Control device for measuring the impedance of the gas sensor with two voltage application resistors which changes the period length of the bidirectional currents flowing through the gas sensor when the temperature change of the resistors exceeds a threshold value

Abstract

A control device (100) for a gas sensor (200) that measures a gas concentration, the control device (100) comprising: a voltage applying section (F1, F2) that applies a voltage for measuring the impedance of the gas sensor (200) to the gas sensor (200), the voltage applying section (F1, F2) being connected in series with a resistor (R14) and another resistor (R15); a control section (110) that controls the operation of the voltage applying section (F1, F2); a sweep measuring section (120) that measures at least one of a current flowing in the gas sensor (200) and a voltage applied to the gas sensor (200), and a temperature measuring section (150), wherein a location at which the temperature is measured by the temperature measuring section (150) is located near the resistor (R14) or the further resistor (R15), wherein the control section (110) performs the following: a first controller which, during a first period (TM11), operates the voltage application section such that a current flows through the gas sensor (200) in a first direction, and a second controller which, during a second period (TM12), operates the voltage application section such that a current flows through the gas sensor (200) in a second direction opposite to the first direction; and wherein the control section (110) changes the length of at least one of the first period (TM11) and the second period (TM12) based on a comparison between a first measured value, which is the absolute value of a value measured by the sweep measuring section (120) during the execution of the first control, and a second measured value, which is the absolute value of a value measured by the sweep measuring section (120) during the execution of the second control, characterized in that, in response to a change in the temperature measured by the temperature measuring section (150) such that an absolute value of a difference between a temperature detected in a first control period and a temperature detected in a second control period following the first control period exceeds a prescribed threshold, the control section (110) performs processing for changing the length of at least one of the first period (TM11) and the second period (TM12).

Description

[Technical field]

[0001] The present disclosure relates to a control device for a gas sensor that measures a gas concentration. [State of the art]

[0002] A gas sensor is provided in the exhaust duct of a vehicle with an internal combustion engine to measure the concentration of a specific gas (e.g., oxygen) contained in the exhaust gas. Like an O2 sensor or an A / F sensor, an oxygen concentration sensor has a solid oxide layer through which oxygen ions can pass and is configured to vary the resulting electromagnetic force according to the oxygen concentration in a detection space.

[0003] To accurately measure the gas concentration by the gas sensor, it is necessary to keep the temperature of the gas sensor within an activation temperature range. Because this activation temperature range is relatively narrow, it is difficult to maintain the temperature of the gas sensor within this range by heating it only with exhaust gas. For this reason, the gas sensor is generally equipped with a heater, and the temperature of the gas sensor is adjusted to be kept within the activation temperature range by turning on the heater.

[0004] It would be possible to provide a separate temperature sensor to measure the temperature of the gas sensor to perform the temperature adjustment as described above. However, such a configuration is undesirable given the increased parts cost. The temperature of the gas sensor is therefore estimated by measuring its impedance and using a correlation relationship between the temperature of the gas sensor and its impedance.

[0005] For example, in an impedance detection device for an oxygen sensor element (i.e., a control device for a gas sensor) described in JP 2004-177178 A, a sweep voltage is applied to the gas sensor while the gas sensor is in a state where the gas sensor's measurement of the gas concentration is temporarily interrupted. The impedance of the gas sensor is then calculated by dividing the amount of voltage increase across the gas sensor by the amount of current increase. After calculating the impedance of the gas sensor, the gas sensor's measurement of the gas concentration is resumed.

[0006] In the control device described in JP 2004-177178 A, after applying the sweep voltage to the gas sensor to calculate the impedance, the sweep voltage is reset to zero, and the gas concentration measurement is restarted. However, applying the sweep voltage causes a charge to accumulate in the gas sensor, which is discharged from the gas sensor after the sweep voltage is reset to zero. As a result, the electromotive force representing the gas sensor's measured value can be altered by the effects of such a discharge. This means that the gas sensor can generate an electromotive force value that deviates from the electromotive force corresponding to the gas concentration.

[0007] To prevent this phenomenon, in JP 2017-53631 A, as well as in DE 10 2015 206 374 A1, DE 10 2008 042 268 A1, and DE 10 2012 200 038 A1, a voltage in the opposite direction to the above sweep voltage (hereinafter also referred to as "backward sweep voltage") is applied to the gas sensor before the sweep voltage is set to zero and the gas concentration measurement is resumed. By applying the voltage in the reverse direction, the discharge of the charge accumulated in the gas sensor can be promoted and the effects of the stored charge on the electromotive force described above can be suppressed.

[0008] Preferably, the absolute value of the reverse sweep voltage should be equal to the absolute value of the sweep voltage to minimize the amount of charge accumulated in the gas sensor when gas concentration measurement is resumed. Furthermore, it is preferable that the length of the period or time period for which the reverse sweep voltage is applied matches the length of the period or time period for which the sweep voltage is applied.

[0009] However, in a circuit for applying a sweep voltage or the like to a gas sensor, the absolute values ​​of the sweep voltage and the reverse sweep voltage may vary due to component tolerances of circuit components and temperature fluctuations. Therefore, it is difficult to precisely match the absolute value of the reverse sweep voltage and the absolute value of the sweep voltage. From a parts cost perspective, it is impractical to strictly control part tolerances or provide separate temperature fluctuation suppression means to precisely match the absolute values ​​of the reverse sweep voltage and the sweep voltage. Therefore, in EP 2 056 099 B1, temperature-compensated measurement of the gas sensor is performed using a temperature sensing element mounted on the circuit board.

[0010] An object of the present disclosure is to provide a control device that suppresses the temperature-dependent change in charge accumulation in a gas sensor caused by impedance measurement and that enables a gas concentration to be accurately measured by the gas sensor without constantly making unnecessary changes.

[0011] This object is achieved by the control device of claim 1 with its features. Advantageous further developments can be found in the associated claims.

[0012] A control device according to the present disclosure is for controlling a gas sensor that measures a gas concentration, and includes a voltage applying section that applies a voltage to the gas sensor to measure the impedance of the gas sensor, a control section that controls the operation of the voltage applying section, and a sweep measuring section that measures the current flowing in the gas sensor or the voltage applied to the gas sensor, or both.The control section performs first control in a first period to operate the voltage applying section so that a current flows in the gas sensor in a first direction, and second control in a second period following the first period to operate the voltage applying section so that a current flows in the gas sensor in a second direction opposite to the first direction, and changes the length of at least one of the first period and the second period based on a comparison between a first measured value and a second measured value, the first measured value being the absolute value of a value measured by the sweep measuring section during execution of the first control, and the second measured value being the absolute value of a value measured by the sweep measuring section during execution of the second control.

[0013] With a control device having such a configuration, after a current is passed through the gas sensor in the first direction in the first period, a current is passed through the gas sensor in the second direction in the second period. The impedance measurement is performed in the first period, and the charge accumulated in the gas sensor is removed in the second period. Furthermore, in the control device, the length of at least one of the first period and the second period is changed based on a first measured value and a second measured value measured by the sweep measurement section.

[0014] Therefore, even if the first measured value and the second measured value differ from each other due to part variations, etc., since the length of at least one of the first period and the second period changes, the charge accumulated in the gas sensor can be kept at approximately zero, so that the electromotive force is prevented from fluctuating due to the accumulated charge after the impedance measurement, and thus the gas concentration can be accurately measured by the gas sensor.

[0015] The present disclosure provides a control device that suppresses charge accumulation in a gas sensor caused by performing impedance measurement and enables accurate measurement of gas concentration by the gas sensor. [Brief description of the drawings]

[0016] It shows / it shows: Fig. 1 is a conceptual diagram illustrating the configuration of a gas sensor and a control device according to a first embodiment; Fig. 2 is a graph showing the time variation of a sweep current flowing in the gas sensor when an impedance measurement is performed; Fig. 3 is a graph showing the time variation of a sweep current flowing in the gas sensor when an impedance measurement is performed; Fig. 4 is a graph showing the time variation of a sweep current flowing in the gas sensor when an impedance measurement is performed; Fig. 5 is a diagram for describing timing in which the length of a second period, etc., is changed; Fig. 6 is a diagram for describing a method for adjusting the length of the second period, etc.; Fig. Fig. 7 is a flowchart of the processing performed by the control device of Fig. 1 is executed; Fig. Fig. 8 is a flowchart of the processing performed by the control device of Fig. 1 is executed; Fig. Fig. 9 is a flowchart of the processing performed by the control device of the Fig. 1 is executed; Fig. 10 is a flowchart of the processing performed by the control device of Fig. 1 is executed; Fig. 11 is a graph showing the relationship between the difference between the first measured value and the second measured value and a change in the electromotive force of the gas sensor; Fig. 12 is a flowchart of processing executed by a control device according to a second embodiment; Fig. 13 is a flowchart of the processing executed by a control device according to the embodiment of the invention; Fig. 14 is a flowchart of processing executed by a control device according to a fourth embodiment; Fig. 15 is a flowchart of processing executed by a control device according to a fifth embodiment; Fig. 16 is a flowchart of processing executed by a control device according to a sixth embodiment; Fig. 17 is a diagram showing the temporal variation of a sweep current flowing in the gas sensor when impedance measurement is performed by a control device according to a seventh embodiment; Fig. 18 is a diagram showing the temporal variation of a sweep current flowing in the gas sensor when impedance measurement is performed by a control device according to the seventh embodiment; Fig. 19 is a flowchart of the processing executed by a control device according to the seventh embodiment; Fig. 20 is a flowchart of processing executed by a control device according to an eighth embodiment; Fig. 21 is a flowchart of processing executed by a control device according to a ninth embodiment; Fig. Figure 22 is a graph showing a relationship between temperature and impedance of a gas sensor; Fig. 23 is a diagram showing the temporal variation of a sweep current flowing in the gas sensor when impedance measurement is performed by a control device according to a comparative example; and Fig. 24 is a graph showing the time variation of the electromotive force of a gas sensor when impedance measurement is performed by a control device according to the comparative example. [Description

[0017] The embodiments are described below with reference to the accompanying drawings. For better understanding, identical components in the respective drawings are designated by the same reference numbers wherever possible, and duplicate descriptions are omitted.

[0018] The respective configurations of a control device 100 and a gas sensor 200 according to the first embodiment will be described with reference to Fig. 1. The gas sensor 200 is provided in an exhaust passage (not shown) of a vehicle and is an O2 sensor for measuring the oxygen concentration of the exhaust gas flowing through the exhaust passage. The control device 100 is a device for measuring a gas concentration using the gas sensor 200 by applying a voltage to the gas sensor 200.

[0019] First, the configuration of the gas sensor 200 will be described. The gas sensor 200 includes a solid oxide layer made of partially stabilized zirconia and a pair of electrode layers formed on opposite sides of the solid oxide layer (both not shown). The exhaust gas flowing through the exhaust passage is supplied to one of the electrode layers. Atmospheric air is introduced into the other electrode layer. In the gas sensor 200, oxygen ions pass through the solid oxide layers according to the difference between the oxygen concentration of the exhaust gas and the oxygen concentration of the atmosphere. An electromotive force with a magnitude corresponding to the oxygen concentration of the exhaust gas is generated by the gas sensor 200.

[0020] Fig. 1 shows an equivalent circuit of the gas sensor 200 configured as described above. Resistors R21 and R22 represent the respective resistance components of the layers of the gas sensor 200. Capacitors C21 and C22 represent the capacitance components of the layers of the gas sensor 200. Power source V20 conceptually represents the generation source of the electromotive force of the gas sensor 200, that is, the electromotive force with a magnitude corresponding to the oxygen concentration of the exhaust gas. The electromotive force is approximately 1 V when the air-fuel ratio of the exhaust gas is richer than the theoretical air-fuel ratio, and approximately 0 V when the air-fuel ratio of the exhaust gas is less than the theoretical air-fuel ratio.In a range where the air-fuel ratio is close to the theoretical air-fuel ratio, the above-mentioned electromotive force changes rapidly between 1 V and 0 V.

[0021] The electromotive force of the gas sensor 200 is output to the control device 100 as a potential difference between the end P21 on one side of the gas sensor 200 and the end P22 on the other side. The end P21 is connected to the terminal T1 of the control device 100. The end P22 is connected to a terminal T2 of the control device 100.

[0022] To accurately measure the oxygen concentration by the gas sensor 200, it is necessary to maintain the temperature of the gas sensor 200 (especially the temperature of the solid oxide layer) within an activation temperature range. Since this activation temperature range is relatively narrow, it is difficult to maintain the temperature of the gas sensor 200 within the activation temperature range only by heating the gas sensor 200 with the exhaust gas. Therefore, a heater HT is provided for heating the gas sensor 200. The temperature of the gas sensor 200 is adjusted to be within the above-mentioned activation temperature range by controlling the magnitude of a current supplied to the heater HT.

[0023] In order for the control device 100 to perform temperature control as described above, it is necessary for the control device 100 to determine the temperature of the gas sensor 200. A temperature sensor may be provided separately to measure the temperature of the gas sensor 200. However, such a configuration is undesirable from the perspective of increasing parts costs.

[0024] For this reason, the control device 100 of the present embodiment periodically measures the impedance of the gas sensor 200 (specifically, the impedance of the solid oxide layer) and estimates the temperature of the gas sensor 200 based on the impedance. A resistor Z20 used in the equivalent circuit of Fig. 1 expresses the impedance of the gas sensor 200.

[0025] Fig. Figure 22 shows the relationship between the temperature of the gas sensor 200 and the impedance. As shown in the diagram, the higher the temperature of the gas sensor 200, the smaller the impedance of the gas sensor 200, which tends to become. Fig. The correspondence relationship shown in Fig. 22 is measured in advance and stored in a storage device (not shown) of the control device 100. The control device 100 estimates the temperature of the gas sensor 200 based on its impedance and the Fig. 22, wherein the impedance of the gas sensor 200 is measured according to a method described below. The control device 100 adjusts the duty cycle of the voltage applied to the heater HT based on the estimated temperature of the gas sensor 200.

[0026] The configuration of the control device 100 is described below, with reference to Fig. 1. The control device 100 is provided with power supply lines PL1 and PL2. The power supply line PL1 is a constant voltage source for applying a predetermined amount of positive polarity offset to the end P22 of the gas sensor 200 with respect to ground potential. The power supply line PL2 is a constant voltage source for supplying operating power to the operational amplifier OP.

[0027] A resistor R11 and a resistor R12 are connected in series between the supply line PL1 and the ground line. A point P11 between the resistor R11 and the resistor R12 is connected to the non-inverting input of the operational amplifier OP.

[0028] The output of the operational amplifier OP is connected to the end P22 of the gas sensor 200 via a resistor R13 and terminal T2. A capacitor C11 is connected between the ground line and an intermediate position on the line extending from the output of the operational amplifier OP.

[0029] The line extending from the output of the operational amplifier OP is branched at an intermediate position, with a branch line connected to the inverting input of the operational amplifier OP. As a result, when the oxygen concentration is measured by the gas sensor 200, the potential of the end P22 of the gas sensor 200 is maintained at the same potential as that of the point P11 (2 V, with the present embodiment). The potential of the end P21 of the gas sensor 200 is obtained by adding the electromotive force of the gas sensor 200 to the potential of the end P22. Thus, the gas sensor 200 changes the potential of the end P22 according to the oxygen concentration. The potential of the end P22 changes between approximately 2 V and 3 V, depending on the oxygen concentration of the exhaust gas.

[0030] The control device 100 is provided with a power supply line PL3 in addition to the power supply lines PL1 and PL2. The power supply line PL3 is a constant voltage source designed to apply a sweep voltage (described below) to the gas sensor 200 when measuring its impedance. A resistor R14, a switching element F1, a switching element F2, and a resistor R15 are connected in series in this order between the power supply line PL3 and the ground line.

[0031] The switching elements F1 and F2 are both field-effect transistors (FETs). The circuits of the switching elements F1 and F2 are individually controlled by an operation control section (hereinafter referred to as the "control section") 110, described below.

[0032] A point P14 between the switching element F1 and the switching element F2 is connected via terminal T1 to the end P21 of the gas sensor 200. A resistor R16 and a capacitor C12 are connected in parallel between a ground line and an intermediate position on the line connecting the point P14 to the terminal T1.

[0033] When the oxygen concentration is measured by the gas sensor 200, the two switching elements F1 and F2 are open. The potential at point P14 is thus equal to the potential at the end P22 plus the electromotive force of the gas sensor 200 and is not influenced by the supply line PL3.

[0034] As described below, when measuring the impedance of the gas sensor 200, the closing and opening of the switching element F1 is controlled at a predetermined time interval while the switching element F2 remains open. This applies a voltage to the gas sensor 200 in one direction from the end P21 to the end P22 (hereinafter also referred to as the "first direction").

[0035] Immediately after measuring the impedance of the gas sensor 200, the switching element F1 is returned to the open state, and the switching element F2 is closed and opened at a predetermined time interval. This applies a voltage to the gas sensor 200 in one direction from the end P22 to the end P21 (hereinafter also referred to as the "second direction").

[0036] The switching elements F1 and F2 that perform the above operation can be considered as parts that apply a voltage to the gas sensor 200 to measure its impedance. Such switching elements F1 and F2 correspond to a "voltage applying device" in the present embodiment.

[0037] The control device 100 further includes a control section 110, a measuring section 120, a heater control section 130, and a mask adjustment section 140. Each of these is configured as a single IC. However, the specific configurations of the control section 110, etc., are not limited to those described above. For example, the control section 110, the measuring section 120, and the heater control section 130 may be configured as a single IC. Furthermore, each of the control sections 110, etc., may be configured as a combination of a plurality of ICs instead of a single IC.

[0038] The control section 110 transmits control signals to each of the switching elements F1 and F2, which are voltage applying units, so as to individually control their opening / closing operation.

[0039] The measuring section 120 measures the current flowing to the gas sensor 200, the voltage applied to the gas sensor 200, etc. As shown in Fig. As shown in Figure 1, the measuring section 120 receives the potential at point P12, between the resistor R13 and the operational amplifier OP, and the potential at point P13, between the resistor R13 and the terminal P22. The measuring section 120 can measure (calculate) the magnitude of the current flowing through the resistor R13, that is, the current flowing through the gas sensor 200, based on the potential difference between points P12 and P13.

[0040] The measuring section 120 also receives the potential occurring at point P15 between point P14 and end P21. The measuring section 120 can measure the potential difference between ends P21 and P22 of the gas sensor 200 based on the potential difference between points P15 and P13.

[0041] When both switching elements F1 and F2 are open and the oxygen concentration measurement is performed by the gas sensor 200, the potential difference between the point P15 and the point P13 is equal to the electromotive force of the gas sensor 200. The measuring section 120 can calculate the current value of the oxygen concentration in the exhaust gas based on the electromotive force of the gas sensor 200.

[0042] As described below, the measuring section 120 has a function of calculating the impedance of the gas sensor 200 based on the amount of change in the voltage applied to the gas sensor 200 (the potential difference between the points P15 and P13) and the amount of change in the current flowing through the gas sensor 200.

[0043] The measuring section 120 includes a sensor temperature estimation section 121 as a function control block. The sensor temperature estimation section 121 is a part that estimates the current temperature of the gas sensor 200 based on the impedance of the gas sensor 200 and the Fig. 22 depicted correspondence relationship.

[0044] In addition to the potentials of point P12, etc., as described above, the measuring section 120 also receives the measured value of a temperature sensor 150. The temperature sensor 150 is provided for measuring the temperature of the control device 100 during operation and corresponds to a "temperature measuring section" in the present embodiment. In the control device 100, the location where the temperature is measured by the temperature sensor 150 is located near the resistor R14 or the resistor R15.

[0045] The heater control section 130 supplies power to the heater HT of the gas sensor 200. The heater control section 130 adjusts the duty cycle of the voltage applied to the heater HT so that the temperature of the gas sensor 200 estimated by the sensor temperature estimation section 121 (i.e., the temperature estimated based on the impedance of the gas sensor 200) is maintained within the activation temperature range.

[0046] The mask setting section 140 sets a mask period TM10. The mask period TM10 is described below.

[0047] An overview of the processing performed by the control device 100 for measuring the impedance of the gas sensor 200 will be described with reference to Fig. 2. As described above, during impedance measurement, a voltage is applied to the gas sensor 200 in the first direction, causing a current to flow in the gas sensor 200. In the following description, the voltage applied to the gas sensor 200 is also referred to as a "sweep voltage," and the current flowing through the gas sensor 200 is also referred to as a "sweep current." Furthermore, with respect to positive and negative values ​​of a sweep voltage and a sweep current, the first direction is referred to as positive and the second direction is referred to as negative, either for the sweep voltage or for a sweep current. Fig. Figure 2 shows the time variation of the sweep current (actually the current flowing through resistor R13) measured by the measuring section 120.

[0048] While the impedance of the gas sensor 200 is being measured, the measurement of the oxygen concentration by the gas sensor 200 cannot be performed. Therefore, the control device 100 sets a mask period TM10 as a period in which the measurement of the oxygen concentration is temporarily prohibited, and measures the impedance during the mask period TM10. In the example of Fig. 2, the period from time t0 to time t40 is set as the mask period TM10. The mask period TM10 is set via the mask setting section 140.

[0049] After the mask period TM10 has elapsed, the measurement of the oxygen concentration by the gas sensor 200 continues. Hereinafter, a period in which the measurement of the oxygen concentration is performed by the gas sensor 200, that is, a period other than a mask period TM10, is also referred to as a "concentration measurement period TM20."

[0050] The setting of the mask period TM10 and the impedance measurement during the mask period TM10 are repeated after a specified time. Thus, the mask period TM10 and the concentration measurement period TM20 are repeated alternately.

[0051] At time t10 immediately after the start of the mask period TM10, the control section 110 begins to open / close the switching element F1 at a predetermined duty cycle while keeping the switching element F2 open. A sweep voltage is applied to the gas sensor 200 in the first direction, from the end P21 to the end P22. The above duty cycle is preset so that the magnitude of the sweep current flowing through the gas sensor 200 corresponds to a predetermined set value (I10). Thus, in the example of Fig. 2 the magnitude of the sweep current after time t10 I10. The state in which a sweep voltage in the first direction is applied to the gas sensor 200 continues for a predetermined first period TM11.

[0052] The control of applying the sweep voltage to the gas sensor 200 in the first period TM11 can be considered as controlling the operation of the switching element F1, which is a voltage applying device, so that a current flows in the first direction in the gas sensor 200. This control is also referred to as the "first control" hereinafter.

[0053] In the first period TM11, the measuring section 120 calculates the impedance of the gas sensor 200 by dividing the amount of increase in the sweep voltage by the amount of increase in the sweep current. The amount of increase in the sweep voltage and the amount of increase in the sweep current are both measured by the measuring section 120.

[0054] It can be assumed that the measurement of the oxygen concentration by the gas sensor 200 can be resumed immediately after the impedance calculation is completed and the first period TM11 ends. However, a charge has been accumulated (i.e., charged) in the gas sensor 200 at the end of the first period TM11 due to the application of the sweep voltage. Therefore, after the first period TM11 ends and the sweep voltage is reset to 0, the charge is discharged from the gas sensor 200 for a relatively long time. As a result, the electromotive force indicating the measured value of the gas sensor 200 may temporarily change due to the effects of the discharge, as described above. Thus, an electromotive force other than the electromotive force corresponding to the gas concentration may be generated from the gas sensor 200.

[0055] Thus, in the control device 100 of the present embodiment, after time t20, when the first period TM11 ends, the switching element F1 is returned to the open state, and the switching element F2 begins to close / open at a predetermined time interval. This applies the sweep voltage to the gas sensor 200 in the second direction, from the end P22 to the end P21. This promotes the discharge of charge from the gas sensor 200.

[0056] The above time interval is set in advance so that the magnitude of the sweep current flowing through the gas sensor 200 corresponds to a predetermined setpoint (-I10). Fig. 2 the magnitude of the sweep current after time t20 -I10. The state in which the sweep voltage is applied to the gas sensor 200 in the second direction is continued for a predetermined second period TM12. In the example of Fig. 2, the period from time t20 to time t30 is the second period TM12. The mask setting section 140 sets the mask period TM10, in which the measurement of the gas concentration is temporarily prohibited, as a period including both the first period TM11 and the second period TM12.

[0057] In the second period TM12, the sweep voltage application controller controls the operation of switching element F2, which is a voltage application device, to apply the sweep voltage to gas sensor 200, so that a current flows in the gas sensor 200 in the second direction opposite to the first direction. This control is also referred to as the "second control" hereinafter.

[0058] The absolute value of the setpoint (I10) of the sweep current flowing through the gas sensor 200 in the first controller and the absolute value of the setpoint (-I10) of the sweep current flowing through the gas sensor 200 in the second controller are equal. That is, the duty cycle during the switching operation of the switching elements F1 and F2 is preset so that the absolute value of the sweep current in the first controller and the absolute value of the sweep current in the second controller become equal.

[0059] Furthermore, the length of the first period TM11, in which the first control is performed, and the length of the second period TM12, in which the second control is performed, are substantially identical. As a result, the amount of charge accumulated in the gas sensor 200 in the first period TM11 and the amount of charge discharged by the gas sensor 200 in the second period TM12 are substantially the same. Thus, at the time when the oxygen concentration measurement by the gas sensor 200 is restarted (time t40), the charge has almost no influence on the electromotive force of the gas sensor 200.

[0060] The mask period TM10, during which the sweep voltage is applied as described above, is repeatedly set as described above. Thus, with the control device 100, the sweep voltage is applied by the switching element F1 or the like (voltage applying device) and the sweep current is measured by the measuring section 120.

[0061] However, if the resistance of resistor R14 deviates from the setpoint, e.g., due to component tolerance or temperature fluctuations, the sweep current value in the first period TM11 may deviate from the setpoint I10. Likewise, the sweep current value in the second period TM12 may deviate from the setpoint -I10.

[0062] Fig. 23 shows an example of the temporal variation of the sweep current in which the sweep voltage is applied to the gas sensor 200 by a control device according to the comparative example. In the example of Fig. 23, the sweep current value in the first period TM11 has reached a value (I11) that is higher than the setpoint (I10) due to the influence of component fluctuations. On the other hand, the sweep current value in the first period TM11 corresponds to the setpoint -I10. In addition, in the example of Fig. 23 the length of the first period TM11 and the length of the second period TM12 are equal.

[0063] If the sweep voltage is as in Fig. 23, the amount of charge accumulated in the gas sensor 200 in the first period TM11 is greater than the amount of charge discharged from the gas sensor 200 in the second period TM12. Thus, at time t40, when the concentration measurement period TM20 begins and the gas concentration measurement is started, the electromotive force of the gas sensor 200 is shifted to the positive side by the influence of the residual charge, thus differing from the electromotive force corresponding to the oxygen concentration.

[0064] In addition, if you repeatedly create the Fig. 23, the amount of charge accumulated in the gas sensor 200 gradually increases, and as shown in Fig. 24, the electromotive force of the gas sensor 200 also gradually increases. Thus, over time, the difference between the actually measured electromotive force of the gas sensor 200 and the electromotive force corresponding to the oxygen concentration (0 V in the example of Fig. 24).

[0065] To prevent such a deviation of the electromotive force, the control device 100 of the present embodiment changes the length of at least one of the first periods TM11 and TM12. A concrete example of this is shown in Fig. 3 described.

[0066] As in Fig. 2 described above, shows Fig. 3, (A) the temporal variation of the sweep current in the case that the respective setpoints (I10 and -I10) of the sweep current are the same in the first period TM11 and in the second period TM12.

[0067] At time t191, the control device 100 measures the value of the sweep current actually flowing through the gas sensor 200 in the first period TM11 in which the first control is performed, with the measurement being performed by the measuring section 120. The time t191 is defined as the time at which a prescribed period (shorter than the first period TM11) has elapsed from the time t10 at which the first period TM11 began. The absolute value of the sweep current measured by the measuring section 120 in the first period TM11 is hereinafter also referred to as the "first measured value."

[0068] At time t291, the control device 100 measures the value of the sweep current actually flowing through the gas sensor 200 in the second period TM12 in which the second control is performed, with the measurement being performed by the measuring section 120. The time t291 is defined as the time at which a prescribed period (shorter than the second period TM12) has elapsed from the time t20 at which the second first period TM12 began. The absolute value of the sweep current measured by the measuring section 120 in the second period TM12 is hereinafter also referred to as the "second measured value."

[0069] Similar to the example described above of Fig. 23 shows Fig. 3, (B) the variation of the sweep current with time in the case that the value of the sweep current in the first period TM11 becomes I11, which is higher than the setpoint I10. In the example of (B) in Fig. 3 the first measured value (I11) is greater than the second measured value (I10).

[0070] When the first measured value is larger than the second measured value, the control section 110 of the control device 100 changes the length of the second period TM12 to be longer than in the case of (A) in Fig. 3. In the example of (B) in Fig. 3, the time at which the second period TM12 ends is changed to time t31, which is later than time t30. As a result, the second period TM12 in (B) is Fig. 3 longer than the first period TM11 in (B) of Fig. 3.

[0071] In the example of Fig. 3, after reaching the first period TM11, there is no change between (A) and (B) in Fig. 3 at the time when the measurement (detection of the first measured value) is carried out by the measuring section 120, ie there is no change in the length of the period from time t10 to time t191. In addition, after reaching the second period TM12, there is no change between (A) and (B) in Fig. 3 at the time at which the measurement (detection of the second measured value) is carried out by the measuring section 120, ie there is no change in the length of the period from time t20 to time t291.

[0072] In addition, in (B) Fig. 3, the mask period TM10 is also extended along with the extension of the second period TM12. Specifically, the time at which the mask period TM10 ends is changed from time t40 to time t45. Through such processing, the mask setting section 140 can prevent the gas concentration measurement from starting before the second period TM12 ends.

[0073] In (B) of Fig. 3, as the second period TM12 becomes longer, the amount of charge released by the gas sensor 200 in the second period TM12 increases. Thus, not only the charge accumulated in the gas sensor 200 in the first period TM11 increases, but also the charge released by the gas sensor 200 in the second period TM12 increases. Thus, the amount of charge accumulated in the gas sensor 200 at the time (time t45) when the gas concentration measurement is restarted can be kept smaller than in the case of the Fig. 23. Since the charge accumulation on the gas sensor 200 is suppressed in the mask period TM10, the gas concentration can be accurately measured with the gas sensor 200.

[0074] Furthermore, if the second measured value becomes smaller than I10 and the first measured value also becomes larger than the second measured value, the second period TM12 is changed to a longer period. In this case, too, the charge accumulation on the gas sensor 200 is suppressed as described above.

[0075] In contrast, an example in which the first measured value becomes smaller than the second measured value is shown by Fig. 4. In Fig. 4 shows (A) the temporal variation of the sweep current, as in Fig. 2 above, in the case that the values ​​of the sweep current in the first period TM11 and in the second period TM12 respectively correspond to the setpoint values ​​(I10 and -I10).

[0076] In Fig. 4, (B) shows the variation of the sweep current with time, where the value of the sweep current in the first period TM11 becomes I09, which is smaller than the setpoint I10. In the example of (B) in Fig. 4 the first measured value (I09) is smaller than the second measured value (I10).

[0077] When the first measured value is smaller than the second measured value, the control section 110 of the control device 100 changes the length of the first period TM11 to be longer than in the case of (A) in Fig. 4. In the example of (B) in Fig. 4, the time at which the first period TM11 ends (which is also the start time of the second period TM12) is changed to the time t21 following t20.

[0078] In addition, the time at which the second period TM12 ends is changed from time t30 to time t32. Thus, the length of the second period TM12 in (B) is Fig. 4 equal to the length of the second period TM12 in (A) of Fig. 4.

[0079] As a result of the above change, the first period TM11 in (B) is Fig. 4 longer than the second period TM12 in (B) of Fig. 4.

[0080] In (B) of Fig. 4, the time at which the measurement is performed by the measuring section 120 (acquisition of the second measured value) in the second period TM12 is changed from time t291 to time t292. However, the length of the period from time t21 to time t292 is equal to the length of the period from time t20 to time t291 in (A) of Fig. 4.

[0081] For this reason, the example of Fig. 4 the time at which the measurement (detection of the second measured value) is carried out by the measuring section 120 after the second period TM12, not between Fig. 4(A) and Fig. 4(B). In addition, the time at which the measurement (acquisition of the first measured value) is performed by the measuring section 120 after the first period TM11 is changed to Fig. 4 not changed between (A) and (B).

[0082] In addition, in (B) Fig. 4, along with the extension of the first period TM11, the mask period TM10 is also extended. Specifically, the time at which the mask period TM10 ends is changed from time t40 to time t46. By performing such processing, the mask setting section 140 can prevent the gas concentration measurement from starting before the end of the second period TM12.

[0083] In (B) of Fig. 4, the amount of charge accumulated per unit time in the gas sensor 200 in the first period TM11 is less than in the case of (A) in Fig. 4. However, since in (B) Fig. 4, since the first period TM11 is long, the amount (total amount) of charge accumulated in the gas sensor 200 in the first period TM11 becomes substantially the same as in the case of (A) in Fig. 4. As a result, the difference between the amount of charge accumulated in the gas sensor 200 in the first period TM11 and the amount of charge released by the gas sensor 200 in the second period TM12 can be kept as small as in the case of (A) in Fig. 4. Since the charge accumulation at the gas sensor 200 is suppressed in the mask period TM10, the gas concentration can be accurately measured with the gas sensor 200.

[0084] If the second measured value becomes greater than I10 and the first measured value becomes smaller than the second measured value, the first period TM11 is also changed to a longer period. In this case, the charge accumulation on the gas sensor 200 is also suppressed as described above.

[0085] In the control device 100 described above, instead of preventing a difference between the absolute values ​​of the sweep current depending on the direction in which the sweep voltage is applied, assuming that a difference occurs, a decrease in measurement accuracy is prevented by adjusting the length of the first period TM11, etc. This eliminates problems such as cost increases due to small part tolerances.

[0086] Note that it would be difficult to immediately implement the above-described changes in the first period TM11 and the second period TM12 during the same mask period TM10 in which the first measurement value and the second measurement value are acquired. Therefore, instead of implementing the length changes of the first period TM11, etc., based on a comparison between the first measurement value and the second measurement value during the mask period TM10 in which the first measurement value, etc., is acquired, the control section 110 implements these changes in the next mask period TM10.

[0087] In the Fig. In the example shown in Figure 5, the first measured value acquired in the mask period TM10, which begins at time t0, is greater than the second measured value taken in the same period. However, in the mask period TM10, the respective lengths of the first period TM11 and the second period TM12 are kept the same.

[0088] In the next mask period TM10, which begins at time t100, the second period TM12 is changed to a longer period by comparing the first measured value and the second measured value acquired in the mask period TM10, which begins at time t0. Thus, the control section 110 changes the length of the first period TM11 or the second period TM12 in the subsequent mask period based on a comparison between the first measured value and the second measured value measured in one mask period.

[0089] In addition, the first and second measured values ​​in the mask period TM10, which begins at time t100, are also recorded, and their respective lengths are compared. Based on the comparison, the length of the first period TM11 or the second period TM12 is further changed in the subsequent mask period TM10.

[0090] As described above, in the control device 100 of the present embodiment, the length of the first period TM11 or the second period TM12 is changed based on a comparison between a first measurement value and a second measurement value, wherein the first measurement value is the absolute value of a value measured by the measuring section 120 when a first control is performed, and the second measurement value is the absolute value of a value measured by the measuring section 120 when a second control is performed.

[0091] The measuring section 120, which detects the first measured value and the second measured value, corresponds to a “sweep measuring section” in the present embodiment.

[0092] The measuring section 120 of the present embodiment has, in addition to the function of acquiring the first measured value and the second measured value, also the function of measuring the potential, etc., of the point P15. However, it would also be possible to use a configuration in which the measuring section 120 only has the function of acquiring the first measured value and the second measured value, namely, in which the measuring section 120 only has the function of measuring the sweep current, while the other functions can be assigned to a separate IC.

[0093] The following describes an example in which the lengths of the first period TM11 and the second period TM12 are changed based on the absolute value (first measurement value) of the sweep current measured by the measuring section 120 in the first period TM11 and the absolute value (second measurement) of the sweep current measured by the measuring section 120 in the second period TM12. However, it would also be possible to change the lengths of the first period TM11 and the second period TM12 based on the absolute value of the sweep voltage measured by the measuring section 120 in the first period TM11 and the absolute value of the sweep voltage measured by the measuring section 120 in the second period TM12.

[0094] That is, an aspect can be applied in which the absolute value of the potential difference between point P15 and point P13 detected in the first period TM11 is used as the first measured value, and the absolute value of the potential difference between point P15 and point P13 detected in the second period TM12 is used as the second measured value. The specific method for changing the first period TM11, etc., in this case would be the same as described above.

[0095] In this case, a configuration could be used in which the measuring section 120, which is the sweep measuring section, has only one function for acquiring the first measured value and the second measured value, namely a function for measuring the sweep voltage, while the other functions can be assigned to a separate IC.

[0096] The control section 110 in the present embodiment changes the lengths of the first period TM11 and the second period TM12 so that the absolute values ​​of the time-integral value of the value measured by the measuring section 120 in the first period TM11 and the time-integral value of the value measured by the measuring section 120 in the second period TM12 coincide with each other.

[0097] The absolute value of the “time integral value of the value measured by the measuring section 120 in the first period TM11” corresponds to the area S1, the absolute value of which is Fig. 6. Such a time integral value can be calculated by substituting the first at time t191 in Fig. 3 is multiplied by the length of the first period TM11. Alternatively, for a more accurate calculation of the time integral value, the first measured value in the first period TM11 can be recorded multiple times, as described in DE 10 2012 200 038 A1, DE 10 2015 207 880 A1, DE 196 52 059 A1, JP 2007-240 188 A, and JP 2006-329 924 A.

[0098] The absolute value of the “time integral value of the value measured by the measuring section 120 in the second period TM12” corresponds to the Fig. 6. Such a time integral value can be calculated by substituting the second value at time t291 in Fig. 3 is multiplied by the length of the second period TM12. Alternatively, for a more accurate calculation of the time integral value, the second measured value can be recorded multiple times in the second period TM12.

[0099] With the present embodiment, the absolute value of the time integral value in the first period TM11 (area S1 in Fig. 6) and the absolute value of the time integral value in the second period TM12 (area S2 in Fig. 6). In this way, the amount of charge accumulated in the gas sensor 200 in the first period TM11 and the amount of charge released by the gas sensor 200 in the second period TM12 can be almost exactly the same. This allows the gas concentration measurement to be performed more accurately because the amount of charge is close to zero at the time the gas concentration measurement begins.

[0100] It should be noted that it would be equally possible for the control section 110 to change both the length of the period TM11 and the length of the second period TM12, instead of changing only the length of one of these periods, in order to change the absolute value of the time integral value in the first period TM11 (area S1 in Fig. 6) and the absolute value of the time integral value in the second period TM12 (area S2 in Fig. 6) to make each other equal.

[0101] Specific processing contents executed by the control device 100 to realize the above-described control will be described below.

[0102] First, the processing for measuring the oxygen concentration is described, which is based on Fig. 7. A number of Fig. The processing steps shown in Fig. 7 are repeatedly executed by the control device 100 after each expiration of a predetermined control period.

[0103] In the first step S01, it is decided whether the current time is a mask period TM10. If the current time is a mask period, the gas concentration measurement by the gas sensor 200 cannot be performed. Fig. The processing sequence shown in Figure 7 is completed.

[0104] If the current time is not a mask period TM10, processing proceeds to step S02. In step S02, the electromotive force of the gas sensor 200 is detected. Specifically, the potential difference between points P15 and P13 is Fig. 1 is detected by the measuring section 120 as the above-mentioned electromotive force.

[0105] In step S03 following step S02, the oxygen concentration corresponding to the electromotive force is calculated, and the operation control of the internal combustion engine is performed based on the oxygen concentration. In addition to the function of controlling the gas sensor 200, the control device 100 in the present embodiment also has a function of controlling the operation of the internal combustion engine. Thus, the control device 100 is configured as a so-called engine ECU.

[0106] Instead of such a structure, the form may be such that the control device 100 is configured as a special device that controls the gas sensor 200 separately from the engine control unit. In this case, a signal indicating the calculated oxygen concentration is output from the control device 100 to the engine control unit. Alternatively, the potential difference between the point P15 and the point P13 may be Fig. 1 unchanged as a signal to display the oxygen concentration to the engine control unit.

[0107] The processing for measuring the impedance of the gas sensor 200 is carried out using Fig. 8. The Fig. The sequence of processing steps shown in Figure 8 is repeatedly executed by the control device 100 after each expiration of a predetermined control period. In addition, the processing is carried out in parallel with the Fig. The sequence of processing steps shown in Figure 7 is carried out.

[0108] In the first step S11, the confirmation of the start condition is performed. The "start condition" is a condition specified as necessary for performing the impedance measurement when changing the first period TM11 and the second period TM12. Further details of the processing performed in step S11 will be described with reference to Fig. 9 described.

[0109] In step S31, it is determined whether the temperature of the gas sensor 200, estimated by the sensor temperature estimation section 121, is above a predetermined temperature. The "predetermined temperature" is a temperature preset as the minimum temperature at which the gas sensor 200 can operate. If the temperature of the gas sensor 200 exceeds the predetermined temperature, processing proceeds to step S32 due to heating by the heater HT. In step S32, it is judged whether the start condition is met.

[0110] On the other hand, if the temperature of the gas sensor 200 does not exceed the predetermined temperature at step S31, processing proceeds to step S33. At step S33, it is judged that the start condition is not met.

[0111] In this way, with the present embodiment, when the heater HT has been turned on and the temperature of the gas sensor 200 estimated by the sensor temperature estimating section 121 exceeds the prescribed temperature, the above start condition is set.

[0112] Thus, the control section 110 supplies power to the heater HT and, after the temperature estimated by the sensor temperature estimation section 121 exceeds the predetermined temperature, begins processing to change the length of at least one of the first period TM11 and the second period TM12. This can prevent unnecessary adjustment of the first period TM11, etc., even though the gas concentration in the gas sensor 200 cannot yet be accurately measured.

[0113] The description continues and returns to Fig. 8. At step S12 following step S11, a decision is made as to whether the start condition at step S11 has been met. If the start condition is not met, processing proceeds to step S27.

[0114] At step S27, the impedance of the gas sensor 200 is measured. Here, the impedance is measured in a state in which the respective lengths of the first period TM11 and the second period TM12 are as in the example of Fig. 23 are retained unchanged. In particular, the processing is identical to the series of processing steps performed after step S13 described below, but step S25 is omitted. Fig. The processing sequence shown in Figure 8 is then terminated.

[0115] If the processing load is a problem, the processing of step S27 may be made identical to the series of steps performed after step S13 as described below, but omitting steps S21, S22, and S25.

[0116] If the start condition is satisfied at step S12, the processing proceeds to step S13. At step S13, the mask setting section 140 performs processing to start a mask period TM10. Thus, the period following step S13 is set as the mask period TM10, which is determined with reference to Fig. 3 etc.

[0117] At step S14 following step S13, the processing for applying a sweep voltage to the gas sensor 200 in a first direction, ie, the first control, is started. As described above, this processing executes the operations for opening and closing the switching element F1 and is performed by the control section 110. The first period TM11, which is Fig. 3 etc., begins from the time at which the processing of step S14 is performed.

[0118] In step S15 following step S14, it is decided whether the time for detecting the sweep current has been reached. The “time for detecting the sweep current” referred to here corresponds, for example, to time t191 in (A) of Fig. 3 and can also be referred to as the "first measurement acquisition time." Here, a decision is made as to whether the current time is the above time, based on whether a predetermined period has passed since the start of the processing of step S14.

[0119] If it is assumed that the current time is not the sweep current detection time, the processing of step S15 is repeatedly executed. If it is assumed that the current is the sweep current detection time, the processing proceeds to step S16.

[0120] At step S16, the value of the sweep current flowing through the gas sensor 200 is measured by the measuring section 120, and the absolute value of the value is detected as the first measured value.

[0121] At step S17 after step S16, the value of the sweep voltage applied to the gas sensor 200 (the potential difference between the points P15 and P13) is detected by the measuring section 120.

[0122] At step S18 following step S17, the impedance of the gas sensor 200 is calculated based on the sweep current value measured in step S16 and the sweep voltage value measured in step S17. Specifically, the impedance is calculated by dividing the amount of increase in the sweep voltage by the amount of increase in the sweep current.

[0123] The impedance calculated in step S18 is used in the control performed by the heater control section 130, that is, the control for adjusting the duty cycle of the voltage HT applied to the heater to maintain the temperature of the gas sensor 200 within the activation temperature range. This control is performed in parallel with the control performed in Fig. 8 shown processing sequence.

[0124] At step S19 following step S18, it is judged whether the first period TM11 has elapsed since the time at which the processing of step S14 was performed. Note that the length of the first period TM11 used for this judgment is the length of the first period TM11 set (changed) at step S25 described below when the Fig. 8 processing sequence was performed in the previous control period.

[0125] If the first period TM11 has not yet elapsed, the processing from step S19 is repeatedly executed and the first control continues. If the first period TM11 has elapsed, the processing proceeds to step S20. At step S20, the processing for applying a sweep voltage to the gas sensor 200 in the second direction, that is, the second control, is started. As described above, this processing executes the operations for opening and closing the switching element F2 and is performed by the control section 110. The second period TM12, shown in Fig. 3, etc., begins at the time when the processing of step S20 is performed.

[0126] In step S21 following step S20, it is decided whether the time for detecting the sweep current has been reached. The “detection time” referred to here corresponds, for example, to time t291 in (A) of Fig. 3 and may also be referred to as the "second measurement value acquisition time." Here, a decision is made as to whether the current time is the above time, based on whether a predetermined period has passed since the start of the processing of step S20.

[0127] If it is assumed that the current time is not the sweep current detection time, the processing of step S21 is repeatedly executed. If it is assumed that the current time is the sweep current detection time, the processing proceeds to step S22.

[0128] In step S22, the value of the sweep current flowing through the gas sensor 200 is measured by the measuring section 120 and the absolute value of this measured value is recorded as a second measured value.

[0129] At step S23 following step S22, it is judged whether the second period TM12 has elapsed from the time at which the processing of step S20 was performed. Note that the length of the second period TM12 used for this judgment is the length of the second period TM12 set (changed) at step S25 as described below when the Fig. 8 processing sequence was performed in the previous control period.

[0130] If the second period TM12 has not yet elapsed, the processing from step S23 is repeated and the second control continues. If the second period TM12 has elapsed, processing proceeds to step S24. In step S24, the switching operation of the switching element F2 is stopped and the switching element F2 is brought into the open state. The second control is thus terminated.

[0131] At step S25 following step S24, processing for changing the length of at least one of the first periods TM11 and the second period TM12 is performed based on the first measurement value acquired at step S16 and the second measurement value acquired at step S22. Further details on the content of the processing performed at step S25 will be described with reference to Fig. 10 described.

[0132] In step S41, it is decided whether the first measured value is greater than the second measured value. If the first measured value is not greater than the second measured value, the processing proceeds to step S42. In step S42, as shown in Fig. 3 under (B), the processing for extending the second period TM12 is performed. The second period TM12, whose length has thus been changed, is used in the judgment of step S23 when the Fig. 8 shown processing sequence is executed in the next control period.

[0133] If the first measured value is not greater than the second measured value at step S41, processing proceeds to step S43. At step S43, it is decided whether the first measured value is smaller than the second measured value. If the first measured value is smaller than the second measured value, processing proceeds to step S44. At step S44, as in Fig. 4 under (B), the processing for extending the first period TM11 is performed. The first period TM11, whose length has thus been changed, is used in the judgment at step S19 when the Fig. 8 shown processing sequence is executed in the next control period.

[0134] If the first measured value in step S43 is not smaller than the second measured value, the Fig. The processing sequence shown in Figure 10 is completed. This means that the first measured value and the second measured value were the same. Thus, the lengths of the first period TM11 and the second period TM12 are not changed.

[0135] The description continues and returns to Fig. 8. At step S26 following step S25, the mask setting section 140 performs the processing for ending the mask period TM10. The time at which this processing is performed corresponds, for example, to time t40 in (A) of Fig. 3.

[0136] The Fig. 3 and Fig. The control form shown in Fig. 4 is realized by the execution of the processing described above by the control device 100.

[0137] The effects of measuring the impedance by this embodiment as described above will be explained with reference to Fig. 11. The values ​​along the horizontal axis in the diagram of Fig. 11 are obtained by subtracting the second measured values ​​from the first measured values, and in this embodiment, these can be referred to as "current differences." The values ​​along the vertical axis in the graph are obtained by subtracting the electromotive force of the gas sensor 200 from the potential difference between points P15 and P13 after repeating the impedance measurement a predetermined number of times. Thus, the values ​​indicate how much the electromotive force of the gas sensor 200, measured by the measuring section 120, changes from the (correct) value corresponding to the gas concentration due to the influence of the accumulated charge. Hereinafter, the values ​​plotted along the vertical axis are also referred to as the "amount of electromotive force fluctuation."

[0138] The line L1 in Fig. 11 expresses the variation of the fluctuation range of the electromotive force over time in the case where the lengths of the first period TM11 and the second period TM12 are not changed but are kept fixed. In this case, as the difference between the first measured value and the second measured value increases, the charge accumulated in the gas sensor 200 also increases, and thus the fluctuation range of the electromotive force also increases.

[0139] In Fig. In Figure 11, points D1, D2, and D3 indicate measured values ​​of the magnitude of the electromotive force change when the lengths of the first period TM11 and the second period TM12 are changed as described above. As indicated by these points D1, etc., with the control performed by the control device 100 of the present embodiment, the electromotive force fluctuation is maintained within a very narrow range (within ±5 mV) regardless of the difference between the first measured value and the second measured value. This makes it possible to accurately measure the gas concentration in the concentration measurement period TM20.

[0140] The second embodiment is based on Fig. 12. This embodiment differs from the first embodiment only in the content of the information displayed at step S11 of Fig. 8, in particular the content of the start condition. The following describes the main points of difference from the first embodiment.

[0141] The Fig. The processing sequence shown in Fig. 12 is a specific processing flow executed at step S11 of Fig. 8 and instead of the Fig. 9 is executed.

[0142] In the first step S51, it is decided whether a predetermined period has elapsed since the heater control section 130 started turning on the heater HT. This "predetermined period" is set as the period required for the temperature of the gas sensor 200 to reach a sufficient temperature (ie, the minimum temperature at which the gas sensor 200 can operate) after the heater HT starts heating.

[0143] If it is judged at step S51 that the predetermined period has elapsed since the heater HT was started to turn on, processing proceeds to step S52. At step S52, it is judged whether the start condition is met.

[0144] If, however, it is judged at step S51 that the predetermined period has not elapsed since the heater HT was started, processing proceeds to step S53. At step S53, it is judged that the start condition is not met.

[0145] As described above, in the present embodiment, the start condition is set as the fact that a predetermined period has elapsed since the heater HT was started. Thus, the control section 110 starts the processing for changing the length of at least one of the first period and the second period only after a predetermined period has elapsed since the heater was started. This can prevent the unnecessary setting of the first period TM11, etc., even when the gas concentration in the gas sensor 200 cannot yet be measured. Even with this form, the same effects as those of the first embodiment can be achieved.

[0146] The embodiment essential to the invention is described with reference to Fig. 13. This embodiment differs from the first embodiment only in the content of the information displayed at step S11 of Fig. 8, in particular the content of the start condition. The following describes the main points of difference from the first embodiment.

[0147] The Fig. The processing sequence shown in Fig. 13 is a specific processing flow executed at step S11 of Fig. 8 and instead of the Fig. 9 is executed.

[0148] In the first step S61, the temperature (casing temperature) of the control device 100 is detected by the temperature sensor 150. In step S62 following step S61, a decision is made as to whether the temperature of the control device 100 detected in step S62 has changed from the temperature of the control device 100 detected in the previous control period. For example, if the absolute value of the difference between the previously detected temperature and the currently detected temperature exceeds a predetermined threshold, it is assumed that the temperature of the control device 100 has changed.

[0149] If it is judged at step S62 that the temperature of the control device 100 has changed, processing proceeds to step S63. At step S63, it is judged whether the start condition is met.

[0150] On the other hand, if it is judged in step S62 that the temperature of the control device 100 has not changed, processing proceeds to step S64. In step S64, it is judged that the start condition is not met.

[0151] As described above, in this embodiment, a temperature change of the control device 100 is set as a start condition. Therefore, when the temperature measured by the temperature sensor 150 changes, the control section 110 starts processing to change the length of at least one of the first period TM11 and the second period TM12. In this way, although the resistance values ​​of the resistor R14, etc., have not changed with the temperature and the need for adjusting the first period TM11, etc. is small, the adjustment of the first period TM11, etc. can be prevented from being performed unnecessarily. Even with this form, the same effects as in the first embodiment can be achieved.

[0152] The fourth embodiment will be described with reference to Fig. 14. This embodiment differs from the first embodiment only in the content of the information displayed at step S11 of Fig. 8, in particular the content of the start condition. The following essentially describes the differences from the first embodiment.

[0153] The Fig. The processing sequence shown in Fig. 14 is a specific processing flow executed at step S11 of Fig. 8 and instead of the Fig. 9 is executed.

[0154] In the first step S71, it is decided whether since the previous execution of the processing of step S13 and the Fig. 8, a predetermined period has passed. If the predetermined period has elapsed, processing proceeds to step S72. In step S72, it is judged whether the start condition is satisfied. Conversely, if it is judged in step S71 that the predetermined period has not elapsed, processing proceeds to step S73. In step S73, it is judged that the start condition is not satisfied.

[0155] As described above, in the present embodiment, the start condition is set so that a predetermined period has elapsed since the processing of step S13 and subsequent steps. Thus, the control section 110 starts processing to change the length of at least one of the first period TM11 and the second period TM12 after each elapse of the predetermined period.

[0156] Since the impedance measurement is performed regularly and appropriately without complex processing, the processing load of the control device 100 can be reduced. Even with such a form, the same effects as in the first embodiment can be achieved.

[0157] A fifth embodiment will be described with reference to Fig. 15. This embodiment differs from the first embodiment only in the content of the data stored in step S25 of Fig. 8. The following describes the main points of difference from the first embodiment.

[0158] The Fig. The processing sequence shown in Fig. 15 is a specific processing flow executed in step S25 of Fig. 8 and instead of the Fig. 10 is executed. This processing is carried out by adding steps S81 and S82 to the beginning of the processing shown in Fig. 10 shown processing sequence is carried out.

[0159] The control device 100 counts the number of sweep voltages applied to the gas sensor 200 (which may be the number of impedance measurements) and stores the number. This number is also referred to below as the "number of applications." In the first step S81, a decision is made as to whether the number of applications has reached a predetermined number. If the number of applications has reached the predetermined number, processing proceeds to step S82.

[0160] At step S82, the number of applications is set to zero. At step S41 and the other steps following step S82, processing similar to that described with reference to Fig. 10. A specific description is therefore not required.

[0161] If the number of applications has not reached the predetermined number at step S81, the Fig. 15 is terminated without changing the length of the first period TM11 or the second period TM12.

[0162] With the control section 110 of this embodiment, as a result of executing the above-described processing, changing the length of at least one of the first period TM11 and the second period TM12 is executed each time the number of times the sweep voltage is applied to the gas sensor 200 reaches a predetermined number. For example, after the processing for changing the length of the first period TM11 has been executed, the length of the first period TM11 is kept unchanged, and the sweep voltage application and impedance measurement are repeatedly performed until the number of applications reaches the predetermined number. This can reduce the processing load of the control device 100 compared to the case where the length of the first period TM11, etc., is changed every control period. Even with such a form, the same effects as those of the first embodiment can be achieved.

[0163] A sixth embodiment will be described with reference to Fig. 16. This embodiment differs from the first embodiment only in the content of the data stored in step S25 of Fig. 8. The following describes the main points of difference from the first embodiment.

[0164] The Fig. The processing sequence shown in Fig. 16 is a specific processing flow executed at step S25 of Fig. 8 and instead of the Fig. 10 shown processing sequence is executed.

[0165] Furthermore, in the present embodiment, as in the fifth embodiment described above, the control device 100 counts the number of application cases. The control device 100 stores the first measurement value and the second measurement value acquired by the measuring section 120 as a history each time the Fig. 8 shown processing sequence is executed.

[0166] In the first step S91, it is determined whether the number of applications has reached a predetermined number. The predetermined number of times is set in advance as the number of first measurement values, etc., required to calculate the respective averages of the first measurement value and the second measurement value. If the number of applications has reached the predetermined number, processing proceeds to step S92. In step S92, the number of applications is set to zero.

[0167] In step S93 following step S92, as in DE 10 2014 205 383 A1, DE 11 2012 005 904 T5, and DE 10 2015 205 971 A1, the average value is calculated from a number of acquired first measured values ​​equal to the predefined number. Additionally, the mean value is calculated from a number of acquired second measured values ​​equal to the predefined number. A decision is then made as to whether the mean value of the first measured values ​​is greater than the mean value of the second measured values.

[0168] If the average value of the first measured values ​​is greater than that of the second measured values, processing proceeds to step S94. In step S94, processing for extending the second period TM12 is performed as shown in Fig. 3 described under (B).

[0169] If it is judged at step S93 that the mean value of the first measured values ​​is not greater than the mean value of the second measured values, processing proceeds to step S95. At step S95, it is decided whether the mean value of the first measured values ​​is smaller than that of the second measured values. If the mean value of the first measured values ​​is smaller than that of the second measured values, processing proceeds to step S96. At step S96, the processing for extending the first period TM11 is performed as shown in Fig. 4 described under (B).

[0170] If the mean value of the first measured values ​​is not smaller than the mean value of the second measured values ​​at step S95, the Fig. The processing sequence shown in Figure 16 is completed. This means that the mean values ​​of the first measured value and the second measured value were equal. Thus, the lengths of the first period TM11 and the second period TM12 are not changed.

[0171] If the number of applications has not reached the predetermined number at step S91, the Fig. 16 is terminated without changing the length of the first period TM11 or the second period TM12.

[0172] In the present embodiment described above, after the sweep voltage is applied to the gas sensor 200 and the sweep current is measured by the measuring section 120 (which could also be a measurement of the sweep voltage), the control section 110 changes the length of at least one of the first periods TM11 and the second period TM12 a plurality of times, the change being effective in the next and subsequent processing periods, and the change being performed based on a comparison between the respective mean values ​​of the first measured values ​​and the second measured values.

[0173] Specifically, when the average value of the first measured values ​​is larger than that of the second measured values, the control section 110 changes the second period TM12 to become longer, with the change taking effect in the next and subsequent processing periods, while when the average value of the first measured values ​​is smaller than that of the second measured values, the control section 110 changes the first period TM11 to become longer, with the change taking effect in the next and subsequent processing periods.

[0174] Even if the first measured value or the second measured value temporarily changes due to noise, etc., the influence on the length of the first period TM11 or the second period TM12 can be reduced. This allows the gas concentration measurement to be performed with greater stability.

[0175] A seventh embodiment will be described next. The control device 100 of this embodiment also changes the length of at least one of the first period TM11 and the second period TM12 to suppress the effects of the accumulated charge on the electromotive force. However, the form of the change differs from that of the first embodiment. A concrete example will be explained with reference to Fig. 17 described.

[0176] As in the case of Fig. 2 shows (A) in Fig. 17 the temporal variation of the sweep current in the case that the value of the sweep current in the first period TM11 and the value of the sweep current in the second period TM12 correspond to the respective setpoints (I10 and -I10).

[0177] (Am Fig. Figure 17 shows the time variation of the sweep current when the value of the sweep current in the first period TM1 becomes I11, which is greater than the setpoint I10. In the example of (B) in Fig. 17 the first measured value (I11) is greater than the second measured value (I10).

[0178] If the first measured value exceeds the second measured value, the control section 110 of this embodiment changes the length of the first period TM11 to be shorter than in the case of (A) in Fig. 17. In the example of (B) in Fig. 17, the time at which the first period TM11 ends (which is also the start time of the second period TM12) is changed to time t19, which precedes time t20.

[0179] In addition, the time at which the second period TM12 ends is changed from time t30 to time t29. Thus, the length of the second period TM12 in (B) is Fig. 17 equal to the length of the second period TM12 in (A) of Fig. 17.

[0180] As a result of the above change, the length of the first period TM11 in (B) is Fig. 17 smaller than that of the first period TM11 in (A) of Fig. 17.

[0181] It should be noted that in (B) of Fig. 17, the mask period TM10 is also shortened along with the shortening of the first period TM11. Specifically, the time at which the mask period TM10 ends is changed from time t40 to time t33. By executing this processing by the mask setting section 140, the transition to the concentration measurement period TM20 and the measurement of the gas concentration can be performed early.

[0182] In (B) of Fig. 17, the amount of charge accumulated per unit time in the gas sensor 200 in the first period TM11 is larger than in the case of (A) in Fig. 17. In (B) of Fig. 17, since the first period TM11 has become short, the amount (total amount) of charge accumulated in the gas sensor 200 in the first period TM11 is, however, almost the same as in the case of (A) in Fig. 17.

[0183] As a result, the difference between the amount of charge accumulated in the gas sensor 200 in the first period TM11 and the amount of charge released by the gas sensor 200 in the second period TM12 can be kept as small as in the case of (A) in Fig. 17. Since the charge accumulation on the gas sensor 200 is suppressed in the mask period TM10, the gas concentration can be accurately measured with the gas sensor 200.

[0184] Furthermore, when the second measured value becomes smaller than I10, and thus the first measured value becomes larger than the second measured value, the first period TM11 is also changed to become shorter. In this case, too, the charge accumulation on the gas sensor 200 is suppressed as described above.

[0185] As described above, when the first measured value is greater than the second measured value, the control section 110 of the present embodiment changes the first period TM11 to be shorter. On this occasion, if it were attempted to measure the first measured value at the same time point (t191) as in (A) of Fig. 17, ie during the first period TM11 in (A) in Fig. 17, the first period TM11 would have already expired by this time, so it would not be possible to obtain the first measured value accurately.

[0186] Therefore, as the first period TM11 becomes shorter as in the present embodiment, the timing at which the measuring section 120 performs the measurement (acquisition of the first measured value) also changes. In the example of (B) in Fig. 17, this timing is changed so that the first measured value is acquired at time t181, which precedes time t191. The period from time t10 to time t181 is shorter than the first period TM11 after the change in the first period TM11. By changing the timing at which the first measured value is acquired as described above, the first measured value in the first period TM11 can be accurately acquired.

[0187] In the example of (B) in Fig. 17, the time at which the second measured value is recorded after reaching the second period TM12 is not changed. In (B) of Fig. 17, the second measured value is taken at time t281, which precedes time t291, but the length of the period from time t19 to time t281 is equal to the length of the period from time t20 to time t291 in (A) of Fig. 17.

[0188] In contrast to the above, an example in which the first measured value becomes smaller than the second measured value is shown using Fig. 18 described. In Fig. Figure 18 (A) shows a case where, as in the case of Fig. 2, the temporal variation of the sweep current is such that the value of the sweep current in the first period TM11 and the value of the sweep current in the second period TM12 agree with the respective setpoints (I10 and -I10).

[0189] (Am Fig. 18 shows the case where the time variation of the sweep current is such that the value of the sweep current in the first period TM11 becomes I09, which is smaller than the setpoint 110. In the example of (B) in Fig. 18 the first measured value (I09) is smaller than the second measured value (I10).

[0190] When the first measured value is smaller than the second measured value, the control section 110 of the control device 100 changes the length of the second period TM12 to be shorter than in the case of (A) in Fig. 18. In the example of (B) in Fig. 18, the time at which the second period TM12 ends is changed to time t29, which precedes time t30.

[0191] As a result of the above change in (B) from Fig. 18 the second period TM12 is made shorter than the first period TM11.

[0192] In (B) of Fig. 18, since the second period TM12 is shortened, the mask period TM10 is also shortened. Specifically, the time at which the mask period TM10 ends is changed from time t40 to time t39. By executing such processing by the mask setting section 140, the transition to the concentration measurement period TM20 and the measurement of the gas concentration can be performed early.

[0193] In (B) of Fig. 17, as the second period TM12 is shortened, the amount of charge released by the gas sensor 200 in the second period TM12 is reduced. Thus, not only the charge accumulated in the gas sensor 200 in the first period TM11 decreases, but also the charge released by the gas sensor 200 in the second period TM12 decreases.

[0194] Thereby, the difference between the amount of charge accumulated in the gas sensor 200 in the first period TM11 and the amount of charge released by the gas sensor 200 in the second period TM12 can be kept as small as in the case of (A) in Fig. 18. Since the charge accumulation on the gas sensor 200 is suppressed in the mask period TM10, the gas concentration can be accurately measured with the gas sensor 200.

[0195] Note that the second period TM12 is also changed to become shorter when the second measured value becomes greater than I10, causing the first measured value to become smaller than the second measured value. In this case, too, charge accumulation on the gas sensor 200 is suppressed as described above.

[0196] As described above, when the first measured value is smaller than the second measured value, the control section 110 of the present embodiment changes the second period TM12 to a shorter one. In this case, if an attempt were made to obtain the second measured value at the same time point (t291) as in (A) of Fig. 18, ie after the start of the second period TM12, the second period TM12 would have already ended by that time, so that it would not be possible to obtain the second measured value accurately.

[0197] Therefore, when the second period TM12 becomes shorter as in the present embodiment, the timing at which the measuring section 120 performs the measurement (acquisition of the second measured value) also changes. In the example of (B) in Fig. 18, the timing is changed so that the first measured value is acquired at time t281 before time t291. The period from time t20 to time t281 is shorter than the second period TM12 after the change. By changing the timing at which the second measured value is acquired as described above, the second measured value can be accurately acquired in the second period TM12.

[0198] In the example of (B) in Fig. 18, the time (1191) at which the first measured value is recorded after reaching the first period TM11 is not changed.

[0199] With this embodiment as described above, if the first period T11 or the second period T12 is shortened, the timing for acquiring the first measured value or for acquiring the second measured value is changed accordingly. If the processing load caused by such a change is a problem, it is better to lengthen the first period T11 or the second period T12 as in the first embodiment ( Fig. 3 and Fig. 4).

[0200] It should be noted that the change in the first period TM11 or the second period TM12 described above is not performed in the current mask period but in the next mask period TM10, as described above for the first embodiment with reference to Fig. 5 described.

[0201] Similar to the method described for the first embodiment, which is based on Fig. 6, the control section 110 of the present embodiment changes the length of the first period TM11 or the second period TM12 so that the respective absolute values ​​of the time integral of the value measured by the measuring section 120 in the first period TM11 (the range S1 in Fig. 6) and the time integral of the value measured by the measuring section 120 in the second period TM12 (the area S2 in Fig. 6) agree with each other.

[0202] Specific processing contents executed by the control device 100 for the above-described control will be described below. Also in this embodiment, processing similar to that of the first embodiment is performed, as described above with reference to FIG. Fig. 7 to 9. However, in the processing carried out by the present embodiment, the Fig. 10 for the first embodiment (ie the processing sequence shown in step S25 of the Fig. 8) by the controller in Fig. 19 replaced by the processing sequence shown.

[0203] In the first step S101 of the Fig. 19, it is decided whether the first measured value is greater than the second measured value. If the first measured value is greater than the second measured value, the processing proceeds to step S102. At step S102, as shown in Fig. 17 under (B), the processing for shortening the first period TM11 is performed. The first period TM11, the length of which has thus been changed, is used in the judgment of step S 19 when the Fig. 8 shown processing sequence is executed in the next control period.

[0204] If, at step S101, the first measured value is not greater than the second measured value, processing proceeds to step S103. At step S103, it is decided whether the first measured value is smaller than the second measured value. If the first measured value is smaller than the second measured value, processing proceeds to step S104. At step S104, the processing for shortening the second period TM12 is performed as shown in Fig. 18 under (B). The second period TM12, whose length has thus been changed, is used in the judgment of step S23 when the Fig. 8 shown processing sequence is executed in the next control period.

[0205] If it is judged at step S103 that the first measured value is not smaller than the second measured value, the Fig. The processing sequence shown in Figure 19 is completed. This means that the first measured value and the second measured value were the same. Thus, the lengths of the first period TM11 and the second period TM12 are not changed.

[0206] As a result of the execution of the above processing by the control device 100, the control of the Fig. 17 and Fig. 18 shown form.

[0207] An eighth embodiment will be described with reference to Fig. 20. This embodiment differs from the seventh embodiment described above only in the content of the data stored in step S25 of Fig. 8. The following describes the main differences from the seventh embodiment.

[0208] The processing sequence in Fig. 20 shows a specific flow of the process at step S25 of Fig. 8 and is used instead of the processing carried out in Fig. 19 shown processing sequence is executed.

[0209] Also in the present embodiment, the control device 100 counts, as in the fifth embodiment ( Fig. 15), the number of use cases. In addition, the control device 100 stores the number of use cases each time the Fig. 8, the first measured value and the second measured value acquired by the measuring section 120 are stored as history.

[0210] In the first step S111, it is decided whether the number of applied voltages has reached a predetermined number. The predetermined number of times is set in advance as the number of first measurement values, etc., required to calculate the respective average values ​​of the first measurement values ​​and the second measurement values. If the number of applications has not reached the predetermined number, the Fig. 20 is terminated without changing the length of the first period TM11 or the second period TM12. When the number of applications has reached the predetermined number, processing proceeds to step S112.

[0211] In step S112, the number of applications is set to zero. In step S113 following step S112, the mean value of a number of acquired first measured values ​​equal to the predetermined number described above is calculated. In addition, the mean value of a number of acquired second measured values ​​equal to the predetermined number described above is calculated. A decision is then made as to whether the mean value of the first measured values ​​is greater than that of the second measured values.

[0212] If the average of the first measured values ​​is greater than the average of the second measured values, processing proceeds to step S114. In step S114, the processing for shortening the first period TM11 is performed as shown in Fig. 17 described under (B).

[0213] If it is determined at step S113 that the average of the first measured values ​​is not greater than the average of the second measured values, processing proceeds to step S115. At step S115, it is decided whether the average of the first measured values ​​is smaller than that of the second measured values. If the average of the first measured values ​​is smaller than that of the second measured values, processing proceeds to step S116. At step S116, the processing for shortening the second period TM12 is executed as shown in Fig. 18 described under (B).

[0214] If it is determined that the mean value of the first measured values ​​is not smaller than that of the second measured values ​​at step S115, the Fig. The processing sequence shown in Figure 20 is completed. This means that the mean value of the first measured value and the mean value of the second measured value were the same. Thus, the lengths of the first period TM11 and the second period TM12 are not changed.

[0215] With this embodiment, as described above, after applying the sweep voltage to the gas sensor 200 and measuring the sweep current by the measuring section 120 (which could also be a measurement of the sweep voltage), the control section 110 changes the length of at least one of the first periods TM11 and the second period TM12 a plurality of times each, the change being effective in the next and subsequent processing periods, and the change being performed based on a comparison between the respective mean values ​​of the first measured values ​​and the second measured values.

[0216] Specifically, when the average value of the first measured values ​​is larger than that of the second measured values, the control section 110 changes the first period TM11 to be shorter, with the change taking effect in the next and subsequent processing periods, while when the average value of the first measured values ​​is smaller than that of the second measured values, the control section 110 changes the second period TM12 to be shorter, with the change taking effect in the next and subsequent processing periods.

[0217] Even if the first or second measured value temporarily changes due to noise, etc., the influence on the length of the first period TM11 or the second period TM12 can be reduced. This allows the gas concentration measurement to be performed with greater stability.

[0218] A ninth embodiment will be described with reference to Fig. 21. This embodiment differs from the first embodiment only in the content of the message displayed at step S25 of Fig. 8. The following describes the main points of difference from the first embodiment.

[0219] The processing sequence in Fig. 21 shows a specific flow of the process at step S25 of Fig. 8 and is used instead of the processing carried out in Fig. 10 shown processing sequence is executed.

[0220] In the first step, S121, it is decided whether the time integral value of the value (sweep current or sweep voltage) measured by the measuring section 120 in the first period TM11 corresponds to a predetermined design value. The absolute value of the "time integral value of the value measured by the measuring section 120 in the first period TM11" corresponds to the Fig. 6. Such a time integral value can be calculated by subtracting the first value at time t191 into Fig. 3 is multiplied by the length of the first period TM11. Alternatively, the first measured value in the first period TM11 can be recorded multiple times to calculate the time integral value more accurately.

[0221] In addition, the "predetermined rated value" referred to here means the time integral value described above in the case where the first measured value corresponds to the target value and the length of the first period TM11 corresponds to the original rated value.

[0222] If the time integral value matches the design value, processing proceeds to step S123, described below, without changing the length of the first period TM11. If the time integral value does not match the design value, processing proceeds to step S122. In step S122, the length of the first period TM11 is changed so that the time integral value matches the target value. For example, if the time integral value is smaller than the design value, the first period TM11 is changed to be longer.

[0223] In step S123, after step S122, it is decided whether the time integral value of the value (sweep current or sweep voltage) measured by the measuring section 120 in the second period TM12 agrees with a predetermined design value. The absolute value of the "time integral value of the value measured by the measuring section 120 in the second period TM12" corresponds to the value specified in Fig. 6. Such a time integral value can be calculated by substituting the second value at time t291 in Fig. 3 is multiplied by the length of the second period TM12. Alternatively, the second measured value can be recorded multiple times in the second period TM12 to calculate the time integral value more accurately.

[0224] In addition, the "predetermined rated value" referred to here means the time integral value described above in the case where the second measured value corresponds to the target value and the length of the second period TM12 corresponds to the original rated value.

[0225] If the time integral value agrees with the design value, the Fig. 21 is terminated without changing the length of the second period TM12. If the time integral value does not match the design value, processing proceeds to step S124. In step S124, the length of the second period TM12 is changed so that the time integral value matches the target value. For example, if the time integral value is smaller than the design value, the second period TM12 is changed to become longer.

[0226] By performing the processing described above, the amount of charge accumulated in the gas sensor 200 in the first period TM11 and the amount of charge released by the gas sensor 200 in the second period TM12 can each be adjusted to approach the design value. This can reduce the difference between the two and accurately measure the gas concentration. Note that it would also be possible to use a form in which only one of the Fig. 21 and the set of processing steps S121 to S122 and the set of processing steps S123 to S124 are executed, the other being omitted.

[0227] As described above, the control section 110 of this embodiment changes the length of at least one of the first period TM11 and the second period TM12 so that at least one of the time integral value of the values ​​measured by the measuring section 120 in the first period TM11 and the time integral value of the values ​​measured by the measuring section 120 in the second period TM12 corresponds to the predetermined design value. The same effects as in the first embodiment can also be achieved with this form.

[0228] When the lengths of both the first period TM11 and the second period TM12 are changed, the mask setting section 140 changes the length of the mask period TM10 so that after the change, both the first period TM11 and the second period TM12 are included in the mask period TM10.

Claims

[1] A control device (100) for a gas sensor (200) that measures a gas concentration, the control device (100) comprising: a voltage applying section (F1, F2) that applies a voltage for measuring the impedance of the gas sensor (200) to the gas sensor (200), the voltage applying section (F1, F2) being connected in series with a resistor (R14) and another resistor (R15); a control section (110) that controls the operation of the voltage applying section (F1, F2); a sweep measuring section (120) that measures at least one of a current flowing in the gas sensor (200) and a voltage applied to the gas sensor (200), and a temperature measuring section (150), wherein a location at which the temperature is measured by the temperature measuring section (150) is located near the resistor (R14) or the further resistor (R15), wherein the control section (110) performs the following: a first controller which, during a first period (TM11), operates the voltage application section such that a current flows through the gas sensor (200) in a first direction, and a second controller that operates the voltage applying section during a second period (TM12) such that a current flows through the gas sensor (200) in a second direction opposite to the first direction; and wherein the control section (110) changes the length of at least one of the first period (TM11) and the second period (TM12) based on a comparison between a first measured value, which is the absolute value of a value measured by the sweep measuring section (120) during the execution of the first control, and a second measured value, which is the absolute value of a value measured by the sweep measuring section (120) during the execution of the second control, characterized by in that, in response to a change in the temperature measured by the temperature measuring section (150) such that an absolute value of a difference between a temperature detected in a first control period and a temperature detected in a second control period following the first control period exceeds a prescribed threshold, the control section (110) performs processing for changing the length of at least one of the first period (TM11) and the second period (TM12). [2] Control device (100) according to claim 1, wherein: in response to the first measured value being greater than the second measured value, the control section (110) changes the length of the second period (TM12) such that it becomes longer; and in response to the first measured value being smaller than the second measured value, the control section (110) changes the length of the first period (TM11) such that it becomes longer. [3] Control device (100) according to claim 1, wherein: in response to the first measured value being greater than the second measured value, the control section (110) changes the length of the first period (TM11) such that it becomes shorter; and in response to the first measured value being smaller than the second measured value, the control section (110) changes the length of the second period (TM12) such that it becomes shorter. [4] Control device (100) according to claim 1, wherein: in response to the change in the first period (TM11) or the second period such that they become shorter, the sweep measuring section (120) changes the time at which the measurement is carried out. [5] Control device (100) according to claim 1, wherein: the application of a voltage by the voltage application section (F1, F2) and the measurement of current or voltage by the sweep measurement section (120) are carried out repeatedly; and the control section (110) changes the length of at least one of the first period (TM11) and the second period (TM12) in the next repetition based on a comparison between the first measured value and the second measured value measured in the current repetition. [6] Control device (100) according to claim 1, further comprising: a mask setting section that sets, as a period including the first period and the second period, a mask period (TM10) in which the measurement of the gas concentration by the gas sensor (200) is temporarily stopped, wherein the mask adjusting section changes the length of the mask period in response to the change in the length of at least one of the first period (TM11) and the second period (TM12). [7] Control device (100) according to claim 1, wherein: the control section (110) changes the length of at least one of the first period (TM11) and the second period (TM12) to effect agreement between the respective absolute values ​​of the time-integral value of a value measured by the sweep measuring section (120) in the first period and the time-integral value of a value measured by the sweep measuring section in the second period (TM12). [8] Control device (100) according to claim 1, wherein: the control section (110) changes the length of at least one of the first period (TM11) and the second period (TM12) so as to cause a match between a predetermined target value and at least one of the time-integral values ​​of a value measured by the sweep measuring section (120) in the first period (TM11) and the time-integral value of a value measured by the sweep measuring section (120) in the second period (TM12). [9] Control device (100) according to claim 1, further comprising: a heater (HT) for heating the gas sensor (200); and a sensor temperature estimation section (121) for estimating the temperature of the gas sensor (200) based on the impedance of the gas sensor (200), wherein, after the temperature estimated by the sensor temperature estimation section exceeds a prescribed temperature, the control section (110) starts processing for changing the length of at least one of the first periods and the second periods. [10] Control device (100) according to claim 1, further comprising: a heater for heating the gas sensor (200), wherein after a prescribed period has elapsed since the heater was started to be switched on, the control section (110) starts processing to change the length of at least one of the first and second periods. [11] Control device (100) according to claim 1, wherein: after the application of a voltage by the voltage application section (F1, F2) and the measurement of current or voltage by the sweep measurement section (120) have been repeated a plurality of times, the control section (110) changes the length of at least one of the first period (TM11) and the second period (TM12) in the next and subsequent iteration based on a comparison between the mean value of the first measured values ​​and the mean value of the second measured values. [12] Control device (100) according to claim 11, wherein: in response to the mean value of the first measured values ​​being greater than the mean value of the second measured values, the control section (110) changes the length of the second period (TM12) to become longer in the next and subsequent iterations; and in response to the mean of the first measured values ​​being less than the mean of the second measured values, the control section (110) changes the length of the first period to become longer in the next and subsequent iterations. [13] Control device (100) according to claim 11, wherein: in response to the mean value of the first measured values ​​being greater than the mean value of the second measured values, the control section (110) changes the length of the first period (TM11) to become shorter in the next and subsequent iterations; and in response to the mean value of the first measured values ​​being smaller than the mean value of the second measured values, the control section (110) changes the length of the second period (TM12) in the next and subsequent iterations to become shorter in the next and subsequent iterations. [14] Control device (100) according to claim 1, wherein: the control section (110) performs processing for changing the length of at least one of the first periods and the second periods after each elapse of a predetermined interval. [15] Control device (100) according to claim 1, wherein: the application of a voltage by the voltage application section (F1, F2) and the measurement of current or voltage by the sweep measurement section (120) are carried out repeatedly; and the control section (110) executes processing for changing the length of at least one of the first period (TM11) and the second period (TM12) each time the number of times the voltage is applied by the voltage applying section (F1, F2) has reached a predetermined number of times.

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