JP2017003463A - Gas sensor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor control device which has a simplified configuration and designed to properly control voltage across a pair of electrodes of a sensor element.SOLUTION: A sensor element 10 comprises a solid electrolyte layer and a pair of electrodes that sandwiches the solid electrolyte layer, and is configured to output element current corresponding to concentration of a predetermined component of a detection target gas when a voltage is applied across the pair of electrodes. A sensor control circuit 30, while applying the voltage across the pair of electrodes of the sensor element 10, temporarily stops applying voltage and then calculates an element voltage Vx, as a voltage across the pair of electrodes while the voltage application is halted. The sensor control circuit controls application voltage VP to be applied across the pair of electrodes based on the element voltage Vx.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gas sensor control device.

  For example, an oxygen concentration sensor (A / F sensor) that detects an oxygen concentration in exhaust gas is known as a gas sensor that detects the concentration of exhaust components of an internal combustion engine. This A / F sensor has a solid electrolyte such as zirconia and a pair of electrodes provided on the surface thereof, and in a state where a predetermined voltage difference is generated between the pair of electrodes, the oxygen concentration in the exhaust gas is controlled. Accordingly, device currents of different magnitudes are output. In this case, for example, a predetermined voltage difference is generated between the pair of electrodes by controlling the voltage applied to the A / F sensor. Then, the air-fuel ratio is obtained based on the element current.

  In the A / F sensor, it is known that the limit current region for detecting the element current shifts to a higher voltage side as the air-fuel ratio becomes leaner, and according to the air-fuel ratio in order to detect the element current accurately. Various techniques for variably setting the applied voltage have been proposed. For example, on the VI characteristic of the A / F sensor, an applied voltage line (applied voltage map) composed of a linear line is determined, and the applied voltage is increased to the higher voltage side as the air-fuel ratio becomes leaner based on the applied voltage line. The technology to shift to is known.

  In addition, as a technique for constructing a sensor control circuit using an ASIC (dedicated IC), the slope of the applied voltage line and the applied voltage (origin voltage) when the element current becomes zero can be changed by changing the hardware constant outside the ASIC. There is known a technique that can be arbitrarily set by (see Patent Document 1). According to such a technique, even when sensor elements having different output characteristics are used, a sensor control circuit can be constructed using a common ASIC. Therefore, it is not necessary to change the ASIC for each A / F sensor model, and the degree of freedom in handling can be increased.

JP 2008-203101A

  In the above-mentioned prior art, even when the A / F sensor type is different, it is possible to cope with it. However, setting for hardware constants outside the ASIC is required for each type. Work exists. Therefore, it is considered that there is room for improvement in order to achieve further simplification.

  The present invention has been made in view of the above circumstances, and its main object is to provide a gas sensor control device capable of appropriately performing voltage control between a pair of electrodes in a sensor element while simplifying the configuration. There is to do.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  The gas sensor control device of the present invention includes a sensor element (10) having a solid electrolyte layer (11) and a pair of electrodes (15, 16) provided so as to sandwich the solid electrolyte layer (11), and a predetermined voltage between the pair of electrodes. A gas sensor that outputs an element current corresponding to the concentration of a predetermined component in the gas to be detected in a state where a difference occurs is a control target. Then, the gas sensor control device includes an energization stop unit that temporarily stops energization from a state in which energization between the pair of electrodes is performed, and after the energization stop unit stops energization, An element voltage calculation unit that calculates an element voltage (Vx) that is a voltage between the pair of electrodes, and a voltage difference that is generated between the pair of electrodes is controlled based on the element voltage calculated by the element voltage calculation unit. Voltage control means.

  In a sensor element having a solid electrolyte layer and a pair of electrodes, an electrode interface capacitance exists between the solid electrolyte layer and each electrode. Therefore, charges are stored in the electrode interface capacitance in the energized state of the sensor element, and the charges stored in the electrode interface capacitance remain for a while after the energization is stopped. That is, in the energized state, in the sensor element, a voltage (VC + VR) obtained by adding the voltage VR at the DC resistance of the solid electrolyte layer or the electrode and the voltage VC at the electrode interface capacitance is generated between the pair of electrodes. Immediately after stopping, only the voltage VC at the electrode interface capacitance is generated between the pair of electrodes in the sensor element. In this case, the voltage VC corresponds to a voltage that generates a limit current in the limit current characteristic that is the VI output characteristic of the sensor element, and a desired limit current is determined depending on whether or not the voltage VC is appropriate. Whether or not the voltage difference between the pair of electrodes is an appropriate value can be determined.

  According to the above configuration, after the energization is stopped from the state of energization between the pair of electrodes, the element voltage that is the voltage between the pair of electrodes in the energization stop state is calculated, and based on the element voltage Thus, the voltage difference generated between the pair of electrodes is controlled. In this case, according to the element voltage after the energization is stopped, it is possible to appropriately grasp the deviation of the voltage difference between the electrodes in the limit current region. In particular, since the voltage difference between the electrodes can be optimized without depending on the magnitude of the direct current resistance, it is not necessary to set constants for voltage control. As a result, voltage control between the pair of electrodes can be appropriately performed in the sensor element while simplifying the configuration.

The block diagram which shows the electrical constitution of a sensor control circuit. Sectional drawing which shows the structure of a sensor element. The figure which shows the output characteristic of a sensor element. The figure which shows the principal part structure of a sensor element, and the equivalent circuit corresponding to the principal part structure. The figure which shows the equivalent circuit of a sensor element. The figure which shows the output characteristic of a sensor element. Explanatory drawing for demonstrating the outline | summary of the applied voltage control of a sensor element. The flowchart which shows the process sequence of applied voltage control. The time chart which shows the change of the voltage difference between electrodes, and element current. The flowchart which shows the process sequence of electric current detection. Explanatory drawing for demonstrating the applied voltage control in case an air fuel ratio changes. Explanatory drawing for demonstrating the applied voltage control in case element temperature changes. The block diagram which shows the electrical constitution of a sensor control circuit in 2nd Embodiment. The flowchart which shows the process sequence of current control in 2nd Embodiment. The time chart which shows the change of the voltage difference between electrodes and element current in 2nd Embodiment. The figure which shows the relationship between the voltage difference of an element voltage and a target value, and a voltage change amount. Explanatory drawing regarding the upper limit setting of an applied voltage.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings. The present embodiment embodies an air-fuel ratio detection device that detects the oxygen concentration (air-fuel ratio: A / F) in the exhaust gas using exhaust gas discharged from an on-vehicle engine (internal combustion engine) as a detected gas. This detection result is used in an air-fuel ratio control system constituted by an engine ECU or the like. In the air-fuel ratio control system, stoichiometric air-fuel ratio control for feedback control of the air-fuel ratio in the vicinity of the stoichiometric control, lean air-fuel ratio control for feedback control of the air-fuel ratio in a predetermined lean region, and the like are appropriately performed.

(First embodiment)
First, the element structure of the A / F sensor will be described with reference to FIG. This A / F sensor is provided in the exhaust pipe of the engine, and generates sensor output corresponding to the oxygen concentration in the exhaust gas with the exhaust gas flowing in the exhaust pipe as a detection target. The A / F sensor includes a sensor element 10 having a solid electrolyte layer and flowing an element current corresponding to the oxygen concentration in the exhaust gas in a voltage applied state. FIG. 2 shows a sensor element having a stacked structure. 10 shows a cross-sectional configuration. The sensor element 10 is actually formed in a long shape extending in the direction orthogonal to the paper surface of FIG. 2, and the entire element is accommodated in a housing or an element cover.

  The sensor element 10 includes a solid electrolyte layer 11, a diffusion resistance layer 12, a shielding layer 13, and an insulating layer 14, which are stacked on the top and bottom of the drawing. A protective layer (not shown) is provided around the element. The rectangular solid electrolyte layer 11 is a partially stabilized zirconia sheet, and a pair of upper and lower electrodes 15 and 16 are disposed opposite to each other with the solid electrolyte layer 11 interposed therebetween. Of the pair of electrodes 15 and 16, the electrode 15 is an exhaust side electrode, and the electrode 16 is an atmosphere side electrode. The diffusion resistance layer 12 is made of a porous sheet for introducing exhaust gas to the electrode 15, and the shielding layer 13 is made of a dense layer for suppressing permeation of exhaust gas. The diffusion resistance layer 12 is provided with an exhaust chamber 17 so as to surround the electrode 15. Both the diffusion resistance layer 12 and the shielding layer 13 are made of a ceramic such as alumina, spinel, zirconia or the like by a sheet molding method or the like, but have different gas permeability due to differences in the average pore diameter and porosity of the porosity. It has become. The diffused resistance layer 12 may be configured by forming pinholes.

  The insulating layer 14 is made of a highly thermally conductive ceramic such as alumina, and an air duct 18 as an air chamber is formed at a portion facing the electrode 16. A heater 19 is embedded in the insulating layer 14. The heater 19 is composed of a linear heating element that generates heat when energized from a battery power source, and heats the entire element by the generated heat.

  In the sensor element 10 having the above-described configuration, the surrounding exhaust gas is introduced from the side portion of the diffusion resistance layer 12, then flows into the exhaust chamber 17 through the diffusion resistance layer 12, and reaches the electrode 15. When the exhaust gas is lean, oxygen in the exhaust gas is decomposed by the electrode 15 and discharged from the electrode 16 to the atmospheric duct 18. On the other hand, when the exhaust is rich, oxygen in the atmospheric duct 18 is decomposed by the electrode 16 and discharged from the electrode 15 to the exhaust side.

  In this embodiment, the exhaust electrode 15 is a negative electrode and the atmospheric electrode 16 is a positive electrode. As shown in FIG. 2, the electrode 15 is negative (−) and the electrode 16 is positive (+). The applied voltage VP applied between them is a positive voltage. Therefore, conversely, the applied voltage VP applied between these electrodes with the electrode 15 being positive (+) and the electrode 16 being negative (-) is a negative voltage.

  FIG. 3 is a diagram showing output characteristics (VI characteristics) of the sensor element 10. In FIG. 3, a characteristic line representing a relationship of the element current IL with respect to the applied voltage VP of the sensor element 10 is shown with the horizontal axis representing voltage and the vertical axis representing current. In the characteristic line of FIG. 3, a straight line portion substantially parallel to the voltage axis that is the horizontal axis is a limit current region that specifies the element current IL as the limit current, and the increase or decrease of the element current IL is the increase or decrease of the air-fuel ratio, that is, the lean.・ It corresponds to the degree of richness. That is, the element current IL increases as the air-fuel ratio becomes leaner, and the element current IL decreases as the air-fuel ratio becomes richer. Further, in the above characteristic line, the lower voltage side than the limit current region is a resistance dominant region that passes through the origin of the VI coordinate and has a slope that depends on the magnitude of the DC resistance Ri of the sensor element 10.

  In the sensor element 10, an appropriate applied voltage VP is determined according to each air-fuel ratio, and the element current IL is detected in a voltage application state of the applied voltage VP. In other words, the limit current region is substantially parallel to the voltage axis as described above, but in detail is slightly raised to the right. In addition, the VI characteristic has a slope corresponding to the DC resistance Ri of the sensor element 10. In this case, in order to accurately detect the air-fuel ratio based on the element current IL, it is necessary to set the applied voltage VP appropriately. For example, as shown in FIG. 3, the applied voltage VP is determined for each air-fuel ratio. Yes. Note that the applied voltage VP at each air-fuel ratio is preferably determined on a straight line L having the same slope as the resistance-dominated region.

  In the present embodiment, focusing on the fact that there is an electrode interface capacitance between the solid electrolyte layer 11 and each of the electrodes 15 and 16 in the sensor element 10, the voltage application is stopped from the voltage application state to the sensor element 10. Later, the applied voltage is controlled based on the voltage (element voltage) generated by the sensor element 10 caused by the charge accumulated in the electrode interface capacitance. The details will be described below.

  First, the configuration of the sensor element 10 will be described again with reference to FIG. FIG. 4 is a diagram showing a main configuration of the sensor element 10 and an equivalent circuit corresponding to the main configuration.

  As shown in FIG. 4, the sensor element 10 is configured by laminating a solid electrolyte layer 11 made of zirconia ZrO2, electrodes 15 and 16 on both sides thereof, and a diffusion resistance layer 12 that restricts the diffusion of exhaust gas. . In this case, the sensor element 10 can be represented by an equivalent circuit composed of a resistor and a capacitor. In this equivalent circuit, Rp1 and Rp2 are electrode lead resistances of the atmosphere side electrode 16 and the exhaust side electrode 15, respectively. Rg is the particle resistance of the solid electrolyte layer 11. Rf1 and Cf1 are the electrode interface resistance and electrode interface capacitance on the electrode 16 side, respectively, and Rf2 and Cf2 are the electrode interface resistance and electrode interface capacitance on the electrode 15 side, respectively.

  Further, when the equivalent circuit of FIG. 4 is simplified, it can be represented as shown in FIG. Rp is an electrode lead resistance, Rg is a particle resistance of the solid electrolyte layer 11, and Rf and Cf are an electrode interface resistance and an electrode interface capacitance, respectively. In this equivalent circuit, the voltage VR is applied to the electrode lead resistance Rp and the particle resistance Rg of the solid electrolyte layer 11 under the condition that a voltage is applied between the pair of electrodes 15 and 16, and the electrode interface resistance Rf and the electrode interface capacitance are applied. The voltage VC is applied to the parallel circuit of Cf.

  Here, in the voltage application state with respect to the pair of electrodes 15, 16, the applied voltage VP has a voltage value corresponding to “VR + VC”. In this voltage application state, charges are stored in the electrode interface capacitance Cf. When the voltage application is stopped from that state, the charge stored in the electrode interface capacitance remains for a while after the voltage application is stopped, and the applied voltage VP shifts to a voltage corresponding to the charge. That is, in the voltage application state, a pair of voltages (VC + VR) obtained by adding the voltage VR applied to the DC resistance of the solid electrolyte layer 11 and the electrodes 15 and 16 and the voltage VC applied to the electrode interface capacitance in the sensor element 10. However, immediately after the voltage application is stopped, only the voltage VC applied to the electrode interface capacitance in the sensor element 10 is generated between the pair of electrodes 15 and 16. In this case, the voltage VC corresponds to a voltage that generates a limit current in the limit current characteristic that is the VI output characteristic of the sensor element 10, and a desired limit current depends on whether or not the voltage VC is appropriate. Whether or not the applied voltage is an appropriate value can be determined.

  This will be described on the VI characteristic of the sensor element 10. In FIG. 6, when the air-fuel ratio is A and VA is applied between the pair of electrodes 15 and 16 of the sensor element 10, the applied voltage VA is the voltage VR corresponding to the DC resistance and the voltage corresponding to the electrode interface capacitance. It corresponds to the added value with VC. When the voltage application between the pair of electrodes 15 and 16 is stopped from this state, the voltage VR corresponding to the DC resistance disappears and only the voltage VC corresponding to the electrode interface capacitance is obtained. In this case, the voltage VC represents a voltage application position in the limit current region α, in other words, whether or not current detection is performed at a desired position in the limit current region α.

  Here, the limit current region α is a substantially flat region, but actually has a slight inclination. Therefore, if the voltage application position in the limit current region α is deviated from a desired position, the current detection value may be deviated, and as a result, an error may occur in the air-fuel ratio detection value.

  Therefore, in the present embodiment, after the voltage application is stopped from the state in which the voltage is applied between the pair of electrodes 15 and 16 of the sensor element 10, the element is the voltage between the pair of electrodes 15 and 16 in the state where the voltage application is stopped. The voltage is calculated, and the applied voltage VP is controlled based on the element voltage. In this case, in particular, the applied voltage VP is feedback-controlled so that the element voltage matches a predetermined target value.

  An outline of feedback control of the applied voltage VP will be described with reference to FIG. In a state where the air-fuel ratio is A and VA1 is applied between the pair of electrodes 15 and 16 of the sensor element 10, the voltage corresponding to the DC resistance is VR, and the voltage corresponding to the electrode interface capacitance is VC1. If the voltage VC1 is detected by stopping the voltage application from this state and the voltage VC1 is smaller than the target value Vtg, the applied voltage VP is increased to the increasing side VA2 according to the difference between the voltage VC1 and the target value Vtg. Be changed. In this case, since the voltage corresponding to the electrode interface capacitance becomes VC2 which is the same as the target value Vtg, current detection is performed at a desired position in the limit current region α. The target value Vtg is, for example, 0.4V.

  Next, a sensor control circuit 30 that realizes the main configuration of the present embodiment will be described with reference to FIG.

  As an outline, the sensor control circuit 30 is connected to the sensor element 10 via a positive side terminal S + connected to the atmosphere side electrode 16 of the sensor element 10 and a negative side terminal S− connected to the exhaust side electrode 15. Yes. The sensor control circuit 30 detects the element current IL flowing through the sensor element 10 and the impedance of the sensor element 10, and outputs the detection result to the engine ECU 50. The engine ECU 50 grasps the air-fuel ratio of the exhaust based on the detection result of the element current IL and appropriately executes air-fuel ratio feedback control and the like, and performs energization control of the heater 19 based on the detection result of the element impedance.

  In the sensor control circuit 30, the AC signal generator 31, the amplifier 32, and the current detection are arranged on the negative terminal S− side of both terminals S + and S− as a configuration for detecting the element current IL and the element impedance. A resistor 33 is provided. The AC signal generation unit 31 outputs an AC signal having a predetermined frequency as an impedance detection signal, and the AC signal is combined with a reference voltage Vref (for example, 2.5 V) and output to the amplifier unit 32. In this case, the voltage on the amplifier unit 32 side at both ends of the current detection resistor 33 is changed in an alternating manner with the reference voltage Vref as a center.

  The element current IL flows through the current detection resistor 33, and the voltage on the sensor element 10 side, that is, the negative terminal voltage VS− changes in accordance with the element current IL at both ends of the current detection resistor 33. For example, when the exhaust gas is lean, current flows from the positive terminal S + to the negative terminal S− in the sensor element 10, so VS− rises. When rich, current flows from the negative terminal S− to the positive terminal S +. Therefore, VS- is lowered. In this case, the negative terminal voltage VS− is detected by the voltage detection unit 34, and the detection signal is input to the current detection unit 35 and the impedance detection unit 36, respectively. The current detection unit 35 detects the element current IL based on the negative terminal voltage VS−. The impedance detector 36 detects the element impedance based on the negative terminal voltage VS−.

  It supplements about impedance detection. In the state where the AC signal is output from the AC signal generation unit 31, the VS-detection signal output from the voltage detection unit 34 is AC-changed with an amplitude corresponding to the element impedance. The amplitude of the detection signal is detected, and a signal corresponding to the amplitude is output as an impedance detection signal. In this case, the engine ECU 50 calculates the element impedance from the amount of change in AC voltage and the amount of change in AC current.

  Further, in the sensor control circuit 30, the element voltage calculation unit 41, the applied voltage control unit 42, the amplifier unit 43, and the switch 44 are arranged on the positive terminal S + side as a configuration for controlling the voltage applied to the sensor element 10. Is provided. Among these, the switch 44 is provided in a voltage application path (that is, an energization path) for the sensor element 10 and is made of, for example, a semiconductor element. The switch 44 corresponds to the opening / closing means. When the switch 44 is closed, a predetermined voltage is applied to the sensor element 10 through the applied voltage control unit 42, and when the switch 44 is opened, the applied voltage to the sensor element 10 is cut off.

  The element voltage calculation unit 41 calculates an element voltage Vx corresponding to the voltage VC corresponding to the electrode interface capacitance of the sensor element 10 after the voltage application is stopped from the state in which the voltage is applied to the sensor element 10. Specifically, the element voltage calculation unit 41 detects the positive side terminal voltage VS + detected by the voltage detection unit 45 and the negative side terminal detected by the voltage detection unit 34 after the switch 44 is switched from on to off. The voltage VS− is input, and the element voltage Vx is calculated from the difference between VS + and VS−.

  The applied voltage control unit 42 compares the element voltage Vx with a target value, and increases or decreases the applied voltage VP based on the magnitude relationship. Thus, voltage feedback is performed so that the element voltage Vx matches the target value. The applied voltage VP output from the applied voltage control unit 42 is combined with a reference voltage Vref (for example, 2.5 V) and output to the amplifier unit 43.

  In the sensor control circuit 30, the functions of voltage application stop, element voltage calculation, and applied voltage control may be realized by executing a software program. In this case, the element voltage calculation unit 41 and the applied voltage control unit 42 are configured by a known microcomputer 40 having a CPU, various memories, an A / D converter, and the like, and are realized as an ASIC, for example. In the following, the details of the processing regarding applied voltage control performed in the sensor control circuit 30 will be described with reference to the flowchart of FIG. The process of FIG. 8 is performed by the microcomputer 40 at a predetermined cycle.

  In FIG. 8, in step S <b> 11, it is determined whether or not an execution condition for executing the feedback process of the applied voltage VP is satisfied. At this time, for example, the execution condition may be satisfied based on the fact that the elapsed time from the previous feedback processing has reached a predetermined time. The predetermined time is, for example, 1 to several msec. If the execution condition of the feedback process is satisfied, the process proceeds to step S12, and if not, the process proceeds to step S21. Note that, when feedback processing is performed as the execution condition is satisfied, the output of an AC signal for impedance detection is temporarily stopped.

  When the execution condition for the feedback process is not satisfied, when the process proceeds to step S21, the switch 44 is turned on (closed). In the subsequent step S22, voltage application to the sensor element 10 is performed with the application voltage VP determined at the present time.

  If the feedback processing execution condition is satisfied, it is determined in step S12 whether or not the switch 44 is currently turned on. If the switch 44 is turned on, the process proceeds to step S13. To the off (open) state.

  Thereafter, in step S14, it is determined whether or not the element voltage Vx can be stably calculated after the switch 44 is turned off. That is, when the switch 44 is switched from the on state to the off state, the internal voltage of the sensor element 10 fluctuates temporarily immediately after the switch 44 is turned off. Therefore, whether or not the element voltage Vx can be stably calculated is determined based on whether or not a predetermined time until the voltage fluctuation is settled after the switch 44 is turned off, that is, whether or not the stabilization waiting time has elapsed. Then, on condition that the element voltage Vx can be stably calculated, the process proceeds to step S15 to calculate the element voltage Vx. At this time, the element voltage Vx is calculated from the difference between the positive terminal voltage VS + and the negative terminal voltage VS−.

  Thereafter, in step S16, it is determined whether or not the element voltage Vx is smaller than the target value Vtg. In step S17, it is determined whether or not the element voltage Vx is larger than the target value Vtg. If Vx <Vtg, the process proceeds to step S18, and the applied voltage VP is changed to the increasing side. If Vx> Vtg, the process proceeds to step S19 to change the applied voltage VP to the decreasing side. At this time, for example, a fixed voltage change amount is determined, and a new applied voltage VP is calculated by adding or subtracting the voltage change amount to the applied voltage VP immediately before switching off. The voltage change amount may be calculated by calculating a deviation between the element voltage Vx and the target value Vtg and performing P feedback calculation or PI feedback calculation based on the deviation. Thereafter, in step S20, it is determined that the current feedback processing is to be temporarily terminated.

  If both steps S16 and S17 are negative, the process proceeds to step S20 without changing the applied voltage VP immediately before the switch is turned off, and it is determined that the current feedback process is temporarily ended. Thereafter, in step S21, the switch 44 is turned on, and in the subsequent step S22, voltage application to the sensor element 10 is performed with the application voltage VP determined at the present time.

  By the way, when the switch 44 is temporarily turned off as described above, the voltage difference between the pair of electrodes 15 and 16 of the sensor element 10 and the element current IL change as shown in FIG. That is, in FIG. 9, when the switch 44 is turned off at timing t1 and the switch 44 is turned on at timing t2, the voltage difference between the pair of electrodes 15 and 16 and the element current IL change as shown in the figure. In this case, a tailing phenomenon occurs in the element current IL when the switch 44 is switched from OFF to ON, and there is a concern that current detection accuracy may be reduced due to this phenomenon. Therefore, in the present embodiment, current detection is prohibited until a predetermined time Td elapses after the switch 44 is turned on, and current detection is performed after timing t3 when the predetermined time Td elapses.

  The current detection unit 35 may manage the period during which the detection of the element current IL is permitted and the period during which the element current IL is prohibited. In this case, the function of the current detection unit 35 is preferably realized as a software process of the microcomputer 40. Specifically, the element current IL is detected by the current detection process shown in FIG.

  In FIG. 10, in step S31, it is determined whether or not the switch 44 is currently on. In subsequent step S32, it is determined whether or not a predetermined time has elapsed since the switch 44 was switched from off to on. judge. If both steps S31 and S32 are YES, detection of the element current IL is permitted. That is, in step S33, the element current IL is detected based on the negative terminal voltage VS−, and then this process is temporarily terminated. If any of steps S31 and S32 is NO, the process is temporarily terminated without detecting the element current IL.

  Next, the specific contents of the applied voltage control will be described by exemplifying the case where the air-fuel ratio changes with the change of the engine operating state and the like, and the case where the temperature of the sensor element 10 changes. FIG. 11 is an explanatory diagram for explaining applied voltage control when the air-fuel ratio changes from A / F 18 to A / F 16, for example. FIG. 12 shows the temperature of the sensor element 10 from 700 ° C. to 600 ° C., for example. It is explanatory drawing for demonstrating the applied voltage control in the case of changing.

  Here, a configuration in which the element voltage Vx matches the target value Vtg by changing the applied voltage VP by a predetermined value in the feedback processing is illustrated. A black circle indicates the target value Vtg, and a white circle indicates the element voltage Vx before reaching the target value Vtg. Further, in FIG. 11 and FIG. 12, parenthesized numerals are attached to indicate the processing order.

  First, in FIG. 11, immediately after the change from A / F18 to A / F16, an applied voltage VP corresponding to A / F18 is applied, and the element voltage Vx after switch-off is the target value Vtg. It is a large value. Therefore, the applied voltage VP is changed to the decreasing side. The processing flow so far is (0) → (1) → (2) → (3).

  Thereafter, the element voltage Vx after the switch-off is compared with the target value Vtg again, and when the element voltage Vx is larger than the target value Vtg, the applied voltage VP is further changed to the decreasing side. The flow of this process is (3) → (4) → (5). Thereafter, the process of (3) → (4) → (5) is repeatedly performed as necessary until the element voltage Vx matches the target value Vtg.

  When the element voltage Vx coincides with the target value Vtg, the applied voltage VP is not changed and is maintained at the value at that time. The flow of this process is (5) → (6) → (7). When the element voltage Vx matches the target value Vtg, the voltage before stopping the voltage application is the target applied voltage, and the voltage (7) matches the voltage (5). Thereafter, every time the change in the air-fuel ratio occurs again, the same processing is performed following the change in the air-fuel ratio.

  In FIG. 12, the limit current region shifts along the voltage axis because the magnitude of the DC resistance Ri differs between the case where the element temperature is 700 ° C. and the case where the element temperature is 600 ° C. Therefore, even if the applied voltage VP is set at a desired position in the limit current region when the device temperature is 700 ° C., the applied voltage VP is changed to the desired current in the limit current region by changing the device temperature to 600 ° C. It will be out of position.

  In this case, immediately after the element temperature changes from 700 ° C. to 600 ° C., the element voltage Vx after the switch-off is a value smaller than the target value Vtg. Therefore, the applied voltage VP is changed to the increasing side. The processing flow so far is (0) → (1) → (2) → (3).

  Thereafter, the element voltage Vx after the switch-off is compared with the target value Vtg again. When the element voltage Vx is smaller than the target value Vtg, the applied voltage VP is further changed to the increasing side. The flow of this process is (3) → (4) → (5). Thereafter, the process of (3) → (4) → (5) is repeatedly performed as necessary until the element voltage Vx matches the target value Vtg.

  When the element voltage Vx coincides with the target value Vtg, the applied voltage VP is not changed and is maintained at the value at that time. The flow of this process is (5) → (6) → (7). As in FIG. 11, the voltage of (7) and the voltage of (5) are the same. Thereafter, every time the change in the element temperature occurs again, the same processing is performed following the change in the element temperature.

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

  After the voltage application is stopped from the state in which the voltage is applied between the pair of electrodes 15 and 16 in the sensor element 10, the element voltage Vx that is the voltage between the pair of electrodes 15 and 16 in the state where the voltage application is stopped is calculated. The applied voltage VP is controlled based on the element voltage Vx. In this case, according to the element voltage Vx after the voltage application is stopped, the deviation of the applied voltage VP in the limit current region can be properly grasped. In particular, since the applied voltage VP can be optimized without depending on the magnitude of the DC resistance Ri, it is not necessary to set a constant for controlling the applied voltage. As a result, the applied voltage control in the sensor element 10 can be appropriately performed while simplifying the configuration.

  For example, even if there are multiple types of A / F sensors and the output characteristics of each sensor are different, there is no need to prepare a separate sensor control circuit for each, and furthermore, setting work for each type of hardware constant outside the ASIC Is also unnecessary. That is, according to the above configuration, it is possible to cope with a plurality of types by common applied voltage control, and it is possible to realize cost reduction in terms of design and manufacturing.

  Further, in the above configuration, even when the element temperature is lowered, appropriate applied voltage control can be continued following the temperature drop. Therefore, it is possible to reduce the element temperature, and the heater power can be saved, so that an effect of power saving can be expected. Thereby, the fuel consumption improvement in a vehicle can also be aimed at.

  Since the feedback control of the applied voltage VP is performed so that the element voltage Vx detected immediately after the voltage application is cut off matches the target value Vtg, even if the applied voltage VP to the sensor element 10 deviates from an appropriate value, The applied voltage VP can be quickly returned to an appropriate value.

  When the switch 44 connected to one electrode of the sensor element 10 is shifted to the on state or the off state, voltage fluctuation temporarily occurs immediately after the switch is turned off. In this regard, in the above configuration, since the element voltage Vx is calculated immediately after the switch-off, when a predetermined stabilization wait time has elapsed, the element voltage Vx is appropriately set while avoiding the influence of the voltage fluctuation after the switch-off. Can be calculated.

  When the switch 44 is turned on after the switch 44 is temporarily turned off, the detection of the element current IL is started after a predetermined time has elapsed after the switch is turned on. Thereby, it is possible to suppress erroneous detection of the element current IL due to the occurrence of tailing immediately after the switch is turned on.

(Second Embodiment)
Next, a second embodiment will be described. In the following description, the same components as those in the above-described embodiment are denoted by the same reference numerals, and overlapping descriptions are omitted as appropriate.

  In the first embodiment, by controlling the applied voltage between the pair of electrodes 15 and 16 in the sensor element 10, a predetermined potential difference is generated between the pair of electrodes 15 and 16, and the element current IL is changed in this state. In the present embodiment, the above-described configuration is changed and a current supply amount between the pair of electrodes 15 and 16 is controlled to cause a predetermined potential difference between the pair of electrodes 15 and 16. In this state, the device current IL is detected. Regarding the voltage control of the sensor element 10, the voltage between the pair of electrodes 15 and 16 in a state where the current supply is stopped after the current supply is stopped from the current supply state (energized state) between the pair of electrodes 15 and 16. A certain element voltage Vx is calculated, and a voltage difference between the pair of electrodes 15 and 16 is controlled based on the element voltage Vx.

  FIG. 13 is a configuration diagram of the sensor control circuit 30 in the present embodiment. 13 will be described focusing on the differences from FIG.

  In FIG. 13, a reference voltage generation unit 61, an amplifier unit 32, and a current detection resistor 33 are provided on the negative terminal S− side of the sensor control circuit 30. The reference voltage generation unit 61 generates and outputs a predetermined reference voltage Vref.

  On the positive terminal S + side, as a configuration for controlling the amount of current supplied to the sensor element 10, an element voltage calculation unit 41, a current control unit 62, an AC signal generation unit 63, and a V-I conversion unit 64 are provided. An amplifier unit 43 and a switch 44 are provided. The current control unit 62 calculates and outputs an instruction voltage Vin corresponding to the amount of current supplied to the sensor element 10. The AC signal generation unit 63 outputs an AC signal having a predetermined frequency as an impedance detection signal. Then, the instruction voltage Vin of the current control unit 62 and the AC signal of the AC signal generation unit 63 are combined and output to the VI conversion unit 64. The V-I converter 64 converts an alternating voltage into an alternating current, and the converted alternating current is supplied to the sensor element 10 via the switch 44.

  When the switch 44 is turned on (closed state), current is supplied to the sensor element 10 based on the instruction voltage Vin (corresponding to the current supply amount) output from the current control unit 62. Moreover, the current supply to the sensor element 10 is stopped by turning off the switch 44 (open state).

  The element voltage calculation unit 41 calculates an element voltage Vx corresponding to the voltage VC corresponding to the electrode interface capacitance of the sensor element 10 after the supply of current to the sensor element 10 is stopped. Specifically, the element voltage calculation unit 41 detects the positive side terminal voltage VS + detected by the voltage detection unit 45 and the negative side terminal detected by the voltage detection unit 34 after the switch 44 is switched from on to off. The voltage VS− is input, and the element voltage Vx is calculated from the difference between VS + and VS−.

  The current control unit 62 compares the element voltage Vx with the target value, and increases or decreases the instruction voltage Vin based on the magnitude relationship. Thus, feedback processing is performed so that the element voltage Vx matches the target value.

  In the sensor control circuit 30, the functions of stopping the current supply, calculating the element voltage, and controlling the current may be realized by executing a software program. In this case, the element voltage calculation unit 41 and the current control unit 62 are configured by a known microcomputer 60 having a CPU, various memories, an A / D converter, and the like, and are realized as an ASIC, for example. Hereinafter, detailed processing contents regarding the current control performed in the sensor control circuit 30 will be described with reference to the flowchart of FIG. The process of FIG. 14 is performed by the microcomputer 60 at a predetermined cycle. Note that the process of FIG. 14 is obtained by changing a part of the process of FIG.

  In FIG. 14, steps S41 to S45 are the same as steps S11 to S15 of FIG. 8, and the switch 44 is temporarily turned off when the execution condition for executing the feedback processing of the instruction voltage Vin is satisfied. The device voltage Vx is calculated from the difference between VS + and VS− in a stable state after switching off.

  Thereafter, in step S46, it is determined whether the element voltage Vx is smaller than the target value Vtg. In step S47, it is determined whether the element voltage Vx is larger than the target value Vtg. If Vx <Vtg, the process proceeds to step S48, and the instruction voltage Vin is changed to the increase side. If Vx> Vtg, the process proceeds to step S49 and the instruction voltage Vin is changed to the decreasing side. At this time, for example, a predetermined voltage change amount is determined, and a new instruction voltage Vin is calculated by adding or subtracting the voltage change amount to the instruction voltage Vin immediately before switching off. The voltage change amount may be calculated by calculating a deviation between the element voltage Vx and the target value Vtg and performing P feedback calculation or PI feedback calculation based on the deviation. Thereafter, in step S50, it is determined that the current feedback processing is to be temporarily terminated.

  If both steps S46 and S47 are negative, the process proceeds to step S50 without changing the instruction voltage Vin immediately before the switch is turned off, and it is determined that the current feedback process is once ended. Thereafter, in step S51, the switch 44 is turned on, and in the subsequent step S52, current supply to the sensor element 10 is performed with the instruction voltage Vin determined at the present time.

  By the way, in the configuration in which the amount of current supplied to the sensor element 10 is controlled by the current control unit 62, when the switch 44 is turned on after the switch 44 is temporarily turned off, current tailing occurs at the beginning of the switch on. It is suppressed. That is, as shown in FIG. 15, when the switch 44 is turned off at the timing t11 and the switch 44 is turned on at the timing t12, the current control by the current control unit 62 starts from the beginning of the switch on, so that tailing occurs. Is suppressed. In this case, the current detection unit 35 starts detecting the element current IL from the beginning of the current supply after the switch 44 is turned on. Therefore, the period during which the element current IL cannot be detected is generally the period from t11 to t12 in FIG. 15, and the air-fuel ratio non-detection period can be shortened.

  In the present embodiment, in the configuration for controlling the amount of current supplied to the sensor element 10, the element voltage Vx in the energization cut-off state is calculated, and current control is performed so that the element voltage Vx matches the target value. Therefore, similarly to the first embodiment configured to control the applied voltage, the voltage difference between the pair of electrodes 15 and 16 in the sensor element 10 can be set to an appropriate value. Thereby, it is possible to appropriately detect the element current IL, that is, the air-fuel ratio, while simplifying the configuration.

  Although not shown in the figure, according to the current control described above, the current supply amount is adjusted by feeding back the element voltage Vx to the target value when the air-fuel ratio changes as the engine operating state changes. Is called. Thereby, the current supply amount is appropriately controlled while following the change in the air-fuel ratio. Even when the temperature of the sensor element 10 changes, the current supply amount is adjusted by feeding back the element voltage Vx to the target value. Thereby, the current supply amount is appropriately controlled while following the change in the element temperature.

(Other embodiments)
For example, the above embodiments may be modified as follows.

  When the applied voltage VP is changed by a predetermined value based on the difference between the element voltage Vx and the target value Vtg in steps S18 and S19 in FIG. 8, the change amount of the applied voltage VP is set to the element voltage Vx and the target value Vtg. When the difference is small, it may be configured to be smaller than when the difference is large. In this case, for example, the voltage change amount may be set based on the voltage difference between the element voltage Vx and the target value Vtg using the relationship of FIG. If the change amount of the applied voltage VP is small when the difference between the element voltage Vx and the target value Vtg is small compared to when the difference is large, the relationship of FIG. 16 is arbitrary, and the voltage difference It is also possible to determine the voltage change amount more finely.

  By making the change amount of the applied voltage VP variable according to the difference between the element voltage Vx and the target value Vtg, even if the difference between the element voltage Vx and the target value Vtg is relatively large, the target value Vtg is reached. Can be accelerated. Further, when the difference between the element voltage Vx and the target value Vtg is relatively small, it is possible to increase the accuracy with which the element voltage Vx matches the target value Vtg.

  Note that when the instruction voltage Vin is changed by a predetermined value based on the difference between the element voltage Vx and the target value Vtg in steps S48 and S49 in FIG. 14, the change amount of the instruction voltage Vin is changed to the element voltage Vx and the target value Vtg. It is good also as a structure made small when compared with the case where the difference is large when the difference with is small.

  When determining whether or not the execution condition of the feedback process is satisfied in step S11 of FIG. 8 or step S41 of FIG. 14, the execution condition is satisfied when the air-fuel ratio changes due to the change of the engine operating state. You may make it determine that. Specifically, when the target air-fuel ratio of the air-fuel ratio feedback control is changed from stoichiometric to either a lean value or a rich value, or vice versa, it is determined that the conditions for executing the feedback processing are satisfied.

  Further, when determining whether or not the execution condition of the feedback processing is successful in step S11 of FIG. 8 or step S41 of FIG. 14, the execution condition is in a state where the temperature change of the sensor element 10 occurs due to the change of the engine operating state. It may be determined that is established. Specifically, it is determined that the conditions for performing the feedback process are satisfied when the exhaust temperature increases in response to a request for acceleration of the vehicle or when the exhaust temperature decreases due to fuel cut during vehicle deceleration.

  When the air-fuel ratio changes or the temperature of the sensor element 10 changes with a change in the engine operating state, the applied voltage VP or current supply amount to the sensor element 10 shifts due to this. In this case, it is determined that the change in the air-fuel ratio due to the change in the engine operating state or the change in the element temperature occurs, and the feedback processing is performed based on the determination result. The feedback process can be implemented. If the switch-off is performed more than necessary for the feedback processing, the detection of the element current IL and the interruption of the impedance detection increase, and there is a concern about the influence on each detection. However, the feedback processing is appropriately performed. Thus, the influence on the detection of the element current IL and the impedance detection can be suppressed.

  When changing to the side where the voltage difference between the pair of electrodes 15 and 16 is increased, it is determined whether or not the voltage difference has reached a predetermined upper limit voltage, and it is determined that the voltage difference has reached the upper limit voltage. In such a case, the increase in voltage difference may be stopped. For example, when the temperature of the sensor element 10 decreases, as shown in FIG. 17, the slope of the VI characteristic decreases, and the limiting current region (flat region) shifts to the high voltage side. In this case, if the applied voltage VP is increased until the element voltage Vx matches the target value, the applied voltage VP becomes excessively large, and there is a concern that the sensor element 10 may be in trouble such as blackening. Therefore, for example, 1V is set as the upper limit value, and the feedback process is stopped when the applied voltage VP reaches the upper limit value.

  Specifically, the microcomputer 40 of the sensor control circuit 30 determines whether or not the applied voltage VP has reached the upper limit value in step S18 of FIG. 8, and when the applied voltage VP has reached the upper limit value, The increase in the applied voltage VP is stopped. When the applied voltage VP reaches the upper limit value, the applied voltage VP may be fixed to a predetermined value (for example, 0.4 V).

  Similarly, in FIG. 14, in step S <b> 48, it is determined whether or not the instruction voltage Vin has reached the upper limit value. When the instruction voltage Vin has reached the upper limit value, the increase in the instruction voltage Vin is stopped. Good.

  The target value Vtg of the element voltage Vx can be set for each air-fuel ratio. In this case, relationship data defining the relationship between the air-fuel ratio and the target value Vtg is prepared in advance, and the target value Vtg is set for each air-fuel ratio using the relationship data.

  In addition to the A / F sensor that can detect the oxygen concentration, the present invention can also be applied to a gas sensor that can detect other gas concentration components such as NOx and HC. For example, it has a plurality of cells formed of a solid electrolyte layer, of which the first cell (pump cell) discharges or draws out oxygen in the gas to be detected and detects the oxygen concentration, and the second cell (sensor cell) The present invention can be applied to a gas sensor that detects the gas concentration of a specific component (NOx, HC, etc.) from the gas after oxygen discharge.

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

  DESCRIPTION OF SYMBOLS 10 ... Sensor element, 11 ... Solid electrolyte layer, 15, 16 ... Electrode, 30 ... Sensor control circuit (gas sensor control apparatus).

Claims (9)

A sensor element (10) having a solid electrolyte layer (11) and a pair of electrodes (15, 16) provided so as to sandwich the solid electrolyte layer (11), and in a state where a predetermined voltage difference is generated between the pair of electrodes A gas sensor control device (30) that controls a gas sensor that outputs an element current according to the concentration of a predetermined component in a gas,
Energization stopping means for temporarily stopping energization from the state of energization between the pair of electrodes;
An element voltage calculating means for calculating an element voltage (Vx) which is a voltage between the pair of electrodes in the state of stopping the energization after stopping the energization by the energization stopping means;
Voltage control means for controlling a voltage difference generated between the pair of electrodes based on the element voltage calculated by the element voltage calculation means;
A gas sensor control device comprising:   The gas sensor control device according to claim 1, wherein the voltage control unit feedback-controls the voltage difference so that the element voltage calculated by the element voltage calculation unit matches a predetermined target value.   The voltage control means makes the change amount when changing the voltage difference smaller when the difference between the element voltage calculated by the element voltage calculation means and the target value is small than when the difference is large. Item 3. The gas sensor control device according to Item 2. Opening / closing means (44) connected to one of the pair of electrodes and opening / closing an energization path for the pair of electrodes,
The energization stop means stops the energization between the pair of electrodes by shifting the open / close means from a closed state to an open state,
4. The device voltage calculation unit according to claim 1, wherein the device voltage calculation unit calculates the device voltage in a state where the energization is stopped when a predetermined time elapses after the switching unit is shifted from the closed state to the open state. The gas sensor control device according to Item. Current detection means for detecting the element current;
5. The gas sensor control device according to claim 4, wherein the current detection unit permits the detection of the element current when a predetermined time elapses after the switching unit shifts from the open state to the closed state. A current supply unit configured to supply current between the pair of electrodes; and a current detection unit configured to detect the element current; and by controlling an amount of current supplied by the current supply unit, A gas sensor control device that generates a predetermined voltage difference,
5. The gas sensor control device according to claim 4, wherein the current detection unit permits detection of the element current when the opening / closing unit shifts from an open state to a closed state and current supply by the current supply unit is started. . When changing to the side that increases the voltage difference between the pair of electrodes by the voltage control means, comprising an upper limit determination means for determining whether the voltage difference has reached a predetermined upper limit voltage,
The gas sensor control device according to any one of claims 1 to 6, wherein an increase in the voltage difference is stopped when it is determined that the voltage difference has reached the upper limit voltage. The gas sensor detects exhaust gas discharged from an internal combustion engine as the detected gas, and detects an oxygen concentration in the exhaust gas,
Air-fuel ratio determination means for determining that a change in the air-fuel ratio occurs with a change in the operating state of the internal combustion engine,
The power supply is stopped by the power supply stop means, the device voltage is calculated by the device voltage calculation means, and the voltage control by the voltage control means is performed when it is determined that the air-fuel ratio changes. The gas sensor control device according to any one of 7. The gas sensor detects exhaust gas discharged from an internal combustion engine as the detected gas, and detects an oxygen concentration in the exhaust gas,
Element temperature determination means for determining that a change in temperature of the sensor element occurs with a change in the operating state of the internal combustion engine;
2. When it is determined that a temperature change of the sensor element occurs, the energization stop by the energization stop unit, the element voltage calculation by the element voltage calculation unit, and the voltage control by the voltage control unit are performed. The gas sensor control apparatus of any one of thru | or 8.

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