CA1127870A - Temperature compensated titania type oxygen sensor - Google Patents
Temperature compensated titania type oxygen sensorInfo
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- CA1127870A CA1127870A CA352,575A CA352575A CA1127870A CA 1127870 A CA1127870 A CA 1127870A CA 352575 A CA352575 A CA 352575A CA 1127870 A CA1127870 A CA 1127870A
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Abstract
TEMPERATURE COMPENSATED TITANIA
TYPE OXYGEN SENSOR
ABSTRACT
A method and apparatus for obtaining an electrical signal which is a function of the 02 content of an exhaust gas of an internal combustion engine. The sensing element is comprised of two resistors, one of which is a zirconia resistor (1), the other of which is a titania resistor (2). Both resistors (1 and 2) have a resistance which varies as a function of the temperature of the exhaust gas to which it is exposed. However, the resistance of one of the resistors (2) also varies as a function of the oxygen content in the exhaust gas. The zirconia resistor (1) is in the feedback loop of an operational amplifier (3) while the titania resistor (2) is in the input circuit of the amplifier (3). Since the gain of the amplifier (3) will change as the ratio of the resistances of the titania resistor and zirconia resistor changes, for a given input, the output of the amplifier will be a function of the oxygen content in an exhaust gas and, hence, a function of the air to fuel ratio being supplied to an internal combustion engine.
TYPE OXYGEN SENSOR
ABSTRACT
A method and apparatus for obtaining an electrical signal which is a function of the 02 content of an exhaust gas of an internal combustion engine. The sensing element is comprised of two resistors, one of which is a zirconia resistor (1), the other of which is a titania resistor (2). Both resistors (1 and 2) have a resistance which varies as a function of the temperature of the exhaust gas to which it is exposed. However, the resistance of one of the resistors (2) also varies as a function of the oxygen content in the exhaust gas. The zirconia resistor (1) is in the feedback loop of an operational amplifier (3) while the titania resistor (2) is in the input circuit of the amplifier (3). Since the gain of the amplifier (3) will change as the ratio of the resistances of the titania resistor and zirconia resistor changes, for a given input, the output of the amplifier will be a function of the oxygen content in an exhaust gas and, hence, a function of the air to fuel ratio being supplied to an internal combustion engine.
Description
7~7~
-1- 360-79-03~0 TEMPERATURE COMPENSATED TITANIA
TYPE OXYGEN SENSOR
BACKGROUND OF THE INV~NTION
This invention is related to an apparatus for sensing the 2 content of an exhaust gas of an automobile engine.
The invention is more particularly related to an improved resistance type oxygen sensor having a titania resistor and a zirconia resistor.
Internal combustion engines, particularly automotive internal combustion engines, have exhaust gases which contain carbon monoxide, nitrogen oxides, and non-oxidized hydrocarbons, i.e. unburned or only partially burned hydrocarbons. All these substances contribute to air pollution. In order to reduce these substances which cause air pollution to a minimum value, it is necessary to clean the exhaust gases from the internal combustion engines as much as possible by effectively removing the largest possible quantity of these substances from the exhaust gases. This means that carbon monoxide and unburned hydrocarbons should be oxidized as completely as possible into their next higher oxidation stage, namely carbon dioxide and water tfor the hydrocarbons), and the nitrogen-oxide compound should be converted to elemental nitro~en and oxygen.
Conversion of the noxious components of exhaust gases to nonpoisonous compounds like carbon dioxide, nitrogen and water can be obtained by subjecting the exhaust gases to after-burning, i.,e. subjecting them to temperatures above about 600C while exposing them to catalysts. In order to succee~ in this method, however, the composition of the exhaust gases must be so controlled that practically complete conversion of the exhaust gases to the non-poisonous compounds is possible. This means that the relationship of air to fuel is close to the stoichiometric value. As a measure of ~he air to fuel .
~ 2~i37~
-1- 360-79-03~0 TEMPERATURE COMPENSATED TITANIA
TYPE OXYGEN SENSOR
BACKGROUND OF THE INV~NTION
This invention is related to an apparatus for sensing the 2 content of an exhaust gas of an automobile engine.
The invention is more particularly related to an improved resistance type oxygen sensor having a titania resistor and a zirconia resistor.
Internal combustion engines, particularly automotive internal combustion engines, have exhaust gases which contain carbon monoxide, nitrogen oxides, and non-oxidized hydrocarbons, i.e. unburned or only partially burned hydrocarbons. All these substances contribute to air pollution. In order to reduce these substances which cause air pollution to a minimum value, it is necessary to clean the exhaust gases from the internal combustion engines as much as possible by effectively removing the largest possible quantity of these substances from the exhaust gases. This means that carbon monoxide and unburned hydrocarbons should be oxidized as completely as possible into their next higher oxidation stage, namely carbon dioxide and water tfor the hydrocarbons), and the nitrogen-oxide compound should be converted to elemental nitro~en and oxygen.
Conversion of the noxious components of exhaust gases to nonpoisonous compounds like carbon dioxide, nitrogen and water can be obtained by subjecting the exhaust gases to after-burning, i.,e. subjecting them to temperatures above about 600C while exposing them to catalysts. In order to succee~ in this method, however, the composition of the exhaust gases must be so controlled that practically complete conversion of the exhaust gases to the non-poisonous compounds is possible. This means that the relationship of air to fuel is close to the stoichiometric value. As a measure of ~he air to fuel .
~ 2~i37~
-2- 360-79-0300 mixture, the symbol lambda has been used. At a value of lambda equal to one, the relationship of air to fuel is stoichiometric. If no excess oxygen is present which exceeds the equilibrium of the various possible reactions, lambda is less than one. If, however, lambda is greater than one, excess oxygen is present in the mixture.
To ensure a value of lambda of approximately one over varying engine conditions, requires that a sensing element be provided which is exposed to the exhaust gases and which determines oxygen content; this sensing element is then connected to a control device which controls the fuel or air supply and provides the correct ratio of fuel and air mixture to the internal combustion engine so that the exhaust gases will have as low a value of noxious components as possible.
One type of oxygen sensor is one wherein various voltages are generated in response to various oxygen contents of a gas. Such a sensor operates on the principle of elemental oxygen concentration and utilizes an ion conductive solid electrolyte and electrodes~ The principles on which a solid electrolyte sensor operates is explained in great detail in U.S. Reissue Patent Re 28,792, reissued April 27, 1976 (previously U.S. Patent
To ensure a value of lambda of approximately one over varying engine conditions, requires that a sensing element be provided which is exposed to the exhaust gases and which determines oxygen content; this sensing element is then connected to a control device which controls the fuel or air supply and provides the correct ratio of fuel and air mixture to the internal combustion engine so that the exhaust gases will have as low a value of noxious components as possible.
One type of oxygen sensor is one wherein various voltages are generated in response to various oxygen contents of a gas. Such a sensor operates on the principle of elemental oxygen concentration and utilizes an ion conductive solid electrolyte and electrodes~ The principles on which a solid electrolyte sensor operates is explained in great detail in U.S. Reissue Patent Re 28,792, reissued April 27, 1976 (previously U.S. Patent
3,400,054). This patent illustrates a solid electrolyte oxygen sensor whi~h, when one side is exposed to exhaust gases and ~n the other side e~posed to ambient air, pro~ides an electrical signal which is a function of elemental oxygen concentration; both sides of the solid electrolyte are covered at least in part with platinum to ~orm electrodes. The electrolyte is generally stabilized æirconia. Another example of such a sensor may be found in U.S. Patent 3,978,006 entitled "Methods for Producing Oxygen-Sensing Element, Particularly For Use With Internal Combustion Engine Exhaust Emission Analysis", issued August 31, 1976.
' ~7~
Another type of oxygen sensor is one wherein the electrical resistance of the sensor changes with the amount of oxygen present in the gas. This type of sensor is generally referred to as a resistance type sensor and the principle of operation of such a sensor is explained in U.S. Patent 3,558,280 entitled "Solid-State Oxygen Gage'l issued January 22, 1971. The use of a titania resistor sensor in a wheatstone bridge circuit to obtain a signal to control the air-fuel ratio of an internal lQ combustion engine is explained in U.S. Patent 3,915,135 entitled "Circuit for Converting a Temperature Dependent Input Signal to a Temperature Independent Output Signal"
issued October 28, 1975.
The resistance type (titania) oxygen sensor has certain disadvantages. For instance, the titania sensor must operate over a range in the order of 300C to 900C, but the electrical resistance of the sensor changes with temperature over that range in a manner that does not permit an unambiguous delineation between a lean air-fuel mixture and a rich air-fuel mixture. Specifically, for a lean air-fuel mixture over the range of 300C and 900C, the dc resistance of a given titania sensor drops from 3 x 108 ohms down to about 2 x 104 ohms. While the dc resistance for a rich air-fuel mixture, over the same range, varies from 5 x 104 ohms down to about 70 ohms.
Therefore, at certain operating temperatures the resistance characteristics for a rich and a lean mixture for the sensor overlap and it would be impossible, with an uncompensated titania sensor, to determine whether the air-fuel ratio is rich or lean. Of course, this is undesirable, as it would not be possible to control the air-fuel mixture because the titania type sensor cannot distinguish between a rich air to fuel mixture and a lean air to fuel mixture.
: . ' ~27~
' ~7~
Another type of oxygen sensor is one wherein the electrical resistance of the sensor changes with the amount of oxygen present in the gas. This type of sensor is generally referred to as a resistance type sensor and the principle of operation of such a sensor is explained in U.S. Patent 3,558,280 entitled "Solid-State Oxygen Gage'l issued January 22, 1971. The use of a titania resistor sensor in a wheatstone bridge circuit to obtain a signal to control the air-fuel ratio of an internal lQ combustion engine is explained in U.S. Patent 3,915,135 entitled "Circuit for Converting a Temperature Dependent Input Signal to a Temperature Independent Output Signal"
issued October 28, 1975.
The resistance type (titania) oxygen sensor has certain disadvantages. For instance, the titania sensor must operate over a range in the order of 300C to 900C, but the electrical resistance of the sensor changes with temperature over that range in a manner that does not permit an unambiguous delineation between a lean air-fuel mixture and a rich air-fuel mixture. Specifically, for a lean air-fuel mixture over the range of 300C and 900C, the dc resistance of a given titania sensor drops from 3 x 108 ohms down to about 2 x 104 ohms. While the dc resistance for a rich air-fuel mixture, over the same range, varies from 5 x 104 ohms down to about 70 ohms.
Therefore, at certain operating temperatures the resistance characteristics for a rich and a lean mixture for the sensor overlap and it would be impossible, with an uncompensated titania sensor, to determine whether the air-fuel ratio is rich or lean. Of course, this is undesirable, as it would not be possible to control the air-fuel mixture because the titania type sensor cannot distinguish between a rich air to fuel mixture and a lean air to fuel mixture.
: . ' ~27~
-4- 360-79-0300 An example of a gas sensor of titania ceramic material which includes a circuit for converting a temperature dependent input signal to a temperature independent output signal to control the air to fuel ratio of an automobile engine is shown in previously mentioned U.S. Patent 3,915,135.
Another example of an 2 sensor system that provides an electrical signal indicative of the 2 content of an exhaust gas which minimizes the temperature effect on the signal is U.S. Patent 4,147,513 entitled "Method and Apparatus for Measuring the 2 Content of a Gas" issued April 3, 1979. This 2 sensor system ancl apparatus describes the use of titania and zirconia resistors connected together in series to obtain a signal which is indicative of the 2 content in the gas.
SUMMARY OF_TEIE INVENTION
This invention provides an oxyyen sensing syste~l which essentially nullifies the effect o~ temperature of the gas on a resistive type oxygen sensing element and is an alternate approach to the system shown in previously discussed U.S. Patents 4,147,513 and 3,915,135.
The invention is a method ancl apparatus for sensing the 2 content of a gas and is characterized by an electrical circuit that includes a titania resistor (1) and a zirconia resistor t2) with the zirconia resistor (2) connected in the feedback loop (input to output) of an amplifier (3). When voltage is applied to the circuit and the resistors are exposed to the heated exhaust gas, an electrical signal can be generated from the circuit that is a function of the oxygen content of the gas.
Accordingly, it is an object of this invention to provide a method and apparatus for determining a relative oxygen content o~ a gas.
3~27æ7q~
Another example of an 2 sensor system that provides an electrical signal indicative of the 2 content of an exhaust gas which minimizes the temperature effect on the signal is U.S. Patent 4,147,513 entitled "Method and Apparatus for Measuring the 2 Content of a Gas" issued April 3, 1979. This 2 sensor system ancl apparatus describes the use of titania and zirconia resistors connected together in series to obtain a signal which is indicative of the 2 content in the gas.
SUMMARY OF_TEIE INVENTION
This invention provides an oxyyen sensing syste~l which essentially nullifies the effect o~ temperature of the gas on a resistive type oxygen sensing element and is an alternate approach to the system shown in previously discussed U.S. Patents 4,147,513 and 3,915,135.
The invention is a method ancl apparatus for sensing the 2 content of a gas and is characterized by an electrical circuit that includes a titania resistor (1) and a zirconia resistor t2) with the zirconia resistor (2) connected in the feedback loop (input to output) of an amplifier (3). When voltage is applied to the circuit and the resistors are exposed to the heated exhaust gas, an electrical signal can be generated from the circuit that is a function of the oxygen content of the gas.
Accordingly, it is an object of this invention to provide a method and apparatus for determining a relative oxygen content o~ a gas.
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-5- 360-79-0300 It is another object of this invention to determine whether the air to fuel mixture supplied to an internal combustion machine is rich or lean~
It is another object of this invention to provide an oxyyen sensing apparatus and method which performs well at temperatures from below 350C to above 850C.
It is another object of this invention to provide a simply constructed oxygen sensor system that has a minimum susceptibility to noise thereby minimizing false output signals.
It is another object of this invention to improve the performance of an oxygen sensing system and method using a titania type oxygen sensor by minimizing the effect of temperature on said sensorD
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic diagram of an electrical circuit used to accomplish the principles of this invention.
FIGURE 2 is a graph of the output voltage of the circuit shown in FIGURE 1 versus l:emperature for rich and lean combustion mixtures.
FIGURES 3 and 4 are diagrams of the switching response of the circuit in FIGURE 1 when the sensing elements are exposed to a gas resulting from combustion of a rich to a lean air to fuel mixture.
FIGURES 5 and 6 is a diagram of the switching response of the circuit in FIGURE 1 (without series or parallel resistors when the sensing elements are exposed to a gas resulting from combustion of a rich to a lean air to f~el mixture.
~27137~
It is another object of this invention to provide an oxyyen sensing apparatus and method which performs well at temperatures from below 350C to above 850C.
It is another object of this invention to provide a simply constructed oxygen sensor system that has a minimum susceptibility to noise thereby minimizing false output signals.
It is another object of this invention to improve the performance of an oxygen sensing system and method using a titania type oxygen sensor by minimizing the effect of temperature on said sensorD
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic diagram of an electrical circuit used to accomplish the principles of this invention.
FIGURE 2 is a graph of the output voltage of the circuit shown in FIGURE 1 versus l:emperature for rich and lean combustion mixtures.
FIGURES 3 and 4 are diagrams of the switching response of the circuit in FIGURE 1 when the sensing elements are exposed to a gas resulting from combustion of a rich to a lean air to fuel mixture.
FIGURES 5 and 6 is a diagram of the switching response of the circuit in FIGURE 1 (without series or parallel resistors when the sensing elements are exposed to a gas resulting from combustion of a rich to a lean air to f~el mixture.
~27137~
-6- 370-79-0300 DETAILED DESCRIPTION OF THE DRAWINGS
FIGURE 1 illustrates an electrical circuit that accomplishes the principles of this invention. The circuit consists of a sensing element 10 comprised of two resistors. The first resistor 1 is comprised of zirconia and the second resistor 2 is comprised of titania. The junction between the two resistors is connected to one of the inputs of an operational amplifier 3. The other input of the operational amplifier 3 is connected to a reference voltage. The zirconia resistor 1 is connected in the feedback loop of the amplifier. In parallel with the zirconia resistor 1 is a resistor 4 and in series with the zirconia resistor 1 is a resistor 5. The inventor believes that it is a function of these two additional resistors 4 and 5 to make the resistance characteristics of the zirconia resistor more closely approximate the resistance values of the titania element at stoichiometr~.
(Lambda equal to 1.0). These additional resistors 4 and 5 may or may not be included in the circuit. A similar circuit is shown in a Society of Automotive Engineers publication No. 790140 published in 1979 and entitled "Titania Exhaust Gas Sensor For Automotive Applications"
by M. J. Esper et al of the Ford ~lotor Company. Power is supplied to the circuit through the operational amplifier 2S 3 at its power input V+.
The resistance of the titania resistor 2 varies as a function of both the temperature and the oxygen content of an exhaust gas from an internal combustion engine. The resistance of the zirconia resistor 1 varies only as a function of the temperature of the exhaust gas. The zirconia resistor 1 may be replaced by any other resistor or combination of resistors that exhibit a change in resistance with respect to temperature that is similar to that of the titania resistor 2 or proportionately similar.
For instance, in the previously identified 1979 SAE
article, it is suggested that the zirconia resistor could ~'7l37~
FIGURE 1 illustrates an electrical circuit that accomplishes the principles of this invention. The circuit consists of a sensing element 10 comprised of two resistors. The first resistor 1 is comprised of zirconia and the second resistor 2 is comprised of titania. The junction between the two resistors is connected to one of the inputs of an operational amplifier 3. The other input of the operational amplifier 3 is connected to a reference voltage. The zirconia resistor 1 is connected in the feedback loop of the amplifier. In parallel with the zirconia resistor 1 is a resistor 4 and in series with the zirconia resistor 1 is a resistor 5. The inventor believes that it is a function of these two additional resistors 4 and 5 to make the resistance characteristics of the zirconia resistor more closely approximate the resistance values of the titania element at stoichiometr~.
(Lambda equal to 1.0). These additional resistors 4 and 5 may or may not be included in the circuit. A similar circuit is shown in a Society of Automotive Engineers publication No. 790140 published in 1979 and entitled "Titania Exhaust Gas Sensor For Automotive Applications"
by M. J. Esper et al of the Ford ~lotor Company. Power is supplied to the circuit through the operational amplifier 2S 3 at its power input V+.
The resistance of the titania resistor 2 varies as a function of both the temperature and the oxygen content of an exhaust gas from an internal combustion engine. The resistance of the zirconia resistor 1 varies only as a function of the temperature of the exhaust gas. The zirconia resistor 1 may be replaced by any other resistor or combination of resistors that exhibit a change in resistance with respect to temperature that is similar to that of the titania resistor 2 or proportionately similar.
For instance, in the previously identified 1979 SAE
article, it is suggested that the zirconia resistor could ~'7l37~
-7- 360-79-0300 be replaced by a densified titania ceramic because the densified titania is relatively insensitive to oxygen changes. Treating the titania resistor 2 with a precious metal such as platinum may also be used to improve its low temperature response.
E X A M P L ~
The following is a table identi~ying the values of components used in an operable embodiment of the invention:
Element Description 1 Resistor comprised of zirconia 2 Resistor comprised of titania 3 Operational amplifier IC (LM 2902) National Semiconductor 4 Resistor 1.5 megohms Resistor 820 ohms V~ 7.5 volts DC
V ref 1.7 volts DC
Typical examples of the resistance of the titania resistor 2 and the zirconia resistor 1 at different temperatures are as follows:
For a rich air to fuel mixture, the resistance of the zirconia resistor 1 at 400C is 1.6 x 106 ohms and at 750C
2.6K ohms for the same air to fuel mixture and temperature range, the resistance of the titania resistor 2 is 7.6K ohms and 180 ohms respectively; for a lean air to fuel mixture, the resistance of the zirconia resistor at 400C is 1.6 x 106 ohms and at 750C, 2.6K ohms; and for the same air to fuel mixture and temperature range, the resistance of the titania resistor is about 2 x 107 ohms and 39K ohms respectively.
, . : ~ -:
7~
E X A M P L ~
The following is a table identi~ying the values of components used in an operable embodiment of the invention:
Element Description 1 Resistor comprised of zirconia 2 Resistor comprised of titania 3 Operational amplifier IC (LM 2902) National Semiconductor 4 Resistor 1.5 megohms Resistor 820 ohms V~ 7.5 volts DC
V ref 1.7 volts DC
Typical examples of the resistance of the titania resistor 2 and the zirconia resistor 1 at different temperatures are as follows:
For a rich air to fuel mixture, the resistance of the zirconia resistor 1 at 400C is 1.6 x 106 ohms and at 750C
2.6K ohms for the same air to fuel mixture and temperature range, the resistance of the titania resistor 2 is 7.6K ohms and 180 ohms respectively; for a lean air to fuel mixture, the resistance of the zirconia resistor at 400C is 1.6 x 106 ohms and at 750C, 2.6K ohms; and for the same air to fuel mixture and temperature range, the resistance of the titania resistor is about 2 x 107 ohms and 39K ohms respectively.
, . : ~ -:
7~
-8- 360-79-0300 FIGURE 2 illustrates the output voltage of the circuit shown in FIGURE 1 for rich and lean air to fuel ratios when the titania resistor 2 and ~irconia resistor 1 are exposed to an exhaust gas from a combustion process. For a lean air to fuel mixture, in this instance lambda approximately 1.07, the output voltage from the operational amplifier 3 from the circuit shown in FIGURE 1 would be about 1.8 volts DC and is shown by curve A. When the air to fuel mixture is rich (lambda approximately 0.93) the output voltage from the operational amplifier shown in FIGURE 1 will be about 6.3 ~olts DC and is shown by curve B.
Accordingly, the signal from the output of the circuit shown in FIGURE 1 can be used to identify rich or lean air to fuel mixtures over a range of operating temperatures.
FIGURES 3 and 4 show graphs of the switching response of the circuit shown in FIGURE 1 when the sensing element 10 is exposed to a gas resulting from combustion of an air to fuel mixture which changes between rich and lean (and vice versa).
FIGURES 5 and 6 are graphs of the switching response of the circuit shown in FIGURE 1, without series and parallel resistors (4 and 5), when the sensing element 10 is exposed to a gas resulting from combustion of an air to fuel mixture which changes between rich and lean (and vice versa).
FIGURES 3 through 6 illustrate that the circuit shown in FIGURE 1 may be used without resistors 4 and 5 and the effects of resistors 4 and 5 on the switching response of the circuit.
OPERATION
When resistors 1 and 2 are exposed to an exhaust gas, the temperature of the exhaust gas and the oxygen content of the exhaust gas will effect the gain of the amplifier 3. Since the gain of the operational amplifier 3 is a function of the ratio of the feedback resistance and the ~2~37~
Accordingly, the signal from the output of the circuit shown in FIGURE 1 can be used to identify rich or lean air to fuel mixtures over a range of operating temperatures.
FIGURES 3 and 4 show graphs of the switching response of the circuit shown in FIGURE 1 when the sensing element 10 is exposed to a gas resulting from combustion of an air to fuel mixture which changes between rich and lean (and vice versa).
FIGURES 5 and 6 are graphs of the switching response of the circuit shown in FIGURE 1, without series and parallel resistors (4 and 5), when the sensing element 10 is exposed to a gas resulting from combustion of an air to fuel mixture which changes between rich and lean (and vice versa).
FIGURES 3 through 6 illustrate that the circuit shown in FIGURE 1 may be used without resistors 4 and 5 and the effects of resistors 4 and 5 on the switching response of the circuit.
OPERATION
When resistors 1 and 2 are exposed to an exhaust gas, the temperature of the exhaust gas and the oxygen content of the exhaust gas will effect the gain of the amplifier 3. Since the gain of the operational amplifier 3 is a function of the ratio of the feedback resistance and the ~2~37~
-9- 360-7~-0300 input resistance, the output of the ampli~ier will vary as the resistance of the æirconia resistor 1 in the feedback loop varies and as the resistance of the titania resistor in the input varies (with the network input voltage being fixed)O
When the resistors 1 and 2 are exposed to an exhaust gas, the temperature of the exhaust gas will change the resistance o both resistors 1 and ~. However, since both resistors have been chosen to have resistances which vary similarly with temperature, the voltage across both resistors 1 and 2 should remain about the same. However, when the oxygen content of the exhaust gas decreases, the resistance of the titania resistor 2 will decrease and when the oxygen content of the e~haust gas increases, the resistance of the titania resistor 2 will increase. When there is a rich air to fuel mixture going into the engine, the 2 content in the exhaust gas is less than would be when a lean air to fuel mixture goes into the exhaust gas.
Conversely, when the titania resistor 2 is exposed to an e~haust gas having more oxygen, i.e., a lean air to fuel mixture, the resistance across the titania resistor 2 increases. Since the ratio of resistance of the titania and zirconia resistors is relatively constant with temperature, the network gain will remain equally constant as the temperature varies. However, since the resistance of the titania resistor 2 will vary for different lean to rich air to fuel mixtures, the gain of the network will be different from the lean to rich air to fuel mixtures.
While a preferred embodiment of this invention has been disclosed, it will apparent to those skilled in the art that changes may be made to the invention as set forth in the appended claims and, in some cases, certain features of the invention may be used to advantage without corresponding use of other features. For example, while only titania and zirconia have been shown as the resistor elements, it has been suggested that other materials may :::
: . . :~ :: ..:
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When the resistors 1 and 2 are exposed to an exhaust gas, the temperature of the exhaust gas will change the resistance o both resistors 1 and ~. However, since both resistors have been chosen to have resistances which vary similarly with temperature, the voltage across both resistors 1 and 2 should remain about the same. However, when the oxygen content of the exhaust gas decreases, the resistance of the titania resistor 2 will decrease and when the oxygen content of the e~haust gas increases, the resistance of the titania resistor 2 will increase. When there is a rich air to fuel mixture going into the engine, the 2 content in the exhaust gas is less than would be when a lean air to fuel mixture goes into the exhaust gas.
Conversely, when the titania resistor 2 is exposed to an e~haust gas having more oxygen, i.e., a lean air to fuel mixture, the resistance across the titania resistor 2 increases. Since the ratio of resistance of the titania and zirconia resistors is relatively constant with temperature, the network gain will remain equally constant as the temperature varies. However, since the resistance of the titania resistor 2 will vary for different lean to rich air to fuel mixtures, the gain of the network will be different from the lean to rich air to fuel mixtures.
While a preferred embodiment of this invention has been disclosed, it will apparent to those skilled in the art that changes may be made to the invention as set forth in the appended claims and, in some cases, certain features of the invention may be used to advantage without corresponding use of other features. For example, while only titania and zirconia have been shown as the resistor elements, it has been suggested that other materials may :::
: . . :~ :: ..:
`, ~ : , ~
,.
37~
-10- 360-79-0300 be used for these resistances so long as the resistance to temperature characteristics of both resistors exposed to the gas are similar or changed in equal proportions so long as one of the materials has a resistance which varies substantially differently than the other resistor with the 2 content of the exhaust gas to which it is exposed.
Further, it has also been pointed out, that additional resistances may be used in the feedback loop of the amplifier to achieve additional advantages. Also, the location of the titania and zirconia resistors may be interchanged. Accordingly, it is intended that the illustrative and descriptive material herein be used to illustrate the principles of the invention and not to limit the scope thereof.
Further, it has also been pointed out, that additional resistances may be used in the feedback loop of the amplifier to achieve additional advantages. Also, the location of the titania and zirconia resistors may be interchanged. Accordingly, it is intended that the illustrative and descriptive material herein be used to illustrate the principles of the invention and not to limit the scope thereof.
Claims (9)
1. An electrochemical oxygen sensing apparatus for obtaining an electrical signal which is a function of the oxygen content in a gas, said sensing apparatus comprising:
an amplifier having an input and an output;
a first resistor having a resistance which varies as a function of the temperature and oxygen content of a gas to which it is exposed, said first resistor electrically connected in series with said amplifier input;
a second resistor having a resistance which varies as a function of the temperature of the gas to which it is exposed, said second resistor having one lead connected to the input of said amplifier and another lead connected to the output of said amplifier, whereby when a voltage is applied to said resistors and said first and second resistors are exposed to a gas, a signal is obtained from the output of said amplifier which is related to the oxygen content of said gas.
an amplifier having an input and an output;
a first resistor having a resistance which varies as a function of the temperature and oxygen content of a gas to which it is exposed, said first resistor electrically connected in series with said amplifier input;
a second resistor having a resistance which varies as a function of the temperature of the gas to which it is exposed, said second resistor having one lead connected to the input of said amplifier and another lead connected to the output of said amplifier, whereby when a voltage is applied to said resistors and said first and second resistors are exposed to a gas, a signal is obtained from the output of said amplifier which is related to the oxygen content of said gas.
2. The apparatus as recited in Claim 1 wherein said second resistor is comprised of zirconia and said second resistor has about the same resistance-temperature characteristics as the first resistor over a predetermined temperature range of said gas.
3. The apparatus as recited in Claim 1 or 2 wherein said first resistor is comprised of titania.
4. A method for obtaining an electrical signal which is a function of the oxygen content of a gas, the method comprising:
connecting a first resistor having a resistance which varies as a function of the temperature and oxygen content of the gas to which it is exposed in series with the input of an amplifier;
connecting a second resistor having a resistance which varies as a function of only the temperature of the gas to which it is exposed to the input and output of said amplifier;
applying a potential to said resistors;
exposing said resistors to said gas; and obtaining from the output of said amplifier a signal which is a function of the resistance of said first and second resistors.
connecting a first resistor having a resistance which varies as a function of the temperature and oxygen content of the gas to which it is exposed in series with the input of an amplifier;
connecting a second resistor having a resistance which varies as a function of only the temperature of the gas to which it is exposed to the input and output of said amplifier;
applying a potential to said resistors;
exposing said resistors to said gas; and obtaining from the output of said amplifier a signal which is a function of the resistance of said first and second resistors.
5. A method for obtaining an electrical signal which is a function of the oxygen content of a gas, the method comprising:
connecting a first resistor, comprised of titania and having a resistance which varies as a function of both the temperature and the oxygen content of a gas to which it is exposed, in series with the input of an amplifier;
connecting a second resistor, comprised of stabilized zirconia and having a resistance which varies as a function of only the temperature of the gas to which it is exposed, to the input and output of said amplifier;
applying a voltage to said resistors; and exposing said resistors to a gas, whereby an electrical signal may be obtained from the output of said amplifier which is a function of the resistance of said first and second resistors and of the oxygen content of said gas.
connecting a first resistor, comprised of titania and having a resistance which varies as a function of both the temperature and the oxygen content of a gas to which it is exposed, in series with the input of an amplifier;
connecting a second resistor, comprised of stabilized zirconia and having a resistance which varies as a function of only the temperature of the gas to which it is exposed, to the input and output of said amplifier;
applying a voltage to said resistors; and exposing said resistors to a gas, whereby an electrical signal may be obtained from the output of said amplifier which is a function of the resistance of said first and second resistors and of the oxygen content of said gas.
6. An electrochemical oxygen sensing apparatus for obtaining an electrical signal which is a function of the oxygen content in a gas, said sensing apparatus comprising:
an amplifier having an input and an output;
a first resistor having a resistance which varies as a function of the temperature and oxygen content of a gas to which it is exposed;
a second resistor having a resistance which varies as a function of the temperature of the gas to which it is exposed and is substantially less sensitive to oxygen than said first resistor; one of said resistors electrically connected to the input of said amplifier, the other of said resistors connected in a feedback loop of said amplifier, whereby when voltage is applied to said apparatus and said first and second resistors are exposed to a gas, a signal is obtained from the output of said amplifier which is related to the oxygen content of said gas.
an amplifier having an input and an output;
a first resistor having a resistance which varies as a function of the temperature and oxygen content of a gas to which it is exposed;
a second resistor having a resistance which varies as a function of the temperature of the gas to which it is exposed and is substantially less sensitive to oxygen than said first resistor; one of said resistors electrically connected to the input of said amplifier, the other of said resistors connected in a feedback loop of said amplifier, whereby when voltage is applied to said apparatus and said first and second resistors are exposed to a gas, a signal is obtained from the output of said amplifier which is related to the oxygen content of said gas.
7. The apparatus as recited in Claim 6 wherein said second resistor is comprised of zirconia and said second resistor has about the same resistance-temperature characteristics as the first resistor over a predetermined temperature range of said gas.
8. The apparatus as recited in Claim 6 or 7 wherein said first resistor is comprised of titania.
9. The apparatus in Claim 6 or 7 wherein said second resistor is in the feedback loop of said amplifier.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US7688079A | 1979-09-19 | 1979-09-19 | |
| US76,880 | 1979-09-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1127870A true CA1127870A (en) | 1982-07-20 |
Family
ID=22134741
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA352,575A Expired CA1127870A (en) | 1979-09-19 | 1980-05-23 | Temperature compensated titania type oxygen sensor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1127870A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11307159B2 (en) | 2017-05-18 | 2022-04-19 | Delphi Technologies Ip Limited | Ionic-conducting resistor for exhaust constituent sensors |
-
1980
- 1980-05-23 CA CA352,575A patent/CA1127870A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11307159B2 (en) | 2017-05-18 | 2022-04-19 | Delphi Technologies Ip Limited | Ionic-conducting resistor for exhaust constituent sensors |
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