JPH0684938B2 - Combustion light air-fuel ratio sensor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a combustion light air-fuel ratio sensor for optically detecting the air-fuel ratio from the state of combustion flame light of an internal combustion engine.

[Background of the Invention]

As a method for detecting the air-fuel ratio from the combustion flame light in the combustion chamber of an internal combustion engine, there is a method described in British Patent No. 1388384. This is because the radiation intensity of the light in the infrared region of the combustion flame changes depending on the air-fuel ratio, and the peak of the intensity coincides with the theoretical air-fuel ratio. However, in the case of this method, there is a problem in that the light intensity changes due to dirt on the flame light detection surface or the like, and sufficient air-fuel ratio detection accuracy cannot be obtained. In addition, the output characteristic having the peak of the stoichiometric air-fuel ratio becomes a binary characteristic, so that the processing becomes complicated.

[Object of the Invention]

The purpose of the present invention is to increase the air-fuel ratio detection error due to the contamination of the combustion flame light detection surface, which is a disadvantage of the above-mentioned conventional technology, and the binary characteristic of the output characteristics with the theoretical air-fuel ratio as the peak. It is an object of the present invention to solve the above problems and provide a combustion light air-fuel ratio sensor that constantly outputs a signal proportional to the air-fuel ratio regardless of the size of dirt on the detection surface.

[Outline of Invention]

In order to achieve the above-mentioned object, the present invention branches a combustion flame light detection end for guiding the combustion flame light from the combustion chamber of the internal combustion engine to the outside, and a plurality of flame lights guided by the detection end. For detecting the peak value of the output electric signal of each of the light receiving means and the light receiving means having different spectral sensitivity characteristics for converting each flame light from the light branching means into an electric signal. Further, a combustion light air-fuel ratio sensor having an arithmetic processing means for calculating an air-fuel ratio signal from the ratio of those peak values is proposed.

The color of the combustion flame in the visible light range changes depending on the air-fuel ratio.
The reason is that the ratio of the emission intensity of radical components (C ₂ , CH, OH) of the combustion gas differs depending on the air-fuel ratio.

In the present invention having the above-mentioned configuration, focusing on the above-mentioned phenomenon, the light emitting means of the at least two kinds of radical components are individually detected by the light receiving means having different spectral sensitivity characteristics, and the arithmetic processing means outputs the output electricity of these light emission intensities. The air-fuel ratio is calculated from the ratio of the signal peak values.

When the air-fuel ratio is obtained in this manner, the detection surface of the combustion flame light detection end is contaminated with carbon or the like, and even when the amount of transmitted light is reduced, the emission intensity ratio of each radical component hardly changes. The air-fuel ratio can be detected accurately without being affected, and the ratio of the emission intensity of each radical component becomes a signal almost proportional to the air-fuel ratio. It is possible to avoid the appearance of a binary characteristic due to the peaked output characteristic.

Example of Invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows the overall configuration of an engine control device using a combustion light air-fuel ratio sensor according to the present invention. A combustion flame light detection end 3 is attached to the combustion chamber 2 of the engine 1 so as to be open, and this is integrated with a spark plug. In this embodiment, in the case of a multi-cylinder engine, it is assumed that the flame light detection end 3 is provided for only one representative cylinder. The combustion flame light derived by the combustion flame light detection end 3 is guided to the optical fiber cable 4, branched into two, and guided to two light receiving elements 5 and 6 having different spectral sensitivity characteristics, respectively. The light receiving elements 5 and 6 are connected to the drive processing circuit 7,
Here, photoelectric conversion is performed, and the signal is guided to the controller 8 composed of a microcomputer. The controller 8 includes an air flow meter 9, an opening sensor for the throttle valve 10,
Various engine information signals such as the crank angle sensor 11 and the water temperature sensor 12 are input. The controller 8 arithmetically processes the two signals from the drive processing circuit 7 to obtain information on the air-fuel ratio. Then, the optimum fuel injection amount and the ignition timing are determined from the various operation information signals and the air-fuel ratio signal, and the control signals are sent to the fuel injection valve 13 and the ignition timing control device 14. Fuel injection valve 13
Then, the valve opening time is controlled by the control signal and the amount of injected fuel is measured. On the other hand, in the ignition timing control device 14, the supply timing of the high voltage applied to the ignition plug 3 is adjusted by the control signal and is sent out. Although a multi-point type fuel injection system is shown as an example here, a single-point type, a carburetor type, etc. can be similarly configured.

FIG. 2 is a detailed view of the combustion flame light detecting end 3. In order to derive the combustion flame light, a quartz glass fiber 15 having a diameter of about 1 mm is arranged so as to penetrate the central axis of the ignition plug. That is, the central electrode portion 16, the central shaft portion of the high voltage terminal shaft 17 is opened,
Put the quartz glass fiber 15 here, and the three parties and the insulator
To fix 18 and maintain airtightness, insert a glass sealing material 19 containing copper as shown in FIG. 2, and when it is in a molten state by being heated in a heating furnace, press the high-voltage terminal 17 downward from above to make it flow into the gaps between the parts. It has been sealed. The flame light detection surface 15a is formed into a spherical shape or a conical shape so that light from the entire combustion chamber can be taken in, whereby an average air-fuel ratio in the combustion chamber can be detected. It should be noted that the plug 20 may be a normal spark plug, and the tip of the plug may be a side electrode.
The fact that 21 is attached is also the same.

FIG. 3 is an example of a detailed diagram of an optical transmission system from the combustion flame light detection end 3 to the light receiving elements 5 and 6. The quartz fiber portion on the side opposite to the combustion chamber of the combustion flame light detection end 3 is connected to the bundle fiber 23 by the connector 22. Further, the high voltage terminal 24 is mounted integrally with the connector 22. This is an example, and in the case of an optical fiber, as is well known, it is electrically non-inductive, so it is possible to integrate the high-voltage cord of the ignition plug and the bundle fiber into a single unit, and configure it according to the application. Just decide the law. The bundle fiber 23 for guiding the combustion flame light to the light receiving elements 5 and 6 is, as is well known, a bundle of several to several tens of fibers with a covering material 25 (cross section A). In the example, the diameter is 250 μm (core diameter 220 μm, cladding diameter 250 μm)
19 multi-component glass fibers are bundled and the outer diameter thereof is about 1.2 mm, which is almost the same as the quartz fiber diameter. By arranging the diameters in this way, the loss at the joint is minimized. This bundle fiber is branched at a branching portion 27 into 10 glass fibers and 9 bundle fibers as shown in the cross sections B and C, and combustion flame light is guided to the light receiving elements 5 and 6 through the connectors 28 and 29. It is configured. An ordinary single-core fiber can be used instead of the bundle fiber 23. In that case, an optical branching device is installed at the rear end of the single-core fiber to guide flame light to each light receiving element.

FIG. 4 shows the spectral sensitivity characteristics a and b of the light receiving elements 5 and 6. The light receiving element 5 has a peak near 430 nm, which is close to the emission wavelength of 432 nm of the CH radical of the combustion gas, and the emission intensity of this CH radical is detected. In addition, the light receiving element 6 is 52
There is a peak near 0 nm, which is close to the emission wavelength of C ₂ · radicals of 516 nm, and this C ₂ · radical emission intensity is detected. Such a light receiving element can be easily realized by using a photodiode for color detection, that is, a so-called color sensor for blue detection (corresponding to a characteristic) and green detection (corresponding to b characteristic).

As shown in FIG. 5, such a light receiving element generally has a characteristic that the output signal changes with the illuminance, and when the operating state of the engine changes and the combustion state changes, It is necessary to correct the illuminance change by some method. Therefore, in the present invention, the light receiving element 5
And take the ratio of the output signals of 6. That is, as described above, when the air-fuel ratio is rich, the combustion flame is reddish (wavelength is large), and when the air-fuel ratio is thin, it is blue (wavelength is small). Due to
The number of flames in any wavelength band has increased, and it is possible to identify and to infer the air-fuel ratio.

FIG. 6 shows the drive processing circuit 7 for the light receiving elements 5 and 6, the microcomputer 35 and the A / D converter 34 in the controller 8. The light receiving elements 5 and 6 are operational amplifiers 30 and 31, respectively.
A plurality of resistors as shown in FIG. 6 are arranged in the circuit configuration to amplify the signal. The operational amplifier used here is a dual power supply type, and the output signal changes from 1 to 10 at the voltage level. The analog output voltage obtained here is sent to the A / D converter via the peak hold circuits 32 and 33, respectively.
After being guided to 34 and converted into a digital signal, it is inputted to the microcomputer 35, and an arithmetic process for obtaining an air-fuel ratio signal from the ratio of both signals is executed. The time chart of the control of FIG. 6 is shown in FIG. 7, and the output signal S6 from the light receiving elements 6 and 5 is slightly delayed after the top dead center signal S11 (FIG. 1) obtained from the crank angle sensor 11. , S5 peak occurs. Therefore, this is held by the peak hold circuits 33 and 32 (dotted lines in S6 and S5 in FIG. 7), and sampling pulses SP1 and SP2 (microcomputer 35 which are delayed from the top dead center S11 by crank angles θ ₁ and θ _2). To A / D converter
(Provided to 34) is taken into the A / D converter 34, where it is converted into a digital signal, and then the ratio of the two is calculated in the micro computer 35 to obtain the air-fuel ratio. The hold value of each output signal S6, S5 is
A command from the micro computer 35 at the crank angle θ ₃ (greater than θ ₁ , θ ₂ and several degrees to several tens of degrees) from the top dead center S11.
It is reset by M ₁ and M ₂ .

By the way, the output signals S5 and S6 from the light receiving elements 5 and 6 have their peak values varying in each cycle. This is because the air-fuel ratio of the air-fuel mixture supplied to the engine combustion chamber fluctuates in each cycle, and if the closed-loop control of the fuel amount is executed each time by the air-fuel ratio signal in each cycle, the fluctuation will further fluctuate. There is a risk of an increased and unstable control system. Therefore, the output signal of the i-th cycle is now S5.
(I), S6 (i) To meantime, at the time of the n cycle _{V 5 = {S5 (n)} + S5 (n-1) + ... + S5 (n-N +
1)} / N ... (1 ) V 6 = {S6 (n) + S6 (n-1) + ... + S6 (n-N +
1)} / N (2) The average values V ₅ and V ₆ for N times are calculated, and the air-fuel ratio is calculated from the ratio of the two to perform control.

Fig. 8 shows the results of the above V ₅ and V ₆ with respect to the air-fuel ratio in this way. Both have the highest output near the theoretical air-fuel ratio A / F = 14.7, and the output is richer or thinner. The output tends to be smaller. This is because the illuminance itself of the combustion flame becomes smaller in a darker region and in a darker region. Therefore, when the ratio of the two, r = V ₆ / V ₅ (3), is obtained, the characteristics shown in FIG. 9 are obtained. That is, in the dark region (Rich), the emission intensity of C ₂ radicals (516 nm) is higher than that of CH radicals (432 nm) (flame becomes reddish), and the ratio r thereof is large. on the other hand,
On the contrary, when the air-fuel ratio region (Lean) becomes thin, C ₂ ·
Since the intensity of light emission becomes smaller and the flame becomes bluish, the ratio r becomes smaller, and as a result, a signal r almost proportional to the change in the air-fuel ratio can be obtained as shown in FIG. Therefore, the signal of the air-fuel ratio A / F can be obtained from the value of r by previously storing the characteristic of FIG. 9 as a function in the microcomputer 35 or by storing it as a map value. . If the absolute value of A / F is not required, the deviation correction control from the predetermined set value may be executed using the value of r itself.

In the above embodiment, only one combustion light air-fuel ratio sensor is attached to the representative cylinder, but this is installed in each cylinder to detect the air-fuel ratio of each cylinder, and the fuel is supplied to each cylinder. If the amount is controlled, more detailed air-fuel ratio control becomes possible. However, in this configuration, for example, in the case of a 4-cylinder engine, the number of light receiving elements is 2 × 4 = 8, and the bundle fiber is also 2
4 branches are required. If other information (knock signal, combustion start timing signal) is to be extracted at the same time, the number of fibers and the number of light receiving elements will increase, which will be complicated and costly. FIG. 10 shows an embodiment for solving these problems, in which light is guided from the flame photodetectors 3A to 3D of each cylinder to the optical coupler 48 by the optical fibers 4A to 4D, respectively. Combine four. In the case of a four-cycle engine, about 3/4 is darkfield, and the explosion process (brightfield) alternates between the cylinders. It can be easily discriminated whether or not there is an electric signal. Optical coupler
The optical signals summarized in 48 are then guided to the optical branching device 49 and branched into the required number of optical paths. In FIG. 10, the light is transmitted to the light receiving elements 50 and 51 for detecting the air-fuel ratio, and the light is transmitted to the light receiving element 52 for detecting the knock and the combustion start timing. If the broken line portion 53 is converted into an optical module, a more compact structure can be obtained. According to this embodiment, the number of optical fibers and the number of light receiving elements can be saved even when the air-fuel ratio detection and the knock signal detection in each cylinder in the case of a multi-cylinder engine are performed.

Further, in the above, the detection of the air-fuel ratio is performed from the intensity of the emission wave table of the C ₂ radical and the CH radical, but even if this is performed by the similar measurement of the CH radical and the OH radical, almost the same result is obtained. The detection accuracy can be further improved by using all the C ₂ , CH, and OH radicals obtained.

〔The invention's effect〕

As described above, according to the present invention, the detection surface of the combustion flame light detection end is contaminated with carbon or the like, and even when the amount of transmitted light is reduced, the ratio of the amount of light of each wavelength hardly changes. There is an effect that the air-fuel ratio can be detected without receiving
Unlike the conventional air-fuel ratio sensor installed in the exhaust pipe, it can be attached to each cylinder to perform air-fuel ratio control for each cylinder without a large delay time, and achieve high-speed control, exhaust gas purification, fuel consumption reduction, and other drivability improvements. . Furthermore, since the detected value and the air-fuel ratio have a one-to-one monotonic characteristic, an accurate value of the air-fuel ratio is not necessary in the case of control, and the ratio r obtained by calculation can be used as it is. There is also an effect that the amount can be reduced.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an engine control device using a combustion light air-fuel ratio sensor according to the present invention, FIG. 2 is a structural diagram of a combustion flame light detection end, and FIG. 3 is a photoelectric conversion unit from the combustion flame light detection end. 4 is a detailed view of the optical transmission section up to FIG. 4, FIG. 4 is a spectral sensitivity characteristic diagram of the light receiving element, FIG. 5 is a characteristic diagram with respect to its illuminance, FIG. 6 is a circuit configuration diagram of the photoelectric conversion signal processing section, and FIG. Time chart, FIG. 8 is a diagram showing the relationship between the air-fuel ratio and the average value of the light-receiving element output, FIG. 9 is a diagram showing the relationship between the air-fuel ratio and the light-receiving element output ratio, and FIG. 10 is the air-fuel ratio detection of multiple cylinders. It is a figure which shows the other Example of this invention suitable for. 3 ... Combustion flame light detection end, 5,6 ... Light receiving element, 7 ... Startup processing circuit, 8 ... Controller.

Claims (4)

[Claims] 1. A combustion flame light detection end for leading out combustion flame light from a combustion chamber of an internal combustion engine to the outside, and an optical branching means for branching the flame light led out by the detection end into a plurality of parts. A light receiving means having different spectral sensitivity characteristics for converting each flame light from the light branching means into an electric signal, and a peak value of each output electric signal of the light receiving means is detected and a ratio of the peak values is detected. And a calculation processing unit for calculating an air-fuel ratio signal from the combustion-light air-fuel ratio sensor. 2. The arithmetic processing means according to claim 1, wherein the peak value of the electric signal from each of the light receiving means having different spectral sensitivity characteristics is N times in an engine cycle (N is an arbitrary plural number). (Indicating the number of times), a combustion light air-fuel ratio sensor having an arithmetic function of calculating from an average value of electric signal peak values. 3. The combustion light space according to claim 1 or 2, wherein the combustion flame light detection end is provided on behalf of one of a plurality of cylinders of an engine. Fuel ratio sensor. 4. The combustion flame light detection end according to claim 1 or 2, wherein the combustion flame light detection end is arranged in each cylinder of the engine, and an optical fiber having the combustion flame light detection end is an optical coupling means. And a light-air-fuel ratio sensor for combustion light, wherein the light-air-fuel ratio sensor is optically connected to the light branching means.