JPH0666176A - Method and device for controlling engine and controller - Google Patents

Abstract

PURPOSE:To reduce the detection quantity of NOx by installing a means for distributing the rich mixed gas in the vicinity of a spark plug when the aimed air-fuel ratio is smaller than a specified value, while distributes the lean mixed gas in other parts. CONSTITUTION:At the intake port 4 of an engine 1, a throttle valve 9, surge tank 10, and an air mixture injector 11 for injection-supplying fuel are arranged in succession. Further, one edge of the air mixture injector 11 is connected with the upstream side of the throttle valve 9 through a passage 41 having an air mixing control valve 42. Further, the air mixing control valve 42 is controlled by an engine control unit 30 on the basis of a variety of detection signals supplied from a variety of sensors 20, 25, and 26 for detecting the operation state of the engine 1. In this case, if the aimed air-fuel ratio is smaller than a specified value, the rich mixed air is distributed in the vicinity of a spark plug, while the lean mixed gas is distributed in other parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine control method and control apparatus, and more particularly to an engine control method and control apparatus that reduces the amount of nitrogen oxide emissions.

[0002]

2. Description of the Related Art Conventionally, the concept of stratifying the in-cylinder air-fuel mixture arrangement is widely known depending on the port shape, the location of the injector, the injection direction, the injection timing, and the like. The merit of this technique is to set the air-fuel ratio in the vicinity of the spark plug to a richer than the average of the entire air-fuel mixture, and as shown by 102 in FIG. 7, compared with a general engine shown by 101 in FIG. The combustion area on the lean side can be expanded, that is, the misfire limit can be further increased.

Further, conventionally, as a technology for improving the atomization state of spray, an air mix injector (hereinafter referred to as "AMI")
JP-A-2-2338 regarding the air amount control method.
There is 67. This is intended to improve combustion stability by introducing assist air during lean operation. The merit of this technology is that the stability during lean operation and the improvement of the misfire limit can be improved relatively easily.

[0004]

However, the above conventional example has the following problems as shown in FIG. That is, FIG. 7 is a characteristic diagram showing the emission amount of nitrogen oxide NOx and the fuel consumption rate be with respect to the air-fuel ratio. According to the characteristic curves 101a to 103a of the fuel consumption rate be, stratification 102a and homogenization 10 compared to general combustion 101a.
Combustion 3a has a smaller fuel consumption rate be and better fuel efficiency. However, in the above-described technique for stratifying the in-cylinder air-fuel mixture arrangement, as shown by the stratification characteristic line 102, when an intermediate air-fuel ratio is used, for example, when the air-fuel ratio A / F = 18 to 20, in general, Compared with the characteristic curve 101 due to the combustion of a typical engine, there is a drawback that the nitrogen oxide NOx emission amount increases.

Further, in the above-mentioned atomization state improving technique of the spray, as shown by the characteristic line 103 of uniformized combustion, the improvement of the misfire limit is relatively smaller than that in the case of stratified combustion, and the merit of lean combustion is obtained. There was a drawback that it could not be pulled out sufficiently.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to solve the above problems, and has the following structure as one means for solving the above problems. That is, when the set target air-fuel ratio is smaller than the first predetermined value, the rich air-fuel mixture is distributed in the vicinity of the spark plug, and the lean air-fuel mixture leaner than the rich air-fuel mixture is provided in the combustion chambers other than the vicinity of the spark plug. When the set target air-fuel ratio is larger than the first predetermined value, the engine control method is such that an air-fuel mixture having a substantially uniform air-fuel ratio is present in the entire combustion chamber.

Further, a stratified supply means for distributing a rich air-fuel mixture in the vicinity of the spark plug and a lean air-fuel mixture leaner than the rich air-fuel mixture in the combustion chamber other than the vicinity of the spark plug, and a stratified supply means for the entire combustion chamber. The uniform supply means for allowing the air-fuel mixture having a uniform air-fuel ratio to exist, the target air-fuel ratio setting means for setting the target air-fuel ratio, and the target air-fuel ratio set by the target air-fuel ratio setting means are smaller than the first predetermined value. Control means for selecting the stratified supply means, and for selecting the uniform supply means when the target air-fuel ratio set by the target air-fuel ratio setting means is larger than the first predetermined value. It shall be the engine control device equipped.

[0008]

With the above-described structure, it is possible to provide an engine control method and a control device for reducing the amount of NOx emitted.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An engine control device according to an embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a diagram showing an example of the overall configuration of this embodiment. In FIG. 2, the piston 2 slides in the combustion chamber 3 of the engine body 1,
An intake port 4 and an exhaust port 6 are connected to the combustion chamber 3.

An intake valve 7 is provided between the intake port 4 and the combustion chamber 3, and an exhaust valve 8 is provided between the exhaust port 6 and the combustion chamber 3.
Are arranged respectively. A throttle valve 9 for controlling the intake air amount is provided on the upstream side of the intake port 4, a surge tank 10 as an intake expansion chamber is provided on the downstream side thereof, and an air mix for injecting and supplying fuel further downstream thereof. A chain ejector (hereinafter referred to as “AMI”) 11 is provided.

FIG. 3 is a sectional view of an essential part showing an example of the AMI 11. As shown in FIG. 3, the AMI 11 is connected to air mixture passages 41a and 41b for supplying assist air for atomizing the fuel. The air mixing passages 41a, 41b are connected to the air mixing passage 41 shown in FIG. 2, an air mixing control valve 42 for controlling the opening and closing of the passage 41 is disposed in the middle of the passage 41, and the other end of the passage 41 is The intake port 4 is connected to the upstream side of the throttle valve 9.

Further, in FIG. 2, an air flow sensor (hereinafter referred to as "AFS") 20a provided in an air flow meter (hereinafter referred to as "AFM") 20a detects an intake air amount to the intake port 4 and detects the air amount. The crank angle sensor 25 outputs an engine rotation speed signal, and the O2 sensor 26 disposed in the exhaust port 6 outputs A /
Output F signal.

A catalyst device (not shown) is arranged downstream of the O 2 sensor 26. Further, an engine control unit (hereinafter referred to as “ECU”) 30 receives signals from the above-mentioned sensors and the like, and sends an ignition timing control signal (not shown), AM to a distributor (not shown).
An injection signal for adjusting the fuel injection amount to I11, an air assist signal for controlling the air control valve 42 to supply assist air to the AMI 11, a swirl signal for controlling the opening and closing of the swirl valve 13, which will be described later, etc. are sent out. . The ECU 30 also stores a map described later in a built-in memory (not shown).

FIG. 4 is a conceptual view showing the relationship between intake and exhaust of the combustion chamber 3, and the intake and exhaust valve side of the combustion chamber 3 (hereinafter referred to as "upper surface side").
FIG. In FIG. 4, the intake air guided to the intake port 4 is introduced into the combustion chamber 3 in the intake stroke.
The intake air introduced into the combustion chamber 3 is mixed with fuel by the AMI 11 at a predetermined timing.

A swirl passage 12 is connected to the combustion chamber 3, and a swirl valve 13 for controlling the opening and closing of the passage is arranged in the middle of the swirl passage 12. When the swirl valve 13 is opened during the intake stroke, a swirl indicated by an arrow S is generated in the peripheral portion of the combustion chamber 3. Further, a spark plug 5 electrically connected to a distributor (not shown) is provided at a substantially central portion on the upper surface side of the combustion chamber 3, and the air-fuel mixture compressed in the compression stroke has a predetermined timing. After being ignited by the spark plug 5 and burning, the air in the combustion chamber 3 is guided to the exhaust port 6 and exhausted in the exhaust stroke.

Next, the combustion control in this embodiment will be described in detail. FIG. 5 is a diagram showing a general relationship between the engine air-fuel ratio and the NOx emission amount, and the horizontal axis shows the air-fuel ratio A / F.
And the vertical axis represents the NOx emission amount. In FIG.
A curve A shows the relationship between the air-fuel ratio A / F and the NOx emission amount in the case of uniform combustion in which the air-fuel mixture having a substantially uniform air-fuel ratio A / F is present in the entire combustion chamber 3 and burned. As shown in the figure, in the uniform combustion, there is a peak of NOx emission amount near the air-fuel ratio A / F = 16, and the NOx emission amount before and after that peak is
x Indicates that the emission amount gradually decreases, and the air-fuel ratio A / F = 20-
The lean burn limit of 25 is reached.

Curve B shows the air-fuel ratio A / F and NOx emission in the case of stratified combustion in which the rich mixture is distributed in the vicinity of the spark plug 5 and the lean mixture is distributed in the peripheral portion of the combustion chamber 3. It is a relationship of quantity. As shown in the figure, in the stratified combustion, there is a peak of NOx emission amount on the relatively lean side of the air-fuel ratio A / F = 18 to 20, and the NOx emission amount gradually decreases at the air-fuel ratio A / F before and after that. It has characteristics and has a combustion region in which the air-fuel ratio A / F of the misfire limit in uniform combustion exceeds 20 to 25.

The characteristics shown in FIG. 5 differ depending on the engine type, and when the characteristics are specifically obtained, the target engine is operated and then measured experimentally. In the present embodiment, from the relationship between the air-fuel ratio A / F and the NOx emission amount shown in FIG. 5, in order to keep the NOx emission amount low, the fuel injection timing is set in the latter half of the intake stroke when the air-fuel ratio A / F is on the latch side. Then, the swirl valve 13 is opened to distribute the rich mixture in the vicinity of the spark plug 5 and the lean mixture in the peripheral portion of the combustion chamber 3 to control the engine so that stratified combustion is achieved.

Further, in the present embodiment, in order to keep the NOx emission amount low, on the lean side of the air-fuel ratio C where the curves A and B intersect, the fuel injection timing is set, for example, in the first half of the intake stroke, and the swirl valve 13 is used. Is closed, and the air-mix control valve 42 is opened to supply assist air to the AMI 11, so that the air-fuel mixture having a substantially uniform air-fuel ratio A is present in the entire combustion chamber 3 so that uniform combustion is achieved. To control.

Further, in this embodiment, in order to maintain combustion on the extremely lean side, the engine is controlled so that stratified combustion occurs on the lean side of the misfire limit of uniform combustion. FIG. 6 is a flow chart showing an example of the combustion control procedure of this embodiment, which is executed by the ECU 30 based on the program stored in the memory inside the ECU 30.

In FIG. 6, the ECU 30 has a step S.
1, the engine speed n represented by the engine speed signal from the crank angle sensor 25, the intake air amount Q represented by the air amount signal from the AFS 20a, and the A2 from the O2 sensor 26.
/ Fm corresponding to the air-fuel ratio A / F represented by the / F signal
Read and. Subsequently, the ECU 30 proceeds to step S2,
The filling amount Ce is calculated by the following equation.

Ce = Ka.multidot.Q / n (1) However, Ka: constant Next, in step S3, the ECU 30 determines the engine speed n based on the target injection amount map fbm stored in the internal memory. Then, the target injection amount Tb is obtained from the filling amount Ce.

Subsequently, the ECU 30 proceeds to step S4,
The actual injection amount Tj is obtained from the measured value A / Fm corresponding to the air-fuel ratio A / F by the air-fuel ratio conversion map ft stored in the internal memory. Subsequently, the ECU 30 causes the step S5
Then, the actual injection amount Tj and the target injection amount Tb are compared, and Tj>
If Tb, lean correction is performed in step S6, and if Tj <Tb, rich correction is performed in step S7, and then step S8 is performed. If Tj = Tb, correction is not performed and step S8 is performed. It should be noted that the ECU 30 uses the step S
In 6, the result of subtracting the air-fuel ratio correction width K from the current air-fuel ratio correction value CFB is substituted into CFB, and in step S7, the result of adding the air-fuel ratio correction width K to the current air-fuel ratio correction value CFB is obtained. Substitute in CFB.

Subsequently, the ECU 30 determines the final injection amount T according to the equation (2) at step S8, and then at step S9.
Then, according to the equation (3), the air-fuel ratio A corresponding to the target injection amount Tb
Find / Fb. T = Tb + CFB (2) A / Fb = fAF (Tb) (3) However, fAF: Air-fuel ratio conversion map stored in the internal memory. The air-fuel ratio A / Fb corresponding to Tb is compared with the use range of the assist air, and if the air-fuel ratio A / Fb is within the range of the following equation, the process proceeds to step S11. /
If Fb is present, the process proceeds to step S12.

KAA- <A / Fb <KAA + (4) However, KAA-: Assist air lower limit air-fuel ratio KAA +: Assist air upper limit air-fuel ratio Note that in step S10, KAA- is shown in FIG. Corresponds to the air-fuel ratio C where curves A and B intersect, and also KAA
+ Corresponds to the misfire limit of uniform combustion at the air-fuel ratio of 20 to 25 shown in FIG.

The ECU 30 sets a flag FAA indicating ON / OFF of the assist air to "1" in step S11, sets "0" to FAA in step S12, and then returns to step S1. The ECU 30 sends an injection signal to the AMI 11 according to the injection amount T set by the above-mentioned combustion control procedure, and mixes the fuel according to the injection amount T with the intake air. That is, the ECU 30 controls the injection amount T so that the air-fuel ratio A / F becomes appropriate according to the engine speed n and the filling amount Ce.

Further, the ECU 30 controls the air mix control valve 42 and the swirl valve 13 in accordance with the flag FAA set by the above combustion control procedure, and if FAA = '0', the air assist signal is given. Yotsute air control valve 42
Is closed and the swirl valve 13 is opened by the swirl signal. Further, if FAA = '1', the air mix control valve 42 is opened by the air assist signal and the swirl valve 13 is closed by the swirl signal. That is, the ECU 30
Is FAA = '0', so that stratified combustion is achieved.
If = '1', the engine is controlled so that uniform combustion is achieved.

As described above, according to this embodiment,
Since the engine is controlled so that the air-fuel ratio A / F becomes stratified combustion on the side closer to the predetermined value and the air-fuel ratio A / F becomes uniform combustion on the side leaner than the predetermined value, over a wide range of the air-fuel ratio, Since it is possible to realize combustion control with a small amount of NOx emissions,
It is possible to prevent the catalyst device that purifies exhaust gas from increasing in size, and
The engine is controlled so that stratified charge combustion is performed on the extremely lean side where the air-fuel ratio A / F exceeds the misfire limit for uniform combustion. Therefore, the misfire limit is sufficiently improved and combustion control that brings out the full advantage of lean combustion is realized. it can.

[0029]

As described above, according to the present invention, it is possible to provide a control method and control device for an engine that emits a small amount of NOx, and it is possible to prevent an increase in size of a catalyst device that purifies exhaust gas.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention.

FIG. 2 is a diagram showing a configuration example of the entire combustion control device of one embodiment according to the present invention.

FIG. 3 is a cross-sectional view of essential parts showing an example of an air mix indicator AMI of the present embodiment.

FIG. 4 is a conceptual diagram showing a relationship between intake and exhaust of a combustion chamber of the present embodiment.

FIG. 5 is a diagram showing a general relationship between an engine air-fuel ratio A / F and NOx emission amount.

FIG. 6 is a flow chart showing an example of a combustion control procedure of the present embodiment.

FIG. 7 is a diagram illustrating a problem of conventional combustion control.

[Explanation of symbols]

 1 Engine Body 2 Piston 3 Combustion Chamber 4 Intake Port 5 Spark Plug 6 Exhaust Port 7 Intake Valve 8 Exhaust Valve 9 Slottle Valve 10 Surge Tank 11 Air Mixer Injector AMI 12 Swirl Passage 13 Swirl Valve 15 Crank Angle Sensor 20 Air Flow Meter AFM 20a Air flow sensor AFS 26 O2 sensor 30 Engine control unit ECU 41 Air mix passage 42 Air mix control valve

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F02D 43/00 U 7536-3G F02M 69/00 310 E 7825-3G

Claims (7)

[Claims] 1. When the set target air-fuel ratio is smaller than a first predetermined value, a rich mixture is distributed in the vicinity of the spark plug, and a combustion chamber other than the vicinity of the spark plug is leaner than the rich mixture. A method of controlling an engine, wherein a lean air-fuel mixture is distributed, and when the set target air-fuel ratio is larger than the first predetermined value, an air-fuel mixture having a substantially uniform air-fuel ratio is present in the entire combustion chamber. 2. When the set target air-fuel ratio exceeds a second predetermined value that is larger than the first predetermined value, a rich mixture is distributed in the vicinity of the spark plug, and in the combustion chamber other than the vicinity of the spark plug. The engine control method according to claim 1, wherein the lean air-fuel mixture is distributed leaner than the rich air-fuel mixture. 3. A stratified supply means for distributing a rich air-fuel mixture in the vicinity of the spark plug and a lean air-fuel mixture leaner than the rich air-fuel mixture in a combustion chamber other than the vicinity of the spark plug; A uniform supply means for allowing an air-fuel mixture having a uniform air-fuel ratio to exist, a target air-fuel ratio setting means for setting a target air-fuel ratio, and a target air-fuel ratio set by the target air-fuel ratio setting means is more than a first predetermined value. Control means for selecting the stratified supply means, and for selecting the uniform supply means when the target air-fuel ratio set by the target air-fuel ratio setting means is larger than the first predetermined value. An engine control device characterized by having. 4. The control means selects the stratified supply means when the target air-fuel ratio set by the target air-fuel ratio setting means exceeds a second predetermined value larger than the first predetermined value. The engine control device according to claim 2, wherein the control device is an engine. 5. The uniform supply means is an assist air control means for causing an air-fuel mixture having a substantially uniform air-fuel ratio to exist throughout the combustion chamber by means of assist air supplied in the vicinity of a fuel injection valve injection port. The engine control device according to claim 3. 6. The stratified supply means is a swirl supply means for supplying intake swirl to the peripheral portion of the combustion chamber, and a fuel injection timing control means for supplying fuel in the latter half of the intake stroke. The engine control device according to claim 3 or 4. 7. The engine control device according to claim 3, wherein the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio.