Variable-energy-spark ignition system for internal combustion engines, particularly for motor vehicles

An ignition system for an internal combustion engine, comprising:

• at least one spark plug;
• at least one ignition coil whose secondary winding is connectible to the at least one spark plug to induce the generation of a spark;
• commutator means adapted to assume first and second conditions which respectively permit and interrupt the flow of a current in the primary winding of the ignition coil;
• electrical sensor means for providing electrical signals indicative of operating conditions of the engine, and
• control means coupled to the commutator means and the electrical sensor means and adapted to pilot the commutator means so as to vary, in accordance with the signals provided by said sensor means, the energy applied to said at least one spark plug for the generation of the sparks;
• wherein the control means include
• monitoring means for monitoring the current flowing in the primary winding of the ignition coil, and
• an electronic control unit arranged to pilot the commutator means in a predetermined manner in accordance with the signals provided by the sensor means and by the monitoring means;
• the said electronic control unit being provided with memory means in which there are stored data indicative of predetermined final values of the current in the primary winding of the ignition coil, associated with various operating conditions of the engine identifiable from the signals from the sensor means, the electronic control unit being further arranged to pilot the commutator means so that, each time a spark needs to be generated, the current flow in the primary winding of the ignition coil is interrupted when its intensity has reached a value associated in the memory means with the operating conditions of the engine indicated by the sensors;
• and
• wherein the monitoring means are arranged to supply the electronic control unit with a signal when the intensity of the current in the primary winding of the ignition coil reaches a threshold value less than the minimum final value stored in the memory means, and in that this unit is arranged to monitor the time taken by the current to reach the threshold value,
• to calculate the further period of time necessary for the current to reach the final value associated with the operating conditions of the engine registered by the sensor means and stored in the memory means, and
• to maintain the commutator means in the first condition for the further period of time.