JP2006105768A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor of low electric power consumption excellent in early stage activity. <P>SOLUTION: This gas sensor is provided with a sensor element 2 provided with a measured gas side electrode 23 and a reference gas side electrode 21 in a solid electrolyte 21, a cylindrical housing 12 for holding the sensor element 2, a measured gas side cover 6 provided in a tip side of the housing 12, and a reference gas side cover 71 provided in a base end side of the housing 12, and an induction coil 5 for induction-heating the sensor element 2 is stored inside the measured gas side cover 6. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas sensor that measures oxygen concentration and the like, for example, a gas sensor installed in an exhaust system of an internal combustion engine.

  As a gas sensor that is installed in an exhaust system of an internal combustion engine and measures the oxygen concentration, NOx concentration, etc. in the exhaust gas, a reference gas using a sensor element provided with a gas side electrode to be measured and a reference gas side electrode on a solid electrolyte body A device that detects a signal corresponding to a concentration difference of a gas to be measured is known.

  Since this type of gas sensor cannot measure the gas concentration unless the sensor element is within a predetermined temperature range, the temperature of the sensor element must be adjusted. In particular, immediately after the internal combustion engine is started, the temperature of the sensor element is about the outside air temperature, and it is necessary to quickly heat the sensor element to a predetermined temperature from this state. For this reason, a heater for heating the sensor element is provided.

As this heater, a ceramic heater having a heating element such as tungsten in an insulating ceramic is known (see, for example, Patent Document 1 or Patent Document 2). Other heaters use external heat sources such as halogen lamps, infrared spheres made of tungsten, and Claude made of silicon carbide (see, for example, Patent Document 3).
JP 2002-14077 A JP 2000-106266 A Japanese Patent Laid-Open No. 11-287784

  The gas sensor that heats the sensor element using the ceramic heater described above is configured to transfer heat by bringing the ceramic heater and the sensor element into contact with each other. However, not all the heat of the ceramic heater is transferred to the sensor element, but a part of the heat of the ceramic heater is radiated to the atmosphere without being used for heating the sensor element. For this reason, it cannot be said that the heat of the ceramic heater is effectively used, and even if the heat generation amount of the heater is increased for early activation, the amount of heat that is not used for heating the sensor element also increases. However, early activity cannot be achieved despite the increase of. In the present specification, “early activation” means that the sensor element operating temperature can be quickly obtained and gas concentration detection can be performed after the start of heating of the sensor element.

  In addition, in a gas sensor using a heat source such as a halogen lamp, heat generated radially from a separately provided heat source needs to be introduced into the heat introduction member to conduct heat, and is not particularly introduced into the heat introduction member. Since heat that is not used for heating the sensor element is generated, early activation cannot be achieved for the increased power consumption of the heater.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a gas sensor having low power consumption and excellent early activity.

  The invention according to claim 1 is a gas sensor comprising a sensor element in which a measured gas side electrode and a reference gas side electrode are provided on a solid electrolyte body, and an induction coil for induction heating the sensor element.

  The present invention uses an induction coil to heat the sensor element. Heating by the induction coil heats the sensor element by generating eddy currents in the measured gas side electrode and the reference gas side electrode provided in the sensor element. And since the electrode itself can be made to generate heat, the gas concentration detection part can be heated quickly, and a gas sensor excellent in early activation while suppressing power consumption can be obtained. Here, the gas concentration detection unit refers to the vicinity of the location where the measured gas side electrode and the reference gas side electrode are provided.

  The invention according to claim 2 is the gas sensor characterized in that the measured gas side electrode is arranged inside the induction coil. The inside of the induction coil has a high magnetic flux density generated by the induction coil, and can effectively heat the sensor element.

  The invention of claim 3 includes a cylindrical housing for holding the sensor element, a measured gas side cover provided on the distal end side of the housing, and a reference gas side cover provided on the proximal end side of the housing. The gas sensor is characterized in that the induction coil is housed in the measured gas side cover. Thus, by arranging the induction coil in the gas side cover to be measured, the sensor element and the induction coil can be integrated, and the attachment of the gas sensor is improved.

  The invention according to claim 4 is the gas sensor characterized in that the sensor element has a conductor portion other than the measured gas side electrode and the reference gas side electrode. Thus, by providing conductor parts other than the electrodes, it is possible to realize even faster activity.

  The invention according to claim 5 is the gas sensor characterized in that the conductor portion has a thickness of 1 to 10 μm. By setting the thickness of the conductor portion within the above range, when an eddy current flows through the conductor portion, sufficient Joule loss due to electric resistance is obtained, and a gas sensor excellent in early activity can be obtained.

  The invention according to claim 6 is a gas sensor characterized by performing signal processing for removing a specific frequency component of the sensor signal. With this configuration, it is possible to realize highly accurate gas concentration detection by removing noise of the AC frequency superimposed on the sensor signal, particularly in the eddy current.

(First embodiment)
A gas sensor 1 according to the present embodiment will be described with reference to FIG. As shown in FIG. 1, the gas sensor 1 includes a sensor element 2, a housing 12 that holds the sensor element 2, a measured gas side cover 6 provided at one end of the housing 12, and a reference gas provided at the other end of the housing 12. It has the side cover 71 and the induction coil 5 arranged inside the measured gas side cover 6.

  In the present specification, the side where the measured gas cover 6 is provided in the axial direction of the gas sensor 1 is the “front end side”, and the side opposite to this side where the reference gas side cover 71 is provided is the “base end side”. Will be described.

  Details will be described below. As shown in FIGS. 1 to 3, the sensor element 2 is configured by laminating a plurality of ceramic sheets. A reference gas side electrode 22 and a measured gas side electrode 23 are provided so as to face a plate-like solid electrolyte body 21 made of zirconia via the solid electrolyte body 21. These electrodes are made of platinum, and are formed by screen printing, sputtering film formation, or the like. Further, a porous diffusion resistance layer 25 and a shielding layer 26 are formed so as to cover the front end side of the measured gas side electrode 23. The porous diffusion resistance layer 25 is made of a porous ceramic such as alumina, and the shielding layer 26 is made of a dense ceramic such as alumina. The amount of the measurement gas that reaches the measurement gas side electrode 23 is regulated by the porous diffusion resistance layer 25 and the shielding layer 26. In addition, duct forming sheets 27 and 29 are provided on the side of the solid electrolyte body 21 where the reference gas side electrode 22 is provided, and a duct 24 that guides the reference gas to the reference gas side electrode 22 is formed.

  The housing 12 is a member having a substantially cylindrical shape made of stainless steel. On the outer diameter surface of the housing 12, there is a flange seated on the exhaust pipe of the internal combustion engine at the center in the axial direction, and a male screw that is coupled to the exhaust pipe is formed on the tip side of the flange. A cylindrical insulator 52 having a through hole 55 is disposed on the inner diameter surface of the housing 12. The sensor element 2 is inserted into the through hole 55, and the insulator 52 and the sensor element 2 are fixed by injecting glass 53 into a space provided on the inner diameter of the base end side of the insulator 52.

  The measured gas side cover 6 has a double structure including an inner cover 61 and an outer cover 62. The measured gas side cover 6 has a bottomed cylindrical shape, and a flange is provided at the open end. The gas side cover 6 to be measured is fixed to the housing 12 by joining the collar portion to the front end side of the housing 12 by caulking, spot welding or the like. The measured gas side cover 6 has a measured gas introduction hole 63 for introducing the measured gas, from which the measured gas is introduced, and the measured gas chamber 64 inside the inner cover 61 is measured. Use a gas atmosphere.

  The reference gas side cover 71 is substantially cylindrical and has a large diameter portion at one end and a small diameter portion at the other end. A step portion 81 is formed between the small diameter portion and the large diameter portion, and an insulating holding member 56 for holding the lead terminal 16 is provided on the inner diameter surface of the large diameter portion. The end portion of the large diameter portion of the reference gas side cover 71 is welded and fixed to the proximal end side of the housing 12 by laser welding, and the end portion of the small diameter portion of the reference gas side cover 71 is sealed by the elastic insulating member 14. . A cylindrical outer cover 72 is caulked and fixed to the outer peripheral surface of the small diameter portion of the reference gas side cover 71 via a water repellent filter 74. Both the reference gas side cover 71 and the outer cover 72 have a reference gas introduction hole 73 for introducing a reference gas, and the reference gas is introduced into the reference gas side electrode 22 through the reference gas introduction hole 73.

  The sensor signal lead-out line 18 is electrically connected to the reference gas side electrode 22 and the measured gas side electrode 23 via the lead terminal 16, and the sensor output passes through the hole provided in the elastic insulating member 14. It is taken out to the outside. A circuit (not shown) for performing signal processing for removing a specific frequency component of the sensor signal is connected to the lead wire.

  The induction coil 5 is formed by spirally winding a conductive wire made of copper, and is bonded and fixed to the inner peripheral surface of the measured gas side cover 6 with an epoxy resin or the like. At this time, the measured gas side electrode 23 of the sensor element 2 is positioned inside the induction coil 5. Lead wires (not shown) are connected to both ends of the conductive wire, and an alternating current is supplied.

  The operation of the gas sensor 1 of the present invention will be described below.

  After starting the internal combustion engine, the induction coil 5 is applied with an alternating voltage. When an alternating current flows through the induction coil 5, an alternating magnetic flux is generated inside the induction coil. This magnetic flux generates eddy currents in the measured gas side electrode 23 and the reference gas side electrode 22, and the electrodes themselves generate heat. For this reason, the gas concentration detection part of the sensor element 2 is heated quickly. At the same time, the exhaust gas in the exhaust pipe of the internal combustion engine is introduced into the measured gas chamber 64 from the measured gas introduction hole 63 of the gas sensor 1. The reference gas is introduced into the reference gas side electrode 22 from the reference gas introduction hole 73 before the internal combustion engine is started.

  After the heating by the induction coil 5 is started, an AC voltage having a frequency different from the applied voltage to the induction coil 5 is applied between the measured gas side electrode 23 and the reference gas side electrode 22 of the sensor element 2, The resistance value of the solid electrolyte body 21 is detected by performing signal processing. When the sensor element temperature rises and the resistance value of the solid electrolyte body 21 reaches a predetermined value, the voltage applied to the induction coil is reduced to adjust the sensor element temperature.

  The gas sensor element that has reached a predetermined temperature outputs a limit current value corresponding to the oxygen concentration in the exhaust gas. The limit current value is, for example, when the state of the exhaust gas is excessive oxygen, a voltage is applied between the reference gas side electrode 22 and the measured gas side electrode 23, and when the voltage is gradually increased, the current eventually becomes It will not change. This current is the limiting current, and the amount of oxygen pumping due to voltage application between the reference gas side electrode 22 and the gas side electrode 23 to be measured is the oxygen in the exhaust gas due to the gas diffusion resistance of the porous layer 24 into the sensor. It is a phenomenon that occurs because it exceeds the inflow. The air-fuel ratio can be obtained by measuring the oxygen concentration from the limit current value. Although noise due to the effect of the eddy current is superimposed on the sensor signal indicating the air-fuel ratio, highly accurate air-fuel ratio can be detected by performing signal processing for removing a specific frequency component of the sensor signal. .

  Further, the temperature of the solid electrolyte body 21 is controlled during the air-fuel ratio detection. This is because when the temperature of the solid electrolyte body 21 is equal to or lower than a predetermined temperature, the solid electrolyte body does not function due to electrical resistance, and there is a high possibility of causing damage or melting of the electrode at a high temperature. It is. When the temperature of the solid electrolyte body 21 is lower than the predetermined temperature, the voltage applied to the induction coil 5 is increased, and when higher than the predetermined temperature, the voltage applied to the induction coil 5 is decreased.

  In order to control the temperature of the solid electrolyte body 21, the temperature of the solid electrolyte body 21 is monitored. As the method, an alternating voltage is applied to the sensor element 2. After applying the sensor element 2 at that time, the obtained current is measured. The element resistance is obtained from the relationship between the current and the AC voltage, and the temperature of the solid electrolyte body 21 can be obtained indirectly from the relational expression between the element complex resistance detected in advance and the temperature of the solid electrolyte 21.

  In addition to the above-described method, the temperature of the solid electrolyte body can be indirectly obtained by measuring the resistance value of the resistor by incorporating a platinum resistor or the like in the element.

(Second Embodiment)
In the present embodiment, as shown in FIG. 4, the conductor portion 28 is provided in the sensor element 2 of the gas sensor of the first embodiment. Other structures and operations are the same as those in the first embodiment.

  When an AC voltage is applied to the induction coil 5, an eddy current flows through the measured gas side electrode 23 and the reference gas side electrode 22, and an eddy current also flows through the conductor portion 28. For this reason, the sensor element 2 can be heated more quickly, and early activation can be realized.

  FIG. 5 shows the element temperature increase rate when the thickness of the conductor portion 28 is changed in the gas sensor of the second embodiment. FIG. 5 shows that the element heating rate is high when the thickness of the conductor portion 28 is 1 to 10 μm. This is because when the thickness of the heating conductor plate is in the range of 1 to 10 μm, the amount of heat generated by the eddy current density and the resistance of the conductor portion 28 increases. Therefore, a gas sensor in which the thickness of the conductor portion 28 is 1 to 10 μm is preferable. When the thickness is less than 1 μm, the resistance when the eddy current flows is high, so that the eddy current itself is difficult to flow. When the thickness is thicker than 10 μm, the eddy current flows much but the resistance is small, so that sufficient Joule loss is obtained. In addition, since it is necessary to supply a larger current, a large current is required, which is not economical.

Sectional drawing of the gas sensor in 1st Embodiment. The expansion | deployment perspective view of the sensor element in 1st Embodiment. 1 is a cross-sectional view taken along line AA in FIG. Sectional drawing of the gas sensor in 2nd Embodiment. The figure which shows the element temperature increase rate in 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Sensor element 5 Inductive coil 6 Gas side cover 12 to be measured 12 Housing 14 Elastic insulating member 21 Solid electrolyte body 22 Reference gas side electrode 23 Gas to be measured side electrode 28 Conductor part

Claims (6)

A gas sensor comprising: a sensor element having a gas electrode to be measured and a reference gas side electrode provided on a solid electrolyte body; and an induction coil for induction heating the sensor element. 2. The gas sensor according to claim 1, wherein the measured gas side electrode is disposed inside the induction coil. 3. A cylindrical housing that holds the sensor element according to claim 1, a measured gas side cover provided on a distal end side of the housing, and a reference gas side cover provided on a proximal end side of the housing. A gas sensor characterized in that the induction coil is housed in the measured gas side cover. 4. The gas sensor according to claim 1, wherein the sensor element has a conductor portion other than the gas side electrode to be measured and the reference gas side electrode. 5. The gas sensor according to claim 4, wherein the conductor portion has a thickness of 1 to 10 μm. 6. The gas sensor according to claim 1, wherein signal processing for removing a specific frequency component of the sensor signal is performed.

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