JP2018116029A - Impedance detection device of oxygen concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect impedance of an oxygen concentration sensor without providing a current detection resistor to the oxygen concentration sensor in series.SOLUTION: An ECU 1 for detecting impedance of an oxygen concentration sensor (hereafter, called a sensor) 3 comprises: a capacitor 7; a switch 11 for charging the capacitor 7 with a prescribed voltage VD output from a voltage generation circuit 9; a switch 12 for discharging from the charged capacitor 7 to the sensor 3; and a control part 19. The control part 19 controls the switches 11, 12 for charging the capacitor 7 with the prescribed voltage VD, then causing the capacitor 7 to discharge to the sensor 3. Then the control part 19 detects a voltage of the capacitor 7 when a prescribed discharge time passed since start of discharge, then, calculates impedance of the sensor 3 using the detected voltage.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an apparatus for detecting impedance of an oxygen concentration sensor.

  As an apparatus for detecting the impedance of an oxygen concentration sensor, for example, there is one described in Patent Document 1 or Patent Document 2. Hereinafter, the oxygen concentration sensor is also simply referred to as a sensor. The impedance of the oxygen concentration sensor is also referred to as sensor impedance or simply impedance.

  In the apparatus of Patent Document 1, a predetermined fixed voltage is applied to a series circuit of a sensor and a current detection resistor to detect a voltage ΔVs across the sensor and a voltage ΔVr across the current detection resistor, and the two voltages ΔVs across the two. , ΔVr, the sensor impedance is calculated. Hereinafter, such a method is referred to as a fixed voltage application method. Since the resistance value of the current detection resistor is known, detecting the voltage ΔVr across the current detection resistor corresponds to detecting the current flowing through the sensor.

  In the apparatus of Patent Document 2, a predetermined fixed current is applied to a series circuit of a sensor and a current detection resistor to detect a voltage ΔVs across the sensor and a voltage ΔVr across the current detection resistor, and the two voltage ΔVs across the two. , ΔVr, the sensor impedance is calculated. Hereinafter, such a method is referred to as a fixed current application method.

Japanese Patent Laid-Open No. 2006-105065 JP-A-2006-3882

  In either of the fixed voltage application method and the fixed current application method, a current detection resistor is provided in series with the sensor, which tends to increase the circuit scale. Furthermore, in order to ensure sufficient detection accuracy of the sensor impedance, at least a current detection resistor with high resistance value accuracy is required, which tends to increase the cost of the device.

  Further, in order to ensure the detection accuracy of the sensor impedance, it is necessary to make the voltage across the sensor ΔVs and the voltage across the current detection resistor ΔVr larger than the voltage detection resolution. However, in the fixed voltage application method, when the sensor impedance is small, the voltage across the sensor ΔVs is small, and when the sensor impedance is large, the voltage across the current detection resistor ΔVr is small. Even in the fixed current application method, when the sensor impedance is small, the voltage ΔVs across the sensor is small.

  For this reason, in the fixed voltage application method, in order to ensure the detection accuracy of the sensor impedance, it is conceivable to increase the voltage applied to the series circuit (hereinafter, applied voltage). Similarly, in the fixed current application method, in order to ensure the detection accuracy of the sensor impedance, it is conceivable to increase the current applied to the series circuit (hereinafter, applied current). However, even if the applied voltage or the applied current is increased, it is necessary that the voltage across the sensor ΔVs does not exceed the rated voltage of the sensor when the sensor impedance is large. Therefore, in each of the above methods in which a current detection resistor is provided in series with the sensor, it is difficult to ensure sensor impedance detection accuracy.

  Therefore, the present disclosure provides a novel technique capable of detecting sensor impedance without providing a current detection resistor in series with the oxygen concentration sensor.

  The impedance detection device of the oxygen concentration sensor of the present disclosure includes a capacitive element (7) having a capacitance, a charging unit (11, 19, S110, S160), a discharging unit (12, 19, S170, S230), A discharge detection unit (17, 19, S180, S190) and an impedance calculation unit (19, S210) are provided.

  The charging unit charges the capacitive element with a predetermined voltage. The discharging unit discharges the oxygen concentration sensor (3) from the capacitive element charged by the charging unit. The during-discharge detection unit detects the voltage of the capacitive element when a predetermined discharge time has elapsed since the start of discharge by the discharge unit. The impedance calculation unit calculates the impedance of the oxygen concentration sensor using the voltage detected by the detection unit during discharge. The impedance calculated by the impedance calculation unit corresponds to the impedance detected by the impedance detection device.

  According to such a configuration, the sensor impedance can be detected without providing a current detection resistor in series with the oxygen concentration sensor. Further, by appropriately setting the discharge time, the voltage detected by the detecting unit during discharge can be set to a voltage within a desired range suitable for sensor impedance detection. For this reason, it is easy to ensure the detection accuracy of the sensor impedance as compared with the conventional method described above.

  In addition, the code | symbol in the parenthesis described in this column and a claim shows the correspondence with the specific means as described in embodiment mentioned later as one aspect, Comprising: The technical scope of this indication is shown. It is not limited.

It is a block diagram which shows the structure of the electronic control apparatus of a 1st embodiment. It is a flowchart showing an impedance detection process. It is a time chart for demonstrating an impedance detection process. It is a flowchart showing the time setting process of 2nd Embodiment. It is a time chart showing the effect | action of a time setting process. It is a flowchart showing the abnormality determination process of 3rd Embodiment. It is a block diagram which shows the structure of the electronic control apparatus of other embodiment.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.
[1. First Embodiment]
[1-1. Constitution]
As shown in FIG. 1, one end of an oxygen concentration sensor (hereinafter referred to as a sensor) 3 is connected to an electronic control device (hereinafter referred to as an ECU) 1 corresponding to the impedance detection device of the first embodiment. The other end of the sensor 3 is connected to the ground line outside the ECU 1. ECU is an abbreviation for “Electronic Control Unit”. Hereinafter, the end of the sensor 3 opposite to the ground line side, that is, the end connected to the ECU 1 is referred to as a positive terminal of the sensor 3.

The sensor 3 is disposed in the exhaust path of the vehicle engine. The sensor 3 is a sensor having a characteristic that an output voltage changes suddenly at a specific air-fuel ratio (for example, a theoretical air-fuel ratio). Such a sensor is called an oxygen sensor or an O ₂ sensor.

For this reason, the ECU 1 detects the output voltage of the sensor 3 and corrects the fuel injection amount to the engine so that the actual air-fuel ratio becomes the specific air-fuel ratio based on the detection result.
Further, the ECU 1 detects the impedance of the sensor 3 to estimate the temperature of the sensor 3 having a correlation with the impedance, so that the estimated temperature of the heater mounted in the sensor 3 becomes the target temperature. To control.

  In FIG. 1, the heater in the sensor 3 is not shown. Further, the heater control and the fuel injection amount correction are not related to the impedance detection device of the present disclosure, and thus detailed description thereof is omitted. Hereinafter, detection of the impedance of the sensor 3 will be described in detail.

  As shown in FIG. 1, the equivalent circuit of the sensor 3 includes a parallel circuit of an interelectrode capacitance 3a and an electrode interface resistance 3b, and an impedance Rs and an electromotive force component 3c of zirconia constituting the element of the sensor 3. , Represented as a series connected circuit. Specifically, the impedance of the sensor 3 to be detected is the impedance Rs of the zirconia. For this reason, hereinafter, “Rs” is used as the sign of the impedance of the sensor 3. Since the sensor 3 has the electrode interface resistance 3b, the ECU 1 applies an AC voltage to the sensor 3 in order to detect the impedance Rs. An alternating voltage is a voltage whose value changes with time.

  The ECU 1 includes a capacitor 7 having electrostatic capacity, a voltage generation circuit 9, a first switch 11, a second switch 12, a third switch 13, a resistor 15, a voltage detection unit 17, a control unit 19, and the like. .

One end of the capacitor 7 is connected to the ground line. Hereinafter, the end portion of the capacitor 7 opposite to the ground line side is referred to as a positive terminal of the capacitor 7.
The voltage generation circuit 9 generates a predetermined voltage (for example, 1.3 V) VD from the power supply voltage Vo, and outputs the predetermined voltage VD from the output unit 9a. The power supply voltage Vo is, for example, a vehicle battery voltage.

  The first switch 11 is provided in a path between the output unit 9 a of the voltage generation circuit 9 and the plus side terminal of the capacitor 7. A path in which the first switch 11 is provided is a charging path from the voltage generation circuit 9 to the capacitor 7. When the first switch 11 is turned on, the charging path is conducted, and the capacitor 7 is charged with the predetermined voltage VD from the voltage generation circuit 9. If the first switch 11 is turned off, the charging path is disconnected.

  The second switch 12 is provided in a path between the plus side terminal of the capacitor 7 and the plus side terminal of the sensor 3. The path where the second switch 12 is provided is a discharge path from the capacitor 7 to the sensor 3. When the second switch 12 is turned on, the discharge path is conducted and the capacitor 7 discharges to the sensor 3. Further, when the second switch 12 is turned off, the discharge path is disconnected.

  The third switch 13 is provided between the positive terminal of the sensor 3 and the ground line. That is, the third switch 13 is provided in parallel with the sensor 3. When the third switch 13 is turned on, both ends of the sensor 3 are conducted, and the charge charged in the sensor 3 is discharged.

  When the second switch 12 is turned on, the third switch 13 is also provided in parallel with the capacitor 7. Therefore, if the third switch 13 is turned on when the second switch 12 is turned on, both ends of the capacitor 7 are also conducted, and the charge charged in the capacitor 7 is discharged.

The resistor 15 is also provided between the positive terminal of the sensor 3 and the ground line, as with the third switch 13. That is, the resistor 15 is also provided in parallel with the sensor 3.
The voltage detection unit 17 detects the voltage of the path connecting the first switch 11 and the plus side terminal of the capacitor 7 as the voltage Va of the plus side terminal of the capacitor 7 (that is, the voltage of the capacitor 7) Va. Further, the voltage detection unit 17 detects the voltage of the path connecting the second switch 12 and the plus side terminal of the sensor 3 as the voltage of the plus side terminal of the sensor 3 (that is, the voltage of the sensor 3) Vb. Hereinafter, the voltage Va is also referred to as a capacitor voltage. The voltage Vb is also referred to as a sensor voltage. When the second switch 12 is on, the capacitor voltage Va and the sensor voltage Vb are the same.

  The voltage detection unit 17 is configured by an A / D converter and is controlled by the control unit 19. And the voltage detection part 17 outputs the digital signal which shows the value of the detected voltages Va and Vb to the control part 19 as a detection result.

  The control unit 19 controls the first switch 11, the second switch 12, the third switch 13, and the voltage detection unit 17, and calculates the impedance Rs of the sensor 3 using the detection result by the voltage detection unit 17.

  The control unit 19 is configured around a known microcomputer having, for example, a CPU and a semiconductor memory (hereinafter referred to as a memory) such as a RAM, a ROM, and a flash memory. The function of the control part 19 is implement | achieved when CPU runs the program stored in the non-transitional tangible recording medium. In this example, the memory corresponds to a non-transitional tangible recording medium that stores a program. Also, by executing this program, a method corresponding to the program is executed. The number of microcomputers constituting the control unit 19 may be one or plural. Further, the method of realizing the function of the control unit 19 is not limited to software, and part or all of the function may be realized using one or a plurality of hardware. For example, when the function of the control unit 19 is realized by an electronic circuit that is hardware, the electronic circuit may be realized by a digital circuit including a large number of logic circuits, an analog circuit, or a combination thereof.

[1-2. processing]
Next, the impedance detection process executed by the control unit 19 to detect the impedance Rs of the sensor 3 will be described with reference to the flowchart of FIG. 2 and the time chart of FIG.

The control unit 19 executes the impedance detection process of FIG. 2 at regular time intervals, for example.
When starting the impedance detection process, the control unit 19 turns on the first switch 11 among the three switches 11 to 13 as shown at time T1 in FIG. 3 in S110. In addition, before the 1st switch 11 is turned on, the electric charge does not remain in the capacitor | condenser 7 by the process of S220 and S240 mentioned later being implemented.

  When the first switch 11 is turned on, the capacitor 7 is charged by the predetermined voltage VD from the voltage generation circuit 9, and therefore the capacitor voltage Va starts to rise as shown in the fourth stage of FIG.

  In the next S120, the control unit 19 waits until a predetermined charging time t1 elapses after the first switch 11 is turned on in S110. The charging time t1 is set to a time shorter than the time for the capacitor 7 to be fully charged.

  When determining that the charging time t1 has elapsed, the control unit 19 proceeds to S130, and detects the capacitor voltage Va at this time as the charging voltage V1, as shown at time T2 in FIG. Specifically, the capacitor voltage Va is detected by the voltage detection unit 17, and the detection result is stored as the charging voltage V1. Therefore, the charging voltage V1 detected in S130 is the capacitor voltage Va during charging of the capacitor 7, and more specifically, the capacitor voltage Va when the charging time t1 has elapsed since the charging of the capacitor 7 was started. is there.

  In the next S140, the control unit 19 waits until a predetermined waiting time tw elapses after the first switch 11 is turned on in S110. The waiting time tw is set to a time longer than the time when the capacitor 7 is considered to be fully charged.

  When determining that the waiting time tw has elapsed, the control unit 19 proceeds to S150, and detects the capacitor voltage Va at this time as the pre-discharge voltage V0, as shown at time T3 in FIG. Specifically, the capacitor voltage Va is detected by the voltage detection unit 17, and the detection result is stored as the pre-discharge voltage V0. The pre-discharge voltage V0 detected in S150 is the capacitor voltage Va before the discharge to the sensor 3 is started, and is also the voltage Va of the capacitor 7 in a fully charged state.

  Thereafter, the control unit 19 proceeds to S160, and turns off the first switch 11 as shown at time T4 in FIG. Even when the first switch 11 is turned off, the capacitor voltage Va remains the pre-discharge voltage V0 detected in S150.

And control part 19 turns ON the 2nd switch 12 among three switches 11-13 as shown in time T5 of Drawing 3 at the following S170.
When the second switch 12 is turned on, the capacitor 7 is discharged to the sensor 3, so that the capacitor voltage Va decreases from the pre-discharge voltage V0 as shown in the fourth stage of FIG. When the second switch 12 is turned on, the sensor voltage Vb becomes the same as the capacitor voltage Va as shown in the fifth stage of FIG.

  In the next S180, the control unit 19 waits until a predetermined discharge time t2 elapses after the second switch 12 is turned on in S170. The discharge time t2 is set to a time shorter than the time when the capacitor 7 is completely discharged.

  When determining that the discharge time t2 has elapsed, the control unit 19 proceeds to S190, and detects the capacitor voltage Va at this time as the discharging voltage V2, as shown at time T6 in FIG. Specifically, the sensor voltage Vb is detected by the voltage detector 17, and the detection result is stored as the discharging voltage V2. At the time when the process of S190 is executed, since the second switch 12 is on, the sensor voltage Vb and the capacitor voltage Va are the same. Therefore, the discharging voltage V2 detected in S190 is the capacitor voltage Va during discharging of the capacitor 7, and more specifically, when the discharging time t2 has elapsed since the discharging from the capacitor 7 to the sensor 3 was started. This is the capacitor voltage Va. In S190, the capacitor voltage Va upstream from the second switch 12 may be detected.

  In the next S200, the control unit 19 calculates the capacitance C of the capacitor 7 by substituting V1 detected in S130 and V0 detected in S150 into the following Expression 2.

尚、式２は、式１を変形したものである。また、式１，２において、「Ｚ」は、電圧生成回路９の既知の出力インピーダンスであり、「ｔ１」は、前述の充電時間ｔ１である。また、式１，２における「Ｖ０」、即ち、満充電状態になったコンデンサ７の電圧Ｖａとしては、Ｓ１５０で検出した値ではなく、電圧生成回路９が出力する所定電圧ＶＤの設計値を用いても良い。

Expression 2 is a modification of Expression 1. In equations 1 and 2, “Z” is a known output impedance of the voltage generation circuit 9, and “t1” is the above-described charging time t1. In addition, as “V0” in Expressions 1 and 2, that is, the voltage Va of the capacitor 7 in the fully charged state, the design value of the predetermined voltage VD output from the voltage generation circuit 9 is used instead of the value detected in S150. May be.

  That is, the control unit 19 charges the capacitor 7 by turning on the first switch 11 from a state in which the electric charge of the capacitor 7 is completely removed, and sets V1 that is a measured value of the capacitor voltage Va during charging as a charging characteristic. The capacitance C of the capacitor 7 is calculated by substituting it into Equation 2 based on it.

  In step S210, the control unit 19 substitutes the V2 detected in step S190, the V0 detected in step S150, and the capacitance C calculated in step S200 into the following equation 4 to obtain the sensor 3 The impedance Rs is calculated.

尚、式４は、式３を変形したものである。また、式３，４において、「ｔ２」は、前述の放電時間ｔ２である。また、式３，４における「Ｖ０」、即ち、放電が開始される前のコンデンサ電圧Ｖａとしては、Ｓ１５０で検出した値ではなく、電圧生成回路９が出力する所定電圧ＶＤの設計値を用いても良い。また、式３，４における「Ｃ」としては、Ｓ２００で算出した値ではなく、コンデンサ７の静電容量Ｃの標準値を用いても良い。

Expression 4 is a modification of Expression 3. In the expressions 3 and 4, “t2” is the above-described discharge time t2. In addition, as “V0” in Expressions 3 and 4, that is, the capacitor voltage Va before the discharge is started, the design value of the predetermined voltage VD output from the voltage generation circuit 9 is used instead of the value detected in S150. Also good. In addition, as “C” in the expressions 3 and 4, the standard value of the capacitance C of the capacitor 7 may be used instead of the value calculated in S200.

  That is, the discharge characteristics when discharging from the capacitor 7 to the sensor 3 are determined by the impedance Rs of the sensor 3 and the capacitance C of the capacitor 7. For this reason, the control unit 19 discharges the capacitor 7 charged with the predetermined voltage VD to the sensor 3, and substitutes V2 which is a measured value of the capacitor voltage Va during discharge into the equation 4 based on the discharge characteristics, thereby impedance Rs. Is calculated.

  In the next S220, the control unit 19 turns on the third switch 13 as shown at time T7 in FIG. Then, since both ends of the sensor 3 are conducted, the charge charged in the sensor 3 is discharged. Further, since the second switch 12 is turned on at this time, both ends of the capacitor 7 become conductive when the third switch 13 is turned on. Therefore, the electric charge charged in the capacitor 7 is also discharged.

  When the control unit 19 turns on the third switch 13 and the time when it is considered that the charges of the sensor 3 and the capacitor 7 are completely discharged, the process proceeds to S230, as shown at time T8 in FIG. The second switch 12 is turned off. Further, in the next S240, the control unit 19 turns off the third switch 13, as shown at time T9 in FIG. 3, and then ends the impedance detection process once. Note that the control unit 19 may turn off the second switch 12 after turning off the third switch 13.

  On the other hand, for example, the control unit 19 uses the voltage detection unit 17 at any timing between turning off the third switch 13 in S240 and turning on the second switch 12 in the next impedance detection process. The sensor voltage Vb is detected as the output voltage of the sensor 3 corresponding to the air / fuel ratio. The output voltage of the sensor 3 here is the output voltage of the electromotive force component 3 c in the sensor 3. Since the sensor 3 is connected to the resistor 15 in parallel, the voltage Vb generated in the resistor 15 can be detected as the output voltage of the sensor 3 corresponding to the air-fuel ratio.

[1-3. effect]
According to the first embodiment described in detail above, the following effects are obtained.
(1a) In the ECU 1, the control unit 19 turns on the first switch 11, charges the capacitor 7 with the predetermined voltage VD, turns off the first switch 11, and then turns on the second switch 12. The sensor 7 is discharged from the capacitor 7. Then, the control unit 19 detects the discharging voltage V2, which is the capacitor voltage Va when the discharging time t2 has elapsed from the start of discharging, and calculates the impedance Rs of the sensor 3 using the detected discharging voltage V2. . According to such an ECU 1, the impedance Rs can be detected without providing a current detection resistor in series with the sensor 3. Further, by appropriately setting the discharge time t2, the discharging voltage V2 detected during discharging can be set to a voltage within a desired range suitable for detecting the impedance Rs. For this reason, it is easy to ensure the detection accuracy of the impedance Rs without increasing the maximum voltage applied to the sensor 3 as compared with the conventional method described above.

  (1b) The control unit 19 detects the pre-discharge voltage V0 that is the capacitor voltage Va before the discharge is started, and calculates the impedance Rs of the sensor 3 using the detected pre-discharge voltage V0. For this reason, compared with the case where the design value of the predetermined voltage VD is used instead of the detection value of the pre-discharge voltage V0, the calculation accuracy (that is, detection accuracy) of the impedance Rs can be improved.

  (1c) The control unit 19 detects the charging voltage V1, which is the capacitor voltage Va when the charging time t1 has elapsed from the start of charging of the capacitor 7, and based on the detected charging voltage V1, The electric capacity C is calculated. Then, the control unit 19 calculates the impedance Rs of the sensor 3 also using the calculated capacitance C. For this reason, compared with the case where the standard value of the capacitance C is used instead of the calculated value of the capacitance C, the calculation accuracy of the impedance Rs can be improved. Further, the capacitance C changes not only due to variations due to individual differences of the capacitors 7, but also changes depending on, for example, temperature, applied voltage, usage period, etc. Even if such changes occur, the actual capacitance C is calculated. Thus, it can be used to calculate the impedance Rs.

  (1d) The ECU 1 includes a first switch 11 for charging the capacitor 7 and a second switch 12 for discharging the capacitor 7 to the sensor 3. For this reason, charging of the capacitor 7 and discharging from the capacitor 7 to the sensor 3 can be performed separately.

  (1e) The ECU 1 includes a third switch 13 provided in parallel with the sensor 3. For this reason, the electric charge charged in the sensor 3 from the capacitor 7 can be discharged by turning on the third switch 13. Therefore, the influence of the charge charged from the capacitor 7 to the sensor 3 can be eliminated with respect to detecting the output voltage of the sensor 3 according to the air-fuel ratio.

  (1f) When the second switch 12 is on, the third switch 13 is a switch provided in parallel to the capacitor 7. For this reason, when the second switch 12 is turned on, the charge of the capacitor 7 can be discharged by turning on the third switch 13. Therefore, before the capacitor 7 is charged next time, the capacitor 7 can be returned to the uncharged initial state, and the calculation accuracy of the capacitance C can be improved.

  (1g) The control unit 19 calculates the impedance Rs of the sensor 3 at regular intervals. For this reason, control of the heater mentioned above can be implemented stably. The control unit 19 also detects the output voltage of the sensor 3 according to the air-fuel ratio at least at regular intervals. For this reason, the correction of the fuel injection amount described above can be performed stably.

  In the present embodiment, the capacitor 7 corresponds to a capacitive element. The first switch 11 and the control unit 19 that performs the processes of S110 and S160 in FIG. 2 correspond to the charging unit. The second switch 12 and the control unit 19 that performs the processes of S170 and S230 in FIG. 2 correspond to a discharge unit. The voltage detection unit 17 and the control unit 19 that performs the processes of S180 and S190 in FIG. 2 correspond to the discharging detection unit. The control unit 19 that performs the process of S210 in FIG. 2 corresponds to an impedance calculation unit. The voltage detection unit 17 and the control unit 19 that performs the process of S150 in FIG. 2 correspond to the pre-discharge detection unit. The voltage detection unit 17 and the control unit 19 that performs the processes of S120 and S130 in FIG. 2 correspond to the charging detection unit. The control unit 19 that performs the process of S200 in FIG. 2 corresponds to a capacity calculation unit. The voltage generation circuit 9 corresponds to a voltage output unit. The first switch 11 corresponds to a charging switch. The second switch 12 corresponds to a discharge switch. The third switch 13 corresponds to a switch provided in parallel with the oxygen concentration sensor. The third switch 13 corresponds to a switch provided in parallel with the capacitive element.

[2. Second Embodiment]
[2-1. Difference from the first embodiment]
Since the basic configuration of the second embodiment is the same as that of the first embodiment, differences will be described below. Note that the same reference numerals as those in the first embodiment indicate the same configuration, and the preceding description is referred to.

The ECU 1 of the second embodiment differs from the first embodiment in that the control unit 19 performs the time setting process of FIG. 4 in order to variably set the discharge time t2 to wait in S180 of FIG.
[2-2. processing]
The control unit 19 executes the time setting process of FIG. 4 between the end of the impedance detection process of FIG. 2 and the start of the next impedance detection process, for example.

  As shown in FIG. 4, in the time setting process, the control unit 19 determines in S310 whether or not the discharging voltage V2 detected in S190 in the current impedance detection process is smaller than the reference voltage Vref. If “V2 <Vref” is determined, the process proceeds to S320. The reference voltage Vref is set to a voltage between the maximum value (that is, the predetermined voltage VD) and the minimum value (that is, 0 V) of the capacitor voltage Va.

  In S320, the controller 19 sets a time obtained by subtracting a predetermined positive adjustment time α from the current discharge time t2 as the next discharge time t2. Then, the time setting process is terminated. The current discharge time t2 is the discharge time t2 used in S180 in the current impedance detection process, and the next discharge time t2 is the discharge time t2 used in S180 in the next impedance detection process.

  If the control unit 19 determines in S310 that “V2 <Vref” is not satisfied, the process proceeds to S330. In S330, the controller 19 sets a time obtained by adding the adjustment time α to the current discharge time t2 as the next discharge time t2. Then, the time setting process is terminated.

  The adjustment time α is an absolute value of the difference between the current discharge time t2 and the reference time t3, for example, as shown in Equation 5 below. As shown in FIG. 5, the reference time t3 is a time from when the discharge from the capacitor 7 to the sensor 3 is started until the capacitor voltage Va becomes the reference voltage Vref. And the control part 19 calculates the reference time t3 by the following formula 6. In Equation 6, the values obtained in S150, S200, and S210 in the current impedance detection process are used as “V0”, “C”, and “Rs”.

［２−３．効果］
以上のような第２実施形態によれば、前述した第１実施形態の効果に加えて、下記の効果を奏する。

[2-3. effect]
According to the second embodiment as described above, the following effects are obtained in addition to the effects of the first embodiment described above.

  The next discharge time t2 is changed according to the result of comparison of the detected current voltage V2 during discharge and the reference voltage Vref. For this reason, the discharge time t2 can be corrected to a time suitable for detecting the impedance Rs. The time suitable for the detection of the impedance Rs here is a time during which the discharging time V2 detected in S190 of FIG. 2 is in the vicinity of the reference voltage Vref.

  Specifically, for example, as shown in FIGS. 5A and 5B, when the discharging voltage V2 detected this time is larger than the reference voltage Vref, the process of S330 in FIG. The next discharge time t2 is changed to a time longer than the current discharge time t2.

  Further, for example, as shown in (b) and (c) in FIG. 5, when the discharging voltage V2 detected this time is smaller than the reference voltage Vref, the next discharge is performed by the process of S320 in FIG. The time t2 is changed to a time shorter than the current discharge time t2.

  By such a change (that is, variable setting) of the discharge time t2, the in-discharge time V2 detected in S190 of FIG. 2 can always be in the vicinity of the reference voltage Vref. For this reason, even if the discharge time constant fluctuates due to a change in impedance Rs, high detection accuracy of impedance Rs can be maintained. That is, it is possible to stably detect the impedance Rs with high accuracy.

  Further, since the absolute value of the difference between the current discharge time t2 and the reference time t3 is set as the adjustment time α, the effect of converging the detected discharging time V2 to the reference voltage Vref is high. However, the adjustment time α can be set to a predetermined fixed value, for example.

In the present embodiment, the control unit 19 that performs the processes of S310 to S330 in FIG. 4 corresponds to the time changing unit.
[3. Third Embodiment]
[3-1. Difference from Second Embodiment]
Since the basic configuration of the third embodiment is the same as that of the second embodiment, differences will be described below. In addition, the same code | symbol as 1st Embodiment and 2nd Embodiment shows the same structure, Comprising: The previous description is referred.

The ECU 1 of the third embodiment is different from the second embodiment in that the control unit 19 performs the abnormality determination process of FIG.
[3-2. processing]
The control unit 19 executes the abnormality determination process in FIG. 6 between, for example, the end of the impedance detection process in FIG. 2 and the start of the next impedance detection process.

  As shown in FIG. 6, in the abnormality determination process, the control unit 19 determines in S410 whether or not the discharging voltage V2 detected in S190 in the current impedance detection process is greater than or equal to a predetermined upper limit threshold Vth1. . If the controller 19 determines in S410 that the discharging voltage V2 is equal to or higher than the upper threshold value Vth1, the controller 19 determines in S420 that a high impedance abnormality has occurred, and then proceeds to S450. The high impedance abnormality is an abnormality that the impedance Rs of the sensor 3 is higher than the normal range.

If the controller 19 determines in S410 that the discharging voltage V2 is not equal to or greater than the upper threshold value Vth1, the process proceeds to S430.
In S430, the control unit 19 determines whether or not the discharging voltage V2 detected in S190 in the current impedance detection process is equal to or lower than a predetermined lower limit threshold Vth2. The lower limit threshold Vth2 is set to a value smaller than the upper limit threshold Vth1. When determining that the discharging voltage V2 is equal to or lower than the lower limit threshold Vth2 in S430, the control unit 19 determines that a low impedance abnormality has occurred in S440, and then proceeds to S450. The low impedance abnormality is an abnormality that the impedance Rs of the sensor 3 is lower than the normal range.

The control unit 19 also proceeds to S450 when determining that the discharging voltage V2 is not equal to or lower than the lower limit threshold Vth2 in S410.
In S450, the control unit 19 determines whether or not the capacitance C calculated in S200 in the current impedance detection process is within a predetermined range. If the controller 19 determines in S450 that the capacitance C is not within the predetermined range, the controller 19 determines in S460 that a circuit abnormality has occurred, and thereafter ends the abnormality determination process. The circuit abnormality is an abnormality in the circuit for detecting the impedance Rs, and is an abnormality in any part of the circuit included in the ECU 1 shown in FIG.

If the controller 19 determines in S450 that the capacitance C is within the predetermined range, the controller 19 ends the abnormality determination process.
[3-3. effect]
According to the third embodiment as described above, the effects of the first embodiment and the second embodiment described above can be obtained, and each of a high impedance abnormality, a low impedance abnormality, and a circuit abnormality can be detected. For example, when disconnection or activation abnormality of the sensor 3 occurs, it can be detected as a high impedance abnormality. Further, when a short circuit failure of the sensor 3 occurs, it can be detected as a low impedance abnormality. Further, when a short circuit failure, an open failure, or a capacity abnormality occurs in the capacitor 7, it can be detected as a circuit abnormality.

  In the present embodiment, the control unit 19 that performs the processes of S410 and S420 in FIG. 6 corresponds to a high impedance abnormality determination unit. The control unit 19 that performs the processes of S430 and S440 in FIG. 6 corresponds to a low impedance abnormality determination unit. The control unit 19 that performs the processes of S450 and S460 in FIG. 6 corresponds to a circuit abnormality determination unit.

Moreover, also in ECU1 of 1st Embodiment, the control part 19 may be comprised so that the abnormality determination process of FIG. 6 may be performed.
[4. Other Embodiments]
As mentioned above, although embodiment of this indication was described, this indication is not limited to the above-mentioned embodiment, and can carry out various modifications.

  For example, the ECU 21 of another embodiment shown in FIG. 7 is provided with a fourth switch 23 parallel to the capacitor 7, in addition to the third switch 13, as compared with the ECU 1 of FIG. 1. The electric charge of the capacitor 7 can also be discharged by turning on the fourth switch 23. In the case of the ECU 21, the capacitor 7 can be discharged by turning on the fourth switch 23 even when the second switch 12 is turned off. Therefore, for example, in the impedance detection process of FIG. 2, the control unit 19 does not perform the processes of S220 and S240. Instead, after turning off the second switch 12 in S230, the third switch 13 and the fourth switch 23 may be turned on for a predetermined time to discharge the sensor 3 and the capacitor 7.

Further, the oxygen concentration sensor to be detected for impedance may be an air-fuel ratio sensor that can obtain an output uniquely corresponding to the air-fuel ratio.
In addition, a plurality of functions of one constituent element in the above-described embodiment may be realized by a plurality of constituent elements, or one function of one constituent element may be realized by a plurality of constituent elements. Further, a plurality of functions possessed by a plurality of constituent elements may be realized by one constituent element, or a single function realized by a plurality of constituent elements may be realized by one constituent element. Moreover, you may abbreviate | omit a part of structure of the said embodiment. Further, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment. In addition, all the aspects included in the technical idea specified from the wording described in the claims are embodiments of the present disclosure.

  In addition to the ECU described above, a system including the ECU as a constituent element, a program for causing a computer to function as the ECU, a non-transition actual recording medium such as a semiconductor memory in which the program is recorded, impedance of the oxygen concentration sensor The present disclosure can also be realized in various forms such as a detection method.

  DESCRIPTION OF SYMBOLS 1, 21 ... ECU, 3 ... Oxygen concentration sensor, 7 ... Condenser, 11 ... 1st switch, 12 ... 2nd switch, 17 ... Voltage detection part, 19 ... Control part

Claims (11)

A capacitive element (7) having a capacitance;
A charging unit (11, 19, S110, S160) for charging the capacitive element at a predetermined voltage;
A discharge unit (12, 19, S170, S230) for discharging the capacitive element charged by the charging unit to the oxygen concentration sensor (3);
A discharge detection unit (17, 19, S180, S190) for detecting the voltage of the capacitive element when a predetermined discharge time has elapsed since the start of discharge by the discharge unit;
An impedance calculation unit (19, S210) for calculating an impedance of the oxygen concentration sensor using a voltage detected by the detection unit during discharge;
An impedance detection device for an oxygen concentration sensor. An impedance detection device for an oxygen concentration sensor according to claim 1,
A pre-discharge detection unit (17, 19, S150) for detecting a pre-discharge voltage that is a voltage of the capacitive element before the discharge by the discharge unit is started;
The impedance calculation unit is configured to calculate the impedance of the oxygen concentration sensor by further using the pre-discharge voltage detected by the pre-discharge detection unit.
Impedance detection device for oxygen concentration sensor. An impedance detection device for an oxygen concentration sensor according to claim 1 or 2,
A charging detection unit (17, 19, S120, S130) for detecting the voltage of the capacitive element when a predetermined charging time has elapsed since the charging by the charging unit was started;
A capacitance calculation unit (19, S200) that calculates the capacitance of the capacitive element based on the voltage detected by the charging detection unit;
The impedance calculation unit is configured to calculate the impedance of the oxygen concentration sensor by further using the capacitance calculated by the capacitance calculation unit.
Impedance detection device for oxygen concentration sensor. The impedance detection device for an oxygen concentration sensor according to any one of claims 1 to 3,
The voltage detected by the detection unit during discharge is compared with a predetermined reference voltage, and the discharge time in the detection unit during discharge when the discharge unit is operated next time is changed according to the comparison result. A time change unit (19, S310 to S330),
Impedance detection device for oxygen concentration sensor. An impedance detection device for an oxygen concentration sensor according to claim 4,
The time changing unit is
When the discharging voltage, which is the voltage detected by the discharging detector, is smaller than the reference voltage, the discharge time is made shorter than the current value, and the discharging voltage is larger than the reference voltage. Is configured to make the discharge time longer than the current value,
Impedance detection device for oxygen concentration sensor. An impedance detection device for an oxygen concentration sensor according to any one of claims 1 to 5,
A voltage output unit (9) for outputting the predetermined voltage;
The charging unit is
A charging switch (11) that is a switch provided in a charging path from the voltage output unit to the capacitive element;
The discharge part is
A discharge switch (12) that is a switch provided in a discharge path from the capacitive element to the oxygen concentration sensor;
Impedance detection device for oxygen concentration sensor. An impedance detection device for an oxygen concentration sensor according to any one of claims 1 to 6,
A switch (13) provided in parallel with the oxygen concentration sensor;
Impedance detection device for oxygen concentration sensor. An impedance detection device for an oxygen concentration sensor according to any one of claims 1 to 7,
It is determined whether or not a discharging voltage that is a voltage detected by the discharging detection unit is equal to or higher than a predetermined upper limit threshold. If the discharging voltage is equal to or higher than the upper limit threshold, it is determined that an abnormality has occurred. A high impedance abnormality determination unit (19, S410, S420),
Impedance detection device for oxygen concentration sensor. The impedance detection device for an oxygen concentration sensor according to any one of claims 1 to 8,
It is determined whether or not the discharging voltage, which is a voltage detected by the discharging detector, is equal to or lower than a predetermined lower threshold, and if the discharging voltage is equal to or lower than the lower threshold, it is determined that an abnormality has occurred. A low impedance abnormality determination unit (19, S430, S440),
Impedance detection device for oxygen concentration sensor. An impedance detection device for an oxygen concentration sensor according to claim 3,
A switch (13, 23) provided in parallel with the capacitive element;
Impedance detection device for oxygen concentration sensor. The oxygen concentration sensor impedance detection device according to claim 3 or 10,
A circuit abnormality determination unit (19) that determines whether or not the capacitance calculated by the capacitance calculation unit is within a predetermined range, and determines that an abnormality has occurred when the capacitance is not within the predetermined range. , S450, S460),
Impedance detection device for oxygen concentration sensor.

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