JP2009156756A - Gas sensor, air fuel ratio control device equipped therewith, and transportation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor having excellent durability to impact from the outside, and suitable for miniaturization. <P>SOLUTION: This gas sensor is equipped with a sensor element 10 having a gas detection part 11 for detecting prescribed gas on a tip part; a housing 20 into which the sensor element 10 is inserted and arranged so that the gas detection part 11 is projected to the lower end side; a terminal 40 connected to the rear end of the sensor element 10; a cover 60 provided on the upper end side of the housing 20, for storing the terminal 40; and a terminal fixing member 70 having a hole 70a into which both the sensor element 10 and the terminal 40 are inserted, for fixing the terminal 40 to the sensor element 10. The sensor element 10 is arranged so that the rear end 10E of the sensor element 10 is positioned at a height lower than the upper end 20E of the housing 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gas sensor. The present invention also relates to an air-fuel ratio control device and a transportation device provided with 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, the fuel concentration is relatively high), the oxygen concentration in the exhaust gas decreases compared to the oxygen concentration 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 (that is, the fuel concentration is relatively low), the oxygen concentration in the exhaust gas increases. For this reason, by measuring the 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 burned under optimal conditions by adjusting the air-fuel ratio. Is possible.

  As an oxygen sensor for measuring the oxygen concentration in the exhaust gas, an electromotive force type oxygen sensor as disclosed in Patent Document 1 or a resistance type oxygen sensor as disclosed in Patent Document 2 is used. Are known. The electromotive force type oxygen sensor detects the difference in oxygen partial pressure between a reference electrode and a measurement electrode (exposed to air and exhaust gas, respectively) provided on the surface of the solid electrolyte layer as an electromotive force. Measure. On the other hand, the resistance type oxygen sensor measures the oxygen concentration by detecting a change in resistivity of the oxide semiconductor layer exposed to the exhaust gas.

  Since the oxygen sensor is provided in the exhaust pipe, the oxygen sensor is required to have excellent resistance to external impacts. Stones may fly around the exhaust pipe during traveling, and when such flying stones collide with the oxygen sensor (called “chipping”), the impact of the impact may damage the inside of the oxygen sensor. It is.

  Patent Document 3 discloses an oxygen sensor excellent in resistance to external impact. FIG. 14 shows an oxygen sensor 800 disclosed in Patent Document 3. As shown in FIG. 14, the oxygen sensor 800 includes a sensor element 810 having a gas detection unit 811 for detecting oxygen at the tip, and a housing 820 through which the sensor element 810 is inserted.

  The sensor element 810 is arranged so that the gas detection unit 811 is exposed on the lower end side of the housing 820. As shown in FIG. 15, this sensor element 810 has a solid electrolyte substrate 812 formed of a material containing zirconia as a main component, and a heater 815 for raising the temperature of the solid electrolyte substrate 812 to a predetermined activation temperature. The heater substrate 816 is stacked.

  The gas detection unit 811 of the sensor element 810 includes a measurement electrode 813 provided on the main surface of the solid electrolyte substrate 812, a reference electrode 814 provided on the back surface of the solid electrolyte substrate 812, and a solid located therebetween. And an electrolyte substrate 812. At the rear end portion of the solid electrolyte substrate 812, a terminal connection electrode 813a electrically connected to the measurement electrode 813 and a terminal connection electrode 814a electrically connected to the reference electrode 814 are provided.

  The heater substrate 816 is made of a ceramic material, and a heater 815 is embedded therein. A terminal connection electrode 815 a electrically connected to the heater 815 is provided at the rear end portion of the heater substrate 816.

  As shown in FIG. 14, the housing 820 has a cylindrical shape, and has a screw portion 820 a formed with a screw thread and a flange portion 820 b protruding outward in the radial direction on its outer surface. The oxygen sensor 800 can be fixed to the exhaust pipe by screwing the screw portion 820a into the screw hole formed in the exhaust pipe.

  An inner protector 831 and an outer protector 832 are provided on the lower end side of the housing 820 so as to cover the gas detector 811 of the sensor element 810. Each of the inner protector 831 and the outer protector 832 is formed with a vent hole 833 for introducing exhaust gas into the interior.

  The oxygen sensor 800 further includes a terminal 840 connected to the rear end of the sensor element 810, a lead wire 850 electrically connected to the sensor element 810 via the terminal 840, and a cover provided on the upper end side of the housing 820. 860 and a terminal fixing member 870 for fixing the terminal 840 to the sensor element 810 are provided.

  The cover 860 is made of a metal material and accommodates the rear end portion of the sensor element 810, the terminal fixing member 870, the terminal 840, the lead wire 850, and the like. A rubber member 862 that seals the cover 860 is disposed near the upper end portion of the cover 860, and the rubber member 862 is fixed by caulking the vicinity of the upper end portion 860a of the cover 860.

  The terminal 840 is made of a metal material. The front end of the terminal 840 is connected to the terminal connection electrodes 813a, 814a and 815a at the rear end of the sensor element 810, whereby the sensor element 810 and the lead wire 850 are electrically connected.

  The lead wire 850 is inserted through a through hole formed in the rubber member 862. A ceramic separator 864 locked by a reduced diameter portion 860b of the cover 860 is provided on the lower side of the rubber member 862, and the lead wire 850 and the terminal 840 are in a through hole 864a formed in the ceramic separator 864. Connected with.

  The terminal fixing member 870 is made of a ceramic material and has a hole into which both the sensor element 810 and the terminal 840 are inserted. The sensor element 810 and the terminal 840 are connected in this hole of the terminal fixing member 870.

  In the oxygen sensor 800, the sensor element 810 and the housing 820 are hermetically sealed with ceramic powder 821. The ceramic powder 821 is, for example, talc and is sandwiched between the first ceramic holder 822 and the second ceramic holder 823. The first ceramic holder 822 is provided to support the ceramic powder 821. The second ceramic holder 823 is provided to compress the ceramic powder 821 by pressing it. The second ceramic holder 823 is fixed by a caulking portion 820 c formed at the upper end portion of the housing 820. An annular packing 824 is disposed between the caulking portion 820c and the second ceramic holder 823.

In the oxygen sensor 800 shown in FIG. 14, a predetermined gap is provided between the inner peripheral surface of the cover 860 and the terminal fixing member 870. Therefore, even if an impact is applied to the cover 860 from the outside, the impact can be absorbed, so that the sensor element 810 can be protected.
JP-A-8-114571 Japanese Patent Laid-Open No. 5-18921 JP 2003-294682 A

  However, when an air gap is provided between the inner peripheral surface of the cover 860 and the terminal fixing member 870 as in the oxygen sensor 800 disclosed in Patent Document 3, the outer diameter of the cover 860 increases by the amount of the air gap. End up. Therefore, the total cross-sectional area of the cover 860 increases and heat from the exhaust pipe is easily transmitted to the upper part of the oxygen sensor 800. Therefore, as a countermeasure, the total length of the oxygen sensor 800 must be increased, and the oxygen sensor 800 is large. Become. In a transport device such as a motorcycle that has a small space around the exhaust pipe and is difficult to place, the increase in the size of the oxygen sensor is a serious problem.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a gas sensor that is excellent in resistance to external impact and is suitable for downsizing.

  A gas sensor according to the present invention includes a sensor element having a gas detection part at a tip part for detecting a predetermined gas, and a housing through which the sensor element is inserted so that the gas detection part protrudes on a lower end side thereof, A terminal connected to a rear end portion of the sensor element; a cover provided on an upper end side of the housing; housing the terminal; and a hole into which both the sensor element and the terminal are inserted; And a terminal fixing member that fixes the sensor element to the sensor element, and the sensor element is disposed such that a rear end of the sensor element is positioned at a height equal to or lower than an upper end of the housing.

  In a preferred embodiment, the housing has a flange that protrudes radially outward, and the sensor element is disposed such that a rear end of the sensor element is positioned at a height equal to or lower than an upper surface of the flange. Has been.

  In a preferred embodiment, the terminal fixing member is disposed such that an upper end of the terminal fixing member is positioned at a height higher than a rear end of the sensor element.

  In a preferred embodiment, the terminal fixing member is arranged such that the upper end of the terminal fixing member is positioned at a height equal to or lower than the upper end of the housing.

  In a preferred embodiment, the terminal fixing member is disposed such that an upper end of the terminal fixing member is located at a height not lower than a rear end of the sensor element and not higher than an upper surface of the flange portion.

  In a preferred embodiment, the gas sensor according to the present invention further includes a glass seal portion formed of a glass material and fixing the sensor element to the housing.

  In a preferred embodiment, the sensor element further includes a substrate that supports the gas detection unit, and the substrate is made of alumina.

  In a preferred embodiment, the terminal is made of a nickel-chromium alloy containing 50 wt% or more of nickel.

  In a preferred embodiment, the cover has a thickness of 0.7 mm or less.

  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, the sensor element is arranged so that the rear end thereof is positioned at a height equal to or lower than the upper end of the housing. In other words, the sensor element does not protrude from the upper end of the housing which is more rigid and difficult to deform than the cover. Therefore, even if the cover is deformed by an external impact, the sensor element is hardly subjected to impact stress, and the occurrence of breakage of the sensor element (for example, breakage of the substrate) is suppressed. Further, in the gas sensor according to the present invention, unlike the conventional gas sensor, it is not necessary to provide a large gap on the inside of the cover for absorbing an external impact, so that the outer diameter of the cover can be reduced. When the outer diameter of the cover is small, heat from the gas detection unit exposed to high temperature is not easily transmitted to the upper part of the gas sensor, so that the gas sensor can be reduced in length by reducing the total length of the gas sensor. Thus, the gas sensor according to the present invention is excellent in resistance to external impacts and is suitable for downsizing.

  When the housing has a flange portion protruding radially outward, the sensor element is preferably arranged so that the rear end thereof is positioned at a height equal to or lower than the upper surface of the flange portion. The flange portion is thicker in the radial direction than the vicinity of the upper end of the housing (the portion above the flange portion), and therefore has a higher rigidity and is difficult to deform. For this reason, the rear end of the sensor element is positioned at a height equal to or lower than the upper surface of the flange portion, so that breakage of the sensor element can be more reliably suppressed.

  In order to sufficiently protect the sensor element from the impact, it is preferable that the sensor element is covered with the terminal fixing member up to the rear end when viewed from the lateral direction (the radial direction of the housing or the cover). That is, the terminal fixing member is preferably arranged so that the upper end thereof is positioned at a height higher than the rear end of the sensor element.

  However, if the upper end of the terminal fixing member protrudes too far from the upper end of the housing, the cover deformed by an external impact may come into contact with the terminal fixing member, which causes impact stress on the sensor element. Sometimes. Therefore, the terminal fixing member is preferably arranged so that its upper end is located at a height below the upper end of the housing, and its upper end is located above the rear end of the sensor element and below the top surface of the flange. More preferably, they are arranged in such a manner.

  The gas sensor according to the present invention is preferably formed of a glass material, and further includes a glass seal portion for fixing the sensor element to the housing. Since the hermetic sealing structure including the glass seal portion requires fewer members than the hermetic sealing structure including ceramic powder such as talc, the total length of the sensor element can be shortened. Therefore, it becomes easy to position the rear end of the sensor element at a height below the upper end of the housing.

  In order to shorten the total length of the sensor element, it is preferable that the substrate of the sensor element is made of alumina. Since an alumina substrate is more resistant to thermal shock than a zirconia substrate, when an alumina substrate is used as a substrate for a sensor element, there is no need to provide an additional configuration for mitigating thermal shock as in the case of using a zirconia substrate. Therefore, the total length of the sensor element can be shortened, and it becomes easy to position the rear end of the sensor element at a height equal to or lower than the upper end of the housing.

  In order to shorten the total length of the sensor element, it is also preferable that the terminal is made of a nickel-chromium alloy containing 50 wt% or more of nickel. If the terminal is made of such a material, the heat resistance of the terminal can be made sufficiently high, so the distance from the gas detector exposed to high temperature to the connection point between the sensor element and the terminal should be shortened. Can do. That is, the overall length of the sensor element can be shortened. Therefore, it becomes easy to position the rear end of the sensor element at a height below the upper end of the housing.

  In order to suppress the transfer of heat from the gas detection unit exposed to high temperature to the upper part of the gas sensor, the thickness of the cover is preferably 0.7 mm or less. A cover having a thickness of 0.7 mm or less is not sufficiently rigid and may be easily deformed when a stepping stone collides, but according to the present invention, even when such a thin cover is used. In addition, the resistance against external impact can be sufficiently increased.

  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.

  ADVANTAGE OF THE INVENTION According to this invention, the gas sensor excellent in the tolerance with respect to the impact from the outside and suitable for size reduction is provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, an oxygen sensor for detecting oxygen will be exemplified, but the present invention is not limited to the oxygen sensor and can be suitably used for gas sensors in general.

  FIG. 1 shows an oxygen sensor 100 according to this embodiment. As shown in FIG. 1, the oxygen sensor 100 includes a sensor element 10 and a housing 20 into which the sensor element 10 is inserted.

  The sensor element 10 includes a gas detection unit 11 for detecting a predetermined gas (in this case, oxygen) and a substrate 12 that supports the gas detection unit 11. The gas detector 11 is provided at the tip of the sensor element 10, and the sensor element 10 is arranged so that the gas detector 11 protrudes (exposes) on the lower end side of the housing 20.

  The sensor element 10 in the present embodiment is a resistance type sensor element. FIG. 2 shows an example of a specific structure of the resistance type sensor element 10. The gas detection unit 11 of the resistance type sensor element 10 includes an oxide semiconductor layer 13 formed of an oxide semiconductor and a detection electrode 14 that detects the resistivity of the oxide semiconductor layer 13.

  The oxide semiconductor layer 13 has a porous structure including minute oxide semiconductor particles, and releases or absorbs oxygen according to the oxygen partial pressure in the atmosphere (that is, exhaust gas). Thereby, since the oxygen vacancy concentration in the oxide semiconductor layer 13 changes, the resistivity of the oxide semiconductor layer 13 changes. As a material of the oxide semiconductor layer 13, for example, titania (titanium dioxide) or ceria (cerium nioxide) can be used.

  The detection electrode 14 is formed from a conductive material, and is typically formed from a metal material such as platinum, a platinum rhodium alloy, or gold. In order to efficiently measure the change in resistivity of the oxide semiconductor layer 13, the portion of the detection electrode 14 that overlaps the oxide semiconductor layer 13 is formed in a comb shape as shown in FIG. Preferably it is. Further, the detection electrode 14 is extended to the rear end portion of the sensor element 10 for connection to a terminal 40 described later.

  The substrate 12 is made of an insulating material, and is typically made of a ceramic material such as alumina. The oxide semiconductor layer 13 and the detection electrode 14 described above are provided on one main surface 12a of the two main surfaces 12a and 12b of the substrate 12 facing each other. A heater 15 for raising the temperature of the gas detection unit 11 is provided on the other main surface 12b.

  The heater 15 is a resistance heating type heating element that performs heating using resistance loss. As a material of the heater 15, 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. Heating is performed by applying a voltage to the heater electrode 15 a extended from the heater 15 to the rear end of the sensor element 10. By detecting the temperature of the gas detection unit 11 (more specifically, the oxide semiconductor layer 13) by the heater 15 and activating it quickly, the detection accuracy at the start of the internal combustion engine can be improved.

  Note that although not illustrated here, a catalyst layer is preferably provided over the oxide semiconductor layer 13. The catalyst layer contains a catalyst metal, and decomposes at least one substance other than the gas to be detected (that is, oxygen) by the catalytic action of the catalyst metal. Specifically, gas or fine particles (for example, hydrocarbons, carbon, nitrogen oxides, etc., which are not completely burned) that adversely affect the detection of oxygen by the gas detector 11 are decomposed, and such gases and fine particles are The adhesion to the surface of the oxide semiconductor layer 13 is prevented. For example, platinum is used as the catalyst metal. The sensor element 10 is not limited to the resistance type sensor element exemplified here, and various known sensor elements can be used.

  The housing 20 is cylindrical as shown in FIG. However, the inner diameter of the housing 20 is not constant in the axial direction. Specifically, the inner diameter of the housing 20 is small on the lower end side of the housing 20 and larger on the upper end side. That is, when the inside of the housing 20 is considered as an insertion hole for the sensor element 10, the sensor element insertion hole has a small diameter portion on the lower end side of the housing 20 and a large diameter portion on the upper end side.

  Further, the outer diameter of the housing 20 is not constant in the axial direction. The housing 20 has, on its outer surface, a threaded portion 20a formed with a thread and a flange portion 20b projecting radially outward. The oxygen sensor 100 can be fixed to the exhaust pipe by screwing the screw portion 20a into the screw hole formed in the exhaust pipe. The housing 20 is typically formed from a metal material (for example, stainless steel).

  A protector 30 is provided on the lower end side of the housing 20 so as to cover the gas detection unit 11 of the sensor element 10. The protector 30 has a double structure composed of an inner protector 31 and an outer protector 32. Each of the inner protector 31 and the outer protector 32 is formed with an opening (vent hole) 33 for introducing exhaust gas into the interior. The opening 33 of the inner protector 31 and the opening 33 of the outer protector 32 are arranged so as not to overlap each other when viewed from the radial direction so that the exhaust gas flowing in the exhaust pipe does not directly hit the gas detection unit 11. It is preferable. The inner protector 31 and the outer protector 32 are made of a metal material such as stainless steel, and are joined to the housing 20 by welding, for example.

  The oxygen sensor 100 according to the present embodiment further includes a terminal 40 connected to the rear end of the sensor element 10, a lead wire 50 electrically connected to the sensor element 10 via the terminal 40, and an upper end side of the housing 20. A provided cover 60, a terminal fixing member 70 that fixes the terminal 40 to the sensor element 10, and a glass seal portion 80 that fixes the sensor element 10 to the housing 20 are provided.

  The terminal 40 is made of a metal material such as stainless steel or nickel alloy. The front end of the terminal 40 is connected to the detection electrode 14 and the heater electrode 15a at the rear end of the sensor element 10, whereby the sensor element 10 and the lead wire 50 are electrically connected.

  The lead wire 50 is made of a metal material (for example, copper) and is covered with an insulating material (resin such as PTFE). The lead wire 50 is further covered with a waterproof cap formed of a resin material (for example, PTFE). The lead wire 50 is connected to the outside (for example, a computer of the air-fuel ratio control apparatus), and is electrically input / output between the sensor element 10 and the outside (for example, output of a detection signal from the sensor element 10, sensor) The supply of power to the element 10 is performed via the lead wire 50.

  The cover 60 has a cylindrical shape (for example, a cylindrical shape) and accommodates the terminal 40 and the lead wire 50. The cover 60 is made of a metal material such as stainless steel, and is joined to the housing 20 by welding, for example. A sealing member 62 that seals the cover 60 is disposed near the upper end of the cover 60.

  The sealing member 62 is made of a rubber material (for example, fluororubber) and has a through hole through which the lead wire 50 is inserted. The lead wire 50 is fixed by caulking the vicinity of the upper end portion 60a of the cover 60 inward, and the cover 60 is sealed.

  The terminal fixing member 70 has a hole 70a into which both the sensor element 10 and the terminal 40 are inserted, and the sensor element 10 and the terminal 40 are connected in the hole 70a. FIG. 3 shows an enlarged view around the terminal fixing member 70. 3A is a cross-sectional view taken along 3A-3A ′ in FIG. 1, and FIG. 3B is a diagram in which components other than the terminal fixing member 70 in FIG. 3A are omitted. .

  As shown in FIG. 3B, the hole 70a of the terminal fixing member 70 includes a sensor element insertion portion 70a1 into which the sensor element 10 is inserted, and a terminal insertion portion 70a2 into which the terminal 40 is inserted. In the present embodiment, the distal end portion of the terminal 40 is configured by folding back a plate material having spring properties, and the distal end portion of such a terminal 40 has a hole as shown in FIG. 1 and FIG. Within 70a, it elastically contacts the detection electrode 14 and the heater electrode 15a of the sensor element 10.

  The glass seal part 80 is formed from a glass material. More specifically, the glass seal portion 80 is formed by melting a glass material by heat treatment and then solidifying it. As the glass material, various known materials (for example, zinc silica borate crystallized glass) can be used as the sealing material. Since the sensor element 10 and the housing 20 are hermetically sealed by the glass seal portion 80, the upper end side of the housing 20, that is, the space where the sealing member 62, the terminal 40, and the lead wire 50 are provided. Intrusion of exhaust gas is prevented. The glass seal portion 80 and the terminal fixing member 70 are disposed in a portion where the inner diameter of the housing 20 is large, that is, in the large diameter portion of the sensor element insertion hole of the housing 20.

  In the oxygen sensor 100 in the present embodiment, the sensor element 10 is disposed such that the rear end 10E of the sensor element 10 is positioned at a height equal to or lower than the upper end 20E of the housing 20. In FIG. 1, a virtual plane P defined by the upper end 20 </ b> E of the housing 20 is indicated by a broken line. 1 illustrates the case where the rear end 10E of the sensor element 10 is located at the same height as the upper end 20E of the housing 20, but the rear end 10E of the sensor element 10 is It may be located below the upper end 20E of the housing 20 (on the gas detection unit 11 side).

  As in this embodiment, the rear end 10E of the sensor element 10 is positioned at a height equal to or lower than the upper end 20E of the housing 20, so that resistance to external impact can be improved. Hereinafter, the reason will be described with reference to FIGS. 4 and 5 as well. FIG. 4 is a view showing an oxygen sensor 900 of a comparative example, and FIG. 5 is a view showing a state where a stone 1 collides with the oxygen sensor 900 of a comparative example.

  An oxygen sensor 900 shown in FIG. 4 is different from the oxygen sensor 100 shown in FIG. 1 in that the rear end 10E of the sensor element 10 is located above the upper end 20E of the housing 20. When the stone 1 collides with the cover 60 of the oxygen sensor 900, as shown in FIG. 5, the cover 60 is deformed, and members (specifically, the lead wires 50 and the terminals 40) in the cover 60 are distorted. Therefore, impact stress is applied to the rear end 10E of the sensor element 10 located above the upper end 20E of the housing 20, and the sensor element 10 is damaged (for example, the substrate 12 is broken). If the sensor element 10 is damaged, the oxygen concentration cannot be normally detected.

  On the other hand, in the oxygen sensor 100 of the present embodiment, the rear end 10E of the sensor element 10 is positioned at a height equal to or lower than the upper end 20E of the housing 20. That is, the sensor element 10 does not protrude from the upper end 20 </ b> E of the housing 20 which is higher in rigidity than the cover 60 and hardly deforms. Therefore, even if the cover 60 is deformed by an external impact, the sensor element 10 is hardly subjected to impact stress, and the occurrence of damage to the sensor element 10 is suppressed. Further, in the oxygen sensor 100 of the present embodiment, unlike the conventional oxygen sensor 800 shown in FIG. 14, it is not necessary to provide a large gap for absorbing an external impact, so the outer diameter of the cover 60 is reduced. be able to. If the outer diameter of the cover 60 is small, the heat from the exhaust pipe is difficult to be transmitted to the upper part of the oxygen sensor 100, so that the total length of the oxygen sensor 100 can be shortened. Therefore, the oxygen sensor 100 as a whole can be downsized. Thus, the oxygen sensor 100 according to the present embodiment is excellent in resistance to external impacts and is suitable for downsizing.

  FIG. 1 illustrates the case where the rear end 10E of the sensor element 10 is located at the same height as the upper end 20E of the housing 20, but in order to suppress damage to the sensor element 10 more reliably, As shown in FIG. 6, the rear end 10 </ b> E of the sensor element 10 is preferably positioned below the upper end 20 </ b> E of the housing 20.

  Further, since the flange portion 20b of the housing 20 is thicker in the radial direction than the vicinity of the upper end 20E of the housing 20 (the portion above the flange portion 20b), it has higher rigidity and is difficult to deform. Therefore, in order to suppress damage of the sensor element 10 more reliably, as shown in FIGS. 7 and 8, the sensor element 10 has a rear end 10E positioned at a height below the upper surface 20b1 of the flange 20b. It is more preferable that they are arranged in the. 7 and 8, the virtual plane P 'defined by the upper surface 20b1 of the flange 20b is indicated by a broken line. In addition, as shown in FIG. 8, the rear end 10E of the sensor element 10 has a lower end than the case where the rear end 10E of the sensor element 10 is located at the same height as the upper surface 20b1 of the upper part 20b. The effect of suppressing breakage of the sensor element 10 is higher when it is located below the upper surface 20b1 of the portion 20b.

  1 and 6 to 8 illustrate the case where the upper end 70E of the terminal fixing member 70 is located at the same height as the rear end 10E of the sensor element 10, but the present invention is not limited to this. . The upper end 70E of the terminal fixing member 70 may be located above the rear end 10E of the sensor element 10 as shown in FIG. 9, or from the rear end 10E of the sensor element 10 as shown in FIG. May be located on the lower side.

  However, in order to sufficiently protect the sensor element 10 from an impact, the sensor element 10 is covered by the terminal fixing member 70 up to the rear end 10E when viewed from the lateral direction (the radial direction of the housing 20 and the cover 60). Preferably it is. That is, as shown in FIGS. 1 and 9, the terminal fixing member 70 is preferably arranged so that the upper end 70 </ b> E is positioned at a height higher than the rear end 10 </ b> E of the sensor element 10.

  If the upper end 70E of the terminal fixing member 70 protrudes too much from the upper end 20E of the housing 20, there is a possibility that the cover 60 deformed by an external impact may come into contact with the terminal fixing member 70. Impact stress may be applied to the element 10 and may eventually lead to damage. Therefore, the upper end 70E of the terminal fixing member 70 is located at the same height as the upper end 20E of the housing 20 as shown in FIG. 1, or is lower than the upper end 20E of the housing 20 as shown in FIG. It is preferably located on the side. That is, it is preferable that the terminal fixing member 70 is disposed so that the upper end 70 </ b> E is positioned at a height equal to or lower than the upper end 20 </ b> E of the housing 20. Further, the upper end 70E of the terminal fixing member 70 is located at the same height as the upper surface 20b1 of the flange 20b as shown in FIG. 7, or from the upper surface 20b1 of the flange 20b as shown in FIG. Is more preferably located on the lower side. That is, it is more preferable that the terminal fixing member 70 is disposed such that the upper end 70E is located at a height not less than the rear end 10E of the sensor element 10 and not more than the upper surface 20b1 of the flange 20b.

  Subsequently, the oxygen sensor 100 in the present embodiment shown in FIG. 1 and the like and the oxygen sensor 900 of the comparative example shown in FIG. 4 are actually prototyped and a chipping test is performed to evaluate the occurrence of breakage of the sensor element 10. The results will be described.

  In the chipping test, the oxygen sensor 100 is held by the cup-shaped holder 2 as shown in FIG. 11 (that is, the portion below the flange 20b of the oxygen sensor 100 is inserted into the hole 2a of the holder 2). ), The hard sphere 3 having a diameter of 16 mm and a weight of 16 g was dropped 120 times from a height of 2 m and collided with the cover 60 as shown in Table 1.

  The evaluation results are shown in Table 2. Table 2 shows the relationship between the protrusion amount (mm) of the rear end 10E of the sensor element 10 from the upper end 20E of the housing 20 and the presence or absence of breakage of the sensor element 10 (specifically, the substrate 12 is bent). ing.

  In the column of the protrusion amount in Table 2, when the rear end 10E of the sensor element 10 is located above the upper end 20E of the housing 20, a positive numerical value is set, which is the same height as the upper end 20E of the housing 20. When it is located, 0 is indicated, and when it is located below the upper end 20E of the housing 20, a negative numerical value is indicated. Further, the difference in height between the upper surface 20b1 of the flange 20b and the upper end 20E of the housing 20 is 2 mm in any example.

  Therefore, Comparative Examples 1 to 6 in Table 2 correspond to the case where the rear end 10E of the sensor element 10 is located above the upper end 20E of the housing 20 as shown in FIG. Moreover, Examples 1-3 correspond to the case where the rear end 10E of the sensor element 10 is located at the same height as the upper end 20E of the housing 20 as shown in FIG. 6 corresponds to the case where the rear end 10E of the sensor element 10 is located below the upper end 20E of the housing 20 (but above the upper surface 20b1 of the flange 20b). Furthermore, Examples 7-9 correspond to the case where the rear end 10E of the sensor element 10 is located at the same height as the upper surface 20b1 of the flange 20b as shown in FIG. This corresponds to the case where the rear end 10E of the sensor element 10 is positioned below the upper surface 20b1 of the flange 20b as shown in FIG.

  Further, “x” in the column of damage of the sensor element 10 in Table 2 means that the substrate 12 is broken, and “◯” and “◎” mean that the substrate 12 is not broken. I mean. However, “◯” means that although the substrate 12 is not bent, a slight decrease in strength has occurred due to minute cracks generated in the substrate 12, whereas “◎” This indicates that there is no such strength reduction.

  As shown in Table 2, in Comparative Examples 1 to 6 in which the rear end 10E of the sensor element 10 is located above the upper end 20E of the housing 20, the sensor element 10 was damaged. In contrast, in Examples 1 to 12 in which the rear end 10E of the sensor element 10 is located at a height equal to or lower than the upper end 20E of the housing 20, the sensor element 10 was not damaged. Therefore, like the oxygen sensor 100 in the present embodiment, the sensor element 10 is arranged such that the rear end 10E is positioned at a height equal to or lower than the upper end 20E of the housing 20, and thus the sensor element 10 is damaged. It can be seen that can be suitably suppressed.

  In Table 2, the results of Examples 7-12 are more preferable than those of Examples 1-6. For this reason, in order to more reliably suppress the occurrence of damage to the sensor element 10, it is preferable to arrange the sensor element 10 so that the rear end 10E is positioned at a height below the upper surface 20b1 of the flange 20b. I understand that.

  As already described, in the oxygen sensor 100 according to this embodiment, the rear end 10E of the sensor element 10 is positioned at a height equal to or lower than the upper end 20E of the housing 20. Therefore, the total length (distance from the front end to the rear end 10E) of the sensor element 10 is shorter than the conventional oxygen sensor 800 as shown in FIG. Hereinafter, a preferable configuration for shortening the overall length of the sensor element 10 will be described.

  In order to shorten the total length of the sensor element 10, it is preferable to provide the glass seal portion 80 as in the present embodiment. Conventionally, as a structure for hermetic sealing in a gas sensor, a hermetic sealing structure including ceramic powder (typically talc) as shown in FIG. 14 has been widely used because of low manufacturing cost. . However, when such a structure is adopted, a member for supporting the ceramic powder, a member for pressing and compressing the ceramic powder, and a caulking portion (the first ceramic holder 822 and the second ceramic holder in the structure shown in FIG. 14). 823, caulking portion 820c) and the like are required, and thus a long space is required in the axial direction of the oxygen sensor. For this reason, the rear end of the sensor element inevitably protrudes above the upper end of the housing. On the other hand, when the glass seal portion 80 is provided as in the present embodiment, an extra member is unnecessary in addition to the glass seal portion 80 itself, so that the overall length of the sensor element 10 can be shortened. Therefore, it becomes easy to position the rear end 10E of the sensor element 10 at a height equal to or lower than the upper end 20E of the housing 20.

  In order to shorten the entire length of the sensor element 10, it is also preferable that the substrate 12 of the sensor element 10 is made of alumina. Hereinafter, the reason will be described.

  In general, in an electromotive force type sensor element, a zirconia substrate having excellent high-temperature stability is used as an oxygen ion conductor. However, since the zirconia substrate is vulnerable to thermal shock, when the sensor element including the zirconia substrate is fixed to the housing by the glass seal portion, it is near the boundary between the portion bonded by the glass seal portion of the zirconia substrate and the portion that is not. There is a problem that stress is concentrated and the zirconia substrate is easily broken.

  In order to solve this problem, Japanese Patent No. 3786330 discloses a method of providing a buffer layer for relaxing stress concentration due to thermal shock so as to be in contact with the lower end surface and the upper end surface of the glass seal portion. . However, in order to provide two buffer layers so as to sandwich the glass seal portion in this way, a long space is required in the axial direction of the oxygen sensor. For this reason, the rear end of the sensor element inevitably protrudes above the upper end of the housing.

  On the other hand, when the substrate 12 is made of alumina, the substrate 12 formed of alumina is more resistant to thermal shock than the zirconia substrate, and thus the buffer layer as described above is unnecessary. Therefore, the overall length of the sensor element 10 can be shortened, and the rear end 10E of the sensor element 10 can be easily positioned at a height equal to or lower than the upper end 20E of the housing 20. Since the substrate 12 formed of alumina is excellent in insulation at high temperatures, it is preferably used for the resistance type sensor element 10 as shown in FIG.

  Further, in order to shorten the overall length of the sensor element 10, it is also preferable that the terminal 40 is formed of a nickel-chromium alloy containing 50 wt% or more of nickel. When the terminal 40 is formed of such a material, the heat resistance of the terminal 40 can be sufficiently increased. Therefore, the distance from the gas detection part 11 exposed to high temperature to the connection location of the sensor element 10 and the terminal 40 can be shortened. That is, the overall length of the sensor element 10 can be shortened. Therefore, it becomes easy to position the rear end 10E of the sensor element 10 at a height equal to or lower than the upper end 20E of the housing 20. As the nickel-chromium alloy containing 50 wt% or more of nickel, for example, Inconel 718 having a composition of 19Cr-53Ni-3Mo-5Nb or Inconel 750 having a composition of 15Cr-78Ni-1Nb can be used.

  As described above, the oxygen sensor 100 according to this embodiment includes (1) the glass seal portion 80, (2) the substrate 12 is made of alumina, and (3) the terminal 40 is nickel containing 50 wt% or more of nickel. -It is preferable to have at least one of the three configurations of being formed from a chromium alloy. Of course, it is more preferable to have two of the three configurations, and most preferable to have all three configurations.

  If the cover 60 is formed thick, the rigidity of the cover 60 is improved and the cover 60 is hard to be deformed. Therefore, the resistance to external impact is increased, but in this case, the heat from the exhaust pipe is increased by the oxygen sensor 100. Therefore, it may be necessary to lengthen the overall length of the oxygen sensor 100. In order to sufficiently suppress the transfer of heat from the exhaust pipe to the upper part of the oxygen sensor 100, the cover 60 preferably has a thickness of 0.7 mm or less. According to the present invention, even when such a thin cover 60 is used, the resistance to external impact can be sufficiently increased. Therefore, it can be said that the present invention is particularly useful when the thickness of the cover 60 is 0.7 mm or less.

  The oxygen sensor 100 in the present embodiment is suitably used for detecting oxygen in exhaust gas discharged from an internal combustion engine of various transport equipment. Since the oxygen sensor 100 according to this embodiment is suitable for downsizing, the oxygen sensor 100 is particularly preferably used for transportation equipment such as a motorcycle having a small space around the exhaust pipe.

  FIG. 12 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. 13 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, 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 optimum 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.

  Although the motorcycle is illustrated here, the oxygen sensor 100 in the present embodiment is also suitably 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. For example, the present invention is also suitably used for a NOx sensor for detecting NOx concentration, a CO sensor for detecting CO concentration, an HC sensor for detecting HC concentration, and the like.

  ADVANTAGE OF THE INVENTION According to this invention, the gas sensor excellent in the tolerance with respect to the impact from the outside and suitable for size reduction is provided. 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 an exploded perspective view showing typically an example of a resistance type sensor element. (A) is sectional drawing along the 3A-3A 'line in FIG. 1, (b) is the figure which abbreviate | omitted components other than the terminal fixing member in (a). It is sectional drawing which shows the oxygen sensor 900 of a comparative example typically. It is a figure which shows a mode when a stone collides with the oxygen sensor 900 of a comparative example. It is sectional drawing which shows typically the oxygen sensor 100 in suitable embodiment of this invention. It is sectional drawing which shows typically the oxygen sensor 100 in suitable embodiment of this invention. It is sectional drawing which shows typically the oxygen sensor 100 in suitable embodiment of this invention. It is sectional drawing which shows typically the oxygen sensor 100 in suitable embodiment of this invention. It is sectional drawing which shows typically the oxygen sensor 100 in suitable embodiment of this invention. It is a figure for demonstrating the method of a chipping test. 1 is a side view schematically showing a motorcycle 500 equipped with an oxygen sensor 100. FIG. Fig. 13 is a diagram schematically showing a control system for an internal combustion engine in the motorcycle 500 shown in Fig. 12. It is sectional drawing which shows the conventional oxygen sensor 800 typically. It is a disassembled perspective view which shows typically the sensor element with which the oxygen sensor 800 is provided.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Sensor element 10E Rear end of sensor element 11 Gas detection part 12 Substrate 13 Oxide semiconductor layer 14 Detection electrode 15 Heater 15a Heater electrode 20 Housing 20E Upper end of housing 20a Screw part 20b Eave part 20b1 Upper part of eaves part 30 Protector 40 Terminal 50 Lead wire 60 Cover 62 Sealing member 70 Terminal fixing member 70a Hole in terminal fixing member 70E Upper end of terminal fixing member 80 Glass seal part 100 Oxygen sensor 500 Motorcycle 600 Internal combustion engine

Claims (12)

A sensor element having a gas detection part for detecting a predetermined gas at the tip part;
A housing in which the sensor element is inserted and arranged so that the gas detection part protrudes on the lower end side;
A terminal connected to the rear end of the sensor element;
A cover provided on the upper end side of the housing and containing the terminal;
A hole for inserting both the sensor element and the terminal, and a terminal fixing member for fixing the terminal to the sensor element,
The sensor element is a gas sensor arranged such that a rear end of the sensor element is positioned at a height equal to or lower than an upper end of the housing. The housing has a flange that protrudes radially outward,
The gas sensor according to claim 1, wherein the sensor element is disposed such that a rear end of the sensor element is positioned at a height equal to or lower than an upper surface of the flange portion.   The gas sensor according to claim 1, wherein the terminal fixing member is arranged such that an upper end of the terminal fixing member is positioned at a height higher than a rear end of the sensor element.   The gas sensor according to claim 3, wherein the terminal fixing member is disposed such that an upper end of the terminal fixing member is positioned at a height equal to or lower than an upper end of the housing.   The gas sensor according to claim 2, wherein the terminal fixing member is disposed such that an upper end of the terminal fixing member is located at a height not less than a rear end of the sensor element and not more than an upper surface of the flange portion.   The gas sensor according to any one of claims 1 to 5, further comprising a glass seal portion formed of a glass material and fixing the sensor element to the housing. The sensor element further includes a substrate that supports the gas detection unit,
The gas sensor according to claim 1, wherein the substrate is made of alumina.   The gas sensor according to any one of claims 1 to 7, wherein the terminal is formed of a nickel-chromium alloy containing nickel of 50 wt% or more.   The gas sensor according to claim 1, wherein the cover has a thickness of 0.7 mm or less.   The gas sensor according to any one of claims 1 to 9, which is an oxygen sensor.   An air-fuel ratio control device comprising the gas sensor according to claim 10.   A transportation device comprising the air-fuel ratio control device according to claim 11.

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