JPH0792450B2 - Oxygen concentration detector - 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 concentration detector,
In particular, the present invention relates to an oxygen concentration detector suitable for detecting the oxygen concentration in a gas containing fixed particles such as automobile engine exhaust.

[0002]

2. Description of the Related Art As a conventional oxygen concentration detector, a system utilizing the principle of an oxygen concentration battery or an oxygen pump using an oxygen ion conductive solid electrolyte such as zirconia, and further, an electronic conductivity in a metal oxide such as titania. There is a method utilizing the oxygen concentration dependency of the above, and it is widely used for detecting the oxygen concentration in the exhaust gas corresponding to the air-fuel ratio for controlling the air-fuel mixture supplied to the automobile engine.

The output signals of these oxygen concentration detectors have a temperature dependency, while the temperature inside the exhaust pipe of an automobile engine in which the oxygen concentration detector is mounted ranges from -50 ° C to +800.
The temperature of the exhaust gas changes from 0 to 100 m / se.
Since it fluctuates to about c, it is necessary to control the temperature according to each purpose.

For example, in order to detect the air-fuel ratio theoretical point using an oxygen concentration battery, it is sufficient to control the temperature to 300 ° C. or higher, whereas in the air-fuel ratio theoretical point detection using the oxygen concentration dependency of electron conductivity. It is necessary to control the temperature within a predetermined range of 500 ° C. or higher, and further, linear detection of the lean region air-fuel ratio using an oxygen pump requires constant temperature control of about 800 ° C. It has been proposed by a person that a heating element is arranged in parallel with a detection element and a heat-sensitive element is arranged in parallel.

In this case, while the engine is in operation, it is necessary to constantly energize and heat it. However, in order to suppress fuel consumption, it is necessary to suppress heating power, and it is necessary to reduce the heat capacity of the heating portion. Small volume desk type, thick film type, thin film type are proposed as elements, and support including detection element,
The base body for conducting is generally becoming elongated in a cylindrical shape, a prismatic shape, and a plate shape.

On the other hand, in the exhaust gas, dust in the intake air, mist, combustion residues of fuel and lubricating oil, engine cylinders,
It is known that solid particles such as sliding abrasion powder of pistons and intake / exhaust valves are included and adhere to and deposit on the combustion chamber and the inner wall of the exhaust pipe. These deposits are carbon, magnesium,
Silicon, phosphorus, sulfur, calcium, chromium, iron, zinc, lead, etc., and heavy ones more than calcium are difficult to vaporize even at 800 ° C.

Therefore, even if the electric current is constantly heated to 800 ° C., these solid particles may adhere to the detection element, gradually accumulate and the output signal changes, and eventually detection becomes impossible. This becomes more remarkable as the detection element becomes smaller.

For example, in the one disclosed in Japanese Patent Laid-Open No. 55-124062, an elongated rectangular plate-shaped base body is coupled and supported in a plug fitting through a packing, and an electrode is provided at one end of the base body. There is a section and a layered heating member, and they are located in the voids inside the plug fitting so as to come into contact with the test gas.

However, with this structure, when it is mounted on an automobile engine exhaust pipe, the oxygen concentration detecting element is inevitably deteriorated due to the adhesion of the solid particles, and the temperature and flow velocity of the exhaust gas are significantly increased. Since the temperature fluctuates abruptly, the temperature of the detection unit fluctuates greatly, and the constant temperature control of the detection unit becomes unstable, resulting in a decrease in detection accuracy.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object thereof is to stably oxygenate for a long period of time even when a test gas contains solid particles and whose temperature and flow velocity fluctuate significantly. An object is to provide an oxygen concentration detector capable of detecting the concentration.

[0011]

According to the present invention, in order to achieve the above object, an oxygen concentration detector is constructed as follows.

That is, a plug having a long and narrow base body having a detection element having an electrode for detecting oxygen concentration and an electric heating element at one end, and a conductive terminal connected to the electrode at the other end mounted on the exhaust pipe wall. The base body which is supported and connected to the metal fitting, and the connecting portion of the base body to the plug metal fitting is set at a position outside the exhaust pipe wall, and which projects from the connecting portion toward the exhaust pipe side. The detection element side is covered with a cap-shaped bottomed tube, and a gas flow hole for allowing a part of the gas in the exhaust pipe to flow is provided in a side wall of the bottomed tube at a position distant from the detection element. At the same time, a gas passage hole is provided in the bottom wall.

[0013]

According to the above construction, firstly, the influence of the exhaust gas temperature on the base body is reduced by the fact that the base body connecting portion of the plug fitting for supporting the elongated plate base body is outside the exhaust pipe. In other words, the degree to which the outside air temperature is received increases, and the second
Since the exhaust flow gently flows around the detection element provided on the base body through the gas flow hole provided on the bottomed tube, the heat exchange with the exhaust is made minute so that the detection element has a built-in electric heating. It is strongly dominated by the element and enhances the thermal management stability of the sensing element.

Further, the fixed particles contained in the exhaust gas operate stably for a long period of time. That is, firstly, heavy solid particles flow through the central portion of the exhaust pipe having a high flow velocity, but in the present invention, the gas flow hole of the bottomed pipe can be located near the inner wall of the exhaust pipe having a slow flow velocity. . Light solid particles flow near the inner wall of the exhaust pipe, but most of the solid particles that pass around the bottomed pipe are trapped on the outer wall of the bottomed pipe and enter the bottomed pipe. In addition to the solid particles flowing out of the bottomed tube along with the flow of gas, only a very small amount of solid particles drifts in the bottomed tube. Even if the very small amount of floating solid particles tries to adhere to the detection element, since the detection element has been red-heated to a high temperature (for example, 800 ° C.) in advance, almost all is burned and vaporized, so that the adhesion volume can be prevented.

[0015]

Embodiments of the present invention will be described in detail with reference to FIGS.

FIG. 1 is a vertical sectional view of an oxygen concentration detector according to one embodiment of the present invention, and FIG. 2 is a lateral sectional view of a main part of FIG.

As shown in these figures, the body of the oxygen concentration detector comprises a plug fitting 3 and a thin cylindrical outer cylinder fitting 13 connected in the axial direction.

The plug fitting 3 has opposite sides of hexagon, and the other parts have a cylindrical shape with a screw 3a on the outer periphery of the lower end. The screw 3 a is for mounting the plug fitting 3 on the wall of the exhaust pipe 14.

Further, a disk-shaped packing 4 having a slotted hole in an inner diameter stepped portion provided at an intermediate position in the axial direction of the plug fitting 3 and an opening peripheral flange 6 of a cap-shaped bottomed tube 6.
and d are fixed by caulking or welding, whereby the opening of the bottomed tube 6 is closed by the packing 4.
The details of the bottomed tube 6 will be described after the substrate 1 with the detection element 1a.

The substrate 1 is made of a partially stabilized zirconia solid electrolyte, and has a layered structure of a detection element 1a having an electrode for detecting oxygen concentration at one end and an electric heating element (not shown), and a detection element at the other end. 1a has an elongated rectangular plate shape having a conductive terminal 1b connected to an electrode of 1a,
The side provided with is formed wide. The detection element 1a is
For example, it is shown in JP-A-59-108951.

The base 1 is inserted into one end of the plug fitting 3 (that is, one end facing the inside of the exhaust pipe when the plug fitting 3 is mounted on the wall of the exhaust pipe 14 and corresponding to the lower end in the figure). Through the central elongated hole of the packing 4 inside the plug fitting 3, the plug fitting 3 is supported and coupled to the plug fitting 3 near the packing 4. Here, the connection of the base 1 to the plug fitting 3 is
This is performed by inserting one end of the base body 1 on the side of the detection element 1a of the base body 1 so as to project toward the exhaust pipe 14 side into the packing 4 fixed in the plug body fitting 3, and further to the inside of the plug body fitting 3 than the packing 4. In, the inorganic filler 7 is injected and solidified to bury the wide end of the base 1 on the side of the conductive terminal 1b to insulate the base 1 to the plug fitting 3 and strengthen the bond.

The connecting portion (near packing 4) of the base 1 to the plug fitting 3 is set at a position outside the exhaust pipe wall when the plug fitting 3 is attached to the exhaust pipe 14.

When assembling the oxygen concentration detector, after fixing the packing 4 and the bottomed tube 6 to the plug fitting 3, the base body 1 is inserted through the packing 4 and the detection element 1a side of the base body 1 is bottomed. Inserted inside the tube 6, injecting liquid inorganic filler 7 into the space above the packing 4 in the plug fitting 3, further inserting the terminal holder 8 and lead plug holder 9 made of alumina or steatite, and The filler 7 is solidified under predetermined drying conditions.

Next, a harness 11 of fluorine resin type insulation coated stranded wire is inserted into the other end of the lead wire 2 via a connector 10, a cylindrical cushion 12 of silicon rubber is inserted, and finally a malleable material is used. A thin-walled cylindrical outer tubular metal fitting 13 is externally inserted, and the flange portion of the expanded pipe portion 13 a is attached to the circumferential groove 3 of the stopper metal fitting 3.
Clamp and fix to c, and then continue to the part 13 of the outer tubular metal fitting 13.
It is formed by crimping b and 13c in a ring shape.

The above-mentioned bottomed tube 6 covers the periphery of the detection element 1a side of the substrate 1 which projects toward the exhaust pipe 14 side from the joint (packing 4), and the bottomed tube 6 has a flange on its side wall. A plurality of louver-shaped gas circulation holes 6b for circulating a part of the gas of the exhaust pipe 14 is provided near the detection element 1a near 6d, and the gas circulation holes 6 are also formed in the bottom wall.
c is provided.

Also, the lower end (tip cylinder wall) 3b of the plug fitting 3
Is extended to the bottom surface of the bottomed tube 6 as shown in the drawing, and the tip end cylindrical wall 3b surrounds the side wall of the bottomed tube 6 and secures an annular space 3c between the bottomed tube 6 and the bottomed tube 6. I am doing it.

The exhaust pipe 14 is welded with a boss metal fitting 15 protruding from the outer wall of the exhaust pipe 14 and provided with a female screw, and the detector main body is screwed and mounted via a gasket ring 16. As a result, the base 1 is positioned so that the support coupling portion 4 to the plug fitting 3 is projected outward from the wall of the exhaust pipe 14, and the detection element 1 a is positioned near the wall of the exhaust pipe 14. Become.

According to the above construction, the inside of the bottomed pipe 6 is gas-exchanged by the following inflow and outflow of the exhaust gas to detect the oxygen concentration in the exhaust gas.

In a steady state, the outer bottom wall of the bottomed pipe 6 is generally exposed to the exhaust flow, so that the vicinity of the outer bottom wall is against the annular gap 3c between the lower end of the plug fitting 3 and the side wall of the bottomed pipe 6. As a result, the air flow is taken in from the annular gap 3c due to the difference in static pressure, enters the bottomed pipe 6 through the gas flow hole 6b, and flows out through the gas flow hole 6c.

When the flow of the exhaust flow is extremely slow and the above-mentioned static pressure difference hardly occurs, the gas inside the bottomed tube 6 is automatically discharged through the gas flow holes 6b and 6c by the gas diffusion action. Instead, the gas in the exhaust pipe is replaced. The gas circulation hole 6c also has a function of preventing a sudden change in the pressure inside the bottomed tube 6 when the exhaust flow suddenly changes.

The oxygen concentration detector according to the present embodiment effectively acts on a large and abrupt change in the exhaust gas flow velocity.

First, since the intake of the exhaust flow is not in the central portion of the exhaust pipe 14 but near the inner wall of the exhaust pipe, there is a gentle fluctuation state, and the pipe wall of the bottomed pipe 6 and the plug metal fitting 3 pipe It is further relaxed by the annular void 3c.

Further, since the base body connecting portion 4 of the plug fitting 3 for supporting the elongated plate-shaped base body 1 is outside the exhaust pipe, it is possible to reduce the influence of the exhaust gas temperature on the base body 1 (in other words, in other words). If you do so, the degree to which the outside air temperature will be affected will increase).

Therefore, the detection element is strongly controlled by the built-in electric heating element by reducing the influence of the exhaust gas temperature and minimizing the heat exchange with the exhaust gas of the detection element by mitigating the exhaust gas flow rate and fluctuations. The stability of temperature control of the detection element is enhanced, and the constant temperature controllability of the detection element 1a is dramatically improved.

Further, the fixed particles contained in the exhaust gas operate stably for a long period of time. That is, firstly, heavy solid particles flow through the central portion of the exhaust pipe 14 having a high flow velocity, but in the present embodiment, the gas flow holes 6b, 6c of the bottomed pipe 6 are provided.
Can be located near the inner wall of the exhaust pipe 14 having a low flow velocity. Light solid particles flow near the inner wall of the exhaust pipe. Of these solid particles, around the bottomed pipe 6 (annular void 3c).
Most of those that pass through the bottom end pipe are trapped on the outer wall of the bottomed pipe 6, and the solid particles that have entered the bottomed pipe are also extremely light in addition to flowing along with the gas flow to the outside of the bottomed pipe. Only a small amount of solid particles will float in the bottomed tube. Even if this very small amount of floating solid particles tries to adhere to the detection element, the detection element is preheated to a high temperature (for example, 800 ° C.) in advance,
Since almost all is vaporized by combustion, the adhered volume can be prevented, and the deterioration of the detection element 1a can be prevented.

In the above embodiments, the base 1 made of elongated rectangular plate-shaped zirconia containing the electrothermal element is used. However, the base 1 may have a columnar shape other than a plate shape, a cylindrical shape, or the like. A prismatic shape or a tubular shape may be used, and the same effect is obtained.

The point is that the elongated base 1 is provided with a detection element and an electric heating element at one end, and the main part of the base 1 is located in the atmosphere outside the wall surface of the exhaust pipe 14, and the base 1 is detected. Any material that allows a relaxed exhaust flow to pass near the element may be used.

[0038]

According to the present invention, it is possible to prevent solid particles from adhering to and depositing on the oxygen concentration detector even in exhaust gas that contains solid particles and whose temperature and flow velocity fluctuate significantly and rapidly. While preventing deterioration of the detection element, it is hardly affected by fluctuations in exhaust gas temperature and flow velocity, so the constant temperature controllability of the detection element is dramatically improved, and the oxygen concentration detector has a stable detection function for a long period of time. Can be guaranteed.

[Brief description of drawings]

FIG. 1 is a vertical sectional view according to an embodiment of the present invention.

FIG. 2 is a side sectional view of a main part of the above embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Base | substrate, 1a ... Detecting element, 1b ... Conductive terminal, 3 ... Plug metal fittings, 4 ... Packing, 6 ... Bottom pipe, 6b, 6c ... Gas distribution hole, 7 ... Inorganic filler, 14 ... Exhaust pipe.

Claims (3)

[Claims] 1. A plug body having a detection element having an electrode for detecting oxygen concentration and an electrothermal element at one end, and an elongated base body having a conductive terminal connected to the electrode at the other end mounted on an exhaust pipe wall. The base body which is supported and connected to the metal fitting, and the connecting portion of the base body to the plug metal fitting is set at a position outside the exhaust pipe wall, and which projects from the connecting portion toward the exhaust pipe side. The detection element side is covered with a cap-shaped bottomed tube, and a gas flow hole for allowing a part of the gas in the exhaust pipe to flow is provided in a side wall of the bottomed tube at a position distant from the detection element. An oxygen concentration detector characterized in that a gas passage hole is also provided in the bottom wall. 2. The coupling of the base body to the plug body fitting is carried out by inserting a packing fixed inside the plug body fitting so that one end of the base body on the detection element side projects toward the exhaust pipe side. And the end of the base body on the side of the conductive terminal is embedded in the inorganic filler injected and solidified in the plug body rather than the packing to strengthen the connection of the plug body to the base body. The oxygen concentration detector according to claim 1. 3. The oxygen concentration detector according to claim 1, wherein the plug metal member is extended so that a cylinder wall at a tip end thereof surrounds a side wall of the bottomed tube.