Engine error detection system
A variety of methods and arrangements for detecting misfire and other engine-related errors are described. In one aspect, a window is assigned to a target firing opportunity for a target working chamber. There is an attempt to fire a target working chamber during the target firing opportunity. A change in an engine parameter (e.g., crankshaft angular acceleration) is measured during the window. A model (e.g., a pressure model) is used to help determine an expected change in the engine parameter during the target firing opportunity. Based on a comparison of the expected change and the measured change in the engine parameter, a determination is made as to whether an engine error (e.g., misfire) has occurred.
1. A method for detecting misfire in an engine, the engine having a plurality of working chambers and being operated in a skip fire manner, the method comprising:
assigning a window to a target firing opportunity;
attempting to fire a target working chamber during the target firing opportunity;
measuring a change in an engine parameter during the target firing opportunity;
using a multi-cylinder pressure model to help determine an expected change in the engine parameter during the target firing opportunity wherein the pressure model involves estimating pressure in a skipped working chamber, wherein the determination of the expected change in the engine parameter accounts for torque added or subtracted from the powertrain by an auxiliary power source;
based on a comparison between the expected change and the measured change, determining whether the target working chamber misfired.
2. A method as recited in claim 1 wherein the engine parameter is crankshaft acceleration.
3. A method as recited in claim 1 wherein the multi-cylinder pressure model involves modeling pressure within each working chamber during a time period between intake valve closure and exhaust valve opening of the target firing opportunity.
4. A method as recited in claim 1 wherein the pressure model takes into account at least one selected from the group consisting of a rise of temperature in a working chamber due to combustion, fuel mass used to fuel combustion, energy conversion efficiency, ignition timing, residual fraction, leakage rate, fuel properties such as heating value, and total mass of mixture in a working chamber.
5. A method as recited in claim 1 further comprising using the pressure model to determine an expected torque generated by the working chambers of the engine during the target firing opportunity.
6. A method as recited in claim 1 wherein the determination of the misfire is based at least in part on A, B and A′ wherein A is the expected change in the engine parameter based on the model, A′ is one of an expected change in the engine parameter based on mass air charge and a low-pass filtered mean of A and B is the measured change in the engine parameter.
7. A method as recited in claim 1 further comprising:
detecting a first offset between the estimated expected change and the measured change in the engine parameter;
adjusting the pressure model based on the first offset; and
repeating the pressure model usage and measurement operations, thereby providing a second expected change and a second measured change in the engine parameter wherein a second offset between the second expected change and the second measured change is reduced relative to the first offset as a result of the model adjustment.
8. A method as recited in claim 1 wherein the auxiliary power source is an electric motor/generator.
9. A misfire detection system for determining whether a particular working chamber in an engine has misfired, the engine being operated in a skip fire manner, the misfire detection system comprising:
an engine parameter measurement module that is arranged to:
assign a window to a target firing opportunity; and
measure a change in an engine parameter during the target firing opportunity; and
a misfire detection module that is arranged to:
use a pressure model to help determine an expected change in the engine parameter during the target firing opportunity wherein the pressure model involves estimating pressure in a skipped working chamber, wherein the determination of the expected change in the engine parameter accounts for torque added or subtracted from the powertrain by an auxiliary power source; and
determine whether the target working chamber misfired based on a comparison between the expected change and the measured change.
10. A misfire detection system as recited in claim 9 wherein the engine parameter is crankshaft acceleration.
11. A misfire detection system as recited in claim 9 wherein the pressure model involves modeling pressure within a working chamber during a time period between intake valve closure and exhaust valve opening.
12. A misfire detection system as recited in claim 9 wherein the multi-cylinder pressure model takes into account at least one selected from the group consisting of a rise of temperature in a working chamber due to combustion, fuel mass used to fuel combustion, energy conversion efficiency, ignition timing, residual fraction, leakage rate, fuel properties such as heating value, and total mass of mixture in a working chamber.
13. A misfire detection system as recited in claim 9 wherein the misfire detection module is further arranged to determine an expected torque generated by the working chambers of the engine during the firing opportunity.
14. A misfire detection system as recited in claim 9 wherein the misfire determination is based at least in part on A, B and A′ wherein A is the expected change in the engine parameter based on the model, A′ is one of a low-pass filtered mean of A and an expected change in the engine parameter based on mass air charge, and B is the measured change in the engine parameter.
15. A misfire detection system as recited in claim 9 wherein the misfire detection module is further arranged to:
detect a first offset between the estimated expected change and the measured change in the engine parameter;
adjust the pressure model based on the first offset; and
repeat the pressure model usage and measurement operations, thereby providing a second expected change and a second measured change in the engine parameter wherein a second offset between the second expected change and the second measured change is reduced relative to the first offset as a result of the model adjustment.
16. A misfire detection system as recited in claim 9 wherein the auxiliary power source is an electric motor/generator.
17. A method for detecting misfire in an engine, the engine having a plurality of working chambers and being operated in a dynamic firing level modulation manner, the method comprising:
assigning a window to a target firing opportunity;
attempting to fire a target working chamber during the target firing opportunity;
measuring a change in an engine parameter during the target firing opportunity;
using a multi-cylinder pressure model to help determine an expected change in the engine parameter during the target firing opportunity wherein the pressure model involves estimating pressure in a skipped working chamber; and
based on a comparison between the expected change and the measured change, determining whether the target working chamber misfired.
18. A method as recited in claim 17 wherein a cam actuated intake valve controls air induction into a cylinder, the cam having a cam profile, and the multi-cylinder pressure model uses different inputs for different cylinders depending on the cam profile.
19. A method as recited in claim 17 wherein the model of the expected change in the engine parameter during the target firing opportunity accounts for torque added to or subtracted from the powertrain by an auxiliary power source.
20. A method as recited in claim 17 wherein the method is performed during dynamic multi-charge level operation of the engine.
21. A method as recited in claim 17 wherein the method is performed during multi-level skip fire operation of the engine.
22. A misfire detection system for determining whether a particular working chamber in an engine has misfired, the engine being operated in a dynamic firing level modulation manner, the misfire detection system comprising:
an engine parameter measurement module that is arranged to:
assign a window to a target firing opportunity; and
measure a change in an engine parameter during the target firing opportunity; and
a misfire detection module that is arranged to:
use a pressure model to help determine an expected change in the engine parameter during the target firing opportunity wherein the pressure model involves estimating pressure in a skipped working chamber; and
determine whether the target working chamber misfired based on a comparison between the expected change and the measured change.
23. A misfire detection system as recited in claim 22 wherein a cam actuated intake valve controls air induction into a cylinder, the cam having a cam profile, and the multi-cylinder pressure model uses different inputs for different cylinders depending on the cam profile.
24. A misfire detection system as recited in claim 22 wherein the model of the expected change in the engine parameter during the target firing opportunity accounts for torque added to or subtracted from the powertrain by an auxiliary power source.
25. A misfire detection system as recited in claim 22 arranged to detect misfires during multi-charge level operation of the engine.
26. A misfire detection system as recited in claim 22 arranged to detect misfires during multi-level skip fire operation of the engine.