Method for estimating the speed of an engine in a predefined position

1. A method for estimating the engine speed of an internal-combustion engine at an angular position of the engine corresponding to a current point (A), in advance for a future engine angular position representing a predefined position of same, said engine comprising:

a target with teeth that is linked to a crankshaft,

a sensor cooperating with the teeth, and

means for managing the engine including means for determining the angular position of the crankshaft, also referred to as the angular position of the engine, and a clock used to determine the time interval between two successive passes of a tooth before the sensor, the method comprising the following steps:

a first step of i) determining the angular position for a first measurement point (A n ) and a second measurement point (A n-1 ) of the sensor and ii) of determining a rotational speed for the first measurement point (A n ) and the second measurement point (A n-1 ) of the sensor,

a second step of determining a gradient (V′(A)) of the rotational speed between the first and second measurement points (A n , A n-1 ) determined in said first step,

a third step of determining at least one gradient of the rotational speed (V′(A n-f )) between two further measurement points, at least one of the two further measurement points being different from the first measurement point (A n ) and the second measurement point (A n-1 ), to thereby obtain at least one other gradient of the rotational speed (V′(A n-f )) in addition to the gradient V′(A) of the speed between the first and second measurement points (A n , A n-1 ) determined in said second step,

using the determined gradient (V′(A)) of the rotational speed between the first and second measurement points (A n , A n-1 ) and the determined at least one other gradient of the rotational speed (V′(A n-f )) between the two further measurement points, approximating the real curve of rotational speed in relation to the angular position using a polynomial function of degree 2, and

using the approximated real curve of rotational speed, calculating in advance an estimated rotational speed at the predefined position, the predefined position being a future angular position of the crankshaft, by application of the polynomial function at said predefined position.

2. The method as claimed in claim 1 , wherein the first measurement point (A n ) and the second measurement point (A n-1 ) are measurement points corresponding to sensor measurements for two successive teeth.

3. The method as claimed in claim 2 , wherein the approximation of the rotational speed in relation to the angular position is determined as the curve of degree 2 passing through the first and second measurement points (A n , A n-1 ) and having a speed gradient variation defined on the basis of the measured speed gradient.

4. A method for predicting an inverse rotation of an engine, further comprising the following steps:

estimating the engine speed at an angular position predetermined using a method according to claim 2 ,

comparing the engine speed at a predetermined threshold as a function of the angular position at which the angular speed was estimated, and

predicting an inverse rotation after the estimated speed is below the predetermined threshold.

5. The prediction method as claimed in claim 4 , wherein the engine speed is estimated at at less than 10° from a top dead center of the engine.

6. The prediction method as claimed in claim 5 , wherein the predetermined threshold is between 240 and 360 rpm (i.e. between 8π and 12π rad/s).

7. A motor management method, further comprising the following steps:

predicting an inverse rotation of an engine as claimed in claim 4 , and

after an inverse rotation is predicted while no starter device is active in the engine, the following combustion is inhibited.

8. The method for managing an engine as claimed in claim 7 , further comprising the following step:

detecting any inverse rotation of the engine and, after such inverse rotation is detected, the prediction method is ended, otherwise it is assumed that the engine is being driven in rotation and the prediction method is continued.

9. The method as claimed in claim 1 , wherein the approximation of the rotational speed in relation to the angular position is determined as the curve of degree 2 passing through the first and second measurement points (A n , A n-1 ) and having a speed gradient variation defined on the basis of the measured speed gradient.

10. The method as claimed in claim 9 , wherein the polynomial estimate is calculated bearing in mind that the speed gradient variation is a constant corresponding to the variation in the speed gradient between, firstly, the speed gradient resulting from the first measurement point and from the second measurement point and, secondly, the distinct speed gradient determined.

11. A method for predicting an inverse rotation of an engine, further comprising the following steps:

estimating the engine speed at an angular position predetermined using a method according to claim 10 ,

comparing the engine speed at a predetermined threshold as a function of the angular position at which the angular speed was estimated, and

predicting an inverse rotation after the estimated speed is below the predetermined threshold.

12. A method for predicting an inverse rotation of an engine, further comprising the following steps:

estimating the engine speed at an angular position predetermined using a method according to claim 9 ,

comparing the engine speed at a predetermined threshold as a function of the angular position at which the angular speed was estimated, and

predicting an inverse rotation after the estimated speed is below the predetermined threshold.

13. A method for predicting an inverse rotation of an engine, further comprising the following steps:

estimating the engine speed at an angular position predetermined using a method according to claim 1 ,

comparing the engine speed at a predetermined threshold as a function of the angular position at which the angular speed was estimated, and

predicting an inverse rotation after the estimated speed is below the predetermined threshold.

14. The prediction method as claimed in claim 13 , wherein the engine speed is estimated close to a top dead center of the engine, i.e. at less than 10° from this top dead center.

15. The prediction method as claimed in claim 14 , wherein the predetermined threshold is between 240 and 360 rpm (i.e. between 8π and 12π rad/s).

16. A motor management method, further comprising the following steps:

predicting an inverse rotation of an engine as claimed in claim 15 , and

after an inverse rotation is predicted while no starter device is active in the engine, the following combustion is inhibited.

17. A motor management method, further comprising the following steps:

predicting an inverse rotation of an engine as claimed in claim 14 , and

after an inverse rotation is predicted while no starter device is active in the engine, the following combustion is inhibited.

18. A motor management method, further comprising the following steps:

predicting an inverse rotation of an engine as claimed in claim 13 , and

after an inverse rotation is predicted while no starter device is active in the engine, the following combustion is inhibited.

19. The method for managing an engine as claimed in claim 18 , further comprising the following step:

detecting any inverse rotation of the engine and, after such inverse rotation is detected, the prediction method is ended, otherwise it is assumed that the engine is being driven in rotation and the prediction method is continued.

20. A device for managing an engine, comprising means for implementing each of the steps of a method as claimed in claim 1 .