Method and system for detecting the misfire of a reciprocating internal combustion engine utilizing a misfire index model

• US 5,576,963 A
• Filed: 10/18/1994
• Issued: 11/19/1996
• Est. Priority Date: 10/18/1994
• Status: Expired due to Fees

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Ribbens, William B., Park, Jaehong
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): LOUIS JACQUES, JACQUES H
• Application Number:
  US08/324,596
• Time in Patent Office: 763 Days
• Field of Search: 364/431.08, 364/431.03, 364/431.01, 364/578, 364/431.04, 364/431.07, 123/416, 123/417, 123/420, 123/425, 123/479, 123/436, 123/419, 123/491, 73/117.3, 73/116, 73/112, 324/379
• US Class Current: 701/111
• CPC Class Codes: G01M 15/11 by detecting misfire

Abstract

A misfire index model-based method and system for detecting misfire in a reciprocating internal combustion engine having an engine cycle frequency in the frequency domain from crankshaft angular velocity. The misfire index model is a function of engine operating condition such as engine load and RPM. Crankshaft angular position is sensed to develop an electrical signal which is a function of the crankshaft angular velocity. The electrical signal contains data which is sampled. The sampled data is transformed to an equivalent frequency domain spectrum including frequency components of the engine cycle frequency and harmonics thereof. A load signal such as mass airflow and an RPM signal are generated. The magnitudes and/or phases of the frequency components and the load and RPM signals are supplied to the misfire index model in an appropriately programmed computer to distinguish between a true misfire and normal cyclic variability which characterizes the combustion process.

Claims

1. A method for detecting the misfire of a reciprocating internal combustion engine with a misfire index model which is a function of engine operating condition, the engine including a plurality of reciprocating components having an engine cycle frequency, at least one cylinder and a crankshaft, the method comprising the steps of:

generating an electrical signal as a function of crankshaft angular velocity, the electrical signal containing data;

sampling the data synchronously with crankshaft angular position at a sampling rate to obtain sampled data;

transforming the sampled data to an equivalent frequency domain spectrum, including frequency components having complex amplitudes at the engine cycle frequency and harmonics thereof;

forming a misfire index based on the complex amplitudes; and

applying a threshold algorithm to the misfire index, which threshold algorithm distinguishes between a true misfire and normal cyclic variability which characterizes the combustion process in each cylinder of the engine to thereby obtain a misfire signal, the step of applying including the step of applying the misfire index to the misfire index model to identify the misfire.

2. The method of claim 1 wherein the threshold algorithm is a mathematical function of engine operating condition.

3. The method of claim 2 wherein the threshold algorithm has mass air flow to the engine and engine RPM as independent variables.

4. The method of claim 1 wherein the frequency components have magnitudes and phases and wherein the magnitudes and phases of the frequency components are applied to the misfire index model to identify the misfire.

5. The method of claim 1 wherein the step of forming includes the step of determining the magnitudes of the complex amplitudes and wherein the step of applying the misfire index includes the step of comparing the magnitudes of the complex amplitudes to an adaptive threshold level.

6. The method of claim 1 wherein the misfire index model includes a combination of two functions which establish an adaptive threshold level and wherein the step of applying the misfire index includes the step of comparing the magnitudes of the complex amplitudes to the adaptive threshold level.

7. The method of claim 6 wherein the adaptive threshold level is a function of at least one engine operating condition.

8. The method of claim 1 further comprising the step of generating a load signal based on engine load, wherein the at least one operating condition includes engine load.

9. The method of claim 8 wherein the load signal is based on mass airflow to the engine.

10. The method of claim 8 wherein the engine has a manifold and wherein the load signal is based on manifold pressure.

11. The method of claim 8 wherein the adaptive threshold level is the function of engine RPM and further comprising the step of generating an RPM signal based on the speed of the engine.

12. The method of claim 8 wherein the operating conditions further include engine manifold absolute pressure.

13. The method of claim 8 wherein the operating conditions further include engine throttle angle position.

14. A system for detecting the misfire of a reciprocating internal combustion engine including a plurality of reciprocating components having an engine cycle frequency, at least one cylinder and a crankshaft, the system comprising:

means for generating an electrical signal as a function of crankshaft angular velocity, the electrical signal containing data;

means for sampling the data synchronously with crankshaft angular position at a sampling rate to obtain sampled data;

means for transforming the sampled data to an equivalent frequency domain spectrum, including frequency components having complex amplitudes at the engine cycle frequency;

means for forming a misfire index based on the complex amplitudes; and

means for applying a threshold algorithm to the misfire index, which threshold algorithm distinguishes between a true misfire and normal cyclic variability which characterizes the combustion process in each cylinder of the engine to thereby obtain a misfire signal, the means for applying including a misfire index model for receiving the misfire index and generating an output signal to identify the misfire.

15. The system of claim 14 wherein the threshold algorithm is a mathematical function of engine operating condition.

16. The system of claim 15 wherein the threshold algorithm has mass air flow to the engine and engine RPM as independent variables.

17. The system of claim 14 wherein the frequency components have magnitudes and phases and wherein the magnitudes and phases of the frequency components are applied to the misfire index model to identify the misfire.

18. The system of claim 14 wherein the means for forming includes means for determining the magnitudes of the complex amplitudes and wherein the means for applying the misfire index includes means for comparing the magnitude of the complex amplitudes to an adaptive threshold level.

19. The system of claim 14 wherein the misfire index model includes a combination of two functions which establish an adaptive threshold level and wherein the means for applying the misfire index includes means for comparing the magnitudes of the complex amplitudes to the adaptive threshold level.

20. The system of claim 19 wherein the adaptive threshold level is a function of at least one engine operating condition.

21. The system of claim 14 further comprising the means for generating a load signal based on engine load, wherein the at least one operating condition includes engine load.

22. The system of claim 21 wherein the load signal is based on mass airflow to the engine.

23. The system of claim 21 wherein the engine has a manifold and wherein the load signal is based on manifold pressure.

24. The system of claim 21 wherein the adaptive threshold level is the function of engine RPM and further comprising means for generating an RPM signal based on the speed of the engine.

25. The system of claim 21 wherein the operating conditions further include engine manifold absolute pressure.

26. The system of claim 21 wherein the operating conditions further include engine throttle angle position.