Gas sensor

Abstract

Provided is a gas sensor having excellent responsiveness. In a gas sensor (10) provided with a sensor element (100) extending in the direction of an axis (O) and a cylindrical protector (51) covering the tip of the sensor element, the protector has a gas introduction hole (56) and a gas discharge hole (53) closer to the tip side than the gas introduction hole, and the inner surface of the protector is provided with a gas inlet (56) and a gas outlet (53). In a region (R) between the gas introduction hole and the gas discharge hole in the axial direction, a reduced-diameter section (55) is provided which is reduced in diameter toward the inside in the radial direction, and the minimum value (D1) of the equivalent circle diameter of the inner surface of the reduced-diameter section is 0.90-0.99 times the maximum value (D2) of the equivalent circle diameter of the inner surface of the protector. Expanded-diameter sections (57a, 57b) are provided on the front end side and the rear end side of the reduced-diameter section, respectively, the expanded-diameter sections (57a, 57b) expanding in diameter further toward the outside in the radial direction than the reduced-diameter section.

Description

TECHNICAL FIELD

[0001] The present application relates to a gas sensor provided with a protective member that covers a sensor element. BACKGROUND

[0002] In the past, as a gas sensor for an internal combustion engine of an automobile or the like, an oxygen sensor provided with a sensor element extending in an axial direction is known (Patent Literature 1). The oxygen sensor also has a cylindrical protective member that covers a front end portion of the sensor element.

[0003] The protective member is provided in order to suppress water in an exhaust pipe from directly falling on the gas sensor element, and has a gas introduction hole that introduces a measured gas into the inside of the protective member and a gas discharge hole that discharges the measured gas inside the protective member to the outside.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2022-61554 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, the measured gas from the outside is introduced into the inside of the protective member from the above-mentioned gas introduction hole, comes into contact with a detection portion disposed at the front end portion of the sensor element, and after the gas concentration is detected, is discharged to the outside from the gas discharge hole. At this time, if the gas replacement of the measured gas to the outside of the protective member is insufficient, there is a problem that the responsiveness of the sensor decreases.

[0009] The present application was completed in view of the above-mentioned circumstances, and aims to provide a gas sensor with excellent responsiveness.

[0010] SOLUTION TO THE PROBLEM

[0011] In order to solve the above-mentioned problem, the gas sensor of the present application is provided with a sensor element extending in an axial direction and a cylindrical protective member that covers a front end portion of the sensor element, and is characterized in that the protective member has a gas introduction hole and a gas discharge hole on a front end side from the gas introduction hole, a reduced diameter portion that is reduced in diameter toward a radially inner side is provided on an inner surface of the protective member in a region R between the gas introduction hole and the gas discharge hole in the axial direction, a minimum value D1 of a circle equivalent diameter of an inner surface of the reduced diameter portion is 0.90 to 0.99 times a maximum value D2 of a circle equivalent diameter of the inner surface of the protective member, and a diameter expansion portion that is expanded in diameter toward a radially outer side compared to the reduced diameter portion is provided on the front end side and the rear end side of the reduced diameter portion in the region R.

[0012] The measured gas introduced from the gas introduction hole into the inside of the protector is detected after coming into contact with the front end side of the sensor element, and is discharged to the outside from the gas discharge hole. Also, when the measured gas flows from the gas introduction hole toward the gas discharge hole, the flow path (the protector) narrows at the reduced diameter portion, so the flow rate increases due to the Venturi effect.

[0013] Thus, the gas replacement of the measured gas to the outside of the protector is promoted, and the responsiveness of the sensor is improved.

[0014] Further, in order to generate the Venturi effect, it is necessary to expand the front end side and the rear end side of the reduced diameter portion compared to the reduced diameter portion. In addition, if the inside space of the protector does not expand at the front end side of the reduced diameter portion, the measured gas is difficult to discharge. Therefore, the expanded diameter portions are respectively provided.

[0015] In the gas sensor of the present application, the reduced diameter portion can also have a straight portion in which the circular equivalent diameter of the inner surface is constant and extends in the axial direction.

[0016] According to the gas sensor, the turbulent flow of the gas is suppressed by the reduced diameter portion, the gas easily flows stably, and the flow rate of the measured gas can be further increased.

[0017] In the gas sensor of the present application, the reduced diameter portion can also be located at a position that is more frontward than the measured gas introduction portion of the sensor element.

[0018] According to the gas sensor, the measured gas flowing from the gas introduction hole toward the reduced diameter portion easily comes into contact with the measured gas introduction portion, and the responsiveness of the sensor can be further improved.

[0019] In the gas sensor of the present application, the sensor element can also overlap at least a part of the reduced diameter portion in the axial direction.

[0020] According to the gas sensor, the sensor element is interposed inside the reduced diameter portion in the radial direction, so the inside space of the protector near the reduced diameter portion decreases in cross-sectional area by an amount corresponding to the thickness of the sensor element. As a result, the minimum value of the circular equivalent diameter of the inner surface of the reduced diameter portion appears to be smaller, and the flow rate of the measured gas can be further increased.

[0021] Effects of the Invention

[0022] According to the present application, a gas sensor having excellent responsiveness can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a sectional view of a gas sensor of an embodiment of the present application.

[0024] Figure 2This is a diagram illustrating an example of the flow velocity distribution when a gas inlet hole, a sensor element, and gas are disposed within the internal space of the inner protective component and discharged from the gas outlet hole.

[0025] Figure 3 It means according to Figure 2 The graph shows the time-varying proportion of gas displacement from the outside of the inner protective component, derived from the velocity distribution. Detailed Implementation

[0026] based on Figures 1-3 The embodiments of the present invention will be described in detail. Figure 1 This is a cross-sectional view of the gas sensor 10 according to an embodiment of the present invention. Figure 2 This is a diagram illustrating an example of the flow velocity distribution when a gas inlet hole 56 and a sensor element 100 are arranged in the internal space of the inner protective member 51, and gas is discharged from the gas outlet hole 53. Figure 3 It means according to Figure 2 The graph shows the time variation of the proportion of gas replacement to the outside of the inner protective component 51, obtained from the flow velocity distribution.

[0027] exist Figure 1 In the gas sensor (oxygen sensor) 10, there are: a sensor element 100; a retainer (ceramic retainer) 15 having a through hole that extends along the axis O and allows the sensor element 100 to be inserted; and a main metal housing 11 that surrounds the radial periphery of the ceramic retainer 15.

[0028] The front end portion of the sensor element 100, where the detection section is formed, protrudes further forward than the ceramic retainer 15 and the main metal housing 11. Thus, the sensor element 100, passing through the through hole, is airtightly fixed in the rear end face (upper side of the figure) of the ceramic retainer 15 by means of the sleeve 17 made of insulating material and the annular washer 23, which compress the sealing members (talc in this example) 16A and 16B disposed in the inner hole 11A of the main metal housing 11 in the front-rear direction.

[0029] Furthermore, the rearward portion of the sensor element 100 protrudes further rearward than the sleeve 17 and the main metal housing 11. Terminal metal pieces 19 are crimped and electrically connected to each electrode pad portion 100B formed at this rearward portion. These terminal metal pieces 19 are located at the front ends of each lead wire 20 extending outward through the cable ring 21. Additionally, the rearward portion of the sensor element 100 including the electrode pad portion 100B is covered by the outer cylinder 14. Further details will follow.

[0030] The sensor element 100 extends along the axis O and is in the shape of a strip plate (plate-shaped) with a detection section for detecting a specific gas component in the gas being detected on the front side (lower side of the figure) facing the object to be measured. The cross-section of the sensor element 100 is rectangular with a constant size from front to back, and is formed into a slender shape with ceramic (solid electrolyte, etc.) as the main body.

[0031] Here, a gas inlet 100A, which is made of a porous layer and communicates with the outside, is provided at the front end of the sensor element 100. The gas to be measured is introduced into the detection section inside the sensor element 100 through the gas inlet 100A.

[0032] In addition, an electrode pad portion 100B is exposed at the rear end of the sensor element 100.

[0033] Furthermore, a porous protective layer made of alumina or spinel can be applied to the front end of the sensor element 100.

[0034] The main metal housing 11 is formed as a cylindrical shape with concentric front and rear diameters, and a smaller diameter at the front end. It has a cylindrical annular portion (hereinafter also referred to as a cylindrical portion) 11B for externally inserting and fixing the protective members 51 and 61 (described later). A thread 11C with a larger diameter for fixing to the engine's exhaust pipe is provided on the outer peripheral surface of the annular portion 11B (top of the figure). Furthermore, a polygonal portion 11D for screwing the gas sensor 10 through the thread 11C is provided behind the thread 11C. A second cylindrical portion 11E is continuously provided behind the polygonal portion 11D. A protective cylinder (outer cylinder) 14 for covering the rear of the gas sensor 10 is externally inserted and welded to the second cylindrical portion 11E. A thin-walled clamping cylindrical portion 11F with a smaller outer diameter is provided behind the second cylindrical portion 11E. Furthermore, the clamping cylindrical portion 11F... Figure 1 Because it is compressed, it bends inward. In addition, a sealing washer (not shown) is installed on the lower surface of the polygonal part 11D for screwing in.

[0035] On the other hand, the main metal housing 11 has an inner hole 11A that extends along the axis O. The inner circumferential surface of the inner hole 11A is tapered, tapering radially inward from the rear end towards the front end, and the front end face of the ceramic retainer 15 is engaged with this tapered portion.

[0036] A ceramic retainer 15, made of insulating ceramic (e.g., alumina) and formed in a generally short cylindrical shape, is disposed on the inner side of the main metal housing 11. As described above, the front end face of the ceramic retainer 15 is engaged with the tapered portion of the inner hole 11A, and the ceramic retainer 15 is pressed from the rear end side by the sealing members 16A and 16B, thereby positioning the ceramic retainer 15 within the main metal housing 11 with a clearance fit.

[0037] On the other hand, the through hole of the ceramic retainer 15 is provided at the center of the ceramic retainer 15 and is formed as a rectangular opening with approximately the same size as the cross-section of the sensor element 100, so that the sensor element 100 can pass through approximately without gaps.

[0038] The sensor element 100 passes through the through hole of the ceramic retainer 15, causing the front end of the sensor element 100 to protrude forward beyond the ceramic retainer 15 and the main metal housing 11.

[0039] On the other hand, in this embodiment, the front end of the sensor element 100 is covered by a bottomed cylindrical protective member (protective cover) 51, 61, which consists of a two-layer (double) structure. The inner protective member 51 faces the sensor element 100, and the outer protective member 61 is embedded in the inner protective member 51. Furthermore, the rear ends of the inner protective member 51 and the outer protective member 61 overlap to form a single unit, and the rear end 51e of the inner protective member 51 is embedded in and welded to the cylindrical portion 11B of the main metal housing 11.

[0040] One or more gas inlet holes 56 are provided on the side wall of the rear end of the inner protective member 51 (in this example, there are, for example, 8 holes provided at equal intervals in the circumferential direction). In addition, one or more gas outlet holes 53 are provided on the side wall of the inner protective member 51 at a position closer to the front end than the gas inlet holes 56 (in this example, there are, for example, 4 holes provided at equal intervals in the circumferential direction).

[0041] On the other hand, for example, eight external gas inlet holes 67 are provided at equal intervals in the circumferential direction on the side wall of the outer protective member 61, and one external gas outlet hole 69 is provided at the bottom center of the front end of the outer protective member 61.

[0042] In addition, the outer gas inlet hole 67 is located at a position that is further forward than the gas inlet hole 56 and further backward than the gas outlet hole 53.

[0043] Furthermore, a reduced diameter portion 55 is provided between the gas inlet hole 56 and the gas outlet hole 53 in the axial direction O of the inner protective member 51, which narrows radially inward. Details of the reduced diameter portion 55 will be described later.

[0044] The inner protective element 51 is equivalent to the "protective element" in the claims, and the gas inlet hole 56 and gas outlet hole 53 of the inner protective element 51 are equivalent to the "gas inlet hole and gas outlet hole" in the claims.

[0045] In addition, such as Figure 1 As shown, each terminal metal piece 19 is elastically pressed and electrically connected to each electrode pad portion 100B formed at the rear end of the sensor element 100. Each terminal metal piece 19 is disposed at the front end of each lead wire 20 extending outward through the cable loop 21. Furthermore, in this example of the gas sensor 10, each terminal metal piece 19 including the pressing portion is disposed in a relative arrangement within each housing portion 18A, which is disposed within an insulating separator 18 disposed within the outer cylinder 14. Moreover, the separator 18 is restricted from radial and frontal movement by a retaining member 25 pressed and fixed within the outer cylinder 14. Furthermore, by externally inserting and welding the front end of the outer cylinder 14 to the second cylindrical portion 11E at the rear end of the main metal housing 11, the rear of the gas sensor 10 is airtightly covered.

[0046] In addition, the lead wire 20 passes through a loop (e.g., rubber) 21 located inside the rear end of the outer cylinder 14 and is led out to the outside. The loop 21 is compressed by narrowing the diameter of the rear end of the outer cylinder 14, thereby maintaining the airtightness of this part.

[0047] Next, the reduced diameter portion 55 of the inner protective member 51 will be described. On the inner surface of the inner protective member 51, a reduced diameter portion 55 is provided in the region R between the gas inlet hole 56 and the gas outlet hole 53 in the axial direction O. The reduced diameter portion 55 is radially reduced inward.

[0048] Furthermore, in region R, there are expansion portions 57a and 57b on the front and rear sides of the reduced diameter portion 55, which are expanded radially outward compared to the reduced diameter portion 55.

[0049] Here, as Figure 1 As shown, the gas to be measured G, introduced into the interior of the inner protective member 51 through the gas inlet hole 56, is detected after contacting the gas to be measured inlet portion 100A disposed at the front end of the sensor element 100, and then discharged to the outside (outer protective member 61) through the gas outlet hole 53. Moreover, as the gas to be measured G flows from the gas inlet hole 56 toward the gas outlet hole 53, the flow path (inner protective member 51) narrows at the diameter reduction portion 55, thus increasing the flow velocity due to the Venturi effect.

[0050] This promotes the displacement of the measured gas G to the outside of the inner protective element 51, thereby improving the sensor's responsiveness.

[0051] Furthermore, in order to generate the Venturi effect, the front and rear ends of the reduced diameter section 55 need to be enlarged compared to the reduced diameter section 55. Additionally, if the internal space of the inner protective member 51 does not expand at the front end of the reduced diameter section 55, the measured gas G will be difficult to escape. Therefore, enlarged diameter sections 57a and 57b are provided respectively.

[0052] However, when the diameter reduction section 55 is excessively reduced, due to displacement or vibration caused by the movement of the vehicle on which the gas sensor 10 is installed, the diameter reduction section 55 may come into contact with the sensor element 100. On the other hand, when the diameter reduction degree of the diameter reduction section 55 is too small, the effect of increasing the flow rate of the measured gas G is reduced.

[0053] Therefore, if the minimum value D1 of the circular equivalent diameter of the inner surface of the reduced diameter portion 55 is 0.90 to 0.99 times the maximum value D2 of the circular equivalent diameter of the inner surface of the inner protective member 51, then the contact between the reduced diameter portion 55 and the sensor element 100 can be suppressed, and the flow rate of the gas G to be measured can be increased.

[0054] If the minimum value D1 is less than 0.90 times the maximum value D2, the reduced diameter section 55 will be excessively reduced in diameter and will come into contact with the sensor element 100.

[0055] If the minimum value D1 exceeds 0.99 times the maximum value D2, the degree of diameter reduction of the narrowing section 55 is too small, and the effect of increasing the flow rate of the measured gas G is reduced.

[0056] Furthermore, the minimum value of the circular equivalent diameter D1 refers to the smallest value among the circular equivalent diameters of the inner surface of the reduced diameter portion 55 measured at multiple locations along the axis O.

[0057] Similarly, the maximum value D2 of the circular equivalent diameter of the inner surface of the inner protective member 51 refers to the maximum value among them when the circular equivalent diameter of the inner surface of the inner protective member 51 is measured at multiple positions along the axis O.

[0058] In addition, when the gas sensor 10 has two or more protective elements, a reduced diameter portion is provided in the innermost protective element facing the sensor element 100.

[0059] Figure 2 , Figure 3 The simulation results represent the proportion of gas displacement to the outside of the inner protective member 51 based on the presence or absence of the reduced diameter section 55. Furthermore, the simulation was conducted using a Siemens Simcenter STAR-CCM+ under the following conditions.

[0060] Gas type: Air

[0061] Gas flow rate: 12 m / s

[0062] Gas temperature: 25℃

[0063] Turbulence model: k-ε model

[0064] The inner diameter of the piping for assembling gas sensor 10 is 56.5 mm.

[0065] like Figure 3 As shown, if the reduced diameter section 55 is provided, the gas replacement ratio increases compared to the case where the reduced diameter section 55 is not provided.

[0066] In addition, Table 1 shows the degree of gas displacement to the outside of the inner protective member 51 at a time 0.2 seconds from the start of the simulation when various changes are made to D1 of the reduced diameter portion 55 to change the value of (D1 / D2).

[0067] Here, in the simulation in Table 1, Figure 1 The gas inlet 100A of the sensor element 100 is not only provided in Figure 1 The surface side of the paper (designated as "surface side" in Table 1) is also provided on the opposite side of the sensor element 100. Figure 1 (The back side of the paper) (let’s call it the “opposite side” in Table 1).

[0068] In this simulation, the proportion of gas displacement to the outside of the inner protective member 51 was determined at the positions of the gas inlet on the front and opposite sides (front side a, opposite side b). Then, the difference between a and b, i.e., |ab|, was used as an indicator of the degree of gas displacement to the outside (of the inner protective member 51).

[0069] The smaller the |ab|, the more equal the proportion of gas replacement in each gas inlet section on the front and opposite sides, and the more uniformly the gas reaches each position of the sensor element. Therefore, it is considered to be a superior degree of gas replacement to the outside.

[0070] Furthermore, according to Table 1, it is believed that within the range of (D1 / D2) of 0.90 to 0.99, |ab| decreases sharply, indicating excellent gas displacement to the outside and uniform gas delivery to the sensor element, which can further improve the sensor's responsiveness.

[0071] This effect is not limited to the structure in which the gas to be measured is introduced into the sensor element 100 on both sides. As a result, the gas replacement ratio is uniform regardless of the position of the sensor element 100, thus enabling a stable high responsiveness.

[0072] In addition, in Table 1, regarding the degree of gas replacement, |ab| < 0.01 is set as "excellent", 0.3 > |ab| ≥ 0.01 is set as "medium", and |ab| ≥ 0.03 is set as "poor".

[0073] [Table 1]

[0074]

[0075] In the gas sensor of this embodiment, the reduced diameter portion 55 may also have a straight portion with a constant circular equivalent diameter on its inner surface and extending along the axis O.

[0076] In this way, by suppressing the turbulence of the gas through the narrowed section 55, the gas can flow more easily and stably, which can further increase the flow rate of the gas G being measured.

[0077] In the gas sensor of this embodiment, the reduced diameter portion 55 may also be located at the front end side of the gas inlet portion 100A of the sensor element 100.

[0078] In this way, the gas G to be measured flowing from the gas inlet 56 toward the narrowed section 55 can easily come into contact with the gas inlet 100A, which can further improve the responsiveness of the sensor.

[0079] In the gas sensor of this embodiment, the sensor element 100 may also overlap with at least a portion of the reduced diameter portion 55 in the axial direction O.

[0080] Thus, the sensor element 100 is located radially inside the reduced diameter portion 55, thereby reducing the cross-sectional area of ​​the internal space of the inner protective member 51 near the reduced diameter portion 55 by an amount corresponding to the thickness of the sensor element 100. As a result, the minimum value D1 of the circular equivalent diameter of the inner surface of the reduced diameter portion appears to become smaller, enabling a further increase in the flow rate of the measured gas G.

[0081] The gas sensor of the present invention can be further modified and its structure can be customized as long as it does not deviate from the spirit of the invention.

[0082] As a sensor element, it is not limited to plate-shaped elements; cylindrical elements can also be used. The protective element is not limited to double protective elements; it can be double or more, or even a single layer.

[0083] Explanation of reference numerals in the attached figures

[0084] 10. Gas sensor; 51. Protective component (inner protective component); 53. Gas exhaust port; 55. Reduced diameter section; 56. Gas inlet port; 57a, 57b. Expanded diameter section; 100. Sensor element; 100A. Gas inlet section to be measured; D1. Minimum value of the equivalent circular diameter of the inner surface of the reduced diameter section; D2. Maximum value of the equivalent circular diameter of the inner surface of the protective component; O. Axis.

Claims

1. A gas sensor comprising a sensor element extending along an axial direction and a cylindrical protective member covering the front end of said sensor element, characterized in that, The protective component has a gas inlet hole and a gas outlet hole located at the front end of the gas inlet hole. On the inner surface of the protective member, in the region R between the gas inlet hole and the gas outlet hole in the axial direction, a diameter-reduced portion is provided that tapers radially inward. The minimum value D1 of the equivalent circular diameter of the inner surface of the reduced diameter section is 0.90 to 0.99 times the maximum value D2 of the equivalent circular diameter of the inner surface of the protective component. In the region R, there are expansion portions on the front and rear sides of the reduced diameter portion, which are radially outward compared to the reduced diameter portion.

2. The gas sensor according to claim 1, characterized in that, The reduced diameter portion has a straight portion with a constant equivalent diameter of the inner surface and extending along the axial direction.

3. The gas sensor according to claim 1 or 2, characterized in that, The reduced diameter section is located at a position closer to the front end than the gas inlet section of the sensor element.

4. The gas sensor according to claim 1 or 2, characterized in that, The sensor element overlaps with at least a portion of the reduced diameter portion in the axial direction.

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