JPH06288283A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To control an injection timing and improve ignition stability so as to suppress an ignition timing when an air-fuel ratio in the vicinity of a sparking plug comes in a rich peak condition. CONSTITUTION:Laser beam having wave length absorbed selectively by gasoline is led in a combustion chamber, and passed into a space in the combustion chamber positioned in the vicinity of a sparking plug. Strength of transmitting beam is detected by a photoelectric transfer element, and an air-fuel ratio at an ignition timing is calculated on the basis of transmitting beam strength and internal cylinder pressure (S3). It is judged whether or not a detected air-fuel ratio is changed in rich direction comparing with a previous time as a result of injection timing control (S4). When rich change of the air-fuel ratio is judged, it is judged whether correction for advancing a previous injection timing is carried out or not (S6). Correction of the injection timing in direction in which rich condition of the air-fuel fuel is obtained is carried out continuously.

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 detecting an air-fuel ratio in the vicinity of a spark plug in a combustion chamber and controlling the injection timing of a fuel injection valve based on the detection result. Regarding the device.

[0002]

2. Description of the Related Art Conventionally, there is known a device for measuring an air-fuel ratio (A / F) of an engine intake air-fuel mixture by detecting combustion light in a combustion chamber. For example, JP-A 1-247
In the air-fuel ratio detection device disclosed in Japanese Patent No. 740, combustion light is taken out by an optical fiber embedded in a spark plug,
The air-fuel ratio is detected by photoelectrically converting the extracted combustion light.

[0003]

By the way, particularly in an engine that burns with a lean air-fuel ratio, the air-fuel ratio near the spark plug is a major factor that determines the ignition limit, so the local air-fuel ratio near the spark plug is detected. Therefore, it is desired to control the air-fuel ratio, and even in the air-fuel ratio detecting device disclosed in the above-mentioned Japanese Patent Laid-Open No. 1-247740, the combustion light is taken out by the optical fiber embedded in the ignition plug, so that the vicinity of the ignition plug is detected. The local air-fuel ratio is detected.

However, the air-fuel ratio in the vicinity of the spark plug is not constant, but is changed by being influenced by the gas flow formed in the combustion chamber, and the ignition timing is reached when the air-fuel ratio falls to the lean side of the air-fuel ratio change, for example. In such a case, ignition may become unstable or misfire may occur. Therefore,
In order to increase the ignition limit, it is necessary to detect the air-fuel ratio immediately before ignition, but conventional local air-fuel ratio detection based on combustion light cannot detect the air-fuel ratio before ignition. There is a problem that it is not possible to perform highly accurate air-fuel ratio control corresponding to the change in air-fuel ratio due to such gas flow, and it is difficult to stably obtain high ignitability.

The present invention has been made in view of the above problems, and detects the local air-fuel ratio in the vicinity of the spark plug before ignition, and based on this, the ignition timing is the timing at which the air-fuel ratio in the vicinity of the spark plug becomes the richest. The present invention aims to improve the ignition performance especially in a lean burn engine by making it possible to meet the above conditions.

[0006]

Therefore, a fuel injection control device for an internal combustion engine according to the present invention is constructed as shown in FIG. In FIG. 1, the transmitted light intensity detecting means faces a combustion chamber in the vicinity of the spark plug, and arranges a pair of optical elements consisting of a light emitting side and a light receiving side so as to face each other with a predetermined gap, and the light emitted from the light source is arranged to It is a means for guiding the photoelectric conversion element through the optical element.

Further, the in-cylinder pressure detecting means detects the in-cylinder pressure of the engine, and the air-fuel ratio calculating means detects the in-cylinder pressure in the in-cylinder pressure detecting means based on the output of the photoelectric conversion element in the transmitted light intensity detecting means. Calculate the air-fuel ratio near the spark plug. Then, the injection timing control means controls the injection timing by the fuel injection valve in a direction in which the air-fuel ratio near the spark plug at the ignition timing becomes thicker based on the air-fuel ratio calculated by the air-fuel ratio calculation means.

[0008]

According to this structure, in the transmitted light intensity detecting means, the light emitted from the light source is guided to the photoelectric conversion element through the gap between the pair of optical elements facing the combustion chamber near the ignition plug. As it passes through the gap near the plug, it will be damped by the fuel present in such space.

The attenuation changes depending on the fuel concentration, and the fact that it changes depending on the fuel concentration also changes depending on the pressure in the combustion chamber (cylinder pressure). Therefore, based on the output of the photoelectric conversion element on which the transmitted light passing through the gap is incident and the in-cylinder pressure detected by the in-cylinder pressure detecting means, the factor of the in-cylinder pressure is excluded and the fuel concentration (air-fuel ratio near the spark plug is eliminated. ) Can be detected.

Here, the air-fuel ratio detection is performed through the absorption of light by the fuel existing near the spark plug in the combustion chamber, and the air-fuel ratio near the spark plug before ignition can be detected. . Therefore, based on the detection result of the air-fuel ratio, the injection timing is advanced / retarded so that the ignition timing comes when the air-fuel ratio which is influenced by the gas flow and fluctuates has a rich peak.

[0011]

EXAMPLES Examples of the present invention will be described below. In FIG. 2 showing the system configuration of the present embodiment, a fuel injection valve 3 is provided in an intake port 2 of an internal combustion engine 1, and the fuel injection is performed on the air sucked through an air cleaner and a throttle valve (not shown). Fuel is intermittently injected and supplied from the valve 3 to form an air-fuel mixture. The fuel injection valve 3 is an electromagnetic fuel injection valve that is driven to open in response to an injection pulse signal output from a control unit 13 having a microcomputer, which will be described later.

The air-fuel mixture is sucked into the combustion chamber 5 through the intake valve 4 and is ignited and burned by spark ignition by the spark plug 6. Exhaust gas from the engine 1 is discharged into the atmosphere via an exhaust valve, a catalyst, and a muffler (not shown). Here, an in-cylinder pressure sensor (in-cylinder pressure detecting means) 7 that detects the pressure (in-cylinder pressure) in the combustion chamber 5 is provided.

Further, the spark plug 6 is integrally provided with a pair of optical elements 9 and 10 for guiding the light beam into the combustion chamber 5 and taking out the light beam passing through the space of the combustion chamber 5 to the outside. ing. As shown in FIGS. 3 and 4, the optical elements 9 and 10 provided integrally with the spark plug 6 emit the laser light emitted from the external laser source (light source) 8 to the combustion chamber at the tip of the spark plug 6. 5 to a position facing the inside of the combustion chamber 5, and the optical surface 9a provided at the tip facing the inside of the combustion chamber 5 causes the other optical element 10
An optical element 9 on the light emitting side for reflecting the laser beam toward
The laser light reflected by the optical surface 9a at the tip of the optical element 9 is arranged to face the optical element 9 with a predetermined gap therebetween, and the incident light is reflected toward the base end side of the spark plug 6. An optical element 10 on the light-receiving side is provided with an optical surface 10a for allowing the optical surface 10a to face the inside of the combustion chamber 5 and guides the laser light reflected by the optical surface 10a to the outside.

That is, the tip of each of the pair of optical elements 9 and 10 faces the inside of the combustion chamber 5, and the tips are arranged so as to face each other with a predetermined gap, and the optical surfaces provided at the tips. The laser light emitted from the laser source 8 is transmitted to the gap space (the space inside the combustion chamber) between the optical elements 9 and 10 by 9a and 10a, and then the transmitted light is extracted to the outside.

The laser light extracted from the inside of the combustion chamber 5 through the optical element 10 is incident on the photoelectric conversion element 11, and the photoelectric conversion element 11 detects the transmitted light intensity of the laser light. Has become. Here, the optical elements 9 and 10 are arranged so as to face each other with the center electrode 6a of the spark plug 6 as the center, and with this configuration, the gap between the pair of optical elements 9 and 10 is the center electrode of the spark plug 6. It crosses the spark gap sandwiched between 6a and the ground electrode 6b. Therefore, the laser light passing through the combustion chamber space from the optical element 9 toward the optical element 10 travels across the spark gap.

In FIG. 2, reference numeral 12 denotes the laser light emitted from the laser source 8 which is reflected by the optical element 9 side, and the laser light extracted through the optical element 10 is converted into a photoelectric conversion element 11.
The laser source 8, the optical elements 9 and 10, the optical component 12, and the photoelectric conversion element 11 constitute an transmitted light intensity detecting means of this embodiment.

Quartz, sapphire or the like can be used as the material of the optical elements 9 and 10, but sapphire is preferably used in consideration of heat resistance and pressure resistance. Furthermore, the combustion chamber 5 determined by the arrangement of the optical elements 9 and 10
It is preferable that the laser light transmission space inside the spark plug be near the spark gap of the spark plug 6, but the optical path of the laser light is not limited to the arrangement of the optical elements that cross the spark gap.
Alternatively, the optical elements 9 and 10 may be provided separately from the spark plug 6.

As the light beam emitted by the laser source 8, a laser beam having a wavelength which is selectively absorbed by the gasoline fuel used is used. Specifically, it is infrared light, and in this embodiment, laser light having a wavelength of 3.39 μm included in the infrared light region is used. The gasoline fuel used in the engine 1 generally has a property of selectively absorbing infrared light, and in the air-fuel mixture, the absorption amount increases substantially in proportion to the gasoline concentration in the air-fuel mixture. That is, when the incident light intensity is I _O , the gasoline concentration is C, and the absorption coefficient is K, the absorption amount I of infrared light by gasoline can be expressed as I = I _O exp ^-KC .

Therefore, if it is possible to irradiate the air-fuel mixture with infrared light of a predetermined intensity and detect how much the infrared light is absorbed by the gasoline, the concentration of gasoline in the air-fuel mixture, in other words, the air-fuel ratio of the air-fuel mixture, can be detected. The fuel ratio can be detected. Here, in this embodiment, the pair of optical elements 9 and 10 are arranged so as to face each other with a space in the combustion chamber 5 as a gap, and the laser light passes through the gap and finally enters the photoelectric conversion element 11. Since the laser light travels across the spark gap of the spark plug 6, the laser light is absorbed by an amount commensurate with the gasoline concentration in the air-fuel mixture existing in the spark gap and is attenuated by the absorption. The laser light will enter the photoelectric conversion element 11.

Further, the fact that the absorption amount of laser light (infrared light) is proportional to the gasoline concentration means that the absorption amount also changes depending on the change in pressure (cylinder pressure) in the combustion chamber. Therefore, the calibration characteristic based on the in-cylinder pressure is measured in advance (see FIG. 5), and the calculation characteristic of the air-fuel ratio using the output of the photoelectric conversion element 11 and the in-cylinder pressure detected by the in-cylinder pressure sensor 7 as parameters ( By setting the conversion map) in advance, the air-fuel ratio around the spark gap of the spark plug 6 can be calculated from the intake stroke when the mixture is sucked to the ignition timing (see FIG. 6).

The control unit 13 inputs the output signal of the photoelectric conversion element 11 and the detection signal of the in-cylinder pressure sensor 7, and calculates the air-fuel ratio around the spark gap of the spark plug 6 according to the characteristics shown in FIG. The injection timing of the fuel injection valve 3 is controlled based on the calculation result. That is, the air-fuel ratio in the vicinity of the spark plug at the ignition timing determines the ignition limit, which is an important factor especially in a lean burn engine in which the ignitability deteriorates, but it is affected by the gas flow in the combustion chamber 5. The air-fuel ratio near the spark plug is not constant and fluctuates. Here, at the ignition timing at the rich peak of the air-fuel ratio fluctuation, a high ignition performance can be obtained even if the average air-fuel ratio is a lean air-fuel ratio, but conversely, at the lean peak, the ignition is performed. When the time comes, ignition may become unstable and misfire may occur.

On the other hand, the phase of the fluctuation of the air-fuel ratio changes with the change of the injection timing by the fuel injection valve 3 (FIG. 6).
(See), the advance / retard control of the injection timing is performed based on the air-fuel ratio in the vicinity of the spark plug 6 before ignition, which is calculated using the output of the photoelectric conversion element 11 and the in-cylinder pressure detection value. It becomes possible to control the injection timing so that the ignition timing is reached at the peak.

The advance / retard control of the injection timing by the control unit 13 will be described with reference to the flowchart of FIG. In the present embodiment, the functions of the air-fuel ratio calculation means and the injection timing control means are provided by the control unit 13 as software, as shown in the flowchart of FIG. In the flowchart of FIG. 7, first, in S1, the basic injection timing (injection start crank angle or injection end crank angle) preset according to the operating conditions is read from the map.

Then, in S2, fuel injection is performed in accordance with the basic injection timing, and in the next S3, the air-fuel ratio at the ignition timing of the air-fuel mixture formed by the fuel injection is converted into the photoelectric conversion element as described above. Calculation is performed based on the transmitted light intensity detected at 11 and the in-cylinder pressure detected by the in-cylinder pressure sensor 7 (see FIG. 5). At S4, the air-fuel ratio in the vicinity of the spark plug 6 at the ignition timing calculated at S3 is compared with the air-fuel ratio at the previous ignition timing, and the air-fuel ratio at the ignition timing is changing in the rich direction compared to the previous time. Determine whether or not.

When the fuel is injected for the first time from S3 to S4, that is, when the injection is performed at the basic injection timing, for example, it is determined that the rich change has been made at S4, and the advance timing control of the injection timing is described for the time being. To do. When the air-fuel ratio at the ignition timing is changing in the rich direction, the routine proceeds to S5, where the air-fuel ratio calculated at this ignition timing is stored as the previous air-fuel ratio.

Next, in S6, it is determined whether or not the injection timing was advanced by the previous injection timing correction. Here, when it is determined that the air-fuel ratio of the ignition timing has changed to the rich direction as a result of advancing the injection timing, the air-fuel ratio of the ignition timing may change to the rich side by further advancing the injection timing. There is, so proceed to S7,
The injection timing is advanced to advance the injection timing by a predetermined minute angle (for example, 1 ° CA). Then, in S8, the history of the correction for advancing the injection timing is stored.

On the other hand, when it is determined in S4 that the air-fuel ratio at the ignition timing has not changed in the rich direction as compared with the previous time, the process proceeds to S9, and it is determined whether or not the previous correction of advancing the injection timing has been performed. As a result of advancing the injection timing, if the air-fuel ratio does not change in the rich direction,
Proceeding to S10, on the contrary, the injection timing is corrected by delaying it by a predetermined minute angle (for example, 1 ° CA), and in S11, the history of the correction of delaying the injection timing is stored.

When it is determined in S9 that the change in the air-fuel ratio in the rich direction has disappeared as a result of delaying the injection timing, conversely, in order to advance the injection timing, S
Proceed to 7. That is, for example, when the air-fuel ratio near the spark plug at the ignition timing changes in the rich direction by advancing the injection timing, the injection timing is gradually advanced until the change in the rich direction stops and When the change is stopped, the injection timing is controlled so that it is delayed in the opposite direction, so that the vicinity of the rich peak of the air-fuel ratio fluctuation coincides with the ignition timing (see FIG. 6).

Here, the transmitted light intensity detected by the photoelectric conversion element 11 having the above-described structure is determined by the pair of optical elements 9 and 10.
Since it is affected only by the air-fuel ratio state in the gap of 1, the local air-fuel ratio in the vicinity of the spark plug 6 can be detected with high accuracy without being affected by the air-fuel ratio in other combustion chamber regions before ignition. Then, based on the detection result of the air-fuel ratio, so that the ignition timing is reached at the rich peak timing of the air-fuel ratio that changes before ignition due to the influence of gas flow, the injection timing is controlled, especially in a lean burn engine, High ignitability can always be obtained without being affected by operating conditions and engine variations.

When the advance / retard correction of the injection timing converges as described above, the injection timing at that time may be learned and stored for each operating condition. Also,
A range in which the injection timing can be changed with respect to the basic injection timing is set in advance, and if the controllable range is exceeded, the injection timing is controlled to reach the ignition timing at the richest air-fuel ratio within the controllable range. It is good to

Further, the angle at which the injection timing is changed stepwise may be a fixed value, or may be changed according to the change width of the air-fuel ratio accompanying the injection timing control.

[0032]

As described above, according to the present invention, the air-fuel ratio in the vicinity of the spark plug before ignition is detected, and the injection timing by the fuel injection valve is controlled based on the detection result, so that the fluctuation of the air-fuel ratio can be reduced. Fuel injection can be performed so that the ignition timing can be reached at the rich peak timing,
As a result, there is an effect that high ignition stability can always be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a system schematic diagram showing an embodiment of the present invention.

FIG. 3 is an enlarged side view of the spark plug tip portion according to the embodiment.

FIG. 4 is an enlarged bottom view of a spark plug tip portion according to the embodiment.

FIG. 5 is a diagram showing an air-fuel ratio corresponding to transmitted light intensity and in-cylinder pressure.

FIG. 6 is a diagram showing how the air-fuel ratio changes before ignition.

FIG. 7 is a flowchart showing injection timing control in the embodiment.

[Explanation of symbols]

 1 Internal Combustion Engine 2 Intake Port 3 Fuel Injection Valve 4 Intake Valve 5 Combustion Chamber 6 Spark Plug 6a Center Electrode 6b Ground Electrode 7 Cylinder Pressure Sensor 8 Laser Source 9, 10 Optical Element 11 Photoelectric Conversion Element 13 Control Unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F02D 45/00 368 S 7536-3G G01N 21/59 Z 7370-2J

Claims (1)

[Claims] 1. A pair of optical elements consisting of a light emitting side and a light receiving side are arranged facing each other with a predetermined gap so as to face a combustion chamber near the spark plug, and light emitted from a light source is photoelectrically transmitted through the pair of optical elements. Transmitted light intensity detection means for guiding to the conversion element, in-cylinder pressure detection means for detecting in-cylinder pressure of the engine, output of the photoelectric conversion element in the transmitted light intensity detection means, and in-cylinder pressure detected by the in-cylinder pressure detection means Air-fuel ratio calculating means for calculating the air-fuel ratio near the spark plug based on the above, and a fuel injection valve for increasing the air-fuel ratio near the spark plug at the ignition timing based on the air-fuel ratio calculated by the air-fuel ratio calculating means. And a fuel injection control device for an internal combustion engine, comprising: