JP6535593B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor disposed and used in an intake passage of an internal combustion engine having an exhaust gas recirculation mechanism.

Among the gas sensors for vehicle use, other than those used in the exhaust passage of an internal combustion engine, there are those which are used by being disposed in the intake passage of an exhaust gas recirculation mechanism that recirculates part of exhaust gas to newly introduced air. In the intake passage of the exhaust gas recirculation mechanism, carbon contained in the exhaust gas, deposits as fine particles such as engine oil (lubricating oil) and water vapor are cooled by newly introduced air that is lower in temperature than the exhaust gas. In the gas sensor disposed in the intake passage of the exhaust gas recirculation mechanism, the sensor element and the cover for covering the sensor element are deposits with high viscosity, and corrosive condensed water in which corrosive substances contained in the exhaust gas are liquefied. It becomes easy to adhere.
In Patent Document 1, a water repellent coating is formed on the porous layer of the sensor element and the outer cover located outside the inner cover covering the sensor element, for the oxygen sensor disposed in the intake passage of the exhaust gas recirculation mechanism. ing. This makes it difficult for deposits to adhere to the porous layer and the outer cover of the sensor element.

Japanese Patent Application Laid-Open No. 10-170474

However, in Patent Document 1, the introduction holes for introducing the measurement gas into the sensor element in the outer cover are equally formed in the circumferential direction. Therefore, the flow of the measurement gas in the intake passage easily contacts the inner cover and the sensor element via the introduction hole, and the deposit and the condensed water contained in the measurement gas easily contact the inner cover and the sensor element . As a result, deposits tend to be deposited around the sensor element and the introduction hole of the inner cover, and the possibility of the sensor element being broken by condensed water increases.
Therefore, further measures are required to more effectively suppress deposition of deposits on the inner cover and the sensor element and corrosion of the inner cover and outer cover by condensed water, and to protect the sensor element from water cracking. It is assumed.

  The present invention has been made in view of such problems, and has been obtained in an attempt to provide a more robust gas sensor against corrosion, deposition of deposits, and water cracking.

One aspect of the present invention is disposed in the intake passage (81) of an internal combustion engine (7) having an exhaust gas recirculation mechanism (8) for recirculating a part of exhaust gas (G) to newly introduced air (A) The gas sensor (1)
A housing (2) having an insertion port (21);
Gas detection which is disposed along the central axis (C) of the housing and is held in the insertion port via the insulator (22) and introduces the mixed gas (M) of the newly introduced air and the exhaust gas A sensor element (3) in which the portion (11) protrudes from the housing;
A cylindrical inner side wall (41) attached to the housing along the central axis, and an inner bottom (42) closing an end of the inner side wall, and the inner bottom and the inner side wall An inner cover (4) provided with inner vents (421, 411) for passing the above mixed gas in the part;
A cylindrical outer sidewall (51) attached to the inner cover or the housing along the central axis, and an outer bottom (52) closing an end of the outer sidewall, and the outer bottom And an outer cover (5) provided with an outer vent hole (521, 511) for passing the mixed gas in the outer side wall portion,
The inner cover is composed of a metal base and a resin coating layer coating the base,
The above outer cover is made of resin,
The outer vent hole in the outer sidewall portion is a half region (X) of the entire region around the central axis in the outer sidewall portion, which is located on the downstream side of the flow of the mixed gas in the intake passage The gas sensor is provided only in the.

In the above gas sensor, the structure of the inner cover and the outer cover, and the structure of the outer vent in the outer cover are devised.
Specifically, the inner cover is formed by covering a metal base with a resin coating layer, while the outer cover is formed by a resin. That is, the outer cover for receiving the flow of the mixed gas of the newly introduced air and the exhaust gas is formed only of the resin without using the metal base. Thereby, even when condensed water contained in the mixed gas collides violently with the outer cover, corrosion of the outer cover can be almost eliminated. Moreover, deposition of deposits on the inner cover can be suppressed by covering the metal base of the inner cover with the resin coating layer.

  Further, the outer vent holes in the outer side wall portion are provided only in a half area located downstream of the flow of the mixed gas in the intake passage among the entire area around the central axis in the outer side wall portion. As a result, the flow of mixed gas in the intake passage collides with the outer side wall portion, and the mixed gas whose collision is weakened to the outer side wall portion to the outer vent in the outer side wall portion wraps around. be introduced. Therefore, it is possible to make it difficult for deposits contained in the mixed gas to be deposited around the inner vent hole in the inner sidewall portion of the inner cover and around the gas detection portion of the sensor element. As a result, it is prevented that the mixed gas hardly reaches the gas detection unit, and responsiveness of gas detection by the gas detection unit is maintained.

In the entire region around the central axis in the outer side wall portion, an outer vent hole is not provided in a half region located on the upstream side of the flow of the mixed gas in the intake passage. Thereby, the condensed water contained in mixed gas becomes difficult to collide with an inner cover and a sensor element. Therefore, the inner cover can be made less likely to be corroded, and the sensor element can be more effectively protected from water-induced cracking due to condensed water.
Therefore, according to the above gas sensor, it is possible to form a more robust gas sensor against corrosion, deposition of deposits, and water cracking.

2 is a cross-sectional view showing a gas sensor disposed in an intake passage of an internal combustion engine having an exhaust gas recirculation mechanism according to Embodiment 1. FIG. Explanatory drawing which shows the inner cover and outer cover concerning Embodiment 1 in the state seen from the axial direction of the gas sensor. Explanatory drawing which shows the outer vent hole in an outer side wall part concerning Embodiment 1 in the state seen from the downstream of the flow of mixed gas. Sectional explanatory drawing which shows the sensor element concerning Embodiment 1. FIG. Sectional explanatory drawing which shows the sensor element concerning Embodiment 1 in the state seen from the direction orthogonal to FIG. FIG. 1 is an explanatory view showing an internal combustion engine having an exhaust gas recirculation mechanism according to a first embodiment. Sectional explanatory drawing which shows the gas sensor concerning Embodiment 2. FIG. Sectional explanatory drawing which shows the other gas sensor concerning Embodiment 2. FIG. Explanatory drawing which shows the outer vent hole in an outer side wall part concerning Embodiment 2 in the state seen from the downstream of the flow of mixed gas. Explanatory drawing which shows the outer vent hole in the other outer side wall part concerning Embodiment 2 in the state seen from the downstream of the flow of mixed gas. Explanatory drawing which shows the outer vent hole in the other outer side wall part concerning Embodiment 2 in the state seen from the downstream of the flow of mixed gas. Explanatory drawing which shows the positional relationship of the inner vent hole in an inner bottom part according to Embodiment 3, and the outer vent hole in an outer bottom part in the state seen from the axial direction of the gas sensor. Explanatory drawing which shows the positional relationship of the inner vent hole in another inner bottom part according to Embodiment 3, and the outer vent hole in another outer bottom part in the state seen from the axial direction of the gas sensor. Explanatory drawing which shows the positional relationship of the inner vent hole in another inner bottom part according to Embodiment 3, and the outer vent hole in another outer bottom part in the state seen from the axial direction of the gas sensor. Explanatory drawing which shows the positional relationship of the inner vent hole in another inner bottom part according to Embodiment 3, and the outer vent hole in another outer bottom part in the state seen from the axial direction of the gas sensor. The graph which shows the relation between the number of cycles (time) which impregnates an outer cover in a solution, and it dries concerning a confirmatory test (times), and the reduction amount (micrometer) of the thickness of an outer cover. The graph which shows the relationship between the time (hr) which the gas sensor was expose | bleached in gas, and 10-90% response time (ms) concerning a verification test.

Preferred embodiments of the above-described gas sensor will be described with reference to the drawings.
(Embodiment 1)
The gas sensor 1 of the present embodiment is used by being disposed in the intake passage 81 of an internal combustion engine 7 having an exhaust gas recirculation mechanism 8 for recirculating a part of the exhaust gas G to the newly introduced air A, as shown in FIG. As shown in FIG. 1, the gas sensor 1 includes a housing 2, a sensor element 3, an inner cover 4 and an outer cover 5. The housing 2 is formed with an insertion port 21 for inserting the sensor element 3.
The sensor element 3 is disposed along the central axis C of the housing 2 and is held in the insertion port 21 of the housing 2 via the insulator 22. The gas detection unit 11 in the sensor element 3 into which the mixed gas M of the newly introduced air A and the exhaust gas G is introduced protrudes from the housing 2.

  The inner cover 4 has a cylindrical inner side wall 41 attached to the housing 2 along the central axis C, and an inner bottom 42 closing an end of the inner side wall 41. The inner bottom portion 42 and the inner side wall portion 41 are provided with inner vent holes 421 and 411 through which the mixed gas M flowing in the intake passage 81 passes. The outer cover 5 has a cylindrical outer side wall 51 attached to the inner cover 4 or the housing 2 along the central axis C, and an outer bottom 52 closing an end of the outer side wall 51. The outer bottom portion 52 and the outer side wall portion 51 are provided with outer vent holes 521 and 511 through which the mixed gas M flowing in the intake passage 81 passes.

  The inner cover 4 is composed of a metal base and a resin coating layer that covers the base. The outer cover 5 is made of resin. As shown in FIG. 1 and FIG. 2, the outer vent hole 511 in the outer side wall 51 is the downstream of the flow of the mixed gas M in the intake passage 81 in the entire area around the central axis C in the outer side wall 51. It is provided only in the half area X located on the side. In FIG. 2, the inner cover 4 is indicated by a broken line.

Hereinafter, the gas sensor 1 of the present embodiment will be described in more detail.
As shown in FIG. 6, the gas sensor 1 is used in an on-vehicle internal combustion engine 7. The exhaust gas recirculation mechanism 8 recirculates a part of the exhaust gas G exhausted from the internal combustion engine 7 to the exhaust passage 82 to the intake passage 81 of the internal combustion engine 7. The exhaust gas recirculation mechanism 8 has a recirculation passage 83 branched from the exhaust passage 82 and connected to the intake passage 81, and a flow control valve 831 for adjusting the flow rate of the exhaust gas G flowing in the recirculation passage 83. There is. The gas sensor 1 of the present embodiment is disposed downstream of the flow of the mixed gas M in the intake passage 81 than the position where the recirculation passage 83 joins.

As shown in FIG. 1, the gas sensor 1 is used by the gas detection unit 11 of the sensor element 3 to detect the oxygen concentration, the specific gas component concentration, and the like of the mixed gas M. The housing 2 has a structure for attaching the gas sensor 1 to a pipe 811 forming an intake passage 81.
The sensor element 3 is formed in an elongated shape along the direction of the central axis C of the housing 2. The central axis C of the sensor element 3 coincides with the central axis C of the housing 2, and the direction of these central axes C is shown as the axial direction L. In FIG. 1, the side where the sensor element 3 is exposed to the inside of the mixed gas M is shown as a tip end side L1 in the axial direction L, and the side opposite to the tip end is shown as a base end side L2. Further, in the same drawing, the upstream side of the flow of the mixed gas M in the intake passage 81 is on the left side, and the direction of this flow is indicated by M1.

  As shown in FIGS. 4 and 5, in the sensor element 3, a solid electrolyte body 31 having oxygen ion conductivity provided with a plurality of electrodes 311 and 312 and a heater 33 for heating the solid electrolyte body 31 are stacked. It is The plurality of electrodes 311 and 312 are provided on one surface of the solid electrolyte body 31 and are a measurement electrode 311 exposed to the mixed gas M, and a reference electrode 312 provided on the other surface of the solid electrolyte body 31 exposed to the atmosphere. It consists of

  The solid electrolyte body 31 and the heater 33 are stacked via the insulator 32. The insulator 32 forms a gas chamber 321 into which the mixed gas M in contact with the measurement electrode 311 is introduced and an atmosphere chamber 322 into which the atmosphere B in contact with the reference electrode 312 is introduced. The measurement electrode 311 and the reference electrode 312 are disposed at the tip of the sensor element 3. The gas detection unit 11 of the sensor element 3 is formed in a portion of the sensor element 3 in which the measurement electrode 311, the reference electrode 312, the gas chamber 321, and the like are arranged. The heater 33 has a heating element 331 at a position facing the measurement electrode 311 and the reference electrode 312, which generates heat by energization.

  As shown in FIGS. 4 and 5, the insulator 32 of the sensor element 3 is provided with a diffusion resistance layer 34 made of a porous body that determines the flow of the mixed gas M introduced into the gas chamber 321. In addition, on the surface of the sensor element 3 including the diffusion resistance layer 34, a porous protection layer 35 for capturing moisture, a poisoning substance to the measurement electrode 311, and the like is provided. The mixed gas M is introduced into the gas chamber 321 through the porous protection layer 35 and the diffusion resistance layer 34.

As shown to FIG. 1, FIG. 2, the inner side wall part 41 of the inner cover 4 is formed in cylindrical shape. The inner vent holes 411 in the inner side wall portion 41 are formed at a plurality of positions on the proximal end L2 in the axial direction L than the position where the gas detection portion 11 of the sensor element 3 is provided. This makes it difficult for the mixed gas M to stay in the inner cover 4, and the response convergence of detection of the oxygen concentration or the specific gas component concentration by the gas detection unit 11 can be improved. The inner vent holes 411 in the inner side wall portion 41 can be provided at equal intervals in the circumferential direction of the inner side wall portion 41.
The inner vent holes 421 in the inner bottom portion 42 are formed at a plurality of locations in the inner bottom portion 42. The inner vents 421 in the inner bottom 42 can be equally spaced around the center of the inner bottom 42.

As shown in FIGS. 1 to 3, the outer side wall 51 of the outer cover 5 is formed in a cylindrical shape. The outer vent hole 511 in the outer side wall portion 51 includes the position in the axial direction L where the gas detection portion 11 of the sensor element 3 is provided, and the tip side L1 and the base in the axial direction L where the gas detection portion 11 is provided It spreads and is formed in each position of end side L2. One outer vent hole 511 in the outer sidewall portion 51 is located at the most downstream center position in the half region X of the outer sidewall portion 51 located on the downstream side of the flow of the mixed gas M in the intake passage 81. It is formed. In the outer side wall portion 51, one large outer vent hole 511 is formed to be spread at each position of the distal end side L1 and the proximal end side L2 of the position in the axial direction L where the gas detection unit 11 is provided.
Outer vents 521 in the outer bottom portion 52 are formed at a plurality of locations in the outer bottom portion 52. Outer vents 521 in the outer bottom 52 may be equally spaced around the center of the outer bottom 52.

The flow of the mixed gas M in the gas sensor 1 is as follows.
As shown in FIG. 1, most of the mixed gas M flowing in the intake passage 81 goes around the outer side wall 51 and the outer bottom 52 and flows from the outer vent hole 511 of the outer side wall 51 into the outer cover 5. Next, a part of the mixed gas M in the outer cover 5 flows from the inner vent hole 411 of the inner side wall portion 41 into the inner cover 4. Then, a part of the mixed gas M in the inner cover 4 passes through the porous protection layer 35 and the diffusion resistance layer 34 and is taken into the gas chamber 321, and the oxygen concentration or the specific gas by the measurement electrode 311 and the reference electrode 312 Used for detection of component concentration.

  Further, the remaining portion of the mixed gas M in the inner cover 4 flows from the inner air hole 421 of the inner bottom portion 42 through the outer air hole 521 of the outer bottom portion 52 and flows into the intake passage 81. At this time, the negative pressure effect is exerted on the outer vent hole 521 of the outer bottom portion 52 by the mixed gas M flowing in the vent passage 81. Thus, the remaining portion of the mixed gas M in the inner cover 4 can easily flow into the intake passage 81 through the inner air holes 421 of the inner bottom portion 42 and the outer air holes 521 of the outer bottom portion 52.

As shown in FIG. 1 and FIG. 2, the inner vent holes 421 in the inner bottom portion 42 and the outer vent holes 521 in the outer bottom portion 52 are formed at mutually offset positions in the lateral direction orthogonal to the central axis C of the housing 2. ing. In other words, when the inner bottom portion 42 and the outer bottom portion 52 are viewed in the axial direction L, the formation portion of the inner vent hole 421 in the inner bottom portion 42 and the formation portion of the outer vent hole 521 in the outer bottom portion 52 overlap each other. Absent. In this way, it is possible to more effectively prevent the entry of condensed water from the outer air holes 521 of the outer bottom portion 52 to the inner air holes 421 of the inner bottom portion 42. And the said negative pressure effect can be operated more effectively.
Further, in the present embodiment, the outer vent holes 521 are formed at the center of the outer bottom portion 52 and at multiple locations around the center, and the inner vent holes 421 are located at multiple locations around the center of the inner bottom portion 42. It is formed.

The metal base of the inner cover 4 is made of stainless steel.
The resin coating layer of the inner cover 4 is made of a fluorine-containing compound (fluororesin) or a silicon-containing compound (silicon resin). The fluorine-containing compound or silicon-containing compound is selected from fluoroalkyl group-containing silane, polytetrafluoroethylene, tetrafluoroethylene / perfluoroalkylvinylether copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, and silica. Can be composed of one or two or more compounds.
The resin coating layer can be provided on the entire surface of the base material constituting the inner cover 4. The resin coating layer can also be provided only on the outer surface of the base material constituting the inner side wall portion 41 of the inner cover 4. The resin coating layer can also be provided only around the inner air vent 411 and the inner air vent 411 in the base material that constitutes the inner side wall portion 41.

  The outer cover 5 is made of a fluorine-containing compound (fluororesin) as a resin. The fluorine compound is composed of one or more compounds selected from polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. Can.

  In the gas sensor 1 of the present embodiment, the inner cover 4 is formed by covering a metal base with a resin coating layer, while the outer cover 5 is formed of resin. That is, the outer cover 5 that receives the flow of the mixed gas M of the newly introduced air A and the exhaust gas G is formed only of resin without using a metal base. Thereby, even when the condensed water contained in the mixed gas M collides with the outer cover 5 violently, the corrosion of the outer cover 5 can be almost eliminated. Moreover, deposition of deposits on the inner cover 4 can be suppressed by covering the metal base of the inner cover 4 with the resin coating layer.

  The outer vent hole 511 in the outer sidewall portion 51 is a half region X of the entire region around the central axis C in the outer sidewall portion 51 located downstream of the flow of the mixed gas M in the intake passage 81. Provided only in As a result, the flow of the mixed gas M in the intake passage 81 collides with the outer side wall 51, and the outer vent hole 511 in the outer side wall 51 collides with the outer side wall 51 and the momentum is weakened. The mixed gas M is introduced so as to wrap around. Therefore, deposits included in the mixed gas M can be less likely to be deposited around the inner air holes 411 in the inner sidewall portion 41 of the inner cover 4 and around the porous protective layer 35 of the sensor element 3. As a result, it is prevented that the mixed gas M does not easily reach the gas detection unit 11, and the responsiveness of gas detection by the gas detection unit 11 is maintained.

  In the entire region around the central axis C in the outer side wall portion 51, the outer vent hole 511 is not provided in the half region located on the upstream side of the flow of the mixed gas M in the intake passage 81. . As a result, condensed water contained in the mixed gas M is less likely to collide with the inner cover 4 and the sensor element 3. Therefore, the inner cover 4 can be made less likely to be corroded, and the sensor element 3 can be protected more effectively from water cracking by condensed water.

  Therefore, according to the gas sensor 1, the gas sensor 1 can be formed more robust against corrosion, deposition of deposits, and water cracking.

Second Embodiment
In this embodiment, various aspects of the outer vent hole 511 provided in the outer side wall portion 51 of the outer cover 5 will be described.
For example, as shown in FIG. 7, the outer vent holes 511 in the outer side wall 51 are located on the left and right sides of the half area X of the outer side wall 51 located downstream of the flow of the mixed gas M in the intake passage 81. It is also possible to form a plurality at the center position along the axial direction L. Further, as shown in FIG. 8, the outer vent hole 511 in the outer side wall 51 is circumferentially located in the circumferential region X of the half of the outer side wall 51 located on the downstream side of the flow of the mixed gas M in the intake passage 81. One can be formed substantially in the entire area.

In addition, the outer vent holes 511 in the outer side wall portion 51 can be formed, for example, in a circular shape as shown in FIG. 9, and as shown in FIG. 10, a rectangular shape elongated in the axial direction L of the outer side wall portion 51 It can also be formed in a rectangular shape that is long in the direction orthogonal to the axial direction L of the outer side wall 51, as shown in FIG. The number of outer vents 511 formed in the outer sidewall portion 51 may be one or more. Further, the shape and arrangement of the outer vent holes 511 in the outer side wall portion 51 may be various modes other than the above.
Also in the present embodiment, the other components of the gas sensor 1 and the components indicated by the reference numerals in the figure are the same as those of the first embodiment, and the same effects as those of the first embodiment can be obtained.

(Embodiment 3)
The present embodiment shows various modes in which the inner vent holes 421 in the inner bottom portion 42 and the outer vent holes 521 in the outer bottom portion 52 are formed at mutually shifted positions in the lateral direction. In addition, in FIGS. 12-15, the inner cover 4 is shown with a broken line.
For example, as shown in FIG. 12, the outer vent holes 521 may be formed only at the center of the outer bottom portion 52, and the inner vent holes 421 may be formed at a plurality of locations around the center of the inner bottom portion 42. Further, as shown in FIG. 13, the outer vent holes 521 are formed at a plurality of locations around the center of the outer bottom portion 52, and the inner vent holes 421 are formed at the center of the inner bottom portion 42 and at a plurality of locations around the center It can also be formed.

Further, as shown in FIG. 14, the outer vent holes 521 may be formed at a plurality of locations around the center of the outer bottom portion 52, and the inner vent holes 421 may be formed at a plurality of locations around the center of the inner bottom portion 42. it can. Further, as shown in FIG. 15, the outer vent holes 521 may be formed at a plurality of locations around the center of the outer bottom portion 52, and the inner vent holes 421 may be formed only at the center of the inner bottom portion 42.
The number of the outer vent holes 521 in the inner vent holes 421 in the inner bottom portion 42 and the outer vent holes 521 in the outer bottom portion 52 can be appropriately changed. Further, the manner of arranging the inner vent holes 421 in the inner bottom portion 42 and the manner of arranging the outer vent holes 521 in the outer bottom portion 52 may be various modes other than the above.
Also in the present embodiment, the other components of the gas sensor 1 and the components indicated by the reference numerals in the figure are the same as those of the first embodiment, and the same effects as those of the first embodiment can be obtained.

  The present invention is not limited to only the embodiments, and it is possible to configure different embodiments without departing from the scope of the invention.

(Confirmation test)
In this confirmation test, a corrosion confirmation test for confirming the degree of corrosion occurring in the outer cover 5 of the gas sensor 1 shown in the first embodiment, and a response for confirming the response of the gas sensor 1 shown in the first embodiment The confirmation test was done.
In the corrosion confirmation test, the following test product, comparative product 1 and comparative product 2 were prepared. The test article consists of an outer cover formed of polytetrafluoroethylene (PTFE). The comparative product 1 is composed of an outer cover formed of a stainless steel base and a resin coating layer of fluoroalkyl group-containing silane (FAS) provided on the surface of the base. The comparative product 2 consists of an outer cover formed of stainless steel.

Then, after impregnating each outer cover of the test article, the comparative article 1 and the comparative article 2 in a solution of ammonium chloride (NH ₄ Cl) for 30 minutes, it is allowed to stand in saturated steam at 60 ° C. and in the atmosphere for 20 hours The cycle was repeated to determine how much the thickness of each outer cover decreased. The measurement results are shown in FIG. In the figure, the relationship between the number of cycles (times) and the reduction amount (μm) of the thickness of the outer cover is shown.
As a result of repeating the cycles of impregnation and drying for the test product, the comparative product 1 and the comparative product 2, the reduction amount of the thickness of the comparative product 1 becomes larger than the reduction of the thickness of the test product. The reduction amount of the thickness of the comparative product 2 was larger than the reduction amount. From this result, it was found that the outer cover which is the test product is superior in corrosion resistance to condensed water as compared with the outer covers of the comparative products 1 and 2.

In the response confirmation test, the following test product, comparative product 1 and comparative product 2 were prepared. The test product was formed of a stainless steel substrate and an inner cover formed of a resin film layer of a fluoroalkyl group-containing silane (FAS) provided on the surface of the substrate, and polytetrafluoroethylene (PTFE). It consists of a gas sensor using an outer cover. The comparative product 1 includes a gas sensor using an inner cover formed of stainless steel and an outer cover formed of polytetrafluoroethylene (PTFE). The comparative product 2 is a gas sensor using only an inner cover formed of stainless steel and not using an outer cover.
The formation states of the respective inner air holes in the inner cover and the respective outer air holes in the outer cover were the same in the test product, the comparative product 1 and the comparative product 2.

Then, when the respective gas sensors of the test article, the comparative article 1 and the comparative article 2 were arranged for a predetermined time in the gas containing a large amount of deposit, the 10-90% response time of each gas sensor was measured. The 10 to 90% response time indicates the time taken for the output when detecting the oxygen concentration or the specific gas component concentration by each gas sensor to be 10% to 90% of the steady value. Further, the A / F (air-fuel ratio) of the gas containing a large amount of deposits was set to 15-18.
The measurement results of 10-90% response time are shown in FIG. In the figure, the relationship between the time (hr) when the gas sensor was exposed to the gas and the 10 to 90% response time (ms) is shown.

  As a result of measuring 10 to 90% response time at a plurality of predetermined times for test article, comparative article 1 and comparative article 2, 10 to 90% response time of comparative article 1 compared to 10 to 90% response time of test article 10 to 90% response time of the comparative product 2 is longer than that of the comparative product 1 of 10 to 90% response time. The reason why the 10 to 90% response time of the comparative products 1 and 2 is increased is considered to be mainly due to the deposition in the gas accumulated in the inner vent holes in the inner sidewall portion. From these results, it was found that the gas sensor which is the test product has less deposition of deposits and is excellent in responsiveness as compared with the gas sensors of the comparative products 1 and 2.

Reference Signs List 1 gas sensor 2 housing 3 sensor element 4 inner cover 41 inner side wall 42 inner bottom 411, 421 inner vent 5 outer cover 51 outer side wall 52 outer bottom 511, 521 outer air vent

Claims (4)

A gas sensor (1) arranged and used in an intake passage (81) of an internal combustion engine (7) having an exhaust gas recirculation mechanism (8) for recirculating a part of exhaust gas (G) to newly introduced air (A) ,
A housing (2) having an insertion port (21);
Gas detection which is disposed along the central axis (C) of the housing and is held in the insertion port via the insulator (22) and introduces the mixed gas (M) of the newly introduced air and the exhaust gas A sensor element (3) in which the portion (11) protrudes from the housing;
A cylindrical inner side wall (41) attached to the housing along the central axis, and an inner bottom (42) closing an end of the inner side wall, and the inner bottom and the inner side wall An inner cover (4) provided with inner vents (421, 411) for passing the above mixed gas in the part;
A cylindrical outer sidewall (51) attached to the inner cover or the housing along the central axis, and an outer bottom (52) closing an end of the outer sidewall, and the outer bottom And an outer cover (5) provided with an outer vent hole (521, 511) for passing the mixed gas in the outer side wall portion,
The inner cover is composed of a metal base and a resin coating layer coating the base,
The above outer cover is made of resin,
The outer vent hole in the outer sidewall portion is a half region (X) of the entire region around the central axis in the outer sidewall portion, which is located on the downstream side of the flow of the mixed gas in the intake passage Gas sensors, provided only in.   The gas sensor according to claim 1, wherein the inner vent in the inner bottom portion and the outer vent in the outer bottom portion are formed at mutually offset positions in a lateral direction orthogonal to the central axis.   The gas sensor according to claim 1, wherein the resin coating layer is configured of a fluorine-containing compound or a silicon-containing compound.   The gas sensor according to any one of claims 1 to 3, wherein the outer cover is made of a fluorine-containing compound as a resin.

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