JP2004184175A - Gas concentration sensor, and air-fuel mixture concentration detector for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect an air-fuel mixture concentration under an operation condition, even in an engine of high rotation type under a high heat load. <P>SOLUTION: When incident optical fibers 35 and emission optical fibers 36 are arranged inside an ignition plug 10, infrared rays emitted from the incident optical fibers 35 are reflected by a mirror 39, the reflected rays are made to get incident into the emission optical fibers 36, and the air-fuel mixture concentration is detected based on intensity of the reflected rays, the number of the emission optical fibers 36 is increased therein more than that of the incident optical fibers 35, and a recovery level of the reflected rays is increase thereby to enhance an S/N ratio. The mirror 39 is made of Si-Cr alloy the same as a plug electrode to enhance heat resistance, and is fixed weldedly to a main body. A ceramic adhesive is used as an adhesive for bundling the optical fibers to be coated, and end faces of the optical fibers are ground together with the adhesive, after cured. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gas concentration sensor used for detecting the concentration of an air-fuel mixture in a combustion chamber of an engine, for example.
[0002]
[Prior art]
In recent years, with the spread of fuel injectors called injectors, it becomes easier to control the timing of fuel injection and the amount of injected fuel, that is, the air-fuel ratio, and to promote higher output, lower fuel consumption, and cleaner exhaust gas. Now you can do it.
However, if the concentration of the air-fuel mixture in the combustion chamber, for example, the state of the concentration distribution, can be detected more accurately, further higher output, lower fuel consumption, cleaner exhaust gas, and the like can be achieved. In order to respond to such a demand, for example, light of a predetermined wavelength or frequency such as infrared light is incident on the gas to be detected, light that has passed through the gas to be detected is extracted, and the concentration of the gas to be detected is determined from the intensity of the light. It has been proposed to detect (for example, see Non-Patent Document 1).
[0003]
Further, using this gas concentration detection technique, two optical waveguides, specifically, an optical fiber are disposed in a spark plug in parallel or substantially in parallel, and one of the optical fibers has the predetermined wavelength or frequency. The light is emitted to the gas to be detected, the light is reflected by a mirror provided on the ignition plug, the reflected light passing through the gas to be detected is incident on the other optical fiber, and the intensity of the reflected light is used to determine the intensity of the reflected light. A gas concentration sensor for detecting the concentration of an air-fuel mixture has been considered.
[0004]
[Non-patent document 1]
Internal combustion engine symposium, '00 / 9, Eiji Tomita et al., "Measurement of hydrocarbon fuel concentration near spark plug in engine cylinder using 3.392 µm infrared absorption method"
[0005]
[Problems to be solved by the invention]
However, there is a situation in which the conventional gas concentration sensor can be used only in a low / medium load state in an actual engine operation state. In particular, motorcycle engines and competition engines use a high rotation range and have a large heat load, so that, for example, the mirror is melted or the adhesive coating the optical fiber is melted. There is. In addition, the light of the predetermined wavelength or frequency is absorbed by a specific component of the air-fuel mixture, but is diffused at the same time. Therefore, the amount of reflected light recovered is small, the sensitivity is low, and so-called S / N is poor. There are also problems.
[0006]
The present invention has been developed to solve the above problems, and has a good S / N, excellent heat resistance, and a gas concentration sensor and an engine for an engine capable of accurately detecting the concentration of air-fuel mixture in a combustion chamber. It is an object of the present invention to provide a mixture concentration detecting device.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the gas concentration sensor according to claim 1 of the present invention is configured such that two or more optical waveguides are arranged in parallel or substantially in parallel, and light of a predetermined wavelength or frequency is transmitted to any one of the optical waveguides. A gas concentration sensor for detecting the concentration of the gas to be detected from the intensity of the reflected light, which is emitted from the gas to the gas to be detected, passes through the gas to be detected, is reflected by a mirror, and is incident on a different optical waveguide. Wherein the number of optical waveguides for entering the reflected light is larger than the number of optical waveguides for emitting light of the predetermined wavelength or frequency to the gas to be detected.
[0008]
In the gas concentration sensor according to claim 2 of the present invention, two or more optical waveguides are disposed in parallel or substantially parallel, and light of a predetermined wavelength or frequency is emitted from any one of the optical waveguides to the gas to be detected. In the gas concentration sensor for detecting the concentration of the gas to be detected based on the intensity of the reflected light, the reflected light that has passed through the gas to be detected and reflected by the mirror is incident on a different optical waveguide. -Cr alloy.
[0009]
According to a third aspect of the present invention, in the gas concentration sensor according to the second aspect, the mirror is fixed by welding.
In the gas concentration sensor according to claim 4 of the present invention, two or more optical waveguides are arranged in parallel or substantially parallel, and light of a predetermined wavelength or frequency is emitted from any one of the optical waveguides to the gas to be detected. Then, passing through the gas to be detected, the reflected light reflected by the mirror is incident on a different optical waveguide, in the gas concentration sensor for detecting the concentration of the gas to be detected from the intensity of the reflected light, the two or more The optical waveguide is fixed so as to be covered with a ceramic adhesive, and after curing, the input / output end faces of the optical waveguide are ground together with the ceramic adhesive.
[0010]
According to a fifth aspect of the present invention, in the gas concentration sensor according to the first to fourth aspects, the two or more optical waveguides are provided in an ignition plug.
Further, according to a sixth aspect of the present invention, there is provided an air-fuel mixture concentration detecting apparatus for an engine according to any one of the first to fifth aspects, wherein the mirror projects from one combustion chamber into the combustion chamber. It is characterized in that two or more concentration sensors are provided to detect the mixture concentration at different parts in the combustion chamber.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described.
FIG. 1 is a schematic configuration showing an example of an engine for a motorcycle and a control device thereof. The engine 1 is a single-cylinder four-stroke engine having a relatively small displacement, and includes a cylinder body 2, a crankshaft 3, a piston 4, a combustion chamber 5, an intake pipe 6, an intake valve 7, an exhaust pipe 8, an exhaust valve 9, An ignition plug (ignition plug) 10 and an ignition coil 11 are provided. A throttle valve 12 that opens and closes in accordance with the accelerator opening is provided in the intake pipe 6, and an injector 13 as a fuel injection device is provided in the intake pipe 6 downstream of the throttle valve 12. . The injector 13 is connected to a filter 18, a fuel pump 17, and a pressure control valve 16 provided in a fuel tank 19. In the figure, reference numeral 30 denotes a laser for generating light of a predetermined wavelength or frequency such as infrared light, reference numeral 31 denotes a chopper (electronic shutter) for cutting out the light generated by the laser 30, and reference numeral 32 denotes a light source to be described later. Reference numeral 33 denotes an optical fiber cable for detecting the intensity of the reflected light.
[0012]
The operating state of the engine 1 is controlled by an engine control unit 15, and the engine control unit 15 includes an arithmetic processing device such as a microcomputer. As means for detecting the control input of the engine control unit 15, that is, the operating state of the engine 1, the crank angle sensor 20 for detecting the rotation angle of the crankshaft 3, that is, the phase, the temperature of the cylinder body 2, or the cooling water A cooling water temperature sensor 21 for detecting a temperature, that is, a temperature of the engine body; an exhaust air-fuel ratio sensor 22 for detecting an air-fuel ratio in the exhaust pipe 8; an intake pressure sensor 24 for detecting an intake pressure in the intake pipe 6; An intake air temperature sensor 25 for detecting the temperature in the pipe 6, that is, the intake air temperature is provided. Then, the engine control unit 15 receives the detection signals of these sensors and outputs control signals to the fuel pump 17, the pressure control valve 16, the injector 13, and the ignition coil 11.
[0013]
The ignition plug 10 incorporates a gas concentration sensor for detecting the concentration of the air-fuel mixture in the combustion chamber 5. Specifically, as shown in FIG. 2, for example, when the combustion chamber 5 side of the ignition plug 10 is the front end and the opposite side is the rear end, the center of the ignition plug 10 is connected to the center electrode 41 from the rear end. A through hole 51 is formed up to the tip of the optical fiber rod 34, and the optical fiber rod 34 is inserted into the through hole 51 to constitute a gas concentration sensor. A cylindrical conductor 52 is provided around the through hole 51, and power is supplied to the center electrode 41 via the conductor 52. Further, as will be described later, since a mirror 39 is provided at the tip of the spark plug 10, a ground electrode 42 is provided beside the center electrode 41, unlike a normal spark plug. Incidentally, reference numeral 29 in the drawing denotes an ignition cable.
[0014]
A transparent sapphire rod 43 for protecting the optical fiber rod 34 from a thermal load is embedded in the tip of the through hole 51. A heat-resistant bracket 53 is erected on the side of the center electrode 41 toward the tip of the spark plug 10, and the tip of the heat-resistant bracket 53 is fixed to the center electrode 41, more precisely, from the sapphire rod 43. Mirrors 39 are provided at intervals. The mirror 39 and the bracket 53 are made of a Ni-Cr alloy conventionally used for a ground electrode of a spark plug, and naturally have a sufficient heat resistance. The mirror 39 is formed at the distal end of the Ni-Cr alloy bracket 53, obtains a sufficient mirror surface by grinding, and is fixed to the spark plug 10 body by welding. When the mirror 39 (bracket 53) is fixed by welding in this manner, heat transfer characteristics are superior to, for example, screwing. Further, the mirror 39 made of the Ni-Cr alloy hardly fogs and does not melt even when exposed to the high temperature of the explosion.
[0015]
On the other hand, a metal connecting member 54 is attached to the rear end of the ignition plug 10, and the through hole 51 is also opened in this connecting member 54, and a female screw is formed at the rear end. ing. The optical fiber rod 34 is inserted from the rear end of the connecting member 54, and a male screw formed on the optical fiber rod 34 is screwed and fixed to a female screw of the connecting member 54. A predetermined gap is formed between the optical fiber rod 34 and the sapphire rod 43 so as to protect the optical fiber rod 34 from the high temperature of the combustion chamber 5.
[0016]
A lens 55 is buried at the center end of the optical fiber rod 34, and a plurality of optical fibers 35, 36, that is, optical waveguides are disposed behind or behind the lens 55 in parallel or substantially parallel. The lens 55 is for adjusting the spread angle of the light emitted from the optical fiber 35 to efficiently guide the light to the gas concentration detector. Instead of mounting the lens 55, the end surface of the sapphire rod 43 may be framed to function as a lens. In addition, a configuration without a lens is also possible. If there is no lens, the efficiency is slightly deteriorated. However, it is possible to accurately detect the gas concentration by using a high output laser 30 or a high sensitivity light intensity detector 32. With this configuration, there is an advantage that it is easy to reduce the size because the number of components incorporated in the ignition plug is reduced.
[0017]
FIG. 3 shows an example of the arrangement of the optical fibers 35 and 36 provided in the optical fiber rod 34. In this example, four optical fibers are provided, one of which is an incident optical fiber 35 for allowing the light of the predetermined wavelength or frequency to be incident on the gas to be detected, and the other three are connected to the mirror. The output optical fiber 36 emits the reflected light to the light intensity detector. The light of a predetermined wavelength or frequency emitted from the incident optical fiber 35 passes through the gap, the sapphire rod 43, passes through the gas to be detected, is reflected by the mirror 39, and is further reflected by the gas to be detected, the sapphire rod 43, and the gap. The light passes through in order and enters the output optical fiber 36. As described above, light of a predetermined wavelength or frequency, for example, infrared light is absorbed by the hydrocarbon of the gas mixture which is the gas to be detected, so if the intensity of the reflected light is detected, the amount of hydrocarbons of the gas mixture, that is, You can see the concentration. However, since the light for concentration detection is absorbed by the air-fuel mixture and diffuses into the air-fuel mixture, there is a problem that the amount of reflected light collected is small. Therefore, in the present embodiment, one of the four optical fibers is an incident optical fiber 35, and the remaining three are an output optical fiber 36, thereby increasing the amount of collected reflected light and improving the concentration detection sensitivity. , So-called S / N is made favorable.
[0018]
The layout of the incident optical fiber 35 and the outgoing optical fiber 36 may be, for example, other than those shown in FIGS. In FIG. 4, one incident optical fiber 35 is provided at the center of the optical fiber rod, and a plurality of outgoing optical fibers 36 are provided on the outer periphery thereof. In FIG. 5, one incident optical fiber 35 is disposed at the center of the optical fiber rod, and a plurality of outgoing optical fibers 36 are disposed on the outer periphery of the optical fiber rod. The diameter of 35 is increased to increase the amount of inspection light incident on the gas to be detected. In FIG. 6, four incident optical fibers 35 are provided at the center of the optical fiber rod, and a plurality of outgoing optical fibers 36 are provided on the outer periphery thereof. Similarly, it is possible to increase the amount of inspection light incident on the gas to be detected. Thus, by making the number of the outgoing optical fibers 36 larger than the number of the incident optical fibers 35, the sensitivity can be improved and the S / N can be improved.
[0019]
The plurality of optical fibers 35 and 36 described above are covered with an adhesive and fixed integrally. In this embodiment, a ceramic adhesive is used as the adhesive. The coating layer of the ceramic adhesive is indicated by reference numeral 37. Conventional adhesives are so-called epoxy adhesives, which are susceptible to heat and easily melt away under normal engine operating conditions. Ceramic adhesives are excellent in heat resistance, but are very difficult to grind after curing. In particular, when used for coating an optical fiber, it becomes necessary to grind the end face of the optical fiber together with the adhesive coating layer 37. The present inventors have made intensive studies and found a technique for grinding the end face of the optical fiber together with the cured ceramic-based adhesive, and have developed a gas concentration sensor of the present embodiment.
[0020]
According to the gas concentration sensor of the present embodiment and the mixture concentration detection device for an engine using the same, since the S / N and heat resistance are excellent, the mixture concentration can be detected with high response from low rotation to high rotation. Becomes possible. FIG. 7A shows the change over time in the mixture concentration when the throttle is opened all at once from a low throttle opening. In this embodiment, the mixture concentration can be detected with a very high response. Therefore, by shortening the sampling period, for example, the change in the mixture concentration during one cycle as shown in FIG. It is also possible to take out the change in the mixture concentration for each rotation speed as shown in FIG.
[0021]
Also, in the present embodiment, the size of the ignition plug 10 incorporating the gas concentration sensor can be reduced due to the above-described improvement in heat resistance, that is, the gas concentration sensor has been successfully reduced in size. Therefore, as shown in FIG. 8, a plurality of gas concentration sensors (ignition plugs 10) are attached to one combustion chamber 5 so that the mirror 39 protrudes into the combustion chamber 5, and the respective gas concentration It is also possible to detect the concentration of the mixture in different parts of the combustion chamber with a sensor. At this time, for example, as shown in FIG. 9, the light from one laser 30 is split by a half mirror 38 and supplied to each gas concentration sensor, or as shown in FIG. By bundling the light from one laser 30 into each of the incident optical fibers 35, it is possible to supply inspection light having the same phase to a plurality of gas concentration sensors. Further, by adjusting the beam diameter of light by interposing a lens at the incident end of each incident optical fiber 35, the efficiency can be improved. If the mixture concentration is detected at a plurality of locations in one combustion chamber 5 in this way, the concentration distribution of the mixture in the combustion chamber 5 can be detected.
[0022]
In the above embodiment, a laser is used as a light source having a predetermined wavelength or frequency, but the light source is not limited to this. For example, infrared light is required to detect the concentration of the air-fuel mixture. However, since infrared light is emitted from a heat source, a heater or the like can be used.
Further, the gas concentration sensor of the present invention can detect the concentration of gas not only in the combustion chamber of the engine but also in various fields, and can be used particularly under a high heat load and high temperature condition. In that case, the wavelength or frequency of the light to be efficiently absorbed by the gas to be detected may be set.
[0023]
【The invention's effect】
As described above, according to the gas concentration sensor according to claim 1 of the present invention, the reflected light is incident on the gas to be detected, rather than the optical waveguide for emitting light of a predetermined wavelength or frequency to the gas to be detected. By increasing the number of optical waveguides, the amount of reflected light recovered is increased, sensitivity is improved, and S / N is improved.
[0024]
Further, according to the gas concentration sensor according to claim 2 of the present invention, the mirror is made of a Ni-Cr alloy, so that the heat resistance of the mirror is improved, and the mirror can be applied to a high rotation type, high heat load engine. Become.
According to the gas concentration sensor according to claim 3 of the present invention, the mirror is fixed by welding, so that the heat transfer characteristics are improved, and the gas concentration sensor can be applied to a higher rotation type and higher heat load engine.
[0025]
According to the gas concentration sensor according to claim 4 of the present invention, two or more optical waveguides are fixed so as to be covered with a ceramic adhesive, and after curing, the input and output of the optical waveguide together with the ceramic adhesive. By grinding the end face, the heat resistance of the optical waveguide coating is improved, and it can be applied to a high-rotation type and high heat load engine.
According to the gas concentration sensor according to claim 5 of the present invention, by arranging two or more optical waveguides in the ignition plug, the air-fuel mixture at the position of the ignition plug most desired to be detected in the combustion chamber of the engine. The concentration can be detected.
[0026]
According to the mixture concentration detecting device for an engine according to claim 6 of the present invention, two or more gas concentration sensors are provided for one combustion chamber such that a mirror projects into the combustion chamber. Since the configuration is such that the mixture concentration is detected at different parts in the combustion chamber, it is possible to detect even the distribution state of the mixture in the combustion chamber.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an engine for a motorcycle and an air-fuel mixture concentration detection device.
FIG. 2 is a detailed view of a gas concentration sensor provided in the ignition plug of FIG.
FIG. 3 is an arrangement diagram of optical fibers of the gas concentration sensor of FIG. 2;
FIG. 4 is an arrangement diagram of optical fibers of the gas concentration sensor of FIG. 2;
FIG. 5 is an arrangement diagram of optical fibers of the gas concentration sensor of FIG. 2;
FIG. 6 is an arrangement diagram of optical fibers of the gas concentration sensor of FIG. 2;
FIG. 7 is an explanatory diagram of a detection result of a mixture concentration by the mixture concentration detecting apparatus of FIG. 1;
FIG. 8 is an explanatory diagram for detecting an air-fuel mixture concentration at multiple points in a combustion chamber.
FIG. 9 is an explanatory diagram of a spectroscopic method of inspection light.
FIG. 10 is an explanatory diagram of a spectroscopic method of inspection light.
[Explanation of symbols]
1 is an engine 3 is a crankshaft 4 is a piston 5 is a combustion chamber 6 is an intake pipe 7 is an intake valve 8 is an exhaust pipe 9 is an exhaust valve 10 is a spark plug 11 is an ignition coil 12 is a throttle valve 13 is an injector 15 is an engine control unit 16 is a pressure control valve 17 is a fuel pump 30 is a laser 31 is a chopper 32 is a light intensity detector 33 is an optical fiber cable 34 is an optical fiber rod 35 is an incident optical fiber 36 is an output optical fiber 37 is an adhesive coating layer 38. Mirror 39 is a mirror

Claims (6)

Two or more optical waveguides are arranged in parallel or substantially in parallel, and light of a predetermined wavelength or frequency is emitted from any one of the optical waveguides to the gas to be detected, passes through the gas to be detected, and is reflected by a mirror. Light is incident on different optical waveguides, and in a gas concentration sensor for detecting the concentration of the gas to be detected from the intensity of the reflected light, the optical waveguide for inputting the reflected light passes the light of the predetermined wavelength or frequency. A gas concentration sensor, wherein the number is larger than that of an optical waveguide for emitting light to a gas to be detected. Two or more optical waveguides are arranged in parallel or substantially in parallel, and light of a predetermined wavelength or frequency is emitted from any one of the optical waveguides to the gas to be detected, passes through the gas to be detected, and is reflected by a mirror. A gas concentration sensor for making light incident on different optical waveguides and detecting the concentration of a gas to be detected from the intensity of the reflected light, wherein the mirror is made of a Ni-Cr alloy. The gas concentration sensor according to claim 2, wherein the mirror is fixed by welding. Two or more optical waveguides are arranged in parallel or substantially in parallel, and light of a predetermined wavelength or frequency is emitted from any one of the optical waveguides to the gas to be detected, passes through the gas to be detected, and is reflected by a mirror. Light is incident on different optical waveguides, and in a gas concentration sensor for detecting the concentration of the gas to be detected from the intensity of the reflected light, the two or more optical waveguides are fixed so as to be covered with a ceramic adhesive and cured. Thereafter, the input / output end face of the optical waveguide is ground together with the ceramic-based adhesive. The gas concentration sensor according to any one of claims 1 to 4, wherein the two or more optical waveguides are provided in an ignition plug. For one combustion chamber, two or more gas concentration sensors according to any one of claims 1 to 5 are provided so that the mirror projects into the combustion chamber, and the mixture concentration at different portions in the combustion chamber is measured. An air-fuel mixture concentration detection device for an engine, wherein the detection is performed.

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