Gas sensor element and the gas sensor containing it

Abstract

Gas sensor element (2) comprising a solid electrolyte material (21) having a cylindrical shape with a base and oxygen ion conductivity, a reference electrode (22) arranged on an inner side surface (212) of the solid electrolyte material (21), a measuring electrode (23) arranged on an outer side surface (213) of the solid electrolyte material (21), and a protective layer (24) covering the outer side surface (213) of the solid electrolyte material (21) together with the measuring electrode (23), and allowing a gas to be measured to pass through the protective layer (24), wherein an end side of the gas sensor element (2) is formed from a leg section (202) whose profile line is straight on an axial cross-section (S), which is a cross-section parallel to an axis (M) of the gas sensor element (2), and a bottom section (201) whose profile line is curved, and the layer thickness (t1) of the protective layer (24) of the soil section (201) is greater than the layer thickness (t2) of the protective layer (24) for the leg section (202), characterized by the fact that the porosity of the protective layer (24) for the soil section (201) is higher than that of the leg section (202).

Description

REFERENCE TO PREVIOUS REGISTRATION

[0001] The present application is based on and claims priority from the earlier Japanese patent application No. 2008-329086 of December 25, 2008, published under JP 2010-151575 A, the description of which is incorporated by reference. BACKGROUND OF THE INVENTION (Field of Invention)

[0002] The invention relates to a gas sensor element that detects the concentration of a specific gas to be measured, and to a gas sensor containing the gas sensor element. (State of the art)

[0003] In the prior art, a gas sensor element is known which includes a solid electrolyte material with a cylindrical shape closed at the bottom and oxygen ion conductivity, a reference electrode arranged on the inner side surface of the solid electrolyte material, a measuring electrode arranged on the outer side surface of the solid electrolyte material, and a protective layer covering the outer side surface of the solid electrolyte material together with the measuring electrode, which allows the passage of the gas to be measured (compare, for example, publication JP 2006-038496 A).

[0004] Such a gas sensor element consists of a leg section whose profile line in the axial cross-section is straight parallel to the axis of the gas sensor element, and a bottom section whose profile line is curved.

[0005] The gas sensor element described above exhibits the problems listed below.

[0006] Because the base section of the gas sensor element has low water resistance and strength, the solid electrolyte material is prone to cracking when exposed to moisture. The following reasons are assumed for this. First, the base section of the solid electrolyte material has the curved shape described above, which easily concentrates thermal stress in the base section. Therefore, the base section cracks easily when wet. Additionally, water that condenses when a car stops collects in the corners of the gas sensor element's cover. This collected water easily comes into contact with the base section of the gas sensor element when the engine starts.

[0007] To solve the problems mentioned above, an increase in the thickness of the protective layer is being considered in order to improve the water resistance of the gas sensor element.

[0008] However, simply increasing the thickness of the protective layer can lead to the following problems. Since increasing the thickness of the protective layer increases the amount of material used to form the layer, and applying the material is time-consuming, the manufacturing costs for the gas sensor element can rise. Furthermore, simply increasing the thickness of the protective layer results in the fatty and lean components of the gas being measured diffusing slowly to the measuring electrode. This can reduce the response time of the gas sensor element.

[0009] Relevant prior art can be found, for example, in US Patent 5,538,612 A, which discloses an oxygen element. Furthermore, US Patent 2003 / 0061862 A1 discloses a gas concentration detection element, US Patent 6,660,145 B2 discloses an oxygen sensor element, US Patent 2002 / 0060152 A1 discloses an oxygen element, US Patent 5,472,591 A discloses an oxygen concentration detector, and JP-H 01203963 A discloses an oxygen sensor element. INVENTION SUMMARY

[0010] The invention was made in view of the known situation described above, and the objective of the present invention is to provide a gas sensor element and a gas sensor containing the gas sensor element, which can be manufactured at low cost and have excellent water resistance and response characteristics.

[0011] To solve the problem, a gas sensor element according to claim 1 is provided according to the invention in one embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] They show: Fig. 1 a sectional view of an end section of a gas sensor element according to a first embodiment; Fig. 2 a sectional view of a gas sensor according to the first embodiment; Fig. 3 a drawing to describe a thermal spraying process according to the first embodiment; Fig. 4A a drawing to describe a condition in which a leg section is sprayed in a different thermal spraying process; Fig. 4B a drawing to describe a condition in which a section of the ground is sprayed in the thermal spraying process; Fig.5 a drawing to describe a further thermal spraying process according to the first embodiment; Fig. 6A a side view of a measuring electrode according to the first embodiment; Fig. 6B a side view of another measuring electrode according to the first example; Fig. 6C a side view of another measuring electrode according to the first embodiment; and Fig. 7 a drawing to describe the layer thicknesses and porosities according to the first implementation example. DETAILED DESCRIPTION OF PREFERRED EXECUTION EXAMPLES

[0013] The gas sensor elements according to the implementation examples include an air-fuel ratio sensor element, which is arranged in an exhaust pipe of various internal combustion engines for vehicles and which is used for an exhaust gas feedback system, as well as an oxygen sensor element that measures the oxygen concentration in an exhaust gas.

[0014] In the present description, one side of a gas sensor, which is inserted, for example, into an exhaust system of an internal combustion engine, is referred to as an end side, and the opposite side of the end side is referred to as a base side.

[0015] In the present description, the thickness of a base section of a protective layer is a value obtained by averaging three layer thicknesses when considering the axial cross-section of the gas sensor element. The first layer thickness is the thickness of the protective layer at a position where the axis of the gas sensor element intersects the base section. The second and third layer thicknesses are the thicknesses of the protective layer at two positions where lines intersect the base section. Each of the lines is inclined at an angle of 30° with respect to the axis from the end face to the base face and is centered at a point where the boundary between the base section and the leg section and the axis intersect (compare Fig. 7).

[0016] The thickness of the leg section of the protective layer is a value calculated by averaging the thicknesses at three arbitrary points when considering the axial cross-section of the gas sensor element. These thicknesses are the thicknesses of the protective layer at the three points within a region extending 5 mm from the boundary between the bottom section and the leg section towards the base (see figure). Fig. 7).

[0017] In the protective layer, the ratio of the layer thickness of the bottom section to the layer thickness of the leg section is preferably 1.1 or more.

[0018] The thickness of the protective layer in the bottom section can be sufficiently greater than that of the leg section. Therefore, a gas sensor element with high water resistance can be obtained.

[0019] Furthermore, if the layer thickness ratio is less than 1.1, the problem described below arises. The amount of water in the gas being measured varies depending on the engine specifications, the exhaust pipe, and other factors. Specifically, in a vehicle that produces a large amount of water, the gas sensor element with a layer thickness ratio of less than 1.1 may struggle to maintain sufficient water resistance.

[0020] Furthermore, the layer thickness ratio for the protective layer is preferably in the range of 1.2 to 2.

[0021] This process allows for the creation of a gas sensor element with sufficiently high water resistance and a sufficiently high response time. Furthermore, if the protective layer is formed by thermal spraying, the solid electrolyte material can be protected from cracking.

[0022] If, on the other hand, the thickness ratio of the protective layer is less than 1.2, achieving a sufficient improvement in water resistance may be difficult.

[0023] If the layer thickness ratio for the protective layer exceeds 2, the sensor's response time at the bottom section will be prolonged. This can reduce the response time of the gas sensor element. Furthermore, the solid electrolyte material can crack if the protective layer is formed by thermal spraying.

[0024] The thickness of the protective layer in the leg section is preferably in the range of 100 to 500 µm.

[0025] This allows for the creation of a gas sensor element that exhibits sufficient response characteristics and a function to protect the electrodes through the protective layer.

[0026] If, on the other hand, the thickness of the protective layer on the leg section is less than 100 µm, the effect of limiting the exhaust gas flow rate may be reduced. As a consequence, the measuring electrode may degrade if the gas sensor element is exposed to a high-temperature atmosphere for an extended period.

[0027] Furthermore, if the thickness of the protective layer on the leg section exceeds 500 µm, the diffusion of gas to the measuring electrode is delayed. This can slow down the sensor's response time, leading to poor emission.

[0028] Furthermore, in the protective layer, the porosity of the soil section is preferably higher than that of the leg section.

[0029] This allows for the creation of a gas sensor element that retains its responsiveness and exhibits excellent water resistance.

[0030] This means that, according to the first example, the thickness of the protective layer in the bottom section is greater than that in the leg section, which improves water resistance and strength. However, this delays the diffusion of the gas to be measured to the measuring electrode in the bottom section, which can reduce the response time of the gas sensor.

[0031] To solve this problem, as described above, the porosity of the protective layer of the bottom section, which has a large layer thickness, is increased. This means that the porosity of the protective layer in the bottom section is higher than that of the leg section. This sufficiently improves gas diffusion in the bottom section and maintains a response behavior equivalent to that of a conventional gas sensor.

[0032] Consequently, a gas sensor element can be obtained that maintains the response behavior immediately after engine start and exhibits excellent water resistance.

[0033] In the present description, the porosity of the protective layer of the soil section is a value obtained by averaging the porosities at arbitrary points in a region of the protective layer between two lines. Each of the lines is inclined at an angle of 30° with respect to the axis centered at a point where the axis intersects a boundary between the soil section and the leg section.

[0034] The porosity of the protective layer of the leg section is a value obtained by averaging the porosities at three arbitrary points in an area, the length of which is 5 mm, and which extends from the boundary between the bottom section and the leg section towards the base side.

[0035] Specifically, porosity is a value obtained by taking images of the points at 400x magnification using a scanning electron microscope, and then dividing the total cross-sectional area of ​​the pores that exist in the scanning electron microscope images by the total area of ​​the scanning electron microscope images.

[0036] Furthermore, in the protective layer the porosity of the soil section is 50% or less, and a porosity ratio, which is a ratio of the porosity of the soil section to the porosity of the leg section, is preferably in the range of 1.1 to 10.

[0037] The protective layer can be achieved with sufficient strength and function to protect the electrodes. Furthermore, a gas sensor element with adequate responsiveness can be obtained.

[0038] If, on the other hand, the porosity of the protective layer in the bottom section exceeds 50%, the strength of the protective layer is reduced. This can cause cracks in the protective layer and even peeling of the protective layer when the gas sensor is used.

[0039] Furthermore, if the porosity ratio is less than 1.1, especially in a vehicle with a small engine displacement, it can be difficult to obtain a gas sensor element with sufficient responsiveness because the gas flow rate is low.

[0040] If the porosity ratio exceeds 10, the effectiveness in restricting the passage of the gas being measured through the protective layer is further reduced, which can make it more difficult to maintain a stable sensor output. Furthermore, the degradation and weakening of the measuring electrode can be accelerated.

[0041] Furthermore, the porosity ratio of the protective layer of the leg section is preferably in the range of 2 to 20%.

[0042] This allows for the creation of a gas sensor element that ensures responsiveness, generates a stable output, and has the effect of sufficiently limiting the passage of the gas to be measured.

[0043] Conversely, if the porosity ratio of the protective layer of the leg section is less than 2%, the diffusion of the gas to the protective layer is considerably delayed, which can reduce the response behavior.

[0044] If the porosity ratio of the protective layer of the leg section exceeds 20%, the limiting effect of the protective layer on the passage of the gas being measured is reduced, making it more difficult to maintain a stable sensor output. Furthermore, it becomes difficult to adequately restrict gas diffusion. As a result, the measuring electrode can deteriorate rapidly.

[0045] Furthermore, the protective layer is preferably made up of at least two layers.

[0046] The gas sensor element, which exhibits excellent durability, can be retained in this process.

[0047] More precisely, a dense structure of the bottom layer, which is contained within the protective layer consisting of at least two layers and is in contact with the measuring electrode, can control the diffusion of the gas being measured, thereby maintaining stable sensor characteristics and preventing the measuring electrode from becoming delaminated. Furthermore, forming the top layer on the bottom layer using a material with a larger specific surface area than that of the bottom layer, or a material with high adsorption capacity for toxic substances, can trap the toxic substances in the gas being measured, thus protecting the measuring electrode.In detail, according to the above description, a gas sensor element with excellent resistance can be obtained using the protective layer formed from at least two layers, which includes a bottom layer mainly for controlling the diffusion of the gas to be measured and an upper layer mainly for trapping the toxic materials.

[0048] Furthermore, the lowest layer of the protective layer in contact with the measuring electrode is preferably made of a metal oxide, the main component of which includes at least aluminium oxide, aluminium oxide magnesium oxide spinel or titanium oxide.

[0049] Since the metal oxide is thermally and chemically stable, a protective layer can be obtained that is difficult to degrade, even when exposed to the gas being measured.

[0050] It is understood that in the present description the main component is defined as a metal oxide whose proportion in the protective layer is more than 50%.

[0051] Furthermore, the gas sensor element preferably comprises a catalytic layer covering the outer surface of the protective layer and formed from a metal oxide whose main component includes at least aluminium oxide, aluminium oxide magnesium oxide spinel and zirconium oxide.

[0052] Since the metal oxide is thermally and chemically stable, the catalytic layer can be preserved, which deteriorates only slightly when exposed to the gas being measured. (First example of implementation)

[0053] Below is an embodiment of a gas sensor element and a gas sensor with the gas sensor element according to the present invention with reference to the Fig. 1 to 7 described.

[0054] A gas sensor 1 according to the present embodiment includes, in accordance with Fig. 1 a solid electrolyte material 21 with a cylindrical shape with a base and oxygen ion conductivity, a reference electrode 22 arranged on the inner side surface 212 of the solid electrolyte material 21, a measuring electrode arranged on the outer side surface 213 of the solid electrolyte material 21, and a protective layer 24 covering the outer side surface 213 of the solid electrolyte material 21 together with the measuring electrode 23, which allows the passage of the gas to be measured.

[0055] The end face of the gas sensor element 2 is according to Fig. 1 formed from a leg section 202, whose profile line is straight on an axial cross-section S parallel to the axis of the gas sensor element 2, and from a bottom section 201, whose profile line is curved.

[0056] The thickness of the protective layer 24 of the soil section 201 is greater than that of the protective layer 24 of the leg section 202.

[0057] The configuration of gas sensor 1 is described in more detail below.

[0058] According to Fig. In addition to the gas sensor element 2, the gas sensor 1 comprises a heating element 11, a housing 12, an atmosphere side cover 13, and an element cover 14. The heating element 11 is embedded within the solid electrolyte material 21 and generates heat through the input of energy. The gas sensor element 2 is embedded within the housing 12. The housing 12 holds the gas sensor element 2. The atmosphere side cover 13 is located on the base side of the housing 12 and covers the base side of the gas sensor element 2. The element cover 14 is located on the end side of the housing 12 and covers the end side of the gas sensor element 2.

[0059] Furthermore, the gas sensor 1 comprises an atmosphere-side insulator element 17, a sleeve 15, leads 16, and contact terminals 18. The atmosphere-side insulator element 17 is arranged to cover the base of the gas sensor element 2. The sleeve 15 is arranged on the base of the atmosphere-side cover 13. The leads 16 are inserted within the sleeve 15. The contact terminals 18 are connected to the leads 16 and electrically connected to the heating element 11 and the gas sensor element 2.

[0060] The element cover 14 comprises according to Fig. 2 gas inlet holes 143 in a bottom surface section and a side surface section.

[0061] In detail, the element cover 14 has a double cover, wherein an outer cover 141 and an inner cover 142 are sealed at the end section of the housing 12.

[0062] The gas to be measured, introduced into a gap between the outer cover 141 and the inner cover 142 through the gas inlet holes 143 formed in the outer cover 141, is introduced within the element cover 14 through the gas inlet holes 143 formed in the inner cover 142.

[0063] The inner cover 142 is formed with the gas inlet holes 143, which are arranged at the end side of the gas sensor 1 with respect to the protective layer 24 of the bottom section 201.

[0064] The gas sensor element 2 contained in the gas sensor 1 is described in more detail below.

[0065] The gas sensor element 2 is an A / F sensor element that is included in an air-fuel ratio sensor that is located in an exhaust pipe of various internal combustion engines for vehicles and that is used for an exhaust gas feedback system, or it is an oxygen sensor element that measures an oxygen concentration in the exhaust gas.

[0066] According to the above description, the gas sensor element 2 comprises the solid electrolyte material 21, the reference electrode 22, the measuring electrode 23 and the protective layer 24, as well as a catalytic layer 25 covering the outer surface of the protective layer 24 and a trapping layer 26 covering the outer surface of the catalytic layer 25.

[0067] The catalytic layer 25 consists of aluminum oxide particles carrying platinum and rhodium. The trapping layer 26 also consists of aluminum oxide particles. The catalytic layer 25 and the trapping layer 26 are arranged on the outer side of the protective layer 24.

[0068] It is understood that the catalytic layer 25 and the trapping layer 26 can be formed from a material other than aluminum oxide. The catalytic layer 25 and the trapping layer 26 can be formed using a metal oxide whose main component includes at least aluminum oxide magnesium oxide spinel or zirconium oxide.

[0069] The catalytic layer 25 and the trapping layer 26 can be formed by immersing the gas sensor element 2 or by printing pastes forming the catalytic layer 25 and the trapping layer 26 onto the measuring electrode 23.

[0070] In the present embodiment, according to Fig.7. The layer thickness t1 of the protective layer 24 of the soil section 201 is a value obtained by averaging the layer thicknesses at three arbitrary points, as described below. More precisely, the layer thickness t1 is a value obtained by averaging the layer thicknesses t11, t12, and t13 when considering an axial cross-section S. The layer thickness t11 is the thickness of the protective layer 24 at a position where an axis M of the gas sensor element 2 passes through the soil section 201.

[0071] The layer thicknesses t12 and t13 are thicknesses of the protective layer 24 at two positions where the lines L, L pass through the soil section 201. The lines L, L are inclined at an angle of 30° with respect to the axis M from the end side to the base side with a center at point 203, where a boundary N between the soil section 201 and the leg section 202 and the axis M intersect.

[0072] According to Fig. 7. The layer thickness t2 of the protective layer 24 of leg section 202 is a value obtained by averaging the layer thicknesses at three arbitrary points described below. More precisely, the layer thickness t2 is a value obtained by averaging the layer thicknesses t21, t22, and t23 when considering the axial cross-section S. The layer thicknesses t21, t22, and t23 are the thicknesses of the protective layer 24 at three arbitrary positions in a region R1, the length of which is 5 mm and extends from the boundary N to the base side.

[0073] In the protective layer 24, the layer thickness ratio of layer thickness t1 of the base section 201 to layer thickness t2 of leg section 202 is 1.1 or more. More precisely, in the present embodiment, the layer thickness ratio is in the range of 1.2 to 2.

[0074] In the case of protective layer 24, the layer thickness t1 of the bottom section 201 can be in the range of 110 to 1000 µm, and the layer thickness t2 of the leg section 202 can be in the range of 100 to 500 µm.

[0075] It is understood that in the gas sensor element 2 according to the present embodiment, the thickness of the protective layer 24 of the base section 201 is preferably in the range of 350 to 550 µm, and the thickness of the protective layer 24 of the leg section 202 is preferably in the range of 260 to 340 µm. This results in a short response time of the sensor, and its water resistance and strength can be improved.

[0076] Furthermore, in protective layer 24, the porosity of soil section 201 is higher than that of leg section 202. More precisely, in protective layer 24, the porosity of soil section 201 is 50% or less, and the porosity ratio, defined as the ratio of the porosity of soil section 201 to the porosity of leg section 202, lies in the range of 1.1 to 10. In the present example, the porosity ratio of protective layer 24 for leg section 202 lies in the range of 2 to 20%. Therefore, the porosity ratio of protective layer 24 for soil section 201 can lie in the range of 2.2 to 50%.

[0077] According to the above description, in the present implementation example, the porosity of the soil section 201 is higher than that of the leg section 202 in the protective layer 24. It is understood that it is preferable for the porosity of the protective layer 24 of the soil section 201 to be in the range of 8 to 20%, and the porosity of the protective layer 24 of the leg section 202 to be in the range of 3 to 7%.

[0078] In the present embodiment, the porosity of the protective layer 24 is measured as follows. The porosity of the protective layer 24 of the soil section 201 is a value obtained by averaging the porosities at arbitrary three points in a region R2 of the protective layer 24 between two lines L, L.

[0079] Lines L and L are inclined at an angle of 30° with respect to axis M, with a center at point 203 where the boundary N between base section 201 and leg section 202 intersects axis M. According to Fig. 7 is the porosity of the protective layer 24 of the soil section 201, a value obtained by averaging the porosities at three arbitrary points in the area R1, the length of which is 5 mm, and which extends from the boundary N to the base side.

[0080] Although the protective layer 24 in the embodiment described above is formed from two layers, the protective layer 24 can be formed from three or more layers or from one layer.

[0081] If the protective layer 24 is formed from two or more layers, the lowest layer of the protective layer 24, which is in contact with the measuring electrode 23, preferably consists of a metal oxide, the main component of which includes at least aluminium oxide, aluminium oxide magnesium oxide spinel or titanium oxide.

[0082] The following is a method for manufacturing the gas sensor element 2 with reference to Fig. 3 described.

[0083] First, the measuring electrode 23 and the reference electrode 22 are applied to the outer side surface 213 and the inner side surface 212 of the solid electrolyte material 21, respectively.

[0084] The solid electrolyte material 21, onto which the measuring electrode 23 is applied according to the preceding description, is then rotated about its axis M. The gas sensor element 2 can be formed by spraying a protective material 4, described below, onto the rotating solid electrolyte material 21. The gas sensor element 2 can thus be easily formed without the use of large equipment, resulting in an excellent gas sensor element.

[0085] Furthermore, according to Fig.3. The protective material 4 is sprayed onto the measuring electrode 23 in a state where the spray angle θ is less than 36°, assuming a direction inclined to an axial direction and the end face with respect to an orthogonal direction to be the positive direction. The orthogonal direction is the direction orthogonal to the axial direction of the gas sensor element 2. This means that the protective material 4 is sprayed in a state where a thermal spray gun 3, which sprays the protective material 4, is inclined at an angle of less than 36° with respect to the orthogonal direction.

[0086] The thermal spray gun 3 comprises a (not shown) nozzle electrode which generates plasma, an (not shown) inlet through which gas is injected, a (not shown) spray outlet through which the protective material 4 fused with the plasma is sprayed onto the solid electrolyte material 21, and a (not shown) tank in which the (not shown) spray powder is stored.

[0087] The thermal spray gun 3, which consumes a power of 35 kW, can be used for this purpose.

[0088] The distribution of the protective material 4 sprayed by the thermal spray gun 3 is dense in a section near an axis M of the thermal spray gun 3 and becomes less dense at angles further away from the axis M. If the spray angle θ is set to less than 36°, the section of the protective material 4 with the less dense distribution shifts to the bottom section 201. Therefore, the bottom section 201 of the protective layer 24 can be formed with a relatively large layer thickness and a relatively high porosity. The remaining section of the protective material 4 with the dense distribution is located on the leg section 202. Thus, the leg section 202 of the protective layer 24 can be formed with a relatively small layer thickness and a relatively low porosity.

[0089] The following describes in more detail a thermal spraying process for the formation of the protective layer 24.

[0090] First, the spray powder stored in the tank is fed from the tank to the spray outlet through a (not shown) feed pipe.

[0091] The spray powder is then melted with the plasma generated between the nozzle electrodes, forming the protective material 4.

[0092] The protective material 4 is then sprayed onto the solid electrolyte material 21 with the plasma emitted from the spray outlet.

[0093] Then, during the thermal spraying process, the protective material 4 is sprayed on in such a way that the spray angle θ is less than 36° according to the above description.

[0094] Specifically, when the protective material 4 is sprayed onto the outer side surface 213 of the solid electrolyte material 21 in a state where the spray angle θ is greater than 9° and less than 36°, the gas sensor element 2 is easily formed, in which the thickness of the protective layer 24 of the bottom section 201 is greater than that of the leg section 202. Consequently, the gas sensor element 2 with high water resistance can be easily obtained according to the following description.

[0095] The thermal spray gun 3 is preferably used at a distance of 50 to 150 mm from the end section of the solid electrolyte material 21.

[0096] In the present embodiment, aluminum oxide with an average particle diameter of 30 µm or less than the spray powder is used. The protective layer 24 with the desired porosity can thus be easily formed.

[0097] If the average particle diameter of the spray powder exceeds 30 µm, the porosity becomes too high, resulting in low water resistance and reduced strength. The element can then easily crack.

[0098] The protective material 4 is then sprayed onto the outer side surface 213 of the solid electrolyte material 21 at a flow rate of 100 to 800 m / s in a state in which the protective material 4 has melted at 1800 to 2200°C.

[0099] The thermal spraying process described above is now complete.

[0100] Instead of the process described above, according to Fig. 4. The spray angle θ can be varied depending on the section to be sprayed.

[0101] When the protective layer 24 of the leg section 202 is formed, the protective material 4 can be applied according to Fig.4A is sprayed in a state where the spray direction is orthogonal to the axis of the gas sensor element 2, i.e., the spray angle θ is 0°, while the thermal spray gun 3 is moved (in the direction of the in Fig. 4A (arrow A shown).

[0102] When the protective layer 24 of the soil section 201 is formed, the protective material 4 can be applied according to Fig. 4B is sprayed while the thermal spray gun 3 is moved (in the direction of the in Fig. 4B (arrow B shown).

[0103] The movements of the thermal spray gun 3 (indicated by arrows A and B) can be continuous or discontinuous. The base section 201 can be subjected to the spraying process exclusively by the thermal spray gun 3, and the leg section 202 can be subjected to the spraying process exclusively by the thermal spray gun 3. Alternatively, the base section 201 and the leg section 202 can be subjected to the spraying process by the same thermal spray gun.

[0104] Furthermore, according to Fig. 5. The thermal spray gun 3 must be fixed. The solid electrolyte material 21 is moved (in the direction of the in Fig. 5 (arrow C) while it is rotated in a state where the solid electrolyte material 21 is inclined relative to the thermal spray gun 3. This allows movement of the solid electrolyte material 21 towards or away from the thermal spray gun 3.

[0105] According to the above description, the thermal spraying process can be carried out using various methods.

[0106] In the present embodiment example, the layer thicknesses of the bottom section 201 and the leg section 202 can be controlled by adjusting the spray angle θ, the movement distance of the thermal spray gun 3, the rotational speed of the solid electrolyte material 21 or the like.

[0107] Furthermore, after completion of the thermal spraying process, the layer thickness of the protective layer 24 of the bottom section 201 and the layer thickness of the protective layer 24 of the leg section 202 can be controlled by grinding down the protective layer 24.

[0108] The catalytic layer 25 is then formed by immersing the solid electrolyte material 21, in which the protective layer 24 is formed, in an aluminum oxide slurry. The catalytic layer 25 can be formed using a slurry whose main component is aluminum oxide magnesium oxide spinel or zirconium oxide instead of aluminum oxide.

[0109] The trapping layer 26 is then formed on the surface of the protective layer 24 by immersing the solid electrolyte material 21 in an aluminum oxide slurry. The trapping layer 26 can also be formed using a slurry whose main component is aluminum oxide magnesium oxide spinel or zirconium oxide instead of aluminum oxide.

[0110] The gas sensor element 2 can be manufactured according to the procedure described above.

[0111] It is understood that the shape of the gas sensor element 2 is not limited to the shape described above.

[0112] In the example described above, according to Fig. 6A the gas sensor element 2 the measuring electrode 23, which is formed substantially on the entire outer side surface 213 of the solid electrolyte material 21. According to Fig. However, according to 6B, the gas sensor element 2 can have the measuring electrode 23 locally formed on the outer side surface 213. Furthermore, according to Fig. 6C the gas sensor element 2 have the measuring electrode 23 without it being formed on the end side of the solid electrolyte material 21.

[0113] The advantages of the present implementation example are described below.

[0114] The thickness of the protective layer 24 of the base section 201 is greater than that of the protective layer 24 of the leg section 202. Consequently, a gas sensor element 2 with high water resistance can be obtained. This means that immediately after the engine starts, the water that condenses on the element cover 14 covering the gas sensor element 2 easily comes into contact with the base section 201 of the solid electrolyte material 21. Therefore, the base section 201 is more prone to cracking due to the water than the leg section 202. Furthermore, when the water in the gas to be measured comes into contact with the gas sensor element 2 during driving, the base section 201, where the thermal stress is more easily concentrated, is more prone to cracking due to the water than the leg section 202.This means that the bottom section 201 of the solid electrolyte material 21 has a lower water resistance and strength than that of the leg section 202 of the solid electrolyte material 21.

[0115] Since the thickness of the protective layer 24 of the bottom section 201 is greater than that of the protective layer 24 of the leg section 202, the bottom section 201 of the solid electrolyte material 21 covered with the protective layer 24 can be adequately protected from direct wetting.

[0116] Consequently, a gas sensor element 2 with higher water resistance can be obtained.

[0117] Furthermore, if, for example, the gas sensor element 2 is manufactured such that the thickness of the protective layer 24 of leg section 202 is as high as in the prior art, and the thickness of the protective layer 24 of the base section 201 is as large as possible, the response behavior of the gas sensor element 2 can be improved compared to a gas sensor element in which the entire protective layer 24 is simply made thicker. In addition, the amount of material used to form the protective layer 24 can be reduced. Therefore, the gas sensor element 2 described above can be manufactured with excellent water resistance and excellent response behavior at low cost.

[0118] Furthermore, since the thickness ratio of the protective layer is in the range of 1.2 to 2, a gas sensor element with sufficiently excellent water resistance and response characteristics can be obtained. If the protective layer is also formed by a thermal spraying process, the solid electrolyte material is protected from cracking.

[0119] Furthermore, since the thickness of the protective layer of the leg section is in the range of 100 to 500 µm, a gas sensor element can be obtained that has sufficient response behavior as well as a function to protect the electrodes through the protective layer.

[0120] Furthermore, in the protective layer 24, the porosity of the base section 201 is 50% or less, and the porosity ratio, which is the ratio of the porosity of the base section 201 to the porosity of the leg section 202, is in the range of 1.1 to 10. Therefore, the protective layer 24 can be obtained with sufficient strength and a function to protect the electrodes. Furthermore, a gas sensor element 2 with sufficient response characteristics can be obtained.

[0121] Furthermore, the porosity ratio for the protective layer 24 of the leg section 202 is in the range of 2 to 20%. Therefore, a gas sensor element 2 can be obtained that ensures the response behavior, generates a stable output, and has sufficient effectiveness to restrict the passage of the gas to be measured.

[0122] Furthermore, since the protective layer 24 is formed from at least two layers, the gas sensor element 2 can be maintained with excellent durability. More precisely, a dense structure of the bottom layer allows diffusion of the gas to be controlled, thereby maintaining stable sensor characteristics and preventing the measuring electrode 23 from peeling off. In addition, forming the upper layer on top of the bottom layer using a material with a larger specific surface area than that of the bottom layer, or a material with a high adsorption capacity for toxic substances, allows the toxic substances in the gas to be trapped, thus protecting the measuring electrode 23.More precisely, according to the above description, a gas sensor element 2 with excellent water resistance can be obtained using the protective layer 24 formed from at least two layers, wherein the lowest layer is mainly for controlling the diffusion of the gas to be measured, and the upper layer is mainly for trapping the toxic substances.

[0123] Furthermore, the lowest layer of the protective layer 24, in contact with the measuring electrode 23, is formed from a metal oxide whose main component includes at least aluminum oxide, aluminum oxide magnesium oxide spinel, or titanium oxide. Since the metal oxide is thermally and chemically stable, the protective layer 24 can be maintained and is hardly affected by deterioration, even when exposed to the gas being measured.

[0124] The gas sensor element 2 has a catalytic layer 25 covering the outer surface of the protective layer 24, and which is formed from a metal oxide whose main component includes at least aluminum oxide, aluminum oxide magnesium oxide spinel, or zirconium oxide. Since the metal oxide is thermally and chemically stable, a catalytic layer 25 can be obtained that deteriorates only minimally, even when exposed to the gas being measured.

[0125] Furthermore, a gas sensor 1 with excellent water resistance and excellent response behavior can be manufactured at low cost using the excellent gas sensor element 2 described above.

[0126] According to the above description, a gas sensor element with excellent water resistance and excellent response behavior and a gas sensor using this gas sensor element can be provided at low cost according to the present embodiment. (Second example)

[0127] The following is an example embodiment of a gas sensor element produced by changing the thickness of the protective layer of the base section and the thickness of the protective layer of the leg section. In this embodiment, the water resistance of the gas sensor element was evaluated.

[0128] More precisely, samples for the gas sensor element were produced by varying the thickness of the protective layer of the base section from 100 to 1000 µm and the thickness of the protective layer of the leg section from 100 to 500 µm. Four samples of each type were produced.

[0129] The porosity of the protective layer for the bottom section and the leg section has been set to a constant 5%.

[0130] For each gas sensor element sample, water droplets were applied to the base and leg sections while the element was heated to 600°C. The number of water droplets was gradually increased. When the element ruptured, the number of water droplets was checked. Additionally, the average number of water droplets for each sample was calculated.

[0131] In the present example, whether the element had cracked or not was determined by an insulation test to check whether the solid electrolyte material had ruptured. Specifically, after testing with water, the gas sensor element was immersed in a liquid containing an aqueous alcohol solution. A DC voltage was then applied to the gas sensor element. If the insulation was maintained, it was determined that the gas sensor element had not cracked. Conversely, if the insulation was not maintained, it was determined that the gas sensor element had cracked.

[0132] Subsequently, for samples with the same layer thickness for the protective layer of the leg section, the number of water droplets for the soil section was determined. Table 1 below shows the evaluation results. In Table 1, an x ​​indicates that the number of water droplets for the soil section was less than that for the leg section, a circle indicates that the number of water droplets for the soil section was equivalent to that for the leg section, and a double circle indicates that the number of water droplets for the soil section was greater than that for the leg section. Table 1 Sample no. Layer thickness (µm) Layer thickness ratio Amount of water droplets when the element was cracked (µL) floor section subsection floor section subsection Evaluation result 1 100 100 1 3 4 × 2 110 100 1,1 4 4 ◯ 3 120 100 1,2 5 4 ⊚ 4 130 100 1, 3 5 4 ⊚ 5 100 100 1,9 7 4 ⊚ 6 200 100 2 7 4 ⊚ 7 200 200 1 7 9 × 8 220 200 1,1 9 9 ◯ 9 240 200 1,2 10 9 ⊚ 10 260 200 1,3 15 9 ⊚ 11 380 200 1,9 25 9 ⊚ 12 400 200 2 25 9 ⊚ 13 300 300 1 15 20 X 14 330 300 1,1 20 20 O 15 360 300 1,2 25 20 ⊚ 16 390 300 1,3 25 20 ⊚ 17 420 300 1,4 25 20 ⊚ 18 450 300 1,5 30 20 ⊚ 19 480 300 1,6 30 20 ⊚ 20 510 300 1,7 30 20 ⊚ 21 540 300 1,8 35 20 ⊚ 22 570 300 1,9 40 20 ⊚ 23 600 300 2 40 20 ⊚ 24 400 400 1 25 30 X 25 440 400 1,1 30 30 O 26 480 400 1,2 30 30 ⊚ 27 520 400 1,3 40 30 ⊚ 28 760 400 1,9 60 30 ⊚ 29 800 400 2 60 30 ⊚ 30 500 500 1 30 40 X 31 550 500 1,1 40 40 O 32 600 500 1,2 40 40 ⊚ 33 650 500 1,3 60 40 ⊚ 34 950 500 1,9 70 40 ⊚ 35 1000 500 2 80 40 ⊚

[0133] As can be seen in Table 1, a circle or double circle is indicated when the thickness of the protective layer of the soil section is equal to or greater than that of the leg section (samples 2 to 6, 8 to 12, 14 to 23, 25 to 29, and 31 to 35 of Table 1). Considering the layer thickness ratios (layer thickness of the soil section divided by layer thickness of the leg section) in this case, the water resistance and strength of the soil section can be improved if the layer thickness ratio is 1.1 or greater. If the layer thickness ratio is in the range of 1.2 to 2, the water resistance and strength of the soil section can be further improved. Furthermore, the layer thicknesses for the protective layer of the soil sections in these cases are in the range of 100 to 500 µm.

[0134] Conversely, if the thickness of the protective layer of the bottom section is less than that of the leg section (samples 1, 7, 13, 24, and 30 from Table 1), the number of water droplets for the bottom section is less than for the leg section when the element tears. This means that the bottom section tears due to water droplets, the number of which is less than that for the leg section. Therefore, this indicates that the bottom section has insufficient water resistance and strength.

[0135] As can be seen from the above description, the water resistance and strength of the soil section can be improved if the thickness of the protective layer of the soil section is greater than that of the leg section.

[0136] Furthermore, if the layer thickness ratio is in the range of 1.2 to 2, the water resistance and strength of the soil section can be sufficiently increased compared to those of the leg section.

[0137] Furthermore, it is evident that it is important that the thickness of the protective layer of the leg section is in the range of 100 to 500 µm, which improves water resistance and strength. (Third embodiment)

[0138] The following describes an embodiment of a gas sensor element produced by changing the porosity of the protective layer of the base section and the porosity of the protective layer of the leg section. The response behavior of the gas sensor element was evaluated in this embodiment.

[0139] More precisely, samples for the gas sensor element were produced by changing the layer thickness of the protective layer of the bottom section in the range of 120 to 420 µm, changing the layer thickness for the protective layer of the leg section in the range of 100 to 300 µm, changing the porosity of the protective layer for the bottom section in the range of 2 to 50% and changing the porosity of the protective layer for the leg section in the range of 2 to 20%.

[0140] Then the response rate for each of the samples was evaluated.

[0141] Specifically, the sensor output was checked while gases simulating a rich and a lean atmosphere, as seen in a real vehicle, were alternately supplied. The period of the sensor output was measured as the response time. The rich gas contained CO, CH4, and C3H8 and was supplied at a rate of λ = 0.99. The lean gas contained O2 and NO and was supplied at a rate of λ = 1.01.

[0142] For each of the sample groups (referred to below as a "category"), whose soil section protection layers have equivalent thickness and porosity, and whose leg section protection layers have equivalent thickness and porosity, the difference in response time was verified with respect to a sample where the porosity of the soil section protection layer was equivalent to that of the leg section protection layer. This means that for each category, the response behavior was evaluated with reference to the reference sample with equivalent porosity. Table 2 below shows the evaluation results. In Table 2, a triangle indicates the case where the response time of the corresponding sample was longer than that of the reference sample (indicated by a dash), and a circle indicates the case where the response time of the corresponding sample was shorter than that of the reference sample. Table 2 category Sample no. floor section thigh section Responsiveness Layer thickness (µm) porosity (%) Layer thickness (µm) porosity (%) Response time (min.) Evaluation result 1 1 420 4 300 5 1,9 Δ 2 420 5 300 5 1,8 - 3 420 5,5 300 5 1,7 ◯ 4 420 20 300 5 1,2 ◯ 5 420 50 300 5 1,0 ◯ 2 6 420 2 300 2 2,4 - 7 420 4 300 2 2,1 ◯ 3 8 420 8 300 8 1,2 - 9 420 16 300 8 0,9 ◯ 4 10 420 11 300 11 0,9 - 11 420 22 300 11 0,7 ◯ 5 12 420 15 300 15 0,7 - 13 420 30 300 15 0,5 ◯ 6 14 420 20 300 20 0,5 - 15 420 40 300 20 0,4 ◯ 7 16 280 5 200 5 1,3 - 17 280 10 200 5 1,0 ◯ 8 18 120 8 100 8 0,4 - 19 120 16 100 8 0,3 ◯

[0143] As can be seen from Table 2, the response time is short in all categories compared to the reference sample if the porosity of the protective layer of the soil section is higher than that of the protective layer of the leg section (samples 3 to 5, 7, 9, 11, 13, 15 and 19). Therefore, circles are entered as evaluation results.

[0144] Conversely, if the porosity of the protective layer of the soil section is lower than that of the protective layer of the leg section, the response time is longer compared to that of the reference sample. Therefore, a triangle is entered as the evaluation result.

[0145] As can be seen from the above description, the response time can be sufficiently shortened if the thickness of the protective layer of the soil section is greater than that of the leg section, and the porosity of the protective layer of the soil section is higher than that of the leg section.

[0146] Furthermore, it is evident that it is important that the porosity of the protective layer of the bottom section is 50% or less, the porosity for the protective layer of the leg section is in the range of 2 to 20%, and the porosity ratio is in the range of 1.1 to 10, which also improves the response behavior.

[0147] The various configurations of the exemplary embodiments described above are summarized below.

[0148] To solve the problem, the embodiments of the invention provide, as one configuration, a gas sensor element comprising a solid electrolyte material with a cylindrical shape, a base, and oxygen ion conductivity, a reference electrode arranged on an inner surface of the solid electrolyte material, a measuring electrode arranged on an outer surface of the solid electrolyte material, and a protective layer covering the outer surface of the solid electrolyte material together with the measuring electrode, and allowing a gas to be measured to pass through the protective layer, wherein an end face of the gas sensor element is formed from a leg section whose profile line is straight on an axial cross-section parallel to an axis of the gas sensor element, and from a base section whose profile line is curved.and wherein the thickness of the protective layer of the soil section is greater than the thickness of the protective layer of the leg section.

[0149] The advantages of the implementation examples are described below.

[0150] The thickness of the protective layer on the base section is greater than that on the leg section. Consequently, a gas sensor element with high water resistance can be obtained. This means that immediately after engine start, water condensing on the element cover easily makes contact with the base section of the solid electrolyte material. Therefore, the base section is much more prone to water damage than the leg section. Furthermore, if water in the gas being measured also makes contact with the gas sensor element during operation, the base section, where thermal stress is easily concentrated, is much more prone to water damage than the leg section. This means that the base section of the solid electrolyte material has lower water resistance and strength than the leg section.

[0151] To solve these problems, according to the exemplary embodiments, the bottom section of the solid electrolyte material covered with the protective layer can be sufficiently protected from getting wet directly, since the thickness of the protective layer for the bottom section is greater than that of the protective layer for the leg section.

[0152] Consequently, a gas sensor element with high water resistance can be obtained.

[0153] Furthermore, if the gas sensor element is manufactured, for example, such that the thickness of the protective layer for the leg section is as large as that in the prior art, and the thickness of the protective layer for the base section is as large as possible, the response behavior of the gas sensor element can be improved compared to a gas sensor element where the entire protective layer is simply made thicker. In addition, the amount of material used to form the protective layer can be reduced. Therefore, the gas sensor element described above can be manufactured with excellent water resistance and response behavior at low cost.

[0154] According to the above description, a gas sensor element can be provided according to the embodiments according to the invention, which can be manufactured at low cost and has excellent water resistance and response behavior.

[0155] Furthermore, the exemplary embodiments provide, as one embodiment, a gas sensor element that detects a concentration of a specific gas to be measured, comprising the gas sensor element, a heating element that is inserted into the solid electrolyte material and generates heat by supplying energy, a housing in which the gas sensor element is inserted and which holds the gas sensor element, an atmosphere-side cover that is arranged on a base side of the housing and that covers a base side of the gas sensor element, and an element cover that is arranged on an end side of the housing and that covers an end side of the gas sensor element.

[0156] The gas sensor element contained in the gas sensor can be manufactured at low cost and exhibits excellent water resistance and response characteristics, as described above. Therefore, a gas sensor element can be obtained that is inexpensive to manufacture and offers excellent water resistance and response characteristics.

[0157] The invention is not limited to the configurations described above, but is further limited by the patent claims.

Claims

[1] Gas sensor element (2) comprising a solid electrolyte material (21) having a cylindrical shape with a base and oxygen ion conductivity, a reference electrode (22) arranged on an inner side surface (212) of the solid electrolyte material (21), a measuring electrode (23) arranged on an outer side surface (213) of the solid electrolyte material (21), and a protective layer (24) covering the outer side surface (213) of the solid electrolyte material (21) together with the measuring electrode (23), and allowing a gas to be measured to pass through the protective layer (24), wherein an end side of the gas sensor element (2) is formed from a leg section (202) whose profile line is straight on an axial cross-section (S), which is a cross-section parallel to an axis (M) of the gas sensor element (2), and a bottom section (201) whose profile line is curved, and the layer thickness (t1) of the protective layer (24) of the soil section (201) is greater than the layer thickness (t2) of the protective layer (24) for the leg section (202), characterized by , that the porosity of the protective layer (24) for the soil section (201) is higher than that of the leg section (202). [2] Gas sensor element (2) according to claim 1, wherein the protective layer (24) has a layer thickness ratio of the layer thickness (t1) for the bottom section (201) to the layer thickness (t2) for the leg section (202) of 1.1 or more. [3] Gas sensor element (2) according to claim 2, wherein the layer thickness ratio of the protective layer (24) is in the range of 1.2 to 2. [4] Gas sensor element (2) according to claim 1, wherein the layer thickness (t2) of the protective layer (24) of the leg section (202) is in the range of 100 to 500 µm. [5] Gas sensor element (2) according to claim 1, wherein the porosity of the protective layer (24) for the bottom section (201) is 50% or less, and a porosity ratio, which is a ratio of the porosity of the protective layer (24) for the bottom section (201) to the porosity of the protective layer (24) for the leg section (202), is in the range of 1.1 to 10. [6] Gas sensor element (2) according to claim 5, wherein the porosity ratio for the protective layer (24) of the leg section (202) is in the range of 2 to 20%. [7] Gas sensor element (2) according to claim 1, wherein the protective layer (24) is formed from at least two layers. [8] Gas sensor element (2) according to claim 7, wherein a bottom layer of the protective layer (24) which contacts the measuring electrode (23) includes a metal oxide, the main component of which includes at least aluminium oxide, aluminium oxide magnesium oxide spinel or titanium oxide. [9] Gas sensor element (2) according to claim 1, further comprising a catalytic layer (25) covering an outer surface of the protective layer (24) and formed from a metal oxide, the main component of which includes at least aluminium oxide, aluminium oxide magnesium oxide spinel or zirconium oxide. [10] Gas sensor (1) which detects a concentration of a specific gas to be measured, comprising: the gas sensor element (2) according to claim 1; a heating element (11) which is inserted within the solid electrolyte material (21) and which generates heat by supplying energy; a housing (12) into which the gas sensor element (2) is inserted and which holds the gas sensor element (2); an atmosphere-side cover (13) arranged on a base side of the housing (12) and covering a base side of the gas sensor element (2); and an element cover (14) which is arranged on one end side of the housing (12) and which covers one end side of the gas sensor element (2).

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