JP2008151735A - Gas sensor, air-fuel ratio control device including the same, and transportation equipment - Google Patents

Abstract

An object of the present invention is to reduce the number of parts of a gas sensor and reduce the number of steps and cost required for assembly.
A gas sensor according to the present invention includes a sensor element 10 having a detection unit 11 for detecting a predetermined gas, a first cover 71 covering the detection unit 11 of the sensor element 10, and a first cover 71. And a second cover 72 for covering. The first cover 71 and the second cover 72 are integrally formed.
[Selection] Figure 1

Description

  The present invention relates to a gas sensor, and more particularly to a gas sensor having a cover that covers a detection portion of a sensor element. The present invention also relates to an air-fuel ratio control device and a transportation device provided with such a gas sensor.

  From the viewpoint of environmental problems and energy problems, it is required to improve the fuel consumption of an internal combustion engine and to reduce the emission amount of regulated substances (such as NOx) contained in the exhaust gas of the internal combustion engine. For this purpose, it is necessary to appropriately control the ratio of fuel to air in accordance with the combustion state so that the fuel can always be burned under optimum conditions. The ratio of air to fuel is called the air / fuel ratio (A / F), and when using a three-way catalyst, the optimum air / fuel ratio is the stoichiometric air / fuel ratio. The stoichiometric air-fuel ratio is an air-fuel ratio in which air and fuel burn without excess or deficiency.

  When the fuel is burned at the stoichiometric air-fuel ratio, certain oxygen is contained in the exhaust gas. When the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, that is, when the fuel concentration is relatively high, the oxygen amount in the exhaust gas decreases compared to the oxygen amount in the case of the stoichiometric air-fuel ratio. On the other hand, when the air-fuel ratio is larger than the stoichiometric air-fuel ratio (the fuel concentration is relatively low), the amount of oxygen in the exhaust gas increases. Therefore, by measuring the oxygen concentration in the exhaust gas using an oxygen sensor, it is estimated how much the air-fuel ratio deviates from the stoichiometric air-fuel ratio, and the fuel burns under optimal conditions by adjusting the air-fuel ratio. It becomes possible to control.

  An oxygen sensor for measuring the oxygen concentration in the exhaust gas is disclosed in Patent Document 1, for example. As disclosed in Patent Document 1, the oxygen sensor includes a cover that covers the detection unit so that the exhaust gas does not directly hit the detection unit for detecting oxygen.

  FIG. 8 schematically shows a conventional oxygen sensor 800. The oxygen sensor 800 includes a sensor element 810 and a housing 820 into which the sensor element 810 is inserted. The housing 820 is made of a metal material such as stainless steel, and the oxygen sensor 800 is fixed to the exhaust pipe of the internal combustion engine by the housing 820.

  The sensor element 810 includes a detection unit 811 for detecting oxygen and a substrate 812 that supports the detection unit 811. The sensor element 810 is disposed on the lower end side of the housing 820 so as to expose the detection unit 811. The sensor element 810 is fixed to the housing 820 by a fixing member 822 formed of a glass material inside the housing 820.

  The sensor element 810 is electrically connected to the lead wire 830 via a terminal portion 840 provided at the end thereof. The lead wire 830 is covered with an insulating resin (PTFE or the like).

  A cylindrical member 850 made of a metal material such as stainless steel is provided at the upper end portion of the housing 820. A rubber member 860 having a through hole through which the lead wire 830 is inserted is disposed inside the tubular member 850. The upper end portion 850a of the tubular member 850 is caulked inward to thereby lead the lead wire 830. Is fixed, and the cylindrical member 850 is sealed.

Two covers 871 and 872 are provided at the lower end portion of the housing 820 so as to cover the detection portion 811 of the sensor element 810. Each of the covers 871 and 872 is formed with circular vent holes 871a and 872a for introducing exhaust gas into the inside. As described above, the detection unit 811 is covered with the covers 871 and 872 so as to prevent the exhaust gas from directly hitting the detection unit 811.
Japanese Patent No. 3493875

  The two covers 871 and 872 of the conventional oxygen sensor 800 are each formed in a cylindrical shape and have a shape that covers the sensor element 810 to the tip. Accordingly, the two covers 871 and 872 are formed as separate parts and attached to the housing 820 by welding or caulking.

  However, the provision of the two covers 871 and 872 as described above causes an increase in the number of parts, which increases the number of steps and cost required for assembly.

  The present invention has been made in view of the above problems, and an object thereof is to reduce the number of parts of the gas sensor and to reduce the number of steps and cost required for assembly.

  A gas sensor according to the present invention includes a sensor element having a detection unit for detecting a predetermined gas, a first cover that covers the detection unit of the sensor element, and a second cover that covers the first cover. The first cover and the second cover are integrally formed.

  In a preferred embodiment, the second cover has a bottomless cylindrical shape.

  In a preferred embodiment, each of the first cover and the second cover has a vent hole extending in a direction from the proximal end portion to the distal end portion of the sensor element.

  In a preferred embodiment, the first cover and the second cover are integrally formed by injection molding.

  In a preferred embodiment, the gas sensor according to the present invention includes a housing that houses the sensor element, and the first cover and the second cover are formed integrally with the housing.

  In a preferred embodiment, the first cover and the second cover are made of a metal material.

  In a preferred embodiment, the gas sensor according to the present invention is an oxygen sensor.

  An air-fuel ratio control apparatus according to the present invention includes a gas sensor having the above-described configuration.

  A transportation device according to the present invention includes an air-fuel ratio control device having the above-described configuration.

  In the gas sensor according to the present invention, since the first cover that covers the detection portion of the sensor element and the second cover that covers the first cover are integrally formed, the structure in which the two covers are formed separately. Compared to this oxygen sensor, the number of parts can be reduced, and the number of steps and cost required for assembly can be reduced.

  The first cover and the second cover can be preferably integrally formed by injection molding.

  The second cover is preferably a bottomless cylinder (that is, the tip is open). When the second cover has a bottomless cylindrical shape, it is easy to integrally form the first cover and the second cover. For example, in the case of using injection molding, the mold can be easily removed after molding, so that it is easy to integrally form the first cover and the second cover.

  Each of the first cover and the second cover preferably has a vent hole extending in a direction from the proximal end portion of the sensor element toward the distal end portion. If the vent hole extends in the direction from the base end portion to the tip end portion of the sensor element, the vent hole can be formed at the same time when the first cover and the second cover are formed by injection molding. Therefore, since it is not necessary to form a vent hole separately, the number of manufacturing steps of the first cover and the second cover can be reduced. Further, regardless of the relative arrangement relationship between the vent hole of the first cover and the vent hole of the second cover (for example, even when they are arranged so as not to overlap each other), the vent hole is provided in the first cover. It can be formed easily.

  The first cover and the second cover are preferably formed integrally with a housing that houses the sensor element. By forming the first cover and the second cover integrally with the housing, the number of parts can be further reduced, and the number of processes and cost required for assembly can be further reduced.

  The first cover and the second cover are typically formed from a metal material.

  The present invention can be widely used for gas sensors in general, and can be suitably used for, for example, an oxygen sensor that detects oxygen.

  The oxygen sensor according to the present invention is suitably used for an air-fuel ratio control device that controls the air-fuel ratio of an internal combustion engine, and the air-fuel ratio control device equipped with the oxygen sensor according to the present invention is suitably used for various transportation equipment.

  According to the present invention, the number of parts of the gas sensor can be reduced, and the number of steps and cost required for assembly can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment.

  1, 2 and 3 show an oxygen sensor 100 in the present embodiment. 1, 2, and 3 are a cross-sectional view, a side view, and a perspective view schematically showing the oxygen sensor 100.

  The oxygen sensor 100 includes a sensor element 10 and a housing 20 that houses the sensor element 10. The housing 20 is formed from a metal material such as stainless steel. The housing 20 has a screw portion 20a formed with a thread (not shown in FIGS. 2 and 3) on its side surface, and the oxygen sensor 100 is fixed to the exhaust pipe of the internal combustion engine by the housing 20. The

  The sensor element 10 includes a detection unit 11 for detecting oxygen and a substrate 12 that supports the detection unit 11. As the sensor element 10, various elements that can detect oxygen can be used. For example, an electromotive force type sensor element using a solid electrolyte as disclosed in JP-A-8-114571 or a resistance-type sensor element as disclosed in JP-A-5-18921 is used. be able to.

  The electromotive force type sensor element measures the oxygen concentration by detecting a difference in oxygen partial pressure between a reference electrode exposed to air and a measurement electrode exposed to exhaust gas as an electromotive force. On the other hand, the resistance type sensor element detects a change in resistivity of the oxide semiconductor layer provided in contact with the exhaust gas. When the oxygen partial pressure in the exhaust gas changes, the oxygen vacancy concentration in the oxide semiconductor layer fluctuates, so that the resistivity of the oxide semiconductor layer changes. Therefore, the oxygen concentration can be measured by detecting this change in resistivity.

  Since the resistance type sensor element does not require a reference electrode unlike the electromotive force type sensor element, the structure of the sensor element itself can be simplified. Therefore, it is preferable to use a resistance type sensor element from the viewpoint of miniaturization of the oxygen sensor 100. As the oxide semiconductor of the resistance type sensor element, for example, titania (titanium dioxide) is used. Further, cerium oxide may be used. Cerium oxide is excellent in durability and stability.

  When the sensor element 10 is an electromotive force type, the detection unit 11 includes a solid electrolyte layer and an electrode. When the sensor element 10 is a resistance type, the detection unit 11 includes an oxide semiconductor layer and an electrode. The substrate 12 of the sensor element 10 is made of an insulating material (for example, a ceramic material such as alumina or silicon nitride), and the detection unit 11 is placed on the tip of the substrate 12 (that is, the tip of the sensor element 10). Is provided.

  The sensor element 10 is inserted and arranged in a holder 21 provided inside the housing 20, and is fixed to the holder 21 by a fixing member 22 provided at the upper end portion of the holder 21. The holder 21 is made of, for example, a ceramic material, and the fixing member 22 is made of, for example, a glass material. The structure for holding and fixing the sensor element 10 to the housing 20 is not limited to the one exemplified here.

  The sensor element 10 is electrically connected to the lead wire 30 via the terminal portion 40. The lead wire 30 is made of a metal material (for example, copper) and is covered with an insulating material (resin such as PTFE). The terminal portion 40 is made of a metal material such as stainless steel or nickel alloy, and is connected to the base end portion (the end portion on which the detection portion 11 is not provided) of the sensor element 10.

  A cylindrical member 50 is provided on the upper end side of the holder 21 so as to cover the terminal portion 40. The cylindrical member 50 is formed from a metal material such as stainless steel. The cylindrical member 50, the holder 21, and the housing 20 are fixed to each other by caulking the upper end portion 20b of the housing 20. A filler 23 for hermetic sealing is provided between the holder 21 and the housing 20. The filler 23 is made of, for example, talc.

  A sealing member 60 that seals the cylindrical member 50 is provided at an upper end portion (an end portion far from the holder 21) 50 a of the cylindrical member 50. The sealing member 60 has a through hole through which the lead wire 30 is inserted. The sealing member 60 is made of a rubber material such as fluoro rubber, and the lead wire 30 is fixed and the cylindrical member 50 is sealed by caulking the upper end portion 50a of the cylindrical member 50 inward. .

  The oxygen sensor 100 further includes a first cover 71 that covers the detection unit 11 of the sensor element 10 and a second cover 72 that covers the first cover 71 on the lower end side of the housing 20. Below, the 1st cover 71 arrange | positioned relatively inside is called an "inner cover", and the 2nd cover 72 arrange | positioned relatively outside is called an "outer cover." The inner cover 71 and the outer cover 72 are formed from a metal material such as stainless steel.

  In this embodiment, the inner cover 71 and the outer cover 72 are integrally formed. That is, the inner cover 71 and the outer cover 72 are not parts formed separately. The inner cover 71 and the outer cover 72 in the present embodiment are also formed integrally with the housing 20. In the conventional oxygen sensor 800 shown in FIG. 8, the cover 871, 872 and the housing 820 are three parts formed separately, whereas the inner cover 71, the outer cover 72, and the housing 20 in the present embodiment. Is one part formed integrally.

  As described above, when the inner cover 71 and the outer cover 72 are integrally formed, the number of parts is reduced compared to an oxygen sensor having a structure in which two covers are formed separately, and a process required for assembly. The number and cost can be reduced. Further, by forming the inner cover 71 and the outer cover 72 integrally with the housing 20 as in this embodiment, the number of parts can be further reduced, and the number of steps and costs required for assembly can be further reduced.

  The inner cover 71 and the outer cover 72 can be integrally formed by, for example, injection molding. Since the inner cover 71 and the outer cover 72 are typically made of a metal material, they can be integrally formed by a technique called metal injection molding (MIM). As its name suggests, MIM is a technology for injection molding of metal materials. In MIM, a metal powder is kneaded with a binder so that injection molding similar to the case where a resin material is used, and after injection molding, the binder is removed by heating to sinter into a single metal.

  Moreover, the inner cover 71 and the outer cover 72 can be integrally formed with the housing 20 by injection molding. FIG. 4 shows the mold 1 used to integrally form the inner cover 71, the outer cover 72 and the housing 20. The mold 1 shown in FIG. 4 has an upper mold 1 a and a lower mold 1 b having surface shapes corresponding to the inner and outer surfaces of the inner cover 71, the outer cover 72, and the housing 20. By performing injection molding using such a mold 1, an integrally formed inner cover 71, outer cover 72 and housing 20 are obtained as shown in FIGS. 4 and 5.

  4 shows the mold 1 for integrally forming the inner cover 71 and the outer cover 72 integrally with the entire housing 20, but the inner cover 71 and the outer cover 72 are only part of the housing 20. You may form integrally.

  As a material of the inner cover 71, the outer cover 72, and the housing 20, a metal material such as stainless steel or an iron-nickel alloy can be used. As the stainless steel, for example, SUS316 can be used.

  As shown in FIG. 1 and the like, each of the inner cover 71 and the outer cover 72 has a cylindrical shape (which is of course not limited to a cylindrical shape), but the inner cover 71 has a bottomed cylindrical shape. On the other hand, the outer cover 72 has a bottomless cylindrical shape. That is, the outer cover 72 has a shape in which the tip is opened.

  If the two covers 871 and 872 are both bottomed cylindrical like the conventional oxygen sensor 800 shown in FIG. 8, it is difficult to form the two covers 871 and 872 integrally. For example, in the case of using injection molding, it is difficult to remove the mold after molding, so it is very difficult to integrally form the two covers 871 and 872.

  On the other hand, when the outer cover 72 has a bottomless cylindrical shape as in this embodiment, it is easy to integrally form the inner cover 71 and the outer cover 72. For example, in the case of using injection molding, the mold can be easily removed after molding (in other words, a simple mold can be used). Therefore, the inner cover 71 and the outer cover 72 can be formed integrally. Easy.

  As shown in FIG. 3, the inner cover 71 and the outer cover 72 are respectively formed with vent holes (gas inlets) 71a and 72a for introducing exhaust gas into the interior. As shown in FIGS. 3 and 5, the vent hole 71 a of the inner cover 71 and the vent hole 72 a of the outer cover 72 are configured so that the exhaust gas flowing in the exhaust pipe does not directly hit the detection unit 11 of the sensor element 10. It is preferable that they are arranged so as not to overlap each other.

  In the present embodiment, the vent hole 71 a of the inner cover 71 and the vent hole 72 a of the outer cover 72 extend in the direction from the proximal end portion of the sensor element 10 toward the distal end portion. In other words, the vent holes 71a and 72a are formed in a slit shape. Thus, when the vent holes 71a and 72a extend in the direction from the base end portion to the tip end portion of the sensor element 10 (corresponding to the direction in which the mold 1 is pulled out as can be seen from FIG. 4), injection molding is performed. Thus, when forming the inner cover 71 and the outer cover 72, the air holes 71a and 72a can be formed at the same time. Therefore, since it is not necessary to form the ventilation holes 71a and 72a separately, the number of manufacturing steps of the inner cover 71 and the outer cover 72 can be reduced. When the vent hole 71a of the inner cover 71 and the vent hole 72a of the outer cover 72 are arranged so as not to overlap each other, the vent hole 71a is formed in the inner cover 71 after injection molding (for example, formed by machining). ) Is difficult due to the outer cover 72 covering the inner cover 71. However, by forming the vent hole 71a of the inner cover 71 into a slit shape at the time of injection molding, regardless of the relative positional relationship between the vent hole 71a of the inner cover 71 and the vent hole 72a of the outer cover 72, A vent hole 71a can be easily provided in the inner cover 71.

  An opening 71b (see FIG. 3) provided in a portion corresponding to the bottom of the inner cover 71 is a hole (gas exhaust port) for exhausting exhaust gas introduced into the oxygen sensor 100. .

  FIG. 6 schematically shows a motorcycle 500 including the oxygen sensor 100 according to this embodiment. The motorcycle 500 includes a main body frame 501 and an internal combustion engine 600. A head pipe 502 is provided at the front end of the main body frame 501. The head pipe 502 is provided with a front fork 503 that can swing in the left-right direction. A front wheel 504 is rotatably supported at the lower end of the front fork 503. A handle 505 is attached to the upper end of the head pipe 502.

  A seat rail 506 is attached so as to extend rearward from the upper rear end of the main body frame 501. A fuel tank 507 is provided above the main body frame 501, and a main seat 508 a and a tandem seat 508 b are provided on the seat rail 506. A rear arm 509 extending rearward is attached to the rear end of the main body frame 501. A rear wheel 510 is rotatably supported at the rear end of the rear arm 509.

  An internal combustion engine 600 is held at the center of the main body frame 501. A radiator 511 is attached to the front portion of the internal combustion engine 600. An exhaust pipe 630 is connected to the exhaust port of the internal combustion engine 600. The exhaust pipe 630 is provided with an oxygen sensor 100, a three-way catalyst 604, and a silencer 606. The oxygen sensor 100 detects oxygen in the exhaust gas flowing through the exhaust pipe 630.

  A transmission 515 is connected to the internal combustion engine 600, and an output shaft 516 of the transmission 515 is attached to a drive sprocket 517. Drive sprocket 517 is connected to rear wheel sprocket 519 of rear wheel 510 via chain 518.

  FIG. 7 shows the main configuration of the control system of the internal combustion engine 600. The cylinder 601 of the internal combustion engine 600 is provided with an intake valve 610, an exhaust valve 606, and a spark plug 608. Further, a water temperature sensor 616 for measuring the temperature of the cooling water for cooling the engine is provided. The intake valve 610 is connected to an intake pipe 622 having an air intake port. The intake pipe 622 is provided with an air flow meter 612, a throttle sensor 614 for a throttle valve, and a fuel injection device 611.

  The air flow meter 612, the throttle sensor 614, the fuel injection device 611, the water temperature sensor 616, the spark plug 608, and the oxygen sensor 100 are connected to a computer 618 that is a control unit. A computer speed signal 620 indicating the speed of the motorcycle 500 is also input to the computer 618.

  When the rider starts the internal combustion engine 600 by a cell motor (not shown), the computer 618 calculates an optimal fuel amount based on the detection signal and the vehicle speed signal 620 obtained from the air flow meter 612, the throttle sensor 614, and the water temperature sensor 616, A control signal is output to the fuel injection device 611 based on the calculation result. The fuel injected from the fuel injection device 611 is mixed with the air supplied from the intake pipe 622, and is injected into the cylinder 601 through the intake valve 610 that is opened and closed at an appropriate timing. The fuel ejected in the cylinder 601 burns and becomes exhaust gas, which is guided to the exhaust pipe 630 through the exhaust valve 606.

  The oxygen sensor 100 detects oxygen in the exhaust gas and outputs a detection signal to the computer 618. The computer 618 determines how much the air-fuel ratio deviates from the ideal air-fuel ratio based on the signal from the oxygen sensor 100. Then, the amount of fuel ejected from the fuel injection device 611 is controlled so as to achieve an ideal air-fuel ratio with respect to the amount of air determined by signals obtained from the air flow meter 612 and the throttle sensor 614. As described above, the air-fuel ratio of the internal combustion engine is appropriately controlled by the air-fuel ratio control device including the oxygen sensor 100 and the computer (control unit) 618 connected to the oxygen sensor 100.

  In the present embodiment, a motorcycle has been described as an example, but the oxygen sensor 100 in the present embodiment is also used for other motor vehicles such as a four-wheeled vehicle. The internal combustion engine is not limited to a gasoline engine, and may be a diesel engine.

  In the present embodiment, the present invention has been described by taking an oxygen sensor as an example. However, the present invention is not limited to an oxygen sensor, and is preferably used as a sensor for detecting various gases. The present invention is also suitably used for, for example, a NOx sensor for detecting NOx concentration. In addition, the present invention is not limited to a type of oxygen sensor (referred to as a “λ sensor”) whose output changes stepwise (steeply) at a specific oxygen concentration (for example, in the vicinity of the theoretical air-fuel ratio), but also from the lean region It is also suitably used for an air-fuel ratio sensor (referred to as “all-range air-fuel ratio sensor”) of a type whose output continuously changes up to a region.

  According to the present invention, the number of parts of the gas sensor can be reduced, and the number of steps and cost required for assembly can be reduced. The present invention is suitably used for various gas sensors including an oxygen sensor.

  The gas sensor according to the present invention is suitably used for an air-fuel ratio control device for various transportation equipment such as passenger cars, buses, trucks, motorcycles, tractors, airplanes, motor boats, and civil engineering vehicles.

It is sectional drawing which shows typically the oxygen sensor 100 in suitable embodiment of this invention. It is a side view showing typically oxygen sensor 100 in a suitable embodiment of the present invention. It is a perspective view showing typically oxygen sensor 100 in a suitable embodiment of the present invention. 2 is a cross-sectional view schematically showing a mold used to integrally form an inner cover, an outer cover, and a housing of the oxygen sensor 100. FIG. It is a side view which shows typically the inner cover, outer cover, and housing which were formed integrally. 1 is a side view schematically showing a motorcycle 500 equipped with an oxygen sensor 100. FIG. FIG. 3 is a diagram schematically showing a control system of an internal combustion engine in a motorcycle 500. It is sectional drawing which shows the conventional oxygen sensor 800 typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Sensor element 11 Detection part 12 Board | substrate 20 Housing 21 Holder 22 Fixing member 23 Filler 30 Lead wire 40 Terminal part 50 Cylindrical member 60 Sealing member 71 1st cover (inner cover)
71a Vent hole (gas inlet) of first cover
72 Second cover (outer cover)
72a Second cover vent hole (gas inlet)
100 Oxygen sensor 500 Motorcycle 600 Internal combustion engine

Claims (9)

A sensor element having a detection unit for detecting a predetermined gas;
A first cover that covers the detection portion of the sensor element;
A second cover covering the first cover,
The gas sensor, wherein the first cover and the second cover are integrally formed.   The gas sensor according to claim 1, wherein the second cover has a bottomless cylindrical shape.   Each of the said 1st cover and the said 2nd cover is a gas sensor of Claim 1 or 2 which has a vent hole extended in the direction which goes to the front-end | tip part from the base end part of the said sensor element.   The gas sensor according to claim 1, wherein the first cover and the second cover are integrally formed by injection molding. A housing for housing the sensor element;
The gas sensor according to claim 1, wherein the first cover and the second cover are formed integrally with the housing.   The gas sensor according to claim 1, wherein the first cover and the second cover are made of a metal material.   The gas sensor according to any one of claims 1 to 6, which is an oxygen sensor.   An air-fuel ratio control apparatus comprising the gas sensor according to claim 7.   A transportation device comprising the air-fuel ratio control device according to claim 8.

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