JP2932887B2 - Air-fuel ratio detection 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 an air-fuel ratio detecting device for an internal combustion engine, and more particularly, to a device capable of directly detecting an air-fuel ratio of an engine intake air-fuel mixture from an air-fuel mixture in a combustion chamber.

[0002]

2. Description of the Related Art Conventionally, there has been known an apparatus 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 extracted by an optical fiber embedded in an ignition plug,
The air-fuel ratio is detected by photoelectrically converting the taken out combustion light.

[0003]

By the way, in the air-fuel ratio detecting device disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 1-247740, as shown in FIG. In addition to the light emission in the area A close to the end face of the optical fiber, all the light emission in the area B relatively far from the end face is extracted.

[0004] Here, the air-fuel ratio may differ between the A region and the B region depending on the gas flow in the combustion chamber. If the air-fuel ratio differs, the flame emission spectrum differs. If the distance from the end face of the optical fiber is different, the intensity changes in inverse proportion to the square of the distance. Therefore, in the configuration in which the combustion light is extracted by the optical fiber, the air-fuel ratio is different, and the light emission in the regions at different distances is mixed and extracted. For example, the air in the A region near the ignition plug, which is the determinant of the ignition limit, is extracted. Even if it is desired to obtain the fuel ratio accurately, there is a fundamental problem that the air-fuel ratio cannot be detected with high accuracy due to the influence of light emission in the B region.

[0005] For this reason, conventionally, it is assumed that the air-fuel ratio is constant in the hollow cone region, or the measurement hollow hollow region is narrowed in the distance direction by shortening the time for taking in the flame emission, so that the combustion light is extracted. It realizes air-fuel ratio detection. However, as described above, the air-fuel ratio in the hollow cone region is not always constant, and if the intake time is shortened, the intensity of the extracted light decreases, resulting in a problem that the measurement accuracy decreases. .

The air-fuel ratio in the vicinity of the spark plug, which is a factor that determines the ignition limit, exhibits a time-series variation strongly depending on the fuel spray particle size and the injection timing. Therefore, in order to control the air-fuel ratio near the spark plug at the ignition timing to improve the ignitability, it is desirable to detect the air-fuel ratio near the spark plug before ignition, but the air-fuel ratio detection based on the combustion light is desired. Cannot detect the air-fuel ratio before ignition,
There is a problem that the air-fuel ratio in the vicinity of the ignition plug at the ignition timing cannot be accurately controlled.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is possible to detect an air-fuel ratio in the vicinity of a spark plug before ignition. It is an object to provide a detection device.

[0008]

An apparatus for detecting the air-fuel ratio of an internal combustion engine according to the present invention is configured as shown in FIG. In FIG. 1, a transmitted light intensity detecting means includes a pair of optical elements each including a light emitting side and a light receiving side facing a combustion chamber of an internal combustion engine and facing each other with a predetermined gap therebetween, and transmits light emitted from a light source to the pair of optical elements. This is a means for guiding to the photoelectric conversion element via the element.

The in-cylinder pressure detecting means detects an in-cylinder pressure of the engine, and the air-fuel ratio calculating means includes an output of the photoelectric conversion element in the transmitted light intensity detecting means and an in-cylinder pressure detected by the in-cylinder pressure detecting means. The air-fuel ratio of the engine intake air-fuel mixture is calculated based on the above. Further, the heating means includes the transmitted light intensity detecting means.
Heating the pair of optical elements in a stage. Here, the pair of optical elements in the transmitted light intensity detection means,
It is preferable to provide the spark plug integrally with the ignition plug of the engine.

[0010] Also, may the cause the heating means selectively operated configure settings <br/> Ke heating control hand stage by operating conditions according to institutional operating conditions. Further, in place of the heating control means based on the operating conditions, a fuel adhesion detecting means for detecting the adhesion state of the fuel to the pair of optical elements in the transmitted light intensity detection means, and the fuel adhesion state is detected by the fuel adhesion detection means. And a heating control unit based on adhesion detection for operating the heating unit when detected.

[0011]

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.
As it passes through the gap, it will be attenuated by the fuel present in such space. The attenuation changes depending on the fuel concentration, and the change depending on the fuel concentration also changes depending on the pressure in the combustion chamber (cylinder pressure). Therefore, the fuel concentration (air-fuel ratio) can be detected based on the output of the photoelectric conversion element on which the transmitted light passing through the gap enters and the in-cylinder pressure detected by the in-cylinder pressure detecting means, excluding the factor of the in-cylinder pressure. I did it. Also, the pair
When the liquid fuel adheres to the optical element, the adhered fuel causes
Light is absorbed and the air-fuel ratio of the mixture
Since the detection cannot be performed well, the pair of optical
A heating means for heating the element is provided.
Fuel can be vaporized early.

In the detection of the air-fuel ratio in the combustion chamber, the air-fuel ratio in the vicinity of the ignition plug particularly greatly affects the ignition limit. Can accurately detect the air-fuel ratio of
Also, the configuration of parts can be simplified. In a further, when the engine operating condition before Symbol fuel adhesion is expected, or, by detecting the fuel adhesion state, by operating the heating means, it is possible to accurately vaporize the fuel adhering to the optical element I made it possible.

[0013]

Embodiments 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 at an intake port 2 of an internal combustion engine 1, and the fuel injection valve 3 is provided for 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.

Then, the air-fuel mixture is sucked into the combustion chamber 5 through the intake valve 4 and 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 (not shown), a catalyst, and a muffler. Here, an in-cylinder pressure sensor (in-cylinder pressure detecting means) 7 for detecting the pressure (in-cylinder pressure) in the combustion chamber 5 is provided, and the ignition plug 6 passes through a cylinder head 8 constituting the combustion chamber 5. A cylindrical optical element 9 constituting an air-fuel ratio detecting device (transmitted light intensity detecting means) is inserted and held in a mounting hole provided in the vicinity.

As shown in FIGS. 3 (a), 3 (b) and 3 (c), a pair of optical elements (triangular prisms) 10 and 10 are provided at the end of the cylindrical optical element 9 facing the combustion chamber 5. 11 are provided integrally. The pair of optical elements 10 and 11 are formed at their distal ends with a light beam that enters from the base end face side of the optical element 9 serving as a base and travels in the combustion chamber 5 along the axial direction of the optical element 9. The optical element 10 on the light emitting side that reflects the light toward the other optical element 11 by the optical surface, and is disposed opposite to the optical element 10 via a predetermined gap, and the light beam reflected by the optical element 10 is reflected by the optical element 10. An optical element 11 on the light receiving side that reflects light toward the optical element 9 by an optical surface formed at the tip.

That is, the light beam travels in a U-turn through the combustion chamber 5 by the pair of optical elements 10 and 11, and the light beam is transmitted from the optical element 10 to the optical element 11. When proceeding toward, the gap between the two,
When the air-fuel mixture passes through the space in the combustion chamber and the air-fuel mixture exists in the combustion chamber 5 from the suction stroke to the ignition, the light beam is transmitted through the optical elements 10 and 11 into the air-fuel mixture. become.

As a material for the optical elements 9, 10, and 11, quartz, sapphire, or the like is used, but sapphire is preferably used in consideration of heat resistance and pressure resistance. Also,
The optical elements 9, 10, and 11 do not need to be formed as a single unit. If the optical surface needs to be polished, the polished surface can be easily polished by, for example, following a divided surface shown by a dotted line in FIG. Alternatively, they may be joined after polishing.

As the light beam, light having a wavelength selectively absorbed by gasoline fuel to be used is used. Specifically, the light is infrared light. In this embodiment, a laser light having a wavelength of 3.39 μm included in the infrared light region is used. A laser beam emitted from a laser source (light source) 12 that emits the laser light is applied to an optical element 13 such as a mirror or a prism.
Is bent in a direction parallel to the axis of the optical element 9,
The light enters at right angles to the base end face of the optical element 9 and proceeds. Then, the light beam is U-turned by the pair of optical elements 10 and 11, passes through the optical element 9 again, and is emitted at a right angle from the base end face. The laser beam emitted from the optical element 9 is bent toward the photoelectric conversion element 14 by the optical element 13 and enters the photoelectric conversion element 14.

In FIG. 2, reference numeral 15 denotes the optical element 9
It is a holder for holding the. The laser light source 12, the optical elements 9, 10, 11, 13 and the photoelectric conversion element 14 constitute the transmitted light intensity detecting means of this embodiment. An output of the photoelectric conversion element 14 and a detection signal from the in-cylinder pressure sensor 7 are input to a control unit 15 having a microcomputer for controlling fuel injection by the fuel injection valve 3. Control unit as air-fuel ratio calculation means
15 detects the air-fuel ratio of the engine intake air-fuel mixture based on these detection signals, and controls the fuel injection based on the detected air-fuel ratio.

Here, the principle of air-fuel ratio detection in this embodiment will be briefly described. The gasoline fuel used for the engine 1 generally has a property of selectively absorbing infrared light,
In the air-fuel mixture, the absorption amount increases substantially in proportion to the gasoline concentration in the air-fuel mixture. That is, the incident light intensity is I
^Assuming that _{O 2} , gasoline concentration is C, and absorption coefficient is K, the absorption amount I can be expressed as I = I _O exp ^−KC .

Therefore, if the mixture is irradiated with infrared light of a predetermined intensity and it is possible to detect how much the infrared light is absorbed by the gasoline, the gasoline concentration in the mixture, in other words, the air of the mixture is empty. The fuel ratio can be detected. Here, in the present embodiment, the pair of optical elements 10 and 11 are opposed to each other with a space in the combustion chamber 5 as a gap, and the laser beam passes through the gap and finally enters the photoelectric conversion element 14. With this configuration, the laser light is absorbed by an amount corresponding to the gasoline concentration in the gas mixture present in the gap, and the laser light attenuated by the absorption enters the photoelectric conversion element 14.

Further, the fact that the absorption amount of the laser light (infrared light) is proportional to the gasoline concentration means that the absorption amount also changes due to a change in the pressure (in-cylinder pressure) in the combustion chamber. Therefore, the calibration characteristics based on the in-cylinder pressure are measured in advance (see FIG. 4), and the calculation characteristics of the air-fuel ratio using the output of the photoelectric conversion element 14 and the in-cylinder pressure detected by the in-cylinder pressure sensor 7 as parameters (see FIG. 4). By setting the conversion map) in the control unit 15 in advance, the combustion chamber 5 can be moved from the intake stroke in which the air-fuel mixture is sucked to the ignition timing.
It is possible to calculate a local air-fuel ratio within the unit (see FIG. 5).

The air-fuel ratio (local air-fuel ratio near the ignition plug 6) detected as described above is used as control information for injection control (injection amount control, injection timing control) by the control unit 15. The air-fuel ratio in the vicinity of the ignition plug at the ignition timing determines the ignition limit, and is an important factor particularly in a lean-burn engine in which the ignitability deteriorates. If the air-fuel ratio can be detected, it is possible to control the air-fuel ratio in the vicinity of the ignition plug with high accuracy and to stably obtain good ignitability.

Further, the transmitted light intensity detected by the photoelectric conversion element 14 is affected only by the air-fuel ratio state in the gap between the pair of optical elements 10 and 11, so that the local air-fuel ratio is changed to other areas in the combustion chamber. And can be detected with high accuracy without being affected by the air-fuel ratio. As the fuel injection control using the detection result of the air-fuel ratio, the injection amount is feedback-controlled so that the detected air-fuel ratio matches the target air-fuel ratio, or the rich peak timing of the air-fuel ratio fluctuation overlaps with the ignition timing. By controlling the injection timing by the injection valve as described above, the air-fuel ratio near the ignition plug can be controlled to a desired state. The injection control will be described later in detail.

By the way, when the optical elements 10 and 11 for guiding the laser beam are arranged facing the combustion chamber 5 as described above, dirt accompanying the combustion adheres to the optical elements 10 and 11 and this dirt is removed. May attenuate the laser light, making it impossible to accurately detect the absorption of the laser light (infrared light) by the gasoline fuel. As a method of correcting the influence of such contamination, as shown in FIG. 6, when there is almost no fuel in the combustion chamber 5 immediately before the intake valve is opened during the exhaust stroke, that is, immediately before the air-fuel mixture is sucked. taking the output a ₁ of the photoelectric conversion element 14. Then, the output A ₁ as a reference intensity for normalization, the output Bn of the photoelectric conversion element 14 in the air-fuel ratio operation period (e.g., the ignition timing before the predetermined section) in the subsequent intake stroke, divided by the reference intensity A ₁ a value Bn / a ₁ was the final detection value.

According to the above method, the reference intensity A ₁ is
It is detected under the condition that there is almost no fuel in the gap between the pair of optical elements 10 and 11, and changes mainly due to the contamination of the optical elements 10 and 11 (including a decrease in output intensity due to deterioration of the laser source). It is estimated to be. Then, if lowering said reference intensity A ₁ by the progress of the soiling, it will be more increased corrects the output Bn of the photoelectric conversion element 14, becomes possible to compensate for the attenuation amount of the laser beam due to contamination.

However, according to the above-described correction method, although the correction calculation can be performed relatively easily, the detection of dirt cannot be performed at the same time as the air-fuel ratio calculation. Since the transmitted light intensity for calculating the fuel ratio is detected, there is a possibility that a deviation may occur with respect to the contamination state at the time of calculating the air-fuel ratio, and that there is no fuel in the gap between the pair of optical elements 10 and 11. , The contamination level is estimated, so that highly accurate correction cannot be expected.

As another method of correcting the influence of the dirt, a light source that emits light having a wavelength that is not absorbed by gasoline but absorbed only by the dirt and attenuated is provided, and a light beam emitted from the light source is It passes through the optical elements 10 and 11 coaxially with the light of the wavelength absorbed by the gasoline used for the air-fuel ratio detection, and absorbs only by the dirt as well as the transmitted light intensity Bn of the wavelength light absorbed by the gasoline as shown in FIG. Is detected by the transmitted light intensity An of the light having the wavelength to be absorbed, and the transmitted light intensity Bn is corrected by the transmitted light intensity An of the light absorbed only by the dirt (Bn / An). There is a method of correcting the attenuation due to light contamination in the region.

According to this correction method, the contamination state at that time can be estimated in synchronization with the calculation of the air-fuel ratio, and the contamination detection can be performed without being affected by the fuel present in the pair of optical elements 10 and 11. Since it can be performed, the calculation load is increased, but highly accurate dirt correction can be performed. Here, the function of the control unit 15 for detecting the air-fuel ratio (gasoline concentration) while performing the above-described correction for dirt will be described with reference to FIG.
This will be described according to the flowchart of FIG. The flowchart of FIG. 8 is simplified and shown as being common to the above two correction methods.

In the flowchart of FIG. 8, first, at S1, the correction light intensity An indicating the attenuation level of the laser light due to dirt is detected. Specifically, the output of the photoelectric conversion element 14 is taken in at a timing immediately before the intake valve opens, or the transmission intensity of light of a wavelength that is not absorbed by gasoline but absorbed only by dirt during the calculation period of the air-fuel ratio. Are sequentially taken.

In the next step S2, the transmitted light intensity Bn for calculating the air-fuel ratio is detected. Then, in S3, the transmitted light intensity Bn for the actual measurement of the air-fuel ratio is divided by the light intensity An for correcting the dirt, and the calculation result is set to I as the light intensity corrected for the dirt. In S4, the gasoline concentration C (air-fuel ratio) is calculated based on the light intensity I subjected to the dirt correction and the in-cylinder pressure detected by the in-cylinder pressure sensor 7.

In S5, n indicating the data number of the air-fuel ratio calculated within the air-fuel ratio calculation period is increased by one, and the next S
At 6, it is determined whether or not the air-fuel ratio is within the actual measurement period (for example, a predetermined section before the ignition timing). If it is not in the actual measurement section, the data number is reset in S7. If it is in the actual measurement section, the flow returns to S1 without performing the reset, and repeats the air-fuel ratio calculation while performing dirt correction. Store in chronological order.

The transmitted light intensity A which is affected by the dirt
When n decreases below a predetermined value, it is determined that it is impossible to detect the desired transmitted light intensity, and it is preferable to shift to the predetermined fail-safe mode. By the way, in the above embodiment, the optical element 9 (air-fuel ratio detector) including the pair of optical elements 10 and 11 is arranged near the ignition plug 6. In order to increase the ignition limit by controlling the fuel ratio, it is desirable to detect the air-fuel ratio at a position as close as possible to the spark plug 6 (electrode portion), and also to reduce the number of parts, assemble, and configure the combustion chamber. In consideration of the space efficiency of the cylinder head, it is preferable that the ignition plug 6 and the pair of optical elements 10 and 11 be provided integrally.

Here, an embodiment in which the pair of optical elements 10 and 11 are provided integrally with the ignition plug 6 will be described with reference to FIGS. 9 to 11, a holder 21 is mounted on a cylinder head by a mounting screw 22. The holder 21 has a terminal 23a and a center shaft 23.
b, spark plug body 23 composed of center electrode 23c and ground electrode 23d
Are held offset from the axis of the holder 21.

The holder 21 includes the ignition plug main body.
A pair of optical elements according to the above-described embodiment is provided in an empty space generated by offsetting and holding 23.
Two cylindrical sapphire rods 24 and 25 corresponding to 10 and 11
Are fixedly penetrated in the axial direction of the holder 21 in parallel at a predetermined interval. The two sapphire rods 24, 25
As shown in FIG. 12, the distal end of each has an optical surface cut at 45 °, and by passing these optical surfaces relative to each other, as in the above-described embodiment, it has passed through one sapphire rod 24. The laser light from the laser source is reflected by the 45 ° optical surface, emitted to the space in the combustion chamber 5, and then enters the other sapphire rod 25.

The laser light incident on the sapphire rod 25 is reflected by the 45 ° optical surface toward the base end of the sapphire rod 25 and proceeds. The laser light extracted through the sapphire rod 25 is guided to the photoelectric conversion element 14. I'm going to be. Here, when the laser light travels through the space from the sapphire rod 24 to the time when the laser light is incident on the sapphire rod 25 side, the laser light, which is infrared light, is absorbed by gasoline existing in the space, and the photoelectric conversion is performed. The degree of absorption, that is, the gasoline concentration, is detected based on the intensity of the laser beam incident on the element 14.

Since the optical surfaces of the sapphire rods 24 and 25 on which the laser light is reflected or transmitted need to be sufficiently polished, for example, the sapphire rods 24 and 25 are separated by a surface shown by a dotted line in FIG. It is good to make it a component structure and to integrate it by welding etc. after polishing. Further, as for the diameters and positions of the sapphire rods 24 and 25, the values of D ₁ , D ₂ and θ shown in FIG. 11 may be increased as long as the diameter of the mounting screw 22 of the holder 21 permits. This is because the larger the rod diameter, the easier it is to process and assemble, so the reflective surface can be enlarged, and by increasing the distance between the rods, the difference in gasoline concentration can be clearly detected as a difference in laser beam attenuation level. You can do it.

In the configuration shown in FIGS. 9 to 11, the two sapphire rods 24 and 25 are formed to have the same diameter from the base end side to the distal end side having the reflection surface, and are fixed to the holder 21. However, the present invention is not limited to such an attachment method. For example, as shown in FIG.
An enlarged flange 26 is provided at an intermediate portion between the sapphire rods 24 and 25 of the holder 21 while the flange portion 26 is provided at an intermediate portion between the sapphire rods 24 and 25.
A step 21b corresponding to the flange 26 is provided. A gasket 27 is sandwiched between both end surfaces of the flange portion 26, and the pressing member 28
Sapphire rod 24,
A configuration may be adopted in which the holder 25 is held by the holder 21 while ensuring sealing performance.

When it is desired to increase the area of the 45 ° optical surface provided on the distal end side of the sapphire rods 24, 25, the sapphire rods 24, 25 may be formed in a prism instead of a cylinder. Further, the sapphire rods 24 and 25 need to face each other with a predetermined gap on the distal end side, but do not need to be separated on the proximal end side. For example, they are integrated as shown in FIG. May be.

In FIG. 14, sapphire rods 24, 25
The sapphire plate-like connecting member 29 is welded so as to be sandwiched between the sapphire rods 24 and 25 so that its cross section is formed in a semicircular shape and its flat side faces are opposed to each other. According to such a configuration, it is not necessary to adjust the optical axes of the sapphire rods 24 and 25 when attaching the sapphire rods 24 and 25 to the holder 21, and the assembly is facilitated. Further, if the base end surface 29a of the plate-shaped connecting member 29 is configured to be brought into contact with and adhered to the processing surface of the holder 21, the end surface 29a functions as a stopper and the sapphire rods 24, 25 are actuated by the pressure of the combustion chamber. Can be prevented from being pushed into the proximal end side.

Further, the light-collecting efficiency may be improved by forming the end faces on the base end side of the sapphire rods 24 and 25 (the input / output faces of the laser beam) in a convex lens shape. Further, in the above embodiment, the optical path of the laser beam moving between the rods on the tip side of the sapphire rods 24 and 25 passes through the vicinity of the spark gap of the ignition plug. In order to detect the affecting air-fuel ratio with high accuracy, it is preferable that the optical path crosses the spark gap so that the local air-fuel ratio near the spark gap can be detected.

FIGS. 15 and 16 show sapphire rods 24 and 25, respectively.
Are integrally provided so as to protrude toward the tip of the ignition plug with the center electrode 23c of the ignition plug interposed therebetween. The laser light reflected by the 45 ° optical surface on the tip side of the sapphire rod 24 is applied to the center electrode 23c. The light enters the sapphire rod 25 through a spark gap between the sapphire rod 25 and the ground electrode 23d. According to this configuration, the air-fuel ratio that affects the ignitability of the ignition plug can be detected more accurately, and highly accurate air-fuel ratio control can be performed without being affected by the air-fuel ratio variation in the combustion chamber 5.

The optical elements 10 and 11 (sapphire rod 2)
The configuration in which (4, 25) is provided integrally with the ignition plug 6 is not limited to the above. However, when the local air-fuel ratio in the combustion chamber 5 is detected, the air-fuel ratio in the spark gap portion of the ignition plug 6 is detected, and the fuel injection is controlled based on the detection result to obtain the desired air-fuel ratio. Figure is desired
As shown in FIGS. 15 and 16, it is preferable to dispose optical elements 10 and 11 on both sides of the spark gap of the ignition plug 6 so that the optical path in the combustion chamber 5 crosses the spark gap.

Next, the state of the air-fuel ratio feedback control and the injection timing control by the control unit 15 using the air-fuel ratio detected by the configuration shown in the above embodiment will be specifically described with reference to the flowchart of FIG. In the flowchart of FIG. 17, first, at S11,
The engine speed Ne is calculated based on a detection signal from a crank angle sensor (not shown). In S12, the throttle valve opening detected by a throttle sensor (not shown) is read as a representative value of the engine load.

Then, in S13, as shown in FIG. 18, the target air-fuel ratio AFR is set by referring to a map in which the target air-fuel ratio is set in advance for each operating region according to the engine load and the engine speed. The map storing the target air-fuel ratio AFR shown in FIG. 18 includes a lean region in which the target air-fuel ratio is set significantly leaner than the stoichiometric air-fuel ratio, a stoichiometric air-fuel ratio region in which the stoichiometric air-fuel ratio is set as the target air-fuel ratio, and a stoichiometric air-fuel ratio region. It is broadly divided into a rich region where a target air-fuel ratio which is slightly richer than the air-fuel ratio is set.

In the next step S14, it is determined whether or not the current operating condition is in a lean region in which an air-fuel ratio significantly leaner than the stoichiometric air-fuel ratio is set as the target air-fuel ratio AFR. Here, when it is determined that the region is the lean region,
Proceeding to S15, in a predetermined section before the ignition timing, from the data in which the air-fuel ratio calculated based on the output of the photoelectric conversion element 14 and the output of the in-cylinder pressure sensor 7 is stored in time series as described above. Then, the minimum air-fuel ratio PAFM (the richest air-fuel ratio in the air-fuel ratio calculation section) at the air-fuel ratio fluctuating in the predetermined section is determined (see FIG. 19).

At S16, the target lean air-fuel ratio AFR is compared with the minimum air-fuel ratio PAFM to determine whether the minimum air-fuel ratio PAFM with respect to the target air-fuel ratio is rich or lean. Here, the minimum air-fuel ratio PA is smaller than the target lean air-fuel ratio.
When FM is determined to be small (rich),
Proceeding to S17, the crank angle position TPAFM at which the minimum air-fuel ratio PAFM was obtained within the predetermined section where the air-fuel ratio detection was performed
Ask for.

In step S18, the current ignition timing TIG is obtained. In the next step S19, the deviation TD between the crank angle position TPAFM at which the air-fuel ratio becomes minimum and the current ignition timing TIG is obtained.
Calculate IFF. Further, in S20, a reference timing TINJ (injection start timing or injection end timing) of the current injection control is obtained.

In S21, the reference timing TINJ is corrected by the deviation TDIFF to obtain
The injection timing is advanced or retarded so that the timing at which the minimum air-fuel ratio PAFM is obtained coincides with the ignition timing TIG. That is, when the fuel is burned at an air-fuel ratio that is significantly leaner than the stoichiometric air-fuel ratio, the ignitability deteriorates. Therefore, even if the average air-fuel ratio is a lean air-fuel ratio, the air-fuel ratio near the spark plug is as rich as possible. Ignition in a state improves ignitability. Therefore, the variation of the air-fuel ratio in a predetermined section before the timing of performing the ignition is obtained, and the injection timing is shifted so that the timing at which the air-fuel ratio becomes richest overlaps the ignition timing. Specifically, when the crank angle position TPAFM appears earlier than the ignition timing TIG, the injection timing is retarded by an amount corresponding to the difference TDIFF.

In the injection timing correction control,
It is preferable that the injection timing be changed only within a predetermined range centered on the basic injection timing. Further, when the operating state has changed, the injection timing is once returned to the reference timing TINJ of the operating state, and the crank angle position TPA is again changed.
It is preferable to make FM coincide with the ignition timing TIG. On the other hand, the injection amount correction for making the air-fuel ratio near the spark plug equal to the target air-fuel ratio is performed outside the lean air-fuel ratio range, and when the minimum air-fuel ratio PAFM is determined to be leaner than the target air-fuel ratio in S16. This is performed in S22 to S25 in the air-fuel ratio range.

In step S22, an average value MAFM of the air-fuel ratio sequentially calculated in a predetermined section before the ignition timing is calculated. In the next S23, the target air-fuel ratio AFR and the average air-fuel ratio MAF are determined.
The difference AFDIFF from M is calculated. In S24, the current injection amount QTp is set, and in the next S25, the deviation AF
Corrected injection amount QAFDIF set corresponding to DIFF
The correction is made by adding F to the injection amount QTp.

According to the correction control of the fuel injection amount, 1
A deviation of the actual air-fuel ratio from the target air-fuel ratio is obtained for each cycle, and a correction according to the deviation can be reflected in the fuel injection amount in the next cycle. Control is possible. In the control of the injection timing and the control of the injection amount as described above, since it is desired to detect the air-fuel ratio of the ignition atmosphere of the ignition plug 6 with high accuracy, the optical elements 10 and 11 are provided between the electrodes of the ignition plug 6. It is desirable to detect the intensity of transmitted light in the configuration of the embodiment shown in FIGS.

In the above description, the deviation AFDIFF is converted into injection amount data. However, a correction coefficient for the injection amount is set based on the deviation ADFIFF, and the correction coefficient is multiplied by the basic injection amount to perform the correction. May be. Further, in this embodiment, the air-fuel ratio of the air-fuel mixture actually sucked into the combustion chamber can be detected by the fuel injected from the fuel injection valve 3.
For example, wall flow correction during transient operation or cold operation can be optimized based on the air-fuel ratio detection result. That is, the fuel injection valve 3
Injection and supply of fuel causes a transport delay due to collision or wall adhesion, and during transient operation or during cold operation, it is necessary to perform an increase correction in anticipation of such a delay. For example, since the air-fuel ratio in the combustion chamber can be detected for each cycle, the excess or deficiency of the increase correction can be quantitatively detected, whereby the increase correction amount for transient operation or cold operation can be optimized.

In the control of the injection timing in the above embodiment, the state of the air-fuel ratio fluctuation before the ignition is detected in time series,
The timing at which the air-fuel ratio peaks on the rich side is determined based on the detection result, and the difference between the rich peak timing and the ignition timing is used as the correction amount of the injection timing. By detecting the change direction of the air-fuel ratio at the ignition timing based on the correction result, an injection timing at which the air-fuel ratio at the ignition timing has a rich peak may be found.

An embodiment of such injection timing control is shown in FIG.
It is shown in the flowchart of 20. First, in S51, a basic injection timing (injection start crank angle or injection end crank angle) set in advance according to operating conditions is read from a map. Then, in S52, fuel injection is performed in accordance with the basic injection timing. In the next S53, the air-fuel ratio of the air-fuel mixture formed by the fuel injection is determined by the transmission detected by the photoelectric conversion element 14 as described above. The calculation is performed at the ignition timing based on the light intensity and the in-cylinder pressure.

In S54, the air-fuel ratio calculated in S53 is compared with the air-fuel ratio at the previous ignition timing, and it is determined whether or not the air-fuel ratio at the ignition timing has changed in the rich direction as compared with the previous time. . When the air-fuel ratio at the ignition timing is changing in the rich direction, the process proceeds to S55, and the air-fuel ratio calculated at the current ignition timing is stored as the previous air-fuel ratio.

Next, in S56, it is determined whether or not the injection timing has been advanced in the previous injection timing correction. Here, when it is determined that the air-fuel ratio of the ignition timing has changed in the rich direction as a result of the advance of the injection timing, there is a possibility that the air-fuel ratio of the ignition timing may change more richly by further advancing the injection timing. Therefore, the process proceeds to S57, and the injection timing is corrected so that the injection timing is advanced by a predetermined minute angle. Then, in S58, the history of performing the correction that further advances the injection timing is stored.

On the other hand, when it is determined in S54 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 S59, and it is determined whether correction has been made to advance the previous injection timing. If the air-fuel ratio does not change in the rich direction as a result of advancing the injection timing,
Proceeding to S60, conversely, a correction for delaying the injection timing by a predetermined minute angle is performed, and in the next S61, the history of the correction for delaying the injection timing is stored.

If it is determined in S59 that the injection timing has been delayed, and that the air-fuel ratio has not changed in the rich direction, the flow proceeds to S59 to advance the injection timing.
Go to 57. That is, for example, when the air-fuel ratio 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 in the rich direction stops. This time, the injection timing is controlled so that the vicinity of the rich peak coincides with the ignition timing.

When the advance / retard correction of the injection timing as described above converges, the injection timing at that time may be learned and stored for each operating condition. In the above embodiment, the embodiment in which the injection timing or the injection amount is corrected based on the air-fuel ratio detected based on the transmitted light intensity of the laser light has been described, but the injection hole of the fuel injection valve faces the combustion chamber. By using the air-fuel ratio detection result by the above configuration for the injection pressure control in a direct injection type spark ignition engine (see Japanese Patent Application No. 4-17738) having a configuration in which fuel injection is performed during the compression stroke, the direct injection type spark ignition engine is used. Ignition performance can be improved.

That is, when the direct injection type spark ignition engine is used to perform lean combustion, it is desired that the air-fuel ratio in the vicinity of the spark plug be made richer than in other stratifications. Should be directed to the vicinity of the spark plug. However, in the case of such a configuration, if the injection pressure is not appropriate,
Fogging of the spark plug occurs, and conversely, it becomes impossible to form an ignitable air-fuel ratio near the spark plug.

Here, by controlling the injection pressure of the direct-injection spark ignition engine based on the air-fuel ratio detection result immediately before ignition based on the transmitted light intensity of the laser light, it is possible to avoid fogging of the spark plug while maintaining a high level. An air-fuel ratio capable of exhibiting ignitability can be stably formed in the vicinity of the ignition plug, and an embodiment will be described below. FIG. 21 shows a system configuration in which the above-described device for detecting the air-fuel ratio based on the transmitted light intensity of the laser beam is incorporated in the direct injection spark ignition engine.
In FIG. 21, the same elements as those in the configuration shown in FIG. 2 are denoted by the same reference numerals.

In the configuration shown in FIG. 21, the injection hole of the fuel injection valve 3 faces the combustion chamber 5, and the spray is directed toward the ignition plug 6. The ignition plug 6 is integrally provided with a pair of optical elements for guiding laser light as shown in FIGS. 15 and 16 described above, and the air-fuel mixture present in the spark gap of the ignition plug is provided by the optical elements. As described above, the transmission intensity of the laser light passing through the inside is detected by the photoelectric conversion element 14, and the air-fuel ratio is calculated based on the output of the photoelectric conversion element 14 and the in-cylinder pressure. The same is true.

In the configuration shown in FIG. 21, the control unit 15 can control the adjustment pressure of the pressure regulator 51 for adjusting the pressure (injection pressure) of the fuel supplied to the direct injection type fuel injection valve 3. I have. The pressure regulator 51 adjusts the pressure of the fuel pumped from the fuel tank 52 by the fuel pump 53 to a predetermined pressure by adjusting the relief amount, for example. The injection pressure may be adjusted by controlling the fuel pump 53.

Then, the control unit 15
As shown in the flowchart, the fuel pressure adjusted by the pressure regulator 51 is controlled, and the injection pulse width given to the electromagnetic fuel injection valve 3 is changed in accordance with the pressure control. In the flowchart of FIG.
In step S72, the engine speed Ne is detected, and in step S72, the engine load (intake air amount) is detected.

In S73, the injection amount (injection pulse width) is calculated based on the information on the rotation and the load. Note that the calculation of the injection pulse width in S73 is performed on the assumption that the injection pressure is adjusted to the basic pressure. In S74, the ignition timing is obtained from the map based on the information on the rotation and the load.

In the next step S75, a preset basic injection pressure Po is set, and is adjusted to the basic injection pressure Po by the pressure regulator 51. Then, in S76, the fuel injection valve 3 is controlled to open at a predetermined injection timing according to the set injection pulse width, and fuel injection is performed. In S77, the air-fuel ratio calculated based on the transmitted light intensity of the laser beam and the in-cylinder pressure is sampled according to the ignition timing obtained in S74, and the air-fuel ratio Ao near the ignition plug 6 at the ignition timing is obtained.

In S78, the air-fuel ratio Ao is compared with the lean limit value Amin of the ignitable air-fuel ratio. When the air-fuel ratio Ao near the ignition plug 6 at the ignition timing is leaner than the lean limit value Amin, the routine proceeds to S79, where a correction is made to increase the injection pressure by a predetermined value. That is, when the air-fuel ratio near the ignition plug 6 at the ignition timing is leaner than the desired air-fuel ratio, the injection pressure is lower than required, and the fuel spray does not reach the vicinity of the injection valve as required. It can be estimated that. Therefore, by performing a correction that further increases the injection pressure, the reaching distance of the fuel injected from the injection valve 3 is extended, the air-fuel ratio near the ignition plug 6 at the ignition timing is further enriched, and the air that provides good ignition is obtained. The ignition is performed in the fuel ratio atmosphere.

On the other hand, when it is determined in S78 that the air-fuel ratio Ao near the ignition plug 6 at the ignition timing is richer than the lean limit value Amin, the process proceeds to S80, and this time the air-fuel ratio Ao and the ignitable air-fuel ratio are compared. Compare with the rich limit value Amax. Here, when it is determined that the air-fuel ratio Ao near the ignition plug 6 at the ignition timing is richer than the rich limit value Amax, the process proceeds to S81, and a correction for reducing the injection pressure by a predetermined value is performed.

That is, when the atmosphere of the ignition plug 6 is the rich limit value A
If the atmosphere is rich, the fuel injection distance from the fuel injection valve 3 is too long, and the ignition plug 6
It is presumed that the fuel spray hits directly to cause wetting, so that the injection distance is reduced by lowering the injection pressure, and the air-fuel ratio near the ignition plug 6 at the ignition timing is made lean.

When the injection pressure is changed in S79 or S81, the intended fuel cannot be injected unless the injection pulse width is corrected according to the change in the injection pressure.
A process for correcting the injection pulse width according to the injection pressure changed in 82 is performed. Then, in S83, the injection pressure P ₁ of a change in the S79 or S81, is set to adjust pressure Po in the pressure regulator 51.

On the other hand, according to the discrimination in S78 and S80, the air-fuel ratio Ao is changed to the lean limit value Amin and the rich limit value A
If it is determined that the air-fuel ratio is within the required air-fuel ratio range sandwiched by max, the injection pressure does not need to be corrected, so that the process jumps from S79 to S83 and proceeds to S84. In S84, the operating conditions (rotation,
It is determined whether or not the load has changed. If the operating conditions are constant and the required fuel amount is constant, the process returns to S76 to control the air-fuel ratio near the ignition plug 6 at the ignition timing to be within the required range. Is adjusted again.

On the other hand, if the required fuel amount changes due to a change in the operating conditions, the flow returns to S71 to calculate the required fuel amount. According to the above embodiment, the injection pressure of the direct injection type fuel injection valve 3 is adjusted so that the air-fuel ratio near the ignition plug 6 at the ignition timing becomes the air-fuel ratio optimal for ignition. Ignition can be performed under conditions.

By the way, the correction of the transmitted light intensity with respect to the contamination of the pair of optical elements 10 and 11 (sapphire rods 24 and 25) has been described above. The fuel flows as a wall flow into the combustion chamber 5, and the liquid fuel adheres to the optical elements 10 and 11 protruding into the combustion chamber 5. There is a possibility that it will be caused by the target fuel.

[0075] Therefore, the pair of optical elements 10 and 11 shown in the previous SL FIGS. 2 and 3, as shown in FIG. 23, the optical element
Bottom portion of the gap 10, 11 is attached a heater (ceramic heater) 31 as a heating means (end face of the optical element 9), and configured to take out to the outside by embedding a heater power supply line 32 to the optical element 9 is there. Then, at the time of the engine operating condition where the liquid fuel adhesion is predicted, or when the adhesion state is detected from the calculated change in the air-fuel ratio, power is supplied to the heater 31 under the control of the control unit 15. Heat is generated, and the optical elements 10 and 11 are heated by the generated heat so that the attached liquid fuel is vaporized at an early stage.

The optical elements 10 and 11 shown in FIG. 23 are of a type separate from the ignition plug 6 shown in FIGS. 2 and 3, but are shown in FIGS. 9 to 11 or FIGS. It is clear that the heater 31 can be attached similarly to the case where the ignition plug 6 is integrated with the ignition plug 6 as described above.
, Regardless of whether they are integrated or separate.

The specific state of the heater control will be described with reference to the flowchart of FIG. 24 and FIGS. 2 and 23.
Note that the software functions of the control unit 15 shown in the flowchart of FIG. 24 correspond to heating control means based on operating conditions, fuel adhesion detection means, and heating control means based on adhesion detection. In the present embodiment, such heating control is performed. For the condition determination, the signals of the water temperature sensor 61 and the start switch 62 (see FIG. 2) are used as described later.

In the flowchart of FIG. 24, first, S
At 31, the cooling water temperature Tw detected by the water temperature sensor 61 is compared with a predetermined temperature. When it is determined that the cooling water temperature Tw representing the engine temperature is lower than the predetermined temperature, the process proceeds to S32, and the elapsed time Ta from the start measured based on the signal of the start switch 62 and the predetermined time are calculated. Compare.

If it is determined that the elapsed time Ta from the start has not reached the predetermined time, the process proceeds to S33, in which power is supplied to the heater 31 to cause the heater 31 to generate heat, thereby causing the optical element 10 to emit heat. , 11 are heated. That is, the heater 31 is caused to generate heat within a predetermined period immediately after the cold start, and the optical element
Even if liquid fuel flows into the combustion chamber 5 and adheres to the optical elements 10 and 11, such liquid fuel can be vaporized at an early stage. The accuracy of the air-fuel ratio detection performed by passing the laser beam through the air-fuel mixture via the elements 10 and 11 can be maintained even during a cold start.

On the other hand, in a lean-burn engine or the like, fuel injection may be performed during the intake stroke. In such a configuration, even if the engine is not immediately after the cold start as described above,
Optical elements 10 and 11 (sapphire rods 24 and 25) are directly drawn into combustion chamber 5 by the injected fuel.
Liquid fuel may adhere to the surface. Here, when the liquid fuel is deposited, the laser light is largely absorbed by the deposited fuel, so that the calculated air-fuel ratio rapidly changes in the rich direction.

Therefore, during the air-fuel ratio calculation period, the first derivative AFDIF of the calculated air-fuel ratio is obtained (see FIG. 25), and the cooling water temperature Tw and the post-start time Ta are determined by the liquid fuel for the optical elements 10 and 11. Even if the adhesion condition is not satisfied, the primary differential value AFDIF is compared with a predetermined value in S34, and when a large change in the air-fuel ratio calculation value is detected, the liquid is applied to the optical elements 10 and 11. It is assumed that the target fuel is attached, and the process proceeds to S33 to supply power to the heater 31.
The detection of the adhesion state based on the air-fuel ratio differential value indicates the function of the control unit 15 as a fuel adhesion detection unit.

In the heater control based on the differential value AFDIF of the air-fuel ratio, in order to avoid frequent ON / OFF control due to the variation of the differential value, a hysteresis is provided in the determination level, or the adhesion state is temporarily determined. It is preferable that the ON-OFF control is performed by forcibly energizing continuously for a predetermined time after the detection, or by setting the differential value to be equal to or less than a determination level and stable for a predetermined time or more.

If the configuration is such that the adhesion of the liquid fuel to the optical elements 10 and 11 is detected from the change in the air-fuel ratio calculation value as described above, the state of the fuel adhesion that is not correlated with the engine operating conditions such as the cooling water temperature Tw is determined. Even in an engine that can detect and shift fuel during the intake stroke and perform fuel injection, the optical element 1
The state of adhesion of the liquid fuel to 0 and 11 can be eliminated at an early stage to maintain the air-fuel ratio detection accuracy.

On the other hand, if the calculated value of the air-fuel ratio is stable, not immediately after the cold start, the routine proceeds to S35, where the heater 31
The power supply to the server to avoid unnecessary power consumption.
When the optical elements 10 and 11 (sapphire rods 24 and 25) are provided integrally with the ignition plug by the configuration shown in FIG. 9 to FIG. 11 or FIG. 15 and FIG.
If the heating control by 31 is performed, the adhesion of the liquid fuel to the optical elements 10 and 11 also causes the fuel wetting of the electrode portion in the spark plug 6 to be estimated. The electrode portion is also heated at the same time, and there is a secondary effect that deterioration of ignitability due to wetting of the spark plug can be avoided.

In the above heater control, the cooling water temperature Tw is used as a parameter representing the engine temperature. However, it is apparent that the temperature of the lubricating oil and the temperature of the intake port may be used. .

[0086]

As described above, according to the present invention, the local air-fuel ratio in the combustion chamber can be detected with high accuracy, and in particular, the air-fuel ratio near the spark plug can be detected before ignition. Therefore, there is an effect that the air-fuel ratio near the spark plug at the ignition timing can be controlled with high accuracy to maintain the ignitability by the spark plug at the best, and a means for heating the optical element.
Air-fuel ratio detection accuracy due to liquid fuel adhesion
This has the effect of avoiding the deterioration of

Further, by providing an optical element for detecting the absorption of light by the fuel integrally with the ignition plug, the configuration of the air-fuel ratio detecting device can be simplified, and the position at a position closer to the ignition plug can be reduced. There is an effect that the air-fuel ratio can be detected. In addition, when the operating condition or the adhesion state in which the adhesion of the liquid fuel to the optical element is predicted is detected, the deterioration of the air-fuel ratio detection accuracy due to the adhesion of the liquid fuel is prevented by heating the optical element. This has the effect that it can be avoided accurately .

[Brief description of the drawings]

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

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

FIG. 3 is a view showing an optical element in the embodiment.

FIG. 4 is a diagram showing an air-fuel ratio corresponding to transmitted light intensity and in-cylinder pressure.

FIG. 5 is a diagram showing changes in transmitted light intensity and in-cylinder pressure according to a crank angle.

FIG. 6 is a diagram showing characteristics of dirt correction based on light intensity immediately before opening of an intake valve.

FIG. 7 is a diagram showing characteristics of stain correction using light of different wavelengths.

FIG. 8 is a flowchart showing a state of an air-fuel ratio calculation involving correction of dirt.

FIG. 9 is a side view showing an example of an ignition plug in which an optical element is integrated.

FIG. 10 is a top view of the ignition plug shown in FIG. 9.

FIG. 11 is a bottom view of the ignition plug shown in FIG. 9;

12 is an enlarged view of the optical element shown in FIG.

FIG. 13 is a view showing another example of a method of attaching an optical element to an ignition plug.

FIG. 14 is a diagram showing an example in which a pair of optical elements are integrated.

FIG. 15 is a side view showing an embodiment in which a spark gap of an ignition plug is used as an optical path.

FIG. 16 is a bottom view of the ignition plug shown in FIG. 16;

FIG. 17 is a flowchart illustrating a fuel injection control using an air-fuel ratio detection result.

FIG. 18 is a diagram showing a map of a target air-fuel ratio.

FIG. 19 is a diagram showing characteristics of air-fuel ratio detection for fuel injection control.

FIG. 20 is a flowchart illustrating another embodiment of the injection timing control.

FIG. 21 is a system diagram showing an embodiment applied to a direct injection spark ignition engine.

FIG. 22 is a flowchart showing injection pressure control in a direct injection spark ignition engine.

FIG. 23 is a structural diagram showing an embodiment in which a heater is attached to an optical element.

FIG. 24 is a flowchart showing on / off control of a heater.

FIG. 25 is a diagram showing a relationship between a differential value of air-fuel ratio detection data and heater control.

FIG. 26 is a diagram for describing a problem of air-fuel ratio detection using conventional combustion light.

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 2 intake port 3 fuel injection valve 4 intake valve 5 combustion chamber 6 ignition plug 7 cylinder pressure sensor 8 cylinder head 9, 10, 11, 13 optical element 12 laser source 14 photoelectric conversion element 15 control unit 21 holder 23 ignition plug Main body 23c Center electrode 23d Ground electrode 24, 25 Sapphire rod 31 Heater 61 Water temperature sensor 62 Start switch

Continuation of front page (56) References JP-A-1-237435 (JP, A) JP-A-1-247740 (JP, A) JP-A-2-19746 (JP, A) JP-A-2-212746 (JP, A) , A) Fully open 1986-33935 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02D 35/00, 45/00 G01N 21/35

Claims (4)

(57) [Claims] 1. A pair of optical elements including a light-emitting side and a light-receiving side facing a combustion chamber of an internal combustion engine with a predetermined gap therebetween, and light emitted from a light source is photoelectrically converted via the pair of optical elements. Transmitted light intensity detecting means for guiding the element, an in-cylinder pressure detecting means for detecting an in-cylinder pressure of an engine, an output of the photoelectric conversion element in the transmitted light intensity detecting means and an in-cylinder pressure detected by the in-cylinder pressure detecting means. Air-fuel ratio calculation means for calculating the air-fuel ratio of the engine intake air-fuel mixture based on the pair of optical elements in the transmitted light intensity detection means.
An air-fuel ratio detection device for an internal combustion engine, comprising: a heating means for heating . 2. The air-fuel ratio detecting device for an internal combustion engine according to claim 1, wherein said pair of optical elements in said transmitted light intensity detecting means are provided integrally with an ignition plug of the engine. Depending on the wherein institution operating condition of the internal combustion engine according to claim 1 or 2, characterized in that a heating control hand stage by operating conditions for selectively operating said heating means Air-fuel ratio detection device. Wherein said heating when the state of adhesion of the fuel is detected in the previous SL transmitted light intensity and the fuel adhesion amount detection means for detecting the state of adhesion of fuel to the pair of optical elements of the detection means, fuel adhesion amount detection means The air-fuel ratio detecting device for an internal combustion engine according to claim 1, further comprising: a heating control unit that detects the adhesion by operating the unit.