JPS61134656A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To prevent the deterioration and injury of an oxygen sensor element owing to the intrusion of foreign matter by providing a hermetic space in the case of the oxygen sensor and communicating the same only with the gap in the oxygen sensor in which a reference electrode is provided. CONSTITUTION:The space 9 between a connector insulator 5 and a keep plate 18 and the space in which the contactor 5a of the insulator 5 is contained are mated to form the hermetic space 9. The space 9 is communicated only with the gap 35 in which the reference electrode 38 and a pump electrode 39 are contained through the spacing at the top end of the oxygen sensor element 1 and the insulator 5. A relatively large amt. of the atm. air which is the reference material can be accumulated into the hermetic space 9 communicating with the gap 35 having the electrode 38 of such oxygen sensor by the above- mentioned constitution and since the hermetic space is hermetically isolated from the outside, the intrusion of the foreign matter such as moisture and salt water into said space is thoroughly prevented.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an oxygen sensor for detecting the oxygen concentration in a gas to be measured, particularly in exhaust gas discharged from an internal combustion engine, and particularly relates to The present invention relates to an oxygen sensor in which a substance can be supplied using a closed space.

(Prior Art) Conventionally, so-called oxygen sensors have been used to detect the concentration of oxygen contained in the exhaust gas of an internal combustion engine, and to optimally control the combustion state of the internal combustion engine based on the detection signal. There are known products that purify fuel and reduce fuel consumption. ] Such an oxygen sensor generally consists of a measurement electrode that is exposed to the gas to be measured, such as exhaust gas, and a reference electrode that is exposed to a reference substance with a constant oxygen concentration, sandwiched between an oxygen ion-conducting positive solid electrolyte. The output from the oxygen ion conduction effect between the two electrodes is used as the detection signal.

By the way, the above-mentioned reference substance is usually the atmosphere, and for this reason, conventional oxygen sensors are provided with an atmosphere intake hole on the outer surface of the case of the oxygen sensor to take in this atmosphere and bring it into contact with the reference electrode. .

(Problem to be Solved by the Invention) However, in the case of an oxygen sensor provided with an atmospheric intake hole as described above, especially when installed in a vehicle such as the one described above, Water may enter, or salt water may enter along the coastline, which may cause damage to the oxygen sensor element or insulation failure.

Furthermore, since the oxygen sensor is used at high temperatures, moisture that has entered the sensor may turn into steam and drive out the atmosphere, which is the reference substance, resulting in an undetectable state.

In order to solve this problem, in addition to eliminating the above-mentioned air intake hole, a microscopic space is created using a porous material around the reference electrode, and an oxygen pump electrode is used to connect the air to this microscopic space. Oxygen sensors have been proposed that take in oxygen from outside air, such as exhaust gas.

For objects with only such a small space,
In order to keep the oxygen partial pressure in this microspace constant, a slight gap is created to exhaust excess gas in the microspace, or when the signal output from the oxygen sensor is read by an external instrument etc. In order to supply oxygen into the microscopic space, it is necessary to keep the oxygen pump running at all times.

However, oxygen pumps do not work well in low-temperature conditions, so it is necessary to apply a high voltage to ensure good operation under these conditions, but applying a high voltage can easily cause electrolysis within the solid electrolyte, causing This may cause deterioration. In order to avoid this, it may be possible to use a heater to constantly heat the oxygen pump section to a high temperature at which the oxygen pump functions sufficiently, but this would consume a large amount of electricity for heating the heater. This heat from the heater causes the element to deteriorate quickly and shortens the life of the heater.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides an airtight space that is substantially airtight in a case that houses an oxygen sensor element, and connects this airtight space with a reference. The present invention is characterized in that an oxygen pump electrode is provided that communicates with the void in which the electrode is accommodated and supplies oxygen to the void.

(Function) Oxygen supplied by the oxygen pump electrode into the cavity housing the reference electrode also flows into the airtight space and is stored therein.

Since this airtight space has a relatively large volume, the reference substance can be sufficiently supplied without constantly operating the oxygen pump. Therefore, for example, even if the oxygen pump part becomes cold and the supply amount temporarily decreases or the oxygen supply stops, you can heat the oxygen pump part to a high temperature with a heater or apply a high voltage to the oxygen pump. This eliminates the need for deterioration of the element and the lifespan of the heater. Of course, it goes without saying that it is possible to completely prevent moisture, salt water, etc. from entering from the outside.

(Example) A first embodiment of the present invention is shown in FIGS. 1 and 2.

The oxygen sensor 100 of this embodiment has an oxygen sensor element 1 formed in the shape of a longitudinal plate housed in a cylindrical metal protective tube body 20.

The oxygen sensor element 1, as shown in an exploded view in FIG.
It has a structure in which plates 31 to 33 made of an oxygen ion conductive solid electrolyte (hereinafter referred to as "solid electrolyte plates") are laminated, and an intermediate solid electrolyte plate 32 is provided with a gap 35 cut in the longitudinal direction. ing. Note that the solid electrolyte plate 32 may be made of insulating ceramics.

One end of the upper surface of the upper 0 solid electrolyte plate 31'' (left side in the figure)
A measuring electrode 37 is attached to the first end),
On its lower surface, a reference electrode 3 is placed opposite to the measurement electrode 37.
8 is attached, and this reference electrode 38 is exposed in the gap 35.

A pump electrode 39 is attached to one end of the upper surface of the lower solid electrolyte plate 33 (also the left end in the figure), and another pump electrode 40 is attached to the lower surface of the solid electrolyte plate 33 at a position opposite to the pump electrode 39. It is attached.

The solid electrolyte plates 31 to 33 are made of YzOz, CaO, Y
bzOi.

Zirconia (ZrOt) containing one or more types of MgO
) is formed from an oxygen ion conductive solid electrolyte whose main component is

On the top surface of the upper solid electrolyte plate 31, a conductor lead 41 that conducts to the measurement electrode 8i37 and a part 43 of the conductor lead that conducts to the reference electrode 38 are provided. Lead 41.4
The other surfaces except the right end in Figure 3 are covered.

A conductor 42 that is electrically connected to the reference electrode 38 is provided on the lower surface of the upper solid electrolyte plate 31, and its tip (right end in the figure)
is electrically connected to the conductor lead 43 on the upper surface of the solid electrolyte plate 31 via the through hole 46 .

Similarly, on the lower surface of the lower solid electrolyte plate 33, a conductor lead 45 that is electrically connected to the pump electrode 40 and a pump electrode 3 are provided.
A conductor lead 48 that becomes a part of the conductor lead electrically connected to the conductor lead 9 is provided, and these conductor leads 45, 48
The other surfaces except the right end in the figure are covered with a protective layer 36 made of a ceramic thin film.

A conductor lead 44 that is electrically connected to the pump electrode 39 is provided on the upper surface of the lower solid electrolyte plate 33, and its tip (
(right end in the figure) is electrically connected to a conductor lead 48 on the lower surface of the solid electrolyte plate 33 via a through hole 47 .

Returning to FIG. 1, the protective tube body 20 has a distal end that connects to the oxygen sensing portion 4 of the oxygen sensor element 1 (the portion where the electrodes 37 to 40 are provided, as shown in FIG. 2). It is composed of a protective cover part 20a that surrounds it, and a protective cylinder part 20b that accommodates parts other than the oxygen detection part 4.

The oxygen sensor element 1 is mounted on the side surface of the protective cover section 20a.
A total of eight measurement gas introduction holes 7, four of which are lined up in the longitudinal direction, are provided at positions on both sides of the width direction, and the measurement gas flowing from these measurement gas introduction holes 7 is detected as oxygen. It is adapted to come into contact with part 4. Further, the oxygen sensor element 1 is attached to the protective tube body 20 at the tip of the protective cover part 20a.
An opening 20c is formed into which a jig for inserting and positioning is inserted.

An oxygen sensor 10 is provided on the outer periphery of the upper end of the protective cylinder portion 20b.
A housing 15 for fixing the 0 to a partition wall 25 that separates the gas to be measured from other parts, such as the exhaust pipe wall of a vehicle, is fitted and fixed, and the housing 15 and the protective cylinder part 20b are fixed to each other. The boundary between the housing 15 and the protective cylindrical portion 20b is sealed by a stainless steel airtight ring 16 so that the gas to be measured does not leak from the boundary.

Further, the central portion of the oxygen sensor element 1 is located within the protective cylinder portion 20b, with the first to third insulators 17°3.2 and the first to third insulators 17°3.2. It is fixed by a second gas-tight member 6.14. Above 1. The second airtight members 6 and 14 have the function of fixing the oxygen sensor element 1 and also of preventing the gas to be measured from entering the inside of the protective cylinder part 20b from the side of the protective cover part 20a. It is made by compacting inorganic fillers such as cement and talc.

A presser plate 1 is placed on the upper surface of the third insulator 2.
8 and the caulking portion 22, the first to third insulators 17
, 3.2 and 1st. This prevents the second airtight members 6, 14 from shifting upward.

Further, above the protective cylinder portion 20b, conductor leads 41 for each electrode provided on both large surfaces of the oxygen sensor element 1 are provided.
．． Lead wire 1 from the external circuit to the end of 43.45.48
1 to 13 and a connector insulator 5 for connecting the earth lead 10 which is in contact with the inner surface of the protective tube body 20. Further, the lead wire 1 is inserted into the upper end of the protective tube portion 20b.
The rubber stopper 8 into which numbers 1 to 13 have been inserted is inserted to completely close the hole. Further, the rubber plug 8 is caulked from the outer periphery of the protective tube body 20, and the caulked portion 21 prevents the rubber plug 8 from being removed and improves airtightness.
1 Connector insulator 5 is press-contacted to the ends of conductor leads 41° 43, 45, 48 for each electrode that appear on both sides of the upper end of oxygen sensor element 1 (this part becomes the connection terminal part). Contactors 5a having spring properties (one is shown in the figure, but there are three other contacts) are provided, and earth leads 1 are connected to these contacts 5a.
0 or lead wires 11 to 13 are connected.

The lower surface of this connector insulator 5 and the pressing plate 18
A space is formed between this space, and this space is surrounded by the holding plate 18 on the lower surface, the protective cylinder part 20b on the side surface, and the lower surface of the connector insulator 5 on the upper surface, and the connector communicating with this space. The upper end of the space in which the contact 5a of the insulator 5 is accommodated is closed off by the lower surface of the rubber stopper 8, the lead wires 11 to 13, and the ground lead 10, so that the rain space is combined to form an airtight space 9. There will be. This airtight space 9 only communicates from the gap between the upper end of the oxygen sensor element 1 and the connector insulator 5 to the gap 35 in which the reference electrode 3 and pump electrode 39 shown in FIG. 2 are accommodated. be.

With the above configuration, the oxygen sensor 100 of the present embodiment can store a relatively large amount of air as a reference substance in the airtight space 9 communicating with the air gap 35 having the reference electrode 38, and Since the space is airtightly isolated from the outside world, it is possible to completely prevent foreign substances such as moisture and salt water from entering and damaging the oxygen sensor, unlike in the past.

In addition, the oxygen consumption in the airtight space 9 due to the operation of the oxygen sensor is controlled by the action of the oxygen pump electrodes 39 and 40 in the gas to be measured (oxygen detection in which the oxygen pump electrode part is exposed to the gas to be measured). 4), oxygen is pumped up and supplied into the cavity 35, and is further stored in the airtight space 9.

It is sufficient to replenish oxygen into the airtight space 9 when the oxygen sensor is operating and at a relatively high temperature (because the capacity of the airtight space 9 is large).
．． Even if the voltage applied to 40 is low, it will work satisfactorily.

Therefore, when the temperature of the oxygen pump electrodes 39 and 40 becomes low, the voltage applied to the oxygen pump electrodes 39 and 40 is low, so that the oxygen ion conductive solid electrolyte does not undergo electrolysis, thereby preventing device deterioration. It will never occur. At this low temperature, the operation of the oxygen pump electrodes 39, 40 is reduced, but since the capacity of the airtight space 9 is large, there is no need to constantly operate the oxygen pump, and the operation of the oxygen sensor is not hindered.

Next, a second embodiment of the present invention will be described using FIG. 3.

FIG. 3 is an exploded view showing another configuration example of the oxygen sensor element, and this oxygen sensor element 60 has the same structure as that shown in FIG. 1, like the oxygen sensor element l of the first embodiment. Assembled to form an oxygen sensor.

As shown in FIG. 3, the measurement electrode 63 and the reference electrode 64 are
Similar to the first embodiment, conductive leads 75 for the measurement electrodes 63 are formed on the upper and lower surfaces of the solid electrolyte plate 61.

Conductor leads 77 and 76 for the reference electrode 64 are formed on the upper and lower surfaces of the solid electrolyte plate 61 and are electrically connected through a through hole 73. The upper surface of the solid electrolyte plate 61 is covered with a protective layer 71 except for the right end portions of the measurement electrode 63 and conductor leads 75 and 76.

An insulating plate 63 made of insulating ceramics and having a void 80 formed therein is laminated on the lower surface of the solid electrolyte plate 61, and another solid electrolyte plate 62 is laminated on the lower surface of this insulating plate 63.

Pump electrodes 65 and 66 are provided on the upper and lower surfaces of the solid electrolyte plate 62 at the left end in the figure, respectively.

On the lower surface of the solid electrolyte plate 62, a heater heating section 67 sandwiched between two heater protective layers 69 and 70 and two heater leads 85 and 86 are laminated with an insulating layer 68 in between. Insulating layer 68 and heater protective layer 69.7
0 has windows 87 to 8 for exposing the pump electrode 66.
9 is formed, and the surface of the pump electrode 66 is further covered with a porous protective layer 72. The heater protective layer 69.70 also includes heater leads 85.86.
Slits 83, 84 are provided to ensure insulation between them.

Furthermore, in this embodiment, the conductor lead 7 of the pump electrode 65
8 is connected to A of the heater heat generating part 67 through the through hole 74.
At this point, the conductor lead 79 of the pump electrode 66 is hit.
It is connected to point B of the 1-ter conductor lead portion 86.

Therefore, the heater power source 8 is connected between the pump electrodes 65 and 66.
2, the partial pressure value of the voltage applied to the heater heat generating section 67 is applied.

With the above configuration, the oxygen sensor of this example has the air gap 8
0 communicates with the airtight space 9 in FIG. 1, the same effect as in the first embodiment can be obtained, that is, the reference substance can be stored and failures due to the intrusion of foreign matter can be prevented.

Furthermore, since the oxygen pump composed of the pump electrodes 65 and 66 and the solid electrolyte plate 62 share the power source 82 for the heater heat generating section 67, there is no need to provide a separate power source for the oxygen pump. Furthermore, since the number of conductor leads appearing in the connector portion (the portion to which the connector insulator 5 is connected) is only four, the connector insulator 5 of the first embodiment can be used as is. Therefore, the connector (not the connector insulator 5, but the lead wires 11 to 1,
3), and of course the connector insulator 5 can also be used in common.

Furthermore, since the voltage applied to the oxygen pump electrodes 65 and 66 uses a partial pressure of the voltage of the heater power supply 82, if the heater heat generating part 67 is formed of a material having a positive temperature coefficient of resistance, the The pressure value becomes lower than the partial pressure value at high temperature (because at low temperature, the ratio of the resistance value of heater heat generating part 67 to the total resistance value of heater leads 85, 86 decreases).

Oxygen pump is 2-3V at low temperature (below 500℃)
Ideally, unless the applied voltage is 1 V or less, element deterioration may occur.

Therefore, as in this embodiment, by extracting the partial pressure value of the applied voltage from a part of the heater heat generating part 67 having a positive temperature coefficient of resistance and applying it to the pump electrode 65,66, it is possible to A voltage of 12 to 16 V (heater power source t source) is applied to the pump electric i65.66 to replenish oxygen into the airtight space 9, and at low temperatures, the partial pressure value decreases to about 1■ to prevent element deterioration. be able to. In the case of a vehicle, this is effective when relatively low-temperature exhaust gas comes into contact with the exhaust gas in many cases, such as when starting the engine.

Further, at low temperatures, the operation of the oxygen pump decreases, but since the capacity of the airtight space 9 is large, the oxygen sensor can continue to operate well. Therefore, the volume of the airtight space 9 only needs to be large enough to store the reference substance (oxygen content of several percent or more), and in particular, as described above, the space inside the protective tube body 20 is utilized. It can be said that it is the most effective thing to do.

Moreover, since a certain amount of the reference substance can be stored in this way, there is no need to constantly operate the oxygen pump, and therefore there is no need to increase the heater power to heat the oxygen pump, which reduces power consumption. Along with the reduction, element deterioration due to heat can also be reduced.

Next, FIG. 4 is a diagram showing a third embodiment of the present invention.

In the oxygen sensor 200 of this embodiment, the first
In addition to the configuration of the oxygen sensor 100 of the embodiment (the element 60 of the second embodiment may be used instead of the oxygen sensor element 1)
A partition wall 23 is provided between the rubber plug 8 and the connector insulator 5 to airtightly isolate them.

This is to prevent organic gas from filling the airtight space 9 and contaminating the airtight space 9, since when the rubber stopper 8 becomes hot, organic gas peculiar to the rubber material may be generated. It is. Therefore, if the rubber stopper 8 is made of another material, the partition wall 23 may become unnecessary.

FIG. 5 shows a fourth embodiment of the invention. In this example,
The cavity 9 for storing the reference gas is kept airtight against the gas to be measured by a first airtight member 6 in which an inorganic filler such as talc or cement is compacted, and the inorganic filler such as talc or cement is further compacted. The second airtight member 14 made of glass or the like is melt-sealed to maintain airtightness against gas components that may be generated at high temperatures from existing equipment such as the upper rubber stopper. Therefore, as shown in FIG. 6, the oxygen sensor element 1 has a through hole 92 communicating with the airtight space at a portion corresponding to the airtight space 9, while the upper end of the gap 90 is airtightly sealed. . Such an oxygen sensor element 1 is, for example, the oxygen sensor element 1 shown in FIGS. 2 and 3.
-, 60 may be closed at the right end, and a through hole penetrating the solid electrolyte plate 31.61 and the protective layer 34.71 may be formed as a through hole communicating with the airtight space.

3 above. The fourth embodiment is a more preferable embodiment when the rubber plug portion 8 becomes relatively high in temperature, for example, in an engine with a high exhaust gas temperature or when an oxygen sensor is installed near the engine.

In addition, in each of the above embodiments, the oxygen pump (pump electrode 6
5.66) is provided in the oxygen detection unit 4, but
This may be provided in another part, for example, a structure may be adopted in which oxygen is drawn from the atmosphere rather than from the gas to be measured and is supplied into the airtight space 9.

In addition, the protective tube body 20 and the insulator 17.2.3 inside it
The shape, quantity, and material of the airtight members 6, 14, etc. are not limited to those in the above embodiment. Therefore, the position of the airtight space 9 is an airtight space 35.80 where the reference electrodes 38 and 64 are provided. It goes without saying that the oxygen sensor may be provided anywhere on the oxygen sensor as long as it has a structure that communicates with the oxygen sensor.

(Effects of the Invention) As described above in detail, the present invention provides an airtight space within the case of the oxygen sensor, and communicates only with the void inside the oxygen sensor element in which the reference electrode is provided. , there is no need to create a hole to introduce a reference material as in the past, and therefore, it completely prevents foreign substances such as water and salt water from entering from the outside and causing deterioration, damage, or inoperability of the oxygen sensor element. can.

Further, an oxygen pump for replenishing oxygen into the airtight space is provided, thereby making it possible to sufficiently store oxygen, which is a reference substance, in the airtight space. Moreover, since the volume of the airtight space can be made sufficiently large, there is no need to constantly operate the oxygen pump.This makes it possible to keep the voltage applied to the oxygen pump low, and the heater Since there is no need to heat the device to a high temperature all the time, the amount of human power needed to heat the heater can be reduced, which also makes it possible to reduce deterioration of the oxygen sensor element.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the configuration of a first embodiment of the present invention, FIG. 2 is an exploded perspective view of an oxygen sensor element constituting the same embodiment, and FIG. 3 is a second embodiment of the present invention. FIG. 4 is an exploded perspective view of an oxygen sensor element. FIG. 4 is a sectional view showing the configuration of a third embodiment of the present invention. FIGS. 5 and 6 are configuration diagrams of a fourth embodiment of the present invention. 100.200...Oxygen sensor 1,60...Oxygen sensor element 17.2.3...(1st to 3rd) insulator 4...Oxygen detection section 5...Connector insulator 8...
・Rubber stopper 6, 14...Airtight member 9...Airtight space 10...Earth leads 11-13...
・Lead wire 15... Housing 20... Protective tube body (case) 20a... Protective cover part 20b... Protective cylinder part 23
...Partition walls 31-33.61-62...Solid electrolyte plates 37, 63
...Measuring electrode 38.64...Reference electrode 39.4
0.65.66...Pump electrode 67...Heater heat generating part 35.80...Gap 41~45.48.75~
79.85.86...Conductor lead song

Claims (1)

[Scope of Claims] 1. An oxygen sensor in which an oxygen sensor element formed mainly using an oxygen ion conductive solid electrolyte and having at least a reference electrode and a measurement electrode is housed in a predetermined case, comprising: an airtight space formed in the airtight space and made substantially airtight; a space provided inside the oxygen sensor element that accommodates the reference electrode and communicates only with the airtight space; and an oxygen ion conduction effect within the space. and at least a pair of oxygen pump electrodes for supplying oxygen. 2. The oxygen sensor element is equipped with a heating heater, and at least one of the conductor leads for the oxygen pump electrode is connected to the heating part of the heating heater or a conductor for the heater in the oxygen sensor element. The oxygen sensor according to claim 1, which is connected to a lead. 3. The oxygen sensor according to claim 2, wherein the heat generating portion of the heating heater is made of a material having a positive temperature coefficient of resistance. 4. One of the pair of oxygen pump electrodes is exposed to the gas to be measured, and the other is provided in a gap accommodating the reference electrode, according to any one of claims 1 to 3. oxygen sensor. 5. The case includes: a protective cover portion that protects a portion of the oxygen sensor element exposed to the gas to be measured; a housing for attaching the oxygen sensor to a partition wall that separates the gas to be measured from other portions; A protective tube that protects the part of the element that is not exposed to the gas to be measured, an airtight member that prevents the gas to be measured from entering the protective tube, and a lead that electrically connects the oxygen sensor element to an external circuit. a rubber plug through which a wire is inserted and which closes an end of the protective cylinder, and the airtight space is surrounded by at least the protective cylinder, an airtight member, a lead wire, the rubber plug, and the oxygen sensor element. An oxygen sensor according to any one of claims 1 to 4. 6. The oxygen sensor according to claim 5, wherein a partition wall is provided between the airtight space and the rubber stopper to airtightly separate the two. 7. The airtight member is formed by compacting an inorganic filler and fixes the oxygen sensor element.
The oxygen sensor according to items 6 to 6. 8. The oxygen sensor according to any one of claims 1 to 7, wherein the oxygen sensor element is formed in a longitudinal plate shape. 9. The oxygen ion conductive positive solid electrolyte is Y_2O_3
, Yb_2O_3, and MgO.