On-board motor vehicle timing measurement system

Claim 1

Apparatus for measuring the timing angle of an internal combustion (IC) engine having a crankshaft mounted ring gear with a plurality of ring gear teeth spaced at substantially equal circumferential intervals, a top dead center (TDC) timing marker, and ignition apparatus, in a system having engine mounted sensors for providing engine sensed signals in each engine cycle, including: a ring gear signal having a series of tooth pulses marking the tooth intervals between passage of successive ring gear teeth past a fixed point in the engine, a TDC signal indicative of the occurrence of TDC in a selected engine cylinder, and an ignition signal indicative of the occurrence of combustion in the selected engine cylinder, the apparatus comprising: timing means, for providing a series of clock pulses; first counter means, for counting the number of ring gear signal tooth pulses occurring in each engine cycle, to provide a whole number tooth interval count signal indicative of the whole number of ring gear tooth intervals in each engine cycle; first signal means, responsive to the pulsed ring gear signal, for providing oppositely polled, first and second bistable signals, each said bistable signal alternating between first and second signal states at each succeeding tooth interval of said ring gear signal, wherein said first and second bistable signals are in opposite ones of said first and second signal states at any time; second and third counter means, each responsive to said timing means and to a related one of said first and second bistable signals, for accumulating the number of said clock pulses occurring in the presence of each said first signal state of the related bistable signal, said second and third counter means each storing therein for the duration of said next succeeding second signal state a sum clock count signal value obtained for each first signal state whereby one of said second and third counter means includes, at any time, a stored sum clock count signal value for an immediately preceeding tooth interval and another one thereof includes an accumulating clock count signal value for a present tooth interval; signal processing means, having memory means for storing signals, and responsive to said engine sensed signal, for sampling said whole number tooth interval count signal value, said sum clock count signal value and said accumulating clock count signal value, to provide a sample value set, at the occurrence of TDC and at the occurrence of combustion in the selected cylinder in each engine cycle; calculating a decimal number tooth interval value for each sample set as equal to the ratio of said accumulating clock count signal sampled value divided by said sum clock count signal sampled value and adding said calculated decimal number value to the sampled whole number tooth interval count signal to provide a total tooth interval signal for each sample set; and providing the difference value between said total tooth interval signals for each sample set as the engine timing signal.