhaust gas temperature becomes 300 degrees or more.)
Such taking into account the wide range of exhaust gas temperature characteristics, catalyst 9 so that it can perform _the NO _x purification in the entire operating range of the lean operation is different catalyst activation temperature range, during lean operation by at least the premixed lean combustion, mainly high temperature lean purifying NO _x NO _x catalyst 9A and low temperature lean N
It has a configuration which is a combination of an O _x catalyst 9B. Note that the catalyst activation temperature range refers to a temperature range in which the catalyst is activated and exhaust gas can be purified.

The high-temperature lean NO _x catalyst 9
A and low temperature lean NO _x catalyst. 9B, CO in the exhaust gas under the stoichiometric air-fuel ratio, but those with a can purify ternary function HC and NO _X, these low temperature lean NO _x catalyst. 9B, in particular, since having a good three-way function, CO in the exhaust gas under the stoichiometric air-fuel ratio, the purification of HC and NO _X is primarily with is performed by low temperature lean NO _x catalyst 9B, the air-fuel ratio is lean operation NO _X purifying a high-temperature lean NO _x catalyst 9A and low temperature lean NO in the exhaust gas when
This is performed by the _x catalyst 9B, whereby the exhaust gas can be reliably purified in the entire operation region of the lean operation.

[0030] Here, to describe in detail the catalyst 9, the high temperature-type lean NO _x catalyst 9A is a NO _x catalytic reduction type catalyst, configured as iridium catalysts having iridium (Ir) as an active metal . Incidentally, the high temperature-type lean NO _x catalyst 9A, the active metal is iridium (I
r) Other than copper (Cu), cobalt (Co), silver (Ag)
May be configured as a catalyst having any one of the above. Further, the high temperature-type lean NO _x catalyst 9A has a high catalytic activity temperature range is about 300 to 550 degrees.

On the other hand, the low temperature-type lean NO _x catalyst 9B is a catalytic reduction type catalyst, composed of platinum-based catalyst. That is, low temperature lean NO _x catalyst. 9B, the noble metal is platinum (Pt), rhodium (Rh), palladium (Pd)
Configured as a system catalyst. Also, low temperature lean NO _x
The catalyst 9B has a low catalytic activity temperature range compared to the high-temperature type lean NO _x catalyst 9A, it is about 150 to 300 degrees.

Next, high-temperature lean in the exhaust gas purifying system the NO _x catalyst 9A and low temperature lean NO _x catalyst 9
When explaining the arrangement of the B, the in the exhaust gas purification system, the catalyst activation temperature range is higher high-temperature lean NO _x catalyst 9A
Downstream of the catalyst activation temperature range is high-temperature lean NO _x catalyst 9
And to arrange the low low-temperature lean NO _x catalyst 9B than A.

[0033] This is because when the exhaust gas temperature is high, mainly, but purification of the NO _x is performed by the hot-type lean NO _x catalyst 9A, the cold-type lean NO _x catalyst 9B of high-temperature type lean NO _x catalyst 9A when placed upstream, low temperature lean NO _x since the catalyst 9B is excellent three-way function as described above, when the exhaust gas temperature is high low temperature lean NO _x catalyst 9
Will HC and CO required for purifying NO _x in the high temperature lean NO _x catalyst 9A is reduced by B, and because it becomes impossible to _the NO _x purification by high-temperature type lean NO _x catalyst 9A.

[0034] The distance between the high temperature-type lean NO _x catalyst 9A and the low temperature-type lean NO _x catalyst. 9B considering the purification efficiency of NO _x, is set to approximately 30 mm. Further, as shown in FIGS. 1 and 2, the exhaust gas purification system includes a heat retaining member 4 as a heat retaining means on the outer periphery of the exhaust passage 3 upstream of the catalyst 9.
0 is attached. This is because the exhaust gas
The heat from the exhaust gas is radiated to the outside through the exhaust passage 3 or the like before reaching the catalyst 9 through the exhaust gas, and the exhaust gas temperature is prevented from rapidly decreasing, thereby suppressing the deterioration of the purification efficiency of the catalyst 9. To do that.

The heat retaining member 40 is attached so as to cover the outer periphery of the exhaust pipe 3b constituting the exhaust passage 3.
It has a two-layered structure of a glass wool 40a on the inside and an outer plate 40b on the outside made of stainless steel, and functions as a heat insulating material. Further, the heat retaining member 40 is attached to a portion immediately downstream of the combustion chamber 1 except for the vicinity of the exhaust manifold 3a in order to prevent the exhaust manifold from being thermally degraded.

In FIG. 1, portion A is formed in a bellows shape with stainless steel having a thickness of about 3 mm. As a result, vibration from the engine is absorbed, and this engine vibration is not transmitted from the exhaust passage 3 downstream of the portion A to the vehicle body via the mounting bracket (not shown). The heat retaining means in such an exhaust gas purification system may be configured as follows. That is, as shown in FIG. 3, the heat retaining means may be configured by forming the exhaust pipe constituting the exhaust passage 3 into a double pipe structure 41.

The double tube structure 41 as the heat retaining means has
An air layer 44 is formed between the inner plate 42 and the outer plate 43, and an air layer 44 is formed between the inner plate 42 and the outer plate 43.
With this, it is possible to have a heat retaining effect. In FIG. 3, arrows indicate the flow of exhaust gas. Further, when the exhaust passage 3 is configured as a double pipe structure 41, since the inner plate 42 and the outer plate 43 have different coefficients of thermal expansion,
The inner plate 42 is divided into a plurality of portions so that the inner plate 42 absorbs thermal deformation. The inner plate 42a and the inner plate 42b divided into a plurality of parts are connected via a steel mesh 45 for preventing gas leakage so that the exhaust gas does not leak. In the seam portion shown in FIG. 3, the downstream inner plate 42b is connected to the upstream inner plate 42a so as to be larger in diameter than the upstream inner plate 42a, and the steel mesh 45 is provided so as not to face the exhaust gas flow. But this is steel mesh 45
The gas leakage prevention effect is not considered to be impaired.

Various sensors are provided for controlling such a direct injection internal combustion engine. First, on the intake passage 2 side,
An air flow sensor 11 for detecting an intake air amount from Karman vortex information, an intake air temperature sensor 12 for detecting an intake air temperature, and an atmospheric pressure sensor 13 for detecting an atmospheric pressure are provided. Potentiometer type throttle sensor 1 for detecting the opening of the throttle 7
4. Idle switch 15 for detecting idling state
Etc. are provided.

In the exhaust passage 3, an oxygen concentration sensor 17 (hereinafter simply referred to as an O ₂ sensor 17) for detecting an oxygen concentration (O ₂ concentration) in the exhaust gas is provided upstream of the catalyst 9.
And a catalyst temperature sensor (high temperature sensor) 26 as catalyst temperature detecting means for detecting the temperature of the catalyst or the vicinity thereof is provided in the downstream portion of the catalyst 9. The catalyst temperature sensor 26 as the catalyst temperature detecting means is a detecting means for detecting or estimating the temperature of the catalyst 9.

Further, as another sensor, a water temperature sensor (cooling water temperature detecting means) for detecting an engine cooling water temperature.
As shown in FIG. 19 and FIG. 4, a crank angle sensor 21 for detecting a crank angle (the crank angle sensor 21 also serves as a rotation speed sensor for detecting an engine rotation speed) and a top death of the first cylinder (reference cylinder). TDC sensors (cylinder discrimination sensors) 22 for detecting points are provided near the cams.

The detection signals from these sensors are input to an electronic control unit (ECU) 23. The ECU 23 is provided with a voltage signal from an accelerator position sensor 24 that detects the amount of depression of an accelerator pedal and a voltage signal from a battery sensor 25 that detects the voltage of a battery, and a cranking switch [or an ignition switch (key switch)] that detects a start time. The signal from the terminal 20 is also input.

The hardware configuration of the ECU 23 is as shown in FIG. 4, but the ECU 23 has a CPU 27 as its main part.
Intake air temperature sensor 12, atmospheric pressure sensor 13, a throttle sensor 14, O ₂ sensor 17, water temperature sensor 19, an accelerator position sensor 24, catalyst temperature sensor 26 and input the detection signal from the battery sensor 25 Interface 28
And an input through an analog / digital converter 30, an air flow sensor 11, a crank angle sensor 21, a TDC sensor 22, an idle switch 15,
Detection signals from the cranking switch 20, the ignition switch, and the like are input via the input interface 29.

Further, the CPU 27 has a ROM for storing program data and fixed value data via a bus line.
31, a RAM 32 that is updated and rewritten sequentially, a free running counter 48, and a battery backup RAM (not shown) that is backed up while the battery is connected by holding the stored contents while the battery is connected. It gives and receives.

The data in the RAM 32 disappears and is reset when the ignition switch is turned off. The fuel injection control signal based on the calculation result by the CPU 27 is output to the solenoid (injector solenoid) 8a of the injector 8 via the injection driver (fuel injection valve driving means) 34 for each cylinder (here, four). It is supposed to be.

Focusing on fuel injection control (air-fuel ratio control), a control signal for fuel injection calculated by the CPU 27 is output via the driver 34, and, for example, the four injectors 8 are sequentially driven. . As described above, in this engine, as a mode of fuel injection, a late injection mode in which fuel injection is performed during a compression stroke (particularly in the latter half of the compression stroke) in order to achieve lean operation by stratified lean combustion and improve fuel efficiency. And the first injection mode, in which fuel is injected during the intake stroke (particularly in the first half of the intake stroke) to achieve lean operation by premixed lean combustion and obtain output by slow acceleration, and stoichiometric operation (stoichiometric air-fuel ratio) by premixed combustion Stoichio mode, in which fuel is injected during the intake stroke in order to achieve higher output than in the previous injection mode, and open loop control to obtain sufficient output during acceleration, starting, etc. And an open loop mode in which premix combustion is performed at an air-fuel ratio.

In the exhaust gas purifying system, the EGR
Equipped with a device 10, the operating state of the EGR device is set respectively to particular above operation mode so as to suppress the NO _X emissions during stratified lean combustion. Here, the EGR device 10
The operation of and the setting of the EGR introduction rate will be described. E
The GR device 10 performs EGR introduction when the operation state of the engine is the stoichiometric mode or the late injection mode,
In the injection mode or the open loop mode, EGR is not introduced. This is because, in the first injection mode, when EGR is turned on, the combustion deteriorates and N
This is because the effect of reducing Ox and improving fuel efficiency is very small.
In particular, if the EGR flow rate is increased, misfire may occur, and it is impossible to introduce a large amount of EGR in this mode.

Note that E performed in the stoichiometric mode
The introduction amount of GR is set smaller in principle than in the latter injection mode. This means that in stoichio mode,
This is mainly because EGR is introduced for the purpose of improving fuel efficiency, and if a large amount of EGR is introduced, combustion deteriorates. The EG during the stoichiometric operation
The introduction rate of R is about 20 to 25% at the maximum, and may be 0 at the minimum.

During stratified lean combustion (late injection mode), as the air-fuel ratio increases, the air-fuel ratio in the vicinity of the ignition plug 35 decreases and the amount of NOx generated increases.
The exhaust gas to be recirculated into the intake passage 2 is set to be large. At this time, the introduction rate of EGR is 30 to 6
It is about 0%. Note that, depending on the engine, from the viewpoint of suppressing deterioration of combustion, the EGR introduction rate during stratified combustion may be set exceptionally lower during specific operation than during stoichiometric operation.

Next, the setting of the EGR introduction rate and the air-fuel ratio during the stratified lean combustion operation will be described with reference to FIG. FIG. 11 shows an example in a general operation state as a stratified lean combustion operation.
The conditions are 500 rpm and a net average effective pressure of 0.3 MPa.

In FIG. 11, the horizontal axis is the air-fuel ratio (A / F).
The vertical axis represents the NOx emission rate, which is the ratio of the NOx emission amount during the stratified lean combustion operation to the NOx emission amount during the stoichiometric operation. In the figure,
A curve L1 indicates a stable combustion limit, and stable combustion by the stratified lean combustion operation cannot be performed outside (ie, to the left or below) the curve. Curve L2 indicates intake air (= fresh air + EG
R) is 0.1 MPa (ie, about 1 atm).
T (throttle fully open), and operation outside this curve (that is, rightward or downward) cannot be performed.

Curves a1 to a3 show the fuel efficiency improvement rate, that is, the improvement rate of the fuel efficiency in the stratified lean combustion operation with respect to the fuel efficiency in the stoichiometric operation. The curve a1 shows the fuel efficiency improvement rate of 10%, and the curve a2 shows the fuel efficiency improvement rate. An improvement rate of 20% and a curve a3 indicate a fuel efficiency improvement rate of 30%. Curves b1 to b3 are EGR
The introduction rate, that is, the ratio of the EGR introduction amount in the intake air amount, is represented by a curve b1 of 0% EGR introduction rate and a curve b2 of EGR introduction rate.
The introduction rate is 20%, and the curve b3 indicates the EGR introduction rate of 40%.

In the stratified lean combustion operation, the curve L in FIG.
1, the operation is possible in the region above L2, and in this region, the air-fuel ratio (A / F) is such that the fuel efficiency improvement rate is high and the NOx reduction rate is high (that is, the NOx emission rate is low).
By setting the EGR introduction rate and the EGR introduction rate, both improvement in fuel efficiency and reduction in NOx are compatible. For example, the stratified lean combustion operation is performed in a region where the fuel efficiency improvement rate is 30% or more and the NOx reduction rate is 90% or more (that is, the NOx emission rate is 10% or more), as in a hatched region in FIG. Thus, it is conceivable to set the air-fuel ratio and the EGR introduction rate. FIG.
In FIG. 1, L3 indicates a NOx reduction rate of 90%.

In the example shown in FIG. 11, the air-fuel ratio is set to about 28
~ 33, the EGR introduction rate is set within a range of about 30-60%, and the fuel efficiency improvement rate is 30% or more and the NOx reduction rate is 90% or more. While achieving, a stratified lean combustion operation by stable combustion can be performed. Of course, FIG. 11 shows one typical example in the latter-stage lean combustion operation, and such a characteristic varies depending on the load state of the engine and the engine speed, and the fuel efficiency improvement rate is high according to each operation state. N
The air-fuel ratio and the EGR introduction rate are set so that the Ox reduction rate becomes high, and control is performed based on these settings. As described above, the present exhaust gas purification system uses lean NO _X
Since the catalyst 9 and the EGR device 10 are provided, the lean NO _X catalyst 9 is mainly used during the lean operation by the premixed lean combustion.
In purify NO _X, there is an advantage that during the lean operation with stratified lean combustion can mainly reliably purify the exhaust gas in a wide range of operating range to suppress the emission of the NO _X by the EGR device 10. In particular, during the lean operation by the stratified lean combustion with a low exhaust gas temperature, the NO
Low temperature _X-can not be reduced correspondingly lean NO _X catalyst 9B
Therefore, there is also an advantage that the exhaust gas purification efficiency can be further improved.

Since the exhaust gas purifying system includes a heat retaining means (heat retaining member 40), heat radiation from the exhaust passage 3 and the like is prevented, a rapid decrease in exhaust gas temperature is suppressed, and purification efficiency of the catalyst 9 is reduced. There is an advantage that it can be suppressed. Furthermore, since the heat retaining member 40 is attached except for the vicinity of the exhaust manifold 3a, there is an advantage that thermal deterioration of the exhaust manifold 3a can be prevented.

[0055] In the exhaust gas purifying system of the present embodiment, cold-type lean NO _x catalyst 9B towards the high-temperature lean N
Because it is composed as having a three-way function better than O _x catalyst 9A, but so as to arrange the low temperature lean NO _x catalyst 9B downstream of the high temperature-type lean NO _x catalyst 9A, high-temperature type lean if configured as having a person of the NO _x catalyst 9A and excellent three-way function, low temperature lean NO _x catalyst 9B upstream of the high temperature-type lean NO _x catalyst 9A
May be arranged.

[0056] Further, the exhaust gas purifying system of the present embodiment is configured as having an even three-way function high temperature lean NO _x catalyst 9A, high-temperature type lean NO _x catalyst 9
A may not have a ternary function. Further, in the exhaust gas purifying system of the present embodiment, the high temperature-type lean NO _x catalyst 9A and low temperature lean NO _x catalyst 9B is configured both as having a three-way function, both have a three-way function High temperature lean NO
_A three-way catalyst may be arranged downstream of the _x catalyst 9A and the low-temperature lean NO _x catalyst 9B.

Further, the exhaust gas purifying system of the present embodiment
Then, high temperature type lean NO_xCatalyst 9A and low temperature lean NO
_xThe catalyst 9B and the catalyst 9B are arranged in series.
The high temperature type lean NO_x
Catalyst 9A and low temperature lean NO _xCatalyst 9B is arranged in parallel
Then, it is switched according to the exhaust gas temperature by a switching valve etc.
You may do it. In this case, high-temperature type and low-temperature type lean N
O_xIf one of the catalysts has no three-way function,
These lean NO_xInstall a three-way catalyst downstream of the catalyst
Is preferred.

[0058] Furthermore, in the exhaust gas purifying system of the present embodiment, the high temperature-type lean NO _x catalyst 9A and low temperature lean NO
_Although a system using two catalysts having different temperature characteristics from the _x catalyst 9B has been described, the present invention is not limited to this embodiment.
Since NO _x emissions during stratified lean combustion by the apparatus can be suppressed, the lean NO _x catalyst may be primarily so as to dispose the one lean NO _x catalysts to be able to purify NO _x during premixed lean combustion. Conversely, when a plurality of catalysts having different temperature ranges are provided as in the present embodiment, it is not necessary to particularly provide an EGR device by setting the amount of catalyst carried.

Next, as the second embodiment, in the first embodiment, the temperature keeping means (the heat retaining member 40) cannot sufficiently prevent the decrease in the exhaust gas temperature during the stratified lean combustion, so that the NO. _{x When the} purification efficiency is deteriorated, the catalyst 9 is determined based on the output from the catalyst temperature sensor 26.
A configuration provided with a temperature raising means for raising the temperature of the device will be described.

This heating means has the function of injecting additional fuel at the end of the expansion step when the exhaust valve 5 is opened, in addition to the fuel injection (main fuel injection) for normal combustion as described above. An injection control means 102 is provided. After the catalyst 9 exceeds the activation temperature, the additional fuel injection control means 102 changes the operation mode of the present engine to the latter lean mode (stratified lean combustion), the temperature of the exhaust gas decreases, and the temperature of the catalyst 9 becomes lower than the activation temperature. that makes _the NO _x purification efficiency is deteriorated lower detected or estimated by the catalyst temperature detecting means 26 is configured to inject additional fuel after expansion step end.

The ECU 23 having such additional fuel injection control means as a temperature raising means will be described.
U23 is provided with a fuel injection control means 101 for selecting an injection mode and setting a fuel injection amount for fuel injection control (injector drive control), as shown in the functional block diagram of FIG. The ECU 23 is further provided with an exhaust gas recirculation amount control means 104 and an ignition timing control means 107.

As shown in FIG. 7, the fuel injection control means 101 has a function (additional fuel injection control means) 102 for performing additional fuel injection when the temperature of the catalyst 9 decreases and a function for controlling fuel injection during normal operation. (Normal fuel injection control means) 1
03 is provided. The additional fuel injection control means 102 as a temperature raising means is configured to reduce the temperature of the catalyst 9 to a predetermined temperature or less based on detection information from a catalyst temperature sensor (catalyst temperature detection means) 26 for detecting the temperature of the catalyst 9 or its vicinity. The additional fuel injection is performed when the fuel pressure drops. That is, the temperature of the catalyst 9 or near the detection by the catalyst temperature sensor 26 (hereinafter, the catalyst temperature of) when theta _CC is detected or estimated to be the predetermined temperature theta ₁ below, the temperature of the catalyst 9 is lowered It is determined that the purification efficiency is deteriorated, and based on this determination, control is performed such that additional fuel injection is performed after the expansion stroke of each cylinder (including the exhaust process).

Thus, by supplying the mixture containing the unburned fuel component to the catalyst 9, the unburned fuel component in the mixture is burned by the catalyst 9, and the temperature of the catalyst 9 can be raised. Note that the predetermined temperature θ ₁ is a catalyst activity target temperature, which is determined according to the catalyst activity lower limit temperature.
It is set as a value obtained by adding a predetermined temperature to the catalyst activity lower limit temperature. This catalyst activity lower limit temperature is about 400 degrees in the lean NO _X catalyst according to the present embodiment.

[0064] Thus, since in the present exhaust gas purification system and an additional fuel injection control unit 102 as a catalyst temperature detecting means 26 and heating device, even when the temperature of the lean NO _x catalyst has decreased by operating conditions stratified lean combustion There is an advantage that the catalyst temperature can be surely raised, thereby suppressing deterioration of the purification efficiency of the catalyst.

Next, as a third embodiment, a function of injecting additional fuel during the expansion stroke (before the end of the expansion stroke) based on the output from the catalyst temperature sensor 26 to the additional fuel injection control means 102 of the second embodiment. Will be described. In the additional fuel injection by the additional fuel injection control means 102 added as the present embodiment, the exhaust gas is reburned, and thereby the exhaust gas having a high temperature is supplied to the catalyst 9, thereby raising the temperature of the catalyst 9. It is about to be activated.

Since this additional fuel injection can surely re-burn in the cylinder and raise the temperature of the catalyst 9 with respect to the additional fuel injection of the second embodiment, immediately after the start when the catalyst 9 does not reach the activation temperature. This is effective when the stratified lean combustion operation is continued for a long time and the temperature of the catalyst 9 is significantly reduced (in an inert state or a state close to an inactive state). For this reason, the additional fuel injection by the additional fuel injection control means 102 in the present embodiment is controlled based on the operating state of the internal combustion engine, in particular, based on the activation state of the catalyst 9, and immediately after the start (in which the catalyst 9 is not activated) As shown in FIG. 8, in an active state) or in a long idling state (a state close to inactive), during the expansion stroke of each cylinder (specifically, when there is a flame during the expansion stroke).
Then, additional fuel injection is performed, and the process ends when the catalyst 9 is activated.

The ECU 23 having such additional fuel injection control means as a temperature raising means will be described.
In U23, as shown in the functional block diagram of FIG. 7, a fuel injection control means for selecting an injection mode and setting a fuel injection amount for the fuel injection control (injector drive control) as in the second embodiment. 101 is provided. Also,
The ECU 23 further includes an exhaust gas recirculation amount control means 1.
04, an ignition timing control means 107 is provided.

The fuel injection control means 101 includes:
Further, a function (additional fuel injection control means) 102 for performing additional fuel injection even when the catalyst 9 is inactive and a function (normal fuel injection control means) 103 for performing fuel injection control during normal operation are provided. The additional fuel injection control means 102 as a temperature raising means is configured to control the catalyst 9 based on detection information from a catalyst temperature sensor (catalyst temperature detecting means) 26 for detecting the temperature of the catalyst 9 or the vicinity thereof in addition to the second embodiment. It is determined whether the catalyst 9 is in the active state or not, and additional fuel injection is performed when the catalyst 9 is not in the active state. That is, the catalyst 9 is not in the active state when the temperature of the catalyst 9 or its vicinity (hereinafter referred to as catalyst temperature) θ _CC detected by the catalyst temperature sensor 26 is detected or estimated to be equal to or lower than the predetermined temperature θ _0. Based on this determination, control is performed so that additional fuel injection is performed during the expansion stroke of each cylinder (see FIG. 8).

Here, the predetermined temperature θ ₀ is a catalyst activity target temperature, which is determined according to the catalyst activity lower limit temperature, and is set, for example, as a value obtained by adding a predetermined temperature to the catalyst activity lower limit temperature. This catalyst activity lower limit temperature is about 400 degrees in the lean NO _X catalyst according to the present embodiment. In addition,
The target temperature θ ₀ as the predetermined temperature (hereinafter, the predetermined temperature is referred to as the target temperature) is set lower than the predetermined temperature θ ₂ of the second embodiment, and may be set to match the catalyst activation temperature.

The additional fuel injection control means 102 as the temperature raising means has a function (injection start timing setting section) 102A for setting the injection start timing T _INJ of the additional fuel injection, as shown by a chain line in FIG. And a function (injection time setting unit) 102B for setting the injection time of the additional fuel in each cycle. Of these, the injection start timing setting unit 102A
Within the expansion stroke of each cylinder, a combustion period during combustion by normal fuel injection (hereinafter referred to as main combustion),
The injection start timing T _INJ is set so that additional fuel injection is performed during a period in which a flame exists (hereinafter, referred to as a flame remaining period).

The reason for setting the injection start timing T _INJ by the additional fuel injection in this way is to cause the fuel injected by the additional fuel injection to burn (hereinafter, referred to as reburning) without providing an additional device. This is because, as shown in FIG. 11, additional fuel injection needs to be performed within the heat generation period due to normal fuel injection. This is because gasoline used as fuel has low self-ignitability and cannot be reliably burned unless there is an ignition source or external energy for chemical decomposition to burn gasoline itself. This is because they have properties. Conversely, as combustion having high self-ignition properties, there is a combustion having a high cetane number such as light oil.

Here, FIG. 11 is a diagram showing the in-cylinder pressure and the heat release rate from the compression stroke to the explosion / expansion stroke.
1, the thin line A is the heat release rate when only normal fuel injection is performed, the thick line B is the heat release rate when additional fuel injection is performed, the broken line C is the in-cylinder pressure when only normal fuel injection is performed, and the thick line. D indicates the in-cylinder pressure when additional fuel injection is performed. Note that the period indicated by the thin line A and the thick line B as the heat generation rate corresponds to the heat generation period.

As shown in FIG. 11, if the additional fuel injection is performed as late as possible in the heat generation period due to the main combustion corresponding to the heat generation rate shown by the line A, the heat Since the generation period is extended and approaches the exhaust stroke, the heat energy obtained by increasing the temperature of the exhaust gas by the reburning can be more effectively used for increasing the temperature of the catalyst 9A.

On the other hand, line D indicates that the cylinder pressure increases when additional fuel injection is performed. When the in-cylinder pressure increases in this way, it is considered that the thermal energy obtained by the reburning is used more for the work for pushing down the piston (the work for expanding the gas). Not preferred. For this reason, it is preferable that the injection start timing T _INJ of the additional fuel be set as late as possible in the expansion stroke in order to effectively utilize the thermal energy obtained by the reburning. Since the injection start time T _INJ must be the flame remaining period,
It is preferable to set as late as possible the flame remaining period.

Here, the setting of the additional fuel injection start timing T _INJ will be described in more detail with reference to the flame extinguishing timing which is the end of the remaining flame period. The flame extinguishing timing is determined by the water temperature θ _W , the exhaust gas It fluctuates under the influence of various parameters such as the recirculation amount (EGR amount), the air-fuel ratio (A / F), and the ignition timing _TIG during main combustion. Therefore, it is necessary to set the injection start timing T _INJ in consideration of the influence of these parameters.

[0076] For example, if you take into account only the water temperature θ _W, water temperature θ _W is low and the combustion is deteriorated, because the flame disappeared timing is early, as the water temperature θ _W is low in order to ensure re-combustion injection start timing T _It is preferable to accelerate _INJ (early expansion stroke). This is because when the engine is cold, the area around the cylinder block is cold, heat can easily escape from the cylinder block, etc., and the space between the flame and the cylinder block (quenching zone) is large. This is because the flame extinguishes before the flame spreads throughout the combustion chamber.

When only the EGR amount is considered, the EG
If the amount of R is large, the ignition delay in the main combustion increases, and the maximum pressure in the combustion chamber and the crank angle corresponding to the maximum pressure fluctuate every cycle. This fluctuation increases as the EGR amount increases, and the flame remaining period also fluctuates with this fluctuation. Therefore, in order to reliably burn the additional fuel, the injection start timing T _INJ of the additional fuel during the expansion stroke must be advanced. Is preferred.

When only A / F is considered, EG
As in the case where only the R amount is considered, as the air-fuel ratio becomes leaner, the ignition delay in the main combustion increases, and the maximum pressure in the combustion chamber and the crank angle corresponding to the maximum pressure fluctuate every cycle. This fluctuation is greater as the fuel becomes leaner, and the flame remaining period also fluctuates with this fluctuation. Therefore, in order to reliably burn the additional fuel, it is preferable to advance T _INJ at the start of injection of the additional fuel during the expansion stroke. .

Further, the ignition timing T for the main combustion_IGOnly consider
The ignition timing T_IGRemaining flame due to advance and retard
Time, that is, the flame extinguishing time fluctuates.
Injection start timing T_INJIs preferably set. this
Is the ignition timing T_IGIs advanced, the combustion period becomes shorter.
This is because the flame disappears earlier, and conversely, the ignition timing T
_IGIs retarded, combustion slows down (combustion speed slows
This is because the flame disappears at a later time.

If the fuel injection amount, that is, the fuel injection time (therefore, the injector drive time) is set by the injection time setting unit 102B, which will be described later, according to each of the above parameters, the exhaust gas can be more efficiently raised. You can warm up. Here, the injection start timing T _INJ is set at an optimal timing (for example, a timing close to the flame extinguishing time) in consideration of the flame extinguishing timing within the flame remaining period according to various parameters. The injection start time T _INJ may be set to a certain time, and the flame extinguishing time may be adjusted by changing various parameters, so that the injection starting time T _INJ becomes an optimal time in consideration of the flame extinguishing time.

For example, when the engine is cold, for example, when the engine is not activated, the injection start timing T _INJ is set as late as possible in the expansion stroke. controls the EGR valve 10a to the exhaust gas recirculation amount is reduced or cut, by delaying the loss of flame timing to the injection start time T _INJ later injection start timing T _INJ is considering flame disappearance time optimal timing May be used.

Similarly, the ignition timing control means 107 controls the ignition system 10 so that the ignition timing _TIG is retarded.
8 may be controlled so that the flame extinction time is delayed until after the injection start time T _INJ , so that the injection start time T _INJ is close to the flame extinction time. The setting of the injection start timing T _INJ in the expansion stroke by the injection start timing setting unit 102A is specifically performed as follows.

That is, the injection start timing setting unit 102A
Start timing T in the expansion stroke _INJThe setting is inflated
Basic fuel that is the basis for additional fuel injection during the stroke
Injection start timing Tb_INJIs the cooling water temperature θ_W, EGR
Quantity, ignition timing T in main combustion _IGTo be corrected by
It is performed by Here, the basic fuel injection start timing Tb
_INJIs detected by the engine speed sensor 21
Based on the engine speed Ne and the target load value Pe,
The stored map [Tb_INJ= F (Pe, Ne)]
Required by

The target load value Pe is calculated by the following equation. Pe = T / (K * Vs) Here, T is a torque, K is a constant, and Vs is a displacement.
The correction by the cooling water temperature theta _W, as shown in FIG. 12 (a), the water temperature correction amount K ₁ from the map (a) which is set in advance from the cooling water temperature theta _W and the water temperature correction coefficient K ₁ Metropolitan sought, the basic fuel injection start timing of the water temperature correction amount K ₁ T
This is performed by adding (Tb _INJ + K ₁ ) to b _INJ . Incidentally, the map (a), as shown in FIG. 12 (a), as the cooling water temperature theta _W is low, the injection start timing T _INJ
Are set earlier (ie, smaller).

Similarly, the correction by the EGR amount and the ignition timing _TIG in the main combustion is performed by _obtaining a correction coefficient or a correction amount from a preset map, and multiplying the correction coefficient or adding the correction amount. Done. At this time, the injection time of the additional fuel (the total injection time in one operation cycle) t _ex is set by the injection time setting unit 102B, and the injection time setting unit 102B remains in the cylinder after the main combustion. The injector drive time t _PLUS is set so that the fuel amount M _fuel corresponding to the excess oxygen is injected.

This is because, when reburning with the additional fuel, surplus oxygen remaining in the cylinder is completely burned with the additional fuel,
This is because the temperature of the exhaust gas can be efficiently increased. The setting of the injector drive time t _PLUS in the expansion stroke by the injection time setting unit 102B is specifically performed as follows.

That is, the setting of the injector drive time t _PLUS in the expansion stroke by the injection time setting unit 102B is as follows:
The basic drive time t _B, which is the basis for additional fuel injection in the expansion stroke, is determined by the injection start timing T _INJ and the catalyst temperature θ.
_The correction is performed by the _CC . here,
The basic drive time t _B is calculated based on the fuel amount M _fuel that can be injected with respect to surplus oxygen in the cylinder after the main combustion. That is, the amount of oxygen remaining in the cylinder after main combustion is determined from the intake air amount Q per cylinder and the target air-fuel ratio (target A / F) determined by the normal fuel injection control means 103 described later. The fuel amount M is calculated based on the oxygen amount.
_fuel is calculated.

The fuel amount M _fuel is obtained by the following equation. _M fuel = Q × (1 / stoichiometric air-fuel ratio -1 / target air-fuel ratio) The correction due to the injection start timing T _INJ of definitive expansion stroke, as shown in FIG. 12 (b), the injection start timing T _INJ correction the correction factor K ₂ from the map (b) which is set in advance is determined from the coefficient K ₂ Prefecture, performed by multiplying the correction coefficient K ₂ to the basic drive time _{t B (t B × K 2} ).

As shown in FIG. 12 (b), the map (b) shows the injection start timing T in order to keep the actual injection amount constant.
_The injector driving time t _PLUS is set to be longer as the _INJ is earlier. That is, in the expansion stroke, when the injection start timing T _INJ is _advanced , the in-cylinder pressure increases and the amount of fuel injected from the injector (the amount per unit time) tends to decrease.
The injector drive time t _PLUS is set to be long.

This is because if the in-cylinder pressure is low, the differential pressure from the injection pressure
, The basic drive time t _BBased on proper
Fuel quantity M_fuelBut the cylinder pressure is high.
When this happens, the differential pressure between the in-cylinder pressure and the injection pressure decreases, and the injection amount decreases
Therefore, the basic driving time t _BInject fuel based on
Therefore, the appropriate amount of fuel M_fuelCan not secure
That's why. Thus, additional fuel during the expansion stroke
Injection is affected by in-cylinder pressure
The injector driving time t_PLUSSettings are important.

The catalyst temperature θ_CCThe correction by
As shown in FIG. 2 (c), the catalyst temperature θ _CCAnd correction coefficient K_Three
And the correction coefficient K from the preset map (c).
_ThreeIs calculated, and the correction coefficient K_ThreeIs the basic drive time t_BTo
Multiply (t_B× K_Three). In addition,
The map (c) shows the catalyst temperature as shown in FIG.
θ_CCIs low, the basic drive time t_BI will not correct
And the catalyst temperature θ_CCIs higher and the goal
Temperature θ₀It gradually decreases to 0 as it approaches
Is set to

This is because the lower the catalyst temperature θ _CC , the lower the catalyst 9
Since the activation of the catalyst 9 is required, a large amount of additional fuel is injected to promote the activation of the catalyst 9, and conversely, the higher the catalyst temperature θ _CC , the more the activation of the catalyst 9 becomes unnecessary. This is to reduce the injection so that unnecessary fuel injection is not performed. Thus, the injector driving time t _PLUS in the expansion stroke is obtained by the following equation.

T _PLUS = t _B × K ₂ × K ₃ Depending on the injection start timing T _INJ and the injector drive time t _{PL US} set in this manner, additional fuel injection is performed as shown in FIG. The fuel injection is performed in the expansion stroke separately from the fuel injection. By the way, the normal fuel injection control means 1
In the normal operation control means 103, the injection mode includes the engine speed (rotation speed) Ne detected from the engine speed sensor 21, the various sensors 106, and the like, and the accelerator pedal depression amount. θ
The target output torque T of the engine is set based on the _ACC , and one of the first injection mode and the second injection mode is selectively set according to the engine speed Ne and the target output torque T. For example, in a region where the engine speed Ne is low and the target torque T is low, the latter-stage injection mode is set. If either the engine speed Ne or the target torque T is not low, the first-stage injection mode or the stoichiometric mode is set.

The fuel injection amount is set as fuel injection time (injector drive time, which is referred to as injector drive pulse width in actual control) t _{AU. In} the case of the stoichiometric mode and the previous injection mode, In the latter case as well, in the late injection mode, the basic drive is first performed by the following equation based on the engine load (amount of intake air per stroke) Q / Ne and a target air-fuel ratio (A / F, hereinafter referred to as AF). time t _p is calculated.

T _p = (Q / Ne) × (1 / AF) × (α
_AIR / α _FUEL ) × (1 / G _INJ ) The engine load Q / Ne is the amount of intake air per stroke, and the amount of intake air Q detected by the air flow sensor 11 is used as the engine speed sensor (crank angle sensor). ) 2
It is obtained by dividing by the engine speed Ne detected at 1. Α _AIR is the air density, α _FUEL is the fuel density, and G _INJ is the injector gain.

The fuel injection time t _AU is calculated by the following equation. t _AU = t _p × f + t _D Here, f is various fuel correction coefficients, and the fuel correction coefficient f is the engine cooling water temperature detected by the water temperature sensor 19, the intake air temperature detected by the intake air temperature sensor 12, The setting is made according to the atmospheric pressure detected by the atmospheric pressure sensor 13 and the like. Further, t _D is the injector dead time (dead time).

Next, the exhaust gas recirculation amount control means 104 will be described. The exhaust gas recirculation amount control means 104 is provided in the EGR device 10 as the exhaust gas recirculation means based on detection information from various sensors 106. It controls the EGR valve 10a. Therefore, the signal from the exhaust gas recirculation amount control means 104 is sent to the fuel injection control means 101.

Here, in addition to the normal function, when the additional fuel injection is performed in the expansion stroke in order to raise the temperature of the exhaust gas in order to activate the catalyst 9, the exhaust gas recirculation amount is reduced or cut. It also has a function of controlling the EGR valve 10a. Therefore, the signal from the fuel injection control means 101 is output to the exhaust gas recirculation amount control means 104.
To be sent to

The ignition timing control means 107 controls the ignition device 1 based on the detection information from the crank angle sensor 21.
This is for controlling the ignition timing T _IG by the ignition plug 35 as 08. Therefore, the ignition timing control means 10
The signal from 7 is sent to the fuel injection control means 101. Here, in addition to the usual functions, the catalyst 9
When the additional fuel injection is performed in the expansion stroke to increase the temperature of the exhaust gas to activate the ignition timing, the ignition timing T _IG
Has a function of retarding the angle. For this reason, the signal from the fuel injection control means 101 is
7.

The ECU 23 having the temperature raising means in the exhaust gas purifying system is configured as described above, so that, for example, the normal fuel injection control is performed as shown in FIG. 9 and the temperature is raised as shown in FIG. Additional fuel injection control (expansion stroke fuel injection control) is performed by additional fuel injection control means 102 as means. First, the normal fuel injection control will be described.

This control is executed at every fixed crank angle. First, the processing of steps A10 to A30 is performed. That is, in step A10, the engine load Q / Ne (that is, the intake air amount per stroke) is calculated from the intake air amount Q detected by the air flow sensor 11 and the rotational speed sensor 21 and the engine rotational speed Ne. Next, step A20
In, as shown in the above equation, based on the engine load Q / Ne, calculating a basic drive time t _p. Step A
30, calculates the fuel injection time t _AU performs a multiplication of various fuel correction coefficient K to the basic drive time t _p.

Then, based on this, normal fuel injection (step A40) is performed. Next, the expansion stroke fuel injection control (additional fuel injection control) by the additional fuel injection control means 102 as the temperature increasing means will be described. This expansion stroke fuel injection control is performed in the lean operation mode in the first injection mode or the second injection mode. Done at time. FIG. 8 shows a case where the expansion stroke fuel injection is performed in the first injection mode.

First, the processing of steps B10 and B20 is performed. That is, the medium temperature θ _CC is read in step B10, and it is determined in step B20 whether the catalyst temperature θ _CC is equal to or lower than the target temperature θ ₀ . As a result, when the catalyst temperature θ _CC is equal to or lower than the target temperature θ ₀ , the processing from Steps B30 to B90 is performed to perform the expansion stroke injection control, and when the catalyst temperature θ _CC is not equal to or lower than the target temperature θ ₀ , The routine returns without performing the expansion stroke injection control.

In the expansion stroke injection control, first, step B
The processing from 30 to B60 is performed to set the injection start timing T _INJ in the expansion stroke. That is, step B30
Reads the target load value (target Pe), the engine speed Ne, the cooling water temperature θ _W , the ignition timing T _IG in the main combustion, and the EGR amount. Next, at step B40, the engine speed Ne
The basic injection start timing Tb _INJ in the expansion stroke is read from a map stored in advance based on the target load value Pe. Then, at step B50, the basic injection start timing T
b _INJ is corrected by the EGR amount, the coolant temperature θ _W , and the ignition timing T _IG in the main combustion, and in step B60, the injection start timing T _INJ in the expansion stroke is set.

Next, the processing of steps B70 to B90 is performed, and the injector drive time t during the expansion stroke is determined.
Set _PLUS . That is, in step B70, the intake air amount Q per cylinder and one cycle and the target A / F are read.
Next, in step B80, the amount of oxygen remaining in the cylinder after the main combustion is obtained from the intake air amount Q per cylinder per cycle and the target A / F, and the fuel amount M _fuel is calculated based on this oxygen amount. . Then, in step B90, the basic drive time t _B of the additional fuel injection in the expansion stroke is changed to the injection start timing T _INJ ,
The injector drive time t _PLUS in the expansion stroke is set by correcting with the catalyst temperature θ _CC . Then, additional fuel injection in the expansion stroke is performed based on this setting.

Since the exhaust gas purifying system of this embodiment is configured as described above, the temperature of the catalyst 9 can be reliably raised even when the catalyst 9 is inactive or inactive depending on the operating state, There is no loss of efficiency. Also, in the present embodiment, additional injection during the expansion stroke,
Since the additional injection after the expansion stroke is selectively used according to the temperature of the catalyst, when the catalyst is in an inactive or nearly inactive state, such as at the time of a low temperature start where activation of the catalyst 9 is required, the expansion is performed. by reheating the exhaust gases in the process, significantly raising the temperature of the exhaust gas, together to efficiently activate the catalyst 9, once the target temperature theta ₀ or target temperature theta ₀ reaches the vicinity, lowering the catalyst temperature In an idle operation state or a deceleration operation state where there is a concern, the catalyst 9 can be activated efficiently by burning the unburned fuel component in the air-fuel mixture by the catalyst 9. When operating the temperature raising means, an operation state (for example, an idling operation state or a deceleration operation state) where the catalyst temperature may be lowered may be detected instead of directly detecting the catalyst temperature.

In the exhaust gas purifying system of the present embodiment, the additional fuel injection control means 102 as the temperature raising means
Although it is configured as having the above functions,
It is not limited to such a configuration. That is, the additional fuel injection control means 102 as the temperature raising means may be configured to inject the additional fuel by a plurality of divided injections during the expansion stroke. Further, the additional fuel injection control means 102 as the temperature raising means is provided with a cylinder setting means for setting the number of cylinders at which the additional fuel is injected during the expansion stroke based on the catalyst temperature, and is set by the cylinder setting means. You may comprise so that injection of additional fuel may be performed in a specific cylinder. Further, the additional fuel injection control means 102 as a temperature raising means is used to perform additional fuel injection during the expansion stroke when the temperature reduction state of the catalyst 9 is detected or estimated based on the detection information from the catalyst temperature detection means 26. May be performed.

Further, in this embodiment, the additional injection during the expansion stroke and the additional injection after the expansion stroke are selectively used according to the catalyst temperature. However, the additional fuel injection control means 102 performs only the additional injection during the expansion stroke. You may set as follows. Furthermore, although the temperature raising means of the present embodiment is effective in that the temperature of the exhaust gas can be raised by an inexpensive system as another device,
The same effect can be obtained even if the temperature of the exhaust gas is raised by another device such as an electric heating catalyst or secondary air device.

[0109]

As described above in detail, according to the exhaust gas purifying system of the present invention according to claim 1, (primarily, NO _X purifying) exhaust gas purification in the wide operating range is an advantage that it is possible is there. Since it is less in this case also deteriorates combustion performed EGR in large quantities at the time of stratified combustion, it is possible to NO _X reduction without sacrificing drivability.

[0110] According to the exhaust gas purifying system of the present invention described in claim 2, during lean operation by the premixed combustion is primarily to purify the NO _X in the lean NO _X catalyst, the exhaust gas recirculation means during the lean operation with stratified combustion NO By purifying _X , there is an advantage that exhaust gas can be reliably purified in a wide range of operation. According to the exhaust gas purification system of the third aspect of the present invention, exhaust gas purification (mainly,
NO _X purification) becomes possible, in particular, during the lean operation with stratified combustion, since the amount of generation of sufficient NO _X was not suppressed by the exhaust gas recirculation means can purify by low-temperature lean NO _X catalyst, a further exhaust gas purification efficiency There is an advantage that it can be improved.

[0111] According to the exhaust gas purifying system of the present invention described in claim 4, also it can be reliably raise the temperature of the catalyst temperature when the temperature of the lean NO _X catalyst is lowered, thereby deteriorating the purification efficiency of the catalyst Can be suppressed. According to the exhaust gas purifying system according to the fifth aspect of the present invention, there is an advantage that heat radiation from an exhaust passage or the like can be prevented, a rapid decrease in exhaust gas temperature can be suppressed, and a decrease in catalyst purification efficiency can be suppressed. . In addition, when the temperature raising means is provided, there is an advantage that the temperature raising efficiency of the catalyst can be improved, and the purification efficiency of the catalyst can be improved.

According to the exhaust gas purifying system of the present invention, there is an advantage that thermal deterioration of the exhaust manifold can be prevented. According to the exhaust gas purifying system of the present invention according to claim 7, exhaust gas purification in the wide operating range (wide exhaust gas temperature characteristics) (mainly, NO _X purification) is advantageous in that it is possible.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an exhaust gas purification system as a first embodiment of the present invention.

FIG. 2 is a view schematically showing a heat retaining means in an exhaust gas purification system according to a second embodiment of the present invention.

FIG. 3 is a view schematically showing a modification of the heat retaining means in the exhaust gas purification system according to the first embodiment of the present invention.

FIG. 4 is a control block diagram in the exhaust gas purification system as the first embodiment of the present invention.

FIG. 5 is a diagram illustrating an operation mode of the engine according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating the setting of an EGR introduction rate and an air-fuel ratio during stratified lean combustion operation in the EGR device according to the first embodiment of the present invention.

FIG. 7 is a control block diagram schematically illustrating a main configuration of a control system of an exhaust gas purification system according to a second embodiment and a third embodiment of the present invention.

FIG. 8 is a diagram showing injection timing of additional fuel in an exhaust gas purification system as a second embodiment of the present invention.

FIG. 9 is a flowchart for explaining normal fuel injection control of an exhaust gas purification system as a second embodiment of the present invention.

FIG. 10 is a flowchart illustrating additional fuel injection control of an exhaust gas purification system as a second embodiment of the present invention.

FIG. 11 is a diagram for explaining an in-cylinder pressure and a heat generation rate when additional fuel injection is performed in an expansion stroke by an exhaust gas purification system according to a second embodiment of the present invention.

FIG. 12 is a diagram showing a map used in additional fuel injection control of an exhaust gas purification system as a second embodiment of the present invention, where (a) shows a cooling water temperature θ _W , (b) shows an injection start timing T _INJ , (C) relates to the catalyst temperature θ _CC .

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Intake passage 2a Surge tank 3 Exhaust passage 3a Exhaust manifold 3b Exhaust pipe 4 Intake valve 5 Exhaust valve 6 Air cleaner 7 Throttle valve 8 Injector (fuel injection valve) 8a Injector solenoid 8b Switching transistor for injector solenoid 9 Exhaust gas purification the catalyst as an exhaust gas purifying catalyst converter 9A high-temperature type lean NO _x catalyst (lean NO _x catalyst) 9B low-temperature lean NO _x catalyst (lean NO _x catalyst) 10 exhaust gas recirculation system (exhaust gas recirculation means) 10b exhaust gas recirculation passage 10a EGR valve 11 the air flow sensor 12 intake air temperature sensor 13 atmospheric pressure sensor 14 throttle sensor 15 idle switch 16 idle speed control valve (ISC valve) 16A bypass passage 17 oxygen concentration sensor (O ₂ 19) Cooling water temperature sensor 20 Cranking switch or ignition switch 21 Crank angle sensor (engine speed sensor) 22 TDC sensor (cylinder discrimination sensor) 23 Electronic control unit (ECU) 24 Accelerator position sensor 25 Battery sensor 26 Catalyst temperature detection Catalyst temperature sensor (detecting means) as means 27 CPU 28, 29 Input interface 30 Analog / digital converter 31 ROM 32 RAM 34 Injection driver (fuel injection valve driving means) 35 Spark plug 40 Heat retaining member (heat retaining means) 40a Glass wool 40b Iron plate 41 Double pipe structure (heat insulation means) 42 Inner plate 42a, 42b Inner plate 43 Outer plate 44 Air layer 45 Steel mesh 50 Air bypass valve (ABV) 50A Bypass path 101 Fuel injection Control means 102 additional fuel injection control unit (heating device) 102A injection start timing setting unit 102B injection time setting unit 103 normal fuel injection control means 104 exhaust gas recirculation amount control means 106 sensors 107 an ignition timing control means 108 ignition device

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display F02D 41/02 301 F02M 25/07 570A B01D 53/36 ZAB F02M 25/07 570 101B (72) Invention Person Daisuke Mibayashi 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Inventor Naoto Yamada 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Invention Hironobu Sato 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation

Claims (7)

[Claims] 1. A injecting fuel directly into a combustion chamber, provided in-cylinder injection type internal combustion engine switching between premixed lean combustion and stratified lean combustion, disposed in the exhaust passage of the engine, mainly NO _x includes a lean NO _x catalyst for purifying, the lean NO _x catalyst, and a catalyst activation temperature range is higher high-temperature lean NO _x catalyst, the catalyst activation temperature range is the high-temperature lean NO _x low low-temperature lean NO of the catalyst _An exhaust gas purification system comprising an _x catalyst. 2. An in-cylinder injection type internal combustion engine which injects fuel directly into a combustion chamber and switches between premixed lean combustion and stratified lean combustion, is provided in an exhaust passage of the engine, and includes at least the premixed fuel. a lean NO _x catalyst for purifying mainly NO _x during lean combustion, characterized in that the exhaust gas and a flue gas recirculation means for recirculating into the intake passage of the engine when the layered lean combustion, the exhaust gas purification system. 3. An in-cylinder injection type internal combustion engine which injects fuel directly into a combustion chamber and switches between premixed lean combustion and stratified lean combustion, is provided in an exhaust passage of the engine, and includes at least the premixed fuel. includes a lean NO _x catalyst for purifying mainly NO _x during lean combustion, the exhaust gas when the layered lean combustion and exhaust gas recirculation means for recirculating into the intake passage of the engine, the lean NO _x catalyst, the catalyst activation temperature range and a high high-temperature lean NO _x catalyst, the catalyst activation temperature range is provided downstream of the high-temperature lean NO _x catalyst is composed of the lower low temperature lean NO _x catalyst than the high-temperature lean NO _x catalyst An exhaust gas purification system characterized by the following. 4. A detecting means for detecting or estimating the temperature of the lean NO _x catalyst, and a Atsushi Nobori means for raising the temperature of the lean NO _x catalyst when the catalyst temperature decrease is detected or estimated by said detection means 2. The device according to claim 1, wherein
An exhaust gas purification system according to any one of claims 1 to 3. 5. The exhaust gas purifying system according to claim 1, wherein a heat retaining means is provided on an outer periphery of said exhaust passage upstream of said lean NO _x catalyst. 6. The exhaust gas purifying system according to claim 5, wherein said heat retaining means is provided except for the vicinity of an exhaust manifold near said combustion chamber. 7. The high temperature lean NO _x catalyst is iridium catalysts, and wherein the low temperature lean NO _x catalyst is a platinum-based catalyst, according to any one of claims 1,3～6 Exhaust gas purification system.