Abnormality detecting apparatus for means for sensing operating parameters of an internal combustion engine

DETAILED DESCRIPTION It is therefore the object of the invention to provide an apparatus for detecting an abnormality in sensing means for sensing operating parameters of an internal combustion engine, which apparatus is capable of performing accurate abnormality determination by preventing erroneous diagnosis in determining whether the sensing means is operating abnormally.
According to the invention, there is provided an abnormality detecting apparatus for detecting abnormality in operating parameter sensing means for sensing a value of an operating parameter of an internal combustion engine in synchronism with generation of pulses of a signal indicative of predetermined rotational angle positions of the engine.
Comparator means determines whether or not the deteced value of the operating parameter lies outside a predetermined range.
First timer means is responsive to results of the determination by the comparator means for measuring, when the detected value of the operating parameter lies outside the predetermined range, time elapsed from the instant at which the detected value of the operating parameter falls outside the predetermined range.
Decision means decides that the operating parameter sensing means is faulty when the elapsed time measured by the first timer means exceeds a first predetermined period of time.
Second timer means is disposed to be reset each time a pulse of the aforementioned rotational angle position signal is generated for measuring time elapsed from the instant at which it becomes reset.
The second timer means is adapted to halt the measuring operation of the first timer means when the elapsed time measured by the second timer means reaches a second predetermined period of time which is shorter than the first predetermined period of time.
Preferably, the abnormality detecting apparatus according to the invention may further comprise generating means for generating reference clock pulses at fixed time intervals.
The second timer means counts a number of pulses generated by the generating means