System for monitoring the sensor responsive to a periodic condition in an internal combustion engine

摘要

A sensor for the variable underpressure in the intake manifold of an engine produces a digital output signal which is sampled at intervals of one half of the period of pressure variation or an odd multiple of such half period, as timed in synchronism with the crankshaft revolution in a phase relation designed to intercept maximum and minimum values of pressure. The two most recent samples are stored in a shift register and their difference is formed by digital subtraction, compensated for changes of sign in successive difference operations to provide an absolute difference value output. The latter is then provided to a threshold stage which provides an output signal if the difference value does not reach a predetermined threshold. The signal of the threshold stage is integrated before it is used to produce an alarm indication or a corrective control function. When such an indication is produced, the value of pressure measured by the sensor is referred to in order to determine whether the malfunction relates to the communication of the vacuum to the sensor or to a defect in the sensor itself.