JP4661013B2 - Internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine, and more particularly, to an internal combustion engine that operates an engine while appropriately selecting two combustion states with greatly different combustion temperatures and oxygen concentrations.
[0002]
[Prior art]
In diesel engines and lean-burn gasoline engines, various measures are taken to reduce soot and nitrogen oxide (NOx) emissions. As one of countermeasures, for example, there is a combustion technique disclosed in a patent publication (No. 30925497).
[0003]
According to the combustion technique disclosed in the patent publication, the ratio of EGR gas contained in intake air supplied for combustion is adjusted by adjusting the supply amount of EGR gas supplied to the combustion chamber and the flow rate of air. In addition, two engine combustions with greatly different combustion temperatures and oxygen concentrations are possible.
[0004]
That is, during high load operation, in order to ensure driver viability, normal combustion is performed while suppressing the ratio of EGR gas contained in the intake air to an appropriate amount. Conversely, during idling and low load operation, EGR gas The combustion temperature and oxygen concentration are lowered by greatly increasing the ratio of soot, and the amount of soot and nitrogen oxide (NOx) produced is reduced. In the following description, the engine combustion in a 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 an EGR rate. Nitrogen oxide may be simply referred to as “NOx”.
[0005]
By the way, in a diesel engine or the like, in its normal combustion state, the engine is operated in a state of excessive air reaching A / F = 30 to 40, and a large amount of oxygen is contained in the intake air used for the combustion. Exists. Further, since this excessive oxygen intake air 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 as the EGR gas.
[0006]
Therefore, simply increasing only the amount of EGR gas slows down changes in the oxygen concentration and the amount of EGR gas, and it takes a certain amount of time to switch to 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. For this reason, in the conventional internal combustion engine, various engine controls have been performed to shorten the time required for switching and to ensure a stable combustion state.
[0007]
More specifically, in addition to the control for increasing the opening 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. In addition, low temperature combustion has been realized by performing various engine controls such as prevention of misfire due to excessive EGR gas and insufficient air amount and fuel injection correction control to compensate for pumping loss associated with intake throttle control. In addition, with regard to the intake throttle control, the EGR gas amount is relatively increased by reducing the air amount itself, and the introduction amount (supply amount) of the EGR gas is increased by lowering the pressure in the intake passage. Also have.
[0008]
As described above, in the conventional internal combustion engine, the switching of the combustion state is optimized by performing various engine controls. Of course, the above-described engine control is also required when returning to the normal combustion state, and the processing content is processed with the control content suitable for the purpose in a timely manner.
[0009]
In recent years, many internal combustion engines are provided with an exhaust purification catalyst in their exhaust passages in order to reduce the discharge amount of particulates such as NOx and soot. Further, the exhaust purification action is promoted by lowering the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst. Note that reducing the air-fuel ratio of the exhaust gas means increasing the ratio of the unburned combustion component to the residual oxygen amount of the exhaust gas. For example, a reducing agent is added to the exhaust passage upstream of the exhaust purification catalyst. Further, by sub-injecting engine fuel, which is a reducing agent, into the cylinder in the latter half of the combustion stroke, a reduction in the air-fuel ratio is promoted.
[0010]
[Problems to be solved by the invention]
By the way, the present inventors have found various improvements regarding the switching of the combustion state described above through further earnest research. That is, paying attention to the transient state corresponding to the combustion switching period, efforts were made to improve various problems that occur in the transient state.
[0011]
First, in a transient state from normal combustion to low-temperature combustion, fluctuations in generated torque and an increase in combustion noise were observed due to a delay in supply of EGR gas. Moreover, in the transient state from low temperature combustion to normal combustion, misfire and increase in smoke were observed due to the delay of air introduction. These various problems associated with transient combustion instability are contrary to the purpose of improving driver viability, reducing engine noise, and suppressing smoke. Improvement of these phenomena is important in the development of internal combustion engines. It becomes a point.
[0012]
Further, during the switching period of the combustion state, feedback control based on the oxygen concentration of the exhaust gas is performed at various places. Therefore, when the above reducing agent is added, the feedback control may fail.
[0013]
The present invention has been made in view of these various problems. Combustion improvement that improves various problems caused by the transient state, improves driver viability, reduces engine noise, suppresses smoke, and the like. To provide technology.
[0014]
[Means for Solving the Problems]
In order to solve the above technical problem, the present invention has the following configuration.
That is, the internal combustion engine of the present invention is
When the proportion of inert gas contained in the intake air used for combustion approaches a predetermined amount, the amount of soot produced during the combustion gradually reaches a peak, and when the proportion is further increased, the amount of soot produced decreases. A first combustion state that suppresses the generation of soot by suppressing the ratio of the inert gas to less than the predetermined amount, and the ratio of the inert gas to a region that exceeds the predetermined amount. An internal combustion engine capable of switching between a second combustion state that suppresses the generation of soot by holding,
When switching from the first combustion state to the second combustion state, or when switching from the second combustion state to the first combustion state, oxygen in the exhaust gas flowing through the exhaust passage of the internal combustion engine Combustion state switching means for changing the ratio of the inert gas based on the concentration;
Reducing agent addition means for adding a reducing agent to the exhaust gas exhausted during engine operation and promoting an exhaust purification action of an exhaust purification catalyst installed in the exhaust passage;
In the process of switching the combustion state from the first combustion state to the second combustion state, or in the process of switching from the second combustion state to the first combustion state, addition of a reducing agent to the exhaust gas is performed. Reducing agent addition prohibition means prohibited for a predetermined period;
It is characterized by providing.
[0015]
In the present invention configured as described above, by providing the reducing agent addition means, the reducing agent is added to the exhaust gas discharged along with the operation of the engine, and the air-fuel ratio of the exhaust gas is forced by the added reducing agent. Has been reduced. Here, the reducing agent addition means may be configured so that the reducing agent can be added to the exhaust gas flowing into the exhaust purification catalyst. For example, the reducing agent addition means, for example, addition of the reducing agent into the exhaust passage or the later stage of the combustion stroke in the cylinder This is a concept including sub-injection and the like.
[0016]
The internal combustion engine of the present invention is a kind of internal combustion engine capable of switching between the two combustion states disclosed in the prior art, and the switching control is based on the oxygen concentration of the exhaust gas. For this reason, when the reducing agent is added at the time of switching of the combustion state, that is, in the transient state leading to the first combustion state or the second combustion state, switching of the appropriate combustion state is affected by the addition. Becomes difficult. Therefore, in the internal combustion engine of the present invention, in addition to the reducing agent addition means, a reducing agent addition prohibiting means for prohibiting addition of the reducing agent in the transient state is further provided, thereby enabling quick switching of the combustion state. Yes.
[0017]
That is, in the process of switching the combustion state, by realizing a means that can accurately determine the oxygen concentration in the exhaust gas, the difficulty of switching the combustion state due to the erroneous determination is avoided. Therefore, various problems in the transient period (transient state) are improved.
[0018]
In addition, 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,
The combustion state switching means includes an EGR amount control means for controlling the supply amount of EGR gas supplied to the combustion chamber through the intake passage, and an air flow control means for controlling the flow rate of air flowing into the combustion chamber through the intake passage. With
When changing the ratio of the inert gas contained in the intake air, at least one of the supply amount of the EGR gas and the air flow rate is adjusted to converge to a target ratio suitable for a desired combustion state. Good.
[0019]
Here, the EGR amount control means may be any means 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 difference between the intake passage and the exhaust passage. There is no particular limitation on the control method such as a method of increasing the amount of EGR gas introduced by increasing the pressure. Similarly, the air flow rate control means only needs to be able to control (adjust) the flow rate of air flowing into the combustion chamber through the intake passage, and can be controlled by an intake throttle valve disposed in the intake passage, The control method is arbitrary, such as adjusting the amount of air by adjusting the supercharging pressure in an on-board internal combustion engine, or adjusting the amount of air by using an exhaust throttle valve in an internal combustion engine equipped with an exhaust throttle valve.
[0020]
In this configuration, the EGR gas supply amount can be adjusted by the EGR amount control means, the air flow rate can be adjusted by the air flow rate control means, and the ratio of EGR gas (inert gas) contained in the intake air can be changed. In order to achieve this, by adjusting at least one of the supply amount of the EGR gas or the air flow rate, the target ratio suitable for the required combustion state is converged. That is, if the supply amount of EGR gas is increased, the ratio of EGR gas contained in the intake air is increased, and if the air flow rate is decreased, the ratio is further increased relatively.
[0021]
The above-mentioned “target ratio” is a ratio set individually for each of the first combustion state and the second combustion state. For example, in the first combustion state, EGR with respect to the intake air is performed. The ratio of gas, that is, the EGR rate is set to less than 50% (preferably less than 45%), and is set to 55% or more (preferably 65% or more) in the second combustion state. In addition, the numerical value illustrated here is an example to the last, Of course, the numerical value is suitably changed in consideration of the combustion characteristics of the internal combustion engine, the traveling state, the operating environment, and the like.
[0022]
Further, regarding the EGR amount control means and the air flow rate control means,
In the combustion state switching means, after the start of switching of the combustion state, the control of the EGR gas amount by the EGR amount control means is performed for a predetermined period with a control amount exceeding a control amount determined in accordance with the target ratio. You may make it hold | maintain.
Further, after the start of switching of the combustion state, the air flow rate control 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.
[0023]
In this configuration, the EGR amount control means and the air flow rate control means are usually controlled beyond the control amount that should be determined in accordance with the target ratio. That is, since the EGR gas amount and the air amount change with a delay from the actual demand, the control amount is overshot for a predetermined period after the start of switching of the combustion state, thereby suppressing the response delay of the EGR gas and air. .
[0024]
In addition, regarding the switching of the combustion state,
Fuel injection switching specific to each combustion state is prepared corresponding to the first combustion state and the second combustion state, and the fuel injection control is switched according to switching of the combustion state. Having means,
In the combustion state switching means, the ratio of the inert gas contained in the intake air may be changed in preference to the switching of the fuel injection control.
[0025]
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. 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 are switched by the fuel injection switching means, so that they are suitable for each combustion state. Realizes fuel injection control. In addition, by changing the ratio of inert gas prior to switching the fuel injection control, the ratio of air and inert gas used for combustion is stabilized, creating a situation that can cope with switching of fuel injection control. Yes.
[0026]
Further, in the present invention, in order to solve the above technical problem, the following configuration may be adopted.
That is, the internal combustion engine of the present invention is
When the proportion of inert gas contained in the intake air used for combustion approaches a predetermined amount, the amount of soot produced during the combustion gradually reaches a peak, and when the proportion is further increased, the amount of soot produced decreases. A first combustion state that suppresses the generation of soot by suppressing the ratio of the inert gas to less than the predetermined amount, and the ratio of the inert gas to a region that exceeds the predetermined amount. An internal combustion engine capable of switching between a second combustion state that suppresses the generation of soot by holding,
Fuel injection control specific to each combustion state prepared for each of the first combustion state and the second combustion state;
Fuel injection corresponding to the requested combustion state at the time of a request for switching from the first combustion state to the second combustion state, or at the time of a request for switching from the second combustion state to the first combustion state Fuel injection switching means for switching to control;
Fuel injection control restraining means for restraining the fuel injection control for a predetermined time in the control state before the switching after the start of switching of the combustion state;
It is characterized by providing.
[0027]
In the internal combustion engine configured as described above, combustion injection control corresponding to the first combustion state and fuel injection control corresponding to the second combustion state are prepared, and these are switched by the fuel injection switching means. The fuel injection control suitable for each combustion state is implemented. In addition, after starting the switching of the combustion state, the fuel injection control is restrained for a predetermined time in the control state before the switching by the injection control restraining means.
[0028]
In other words, 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, it should be an appropriate switching that should be the proper fuel injection control switching. End up. Therefore, the fuel injection control switching timing is optimized by constraining the fuel injection control for a predetermined time in the control state before switching.
[0029]
Here, the predetermined time is set in consideration of the above circumstances, and is set by the time required for the air-fuel ratio (ratio of air and inert gas) in the combustion chamber to reach a predetermined ratio. It is desirable to do. Further, 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.
[0030]
Further, regarding the injection control restraint means,
The fuel injection control restraining means may shift to the normal fuel injection control state while gradually changing the fuel injection control after the predetermined time has elapsed.
[0031]
In this configuration, gradual change control is performed in switching of fuel injection control. Note that the gradual change control is control for gradually changing the combustion injection amount, the combustion injection timing, the combustion injection pressure, and the like to shift to a desired fuel injection state within a predetermined period.
[0032]
Further, regarding the injection control restraint means,
The fuel injection control restraint means may release the restraint state of the combustion injection control when the oxygen concentration of the intake air provided for combustion reaches a predetermined oxygen concentration. That is, if the oxygen concentration of the intake air supplied to the combustion chamber is a predetermined oxygen concentration, it can be said that the ratio of the inert gas to the intake air is the target rate, and the restraint state is based on this condition. Decide whether or not to cancel.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the internal combustion engine according to the present invention will be described.
Note that the structure of the internal combustion engine described below is merely an embodiment of the present invention, and details thereof can be arbitrarily changed without departing from the scope of the claims.
[0034]
<Outline of diesel engine>
As shown in FIG. 1, the internal combustion engine 1 shown in the present embodiment is a diesel engine, and includes a fuel supply system, an intake system, an exhaust system, a control system, etc., in addition to four cylinders 2 forming a combustion chamber. It is provided as a main component.
[0035]
The fuel supply system includes a fuel injection valve 3, a pressure accumulation 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 serving as a fuel distribution pipe. The common rail 4 is connected to a fuel pump 6 via a 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.
[0036]
In the fuel supply system configured as described above, first, fuel in a fuel tank (not shown) is pumped up by the fuel pump 6. The pumped fuel is supplied to the common rail 4 through 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 is distributed to each fuel injection valve 3. When a drive voltage is applied to the fuel injection valve 3 and the fuel injection valve 3 is opened, the fuel is injected into the cylinder 2 through the fuel injection valve 3.
[0037]
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, and forms an intake passage for supplying air to each cylinder 2.
[0038]
The intake pipe 9 forms a passage that guides air (fresh air) sucked 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 via the intake pipe 9 to each cylinder 2. Further, an air flow meter 11 that measures the amount of air flowing into the intake pipe 9 and an intake air temperature sensor 12 that measures the temperature of the air are provided in the vicinity of the connection portion between the intake pipe 9 and the air cleaner box 10.
[0039]
Further, 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 pressure in the intake branch pipe 8 are provided immediately downstream of the throttle valve 13.
[0040]
Further, in the intake passage from the air cleaner box 10 to the throttle valve 13, a compressor housing 15a of a turbocharger 15 that compresses air and an intercooler 16 that cools the intake air compressed in the compressor housing 15a are provided. Yes.
[0041]
In the intake system configured as described above, first, air to be supplied to each cylinder 2 flows into the air cleaner box 10 due to generation of negative pressure accompanying engine operation. The air that has flowed into the air cleaner box 10 is removed of dust and dirt in the air cleaner box 10, and then flows into the compressor housing 15 a of the turbocharger 15 through the intake pipe 9. The air flowing into the compressor housing 15a is compressed by a compressor wheel (not shown) and then cooled by the intercooler 16. Then, the flow rate is adjusted by the throttle valve 13 as necessary, and then flows into the intake branch pipe 8. The air that has flowed into the intake branch pipe 8 is distributed to each cylinder 2 via each branch pipe, and is burned together with the fuel injected and supplied from the fuel injection valve 3. The outputs of various sensors are input to an electronic control unit 30 described later, and are fed back to, for example, fuel injection control (basic engine control) processed in the electronic control unit 30.
[0042]
The exhaust system includes 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 engine combustion is discharged to the outside of the engine. Further, it has an EGR device 20, a catalytic converter 52, a reducing agent addition device 60, and the like, and has a function as an exhaust purification device that purifies particulates such as nitrogen oxide (NOx) and soot contained in the exhaust gas. .
[0043]
The exhaust branch pipe 18 is connected to an exhaust port 18 a provided for each cylinder 2 and forms a passage for collecting exhaust gas flowing out from each exhaust port 18 a and leading it to the turbine housing 15 b of the turbocharger 15. Further, the exhaust pipe 19 forms a passage from the turbine housing 15b to a silencer (not shown).
[0044]
The EGR device 20 that is one of the exhaust gas purification devices includes an EGR passage 25, an EGR valve 26, an EGR cooler 27, and the like, and reduces the amount of nitrogen oxide (NOx) generated by engine combustion. 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 an electrical on-off valve provided in the EGR passage 25, and is based on a combustion state switching control program or the like processed in the electronic control unit 30 and the exhaust gas flowing in the EGR passage 25 ( EGR gas) is adjusted. The EGR cooler 27 cools the exhaust gas flowing through the EGR passage 25 using engine cooling water as a heat medium. In the following description, the exhaust gas flowing through the EGR passage 25 may be referred to as EGR gas.
[0045]
According to the EGR device 20 configured as described above, a part of the exhaust gas flowing in the exhaust branch pipe 18 flows into the EGR passage 25 at a flow rate corresponding to the opening amount of the EGR valve 26. The EGR gas (exhaust gas) that has flowed into the EGR passage 25 flows into the EGR cooler 27 that is disposed in the path of the EGR passage 25. The EGR gas that has flowed into the EGR cooler 27 is cooled when passing through the EGR cooler 27 and flows into the intake branch pipe 8. The EGR gas that has flowed into the intake branch pipe 8 is mixed with the air (fresh air) that flows from the upstream side of the intake branch pipe 8 to form intake air. It is burned together with the fuel injected from the fuel injection valve 3. That is, in the present invention, the intake air used for combustion is a mixed gas of air (fresh air) and EGR gas.
[0046]
In the exhaust gas that becomes EGR gas, water vapor (H ₂ O) and carbon dioxide (CO ₂ ) And other inert gases. For this reason, when exhaust gas containing the inert gas together with air flows into each cylinder 2, the combustion temperature at the time of combustion decreases due to the mixing of the inert gas. As a result, generation of nitrogen oxides (NOx) is suppressed.
[0047]
Next, the catalytic converter 52 that is one of the exhaust purification devices will be described.
The catalytic converter 52 includes a casing 53 and various exhaust purification catalysts 52 a and 52 b provided in the casing 53, and has an exhaust purification action of purifying harmful substances in the exhaust gas discharged from the engine body 1.
[0048]
More specifically, the exhaust purification catalyst is arranged in the vicinity of the outlet of the turbine housing 15b. In the casing 53, the NOx storage reduction catalyst 52a and the particulate filter 52b are arranged in this order from the upstream side. In the following description, the NOx storage reduction catalyst 52a may be simply referred to as the NOx catalyst 52a. Nitrogen oxide (NOx) may be simply referred to as NOx.
[0049]
The NOx catalyst 52a, which is one of the exhaust purification catalysts, has an exhaust purification action that mainly purifies NOx in the exhaust gas. More specifically, when the oxygen concentration of the exhaust gas flowing into the NOx catalyst 52a is high, NOx in the exhaust gas is absorbed, and when the oxygen concentration in the exhaust gas is low, that is, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 52a is Nitrogen dioxide (NO2) absorbs the NOx absorbed when it is low. ₂ ) And nitric oxide (NO) in the form of nitrogen monoxide (NO), reduced and released into the exhaust gas, and reacted with unburned combustion components (CO, HC) contained in the exhaust gas. ₂ O) and carbon dioxide (CO ₂ ) Has an exhaust purification action that purifies oxidation.
[0050]
The composition is, for example, alumina (Al ₂ O _Three ) As a carrier, an alkali metal such as potassium (K), sodium (Na), lithium (Li), cesium (Cs), or an alkaline earth such as barium (Ba), calcium (Ca), or the like on the carrier, or At least one selected from rare earths such as lanthanum (La) and yttrium (Y) and a noble metal such as platinum (Pt) are supported.
[0051]
If a supplementary explanation of the exhaust purification action is given here, in a diesel engine, engine combustion is usually performed in an oxygen-excess atmosphere. For this reason, the oxygen concentration in the exhaust gas discharged with combustion hardly decreases until the above reduction / release action is promoted, and unburned combustion components (CO, HC) contained in the exhaust gas. The amount of is also negligible. For this reason, in this embodiment, engine fuel (HC), which is a reducing agent, is injected and supplied into the exhaust gas, thereby promoting reduction in oxygen concentration and supplementing hydrocarbon (HC), which is an unburned combustion component, and exhaust gas. Promotes the cleansing action. The supply of the reducing agent is performed by a reducing agent adding device 60 described later. Details thereof will be described later.
[0052]
One particulate filter 52b has an exhaust purification action of oxidizing and burning particulates such as soot contained in the exhaust gas. More specifically, it has a filter 58 carrying an activated oxygen release agent, and has an exhaust purification action that removes (purifies) particulates collected on the filter 58 by oxidizing and burning them with the activated oxygen. ing.
[0053]
As shown in FIG. 6, the filter 58 alone has a honeycomb shape formed of a porous material such as cordierite, and includes a plurality of flow paths 55 and 56 extending in parallel with each other. More specifically, an exhaust gas inflow passage 55 whose downstream end is closed by a plug 55a and an exhaust gas outflow passage 56 whose upstream end is closed by a plug 56a are provided, and each exhaust gas inflow passage 55 and exhaust gas are provided. The outflow passages 56 are arranged side by side in the vertical and horizontal directions of the filter 58 through thin partition walls 57. It is formed in a so-called wall flow type.
[0054]
Further, alumina (Al ₂ O _Three ), Etc., and a noble metal catalyst such as platinum (Pt) on the support, and if there is excess oxygen in the surroundings, the excess oxygen is occluded, and conversely the oxygen concentration When it decreases, it carries an active oxygen release agent that releases the stored oxygen in the form of active oxygen.
[0055]
In addition, as active oxygen release agents, potassium (K), sodium (Na), lithium (Li), cesium (Cs), alkali metals such as rubidium (Rb), barium (Ba), calcium (Ca), strontium Use at least one selected from alkaline earth metals such as (Sr), rare earths such as lanthanum (La) and yttrium (Y), and transition metals such as cerium (Ce) and tin (Sn) Can do.
[0056]
Preferably, the alkali metal or alkaline earth metal has a higher ionization tendency than calcium (Ca), that is, potassium (K), lithium (Li), cesium (Cs), rubidium (Rb), barium (Ba), strontium. (Sr) or the like may be used.
[0057]
In the particulate filter 52b configured as described above, first, the exhaust gas flowing into the exhaust gas inflow passage 55 is exhaust gas inflow passage 55 → the partition wall 57 → the exhaust gas outflow passage 56 as shown by the arrow a in FIG. The particulates such as soot contained in the exhaust gas are collected on the surface and inside of the partition wall 57. The particulates collected in the partition wall 57 are oxidized by the activated oxygen that increases by changing the oxygen concentration of the exhaust gas flowing into the partition wall 57 a plurality of times, and finally burned out without emitting a luminous flame. 58 is removed from above.
[0058]
Thus, in the present embodiment, the NOx storage reduction catalyst 52a and the particulate filter 52b are disposed in the exhaust passage to purify the NOx and soot particles contained in the exhaust gas.
[0059]
In the present 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 temperature of the particulate filter 52b is raised by utilizing the reaction heat accompanying the oxidation / reduction reaction in the NOx storage reduction catalyst 52a. For example, the activated oxygen from the NOx storage reduction catalyst 52a released due to the oxidation / reduction reaction in the NOx storage reduction catalyst 52a is used for the exhaust gas purification action of the particulate filter 52b. . The occlusion reduction type NOx catalyst 52a carries a substance substantially the same as the activated oxygen release agent, as is apparent from the above. Therefore, it can be said that the NOx storage reduction catalyst 52a has a function as an activated oxygen release agent. In the present embodiment, an oxidation catalytic converter 59 for oxidizing and purifying unburned fuel components in the exhaust gas is provided downstream of the catalytic converter 52.
[0060]
Next, the reducing agent addition device 60 that promotes the exhaust purification action of the exhaust purification catalyst will be described.
The reducing agent addition device 60 includes a reducing agent addition valve 61, a reducing agent supply path 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. The engine fuel, which is a reducing agent, is performed in the exhaust gas so that the fuel ratio becomes the same.
[0061]
The reducing agent addition valve 61 is provided at a collecting portion of the exhaust branch pipe 18 and is an electric valve that opens when a predetermined voltage is applied under a reducing agent addition program processed in an electronic control unit described later. It is a type on-off valve. 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 path 62 and maintains the fuel pressure in the reducing agent supply path 62 at a predetermined fuel pressure. The fuel pressure sensor 63 detects the fuel pressure in the reducing agent supply path 62. The emergency shutoff valve 66 stops the fuel supply into the reducing agent supply path 62 when an abnormality occurs in the pressure in the reducing agent supply path 62.
[0062]
In the reducing agent addition device 60 configured as described above, the fuel discharged from the fuel pump 6 is maintained at a predetermined fuel pressure by the fuel pressure control valve 64 and then supplied to the reducing agent addition valve 61 through the reducing agent supply path 62. The 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 path 62 is added into the exhaust branch pipe 18 through the reducing agent addition valve 61. Is done. The fuel (reducing agent) supplied to the exhaust branch pipe 18 is stirred in the turbine housing 15 b and then flows into the catalytic converter 52 through the exhaust pipe 19. Therefore, the exhaust gas having a low oxygen concentration and mixed with hydrocarbon (HC), which is an unburned combustion component, flows into the catalytic converter 52, thereby promoting the exhaust purification action.
[0063]
Note that the amount of addition of the reducing agent and the timing of addition are as follows: the output of the air-fuel ratio sensor (A / F sensor) 74 provided downstream of the catalytic converter 52, the exhaust gas temperature sensor provided upstream and downstream of the particulate filter 52b ( (Not shown) and the operation history recorded in the electronic control unit 30 to be described later. Details thereof will be described later.
[0064]
Next, the control system will be described.
The control system includes a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Central Control Device) 34, an input port 35, and an output port 36 connected to each other by a bidirectional bus 31. Electronic control unit 30 (ECU), which controls fuel injection control (basic engine control) for obtaining engine output, reducing agent addition control for accelerating exhaust purification, and operation of EGR valve 26, throttle valve 13 and the like Thus, the combustion state switching control for switching the combustion state of the engine body is executed.
[0065]
In addition to the output signals of the various sensors described above, the input port 35 includes a load sensor 41 that detects the amount of depression of the accelerator pedal 40, a crank angle sensor 42 that detects the rotational speed of the crankshaft 1a, and a vehicle speed sensor 43 that measures the vehicle speed. Are input via the corresponding A / D converter 37 or directly. On the other hand, the fuel injection valve 3, the reducing agent addition valve 61, the actuator 14 for driving the throttle valve, the EGR valve 26, and the like are connected to the output port 36 through corresponding drive circuits 38.
[0066]
The ROM 32 is provided with a program for processing the above-described various controls, a control map that is referred to when the program is executed, and the like corresponding to each device. 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. In the CPU 34, the output signals of the various sensors recorded on the RAM 33 and the control map developed on the ROM 32 are compared on a desired program, and various control signals output in the processing process are compared via the output port 36. Various devices are centrally managed by outputting to the corresponding devices.
[0067]
Next, the reducing agent addition control and the combustion state switching control for switching the combustion state will be described in detail.
[0068]
<Reducing agent addition control>
In the reducing agent addition control (reducing agent addition control program), first, the CPU 34 determines whether or not a condition for adding fuel as a reducing agent is satisfied. Here, the reducing agent addition start condition is that when the output value of the exhaust temperature sensor reaches a predetermined value and the temperature in the catalytic converter 52 is considered to have reached the activation temperature of various exhaust purification catalysts, It is considered that the number of mileage of the vehicle and the running time of the vehicle have reached a predetermined value, and the amount of NOx stored in the NOx catalyst 52a and the amount of particulates collected in the particulate filter 52b have reached a predetermined amount. Is set as a starting condition for the addition of the reducing agent.
[0069]
Then, the CPU 34 permits the addition of the reducing agent by the reducing agent addition device 60 upon receipt of these conditions. The reducing agent is added so that the air-fuel ratio of the exhaust gas flowing into the catalytic converter 52 changes in a spike manner with a relatively short period. At that time, the CPU 34 reads the output value of the air-fuel ratio sensor 74 provided downstream of the catalytic converter 52 and feeds back the output value to the addition amount of the reducing agent, thereby adjusting the addition amount of the reducing agent to an appropriate amount. That is, feedback control based on the output value of the air-fuel ratio sensor 74 is executed.
[0070]
In this embodiment, a lean mixture sensor is used as the air-fuel ratio sensor 74, but of course, an oxygen concentration sensor (O ₂ Sensor) or the like may be used. Further, although the air-fuel ratio sensor 74 is installed downstream of the catalytic converter 52, it can also be arranged upstream of the catalytic converter 52. When installed downstream of the catalytic converter 52, there can be obtained an advantage that soot can be prevented from adhering to the air-fuel ratio sensor 74.
[0071]
Subsequently, 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 explained.
[0072]
The diesel engine shown in the present embodiment is a kind of internal combustion engine disclosed in the prior art, and by greatly increasing the ratio of inert gas to intake air, the growth of smoke generated during combustion is increased. Adopting combustion technology to suppress.
[0073]
FIG. 2 is a graph obtained in accordance with actual experimental results, and shows the correlation between the ratio of the inert gas to the intake air and the amount of smoke generated by the combustion. In the following description, the ratio of the inert gas to the intake air may be simply referred to as an EGR rate.
[0074]
As can be seen from FIG. 2, the amount of soot reaches a peak between about 40% and 50% of the EGR rate, and in the region where the EGR rate is 55% or more, almost no soot is generated. Therefore, if the engine is operated in the region where the EGR rate is 55% or more, preferably, the EGR rate is 65% or more, the engine can be operated while substantially reducing the amount of soot discharged.
[0075]
However, in the operation with an EGR rate of 65% or more, there is a problem that the engine output cannot be sufficiently obtained due to a shortage of air amount or a decrease in combustion pressure. On the other hand, in the region where the engine output is sufficiently high, the generation of soot is slightly seen in the region where the EGR rate is less than 40%, but the generation amount is sufficiently smaller than the operation region where the EGR rate is 40% to 50%. It has become.
[0076]
Therefore, when the engine is not required to output much, such as idling and low-load running, the engine is operated with the EGR rate maintained at 65% or more. When sufficient engine output is required such as during high-load running, EGR By operating the engine while keeping the rate below 40%, a comfortable driving state is secured while suppressing the occurrence of soot.
[0077]
That is, in the diesel engine shown in the present embodiment, soot emission control and operation are performed by switching the combustion state in a stepped manner so as to avoid operation at an EGR rate of 40% to 50% at which the soot generation amount reaches a peak. The balance of sex is secured.
[0078]
In addition, the numerical value illustrated above, ie, the specific numerical value of the EGR rate, is merely an example, and the numerical value slightly changes depending on the combustion characteristics unique to the applied internal combustion engine and the cooling temperature of the EGR gas. However, soot emission characteristics, ie, the presence of peaks, are common to all internal combustion engines.
[0079]
The switching of the combustion state is determined in consideration of, for example, the engine required torque calculated at the time of the fuel injection control process that is the basic engine control. That is, in the combustion state switching control, as one control, in response to the engine required torque being equal to or lower than a predetermined lower limit value, an operation at an EGR rate of 65% or higher is selected, and the engine required torque is equal to or higher than a predetermined upper limit value. Is reached, combustion state selection control for selecting operation at an EGR rate of less than 40% is executed.
[0080]
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 switching threshold value between acceleration traveling and deceleration traveling, frequent switching near the threshold is suppressed. .
[0081]
Subsequently, detailed control contents of the combustion state switching control (combustion state switching control program) will be described.
In the following description, an operation region at an EGR rate of 65% or more is sometimes referred to as “low temperature combustion”, and an operation region at an EGR rate of less than 40% is sometimes referred to as “normal combustion”.
[0082]
In this control, in addition to the above-described combustion state selection control, (1) EGR rate variable control for changing the EGR rate by changing the opening degree of the EGR valve 26 and the throttle valve 13 is performed. (2) By switching to fuel injection control suitable for each combustion state, engine control such as fuel injection switching control that stabilizes the combustion state is performed to realize switching of the combustion state.
[0083]
That is, in this embodiment, the combustion state switching control is control that collectively processes 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. Further, by controlling the EGR valve 26, the throttle valve 13, the fuel injection control and the like based on these various controls, 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.
[0084]
3 and 4 show the changes in the EGR valve 26 opening, the throttle valve 13 opening, and the combustion injection control over time, which change in the process of the combustion state switching control, in accordance with changes in the combustion states. Show.
[0085]
Hereinafter, with reference to FIG.3 and FIG.4, the various control content processed in the switching process of the combustion state is explained in full detail.
[0086]
First, with reference to FIG. 3, the control content processed when switching from normal combustion to low-temperature combustion will be described.
When switching from normal combustion to low-temperature combustion, the combustion state at an EGR rate of less than 40% is switched to a combustion state at an EGR rate of 65% or more. That is, the EGR rate variable control for increasing the EGR rate by increasing the opening of the EGR valve 26 and decreasing the opening of the throttle valve 13 is executed.
[0087]
In the EGR rate variable control, the opening amounts of the valve bodies 26 and 13 are 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, and the opening degrees of the EGR valve 26 and the throttle valve 13 are controlled so that the air-fuel ratio sensor 74 can obtain a predetermined output. .
[0088]
Here, the predetermined output is a value output when the ratio of the inert gas to the intake air (EGR rate) reaches the target rate, and the EGR rate and exhaust gas obtained in various preliminary experiments. It is defined by the correspondence with the oxygen concentration inside.
[0089]
More specifically, when the valve opening control of the EGR valve 26 and the throttle valve 13 is finished and the amount of EGR gas supplied to the combustion chamber reaches a target ratio and a predetermined oxygen content, it is naturally included in the intake air. The amount of oxygen (oxygen concentration) also becomes a predetermined amount. Also, the oxygen concentration in the exhaust gas generated by the combustion of the intake air is necessarily proportional to the amount of oxygen in the intake air. That is, the EGR rate can be estimated by detecting the oxygen concentration in the exhaust gas.
[0090]
The EGR rate is generally a numerical value defined by the supply amount of EGR gas supplied to the intake passage. However, focusing on the amount of oxygen contained in the EGR gas, the EGR gas supplied to the intake passage is The amount of oxygen inside decreases with time depending on the amount of oxygen in the exhaust gas generated by combustion of the intake air mixed with EGR gas. Therefore, the EGR rate defined without considering the oxygen concentration in the exhaust gas is not a true EGR rate, and as shown in the present embodiment, the EGR rate is changed based on the oxygen concentration in the exhaust gas. This makes it possible to manage the EGR rate accurately.
[0091]
Further, regarding the EGR rate variable control, in the present combustion state switching control, overshoot control for forcibly changing the EGR rate is performed in preference to the feedback control based on the output of the air-fuel ratio sensor.
[0092]
That is, the supply amount of EGR gas and the flow rate of air change over time with a delay in controlling the valve bodies 26 and 13. For this reason, the response speed of the EGR rate (by increasing the control amount of each valve element 13, 26 that should be determined in accordance with the target ratio (EGR rate) originally required at the time of low-temperature combustion is temporarily increased. Speed of change).
[0093]
This overshoot control is executed after the start of switching of the combustion state, and when the oxygen concentration in the exhaust gas is reduced to a predetermined oxygen concentration, the air flow rate obtained at the output of the air flow meter 11 is a predetermined value. In response to the reduction in the air flow rate, the control is switched to feedback control based on the output of the air-fuel ratio sensor 74. In the present embodiment, the response speed of the EGR rate is improved by setting the EGR valve 26 in a substantially fully open state and the throttle valve 13 in a substantially fully closed state in the overshoot control process.
[0094]
On the other hand, in the fuel injection switching control, corrections such as increasing the combustion injection pressure, increasing the fuel injection amount, advancing the fuel injection timing, and switching from multiple injection (multi injection) to single injection (single injection), etc. Execute control. These correction contents are recorded in the electronic control unit 30 as fuel injection control for low-temperature combustion. When switching to low-temperature combustion, subsequent fuel injection control is performed based on the fuel injection control for low-temperature combustion. It is processed.
[0095]
The correction of the combustion injection control is intended to improve various combustion defects that occur during low temperature combustion. That is, during low-temperature combustion, the combustion temperature decreases and the amount of oxygen that contributes to combustion also decreases. Therefore, combustion under severe conditions is required, and in the fuel injection control that has been performed during normal combustion, misfire, reduction in combustion pressure, insufficient engine output, increase in combustion noise (diesel knock), etc. Problem arises. Therefore, the above-mentioned various corrections are performed to optimize the improvements in ignition delay, suppression of pressure rise in the flame propagation period, shortening of the direct combustion period and the late combustion period, etc. to ensure a good combustion state during low temperature combustion. ing.
[0096]
In the present embodiment, the fuel injection control switching is processed after the previous EGR rate variable control. That is, after the start of switching of the combustion state, fuel injection restriction control is performed in which the fuel injection control is restricted for a predetermined time in the control state before the switching.
[0097]
More specifically, the fuel injection control is optimized by including a control delay (standby time) in the correction of the fuel injection control so as to cope with the response delay of the EGR gas amount and the air amount.
[0098]
Note that the delay time in the correction control is determined in consideration of various conditions. More specifically, the time until the cumulative crank cycle number reaches the predetermined crank cycle number from the start of the switching of the combustion state, and the time until the air amount, the intake branch pipe pressure, the intake branch pipe temperature reaches the predetermined value, In addition, it is determined in consideration of various conditions such as how much the fuel injection amount before switching the combustion state is, and when these conditions are satisfied, correction of the fuel injection control is started.
[0099]
Note that the cumulative crank cycle number corresponds to how far the stroke of intake → compression → combustion → exhaust has progressed, and exhaust gas to the intake system (EGR gas) is detected by detecting this cumulative crank cycle number. The amount of wraparound, that is, the EGR rate can be roughly estimated. Further, changes in the air amount, the intake branch pipe pressure, and the intake branch pipe temperature will be described. During low-temperature combustion, the air amount and the intake branch pipe pressure decrease, and the intake branch pipe temperature rises. Therefore, if these changes are detected, the EGR rate can be estimated. Further, since the amount of exhaust gas (EGR gas) is determined by the fuel injection amount before switching the combustion state, the amount of EGR gas wraparound can be estimated from the fuel injection amount.
[0100]
Thus, in the internal combustion engine shown in the present embodiment, it is determined whether or not the amount of change in 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 predetermined. In response to the decrease in the oxygen concentration, the restraint state of the fuel injection control is released.
[0101]
Further, in the present embodiment, gradual change control is performed with respect to correction of fuel injection control. In this gradual change control, control gains for various corrections are determined in order to finish the correction within a predetermined period. That is, since the correction related to fuel injection is caused by the magnitude of torque shock or the like, the torque shock or the like during fuel injection correction control is suppressed by changing the correction while gradually changing the correction.
[0102]
Next, with reference to FIG. 4, control contents to be processed when returning from low temperature combustion to normal combustion will be described.
When switching from low temperature combustion to normal combustion, the combustion state at an EGR rate of 65% or more is switched to a combustion state at an EGR rate of less than 40%. That is, the EGR rate variable control is performed to reduce the EGR rate by decreasing the opening of the EGR valve 26 and increasing the opening of the throttle valve 13.
[0103]
Similarly, when switching from low temperature combustion to normal combustion, the EGR rate variable control performs feedback control based on the air-fuel ratio (oxygen concentration) of the exhaust gas flowing through the exhaust passage. 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 normal combustion, the opening degree of the EGR valve 26 is substantially fully closed, and the throttle valve 13 is substantially fully open.
[0104]
On the other hand, in the fuel injection switching control, correction control is executed 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. These correction contents are also recorded on the electronic control unit 30 as described above. When switching to normal combustion, the subsequent fuel injection control is processed based on the fuel injection control for normal combustion.
[0105]
The correction related to the combustion injection control is correction control for obtaining driver viability at the time of normal combustion, and the correction value and the like are almost the same as the basic fuel injection control.
[0106]
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, and the target request. In order to obtain torque, control signals output to the fuel injection valve 3 and the fuel pump 6 are updated in a timely manner to correct the fuel supply amount in the fuel supply system.
[0107]
Also in the fuel injection control switching 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, at the start of correction of the fuel injection control, a gradual change control is performed to avoid a torque shock associated with switching of the fuel injection control. The setting of the delay time is determined in consideration of the various conditions described above.
[0108]
Thus, in the internal combustion engine shown in the present embodiment, overshoot control for overshooting the control amounts of the valve bodies 13 and 26 is performed. Fuel injection restraint control is performed in which a control delay is provided for correction of combustion injection control. By processing additional control such as gradual change control in switching of fuel injection control during the transition period of the combustion state, various problems in the transition period are improved.
[0109]
That is, since the combustion state is quickly switched by the overshoot control, the combustion unstable state in the transient period accompanying the response delay of the EGR gas amount and the air amount is improved. Further, by performing fuel injection restraint control and gradual change control, the fuel injection control is optimized, thereby improving driver viability, reducing engine noise, and suppressing smoke.
[0110]
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.
[0111]
On the other hand, in the internal combustion engine shown in the present embodiment, as described above, a reducing agent is added to the exhaust gas so as to promote purification of particulates such as NOx and soot. In addition, the addition is performed in the exhaust branch pipe 18 with the expectation of the agitation effect in the turbocharger and gasification due to exhaust heat, so when adding the reducing agent, the exhaust gas mixed with the reducing agent (engine fuel) is used. The exhaust passage will be filled.
[0112]
On the other hand, the EGR rate variable control is performed on the basis of the output of the air-fuel ratio sensor 74 installed downstream of the catalytic converter 52 in order to avoid soot adhesion and the like. 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 air-fuel ratio (oxygen concentration) of the original exhaust gas. A different air-fuel ratio is detected. That is, when the reducing agent is added, consistency between the output of the air-fuel ratio sensor 74 and the target EGR rate is not ensured, making it difficult to switch the combustion state appropriately.
[0113]
Therefore, in the internal combustion engine shown in the present embodiment, in addition to the various controls described above, reducing agent addition prohibition control is executed so that the combustion state can be switched appropriately. Hereinafter, this reducing agent addition prohibition control will be described.
[0114]
This reducing agent addition prohibition control is added to the combustion state switching control, and is processed in the transition state of the combustion state, that is, in a transient state from low temperature combustion to normal combustion and in a transient state from normal combustion to low temperature combustion. Yes.
[0115]
Further, the processing content will be described. In this control, the addition of the reducing agent into the exhaust gas is prohibited until the above-described EGR rate variable control is completed. More specifically, the valve opening signal output to the reducing agent addition valve 61 is interrupted, and even if an output result indicating that the reducing agent should be added is obtained in the above-described reducing agent addition control, it is based on the output result. The valve opening control of the reducing agent addition valve 61 is not performed. For this reason, during the EGR rate variable control period, the normal oxygen concentration is detected by the air-fuel ratio sensor 74, so that appropriate switching to each combustion state becomes possible.
[0116]
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.
[0117]
First, the electronic control unit 30 determines whether or not the combustion state should be switched by processing of the combustion state selection control based on various conditions such as the engine required torque (step 101). Subsequently, in response to the combustion state switching request, the reducing agent addition prohibition control is processed (step 102). When the determination at step 101 is negative, this control is temporarily terminated.
[0118]
Subsequently, the electronic control unit 30 starts the above-described EGR rate variable control to switch the combustion state (step 103). In synchronism with this, the fuel injection switching control is started to start switching of the fuel injection control (step 106).
[0119]
In the EGR rate variable control in step 103, overshoot control is processed first (step 104), and then feedback control based on the air-fuel ratio sensor 74 is processed (step 105).
[0120]
On the other hand, in the fuel injection switching control in step 106, first, fuel injection restraint control is processed, and switching of fuel injection control is restrained for a predetermined time (step 107). Subsequently, 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). 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 the present processing routine.
[0121]
As described above, in the present embodiment, various controls are performed in the transient state corresponding to the switching period of the combustion state, and the driver viability is reduced due to the unstable combustion in the transient state, the engine noise is increased, and Efforts are being made to improve phenomena such as smoke.
[0122]
The above-described configuration is merely an example of the present invention, and details thereof can be changed as desired. For example, in the above, when the reducing agent is added, the reducing agent is added to the exhaust passage. However, by sub-injecting engine fuel as the reducing agent into the cylinder in the latter half of the combustion stroke, the air-fuel ratio of the exhaust gas is lowered. You may let them. In the above description, a diesel engine has been described as an example. However, the present invention is also useful in a lean combustion gasoline engine.
[0123]
Regarding the reducing agent addition prohibition control, the reducing agent addition prohibition period is from the start of combustion state switching to the end of switching, but the addition of reducing agent should be prohibited from the end of overshoot control. Also good. Further, the addition of the reducing agent may be permitted upon the start of switching of the fuel injection control.
[0124]
As for the combustion state switching control, switching in consideration of the temperature of the exhaust purification catalyst and the temperature of the exhaust gas is also possible. As a background to this, the technique of low-temperature combustion shown 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 has a considerable amount of heat energy, so when the temperature of the air (outside air) itself is low or when the fuel injection amount is small. The effect of maintaining the exhaust gas temperature at a high temperature is expected. Therefore, the exhaust gas mixed with the EGR gas flows into the exhaust purification catalyst, so that the exhaust purification catalyst can be warmed up early. Even in this case, when the combustion state is switched, smoke is generated, engine noise is increased, and the like. Therefore, these various problems can be solved by performing various engine controls in the transient state described above.
[0125]
As for the fuel injection switching control, even if the gradual change control is started from the end of the overshoot control, the same effect as the above description can be obtained. The delay time can be set in advance in various preliminary experiments.
[0126]
【The invention's effect】
As described above, according to the present invention, during the transition period of the combustion state, the addition of the reducing agent to the exhaust purification catalyst is prohibited, and the control amount of each valve body is overshot, and the delay time is corrected for the correction of the combustion injection control. It is possible to improve various problems caused in the transient state by performing various controls such as providing and gradually changing the fuel injection control. Therefore, improvement of driver viability, reduction of engine noise, suppression of smoke, and the like are achieved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an internal combustion engine according to an embodiment.
FIG. 2 is a graph for explaining the correlation between the generation amount of soot 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 order of various controls that are processed when the combustion state is switched.
FIG. 6 is a diagram for explaining the internal structure of the particulate filter.
[Explanation of symbols]
1 Internal combustion engine (engine body)
1a Crankshaft
2-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 equipment
23 Supercharging pressure sensor
24 Intake air 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 NOx storage reduction catalyst
52b Particulate filter
53 Casing
55 Exhaust gas inflow passage
55a stopper
56 Exhaust gas outflow passage
56a stopper
57 Bulkhead
58 Filter
59 Oxidation Catalytic Converter
60 Reducing agent addition device
61 Reducing agent addition valve
62 Reducing agent supply path
63 Fuel pressure sensor
64 Fuel pressure control valve
66 Emergency shut-off valve
74 Air-fuel ratio sensor

Claims (7)

When the proportion of inert gas contained in the intake air used for combustion approaches a predetermined amount, the amount of soot produced during the combustion gradually reaches a peak, and when the proportion is further increased, the amount of soot produced decreases. A first combustion state that suppresses the generation of soot by suppressing the ratio of the inert gas to less than the predetermined amount, and the ratio of the inert gas to a region that exceeds the predetermined amount. An internal combustion engine capable of switching between a second combustion state that suppresses the generation of soot by holding,
When switching from the first combustion state to the second combustion state, or when switching from the second combustion state to the first combustion state, oxygen in the exhaust gas flowing through the exhaust passage of the internal combustion engine Combustion state switching means for changing the ratio of the inert gas based on the concentration;
Reducing agent addition means for adding a reducing agent to the exhaust gas exhausted during engine operation and promoting an exhaust purification action of an exhaust purification catalyst installed in the exhaust passage;
In the process of switching the combustion state from the first combustion state to the second combustion state, or in the process of switching from the second combustion state to the first combustion state, addition of a reducing agent to the exhaust gas is performed. Reducing agent addition prohibition means prohibited for a predetermined period;
An internal combustion engine comprising: The inert gas is EGR gas introduced from the exhaust passage into the intake passage of the internal combustion engine,
The combustion state switching means includes an EGR amount control means for controlling the supply amount of EGR gas supplied to the combustion chamber through the intake passage, and an air flow control means for controlling the flow rate of air flowing into the combustion chamber through the intake passage. With
When changing the ratio of the inert gas contained in the intake air, 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 internal combustion engine according to claim 1. In the combustion state switching means, after the start of switching of the combustion state, the control of the EGR gas amount by the EGR amount control means is performed for a predetermined period with a control amount exceeding a control amount determined in accordance with the target ratio. The internal combustion engine according to claim 2, wherein the internal combustion engine is held. In the combustion state switching means, after the start of switching of the combustion state, the control of the air flow rate by the air flow rate control means is performed for a predetermined period with a control amount exceeding a control amount determined according to the target ratio. The internal combustion engine according to claim 2 or 3, wherein the internal combustion engine is held. Fuel injection switching specific to each combustion state is prepared corresponding to the first combustion state and the second combustion state, and the fuel injection control is switched according to switching of the combustion state. Having means,
The internal combustion engine according to any one of claims 1 to 4, wherein the combustion state switching means changes the ratio of the inert gas contained in the intake air in preference to the switching of the fuel injection control. When the proportion of inert gas contained in the intake air used for combustion approaches a predetermined amount, the amount of soot produced during the combustion gradually reaches a peak, and when the proportion is further increased, the amount of soot produced decreases. A first combustion state that suppresses the generation of soot by suppressing the ratio of the inert gas to less than the predetermined amount, and the ratio of the inert gas to a region that exceeds the predetermined amount. An internal combustion engine capable of switching between a second combustion state that suppresses the generation of soot by holding,
Fuel injection control specific to each combustion state prepared for each of the first combustion state and the second combustion state;
Fuel injection corresponding to the requested combustion state at the time of a request for switching from the first combustion state to the second combustion state, or at the time of a request for switching from the second combustion state to the first combustion state Fuel injection switching means for switching to control;
Fuel injection control restraint means for restraining the fuel injection control for a predetermined time in the control state before the switching after the start of switching of the combustion state ,
The internal combustion engine characterized in that the fuel injection control restraint means releases the restraint state of the combustion injection control when the oxygen concentration of the intake air supplied for combustion reaches a predetermined oxygen concentration . The internal combustion engine according to claim 6, wherein the fuel injection control restraining means shifts the fuel injection control to a normal fuel injection control state while gradually changing the fuel injection control after the predetermined time has elapsed.

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