JP3257432B2 - Oxygen sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor used in an internal combustion engine or the like, and more particularly, to a cover having a multi-tube structure provided with an inner cover for covering a sensor element and an outer cover for further covering the cover. The present invention relates to an oxygen sensor having the same.

[0002]

2. Description of the Related Art An oxygen sensor generally comprises a sensor element formed of a solid electrolyte such as zirconia and a cover for covering the outer peripheral side of the element. In such an oxygen sensor, a gas to be detected is introduced into the inside of the cover through an introduction hole formed in the cover. Then, when this gas comes into contact with the sensor element, a signal corresponding to the oxygen concentration of the detection gas is output from the element.

[0003] The oxygen sensor as described above has been conventionally used for air-fuel ratio control of an internal combustion engine. For example, as shown in FIG. 8, an oxygen sensor (exhaust-side oxygen sensor) 102 is provided in an exhaust passage 101 of the internal combustion engine 100, and the oxygen concentration of the exhaust is detected by the sensor 102. And
The air-fuel ratio is feedback-controlled based on the detected oxygen concentration.

The internal combustion engine 100 has an exhaust gas recirculation device (EGR device) for reducing NOx (nitrogen oxides) in exhaust gas, or exhaust gas and mixed gas leaked into a crankcase (not shown) of the engine 100. Blow-by gas reduction device (P
CV device) may be provided.

As shown in FIG. 8, this EGR device 200
In the embodiment, the exhaust passage 101 and the intake passage 103 are connected by the EGR passage 201. This EGR passage 201
Is provided with a flow control valve 202, and the amount (EG) of EGR gas (exhaust gas) returned from the exhaust passage 101 to the intake passage 103 through the EGR passage 201 by the valve 202
R amount) is adjusted.

In the PCV device 300, the internal combustion engine 1
00 cylinder head cover (not shown) and the intake passage 1
03, a portion upstream of the throttle valve 104 is communicated with a pressure passage 301, and the inside of a crankcase (not shown) of the internal combustion engine 100 and the throttle valve 1
04 and the intake passage 103 downstream of the PCV passage 302
Communication. In the middle of the PCV passage 302,
A flow control valve 303 is provided, and the amount of blow-by gas (PCV amount) introduced into the intake passage 103 from the inside of the crankcase through the PCV passage 302 by the valve 303.
Is to be adjusted.

As described above, the EGR device 200 or the PCV
In the internal combustion engine 100 provided with the device 300, E
The oxygen concentration of the intake air becomes different depending on the change in the GR amount and the PCV amount. As a result, it is difficult to control the actual air-fuel ratio by accurately following the change in the target air-fuel ratio.

Therefore, as shown in FIG. 8, in addition to the above-described exhaust-side oxygen sensor 102, another oxygen sensor (intake-side oxygen sensor) 105 is provided in the intake passage 103 downstream of the EGR passage 201 or the PCV passage 302. A method of detecting the oxygen concentration of the intake air including the influence of the EGR gas or the blow-by gas by the intake oxygen sensor 105 is also adopted. In this way, the control accuracy in the air-fuel ratio control described above can be improved by referring to the oxygen concentration of the intake air.

By the way, in each of the oxygen sensors 102 and 105 provided in the exhaust passage 101 or the intake passage 103, the internal combustion engine 100 is constantly exposed to exhaust gas or intake air containing EGR gas and blow-by gas when the internal combustion engine 100 is in an operating state. Therefore, the following problems cannot be ignored. That is, the intake and exhaust contain fine particles (hereinafter, referred to as “deposits”) composed of a mixture of carbon, engine oil, and the like, and the deposits are contained in the sensor elements inside the covers 106 and 107 of the oxygen sensors 102 and 105. (Not shown), the detection accuracy of the oxygen sensor may be deteriorated.

[0010] In view of this, the cover covering the sensor element has a double-pipe structure (for example, an "oxygen sensor" described in Japanese Patent Application Laid-Open No. 5-26842) to prevent the deposit from adhering to the sensor element. It is possible to do.

[0011]

However, even in an oxygen sensor employing a cover having a double-tube structure, a large amount of deposit adheres to each cover, although deposition of the deposit on the sensor element is suppressed. There is a problem that the introduction hole formed in the cover is clogged. When such clogging of the introduction hole occurs, the detection accuracy of the oxygen sensor, particularly the responsiveness, may be deteriorated.

In particular, as described above, in the oxygen sensor 105 provided in the intake passage 103,
Since the temperature of the intake air (including the EGR gas or the blow-by gas) passing through the exhaust gas is lower than the exhaust gas temperature and the viscosity of the deposit tends to be relatively high, the clogging of the introduction hole as described above occurs more frequently. The situation is easy to do.

The present invention has been made in view of such circumstances, and an object thereof is to suppress the introduction hole formed in a cover of an oxygen sensor from being clogged by a deposit.

[0014]

In order to achieve the above object, according to the first aspect of the present invention, a sensor element for detecting the oxygen concentration of gas and a sensor element are provided so as to cover the sensor element.
In an oxygen sensor including an inner cover having an introduction hole for introducing a gas therein and an outer cover provided to cover a side portion of the inner cover, the introduction hole is a side portion of the cylindrical inner cover. And at least its inner peripheral surface is
The outer cover is covered with a water-repellent coating and has a bottomless cylindrical shape having no introduction hole.

According to the above configuration, the gas whose oxygen concentration is detected by the sensor element is introduced into the inside of the outer cover after the gas is introduced into the inside of the outer cover from the bottom opening of the outer cover and then passes through the introduction hole. Will be introduced. Therefore, since the gas flow does not directly collide with the side surface of the inner cover, the amount of deposit adhering to the side surface of the inner cover is reduced. In addition, the affinity between the inner peripheral surface of the introduction hole and the deposit
The amount of deposit adhering to the inner peripheral surface
Decrease.

In order to achieve the above object, according to the second aspect of the present invention, in the oxygen sensor according to the first aspect,
The purpose of the outer cover is that the bottom of the outer cover extends in the axial direction more than the bottom of the inner cover.

According to the above configuration, the gas is introduced into the inside of the outer cover by bypassing the bottom peripheral portion of the outer cover, so that the amount of deposit adhering to the side surface of the inner cover is further reduced.

In order to achieve the above object, according to the third aspect of the present invention, in the oxygen sensor according to the first or second aspect, the outer cover has an inner flange extending inward at a bottom opening thereof. It is intended.

According to the above structure, the gas is introduced into the outer cover by bypassing the inner flange, and the moving path to the inner cover becomes longer, so that the deposit adhering to the side surface of the cover is formed. Is further reduced.

[0020]

[0021]

According to a fourth aspect of the present invention, in the oxygen sensor according to any one of the first to third aspects, the outer surface of the inner cover and the inner surface of the outer cover are provided with a water-repellent coating. It is intended that the coating is performed.

According to the above construction, any one of claims 1 to 3 is provided.
In addition to the effects of the invention described above, the amount of deposits attached to the outer surface of the inner cover and the inner surface of the outer cover is reduced .

[0024]

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] The present invention relates to an EG for a diesel engine.
A first embodiment applied to an oxygen sensor used for R amount feedback control will be described with reference to FIGS.

FIG. 1 shows a schematic configuration of a diesel engine system. As shown in FIG. 1, an intake pipe 12 is connected to the diesel engine 11, and intake air is introduced into a combustion chamber (not shown) of the engine 11 through the pipe 12. A throttle valve 13 is provided in the intake pipe 12 and controls the amount of intake air introduced into the combustion chamber by the valve 13. And, the intake air introduced into the combustion chamber,
Fuel injected from an injector (not shown) is mixed in the combustion chamber, and the air-fuel mixture is burned, so that a driving force is obtained for the engine 11. After combustion, the exhaust gas is introduced into the exhaust pipe 14 from the combustion chamber, and then is discharged outside through a catalyst or the like (not shown).

The engine 11 further includes an exhaust gas recirculation device (E
GR device 15 is provided. This EGR device 15
Is a throttle valve 13 in the exhaust pipe 14 and the intake pipe 12.
An EGR passage 16 that communicates with a portion on the downstream side is provided, and a flow regulating valve 17 provided in the middle of the EGR passage 16. Part of the exhaust gas in the exhaust pipe 14 passes through the EGR passage 16 and is returned into the intake pipe 12. As described above, the amount of exhaust gas that passes through the EGR passage 16 and returns to the intake pipe 12 (EG
The R amount) is adjusted by controlling the opening degree of the flow control valve 17 by an electronic control unit (not shown) of the engine 11.

In this engine system, an oxygen sensor 20 is provided in the intake pipe 12 at a position downstream of the opening of the EGR passage 16. The oxygen sensor 20 detects the oxygen concentration of the intake air including the EGR gas introduced into the intake pipe 12 through the EGR passage 16 and outputs a detection signal to the electronic control unit. The electronic control unit executes the EGR amount feedback control based on the detection signal from the oxygen sensor 20.

FIG. 2 is a cross-sectional view showing a front end portion of the oxygen sensor 20. As shown in FIG.
0 is a sensor element 2 formed in a rod shape by zirconia
1, a cover 22 having a double pipe structure provided so as to cover the outer periphery of the sensor element 21, and a housing 23 for fixing the sensor element 21 and the cover 22.

The sensor element 21 has a portion for detecting the oxygen concentration at the tip side, and a signal corresponding to the oxygen concentration of the intake air coming into contact with the portion is provided by a pair of electrodes ( (Not shown). The sensor element 21 has a built-in heater (not shown) that is controlled to be energized by the electronic control unit. The sensor element 21 is heated to a predetermined activation temperature (for example, 60
0 ° C.).

The oxygen sensor 20 includes a housing 23
Is fixed to the intake pipe 12 so that its distal end portion (lower portion in the figure) protrudes into the pipe 12, in the axial direction of the pipe 12, that is, in the flow direction of the intake air. It is attached to the pipe 12 so as to be substantially perpendicular to the pipe (see FIG. 1).

The cover 22 according to this embodiment includes an inner cover 26 that covers the sensor element 21 and an outer cover 25 that covers the side of the cover 26. Each of these covers 25 and 26 is made of stainless steel. Further, each of the covers 25 and 26 is fixed to the housing 23 such that a gap for allowing the intake air to flow quickly is formed therebetween.

The inner cover 26 has a cylindrical shape with a bottom, and a side portion thereof has an introduction hole 3 for introducing air into the inside.
A plurality of 0s are formed. In consideration of the responsiveness of the oxygen sensor 20, the introduction holes 30 have a diameter of, for example, 1 to 3 mm, and the number thereof is desirably 4 to 8.

On the other hand, the outer cover 25 has a bottomless cylindrical shape whose bottom portion is open. The outer cover 25 is different from the inner cover 26 in that an introduction hole is not formed in a side portion thereof. Further, the bottom of the outer cover 25
The inner cover 26 extends beyond the bottom of the inner cover 26 in the axial direction (vertical direction in FIG. 2). Therefore, the inner cover 2
6 is completely exposed by the outer cover 25 without being exposed.

Further, in this embodiment, both covers 2
5 and 26 are covered with an FAS film (not shown) made of fluoroalkylsilane (hereinafter simply referred to as “FAS”) on the entire surface (including the inner peripheral surface of the introduction hole 30). The FAS film is bonded to the covers 25 and 26 (stainless steel) by oxygen in the silane, and has a structure in which a fluoroalkyl group is bonded to the silane. Due to the presence of the fluoroalkyl group, the FAS coating has water repellency.

Next, the operation and effect of this embodiment will be described. When the operation of the engine 11 is started, a flow of intake air toward the combustion chamber is formed inside the intake pipe 12. In addition, the flow control valve 1 of the EGR device 15
7 is opened, EGR is provided inside the intake pipe 12.
EGR gas is introduced through the passage 16 and mixed with the intake air.

Since the introduction hole is not formed in the outer cover 25 and the bottom of the outer cover 25 extends more in the axial direction than the bottom of the inner cover 26, a part of the intake air is supplied as shown in FIG. As shown by the arrow A1, it collides with the side surface of the outer cover 25, bypasses the extended portion of the cover 25, and is introduced into the inside from the bottom opening. Further, as indicated by an arrow A2, the intake air passing through the bottom side of the outer cover 25 is:
Since the bottom of the cover 25 is extended, the cover 25 is not directly introduced into the inside of the cover 25, but is introduced in a partially stagnated state. The intake air is supplied to the inner cover 26.
After passing through the gap between the inner cover 26 and the outer cover 25, it is introduced into the inner cover 26 through each introduction hole 30 and contacts the sensor element 21.

As described above, in the oxygen sensor according to the present embodiment, the intake air does not directly collide with the inner cover 26. Further, the deposit contained in the intake air has a large inertial force and its flow direction tends to be hard to change. Therefore, when the intake air is introduced into the outer cover 25 in a stagnant state (arrow A2). ), The amount of deposit contained in the intake air is relatively small.

Therefore, according to this embodiment, the amount of the deposit adhering to the side surface of the inner cover 26 can be reduced, and the clogging of the introduction hole 30 can be suppressed. As a result, a predetermined responsiveness of the oxygen sensor 20 can be ensured, and deterioration of the detection accuracy can be prevented.

By the way, as in the present embodiment, in order to prevent the intake air from directly colliding with the inner cover 26, for example, the following configuration may be adopted. That is, the outer cover is formed in a cylindrical shape with a bottom, and a side opening having an opening area similar to that of the bottom opening is formed on a side of the outer cover. Then, the housing of the oxygen sensor is fixed to the intake pipe 12 such that the side where the side opening is formed faces downstream in the flow direction of the intake air.

According to such a configuration, the intake air passing through the side opening is introduced into the inside of the outer cover in a stagnant state similarly to the present embodiment, and is included in the introduced intake air. Since the amount of deposit is reduced, it is possible to suppress clogging of the introduction hole. However, when the above configuration is adopted, the housing is connected to the intake pipe 12.
When fixing the oxygen sensor, it is necessary to make sure that the side opening of the outer cover is directed to the downstream side in the flow direction of the intake air, so that the mounting work of the oxygen sensor becomes complicated.

In this regard, according to the present embodiment, the oxygen sensor 20 can be easily attached to the intake pipe 12 without causing such complication. Further, in the present embodiment, the introduction hole is not formed in the outer cover 25, and furthermore, the bottom is extended in the axial direction from the bottom of the inner cover 26, and the inner cover 26 is completely formed by the outer cover 25. It is covered. Therefore, heat radiation to the outside of the inner cover 26 is effectively suppressed by the outer cover 25, and the inner cover 26 is maintained at a high temperature by the heat of the heater. As a result, according to the present embodiment, even if a deposit adheres to the inner cover 26, the deposit is burned and removed by the heat of the cover 26. Clogging can be further suppressed.

Further, in the oxygen sensor 20 attached to the intake pipe 12, since the intake air is at a low temperature, the power consumption of the heater tends to increase as compared with, for example, the oxygen sensor attached to the exhaust pipe 13. In this regard, according to the outer cover 25 of the present embodiment, since the heat radiation to the outside can be effectively suppressed as described above, it is preferable in reducing the power consumption of the heater.

In this embodiment, both covers 25, 2
6 is coated with a water-repellent FAS film, so that the affinity between the surfaces of the covers 25 and 26 and the deposit is reduced. As a result, according to the present embodiment, it becomes difficult for the deposit to adhere to the inner peripheral surface of the introduction hole 30, and it is possible to suppress clogging of the hole 30 due to the deposit. Furthermore, according to the present embodiment, the outer cover 2
Similarly, the deposit hardly adheres to the inner surface of the inner cover 5 and the outer surface of the inner cover 26.
It is possible to prevent the gap between 5, 26 from decreasing due to adhesion of the deposit. When the size of the gap is reduced, the intake air cannot flow quickly between the two covers 25 and 26, and the responsiveness of the oxygen sensor decreases. According to the present embodiment, such responsiveness is reduced. Drops can be avoided.

Further, in the oxygen sensor 20 attached to the intake pipe 12 as in the present embodiment, since the temperature of the intake air is relatively low and the adhesiveness of the deposit is high, the deposit adheres to the inner cover 26. And the clogging of the introduction hole 30 is more likely to occur. In this regard, according to the present embodiment, such clogging of the introduction hole 30 can be suitably suppressed.

[Second Embodiment] Next, a second embodiment of the present invention will be described. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 3 shows the oxygen sensor 20 according to this embodiment.
It is sectional drawing which shows the front-end | tip part of this. In this embodiment, the shape of the outer cover 25 has the feature. That is, as shown in the figure, an inner flange 40 is formed at the bottom side opening portion of the outer cover 25 by extending a peripheral portion thereof into the cover 25 over the entire circumference. Therefore,
The side section of the outer cover 25 has a substantially L-shape.

In this embodiment constructed as described above, as shown by the arrow A3 in FIG.
And moves to the inside of the outer cover 25, so that the movement distance becomes longer. As a result, the intake air reaches the inner cover 26 in a stagnant state,
When the intake air becomes stagnant in this manner, the amount of deposit contained therein decreases. As a result, according to the present embodiment, the amount of the deposit adhering to the inner cover 26 is further reduced, and the clogging of the introduction hole 30 can be suppressed more reliably.

Further, in the present embodiment, the heat retention of the outer cover 25 is improved by the inner flange 40, so that the heat radiation to the outside of the inner cover 26 is further suppressed. Therefore, the amount of deposit burned and removed by the heat of the inner cover 26 maintained at a higher temperature increases, and the clogging of the introduction hole 30 can be further suppressed. In addition, the power consumption of the heater can be further reduced.

[Third Embodiment] Next, a third embodiment of the present invention will be described. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 4 shows an oxygen sensor 20 according to this embodiment.
FIG. 5 is a cross-sectional view showing a tip side portion of FIG.
It is sectional drawing along the line. As shown in each drawing, in the present embodiment, the inner cover 2 is not provided inside the sensor element 21.
6, a heater 31 for activating the sensor element 21 is formed by a platinum pattern.

In this embodiment, the inner cover 26 is
The heater 31 is formed in a cylindrical shape having a bottom with alumina which is an insulating ceramic material, and the heater 31 is provided therein. Since the inner cover 26 is heated to a high temperature by the heat of the heater 31, its surface is not covered with the FAS film for suppressing the adhesion of the deposit.

FIG. 6 is a perspective view showing the heater 31. As shown in the figure, the heater 31 includes lead portions 31 provided inside each side portion of the inner cover 26.
a and a heat generating portion 31b connected to each lead portion 31a. The heat generating portion 31 b is provided inside the bottom portion of the inner cover 26, and is arranged so as to cover the front end portion of the sensor element 21.

Each end of the lead portion 31a is electrically connected to an electronic control unit of the engine 11, and a voltage is applied to the heat generating portion 31b by the device through the lead portion 31a to supply a predetermined current. Swept away. Thus, the heating part 3
When a current flows through the sensor element 1b, the part 31b is heated to a temperature higher than the activation temperature of the sensor element 21 (for example, 700 ° C.).
The temperature rises up to.

In this embodiment configured as described above,
The inner cover 26 is heated to a temperature equal to or higher than the combustion temperature of the deposit (for example, 600 ° C.) by the heat of the heater 31.
Therefore, even if the deposit adheres to the inner cover 26, the deposit is reliably burned and removed by the heat of the cover 26. As a result, according to the present embodiment, clogging of the introduction hole 30 can be reliably suppressed.

In the present embodiment, the heater 31 is provided not on the outer cover 25 but on the inner cover 26 located closer to the sensor element 21. Therefore, according to the present embodiment, the sensor element 21 can be heated to activate the sensor element 21. For this reason, for example, unlike the configuration in which the heater 31 is provided on the outer cover 25, it is not necessary to separately provide a heater for heating the sensor element, and the configuration of the oxygen sensor 20 can be simplified.

In addition, in this embodiment, the heater 31 is provided inside the inner cover 26. For this reason, for example, as compared with the case where the heater 31 is provided on the surface of the inner cover 26, damage such as disconnection of the pattern of the heater 31 can be prevented, and the durability of the oxygen sensor 20 can be improved. .

Further, in this embodiment, as in the first embodiment, since the outer cover 25 suppresses heat radiation from the inner cover 26 to the outside, the inner cover 26 is maintained at a high temperature. As a result, the deposit attached to the inner cover 26 can be reliably burned and removed, and the power consumption of the heater 31 can be reduced.

Each of the above embodiments can be implemented by changing the configuration as in the other embodiments described below. According to these other embodiments, substantially the same functions and effects as those of the above embodiments can be obtained.

In the first and second embodiments, the entire surfaces of the outer cover 25 and the inner cover 26 are covered with the FAS film. On the other hand, only the inner peripheral surface of the introduction hole 30 may be partially covered with the same FAS coating. Further, in addition to the inner peripheral surface of the introduction hole 30, only the inner surface of the outer cover 25 and the outer surface of the inner cover have the same F
It may be covered with an AS film.

In the first and second embodiments, the surfaces of both covers 25 and 26 are covered with the FAS film. On the other hand, the surfaces of both covers 25 and 26 may be covered with a water-repellent film having predetermined water-repellency and heat resistance other than the FAS film. For example, the surface of the outer cover 25 having a relatively low maximum temperature may be covered with a fluororesin film instead of the FAS film. Also, F
A fluororesin film may be formed on the AS film. In this case, the FAS coating has a high affinity for the fluororesin because the fluoroalkyl group is unevenly distributed on the surface,
A more closely adhered fluororesin coating can be obtained.

In the third embodiment, the inner cover 2
6, the cover 26 is heated and the sensor element 21 is heated to activate it. On the other hand, a heater for activating the sensor element 21 can be separately provided on the element 21.

In the third embodiment, the inner cover 2
Alumina, which is an insulating ceramic material, was selected as the material for forming No. 6. On the other hand, for example, silicon nitride, silicon carbide, and zirconia may be selected.

In the third embodiment, the inner cover 2
6, a heater 31 is provided inside. On the other hand, for example, a heater may be provided on the surface of the inner cover 26.

In the third embodiment, platinum is used as a material for forming the heater 31. On the other hand, the heater may be made of, for example, tungsten.

As shown in FIG. 7, an inner flange 40 similar to that of the second embodiment may be formed at the bottom opening of the outer cover 25 in the third embodiment. According to this structure, similarly to the second embodiment, the amount of the deposit adhering to the inner cover 26 can be further reduced and the clogging of the introduction hole 30 can be suppressed. Further, by keeping the inner cover 26 at a higher temperature,
In addition to burning and removing the deposit attached to the heater 31, the power consumption of the heater 31 can be further reduced.

In the above embodiments, the cover 22 of the oxygen sensor 20 is constituted by the inner cover 26 and the outer cover 25. On the other hand, for example, a cover that covers the outer cover 25 may be further provided.

In the above embodiments, the present invention is embodied as the oxygen sensor 20 attached to the intake pipe 12 of the diesel engine 11. On the other hand, the present invention can also be applied to an exhaust pipe 14 of a diesel engine 11 or an oxygen sensor attached to an intake pipe or an exhaust pipe of a gasoline engine. Further, the present invention is not limited to an engine, and can be applied to an oxygen sensor used in various combustion devices.

In each of the above embodiments, the present invention is applied to an oxygen sensor 2 used in an engine 11 having an EGR device 15.
Although it has been embodied as 0, it can also be embodied as an oxygen sensor used in an engine having the above-described PCV device or an engine having both the EGR device 15 and the PCV device.

The technical ideas that can be grasped from the above embodiments will be described below together with their effects. (A) The oxygen sensor according to any one of claims 1 to 4, wherein the water-repellent coating is formed of fluoroalkylsilane. According to such a configuration, the affinity between the surface of the cover and the deposit is reduced by the water repellency of the fluoroalkyl group in the fluoroalkylsilane, whereby the deposit can be suppressed from adhering to the cover.

[0071]

( B ) The oxygen sensor according to any one of claims 1 to 4 is mounted on an intake pipe of an internal combustion engine provided with at least one of an exhaust gas recirculation device and a blow-by gas reduction device. I do.

As described above, in the oxygen sensor attached to the intake pipe of the internal combustion engine, as described above, since the soot contained in the intake air has high adhesiveness, the introduction hole tends to be clogged. The configuration described in ( b ) is preferable in that the clogging of the introduction hole in the oxygen sensor cover, which tends to be as described above, is suppressed.

[0074]

According to the first aspect of the present invention, the introduction hole is formed in the side of the inner cover, and the shape of the outer cover is a bottomless cylinder having no introduction hole. Therefore, the gas flow does not directly collide with the side surface of the inner cover, and the amount of deposit adhering to the side surface of the inner cover is reduced. In addition, at least the inner peripheral surface of the introduction hole is water repellent
Affinity with deposits because of coating
And the amount of deposit adhering to the inner peripheral surface decreases.
You. As a result, according to the present invention, it is possible to prevent the introduction hole of the inner cover from being clogged by the deposit.

According to the second aspect of the invention, in the oxygen sensor according to the first aspect, the bottom of the outer cover extends in the axial direction more than the bottom of the inner cover. Therefore, the gas is introduced into the inside of the outer cover by bypassing the bottom peripheral portion of the outer cover, so that the amount of the deposit adhering to the side surface of the inner cover is further reduced. As a result, according to the present invention, clogging of the introduction hole can be further suppressed.

According to the third aspect of the present invention, the first or second aspect is provided.
In the described oxygen sensor, an inner flange extending inward is provided at the bottom opening of the outer cover. Therefore, the gas is introduced into the outer cover by bypassing the inner flange, and the moving path to reach the inner cover becomes longer, so that the amount of the deposit adhering to the side surface of the cover is further reduced. As a result, according to the present invention, clogging of the introduction hole can be further suppressed.

[0077]

[0078] In the invention as set forth in claim 4, claim 1乃
In the oxygen sensor according to any one of the first to third aspects, the outer surface of the inner cover and the inner surface of the outer cover are covered with a water-repellent coating. Therefore, the amount of deposits adhering to the outer surface of the inner cover and the inner surface of the outer cover is reduced. As a result, according to the present invention, the size of the gap between the two covers is suppressed from being reduced by the deposit, and the response of the oxygen sensor is prevented from being reduced due to the reduction in the gap. can do.

[0079]

[0080]

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a diesel engine system according to a first embodiment.

FIG. 2 is a cross-sectional view showing a tip side portion of the oxygen sensor according to the first embodiment.

FIG. 3 is a cross-sectional view showing a tip side portion of an oxygen sensor according to a second embodiment.

FIG. 4 is a cross-sectional view showing a tip side portion of an oxygen sensor according to a third embodiment.

FIG. 5 is a sectional view taken along the line 5-5 in FIG. 4;

FIG. 6 is a perspective view showing a heater of the oxygen sensor.

FIG. 7 is a cross-sectional view showing a distal end portion of an oxygen sensor according to another embodiment.

FIG. 8 is a schematic configuration diagram showing a system of an internal combustion engine provided with an EGR device and a PCV device.

[Explanation of symbols]

20 oxygen sensor, 21 sensor element, 25 outer cover, 26 inner cover, 30 introduction hole, 31 heater
40 ... Inner flange.

Claims (4)

(57) [Claims] 1. A sensor element for detecting the oxygen concentration of a gas, an inner cover provided to cover the sensor element and having an introduction hole for introducing the gas therein, and a side portion of the inner cover. An oxygen sensor comprising an outer cover provided so as to cover the inner cover, wherein the introduction hole is formed in a side portion of the cylindrical inner cover, and at least the inner peripheral surface thereof is covered with a water-repellent coating.
The oxygen sensor is characterized in that the outer cover has a bottomless cylindrical shape without the introduction hole. 2. The oxygen sensor according to claim 1, wherein a bottom portion of the outer cover extends in an axial direction from a bottom portion of the inner cover. 3. The oxygen sensor according to claim 1, wherein the outer cover has an inner flange extending inward at a bottom opening portion. 4. The oxygen sensor according to claim 1, wherein an outer surface of the inner cover and the outer surface.
An oxygen sensor, wherein an inner surface of a cover is covered with a water-repellent coating .