Control system

An air-fuel ratio control system for an internal combustion engine having an intake passage, an exhaust passage, air-fuel mixture supply means, and electro-magnetic means for correcting the air-fuel ratio of the air-fuel mixture supplied by said air-fuel mixture supply means, the system comprising

• dither signal generating circuit means for producing a periodical dither signal having a pattern of pulses which comprises a plurality of alternate positive excursions and negative excursions,
• at least one of said positive excursions being lower than another of said positive excursions and at least one of said negative excursions being shallower than the another of said positive excursions,
• said dither signal defining a center line having a level,
• a shift control circuit means for shifting the level of the center line of said dither signal,
• driving circuit means for producing a driving output according to said dither signal for driving said electro-magnetic means,
• detecting means for sensing the concentration of a constituent of the exhaust gases passing through said exhaust passage,
• said detecting means including means for distinguishing values higher than a reference value corresponding to the stoichiometric air-fuel ratio from lower values with a steep change,
• comparing circuit means for comparing said output signal of the distinguishing means with reference pulses having the same period as that of corresponding of said pulses of said dither signal and for producing a control signal corresponding to said dither signal but said control signal omitting corresponding portions of the dither signal from time to time dependent on the output signal of the distinguishing means,
• a shift signal generating circuit means for producing a shift signal dependent on said control signal for shifting the level of said center line of said dither signal from time to time via said shift control circuit means.

A feedback control system comprising

• a dither signal generating circuit means for continuously generating a periodical, initial dither signal having a pattern of pulses having a period which comprises a plurality of alternating positive excursions and negative excursions,
• at least one of said excursions of at least either of said positive excursions and said negative excursions having a level different from another of said excursions of said either of said positive excursions and said negative excursions, said dither signal defining a center line having a level,
• shift control circuit means for shifting said initial dither signal along with the level of the center line of said initial dither signal whereby producing a shifted dither signal,
• controlled output producing means operatively connected to an output of said shift control circuit means for producing at a location a controlled output as a function of said shifted dither signal, said controlled output varying with a dither pattern substantially according to said shifted dither signal,
• means for sensing the controlled output and distinguishing values of said controlled output higher than a desired value from values of said controlled output lower than said desired value and providing a control signal substantially corresponding to said shifted dither signal but omitting portions of said control signal corresponding to portions of the controlled output respectively above and below said desired value from time to time,
• a shift signal generating circuit means connected to said shift control circuit means and for producing a shift signal dependent on said control signal for shifting, via said shift control circuit means, said initial dither signal along with the level of the center line thereof from time to time in a direction compensatingly opposite to deviations of said controlled output from said desired value, and said shift signal generating circuit means for not producing a shift signal when a deviation of said controlled output is such that level-wise centralmost of said at least one of said excursions of said of said positive excursions and said negative excursions and another of said excursions are between said desired value.

A feedback control system comprising

• a dither signal generating circuit means for continuously generating a periodical, initial dither signal having a pattern of pulses having a repeating cycle of a period comprising only a plurality of more than one of said pulses and which comprises a plurality of alternating positive excursions and negative excursions, said dither signal defining a center line having a level,
• shift control circuit means for shifting said initial dither signal along with the level of the center line of said initial dither signal whereby producing a shifted dither signal,
• controlled output producing means operatively connected to an output of said shift control circuit means for producing at a location a controlled output as a function of said shifted dither signal, said controlled output varying with a dither pattern substantially according to said shifted dither signal,
• means for sensing the controlled output and distinguishing values of said controlled output higher than a desired value from values of said controlled output lower than said desired value providing a control signal thereof substantially corresponding to said shifted dither signal but omitting portions of said control signal corresponding to portions of the controlled output respectively higher and lower than said desired value from time to time,
• a shift signal generating circuit means connected to said shift control circuit means and for producing a shift signal dependent on said control signal for level-wise shifting, via said shift control circuit means, of said initial dither signal along with the level of the center line thereof from time to time, said shift control circuit means dependent on said shift signal for shifting said initial dither signal along with the level of said center line of said initial dither signal in a direction and magnitude compensatingly opposite to predetermined ranges of deviations of a center line of said controlled output from said desired value, and said shift signal generating circuit means for not producing said shift signal when said shift signal represents a condition of said controlled output in a level-wise central range with respect to said desired value.