Method and device for detecting reverse rotation of an internal combustion engine

A method for detecting the direction of rotation of an internal combustion engine, said engine being associated with:

• a toothed target (3) rotationally fixed to a shaft (4) of the engine, said toothed target comprising a series of teeth comprising on the one hand n real teeth (31) which are regularly spaced, followed by m dummy teeth forming a reference zone (32) on the other hand, where n and m are non-zero integers;
• a sensor (2) arranged to generate a substantially periodic sensor signal having active edges between a first signal level and a second signal level in response to the passage of the real teeth of the toothed target in front of said sensor;
• and
• a management unit (1) configured to measure, for each tooth of index k in the series of teeth, the period of time, referred to as the period T(k) of the tooth k, separating said tooth k from the preceding tooth of index k−1 in the series of teeth;
• wherein,
• the sensor signal further exhibiting at least one transition between the first signal level and the second signal level in a portion of the sensor signal corresponding to passage of the reference zone (32) of the toothed target in front of the sensor, the method comprises the following steps executed for at least some of the values of the index k associated with the teeth of the target:
• a) calculation of a first product by multiplying N times the period T(k−N/2) of the tooth k−N/2, where N is an even integer equal to or greater than 2,
• b) calculation of a second product by multiplying between themselves the periods T(k−i) of the teeth i, with i being between 0 and N/2−1, and between N/2+1 and N,
• c) calculation of the ratio, denoted R′(k), between the first product and the second product, and
• d) detection of the direction of rotation of the target, and therefore of the engine, in case of correspondence of the ratio R′(k) with a first noteworthy value and with a second noteworthy value which are representative, respectively, of rotation in a normal direction of rotation and of rotation in a reverse direction of rotation to said normal direction of rotation.