SENSORELEMENT

Abstract

Sensor element incorporated into a gas sensor that detects a predetermined gas component in a measuring gas, wherein the sensor element comprises: an element base comprising: an elongated planar ceramic body made of an oxygen ion-conducting solid electrolyte and having a gas inlet at one end section thereof; at least one inner chamber located within the ceramic body and connected to the gas inlet at a predetermined diffusion resistance; at least one electrochemical pump cell comprising an outer pump electrode located on an outer surface of the ceramic body, an inner pump electrode arranged to point towards the at least one inner chamber, and a solid electrolyte located between the outer pump electrode and the inner pump electrode, wherein the at least one electrochemical pump cell pumps oxygen in and out between the at least one inner chamber and an outer surface; and a heating device embedded in a predetermined area on one side of one end section of the ceramic body, and a protective layer of the front end, which is porous and covers a surface of the front end and four side surfaces in a predetermined area of ​​the element base on one end section, wherein The protective layer of the front end has an extension that partially extends into the gas inlet and is attached to an inner wall surface of the ceramic body, which delimits the gas inlet without completely filling the gas inlet.

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The present invention relates to a gas sensor that detects a predetermined gas component in a measuring gas, and in particular to a structure of a front end section of a sensor element that is included in the gas sensor. Description of the state of the art

[0002] A gas sensor for determining the concentration of a desired gas component in a sample gas is known. This gas sensor comprises a sensor element made of an oxygen-ion-conducting solid electrolyte, such as zirconium oxide (ZrO2), and includes electrodes on its surface and interior. The sensor element also includes a protective layer formed from a porous body (porous protective layer) at an end section where a gas inlet is provided for introducing the sample gas (see, for example, JP 2013-64605A, Japanese Patent JP 5533767B2, and Japanese Patent JP 4583187B2).

[0003] The aforementioned gas sensor is primarily installed on the exhaust pipe of an internal combustion engine, such as a vehicle engine, and is used to detect a specific gas component contained in the exhaust gas from the engine and to measure the concentration of that gas component. When used in such an application, the sensor element is frequently subjected to thermal shock due to repeated heating during engine operation and cooling when the engine is not in use. To achieve stable long-term operation of the gas sensor, it is necessary to ensure that the porous protective layer is designed to prevent delamination and subsequent detachment after repeated thermal shock.

[0004] Such delamination and further delamination, which occur during long-term use of the gas sensor, are not preferred, since the introduction path of the measuring gas increases more than was expected in the product design, the diffusion resistance of the measuring gas decreases, and as a result, the output from the sensor element increases to more than a predetermined value.

[0005] Regarding this point, JP 2013 - 64 605 A discloses a structure in which a side surface of a sensor element is covered with a layer of inorganic fibers and a protective layer is provided over the layer to prevent delamination of the protective layer due to thermal shock and the like.

[0006] Japanese patent JP 5 533 767 B2 discloses a structure of a gas sensor element comprising a porous protective layer provided on a section exposed to a measuring gas, wherein an upper end surface of the porous protective layer and the surface of the sensor element form a contact angle of 80° or less, and the upper end surface of the porous protective layer is gently curved such that it has an upwardly convex, substantially arc-like or substantially parabolic shape in a plane direction of the sensor element, thereby reducing the likelihood of delamination of the porous protective layer occurring when the gas sensor element is subjected to shock or vibration.

[0007] Japanese patent JP 4 583 187 B2 discloses a structure in which two or more porous ceramic layers are provided outside a ceramic heating element which includes a sensor section on its surface or interior, and an inclined section which satisfies a predetermined shape condition is provided at an end section of an outermost ceramic layer, such that delamination of the porous ceramic layers from the ceramic heating element is prevented due to a small difference in the coefficient of thermal expansion between the ceramic heating element and the porous layers.

[0008] None of JP 2013 - 64 605 A, Japanese patent JP 5 533 767 B2 and Japanese patent JP 4 583 187 B2 discloses or suggests a structure of a sensor element with a gas inlet in a surface of the front end thereof for positively ensuring the adhesion of a porous protective layer to the surface of the front end.

[0009] Furthermore, US 2015 / 0 276 661 A1 deals with a foil-laminated structure, a method for manufacturing it, and a gas sensor; US 4 824 549 A relates to an oxygen measuring device adapted to measure exhaust gases and used in particular for a combustion control system for internal combustion engines and industrial furnaces; US 2009 / 0 242 404 A1 describes a gas sensor for measuring the concentration of a predetermined gas component in a sample gas, in particular a gas sensor for measuring the concentration of nitrogen oxide; and US 2014 / 0 291 150 A1 deals with a gas sensor element and a gas sensor used to determine the concentration of a specific gas contained, for example, in a combustion gas or exhaust gas of a combustion chamber or internal combustion engine. SUMMARY

[0010] The present invention relates to a gas sensor that detects a predetermined gas component in a measuring gas, and in particular relates to a structure of a front end section of a sensor element that is included in the gas sensor.

[0011] According to the present invention, a sensor element incorporated into a gas sensor that detects a predetermined gas component in a measuring gas comprises: an element base comprising: an elongated planar ceramic body made of an oxygen-ion-conducting solid electrolyte and having a gas inlet at an end section thereof; at least one inner chamber located within the ceramic body and connected to the gas inlet at a predetermined diffusion resistance;at least one electrochemical pump cell comprising an outer pump electrode located on an outer surface of the ceramic body, an inner pump electrode arranged to be directed towards the at least one inner chamber, and a solid electrolyte located between the outer pump electrode and the inner pump electrode, wherein the at least one electrochemical pump cell pumps oxygen in and out between the at least one inner chamber and an outer surface;and a heating device embedded in a predetermined area on one side of one end section of the ceramic body, and a front-end protective layer that is porous and covers a front-end surface and four side surfaces in a predetermined area of ​​the element base on one end section, the front-end protective layer having an extension that partially extends into the gas inlet and is attached to an inner wall surface of the ceramic body that delimits the gas inlet without completely filling the gas inlet.

[0012] Accordingly, a sensor element can be obtained in which delamination and furthermore detachment of the porous protective layer of the front end on one side of the surface of the front end of the element, which are caused by the application of a thermal shock, are suppressed in a suitable manner and adhesion of the protective layer of the front end to the element base is ensured in a suitable manner.

[0013] Preferably, the sensor element according to the present invention further comprises a buffer layer which is porous, has a higher porosity than the protective layer of the front end and is located outside the four side surfaces of the element base, wherein the protective layer of the front end is located further outside the buffer layer.

[0014] In this case, a so-called anchoring effect occurs between the protective layer of the front end and the buffer layer, and delamination of the protective layer of the front end from the element base, which is caused by a difference in the coefficient of thermal expansion between the protective layer of the front end and the element base, is consequently suppressed in a more suitable way when the sensor element is in use.

[0015] It is therefore an object of the present invention to provide a sensor element for a gas sensor in which the adhesion of a porous protective layer of the front end to an element base on one side of a surface of the front end is ensured in a suitable manner. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic perspective view of the outside of a sensor element (gas sensor element) 10; Fig.Figure 2 is a schematic diagram showing the structure of a gas sensor 100, including a sectional view along the longitudinal direction of the sensor element 10; Fig. Figure 3 is an enlarged view in the vicinity of a section Q on one side of an end section E1 of the sensor element 10; Fig. Figure 4 is a diagram describing the size of each section of a gas inlet 105 on one side of a surface of the front end 101e; Fig. Figure 5 is a flowchart of the processing during the manufacture of the sensor element 10; Fig. Figure 6 schematically shows the formation of a protective layer at the front end 2 by plasma spraying; and Fig. Figure 7 is a schematic block diagram of the gas sensor 100 in a case where the sensor element 10 includes a buffer layer 180. DESCRIPTION OF PREFERRED DESIGNS<Overview of the sensor element and the gas sensor>

[0016] The Fig. Figure 1 is a schematic perspective view of the exterior of a sensor element (gas sensor element) 10 according to an embodiment of the present invention. Fig. Figure 2 is a schematic diagram showing the structure of a gas sensor 100, including a sectional view along the longitudinal direction of the sensor element 10. The sensor element 10 is a key component of the gas sensor 100, which detects a predefined gas component in a sample gas and measures its concentration. The sensor element 10 is a so-called limiting-flow gas sensor element.

[0017] In addition to the sensor element 10, the gas sensor 100 mainly comprises a pump cell power supply 30, a heating device power supply 40 and a control unit 50.

[0018] As it is in the Fig.As shown in Figure 1, the sensor element 10 has a structure in which an end section of an elongated planar element base 1 is covered with a porous protective layer of the front end 2.

[0019] As it is in the Fig.As shown in Figure 2, the element base 1 comprises an elongated planar ceramic body 101 as a main structure. Main surface protective layers 170 are provided on two main surfaces of the ceramic body 101. In the sensor element 10, the front end protective layer 2 is further provided outside both an end surface (a front end surface 101e of the ceramic body 101) and four side surfaces on a front end section. The four side surfaces, which are different from opposite end surfaces in the longitudinal direction of the sensor element 10 (or the element base 1 or the ceramic body 101), are hereinafter simply referred to as the side surfaces of the sensor element 10 (or the element base 1 or the ceramic body 101).

[0020] The ceramic body 101 is made of a ceramic containing zirconium oxide (yttrium-stabilized zirconium oxide) as a main component, which is an oxygen-ion-conducting solid electrolyte. Various components of the sensor element 10 are provided both outside and inside the ceramic body 101. The ceramic body 101 with this configuration has a high density and is airtight. The [missing information] Fig. The setup of sensor element 10 shown in Figure 2 is merely an example and the specific setup of sensor element 10 is not limited to this setup.

[0021] The one in Fig.The sensor element 10 shown in Figure 2 is a so-called gas sensor element of the three-chamber series structure type, comprising a first inner chamber 102, a second inner chamber 103, and a third inner chamber 104 within the ceramic body 101. That is, in the sensor element 10, the first inner chamber 102 is connected via a first diffusion control element 110 and a second diffusion control element 120 to a gas inlet 105, which is open to the outside on one side of an end section E1 of the ceramic body 101 (in particular, in connection with the outside through the protective layer of the front end 2), the second inner chamber 103 is connected to the first inner chamber 102 via a third diffusion control element 130, and the third inner chamber 104 is connected to the second inner chamber 103 via a fourth diffusion control element 140. A path from the gas inlet 105 to the third inner chamber 104 is also referred to as the gas distribution part.In the sensor element 10 according to the present embodiment, the distribution part is provided straight along the longitudinal direction of the ceramic body 101.

[0022] The first diffusion control part 110, the second diffusion control part 120, the third diffusion control part 130 and the fourth diffusion control part 140 are each provided as two slots that are vertically in the Fig. The two diffusion control units are arranged. The first diffusion control unit 110, the second diffusion control unit 120, the third diffusion control unit 130, and the fourth diffusion control unit 140 provide a predetermined diffusion resistance for a sample gas passing through them. A buffer chamber 115, which buffers pulsations of the sample gas, is provided between the first diffusion control unit 110 and the second diffusion control unit 120.

[0023] An outer pump electrode 141 is provided on an outer surface of the ceramic body 101, and an inner pump electrode 142 is provided in the first inner chamber 102. Furthermore, an auxiliary pump electrode 143 is provided in the second inner chamber 103, and a measuring electrode 145 is provided in the third inner chamber 104. In addition, a reference gas inlet 106, which is connected to the outer surface and through which a reference gas is introduced, is provided on one side of the other end section E2 of the ceramic body 101, and a reference electrode 147 is provided in the reference gas inlet 106.

[0024] In a case where a measurement target of the sensor element 10 is, for example, NOx in the measuring gas, the concentration of a NOx gas in the measuring gas is calculated by a procedure described below.

[0025] First, the sample gas, which has been introduced into the first inner chamber 102, is adjusted by the pumping action (pumping oxygen in or out) of a main pump cell P1 so that it has an approximately constant oxygen concentration, and then introduced into the second inner chamber 103. The main pump cell P1 is an electrochemical pump cell comprising the outer pump electrode 141, the inner pump electrode 142, and a ceramic layer 101a, which is a section of the ceramic body 101 located between these electrodes. In the second inner chamber 103, oxygen in the sample gas is pumped out of the element by the pumping action of an auxiliary pump cell P2, which is also an electrochemical pump cell, so that the sample gas is in a state with a sufficiently low oxygen partial pressure.The auxiliary pump cell P2 comprises the outer pump electrode 141, the auxiliary pump electrode 143 and a ceramic layer 101b, which is a section of the ceramic body 101 located between these electrodes.

[0026] The outer pump electrode 141, the inner pump electrode 142, and the auxiliary pump electrode 143 are each designed as a porous cermet electrode (e.g., a cermet electrode made of ZrO2 and Pt containing 1% Au). The inner pump electrode 142 and the auxiliary pump electrode 143, which are to be in contact with the measuring gas, are each designed using a material with reduced or no reducing capacity with respect to a NOx component in the measuring gas.

[0027] NOx in the measuring gas, which has been brought into a state of low oxygen partial pressure by the auxiliary pump cell, is introduced into the third inner chamber 104 and reduced or decomposed by the measuring electrode 145, which is provided in the third inner chamber 104. The measuring electrode 145 is a porous cermet electrode that also acts as an NOx reduction catalyst, reducing NOx present in the atmosphere in the third inner chamber 104. During the reduction or decomposition, the potential difference between the measuring electrode 145 and the reference electrode 147 is kept constant. Oxygen ions generated by the aforementioned reduction or decomposition are pumped out of the element by a measuring pump cell P3. The measuring pump cell P3 comprises the outer pump electrode 141, the measuring electrode 145, and a ceramic layer 101c, which is a section of the ceramic body 101 located between these electrodes.The measuring pump cell P3 is an electrochemical pump cell that pumps out oxygen that has been generated by the decomposition of NOx in the atmosphere around the measuring electrode 145.

[0028] The pumping (injection or removal of oxygen) of the main pump cell P1, the auxiliary pump cell P2, and the measuring pump cell P3 is achieved under the control of the control unit 50 by the pump cell power supply (variable power supply) 30, which applies a voltage required for pumping via electrodes arranged in each of the pump cells. In the case of the measuring pump cell P3, a voltage is applied to the outer pump electrode 141 and the measuring electrode 145 such that the potential difference between the measuring electrode 145 and the reference electrode 147 is maintained at a predetermined value. The pump cell power supply 30 is typically provided for each pump cell.

[0029] The control unit 50 detects a pump current Ip2 flowing between the measuring electrode 145 and the outer pump electrode 141, according to the amount of oxygen pumped out through the measuring pump cell P3, and calculates a NOx concentration in the measuring gas on the basis of a linear relationship between a current value (NOx signal) of the pump current Ip2 and the concentration of decomposed NOx.

[0030] The gas sensor 100 preferably comprises a plurality of electrochemical sensor cells, not shown, which detect the potential difference between each pump electrode and the reference electrode 147, and each pump cell is controlled by the control device 50 on the basis of a signal detected by each sensor cell.

[0031] In the sensor element 10, a heating device 150 is embedded in the ceramic body 101. The heating device 150 is located below the gas distribution part in the Fig.2 over an area from the vicinity of one end section E1 to at least one location of the formation of the measuring electrode 145 and the reference electrode 147. The heating device 150 is primarily provided for heating the sensor element 10 to increase the oxygen ion conductivity of the solid electrolyte that forms the ceramic body 101 when the sensor element 10 is in use. In particular, the heating device 150 is provided such that it is surrounded by an insulating layer 151.

[0032] The heating device 150 is a resistance heater, made, for example, of platinum. The heating device 150 generates heat by being supplied with electricity by the heating device power supply 40, under the control carried out by the control unit 50.

[0033] The sensor element 10 according to the present embodiment is heated during use by the heating device 150 so that the temperature is at least 500 °C or more in a section from the first inner chamber 102 to the second inner chamber 103. In some cases, the sensor element 10 is heated so that the temperature of the entire gas distribution section, from the gas inlet 105 to the third inner chamber 104, is 500 °C or more. This serves to increase the oxygen ion conductivity of the solid electrolyte that forms each pump cell and to enable each pump cell to function. In this case, the temperature in the vicinity of the first inner chamber 102, which will be the highest temperature, will be approximately 700 °C to 800 °C.

[0034] In the following description, of the two main surfaces of the ceramic body 101, one main surface (or an outer surface of the sensor element 10, which has the main surface) is located on the upper side in the Fig. 2 and is located on a side where the main pump cell P1, the auxiliary pump cell P2 and the measuring pump cell P3 are predominantly provided, also referred to as the pump surface, and a main surface (or an outer surface of the sensor element 10 which has the main surface) which is located on the lower side in the Fig.2 and located on a side where the heating device 150 is provided, is also referred to as the heating device surface. In other words, the pump surface is a major surface located closer to the gas inlet 105, the three inner chambers and the pump cells than to the heating device 150, and the heating device surface is a major surface located closer to the heating device 150 than to the gas inlet 105, the three inner chambers and the pump cells.

[0035] A plurality of electrode terminals 160 are provided on the respective main surfaces of the ceramic body 101 on the side of the other end section E2 to provide an electrical connection between the sensor element 10 and the outside. These electrode terminals 160 are electrically connected to the aforementioned five electrodes, opposite ends of the heating device 150, and a connection for sensing the heating device resistance (not shown) via terminals provided within the ceramic body 101 (not shown), thus establishing a predetermined correspondence relationship. The application of a voltage from the pump cell power supply 30 to each pump cell of the sensor element 10 and the heating by the heating device 150, by being supplied with current from the heating device power supply 40, are therefore carried out via the electrode terminals 160.

[0036] The sensor element 10 further comprises the aforementioned main surface protective layers 170 (170a, 170b) on the pump surface and the heating element surface of the ceramic body 101. The main surface protective layers 170 are aluminum oxide layers with a thickness of approximately 5 µm to 30 µm and pores with a porosity of approximately 20% to 40%. They are provided to prevent the adhesion of any foreign material and toxic substances to the main surfaces (the pump surface and the heating element surface) of the ceramic body 101 and the external pump electrode 141 provided on the pump surface. The main surface protective layer 170a on the pump surface thus acts as a pump electrode protective layer to protect the external pump electrode 141.

[0037] In the present embodiment, the porosity is obtained by applying a known image processing method (e.g., binary processing) to a scanning electron microscope (SEM) image of an evaluation target.

[0038] The main surface protective layers 170 are provided essentially over the entire pump surface and the heating device surface, except for the electrode terminals 160 in the Fig. 2 partially exposed, however this is only an example. The main surface protective layers 170 can be provided locally in the vicinity of the outer pump electrode 141 on the side of one end section E1, compared to the case described in the Fig. 2 is shown. <details der schutzschicht des vorderen endes>

[0039] In the sensor element 10, the outer protective layer of the front end 2, which is a porous layer made of aluminum oxide with a purity of 99.0% or more, is provided around an outermost circumference in a predetermined area of ​​the one end section E1 of the element base 1, which has the structure described above.

[0040] In the following description, a section of the protective layer of the front end 2 that is in contact with the surface of the front end 101e of the ceramic body 101 is referred to as the end surface section 201, and a section of the protective layer of the front end 2 that is in contact with the four side surfaces, including the two main surfaces (the pump surface and the heating device surface) on which the main surface protective layers 170 are provided, is referred to as the side surface section 202.

[0041] The protective layer of the front end 2 is positioned to surround a section of the element base 1 where the temperature rises during use of the gas sensor 100, thus providing water resistance in that section. The protective layer of the front end 2 prevents water-induced cracking of the element base 1 due to thermal shock caused by a local temperature drop upon direct exposure of the section to water.

[0042] Since the protective layer of the front end 2 is a porous layer, gas always flows between the gas inlet 105 and the outer surface, regardless of the presence of the protective layer of the front end 2. This means that the introduction of the measuring gas into the element base 1 (ceramic body 101) through the gas inlet 105 is carried out without any problems.

[0043] The protective layer of the front end 2 is preferably designed to have a thickness of 150 µm or more and 600 µm or less. A thickness of less than 150 µm for the protective layer of the front end 2 is not preferred because the reduced strength of the protective layer itself decreases thermal shock resistance, water resistance, and resistance to impact caused by vibration and other factors. On the other hand, a thickness of more than 600 µm for the protective layer of the front end 2 is not preferred because the increased heat capacity of the protective layer of the front end 2 leads to increased power consumption when the heating device 150 performs heating, and the increased gas diffusion time impairs the response of the sensor element 10.

[0044] The protective layer of the front end 2 preferably has a porosity of 15% to 40%. In this case, adhesion to the element base 1, particularly to the main surface protective layers 170, which are in contact with most of the protective layer of the front end 2, is adequately ensured. A porosity of less than 15% for the protective layer of the front end 2 is not preferred because the diffusion resistance increases and the response of the sensor element 10 is impaired. On the other hand, a porosity of more than 40% is not preferred because adhesion to the element base 1 (in particular, adhesion to the surface of the front end 101e and the main surface protective layers 170) is reduced and the strength of the protective layer of the front end 2 is not ensured.

[0045] Fig. 3 and Fig. Figure 4 shows diagrams describing further details of the protective layer of the front end 2 in the vicinity of the gas inlet 105. Fig. Figure 3 is an enlarged view in the vicinity of a section Q on one end section E1 of the sensor element 10, which is located in the Fig. 2 is shown by a dashed line, and the Fig. Figure 4 is a diagram to describe the size of each section of the gas inlet 105 on the surface of the front end 101e.

[0046] Although this is for illustrative purposes in the Fig. In simplified terms, the protective layer of the front end 2 of the sensor element 10 has an extension 201a that extends partially from the end surface section 201, which adheres to the surface of the front end 101e of the ceramic body 101, into the gas inlet 105, as shown in the Fig. Figure 3 shows the extension 201a being attached to an inner wall surface 101f, which delimits the gas inlet 105 on four sides in the ceramic body 101 without completely filling the gas inlet. Fixing only two opposing sections of the inner wall surface 101f is shown in the Fig. 3 shown for illustrative purposes.

[0047] The aforementioned thickness of the protective layer of the front end 2 refers to the thickness of a section of the protective layer of the front end 2, excluding extension 201a.

[0048] In particular, the extension 201a is formed in an area corresponding to the size of the gas inlet 105 of the sensor element 10. The gas inlet 105 is provided such that the distance L0 from the surface of the front end 101e of the ceramic body 101 to an innermost part of the gas inlet 105 (the beginning of the first diffusion control part 110) satisfies the equation 100 µm ≤ L0 ≤ 500 µm.

[0049] A distance L0 of less than 100 µm is not preferred because it is likely that formation particles of the protective layer of the front end 2, which are scattered during the formation of the protective layer of the front end 2 (especially the extension 201a), will penetrate into the first diffusion control part 110, causing a blockage and increasing the diffusion resistance more than expected in the design.

[0050] On the other hand, a distance L0 of more than 500 µm is not preferred, as it is necessary to shorten the diffusion control section to maintain a given element size, and it becomes difficult to achieve the desired diffusion resistance, or the element size is increased to ensure the diffusion control section.

[0051] The extension 201a is designed such that a formation area L1 of the extension 201a from the surface of the front end 101e in the longitudinal direction of the element is 8% or more and 75% or less of the distance L0 (0.08 ≤ L1 / L0 ≤ 0.75), wherein, in other words, an adhesion ratio of the extension 201a from the side of the surface of the front end in the gas inlet 105 is 8% or more and 75% or less.

[0052] In the sensor element 10 according to the present embodiment, the protective layer of the front end 2, which surrounds the section of the element base 1 where the temperature becomes high when the gas sensor 100 is in use, has the extension 201a in the manner mentioned above, so that the adhesion of the protective layer of the front end 2 to the surface of the front end 101e of the ceramic body 101, which is the end surface of the element base 1, is better ensured compared to that in a conventional sensor element.

[0053] A ratio L1 / L0 of less than 0.08 is not preferred, as the effect of ensuring liability under extension 201a is not sufficiently preserved.

[0054] On the other hand, an L1 / L0 ratio greater than 0.75 is not preferred, as the extension 201a then resembles the diffusion control section with a slot-like shape, and the operation of each pump cell of the sensor element 10 differs from the operation expected during the design process. There is a problem in that the formation of the extension 201a is difficult and leads to higher costs.

[0055] The gas inlet 105 preferably has an aspect ratio t / w, which is a ratio of an opening height (thickness) t to an opening width w of the gas inlet 105, of 0.015 to 0.15 and an opening area S = wt of 0.1 mm². 2 up to 0.9 mm 2 on.

[0056] An aspect ratio t / w of less than 0.015 or an opening area S of less than 0.1 mm 2 is not preferred because the formation of extension 201a is difficult.

[0057] On the other hand, an aspect ratio t / w of more than 0.15 or an opening area S of more than 0.9 mm 2 This is possible by increasing at least one of the opening width w and the opening height t, but is not preferred, as a discrepancy regarding the size and shape of the interior becomes significant, and in this case, productivity decreases due to the difficulty of simultaneous formation with the interior.

[0058] In the Fig. 3 is a groove g formed between two sections of the extension 201a, which is located in the Fig. 3 is formed vertically. However, this is merely an example and not necessarily required. That is, a section forming the groove g can be embedded by a material to form the protective layer of the front end 2.

[0059] The extension 201a of the protective layer of the front end 2 appropriately suppresses delamination and furthermore detachment of the protective layer of the front end 2 on the surface of the front end of the element base 1, even if the sensor element 10 is frequently subjected to thermal shock due to repeated heating and cooling during long-term use. That is, it can be assumed that the sensor element 10, even during long-term use, is less likely to experience a change in sensitivity caused by delamination and furthermore detachment of the protective layer of the front end, and consequently exhibits high reliability.

[0060] As described above, in the present embodiment, the protective layer of the front end is provided as the porous layer in the element base of the sensor element incorporated into the gas sensor, extending at least around the portion where the temperature becomes high during gas sensor use. A portion of the protective layer of the front end extends partially into the gas inlet on one end section of the element base and is attached to the inner surface of the gas inlet without completely filling it. In this way, a sensor element can be obtained in which delamination and furthermore, peeling of the protective layer of the front end on the surface side of the front end of the element base, caused by the application of thermal shock, are appropriately suppressed. <Verfahren zur Herstellung eines Sensorelements>

[0061] An example of a method for manufacturing the sensor element 10 with a structure and features as described above is described next. Fig. Figure 5 is a flowchart of the processing during the manufacture of sensor element 10.

[0062] In the production of element base 1, a plurality of unstructured layers (not shown) are first produced, which are green layers containing the oxygen ion-conducting solid electrolyte, such as zirconium oxide, as a ceramic component and have no structure formed on it (step S1).

[0063] The unstructured layers have multiple layer holes used for positioning during printing and lamination. These layer holes are formed in the unstructured layers prior to the formation of any structure, for example, by die-cutting with a die-cutting machine. Green layers corresponding to a section of the ceramic body 101 containing an interior also include sections corresponding to the interior, which were formed beforehand, for example, by die-cutting as described above. The unstructured layers need not be of the same thickness and can have different thicknesses according to corresponding sections of the ultimately formed element base 1.

[0064] After the production of the unstructured layers according to the respective layers, structure printing and drying are carried out with the individual unstructured layers (step S2). In particular, a structure of various electrodes, a structure of the heating device 150 and the insulating layer 151, a structure of the electrode terminals 160, a structure of the main surface protective layers 170, a structure of internal wiring (not shown), and the like are formed. The application or arrangement of a sublimable (disappearing) material to form the first diffusion control part 110, the second diffusion control part 120, the third diffusion control part 130, and the fourth diffusion control part 140 is also carried out during structure printing.

[0065] The structures are printed onto the unstructured layers using a known screen printing technology by applying structure-forming pastes, which are pre-produced with the properties required for the respective design objectives. A known drying device can be used for drying after printing.

[0066] After structural printing on each of the unstructured layers, a bonding paste is printed and dried to laminate and join the green layers (step S3). The established screen printing technology can be used to print the bonding paste, and the established drying equipment can be used for drying after printing.

[0067] The green layers, to which an adhesive has been applied, are then stacked in a predetermined sequence, and the stacked green layers are pressed under predetermined temperature and pressure conditions to form a laminated body (step S4). Specifically, the pressing is carried out by stacking and holding the green layers as the lamination target on a predetermined laminating device (not shown) while the green layers are positioned at the layer holes, and then heating and applying pressure to the green layers along with the laminating device using a laminating machine, such as a known hydraulic press. The pressure, temperature, and time for heating and applying pressure depend on the laminating machine used, and these conditions can be appropriately determined to achieve good lamination.

[0068] After the laminated body has been obtained in the manner described above, the laminated body is cut out at a plurality of places to obtain unit bodies, which eventually become the individual element bases 1 (step S5).

[0069] The resulting unit bodies are then each fired at a firing temperature of approximately 1300 °C to 1500 °C (step S6). This produces the element base 1. That is, the element base 1 is produced by the integrated firing of the ceramic body 101, which is made from the solid electrolyte, the electrodes, and the main surface protective layers 170. The integrated firing is carried out in such a way that the electrodes each exhibit sufficient adhesion strength in the element base 1.

[0070] After the element base 1 has been manufactured in this way, the protective layer of the front end 2 is formed with respect to the element base 1. The protective layer of the front end 2 is formed by a plasma spraying process. Fig. Figure 6 schematically shows the formation of the protective layer of the front end 2 by plasma spraying.

[0071] The protective layer of the front end 2 is formed by plasma spraying a slurry containing an aluminum oxide powder as material for forming the protective layer of the front end 2 at a predetermined formation target location (step S7).

[0072] Especially as it is in the Fig. As shown in Figure 6, after the element base 1 has been tilted to a predetermined angle α with one side of the surface of the front end 101e facing upwards, the element base 1 is continuously rotated about the longitudinal direction of the element, as indicated by arrow AR1, while the angle α is changed. During the rotation, the slurry is thermally sprayed by a thermal spray gun 1000 in the direction of the side of the surface of the front end 101e, as indicated by arrow AR2. The slurry consequently adheres to the side surfaces of the element base 1, the end surface of the element base 1 (the surface of the front end 101e of the ceramic body 101), and a predetermined area in the gas inlet 105.

[0073] The aluminum oxide powder is a powder with a maximum particle diameter of 50 µm or less and D 50 Suitable for sizes of 23 µm or less.

[0074] The inclination angle α and a rotational speed of the element base 1 are set in a suitable manner so that the slurry adheres to the inner wall surface 105f, which delimits the gas inlet 105, in such a way that the adhesion ratio has a predetermined value within 8% to 75% in the protective layer of the front end 2 finally formed.

[0075] The sensor element 10 is completed by the formation of the thermally sprayed film.

[0076] The sensor element 10 thus obtained is received in a specified housing and installed in the body, which is not shown, of the gas sensor 100. <modifizierungen>

[0077] The aforementioned embodiments relate to a sensor element with three internal chambers; however, the sensor element need not necessarily have a three-chamber design. That is, the design in which the extension, which partially extends into the gas inlet, is provided for the protective layer of the front end—which is the porous layer surrounding the end surface and the predetermined area of ​​the side surfaces on one end section of the element base—is applicable to a sensor element with one internal chamber or two internal chambers.

[0078] Although the protective layer of the front end 2 is provided directly on the element base 1 in the embodiment described above, the protective layer of the front end 2 does not necessarily have to be provided directly on the element base 1. Fig. Figure 7 is a schematic block diagram of the gas sensor 100 in a case where the sensor element 10 includes a buffer layer 180 between the element base 1 and the protective layer of the front end 2.

[0079] The one in Fig. The sensor element 10 shown in Figure 7 comprises the buffer layer 180 outside the four side surfaces (on an outer circumference that is different from the surface of the front end 101e) of the element base 1 on one end section E1. The protective layer of the front end 2 is provided further outside of the buffer layer 180. In the Fig. Figure 7 shows a pump surface-side section 180a and a heating device-side section 180b of the buffer layer 180.

[0080] The buffer layer 180 is a porous layer made of aluminum oxide and has a relatively high porosity of 30% to 50% and a thickness of 20 µm to 50 µm.

[0081] In a case where the buffer layer 180 is provided, the protective layer of the front end 2 preferably has a lower porosity than the buffer layer 180. If the buffer layer 180 has a higher porosity, a so-called anchoring effect acts between the protective layer of the front end 2 and the buffer layer 180 as the underlying layer. Due to the effect of the anchoring effect, delamination of the protective layer of the front end 2 from the element base 1, which is caused by a difference in thermal expansion between the protective layer of the front end 2 and the element base 1, is suppressed in a more suitable manner when the sensor element 10 is in use.

[0082] The buffer layer 180, together with the front-end protective layer 2 and the main surface protective layers 170, serves to prevent poisoning of the sensor element 10 and its exposure to water. In particular, the buffer layer 180 exhibits better thermal insulation properties than the front-end protective layer 2 and the main surface protective layers 170, provided that the buffer layer 180 has a higher porosity than the front-end protective layer 2. This contributes to an improvement in the water resistance of the sensor element 10.

[0083] The buffer layer 180 also plays a role as the underlying layer when the protective layer of the front end 2 is formed with respect to the element base 1. In this respect, the buffer layer 180 only needs to be formed on the side surfaces of the element base 1 in at least an area surrounded by the protective layer of the front end 2.

[0084] The production of the sensor element 10, which includes the buffer layer 180, as described in the Fig. As shown in 7, furthermore, by carrying out, with respect to a single element body defined by the in the Fig. The process shown in Figure 5 involves the formation (application and drying) of a structure, which ultimately becomes the buffer layer 180, and then firing. The formation of the structure is carried out using a pre-prepared paste, so that the desired buffer layer 180 is ultimately formed. That is, the element base 1 of the sensor element 10, which is in the Fig. 7 is formed by integrated firing of the ceramic body 101, which is made from the solid electrolyte, the electrodes, the main surface protective layers 170 and the buffer layer 180. [Examples]

[0085] Five types of sensor elements 10 (examples 1 to 5) were produced with adhesion ratios of the extension 201a of the protective layer of the front end 2 to the inner wall surface 101f of 10%, 30%, 50%, 60%, and 75%. The gas inlet 105 was adjusted to have a distance L0 of 300 µm, an aspect ratio t / w of an opening of 0.08, and an opening area S of 0.5 mm². 2 exhibited [unclear].

[0086] For comparison, two types of sensor elements (Comparison Examples 1 and 2) with L1 / L0 ratios of 85% and 90%, respectively, and two types of sensor elements (Comparison Examples 3 and 4), each comprising the protective layer of the front end 2 without extension 201a, were fabricated. All comparison examples were fabricated under the same conditions as Examples 1 to 5, except for the formation of extension 201a.

[0087] A heating / cooling cycle test, in which heating and cooling and atmospheric changes were cyclically repeated, was performed with each of the obtained sensor elements to assess resistance to thermal shock, and whether the protective layer of the front end 2 was delaminated from the surface of the front end 101e was determined after the test (Determination 1).

[0088] In the heating / cooling cycle test, a temperature profile of "held at 950 °C for five minutes" followed by "held at 300 °C for five minutes" was set as a heating and cooling cycle, and this was repeated 600 times. The test gas atmosphere was an exhaust gas atmosphere with λ = 1.1 at 950 °C and an ambient atmosphere at 300 °C. X-ray CT imaging was used to determine whether the protective layer of the front end 2 was delaminated.

[0089] A pump current Ip0 in the main pump cell P1 of each sensor element was measured before and after the heating / cooling cycle test to evaluate the validity of the sensor element's operation. The pump current Ip0 was measured in a model gas atmosphere containing oxygen at an O2 concentration of 20.5 mol% and nitrogen gas as the remainder.

[0090] The ratio of the difference in pump current Ip0 before and after the test to the pump current Ip0 value before the test was calculated, and whether a significant change in sensitivity occurred before and after the heating / cooling cycle test was determined using the magnitude of this ratio (Determination 2). The magnitude of the pump current Ip0 value after the test itself was also determined (Determination 3).

[0091] The adhesion ratio and the results of measures 1 to 3 for each sensor element are shown as a list. [Table 1] level Adhesion ratio of the protective layer of the front end [%] Provision 1 Provision 2 Provision 3 Example 1 10 ◯ ◯ ◯ Example 2 30 ◯ ◯ ◯ Example 3 50 ◯ ◯ ◯ Example 4 60 ◯ ◯ ◯ Example 5 75 ◯ ◯ ◯ Comparative example 1 85 ◯ ◯ × Comparative example 2 90 ◯ ◯ × Comparative example 3 - × × ◯ Comparative example 4 - × × ◯

[0092] Regarding determination 1, Table 1 shows a cross for a sensor element in which delamination has been detected, and a circle for a sensor element in which delamination has not been detected, using X-ray CT.

[0093] Regarding determination 2, if the ratio is 5% or less, it is determined that there is no significant change in sensitivity in the sensor element before and after the heating / cooling cycle test, and a circle is indicated in Table 1. If the ratio exceeds 5%, it is determined that there is a significant change in sensitivity in the sensor element before and after the heating / cooling cycle test, and a cross is indicated in Table 1.

[0094] Regarding provision 3, if the pump current Ip0 is 1 mA or more, it is determined that the pump current Ip0 is of sufficient magnitude, and a circle is indicated in Table 1. If the pump current Ip0 is less than 1 mA, it is determined that the pump current Ip0 is of insufficient magnitude, and a cross is indicated in Table 1.

[0095] In Table 1, a circle is indicated for each of provisions 1 to 3 for the sensor elements in examples 1 to 5. In contrast, for the sensor elements in comparison examples 1 and 2, a cross is indicated for provision 3, while a circle is indicated for provisions 1 and 2, and for the sensor elements in comparison examples 3 and 4, a cross is indicated for provisions 1 and 2, while a circle is indicated for provision 3.

[0096] The results shown in Table 1 demonstrate that, in the aforementioned embodiment, providing the protective layer at the front end for the sensor element, extending the protective layer from the front end surface into the gas inlet, and attaching the extension to the inner wall surface of the gas inlet effectively suppresses delamination and peeling of the protective layer from the front end surface caused by thermal shock. The results also show that the significant sensitivity change caused by thermal shock does not occur when delamination and peeling are prevented.The results also show that in this case, an output from the sensor element is ensured in a suitable manner if the adhesion ratio (from the side of the surface of the front end) to the inner wall surface of the gas inlet has a value in the range of 8% or more and 75% or less.< / modifizierungen> < / details>

Claims

[1] Sensor element incorporated into a gas sensor which detects a predetermined gas component in a sample gas, wherein the sensor element comprises: an element base comprising: an elongated planar ceramic body made of an oxygen ion-conducting solid electrolyte and having a gas inlet at one end section thereof; at least one inner chamber located within the ceramic body and connected to the gas inlet at a predetermined diffusion resistance; at least one electrochemical pump cell comprising an outer pump electrode located on an outer surface of the ceramic body, an inner pump electrode arranged to point towards the at least one inner chamber, and a solid electrolyte located between the outer pump electrode and the inner pump electrode, wherein the at least one electrochemical pump cell pumps oxygen in and out between the at least one inner chamber and an outer surface; and a heating device embedded in a predetermined area on one side of one end section of the ceramic body, and a protective layer of the front end, which is porous and covers a surface of the front end and four side surfaces in a predetermined area of ​​the element base on one end section, wherein The protective layer of the front end has an extension that partially extends into the gas inlet and is attached to an inner wall surface of the ceramic body, which delimits the gas inlet without completely filling the gas inlet. [2] Sensor element according to claim 1, wherein 100μm≤L0≤500μm, and 0.08≤L1 / L0≤0.75, where L0 is the distance from a surface of the front end of the ceramic body to an innermost part of the gas inlet and L1 is a formation area of ​​the extension from the surface of the front end in a longitudinal direction of the sensor element. [3] Sensor element according to claim 2, wherein an aspect ratio t / w, which is a ratio of an opening height t to an opening width w of the gas inlet, is between 0.015 and 0.15, and an opening area S of the gas inlet 0.1 mm 2 up to 0.9 mm 2 amounts. [4] Sensor element according to one of claims 1 to 3, furthermore a buffer layer which is porous, has a higher porosity than the protective layer of the front end and is located outside the four side surfaces of the element base, wherein the protective layer of the front end is located further outside the buffer layer.

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