Digital circuitry for spark timing and exhaust gas recirculation control

Claim 1

A spark timing and exhaust gas recirculation control system for an internal combustion engine, said system including: a signal processing circuit for developing an output which is a complex function of two variable input signals representing different engine conditions, said circuit comprising: programmable transfer function means for receiving an input signal and producing an output signal having a selectable predetermined relationship to the input signal; means coupled to said programmable transfer function means for supplying a first analog input signal related to a first engine condition to said transfer function means while selecting a first transfer relationship therefor; first storage means coupled to said transfer function means for storing a quantity related to the output of said transfer function means produced in response to said first input signal; said supplying and selecting means including circuitry for supplying a second analog input signal related to a second engine condition to said transfer function means, after said first input signal, while selecting a second relationship for said transfer function means; and means coupled to said first storage means for multiplying the output of said programmable transfer function means produced in response to said second input signal by a factor related to said stored quantity to produce a complex output analog control signal, whereby a single programmable transfer function means can sequentially process two variable input signals related to engine conditions and develop a complex output signal control which is a product function of both of the input signals; and wherein said programmable transfer function means includes a function generator comprising: analog to digital converter means for receiving an input analog signal and producing a first output digital signal related to said input signal; and read only memory means coupled to said analog to digital converter means for receiving said first output digital signal as an input and producing a second output digital signal having a selectable predetermined functional relationship with respect to said first output digital signal; and wherein said multiplying means includes: digital to analog converter means coupled between said read only memory means and said storage means for receiving said second digital output signal and producing a first analog output signal related to said second digital output signal; and wherein said analog to digital (A/D) converter means comprises: at least one capacitor: first means coupled to said capacitor for setting the charge on said capacitor to a first predetermined charge level; second means coupled to said capacitor for subsequently altering the charge on said capacitor from said first predetermined charge level at a predetermined rate; means coupled to said capacitor for comparing the charge on said capacitor to a predetermined reference level and producing a digital signal related to the duration of time between the time of starting to alter the charge on said capacitor at said predetermined rate and the time that the charge on said capacitor is equal to the predetermined reference level; and means for sequentially activating said first and second means and maintaining said first predetermined charge level at a fixed value while determining said first predetermined rate directly in accordance with the variable magnitude of one of said input signals, whereby said produced digital signal is a function of the inverse of the magnitude of said one of said input signals.