JP2006250695A - Method and device for controlling oxygen concentration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for controlling an oxygen concentration sensor that can control the oxygen concentration sensor in a state allowing detection of appropriate oxygen concentration value regardless of whether the state of the oxygen concentration sensor is normal or failure, and can determine abnormality at an early stage. <P>SOLUTION: The control device comprises the oxygen concentration sensor 1 for detecting oxygen concentration in exhaust gas, an element impedance detecting means 32a that switches the applied voltage to the oxygen concentration sensor from a reference voltage at the detection time of the oxygen concentration to a sweep voltage for detecting the element impedance for temperature control, and detects element impedance based on the voltage value ΔVi corresponding to the voltage variation ΔVo and current variation at that time, and a pull-back control means 32b for discharging the charges by the sweep voltage when the applied voltage is returned from the sweep voltage to the reference voltage. The pull-back control means 32b sets the charging time value of the charged charges based on the voltage value ΔVi. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control method and a control apparatus for an oxygen concentration sensor that discharges a charged charge after applying a sweep voltage to detect element impedance of the oxygen concentration sensor.

  In recent years, the oxygen concentration in exhaust gas is detected by an oxygen concentration sensor, and based on the oxygen concentration value detected by the oxygen concentration sensor, the air-fuel ratio of the air-fuel mixture sucked into the engine is feedback-controlled, so that the exhaust gas by the catalyst Automobile air-fuel ratio control systems that enhance gas purification performance have been put into practical use.Generally, the output voltage of the oxygen concentration sensor is highly temperature dependent, and the element temperature must be set to maintain good oxygen concentration detection accuracy. For example, it is necessary to maintain an active temperature of about 600 ° C. or higher.

  Therefore, a heater is attached to the oxygen concentration sensor, and the power supply to the heater is feedback-controlled so that the element temperature is kept above the activation temperature by the heat generated by the heater, and the element impedance of the oxygen concentration sensor is further controlled. Focusing on the fact that (element resistance) changes according to the element temperature, the element impedance is detected, and the energization to the heater is feedback controlled based on the element temperature calculated from the element impedance. Yes.

As a technique for detecting the element impedance of the oxygen concentration sensor, as shown in the following Patent Document 1, the element applied voltage is switched from a reference voltage at the time of detecting the oxygen concentration to a sweep voltage for detecting the element impedance. Has been proposed to detect the element impedance from the voltage change ΔVo and the voltage change ΔVi according to the current change caused by the voltage change ΔVo. After applying the sweep voltage, the element current is quickly converged to the normal state. Therefore, the device applied voltage is switched to a pullback voltage that is swung to the opposite side of the reference voltage by the voltage difference between the reference voltage and the sweep voltage, and the charge accumulated in the capacitive component of the element of the oxygen concentration sensor during the sweep is changed. When the discharge is promoted and the pull-back voltage is held for the same time as the sweep time to finish discharging the charge due to the capacitive component of the element It is configured to return the device application voltage Vo to a reference voltage.

On the other hand, for example, as shown in FIG. 1B, a reference voltage is supplied from a vehicle battery Bat and a sweep voltage is applied via an RC circuit when detecting element impedance. The element impedance of the oxygen concentration sensor can be detected so that an accurate limit current value can be detected by quickly discharging the charge charged in the RC circuit by the sweep voltage through a resistor when returning to the reference voltage. Proposals have been made to perform pullback control (pullback control) with a discharge time based on a pullback time (discharge time) map data composed of detected oxygen concentration values. The above pull-back time map data is set so that the discharge time is shorter as the element impedance is lower and the oxygen concentration value is higher, and conversely, the discharge time is longer as the element impedance is higher and the oxygen concentration value is lower. A value read from the pull-back time map data based on the element impedance detected at the time of voltage application and the immediately preceding detected oxygen concentration value is set as the pull-back time.
JP 2000-28575 A

However, according to the pull-back control based on the above-described discharge time map data, since the discharge time is set based on the element impedance and the oxygen concentration value detected at the time of the previous sweep voltage application, the element impedance of the active temperature or higher is set. In a small situation, if a high impedance abnormality due to disconnection occurs when applying a sweep voltage, the pullback time set by the discharge time map data is set to be extremely short, and the charge charge of the RC circuit etc. cannot be discharged sufficiently, When the limit current value is detected in such a state, there is a problem that the value becomes extremely inaccurate and may hinder the above-described air-fuel ratio control.

  In view of the above-described conventional drawbacks, the present invention controls an oxygen concentration sensor that is capable of detecting an appropriate oxygen concentration value regardless of whether the oxygen concentration sensor is normal or malfunctioning, and can perform an abnormality determination at an early stage. A control method and a control apparatus are provided.

  In order to achieve the above object, a first characteristic configuration of a method for controlling an oxygen concentration sensor according to the present invention includes a step of applying a reference voltage to the oxygen concentration sensor to detect a current value according to the oxygen concentration, and Switching the voltage applied to the concentration sensor from a reference voltage to a sweep voltage, detecting the element impedance of the oxygen concentration sensor based on the change state of the output value from the oxygen concentration sensor at that time, and applying the sweep voltage And a step of discharging the charged charge charged by applying the sweep voltage, and applying a discharge time for discharging the charged charge to the oxygen concentration sensor. The voltage is set based on the amount of change in the current of the oxygen concentration sensor that occurs when the voltage is switched from the reference voltage to the sweep voltage.

  Since the discharge time for discharging the charge accumulated in the circuit by applying the sweep voltage is set based on the current change amount ΔI detected when the sweep voltage is applied, the current change ΔI is large when the element impedance is small. Thus, since the current change ΔI is small when the element impedance is large, the amount of charge transfer increases as the element impedance decreases, and accordingly, the amount of charge accumulated in the circuit increases accordingly. According to the above-described feature configuration, since an appropriate discharge time is set based on the current change amount ΔI, the limit current value can be accurately detected thereafter, and the sensor element is disconnected while the sweep voltage is applied. However, the charging current in the circuit is reliably discharged, and the abnormal state of the oxygen concentration sensor can be detected quickly.

  The second feature configuration is that, in addition to the first feature configuration described above, the discharge time is set by a linear function with the amount of change in the current of the oxygen concentration sensor as a variable. Accordingly, it is possible to easily set an appropriate discharge time so that the discharge time is long when the current change amount ΔI is large, and conversely, when the current change amount is small, the discharge time is shortened.

  In the third feature configuration, in addition to the first feature configuration described above, discharge time map data in which the discharge time is set long when the amount of change in the current of the oxygen concentration sensor is large and short when it is small. Thus, if configured in this way, an appropriate discharge time can be easily set as described above.

  The first characteristic configuration of the control device for the oxygen concentration sensor according to the present invention is that the voltage applied to the oxygen concentration sensor is switched from a reference voltage for detecting a current value corresponding to the oxygen concentration to a sweep voltage, and the oxygen concentration sensor at that time Element impedance detection means for detecting the element impedance of the oxygen concentration sensor based on the change state of the output value from the output, and pullback control means for discharging the charge charged by application of the sweep voltage after application of the sweep voltage; The pull-back control means switches the voltage applied to the oxygen concentration sensor from the reference voltage to the sweep voltage for a discharge time for discharging the charged charge. The oxygen concentration sensor is set based on the amount of change in the current of the oxygen concentration sensor.

In the second characteristic configuration, in addition to the first characteristic configuration described above, the pullback control unit is configured to change the discharge time of the charge charge based on a linear function using the change amount of the current of the oxygen concentration sensor as a variable. Is configured to be set.

  In the third feature configuration, in addition to the first feature configuration described above, the pullback control means is configured such that the discharge time of the charge charge is long and small when the change amount of the current of the oxygen concentration sensor is large. Is set based on the discharge time map data set short.

  In the fourth feature configuration, in addition to the third feature configuration described above, the discharge time map data includes a deviation between an oxygen concentration value detected immediately after discharge and an average value of oxygen concentration values detected before and after the discharge. This configuration makes it possible to always compensate for an appropriate discharge time in response to variations in components including the oxygen sensor and changes over time. .

  As described above, according to the present invention, the oxygen concentration sensor is controlled so that an appropriate oxygen concentration value can be detected regardless of whether the oxygen concentration sensor is normal or faulty, and abnormality determination can be performed at an early stage. A control method and a control apparatus can be provided.

  A control method and a control apparatus for an oxygen concentration sensor according to the present invention will be described below with reference to the drawings. As shown in FIG. 1A, an air-fuel ratio sensor (hereinafter referred to as “A / F sensor”) as a limiting current type oxygen concentration sensor 1 attached to an exhaust pipe 20 extending from an engine body 10 is provided. The engine control computer (hereinafter referred to as “ECU”) 30 is controlled by an oxygen concentration detection circuit 32 and a heater control circuit 34, and outputs a linear air-fuel ratio detection signal proportional to the oxygen concentration in the exhaust gas. To do.

As shown in FIG. 2, the A / F sensor 1 protrudes toward the inside of the exhaust pipe 20, has a U-shaped cross section, and has a plurality of small holes 12 communicating with the inside and outside of the cover on its peripheral wall. Cover 10, a sensor main body 14 that generates a limit current corresponding to an oxygen concentration in a lean region of the air-fuel ratio, or a concentration of unburned gas such as CO or HC in a rich region of the air-fuel ratio, and a heater 16. Yes. In the sensor body 14, an exhaust gas side electrode layer 14b is fixed to the outer surface of the low-cylindrical solid electrolyte layer 14a, an atmosphere side electrode layer 14c is fixed to the inner surface, and the outside of the exhaust gas side electrode layer 14b. The diffusion resistance layer 14d is plasma sprayed. The solid electrolyte layer 14a is an oxygen ion conductive oxide in which a stabilizer such as CaO, MgO, Y ₂ O ₃ , Yb ₂ O ₃ or the like is dissolved in ZrO ₂ , HfO ₂ , ThO ₂ , Bi ₂ O ₂ or the like. The diffusion resistance layer 14d is composed of a sintered body, and is composed of a heat-resistant inorganic material such as alumina, magnetic material, siliceous material, spinel, or mullite. Both the exhaust gas side electrode layer 14b and the atmosphere side electrode layer 14c are made of a noble metal having high catalytic activity such as platinum, and the surface thereof is subjected to porous chemical plating or the like. The heater 16 is accommodated inside the atmosphere-side electrode layer 14c, and the sensor main body 14 is heated by the generated heat.

  The sensor body 14 generates a limiting current determined by the area of the exhaust gas side electrode layer 14b, the thickness of the diffusion resistance layer 14d, the porosity, and the average pore diameter in the lean region from the stoichiometric air-fuel ratio. To do. Further, in a rich region from the stoichiometric air-fuel ratio, the concentration of unburned gas such as carbon monoxide changes almost linearly with respect to the air-fuel ratio, and a limit current corresponding to the unburned gas concentration is generated. The limit current exhibits a linear characteristic corresponding to the oxygen concentration, but is activated at a temperature of about 600 ° C. or higher, and the sensor body 14 is controlled to the activation temperature range by heating by the heater 16.

As shown in FIG. 3, the A / F sensor 1 has an inflow current I to the solid electrolyte layer 14a and an applied voltage V having a linear characteristic, and a straight line portion L parallel to the voltage axis V is the limit current. The increase / decrease in the limit current corresponds to the increase / decrease in the air-fuel ratio. That is, the limit current increases as the air-fuel ratio becomes leaner, and the limit current decreases as the air-fuel ratio becomes richer.

  In the above-described voltage-current characteristics, the voltage region lower than the straight line portion parallel to the voltage axis V is the resistance dominant region, and the slope of the straight line portion in the resistance dominant region indicates the internal resistance of the solid electrolyte layer 14a, that is, the element impedance. . Since this element impedance changes with temperature change, the element impedance increases when the temperature of the sensor main body 32 decreases.

The specific configurations of the oxygen concentration detection circuit 32 and the A / F sensor 1 shown in FIG. 1A are as shown in FIG. 1B, and the reference voltage application battery Bat ( The A / F sensor 1 connected in series with the DC12V), an O ₂ sensor voltage detection port for inputting a current flowing through the A / F sensor 1 as a sensor voltage via a resistor R1, and the A / F A sweep voltage control port for controlling a sweep circuit composed of a transistor Tr1, a resistor R2, and a capacitor C1 in order to lower a voltage value applied to the sensor 1 and sweep it to a resistance control region, and a voltage due to an element impedance in the swept state The impedance voltage ΔVo detection port for inputting the drop and the impedance current Δ for inputting the voltage corresponding to the element current via the shunt resistor R3 in the same swept state. o A detection port, a transistor Tr2 and a resistor, each of which is an A / D input port or an output port of the ECU 30 is a pull-back control port that discharges the charge charged by the sweep voltage after the sweep voltage is applied and returns to the reference voltage. Connected to and configured.

  An element impedance detection means 32a is configured by an ECU that performs sweep control from the sweep circuit and the sweep voltage control port, and calculates and derives the element impedance by the A / D input of the impedance voltage ΔVo detection port and the impedance current ΔVo detection port shell. The retraction control means 32b is constituted by the discharge circuit and the ECU that performs retraction control from the retraction control port, and the oxygen concentration detection circuit 32, the A / F sensor 1, and the ECU constitute a control device for the oxygen concentration sensor. ing.

Specifically, the O ₂ sensor voltage detection port, the impedance voltage ΔVo detection port, and the impedance current ΔVi detection port are connected to the A / D input port, respectively, and the sweep voltage control port and the pullback control port are connected to the output port. ing. A resistor and diode for absorbing surge and a capacitor for absorbing noise are connected to the impedance voltage ΔVo detection port and the impedance current ΔVi detection port, respectively.

FIG. 4A shows the operation of oxygen concentration detection and element impedance detection by the ECU 30 that controls the oxygen concentration detection circuit 32 described above. That is, as indicated by the circled numbers 1, 2, 3, and 4 in the figure, the oxygen concentration value is taken from the O ₂ sensor voltage detection port at a predetermined detection cycle (here, 4 msec. Interval). A sweep signal is periodically output from the sweep voltage control port for a predetermined time at an interval longer than the oxygen concentration detection interval. With this signal, the transistor Tr1 is turned on, and a DC5V sweep voltage is applied to one end of the shunt resistor R3 via the resistor R2.

  A voltage ΔVi corresponding to the impedance voltage ΔVo and the impedance current is detected based on the voltage values input from the impedance voltage ΔVo detection port and the impedance current ΔVi detection port after a predetermined time from the start of the sweep. The ECU 30 calculates the impedance current ΔI from the ratio between the two voltages and the resistance value of the shunt resistor R3, and calculates and derives the element impedance based on the ratio with the impedance voltage ΔVo.

The heater control circuit 34 supplies power from the battery power source to the heater 16 by duty control so that the calculated element impedance decreases to a value indicating a predetermined active temperature region and is maintained in that region.

  After the control signal from the sweep voltage control port is turned off, a pullback control signal is output from the pullback control port, and the transistor Tr2 is turned on by this pullback control signal, and the capacitor C1 or A / F is applied during the sweep voltage application. The electric charge charged in the internal capacitance of the sensor 1 is quickly discharged through the resistor R4 to prepare for the next oxygen concentration detection timing.

  Here, when the sweep voltage is applied to detect the impedance voltage ΔVo and the voltage ΔVi corresponding to the impedance current, as shown in FIG. 4B, the element impedance of the A / F sensor 1 is detected once. The sweep control for switching the element applied voltage from the reference voltage to the sweep voltage is performed at least twice, and only one of the impedance voltage ΔVo and the voltage ΔVi corresponding to the impedance current is A / D converted during one sweep. Thus, it may be configured to shorten the sweep time per time.

  In any case, the pulse width of the pullback control signal output from the pullback control port, that is, the discharge time, needs to ensure a sufficient time to discharge the charge charged by the sweep voltage. As shown in FIG. 5 (a), if it is too long, the next oxygen concentration detection timing overlaps and cannot be detected accurately. If it is too short, the charged charge remains and cannot be detected accurately. In particular, if a fault such as disconnection occurs in the A / F sensor 1 when the sweep voltage is applied, even if the pull-back control is performed with a pulse width of a time that can be sufficiently discharged under normal conditions, the discharge is not sufficiently performed, and accurate oxygen concentration detection is possible. It becomes impossible.

  Therefore, the present invention is configured to set the discharge time of the charge charge based on the voltage value ΔVi corresponding to the impedance current. That is, since the discharge time for discharging the charge accumulated in the circuit by applying the sweep voltage is set based on the change amount ΔI of the current detected at the time of applying the sweep voltage or the corresponding voltage value ΔVi, Focusing on the fact that the amount of charge transfer increases as the element impedance decreases, and therefore the amount of charge stored in the circuit increases accordingly, the discharge time is set based on the current change ΔI or the corresponding voltage value ΔVi. By configuring as described above, it becomes possible to set an appropriate discharge time, and it becomes possible to accurately detect the limit current value, and even if the sensor element is disconnected during the sweep voltage application, Since the charging current is discharged quickly, the abnormal state of the oxygen concentration sensor can be detected quickly.

  Specifically, the discharge time of the charge charge can be set based on a linear function (discharge time T = α × ΔI) having the current change ΔI or a value corresponding thereto as a variable. Here, the proportionality constant α is appropriately set by experiment.

  Furthermore, the discharge time map data set long when the current change ΔI or the corresponding voltage value ΔVi is large and short when the current change ΔI or the corresponding voltage value ΔVi is small is stored in the memory constituting the ECM, You may comprise so that it may set based on the value.

The discharge time map data can be configured as one-dimensional map data corresponding to the current change ΔI as shown in FIG. 6A, and as shown in FIG. 6B, the current change ΔI and It can be configured as two-dimensional map data based on the O ₂ sensor voltage. Note that when an intermediate value of the map is indicated, the value is calculated based on an interpolation method.

In this case, it is preferable to include map data correction means for correcting the discharge time map data based on a deviation between an oxygen concentration value detected immediately after discharge and an average value of oxygen concentration values detected before and after the discharge, This makes it possible to always compensate for an appropriate discharge time in response to variations in components including the oxygen sensor and changes over time.

In the process of detecting the element impedance in this way, even when the oxygen concentration sensor fails due to disconnection or the like during the sweep control, the electric charge accumulated in the capacitor or the like included in the sweep circuit is surely ensured by the discharge circuit. Therefore, the influence of the accumulated charge on the value input from the O ₂ sensor voltage detection port is eliminated, and as a result, the abnormality of the oxygen concentration sensor can be reliably detected. When the above-described failure occurs when the circuit shown in FIG. 1 is adopted, the value input from the O ₂ sensor voltage detection port indicates 0 V, and the disconnection abnormality is detected by the oxygen concentration sensor abnormality detection means built in the ECU 30. It is detected quickly.

  The element impedance detection operation by the ECU 30 described above is shown in the flowchart of FIG.

  That is, the oxygen concentration sensor control apparatus according to the present invention includes an oxygen concentration sensor that outputs a limit current value corresponding to the oxygen concentration in the gas to be detected in accordance with the application of the reference voltage, and the applied voltage to the oxygen concentration sensor is the oxygen concentration sensor. An element that switches from a reference voltage at the time of concentration detection to a sweep voltage for detecting an element impedance for temperature control, and detects the element impedance based on a voltage change ΔVo and a current change ΔI or a corresponding voltage value ΔVi Impedance detection means; and pull back control means for discharging the charge charged by the sweep voltage when the applied voltage is returned from the sweep voltage to the reference voltage. The pull back control means determines the discharge time of the charge charge. The current change ΔI or the voltage value ΔVi corresponding to the current change ΔI is set.

  In the embodiment described above, the element impedance is calculated and derived by detecting the voltage value ΔVi corresponding to the current change ΔI during the sweep control. However, the current detection circuit is provided to directly detect the current change ΔI. It may be.

  In the embodiment described above, the oxygen concentration detection circuit 32 is directly controlled by the microcomputer constituting the ECU 30, but the oxygen concentration detection circuit 32 is controlled by the slave computer controlled by the microcomputer constituting the ECU 30. It may be configured so that.

  The above-described embodiment is merely an example of the present invention, and it is needless to say that the specific circuit configuration of each block can be appropriately changed and designed within the scope of the effects of the present invention.

(A) is a block diagram of a control device for an oxygen concentration sensor, and (b) is a circuit diagram of an oxygen concentration detection control circuit. Explanatory drawing showing the structure of the oxygen concentration sensor Oxygen concentration sensor characteristic explanatory diagram Device impedance detection timing chart of oxygen concentration sensor Device impedance detection timing chart of oxygen concentration sensor Illustration of discharge time map data Flow chart showing oxygen concentration detection procedure by oxygen concentration sensor

Explanation of symbols

1: Oxygen concentration sensor (A / F sensor)
10: Engine body 20: Exhaust pipe 30: Engine control computer (ECU)
32: Oxygen concentration detection circuit 32a: Element impedance detection means 32b: Pullback control means 34: Heater control circuit

Claims (7)

A step of applying a reference voltage to the oxygen concentration sensor to detect a current value corresponding to the oxygen concentration, and switching a voltage applied to the oxygen concentration sensor from a reference voltage to a sweep voltage, and an output from the oxygen concentration sensor at that time An oxygen concentration sensor comprising: detecting an element impedance of the oxygen concentration sensor based on a change state of the value; and discharging a charged charge charged by the application of the sweep voltage after the application of the sweep voltage. A control method,
The oxygen concentration for setting the discharge time for discharging the charged charge based on the amount of change in the current of the oxygen concentration sensor that occurs when the voltage applied to the oxygen concentration sensor is switched from the reference voltage to the sweep voltage. Sensor control method.   2. The method of controlling an oxygen concentration sensor according to claim 1, wherein the discharge time is set by a linear function having a change amount of the current of the oxygen concentration sensor as a variable.   2. The method of controlling an oxygen concentration sensor according to claim 1, wherein the discharge time is set based on discharge time map data set long when the change amount of the current of the oxygen concentration sensor is large and short when it is small. The applied voltage to the oxygen concentration sensor is switched from a reference voltage for detecting a current value according to the oxygen concentration to a sweep voltage, and the element impedance of the oxygen concentration sensor based on the change state of the output value from the oxygen concentration sensor at that time An oxygen concentration sensor control device comprising: an element impedance detection means for detecting the charge impedance; and a pullback control means for discharging the charge charged by the application of the sweep voltage after the sweep voltage is applied,
The pullback control means sets a discharge time for discharging the charged charge to a change amount of the current of the oxygen concentration sensor generated when the voltage applied to the oxygen concentration sensor is switched from the reference voltage to the sweep voltage. Control device for oxygen concentration sensor to be set based on.   5. The oxygen concentration sensor control device according to claim 4, wherein the pull-back control means sets the discharge time of the charge charge based on a linear function having the amount of change in the current of the oxygen concentration sensor as a variable.   5. The pull-back control means sets the discharge time of the charge charge based on discharge time map data set long when the change amount of the current of the oxygen concentration sensor is large and short when it is small. Oxygen concentration sensor control device.   The oxygen concentration sensor according to claim 6, wherein the discharge time map data is corrected based on a deviation between an oxygen concentration value detected immediately after discharge and an average value of oxygen concentration values detected before and after the discharge. Control device.

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