Gas sensor

Abstract

Provided is a gas sensor that, in a configuration in which a filter is disposed between an outer cylinder and a protective outer cylinder, can inhibit the gas permeation hole of the protective outer cylinder from being clogged by foreign matter and stably introduce external gas to the internal sensor element via the filter. A gas sensor (1) includes: a sensor element; an outer cylinder that is cylindrical, has a first gas permeation hole that introduces external gas to the inside of the outer cylinder; a filter that is disposed on the radial outside of the outer cylinder in a manner that clogs the first gas permeation hole and has gas permeability; and a protective outer cylinder that is cylindrical, surrounds the filter from the radial outside, and has a second gas permeation hole that communicates with the first gas permeation hole via the filter. A gap is provided between the outer surface of the filter and the inner surface of the protective outer cylinder that surrounds the second gas permeation hole. The area of the gap in a cross section that passes through the second gas permeation hole in the axial direction is more than half the opening area of the second gas permeation hole that is located on the cross section and directly opposes the gap.

Description

TECHNICAL FIELD

[0001] The present application relates to a gas sensor provided with a sensor element exposed to a detected gas and detecting a specific gas component therein. BACKGROUND

[0002] As a gas sensor that performs fuel consumption rate improvement and combustion control of an internal combustion engine such as an automobile engine, an oxygen sensor that detects an oxygen concentration in exhaust gas, and an air-fuel ratio sensor are known.

[0003] The detection unit of the sensor element has a reference electrode exposed to an external gas that is a reference of the oxygen concentration, and a detection electrode exposed to the detected gas, and it is necessary to introduce the external gas to the sensor element housed inside the outer cylinder. Therefore, a gas sensor is disclosed in which a gas-permeable hole is provided in the side surface of the outer cylinder (housing), and a waterproof filter is disposed in the gas-permeable hole (for example, refer to Patent Document 1).

[0004] In this gas sensor, the external gas introduced from the gas-permeable hole of the housing permeates the filter, passes through the gap of the internal member disposed inside the filter, and reaches the sensor element. In addition, a gap is provided between the housing and the filter, and even if a water droplet enters the inside from the gas-permeable hole, the filter blocks the permeation of the water droplet, and causes the moisture to be discharged to the gap.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-75066 Figure 3 ) SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] However, when mud splashes on the gas-permeable hole of the housing along with the running of the automobile, etc., the mud dries and solidifies to clog the gas-permeable hole when the gas sensor becomes high temperature due to exhaust gas, etc. Therefore, it is possible that the external gas is difficult to pass through the filter and be introduced into the gas sensor. In particular, the larger the diameter of the gas-permeable hole, the easier it is for the mud to enter the hole, and therefore, there is a tendency to easily clog.

[0010] On the other hand, if the diameter of the gas-permeable hole is too small, the gas permeability is reduced first, and finally the external gas is difficult to be introduced into the gas sensor.

[0011] The present application was completed in view of this situation, and aims to provide a gas sensor that, in a configuration in which a filter is disposed between the outer cylinder and the protective outer cylinder, can suppress clogging of the gas-permeable hole of the protective outer cylinder by foreign matter, and can stably introduce the external gas to the sensor element inside via the filter.

[0012] Solution to the problem

[0013] To achieve the above object, a gas sensor according to a first aspect of the present application includes: a sensor element extending in an axial direction; an outer cylinder which is cylindrical, which accommodates a rear end side of the sensor element, and which has a first gas permeable hole through which an external gas is introduced into an inside thereof; a filter which is made of resin, which is disposed on a radially outer side of the outer cylinder in a manner of blocking the first gas permeable hole, and which has gas permeability; and a protective outer cylinder which is cylindrical, which surrounds the filter from a radially outer side, and which has a second gas permeable hole which communicates with the first gas permeable hole via the filter, characterized in that a gap is provided between an outer surface of the filter and an inner surface of the protective outer cylinder which surrounds the second gas permeable hole, and an area S1 of the gap in a cross section of the second gas permeable hole in the axial direction is more than half of an opening area S2 of the second gas permeable hole on the cross section and directly opposite to the gap.

[0014] If the opening area S2 is large, mud water easily enters the hole, and thus, becomes easy to clog. On the other hand, if the opening area S2 is too small, gas permeability is reduced first. Therefore, according to the gas sensor, since it is configured as S1 ≥ (S2) / 2, the area S1 is relatively large compared to the area S2, and there is a large margin for discharging foreign matter such as mud water to the gap.

[0015] Therefore, even if foreign matter such as mud water splashes into the second gas permeable hole, it can easily fall to the gap and be discharged. Thus, even if mud water or the like entering the second gas permeable hole dries and solidifies when the gas sensor becomes high temperature, it takes time until the second gas permeable hole is completely clogged. As a result, even if the opening area S2 is relatively large, it is possible to suppress clogging of the second gas permeable hole by mud water (foreign matter), and it is possible to stably introduce an external gas to the sensor element inside via the filter. Furthermore, it is also possible to suppress a case where the opening area S2 is too small and gas permeability is reduced.

[0016] Further, the gas sensor of the second aspect of the present application includes: a sensor element extending in an axial direction; an outer cylinder that is cylindrical and that houses a rear end side of the sensor element and has a first gas permeable hole through which an external gas is introduced into an inside thereof; a filter that is made of resin, that is disposed on a radially outer side of the outer cylinder in a manner of blocking the first gas permeable hole, and that has gas permeability; and a protective outer cylinder that is cylindrical, that surrounds the filter from a radially outer side, and that has a second gas permeable hole that communicates with the first gas permeable hole via the filter, characterized in that a gap is provided between an outer surface of the filter and an inner surface of the protective outer cylinder that surrounds the second gas permeable hole, and an average thickness t1 of the gap in a cross section that passes through the second gas permeable hole in the axial direction is larger than a maximum width w1 of the second gas permeable hole.

[0017] In the gas sensor of the second aspect, when mud or the like splashes into the second gas permeable hole, mud or the like of a size (amount) equal to or greater than the maximum width w1 of the second gas permeable hole cannot enter the inside (gap) of the gas sensor at one time. Therefore, when t1 > w1 is provided, even if the maximum amount of mud or the like enters the gap from the second gas permeable hole, the mud or the like can be discharged (accommodated) into the gap. Thus, even if the mud or the like that enters the second gas permeable hole dries and solidifies when the gas sensor becomes high temperature, time is taken until the second gas permeable hole is completely blocked.

[0018] As a result, in the embodiment of the second aspect, it is possible to suppress the second gas permeable hole of the protective outer cylinder from being blocked by mud or the like (foreign matter), and it is possible to stably introduce an external gas to the sensor element inside via the filter.

[0019] In the gas sensor of the first aspect or the second aspect, the protective outer cylinder can have two pressing portions that press the filter in the axial direction, at positions on a tip end side and a rear end side of the second gas permeable hole.

[0020] In a region between the two pressing portions, the filter bulges to a radially outer side, and a minute gap is generated between the outer cylinder and the filter. Therefore, by disposing the first gas permeable hole in a region formed by the gap, it is possible to more reliably ensure the gas permeability of the gap and the first gas permeable hole 1.

[0021] In the gas sensor of the first aspect or the second aspect, the second gas permeable hole can overlap the center in the axial direction of the gap.

[0022] According to the gas sensor, since the second gas permeable hole is opened near the center in the axial direction of the gap, mud or the like foreign matter is easily discharged to the gap.

[0023] Effects of the Invention

[0024] According to the present application, in the configuration of the gas sensor in which the filter is sandwiched between the outer cylinder and the protective outer cylinder, the gas permeation hole of the protective outer cylinder can be prevented from being clogged by foreign matter, and the outside gas can be stably introduced to the sensor element inside via the filter. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a sectional view of the gas sensor according to the embodiment of the first technical solution of the present application along the axial direction.

[0026] Figure 2 is a sectional view along the A-A line of Figure 1 .

[0027] Figure 3 is a partially enlarged sectional view of the gas sensor around the second gas permeation hole.

[0028] Figure 4 is a sectional view showing the area S1 and the opening area S2.

[0029] Figure 5 is a sectional view showing the state in which the mud water entering from the second gas permeation hole is discharged to the gap.

[0030] Figure 6 is a graph showing the calculation method of S1, S2 in the case where the plurality of second gas permeation holes and the gap exist in the cross section.

[0031] Figure 7 is a graph showing the appearance of the protective outer cylinder.

[0032] Figure 8 is a sectional view of the gas sensor according to the embodiment of the second technical solution of the present application along the axial direction.

[0033] Figure 9 is a sectional view along the B-B line of Figure 8 .

[0034] Figure 10 is a partially enlarged sectional view of the gas sensor around the second gas permeation hole in the embodiment of the second technical solution.

[0035] Figure 11 is a sectional view showing the state in which the mud water entering from the second gas permeation hole is discharged to the gap.

[0036] Figure 12 is a graph showing the appearance of the protective outer cylinder.

[0037] Figure 13 is a graph showing the gas permeation amount of air from the second gas permeation hole to the outside of the gas sensor when the (S1 / S2) of the actual gas sensor is changed.

[0038] Figure 14 is a sectional view along the axial direction of a gas sensor which is a modification of the embodiment of the first technical solution of the present application.

[0039] Explanation of Reference Numerals

[0040] 1, 1B, 1C, gas sensor; 10, sensor element; 144, 344, outer cylinder; 144h, 344h, first gas permeable hole; 180, 380, filter; 180f, outer surface of filter; 190, 290, 390, protective outer cylinder; 190i, 290i, inner surface of protective outer cylinder; 190h, 190hx, 290h, 390h, second gas permeable hole; O, axial line; Ce, center in the axial direction of gap; G1, G1x, G2, gap; C1, C2, compression portion. DETAILED DESCRIPTION

[0041] Hereinafter, the embodiment of the present application will be described.

[0042] Figure 1 is a sectional view along the axial direction of a gas sensor (oxygen sensor) 1 of the embodiment of the first technical solution of the present application, Figure 2 is a sectional view along Figure 1 the A-A line of Figure 3 is a partial enlarged sectional view of the gas sensor 1 around the second gas permeable hole 190h, Figure 4 is a sectional view showing the area S1 and the opening area S2, Figure 5 is a sectional view showing the state in which the mud water M entering from the second gas permeable hole 190h is discharged to the gap, Figure 6 is a diagram showing the calculation method of S1, S2 indicating the presence of the plurality of second gas permeable holes 190h and the gap G1 in the cross section, Figure 7 is a diagram showing the appearance of the protective outer cylinder 190.

[0043] The gas sensor 1 is an oxygen sensor which detects the oxygen concentration in the exhaust gas of an automobile, various internal combustion engines.

[0044] In Figure 1In the embodiment, the gas sensor 1 includes a main body metal case 138 which is a cylindrical shape, the main body metal case 138 having a threaded portion 139 formed on an outer surface for fixing to an exhaust pipe, a sensor element 10 which forms a plate-like shape extending in a direction of an axis O (a length direction of the gas sensor 1: a vertical direction in the drawing), an outer cylinder 144 which is a cylindrical shape, the outer cylinder 144 being mounted to the main body metal case 138 and extending to a rear end side, and covering a rear end portion of the sensor element 10, a protective outer cylinder 190 which is a cylindrical shape, the protective outer cylinder 190 covering the outer cylinder 144, a filter 180 which is sandwiched between the outer cylinder 144 and the protective outer cylinder 190, and other components.

[0045] A plurality of electrode pads (not shown) are arranged on both surfaces of the rear end side of the sensor element 10. On the other hand, a gas detection portion 11 of the top end of the sensor element 10 is covered with a porous protective layer 14 of alumina or the like.

[0046] The main body metal case 138 is composed of stainless steel, and has a substantially cylindrical shape having a through-hole 154 extending in the axial direction and a slope portion 152 protruding to a radially inner side of the through-hole 154. The sensor element 10 is disposed in the through-hole 154 in such a manner that the top end portion of the sensor element 10 protrudes from the top end of the through-hole 154. Further, the slope portion 152 is formed as an inwardly tapered surface inclined with respect to a plane perpendicular to the axial direction.

[0047] In addition, inside the through-hole 154 of the main body metal case 138, a ceramic holder 151 of alumina which is a substantially ring-like shape, a powder filling layer 153 (hereinafter, also referred to as a talc ring 153), and a ceramic sleeve 106 are sequentially stacked in a state of surrounding the radial periphery of the sensor element 10 from the top end side to the rear end side.

[0048] Further, a compression packing 157 is disposed between the ceramic sleeve 106 and the rear end portion 140 of the main body metal case 138. In addition, the rear end portion 140 of the main body metal case 138 is compressed in such a manner as to press the ceramic sleeve 106 to the top end side with the compression packing 157 interposed.

[0049] On the other hand, as shown in FIG. 1, an outer protective member 142 and an inner protective member 143 which are metal (for example, stainless steel or the like) double protective members covering the protruding portion of the sensor element 10 and having a plurality of hole portions are mounted to the outer periphery of the top end side (below the Figure 1 Figure 1 of the main body metal case 138 by welding or the like.

[0050] ​An outer cylinder 144 is fixed to the outer periphery of the rear end side of the main metal housing 138. Furthermore, the partition includes two components: a top-side partition 90 and a rear-side partition 95. A rear-side terminal metal piece 40 is held in the rear-side partition 95. The rear ends of the rear-side terminal metal piece 40 are connected to leads 146, which extend towards the rear end side of the rear-side partition 95.

[0051] Furthermore, at the rear end 144e of the outer cylinder 144 Figure 1 A rubber washer 170 is provided at the opening (above) of the rear end partition 95, and the washer 170 is formed with six leads 146 for leading out from the rear end partition 95. Figure 1 Only two through-holes 170h are shown in the image. The rear end 144e is pressed radially inward to fix the washer 170 to the inside of the outer cylinder 144.

[0052] Furthermore, on the rear end side of the sensor element 10 protruding from the rear end 140 of the main metal housing 138 ( Figure 1 A top side partition 90 is disposed above the outer cylinder 144, the top side partition 90 having a flange 90p projecting radially outward from the outer surface. The top side partition 90 is held inside the outer cylinder 144 by abutting the flange 90p against the outer cylinder 144 via the retaining member 169.

[0053] Furthermore, a rear-end partition 95 is disposed between the washer 170 and the top-side partition 90. Through the elastic force of the washer 170, the rear-end partition 95 presses the top-side partition 90 towards the top. As a result, the flange 90p is pressed towards the retaining member 169, and the top-side partition 90 and the rear-end partition 95 are held together inside the outer cylinder 144 in a connected state (that is, without separation in the axial direction O).

[0054] Four top-side terminal metal pieces 30 are maintained on the top-side partition 90, and four rear-side terminal metal pieces 40 are also maintained on the rear-side partition 95.

[0055] Furthermore, the top-side terminal metal member 30 and the rear-side terminal metal member 40 are respectively disposed on the top side and the rear side and are connected to each other. In detail, the rear-side of the top-side terminal metal member 30 forms a cylindrical portion 33, which becomes a pointed cylindrical portion into which the top of the rear-side terminal metal member 40 is inserted.

[0056] Furthermore, the electrode pads disposed on the rear end side of the sensor element 10 are electrically connected to the top end terminal metal piece 30, so that the sensor output signal is taken out to the outside from the top end terminal metal piece 30 and the rear end terminal metal piece 40 via the lead wire 146, and power is supplied to the heater section via the rear end terminal metal piece 40 and the top end terminal metal piece 30.

[0057] In addition, a lead wire 146 is crimped to the rear end side of the rear end side terminal metal piece 40, and the lead wire 146 is led to the outside via a lead wire through-hole 170h of the grommet 170.

[0058] The sensor element 10 itself is a publicly known structure, although not shown, and includes a gas detecting portion having a solid electrolyte body of oxygen ion permeability and a pair of electrodes, and a heater portion that heats and maintains the gas detecting portion at a constant temperature. Further, the pair of electrodes of the gas detecting portion includes a reference electrode exposed to an external gas that is a reference of oxygen concentration, and a detection electrode exposed to a detected gas.

[0059] Furthermore, in order to introduce the external gas to the sensor element 10 housed in the inside of the outer cylinder 144, a plurality of first gas permeation holes 144h are provided at the side surface of the outer cylinder 144 at equal intervals in the circumferential direction. Further, on the radially outer side of the outer cylinder 144, a filter 180 made of a gas-permeable resin (for example, PTFE) is disposed in a manner to plug the first gas permeation holes 144h. Furthermore, on the outer side of the filter 180, a protective outer cylinder 190 made of metal is sleeved in a manner to surround the filter 180 from the radially outer side.

[0060] The protective outer cylinder 190 is also provided with a second gas permeation hole 190h in a manner to overlap the first gas permeation hole 144h across the filter 180. The second gas permeation hole 190h communicates with the first gas permeation hole 144h via the filter 180, and thus, the external gas can be introduced and discharged with respect to the inside of the gas sensor 1 via each of the gas permeation holes 144h, 190h and the filter 180.

[0061] The filter 180 has water resistance and can permeate gas but can prevent the entry of moisture.

[0062] Further, "communicates with the first gas permeation hole 144h via the filter 180" means that the second gas permeation hole 190h and the first gas permeation hole 144h do not necessarily overlap, as long as the external gas permeates from the second gas permeation hole 190h to the inside of the filter 180 via the outer surface of the filter 180 opposite to the second gas permeation hole 190h, the external gas reaches the first gas permeation hole 144h in the inside of the filter 180, and the external gas is introduced to the inside of the gas sensor 1 from the first gas permeation hole 144h.

[0063] That is, as long as the second gas permeation hole 190h is opposite to the outer surface of the filter 180 and the first gas permeation hole 144h is opposite to the inner surface of the filter 180. Further, it can also be that the first gas permeation hole 144h is in contact with the inner surface of the filter 180.

[0064] Furthermore, the outer cylinder 144, the filter 180, and the protective outer cylinder 190 are integrally fixed by the pressing portions C1, C2 pressed from the outer side of the protective outer cylinder 190 across the filter 180.

[0065] The pressing part C1 is located on the top side of the first vent 144h and the second vent 190h, and the pressing part C2 is located on the rear side of the first vent 144h and the second vent 190h.

[0066] Next, refer to Figures 3-5 The characteristic parts of the gas sensor 1 according to the first embodiment of the present invention will be described.

[0067] like Figure 3 As shown, a gap G1 is provided between the outer surface 180f of the filter 180 and the inner surface 190i of the protective outer cylinder 190 surrounding the second vent 190h. That is, the outer surface 180f of the filter 180 and the inner surface 190i of the second vent 190h are separated. Furthermore, the gap G1 is visible in cross-section. Figure 4 (Across the cross section passing through the second vent 190h along axis O, and...) Figure 3 The area S1 in the same cross section is more than half of the opening area S2 of the second vent 190h on that cross section.

[0068] Here, "enclosing the second vent 190h" means "including the outer edge of the second vent 190h and its surroundings".

[0069] If the opening area S2 is large, mud and water can easily enter the hole, making it prone to clogging. On the other hand, if the opening area S2 is too small, the air permeability will decrease.

[0070] Therefore, in the first technical solution of the present invention, it was found that by focusing on the ratio of the area S1 of the gap G1 to the opening area S2 rather than just controlling the size of the opening area S2, it is possible to suppress the blockage caused by the drying of mud and water even without making the opening area S2 too small.

[0071] In other words, when the area is set to S1≥(S2) / 2, the area S1 is relatively larger than the area S2, and the room for discharge of mud, water and other foreign objects into the gap G1 becomes larger.

[0072] Therefore, as Figure 5 As shown, even if muddy water M splashes into the second vent 190h, it can easily fall into the gap G1 and be discharged. Therefore, even if the muddy water M that enters the second vent 190h dries and solidifies when the gas sensor 1 becomes hot, it will take time for the second vent 190h to be completely blocked.

[0073] As a result, even if the opening area S2 is relatively large, it is possible to prevent the second vent 190h from being blocked by mud and water M (foreign matter), and to stably introduce external gas into the internal sensor element 10 through the filter 180. In addition, it is also possible to prevent the opening area S2 from becoming too small and reducing air permeability.

[0074] Furthermore, the situation where area S1 becomes relatively too large compared to area S2 refers to either an increase in the length of gap G1 in at least one direction, either the axial direction O or the radial direction, or a decrease in the opening area S2. In the former case, the length increases, and the size of gas sensor 1 in either the axial or width direction increases, potentially interfering with other layout elements within the vehicle. In the latter case, air permeability may sometimes decrease. Therefore, setting (S1 / S2) ≤ 5 is preferable.

[0075] Furthermore, if the opening area S2 is too small, the air permeability may sometimes decrease. Therefore, S2 is set to ≥ 1.0 mm. 2 better.

[0076] In addition, such as Figure 6 As shown, when observing the cross-section passing through the second vent hole 190h along the axis O, sometimes multiple (in) Figure 6 (There are two in the middle) The second vent is 190h.

[0077] In this case, when calculating S1 and S2, S1 and S2 are determined for the second vent 190h that is directly opposite to the specific gap G1.

[0078] For example, in Figure 6 In the case of a second vent 190h directly opposite the gap G1 on the right side, S1 and S2 are calculated respectively. On the other hand, for a second vent 190hx directly opposite the gap G1x on the left side, S1x and S2x are calculated respectively.

[0079] In other words, instead of adding up all S1 and S2 seen on the cross-section, S1 and S2 are calculated separately for each of the second vent holes 190h directly opposite each gap G1. This is because the anti-clogging effect of the second vent hole 190h only works effectively for the gap G1 directly opposite to the second vent hole 190h, and has no effect between the separated right-side gap G1 and the left-side second vent hole 190hx.

[0080] Therefore, when there are two or more second vent holes 190h directly opposite a gap G1, the opening area S2 is the sum of the opening areas of the two second vent holes 190h.

[0081] In addition, such as Figure 7As shown, in the embodiment of the first technical solution, a protrusion 190p is formed between the pressing portions C1 and C2 in the protective outer cylinder 190. The protrusion 190p is continuously connected in the circumferential direction and protrudes radially outward. A total of four second vent holes 190h are equally spaced in the circumferential direction of the protrusion 190p. Moreover, the protrusion 190p is separated from the outer surface 180f of the filter 180, thereby forming a gap G1.

[0082] In other words, such as Figure 2 As shown, gap G1 is formed as a continuous loop.

[0083] Next, refer to Figures 8-12 The gas sensor (oxygen sensor) 1B according to the second embodiment of the present invention will be described. Figure 8 This is a partial cross-sectional view along axis O of the gas sensor 1B according to the second technical solution embodiment. Figure 9 It is along Figure 8 A cross-sectional view of the BB line. Figure 10 This is a partially enlarged cross-sectional view of the gas sensor 1B surrounding the second vent 290h. Figure 11 This is a cross-sectional view showing the state in which the mud and water M entering from the second vent 290h is discharged into the gap. Figure 12 This is a diagram showing the appearance of the protective outer cylinder 290.

[0084] Furthermore, apart from the different shapes of the protective outer cylinder 290 and the gap G2, the gas sensor 1B of the second technical solution embodiment has the same structure as the gas sensor 1 of the first technical solution embodiment. Therefore, the designation and description of the reference numerals for the parts with the same structure are appropriately omitted.

[0085] like Figure 9 , Figure 12 As shown, in the second technical embodiment, four quadrangular cylindrical protrusions 290p are formed between the clamping portions C1 and C2 in the protective outer cylinder 290. These protrusions are equally spaced in the circumferential direction and protrude radially outward. A second vent hole 290h is opened on the side (top surface of the cylinder) of each protrusion 290p. Furthermore, the protrusion 290p is separated from the outer surface 180f of the filter 180, thereby forming a gap G2.

[0086] Thus, a gap G2 is provided between the outer surface 180f of the filter 180 and the inner surface 290i of the protective outer cylinder 290 surrounding the second vent 290h. That is, the outer surface 180f and the inner surface 290i are separated.

[0087] Furthermore, gap G2 is mainly formed intermittently at equal intervals in the circumferential direction. Among them, in Figure 9In the example, there is also a slight gap between the outer surface 180f of the filter 180 and the inner surface 290i of the second vent 290h, between adjacent gaps G2 in the circumferential direction. This gap can also be considered as part of the gap G2 as long as it has the function of draining (accommodating) mud and water entering from the second vent 290h.

[0088] Moreover, in the second technical solution of the present invention, Figure 10 The average thickness t1 of the gap G2 (the section passing through the second vent 290h along the axis O) is greater than the maximum width w1 of the second vent 190h.

[0089] like Figure 11 As shown, when muddy water M splashes onto the second vent 290h, a quantity (amount) of muddy water M exceeding the maximum width w1 of the second vent 290h cannot enter the gas sensor interior (gap G2) at once. Therefore, when t1 > w1, even if the maximum amount of muddy water M enters the gap G2 from the second vent 290h, it can still be discharged (accommodated) into the gap G2. Consequently, even if the muddy water M entering the second vent 290h dries and solidifies when the gas sensor 1B reaches a high temperature, it will still take time for the second vent 190h to be completely blocked.

[0090] As a result, in the implementation of the second technical solution, it is also possible to prevent the second vent hole 290h of the protective outer cylinder 290 from being blocked by mud and water M (foreign matter), and to stably introduce external gas into the internal sensor element 10 through the filter 180.

[0091] Here, the maximum width w1 of the second vent 290h is the maximum length of the second vent 290h along the axis O. Furthermore, the average thickness t1 is... Figure 10 The average thickness of the gaps between three equally spaced points M1 to M3 along the axis O in the cross section.

[0092] M1 to M3 are obtained by calculating... Figure 10 The length of the axis in the cross section along the O direction is obtained by dividing the two connection points P1 and P2 of the filter 180 and the second vent 290h into four equal parts.

[0093] Furthermore, at each point M1 to M3, the distance (thickness of gap G2) between the outer surface 180f of the filter 180 and the inner surface 290i of the protective outer cylinder 290 in a direction orthogonal to the axis O (radial) is measured, and t1 is determined as described above. For example, as Figure 10 As shown, the distance at point M3 is denoted by t13.

[0094] The present application is not limited to the above-described embodiments, and of course various modifications and equivalents included in the idea and scope of the present application are also involved.

[0095] The sensor element is not limited to the above-described plate-shaped element, and can be a cylindrical shape. Furthermore, the positions and number of the first gas permeable hole and the second gas permeable hole are not limited to the above-described.

[0096] As the gas sensor, in addition to the oxygen sensor and the full-area gas sensor, a NOx sensor can be cited.

[0097] Furthermore, for example, as shown in Figure 1 , at least a part of the first gas permeable hole 144h can be positioned between the pressing portion C1 and the pressing portion C2 in the axial O direction. Although not shown, in the region between the pressing portion C1 and the pressing portion C2, the filter 180 bulges to the radial outer side, and a slight gap is generated between the outer tube 144 and the filter 180. By providing the first gas permeable hole 144h in the region formed by the gap, the gap G1 and the gas permeability of the first gas permeable hole 144h can be more reliably ensured.

[0098] In addition, the filter 180 of the present embodiment has a through hole only in the thickness direction (radial direction of the gas sensor 1), is gas permeable in the radial direction, and is not gas permeable in the circumferential direction and the axial direction. However, this is not limiting.

[0099] Furthermore, as shown in Figure 10 , the second gas permeable hole 290h can overlap the center Ce in the axial O direction of the gap G2. In this case, the second gas permeable hole 290h is opened in the vicinity of the center Ce in the axial O direction of the gap G2, and thus foreign matter such as mud is easily discharged to the gap G2.

[0100] In addition, in the gas sensor 1 of the first technical solution embodiment, when viewed from the radial outer side toward the inner side, the second gas permeable hole 190h and the first gas permeable hole 144h do not overlap, but the second gas permeable hole 190h and the first gas permeable hole 144h can at least partially overlap.

[0101] Furthermore, as an example of the above-described "the positions and number of the first gas permeable hole and the second gas permeable hole are not limited to the above-described", as shown in Figure 14 , a gas sensor 1C of a modification example of the gas sensor of the first technical solution embodiment can be exemplified.

[0102] In addition, the gas sensor 1C is the same structure as the gas sensor 1 of the first technical solution embodiment except that the shapes of the outer tube 344, the filter 380, and the protective outer tube 390 are different, and thus the representation and explanation of the reference numerals of the same structure parts are appropriately omitted.

[0103] AsFigure 14 As shown, the gas sensor 1C has the following features: the rear end 344e of the outer tube 344 is located on the top end side than the top end of the gasket 170, and the rear end 344e of the outer tube 344 forms a straight open end. Therefore, in the gas sensor 1C, the 1st gas permeable hole 344h having the function of introducing the outside gas to the inside of the outer tube 344 is not a side hole as in the gas sensor 1, but is formed in a face (dotted line) passing through the rear end 344e (open end). Figure 14

[0104] Further, a gap through which the outside gas passes is formed between the 1st gas permeable hole 344h and the top end of the gasket 170.

[0105] Further, in order to "plug the 1st gas permeable hole 344h", the filter 380 is disposed on the radial outer side of the outer tube 344, and on the radial outer side of the above-mentioned gap covered by the gasket 170 from the rear end side of the outer tube 344.

[0106] Further, in this example, the rear end 344e of the outer tube 344 is located at a position on the top end side than the 2nd gas permeable hole 390h of the protective outer tube 390.

[0107] Further, the top end side of the filter 380 is sandwiched by the rear end 344e side of the outer tube 344 and the top end side of the protective outer tube 390. On the other hand, the rear end side of the filter 380 is narrowed, and is sandwiched by the top end side of the gasket 170 and the rear end side of the protective outer tube 390.

[0108] That is, in other words, in the gas sensor 1C, (i) the 1st gas permeable hole 344h is the rear end 344e (open end) of the outer tube 344; (ii) the gasket 170 is separately disposed at a position on the rear end side than the rear end 344e of the outer tube 344; (iii) the filter 380 is disposed on the radial outer side of the outer tube 344 and on the radial outer side of the gap between the outer tube 344 and the gasket 170; (iv) the rear end 344e of the outer tube 344 is located at a position on the top end side than the 2nd gas permeable hole 390h of the protective outer tube 390.

[0109] Further, in this example, only one filter 380 is disposed, but a plurality of filters can also be disposed.

[0110] In such a gas sensor 1C, by making the area S1 be half or more of the open area S2, the above-mentioned effects can also be exerted.

[0111] Further, by making the rear end 344e of the outer tube 344 a straight open end, the gas sensor 1C can also be applied as a modified example of the gas sensor of the embodiment of the 2nd technical solution.

[0112]

EMBODIMENT

[0113] ​As Figure 1 The gas sensor 1 shown in FIG. 1 was manufactured, and gas sensors in which S1 / S2 was changed variously were manufactured. The prescribed slurry was poured into the second gas permeation holes 190h of each gas sensor, and the slurry was introduced into the gap Gl. Thereafter, the gas sensor was held at a prescribed temperature of 100°C or higher and 300°C or lower for a prescribed time to dry the slurry, and this process was repeated a prescribed number of times of 50 or more and 600 or less.

[0114] Thereafter, air at a prescribed pressure was introduced into the inside of the outer cylinder 144 of the gas sensor, and every unit time, the gas permeation amount of the air that had passed through the gas sensor from all of the second gas permeation holes 190h was measured.

[0115] In Figure 13 The results obtained are shown.

[0116] It was confirmed that when S1 / S2 was made to be 1 / 2 or more, the gas permeation amount increased sharply, and clogging of the second gas permeation holes 190h could be suppressed.

[0117] In addition, Figure 13 The vertical axis is a relative value when the prescribed gas permeation amount is taken to be 1.

Claims

1. A gas sensor comprising: a sensor element extending in an axial direction; an outer cylinder which is cylindrical, which houses a rear end side of the sensor element, and which has a first gas permeable hole through which an external gas is introduced into an inside of the outer cylinder; a filter which is made of resin, which is arranged on a radially outer side of the outer cylinder in a manner of blocking the first gas permeable hole, and which has gas permeability; and a protective outer cylinder which is cylindrical, which surrounds the filter from a radially outer side, and which has a second gas permeable hole which communicates with the first gas permeable hole via the filter, characterized in that a gap is provided between an outer surface of the filter and an inner surface of the protective outer cylinder which surrounds the second gas permeable hole, an area SI in a cross section of the gap which passes through the second gas permeable hole in the axial direction is more than half of an opening area S2 of the second gas permeable hole which is located on the cross section and directly opposes the gap, and (SI / S2) ≤ 5.

2. A gas sensor comprising: a sensor element extending in an axial direction; an outer cylinder which is cylindrical, which houses a rear end side of the sensor element, and which has a first gas permeable hole through which an external gas is introduced into an inside of the outer cylinder; a filter which is made of resin, which is arranged on a radially outer side of the outer cylinder in a manner of blocking the first gas permeable hole, and which has gas permeability; and a protective outer cylinder which is cylindrical, which surrounds the filter from a radially outer side, and which has a second gas permeable hole which communicates with the first gas permeable hole via the filter, characterized in that a gap is provided between an outer surface of the filter and an inner surface of the protective outer cylinder which surrounds the second gas permeable hole, in a cross section of the gap which passes through the second gas permeable hole in the axial direction, an average thickness tl is larger than a maximum width wl, the average thickness tl is a thickness which is obtained by averaging radial thicknesses of respective gaps of three points which are equally spaced in the axial direction in the cross section which passes through the second gas permeable hole, the three points are obtained by obtaining two contact points Pl, P2 of the filter and the protective outer cylinder which are spaced apart from each other in the axial direction in the cross section and equally dividing a length in the axial direction between the contact points Pl, P2 into four, and the maximum width wl is a maximum length in the axial direction of the second gas permeable hole.

3. The gas sensor according to claim 1 or 2, characterized in that the protective outer cylinder has two press portions which press the filter in a position which is closer to a top end side and a rear end side than the second gas permeable hole in the axial direction, and at least a part of the first gas permeable hole is located between the two press portions.

4. The gas sensor according to claim 1 or 2, characterized in that the second gas permeable hole overlaps a center in the axial direction of the gap.

5. The gas sensor according to claim 3, characterized in that the second gas permeable hole overlaps the center in the axial direction of the gap. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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