JP2007327941A - Gas sensor, and internal combustion engine and transportation equipment equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve detection accuracy of a resistance type gas sensor equipped with an oxide semiconductor layer formed from an oxide containing cerium. <P>SOLUTION: This gas sensor 10 which is the resistance type gas sensor is equipped with the oxide semiconductor layer 11 formed from the oxide containing cerium, and a detection electrode 12 for detecting a resistivity of the oxide semiconductor layer 11. The oxide semiconductor layer 11 contains an alumina-containing layer 11a containing alumina, and the detection electrode 12 is provided so as to be in contact with the alumina-containing layer 11a. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a gas sensor, and more particularly, to a resistance type gas sensor including an oxide semiconductor layer. The present invention also relates to an internal combustion engine 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 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 (fuel concentration is low), the amount of oxygen in the exhaust gas increases. Therefore, by measuring the amount of oxygen or oxygen concentration in the exhaust gas, it is estimated how much the air-fuel ratio deviates from the stoichiometric air-fuel ratio, and the fuel is combusted under optimum conditions by adjusting the air-fuel ratio. It becomes possible to control.

  As an oxygen sensor for measuring the oxygen concentration in the exhaust gas, an oxygen sensor using a solid electrolyte as disclosed in Patent Document 1 or a resistance-type oxygen sensor as disclosed in Patent Document 2 It has been known.

  An oxygen sensor using a solid electrolyte measures an oxygen concentration by detecting a difference in oxygen partial pressure between a reference electrode and a measurement electrode as an electromotive force. For this reason, in this type of oxygen sensor, it is necessary to expose the measurement electrode and the reference electrode to exhaust gas and air, respectively. Therefore, the structure of the oxygen sensor itself is complicated, and the structure for attaching the oxygen sensor to the exhaust pipe is also complicated. Further, since the structure is complicated, there is a problem that it is difficult to reduce the size of the oxygen sensor.

  On the other hand, the resistance-type oxygen sensor detects a change in resistivity of the oxide semiconductor layer provided so as to be 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 oxygen sensor does not require a reference electrode, the structure of the oxygen sensor itself can be simplified. Further, the structure for attaching the oxygen sensor to the exhaust pipe can be simplified.

  As an oxide semiconductor used for a resistance-type oxygen sensor, cerium oxide is considered promising from the viewpoint of durability and stability. As disclosed in Patent Document 3, the responsiveness of a resistance-type oxygen sensor using cerium oxide can be improved by setting the average particle size of the cerium oxide fine particles contained in the oxide semiconductor layer to 200 nm or less. it can.

Further, as disclosed in Patent Document 4, when zirconium is added to an oxide containing cerium, the electronic conductivity of the oxide semiconductor layer increases, and the oxygen partial pressure dependency of the output of the oxygen sensor increases. Detection accuracy can be improved.
JP-A-8-114571 Japanese Patent Laid-Open No. 5-18921 JP 2003-149189 A JP 2004-93547 A

  However, in recent years, interest in environmental issues has further increased, and it is required to detect oxygen concentration with higher accuracy.

  The present invention has been made in view of the above problems, and an object thereof is to improve the detection accuracy of a resistance type gas sensor including an oxide semiconductor layer formed from an oxide containing cerium.

  The gas sensor according to the present invention is a resistance type gas sensor comprising an oxide semiconductor layer formed of an oxide containing cerium and a detection electrode for detecting a resistivity of the oxide semiconductor layer, wherein the oxide semiconductor The layer includes an alumina-containing layer containing alumina, and the detection electrode is provided in contact with the alumina-containing layer, thereby achieving the above-described object.

  In a preferred embodiment, the alumina-containing layer contains 4.5 wt% or more and 12 wt% or less of alumina.

  In a preferred embodiment, only a part of the oxide semiconductor layer is the alumina-containing layer.

  In a preferred embodiment, all of the oxide semiconductor layer is the alumina-containing layer.

  In a preferred embodiment, the oxide semiconductor layer has a porous structure including oxide semiconductor particles, and the average particle diameter of the oxide semiconductor particles is 200 nm or less.

  In a preferred embodiment, the alumina-containing layer has a porous structure including oxide semiconductor particles and alumina particles, and the average particle size of the alumina particles is larger than the average particle size of the oxide semiconductor particles. .

  In a preferred embodiment, the oxide forming the oxide semiconductor layer further contains zirconium.

  Alternatively, a gas sensor according to the present invention is a resistance type gas sensor comprising an oxide semiconductor layer formed of an oxide containing cerium and a detection electrode for detecting a resistivity of the oxide semiconductor layer, The oxide semiconductor layer contains alumina, and the alumina contained in the oxide semiconductor layer has a concentration distribution such that the concentration is relatively high on the detection electrode side, whereby the above object is achieved. .

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

  The internal combustion engine by this invention is provided with the gas sensor which has the said structure.

  A transportation device according to the present invention includes an internal combustion engine having the above-described configuration.

  The gas sensor according to the present invention is a resistance type gas sensor including an oxide semiconductor layer formed of an oxide containing cerium. In the gas sensor according to the present invention, the oxide semiconductor layer includes an alumina-containing layer containing alumina, and the detection electrode is provided in contact with the alumina-containing layer. As a result, the resistivity of the oxide semiconductor layer in an atmosphere with a low oxygen partial pressure (that is, on the fuel rich side) is reduced, and the oxygen partial pressure dependency of the sensor output is increased. Therefore, detection accuracy is improved.

  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.

  First, the structure of the gas sensor 10 in the present embodiment will be described with reference to FIGS. 1 and 2. 1 and 2 are an exploded perspective view and a cross-sectional view schematically showing the gas sensor 10, respectively. As shown in FIGS. 1 and 2, the gas sensor 10 is a resistance type including an oxide semiconductor layer 11 formed of an oxide containing cerium and a detection electrode 12 that detects the resistivity of the oxide semiconductor layer 11. This is an oxygen sensor.

  The oxide semiconductor layer 11 and the detection electrode 12 are supported by the substrate 13. The substrate 13 is made of an insulator such as alumina or magnesia. The substrate 13 has a main surface 13a and a back surface 13b facing each other, and the oxide semiconductor layer 11 and the detection electrode 12 are provided on the main surface 13a.

  The oxide semiconductor layer 11 has a porous structure and releases or absorbs oxygen according to the oxygen partial pressure of the atmosphere. As a result, the oxygen vacancy concentration in the oxide semiconductor layer 11 changes, and the resistivity of the oxide semiconductor layer 11 changes. By measuring this change in resistivity with the detection electrode 12, the oxygen concentration is detected. can do.

  As an oxide that forms the oxide semiconductor layer 11, for example, cerium oxide or a composite of cerium oxide and zirconium oxide can be used. By using an oxide containing zirconium in addition to cerium, detection accuracy is improved as described in Patent Document 4. The oxide semiconductor layer 11 typically contains mainly cerium oxide (that is, 50 mol% or more).

  The detection electrode 12 is made of a conductive material, for example, a metal material such as platinum, a platinum rhodium alloy, or gold. The detection electrode 12 is preferably formed in a comb shape so that the change in resistivity of the oxide semiconductor layer 11 can be efficiently measured.

  A heater 14 for raising the temperature of the oxide semiconductor layer 11 is provided on the back surface 13 b side of the substrate 13. The heater 14 in the present embodiment is a resistance heating type heating element that performs heating using resistance loss. When a voltage is applied to the electrode 14a extended from the heater 14, a current flows through the heating element formed in a predetermined shape, and the heating element generates heat, whereby heating is performed. Heat is transferred to the oxide semiconductor layer 11 through the substrate 13. The heating element is often formed from a metal material. By detecting the temperature of the oxide semiconductor layer 11 by the heater 14 and quickly activating it, the detection accuracy at the start of the internal combustion engine can be improved.

  As shown in FIG. 2, the oxide semiconductor layer 11 of the gas sensor 10 in this embodiment is configured by laminating an alumina-containing layer 11a to which alumina is added and an alumina non-containing layer 11b to which alumina is not added. ing. That is, the oxide semiconductor layer 11 includes an alumina-containing layer 11a containing alumina. The detection electrode 12 is provided in contact with the alumina-containing layer 11a. In other words, the alumina containing layer 11a and the alumina non-containing layer 11b are laminated in this order from the detection electrode 12 side along the thickness direction of the gas sensor 10 (direction perpendicular to the main surface 13a of the substrate 13). 11 a is located on the detection electrode 12 side in the oxide semiconductor layer 11.

  As described above, when the oxide semiconductor layer 11 includes the alumina-containing layer 11a, the detection accuracy of the gas sensor 10 is improved. Hereinafter, the reason will be described.

  The inventor of the present application has made various studies in order to improve the detection accuracy of the resistance type gas sensor. As a result, when alumina is added to the oxide containing cerium, the surprising phenomenon that the resistivity of the oxide semiconductor layer decreases. I found Alumina is known to have high electrical insulation, and conventionally alumina has not been used for the purpose of reducing the electrical resistance of materials. Of course, no example of adding alumina for the purpose of reducing the resistivity of an oxide semiconductor for a gas sensor has been reported.

  In FIG. 3, the gas sensor 10 according to the present embodiment is actually prototyped, and the resistivity of the oxide semiconductor layer 11 (that is, the sensor output) is changed by changing the amount of alumina added (weight fraction of alumina in the alumina-containing layer 11a). The result of having measured is shown. FIG. 3 is a graph with lambda (λ) on the horizontal axis and sensor output on the logarithmic axis on the vertical axis. Note that lambda (λ) is a value indicating how much the actual air-fuel ratio deviates from the stoichiometric air-fuel ratio, and a relational expression of λ = (amount of supplied air) / (theoretical required air amount). It is represented by When λ = 1 (the center of the graph), the air-fuel ratio matches the stoichiometric air-fuel ratio. On the other hand, when λ <1 (left side of the graph), the amount of supplied air is insufficient, and the air-fuel mixture is rich (that is, the rich side). When λ> 1 (right side of the graph), the amount of supplied air is excessive and the air-fuel mixture is lean (that is, the lean side).

  As can be seen from FIG. 3, the resistivity on the rich side is greatly reduced by adding alumina. As a result, the oxygen partial pressure dependency of the sensor output is increased, and the detection accuracy is improved. Note that although the mechanism by which the resistivity of the oxide semiconductor layer 11 decreases due to the addition of alumina is not clear, it has been experimentally confirmed that the resistivity decreases on the rich side.

  FIG. 4 shows the relationship between the resistivity of the oxide semiconductor layer 11 on the rich side and the amount of alumina added. In FIG. 4, the resistivity is shown as a relative value when the resistivity when the amount of alumina added is 0 wt% is 100%.

  As shown in FIG. 4, when the amount of alumina added is 0 wt% to about 5 wt%, the resistivity greatly decreases as the amount of alumina increases, and when the amount of alumina added exceeds about 5 wt%, the amount of alumina increases. The resistivity increases slightly. As can be seen from FIG. 4, the resistivity of the oxide semiconductor layer 11 can be sufficiently reduced to 20% or less by setting the alumina content of the alumina-containing layer 11a to 4.5 wt% or more and 12 wt% or less. .

  The gas sensor 10 in this embodiment can be manufactured as follows, for example.

  First, the substrate 13 is prepared. It is preferable that the substrate 13 has an insulating surface and has heat resistance such that deformation or the like does not substantially occur at the heat treatment temperature performed in the following steps and the use temperature of the gas sensor 10. In the prototype gas sensor whose data is shown in FIGS. 3 and 4, an alumina substrate having a thickness of 0.635 mm, a width of 5 mm, and a length of 15 mm was used.

  Next, the detection electrode 12 is formed on the main surface 13 a of the substrate 13. The detection electrode 12 is made of a material that is conductive and has a heat resistance comparable to that of the substrate 13. As a method for forming the detection electrode 12, for example, a screen printing method can be used. In the prototype, a platinum paste is applied on the main surface 13a using a screen printing method and then baked, so that the thickness is 8 μm, the width is 100 μm, and the distance between the comb-like electrodes is 100 μm. The detection electrode 12 was formed.

  Subsequently, the oxide semiconductor layer 11 is formed so as to cover the detection electrode 12. Specifically, first, two types of slurry containing oxide semiconductor particles are prepared. Alumina particles are added to one slurry, and alumina particles are not added to the other slurry.

  Next, the alumina-containing layer 11a having a porous structure is formed by applying the slurry to which the alumina particles are added to the main surface 13a of the substrate 13 so as to cover the detection electrode 12, and then baking the slurry. To do.

  Then, the alumina non-containing layer 11b having a porous structure is formed by applying the slurry to which the alumina particles are not added onto the alumina-containing layer 11a and then baking the slurry. In this way, the oxide semiconductor layer 11 is formed.

In the prototype example, a slurry containing particles (average particle diameter: 10 nm to 50 nm) of a composite oxide (expressed by a chemical formula of Ce _0.8 Zr _0.2 O _2-δ ) containing cerium as a main component and 20 mol% of zirconium is added. The non-alumina-containing layer 11b was formed so that the thickness after firing was 5 μm. Further, the alumina-containing layer 11a is prepared by adding 5 mol% of alumina (average particle diameter: 200 nm to 800 nm) to the above-described slurry for the non-alumina-containing layer 11b so that the thickness after firing becomes 5 μm. Formed.

  As described above, the heater 14 is formed on the back surface 13 b of the substrate 13 separately from the formation of the detection electrode 12 and the oxide semiconductor layer 11 on the main surface 13 a of the substrate 13. As a material of the heater 14, a metal material such as platinum or tungsten can be used. Moreover, a nonmetallic material can also be used, for example, good conductor oxides, such as rhenium oxide, can be used. As a method for forming the heater 14, a screen printing method is preferably used.

  In this way, the gas sensor 10 can be manufactured. In the present embodiment, as shown in FIG. 2, only a part of the oxide semiconductor layer 11 is the alumina-containing layer 11a. However, as shown in FIG. All may be the alumina containing layer 11a.

  From the viewpoint of reducing the resistance of the oxide semiconductor layer 11, it is preferable that alumina is unevenly distributed on the detection electrode 12 side. That is, it is preferable that only part of the oxide semiconductor layer 11 is the alumina-containing layer 11a. In FIG. 6, when only a part of the oxide semiconductor layer 11 is the alumina-containing layer 11a (that is, alumina is unevenly distributed on the detection electrode 12 side), the entire oxide semiconductor layer 11 is the alumina-containing layer 11a. For a certain case (that is, alumina is ubiquitous throughout the oxide semiconductor layer 11), the resistivity of the oxide semiconductor layer 11 is shown (the vertical axis is a logarithmic axis).

  As can be seen from FIG. 6, the resistivity is lower when only part of the oxide semiconductor layer 11 (only the part on the detection electrode 12 side) is the alumina-containing layer 11a. This is presumed to be because if the alumina particles are present in the entire oxide semiconductor layer 11, the oxygen in the exhaust gas is likely to be prevented from being taken into the oxygen vacancies. As shown in FIG. 2, only part of the oxide semiconductor layer 11 is the alumina-containing layer 11a, and the other part that is in contact with the exhaust gas is the alumina-free layer 11b. Incorporation is preferably performed, and the resistance of the oxide semiconductor layer 11 can be further reduced.

  On the other hand, as shown in FIG. 5, when the oxide semiconductor layer 11 is entirely made of the alumina-containing layer 11 a, two types of slurry are prepared when the oxide semiconductor layer 11 is formed, or a coating process and a firing process. Therefore, it is not necessary to perform the measurement twice, so that the manufacturing of the gas sensor 10 can be simplified and the cost can be reduced.

  In the description so far, the concentration of alumina in the oxide semiconductor layer 11 changes in two steps along the thickness direction of the gas sensor 10 (configuration shown in FIG. 2), or the case where it is almost constant ( Although the configuration shown in FIG. 5 is illustrated, the concentration of alumina in the oxide semiconductor layer 11 may change in three or more steps along the thickness direction of the gas sensor 10, or may be linear (continuous). It may change to. However, from the viewpoint of reducing the resistance of the oxide semiconductor layer 11, it is preferable that the alumina concentration is relatively low on the side of the oxide semiconductor layer 11 in contact with the exhaust gas (even if the oxide semiconductor layer 11 is entirely formed). That is, even when alumina is contained), that is, it is preferable that the alumina contained in the oxide semiconductor layer 11 has a concentration distribution in which the concentration is relatively high on the detection electrode 12 side. In other words, the alumina concentration in the oxide semiconductor layer 11 is preferably higher on the detection electrode 12 side than on the surface side of the gas sensor 10.

  As already described, the oxide semiconductor layer 11 has a porous structure including oxide semiconductor particles. When the average particle diameter of oxide semiconductor particles containing cerium is made small, specifically 200 nm or less, the movement distance of oxygen vacancies in the particles is reduced, and the surface area of the oxide semiconductor is increased. Since the output response time with respect to the concentration change is shortened, the responsiveness of the gas sensor 10 is improved. In addition, when the average particle size of the oxide semiconductor particles is reduced, the number of junctions between the oxide semiconductor particles is increased, so that an effect of improving the strength of the porous structure can be obtained.

  The average particle size of the alumina particles is preferably larger than the average particle size of the oxide semiconductor particles. When the average particle size of the alumina particles is larger than the average particle size of the oxide semiconductor particles, the relatively small oxide semiconductor particles are disposed so as to surround the relatively large alumina particles. Is prevented from becoming too dense. Therefore, the porosity of the porous structure is increased.

So far, the case where alumina is added to the oxide semiconductor layer 11 has been described. FIG. 7 shows the resistivity (relative value) when 5 wt% of silica / barium oxide (SiO ₂ / BaO) is added instead of alumina. As can be seen from FIG. 7, the resistivity did not decrease much when silica / barium oxide was added compared to when nothing was added. This shows that alumina is particularly suitable for reducing the resistivity of the oxide semiconductor layer 11.

FIG. 7 also shows the resistivity when 5 wt% of silica / alumina (SiO ₂ .Al ₂ O ₃ ) is added instead of alumina. As can be seen from FIG. 7, when silica / alumina was added, the resistivity was greatly reduced compared to when nothing was added. Thus, alumina may not be added to the oxide semiconductor layer 11 alone, and a composite such as silica-alumina may be added. That is, part or all of the oxide semiconductor layer 11 only needs to contain alumina as a component. In the example shown in FIG. 7, the ratio of alumina in the total added silica / alumina is 1/4, and the amount added is 1.25 wt% in terms of alumina.

For reference, FIG. 8 shows the resistivity (relative value) when 5 wt% of silica / calcium oxide (SiO ₂ / CaO) is added instead of alumina. As can be seen from FIG. 8, when silica / calcium oxide was added, the resistivity was increased 100 times or more compared to when nothing was added. This also shows that it is preferable to use alumina in order to reduce the resistivity of the oxide semiconductor layer 11.

  Next, a configuration for actually attaching the gas sensor 10 to the exhaust pipe of the internal combustion engine will be described with reference to FIGS. 9 (a), 9 (b) and FIG.

  As shown in FIGS. 9A and 10, the gas sensor 10 is held by the first housing 20 at the base end portion thereof. The first housing 20 is a ceramic guide formed from, for example, ceramic. The gas sensor 10 is further held in the second housing 21 together with the first housing 20. The second housing 21 is a metal case made of stainless steel, for example. The surface of the second housing 21 is threaded, and the second housing 21 is fixed to the exhaust pipe by a nut 22 that is screwed to the screw.

  In actual use, as shown in FIG. 9B, a protective cap 25 is provided so as to cover the gas sensor 10. The detection result by the gas sensor 10 is output to the control device via the detection line 24. The inside of the first housing 20 is hermetically sealed with a filler (for example, talc powder) 23.

  Next, a vehicle including the gas sensor 10 according to this embodiment and using an internal combustion engine as a drive source will be described. FIG. 11 schematically shows a motorcycle 300 provided with the gas sensor 10.

  The motorcycle 300 includes a main body frame 301 and an engine (internal combustion engine) 100, as shown in FIG. A head pipe 302 is provided at the front end of the main body frame 301. The head pipe 302 is provided with a front fork 303 that can swing in the left-right direction. A front wheel 304 is rotatably supported at the lower end of the front fork 303. A handle 305 is attached to the upper end of the head pipe 302.

  A seat rail 306 is attached so as to extend rearward from the upper rear end of the main body frame 301. A fuel tank 307 is provided above the main body frame 301, and a main seat 308 a and a tandem seat 308 b are provided on the seat rail 306. A rear arm 309 extending backward is attached to the rear end of the main body frame 301. A rear wheel 310 is rotatably supported at the rear end of the rear arm 309.

  The engine 100 is held at the center of the main body frame 301. A radiator 311 is attached to the front portion of the engine 100. An exhaust pipe 312 is connected to the exhaust port of the engine 100. As will be described in detail below, the exhaust pipe is provided with a gas sensor 10, a three-way catalyst 104, and a silencer 106 in the order closer to the engine 100. The tip of the gas sensor 10 is exposed in a passage through which the exhaust gas passes through the exhaust pipe 312, and the gas sensor 10 detects oxygen in the exhaust gas. The heater 14 shown in FIG. 1 or the like is attached to the gas sensor 10, and the temperature of the oxide semiconductor layer 11 is raised by the heater 14 when the engine 100 is started (for example, the temperature is raised to 700 ° C. in 5 seconds). Thereby, the detection sensitivity of the oxide semiconductor layer 11 is increased.

  A transmission 315 is connected to the engine 100, and an output shaft 316 of the transmission 315 is attached to a drive sprocket 317. The drive sprocket 317 is connected to the rear wheel sprocket 319 of the rear wheel 310 via a chain 318.

  FIG. 12 shows the main configuration of the control system of engine 100. An intake valve 110, an exhaust valve 106, and a spark plug 108 are provided in the cylinder 101 of the engine 100. A water temperature sensor 116 that measures the temperature of cooling water for cooling the engine is also provided. The intake valve 110 is connected to an intake pipe 122 having an air intake port. The intake pipe 122 is provided with an air flow meter 112, a throttle sensor 114 for a throttle valve, and a fuel injection device 111.

  The air flow meter 112, the throttle sensor 114, the fuel injection device 111, the water temperature sensor 116, the spark plug 108, and the gas sensor 10 are connected to a computer 118 that is a control unit. A computer speed signal 120 indicating the speed of the motorcycle 300 is also input to the computer 118.

  When the rider starts the engine 100 by a cell motor (not shown), the computer 118 calculates an optimal fuel amount based on the detection signal and the vehicle speed signal 120 obtained from the air flow meter 112, the throttle sensor 114, and the water temperature sensor 116. Based on the result, a control signal is output to the fuel injection device 111. The fuel injected from the fuel injection device 111 is mixed with the air supplied from the intake pipe 122 and injected into the cylinder 101 via the intake valve 110 that is opened and closed at an appropriate timing. The fuel ejected in the cylinder 101 burns and becomes exhaust gas, which is guided to the exhaust pipe 312 through the exhaust valve 106.

  The gas sensor 10 detects oxygen in the exhaust gas and outputs a detection signal to the computer 118. The computer 118 determines how much the air-fuel ratio deviates from the ideal air-fuel ratio based on the signal from the gas sensor 10. Then, the amount of fuel ejected from the fuel injection device 111 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 112 and the throttle sensor 114. As described above, the air-fuel ratio of the internal combustion engine is appropriately controlled by the air-fuel ratio control apparatus including the gas sensor 10 and the computer (control unit) 118 connected to the gas sensor 10.

  FIG. 13 shows a control flow of the heater 14 of the gas sensor 10. When engine 100 is started and the main switch is turned on (step S1), energization of heater 14 is started (step S2). Next, the temperature of the heater 14 is detected (step S3), and it is determined whether the temperature of the heater 14 is lower than a set temperature (step S4). The temperature of the heater 14 can be detected by detecting the current flowing through the heater 14 using the fact that the resistance value of the heater 14 changes depending on the temperature. If the temperature of the heater 14 is lower than the set temperature, the heater 14 is subsequently energized (step S2). On the other hand, when the temperature of the heater 14 is equal to or higher than the set temperature, the energization to the heater 14 is stopped for a certain time (step S5), and the energization to the heater 14 is started again (step S2). Temperature detection is performed (step S3). With such a control flow, the temperature of the heater 14 is kept constant.

  In the motorcycle 300 provided with the gas sensor 10 in the present embodiment, the oxygen concentration in the exhaust gas and its change can be detected with excellent detection accuracy immediately after the engine 100 is started. For this reason, even at the time of starting, fuel and air can be mixed at an appropriate air-fuel ratio, the fuel can be burned under optimum conditions, and the concentration of regulated substances including NOx in the exhaust gas can be reduced. It is also possible to improve fuel consumption.

  Although a motorcycle is illustrated here, the present invention is also suitably used for other transportation equipment such as a four-wheeled vehicle. The internal combustion engine is not limited to a gasoline engine, and may be a diesel engine.

  ADVANTAGE OF THE INVENTION According to this invention, the detection accuracy of a resistance type gas sensor provided with the oxide semiconductor layer formed from the oxide containing cerium can be improved. Since the gas sensor according to the present invention has excellent detection accuracy, it can be suitably used for internal combustion engines for various transportation equipment such as passenger cars, buses, trucks, motorcycles, tractors, airplanes, motor boats, and civil engineering vehicles.

1 is an exploded perspective view schematically showing a gas sensor 10 in a preferred embodiment of the present invention. It is sectional drawing which shows typically the gas sensor 10 in suitable embodiment of this invention. It is a graph which shows the relationship between the lambda ((lambda)) when changing the addition amount of an alumina, and sensor output (the resistivity of an oxide semiconductor layer), and a vertical axis | shaft is a logarithmic axis. It is a graph which shows the relationship between the resistivity in the rich side of an oxide semiconductor layer, and an alumina addition amount. It is sectional drawing which shows typically the gas sensor 10 in suitable embodiment of this invention. Lambda (λ) and sensor output (resistivity of oxide semiconductor layer) for the case where only part of the oxide semiconductor layer is an alumina-containing layer and the case where all of the oxide semiconductor layer is an alumina-containing layer The vertical axis is a logarithmic axis. When 5 wt% of silica / barium oxide (SiO ₂ · BaO) is added to the oxide semiconductor layer, when 5 wt% of silica / alumina (SiO ₂ / Al ₂ O ₃ ) is added, and when nothing is added, It is a graph which shows the resistivity of an oxide semiconductor layer. For the case where silica calcium oxide (SiO ₂ · CaO) was not added and when nothing was added 5 wt% to the oxide semiconductor layer is a graph showing the resistivity of the oxide semiconductor layer. (A) And (b) is a perspective view which shows typically the structure for fixing the gas sensor 10 to an exhaust pipe, (a) shows the state which removed the protective cap, (b) shows a protective cap. The attached state is shown. It is sectional drawing which shows typically the structure for fixing the gas sensor 10 to an exhaust pipe. 1 is a diagram schematically illustrating an example of a motorcycle including a gas sensor 10. FIG. FIG. 12 is a diagram schematically showing an engine control system in the motorcycle shown in FIG. 11. 4 is a flowchart illustrating an example of a control flow of the gas sensor 10.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Gas sensor 11 Oxide semiconductor layer 11a Alumina containing layer 11b Alumina non-containing layer 12 Detection electrode 13 Board | substrate 14 Heater 20 1st housing 21 2nd housing 23 Filling material 25 Protection cap 100 Engine 300 Motorcycle

Claims (11)

An oxide semiconductor layer formed from an oxide containing cerium;
A detection electrode for detecting a resistivity of the oxide semiconductor layer;
A resistance type gas sensor comprising:
The oxide semiconductor layer includes an alumina-containing layer including alumina,
The gas sensor provided so that the detection electrode may contact the alumina content layer.   The gas sensor according to claim 1, wherein the alumina-containing layer contains 4.5 wt% or more and 12 wt% or less of alumina.   The gas sensor according to claim 1 or 2, wherein only part of the oxide semiconductor layer is the alumina-containing layer.   The gas sensor according to claim 1 or 2, wherein the entire oxide semiconductor layer is the alumina-containing layer.   5. The gas sensor according to claim 1, wherein the oxide semiconductor layer has a porous structure including oxide semiconductor particles, and an average particle diameter of the oxide semiconductor particles is 200 nm or less.   The alumina-containing layer has a porous structure including oxide semiconductor particles and alumina particles, and the average particle size of the alumina particles is larger than the average particle size of the oxide semiconductor particles. The gas sensor according to Crab.   The gas sensor according to claim 1, wherein the oxide forming the oxide semiconductor layer further contains zirconium. An oxide semiconductor layer formed from an oxide containing cerium;
A detection electrode for detecting a resistivity of the oxide semiconductor layer;
A resistance type gas sensor comprising:
The oxide semiconductor layer includes alumina,
A gas sensor having a concentration distribution such that alumina contained in the oxide semiconductor layer has a relatively high concentration on the detection electrode side.   The gas sensor according to any one of claims 1 to 8, which is an oxygen sensor.   An internal combustion engine comprising the gas sensor according to claim 9.   A transportation device comprising the internal combustion engine according to claim 10.

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