JP6455389B2 - Sensor control device - Google Patents

Description

  The present invention relates to a sensor control device applied to a gas sensor for detecting a specific component concentration in a gas to be detected.

  Conventionally, for example, a gas sensor having a solid electrolyte and a pair of electrodes provided with the solid electrolyte sandwiched between them is used as a sensor for detecting the oxygen concentration contained in the exhaust of an in-vehicle engine. This type of gas sensor is configured to flow an element current according to the oxygen concentration of the exhaust gas in a state where one of the pair of electrodes is exposed to the exhaust gas and the other electrode is exposed to the atmosphere. In this case, since the electrode is exposed to exhaust gas or air, there is a concern that the electrode is poisoned by poisoning substances such as silicon and sulfur contained in the exhaust gas or air. For this reason, various techniques for suppressing the poisoning of the electrodes have been proposed.

  For example, in the one described in Patent Document 1, a poisoning prevention layer is formed on the electrode surface, and the poisoning substance is trapped by the poisoning prevention layer, thereby suppressing the poisoning substance from reaching the electrode. The electrode is prevented from being poisoned.

JP 2005-227300 A

  By the way, when forming a poisoning prevention layer on the electrode surface, there is a concern that an advanced manufacturing technique is required. In addition, when a poisoning prevention layer is formed on the atmosphere-side electrode surface, it becomes difficult for oxygen from the atmosphere to reach the atmosphere-side electrode surface when detecting rich gas components, and the oxygen concentration detection accuracy and responsiveness are reduced. There is concern about the decline.

  This invention is made | formed in view of the said situation, The main objective is to provide the sensor control apparatus which can suppress appropriately that the atmosphere side electrode poisons.

  The sensor control device according to the present invention has a sensor element (30) including a solid electrolyte layer (31) and a pair of electrodes (35, 36) provided on both sides of the solid electrolyte layer, and the pair of electrodes. One of them is a gas side electrode (35) exposed to the gas to be detected, and the other is a gas sensor (20) which is an atmosphere side electrode (36) provided in an air duct (37) into which air is introduced from the outside. When it is determined that the atmosphere-side electrode is in a poisoned environment, and an environment determination unit that determines whether the atmosphere-side electrode is in a poisoned environment when the gas sensor output is not used. And a pumping execution unit for pumping oxygen from the gas side electrode to the atmosphere side electrode.

  When the gas sensor output is not used, the gas sensor and its surroundings are in a high-temperature atmosphere, and the atmosphere contains poisonous substances such as silicon, sulfur, phosphorus, ammonia, hydrocarbons, and gas phase metals. Is supplied to the atmosphere side electrode, the atmosphere side electrode may be poisoned. In this case, since an insulator is formed on the atmosphere side electrode by the poisoning substance, there is a concern that the current is inhibited by the insulator and the detection accuracy and responsiveness of the gas sensor are lowered.

  In this regard, according to the above configuration, when it is determined that the atmosphere-side electrode is in a poisoned environment when the gas sensor output is shifted to a non-use state, oxygen is supplied from the gas-side electrode to the atmosphere-side electrode. It was set as the structure which implements pumping. In this case, the atmosphere duct in which the atmosphere side electrode is provided is filled with oxygen, and poisonous substances contained in the atmosphere are suppressed from flowing into the atmosphere duct. Thereby, poisoning of the atmosphere side electrode can be appropriately suppressed. In addition, it is possible to suppress the poisoning of the atmosphere side electrode without providing a poisoning prevention layer on the surface of the atmosphere side electrode, and the detection accuracy caused by providing the poisoning prevention layer on the surface of the atmosphere side electrode A decrease in responsiveness can be avoided.

The block diagram which shows the whole engine control system. (A) is sectional drawing which shows the inside of the whole A / F sensor, (b) is sectional drawing which shows the inside of the sensor element which comprises the sensor. The figure which shows the output characteristic of an A / F sensor. The figure which shows the outline | summary of a pumping process. The flowchart which shows the procedure of a pumping process. The figure which shows the relationship between a stop period and pumping time, and an engine load.

  Hereinafter, an engine control system according to the present embodiment will be described with reference to the drawings. In this embodiment, an exhaust gas discharged from an engine mounted on a vehicle is used as a detected gas, and an A / F sensor is used to detect an oxygen concentration (air-fuel ratio: A / F) in the exhaust gas. An engine control system that performs various engine controls based on the output of the engine will be described. In the control system, stoichiometric combustion control in which the air-fuel ratio is stoichiometrically or near the stoichiometric air-fuel ratio feedback control, lean air-fuel ratio control in which the air-fuel ratio is feedback-controlled in a predetermined lean region, and the like are appropriately performed.

  First, an overall outline of the engine control system will be described with reference to FIG. The engine 10 is, for example, a gasoline engine, and includes an electronically controlled throttle valve 11, a fuel injection valve 12, an ignition device 13, and the like. The exhaust pipe 14 of the engine 10 is provided with a catalyst 15 made of, for example, a three-way catalyst as an exhaust purification device. An A / F sensor 20 is provided upstream of the catalyst 15 in the exhaust pipe 14 and outputs an air-fuel ratio signal corresponding to the oxygen concentration in the exhaust to the ECU 17.

  The ECU 17 is mainly composed of a microcomputer including a known CPU, ROM, RAM and the like, and based on various control programs stored in the ROM, for example, an air-fuel ratio feedback based on an actual air-fuel ratio. Implement control.

  More specifically, in the air-fuel ratio feedback control, the target air-fuel ratio is stoichiometric (A / F = 14.7), and the fuel injection valve 12 uses the actual air-fuel ratio detected by the A / F sensor 20 so as to match the target air-fuel ratio. Control the fuel injection amount.

  Next, the configuration of the A / F sensor 20 will be described with reference to FIG. 2A is a cross-sectional view showing the entire inside of the A / F sensor 20, and FIG. 2B is a cross-sectional view showing the inside of the sensor element 30 constituting the sensor 20 (A-A in FIG. 2A). It is a line sectional view, except for the cover section.

  As shown in FIG. 2A, the A / F sensor 20 has an exhaust side cover 22, a housing part 23, and an atmosphere side cover 24, and has a substantially cylindrical shape as a whole. And the elongate sensor element 30 is accommodated in the inside. The A / F sensor 20 is attached to the wall portion of the exhaust pipe 14 by the housing portion 23, and the exhaust side cover 22 is arranged in the exhaust pipe 14 in the attached state. The exhaust side cover 22 has a double structure by an outer cover 25 and an inner cover 26, and exhaust circulation ports 27 for taking in exhaust gas are formed in the peripheral walls of these covers, respectively. The sensor element 30 is inserted and held in a through hole provided in an insulating member 29 inserted in the housing portion 23, and the tip end portion of the sensor element 30 protrudes from the housing portion 23 to the inside of the exhaust pipe 14 and enters the exhaust side cover 22. Contained. The atmosphere side cover 24 is fixed to the upper end side of the housing part 23. At the opposing position of the peripheral wall of the atmosphere side cover 24, an air circulation port 28 for taking the atmosphere into the atmosphere space S provided in the atmosphere side cover 24 is formed. The atmosphere taken into the atmosphere space S is guided into the sensor element 30.

  As shown in FIG. 2B, the sensor element 30 includes a solid electrolyte layer 31, a diffusion resistance layer 32, a shielding layer 33, and an insulating layer 34, which are stacked in the vertical direction in the figure. A protective layer (not shown) is provided around the element 30. The rectangular plate-shaped solid electrolyte layer 31 (solid electrolyte body) is a partially stabilized zirconia sheet, and a pair of upper and lower exhaust-side electrodes 35 and air-side electrodes 36 are disposed opposite to each other with the solid electrolyte layer 31 interposed therebetween. . The exhaust side electrode 35 and the atmosphere side electrode 36 are formed of a noble metal such as platinum Pt. The diffusion resistance layer 32 is composed of a porous sheet for introducing exhaust gas into the exhaust side electrode 35, and the shielding layer 33 is composed of a dense layer for suppressing permeation of exhaust gas. An exhaust chamber 39 is formed in the diffusion resistance layer 32 so as to surround the exhaust side electrode 35. Each of these layers 32 and 33 is formed by molding a ceramic such as alumina or zirconia by a sheet forming method or the like, but the gas permeability is different due to the difference in the average pore diameter and porosity of the porosity.

  The insulating layer 34 is made of ceramics such as alumina and zirconia, and an air duct 37 is formed at a portion facing the air-side electrode 36. In addition, a heater 38 made of platinum Pt or the like is embedded in the insulating layer 34. The heater 38 is a linear heating element that generates heat when energized from a battery power source, and heats the entire element by the generated heat. The heater 38 may be configured to be externally attached to the sensor element 30 other than the configuration embedded in the insulating layer 34 (configuration built in the sensor element 30).

  In the sensor element 30 having the above-described configuration, the surrounding exhaust is introduced from the side portion of the diffusion resistance layer 32 and reaches the exhaust side electrode 35. When the sensor element 30 is in an active state when the exhaust gas is lean, oxygen in the exhaust gas is decomposed by the exhaust side electrode 35 and discharged from the atmosphere side electrode 36 to the atmospheric duct 37. That is, oxygen is pumped to the atmosphere side electrode 36 side. Then, the oxygen discharged into the air duct 37 is discharged into the air space S. On the other hand, if the sensor element 30 is in an active state when the exhaust gas is rich, the oxygen in the atmospheric duct 37 is decomposed by the atmospheric electrode 36 and discharged from the exhaust electrode 35 to the exhaust chamber 39. That is, oxygen pumping to the exhaust side electrode 35 side is performed.

  In this embodiment, the exhaust side electrode 35 is a negative electrode and the atmosphere side electrode 36 is a positive electrode, and the exhaust side electrode 35 is negative (−) and the atmosphere side electrode 36 is positive (+) as shown in FIG. The applied voltage applied between the electrodes is a positive voltage. Therefore, conversely, the exhaust side electrode 35 is positive (+) and the exhaust side electrode 35 is negative (-), and the applied voltage applied between these electrodes is a negative voltage.

  FIG. 3 is a diagram showing the voltage-current characteristics (VI characteristics) of the A / F sensor 20, and particularly shows the characteristics in the atmospheric detection state. In FIG. 3, the flat portion on the low voltage side parallel to the voltage axis (horizontal axis) is a limit current region for specifying an element current (limit current) that is an output value of the A / F sensor 20. The increase / decrease corresponds to the increase / decrease of the air-fuel ratio (that is, the degree of lean / rich). That is, the device current increases as the air-fuel ratio becomes leaner, and the device current decreases as the air-fuel ratio becomes richer.

  RG indicated by the primary straight line represents an applied voltage line for determining the value of the applied voltage to the sensor element 30. In order to accurately detect the air-fuel ratio, it is necessary to correctly control the applied voltage value on the limit current region of the VI characteristic, and an applied voltage line indicated by a primary straight line in FIG. On the line, the applied voltage value is determined in accordance with each element current value.

  In this VI characteristic, the lower voltage side than the limit current region is a resistance dominant region, and the slope of the primary straight line portion in the resistance dominant region is specified by the DC internal resistance Ri of the sensor element 30. The DC internal resistance Ri changes according to the element temperature, and the DC internal resistance Ri increases as the element temperature decreases. That is, at this time, the slope of the primary straight line portion of the resistance dominating region becomes small (the straight line portion lies down). Further, when the element temperature rises, the DC internal resistance Ri decreases. That is, at this time, the slope of the primary straight line portion of the resistance dominating region becomes large (the straight line portion stands up). Further, in this VI characteristic, a flat portion on the higher voltage side than the limit current region is a water decomposition region, and water contained in the exhaust gas is decomposed by voltage application in this water decomposition region.

  In the VI characteristic in the atmosphere detection state, an oxygen concentration output in the atmosphere is obtained in the limit current region in a state where the voltage V1 is applied as the atmosphere detection voltage to the sensor element 30. Further, the voltage V2 is a voltage corresponding to the upper limit value of the limit current region in the atmospheric detection state, and the voltage V3 is a voltage corresponding to the upper limit value of the water decomposition region. When a voltage equal to or higher than the voltage V3 is applied to the sensor element 30, blackening occurs in which the solid electrolyte layer 31 is blackened, and there is a concern about element deterioration due to a decrease in ionic conductivity of the solid electrolyte layer 31. The voltages V1 to V3 are, for example, V1 = 0.6V, V2 = 1.1V, and V3 = 1.6V.

  By the way, when the A / F sensor 20 shifts to a non-use state when the engine stops, that is, when the output of the A / F sensor 20 shifts to a state where the output is not used, the gas sensor and its surroundings become a high temperature atmosphere. In addition, the atmosphere-side electrode 36 may be poisoned when the atmosphere containing poisoning substances such as silicon, sulfur, phosphorus, ammonia, hydrocarbons, and metals in a gas phase is supplied to the atmosphere-side electrode 36 side. In this case, since an insulator is formed on the atmosphere side electrode 36 by the poisoning substance, the current is inhibited by the insulator, and the detection accuracy and responsiveness of the A / F sensor 20 are lowered.

  Specifically, the running wind cannot be obtained immediately after the engine is stopped. As a result, various members of the engine 10, the exhaust pipe 14, and the like remain in a high temperature state, and outgas including poisonous substances is generated from the various members and the outgas stays around the vehicle. In particular, when the operation state immediately before the engine is stopped is a high load operation state (for example, A / F is 12 or less, the exhaust pressure is 150 kPa or more, etc.), the outgas increases. In this case, since the inside of the air duct 37 of the sensor element 30 becomes a poisoning environment with a lot of poisoning substances, an insulator is easily formed on the atmosphere side electrode 36 by the poisoning substances.

  Therefore, in this embodiment, when it is determined that the atmosphere side electrode 36 is in a poisoned environment when the output of the A / F sensor 20 is not used, the exhaust side electrode 35 is changed to the atmosphere side electrode 36. On the other hand, oxygen pumping is performed. At this time, the ECU 17 maintains the active state by setting the sensor element 30 to a predetermined temperature, and sets the applied voltage of the sensor element 30 to a predetermined positive voltage. Thereby, as shown in FIG. 4, the oxygen pumping to the atmosphere side electrode 36 is performed. When oxygen is pumped into the atmosphere-side electrode 36, the atmosphere duct 37 is filled with oxygen, and then the atmosphere space S is filled with oxygen.

  Next, the procedure of the pumping process performed by ECU17 is demonstrated using the flowchart of FIG.

  First, in step S11, it is determined whether or not an ignition switch (not shown) is in an off state. When YES is determined in the step S11, the process proceeds to a step S12 so as to determine whether or not it is a poisoned environment. At this time, when the elapsed time from the engine stop is within the predetermined stop period Ta, it is determined that the atmosphere side electrode 36 is in a poisoned environment based on the operation state immediately before the engine stop being the high load operation state. To do. In addition, it is good to set it as a high load driving | running state when the integrated value of the engine load (for example, accelerator opening) from the time of an engine stop to the time of a predetermined period is more than a predetermined value.

  If “YES” in the step S12, the process proceeds to a step S13 to determine whether or not the pumping process is being performed. If NO in step S13, the process proceeds to step S14 to start the pumping process. At this time, the sensor element 30 is maintained at a predetermined activation temperature by the heating of the heater 38. Specifically, the heater temperature is controlled within the range of the upper and lower limit temperatures, where the activation temperature of the sensor element 30 is set as the lower limit temperature, and the temperature at which the degree of poisoning of the atmosphere side electrode 36 by the poisoning substance is increased. Specifically, the element temperature is set to 400 to 800 ° C. In addition, it is 600-700 degreeC more desirably.

  Further, by maintaining the applied voltage of the sensor element 30 within a predetermined range equal to or higher than the voltage V1 that is an applied voltage at the time of atmospheric detection, oxygen pumping to the atmosphere side electrode 36 is performed at the time of atmospheric detection. Specifically, the applied voltage is set to 0.6 to 1.6V. In particular, in the present embodiment, the voltage V2 is set as the lower limit voltage and the voltage V3 at which blackening occurs is set as the upper limit voltage in order to stably fill the atmosphere duct 37 and the atmosphere space S with oxygen, and within the range of the upper and lower limit voltages. Control the voltage.

  On the other hand, if “YES” in the step S13, the process proceeds to a step S15 to determine whether it is the end timing of the pumping process. At this time, when the elapsed time from the start of the pumping process exceeds the pumping time Tb, it is determined that it is the end timing of the pumping process. If YES in step S15, the process proceeds to step S16, and the pumping process is terminated.

  As mentioned above, according to this embodiment explained in full detail, the following outstanding effects are acquired.

  According to the above configuration, when it is determined that the atmosphere side electrode 36 is in a poisoned environment when the output of the A / F sensor 20 is not used, the exhaust side electrode 35 is changed to the atmosphere side electrode 36. On the other hand, oxygen pumping was implemented. In this case, the atmosphere duct 37 provided with the atmosphere-side electrode 36 is filled with oxygen, and poisonous substances contained in the atmosphere are prevented from flowing into the atmosphere duct 37. Thereby, poisoning of the atmosphere side electrode 36 can be suppressed appropriately. Further, the poisoning of the atmosphere-side electrode 36 can be suppressed without providing the poisoning-preventing layer on the surface of the atmosphere-side electrode 36, resulting from the provision of the poisoning-preventing layer on the surface of the atmosphere-side electrode 36. A decrease in detection accuracy and responsiveness can be avoided.

  When it is determined that the atmosphere-side electrode 36 is in a poisoned environment, oxygen is pumped to the atmosphere-side electrode 36 side with a predetermined applied voltage equal to or higher than the voltage V1 as an atmosphere detection voltage that is an applied voltage at the time of atmosphere detection. The configuration. In this case, the atmospheric duct 37 can be filled with oxygen. As a result, the atmosphere side electrode 36 can be suitably prevented from being poisoned.

  When it is determined that the atmosphere-side electrode 36 is in a poisoned environment, a predetermined applied voltage between the voltage V2 corresponding to the upper limit value of the limit current region and the voltage V3 corresponding to the upper limit value of the water splitting region It was set as the structure which pumps oxygen. In this case, it is possible to stably fill not only the atmospheric duct 37 but also the atmospheric space S provided in the atmospheric side cover 24 with oxygen while suppressing the occurrence of blackening. As a result, it is possible to enhance the suppression effect of the atmosphere side electrode 36 being poisoned while suppressing the occurrence of blackening.

  When it is determined that the atmosphere side electrode 36 is in a poisoned environment, the sensor element 30 is maintained in an active state by heating the heater 38. In this case, oxygen pumping can be performed stably, so that the atmosphere side electrode 36 can be stably prevented from being poisoned.

  If the element temperature is too high, there is a concern that poisoning of the atmosphere side electrode 36 by the poisoning substance is promoted. In this respect, since the upper limit temperature is set and the heater heating is performed below the upper limit temperature, the poisoning of the atmosphere side electrode 36 can be suitably suppressed.

  Pumping is performed so that the atmosphere duct 37 and the atmosphere space S are filled with oxygen. For this reason, the surface of the atmosphere-side electrode 36 can be stably filled with oxygen. As a result, the effect of suppressing the atmosphere side electrode 36 from being poisoned can be enhanced.

  When the elapsed time from the engine stop is within the stop period Ta, the atmosphere side electrode 36 is determined to be in a poisoned environment. For this reason, even if it becomes a case where the atmosphere side electrode 36 becomes easy to be poisoned by an engine stop, it can suppress appropriately that the atmosphere side electrode 36 is poisoned.

  When the elapsed time from the engine stop is within the stop period Ta, the atmosphere-side electrode 36 is determined to be in a poisoned environment based on the high-load operation state immediately before the engine stop. In this case, since the determination accuracy of the poisoning environment can be improved, the necessity of the pumping process can be appropriately determined. For this reason, it can suppress appropriately that the atmosphere side electrode 36 is poisoned, suppressing that a battery electrode is consumed by unnecessary pumping.

(Other embodiments)
The above embodiment may be modified as follows, for example.

  The atmosphere side electrode 36 is determined to be in a poisoned environment based on the ignition switch being in the off state, but the atmosphere is based on the ignition switch being in the on state and the vehicle being stopped. It may be configured to determine that the side electrode 36 is in a poisoned environment. In this case, when the elapsed time from the stop is within a predetermined stop duration, and it is determined that the atmosphere-side electrode 36 is in a poisoned environment when the driving state immediately before the vehicle stops is a high-load driving state. Good.

  In the engine control system in which the air-fuel ratio feedback control based on the sensor output is interrupted when the engine 10 is in a high load operation state, it is determined that the atmosphere side electrode 36 is in a poisoned environment when the interruption is performed. It is good also as a structure.

  During high-load operation of the engine 10 (for example, A / F is 12 or less, exhaust pressure is 150 kPa or more, etc.), outgas containing poisonous substances is generated. Further, during high load operation, the exhaust becomes rich and oxygen in the atmospheric duct 37 is exhausted to the exhaust chamber 39. In this case, since the outgas containing poisonous substance easily enters the atmospheric duct 37 even when the vehicle is in a driving state, the atmosphere side electrode 36 is considered to be in a poisoning environment. In this regard, according to the above, when the engine 10 is in a high load operation state, when the air-fuel ratio feedback control based on the sensor output is interrupted, it is determined that the atmosphere-side electrode 36 is in a poisoned environment, and the atmosphere 10 Oxygen pumping is performed on the side electrode 36 side. For this reason, even when the vehicle is in a driving state, the opportunity to pump oxygen to the atmosphere side electrode 36 can be appropriately determined.

  The engine load (for example, accelerator) for the stop period Ta for determining that the atmosphere side electrode 36 is in a poisoned environment or the pumping time Tb for determining the end of the pumping process is a predetermined time after the engine stop. It is good also as a structure set variably based on the integrated value of an opening degree. In this case, as shown in FIG. 6, the stop period Ta or the pumping time Tb may be set to be larger as the integrated value of the engine load is larger.

  It can be considered that as the integrated value of the engine load is larger, the outgas generation time after the engine is stopped is longer and the generation amount is larger. In this regard, according to the above-described configuration, the pumping time Tb is set to be larger as the integrated value of the engine load from the time when the engine is stopped to a time point that is a predetermined time backward is larger. In this case, since the pumping time Tb can be changed according to the generation time and the generation amount of outgas, it is possible to suitably suppress the atmosphere side electrode 36 from being poisoned.

  Further, the stop period Ta is set to be larger as the integrated value of the engine load from the time when the engine is stopped to a time point that is a predetermined time later is larger. In this case, since it is grasped whether or not the poisoning environment is continuing, it is possible to improve the determination accuracy of the poisoning environment.

  -It is good also as a structure which terminates a pumping process, when an engine water temperature falls below predetermined temperature.

  In addition to the A / F sensor 20 and the O2 sensor whose oxygen concentration is a detection target, the present invention can be applied to a gas sensor whose detection target is another gas concentration component. For example, a composite type gas sensor has a plurality of cells formed of a solid electrolyte layer, and in the first cell (pump cell), oxygen in the gas to be detected is discharged or pumped and the oxygen concentration is detected. In the two cells (sensor cell), the gas concentration of the specific component is detected from the gas after the oxygen is discharged. This gas sensor is embodied as, for example, a NOx sensor that detects the NOx concentration in the exhaust gas, and can also be embodied as a sensor control device that targets this NOx sensor. Further, in addition to the first cell and the second cell, a gas sensor having a plurality of cells such as a third cell (monitor cell or second pump cell) for detecting a residual oxygen concentration after oxygen discharge may be used.

  -It can also be embodied as a sensor control device for a gas sensor provided in an intake passage of the engine 10 or a gas sensor used in other types of engines such as a diesel engine in addition to a gasoline engine. The gas sensor may be a gas to be detected other than exhaust gas or used for purposes other than automobiles.

  As an electromotive force output type gas sensor, in addition to a sensor that generates an electromotive force between electrodes according to the oxygen concentration (O2 concentration) in the exhaust gas, an electromotive force is generated between the electrodes according to the concentration of NOx or CO containing oxygen components. A sensor that generates electric power may be used. That is, when NOx and CO are decomposed at one electrode to generate oxygen ions and a difference in oxygen partial pressure occurs on both sides of the solid electrolyte layer, an electromotive force is generated according to the difference in oxygen partial pressure. At this time, an electromotive force based on the Nernst equation is generated. The present invention can also be applied to a gas sensor having such a configuration. In this case, the pumping process may be terminated based on the oxygen partial pressure.

  17 ... ECU (sensor control device), 20 ... A / F sensor (gas sensor), 30 ... sensor element, 31 ... solid electrolyte layer, 35 ... exhaust side electrode (gas side electrode), 36 ... atmosphere side electrode, 37 ... atmosphere duct.

Claims (11)

It has a sensor element (30) including a solid electrolyte layer (31) and a pair of electrodes (35, 36) provided on both sides of the solid electrolyte layer, and one of the pair of electrodes is a gas to be detected. Is applied to the gas sensor (20), which is an atmosphere side electrode (36) provided in an air duct (37) into which air is introduced from the outside.
An environment determination unit that determines whether or not the atmosphere side electrode is in a poisoned environment when the gas sensor output is shifted to a non-use state;
A pumping execution unit that performs oxygen pumping from the gas side electrode to the atmosphere side electrode when it is determined that the atmosphere side electrode is in a poisoned environment;
A sensor control device (17). The gas sensor is a limiting current type gas concentration sensor configured to flow an element current according to an oxygen concentration each time a predetermined voltage is applied to the pair of electrodes.
When it is determined that the atmosphere-side electrode is in a poisoned environment, the pumping unit applies an atmospheric detection voltage, which is an applied voltage at the time of atmospheric detection, or a predetermined voltage on a higher voltage side to the pair of electrodes. The sensor control apparatus according to claim 1, wherein the pumping of oxygen is performed from the gas side electrode to the atmosphere side electrode by applying. The gas sensor is a limiting current type gas concentration sensor configured to flow an element current according to an oxygen concentration each time a predetermined voltage is applied to the pair of electrodes.
The pumping unit, when it is determined that the atmosphere side electrode is in a poisoned environment, a first voltage corresponding to an upper limit value of a limit current region, a voltage higher than the first voltage, and a water decomposition region 3. The pumping of oxygen is performed from the gas side electrode to the atmosphere side electrode by applying a predetermined voltage between the second voltage corresponding to the upper limit value of the gas to the pair of electrodes. Sensor control device. The gas sensor includes a heater (38) for heating the sensor element,
4. The sensor according to claim 1, further comprising a heater control unit configured to maintain the sensor element in an active state by heating the heater when it is determined that the atmosphere-side electrode is in a poisoned environment. Control device.   When it is determined that the atmosphere side electrode is in a poisoning environment, the heater control unit heats the heater with a temperature at which the degree of poisoning of the atmosphere side electrode due to the poisoning substance is increased as an upper limit temperature. The sensor control apparatus of Claim 4 which controls. The gas sensor has an atmosphere side cover part (24) provided with an introduction port (28) for accommodating the sensor element and introducing the atmosphere into the internal space (S), and the atmosphere introduced from the introduction port is It has a configuration that flows into the air duct from an internal space,
6. The sensor control device according to claim 1, wherein the pumping unit performs the pumping so that the atmospheric duct and the internal space are filled with oxygen in the gas sensor. 7. The gas sensor is an exhaust sensor that detects the concentration of a specific component in the exhaust with the exhaust discharged from the in-vehicle engine (10) as a detection target,
The sensor control according to any one of claims 1 to 6, wherein the environment determination unit determines that the atmosphere-side electrode is in a poisoned environment when it is within a predetermined stop period immediately after the operation of the engine is stopped. apparatus.   The environment determination unit determines that the atmosphere-side electrode is in a poisoned environment based on the fact that the operation state immediately before the engine is stopped is a high-load operation state when the engine is within the stop period. The sensor control device according to 1.   The pumping execution unit is configured to end the pumping after a lapse of a predetermined pumping time from the start of the pumping, and variably set the pumping time according to a load immediately before the engine is stopped. The sensor control apparatus according to 7 or 8.   The sensor control device according to any one of claims 7 to 9, wherein the environment determination unit variably sets the stop period according to a load immediately before the engine is stopped. The gas sensor is an exhaust sensor that detects the oxygen concentration in the exhaust gas with the exhaust gas discharged from the in-vehicle engine (10) as a detection target,
Applied to a control system that performs air-fuel ratio feedback control based on the detection result of the oxygen concentration and interrupts the air-fuel ratio feedback control when the engine is in a high-load operation state,
The said environment determination part determines that the said atmosphere side electrode exists in poisonous environment, when it transfers to the state which does not use the output of the said gas sensor by the said air-fuel ratio feedback control being interrupted. The sensor control device according to any one of claims.

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