Method for precise synchronization of a combustion engine

1. An exact synchronization method for determining an angular position of an engine, modulo one engine cycle, by a crankshaft sensor comprising a crankshaft detector facing a crankshaft toothed wheel, performing two revolutions per engine cycle, and comprising a large number of regular teeth and at least one marker, the crankshaft detector being able to produce a “tooth” event corresponding to each of said teeth, and a “marker” event for a marker, and at least one camshaft sensor, each camshaft sensor comprising a camshaft detector facing a camshaft toothed wheel, performing one revolution per engine cycle, and comprising a small number of teeth, advantageously irregular, a camshaft detector being able to produce a “start of tooth” event for each rising edge and/or an “end of tooth” event for each falling edge, the method comprising:

estimating a continuous estimated interval assumed to contain the angular position,

on receipt of a “marker” event, determining an angular position corresponding to each one of the possible occurrences of this marker, and

comparing the determined angular positions with the estimated interval:

if none of the determined angular positions belongs to the estimated interval, or if more than one of the determined angular positions belongs to the estimated interval, then exact synchronization is not achieved,

if exactly one of the determined angular positions belongs to the estimated interval (IP), then this angular position is the angular position of the engine, and exact synchronization is achieved.

2. The method as claimed in claim 1 , wherein, in the comparison step, the estimated interval is replaced by the estimated interval increased by a tolerance margin.

3. The method as claimed in claim 2 , wherein the tolerance margin is equal to a portion of an angular span of a variable-timing device.

4. The method as claimed in claim 1 , wherein the estimated interval from the estimation step is used in the comparison step only if its span is below a validation threshold.

5. The method as claimed in claim 1 , applying, in parallel, an alternative exact synchronization method, which may prove slower, but has to be convergent.

6. The method as claimed in claim 1 , wherein as long as exact synchronization is not achieved, the method reiterates the estimation and comparison operations.

7. An engine control method, wherein the method uses an estimated synchronization method that produces a continuous estimated interval in order to command an injection of fuel, and an exact synchronization method as claimed in claim 1 to command ignition.

8. The method as claimed in claim 7 , wherein the estimated synchronization method is merged with the estimation step of the exact synchronization method.

9. The method as claimed in claim 7 , wherein injection is permitted only if the span of the continuous estimated interval is below a threshold.

10. The method as claimed in claim 7 , wherein injection is forbidden if the comparison step does not conclude that exact synchronization has been achieved.

11. The method as claimed in claim 3 , wherein the portion of the angular span is 75%.

12. The method as claimed in claim 8 , wherein injection is permitted only if the span of the continuous estimated interval is below a threshold.

13. The method as claimed in claim 8 , wherein injection is forbidden if the comparison step does not conclude that exact synchronization has been achieved.

14. The method as claimed in claim 9 , wherein injection is forbidden if the comparison step does not conclude that exact synchronization has been achieved.

15. The method as claimed in claim 7 , wherein injection is permitted only if the span of the continuous estimated interval is equal to the validation threshold.

16. The method as claimed in claim 8 , wherein injection is permitted only if the span of the continuous estimated interval is equal to the validation threshold.