Method for controlling the rotation of a vehicle engine camshaft

A method for controlling the rotation of a camshaft of an internal combustion engine of an automotive vehicle, said vehicle comprising said engine, said engine comprising a camshaft and an angular-position measurement sensor, said camshaft being configured to be rotated in a direction referred to as nominal, said nominal direction of rotation being the opposite of a direction of rotation said to be the “reverse” direction, said measurement sensor comprising:

• a toothed target, fixed to the camshaft and comprising on its periphery a plurality of teeth having uneven angular lengths, each tooth having a leading edge and a trailing edge,
• a sensitive element, configured to emit a signal the variations of which are indicative of the passage of the leading edges and of the trailing edges of the teeth, and
• an electronic control unit containing, in memory, for each edge of the toothed target, a set of predetermined “nominal” time interval (Tnom,n), a set of nominal ratios (Rnom,n) and at least one “reverse” time interval (Tinv,n), these having been predetermined from a theoretical model of the speed of reverse rotation of the camshaft, said model having been created in advance using measurements from a camshaft of a calibration engine-rotating in the reverse direction,
• said method comprising the steps of:
• passage (E1) of an edge of a tooth of the toothed target past the sensitive element,
• detection (E2), by the sensitive element, of the passage of said edge,
• generation (E3), by the sensitive element, of a signal indicative of the detected passage of the edge,
• determination (E4), by the electronic control unit, of an identification time interval (Tn) corresponding to the duration separating two successive edges in the generated signal,
• calculation (E5), by the electronic control unit, of an identification ratio (Rmes,n) from at least one predetermined identification time interval (Tn),
• determination (E6), by the electronic control unit, of the theoretical edge corresponding to the detected passage of the signal edge on the basis of the last edge validated during the preceding iteration of the method,
• calculation (E8*), by the electronic control unit, of a theoretical “reverse” ratio (Rinv,n), from a plurality of nominal time intervals and from the at least one reverse time interval (Tinv,n) stored in memory,
• comparison (E9*), by the electronic control unit between the calculated identification ratio (Rmes,n), the nominal ratio (Rnom,n) corresponding to the theoretical edge and the reverse ratio (Rinv,n),
• if the identification ratio (Rmes,n) is closer to the expected nominal ratio (Rnom,n) than to the reverse ratio (Rinv,n), validation (E10) of the nominal direction of rotation of the camshaft and validation of the edge,
• if the identification ratio (Rmes,n) is closer to the reverse ratio (Rinv,n) than to the expected nominal ratio (Rnom,n), detection (E10*), by the electronic control unit of a reverse rotation of the camshaft and interruption of the injection of fuel into the engine.