JP2001003794A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To feed secondary fuel in an amount and being a component optimum to NOx reduction to an NOx catalyst. SOLUTION: In this control device, an NOx catalyst 15 capable of reducing NOx in oxidation atmosphere in arranged in an engine exhaust passage. At an engine expansion stroke or an exhaust stroke consecutive to main fuel injection, second secondary fuel injection is effected from a fuel injection valve 17 arranged in a cylinder and secondary fuel is fed to the NOx catalyst 15. A cylinder temperature is determined by a cylinder temperature sensor 38. Based on a cylinder temperature, secondary fuel injection timing is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

BACKGROUND OF THE INVENTION capable of reducing NO _X in an oxidizing atmosphere NO _X
Placing the catalyst into the engine exhaust passage, a secondary fuel by performing secondary fuel injection for the second time from the fuel injection valve disposed in the cylinder in a subsequent engine expansion stroke or exhaust stroke in the main fuel injection in the NO _X catalyst 2. Description of the Related Art An exhaust gas purifying apparatus for an internal combustion engine which supplies the exhaust gas is known (see Japanese Patent Application Laid-Open No. Hei 4-231645).

[0003]

[SUMMARY OF THE INVENTION] NO _X catalyst in N
O _X purification rate depends on the amount and components of the secondary fuel flowing to the NO _X catalyst, the amount and components of the secondary fuel flowing to the NO _X catalyst depends on the in-cylinder temperature at the time when the secondary fuel injection is performed I do. Thus, 2 of the optimal quantity and components for of the NO _X reduction
In order to supply the secondary fuel to the NO _X catalyst, it is necessary to determine the secondary fuel injection timing based on the in-cylinder temperature. However, the above-mentioned publication does not suggest anything about this point.

Accordingly, an object of the present invention is to provide NO_XFor reduction
NO for optimal amount and composition of secondary fuel _XSupply to the catalyst
To provide an exhaust gas purification device for an internal combustion engine that can
You.

[0005]

[MEANS FOR SOLVING THE PROBLEMS]
According to the present invention, NO in an oxidizing atmosphere_XN that can reduce
O_XPlacing the catalyst in the engine exhaust passage and pulling it for main fuel injection
In the subsequent engine expansion stroke or exhaust stroke,
The second fuel injection from the selected fuel injection valve
NO fuel_XInternal combustion engine exhaust supplied to the catalyst
In the purifier, the temperature inside the cylinder is calculated based on the temperature inside the cylinder.
The secondary fuel injection timing is determined. That is,
When the temperature in the cylinder fluctuates according to the engine operating condition,
Secondary fuel injection is performed when the internal temperature is optimal, and
NO secondary fuel of appropriate amount and composition _XSupplied to the catalyst.

[0006]

FIG. 1 shows a case where the present invention is applied to a diesel engine. However, the present invention can be applied to a spark ignition type engine. Referring to FIG. 1, 1 indicates an engine body, 2 indicates a piston, 3 indicates a combustion chamber, 4 indicates an intake port, 5 indicates an intake valve, 6 indicates an exhaust port, and 7 indicates an exhaust valve. The intake port 4 is connected to a surge tank 9 via a corresponding intake branch pipe 8, and the surge tank 9 is connected to an air cleaner 11 via an intake duct 10. A throttle valve 12 is arranged in the intake duct 4. On the other hand, the exhaust port 6 is connected via an exhaust manifold 13 and an exhaust pipe 14 to a casing 16 containing a NO _X catalyst 15.

In the combustion chamber 3, for example, an electromagnetic fuel injection valve 17 for directly injecting fuel into the combustion chamber 3 is arranged. Each fuel injection valve 17 is connected to a fuel pump (not shown) capable of controlling the discharge amount via a common fuel pressure accumulating chamber 18. The discharge amount of the fuel pump is controlled such that the fuel pressure in the fuel pressure accumulating chamber 18 becomes the target fuel pressure. Electronic control unit (EC
U) 30 is composed of a digital computer, and a ROM (read only memory) 32 and a RAM (random access memory) 3 interconnected via a bidirectional bus 31.
3. CPU (microprocessor) 34, B-RAM (backup RAM) 35 constantly connected to a power source,
An input port 36 and an output port 37 are provided. In the combustion chamber 3, an in-cylinder temperature sensor 38 that generates an output voltage proportional to the temperature in the combustion chamber 3, that is, the in-cylinder temperature TC is arranged. The depression amount sensor 39 generates an output voltage proportional to the depression amount DEP of the accelerator pedal. The output voltages of these sensors 38 and 39 are respectively A
The data is input to the input port 36 via the D converter 40. Further, the input port 36 is connected to a rotation speed sensor 41 that generates an output pulse representing the engine rotation speed N. On the other hand, the output port 37 is connected to each fuel injection valve 7 via the corresponding drive circuit 42.

[0008] NO_XCatalyst 15 is zeolite, ferriera
Ite, mordenite, alumina Al _TwoO_Three, Titania T
iO_TwoPt supported on a porous carrier such as
Such as radium Pd, rhodium Rh, iridium Ir
Precious metals, copper Cu, iron Fe, cobalt Co, nickel N
Transitions such as i, chromium Cr, vanadium V, titanium Ti
It comprises a transfer metal or an oxide of these transition metals. Ze
High silica content such as ZSM-5 type as olilite
Zeolites can be used. This NO_XCatalyst 15
Is, for example, hydrocarbon HC, carbon monoxide CO, ammonia N
H_Three, Hydrogen H_TwoIn an oxygen atmosphere containing a reducing agent such as
NO_XSelectively reacts with the reducing agent, thereby
NO_XTo nitrogen N_TwoCan be reduced to That is,
NO_XIn the catalyst 15, the exhaust gas flowing in contains the reducing agent
NO in the inflowing exhaust gas even in an oxygen atmosphere
_XTo reduce.

[0009] Always in order to reduce smoke and particulates exhausted from the engine is a diesel engine of FIG. 1, the oxygen excess combustion has been performed, thus flowing to the NO _X catalyst 15 exhaust is typically maintained in an oxygen atmosphere Have been. In this case, unburned HC or CO discharged from the engine acts as a reducing agent, and as a result, NO _X is reduced in the NO _X catalyst 15. However, compared to the unburned HC amount discharged from the diesel engine, N
O _X amount overwhelmingly, i.e. reducing agents for favorably purify NO _X becomes insufficient. Therefore, in the present embodiment, in the engine expansion stroke or the exhaust stroke subsequent to the main fuel injection performed around the compression top dead center, the second fuel injection from the fuel injection valve 17, that is, the secondary fuel injection is performed to discharge the secondary fuel. and then supplied to the NO _X catalyst 15 as a reducing agent. The secondary fuel hardly contributes to the engine output.

[0010] Figure 2 is a cylinder temperature TC at the time when the secondary fuel injection is performed, HC in the exhaust gas flowing to the NO _X catalyst 15
It is an experimental result showing the relationship between the component concentration CHC and the NO _X purification rate PENO _X. As can be seen from FIG. 2, the HC component concentration CHC and the NO _X purification rate PENO _X are different from the in-cylinder temperature TC.
Becomes lower when the in-cylinder temperature TC increases. This is believed to be due to the following reasons. That is, the amount and extent of the reforming or cracking of the reforming or cracking caused to be secondary fuel is low in the cylinder as the cylinder temperature TC becomes lower, thus NO _X HC effective light for the reduction is decreased . The cylinder temperature T
As C becomes higher, the amount of secondary fuel that is completely burned in the cylinder increases, and thus, also in this case, the amount of light HC decreases.

Referring still to FIG. 2, the HC component concentration C
HC becomes maximum when the in-cylinder temperature TC is TOPT, and at this time, the NO _X purification rate PENO _X also becomes maximum. Therefore,
This TOP is referred to as an optimum in-cylinder temperature.
NO if secondary fuel injection is performed when is at the optimal temperature TOPT
_{The X} catalyst 15 can satisfactorily purify NO _X. Note that when the in-cylinder temperature TC is the optimum temperature TOPT, 2
Doing next fuel injection, the proportion of light components of HC flowing into the NO _X catalyst 15 (for example _of C ₁₀ or less) has also confirmed that high.

The optimum in-cylinder temperature TOPT is determined by the engine operating state.
It is determined according to. In the present embodiment, the optimum in-cylinder temperature TOPT
Is determined in advance by experiments, and
The relation between the depression amount DEP of the cell pedal and the engine speed N
The form of the map shown in FIG.
Is remembered. Therefore, in this embodiment, NO_Xcatalyst
Optimizing the quantity and quality of secondary fuel supplied to 15
Can be. That is, NO_XLight to be supplied to the catalyst 15
Increasing components and reducing soluble organic components (SOF)
can do. As a result, NO _XIn catalyst 15
NO_XCan be satisfactorily purified, and NO_XTouch
It is possible to prevent the medium 15 from being poisoned by SOF.
You.

FIG. 4 shows a routine for calculating the secondary fuel injection timing SFIT according to this embodiment. This routine is executed by interruption every predetermined set crank angle. Referring to FIG. 4, first, step 60 is executed.
Then, the basic secondary fuel injection timing ITB is calculated. The basic secondary fuel injection timing ITB is a secondary fuel injection timing corresponding to a crank angle at which the in-cylinder temperature TC becomes the optimum in-cylinder temperature TOPT, and is obtained in advance by an experiment. The basic secondary fuel injection timing ITB is stored in the ROM 32 in advance in the form of a map shown in FIG. In the following step 61, the optimum in-cylinder temperature TOPT is calculated from the map of FIG. In the following step 62, the actual in-cylinder temperature TC is read. Next step 63
Then, the temperature difference DIF, which is the difference (TC-TOPT) between the actual in-cylinder temperature TC and the optimum in-cylinder temperature TOPT, is calculated.
In the following step 64, a correction coefficient ITK is calculated. This correction coefficient ITK is for maintaining the in-cylinder temperature TC at the secondary fuel injection timing at the optimum in-cylinder temperature TOPT. As shown in FIG. 6, when DIF> 0, IT
K> 0, that is, the secondary fuel injection timing SFIT is advanced. When DIF = 0, ITK = 0, and when DIF <0, ITK <0, that is, the secondary fuel injection timing SFIT is retarded. . The correction coefficient ITK is stored in advance in the ROM 32 in the form of a map shown in FIG.
Is stored within. In the following step 65, the secondary fuel injection timing SFIT is calculated based on the following equation.

SFIT = ITB + ITK In the above embodiment, the in-cylinder temperature sensor 38 is arranged in the combustion chamber 3 so as to directly detect the in-cylinder temperature TC. However, for example, an in-cylinder pressure sensor for detecting an in-cylinder pressure in the combustion chamber 3 or an exhaust temperature sensor for detecting the temperature of exhaust gas in an engine exhaust passage is provided. Can be detected indirectly. Further, a needle lift sensor for detecting a lift amount of the needle of the fuel injection valve 17 is attached to the fuel injection valve 17 to detect an actual secondary fuel injection timing,
The fuel injection valve can be controlled so that the actual secondary fuel injection timing coincides with the calculated secondary fuel injection timing SFIT.

[0015]

The secondary fuel optimal amount and components for of the NO _X reduction according to the present invention can be supplied to the NO _X catalyst.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a cylinder temperature TC at the time when secondary fuel injection is performed.
If, HC component concentration CHC in the exhaust gas flowing to the NO _X catalyst
FIG. 7 is a diagram showing the relationship between the NOx conversion rate and the NO _X purification rate PENO _X.

FIG. 3 is a diagram showing an optimum in-cylinder temperature TOPT.

FIG. 4 is a flowchart showing a routine for calculating a secondary fuel injection timing SFIT.

FIG. 5 is a diagram showing basic secondary fuel injection timing.

FIG. 6 is a diagram showing a correction coefficient ITK.

[Explanation of symbols]

1 ... engine body 3 ... combustion chamber 13 ... Temperature sensor exhaust manifold 15 ... NO _X catalyst 17 ... fuel injection valves 38 in the cylinder

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) F02D 41/04 335 F02D 41/04 335A F term (Reference) 3G091 AA18 AB05 BA14 CB02 CB03 EA01 EA07 EA15 GB01W GB05W GB06W GB07W GB09X GB10X 3G301 HA02 JA25 MA14 MA19 MA26 PC05Z PE01Z PF03Z

Claims (1)

[Claims] 1. A possible reduction of NO _X in an oxidizing atmosphere NO _X
Placing the catalyst into the engine exhaust passage, a secondary fuel by performing secondary fuel injection for the second time from the fuel injection valve disposed in the cylinder in a subsequent engine expansion stroke or exhaust stroke in the main fuel injection in the NO _X catalyst In the exhaust gas purifying apparatus for an internal combustion engine, the in-cylinder temperature is determined, and based on the in-cylinder temperature,
An exhaust gas purification device for an internal combustion engine, which determines the next fuel injection timing.