JPH10123089A - Oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain an introduction hole formed in an oxygen sensor cover from clogging without inviting a large increase is costs. SOLUTION: An oxygen sensor 20 is provided with a layered sensor element 24 of three layers of sheets 21, 22 and 23 formed of a solid electrolyte such as a zirconia element or the like, and a cover 25 separated by a predetermined distance from an outer periphery of the element 24. Each of the sensor element 24 and cover 25 is like a quadrangular prism having a front end part closed. A cross section of each of the sensor element 24 and cover 25 is quadrilateral. Any part of the cover 25 facing to the sensor element 24 is in parallel to the element 24.

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, and more particularly, to an oxygen sensor in which the outer periphery of a stacked sensor element is covered by a cover having an introduction hole.

[0002]

2. Description of the Related Art As a configuration of a stacked type oxygen sensor, a sensor element formed by stacking a plurality of solid electrolyte (zirconia etc.) sheets so as to form an internal space, and provided on the inner and outer surfaces of the element. Generally, a device provided with a pair of electrodes is used. In this oxygen sensor, a heater is built in a part of the solid electrolyte sheet, and the heat of the heater heats the sensor element to a predetermined activation temperature. A cover for protecting the sensor element is provided on the outer periphery of the sensor element, and the cover has a plurality of introduction holes for introducing gas into the cover.

When a reference gas having a known oxygen concentration is supplied to the internal space of the sensor element, an electrode provided on the inner surface of the element comes into contact with the reference gas. On the other hand, by disposing the oxygen sensor in the atmosphere of the detection gas to be detected, the electrode provided on the outer surface of the sensor element comes into contact with the detection gas passing through the introduction hole of the cover. As described above, when the electrodes having different oxygen concentrations come into contact with the respective electrodes, an electromotive force is generated between the two electrodes in accordance with the difference between the oxygen concentrations of the two gases, or a current flows.
Therefore, the oxygen concentration of the detection gas can be known from the magnitude of the electromotive force or the current value.

In the air-fuel ratio control of an internal combustion engine using the above-described stacked oxygen sensor, an oxygen sensor (exhaust-side oxygen sensor) provided in an exhaust passage 101 of the internal combustion engine 100 as shown in FIG. The exhaust gas oxygen concentration is detected by 102, and the actual air-fuel ratio is calculated based on the oxygen concentration. Then, feedback control is performed so that the air-fuel ratio becomes a target air-fuel ratio (normally, a stoichiometric air-fuel ratio).

In the internal combustion engine 100, an exhaust gas recirculation device (EGR device) for reducing NOx (nitrogen oxide) in the exhaust gas or an exhaust gas leaked into a crankcase (not shown) of the engine 100 is used. In some cases, a blow-by gas reducing device (PCV device) for discharging an air-fuel mixture or the like (blow-by gas) is used.

As shown in FIG. 5, this EGR device 200
The exhaust passage 101 and the intake passage 103 are communicated with each other by an EGR passage 201, and the amount (EGR amount) of EGR gas (exhaust gas) returned from the exhaust passage 101 to the intake passage 103 through the passage 201 is adjusted by the flow control valve 202. Is done.

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 by a pressure passage 301, and a crankcase (not shown) of the internal combustion engine 100 and an intake passage 103
And the portion downstream of the throttle valve 104 is P
They are communicated by the CV passage 302. A flow control valve 303 is provided in the middle of the PCV passage 302, and regulates the amount of blow-by gas (PCV amount) introduced into the intake passage 103 from inside the crankcase by the valve 303.

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 may be difficult to control the actual air-fuel ratio by accurately following the change in the target air-fuel ratio.

Therefore, conventionally, as shown in FIG. 5, in addition to the above-described exhaust-side oxygen sensor 102, an intake passage 103 is provided.
Also, another oxygen sensor (intake side oxygen sensor) 105 is provided on the downstream side of the portion where the EGR passage 201 or the PCV passage 302 is connected, and the intake side oxygen sensor 105 causes the intake including the influence of EGR gas or blow-by gas. A method of detecting the oxygen concentration of the air is also taken. 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.

[0010]

The internal combustion engine 1
The oxygen sensors 102 and 105 provided in the exhaust passage 101 or the intake passage 103 are always exposed to exhaust air or intake air containing EGR gas and blow-by gas when the internal combustion engine is in an operating state. For,
The following issues are also not negligible.

That is, the intake and exhaust contain a mixture of carbon and engine oil (hereinafter referred to as "soot").
Then, this soot is covered by the cover 1 of the oxygen sensors 102 and 105.
06,107. However, the soot attached to the surfaces of the covers 106 and 107
In many cases, the fuel is removed by burning due to the heat of the covers 106 and 107 heated by the heaters 2 and 105 (not shown). However, when the amount of soot contained in the intake and exhaust air increases, soot gradually accumulated on the surfaces of the covers 106 and 107 may cause clogging of an introduction hole (not shown). . If such clogging of the introduction hole occurs, a difference occurs in the oxygen concentration between the inside and outside of the covers 106 and 107, and the detection accuracy of the oxygen sensors 102 and 105, particularly the responsiveness, deteriorates.

In particular, in the intake-side oxygen sensor 105, the temperature of the intake air (including the EGR gas or the blow-by gas) passing through the intake passage 103 is lower than the exhaust temperature. The cover 107 also tends to be relatively low in temperature, and the amount of soot removed by burning by the heat of the cover 107 is small. That is, the intake side oxygen sensor 105 is in a state where clogging of the introduction hole is more likely to occur.

Conventionally, in order to prevent the sensor performance from being deteriorated due to such clogging of the introduction hole, a ceramic heater is separately provided inside the cover, and soot adhering to the cover is burned and removed by the heat of the heater. Like
Alternatively, an oxygen sensor has been known which removes soot by forcibly discharging compressed air supplied from the compressed air source into the inside of the cover from an inlet hole (for example, Japanese Utility Model Publication No. 64-48664). reference).

However, in such an oxygen sensor, there is a problem that a significant increase in cost occurs because it is necessary to separately provide a heater on the cover or prepare a compressed air source.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an oxygen sensor which can suppress clogging in an introduction hole of a cover without causing a large increase in cost. .

[0016]

In order to achieve the above object, according to the first aspect of the present invention, a detector for detecting the oxygen concentration of gas and a heater for heating the detector are provided. A cover is provided so as to cover the outer peripheral surface of the stacked sensor element formed by stacking, and in the oxygen sensor in which an introduction hole for flowing a gas to be detected is formed in the cover,
The gist of the cover is that at least a part of the surface facing the outer peripheral surface of the sensor element has a shape parallel to the outer peripheral surface.

In the above configuration, the heater unit heats the detection unit to activate the detection unit. At this time, radiant heat is radiated toward the cover from the outer peripheral surface of the heater and the heated detector, that is, the outer peripheral surface of the sensor element. On the other hand, the cover has a shape in which at least a part of the surface facing the outer peripheral surface of the sensor element is parallel to the outer peripheral surface. Therefore, according to the configuration, the radiant heat radiated from the sensor element is efficiently absorbed by the cover.

In order to achieve the above object, the present invention according to claim 2, according to the structure of the invention described in claim 1, is characterized in that the cross-sectional shape crossing the lamination surface of the sensor element and the cross-sectional shape in the same direction of the cover are different. The intent is to make them approximately the same.

According to the above configuration, since the cross-sectional shape of the sensor element in the same direction as the cross-section crossing the lamination surface is substantially the same, the inner wall surface of the cover is parallel to the outer peripheral surface of the sensor element over the entire circumference. It is arranged in a suitable position.
Therefore, the radiant heat radiated from the sensor element is more efficiently absorbed by the cover.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment A first embodiment in which the present invention is embodied as an intake-side oxygen sensor for a diesel engine will be described below with reference to FIGS.

FIG. 1 shows a schematic configuration of a diesel engine (hereinafter simply referred to as “engine”) 11 in the present embodiment. As shown in FIG. 1, an intake pipe 12 and an exhaust pipe 13 are connected to a combustion chamber (not shown) of the engine 11.

The intake air taken into the intake pipe 12 through an air cleaner (not shown) or the like passes through the pipe 12 and is taken into a combustion chamber (not shown) of the engine 11.
A throttle valve 14 is provided in the intake pipe 12.
The valve 14 regulates the amount of intake air. Fuel injected from an injector (not shown) and intake air are mixed in the combustion chamber, and the air-fuel mixture explodes and burns, so that a driving force is obtained in the engine 11. After the combustion, the exhaust gas is introduced into the exhaust pipe 13 from the combustion chamber, and then discharged outside through a catalyst or the like (not shown).

The engine 11 is provided with an EGR device 15. The EGR device 15 includes an EGR passage 16 communicating the exhaust pipe 13 and a portion of the intake pipe 12 downstream of the throttle valve 14, and a flow regulating valve 17 provided in the passage 16. . Part of the exhaust gas in the exhaust pipe 13 passes through the EGR passage 16 and is returned into the intake pipe 12. The flow control valve 17 is an electronic control unit (not shown).
, The amount of exhaust gas passing through the EGR passage 16 is adjusted.

In the EGR device 15, a part of the intake air introduced into the combustion chamber of the engine 11 is exhausted (E
(GR gas), that is, an inert gas that is not used for combustion is mixed, and the maximum temperature of the combustion gas in the combustion chamber is reduced, thereby reducing NOx.

In the intake pipe 12, an oxygen sensor 20 is provided at a position downstream of the opening 16 a of the EGR passage 16.
Are attached such that their tips project into the intake pipe 12. The oxygen sensor 20 is connected to the throttle valve 14
And detects the oxygen concentration of the intake air composed of the EGR gas and the air that has passed through, and outputs a detection signal to the electronic control unit. The electronic control unit executes air-fuel ratio control of the engine 11 based on a detection signal from the oxygen sensor 20 and a detection signal from another oxygen sensor (not shown) separately provided in the exhaust pipe 13.

FIG. 2 shows the tip of the oxygen sensor 20 in an enlarged manner. As shown in FIG. 1, the oxygen sensor 20 includes sheets 21, 22, 2 made of a solid electrolyte such as a zirconia element.
3 is stacked in three layers, and
4 and a cover 25 made of an iron material provided at a predetermined interval on the outer periphery of the cover 4. Both the sensor element 24 and the cover 25 are fixed to a housing (not shown) of the oxygen sensor 20.

FIG. 3 shows a cross section (a cross section taken along line 3-3 in FIG. 2) orthogonal to the lamination plane of each of the sheets 21 to 23. The sensor element 24 is formed in a quadrangular cylindrical shape with its tip end closed, and has an air introduction space 26 inside. In the drawing, an outer electrode 27 made of platinum is provided on the outer surface of the sheet 21 arranged in the upper stage. A diffusion-controlling layer 28 is formed on the outer surface of the sheet 21 so as to cover the outer electrode 27. An inner electrode 29 made of platinum is provided on the inner surface of the sheet 21 at a position corresponding to the outer electrode 27.

A heater 30, which is controlled to be energized by an electronic control unit, is embedded inside the leading end of the sheet 23 arranged in the lower part of FIG. The sensor element 24 is heated by the heat of the heater 30 until the activation temperature (700 ° C.) or higher.

The cover 25, like the sensor element 24, has a rectangular cylindrical shape with a closed end. Therefore, as shown in FIG. 3, the sensor element 24 and the cover 25 have a rectangular cross section, and the portion of the cover 25 facing the sensor element 24 is parallel to the element 24. . In the present embodiment, the sensor element 24 and the cover 25 are arranged so as to be as close as possible to the extent that they do not come into contact with each other taking into account the dimensional tolerance and the assembly tolerance of the components 24 and 25.

The cover 25 has a plurality of introduction holes 31 formed all around. The intake air passing through the intake pipe 12 is introduced into the inside of the cover 25 through the introduction hole 31 and comes into contact with the outer electrode 27 via the diffusion-controlling layer 28. On the other hand, the atmosphere whose oxygen concentration is known is introduced into the atmosphere introduction space 26, and the atmosphere comes into contact with the inner electrode 29. Thus, both electrodes 27,
When the intake air and the atmosphere having different oxygen concentrations come into contact with 29, a current having a magnitude corresponding to the oxygen concentration difference flows between the two electrodes 27 and 29. In the oxygen sensor 20 according to the present embodiment, the oxygen concentration of the intake air can be detected from the magnitude of the current value.

Next, the operation and effects of the above-described embodiment will be described. When the operation of the engine 11 is started, a predetermined amount of EGR gas flows into the intake pipe 12 through the EGR passage 16. The EGR gas contains soot containing carbon, oil, and the like, and this soot tends to accumulate on the outer peripheral surface of the cover 25 of the oxygen sensor 20. The heater 30 generates heat by being controlled by the electronic control unit, and the heat causes the sensor element 24,
Particularly, the tip of the element 24 provided with the electrodes 27 and 29 is heated. As a result, the sensor element 24 is heated to a predetermined temperature (700 ° C.) and activated.

Radiation heat is radiated to the outside from the outer peripheral surface of the sensor element 24 whose temperature has risen due to the heat of the heater 30. Then, the temperature of the cover 25 on the outer periphery of the sensor element 24 rises by absorbing the radiant heat.

Here, as shown by a dashed line in FIG. 3, when a cover having a circular cross section is employed as the cover 25, the cover 25 has no portion parallel to the outer peripheral surface of the sensor element 24. The radiant heat radiated from the surface cannot be efficiently absorbed.

In this regard, in the present embodiment, the cross-sectional shape of the cover 25 is made to be a quadrangle like the sensor element 24. Therefore, the sensor element 24
Any portion facing the outer peripheral surface is parallel to the outer peripheral surface. Therefore, the radiant heat radiated from the outer peripheral surface of the sensor element 24 is efficiently absorbed by the cover 25. In particular, in the present embodiment, since the outer peripheral surface of the sensor element 24 and the cover 25 are as close as possible, most of the radiant heat can be absorbed.

As a result, the cover 25 is heated to a higher temperature, and the heat can burn and remove the soot attached to the outer peripheral surface of the cover 25. in this way,
According to the present embodiment, even if soot adheres to the cover 25, the soot is quickly removed, so that the introduction hole 31
Can be prevented from being clogged by soot that has accumulated. Therefore, due to the clogging of the introduction hole 31, a difference occurs in the oxygen concentration inside and outside the cover 25,
It is possible to prevent the detection accuracy of the oxygen sensor 20, particularly the response, from deteriorating.

Further, according to the present embodiment, the clogging of the introduction hole 31 can be suppressed as described above only by changing the shape of the cover 25. Therefore, unlike the configuration in which the heater 30 for burning and removing soot on the cover 25 is separately provided, the above-described clogging can be suppressed without causing a significant increase in cost.

As described above, the exhaust pipe 13 is attached to the cover 25 of the oxygen sensor 20 attached to the intake pipe 12.
The amount of soot deposited is greater than the cover of the oxygen sensor attached to the sensor. Further, in the diesel engine 11 as in the present embodiment, the amount of soot deposited on the cover 25 is relatively larger than that in the gasoline engine. For this reason, the oxygen sensor 20 attached to the intake pipe 12 of the diesel engine 11 as in the present embodiment is provided with an inlet 31 made of soot.
Tends to be easily clogged. In this embodiment,
This is extremely effective in preventing clogging of the introduction hole 31 of the oxygen sensor 20 attached to the intake pipe 12 of the diesel engine 11.

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to FIG.
This embodiment is different from the first embodiment only in the cross-sectional shape of the cover 25. That is, as shown in FIG. 4, the cover 25 in the present embodiment has a barrel-shaped cross section. That is, the cover 25 is formed such that the upper and lower opposing portions in FIG. 4 are parallel. The cover 25 in the present embodiment is formed into a cylindrical shape with a bottom by drawing, and then is pressed from above and below in FIG. 4 to form parallel opposing portions.

Unlike the first embodiment, in this embodiment, the cover 25 has a barrel shape in cross section, so that the cover 25
Can be formed by a combination of the above-described cylindrical drawing and pressing. For example, when forming a cover 25 having a rectangular cross section as in the first embodiment, a rectangular cylinder drawing process is generally employed. The processing has a high yield and good formability. For this reason, according to the present embodiment, the manufacturing cost of the oxygen sensor 20 can be kept low, and the distance between the sensor element 24 and the cover 25 is set smaller by improving the dimensional accuracy during processing. 25 can increase the amount of heat absorbed.

The present invention can be embodied as another embodiment described below in addition to the above embodiments. In these other embodiments, substantially the same operation and effects as those of the above embodiments can be obtained.

(1) In each of the above embodiments, the oxygen sensor 2
0 is the intake pipe 12 of the engine 11 equipped with the EGR device 15.
It is designed to be attached to. On the other hand, the oxygen sensor 20 according to the present invention may be attached to the intake pipe 12 of the engine 11 having the PCV device.

(2) In the above embodiments, the oxygen sensor 2
0 is attached to the intake pipe 12 of the diesel engine 11. On the other hand, the oxygen sensor 20 may be attached to the exhaust pipe 13 of the diesel engine 11. Further, the exhaust pipe 13 of the gasoline engine, the EGR
The oxygen sensor 20 according to the present invention may be attached to the intake pipe 12 of the gasoline engine provided with the device 15 or the PCV device.

(3) In each of the above embodiments, the cover 2
Material with high heat absorption rate (eg graphite) on the inner surface of 5
Is coated, the absorptance of radiant heat radiated from the sensor element 24 can be increased. When the inner surface of the cover 25 is mirror-shaped, the absorption rate of radiant heat is low. Therefore, processing the inner surface into a satin shape is effective in increasing the absorption rate of radiant heat. According to these configurations, the temperature of the cover 25 can be further increased, and clogging of the introduction hole 31 by soot can be reliably suppressed.

(4) In each of the above embodiments, the cover 2
5 was made of an iron material. On the contrary,
The cover 25 may be formed of a metal material having high thermal conductivity, such as copper, aluminum, zinc, and nickel steel.

(5) In each of the above embodiments, FIGS.
As shown in (1), the distance between the sensor element 24 and the cover 25 in the vertical direction is substantially equal. The total amount of radiant heat radiated from the sheet 23 containing the heater 30 is larger than that radiated from the sheet 21. For this reason,
The cover 25 is configured such that the distance between the sheet 21 and the cover 25 is relatively shorter than the distance between the sheet 23 and the cover 25.
By disposing the sensor element 24 and the sensor element 24, heat may be uniformly transmitted from the outer peripheral surface of the sensor element 24 to the cover 25.

The technical ideas that can be grasped from the above embodiments are described below together with their effects. (1) In the oxygen sensor according to the first aspect, the sensor is attached to an intake pipe of an internal combustion engine provided with an exhaust gas recirculation device or a blow-by gas reduction device.

As described above, in the oxygen sensor attached to the intake pipe of the internal combustion engine, since the temperature of the cover is relatively low as described above, the amount of soot burned and removed by the heat is small. For this reason, in the oxygen sensor, clogging of the introduction hole tends to easily occur. The above (a)
The configuration described in (1) is preferable in that the clogging of the introduction hole in the oxygen sensor having the above tendency is prevented.

[0048]

According to the first aspect of the present invention, the cover for covering the sensor element has a shape in which at least a part of the surface facing the outer peripheral surface of the sensor element is parallel to the outer peripheral surface. . Therefore, the radiant heat radiated from the outer peripheral surface of the sensor element is efficiently absorbed by the cover. As a result, the soot attached to the surface can be burned and removed by the heat of the cover whose temperature has been raised to a high temperature. For this reason,
The clogging of the introduction hole due to soot can be suppressed without increasing the manufacturing cost only by changing the shape of the cover.

According to a second aspect of the present invention, in the configuration of the first aspect, the cross-sectional shape of the sensor element across the lamination surface is substantially the same as the cross-sectional shape in the same direction of the cover. . Therefore, since the inner wall surface of the cover is disposed at a position parallel to the outer peripheral surface of the sensor element over the entire circumference, radiant heat radiated from the element is more efficiently absorbed by the cover. As a result, the soot can be burned and removed by the heat of the cover whose temperature has been further raised to a high temperature, so that clogging of the introduction hole can be more reliably suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an engine system.

FIG. 2 is a perspective view showing a tip portion of the oxygen sensor.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a cross-sectional view of an oxygen sensor according to another embodiment.

FIG. 5 is a schematic configuration diagram of an internal combustion engine including an oxygen sensor.

[Explanation of symbols]

21 ... sheet, 25 ... cover, 27 ... outer electrode, 29 ...
Inside electrode, 23 ... sheet, 30 ... heater, 31 ... introduction hole.

Claims (2)

[Claims] A cover is provided so as to cover an outer peripheral surface of a stacked sensor element in which a detection unit for detecting the oxygen concentration of a gas and a heater unit for heating the detection unit are stacked. In the oxygen sensor having an introduction hole through which a gas to be detected flows through the cover, the cover has a shape in which at least a part of a surface facing the outer peripheral surface of the sensor element is parallel to the outer peripheral surface. An oxygen sensor, comprising: 2. The oxygen sensor according to claim 1, wherein a cross-sectional shape of the sensor element crossing a lamination surface and a cross-sectional shape of the cover in the same direction are substantially the same.