Engine Management

A little dental work, or what to do about missing teeth.

The more advanced timing wheels on motors have high tooth count and also throw in areas where teeth are deleted, in order to provide sub-timing to catch ignition in less than one full crank. It is my observation, this is overkill, because, the increase in processing needed for high level detection, often results in missing the special event, and it still requires multiple rotations to capture timing.  However, because they didn't listen to me, and implemented missing teeth anyway, coding must be made to mitigate the event.

There are two processes that must be implemented, first is detection of the missing tooth event. The second is compensating for the event.  Detecting the event requires notification of the potential for a missing event, so a calibration value of missing teeth is needed. Missing teeth is not the total number of missing teeth. It is the number of missing teeth together. Meaning it is possible to have a missing tooth at 10 degrees and a second at 100 degrees, even though in total, there are two missing teeth, the value of missing teeth in calibration is still one. I hope that is clear enough.

The detection of a missing tooth event, is; first, is there a missing tooth (missing > 0), and when the measured Diff value tmpDiff (current) is greater than 1.5 times the previous Diff (crkDiff). Because the change in crkDiff from tooth to tooth is relatively small, if the change in crkDiff is greater than 1.5 times, it is the indication of a missing tooth event. Once the missing tooth event has been detected, a correction to operating variables is required. First, update the cam angle, then correct for error, repeating once for each missing tooth. This operation is performed in the crank interrupt. Because it only requires comparison and addition, the impact is very slight.

    if (isInt0Low() ^ isCrkRising()) {
        tmOut = QUART_SEC;
/**************************************************************************************************
  use the cam signal to locate the tooth
**************************************************************************************************/
        if (isCamDet()) {
            setCamDet(false);                       /* cam detected so clear the flag */
            camAngle = 0;
            camError = 0;
        } else {
/**************************************************************************************************
        Because tooth angle may not be an even division, an error correction is performed
        at each update. If the error exceeds the threshold, the angle value is incremented,
        and the threshold value is removed from the error.
**************************************************************************************************/
            camAngle += toothAngle;
            camError += toothError; if (toothError >= teeth) { camAngle++; camError -= teeth; }
        }
/**************************************************************************************************
        Special case op for missing tooth, if no missing tooth, then skip this whole part.
        The detection of an event is both there is a missing tooth, and the DIFF is longer
        than 1.5 of the previous event DIFF.
**************************************************************************************************/
        if ((missing > 0) && (tmpDiff > (crkDiff + (crkDiff / 2)))) {
/**************************************************************************************************
        Missing tooth detected, so correct the angle for one missing tooth (at least)
**************************************************************************************************/
            camAngle += toothAngle; camError += toothEr; if (camError >= toothCt) { curAngl++; camError -= toothCt; }
/**************************************************************************************************
            If more missing teeth, correct again for each (math runs fast, so little or
            no impact)
**************************************************************************************************/
            if (missing > 1) { camAngle += toothAngle; camError += toothEr; if (camError >= toothCt) { curAngl++; camError -= toothCt; } }
            if (missing > 2) { camAngle += toothAngle; camError += toothEr; if (camError >= toothCt) { curAngl++; camError -= toothCt; } }
/**************************************************************************************************
            If there was a missing tooth the value of tmpDiff is extended, so replace
            tmpDiff with the old value of DIFF to prevent calculation problems.
**************************************************************************************************/
            tmpDiff = crkDiff;
        }
        crkTime = tmpTime;
        crkDiff = tmpDiff;

The value of "missing" is read from calibration at engine stop.

/* Calibration value in future, but for now just provide a constant */
SWord getCrankToothCt(void) { return 4; }
SWord getCrankToothMissing(void) { return 0; }

       missing = getCrankToothMissing();

TTFN,

Jack

A little dental work, or what to do about missing teeth.

The more advanced timing wheels on motors have high tooth count and also throw in areas where teeth are deleted, in order to provide sub-timing to catch ignition in less than one full crank. It is my observation, this is overkill, because, the increase in processing needed for high level detection, often results in missing the special event, and it still requires multiple rotations to capture timing.  However, because they didn't listen to me, and implemented missing teeth anyway, coding must be made to mitigate the event.

There are two processes that must be implemented, first is detection of the missing tooth event. The second is compensating for the event.  Detecting the event requires notification of the potential for a missing event, so a calibration value of missing teeth is needed. Missing teeth is not the total number of missing teeth. It is the number of missing teeth together. Meaning it is possible to have a missing tooth at 10 degrees and a second at 100 degrees, even though in total, there are two missing teeth, the value of missing teeth in calibration is still one. I hope that is clear enough.

The detection of a missing tooth event, is; first, is there a missing tooth (missing > 0), and when the measured Diff value tmpDiff (current) is greater than 1.5 times the previous Diff (crkDiff). Because the change in crkDiff from tooth to tooth is relatively small, if the change in crkDiff is greater than 1.5 times, it is the indication of a missing tooth event. Once the missing tooth event has been detected, a correction to operating variables is required. First, update the cam angle, then correct for error, repeating once for each missing tooth. This operation is performed in the crank interrupt. Because it only requires comparison and addition, the impact is very slight.

    if (isInt0Low() ^ isCrkRising()) {
        tmOut = QUART_SEC;
/**************************************************************************************************
  use the cam signal to locate the tooth
**************************************************************************************************/
        if (isCamDet()) {
            setCamDet(false);                       /* cam detected so clear the flag */
            camAngle = 0;
            camError = 0;
        } else {
/**************************************************************************************************
        Because tooth angle may not be an even division, an error correction is performed
        at each update. If the error exceeds the threshold, the angle value is incremented,
        and the threshold value is removed from the error.
**************************************************************************************************/
            camAngle += toothAngle;
            camError += toothError; if (toothError >= teeth) { camAngle++; camError -= teeth; }
        }
/**************************************************************************************************
        Special case op for missing tooth, if no missing tooth, then skip this whole part.
        The detection of an event is both there is a missing tooth, and the DIFF is longer
        than 1.5 of the previous event DIFF.
**************************************************************************************************/
        if ((missing > 0) && (tmpDiff > (crkDiff + (crkDiff / 2)))) {
/**************************************************************************************************
        Missing tooth detected, so correct the angle for one missing tooth (at least)
**************************************************************************************************/
            camAngle += toothAngle; camError += toothEr; if (camError >= toothCt) { curAngl++; camError -= toothCt; }
/**************************************************************************************************
            If more missing teeth, correct again for each (math runs fast, so little or
            no impact)
**************************************************************************************************/
            if (missing > 1) { camAngle += toothAngle; camError += toothEr; if (camError >= toothCt) { curAngl++; camError -= toothCt; } }
            if (missing > 2) { camAngle += toothAngle; camError += toothEr; if (camError >= toothCt) { curAngl++; camError -= toothCt; } }
/**************************************************************************************************
            If there was a missing tooth the value of tmpDiff is extended, so replace
            tmpDiff with the old value of DIFF to prevent calculation problems.
**************************************************************************************************/
            tmpDiff = crkDiff;
        }
        crkTime = tmpTime;
        crkDiff = tmpDiff;

The value of "missing" is read from calibration at engine stop.

/* Calibration value in future, but for now just provide a constant */
SWord getCrankToothCt(void) { return 4; }
SWord getCrankToothMissing(void) { return 0; }

       missing = getCrankToothMissing();

TTFN,

Jack