JPH10170475A - Oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain a deposit from adhering to a cover of an oxygen sensor thereby clogging an introduction hole of the cover. SOLUTION: An oxygen sensor 23 mounted to a suction pipe of a vehicle diesel engine is provided with an element 24 of a solid electrolyte such as zirconia or the like, and a cover 25 covering an outer periphery of the element 24 and having a plurality of introduction holes 28. A plurality of alumina particles 29 are enclosed in a space 31 between the electrode 24 and cover 25. The alumina particles 29 remove a deposit adhering to the neighborhood of the introduction holes 28 while moving in the cover 25 consequent to vibrations of the engine and vehicle.

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 an element for measuring the oxygen concentration of a gas, and a gas covering the element and flowing a gas to be measured. An oxygen sensor including a cover having an introduction hole.

[0002]

2. Description of the Related Art An oxygen sensor generally includes an element formed of a solid electrolyte (zirconia or the like) having an internal space, and a pair of electrodes provided on the inner and outer surfaces of the element. (See, for example, JP-A-5-26)
An oxygen sensor described in Japanese Patent Publication No. 842. ). A cover is provided on the outer periphery of the element to protect the element,
The cover has a plurality of introduction holes for introducing gas therein. In the oxygen sensor, when the gas introduced into the cover through the introduction hole comes into contact with the surface of the element, an output signal corresponding to the oxygen concentration of the gas is output from each electrode.

For example, in the air-fuel ratio control of an internal combustion engine, the oxygen concentration of exhaust gas is detected by an oxygen sensor (exhaust-side oxygen sensor) provided in an exhaust passage of the engine, and an actual oxygen concentration is detected based on the oxygen concentration. An air-fuel ratio is calculated. Then, feedback control is performed so that the air-fuel ratio becomes a target air-fuel ratio (normally, a stoichiometric air-fuel ratio).

In an internal combustion engine equipped with an exhaust gas recirculation device (EGR device) or a blow-by gas reduction device (PCV device), an oxygen sensor is also attached to an intake pipe of the internal combustion engine to detect intake air detected by the sensor. A method of improving the control accuracy of the air-fuel ratio control by referring to the oxygen concentration and the oxygen concentration of the exhaust gas together has been taken.

[0005]

Each of the oxygen sensors provided in the exhaust passage or the intake passage of the internal combustion engine emits exhaust gas or EG when the internal combustion engine is in operation.
Since it is constantly exposed to intake air containing R gas and blow-by gas, the following problems cannot be ignored.

That is, the intake and exhaust contain a mixture of carbon and engine oil (hereinafter referred to as "deposit"), and this deposit adheres to the cover of the oxygen sensor. Then, there is a problem that the deposits gradually deposited on the surface of the cover cause clogging of the introduction hole (not shown). If such clogging of the introduction hole occurs, a difference occurs in the oxygen concentration inside and outside the cover, and the detection accuracy of the oxygen sensor, particularly the response, deteriorates.

In particular, since the temperature of the intake air is lower than that of the exhaust gas and the stickiness of the deposit is large, the deposit on the intake oxygen sensor tends to adhere to the cover more easily than the oxygen on the exhaust gas. is there. That is, the intake side oxygen sensor is in a state where clogging of the introduction hole is more likely to occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent a deposit attached to a cover of an oxygen sensor from clogging an introduction hole of the cover.

[0009]

In order to achieve the above object, the present invention provides an element for measuring the oxygen concentration of a gas, and an introduction hole which covers the element and through which a gas to be measured flows. In the oxygen sensor provided with the cover described above, a deposit removing member that cannot pass through the introduction hole is movably disposed inside the cover.

In the above structure, when the oxygen sensor is provided in, for example, an internal combustion engine of a vehicle, the deposit removing member moves irregularly inside the cover due to vibrations accompanying the running of the vehicle or vibrations of the internal combustion engine. . By this movement, the deposit attached to the vicinity of the introduction hole in the cover is removed by the deposit removing member.

[0011]

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 provided in a vehicle 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 the engine 11. The intake air that has been taken into the intake pipe 12 after passing through an air cleaner (not shown) or the like passes through the pipe 12 and is taken into the combustion chamber (not shown) of the engine 11. A throttle valve 14 is provided in the intake pipe 12, and the amount of intake air taken into the combustion chamber of the engine 11 is adjusted according to the opening of the valve 14. 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.
The exhaust gas after combustion is introduced into the exhaust pipe 13 from the combustion chamber,
It is discharged outside after passing through a catalyst or the like (not shown).

The engine 11 is provided with an EGR device 15. The EGR device 15 is an EGR device that connects the exhaust pipe 13 with the intake pipe 12 downstream of the throttle valve 14.
The apparatus includes a passage 16 and a flow control valve 17 provided in the middle of 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 for the engine 11 (not shown).
, The amount of exhaust gas passing through the EGR passage 16 is adjusted. Exhaust gas (EGR gas), that is, an inert gas that is not subjected to combustion, is mixed into a part of the intake air introduced into the combustion chamber of the engine 11, and the maximum temperature of the combustion gas in the combustion chamber is reduced. It is planned.

The engine 11 has a blow-by gas reducing device (PC) for discharging exhaust gas and air-fuel mixture (blow-by gas) leaked into a crankcase (not shown).
V device) 18 is provided. This PCV device 18
A pressure passage 19 connects the inside of a cylinder head cover (not shown) with the intake pipe 12 upstream of the throttle valve 14, and the inside of a crankcase (not shown) and the intake pipe 12 downstream of the throttle valve 14. Are communicated by the PCV passage 20. A flow regulating valve 21 is provided in the middle of the PCV passage 20, and regulates the amount of blow-by gas (PCV amount) introduced into the intake pipe 12 from inside the crankcase by the valve 21.

An oxygen sensor 23 is attached to the intake pipe 12 at a position downstream of the openings 16 a and 20 a of the EGR passage 16 and the PCV passage 20. It protrudes vertically downward. The oxygen sensor 23 is a throttle valve 1
4 detects the oxygen concentration of the intake air composed of the air that has passed through No. 4 and the EGR gas and the blow-by gas, and the detection signal (current)
Is output 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 23 and a detection signal from an oxygen sensor (not shown) separately provided in the exhaust pipe 13.

FIG. 2 shows the tip of the oxygen sensor 23. As shown in FIG.
And a cover 25 provided so as to cover the outer periphery of the element 24. Both the element 24 and the cover 25 are fixed to the housing 26 of the oxygen sensor 23.

The element 24 is formed in the shape of a test tube by a solid electrolyte such as a zirconia element or the like, and platinum electrodes (not shown) are provided on the inner and outer surfaces, respectively. Further, a heater (not shown) controlled by an electronic control unit is provided inside the element 24, and the element 24 is heated to a predetermined activation temperature or higher by the heater.

The cover 25 is formed of a stainless steel material and has a cylindrical shape with a bottom, and an introduction hole 28 is formed in each of a side portion and a bottom portion. Each of the introduction holes 28 has a tapered hole shape whose diameter is increased from the outside to the inside of the cover 25, and has an inner peripheral wall surface inclined toward the inside of the cover 25.

In this embodiment, the element 24 and the cover 2
5, a plurality of alumina particles 29 are interposed. The alumina particles 29 have a spherical shape having a plurality of protrusions 30 on the outer peripheral surface, and are formed in a shape that cannot pass through the introduction hole 28. Further, a space 31 is formed between the element 24 and the cover 25 so that the alumina particles 29 can move to some extent.

Next, the operation and effect of the embodiment constructed as described above will be described. FIG. 3 shows the cover 2
5 shows one of the introduction holes 28 formed in an enlarged manner. When the operation of the engine 11 is started, predetermined amounts of EGR gas and blow-by gas flow into the intake pipe 12 through the EGR passage 16 and the PCV passage 20. E
As described above, the GR gas and the blow-by gas include a deposit containing carbon, oil, and the like. Therefore, a part of the deposit included in the intake air adheres to the outer peripheral surface of the cover 25 and the inner peripheral wall surface of the introduction hole 28 as shown in FIG.

The alumina particles 29 in the cover 25 are located at the bottom of the cover 25 when the engine 11 and the vehicle are both stopped, but the operation of the engine 11 is started and the vehicle is in a running state. As a result, the inside of the cover 25 moves irregularly due to the vibration of the engine 11 and the vehicle. Then, the deposit attached to the inner peripheral wall surface of the introduction hole 28 is removed by being scraped off by the projections 30 of the alumina particles 29. The deposit thus removed falls to the bottom of the cover 25,
It is discharged to the outside (inside of the intake pipe 12) through the inlet hole 28 at the bottom or burns by contacting the element heated to a high temperature by the heat of the heater.

Therefore, according to the present embodiment, the introduction hole 28
By removing the deposits adhered to the inner peripheral wall surface by the alumina particles 29, clogging of the holes 28 can be suppressed.

By the way, unlike the present embodiment, a heater is provided inside the cover 25 in order to prevent the introduction hole 28 from being clogged, and the deposit attached to the outer peripheral surface of the cover 25 is burned by the heat of the heater. To remove it. However, according to such a configuration, since the cover 25 needs to be heated by the heater, the power consumption of the oxygen sensor 23 increases, which is not preferable.

In this respect, in the present embodiment, the alumina particles 29 are moved inside the cover 25 by the vibration of the engine 11 or the vehicle, and the deposits are removed by the movement. Clogging of the introduction hole 28 can be prevented without causing a problem such as increase.

Further, in this embodiment, the deposit attached to the cover 25 can be removed, and the poisoning substance attached to the surface of the element 24 can be removed. That is, the oil introduced from the PCV passage 20 into the intake pipe 12 contains phosphorus (P) and zinc (Zn), and these compounds (Zn3 (PO4) 2 etc.) May adhere to the surface. When the poisoning substance adheres to the surface of the element 24 as described above, there is a concern that the detection accuracy of the oxygen sensor 23 is reduced.

However, according to the present embodiment, since the outermost surface layer of the element 24 is thinly scraped off by the alumina particles 29 and the poisonous substance can be removed, the oxygen sensor 23 caused by the adhesion of the substance is removed. A decrease in detection accuracy can be prevented.

Further, in the present embodiment, the alumina particles 29
Since the plurality of protrusions 30 are formed on the surface of
9 and the cover 25 are in point contact with each other.
29 has a very small contact area.

For example, when substantially spherical alumina particles without such projections 30 are used, the cover 25
The contact area with the cover 25 is increased, and the particles may adhere to the cover 25 due to the adhesion of the deposit.

In this respect, according to the present embodiment, the deposit can be efficiently removed by the projections 30 without causing the fixation of the alumina particles 29 as described above. In addition, the introduction hole 28 in the present embodiment is
5 has a tapered hole shape whose diameter increases from the outside toward the inside. For this reason, the deposit attached to the inner peripheral wall surface of the introduction hole 28 is easily scraped off by the projections 30 of the alumina particles 29, and the deposit can be efficiently removed.

In addition, in this embodiment, when the vehicle is not running just after the engine 11 is started, the alumina particles 29 are often located at the bottom of the cover 25. The introduction hole 28 formed at the bottom is substantially closed by the particles 29. As a result, according to the present embodiment, since the diffusion of heat through the introduction hole 29 is reduced, the element 24 can be efficiently heated by the heater when the engine 11 starts.
The element 24 can be activated early.

In the present embodiment, when the element 24 is heated by the heat of the heater, the alumina particles 2 are heated by the heat.
9 is also heated at the same time and its temperature rises. Since the alumina particles 29 have a predetermined heat capacity, the particles 29 act as a kind of heat storage material by heating and raising the temperature. As a result, according to the present embodiment, the cover 25
Of the heater can be improved, and the power consumption of the heater can be reduced. Experiments have confirmed that the configuration of the present embodiment can reduce the power consumption of the heater by 5 to 10%.

FIG. 4 shows the results of an experiment performed to confirm the effect of the present embodiment. Hereinafter, the operating conditions of the engine 11 in this experiment will be described. Engine rotation speed: 1200 rpm EGR rate (volume ratio of EGR gas to total intake amount):
15% Amount of engine oil introduced into the intake pipe 12 through the PCV passage 20: 10 ml / hour. In this experiment, the oxygen concentration of the intake air was changed from 15% to 2%.
The response time of the oxygen sensor 23 when increasing to 0% is measured every 50 hours. Here, the response time is the time from when the oxygen concentration increases to when the detection signal (current) reaches 63% of the normal output value corresponding to the oxygen concentration of 20%.

The solid line in FIG. 4 shows the change in the response time of the oxygen sensor 23 in this embodiment, and the dashed line shows the change in the cover 25.
The change of the response time in the oxygen sensor having no alumina particles 29 is shown as a comparative example.

As shown in the figure, in the comparative example, it can be seen that the response time increases because the opening area of the introduction hole 28 gradually decreases due to the deposition of the deposit over time. After 100 hours from the start of the experiment, the response time has reached 600 msec., And it is difficult to perform normal air-fuel ratio control using the oxygen sensor.

On the other hand, the oxygen sensor 2 of the present embodiment
In No. 3, the response time hardly increased even 200 hours after the start of the experiment. That is, according to the present embodiment,
Deposits and elements 24 attached to the inner peripheral wall surface of the introduction hole 28
By removing the poisoning substances adhered to the surface of the substrate with the alumina particles 29, good responsiveness can be secured for a long period of time.

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

FIG. 5 shows the oxygen sensor 23 in this embodiment.
2 shows a tip portion of the camera. As shown in the figure, the cover 25 in the present embodiment has a double pipe structure including an outer cover 25a and an inner cover 25b. The covers 25a and 25b are fixed to the housing 26. As in the first embodiment, introduction holes 28a and 28b are formed in the sides and the bottom of each of the covers 25a and 25b, each having a tapered shape through which alumina particles (not shown) cannot pass. . The introduction holes 28a and 28b formed on the sides of the covers 25a and 25b are
3 are displaced in the axial direction (vertical direction in FIG. 5). Thus, the intake air that has passed through the introduction hole 28a of the outer cover 25a once collides with the side of the inner cover 25b, and is then introduced into the cover 25b. As a result, most of the deposits, poisoning substances, water droplets, and the like contained in the intake air adhere to the side of the inner cover 25b, so that these deposits and the like are prevented from adhering to the element 24.

The diameter and the number of the introduction holes 28a and 28b are determined in consideration of the responsiveness of the oxygen sensor 23 and the heat retention of the cover 25. For example, the diameter of the introduction hole 28a of the outer cover 25a is 1.0 to 2.0 mm, and the diameter of the introduction hole 28b of the inner cover 25b is 1.0 to 3.0 m.
m, and each cover 25a,
Suitably, the number of inlet holes 28a, 28b formed on the side of 25b is 8 to 24, and the number of inlet holes 28a, 28b formed on the bottom is 1 to 4.

A plurality of alumina particles (not shown) are interposed in the gap 32 between the outer cover 25a and the inner cover 25b. The gap 32 has a size that does not restrict the movement of the alumina particles due to the vibration of the engine 11 and the vehicle. Also, between the inner cover 25b and the element 24,
A plurality of alumina particles (not shown) as in the first embodiment
Is interposed.

According to this embodiment, the same effects as those of the first embodiment can be obtained, and the activation time of the element 24 can be shortened by improving the heat retaining property of the cover 25. In addition, it is possible to more reliably suppress the deposit, poisoning substance, water droplet, and the like from adhering to the element 24.

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

(1) In the first embodiment, when the vibration of the engine 11 or the vehicle is small, the alumina particles 29 are often located at the bottom of the cover 25. For this reason, in the introduction hole 28 formed on the upper side of the cover 25, the amount of deposit removal by the alumina particles 29 tends to be relatively smaller than in the introduction hole 28 formed on the lower side. In consideration of this point, for example, a cover 25 having a configuration as shown in FIG. 6 can be employed.

That is, the partition plate 40 that partitions the inside of the cover 25 into upper and lower portions is fixed to the inner peripheral wall of the cover 25. This partition plate 40 has an insertion hole 40a in the center,
The element 24 is inserted in a. And the cover 25
Inside, the same alumina particles (not shown) as in the first embodiment are provided on the upper and lower sides of the partition plate 40, respectively. Here, the diameter of the insertion hole 40a is such that the gap 41 formed between the inner peripheral surface of the hole 40a and the outer peripheral surface of the element 24 does not allow alumina particles (not shown) to pass therethrough. Is set so as not to impede the distribution of

In such a configuration, the introduction hole 28 located above the partition plate 40 is formed by alumina particles located above the plate 40, and the introduction hole 28 located below the partition plate 40 is defined by the plate 40. The deposits attached to the respective inner peripheral wall surfaces are removed by the alumina particles on the lower side.
For this reason, according to the above configuration, the deposit can be more efficiently removed and the clogging can be prevented.

(2) In the second embodiment, alumina particles are provided both in the gap 32 between the covers 25a and 25b and in the inner cover 25b. On the contrary,
Alumina particles may be interposed only in the gap 32. In this case, the introduction hole 28b of the inner cover 25b
In order to remove the deposit, it is desirable to form a tapered hole whose diameter is increased from the inside to the outside of the cover 25b, contrary to the shape shown in FIG.

(3) In the above embodiments, alumina particles are used as the deposit removing member for removing the deposit on the cover 25. On the other hand, as a material of the deposit removing member, for example, a ceramic material such as zirconia, cordierite, mullite, or a stainless material may be used. Also, alumina particles 29
Is not limited to the shape shown in the first embodiment. For example, FIG.
Shapes as shown in (b) and (c) can also be adopted.

(4) In each of the above embodiments, the oxygen sensor 2
3 is attached to the intake pipe 12 of the engine 11 provided with the EGR device 15 and the PCV device 18. On the other hand, the oxygen sensor 23 according to the present invention may be attached to the intake pipe 12 of the engine 11 provided with only one of the devices 15 and 18.

(5) In the above embodiments, the oxygen sensor 2
3 was attached to the intake pipe 12 of the diesel engine 11. On the other hand, the oxygen sensor 23 may be attached to the exhaust pipe 13 of the diesel engine 11. Further, the oxygen sensor according to the present invention may be attached to an exhaust pipe of a gasoline engine or an intake pipe of a gasoline engine provided with an EGR device or a PCV device.

The technical ideas that can be grasped from the above embodiment will be 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, as described above, the adhesion of the deposit contained in the intake air is large, so that the introduction hole tends to be clogged. The configuration described in (a) above is preferable in that the clogging in the introduction hole of the oxygen sensor, which tends to be as described above, is suppressed.

(B) In the oxygen sensor according to the first aspect, the deposit removing member has a plurality of projections on an outer surface thereof. According to such a configuration, the contact state between the deposit removing member and the cover becomes a point contact, and the contact area between them becomes extremely small. As a result, the deposit removing member can be prevented from sticking to the cover, and the deposit can be effectively removed by the protrusion.

(C) In the oxygen sensor according to the first aspect, the introduction hole has a shape in which an inner peripheral wall surface is directed toward the inside of the cover.
According to such a configuration, the deposit attached to the inner peripheral wall surface can be easily removed by the deposit removing member.

[0053]

According to the first aspect of the present invention, the deposit removing member that cannot pass through the introduction hole is movably disposed inside the cover. Therefore, for example, due to vibration of an internal combustion engine or the like to which the oxygen sensor is attached, the deposit removing member moves irregularly inside the cover. By the movement of the deposit removing member, the deposit attached to the vicinity of the introduction hole in the cover is removed. As a result, clogging of the introduction hole due to the deposit can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a diesel engine and the like in a first embodiment.

FIG. 2 is a cross-sectional view showing a tip portion of the oxygen sensor.

FIG. 3 is a sectional view showing the vicinity of an introduction hole in a cover.

FIG. 4 is a graph showing a temporal change in responsiveness of the oxygen sensor.

FIG. 5 is a cross-sectional view illustrating a tip portion of an oxygen sensor according to a second embodiment.

FIG. 6 is a cross-sectional view showing a tip portion of an oxygen sensor according to another embodiment.

FIG. 7 is a perspective view showing the shape of alumina particles according to another embodiment.

[Explanation of symbols]

24 ... element, 25 ... cover, 25a ... outer cover, 25b
... inner cover, 28 (a, b) ... introduction holes, 29 ... alumina particles.

Claims (1)

[Claims] 1. An oxygen sensor comprising: an element for measuring the oxygen concentration of a gas; and a cover that covers the element and has an introduction hole through which a gas to be measured flows. An oxygen sensor, wherein a deposit removing member that cannot pass through the introduction hole is movably arranged.