Electronic ignition timing system using digital rate multiplication

摘要

An electronic ignition timing system for an internal combustion engine which rotates a crankshaft is disclosed. The ignition system comprises a plurality of variable engine condition sensors which produce corresponding analog output signals and a crankshaft position sensor. A timing control logic circuit periodically multiplexes each of the variable engine condition sensors such that they are sequentially connected as inputs to an analog to digital (A/D) converter which produces an output signal comprising a pulse train for each of the multiplexed engine conditions. The total number of pulses in each pulse train is related to the magnitude of the variable engine condition currently being connected to the A/D converter. In addition, high resolution crankshaft position pulses are produced, preferably by an electronic angle divider which receives coarse crankshaft position pulses and produces high resolution crankshaft position pulses. The variable engine condition pulse trains and the high resolution crankshaft position pulses are then multiplexed to produce an input signal to a binary rate multiplier (BRM) which has its output connected to a counter. The input signal going to the BRM is monitored by a separate counter which controls the output of a read only memory (ROM) that determines the multiplication factor M of the BRM. The use of this separate counter to monitor the inputs of the BRM results in producing an output count from the BRM which is a non-linear function of the input signal, and this is accomplished with the use of a minimum number of memory cells in the ROM. A count related to the output count of the BRM for all of the multiplexed inputs is loaded into a phase counter which then proceeds to count down at a rate determined by the high resolution crankshaft position pulses. A latch circuit is then used to generate a spark timing signal when the count of the phase counter reaches a predetermined count. The spark timing pulses are produced at predetermined engine crankshaft positions related to the output count of the BRM wherein the output count is the summation of a plurality of non-linear output functions relating engine spark timing to the plurality of multiplexed variable engine conditions, including engine speed.