JPH06280669A - Air fuel ratio detector for internal combustion engine - Google Patents

Abstract

PURPOSE:To detect air fuel ratio near an ignition plug before ignition timing with high accuracy. CONSTITUTION:A laser beam having the wave length for selectively absorbing gasoline is emitted from a laser sorce 12. After the laser beam is passed through a space in a combustion chamber 5 by a pair of optical elements 10, 11, it is conducted to a photoelectric transfer element 14. Here, the laser beam is absorbed according to the concentration of gasoline present in a gap between a pair of optical elements 10, 11 so that the brightness of a transmitting beam incident on the photoelectric transfer element 14 is changed and affected by pressure in the cylinder. Then, in a control unit 15, an air fuel ratio is calculated on the basis of the pressure in the cylinder detected by a pressure-in-cylinder sensor 7 and the output of the photoelectric transfer element 14.

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 for directly detecting the air-fuel ratio of an engine intake air-fuel mixture from the air-fuel mixture in a combustion chamber.

[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, in the air-fuel ratio detecting device disclosed in the above-mentioned Japanese Patent Laid-Open No. 1-247740, as shown in FIG. 26, in the region where the combustion light is taken out by the optical fiber (hollow cone region). In addition to the light emission in the area A near the end face of the optical fiber, all the light emission in the area B relatively far from the end face is extracted.

Here, the air-fuel ratio may be different between the A region and the B region depending on the gas flow in the combustion chamber, and the flame emission spectrum is different when the air-fuel ratio is different. Further, if the distance from the end face of the optical fiber is different, the intensity thereof changes in inverse proportion to the square of the distance. Therefore, in the configuration in which the combustion light is taken out by the optical fiber, the lights emitted in the regions with different air-fuel ratios and different distances are mixed and taken out. For example, the air in the region A near the spark plug, which is the deciding factor of the ignition limit, is taken out. Even if it is desired to accurately obtain the fuel ratio, there is a theoretical problem that the light emission in the region B influences and highly accurate air-fuel ratio detection cannot be performed.

Therefore, conventionally, by taking out the combustion light, it is considered that the air-fuel ratio is constant in the hollow cone region, and the measurement hollow cone region is narrowed in the distance direction by shortening the time for capturing flame emission. 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 light extracted decreases, resulting in a decrease in measurement accuracy. .

Further, the air-fuel ratio in the vicinity of the spark plug, which is a factor that determines the ignition limit, shows a time-series variation that strongly depends on the injection timing in addition to the particle size of the fuel spray. Therefore, in order to control the air-fuel ratio near the spark plug at the ignition timing in order to improve the ignitability, it is desirable to detect the air-fuel ratio near the spark plug before ignition. Then, it is not possible to detect the air-fuel ratio before ignition,
There is a problem that the air-fuel ratio near the spark plug at the ignition timing cannot be accurately controlled.

The present invention has been made in view of the above problems, and the air-fuel ratio in the vicinity of the spark plug can be detected before ignition, and, still, the local air-fuel ratio can be detected with high accuracy. An object is to provide a detection device.

[0008]

Therefore, an air-fuel ratio detecting apparatus 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 of an internal combustion engine by arranging a pair of optical elements including a light emitting side and a light receiving side so as to face each other with a predetermined gap, and the light emitted from a light source is transmitted to the pair of optical elements. It is a means for leading to the photoelectric conversion element through the 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 output of the photoelectric conversion element in the transmitted light intensity detecting means and the in-cylinder pressure detected by the in-cylinder pressure detecting means. Based on and, the air-fuel ratio of the engine intake air-fuel mixture is calculated. Here, it is preferable that the pair of optical elements in the transmitted light intensity detecting means are integrally provided on an ignition plug of an engine.

Further, there are provided heating means for heating the pair of optical elements in the transmitted light intensity detecting means, and heating control means under operating conditions for selectively operating the heating means according to engine operating conditions. Good to configure. Furthermore,
Instead of the heating control means based on the operating conditions, a fuel adhesion detection means for detecting the adhesion status of fuel to the pair of optical elements in the transmitted light intensity detection means, and the fuel adhesion status is detected by the fuel adhesion detection means. It is also possible to provide a heating control means based on adhesion detection for operating the heating means at this time.

[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 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, the fuel concentration (air-fuel ratio) can be detected by excluding the factor of the in-cylinder pressure 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. I did it.

Further, in detecting the air-fuel ratio in the combustion chamber, in particular, the air-fuel ratio near the ignition plug greatly affects the ignition limit. Therefore, by providing the pair of optical elements integrally with the ignition plug, Can accurately detect the air-fuel ratio of
Also, the parts configuration can be simplified. Further, if liquid fuel adheres to the pair of optical elements, the adhered fuel absorbs light, which makes it impossible to accurately detect the air-fuel mixture. Therefore, a heating means for heating the pair of optical elements is provided, and the engine is operated under the engine operating conditions where the fuel adhesion is predicted, or the fuel adhesion state is detected, and the heating means is operated to adhere to the optical element. It was made possible to vaporize the fuel that was made earlier.

[0013]

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.

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, a catalyst, and a muffler (not shown). Here, an in-cylinder pressure sensor (in-cylinder pressure detection means) 7 for detecting the pressure (in-cylinder pressure) in the combustion chamber 5 is provided, and the cylinder head 8 forming the combustion chamber 5 is penetrated to the spark plug 6 A cylindrical optical element 9 forming an air-fuel ratio detection device (transmitted light intensity detection means) is fitted 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 are provided at the tip 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 tips with a light beam which is incident from the base end face side of the optical element 9 serving as a base body and advances toward the inside of the combustion chamber 5 along the axial direction of the optical element 9. The optical element 10 on the light emitting side which is reflected by the optical surface toward the other optical element 11, and the optical element 10 which is arranged to face the optical element 10 with a predetermined gap therebetween, and which reflects the light beam reflected by the optical element 10. The optical element 11 on the light receiving side reflects the light toward the optical element 9 by the optical surface formed at the tip.

That is, the light beam is configured to travel in a U-turn through the combustion chamber 5 by the pair of optical elements 10 and 11, and the light beam travels from the optical element 10 to the optical element 11. When going towards, the gap between the two,
When the mixture passes through the space in the combustion chamber and the mixture exists in the combustion chamber 5 from the intake stroke to the ignition, the light beam is transmitted through the mixture through the optical elements 10 and 11. become.

Although quartz, sapphire or the like is used as the material of the optical elements 9, 10 and 11, sapphire is preferably used in consideration of heat resistance and pressure resistance. Also,
The optical elements 9, 10 and 11 do not have to be formed as one piece, and when polishing of the optical surface is required, for example, according to the division surface shown by the dotted line in FIG. Alternatively, the structure may be a three-part configuration, and the components may be joined after polishing.

As the light beam, light having a wavelength that 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 laser beam emitted from the laser source (light source) 12 that emits the laser light is an optical element 13 including a mirror and a prism.
Is bent in a direction parallel to the axis of the optical element 9 by
The light enters at a right angle to the base end face of the optical element 9 and proceeds. Then, it makes a U-turn by the pair of optical elements 10 and 11, passes through the optical element 9 again, and exits 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, 15 is the optical element 9 described above.
Is a holder for holding. The laser 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. The output of the photoelectric conversion element 14 and the detection signal from the in-cylinder pressure sensor 7 are input to a control unit 15 containing a microcomputer for controlling fuel injection by the fuel injection valve 3. Control unit as means for calculating air-fuel ratio
Reference numeral 15 detects the air-fuel ratio of the engine intake air-fuel mixture based on these detection signals, and controls fuel injection based on the detected air-fuel ratio.

Here, the principle of air-fuel ratio detection in this embodiment will be briefly described. Gasoline fuel used in 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
_{When O 2} , the gasoline concentration are C and the absorption coefficient is K, the absorption amount I 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 infrared light is absorbed by the gasoline, it is possible to detect the concentration of gasoline in the air-fuel mixture, in other words, the air in the air-fuel mixture. The fuel ratio can be detected. Here, in the present embodiment, the pair of optical elements 10 and 11 are arranged so as to face each other with the space in the combustion chamber 5 as a gap, and the laser light passes through the gap and finally enters the photoelectric conversion element 14. Due to the constitution, the laser light is absorbed by an amount commensurate with the gasoline concentration in the air-fuel mixture existing in the gap, and the laser light attenuated by such absorption enters the photoelectric conversion element 14.

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. 4), and the air-fuel ratio calculation characteristic using the output of the photoelectric conversion element 14 and the in-cylinder pressure detected by the in-cylinder pressure sensor 7 as parameters ( By setting the conversion map) in the control unit 15 in advance, the combustion chamber 5 can be operated from the intake stroke when the mixture is sucked to the ignition timing.
It is possible to calculate the local air-fuel ratio in the inside (see FIG. 5).

The air-fuel ratio (local air-fuel ratio in the vicinity of the spark 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 spark plug at the ignition timing will determine the ignition limit, and is an important factor especially in a lean-burn engine in which the ignitability deteriorates. If the air-fuel ratio can be detected, it becomes possible to control the air-fuel ratio in the vicinity of the spark plug with high accuracy and stably obtain good ignitability.

Further, since 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, the local air-fuel ratio is changed to another combustion chamber area. It 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 to match the detected air-fuel ratio with the target air-fuel ratio, and the rich peak timing of 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 spark 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 light are arranged so as to face the inside of the combustion chamber 5 as described above, stains due to combustion adhere to the optical elements 10 and 11, and the amount of the stains is increased. There is a possibility that the absorption of the laser light (infrared light) by the gasoline fuel cannot be accurately detected by attenuating the laser light. As a method of correcting the influence of such dirt, as shown in FIG. 6, immediately before the intake valve is opened during the exhaust stroke, that is, immediately before the air-fuel mixture is sucked, when there is almost no fuel in the combustion chamber 5, The output A ₁ of the photoelectric conversion element 14 is taken in. Then, using this output A ₁ as the reference intensity for normalization, the output Bn of the photoelectric conversion element 14 in the subsequent air-fuel ratio calculation period in the intake stroke (for example, a predetermined section before the ignition timing) is 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 almost no fuel is present in the gap between the pair of optical elements 10 and 11, so it changes mainly due to the contamination of the optical elements 10 and 11 (including the decrease of output intensity due to deterioration of the laser source). It is estimated to be. If the reference intensity A ₁ decreases due to the progress of dirt, the output Bn of the photoelectric conversion element 14 is corrected to be increased, and the attenuation of the laser light due to dirt can be compensated.

However, according to the above-mentioned correction method, although the correction calculation can be performed relatively easily, the dirt cannot be detected at the same time as the air-fuel ratio calculation. Since the transmitted light intensity for fuel ratio calculation is detected, there is a risk of deviation from the dirt state during air-fuel ratio calculation, and there is no fuel in the gap between the pair of optical elements 10 and 11. Since the dirt level is estimated by, high precision correction cannot be expected.

As another method for correcting the influence of the dirt, a light source which emits light having a wavelength which is not absorbed by gasoline but is absorbed only by the dirt and attenuated is provided, and the light beam emitted from the light source is Passing through the optical elements 10 and 11 coaxially with the light of the wavelength absorbed by gasoline used for air-fuel ratio detection, as shown in FIG. 7, at the same time as the transmitted light intensity Bn of the light absorbed by gasoline, it is absorbed only by dirt. The wavelength absorbed by gasoline is detected by detecting the transmitted light intensity An of the light having a wavelength that is absorbed, and correcting the transmitted light intensity Bn with the transmitted light intensity An of the light that is absorbed only by the dirt (Bn / An). There is a method of correcting the attenuation due to the dirt of the light in the area.

According to such a correction method, the dirt state at that time can be estimated in synchronization with the calculation of the air-fuel ratio, and the dirt can be detected without being affected by the fuel existing in the pair of optical elements 10 and 11. Since it can be performed, a high-precision stain correction can be performed although the calculation load increases. Here, the function of the control unit 15 for detecting the air-fuel ratio (gasoline concentration) while correcting the dirt as described above is shown in FIG.
It will be described in accordance with the flowchart of. The flow chart of FIG. 8 is simplified and shown as being common to the above two correction methods.

In the flow chart of FIG. 8, first, in 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 the timing immediately before the intake valve is opened, or the transmission intensity of light having a wavelength that is not absorbed by gasoline and is absorbed only by dirt within the calculation period of the air-fuel ratio. Sequentially take in.

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

At S5, n, which indicates the data number of the air-fuel ratio calculated within the air-fuel ratio calculation period, is increased by 1, and the next S
At 6, it is determined whether or not it is within the actual measurement period of the air-fuel ratio (for example, a predetermined section before the ignition timing). Then, 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 the air-fuel ratio calculation is repeated while performing the dirt correction, and the calculation result is obtained. Store in time series.

The transmitted light intensity A which is affected by the amount of dirt
If n is lower than a predetermined value, it is determined that the desired transmitted light intensity cannot be detected, and the predetermined fail-safe mode may be set. In the above embodiment, the optical element 9 (air-fuel ratio detector) including the pair of optical elements 10 and 11 is arranged in the vicinity of the spark plug 6, but the electrode atmosphere of the spark plug 6 is empty. In order to control the fuel ratio and raise the ignition limit, it is desirable to detect the air-fuel ratio at a position as close as possible to the spark plug 6 (electrode part), and also to reduce the number of parts, to assemble and to form a combustion chamber. Considering the space efficiency in the cylinder head, it is preferable to integrally provide the spark plug 6 and the pair of optical elements 10 and 11.

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

Further, the holder 21 includes the spark plug body.
The pair of optical elements in the above embodiment is provided in a vacant space portion generated by offsetting and holding 23.
Two cylindrical sapphire rods 24 and 25 corresponding to 10 and 11
Are fixed in parallel with each other with a predetermined interval so as to penetrate the holder 21 in the axial direction. The two sapphire rods 24, 25
The tip portion of each has an optical surface cut at 45 °, as shown in FIG. 12, and the optical surfaces are made to face each other, and as in the above-described embodiment, one of the sapphire rods 24 has passed through. The laser light from the laser source is reflected by the optical surface of 45 °, 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 in the direction of the base end of the sapphire rod 25 and travels, and the laser light extracted through the sapphire rod 25 is guided to the photoelectric conversion element 14. I'm allowed to do it. Here, when the laser light is emitted from the sapphire rod 24 and travels in the space until it is incident on the sapphire rod 25 side, the laser light that is infrared light is absorbed by the gasoline existing in the space, and photoelectric conversion is performed. The absorption degree, that is, the gasoline concentration is detected by the intensity of the laser light 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 indicated by a dotted line in FIG. It is preferable that the components are configured and integrated after welding by welding or the like. Further, the diameters and positions of the sapphire rods 24 and 25 are preferably set to large values of D ₁ , D ₂ and θ shown in FIG. 11 as long as the diameter of the mounting screw 22 of the holder 21 allows. This is because the thicker the rod, the easier it is to process and assemble, and the larger the reflecting surface can be made.Also, by increasing the distance between the rods, the difference in gasoline concentration can be clearly detected as the difference in the laser light attenuation level. You can do it.

In the structure 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 tip side having the reflecting surface, and are fixed to the holder 21. However, the mounting method is not limited to this. For example, as shown in Figure 13, sapphire rod 2
The enlarged flange portion 26 is provided in the middle of 4 and 25, while the sapphire rods 24 and 25 of the holder 21 have mounting holes 21a.
A step portion 21b corresponding to the flange portion 26 is provided on the. Then, the gasket 27 is sandwiched between both end surfaces of the flange portion 26, and the flange portion 26 is inserted from the base end side by the pressing member 28.
Push in the upper end surface of the sapphire rod 24,
25 may be configured to be held by the holder 21 while ensuring the sealing property.

When it is desired to increase the area of the 45 ° optical surface provided on the tip side of the sapphire rods 24 and 25, the sapphire rods 24 and 25 may be formed into a prism rather than a cylinder. Further, the sapphire rods 24 and 25 need to face each other with a predetermined gap on the distal end side, but they do not have to be separate bodies on the proximal end side, and are integrated as shown in FIG. 14, for example. May be.

In FIG. 14, sapphire rods 24, 25
Has a semicircular cross-section, and plate-like connecting members 29 made of sapphire are sandwiched between the sapphire rods 24 and 25 and welded with their flat side surfaces facing 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 to the holder 21, and the assembling becomes easy. If the base end side end surface 29a of the plate-like connecting member 29 is brought into contact with and bonded to the machined surface of the holder 21, the end surface 29a serves as a stopper and the sapphire rods 24, 25 are pressed by the combustion chamber pressure. Can be prevented from being pushed toward the base end side.

Further, the light condensing efficiency may be improved by forming the end faces (laser light input / output faces) of the sapphire rods 24, 25 on the base end side into a convex lens shape. Further, in the above-mentioned embodiment, the optical path of the laser beam moving between the rods on the tip side of the sapphire rods 24, 25 is configured to pass near the spark gap of the spark plug, but the ignition performance by the spark plug is further improved. In order to detect the air-fuel ratio that varies depending on the accuracy, the optical path may cross the spark gap so that the local air-fuel ratio near the spark gap can be detected.

15 and 16 show sapphire rods 24 and 25.
Of the sapphire rod 24, the laser beam reflected by the 45 ° optical surface on the tip side of the sapphire rod 24 is used as the center electrode 23c. The light enters the sapphire rod 25 side through the spark gap between the ground electrode and the ground electrode 23d. With this configuration, the air-fuel ratio that affects the ignitability of the spark plug can be detected more accurately, and highly accurate air-fuel ratio control is possible without being affected by the air-fuel ratio variation in the combustion chamber 5.

The optical elements 10 and 11 (sapphire rod 2
However, the configuration in which (4, 25) is integrally provided with the spark plug 6 is not limited to the above. However, in the case of detecting the local air-fuel ratio in the combustion chamber 5, the air-fuel ratio of the spark gap portion of the spark plug 6 is detected, and the fuel injection is controlled based on the detection result so as to obtain the desired air-fuel ratio. So the figure is
As shown in FIGS. 15 and 16, it is preferable that the optical elements 10 and 11 are arranged on both sides of the spark gap of the spark 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 concretely described with reference to the flowchart of FIG. In the flowchart of FIG. 17, first, in S11,
The engine speed Ne is calculated based on a detection signal from a crank angle sensor (not shown). Further, in S12, the throttle valve opening detected by the 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 the 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 that stores the target air-fuel ratio AFR shown in FIG. 18 is a lean region that sets a target air-fuel ratio that is significantly leaner than the theoretical air-fuel ratio, a theoretical air-fuel ratio region that sets the theoretical air-fuel ratio as the target air-fuel ratio, and a theoretical It is roughly divided into a rich region in which a target air-fuel ratio that 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 the lean range where the target air-fuel ratio AFR is set to an air-fuel ratio which is significantly leaner than the stoichiometric air-fuel ratio. Here, when it is determined that the region is lean,
The process proceeds to S15, where 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 a time series in a predetermined section before the ignition timing. , The minimum air-fuel ratio PAFM (the richest air-fuel ratio in the air-fuel ratio calculation section) at the air-fuel ratio fluctuating within the predetermined section is obtained (see FIG. 19).

Then, in S16, the target lean air-fuel ratio AFR is compared with the minimum air-fuel ratio PAFM to determine the rich lean of the minimum air-fuel ratio PAFM with respect to the target air-fuel ratio. Here, the minimum air-fuel ratio PA rather than the target lean air-fuel ratio
When it is determined that the FM is small (rich),
Proceeding to S17, the crank angle position TPAFM at which the minimum air-fuel ratio PAFM is obtained within the predetermined section where the air-fuel ratio detection is performed.
Ask for.

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

Then, in S21, the reference timing TINJ is corrected by the deviation TDIFF,
The injection timing is advanced / retarded so that the timing at which the minimum air-fuel ratio PAFM is obtained matches the ignition timing TIG. That is, when the combustion is performed at an air-fuel ratio that is significantly leaner than the stoichiometric air-fuel ratio, the ignitability deteriorates, so even if the average air-fuel ratio is lean, the air-fuel ratio near the spark plug is as rich as possible. Ignition in this state enhances ignitability. Therefore, the variation of the air-fuel ratio in the predetermined section before the ignition timing is obtained, and the injection timing is shifted so that the timing when the air-fuel ratio becomes the 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 deviation TDIFF.

In the injection timing correction control,
It is preferable to allow the change of the injection timing only within a predetermined range around the basic injection timing. When the operating state changes, the injection timing is once returned to the reference timing TINJ of the operating state, and the crank angle position TPA is again set.
It is advisable to make FM coincide with the ignition timing TIG. On the other hand, the injection amount correction for matching the spark plug vicinity air-fuel ratio with the target air-fuel ratio is performed outside the lean air-fuel ratio region, and the lean 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.

At S22, the average value MAFM of the air-fuel ratio successively calculated within the predetermined section before the ignition timing is calculated. Next, in S23, the target air-fuel ratio AFR and the average air-fuel ratio MAF
The deviation AFDIFF from M is calculated. In S24, the current injection amount QTp is set, and in the next S25, the deviation AF is set.
Corrected injection amount QAFDIF set corresponding to DIFF
F is added to the injection amount QTp for correction.

According to the correction control of the fuel injection amount, 1
It is possible to obtain the deviation of the actual air-fuel ratio from the target air-fuel ratio for each cycle, and to correct the deviation according to the deviation in the fuel injection amount in the next cycle. It can be controlled. In the control of the injection timing and the control of the injection amount as described above, it is desired to detect the air-fuel ratio of the ignition atmosphere of the spark plug 6 with high accuracy, so that the optical elements 10 and 11 are provided between the electrodes of the spark plug 6. It is desirable to detect the transmitted light intensity with the configuration of the embodiment shown in FIGS. 15 and 16 which is integrated with the ignition plug as a configuration for passing the laser light.

In the above description, the deviation AFDIFF is converted into the injection amount data. However, the correction coefficient of the injection amount is set from the deviation AFDIFF, and the basic injection amount is multiplied by the correction coefficient to perform the correction. May be. Further, in the present embodiment, the air-fuel ratio of the air-fuel mixture actually sucked into the combustion chamber by the fuel injected from the fuel injection valve 3 can be detected,
For example, wall flow correction during transient operation or cold can be optimized based on the air-fuel ratio detection result. That is, the fuel injection valve 3
The fuel injected and supplied from the fuel tank has a transportation delay due to collisions and adherence to the wall surface, and during transient operation or during cold, it is necessary to correct the fuel consumption increase in consideration of such delay. For example, since the air-fuel ratio in the combustion chamber can be detected for each cycle, excess or deficiency of the increase correction can be quantitatively detected, and thereby 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 ignition is detected in time series,
The timing at which the air-fuel ratio peaks on the rich side is obtained based on the detection result, and the deviation amount between the rich peak timing and the ignition timing is used as the correction amount of the injection timing, but the injection timing is advanced / retarded, The injection timing at which the air-fuel ratio at the ignition timing becomes a rich peak may be found by detecting the changing direction of the air-fuel ratio at the ignition timing based on the correction result.

An example of such injection timing control is shown in FIG.
It is shown in the flow chart of 20. First, in S51, 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 S52, fuel injection is performed in accordance with the basic injection timing, and in next S53, the air-fuel ratio of the air-fuel mixture formed by such fuel injection is detected by the photoelectric conversion element 14 as described above. The ignition timing is calculated based on the light intensity and the cylinder pressure.

At S54, the air-fuel ratio calculated at S53 is compared with the air-fuel ratio at the previous ignition timing to determine whether 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 routine proceeds to S55, where the air-fuel ratio calculated at this ignition timing is stored as the previous air-fuel ratio.

Next, in S56, 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 in the rich direction as a result of advancing the injection timing, the air-fuel ratio of the ignition timing may change more richly by advancing the injection timing. Therefore, the process proceeds to S57, and the injection timing for advancing the injection timing by a predetermined minute angle is corrected. Then, in S58, the history of 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 compared to the previous time, the routine proceeds to S59, where 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 S60, on the contrary, the injection timing is corrected by delaying it by a predetermined minute angle, and in S61, the history of the correction of delaying the injection timing is stored.

When it is determined in S59 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
Continue 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 the change in the rich direction stops. This time, by conversely delaying, 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 has converged, the injection timing at that time may be learned and stored for each operating condition. In the above-mentioned embodiment, the embodiment is shown 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, but the injection hole of the fuel injection valve is made to face the combustion chamber. By using the air-fuel ratio detection result of the above configuration for injection pressure control in a direct injection spark ignition engine (see Japanese Patent Application No. 4-17738) configured to perform fuel injection during the compression stroke, the direct injection spark ignition engine The ignition performance can be improved.

That is, when lean combustion is performed in the direct injection spark ignition engine, stratification that enriches the air-fuel ratio in the vicinity of the spark plug as compared with the others is desired. For that purpose, atomization by the fuel injection valve is required. Should be directed near 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 in the vicinity of the spark plug.

Here, by controlling the injection pressure of the direct injection type 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 the fog of the spark plug and to increase it. It becomes possible to stably form an air-fuel ratio capable of exhibiting ignitability in the vicinity of the spark plug, and the following examples will be described. FIG. 21 shows a system configuration in which a device for detecting the air-fuel ratio based on the transmitted light intensity of the laser light described above is incorporated in the direct injection spark ignition engine.
In FIG. 21, the same elements as those in the configuration shown in FIG. 2 described above are designated by the same reference numerals.

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

In the structure shown in FIG. 21, the control unit 15 can control the adjusting pressure of the pressure adjuster 51 for adjusting the pressure (injection pressure) of the fuel supplied to the direct injection type fuel injection valve 3. There is. The pressure adjuster 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. Note that the injection pressure may be adjusted by controlling the fuel pump 53.

The control unit 15 is shown in FIG.
The fuel pressure adjusted by the pressure adjuster 51 is controlled as shown in the flow chart of FIG. 1, and the injection pulse width given to the electromagnetic fuel injection valve 3 is changed corresponding to the pressure control. In the flowchart of FIG. 22, S71
At S72, the engine speed Ne is detected, and at S72, the engine load (intake air amount) is detected.

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

At the next step S75, a preset basic injection pressure Po is set and adjusted by the pressure adjuster 51 to the basic injection pressure Po. 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 light and the in-cylinder pressure is sampled in accordance with the ignition timing obtained in S74, and the air-fuel ratio Ao near the spark 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. Then, when the air-fuel ratio Ao near the spark plug 6 at the ignition timing is leaner than the lean limit value Amin, the routine proceeds to S79, where correction is performed to increase the injection pressure by a predetermined value. That is, when the air-fuel ratio in the vicinity of the spark plug 6 at the ignition timing is leaner than the desired air-fuel ratio, the injection pressure is lower than the request, so the fuel spray does not reach the vicinity of the injection valve as requested. It can be presumed. Therefore, by performing a correction to further increase the injection pressure, the arrival distance of the fuel injected from the injection valve 3 is extended, the air-fuel ratio near the spark plug 6 at the ignition timing is made richer, and good ignition is obtained. Ignition is performed in a fuel ratio atmosphere.

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

That is, the atmosphere of the spark plug 6 is the rich limit value A.
In a rich atmosphere exceeding max, the distance reached by the fuel injected from the fuel injection valve 3 is too long, and the spark plug 6
Since it is estimated that the fuel spray directly hits and causes wetting, the reaching distance is shortened by lowering the injection pressure, and the air-fuel ratio near the spark plug 6 at the ignition timing is made lean.

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

On the other hand, the air-fuel ratio Ao is determined to be lean limit value Amin and rich limit value A by the determinations in S78 and S80.
If it is determined that the air-fuel ratio is within the required air-fuel ratio range sandwiched by max, it is not necessary to correct the injection pressure. Therefore, steps S79 to S83 are skipped and the process proceeds to step S84. At S84, operating conditions (rotation,
Load) has changed, and 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 spark plug 6 at the ignition timing within the required range. Make the injection pressure adjustment again.

On the other hand, when the operating condition changes and the required fuel amount changes, the process returns to S71 to calculate the required fuel amount. According to the above-described embodiment, the injection pressure by the direct injection type fuel injection valve 3 is adjusted so that the air-fuel ratio near the spark plug 6 at the ignition timing becomes the optimum air-fuel ratio for ignition. Ignition can be performed under certain conditions.

By the way, the correction of the transmitted light intensity with respect to the dirt of the pair of optical elements 10 and 11 (sapphire rods 24 and 25) has been described above. However, since the vaporization property of the fuel is deteriorated at the time of cold or starting, The fuel becomes a wall flow and flows into the combustion chamber 5, and the liquid fuel adheres to the optical elements 10 and 11 protruding into the combustion chamber 5, and the liquid intensity is attenuated beyond the limit of the correction control. There are fears caused by statically attached fuel.

Therefore, for example, with respect to the pair of optical elements 10 and 11 shown in FIGS. 2 and 3, as shown in FIG. 23, the bottom surface portion of the gap between the optical elements 10 and 11 (the end surface of the optical element 9) is shown. A heater (ceramic heater) 31 serving as a heating means is attached to the above, and a heater power supply line 32 is embedded in the optical element 9 and taken out to the outside. The control unit is operated under the engine operating conditions in which the liquid fuel adhesion is predicted, or when the adhered state is detected from the change in the calculated air-fuel ratio.
Power is supplied to the heater 31 to generate heat by the control of 15, and the optical elements 10 and 11 are warmed by the generated heat,
The attached liquid fuel should be vaporized early.

The optical elements 10 and 11 shown in FIG. 23 are of a type different from the spark plug 6 shown in FIGS. 2 and 3, but are shown in FIGS. 9 to 11 or FIGS. 15 and 16. It is obvious that the heater 31 can be attached in the same manner even in the case of being integrated with the spark plug 6 as described above.
It shall be carried out according to common specifications regardless of whether it is an integrated type or a separate type.

A concrete heater control will be described in accordance with the flowchart of FIG. 24 and with reference to FIGS. 2 and 23.
The software function of the control unit 15 shown in the flow chart of FIG. 24 corresponds to the heating control means according to the operating conditions, the fuel adhesion detection means, and the heating control means by the adhesion detection. In the present embodiment, such heating control is performed. As will be described later, the signals of the water temperature sensor 61 and the start switch 62 (see FIG. 2) are used for the condition determination.

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. Then, 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 To compare.

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

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

Therefore, within the air-fuel ratio calculation period, the calculated first derivative value AFDIF of the air-fuel ratio is obtained (see FIG. 25), and the cooling water temperature Tw and the post-starting time Ta are 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 calculated air-fuel ratio value is detected, the liquid is fed to the optical elements 10 and 11. It is estimated that the static fuel is attached, and the process proceeds to S33, in which power is supplied to the heater 31.
The detection of the adhesion state based on such an air-fuel ratio differential value shows the function of the control unit 15 as the fuel adhesion detection means.

Incidentally, 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 adhered state is temporarily set. It is preferable that the ON-OFF control condition is such that the current is forcibly energized continuously for a predetermined time when detected, or that the differential value is stable below the judgment level for a predetermined time or more.

As described above, with the structure for detecting the adherence of the liquid fuel to the optical elements 10 and 11 from the fluctuation of the calculated air-fuel ratio value, the fuel adhered state which does not correlate with the engine operating conditions such as the cooling water temperature Tw is detected. Even in an engine that can detect and inject fuel during the intake stroke, the optical element 1
The state of liquid fuel adhesion to 0 and 11 can be eliminated early to maintain the air-fuel ratio detection accuracy.

On the other hand, immediately after the cold start and when the calculated air-fuel ratio is still stable, the routine proceeds to S35, where the heater 31
Stop the power supply to and avoid unnecessary power consumption.
When the optical elements 10 and 11 (sapphire rods 24 and 25) are integrally provided to the spark plug by the configuration shown in FIGS. 9 to 11 or FIGS. 15 and 16, the heater is configured as described above.
If the heating control by 31 is performed, the adhesion of the liquid fuel to the optical elements 10 and 11 also makes it possible to estimate the wetting of the electrode portion of the spark plug 6, so that the spark plug 6 is heated by heating the optical elements 10 and 11. The electrode part of 1 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 was used as a parameter representing the engine temperature, but it is obvious that the temperature of the lubricating oil, the temperature of the intake port, etc. 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 in the vicinity of the spark plug at the ignition timing can be controlled with high accuracy, and the ignitability of the spark plug can be optimally maintained.

Further, by integrally providing the spark plug with an optical element for detecting the absorption of light by the fuel, the structure of the air-fuel ratio detecting device can be simplified, and at a position closer to the spark plug. There is an effect that the air-fuel ratio can be detected. Further, when the operating condition or the adhered state in which the liquid fuel is expected to adhere to the optical element is detected, by heating the optical element, the deterioration of the air-fuel ratio detection accuracy due to the liquid fuel adhered is deteriorated. The effect is that it can be avoided.

[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 a diagram showing an optical element in the same example.

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 stain correction based on light intensity immediately before opening of an intake valve.

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

FIG. 8 is a flow chart showing a state of air-fuel ratio calculation accompanied by dirt correction.

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 spark plug shown in FIG. 9.

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

FIG. 12 is an enlarged view of the optical element shown in FIG. 9.

FIG. 13 is a diagram showing another example of a method of attaching the optical element to the spark 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.

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

FIG. 17 is a flowchart showing fuel injection control using the 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 showing another embodiment of 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 the 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 explaining a problem of conventional air-fuel ratio detection using combustion light.

[Explanation of symbols]

 1 Internal Combustion Engine 2 Intake Port 3 Fuel Injection Valve 4 Intake Valve 5 Combustion Chamber 6 Spark 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 Spark Plug Main unit 23c Center electrode 23d Ground electrode 24, 25 Sapphire rod 31 Heater 61 Water temperature sensor 62 Start switch

Claims (4)

[Claims] 1. A pair of optical elements consisting of a light emitting side and a light receiving side facing each other in a combustion chamber of an internal combustion engine are arranged to face each other with a predetermined gap, and light emitted from a light source is photoelectrically converted through the pair of optical elements. The transmitted light intensity detecting means for guiding the element, the in-cylinder pressure detecting means for detecting the in-cylinder pressure of the engine, the output of the photoelectric conversion element in the transmitted light intensity detecting means and the in-cylinder pressure detected by the in-cylinder pressure detecting means. An air-fuel ratio detecting device for an internal combustion engine, comprising: an air-fuel ratio calculating means for calculating an air-fuel ratio of an engine intake air-fuel mixture based on the above. 2. The air-fuel ratio detecting device for an internal combustion engine according to claim 1, wherein the pair of optical elements in the transmitted light intensity detecting means are provided integrally with an ignition plug of the engine. 3. A heating means for heating the pair of optical elements in the transmitted light intensity detecting means, and a heating control means under operating conditions for selectively operating the heating means according to engine operating conditions. The air-fuel ratio detection device for an internal combustion engine according to claim 1 or 2, characterized in that. 4. A heating means for heating the pair of optical elements in the transmitted light intensity detecting means, and a fuel adhesion detecting means for detecting an adhesion state of fuel to the pair of optical elements in the transmitted light intensity detecting means, 3. The internal combustion engine according to claim 1, further comprising: a heating control unit that detects the adhesion of the fuel and that operates the heating unit when the adhesion state of the fuel is detected by the fuel adhesion detection unit. Air-fuel ratio detector for engines.