Fail safe devices for use with devices for limiting the speed of revolution of an internal combustion engine

A fail-safe device for isolating an electronic revolution limiter associated with an electronic ignition system for an internal combustion engine including a spark ignition coil, the revolution limiter being of the type having an output stage including a semiconductor breakdown device in series with a semiconductor switch for connection in parallel with an output stage of the electronic ignition system, wherein the semiconductor switch is rendered conductive at engine speeds above a predetermined limiting speed to prevent the generation of ignition pulses by limiting the voltage applied to operate the ignition coil;

• the fail-safe device comprising detecting means arranged to be coupled to the output stage of the revolution limiter for detecting if the semiconductor switch is conductive such as to prevent the generation of ignition pulses at an engine speed lower than the predetermined limiting speed thus indicating that a fault has developed in the revolution limiter, and for providing a corresponding detecting signal containing pulses at a rate proportional to the engine speed;
• and interrupt means coupled to said detecting means and arranged to be connected to the revolution limiter for isolating the revolution limiter from the electronic ignition system in accordance with said detecting signal.