WO2023181292A1 - Air-fuel ratio control device - Google Patents

Air-fuel ratio control device Download PDF

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Publication number
WO2023181292A1
WO2023181292A1 PCT/JP2022/014124 JP2022014124W WO2023181292A1 WO 2023181292 A1 WO2023181292 A1 WO 2023181292A1 JP 2022014124 W JP2022014124 W JP 2022014124W WO 2023181292 A1 WO2023181292 A1 WO 2023181292A1
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unit
value
control
temperature
section
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PCT/JP2022/014124
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French (fr)
Japanese (ja)
Inventor
勝明 和知
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日立Astemo株式会社
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Priority to PCT/JP2022/014124 priority Critical patent/WO2023181292A1/en
Publication of WO2023181292A1 publication Critical patent/WO2023181292A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D45/00—Electrical control not provided for in groups F02D41/00 - F02D43/00

Definitions

  • the present invention relates to an air-fuel ratio control device that includes a resistance-type oxygen sensor that is provided in contact with the exhaust gas of an internal combustion engine that has exhaust pulsation.
  • Patent Document 1 it has been known to perform air-fuel ratio feedback control in the internal combustion process of an internal combustion engine based on the air-fuel ratio obtained from the output information of an oxygen sensor provided in contact with the exhaust gas of the internal combustion engine (for example, Patent Document 1 reference).
  • a resistance-type oxygen sensor that detects oxygen based on the internal resistance of a detection part is used as an oxygen sensor.
  • a first value indicating the oxygen content in the exhaust gas is determined based on the resistance of the detection section of the oxygen sensor.
  • a second value indicating the temperature of the oxygen sensor is determined based on the resistance of the heater portion of the oxygen sensor. The air-fuel ratio as a function of the first value and the second value is then determined as a third value.
  • the function for determining the third value includes a second value that affects the first value in real time, so even if the output characteristics change due to the temperature of the oxygen sensor, The air-fuel ratio is calculated based on the detected resistance value of the detection section of the oxygen sensor.
  • an object of the present invention is to appropriately compensate for the temperature characteristics of a resistance-type oxygen sensor, including the differences in characteristics between individual sensors, thereby achieving high robustness.
  • An object of the present invention is to provide an air-fuel ratio control device that can realize air-fuel ratio feedback control using a resistance-type oxygen sensor.
  • the air-fuel ratio control device of the present invention includes: An air-fuel ratio control device for an internal combustion engine, comprising a resistance-type oxygen sensor having a detection section provided in contact with exhaust gas of an internal combustion engine having exhaust pulsation, and a heater section adjacent to the detection section, a target value setting unit that sets a control target value related to an excess air ratio based on the operating state of the internal combustion engine; a detection unit temperature estimation unit that calculates the temperature of the detection unit based on the resistance value of the heater unit; a detected value reading unit that reads a resistance value of the detection unit to obtain a detection value of the detection unit; an excess rate calculation unit that calculates the excess air rate from the detected value and the temperature of the detection unit; A PD/PID that calculates a deviation between the excess air ratio and the control target value, and performs feedback control of the excess air ratio using the deviation and the derivative of the deviation, or the deviation, the integral of the deviation, and the derivative of the deviation as elements.
  • control unit a control unit; a PI control unit that performs feedback control of the excess air ratio using a deviation between the excess air ratio and the control target value and an integral of the deviation as elements; a control unit selection unit that selects which of the PI control unit or the PD/PID control unit to use for the feedback control; a characteristic checking unit that checks whether the detected value and the temperature of the detection unit correspond to each predetermined characteristic; a calibration unit that calibrates the detection unit temperature estimation unit and the detected value reading unit, respectively, based on the inspection;
  • the control section selection section is configured to be able to perform alternative selection of the PD/PID control section or the PI control section according to the detection value in the characteristic inspection section and the inspection result of the temperature of the detection section. It is characterized by being configured.
  • the characteristic checking section checks whether the detected value of the detecting section and the temperature of the detecting section correspond to each predetermined characteristic, and based on this, the detecting section temperature estimating section and the detected value reading section are connected to the calibration section.
  • the PD/PID control section or the PI control section is selected by the control section selection section according to the inspection result.
  • the reliability of the excess air ratio ⁇ calculated by the excess air ratio calculation unit is not guaranteed, so feedback from the PD/PID unit using this excess air ratio as a trigger is applied. Can not do it.
  • the characteristics of resistance-type oxygen sensors vary depending on the individual resistance-type oxygen sensors, and since there are large individual differences, the progress state of calibration also differs each time.
  • the characteristic inspection section checks whether the detection value of the detection section and the temperature of the detection section correspond to each predetermined characteristic, and based on this inspection, the control section selection section selects the PD/PID.
  • the control unit or the PI control unit is alternatively selected.
  • control section selection section grasps the progress of calibration for each resistance-type oxygen sensor, and determines that the calibration has progressed sufficiently to the extent that the control followability expected for PID or PD control can be achieved. If it is determined, the PD/PID control section can be selected to perform feedback control of the excess air ratio by PD/PID control. On the other hand, if it is determined that such a state does not exist, the PI control section can be selected to perform feedback control of the excess air ratio by PI control.
  • the calibration unit is configured to perform a lean air-fuel ratio range for determining whether the peak value of the wave height of the detected value due to exhaust pulsation of the internal combustion engine corresponds to which air-fuel ratio region of a rich region, a stoichiometric region, or a lean region.
  • the characteristic inspection unit may determine the progress state of the calibration by comparing the peak value with at least one of the lean-side threshold value and the rich-side threshold value.
  • the data map is calibrated based on the comparison between the data map and the peak value described above, and the progress state of the calibration is checked by comparing the peak value with at least one side of the lean side threshold or the rich side threshold. It will be judged. Therefore, by referring to the progress state of this calibration as the inspection result in the characteristic inspection section, the control section selection section can control the PD/PID control section or the PI control By appropriately selecting the air-fuel ratio feedback control, it is possible to ensure appropriate implementation of air-fuel ratio feedback control and suppress deterioration of emission performance.
  • a calibration reset unit configured to be able to issue an initialization command to initialize the correspondence in the data map
  • the control unit selection unit may be configured to select the PI control unit for a predetermined period after receiving a reset command from the calibration reset unit.
  • PI control when a reset command is received from the calibration reset section, feedback control by PI control is performed at least for a predetermined period, so that the characteristic inspection section performs an inspection during that time. , and is configured to appropriately determine the progress state of the calibration while steadily progressing recalibration by the calibration unit according to the result, and to appropriately select the PD/PID control unit or the PI control unit. can do. For example, if a failure is actually detected and confirmed in the detection part or heater part of an oxygen sensor, the repair work involves replacing the oxygen sensor body with a normal one and also issuing a reset command from the calibration reset part.
  • the calibration parameters stored in the air-fuel ratio control device are reset, but even if the characteristics of the replaced resistance-type oxygen sensor are large due to individual differences, the PI control section cannot be selected. Therefore, air-fuel ratio feedback control can be performed without any problem and deterioration of emission performance can be suppressed.
  • the on-board diagnostic section is configured to be able to diagnose abnormality or failure of the detection section or the heater section of the resistance-type oxygen sensor
  • the control section selection section is arranged in the on-board diagnostic section.
  • the sensor may be configured to select the PI control unit when it is determined that the detection unit or the heater unit of the resistance-type oxygen sensor is abnormal.
  • the detection section or heater section of the resistance type oxygen sensor is abnormal, even temporarily, it becomes difficult for the PD/PID control section to perform appropriate feedback control; however, in such a case, the PI control section Since this is selected, air-fuel ratio feedback control can be continued without any problem and deterioration of emission performance can be suppressed.
  • the calibration unit is configured to temporarily suspend control related to calibration when the on-board diagnosis unit determines that the detection unit or the heater unit of the resistance-type oxygen sensor is abnormal. may be done.
  • the control section selection section selects the control section of the calibration section.
  • the calibration control unit may be configured to restart control related to calibration and select the PI control unit in a predetermined period after the restart.
  • the PI control Since air-fuel ratio feedback is performed, the calibration section steadily progresses in calibrating the data map, and the progress of this calibration is appropriately determined, thereby determining the selection of the PD/PID control section or the PI control section. The deterioration of emission performance can be suppressed by making appropriate selections.
  • FIG. 1 is a schematic diagram schematically showing the configuration of main parts of an internal combustion engine including an air-fuel ratio control device according to an embodiment of the present invention.
  • 2 is a block diagram showing the main configuration of an ECU of the internal combustion engine of FIG. 1.
  • FIG. 3 is a flowchart showing an excess rate calculation process in which an excess air rate is calculated by an excess rate calculation unit in the ECU of FIG. 2.
  • FIG. 4 is a graph showing how the excess air ratio in the stoichiometric region is calculated in the process of FIG. 3.
  • 4 is a diagram showing a graph corresponding to a lookup table for calculating a lean side threshold value LREF and a rich side threshold value RREF, and a data map for calculating an excess air ratio in the process of FIG. 3.
  • FIG. 3 is a schematic diagram schematically showing the configuration of main parts of an internal combustion engine including an air-fuel ratio control device according to an embodiment of the present invention.
  • FIG. 3 is a flowchart showing an excess rate calculation
  • FIG. 4 is a graph schematically showing how the excess air ratio ⁇ calculated by the process of FIG. 3 changes;
  • FIG. 3 is a waveform diagram showing a voltage waveform representing a change in a voltage value output by a voltage calculation unit over time obtained while driving a vehicle equipped with an internal combustion engine.
  • 3 is a diagram showing an example of an inspection by a characteristic inspection section and calibration by a calibration section in the ECU of FIG. 2.
  • FIG. It is a figure which shows the other example of the inspection by the said characteristic inspection part and calibration by a calibration part.
  • It is a figure which shows another example of the inspection by the said characteristic inspection part and calibration by a calibration part.
  • It is a figure which shows yet another example of the inspection by the said characteristic inspection part and calibration by a calibration part.
  • 3 is a block diagram showing the configuration of a feedback coefficient calculating section in the ECU of FIG. 2.
  • FIG. 3 is a diagram showing an example of an alternative temperature Tsub obtained by an alternative temperature preparation section in the ECU of
  • FIG. 1 shows the configuration of the main parts of a four-stroke internal combustion engine equipped with an air-fuel ratio control device according to an embodiment of the present invention.
  • This air-fuel ratio control device has a function of performing air-fuel ratio feedback control based on the deviation between the excess air ratio obtained based on the oxygen concentration in the exhaust gas of the internal combustion engine and the target excess air ratio.
  • an engine body 1 of this internal combustion engine has an intake pipe 2 provided at an intake port, and an air cleaner 4 provided in the intake pipe 2 that controls the amount of intake air supplied to the intake port. and a throttle valve 3 that is adjusted according to the
  • the throttle valve 3 is provided with a throttle sensor 5 that detects the opening degree of the throttle valve 3.
  • a fuel injection valve 6 for injecting fuel is provided near the intake port of the intake pipe 2. Fuel is fed under pressure to the fuel injection valve 6 from a fuel tank (not shown) by a fuel pump.
  • the intake pipe 2 is provided with an intake pressure sensor 7 that detects the intake pressure in the intake pipe 2 and an intake temperature sensor 8 that detects the temperature of the intake air in the intake pipe 2.
  • an exhaust pipe 10 connected to an exhaust port of the engine body 1, a catalyst 11 for reducing unburned components in the exhaust gas from the exhaust pipe 10 and an oxygen sensor 12 for detecting the oxygen concentration in the exhaust gas are provided.
  • a spark plug 13 connected to an ignition device 14 is fixed to the engine body 1.
  • the ECU (electronic control unit) 15 issues an ignition timing command to the ignition device 14, spark discharge occurs within the cylinder combustion chamber of the engine body 1.
  • Analog voltages indicating respective detection values of the throttle sensor 5, intake pressure sensor 7, intake temperature sensor 8, oxygen sensor 12, cooling water temperature sensor 17, and atmospheric pressure sensor 20 that detects atmospheric pressure are input to the ECU 15. .
  • the above-mentioned fuel injection valve 6 is connected to the ECU 15.
  • a signal indicating the rotational angular position of the crankshaft 18 from the crank angle sensor 19 is further input to the ECU 15. That is, the crank angle sensor 19 includes a plurality of convex portions provided at predetermined angle intervals (for example, 15 degrees) on the outer circumference of the rotor 19a that rotates in conjunction with the crankshaft 18, and arranged near the outer circumference of the rotor 19a.
  • the pickup 19b detects it magnetically or optically, and the pickup 19b generates a pulse (crank signal) every time the crankshaft 18 rotates by a predetermined angle.
  • crank angle sensor 19 outputs a signal indicating the reference angle to the ECU 15 every time the piston 9 reaches the top dead center or every time the crankshaft 18 rotates 360 degrees.
  • FIG. 2 shows the main configuration of the ECU 15.
  • an oxygen sensor 12 that supplies a detection signal of the oxygen concentration in the exhaust gas to the ECU 15 is a detection unit that is provided in contact with the exhaust gas of an internal combustion engine that has exhaust pulsation and detects the oxygen concentration in the exhaust gas.
  • the sensor element 12a is provided with a sensor element 12a as a sensor element 12a, and a sensor heater 12b as a heater part that is adjacent to the sensor element 12a and heats the sensor element 12a.
  • the sensor element 12a has a resistance value that changes substantially stepwise when the exhaust gas of the internal combustion engine has an oxygen concentration near the stoichiometric value, and the detected value obtained from the resistance value is determined by the temperature of the sensor element 12a and the exhaust pulsation. It exhibits a pulse waveform with a peak value corresponding to the wave height.
  • a titania oxygen sensor which is a resistance type oxygen sensor whose resistance value changes depending on the oxygen concentration, is used.
  • the ECU 15 includes a heater controller 22 that controls the sensor heater 12b, a temperature calculation section 23 as a detection section temperature estimation section that calculates a temperature value T indicating the temperature of the sensor element 12a, and an output signal of the sensor element 12a, which is connected to the exhaust gas.
  • a voltage calculation unit 24 is provided as a detection value reading unit that converts into a voltage value VHG as a detection value indicating the oxygen concentration in the air.
  • the temperature of the sensor heater 12b is controlled by the heater controller 22 by performing pulse width modulation (PWM) control by the ECU 15 on the amount of current I supplied to the sensor heater 12b from an unillustrated power source (storage battery). Further, the temperature value T is calculated by the temperature calculation unit 23 by, for example, reading each value of the heater voltage and the current amount I applied to the sensor heater 12b with the ECU 15 to determine the resistance value of the sensor heater 12b, and calculating the resistance value of the sensor heater 12b. This is done by converting using table data or a calculation formula prepared in advance in the ECU 15 that indicates the correspondence between the heater resistance value and the temperature value T. The calculation results from the temperature calculation section 23 and the voltage calculation section 24 are supplied to an alternative value calculation section 26 of the excess rate calculation section 25, which will be described later.
  • PWM pulse width modulation
  • the ECU 15 also includes a rotational speed calculation unit 27 that calculates the rotational speed NE and angular velocity NETC of the internal combustion engine based on the detection results of the crank angle sensor 19, and a rotational speed calculation unit 27 that calculates the rotational speed NE and angular velocity NETC of the internal combustion engine based on the detection results of the crank angle sensor 19, and a It includes an excess air ratio calculation section 25 that calculates an excess air ratio ⁇ based on the voltage value VHG and the angular velocity NETC from the rotational speed calculation section 27.
  • the ECU 15 includes a target value calculation unit 28 as a target value setting unit that calculates an excess air ratio ⁇ cmd as a control target value based on an estimated value of the amount of oxygen stored in the catalyst 11 and the operating state of the internal combustion engine, and a rotation speed
  • the basic injection amount calculation section 29 calculates the basic injection amount BJ based on the rotational speed NE from the calculation section 27 and the pressure PM in the intake pipe 2 from the intake pressure sensor 7, and the excess rate calculation section 25 calculates the basic injection amount BJ.
  • a feedback coefficient calculation section 30 that calculates a feedback coefficient k for correcting the basic fuel injection amount BJ calculated by the basic injection amount calculation section 29 in order to make the excess air ratio ⁇ match the target excess air ratio ⁇ cmd; It includes an injection amount calculation unit 31 that calculates the injection amount Ti based on the basic injection amount BJ and operates the fuel injection valve 6.
  • the calculation is performed based on the deviation P between the excess air ratio ⁇ and the target excess air ratio ⁇ cmd and the derivative D of the deviation, or the deviation P, the integral I of the deviation, and the derivative D of the deviation.
  • PD/PID control based on the excess air ratio ⁇ and the target excess air ratio ⁇ cmd, or PI control executed based on the deviation P between the excess air ratio ⁇ and the target excess air ratio ⁇ cmd and the integral I of the deviation is selectively performed and feedback is performed as described later.
  • a coefficient k is calculated. Based on the injection amount Ti calculated by the injection amount calculating section 31 based on the feedback coefficient k and the basic injection amount BJ, the fuel injection valve 6 is opened for a corresponding time. Thus, an amount of fuel is injected into the cylinder combustion chamber of the engine body 1 in an amount corresponding to the feedback coefficient k based on the comparison between the excess air ratio ⁇ and the target excess air ratio ⁇ cmd.
  • the excess ratio calculation unit 25 linearizes the voltage value VHG with respect to the excess air ratio while compensating for its temperature characteristics.
  • the excess air ratio ⁇ of the exhaust gas is calculated using the data LD obtained. However, as will be described later, this calculation is applied when the voltage value VHG is less than or equal to the lean side threshold value LREF, and when the voltage value VHG is larger than the lean side threshold value LREF, the excess air ratio ⁇ is determined by another method.
  • the excess rate calculation unit 25 includes a torque calculation unit 32 that calculates the torque value TQ of the internal combustion engine based on the crank angular speed NETC of the internal combustion engine, and a limit threshold setting unit 33 that sets a conversion limit threshold for the above-mentioned linearization conversion. , a storage unit 34 that stores data necessary for calculating an alternative value R for the excess air ratio ⁇ , a data map and a look-up table to be described later, and an alternative value calculation unit 26 that calculates the alternative value R.
  • the limit threshold value setting unit 33 sets a lean side threshold value LREF, which is a conversion limit threshold value on the lean side, and a rich side threshold value RREF, which is a conversion limit threshold value on the rich side, as conversion limit threshold values, with respect to the voltage value VHG from the voltage calculation unit 24.
  • LREF lean side threshold value
  • RREF rich side threshold value
  • T conversion limit threshold
  • FIG. 5 shows the first scale value G1 in the horizontal direction in FIG. 5 corresponding to the temperature value T calculated by the temperature calculation unit 23, and the voltage value VHG calculated by the voltage calculation unit A data map is posted that has a second scale value G2 in the vertical direction in FIG. Furthermore, examples of look-up tables corresponding to graphs 35 and 36 for determining the lean-side threshold LREF and the rich-side threshold RREF are shown superimposed on the data map.
  • the data map associates a plurality of excess air ratio values with a plurality of first scale values G1 for the temperature value T and a plurality of second scale values G2 for the voltage value VHG (detected value). This is what is shown.
  • the lookup table shows the correspondence between the rich side threshold value RREF and the lean side threshold value LREF for determining whether the voltage value VHG corresponds to a rich area, a stoichiometric area, or a lean air-fuel ratio area with the first scale value G1. It shows the relationship.
  • Graph 35 shows, for example, when the excess air ratio ⁇ as the boundary between the lean region and the stoichiometric region is 1.02, and the points on the data map whose coordinates are the voltage value VHG and temperature value T that have this value are plotted. This is a graph obtained by finding multiple points and connecting these multiple points by line interpolation. Further, the graph 36 shows, for example, that the excess air ratio ⁇ as the boundary between the stoichiometric region and the rich region is 0.98, and the voltage value VHG and temperature value T corresponding to this value are set as coordinates on the data map. This is a graph obtained by finding points and connecting each of these points by line interpolation.
  • the limit threshold setting unit 33 determines that the voltage value v0 derived from the coordinate t0 is in the lean region and the stoichiometric range. It can be set as the lean-side threshold LREF for the boundary with the region.
  • the voltage value v1 derived from the coordinate t0 is It can be set as a rich-side threshold RREF.
  • the storage unit 34 also stores, as data necessary for calculating the alternative value R, the execution time Ti1 of the fuel injection by the fuel injection valve 6, the torque value TQ1, the excess air ratio ⁇ b regarding the conversion limit threshold LREF is stored.
  • the excess rate calculation unit 25 calculates a substitute value R for the exhaust air in place of the excess air rate ⁇ as the linearized data LD. Regarded as excess rate ⁇ .
  • FIG. 3 shows an excess rate (lambda) calculation process in which the excess air rate ⁇ is calculated by the excess rate calculation unit 25. Note that the control by the ECU 15 including this excess rate calculation process is executed in synchronization with the stroke of the internal combustion engine based on a pulse signal from the crank angle sensor 19 indicating the rotational angular position of the crankshaft 18.
  • step S1 the torque calculation section 32 calculates the torque TQ (DCBCP) of the internal combustion engine based on the crank angular speed NETC from the rotational speed calculation section 27.
  • step S2 when the disconnection state of the sensor heater 12b is not detected when reading the resistance of the sensor heater 12b, in step S2, the limit threshold setting unit 33 Accordingly, the lean side threshold LREF and the rich side threshold RREF are respectively set using the first and second lookup tables (VHGLREF_N, VHGRREF_N) corresponding to the graphs 35 and 36 in FIG.
  • step S3 a voltage value VHG is acquired from the voltage calculation unit 24, and the voltage value VHG is corrected by a deviation VD obtained by a voltage difference confirmation unit 43, which will be described later, to obtain a control voltage value (detected value).
  • a voltage difference confirmation unit 43 which will be described later, to obtain a control voltage value (detected value).
  • step S4 the above-mentioned data map (FIG. 5) is scanned based on the temperature value T obtained in step S2 and the voltage value VHGcon obtained in step S3.
  • Data LD is obtained which has been linearized into excess air ratio ⁇ while being compensated.
  • step S5 it is determined whether the voltage value VHGcon acquired in step S3 is smaller than the rich-side threshold value RREF set in step S2. If it is determined that it is small, the flag F_DETECT is set to zero in the subsequent step S6, and the process proceeds to step S16, where the value of the data LD is set as the excess air ratio ⁇ value LAMBDA, and the excess ratio calculation process of FIG. 3 is ended. do.
  • step S7 the voltage value VHGcon acquired in step S3 is greater than the lean threshold LREF set in step S2. Determine whether or not.
  • step S7 when it is determined that the voltage value VHGcon is not large, in step S8, the voltage value lref of the lean side threshold LREF, the voltage value rref of the rich side threshold RREF, and the voltage value lref acquired in step S2 are determined.
  • the excess air ratio ⁇ is calculated as data LD obtained by linearizing the excess air ratio while compensating for the temperature characteristics of 12, and the process proceeds to step S9.
  • the excess air ratio ⁇ as the linearized data LD in step S8 is set in advance by numerically setting the excess air ratio ⁇ as the boundary between the predetermined stoichiometric region and the lean region.
  • a variable #LLMD (for example, 1.02) that can set If there is, it can be represented by a graph as shown in FIG. In this graph, the horizontal axis in the horizontal direction in FIG. 4 is the voltage value VHG, and the vertical axis in the vertical direction in FIG. 4 is the excess air ratio ⁇ . Therefore, for example, when the voltage value VHG is vhg1, the corresponding value ⁇ 1 of the excess air ratio ⁇ can be calculated using the following equation (2).
  • ⁇ 1 (((vhg1-rref) ⁇ (lref-rref)) ⁇ (#LLMD-#RLMD))+#RLMD (2)
  • step S9 the execution time Ti of the immediately preceding fuel injection by the fuel injection valve 6 and the torque TQ calculated in step S1 are respectively set as Ti1 and TQ1, and the excess air ratio ⁇ regarding the lean side threshold value LREF is stored as ⁇ b in the storage unit 34. .
  • the countdown timer value TIMER indicating the valid time of the memory is reset to its predetermined initial value #TMINT.
  • the flag F_DETECT is set to 1, and the process proceeds to step S16, where the value of the data LD acquired in step S8 is set as the excess air ratio ⁇ value LAMBDA, and the excess ratio calculation process of FIG. 3 is ended.
  • the value of the data LD acquired in step S8 is stored as ⁇ b.
  • the exponential moving average ⁇ a of the excess air ratio ⁇ (data LD) obtained by the following equation (3) is stored as ⁇ b.
  • ⁇ a LD ⁇ k1+ ⁇ ab ⁇ (1-k1) (3)
  • k1 is a moving average coefficient
  • ⁇ ab is a moving average value in the previous control cycle stored in the storage unit 34.
  • 0.34 is used as the moving average coefficient k1.
  • the storage unit 34 stores moving average values as the fuel injection execution time Ti1 and the torque value TQ1, respectively.
  • the exponential moving average TiFLT of the fuel injection execution time Ti is calculated using the following equation (4) and stored as Ti1
  • the exponential moving average TQFLT of the torque value TQ is calculated using the following equation (5) and stored as Ti1. is stored as.
  • TiFLT Ti ⁇ k2+TiFLTb ⁇ (1-k2)
  • TQFLT TQ ⁇ k3+TQFLTb ⁇ (1-k3) (5)
  • k2 and k3 are moving average coefficients
  • TiFLTb and TQFLTb are moving average values in the previous control cycle stored in the storage unit 34.
  • different values can be used as the moving average coefficients k1, k2, and k3.
  • step S7 if it is determined that the voltage value VHGcon acquired in step S3 is larger than the lean side threshold value LREF, in step S10, it is determined whether the above-mentioned countdown timer value TIMER has reached zero. judge. If TIMER has reached zero, the flag F_DETECT is reset to 0 (step S11).
  • step S14 it is determined whether the value of the data LD set in step S13 is larger than a predetermined upper limit value #LLMT. If the value of data LD set in step S13 is larger than upper limit value #LLMT, the value of data LD is set to upper limit value #LLMT (step S15). In this case, for example, 1.25 can be used as the upper limit value #LLMT.
  • step S12 the storage unit 34 does not store valid values regarding the excess air ratio ⁇ b, the fuel injection execution time Ti1, and the torque value TQ1 regarding the lean side threshold value LREF. Therefore, the alternative value R cannot be calculated. Also in this case, the value of data LD is set to the upper limit value #LLMT (step S15).
  • step S13 or step S15 The value of the data LD set in step S13 or step S15 is then set as the excess air ratio ⁇ value LAMBDA (step S16), thereby ending the excess ratio calculation process of FIG.
  • the ECU 15 converts the excess air rate ⁇ value LAMBDA calculated in the excess rate calculation process of FIG.
  • the amount of fuel injected by the fuel injection valve 6 is controlled via the feedback coefficient calculation unit 30 so as to match the rate ⁇ cmd.
  • FIG. 6 is a graph schematically showing how the excess air ratio ⁇ value LAMBDA calculated by the excess air ratio calculation process of FIG. 3 changes.
  • the horizontal axis of the graph is a numerical value indicating the passage of time, and the vertical axis is the excess air ratio ⁇ .
  • Graph 37 in FIG. 6 shows that the actual exhaust air excess rate gradually increases at a constant rate of change in the range from the left end side to near the center of the horizontal axis in the left-right direction in FIG.
  • the voltage value VHG read by the voltage calculation unit 24 of the ECU 15 is The figure shows a numerical change in the excess air ratio ⁇ value when the excess air ratio ⁇ value is calculated using data directly linearized with respect to the excess air ratio while compensating for temperature characteristics.
  • the graph 38 shows that when the actual excess air ratio of the exhaust gas is gradually increased or decreased at a constant rate of change from the left end to the right end of the horizontal axis, the voltage value VHG from the voltage calculation unit 24 is on the lean side.
  • the excess air ratio ⁇ value is calculated using the data map described above ( Figure 5) or the data obtained by directly linearizing the voltage value VHG using equation (2).
  • the voltage value VHG from the voltage calculation unit 24 exceeds the voltage value lref of the lean side range value LREF (corresponding to the value of excess air ratio ⁇ of 1.020), the voltage value VHG is linearized.
  • the graph shows the numerical change in the excess air ratio ⁇ value when the substitute value R obtained by the above-mentioned formula (1) is used as the excess air ratio ⁇ value in place of the above data.
  • the voltage value VHG from the voltage calculation unit 24 in response thereto is proportional (linear) to the actual excess air ratio ⁇ of the exhaust gas. ), so if the actual excess air ratio of the exhaust gas is 1.020 or less, graphs 37 and 38 both linearly follow the constant change in the actual excess air ratio of the exhaust gas. However, if the excess air ratio of the exhaust exceeds 1.020, the voltage value VHG, which exhibits nonlinearity under that situation, will rapidly change in the increasing direction.
  • the graph 37 showing the excess air ratio ⁇ value based on the linearized data similarly changes steeply and non-linearly in the increasing direction.
  • the excess ratio calculation unit 25 can interlock with the actual excess air ratio of exhaust gas over the entire range of the graph in FIG. It can be seen that the excess air ratio ⁇ value that changes proportionally can be supplied to the feedback coefficient calculation unit 30. This suppresses interruption of the calculation of the feedback coefficient k by the feedback coefficient calculation unit 30.
  • the excess rate calculation section 25 includes a characteristic inspection section 40 that inspects the characteristics of the voltage value VHG (detected value) that changes according to the variation in the resistance value, and a characteristic inspection section 40 that inspects the characteristics of the voltage value VHG (detected value) that changes according to the variation in the resistance value, and uses the above-mentioned data map and lookup based on the inspection results. and a calibration section 41 that calibrates the up-table.
  • the characteristic checking unit 40 includes a temperature difference checking unit 42 that checks the deviation amount TD of the temperature T of the sensor element 12a from the reference value and sets the temperature Tcon for control, and a temperature difference checking unit 42 that checks the deviation amount TD of the temperature T of the sensor element 12a from the reference value and sets the temperature Tcon for control, and It has a voltage difference confirmation unit 43 that confirms the deviation VD between the average value VHGSTD and the lean side threshold value LREF and sets the control voltage value (detected value) VHGcon, and the set control temperature Tcon and the control voltage
  • the output characteristic of the oxygen sensor 12 connected to the ECU 15 is checked according to the value (detection value) VHGcon.
  • control temperature Tcon is set to be the same as the engine temperature and intake air temperature at room temperature and before startup.
  • the temperature difference confirmation unit 42 substantially moves the lookup table corresponding to the data map and graphs 35 and 36 in parallel in the left-right direction (in the direction of the first scale value G1) in FIG. .
  • the voltage difference confirmation unit 43 determines the voltage value VHG obtained from the resistance value of the sensor element 12a.
  • the deviation VD between the average value VHGSTD and the lean side threshold value LREF within a predetermined period of time is obtained.
  • the wave height of the voltage value VHG becomes almost zero (state where the voltage value VHG does not move) and the standard resistance value decreases.
  • the voltage value VHGref that can be read from the sensor element 12a has the same value as the graphs 35 and 36 (the voltage value VHGref and the graphs 35 and 36 overlap). That is, when the control temperature Tcon is below a predetermined value, the standard voltage value VHGref becomes equal to graph 35 (lean side threshold value LREF), so this is the standard for setting the control voltage value (detected value) VHGcon.
  • the value can be determined by scanning the look-up table corresponding to graph 35 at the sufficiently low temperature Tcon.
  • the above average value VHGSTD can be obtained from the arithmetic average value of the voltage values VHG read many times in a period of 5 seconds, for example, thereby reducing the influence of quantization errors in reading the voltage values VHG.
  • control voltage value (detected value) VHGcon is corrected to be the same as the graph 35 (lean side threshold value LREF) when the control temperature Tcon is below a predetermined value.
  • the voltage difference confirmation unit 43 substantially translates the data map in the vertical direction (in the direction of the second scale value G2) in FIG. 5 .
  • the characteristic inspection unit 40 sets the target excess air ratio ⁇ cmd to near the stoichiometric value through the target value calculation unit 28, and obtains the peak value of the voltage value VHGcon. , it is checked whether this peak value corresponds to any of the air-fuel ratio regions.
  • the first and second lookup tables corresponding to the data map and graphs 35 and 36 are calibrated based on the results of the above inspection.
  • FIG. 7 shows a voltage obtained by the characteristic inspection unit 40 while driving a vehicle equipped with an oxygen sensor 12 having a standard resistance value in an internal combustion engine with the target excess air ratio ⁇ cmd set near the stoichiometric value.
  • a voltage waveform 44 representing the change over time of the value (detected value) VHGref is shown.
  • an air-fuel ratio waveform 45 indicating the waveform of an output signal from a wideband air-fuel ratio sensor temporarily installed for verification purposes.
  • the exhaust gas in the exhaust pipe and the oxygen concentration contained in the exhaust gas are pulsating, so as shown in FIG.
  • the voltage waveform 44 of the voltage value (detected value) VHGref and the air-fuel ratio waveform 45 of the attached air-fuel ratio sensor are observed as waveforms with wave heights that change oscillally over time, but especially when the air-fuel ratio During the illustrated period P in which the fuel ratio waveform 45 crosses the level where the excess air ratio ⁇ is 1.0, the resistance value of the sensor element 12a naturally changes steeply in a stepwise manner at the oxygen concentration near the stoichiometric range.
  • the wave height M of the voltage waveform 44 (the wave height value of the detected value) is observed as a waveform that oscillates significantly compared to the wave height of the air-fuel ratio waveform 45 during the same period P.
  • the first and second lookup tables corresponding to the graph 35 (lean side threshold LREF) and graph 36 (rich side threshold RREF) are created along the wave height transition of the voltage waveform 44 that oscillates greatly in this way. are set respectively.
  • the rich-side peak near the lower rich-side threshold RREF in FIG. 46 many of them are located approximately above the rich-side threshold RREF, while many of the lean-side peaks 47 near the upper lean-side threshold LREF in FIG. 7 are located approximately above the lean-side threshold LREF.
  • the voltage value of the oxygen sensor 12 actually connected to the ECU 15 is adjusted while performing feedback control of the air-fuel ratio so as to reproduce the state of the illustrated period P by setting the target excess air ratio ⁇ cmd near the stoichiometric value.
  • Detection value By measuring the wave height M expressed by VHGcon with the ECU 15 and checking whether the peak of the wave height M matches the lean side threshold LREF and the rich side threshold RREF, the standard It is possible to grasp and obtain how much the characteristic deviation of the voltage value VHGcon from the characteristic of the voltage value VHGref at a certain resistance value is.
  • the characteristic inspection unit 40 sets the target excess air ratio ⁇ cmd near the stoichiometric value and performs air-fuel ratio feedback control, while checking the wave height of the voltage value (detection value) VHGcon of the oxygen sensor 12 connected to the ECU 15. It is configured to acquire the peak value of the wave height M and check whether the peak value of the wave height M corresponds to a rich region, a stoichiometric region, or a lean region. Also, based on the inspection results, the calibration unit 41 performs affine transformation on the data map and the first and The second lookup table can be calibrated.
  • the calibration unit 41 enlarges or reduces the plurality of first scale values G1 and the plurality of second scale values G2 in a manner of so-called affine transformation, thereby adjusting the data map and the first and second lookup tables. It is provided with a first calibration magnification value C1 and a second calibration magnification value C2 for calibrating.
  • the calibration unit 41 calculates the lean side peak value 47v of the control voltage value VHGcon that changes over time and the graph 35 (lean side threshold value LREF). For example, when the lean side peak value 47v is in the lean region, when comparing the data map and the first lookup table corresponding to When the lean side peak value 47v is in the stoichiometric region, the first calibration magnification value C1 is decreased and the data map and the first lookup table are expanded to the left in FIG. 8B. Reduce towards.
  • the calibration unit 41 multiplies the first scale value G1 of the data map and the first lookup table by the increased or decreased first calibration magnification value C1, thereby converting the data map and the first look up in a manner of so-called affine transformation. Calibrate by substantially expanding or contracting the uptable. Note that 0 Kelvin (minus 273.15 degC; absolute zero) can be adopted as the expansion/contraction origin of the first scale value G1.
  • Tk degree Celsius temperature
  • the calibration unit 41 compares the rich-side peak value 46v of the control voltage value VHGcon that changes with the passage of time with the second look-up table corresponding to the graph 36 (rich-side threshold value RREF), For example, when the peak value 46v on the rich side is in the rich region, the second calibration magnification value C2 is increased to enlarge the data map and the second lookup table downward in FIG. When the peak value 46v is in the stoichiometric region, the second calibration magnification value C2 is decreased to reduce the data map and the second lookup table upward in FIG. 8C.
  • the calibration unit 41 multiplies the second scale value G2 of the data map and the second lookup table by the increased or decreased second calibration magnification value C2, thereby converting the data map and the second look up in the manner of so-called affine transformation. Calibrate by substantially expanding or contracting the uptable.
  • the value of the graph 35 (lean side threshold value LREF) when the above-mentioned control temperature Tcon is below a predetermined value can be adopted as the expansion/contraction origin of the second scale value G2.
  • the first calibration magnification value C1 or the second calibration magnification value C1 or The calibration unit 41 can be configured to include a transition process in which the second calibration magnification value C2 is gradually increased or decreased to gradually transition to the calibration complete state.
  • the on-board diagnosis in the ECU 15 definitively diagnoses that the signal line between the sensor heater 12b of the titania type oxygen sensor 12 and the temperature calculation unit 23 is disconnected or short-circuited, , the above transition process (increase or decrease) for the first calibration magnification value C1 is interrupted, and the first calibration magnification value C1 is reset to a default value (for example, a value such as #1.0 times).
  • a titania oxygen sensor which is an embodiment of a resistance-type oxygen sensor
  • the oxygen sensor 12a if the temperature of the sensor element 12a is too low or too high, the sensor element The resistance value of 12a is difficult to respond to the air-fuel ratio, resulting in a narrow dynamic range.
  • the temperature of the sensor element 12a is too low (for example, 280 degC or lower) or too high (for example, 870 degC or higher), as can be understood from FIG.
  • the resolution of the excess rate ⁇ is extremely reduced. This makes it difficult to control using the differential term of the deviation in PID or PD control, making it difficult to maintain the control followability expected of PID or PD control (including pseudo differential terms). There is a possibility that the accuracy of feedback control regarding the excess rate ⁇ may decrease.
  • the temperature of the sensor element 12a is too low (for example, 280 degC or lower) or too high (for example, 870 degC or higher), feedback control using PID or PD control including control using a differential term is performed. It is possible that there is no such thing.
  • the control temperature Tcon is lower than the second temperature or the third temperature
  • the PI control is selected and a step of switching to the PI control is performed.
  • the feedback coefficient calculation unit 30 calculates the deviation P between the excess air ratio ⁇ obtained according to the control temperature Tcon and the target excess air ratio ⁇ cmd, the differential D of the deviation P,
  • the PD/PID control unit 49 calculates the feedback coefficient k based on the deviation P, the integral I of the deviation, and the differential D of the deviation, and the excess air ratio ⁇ and the target excess air ratio calculated according to the control temperature Tcon.
  • a PI control unit 50 that calculates a feedback coefficient k based on a deviation P with respect to ⁇ cmd and an integral I of the deviation P, and which of the PI control unit 50 or the PD/PID control unit 49 is used to calculate the feedback coefficient k.
  • a control unit selection unit 51 selects the control temperature Tcon, and a plurality of temperature setting values regarding the control temperature Tcon are read from the storage unit 34, and based on the plurality of temperature setting values and the first calibration magnification value C1, the first calibration magnification value C1 is selected from the lowest one.
  • a temperature threshold setting section 52 that sets the first, second, third, and fourth temperatures t1, t2, t3, and t4, respectively, and a PI control section 50 or a PD/PID control section 49 according to the control temperature Tcon.
  • an activation determination unit 53 that determines whether or not to permit execution of the feedback control, and a deviation P between an excess air ratio ⁇ and a target excess air ratio ⁇ cmd determined according to an alternative temperature Tsub, which will be described later, and an integral I of the deviation.
  • a fault PI control unit 59 that calculates a feedback coefficient k based on the following.
  • the activation determination unit 53 allows execution of feedback control via the PI control unit 50 or the PD/PID control unit 49 when the control temperature Tcon is higher than the first temperature t1 and lower than the fourth temperature t4. do.
  • the control unit selection unit 51 selects the PD/PID control unit when the control temperature Tcon is higher than the second temperature t2 and lower than the third temperature t3. 49 is selected, and when the control temperature Tcon is lower than the second temperature t2 or higher than the third temperature t3, the PI control unit 50 is selected.
  • the feedback coefficient calculation unit 30 calculates the deviation P between the excess air ratio ⁇ and the target excess air ratio ⁇ cmd, and the deviation P of the deviation P. Calculate the feedback coefficient k based on the differentiation, or the deviation P, the integral of the deviation P, and the differentiation of the deviation P, and if the PI control unit 50 is selected, calculate the feedback coefficient k based on the deviation P, the integral of the deviation P, and the Based on this, a feedback coefficient k is calculated. Thereby, appropriate feedback control is performed depending on whether the control temperature Tcon is too low or too high.
  • the oxygen sensor 12 is used for a long period of time and the signal line from the sensor heater 12b is disconnected due to some external factor, the resistance value of the sensor heater 12b cannot be read accurately. This makes it difficult to accurately calculate the temperature value T of the sensor element 12a. In this case, if no measures are taken, air-fuel ratio control by the oxygen sensor 12, which is highly temperature dependent, cannot be continued.
  • an alternative temperature preparation unit 54 is used that prepares an alternative temperature Tsub to be used as an alternative to the control temperature Tcon when the resistance value of the sensor heater 12b cannot be read.
  • the alternative temperature preparation unit 54 sets a plurality of voltage values corresponding to a lean side peak value 47v of the wave height of the voltage value VHG of the sensor element 12a due to exhaust pulsation and a plurality of temperature values corresponding thereto as coordinates.
  • a third look-up table 55 and a fourth look-up table 56 whose coordinates are a plurality of voltage values corresponding to the rich-side peak value 46v of the wave height of the voltage value VHGcon and a plurality of temperature values corresponding thereto.
  • These third and fourth lookup tables 55 and 56 are stored in the storage unit 34.
  • the third lookup table 55 is set in a so-called inverse functional relationship with the lookup table corresponding to the graph 35 (lean side threshold LREF). That is, in this embodiment, the third lookup table 55 sets, for example, the excess air ratio ⁇ as the boundary between the lean region and the stoichiometric region to 1.02, and determines the voltage value VHG and temperature value T that will result in this value. It is expressed by a graph obtained by finding multiple points on the data map as coordinates and connecting these multiple points by line interpolation. The correspondence relationship with the second scale value G2 is shown.
  • the fourth lookup table 56 sets, for example, the excess air ratio ⁇ as the boundary between the stoichiometric region and the rich region to 0.98, and the voltage value VHG and temperature value that result in this value. It is expressed by a graph obtained by finding multiple points on the above data map with T as the coordinate and connecting these multiple points by line interpolation, and multiple temperature values are expressed with respect to the voltage value VHG (detected value). are shown in correspondence with the plurality of second scale values G2.
  • an alternative temperature preparation section 54 for example, if the lean side peak value 47v (see FIG. 7) of the wave height of the voltage value VHG of the sensor element 12a is 3.0 volts, as shown in FIG. , it can be seen from the third lookup table 55 that the corresponding alternative temperature value Tsub is 650 degC. That is, the alternative temperature preparation unit 54 can use the third lookup table to obtain the alternative temperature Tsub based on the lean side peak value 47v, and prepare this as the alternative temperature for the control temperature Tcon.
  • the alternative temperature value Tsub is 400 degC. That is, the alternative temperature preparation unit 54 can obtain the alternative temperature Tsub using the fourth lookup table and prepare this as the alternative temperature for the control temperature Tcon. In this way, even if the signal line from the sensor heater 12b is disconnected due to some external factor, the substitute temperature Tsub is determined as a substitute temperature for the control temperature Tcon, and the air-fuel ratio is determined by the oxygen sensor 12, which is highly temperature dependent. It becomes possible to continue control.
  • the alternative temperature preparation section 54 prepares the alternative temperature for the sensor element 12a at the peak of the wave height of the voltage value VHG of the sensor element 12a. This is done by checking the value.
  • the excess air ratio calculated from the alternative temperature Tsub and the voltage value VHG from the voltage calculation unit 24 ⁇ is a value that includes ambiguity in immediacy (real-time) and has a large detection delay. This means that the accuracy of PD/PID control based on the amount of change in deviation (differential term) with respect to the excess air ratio ⁇ may be significantly reduced.
  • PD/PID control is not performed, and limited control is performed only by PI control, which is a control method that does not include a differential term.
  • the alternative temperature preparation unit 54 is executed (step S2B).
  • the alternative temperature Tsub is determined from the lean side peak value 47v or the rich side peak value 46v as described above.
  • step S2B the limit threshold setting unit 33 is executed (step S2B).
  • the limit threshold value setting unit 33 sets a lean side threshold value LREF and a rich side threshold value RREF based on the alternative temperature value Tsub using the first and second lookup tables corresponding to the graphs 35 and 36 in FIG.
  • step S3B the voltage value VHG obtained from the voltage calculation section 24 is corrected by the deviation VD obtained from the voltage difference confirmation section 43, and a voltage value (detected value) VHGcon for control is set.
  • step S4B the above-mentioned data map (FIG. 5) is scanned based on the alternative temperature Tsub and the voltage value VHGcon obtained in step S3B, and data LD is obtained.
  • step S6 the flag F_DETECT is set to zero, and the process proceeds to step S16, where the value of the data LD is set as the excess air ratio ⁇ value LAMBDA. In this way, the excess rate calculation process shown in FIG. 3 in the event of a failure such as a disconnection of the sensor heater 12b is completed.
  • the activation determining unit 53 and the control unit selecting unit 51 detect that the signal line between the sensor heater 12b of the titania oxygen sensor 12 and the temperature calculating unit 23 is disconnected or short-circuited by the on-board diagnostic unit 62 in the ECU 15.
  • the alternative temperature Tsub is higher than the first temperature t1 and lower than the fourth temperature t4
  • the failure only allows execution of feedback control via the failure PI control unit 59. It has a time activation determining section.
  • the activation determination unit 53 and the control unit selection unit 51 permit PD/PID control when it is diagnosed that the signal line between the sensor heater 12b and the temperature calculation unit 23 is disconnected or short-circuited. It is configured not to.
  • the fault PI control unit 59 calculates the feedback coefficient k based on the deviation between the excess air ratio ⁇ obtained according to the alternative temperature Tsub and the target excess air ratio ⁇ cmd and the integral of the deviation, and thereby, Feedback control of the excess air ratio ⁇ can be performed by PI control. Therefore, even if it is diagnosed that the signal line between the sensor heater 12b and the temperature calculation unit 23 is disconnected or short-circuited, appropriate feedback control is continued.
  • control section selection section 51 selects the control voltage value (detected value) VHGcon in the characteristic inspection section 40 and the control
  • the PD/PID control unit 49 or the PI control unit 50 is configured to be selected depending on the inspection result of the operating temperature Tcon.
  • the calibration unit 41 sets the lean side threshold LREF and the rich side threshold RREF respectively to the first scale value G1 related to the control temperature Tcon and the first scale value G1 related to the control voltage value (detected value) VHGcon.
  • the first scale value G1 and the second scale value G2 regarding the correspondence in the data map are each calibrated based on the comparison between the data map respectively associated with the second scale value G2 and the peak values 46v and 47v. It is composed of
  • the calibration unit 41 adjusts the By gradually increasing or decreasing the calibration magnification value C1 or the second calibration magnification value C2, the calibration can be gradually progressed (learning) to a calibration completed state.
  • the characteristic inspection unit 40 compares the peak values 46v and 47v with at least one side of the rich side threshold RREF or the lean side threshold LREF to which the above-mentioned calibration is reflected, thereby checking the progress of the calibration by the calibration unit 41.
  • the control unit selection unit 51 calculates the difference between the peak value 46v and the rich side threshold RREF, or the peak value 46v and the lean side threshold LREF, and considers the difference as the progress state of the calibration by the calibration unit 41,
  • the progress state of this calibration can be used as the inspection result of the control voltage value VHGcon and the control temperature Tcon in the characteristic inspection section 40 to select the PD/PID control section 49 or the PI control section 50.
  • the control unit selection unit 51 determines the calibration progress state. It is possible to select the above-mentioned PD/PID control section 49 by assuming that the calibration is completed. Alternatively, if the difference between the peak value 46v and the rich side threshold RREF, or the difference between the peak value 46v and the lean side threshold LREF is larger than a predetermined threshold, the calibration progress state is the calibration incomplete state. In this case, the PI control unit 50 can be selected.
  • priority is given to determining whether or not to allow the execution of the feedback control by the above-mentioned activation determining section 53 and determining whether or not to permit the execution of the air-fuel ratio feedback control by the PI control section 50.
  • the PI control unit 50 and PD/PID control unit 49 are not selected, that is, feedback control is stopped.
  • control temperature Tcon is lower than the second temperature t2 or higher than the third temperature t3, and therefore execution of feedback control by the PI control unit 50 is selected, even if the peak value is 46V. Even if the rich side threshold RREF or the difference between the peak value 46v and the lean side threshold LREF is less than a predetermined threshold, the PD/PID control unit 49 is not allowed to perform control.
  • control temperature Tcon is higher than the second temperature t2 and lower than the third temperature t3, and the control temperature Tcon is such that execution of feedback control by the PD/PID control unit 49 can be selected. If the difference between the peak value 46v and the rich side threshold RREF or between the peak value 46v and the lean side threshold LREF is larger than a predetermined threshold and it is considered that the calibration is still incomplete, the PI control unit Execution of feedback control by 50 is selected.
  • the ECU 15 includes a calibration reset section 61 and the above-mentioned on-board diagnostic section 62, which output a trigger signal that causes the control section selection section 51 to make a selection based on the inspection result of the characteristic inspection section 40 (see FIG. 2). .
  • the calibration reset unit 61 is configured to be able to issue, to the control unit selection unit 51, an initialization command Rs that initializes the correspondence in the data map described above as the trigger signal.
  • the on-board diagnostic unit 62 is configured to be capable of diagnosing a failure such as a disconnection in the sensor element (detection unit) 12a or the sensor heater 12b (heater unit) of the titania oxygen sensor 12.
  • a failure such as a disconnection in the sensor element (detection unit) 12a or the sensor heater 12b (heater unit) of the titania oxygen sensor 12.
  • the on-board diagnostic unit 62 determines that there is an abnormality in the sensor element 12a or the sensor heater 12b
  • the on-board diagnostic unit 62 sends an abnormality signal As indicating this to the control unit selection unit 51 as the trigger signal. will be issued.
  • control unit selection unit 51 When the control unit selection unit 51 receives the initialization command Rs from the calibration reset unit 61, it preferentially selects the PI control unit 50 in a predetermined period thereafter.
  • This predetermined period is set to be a sufficient period required for the characteristics inspection section 40 to repeatedly perform inspections and for the calibration section 41 to determine the progress state of the above-mentioned calibration according to the results. Ru.
  • control unit selection unit 51 selects the PI control unit 50 when receiving the abnormality signal As from the on-board diagnosis unit 62.
  • the accurate temperature value Tcon of the sensor element 12a cannot be obtained, so the excess air ratio ⁇ obtained from the substitute value Tsub (see steps S2B to S43B, S6, and S16 in FIG. 3) )
  • the fault PI control unit 59 is selected as the PI control unit 50.
  • PI control by the failure PI control section 59 is selected until the abnormality signal As is released. Note that when the fault PI control section 59 performs PI control in response to the abnormal signal As, the above-mentioned calibration control by the calibration section 41 is interrupted (temporarily stopping calculation and updating of calibration values). ).
  • the control unit selection unit 51 selects the PI control unit 50 for a predetermined period after the cancellation.
  • This predetermined period is such that after the cancellation, the calibration unit 41 repeatedly performs the inspection by the characteristic inspection unit 40 as described above, and depending on the result, the calibration unit 41 indicates the progress status of the calibration described above. A period sufficient to allow a decision to be made will be set.
  • the temperature of the sensor element 12a of the oxygen sensor 12 when the temperature of the sensor element 12a of the oxygen sensor 12 is below the first temperature t1 which is too low or above the fourth temperature t4 which is too high, no feedback control is performed.
  • the control temperature when the control temperature is lower than the second temperature t2 or higher than the third temperature t3, feedback control is performed via the PI control unit 50, and the temperature of the sensor element 12a of the oxygen sensor 12 is lower than the second temperature t2.
  • feedback control is performed via the PD/PID control unit 49, so it is possible to substantially expand the operating temperature range of feedback control, improve availability, and improve exhaust purification performance. can.
  • the temperature corresponding to the peak value of the voltage value VHG from the voltage calculation unit 24 is determined, and the determined temperature is used for control in the excess rate calculation unit 25.
  • the prepared alternative temperature Tcon can be used. Since a failure PI control unit 59 is provided that calculates a feedback coefficient k based on the deviation P between the excess air ratio ⁇ obtained using Tsub and the target excess air ratio ⁇ cmd and the integral I of the deviation, it is possible to prevent a failure of the heater unit. Feedback control of the excess air ratio can be continued even at the same time.
  • control unit selection unit 51 selectively selects the PD/PID control unit 49 or the PI control unit 50 according to the inspection results of the detected value VHGcon, the control temperature Tcon, and the control temperature Tcon in the characteristic inspection unit 40. Since the oxygen sensor 12 is configured to be able to perform the following, it is possible to select an appropriate control according to the inspection result in accordance with differences in characteristics due to individual differences in the oxygen sensor 12. As a result, highly robust air-fuel ratio feedback control using the titania-type oxygen sensor 12 can be realized.
  • the data map is also calibrated based on the comparison between the data map and the peak value described above, and the progress of the calibration is determined by comparing the peak value with at least one of the lean threshold or the rich threshold. Therefore, the control unit selection unit 51 can appropriately select the PD/PID control unit 49 or the PI control unit 50 by referring to the progress state of this calibration as the inspection result in the characteristic inspection unit 40. can.
  • control unit selection unit 51 receives the initialization command Rs from the calibration reset unit 61, it selects the PI control unit for a predetermined period thereafter, so that the data is not stored in the predetermined period. While the map calibration is progressing, the progress state of the calibration can be appropriately determined, and the alternative selection of the PD/PID control unit 49 or the PI control unit 50 can be appropriately performed.
  • control unit selection unit 51 selects the PI control unit 50 when it is determined that the sensor element 12a or the sensor heater 12b of the oxygen sensor 12 is temporarily abnormal. It is possible to prevent inaccurate feedback control from being performed by the control unit 49.
  • control unit selection unit 51 selects a PI control unit in a predetermined period after the cancellation. 50 is selected, the calibration of the data map is progressing in the meantime, the progress state of this calibration is appropriately determined, and the alternative selection of the PD/PID control unit 49 or the PI control unit 50 is appropriately performed. I can do it.
  • the plurality of first scale values G1 of the data map and the first and second lookup tables, and the first, second, third, and fourth temperatures t1, t2, t3, t4 Although the calibration is performed by multiplying each of the values by the first calibration magnification value C1 (Equation (6a) and Equation (6b)), the present invention is not limited to this. For example, even with a configuration in which the temperature value is multiplied by the reciprocal of the first calibration magnification value C1, it is possible to substantially enlarge or reduce the data map and lookup table, and at this time, the data map and the lookup table can be substantially enlarged or reduced.
  • the pre-calibration values of the plurality of first scale values G1 or the plurality of first to fourth temperature setting values are Tk (degrees Celsius temperature), the first control scale values after calibration or the first and second temperature settings after calibration.
  • Tkcal is the third and fourth temperatures t1, t2, t3, and t4
  • Temp is the temperature value T from the temperature calculation unit 23 or the alternative temperature Tsub from the alternative temperature preparation unit 54, Tkcal and the control temperature
  • Tcon temperature in degrees Celsius
  • the reference value Tref for setting the temperature Tcon may be calculated from only one of them.
  • Characteristic inspection section 41... Calibration section, 42... Temperature difference confirmation section, 43...Voltage difference confirmation unit, 44...Voltage waveform, 45...Air-fuel ratio waveform, 46...Rich side peak, 47...Lean side peak, 46v, 47v...Peak value, 48...Feedback control unit, 49...PD ⁇ PID control unit, 50...PI control unit, 51...Control unit selection unit, 52...Temperature threshold setting unit, 53...Activity determination unit, 54...Alternative temperature preparation unit, 55...Third lookup table, 56...-Fourth Lookup table, 58... Graph, 59... PI control unit at the time of failure, 61... Calibration reset unit, 62... On-board diagnostic unit.

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  • Chemical & Material Sciences (AREA)
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Abstract

 Provided is an air-fuel ratio control device that can perform air-fuel ratio feedback control with a resistive oxygen sensor having high robustness. This air-fuel ratio control device comprises: a PD/PID control unit (49) and a PI control unit (50) that perform feedback control of an excess air rate; a control unit selection unit (51) that selects one of the controls units; a characteristic inspection unit that inspects whether a detection value of a titania oxygen sensor and a temperature of a detection unit correspond to respective prescribed characteristics; and a calibration unit that, on the basis of the inspection, calibrates first and second scale values (G1, G2) of a data map for finding the excess air rate from the detection value and the temperature. The control unit selection unit (51) performs the alternative selection of the PD/PID control unit or the PI control unit in accordance with the inspection result.

Description

空燃比制御装置Air fuel ratio control device
　本発明は、排気脈動を有する内燃機関の排気に接するように設けられる抵抗型酸素センサを備える空燃比制御装置に関する。 The present invention relates to an air-fuel ratio control device that includes a resistance-type oxygen sensor that is provided in contact with the exhaust gas of an internal combustion engine that has exhaust pulsation.
　従来、内燃機関の排気に接するように設けられた酸素センサの出力情報により得られる空燃比に基づき、内燃機関の内燃プロセスにおける空燃比フィードバック制御を行うことが知られている（例えば、特許文献１参照）。 Conventionally, it has been known to perform air-fuel ratio feedback control in the internal combustion process of an internal combustion engine based on the air-fuel ratio obtained from the output information of an oxygen sensor provided in contact with the exhaust gas of the internal combustion engine (for example, Patent Document 1 reference).
　特許文献１の技術では、酸素センサとして、検出部の内部抵抗に基づいて酸素を検出する抵抗型酸素センサが用いられる。この酸素センサでは、排気ガス中の酸素含有量を示す第１の値が、酸素センサの検出部の抵抗に基づいて決定される。また、酸素センサの温度を示す第２の値が、酸素センサのヒータ部分の抵抗に基づいて決定される。そして、第１の値及び第２の値の関数としての空燃比が、第３の値として決定される。 In the technique of Patent Document 1, a resistance-type oxygen sensor that detects oxygen based on the internal resistance of a detection part is used as an oxygen sensor. In this oxygen sensor, a first value indicating the oxygen content in the exhaust gas is determined based on the resistance of the detection section of the oxygen sensor. Further, a second value indicating the temperature of the oxygen sensor is determined based on the resistance of the heater portion of the oxygen sensor. The air-fuel ratio as a function of the first value and the second value is then determined as a third value.
　この技術によれば、第３の値を決定するための関数に、第１の値にリアルタイムで影響を及ぼす第２の値が含まれるので、酸素センサの温度によりその出力特性が変化しても、検出された酸素センサの検出部の抵抗値に基づいて空燃比が算出される。 According to this technology, the function for determining the third value includes a second value that affects the first value in real time, so even if the output characteristics change due to the temperature of the oxygen sensor, The air-fuel ratio is calculated based on the detected resistance value of the detection section of the oxygen sensor.
米国特許第８９５９９８７号公報US Patent No. 8959987
　ところで、抵抗型酸素センサの一態様であるチタニア酸素センサを採用した場合、チタニア酸素センサの検出部の温度が低すぎるか又は高すぎる場合には、そうでない場合と比較して、検出部の抵抗値が空燃比に対して応動し難く、ダイナミックレンジが狭くなる。その帰結として、検出部の温度が低すぎるか又は高すぎる場合には、チタニア酸素センサの検出値に基づく空気過剰率の分解能が極端に低下し、空燃比フィードバック制御の精度が大きく低下するおそれがある。そして、かかるチタニア酸素センサの温度特性による検出値のずれは、個々のチタニア酸素センサの個体によっても異なり、個体差も大きい。 By the way, when a titania oxygen sensor, which is an embodiment of a resistance-type oxygen sensor, is adopted, if the temperature of the detection part of the titania oxygen sensor is too low or too high, the resistance of the detection part will be lower than in the case where it is not. The value is difficult to respond to the air-fuel ratio, and the dynamic range becomes narrow. As a result, if the temperature of the detection part is too low or too high, the resolution of the excess air ratio based on the detection value of the titania oxygen sensor will be extremely reduced, and the accuracy of air-fuel ratio feedback control may be greatly reduced. be. The deviation in the detected value due to the temperature characteristics of such a titania oxygen sensor varies depending on the individual titania oxygen sensor, and there are large individual differences.
　本発明の目的は、かかる従来技術の問題点に鑑み、抵抗型酸素センサの温度特性を、センサの個体毎の特性の相違をも含めて適切に補償することにより、ロバストネス（堅牢性)の高い抵抗型酸素センサによる空燃比フィードバック制御を実現できる空燃比制御装置を提供することにある。 In view of the problems of the prior art, an object of the present invention is to appropriately compensate for the temperature characteristics of a resistance-type oxygen sensor, including the differences in characteristics between individual sensors, thereby achieving high robustness. An object of the present invention is to provide an air-fuel ratio control device that can realize air-fuel ratio feedback control using a resistance-type oxygen sensor.
　本発明の空燃比制御装置は、
　排気脈動を有する内燃機関の排気に接するように設けられる検出部と、該検出部に隣接するヒータ部とを有する抵抗型酸素センサを備える内燃機関の空燃比制御装置であって、
　前記内燃機関の作動状態に基づき空気過剰率に係る制御目標値を設定する目標値設定部と、
　前記ヒータ部の抵抗値に基づいて前記検出部の温度を求める検出部温度推定部と、
　前記検出部の抵抗値を読み取って該検出部の検出値を求める検出値読取部と、
　前記検出値及び前記検出部の温度から前記空気過剰率を算出する過剰率算出部と、
　前記空気過剰率と前記制御目標値との偏差を求め、該偏差及び該偏差の微分、又は該偏差、該偏差の積分及び該偏差の微分を要素として前記空気過剰率をフィードバック制御するＰＤ・ＰＩＤ制御部と、
　前記空気過剰率と前記制御目標値との偏差及び該偏差の積分を要素として前記空気過剰率をフィードバック制御するＰＩ制御部と、
　前記フィードバック制御に、前記ＰＩ制御部又は前記ＰＤ・ＰＩＤ制御部のいずれを使用するかを選択する制御部選択部と、
　前記検出値及び前記検出部の温度が各所定の特性に該当するか否かを点検する特性点検部と、
　前記検出部温度推定部及び前記検出値読取部を、前記点検に基づいてそれぞれ較正する較正部とを備え、
　前記制御部選択部は、前記特性点検部における前記検出値及び前記検出部の温度の点検結果に応じて、前記ＰＤ・ＰＩＤ制御部又は前記ＰＩ制御部の択一的選択を実行し得るように構成されることを特徴とする。 The air-fuel ratio control device of the present invention includes:
An air-fuel ratio control device for an internal combustion engine, comprising a resistance-type oxygen sensor having a detection section provided in contact with exhaust gas of an internal combustion engine having exhaust pulsation, and a heater section adjacent to the detection section,
a target value setting unit that sets a control target value related to an excess air ratio based on the operating state of the internal combustion engine;
a detection unit temperature estimation unit that calculates the temperature of the detection unit based on the resistance value of the heater unit;
a detected value reading unit that reads a resistance value of the detection unit to obtain a detection value of the detection unit;
an excess rate calculation unit that calculates the excess air rate from the detected value and the temperature of the detection unit;
A PD/PID that calculates a deviation between the excess air ratio and the control target value, and performs feedback control of the excess air ratio using the deviation and the derivative of the deviation, or the deviation, the integral of the deviation, and the derivative of the deviation as elements. a control unit;
a PI control unit that performs feedback control of the excess air ratio using a deviation between the excess air ratio and the control target value and an integral of the deviation as elements;
a control unit selection unit that selects which of the PI control unit or the PD/PID control unit to use for the feedback control;
a characteristic checking unit that checks whether the detected value and the temperature of the detection unit correspond to each predetermined characteristic;
a calibration unit that calibrates the detection unit temperature estimation unit and the detected value reading unit, respectively, based on the inspection;
The control section selection section is configured to be able to perform alternative selection of the PD/PID control section or the PI control section according to the detection value in the characteristic inspection section and the inspection result of the temperature of the detection section. It is characterized by being configured.
　本発明において、検出部の検出値及び検出部の温度が各所定の特性に該当するか否かが特性点検部により点検され、これに基づいて検出部温度推定部及び検出値読取部が較正部により較正されるとともに、該点検結果に応じて、ＰＤ・ＰＩＤ制御部又はＰＩ制御部が制御部選択部により選択される。 In the present invention, the characteristic checking section checks whether the detected value of the detecting section and the temperature of the detecting section correspond to each predetermined characteristic, and based on this, the detecting section temperature estimating section and the detected value reading section are connected to the calibration section. The PD/PID control section or the PI control section is selected by the control section selection section according to the inspection result.
　ここで、較正部による較正が未完了の状態では、過剰率算出部により算出される空気過剰率λの確からしさが保証されないので、この空気過剰率をトリガとするＰＤ・ＰＩＤ部によるフィードバックを適用することができない。また、抵抗型酸素センサについては、その特性が個々の抵抗型酸素センサによって異なり、個体差も大きいので、較正の進捗状態も都度異なる。 Here, if the calibration by the calibration unit is not completed, the reliability of the excess air ratio λ calculated by the excess air ratio calculation unit is not guaranteed, so feedback from the PD/PID unit using this excess air ratio as a trigger is applied. Can not do it. Furthermore, the characteristics of resistance-type oxygen sensors vary depending on the individual resistance-type oxygen sensors, and since there are large individual differences, the progress state of calibration also differs each time.
　そこで、本発明では、検出部の検出値及び検出部の温度が各所定の特性に該当するか否かが特性点検部により点検され、この点検に基づいて、制御部選択部により、ＰＤ・ＰＩＤ制御部又はＰＩ制御部が択一的に選択される。 Therefore, in the present invention, the characteristic inspection section checks whether the detection value of the detection section and the temperature of the detection section correspond to each predetermined characteristic, and based on this inspection, the control section selection section selects the PD/PID. The control unit or the PI control unit is alternatively selected.
　これにより、制御部選択部は、抵抗型酸素センサ毎に較正の進捗状況を把握し、ＰＩＤ又はＰＤ制御に期待される制御追従性を実現できる程度にまで十分に較正が進捗した状態にあると判断される場合には、ＰＤ・ＰＩＤ制御部を選択してＰＤ・ＰＩＤ制御による空気過剰率のフィードバック制御を実施させることができる。一方、かかる状態にないと判断される場合には、ＰＩ制御部を選択してＰＩ制御による空気過剰率のフィードバック制御を実施させることができる。 As a result, the control section selection section grasps the progress of calibration for each resistance-type oxygen sensor, and determines that the calibration has progressed sufficiently to the extent that the control followability expected for PID or PD control can be achieved. If it is determined, the PD/PID control section can be selected to perform feedback control of the excess air ratio by PD/PID control. On the other hand, if it is determined that such a state does not exist, the PI control section can be selected to perform feedback control of the excess air ratio by PI control.
　したがって、本発明によれば、抵抗型酸素センサ毎の特性を、その相違をも含めて適切に補償しつつ、ＰＩＤ・ＰＤ制御とＰＩ制御を適切に選択して実施できるので、抵抗型酸素センサによるロバストネス（堅牢性)の高い空燃比フィードバック制御を実現できる空燃比制御装置を提供することができる。 Therefore, according to the present invention, it is possible to appropriately select and implement PID/PD control and PI control while appropriately compensating for the characteristics of each resistance-type oxygen sensor, including the differences. It is possible to provide an air-fuel ratio control device that can realize air-fuel ratio feedback control with high robustness.
　本発明において、前記較正部は、前記内燃機関の排気脈動による前記検出値の波高の尖頭値がリッチ領域、ストイキ領域又はリーン領域の何れの空燃比領域に該当するかを判別するためのリーン側閾値及びリッチ側閾値のそれぞれを前記検出部の温度に係る第１目盛値及び前記検出値に係る第２目盛値にそれぞれ対応付けたデータマップと、前記尖頭値との対比に基づいて前記データマップにおける前記対応付けに関する前記第１目盛値及び前記第２目盛値を各較正するように構成されており、
　前記特性点検部は、前記尖頭値を前記リーン側閾値又は前記リッチ側閾値の少なくとも一方側と比較することによって前記較正の進捗状態を判定するものであってもよい。 In the present invention, the calibration unit is configured to perform a lean air-fuel ratio range for determining whether the peak value of the wave height of the detected value due to exhaust pulsation of the internal combustion engine corresponds to which air-fuel ratio region of a rich region, a stoichiometric region, or a lean region. Based on the comparison between the peak value and a data map in which the side threshold value and the rich side threshold value are respectively associated with the first scale value related to the temperature of the detection unit and the second scale value related to the detected value, configured to calibrate each of the first scale value and the second scale value regarding the correspondence in the data map,
The characteristic inspection unit may determine the progress state of the calibration by comparing the peak value with at least one of the lean-side threshold value and the rich-side threshold value.
　これによれば、上述のデータマップと尖頭値との対比に基づいてデータマップが較正され、尖頭値をリーン側閾値又はリッチ側閾値の少なくとも一方側と比較することによって較正の進捗状態が判定される。したがって、制御部選択部は、特性点検部における点検結果としてこの較正の進捗状態を参照することにより、抵抗型酸素センサの個体差による特性の差異が大きい場合でも、ＰＤ・ＰＩＤ制御部又はＰＩ制御部を適切に選択して空燃比フィードバック制御の適切な実施を担保し、エミッション性能の悪化を抑制することができる。 According to this, the data map is calibrated based on the comparison between the data map and the peak value described above, and the progress state of the calibration is checked by comparing the peak value with at least one side of the lean side threshold or the rich side threshold. It will be judged. Therefore, by referring to the progress state of this calibration as the inspection result in the characteristic inspection section, the control section selection section can control the PD/PID control section or the PI control By appropriately selecting the air-fuel ratio feedback control, it is possible to ensure appropriate implementation of air-fuel ratio feedback control and suppress deterioration of emission performance.
　この場合、前記データマップにおける前記対応付けを初期化する初期化指令を発行可能に構成された較正リセット部を備え、
、前記制御部選択部は、該較正リセット部からのリセット指令を受けた場合、それ以降の予め定められた期間、前記ＰＩ制御部を選択するように構成されてもよい。 In this case, a calibration reset unit configured to be able to issue an initialization command to initialize the correspondence in the data map,
, the control unit selection unit may be configured to select the PI control unit for a predetermined period after receiving a reset command from the calibration reset unit.
　これによれば、較正リセット部からのリセット指令を受けた場合には、少なくとも予め定められた期間の間は、ＰＩ制御によるフィードバック制御が行われるので、その間に、特性点検部による点検を実施し、その結果に応じて、較正部による再較正を着実に進捗させつつこの較正の進捗状態を適切に判定して、ＰＤ・ＰＩＤ制御部又はＰＩ制御部の択一的選択を適切に行うよう構成することができる。たとえば、酸素センサの検出部又はヒータ部について実際に故障が検出確定された場合には、その修復作業として酸素センサ本体を正常品へと交換することと共に、較正リセット部からのリセット指令を介して空燃比制御装置に記憶されている較正パラメータのリセットが行われるが、そのように交換された、抵抗型酸素センサの個体差による特性の差異が大きい場合であっても、ＰＩ制御部を選択して空燃比フィードバック制御を支障なく行いエミッション性能の悪化を抑制することができる。 According to this, when a reset command is received from the calibration reset section, feedback control by PI control is performed at least for a predetermined period, so that the characteristic inspection section performs an inspection during that time. , and is configured to appropriately determine the progress state of the calibration while steadily progressing recalibration by the calibration unit according to the result, and to appropriately select the PD/PID control unit or the PI control unit. can do. For example, if a failure is actually detected and confirmed in the detection part or heater part of an oxygen sensor, the repair work involves replacing the oxygen sensor body with a normal one and also issuing a reset command from the calibration reset part. The calibration parameters stored in the air-fuel ratio control device are reset, but even if the characteristics of the replaced resistance-type oxygen sensor are large due to individual differences, the PI control section cannot be selected. Therefore, air-fuel ratio feedback control can be performed without any problem and deterioration of emission performance can be suppressed.
　本発明において、前記抵抗型酸素センサの検出部又は前記ヒータ部の異常乃至故障の診断を実行可能に構成されたオンボード診断部を有し、前記制御部選択部は、前記オンボード診断部において前記抵抗型酸素センサの検出部又は前記ヒータ部が異常であると判定された場合には、前記ＰＩ制御部を選択するように構成されてもよい。 In the present invention, the on-board diagnostic section is configured to be able to diagnose abnormality or failure of the detection section or the heater section of the resistance-type oxygen sensor, and the control section selection section is arranged in the on-board diagnostic section. The sensor may be configured to select the PI control unit when it is determined that the detection unit or the heater unit of the resistance-type oxygen sensor is abnormal.
　これによれば、一時的であれ抵抗型酸素センサの検出部又はヒータ部が異常である場合には、ＰＤ・ＰＩＤ制御部による適切なフィードバック制御が困難となるが、かかる場合にＰＩ制御部が選択されるので、空燃比フィードバック制御を支障なく続行し、エミッション性能の悪化を抑制することができる。 According to this, if the detection section or heater section of the resistance type oxygen sensor is abnormal, even temporarily, it becomes difficult for the PD/PID control section to perform appropriate feedback control; however, in such a case, the PI control section Since this is selected, air-fuel ratio feedback control can be continued without any problem and deterioration of emission performance can be suppressed.
　また、前記較正部は、前記オンボード診断部において前記抵抗型酸素センサの検出部又は前記ヒータ部が異常であると判定された場合には、較正に係る制御を一時的に中断するように構成されてもよい。 Further, the calibration unit is configured to temporarily suspend control related to calibration when the on-board diagnosis unit determines that the detection unit or the heater unit of the resistance-type oxygen sensor is abnormal. may be done.
　これによれば、一時的であれ抵抗型酸素センサの検出部又はヒータ部が異常である場合に、異常な検出部又はヒータ部からの値に基づく較正が行われることを抑制することができる。 According to this, even if the detection section or heater section of the resistance type oxygen sensor is abnormal, even temporarily, it is possible to suppress the calibration based on the value from the abnormal detection section or heater section from being performed.
　この場合、前記制御部選択部は、前記オンボード診断部により前記抵抗型酸素センサの検出部又は前記ヒータ部の異常が検出された後に該異常の検出が解除されたとき、前記較正部の前記較正に係る制御を再開するとともに、該再開以降の予め定められた期間において前記ＰＩ制御部を選択するように構成されてもよい。 In this case, when the on-board diagnosis section detects an abnormality in the detection section or the heater section of the resistance-type oxygen sensor and then the detection of the abnormality is canceled, the control section selection section selects the control section of the calibration section. The calibration control unit may be configured to restart control related to calibration and select the PI control unit in a predetermined period after the restart.
　これによれば、異常の検出が解除された後、特性点検部における点検結果として、較正の進捗状態を参照されるまでにある程度の期間を要するところ、少なくとも予め定められた期間においてはＰＩ制御による空燃比フィードバックが行われるので、その間に較正部によるデータマップの較正を着実に進捗させつつこの較正の進捗状態を適切に判定して、これにより、ＰＤ・ＰＩＤ制御部又はＰＩ制御部の択一的選択を適切に行いエミッション性能の悪化を抑制することができる。 According to this, after the abnormality detection is canceled, it takes a certain period of time before the calibration progress status is referred to as the inspection result in the characteristic inspection section, but at least during a predetermined period, the PI control Since air-fuel ratio feedback is performed, the calibration section steadily progresses in calibrating the data map, and the progress of this calibration is appropriately determined, thereby determining the selection of the PD/PID control section or the PI control section. The deterioration of emission performance can be suppressed by making appropriate selections.
本発明の一実施形態に係る空燃比制御装置を備える内燃機関の主要部の構成を模式的に示す模式図である。1 is a schematic diagram schematically showing the configuration of main parts of an internal combustion engine including an air-fuel ratio control device according to an embodiment of the present invention. 図１の内燃機関のＥＣＵにおける主要な構成を示すブロック図である。2 is a block diagram showing the main configuration of an ECU of the internal combustion engine of FIG. 1. FIG. 図２のＥＣＵにおいて過剰率算出部により空気過剰率を算出する過剰率算出処理を示すフローチャートである。3 is a flowchart showing an excess rate calculation process in which an excess air rate is calculated by an excess rate calculation unit in the ECU of FIG. 2. FIG. 図３の処理において、ストイキ領域における空気過剰率を算出する様子を示すグラフである。4 is a graph showing how the excess air ratio in the stoichiometric region is calculated in the process of FIG. 3. 図３の処理において、リーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦを求めるためのルックアップテーブルに対応するグラフ、及び空気過剰率を算出するためのデータマップを示す図である。4 is a diagram showing a graph corresponding to a lookup table for calculating a lean side threshold value LREF and a rich side threshold value RREF, and a data map for calculating an excess air ratio in the process of FIG. 3. FIG. 図３の処理によって算出される空気過剰率λの変化の様子を模式的に示すグラフである。4 is a graph schematically showing how the excess air ratio λ calculated by the process of FIG. 3 changes; 内燃機関を搭載した車両を運転しながら得られた時間経過に伴い、電圧算出部が出力する電圧値の変化を表す電圧波形を示す波形図である。FIG. 3 is a waveform diagram showing a voltage waveform representing a change in a voltage value output by a voltage calculation unit over time obtained while driving a vehicle equipped with an internal combustion engine. 図２のＥＣＵにおける特性点検部による点検及び較正部による較正の一例を示す図である。3 is a diagram showing an example of an inspection by a characteristic inspection section and calibration by a calibration section in the ECU of FIG. 2. FIG. 前記特性点検部による点検及び較正部による較正の他の例を示す図である。It is a figure which shows the other example of the inspection by the said characteristic inspection part and calibration by a calibration part. 前記特性点検部による点検及び較正部による較正の別の例を示す図である。It is a figure which shows another example of the inspection by the said characteristic inspection part and calibration by a calibration part. 前記特性点検部による点検及び較正部による較正のさらに別の例を示す図である。It is a figure which shows yet another example of the inspection by the said characteristic inspection part and calibration by a calibration part. 図２のＥＣＵにおけるフィードバック係数演算部の構成を示すブロック図である。3 is a block diagram showing the configuration of a feedback coefficient calculating section in the ECU of FIG. 2. FIG. 図２のＥＣＵにおける代替温度準備部により求められる代替温度Ｔｓｕｂの例を示す図である。3 is a diagram showing an example of an alternative temperature Tsub obtained by an alternative temperature preparation section in the ECU of FIG. 2. FIG.
　以下、図面を用いて本発明の実施形態を説明する。図１は、本発明の一実施形態に係る空燃比制御装置を備える４サイクル形式の内燃機関の主要部の構成を示す。この空燃比制御装置は、内燃機関の排気中の酸素濃度に基づいて得られる空気過剰率と、目標空気過剰率との偏差に基づいて空燃比フィードバック制御を行う機能を有する。 Hereinafter, embodiments of the present invention will be described using the drawings. FIG. 1 shows the configuration of the main parts of a four-stroke internal combustion engine equipped with an air-fuel ratio control device according to an embodiment of the present invention. This air-fuel ratio control device has a function of performing air-fuel ratio feedback control based on the deviation between the excess air ratio obtained based on the oxygen concentration in the exhaust gas of the internal combustion engine and the target excess air ratio.
　同図に示すように、この内燃機関の機関本体１は、吸入ポートに設けられた吸気管２と、吸気管２内に設けられてエアクリーナ４から吸入ポートに供給される吸気の量を開度に応じて調整するスロットル弁３とを備える。 As shown in the figure, an engine body 1 of this internal combustion engine has an intake pipe 2 provided at an intake port, and an air cleaner 4 provided in the intake pipe 2 that controls the amount of intake air supplied to the intake port. and a throttle valve 3 that is adjusted according to the
　スロットル弁３には、スロットル弁３の開度を検出するスロットルセンサ５が設けられる。吸気管２の吸入ポート近傍には、燃料を噴射する燃料噴射弁６が設けられる。燃料噴射弁６には、図示しない燃料タンクから燃料ポンプによって燃料が圧送される。 The throttle valve 3 is provided with a throttle sensor 5 that detects the opening degree of the throttle valve 3. A fuel injection valve 6 for injecting fuel is provided near the intake port of the intake pipe 2. Fuel is fed under pressure to the fuel injection valve 6 from a fuel tank (not shown) by a fuel pump.
　吸気管２には、吸気管２における吸気圧を検出する吸気圧センサ７及び吸気管２内の吸入空気の温度を検出する吸気温センサ８が設けられる。機関本体１の排気ポートに連結された排気管１０内には、排気管１０の排気中の未燃焼成分を低減させる触媒１１及び排気中の酸素濃度を検出する酸素センサ１２が設けられる。 The intake pipe 2 is provided with an intake pressure sensor 7 that detects the intake pressure in the intake pipe 2 and an intake temperature sensor 8 that detects the temperature of the intake air in the intake pipe 2. In an exhaust pipe 10 connected to an exhaust port of the engine body 1, a catalyst 11 for reducing unburned components in the exhaust gas from the exhaust pipe 10 and an oxygen sensor 12 for detecting the oxygen concentration in the exhaust gas are provided.
　機関本体１には、点火装置１４に接続された点火プラグ１３が固着される。ＥＣＵ（電子制御ユニット）１５が点火装置１４に対して点火タイミングの指令を発することにより、機関本体１のシリンダ燃焼室内で火花放電が生じる。 A spark plug 13 connected to an ignition device 14 is fixed to the engine body 1. When the ECU (electronic control unit) 15 issues an ignition timing command to the ignition device 14, spark discharge occurs within the cylinder combustion chamber of the engine body 1.
　ＥＣＵ１５には、スロットルセンサ５、吸気圧センサ７、吸気温センサ８、酸素センサ１２、冷却水温センサ１７、及び大気圧を検出する大気圧センサ２０のそれぞれの検出値を示すアナログ電圧が入力される。また、ＥＣＵ１５には、上記の燃料噴射弁６が接続される。 Analog voltages indicating respective detection values of the throttle sensor 5, intake pressure sensor 7, intake temperature sensor 8, oxygen sensor 12, cooling water temperature sensor 17, and atmospheric pressure sensor 20 that detects atmospheric pressure are input to the ECU 15. . Moreover, the above-mentioned fuel injection valve 6 is connected to the ECU 15.
　ＥＣＵ１５には、さらに、クランク角度センサ１９からのクランク軸１８の回転角度位置を示す信号が入力される。すなわち、クランク角度センサ１９は、クランク軸１８に連動して回転するロータ１９ａの外周に所定角度（例えば、１５度）毎に設けられた複数の凸部を、ロータ１９ａの外周近傍に配置されたピックアップ１９ｂによって磁気的あるいは光学的に検出し、ピックアップ１９ｂからクランク軸１８の所定角度の回転毎にパルス（クランク信号）を発生する。 A signal indicating the rotational angular position of the crankshaft 18 from the crank angle sensor 19 is further input to the ECU 15. That is, the crank angle sensor 19 includes a plurality of convex portions provided at predetermined angle intervals (for example, 15 degrees) on the outer circumference of the rotor 19a that rotates in conjunction with the crankshaft 18, and arranged near the outer circumference of the rotor 19a. The pickup 19b detects it magnetically or optically, and the pickup 19b generates a pulse (crank signal) every time the crankshaft 18 rotates by a predetermined angle.
　具体的には、クランク角度センサ１９は、ピストン９が上死点に至る毎に、又はクランク軸１８が３６０度回転する毎に基準角度を示す信号をＥＣＵ１５に出力する。 Specifically, the crank angle sensor 19 outputs a signal indicating the reference angle to the ECU 15 every time the piston 9 reaches the top dead center or every time the crankshaft 18 rotates 360 degrees.
　図２は、ＥＣＵ１５における主要な構成を示す。同図に示すように、ＥＣＵ１５に排気中の酸素濃度の検出信号を供給する酸素センサ１２は、排気脈動を有する内燃機関の排気に接するように設けられて排気中の酸素濃度を検出する検出部としてのセンサ素子１２ａと、センサ素子１２ａに隣接してセンサ素子１２ａを加熱するヒータ部としてのセンサヒータ１２ｂとを備える。 FIG. 2 shows the main configuration of the ECU 15. As shown in the figure, an oxygen sensor 12 that supplies a detection signal of the oxygen concentration in the exhaust gas to the ECU 15 is a detection unit that is provided in contact with the exhaust gas of an internal combustion engine that has exhaust pulsation and detects the oxygen concentration in the exhaust gas. The sensor element 12a is provided with a sensor element 12a as a sensor element 12a, and a sensor heater 12b as a heater part that is adjacent to the sensor element 12a and heats the sensor element 12a.
　センサ素子１２ａは、内燃機関の排気がストイキメトリック近傍の酸素濃度である際に略ステップ状に変化する抵抗値を有し、該抵抗値から求める検出値がセンサ素子１２ａの温度と前記排気脈動とに応じた波高値を有するパルス波状を呈する。センサ素子１２ａとしては、本実施形態では、酸素濃度に応じて抵抗値が変化する抵抗型酸素センサであるチタニア酸素センサが用いられる。 The sensor element 12a has a resistance value that changes substantially stepwise when the exhaust gas of the internal combustion engine has an oxygen concentration near the stoichiometric value, and the detected value obtained from the resistance value is determined by the temperature of the sensor element 12a and the exhaust pulsation. It exhibits a pulse waveform with a peak value corresponding to the wave height. As the sensor element 12a, in this embodiment, a titania oxygen sensor, which is a resistance type oxygen sensor whose resistance value changes depending on the oxygen concentration, is used.
　ＥＣＵ１５は、センサヒータ１２ｂを制御するヒータ制御器２２と、センサ素子１２ａの温度を示す温度値Ｔを算出する検出部温度推定部としての温度算出部２３と、センサ素子１２ａの出力信号を、排気中の酸素濃度を示す検出値としての電圧値ＶＨＧに変換する検出値読取部としての電圧算出部２４とを備える。 The ECU 15 includes a heater controller 22 that controls the sensor heater 12b, a temperature calculation section 23 as a detection section temperature estimation section that calculates a temperature value T indicating the temperature of the sensor element 12a, and an output signal of the sensor element 12a, which is connected to the exhaust gas. A voltage calculation unit 24 is provided as a detection value reading unit that converts into a voltage value VHG as a detection value indicating the oxygen concentration in the air.
　ヒータ制御器２２によるセンサヒータ１２ｂの温度の制御は、不図示の電源（蓄電池）からセンサヒータ１２ｂに供給される通電電流量ＩをＥＣＵ１５でパルス幅変調（ＰＷＭ）制御することにより行われる。また、温度算出部２３による温度値Ｔの算出は、たとえば、センサヒータ１２ｂに印加されたヒータ電圧及び通電電流量Ｉの各値をＥＣＵ１５で読み取ってセンサヒータ１２ｂの抵抗値を求め、該抵抗値を、ＥＣＵ１５に予め準備されたヒータ抵抗値及び温度値Ｔ間の対応関係を示すテーブルデータあるいは計算式によって換算することにより行われる。温度算出部２３及び電圧算出部２４における算出結果は、後述する過剰率算出部２５の代替値演算部２６に供給される。 The temperature of the sensor heater 12b is controlled by the heater controller 22 by performing pulse width modulation (PWM) control by the ECU 15 on the amount of current I supplied to the sensor heater 12b from an unillustrated power source (storage battery). Further, the temperature value T is calculated by the temperature calculation unit 23 by, for example, reading each value of the heater voltage and the current amount I applied to the sensor heater 12b with the ECU 15 to determine the resistance value of the sensor heater 12b, and calculating the resistance value of the sensor heater 12b. This is done by converting using table data or a calculation formula prepared in advance in the ECU 15 that indicates the correspondence between the heater resistance value and the temperature value T. The calculation results from the temperature calculation section 23 and the voltage calculation section 24 are supplied to an alternative value calculation section 26 of the excess rate calculation section 25, which will be described later.
　また、ＥＣＵ１５は、クランク角度センサ１９の検出結果に基づいて内燃機関の回転速度ＮＥ及び角速度ＮＥＴＣを算出する回転速度演算部２７と、温度算出部２３からの温度値Ｔ、電圧算出部２４からの電圧値ＶＨＧ、及び回転速度演算部２７からの角速度ＮＥＴＣに基づいて空気過剰率λを算出する過剰率算出部２５とを備える。 The ECU 15 also includes a rotational speed calculation unit 27 that calculates the rotational speed NE and angular velocity NETC of the internal combustion engine based on the detection results of the crank angle sensor 19, and a rotational speed calculation unit 27 that calculates the rotational speed NE and angular velocity NETC of the internal combustion engine based on the detection results of the crank angle sensor 19, and a It includes an excess air ratio calculation section 25 that calculates an excess air ratio λ based on the voltage value VHG and the angular velocity NETC from the rotational speed calculation section 27.
　さらに、ＥＣＵ１５は、制御目標値としての空気過剰率λｃｍｄを触媒１１における貯蔵酸素量の推定値や内燃機関の作動状態に基づいて算出する目標値設定部としての目標値演算部２８と、回転速度演算部２７からの回転速度ＮＥ、及び吸気圧センサ７からの吸気管２内の圧力ＰＭに基づいて基本噴射量ＢＪを算出する基本噴射量演算部２９と、過剰率算出部２５により算出された空気過剰率λを目標空気過剰率λｃｍｄに一致させるべく、基本噴射量演算部２９が算出した基本燃料噴射量ＢＪを補正するためのフィードバック係数ｋを求めるフィードバック係数演算部３０と、フィードバック係数ｋ及び基本噴射量ＢＪに基づいて噴射量Ｔｉを算出するとともに、燃料噴射弁６を作動させる噴射量演算部３１とを備える。 Furthermore, the ECU 15 includes a target value calculation unit 28 as a target value setting unit that calculates an excess air ratio λcmd as a control target value based on an estimated value of the amount of oxygen stored in the catalyst 11 and the operating state of the internal combustion engine, and a rotation speed The basic injection amount calculation section 29 calculates the basic injection amount BJ based on the rotational speed NE from the calculation section 27 and the pressure PM in the intake pipe 2 from the intake pressure sensor 7, and the excess rate calculation section 25 calculates the basic injection amount BJ. A feedback coefficient calculation section 30 that calculates a feedback coefficient k for correcting the basic fuel injection amount BJ calculated by the basic injection amount calculation section 29 in order to make the excess air ratio λ match the target excess air ratio λcmd; It includes an injection amount calculation unit 31 that calculates the injection amount Ti based on the basic injection amount BJ and operates the fuel injection valve 6.
　フィードバック係数演算部３０においては、空気過剰率λと目標空気過剰率λｃｍｄとの偏差Ｐ及び該偏差の微分Ｄ、又は該偏差Ｐ、該偏差の積分Ｉ及び該偏差の微分Ｄに基づいて実行されるＰＤ・ＰＩＤ制御、もしくは、空気過剰率λと目標空気過剰率λｃｍｄとの偏差Ｐ及び該偏差の積分Ｉに基づいて実行されるＰＩ制御が、後述するように、選択的に行われてフィードバック係数ｋが演算される。噴射量演算部３１によりフィードバック係数ｋ及び基本噴射量ＢＪに基づいて算出される噴射量Ｔｉに基づき、これに対応する時間だけ、燃料噴射弁６が開弁される。而して、機関本体１のシリンダ燃焼室内には空気過剰率λと目標空気過剰率λｃｍｄとの比較に基づいた上記フィードバック係数ｋに応じた量の燃料が噴射される。 In the feedback coefficient calculation unit 30, the calculation is performed based on the deviation P between the excess air ratio λ and the target excess air ratio λcmd and the derivative D of the deviation, or the deviation P, the integral I of the deviation, and the derivative D of the deviation. PD/PID control based on the excess air ratio λ and the target excess air ratio λcmd, or PI control executed based on the deviation P between the excess air ratio λ and the target excess air ratio λcmd and the integral I of the deviation, is selectively performed and feedback is performed as described later. A coefficient k is calculated. Based on the injection amount Ti calculated by the injection amount calculating section 31 based on the feedback coefficient k and the basic injection amount BJ, the fuel injection valve 6 is opened for a corresponding time. Thus, an amount of fuel is injected into the cylinder combustion chamber of the engine body 1 in an amount corresponding to the feedback coefficient k based on the comparison between the excess air ratio λ and the target excess air ratio λcmd.
　過剰率算出部２５は、電圧算出部２４からの電圧値ＶＨＧ及び温度算出部２３からの温度値Ｔに基づき、電圧値ＶＨＧを、その温度特性を補償しつつ空気過剰率に対してリニアライズ変換したデータＬＤを用いて排気の空気過剰率λを算出するものである。ただし、この算出は、後述するように、電圧値ＶＨＧがリーン側閾値ＬＲＥＦ以下の場合に適用され、電圧値ＶＨＧがリーン側閾値ＬＲＥＦより大きいときには、別の方法で空気過剰率λが求められる。 Based on the voltage value VHG from the voltage calculation unit 24 and the temperature value T from the temperature calculation unit 23, the excess ratio calculation unit 25 linearizes the voltage value VHG with respect to the excess air ratio while compensating for its temperature characteristics. The excess air ratio λ of the exhaust gas is calculated using the data LD obtained. However, as will be described later, this calculation is applied when the voltage value VHG is less than or equal to the lean side threshold value LREF, and when the voltage value VHG is larger than the lean side threshold value LREF, the excess air ratio λ is determined by another method.
　過剰率算出部２５は、内燃機関のクランク角速度ＮＥＴＣに基づいて内燃機関のトルク値ＴＱを算出するトルク演算部３２と、上述のリニアライズ変換についての変換限界閾値を設定する限界閾値設定部３３と、空気過剰率λの代替値Ｒを算出するのに必要なデータや、後述するデータマップ及びルックアップテーブルを記憶する記憶部３４と、代替値Ｒを算出する代替値演算部２６とを備える。 The excess rate calculation unit 25 includes a torque calculation unit 32 that calculates the torque value TQ of the internal combustion engine based on the crank angular speed NETC of the internal combustion engine, and a limit threshold setting unit 33 that sets a conversion limit threshold for the above-mentioned linearization conversion. , a storage unit 34 that stores data necessary for calculating an alternative value R for the excess air ratio λ, a data map and a look-up table to be described later, and an alternative value calculation unit 26 that calculates the alternative value R.
　限界閾値設定部３３は、変換限界閾値として、リーン側の変換限界域値であるリーン側閾値ＬＲＥＦ及びリッチ側の変換限界閾値であるリッチ側閾値ＲＲＥＦを、電圧算出部２４からの電圧値ＶＨＧについて設定する。ただし、チタニア型のセンサ素子１２ａは、温度が変化すると、出力値のダイナミックレンジ（センサ出力電圧の線形領域の最小値と最大値の各値）が変化するため、温度算出部２３からの温度値Ｔに応じて変換限界閾値を変化させる必要がある。 The limit threshold value setting unit 33 sets a lean side threshold value LREF, which is a conversion limit threshold value on the lean side, and a rich side threshold value RREF, which is a conversion limit threshold value on the rich side, as conversion limit threshold values, with respect to the voltage value VHG from the voltage calculation unit 24. Set. However, in the titania type sensor element 12a, when the temperature changes, the dynamic range of the output value (minimum and maximum values in the linear region of the sensor output voltage) changes. It is necessary to change the conversion limit threshold according to T.
　図５を併せて参照して、該図５は、温度算出部２３が算出する温度値Ｔに対応する図５において左右方向の第１目盛値Ｇ１と、電圧算出部２４が算出する電圧値ＶＨＧに対応する図５において上下方向の第２目盛値Ｇ２とを有するとともに、電圧値ＶＨＧ及び温度値Ｔを座標として対応付けられた複数個の前記データＬＤの数値が設定されているデータマップを掲出したものであり、しかも、リーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦを求めるためのグラフ３５、３６に対応するルックアップテーブルの各一例をデータマップ上に夫々重ね合わせた図として示している。 Referring also to FIG. 5, FIG. 5 shows the first scale value G1 in the horizontal direction in FIG. 5 corresponding to the temperature value T calculated by the temperature calculation unit 23, and the voltage value VHG calculated by the voltage calculation unit A data map is posted that has a second scale value G2 in the vertical direction in FIG. Furthermore, examples of look-up tables corresponding to graphs 35 and 36 for determining the lean-side threshold LREF and the rich-side threshold RREF are shown superimposed on the data map.
　すなわち、データマップは、複数の空気過剰率値を、温度値Ｔについての複数の第１目盛値Ｇ１、及び電圧値ＶＨＧ（検出値）についての複数の第２目盛値Ｇ２との対応関係を付けて示すものである。ルックアップテーブルは、電圧値ＶＨＧがリッチ領域、ストイキ領域又はリーン領域の何れの空燃比領域に該当するかを判別するためのリッチ側閾値ＲＲＥＦ及びリーン側閾値ＬＲＥＦを第１目盛値Ｇ１との対応関係を付けて示すものである。 That is, the data map associates a plurality of excess air ratio values with a plurality of first scale values G1 for the temperature value T and a plurality of second scale values G2 for the voltage value VHG (detected value). This is what is shown. The lookup table shows the correspondence between the rich side threshold value RREF and the lean side threshold value LREF for determining whether the voltage value VHG corresponds to a rich area, a stoichiometric area, or a lean air-fuel ratio area with the first scale value G1. It shows the relationship.
　このようなデータマップと、グラフ３５、３６に対応するルックアップテーブルとをＥＣＵ１５内の記憶部３４に予め記憶しておくことにより、これらを用いて電圧値ＶＨＧをリニアライズ変換したデータＬＤと、リーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦとを容易に取得して設定することができる。 By storing such a data map and a lookup table corresponding to the graphs 35 and 36 in advance in the storage unit 34 in the ECU 15, data LD obtained by linearizing the voltage value VHG using these data, The lean side threshold LREF and the rich side threshold RREF can be easily acquired and set.
　グラフ３５は、例えば、リーン領域とストイキ領域との境界としての空気過剰率λを１．０２とし、この値となるような電圧値ＶＨＧ及び温度値Ｔを座標とした上記データマップ上の点を複数点求め、これら複数の点の間をそれぞれ線補間で結んだグラフである。またグラフ３６は、例えば、ストイキ領域とリッチ領域との境界としての空気過剰率λを０．９８とし、この値に対応する電圧値ＶＨＧ及び温度値Ｔを座標とした上記データマップ上の複数の点を求め、これら複数の点の相互間をそれぞれ線補間で結んだグラフである。 Graph 35 shows, for example, when the excess air ratio λ as the boundary between the lean region and the stoichiometric region is 1.02, and the points on the data map whose coordinates are the voltage value VHG and temperature value T that have this value are plotted. This is a graph obtained by finding multiple points and connecting these multiple points by line interpolation. Further, the graph 36 shows, for example, that the excess air ratio λ as the boundary between the stoichiometric region and the rich region is 0.98, and the voltage value VHG and temperature value T corresponding to this value are set as coordinates on the data map. This is a graph obtained by finding points and connecting each of these points by line interpolation.
　例えば、限界閾値設定部３３は、グラフ３５に対応するルックアップテーブルからは、温度算出部２３からの温度値Ｔがｔ０である場合、その座標ｔ０から導かれる電圧値ｖ０を、リーン領域とストイキ領域との境界についてのリーン側閾値ＬＲＥＦとして設定することができる。同様に、グラフ３６に対応するルックアップテーブルからは、温度算出部２３からの温度値Ｔがｔ０である場合、その座標ｔ０から導かれる電圧値ｖ１を、ストイキ領域とリッチ領域との境界についてのリッチ側閾値ＲＲＥＦとして設定することができる。 For example, from the lookup table corresponding to the graph 35, if the temperature value T from the temperature calculation unit 23 is t0, the limit threshold setting unit 33 determines that the voltage value v0 derived from the coordinate t0 is in the lean region and the stoichiometric range. It can be set as the lean-side threshold LREF for the boundary with the region. Similarly, from the lookup table corresponding to the graph 36, when the temperature value T from the temperature calculation unit 23 is t0, the voltage value v1 derived from the coordinate t0 is It can be set as a rich-side threshold RREF.
　また、記憶部３４は、代替値Ｒの算出に必要なデータとして、電圧算出部２４からの電圧値ＶＨＧが変換限界閾値ＬＲＥＦ以下のとき、燃料噴射弁６による燃料噴射の実行時間Ｔｉ１、トルク値ＴＱ１、変換限界閾値ＬＲＥＦに関する空気過剰率λｂを記憶する。 The storage unit 34 also stores, as data necessary for calculating the alternative value R, the execution time Ti1 of the fuel injection by the fuel injection valve 6, the torque value TQ1, the excess air ratio λb regarding the conversion limit threshold LREF is stored.
　代替値演算部２６は、電圧値ＶＨＧが変換限界閾値ＬＲＥＦを超えているとき、該超えるより前の燃料噴射の実行時間をＴｉ２、トルク値をＴＱ２として、次式（１）により代替値Ｒを算出する。
　Ｒ＝（（Ｔｉ１÷Ｔｉ２）÷（ＴＱ１÷ＴＱ２））×λｂ　　　（１） When the voltage value VHG exceeds the conversion limit threshold LREF, the substitute value calculation unit 26 calculates the substitute value R using the following equation (1), assuming that the execution time of the fuel injection before the exceedance is Ti2 and the torque value is TQ2. calculate.
R=((Ti1÷Ti2)÷(TQ1÷TQ2))×λb (1)
　そして、過剰率算出部２５は、電圧値ＶＨＧが変換限界閾値ＬＲＥＦを超えている場合には、上述のリニアライズ変換したデータＬＤとしての空気過剰率λに代えて、代替値Ｒを排気の空気過剰率λとみなす。 Then, when the voltage value VHG exceeds the conversion limit threshold LREF, the excess rate calculation unit 25 calculates a substitute value R for the exhaust air in place of the excess air rate λ as the linearized data LD. Regarded as excess rate λ.
　図３は、過剰率算出部２５における空気過剰率λを算出する過剰率（ラムダ）算出処理を示す。なお、この過剰率算出処理を含むＥＣＵ１５による制御は、クランク角度センサ１９からのクランク軸１８の回転角度位置を示すパルス信号に基づき、内燃機関の行程に同期して実行される。 FIG. 3 shows an excess rate (lambda) calculation process in which the excess air rate λ is calculated by the excess rate calculation unit 25. Note that the control by the ECU 15 including this excess rate calculation process is executed in synchronization with the stroke of the internal combustion engine based on a pulse signal from the crank angle sensor 19 indicating the rotational angular position of the crankshaft 18.
　過剰率算出処理が開始されると、ステップＳ１において、トルク演算部３２により、回転速度演算部２７からのクランク角速度ＮＥＴＣに基づいて内燃機関のトルクＴＱ（ＤＣＢＣＰ）を算出する。 When the excess rate calculation process is started, in step S1, the torque calculation section 32 calculates the torque TQ (DCBCP) of the internal combustion engine based on the crank angular speed NETC from the rotational speed calculation section 27.
　なお、トルクＴＱの算出に際しては、内燃機関における吸気、圧縮、燃焼膨張、排気の各行程を有する内燃機関の連続する２つの行程の各々に対応した内燃機関のクランク軸の２つの角速度が算出され、これに基づき、内燃機関が発生する発生トルクが精度よく算出される（特許第６２５４６３３号公報参照）。 In addition, when calculating the torque TQ, two angular velocities of the crankshaft of the internal combustion engine corresponding to each of two consecutive strokes of the internal combustion engine, which has each stroke of intake, compression, combustion expansion, and exhaust, are calculated. , Based on this, the generated torque generated by the internal combustion engine is calculated with high accuracy (see Japanese Patent No. 6254633).
　次に、センサヒータ１２ｂの抵抗を読み取る際にセンサヒータ１２ｂの断線状態が検出されていない場合に、ステップＳ２において、温度算出部２３からの温度値Ｔ（ＨＧＴＥＭＰ）に基づき、限界閾値設定部３３により、図５のグラフ３５、３６に対応する第１及び第２ルックアップテーブル（ＶＨＧＬＲＥＦ＿Ｎ、ＶＨＧＲＲＥＦ＿Ｎ）を用いて、リーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦをそれぞれ設定する。 Next, when the disconnection state of the sensor heater 12b is not detected when reading the resistance of the sensor heater 12b, in step S2, the limit threshold setting unit 33 Accordingly, the lean side threshold LREF and the rich side threshold RREF are respectively set using the first and second lookup tables (VHGLREF_N, VHGRREF_N) corresponding to the graphs 35 and 36 in FIG.
　次に、ステップＳ３において、電圧算出部２４から電圧値ＶＨＧを取得し、該電圧値ＶＨＧを後述する電圧差確認部４３で得られる偏差ＶＤにより補正して、制御用の電圧値（検出値）ＶＨＧｃｏｎを設定する。 Next, in step S3, a voltage value VHG is acquired from the voltage calculation unit 24, and the voltage value VHG is corrected by a deviation VD obtained by a voltage difference confirmation unit 43, which will be described later, to obtain a control voltage value (detected value). Set up VHGcon.
　次に、ステップＳ４において、ステップＳ２で取得した温度値Ｔ、ステップＳ３で取得した電圧値ＶＨＧｃｏｎに基づき上述のデータマップ（図５）が走査され、かくして、電圧値ＶＨＧｃｏｎの値をその温度特性を補償しつつ空気過剰率λへとリニアライズ変換したデータＬＤが取得される。 Next, in step S4, the above-mentioned data map (FIG. 5) is scanned based on the temperature value T obtained in step S2 and the voltage value VHGcon obtained in step S3. Data LD is obtained which has been linearized into excess air ratio λ while being compensated.
　次に、ステップＳ５において、ステップＳ３で取得した電圧値ＶＨＧｃｏｎが、ステップＳ２で設定したリッチ側閾値ＲＲＥＦよりも小さいか否かを判定する。小さいと判定した場合には、続くステップＳ６においてフラグＦ＿ＤＥＴＥＣＴをゼロに設定しつつステップＳ１６に進み、上記データＬＤの値を空気過剰率λ値ＬＡＭＢＤＡとして設定し、図３の過剰率算出処理を終了する。 Next, in step S5, it is determined whether the voltage value VHGcon acquired in step S3 is smaller than the rich-side threshold value RREF set in step S2. If it is determined that it is small, the flag F_DETECT is set to zero in the subsequent step S6, and the process proceeds to step S16, where the value of the data LD is set as the excess air ratio λ value LAMBDA, and the excess ratio calculation process of FIG. 3 is ended. do.
　ステップＳ５において、電圧値ＶＨＧｃｏｎがリッチ側閾値ＲＲＥＦよりも小さくはないと判定した場合には、ステップＳ７において、ステップＳ３で取得した電圧値ＶＨＧｃｏｎが、ステップＳ２で設定したリーン側閾値ＬＲＥＦよりも大きいか否かを判定する。 If it is determined in step S5 that the voltage value VHGcon is not smaller than the rich threshold RREF, then in step S7 the voltage value VHGcon acquired in step S3 is greater than the lean threshold LREF set in step S2. Determine whether or not.
　ステップＳ７において、上記電圧値ＶＨＧｃｏｎが大きくはないと判定した場合には、ステップＳ８において、ステップＳ２で取得したリーン側閾値ＬＲＥＦの電圧値ｌｒｅｆ及びリッチ側閾値ＲＲＥＦの電圧値ｒｒｅｆと、電圧値ｌｒｅｆに対応する所定のストイキ領域とリーン領域との境界としての空気過剰率λ値（この実施の形態においては、λ＝１．０２）と、電圧値ｒｒｅｆに対応する所定のリッチ領域とストイキ領域との境界としての空気過剰率λ値（この実施の形態においては、λ＝０．９８）と、ステップＳ３で取得した電圧値ＶＨＧとに基づき、電圧算出部２４からの電圧値ＶＨＧを、酸素センサ１２の温度特性を補償しつつ空気過剰率に対してリニアライズ変換したデータＬＤとしての空気過剰率λを算出し、ステップＳ９に進む。 In step S7, when it is determined that the voltage value VHGcon is not large, in step S8, the voltage value lref of the lean side threshold LREF, the voltage value rref of the rich side threshold RREF, and the voltage value lref acquired in step S2 are determined. The excess air ratio λ value (in this embodiment, λ=1.02) as a boundary between a predetermined stoichiometric region and a lean region corresponding to , and a predetermined rich region and stoichiometric region corresponding to a voltage value rref. Based on the excess air ratio λ value as a boundary (in this embodiment, λ=0.98) and the voltage value VHG acquired in step S3, the voltage value VHG from the voltage calculation unit 24 is The excess air ratio λ is calculated as data LD obtained by linearizing the excess air ratio while compensating for the temperature characteristics of 12, and the process proceeds to step S9.
　図４を併せて参照して、上記ステップＳ８におけるリニアライズ変換したデータＬＤとしての空気過剰率λは、前記所定のストイキ領域とリーン領域との境界としての空気過剰率λを予め数値設定することが可能な変数＃ＬＬＭＤ(たとえば１．０２）、及び、前記所定のリッチ領域とストイキ領域との境界としての空気過剰率λを予め設定することが可能な変数＃ＲＬＭＤ（たとえば０．９８）であるとすれば、図４に示すようなグラフで表すことができる。該グラフの、図４において左右方向の横軸は電圧値ＶＨＧであり、図４において上下方向の縦軸は空気過剰率λである。したがって、例えば電圧値ＶＨＧがｖｈｇ１である場合、これに対応する空気過剰率λの値λ１は、次式（２）により算出することができる。
　λ1=(((vhg1-rref)÷(lref-rref))×(#LLMD-#RLMD))＋＃RLMD　　（２） Referring also to FIG. 4, the excess air ratio λ as the linearized data LD in step S8 is set in advance by numerically setting the excess air ratio λ as the boundary between the predetermined stoichiometric region and the lean region. A variable #LLMD (for example, 1.02) that can set If there is, it can be represented by a graph as shown in FIG. In this graph, the horizontal axis in the horizontal direction in FIG. 4 is the voltage value VHG, and the vertical axis in the vertical direction in FIG. 4 is the excess air ratio λ. Therefore, for example, when the voltage value VHG is vhg1, the corresponding value λ1 of the excess air ratio λ can be calculated using the following equation (2).
λ1=(((vhg1-rref)÷(lref-rref))×(#LLMD-#RLMD))+#RLMD (2)
　ステップＳ９では、燃料噴射弁６による直前の燃料噴射の実行時間Ｔｉ、ステップＳ１で算出したトルクＴＱをそれぞれＴｉ１、ＴＱ１とし、リーン側閾値ＬＲＥＦに関する空気過剰率λをλｂとして記憶部３４により記憶する。ほぼ同時に、前記記憶の有効時間を示すカウントダウンタイマー値ＴＩＭＥＲをその所定の初期値である＃ＴＭＩＮＴでリセットする。続いて、フラグＦ＿ＤＥＴＥＣＴを１に設定するとともにステップＳ１６に進み、上記ステップＳ８で取得したデータＬＤの値を、空気率過剰率λ値ＬＡＭＢＤＡとして設定し、図３の過剰率算出処理を終了する。 In step S9, the execution time Ti of the immediately preceding fuel injection by the fuel injection valve 6 and the torque TQ calculated in step S1 are respectively set as Ti1 and TQ1, and the excess air ratio λ regarding the lean side threshold value LREF is stored as λb in the storage unit 34. . Almost simultaneously, the countdown timer value TIMER indicating the valid time of the memory is reset to its predetermined initial value #TMINT. Subsequently, the flag F_DETECT is set to 1, and the process proceeds to step S16, where the value of the data LD acquired in step S8 is set as the excess air ratio λ value LAMBDA, and the excess ratio calculation process of FIG. 3 is ended.
　このとき、λｂとしては、ステップＳ８で取得したデータＬＤの値が記憶される。その際に、データＬＤの値の移動平均をλｂとして記憶するのが好ましい。例えば、次式（３）で求められる空気過剰率λ（データＬＤ）の指数移動平均λａがλｂとして記憶される。
　　λａ＝ＬＤ×ｋ１＋λａｂ×（１－ｋ１）　　　　　　　　（３） At this time, the value of the data LD acquired in step S8 is stored as λb. At that time, it is preferable to store the moving average of the values of the data LD as λb. For example, the exponential moving average λa of the excess air ratio λ (data LD) obtained by the following equation (3) is stored as λb.
λa=LD×k1+λab×(1-k1) (3)
　ここで、ｋ１は移動平均係数であり、λａｂは記憶部３４が記憶している前回制御周期での移動平均値である。移動平均係数ｋ１としては、例えば０．３４が用いられる。 Here, k1 is a moving average coefficient, and λab is a moving average value in the previous control cycle stored in the storage unit 34. For example, 0.34 is used as the moving average coefficient k1.
　また、このとき、記憶部３４は、燃料噴射の実行時間Ｔｉ１及び前記トルク値ＴＱ１として、それぞれ移動平均値を記憶するのが好ましい。例えば、燃料噴射の実行時間Ｔｉの指数移動平均ＴｉＦＬＴが次式（４）で求められてＴｉ１として記憶されるとともに、前記トルク値ＴＱの指数移動平均ＴＱＦＬＴが次式（５）で求められてＴＱ１として記憶される。
　ＴｉＦＬＴ＝Ｔｉ×ｋ２＋ＴｉＦＬＴｂ×（１－ｋ２）　　　　（４）
　ＴＱＦＬＴ＝ＴＱ×ｋ３＋ＴＱＦＬＴｂ×（１－ｋ３）　　　　（５） Moreover, at this time, it is preferable that the storage unit 34 stores moving average values as the fuel injection execution time Ti1 and the torque value TQ1, respectively. For example, the exponential moving average TiFLT of the fuel injection execution time Ti is calculated using the following equation (4) and stored as Ti1, and the exponential moving average TQFLT of the torque value TQ is calculated using the following equation (5) and stored as Ti1. is stored as.
TiFLT=Ti×k2+TiFLTb×(1-k2) (4)
TQFLT=TQ×k3+TQFLTb×(1-k3) (5)
　ここで、ｋ２、ｋ３は移動平均係数であり、ＴｉＦＬＴｂ、ＴＱＦＬＴｂは記憶部３４が記憶している前回制御周期での移動平均値である。この実施の形態においては、移動平均係数ｋ１、ｋ２、及びｋ３として、それぞれ異なる値を用いることができる。 Here, k2 and k3 are moving average coefficients, and TiFLTb and TQFLTb are moving average values in the previous control cycle stored in the storage unit 34. In this embodiment, different values can be used as the moving average coefficients k1, k2, and k3.
　次に、ステップＳ７において、ステップＳ３で取得した電圧値ＶＨＧｃｏｎがリーン側閾値ＬＲＥＦよりも大きいと判定した場合には、ステップＳ１０において、上述のカウントダウンタイマー値ＴＩＭＥＲがゼロに到達しているか否かを判定する。そして、ＴＩＭＥＲがゼロに到達しているならば、フラグＦ＿ＤＥＴＥＣＴを０にリセットする（ステップＳ１１）。 Next, in step S7, if it is determined that the voltage value VHGcon acquired in step S3 is larger than the lean side threshold value LREF, in step S10, it is determined whether the above-mentioned countdown timer value TIMER has reached zero. judge. If TIMER has reached zero, the flag F_DETECT is reset to 0 (step S11).
　次に、ステップＳ１２に進み、フラグＦ＿ＤＥＴＥＣＴ＝１であるか否かを判定する。Ｆ＿ＤＥＴＥＣＴ＝１であるならば、記憶部３４にリーン側閾値ＬＲＥＦに関する空気過剰率λｂ、燃料噴射の実行時間Ｔｉ１、及び、トルク値ＴＱ１が記憶されていることを示すので、ステップＳ１３に進み、代替値演算部２６において、上述の式（１）により代替値Ｒを算出するとともに、データＬＤの値を代替値Ｒに設定する。 Next, the process proceeds to step S12, and it is determined whether the flag F_DETECT=1. If F_DETECT=1, this indicates that the excess air ratio λb, the fuel injection execution time Ti1, and the torque value TQ1 regarding the lean side threshold value LREF are stored in the storage unit 34, so the process advances to step S13 and the alternative The value calculation unit 26 calculates the alternative value R using the above equation (1) and sets the value of the data LD as the alternative value R.
　次に、ステップＳ１４において、ステップＳ１３で設定したデータＬＤの値が所定の上限値＃ＬＬＭＴよりも大きいか否かを判定する。ステップＳ１３で設定したデータＬＤの値が上限値＃ＬＬＭＴよりも大きい場合には、データＬＤの値を上限値＃ＬＬＭＴに設定する（ステップＳ１５）。この場合、上限値＃ＬＬＭＴとして、例えば１．２５を用いることができる。 Next, in step S14, it is determined whether the value of the data LD set in step S13 is larger than a predetermined upper limit value #LLMT. If the value of data LD set in step S13 is larger than upper limit value #LLMT, the value of data LD is set to upper limit value #LLMT (step S15). In this case, for example, 1.25 can be used as the upper limit value #LLMT.
　なお、上記ステップＳ１２において、Ｆ＿ＤＥＴＥＣＴ＝０であるならば、記憶部３４にリーン側閾値ＬＲＥＦに関する空気過剰率λｂ、燃料噴射の実行時間Ｔｉ１、及び、トルク値ＴＱ１に関する有効な値が記憶されていないことを示すので、代替値Ｒを算出することができない。この場合も、データＬＤの値は上記上限値＃ＬＬＭＴに設定される（ステップＳ１５）。 Note that if F_DETECT=0 in step S12 above, the storage unit 34 does not store valid values regarding the excess air ratio λb, the fuel injection execution time Ti1, and the torque value TQ1 regarding the lean side threshold value LREF. Therefore, the alternative value R cannot be calculated. Also in this case, the value of data LD is set to the upper limit value #LLMT (step S15).
　而して、上記ステップＳ１３又はステップＳ１５で設定されたデータＬＤの値は空気率過剰率λ値ＬＡＭＢＤＡとして設定され(ステップＳ１６）、これにより、図３の過剰率算出処理を終了する。 The value of the data LD set in step S13 or step S15 is then set as the excess air ratio λ value LAMBDA (step S16), thereby ending the excess ratio calculation process of FIG.
　図３の過剰率算出処理が終了すると、ＥＣＵ１５は、図３の過剰率算出処理で算出された空気過剰率λ値ＬＡＭＢＤＡを、上述のように、目標値演算部２８からの目標とする空気過剰率λｃｍｄに一致させるべく、フィードバック係数演算部３０を介して燃料噴射弁６による燃料の噴射量を制御する。 When the excess rate calculation process of FIG. 3 is completed, the ECU 15 converts the excess air rate λ value LAMBDA calculated in the excess rate calculation process of FIG. The amount of fuel injected by the fuel injection valve 6 is controlled via the feedback coefficient calculation unit 30 so as to match the rate λcmd.
　図６は、図３の過剰率算出処理によって算出される空気過剰率λ値ＬＡＭＢＤＡの変化の様子を模式的に示すグラフである。グラフの横軸は時間経過を示す数値であり、縦軸は空気過剰率λである。 FIG. 6 is a graph schematically showing how the excess air ratio λ value LAMBDA calculated by the excess air ratio calculation process of FIG. 3 changes. The horizontal axis of the graph is a numerical value indicating the passage of time, and the vertical axis is the excess air ratio λ.
　図６におけるグラフ３７は、図６において左右方向の横軸の、左端側から中央付近までの範囲において、実際の排気の空気過剰率を一定の変化率で徐々に増加させ、且つ、続く上記横軸の中央付近から右端側までの範囲において、実際の排気の空気過剰率を一定の変化率で徐々に減少させた場合において、それをＥＣＵ１５の電圧算出部２４で読み取った電圧値ＶＨＧを、その温度特性を補償しつつ空気過剰率に対して直接的にリニアライズ変換したデータを用いて空気過剰率λ値を算出した場合の空気過剰率λ値の数値変化を示す。 Graph 37 in FIG. 6 shows that the actual exhaust air excess rate gradually increases at a constant rate of change in the range from the left end side to near the center of the horizontal axis in the left-right direction in FIG. In the range from near the center of the shaft to the right end side, when the actual excess air ratio of the exhaust gas is gradually decreased at a constant rate of change, the voltage value VHG read by the voltage calculation unit 24 of the ECU 15 is The figure shows a numerical change in the excess air ratio λ value when the excess air ratio λ value is calculated using data directly linearized with respect to the excess air ratio while compensating for temperature characteristics.
　グラフ３８は、同様に、上記横軸の左端から右端まで実際の排気の空気過剰率を一定の変化率で徐々に増加乃至減少させた場合において、電圧算出部２４からの電圧値ＶＨＧがリーン側域値ＬＲＥＦの電圧値ｌｒｅｆ以下であるときは、上述のデータマップ（図５）又は式（２）で電圧値ＶＨＧを直接的にリニアライズ変換したデータを用いて空気過剰率λ値を算出しているが、電圧算出部２４からの電圧値ＶＨＧがリーン側域値ＬＲＥＦの電圧値ｌｒｅｆ（空気過剰率λの値１．０２０に対応）を超える場合には、上記電圧値ＶＨＧをリニアライズ変換したデータに代えて上述の数式（１）により取得した代替値Ｒを空気過剰率λ値としたときのその空気過剰率λ値の数値変化を示している。 Similarly, the graph 38 shows that when the actual excess air ratio of the exhaust gas is gradually increased or decreased at a constant rate of change from the left end to the right end of the horizontal axis, the voltage value VHG from the voltage calculation unit 24 is on the lean side. When the voltage value lref is below the threshold value LREF, the excess air ratio λ value is calculated using the data map described above (Figure 5) or the data obtained by directly linearizing the voltage value VHG using equation (2). However, if the voltage value VHG from the voltage calculation unit 24 exceeds the voltage value lref of the lean side range value LREF (corresponding to the value of excess air ratio λ of 1.020), the voltage value VHG is linearized. The graph shows the numerical change in the excess air ratio λ value when the substitute value R obtained by the above-mentioned formula (1) is used as the excess air ratio λ value in place of the above data.
　斯くして、実際の排気の空気過剰率が１．０２０以下の場合には、それに応答する電圧算出部２４からの電圧値ＶＨＧは上記実際の排気の空気過剰率λに対して比例的（線形）に変化するため、実際の排気の空気過剰率が１．０２０以下の場合には、グラフ３７及びグラフ３８は共に、上記実際の排気の空気過剰率の上記一定変化に追従して直線的に推移しているが、排気の空気過剰率が１．０２０を超える場合には、その状況下での非線形性を呈する電圧値ＶＨＧが急激に増加方向に変化するため、電圧値ＶＨＧを直接的にリニアライズ変換したデータに基づく空気過剰率λ値を示すグラフ３７も同じく増加方向へと急峻且つ非線形に変化する。一方、グラフ３８では、排気の空気過剰率が１．０２０（上記＃ＬＬＭＤ）を超える場合にも空気過剰率λ値ＬＡＭＢＤＡが排気の空気過剰率（空燃比）に対して直線状に変化しており、実際の排気の空気過剰率と連動している。 Thus, when the actual excess air ratio of the exhaust gas is 1.020 or less, the voltage value VHG from the voltage calculation unit 24 in response thereto is proportional (linear) to the actual excess air ratio λ of the exhaust gas. ), so if the actual excess air ratio of the exhaust gas is 1.020 or less, graphs 37 and 38 both linearly follow the constant change in the actual excess air ratio of the exhaust gas. However, if the excess air ratio of the exhaust exceeds 1.020, the voltage value VHG, which exhibits nonlinearity under that situation, will rapidly change in the increasing direction. The graph 37 showing the excess air ratio λ value based on the linearized data similarly changes steeply and non-linearly in the increasing direction. On the other hand, in graph 38, even when the excess air ratio of the exhaust exceeds 1.020 (#LLMD above), the excess air ratio λ value LAMBDA changes linearly with the excess air ratio (air-fuel ratio) of the exhaust. This is linked to the actual exhaust air excess rate.
　したがって、過剰率算出処理により、電圧値ＶＨＧがリーン側閾値ＬＲＥＦ以下の場合には、上述のリニアライズ変換したデータを用いて空気過剰率λを算出し、電圧値ＶＨＧがリーン側閾値ＬＲＥＦを超える場合には、上述の数式（１）で空気過剰率λを算出する（グラフ３８）ことにより、過剰率算出部２５は、図６のグラフの全範囲にわたって実際の排気の空気過剰率と連動し比例的に変化する空気過剰率λ値をフィードバック係数演算部３０に供給できることがわかる。これにより、フィードバック係数演算部３０によるフィードバック係数ｋの演算の中断が抑制される。 Therefore, in the excess ratio calculation process, if the voltage value VHG is less than the lean side threshold LREF, the excess air ratio λ is calculated using the linearized data described above, and the voltage value VHG exceeds the lean side threshold LREF. In this case, by calculating the excess air ratio λ using the above-mentioned formula (1) (graph 38), the excess ratio calculation unit 25 can interlock with the actual excess air ratio of exhaust gas over the entire range of the graph in FIG. It can be seen that the excess air ratio λ value that changes proportionally can be supplied to the feedback coefficient calculation unit 30. This suppresses interruption of the calculation of the feedback coefficient k by the feedback coefficient calculation unit 30.
　ところで、製造公差等によりセンサ素子１２ａ（検出部）やセンサヒータ１２ｂ（ヒータ部）の抵抗値がばらつくと、これらの抵抗値に基づいて得られる空気過剰率も不正確なものとなり、空燃比フィードバック制御に支障を来たすおそれがある。 By the way, if the resistance values of the sensor element 12a (detection section) and the sensor heater 12b (heater section) vary due to manufacturing tolerances, the excess air ratio obtained based on these resistance values will also be inaccurate, and the air-fuel ratio feedback Control may be impaired.
　そこで、過剰率算出部２５は、上記の抵抗値のばらつきに応じて変化する電圧値ＶＨＧ（検出値）の特性を点検する特性点検部４０と、その点検結果に基づいて上述のデータマップ及びルックアップテーブルを較正する較正部４１とを備える。 Therefore, the excess rate calculation section 25 includes a characteristic inspection section 40 that inspects the characteristics of the voltage value VHG (detected value) that changes according to the variation in the resistance value, and a characteristic inspection section 40 that inspects the characteristics of the voltage value VHG (detected value) that changes according to the variation in the resistance value, and uses the above-mentioned data map and lookup based on the inspection results. and a calibration section 41 that calibrates the up-table.
　特性点検部４０は、センサ素子１２ａの温度Ｔの基準値からのずれ量ＴＤを確認して制御用の温度Ｔｃｏｎを設定する温度差確認部４２と、センサ素子１２ａの電圧値ＶＨＧの所定時間内における平均値ＶＨＧＳＴＤとリーン側閾値ＬＲＥＦとの偏差ＶＤを確認して制御用の電圧値（検出値）ＶＨＧｃｏｎを設定する電圧差確認部４３とを有し、設定した制御用温度Ｔｃｏｎ及び制御用電圧値（検出値）ＶＨＧｃｏｎとに応じて、ＥＣＵ１５に接続された酸素センサ１２の出力特性を点検するように構成される。 The characteristic checking unit 40 includes a temperature difference checking unit 42 that checks the deviation amount TD of the temperature T of the sensor element 12a from the reference value and sets the temperature Tcon for control, and a temperature difference checking unit 42 that checks the deviation amount TD of the temperature T of the sensor element 12a from the reference value and sets the temperature Tcon for control, and It has a voltage difference confirmation unit 43 that confirms the deviation VD between the average value VHGSTD and the lean side threshold value LREF and sets the control voltage value (detected value) VHGcon, and the set control temperature Tcon and the control voltage The output characteristic of the oxygen sensor 12 connected to the ECU 15 is checked according to the value (detection value) VHGcon.
　温度差確認部４２は、内燃機関が停止した状態で、センサ素子１２ａの温度Ｔがセンサ素子１２ａの雰囲気温度に収束するに足る所定時間が経過した場合に、温度Ｔの基準値からのずれ量ＴＤを取得する。そして、温度差確認部４２は、電圧値ＶＨＧの特性の点検並びに過剰率算出部２５で用いる制御用の温度として、センサ素子１２ａの温度Ｔを、ずれ量ＴＤに基づいて補正した値Ｔｃｏｎ（この実施の形態においてはＴｃｏｎ＝Ｔ＋ＴＤ）を設定する。 The temperature difference confirmation unit 42 determines the amount of deviation of the temperature T from the reference value when a predetermined time period sufficient for the temperature T of the sensor element 12a to converge to the ambient temperature of the sensor element 12a has passed while the internal combustion engine is stopped. Get TD. Then, the temperature difference confirmation unit 42 uses the temperature T of the sensor element 12a as a control temperature to be used in the inspection of the characteristics of the voltage value VHG and the excess rate calculation unit 25, as a value Tcon (this value Tcon) corrected based on the deviation amount TD. In the embodiment, Tcon=T+TD) is set.
　上記の温度Ｔｃｏｎを設定するための基準値Ｔｒｅｆは、例えば、冷却水温センサ１７により得られるエンジン温度に吸気温センサ８により得られる吸気温度を加えて２で除する｛Ｔｒｅｆ＝（エンジン温度＋吸気温度）÷２｝ことにより求めることができる。これにより、冷却水温センサ１７及び吸気温センサ８の各読取での量子化誤差による影響を軽減して上記制御用の温度Ｔｃｏｎを精度よく設定することができる。 The reference value Tref for setting the above-mentioned temperature Tcon is determined by adding the intake air temperature obtained by the intake air temperature sensor 8 to the engine temperature obtained by the cooling water temperature sensor 17 and dividing the result by 2 {Tref=(engine temperature + intake air temperature). temperature)÷2}. Thereby, the influence of quantization errors in each reading of the cooling water temperature sensor 17 and the intake air temperature sensor 8 can be reduced, and the control temperature Tcon can be set with high accuracy.
　この場合、制御用の温度Ｔｃｏｎは、常温下かつ始動前のエンジン温度及び吸気温度と同じになるように設定される。かくして、温度差確認部４２は、上記のデータマップ及びグラフ３５、３６に対応するルックアップテーブルを、図５において左右方向（第１目盛値Ｇ１方向）へと実質的に平行移動させることになる。 In this case, the control temperature Tcon is set to be the same as the engine temperature and intake air temperature at room temperature and before startup. Thus, the temperature difference confirmation unit 42 substantially moves the lookup table corresponding to the data map and graphs 35 and 36 in parallel in the left-right direction (in the direction of the first scale value G1) in FIG. .
　続いて、電圧差確認部４３は、センサ素子１２ａの上記制御用の温度Ｔｃｏｎが所定値以下（例えば、上記基準値Ｔｒｅｆに同じ）の場合に、センサ素子１２ａの抵抗値から求める電圧値ＶＨＧの所定時間内における平均値ＶＨＧＳＴＤとリーン側閾値ＬＲＥＦとの偏差ＶＤを取得する。そして、電圧差確認部４３は、上述の特性の点検及び過剰率算出部２５で用いる制御用の電圧値（検出値）として、前記抵抗値から求める電圧値ＶＨＧを偏差ＶＤに基づいて補正した電圧値ＶＨＧｃｏｎ（＝ＶＨＧ＋ＶＤ）を設定する。 Subsequently, when the control temperature Tcon of the sensor element 12a is below a predetermined value (for example, the same as the reference value Tref), the voltage difference confirmation unit 43 determines the voltage value VHG obtained from the resistance value of the sensor element 12a. The deviation VD between the average value VHGSTD and the lean side threshold value LREF within a predetermined period of time is obtained. Then, the voltage difference confirmation unit 43 corrects the voltage value VHG obtained from the resistance value based on the deviation VD as a control voltage value (detected value) used in the characteristic inspection and excess rate calculation unit 25 described above. Set the value VHGcon (=VHG+VD).
　この場合、センサ素子１２ａの温度Ｔｃｏｎが充分に低く酸素センサが不活性となる状況では、電圧値ＶＨＧの波高がほぼゼロ（電圧値ＶＨＧが動かない状態）になるとともに、標準的な抵抗値を有するセンサ素子１２ａから読み取り可能な電圧値ＶＨＧｒｅｆは、上記グラフ３５及びグラフ３６と同一値になる（電圧値ＶＨＧｒｅｆとグラフ３５、３６が重なり合う）。すなわち、上記制御用の温度Ｔｃｏｎが所定値以下の場合に、標準電圧値ＶＨＧｒｅｆはグラフ３５（リーン側閾値ＬＲＥＦ）に等しくなるので、制御用の電圧値（検出値）ＶＨＧｃｏｎを設定するための基準値は、グラフ３５に対応するルックアップテーブルを上記充分に低い温度Ｔｃｏｎで走査することにより、求めることができる。また、上記の平均値ＶＨＧＳＴＤは、例えば、５秒間の期間で多数回読み取った電圧値ＶＨＧの相加平均値から求めることができ、これにより、電圧値ＶＨＧの読取における量子化誤差による影響を軽減して偏差ＶＤを取得するとともに、制御用の電圧値ＶＨＧｃｏｎを精度よく設定することができる。 In this case, in a situation where the temperature Tcon of the sensor element 12a is sufficiently low and the oxygen sensor becomes inactive, the wave height of the voltage value VHG becomes almost zero (state where the voltage value VHG does not move) and the standard resistance value decreases. The voltage value VHGref that can be read from the sensor element 12a has the same value as the graphs 35 and 36 (the voltage value VHGref and the graphs 35 and 36 overlap). That is, when the control temperature Tcon is below a predetermined value, the standard voltage value VHGref becomes equal to graph 35 (lean side threshold value LREF), so this is the standard for setting the control voltage value (detected value) VHGcon. The value can be determined by scanning the look-up table corresponding to graph 35 at the sufficiently low temperature Tcon. In addition, the above average value VHGSTD can be obtained from the arithmetic average value of the voltage values VHG read many times in a period of 5 seconds, for example, thereby reducing the influence of quantization errors in reading the voltage values VHG. In addition to obtaining the deviation VD, it is possible to accurately set the control voltage value VHGcon.
　斯くして、制御用の電圧値（検出値）ＶＨＧｃｏｎは制御用の温度Ｔｃｏｎが所定値以下の場合のグラフ３５（リーン側閾値ＬＲＥＦ）と同じになるように補正される。これにより、電圧差確認部４３は、上記のデータマップを、図５において上下方向（第２目盛値Ｇ２方向）へと実質的に平行移動させることになる。 In this way, the control voltage value (detected value) VHGcon is corrected to be the same as the graph 35 (lean side threshold value LREF) when the control temperature Tcon is below a predetermined value. As a result, the voltage difference confirmation unit 43 substantially translates the data map in the vertical direction (in the direction of the second scale value G2) in FIG. 5 .
　実際にＥＣＵ１５に接続された酸素センサ１２の点検に際しては、特性点検部４０は、目標値演算部２８を通じて目標空気過剰率λｃｍｄをストイキメトリック近傍に設定して電圧値ＶＨＧｃｏｎの波高値を取得するとともに、この波高値が空燃比領域の何れかに該当するかを点検する。 When actually inspecting the oxygen sensor 12 connected to the ECU 15, the characteristic inspection unit 40 sets the target excess air ratio λcmd to near the stoichiometric value through the target value calculation unit 28, and obtains the peak value of the voltage value VHGcon. , it is checked whether this peak value corresponds to any of the air-fuel ratio regions.
　また、較正部４１による較正に際しては、上記点検の結果を受けて、上記データマップ及びグラフ３５、３６に対応する第１及び第２ルックアップテーブルが較正される。 Furthermore, when performing calibration by the calibration unit 41, the first and second lookup tables corresponding to the data map and graphs 35 and 36 are calibrated based on the results of the above inspection.
　図７には、特性点検部４０により、目標空気過剰率λｃｍｄをストイキメトリック近傍に設定した状態で内燃機関に標準的な抵抗値を有する酸素センサ１２を搭載した車両を運転しながら得られた電圧値（検出値）ＶＨＧｒｅｆについて、その時間経過に伴う変化を表す電圧波形４４が示されている。また図７には、検証用として臨時に併設した広帯域（ワイドバンド）空燃比センサの出力信号の波形を示す空燃比波形４５が併せて示されている。 FIG. 7 shows a voltage obtained by the characteristic inspection unit 40 while driving a vehicle equipped with an oxygen sensor 12 having a standard resistance value in an internal combustion engine with the target excess air ratio λcmd set near the stoichiometric value. A voltage waveform 44 representing the change over time of the value (detected value) VHGref is shown. Also shown in FIG. 7 is an air-fuel ratio waveform 45 indicating the waveform of an output signal from a wideband air-fuel ratio sensor temporarily installed for verification purposes.
　４サイクル内燃機関において、排気管内の排気及び当該排気に含まれる酸素濃度は脈動をしているので、図７に示すように、標準的な抵抗値を有する酸素センサ１２のセンサ素子１２ａから読み取られる電圧値（検出値）ＶＨＧｒｅｆの電圧波形４４及び併設された空燃比センサの空燃比波形４５は、時間の経過に伴い振動的に遷移する波高を有した波形として観測されるのであるが、特に空燃比波形４５が、空気過剰率λが１．０となるレベルを跨ぐ図示の期間Ｐにおいては、元よりセンサ素子１２ａの抵抗値はストイキメトリック近傍の酸素濃度においてステップ（階段）状に急峻な変化をする特性を有していることから、電圧波形４４の波高Ｍ（検出値の波高値）は同期間Ｐにおける空燃比波形４５の波高と比して非常に大きく振動する波形として観測される。そして、このように大きく振動する電圧波形４４の波高の遷移に沿うように、上記のグラフ３５（リーン側閾値ＬＲＥＦ）及びグラフ３６（リッチ側閾値ＲＲＥＦ）に対応する第１及び第２ルックアップテーブルがそれぞれ設定されている。 In a four-stroke internal combustion engine, the exhaust gas in the exhaust pipe and the oxygen concentration contained in the exhaust gas are pulsating, so as shown in FIG. The voltage waveform 44 of the voltage value (detected value) VHGref and the air-fuel ratio waveform 45 of the attached air-fuel ratio sensor are observed as waveforms with wave heights that change oscillally over time, but especially when the air-fuel ratio During the illustrated period P in which the fuel ratio waveform 45 crosses the level where the excess air ratio λ is 1.0, the resistance value of the sensor element 12a naturally changes steeply in a stepwise manner at the oxygen concentration near the stoichiometric range. Therefore, the wave height M of the voltage waveform 44 (the wave height value of the detected value) is observed as a waveform that oscillates significantly compared to the wave height of the air-fuel ratio waveform 45 during the same period P. Then, the first and second lookup tables corresponding to the graph 35 (lean side threshold LREF) and graph 36 (rich side threshold RREF) are created along the wave height transition of the voltage waveform 44 that oscillates greatly in this way. are set respectively.
　すなわち、図示の期間Ｐにおいて、標準的な抵抗値を有する酸素センサ１２から得られる電圧波形４４での各波高Ｍの尖頭のうち、図７において下方のリッチ側閾値ＲＲＥＦに近いリッチ側尖頭４６は、多数のものがほぼリッチ側閾値ＲＲＥＦ上に位置する一方、図７において上方のリーン側閾値ＬＲＥＦに近いリーン側尖頭４７は、多数のものがほぼリーン側閾値ＬＲＥＦ上に位置する。 That is, in the illustrated period P, among the peaks of each wave height M in the voltage waveform 44 obtained from the oxygen sensor 12 having a standard resistance value, the rich-side peak near the lower rich-side threshold RREF in FIG. 46, many of them are located approximately above the rich-side threshold RREF, while many of the lean-side peaks 47 near the upper lean-side threshold LREF in FIG. 7 are located approximately above the lean-side threshold LREF.
　換言すると、目標空気過剰率λｃｍｄをストイキメトリック近傍に設定して図示の期間Ｐの状態を再現する如くに空燃比のフィードバック制御を実施しながら前記実際にＥＣＵ１５に接続された酸素センサ１２の電圧値（検出値）ＶＨＧｃｏｎが表出する波高ＭをＥＣＵ１５で計測するとともに、その波高Ｍの尖頭がリーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦと合致しているか否かを点検することにより、上記標準的な抵抗値での電圧値ＶＨＧｒｅｆの特性からの電圧値ＶＨＧｃｏｎの特性ずれが如何ほどであるかを把握し、取得することができる。 In other words, the voltage value of the oxygen sensor 12 actually connected to the ECU 15 is adjusted while performing feedback control of the air-fuel ratio so as to reproduce the state of the illustrated period P by setting the target excess air ratio λcmd near the stoichiometric value. (Detection value) By measuring the wave height M expressed by VHGcon with the ECU 15 and checking whether the peak of the wave height M matches the lean side threshold LREF and the rich side threshold RREF, the standard It is possible to grasp and obtain how much the characteristic deviation of the voltage value VHGcon from the characteristic of the voltage value VHGref at a certain resistance value is.
　斯くして、特性点検部４０は、目標空気過剰率λｃｍｄをストイキメトリック近傍に設定して空燃比フィードバック制御を実施しながら、ＥＣＵ１５に接続された酸素センサ１２の電圧値（検出値）ＶＨＧｃｏｎについて波高Ｍの尖頭値を取得し、該波高Ｍの尖頭値がリッチ領域、ストイキ領域又はリーン領域の何れかに該当するかを点検するように構成される。また、この点検結果に基づいて、較正部４１は、波高Ｍの尖頭値が前記リッチ側閾値ＲＲＥＦ及びリーン側閾値ＬＲＥＦに適合するように、アフィン変換を施して前記データマップ及び前記第１及び第２ルックアップテーブルを較正することができる。 In this way, the characteristic inspection unit 40 sets the target excess air ratio λcmd near the stoichiometric value and performs air-fuel ratio feedback control, while checking the wave height of the voltage value (detection value) VHGcon of the oxygen sensor 12 connected to the ECU 15. It is configured to acquire the peak value of the wave height M and check whether the peak value of the wave height M corresponds to a rich region, a stoichiometric region, or a lean region. Also, based on the inspection results, the calibration unit 41 performs affine transformation on the data map and the first and The second lookup table can be calibrated.
　具体的には、較正部４１は、所謂アフィン変換の要領で、複数の第１目盛値Ｇ１及び複数の第２目盛値Ｇ２を拡大又は縮小することによりデータマップ及び第１及び第２ルックアップテーブルを較正するための第１較正倍率値Ｃ１及び第２較正倍率値Ｃ２を備えている。 Specifically, the calibration unit 41 enlarges or reduces the plurality of first scale values G1 and the plurality of second scale values G2 in a manner of so-called affine transformation, thereby adjusting the data map and the first and second lookup tables. It is provided with a first calibration magnification value C1 and a second calibration magnification value C2 for calibrating.
　図８Ａ～図８Ｄを併せて参照しつつ詳述すると、較正部４１は、時間の経過に伴って変化する制御用の電圧値ＶＨＧｃｏｎのリーン側尖頭値４７ｖとグラフ３５（リーン側閾値ＬＲＥＦ）に対応する第１ルックアップテーブルとを対比した際に、例えば、リーン側尖頭値４７ｖがリーン領域にある場合には第１較正倍率値Ｃ１を増加してデータマップ及び第１ルックアップテーブルを図８Ａにおいて右側方向に向けて拡大し、リーン側尖頭値４７ｖがストイキ領域にある場合には第１較正倍率値Ｃ１を減少してデータマップ及び第１ルックアップテーブルを図８Ｂにおいて左側方向に向けて縮小する。 To explain in detail with reference to FIGS. 8A to 8D, the calibration unit 41 calculates the lean side peak value 47v of the control voltage value VHGcon that changes over time and the graph 35 (lean side threshold value LREF). For example, when the lean side peak value 47v is in the lean region, when comparing the data map and the first lookup table corresponding to When the lean side peak value 47v is in the stoichiometric region, the first calibration magnification value C1 is decreased and the data map and the first lookup table are expanded to the left in FIG. 8B. Reduce towards.
　すなわち、較正部４１は、上記増加又は減少した第１較正倍率値Ｃ１をデータマップ及び第１ルックアップテーブルの第１目盛値Ｇ１に乗じることにより、所謂アフィン変換の要領でデータマップ及び第１ルックアップテーブルを実質的に拡大又は縮小することで較正をする。なお、第１目盛値Ｇ１の拡縮原点には、０ケルビン（マイナス２７３．１５ｄｅｇＣ；絶対零度）を採用することができる。このとき、記憶部３４に記憶されている複数の第１目盛値Ｇ１の較正前の値をＴｋ（摂氏温度）とした場合、較正後の制御用第１目盛値Ｔｋｃａｌは、次式（６ａ）により求められる。
Ｔｋｃａｌ＝（Ｔｋ＋２７３．１５）×Ｃ１－２７３．１５　　（６ａ） That is, the calibration unit 41 multiplies the first scale value G1 of the data map and the first lookup table by the increased or decreased first calibration magnification value C1, thereby converting the data map and the first look up in a manner of so-called affine transformation. Calibrate by substantially expanding or contracting the uptable. Note that 0 Kelvin (minus 273.15 degC; absolute zero) can be adopted as the expansion/contraction origin of the first scale value G1. At this time, if the value before calibration of the plurality of first scale values G1 stored in the storage unit 34 is Tk (degree Celsius temperature), the first scale value for control after calibration Tkcal is calculated by the following equation (6a). It is determined by
Tkcal=(Tk+273.15)×C1-273.15 (6a)
　また、較正部４１は、時間の経過に伴って変化する制御用の電圧値ＶＨＧｃｏｎのリッチ側尖頭値４６ｖとグラフ３６（リッチ側閾値ＲＲＥＦ）に対応する第２ルックアップテーブルとを対比した際に、例えば、リッチ側尖頭値４６ｖがリッチ領域にある場合には第２較正倍率値Ｃ２を増加してデータマップ及び第２ルックアップテーブルを図８Ｄにおいて下方向に向けて拡大し、リッチ側尖頭値４６ｖがストイキ領域にある場合には第２較正倍率値Ｃ２を減少してデータマップ及び第２ルックアップテーブルを図８Ｃにおいて上方向に向けて縮小する。 Further, when the calibration unit 41 compares the rich-side peak value 46v of the control voltage value VHGcon that changes with the passage of time with the second look-up table corresponding to the graph 36 (rich-side threshold value RREF), For example, when the peak value 46v on the rich side is in the rich region, the second calibration magnification value C2 is increased to enlarge the data map and the second lookup table downward in FIG. When the peak value 46v is in the stoichiometric region, the second calibration magnification value C2 is decreased to reduce the data map and the second lookup table upward in FIG. 8C.
　すなわち、較正部４１は、上記増加又は減少した第２較正倍率値Ｃ２をデータマップ及び第２ルックアップテーブルの第２目盛値Ｇ２に乗じることにより、所謂アフィン変換の要領でデータマップ及び第２ルックアップテーブルを実質的に拡大又は縮小することで較正する。なお、第２目盛値Ｇ２の拡縮原点には、上述の制御用の温度Ｔｃｏｎが所定値以下の場合のグラフ３５（リーン側閾値ＬＲＥＦ）の値を採用することができる。 That is, the calibration unit 41 multiplies the second scale value G2 of the data map and the second lookup table by the increased or decreased second calibration magnification value C2, thereby converting the data map and the second look up in the manner of so-called affine transformation. Calibrate by substantially expanding or contracting the uptable. In addition, the value of the graph 35 (lean side threshold value LREF) when the above-mentioned control temperature Tcon is below a predetermined value can be adopted as the expansion/contraction origin of the second scale value G2.
　このとき、上記制御用の温度Ｔｃｏｎが所定値以下の場合のグラフ３５の値をＬＲＥＦａｎｃｈｏｒ、記憶部３４に記憶されている複数の第２目盛値Ｇ２の較正前の値をＶｋとした場合、較正後の制御用第２目盛値Ｖｋｃａｌは、次式（７）により求められる。
　　Vkcal=(Vk-LREFanchor)×C2+LREFanchor　　　　　　　　　（７） At this time, if the value of the graph 35 when the control temperature Tcon is below a predetermined value is LREFanchor, and the pre-calibration value of the plurality of second scale values G2 stored in the storage unit 34 is Vk, then the calibration The subsequent control second scale value Vkcal is determined by the following equation (7).
Vkcal=(Vk-LREFanchor)×C2+LREFanchor (7)
　なお、本実施の形態においては、上記第１較正倍率値Ｃ１及び第２較正倍率値Ｃ２の増加又は減少を行う場合に、所定の漸増率及び漸減率を介在させて第１較正倍率値Ｃ１又は第２較正倍率値Ｃ２を漸増又は漸減させて徐々に較正完了状態へと移行させる移行処理を含むように較正部４１を構成することができる。このとき、ＥＣＵ１５におけるオンボード診断により、チタニア型の酸素センサ１２のセンサヒータ１２ｂと温度算出部２３との間の信号線が断線又は短絡しているとの故障状態が確定診断された場合には、第１較正倍率値Ｃ１についての上記移行処理（増加又は減少）は中断され、第１較正倍率値Ｃ１はデフォルト値（例えば＃１．０倍などの値）にリセットされる。 In this embodiment, when increasing or decreasing the first calibration magnification value C1 and the second calibration magnification value C2, the first calibration magnification value C1 or the second calibration magnification value C1 or The calibration unit 41 can be configured to include a transition process in which the second calibration magnification value C2 is gradually increased or decreased to gradually transition to the calibration complete state. At this time, if the on-board diagnosis in the ECU 15 definitively diagnoses that the signal line between the sensor heater 12b of the titania type oxygen sensor 12 and the temperature calculation unit 23 is disconnected or short-circuited, , the above transition process (increase or decrease) for the first calibration magnification value C1 is interrupted, and the first calibration magnification value C1 is reset to a default value (for example, a value such as #1.0 times).
　一方、酸素センサ１２として、抵抗型酸素センサの一態様であるチタニア酸素センサを採用した場合、センサ素子１２ａの温度が低すぎるか又は高すぎる場合には、そうでない場合と比較して、センサ素子１２ａの抵抗値が空燃比に対して応動し難く、ダイナミックレンジが狭くなる。その帰結として、センサ素子１２ａの温度が低すぎる（例えば、２８０ｄｅｇＣ以下）か又は高すぎる（例えば、８７０ｄｅｇＣ以上）場合には、図５から理解されるように、酸素センサ１２の検出値に基づく空気過剰率λの分解能が極端に低下する。これにより、ＰＩＤ又はＰＤ制御における偏差の微分項での制御が困難になることから、ＰＩＤ又はＰＤ制御（疑似的な微分項を含む）に期待される制御追従性を保つことが難しくなり、空気過剰率λについてのフィードバック制御の精度が低下するおそれがある。 On the other hand, when a titania oxygen sensor, which is an embodiment of a resistance-type oxygen sensor, is adopted as the oxygen sensor 12, if the temperature of the sensor element 12a is too low or too high, the sensor element The resistance value of 12a is difficult to respond to the air-fuel ratio, resulting in a narrow dynamic range. As a result, if the temperature of the sensor element 12a is too low (for example, 280 degC or lower) or too high (for example, 870 degC or higher), as can be understood from FIG. The resolution of the excess rate λ is extremely reduced. This makes it difficult to control using the differential term of the deviation in PID or PD control, making it difficult to maintain the control followability expected of PID or PD control (including pseudo differential terms). There is a possibility that the accuracy of feedback control regarding the excess rate λ may decrease.
　そこで、本実施形態ではセンサ素子１２ａの温度が低すぎる（例えば、２８０ｄｅｇＣ以下）か又は高すぎる（例えば、８７０ｄｅｇＣ以上）場合には、微分項での制御を含むＰＩＤ又はＰＤ制御によるフィードバック制御を行わないことを可能としている。 Therefore, in this embodiment, if the temperature of the sensor element 12a is too low (for example, 280 degC or lower) or too high (for example, 870 degC or higher), feedback control using PID or PD control including control using a differential term is performed. It is possible that there is no such thing.
　ただしこの場合、センサ素子１２ａの温度が低すぎるか又は高すぎることに基づいて直ちに微分制御を含むフィードバック制御を停止するのではなく、制御用温度Ｔｃｏｎが第２温度よりも低いか又は第３温度よりも高いときにはＰＩ制御を選択することにより、ＰＩ制御へ切り替える段階を踏むように構成している。 However, in this case, rather than immediately stopping the feedback control including differential control based on the temperature of the sensor element 12a being too low or too high, the control temperature Tcon is lower than the second temperature or the third temperature When the value is higher than , the PI control is selected and a step of switching to the PI control is performed.
　具体的には、図９に示すように、フィードバック係数演算部３０は、制御用温度Ｔｃｏｎに応じて求めた空気過剰率λと目標空気過剰率λｃｍｄとの偏差Ｐ及び該偏差Ｐの微分Ｄ、又は、該偏差Ｐ、該偏差の積分Ｉ及び該偏差の微分Ｄに基づきフィードバック係数ｋを求めるＰＤ・ＰＩＤ制御部４９と、制御用温度Ｔｃｏｎに応じて求めた空気過剰率λと目標空気過剰率λｃｍｄとの偏差Ｐ及び該偏差Ｐの積分Ｉに基づきフィードバック係数ｋを求めるＰＩ制御部５０と、フィードバック係数ｋの演算に前記ＰＩ制御部５０又は前記ＰＤ・ＰＩＤ制御部４９のいずれを使用するかを選択する制御部選択部５１と、前記制御用温度Ｔｃｏｎに関する複数の温度設定値を記憶部３４より読み出し、この複数の温度設定値及び前記第１較正倍率値Ｃ１に基づいて、低い方から第１、第２、第３、第４温度ｔ１、ｔ２、ｔ３、ｔ４をそれぞれ設定する温度閾値設定部５２と、制御用温度Ｔｃｏｎに応じて、ＰＩ制御部５０又はＰＤ・ＰＩＤ制御部４９を介したフィードバック制御の実行を許容するか否かを判断する活性判断部５３と、後述する代替温度Ｔｓｕｂに応じて求めた空気過剰率λと目標空気過剰率λｃｍｄとの偏差Ｐ及び該偏差の積分Ｉに基づきフィードバック係数ｋを求める故障時ＰＩ制御部５９とを備える。 Specifically, as shown in FIG. 9, the feedback coefficient calculation unit 30 calculates the deviation P between the excess air ratio λ obtained according to the control temperature Tcon and the target excess air ratio λcmd, the differential D of the deviation P, Alternatively, the PD/PID control unit 49 calculates the feedback coefficient k based on the deviation P, the integral I of the deviation, and the differential D of the deviation, and the excess air ratio λ and the target excess air ratio calculated according to the control temperature Tcon. A PI control unit 50 that calculates a feedback coefficient k based on a deviation P with respect to λcmd and an integral I of the deviation P, and which of the PI control unit 50 or the PD/PID control unit 49 is used to calculate the feedback coefficient k. A control unit selection unit 51 selects the control temperature Tcon, and a plurality of temperature setting values regarding the control temperature Tcon are read from the storage unit 34, and based on the plurality of temperature setting values and the first calibration magnification value C1, the first calibration magnification value C1 is selected from the lowest one. A temperature threshold setting section 52 that sets the first, second, third, and fourth temperatures t1, t2, t3, and t4, respectively, and a PI control section 50 or a PD/PID control section 49 according to the control temperature Tcon. an activation determination unit 53 that determines whether or not to permit execution of the feedback control, and a deviation P between an excess air ratio λ and a target excess air ratio λcmd determined according to an alternative temperature Tsub, which will be described later, and an integral I of the deviation. and a fault PI control unit 59 that calculates a feedback coefficient k based on the following.
　温度閾値設定部５２において、記憶部３４から読み出した複数の温度設定値を＃Ｔｌｅｖｅｌとした場合、較正後の第１、第２、第３、第４温度ｔ１、ｔ２、ｔ３、ｔ４を示すＴｎ（ｎ＝１～４）は、次式（６ｂ）により求められる。
　　Tn(n=1～4)=(#Tlevel+273.15)×C1-273.15　　　　　　　（６ｂ） In the temperature threshold setting unit 52, when the plurality of temperature setting values read from the storage unit 34 are #Tlevel, Tn indicating the first, second, third, and fourth temperatures t1, t2, t3, and t4 after calibration (n=1 to 4) is determined by the following equation (6b).
Tn(n=1~4)=(#Tlevel+273.15)×C1-273.15 (6b)
　活性判断部５３は、制御用温度Ｔｃｏｎが、第１温度ｔ１よりも高くかつ第４温度ｔ４よりも低いときに、ＰＩ制御部５０又はＰＤ・ＰＩＤ制御部４９を介したフィードバック制御の実行を許容する。 The activation determination unit 53 allows execution of feedback control via the PI control unit 50 or the PD/PID control unit 49 when the control temperature Tcon is higher than the first temperature t1 and lower than the fourth temperature t4. do.
　制御部選択部５１は、活性判断部５３が前記フィードバック制御の実行を許容する場合に、制御用温度Ｔｃｏｎが第２温度ｔ２よりも高くかつ第３温度ｔ３よりも低いときには、ＰＤ・ＰＩＤ制御部４９を選択し、制御用温度Ｔｃｏｎが第２温度ｔ２よりも低いか又は第３温度ｔ３よりも高いときには、ＰＩ制御部５０を選択する。 When the activation determination unit 53 allows execution of the feedback control, the control unit selection unit 51 selects the PD/PID control unit when the control temperature Tcon is higher than the second temperature t2 and lower than the third temperature t3. 49 is selected, and when the control temperature Tcon is lower than the second temperature t2 or higher than the third temperature t3, the PI control unit 50 is selected.
　而してフィードバック係数演算部３０は、上記制御部選択部５１においてＰＤ・ＰＩＤ制御部４９が選択された場合には、空気過剰率λと目標空気過剰率λｃｍｄとの偏差Ｐ及び該偏差Ｐの微分、又は該偏差Ｐ、該偏差Ｐの積分及び該偏差Ｐの微分に基づいてフィードバック係数ｋを算出し、ＰＩ制御部５０が選択された場合には、該偏差Ｐ及び該偏差Ｐの積分に基づいてフィードバック係数ｋを算出する。これにより、制御用温度Ｔｃｏｎが低すぎたり高すぎたりする場合に応じて、適切なフィードバック制御が行われる。 When the PD/PID control unit 49 is selected in the control unit selection unit 51, the feedback coefficient calculation unit 30 calculates the deviation P between the excess air ratio λ and the target excess air ratio λcmd, and the deviation P of the deviation P. Calculate the feedback coefficient k based on the differentiation, or the deviation P, the integral of the deviation P, and the differentiation of the deviation P, and if the PI control unit 50 is selected, calculate the feedback coefficient k based on the deviation P, the integral of the deviation P, and the Based on this, a feedback coefficient k is calculated. Thereby, appropriate feedback control is performed depending on whether the control temperature Tcon is too low or too high.
　他方、酸素センサ１２を長期間使用する状況下で、何らかの外的要因でセンサヒータ１２ｂからの信号線が断線したりすると、センサヒータ１２ｂの抵抗値が正確に読み取れないので、温度算出部２３によりセンサ素子１２ａの温度値Ｔを正確に算出することが困難となる。この場合、何らの対策も講じられない場合には、温度依存性の高い酸素センサ１２による空燃比制御が継続できなくなる。 On the other hand, if the oxygen sensor 12 is used for a long period of time and the signal line from the sensor heater 12b is disconnected due to some external factor, the resistance value of the sensor heater 12b cannot be read accurately. This makes it difficult to accurately calculate the temperature value T of the sensor element 12a. In this case, if no measures are taken, air-fuel ratio control by the oxygen sensor 12, which is highly temperature dependent, cannot be continued.
　そこで、本実施形態においては、センサヒータ１２ｂの抵抗値が読み取れなくなった場合の制御用温度Ｔｃｏｎの代替として使用する代替温度Ｔｓｕｂを準備する代替温度準備部５４が用いられる。 Therefore, in this embodiment, an alternative temperature preparation unit 54 is used that prepares an alternative temperature Tsub to be used as an alternative to the control temperature Tcon when the resistance value of the sensor heater 12b cannot be read.
　ここで代替温度準備部５４は、排気脈動によるセンサ素子１２ａの電圧値ＶＨＧの波高のリーン側尖頭値４７ｖに対応する複数個の電圧値及びこれに対応する複数個の温度値を座標とした第３ルックアップテーブル５５と、電圧値ＶＨＧｃｏｎの波高のリッチ側尖頭値４６ｖに対応する複数個の電圧値及びこれに対応する複数個の温度値を座標とした第４ルックアップテーブル５６とを有しており、これら第３、第４ルックアップテーブル５５、５６は記憶部３４に記憶される。 Here, the alternative temperature preparation unit 54 sets a plurality of voltage values corresponding to a lean side peak value 47v of the wave height of the voltage value VHG of the sensor element 12a due to exhaust pulsation and a plurality of temperature values corresponding thereto as coordinates. A third look-up table 55 and a fourth look-up table 56 whose coordinates are a plurality of voltage values corresponding to the rich-side peak value 46v of the wave height of the voltage value VHGcon and a plurality of temperature values corresponding thereto. These third and fourth lookup tables 55 and 56 are stored in the storage unit 34.
　図１０を参照して、第３ルックアップテーブル５５は、前記グラフ３５（リーン側閾値ＬＲＥＦ）に対応するルックアップテーブルとはいわゆる逆関数の関係に設定されている。すなわちこの実施の形態において、第３ルックアップテーブル５５は、例えばリーン領域とストイキ領域との境界としての空気過剰率λを１．０２とし、この値となるような電圧値ＶＨＧ及び温度値Ｔを座標とした上記データマップ上の点を複数点求め、これら複数の点の間をそれぞれ線補間で結んだグラフで表現されるもので、複数の温度値を電圧値ＶＨＧ（検出値）についての複数の第２目盛値Ｇ２との対応関係を付けて示している。 Referring to FIG. 10, the third lookup table 55 is set in a so-called inverse functional relationship with the lookup table corresponding to the graph 35 (lean side threshold LREF). That is, in this embodiment, the third lookup table 55 sets, for example, the excess air ratio λ as the boundary between the lean region and the stoichiometric region to 1.02, and determines the voltage value VHG and temperature value T that will result in this value. It is expressed by a graph obtained by finding multiple points on the data map as coordinates and connecting these multiple points by line interpolation. The correspondence relationship with the second scale value G2 is shown.
　また、この実施の形態において、第４ルックアップテーブル５６は、例えば、ストイキ領域とリッチ領域との境界としての空気過剰率λを０．９８とし、この値となるような電圧値ＶＨＧ及び温度値Ｔを座標とした上記データマップ上の点を複数点求め、これら複数の点の間をそれぞれ線補間で結んだグラフで表現されるもので、複数の温度値を電圧値ＶＨＧ（検出値）についての複数の第２目盛値Ｇ２との対応関係を付けて示している。 In addition, in this embodiment, the fourth lookup table 56 sets, for example, the excess air ratio λ as the boundary between the stoichiometric region and the rich region to 0.98, and the voltage value VHG and temperature value that result in this value. It is expressed by a graph obtained by finding multiple points on the above data map with T as the coordinate and connecting these multiple points by line interpolation, and multiple temperature values are expressed with respect to the voltage value VHG (detected value). are shown in correspondence with the plurality of second scale values G2.
　このような代替温度準備部５４において、例えば、センサ素子１２ａの電圧値ＶＨＧの波高のリーン側尖頭値４７ｖ（図７参照）が、３．０ｖｏｌｔであるとすれば、図１０に示すように、第３ルックアップテーブル５５により、対応する代替温度値Ｔｓｕｂは６５０ｄｅｇＣとなることがわかる。すなわち、代替温度準備部５４は、リーン側尖頭値４７ｖに基づき、第３ルックアップテーブルを用いて代替温度Ｔｓｕｂを求め、これを制御用温度Ｔｃｏｎの代替温度として準備することができる。 In such an alternative temperature preparation section 54, for example, if the lean side peak value 47v (see FIG. 7) of the wave height of the voltage value VHG of the sensor element 12a is 3.0 volts, as shown in FIG. , it can be seen from the third lookup table 55 that the corresponding alternative temperature value Tsub is 650 degC. That is, the alternative temperature preparation unit 54 can use the third lookup table to obtain the alternative temperature Tsub based on the lean side peak value 47v, and prepare this as the alternative temperature for the control temperature Tcon.
　同様にして、例えば、センサ素子１２ａの電圧値ＶＨＧの波高のリッチ側尖頭値４６ｖ（図７参照）が１．０ｖｏｌｔであるとすれば、図１０に示すように、第４ルックアップテーブル５６により、代替温度値Ｔｓｕｂは４００ｄｅｇＣであることがわかる。すなわち、代替温度準備部５４は、第４ルックアップテーブルを用いて代替温度Ｔｓｕｂを求め、これを制御用温度Ｔｃｏｎの代替温度として準備することができる。斯くして、何らかの外的要因でセンサヒータ１２ｂからの信号線が断線した場合であっても、制御用温度Ｔｃｏｎの代替温度として代替温度Ｔｓｕｂを求めて温度依存性の高い酸素センサ１２による空燃比制御を継続させることが可能となる。 Similarly, if the rich-side peak value 46v (see FIG. 7) of the wave height of the voltage value VHG of the sensor element 12a is 1.0 volt, as shown in FIG. It can be seen that the alternative temperature value Tsub is 400 degC. That is, the alternative temperature preparation unit 54 can obtain the alternative temperature Tsub using the fourth lookup table and prepare this as the alternative temperature for the control temperature Tcon. In this way, even if the signal line from the sensor heater 12b is disconnected due to some external factor, the substitute temperature Tsub is determined as a substitute temperature for the control temperature Tcon, and the air-fuel ratio is determined by the oxygen sensor 12, which is highly temperature dependent. It becomes possible to continue control.
　ところで、上述のように、センサヒータ１２ｂからの信号線が断線等した場合に、代替温度準備部５４でのセンサ素子１２ａの代替温度の準備は、センサ素子１２ａの電圧値ＶＨＧの波高の尖頭値を確認することによって行われる。この場合、この代替温度Ｔｓｕｂとセンサ素子１２ａの電圧値ＶＨＧとの相互の時系列を調停することが難しくなることから、代替温度Ｔｓｕｂと電圧算出部２４からの電圧値ＶＨＧから求められる空気過剰率λは、即時性（リアルタイム性）においてあいまいさを含む、検出遅れの大きい値となる。これは、空気過剰率λに対する偏差の変化量（微分項）に基づくＰＤ・ＰＩＤ制御の精度が大きく低下するおそれがあることを意味する。 By the way, as described above, when the signal line from the sensor heater 12b is disconnected, the alternative temperature preparation section 54 prepares the alternative temperature for the sensor element 12a at the peak of the wave height of the voltage value VHG of the sensor element 12a. This is done by checking the value. In this case, since it becomes difficult to arbitrate the mutual time series between the alternative temperature Tsub and the voltage value VHG of the sensor element 12a, the excess air ratio calculated from the alternative temperature Tsub and the voltage value VHG from the voltage calculation unit 24 λ is a value that includes ambiguity in immediacy (real-time) and has a large detection delay. This means that the accuracy of PD/PID control based on the amount of change in deviation (differential term) with respect to the excess air ratio λ may be significantly reduced.
　そこで、本実施形態では、センサヒータ１２ｂ断線等の異常乃至故障の時には、ＰＤ・ＰＩＤ制御は行わずに、微分項を含まない制御法であるＰＩ制御のみによる限定された制御が行われる。 Therefore, in this embodiment, in the event of an abnormality or failure such as a disconnection of the sensor heater 12b, PD/PID control is not performed, and limited control is performed only by PI control, which is a control method that does not include a differential term.
　図３に注目して、該図３の過剰率算出処理では、センサヒータ抵抗を読み取る際にセンサヒータ１２ｂの断線状態が検出される場合、代替温度準備部５４が実行される（ステップＳ２Ｂ）。代替温度準備部５４では、上述したようにリーン側尖頭値４７ｖ又はリッチ側尖頭値４６ｖから代替温度Ｔｓｕｂが求められる。 Paying attention to FIG. 3, in the excess rate calculation process of FIG. 3, if a disconnection state of the sensor heater 12b is detected when reading the sensor heater resistance, the alternative temperature preparation unit 54 is executed (step S2B). In the alternative temperature preparation section 54, the alternative temperature Tsub is determined from the lean side peak value 47v or the rich side peak value 46v as described above.
　次に、限界閾値設定部３３が実行される（ステップＳ２Ｂ）。限界閾値設定部３３では、代替温度値Ｔｓｕｂに基づき、図５のグラフ３５、３６に対応する第１、第２ルックアップテーブルを用いて、リーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦを設定する。ステップＳ３Ｂにおいて、電圧算出部２４から得られた電圧値ＶＨＧを電圧差確認部４３で得られたる偏差ＶＤにより補正して、制御用の電圧値（検出値）ＶＨＧｃｏｎを設定する。次に、ステップＳ４Ｂにおいては、代替温度Ｔｓｕｂ及びステップＳ３Ｂで取得した電圧値ＶＨＧｃｏｎに基づき上述のデータマップ（図５）が走査され、データＬＤが取得される。続くステップＳ６においてフラグＦ＿ＤＥＴＥＣＴをゼロに設定しつつステップＳ１６に進み、上記データＬＤの値を空気率過剰率λ値ＬＡＭＢＤＡとして設定する。斯くして、センサヒータ１２ｂ断線等の故障時における図３の過剰率算出処理を終了する。 Next, the limit threshold setting unit 33 is executed (step S2B). The limit threshold value setting unit 33 sets a lean side threshold value LREF and a rich side threshold value RREF based on the alternative temperature value Tsub using the first and second lookup tables corresponding to the graphs 35 and 36 in FIG. In step S3B, the voltage value VHG obtained from the voltage calculation section 24 is corrected by the deviation VD obtained from the voltage difference confirmation section 43, and a voltage value (detected value) VHGcon for control is set. Next, in step S4B, the above-mentioned data map (FIG. 5) is scanned based on the alternative temperature Tsub and the voltage value VHGcon obtained in step S3B, and data LD is obtained. In the following step S6, the flag F_DETECT is set to zero, and the process proceeds to step S16, where the value of the data LD is set as the excess air ratio λ value LAMBDA. In this way, the excess rate calculation process shown in FIG. 3 in the event of a failure such as a disconnection of the sensor heater 12b is completed.
　また、上記活性判断部５３及び制御部選択部５１は、ＥＣＵ１５におけるオンボード診断部６２により、チタニア酸素センサ１２のセンサヒータ１２ｂと温度算出部２３との間の信号線が断線又は短絡していると診断された場合に、代替温度Ｔｓｕｂが、前記第１温度ｔ１よりも高くかつ前記第４温度ｔ４よりも低いときに、故障時ＰＩ制御部５９を介したフィードバック制御の実行のみを許容する故障時活性判断部を有している。換言すると、活性判断部５３及び制御部選択部５１は、センサヒータ１２ｂと温度算出部２３との間の信号線が断線又は短絡していると診断された場合には、ＰＤ・ＰＩＤ制御を許可しないように構成されている。 In addition, the activation determining unit 53 and the control unit selecting unit 51 detect that the signal line between the sensor heater 12b of the titania oxygen sensor 12 and the temperature calculating unit 23 is disconnected or short-circuited by the on-board diagnostic unit 62 in the ECU 15. When the alternative temperature Tsub is higher than the first temperature t1 and lower than the fourth temperature t4, the failure only allows execution of feedback control via the failure PI control unit 59. It has a time activation determining section. In other words, the activation determination unit 53 and the control unit selection unit 51 permit PD/PID control when it is diagnosed that the signal line between the sensor heater 12b and the temperature calculation unit 23 is disconnected or short-circuited. It is configured not to.
　而して、故障時ＰＩ制御部５９は、代替温度Ｔｓｕｂに応じて求めた空気過剰率λと目標空気過剰率λｃｍｄとの偏差及び偏差の積分に基づいてフィードバック係数ｋを算出し、これにより、ＰＩ制御による空気過剰率λのフィードバック制御を行うことができる。したがって、センサヒータ１２ｂと温度算出部２３との間の信号線が断線又は短絡していると診断された場合においても、適切なフィードバック制御が続行される 。 Then, the fault PI control unit 59 calculates the feedback coefficient k based on the deviation between the excess air ratio λ obtained according to the alternative temperature Tsub and the target excess air ratio λcmd and the integral of the deviation, and thereby, Feedback control of the excess air ratio λ can be performed by PI control. Therefore, even if it is diagnosed that the signal line between the sensor heater 12b and the temperature calculation unit 23 is disconnected or short-circuited, appropriate feedback control is continued.
　さらに、制御部選択部５１は、上述の制御用温度Ｔｃｏｎに応じてＰＤ・ＰＩＤ制御又はＰＩ制御部を選択することに加えて、特性点検部４０における制御用電圧値（検出値）ＶＨＧｃｏｎ及び制御用温度Ｔｃｏｎの点検結果に応じて、ＰＤ・ＰＩＤ制御部４９又はＰＩ制御部５０の選択を実行し得るよう構成される。 Furthermore, in addition to selecting the PD/PID control or the PI control section according to the above-mentioned control temperature Tcon, the control section selection section 51 selects the control voltage value (detected value) VHGcon in the characteristic inspection section 40 and the control The PD/PID control unit 49 or the PI control unit 50 is configured to be selected depending on the inspection result of the operating temperature Tcon.
　具体的には、上述のように、較正部４１は、リーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦのそれぞれを制御用温度Ｔｃｏｎに係る第１目盛値Ｇ１及び制御用電圧値（検出値）ＶＨＧｃｏｎ係る第２目盛値Ｇ２にそれぞれ対応付けたデータマップと、尖頭値４６ｖ、４７ｖとの対比に基づいて、該データマップにおける該対応付けに関する第１目盛値Ｇ１及び第２目盛値Ｇ２を各較正するように構成されている。 Specifically, as described above, the calibration unit 41 sets the lean side threshold LREF and the rich side threshold RREF respectively to the first scale value G1 related to the control temperature Tcon and the first scale value G1 related to the control voltage value (detected value) VHGcon. The first scale value G1 and the second scale value G2 regarding the correspondence in the data map are each calibrated based on the comparison between the data map respectively associated with the second scale value G2 and the peak values 46v and 47v. It is composed of
　この較正に際し、上述のように、較正部４１は、上記第１較正倍率値Ｃ１及び第２較正倍率値Ｃ２の増加又は減少を行う場合に、所定の漸増率及び漸減率を介在させて第１較正倍率値Ｃ１又は第２較正倍率値Ｃ２を漸増又は漸減させて徐々に較正完了状態へと較正を進捗（学習）させることができる。 In this calibration, as described above, when increasing or decreasing the first calibration magnification value C1 and the second calibration magnification value C2, the calibration unit 41 adjusts the By gradually increasing or decreasing the calibration magnification value C1 or the second calibration magnification value C2, the calibration can be gradually progressed (learning) to a calibration completed state.
　そして、特性点検部４０は、尖頭値４６ｖ、４７ｖを、上記較正が反映されているリッチ側閾値ＲＲＥＦ又はリーン側閾値ＬＲＥＦの少なくとも一方側と比較することによって、較正部４１による較正の進捗状態を判定する。たとえば、制御部選択部５１は、尖頭値４６ｖとリッチ側閾値ＲＲＥＦ、又は尖頭値４６ｖとリーン側閾値ＬＲＥＦとの差を算出して当該差を較正部４１による較正の進捗状態とみなし、この較正の進捗状態を、特性点検部４０における制御用電圧値ＶＨＧｃｏｎ及び制御用温度Ｔｃｏｎの点検結果として、ＰＤ・ＰＩＤ制御部４９又はＰＩ制御部５０の選択を実行することができる。 Then, the characteristic inspection unit 40 compares the peak values 46v and 47v with at least one side of the rich side threshold RREF or the lean side threshold LREF to which the above-mentioned calibration is reflected, thereby checking the progress of the calibration by the calibration unit 41. Determine. For example, the control unit selection unit 51 calculates the difference between the peak value 46v and the rich side threshold RREF, or the peak value 46v and the lean side threshold LREF, and considers the difference as the progress state of the calibration by the calibration unit 41, The progress state of this calibration can be used as the inspection result of the control voltage value VHGcon and the control temperature Tcon in the characteristic inspection section 40 to select the PD/PID control section 49 or the PI control section 50.
　例えば、制御部選択部５１は、尖頭値４６ｖとリッチ側閾値ＲＲＥＦ、又は尖頭値４６ｖとリーン側閾値ＬＲＥＦとの差が、あらかじめ定められた閾値以下である場合には、較正の進捗状態が較正完了状態であるとみなし、上述のＰＤ・ＰＩＤ制御部４９を選択することができる。あるいは、尖頭値４６ｖとリッチ側閾値ＲＲＥＦ、又は尖頭値４６ｖとリーン側閾値ＬＲＥＦとの差が、あらかじめ定められた閾値よりも大きい場合には、較正の進捗状態が較正未完了状態であるとみなし、この場合はＰＩ制御部５０を選択することができる。 For example, if the difference between the peak value 46v and the rich side threshold RREF, or between the peak value 46v and the lean side threshold LREF is less than or equal to a predetermined threshold, the control unit selection unit 51 determines the calibration progress state. It is possible to select the above-mentioned PD/PID control section 49 by assuming that the calibration is completed. Alternatively, if the difference between the peak value 46v and the rich side threshold RREF, or the difference between the peak value 46v and the lean side threshold LREF is larger than a predetermined threshold, the calibration progress state is the calibration incomplete state. In this case, the PI control unit 50 can be selected.
　ただし、この選択に際しては、上述の活性判断部５３によるフィードバック制御の実行を許容するか否かの判断と、ＰＩ制御部５０による空燃比フィードバック制御の実行を許容するか否かの判断とが優先とされており、たとえば上述のように、センサ素子１２ａの温度Ｔｃｏｎが低すぎる第１温度ｔ１以下であるか又は高すぎる第４温度ｔ４以上の場合（不活性温度）には、ＰＩ制御部５０及びＰＤ・ＰＩＤ制御部４９の双方が選択されず、すなわち、フィードバック制御が停止される。 However, when making this selection, priority is given to determining whether or not to allow the execution of the feedback control by the above-mentioned activation determining section 53 and determining whether or not to permit the execution of the air-fuel ratio feedback control by the PI control section 50. For example, as described above, when the temperature Tcon of the sensor element 12a is below the too low first temperature t1 or above the too high fourth temperature t4 (inert temperature), the PI control unit 50 and PD/PID control unit 49 are not selected, that is, feedback control is stopped.
　また、制御用温度Ｔｃｏｎが第２温度ｔ２よりも低いか又は第３温度ｔ３よりも高く、これによりＰＩ制御部５０によるフィードバック制御の実行が選択される温度条件下では、たとえ尖頭値４６ｖとリッチ側閾値ＲＲＥＦ、又は尖頭値４６ｖとリーン側閾値ＬＲＥＦとの差があらかじめ定められた閾値以下であったとしても、ＰＤ・ＰＩＤ制御部４９による制御の実行が許容されることはない。 In addition, under temperature conditions where the control temperature Tcon is lower than the second temperature t2 or higher than the third temperature t3, and therefore execution of feedback control by the PI control unit 50 is selected, even if the peak value is 46V. Even if the rich side threshold RREF or the difference between the peak value 46v and the lean side threshold LREF is less than a predetermined threshold, the PD/PID control unit 49 is not allowed to perform control.
　他方、制御用温度Ｔｃｏｎが第２温度ｔ２よりも高くかつ第３温度ｔ３よりも低く、ＰＤ・ＰＩＤ制御部４９によるフィードバック制御の実行が選択されうる制御用温度Ｔｃｏｎの条件下であっても、尖頭値４６ｖとリッチ側閾値ＲＲＥＦ、又は尖頭値４６ｖとリーン側閾値ＬＲＥＦとの差があらかじめ定められた閾値よりも大きく、依然として較正未完了状態であるとみなされる場合には、ＰＩ制御部５０によるフィードバック制御の実行が選択される。 On the other hand, even if the control temperature Tcon is higher than the second temperature t2 and lower than the third temperature t3, and the control temperature Tcon is such that execution of feedback control by the PD/PID control unit 49 can be selected, If the difference between the peak value 46v and the rich side threshold RREF or between the peak value 46v and the lean side threshold LREF is larger than a predetermined threshold and it is considered that the calibration is still incomplete, the PI control unit Execution of feedback control by 50 is selected.
　ＥＣＵ１５は、この特性点検部４０の点検結果に基づく選択を制御部選択部５１に実行させるトリガ信号を出力するものとして、較正リセット部６１及び上述のオンボード診断部６２を備える（図２参照）。較正リセット部６１は、前記トリガ信号として、上述のデータマップにおける対応付けを初期化する初期化指令Ｒｓを、制御部選択部５１に対して発行可能に構成される。 The ECU 15 includes a calibration reset section 61 and the above-mentioned on-board diagnostic section 62, which output a trigger signal that causes the control section selection section 51 to make a selection based on the inspection result of the characteristic inspection section 40 (see FIG. 2). . The calibration reset unit 61 is configured to be able to issue, to the control unit selection unit 51, an initialization command Rs that initializes the correspondence in the data map described above as the trigger signal.
　一方、オンボード診断部６２は、上述のように、チタニア酸素センサ１２のセンサ素子（検出部）１２ａ又はセンサヒータ１２ｂ（ヒータ部）における断線などの故障診断を実行可能に構成される。そして、オンボード診断部６２は、センサ素子１２ａ又はセンサヒータ１２ｂに異常がある旨の判定をした場合には、その旨を示す異常信号Ａｓを、前記トリガ信号として、制御部選択部５１に対して発行する。 On the other hand, as described above, the on-board diagnostic unit 62 is configured to be capable of diagnosing a failure such as a disconnection in the sensor element (detection unit) 12a or the sensor heater 12b (heater unit) of the titania oxygen sensor 12. When the on-board diagnostic unit 62 determines that there is an abnormality in the sensor element 12a or the sensor heater 12b, the on-board diagnostic unit 62 sends an abnormality signal As indicating this to the control unit selection unit 51 as the trigger signal. will be issued.
　制御部選択部５１は、較正リセット部６１から初期化指令Ｒｓを受けた場合、それ以後の予め定められた期間では、ＰＩ制御部５０を優先的に選択する。この予め定められた期間としては、特性点検部４０による点検が反復的に実行され、その結果に応じて較正部４１に上述の較正の進捗状態を判定するまでに要する、十分な期間が設定される。 When the control unit selection unit 51 receives the initialization command Rs from the calibration reset unit 61, it preferentially selects the PI control unit 50 in a predetermined period thereafter. This predetermined period is set to be a sufficient period required for the characteristics inspection section 40 to repeatedly perform inspections and for the calibration section 41 to determine the progress state of the above-mentioned calibration according to the results. Ru.
　また、制御部選択部５１は、オンボード診断部６２から異常信号Ａｓを受けた場合には、ＰＩ制御部５０を選択する。ただし、この場合には、上述のように、センサ素子１２ａの正確な温度値Ｔｃｏｎが得られないので、代替値Ｔｓｕｂにより求めた空気過剰率λ（図３のステップＳ２Ｂ～Ｓ４３Ｂ、Ｓ６、Ｓ１６参照）によりＰＩ制御を行うために、ＰＩ制御部５０として、故障時ＰＩ制御部５９が選択される。故障時ＰＩ制御部５９によるＰＩ制御は、異常信号Ａｓが解除されるまで選択される。なお、このように異常信号Ａｓを受けて故障時ＰＩ制御部５９によるＰＩ制御が行われる際には、上述の較正部４１による較正制御は中断される（一時的に較正値の算出更新を停止）。 Further, the control unit selection unit 51 selects the PI control unit 50 when receiving the abnormality signal As from the on-board diagnosis unit 62. However, in this case, as described above, the accurate temperature value Tcon of the sensor element 12a cannot be obtained, so the excess air ratio λ obtained from the substitute value Tsub (see steps S2B to S43B, S6, and S16 in FIG. 3) ), the fault PI control unit 59 is selected as the PI control unit 50. PI control by the failure PI control section 59 is selected until the abnormality signal As is released. Note that when the fault PI control section 59 performs PI control in response to the abnormal signal As, the above-mentioned calibration control by the calibration section 41 is interrupted (temporarily stopping calculation and updating of calibration values). ).
　この場合、制御部選択部５１は、一時的に異常信号Ａｓを受けた後に、その異常信号Ａｓが解除されたときには、該解除後の予め定められた期間においてＰＩ制御部５０を選択する。この予め定められた期間としては、該解除後に、較正部４１によって、上述のように特性点検部４０による点検が反復的に実行され、その結果に応じて較正部４１に上述の較正の進捗状態を判断させるに十分な期間が設定される。 In this case, when the abnormal signal As is canceled after temporarily receiving the abnormal signal As, the control unit selection unit 51 selects the PI control unit 50 for a predetermined period after the cancellation. This predetermined period is such that after the cancellation, the calibration unit 41 repeatedly performs the inspection by the characteristic inspection unit 40 as described above, and depending on the result, the calibration unit 41 indicates the progress status of the calibration described above. A period sufficient to allow a decision to be made will be set.
　以上のように、本実施形態によれば、酸素センサ１２のセンサ素子１２ａの温度が低すぎる第１温度ｔ１以下であるか又は高すぎる第４温度ｔ４以上の場合には、フィードバック制御を行なわず、制御用温度が第２温度ｔ２よりも低いか又は第３温度ｔ３よりも高いときにはＰＩ制御部５０を介したフィードバック制御を行い、酸素センサ１２のセンサ素子１２ａの温度が第２温度ｔ２よりも高くかつ第３温度ｔ３よりも低いときには、ＰＤ・ＰＩＤ制御部４９を介したフィードバック制御を行うので、フィードバック制御の作動温度範囲を実質的に広げて可用性を向上させ、排気浄化性能を高めることができる。 As described above, according to the present embodiment, when the temperature of the sensor element 12a of the oxygen sensor 12 is below the first temperature t1 which is too low or above the fourth temperature t4 which is too high, no feedback control is performed. , when the control temperature is lower than the second temperature t2 or higher than the third temperature t3, feedback control is performed via the PI control unit 50, and the temperature of the sensor element 12a of the oxygen sensor 12 is lower than the second temperature t2. When the temperature is high and lower than the third temperature t3, feedback control is performed via the PD/PID control unit 49, so it is possible to substantially expand the operating temperature range of feedback control, improve availability, and improve exhaust purification performance. can.
　また、較正された第１～第４ルックアップテーブルに基づき、電圧算出部２４からの電圧値ＶＨＧの尖頭値に対応する温度を求め、求めた温度を過剰率算出部２５で使用する制御用温度Ｔｃｏｎの代替温度Ｔｓｕｂとして準備するとともに、酸素センサ１２のセンサヒータ１２ｂから信号線が断線又は短絡等してセンサヒータ１２ｂの温度を温度算出部２３が正しく算出できない場合でも、準備された代替温度Ｔｓｕｂを使用して求めた空気過剰率λと目標空気過剰率λｃｍｄとの偏差Ｐ及び該偏差の積分Ｉに基づきフィードバック係数ｋを求める故障時ＰＩ制御部５９を設けているので、ヒータ部の故障時においても、空気過剰率のフィードバック制御を継続することができる。 Further, based on the calibrated first to fourth lookup tables, the temperature corresponding to the peak value of the voltage value VHG from the voltage calculation unit 24 is determined, and the determined temperature is used for control in the excess rate calculation unit 25. In addition to preparing an alternative temperature Tsub for the temperature Tcon, even if the temperature calculating section 23 cannot correctly calculate the temperature of the sensor heater 12b due to disconnection or short circuit of the signal line from the sensor heater 12b of the oxygen sensor 12, the prepared alternative temperature Tcon can be used. Since a failure PI control unit 59 is provided that calculates a feedback coefficient k based on the deviation P between the excess air ratio λ obtained using Tsub and the target excess air ratio λcmd and the integral I of the deviation, it is possible to prevent a failure of the heater unit. Feedback control of the excess air ratio can be continued even at the same time.
　また、制御部選択部５１は、特性点検部４０における検出値ＶＨＧｃｏｎ及び制御用温度Ｔｃｏｎ及び制御用温度Ｔｃｏｎの点検結果に応じて、ＰＤ・ＰＩＤ制御部４９又はＰＩ制御部５０の択一的選択を実行し得るように構成されているので、該点検結果に応じた適切な制御の選択を、酸素センサ１２の個体差による特性の差異に応じて行うことができる。これにより、チタニア型の酸素センサ１２によるロバストネス（堅牢性)の高い空燃比フィードバック制御を実現することができる。 Further, the control unit selection unit 51 selectively selects the PD/PID control unit 49 or the PI control unit 50 according to the inspection results of the detected value VHGcon, the control temperature Tcon, and the control temperature Tcon in the characteristic inspection unit 40. Since the oxygen sensor 12 is configured to be able to perform the following, it is possible to select an appropriate control according to the inspection result in accordance with differences in characteristics due to individual differences in the oxygen sensor 12. As a result, highly robust air-fuel ratio feedback control using the titania-type oxygen sensor 12 can be realized.
　また、上述のデータマップと尖頭値との対比に基づいてデータマップが較正され、尖頭値をリーン側閾値又はリッチ側閾値の少なくとも一方側と比較することによって較正の進捗状態が判定されるので、制御部選択部５１は、特性点検部４０における点検結果としてこの較正の進捗状態を参照することにより、ＰＤ・ＰＩＤ制御部４９又はＰＩ制御部５０の択一的選択を適切に行うことができる。 The data map is also calibrated based on the comparison between the data map and the peak value described above, and the progress of the calibration is determined by comparing the peak value with at least one of the lean threshold or the rich threshold. Therefore, the control unit selection unit 51 can appropriately select the PD/PID control unit 49 or the PI control unit 50 by referring to the progress state of this calibration as the inspection result in the characteristic inspection unit 40. can.
　また、制御部選択部５１は、較正リセット部６１からの初期化指令Ｒｓを受けた場合、それ以降の予め定められた期間、ＰＩ制御部を選択するので、その予め定められた期間に、データマップの較正を進捗させつつこの較正の進捗状態を適切に判定して、ＰＤ・ＰＩＤ制御部４９又はＰＩ制御部５０の択一的選択を適切に行うことができる。 Further, when the control unit selection unit 51 receives the initialization command Rs from the calibration reset unit 61, it selects the PI control unit for a predetermined period thereafter, so that the data is not stored in the predetermined period. While the map calibration is progressing, the progress state of the calibration can be appropriately determined, and the alternative selection of the PD/PID control unit 49 or the PI control unit 50 can be appropriately performed.
　また、制御部選択部５１は、酸素センサ１２のセンサ素子１２ａ又はセンサヒータ１２ｂが一時的に異常であると判定された場合には、ＰＩ制御部５０を選択するので、かかる場合にＰＤ・ＰＩＤ制御部４９により不正確なフィードバック制御が行われてしまうことを防止することができる。 Further, the control unit selection unit 51 selects the PI control unit 50 when it is determined that the sensor element 12a or the sensor heater 12b of the oxygen sensor 12 is temporarily abnormal. It is possible to prevent inaccurate feedback control from being performed by the control unit 49.
　また、制御部選択部５１は、酸素センサ１２のセンサ素子１２ａ又はセンサヒータ１２ｂの異常が検出された後に該異常の検出が解除されたとき、該解除以降の予め定められた期間においてＰＩ制御部５０が選択されるので、その間にデータマップの較正を進捗させつつこの較正の進捗状態を適切に判定して、ＰＤ・ＰＩＤ制御部４９又はＰＩ制御部５０の択一的選択を適切に行うことができる。 Furthermore, when the detection of an abnormality in the sensor element 12a or the sensor heater 12b of the oxygen sensor 12 is canceled after the detection of the abnormality, the control unit selection unit 51 selects a PI control unit in a predetermined period after the cancellation. 50 is selected, the calibration of the data map is progressing in the meantime, the progress state of this calibration is appropriately determined, and the alternative selection of the PD/PID control unit 49 or the PI control unit 50 is appropriately performed. I can do it.
　以上、本発明の実施の形態について説明したが、本発明は上記実施の形態に限定されるものではなく、特許請求の範囲に記載された本発明を逸脱することなく種々の設計変更を行うことが可能である。 Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various design changes can be made without departing from the scope of the invention described in the claims. is possible.
　例えば、上述の実施の形態では、データマップ及び第１、第２ルックアップテーブルの複数の第１目盛値Ｇ１、及び、第１、第２、第３、第４温度ｔ１、ｔ２、ｔ３、ｔ４にそれぞれ第１較正倍率値Ｃ１を乗じる（式（６ａ）、式（６ｂ））ことにより較正するものであったが、本発明はこれに限定されない。例えば、温度値に上記第１較正倍率値Ｃ１の逆数を乗じる構成であってもデータマップ及びルックアップテーブルを実質的に拡大又は縮小することが可能であり、このとき、記憶部３４に記憶されている複数の第１目盛値Ｇ１の較正前の値又は複数の第１～第４温度設定値をＴｋ（摂氏温度）、較正後の制御用第１目盛値または較正後の第１、第２、第３、第４温度ｔ１、ｔ２、ｔ３、ｔ４をＴｋｃａｌ、温度算出部２３からの温度値Ｔ又は代替温度準備部５４からの代替温度ＴｓｕｂをＴｅｍｐとした場合に、Ｔｋｃａｌ及び制御用の温度値Ｔｃｏｎ（摂氏温度）は、次式（６ｃ）により求めることができる。
　　Tkcal=Tk
　　Tcon=(Temp+TD+273.15)×(1/C1)-273.15　　　　　　　　（６ｃ） For example, in the embodiment described above, the plurality of first scale values G1 of the data map and the first and second lookup tables, and the first, second, third, and fourth temperatures t1, t2, t3, t4 Although the calibration is performed by multiplying each of the values by the first calibration magnification value C1 (Equation (6a) and Equation (6b)), the present invention is not limited to this. For example, even with a configuration in which the temperature value is multiplied by the reciprocal of the first calibration magnification value C1, it is possible to substantially enlarge or reduce the data map and lookup table, and at this time, the data map and the lookup table can be substantially enlarged or reduced. The pre-calibration values of the plurality of first scale values G1 or the plurality of first to fourth temperature setting values are Tk (degrees Celsius temperature), the first control scale values after calibration or the first and second temperature settings after calibration. , Tkcal is the third and fourth temperatures t1, t2, t3, and t4, and Temp is the temperature value T from the temperature calculation unit 23 or the alternative temperature Tsub from the alternative temperature preparation unit 54, Tkcal and the control temperature The value Tcon (temperature in degrees Celsius) can be determined by the following equation (6c).
Tkcal=Tk
Tcon=(Temp+TD+273.15)×(1/C1)-273.15 (6c)
　上述の式（６ｃ）を用いる構成であっても、実際に計測した電圧値（検出値）ＶＨＧｃｏｎの波高値がリッチ側及びリーン側閾値に合致する（波高の尖頭が閾値に重なる）ように較正して正確な空気過剰率を算出し、適切な空燃比フィードバック制御を行うことができる。 Even in the configuration using the above formula (6c), it is necessary to make sure that the peak value of the actually measured voltage value (detected value) VHGcon matches the rich side and lean side threshold values (the peak of the wave height overlaps the threshold value). It is possible to calibrate and calculate an accurate excess air ratio and perform appropriate air-fuel ratio feedback control.
　また、上述の実施の形態では、温度Ｔｃｏｎを設定するための基準値Ｔｒｅｆを、冷却水温センサ１７により得られるエンジン温度に吸気温センサ８により得られる吸気温度を加えて２で除する｛Ｔｒｅｆ＝（エンジン温度＋吸気温度）÷２｝ことにより設定しているが、これに限定されることなく、例えば、冷却水温センサ１７により得られるエンジン温度又は吸気温センサ８により得られる吸気温度のいずれか一方のみから温度Ｔｃｏｎを設定するための基準値Ｔｒｅｆを算出するようにしてもよい。 Further, in the embodiment described above, the reference value Tref for setting the temperature Tcon is calculated by adding the intake air temperature obtained by the intake air temperature sensor 8 to the engine temperature obtained by the cooling water temperature sensor 17 and dividing by 2 {Tref= (engine temperature + intake air temperature) ÷ 2}, but is not limited to this, for example, either the engine temperature obtained by the cooling water temperature sensor 17 or the intake air temperature obtained by the intake air temperature sensor 8. The reference value Tref for setting the temperature Tcon may be calculated from only one of them.
　１…機関本体、２…吸気管、３…スロットル弁、４…エアクリーナ、５…スロットルセンサ、６…燃料噴射弁、７…吸気圧センサ、８…吸気温センサ、９…ピストン、１０…排気管、１１…触媒、１２…酸素センサ、１２ａ…センサ素子（検出部）、１２ｂ…センサヒータ、１３…点火プラグ、１４…点火装置、１５…ＥＣＵ（電子制御ユニット）、１７…冷却水温センサ、１８…クランク軸、１９…クランク角度センサ、１９ａ…ロータ、１９ｂ…ピックアップ、２０…大気圧センサ、２２…ヒータ制御器、２３…温度算出部、２４…電圧算出部、２５…過剰率算出部、２６…代替値演算部、２７…回転速度演算部、２８…目標値演算部、２９…基本噴射量演算部、３０…フィードバック係数演算部、３１…噴射量演算部、３２…トルク演算部、３３…限界閾値設定部、３４…記憶部、３５～３８、３５ｂ、３６ｂ、３５ｃ、３６ｃ、３５ｄ、３６ｄ、３５ｅ、３６ｅ…グラフ、４０…特性点検部、４１…較正部、４２…温度差確認部、４３…電圧差確認部、４４…電圧波形、４５…空燃比波形、４６…リッチ側尖頭、４７…リーン側尖頭、４６ｖ、４７ｖ…尖頭値、４８…フィードバック制御部、４９…ＰＤ・ＰＩＤ制御部、５０…ＰＩ制御部、５１…制御部選択部、５２…温度閾値設定部、５３…活性判断部、５４…代替温度準備部、５５…第３ルックアップテーブル、５６…～第４ルックアップテーブル、５８…グラフ、５９…故障時ＰＩ制御部、６１…較正リセット部、６２…オンボード診断部。 1... Engine body, 2... Intake pipe, 3... Throttle valve, 4... Air cleaner, 5... Throttle sensor, 6... Fuel injection valve, 7... Intake pressure sensor, 8... Intake temperature sensor, 9... Piston, 10... Exhaust pipe , 11... Catalyst, 12... Oxygen sensor, 12a... Sensor element (detection section), 12b... Sensor heater, 13... Spark plug, 14... Ignition device, 15... ECU (electronic control unit), 17... Cooling water temperature sensor, 18 ...Crankshaft, 19...Crank angle sensor, 19a...Rotor, 19b...Pickup, 20...Atmospheric pressure sensor, 22...Heater controller, 23...Temperature calculation section, 24...Voltage calculation section, 25...Excess rate calculation section, 26 ...Alternative value calculation section, 27...Rotational speed calculation section, 28...Target value calculation section, 29...Basic injection amount calculation section, 30...Feedback coefficient calculation section, 31...Injection amount calculation section, 32...Torque calculation section, 33... Limit threshold setting section, 34... Storage section, 35 to 38, 35b, 36b, 35c, 36c, 35d, 36d, 35e, 36e... Graph, 40... Characteristic inspection section, 41... Calibration section, 42... Temperature difference confirmation section, 43...Voltage difference confirmation unit, 44...Voltage waveform, 45...Air-fuel ratio waveform, 46...Rich side peak, 47...Lean side peak, 46v, 47v...Peak value, 48...Feedback control unit, 49...PD・PID control unit, 50...PI control unit, 51...Control unit selection unit, 52...Temperature threshold setting unit, 53...Activity determination unit, 54...Alternative temperature preparation unit, 55...Third lookup table, 56...-Fourth Lookup table, 58... Graph, 59... PI control unit at the time of failure, 61... Calibration reset unit, 62... On-board diagnostic unit.

Claims (6)

  1. 　排気脈動を有する内燃機関の排気に接するように設けられる検出部と、該検出部に隣接するヒータ部とを有する抵抗型酸素センサを備える内燃機関の空燃比制御装置であって、
    　前記内燃機関の作動状態に基づき空気過剰率に係る制御目標値を設定する目標値設定部と、
    　前記ヒータ部の抵抗値に基づいて前記検出部の温度を求める検出部温度推定部と、
    　前記検出部の抵抗値を読み取って該検出部の検出値を求める検出値読取部と、
    　前記検出値及び前記検出部の温度から前記空気過剰率を算出する過剰率算出部と、
    　前記空気過剰率と前記制御目標値との偏差を求め、該偏差及び該偏差の微分、又は該偏差、該偏差の積分及び該偏差の微分を要素として前記空気過剰率をフィードバック制御するＰＤ・ＰＩＤ制御部と、
    　前記空気過剰率と前記制御目標値との偏差及び該偏差の積分を要素として前記空気過剰率をフィードバック制御するＰＩ制御部と、
    　前記フィードバック制御に、前記ＰＩ制御部又は前記ＰＤ・ＰＩＤ制御部のいずれを使用するかを選択する制御部選択部と、
    　前記検出値及び前記検出部の温度が各所定の特性に該当するか否かを点検する特性点検部と、
    　前記検出部温度推定部及び前記検出値読取部を、前記点検に基づいてそれぞれ較正する較正部とを備え、
    　前記制御部選択部は、前記特性点検部における前記検出値及び前記検出部の温度の点検結果に応じて、前記ＰＤ・ＰＩＤ制御部又は前記ＰＩ制御部の択一的選択を実行し得るよう構成されることを特徴とする空燃比制御装置。     An air-fuel ratio control device for an internal combustion engine, comprising a resistance-type oxygen sensor having a detection section provided in contact with exhaust gas of an internal combustion engine having exhaust pulsation, and a heater section adjacent to the detection section,
    a target value setting unit that sets a control target value related to an excess air ratio based on the operating state of the internal combustion engine;
    a detection unit temperature estimation unit that calculates the temperature of the detection unit based on the resistance value of the heater unit;
    a detected value reading unit that reads a resistance value of the detection unit to obtain a detection value of the detection unit;
    an excess rate calculation unit that calculates the excess air rate from the detected value and the temperature of the detection unit;
    A PD/PID that calculates a deviation between the excess air ratio and the control target value, and performs feedback control of the excess air ratio using the deviation and the derivative of the deviation, or the deviation, the integral of the deviation, and the derivative of the deviation as elements. a control unit;
    a PI control unit that performs feedback control of the excess air ratio using a deviation between the excess air ratio and the control target value and an integral of the deviation as elements;
    a control unit selection unit that selects which of the PI control unit or the PD/PID control unit to use for the feedback control;
    a characteristic checking unit that checks whether the detected value and the temperature of the detection unit correspond to each predetermined characteristic;
    a calibration unit that calibrates the detection unit temperature estimation unit and the detected value reading unit, respectively, based on the inspection;
    The control section selection section is configured to be able to perform alternative selection of the PD/PID control section or the PI control section according to the detection value in the characteristic inspection section and the inspection result of the temperature of the detection section. An air-fuel ratio control device characterized by:
  2. 　前記較正部は、前記内燃機関の排気脈動による前記検出値の波高の尖頭値がリッチ領域、ストイキ領域又はリーン領域の何れの空燃比領域に該当するかを判別するためのリーン側閾値及びリッチ側閾値のそれぞれを前記検出部の温度に係る第１目盛値及び前記検出値に係る第２目盛値にそれぞれ対応付けたデータマップと、前記尖頭値との対比に基づいて前記データマップにおける前記対応付けに関する前記第１目盛値及び前記第２目盛値とを各較正するように構成されており、
    　前記特性点検部は、前記尖頭値を前記リーン側閾値又は前記リッチ側閾値の少なくとも一方側と比較することによって前記較正の進捗状態を判定することを特徴とする請求項１に記載の空燃比制御装置。     The calibration unit includes a lean-side threshold value and a rich-side threshold value for determining which air-fuel ratio region of a rich region, a stoichiometric region, or a lean region the peak value of the wave height of the detected value due to exhaust pulsation of the internal combustion engine corresponds to. A data map in which each of the side threshold values is associated with a first scale value related to the temperature of the detection unit and a second scale value related to the detected value, respectively, and the peak value in the data map. The first scale value and the second scale value regarding the correspondence are each calibrated,
    The air-fuel ratio according to claim 1, wherein the characteristic inspection unit determines the progress state of the calibration by comparing the peak value with at least one of the lean side threshold value and the rich side threshold value. Control device.
  3. 　前記データマップにおける前記対応付けを初期化する初期化指令を発行可能に構成された較正リセット部を備え、
    　前記制御部選択部は、前記較正リセット部からの初期化指令を受けた場合、それ以降の予め定められた期間、前記ＰＩ制御部を選択するように構成されることを特徴とする請求項２に記載の空燃比制御装置。     comprising a calibration reset unit configured to be able to issue an initialization command to initialize the correspondence in the data map;
    2. The control unit selection unit is configured to select the PI control unit for a predetermined period after receiving an initialization command from the calibration reset unit. The air-fuel ratio control device described in .
  4. 　前記抵抗型酸素センサの検出部又は前記ヒータ部の異常乃至故障の診断を実行可能に構成されたオンボード診断部を有し、
    　前記制御部選択部は、前記オンボード診断部において前記抵抗型酸素センサの検出部又は前記ヒータ部が異常であると判定された場合には、前記ＰＩ制御部を選択するように構成されることを特徴とする請求項２に記載の空燃比制御装置。     an on-board diagnostic unit configured to be capable of diagnosing an abnormality or failure of the detection unit or the heater unit of the resistance-type oxygen sensor;
    The control unit selection unit may be configured to select the PI control unit when the on-board diagnosis unit determines that the detection unit of the resistive oxygen sensor or the heater unit is abnormal. The air-fuel ratio control device according to claim 2, characterized in that:
  5. 　前記較正部は、前記オンボード診断部において前記抵抗型酸素センサの検出部又は前記ヒータ部が異常であると判定された場合には、前記較正に係る制御を一時的に中断するように構成されることを特徴とする請求項４に記載の空燃比制御装置。 The calibration unit is configured to temporarily interrupt the control related to the calibration when the on-board diagnosis unit determines that the detection unit or the heater unit of the resistance-type oxygen sensor is abnormal. 5. The air-fuel ratio control device according to claim 4.
  6. 　前記制御部選択部は、前記オンボード診断部により前記抵抗型酸素センサの検出部又は前記ヒータ部の異常が検出された後に該異常の検出が解除されたとき、前記中断した前記較正部の前記較正に係る制御を再開するとともに、該再開以降の予め定められた期間において前記ＰＩ制御部を選択するように構成されることを特徴とする請求項５に記載の空燃比制御装置。
     
          The control section selection section is configured to select the control section of the interrupted calibration section when the on-board diagnostic section detects an abnormality in the detection section or the heater section of the resistance-type oxygen sensor and then cancels the detection of the abnormality. The air-fuel ratio control device according to claim 5, wherein the air-fuel ratio control device is configured to restart control related to calibration and select the PI control section in a predetermined period after the restart.
PCT/JP2022/014124 2022-03-24 2022-03-24 Air-fuel ratio control device WO2023181292A1 (en)

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JPH07127502A (en) * 1993-11-05 1995-05-16 Nippondenso Co Ltd Air-fuel ratio controller for internal combustion engine
JPH08338289A (en) * 1995-06-09 1996-12-24 Honda Motor Co Ltd Air-fuel ratio control device
JPH09291843A (en) * 1996-02-28 1997-11-11 Toyota Motor Corp Air-fuel ratio controller for internal combustion engine
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JP2013142683A (en) * 2012-01-13 2013-07-22 Ngk Spark Plug Co Ltd Gas sensor processing device

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07127502A (en) * 1993-11-05 1995-05-16 Nippondenso Co Ltd Air-fuel ratio controller for internal combustion engine
JPH08338289A (en) * 1995-06-09 1996-12-24 Honda Motor Co Ltd Air-fuel ratio control device
JPH09291843A (en) * 1996-02-28 1997-11-11 Toyota Motor Corp Air-fuel ratio controller for internal combustion engine
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