Abstract: An ignition timing control system for vehicle internal combustion engines, in which the basic ignition timing is determined for a detected engine speed and load and when knock occurs, the basic ignition timing is retarded by a unit amount. A counter is provided for determining the occurrence rate of knock, the value of which is incremented each time knock occurs and is decrement if no knock occurs within a predetermined number of firings. Based on the counter values, a period is determined. When knock occurs, the retard adjustment is started and is continued for the period even when knock has ceased in the course of retard adjustment. The predetermined number of firings for defining a wait period before the counter value is decremented is set to equal the number of cylinders of the engine concerned. Alternatively, the predetermined number of firings can be varied with the knock occurrence rate counter value.

Abstract: An air-fuel ratio control method for an internal combustion engine. An amount of fuel to be supplied to the engine is calculated in response to operating conditions of the engine and output from an exhaust gas ingredient concentration sensor, to thereby feedback-control the air-fuel ratio of a mixture supplied to the engine to a desired air-fuel ratio. The method comprises the steps of (1) calculating a fuel cooling correction value for compensating for a change in an actual air-fuel ratio caused by cooling effects of actually-injected fuel, according to at least one parameter which can determine the amount of fuel to be supplied to the engine, and (2) calculating the amount of fuel to be supplied to the engine by the use of the fuel cooling correction value.

Abstract: An air-fuel ratio control method for an internal combustion engine. The air-fuel ratio of an air-fuel mixture supplied to the engine is feedback-controlled to a desired air-fuel ratio in response to output from an exhaust gas ingredient concentration sensor. When the desired air-fuel ratio is to be changed in a leaning direction from a value equal to or leaner than a stoichiometric air-fuel ratio, it is changed at a larger rate until it reaches a predetermined value than after it has reached the predetermined value. The predetermined value is set to a value slightly leaner than an air-fuel ratio at which the amount of emission of NO.sub.X increases.

Abstract: An air-fuel ratio control method for an internal combustion engine, in which the air-fuel ratio of a mixture supplied to the engine is feedback-controlled to a desired air-fuel ratio in response to output from an exhaust gas ingredient concentration sensor. When the engine is in a predetermined decelerating condition, fuel supply to the engine is cut off. The rate of correction of the air-fuel ratio of the mixture by the feedback control is set to a larger value before a predetermined time period elapses after the engine shifted from the predetermined decelerating condition to another operating condition, than values to be set after the predetermined time period has elapsed.

Abstract: An air-fuel ratio control method for an internal combustion engine, in which the air-fuel ratio of a mixture supplied to the engine is feedback-controlled to a desired air-fuel ratio in response to output from an exhaust gas ingredient concentration sensor. When the engine is in a predetermined accelerating condition, fuel supply to the engine is increased. The rate of correction of the air-fuel ratio of the mixture by the feedback control is set to a smaller value when the engine is in the predetermined accelerating condition, than values to be set when the engine is in other operating conditions.

Abstract: A system for controlling ignition timing of a vehicle internal combustion engine, in which a plurality of sets of ignition timing control characteristics are established in response to the octane numbers of different kinds of fuel which may intentionally or unintentionally be used in the vehicle. The system infers the octane number of the fuel being used from the occurrence state of knock and selects the set of control characteristics corresponding to the selected fuel octane number, whereafter it determines the ignition timing based on the selected set of control characteristics.

Abstract: A knocking control system for an internal combustion engine with inlet valves and exhaust valves having valve timing thereof controlled depending on operating conditions of the engine. It is determined whether or not knocking has occurred in the engine on the basis of a detection parameter indicative of knocking and at least one discrimination parameter. The operation of the engine is controlled by the use of at least one control parameter in response to the determination result, so as to eleminate knocking. The values of the discrimination and control parameters are selected in accordance with the actual valve timing. When abnormality in the valve timing control is detected, the valve timing is held at predetermined valve timing irrespective of engine operating conditions, and values of the at least one discriminating parameter and the at least one control parameter are selected, which correspond to the held predetermined valve timing.

Abstract: An idling speed control system for controlling idling rotational speed of an internal combustion engine. A vacuum-operated actuator having a diaphragm defining a vacuum chamber controls opening and closing of a throttle valve in response to pressures supplied from a change-over control valve to the vacuum chamber. The change-over control valve selectively supplies the vacuum chamber with a first control pressure for opening the throttle valve and a second control pressure for closing same. An electronic control unit generates an on-off control pulse signal having a pulse repetition period corresponding to rotational speed of the engine, one of on-period or off-period of the on-off control pulse signal having a predetermined constant value, and supplies the change-over control valve with the on-off control pulse signal.

Abstract: An idling speed control system for controlling idling rotational speed of an internal combustion engine. A vacuum-operated actuator having a diaphragm defining a vacuum chamber controls opening and closing of a throttle valve in response to pressures suppliedfrom a change-over control valve to the vacuum chamber. The change-over control valve selectively supplies the vacuum chamber with a first control pressure for opening the throttle valve and a second control pressure for closing same. An electronic control unit generates an on-off control pulse signal having a pulse repetition period corresponding to rotational speed of the engine, one of on-period or off-period of the on-off control pulse signal having a predetermined constant value, and supplies the change-over control valve with the on-off control pulse signal.

Abstract: An idling speed control system for controlling idling rotational speed of an internal combustion engine. A vacuum-operated actuator having a diaphragm defining a vacuum chamber controls opening and closing of a throttle valve in an intake passage of the engine in response to first and second control pressures supplied from a change-over control valve to the vacuum chamber.

Abstract: A vacuum-operated actuator controls opening and closing of a throttle valve in an intake passage of an internal combustion engine in response to pressure in a vacuum chamber thereof. A change-over control valve supplies the vacuum chamber, selectively, with first and second control pressures for opening and closing the throttle valve, respectively. An electronic control unit controls the engine idling rotational speed by generating an on-off control pulse signal having a period corresponding to the engine rotational speed, and supplying the change-over control valve with the on-off control pulse signal to cause same to supply the vacuum chamber with the first or second control pressure.