Control device for internal combustion engine
A novel control device for an internal combustion engine capable of highly accurately estimating an EGR amount (rate) during the transient state is provided. A first EGR rate is determined using, as an input, a detection signal of an EGR sensor provided on the downstream side of a throttle valve which adjusts the flow rate of a mixed gas of air and EGR gas flowing through an intake pipe, a second EGR rate is estimated by calculating a predetermined equation using, as an input, at least a detection signal of an air flow sensor and an EGR valve opening degree sensor, a third EGR rate is determined by carrying out delay processing on the second EGR rate corresponding to a response delay of the EGR sensor, and the second EGR rate is subjected to learning correction by reflecting a difference between the third EGR rate and the first EGR rate.
1. A control device for an internal combustion engine, the internal combustion engine including:
an external EGR device with an EGR valve configured to recirculate exhaust gas from an exhaust system to an intake system of the internal combustion engine,
an air flow sensor provided in the intake system of the internal combustion engine and measuring an air flow rate of air taken into the internal combustion engine, and
an EGR sensor detecting an EGR rate of a mixed gas mixed with the exhaust gas,
the control device for the internal combustion engine comprising:
a processor configured to
estimate the EGR rate of the mixed gas according to at least the air flow sensor and the EGR sensor,
determine a first EGR rate using, as an input, a detection signal of the EGR sensor provided on a downstream side of a throttle valve which adjusts a flow rate of the mixed gas flowing through the intake system and a second detection signal of a sensor at an intake of the intake system,
calculate a second EGR rate, based on a predetermined equation using, as an input, one or more detection signals of at least the air flow sensor, an opening degree sensor of the EGR valve, and an opening degree sensor of the throttle valve,
carry out response delay processing by calculating a measurement response delay of the EGR sensor as a lag on the second EGR rate to determine a third EGR rate,
determine whether dew condensation is present in the intake system when an estimated water vapor partial pressure in the intake system becomes equal to or higher than a saturated water vapor pressure, and
when the dew condensation is not present, correct the second EGR rate based on a difference between the third EGR rate and the first EGR rate, and
when the dew condensation is present, correction of the second EGR rate is not executed, a partial pressure difference corresponding to the dew condensation is calculated and an EGR rate difference is calculated.
2. The control device for the internal combustion engine according to claim 1 , wherein
the EGR sensor is at least constituted by a mixed gas humidity sensor provided in the intake system and configured to detect humidity of the mixed gas.
3. The control device for the internal combustion engine according to claim 2 , wherein
the EGR sensor is constituted by an atmospheric humidity sensor provided in the intake system and configured to detect humidity of air in addition to the mixed gas humidity sensor.
4. The control device for the internal combustion engine according to claim 1 , wherein
the EGR sensor is constituted by an intake-side oxygen concentration sensor provided in the intake system and configured to detect an oxygen concentration of the mixed gas.
5. The control device for the internal combustion engine according to claim 1 , wherein
the processor calculates a physical model comprising a plurality of mathematical equations that simulate behavior of the mixed gas to calculate the second EGR rate.
6. The control device for the internal combustion engine according to claim 5 , wherein
the processor carries out the correction on the second EGR rate when the third EGR rate and the first EGR rate are deviated from each other by at least a predetermined value.
7. The control device for the internal combustion engine according to claim 6 , wherein
the correction by the processor is executed when an opening area of the EGR valve used in the physical model is corrected.
8. The control device for the internal combustion engine according to claim 7 , wherein
the correction by the processor decreases the opening area of the EGR valve when the third EGR rate is greater than the first EGR rate, and
the correction by the processor increases the opening area of the EGR valve when the third EGR rate is smaller than the first EGR rate.
9. The control device for the internal combustion engine according to claim 1 , wherein
the estimated water vapor partial pressure is calculated from a pressure and a temperature of the mixed gas in the intake system.
10. The control device for the internal combustion engine according to claim 1 , wherein
the processor decreases an opening area of the EGR valve and retards ignition timing of an ignition plug when it is determined that the dew condensation is present.