Gas sensor element and gas sensor

Abstract

To provide a gas sensor element and a gas sensor capable of accurately detecting temperature of a detection electrode.SOLUTION: A gas sensor element 2 is used for a gas sensor 1 utilizing mixed potential. The gas sensor element 2 comprises: a solid electrolyte 21 having a first surface 201 and a second surface 202; a detection electrode 22 provided on the first surface of the solid electrolyte and in contact with a detection object gas G; a reference electrode 23 provided in a position of the second surface of the solid electrolyte opposite the detection electrode and in contact with a reference gas A; a temperature detection part 25 provided on the solid electrolyte; an insulator 3 arranged facing the second surface of the solid electrolyte, so as to have a duct 24 for circulating the reference gas between the second surface and the insulator; and a heater 411 arranged together with the insulator and controlled based on the temperature detected by the temperature detection part.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a gas sensor element and a gas sensor. [Background technology]

[0002] Gas sensors are disposed in the exhaust pipe of an internal combustion engine of a vehicle and are used to detect the concentration of a specific gas component, oxygen concentration, etc., in the exhaust gas flowing through the exhaust pipe as the detection target gas. In addition to air-fuel ratio sensors and NOx sensors, some gas sensors detect the mixed potential of a specific gas component, such as ammonia gas or hydrocarbon gas, and oxygen gas by using a detection electrode that has catalytic activity for the specific gas component and oxygen gas.

[0003] An example of a gas sensor that utilizes a mixed potential is shown in Patent Document 1. The gas sensor described in Patent Document 1 has an insulating layer and a solid electrolyte layer laminated on the insulating layer. A reference gas chamber through which a reference gas can flow is provided between the insulating layer and the solid electrolyte layer. A detection electrode is provided on the surface of the solid electrolyte layer, and the detection electrode is capable of contacting a gas to be detected. In addition, a reference electrode is provided on the back surface of the solid electrolyte layer in an area facing the reference gas chamber, and the reference electrode is capable of contacting the reference gas. Furthermore, the gas sensor has a temperature detection means for detecting the temperature of the detection electrode in the outermost layer located on the opposite side of the insulating layer from the detection electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5134399 Summary of the Invention [Problem to be solved by the invention]

[0005] In the gas sensor described in Patent Document 1, the temperature detection means is provided on the surface of the gas sensor opposite to the detection electrode. Therefore, there is a possibility that a difference may occur between the temperature of the detection electrode and the temperature detection means. As a result, there is a problem that it is difficult to detect the temperature of the detection electrode with high accuracy.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to provide a gas sensor element and a gas sensor capable of detecting the temperature of a detection electrode with high accuracy. [Means for solving the problem]

[0007] The present invention No. one of The aspect is A gas sensor element (2) for use in a gas sensor (1) that utilizes a mixed potential, a solid electrolyte body (21) having a first surface (201) and a second surface (202); a detection electrode (22) provided on the first surface of the solid electrolyte body and in contact with the target gas (G); a reference electrode (23) provided on the second surface of the solid electrolyte body at a position opposite to the detection electrode and in contact with a reference gas (A); a temperature detection unit (25) provided on the solid electrolyte body; an insulator (3) disposed opposite the second surface of the solid electrolyte body and having a duct (24) between the insulator and the second surface through which the reference gas flows; a heater (411) disposed in the insulator and controlled based on the temperature detected by the temperature detection unit. 、 the temperature detection unit is provided on the first surface of the solid electrolyte body, It has a long and narrow shape in the longitudinal direction (X), The gas sensor element has the detection electrode and the temperature detection portion disposed adjacent to each other in a width direction (W) perpendicular to both the opposing direction (D) of the first surface and the second surface and the longitudinal direction. A second aspect of the present invention is A gas sensor element (2) for use in a gas sensor (1) that utilizes a mixed potential, a solid electrolyte body (21) having a first surface (201) and a second surface (202); a detection electrode (22) provided on the first surface of the solid electrolyte body and in contact with the target gas (G); a reference electrode (23) provided on the second surface of the solid electrolyte body at a position opposite to the detection electrode and in contact with a reference gas (A); a temperature detection unit (25) provided on the solid electrolyte body; an insulator (3) disposed opposite the second surface of the solid electrolyte body and having a duct (24) between the insulator and the second surface through which the reference gas flows; a heater (411) disposed in the insulator and controlled based on the temperature detected by the temperature detection unit; the temperature detection unit is provided on the second surface of the solid electrolyte body, It has a long and narrow shape in the longitudinal direction. The reference electrode and the temperature detection portion are provided adjacent to each other in a width direction perpendicular to both the opposing direction of the first surface and the second surface and the longitudinal direction of the gas sensor element. A third aspect of the present invention is A gas sensor element (2) for use in a gas sensor (1) that utilizes a mixed potential, a solid electrolyte body (21) having a first surface (201) and a second surface (202); a detection electrode (22) provided on the first surface of the solid electrolyte body and in contact with the target gas (G); a reference electrode (23) provided on the second surface of the solid electrolyte body at a position opposite to the detection electrode and in contact with a reference gas (A); a temperature detection unit (25) provided on the solid electrolyte body; an insulator (3) disposed opposite the second surface of the solid electrolyte body and having a duct (24) between the insulator and the second surface through which the reference gas flows; a heater (411) disposed in the insulator and controlled based on the temperature detected by the temperature detection unit; The ratio Ss / St of the area Ss of the detection electrode to the area St of the temperature detection portion is given by: 0.5 ≦ Ss / St ≦ 2.0 The gas sensor element has the following characteristics.

[0008] The present invention fourth The embodiment of the present invention is a gas sensor (1) that utilizes a mixed potential, The gas sensor (1) has the above gas sensor element. Effect of the Invention

[0009] Since the temperature detection portion is provided in the solid electrolyte body, the temperature of the detection electrode provided in the solid electrolyte body can be detected with high accuracy, thereby improving the accuracy of the gas sensor element compared to a case in which the temperature detection portion is provided in a portion other than the solid electrolyte body.

[0010] As described above, according to the above aspects, it is possible to provide a gas sensor element and a gas sensor that can detect the temperature of the detection electrode with high accuracy.

[0011] In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate a correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief description of the drawings]

[0012] [Figure 1] 2 showing the gas sensor and the gas sensor element according to the first embodiment. FIG. [Diagram 2] 2 is a view taken along the line II in FIG. 1, showing the gas sensor element according to the first embodiment. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1 showing a gas sensor and a sensor element according to the first embodiment; [Figure 4] FIG. 1 is an explanatory diagram showing an internal combustion engine in which a gas sensor is disposed according to a first embodiment. [Diagram 5] FIG. 2 is a partially enlarged view of the gas sensor element according to the first embodiment taken along the line II in FIG. [Figure 6] 5 is a graph showing a change in a voltage output from a detection electrode relative to the surface temperature of the detection electrode according to the first embodiment. [Figure 7] FIG. 4 is an explanatory diagram showing a detection electrode and a temperature detection unit according to Experimental Example 1. [Figure 8] FIG. 11 is an explanatory diagram showing a detection electrode and a temperature detection unit according to Experimental Example 2. [Figure 9] FIG. 11 is an explanatory diagram showing a detection electrode and a temperature detection unit according to Experimental Example 3. [Figure 10] 6 is a graph showing changes over time in the temperature of a gas to be detected, the electrical resistance value of a temperature detection portion, and the mixed potential output output from a detection electrode, according to Experimental Example 1. [Figure 11] 10 is a graph showing changes over time in the temperature of the detection target gas, the electrical resistance value of the temperature detection portion, and the mixed potential output output from the detection electrode, according to Experimental Example 2. [Figure 12] 10 is a graph showing changes over time in the temperature of the detection target gas, the electrical resistance value of the temperature detection portion, and the mixed potential output output from the detection electrode, according to Experimental Example 3. [Figure 13] 2 is a view showing a gas sensor element according to a second embodiment, taken along the line II in FIG. 1; [Figure 14] FIG. 11 is an explanatory diagram showing a second surface of the solid electrolyte body according to the second embodiment. [Figure 15]2 is a view showing the gas sensor element according to a third embodiment, taken along the line II in FIG. 1 . [Figure 16] 2 is a view showing the gas sensor element according to a fourth embodiment, taken along the line II in FIG. 1 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] <Embodiment 1> The gas sensor element and the gas sensor of the first embodiment will be described with reference to FIGS.

[0014] (Gas sensor element 2) First, the gas sensor element of this embodiment will be described. The gas sensor element 2 of this embodiment is an element used in a gas sensor 1 (described in detail later) that utilizes a mixed potential. As shown in Figs. 1 to 3, the gas sensor element 2 includes a solid electrolyte body 21, a detection electrode 22, a reference electrode 23, a temperature detection portion 25, an insulator 3, and a heater 411.

[0015] The solid electrolyte body 21 has a first surface 201 and a second surface 202. The detection electrode 22 is provided on the first surface 201 of the solid electrolyte body 21 and is in contact with the detection target gas G. The reference electrode 23 is provided on the second surface 202 of the solid electrolyte body 21 at a position opposite to the detection electrode 22 and is in contact with the reference gas A. The temperature detection unit 25 is provided on the solid electrolyte body 21.

[0016] The insulator 3 faces the second surface 202 of the solid electrolyte body 21, and has a duct 24 through which a reference gas flows between the insulator 3 and the second surface 202. The heater 411 is disposed in the insulator 3, and is controlled based on the temperature detected by the temperature detection unit 25.

[0017] 1 to 3, the gas sensor element 2 is formed by laminating a solid electrolyte body 21 provided with a detection electrode 22 and a reference electrode 23, and an insulator 3 in which a heater 411 is embedded. The gas sensor element 2 is formed in an elongated shape. A portion of the gas sensor element 2 on a tip side X1 in a longitudinal direction X is accommodated in a cover constituting a gas sensor 1 and is disposed in an exhaust pipe 71. In the gas sensor element 2, a direction in which a first surface 201 and a second surface 202 (to be described later) of the solid electrolyte body 21 face each other perpendicular to the longitudinal direction X is referred to as a facing direction D, and a direction perpendicular to both the longitudinal direction X and the facing direction D is referred to as a width direction W.

[0018] (Solid electrolyte body 21) 1 to 3, the solid electrolyte body 21 is formed in a plate shape and is made of a zirconia material having a property of conducting oxygen ions at a predetermined temperature. The zirconia material can be made of various materials containing zirconia as a main component. As the zirconia material, stabilized zirconia or partially stabilized zirconia in which a part of zirconia is replaced by a rare earth metal element such as yttria (yttrium oxide) or an alkaline earth metal element can be used.

[0019] The first surface 201 of the solid electrolyte body 21 exposed to the target gas G forms the outermost surface of the gas sensor element 2. The detection electrode 22 provided on the first surface 201 is formed in a state where the target gas G can easily come into contact with it. The detection electrode 22 has a rectangular shape that is elongated in the longitudinal direction X. In this embodiment, a protective layer 223 made of a porous ceramic material or the like is provided on the surface of the detection electrode 22. The protective layer 223 covers the entire surface of the detection electrode 22. It is also possible to configure the detection electrode 22 without providing the protective layer 223 on the surface of the detection electrode 22.

[0020] The reference electrode 23 provided on the second surface 202 of the solid electrolyte body 21 is exposed to the air as the reference gas A. A duct 24 through which the air is introduced is formed adjacent to the second surface 202 of the solid electrolyte body 21. The reference electrode 23 has a rectangular shape that is elongated in the longitudinal direction X. The shape and size of the detection electrode 22 and the shape and size of the reference electrode 23 are formed to be substantially the same. "Substantially the same" includes the case where they are the same, and also includes the case where they are not the same but are considered to be substantially the same. The shape of the detection electrode 22 and the shape of the reference electrode 23 may be different from each other.

[0021] (detection electrode 22) As shown in FIGS. 1 to 3, the detection electrode 22 is provided on a first surface 201 of the solid electrolyte body 21 that is exposed to a detection target gas G containing oxygen and ammonia. The detection electrode 22 contains a precious metal having catalytic activity for ammonia and oxygen, and a zirconia material that serves as a common material when sintered with the solid electrolyte body 21. The precious metal constituting the detection electrode 22 may be gold (Au), a platinum (Pt)-gold alloy, a platinum-palladium alloy, a palladium-gold alloy, or the like. The detection electrode 22 may contain a metal oxide or an oxide having a perovskite structure (perovskite-type oxide) in addition to the precious metal and the zirconia material, or instead of the precious metal.

[0022] 1 and 2, a lead portion 221 connected to the detection electrode 22 is provided on the first surface 201 of the solid electrolyte body 21. The lead portion 221 is used to electrically connect the detection electrode 22 to the outside of the gas sensor 1.

[0023] (Reference electrode 23) 1 to 3, the reference electrode 23 is provided on a second surface 202 of the solid electrolyte body 21, the second surface 202 being opposite to the first surface 201. The second surface 202 and the reference electrode 23 provided on the second surface 202 are exposed to the air as a reference gas A. The reference electrode 23 contains a precious metal having catalytic activity against oxygen, and a zirconia material which is a common material when sintered with the solid electrolyte body 21. The precious metal constituting the reference electrode 23 may be platinum (Pt), etc.

[0024] The reference electrode 23 in this embodiment is formed at a position facing the detection electrode 22 via the solid electrolyte body 21. A lead portion 231 connected to the reference electrode 23 is provided on the second surface 202 of the solid electrolyte body 21.

[0025] In the gas sensor element 2, a detection cell through which oxygen ions are conducted is formed by the detection electrode 22, the reference electrode 23, and a portion of the solid electrolyte body 21 sandwiched between the detection electrode 22 and the reference electrode 23. The temperature of the gas sensor element 2 generated by the heater 411 is controlled so that the temperature of the detection cell becomes a predetermined operating temperature.

[0026] (Temperature detection unit 25) 2 and 3, the temperature detection unit 25 is provided on a first surface 201 of the solid electrolyte body 21, which is exposed to a detection target gas G containing oxygen and ammonia. The temperature detection unit 25 is provided on the first surface 201 of the solid electrolyte body 21 adjacent to the detection electrode 22 in the width direction W.

[0027] 2, a lead portion 225 connected to the temperature detection portion 25 is provided on the first surface 201 of the solid electrolyte body 21. The lead portion 225 is used to electrically connect the temperature detection portion 25 to the outside of the gas sensor 1. As shown in FIG. 3, the sensor control unit 5 detects the temperature of the portion where the temperature detection portion 25 is disposed based on a change in the electrical resistance value of the temperature detection portion 25.

[0028] The temperature detection unit 25 and the lead portion 225 contain platinum (Pt) and alumina (Al2O3). The temperature detection unit 25 and the lead portion 225 can be formed by applying a metal paste containing platinum and alumina in a predetermined shape to the first surface 201 of the solid electrolyte body 21 and then firing the paste.

[0029] As shown in FIG. 2, the temperature detection unit 25 has a plurality of straight portions 226 extending along the longitudinal direction X, and a plurality of folded portions 227 that connect the ends of the straight portions 226 and fold back adjacent straight portions 226 in the width direction W. The straight portions 226 are formed parallel to the longitudinal direction X. Of the straight portions 226, two straight portions 226 located at both ends in the width direction W are connected to the lead portions 225. The width dimension of the lead portions 225 in the width direction is set to be larger than the width dimension of the straight portions 226 in the width direction W and the width dimension of the folded back portions 227 in the longitudinal direction. As a result, the electrical resistance value per unit length of the lead portions 225 is smaller than the electrical resistance values ​​per unit length of the straight portions 226 and the folded back portions 227. As a result, the change in the electrical resistance value of the temperature detection unit 25 can be detected by the sensor control unit 5 via the lead portions 225.

[0030] (insulating layer 26) 2, the first surface 201 of the solid electrolyte body 21 is provided with an insulating layer 26 having a rectangular shape elongated in the longitudinal direction X. The insulating layer 26 is provided at a position overlapping the temperature detection unit 25 and the lead portion 225 when viewed from the facing direction D. The insulating layer 26 is interposed between the solid electrolyte body 21, the temperature detection unit 25, and the lead portion 225. This electrically insulates the solid electrolyte body 21 from the temperature detection unit 25 and the lead portion 225. The insulating layer 26 is formed by applying a metal paste containing alumina (Al2O3) to the first surface 201 of the solid electrolyte body 21 and then firing the paste.

[0031] (Insulator 3) 1 and 3, the insulator 3 is formed of a spacer insulator portion 31 provided with a cutout portion forming the duct 24, and a heater insulator portion 32 in which a heater 411 is embedded. The insulator 3 is made of an insulating ceramic material such as alumina. The duct 24 is formed from the position where the reference electrode 23 is disposed to the position of the base end side X2 in the longitudinal direction X. Air as a reference gas A is introduced into the duct 24 from an opening 241 formed at the position of the base end side X2 in the longitudinal direction X.

[0032] (Heater 411) As shown in FIG. 1 and FIG. 3, a heater 411 that generates heat when electricity is applied is embedded in the heater insulator portion 32 of the insulator 3. A heater lead portion 412 is connected to the heater 411. The heater 411 is disposed at a position facing the detection electrode 22, the reference electrode 23, and the temperature detection portion 25 in the stacking direction D. A current control portion 52 for applying current to the heater 411 is connected to the heater 411 via the heater lead portion 412. The current control portion 52 is formed using a drive circuit or the like that applies a voltage that has been subjected to PWM (pulse width modulation) control or the like to the heater 411. The current control portion 52 is formed in the sensor control unit 5.

[0033] The heater 411 is formed of a linear conductor that meanders with straight and curved portions. The straight portions of the heater 411 in this embodiment are formed parallel to the longitudinal direction X. The heater lead portion 412 is formed of a linear conductor. The resistance value per unit length of the heater 411 is greater than the resistance value per unit length of the heater lead portion 412. The heater lead portion 412 is drawn out to a portion on the base end side X2 in the longitudinal direction X. The heater 411 and the heater lead portion 412 contain a metallic material having electrical conductivity.

[0034] The cross-sectional area of ​​the heater 411 is smaller than that of the heater lead portion 412, and the resistance value per unit length of the heater 411 refers to the cross-sectional area in a plane perpendicular to the extension direction of the heater 411 and the heater lead portion 412. When a voltage is applied to the pair of heater leads 412, the heater 411 generates heat due to Joule heat, and the periphery of the detection electrode 22 and the reference electrode 23 is heated by this heat.

[0035] The target operating temperature of the detection cell of the gas sensor element 2, which is controlled by energizing the heater 411, is set as a specific temperature within a temperature range of 350° C. to 550° C. The temperature of the detection electrode 22 (detection cell) is controlled to the target operating temperature by the amount of electricity supplied to the heater 411 by the electricity supply control unit 52. The electricity supply control unit 52 controls the amount of electricity supplied to the heater 411 based on the temperature detected by the temperature detection unit 25. However, during a transitional period of detection, etc., the temperature of the detection electrode 22 (detection cell) changes within the operating temperature range due to the influence of changes in the temperature, flow rate, etc. of the detection gas.

[0036] (Ratio of area Ss of detection electrode 22 to area St of temperature detection section 25) In the gas sensor element 2 utilizing the mixed potential, the reaction rate on the detection electrode 22 easily changes depending on the surface temperature of the detection electrode 22. Therefore, the temperature dependency of the detection electrode 22 is very large, and therefore temperature management of the detection electrode 22 is important.

[0037] 6 shows the change in the voltage output of the detection electrode 22 with respect to the surface temperature of the detection electrode 22. The measurement conditions were an N2 atmosphere containing 10% O2, and the temperature of the detection target gas G was 250°C. "100 ppm", "50 ppm", and "10 ppm" shown in the figure are the concentrations of NH3 in the detection target gas G.

[0038] In the temperature range from 300°C to 550°C, as the NH3 concentration in the target detection gas G increases from 10 ppm, 50 ppm, to 100 ppm, the voltage output from the detection electrode 22 also increases. Furthermore, at a constant NH3 concentration, a graph showing the change in the voltage output from the detection electrode 22 versus the surface temperature of the detection electrode is convex upward, with the voltage output reaching a maximum value at approximately 350°C.

[0039] For example, when the surface temperature of the detection electrode 22 drops from 400°C to 350°C, the voltage output of the detection electrode 22 increases even if the concentration of NH3 in the detection target gas G has not changed. This may cause the detection result to appear as if the concentration of NH3 is high.

[0040] In this embodiment, the temperature of the detection electrode 22 is detected by temperature detection units 25 arranged adjacent to each other in the width direction W of the detection electrode 22, and the temperature of the detection electrode 22 is managed by controlling the heater 411 based on this temperature.

[0041] In order to improve the accuracy of the temperature control of the detection electrode 22, it is preferable that the ratio of the area Ss of the detection electrode 22 to the area St of the temperature detection portion 25 is within a predetermined range. This will be explained in detail below.

[0042] As shown by the two-dot chain line in Fig. 5, the area Ss of the detection electrode 22 in this embodiment is the area of ​​a region surrounded by the outline of the detection electrode 22. For ease of explanation, the rectangle of the two-dot chain line indicating the area Ss of the detection electrode 22 is drawn slightly larger than the outline of the detection electrode 22. For ease of explanation, the protective layer 223 and the insulating layer 26 are omitted in Fig. 5.

[0043] As shown by the two-dot chain line in Fig. 5, the area St of the temperature detection unit 25 in this embodiment is a rectangular region surrounded by both ends of the temperature detection unit 25 in the longitudinal direction X and both ends of the temperature detection unit 25 in the width direction W. This will be described in detail below. The boundary of the area St of the temperature detection unit 25 in the longitudinal direction X is determined by the tip end of the folded-back portion 227A on the tip end side in the longitudinal direction X and the base end of the folded-back portion 227B on the base end side in the longitudinal direction X, among the folded-back portion 227. In addition, the boundary of the area St of the temperature detection unit 25 in the width direction W is determined by the straight line portions 226A and 226B located at both ends in the width direction W, among the straight line portions 226. For ease of explanation, the rectangle indicated by the two-dot dashed line indicating the area St of the temperature detection unit 25 is drawn slightly larger than the tip end of the folded portion 227A on the tip end side in the longitudinal direction X, the base end of the folded portion 227B on the base end side in the longitudinal direction X, and the straight portions 226A, 226B located at both ends in the width direction W.

[0044] The ratio Ss / St of the area Ss of the detection electrode 22 to the area St of the temperature detection section 25 is preferably 0.5≦Ss / St≦2.0. By satisfying 0.5≦Ss / St≦2.0, the responsiveness of the detection electrode 22 to the temperature change and the responsiveness of the temperature detection section 25 to the temperature change can be made to be approximately the same. As a result, even if the temperature of the detection electrode 22 changes suddenly due to a sudden change in the temperature of the detection target gas G, the temperature of the temperature detection section 25 also changes in response to the temperature change of the detection electrode 22, so that the temperature of the detection electrode 22 can be detected with high accuracy. As a result, the temperature of the detection electrode 22 can be appropriately controlled, so that the accuracy of the gas sensor element 2 can be improved. The value of Ss / St is not limited to the above range.

[0045] (Experimental Example) Next, the relationship between the ratio Ss / St of the area Ss of the detection electrode 22 to the area St of the temperature detection section 25 and the mixed potential output will be described with reference to Experimental Examples 1 to 3.

[0046] (Experimental Example 1) In the gas sensor element 2 according to the experimental example 1, the ratio Ss / St of the area Ss of the detection electrode 22 to the area St of the temperature detection portion 25 is 1.0. As shown in Fig. 7, the detection electrode 22 and the temperature detection portion 25 are set to have the same area. In addition, the center Cs of the detection electrode 22 in the longitudinal direction X and the width direction W and the center Ct of the temperature detection portion 25 in the longitudinal direction X and the width direction W are arranged to be at the same position in the longitudinal direction X.

[0047] FIG. 10 shows changes over time in the temperature of the detection target gas G, the electrical resistance value of the temperature detection portion 25, and the mixed potential output output from the detection electrode 22 when Ss / St=1.0.

[0048] Five seconds after the start of the experiment, when the temperature of the temperature detection target gas G drops from 250°C to 200°C, the temperature of the temperature detection section 25 drops once, and the electrical resistance value of the temperature detection section 25 drops accordingly. Then, the sensor control unit 5 increases the current flowing through the heater 411 to increase the temperature of the heater 411. As a result, the temperature of the temperature detection section 25 rises again, and the electrical resistance value of the temperature detection section 25 also rises. When the temperature of the temperature detection section 25 exceeds 400°C, the sensor control unit 5 reduces the current flowing through the heater 411 to lower the temperature of the heater 411. As a result, the temperature of the temperature detection section 25 is controlled to 400°C.

[0049] When the temperature of the temperature detection target gas G drops from 250°C to 200°C, the temperature of the detection electrode 22 increases slightly due to heating of the heater 411 by the sensor control unit 5 based on the drop in the electrical resistance value of the temperature detection section 25. This causes a slight increase in the mixed potential output output from the detection electrode 22. Thereafter, after the temperature of the temperature detection section 25 is controlled to 400°C, the temperature of the detection electrode 22 is also controlled to 400°C, and the mixed potential output returns to the value when the temperature of the temperature detection target gas G was 250°C.

[0050] As described above, when Ss / St=1.0, the temperature of the detection electrode 22 can be controlled with high precision when the temperature of the target gas G changes.

[0051] (Experimental Example 2) In the gas sensor element 2 according to the experimental example 2, the ratio Ss / St of the area Ss of the detection electrode 22 to the area St of the temperature detection portion 25 is 0.5. As shown in Fig. 8, the area of ​​the temperature detection portion 25 is set to be twice as large as that of the detection electrode 22. In addition, the center Cs of the detection electrode 22 in the longitudinal direction X and the width direction W and the center Ct of the temperature detection portion 25 in the longitudinal direction X and the width direction W are disposed so as to be at the same position in the longitudinal direction X.

[0052] 11 shows the changes over time in the temperature of the detection target gas G, the electrical resistance value of the temperature detection portion 25, and the mixed potential output output from the detection electrode 22 when Ss / St=0.5. The measurement conditions are the same as in the first experimental example.

[0053] Five seconds after the start of the experiment, when the temperature of the gas G to be detected falls from 250°C to 200°C, the temperature of the temperature detection unit 25 falls once, and the electrical resistance value of the temperature detection unit 25 falls accordingly. The amount of fall in the electrical resistance value is smaller than that of Experimental Example 1. Thereafter, the sensor control unit 5 increases the current flowing through the heater 411 to raise the temperature of the heater 411. As a result, the temperature of the temperature detection unit 25 rises again, and the electrical resistance value of the temperature detection unit 25 also rises. When the temperature of the temperature detection unit 25 exceeds 400°C, the sensor control unit 5 reduces the current flowing through the heater 411 to lower the temperature of the heater 411. As a result, the temperature of the temperature detection unit 25 is controlled to 400°C.

[0054] When the temperature of the temperature detection target gas G drops from 250°C to 200°C, the temperature of the detection electrode 22 increases slightly due to heating of the heater 411 by the sensor control unit 5 based on the drop in the electrical resistance value of the temperature detection section 25. As a result, the mixed potential output output from the detection electrode 22 also increases slightly. The amount of increase in the mixed potential output is slightly larger than in Experimental Example 1. Thereafter, after the temperature of the temperature detection section 25 is controlled to 400°C, the temperature of the detection electrode 22 is also controlled to 400°C, and the mixed potential output also returns to the value when the temperature of the temperature detection target gas G was 250°C.

[0055] As described above, even when Ss / St=0.5, the temperature of the detection electrode 22 can be controlled with high precision when the temperature of the target gas G changes.

[0056] (Experimental Example 3) In the gas sensor element 2 of Experimental Example 3, the ratio Ss / St of the area Ss of the detection electrode 22 to the area St of the temperature detection portion 25 is 2.0. As shown typically in Fig. 9, the area of ​​the detection electrode 22 is set to be twice as large as that of the temperature detection portion 25. In addition, the center Cs of the detection electrode 22 in the longitudinal direction X and width direction W and the center Ct of the temperature detection portion 25 in the longitudinal direction X and width direction W are disposed to be at the same position in the longitudinal direction X.

[0057] 12 shows the changes over time in the temperature of the detection target gas G, the electrical resistance value of the temperature detection portion 25, and the mixed potential output output from the detection electrode 22 when Ss / St=2.0. The measurement conditions are the same as in Experimental Example 1.

[0058] In the gas sensor element 2 of Experimental Example 3, Ss / St=2.0, and the area St of the temperature detection section 25 is smaller than the area Ss of the detection electrode 22. Therefore, the temperature detection section 25 is capable of detecting local temperature changes, and the sensitivity of the temperature detection section 25 is higher than that of the detection electrode 22. As a result, even if the temperature of the temperature detection target gas G is set to 250° C. during the period from the start of the experiment until 5 seconds later, the temperature detection section 25 detects local temperature changes, and the electrical resistance value repeatedly increases and decreases. Then, the sensor control unit 5 repeatedly turns the heater 411 on and off in accordance with the change in the electrical resistance value of the temperature detection section 25.

[0059] When the temperature of the gas G to be detected falls from 250°C to 200°C, the temperature of the temperature detection unit 25 falls once, and the electrical resistance value of the temperature detection unit 25 falls accordingly. Then, the sensor control unit 5 increases the current flowing through the heater 411 to raise the temperature of the heater 411. As a result, the temperature of the temperature detection unit 25 rises again, and the electrical resistance value of the temperature detection unit 25 also rises. When the temperature of the temperature detection unit 25 exceeds 400°C, the sensor control unit 5 reduces the current flowing through the heater 411 to lower the temperature of the heater 411. As a result, the temperature of the temperature detection unit 25 is controlled to 400°C. In the experimental example 3, even when the temperature of the temperature detection unit 25 is controlled to 400°C, the temperature detection unit 25 detects a local temperature change, and the electrical resistance value increases and decreases repeatedly. As a result, the sensor control unit 5 repeatedly turns the heater 411 on and off.

[0060] Even when the temperature of the temperature detection target gas G drops from 250°C to 200°C, the temperature of the detection electrode 22 hardly changes. Therefore, the mixed electrode potential output from the detection electrode 22 hardly changes either. Furthermore, even after the temperature of the temperature detection unit 25 is controlled to 400°C, the temperature of the detection electrode 22 hardly changes and the mixed electrode potential output from the detection electrode 22 hardly changes either. The amount of change in the mixed potential output is smaller than that in the first experimental example.

[0061] As described above, when Ss / St=2.0, the temperature of the detection electrode 22 can be controlled with high precision when the temperature of the target gas G changes.

[0062] In the gas sensor element 2 of this embodiment, the temperature detection section 25 is provided in the solid electrolyte body 21, and therefore it is possible to accurately detect the temperature of the detection electrode 22 provided in the solid electrolyte body 21. This makes it possible to improve the accuracy of the gas sensor element 2 compared to a case in which the temperature detection section 25 is provided in a portion other than the solid electrolyte body 21.

[0063] Furthermore, in this embodiment, since the temperature detection unit 25 is provided on the first surface 201 of the solid electrolyte body 21 on which the detection electrode 22 is provided, the temperature of the detection electrode 22 can be detected with even greater accuracy.

[0064] The gas sensor element 2 of this embodiment is formed long in the longitudinal direction X. Therefore, in the region of the gas sensor element 2 near the end in the longitudinal direction X, heat is easily dissipated to the outside, while heat is easily trapped near the center position in the longitudinal direction X. In this way, the gas sensor element 2 is prone to temperature distribution in the longitudinal direction X. On the other hand, the temperature distribution in the width direction W perpendicular to the longitudinal direction X is smaller than that in the longitudinal direction X. Therefore, since the detection electrode 22 and the temperature detection portion 25 are provided adjacent to each other in the width direction, the temperature of the detection electrode 22 can be detected with high accuracy. As a result, the accuracy of the gas sensor element 2 can be improved.

[0065] In this embodiment, the ratio Ss / St of the area Ss of the detection electrode 22 to the area St of the temperature detection section 25 is 0.5 or more and 2.0 or less, so that the responsiveness of the detection electrode 22 to the temperature change and the responsiveness of the temperature detection section 25 to the temperature change can be made to be approximately the same. As a result, even if the temperature of the detection electrode 22 changes suddenly due to a sudden change in the temperature of the detection target gas G, the temperature of the temperature detection section 25 also changes in response to the temperature change of the detection electrode 22, so that the temperature of the detection electrode 22 can be detected with high accuracy. As a result, the temperature of the detection electrode 22 can be appropriately controlled, so that the accuracy of the gas sensor element 2 can be improved.

[0066] (Gas sensor 1) Next, the gas sensor 1 of this embodiment will be described. As illustrated in Figures 1 and 3, the gas sensor 1 of this embodiment is of a mixed potential type, and includes the gas sensor element 2 of this embodiment.

[0067] An example of a detailed configuration of the gas sensor 1 of the present embodiment will be described below, but the gas sensor 1 of the present embodiment is not limited to the following configuration.

[0068] 1 and 3, the gas sensor 1 includes a gas sensor element 2 and a detection unit 51. The detection unit 51 is configured to detect a mixed potential that occurs between the detection electrode 22 and the reference electrode 23 and is based on the concentration of a specific gas component and the concentration of oxygen.

[0069] 4, the gas sensor 1 is disposed in an exhaust pipe 71 of an internal combustion engine 7 of a vehicle. A gas G to be detected by the gas sensor 1 is exhaust gas exhausted from the internal combustion engine 7 to the exhaust pipe 71. The gas sensor 1 is disposed in the exhaust pipe 71 at a position downstream of a catalyst 72 that reduces NOx in the flow of exhaust gas, and detects the concentration of ammonia gas flowing out from the catalyst 72.

[0070] As shown in Fig. 1, the gas sensor 1 of this embodiment is of a mixed potential type. The gas sensor 1 detects a mixed potential based on the ammonia gas concentration and the oxygen gas concentration as specific gas component concentrations, and corrects the mixed potential by the oxygen gas concentration to detect the ammonia gas concentration. The detection unit 51 is configured to detect, as the mixed potential, a potential difference ΔV between the detection electrode 22 and the reference electrode 23 that occurs when a reduction current due to an electrochemical reduction reaction of oxygen (hereinafter simply referred to as a reduction reaction) and an oxidation current due to an electrochemical oxidation reaction of ammonia (hereinafter simply referred to as an oxidation reaction) become equal.

[0071] As shown in FIGS. 1 and 3, the detection unit 51 of the gas sensor 1 detects the ammonia concentration in the detection target gas G based on a potential difference (voltage) ΔV as a mixed potential generated between the detection electrode 22 and the reference electrode 23.

[0072] The detection unit 51 is formed in a sensor control unit 5 connected to an engine control unit 50 of a vehicle. The detection unit 51 has a potential difference detection circuit 511 that detects a potential difference ΔV occurring between the detection electrode 22 and the reference electrode 23, and an arithmetic processing unit 512 that obtains an ammonia concentration by correcting the potential difference ΔV by the potential difference detection circuit 511 with the oxygen concentration. The arithmetic processing unit 512 can obtain an ammonia concentration by using a relationship map in which the relationship between the potential difference ΔV and the ammonia concentration is obtained using the oxygen concentration as a parameter, and collating the potential difference ΔV and the oxygen concentration with the relationship map. Furthermore, the ammonia concentration can be corrected based on the temperature of the detection electrode 22 detected by the temperature detection unit 25.

[0073] In the detection electrode 22, when ammonia and oxygen are present in the detection target gas G that contacts the detection electrode 22, an oxidation reaction of ammonia and a reduction reaction of oxygen proceed simultaneously. The oxidation reaction of ammonia is typically represented by the formula: 2NH3+3O 2- →N2+3H2O+6e - The reduction reaction of oxygen is typically represented by O2 + 4e - →2O 2-The mixed potential of ammonia and oxygen at the detection electrode 22 occurs as a potential when the oxidation reaction (rate) of ammonia and the reduction reaction (rate) of oxygen at the detection electrode 22 become equal.

[0074] Although not shown in the figure, the oxygen gas concentration is detected by an oxygen sensor separate from the gas sensor 1. The oxygen sensor is disposed in the exhaust pipe 71 at a position downstream of the catalyst 72. Then, in the detection unit 51, the mixed potential is corrected using the oxygen gas concentration detected by the oxygen sensor, and the ammonia gas concentration is obtained.

[0075] As shown in FIG. 3, a catalyst 72 for reducing NOx and a reducing agent supplying device 73 for supplying a reducing agent K containing ammonia to the catalyst 72 are arranged in the exhaust pipe 71. The catalyst 72 is a catalyst carrier to which ammonia is attached as the reducing agent K of NOx. The amount of ammonia attached to the catalyst carrier of the catalyst 72 decreases with the reduction reaction of NOx. When the amount of ammonia attached to the catalyst carrier becomes small, the reducing agent supplying device 73 newly replenishes ammonia to the catalyst carrier. The reducing agent supplying device 73 is arranged in the exhaust pipe 71 at a position upstream of the catalyst 72 in the flow of exhaust gas, and supplies ammonia gas generated by injecting urea water to the exhaust pipe 71. The ammonia gas is generated by hydrolysis of the urea water. A tank 731 of urea water is connected to the reducing agent supplying device 73.

[0076] The internal combustion engine 7 of this embodiment is a diesel engine that uses the self-ignition of diesel fuel for combustion operation. The catalyst 72 is a selective catalytic reduction (SCR) catalyst that chemically reacts NOx (nitrogen oxides) with ammonia (NH3) to reduce them to nitrogen (N2) and water (H2O).

[0077] Although not shown in the figure, an oxidation catalyst (DOC) that converts (oxidizes) NO to NO2 and reduces CO and HC (hydrocarbons), a filter (DPF) that collects particulates, etc. may be arranged in the exhaust pipe 71 upstream of the catalyst 72.

[0078] As described above, according to this embodiment, it is possible to provide the gas sensor element 2 and the gas sensor 1 that can detect the temperature of the detection electrode with high accuracy.

[0079] <Embodiment 2> Next, a second embodiment will be described with reference to Fig. 13 and Fig. 14. As shown in Fig. 13, in a gas sensor element 2 of this embodiment, a detection electrode 22 is provided on a first surface 201 of a solid electrolyte body 21.

[0080] 14, a reference electrode 23 and a temperature detection unit 25 are provided on the second surface 202 of the solid electrolyte body 21. The reference electrode 23 is provided on the second surface 202 of the solid electrolyte body 21 at a position overlapping the detection electrode 22 formed on the first surface 201 when viewed from the opposing direction D. The temperature detection unit 25 is provided on the second surface 202 of the solid electrolyte body 21 adjacent to the reference electrode 23 in the width direction W.

[0081] 14, a lead portion 225 connected to the temperature detection portion 25 is provided on the second surface 202 of the solid electrolyte body 21. The lead portion 225 is used to electrically connect the temperature detection portion 25 to the outside of the gas sensor 1. Since the structures of the temperature detection portion 25 and the lead portion 225 are similar to those of the first embodiment, the same reference numerals are used for the overlapping configurations and the description thereof will be omitted.

[0082] (insulating layer 26) A rectangular insulating layer 26 extending in the longitudinal direction X is provided on the second surface 202 of the solid electrolyte body 21 at a position overlapping the temperature detection unit 25 and the lead portion 225 when viewed from the facing direction D. The insulating layer 26 is interposed between the solid electrolyte body 21, the temperature detection unit 25, and the lead portion 225. This electrically insulates the solid electrolyte body 21 from the temperature detection unit 25 and the lead portion 225. The insulating layer 26 is formed from the same material by the same manufacturing method as in the first embodiment.

[0083] The temperature detection unit 25 of this embodiment is provided on the second surface 202 of the solid electrolyte body 21. As a result, the temperature detection unit 25 does not come into contact with the highly reactive target gas G, and thus the temperature detection unit 25 is prevented from being altered by the target gas G. This improves the reliability of the temperature detection unit 25.

[0084] In this embodiment, the reference electrode 23 is provided on the second surface 202 of the solid electrolyte body 21 at a position facing the detection electrode 22 provided on the first surface 201. The reference electrode 23 and the temperature detection unit 25 are provided adjacent to each other in the width direction W. Therefore, the detection electrode 22 and the temperature detection unit 25 are disposed relatively close to each other with the solid electrolyte body 21 interposed therebetween, so that the temperature of the detection electrode 22 can be detected with high accuracy. As a result, the accuracy of the gas sensor element 2 can be improved.

[0085] Other configurations, functions, effects, etc. of the gas sensor 1 of this embodiment are the same as those of embodiment 1. In this embodiment, too, the components denoted by the same reference numerals as those in embodiment 1 are the same as those in embodiment 1.

[0086] <Embodiment 3> Next, a third embodiment will be described with reference to FIG. 15. In the gas sensor element 2 of this embodiment, the detection electrode 22 is provided at a position closer to the tip end of the first surface 201 of the solid electrolyte body 21 in the longitudinal direction X. The temperature detection section 25 is provided at a position closer to the base end than the detection electrode 22 in the longitudinal direction X. In this manner, in this embodiment, the detection electrode 22 and the temperature detection section 25 are provided side by side in the longitudinal direction X. This allows the gas sensor element 2 to be miniaturized in the width direction W. Note that the temperature detection section 25 may be provided closer to the tip end and the detection electrode 22 closer to the base end in the longitudinal direction X.

[0087] Other configurations, functions, effects, etc. of the gas sensor 1 of this embodiment are the same as those of embodiment 1. In this embodiment, too, the components denoted by the same reference numerals as those in embodiment 1 are the same as those in embodiment 1.

[0088] <Embodiment 4> Next, a fourth embodiment will be described with reference to Fig. 16. In the gas sensor element 2 of this embodiment, a detection electrode 22 is provided at a position slightly toward the base end side in the longitudinal direction X from the tip end of the first surface 201 of the solid electrolyte body 21. In the width direction W, both side edges of the detection electrode 22 are provided with a gap between them and both side edges of the solid electrolyte body 21. A lead portion 221 extending in the longitudinal direction X is connected to the detection electrode 22.

[0089] An insulating layer 26 having an elongated U-shape in the longitudinal direction X as a whole is formed on the first surface 201 of the solid electrolyte body 21 at positions near both side edges in the width direction W and at a position near the tip end in the longitudinal direction X. The detection electrode 22 and the lead portion 221 are formed in an area of ​​the first surface 201 of the solid electrolyte body 21 that is not covered by the insulating layer 26.

[0090] A temperature detection unit 25 is formed on the surface of the insulating layer 26 opposite the solid electrolyte body 21, at a position closer to the tip end in the longitudinal direction X. The temperature detection unit 25 has an overall U-shape. A lead portion 225 extending along the longitudinal direction X is formed on an end of the temperature detection unit 25 on the base end side in the longitudinal direction X. The temperature detection unit 25 and the lead portion 225 are electrically insulated from the solid electrolyte body 21 by the insulating layer 26.

[0091] The temperature detection unit 25 has two side parts 325 formed with a gap between them on both sides of the detection electrode 22 in the width direction W, and a connecting part 326 that connects the tips of the two side parts 325 and is formed with a gap between them and the tip of the detection electrode 22 in the longitudinal direction X. As a result, the tip side of the detection electrode 22 in the longitudinal direction X and both sides in the width direction W are surrounded by the temperature detection unit 25.

[0092] The side portion 325 of the temperature detection unit 25 has a plurality of first straight portions 327 extending in the width direction W, and a plurality of first folded portions 328 connecting ends of the plurality of first straight portions 327 to connect adjacent first straight portions 327 in the longitudinal direction X in a folded-back manner. In addition, the connecting portion 326 of the temperature detection unit 25 has a plurality of second straight portions 329 extending in the longitudinal direction, and a plurality of second folded portions 330 connecting ends of the plurality of second straight portions 329 to connect adjacent second straight portions 329 in the width direction W in a folded-back manner.

[0093] Since the temperature detection section 25 of this embodiment surrounds the detection electrode 22 on three sides, the temperature of the detection electrode 22 can be detected with high accuracy.

[0094] As described above, the gas sensor element 2 of this embodiment is formed to be elongated in the longitudinal direction X, and therefore the gas sensor element 2 is prone to temperature distribution in the longitudinal direction X. On the other hand, the temperature distribution in the width direction W is smaller than that in the longitudinal direction X. In this embodiment, the detection electrode 22 and the temperature detection portion 25 are formed symmetrically with respect to the longitudinal direction X, and therefore the temperature of the detection electrode 22 can be detected with high accuracy.

[0095] Other configurations, functions, effects, etc. of the gas sensor 1 of this embodiment are the same as those of embodiment 1. In this embodiment, too, the components denoted by the same reference numerals as those in embodiment 1 are the same as those in embodiment 1.

[0096] The present invention is not limited to the respective embodiments, and further different embodiments can be configured without departing from the scope of the present invention. The present invention also includes various modified examples, modifications within the scope of equivalents, etc. Furthermore, the combinations and forms of various components envisioned from the present invention are also included in the technical spirit of the present invention. [Explanation of symbols]

[0097] 1...gas sensor, 2...gas sensor element, 3...insulator, 5...sensor control unit, 21...solid electrolyte body, 22...detection electrode, 23...reference electrode, 24...duct, 25...temperature detection section, 201...first surface, 202...second surface, 411...heater

Claims

1. A gas sensor element (2) for use in a gas sensor (1) that utilizes a mixed potential, A solid electrolyte body (21) having a first surface (201) and a second surface (202); a detection electrode (22) provided on the first surface of the solid electrolyte body and in contact with a detection target gas (G); a reference electrode (23) provided on the second surface of the solid electrolyte body at a position opposite to the detection electrode and in contact with a reference gas (A); A temperature detection unit (25) provided on the solid electrolyte body; an insulator (3) disposed opposite the second surface of the solid electrolyte body and having a duct (24) between the insulator and the second surface through which the reference gas flows; a heater (411) disposed in the insulator and controlled based on the temperature detected by the temperature detection unit; the temperature detection unit is provided on the first surface of the solid electrolyte body, It has an elongated shape in the longitudinal direction (X), The gas sensor element, wherein the detection electrode and the temperature detection portion are provided adjacent to each other in a width direction (W) perpendicular to both the opposing direction (D) of the first surface and the second surface and the longitudinal direction.

2. A gas sensor element (2) for use in a gas sensor (1) that utilizes a mixed potential, A solid electrolyte body (21) having a first surface (201) and a second surface (202); a detection electrode (22) provided on the first surface of the solid electrolyte body and in contact with a detection target gas (G); a reference electrode (23) provided on the second surface of the solid electrolyte body at a position opposite to the detection electrode and in contact with a reference gas (A); A temperature detection unit (25) provided on the solid electrolyte body; an insulator (3) disposed opposite the second surface of the solid electrolyte body and having a duct (24) between the insulator and the second surface through which the reference gas flows; a heater (411) disposed in the insulator and controlled based on the temperature detected by the temperature detection unit; the temperature detection unit is provided on the second surface of the solid electrolyte body, It has a long and narrow shape in the longitudinal direction. The gas sensor element has the reference electrode and the temperature detection portion disposed adjacent to each other in a width direction perpendicular to both the opposing direction of the first surface and the second surface and the longitudinal direction.

3. A gas sensor element (2) for use in a gas sensor (1) that utilizes a mixed potential, A solid electrolyte body (21) having a first surface (201) and a second surface (202); a detection electrode (22) provided on the first surface of the solid electrolyte body and in contact with a detection target gas (G); a reference electrode (23) provided on the second surface of the solid electrolyte body at a position opposite to the detection electrode and in contact with a reference gas (A); A temperature detection unit (25) provided on the solid electrolyte body; an insulator (3) disposed opposite the second surface of the solid electrolyte body and having a duct (24) between the insulator and the second surface through which the reference gas flows; a heater (411) disposed in the insulator and controlled based on the temperature detected by the temperature detection unit; The ratio S / S of the area S of the detection electrode to the area S of the temperature detection portion is 0.5≦Ss / St≦2.0 A gas sensor element.

4. A gas sensor (1) utilizing a mixed potential, A gas sensor (1) comprising a gas sensor element according to any one of claims 1 to 3.

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