Method for diagnosing a variable-lift camshaft follower

1. A method for diagnosing a variable-lift camshaft follower which transmits opening and closing motion from a camshaft of an internal combustion engine to a combustion valve of said internal combustion engine, said variable-lift camshaft follower being switchable between a high-lift mode which opens said combustion valve by a first magnitude and a low-lift mode which opens said combustion valve by a second magnitude that is less than said first magnitude, said method comprising:

detecting a first knock using a spark knock sensor of said internal combustion engine;

retarding ignition timing of said internal combustion engine after detecting said first knock such that said ignition timing is retarded sufficiently to ensure that spark knock is no longer possible;

detecting a second knock using said spark knock sensor after retarding said ignition timing sufficiently to ensure that spark knock is no longer possible;

determining that said variable-lift camshaft follower is not functioning as desired based on said second knock; and

activating a malfunction alert based on said determining that said variable-lift camshaft follower is not functioning as desired.

2. A method as in claim 1 further comprising limiting the rotational rate of said internal combustion engine based on said determining that said variable-lift camshaft follower is not functioning as desired.

3. A method as in claim 1 wherein said internal combustion engine comprises a plurality of combustion chambers and a crankshaft and wherein said variable-lift camshaft follower is one of a plurality of variable-lift camshaft followers such that each one of said plurality of variable-lift camshaft followers is associated with a respective one of said plurality of combustion chambers, said method further comprising:

indexing said second knock to the rotational position of said crankshaft; and

determining which one of said plurality of combustion chambers is associated with said variable-lift camshaft follower that is not functioning as desired based on said indexing of said second knock to the rotational position of said crankshaft.

4. A method as in claim 3 further comprising reporting which one of said plurality of combustion chambers is associated with said variable-lift camshaft follower that is not functioning as desired.

5. A method as in claim 1 further comprising:

determining that the rotational rate of said internal combustion engine is above a first threshold when said second knock is detected;

waiting for the rotational rate of said internal combustion engine to fall below a second threshold that is less than said first threshold;

determining that said second knock has ceased after the rotational rate of said internal combustion engine falls below said second threshold; and

determining that said variable-lift camshaft follower is in said low-lift mode when said variable-lift camshaft follower has been commanded to be in said high-lift mode based on said second knock ceasing after the rotational rate of said internal combustion engine falls below said second threshold.

6. A method as in claim 5 wherein said waiting for the rotational rate of said internal combustion engine to fall below the second threshold includes limiting the rotational rate of said internal combustion engine to be below said second threshold.

7. A method as in claim 5 wherein said internal combustion engine comprises a plurality of combustion chambers and a crankshaft and wherein said variable-lift camshaft follower is one of a plurality of variable-lift camshaft followers such that each one of said plurality of variable-lift camshaft followers is associated with a respective one of said plurality of combustion chambers, said method further comprising:

indexing said second knock to the rotational position of said crankshaft; and

determining which one of said plurality of combustion chambers is associated with said variable-lift camshaft follower that is not functioning as desired based on said indexing of said second knock to the rotational position of said crankshaft.

8. A method as in claim 7 further comprising reporting which one of said plurality of combustion chambers is associated with said variable-lift camshaft follower that is not functioning as desired.

9. A method as in claim 5 wherein said first threshold is greater than said second threshold.

10. A method as in claim 1 further comprising:

determining that the rotational rate of said internal combustion engine is above a first threshold when said second knock is detected;

waiting for the rotational rate of said internal combustion engine to fall below a second threshold that is less than said first threshold;

determining that said second knock has continued after the rotational rate of said internal combustion engine falls below said second threshold; and

determining that a catastrophic failure of said variable-lift camshaft follower has occurred based on said second knock continuing after the rotational rate of said internal combustion engine falls below said second threshold.

11. A method as in claim 10 further comprising limiting the rotational rate of said internal combustion engine based on said determining that said catastrophic failure of said variable-lift camshaft follower has occurred.

12. A method as in claim 1 further comprising:

determining, when said second knock is determined, that the rotational rate of said internal combustion engine is below a threshold when said variable-lift camshaft follower has been commanded to be in said high-lift mode; and

determining that a catastrophic failure of said variable-lift camshaft follower has occurred based on determining that the rotational rate of said internal combustion engine is below said threshold when said variable-lift camshaft follower has been commanded to be in said high-lift mode.

13. A method as in claim 12 further comprising limiting the rotational rate of said internal combustion engine based on said determining that said catastrophic failure of said variable-lift camshaft follower has occurred.

14. A method as in claim 1 further comprising determining that a catastrophic failure of said variable-lift camshaft follower has occurred based on said second knock and said variable-lift camshaft follower being commanded to said low-lift mode.

15. A method as in claim 14 further comprising limiting the rotational rate of said internal combustion engine based on said determining that said catastrophic failure of said variable-lift camshaft follower has occurred.