阅读说明：本技术 气体传感器及气体传感器的控制方法 (Gas sensor and method for controlling gas sensor ) 是由 关谷高幸 渡边悠介 于 2020-03-27 设计创作，主要内容包括：一种气体传感器(10)及气体传感器的控制方法,气体传感器(10)具备：加热器部(110),其承担对传感器元件(12)进行加热并保温的温度调整作用；泵驱动控制部(200),其至少控制针对被测定气体流通部(50)的泵驱动；测定用泵单元(90),其基于基准电极(60)与测定电极(92)之间产生的电动势而对被测定气体中的特定气体浓度进行检测；加热器控制部(202),其对加热器部(110)进行控制；以及泵停止部(204A),其在利用加热器控制部(202)对加热器部(110)的通电停止之后使得基于泵驱动控制部(200)的泵驱动停止。(A gas sensor (10) and a method for controlling the gas sensor, the gas sensor (10) comprising: a heater unit (110) that performs a temperature adjustment function for heating and maintaining the temperature of the sensor element (12); a pump drive control unit (200) that controls at least the pump drive for the gas flow unit (50) to be measured; a measurement pump unit (90) that detects the concentration of a specific gas in a measurement gas on the basis of an electromotive force generated between a reference electrode (60) and a measurement electrode (92); a heater control unit (202) that controls the heater unit (110); and a pump stop unit (204A) that stops the pump drive by the pump drive control unit (200) after the heater unit (110) is stopped by the heater control unit (202).)

1. A gas sensor (10) characterized in that,

the gas sensor (10) is provided with a sensor element (12), a heater unit (110), a pump drive control means (200), a detection means (90), a heater control means (202), and a pump stop means (204A),

the sensor element (12) has:

a laminate (25) in which a plurality of oxygen ion conductive solid electrolyte layers are laminated to form a laminate (25), and in which a measurement gas flow section (50) through which a measurement gas is introduced and flows and a reference gas introduction space (52) through which a reference gas that is a reference for detecting the concentration of a specific gas in the measurement gas is introduced are provided inside the laminate (25);

a reference electrode (60), wherein the reference electrode (60) is formed inside the laminated body, and the reference gas is introduced into the reference electrode (60) through the reference gas introduction space;

a measurement electrode (92) and an inner pump electrode (64), wherein the measurement electrode (92) and the inner pump electrode (64) are arranged on the inner circumferential surface of the gas flow part to be measured; and

a gas-to-be-measured electrode disposed in a portion of the laminate exposed to the gas to be measured,

the heater part (110) performs a temperature adjustment function of heating and keeping the temperature of the sensor element,

the pump drive control means (200) controls at least the pump drive to the gas flow portion to be measured,

the detection means (90) detects the concentration of a specific gas in the gas to be measured based on the electromotive force generated between the reference electrode and the measurement electrode,

the heater control mechanism (202) controls the heater section,

the pump stop mechanism (204A) stops the pump driving by the pump driving control mechanism after the energization of the heater portion by the heater control mechanism is stopped.

2. The gas sensor according to claim 1,

the gas sensor further comprises a timer mechanism (206), the timer mechanism (206) performs timing based on the stop of the energization of the heater unit (110),

the pump stopping means (204B) stops the pump driving when a predetermined time (Ta) has elapsed after the time counting means (206) counts the time.

3. The gas sensor according to claim 1,

the gas sensor further comprises a temperature measurement means (208), wherein the temperature measurement means (208) measures the temperature of the laminate (25),

the pump stop mechanism (204C) stops the driving of the pump when the temperature of the stacked body (25) reaches a preset low temperature.

4. The gas sensor according to claim 1,

the gas sensor further comprises a temperature measuring means (208), wherein the temperature measuring means (208) measures the temperature of a specific portion of the laminate (25),

the difference between the temperature of the specific portion when the heater section (110) is energized by the heater control means (202) and the temperature of the specific portion when the pump drive is stopped by the pump stop means (204D) is 200 ℃ or more.

5. The gas sensor according to claim 4,

the specific portion of the laminated body (25) is the heater section (110).

6. The gas sensor according to claim 5,

the temperature measuring means (208) measures the temperature of the specific portion based on the resistance value of the heater (114) constituting the heater section (110).

7. The gas sensor according to any one of claims 1 to 6,

the delay time from the stop time of the heater unit (110) to the drive stop time of each pump unit is 10 seconds or more.

8. The gas sensor according to any one of claims 1 to 7,

the temperature difference between the time of stopping the driving and the time of driving is 200 ℃ or more.

9. A method for controlling a gas sensor having a sensor element (12) and a heater unit (110), the heater unit (110) having a temperature adjustment function of heating and keeping the temperature of the sensor element (12),

the sensor element (12) has:

a laminate (25) in which a plurality of oxygen ion conductive solid electrolyte layers are laminated to form a laminate (25), and in which a measurement gas flow section (50) through which a measurement gas is introduced and flows and a reference gas introduction space (52) through which a reference gas that is a reference for detecting the concentration of a specific gas in the measurement gas is introduced are provided inside the laminate (25);

a reference electrode (60), wherein the reference electrode (60) is formed inside the laminated body (25), and the reference gas is introduced into the reference electrode (60) through the reference gas introduction space (52);

a measurement electrode (92) and an inner pump electrode (64), wherein the measurement electrode (92) and the inner pump electrode (64) are arranged on the inner circumferential surface of the gas flow section (50) to be measured; and

a gas-to-be-measured electrode disposed at a portion of the laminate (25) exposed to the gas to be measured,

the control method of the gas sensor is characterized by comprising the following steps:

controlling at least pump driving of the gas flow unit (50) to be measured;

detecting a specific gas concentration in the measurement gas based on an electromotive force generated between the reference electrode (60) and the measurement electrode (92); and

and stopping the pump driving after the energization of the heater section (110) is stopped.

10. The control method of a gas sensor according to claim 9,

further comprising: a step of performing timing based on the stop of energization of the heater section (110),

and stopping the pump drive at a stage when a predetermined time (Ta) has elapsed after the stop of the energization of the heater unit (110).

11. The control method of a gas sensor according to claim 9,

further comprising: a step of measuring the temperature of the laminate,

and stopping the driving of the pump when the temperature of the stacked body reaches a preset low temperature.

12. The control method of a gas sensor according to claim 9,

further comprising: a step of measuring the temperature of a specific portion of the laminate,

the difference between the temperature of the specific portion when the heater portion is energized and the temperature of the specific portion when the pump is stopped is 200 ℃ or more.

13. The control method of a gas sensor according to claim 12,

the specific portion of the laminated body is the heater section.

14. The control method of a gas sensor according to claim 13,

in the step of measuring the temperature of the specific portion of the stacked body, the temperature of the specific portion is measured based on a resistance value of a heater constituting the heater section.

Technical Field

The present invention relates to a gas sensor and a method for controlling the gas sensor.

Background

The gas sensor described in japanese patent application laid-open No. 2018-077115 solves the problems that: the deterioration of the measurement accuracy of the gas sensor due to the adsorption of a substance to the electrode is suppressed without causing an unusable time.

In order to solve the above problem, a gas sensor described in japanese patent application laid-open No. 2018-077115 includes: a sensor element composed of an oxygen ion conductive solid electrolyte; at least one electrode provided on the sensor element and in contact with the gas to be measured; and a control means for controlling the gas sensor, wherein when the gas sensor is activated, the sensor element is heated by a heater provided in the sensor element for a predetermined time Δ T and at a temperature T2 higher than a predetermined drive temperature T1, and then the temperature of the sensor element is reduced to the drive temperature T1.

Disclosure of Invention

However, platinum and a material in which a trace amount of a substance is added to platinum are used for the electrodes of the sensor element as described above. The sensor element utilizes electrochemical properties, and in order to use these properties, it is necessary to have a high temperature (600 to 900 ℃). Due to the presence of oxygen (O) in the exhaust gas₂) Thus, the gas sensor makes O in the exhaust gas₂And NO separation. The separated NO is decomposed into O by catalytic reaction of another electrode₂And N₂According to the O₂Concentration of (2) determining the NO concentration. When the catalytic electrode is at O₂When exposed, Pt and Rh of the electrode are PtO and PtO₂、Rh₂O₃Etc. which evaporate at lower temperatures than Pt, Rh. Further, when Pt and Rh are oxidized, catalytic reactivity is deteriorated, and further, gas decomposition ability is lowered, and as a result, there is a possibility that sensor sensitivity is causedAnd decreases.

An object of the present invention is to provide a gas sensor and a method for controlling the gas sensor, which can suppress oxidation of a catalytic electrode and can suppress a decrease in sensor sensitivity.

A gas sensor according to one aspect of the present invention includes a sensor element, a heater unit, a pump drive control mechanism, a detection mechanism, a heater control mechanism, and a pump stop mechanism, the sensor element including: a laminate body in which a plurality of oxygen ion conductive solid electrolyte layers are laminated, and which is provided with a measurement gas flow section for introducing and flowing a measurement gas and a reference gas introduction space for introducing a reference gas serving as a detection reference for a specific gas concentration in the measurement gas; a reference electrode formed inside the laminated body, the reference gas being introduced into the reference electrode through the reference gas introduction space; a measurement electrode and an inner pump electrode disposed on an inner peripheral surface of the gas flow portion to be measured; and a gas-to-be-measured side electrode disposed in a portion of the stacked body exposed to the gas to be measured, wherein the heater portion performs a temperature adjustment function of heating and holding the sensor element, the pump drive control means controls at least pump drive to the gas-to-be-measured circulation portion, the detection means detects a specific gas concentration in the gas to be measured based on an electromotive force generated between the reference electrode and the measurement electrode, the heater control means controls the heater portion, and the pump stop means stops the pump drive by the pump drive control means after energization of the heater portion by the heater control means is stopped.

A method for controlling a gas sensor according to an aspect of the present invention includes a sensor element and a heater unit that performs a temperature adjustment function of heating and maintaining the temperature of the sensor element, the sensor element including: a laminate body in which a plurality of oxygen ion conductive solid electrolyte layers are laminated, and which is provided with a measurement gas flow section for introducing and flowing a measurement gas and a reference gas introduction space for introducing a reference gas serving as a detection reference for a specific gas concentration in the measurement gas; a reference electrode formed inside the laminated body, the reference gas being introduced into the reference electrode through the reference gas introduction space; a measurement electrode and an inner pump electrode disposed on an inner peripheral surface of the gas flow portion to be measured; and a gas-to-be-measured side electrode disposed in a portion of the stacked body exposed to the gas to be measured, the gas sensor control method including: controlling at least pump driving of the gas flow unit to be measured; detecting a specific gas concentration in the measurement gas based on an electromotive force generated between the reference electrode and the measurement electrode; and stopping the driving of the pump after the energization of the heater portion is stopped.

According to the present invention, oxidation of the catalytic electrode can be suppressed, and a decrease in sensor sensitivity can be suppressed.

Drawings

Fig. 1 is a sectional view showing a gas sensor according to the present embodiment.

Fig. 2 is a block diagram showing the structure of the first gas sensor.

Fig. 3 is a block diagram showing the structure of the gas sensor according to the comparative example.

Fig. 4A to 4C are timing charts showing control operations of the gas sensor according to the comparative example.

Fig. 5A to 5C are timing charts showing an example of the control operation of the first gas sensor according to the present embodiment.

Fig. 6 is a block diagram showing the structure of the second gas sensor.

Fig. 7 is a block diagram showing the structure of the third gas sensor.

Fig. 8 is a block diagram showing the structure of the fourth gas sensor.

Fig. 9 is table 1 showing the pump stop delay time, light-off time, and temperature difference during sensor driving in examples 1 to 5 and comparative example.

Fig. 10 is a graph showing the change in the light-off time with respect to the pump-off delay time.

Fig. 11 is a graph showing a change in the light-off time with respect to the temperature difference when the sensor is driven.

Fig. 12 is a graph showing changes in the surface temperature of the gas sensor with respect to the elapsed time (pump stop delay time) after the heater is stopped.

Fig. 13 is a block diagram showing an example of a power supply system of the sensor controller.

Detailed Description

A gas sensor and a method for controlling a gas sensor according to the present invention will be described in detail below with reference to the accompanying drawings by referring to preferred embodiments.

As shown in fig. 1, the gas sensor 10 according to the present embodiment includes a sensor element 12. The sensor element 12 has an elongated rectangular parallelepiped shape, and the longitudinal direction (the left-right direction in fig. 1) of the sensor element 12 is the front-rear direction, and the thickness direction (the up-down direction in fig. 1) of the sensor element 12 is the up-down direction. The width direction of the sensor element 12 (the direction perpendicular to the front-rear direction and the up-down direction) is the left-right direction.

As shown in fig. 1, the sensor element 12 is an element having a laminate 25 in which six layers each made of zirconium oxide (ZrO) are laminated in this order from the lower side in the drawing₂) A first substrate layer 14, a second substrate layer 16, a third substrate layer 18, a first solid electrolyte layer 20, a separation layer 22, and a second solid electrolyte layer 24, which are made of a plasma-conductive solid electrolyte. In addition, the solid electrolyte forming these six layers is a dense and airtight solid electrolyte. The sensor element 12 is manufactured, for example, in the following manner: the ceramic green sheets corresponding to the respective layers are subjected to predetermined processing, printing of circuit patterns, and the like, and then stacked, and further fired to be integrated.

At one end (left side in fig. 1) of the sensor element 12, between the lower surface of the second solid electrolyte layer 24 and the upper surface of the first solid electrolyte layer 20, the gas introduction port 30, the first diffusion rate control portion 32, the buffer space 34, the second diffusion rate control portion 36, the first internal cavity 38, the third diffusion rate control portion 40, the second internal cavity 42, the fourth diffusion rate control portion 44, and the third internal cavity 46 are formed adjacently so as to communicate in order.

The gas introduction port 30, the buffer space 34, the first internal cavity 38, the second internal cavity 42, and the third internal cavity 46 are spaces inside the sensor element 12 provided in a form in which the separator 22 is hollowed out, an upper portion of the space being defined by a lower surface section of the second solid electrolyte layer 24, a lower portion of the space being defined by an upper surface section of the first solid electrolyte layer 20, and side portions of the space being defined by side surface sections of the separator 22.

The first diffusion rate controlling section 32, the second diffusion rate controlling section 36, and the third diffusion rate controlling section 40 are each provided with 2 horizontally long (the longitudinal direction of the opening is the direction perpendicular to the drawing) slits. In addition, the fourth diffusion rate control section 44 is provided to: 1 slit which is formed transversely long (the longitudinal direction of the opening is the direction perpendicular to the drawing) as a gap with the lower surface of the second solid electrolyte layer 24. A region from the gas inlet 30 to the third internal cavity 46 is also referred to as a measurement gas flowing portion 50.

Further, a reference gas introduction space 52 is provided between the upper surface of the third substrate layer 18 and the lower surface of the separator 22 at a position farther from one end side than the gas flow portion 50 to be measured, and at a position where the side portion is defined by the side surface section of the first solid electrolyte layer 20. For example, the atmosphere is introduced into the reference gas introduction space 52 as a reference gas for measuring the NOx concentration.

The atmosphere introduction layer 54 is made of ceramic such as porous alumina and is exposed to the reference gas introduction space 52. The reference gas is introduced into the atmosphere introduction layer 54 through the reference gas introduction space 52. The atmosphere introduction layer 54 is formed to cover the reference electrode 60. The atmosphere introduction layer 54 applies a predetermined diffusion resistance to the reference gas in the reference gas introduction space 52, and introduces the reference gas to the reference electrode 60. The atmosphere introduction layer 54 is formed by: the reference gas introduction space 52 is exposed only at a position closer to the rear end side (right side in fig. 1) of the sensor element 12 than the reference electrode 60. In other words, the reference gas introduction space 52 is not formed right above the reference electrode 60. However, the reference electrode 60 may be formed directly below the reference gas introduction space 52 in fig. 1.

The reference electrode 60 is an electrode formed so as to be sandwiched between the upper surface of the third substrate layer 18 and the first solid electrolyte layer 20, and as described above, an atmosphere introduction layer 54 communicating with the reference gas introduction space 52 is provided around the reference electrode. The reference electrode 60 is formed directly on the upper surface of the third substrate layer 18, and is covered with the atmosphere introduction layer 54 except for a portion in contact with the upper surface of the third substrate layer 18. As will be described later, the oxygen concentration (oxygen partial pressure) in the first internal cavity 38, the second internal cavity 42, and the third internal cavity 46 can be measured by the reference electrode 60. The reference electrode 60 is formed as a porous cermet electrode (e.g., Pt and ZrO)₂The cermet electrode of (a).

The gas introduction port 30 of the gas flow portion 50 is a site that is open to the outside space, and the gas to be measured enters the sensor element 12 from the outside space through the gas introduction port 30. The first diffusion rate controller 32 is a part that applies a predetermined diffusion resistance to the gas to be measured entering from the gas inlet 30. The buffer space 34 is a space provided for guiding the gas to be measured introduced from the first diffusion rate control unit 32 to the second diffusion rate control unit 36. The second diffusion rate controller 36 is a portion that applies a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 34 into the first internal cavity 38. When the gas to be measured is introduced into the first internal cavity 38 from outside the sensor element 12, the gas to be measured that has suddenly entered the sensor element 12 from the gas introduction port 30 due to a pressure variation of the gas to be measured in the external space (pulsation of the exhaust pressure in the case where the gas to be measured is an exhaust gas of an automobile) is not directly introduced into the first internal cavity 38, but is introduced into the first internal cavity 38 after the concentration variation of the gas to be measured is eliminated by the first diffusion rate control unit 32, the buffer space 34, and the second diffusion rate control unit 36. Thus, the concentration of the gas to be measured introduced into the first internal cavity 38 varies to a negligible extent. The first internal cavity 38 is configured to: a space for adjusting the oxygen partial pressure in the gas to be measured introduced by the second diffusion rate control unit 36. The main pump unit 62 described later is operated to adjust the oxygen partial pressure.

The main pump cell 62 is an electrochemical pump cell including an inner pump electrode 64, an outer pump electrode 66, and the second solid electrolyte layer 24 sandwiched between these electrodes, wherein the inner pump electrode 64 is provided on the inner surface of the first internal cavity 38, and the outer pump electrode 66 is provided so as to be exposed to the external space in a region corresponding to the inner pump electrode 64 on the upper surface of the second solid electrolyte layer 24.

The inner pump electrode 64 is formed such that: solid electrolyte layers (first solid electrolyte layer 20 and second solid electrolyte layer 24) above and below the first internal cavity 38 and a spacer layer 22 constituting a sidewall are formed so as to partition the solid electrolyte layers. Specifically, the top electrode portion 64a of the inner pump electrode 64 is formed on the lower surface of the second solid electrolyte layer 24 constituting the top surface of the first internal cavity 38, the bottom electrode portion 64b is formed directly on the upper surface of the first solid electrolyte layer 20 constituting the bottom surface, and the side electrode portions (not shown) are formed on the side wall surfaces (inner surfaces) of the separator 22 constituting the two side walls of the first internal cavity 38, whereby the top electrode portion 64a and the bottom electrode portion 64b are connected to each other and arranged in a tunnel shape at the arrangement positions of the side electrode portions.

The inner pump electrode 64 and the outer pump electrode 66 are formed as porous cermet electrodes (e.g., Pt and ZrO containing 1% Au)₂The cermet electrode of (a). The inner pump electrode 64 that is in contact with the measurement target gas is formed using a material that reduces the reducing ability for the NOx component in the measurement target gas.

In the main pump unit 62, by applying a required pump voltage Vp0 between the inner pump electrode 64 and the outer pump electrode 66 and causing a pump current Ip0 to flow between the inner pump electrode 64 and the outer pump electrode 66 in the positive or negative direction, oxygen in the first internal cavity 38 can be sucked into the external space or oxygen in the external space can be sucked into the first internal cavity 38.

In order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 38, the electrochemical sensor unit, i.e., the main pump control oxygen partial pressure detection sensor unit 70 (referred to as the main pump control sensor unit 70) is configured to include the inner pump electrode 64, the second solid electrolyte layer 24, the separator 22, the first solid electrolyte layer 20, and the reference electrode 60.

The oxygen concentration (oxygen partial pressure) in the first internal cavity 38 is known by measuring the electromotive force V0 of the sensor unit 70 for main pump control. Further, the pump current Ip0 is controlled by feedback-controlling the pump voltage Vp0 of the variable power supply 72 so that the electromotive force V0 is constant. This can maintain the oxygen concentration in the first internal cavity 38 at a predetermined constant value.

The third diffusion rate controller 40 is configured to: the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 62 in the first internal cavity 38, is guided to the second internal cavity 42 by applying a predetermined diffusion resistance to the gas to be measured.

The second internal cavity 42 is provided as a space for performing the following processes: the oxygen partial pressure of the gas to be measured introduced by the third diffusion rate control unit 40 after the oxygen concentration (oxygen partial pressure) has been adjusted in the first internal cavity 38 in advance is further adjusted by the auxiliary pump unit 74. This makes it possible to accurately maintain the oxygen concentration in the second internal cavity 42 constant, and therefore, the gas sensor 10 can measure the NOx concentration with high accuracy.

The auxiliary pump cell 74 is an auxiliary electrochemical pump cell including an auxiliary pump electrode 76, an outer pump electrode 66 (not limited to the outer pump electrode 66, and any appropriate electrode on the outer side of the sensor element 12), and the second solid electrolyte layer 24, wherein the auxiliary pump electrode 76 is provided on the inner surface of the second internal cavity 42.

The auxiliary pump electrode 76 is disposed within the second internal cavity 42 such that: the tunnel-shaped configuration is the same as the inner pump electrode 64 disposed within the first internal cavity 38 described above. That is, a top electrode portion 80a is formed on the second solid electrolyte layer 24 constituting the top surface of the second internal cavity 42, a bottom electrode portion 80b is formed directly on the upper surface of the first solid electrolyte layer 20 constituting the bottom surface of the second internal cavity 42, and side electrode portions (not shown) connecting the top electrode portion 80a and the bottom electrode portion 80b are formed on the two wall surfaces of the separator 22 constituting the side walls of the second internal cavity 42, respectively, thereby forming a tunnel-like structure. Similarly to the inner pump electrode 64, the auxiliary pump electrode 76 is also formed using a material that reduces the reducing ability for the NOx component in the measurement gas.

The auxiliary pump unit 74 can suck oxygen in the atmosphere in the second internal cavity 42 to the external space or can suck oxygen from the external space into the second internal cavity 42 by applying a required voltage Vp1 between the auxiliary pump electrode 76 and the outer pump electrode 66.

In order to control the oxygen partial pressure in the atmosphere in the second internal cavity 42, an auxiliary pump control oxygen partial pressure detection sensor unit 82 (referred to as an auxiliary pump control sensor unit 82), which is an electrochemical sensor unit, is configured to include the auxiliary pump electrode 76, the reference electrode 60, the second solid electrolyte layer 24, the separator 22, and the first solid electrolyte layer 20.

The auxiliary pump unit 74 pumps by the variable power supply 84, and controls the voltage of the variable power supply 84 based on the electromotive force V1 detected by the auxiliary pump control sensor unit 82. Thereby, the oxygen partial pressure in the atmosphere inside the second internal cavity 42 is controlled to be: a lower partial pressure that has substantially no effect on the determination of NOx.

At the same time, the pump current Ip1 is used to control the electromotive force of the main pump control sensor unit 70. Specifically, the pump current Ip1 is input as a control signal to the main pump control sensor unit 70, and the electromotive force V0 thereof is controlled, whereby the gradient of the oxygen partial pressure in the gas to be measured introduced from the third diffusion rate control portion 40 into the second internal cavity 42 is controlled to be constant at all times. When used as a NOx sensor, the oxygen concentration in the second internal cavity 42 is maintained at a constant value of about 0.001ppm by the action of the main pump unit 62 and the auxiliary pump unit 74.

The fourth diffusion rate controller 44 is configured to: a predetermined diffusion resistance is applied to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump unit 74 in the second internal cavity 42, and the gas to be measured is guided to the third internal cavity 46. The fourth diffusion rate control portion 44 plays a role of limiting the amount of NOx flowing into the third internal cavity 46.

The third internal cavity 46 is provided as a space for performing the following processes: the concentration of nitrogen oxide (NOx) in the gas to be measured is measured with respect to the gas to be measured introduced through the fourth diffusion rate control unit 44 after the oxygen concentration (oxygen partial pressure) has been adjusted in the second internal cavity 42 in advance. The NOx concentration is measured mainly in the third internal cavity 46 by the operation of the measurement pump unit 90.

The measurement pump unit 90 measures the NOx concentration in the gas to be measured in the third internal cavity 46. The measurement pump cell 90 is an electrochemical pump cell including a measurement electrode 92, the outer pump electrode 66, the second solid electrolyte layer 24, the separator 22, and the first solid electrolyte layer 20, wherein the measurement electrode 92 is directly provided on the upper surface of the first solid electrolyte layer 20 at a position facing the third internal cavity 46. The measurement electrode 92 is a porous cermet electrode. The measurement electrode 92 also functions as an NOx reduction catalyst that reduces NOx present in the atmosphere in the third internal cavity 46.

The measurement pump unit 90 can detect the amount of oxygen generated by decomposition of nitrogen oxides in the atmosphere around the measurement electrode 92 by sucking the oxygen out as the pump current Ip 2.

In order to detect the partial pressure of oxygen around the measurement electrode 92, the electrochemical sensor unit, i.e., the sensor unit 83 for pump control for measurement is configured to include the first solid electrolyte layer 20, the measurement electrode 92, and the reference electrode 60. The variable power supply 94 is controlled based on the electromotive force V2 detected by the measurement pump control sensor unit 83.

The gas to be measured introduced into the second internal cavity 42 passes through the fourth diffusion rate controller 44 under the condition that the oxygen partial pressure is controlled, and reaches the measurement electrode 92 in the third internal cavity 46. Nitrogen oxide in the measurement gas around the measurement electrode 92 is reduced (2NO → N)₂+O₂) Thereby generating oxygen. The generated oxygen is pumped by the measurement pump unit 90, and at this time, the voltage Vp2 of the variable power supply 94 is controlled so that the electromotive force V2 detected by the measurement pump control sensor unit 83 is constant. Since the amount of oxygen generated around the measurement electrode 92 is proportional to the concentration of nitrogen oxide in the measurement gas, the concentration of nitrogen oxide in the measurement gas is calculated by the pump current Ip2 in the measurement pump cell 90.

The electrochemical sensor cell 96 includes the second solid electrolyte layer 24, the separator 22, the first solid electrolyte layer 20, the third substrate layer 18, the outer pump electrode 66, and the reference electrode 60, and is configured to be able to detect the partial pressure of oxygen in the gas to be measured outside the sensor by using the electromotive force Vref obtained by the sensor cell 96.

The electrochemical reference gas control pump cell 100 includes the second solid electrolyte layer 24, the separator 22, the first solid electrolyte layer 20, the third substrate layer 18, the outer pump electrode 66, and the reference electrode 60. The reference gas adjustment pump cell 100 performs pumping by flowing a control current Ip3 by a voltage Vp3 applied by a variable power supply 102 connected between the outer pump electrode 66 and the reference electrode 60. Thus, the reference gas adjustment pump unit 100 sucks oxygen from the space around the outer pump electrode 66 into the space around the reference electrode 60 (the atmosphere introduction layer 54). The voltage Vp3 of the variable power supply 102 is predefined as: so that the control current Ip3 becomes a dc voltage of a prescribed value (a constant value of dc current).

In addition, the reference gas adjusting pump unit 100 is previously definedThe area of the reference electrode 60, the control current Ip3, the voltage Vp3 of the variable power supply 102, and the like, so that the average current density of the reference electrode 60 when the control current Ip3 flows exceeds 0 μ a/mm²And less than 400 muA/mm². Here, the average current density means: the current density obtained by dividing the average value of the control current Ip3 by the area S of the reference electrode 60. The area S of the reference electrode 60 is the area of the portion of the reference electrode 60 facing the atmosphere introduction layer 54, and in the present embodiment, is the area of the upper surface of the reference electrode 60 (the longitudinal length × the lateral width). Since the vertical thickness of the reference electrode 60 is very small compared to the longitudinal length and the lateral width of the reference electrode 60, the area of the side surface (the longitudinal, lateral, and left-right surfaces) of the reference electrode 60 can be ignored. The average value of the control current Ip3 is set to: the time-averaged value is obtained for a predetermined period of time long enough to ignore instantaneous changes in the control current Ip 3. The average current density is preferably set to 200. mu.A/mm²Hereinafter, it is more preferable to set the concentration to 170. mu.A/mm²It is more preferable to set the thickness to 160. mu.A/mm²The following. The area S of the reference electrode 60 is preferably set to 5mm²The following. Although not particularly limited, the reference electrode 60 has a length in the front-rear direction of, for example, 0.2 to 2mm and a width in the left-right direction of, for example, 0.2 to 2.5 mm. The average value of the control current Ip3 is, for example, 1 to 100 μ A. The average value of the control current Ip3 is preferably more than 1 μ a, more preferably 4 μ a or more, further preferably 5 μ a or more, and further preferably 8 μ a or more.

In the gas sensor 10 having such a configuration, the main pump means 62 and the auxiliary pump means 74 are operated to supply the measurement target gas, whose oxygen partial pressure is always kept constant at a low value (a value that does not substantially affect the measurement of NOx), to the measurement pump means 90. Therefore, oxygen generated by the reduction of NOx is sucked out by the measurement pump cell 90 in a substantially direct proportion to the NOx concentration in the measurement target gas, and the NOx concentration in the measurement target gas can be known based on the pump current Ip2 flowing therethrough.

The sensor element 12 further includes a heater unit 110 that performs a temperature adjustment function of heating and holding the sensor element 12, so as to improve oxygen ion conductivity of the solid electrolyte. The heater section 110 includes a heater connector electrode 112, a heater 114, a through hole 116, a heater insulating layer 118, a pressure release hole 120, and a lead wire 122.

The heater connector electrode 112 is an electrode formed so as to be in contact with the lower surface of the first substrate layer 14. By connecting the heater connector electrode 112 to an external power supply, power can be supplied from the outside to the heater portion 110.

The heater 114 is a resistor body formed so as to be sandwiched between the second substrate layer 16 and the third substrate layer 18 from the upper and lower sides. The heater 114 is connected to the heater connector electrode 112 via the lead wire 122 and the through hole 116, and generates heat by supplying power from the outside through the heater connector electrode 112, thereby heating and insulating the solid electrolyte forming the sensor element 12.

The heater 114 is buried in the entire region from the buffer space 34 to the third internal cavity 46, and the entire sensor element 12 can be adjusted to a temperature at which the solid electrolyte is activated.

The heater insulating layer 118 is an insulating layer containing porous alumina formed on the upper and lower surfaces of the heater 114 from an insulator such as alumina. The heater insulating layer 118 is formed for the purpose of: electrical insulation between the second substrate layer 16 and the heater 114 and electrical insulation between the third substrate layer 18 and the heater 114 are achieved.

The pressure release hole 120 is a portion provided so as to penetrate the third substrate layer 18 and communicate with the reference gas introduction space 52, and the purpose of forming the pressure release hole 120 is to: the increase in internal pressure accompanying the increase in temperature in the heater insulating layer 118 is alleviated.

Actually, the variable power sources 72, 84, 94, 102 and the like shown in fig. 1 are connected to the respective electrodes via unillustrated lead wires, connectors, and lead wires formed in the sensor element 12.

Next, an example of a method for manufacturing the gas sensor 10 will be described below. First, 6 unfired ceramic green sheets containing an oxygen ion conductive solid electrolyte such as zirconia as a ceramic component were prepared. A plurality of sheet holes, required through holes, and the like for positioning at the time of printing or stacking are formed in advance in the green sheet. In addition, a space constituting the gas flow portion 50 to be measured is provided in advance in the green sheet constituting the separator 22 by punching or the like. Then, pattern printing processing and drying processing for forming various patterns on the respective ceramic green sheets are performed in correspondence with the first substrate layer 14, the second substrate layer 16, the third substrate layer 18, the first solid electrolyte layer 20, the separator 22, and the second solid electrolyte layer 24, respectively. Specifically, the pattern to be formed is, for example, the pattern of each electrode described above, the lead wire 122 connected to each electrode, the atmosphere introduction layer 54, the heater section 110, and the like. Pattern printing was performed as follows: a paste for pattern formation prepared in accordance with the characteristics required for each object to be formed is applied to the green sheet by a known screen printing technique. For the drying treatment, a known drying method is also used. After the pattern printing and drying are completed, printing and drying treatment of a paste for bonding for laminating and bonding the green sheets corresponding to the respective layers is performed. Then, the green sheets formed with the adhesive paste are positioned by sheet holes, stacked in a predetermined order, and subjected to pressure bonding under predetermined temperature and pressure conditions to produce a single stacked body 25. The laminate 25 thus obtained includes a plurality of sensor elements 12. The laminated body 25 is cut and cut into the size of the sensor element 12. Then, the cut laminate 25 is fired at a predetermined firing temperature to obtain the sensor element 12.

Here, a plurality of examples of the gas sensor 10 according to the present embodiment will be described with reference to fig. 2 to 8.

First, as shown in fig. 2, the gas sensor according to the first embodiment (hereinafter referred to as a first gas sensor 10A) includes the sensor element 12, the pump drive control unit 200, the heater control unit 202, and the first pump stop unit 204A.

The pump drive control unit 200 controls at least the pump drive (the suction of oxygen from the gas to be measured flow unit 50) for the gas to be measured flow unit 50 (see fig. 1). The heater control section 202 controls energization/stoppage to the heater section 110. The first pump stopping portion 204A stops the pump driving by the pump driving control portion 200 after the energization of the heater portion 110 by the heater control portion 202 is stopped.

The pump drive control unit 200, the heater control unit 202, and the first pump stop unit 204A are each configured by 1 or more electronic circuits including, for example, 1 or more CPUs (central processing units), a storage device, and the like. The electronic circuit is also a software functional section that realizes a predetermined function by the CPU executing a program stored in the storage device, for example. Of course, the integrated circuit may be an integrated circuit such as an FPGA (Field-Programmable Gate Array) in which a plurality of electronic circuits are connected according to functions. The same applies to the following.

On the other hand, as shown in fig. 3, the gas sensor 1000 according to the comparative example includes the sensor element 12, the pump drive control unit 200, and the heater control unit 202.

The pump drive control unit 200 controls at least the pump drive to the gas flow unit to be measured 50 (the suction of oxygen from the gas flow unit to be measured 50). The heater control section 202 controls energization/stoppage to the heater section 110.

Here, a control method of the first gas sensor 10A will be described in comparison with the control method of the comparative example.

First, as shown in fig. 3 and 4A to 4C, the control method of the comparative example is as follows: the ON signal is input to the pump drive control unit 200 and the heater control unit 202 to drive the various pump units, and the heater unit 110 is also energized. Then, as shown in fig. 4B, the temperature of the sensor element 12 (hereinafter referred to as the sensor temperature) is substantially maintained at the first temperature Tha (for example, 800 ℃) which is a high temperature.

Then, as shown in fig. 4C, at the energization stop time ta, an OFF signal is input to the pump drive control unit 200 and the heater control unit 202 to stop driving of the various pump units and also stop energization of the heater unit 110. At this time, as shown in fig. 4B, the sensor temperature gradually decreases after the energization of the heater portion 110 is stopped, but the sensor temperature is maintained at a high temperature equal to or higher than a predetermined temperature Thb (e.g., 500 ℃) for a certain period Ta. Immediately after the energization of the heater portion 110 is stopped, the temperature does not drop immediately, and the high temperature state temporarily continues. When the exhaust gas enters the gas flow portion 50 to be measured, which is not driven by the pump, in a high temperature state, the catalytic electrodes (the reference electrode 60, the inner pump electrode 64, the auxiliary pump electrode 76, the measurement electrode 92, and the like) are oxidized by oxygen contained therein. That is, oxidation of the catalyst electrode occurs during the above-described fixed period Ta. Further, the influence of the electrode oxidation described above causes not only a decrease in sensitivity of the gas sensor 1000 but also a delay in time (light-off time) until the gas sensor 1000 is stabilized after being driven.

On the other hand, as shown in fig. 2 and fig. 5A to 5C, the first pump stopping unit 204A of the first gas sensor 10A delays the input OFF signal, and outputs the OFF signal to the pump drive control unit 200 after the energization of the heater unit 110 by the heater control unit 202 is stopped. That is, the pump drive by the pump drive control unit 200 is stopped at time tb that is later than the energization stop time ta for the heater unit 110.

Accordingly, the pump driving by the pump drive control unit 200 is continued from the energization stop time ta to the time tb with respect to the heater unit 110, whereby oxygen is sucked out from the measurement gas flowing unit 50. As a result, oxidation of the reference electrode 60, the measurement electrode 92, and the like is suppressed, and a decrease in sensitivity of the first gas sensor 10A can be suppressed.

In addition, as described above, since the electrode oxidation is suppressed, the time (light-off time) until the first gas sensor 10A is stabilized after being driven is also advanced. The NOx concentration can be known at a time earlier than the time of engine start because the light-off time is advanced, and the product quality can be improved.

Next, as shown in fig. 6, the gas sensor according to the second embodiment (hereinafter referred to as the second gas sensor 10B) has the same configuration as the first gas sensor 10A described above, but differs in that it includes a second pump stop unit 204B and a timer mechanism 206 to which an OFF signal is input. Note that description of a portion overlapping with the first gas sensor 10A is omitted.

As shown in fig. 5A to 5C, the timer mechanism 206 outputs the OFF signal to the second pump stop unit 204B at a time when a predetermined time Tb has elapsed after the energization stop time ta at which the OFF signal is input. The second pump stop unit 204B outputs an OFF signal to the pump drive control unit 200 based on the input of the OFF signal from the timer mechanism 206. That is, the pump drive by the pump drive control unit 200 is stopped at a time Tb when a predetermined time Tb has elapsed after the time ta at which the energization to the heater unit 110 is stopped.

Further, the predetermined time Tb counted by the timer mechanism 206 is set to a time at which the temperature reaches the temperature of the environment in which the reference electrode 60, the measurement electrode 92, and the like are difficult to oxidize, so that the reference electrode 60, the measurement electrode 92, and the like are exposed to the environment in which oxidation is difficult after the pump driving by the pump driving control unit 200 is stopped, and therefore, the sensitivity of the second gas sensor 10B can be suppressed from being lowered. Further, as described above, the time (light-off time) until the second gas sensor 10B is stabilized after being driven is also advanced.

Next, as shown in fig. 7, the gas sensor according to the third embodiment (hereinafter referred to as a third gas sensor 10C) has the same configuration as the first gas sensor 10A described above, but differs in that it includes a third pump stopping portion 204C and a temperature measuring portion 208 that measures the temperature of the sensor element 12 (sensor temperature). Note that description of a part overlapping with the first gas sensor 10A is omitted.

The temperature measuring unit 208 measures the temperature of the sensor element 12 (sensor temperature Th), and supplies the sensor temperature Th to the third pump stopping unit 204C. The temperature measuring unit 208 measures the temperature of a specific portion of the sensor element 12. The specific portion may be, for example, the lower surface, the side surface, or the like of the stacked body 25, or may be the heater unit 110.

The third pump stop unit 204C compares the input sensor temperature Th with a preset threshold temperature Tth, and outputs an OFF signal to the pump drive control unit 200 when the sensor temperature Th is equal to or lower than the threshold temperature Tth. For example, as shown in fig. 5B and 5C, the third pump stop unit 204C outputs an OFF signal to the pump drive control unit 200 at a time Tb when the sensor temperature Th becomes equal to or less than the threshold temperature Tth, that is, at a time Tb when a predetermined time Tb has elapsed after the time ta when the energization of the heater unit 110 is stopped.

Since the predetermined time Tb is set to a time at which the temperature of the environment in which the reference electrode 60, the measurement electrode 92, and the like are difficult to oxidize is reached, the reference electrode 60, the measurement electrode 92, and the like are exposed to the environment in which the oxidation is difficult after the pump driving by the pump drive control unit 200 is stopped, and therefore, the sensitivity of the third gas sensor 10C can be suppressed from being lowered. Further, as described above, the time (light-off time) until the third gas sensor 10C is stabilized after being driven is also advanced.

Next, as shown in fig. 8, the gas sensor according to the fourth embodiment (hereinafter referred to as a fourth gas sensor 10D) has the same configuration as the third gas sensor 10C described above, but differs in that it includes a fourth pump stopping unit 204D and a temperature difference calculating unit 210. Note that description of a part overlapping with the third gas sensor 10C is omitted.

The temperature difference calculation unit 210 calculates a difference (temperature difference Δ Th) between the first temperature Tha and the current sensor temperature Th from the temperature measurement unit 208, and outputs the difference to the fourth pump stop unit 204D.

The fourth pump stop unit 204D compares the input temperature difference Δ Th with a preset target temperature difference Δ Tth, and outputs an OFF signal to the pump drive control unit 200 when the temperature difference Δ Th is equal to or greater than the target temperature difference Δ Tth. That is, at a time Tb when the temperature difference Δ Th becomes equal to or greater than the target temperature difference Δ Tth after the time ta when the energization of the heater portion 110 is stopped, that is, at a time Tb when the predetermined time Tb has elapsed, the OFF signal is output to the pump drive control portion 200 to stop the pump drive.

As described above, by setting the predetermined time Tb to a time at which the temperature of the environment in which the reference electrode 60, the measurement electrode 92, and the like are difficult to oxidize is reached, the reference electrode 60, the measurement electrode 92, and the like are exposed to the environment in which oxidation is difficult after the pump driving by the pump drive control unit 200 is stopped, and therefore, a decrease in sensitivity of the fourth gas sensor 10D can be suppressed. Further, as described above, the time (light-off time) until the fourth gas sensor 10D is stabilized after being driven is also advanced.

Examples

As shown in fig. 5A to 5C, the gas sensors according to examples 1 to 5 and comparative example were driven in the atmosphere for 10 minutes, and then the driving of the gas sensors was stopped. In this case, the time from the heater stop time ta to the drive stop time Tb of each pump unit when the gas sensor is stopped, that is, the pump stop delay time Tb, differs in examples 1 to 5 and comparative example. The light-off time Tc and the temperature difference between the sensor driving times in examples 1 to 5 and comparative examples were confirmed. The results are shown in table 1 of fig. 9.

In table 1 of fig. 9, "pump stop delay time Tb" is: the delay time from the heater stop time ta to the drive stop time tb of the various pump units. As described above, the "light-off time Tc" is: the time until the gas sensor is stabilized after being driven. The "temperature difference from the sensor driving" is: the difference between the surface temperature of the gas sensor during sensor driving and the surface temperature of the gas sensor after the heater is stopped.

In addition, based on the results of table 1 described above, fig. 10 shows the change in the light-off time Tc with respect to the pump stop delay time Tb, and fig. 11 shows the change in the light-off time Tc with respect to the temperature difference from the sensor driving time. Fig. 12 shows a change in the surface temperature of the gas sensor with respect to the elapsed time (pump stop delay time Tb) after the heater is stopped.

[ examination ]

As can be seen from the results of table 1 and fig. 10 of fig. 9: in examples 1 to 5, the light-off time Tc was shortened as compared with the comparative examples. That is, the pump stop delay time Tb is preferably 10 seconds or longer, more preferably 20 seconds or longer, and further preferably 30 seconds or longer.

From the results of table 1 and fig. 11 of fig. 9, it is understood that: in examples 1 to 5, the light-off time Tc was shortened as compared with the comparative examples. That is, the temperature difference from the sensor at the time of driving is preferably 200 ℃ or more, more preferably 350 ℃ or more, and further preferably 435 ℃ or more.

As can be seen from the results of table 1 and fig. 12 of fig. 9: as the pump stop delay time Tb (elapsed time) extends, the surface temperature of the gas sensor decreases. From the results of fig. 11, it can also be seen that: the temperature difference from the sensor at the time of driving is preferably 200 ℃ or more, more preferably 350 ℃ or more, and further preferably 435 ℃ or more, and thus the elapsed time is preferably 10 seconds or more, more preferably 20 seconds or more, and further preferably 30 seconds or more.

The above embodiments are summarized below.

[1] The present embodiment includes a sensor element 12, a heater unit 110, a pump drive control unit 200, a measurement pump unit 90, a heater control unit 202, and a first pump stop unit 204A, wherein the sensor element 12 includes: a laminate 25 in which a plurality of oxygen ion conductive solid electrolyte layers are laminated, the laminate 25 having a measurement gas flow section 50 for introducing and flowing a measurement gas and a reference gas introduction space 52 for introducing a reference gas as a detection reference for detecting a specific gas concentration in the measurement gas, provided inside the laminate 25; a reference electrode 60 formed inside the laminated body 25, the reference electrode 60 being configured to introduce a reference gas into the reference electrode 60 through a reference gas introduction space 52; a measurement electrode 92 and an inner pump electrode 64, the measurement electrode 92 and the inner pump electrode 64 being disposed on the inner circumferential surface of the measurement gas flow section 50; and a gas-to-be-measured side electrode disposed at a portion exposed to the gas to be measured in the stacked body 25, the heater unit 110 performs a temperature adjustment function of heating and holding the sensor element 12, the pump drive control unit 200 controls at least pump drive to the gas-to-be-measured circulation unit 50 (sucking oxygen from the gas-to-be-measured circulation unit 50), the measurement pump unit 90 detects a specific gas concentration in the gas to be measured based on an electromotive force generated between the reference electrode 60 and the measurement electrode 92, the heater control unit 202 controls the heater unit 110, and the first pump stop unit 204A stops the pump drive by the pump drive control unit 200 after the energization of the heater unit 110 by the heater control unit 202 is stopped.

In a certain period Ta after the heater control unit 202 stops the energization of the heater unit 110, an environment in which the catalytic electrodes such as the reference electrode 60 and the measurement electrode 92 are easily oxidized is formed. Immediately after the energization to the heater portion 110 is stopped, the temperature does not drop immediately, and the high temperature state continues for a while. When the exhaust gas enters the gas flow portion 50 to be measured, which is not driven by the pump, in a high temperature state, the catalytic electrode is oxidized by oxygen therein.

The influence of the oxidation of the electrode causes not only a decrease in sensitivity of the gas sensor but also a delay in time (light-off time) until the gas sensor is stabilized after being driven.

In contrast, in the present embodiment, by continuing the pump driving by the pump drive control unit 200 for at least the fixed period Ta, the oxygen is sucked out from the measurement gas passage 50 during the fixed period Ta, oxidation of the reference electrode 60, the measurement electrode 92, and the like is suppressed, and a decrease in sensitivity of the gas sensor can be suppressed. Further, as described above, since the electrode oxidation is suppressed, the time (light-off time) until the gas sensor is stabilized after being driven is also advanced. The NOx concentration can be known at a time earlier than the time of engine start because the light-off time is advanced, and the product quality can be improved.

[2] In the present embodiment, the pump driving device further includes a timer mechanism 206, the timer mechanism 206 performs a timer based on the stop of energization of the heater unit 110, and the second pump stop unit 204B stops the pump driving when the timer mechanism 206 counts at least a certain period Ta.

When the energization of the heater unit 110 by the heater control unit 202 is stopped, the temperature of the gas flow portion to be measured 50 is lowered. During a fixed period Ta in which the temperature of the gas flow portion 50 to be measured is high, an environment in which the reference electrode 60, the measurement electrode 92, and the like are easily oxidized is formed. By continuing the pump driving by the pump driving control unit 200 at least for the fixed period Ta, the oxidation of the reference electrode 60, the measurement electrode 92, and the like is suppressed during the fixed period Ta.

Further, by setting the predetermined time Tb for which the timer mechanism 206 counts time to the predetermined time Tb at a temperature at which the temperature reaches the environment in which the reference electrode 60, the measurement electrode 92, and the like are less likely to be oxidized, the reference electrode 60, the measurement electrode 92, and the like are exposed to the environment in which oxidation is less likely to occur after the pump driving by the pump drive control unit 200 is stopped, and therefore, a decrease in sensitivity of the gas sensor can be suppressed. Further, as described above, the time (light-off time) until the gas sensor is stabilized after being driven is also advanced.

[3] In the present embodiment, the apparatus further includes a temperature measuring unit 208, the temperature measuring unit 208 measures the temperature of the stacked body 25, and the third pump stopping unit 204C stops the pump driving at a stage when the temperature of the stacked body 25 reaches a preset low temperature.

When the energization of the heater section 110 by the heater control section 202 is stopped, the temperature of the specific portion of the stacked body 25 is lowered. During a certain period Ta in which the temperature of the specific portion is high, an environment in which the reference electrode 60, the measurement electrode 92, and the like are easily oxidized is formed. By continuing the pump driving by the pump drive control unit 200 during the fixed period Ta, the oxidation of the reference electrode 60, the measurement electrode 92, and the like during the fixed period Ta is suppressed.

Since the temperature of the specific portion is set to a preset low temperature, that is, a temperature in an environment in which the reference electrode 60, the measurement electrode 92, and the like are difficult to oxidize, the reference electrode 60, the measurement electrode 92, and the like are exposed to the environment in which oxidation is difficult after the pump driving by the pump driving control unit 200 is stopped, and therefore, a decrease in sensitivity of the gas sensor can be suppressed. Further, as described above, the time (light-off time) until the gas sensor is stabilized after being driven is also advanced.

[4] In the present embodiment, the temperature measuring unit 208 is further provided, and the temperature measuring unit 208 measures the temperature of the specific portion of the laminated body 25, and the difference between the temperature of the specific portion when the heater control unit 202 supplies the electric power to the heater unit 110 and the temperature of the specific portion when the pump driving is stopped by the fourth pump stopping unit 204D is equal to or higher than a predetermined temperature (200 ℃).

In a period in which the temperature difference after the energization of the heater portion 110 by the heater control portion 202 is stopped is less than 200 ℃, an environment in which the reference electrode 60, the measurement electrode 92, and the like are easily oxidized is formed. By continuing the pump driving by the pump drive control unit 200 during this period, the oxidation of the reference electrode 60, the measurement electrode 92, and the like during the above-described fixed period Ta is suppressed. On the other hand, when the temperature difference is 200 ℃ or more, the pump driving is stopped by the fourth pump stopping portion 204D because the reference electrode 60, the measurement electrode 92, and the like are in an environment in which oxidation is difficult.

[5] In the present embodiment, the specific portion of the stacked body 25 is the heater section 110. Measuring the temperature of the heater portion 110 means measuring a portion of the stacked body 25 having the highest temperature. Therefore, the pump drive by the pump drive control unit 200 can be reliably continued while the gas flow unit 50 to be measured is in the high-temperature state with reference to the temperature of the heater unit 110. This can suppress oxidation of the reference electrode 60, the measurement electrode 92, and the like, and can suppress a decrease in sensitivity of the gas sensor. Of course, the light-off time can also be advanced.

[6] In the present embodiment, the temperature measuring unit 208 measures the temperature of a specific portion based on the resistance value of the heater 114 constituting the heater unit 110. When the heater 114 is made of, for example, platinum, the resistance of the heater 114 increases as the temperature of the specific portion increases. Therefore, the temperature of the specific portion can be measured based on the resistance value of the heater 114.

[7] In the present embodiment, the delay time (pump stop delay time) from the stop time of the heater 114 to the drive stop time of each of the pump units is preferably 10 seconds or more, more preferably 20 seconds or more, and further preferably 30 seconds or more.

[8] In the present embodiment, the temperature difference between the time when the gas sensor is stopped and the time when the gas sensor is driven is preferably 200 ℃ or more, more preferably 350 ℃ or more, and still more preferably 500 ℃ or more.

[9] The control method of the gas sensor according to the present embodiment includes a sensor element 12 and a heater unit 110, the heater unit 110 having a temperature adjustment function of heating and holding the sensor element 12, the sensor element 12 including: a laminate 25 in which a plurality of oxygen ion conductive solid electrolyte layers are laminated, the laminate 25 having a measurement gas flow section 50 for introducing and flowing a measurement gas and a reference gas introduction space 52 for introducing a reference gas as a detection reference for a specific gas concentration in the measurement gas, provided inside the laminate 25; a reference electrode 60 formed inside the laminated body 25, the reference electrode 60 being configured to introduce a reference gas into the reference electrode 60 through a reference gas introduction space 52; a measurement electrode 92 and an inner pump electrode 64, the measurement electrode 92 and the inner pump electrode 64 being disposed on the inner circumferential surface of the measurement gas flow section 50; and a gas-to-be-measured side electrode (such as the outer pump electrode 66) disposed at a portion of the stacked body 25 exposed to the gas to be measured, wherein the gas sensor control method includes the steps of: a step of controlling at least pump driving of the gas flow portion to be measured 50 (sucking oxygen from the gas flow portion to be measured 50) (pump driving control); a step (detection means) of detecting the concentration of a specific gas in the gas to be measured based on the electromotive force generated between the reference electrode 60 and the measurement electrode 92; and stopping the pump driving after the energization of the heater portion 110 is stopped.

During a certain period Ta after the energization of the heater portion 110 is stopped, an environment in which the reference electrode 60, the measurement electrode 92, and the like are easily oxidized is formed. Immediately after the energization of the heater portion 110 is stopped, the temperature does not drop immediately, and the high temperature state continues for a while. When the exhaust gas enters the gas flow portion 50 to be measured, which is not driven by the pump, in a high temperature state, the catalytic electrode is oxidized by oxygen therein.

The influence of the oxidation of the electrode causes not only a decrease in sensitivity of the gas sensor but also a delay in time (light-off time) until the gas sensor is stabilized after being driven.

In contrast, in the present embodiment, by continuing the pump driving for at least a certain period Ta after the energization of the heater unit 110 is stopped, oxygen is sucked out from the measurement gas flowing unit 50 at least for the certain period Ta, oxidation of the reference electrode 60, the measurement electrode 92, and the like is suppressed, and a decrease in sensitivity of the gas sensor can be suppressed. Further, as described above, since the electrode oxidation is suppressed, the time (light-off time) until the gas sensor is stabilized after being driven is also advanced. The NOx concentration can be known at a time earlier than the time of engine start because the light-off time is advanced, and the product quality can be improved.

[10] In this embodiment, the present invention further includes: the step of timing based on the stop of the energization of the heater portion 110 stops the pump driving at a stage when at least a certain period Ta elapses after the energization of the heater portion 110 is stopped.

When the energization of the heater 110 is stopped, the temperature of the measured gas flowing portion 50 is lowered. During a certain period Ta in which the temperature of the gas flow portion 50 to be measured is high, the atmosphere is easily oxidized such as the reference electrode 60 and the measurement electrode 92. By continuing the pump driving for the fixed period Ta, oxidation of the reference electrode 60, the measurement electrode 92, and the like is suppressed for the fixed period Ta.

Further, by setting the time period Ta to reach the temperature at which the reference electrode 60, the measurement electrode 92, and the like are formed in the environment that is difficult to oxidize, the reference electrode 60, the measurement electrode 92, and the like are exposed to the environment that is difficult to oxidize after the pump driving is stopped, and therefore, the sensitivity of the gas sensor can be suppressed from being lowered. Further, as described above, the time (light-off time) until the gas sensor is stabilized after being driven is also advanced.

[11] In this embodiment, the present invention further includes: the step of measuring the temperature of the stacked body 25 stops the pump driving when the temperature of the stacked body 25 reaches a preset low temperature.

When the energization of the heater section 110 is stopped, the temperature of a specific portion of the stacked body 25 is lowered. During a certain period Ta in which the temperature of the specific portion is high, an environment in which the reference electrode 60, the measurement electrode 92, and the like are easily oxidized is formed. By continuing the pump driving for the fixed period Ta, oxidation of the reference electrode 60, the measurement electrode, and the like can be suppressed for the fixed period Ta.

Further, since the temperature of the specific portion is set to a preset low temperature, that is, a temperature in an environment in which the reference electrode 60, the measurement electrode 92, and the like are difficult to oxidize, the reference electrode 60, the measurement electrode 92, and the like are exposed to the environment in which oxidation is difficult after the pump driving is stopped, and therefore, a decrease in sensitivity of the gas sensor can be suppressed. Further, as described above, the time (light-off time) until the gas sensor is stabilized after being driven is also advanced.

[12] In this embodiment, the present invention further includes: the step of measuring the temperature of the specific portion of the laminated body 25 is such that the difference between the temperature of the specific portion when the heater 110 is energized and the temperature of the specific portion when the pump drive is stopped is 200 ℃ or more.

In a certain period Ta in which the temperature difference after the stop of energization of the heater portion 110 is less than 200 ℃, an environment in which the reference electrode 60, the measurement electrode 92, and the like are easily oxidized is formed. By continuing the pump driving for the fixed period Ta, oxidation of the reference electrode 60, the measurement electrode 92, and the like can be suppressed for the fixed period Ta. On the other hand, when the temperature difference is 200 ℃ or more, the pump driving is stopped because the reference electrode 60, the measurement electrode 92, and the like are in an environment in which oxidation is difficult.

[13] In the present embodiment, the specific portion of the stacked body 25 is the heater section 110. Measuring the temperature of the heater portion 110 means measuring a portion of the stacked body 25 having the highest temperature. Therefore, the pump driving can be reliably continued while the gas flow portion 50 to be measured is in a high temperature state with reference to the temperature of the heater portion 110. This can suppress oxidation of the reference electrode 60, the measurement electrode 92, and the like, and can suppress a decrease in sensitivity of the gas sensor. Of course, the light-off time can also be advanced.

[14] In the present embodiment, in the step of measuring the temperature of the specific portion of the laminated body 25, the temperature of the specific portion is measured based on the resistance value of the heater 114 constituting the heater portion 110. When the heater 114 is made of, for example, platinum, the resistance of the heater 114 increases as the temperature of the specific portion increases. Therefore, the temperature of the specific portion can be measured based on the resistance value of the heater 114.

The gas sensor and the method for controlling the gas sensor according to the present invention are not limited to the above embodiments, and various configurations may be adopted without departing from the spirit of the present invention.

In the above embodiment, the reference gas is set to be atmospheric gas, but the present invention is not limited to this as long as it is a gas that is a reference for detecting the concentration of a specific gas in a measurement gas. For example, a gas adjusted to a predetermined oxygen concentration (> oxygen concentration of the gas to be measured) may be filled as the reference gas.

In the above embodiment, the sensor element 12 detects the NOx concentration in the measurement target gas, but the present invention is not limited to this, as long as the concentration of the specific gas in the measurement target gas is detected. For example, the oxygen concentration in the gas to be measured can be detected.

In carrying out the present invention, various means for improving reliability as automobile parts may be added within a range not to impair the idea of the present invention.

As shown in fig. 13, the sensor controller 300 to which the pump drive control unit 200 and the like are mounted supplies electric power from an external power supply 302 (a battery of an automobile or the like) to the heater control unit 202 and the like via a power supply unit 304. Therefore, when the power to the sensor controller 300 is forcibly turned off by turning off the power to the vehicle (the driver stops the engine), the heater 114 and the pump of the sensor element 12 may be turned off at the same time.

Therefore, the sensor controller 300 may be provided with a backup power supply 306 for driving the pump, a battery, and the like, in order to continue driving the heater 114, the pump, and the like even after the power failure. Thus, even when the energization is forcibly turned off, the sensor element 12 continues pumping by the power supply from the backup power source 306, the battery, or the like.