WE CLAIM:
1. An air-fuel ratio control device for an internal-combustion engine equipped with
a resistive oxygen sensor having a detection unit provided in contact with exhaust of an
5 internal-combustion engine having exhaust pulsation, and a heater unit adjacent to the
detection unit, the air-fuel ratio control device comprising:
a desired value setting unit that sets a desired control value related to an excess
air ratio based on an operating state of the internal-combustion engine;
a detection unit temperature estimation unit that determines a temperature of the
10 detection unit based on a resistance value of the heater unit;
a detection value reading unit that determines a detection value of the detection
unit by reading a resistance value of the detection unit;
an excess ratio calculation unit that calculates the excess air ratio from the
detection value and the temperature of the detection unit;
15 a PD/PID control unit that determines a difference between the excess air ratio
and the desired control value to perform feedback control of the excess air ratio by using,
as factors, the difference and a differential of the difference, or the difference, an integral
of the difference and a differential of the difference;
a PI control unit that performs feedback control of the excess air ratio by using,
20 as factors, a difference between the excess air ratio and the desired control value and an
integral of the difference;
a control unit selection unit that selects the PI control unit or the PD/PID control
unit to be used for the feedback control;
a characteristic inspection unit that inspects whether the detection value and the
25 temperature of the detection unit correspond to predetermined characteristics; and
a calibration unit that calibrates the detection unit temperature estimation unit and
the detection value reading unit based on the inspection,
wherein the control unit selection unit is configured to be capable of alternatively
selecting the PD/PID control unit or the PI control unit according to an inspection result of
30 the detection value and the temperature of the detection unit in the characteristic inspection unit,
the calibration unit is configured to calibrate a first graduation value and a second
graduation value for association in a data map based on comparison between the data map,
which associates a lean-side threshold value and a rich-side threshold value for determining
5 correspondence of a peak value of a wave height of the detection value due to exhaust
pulsation of the internal-combustion engine to an air-fuel ratio region of a rich region, a
stoichiometric region, or a lean region with the first graduation value related to a
temperature of the detection unit and the second graduation value related to the detection
value, respectively, and the peak value, and
10 the characteristic inspection unit determines a progress state of the calibration by
comparing the peak value with at least one of the lean-side threshold value and the richside threshold value.
2. The air-fuel ratio control device according to claim 1, comprising:
15 a calibration reset unit configured to be capable of issuing an initialization
command for initializing the association in the data map,
wherein the control unit selection unit is configured to select, in a case where an
initialization command is received from the calibration reset unit, the PI control unit for a
predetermined period of time thereafter.
20
3. The air-fuel ratio control device according to claim 1, comprising:
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 resistive oxygen
sensor,
25 wherein the control unit selection unit is configured to select the PI control unit
in a case where the on-board diagnostic unit determines that the detection unit or the heater
unit of the resistive oxygen sensor is abnormal.
4. The air-fuel ratio control device according to claim 4, wherein the calibration
30 unit is configured to temporarily interrupt control related to the calibration in a case where
the on-board diagnostic unit determines that the detection unit or the heater unit of the
resistive oxygen sensor is abnormal.
5. The air-fuel ratio control device according to claim 5, wherein the control unit
5 selection unit is configured to resume control related to the interrupted calibration of the
calibration unit, and selects the PI control unit in a predetermined period of time after the
resumption in a case where the abnormality detection is cleared after the abnormality of
the detection unit or the heater unit of the resistive oxygen sensor is detected by the onboard diagnostic unit.