JP2012047535A - Gas concentration detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas concentration detector capable of accurately detecting short circuit of a gas sensor even when a resistance value of a powder layer is reduced by moisture absorption while suppressing an increase of manufacturing costs.SOLUTION: A resistance value Ra of a power supply side resistor 251 and a resistance value Rb of a reference potential side resistor 252 constituting a voltage dividing circuit 250 of a circuit 200 for gas sensors are set to the following range in order to suppress the decrease of offset voltage to be generated by the voltage dividing circuit 250 and to suppress current flowing through the voltage dividing circuit 250 to 1 mA or less when resistance of the powder layer of an oxygen sensor 100 is decreased by the moisture absorption.

Description

  The present invention relates to a gas concentration detection apparatus having a gas sensor.

  A gas sensor for measuring oxygen concentration, etc., comprising a bottomed cylindrical detection element, inner and outer electrodes provided on the inner and outer sides of the detection element, a casing covering the detection element, and the like Are known. When measuring the oxygen concentration using this gas sensor, the bottom side of the detection element is in contact with the gas to be measured, and the opening side of the detection element is in contact with a reference gas such as the atmosphere. Then, the oxygen concentration in the measurement gas is measured based on the electromotive force generated in the detection element according to the difference between the oxygen concentration of the measurement gas and the oxygen concentration of the reference gas.

  When this gas sensor is used to measure the oxygen concentration in the exhaust gas from the vehicle engine, when the air-fuel ratio of the exhaust gas is rich, the oxygen concentration in the exhaust gas is low, so the electromotive force increases. The output voltage of the gas sensor approaches a predetermined value. On the other hand, when it is lean, the output voltage approaches 0V, but when the gas sensor is short-circuited, the output voltage from the gas sensor becomes 0V. For this reason, there is a problem that it is impossible to distinguish between a lean state and a short circuit, and a short circuit of the gas sensor cannot be detected.

  In order to solve such a problem, a voltage dividing circuit including a resistor connected to a power source and a resistor connected to a reference potential is provided on the apparatus side where the gas sensor is mounted to generate an offset voltage. Application to the outer electrode of the gas sensor is performed. By doing so, the output voltage of the gas sensor when it is lean can be set to a voltage value larger than 0 V, and a short circuit of the gas sensor can be detected.

  By the way, in such a gas sensor, the detection element is held from the outside by a metal shell constituting a part of the casing. The metal shell is connected to a reference potential, but an insulator and a powder layer that seals a gap formed between the insulator and the metal shell are provided between the detection element and the metal shell. It is electrically insulated from the metallic shell.

  However, if moisture absorption occurs in the powder layer, the resistance value of the powder layer decreases and the detection element and the metal shell are electrically connected via the powder layer, and current flows from the detection element to the metal shell. End up. As a result, the offset voltage applied to the outer electrode is lowered, and there is a risk of erroneous detection of a short circuit of the gas sensor.

  Here, Patent Document 1 describes providing an insulating layer that covers the outer electrode of the detection element of the gas sensor. By doing so, even when the resistance value of the powder layer is reduced due to moisture absorption, the detection element and the metal shell can be electrically insulated, and erroneous detection of a short circuit of the gas sensor can be prevented. .

JP 2006-234790 A

  However, the insulating layer described above needs to have sufficient insulation, and if the gas sensor is used for measuring the oxygen concentration in the exhaust gas from the engine, it needs to have sufficient heat resistance, durability, etc. Therefore, there is a possibility that the manufacturing cost of the gas sensor will increase significantly.

  The invention of the present application has been made in view of the above problems, and can detect a short circuit of a gas sensor with high accuracy even when the resistance value of a powder layer is reduced due to moisture absorption while suppressing an increase in manufacturing cost. An object is to provide an apparatus.

  The present invention made to solve the above problems is formed in a bottomed cylindrical shape with a closed tip, and the concentration of the gas to be measured in which the inner electrode and the outer electrode are provided on the inner side and the outer side, respectively. The detection element to be detected, the detection element is held from the outside, the metal fitting connected to the sensor-side reference potential is filled, and the gap between the detection element and the metal fitting is filled, and the detection element and the metal fitting are electrically insulated. And a gas sensor circuit connected to an inner electrode and an outer electrode, and a signal corresponding to the concentration of the gas to be measured is input from the gas sensor. The gas sensor circuit divides the voltage generated by the power supply by the power supply resistance connected directly to the power supply or through another resistor and the reference potential resistance connected to the circuit reference potential. Electric It generates, comprises a voltage divider circuit for inputting the offset voltage to the outer electrode of the gas sensor. Then, the resistance value Ra of the power supply side resistor is suppressed in order to suppress a decrease in the offset voltage when the resistance value of the seal layer decreases due to moisture absorption of the seal layer and the outside of the detection element and the metal shell are electrically connected. And the resistance value Rb of the reference potential side resistor are set according to the equations (1) and (2), respectively.

  Vcc is the difference between the voltage value of the voltage generated by the power supply and the voltage value of the circuit side reference potential, and Va is the offset voltage when the detection element and the metal shell are electrically insulated. The value of t is 0.7 or more and less than 1.

  In addition, the “voltage generated by the power supply” means that if the power supply side resistance of the gas sensor circuit is connected to the power supply through another resistance, the voltage to the power supply side resistance through the other resistance. It may mean an applied voltage.

  Further, the sensor-side reference potential and the circuit-side reference potential may be generated by, for example, a casing of a system in which the gas concentration detection device is mounted. The sensor-side reference potential and the circuit-side reference potential are , May be the same potential or substantially the same potential.

  As described above, when the resistance value of the powder layer (corresponding to the seal layer) decreases due to moisture absorption, the outside of the detection element and the sensor-side reference potential are electrically connected, and the offset voltage applied to the outer electrode of the detection element. Will fall.

  However, by setting the resistance values Ra and Rb of the power supply side resistance and the reference potential side resistance of the voltage dividing circuit that generates the offset voltage to be low, a decrease in the offset voltage when the resistance value of the powder layer is reduced due to moisture absorption is suppressed. be able to. FIG. 4 shows a graph showing the relationship between the offset voltage and the resistance value Rx of the powder layer when the offset voltage at normal time (when moisture absorption does not occur in the powder layer) is 1.5V. Yes. The graph of FIG. 4 shows the case where the resistance value Ra of the power supply side resistance and the resistance value Rb of the reference potential side resistance are 560 kΩ and 240 kΩ, 56 kΩ and 24 kΩ, and 5.6 kΩ and 2.4 kΩ. The relationship between the offset voltage and the resistance value Rx is shown. From the graph, it can be seen that the lower the resistance values Ra and Rb, the more the offset voltage can be suppressed from decreasing as the resistance value Rx decreases.

  For this reason, assuming the minimum value of the resistance value Rx of the powder layer that decreases due to moisture absorption, and setting the resistance value Ra of the power supply side resistance and the resistance value Rb of the reference potential side resistance based on the minimum value, A decrease in offset voltage when moisture absorption occurs in the layer can be suppressed. Based on such an idea, the ranges of the resistance values Ra and Rb are determined by the above formulas (1) and (2).

  Next, how the above formulas (1) and (2) are derived will be described with reference to FIG. In the following description, it is assumed that the gas sensor and the gas sensor circuit of the present invention correspond to 100 and 200 in FIG. 1, respectively. However, the gas sensor and the gas sensor circuit of the present invention are configured as shown in FIG. Note that this is not a limitation.

  The gas sensor circuit 200 is connected to a power source 400 that generates a voltage of 5 V, and includes a first terminal 210 and a second terminal 220 connected to the inner electrode and the outer electrode of the gas sensor 100, respectively. In addition, the gas sensor circuit 200 generates an offset voltage by the power supply side resistor 251 connected to the power supply 400 and the reference potential side resistor 252 connected to the circuit side reference potential 240, and the gas sensor circuit 200 A voltage dividing circuit 250 is applied to the outer electrode.

  When the resistance value Rx of the powder layer of the gas sensor decreases due to moisture absorption, the outside of the detection element and the sensor side reference potential 500 are electrically connected, so that the powder is between the second terminal 220 and the sensor side reference potential 500. The layer resistance 300 is formed.

  Here, when moisture absorption does not occur in the powder layer, the resistance values Ra and Rb have the following relationship.

  In addition, Va ′ can be expressed as follows as an offset voltage when moisture absorption occurs in the powder layer and the powder layer resistance 300 is formed.

  Here, when moisture absorption of the powder layer occurs, assuming that the voltage value to be maintained as a minimum as the offset voltage is t × Va [V] (t is a coefficient of 0.7 or more and less than 1), the following equation is established. .

  Then, by substituting equation (3) into equation (5) and eliminating Rb, the following equation is obtained.

  Here, although details will be described later, the lowest value of the resistance value Rx of the powder layer when moisture absorption occurs is assumed to be 0.1 MΩ from the experimental results. For this reason, Formula (1) mentioned above is guide | induced from Formula (6).

  Similarly for Rb, the following relationship can be derived by substituting Equation (3) into Equation (5) and eliminating Ra.

  Since the minimum value of the resistance value Rx of the powder layer when moisture absorption occurs is assumed to be 0.1 MΩ, Equation (2) described above is derived from Equation (7).

  That is, the resistance value Rx of the power supply side resistance of the voltage dividing circuit and the resistance value Rb of the reference potential side resistance of the voltage dividing circuit are only set according to the equations (1) and (2), and the resistance value Rx of the powder layer is reduced to 0.1 MΩ by moisture absorption Even when the voltage drops, the offset voltage can be maintained at 70% or more of the normal value. Therefore, without providing an insulating layer or the like covering the outer electrode of the detection element of the gas sensor, it is possible to sufficiently suppress a decrease in offset voltage when moisture absorption of the powder layer occurs, and prevent erroneous detection of a short circuit of the gas sensor. Can do it. For this reason, according to the present invention, it is possible to accurately detect a short circuit of the gas sensor even when the resistance value of the powder layer is reduced due to moisture absorption while suppressing an increase in manufacturing cost.

  On the other hand, by reducing the resistance value Ra of the power supply side resistance and the resistance value Rb of the reference potential side resistance, the current flowing through the voltage dividing circuit increases, and the power consumption in the gas sensor circuit increases. Here, when the current flowing through the dividing circuit when moisture absorption does not occur in the powder layer is Ia, the resistance values Ra and Rb, the power supply voltage Vcc, the offset voltage Va, and Ia are as follows. A relationship is established.

From Expressions (8) and (9), it is possible to determine a range of resistance values Ra and Rb when the current Ia flowing through the voltage dividing circuit of the gas sensor circuit is set to a predetermined value or less.
Therefore, in the gas concentration detection device according to the present invention, the resistance value Ra of the power supply side resistance and the resistance value Rb of the reference potential side resistance are set according to the equations (10) and (11), respectively. Features.

  By doing so, the current flowing through the voltage dividing circuit of the gas sensor circuit can be suppressed to 1 mA or less, and an increase in power consumption in the gas sensor circuit can be suppressed.

It is a block diagram which shows the structure of a gas concentration detection apparatus. It is sectional drawing of an oxygen sensor. It is a graph which shows the measurement result of the resistance value of the powder layer of an oxygen sensor in a high temperature and high humidity environment. It is a graph which shows the relationship between resistance value Rx of the powder layer of an oxygen sensor, and offset voltage.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments of the present invention are not limited to the following embodiments, and various forms can be adopted as long as they belong to the technical scope of the present invention.

[Description of configuration]
FIG. 1 is a block diagram showing a configuration of a gas concentration detection device 1 of the present embodiment. The gas concentration detection apparatus 1 measures the oxygen concentration in the exhaust gas using the oxygen sensor 100 for measuring the oxygen concentration in the exhaust gas from the engine of the vehicle, and the oxygen sensor 100, and various types of measurement are performed according to the measurement results. The gas sensor circuit 200 performs processing.

  The gas sensor circuit 200 includes a first terminal 210 and a second terminal 220 connected to the oxygen sensor 100. The second terminal 220 is connected to a power supply 400 that generates a voltage of 5V via a step-down resistor 230. Connected. Further, an offset voltage of 1.5 V is generated by the power supply side resistor 251 connected to the power supply 400 and the reference potential side resistor 252 connected to the circuit side reference potential 240 and applied to the oxygen sensor 100 from the second terminal 220. And a differential amplifier circuit 260 that amplifies the potential difference between the first terminal 210 and the second terminal 220.

  Further, the first terminal 210 of the gas sensor circuit 200 and the output terminal of the differential amplifier circuit 260 are connected to a microcomputer that measures the oxygen concentration and detects a short circuit of the oxygen sensor 100 based on the voltages of these terminals. Yes. The gas sensor circuit 200 may be provided integrally with the oxygen sensor 100, or may be configured as a part of an engine control unit (ECM), a powertrain control module (PCM), or the like. Further, it may be provided between the oxygen sensor 100 and the ECM or PCM.

  Next, the configuration of the oxygen sensor 100 will be described using the cross-sectional view of the oxygen sensor 100 shown in FIG. In the following description, the lower side in FIG. 2 is described as the front end side of the oxygen sensor 100, and the upper side is described as the rear end side of the oxygen sensor 100.

The oxygen sensor 100 includes a detection element 110 formed in a bottomed cylindrical shape having a closed end with an oxygen ion conductive solid electrolyte body mainly composed of zirconia (ZrO ₂ ), and disposed inside the detection element 110. It is composed of a rod-shaped ceramic heater 120, a casing 130 that houses the detection element 110, and the like.

  The detection element 110 is configured as a detection unit 111 whose tip is in contact with the gas to be measured, and an outer electrode 112 used for measuring the voltage of the detection element 110 on the outer side and the inner side, respectively. And an inner electrode 113 are provided. Note that these electrodes may be configured as porous electrodes formed of Pt or a Pt alloy.

In addition, the ceramic heater 120 has a heat generating part 121 that heats the detecting part 111 of the detecting element 110 with a resistance heat generating line.
The casing 130 holds the detection element 110 and has a metallic metal shell 131 that projects the detection portion 111 into the exhaust pipe and the like, and a cylindrical shape connected to the rear end side opening of the metal shell 131. An inner cylinder member 132 and a cylindrical outer cylinder member 133 connected to the rear end opening of the inner cylinder member 132 are provided. Further, a reference gas space 134 in which the reference gas is accumulated is formed inside the inner cylinder member 132 and the outer cylinder member 133.

  Further, insulators 140 and 142 made of insulating ceramic and a powder layer 141 made of talc and the like are provided between the metal shell 131 and the detection element 110, and the rear end of the metal shell 131. By crimping the side, the metal shell 131 and the detection element 110 are sealed in an airtight state.

  The oxygen sensor 100 includes an outer electrode lead wire 150, an inner electrode lead wire 151 connected to the gas sensor circuit 200, and a heater lead wire 152 that supplies power to the ceramic heater 120.

  The outer electrode lead wire 150 and the inner electrode lead wire 151 are disposed in the reference gas space 134 through the seal member 153 and the separator 154. The outer electrode lead wire 150 is connected to the element outer surface fixing bracket 155 in contact with the outer electrode 112, and the inner electrode lead wire 151 is connected to the element inner surface fixing bracket 156 in contact with the inner electrode 113. Is done. The outer electrode lead wire 150 and the inner electrode lead wire 151 are connected to the second terminal 220 and the first terminal 210 (see FIG. 1) of the gas sensor circuit 200, respectively.

The heater lead wire 152 is also inserted into the oxygen sensor 100 through the seal member 153 and the separator 154 and connected to the ceramic heater 120.
The metal shell 131 is connected to the sensor side reference potential 500. The sensor-side reference potential 500 and the circuit-side reference potential 240 may be generated by, for example, the vehicle body of a vehicle on which the gas concentration detection device 1 is mounted. The potential 240 may be the same potential or almost the same potential.

[Measurement of oxygen concentration]
Next, measurement of oxygen concentration using the oxygen sensor 100 will be described. In the oxygen sensor 100, when the reference gas is accumulated in the reference gas space 134 and the detection unit 111 of the detection element 110 is brought into contact with the measurement gas, the oxygen concentration in the measurement gas and the oxygen concentration in the reference gas are determined. In response to the difference, an electromotive force is generated in the detection element 110, and the voltage of the inner electrode 113 changes. The gas sensor circuit 200 measures the voltage of the inner electrode 113 with the inner electrode lead wire 151, and measures the oxygen concentration in the gas to be measured based on the measured voltage.

  In the present embodiment, the oxygen sensor 100 is used for measuring the oxygen concentration in the exhaust gas. When the air-fuel ratio of the exhaust gas is rich, the oxygen concentration in the exhaust gas is lower than that of the reference gas, so the electromotive force approaches 1 V. When the exhaust gas is lean, the oxygen concentration in the exhaust gas is the reference gas. The electromotive force approaches 0 V because it is close to the oxygen concentration. As already described, since the 1.5 V offset voltage generated by the voltage dividing circuit 250 of the gas sensor circuit 200 is applied to the outer electrode 112 of the oxygen sensor 100, the voltage of the inner electrode 113 is It changes in the range of 1.5V-2.5V at the normal time.

  In addition, there is a failure mode in which exhaust gas flows into the inside of the detection element 110 (normally exposed to the reference gas) due to breakage of the oxygen sensor 100 or the like. Accordingly, when the outer side of the detection element 110 is exposed to a gas having a higher oxygen concentration, the voltage value of the inner electrode 113 becomes lower than the voltage value of the outer electrode 112. At this time, if an offset voltage of 1.5V is applied to the outer electrode 112, the voltage of the inner electrode 113 changes between 1.5V and 0.5V. This failure mode is called output shift (CSD).

  When a short circuit occurs on the first terminal 210 side (inner electrode lead wire 151 side) of the oxygen sensor 100, the voltage output from the inner electrode lead wire 151 becomes 0 V, and the second terminal 220 side ( When a short circuit occurs on the outer electrode lead wire 150 side, the voltage output from the inner electrode lead wire 151 changes in the range of 0V to 1.0V.

  For this reason, the gas sensor circuit 200 uses 0.3 V as the threshold for determining the short circuit of the oxygen sensor 100, and when the voltage at the first terminal 210 falls below 0.3 V, the oxygen sensor 100 is short-circuited. judge.

[Moisture absorption of powder layer]
Incidentally, an electrically insulating powder layer 141 is provided between the metal shell 131 of the oxygen sensor 100 and the detection element 110. When moisture absorption occurs in the powder layer 141, the powder layer 141 is provided. The resistance value of the metal shell 131 and the outer side of the detection element 110 are electrically connected. At this time, the outer side of the detection element 110 and the metal shell 131 are connected by the powder layer resistance formed on the powder layer 141, but the metal shell 131 is connected to the sensor-side reference potential 500. As shown in FIG. 1, the powder layer resistor 300 is formed between the second terminal 220 and the sensor-side reference potential 500.

  As a result, a current flows from the second terminal 220 to the sensor-side reference potential 500 via the powder layer resistor 300, so that the offset voltage applied to the outer electrode 112 decreases, and the normal state (powder layer) The lower limit value of the voltage of the inner electrode 113 is reduced as compared with the case where no moisture absorption occurs. When the lower limit value is less than 0.3 V, the gas sensor circuit 200 can detect that a short circuit has occurred even if the oxygen sensor 100 has not short circuited.

Here, the range of the resistance value of the powder layer that decreases due to moisture absorption will be examined.
An experiment was conducted to measure the resistance value of the powder layer 141 by leaving the oxygen sensor 100 in a high-temperature and high-humidity environment at a temperature of 60 ° C. and a humidity of 98% for about 500 hours. FIG. 3 shows a graph showing the measurement result of the resistance value Rx of the powder layer 141 in the experiment. The experiment was carried out in a vehicle for a predetermined period of time and used as a durable product No1, No2 which is an oxygen sensor 100 used for measuring an oxygen concentration for exhaust gas, and a NEW product No1, a unused oxygen sensor 100. The test was conducted for No.4.

  From the measurement results, it was found that the resistance value Rx of the powder layer 141 when the oxygen sensor 100 was left in the high temperature and high humidity environment was at least about 0.5 MΩ. For this reason, the range of the resistance value Rx of the powder layer resistor 300 formed by the powder layer 141 of the oxygen sensor 100 can be assumed to be 0.1 MΩ or more.

[Resistance value of voltage divider circuit resistance]
In the present embodiment, the threshold for short circuit detection based on the voltage value of the first terminal 210 is 0.3V. As described above, even if the output shift (CSD) failure occurs in the oxygen sensor 100 and the sensor output is 1.0 V lower than the offset voltage, the threshold value is set to 0. Set to 3V.

  That is, assuming that the short-circuit detection threshold is 0.3 V and the minimum value of the offset voltage is 90% (1.35 V) of the normal value (1.5 V), the output shift (CSD) is temporarily assumed. This is because even if a failure occurs, the voltage value of the first terminal 210 can be ensured to be 0.35 V or higher, so that a short circuit can always be detected normally.

  Therefore, Vcc = 5.0V, Va = 1.5V, and t = 0.9, and the resistance values Ra and Rb are set in the following ranges based on the above formulas (1) and (2).

  Further, in order to set the current flowing through the voltage dividing circuit 250 to 1 mA or less, the resistance values Ra and Rb are set to the following ranges based on the above-described equations (10) and (11).

[effect]
According to the gas concentration detection device 1 of the present embodiment, even when the resistance value Rx of the powder layer 141 is reduced to 0.1 MΩ due to moisture absorption, the offset voltage can be maintained at 90% or more of the normal value. Therefore, it is possible to sufficiently suppress a decrease in offset voltage when moisture absorption of the powder layer 141 occurs without providing an insulating layer or the like that covers the outer electrode 112 of the detection element 110 of the oxygen sensor 100. It is possible to prevent erroneous detection of a short circuit. For this reason, it is possible to accurately detect a short circuit of the oxygen sensor 100 when the resistance value of the powder layer 141 is reduced due to moisture absorption while suppressing an increase in manufacturing cost.

Further, the current flowing through the voltage dividing circuit 250 of the gas sensor circuit 200 can be suppressed to 1 mA or less, and an increase in power consumption in the gas sensor circuit 200 can be suppressed.
[Other Embodiments]
(1) In the present embodiment, the gas concentration detection device 1 including the oxygen sensor 100 has been described as an example. However, the present invention is not limited to this, and the present invention is a gas sensor that detects gas other than oxygen. It can also be applied to.
(2) In the present embodiment, the case where the oxygen sensor 100 is used for measuring exhaust gas from the engine of the vehicle has been described as an example. However, even when the oxygen sensor 100 is used for other purposes. The present invention can be applied.
(3) In this embodiment, the voltage of the power supply 400 is 5.0 V, the normal offset voltage is 1.5 V, and the short-circuit determination threshold is 0.3 V. However, the present invention is limited to these values. There is nothing. In addition, when the resistance value Rx of the powder layer 141 decreases due to moisture absorption, the minimum value of the offset voltage is 1.35 V, which is 90% of the normal time, but this minimum value is also limited to this. And is determined as appropriate according to the offset voltage and the threshold for short-circuit determination.
(4) In the gas sensor circuit 200 of FIG. 1, the voltage dividing circuit 250 directly divides the voltage of the power source 400, but a resistor or the like is interposed between the voltage dividing circuit 250 and the power source 400. The power supply voltage once lowered may be divided by the voltage dividing circuit 250. For example, even if the voltage value of the power supply 400 is 12V, the voltage dividing circuit 250 may generate an offset voltage after stepping down to 5V by a resistor or the like. Similarly, the step-down resistor 230 may step down the voltage of the power supply 400 or may be omitted.
(5) In the gas sensor circuit 200 of FIG. 1, the circuit-side reference potential 240 has been described as 0 V, but there is no problem even if the circuit-side reference potential 240 is raised to 0.1 V or the like. In that case, the difference between the voltage value of the voltage generated by the power supply 400 and the voltage value of the circuit-side reference potential 240 is expressed as Vcc in the equations (1) to (13).
If this is the case, the equations of (Equation 1) to (Equation 13) can be used as they are.

[Correspondence with Claims]
The correspondence between the terms used in the description of the above embodiment and the terms used in the description of the claims is shown.

  The oxygen sensor 100 corresponds to a gas sensor, and the powder layer 141 corresponds to a seal layer.

  DESCRIPTION OF SYMBOLS 1 ... Gas concentration detection apparatus, 100 ... Oxygen sensor, 110 ... Detection element, 111 ... Detection part, 112 ... Outer electrode, 113 ... Inner electrode, 120 ... Ceramic heater, 121 ... Heat-generating part, 130 ... Casing, 131 ... Metal fitting 132 ... Inner cylinder member, 133 ... Outer cylinder member, 134 ... Reference gas space, 140 ... Insulator, 141 ... Powder layer, 142 ... Insulator, 150 ... Lead wire for outer electrode, 151 ... Lead wire for inner electrode, 152 ... Heater lead wire, 153... Sealing member, 154... Separator, 155... Element outer surface fixing bracket, 156... Element inner surface fixing bracket, 200 ... Circuit for gas sensor, 210 ... First terminal, 220. , 240 ... circuit side reference potential, 250 ... voltage dividing circuit, 251 ... power supply side resistance, 252 ... reference potential side resistance, 260 ... differential Width circuit, 300 ... powder layer resistance, 400 ... power supply, 500 ... sensor reference potential.

Claims (2)

A detection element for detecting the concentration of the gas to be measured, which is formed in a bottomed cylindrical shape with a closed tip and provided with an inner electrode and an outer electrode on the inner side and the outer side, respectively;
A metal shell that holds the detection element from the outside and is connected to a sensor-side reference potential;
A sealing layer that fills a gap between the detection element and the metal shell and electrically insulates the detection element and the metal shell;
A gas sensor comprising:
A gas sensor circuit connected to the inner electrode and the outer electrode, to which a signal corresponding to the concentration of the gas to be measured is input from the gas sensor;
A gas concentration detection device comprising:
The gas sensor circuit divides a voltage generated by the power source by a power source side resistor connected to the power source directly or through another resistor and a reference potential side resistor connected to the circuit side reference potential. A voltage dividing circuit that generates an offset voltage and inputs the offset voltage to the outer electrode of the gas sensor;
The resistance value Ra of the power supply side resistance and the resistance value Rb of the reference potential side resistance are set according to the equations (1) and (2), respectively.
A gas concentration detection device characterized by the above.


Vcc is the difference between the voltage value of the voltage generated by the power supply and the voltage value of the circuit-side reference potential, and Va is electrically insulated from the detection element and the metal shell. In this case, the value of t is 0.7 or more and less than 1. The gas concentration detection apparatus according to claim 1,
Furthermore, the resistance value Ra of the power source side resistor and the resistance value Rb of the reference potential side resistor are set according to the equations (3) and (4), respectively.
A gas concentration detection device characterized by the above.