JPH0244242A - Fault detection type oxygen sensor - Google Patents

Abstract

PURPOSE:To enable detection of the presence of a fault in a sensor itself quickly and accurately without erroneous detection by arranging a specified resistor on a superpower output circuit positioned within a sensor body so as to be in series with respect to a measuring electrode or a reference electrode. CONSTITUTION:For example, a resistor 42 has conductor sections 52 and 53 comprising a Pt-Au alloy or the like formed on upper and lower end faces of a prismatic ceramic porcelain 50, a resistance section 54 of a resistance value R formed on the side thereof and conductor sections 52 and 53 connected to the resistance section 54. The resistance section 54 herein used is a lutenium oxide based thick film resistance in view of resistance to heat. Moreover, an overcoat glass is applied thereon to reduce a change in resistance at a high temperature. Therefore, this resistor 42 is interposed between a connection terminal 40 and a lead metal 44 to be connected in series to a reference electrode 16. As a result, the resistance value R serves to expand a change in an electromotive force Es attribute to a fine current (i) flowing in from a control computer B thereby assuring accurate detection of a fault eliminating erroneous detection.

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to a failure detection type oxygen sensor, and in particular, the present invention relates to a failure detection type oxygen sensor. The present invention relates to an oxygen sensor used in a system that detects the presence or absence of a failure based on a signal corresponding to a pulsed current.

(Background technology) Conventionally, air-fuel ratio detection devices detect the oxygen concentration contained in the exhaust gas (combustion exhaust gas) of an automobile internal combustion engine, and optimally control the combustion state of the internal combustion engine based on the detected signal. So-called oxygen sensors are known that purify exhaust gas and reduce fuel consumption.

By the way, the oxygen concentration detection element used in this type of oxygen sensor typically determines the oxygen concentration using the principle of an oxygen concentration battery using an oxygen ion conductive solid electrolyte such as zirconia porcelain. Structures have been put into practical use, in which each solid electrolyte has a
Combustion exhaust gas obtained by detecting the electromotive force caused by the difference in oxygen concentration between the measurement electrode exposed to the measured gas and the reference electrode exposed to the reference gas with the reference oxygen concentration, and then burning at the stoichiometric air-fuel ratio. Based on this, it is determined whether the gas to be measured is in a lean atmosphere or a rich atmosphere, using a gas in a neutral atmosphere as the boundary, and based on this, the combustion The engine that generates the exhaust gas is controlled so that the combustion exhaust gas is in a range near the stoichiometric air-fuel ratio where the three-way catalyst that purifies the exhaust gas is effective.

In this way, such an oxygen sensor mainly controls harmful components in the exhaust gas, such as nitrogen, by managing the oxygen concentration in the combustion exhaust gas and maintaining the appropriate air-fuel ratio of the internal combustion engine that generates the exhaust gas. The output of the electromotive force to be detected is the function of such an oxygen sensor, since it is used for the purpose of reducing the amount of oxides (No,), -carbon oxides (CO), hydrocarbons (HC), etc. Circuit (detection circuit)
If the electromotive force is damaged due to disconnection, short circuit, etc., normal electromotive force cannot be detected, and therefore,
This will cause an increase in the amount of harmful components in the exhaust gas.

For this reason, it is necessary to detect whether the oxygen sensor is functioning normally and, if it is unable to output a normal electromotive force, notify the malfunction by lighting a warning light, etc., and take some countermeasures. However, conventional failure detection methods turn on a warning light when the heater built into the oxygen sensor is disconnected, or determine the failure state based on the length of time that the detected electromotive force signal is in an abnormal state. Because of this, there are various problems inherent in it.

In other words, the former method, which detects failures due to heater disconnection, etc., does not directly detect failures in the electromotive force detection system, so there are many cases of false detection; In the fault detection method based on length,
In order to avoid false positive detection, the presence or absence of a failure is determined based on the continuation of an abnormal state for a long period of time, so it takes time to detect a failure. The demand for detection could not be fully met.

(Solution Division B) By the way, as a direct failure detection method for such an oxygen sensor, it is also possible to use a measuring electrode that constitutes the oxygen concentration detection element of the oxygen sensor, in its electromotive force output circuit (detection circuit). By passing a predetermined minute current in pulse form from the outside between the electrode and the reference electrode, the electromotive force detected by the oxygen concentration detection element according to the principle of an oxygen concentration battery is changed (increased). A system is conceivable in which the presence or absence of a failure is detected based on a signal corresponding to the pulsed current that is output superimposed on the electromotive force, in other words, based on the degree of increase in the electromotive force.

According to this fault detection system, the presence or absence of a fault is determined based on the degree of change in electromotive force caused by instantaneous application of a predetermined fault detection current.
Failure detection does not require much time and can fully meet the demand for speedy failure detection in recent years, but the change (increase) in electromotive force due to the application of such failure detection current is simply due to the increase in oxygen in the oxygen sensor. This is due to the internal resistance of the concentration detection element, and such internal resistance has a large temperature dependence, with a resistance value of several hundred ohms or less at temperatures above 600'C, which reduces the rate of change in the detected electromotive force. becomes smaller, which increases the possibility of false positive detection. Of course, if such a failure detection current is applied as a large current, the degree of change in the output electromotive force will increase, but due to the oxygen pumping effect between the measurement electrode and the reference electrode due to such a large current, oxygen The solid electrolyte constituting the oxygen concentration detecting element of the sensor is subject to deterioration, causing problems such as reduced durability.

(Solution Means) Here, the present invention has been made against this background, and in order to solve the above problems,
The oxygen concentration battery has an oxygen ion conductive solid electrolyte, a measurement electrode that is brought into contact with combustion exhaust gas as a gas to be measured, and a reference electrode that is brought into contact with a reference gas, each of which is provided in contact with the solid electrolyte. According to the principle, the electromotive force caused by the oxygen concentration difference between the combustion exhaust gas and the reference gas is output, and by passing a predetermined current in a pulse form from the outside to the output circuit of the electromotive force, the electromotive force is In an oxygen sensor used in a system that detects the presence or absence of a failure based on a signal corresponding to the pulsed current that is output in a superimposed manner, an output circuit for the electromotive force located in the main body of the oxygen sensor is provided. , a predetermined resistor is provided so as to be located in series with the measurement electrode or the reference electrode.

Furthermore, in this case, as a more preferable form for downsizing and high reliability, an oxygen ion conductive solid electrolyte, and measurement electrodes provided in contact with the solid electrolyte and brought into contact with the combustion exhaust gas, which is the gas to be measured, are provided. It has a measurement electrode that is brought into contact with the reference gas and a reference electrode that is brought into contact with the reference gas, and outputs an electromotive force due to the oxygen concentration difference between the combustion exhaust gas and the reference gas based on the principle of an oxygen concentration battery. On the other hand, by passing a predetermined current in a pulse form from the outside into the output circuit of the electromotive force, the presence or absence of a failure is detected based on a signal corresponding to the pulsed current that is output superimposed on the electromotive force. In the oxygen sensor used in the system, in particular, a predetermined resistor arranged in series with the measurement electrode or the reference electrode is provided on the output circuit of the electromotive force on the plate-shaped oxygen concentration detection element. You can also do that.

(Function) By the way, the electromotive force detection circuit (extraction circuit) of the failure detection type oxygen sensor according to the present invention can be schematically shown, for example, as shown in FIG. Here, the oxygen sensor A has an internal circuit of the sensor body surrounded by a broken line, and is connected to an external control computer B at a connection point a formed by a connector or the like.

This control computer B, at connection point = b,
The inside and outside of the sensor are connected to each other and have at least an internal circuit surrounded by a broken line, and the air-fuel ratio in a combustion device such as an internal combustion engine of an automobile is determined based on the electromotive force output taken out from the oxygen sensor. It's meant to be controlled.

In other words, oxygen sensor A, as is well known,
It has a solid electrolyte that conducts oxygen ions, and a measurement electrode that is brought into contact with combustion exhaust gas, which is the gas to be measured, and a reference electrode that is brought into contact with a reference gas, which are provided in contact with the solid electrolyte, respectively, and are arranged in contact with the solid electrolyte. The principle of the battery is to generate an electromotive force E due to the difference in oxygen concentration between the combustion exhaust gas and the reference gas. Note that this oxygen sensor has its own internal resistance R.

The resistor according to the present invention, which has a resistance value of It is being

On the other hand, in the control computer B, the electromotive force E taken out from the oxygen sensor A is compared with a predetermined control value through an amplifier (AMP), and based on that, the air-fuel ratio of a combustion device such as an internal combustion engine of a car is determined. A control signal is output to control the Also, for the circuit leading to the amplifier (AMP) in the control computer B, the electric a! XE is connected through a resistor R1, and a constant current given by this power source E and resistor R1 is passed in pulse form to the electromotive force output circuit at regular intervals by the switch means SW, and then the oxygen sensor A It is designed to be guided by the side. When this current i is applied, the output voltage of the oxygen sensor A changes depending on the resistances R and R8 on the sensor side. That is, a signal (voltage) corresponding to the pulsed current i is superimposed on the electromotive force E and output, and a change in the electromotive force based on such superposition is detected by the control computer B. That's what happens.

Therefore, in such a failure detection system, in an operating state where the oxygen sensor A detects an electromotive force based on the oxygen concentration in the combustion exhaust gas, which is the gas to be measured, the control computer B sends a signal to the oxygen sensor A side. The change in electromotive force based on the pulsed current i that is passed through is detected by the control computer B, and the difference in voltage between when the pulsed current i is passed and when it is not is used to detect failures. Since such a pulsed current i is passed to the oxygen sensor A side at regular intervals, the voltage difference described above is always constant while the oxygen sensor A is in operation. This makes it possible to constantly monitor failures during operation of the oxygen sensor A.

In such a failure detection system, if a short circuit occurs inside oxygen sensor A or between connection points a and b, even if the failure detection current i is passed in a pulsed manner as described above, A corresponding increase (change) in the electromotive force is not observed, and if there is an interruption within the oxygen sensor A or between the connection point a and b, and electrical continuity cannot be established, the computer B The voltage of the power supply E inside the device will be directly applied to the amplifier (AMP).In any case, if the electromotive force of the oxygen sensor A is detected by the control computer, such an electromotive force can be avoided. Changes in power make it possible to detect failures such as short circuits and disconnections.

In addition, a resistor (R) installed on the electromotive force output circuit located inside the main body of the oxygen sensor A magnifies the change in the electromotive force E due to the pulsed minute current i flowing from the control computer B. This eliminates the possibility of false detection and ensures accurate failure detection. In short, by inserting a resistor (R) inside the sensor, it is necessary to maintain a stable resistance value in the temperature range in which the sensor is used.For this purpose, the resistance value R of the resistor is preferably 1. A value of about Ω to 100Ω will be adopted.

Furthermore, as the resistor R, one having a stable resistance value, that is, one whose resistance value does not substantially change even in a high temperature range of generally 150° C. or higher, is advantageously used, and furthermore, one having temperature dependence is used. However, as long as it has positive temperature dependence, it can be used in the same way.

In addition, the failure detection current i flowing from the control computer B is approximately 0.1 to 100 μA, especially 1
A current of about ~10 μA is preferably adopted, and such a current i is caused to flow to the electromotive force output circuit at regular intervals by the switch means SW, but the energization time and energization interval etc. It will be selected as appropriate depending on conditions such as the time required for detection.

(Examples) Hereinafter, some examples according to the present invention will be described based on the drawings to clarify the present invention more specifically.

First, a failure detection type oxygen sensor according to an example of the present invention shown in FIG. 2 has a well-known test tube-shaped oxygen concentration detection element 10. In addition, as in the conventional case, this oxygen concentration detection element 10 includes an oxygen ion conductive solid electrolyte 12 such as zirconia porcelain, and measurement electrodes 14 made of platinum or the like formed on the outer and inner surfaces of the solid electrolyte 12, respectively.
and a reference electrode 16. The oxygen concentration detection element 10 is housed in a housing attached to a partition wall that partitions the combustion exhaust gas and the atmosphere, and the combustion exhaust gas as the gas to be measured introduced through the window 22 of the protective cover 20 is exposed to the oxygen concentration. Concentration detection element 10
It is adapted to be brought into contact with a measurement electrode 14 formed on the outer surface of the. Further, the reference electrode 16 formed on the inner surface of the oxygen concentration detection element 10 is connected to a suitable ventilation part provided in a bottomed cylindrical metal cap 24 attached to the atmosphere side opening part of the housing 18 or such. It is designed to come into contact with the atmosphere that is introduced through the gap in the attachment area of the cap.

Further, the oxygen concentration detection element 10 is attached to the housing 18 by the pressing force of a disc spring 30 disposed at the end of the cap via the first insulator 26 and the second insulator 28 housed in the cap 24. It is designed to be pressed down, thereby achieving electrical continuity and sealing against exhaust gas. Note that 32 is a holding cylinder for holding the first and second insulators 26 and 28, one end of which is fitted into the inner hole of the housing 18 and fixed, and Second insulator 26.
A metal washer 34 is interposed between 28.

An external lead wire 36 connected to an electromotive force measurement system such as an external control computer is connected to the grommet 3 with respect to the reference electrode 16 of the oxygen concentration detection element IO.
8, the connection terminal 40, the resistor 42, and the lead fitting 44 are fixed and supported on the bottom of the cap 24.
are electrically connected via. More specifically, the resistor 42 is arranged between the first insulator 26 and the second insulator 28, fixed by the pressing force of the wave spring 46, and Due to the pressing force of the wave spring 46, the connection terminal 40 and the reference electrode 16, which are caulked and fixed to the external lead wire 36, are electrically connected.
This is achieved by bringing the lead metal fittings 44 connected to the conductive parts of the upper and lower end surfaces of the resistor 42 into contact. Note that the lead fitting 44 and the reference electrode 16
The connection is made by pinching the connection piece provided at the end of the lead metal fitting 44 between the oxygen concentration detection element 10 and the first insulator 26, so that the connection is made to the end surface of the oxygen concentration detection element 10. This is done by contacting a reference electrode 16 extending up to .

Further, the resistor 42 is, for example, as shown in FIG.
Conductive portions 52 and 52 made of a Pt-Au alloy or the like are formed on the upper and lower end surfaces of the columnar ceramic porcelain 50, respectively, and a resistance portion 54 having a predetermined resistance value is formed on the side surface of the columnar ceramic porcelain 50, and This resistance section 54
The conductive portions 52 and 52 on the upper and lower end surfaces are connected to each other. Note that, from the viewpoint of heat resistance, a ruthenium oxide thick film resistor is advantageously used as the resistor portion 54, and an overcoat glass is further applied thereon to reduce resistance changes at high temperatures. The configuration will be advantageously adopted.

Therefore, the resistor 42 having such a structure is connected to the connecting terminal 40.
By being interposed between the resistor 42 and the lead fitting 44, the resistor 42 is connected in series to the reference electrode 16 on the electromotive force output circuit within the sensor body, and the resistor 42 42 (more precisely, the resistance section 54) is applied to the electromotive force output circuit, and as a result, as described above, the control device such as the control computer or the electromotive force detection This can advantageously cause a change in electromotive force based on a minute fault detection current from the device.

On the other hand, the measurement electrode 14 of the oxygen concentration detection element 10 is electrically connected to the housing 18 and grounded through it.

Note that the resistor 42 having a predetermined resistance value can be placed anywhere inside the sensor body including the oxygen concentration detection element IO, the housing 18, and the cap 24, but it is preferable that the resistor 42 has a predetermined resistance value. In order to prevent 42 from being exposed to high temperature conditions and causing a large change in its resistance value or from being degraded or destroyed, it should be placed at a location away from the oxygen concentration detection element 10 where high temperatures act, in other words, from outside. It is desirable to arrange it at a position closer to the connection part with the lead wire 36. Further, the resistor 42 does not necessarily need to be housed in an insulator as illustrated, but such housing in an insulator may cause the conductive portion 52 of the resistor 42 to come into contact with the cap 24, which is the ground electrode. This is advantageous in that there is no fear.

Furthermore, the electrical connection between the resistor 42, the connecting terminal 40, and the lead metal fitting 44 is preferably structured so that electrical continuity is achieved through contact, as shown in the example, but brazing, soldering, etc. It goes without saying that there is no problem even if the electrical connection is made using other connection methods.

In another example of the failure detection type oxygen sensor according to the present invention shown in FIG. It is pressed into the end opening of the element 10, thereby establishing electrical continuity between the resistor 56 and the electromotive force 16 inside the oxygen concentration detection element 10.

Note that, like the resistor in the previous example, this resistor 56 is constructed by providing a conductive portion at both ends of a ceramic cylindrical body and a resistor portion made of a thick film resistor that provides a predetermined resistance value on the side surface.

In the oxygen sensor of this embodiment, the cap is divided into two parts, a first cap 62 and a second cap 64, and the base of the first cap 62 is covered with talc 66 as in the conventional case. , a one shear 68, and a heat compensating metal 70, the housing 18 is caulked and fixed to the atmosphere side opening of the housing 18. Further, the connection terminal 40 fixed to the external lead wire 36 by the caulking metal fitting 72 is pressed against the conductive part at the end of the resistor 56 by the pressing force of the spring 58, thereby establishing electrical continuity between them. is now being done. Note that both 74 and 76 are insulators.

Furthermore, in different embodiments of the present invention shown in FIGS. 5 and 6, unlike the test tube-shaped or bottomed cylindrical oxygen concentration detection element 10 as in the above two examples, a plate-shaped oxygen concentration detection element 10 is used. The element 80 is used, and a chip resistor 82 as a resistor is provided by brazing to the electromotive force output circuit of the oxygen concentration detection element 80.

That is, as is clear from FIG. 6, in this oxygen concentration detection element 80, a measurement electrode 86 is formed on the side of a plate-shaped solid electrolyte 84 exposed to combustion exhaust gas, and a reference electrode 88 is formed on the opposite side. Furthermore, it has a structure in which a spacer member 92 for forming an air passage 90 and a plate-like lid member 94 are sequentially laminated and integrated on the side where the reference electrode 88 is provided. .

The reference electrode 8 of the oxygen concentration detection element 80 is brought into contact with the atmosphere guided through the air passage 90, while the lead portion 96 is connected to the solid electrolyte through a through hole 98 provided in the solid electrolyte 84. 84
A chip resistor 82 is taken out on the side where the measurement electrode 86 is formed, and has a predetermined resistance value at the taken out part.
are connected in series to the reference electrode 88.

In this way, even if the chip resistor 82 as a resistor is provided on the oxygen concentration detection element 80 to provide a predetermined resistance value, the same functions and effects as in the above embodiment can be obtained. It can be done. Note that instead of the chip resistor 82 as the resistor used here, it is also possible to configure a part of the lead portion 96 of the reference electrode 88 with a thick film resistor similar to the previous example.

In addition, -b Although not illustrated, it goes without saying that the present invention can be implemented in various forms without departing from the spirit of the present invention, and such embodiments include: It should be understood that both fall within the scope of the present invention.

(Effect of the invention) As is clear from the above explanation, by passing a predetermined minute current in a pulse form from the outside into the output circuit of the electromotive force generated by the principle of an oxygen concentration battery, the electromotive force is superimposed and output. If the failure detection type oxygen sensor according to the present invention is used in a system that detects failure or non-failure based on the signal corresponding to the pulsed current generated, there is almost no possibility of false detection, and the oxygen sensor itself This makes it possible to accurately and quickly detect the presence or absence of a failure.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of an electromotive force output circuit using an oxygen sensor according to the present invention, and FIG. 2 is a cross-sectional explanatory diagram showing an example of a failure detection type oxygen sensor according to the present invention. 3 is a perspective explanatory view of a resistor used in the oxygen sensor of FIG. 2, and FIG. 4 is a cross-sectional explanatory view corresponding to FIG. 2 showing another example of the oxygen sensor according to the present invention.
FIG. 5 is a perspective view showing another example of the oxygen concentration detection element of the oxygen sensor according to the present invention, and FIG. 6 is an exploded view of the oxygen concentration detection element shown in FIG. 5. 1, o, so: oxygen concentration detection element 12.84: solid electrolyte 14.86: measurement electrode is, 8s: reference electrode 18: housing 26: first insulator 30: disc spring 36: external lead wire 42: resistance Body 46 Two wave spring 50: Column ceramic porcelain 52: Conductive part 54: Resistance part 56: Resistor 58: Coil spring 60: Graphite powder 74.76: Insulator 90; Air passage 94: Cover member 98 Varnish through hole 24: Cap 28: Second insulator 32: Protective cylinder 40: Connection terminal 44: Lead metal fittings 82: Chimp resistor 92 Nice spacer member 96: Lead portion Figure 2 Procedure amendment (voluntary) September 4, 1999 ■. 2゜3゜4゜Indication of the case 1985 Patent application No. 194264 Name of the invention Relationship to the person who corrects failure detection type oxygen sensor Case Name of patent applicant Name (406) Nippon Insulator Co., Ltd. Rijin's representative specification Column 6 of Detailed Description of the Invention, Contents of Amendment (1) "It can be done." on page 21, line 8 of the specification has been changed to "It is possible, and the resistor is provided on the oxygen concentration detection element in this way." In this case, it is obvious that this embodiment is advantageous compared to the above embodiment because no structural changes other than the oxygen concentration detection element are required. (2) As shown in red on the attached sheet in Figure 4 of the drawings, the code is 40.
and its leader line. that's all

Claims (1)

[Scope of Claims] A system comprising an oxygen ion conductive solid electrolyte, and a measurement electrode that is brought into contact with combustion exhaust gas, which is a gas to be measured, and a reference electrode that is brought into contact with a reference gas, which are provided in contact with the solid electrolyte, respectively. However, according to the principle of an oxygen concentration battery, an electromotive force caused by the difference in oxygen concentration between the combustion exhaust gas and the reference gas is output, and a predetermined current is passed in a pulse form from the outside to the output circuit of the electromotive force. An oxygen sensor used in a system for detecting the presence or absence of a failure based on a signal corresponding to the pulsed current superimposed on the electromotive force, and the oxygen sensor located in the main body of the oxygen sensor. A failure detection type oxygen sensor, comprising a predetermined resistor arranged in series with the measurement electrode or the reference electrode on the electromotive force output circuit.