JP2003097256A - Internal combustion engine - Google Patents

Abstract

(57) [Problem] To provide a combustion improvement technique capable of improving driver variability, reducing engine noise, suppressing smoke, and the like when switching the combustion state. An internal combustion engine (1) capable of switching between two combustion states having greatly different EGR rates.
The GR rate is adjusted based on the oxygen concentration of the exhaust gas, and a catalytic converter 52 and a reducing agent adding device 60 for adding a reducing agent to the catalytic converter 52 are provided in the exhaust passage.
When the EGR rate is changed to switch the combustion state, the addition of the reducing agent by the reducing agent adding device 60 is prohibited. When switching the combustion state, the EGR
The opening amounts of the valve 16 and the throttle valve 13 are overshot. Further, when the fuel injection system is switched in accordance with the switching of the combustion state, the switching is temporarily prohibited. At the time of the switching, the control is switched to the normal fuel injection control while gradually changing.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an internal combustion engine,
More specifically, the present invention relates to an internal combustion engine that performs engine operation while appropriately selecting two combustion states that greatly differ in combustion temperature and oxygen concentration.

[0002]

2. Description of the Related Art In diesel engines and lean-burn gasoline engines, various measures are taken to reduce the emission of soot and nitrogen oxides (NOx). As one of the countermeasures, for example, there is a combustion technique disclosed in Japanese Patent Publication (No. 30925497).

According to the combustion technique disclosed in the patent publication, the EGR gas contained in the intake air supplied for combustion is adjusted by adjusting the supply amount of EGR gas and the flow rate of air supplied to the combustion chamber. By adjusting the ratio, two engine combustions with greatly different combustion temperatures and oxygen concentrations are possible.

That is, at the time of high load operation, the EG contained in the intake air is ensured in order to secure the driver's ability.
Perform normal combustion while suppressing the ratio of R gas to an appropriate amount,
Conversely, during idling and during low load operation, the proportion of EGR gas is greatly increased to lower the combustion temperature and oxygen concentration, and the amount of soot and nitrogen oxides (NOx) produced is reduced. In the following description, the engine combustion in the state where the combustion temperature and the oxygen concentration are low may be referred to as "low temperature combustion". Further, the ratio of EGR gas contained in the intake air (EGR gas amount / (EGR gas amount + air amount)) may be simply referred to as the EGR rate. Further, the nitrogen oxide may be simply referred to as “NOx”.

By the way, in a diesel engine or the like, in its normal combustion state, engine operation is performed in a state of excess air reaching A / F = 30 to 40, and the intake air used for the combustion contains There is a large amount of oxygen. Further, since the intake air having an excessive oxygen content is burned, a large amount of oxygen remains in the exhaust gas. That is, a large amount of oxygen is mixed in the exhaust gas which is the EGR gas.

Therefore, simply increasing only the EGR gas amount slows down the changes in the oxygen concentration and the EGR gas amount, and it took some time to switch to the low temperature combustion realized at a high EGR rate. Further, during the switching period (transient state), the EGR rate fluctuates greatly, and the combustion state becomes unstable. Therefore, in the conventional internal combustion engine, various engine controls are performed to reduce the time required for switching and to ensure a stable combustion state.

More specifically, in addition to the control for increasing the opening degree of the EGR valve, the intake throttle control for significantly reducing the oxygen concentration in the intake air by reducing the air amount itself is performed. Also, E
Low temperature combustion has been realized by performing various engine controls such as misfire prevention due to excessive GR gas and insufficient air amount, and fuel injection correction control that compensates for pumping loss associated with intake throttle control. Regarding the intake throttle control, the EGR gas amount is relatively increased by reducing the air amount itself, and the EG is reduced by decreasing the pressure in the intake passage.
It also has the function of increasing the amount of R gas introduced (supply amount).

As described above, in the conventional internal combustion engine, the combustion state is properly switched by performing various engine controls. The engine control described above is, of course, also required when returning to the normal combustion state, and the processing content thereof is timely processed with the control content suitable for the purpose.

Further, in recent years, many internal combustion engines are equipped with an exhaust gas purification catalyst in their exhaust passages in order to reduce the emission amount of fine particles such as NOx and soot. Further, the exhaust gas purification action is promoted by reducing the air-fuel ratio of the exhaust gas flowing into the exhaust gas purification catalyst. still,
Decreasing the air-fuel ratio of the exhaust gas means increasing the ratio of unburned combustion components to the residual oxygen amount of the exhaust gas, for example, adding a reducing agent to the exhaust passage upstream of the exhaust purification catalyst, By sub-injecting the engine fuel, which is a reducing agent, into the cylinder in the latter part of the combustion stroke, the reduction of the air-fuel ratio is promoted.

[0010]

DISCLOSURE OF THE INVENTION By the way, the present inventors have made various studies and found various improvements in switching the combustion state. That is, attention was paid to the transient state corresponding to the combustion switching period, and efforts were made to improve various problems occurring in the transient state.

First, in the transient state from normal combustion to low temperature combustion, fluctuations in generated torque and an increase in combustion noise were observed due to the delay in the supply of EGR gas. Also, in the transient state from low temperature combustion to normal combustion, misfire and smoke were increased due to the delay of air introduction. Various problems associated with combustion instability in these transient states go against the purpose of improving driver bilities, reducing engine noise, and suppressing smoke, and improving these phenomena is important in the development of internal combustion engines. It will be a point.

Further, during the combustion state switching period, feedback control based on the oxygen concentration of the exhaust gas is performed at various places. Therefore, if the above reducing agent is added, the feedback control may fail.

The present invention has been made in view of these various problems, and it is intended to improve various problems occurring in the transient state thereof, to improve the driver's ability, to reduce engine noise, and to suppress smoke. It is to provide a combustion improvement technology that can be achieved.

[0014]

In order to solve the above technical problems, the present invention has the following configuration. That is, the internal combustion engine of the present invention, when the proportion of the inert gas contained in the intake air used for combustion approaches a predetermined amount, the production amount of soot produced during the combustion gradually reaches its peak, When it is further increased, it has a combustion characteristic that the amount of soot produced decreases, and further, the first combustion state in which the generation of soot is suppressed by suppressing the ratio of the inert gas to less than the predetermined amount, and the inert gas An internal combustion engine capable of switching between a second combustion state in which the generation of soot is suppressed by maintaining the ratio in a region exceeding the predetermined amount, and the second combustion state is changed from the first combustion state. At the time of switching to the state or at the time of switching from the second combustion state to the first combustion state, the proportion of the inert gas is adjusted based on the oxygen concentration of the exhaust gas flowing through the exhaust passage of the internal combustion engine. Changing combustion state Replacement means, a reducing agent addition means for adding a reducing agent to the exhaust gas discharged along with engine operation, and promoting the exhaust purification action of the exhaust purification catalyst installed in the exhaust passage, and the combustion state of the first combustion. In the process of switching from the state to the second combustion state or in the process of switching from the second combustion state to the first combustion state, reducing agent addition prohibition for inhibiting addition of reducing agent to exhaust gas for a predetermined period Means and
It is characterized by including.

In the present invention thus constituted, the reducing agent adding means is provided to add the reducing agent to the exhaust gas discharged along with the operation of the engine, and the exhaust gas is exhausted by the added reducing agent. The fuel ratio is forcibly reduced. Here, the reducing agent adding means may be any structure capable of adding the reducing agent to the exhaust gas flowing into the exhaust purification catalyst, and for example, adding the reducing agent into the exhaust passage or the cylinder in the latter stage of the combustion stroke. This is a concept including sub injection in the above.

The internal combustion engine of the present invention is one of the internal combustion engines capable of switching between the two combustion states disclosed in the prior art, and the switching control is performed based on the oxygen concentration of the exhaust gas. There is. Therefore, when the above-mentioned reducing agent is added at the time of switching the combustion state, that is, in the transient state leading to the first combustion state or the second combustion state, the switching of the appropriate combustion state is affected by the addition of the reducing agent. Becomes difficult. Therefore, in the internal combustion engine of the present invention, in addition to the reducing agent addition means, by further providing a reducing agent addition prohibiting means for prohibiting addition of the reducing agent in the transient state,
It enables quick switching of the combustion state.

That is, in the process of switching the combustion state, by realizing means for accurately determining the oxygen concentration in the exhaust gas, it is possible to avoid the difficulty of switching the combustion state due to the erroneous determination. Therefore, various problems in the transient period (transient state) are improved.

Regarding the switching of the combustion state, the inert gas is EGR gas introduced from the exhaust passage into the intake passage of the internal combustion engine, and the combustion state switching means passes through the intake passage to the combustion chamber. EGR supplied to
EGR amount control means for controlling the gas supply amount and air flow rate control means for controlling the flow rate of the air flowing into the combustion chamber through the intake passage are provided, and when changing the ratio of the inert gas contained in the intake air, It is also possible to adopt a configuration in which at least one of the EGR gas supply amount and the air flow rate is adjusted to converge to a target ratio suitable for a desired combustion state.

The EGR amount control means may be any device that can control (adjust) the supply amount of EGR gas flowing into the combustion chamber. For example, not only the existing EGR valve but also the intake passage and the exhaust gas can be used. EG by increasing the differential pressure in the passage
There is no particular limitation on the control method such as a method of increasing the amount of R gas introduced. In addition, the air flow rate control means similarly,
Anything that can control (adjust) the flow rate of air flowing into the combustion chamber through the intake passage may be used, such as control by the intake throttle valve arranged in the intake passage or adjustment of the supercharging pressure in an internal combustion engine equipped with a supercharger. The control method is arbitrary, such as the adjustment of the air amount by means of, or in an internal combustion engine equipped with an exhaust throttle valve, the adjustment of the amount of air by the exhaust throttle valve.

In this structure, the EGR amount control means controls the EG
The supply amount of R gas can be adjusted, the flow rate of air can be adjusted by the air flow rate control unit, and the EGR included in the intake air can be adjusted.
When changing the ratio of the gas (inert gas), at least one of the supply amount and the air flow rate of the EGR gas is adjusted to converge the target ratio suitable for the required combustion state. That is, if the supply amount of EGR gas is increased, the ratio of EGR gas contained in the intake air will be increased, and if the air flow rate is decreased, the ratio will be relatively increased.

The above-mentioned "target ratio" means the first
Of the EGR gas relative to the intake air in the first combustion state, that is, the EGR rate is less than 50% ( The EGR rate is preferably less than 45%) and is set to 55% or more (preferably 65% or more) in the second combustion state. It should be noted that the numerical values illustrated here are merely examples, and, of course, the numerical values are appropriately changed in consideration of the combustion characteristics of the internal combustion engine, the traveling condition, the operating environment, and the like.

With respect to the EGR amount control means and the air flow rate control means, the combustion state switching means controls the EGR gas amount by the EGR amount control means after the combustion state is switched. You may make it hold | maintain for a predetermined period with the control amount exceeding the control amount determined according to a ratio. Further, after the switching of the combustion state is started, the control of the air flow rate by the air flow rate control means may be held for a predetermined period with a control amount exceeding a control amount determined in accordance with the target ratio. Good.

In this configuration, the EGR amount control means and the air flow rate control means are controlled to exceed the control amount which should be determined in accordance with the target ratio. That is, since the EGR gas amount and the air amount change later than the actual demand, after the switching of the combustion state is started, the control amount is overshot for a predetermined period to suppress the response delay of the EGR gas and the air. .

Regarding switching of combustion states, combustion injection control specific to each combustion state is prepared corresponding to the first combustion state and the second combustion state, and in response to the switching of the combustion states. The combustion state switching means may change the ratio of the inert gas contained in the intake air in preference to the switching of the fuel injection control.

In the internal combustion engine of the present invention, the combustion state is switched by changing the ratio of the inert gas contained in the intake air, but at the same time, the fuel injection control is also changed in time according to the switching request. That is, the combustion injection control corresponding to the first combustion state and the fuel injection control corresponding to the second combustion state are prepared, and these are switched by the fuel injection switching means to suit each combustion state. Realize fuel injection control. Also, prior to the switching of the fuel injection control,
By changing the ratio of the inert gas, the ratio of the air supplied to the combustion and the inert gas is stabilized, and the situation in which the fuel injection control can be switched is created.

Further, the present invention may have the following configurations in order to solve the above technical problems. That is, the internal combustion engine of the present invention, when the proportion of the inert gas contained in the intake air used for combustion approaches a predetermined amount, the production amount of soot produced during the combustion gradually reaches its peak, When it is further increased, it has a combustion characteristic that the amount of soot produced decreases, and further, the first combustion state in which the generation of soot is suppressed by suppressing the ratio of the inert gas to less than the predetermined amount, and the inert gas An internal combustion engine capable of switching between a second combustion state in which the generation of soot is suppressed by maintaining the ratio in a region exceeding the predetermined amount, the first combustion state, and the second combustion state. Fuel injection control specific to each combustion state prepared for each of the combustion states, at the time of requesting switching from the first combustion state to the second combustion state, or from the second combustion state to the first combustion When a request to switch to the Fuel injection switching means for switching to fuel injection control corresponding to the required combustion state, and fuel injection control restraining means for restraining the fuel injection control for a predetermined period of time in the control state before switching after switching the combustion state. It is characterized by being provided.

In the internal combustion engine configured as described above, the first
Fuel injection control corresponding to each combustion state and fuel injection control corresponding to the second combustion state are prepared, and fuel injection control suitable for each combustion state is performed by switching them by the fuel injection switching means. To do. After the start of switching the combustion state, the injection control restraining means restrains the fuel injection control in the control state before the switching for a predetermined time.

That is, if the combustion injection control is switched before the ratio of the inert gas (EGR gas) contained in the intake air reaches the target ratio, the proper switching of the fuel injection control should be originally made. The switching will be appropriate. Therefore, the fuel injection control switching timing is optimized by restraining the fuel injection control in the control state before switching for a predetermined time.

The predetermined time is set in consideration of the above circumstances, and is the time required for the air-fuel ratio (ratio of air and inert gas) in the combustion chamber to reach the predetermined ratio. It is desirable to set with. The time required to reach the predetermined ratio can be obtained by various preliminary experiments or can be estimated from various data that can be acquired during engine operation, and the time can be calculated by various methods.

Further, regarding the injection control restraint means, the fuel injection control restraint means may shift the fuel injection control to a regular fuel injection control state while gradually changing the fuel injection control after the lapse of the predetermined time. .

With this configuration, the gradual change control is performed when the fuel injection control is switched. The gradual change control is to gradually change the combustion injection amount, the combustion injection timing, the combustion injection pressure, etc.
This is a control for shifting to a desired fuel injection state within a predetermined period.

With respect to the injection control restraint means, the fuel injection control restraint means releases the restraint state of the combustion injection control when the oxygen concentration of intake air used for combustion reaches a predetermined oxygen concentration. You may do it. That is, if the oxygen concentration of the intake air supplied to the combustion chamber reaches a predetermined oxygen concentration, it can be said that the ratio of the inert gas to the intake air is the target ratio. Decide whether or not to cancel.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of an internal combustion engine according to the present invention will be described below. It should be noted that the structure of the internal combustion engine shown below is merely one embodiment of the present invention, and its details can be arbitrarily changed without departing from the scope of the claims.

<Outline of Diesel Engine> As shown in FIG. 1, the internal combustion engine 1 according to the present embodiment is a diesel engine, and in addition to four cylinders 2 forming a combustion chamber, a fuel supply system and an intake system. , An exhaust system, a control system, etc. are provided as main components.

The fuel supply system includes a fuel injection valve 3, a pressure accumulating chamber (hereinafter referred to as a common rail) 4, a fuel supply pipe 5, a fuel pump 6, and the like, and supplies fuel to each cylinder 2. The fuel injection valve 3 is an electromagnetically driven on-off valve provided for each cylinder 2, and each fuel injection valve 3 is connected to a common rail 4 that serves as a fuel distribution pipe. Further, the common rail 4 is connected to the fuel pump 6 via the fuel supply pipe 5. The fuel pump 6 is rotationally driven using the rotation of the crankshaft 1a, which is the output shaft of the internal combustion engine 1, as a drive source.

In the fuel supply system constructed as described above, first, the fuel in the fuel tank (not shown) is pumped up by the fuel pump 6. The pumped fuel is supplied to the common rail 4 via the fuel supply pipe 5. Subsequently, the fuel supplied to the common rail 4 is increased to a predetermined fuel pressure in the common rail 4 and distributed to each fuel injection valve 3. Then, when the drive voltage is applied to the fuel injection valve 3 and the fuel injection valve 3 opens, the fuel is injected into the cylinder 2 via the fuel injection valve 3.

On the other hand, the intake system includes an intake pipe 9, a throttle valve 13, an intake branch pipe 8, an air cleaner box 10, an intercooler 16 and the like to form an intake passage for supplying air to each cylinder 2. .

The intake pipe 9 forms a passage for guiding the air (fresh air) taken in through the air cleaner box 10 to the intake branch pipe 8. The intake branch pipe 8 forms a passage for distributing the air flowing in through the intake pipe 9 to each cylinder 2. An air flow meter 11 for measuring the amount of air flowing into the intake pipe 9 and an intake air temperature sensor 12 for measuring the temperature of the air are provided near the connecting portion between the intake pipe 9 and the air cleaner box 10.

A throttle valve 13 (intake throttle valve) for adjusting the flow rate of air is provided immediately upstream of the intake branch pipe 8. The throttle valve 13 is opened and closed by an actuator 14 composed of a stepper motor or the like, and the actuator 14 is controlled based on a combustion state switching control program processed in an electronic control unit 30 described later. An intake air temperature sensor 24 that measures the temperature in the intake branch pipe 8 and a supercharging pressure sensor 23 that measures the pipe internal pressure in the intake branch pipe 8 are provided immediately downstream of the throttle valve 13.

In the intake passage from the air cleaner box 10 to the throttle valve 13, a compressor housing 15a of a turbocharger 15 for compressing air,
And an intercooler 16 for cooling the intake air compressed in the compressor housing 15a.

In the intake system thus constructed, first,
The air to be supplied to each cylinder 2 flows into the air cleaner box 10 due to the negative pressure generated by the engine operation. The air that has flowed into the air cleaner box 10 has its dust removed in the air cleaner box 10, and then flows into the compressor housing 15 a of the turbocharger 15 via the intake pipe 9. Compressor housing 15a
The air that has flowed into is compressed by a compressor wheel (not shown) and then cooled by the intercooler 16. Then, after the flow rate is adjusted by the throttle valve 13 as necessary, it flows into the intake branch pipe 8. The air flowing into the intake branch pipe 8 is distributed to each cylinder 2 through each branch pipe,
The fuel is combusted together with the fuel injected and supplied from the fuel injection valve 3. Outputs of various sensors are input to an electronic control unit 30 described later, and for example, the electronic control unit 30 is used.
It is fed back to the fuel injection control (basic engine control) etc. which is processed inside.

The exhaust system is provided with an exhaust branch pipe 18 and an exhaust pipe 19, and forms an exhaust passage through which exhaust gas discharged from each cylinder 2 due to combustion of the engine is discharged to the outside of the engine. Also, E
GR device 20, catalytic converter 52, reducing agent addition device 6
0, etc., and nitrogen oxides (NO
It has a function as an exhaust gas purification device that purifies fine particles such as x) and soot.

The exhaust branch pipe 18 is connected to the exhaust port 18a provided for each cylinder 2 and also the exhaust port 18a.
Exhaust gas flowing out from the turbocharger 15
And a passage leading to the turbine housing 15b is formed. Further, the exhaust pipe 19 forms a passage from the turbine housing 15b to a silencer (not shown).

EGR device 20 which is one of the exhaust purification devices
Is an EGR passage 25, an EGR valve 26, an EGR cooler 27.
Etc., and nitrogen oxides (NO
The production amount of x) is reduced. The EGR passage 25 forms a passage that bypasses the engine body 1 and connects the exhaust branch pipe 18 and the intake branch pipe 8. The EGR valve 26 is provided in the EGR passage 2
5 is an electric on-off valve provided in FIG. 5, and regulates the flow rate of exhaust gas (EGR gas) flowing in the EGR passage 25 based on a combustion state switching control program processed in the electronic control unit 30. Is going. The EGR cooler 27 uses the engine cooling water as a heat medium for the EGR passage 25.
The exhaust gas flowing inside is cooled. In the following description, the exhaust gas flowing through the EGR passage 25 may be referred to as EGR gas.

According to the EGR device 20 configured as described above, a part of the exhaust gas flowing in the exhaust branch pipe 18 is EG
It flows into the EGR passage 25 at a flow rate corresponding to the opening amount of the R valve 26. The EGR gas (exhaust gas) that has flowed into the EGR passage 25 is arranged in the EGR passage 25.
It flows into the cooler 27. The EGR gas flowing into the EGR cooler 27 is cooled when passing through the EGR cooler 27 and flows into the intake branch pipe 8. Then, the EGR gas flowing into the intake branch pipe 8 forms intake air while mixing with the air (fresh air) flowing from the upstream of the intake branch pipe 8, and the intake air mixed with the EGR gas flowing into each cylinder 2 is The fuel is combusted together with the fuel injected from the fuel injection valve 3. That is,
In the present invention, the intake air used for combustion is air (fresh air).
And a mixed gas of EGR gas.

The exhaust gas to be the EGR gas contains an inert gas such as water vapor (H ₂ O) and carbon dioxide (CO ₂ ). Therefore, when the exhaust gas containing the inert gas flows into each cylinder 2 together with the air, the combustion temperature at the time of combustion is lowered due to the mixing of the inert gas. As a result, the production of nitrogen oxides (NOx) is suppressed.

Next, the catalytic converter 52 which is one of the exhaust gas purification devices will be described. Catalytic converter 52
Is composed of a casing 53 and various exhaust purification catalysts 52a and 52b provided in the casing 53,
It has an exhaust gas purification function of purifying harmful substances in the exhaust gas discharged from the engine body 1.

More specifically, the turbine housing 15b
The NOx catalyst 52a and the particulate filter 52b are arranged in this order from the upstream side in the casing 53 of the exhaust purification catalyst. In the following description, the NOx storage reduction catalyst 52 will be described.
The a may be simply referred to as the NOx catalyst 52a. Also,
Nitrogen oxide (NOx) may be simply referred to as NOx.

NOx catalyst 52 which is one of the exhaust purification catalysts
"a" has an exhaust gas purification action for mainly purifying NOx in the exhaust gas. More specifically, the NOx catalyst 52
When the oxygen concentration of the exhaust gas flowing into a is high, NOx in the exhaust gas is absorbed, and when the oxygen concentration in the exhaust gas is low, that is, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 52a is low, it is absorbed. The existing NOx is reduced and released into the exhaust gas in the form of nitrogen dioxide (NO ₂ ) or nitric oxide (NO), and the unburned combustion component (C
It has an exhaust gas purification effect of oxidizing and purifying water vapor (H ₂ O) and carbon dioxide (CO ₂ ) by reacting with O, HC).

The composition is, for example, alumina (Al
₂ O ₃ ) as a carrier, and potassium (K), sodium (Na), lithium (Li), cesium (C
Alkali metals such as s), alkaline earths such as barium (Ba) and calcium (Ca), or lanthanum (L)
a) and at least one selected from rare earths such as yttrium (Y) and a noble metal such as platinum (Pt).

Incidentally, as a supplementary explanation of the exhaust gas purifying action, in a diesel engine, engine combustion is usually performed in an oxygen excess atmosphere. Therefore, the oxygen concentration in the exhaust gas discharged along with the combustion hardly decreases until the reduction / release action is promoted, and the unburned combustion components (CO, HC) contained in the exhaust gas. The amount of is very small. Therefore, in the present embodiment, by injecting and supplying the engine fuel (HC), which is a reducing agent, into the exhaust gas, the reduction of the oxygen concentration is promoted and the hydrocarbon (H
C) and the like are supplemented to promote the exhaust gas purification action. In addition,
The reducing agent is injected and supplied by a reducing agent addition device 60 described later. The details will be described later.

One particulate filter 52b
Has an exhaust gas purification effect of oxidizing and burning fine particles such as soot contained in the exhaust gas. More specifically, it has a filter 58 carrying an activated oxygen releasing agent, and has an exhaust gas purifying action of removing (purifying) the fine particles collected on the filter 58 by oxidizing and burning them with the activated oxygen. ing.

As shown in FIG. 6, the filter 58 alone has a honeycomb shape formed of a porous material such as cordierite, and has a plurality of channels 55 and 56 extending in parallel with each other. There is. More specifically, an exhaust gas inflow passage 55 whose downstream end is closed by a plug 55a,
Exhaust gas outflow passage 5 whose upstream end is closed by a plug 56a
6, and the exhaust gas inflow passages 55 and the exhaust gas outflow passages 56 are arranged side by side in the vertical and horizontal directions of the filter 58 via a thin partition wall 57. The so-called wall flow type is formed.

Further, a layer of a carrier made of alumina (Al ₂ O ₃ ) or the like is provided on the surface and inside pores of the partition wall 57, and platinum (Pt) or the like is formed on the carrier. In addition to the noble metal catalyst, it carries an active oxygen releasing agent that occludes the excess oxygen when it exists in the surroundings and conversely releases the occluded oxygen in the form of active oxygen when the oxygen concentration decreases.

As the active oxygen releasing agent, potassium (K), sodium (Na), lithium (Li), cesium (Cs), alkali metals such as rubidium (Rb), barium (Ba), calcium (Ca). ), At least one selected from alkaline earth metals such as strontium (Sr), rare earths such as lanthanum (La) and yttrium (Y), and transition metals such as cerium (Ce) and tin (Sn). Can be used.

Also, preferably, an alkali metal or alkaline earth metal having a higher ionization tendency than calcium (Ca), that is, potassium (K), lithium (Li), cesium (Cs), rubidium (Rb), barium (Ba). ),
It is preferable to use strontium (Sr) or the like.

In the particulate filter 52b thus constructed, first, the exhaust gas flowing into the exhaust gas inflow passage 55 is exhaust gas inflow passage 55 → partition 57 → exhaust gas as shown by an arrow a in FIG. The soot and other fine particles contained in the exhaust gas that flow in the order of the outflow passage 56 are collected on the surface and inside of the partition wall 57. Partition wall 5
The fine particles collected in 7 are oxidized by the activated oxygen that increases by changing the oxygen concentration of the exhaust gas flowing into the partition wall 57 multiple times, and finally burnt out without emitting a luminous flame and the filter 58. Removed from above.

As described above, in this embodiment, the NOx contained in the exhaust gas is arranged by arranging the NOx storage reduction catalyst 52a and the particulate filter 52b in the exhaust passage.
Purifies fine particles such as Ox and soot.

In this embodiment, as described above, the NOx storage reduction catalyst 52a and the particulate filter 52b are arranged in series. The reason for this is that the particulate heat filter 52b is used by utilizing the reaction heat associated with the oxidation / reduction reaction in the NOx storage reduction catalyst 52a.
To raise the temperature. The reason is that the activated oxygen from the storage reduction type NOx catalyst 52a released due to the oxidation / reduction reaction in the storage reduction type NOx catalyst 52a is used for the exhaust gas purification action of the particulate filter 52b. . The storage reduction type NOx catalyst 52a
As is clear from the above, it carries a substance substantially similar to the activated oxygen releasing agent. Therefore, the storage reduction type NO
It can be said that the x catalyst 52a has a function as an activated oxygen releasing agent. In addition, in the present embodiment, an oxidation catalytic converter 59 that purifies the unburned fuel components in the exhaust gas by oxidation is provided downstream of the catalytic converter 52.

Next, the reducing agent addition device 60 for promoting the exhaust gas purification action of the exhaust gas purification catalyst will be described. The reducing agent addition device 60 includes a reducing agent addition valve 61, a reducing agent supply passage 62, a fuel pressure control valve 64, a fuel pressure sensor 63, an emergency shutoff valve 66, and the like, and the air-fuel ratio of the exhaust gas flowing into the catalytic converter 52 is a target air-fuel ratio. The engine fuel, which is a reducing agent, is introduced into the exhaust gas so as to obtain a fuel ratio.

The reducing agent addition valve 61 is provided in the collecting portion of the exhaust branch pipe 18, and is opened when a predetermined voltage is applied under a reducing agent addition program processed in an electronic control unit described later. It is an electric on-off valve that operates. The reducing agent supply passage 62 forms a passage for guiding a part of the fuel pumped up by the fuel pump 6 to the reducing agent addition valve 61. The fuel pressure control valve 64 is arranged in the middle of the reducing agent supply passage 62 and maintains the fuel pressure in the reducing agent supply passage 62 at a predetermined fuel pressure. The fuel pressure sensor 63 detects the fuel pressure in the reducing agent supply passage 62. The emergency cutoff valve 66 stops the fuel supply to the reducing agent supply passage 62 when the pressure in the reducing agent supply passage 62 becomes abnormal.

Reducing agent adding device 60 configured as described above
Then, the fuel discharged from the fuel pump 6 is supplied to the reducing agent addition valve 61 through the reducing agent supply passage 62 after the fuel pressure control valve 64 maintains the predetermined fuel pressure. Then, when a predetermined voltage is applied to the reducing agent addition valve 61 and the reducing agent addition valve 61 is opened, the fuel in the reducing agent supply passage 62 is added to the exhaust branch pipe 18 through the reducing agent addition valve 61. To be done. Fuel (reducing agent) supplied to the exhaust branch pipe 18
Is stirred in the turbine housing 15b, and then flows into the catalytic converter 52 through the exhaust pipe 19. Therefore, the catalytic converter 52 has a low oxygen concentration, and
Exhaust gas mixed with hydrocarbon (HC), which is an unburned combustion component, flows in, and thus the above-described exhaust gas purification action is promoted.

The amount and timing of addition of the reducing agent are determined by the output of the air-fuel ratio sensor (A / F sensor) 74 provided downstream of the catalytic converter 52 and the exhaust gas provided upstream and downstream of the particulate filter 52b. It is determined in consideration of the output of a temperature sensor (not shown) and the operation history recorded in the electronic control unit 30 described later. The details will be described later.

Next, the control system will be described. The control system is a ROM connected to each other by a bidirectional bus 31.
A so-called electronic control unit 30 (ECU) including a (read only memory) 32, a RAM (random access memory) 33, a CPU (central control unit) 34, an input port 35, and an output port 36, in order to obtain an engine output. In addition to the fuel injection control (basic engine control), the reducing agent addition control for promoting the exhaust purification action, and the combustion state switching control for switching the combustion state of the engine body by operating the EGR valve 26, the throttle valve 13 and the like. Is running.

At the input port 35, in addition to the output signals of the various sensors described above, a load sensor 41 for detecting the depression amount of the accelerator pedal 40, a crank angle sensor 42 for detecting the rotation speed of the crankshaft 1a, and a vehicle speed are measured. The vehicle speed sensor 43 or the like is directly input via the corresponding A / D converter 37. On the other hand, at the output port 36, the fuel injection valve 3, the reducing agent addition valve 61, the throttle valve driving actuator 14, and the EG via the corresponding drive circuit 38.
The R valve 26, etc. are connected.

Further, the ROM 32 is provided with a program for processing the above various controls, a control map referred to when the program is executed, and the like corresponding to each device. Further, in the RAM 33, output signals of various sensors input to the input port 35, control signals output to the output port 36, and the like are recorded as an operation history of the internal combustion engine. The CPU 34 compares the output signals of the various sensors recorded on the RAM 33 with the control map developed on the ROM 32 on a desired program, and outputs the various control signals output during the processing through the output port 36. Various devices are centrally managed by outputting to corresponding devices.

Next, the reducing agent addition control and the combustion state switching control for switching the combustion state will be described in detail.

<Reducing Agent Addition Control> In the reducing agent addition control (reducing agent addition control program), the CPU 34 first determines whether or not the conditions for adding the fuel that is the reducing agent are satisfied. Here, as the reducing agent addition start condition, when it is considered that the output value of the exhaust gas temperature sensor reaches a predetermined value and the temperature in the catalytic converter 52 reaches the activation temperature of various exhaust gas purification catalysts, The NO occluded in the NOx catalyst 52a when the number of mileages of the vehicle and the traveling time of the vehicle have reached a predetermined value.
When the storage amount of x and the collection amount of the particulates collected by the particulate filter 52b are considered to have reached a predetermined amount, the addition condition of the reducing agent is set.

Then, the CPU 34 accepts the establishment of these conditions and permits the reducing agent addition device 60 to add the reducing agent. The reducing agent is added by the catalytic converter 52.
The air-fuel ratio of the exhaust gas flowing into the engine is changed so as to change like a spike in a relatively short cycle. Further, at that time, in the CPU 34, the air-fuel ratio sensor 74 provided downstream of the catalytic converter 52.
The output value of is read, and the output value is fed back to the addition amount of the reducing agent to adjust the addition amount of the reducing agent to an appropriate amount. That is, the feedback control based on the output value of the air-fuel ratio sensor 74 is executed.

In this embodiment, the air-fuel ratio sensor 7
The lean mixture sensor is adopted as 4,
Of course, an oxygen concentration sensor (O ₂ sensor) or the like may be used. Although the air-fuel ratio sensor 74 is installed downstream of the catalytic converter 52, it may be installed upstream of the catalytic converter 52. The catalytic converter 52
When installed on the downstream side, there is an advantage that soot can be prevented from adhering to the air-fuel ratio sensor 74.

Next, the combustion state switching control will be described. <Combustion state switching control> First, before explaining the detailed control contents, the combustion characteristics of the internal combustion engine will be described.

The diesel engine shown in the present embodiment is a kind of the internal combustion engine disclosed in the above-mentioned prior art, in which the ratio of the inert gas to the intake air is greatly increased so that the smoke produced during the combustion. Combustion technology that suppresses the growth of is adopted.

FIG. 2 is a graph obtained in accordance with the actual experimental results, and shows the correlation between the ratio of the inert gas to the intake air and the amount of smoke produced by the combustion. . In the following description, the ratio of the inert gas to the intake air may be simply referred to as the EGR rate.

As can be seen from FIG. 2, the soot generation amount reaches a peak when the EGR rate is between about 40% and 50%, and E
In the region where the GR rate is 55% or more, soot is hardly generated. Therefore, if the engine operation is performed in the region where the EGR rate is 55% or more, preferably the EGR rate is 65% or more, the engine operation can be performed while the soot emission amount is substantially zero.

However, in the operation at the EGR rate of 65% or more, there arises a problem that the engine output cannot be sufficiently obtained due to the shortage of the air amount and the decrease of the combustion pressure. On the other hand, in the region where the EGR rate is less than 40% where sufficient engine output is obtained,
Although the generation of soot is slightly observed, the amount generated is
The EGR rate is sufficiently small as compared with the operating range of 40% to 50%.

Therefore, when the engine output is not so much required, such as when the engine is idling or running at a low load, E
When engine operation is performed with the GR rate maintained at 65% or higher, and when sufficient engine output is required during high load running, EGR
By operating the engine while keeping the rate below 40%, a comfortable operating state is secured while suppressing the generation of soot.

That is, in the diesel engine shown in the present embodiment, the EGR rate at which the amount of soot generated peaks is 40%.
By switching the combustion state in steps so as to avoid the operation at -50%, compatibility of soot emission control and drivability is ensured.

The values exemplified above, that is, EGR
The specific numerical value of the rate is merely an example, and the numerical value slightly changes depending on the combustion characteristics specific to the applied internal combustion engine and the cooling temperature of the EGR gas. However, the emission characteristics of soot, that is, the presence of a peak, can be said to be common to all internal combustion engines.

Further, the switching of the combustion state is determined in consideration of, for example, the engine required torque calculated during the processing of the fuel injection control which is the basic engine control. That is, in the combustion state switching control, as one of the controls, the engine required torque becomes equal to or lower than the predetermined lower limit value, and the EG
When the operation at the R rate of 65% or more is selected and the engine required torque reaches or exceeds the predetermined upper limit value, the combustion state selection control for selecting the operation at the EGR rate of less than 40% is executed.

A hysteresis is provided between the predetermined upper limit value and the predetermined lower limit value. This hysteresis suppresses frequent switching of the combustion state. For example, by changing the threshold value for switching between acceleration traveling and deceleration traveling, frequent switching near the threshold is suppressed. .

Next, detailed control contents of the combustion state switching control (combustion state switching control program) will be described.
In the following description, the operating range at an EGR rate of 65% or more may be referred to as “low temperature combustion”, and the operating range at an EGR rate of less than 40% may be referred to as “normal combustion”.

In the present control, in addition to the combustion state selection control described above, (1) EGR rate variable control for changing the EGR rate by changing the opening of the EGR valve 26 and the throttle valve 13 is carried out. (2) The combustion state is switched by performing engine control such as fuel injection switching control for stabilizing the combustion state by switching to the fuel injection control suitable for each combustion state.

That is, the combustion state switching control in the present embodiment is a control for collectively processing the opening control of the EGR valve 26, the opening control of the throttle valve 13, the switching control of the combustion injection control, and the like. . Also, based on these various controls, EG
By controlling the R valve 26, the throttle valve 13, the fuel injection control and the like, the EGR amount control means, the air flow rate control means, the fuel injection switching means and the like according to the present invention are realized.

3 and 4, the opening of the EGR valve 26, the opening of the throttle valve 13, and the change over time of the combustion injection control, which change in the process of the combustion state switching control, are shown as changes in each combustion state. It is shown immediately.

Hereinafter, various control contents processed in the combustion state switching process will be described in detail with reference to FIGS. 3 and 4.

First, with reference to FIG. 3, description will be given of the control contents to be processed when the normal combustion is switched to the low temperature combustion.
EGR rate of 4 when switching from normal combustion to low temperature combustion
The combustion state at less than 0% is switched to the combustion state at an EGR rate of 65% or more. That is, the opening degree of the EGR valve 26 is increased, the opening degree of the throttle valve 13 is decreased, and the EGR rate variable control for increasing the EGR rate is executed.

In the EGR rate variable control, the opening amount of each valve body 26, 13 is controlled mainly based on the air-fuel ratio (oxygen concentration) of the exhaust gas flowing through the exhaust passage. That is, the output of the air-fuel ratio sensor 74 provided downstream of the catalytic converter 52 is fed back to the air-fuel ratio sensor 74.
The opening degrees of the EGR valve 26 and the throttle valve 13 are controlled so that a predetermined output can be obtained.

The predetermined output is a value output when the ratio of the inert gas to the intake air (EGR rate) reaches the target ratio, and the EGR rate obtained in various preliminary experiments. And the oxygen concentration in the exhaust gas.

More specifically, the valve opening control of the EGR valve 26 and the throttle valve 13 is completed, and E supplied to the combustion chamber.
When the GR gas amount reaches the target ratio and the predetermined contained oxygen amount, the oxygen amount (oxygen concentration) naturally contained in the intake air also becomes the predetermined amount. Further, the oxygen concentration in the exhaust gas generated by the combustion of the intake air is inevitably proportional to the oxygen amount of the intake air. That is, the EGR rate can be estimated by detecting the oxygen concentration in the exhaust gas.

The EGR rate is generally a numerical value defined by the supply amount of the EGR gas supplied to the intake passage. However, if attention is paid to the amount of oxygen contained in the EGR gas, the EGR rate is supplied to the intake passage. The amount of oxygen in the EGR gas that is generated decreases over time due to the amount of oxygen in the exhaust gas that is generated by the combustion of intake air mixed with the EGR gas. Therefore, the EGR rate defined without considering the oxygen concentration in the exhaust gas cannot be said to be the true EGR rate, and as shown in the present embodiment, the EGR rate is based on the oxygen concentration in the exhaust gas.
By changing the rate, it becomes possible to accurately manage the EGR rate.

Regarding the EGR rate variable control, in the combustion state switching control, the overshoot control for forcibly changing the EGR rate is executed prior to the feedback control based on the output of the air-fuel ratio sensor.

That is, the supply amount of EGR gas and the flow rate of air change with time after the control of the valve bodies 26, 13. Therefore, each valve element 1 that should be originally determined in accordance with the target ratio (EGR rate) required at low temperature combustion
By temporarily increasing the control amounts of 3, 26, EGR
The rate of response (rate of change) is being accelerated.

The overshoot control is executed after the switching of the combustion state is started, and when the oxygen concentration in the exhaust gas is reduced to a predetermined oxygen concentration, and the air flow rate obtained by the output of the air flow meter 11 is reached. Is reduced to a predetermined air flow rate, the feedback control is switched to the feedback control based on the output of the air-fuel ratio sensor 74. In the present embodiment, in the overshoot control process, the EGR valve 26 is set to a substantially fully open state, and the throttle valve 13
Is substantially closed to improve the response speed of the EGR rate.

On the other hand, in the fuel injection switching control, the combustion injection pressure is increased, the fuel injection amount is increased, the fuel injection timing is advanced, and the multiple injections (multi injection) are switched to the single injection (single injection). Correction control such as. The contents of these corrections are recorded in the electronic control unit 30 as fuel injection control for low temperature combustion,
At the time of switching to the low temperature combustion, the subsequent fuel injection control is processed based on the fuel injection control for the low temperature combustion.

The correction of these combustion injection controls is intended to improve various combustion defects that occur during low temperature combustion. That is, at low temperature combustion, the combustion temperature decreases,
Also, the amount of oxygen contributing to combustion is reduced. Therefore, combustion under severe conditions is required, and in the fuel injection control that was performed during normal combustion, misfire, decrease in combustion pressure, insufficient engine output, increase in combustion noise (diesel knock), etc. Problem arises. Therefore, by performing the various corrections described above to optimize ignition delay, suppression of pressure rise during the flame propagation period, shortening of the direct combustion period and late combustion period, etc., a good combustion state at low temperature combustion is secured. ing.

Further, in the present embodiment, the switching of the fuel injection control is processed after the previous EGR rate variable control. That is, after the switching of the combustion state is started, the fuel injection control is performed to restrain the fuel injection control for a predetermined time in the control state before the switching.

More specifically, the fuel injection control is optimized by including the control delay (standby time) in the correction of the fuel injection control in order to respond to the response delay of the EGR gas amount and the air amount.

The delay time in the correction control is
It is decided in consideration of various conditions. More specifically, the time from the start of switching the combustion state until the cumulative number of crank cycles reaches a predetermined number of crank cycles, and the time until the air amount, the pressure in the intake branch pipe, and the temperature in the intake branch pipe reach a predetermined value, Also, it is determined in consideration of various conditions such as the fuel injection amount before switching the combustion state,
In response to the satisfaction of these conditions, the correction of the fuel injection control is started.

The cumulative crank cycle number corresponds to the progress of the intake stroke → compression → combustion → exhaust stroke. By detecting the cumulative crank cycle number, the exhaust gas to the intake system ( The amount of entrainment of EGR gas, that is, the EGR rate can be roughly estimated. Further, changes in the air amount, the pressure in the intake branch pipe, and the temperature in the intake branch pipe will be described. At low temperature combustion, the air amount and the pressure in the intake branch pipe decrease, and the temperature in the intake branch pipe rises. Therefore, the EGR rate can be estimated by detecting these changes.
Further, since the amount of exhaust gas (EGR gas) is determined by the fuel injection amount before switching the combustion state, the wraparound amount of EGR gas can be estimated from the fuel injection amount.

As described above, in the internal combustion engine according to the present embodiment, it is determined whether or not the change amount of the EGR rate, that is, the oxygen concentration of the intake air supplied into the combustion chamber has reached the predetermined oxygen concentration, and the oxygen concentration is changed. The restraint state of the fuel injection control is released in response to the decrease in the concentration to the predetermined oxygen concentration.

Further, in the present embodiment, the gradual change control is executed for the correction of the fuel injection control. In this gradual change control, control gains for various corrections are determined in order to end the correction within a predetermined period. That is, since the correction related to the fuel injection is caused by the torque shock or the like, the correction is gradually changed to suppress the torque shock during the fuel injection correction control.

Next, with reference to FIG. 4, description will be given of the contents of control executed when returning from low temperature combustion to normal combustion. When switching from low temperature combustion to normal combustion, EGR
The combustion state at the rate of 65% or more is switched to the combustion state at the EGR rate of less than 40%. That is, the opening degree of the EGR valve 26 is decreased and the opening degree of the throttle valve 13 is increased to increase the EG
The EGR rate variable control for reducing the R rate is executed.

Also, when the low temperature combustion is switched to the normal combustion, the EGR rate variable control similarly performs feedback control based on the air-fuel ratio (oxygen concentration) of the exhaust gas flowing through the exhaust passage. Further, prior to the feedback control, overshoot control of the valve bodies 13 and 26 is performed. In the overshoot control at the time of switching to the normal combustion, the opening degree of the EGR valve 26 is in a substantially fully closed state, and the throttle valve 13 is in a substantially fully opened state.

On the other hand, in the fuel injection switching control, correction control such as reducing the combustion injection pressure, reducing the fuel injection amount, retarding the fuel injection timing, and switching from single injection to multiple injections is executed. Note that these correction contents are also recorded on the electronic control unit 30 in the same manner as above, and when switching to normal combustion, the subsequent fuel injection control is processed based on the fuel injection control for normal combustion.

The correction related to the combustion injection control is a correction control for obtaining the driver's bilility at the time of normal combustion, and the correction value and the like are the contents of the control that are roughly marred to the basic fuel injection control. There is.

The basic combustion injection control will be described. In the basic fuel injection control, the "target required torque" required for the current engine operation is calculated based on the output signals of the crank angle sensor 42 and the load sensor 41, In order to obtain this target required torque, the control signals output to the fuel injection valve 3 and the fuel pump 6 are updated at appropriate times to correct the fuel supply amount in the fuel supply system.

Further, also in the switching of the fuel injection control caused by switching to the normal combustion, in this embodiment, the control delay (standby time) is included to optimize the fuel injection switching control. Further, when the correction of the fuel injection control is started, the gradual change control is executed to avoid the torque shock accompanying the switching of the fuel injection control.
The delay time is set in consideration of the various conditions described above.

As described above, in the internal combustion engine according to the present embodiment, the overshoot control for overshooting the control amounts of the valve bodies 13 and 26 is performed. A fuel injection restraint control is provided in which a control delay is provided to correct the combustion injection control. Performs gradual change control when switching fuel injection control,
By processing additional control such as the above in the transient period of the combustion state, various problems in the transient period are improved.

That is, since the combustion state is swiftly switched by the overshoot control, the combustion instability state in the transient period due to the response delay of the EGR gas amount and the air amount is improved. Further, the fuel injection control and the gradual change control are performed to optimize the fuel injection control, thereby improving the driver's ability, reducing engine noise, and suppressing smoke.

By the way, during the transition period from the normal combustion to the low temperature combustion and during the transition period from the low temperature combustion to the normal combustion, the variable control of the EGR rate is performed based on the oxygen concentration (air-fuel ratio) of the exhaust gas as described above. ing.

On the other hand, in the internal combustion engine shown in this embodiment,
As described above, a reducing agent is added to the exhaust gas in order to promote purification of fine particles such as NOx and soot. Further, since the addition is carried out in the exhaust branch pipe 18 with the expectation of the stirring effect in the turbocharger and the gasification by the exhaust heat, when the reducing agent is added, the exhaust gas mixed with the reducing agent (engine fuel) is used. The exhaust passage will be filled.

On the other hand, the air-fuel ratio sensor 74 installed downstream of the catalytic converter 52 in order to avoid soot adhesion and the like.
The EGR rate variable control is performed on the basis of the output of. Therefore, when the reducing agent is added, the air-fuel ratio of the exhaust gas mixed with the reducing agent is detected by the air-fuel ratio sensor 74. As a result, the air-fuel ratio sensor 74 detects the original air-fuel ratio of the exhaust gas (oxygen concentration). Will detect an air-fuel ratio different from That is, when the reducing agent is added, the air-fuel ratio sensor 7
Since the consistency between the output of No. 4 and the target EGR rate is not ensured, it becomes difficult to appropriately switch the combustion state.

Therefore, in the internal combustion engine shown in this embodiment,
In addition to the various controls described above, a reducing agent addition prohibition control is executed so that the combustion state can be appropriately switched. Hereinafter, the reducing agent addition prohibition control will be described.

This reducing agent addition prohibition control is added to the combustion state switching control and is performed during the combustion state switching period, that is, in the transient state from low temperature combustion to normal combustion and in the transient state from normal combustion to low temperature combustion. Is being processed.

The processing contents will be described below.
In this control, addition of the reducing agent to the exhaust gas is prohibited until the EGR rate variable control is completed. More specifically, even if the output signal indicating that the reducing agent should be added is obtained in the above-mentioned reducing agent addition control by shutting off the valve opening signal output to the reducing agent addition valve 61, it is based on the output result. The opening control of the reducing agent addition valve 61 is not performed. Therefore, during the EGR rate variable control period, the air-fuel ratio sensor 74 detects the normal oxygen concentration, and thus,
Appropriate switching to each combustion state becomes possible.

Note that FIG. 5 shows a series of processing contents in the above-described combustion state switching control (combustion state switching control program) based on the present reducing agent addition prohibition control.

First, the electronic control unit 30 determines whether or not the combustion state should be switched by the processing of the combustion state selection control based on various conditions such as the engine required torque (step 101). Subsequently, in response to the request for switching the combustion state, the above-mentioned reducing agent addition prohibition control is processed (step 1
02). When the result in step 101 is negative, this control is temporarily terminated.

Then, the electronic control unit 30 starts the above EGR rate variable control to switch the combustion state (step 103). Further, in synchronization with this, the fuel injection switching control is started to start switching the fuel injection control (step 106).

In the EGR rate variable control in step 103, the overshoot control is processed first (step 1
04), and subsequently, the feedback control based on the air-fuel ratio sensor 74 is processed (step 105).

On the other hand, in the fuel injection switching control in step 106, first, the fuel injection restraint control is processed to restrain the switching of the fuel injection control for a predetermined time (step 10).
7). Then, when the oxygen concentration of the intake air supplied to the combustion chamber approaches the desired oxygen concentration, switching of the fuel injection control based on the gradual change control is processed (step 108). Then, the electronic control unit 30 receives the end of the fuel injection switching control, cancels the reducing agent addition prohibition control (step 109), and ends this processing routine.

As described above, in the present embodiment, various controls are performed in the transient state corresponding to the combustion state switching period, and the driver's viability is lowered due to combustion instability in the transient state, and engine noise is reduced. We are working to improve phenomena such as increase and smoke.

The above-described structure is merely an embodiment of the present invention, and its details can be changed as desired. For example, in the above, when adding the reducing agent, the reducing agent is added to the exhaust passage, but by sub-injecting the engine fuel that is the reducing agent into the cylinder in the latter stage of the combustion stroke, the air-fuel ratio of the exhaust gas is reduced. You may let me. Although the diesel engine has been described above as an example, the present invention is also useful in a lean-burn gasoline engine and the like.

Regarding the reducing agent addition prohibition control, the reducing agent addition prohibition period is from the start of the switching of the combustion state to the end of the switching, but the addition of the reducing agent is prohibited from the end of the overshoot control. You may do it. Further, the addition of the reducing agent may be permitted upon the start of switching the fuel injection control.

Regarding the combustion state switching control,
Switching is possible in consideration of the temperature of the exhaust purification catalyst and the temperature of the exhaust gas. As a background for this, the low temperature combustion technique described in the present embodiment may be used for warming up the exhaust purification catalyst. That is, the EGR gas itself is an inert gas that absorbs heat energy, but since the gas itself has considerable heat energy, when the temperature of the air (outside air) itself is low or when the fuel injection amount is small. , The effect of keeping the temperature of the exhaust gas high. Therefore, the exhaust gas containing the EGR gas is caused to flow into the exhaust purification catalyst, whereby the exhaust purification catalyst is quickly warmed up. Even in this case, smoke is generated and engine noise is increased when the combustion state is switched. Therefore, by performing various engine controls in the above transient state, these problems can be solved.

Regarding the fuel injection switching control,
Even if the gradual change control is started after the above overshoot control is completed, the same effect as the above description can be obtained. Further, the delay time can be set in advance by various preliminary experiments.

[0126]

As described above, according to the present invention, in the combustion injection control, the addition of the reducing agent to the exhaust purification catalyst is prohibited during the transient period of the combustion state, and the control amount of each valve body is overshooted. By performing various controls such as providing a delay time for correction and gradually changing the fuel injection control, it is possible to improve various problems caused in the transient state. Therefore, it is possible to improve the driver's ability, reduce engine noise, and suppress smoke.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine according to the present embodiment.

FIG. 2 is a graph for explaining the correlation between the amount of soot generated and the EGR rate.

FIG. 3 is a time chart showing changes with time of various controls processed when switching from normal combustion to low temperature combustion.

FIG. 4 is a time chart showing changes with time of various controls processed at the time of transition from low temperature combustion to normal combustion.

FIG. 5 is a flowchart for explaining the processing sequence of various controls that are performed when switching the combustion state.

FIG. 6 is a view for explaining the internal structure of a particulate filter.

[Explanation of symbols] 1 Internal combustion engine (engine body) 1a crankshaft Two cylinder 3 Fuel injection valve 4 common rail 5 Fuel supply pipe 6 Fuel pump 8 intake branch pipe 9 Intake pipe 10 air cleaner box 11 Air flow meter 12 Intake air temperature sensor 13 Throttle valve 14 Actuator 15 Turbocharger 15a Compressor housing 15b turbine housing 16 Intercooler 18 Exhaust branch pipe 18a exhaust port 19 Exhaust pipe 20 EGR device 23 Supercharging pressure sensor 24 Intake temperature sensor 25 EGR passage 26 EGR valve 27 EGR cooler 30 electronic control unit 31 bidirectional bus 35 input ports 36 output ports 37 A / D converter 38 Drive circuit 40 accelerator pedal 41 Load sensor 42 crank angle sensor 43 Vehicle speed sensor 52 catalytic converter 52a Storage reduction type NOx catalyst 52b Particulate filter 53 casing 55 Exhaust gas inflow passage 55a stopper 56 Exhaust gas outflow passage 56a stopper 57 partitions 58 Filter 59 Oxidation catalytic converter 60 Reductant addition device 61 Reductant addition valve 62 Reductant supply path 63 Fuel pressure sensor 64 Fuel pressure control valve 66 Emergency shutoff valve 74 Air-fuel ratio sensor

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/28 301 F02D 21/08 301B 3G301 F02D 21/08 301 301D 4D048 41/02 301E 41/02 301 41/04 310Z 41/04 310 325Z 325 43/00 301G 43/00 301 301N 301T F02M 25/07 570D F02M 25/07 570 570J B01D 53/36 103B (72) Inventor Tatsuyu Sugiyama Toyota City, Aichi Prefecture Toyota-cho 1 Toyota Auto Car Company (72) Inventor Yasuhiko Otsubo 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Takekazu Ito 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Atsushi Tahara 1 Toyota Town, Toyota City, Aichi Prefecture F-term in Toyota Motor Corporation (reference) 3G062 AA01 BA02 BA04 BA05 BA06 DA01 DA02 DA04 DA06 EA10 EB15 ED08 ED14 GA04 GA06 G A09 GA15 GA17 GA25 3G084 AA01 AA04 BA04 BA05 BA11 BA20 BA24 DA10 DA15 DA39 EC01 EC03 FA00 FA05 FA10 FA18 FA19 FA26 FA29 FA38 3G090 AA03 BA01 DA10 DA12 DA15 DA18 DA19 DA20 EA01 EA02 AB01 A14 A11 A02 A11 A02 A11 A11 AA02 A11 A11 AA02 BA19 BA33 CA13 CA18 CB02 CB03 CB07 CB08 DA01 DA02 DA05 DA07 DB10 DC01 DC06 EA00 EA01 EA03 EA07 EA17 EA30 EA31 EA34 EA39 FA12 FA13 FA14 FB10 FB12 FC37 HA36 GB16 HA16 GB16 HA16 GB16W16 GB16W16 GB16W16 GB16W16 GB16W16 GB16W16 GB16W16 GB16W16 GB16W16 GB16W16 GB16W16 GB16W16 GB06WW16 GB16WQW16 GB06WW16 GB06WW16 GB16WQW16 GB06WWQWGBO 16 GBWYGW04 HA47 HB03 HB05 HB06 3G092 AA02 AA06 AA13 AA17 AA18 AB03 AB20 BA07 BB04 BB06 BB08 DB03 DC03 DC08 DC09 DC15 DE03S DF03 DF06 DG07 EA01 EA02 EA05 EA06 EA07 EA11 EA16 EA22 EC01 FA03 FA04 FA05 FA14 FA17 FA18 FA24 FB06 HA06X HA15X HB01X HB02X HD01Z HD04X HD04Z HD07X HE01Z HE03Z HF08Z HF09Z 3G301 HA02 HA11 HA13 HA15 JA03 JA21 JA37 LA00 LA01 LB06 MA00 MA18 PA17Z PB08Z PD02Z PE03Z PF01Z PF03Z 4D048 AA06 AA14 AB01 AB02 AC02 BA03X BA14X BA15X

Claims (8)

[Claims] 1. When the ratio of the inert gas contained in the intake air used for combustion approaches a predetermined amount, the amount of soot generated during the combustion gradually reaches a peak, and when the ratio is further increased, the soot is increased. The first combustion state that suppresses the generation of soot by suppressing the proportion of the inert gas to less than the predetermined amount, and the proportion of the inert gas are the same as those described above. An internal combustion engine capable of switching between a second combustion state in which generation of soot is suppressed by holding in a region exceeding a fixed amount, and switching from the first combustion state to the second combustion state. At the time, or at the time of switching from the second combustion state to the first combustion state, a combustion state in which the proportion of the inert gas is changed based on the oxygen concentration of the exhaust gas flowing through the exhaust passage of the internal combustion engine. Switching means and engine The reducing agent is added to the exhaust gas discharged due to the rolling,
A reducing agent addition means for promoting the exhaust gas purification action of the exhaust gas purification catalyst installed in the exhaust passage, and a process of switching the combustion state from the first combustion state to the second combustion state, or the second combustion state. An internal combustion engine, comprising: a reducing agent addition prohibiting means for prohibiting addition of the reducing agent to the exhaust gas for a predetermined period in the process of switching from the state to the first combustion state. 2. The EGR gas introduced into the intake passage of the internal combustion engine from the exhaust passage, and the combustion state switching means supplies the EGR gas to the combustion chamber through the intake passage. And an air flow rate control means for controlling the flow rate of the air flowing into the combustion chamber through the intake passage, and when changing the proportion of the inert gas contained in the intake air, Of the EGR gas supply amount and the air flow rate,
The internal combustion engine according to claim 1, wherein at least one of them is adjusted to converge to a target ratio suitable for a desired combustion state. 3. The combustion state switching means, after starting the switching of the combustion state, performs the EGR by the EGR amount control means.
The internal combustion engine according to claim 2, wherein control of the gas amount is held for a predetermined period at a control amount that exceeds a control amount that is determined according to the target ratio. 4. The combustion state switching means, after starting the combustion state switching, controls the air flow rate by the air flow rate control means to exceed a control amount determined in accordance with the target ratio. The internal combustion engine according to claim 2, wherein the internal combustion engine holds the amount for a predetermined period. 5. Combustion injection control specific to each combustion state is prepared corresponding to the first combustion state and the second combustion state, and the fuel injection control is performed according to switching of the combustion state. 5. The fuel injection switching means for switching the fuel injection control means, wherein the combustion state switching means changes the proportion of the inert gas contained in the intake air prior to the switching of the fuel injection control. Internal combustion engine according to any one of 1. 6. When the ratio of the inert gas contained in the intake air used for combustion approaches a predetermined amount, the amount of soot generated during the combustion gradually reaches a peak, and when the ratio is further increased, the soot is increased. The first combustion state that suppresses the generation of soot by suppressing the proportion of the inert gas to less than the predetermined amount, and the proportion of the inert gas are the same as those described above. An internal combustion engine capable of switching between a second combustion state in which generation of soot is suppressed by holding in a region exceeding a fixed amount, each of the first combustion state and the second combustion state. Fuel injection control peculiar to each combustion state, prepared when the switching request from the first combustion state to the second combustion state is requested, or switching from the second combustion state to the first combustion state On demand, the requested combustion Fuel injection control means for switching to fuel injection control corresponding to the state, and fuel injection control restraining means for restraining the fuel injection control for a predetermined time in the control state before switching after switching the combustion state. Internal combustion engine. 7. The internal combustion engine according to claim 6, wherein the fuel injection control restraining means gradually shifts the fuel injection control to a normal fuel injection control state after the lapse of the predetermined time. organ. 8. The fuel injection control restraint means releases the restraint state of the combustion injection control when the oxygen concentration of intake air used for combustion reaches a predetermined oxygen concentration. Item 6. An internal combustion engine according to item 6 or 7.