Abstract: An automatic choke system has a thermostatic spring connected to a choke valve, and a heater for heating the thermostatic spring so as to open the choke valve. A control circuit is provided for controlling the current passing through the heater. At starting of an engine, when cooling water temperature is lower than a predetermined temperature the control circuit operates to decrease the current so as to slowly open the choke valve. When the cooling water temperature is higher than a predetermined temperature, a rated current is supplied to the heater so as to quickly open the choke valve.

Abstract: An air-fuel ratio control system for an internal combustion engine has an electromagnetic valve for correcting the air-fuel ratio of air-fuel mixture, an O.sub.2 sensor for detecting oxygen concentration in exhaust gases, and a feedback control circuit including a pulse generating circuit for generating pulses, the duty ratio of which is dependent on the oxygen concentration. The system has an engine deceleration detecting circuit and a light load detecting circuit for producing a deciding signal. Pulses having a fixed duty ratio are applied to the electromagnetic valve in response to the deciding signal so as to enrich the air-fuel mixture at the deceleration when the throttle valve closes.

Abstract: An air-fuel ratio control system for an internal combustion engine has an electromagnetic valve for correcting the air-fuel ratio of air-fuel mixture, and an O.sub.2 sensor for detecting oxygen concentration in exhaust gases. An engine coolant temperature sensor is provided for producing an engine temperature signal when the temperature is higher than a predetermined value, and an O.sub.2 sensor condition detecting circuit is provided for producing a non-activation signal when the O.sub.2 sensor is not activated. Engine restart operation is detected by the engine temperature signal and non-activation signal. When the restarting of the engine detected, pulses with a duty ratio of which is dependent on the coolant temperature are applied to the electromagnetic valve, so as to prevent extreme enrichment of the air-fuel mixture.

Abstract: An air-fuel ratio control system for an internal combustion engine has an electromagnetic valve for correcting the air-fuel ratio of air-fuel mixture, and an O.sub.2 sensor for detecting oxygen concentration in exhaust gases. A detecting circuit is provided for producing an acceleration signal when the engine is accelerated at cold engine operation. A pulse generating circuit is provided for producing a plurality of pulses, the duty ratios of which are proper for air-fuel ratio at acceleration in cold engine operation. A changeover switch is provided to respond to the acceleration signal for applying the pulses to the electromagnetic valve so as to control the air-fuel ratio.

Abstract: An air-fuel ratio control system for an internal combustion engine has an electromagnetic valve for correcting the air-fuel ratio of air-fuel mixture, an O.sub.2 sensor for detecting oxygen concentration in exhaust gases, and a feedback control circuit including a PI circuit, and a pulse generating circuit responsive to the output of the PI circuit for generating pulses, the duty ratio of which is dependent on the output of the PI circuit. A steady state detecting circuit is provided for producing a steady state signal when the magnitude of acceleration of the engine is within a predetermined range. The constant of the PI circuit is decreased by the steady state signal for preventing overshooting of the air-fuel ratio control.

Abstract: A low-pass filter circuit for suppressing a subcarrier contained in an FM stereo demodulation signal in which the output signal of the circuit is unaffected by magnetic distortion. The FM stereo demodulation signal is applied through a low-pass filter to n sample-and-hold circuits connected in parallel with one another. The outputs of the sample-and-hold circuits are summed to form an output signal in which the subcarrier signal has been suppressed. The n sample-and-hold circuits are driven with a corresponding number of sampling pulse signals of different phases.

Abstract: An ignition timing control system with an exhaust gas recirculation (EGR) system has a primary vacuum-advance mechanism operated by vacuum in an intake passage of an engine to advance the ignition timing of the engine, and a secondary vacuum-advance mechanism operated by vacuum in the intake passage to advance the ignition timing in addition to the operation of the primary vacuum-advance mechanism. A first solenoid operated valve is provided to render the secondary vacuum-advance mechanism inoperative. A second solenoid operated valve is provided for cutting off the EGR system. An electronic control unit responds to engine operating conditions in a low engine speed range except idling operation for closing the first and second solenoid operated valve to cut off the EGR system and to cut off the secondary vacuum-advance mechanism, thereby stopping the advancing of the ignition timing.

Abstract: A multipath distortion reducing circuit particularly adapted for use with stereophonic receiving circuits in which the amount of mixing between right and left channels is reduced. In accordance with the invention, the envelope of the received FM signal is AM detected, and the envelope detected circuit is multiplied by the FM detected signal differentiated to provide a distortion cancelling signal. The distortion cancelling signal is summed with the detected FM signal to provide an output having a reduced multipath distortion component.