JP2016080406A - Gas sensor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately perform a control of current application in the case that electromotive force characteristics of a gas sensor are shifted.SOLUTION: A CO2 sensor 16 includes a sensor element 31 having a solid electrolytic layer 32 and a pair of electrodes 33, 34 provided at a position sandwiching a solid electrolytic layer 32, and outputs a signal of electromotive force according to an air fuel ratio of an exhaust gas with the exhaust gas of an engine as a detection object. A microcomputer 41 executes a current application by a constant current circuit 43 based on a demand value of a current applied to the sensor element 31, and includes: characteristic control means for causing electromotive force characteristics of the sensor element 31 to be shifted; and current correction means for correcting the application current from the demand value to a temporarily increased side or reduced side according to a form of the current application when the current application by a constant current circuit 43 is started.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a gas sensor control device that detects an air-fuel ratio based on a detection signal of a gas sensor.

  For example, in a vehicular engine, an electromotive force output type gas sensor (so-called O2 sensor) that detects an oxygen concentration by using exhaust discharged from the engine as a detection target is generally used. This gas sensor has an electromotive force cell that outputs different electromotive force signals depending on whether the air-fuel ratio of exhaust is rich or lean. Specifically, if the air-fuel ratio is rich, an electromotive force signal of about 0.9 V If the air-fuel ratio is lean, an electromotive force signal of about 0 V is output.

  Further, in such a gas sensor, there is a technique in which a current is passed between a pair of electrodes provided at a position sandwiching the solid electrolyte layer, thereby shifting an electromotive force characteristic (output characteristic) of the gas sensor to a lean side or a rich side. Proposed. For example, in the gas sensor control device of Patent Document 1, when it is determined that there is a change request for changing the electromotive force characteristics of the gas sensor, the direction of the constant current applied between the pair of electrodes is determined based on the change request. At the same time, the constant current circuit is controlled so that a constant current flows in the determined direction. The electromotive force characteristics of the gas sensor are suitably controlled by supplying the constant current.

JP 2012-63345 A

  However, when an electromotive force characteristic is shifted by applying a current between a pair of electrodes of the gas sensor, it takes time until the characteristic is actually changed after the current application. For this reason, when the target value of the air-fuel ratio is changed by the characteristic shift of the electromotive force cell, for example, when switching from stoichiometric feedback control to lean feedback control, the controllability is reduced due to the delay in the change in the electromotive force characteristic. Is concerned. In such a case, there is a concern about the occurrence of inconveniences such as the fuel injection amount becoming smaller or larger than intended.

  The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a gas sensor control device that can appropriately control current application when shifting the electromotive force characteristics of the gas sensor. .

  The gas sensor control device of the present invention has an electromotive force cell (31) including a solid electrolyte body (32) and a pair of electrodes (33, 34) provided at a position between which the solid electrolyte body is sandwiched. The present invention is applied to a gas sensor (16) that outputs an electromotive force signal corresponding to the air-fuel ratio of the exhaust gas with the exhaust gas of 10) as a detection target. A predetermined current can be applied between the pair of electrodes of the electromotive force cell by the energizing means (43). Then, the gas sensor control device performs a current application by the energization unit based on a required value of an applied current applied to the electromotive force cell, and shifts the electromotive force characteristic of the electromotive force cell, And a current correcting unit that temporarily corrects the applied current from a required value to an increase side or a decrease side according to a mode of current application when starting current application by the energization unit.

  When current is applied to the electromotive force cell to shift the electromotive force characteristic (λ inflection point), the controllability is reduced due to the delay in the change in the electromotive force characteristic, and the fuel is implemented based on the detection signal of the gas sensor. There are concerns about inconveniences such as the fuel injection amount being too small or excessive in the injection amount control. In this regard, in the above configuration, when the current application by the energization means is started, the applied current is temporarily corrected from the required value to the increase side or the decrease side according to the mode of current application. Inconveniences (such as deviations in fuel injection amount) caused by response delays when shifting the engine can be corrected by temporary current correction. As a result, it is possible to appropriately control the current application when shifting the electromotive force characteristics of the gas sensor.

The schematic block diagram which shows the whole engine control system. The figure which shows the cross-sectional structure of a sensor element, and the schematic structure of a sensor control part. The electromotive force characteristic figure which shows the relationship between an air fuel ratio and the electromotive force of a sensor element. The figure which shows the limiting current characteristic of a sensor element. Schematic for demonstrating reaction of the gas component in a sensor element. The figure which shows the relationship between the applied current of a sensor element, and A / F of a characteristic inflection point. The electromotive force characteristic figure which shows the relationship between an air fuel ratio and the electromotive force of a sensor element. The flowchart which shows the process sequence of a characteristic shift. The figure which shows the correlation with the request | requirement shift amount of an electromotive force characteristic, and an applied current. The figure which shows the correlation with the shift amount of an electromotive force characteristic, and an electric current correction value. The time chart for demonstrating operation | movement of 1st Embodiment. The time chart for demonstrating operation | movement of 2nd Embodiment. The figure which shows the correlation with the shift amount of an electromotive force characteristic, and an electric current correction value. The figure which shows the correlation with the shift amount of an electromotive force characteristic, and the length of a correction period.

(First embodiment)
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. In the present embodiment, an engine control system that uses a gas sensor provided in an exhaust pipe of an in-vehicle engine (internal combustion engine) and performs various controls of the engine based on the output of the gas sensor will be described. In this control system, an electronic control unit (hereinafter referred to as ECU) is used as a center to control the fuel injection amount, control the ignition timing, and the like. FIG. 1 is a configuration diagram showing an overall outline of the present system.

  In FIG. 1, an 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 (exhaust part) of the engine 10 is provided with catalysts 15a and 15b as exhaust purification devices. Each of the catalysts 15a and 15b is, for example, a three-way catalyst, of which the catalyst 15a is a first catalyst as an upstream catalyst, and the catalyst 15b is a second catalyst as a downstream catalyst. As is well known, the three-way catalyst purifies CO (carbon monoxide), HC (hydrocarbon), NOx (nitrogen oxides such as NO), which are harmful three components of exhaust gas. Is formed by supporting a metal such as platinum, palladium, or rhodium on a ceramic carrier. In this case, in the three-way catalyst, CO and HC that are rich components are purified by an oxidizing action, and NOx that is a lean component is purified by a reducing action.

  O2 sensors 16 and 17 are provided on the upstream side of the first catalyst 15a and between the catalysts 15a and 15b (on the downstream side of the first catalyst 15a and on the upstream side of the second catalyst 15b), respectively. The O2 sensors 16 and 17 output different electromotive force signals depending on whether the air-fuel ratio of the exhaust is rich or lean.

  In addition, the present system includes a throttle opening sensor 21 that detects the opening of the throttle valve 11 and a crank angle sensor that outputs a rectangular crank angle signal at every predetermined crank angle of the engine (for example, at a cycle of 30 ° CA). 22. Various sensors such as an air amount sensor 23 for detecting the intake air amount of the engine 10 and a cooling water temperature sensor 24 for detecting the temperature of the engine cooling water are provided.

  The ECU 25 is mainly composed of a microcomputer (microcomputer) composed of a well-known CPU, ROM, RAM, and the like, and executes various control programs stored in the ROM, so that the engine can be operated according to the engine operating state each time. 10 various controls are executed. That is, the ECU 25 inputs signals from the various sensors and the like, calculates the fuel injection amount and ignition timing based on the various signals, and controls the driving of the fuel injection valve 12 and the ignition device 13.

  In particular, regarding fuel injection amount control, the ECU 25 performs air-fuel ratio feedback control based on detection signals from the O2 sensors 16 and 17 on the upstream side and downstream side of the first catalyst. In this case, the ECU 25 performs main feedback control so that the front air-fuel ratio detected by the upstream O2 sensor 16 becomes the target air-fuel ratio (for example, the theoretical air-fuel ratio), and the front air-fuel ratio changes to rich or lean. Then, the sub-feedback control is performed in which the delay time from when the rich determination or the lean determination is actually made is variably set based on the rear air-fuel ratio detected by the downstream O2 sensor 17. The main feedback control and sub feedback control will be briefly described below.

  The ECU 25 becomes rich when the rich delay time elapses after the output value V1 (corresponding to the front air-fuel ratio) of the upstream O2 sensor 16 becomes richer than a reference value (for example, 0.45 V). When the lean delay time elapses after V1 becomes leaner than the reference value, the lean determination that the air-fuel ratio becomes lean is performed. Then, the ECU 25 increases or decreases the feedback correction value (injection correction value) by skip and integration based on the rich / lean determination result, and corrects the fuel injection amount by the feedback correction value. Such control corresponds to main feedback control. Further, the ECU 25 variably controls the rich delay time and the lean delay time depending on whether the output value V2 (corresponding to the rear air-fuel ratio) of the downstream O2 sensor 17 is rich or lean as sub feedback control. In this case, if the output value V2 is larger than the reference value (if the rear air-fuel ratio is rich), at least one of shortening the rich delay time and extending the lean delay time is performed. If the output value V2 is smaller than the reference value (if the rear air-fuel ratio is lean), at least one of extending the rich delay time and shortening the lean delay time is performed.

  In addition, air-fuel ratio learning is performed when air-fuel ratio feedback control is performed. An air-fuel ratio learning value is calculated based on the feedback correction value, and the air-fuel ratio learning value is stored in a backup memory such as an EEPROM. . In this case, a plurality of operation regions divided according to the engine speed and engine load are determined, and the air-fuel ratio learning value is calculated and stored for each operation region. In the air-fuel ratio learning, a steady-state feedback correction value shift caused by individual differences in the injectors, changes over time, and the like is calculated and stored as an air-fuel ratio correction value.

  Next, the configuration of the O2 sensors 16 and 17 will be described. Although the O2 sensors 16 and 17 have the same basic configuration, the O2 sensor 16 will be particularly described here. The O2 sensor 16 has a sensor element 31 having a cup-type structure, and FIG. Actually, the sensor element 31 is configured such that the entire element is accommodated in a housing or an element cover, and is disposed in the engine exhaust pipe. The sensor element 31 corresponds to an electromotive force cell.

  In the sensor element 31, the solid electrolyte layer 32 is formed in a cup shape in cross section, an exhaust side electrode 33 is provided on the outer surface, and an air side electrode 34 is provided on the inner surface. These electrodes 33 and 34 are provided in a layered manner on the surface of the solid electrolyte layer 32. The solid electrolyte layer 32 is made of an oxygen ion conductive oxide sintered body in which CaO, MgO, Y2O3, Yb2O3 or the like is dissolved as a stabilizer in ZrO2, HfO2, ThO2, Bi2O3 or the like. Each of the electrodes 33 and 34 is made of a noble metal having high catalytic activity such as platinum, and the surface thereof is subjected to porous chemical plating or the like. Each electrode 33 and 34 is a pair of counter electrodes (sensor electrodes). The internal space surrounded by the solid electrolyte layer 32 is an atmosphere chamber 35 (reference chamber) into which the atmosphere as a reference gas is introduced, and a heater 36 is accommodated in the atmosphere chamber 35. The heater 36 has a heat generation capacity sufficient to activate the sensor element 31, and the entire sensor element is heated by the heat generation energy. The activation temperature of the O2 sensor 16 is, for example, about 500 to 650 ° C. The atmosphere chamber 35 is maintained at a predetermined oxygen concentration by introducing the atmosphere as a reference gas.

  In the sensor element 31, the outside (on the electrode 33 side) of the solid electrolyte layer 32 is an exhaust atmosphere, and the inside (on the electrode 34 side) is an air atmosphere. The difference in oxygen concentration between these two (difference in oxygen partial pressure) Accordingly, an electromotive force is generated between the electrodes 33 and 34. That is, different electromotive forces are generated depending on whether the air-fuel ratio is rich or lean. In this case, from the atmosphere side electrode 34 that is the reference side electrode, the exhaust side electrode 33 has a low oxygen concentration, and in the sensor element 31, the atmosphere side electrode 34 is the positive side and the exhaust side electrode 33 is the negative side. An electromotive force is generated. Thereby, the O2 sensor 16 outputs an electromotive force signal corresponding to the oxygen concentration (that is, the air-fuel ratio) of the exhaust gas.

  FIG. 3 is an electromotive force characteristic diagram showing the relationship between the air-fuel ratio of the exhaust gas and the electromotive force of the sensor element 31. In FIG. 3, the horizontal axis is the excess air ratio λ, and λ = 1 is the stoichiometric (theoretical air-fuel ratio). The sensor element 31 has a characteristic that the electromotive force varies depending on whether the air-fuel ratio is rich or lean, and the electromotive force changes suddenly near the stoichiometric range. Specifically, the sensor electromotive force at the time of rich is about 0.9V, and the sensor electromotive force at the time of lean is about 0V.

  Further, in the O2 sensor 16 of this embodiment, a part of the configuration is changed with respect to a general O2 sensor. In the sensor element 31 shown in FIG. 2, the exhaust side and the atmosphere side of the solid electrolyte layer 32 are changed. A gas diffusion resistance layer 37 that restricts the diffusion of the exhaust is provided on the exhaust side. The gas diffusion resistance layer 37 is made of a porous material such as alumina, spinel, or zirconia, and is provided on the outer surface of the sensor element 31 so as to cover the exhaust-side electrode 33. Thus, the exhaust gas passes through the gas diffusion resistance layer 37 with a predetermined transmittance and reaches the exhaust-side electrode 33.

  Although the sensor element 31 having the above configuration is basically an electromotive force cell that outputs an electromotive force, a limit current that outputs a limit current corresponding to the oxygen concentration by applying a voltage between the pair of electrodes 33 and 34. It has characteristics. More specifically, the A / F region (oxygen concentration region) in which the limit current output is possible varies depending on the form of the gas diffusion resistance layer 37 (for example, the layer thickness or pinhole diameter), for example, the thickness of the gas diffusion resistance layer 37 As A becomes larger, the A / F capable of outputting a limit current is expanded to the lean side. Specifically, as shown in FIG. 4A, when the thickness of the gas diffusion resistance layer 37 is 100 μm, it becomes possible to output a limit current with A / F = 15 as the maximum value on the lean side. . As shown in FIG. 4B, when the thickness of the gas diffusion resistance layer 37 is 200 μm, the limit current can be output with A / F = 16 as the maximum value on the lean side. Further, as shown in FIG. 4C, when the thickness of the gas diffusion resistance layer 37 is 300 μm, it is possible to output a limit current with A / F = 18 as the maximum value on the lean side.

  As shown in FIG. 2, a sensor control unit 40 is connected to the sensor element 31 (O2 sensor 16), and an electromotive force is generated in the sensor element 31 in accordance with the air-fuel ratio (oxygen concentration) of the exhaust. A sensor detection signal (electromotive force signal) corresponding to the electromotive force is output to the microcomputer 41 in the sensor control unit 40. The microcomputer 41 takes in the electromotive force signal output from the sensor element 31 via an A / D converter or the like, and calculates the air / fuel ratio of exhaust (particularly, the air / fuel ratio downstream of the catalyst) based on the electromotive force signal. The sensor control unit 40 is provided in the ECU 25 shown in FIG. In the ECU 25, a microcomputer 41 is provided as a calculation means having an engine control function and a sensor control function. In this case, the microcomputer 41 calculates the engine rotation speed and the intake air amount based on the detection results of the various sensors described above. However, the ECU 25 may have a configuration in which a microcomputer for engine control and a microcomputer for sensor control are provided separately.

  The microcomputer 41 determines the active state of the sensor element 31 and controls the driving of the heater 36 through the heater driving circuit 42 based on the determination result.

  In the present embodiment, in order to change the output characteristics (electromotive force characteristics) of the O2 sensor 16, a configuration in which a predetermined constant current is supplied between the pair of electrodes 33 and 34 in the sensor element 31 (a configuration in which oxygen pumping is performed). The controllability in air-fuel ratio feedback control is improved by changing the output characteristics. The principle that the sensor output characteristics are changed when a constant current is passed in the direction from the exhaust side to the atmosphere side is as follows.

  As shown in FIG. 5, CO, HC, NOx, and O2 exist in the vicinity of the exhaust side electrode 33 of the O2 sensor 16, and in this situation, the exhaust gas is exhausted from the atmosphere side electrode 34 through the solid electrolyte layer 32. A current is passed through the sensor element 31 so that oxygen ions move to the side electrode 33. That is, oxygen pumping is performed in the sensor element 31. In this case, in the exhaust-side electrode 33, oxygen that has moved to the exhaust-side electrode 33 through the solid electrolyte layer 32 reacts with CO and HC to generate CO2 and H2O. As a result, CO and HC in the vicinity of the exhaust side electrode 33 are removed, and the equilibrium point of the gas reaction in the vicinity of the exhaust side electrode of the O 2 sensor 16 is shifted to the rich side. That is, the sensor electromotive force characteristic indicating the relationship between the excess air ratio λ and the electromotive force is shifted to the rich side as a whole, and accordingly, the electromotive force becomes the stoichiometric value (0.45 V), that is, rich / lean. The inflection point shifts to the rich side.

  As shown in FIG. 2, in the sensor control unit 40, a constant current circuit 43 as an energizing unit is connected in the middle of an electrical path that electrically connects the atmosphere side electrode 34 of the sensor element 31 and the microcomputer 41. . The constant current circuit 43 allows a constant current to flow through the solid electrolyte layer 32 in the sensor element 31 in at least one of the direction from the exhaust side electrode 33 to the atmosphere side electrode 34 and the direction from the atmosphere side electrode 34 to the exhaust side electrode 33. It is possible. Further, the constant current circuit 43 may have a PWM drive unit and may be configured to be able to adjust current by PWM control (duty control). In this case, according to the constant current circuit 43, a current flows in the sensor element 31 either through the solid electrolyte layer 32 in the direction from the exhaust side to the atmosphere or from the atmosphere to the exhaust side. Oxygen ions move in the electrolyte layer 32. In the present embodiment, the constant current circuit 43 supplies a constant current based on a command from the microcomputer 41.

  Here, in the sensor element 31 having the gas diffusion resistance layer 37 as described above, the shift amount of the electromotive force characteristic can be expanded by supplying a constant current. That is, the lean shift amount and rich shift amount of the electromotive force characteristics can be expanded. When this is compared with the matter described in FIG. 4, it is as follows.

  As shown in FIG. 4A, when the thickness of the gas diffusion resistance layer 37 is set to 100 μm and the limit current output up to A / F = 15 is enabled, by passing a constant current through the sensor element 31, The electromotive force characteristic can be lean-shifted so that the rich / lean inflection point is A / F = 15. As shown in FIG. 4B, when the thickness of the gas diffusion resistance layer 37 is set to 200 μm and the limit current output up to A / F = 16 is enabled, by passing a constant current through the sensor element 31, The electromotive force characteristic can be lean-shifted so that the rich / lean inflection point is A / F = 16. In addition, when the thickness of the gas diffusion resistance layer 37 is set to 300 μm and the limit current output up to A / F = 18 is enabled as shown in FIG. 4C, a constant current is passed through the sensor element 31. Thus, the electromotive force characteristic can be lean-shifted so that the rich / lean inflection point is A / F = 18.

  In the sensor element 31, it has been confirmed that the shift amount can be increased by increasing the applied current in addition to increasing the shift amount by increasing the thickness of the gas diffusion resistance layer 37. FIG. 6 shows the relationship between the applied current of the sensor element 31 and the A / F of the characteristic inflection point when the electromotive force characteristic is shifted. FIG. 6 shows the relationship between the applied current and the A / F of the characteristic inflection point when the thickness of the gas diffusion resistance layer 37 is 100 μm, 200 μm, and 300 μm.

  According to FIG. 6, when the lean shift is performed so that the rich / lean inflection point is A / F = 15, the applied current is about 2.5 mA if the thickness of the gas diffusion resistance layer 37 is 300 μm. If the thickness of the gas diffusion resistance layer 37 is 200 μm, the applied current should be about 3.4 mA, and if the thickness of the gas diffusion resistance layer 37 is 100 μm, the applied current should be about 5.8 mA. .

  In the O2 sensor 16 provided on the upstream side of the catalyst, the shift amount required as a rich shift or lean shift of the electromotive force characteristic is larger than that of the O2 sensor 17 on the downstream side of the catalyst. On the other hand, in the sensor element 31 that enables electromotive force output and has the gas diffusion resistance layer 37 on the exhaust side of the solid electrolyte layer 32, limit current output under a predetermined voltage application state is possible. By adopting such a configuration, it is possible to extend the shift amount of the electromotive force characteristic. In such a case, by using the sensor element 31 having the gas diffusion resistance layer 37, a preferable countermeasure can be taken even if the required amount of rich shift or lean shift of the electromotive force characteristic increases.

  When supplying a constant current to the sensor element 31, if the voltage level of the electromotive force characteristic is shown in detail, the electromotive force characteristic is considered to shift as shown in FIG. That is, when a constant current is passed between the pair of electrodes 33 and 34 of the sensor element 31 in the direction from the exhaust side to the atmosphere (when a negative current is applied), the electromotive force characteristic of the sensor element 31 is shifted to the rich side. Conversely, when a constant current is passed between the pair of electrodes 33 and 34 in the direction from the atmosphere side to the exhaust side (when a positive current is applied), the electromotive force characteristic of the sensor element 31 is shifted to the lean side. In this case, in the sensor element 31 having the gas diffusion resistance layer 37 as described above, the electromotive force characteristic (λ) can be shifted to the rich side and the lean side by about 20% at the maximum (for example, about 3 to 10%). .

  By the way, when the electromotive force characteristic (λ inflection point) is shifted by applying a current to the sensor element 31, the controllability is lowered due to the delay in the change in the electromotive force characteristic, and based on the detection signal of the O 2 sensor 16. There is a concern that the fuel injection amount may be too small or excessive in the fuel injection amount control to be performed.

  Therefore, in this embodiment, when current application to the sensor element 31 is started, the applied current is temporarily corrected from the required value to the increase side or the decrease side according to the mode of current application. Specifically, when the current application to the sensor element 31 causes the electromotive force characteristic to undergo a lean shift, the applied current is temporarily corrected to increase the lean shift, and the current application to the sensor element 31 is initiated. When the power characteristic is to be richly shifted, the applied current is temporarily corrected so as to increase the rich shift. In short, the deviation of the fuel injection amount caused by the response delay when shifting the electromotive force characteristics is corrected by temporary current correction.

  Next, the characteristic shift process performed by the microcomputer 41 will be described in detail. FIG. 8 is a flowchart showing a processing procedure of characteristic shift, and this processing is repeatedly performed by the microcomputer 41 at a predetermined cycle.

  In FIG. 8, in step S11, it is determined whether or not there is a request for shifting the electromotive force characteristic (λ inflection point) for the sensor element 31, and if there is a request, the process proceeds to the subsequent step S12. In the present embodiment, it is assumed that the electromotive force characteristic is lean-shifted and rich-shifted, and whether or not a lean shift or rich shift request is generated based on the engine operating state each time. Determine whether. For example, when the engine 10 is cold-started or when low fuel consumption driving is performed in order to improve fuel consumption, it is determined that a lean shift is required, and high load for protecting the catalyst or the like at high load is obtained. When the load increase is performed, it is determined that a request for rich shift has occurred. Step S11 is also affirmed when shifting from the lean shift or rich shift state to the original state. If there is no request, this processing is terminated as it is.

  In step S12, the required shift amount in the current characteristic shift is set. At this time, the λ shift amount on the lean shift side or the rich shift side is set as the required shift amount based on the current engine operating state. In the subsequent step S13, the value of the applied current is determined based on the required shift amount. Here, as shown in FIG. 9, the correlation between the required shift amount of the electromotive force characteristics and the applied current is determined in advance, and the value of the applied current is obtained based on the correlation.

  Thereafter, in step S14, a current application command signal is output to the constant current circuit 43, and the applied current determined in step S13 is supplied from the constant current circuit 43 as a constant current.

  Thereafter, in step S15, it is determined whether or not the present time is immediately after the start of current application to the sensor element 31 and is within the correction period in which the increase / decrease correction of the applied current is performed. If it is within the correction period, the process proceeds to the subsequent step S16, and if it is not within the correction period, the present process is terminated.

  In step S16, it is determined whether or not the current characteristic shift is a shift toward the lean side. If the shift is to the lean side, the process proceeds to step S17, and the process of correcting the applied current to the side that increases the shift amount on the lean side is performed. For example, when a positive current starts flowing from a state where no applied current is flowing, the positive current is temporarily increased. If the shift is to the rich side, the process proceeds to step S18, and the process of correcting the applied current to the side to increase the shift amount on the rich side is performed. For example, when a negative current starts flowing from a state where no applied current is flowing, the negative current is temporarily increased.

  In the present embodiment, the current correction value for increasing / decreasing the applied current is variably set based on the required shift amount of the electromotive force characteristics (that is, the change width of the applied current). The current correction value is set using the relationship. In FIG. 10, the current correction value is calculated as a positive value when shifting to the lean side, and a relationship is defined such that the current correction value (positive value) increases as the shift amount to the lean side increases. In addition, the current correction value is calculated as a negative value when shifting to the rich side, and a relationship is defined such that the current correction value (negative value) increases as the shift amount to the rich side increases.

  In particular, after the start of current application, the current correction value is gradually decreased from the initial value with the passage of time within the correction period. Therefore, within the period in which step S15 is YES, the gradual decrease calculation of the positive current correction value is repeatedly performed every time step S17, while the gradual decrease calculation of the negative current correction value is repeatedly performed every time step S18 is performed. Is done. In the present embodiment, a period from when the current correction value is gradually subtracted to 0 is defined as a correction period.

  FIG. 11 is a time chart specifically showing an operation when the air-fuel ratio control is switched from the stoichiometric control to the lean control.

  In FIG. 11, the stoichiometric feedback control is performed before the timing t1, and the applied current is zero. Then, at timing t1, a predetermined applied current is applied to the sensor element 31 based on the lean shift request. At this time, if the change width of the applied current is ΔI, a current correction value is calculated based on the change width ΔI, and the applied current is corrected by the current correction value. Here, since a lean shift is assumed, a positive current correction value is calculated.

  In the correction period from timing t1 to t2, the correction of the applied current is performed using the current correction value that is gradually reduced, and the correction ends at timing t2 when the current correction value becomes zero. The correction period may be a predetermined period, and the correction of the applied current may be terminated when the predetermined period elapses.

  Further, at timing t3, a request for returning the air-fuel ratio control from lean control to stoichiometric control is generated, which corresponds to a request for shifting the electromotive force characteristic to the rich side. In this case, at timing t3, when the applied current is changed to 0 (corresponding to a change to the negative side), the applied current is corrected based on the change width ΔI at that time. Here, a negative current correction value is calculated. In the correction period from timing t3 to t4, the applied current is corrected using the current correction value that is gradually reduced, and the correction ends at timing t4 when the current correction value becomes zero.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  When a current is applied to the sensor element 31 to shift the electromotive force characteristic (λ inflection point), the controllability is reduced due to a delay in the change in the electromotive force characteristic, which is performed based on the detection signal of the O 2 sensor 16. In the fuel injection amount control, there is a concern that the fuel injection amount becomes too small or too large. In this regard, in the above configuration, when the current application to the sensor element 31 is started, the applied current is temporarily corrected from the required value to the increase side or the decrease side according to the current application mode. Inconveniences (such as deviations in fuel injection amount) due to response delays when shifting the power characteristics can be corrected by temporary current correction. As a result, it is possible to appropriately control the current application when shifting the electromotive force characteristics of the O2 sensor 16 (sensor element 31).

  When the electromotive force characteristic of the sensor element 31 is shifted to the lean side, the change of the feedback correction value to the decrease side is delayed due to the response delay of the characteristic shift, even though the shift request is generated. Can be considered. In addition, when the electromotive force characteristic of the sensor element 31 is shifted to the rich side, the feedback correction value is changed to the increase side due to the response delay of the characteristic shift even though the shift request is generated. It can be delayed. In this regard, the configuration is such that the applied current is increased to the positive side (the side that increases the lean shift amount) when shifting to the lean side, and the applied current is increased to the negative side (the side that increases the rich shift amount) when shifting to the rich side. Therefore, the deviation of the feedback correction value due to the response delay of the characteristic shift can be corrected appropriately.

  It is considered that as the change width (required shift amount) of the applied current is larger, the delay time until shifting to the desired electromotive force characteristic is increased. In this respect, since the correction value of the applied current is set based on the change width (required shift amount) of the applied current, the increase / decrease correction of the applied current can be appropriately performed according to the necessary situation.

  When the current application to the sensor element 31 is performed to shift the electromotive force characteristic, the electromotive force characteristic gradually shifts to a desired characteristic with a delay in response. In this case, since the current correction value after the start of current application is gradually decreased within the correction period, the applied current correction can be performed while corresponding to the actual shift state of the electromotive force characteristics. Thereby, appropriate applied current correction can be implemented.

(Second Embodiment)
Next, the second embodiment will be described focusing on differences from the first embodiment. In the present embodiment, the microcomputer 41 performs a shift from one to the other of the first characteristic when the current is not applied to the sensor element 31 and the second characteristic when the current is applied. The “first process” and the “second process” for performing the shift from one of the lean shift characteristic and the rich shift characteristic to the other in the second characteristic are performed. That is, when a lean shift request or a rich shift request occurs during the execution of the stoichiometric control, the microcomputer 41 applies a current according to the request to the sensor element 31 to shift the electromotive force characteristic (first step). Equivalent to one process). Further, when a request for a rich shift occurs during the lean shift of the electromotive force characteristics, or when a request for a lean shift occurs during the rich shift of the electromotive force characteristics, the microcomputer 41 outputs a current corresponding to the request to the sensor element. The process (equivalent to a 2nd process) which applies to 31 and shifts an electromotive force characteristic is implemented.

  When the electromotive force characteristic is shifted by the second process, the λ inflection point is changed from the lean side to the rich side or vice versa across the stoichiometry. Here, when the λ inflection point straddles the stoichiometry (second process), the characteristic is obtained even when the required shift amount is the same as compared with the case where the λ inflection point does not straddle the stoichiometry (first process). It is thought that the delay of the shift becomes large. Therefore, in this embodiment, the degree of increase / decrease correction of the applied current with respect to the required shift amount of the electromotive force characteristic is changed according to which of the first process and the second process is performed.

  FIG. 12 is a time chart specifically showing an operation when the air-fuel ratio control is switched from the stoichiometric control to the lean control and then switched to the rich control.

  In FIG. 12, the stoichiometric feedback control is performed before the timing t11, and the applied current is zero. At a timing t11, a predetermined applied current is applied to the sensor element 31 based on the lean shift request. At this time, a positive current correction value is calculated based on the change width ΔI1 of the applied current, and the applied current is corrected by the current correction value. The current correction value may be calculated based on the correlation L1 for the first process in FIG.

  Then, in the correction period from timing t11 to t12, the correction of the applied current is performed using the current correction value, and the correction ends at timing t12 when the current correction value becomes zero.

  Further, at timing t13, a request for changing the air-fuel ratio control from lean control to rich control (a rich shift request across the stoichiometry) is generated. In this case, at the timing t13, the applied current is corrected based on the change width ΔI2 of the applied current. The current correction value may be calculated based on the correlation L2 for the second process in FIG. In FIG. 13, the correlation L <b> 2 has a larger degree of increase / decrease correction with respect to the required shift amount (change width of applied current) of the electromotive force characteristics than the correlation L <b> 1.

  In the correction period from timing t13 to t14, correction of the applied current is performed using the current correction value that is gradually reduced, and the correction ends at timing t14 when the current correction value becomes zero.

  As described above, according to the second embodiment, the first process for shifting the electromotive force characteristic with stoichiometric rich and lean and the second process for shifting the electromotive force characteristic with lean and rich can be performed. Even if any of stoichiometric control, lean control, and rich control is performed, it is possible to shift to any desired electromotive force characteristics.

  In addition, since the degree of increase / decrease correction of the applied current with respect to the required shift amount of the electromotive force characteristic is changed depending on which of the first process and the second process is performed, a more appropriate treatment can be realized.

  Unlike the above, the λ inflection point does not straddle the stoichiometric (first process) and the λ inflection point straddles the stoichiometric (second process) with respect to the required shift amount of the electromotive force characteristic. The degree of increase / decrease correction of the applied current may be the same. In addition, when the λ inflection point does not straddle the stoichiometry (first process), the applied current increases or decreases with respect to the required shift amount of the electromotive force characteristics as compared with the case where the λ inflection point straddles the stoichiometry (second process). The degree of correction may be increased.

(Other embodiments)
You may change the said embodiment as follows, for example.

  -It is considered that the longer the change width (required shift amount) of the applied current, the longer the delay time until shifting to the desired electromotive force characteristics. In view of this point, the correction period for correcting the applied current may be variably set based on the change width (required shift amount) of the applied current. Specifically, in step S15 in FIG. 8, the length of the correction period is set using the relationship in FIG. In FIG. 14, a relationship is set such that the length of the correction period increases as the amount of shift to the lean side or the rich side increases. Thereby, the increase / decrease correction of the applied current can be appropriately performed according to the necessary situation.

  Both the process of setting the current correction value variably based on the change width (requested shift amount) of the applied current and the process of setting the correction period variably based on the change width (requested shift amount) of the applied current are both performed. The structure to implement may be sufficient.

  In the case where the applied current is temporarily corrected when the current application to the sensor element 31 is started, a configuration in which a constant amount of current correction value is used throughout the correction period (a configuration in which the initial value is continuously used) may be employed. In addition, instead of setting the current correction value variably based on the change width of the applied current or the required shift amount of the electromotive force characteristics, a configuration using a predetermined current correction value determined in advance may be used. .

  As an O2 sensor having a gas diffusion resistance portion, a configuration having a pinhole of a predetermined diameter may be used instead of the configuration having a gas diffusion resistance layer having a predetermined thickness.

  The gas sensor may be a so-called two-cell gas sensor including an electromotive force cell and a pump cell in addition to the O2 sensor having the above configuration. In this case, the electromotive force characteristics of the electromotive force cell of the two-cell gas sensor can be suitably changed, and proper air-fuel ratio detection can be realized. Further, as the electromotive force cell (sensor element), it is also possible to use a laminated type structure in addition to the cup type structure.

  DESCRIPTION OF SYMBOLS 10 ... Engine (internal combustion engine), 16 ... O2 sensor (gas sensor), 31 ... Sensor element (electromotive force cell), 32 ... Solid electrolyte layer, 33 ... Exhaust side electrode, 34 ... Air side electrode, 41 ... Microcomputer (characteristic control) Means, current correction means), 43... Constant current circuit (energization means).

Claims (7)

An electromotive force cell (31) including a solid electrolyte body (32) and a pair of electrodes (33, 34) provided at a position sandwiching the solid electrolyte body, and detecting exhaust of the internal combustion engine (10) as a detection target A gas sensor control device (41) applied to a gas sensor (16) for outputting an electromotive force signal corresponding to an air-fuel ratio of the exhaust,
A predetermined current can be applied between the pair of electrodes of the electromotive force cell by the energizing means (43),
Characteristic control means for performing current application by the energization means based on a required value of an applied current applied to the electromotive force cell, and shifting the electromotive force characteristics of the electromotive force cell;
Current correction means for temporarily correcting the applied current from the required value to the increase side or the decrease side according to the mode of current application when starting the current application by the energization means;
A gas sensor control device comprising:   The current correction means, when the current application by the energization means shifts the electromotive force characteristic to the lean side, temporarily corrects the applied current to the side to increase the lean side shift amount, 2. The gas sensor control device according to claim 1, wherein when the current application by the energizing means shifts the electromotive force characteristic to the rich side, the applied current is temporarily corrected to a side to increase the rich side shift amount. .   The gas sensor control device according to claim 1, further comprising a correction value setting unit configured to set a correction value of the applied current by the current correction unit based on a change width of the applied current or a required shift amount of the electromotive force characteristic. .   4. The apparatus according to claim 1, further comprising a period setting unit that sets a length of a correction period for correcting the applied current by the current correcting unit based on a change width of the applied current or a required shift amount of the electromotive force characteristic. The gas sensor control device according to claim 1.   5. The current correction means sets an initial value of a correction value for correcting the applied current at the start of current application by the energization means, and thereafter gradually reduces the correction value within a correction period. The gas sensor control device according to any one of the above.   The characteristic control means includes a first process for performing a shift from one of the first characteristic when the current is not applied by the energization means and the second characteristic when the current is applied to the other. 6. The gas sensor according to claim 1, wherein in the second characteristic, a second process for performing a shift from one of a lean shift characteristic and a rich shift characteristic to the other can be respectively performed. Control device.   The current correction unit changes a degree of increase / decrease correction of the applied current with respect to the required shift amount of the electromotive force characteristic depending on whether the first process or the second process is performed by the characteristic control unit. The gas sensor control device according to claim 6.

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