JPH07280771A - Oxygen sensor - Google Patents

Abstract

(57) [Summary] [Purpose] To activate the zirconia tube in a short time and prevent damage to the zirconia tube due to stress concentration. [Structure] The zirconia tube 21 is attached to the lid portion 2 on the tip side.
2, a thin-walled cylindrical portion 23 that has a diameter T approximately equal to the outer diameter D1 of the lid portion 22 and extends, and the thin-walled tubular portion 23.
From the first inflection point k1 to the taper-shaped taper cylinder portion 24 which gradually increases the outer diameter dimension to the outer diameter dimension D2, and from the taper cylinder portion 24 through the second inflection point k2. It is composed of a thick flange portion 25 having an enlarged diameter. Therefore, since the zirconia tube 21 is thinned by the thin-walled cylinder portion 23, the internal resistance is reduced and the activation start temperature is lowered, and the volume of the entire zirconia tube 21 is reduced, and the activation start temperature is shortened in a short time. Is heated in. The stress applied to the zirconia tube 21 is the first inflection point k1.
And the second inflection point k2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor suitable for detecting the oxygen concentration in the exhaust gas of an automobile, for example.

[0002]

2. Description of the Related Art Generally, in an engine of an automobile or the like, an oxygen sensor (O ₂ sensor) is attached to an exhaust pipe or the like to constantly detect the oxygen concentration in exhaust gas in order to optimally perform feedback control of an air-fuel ratio. However, it is used for air-fuel ratio control.

As a conventional oxygen sensor, for example, a heater-less oxygen sensor will be described with reference to FIGS. 5 and 6.

In the figure, reference numeral 1 denotes a stepped tubular sensor body that constitutes the body of the oxygen sensor. The sensor body 1 has a threaded portion 2A formed on the outer periphery at one end and a tubular fit at the other end. The holder 2 that has become the joining portion 2B is fixed at one end side to the fitting portion 2B of the holder 2 through the caulking portion 3A, and at the other end side, the step portion 3 is formed.
B, a stepped tubular cap 3 having a reduced diameter portion 3C, and the like, which are made of a metallic material such as stainless steel. A cylindrical insulating cylinder 4 made of a ceramic material such as alumina is inserted into the holder 2 and the cap 3. The sensor body 1 is adapted to be attached to an exhaust pipe (not shown) of an automobile via the male screw portion 2A of the holder 2.

Reference numeral 5 denotes a zirconia tube whose base side is attached to one end side of the sensor body 1 and whose tip side projects from the sensor body 1 and extends into the exhaust pipe. The zirconia tube 5 is made of a ceramic material such as zirconium oxide. It is integrally molded into a cylindrical shape with a lid. In addition, as shown in FIG. 6, the zirconia tube 5 has a lid portion 6 located on the distal end side and formed in a hemispherical shape, and extends from the lid portion 6 toward the proximal end side. A taper cylindrical portion 7 formed in a taper shape in which the outer diameter dimension gradually increases from the diameter dimension d1 to the outer diameter dimension d2 on the extension side, and the extension side of the taper tube portion 7 serves as an inflection point k and the shoulder portion 8A, the zirconia tube 5 has a flange portion 8 having a thickened diameter, and the shoulder portion 8A of the flange portion 8 has a ring-shaped washer 9 for holding the holder 2
It is fixed to the sensor body 1 by being pressed by the shoulder portion 2C.

The zirconia tube 5 allows oxygen ions to pass through when a difference in oxygen concentration between the inside and the outside occurs.
An electromotive force (detection signal) is generated between them.
The inside and outside of the zirconia tube 5 is coated with porous platinum (not shown), and the platinum layer serves to amplify the electromotive force (catalyst).

Of the zirconia tubes 5, 10 and 11,
Showing the inner electrode and the outer electrode respectively provided on the outer surface,
Each of the electrodes 10 and 11 is formed by applying a paste material made of platinum and zirconia to the inner and outer surfaces of the zirconia tube 5 to extend in a strip shape. The other end of the inner electrode 10 extends to the end surface of the flange portion 8 of the zirconia tube 5 to form a connecting portion 10A, which is connected to a contact plate 12 described later. Further, the outer electrode 11 is a shoulder portion 2C of the holder 2.
Is connected via a washer 9 and is grounded to the exhaust pipe side.

Reference numeral 12 denotes a contact plate arranged in the insulating cylinder 4, which is formed by bending a conductive metal plate, and has a disk-shaped contact portion on one end side thereof. 12A and a connecting portion 12B connected to the lead wire 13 are provided on the other end side. The contact portion 12A of the contact plate 12 is sandwiched between the end surface of the flange portion 8 of the zirconia tube 5 and the insulating cylindrical body 4 by the spring force of the disc spring 14, and is connected to the connecting portion 10A of the inner electrode 10. .

Further, 15 is a seal member which is disposed in the reduced diameter portion 3C of the cap 3 and seals the periphery of the lead wire 13, and 16 is a protector fixed to the holder 2 so as to protect the zirconia tube 5. The protector 16 is provided with elongated holes 16A, 16A, ... For introducing exhaust gas.

The oxygen sensor according to the prior art has the above-mentioned structure. The sensor body 1 is attached to the exhaust pipe by screwing the male screw portion 2A of the holder 2 to the exhaust pipe, and the tip side of the zirconia tube 5 is attached. Is projected into the exhaust pipe together with the protector 16 to detect the oxygen concentration in the exhaust gas. That is, since the exhaust gas is a waste gas obtained by burning a mixture of air and fuel, the oxygen concentration in the exhaust gas is lower than the atmosphere inside the zirconia tube 5, and the inside and outside of the zirconia tube 5 are reduced. There is a large oxygen concentration difference between and.

Therefore, oxygen ions pass through the zirconia tube 5 from the inside to the outside, and an electromotive force is generated between the inner electrode 10 and the outer electrode 11. Since this electromotive force increases / decreases according to the change in oxygen concentration in the exhaust gas, the electromotive force due to this change in oxygen concentration is used as a detection signal through the contact plate 12, the lead wire 13, etc. to an external control unit (not shown). ), And the control unit corrects the fuel injection amount and the like based on this detection signal, and feedback-controls the air-fuel ratio.

[0012]

By the way, in the oxygen sensor, the zirconia tube 5 has a predetermined temperature, for example, 320.
It is activated at ˜350 ° C. and starts control (outputs a detection signal). Oxygen sensors without heaters require a longer time to start control than oxygen sensors with heaters. It is inferior in terms of starting characteristics.

In particular, in the above-mentioned heaterless oxygen sensor, the zirconia tube 5 is composed of the lid portion 6, the taper tube portion 7 and the flange portion 8. The taper tube portion 7 has an outer diameter dimension d1 of the lid portion 6. Since the outer diameter is gradually increased and the outer diameter is tapered on the extension side, the tapered cylindrical portion 7 becomes thick as a whole and the volume of the zirconia tube 5 becomes large. .

As a result, not only the internal resistance of the zirconia tube 5 increases due to the thickening of the tapered cylindrical portion 7 and the temperature at which the zirconia tube 5 is activated to start generating electromotive force increases, but also due to the increase in volume, zirconia increases. Tube 5
It takes time for the exhaust gas to be heated to a temperature at which electromotive force is generated, and there is a problem that the uncontrollable time from the engine start to the start of the air-fuel ratio control becomes long.

Further, in the conventional zirconia tube 5, since the flange portion 8 is formed from the tapered cylindrical portion 7 via the inflection point k, stress due to vibration or the like is concentrated at this inflection point k. As a result, a crack or the like is likely to occur near the inflection point k of the zirconia tube 5, and the oxygen sensor has a short life.

The present invention has been made in view of the above-mentioned problems of the prior art, and provides an oxygen sensor capable of activating a zirconia tube in a short time and preventing damage to the zirconia tube due to stress concentration. With the goal.

[0017]

In order to solve the above-mentioned problems, the structure of the oxygen sensor adopted by the present invention is such that the sensor main body and the base end side are attached to the sensor main body, and the front end side protrudes from the sensor main body. It consists of a cylindrical zirconia tube with a lid, and a contact plate that is provided in the sensor body and outputs an oxygen concentration change signal detected by the zirconia tube.

The oxygen sensor employed in the present invention is characterized in that the zirconia tube extends into a lid portion located on the distal end side and a tubular body having substantially the same diameter from the lid portion toward the base end side. A thin-walled tubular portion, a taper-shaped tubular portion formed in a tapered shape in which the outer diameter dimension gradually increases with the extension side of the thin-walled tubular portion as a first inflection point, and the extension side of the tapered tubular portion is a second The inflection point is formed of a thick flange portion which is thickened and fixed to the sensor body.

The outer peripheral side of the tapered cylindrical portion may be a tapered surface that linearly expands from the first inflection point toward the second inflection point.

Further, the outer peripheral side of the taper cylinder portion has a first
It may be an arcuate taper surface that expands in an arcuate shape from the inflection point to the second inflection point.

[0021]

With the above construction, the zirconia tube is thinned by the thin-walled cylindrical portion to reduce the internal resistance, and the temperature at which the zirconia tube is activated to start generating an electromotive force is lowered. Is heated up. Further, the stress applied to the zirconia tube is dispersed at the first inflection point and the second inflection point.

[0022]

EXAMPLE An oxygen sensor (O) according to an example of the present invention will be described below.
₂ sensors) will be described with reference to FIGS. In the embodiment, the same components as those of the conventional technique shown in FIGS. 5 and 6 described above are designated by the same reference numerals, and the description thereof will be omitted.

First, FIGS. 1 and 2 show an oxygen sensor without a heater as an oxygen sensor according to a first embodiment of the present invention.

In the figure, reference numeral 21 indicates the sensor body 1 on the base end side.
The zirconia tube according to the present embodiment, which is attached to one end side of the zirconia, has a tip end side protruding from the sensor body 1 and extending into an exhaust pipe (not shown).
Is integrally formed in a cylindrical shape with a lid from a ceramic material such as zirconium oxide. As shown in FIG. 2, the zirconia tube 21 has a hemispherical lid portion 22 located on the distal end side and a lid portion 22 extending from the lid portion 22 toward the proximal end side. The diameter is approximately the same as the diameter D1 and the lid 2
Thin-walled cylindrical portion 2 having a wall thickness dimension T equivalent to 2
3 and a tapered cylindrical portion 24 formed into a tapered shape having an outer diameter dimension D2 on the proximal end side by gradually increasing the outer diameter dimension with the extension side of the thin-walled cylindrical portion 23 as the first inflection point k1. ,
The extended side of the tapered cylindrical portion 24 is defined as the second inflection point k2, and the thick-walled flange portion 25 is thickened through the shoulder portion 25A.
And the outer peripheral surface of the tapered cylindrical portion 24 has a first
Is a taper surface 24A that linearly expands from the inflection point k1 to the second inflection point k2.

The first inflection point k1 is defined by the lid portion 22.
The thin cylinder portion 23 is arranged at a position separated from the tip by a dimension L1 and extends to the first inflection point k1. The dimension L1 from the tip of the lid portion 22 to the first inflection point k1, that is, the length dimension of the thin-walled tubular portion 23 is the length from the tip of the lid portion 22 to the second.
The dimension L2 up to the inflection point k2 is set to 40 to 95%, preferably 40 to 80%.

The zirconia tube 21 of the oxygen sensor according to this embodiment has the above-mentioned structure, and its basic operation is not different from that of the prior art.

However, in this embodiment, the zirconia tube 21 is located at the tip end side and the lid portion 2 is formed in a hemispherical shape.
2, a thin-walled cylindrical portion 23 that has a diameter T approximately equal to the outer diameter D1 of the lid portion 22 and extends, and the thin-walled tubular portion 23.
From the first inflection point k1 to the outer diameter dimension, the taper cylindrical portion 24 is formed in a tapered shape so as to have the outer diameter dimension D2, and the second inflection point k2 from the tapered cylindrical portion 24. And the thick-walled flange portion 25 having a large diameter through the thin-walled tubular portion 23, the thin-walled tubular portion 23 can reduce the thickness of the zirconia tube 21 to significantly reduce the internal resistance. The temperature at which 21 is activated and begins to generate an electromotive force is, for example, 320 to 350 in the related art.
It was possible to reduce the temperature from ℃ to about 250 ℃. Further, since the entire volume of the zirconia tube 21 can be reduced by the thin-walled tubular portion 23, the entire zirconia tube 21 can be easily heated, and the zirconia tube 21 can be activated in a short time. You can

Thus, according to this embodiment, the temperature at which the zirconia tube 21 is activated to start generating electromotive force can be set low, and the zirconia tube 2 can be set.
Since 1 can be heated to this activation start temperature in a short time, the uncontrollable time from the engine start to the activation of the zirconia tube 21 to generate electromotive force can be significantly shortened, and the engine start time can be shortened. It is possible to stabilize the air-fuel ratio over time and improve reliability.

Further, since the thin-walled cylinder portion 23 of the zirconia tube 21 is provided with the first inflection point k1,
In the prior art, the inflection point k (in the embodiment, the second inflection point k
The stress concentrated in 2) can be dispersed to the side of the first inflection point k1.
1 can be prevented and the life of the oxygen sensor can be greatly extended.

Next, FIG. 3 shows a second embodiment of the present invention.

In the figure, 31 indicates a zirconia tube according to the present embodiment, and the zirconia tube 31 is located at the tip end side and is formed in a hemispherical shape, substantially like the zirconia tube 21 according to the first embodiment. Lid 32
And a thin-walled cylindrical portion 33 extending with a wall thickness dimension T substantially the same as the outer diameter dimension D1 of the lid portion 32, and the outer diameter dimension gradually increasing from the thin-walled cylindrical portion 33 through the first inflection point k1. And the taper tube portion 34 formed in a taper shape having an outer diameter dimension D2.
And a thick flange portion 35 whose diameter is increased through the shoulder portion 35A, with the extension side of the taper tubular portion 34 as the second inflection point k2. Three
The outer peripheral surface of No. 4 has a first inflection point k1 to a second inflection point k2.
It is an arcuate tapered surface 34A that expands in an arcuate shape with a radius dimension R toward.

Thus, in this embodiment having the above-described structure, it is possible to obtain substantially the same effect as that of the first embodiment, but in particular, in this embodiment, the outer circumference of the tapered cylindrical portion 34 is By forming the arcuate tapered surface 34A, the stress applied to the zirconia tube 31 is applied to the first inflection point k1 and the second inflection point k2, and the arcuate taper surface 3 is formed.
4A can be dispersed to prevent stress concentration, and the zirconia tube 31 can be reliably prevented from being damaged.

Next, FIG. 4 shows an oxygen sensor with a heater as an oxygen sensor according to a third embodiment of the present invention.

Reference numeral 41 denotes a contact pipe as a contact plate according to the present embodiment, which is disposed in the insulating cylinder 4 in order to lead the detection signal from the zirconia tube 21 to the outside. The contact pipe 41 has a conductive property. The heater 42 is formed of a metallic material in a stepped cylinder shape, and a heater 42 described later is positioned on the inner circumference of the tip end side thereof. The tip end of the contact pipe 41 is the zirconia tube 21.
It is inserted inside and is connected to the inner electrode 10.

Reference numeral 42 denotes a heater which is positioned in the contact pipe 41 and whose tip side extends axially in the zirconia tube 21. The heater 42 is formed of a ceramic material such as alumina into a rod shape having a small diameter.
A heater pattern (not shown) made of a material such as tungsten is formed on the outer peripheral side of the heater 42, and the heater pattern is connected to the nickel wires 43A and 43B. The heater 42 has its tip end extended into the zirconia tube 21, and heats the zirconia tube 21 from the inside to heat it to a predetermined temperature, thereby activating the zirconia tube 21 in an early stage. It is like this.

Reference numerals 44A and 44B are power supply lead wires for supplying power to the heater 42 from the outside.
B is introduced into the contact pipe 41, and its tip is connected to the nickel wires 43A and 43B.

Reference numeral 45 is an output lead wire connected to the contact pipe 41 via a terminal 46, and the output lead wire 45 is for outputting a detection signal from the zirconia tube 21 to the outside.

Thus, even in this embodiment having such a structure, it is possible to obtain substantially the same effect as each of the above embodiments, but in particular, in this embodiment, the heater 42 is provided in the zirconia tube 21. Since it is configured, the zirconia tube 21 can be further heated to a predetermined temperature in a short time by the effect of the thinned zirconia tube 21 and the heating effect of the heater 42, and the uncontrollable time can be significantly shortened. You can

[0039]

As described in detail above, according to the present invention, the zirconia tube is extended into a lid portion located on the distal end side and a tubular body having substantially the same diameter from the lid portion toward the base end side. A thin-walled tubular portion, a taper-shaped tubular portion formed in a tapered shape in which the outer diameter dimension gradually increases with the extension side of the thin-walled tubular portion as a first inflection point, and the extension side of the tapered tubular portion is a second Since it is composed of a thick flange portion that is thickened as an inflection point and is fixed to the sensor body, the internal resistance of the zirconia tube can be reduced by thinning the thin tubular portion, and the zirconia tube The activation start temperature can be set low, and the volume can be reduced by thinning the zirconia tube to the activation start temperature in a short time.For example, an oxygen sensor can detect exhaust gas. When used for Zirconia tube is heated from the engine start to activation, it is possible to significantly reduce the uncontrolled time to produce the electromotive force.

Further, by providing the zirconia tube with the first inflection point and the second inflection point, the stress applied to the zirconia tube is dispersed into the first inflection point and the second inflection point. Therefore, damage to the zirconia tube due to stress concentration can be prevented and the life of the oxygen sensor can be extended.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an oxygen sensor using a zirconia tube according to a first embodiment of the present invention.

FIG. 2 is an enlarged vertical sectional view showing a zirconia tube in FIG.

FIG. 3 is a vertical sectional view showing a zirconia tube according to a second embodiment of the present invention.

FIG. 4 is a vertical sectional view showing an oxygen sensor according to a third embodiment of the present invention.

FIG. 5 is a vertical sectional view showing an oxygen sensor according to a conventional technique.

6 is an enlarged vertical sectional view showing the zirconia tube in FIG.

[Explanation of symbols]

 1 Sensor Main Body 12 Contact Plate 21, 31 Zirconia Tube 22, 32 Lid 23, 33 Thin-walled Cylinder 24, 34 Tapered Cylinder 24A Tapered Surface 34A Arc Tapered Surface 25, 35 Thick Flange 41 Contact Pipe (Contact Plate) k1 1st inflection point k2 2nd inflection point D1 Outer diameter dimension of lid D2 Outer diameter dimension of taper cylinder extension side T Wall thickness dimension

Claims (3)

[Claims] 1. A sensor body, a cylindrical zirconia tube with a base end attached to the sensor body and a tip end protruding from the sensor body, and oxygen provided in the sensor body and detected by the zirconia tube. In an oxygen sensor including a contact plate that outputs a concentration change signal, the zirconia tube extends from a lid located on the tip side to a tubular body having substantially the same diameter from the lid toward the proximal side. The thin-walled tubular portion, the taper tubular portion formed in a tapered shape in which the outer diameter dimension gradually increases with the extension side of the thin-walled tubular portion as the first inflection point, and the extension side of the tapered tubular portion is the second inflection point. An oxygen sensor, comprising: a thick-walled flange portion which is thickened as a bending point and fixed to the sensor body. 2. The oxygen sensor according to claim 1, wherein an outer peripheral side of the tapered cylindrical portion is a tapered surface that linearly expands from a first inflection point toward a second inflection point. 3. The oxygen sensor according to claim 1, wherein an outer peripheral side of the taper cylinder portion is an arcuate tapered surface that expands in an arcuate shape from a first inflection point toward a second inflection point. .