Misfire detection in internal combustion engines

• US 5,509,302 A
• Filed: 05/02/1994
• Issued: 04/23/1996
• Est. Priority Date: 05/02/1994
• Status: Expired due to Term

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: Saturn (CCL Industries Incorporated)
• Inventors: Drexel, Jeffrey R., Nitz, Larry T.
• Primary Examiner(s): Chilcot, Richard
• Assistant Examiner(s): MCCALL, ERIC SCOTT
• Application Number:
  US08/236,812
• Time in Patent Office: 722 Days
• Field of Search: 73/116, 73/117.3, 123/419, 123/436, 364/431.07, 364/431.08
• US Class Current: 73/114.05
• CPC Class Codes: G01M 15/11 by detecting misfire

Abstract

Internal combustion engine misfires are diagnosed through monitoring of change in engine speed wherein an acceleration spike index is generated for each cylinder event over a number of engine cycles in a test period and is corrected in accord with sensed part tolerancing, and wherein the corrected acceleration spike index is compared to at least one misfire threshold. For each engine cylinder, a degree of misfire severity is diagnosed at the end of the test period in accord with the frequency of excursions by the corresponding misfire index above the at least one misfire threshold.

Claims

1. A method for diagnosing misfires in an automotive internal combustion engine having an output shaft with a predetermined number of spaced reference points and a predetermined desired spacing between the predetermined number of spaced reference points, comprising the steps of:

sensing a rate of rotation between consecutive sets of the reference points on the output shaft;

sensing a magnitude of a transient rate of rotation characterized by a decrease in the rate of rotation followed by an increase in the rate of rotation;

estimating an actual spacing between the predetermined number of spaced reference points;

generating a spacing error as a difference between the desired spacing and the estimated actual spacing;

generating a transient condition correction value as a predetermined function of the spacing error;

adjusting the sensed magnitude of the transient rate of rotation in accord with the generated transient condition correction value;

comparing the adjusted sensed magnitude to a predetermined misfire threshold value; and

detecting an engine misfire when the adjusted sensed magnitude exceeds the misfire threshold value.

2. The method of claim 1, wherein the step of detecting an engine misfire further comprises the steps of:

attributing the sensed transient rate of rotation to a responsible cylinder a cylinder event of which significantly contributed to the sensed transient rate of rotation when the adjusted sensed magnitude exceeds the misfire threshold value;

adjusting a misfire counter corresponding to the responsible cylinder; and

indicating the detected misfire when the adjusted misfire counter exceeds a predetermined counter threshold value.

3. The method of claim 1, further comprising the steps of:

sensing engine speed;

sensing engine load; and

wherein at least a predetermined one of the group including the predetermined misfire threshold value and the predetermined counter threshold value is determined as a predetermined function of sensed engine speed and sensed engine load.

4. A method for diagnosing misfires in an automotive internal combustion engine over a test period including a predetermined number of engine cycles, wherein the engine has a plurality of cylinders and a corresponding plurality of misfire counters and the engine cycle is defined to include a combustion event for each of the plurality of cylinders, comprising the steps of:

for each of the predetermined number of engine cycles,

(a) for each of the plurality of cylinders, sensing the magnitude of an engine speed transient corresponding to the cylinder wherein the engine speed transient is characterized by an engine speed decrease in a first predetermined reference period followed by an engine speed increase in a second predetermined reference period following the first predetermined reference period;

(b) determining a largest sensed engine speed transient magnitude over the engine cycle;

(c) comparing the determined largest magnitude to a predetermined threshold value;

(d) identifying the cylinder corresponding to the determined largest magnitude when the determined largest magnitude exceeds the predetermined threshold value;

(e) adjusting the counter corresponding to the identified cylinder when the determined largest magnitude exceeds the predetermined threshold value;

upon completion of the test period, comparing each of the plurality of counters to a predetermined count threshold value; and

indicating a misfire in any of the plurality of cylinders having a corresponding counter that, upon completion of the test period, exceeds the predetermined count threshold value.

5. The method of claim 4, further comprising the steps of:

further, for each of the predetermined number of engine cycles,

(a) determining a second largest magnitude as a second largest sensed engine speed transient magnitude over the engine cycle;

(b) comparing the second largest magnitude to the predetermined threshold value;

(c) identifying the cylinder corresponding to the second largest magnitude when the second largest magnitude exceeds the predetermined threshold value; and

(d) adjusting the counter corresponding to the identified cylinder when the second largest magnitude exceeds the predetermined threshold value.

6. The method of claim 4, further comprising the steps of:

sensing engine speed;

sensing engine load;

and wherein at least a predetermined one of the group consisting of the predetermined threshold value and the predetermined count threshold value is determined as a predetermined function of engine speed and engine load.

7. A misfire detection method for an automotive internal combustion engine having a plurality of cylinders and having an output shaft with a predetermined number of spaced reference points about the shaft and with a predetermined desired spacing between the predetermined number of reference points about the shaft, comprising the steps of:

sensing engine speed;

sensing a deceleration magnitude as a magnitude of an engine speed decrease over a first reference period;

sensing an acceleration magnitude as a magnitude of an engine speed increase over a second reference period following the first reference period;

estimating an actual spacing between the predetermined number of spaced reference points about the shaft;

calculating a spacing error as a difference between the predetermined desired spacing and the estimated actual spacing;

determining an engine speed transient correction value as a predetermined function of the calculated spacing error;

generating an engine speed change value as a predetermined function of the sensed deceleration magnitude, the sensed acceleration magnitude and the calculated spacing error to correct the engine speed change value in accord with the calculated spacing error;

comparing the generated engine speed change value to a predetermined threshold value;

sensing occurrence of an engine speed transient when the engine speed change value exceeds the predetermined threshold value;

attributing the sensed engine speed transient to a responsible one of the plurality of cylinders, wherein a cylinder event of the responsible one contributed primarily to the occurrence of the engine speed transient;

adjusting a transient count value to indicate the sensed occurrence; and

detecting a misfire when the transient count value exceeds a predetermined count threshold value.