Gas sensor element and method for manufacturing the same, and gas sensor

Abstract

The present invention provides a method for manufacturing a gas sensor element, a gas sensor element, and a gas sensor that can easily form an inner protective layer and an outer protective layer by an immersion method and reduce the uneven thickness of the layers caused by the immersion method. The inner protective layer and the outer protective layer are sequentially covered on the detection part of the gas sensor element, and the manufacturing method includes a first immersion step, in which the top side of the gas sensor element is immersed in a first slurry for the inner protective layer to form a first coating film of the first slurry on the top surface and the peripheral surface of the gas sensor element; a drying step, in which the first coating film is dried to solidify; a second immersion step, in which the top side of the gas sensor element is immersed in a second slurry for the outer protective layer without removing the first coating film, so that a second coating film of the second slurry is formed on the entire surface of the solidified first coating film; and a grinding step, in which the second coating film is ground without grinding the solidified first coating film to remove a part of the second coating film.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a gas sensor element suitable for detecting the gas concentration of a specific gas contained in combustion gas or exhaust gas of a burner, an internal combustion engine, etc., a gas sensor element, and a gas sensor. Background Art

[0002] A gas sensor for detecting the concentration of a specific component (oxygen, etc.) contained in the exhaust gas of an internal combustion engine is known. This gas sensor has a plate-shaped gas sensor element extending elongatedly inside. A detection unit for detecting the specific component is provided at the top end of the gas sensor element. The detection unit is composed of an electrode, etc., and the top end of the gas sensor element provided with such a detection unit is exposed to the exhaust gas.

[0003] In addition to specific components, exhaust gas also contains toxic substances such as silicon and phosphorus. Such toxic substances sometimes adhere to the top portion of the gas sensor element (detection portion, etc.). In addition, exhaust gas also contains moisture. Such moisture, condensed water from the exhaust pipe, and other moisture sometimes adhere to the top portion of the gas sensor element. When moisture adheres to the gas sensor element, it is possible to cause cracks and other damage to the gas sensor element. Therefore, a porous protective layer is formed at the top portion of the conventional gas sensor element to suppress the adhesion of toxic substances and the contact of moisture (water droplets). The porous protective layer is formed to cover the detection portion at the top portion of the gas sensor element.

[0004] In addition, there is also a known technique of stacking an inner protective layer and an outer protective layer having different porosities to form a porous protective layer. For such a two-layer protective layer, for example, if the porosity of the inner protective layer is increased, it is possible to utilize the capillary phenomenon to suppress water from the outside from penetrating from the outer protective layer to the inner protective layer.

[0005] As a prior art for forming such a porous protective layer on a gas sensor element, for example, a method of immersing a gas sensor element in a slurry for a porous protective layer (immersion method) is known (see Patent Document 1). In this method, the top end of the gas sensor element is immersed in the slurry so that the slurry adheres to the top end. Thereafter, the adhered slurry is fired to form a porous protective layer on the top end of the gas sensor element.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2017-203716 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] In the above-mentioned method of immersing the gas sensor element in the slurry, there is a problem that it is difficult to control the thickness of the porous protective layer. For example, the corners of the gas sensor element become parts that are difficult to adhere to the slurry compared to other parts. When you want to increase the thickness of the porous protective layer at such corners, it will cause more slurry than required to be attached to most parts of the gas sensor element except the corners. When the slurry in such a state is baked, the result is that a porous protective layer with a large thickness (volume) is formed. In this case, the heat capacity of the porous protective layer becomes too large, and the activation of the gas sensor element after heating is delayed.

[0011] Therefore, in the above-mentioned prior art, in order to reduce the thickness of the porous protective layer, after calcination, the excess portion around the porous protective layer is cut off by a cutter, etc. However, when the porous protective layer is cut off after calcination, the porous protective layer is hardened by calcination, and the force required for cutting is increased, so that the porous protective layer may be damaged.

[0012] On the other hand, a porous protective layer can be formed by spray coating, but there are problems that skill is required to form a porous protective layer of uniform thickness and the adhesion rate is reduced, resulting in increased costs.

[0013] An object of the present invention is to provide a method for manufacturing a gas sensor element, a gas sensor element, and a gas sensor, which can easily form an inner protective layer and an outer protective layer by a dipping method and reduce uneven thickness of the layers caused by the dipping method.

[0014] Solutions for solving problems

[0015] In order to solve the above-mentioned problems, the manufacturing method of the gas sensor element of the present invention covers a porous inner protective layer and a porous outer protective layer having a porosity different from that of the inner protective layer in sequence as a porous protective layer in a detection portion arranged on the top side of the gas sensor element extending in the axial direction, and the manufacturing method of the gas sensor element includes the following steps: a first immersion step, in which the top side of the gas sensor element is immersed in a first slurry for the inner protective layer, thereby forming a first coating of the first slurry on the top surface and the peripheral surface of the gas sensor element; a drying step, in which the first coating is dried to solidify; a second immersion step, in which the top side of the gas sensor element is immersed in a second slurry for the outer protective layer without removing the first coating, thereby forming a second coating of the second slurry on the entire surface of the solidified first coating; and a grinding step, in which the second coating is ground without grinding the solidified first coating to remove a part of the second coating.

[0016] According to the manufacturing method of the gas sensor element, since both the inner protective layer and the outer protective layer are formed by the dipping method, it is not necessary to have skilled operation like the spraying method, and it is possible to suppress the cost increase and simply form. In addition, since the outer protective layer is formed to have a thickness that is approximately uniform in the axial direction, it is also possible to reduce the uneven thickness of the layer and suppress the delay in activation due to excessive heat capacity. Here, the thickness of the protective layer is the sum of the thickness of the inner protective layer and the thickness of the outer protective layer.

[0017] In addition, the inner protective layer is still formed by the dipping method, and the thickness in the axial direction is not uniform. However, since the thickness in the axial direction of the outer protective layer located outside the inner protective layer is formed to be substantially uniform, the thickness of the outer shape of the porous protective layer composed of the inner protective layer and the outer protective layer is formed to be substantially uniform. As a result, the increase in heat capacity caused by the uneven thickness of the entire layer can be suppressed.

[0018] In addition, in the inner protective layer formed by the dipping method, although the thickness of the corner portion on the top side becomes thinner, the thickness of the outer protective layer compensates for this amount, and the thickness of the corner portion is ensured for the entire porous protective layer. In other words, the disadvantage caused by the reduction of the thickness of the corner portion caused by the dipping method can also be eliminated.

[0019] Moreover, since the first coating film is dried and solidified by the drying process after the first dipping process, it is possible to suppress undesirable situations such as the first coating film and the second coating film being mixed due to the second dipping process not being dried, or the first coating film flowing down during the second dipping process.

[0020] In addition, when the solidified first coating film is ground, the first coating film may be damaged or the grinding die used for grinding may be deformed. Therefore, in the grinding process, since the solidified first coating film is not ground, such an undesirable situation can be avoided.

[0021] In the method for manufacturing a gas sensor element of the present invention, in the grinding step, grinding may be performed so that the surface of the second coating film after grinding becomes a flat surface.

[0022] When grinding is performed in this manner, the second coating film and the outer protective layer are formed flat (in a straight line shape).

[0023] In the manufacturing method of the gas sensor element of the present invention, the grinding process may also include: a circumferential surface grinding process, grinding and removing a circumferential portion of the second coating; and a top surface grinding process, grinding and removing a top end side portion of the second coating, and the top surface grinding process is performed after the circumferential surface grinding process.

[0024] When the peripheral surface grinding step is performed first and then the top surface grinding step where slurry is likely to drip due to gravity is performed, the top surface after grinding can be prevented from sagging after a period of time after the top surface grinding step, and the ground shape can be maintained.

[0025] The gas sensor element of the present invention extends along the axial direction, is in the shape of a plate with relative main surfaces and has a detection portion on the top side, includes a porous protective layer covering the detection portion, the porous protective layer includes an inner protective layer and a porous outer protective layer with a porosity different from that of the inner protective layer and covering the inner protective layer, the inner protective layer has a region where the thickness is the largest along the axial direction, and the thickness becomes thinner as it moves from the region toward the top side and the rear end side, the outer protective layer has a flat top surface and flat side surfaces, and when viewed from a direction perpendicular to the main surface, the radially outermost rear end edge of the outer protective layer is a shape that is recessed toward the top side relative to the rear end from the center of the width direction of the gas sensor element.

[0026] According to the gas sensor element, since both the inner protective layer and the outer protective layer are formed by the dipping method, it is not necessary to have skilled operation like the spraying method, and it is possible to suppress the cost increase and form it simply. In addition, since the outer protective layer is formed to have a substantially uniform thickness in the axial direction, it is also possible to reduce the unevenness of the layer thickness and suppress the delay of activation due to excessive heat capacity.

[0027] In addition, the inner protective layer is still formed by the dipping method, and the thickness in the axial direction is not uniform. However, since the thickness in the axial direction of the outer protective layer located outside the inner protective layer is formed to be substantially uniform, the thickness of the outer shape of the porous protective layer composed of the inner protective layer and the outer protective layer is formed to be substantially uniform. As a result, the increase in heat capacity caused by the uneven thickness of the entire layer can be suppressed.

[0028] In addition, in the inner protective layer formed by the dipping method, although the thickness of the corner portion on the top side becomes thinner, the thickness of the outer protective layer compensates for this amount, and the thickness of the corner portion is ensured for the entire porous protective layer. In other words, the disadvantage caused by the reduction of the thickness of the corner portion caused by the dipping method can also be eliminated.

[0029] In the case where only the side surfaces of the outer protective layer are straight (flat) but the top surface is not flat, it is difficult to sufficiently reduce the thickness unevenness. Therefore, the top surface and the side surfaces are both flat.

[0030] A gas sensor according to the present invention is characterized in that the gas sensor includes the above-mentioned gas sensor element.

[0031] Effects of the Invention

[0032] According to the present invention, it is possible to obtain a gas sensor element in which the inner protective layer and the outer protective layer can be easily formed by the dipping method and the unevenness of the layer thickness caused by the dipping method can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a cross-sectional view of the gas sensor cut along the axial direction.

[0034] Figure 2 It is an exploded perspective view schematically showing a detection element portion and a heater portion constituting a gas sensor element.

[0035] Figure 3 It is a cross-sectional view schematically showing the structure of the tip end side of the gas sensor element cut along the axial direction.

[0036] Figure 4 It is a cross-sectional view schematically showing the structure of the tip end side of the gas sensor element cut in a direction perpendicular to the axial direction.

[0037] Figure 5 This is a perspective view of the gas sensor element body as viewed from the tip side.

[0038] Figure 6 This is a front view showing the shape of the outer protective layer when viewed from a direction perpendicular to the main surface of the gas sensor element.

[0039] Figure 7 This is an explanatory diagram showing a state in which the gas sensor element main body is on standby above the immersion tank in the first immersion step.

[0040] Figure 8 This is a diagram showing a drying step of drying and curing the first coating film to form an unfired inner protective layer.

[0041] Fig. 9 This is an explanatory diagram showing a state in which the gas sensor element main body is on standby above the immersion tank in the second immersion step.

[0042] Fig.10 It is a top view of the grinding die.

[0043] Fig.11This is a top view of the grinding mold in a state where the gas sensor element is rotated 90 degrees and the gap is narrowed.

[0044] Fig.12 It is an explanatory diagram showing a state in which the tip portion of the gas sensor element body lowered from the standby position is immersed in the slurry in the dipping tank in the first dipping step and the second dipping step.

[0045] Fig.13 This is an explanatory diagram showing how a part of the peripheral surface coating film (excess coating film) formed on the peripheral surface of the tip end portion of the gas sensor element body is removed by a grinding jig in the grinding step.

[0046] Fig.14 This is an explanatory diagram showing how a part of the peripheral surface coating film (excess coating film) formed on the peripheral surface when the gas sensor element body is rotated 90 degrees is removed by a grinding jig in the grinding step.

[0047] Fig.15 This is an explanatory diagram showing how a portion of a tip coating film (excess coating film) formed on the tip surface of the tip portion of the gas sensor element body is removed by a grinding tool in a grinding step.

[0048] Fig.16 This is an explanatory diagram showing a state in which the grinding tool returns to the retracted position after the grinding step.

[0049] Description of Reference Numerals

[0050] 1. Gas sensor; 20. Porous protective layer; 21. Inner protective layer; 22. Outer protective layer; 22s. Side of the outer protective layer; 22t. Top surface of the outer protective layer; 22f. The radially outermost rear end edge of the outer protective layer; 100. Gas sensor element; 100b. Top end of the sensor element; 100c. Top surface of the gas sensor element; 100d. Peripheral surface of the gas sensor element; 101, 111. Main surface (protective layer 111 and first substrate); 150. Detection part; 700. First coating; 800. Second coating; L. Axis; R. Area where the thickness of the inner protective layer is the largest; P1, P2. The rear end of the radially outermost rear end edge of the outer protective layer; S1. First slurry; S2. Second slurry. DETAILED DESCRIPTION

[0051] Hereinafter, various embodiments of the present invention will be described with reference to the drawings, but the present invention should not be construed as being limited thereto.

[0052] First, the structure of a gas sensor (oxygen sensor) 1 including a gas sensor element 100 according to the present embodiment will be described. Figure 1is a cross-sectional view of the gas sensor 1 cut along the axis L direction, Figure 2 2 is an exploded perspective view schematically showing the detection element section 300 and the heater section 200 constituting the gas sensor element 100. Figure 1 The lower side of the gas sensor 1 shown is referred to as the "top side", and the opposite side ( Figure 1 The upper side of the rear end is called the "rear end side".

[0053] like Figure 1 As shown, the gas sensor 1 includes: a gas sensor element 100 including a stacked body of a detection element portion 300 and a heater portion 200; a main metal shell 30 for holding the gas sensor element 100 and the like in an internal manner; and a protective member 24 mounted on the top end portion of the main metal shell 30. The gas sensor element 100 is in the shape of a plate extending elongated as a whole, and is arranged such that its length direction is along the axis L. In addition, as described later, a porous protective layer 20 is formed on the top end side of the gas sensor element 100.

[0054] like Figure 2 As shown, the heater part 200 is in the shape of a plate extending elongatedly as a whole, and has a first substrate 101 and a second substrate 103 mainly made of alumina, and a heating element 102 mainly made of platinum sandwiched by the first substrate 101 and the second substrate 103. The heating element 102 has a heating portion 102a located at the top end side and a pair of heater lead portions 102b extending from the heating portion 102a along the length direction (axis L direction) of the first substrate 101. In addition, the end of the heater lead portion 102b is electrically connected to the heater side gasket 120 via a conductor formed in the heater side through hole 101a provided in the first substrate 101.

[0055] Similar to the heater unit 200, the detection element unit 300 is in the shape of a plate extending elongated as a whole, and includes an oxygen concentration detection element 130 and an oxygen pump element 140. The oxygen concentration detection element 130 is composed of a first solid electrolyte body 105, and a first electrode 104 and a second electrode 106 formed on both surfaces of the first solid electrolyte body 105. The first electrode 104 is composed of a first electrode portion 104a and a first lead portion 104b extending from the first electrode portion 104a along the length direction (axis L direction) of the first solid electrolyte body 105. The second electrode 106 is composed of a second electrode portion 106a and a second lead portion 106b extending from the second electrode portion 106a along the length direction (axis L direction) of the first solid electrolyte body 105.

[0056] The end of the first lead portion 104b is electrically connected to the detection element side pad 121 via conductors formed in the first through hole 105a provided in the first solid electrolyte body 105, the second through hole 107a provided in the insulating layer 107 described later, the fourth through hole 109a provided in the second solid electrolyte body 109, and the sixth through hole 111a provided in the protective layer 111. The end of the second lead portion 106b is electrically connected to the detection element side pad 121 via conductors formed in the third through hole 107b provided in the insulating layer 107 described later, the fifth through hole 109b provided in the second solid electrolyte body 109, and the seventh through hole 111b provided in the protective layer 111.

[0057] The oxygen pump element 140 is composed of a second solid electrolyte body 109 and a third electrode 108 and a fourth electrode 110 formed on both surfaces of the second solid electrolyte body 109. The third electrode 108 is composed of a third electrode portion 108a and a third lead portion 108b extending from the third electrode portion 108a along the longitudinal direction (axis L direction) of the second solid electrolyte body 109. The fourth electrode 110 is composed of a fourth electrode portion 110a and a fourth lead portion 110b extending from the fourth electrode portion 110a along the longitudinal direction (axis L direction) of the second solid electrolyte body 109.

[0058] The end of the third lead portion 108b is electrically connected to the detection element side pad 121 via conductors formed in the fifth through hole 109b provided in the second solid electrolyte body 109 and the seventh through hole 111b provided in the protective layer 111. The end of the fourth lead portion 110b is electrically connected to the detection element side pad 121 via a conductor formed in the eighth through hole 111c provided in the protective layer 111. The second lead portion 106b and the third lead portion 108b have the same potential.

[0059] The first solid electrolyte body 105 and the second solid electrolyte body 109 are composed of a partially stabilized zirconia sintered body obtained by adding yttrium oxide (Y2O3) or calcium oxide (CaO) as a stabilizer to zirconium oxide (ZrO2).

[0060] The heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heater side gasket 120 and the detection element side gasket 121 can be formed of platinum group elements. Suitable platinum group elements for forming the above components include Pt, Rh, Pd, etc. In addition, the above platinum group elements may be used alone or in combination of two or more.

[0061] The heating element 102 is preferably formed mainly of Pt from the viewpoint of heat resistance and oxidation resistance. In addition, the heating element 102 preferably contains a ceramic component in addition to the platinum group element as the main component. The ceramic component is preferably the same component as the material of the main body on the stacked side from the viewpoint of fixation.

[0062] Furthermore, an insulating layer 107 is formed between the oxygen pump element 140 and the oxygen concentration detection element 130. The insulating layer 107 includes an insulating portion 114 and a diffusion resistor portion 115. A hollow measurement chamber 107c is formed in the insulating portion 114 of the insulating layer 107 at positions corresponding to the second electrode portion 106a and the third electrode portion 108a. The measurement chamber 107c is connected to the outside in the width direction of the insulating layer 107, and a diffusion resistor portion 115 is arranged in the connected portion to achieve gas diffusion between the outside and the measurement chamber 107c under a predetermined speed regulation condition.

[0063] The insulating portion 114 is not limited as long as it is a ceramic sintered body having insulating properties, and is made of, for example, oxide-based ceramics such as alumina and mullite.

[0064] The diffusion resistor portion 115 is a porous body formed of alumina. The diffusion resistor portion 115 formed of the porous body is used to adjust the speed of the detection gas flowing into the measurement chamber 107 c .

[0065] In addition, a protective layer 111 is formed on the surface of the second solid electrolyte body 109 in such a manner as to sandwich the fourth electrode 110. The protective layer 111 includes a porous electrode protection portion 113a for protecting the fourth electrode portion 110a from poisoning in such a manner as to sandwich the fourth electrode portion 110a, and a reinforcing portion 112 for protecting the second solid electrolyte body 109 in such a manner as to sandwich the fourth lead portion 110b. In addition, the gas sensor element 100 of the present embodiment adjusts the direction and magnitude of the current flowing between the electrodes of the oxygen pump element 140 so that the voltage (electromotive force) generated between the electrodes of the oxygen concentration detection element 130 becomes a predetermined value (for example, 450 mV), and becomes an oxygen sensor element that linearly detects the oxygen concentration in the measured gas corresponding to the current flowing to the oxygen pump element 140.

[0066] Here, Figure 2 The protective layer 111 and the first substrate 101 shown correspond to the "opposing main surfaces" in the claims. That is, when observing the cross section of the gas sensor element 100 perpendicular to the axis L, a rectangular cross section is formed, in which the outer edge formed by the protective layer 111 and the first substrate 101 is the long side and the two sides along the stacking direction are the short sides.

[0067] Back to Figure 1The main metal shell 30 is made of SUS430 and includes an external thread portion 31 for mounting the gas sensor 1 on the exhaust pipe and a hexagonal portion 32 against which the mounting tool is abutted during mounting. In addition, the main metal shell 30 is provided with a metal shell side step portion 33 protruding toward the radial inner side, and the metal shell side step portion 33 supports a metal retainer 34 for holding the gas sensor element 100. Moreover, a ceramic retainer 35 and a steatite 36 are arranged in order from the top end side on the inner side of the metal retainer 34.

[0068] The talc 36 includes a first talc 37 disposed in the metal holder 34 and a second talc 38 disposed at the rear end of the metal holder 34. By compressing and filling the first talc 37 in the metal holder 34, the gas sensor element 100 is fixed to the metal holder 34. In addition, by compressing and filling the second talc 38 in the main metal housing 30, the sealing property between the outer surface of the gas sensor element 100 and the inner surface of the main metal housing 30 is ensured.

[0069] Furthermore, an alumina sleeve 39 is disposed on the rear end side of the second talc 38. The sleeve 39 is formed into a multi-stage cylindrical shape, and an axial hole 39a is provided along the axis L. The gas sensor element 100 is penetrated inside the sleeve 39 including the axial hole 39a. Furthermore, the pressing portion 30a at the rear end side of the main metal shell 30 is bent inward, and the sleeve 39 is pressed toward the front end side of the main metal shell 30 via the stainless steel ring member 40 by means of the pressing portion 30a.

[0070] Furthermore, a metal protective member 24 is attached by welding to the outer periphery of the top end side of the main metal shell 30. The protective member 24 is formed into a double-layer structure, and an outer protective member 41 having a bottomed cylindrical shape with the same outer diameter is arranged on the outside, and an inner protective member 42 having a bottomed cylindrical shape with the outer diameter of the rear end portion 42a formed larger than the outer diameter of the top end portion 42b is arranged on the inside. Such a protective member 24 covers the top end portion of the gas sensor element 100 protruding from the top end of the main metal shell 30 and has a plurality of air inlet holes 24a.

[0071] The front end side of the outer cylinder 25 made of SUS430 is inserted into the rear end side of the main metal shell 30. The outer cylinder 25 has a front end portion 25a whose front end side is enlarged in diameter, and the front end portion 25a is fixed to the main metal shell 30 by laser welding or the like. A partition 50 is arranged inside the rear end side of the outer cylinder 25, and a retaining member 51 is interposed in a gap formed between the partition 50 and the outer cylinder 25. The retaining member 51 is engaged with a protrusion 50a protruding outward from the circumference of the partition 50, and is fixed between the compressed outer cylinder 25 and the partition 50.

[0072] In addition, the separator 50 is provided with a through hole 50b for inserting various lead wires 11, 12, and 13 for the detection element unit 300 and the heater unit 200 so as to penetrate from the front end side to the rear end side. Figure 1 In the figure, for the sake of convenience, only three leads 11, 12, and 13 are shown, and the illustration of the other leads is omitted. The through hole 50b contains a connection terminal 16, which connects the above-mentioned leads 11, etc. and the detection element side gasket 121 of the detection element part 300 and the heater side gasket 120 of the heater part 200. Each lead 11, etc. is formed into a structure that can be connected to a connector not shown outside, and the electrical signal is input and output between the external device such as the ECU and each lead 11, etc. through such a connector.

[0073] Furthermore, a substantially cylindrical rubber cover 52 is disposed on the rear end side of the separator 50 for closing the opening 25b on the rear end side of the outer tube 25. The rubber cover 52 is pressed radially inward by the outer tube 25 while being accommodated in the rear end of the outer tube 25, thereby being fixed to the outer tube 25. In addition, the rubber cover 52 is also provided with through holes 52a for inserting the lead wires 11 and the like so as to penetrate from the front end side to the rear end side.

[0074] Next, refer to Figure 3 to Figure 6 , the porous protective layer 20 will be described. In the present invention, the porous protective layer 20 includes an inner protective layer 21 and an outer protective layer 22 covering the inner protective layer 21. The inner protective layer 21 and the outer protective layer 22 are both porous and have different porosities.

[0075] In addition, in the present embodiment, the porosity of the inner protective layer 21 is set larger than the porosity of the outer protective layer 22. When water comes in contact with the inner protective layer 21 from the outside, the capillary phenomenon can be used to suppress the water from penetrating from the outer protective layer 22 to the inner protective layer 21, thereby improving the water resistance.

[0076] The porosity of the inner protective layer 21 does not necessarily need to be larger than the porosity of the outer protective layer 22 , and the porosity of the inner protective layer 21 may be set smaller than the porosity of the outer protective layer 22 for other purposes.

[0077] Figure 3 1 is a cross-sectional view schematically showing the structure of the top end side of the gas sensor element 100 cut along the axis L direction. Figure 4 2 is a cross-sectional view schematically showing the structure of the top end side of the gas sensor element 100 cut in a direction perpendicular to the axis L direction. Figure 3 and Figure 4As shown, a porous protective layer 20 (an inner protective layer 21 and an outer protective layer 22) is formed on the top side of the gas sensor element 100. In addition, in this specification, the gas sensor element 100 in a state where the porous protective layer 20 is not formed is sometimes specifically referred to as a "gas sensor element body 100a".

[0078] A detection unit 150 for detecting a specific component (oxygen, etc.) contained in the exhaust gas is provided at the top end 100b of the gas sensor element body 100a. The detection unit 150 is mainly composed of the electrode units (the first electrode unit 104a, the second electrode unit 106a, the third electrode unit 108a, and the fourth electrode unit 110a) of the detection element unit 300 and the measurement chamber 107c. A porous protective layer 20 is formed at the top end 100b of the gas sensor element body 100a so as to cover the periphery of such a detection unit 150. Pores of a three-dimensional network structure are formed in the porous protective layer 20 (the inner protective layer 21 and the outer protective layer 22) so that gas can pass through.

[0079] Figure 5 This is a perspective view of the gas sensor element main body 100a as viewed from the top end side. Figure 5 The outer protective layer 22 (porous protective layer 20) is virtually shown in the figure. The outer protective layer 22 (porous protective layer 20) is formed on the top end portion 100b of the gas sensor element body 100a so as to cover the top end surface 100c and the peripheral surface 100d of the top end portion 100b of the gas sensor element body 100a.

[0080] The inner protective layer 21 and the outer protective layer 22 constituting the porous protective layer 20 can be formed by bonding, for example, one or more ceramic particles selected from the group consisting of titanium dioxide, aluminum oxide, spinel, zirconium oxide, mullite, zircon and cordierite by calcination or the like. By sintering the slurry containing these particles, pores can be formed between the ceramic particles. Alternatively, a burnable pore-forming material formed of carbon, resin beads, an organic or inorganic binder, etc. may be added to the slurry containing the above particles.

[0081] Furthermore, if the ratio of the burnable pore-forming material added to the slurry is increased, the porosity of the layer increases. Therefore, the porosity of the inner protective layer 21 and the outer protective layer 22 can be changed by adjusting the ratio of the pore-forming material.

[0082] Next, refer to Figure 6 , the characteristic parts of the gas sensor element 100 according to the embodiment of the present invention will be described.

[0083] like Figure 6As shown, when viewed from a direction perpendicular to the main surface (protective layer 111 ), the inner protective layer 21 has a region R along the axis L where the thickness t becomes the largest, and the thickness becomes thinner from the region R toward the front end and the rear end.

[0084] On the other hand, the outer protective layer 22 has a top face 22t and four side faces 22s, and the top face and the side faces are all flat faces. Therefore, the outer protective layer 22 has the smallest thickness in the region R, and its thickness increases from the region R toward the front end side and the rear end side. Moreover, the side face 22s is a straight line shape (roughly parallel to the axis L direction), and the radially outermost rear edge 22f of the outer protective layer 22 is a shape that is concave toward the top end side relative to the rear end P1, P2 in the center of the width direction of the gas sensor element 100. In other words, it is a shape that is concave toward the top end side from the rear end P1, P2 toward the center sandwiched by P1 and P2. In addition, the surface of the portion where the top face 22t and the side face 22s in the outer protective layer 22 are connected (the portion covering the corner of the sensor element) is formed as a curved surface, which is not shown in the figure.

[0085] Here, Figure 3 It is from Figure 6 A cross-sectional view viewed in a vertical direction (that is, in a direction parallel to the main surface), such as Figure 3 As shown in FIG. 1 , the “rear edge 22f” refers to the rear edge of the side 22s (that is, the radially outermost side) of the outer protective layer 22. Figure 3 As shown, the surface of the outer cover layer 22 facing the rear end is formed to be inclined, and the shape of the rear end edge also changes depending on the position in the thickness direction of the outer cover layer 22.

[0086] In other words, “the rear edge 22f is recessed toward the tip side from the rear ends P1 and P2 toward the center sandwiched between P1 and P2” means that at any position C1 in the region between the rear ends P1 and P2 in the width direction of the gas sensor element 100, the rear edge 22f is located at a position greater than Figure 6 The virtual line VL connecting the rear ends P1 and P2 in FIG.

[0087] First, “the thickness of the inner protective layer 21 becomes thinner as it moves from region R toward the top end side and the rear end side” means that the inner protective layer 21 is formed by the dipping method, and due to the flow of the slurry, the thickness on the top end side and the thickness on the rear end side (especially the thickness of the corner 21e on the top end side) becomes thinner.

[0088] In addition, “the rear end edge 22f is recessed toward the top end side from the rear ends P1 and P2 toward the center” means that the outer protective layer 22 is also formed by the dipping method, and when the gas sensor element 100 is immersed in the slurry, the friction between the surface of the gas sensor element 100 and the slurry is utilized to maintain the recessed shape of the central portion to adhere the slurry.

[0089] On the other hand, "the top surface and the side surface are flat surfaces" and "the side surface 22s is a straight line shape" mean that if a general impregnation method is used, then the outer protective layer 22 should also have an area with the largest thickness along the axis L direction, similar to the inner protective layer 21, and the thick part is corrected by the manufacturing method described later to make the surface flat and form a roughly uniform thickness in the axis L direction.

[0090] Thus, for the gas sensor element 100 of the embodiment of the present invention, both the inner protective layer 21 and the outer protective layer 22 are formed by the dipping method, so that unlike the spraying method, it is not necessary to have skilled operation, and it is possible to suppress the cost increase and form it simply. In addition, since the outer protective layer 22 is formed to have a substantially uniform thickness in the direction of the axis L, it is also possible to reduce the unevenness of the layer thickness, and suppress the situation where the activation is delayed due to excessive heat capacity.

[0091] In addition, the inner protective layer 21 is still formed by the dipping method, and the thickness in the direction of the axis L is non-uniform, but since the thickness in the direction of the axis L of the outer protective layer 22 located outside the inner protective layer 21 is formed to be substantially uniform, the thickness of the outer shape of the porous protective layer 20 composed of the inner protective layer 21 and the outer protective layer 22 is formed to be substantially uniform. As a result, the increase in heat capacity caused by the non-uniform thickness of the entire layer can be suppressed.

[0092] In addition, if Figure 6 As shown in FIG. 1 , in the inner protective layer 21 formed by the dipping method, although the thickness of the corner portion 21e on the top side is reduced, the thickness of the outer protective layer 22 is compensated by the amount thereof, and the thickness of the corner portion is ensured for the entire porous protective layer 20. In other words, the disadvantage caused by the reduction in the thickness of the corner portion 21e caused by the dipping method can also be eliminated.

[0093] The gas sensor element 100 is used in the gas sensor 1 as described above.

[0094] Next, a method for manufacturing a gas sensor element according to an embodiment of the present invention will be described. The method for manufacturing a gas sensor element according to this embodiment includes a first dipping step, a drying step, a second dipping step, and a grinding step.

[0095] The first immersion step is a step in which the top end side of the gas sensor element body 100a (gas sensor element 100) is immersed in a slurry (hereinafter simply referred to as "slurry") S1 for forming the inner protective layer 21, thereby forming a first coating film 700 of the slurry S1 on the top end surface 100c and the peripheral surface 100d of the top end portion 100b of the gas sensor element body 100a.

[0096] In addition, the slurry for forming the outer protective layer 22 used in the second dipping step described later is referred to as “slurry S2 ”.

[0097] The slurries S1 and S2 are similar to the materials used in the impregnation process in the past, for example, a solution containing one or more ceramic particles selected from the group consisting of titanium dioxide, aluminum oxide, spinel, zirconium oxide, mullite, zircon and cordierite. The slurries S1 and S2 are preferably formed at a shear rate of 0.1 s compared to the materials used in the past. -1 The viscosity is set higher, preferably, the shear rate is 10s -1 The viscosity is set lower.

[0098] For the viscosity (mPa·s) of slurries S1 and S2, for example, at room temperature (23°C) and at a shear rate of 0.1s -1 It is preferably set to 43000 mPa·s or more at a shear rate of 10 s -1 It is preferably set to 2500 mPa·s or less.

[0099] The viscosity of the slurries S1 and S2 is not particularly limited unless the purpose of the present invention is impaired. For example, at room temperature (23° C.), the viscosity of the slurries S1 and S2 is 0.1 s -1 When the shear rate is set to 65000mPa·s, -1 When the viscosity of the slurries S1 and S2 is set as described above, it is easy to adjust the thickness of the coating film 700 formed by the slurry on the gas sensor element body 100a in the grinding process described later. In addition, the viscosity of the slurries S1 and S2 is appropriately adjusted by adding an organic binder formed of, for example, a synthetic resin, a natural polymer, etc., alumina sol, water, etc. to the slurries S1 and S2. In addition, the viscosity of the slurry S is measured using a viscometer (rheometer MCR102: manufactured by Anton-Paar).

[0100] Here, an example of preparing the slurry used in the first impregnation step and the second impregnation step is described. Titanium dioxide powder, spinel powder, alumina sol, organic binder (e.g., acrylic copolymer), dispersant (e.g., anionic polymer dispersant), defoamer (e.g., amide wax defoamer) and water are prepared in a predetermined ratio, and the above materials are mixed for a predetermined time to obtain the desired slurry.

[0101] Figure 7 4 is an explanatory diagram showing a state in which the gas sensor element body 100a is on standby above the immersion tank 400 in the first immersion step. Figure 72 shows the state of the gas sensor element main body 100a and the like before the immersion step starts. Figure 7 4 shows a container-shaped immersion tank 400 for containing slurry S1 and having an upper opening, and a gas sensor element main body 100 a standing by in a stationary state above the immersion tank 400 .

[0102] The gas sensor element body 100a is fixed by a predetermined jig so that its longitudinal direction is along the vertical direction and its top end 100b faces downward. The top end 100b of the gas sensor element body 100a is in a state facing the slurry S1 contained in the immersion tank 400. Figure 7 In the figure, the surface of the gas sensor element body 100a on which the electrode protecting portion 113a is formed (the protecting layer 111, that is, the main surface) is shown facing the front side of the paper.

[0103] In addition, if Figure 7 As shown in FIG. 4 , the position where the gas sensor element body 100 a stands still and waits above the immersion tank 400 is referred to as a “waiting position”.

[0104] The gas sensor element body 100a is configured to be able to reciprocate between a standby position and a position (immersion position described later) inside the immersion tank 400 located below it in the up-down direction (vertical direction) while being fixed to a predetermined jig. The mechanism for reciprocating the gas sensor element body 100a is not particularly limited as long as it does not impair the purpose of the present invention, and a known reciprocating mechanism using a servo motor or the like can be applied.

[0105] In the first immersion step, the tip portion 100 b of the gas sensor element body 100 a that has been lowered from the standby position is immersed in the slurry in the immersion tank 400 .

[0106] The height position of the tip portion 100b immersed in the slurry is set so as not to contact the bottom of the immersion tank 400 and the slurry S1 is attached to the tip surface 100c and the peripheral surface 100d of the tip portion 100b.

[0107] The position of the gas sensor element body 100a immersed in the slurry so that the slurry adheres to the top surface 100c and the peripheral surface 100d is referred to as the "immersion position" (refer to the second immersion step described later). Fig.12 The gas sensor element body 100a may be left at rest at the immersion position for a predetermined time as required, or may be pulled up directly after reaching the immersion position.

[0108] like Figure 8As shown, by the first dipping step, the tip portion 100b of the gas sensor element body 100a is dipped in the slurry S1, so that the first coating film 700 of the slurry S1 can be formed on the tip surface 100c and the peripheral surface 100d of the tip portion 100b. In addition, the tip portion 100b of the gas sensor element body 100a dipped in the slurry is then pulled up and handed over to the next drying step.

[0109] like Figure 8 As shown, the drying process is a process for drying and solidifying the first coating film 700 to form the unfired inner protective layer 21x. This is because, when the second dipping process is performed without drying the first coating film 700, the first coating film 700 and the second coating film 800 described later are mixed, or the first coating film 700 flows down during the second dipping process.

[0110] In addition, "curing" does not mean that the water content does not need to be completely reduced to zero, and it is sufficient to maintain the solidified shape so that the first coating film 700 does not flow down during the second dipping step and does not mix with the second coating film 800 (mainly to form the desired inner and outer protective layers respectively after baking).

[0111] In addition, since the grinding process described later is not performed after the first dipping process, the first coating film 700 (and the unfired inner protective layer 21x after drying) is still formed by the dipping method, and the thickness in the direction of the axis L is not uniform. However, as described above, the thickness of the outer shape of the porous protective layer 20 composed of the inner protective layer 21 and the outer protective layer 22 is formed to be approximately uniform, so there is no problem even if the thickness of the first coating film 700 remains uneven.

[0112] In order to ensure the thickness of the inner protective layer 21 , the first immersion step and the drying step may be performed a plurality of times as necessary.

[0113] After the drying step, the next second dipping step is performed.

[0114] Fig. 9 4 is an explanatory diagram showing a state in which the gas sensor element body 100a is on standby above the immersion tank 450 in the second immersion step. Fig. 9 2 shows the state of the gas sensor element main body 100a and the like before the immersion step starts. Fig. 9 4 shows a container-shaped immersion tank 450 for containing slurry S2 which is opened at the top, and a gas sensor element main body 100 a which is stationary and waiting at a “waiting position” above the immersion tank 450 .

[0115] The arrangement state of the gas sensor element main body 100a at the "standby position" is different from Figure 7The same is true for the first impregnation step. In addition, through the first impregnation step and the drying step, the unfired inner protective layer 21x is formed on the tip portion 100b of the gas sensor element body 100a.

[0116] In addition, if Fig. 9 As shown, a grinding jig 500 and a grinding tool 600 used in a grinding process performed after the immersion process are arranged between the gas sensor element body 100 a in the standby position and the immersion tank 450 .

[0117] Fig.10 1 is a plan view of the grinding die 500. The grinding die 500 includes a pair of movable cutters 501 and 502 arranged to be spaced apart in the horizontal direction, and a moving mechanism (an actuator such as a servomotor and a feed screw) for moving the movable cutters 501 and 502.

[0118] Each movable blade 501, 502 is substantially rectangular, and its opposite sides E, E are parallel to each other and separated by a predetermined interval D1 to form an opening (gap) 503. The size (interval D1) of the opening 503 is set so that the gas sensor element body 100a can pass between the sides E, E at the edge of the opening 503.

[0119] In the standby position, the tip portion 100b of the gas sensor element body 100a is arranged to be accommodated inside the opening 503 in a plan view. Fig.10 In FIG. 5 , the top end portion 100 b of the gas sensor element main body 100 a in a state of being accommodated inside the opening 503 in a plan view is virtually shown.

[0120] A pair of sides E and E forming the periphery of the opening 503 function as grinding tools. The excess second coating 800 located on the side of the movable tools 501 and 502 relative to the sides E and E is ground by the sides E and E when passing through the opening 503, and the thickness (width) of the second coating 800 is adjusted to the interval D1.

[0121] In addition, Fig.10 In the case of , the thickness (width) of the second coating film 800 in the direction parallel to the protective layer 111 (main surface) is adjusted to be only the distance D1.

[0122] Therefore, if Fig.11 As shown, the gas sensor element body 100a (and the tip portion 100b) is rotated 90 degrees (in Fig.11 ), and by further narrowing the interval D2, the thickness (width) of the second coating film 800 extending in a direction perpendicular to the protective layer 111 (main surface) can be adjusted to the interval D2, which will be described in detail later.

[0123] In addition, you can also Fig. 9Before grinding Fig.11 The main surface side of the top end portion 100b may also be Fig.11 , Fig. 9 Before Fig.15 The order of grinding the top.

[0124] like Fig. 9 As shown, the grinding tool 600 is retracted to a position outside the opening 503 so as not to overlap with the opening 503 in the up-down direction. This position is referred to as a “retracted position” of the grinding tool 600 .

[0125] In the present embodiment, the grinding tool 600 is disposed on the upper surface 500a side of the grinding mold 500. The grinding tool 600 is disposed at a height position such that a gap is formed between the grinding tool 600 and the upper surface 500a of the grinding mold 500.

[0126] Fig.12 1 is an explanatory diagram showing a state in which the top end 100b of the gas sensor element body 100a lowered from the standby position is immersed in the slurry S2 in the immersion tank 450 in the immersion process. Figure 7 ) moves downward, the tip portion 100b passes through the opening 503 of the grinding mold 500 from the upper side to the lower side. At this time, the tip portion 100b passes through the opening 503 without contacting the grinding mold 500. Thereafter, the gas sensor element body 100a moves further downward, and the tip portion 100b is immersed in the slurry contained in the immersion tank 450.

[0127] The height position of the tip portion 100b immersed in the slurry is set so as not to contact the bottom of the immersion tank 450, and the slurry is attached to the tip surface 100c and the peripheral surface 100d of the tip portion 100b.

[0128] In addition, if Fig.12 As shown, the position of the gas sensor element body 100a immersed in the slurry in such a manner that the slurry adheres to the top surface 100c and the peripheral surface 100d is called the "immersion position" (common to both the first immersion step and the second immersion step). The gas sensor element body 100a can be left stationary at the immersion position for a predetermined time as needed, or can be pulled up directly after reaching the immersion position.

[0129] By such an immersion process, the top portion 100b of the gas sensor element body 100a is immersed in the slurry, so that the slurry coating films 700 and 800 are formed on the top surface 100c and the peripheral surface 100d of the top portion 100b (the first immersion process and the second immersion process). In addition, the top portion 100b of the gas sensor element body 100a immersed in the slurry is then pulled up, handed over to the drying process in the first immersion process, and handed over to the grinding process in the second immersion process.

[0130] The grinding step is a step of grinding the coating film 800 of the slurry S2 formed in the second dipping step and attached to the top end portion 100b of the gas sensor element body 100a to remove a portion of the coating film 800. Fig.10 , Fig.11 As shown in FIG. 1 , when the top end 100b of the gas sensor element body 100a is pulled up from the slurry S2 after the second immersion step, a coating film 800 composed of the attached matter of the slurry is formed on the top end 100b. Furthermore, when the thickness of the coating film 800 formed on the top end 100b exceeds the thickness required as the porous protective layer 20 after the second immersion step, the excess amount of the coating film is removed by the grinding step.

[0131] In addition, in this specification, the thickness of the coating film 800 required as the porous protective layer 20 is referred to as “required thickness”.

[0132] In this specification, the coating film formed on the peripheral surface 100d of the tip portion 100b among the coating films 800 attached to the tip portion 100b after the dipping process is referred to as "peripheral surface coating film 801", and the coating film formed on the tip surface 100c of the tip portion 100b among the coating films 800 attached to the tip portion 100b after the dipping process is referred to as "tip coating film 802". In this specification, the coating film located on the tip side of the tip surface 100c of the tip portion 100b in the axial direction (axis L direction) is referred to as the tip coating film 802.

[0133] The grinding process of this embodiment includes a process of removing a portion (excess coating film) 801a of the circumferential surface coating film 801 formed on the circumferential surface 100d of the top end portion 100b in the coating film 800 attached to the top end portion 100b using a grinding mold 500 (circumferential surface grinding process), and a process of removing a portion (excess coating film) 802a of the top end coating film 802 formed on the top end surface 100c of the top end portion 100b in the coating film 800 attached to the top end portion 100b using a grinding tool 600 (top end surface grinding process).

[0134] Furthermore, the excess coating film 801a is Fig.10As shown in FIG. 1 , a coating film having a thickness in a direction parallel to the protective layer 111 (main surface) is formed as a coating film 801a1, and the excess coating film 801a is Fig.11 As shown in the figure, a coating film having a thickness in a direction perpendicular to the protective layer 111 (main surface) is used as coating film 801a2.

[0135] In this embodiment, the peripheral surface grinding step is performed first and the top surface grinding step is performed later. However, in consideration of the situation that the slurry drips due to gravity, the peripheral surface grinding step may be performed first and the top surface grinding step may be performed last.

[0136] Fig.13 1 is an explanatory diagram showing how a portion (excess coating film) 801a1 of the peripheral surface coating film 801 formed on the peripheral surface 100d of the top end portion 100b of the gas sensor element body 100a is removed by the grinding die 500 in the grinding step. Fig.13 The contents of the above-mentioned peripheral surface grinding process are shown in FIG. When the peripheral surface coating film 801 exceeding the required thickness is attached to the top end portion 100b of the pulled-up gas sensor element body 100a after the immersion process, the excess amount of coating film (excess coating film) 801a1 is ground by the edges E, E when the top end portion 100b passes through the opening 503 (a pair of sides E, E) of the grinding mold 500 from the lower side to the upper side. In this way, when the top end portion 100b passes through the sides E, E, the excess coating film 801a1 is separated from the peripheral surface coating film 801 of the required thickness.

[0137] Thus, the thickness (width) of the second coating film 800 in the direction parallel to the protective layer 111 (main surface) is adjusted to the distance D1.

[0138] In the above embodiment, the following operation is performed: by pulling up the gas sensor element body 100a, the grinding mold 500 is relatively moved toward the top end surface 100c and grinding is performed using the sides E, E. Alternatively, the grinding mold 500 is relatively moved toward the rear end of the gas sensor element body 100a by pulling down the gas sensor element body 100a and grinding is performed. However, in the case of adopting the above embodiment, there is no possibility that the separated excess coating film 801a1 will adhere to the gas sensor element body 100a, so it is preferred.

[0139] In addition, a part of the separated excess coating film 801a1 falls due to its own weight and returns to the immersion tank 450. The grinding die 500 is formed by, for example, a member obtained by processing a metal plate into a predetermined shape. The size (interval D1) of the opening 503 of the grinding die 500 is set so that, as described above, the gas sensor element body 100a can pass therethrough and the coating film 800 (peripheral coating film 801) of the required thickness for forming the porous protective layer 20 is formed around the tip portion 100b after the peripheral grinding step.

[0140] When the viscosity of the slurry is high, the slurry may not return to the immersion tank 450 but may adhere to the grinding die 500 . Therefore, it is better to remove it appropriately.

[0141] Fig.14 This is an explanatory diagram showing how a portion (excess coating film) 801a2 of the peripheral surface coating film 801 formed on the peripheral surface 100d of the tip portion 100b of the gas sensor element body 100a is removed by the grinding jig 500 in the grinding step. Fig.14 Although Fig.13 Same as, but with Fig.11 Similarly, the gas sensor element main body 100a (and the tip portion 100b) is rotated 90 degrees (at Fig.14 The grinding process is performed in a state where the interval D2 is further narrowed than the interval D1).

[0142] Specifically, in Fig.13 In the process, after removing the excess coating film 801a1, the top end portion 100b is pulled up again from the second dipping step (that is, in Fig.13 After grinding, the top end 100b is moved downward through the opening 503 of the interval D1, the moving mechanism is activated and the interval is narrowed to D2, and then the top end 100b is pulled up by passing through the opening 503 of the interval D2.

[0143] In addition, when the tip portion 100 b is moved downward through the opening 503 of the interval D1 , it is desirable to adjust the height so that the tip portion 100 b is not immersed in the dipping tank 450 again.

[0144] exist Fig.14 In the embodiment, when the peripheral coating film 801 having a thickness exceeding the required thickness is attached to the tip portion 100b, the excess coating film (excess coating film) 801a2 is ground by the edges E, E when the tip portion 100b passes through the opening 503 (a pair of edges E, E) of the grinding die 500 from the lower side to the upper side. In this way, when the tip portion 100b passes through the edges E, E, the excess coating film 801a2 is separated from the peripheral coating film 801 having a required thickness.

[0145] Thus, the thickness (width) of the second coating film 800 in the direction perpendicular to the protective layer 111 (main surface) is adjusted to the distance D2.

[0146] As described above, the thickness (width) of the second coating film 800 is adjusted to the intervals D1 and D2 by the grinding die 500 .

[0147] In addition, in the above embodiment, the following actions are performed: by pulling up the gas sensor element body 100a, the grinding mold 500 is relatively moved toward the top end surface 100c and grinding is performed using the sides E, E. Alternatively, conversely, by pulling down the gas sensor element body 100a, the grinding mold 500 is relatively moved toward the rear end of the gas sensor element body 100a and grinding is performed. However, in the case of adopting the above embodiment, there is no possibility that the separated excess coating film 801a2 will adhere to the gas sensor element body 100a, so it is preferred.

[0148] Furthermore, in the above-mentioned embodiment, in Fig.13 After grinding the peripheral coating film 801 in the direction parallel to the protective layer 111 (main surface) shown in FIG. Fig.14 The operation shown is to grind the peripheral surface coating film 801 in the direction perpendicular to the protective layer 111 (main surface), but the grinding order may be reversed.

[0149] Fig.15 1 is an explanatory diagram showing how a portion (excess coating film) 802a of the tip coating film 802 formed on the tip surface 100c of the tip portion 100b of the gas sensor element body 100a is removed by the grinding tool 600 in the grinding process. Fig.15 The content of the top end surface grinding process is shown in FIG. After the peripheral surface grinding process, for the gas sensor element body 100a passing through the opening 503 of the grinding mold 500 from the bottom to the top, in order to perform the top end surface grinding process, the position of the top end surface 100c of the top end portion 100b is moved upward to a predetermined specified height position.

[0150] The predetermined height position of the distal end surface 100 c for the distal end surface grinding step is set so that the thickness of the distal end coating film 802 formed on the distal end surface 100 c becomes a thickness required as the porous protective layer 20 after the distal end surface grinding step.

[0151] In the case of this embodiment, the height position of the top surface 100c during the top surface grinding process is set to be the same as the height position of the top surface 100c of the gas sensor element body 100a stationary at the above-mentioned standby position. In other embodiments, the height position of the top surface 100c during the top surface grinding process may also be different from the height position of the top surface 100c of the gas sensor element body 100a stationary at the standby position.

[0152] exist Fig.15 The gas sensor element body 100a is shown in a state of being stationary at a standby position. In this state, a coating film 800 including a peripheral surface coating film 801 whose thickness is adjusted by removing excess coating films 801a1 and 801a2 is formed at the top end portion 100b of the gas sensor element body 100a. When the top coating film 802 formed on the top end surface 100c of such a coating film 800 exceeds the required thickness, the excess amount of coating film (excess coating film 802a) is ground by the grinding tool 600.

[0153] The grinding tool 600 is formed, for example, by processing a metal plate into a predetermined shape. The grinding tool 600 is configured using a known reciprocating mechanism, etc., so that its top end 601 can reciprocate in the horizontal direction. In the grinding process, the height position of the top end 601 of the grinding tool 600 and the height position of the top end 100b of the gas sensor element body 100a are set so that the top coating film 802 of the required thickness remains on the top surface 100c.

[0154] In addition, Fig. 9 In the embodiment, the gas sensor element body 100a is configured such that its length direction is along the vertical direction (up and down direction). The axial direction (axis L direction) of the gas sensor element body 100a is along the vertical direction. Therefore, it can be said that the grinding tool 600 moves in a direction perpendicular to the axial direction of the gas sensor element body 100a.

[0155] The grinding tool 600 is kept in the same state during the first and second immersion steps and the peripheral surface grinding step. Fig. 9When the gas sensor element body 100a returns to the standby position and stops after the peripheral surface grinding process, the grinding tool 600 moves in the horizontal direction to grind the excess coating 802a of the top coating 802. The grinding tool 600 moves horizontally from the retreat position to the gas sensor element body 100a side with its top end 601, and moves horizontally in a manner that straddles the opening 503 in the longitudinal direction above the opening 503. When the grinding tool 600 moves horizontally in a manner that straddles the opening 503, the top end 601 is formed into a shape that shaves off the excess coating 802a exceeding the required thickness from the top coating 802 of the required thickness. In this way, when the top coating 802 formed on the top surface 100c exceeds the required thickness, the excess amount of coating (excess coating 802a) is ground by the grinding tool 600.

[0156] Fig.16 This is an explanatory diagram showing the grinding tool 600 returning to the retreat position after the grinding process. After grinding the excess coating film 802a of the tip coating film 802, the grinding tool 600 moves horizontally in the opposite direction to the grinding process to return to the retreat position.

[0157] Through the above-described grinding steps (peripheral surface grinding step, distal end surface grinding step), the coating film 800 formed on the distal end portion 100b of the gas sensor element body 100a is adjusted so as not to have an excessively large thickness.

[0158] In addition, it is preferred that the cured first coating 700 is not ground during the grinding process. When the cured first coating 700 is ground, it is possible that the first coating 700 is damaged or the movable cutters 501, 502 (sides E, E) are deformed. Specifically, "the cured first coating 700 is not ground" means that the intervals D1 and D2 are respectively larger than the thickness of the cured first coating 700. In addition, for example, the thickness of the first coating 700 after curing based on a specified immersion time, the viscosity of the slurry S1, etc. may be measured in advance, and the intervals D1 and D2 may be set based on the measured values.

[0159] After the grinding step, when the coating film 800 having a sufficient thickness for forming the porous protective layer 20 is formed on the top end portion 100b of the gas sensor element body 100a, the gas sensor element body 100a is transferred to the baking step as needed. In addition, a second drying step of drying the coating film 800 may be provided before the baking step.

[0160] The calcining step is a step of calcining the coating film 800 after the grinding step to obtain the porous protective layer 20. The calcining temperature and calcining time in the calcining step are not particularly limited as long as the porous protective layer 20 can be obtained by sintering the coating film 800, and can be appropriately set according to the purpose. The calcining step is performed, for example, at 1000° C. for three hours.

[0161] As described above, in the method for manufacturing the gas sensor element of the present embodiment, the porous protective layer 20 is covered on the top end portion 100b of the gas sensor element 100 (gas sensor element body 100a) where the detection portion 150 is arranged, through the first immersion step, the drying step, the second immersion step, and the grinding step, so that the gas sensor element 100 including the porous protective layer 20 as described above can be obtained (see Figure 3 to Figure 5 According to the method for manufacturing the gas sensor element of the present embodiment, the thickness of the coating film 800 formed of the slurry S2 constituting the outer protective layer 22 can be adjusted to a desired thickness through the grinding step.

[0162] Therefore, according to the manufacturing method of the gas sensor element of this embodiment, since both the inner protective layer 21 and the outer protective layer 22 are formed by the dipping method, it is not necessary to have skilled operation like the spraying method, and it is possible to suppress the cost increase and simply form. In addition, since the outer protective layer 22 is formed to have a substantially uniform thickness in the direction of the axis L by the grinding process, it is also possible to reduce the unevenness of the layer thickness and suppress the delay of activation due to excessive heat capacity.

[0163] In addition, the inner protective layer 21 is still formed by the dipping method without the grinding process, so the thickness in the direction of the axis L is uneven (refer to Figure 6 ), but since the thickness of the outer protective layer 22 located outside the inner protective layer 21 in the direction of the axis L is made substantially uniform by the grinding process, the thickness of the outer shape of the porous protective layer 20 formed by combining the inner protective layer 21 and the outer protective layer 22 becomes substantially uniform. As a result, the increase in heat capacity caused by uneven thickness of the entire layer can be suppressed.

[0164] In addition, if Figure 6 As shown in FIG. 1 , in the inner protective layer 21 formed by the dipping method, although the thickness of the corner portion 21e on the top end side is reduced, the thickness of the outer protective layer 22 is compensated by the amount thereof, and the thickness of the corner portion is ensured for the entire porous protective layer 20. In other words, the disadvantage caused by the reduction in the thickness of the corner portion 21e caused by the dipping method can also be eliminated.

[0165] In addition, it is preferable to arrange the grinding tool 600 on the upper surface 500a side of the grinding mold 500 and perform the top surface grinding process in a state away from the upper surface 500a, compared with the case where the grinding tool 600 is arranged on the lower surface side of the grinding mold 500. This is because it is difficult for the horizontal movement of the grinding tool 600 to be hindered by the influence of the solidified material such as the removed excess coating film 802a.

[0166] The present invention is not limited to the above-described embodiments, and it is apparent that various modifications and equivalents included in the concept and scope of the present invention are also possible.

[0167] In the above-mentioned embodiment, the grinding mold 500 is arranged directly above the immersion tank 450, and when the gas sensor element body 100a is moved in a process other than the grinding process such as the immersion process, the gas sensor element body 100a and the coating films 700 and 800 are moved in a manner that does not contact the grinding mold 500, but is not limited to this form.

[0168] For example, the grinding mold 500 may be arranged at a different position instead of being arranged directly above the dipping tank 450. In this case, during the dipping process, it is not necessary to move the gas sensor element body 100a with high precision so that the gas sensor element body 100a and the coating films 700 and 800 do not contact the grinding mold 500, and the gas sensor element body 100a only needs to be moved up and down in coordination with the area where the slurry is desired to be attached.

[0169] Then, after the immersion step, the grinding jig 500 and the gas sensor element body 100 a are relatively moved so as to approach each other, and the grinding step may be performed.

[0170] Furthermore, in the above embodiment, the grinding die 500 includes a pair of movable blades 501 and 502 and the coating films 700 and 800 are ground by adjusting the interval between the movable blades 501 and 502. However, the present invention is not limited thereto and a frame-shaped grinding die of a predetermined size may be used.

[0171] Alternatively, in the grinding process, the surface of the second coating film after grinding is made flat. When such grinding is performed, the second coating film and the outer protective layer become flat (straight line shape). As the gas sensor element 100, in addition to the oxygen sensor element, a NOx sensor element or the like can be used.

[0172] The shape of the opening 503 (sides E, E) is not limited to the above, and may be appropriately set to a shape other than a straight line according to the desired shape of the porous protective layer.

[0173] The porous protective layer of the gas sensor element manufactured by the above-mentioned manufacturing method may be subjected to cutting processing such as laser or a cutter to finely adjust the shape of the porous protective layer as necessary.

[0174] The present invention has been described in detail with reference to the above embodiments. However, the present invention should not be construed as being limited thereto. It will be apparent to those skilled in the art that various changes may be made to the form and details of the present invention as shown and described above. These changes are intended to be included within the spirit and scope of the appended claims. This application is based on Japanese Patent Application No. 2020-135828 filed on August 11, 2020, and all of its disclosures are incorporated herein by reference.

Claims

1. A method for manufacturing a gas sensor element, comprising: sequentially covering a porous inner protective layer and a porous outer protective layer having a porosity different from that of the inner protective layer as a porous protective layer on a detection portion disposed on the tip side of a gas sensor element extending in an axial direction, wherein: The method for manufacturing the gas sensor element comprises the following steps: a first dipping step of dipping the tip side of the gas sensor element into a first slurry for an inner protective layer, thereby forming a first coating film of the first slurry on the tip surface and the peripheral surface of the gas sensor element; A drying step of drying the first coating film to solidify it; a second dipping step of dipping the tip side of the gas sensor element into a second slurry for an outer protective layer without removing the first coating film, thereby forming a second coating film of the second slurry on the entire surface of the cured first coating film; as well as The grinding step is to grind the second coating film so as not to grind the cured first coating film, thereby removing a part of the second coating film.

2. The method for manufacturing a gas sensor element according to claim 1, wherein: In the grinding step, grinding is performed so that the surface of the second coating film after grinding becomes a flat surface.

3. The method for manufacturing a gas sensor element according to claim 1 or 2, characterized in that: The grinding step includes: a peripheral surface grinding step of grinding and removing a portion of the second coating film in the peripheral direction; and a top surface grinding step of grinding and removing a portion of the top side of the second coating film. The top end surface grinding step is performed after the peripheral surface grinding step.

4. A gas sensor element extending in an axial direction, in a plate shape having opposite main surfaces and having a detection portion at the tip side, comprising a porous protective layer covering the detection portion, characterized in that: The porous protective layer includes an inner protective layer and a porous outer protective layer having a porosity different from that of the inner protective layer and covering the inner protective layer. The inner protective layer has a region where the thickness is the largest along the axial direction, and the thickness becomes thinner as it goes from the region toward the front end side and the rear end side. The outer protective layer has a flat top surface and flat side surfaces, When viewed from a direction perpendicular to the main surface, the radially outermost rear end edge of the outer protection layer is shaped so that the center in the width direction of the gas sensor element is recessed toward the tip side relative to the rear end.

5. A gas sensor, characterized in that: This gas sensor has the gas sensor element according to claim 4.

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