Method and processing system of sensed ionization current data for real time estimation of combustion chamber pressure in a spark ignition engine

Patent metadata

Field	Value
Publication number	US-9752548-B2
Application number	US-201414272980-A
Country	US
Kind code	B2
Filing date	May 8, 2014
Priority date	May 9, 2013
Publication date	Sep 5, 2017
Grant date	Sep 5, 2017

Abstract

The pressure in the combustion chamber of an electronically controlled spark plug ignition engine may be estimated in real time mode without specific sensors by processing sensed ionization current data to calculate features of the current waveform proven to be correlated to the pressure inside the engine cylinders and correlating them on the basis of a look up table of time invariant correlation coefficients generated through a calibration campaign of tests on a test engine purposely equipped with sensors. A mathematical model of the electrical and physical spark plug ignition system and combustion chamber of the engine is refined during calibration by iteratively testing the interactive performance of correlation coefficients of related terms of a mathematical expression of the model and comparing the expressed pressure value with the real pressure value as measured by a sensor.

First claim

What is claimed is:

1. A method of real-time evaluation of at least pressure in a combustion chamber of an electronically controlled spark plug ignition engine by sensing an ionization current flowing through a spark plug, the method comprising:
refining a mathematical model of the electronically controlled spark plug ignition engine and the combustion chamber through a calibration campaign of tests conducted on a test engine equipped with specific sensors of combustion chamber pressure, and a first engine parameter by iteratively testing interactive performance of correlation coefficients of related terms of a mathematical expression of the mathematical model and comparing an estimated pressure value generated by the mathematical model with a pressure value as measured by a sensor;
storing in a matrix or look-up table a set of time invariant correlation coefficients of the terms when a residual mismatch between the estimated pressure value generated by the mathematical model compared with the measured value remains within a maximum spread; and
sensing the ionization current in the electronically controlled spark plug ignition engine when the electronically controlled spark plug ignition engine is running, measuring or calculating at least one or more significant features of a waveform of the sensed ionization current and processing the at least one or more significant features of the waveform together with the matrix or look-up table and with a set of actual values of parameters of the electronically controlled spark plug ignition engine when the electronically controlled spark plug ignition engine is running for producing an evaluated value of the combustion chamber pressure.

2. The method of claim 1 , wherein the one or more significant features of the waveform of the sensed ionization current comprise one or more features selected from the group consisting of:
a time delay of a beginning of an oscillatory decay phase of the ionization current from an electronically controlled generation of a trigger signal of a spark plug discharge,
a calculated amplitude of a first ringing frequency peak in a frequency domain,
a calculated asymptotic current value,
a calculated amplitude of resonance peaks or envelope function, and
a time width of current peaks of the oscillatory decay phase of the ionization current.

3. The method of claim 2 , wherein the one or more significant features of the waveform of the sensed ionization current comprises a time delay of a beginning of an oscillatory decay phase of the ionization current subsequent to a trigger signal of a spark plug discharge, the method further comprising
defining a length of a data acquisition time interval following the time delay, wherein the measuring or calculating the at least one or more significant features of the waveform of the sensed ionization current comprises measuring the ionization current during the length of the data acquisition time interval.

4. The method of claim 1 , further comprising:
processing acquired data of the ionization current over a programmable data acquisition time interval for outputting instantaneous values of the at least one or more significant features of the waveform;
averaging over a given number of engine cycles the measured or calculated at least one or more significant features of the waveform for selectively outputting the instantaneous or the averaged values of the at least one or more significant features of the waveform to produce continuously updated vectors of values of the at least one or more significant features of the waveform for the given number of engine cycles; and
feeding the selected instantaneous or averaged values of the at least one or more significant features of the waveform together with the set of time invariant correlation coefficients of the matrix or look-up table and with the set of actual values of parameters of the electronically controlled spark plug ignition engine when the electronically controlled spark plug ignition engine is running to a correlator embedding the mathematical model of the electronically controlled spark plug ignition engine and combustion chamber for generating on respective outputs correspondingly evaluated instantaneous and averaged values of the combustion chamber pressure.

5. The method of claim 1 , wherein one or more spark discharges are commanded after ignition has taken place for gathering multiple estimated instantaneous values of pressure in the combustion chamber over a complete ignition-flame propagation-full combustion-exhaust process.

6. The method of claim 1 , wherein the first engine parameter comprises
ambient temperature; or
air/fuel ratio or correspondent throttle.

7. The method of claim 2 , wherein calculating the amplitude of the first ringing frequency peak comprises calculating a Fast Fourier Transform (FFT) of the sensed ionization current.

8. A method comprising:
refining a mathematical model of a spark plug ignition system, the mathematical model comprising a set of time-invariant coefficients, wherein refining the mathematical model comprises:
monitoring an ionization current of a test engine,
monitoring a pressure of a combustion chamber of the test engine by measuring a pressure sensor,
generating the set of time-invariant coefficients based on the monitored ionization current of the test engine and the monitored pressure of the combustion chamber of the test engine,
estimating a pressure of the combustion chamber of the test engine based on the generated set of time-invariant coefficients,
comparing the estimated pressure of the combustion chamber of the test engine with the measured pressure of the combustion chamber of the test engine,
regenerating the set of time-invariant coefficients when a residual mismatch between the estimated pressure of the combustion chamber of the test engine and the measured pressure of the combustion chamber of the test engine is higher than a predetermined threshold, and
storing the set of time-invariant coefficients when the residual mismatch between the estimated pressure of the combustion chamber of the test engine and the measured pressure of the combustion chamber of the test engine is lower than the predetermined threshold; and

applying the mathematical model to a running engine to obtain real-time estimated values of pressure of a combustion chamber of the running engine, wherein the applying the mathematical model comprises
monitoring an ionization current of the running engine, and
estimating a pressure of the combustion chamber of the running engine based on the monitored ionization current of the running engine and the mathematical model.

9. The method of claim 8 , wherein
monitoring the ionization current of the running engine comprises determining a time delay between an ignition trigger signal and a beginning of an oscillatory decay phase of the monitored ionization current of the running engine; and
the estimating the pressure of the combustion chamber of the running engine is further based on the determined time delay.

10. The method of claim 9 , wherein monitoring the ionization current of the running engine further comprises blanking a data-acquisition process during the time delay.

11. The method of claim 8 , wherein
monitoring the ionization current of the running engine comprises determining an amplitude of a first harmonic peak of a decaying oscillatory phase of the ionization current of the running engine; and
the estimating the pressure of the combustion chamber of the running engine is further based on the amplitude of the first harmonic peak.

12. The method of claim 11 , wherein the determining the amplitude of the

Assignees

• St Microelectronics Srl

Inventors

• Patti Davidegiuseppe
• Paparo Mario

Classifications

• F02D35/024

  using an estimation · CPC title

• F02D35/021

  using an ionic current sensor · CPC title

• F02D41/2422

  Selective use of one or more tables · CPC title

• F02P17/12 Primary

  Testing characteristics of the spark, ignition voltage or current (testing of sparking plugs H01T13/60) · CPC title

• G01M15/09

  by monitoring pressure in fluid ducts, e.g. in lubrication or cooling parts · CPC title