Gas sensor

Abstract

[Problem] To provide a gas sensor that has excellent responsiveness. [Solution] A gas sensor 10 comprising: a sensor element 100 that extends in an axis O direction; and a tubular protector 51 that covers a tip end section of the sensor element, wherein the protector has a gas introduction hole 56, and a gas discharge hole 53 that is further to the tip end side than the gas introduction hole, a diameter reduction section 55 in which the diameter is reduced toward the inside in a radial direction is provided to the inner surface of the protector, in a region R between the gas introduction hole and the gas discharge hole in the axis direction, the minimum value D1 of the equivalent circle diameter of the inner surface of the diameter reduction section is 0.90-0.99 of the maximum value D2 of the equivalent circle diameter of the inner surface of the protector, and in the region R, diameter increase sections 57a, 57b in which the diameter is increased toward the outside in the radial direction relative to the diameter reduction section are respectively provided to the tip end side and the rear end side of the diameter reduction section.

Description

Gas Sensor

[0001] The present invention relates to a gas sensor provided with a protector that covers a sensor element.

[0002] Conventionally, an oxygen sensor having an axially extending sensor element has been known as a gas sensor for use in an internal combustion engine of an automobile or the like (see Patent Document 1). This oxygen sensor further includes a cylindrical protector that covers the tip of the sensor element. The protector is provided to prevent moisture in the exhaust pipe from directly contacting the gas sensor element, and has a gas inlet port for introducing a gas to be measured into the protector and a gas outlet port for discharging the gas to be measured from the protector.

[0003] Japanese Patent Publication No. 2022-61554

[0004] The external measurement gas is introduced into the protector through the gas inlet, contacts the detector located at the tip of the sensor element to detect the gas concentration, and then is discharged to the outside through the gas outlet. If the measurement gas is not sufficiently replaced with gas outside the protector, the sensor's response may be impaired. The present invention has been made in light of this situation, and aims to provide a gas sensor with excellent response.

[0005] In order to solve the above-mentioned problems, the gas sensor of the present invention includes a sensor element extending in an axial direction and a cylindrical protector covering a tip end of the sensor element, wherein the protector has a gas inlet hole and a gas exhaust hole located tip-side of the gas inlet hole, and a reduced diameter section whose diameter decreases radially inward is provided on the inner surface of the protector in a region R between the gas inlet hole and the gas exhaust hole in the axial direction, and a minimum value D1 of the circle-equivalent diameter of the inner surface of the reduced diameter section is 0.90 to 0.99 of a maximum value D2 of the circle-equivalent diameter of the inner surface of the protector, and an increased diameter section whose diameter increases radially outward from the reduced diameter section is provided on the tip end and rear end sides of the reduced diameter section in the region R.

[0006] The measurement gas introduced into the protector through the gas inlet comes into contact with the tip of the sensor element, is detected, and then is discharged to the outside through the gas outlet. As the measurement gas flows from the gas inlet toward the gas outlet, the flow path (protector) narrows at the reduced diameter section, increasing the flow rate due to the Venturi effect. This promotes gas displacement of the measurement gas outside the protector, improving the sensor's responsiveness. For the Venturi effect to occur, the leading and trailing ends of the reduced diameter section must be larger in diameter than the reduced diameter section. Furthermore, if the internal space of the protector does not expand at the leading end of the reduced diameter section, it will be difficult for the measurement gas to be discharged. For this reason, the expanded diameter sections are provided.

[0007] In the gas sensor of the present invention, the reduced diameter portion may have a straight portion extending in the axial direction and having a constant inner circle equivalent diameter, whereby turbulence of the gas is suppressed in the reduced diameter portion, facilitating a stable gas flow, and further increasing the flow rate of the measurement gas.

[0008] In the gas sensor of the present invention, the reduced diameter portion may be located closer to the tip of the measurement gas inlet of the sensor element than the measurement gas inlet, so that the measurement gas flowing from the gas inlet hole toward the reduced diameter portion can more easily come into contact with the measurement gas inlet, thereby further improving the responsiveness of the sensor.

[0009] In the gas sensor of the present invention, the sensor element may overlap at least a portion of the reduced diameter portion in the axial direction. In this gas sensor, the sensor element is disposed radially inside the reduced diameter portion, thereby reducing the cross-sectional area of ​​the internal space of the protector near the reduced diameter portion by the thickness of the sensor element. As a result, the minimum value of the equivalent circle diameter of the inner surface of the reduced diameter portion appears smaller, thereby further increasing the flow rate of the measurement gas.

[0010] According to the present invention, a gas sensor with excellent response can be obtained.

[0011] 1 is a cross-sectional view of a gas sensor according to an embodiment of the present invention, and is a diagram showing an example of a simulation of flow velocity distribution when a gas inlet and a sensor element are disposed in the internal space of an inner protector and gas is discharged from a gas outlet hole. 2 is a diagram showing the time change of the rate of gas replacement to the outside of the inner protector obtained from the flow velocity distribution in FIG.

[0012] An embodiment of the present invention will be described in detail with reference to Fig. 1 to Fig. 3. Fig. 1 is a cross-sectional view of a gas sensor 10 according to an embodiment of the present invention, Fig. 2 is a diagram showing an example of a simulation of flow velocity distribution when a gas inlet hole 56 and a sensor element 100 are disposed in the internal space of an inner protector 51 and gas is discharged from a gas outlet hole 53, and Fig. 3 is a diagram showing the time change in the rate of gas displacement to the outside of the inner protector 51, calculated from the flow velocity distribution in Fig. 2.

[0013] 1 , a gas sensor (oxygen sensor) 10 includes a sensor element 100, a holder (ceramic holder) 15 having a through-hole penetrating in the direction of axis O for inserting the sensor element 100, and a metallic shell 11 surrounding the ceramic holder 15 in the radial direction. A portion of the sensor element 100 near the front end where a detection portion is formed protrudes forward beyond the ceramic holder 15 and the metallic shell 11. The sensor element 100 thus inserted through the through-hole is fixed in place inside the metallic shell 11 while maintaining airtightness in the front-to-rear direction on the rear end face side (upper side in the figure) of the ceramic holder 15 by compressing sealing materials (talc in this example) 16A and 16B arranged in an inner hole 11A of the metallic shell 11 in the front-to-rear direction via a sleeve 17 and a ring washer 23 made of an insulating material.

[0014] The rear end portion of the sensor element 100 protrudes rearward beyond the sleeve 17 and the metal shell 11, and terminal fittings 19 provided at the tip of each lead wire 20 drawn to the outside through a grommet 21 are crimped and electrically connected to each electrode pad portion 100B formed in the rear end portion. The rear end portion of the sensor element 100 including the electrode pad portion 100B is covered by an outer tube 14. This will be explained in more detail below.

[0015] The sensor element 100 extends along the axis O and has a strip-like (plate-like) shape with a detection section for detecting a specific gas component in a gas to be detected at its tip (lower side in the figure) facing the measurement target. The cross section of the sensor element 100 is rectangular (rectangular) with a fixed size at both ends and is formed as an elongated structure primarily made of ceramic (e.g., solid electrolyte). A measurement gas inlet 100A, made of, for example, a porous layer and communicating with the outside, is provided at the tip end of the sensor element 100. The measurement gas is introduced into the detection section inside the sensor element 100 through the measurement gas inlet 100A. An electrode pad 100B is exposed near the rear end of the sensor element 100. The tip end of the sensor element 100 may be covered with a porous protective layer made of alumina, spinel, or the like.

[0016] The metal shell 11 has a cylindrical shape with different diameters at the front and rear ends, with a smaller diameter at the front end. The metal shell 11 has a cylindrical annular portion (hereinafter also referred to as the cylindrical portion) 11B for fitting and securing protectors 51 and 61 (described later). The rear (upper portion in the figure) of the metal shell 11 has a larger-diameter thread 11C on its outer surface for fastening to an engine exhaust pipe. The rear of the metal shell 11 has a polygonal portion 11D for threading the gas sensor 10 with the thread 11C. A second cylindrical portion 11E is connected to the rear of the polygonal portion 11D. A protective tube (outer tube) 14 is fitted and welded to cover the rear of the gas sensor 10. The second cylindrical portion 11E has a smaller outer diameter and a thinner crimping cylindrical portion 11F. In FIG. 1, the crimping cylindrical portion 11F is bent inward for crimping. A gasket (not shown) is attached to the underside of the polygonal portion 11D for sealing when screwed. On the other hand, the metallic shell 11 has an inner hole 11A that penetrates in the direction of the axis O. The inner peripheral surface of the inner hole 11A is tapered radially inward from the rear end side to the front end side, and the front-facing surface of the ceramic holder 15 is engaged with this tapered portion.

[0017] A ceramic holder 15 made of insulating ceramic (e.g., alumina) and formed in a roughly short cylindrical shape is disposed inside the metallic shell 11. As described above, the front-facing surface of the ceramic holder 15 is engaged with the tapered portion of the inner hole 11A, and the ceramic holder 15 is pressed from the rear end side by the seal materials 16A and 16B, thereby positioning the ceramic holder 15 within the metallic shell 11 and providing a clearance fit. Meanwhile, the through-hole of the ceramic holder 15 is provided at the center of the ceramic holder 15 and is a rectangular opening having dimensions substantially the same as the cross section of the sensor element 100 so that the sensor element 100 can pass through it with almost no gap. The sensor element 100 is passed through the through-hole of the ceramic holder 15, with the front end of the sensor element 100 protruding forward of the ceramic holder 15 and the metallic shell 11.

[0018] Meanwhile, in this embodiment, the tip portion of the sensor element 100 is covered with bottomed cylindrical protectors (protective covers) 51, 61 having a two-layer (double) structure. Of these, the inner protector 51 faces the sensor element 100, and the outer protector 61 is fitted onto the inner protector 51. The rear ends of the inner protector 51 and the outer protector 61 overlap and become one unit, and a rear end 51e of the inner protector 51 is fitted onto the cylindrical portion 11B of the metallic shell 11 and welded thereto.

[0019] One or more gas inlet holes 56 (e.g., eight holes equally spaced circumferentially in this example) are provided in the side wall of the rear end of the inner protector 51. One or more gas exhaust holes 53 (e.g., four holes equally spaced circumferentially in this example) are also provided in the side wall of the inner protector 51, closer to the tip of the gas inlet holes 56. Meanwhile, eight outer gas inlet holes 67 are provided in the side wall of the outer protector 61, spaced equally circumferentially, and one outer gas exhaust hole 69 is provided in the center of the bottom of the tip of the outer protector 61. The outer gas inlet hole 67 is located more distally than the gas inlet hole 56 and more proximal than the gas exhaust hole 53. Furthermore, a tapered portion 55, whose diameter tapers radially inward, is provided in the inner protector 51 between the gas inlet hole 56 and the gas exhaust hole 53 in the axial direction O. Details of the tapered portion 55 will be described later. The inner protector 51 corresponds to the "protector" in the claims, and the gas inlet hole 56 and the gas outlet hole 53 of the inner protector 51 correspond to the "gas inlet hole and gas outlet hole" in the claims.

[0020] 1, terminal fittings 19 provided at the tips of lead wires 20 extending through grommets 21 are pressed against and electrically connected to electrode pads 100B formed near the rear end of the sensor element 100 due to their spring properties. In the gas sensor 10 of this embodiment, the terminal fittings 19, including the pressure-contact portions, are disposed opposite each other in housings 18A provided in an insulating separator 18 disposed within the outer tube 14. The separator 18 is restricted from radial and tip-side movement by a retaining member 25 crimped and fixed within the outer tube 14. The tip of the outer tube 14 is fitted and welded to a second cylindrical portion 11E near the rear end of the metal shell 11, thereby airtightly covering the rear of the gas sensor 10. The lead wire 20 is passed through a grommet (e.g., rubber) 21 located inside the rear end of the outer tube 14 and pulled out to the outside, and the rear end of the outer tube 14 is crimped to reduce the diameter and compress this grommet 21, thereby maintaining airtightness in this area.

[0021] Next, a description will be given of the reduced diameter portion 55 of the inner protector 51. The reduced diameter portion 55, which reduces in diameter radially inward, is provided in a region R on the inner surface of the inner protector 51 between the gas inlet hole 56 and the gas outlet hole 53 in the direction of the axis O. Furthermore, in the region R, expanded diameter portions 57a and 57b, which expand in diameter radially outward beyond the reduced diameter portion 55, are provided at the front and rear ends, respectively, of the reduced diameter portion 55.

[0022] As shown in FIG. 1 , the measurement gas G introduced into the inner protector 51 through the gas inlet 56 comes into contact with the measurement gas inlet 100A located at the tip of the sensor element 100 and is detected. The gas is then discharged to the outside (outer protector 61) through the gas outlet 53. As the measurement gas G flows from the gas inlet 56 toward the gas outlet 53, the flow path (inner protector 51) narrows at the reduced-diameter portion 55, increasing the flow rate due to the Venturi effect. This promotes gas displacement of the measurement gas G to the outside of the inner protector 51, improving the sensor's responsiveness. For the Venturi effect to occur, the leading and trailing ends of the reduced-diameter portion 55 must be larger in diameter than the reduced-diameter portion 55. Furthermore, if the internal space of the inner protector 51 does not expand at the leading end of the reduced-diameter portion 55, it becomes difficult for the measurement gas G to be discharged. For this reason, the expanded-diameter portions 57a and 57b are provided.

[0023] However, if the diameter of the reduced diameter portion 55 is reduced too much, there is a risk that the reduced diameter portion 55 may come into contact with the sensor element 100 due to misalignment or vibration caused by, for example, the running of the vehicle in which the gas sensor 10 is installed. On the other hand, if the degree of reduction of the reduced diameter portion 55 is too small, the effect of increasing the flow rate of the measurement gas G is reduced. Therefore, if the minimum value D1 of the equivalent circle diameter of the inner surface of the reduced diameter portion 55 is 0.90 to 0.99 of the maximum value D2 of the equivalent circle diameter of the inner surface of the inner protector 51, it is possible to increase the flow rate of the measurement gas G while suppressing contact of the reduced diameter portion 55 with the sensor element 100.

[0024] If the minimum value D1 is less than 0.90 of the maximum value D2, the diameter of the reduced diameter portion 55 is reduced too much and comes into contact with the sensor element 100. If the minimum value D1 exceeds 0.99 of the maximum value D2, the degree of reduction of the reduced diameter portion 55 is too small, and the effect of increasing the flow rate of the measurement gas G is reduced.

[0025] The minimum value D1 of the equivalent circle diameter refers to the smallest value among the equivalent circle diameters of the inner surface of the reduced diameter portion 55 measured at multiple positions in the direction of the axis O. Similarly, the maximum value D2 of the equivalent circle diameter of the inner surface of the inner protector 51 refers to the largest value among the equivalent circle diameters of the inner surface of the inner protector 51 measured at multiple positions in the direction of the axis O. Furthermore, if the gas sensor 10 has two or more protectors, the reduced diameter portion is provided in the innermost protector facing the sensor element 100.

[0026] 2 and 3 show the results of a simulation of the rate of gas replacement to the outside of the inner protector 51 with and without the reduced diameter portion 55. The simulation was performed using a "Simcenter STAR-CCM+" manufactured by Siemens under the following conditions: Gas type: air Gas flow velocity: 12 m / s Gas temperature: 25°C Turbulence model: k-ε model Inner diameter of pipe to which the gas sensor 10 is attached: 56.5 mm As shown in FIG. 3, it can be seen that the rate of gas replacement increases when the reduced diameter portion 55 is provided compared to when the reduced diameter portion 55 is not provided.

[0027] Table 1 shows the degree of gas displacement to the outside of the inner protector 51 at 0.2 seconds (sec) after the start of the simulation when the diameter D1 of the reduced diameter portion 55 is varied and the value of (D1 / D2) is varied. In the simulation shown in Table 1, the measurement gas inlet 100A of the sensor element 100 shown in FIG. 1 is provided not only on the front side of the paper in FIG. 1 (referred to as the "front side" in Table 1) but also on the opposite side of the sensor element 100 (referred to as the "opposite side" in Table 1). In this simulation, the proportions of gas displacement to the outside of the inner protector 51 (front side a, opposite side b) were calculated at the positions of the measurement gas inlet on the front side and the opposite side. The difference between a and b, |ab|, was used as an index of the degree of gas displacement to the outside (of the inner protector 51). The smaller |ab| is, the more equivalent the gas replacement rate is at each measurement gas inlet on the front and opposite sides, and the more uniform the gas reaches each position on the sensor element. This indicates a better degree of gas replacement to the outside.

[0028] According to Table 1, |ab| rapidly decreases when (D1 / D2) is in the range of 0.90 to 0.99, indicating an excellent degree of gas replacement to the outside, with gas uniformly reaching the sensor element and further improving the sensor's responsiveness. This effect is not limited to a structure in which the measurement gas inlet 100A is provided on each side of the sensor element 100. As a result, the gas replacement rate is uniform regardless of the position on the sensor element 100, resulting in stable, high responsiveness. In Table 1, |ab| < 0.01 indicates an excellent degree of gas replacement, 0.3 > |ab| ≥ 0.01 indicates a moderate degree, and |ab| ≥ 0.03 indicates a poor degree.

[0029]

[0030] In the gas sensor of this embodiment, the reduced diameter portion 55 may have a straight portion whose inner surface has a constant equivalent circle diameter and extends in the direction of the axis O. In this case, the reduced diameter portion 55 suppresses turbulence of the gas, facilitating a stable gas flow, and further increasing the flow rate of the measurement gas G.

[0031] In the gas sensor of this embodiment, the reduced diameter portion 55 may be located closer to the tip of the measurement gas inlet 100A of the sensor element 100. In this case, the measurement gas G flowing from the gas inlet 56 toward the reduced diameter portion 55 can more easily come into contact with the measurement gas inlet 100A, thereby further improving the responsiveness of the sensor.

[0032] In the gas sensor of this embodiment, the sensor element 100 may overlap at least a portion of the reduced diameter portion 55 in the direction of the axis O. In this case, the sensor element 100 is disposed radially inside the reduced diameter portion 55, and the cross-sectional area of ​​the internal space of the inner protector 51 near the reduced diameter portion 55 is reduced by the thickness of the sensor element 100. As a result, the minimum value D1 of the circle-equivalent diameter of the inner surface of the reduced diameter portion appears smaller, and the flow rate of the measurement gas G can be further increased.

[0033] The gas sensor of the present invention can be embodied by appropriately modifying its structure and configuration as long as it does not deviate from the gist of the present invention. The sensor element is not limited to a plate-shaped element, but a cylindrical element may also be used. The protector is not limited to a double protector, but may be double or more, or may be single.

[0034] 10 Gas sensor 51 Protector (inner protector) 53 Gas discharge hole 55 Reduced diameter portion 56 Gas introduction hole 57a, 57b Expanded diameter portion 100 Sensor element 100A Measured gas introduction portion D1 Minimum value of the circle equivalent diameter of the inner surface of the reduced diameter portion D2 Maximum value of the circle equivalent diameter of the inner surface of the protector O Axis

Claims

1. A gas sensor comprising: a sensor element extending in an axial direction; and a cylindrical protector covering a tip end of the sensor element; wherein the protector has a gas inlet and a gas exhaust hole located tipward of the gas inlet; a reduced diameter section whose diameter decreases radially inward is provided on an inner surface of the protector in a region R between the gas inlet and the gas exhaust hole in the axial direction; a minimum value D1 of the circle-equivalent diameter of the inner surface of the reduced diameter section is 0.90 to 0.99 of a maximum value D2 of the circle-equivalent diameter of the inner surface of the protector; and wherein, in the region R, at the tip end and rear end of the reduced diameter section, expanded diameter sections whose diameter increases radially outward beyond the reduced diameter section are respectively interposed.

2. The gas sensor according to claim 1, wherein the reduced diameter portion has a straight portion extending in the axial direction and having a constant equivalent circle diameter on the inner surface.

3. The gas sensor according to claim 1 or 2, wherein the reduced diameter portion is located closer to the tip of the sensor element than the measurement gas inlet portion.

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

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