Gas sensor element manufacturing method, gas sensor element, and gas sensor

Abstract

To provide a manufacturing method of a gas sensor element including a porous protective layer with reduced defects derived from air bubbles and excellent in water resistance.SOLUTION: A manufacturing method includes: a first immersion step S101 of immersing a tip in first slurry to form a first coated film made of the first slurry at the tip so as to accommodate a detection part; a first drying step S103 of drying the first coated film to for a first dry film at the tip; a second immersion step S104 of immersing the tip with the first dry film formed thereon in second slurry containing same dispersoid as the first slurry or a similar type of dispersoid to major components of the first slurry to form second coated film made of the second slurry on teh first dry film so as to expose a rear end of the first dry film and accommodate the detection part; a second drying step S106 of drying the second coated film to form a second dry film on the first dry film so as to expose the tip; and a calcination step S107 of firing the first dry film and the second dry film to form at the tip a sintered body of the first dry film and the second dry film composing a porous protective layer.SELECTED DRAWING: Figure 7

Description

[Technical field]

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

[0002] There is known a gas sensor for detecting the concentration of a specific component (oxygen, etc.) contained in exhaust gas from an internal combustion engine. This type of gas sensor includes an elongated plate-like gas sensor element therein. A detection portion for detecting the specific component is provided at the tip of the gas sensor element. A porous protective layer is formed at the tip of the gas sensor element so as to cover the detection portion (see, for example, Patent Document 1).

[0003] The porous protective layer is provided for the purpose of mitigating the thermal shock applied to the gas sensor element when water droplets derived from moisture contained in the exhaust gas come into contact with the gas sensor element. When starting an internal combustion engine, the moisture in the exhaust gas condenses into water droplets, which may fly toward the gas sensor element together with the exhaust gas. Since the gas sensor element is used in a state where it is heated to a high temperature, if water droplets adhere to the gas sensor element in such a state, the water droplets instantly evaporate, and a thermal shock is applied to the gas sensor element. The porous protective layer also has a function of suppressing the adhesion of poisonous substances (silicon, phosphorus, etc.) contained in the exhaust gas to the detection unit.

[0004] For example, as shown in Patent Document 1, a gas sensor element having a multi-layered porous protective layer is known. This porous protective layer has an inner porous protective layer and an outer porous protective layer which have different porosities and densities. The inner porous protective layer is formed so as to cover the tip of the gas sensor element, and the outer porous protective layer is formed so as to be superimposed on the inner porous protective layer. The outer porous protective layer has a smaller porosity and a higher density than the inner porous protective layer. Such an outer porous protective layer and inner porous protective layer are formed on the tip of the gas sensor element, for example, by dipping (dip method). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-93330 A Summary of the Invention [Problem to be solved by the invention]

[0006] When manufacturing a gas sensor element having a multi-layered porous protective layer, the outer porous protective layer may be formed in a multi-layered manner through multiple dipping steps. For example, when the outer porous protective layer is composed of a first protective layer and a second protective layer overlaid on the first protective layer, the two-layered outer porous protective layer is formed through at least two dipping steps.

[0007] In this case, first, in order to form the first protective layer, the tip of the gas sensor element is immersed in a predetermined slurry, and a first coating film is formed on the tip of the gas sensor element. After that, the thickness of the first coating film is appropriately adjusted, and the first coating film is dried to obtain a first dry film. Next, the tip of the gas sensor element on which the first dry film is formed is immersed in the slurry, and a second coating film is formed on the first dry film. After that, the thickness of the second coating film is appropriately adjusted, and the second coating film is dried to obtain a second dry film. After the first dry film and the second dry film are formed in this way, they are fired to obtain a porous protective layer (outer porous protective layer).

[0008] When the porous protective layer is formed through multiple dipping processes, a coating film made of a slurry is formed so as to cover the previously formed dry film. Then, air bubbles present in the dry film move toward the coating film, and the moved air bubbles break, etc., which may cause defects such as concave (crater-like) depressions on the surface of the coating film. This is presumably because some of the moisture contained in the coating film moves so as to penetrate into the dry film, and the air bubbles previously present in the dry film are pushed toward the coating film by the penetrated moisture. When such defects are formed, the thickness of the finally obtained porous protective layer (the thickness of the part where the defects are formed) may be insufficient, and the water resistance of the gas sensor element may be reduced.

[0009] An object of the present invention is to provide a manufacturing method for a gas sensor element having a porous protective layer that is excellent in water resistance and in which defects caused by air bubbles are suppressed, a gas sensor element, and a gas sensor. [Means for solving the problem]

[0010] The means for solving the above problems are as follows. <1> A method for manufacturing a gas sensor element comprising a rod-shaped body portion having a rod shape extending from front to back and including a detection portion at its tip portion for detecting a specific gas component, and a porous protective layer covering the tip portion, the method comprising the steps of: a first dipping step of dipping the tip portion into a first slurry to form a first coating film made of the first slurry on the tip portion so as to enclose the detection portion; a first drying step of drying the first coating film to form a first dry film on the tip portion; and a second drying step of drying the tip portion on which the first dry film has been formed, the second drying step being performed by applying a solution having the same main component as the first slurry or the same main component as the first slurry. a second dipping step of dipping the first dry film in a second slurry containing a type of dispersoid to form a second coating film made of the second slurry on the first dry film so that a rear end of the first dry film is exposed and the detection portion is enclosed therein; a second drying step of drying the second coating film to form a second dry film on the first dry film so that the end is exposed; and a firing step of firing the first dry film and the second dry film to form a sintered body of the first dry film and the second dry film that constitute the porous protective layer at the tip portion.

[0011] <2> In the first dipping step, the first coating film is formed so as to cover an area between the tip surface of the rod-shaped main body and a first reference position that is a predetermined first length away from the detection unit toward the rear end side of the rod-shaped main body, and in the second dipping step, the second coating film is formed so as to cover an area between the tip surface and a second reference position that is a second length away from the detection unit toward the rear end side of the rod-shaped main body, the second length being shorter than the first length. <1> A method for manufacturing the gas sensor element according to claim 1.

[0012] <3> In the second immersion step, the second coating film is formed so as to cover a portion of the tip portion that is to have a higher temperature than a portion of the end portion when the gas sensor element is used. <1> or <2> A method for manufacturing the gas sensor push element according to claim 1.

[0013] <4> The porous protective layer has an outer porous protective layer made of the sintered body of the first dry film and the second dry film, and an inner porous protective layer interposed between the outer porous protective layer and the tip portion and formed on the tip portion so as to encapsulate the detection portion, and in the first immersion step, an inner dry film for forming the inner porous protective layer is formed in advance on the tip portion immersed in the first slurry so as to encapsulate the detection portion, and the first coating film made of the first slurry is formed so as to cover the inner dry film on the tip portion. <1> from <3> 13. A method for manufacturing the gas sensor element according to any one of the above.

[0014] <5> The method further includes a first thickness adjusting step of removing a part of the first coating film to adjust the thickness of the first coating film before the first drying step. <1> from <4> 13. A method for manufacturing the gas sensor element according to any one of the above.

[0015] <6> The method further includes a second thickness adjusting step of removing a part of the second coating film to adjust the thickness of the second coating film before the second drying step. <1> from <5> 13. A method for manufacturing the gas sensor element according to any one of the above.

[0016] <7> A gas sensor element comprising: a rod-shaped main body portion having a rod shape extending from front to back and including a detection portion at its tip portion for detecting a specific gas component; and a porous protective layer covering the tip portion, wherein the porous protective layer comprises: a first protective layer formed around the entire circumference at least in the axial direction in a region where the detection portion is provided; and a second protective layer having the same main component as the first protective layer and provided outside the first protective layer so that a rear end portion of the first protective layer is exposed together with the region where the detection portion is provided at least in the axial direction, and the porosity of the first protective layer and the porosity of the second protective layer are approximately the same.

[0017] <8> The first protective layer is formed so as to cover an area between a tip end surface of the rod-shaped main body and a first reference position that is a predetermined first length away from the detection unit toward the rear end side of the rod-shaped main body, and the second protective layer is formed so as to cover an area between the tip end surface and a second reference position that is a second length away from the detection unit toward the rear end side of the rod-shaped main body, the second length being shorter than the first length. <7> The gas sensor element according to claim 1 .

[0018] <9> The second protective layer covers a portion of the tip portion that becomes hotter than a portion where the end portion is formed during use. <7> or <8> The gas sensor element according to claim 1 .

[0019] <10> The porous protective layer includes an outer porous protective layer including the first protective layer and the second protective layer, and an inner porous protective layer interposed between the outer porous protective layer and the tip portion and formed on the tip portion so as to enclose the detection portion. <7> from <9> 13. The gas sensor element according to claim 12,

[0020] <11> The above <7> from <10> A gas sensor comprising the gas sensor element according to any one of the above. Effect of the Invention

[0021] According to the present invention, it is possible to provide a manufacturing method for a gas sensor element having a porous protective layer with excellent water resistance in which defects caused by air bubbles are suppressed, a gas sensor element, and a gas sensor. [Brief description of the drawings]

[0022] [Figure 1] FIG. 2 is a cross-sectional view of the gas sensor according to the first embodiment taken along the axial direction. [Diagram 2] FIG. 2 is an exploded perspective view showing a schematic diagram of a detection element and a heater portion that constitute the gas sensor element; [Diagram 3] FIG. 2 is an enlarged schematic diagram of the tip side of the gas sensor element shown in FIG. 1. [Figure 4] An explanatory diagram of the gas sensor element as viewed from the tip side along the axial direction. [Diagram 5] Cross section of line AA in Figure 3 [Figure 6] Cross section of line BB in Figure 4 [Figure 7] 1 is a flow chart showing a method for manufacturing the gas sensor element according to the embodiment; [Figure 8] FIG. 13 is an explanatory diagram showing a state in which the gas sensor element body is waiting above the dipping tank in the first immersion step. [Figure 9] FIG. 11 is an explanatory diagram showing a state in which the tip portion of the gas sensor element body, which has been lowered from the standby position, is immersed in the first slurry in the dipping tank in the first immersion step. [Figure 10] FIG. 13 is an explanatory diagram showing a state in which a part (excess coating film) of the first peripheral surface coating film formed on the peripheral surface of the tip portion of the gas sensor element body is removed by using a scraping die in the first thickness adjustment process. [Figure 11] FIG. 11 is an explanatory diagram showing a state in which a part (excess coating film) of the first tip coating film formed on the tip surface of the gas sensor element body is removed by using a scraping blade in the first thickness adjustment process. [Figure 12] FIG. 13 is a schematic explanatory diagram showing the tip side of the gas sensor element body after the first drying process. [Figure 13] A schematic diagram of the second immersion process [Figure 14] FIG. 13 is an explanatory diagram showing a state in which a part (excess coating film) of the second peripheral surface coating film formed on the peripheral surface of the tip portion of the gas sensor element body is removed by using a scraping die in the second thickness adjustment process. [Figure 15] FIG. 11 is an enlarged vertical cross-sectional view of the gas sensor element body in the vicinity of its tip portion after the second thickness adjustment process; [Figure 16] FIG. 13 is a schematic explanatory diagram showing the tip side of the gas sensor element body after the second drying process. [Figure 17] FIG. 17 is a vertical sectional view of the gas sensor element body after the second drying step shown in FIG. 16; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] <Embodiment 1> A first embodiment of the present invention will be described below with reference to Figs. 1 to 17. First, a configuration of a gas sensor (oxygen sensor) 1 including a gas sensor element 100 manufactured by a manufacturing method for a gas sensor element according to this embodiment will be described. Fig. 1 is a cross-sectional view of the gas sensor 1 according to the first embodiment cut along the axis L direction, and Fig. 2 is an exploded perspective view showing a detection element portion 300 and a heater portion 200 which constitute the gas sensor element 100. In this specification, the lower side of the gas sensor 1 shown in Fig. 1 is referred to as the "front end side", and the opposite side (the upper side in Fig. 1) is referred to as the "rear end side".

[0024] 1, the gas sensor 1 includes a gas sensor element 100 formed of a laminate of a detection element portion 300 and a heater portion 200, a metal shell 30 that holds the gas sensor element 100 and the like in a manner that accommodates them therein, and a protector 24 that is attached to the tip of the metal shell 30. The gas sensor element 100 is generally in the form of an elongated plate (rod) and is disposed such that its longitudinal direction is aligned with the direction of the axis L. As will be described later, a porous protective layer 60 is formed on the tip side of the gas sensor element 100.

[0025] 2, the heater section 200 has an elongated plate shape overall, and includes a first base 101 and a second base 103 mainly made of alumina, and a heating element 102 mainly made of platinum and sandwiched between the first base 101 and the second base 103. The heating element 102 has a heating portion 102a located at the tip side, and a pair of heater lead portions 102b extending from the heating portion 102a along the longitudinal direction (axis L direction) of the first base 101. The ends of the heater lead portions 102b are electrically connected to the heater side pads 120 via conductors formed in heater side through holes 101a provided in the first base 101.

[0026] The detection element section 300, like the heater section 200, is generally in the shape of a long and thin plate, and includes an oxygen concentration detection cell 130 and an oxygen pump cell 140. The oxygen concentration detection cell 130 is composed of a first solid electrolyte body 105, and a first electrode 104 and a second electrode 106 formed on both sides of the first solid electrolyte body 105. The first electrode 104 is composed of a first electrode section 104a and a first lead section 104b extending from the first electrode section 104a along the longitudinal direction (axis L direction) of the first solid electrolyte body 105. The second electrode 106 is composed of a second electrode section 106a and a first lead section 104b extending from the second electrode section 106a along the longitudinal 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 longitudinal direction of the first solid electrolyte body 105 (the direction of the axis L).

[0027] An end of the first lead portion 104b is electrically connected to the detection element side pad 121 via conductors formed in a first through hole 105a provided in the first solid electrolyte body 105, a second through hole 107a provided in the insulating layer 107 described later, a fourth through hole 109a provided in the second solid electrolyte body 109, and a sixth through hole 111a provided in the protective layer 111. An end of the second lead portion 106b is electrically connected to the detection element side pad 121 via conductors formed in a third through hole 107b provided in the insulating layer 107 described later, a fifth through hole 1-9b provided in the second solid electrolyte body 109, and a seventh through hole 111b provided in the protective layer 111.

[0028] The oxygen pump cell 140 is composed of a second solid electrolyte body 109, and a third electrode 108 and a fourth electrode 110 formed on both sides 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.

[0029] An end of the third lead portion 108b is electrically connected to the detection element side pad 121 via a conductor formed in a fifth through hole 109b provided in the second solid electrolyte body 109 and a seventh through hole 111b provided in the protective layer 111. An end of the fourth lead portion 110b is electrically connected to the detection element side pad 121 via a conductor formed in an eighth through hole 111c provided in the protective layer 111. The second lead portion 106b and the third lead portion 108b are at the same potential.

[0030] The first solid electrolyte body 105 and the second solid electrolyte body 109 are made of zirconia (ZrO 2 ) with yttria (Y 2 O 3 ) or calcia (CaO) is added to form a partially stabilized zirconia sintered body.

[0031] The heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heater side pad 120, and the detection element side pad 121 can be formed of a platinum group element. Suitable platinum group elements for forming these include Pt, Ph, Pd, etc. These platinum group elements may be used alone or in combination of two or more kinds.

[0032] From the viewpoint of heat resistance and oxidation resistance, the heating element 102 etc. is preferably formed mainly of Pt. Also, the heating element 102 etc. preferably contains a ceramic component in addition to the platinum group element which is the main component. From the viewpoint of adhesion, this ceramic component is preferably the same component as the main material on the laminated side.

[0033] An insulating layer 107 is formed between the oxygen pump cell 140 and the oxygen concentration detection cell 130. The insulating layer 107 is composed of an insulating portion 114 and a diffusion resistance portion 115. A hollow measurement chamber 107c is formed in the insulating portion 114 of the insulating layer 107 at a position corresponding to the second electrode portion 106a and the third electrode portion 108a. The measurement chamber 107c communicates with the outside in the width direction of the insulating layer 107, and a diffusion resistance portion 115 that realizes gas diffusion between the outside and the measurement chamber 107c under a predetermined rate-controlling condition is disposed in the communicating portion.

[0034] The insulating portion 114 is not limited as long as it is a ceramic sintered body having insulating properties, and may be made of, for example, an oxide-based ceramic such as alumina or mullite.

[0035] The diffusion resistance portion 115 is a porous body made of alumina, and the speed at which the detection gas flows into the measurement chamber 107c is adjusted by the diffusion resistance portion 115 made of this porous body.

[0036] A protective layer 111 is formed on the surface of the second solid electrolyte body 109 so as to sandwich the fourth electrode 110. The protective layer 111 is composed of a porous electrode protective portion 113a for protecting the fourth electrode portion 110a from poisoning by sandwiching the fourth electrode portion 110a, and a reinforcing portion 112 for protecting the second solid electrolyte body 109 by sandwiching the fourth lead portion 110b. In the gas sensor element 100 of this embodiment, the direction and magnitude of the current flowing between the electrodes of the oxygen pump cell 140 are adjusted so that the voltage (electromotive force) generated between the electrodes of the oxygen concentration detection cell 130 becomes a predetermined value (for example, 450 mV), and the oxygen concentration in the measurement gas is linearly detected according to the current flowing through the oxygen pump cell 140.

[0037] Returning to FIG. 1, the metal shell 30 is made of SUS430 and includes a male thread portion 31 for mounting the gas sensor 1 to an exhaust pipe and a hexagonal portion 32 to which a mounting tool is applied during mounting. The metal shell 30 is also provided with a metal-side step portion 33 that protrudes radially inward, and the metal-side step portion 33 supports a metal holder 34 for holding the gas sensor element 100. Inside the metal holder 34, a ceramic holder 35 and talc 36 are arranged in this order from the front end. The talc 36 is composed of a first talc 37 arranged in the metal holder 34 and a second talc 38 arranged at the rear end of the metal holder 34. The first talc 37 is compressed and filled in the metal holder 34, thereby fixing the gas sensor element 100 to the metal holder 34. The second talc 38 is compressed and filled in the metal shell 30, thereby ensuring sealing between the outer surface of the gas sensor element 100 and the inner surface of the metal shell 30. An alumina sleeve 39 is disposed on the rear end side of the second talc 38. The sleeve 39 is formed in a multi-stage cylindrical shape and has an axial hole 39a formed along the axis L. The gas sensor element 100 is inserted into the sleeve 39 including the axial hole 39a. A crimped portion 30a on the rear end side of the metallic shell 30 is bent inward, and the sleeve 39 is pressed against the front end side of the metallic shell 30 via a stainless steel ring member 40 by the crimped portion 30a.

[0038] A metal protector 24 is attached by welding to the outer periphery of the front end side of the metal shell 30. The protector 24 has a double structure, with a cylindrical outer protector 41 with a uniform outer diameter arranged on the outside and a cylindrical inner protector 42 with a rear end 42a having an outer diameter larger than that of a front end 42b arranged on the inside. The protector 24 covers the front end of the gas sensor element 100 protruding from the front end of the metal shell 30 and has a plurality of gas intake holes 24a.

[0039] The front end side of an outer tube 25 made of SUS430 is inserted into the rear end side of the metal shell 30. The outer tube 25 has a front end portion 25a with an expanded diameter at the front end side, and the front end portion 25a is fixed to the metal shell 30 by laser welding or the like. A separator 50 is disposed inside the rear end side of the outer tube 25, and a holding member 51 is interposed in a gap formed between the separator 50 and the outer tube 25. The holding member 51 is fixed between the crimped outer tube 25 and the separator 50 while engaging with a protruding portion 50a that protrudes outward from the peripheral surface of the separator 50.

[0040] Further, the separator 50 is provided with a through hole 50b penetrating from the front end side to the rear end side for inserting various lead wires 11, 12, 13 for the detection element section 300 and the heater section 200. For convenience of explanation, only three lead wires 11, 12, 13 are shown in FIG. 1, and the other lead wires are omitted. A connection terminal 16 is accommodated in the through hole 50b for connecting the lead wires 11, etc. to the detection element side pad 121 of the detection element section 300 and the heater side pad 120 of the heater section 200. Each lead wire 11, etc. is configured to be connectable to a connector (not shown) on the outside, and input and output of electric signals are performed between an external device such as an ECU and each lead wire 11, etc. via such a connector.

[0041] Furthermore, a substantially cylindrical rubber cap 52 is disposed on the rear end side of the separator 50 to close the opening 25b on the rear end side of the outer tube 25. This rubber cap 52 is fixed to the outer tube 25 by crimping the outer tube 25 radially inward while being accommodated in the rear end of the outer tube 25. The rubber cap 52 is also provided with through holes 52a penetrating from the front end side to the rear end side for inserting the lead wires 11 and the like.

[0042] Fig. 3 is an enlarged view showing a schematic diagram of the tip side of the gas sensor element 100 shown in Fig. 1. As shown in Fig. 3, a porous protective layer 60 is formed on the tip side of the gas sensor element 100. In this specification, the gas sensor element 100 in a state in which the porous protective layer 60 is not formed is particularly referred to as a "gas sensor element main body (rod-shaped main body portion) 100a." Fig. 4 is an explanatory view showing the gas sensor element 100 as viewed from the tip side along the axis L direction.

[0043] The gas sensor element body 100a has a rod shape extending from front to rear, and is provided at its tip with a detection section 150 for detecting a specific gas component (oxygen, etc.) contained in exhaust gas. The detection section 150 is mainly composed of each electrode section (first electrode section 104a, second electrode section 106a, third electrode section 108a, and fourth electrode section 110a) of the detection element section 300, a measurement chamber 107c, and an electrode protection section 113a. FIG. 3 shows a porous electrode protection section 113a, which is a part of the detection section 150 and is formed so as to overlap with the fourth electrode section 110a in the thickness direction of the gas sensor element body 100a. A porous protection layer 60 is formed at the tip section 100b of the gas sensor element body 100a so as to cover the periphery of the detection section 150. The porous protection layer 60 has pores of a three-dimensional network structure so as to allow gas permeation.

[0044] As shown in FIG. 3, the porous protective layer 60 is formed on the front end portion 100b of the gas sensor element body 100a so as to cover a front end face 100c and a peripheral face 100d of the front end portion 100b of the gas sensor element body 100a.

[0045] The porous protective layer 60 can be formed by binding one or more ceramic particles selected from the group consisting of titania, alumina, spinel, zirconia, mullite, zircon, and cordierite by firing or the like. Pores can be formed between the ceramic particles by sintering a slurry containing these particles. Note that a burnable pore-forming material made of carbon, resin beads, organic or inorganic binder, or the like may be added to the slurry containing the above particles.

[0046] The porous protective layer 60 of this embodiment is a multi-layer type, and includes an inner porous protective layer 61 and an outer porous protective layer 62. Fig. 5 is a cross-sectional view taken along line AA in Fig. 3, and Fig. 6 is a cross-sectional view taken along line BB in Fig. 4. The inner porous protective layer 61 and the outer porous protective layer 62 are different in density, porosity (%), main components, etc. Specifically, the inner porous protective layer 61 has a structure with a lower density and a higher porosity (%) than the outer porous protective layer 62. The porosity of the inner porous protective layer 61 is, for example, 20 to 50%, and the porosity of the outer porous protective layer 62 is 10 to 20%.

[0047] The inner porous protective layer 61 is formed on the tip portion 100b of the gas sensor element body 100a so as to enclose the detection portion 150 therein.

[0048] The outer porous protective layer 62 is formed so as to overlap the inner porous protective layer 61 and to cover the tip portion 100b of the gas sensor element body 100a. Such an outer porous protective layer 62 is formed so as to enclose the inner porous protective layer 61. In particular, the outer porous protective layer 62 of this embodiment has a multi-layer structure and is formed through a plurality of dipping steps as described later.

[0049] The outer porous protective layer 62 comprises a first protective layer 63 formed around the entire circumference in at least the region R in the axial direction where the detection section 150 is provided, and a second protective layer 64 whose main component is the same as that of the first protective layer 63 and which is provided on the outside of the first protective layer 63 so that the rear end portion 63a of the first protective layer 63 is exposed, together with the region R in which the detection section 150 is provided in at least the axial direction L.

[0050] The "region R in which the detection section 150 is provided in the direction of the axis L" refers to a region of a minimum size in the direction of the axis L that includes each part constituting the detection section 150 (the first electrode section 104a, the second electrode section 106a, the third electrode section 108a, the fourth electrode section 110a, the measurement chamber 107c, and the electrode protection section 113a) when the gas sensor element body 100a is viewed in the thickness direction as shown in FIG.

[0051] Furthermore, between the first protective layer 63 and the second protective layer 64, "the main components are the same" means that the ceramic components constituting the first protective layer 63 are the same or are 90% or more the same as the ceramic components constituting the second protective layer 64.

[0052] The porosity of the first protective layer 63 and the porosity of the second protective layer 64 are approximately the same. The porosity of the first protective layer 63 and the porosity of the second protective layer 64 are lower than the porosity of the inner porous protective layer 61.

[0053] Since the rear end 63a of the first protective layer 63 is not covered with the second protective layer 64 and is exposed, the rear portion of the outer porous protective layer 62 is stepped by the end 63a of the first protective layer 63 and the end 64a of the second protective layer 64. Therefore, although the first protective layer 63 and the second protective layer 64 are integrated with each other in a sintered body state, the end 63a of the first protective layer 63 and the end 64a of the second protective layer 64 can be clearly distinguished. Therefore, even in the portion where the first protective layer 63 and the second protective layer 64 overlap each other, the boundary between the first protective layer 63 formed by the first coating film (first dry film) described later and the second protective layer 64 formed by the second coating film (second dry film) can be estimated from the thickness of the end 63a of the first protective layer 63 and the thickness of the end 64a of the second protective layer 64.

[0054] In addition, in each cross-sectional view of Figures 5 and 6, the boundary line between the first protective layer 63 and the second protective layer 64, which is inferred from the end 63a of the first protective layer 63 and the end 64a of the second protective layer 64, is virtually shown.

[0055] The gas sensor 1 described above uses the gas sensor element 100 manufactured by the manufacturing method of this embodiment.

[0056] Next, a method for manufacturing the gas sensor element according to the embodiment 1 will be described. Fig. 7 is a flow diagram showing the method for manufacturing the gas sensor element according to the present embodiment. As shown in Fig. 7, the method for manufacturing the gas sensor element according to the present embodiment includes a first immersion step S101, a first thickness adjustment step S102, a first drying step S103, a second immersion step S104, a second thickness adjustment step S105, a second drying step S106, and a firing step S107.

[0057] The first immersion step S101 is an immersion step for forming the first protective layer 63 of the outer porous protective layer 62. Specifically, the first immersion step S101 is a step for immersing the tip portion 100b of the gas sensor element body 100a (gas sensor element 100) in a first slurry S1 to form a first coating film made of the first slurry on the tip portion 100b so as to encapsulate the detection portion 150.

[0058] The first slurry S1 is a slurry for forming the first protective layer 63, and for example, a slurry for forming an outer porous protective layer in a conventional gas sensor element is used as the first slurry S1. The first slurry S1 is obtained by mixing, for example, titania powder, spinel powder, alumina sol, an organic binder (for example, an acrylic copolymer), a dispersant (for example, an anionic polymer dispersant), an antifoaming agent (for example, an amide wax-based antifoaming agent), and water in a predetermined ratio, and mixing them for a predetermined time.

[0059] FIG. 8 is an explanatory diagram showing a state in which the gas sensor element body 100a is waiting above the dipping tank 400 in the first immersion step S101. FIG. 8 shows the container-shaped dipping tank 400 that is open upward and contains the first slurry S1, and the gas sensor element body 100a that is waiting in a stationary state above the dipping tank 400. The gas sensor element body 100a is fixed using a predetermined jig (not shown) with its longitudinal direction (axis L direction) aligned vertically and its tip portion 100b facing downward. The tip portion 100b of the gas sensor element body 100a faces the first slurry S1 contained in the dipping tank 400. In FIG. 8, the surface of the gas sensor element body 100a on the side where the electrode protection portion 113a, which is a part of the detection portion 150, is formed is shown facing the front side of the paper.

[0060] As shown in FIG. 8, the inner dry film 610 for forming the inner porous protective layer 61 is formed in advance on the tip portion 100b of the gas sensor element body 100a to be immersed in the first slurry S1 so as to enclose the detection portion 150. The inner dry film 610 is formed by drying an inner coating film made of the slurry formed by immersing the tip portion 100b of the gas sensor element body 100a in the slurry for forming the inner porous protective layer 61. In the first immersion step S101, a first coating film 630 made of the first slurry S1 is formed so as to cover the inner dry film 610 of the tip portion 100b. As shown in FIG. 8, the position where the gas sensor element body 100a is stationary above the dipping tank 400 is referred to as a "standby position".

[0061] The gas sensor element body 100a is configured to be movable up and down (vertical direction) between a standby position and a position (a dipping position to be described later) inside the dipping tank 400 located below the standby position while being fixed to a predetermined jig. There are no particular limitations on the mechanism for moving the gas sensor element body 100a back and forth as long as it does not impair the object of the present invention, and a known reciprocating mechanism using a servo motor or the like is applied.

[0062] As shown in FIG. 8, a leveling die 500 and a leveling blade 600 are disposed between the gas sensor element body 100a at the standby position and the dipping tank 400 to be used in the first thickness adjustment step (first leveling step) performed after the first immersion step. The leveling die 500 includes a plate-shaped leveling body 501 disposed along the horizontal direction, a through hole 502 provided inside the leveling body 501 in a manner penetrating in the thickness direction, and an opening edge 503 surrounding the through hole 502. The sizes of the through hole 502 and the opening edge 503 are set so that the gas sensor element body 100a on which the inner dry film 610 is formed can pass through the through hole 502 located in the opening edge 503. At the standby position, the tip 100b of the gas sensor element body 100a on which the inner dry film 610 is formed is disposed so as to be contained inside the opening edge 503 when viewed in a plan view.

[0063] 8, the scraping blade 600 is retracted to a position outside the through-hole 502 so as not to overlap with the through-hole 502 in the vertical direction, and this position is referred to as the "retracted position" of the scraping blade 600. In this embodiment, the scraping blade 600 is disposed on the upper surface 500a side of the scraping die 500. The scraping blade 600 is disposed at a height position such that a gap is formed between the scraping blade 600 and the upper surface 500a of the scraping die 500.

[0064] 9 is an explanatory diagram showing a state in which the tip portion 100b of the gas sensor element body 100a, which has been lowered from the standby position, is immersed in the first slurry S1 in the dipping tank 400 in the first immersion step S101. When the gas sensor element body 100a (see FIG. 8) waiting at the standby position moves downward, the tip portion 100b on which the inner dry film 610 is formed passes through the through hole 502 in the opening edge portion 503 of the scraping mold 500 from the upper side to the lower side. At that time, the tip portion 100b on which the inner dry film 610 is formed passes through the through hole 502 without coming into contact with the opening edge portion 503. Thereafter, the gas sensor element body 100a further moves downward, and the tip portion 100b is immersed in the first slurry S1 contained in the dipping tank 400. The height position of the tip portion 100b immersed in the first slurry S1 is set so that the tip portion 100b does not come into contact with the bottom of the dipping tank 400 and the first slurry S1 covers the inner dry film 610 formed on the tip portion 100b. More specifically, the height position of the tip portion 100b immersed in the first slurry S1 is set so that the first slurry S1 covers an area R1 between the tip surface 100c of the gas sensor element body (rod-shaped body portion) 100a and a first reference position M1, which is a position from the rear end of the detection portion 150 toward the rear end side of the gas sensor element body 100a (i.e., the upper side in FIG. 9) by a predetermined first length L1 in the axial direction L. The position of the gas sensor element body 100a thus set is referred to as the "first immersion position". The gas sensor element body 100a may be stationary at the first immersion position for a predetermined time as necessary, or may be immediately pulled up after reaching the first immersion position. In FIG. 9, the position corresponding to the tip end surface 100c in the direction of the axis L is indicated by the symbol M0.

[0065] By such a first immersion process S101, the tip portion 100b of the gas sensor element body 100a is immersed in the first slurry S1, so that a first coating film 630 made of the first slurry S1 is formed so as to encapsulate the detection portion 150 and the inner dry film 610.

[0066] Such a first coating film 630 is formed so as to cover an area R1 between the tip surface 100c of the gas sensor element body (rod-shaped body portion) 100a and a first reference position M1, which is a position a predetermined first length L1 away from the detection portion 150 toward the rear end side of the gas sensor element body 100a, in the direction of the axis L. The "first length L1" is determined based on the range in which at least the porous protective layer 60 needs to be formed for the purpose of ensuring water resistance, etc., within the range from the rear end of the detection portion 150 toward the rear end side of the gas sensor element body 100a in the longitudinal direction (direction of the axis L) of the gas sensor element body 100a.

[0067] The tip portion 100b of the gas sensor element body 100a immersed in the first slurry S1 is then pulled up and subjected to the next first thickness adjusting step S102.

[0068] The first thickness adjustment step S102 is a step of adjusting the thickness of the first coating film 630 by scraping off the first coating film 630 made of the first slurry S1 adhering to the tip portion 100b of the gas sensor element body 100a and removing a part of the first coating film 630. As described above, after the first immersion step S101, when the tip portion 100b of the gas sensor element body 100a is pulled up from the first slurry S1, the first coating film 630 made of the adhering matter of the first slurry S1 is formed on the tip portion 100b. Then, after the first immersion step S101, if the thickness of the first coating film 630 formed on the tip portion 100b exceeds the thickness required for the first protective layer 63 (outer porous protective layer 62), the excess coating film is removed in the first thickness adjustment step S102.

[0069] In this specification, of the first coating film 630 attached to the tip portion 100b after the first immersion step S101, the coating film formed on the peripheral surface 100d of the tip portion 100b is referred to as the "first peripheral surface coating film 631," and the coating film formed on the tip surface 100c of the tip portion 100b is referred to as the "first tip coating film 632." In this specification, the coating film located further forward than the tip surface 100c of the tip portion 100b in the axis L direction is referred to as the first tip coating film 632.

[0070] The first thickness adjustment process S102 of this embodiment includes a process of removing a part (excessive coating film) 631a of the first peripheral surface coating film 631 formed on the peripheral surface 100d of the tip portion 100b, out of the first coating film 630 attached to the tip portion 100b, using the scraping mold 500 (peripheral surface scraping process), and a process of removing a part (excessive coating film) 632a of the first tip coating film 632 formed on the tip surface 100c of the tip portion 100b, using the scraping blade 600 (tip surface scraping process). In this embodiment, the peripheral surface scraping process is performed first, and then the tip surface scraping process is performed.

[0071] Fig. 10 is an explanatory diagram showing how a part (excess coating) 631a of the first peripheral surface coating 631 formed on the peripheral surface 100d of the tip portion 100b of the gas sensor element body 100a is removed by using the scraping mold 500 in the first thickness adjusting step S102. Fig. 10 shows the content of the peripheral surface scraping step described above. If the first peripheral surface coating 631 of a thickness exceeding the required thickness is attached to the tip portion 100b of the gas sensor element body 100a that has been pulled up after the first immersion step S101, the excess coating (excess coating) 631a is scraped off by the opening edge portion 503 when the tip portion 100b passes through the opening edge portion 503 of the scraping mold 500 (through hole 502) from the bottom to the top. In this manner, when the tip portion 100b passes through the opening edge portion 503, the excess coating film 631a is separated from the first peripheral surface coating film 631 of the required thickness.

[0072] A part of the separated excess coating film 631a falls due to its own weight or the like and is returned to the dipping tank 400. The scraping mold 500 is, for example, made of a metal plate material processed into a predetermined shape. The size of the opening edge portion 503 (the size of the through hole 502) of the scraping mold 500 is set so that the tip portion 100b of the gas sensor element body 100a on which the inner dry film 610 is formed can pass through, as described above, and the first coating film 630 (first peripheral coating film 631) having a thickness necessary for forming the first protective layer 63 of the outer porous protective layer 62 is formed around the inner dry film 610 of the tip portion 100b after the peripheral scraping process. In this embodiment, the opening edge portion 503 has a rectangular shape in a plan view and is fixed using a fixing device not shown. The longitudinal direction (long side direction) of the opening edge portion 503 is arranged along the short side direction (width direction) of the gas sensor element body 100a, and the short side direction (short side direction) of the opening edge portion 503 is arranged along the thickness direction of the gas sensor element body 100a.

[0073] FIG. 11 is an explanatory diagram showing how a part (excessive coating) 632a of the first tip coating 632 formed on the tip surface 100c of the gas sensor element body 100a is removed using the scraping blade 600 in the first thickness adjustment step S102. FIG. 11 shows the contents of the tip surface scraping step described above. After the peripheral surface scraping step, the gas sensor element body 100a that has passed from the bottom to the top inside the opening edge portion 503 of the scraping mold 500 moves upward so that the position of the tip surface 100c of the tip portion 100b is at a predetermined height position determined in advance for the tip surface scraping step. The predetermined height position of the tip surface 100c for the tip surface scraping step is set so that the thickness of the first tip coating 632 formed on the tip surface 100c becomes a thickness required for the first protective layer 63 of the outer porous protective layer 62 after the tip surface scraping step. In the present embodiment, the height position of the tip surface 100c when the tip surface scraping process is performed is set to be the same as the height position of the tip surface 100c of the gas sensor element body 100a stopped at the standby position described above. In other embodiments, the height position of the tip surface 100c when the tip surface scraping process is performed may be different from the height position of the tip surface 100c of the gas sensor element body 100a stopped at the standby position.

[0074] 11 shows the gas sensor element body 100a in a stationary state at the standby position. In this state, a first coating film 630 including a first peripheral surface coating film 631 in which an excess coating film 631a has been removed and the thickness has been adjusted is formed on the tip portion 100b of the gas sensor element body 100a. If a first tip coating film 632 formed on the tip surface 100c of such a first coating film 630 exceeds a required thickness, the excess coating film (excess coating film 632a) is scraped off by the scraping blade 600.

[0075] The scraping blade 600 is made of, for example, a metal plate material processed into a predetermined shape. The scraping blade 600 is configured by using a known reciprocating mechanism or the like so that the tip 601 can reciprocate along the horizontal direction. In the first thickness adjustment step S102, the height position of the tip 601 of the scraping blade 600 and the height position of the tip 100b of the gas sensor element body 100a are set so that the first tip coating film 632 of a required thickness is left on the tip surface 100c. In FIG. 11 and the like, the gas sensor element body 100a is arranged so that its longitudinal direction is along the vertical direction (up and down direction). The axis L direction of such a gas sensor element body 100a is in a state along the vertical direction. Therefore, it can be said that the scraping blade 600 moves along a direction perpendicular to the axis L direction of the gas sensor element body 100a.

[0076] During the first immersion step and the peripheral surface scraping step, the scraping blade 600 remains stationary at the retreated position as shown in FIG. 8 and the like. When the gas sensor element body 100a is returned to the standby position after the peripheral surface scraping step and remains stationary, the scraping blade 600 moves horizontally to scrape off the excess coating film 632a of the first tip coating film 632. The tip 601 of the scraping blade 600 moves horizontally from the retreated position toward the gas sensor element body 100a, and further moves horizontally above the opening edge 503 to cross the opening edge 503 in the longitudinal direction. When the scraping blade 600 moves horizontally to cross the opening edge 503, the tip 601 scrapes off the excess coating film 632a that exceeds the required thickness from the first tip coating film 632 of the required thickness. In this way, if the first tip coating film 632 formed on the tip surface 100c exceeds the required thickness, the excess coating film (excess coating film 632a) is scraped off by the scraping blade 600. After scraping off the excess coating film of the first tip coating film 632, the scraping blade 600 moves horizontally in the opposite direction to that during scraping so as to return to the retracted position.

[0077] By undergoing the above-described first thickness adjusting step S102, the thickness of the first coating film 630 formed on the tip portion 100b of the gas sensor element body 100a is adjusted.

[0078] After the first thickness adjusting step S102, the first coating film 630 formed on the tip portion 100b of the gas sensor element body 100a is dried in a first drying step S103 to become a first dry film 633. The first drying step S103 is a step of drying the first coating film 630 to form the first dry film 633 on the tip portion 100b of the gas sensor element body 100a.

[0079] The first drying step S103 is performed, for example, by placing the gas sensor element body 100a in a heating tank and heating it at a temperature condition of 80°C to 120°C for 1 to 5 minutes. FIG. 12 is an explanatory diagram that shows a schematic view of the front end side of the gas sensor element body 100a after the first drying step S103. As shown in FIG. 12, a first dry film 633 is formed on the front end portion 100b of the gas sensor element body 100a. The first dry film 633 is formed so as to cover a region R1 between the front end surface 100c of the gas sensor element body (rod-shaped main body portion) 100a and a first reference position M1, which is a position that is a predetermined first length L1 away from the rear end of the detection portion 150 toward the rear end side of the gas sensor element body 100a (i.e., the upper side of FIG. 12) in the axial direction L. In FIG. 12, the position corresponding to the front end surface 100c in the axial direction L is indicated by the symbol M0. FIG. 12 also shows the rear end 633a of the first dry film 633 at the first reference position M1.

[0080] Subsequently, as shown in Fig. 7, after the first drying step S103, the second immersion step S104 is performed. Fig. 13 is an explanatory diagram showing the content of the second immersion step S104. The second immersion step S104 is an immersion step for forming the second protective layer 64 of the outer porous protective layer 62. Specifically, the second immersion step S104 is a step of immersing the tip portion 100b of the gas sensor element body 100a (gas sensor element 100) on which the first dry film 633 is formed, into the second slurry S2, and forming a second coating film 640 made of the second slurry S2 on the first dry film 633 so that the rear end portion 633a of the first dry film 633 is exposed and the detection portion 150 is enclosed therein.

[0081] The second immersion step S104 of this embodiment is performed by using another dipping tank 400A prepared separately from the dipping tank 400 used in the first immersion step S101. The basic configuration of the dipping tank 400A is the same as that of the dipping tank 400. The second slurry S2 contained in the dipping tank 400A is a slurry for forming the second protective layer 64, and is composed of "the same slurry as the first slurry S1" or "a slurry containing the same type of dispersoid as the main component of the first slurry S1."

[0082] When the same slurry as the first slurry S1 is used as the second slurry S2, the first slurry S1 to be used as the second slurry S2 is prepared separately from the first slurry S1 used in the first immersion step S101.

[0083] In addition, in this specification, "a slurry containing the same type of dispersoid as the main component of the first slurry S1" means a slurry containing dispersoids that are the same or 90% or more the same as the substances (dispersoids) dispersed in the dispersion medium (water) among the components constituting the first slurry S1.

[0084] The dispersion medium used in the second slurry S2 is preferably the same type as the dispersion medium used in the first slurry S2.

[0085] 13 is an explanatory diagram showing a state in which the tip portion 100b of the gas sensor element body 100a, which has been lowered from the standby position, is immersed in the second slurry S2 in the dipping tank 400A in the second immersion step S104. Before the second immersion step S104 is started, the gas sensor element body 100a is waiting at a standby position above the dipping tank 400A, as in the first immersion step S101. At this time, the gas sensor element body 100a is fixed using a predetermined jig (not shown) along its longitudinal direction (axis L direction) with its tip portion 100b facing downward.

[0086] 13, when the second immersion step S104 is started, the gas sensor element body 100a moves downward and passes through the through hole 502A in the opening edge portion 503A of the scraping mold 500A used in the second thickness adjustment step S105 described later from the top to the bottom. At that time, the tip portion 100b on which the first dry film 633 is formed passes through the through hole 502A without coming into contact with the opening edge portion 503A. Thereafter, the gas sensor element body 100a moves further downward, and the tip portion 100b is immersed in the second slurry S2 contained in the dipping tank 400A. The height position of the tip portion 100b immersed in the second slurry S2 is set so that the tip portion 100b does not contact the bottom of the dipping tank 400A, the rear end portion 633a of the first dry film 633 is exposed, and the second coating film 640 made of the second slurry S2 is formed on the first dry film 633 so as to enclose the detection portion 150. More specifically, the height position of the tip portion 100b immersed in the second slurry S2 is set so that the second slurry S2 covers a region R2 between the tip surface 100c of the gas sensor element body (rod-shaped body portion) 100a and the second reference position M2, which is a position from the rear end of the detection portion 150 toward the rear end side of the gas sensor element body 100a (i.e., the upper side of FIG. 13) by a second length L2 shorter than the first length L1 described above, in the axial direction L. The position of the gas sensor element body 100a set in this manner is referred to as the "second immersion position." The gas sensor element body 100a may be kept stationary at the second immersion position for a predetermined time, or may be pulled up immediately after reaching the second immersion position, as required. In Fig. 13, the position corresponding to the tip end surface 100c in the direction of the axis L is indicated by the symbol M0.

[0087] In the second immersion step S104, similarly to the first immersion step S101, the gas sensor element body 100a is configured to be able to reciprocate between a standby position and a position (second immersion position) inside the dipping tank 400A located therebelow.

[0088] As shown in FIG. 13, a leveling mold 500A and a leveling blade 600A to be used in a second thickness adjusting step (second leveling step) performed after the second immersion step are disposed at a predetermined position above the dipping tank 400A.

[0089] By the second immersion process S104 as described above, the tip portion 100b of the gas sensor element body 100a is immersed in the second slurry S2, so that the rear end portion 633a of the first dry film 633 is exposed and a second coating film 640 made of the second slurry S2 is formed on the first dry film 633 so as to encapsulate the detection portion 150.

[0090] Such a second coating 640 is formed so as to cover a region R2 between the tip end surface 100c of the gas sensor element body (rod-shaped body portion) 100a and a second reference position M2, which is a position away from the rear end of the detection portion 150 toward the rear end side of the gas sensor element body 100a by a second length L2 that is shorter than the above-mentioned first length L1, in the direction of the axis L. The "second length L2" is determined based on the range from the rear end of the detection portion 150 toward the rear end side of the gas sensor element body 100a in the longitudinal direction (direction of the axis L) of the gas sensor element body 100a, where water resistance is particularly required.

[0091] The second coating 640 is formed so as to cover a portion of the tip portion 100b that will become hotter than the portion where the end portion 633a of the first dry film 633 is formed when the gas sensor element 100 is in use.

[0092] In the second immersion step S104, the tip portion 100b of the gas sensor element body 100a immersed in the second slurry S2 is then pulled up and subjected to the next second thickness adjustment step S105.

[0093] The second thickness adjustment step S105 is a step of scraping off the second coating film 640 made of the second slurry S2 attached to the tip portion 100b of the gas sensor element body 100a, thereby removing a part of the second coating film 640, thereby adjusting the thickness of the second coating film 640. If the thickness of the second coating film 640 formed on the tip portion 100b after the second immersion step S104 exceeds the thickness required for the second protective layer 64 (outer porous protective layer 62), the excess part of the coating film is removed in the second thickness adjustment step S105.

[0094] In this specification, of the second coating film 640 attached to the tip portion 100b after the second immersion step S104, the coating film formed on the peripheral surface 100d of the tip portion 100b is referred to as the "second peripheral surface coating film 641," and the coating film formed on the tip surface 100c of the tip portion 100b is referred to as the "second tip coating film 642." In this specification, the coating film located further forward than the tip surface 100c of the tip portion 100b in the axis L direction is referred to as the second tip coating film 642.

[0095] The second thickness adjustment process S105 of this embodiment, like the first thickness adjustment process S102 described above, includes a process of removing a portion (excess coating) 631a of the second peripheral surface coating 641 formed on the peripheral surface 100d of the tip portion 100b, of the second coating film 640 adhering to the tip portion 100b, using the scraping mold 500A (peripheral surface scraping process), and a process of removing a portion (excess coating) of the second tip coating 642 formed on the tip surface 100c of the tip portion 100b, using the scraping blade 600A (tip surface scraping process).

[0096] The basic configuration of the leveling mold 500A is the same as that of the leveling mold 500 in the first thickness adjustment process described above, and comprises a plate-shaped leveling main body 501A arranged along the horizontal direction, a through hole 502A provided inside this leveling main body 501A and penetrating in the thickness direction, and an opening edge portion 503A surrounding this through hole 502A.

[0097] The basic configuration of the rasp blade 600A is also the same as that of the rasp blade 600 in the first thickness adjustment step described above. As shown in Fig. 13, the rasp blade 600A is retracted to a position outside the through hole 502A so as not to overlap with the through hole 502A in the vertical direction. The rasp blade 600A is also disposed on the upper surface 500Aa side of the rasp mold 500A.

[0098] Fig. 14 is an explanatory diagram showing how a part (excess coating) 641a of the second peripheral surface coating 641 formed on the peripheral surface 100d of the tip portion 100b of the gas sensor element body 100a is removed by using the scraping mold 500A in the second thickness adjustment step S105. Fig. 14 shows the content of the peripheral surface scraping step in the second thickness adjustment step S105. If the second peripheral surface coating 641 of a thickness exceeding the required thickness is attached to the tip portion 100b of the gas sensor element body 100a that is pulled up after the second immersion step S104, the excess coating (excess coating) 641a is scraped off by the opening edge portion 503A when the tip portion 100b passes through the opening edge portion 503A (through hole 502A) of the scraping mold 500A from the bottom to the top. In this manner, when the tip portion 100b passes through the opening edge portion 503A, the excess coating film 641a is separated from the second peripheral surface coating film 641 of the required thickness.

[0099] The size of the opening edge 503A of the scraping mold 500A (the size of the through hole 502A) is set so that the tip portion 100b of the gas sensor element body 100a can pass through it when it descends from the waiting position in the second immersion process S104, and so that a second coating film 640 (second peripheral coating film 641) of a thickness required to form the second protective layer 64 is formed around the first dry film 633 of the tip portion 100b when the gas sensor element body 100a is pulled up from the second slurry S2.

[0100] Thereafter, the gas sensor element body 100a is pulled further upward, and a part of the second tip coating film 642 formed on the tip surface 100c is removed using the scraping blade 600A. The method of adjusting the thickness of the second tip coating film 642 using the scraping blade 600A is basically the same as the method of adjusting the thickness of the first tip coating film 632 using the scraping blade 600 in the first thickness adjustment step. The scraping blade 600A is configured using a known reciprocating mechanism or the like so that the tip portion 601A can reciprocate along the horizontal direction.

[0101] Fig. 15 is an enlarged longitudinal sectional view of the gas sensor element body 100a near the tip portion 100b after the second thickness adjustment process. As shown in Fig. 15, a first dry film 633 is formed so as to cover the inner dry film 613 formed on the tip portion 100b. Then, a second coating film 640 is formed so as to be superimposed on the first dry film 633. As described above, the rear end 633a of the first dry film 633 is not covered with the second coating film 640, and protrudes from the end 640a of the second coating film 640 toward the rear end side of the gas sensor element body 100a.

[0102] In this way, when the second coating film 640 is formed on the first dry film 633, the air bubbles present in the first dry film 633 move toward the second coating film 640, and the bubbles are prevented from bursting so as to break through the second coating film 640. This is because, even if some of the moisture contained in the second coating film 640 moves so as to soak into the first dry film 633 (see the arrow indicated by the reference numeral 70), the air bubbles present in the first dry film 633 move toward the rear end 633a of the first dry film 633 and are released from the end 633a to the outside. Since the rear end 633a of the first dry film 633 is not covered with the second coating film 640, the end 633a of the first dry film 633 can function as an "exit" for the air bubbles generated in the first dry film 633.

[0103] After the second thickness adjustment step, a second drying step S106 is performed as shown in Fig. 7. The second drying step is a step of drying the second coating film 640 to form a second dry film 643 on the first dry film 633 so that the end portion 633a is exposed. Through this second drying step S106, the second coating film 640 is dried to become the second dry film 643.

[0104] The second drying step S106 is performed, for example, by placing the gas sensor element body 100a in a heating tank and heating it at a temperature of 80 to 120° C. for 1 to 5 minutes, as in the first drying step S103 described above. FIG. 16 is an explanatory diagram that shows a schematic view of the front end side of the gas sensor element body 100a after the second drying step S106. As shown in FIG. 16, a second dry film 643 is formed on the front end portion 100b of the gas sensor element body 100a. In the axial direction L (longitudinal direction), the second dry film 643 is formed so as to cover a region R2 between the front end surface 100c of the gas sensor element body (rod-shaped main body portion) 100a and a second reference position M2, which is a position from the rear end of the detection portion 150 toward the rear end side of the gas sensor element body 100a by a second length L2 that is shorter than the first length l1 described above. In FIG. 16, the position corresponding to the front end surface 100c in the axial direction L is indicated by the symbol M0. In addition, in FIG. 16, the rear end 643a of the second dry film 643 is shown at the second reference position M2, and the rear end 633a of the first dry film 633 is shown at the first reference position M1.

[0105] Fig. 17 is a longitudinal sectional view of the gas sensor element body 100a after the second drying step S106 shown in Fig. 16. Fig. 17 shows a schematic cross-sectional configuration of the gas sensor element body 100a cut along the axis L direction. In the longitudinal direction (axis L direction), a range Ha from the tip surface 100c (position M0) of the gas sensor element body 100a to the second reference position M2 has a higher temperature due to heat generation by the heater section 200 when the gas sensor 1 is used, compared with a range Hb from the second reference position M2 to the first reference position M1. A second coating film 640 (second dry film 643) for forming the second protective layer 64 of the gas sensor 1 is formed so as to cover such a range Ha.

[0106] 7, the second drying step S106 is followed by the firing step S107. The firing step S107 is a step of firing the first dry film 633 and the second dry film 643 to form a sintered body of the first dry film 633 and the second dry film 643 constituting the porous protective layer 60 at the tip portion 100b. The firing temperature, firing time, and other conditions in the firing step are not particularly limited as long as the first dry film 633, the second dry film 643, and the like are sintered to obtain the porous protective layer 60, and are appropriately set according to the purpose. The firing step is performed, for example, at 1080° C. for 3 hours.

[0107] Through this firing step S107, the first dry film 633 becomes the first protective layer 63 after firing, and the second dry film 643 becomes the second protective layer 64 after firing. That is, through firing the first dry film 633 and the second dry film 643, an outer porous protective layer 62 consisting of the first protective layer 63 and the second protective layer 64 is formed. Through the firing step S107, the inner dry film 613 becomes the inner porous protective layer 61 after firing (see FIGS. 3 to 6).

[0108] As described above, in the manufacturing method of the gas sensor element of this embodiment, the gas sensor element 100 having the porous protective layer 60 formed on the tip portion 100b of the gas sensor element body 100a is obtained through the first immersion process S101, the first thickness adjustment process S102, the first drying process S103, the second immersion process S104, the second thickness adjustment process S105, the second drying process S106 and the firing process S107.

[0109] In particular, in the manufacturing method of the gas sensor element of this embodiment, when forming the second coating film 640 in the second immersion step S104, the second coating film 640 is formed on the first dry film 633 so that the rear end portion 633a of the first dry film 633 is exposed, thereby obtaining a gas sensor element 100 having a porous protective layer 60 with excellent water resistance and in which defects caused by air bubbles are suppressed.

[0110] <Other embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention.

[0111] (1) In the above-mentioned embodiment 1, the porous protective layer formed on the tip portion of the gas sensor element body includes an inner porous protective layer. However, as long as the object of the present invention is not impaired, for example, in other embodiments, the first coating film may be formed directly on the tip portion of the gas sensor element body.

[0112] (2) In the above-mentioned embodiment 1, in the first immersion step, the first coating film is formed on the tip portion of the gas sensor element body by a single dipping (immersion step). However, as long as the object of the present invention is not impaired, for example, in other embodiments, in the first immersion step, the tip portion of the gas sensor element body may be immersed in the first slurry multiple times for the purpose of ensuring the thickness of the first coating film, etc.

[0113] (3) In the above-mentioned embodiment 1, in the second immersion step, the second coating film is formed on the tip portion of the gas sensor element body by a single dipping (immersion step). However, as long as the object of the present invention is not impaired, for example, in other embodiments, in the second immersion step, the tip portion of the gas sensor element body may be immersed in the second slurry multiple times for the purpose of ensuring the thickness of the second coating film, etc. [Explanation of symbols]

[0114] 1...gas sensor, 60...porous protective layer, 61...inner porous protective layer, 62...outer porous protective layer, 63...first protective layer, 63a...end, 64...second protective layer, 100...gas sensor element, 100a...gas sensor element main body (rod-shaped main body), 100b...tip, 150...detection section, 630...first coating film, 633...first dried film, 633a...end, 640...second coating film, 643...second dried film, S1...first slurry, S2...second slurry, S101...first immersion step, S103...first drying step, S104...second immersion step, S106...second drying step, S107...firing step

Claims

1. A method for manufacturing a gas sensor element comprising a rod-shaped body portion extending from front to back and including a detection portion at a tip end thereof for detecting a specific gas component, and a porous protective layer covering the tip end, comprising: a first dipping step of dipping the tip portion into a first slurry to form a first coating film made of the first slurry on the tip portion so as to encapsulate the detection portion; a first drying step of drying the first coating film to form a first dry film on the tip portion; a second immersion step of immersing the tip portion on which the first dry film is formed in a second slurry that is the same as the first slurry, to form a second coating film made of the second slurry on the first dry film so that a rear end of the first dry film is exposed and the detection unit is enclosed therein; a second drying step of drying the second coating film to form a second dry film on the first dry film so that the end portion is exposed; and a firing step of firing the first dry film and the second dry film to form a sintered body of the first dry film and the second dry film that constitute the porous protective layer at the tip portion.

2. In the first immersion step, the first coating film is formed so as to cover an area between a tip surface of the rod-shaped main body and a first reference position that is a predetermined first length away from the detection unit toward a rear end side of the rod-shaped main body, 2. The method for manufacturing a gas sensor element according to claim 1, wherein in the second immersion step, the second coating film is formed so as to cover an area between the tip surface and a second reference position that is spaced from the detection portion by a second length that is shorter than the first length toward a rear end side of the rod-shaped main body.

3. 3. The method for manufacturing a gas sensor element according to claim 1, wherein in the second immersion step, the second coating film is formed so as to cover a portion of the tip portion that will have a higher temperature than a portion of the end portion when the gas sensor element is used.

4. the porous protective layer has an outer porous protective layer made of the sintered body of the first dry film and the second dry film, and an inner porous protective layer interposed between the outer porous protective layer and the tip portion and formed on the tip portion so as to enclose the detection portion; 4. The method for manufacturing a gas sensor element according to claim 1, wherein in the first immersion step, an inner dry film for forming the inner porous protective layer is pre-formed on the tip portion immersed in the first slurry so as to enclose the detection portion, and the first coating film made of the first slurry is formed so as to cover the inner dry film of the tip portion.

5. 5. The method for manufacturing a gas sensor element according to claim 1, further comprising a first thickness adjusting step of removing a part of the first coating film to adjust a thickness of the first coating film before the first drying step.

6. 6. The method for manufacturing a gas sensor element according to claim 1, further comprising a second thickness adjusting step of removing a part of the second coating film to adjust a thickness of the second coating film before the second drying step.

7. A gas sensor element comprising a rod-shaped body portion extending from front to back and including a detection portion at a tip end thereof for detecting a specific gas component, and a porous protective layer covering the tip end, the porous protective layer includes a first protective layer formed around the entire circumference at least in the axial direction in a region where the detection unit is provided, and a second protective layer whose main component is the same as that of the first protective layer, which is provided at least in the axial direction in a region where the detection unit is provided, and which is provided outside the first protective layer so that a rear end of the first protective layer is exposed; The gas sensor element, wherein the porosity of the first protective layer and the porosity of the second protective layer are approximately the same.

8. the first protective layer is formed so as to cover an area between a tip surface of the rod-shaped main body and a first reference position that is a predetermined first length away from the detection unit toward a rear end side of the rod-shaped main body, 8. The gas sensor element according to claim 7, wherein the second protective layer is formed so as to cover an area between the tip surface and a second reference position that is spaced from the detection portion by a second length that is shorter than the first length toward a rear end side of the rod-shaped main body.

9. 9. The gas sensor element according to claim 7, wherein the second protective layer covers a portion of the tip portion that becomes hotter than a portion where the end portion is formed during use.

10. 10. The gas sensor element according to claim 7, wherein the porous protective layer comprises an outer porous protective layer including the first protective layer and the second protective layer, and an inner porous protective layer interposed between the outer porous protective layer and the tip portion and formed on the tip portion so as to encapsulate the detection portion.

11. A gas sensor comprising the gas sensor element according to any one of claims 7 to 10.

Images