JP2014025726A - Protective cover structure for gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective cover structure for a gas sensor, capable of reliably blocking adhesion of a water droplet to a sensor element arranged inside a gas flow passage.SOLUTION: A protective cover 130 for protecting a bar shape sensor element 121 projecting from a gas flow passage wall 111 into a gas flow passage 110 includes: a first cover 140 that has a first cylindrical wall portion 141 projecting from the gas flow passage wall 111 so as to cover the outer periphery part of the sensor element 121 and an end wall portion 142 covering the tip of the sensor element 121, where a gas flow-in ventilation hole 144 is formed only on the downstream side of the gas flow passage in the first cylindrical wall portion 141 and a gas flow-out ventilation hole 145 is formed in the end wall portion 142; and a guide member 151 that is arranged on the downstream side of the gas flow passage with respect to the sensor element 121 so as to catch gas flowing into the downstream side of the sensor element 121 after detouring the outer periphery of the first cover 140 and to suppress a flow rate of the gas flowing toward the downstream side, where the gas flows between the sensor element 121 and the first cover 140.

Description

  The present invention relates to a protective cover structure for a gas sensor suitable for protecting a gas sensor for detecting a gas component contained in intake air or exhaust gas in an intake passage or an exhaust passage of an internal combustion engine.

Gas sensors such as an air-fuel ratio sensor (A / F sensor), an oxygen sensor (O ₂ sensor), and a NOx sensor are provided in an intake passage and an exhaust passage of an internal combustion engine in order to detect gas components contained in the intake air and exhaust gas. Equipped. Such a gas sensor generally includes a sensor element, a heater that activates the sensor element, and a protective cover (also simply referred to as a cover) that covers the sensor element. The cover has a vent hole for introducing intake air and exhaust gas into the sensor element. The reason why the sensor element is covered with the cover is to prevent water droplets from adhering to the sensor element and to keep the sensor element warm.

  The prevention of water droplet adhesion to the sensor element will be described. If minute water droplets contained in the intake air or exhaust gas collide with and adhere to the sensor element, the temperature of the sensor element is drastically lowered, which may cause a crack in the sensor element and cause damage. Further, when water droplets adhere to the sensor element, the sensitivity of the sensor element may be reduced even when no cracks are generated. Therefore, from the viewpoint of preventing water droplets from adhering to the sensor element, the sensor element is covered with a cover. Techniques related to this are disclosed in, for example, Patent Documents 1 and 2.

The reason why water droplets are contained in the intake and exhaust air is as follows. The reason why the water droplets are included in the intake air is that the water (water vapor) included in the intake air is condensed by the intercooler to become minute water droplets. When EGR is introduced into the intake passage, a gas sensor is disposed immediately upstream of the intake manifold. Therefore, intake gas including water droplets cooled by an intercooler upstream from this gas sensor flows through the gas sensor, and water droplets are generated. Easy to collide. Also, water droplets are included in the exhaust gas because water (H ₂ O) generated by the reaction of hydrocarbons as fuel with oxygen by combustion and HC, CO, NOx in the exhaust gas is purified by the exhaust gas purification device. This is because a part of the water (H ₂ O) generated at the time of condensation is condensed into minute water droplets. The exhaust gas containing water droplets circulates in the gas sensor disposed downstream of the exhaust gas purification device, and the water droplets easily collide.

  In the technique disclosed in Patent Document 1, the sensor element with the tip protruding into the exhaust passage is covered with a cylindrical inner cover, the inner cover is further covered with a cylindrical outer cover, and the cover has a double structure. The vent holes are shifted from each other in the upstream and downstream portions of each cylindrical part of the outer cover and the inner cover, and even if water drops enter from the vent hole of the outer cover, they hit the wall of the inner cover (the inner part of the vent hole) A configuration in which water droplets are prevented from entering the inner cover is shown. The inner cover has a vent hole on the front end, but the front end faces the downstream of the exhaust passage so that it cannot be seen directly from the exhaust inflow direction, preventing water droplets from entering from the front end of the inner cover. It has come to be.

  In the technique disclosed in Patent Document 2, the sensor element whose tip is protruded into the exhaust passage is covered with a cover having a double structure of the inner cover and the outer cover, and the exhaust is introduced into the inside from the second vent hole of the outer cover. And a gas flow path that enters the inside of the inner cover through the first vent hole of the inner cover and reaches the tip of the sensor element. At least one of the inner cover and the outer cover is a second vent hole of the gas flow path. And an inner wall member arranged so as to narrow the width of at least a part of the flow path extending from the first vent hole to the gas introduction hole. The inner wall member makes it difficult for a liquid such as water to reach the sensor element through the gas flow path.

  The temperature retention of the sensor element will be described. Since the sensor element is not activated unless the temperature is raised to a certain temperature range, the sensor is equipped with a heater. Therefore, the sensor element is covered with a cover from the viewpoint of activating the sensor element more efficiently and maintaining the temperature of the activated sensor element so as to maintain the activation temperature range. A technique related to this is disclosed in Patent Document 3, for example.

JP 2009-85603 A Japanese Patent No. 4856751 Japanese Patent Laid-Open No. 9-329043

Since it is desirable to reliably avoid damage to the sensor element, it is an important issue to prevent water droplets from adhering to the sensor element.
However, with the techniques of Patent Documents 1 and 2, there is a possibility that water droplets cannot be reliably prevented from adhering to the sensor element.
That is, in Patent Document 1, it seems that even if water droplets enter the inside from the vent hole of the outer cover, it is assumed that the water droplets hit the wall of the inner cover and the water droplets are prevented from entering the inner cover. Water droplets that have entered the inside through the vent hole on the upstream side of the cylindrical part of the cover ride on the strong gas flow when flowing between the outer cover and the inner cover, and are shifted from the vent hole in the outer cover. There is a risk of entering the inside through the vent hole on the upstream side of the cylindrical portion of the inner cover. Further, after the water droplet hits the wall portion of the inner cover, it may reach the lower air vent through the wall portion and enter the inside through this air vent.

  Moreover, in patent document 2, although the inner wall member which narrows the width | variety of a flow path is provided in the gas flow path part from the 2nd ventilation hole of an outer cover to the 1st ventilation hole of an inner cover, a flow path width is narrowed. This makes it difficult for water droplets contained in the gas to enter the first vent hole of the inner cover. However, the water droplets contained in the gas also ride on the strong gas flow in the space between the outer cover and the inner cover. There is a risk of entering the first vent hole of the cover.

  The present invention was devised in view of the above problems, and provides a protective cover structure for a gas sensor that can reliably prevent water droplets from adhering to a sensor element installed in a gas flow path. It is an object.

  (1) The protective cover structure for a gas sensor of the present invention is a protective cover structure for a gas sensor that protects a rod-shaped sensor element protruding from a gas flow path wall into the gas flow path, and covers the outer periphery of the sensor element. A first cylindrical wall portion projecting from the gas flow channel wall and an end wall portion covering the tip of the sensor element, and the first cylindrical wall portion is downstream of the gas flow channel. A first cover in which a gas inflow vent is formed only on the side, and a gas outflow vent is formed in the end wall, and provided on the downstream side of the gas flow path with respect to the sensor element. A guide member that bypasses the outer periphery of one cover and captures the gas flowing into the downstream side of the sensor element, and suppresses the gas flow rate to the downstream side of the gas flowing between the first cover and at least It is characterized by having. It is also preferable that the guide member has a guide surface that reflects the trapped gas toward the first cover.

(2) The guide member includes a second cylindrical wall portion protruding from the gas flow path wall so as to cover an outer periphery of the first cylindrical wall portion of the first cover, and the second cylindrical wall. It is preferable that the second cover has an opening end portion formed at an end portion of the portion, and a gas circulation vent is formed on the upstream side of the gas flow path of the second cylindrical wall portion. .
Of course, the guide member is not limited to a cover that covers the entire outer periphery of the first cylindrical wall portion of the first cover, but in this case, the downstream side of the outer periphery of the first cylindrical wall portion of the first cover. It is preferable that it is a cylindrical wall member which covers partially.

  (3) Water that captures water droplets contained in the gas flowing in the gas flow path that is between the first cylindrical wall portion and the second cylindrical wall portion and bypasses the outer periphery of the first cover. A trapping wall, and a conduction portion that guides the gas downstream of the water trapping wall, and drops the water droplets trapped by the water trapping wall from the opening end of the second cover. It is preferable that a separation guide for separating the water droplets from the gas is provided.

(4) In this case, it is preferable that the water capturing wall portion is provided with a water guide portion that guides the captured water droplets to the inner wall of the second cylindrical wall portion of the second cover.
(5) In addition, the outer surface of the portion where the gas inflow vent or the gas flow vent is formed in at least one of the first cylindrical wall and the second cylindrical wall. It is preferable that a cylindrical projecting wall protrudes outward.

(6) The gas inflow hole and the gas circulation hole are located above the first cylindrical wall portion or the intermediate portion in the axial direction of the second cylindrical wall portion in the gravity direction. It is preferable to arrange on the wall side.
(7) In this case, it is preferable that the gas inflow hole and the gas circulation hole are disposed at a position separated from the gas flow path wall by a certain distance.

  (1) According to the protective cover structure of the gas sensor of the present invention, the gas flowing in the gas flow path bypasses the outer periphery of the first cover, flows into the downstream side of the sensor element, is captured by the guide member, and is downstream The flow rate to is suppressed. At this time, the water droplets contained in the gas have a remarkably larger specific gravity than the other gas components, so that the water droplets are unlikely to stay between the first cover and the upstream as in the case of the gas components due to their own weight, and most of them are transmitted through the guide member. And dripping. As a result, a gas component from which water droplets have been removed exists between the upstream first cover and flows into the inside from the gas inflow vent hole of the first cover and flows through the sensor element. It flows out from the gas outflow vent of the first cover. Therefore, the gas component can be detected by the sensor element while reliably preventing water droplets from adhering to the sensor element in the first cover.

  (2) Further, the guide member is constituted by a second cover having a second cylindrical wall portion protruding from the gas flow path wall so as to cover the outer periphery of the first cylindrical wall portion of the first cover, and the second cylinder If the opening end is formed at the end of the cylindrical wall and the gas flow vent is formed upstream of the gas flow path of the second cylindrical wall, the inner wall surface on the downstream side of the second cylindrical wall Serves as a guide surface, and the gas that has flowed into the second cover from the gas circulation vent hole is reliably captured by the guide surface, and the gas component from which water droplets have been removed is reflected to the upstream first cover side. it can.

  (3) In this case, in the gas flow path that bypasses the outer periphery of the first cover between the first cylindrical wall portion and the second cylindrical wall portion, the water capturing wall portion that captures water droplets, and the gas is captured by water. And a conducting part that leads to the downstream side of the wall part, and a guide is provided that separates the water droplets from the gas by dropping the water droplets captured by the water capturing wall part from the opening end of the second cover. Even before reaching the surface, water droplets can be separated from the gas, and adhesion of water droplets to the sensor element can be more reliably prevented.

(4) In order to prevent the movement of the water droplets to the first cover side if the water capturing wall portion is provided with a water guide portion that guides the captured water droplets to the inner wall of the second cylindrical wall portion of the second cover, It is possible to more reliably prevent water droplets from adhering to the sensor element in the first cover.
(5) Cylinder facing outward on the outer surface of the first cylindrical wall portion where the gas inflow hole is formed or the outer surface of the second cylindrical wall portion where the gas flow hole is formed. If the projection wall is formed in a projecting manner, the projection wall more reliably prevents water droplets from entering the inside of the vent hole, so that adhesion of water droplets to the sensor element in the first cover is further prevented. be able to.

(6) When the gas inflow vent hole and the gas flow vent hole are arranged on the gas flow path wall side above the first cylindrical wall portion or the middle portion in the axial direction of the second cylindrical wall portion in the gravity direction. Water droplets having a significantly higher specific gravity than other gas components are unlikely to enter the vent hole due to their own weight, and can more reliably prevent water droplets from adhering to the sensor element.
(7) If the gas inflow vent and the gas circulation vent are arranged at a position spaced apart from the gas flow path wall by a certain distance, it is difficult for water droplets that have traveled along the gas flow path wall to enter from the vent hole. In particular, when a protruding wall is provided, it becomes more difficult to enter, and adhesion of water droplets to the sensor element can be more reliably prevented.

It is a figure which shows the protective cover structure of the gas sensor concerning 1st Embodiment of this invention, (a) is the longitudinal cross-sectional view fractured | ruptured along the distribution direction of the gas flow path, (b) is the cross section of the half part Figures [B-B cross-sectional view of (a)], (c) is an upstream side view of the half [C view of (a)], (d) is the gas flow path of the half. Longitudinal sectional view broken along a direction orthogonal to the flow direction [cross-sectional view taken along line DD in (b)], (e) is a perspective view of the separation guide (viewed along arrow E in (d)), (f ) Is a diagram showing the shape of the separation guide before completion. It is a block diagram which shows the intake / exhaust system of the engine for motor vehicles equipped with the protective cover structure of the gas sensor concerning each embodiment of this invention. It is sectional drawing of the gas flow path wall part which shows the installation structure of the gas sensor concerning each embodiment of this invention, and its protective cover. It is a figure which shows the protective cover structure of the gas sensor concerning 2nd Embodiment of this invention, (a) is the longitudinal cross-sectional view fractured | ruptured along the distribution direction of the gas flow path, (b) is the upstream of the half part Side view [C 'arrow view of (a)], (c) is a longitudinal sectional view (D'-D' of (a), broken along a direction orthogonal to the flow direction of the gas flow path of the half part. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 4 are diagrams for explaining an embodiment of the invention. FIG. 1 is a diagram for explaining a first embodiment. FIG. 4 is a diagram for explaining a second embodiment. It is a figure explaining the matter common to both embodiment.
<First Embodiment>
First, the first embodiment will be described.

First, an automotive engine (internal combustion engine) to which a protective cover structure for a gas sensor according to the present embodiment is applied and an intake / exhaust system thereof will be described.
As shown in FIG. 2, the engine 1 according to this embodiment is a common rail diesel engine. The engine 1 is a multi-cylinder direct injection type (only one cylinder is shown in FIG. 1). A plurality of cylinders 2 are formed in a cylinder block 1B of the engine 1, and a piston 3 that reciprocates in the vertical direction in the figure is provided in each cylinder 2. The piston 3 is connected to the crankshaft via a connecting rod. The piston 3 is formed with a cavity 3a serving as a combustion chamber on the top surface. The plurality of cylinders 2 are provided side by side in a direction orthogonal to the paper surface of FIG. 1, and all the cylinders 2 have the same configuration.

  The cylinder head 1H above the cylinder 2 is provided with an injector 4 and a glow plug 5. The injector 4 has a tip projecting from the in-cylinder space of the cylinder 2 and directly injects fuel into the cylinder 2. The injection direction of the fuel injected from the injector 4 is set to a direction toward the cavity 3 a of the piston 3. A fuel pipe is connected to the base end of the injector 4, and pressurized fuel is supplied to the injector 4 from the fuel pipe. The glow plug 5 is driven and controlled so as to improve the combustion during the cold operation of the engine 1.

  The cylinder head 1H is provided with an intake port 6 and an exhaust port 7 communicating with the in-cylinder space of the cylinder 2, and an intake valve 8 and an exhaust valve 9 for opening and closing these ports 6 and 7 are provided. An intake system 10 having various devices attached to the intake passage 11 is connected to the upstream side of the intake port 6, and an exhaust system 20 having various devices attached to the exhaust passage 21 is connected to the downstream side of the exhaust port 7. It is connected. The engine 1 is equipped with a turbocharger 30, an intercooler 40, a low pressure EGR device 50, a high pressure EGR device 60 and an exhaust purification catalyst device 70 in the intake and exhaust systems 10 and 20.

  A fuel supply device 80 is connected to the injector 4. The fuel supply device 80 includes a common rail 81, a fuel injection pump 82 connected to the common rail 81, a fuel tank (not shown), and a fuel pressure sensor 83 that outputs a common rail pressure Pcm. The fuel stored in the common rail 81 is supplied from a fuel injection pump 82 driven by the engine 1 via a high pressure pipe 84. The fuel pressure (common rail pressure Pcm) stored in the common rail 81 is detected by the fuel pressure sensor 83, and a detection signal is input to a control unit (not shown).

  The intake system 10 will be described. From the upstream side, an air cleaner 12, a first intake throttle valve (throttle valve) 13, an outlet 53 of an EGR passage 51 of the low-pressure EGR device 50, and a compressor 31 of a turbocharger 30 are provided in the intake passage 11. , An intercooler 40, a second intake throttle valve (throttle valve) 14, an outlet 63 of an EGR passage 61 of the high-pressure EGR device 60 are provided in this order, and an intake manifold is connected to the downstream end of the intake passage 11 via a surge tank 15. (Hereinafter referred to as intake manifold) 16 is connected, and each downstream end of intake manifold 16 is connected to intake port 6.

  Exhaust system 20 will be described. Exhaust passage 21 is connected to a collecting portion at the downstream end of an exhaust manifold (hereinafter referred to as an exhaust manifold) 22 connected to the exhaust port 7 at each upstream end. From the inlet 62 of the EGR passage 61 of the high pressure EGR device 60, the turbine 32 of the turbocharger 30, the front stage portion 70a of the exhaust purification catalyst device 70, the inlet 52 of the EGR passage 51 of the low pressure EGR device 50, and the exhaust purification catalyst device 70. The rear stage part 70b is equipped in order.

The upstream stage 70a of the exhaust purification catalyst device 70 is equipped with an oxidation catalyst 71 and a diesel particulate filter (hereinafter simply referred to as DPF) 72 from the upstream side, and the upstream stage 70b of the exhaust purification catalyst device 70 is upstream. Two storage reduction catalysts (NO _X trap catalysts) 73 and 74 are installed in this order from the side.
Further, in the low pressure EGR device 50, an EGR cooler 54 is interposed in the middle portion of the EGR flow path 51, and a low pressure EGR valve 55 is equipped at the outlet 53 of the EGR flow path 51. In the high pressure EGR device 60, an EGR cooler 64 is interposed in the middle portion of the EGR flow path 61, and a high pressure EGR valve 65 is provided at the outlet 63 of the EGR flow path 61.

  Such intake and exhaust systems 10 and 20 of the engine 1 are equipped with various sensors for acquiring information such as for controlling the engine 1. For example, an air flow sensor or an intake air temperature sensor 101 is provided in the vicinity of the outlet of the air cleaner 12, and an air-fuel ratio sensor (A / F sensor) 102 is provided downstream of the second intake throttle valve 14 in the intake passage 11. An intake system pressure sensor 103 is provided upstream of the downstream surge tank 15, and a temperature sensor 104 is provided in the surge tank 15. Further, a differential pressure sensor 105 is provided at the front stage portion 70a of the exhaust purification catalyst device 70 in the exhaust passage 21, and the air-fuel ratio sensors 106 and 107 are provided at the upstream portion and the downstream portion of the rear stage portion 70b of the exhaust purification catalyst device 70, respectively. Is equipped.

  Examples of the gas sensor according to the present embodiment include air-fuel ratio sensors 102, 106, and 107 provided in each part. The protective cover structure of the gas sensor according to the present embodiment is applied to all or part of the air-fuel ratio sensors 102, 106, and 107 as the gas sensors. In addition, about each gas sensor illustrated in FIG. 2, it shows presence and does not show the arrangement direction.

Here, a protective cover structure of a gas sensor such as an air-fuel ratio sensor according to the present embodiment will be described.
As shown in FIG. 1 (a), a gas sensor 120 is provided in a gas flow path 110 through which gas (intake or exhaust) such as an intake passage or an exhaust passage flows. The gas sensor 120 includes a rod-shaped sensor element 121 projecting downward from the wall portion (gas channel wall) 111 of the gas channel 110 into the gas channel 110, and the sensor element 121 is heated to an activation temperature. A heater (not shown) that overheats and a protective cover 130 that is disposed around the sensor element 121 and protects the sensor element 121 are provided.

  In FIG. 1A, the vertical direction in the drawing indicates the vertical direction, and the gas sensor 120 is installed at a position vertically above the gas flow path wall 111 of the gas flow path 110 so as to face vertically downward. This is because water droplets are dropped so as to be separated from the gas sensor 120 using gravity applied to the water droplets, and the direction of the gas sensor 120 is not required to be vertical. At least the front end side of the gas sensor 120 may be vertically lower than the base end side.

The protective cover 130 includes a first cover 140 that covers the sensor element 121 and a second cover 150 that covers the first cover 140.
The first cover 140 has an end formed through a first cylindrical wall portion 141 projecting from the gas flow path wall 111 and a tapered portion 143 that gradually decreases in diameter at the tip portion of the first cylindrical wall portion 141. Wall part 142. The first cylindrical wall portion 141 is disposed concentrically or substantially concentrically with the sensor element 121 so as to cover the outer periphery of the sensor element 121, and the end wall portion 142 is slightly separated from the tip end portion 122 of the sensor element 121. Is covered.

  A gas inflow hole 144 is formed in the first cylindrical wall portion 141 only in a half portion on the downstream side of the gas flow path 110 with respect to the sensor element 121. In addition, the gas inflow vent hole 144 is a portion closer to the gas flow path wall 111 than the intermediate portion in the axial direction of the first cover 140, and is disposed at a position separated from the gas flow path wall 111 by a certain distance or more. Yes. Here, the gas inflow vent hole 144 is located in the vicinity of the base portion thereof, but is disposed at a position separated from the gas flow path wall 111 by a certain distance. Further, here, only one gas inflow hole 144 is provided on the most downstream side of the gas flow path 110.

The gas that has entered the inside of the first cover 140 from the gas inflow hole 144 at the base of the first cover 140 circulates around the sensor element 121 in the first cover 140, and the first cylindrical wall portion. 141 flows along the inner peripheral surface of the taper portion 143 toward the front end side of the first cover 140, and flows out of the first cover 140 from the gas outflow vent hole 145 of the end wall portion 142.
The second cover 150 has an opening formed through a second cylindrical wall portion 151 projecting from the gas flow path wall 111 and a tapered portion 153 that gradually decreases in diameter at the distal end portion of the second cylindrical wall portion 151. And an end 152. The second cylindrical wall portion 151 is arranged concentrically or substantially concentrically with the first cylindrical wall portion 141 so as to cover the outer peripheral portion of the first cylindrical wall portion 141 of the first cover 140, and the tapered portion 153 is the first cover. 140 is located so as to cover the outer periphery of the tapered portion 143, and the opening end portion 152 slightly protrudes in a direction away from the gas flow path wall 111 than the end wall portion 142 of the first cover 140.

  In addition, the second cylindrical wall 151 of the second cover 150 is formed with a gas circulation vent 154 only in a half portion on the upstream side of the gas passage 110 with respect to the sensor element 121. This gas circulation vent 154 is also located closer to the gas flow path wall 111 than the axially intermediate portion of the second cover 150, and is disposed at a location separated from the gas flow path wall 111 by a certain distance or more. . Here, the gas circulation vent 154 is in the vicinity of the base, but is disposed at a position separated from the gas flow path wall 111 by a certain distance. Further, here, only three gas circulation holes 154 are provided side by side.

  It is noted that the gas inflow hole 144 and the gas flow hole 154 are disposed in a portion closer to the gas flow path wall 111 than the intermediate portion in the axial direction of the covers 140 and 150, which is much more specific than other gas components. This is because a large water droplet is difficult to enter the gas inflow hole 144 and the gas circulation hole 154 due to its own weight and can more reliably prevent the water droplet from adhering to the sensor element 121.

  Further, the gas inflow hole 144 and the gas circulation hole 154 are separated from the gas flow path wall 111 by a certain distance or more because the air holes 144 and 154 are separated from the gas flow path wall 111 by a certain distance. This is because it is difficult for water droplets that have traveled through the gas flow path wall 111 to enter from the vent holes 144 and 154, and the adhesion of water droplets to the sensor element 121 can be more reliably prevented.

  In the second cylindrical wall portion 151, the cylindrical inner peripheral surface 151 a on the downstream side of the gas flow path 110 with respect to the sensor element 121 bypasses the outer periphery of the first cover 140, and the first cover 140 and the second cover 151. It functions as a guide surface that flows through a flow path space (gas flow path) 160 formed between the cover 150 and the gas that flows into the downstream side of the sensor element 121 and reflects it to the first cover 140 side. That is, the second cover 150 is configured as a guide member having the guide surface 151a. Therefore, the guide surface 151a of the present embodiment is formed in a semi-cylindrical inner peripheral surface shape.

  Further, as shown in FIGS. 1A and 1C, the outer surface of the second cylindrical wall portion 151 of the second cover 150 where the gas flow holes 154 are formed, and the first cover 140. Cylindrical projecting walls 155 and 146 protrude outwardly from the outer surface of the cylindrical wall portion 141 where the gas inflow vent holes 144 are formed. The protruding walls 155 and 146 are for preventing water droplets from entering the covers 150 and 140 from the gas flow vent holes 154 and the gas inflow vent holes 144.

  When water droplets are contained in the gas that travels from the gas circulation vent 154 to the inside of the second cover 150, most of the water droplets are captured by the outer surface or inner surface of the projection wall 155, and the outer wall surface of the second cover 150 or Drip along the inner wall. Also, even if water droplets are contained in the gas flowing into the first cover 140 from the gas inflow hole 144, most of the water droplets are captured by the outer surface of the projection wall 146 and are outside the first cover 140. Drip along the wall. Even if a water droplet enters the inside of the protruding wall 146, it is captured by the inner surface of the protruding wall 146 and drops along the inner wall surface of the first cover 140.

  As shown in FIGS. 1B and 1D, the space between the first cylindrical wall portion 141 and the second cylindrical wall portion 151 is a gas flow path that bypasses the outer periphery of the first cover 140. The gas flow path 160 is provided with a separation guide 170 that separates water droplets contained in the flowing gas from other gas components. As shown in FIG. 1 (f), the separation guide 170 is cut from one of the long side portions of the elongated plate-shaped member toward the other of the long side portions, and the one long side portion 171 is used as a base. A plurality of strip pieces 172 and 173 that can be bent on the other long side portion side are formed, and the other long side portion side is alternately bent.

  As a result, as shown in FIG. 1 (e), the strips 172 bent to the downstream side of the gas flow channel 160 and the strips 173 bent to the upstream side of the gas flow channel 160 are alternately arranged, and each strip piece. 172 and one surface (upstream surface) of each strip piece 173 capture water droplets contained in the gas flowing through the gas flow path 160, and each strip piece 172 and each strip piece 173 function as a water capturing wall portion. . Further, a gap 174 is formed between the strip piece 172 and the strip piece 173, and the gap 174 serves as a conduction portion that guides the gas flowing through the gas flow path 160 to the downstream side of the respective strip pieces 172 and 173. Function.

  In the present embodiment, as shown in FIG. 1F, each strip 172, 173 has lower edges 172a, 173a extending from one long side portion 171 as the base toward the other long side portion as the tip. As shown in FIGS. 1B and 1D, one of the base portions in the middle portion (position where the sensor element 121 is present in a side view) in the gas flow path 160 is inclined. The long side portion 171 is coupled to the outer periphery of the first cover 140, and the tip side is coupled to the inner periphery of the second cover 150. Thereby, the water droplets captured by the respective strip pieces 172 and 173 are guided to the inner periphery of the second cover 150 through the respective lower edges (water guide portions) 172a and 173a, and from the inner peripheral surface of the second cover 150. It comes to dripping.

  As described above, since the gas sensor 120 has directionality in the gas inflow hole 144 and the gas circulation hole 154, the conventional screw-in type cannot be mounted with sufficient directionality. Therefore, as shown in FIG. 3, it is preferable to fix the gas sensor 120 to the support 181 in advance so that the direction is aligned, and to attach the support 181 to the gas flow path wall 111 by bolts 182 at a plurality of locations. At the time of this attachment, a gasket 180 is interposed between the flange portion 124 provided at the base of the protruding portion 123 that protrudes outward from the gas flow path wall 111 of the gas sensor 120 and the gas flow path wall 111 to provide a sealing property. Secure.

Since the protective cover structure of the gas sensor according to the first embodiment of the present invention is configured as described above, the following operations and effects can be obtained.
First, the gas flowing in the gas flow path 110 passes between the second cover 150 and the first cover 140 inside the second cover 150 from the gas circulation vent 154 provided on the upstream side of the second cover 150. Enter the space (gas flow path) 160. At this time, since the gas circulation vent 154 is disposed in a portion closer to the gas flow path wall 111 than the intermediate portion in the axial direction of the second cover 150, water droplets having a significantly higher specific gravity than other gas components Therefore, it is difficult to enter the gas circulation vent 154. In addition, since the gas circulation vent 154 is separated from the gas flow path wall 111 by a certain distance or more, water droplets that have traveled through the gas flow path wall 111 do not easily enter the gas flow ventilation hole 154. Furthermore, since the outer surface or the inner peripheral surface of the cylindrical projection wall 155 protruding toward the outside (upstream side of the gas flow) in the gas flow vent hole 154 captures water droplets contained in the gas, The water drops drop downward along the outer wall surface or the inner wall surface of the second cylindrical wall portion 151 of the second cover 150.

  The gas that has entered the gas flow path 160 then reaches the separation guide 170. In this separation guide 170, one surface (upstream surface) of each strip piece 172, 173 captures water droplets contained in the flowing gas, and the remaining gas is downstream from each strip piece 172, 173 through each gap 174. Led to the side. The water droplets captured by the strip pieces 172 and 173 drop along the strip pieces 172 and 173, but the lower edges 172 a and 173 a of the strip pieces 172 and 173 are lowered toward the inner periphery of the second cover 150. Therefore, the water droplets are guided by the lower edges 172 a and 173 a and are dropped from the inner peripheral surface of the second cover 150 while being separated from the first cover 140.

  The gas flowing downstream from the separation guide 170 in the gas flow path 160 is captured by the cylindrical inner peripheral surface (guide surface) 151a on the downstream side of the second cylindrical wall portion 151 and is moved to the first cover 140 side. Reflected. Accordingly, gas flows into the first cover 140 through the gas inflow vent hole 144 formed on the downstream side of the separation guide 170 of the first cover 140. Since the guide surface 151a is formed in a semicylindrical inner peripheral surface shape, the gas is smoothly reflected to the first cover 140 side.

  Since the gas inflow vent hole 144 is disposed in a portion closer to the gas flow path wall 111 than the intermediate portion in the axial direction of the first cover 140, water droplets having a significantly higher specific gravity than other gas components flow into the gas due to their own weight. It is difficult to enter the ventilation hole 144 for use. Further, since the gas inflow vent hole 144 is separated from the gas flow path wall 111 by a certain distance or more, water droplets that have traveled through the gas flow path wall 111 are difficult to enter from the gas inflow vent hole 144. In addition, even if water is contained in the gas that travels from the gas inflow hole 144 to the inside of the first cover 140, most of the water droplet is captured by the outer surface of the projection wall 146 and is outside the first cover 140. Drip along the wall. Even if a water droplet enters the inside of the protruding wall 146, it is captured by the inner surface of the protruding wall 146 and drops along the inner wall surface of the first cover 140.

In this way, after removing water droplets from the gas in a plurality of stages, the gas is guided to the sensor element 121, so that it is possible to reliably prevent water droplets from adhering to the sensor element 121, and water droplets to the sensor element 121. As a result, it is possible to reliably eliminate the possibility of causing cracks in the sensor element 121 and causing damage, and to detect gas components.
Second Embodiment
Next, a second embodiment will be described.

The present embodiment is characterized by the number and arrangement of the gas circulation vents 154 and the gas inflow vents 144, and is otherwise the same as the first embodiment.
That is, in the first embodiment, three gas circulation vents 154 are provided side by side and only one gas inflow vent 144 is provided, but the number is not limited. In the present embodiment, as shown in FIGS. 4A to 4C, the gas circulation vents 154 are provided side by side and vertically in a large number, and the gas inflow vent holes 144 are also provided side by side and in a vertical and numerous manner. However, the gas flow vent holes 154 and the gas inflow vent holes 144 are arranged in a staggered manner, so that the distance between the upper and lower sides of the gas flow vent holes 154 and the gas inflow vent holes 144 is ensured. The water droplets trapped and dropped by the gas vent hole 154 and the gas inflow vent hole 144 are prevented from entering the inside from the lower gas flow vent hole 154 and the gas inflow vent hole 144 as much as possible.

  According to the protective cover structure of the gas sensor of the present embodiment, since a large number of gas circulation holes 154 and gas inflow holes 144 are formed, it is possible to promote the flow of gas into the first cover 140. As a result, there is an increased risk of water droplets entering the first cover 140 together with the gas. However, the staggered arrangement of the gas circulation vents 154 and the gas inflow vents 144 can suppress such an increase in risk. it can.

<Others>
As mentioned above, although embodiment of this invention was described, this invention is not limited to this embodiment, In the range which does not deviate from the meaning of this invention, this embodiment can be changed suitably and can be implemented.
For example, in the above-described embodiment, a gas sensor such as an air-fuel ratio sensor provided in an intake / exhaust system of an automobile engine is exemplified, but the present invention can also be applied to other gas sensors such as an oxygen sensor and a NOx sensor. In addition, the present invention is not limited to an automobile engine, as long as it is a gas sensor in which water droplets are a concern. Applicable.

Further, the guide member is not limited to the one that covers the entire outer periphery of the first cylindrical wall portion 141 of the first cover 140 like the second cover 150, but may be a member that is partially disposed downstream of the first cover 140. Good. However, in this case, a cylindrical wall member that partially covers the downstream side of the outer periphery of the first cylindrical wall 141 of the first cover 140 is preferable.
In the above embodiment, the second cover 150 serving as the guide member is provided with the guide surface 151a that captures the gas flowing into the downstream side of the sensor element 121 and reflects it to the first cover 140 side. Is not necessarily required to capture the gas flowing into the downstream side of the sensor element 121 and reflect it to the first cover 140 side, and can suppress the flow rate of the gas between the first cover 140 and the downstream side. That's fine. For example, the guide surface 151a may only be able to suppress the flow rate of the gas to the downstream side.

  If the flow rate of the gas to the downstream side can be suppressed, the gas stays between the guide member and the first cover 140 upstream thereof. Since the water droplets contained in the staying gas have a remarkably larger specific gravity than other gas components, most of the water droplets are dripped along the guide surface by its own weight. On the other hand, since the gas component does not drip, there is a gas component from which water droplets have been removed between the guide member and the first cover 140- upstream of the guide member. The gas flows into the cover 140 from the gas inflow hole 144, flows through the sensor element 121, and flows out from the gas outflow hole 145 of the first cover 140. Therefore, the gas component can be detected by the sensor element 121 while reliably preventing water droplets from adhering to the sensor element 121 in the first cover 140.

  Further, the separation guide 170 is not essential. Further, the structure of the separation guide 170 may be any as long as it has a water capturing wall portion that captures water droplets contained in the flowing gas and a conduction portion that guides the gas downstream from the water capturing wall portion. It is not limited to.

DESCRIPTION OF SYMBOLS 110 Gas flow path 111 Gas flow path wall 120 Gas sensor 121 Sensor element 130 Protective cover 140 1st cover 141 1st cylindrical wall part 142 End wall part 144 Gas inflow ventilation hole 145 Gas outflow ventilation hole 150 2nd cover (guide) Element)
151 2nd cylindrical wall part 151a Guide surface 152 Opening end part 154 Ventilation hole 155,146 Protrusion wall 170 Separation guides 172,173 Strip strip (water capturing wall part)
172a, 173a Lower edge (water guide part)
174 Clearance (conduction part)

Claims (7)

A protective cover structure for a gas sensor that protects a rod-shaped sensor element protruding from the gas flow path wall into the gas flow path,
A first cylindrical wall portion projecting from the gas flow path wall so as to cover an outer peripheral portion of the sensor element; and an end wall portion covering a distal end portion of the sensor element; A first cover in which a gas inflow vent is formed only on the downstream side of the gas flow path, and a gas outflow vent is formed in the end wall;
Provided on the downstream side of the gas flow path with respect to the sensor element, catches the gas that flows around the outer periphery of the first cover and flows into the downstream side of the sensor element, and at least between the first cover and the sensor element. A protective cover structure for a gas sensor, comprising: a guide member that suppresses a gas flow rate of the flowing gas toward the downstream side. The guide member includes a second cylindrical wall portion protruding from the gas flow path wall so as to cover an outer periphery of the first cylindrical wall portion of the first cover, and an end of the second cylindrical wall portion. An opening end portion formed in the portion, and a second cover in which a gas circulation vent is formed on the upstream side of the gas flow path of the second cylindrical wall portion, The protective cover structure of the gas sensor according to claim 1. A water capturing wall portion that traps water droplets contained in the flowing gas in a gas flow path that is between the first cylindrical wall portion and the second cylindrical wall portion and bypasses the outer periphery of the first cover. And a conduction part that guides the gas to the downstream side of the water capturing wall part, and drops the water droplets captured by the water capturing wall part from the opening end of the second cover. The protective cover structure for a gas sensor according to claim 2, wherein a separation guide for separating water droplets is provided. The gas sensor according to claim 3, wherein the water trapping wall portion is provided with a water guide portion that guides the trapped water droplets to an inner wall of the second cylindrical wall portion of the second cover. Protective cover structure. The outer surface of the portion where the gas inflow hole or the gas circulation hole is formed in at least one of the first and second cylindrical wall portions is an outer side. The protective cover structure for a gas sensor according to any one of claims 2 to 4, wherein a cylindrical protruding wall is provided so as to project toward the surface. The gas inflow vent and the gas circulation vent are on the gas flow channel wall side in the gravity direction above the intermediate portion in the axial direction of the first cylindrical wall portion or the second cylindrical wall portion. The protective cover structure for a gas sensor according to any one of claims 2 to 5, wherein the protective cover structure is disposed. 7. The protective cover structure for a gas sensor according to claim 6, wherein the gas inflow vent hole and the gas flow vent hole are disposed at a position spaced apart from the gas flow path wall by a predetermined distance.

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