Digital advance control device for internal combustion engines

Claim 1

A digital advance control system for internal combustion engines comprising a digital computer which receives signals representative of operating parameters of the engine, a detector for measuring the speed of the engine and a tachometer device for supplying signals to the digital computer at a frequency which is a multiple of that produced by the detector, said computer having a memory and operating in response to the input data for addressing said memory and producing at an output thereof a group of bit signals corresponding to a number which is related to the number of signals from said tachometer device which corresponds to the ignition angle of the engine, a variable attenuation circuit coupled to the computer output, said circuit comprising: first subtracter means for receiving at one input thereof the higher order bits of said computer output, reversible counter means, the higher order bits of the output of said reversible counter means being supplied to another input of said first subtracter means, means for supplying clock pulses to said reversible counter means, second subtracter means for receiving and comparing the lower order bits of the computer output and of the reversible counter means, said second subtracter means including means for supplying to said first subtracter means digital signals defining a number and a sign for effecting the carry-over of borrows in dependence on its sign, preselection counter means having an input for receiving the output of said first subtracter means, the output of said preselection counter means controlling said means for supplying clock pulses to said reversible counter means.

Claim 7

A system according to either of claims 2 or 3 wherein the pulse supplied by the preselection counter is applied to the addressing circuit for triggering the interpolation.