JP2003148132A - Exhaust emission control device and method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent regeneration inhibition of fine particles due to combustion instability, exhaust gas deterioration and filter clogging of additional fuel, etc., caused by various situations of an internal combustion engine and an exhaust passage, when a particulate filter is regenerated by oxidation and burning of fine particles trapped in the particulate filter by adding fuel. SOLUTION: A fuel addition means in a combustion chamber to add a part of fuel injected in the combustion chamber 20 as secondary injection fuel, and a fuel addition means in an exhaust passage to inject fuel directly and add it into the exhaust passage, are used as a fuel addition method. When a secondary fuel injection is possible and a bed temperature of a particulate filter 42a is not less than the first temperature, the fuel addition means in the combustion chamber is used. When an exhaust passage temperature is not less than the second temperature and the bed temperature of the particulate filter 42a is not less than the third temperature, the fuel addition means in the exhaust passage is used. When satisfying the conditions that both the fuel addition means in the combustion chamber and the fuel addition means in an exhaust passage can be performed, either means or both means are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology of an exhaust gas purification apparatus for an internal combustion engine, and more particularly to a fuel addition control technology.

[Prior art]

In recent years, in internal combustion engines mounted on automobiles and the like, carbon monoxide (CO) and hydrocarbons (HC) contained in the exhaust gas are discharged before the exhaust gas discharged from the internal combustion engine is released into the atmosphere. It is required to improve exhaust emission by purifying or removing toxic gas components such as nitrogen oxides (NOx).

Particularly, in a compression ignition type diesel engine that uses light oil as a fuel, carbon monoxide (CO) and hydrocarbon (H
In addition to C), nitrogen oxides (NOx), etc., it is important to purify or remove soot contained in the exhaust gas and particulates called PM (Particulate Matter) such as SOF (Solbule Organic Fraction). Is.

The main component of the fine particles is black smoke (soot) caused by the fuel, but it is also a mixture of various components,
The component is divided into black smoke (soot) which is an insoluble component, unburned fuel component which is a soluble component (SOF) and unburned oil component which is a soluble component (SOF) depending on whether or not it is soluble in an organic solvent.

It is considered that soot is caused by a complicated reaction when fuel burns in a state of insufficient air. In summary, the fuel molecule undergoes a dehydrogenation reaction by thermal decomposition, and a nucleus of fine particles (soot precursor) is generated. Substance), and the nuclei aggregate and coalesce to form soot. In diesel combustion, a large amount of soot is produced during diffusion combustion, but re-combustion occurs by introducing air into the flame in the latter stage of combustion, and soot is rapidly reduced.
Sulfate is the oxidation of sulfur during combustion and is in the form of a sulfuric acid mist that is bound to water.

For this reason, in a diesel engine, a particulate filter made of a base material having a large number of small pores of entrained air bubbles incorporated therein and having an increased specific surface area per unit volume is arranged in the exhaust passage. A method is known in which exhaust gas is flowed through the pores to adsorb and collect the fine particles in the exhaust gas on the surface.

By the way, when the amount of fine particles trapped in the particulate filter increases excessively, the exhaust passage in the particulate filter is blocked, and the flow of exhaust gas is obstructed.

When the flow of exhaust gas is blocked by the particulate filter, the exhaust pressure rises in the exhaust passage upstream of the particulate filter, and the exhaust pressure acts as back pressure on the internal combustion engine.

Therefore, it is necessary to regenerate the particulate filter by purifying the collected particulates before the particulates collected by the particulate filter increase excessively.

As a method of regenerating the particulate filter, there is a method of oxidizing, that is, burning, the collected fine particles by making the inside of the particulate filter an oxidizing atmosphere.

However, the fine particles are approximately 500 ° C to 700 ° C.
In order to oxidize the collected fine particles, the ambient temperature of the particulate filter is raised to a high temperature of 500 ° C. to 700 ° C., and the surrounding area of the particulate filter is made an oxygen excess atmosphere. There must be.

However, since the diesel engine performs lean combustion operation with excess air in most operating regions, the combustion temperature of the air-fuel mixture is likely to be low, and accordingly the temperature of exhaust gas is also likely to be low. Therefore, in a diesel engine, it is difficult to raise the atmospheric temperature of the particulate filter to 500 ° C. or higher by utilizing the heat of exhaust gas.

On the other hand, in the past, Japanese Patent Publication No. 7-1062
A diesel exhaust particle filter as described in Japanese Patent No. 90 has been proposed. The filter for diesel exhaust particles described in this publication has a catalyst material containing a mixture of a platinum group metal and an alkaline earth metal oxide supported on a particulate filter, and thereby has a temperature of about 350 ° C.
Ignition and combustion of fine particles can be performed even under relatively low temperature conditions of up to 400 ° C.

On the other hand, the exhaust gas temperature of the diesel engine is
In the high load operating region, the temperature may rise to 350 ° C. or higher, but in the low load operating region, it hardly rises to 350 ° C. or higher. Therefore, when the diesel engine is operated at a low load, especially when the fuel injection is stopped as in the case where the diesel engine is in the decelerating operation state, low temperature exhaust gas is discharged from the diesel engine, so the particulates are discharged. It is assumed that the filter is cooled by the low temperature exhaust gas and the particulate oxidation ability of the particulate filter is reduced.

Therefore, in order to oxidize the particulates on the particulate filter during low load operation, it is necessary to raise the temperature of the particulate filter to a temperature at which the particulates can be oxidized at a minimum.

As one of the means for raising the temperature of the particulate filter, a fuel is added on the particulate, and the heat released when the fuel oxidizes raises the particulate filter bed temperature to oxidize the particulates. There is a means to burn.

There are the following methods for supplying fuel for raising the particulate filter bed temperature. Part of the fuel injected into the cylinder of the engine as a power source,
By performing a secondary fuel injection that is injected after the end of the combustion process of the injected fuel that is normally performed in the cylinder, a method of including unburned unburned fuel in the exhaust gas and discharging and adding it to the exhaust passage, A method of providing a fuel injection device in the exhaust passage and directly injecting and adding the fuel into the exhaust gas.

[0018]

The method of adding as unburned fuel in the cylinder is that the added fuel is in a sufficiently vaporized state. Since the fuel is sprayed in a mist state in a high-temperature combustion chamber and evaporated, and the fuel becomes sufficiently vaporized, the combustion reactivity on the particulate filter improves, so the particulate filter bed temperature becomes It becomes possible to react even near the minimum temperature at which reaction is possible.

Further, even if the temperature distribution of the particulate filter is non-uniform and only the downstream side reaches the reaction temperature and the upstream side does not reach the reaction temperature, if it is vaporized fuel, it will pass through the upstream side and the downstream side. React on the side,
As a result, it becomes possible to raise the temperature of the entire particulate filter to a temperature at which it can react.

However, in the method of adding as unburned fuel in the cylinder, since a part of the fuel converted to power is used as the fuel for the reaction, the absolute amount thereof is limited,
Further, when the engine is under a high load, there is a problem in that it may be impossible to supply unburned fuel due to concern about a decrease in torque.

On the other hand, in the method of injecting and adding the fuel into the exhaust passage, the fuel is supplied and injected by a system different from the system for supplying the fuel to the cylinder in the engine, and therefore the injection amount It is also possible to increase the fuel consumption, and fuel can be added without being restricted by the operating state of the engine.

However, in the method of injecting fuel into the exhaust passage and adding it, since the liquid fuel is injected in the form of mist, in order to change it into a gas state in which it easily reacts, the injected fuel is used. In order to enable vaporization in a short time, the exhaust gas temperature at the injection position of the exhaust passage needs to be high to some extent. Since the added fuel is not completely gas, when it reacts on the particulate filter, it deprives the particulate filter bed temperature as latent heat when the fuel is changed from liquid to gas. Therefore, the bed temperature of this particulate filter also needs to be higher than the temperature required for the minimum reaction. In addition, when fuel is injected, some fuel adheres to the exhaust pipe around the injection point, so if the exhaust pipe temperature is low, it accumulates as a liquid as it is, and especially when injecting at a trap-shaped place such as a collecting pipe (manifold) There are problems such as the need for countermeasures.

The present invention has been made in view of the above problems, and based on various conditions of an internal combustion engine and an exhaust system,
An object is to adopt an efficient fuel addition method to remove fine particles deposited on the particulate filter.

[0024]

In order to solve the above problems, a filter provided in an exhaust passage of an internal combustion engine for collecting fine particles in exhaust gas, and a power used in a combustion chamber of the internal combustion engine A combustion chamber fuel addition means for injecting fuel separately from the main fuel injection for conversion, and an exhaust passage fuel addition means for injecting fuel into the exhaust gas. In the exhaust gas purification device provided, when secondary fuel injection is possible in the combustion chamber and the filter bed temperature is equal to or higher than a first temperature at which the gaseous fuel is oxidized and reacted, fuel addition in the combustion chamber is performed. A fuel is added by the means, the exhaust gas temperature is equal to or higher than a second temperature at which the fuel injected in the exhaust passage is not condensed, and the filter bed temperature causes an oxidation reaction of the gaseous fuel containing droplets. If above temperature The exhaust gas purification device for an internal combustion engine is characterized in that the fuel is added by the fuel addition means in the exhaust passage.

According to the present invention, the secondary fuel injection in the combustion chamber and the fuel injection in the exhaust passage are selectively used depending on the temperature condition of the engine peripheral elements which changes according to the operating condition of the internal combustion engine. Then, the fuel is added to the filter.

This means that the condition of the internal combustion engine is that the internal combustion engine is in a low load state and secondary fuel injection is possible in the combustion chamber, and that the filter bed temperature is equal to or higher than a predetermined temperature. If the temperature conditions are met, fuel is added to the filter by performing secondary fuel injection in the combustion chamber. If the conditions of the exhaust passage where the temperature of the exhaust passage is higher than a certain temperature and fuel can be injected in the exhaust passage and the condition of the filter floor temperature that the filter floor temperature is equal to or higher than a predetermined temperature are met, the exhaust passage Fuel is added to the filter by injecting fuel therein.

When both of the condition settings that determine the above two means are satisfied, that is, secondary fuel injection is possible in the combustion chamber, and the filter bed temperature oxidizes the gaseous fuel. It is higher than each of the first temperature for reacting and the third temperature for oxidizing the gaseous fuel containing droplets, and the exhaust passage temperature is equal to or higher than the second temperature at which the fuel injected in the exhaust passage is not condensed. In some cases,
The fuel is added using one or both of the fuel addition means in the combustion chamber and the fuel addition means in the exhaust passage.

When performing the fuel addition means for both the fuel addition in the combustion chamber and the fuel addition in the exhaust passage, the condition of the filter bed temperature is set in each of the fuel addition means. The first temperature, which is the bed temperature condition, is the minimum temperature at which the gaseous fuel can undergo an oxidation reaction on the filter. The third temperature, which is the condition of the filter bed temperature of the fuel addition means in the exhaust passage, is on this filter even if the latent heat required for the gaseous fuel containing droplets to become a complete gas is deprived on this filter. This is the minimum temperature at which the fuel can react. Therefore, the third temperature becomes higher than the first temperature because the fuel has latent heat for transferring to gas.

The addition of fuel to the filter by the fuel addition means in the combustion chamber under the condition of the first temperature is added to the filter by the fuel which is injected in the combustion chamber in the high temperature state and is completely vaporized. The reactivity becomes good. for that reason,
Although it is possible to cause a temperature rising reaction even at the first temperature which is a low temperature range, the addition of fuel to the filter by the fuel injection in the exhaust passage on the condition of the third temperature causes the liquid to be atomized. After that, the fuel is added to the filter after being vaporized by the atmosphere at the injection position. Therefore, not all injected fuel may be vaporized depending on the surrounding atmosphere.
The fuel is added at the third temperature, which is a high temperature range to some extent.

In connection with the first and third temperatures, the second temperature which is the exhaust temperature is a temperature at which the fuel injected into the exhaust passage does not condense, that is, the fuel is introduced into the exhaust passage. It is the temperature at which the added fuel can be kept so as not to accumulate in the exhaust passage as a liquid when added.

The filter retains the nitrogen oxides in the exhaust gas when the oxygen concentration in the exhaust gas is high, and retains the nitrogen oxides when the oxygen concentration decreases and fuel as a reducing agent exists. It is possible to carry an occlusion-reduction type NOx catalyst that reduces NO.

In addition to the characteristics described above, the NOx storage reduction catalyst activates oxygen in the exhaust gas when the oxygen concentration in the exhaust gas is high, lowers the oxygen concentration, and the fuel as a reducing agent is present. When this is done, nitrogen oxides are reduced and active oxygen is also produced. Therefore, the active oxygen serves to purify the nitrogen oxides in the exhaust gas and at the same time, plays a role of an oxidant when burning the fine particles.

By carrying out the present invention, it becomes possible to efficiently remove the particulates deposited on the particulate filter according to various conditions of the internal combustion engine and the exhaust system.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment in which the fuel injection control device and method for an internal combustion engine according to the present invention are applied to a diesel engine system will be described below.

In FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 1 includes a fuel supply system 10, a combustion chamber 20, and an intake system 3.
It is an in-line four-cylinder diesel engine system mainly composed of 0 and an exhaust system 40.

The fuel supply system 10 includes a supply pump 11,
A pressure accumulating chamber (common rail) 12, a fuel injection valve 13, a shutoff valve 14, a fuel addition nozzle 17, an engine fuel passage P1 and an addition fuel passage P2 are provided.

The supply pump 11 is a fuel tank (not shown)
The fuel drawn up is made into a high pressure and supplied to the common rail 12 through the engine fuel passage P1. The common rail 12 has a function of holding (accumulating) the high-pressure fuel supplied from the supply pump 11 at a predetermined pressure, and distributes the accumulated fuel to each fuel injection valve 13. The fuel injection valve 13 is an electromagnetic valve having an electromagnetic solenoid (not shown) inside, and is opened appropriately to supply and inject fuel into the combustion chamber 20.

On the other hand, the supply pump 11 supplies a part of the fuel pumped up from the fuel tank to the fuel addition nozzle 17 through the addition fuel passage P2. A shutoff valve 14 is arranged in the fuel passage P2 from the supply pump 11 toward the fuel addition nozzle 17. In an emergency, the shutoff valve 14 shuts off the additional fuel passage P2 and stops the fuel supply.
The fuel addition nozzle 17 is an electromagnetic valve similar to the fuel injection valve 13, and is an exhaust passage fuel addition means in the present invention for injecting and adding fuel as a reducing agent into the exhaust system 40.

The intake system 30 forms a passage (intake passage) for intake air supplied into each combustion chamber 20. On the other hand, the exhaust system 40 forms a passage (exhaust passage) for exhaust gas discharged from each combustion chamber 20.

The engine 1 is also provided with a known supercharger (turbocharger) 50. The turbocharger 50 includes a turbine wheel 52 and a compressor 53 that are connected via a shaft 51. One compressor 53 is exposed to intake air in the intake system 30, and the other turbine wheel 52 is exposed to exhaust gas in the exhaust system 40. The turbocharger 50 having such a structure has an effect of increasing the intake pressure (supercharging effect) by rotating the compressor 53 using the exhaust flow (exhaust pressure) received by the turbine wheel 52.

In the intake system 30, the turbocharger 5
The intercooler 31 provided at 0 forcibly cools the intake air whose temperature has risen due to supercharging. The throttle valve 32, which is provided further downstream than the intercooler 31, is an electronically controlled on-off valve whose opening can be adjusted steplessly, and reduces the flow passage area of the intake passage under predetermined conditions. , Has a function of adjusting (reducing) the supply amount of the intake air.

The engine 1 is also provided with an exhaust gas recirculation passage (EGR passage) 60 that bypasses the upstream side (intake system 30) and the downstream side (exhaust system 40) of the combustion chamber 20. Specifically, the EGR passage 60 connects the exhaust collecting pipe 40a upstream of the turbocharger 50 in the exhaust system 40 and the downstream side of the throttle valve 32 in the intake system 30. The EGR passage 60 has a function of appropriately returning a part of the exhaust gas to the intake system 30. The EGR passage 60 is opened and closed steplessly by electronic control, and an EGR valve 61 capable of freely adjusting the flow rate of exhaust gas flowing through the passage and an EGR passage 6 are provided.
EGR for cooling exhaust gas passing through 0 (circulation)
A cooler 62 is provided.

Further, in the exhaust system 40, an exhaust passage 40b along a flow path of exhaust gas is provided downstream of a portion where an exhaust collecting pipe 40a connected to a combustion chamber and a turbine wheel 52 are provided, and NOx is provided downstream thereof. Catalyst casing 42,
Further, the exhaust passage 40c is sequentially connected downstream. NO
The x-catalyst casing 42 has an occlusion reduction type N that purifies harmful components such as NOx contained in the exhaust gas as described later.
An Ox catalyst 42b and a particulate filter 42a that purifies particulates (PM) such as soot contained in the exhaust gas together with harmful components such as NOx are housed (see FIG. 3).

Various sensors are attached to each part of the engine 1 to output signals relating to the environmental conditions of the part and the operating state of the engine 1.

That is, the rail pressure sensor 70 outputs a detection signal corresponding to the pressure of the fuel stored in the common rail 12. The fuel pressure sensor 71 has an additional fuel passage P2.
A detection signal corresponding to the pressure (fuel pressure) Pg of the fuel introduced into the fuel addition nozzle 17 among the fuel flowing inside is output. The air flow meter 72 outputs a detection signal according to the flow rate (intake amount) Ga of intake air upstream of the throttle valve 32 in the intake system 30. Air-fuel ratio (A / F) sensor 7
3 outputs a detection signal that continuously changes according to the oxygen concentration in the exhaust gas upstream of the catalyst casing 42 of the exhaust system 40. The exhaust temperature sensor 74 is the same as the exhaust system 40.
A detection signal corresponding to the exhaust gas temperature (exhaust temperature) TEX is output downstream of the catalyst casing 42. Similarly, the NOx sensor 75 outputs a detection signal that continuously changes according to the NOx concentration in the exhaust gas downstream of the catalyst casing 42 of the exhaust system 40. Catalyst inflow exhaust temperature sensor 7
8 outputs a detection signal according to the temperature of the exhaust gas flowing in at the inlet of the catalyst casing 42. Catalyst temperature sensor 7
9 outputs a detection signal in the catalyst casing 42 according to the catalyst bed temperature. The pressure sensor 90 is the catalyst casing 4
2 is provided upstream and outputs a detection signal corresponding to the pressure in the exhaust passage.

Further, the accelerator opening sensor 76 is attached to an accelerator pedal (not shown) of the engine 1 and outputs a detection signal which is a basis of the work amount required in the engine 1 according to the depression amount ACC of the pedal. The crank angle sensor 77 outputs a detection signal (pulse) every time the output shaft (crankshaft) of the engine 1 rotates by a certain angle. Each of these sensors 70 to 79, 90 is an electronic control unit (EC
U) 80 is electrically connected.

As shown in FIG. 2, the ECU 80 includes a central processing unit (CPU) 81 and a read-only memory (RO).
M) 82, random access memory (RAM) 83, backup RAM 84 in which stored information is not erased even after operation stop, timer counter 85, etc., external input circuit 86 including A / D converter, and external output circuit 87. , A logical operation circuit configured by being connected by a bidirectional bus 88.

The ECU 80 inputs the detection signals of the various sensors through an external input circuit, and in the CPU 81 of the ECU 80 based on these signals, a program stored in the ROM 82 is used to detect fuel injection of the engine 1 or the like. In addition to performing basic control, various controls related to the operating state of the engine 1, such as determining the supply amount of fuel injection related to addition of a reducing agent (fuel that functions as a reducing agent) and reducing agent (fuel) addition control regarding the addition timing, etc. I do.

The N provided in the fuel supply system 10 and the exhaust system 40 for supplying fuel to each cylinder through the fuel injection valve 13.
The Ox catalyst and the particulate filter, and the ECU 80 that controls the functions of the fuel supply section 10, the NOx catalyst and the particulate filter, and the like together constitute the exhaust gas purification device of the engine 1 according to the present embodiment. The fuel addition control or the like outputs an instruction signal related to the control E
It is carried out through the operation of various members constituting the exhaust emission control device including the CU80.

Next, of the components of the engine 1 described above, the configuration and function of the catalyst casing 42 provided in the exhaust system 40 will be described in detail.

FIG. 3 shows the catalyst casing 42 shown in FIG.
FIG. 3 is a cross-sectional view showing, in an enlarged manner, with a part of its internal structure. The catalyst casing 42 has a storage reduction type NO inside.
Particulate filter 42 carrying x catalyst 42b
accommodates a.

The NOx catalyst 42b is made of, for example, alumina (A
L ₂ O ₃ ) as the main material, and the surface of this carrier is N
Functions as an Ox absorbent, for example, potassium (K), sodium (Na), lithium (Li), cesium (C
Alkali metal such as s), alkaline earth metal such as barium (Ba), calcium (Ca), or rare earth such as yttrium (Y), and platinum (e.g. platinum (metal) that functions as an oxidation catalyst (precious metal catalyst)). It is constituted by carrying a noble metal such as Pt).

The particulate filter 42a is made of a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage is closed as shown by the arrow since it is closed. It passes through the surrounding partition wall made of a porous material and flows out to the adjacent exhaust gas inflow passage.

In the present embodiment, the carrier layer made of alumina or the like is formed on the surface of the partition wall of the particulate filter 42a and on the inner wall surface of the pores of the partition wall, and on this carrier. A NOx catalyst 42b including a noble metal catalyst and a NOx absorbent is carried.

The NOx absorbent has a characteristic that it retains NOx when the oxygen concentration in the exhaust gas is high and releases NOx when the oxygen concentration in the exhaust gas is low. Further, when NOx is released into the exhaust gas, HC is contained in the exhaust gas.
If CO, CO, etc. are present, the noble metal catalyst promotes the oxidation reaction of these HC and CO, thereby converting NOx into an oxidizing component, HC
A redox reaction using CO or CO as a reducing component occurs between the two. That is, HC and CO are oxidized to CO ₂ and H ₂ O,
NOx is reduced to N ₂ .

Further, the noble metal catalyst forming the NOx catalyst 42b promotes the oxidation of HC, and the bed temperature is raised by the heat of the oxidation reaction of HC.

When the NOx absorbent holds a predetermined limit amount of NOx even when the oxygen concentration in the exhaust gas is high, the NOx absorbent does not hold NOx any more. In the engine 1, before the NOx retention amount of the NOx catalyst 42b housed in the catalyst casing 42 reaches a limit, the reducing agent is added and supplied upstream of the catalyst casing 42 in the exhaust passage to activate the NOx catalyst 42b. The control of reducing and purifying the retained NOx and recovering the NOx retaining capacity of the NOx catalyst 42b is repeated at predetermined intervals.

In the particulate filter 42a, the NOx catalyst 42b supported on the surface thereof is N
The repeated holding, reduction and purification of Ox are as described above. On the other hand, the NOx catalyst 42b rises in temperature in the process of purifying NOx, and secondarily produces active oxygen. Have characteristics. When exhaust gas passes through the particulate filter 42a, PM components such as soot contained in the exhaust gas are captured by the porous material. Here, the active oxygen generated by the NOx catalyst 42b is
Since it has extremely high reactivity (activity) as an oxidant,
The trapped PM component reacts rapidly with the active oxygen without emitting a bright flame and is purified in a state where the temperature is raised by the addition of fuel.

The NOx purification will be specifically described below.

Generally, in a diesel engine, the oxygen concentration of the mixture of fuel and air used for combustion in the combustion chamber is high in most operating regions. The oxygen concentration of the air-fuel mixture used for combustion is normally reflected in the oxygen concentration in the exhaust gas as it is after subtracting the oxygen used for combustion, and the oxygen concentration (air-fuel ratio) in the air-fuel mixture is high. For example, the oxygen concentration (air-fuel ratio) in the exhaust gas also basically becomes high.

On the other hand, as described above, the NOx catalyst 42b
Has the property of holding NOx if the oxygen concentration in the exhaust gas is high, and reducing NOx to NO ₂ or NO if it is low, so long as the oxygen concentration in the exhaust gas is high.
Keep holding. However, the NOx of the NOx catalyst 42b concerned
There is a limit to the holding amount, and when the NOx catalyst 42b holds the limiting amount of NOx, NOx in the exhaust gas is not held by the NOx catalyst 42b and passes through the catalyst casing 42 as it is.

In order to restore the NOx retention function of the NOx catalyst, it is necessary to add a reducing agent to the NOx absorbent.
Due to the structure of the engine, when normal fuel injection is performed, exhaust gas having a low oxygen concentration, that is, containing a large amount of fuel that is a reducing agent is difficult to be discharged.

Therefore, in addition to the main fuel injection for power conversion that is performed in the combustion chamber of the internal combustion engine, a method for performing secondary fuel injection that mainly injects fuel as unburned fuel, and a method provided in the exhaust passage, The fuel is added to the exhaust gas by a method of injecting the fuel into the exhaust gas to increase the amount of the reducing agent component in the exhaust gas, and the reducing component restores the NOx retention action.

The ECU 80 of the engine 1 continuously observes the NOx concentration in the exhaust gas downstream of the NOx catalyst 42b based on the output signal of the NOx sensor 75. NOx
The NOx retention capacity (retention efficiency) of the catalyst 42b can be retained by the NOx catalyst 42b as the NOx amount retained by the NOx catalyst 42b increases, in other words, the NOx amount retained by the NOx catalyst 42b can be retained by the NOx catalyst 42b. NO
It becomes lower as it approaches the maximum amount (saturation amount) of x. That is, as the amount of NOx retained in the NOx catalyst 42b increases, the concentration of NOx that passes through the catalyst casing 42 and is discharged downstream also increases. Since there is a sufficient correlation between the transitional states of the two, the Nx in the NOx catalyst 42b is determined based on the transitional state of the NOx concentration.
The amount of Ox retained can be grasped.

Therefore, the ECU 80 controls the catalyst casing 4
2 When the NOx concentration in the downstream reaches a predetermined concentration, it is judged that the NOx holding amount in the NOx catalyst 42b has reached a predetermined amount, and the fuel addition means is used to include the unburned fuel in the exhaust gas. As a result, fuel is added upstream of the catalyst casing 42 of the exhaust system 40 to temporarily increase the amount of reducing components in the exhaust gas flowing into the catalyst casing 42, lower the air-fuel ratio, and reduce NOx in the catalyst. Reacts with the fuel that is a reducing agent to purify it.

Next, the fine particles contained in the exhaust gas (hereinafter P
Purification of (referred to as M) will be described.

Similar to the purification of NOx, the purification of PM is also performed by using the fuel, but the purification of NOx is performed by utilizing the chemical reaction between HC and NOx which are the main components of the fuel. On the other hand, in the purification of PM, mainly by using HC as a heat source to raise the temperature, PM and oxygen (O ₂ ) are activated by the temperature and oxidized to purify.

Therefore, regarding the purification of PM, the added fuel is used as a heat source in the particulate filter 42a, that is, the purification is performed based on the combustion reactivity of the fuel.

The main control method is as follows: the operation history in which the output signals of the accelerator opening sensor 76, the crank angle sensor 77, the timer counter 85, etc. are accumulated in the backup RAM 84, and the pressure sensor 90 installed in the exhaust passage. The CPU 81 compares it with a program stored in the ROM 82 to determine whether to add fuel, which is a purification method, based on the signal from the above.

NO for the above method for adding fuel
Similarly to the fuel addition in the x catalyst 42b, as shown in FIG. 4, a part of the main fuel injection for power conversion performed in the combustion chamber of the internal combustion engine is injected after the combustion process to generate unburned fuel. A method of performing secondary fuel injection (combustion chamber fuel addition means) and a method of providing a fuel injection device in the exhaust passage to inject fuel directly into the exhaust gas as shown in FIG. 5 (exhaust passage fuel addition) Means). Since each of the above methods has different characteristics, those characteristics are also one factor of the judgment factor.

The features of the above-mentioned fuel addition means in the combustion chamber and the fuel addition means in the exhaust passage will be described below.

Regarding the fuel addition means in the combustion chamber, since the fuel is injected in the combustion chamber, the fuel in the combustion chamber must be sufficiently vaporized by the heat in the combustion chamber.
As the catalyst bed temperature flows into the first temperature (20), the catalyst bed temperature is the minimum temperature at which the vaporized and activated fuel can react.
It is possible to raise the temperature even at 0 ° C), and the injection amount depends on the fuel amount required from the accelerator pedal depression amount, and the injection amount cannot be changed directly. However, there is a torque step in the engine when the engine load is large, or when secondary fuel injection is performed at the time of starting the engine, so fuel addition cannot be performed in these conditions. Can be mentioned.

With regard to the fuel addition means in the exhaust passage, the temperature inside the exhaust passage is the second because the fuel is injected into the exhaust passage.
If it is not higher than the temperature (assuming about 300 ° C), it may vaporize and adhere to the inner surface of the exhaust passage to form a liquid pool. All the injected fuel does not vaporize and remains in a droplet state. Since it may flow into the catalyst casing 42, even if the latent heat necessary for the fuel, which is a gas containing droplets, to become a complete gas on the filter is taken away, the minimum amount of fuel that can react on the filter The temperature is higher than the third temperature, which is higher than the first temperature (assuming about 250 ° C), and the fuel injection from a system different from the fuel system added to the engine affects the operation of the engine. However, the injection amount can be directly controlled, and the injection amount can be increased.

In summary of the above characteristics, the fuel addition means in the combustion chamber can add fuel even if the catalyst bed temperature is low, but the injection amount is not so large depending on the operating conditions of the engine, and the injection amount is small. It is also difficult to adjust. Regarding the fuel addition means in the exhaust passage, the injection amount can be adjusted regardless of the operating condition of the engine, but the catalyst bed temperature needs to be high to some extent, and the exhaust passage temperature is also limited. Become.

A program regarding whether or not fuel can be added will be described with the above conditions taken into consideration. First, when PM is required to be accumulated and removed, the temperature sensor 74 measures the catalyst outlet gas temperature. Here, the catalyst outlet gas temperature is measured because when the catalyst casing 42 is on the high temperature side (≧ 700 ° C.), the temperature is further increased by adding fuel, and as a result, the NOx catalyst 42b is thermally deteriorated. The main purpose is to prevent.

Next, whether or not fuel can be added to the combustion chamber will be described. After measuring the catalyst outlet gas temperature, the engine 1 is measured by the accelerator opening sensor 76 and the crank angle sensor 77.
Determine whether the load is heavy and measure the engine cooling water temperature with a water temperature gauge (not shown). The water temperature is measured here, especially since the rotation is unstable immediately after the engine 1 is started, and fuel cannot be added in this state. Therefore, it is determined whether or not the warm-up operation is finished after the engine 1 is started. The engine cooling water temperature was adopted as one of the materials. Next, the catalyst bed temperature is measured by the catalyst bed temperature sensor 79, and if the temperature is equal to or higher than a predetermined first temperature (200 ° C.), fuel is added in the combustion chamber.

Next, whether or not fuel can be added to the exhaust passage will be described. Similarly, after measuring the catalyst outlet gas temperature,
The catalyst inlet gas temperature sensor 78 measures the catalyst inlet gas temperature. Originally, it is desirable to measure the temperature at the fuel injection position, but the catalyst inlet gas temperature is measured due to problems such as sensor arrangement, and the temperature at the fuel injection position is estimated from that value. When the catalyst inlet gas temperature is equal to or higher than the predetermined second temperature (300 ° C.), the catalyst bed temperature sensor 79 then measures the catalyst bed temperature, and if the temperature is equal to or higher than the predetermined third temperature (250 ° C.), exhaust is performed. Fuel is added in the passage, and the fuel addition control for PM regeneration is completed.

Hereinafter, E of the engine 1 according to this embodiment will be described.
Regarding the "fuel addition control" executed by the CU 80, a specific processing procedure will be described with reference to the flowchart shown in FIG.

FIG. 6 shows the processing contents of the "particulate filter PM regeneration routine" which is carried out to control the fuel addition method and the addition amount required for regeneration when performing the PM regeneration control. This routine process is executed by the ECU 80.
The execution of the engine 1 is started at the same time when the engine 1 is started.

When the processing shifts to this routine, the ECU
In step S101, the controller 80 determines whether PM regeneration is necessary by checking the accelerator opening sensor 76 and the crank angle sensor 7.
7. Whether or not regeneration control is necessary is determined from the operation history obtained by accumulating data of the timer counter 85 and the pressure sensor 90, and if it is determined that it is not necessary, the process proceeds to S112 and fuel addition and exhaust in the combustion chamber are performed. Without adding fuel in the passage, normal combustion is executed in S113 to end this routine, and if necessary, proceed to the next step.

Next, in step S102, the condition of the catalyst casing 42 is judged from the catalyst outlet gas temperature. Here, if the outlet gas temperature is ≧ 700 ° C., the process proceeds to S112, where S1 is performed without adding fuel in the combustion chamber and fuel in the exhaust passage.
In step 13, normal combustion is executed to end this routine. When the temperature of the discharged gas is <700 ° C., the process proceeds to the next step.

Next, in S103 and subsequent steps, it is determined whether fuel addition in the combustion chamber can be performed. First, in S103,
The cooling water temperature of the engine 1 is measured. If the water temperature <60 ° C., the process proceeds to S107 without adding fuel in the combustion chamber, and then proceeds to S108, and if the water temperature ≧ 60 ° C., proceeds to the next step.

Next, in S104, the load state of the engine is determined. If the load is high, the process proceeds to S107 without adding fuel in the combustion chamber, and then proceeds to S108. If the load is low, the process proceeds to the next step.

Next, in S105, the catalyst bed temperature is measured. If the catalyst bed temperature <200 ° C., the process proceeds to S107 without adding fuel in the combustion chamber, and then proceeds to S108. If the catalyst bed temperature ≧ 200 ° C., proceeds to S106 and performs fuel addition in the combustion chamber, and then proceeds to S108.

Next, in S108 and thereafter, it is judged whether or not the means for adding fuel in the exhaust passage can be performed. First, S10
At 8, the temperature of gas entering the catalyst is measured. Input gas temperature <300
If the temperature is ° C, the process proceeds to S111 to end this routine without adding fuel in the exhaust passage, and if the inlet gas temperature is ≥300 ° C, the process proceeds to the next step.

In step S109, the catalyst bed temperature is measured. If the catalyst bed temperature is <250 ° C., the routine proceeds to S111 to end the routine without adding fuel in the exhaust passage, and if the catalyst bed temperature ≧ 250 ° C., proceeds to S110 to add fuel in the exhaust passage and then terminates this routine. To do.

In this routine, the possibility of adding fuel in the combustion chamber was discussed, and then the possibility of adding fuel in the exhaust passage was discussed. These two fuel additions are performed independently of each other. Although expressed in parallel, for the convenience of processing, as described above, the fuel addition in the combustion chamber was first performed, and then the fuel addition in the exhaust passage was performed. Therefore, on the contrary, even if the possibility of adding fuel in the exhaust passage is discussed first and then the possibility of adding fuel in the combustion chamber is discussed, there is no difference in actual control.

In the present embodiment, the predetermined temperature is set under each condition, but it is not limited to this value in practice, and each internal combustion engine and exhaust system has a unique value.
It shall be based on that value. In addition, the routine S10
In step 8, the catalyst inlet gas temperature was used as the determination condition, but this is one means for estimating the temperature of the fuel injection position in the exhaust passage as described above, and other means such as water temperature, intake temperature, injection The temperature may be estimated by calculating from the amount, the number of revolutions, and the like. The point is that the means does not matter as long as the temperature at the fuel injection position can be estimated. This also applies to other condition settings. For example, in steps S103 and S104, the water temperature and the load state of the engine are discussed. This is the condition setting of whether the engine can perform the secondary injection. Then, S103 and S104 are only one means of expressing it.

Further, under the condition that both the fuel addition in the combustion chamber and the fuel addition in the exhaust passage can be executed, both fuels may be added, or only one of them may be added. For example, even when the temperature condition of the exhaust system is sufficient to add fuel in the exhaust passage, it is necessary to add fuel in the combustion chamber only and add fuel in the exhaust passage if the engine is idling. On the contrary, when the engine is operating such that high load state and low load state are alternately repeated, it is only necessary to add fuel in the exhaust passage without adding fuel in the combustion chamber at that low load. PM
It is fully possible to regenerate.

【The invention's effect】

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when raising the temperature of the particulate filter having the function of oxidizing PM in the exhaust gas, the PM according to various conditions of the internal combustion engine and the exhaust system is It is possible to add fuel in order to efficiently and more accurately remove.

That is, by selecting the fuel addition method suitable for the regeneration of PM according to the operating condition of the internal combustion engine and the temperature property of the exhaust system, PM is burned on the particulate filter. It becomes possible to burn PM without causing instability, deterioration of exhaust gas components passing through the catalyst casing, and clogging of the catalyst casing with the added fuel.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a diesel engine system according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram of a configuration around an ECU according to the same embodiment.

FIG. 3 is a conceptual sectional view of a catalyst casing according to the same embodiment.

FIG. 4 is a schematic cross-sectional view of an engine and an exhaust system showing fuel addition in a combustion chamber according to the same embodiment.

FIG. 5 is a schematic cross-sectional view of an engine and an exhaust system showing fuel addition in a fuel exhaust passage according to the same embodiment.

FIG. 6 is a flowchart showing PM regeneration control according to the embodiment.

[Explanation of symbols]

1 engine (internal combustion engine) 10 Fuel supply system 11 Supply pump 12 common rail (accumulation chamber) 13 Fuel injection valve 14 Control valve 17 Fuel addition nozzle 20 Combustion chamber 30 Intake system 31 Intercooler 32 Throttle valve 40 exhaust system 40a Exhaust collecting pipe 40b, c exhaust passage 42 catalyst casing 42a particulate filter 42b NOx storage reduction catalyst (NOx catalyst) 42c plugging 43 Fuel injection pool 50 turbocharger 51 shaft 52 turbine wheel 53 Compressor 60 EGR passage 61 EGR valve 62 EGR cooler 70 Rail pressure sensor 71 Combustion sensor 72 Air flow meter 73 Air-fuel ratio (A / F) sensor 74 Exhaust temperature sensor 75 NOx sensor 76 Accelerator position sensor 77 Crank angle sensor 78 Catalyst inflow exhaust temperature sensor 80 Electronic Control Unit (ECU) 81 Central processing unit (CPU) 82 Read-only memory (ROM) 83 Random access memory (RAM) 84 Backup RAM 85 timer counter 86 External input circuit 87 External output circuit 88 two-way bus 90 Pressure sensor P1 engine fuel passage P2 additional fuel passage

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/24 F01N 3/24 R F02D 41/04 385 F02D 41/04 385E 385M (72) Inventor Taro Aoyama 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Yasuhiko Otsubo 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Takekazu Ito 1 Toyota Town, Toyota City, Aichi Prefecture Address Toyota Motor Co., Ltd. (72) Inventor Atsushi Tahara 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto Car Co., Ltd. F-term (reference) 3G090 AA03 BA01 DA02 DA12 DA18 DA20 DB07 3G091 AA10 AA11 AA18 AB04 AB06 AB09 BA04 CA18 CA26 DA03 EA01 EA05 EA07 EA16 EA17 EA18 EA34 GA06 GB02W GB03W GB04W GB05W GB06W GB10X 3G301 HA02 HA11 HA13 JA24 JA2 5 KA08 KA16 LA03 LB11 MA19 MA23 NE13 PA01Z PB08Z PD11Z PD12Z PE03Z PE08Z

Claims (7)

[Claims] 1. A fuel is injected separately from a filter provided in an exhaust passage of an internal combustion engine for collecting fine particles in exhaust gas and a main fuel injection for power conversion performed in a combustion chamber of the internal combustion engine. In an exhaust gas purification device provided with a fuel addition device in a combustion chamber for secondary fuel injection and a fuel addition device in an exhaust passage provided in an exhaust passage for injecting fuel into exhaust gas, When the secondary fuel injection is possible and the filter bed temperature is equal to or higher than the first temperature for oxidizing the gaseous fuel, the fuel is added by the fuel addition means in the combustion chamber, and the exhaust gas temperature becomes the exhaust passage. When the temperature is not lower than the second temperature at which the fuel injected in step S3 is not condensed and the filter bed temperature is not lower than the third temperature at which the gaseous fuel containing droplets is oxidized, the fuel addition means in the exhaust passage Add fuel by An exhaust emission control device for an internal combustion engine, which is characterized in that: 2. A first temperature at which a secondary fuel injection can be performed in the combustion chamber, and the filter bed temperature is a first temperature at which a gaseous fuel is oxidized, and a gaseous fuel containing droplets is oxidized at a third temperature. If the exhaust passage temperature is higher than or equal to a second temperature at which the fuel injected in the exhaust passage is not condensed, the combustion chamber fuel addition means and the exhaust passage fuel addition are performed. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein fuel is added by using one or both of the means. 3. The first temperature, which is the filter bed temperature, is a temperature of 200 ° C. or higher at which a gaseous fuel can undergo an oxidation reaction,
The third temperature is a temperature of 250 ° C. or higher at which a gaseous fuel containing droplets can undergo an oxidation reaction, and the third temperature is higher than the first temperature. Exhaust gas purification device for internal combustion engine. 4. The internal combustion engine according to claim 1, wherein the second temperature, which is the exhaust gas temperature, is a temperature of 300 ° C. or higher at which the fuel injected into the exhaust passage does not condense. Exhaust gas purification device for engines. 5. The filter retains nitrogen oxides in the exhaust gas when the oxygen concentration in the exhaust gas is high, and retains the nitrogen oxides in the exhaust gas when the oxygen concentration is low and fuel as a reducing agent is present. An occlusion reduction type NOx catalyst for reducing nitrogen oxides is supported.
An exhaust emission control device for an internal combustion engine according to any one of claims. 6. A filter, which is provided in an exhaust passage of an internal combustion engine, for collecting particulates in exhaust gas, and a secondary fuel in addition to a main injection fuel for power conversion performed in a combustion chamber of the internal combustion engine. In the exhaust purification method of adding fuel by appropriately selecting the first method of injecting and adding fuel and the second method of directly injecting fuel into the exhaust gas in the exhaust passage to add fuel, If the secondary fuel can be injected in the combustion chamber and the filter bed temperature is at a temperature higher than the temperature at which the gaseous fuel can undergo the oxidation reaction, the first method of adding the unburned fuel is adopted, and the exhaust gas If the temperature of the exhaust gas in the passage is equal to or higher than the temperature at which the fuel injected into the exhaust passage does not condense, and the filter bed temperature is equal to or higher than the temperature at which the gaseous fuel containing droplets can undergo the oxidation reaction, the direct fuel is used. Exhaust purification adopting the second method of adding Law. 7. A temperature at which a secondary fuel can be injected in a combustion chamber, and the filter bed temperature is a temperature at which a gaseous fuel can undergo an oxidation reaction and a gaseous fuel containing liquid droplets can undergo an oxidation reaction. If the exhaust gas temperature in the exhaust passage is higher than each temperature and is higher than the temperature at which the fuel injected into the exhaust passage does not condense, the first method of adding the unburned fuel and the second method of adding the direct fuel 7. The exhaust gas purification method according to claim 6, wherein one or both of the above are adopted.