JP4965356B2 - Degradation judgment method of gas sensor - Google Patents

Description

  The present invention relates to a gas sensor deterioration determination method for determining whether or not a sensor element has deteriorated.

  In general, a gas sensor that detects an oxygen concentration in exhaust gas is used for combustion control of an internal combustion engine. As such a gas sensor, two cells equipped with electrodes on both sides of a solid electrolyte body mainly composed of zirconia or the like are arranged so as to sandwich the measurement chamber, and exhaust gas is introduced into the measurement chamber via a diffusion-controlled layer. Thus, there is a full-range air-fuel ratio sensor that detects oxygen contained in exhaust gas. Further, the exhaust gas contains a poisoning substance such as phosphorus. When the poisoning substance adheres to the diffusion-controlling layer, the porous material constituting the diffusion-controlling layer is vitrified, and pores of the diffusion-controlling layer are formed. It will be blocked. As a result, the diffusion-controlled state of the exhaust gas changes, and the detection accuracy of the gas sensor may decrease. Therefore, a porous protective layer (poisoning prevention layer) made of ceramic such as alumina magnesia spinel for preventing poisoning of the diffusion control layer is formed on the surface of the sensor element.

By the way, in order to respond to the recent tightening of exhaust gas regulations, more precise combustion control of an internal combustion engine is required. For this reason, higher measurement accuracy is also required for the gas sensor, and it is very important to accurately detect the deterioration state of the gas sensor. Thus, various methods have been proposed so far for determining whether or not a gas sensor has failed or deteriorated. For example, the element impedance is detected based on the element temperature of the air-fuel ratio sensor, and the detected element impedance is sequentially compared with three reference values, so that any one of normal, heater deterioration, heater disconnection, and sensor disconnection is detected. An air-fuel ratio detection device that determines whether or not the vehicle is in a state has been proposed (see Patent Document 1).
JP 2000-193635 A

  However, when deposits are deposited on the outer surface of the sensor element (or a protective layer covering the sensor element) or when deposits are deposited on the inner surface of the protector arranged so as to cover the periphery of the sensor element, It affects the heating of the sensor element by the heater.

  Specifically, when deposits accumulate on the outer surface of the sensor element, the heat capacity of the sensor element increases, so even if a predetermined voltage (power) is applied to the heater so that the predetermined temperature is assumed in advance. The sensor element is not heated up to the predetermined temperature.

  In addition, when deposits accumulate on the inner surface of a member such as a protector arranged so as to cover the periphery of the sensor element, the radiant heat of the member such as the protector is reduced, so that the predetermined temperature is assumed in advance. Even if a predetermined voltage (electric power) is applied to the heater, the sensor element is not heated to the predetermined temperature.

  In the above-described conventional air-fuel ratio detection device, the influence when deposits accumulate on such a sensor element (or a protective layer covering the sensor element) and the members disposed around the sensor element (for example, the tip of the sensor element) It does not take into account the effects of deposits on the inner surface of the protector that covers the part. That is, it does not consider that the influence of heating on the sensor element by the heater changes.

  For this reason, even if a predetermined voltage (power) is applied to the heater due to these effects, if the sensor element is not heated to a predetermined temperature that is assumed in advance, the predetermined temperature (or the applied voltage (supply to the heater) The internal resistance value of the sensor element increases with respect to the electric power)). When the gas sensor deterioration is determined based on the internal resistance value, there is a possibility that the sensor element is erroneously determined to be deteriorated even though the sensor element itself is not deteriorated.

  The present invention has been made to solve the above problem, and an object of the present invention is to provide a gas sensor deterioration determination method that accurately determines whether or not a sensor element has deteriorated.

In order to solve the above-described problem, a method for determining deterioration of a gas sensor according to a first aspect of the present invention includes a solid electrolyte body whose electrical characteristics change according to the concentration of a specific gas in a gas to be measured, and a solid electrolyte body formed on the solid electrolyte body A sensor element having a pair of electrodes and a heater for heating the sensor element, and a tip portion of the sensor element is covered with a protector having a through hole for introducing the gas to be measured. a deterioration determination method of the gas sensor determines whether the gas sensor have has deteriorated, in a state where the gas sensor is exposed to an atmosphere of a predetermined temperature, the inside of the sensor element when electric power is supplied to the pre-Symbol heater the resistance value, the internal resistance value acquisition step of acquiring the several different that supply power to the heater, based on a plurality of the internal resistance value obtained in the internal resistance value acquisition step The sensor element and a degradation determiner step whether is deteriorated.

Further, the deterioration determination method of the gas sensor of the invention according to claim 1, in addition to the above configuration of the invention, in the deterioration determination process, a plurality of the internal resistance value obtained in the internal resistance value acquisition step, the respective A straight line is calculated by an Arrhenius plot based on each power supplied to the heater from which an internal resistance value is obtained, and a theoretical internal resistance value when the heater is not energized is calculated based on the straight line. When the internal resistance value is obtained for a straight line having the same inclination as the reference line obtained by the same method as the method for obtaining the straight line and passing through the theoretical internal resistance value, It is characterized in that it is determined whether or not the sensor element is deteriorated based on a true theoretical internal resistance value calculated and obtained by substituting the calculated power .

According to the deterioration determination process of the gas sensor of the invention according to claim 1, in a state exposed gas sensor to an atmosphere of a predetermined temperature, the internal resistance of the sensor element at the time of applying a power to the heater, to the heater Obtain for multiple different power supplies . In a state where the gas sensor is exposed to an atmosphere of a predetermined temperature, when applying the power heater, the sensor element and the atmosphere at a predetermined temperature, it is heated by the heater. For this reason, compared with the case where a sensor element is heated only with a heater, a sensor element becomes easy to be heated to the predetermined temperature assumed beforehand.

Further, when the presence or absence of deterioration of the sensor element itself is determined based on only one point of the internal resistance value of the sensor element, heat from the heater is appropriately conducted to the sensor element, and the temperature of the sensor element is determined by the atmosphere at a predetermined temperature and the heater. Assuming that is at a predetermined temperature, there is no choice but to perform deterioration determination. Therefore, the cause as described above, even by applying a predetermined power to the heater to a predetermined temperature which has been previously assumed, when the sensor element to its predetermined temperature is no longer heated, have previously assumed The internal resistance value increases with respect to the predetermined temperature (or the power supplied to the heater). Therefore, when the gas sensor deterioration determination is performed based on the internal resistance value, it may be erroneously determined that the sensor element has deteriorated even though the sensor element has not deteriorated.

In contrast, in the gas sensor deterioration determination method of the present invention, the internal resistance, by using a plurality of the relationship between test sheet was power to the heater when acquiring the internal resistance value, the sensor element by the heater Considering that the influence of heating changes, the presence or absence of deterioration of the sensor element itself is determined. For this reason, according to the deterioration determination method for a gas sensor of the present invention, the influence of heating on the sensor element by the heater changes while using an atmosphere at a predetermined temperature and a plurality of internal resistance values of the sensor element heated by the heater. Regardless of the fact, the presence or absence of deterioration of the sensor element itself can be accurately determined.

According to the gas sensor deterioration determination method of the first aspect of the invention, in addition to the effects of the invention, a plurality of the internal resistance values acquired in the internal resistance value acquisition step and the internal resistance values are obtained. A straight line is calculated by an Arrhenius plot based on each supply power to the heater, a theoretical internal resistance value when the heater is not energized is calculated based on the straight line, and the straight line is calculated using a gas sensor in an initial state. Substituting the power supplied when acquiring the internal resistance value for a straight line that has the same slope as the reference line, which is the straight line obtained by the same method as that obtained, and passes through the theoretical internal resistance value Whether or not the sensor element has deteriorated is determined based on the true theoretical internal resistance value calculated and obtained in step (1) .

The theoretical internal resistance value when no electric power is applied to the heater includes the case where deposits are deposited on the sensor element (or the protective layer covering the sensor element) as described above, or the members disposed around the sensor element. Does not include the effects of deposits. Therefore, based on this theoretical internal resistance value, it can be more accurately determined whether or not the sensor element itself has deteriorated.

According to the gas sensor deterioration determination method of the first aspect of the invention, in addition to the effects of the invention described above, the tip of the sensor element is covered with a protector having a measurement gas intake hole. This protector is warmed by the heat generated when electric power is applied to the heater, and has the effect of directly warming the air in contact with the sensor element by radiant heat. By using the gas sensor for a long period of time, when deposits accumulate on the inner surface of the protector, the effect of this radiant heat is reduced compared to the initial state. When the gas sensor deterioration determination method of the present invention is applied to a gas sensor having such a configuration, it is erroneously determined that the sensor element itself has deteriorated due to the influence of the reduction of radiant heat, although it has not deteriorated. Can be avoided.

  Hereinafter, an embodiment of a gas sensor deterioration determination method embodying the present invention will be described with reference to the drawings. First, the structure of the gas sensor 1 is demonstrated with reference to FIGS. 1-3 as an example of the gas sensor provided to the degradation determination method of the gas sensor which concerns on this invention. FIG. 1 is a longitudinal sectional view of the gas sensor 1. FIG. 2 is a perspective view showing the external appearance of the sensor element 10. FIG. 3 is an exploded perspective view of the sensor element 10.

  In the following drawings, the vertical direction in FIGS. 1 and 2 and the horizontal direction in FIG. 3 are the directions of the axis O of the gas sensor 1 (or sensor element 10). This axis O direction is indicated by a one-dot chain line in FIGS. 1 and 2 and indicated by an arrow in FIG. 1 and 2, the lower side in FIG. 3 is the tip side of the gas sensor 1 (or sensor element 10), the upper side in FIGS. 1 and 2, and the right side in FIG. 3 is the gas sensor 1 (or The sensor element 10) will be described as the rear end side.

  A gas sensor 1 shown in FIG. 1 is attached to an exhaust pipe (not shown) of an automobile, and a tip portion 11 of a sensor element 10 held inside is exposed to exhaust gas flowing in the exhaust pipe, and the exhaust gas in the exhaust gas This is a so-called full-range air-fuel ratio sensor that detects the air-fuel ratio of exhaust gas from the oxygen concentration. From the sensor element 10, when the air-fuel ratio of the exhaust gas is lean, a detection value (current value) corresponding to the amount of oxygen surplus with respect to the theoretical air-fuel ratio is obtained, and when it is rich, the unburned gas A detection value (current value) corresponding to the amount of oxygen necessary to completely burn the gas is obtained. Based on these detection values, the air-fuel ratio of the exhaust gas is obtained by a sensor control circuit (not shown) and output to an ECU (electronic control unit) for use in air-fuel ratio feedback control or the like.

  The sensor element 10 is a narrow and plate-like element extending in the direction of the axis O, and includes a detection element 3 and a heater element 4 (to be described later in FIG. 1, the sheet thickness direction is the sheet thickness direction and the sheet width direction is the sheet width. Shown as direction.) The gas sensor 1 holds the sensor element 10 in the metal cup 20, and further supports the metal cup 20 in a metal shell 50 to be attached to an exhaust pipe (not shown) of the automobile, thereby It has a structure held in the metal shell 50. The detailed structure of the sensor element 10 will be described later.

  A metal metal cup 20 having a bottomed cylindrical shape in which the sensor element 10 is inserted is disposed inside the central portion 13 of the sensor element 10 at a slightly distal end side. The metal cup 20 is a holding member for holding the sensor element 10 in the metal shell 50, and the tip end portion 11 of the sensor element 10 protrudes from the opening 25 at the bottom of the cylinder. Moreover, the front-end | tip peripheral part 23 of the edge part of a cylinder bottom is formed in the taper shape over the outer peripheral surface. In the metal cup 20, an alumina ceramic ring 21 and a talc ring 22 obtained by compressing and solidifying talc powder are accommodated in a state where the sensor element 10 is inserted through the ring. The talc ring 22 is crushed in the metal cup 20 so as to be filled in detail, whereby the sensor element 10 is positioned and held in the metal cup 20.

  The sensor element 10 integrated with the metal cup 20 is surrounded and held by a cylindrical metal shell 50. The metal shell 50 is for attaching and fixing the gas sensor 1 to an exhaust pipe (not shown) of an automobile, and is made of a low carbon steel such as SUS430. A male thread 51 for attachment to the exhaust pipe is formed on the outer peripheral tip side of the metal shell 50. A distal end engaging portion 56 to which a protector 8 described later is engaged is formed on the distal end side of the male screw portion 51. A tool engaging portion 52 that engages a tool for attachment to the exhaust pipe is formed at the center of the outer periphery of the metal shell 50. The front end surface of the tool engaging portion 52 and the rear end of the male screw portion 51 are formed. In between, a gasket 55 is inserted to prevent gas escape when attached to the exhaust pipe. Further, the rear end side of the tool engaging portion 52 is engaged with a rear end engaging portion 57 to be engaged with an outer cylinder 65 described later, and the sensor element 10 is caulked and held in the metal shell 50 on the rear end side. For this purpose, a caulking portion 53 is formed.

  Further, a step portion 54 is formed in the vicinity of the male screw portion 51 on the inner periphery of the metal shell 50. The step 54 is engaged with the peripheral edge 23 of the tip of the metal cup 20 that holds the sensor element 10. Further, a talc ring 26 is loaded on the inner periphery of the metal shell 50 from the rear end side of the metal cup 20 with the sensor element 10 inserted therethrough. A cylindrical sleeve 27 is fitted into the metal shell 50 so as to hold the talc ring 26 from the rear end side. A shoulder portion 28 having a step shape is formed on the outer periphery of the rear end side of the sleeve 27, and an annular caulking packing 29 is disposed on the shoulder portion 28. In this state, the crimping portion 53 of the metal shell 50 is crimped so as to press the shoulder portion 28 of the sleeve 27 toward the distal end side via the crimping packing 29. The talc ring 26 pressed by the sleeve 27 is crushed in the metal shell 50 and filled in details. The metal cup 20 and the sensor element 10 are positioned and held in the metal shell 50 by the talc ring 26 and the talc ring 22 loaded in the metal cup 20 in advance. The airtightness in the metal shell 50 is maintained by the caulking packing 29 interposed between the caulking portion 53 and the shoulder portion 28 of the sleeve 27, and the outflow of combustion gas is prevented.

  From the tip end (tip engaging portion 56) of the metal shell 50, the tip end portion 11 of the sensor element 10 held inside protrudes. A protector 8 for protecting the distal end portion 11 of the sensor element 10 from breakage due to moisture etc. is fitted to the distal end engaging portion 56, and is fixed by spot welding or laser welding. The protector 8 is a double structure constituted by a bottomed cylindrical inner protector 90 and a cylindrical outer protector 80 that surrounds the periphery in the radial direction with a gap between the outer peripheral surface of the inner protector 90. Have

  The inner protector 90 has a plurality of inner introduction holes 95 at the rear end side of the peripheral wall 92, a plurality of drain holes 96 at the front end side of the peripheral wall 92, and a discharge port 97 at the bottom wall 93. Then, the base end portion 91 on the opening end side (rear end side) is engaged with the outer periphery of the front end engaging portion 56, and in this state, the outer periphery is made a round and laser welding is performed, and the inner protector 90 is the metal shell 50. It is fixed to. Further, the outer protector 80 has a plurality of outer introduction holes 85 opened on the distal end side of the peripheral wall 82. The base end portion 81 on the opening end side is engaged with the outer periphery of the base end portion 91 of the inner protector 90, and laser welding is performed on the outer periphery in this state, and the outer protector 80 and the inner protector 90 together with the metal shell 50 is fixed. Furthermore, the tip 83 of the outer protector 80 is bent inward toward the peripheral wall 92 of the inner protector 90 so as to close the gap between the outer protector 80 and the inner protector 90.

  The exhaust gas (measured gas) introduced from the outer introduction hole 85 into the gap between the outer protector 80 and the inner protector 90 generates a swirling flow in a state of surrounding the outer periphery of the peripheral wall 92 of the inner protector 90, Separated into moisture. The gas component is introduced into the inner protector 90 from the inner introduction hole 95, contacts the sensor element 10, and is discharged to the outside from the discharge port 97. On the other hand, moisture enters the inner protector 90 through the drain hole 96 and is discharged to the outside through the discharge port 97. With such a configuration, the distal end portion 11 of the sensor element 10 is protected from breakage due to thermal shock caused by water exposure. The protector 8 including the outer protector 80 and the inner protector 90 corresponds to the “protector” of the present invention. The inner introduction hole 95 and the outer introduction hole 85 correspond to the “through hole” of the present invention.

  On the other hand, the rear end portion 12 of the sensor element 10 held inside protrudes from the rear end (caulking portion 53) of the metal shell 50. As will be described later, the rear end portion 12 of the sensor element 10 has electrode pads 231, 232, 233, 241, and 242 made of platinum (Pt) for taking out electrodes from the detection element 3 and the heater element 4 constituting the sensor element 10. 2 and 3) are formed. Insulating ceramics that internally hold five connection terminals 61 (two of which are shown in FIG. 1) that contact (electrically connect) each of the electrode pads 231 to 233, 241, and 242. A cylindrical separator 60 is formed on the rear end portion 12 of the sensor element 10. The separator 60 also accommodates and protects the connecting portions between the five lead wires 64 (three of which are shown in FIG. 1) drawn to the outside of the gas sensor 1 and the connection terminals 61. Yes.

  Next, the outer cylinder 65 is made of stainless steel (for example, SUS304) and has a cylindrical shape. The outer cylinder 65 is attached to the rear end side of the metal shell 50 and exposed from the rear end of the metal shell 50. The separator 60 is covered and protected. The outer cylinder 65 has an opening end 66 on its front end side engaged with the outer periphery of the rear end engaging portion 57 of the metal shell 50 and is crimped from the outer peripheral side, and makes a round around the outer periphery, and the rear end engaging portion 57. And is fixed to the metal shell 50 by laser welding.

  Further, a metal-made cylindrical holding metal fitting 70 is disposed in the gap between the outer cylinder 65 and the separator 60. The holding metal fitting 70 has a support portion 71 formed by bending the rear end of the holding member 70 inward, and a support portion 71 is provided with a flange portion 62 provided in a hook shape on the outer periphery of the rear end side of the separator 60 inserted into the holding metal fitting 70. And the separator 60 is supported. In this state, the outer peripheral surface of the outer cylinder 65 at the portion where the holding metal fitting 70 is disposed is crimped, and the holding metal fitting 70 that supports the separator 60 is fixed to the outer cylinder 65.

  A fluorine rubber grommet 75 is fitted into the opening on the rear end side of the outer cylinder 65. The grommet 75 has five insertion holes 76 (one of which is shown in FIG. 1), and the five lead wires 64 drawn from the separator 60 are inserted into each insertion hole 76 in an airtight manner. ing. In this state, the grommet 75 is crimped from the outer periphery of the outer cylinder 65 while pressing the separator 60 toward the front end side, and is fixed to the rear end of the outer cylinder 65.

  Next, the sensor element 10 will be described. First, the external configuration of the sensor element 10 will be described. A sensor element 10 shown in FIG. 2 is an element in which a detection element 3 and a heater element 4 formed in a thin plate shape extending in the direction of the axis O and stacked in the thickness direction are integrated. The tip portion 11 of the sensor element 10 is mainly configured by a portion in which the detection element 3 is provided with a gas detection chamber 132 (see FIG. 3) for taking in the exhaust gas and detecting the oxygen concentration in the exhaust gas. A detecting unit 14 is provided. In order to protect the detection unit 14 from poisoning due to deposits (toxic substances such as fuel ash and oil components) in the exhaust gas, the tip 11 of the sensor element 10 covers the entire circumference around the tip of the element. Thus, it is covered with the protective layer 9. The protective layer 9 is made of a composite powder in which the fine powder covers the coarse powder, and pores that are not filled with the fine powder are dispersed in the gaps between the composite powders. The composite powder (coarse powder and fine powder) is, for example, a composite oxide powder containing titania powder having a peak at a particle size of 1 μm or less and alumina such as spinel having a peak at a particle size of 10 μm or more.

  Further, among the outer surfaces orthogonal to the thickness direction of the sensor element 10 at the rear end portion 12 of the sensor element 10, the main surface 15 which is the outer surface on the detection element 3 side has five connection terminals 61 ( The electrode pads 231, 232, and 233 are formed in contact with and electrically connected to each of three of them (see FIG. 1). Similarly, the back surface 16 which is the outer surface of the heater element 4 on the opposite side of the thickness direction from the main surface 15 is also electrically connected in contact with the remaining two connection terminals 61 in pairs. Pads 241 and 242 are formed. The ridge angles formed by two adjacent surfaces of the main surface 15, the back surface 16, and the side surfaces 17 and 18 forming the outer surface of the sensor element 10 are chamfered by cutting or cutting in the manufacturing process of the sensor element 10, respectively. The chamfered portions 32, 34, 42 and 44 are formed. Further, the ridge angle between the rear end face 18 and the side face 17 is also chamfered as a chamfer 46.

  Next, the structure of the sensor element 10 will be described with reference to FIG. As shown in FIG. 3, each of the detection element 3 and the heater element 4 constituting the sensor element 10 has a plate-like member (insulating bases 110 and 130 and solid electrolyte bodies 120 and 140 constituting the detection element 3). In addition, an electrode or the like is sandwiched between insulating bases 160, 170) constituting the heater element 4 and laminated in the thickness direction. In the following description, the outer surface of each member arranged on the main surface 15 side of the sensor element 10 (the upper side in FIG. 3) is referred to as a “main surface” following the sensor element 10, and the back surface 16 side ( Similarly, the outer surface of each member arranged on the lower side of the sheet of FIG. 3 is referred to as a “back surface”.

  In the detection element 3, the insulating bases 110 and 130 mainly composed of insulating alumina and the solid electrolyte bodies 120 and 140 mainly composed of zirconia are separated from the main surface side toward the back surface side. The electrolyte body 120, the insulating base 130, and the solid electrolyte body 140 are stacked in this order. The solid electrolyte bodies 120 and 140 correspond to the “solid electrolyte body” of the present invention. A pair of electrodes 180 and 190 and a pair of electrodes 200 and 210 made of a conductive pattern mainly composed of platinum are formed on both surfaces of the solid electrolyte body 120 and the solid electrolyte body 140, respectively. These electrodes 180 and 190 and electrodes 200 and 210 correspond to the “electrodes” of the present invention. The insulating bases 110 and 130 and the solid electrolyte bodies 120 and 140 are each formed as a narrow plate having substantially the same size.

  The electrode 180 formed on the main surface of the solid electrolyte body 120 (as described above, the surface on the main surface 15 side of the sensor element 10 shown in FIG. 2) is on the front end side (the left hand side in the figure). ) To the rear end side (right hand side in the drawing), and a wide electrode portion 181 is formed on the leading end side of the lead portion 183. The insulating base 110 is laminated on the main surface side of the solid electrolyte body 120, and the electrode 180 is sandwiched therebetween. Further, a through hole 113 is formed at a position corresponding to the position of the rear end portion 182 of the lead portion 183 of the electrode 180 on the rear end side of the insulating substrate 110, and the through hole conductor 234 is formed in the through hole 113. Intervened. An electrode pad 231 is formed at a position on the rear end side corresponding to the through-hole 113 on the main surface of the insulating base 110 serving as the main surface 15 (see FIG. 2) of the sensor element 10. The electrode pad 231 is electrically connected to the rear end portion 182 of the lead portion 183 of the electrode 180 through the through-hole conductor 234.

  Next, an opening 111 penetrating in the thickness direction is provided at a position where the electrode portion 181 is disposed on the distal end side of the insulating base 110. In the opening 111, a porous layer 112 is provided which is mainly made of alumina and is porous like the insulating base 110. The electrode portion 181 of the electrode 180 is configured to communicate with the outside air via the porous layer 112.

  On the other hand, on the back surface of the solid electrolyte body 120, an electrode 190 that is paired with the electrode 180 is formed. Like the electrode 180, a lead portion 193 extending from the front end side to the rear end side of the solid electrolyte body 120; And a wide electrode portion 191 on the leading end side of the lead portion 193. The electrode part 191 is disposed at a position facing the electrode part 181 of the electrode 180 with the solid electrolyte body 120 interposed therebetween. Further, a through hole 124 and a through hole 114 are formed at positions corresponding to the rear end portion 192 of the lead portion 193 of the electrode 190 on the rear end side of the solid electrolyte body 120 and the insulating base 110, respectively. A through-hole conductor 237 and a through-hole conductor 235 are interposed in each of the through holes 124 and 114, and both are electrically connected when stacked. An electrode pad 232 is formed at a position corresponding to the through hole 114 on the main surface on the rear end side of the insulating base 110. The electrode pad 232 is disposed at a position aligned with the electrode pad 231 in the width direction on the main surface on the rear end side of the insulating base 110. The electrode pad 232 is electrically connected to the rear end 192 of the lead portion 193 of the electrode 190 via the through-hole conductor 237 and the through-hole conductor 235.

  Further, the insulating base 130 is laminated on the back surface side of the solid electrolyte body 120 in a state where the electrode 190 is sandwiched between the solid electrolyte body 120. An opening 131 that penetrates in the thickness direction of the electrode body 191 is also provided at a position where the electrode portion 191 is disposed on the distal end side of the insulating base 130. The opening 131 is closed by the solid electrolyte body 120 and the solid electrolyte body 140 that are stacked on both sides of the insulating base 130 in the thickness direction, and the inside is configured as a gas detection chamber 132. The electrode portion 191 of the electrode 190 is disposed in the gas detection chamber 132. A detection unit 14 for detecting the oxygen concentration in the exhaust gas is configured around the gas detection chamber 132 disposed at the distal end 39 (the left hand side in FIG. 3) of the detection element 3.

  In addition, diffusion limiting parts 133 are provided on the side walls of the opening 131 on both sides in the width direction of the insulating base 130. The diffusion control part 133 is formed as a porous body made of alumina, and the exhaust gas around the detection element 3 is introduced into the gas detection chamber 132 through the diffusion control part 133. The diffusion control unit 133 is provided to limit the amount of exhaust gas flowing into the gas detection chamber 132 when exhaust gas is introduced.

  Next, the solid electrolyte body 140 is laminated on the back side of the insulating substrate 130. On the main surface of the solid electrolyte body 140, similarly to the electrodes 180 and 190, a lead portion 203 extending from the front end side to the rear end side of the solid electrolyte body 140 and a wide portion at the front end side of the lead portion 203 were formed. An electrode 200 having an electrode portion 201 is formed. The electrode part 201 of the electrode 200 is also exposed in the gas detection chamber 132. A through hole 134 is also formed at a position corresponding to the rear end portion 202 of the lead portion 203 of the electrode 200 on the rear end side of the insulating base 130. The formation position of the through hole 134 also corresponds to the formation position of the rear end portion 192 of the lead portion 193 of the electrode 190 on the main surface side of the insulating base 130. The rear end portion 192 of the lead portion 193 of the electrode 190 and the rear end portion 202 of the lead portion 203 of the electrode 200 are electrically connected via the through-hole conductor 239 interposed inside the through hole 134. Yes. That is, the electrode 190, the electrode 200, and the electrode pad 232 are electrically connected to each other.

  On the other hand, an electrode 210 that is paired with the electrode 200 is also formed on the back surface of the solid electrolyte body 140. Similarly, the lead portion 213 extending from the front end side to the rear end side of the solid electrolyte body 140, and the lead portion 213 And an electrode portion 211 formed wide at the tip portion. The electrode part 211 is disposed at a position facing the electrode part 201 of the electrode 200 with the solid electrolyte body 140 interposed therebetween. Meanwhile, an electrode pad 233 is formed between the electrode pad 231 and the electrode pad 232 on the main surface on the rear end side of the insulating base 110. The arrangement position of the rear end portion 212 of the lead portion 213 of the electrode 210 corresponds to the formation position of the electrode pad 233 in the thickness direction. Through holes 115 and 125 that penetrate through the insulating base 110, the solid electrolyte body 120, the insulating base 130, and the solid electrolyte body 140 that are interposed between the rear end portion 212 of the electrode 210 and the electrode pad 233 and continue in the thickness direction. , 135, and 145 are formed. Through-hole conductors 236, 238, 240, and 241 are also interposed in these through-holes 115, 125, 135, and 145, respectively, so that the electrode pad 233 and the electrode 210 are electrically connected.

  Next, the configuration of the heater element 4 will be described. The heater element 4 has a structure in which a heating resistor 220 made of a refractory metal such as tungsten or molybdenum is sandwiched between the back surface of an insulating substrate 160 mainly composed of insulating alumina and the main surface of the insulating substrate 170. It has become. The heating resistor 220 is composed of one conductive pattern connected in the heater element 4. The heating resistor 220 has a heating portion 221 having a pattern with a small cross-sectional area so as to generate mainly heat, and the heating portion 221 is a tip portion 49 of the heater element 4 (left hand in FIG. 3). Side). The two lead portions 223 respectively connected to both ends of the heat generating portion 221 have a cross-sectional area larger than that of the heat generating portion 221, and in a state of being parallel to the width direction, the direction of the axis O (the direction indicated by the arrow 600 in FIG. 3). ) To the rear end side of the insulating bases 160 and 170 (right hand side in FIG. 3). On the other hand, two electrode pads 241 and 242 are arranged in a row in the width direction of the insulating substrate 170 on the rear end side on the back surface on the rear end side of the insulating substrate 170 that becomes the back surface 16 of the sensor element 10. The rear end portions 222 of the two lead portions 223 of the heating resistor 220 are through through-hole conductors 243 and 244 respectively interposed in two through-holes 173 and 174 formed on the rear end side of the insulating base 170. The electrode pads 241 and 242 are electrically connected to each other.

  The heater element 4 is integrally configured as the sensor element 10 by sandwiching the electrode 210 between the main surface of the insulating base 160 and the back surface of the solid electrolyte body 140 of the detection element 3 and being laminated together with the detection element 3. The

  The detection element 3 of such a sensor element 10 includes an exhaust gas (measured object) that flows into the gas detection chamber 132 in the detection unit 14 that is configured around the gas detection chamber 132 provided at the tip end 39 of the sensor element 10. The air-fuel ratio of the exhaust gas is detected according to the concentration of oxygen (specific gas) in the gas). The mechanism will be briefly described here.

  A solid electrolyte body made of zirconia exhibits insulation at room temperature but is activated in a high temperature environment (for example, 600 ° C. or higher) and exhibits oxygen ion conductivity. When a platinum electrode is provided in each of the two chambers separating the solid electrolyte body using this property, an electromotive force (potential difference) is generated between the two electrodes at this time due to the oxygen partial pressure difference between the two chambers.

  Therefore, the current flowing between the electrode 180 and the electrode 190 is controlled so that the potential difference between the electrodes 200 and 210 is kept constant. When the air-fuel ratio of the exhaust gas flowing into the gas detection chamber 132 is rich, there is almost no oxygen in the exhaust gas, and oxygen is introduced into the gas detection chamber 132 from the outside of the detection element 3 between the electrodes 180 and 190. Control is made so that the electrons are moved in the direction of pumping. On the other hand, when the air-fuel ratio of the exhaust gas flowing into the gas detection chamber 132 is lean, a large amount of oxygen exists in the exhaust gas, so oxygen is transferred from the gas detection chamber 132 to the outside between the electrodes 180 and 190. Control is made so that electrons are moved in the direction of pumping. From the direction and magnitude of the current obtained at this time, it is possible to detect the air-fuel ratio of the exhaust gas relative to the air-fuel ratio (theoretical air-fuel ratio) when the voltage at the boundary is shown. Note that the solid electrolyte bodies 120 and 140 are promoted to be activated or stabilized early by the heater element 4 laminated together with the detection element 3.

  Next, a gas sensor deterioration determination method according to the present embodiment for determining whether or not the gas sensor 1 having the above-described configuration has deteriorated will be described with reference to FIGS. 4 and 5. FIG. 4 is a graph in which the power supplied to the heater element 4 and the internal resistance value Rpvs of the sensor element 10 corresponding to the supplied power are plotted (Arrhenius plot) under the condition where the gas sensor 1 is exposed to an atmosphere of a predetermined temperature. is there. FIG. 5 is a flowchart showing the procedure of the deterioration determination method of the gas sensor 1. In the following description, a factor that prevents heat from the heater element 4 from being properly conducted to the sensor element 10 and a factor other than deterioration of the sensor element 10 itself is referred to as an “external factor”. Examples of the external factor include a case where an adhering matter is deposited on the sensor element 10 or the protective layer 9 covering the sensor element 10 and a case where an adhering matter is deposited on the inner surface of the protector 8.

  First, the determination principle of the deterioration determination method of the gas sensor 1 of the present embodiment will be briefly described with reference to the graph 500 of FIG.

  There is a positive correlation expressed by a linear expression between the reciprocal of the temperature of the sensor element 10 and the logarithm of the internal resistance value Rpvs of the sensor element 10. Since the predetermined power is supplied to the heater element 4 so that the temperature of the sensor element 10 becomes a predetermined temperature, the temperature of the sensor element 10 and the power supplied to the heater element 4 are substantially proportional in the measurement range. There is a relationship. Therefore, there is also a positive correlation expressed by a linear expression between the reciprocal of the power supplied to the heater element 4 and the logarithm of the internal resistance value Rpvs of the power sensor element 10. The deterioration determination method for the gas sensor 1 of the present embodiment uses the positive correlation.

  In order to obtain the positive correlation, first, a plurality of different electric powers are supplied to the heater element 4 in a state where the gas sensor 1 in the initial state is exposed to an atmosphere of a predetermined temperature (for example, 750 ° C.), and corresponding to each supply electric power. The internal resistance value Rpvs to be acquired is acquired. When the power supplied to the heater element 4 and the internal resistance value Rpvs are Arrhenius plotted, a reference line 512 passing through the reference measurement points 504 and 505 as shown in FIG. 4 is obtained. Note that the horizontal axis of the Arrhenius plot in FIG. 4 is the reciprocal of the power supplied to the heater element 4. Also, the vertical axis of the Arrhenius plot in FIG. 4 is the logarithm of the internal resistance value Rpvs of the sensor element 10 when the power is supplied. The amount of heating of the sensor element 10 by the heater element 4 is reflected in the slope of the straight line obtained by the Arrhenius plot. For this reason, when the heat from the heater element 4 is appropriately conducted to the sensor element 10 and the sensor element 10 is heated to a predetermined target temperature, the reference line 512 obtained using the gas sensor 1 in the initial state and It can be said that a straight line having the same inclination is obtained.

  On the other hand, when deposits are deposited on the sensor element 10 or the protective layer 9 covering the sensor element 10, the heat from the heater element 4 is not properly conducted to the sensor element 10, and the sensor element 10 is not heated to the target temperature. . Further, when deposits accumulate on the inner surface of the protector 8, the radiant heat from the protector 8 is reduced compared to the initial state, and the sensor element 10 is not heated to the target temperature. When such an external factor has occurred, the slope is gentle compared to the reference line 512 obtained using the gas sensor 1 in the initial state, for example, a straight line 511 passing through the measurement point 501 and the measurement point 502. A straight line is obtained. The logarithmic difference (illustrated by an arrow 523) of the internal resistance value Rpvs in the electric power W2 (two-dot chain line 551) between the gas sensor 1 in the initial state and the gas sensor 1 causing the external factor is affected by the external factor. Minute (illustrated by an arrow 521) and an influence due to deterioration of the sensor element 10 itself (illustrated by an arrow 522) are included. As the influence of the external factor and the influence of the deterioration of the sensor element 10 itself, only one internal resistance value (for example, measurement point 501) when the same power is supplied is used as a reference value (reference measurement point 504). ) And cannot be distinguished from just comparison.

  Here, when the above Arrhenius plot is obtained using internal resistance values when a plurality of different electric powers are supplied, the electric power is not supplied to the heater element 4 based on the straight line 511 (two-dot chain line 553). The theoretical internal resistance value (calculation point 503), which is the theoretical internal resistance value of This theoretical internal resistance value does not include the effect of heating by the heater element 4, that is, the influence of external factors. Therefore, using this theoretical internal resistance value, it is possible to accurately determine whether or not the sensor element 10 itself has deteriorated. A method of actually measuring the internal resistance value of the sensor element 10 when the sensor element 10 is heated only by the temperature of the atmosphere without supplying power to the heater element 4 and power is not supplied to the heater element 4 is also considered. It is done. However, in the present embodiment, from the viewpoint of more reliably stabilizing the temperature of the sensor element 10, the sensor element 10 is heated by the atmosphere at a predetermined temperature and the heater element 4, and the theoretical internal resistance value (calculation point) is calculated as described above. 503).

  In the present embodiment, further, the heater element 4 is such that the temperature of the sensor element 10 becomes the temperature at the time of measurement from a straight line 513 that passes through the calculation point 503 indicating the theoretical internal resistance value and has the same inclination as the reference line 512. The internal resistance value (calculation point 507) when power is supplied to is calculated as the true internal resistance value. Whether or not the sensor element 10 itself has deteriorated is determined based on whether or not the true internal resistance value falls within a predetermined range that satisfies the standard.

  In this embodiment, in order to expose the gas sensor 1 to an atmosphere having a predetermined temperature, the gas sensor 1 is arranged in a furnace heated so that the atmosphere has a predetermined temperature. The predetermined temperature of the atmosphere to which the gas sensor 1 is exposed is set to, for example, a temperature higher than the outside air and lower than the durable temperature of each member constituting the gas sensor 1. The predetermined temperature of the atmosphere is more preferable as compared with the case where the difference from the actual use temperature is larger as the temperature is closer to the actual use temperature of the sensor element 10 when the gas sensor 1 detects the concentration of the specific gas in the gas to be measured. . Whether or not the sensor element 10 itself has deteriorated is because it is preferable to examine the temperature at which the gas sensor 1 is actually used, that is, the sensor element 10 that has reached the actual use temperature. Further, when the sensor element 10 is close to the actual use temperature when detecting the concentration of the specific gas in the gas to be measured, the power supplied to the heater element 4 is small in order to heat the sensor element 10 to the target temperature. Tesumu. This is because the influence of heating by the heater element 4 can be reduced. In the present embodiment, the target temperature of the sensor element 10 when using the gas sensor 1 is 830 ° C., and the furnace temperature, which is the temperature of the atmosphere, is 750 ° C.

  Next, a deterioration determination method for the gas sensor 1 of the present embodiment will be described with reference to the flowcharts of FIGS. 4 and 5.

  As shown in the flowchart of FIG. 5, first, in a state where the gas sensor 1 is exposed to an atmosphere heated to a furnace temperature of 750 ° C. in the furnace, the heater element 4 is supplied with electric power W1 (indicated by a two-dot chain line 552 in FIG. 4). ) And the internal resistance value Rpvs1 of the sensor element 10 is measured (S5). Subsequently, in a state where the gas sensor 1 is exposed to an atmosphere at a furnace temperature of 750 ° C., electric power W2 (shown by a two-dot chain line 551 in FIG. 4) is supplied to the heater element 4, and an internal resistance value Rpvs2 of the sensor element 10 is obtained. Measure (S10).

  The internal resistance value refers to the internal resistance value of the solid electrolyte bodies 120 and 140 obtained by supplying a predetermined current or voltage to any of the solid electrolyte bodies 120 and 140 constituting the gas sensor. Is. Since this internal resistance value can be obtained by a known method, a detailed description in this embodiment is omitted. Specifically, for example, the internal resistance value has a predetermined magnitude with respect to the solid electrolyte body 140, for example. Then, the internal resistance value of the solid electrolyte body is obtained from the voltage at that time.

  In S5 and S10, the electric power W1 and W2 supplied to the heater element 4 is appropriately determined in consideration of the temperature of the atmosphere to which the gas sensor 1 is exposed and the relationship between the temperature of the sensor element 10 and the internal resistance value. In the present embodiment, the electric power W2 is measured by the temperature of the sensor element 10 in the initial state by the atmosphere of the furnace temperature of 750 ° C. and the heater element 4 to which the electric power W2 is supplied. The electric power (for example, 4.7 W) is set such that the actual use temperature (for example, 830 ° C.) is reached. In addition, the power W1 is set to be lower than the power W2 (for example, 2W). The order of supplying the electric power W1 and W2 to the heater element 4 is not limited to the above-described order, but from the viewpoint of efficiently heating the heater element 4 and quickly determining deterioration, supply the electric power in ascending order. Is preferred. In addition, said S5 and S10 are corresponded to the "internal resistance value acquisition process" of this invention.

  Subsequently, an Arrhenius plot similar to that in FIG. 4 is obtained using Rpvs1 measured in S5 and Rpvs2 measured in S10, and a theoretical internal resistance value when power is not supplied to the heater element 4 is calculated ( S15). The vertical axis of the Arrhenius plot is the logarithm of the internal resistance value Rpvs of the sensor element 10 corresponding to the power supplied to the heater element 4. The horizontal axis of the Arrhenius plot is the power supplied to the heater element 4. Specifically, first, as shown in FIG. 4, a measurement point 502 based on the internal resistance value Rpvs1 when supplying power W1 measured in S5 and a measurement based on the internal resistance value Rpvs2 when supplying power W2 measured in S10. A straight line 511 is obtained from the point 501. Then, the theoretical internal resistance value (calculation point 503) when power is not supplied to the heater element 4 is calculated by substituting 0 W of power into the linear expression representing the straight line 511.

  The horizontal axis of the Arrhenius plot may be the reciprocal of the temperature of the sensor element 10 when the predetermined power is supplied to the heater element 4 in a state where the gas sensor 1 in the initial state is exposed to an atmosphere of the predetermined temperature.

  Subsequently, a true internal resistance value when power W2 is supplied to the heater element 4 is calculated based on the theoretical internal resistance value calculated in S15 and a predetermined reference line (S20). The “true internal resistance value when the power W2 is supplied to the heater element 4” means that the sensor element 10 assumed when the power W2 is supplied to the heater element 4 under the condition not affected by external factors. This is the theoretical internal resistance value. The reference line used in S20 is the same as the reference line 512 in FIG. 4, and is determined by the following procedure, for example. First, a large number (for example, 100) of gas sensors 1 in an initial state (new) are prepared, and each gas sensor 1 is exposed to an atmosphere at a predetermined temperature (for example, 750 ° C.) similar to the atmosphere in S5 and S10. For each gas sensor 1, as in S 5 and S 10, a plurality of different powers are supplied to the heater element 4, and a plurality of relationships between the power supplied to the heater element 4 and the internal resistance of the sensor element 10 are acquired. Then, the supply power is plotted on the horizontal axis and the logarithm of the internal resistance value Rpvs of the sensor element 10 corresponding to the supply power is plotted on the vertical axis (Arrhenius plot), and a reference line 512 as shown in FIG. 4 is calculated. The calculation procedure of the true internal resistance value (calculation point 507) when the power W2 is supplied to the heater element 4 first passes through the theoretical internal resistance value (calculation point 503) calculated in S15, and the reference line 512 and A straight line 513 having the same inclination is calculated. Then, the power W2 is substituted into a linear expression representing the straight line 513.

  Subsequently, it is determined whether or not the true internal resistance value calculated in S20 satisfies the standard (S25). In the present embodiment, whether or not the true internal resistance value satisfies the standard is determined based on whether or not the true internal resistance value when the power W2 is supplied falls within a predetermined range. When the internal resistance value is within the predetermined range, it is determined that the standard is satisfied. The predetermined range defining the standard is appropriately determined in consideration of the application of the gas sensor 1, the accuracy of deterioration determination, and the like. When the true internal resistance value calculated in S20 satisfies the standard (S25: Yes), it is determined as a pass determination (the sensor element 10 provided in the gas sensor 1 is not deteriorated) (S30). On the other hand, when the true internal resistance value calculated in S20 does not satisfy the standard (S25: Yes), it is determined as a failure determination (the sensor element 10 provided in the gas sensor 1 itself has deteriorated) (S35). In addition, said S15, S20, S25, S30, and S35 are corresponded to the "deterioration determination process" of this invention. Following S30 or S35, the deterioration determination is terminated.

  As described above, the deterioration determination of the gas sensor 1 of the present embodiment is performed. According to the deterioration determination method for the gas sensor 1 of the present embodiment, two different electric powers W1 and W2 are supplied to the heater element 4 in a state where the gas sensor 1 is exposed to an atmosphere at a furnace temperature of 750 ° C. When the W1 and W2 are supplied, the internal resistance values Rpvs1 and Rpvs2 of the sensor elements 10 corresponding to the W1 and W2 are acquired (S5 and S10). Thus, when electric power is supplied to the heater element 4 in a state where the gas sensor 1 is exposed to the atmosphere at the predetermined temperature, the sensor element 10 is heated by both the atmosphere at the predetermined temperature and the heater element 4. For this reason, compared with the case where the sensor element 10 is heated only by the heater element 4 or only the atmosphere to which the gas sensor 1 is exposed, the sensor element 10 is easily heated to a temperature assumed in advance. Since the internal resistance value of the sensor element 10 is affected by the temperature of the sensor element 10 itself, a highly reliable internal resistance value can be obtained under conditions in which the sensor element 10 is heated to a temperature assumed in advance. The presence or absence of deterioration can be appropriately determined using this internal resistance value.

  Further, when it is determined whether the sensor element 10 itself has deteriorated or not by only one point of the internal resistance value of the sensor element 10, heat from the heater element 4 is conducted to the sensor element 10, and the temperature of the sensor element 10 is assumed in advance. However, there is no choice but to perform deterioration judgment on the premise that the temperature has reached a predetermined temperature. When the temperature of the sensor element 10 is lower than a predetermined temperature due to an external factor, it may be erroneously determined that the sensor element 10 is deteriorated although the sensor element 10 itself is not deteriorated. On the other hand, in the degradation determination method of the present embodiment, using a plurality of relationships (W1 and Rpvs1, W2 and Rpvs2) between the internal resistance value and the power supplied to the heater when acquiring the internal resistance value, A theoretical internal resistance value (calculation point 503) when power is not supplied to the sensor element 10 is obtained. This theoretical internal resistance value does not include the influence of the sensor element 10 being heated by the heater element 4, that is, the influence of external factors. For this reason, based on this theoretical internal resistance value, it can be determined more accurately whether or not the sensor element 10 itself has deteriorated.

  In the present embodiment, the true internal resistance value (calculated point 507 in FIG. 4) when the power W2 is supplied to the heater element 4 calculated based on the theoretical internal resistance value (calculated point 503 in FIG. 4) It is determined whether or not the sensor element 10 itself has deteriorated (S30, S35) depending on whether or not it is within a predetermined range that satisfies the standard (S25). By determining whether or not the sensor element 10 itself has deteriorated using this true internal resistance value, the sensor element 10 itself is subjected to a condition that the sensor element 10 is heated to a temperature at which the gas sensor 1 is used. It can be determined whether or not the battery has deteriorated.

  As in this embodiment, in the gas sensor 1 including the protector 8, when the gas sensor 1 is used for a long period of time, when deposits are deposited on the inner surface of the protector 8, the effect of this radiant heat is reduced compared to the initial state. To do. When the gas sensor deterioration determination method of the present invention is applied to the gas sensor 1 having such a configuration, the sensor element 10 itself is not deteriorated due to the influence of the reduction of radiant heat, but is deteriorated. An erroneous determination can be avoided, and the above-described effects can be obtained particularly suitably.

  The present invention is not limited to the embodiment described in detail above, and various modifications may be made without departing from the scope of the present invention. For example, in the above-described embodiment, the case where the gas sensor deterioration determination method of the present invention is applied to the gas sensor 1 which is a so-called full-range air-fuel ratio sensor is exemplified, but the configuration, usage, and the like of the gas sensor are not limited thereto. For example, in the present embodiment, considering that the resistance value of the heater element 4 changes, power is supplied to the heater element 4. However, when the change in the resistance value of the heater element 4 can be ignored, etc. A voltage may be used.

  Further, for example, the sensor element 10 may not include the protector 8 and the protective layer 9, and the sensor element 10 and the heater element 4 may be provided separately. Further, for example, an oxygen sensor, a NOx sensor, an HC sensor, etc., a solid electrolyte body whose electrical characteristics change according to the concentration of a specific gas in the gas to be measured, and a pair of electrodes formed on the solid electrolyte body It can be applied to deterioration determination of a gas sensor having a sensor element having a heater and a heater for heating the sensor element.

  Further, in the above embodiment, in S5 and S10 in FIG. 5, two different electric powers are supplied, and the internal resistance values of the corresponding sensor elements are obtained when the respective electric powers are supplied. Not. For example, the internal resistance value of the sensor element when power is supplied to the heater element 4 in a state where the gas sensor is exposed to an atmosphere of a predetermined temperature may be acquired for three or more different electric powers. When an Arrhenius plot (see FIG. 4) similar to that in the above embodiment is obtained using three or more internal resistance values, an approximate straight line may be obtained from each measurement point. When an internal resistance value of 3 or more is used, an approximate straight line with higher reliability can be obtained.

  In the above embodiment, the true internal resistance value at the time of supplying power W2 is obtained from the theoretical internal resistance value calculated in S15 of FIG. 5 and the reference line, and the true internal resistance value is predetermined. Whether or not the sensor element 10 itself has deteriorated is determined based on whether or not it is within the range, but is not limited thereto. For example, it is determined whether or not the sensor element 10 itself has deteriorated depending on whether or not the theoretical internal resistance value (calculation point 503) calculated in S15 of FIG. 5 is within a predetermined range. May be. In this case, as in S20 of FIG. 5, since it is not necessary to calculate the true internal resistance value when the power W2 is supplied, the processing can be simplified. Further, for example, from a plurality of relationships between the power supplied to the heater element 4 and the internal resistance value of the sensor element 10 acquired in S5 and S10 in FIG. 5 and predetermined relationship data (map data and calculation formula), It may be determined whether or not the sensor element 10 itself has deteriorated.

  Moreover, in the said embodiment, although the gas sensor 1 was arrange | positioned in the furnace heated to predetermined temperature and the deterioration determination process was performed, it is not limited to this. For example, the method for determining deterioration of a gas sensor according to the present invention may be executed in various apparatuses and systems equipped with the gas sensor. For example, the present invention may be applied to a system in which a gas sensor is attached to an exhaust pipe (not shown) of an automobile. In this case, for example, a program for executing the deterioration determination process is stored in advance in a storage device (for example, ROM) provided in the ECU. Then, in the process execution means (for example, CPU) provided in the ECU, the temperature of the exhaust gas from the automobile, which is the gas to be measured, becomes substantially constant during the period when the deterioration determination process is being executed (the exhaust gas having a predetermined temperature). The deterioration determination process of the gas sensor according to the present invention is executed at the timing. Thus, when it is made to execute in various devices and systems equipped with a gas sensor, it can be detected during use of the gas sensor whether or not the sensor element is in an abnormal state.

  In the above embodiment, the presence or absence of the influence of an external factor may be determined. In this case, for example, the presence or absence of the influence of an external factor may be determined according to whether or not the slope of the straight line obtained in S15 of FIG. 5 is within a specified value. Further, for example, from a plurality of relationships between the power supplied to the heater element 4 and the internal resistance value of the sensor element 10 acquired in S5 and S10 in FIG. 5 and predetermined relationship data (map data and calculation formula), You may make it judge the presence or absence of the influence of an external factor. In this case, in addition to whether or not the sensor element 10 itself has deteriorated, it is possible to accurately determine whether or not the sensor element 10 is affected by an external factor.

  The present invention can be applied to a specific gas measurement system equipped with a gas sensor in addition to a method for determining deterioration of a gas sensor using a TF (Thick Film) type element such as an oxygen sensor, a NOx sensor, or an HC sensor.

1 is a longitudinal sectional view of a gas sensor 1. FIG. 1 is a perspective view showing an external appearance of a sensor element 10. FIG. 1 is an exploded perspective view of a sensor element 10. FIG. The power supplied to the heater element 4 or the temperature of the sensor element 10 when power is supplied to the heater element 4 and the internal resistance of the sensor element 10 corresponding to the supplied power under the condition where the gas sensor 1 is exposed to an atmosphere of a predetermined temperature. It is the graph which plotted value Rpvs (Arrhenius plot). 4 is a flowchart showing a procedure of a method for determining deterioration of the gas sensor 1.

DESCRIPTION OF SYMBOLS 1 Gas sensor 3 Detection element 4 Heater element 8 Protector 10 Sensor element 11 Tip part 80 Outer protector 85 Outer introduction hole 90 Inner protector 95 Inner introduction hole 120,140 Solid electrolyte body 180,190,200,210 Electrode

Claims (1)

A sensor element having a solid electrolyte body whose electrical characteristics change according to the concentration of a specific gas in the gas to be measured, and a pair of electrodes formed on the solid electrolyte body, and a heater for heating the sensor element The sensor element has a tip end portion for determining whether or not a gas sensor covered with a protector having a through-hole for introducing the gas to be measured has deteriorated.
In a state in which atmosphere the gas sensor has been exposed at a predetermined temperature, the internal resistance value of the internal resistance of the sensor element when electric power is supplied to the pre-Symbol heater, to obtain the several different that supply power to the heater Acquisition process;
A deterioration determination step of determining whether or not the sensor element is deteriorated based on the plurality of internal resistance values acquired in the internal resistance value acquisition step,
In the deterioration determination step ,
A plurality of the internal resistance value obtained in the internal resistance value acquisition step, calculates a straight line by Arrhenius plot based on the power supplied to the said heater each internal resistance value is obtained,
Calculate the theoretical internal resistance value when the heater is not energized based on the straight line,
Using the gas sensor in the initial state, the internal resistance value is obtained with respect to a straight line having the same inclination as the reference line obtained by the same method as the method for obtaining the straight line and passing through the theoretical internal resistance value. A gas sensor deterioration determination method, comprising: determining whether or not the sensor element has deteriorated based on a true theoretical internal resistance value calculated by substituting electric power supplied at the time .

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