Air flow amount adjusting system for an internal combustion engine

In an additional air supply system for an internal combustion engine comprising:

• a combustion chamber for producing combustion therein;
• an intake system operatively communicated with said combustion chamber for supplying thereto an air-fuel mixture;
• an exhaust system operatively communicated with said combustion chamber for conveying an exhaust gas from said combustion chamber to the atmosphere;
• an additional air supply pipe communicated with at least one of said intake and exhaust systems for supplying additional air thereto, thereby controlling the air-fuel ratio of said air-fuel mixture at a desired value;
• air-fuel ratio detecting means disposed in said exhaust system for detecting the air-fuel ratio of the air-fuel mixture supplied with said additional air;
• control means operatively disposed in said additional air supply pipe for controlling the amount of the additional air to be supplied;
• drive means operatively connected with said control means for driving the same;
• and
• a control circuit electrically connected with said air-fuel ratio detecting means and said drive means for intermittently actuating said drive means in response to the detected air-fuel ratio;
• the improved control circuit comprising:
• an air fuel ratio discriminating circuit connected with said air-fuel ratio detecting means for comparing the output from said detecting means with a preset level and for generating a high level or a low level signal based on the comparison;
• means for stopping the actuation of said drive means in response to change of said signal from one level to the other for a period following a level change to prevent an erroneous operation of said control means, including a first monostable multivibrator connected to said discriminating circuit for producing a timing pulse for a predetermined period following change from a first to a second level, a second monostable multivibrator connected to said discriminating circuit for producing a timing pulse for a predetermined period following change from said second to said first level, logic means connected to said first and second multivibrators and said discriminating circuit and connected to said driving means for causing actuation of said driving means in accordance with said signal from said discriminating means and preventing actuation during said timing pulses.