JP3340051B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly, to a fuel injection valve which includes a nitrogen oxide adsorbent in an exhaust system of the internal combustion engine and injects fuel into a combustion chamber of the internal combustion engine. The present invention relates to a fuel injection control device for an internal combustion engine that controls the amount of fuel supplied to a direct injection type internal combustion engine having the same.

[0002]

2. Description of the Related Art When the air-fuel ratio of exhaust gas is lean, nitrogen oxides (hereinafter referred to as NOx) are absorbed, and when the air-fuel ratio of exhaust gas is enriched to lower the oxygen concentration in the exhaust gas, the absorbed NOx is reduced. A NOx absorbent that emits NOx is disposed in the exhaust passage of the diesel engine. Normally, NOx discharged from the diesel engine is absorbed by the NOx absorbent, and when NOx is to be released from the NOx absorbent, the NOx absorbent is located upstream of the NOx absorbent. A method in which a liquid reducing agent is supplied into the exhaust passage to reduce the concentration of oxygen in the exhaust gas flowing into the NOx absorbent, thereby releasing NOx from the NOx absorbent and reducing the released NOx by the reducing agent (rich method). -Spike control is known (International Publication No. WO93 / 07)
363).

Further, as an improvement of the above technology, NOx is absorbed when the air-fuel ratio of the exhaust gas is lean, and the absorbed NOx is reduced when the air-fuel ratio in the exhaust gas is enriched to lower the oxygen concentration in the exhaust gas. The NOx absorbent to be released is arranged in the exhaust passage of the diesel engine, and the main injection is usually performed in the combustion chamber near the compression top dead center, and the NOx
When Ox is to be released, fuel is injected again (sub-injection) as a NOx reducing agent into the combustion chamber in the explosion stroke or exhaust stroke after completion of the main injection, thereby increasing the reactivity of the reducing agent with respect to NOx and thereby reducing NOx from the NOx absorbent. There is known a method of satisfactorily releasing NOx and satisfactorily reducing the released NOx (JP-A-6-212961).

[0004]

However, in the latter conventional method, when the NOx is released from the NOx absorbent, the main injection is performed to perform normal combustion, and then the fuel is used as the NOx reducing agent. Is sub-injected, thereby reducing the effect of improving fuel economy, which is the greatest advantage of directly injecting fuel into the combustion chamber.

[0005] Further, the sub-injection is performed in the expansion stroke or the exhaust stroke in which the gas temperature in the combustion chamber is high after the fuel which has been injected in the intake stroke or the compression stroke is burned. Burning in or NOx absorbents,
The degree of air-fuel ratio enrichment of the exhaust gas is reduced, and
NOx saturated in the NOx absorbent cannot be reduced efficiently.

An object of the present invention is to provide a fuel injection control device for an internal combustion engine that can improve fuel efficiency and can efficiently reduce NOx without burning fuel as a reducing agent.

[0007]

According to a first aspect of the present invention, there is provided a fuel injection control apparatus for an internal combustion engine, which is provided in an exhaust system of the internal combustion engine and includes a nitrogen oxide in an exhaust gas of the internal combustion engine. A nitrogen oxide adsorbent for adsorbing fuel and a fuel injection valve for injecting fuel into a combustion chamber of the internal combustion engine, wherein the nitrogen oxide adsorbent
For determining whether or not nitrogen oxides are saturated in a room
Nitrogen oxidation adsorbed on said nitrogen oxide adsorbent
When the object is saturated, the intake stroke or compression of the internal combustion engine
Without performing fuel injection in stroke, the internal combustion engine of the nitrogen oxides adsorbed exhaust line as in controlling the fuel injection timing of the fuel injection valve to inject Oite fuel into the nitrogen oxide adsorbent A fuel injection timing control means for reducing the fuel.

According to the fuel injection control device for an internal combustion engine of the first aspect, the nitrogen oxides adsorbed by the nitrogen oxide adsorbent become saturated.
When the sum is to reduce the nitrogen oxides adsorbed onto the nitrogen oxide adsorbing agent, a fuel injection valve for injecting fuel into the combustion chamber only in the exhaust stroke of the internal combustion engine. That is, at this time, no fuel is injected into the combustion chamber during the intake stroke or the compression stroke of the internal combustion engine. Therefore, the fuel is injected into the combustion chamber in the exhaust stroke at a low gas temperature in the combustion chamber, so that the injected fuel is not burned in the exhaust system or the nitrogen oxide adsorbent and the exhaust gas is discharged. The air-fuel ratio can be made sufficiently rich, so that the nitrogen oxides adsorbed by the nitrogen oxide adsorbent can be efficiently reduced. Further, in addition to not injecting fuel into the combustion chamber during the intake stroke or the compression stroke of the internal combustion engine, fuel efficiency can be improved by the above-described enrichment effect.

A fuel injection control device for an internal combustion engine according to claim 2 is the fuel injection control device for an internal combustion engine according to claim 1 , wherein
Before SL fuel injection timing control means, when the nitrogen oxide adsorbed to the nitrogen oxide adsorbent is not saturated, line injection of fuel in the intake stroke or compression stroke of the internal combustion engine
And controlling the fuel injection timing of Uyo urchin the fuel injection valve.

[0010]

According to a third aspect of the present invention, in the fuel injection control device for an internal combustion engine according to the first or second aspect, the internal combustion engine is a gasoline engine.

According to the fuel injection control device for an internal combustion engine of the third aspect, it is possible to efficiently reduce the nitrogen oxides adsorbed on the nitrogen oxide adsorbent provided in the exhaust system of the gasoline engine.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fuel injection control device for an internal combustion engine according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a fuel injection control device according to an embodiment of the present invention and an internal combustion engine (hereinafter referred to as “engine”) to which the device is applied. In the figure,
Reference numeral 1 denotes an internal combustion engine, which is a DOHC in-line four-cylinder gasoline engine in which each cylinder is provided with a pair of an intake valve and an exhaust valve (not shown).

The intake pipe 2 of the engine 1 is connected to a combustion chamber 25 of each cylinder of the engine 1 through a branch portion (intake manifold) 11.
Communicate with A throttle valve 3 is provided in the intake pipe 2. The throttle valve 3 has a throttle valve opening (θT
H) The sensor 4 is connected, and the throttle valve opening θT
An electric signal corresponding to H is output and supplied to an electronic control unit (hereinafter referred to as “ECU”) 5.

An intake air temperature (TA) sensor 8 is mounted on the intake pipe 2 upstream of the throttle valve 3, and a detection signal is supplied to the ECU 5. An expanded chamber 9 is provided between the throttle valve 3 of the intake pipe 2 and the intake manifold 11, and the chamber 9 has an intake pipe absolute pressure (PB
A) The sensor 10 is attached. PBA sensor 1
The detection signal of 0 is supplied to the ECU 5.

The main body of the engine 1 has an engine water temperature (T
W) The sensor 13 is mounted, and the detection signal is EC
It is supplied to U5. The ECU 5 is connected to a crank angle position sensor 14 that detects a rotation angle of a crankshaft (not shown) of the engine 1, and supplies a signal corresponding to the rotation angle of the crankshaft to the ECU 5. The crank angle position sensor 14 outputs a signal pulse (hereinafter referred to as a “CYL signal pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1, and a top dead center (TDC) at the start of an intake stroke of each cylinder. ) At a crank angle position before a predetermined crank angle (in the case of a four-cylinder engine, the crank angle is 18).
A TDC sensor that outputs a TDC signal pulse and a pulse (hereinafter referred to as a “CRK signal pulse”) at a constant crank angle cycle (for example, a 30-degree cycle) shorter than the TDC signal pulse
), And a CYL signal pulse, a TDC signal pulse, and a CRK signal pulse
It is supplied to U5. These signal pulses are used for various timing controls such as fuel injection timing, ignition timing, and the like, and detection of the engine speed NE.

The fuel injection valve 12 is provided in the combustion chamber 25 of each cylinder, and injects fuel into the combustion chamber 25 of each cylinder. Each fuel injection valve 12 is connected to a fuel distribution pipe 27 via a corresponding fuel supply conduit 26, and the fuel distribution pipe 27 is connected to a fuel tank 41 via a fuel supply pump 28. Further, each fuel injection valve 12 is electrically connected to the ECU 5, and a signal from the ECU 5 controls a fuel injection timing and a fuel injection time (valve opening time). An ignition plug (not shown) of the engine 1 is also electrically connected to the ECU 5, and the ECU 5 controls the ignition timing θIG. In the present embodiment, the ECU 5 constitutes fuel injection timing control means and saturation determination means.

The exhaust pipe 16 has a branch portion (exhaust manifold) 1
5 is connected to each combustion chamber 25 of the engine 1. A wide area air-fuel ratio sensor (hereinafter, referred to as a “LAF sensor”) 17 is provided in the exhaust pipe 16 immediately downstream of a portion where the branch portions 15 are gathered. Further, the LAF of the exhaust pipe 16
A three-way catalyst 19 directly below and a three-way catalyst 20 below the floor are disposed downstream of the sensor 17, and an oxygen concentration sensor (hereinafter referred to as an “O2 sensor”) 18 is provided between these three-way catalysts 19 and 20. It is installed. The three-way catalysts 19 and 20 are
It purifies HC, CO, NOx, etc. in exhaust gas. An exhaust gas temperature (TG) sensor 35 is attached to the exhaust pipe 16 downstream of the three-way catalyst 20, and a detection signal is supplied to the ECU 5.

The three-way catalyst 19 has a nitrogen oxide (NOx) adsorption catalyst (hereinafter referred to as a "NOx adsorption catalyst") as a nitrogen oxide adsorbent. Hereinafter, the NOx adsorption catalyst will be described.

The NOx adsorption catalyst uses, for example, alumina as a carrier, and, for example, potassium K, sodium Na,
At least one selected from an alkali metal such as lithium Li and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, a rare earth such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt are supported. ing. When the air-fuel ratio in the exhaust gas is lean and the oxygen concentration in the exhaust gas is high, the NOx adsorption catalyst absorbs NOx, and releases the absorbed NOx when the air-fuel ratio is rich and the oxygen concentration in the exhaust gas decreases. NOx is absorbed and released.

In the above NOx adsorbing catalyst, NOx in which at least one selected from alkali metals, alkaline earths, and rare earths and a noble metal are supported on alumina as the adsorbing catalyst.
An adsorption catalyst is used. However, instead of using such a NOx adsorption catalyst, a composite oxide of alkaline earth and copper, that is, a Ba-Cu-O-based NOx adsorption catalyst can also be used. As such a complex oxide of alkaline earth and copper, for example, MnO ₂ .BaCuO ₂ can be used, and in this case, platinum Pt or cerium Ce can also be added.

In this MnO ₂ .BaCuO ₂ NOx adsorbing catalyst, copper Cu has the same catalytic effect as platinum Pt of the NOx adsorbing catalyst described above. When the air-fuel ratio is lean, NOx is oxidized by copper Cu. (2NO + O ₂ → 2
NO ₂ ) nitrate ions are diffused into the NOx adsorption catalyst in the form of NO ₃ ⁻ .

On the other hand, if the air-fuel ratio is made rich, NO
NOx is released from the x adsorption catalyst, and this NOx is
Is reduced by the catalytic action of However,
The NOx reducing power of copper Cu is weaker than the NOx reducing power of platinum Pt. Therefore, when a Ba—Ca—O-based adsorption catalyst is used, NOx that is not reduced when NOx is released is lower than that of the NOx adsorption catalyst described above. The amount increases slightly. The increased NOx is processed by the three-way catalyst 20.

Returning to FIG. 1, the LAF sensor 17 is connected to the ECU 5 via a low-pass filter 22, outputs an electric signal substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas, and outputs the electric signal. Supply to ECU5. The output of the O2 sensor 18 has a characteristic that the output sharply changes before and after the stoichiometric air-fuel ratio, and the output becomes high level on the rich side and low level on the lean side from the stoichiometric air-fuel ratio. O2
The sensor 18 is connected to the ECU 5 via a low-pass filter 23.
The detection signal is supplied to the ECU 5.

An exhaust gas recirculation mechanism 30 for recirculating a part of the exhaust gas to the intake pipe is provided. The mechanism 30 includes an exhaust gas recirculation path 31 connecting the chamber 9 of the intake pipe 2 and the exhaust pipe 16, and an exhaust gas recirculation path. An exhaust gas recirculation valve (EGR valve) 32 is provided in the middle of 31 and controls an exhaust gas recirculation amount, and a lift sensor 33 that detects a valve opening of the EGR valve 32 and supplies a detection signal to the ECU 5. The EGR valve 32 is an electromagnetic valve having a solenoid, and the solenoid is connected to the ECU 5,
The valve opening is configured to be linearly changed by a control signal from the ECU 5.

An atmospheric pressure (PA) sensor 21 for detecting the atmospheric pressure is connected to the ECU 5, and a detection signal is supplied to the ECU 5.

The ECU 5 has an input circuit having a function of shaping input signal waveforms from the above-described various sensors, correcting a voltage level to a predetermined level, and changing an analog signal value to a digital signal value, and a central processing circuit. (CPU), a storage circuit including a ROM and a RAM for storing various arithmetic programs executed by the CPU, various maps and arithmetic results described later, and drive signals to various solenoid valves such as the fuel injection valve 12 and the ignition plug. And an output circuit for outputting the same.

The ECU 5 determines various engine operating states such as a feedback control operating area and an open loop control operating area according to the outputs of the LAF sensor 17 and the O2 sensor 18 based on the various engine operating parameter signals described above. The fuel injection time TOUT of the fuel injection valve 12 is calculated by the following equation according to the engine operating state, and a signal for driving the fuel injection valve 12 is output based on the calculation result.

TOUT (N) = TIMF × KTOTAL
× KCMDM × KLAF Here, N represents a cylinder number, and a parameter with this is calculated for each cylinder. In the present embodiment, the fuel supply amount to the engine is calculated as the fuel injection time,
Since this corresponds to the amount of fuel to be injected, TOUT is also called a fuel injection amount or a fuel amount.

The TIMF is a basic fuel amount corresponding to the intake air amount. The basic fuel amount TIMF is basically set according to the engine speed NE and the absolute pressure PBA in the intake pipe. It is desirable to model the intake system from the valve 3 to the combustion chamber of the engine 1 and make corrections based on the intake system model taking into account the delay of the intake air. In that case, the throttle opening θTH and the atmospheric pressure PA are further used as detection parameters.

KTOTAL is an engine water temperature correction coefficient KTW set according to the engine water temperature TW, and an EGR correction coefficient K set according to the exhaust gas recirculation amount during execution of the exhaust gas recirculation.
This is a correction coefficient calculated by multiplying all feedforward correction coefficients such as EGR.

KCMDM is a final target air-fuel ratio coefficient calculated by performing fuel cooling correction according to a target air-fuel ratio coefficient KCMD value determined according to the engine speed NE, the intake pipe absolute pressure PBA, and the like. The target air-fuel ratio coefficient KCMD is
Proportional to the reciprocal of the air-fuel ratio A / F, that is, the fuel-air ratio F / A,
Since the value is 1.0 at the stoichiometric air-fuel ratio, it is also called a target equivalent ratio. KLAF is an air-fuel ratio correction coefficient calculated according to a deviation between the detected equivalent ratio KACT as an output of the LAF sensor 17 and the target equivalent ratio KCMD.

In the present embodiment, the functions such as the calculation of the fuel injection time TOUT (N) described above are realized by arithmetic processing by the CPU of the ECU 5. Therefore, the contents of the processing will be concretely described with reference to the flowchart of this processing. Will be explained.

FIG. 2 shows a program of a fuel injection process of the fuel injection valve. This process is executed in synchronization with each generation of the TDC signal pulse.

First, in step S1, the fuel injection time TOUT (N) of the fuel injection valve 12 is calculated by the above equation.
The target air-fuel ratio coefficient KCMD and the air-fuel ratio correction coefficient KLAF in the above equation are calculated by the processing of FIG.

Next, in step S2, it is determined whether or not a NOx release flag FREL indicating "1" to release saturated NOx in the NOx adsorption catalyst in the three-way catalyst 19 is "1". This flag FREL is set in the processing of FIG. 4 described later.

If the answer to the determination in step S2 is negative (NO), and NOx is not saturated in the NOx adsorbing catalyst in the three-way catalyst 19, it is not necessary to release NOx in the catalyst. Proceeding to step S3, a normal fuel injection process described later is performed, while the answer to the determination in step S2 is affirmative (YE
S), the NOx adsorbing catalyst in the three-way catalyst 19
If Ox is saturated and it is necessary to release NOx in the catalyst, the process proceeds to step S4, and a rich spike fuel injection process described later is performed.

FIG. 3 shows a program for calculating the target air-fuel ratio coefficient KCMD and the air-fuel ratio correction coefficient KLAF. This processing is executed in synchronization with the processing of FIG.

First, in a step S11, it is determined whether or not the engine 1 is in a start mode, and the answer is affirmative (YE
In the case of S), the KLAF value is set to 1.0 (step S16), and this processing ends. If the answer to step S11 is negative (NO), that is, if the engine 1 is not in the start mode, a KCMD calculation process is executed (step S1).
2) It is determined whether or not the LAF sensor 12 is in an active state (a state where oxygen concentration can be detected) (step S1).
3). If the answer is negative (NO), the step S
Proceeding to 16, when affirmative (YES), an equivalent ratio KACT representing the detected air-fuel ratio is calculated based on the output of the LAF sensor 12 (step S14), and the target equivalent ratio KCMD and the detected equivalent ratio KACT are calculated. The air-fuel ratio correction coefficient KLAF is calculated so as to match (step S1).
5), end this processing.

According to the processing of FIG. 3, when the engine 1 is not in the start mode and the LAF sensor 12 is in the active state,
The KLAF value is calculated such that the detected equivalent ratio KACT matches the target equivalent ratio KCMD.

FIG. 4 shows a program for determining the NOx release flag FREL used in step S2 of FIG. 2, and this processing is executed in synchronization with the processing of FIG.

First, at step S20, the LAF sensor 17
It is determined whether or not the detected equivalence ratio KACT as the output of is smaller than 1.0, that is, whether or not the air-fuel ratio is lean. In step S20, when KACT ≧ 1.0, that is, when the air-fuel ratio is rich, the process proceeds to step S21, and the down-count timer tmREL started in step S24 described later.
It is determined whether or not the value of 1 is “0”. At first tmR
Since EL1> 0, step S22 is skipped and the down count timer tmREL2 is set to the predetermined time TMRE.
L2 (for example, 5 seconds) is set and started (step S23), and this processing is ended.

In step S21, tmREL1 = 0
Then, the process proceeds to step S22, where the integrated engine speed ΣNE is reset to zero. As a result, when the state where the detected equivalent ratio KACT is equal to or greater than 1.0 and the air-fuel ratio is rich has continued for the predetermined time tmREL1 (YES in step S21), the integrated engine speed ΣNE is reset to 0 (step S22). The process proceeds to step S23.

In step S20, KACT <1.0
In other words, when the air-fuel ratio is lean, a predetermined time TMREL1 (for example, 10 seconds) is set in the down-count timer tmREL1 and started (step S).
24) Then, the accumulated engine speed up to the previous timeΣNE
Is added to the current engine speed NE to calculate a current integrated engine speed ΣNE (step S25). Next, at step S26, the current integrated engine speed ΣN
It is determined whether E is larger than a predetermined value SNE. The predetermined value SNE indicates the integrated engine speed at which the NOx adsorbing catalyst has absorbed the NOx amount of, for example, 80% of the NOx adsorbing ability, that is, it is estimated that the NOx adsorbing catalyst is substantially saturated. Step S26 corresponds to saturation determination means.

In the discrimination in step S26, initially, ΣN
Since E ≦ SNE, step S23 is executed to end this processing. On the other hand, when ΣNE> SNE, ie, N
If it is estimated that the NOx amount of 80% of the NOx adsorption capacity is adsorbed on the Ox adsorption catalyst, step S2
Proceeding to 7, it is determined whether or not the exhaust gas temperature TG detected by the TG sensor 35 is lower than a predetermined value TG0, for example, 200 ° C. If TG <TG0 in step S27, the processing in step S23 is executed to end this processing, while TG ≧ TG0.
If TG0, the NOx release flag FREL is set to "1" (step S28).

Next, it is determined whether or not the value of the timer tmREL2 started in step S23 is "0" (step S29). At first, since tmREL2> 0, steps S30 and S31 are skipped and the present process is terminated. On the other hand, when tmREL2 = 0, the NOx release flag FREL is set to “0” (step S30).
The accumulated engine speed ΣS is reset to 0 (step S31), and the process ends.

According to the processing of FIG. 4, KACT <1.0,
Σ When NE> SNE and TG ≧ TG0, the NOx release flag FREL is set to “1”, and thereafter, for a predetermined time (t
After mREL2), the NOx release flag is reset to “0”.

The normal fuel injection processing in step S3 in FIG. 2 is performed as follows.

FIG. 5 is an explanatory diagram for explaining the fuel injection timing in the normal fuel injection processing.

FIG. 5 shows one cycle consisting of the intake, compression, expansion and exhaust strokes of the engine 1. The intake valve starts to open just before TDC at the start of the intake stroke and closes immediately after bottom dead center (BDC) at the end of the intake stroke. The exhaust valve starts to open just before BDC at the end of the expansion stroke and closes immediately after TDC at the start of the intake stroke. The opening timings of the intake valve and the exhaust valve overlap before and after TDC at the start of the intake stroke.

In the fuel injection of the fuel injection valve 12 into the combustion chamber 25, first, the intake stroke injection is performed in the first half of the intake stroke, and then the compression stroke injection is performed in the second half of the compression stroke. The fuel injection time TOUT of the fuel injection valve 12
The fuel injection time TOUT (N) of the fuel injection valve 12 calculated by the calculation formula (N) corresponds to the sum of the intake stroke injection and the compression stroke injection. After the fuel is injected into the combustion chamber 25, the air-fuel mixture in the combustion chamber 25 is ignited by the operation of the ignition plug, and the process proceeds to the expansion stroke. In FIG. 5, no fuel injection is performed in a region Z that extends over the expansion stroke and the exhaust stroke after the completion of the compression stroke injection.

The fuel injection process for rich spikes in step S4 in FIG. 2 is performed as follows.

FIG. 6 is an explanatory diagram for explaining the fuel injection timing in the rich spike fuel injection process.
This rich spike fuel injection process is executed at the time of NOx release and reduction from the NOx adsorption catalyst (step S4 in FIG. 2).

FIG. 6 shows one cycle consisting of the intake, compression, expansion, and exhaust strokes of the engine 1. The opening and closing timings of the intake valve and the exhaust valve are the same as in the case of FIG.

The intake stroke injection in the intake stroke and the compression stroke injection in the compression stroke performed in the normal fuel injection processing in step S3 in FIG. 2 are not performed in the fuel injection processing for the rich spike. However, as shown in FIG. 6, the fuel valve 1 is located at a later stage of the zone Z that extends over the expansion stroke and the exhaust stroke after the completion of the compression stroke injection, that is, at the center of the exhaust stroke.
2, the exhaust stroke injection is performed.

As described above, in the present embodiment, N
At the time of NOx release reduction from the Ox adsorption catalyst, the intake stroke injection in the intake stroke and the compression stroke injection in the compression stroke are not executed, and the fuel injection in the zone Z is performed only in the exhaust stroke as the exhaust stroke injection (FIG. 6).

According to the fuel injection process for rich spikes, when the NOx adsorbed by the NOx adsorbing catalyst is reduced, the combustion chamber 25 is reduced only during the exhaust stroke of the engine 1.
At this time, no fuel is injected into the combustion chamber 25 during the intake stroke or the compression stroke of the engine 1. Therefore, the fuel is injected into the combustion chamber 25 in the exhaust stroke in a state where the gas temperature in the combustion chamber 25 is low, so that the injected fuel does not burn in the exhaust system or the NOx adsorption catalyst, and the exhaust gas does not burn. The air-fuel ratio of the gas can be made sufficiently rich, so that NOx adsorbed on the NOx adsorption catalyst can be efficiently reduced. Further, in addition to not performing injection during the intake stroke or the compression stroke of the engine 1, fuel efficiency can be improved by the above-described enrichment effect.

According to the above-described conventional technique, when the NOx adsorption catalyst is reduced, after performing the intake stroke injection in the intake stroke and the compression stroke injection (main injection) in the compression stroke, the fuel injection (sub-injection) in the expansion stroke in the region Z, for example, is performed. Injection).

FIG. 7 shows a comparison of the fuel efficiency improvement effect between the present invention and the prior art. FIG. 7 shows the release amount (ppm) of NOx when the NOx reduction treatment is performed when the NOx adsorption medium is saturated with NOx.

As can be seen from the figure, in order to obtain the same NOx releasing effect, the method according to the present invention can further improve the fuel efficiency as compared with the method according to the prior art.

In the above embodiment, the fuel injection amount TO
When the UT (N) is small, the excess air ratio can be reduced by closing the throttle valve 3 to a certain opening degree,
With a small exhaust stroke injection amount, the air-fuel ratio of the exhaust gas can be made rich to release NOx from the NOx adsorbent. Similar effects can be obtained even if the exhaust gas is recirculated by the exhaust recirculation mechanism 30.

In the above embodiment, the case where the present invention is applied to the direct injection type gasoline engine has been described, but the present invention may be applied to a direct injection type diesel engine.

[0064]

As described above in detail, according to the fuel injection control apparatus for an internal combustion engine of the first aspect, nitrogen oxide adsorption
When the nitrogen oxides adsorbed on material is saturated, in order to reduce nitrogen oxides adsorbed onto the nitrogen oxide adsorbing agent, injecting the fuel to the fuel injection valve combustion chamber only in the exhaust stroke of the internal combustion engine I do. That is, at this time, no fuel is injected into the combustion chamber during the intake stroke or the compression stroke of the internal combustion engine.
Therefore, since the fuel is injected into the combustion chamber in the exhaust stroke while the gas temperature in the combustion chamber is low, the injected fuel does not burn in the exhaust system or the nitrogen oxide adsorbent, and the exhaust gas Therefore, the air-fuel ratio can be sufficiently enriched, and thus the nitrogen oxides adsorbed by the nitrogen oxide adsorbent can be efficiently reduced. Further, in addition to not injecting fuel into the combustion chamber during the intake stroke or the compression stroke of the internal combustion engine, fuel efficiency can be improved by the above-described enrichment effect.

[0065]

According to the fuel injection control device for an internal combustion engine of the third aspect, it is possible to efficiently reduce the nitrogen oxides adsorbed by the nitrogen oxide adsorbent provided in the exhaust system of the gasoline engine.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a flowchart of a program of a fuel injection process.

FIG. 3 shows a target air-fuel ratio coefficient KCMD and an air-fuel ratio correction coefficient K
It is a flowchart of a program of LAF calculation processing.

FIG. 4 is a flowchart of a program for determining a NOx release flag FREL.

FIG. 5 is an explanatory diagram for explaining a fuel injection timing in a normal fuel injection process.

FIG. 6 is an explanatory diagram for explaining a fuel injection timing in a rich spike fuel injection process.

FIG. 7 is a graph for comparing and explaining the effect of the present invention and the effect of the conventional technique.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 internal combustion engine 2 intake pipe 5 ECU (fuel injection timing control means, saturation determination means) 12 fuel injection valve 16 exhaust pipe 17 wide area air-fuel ratio sensor 18 O2 sensor 19 immediately below three-way catalyst (nitrogen oxide adsorbent) 20 below floor three-way Catalyst 25 Combustion chamber 28 Fuel pump 41 Fuel tank

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 41/02 325 F02D 41/02 325A ZAB ZAB 41/04 335 41/04 335Z 385 385Z ZAB ZAB 41/34 ZAB 41/34 ZABF (58) Fields surveyed (Int.Cl. ⁷ , DB name) F01N 3/08-3/36 F02D 41/02-41/04 F02D 41/34

Claims (3)

(57) [Claims] A nitrogen oxide adsorbent that is provided in an exhaust system of an internal combustion engine and adsorbs nitrogen oxide in exhaust gas of the internal combustion engine; and a fuel injection valve that injects fuel into a combustion chamber of the internal combustion engine. In a fuel injection control device for an internal combustion engine having
Whether nitrogen oxides are saturated in the nitrogen oxide adsorbent
The nitrogen oxide adsorbent, comprising a saturation determination means for determining
When the nitrogen oxides adsorbed on the
Inject fuel during the intake or compression stroke of the Seki
And without the fuel injection timing for reducing nitrogen oxides exhaust line as in controlling the fuel injection timing of the fuel injection valve to inject the Oite fuel adsorbed to the nitrogen oxide adsorbent of the internal combustion engine A fuel injection control device for an internal combustion engine, comprising control means. 2. A pre-Symbol fuel injection timing control means, when the nitrogen oxide adsorbed to the nitrogen oxide adsorbent is not saturated, performs fuel injection in the intake stroke or compression stroke of the internal combustion engine the fuel injection control apparatus for an internal combustion engine according to claim 1, characterized in that to control the fuel injection timing of I urchin the fuel injection valve. 3. The fuel injection control device for an internal combustion engine according to claim 1, wherein the internal combustion engine is a gasoline engine.