Abstract: Failure of a valve timing changeover control system of an internal combustion engine is detected by comparing a present value of an air-fuel ratio feedback control correction coefficient which is varied in response to output from an O.sub.2 sensor with a predetermined value of the correction coefficient obtained based on values of same obtained during the feedback control of the air-fuel ratio. Alternatively, or in combination, failure of the valve timing changeover control system is detected by determining whether a present value of the correction coefficient obtained with respect to each of a plurality of cylinders of the engine in response to output from each of O.sub.2 sensors corresponding to the each cylinder is outside a predetermined range of deviation of values of the correction coefficient from a reference value, the deviation resulting from differences in characteristics between the cylinders.

Abstract: Failure of a valve timing changeover control system of an internal combustion engine is detected by the steps of: (1) setting a predetermined state of intake air to be supplied to the engine depending on a control signal for controlling changeover of valve timing, (2) detecting a state of intake air being supplied to the engine, (3) comparing the detected state of intake air with the set predetermined state of intake air, and (4) detecting from the result of the combustion whether or not there is failure in the valve timing changeover control system.

Abstract: A control method for a valve-timing changeover in an engine having a valve operating mechanism capable of operating the intake valves or exhaust valves, or both, in a different manner, known as valve timing, such as the magnitude of valve lift or the duration the valve remains open, for improving the operation of the engine at different engine speeds. The control method uses various parameters to cause the changeover to occur when the engine output is substantially the same in the two different valve timing speed ranges between which the changeover is being made to minimize any shock loading during the changeover. In a fuel injection type engine, the preset quantities of fuel injection that would normally be supplied to the engine for those two different valve timing speed ranges are used to determine the engine output and return the proper time for the changeover.

Abstract: A method for detecting an irregularity in the valve-timing changeover in an engine having a valve operating mechanism capable of operating the intake valves or exhaust valves, or both, in a different manner, known as valve timing, such as the magnitude of valve lift or the duration the valve remains open, for improving the operation of the engine at different engine speeds. The method compares the oil pressure in the supply passage to the valve timing changeover mechanism with the oil pressure that should exist after the changeover caused by the latest instruction to determine an irregularity if the pressures are not equal. A time delay may be used to accommodate the inherent time lay in the changeover to avoid a premature determination of an irregularity. An alarm may be energized or a fail-safe procedure initiated when an irregularity is detected.

Abstract: An intake air flow control apparatus for an internal-combustion engine, which includes a valve lift characteristic control means for variable control of the lift characteristics of intake and exhaust valves for the internal-combustion engine and a deceleration intake control means for controlling the quantity of intake air to be supplied to the downstream side of the intake throttle valve during the deceleration operation of the engine, comprises an intake control characteristic change means for changing the control characteristics of the deceleration intake control means in response to the valve lift characteristic control.

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: A failsafe method in connection with valve timing-changeover control for an internal combustion engine. An abnormality in a control system of the engine is detected. A changeover-instructing signal is generated for changing the valve timing to the low speed valve timing in both of the lower and higher engine speed regions, when the abnormality is detected. When the abnormality is detected, the air-fuel ratio of an air-fuel mixture to be supplied to the engine is enriched when the engine is in a predetermined operating condition determined by the detected value of at least one engine parameter. The enriching of the air-fuel ratio of the air-fuel mixture is carried out by multiplying a basic fuel injection period by a correction coefficient or selecting a suitable basic fuel injection period map.

Abstract: An engine control apparatus wherein an engine output can be adjusted in accordance with an allowable revolution speed of the engine at each valve timing so that while the engine can operate at a revolution speed of up to the highest allowable speed range when operating at a valve timing at which the allowable revolution in speed is high, it can nevertheless operate advantageously without experiencing damage to the timing belt and valve jump even when operated at a valve timing having a lower allowable revolution speed range.

Abstract: A fuel control apparatus is provided for an engine which is primarily used for a vehicle so as to permit the changing of a valve opening-closing timing and/or a valve lift amount for a valve on at least one of an intake side and an exhaust side. Accordingly, to the present invention, the fuel supply to the engine can thus be properly adjusted or corrected in each of the operation ranges with different valve timings so as to improve engine drivability.

Abstract: A control method for a valve-timing changeover in an engine having a valve operating mechanism capable of operating the intake valves or exhaust valves, or both, in a different manner, known as valve timing, such as the magnitude of valve lift or the duration the valve remains open, for improving the operation of the engine at different engine speeds. The control method uses a high-load determinant reference valve established experimentally based on engine revolution speed and calculated in terms of fuel injection quantity to cause the changeover to high-speed valve-timing to occur under high-load conditions when the actual fuel injection quantity being supplied at that engine revolution speed exceeds the high-load determinant reference value.

Abstract: A method for indicating a shift operation for a manual transmission gear includes a step for comparing a detected vehicle speed with a reference speed which is determined and changed on the basis of a detected engine temperature and a step for indicating the shift operation on this basis of a result of the comparison. When a temperature parameter relating to the engine operation is lower than a predetermined reference temperature value, the reference vehicle speed is raised so that the indication of the shift operation will not be generated.

Abstract: An apparatus for sensing the concentration of oxygen in a gas such as engine exhaust gas includes an oxygen concentration sensor formed of an oxygen pump element and a sensor cell element, each based on a solid electrolytic member formed of a material such as ZrO.sub.2, and is provided with a limiter circuit which functions to reduce the level of current supplied to the oxygen pump element when a voltage produced by the sensor cell element indicates that this current level is such as to produce a "blackening" phenomenon whereby deterioration of the oxygen pump element will occur and oxygen concentration sensing reliability will be lowered.

Abstract: An oxygen concentration sensing apparatus includes an oxygen pump element and a sensor cell element to be placed in a gas under measurement, and a device for generating a voltage value command indicating a voltage to be generated across electrodes of the sensor cell element. A current limit device is provided so that the supply of the voltage value command is stopped to decrease a pump current to the oxygen pump element gradually when the voltage generated across the electrodes of the sensor cell element exceeds a first predetermined voltage, and the pump current to the oxygen pump element is reduced immediately when the voltage generated across the electrodes of the sensor cell element exceeds a second predetermined voltage which is higher than the first predetermined voltage.

Abstract: An air intake side secondary air supply system for an internal combustion engine having an air intake side secondary air supply system includes an oxygen concentration sensor, and controls a duty ratio of opening and closing of an open/close valve disposed in the air intake side secondary air supply passage by determining a valve open period within each duty cycle of control operation in accordance with a result of comparison between the level of the output signal of the oxygen concentration sensor and a level corresponding to a target air-fuel ratio. The duty ratio of opening and closing of the open/close valve is maintained within a predetermined duty ratio range so as to improve effectiveness of the control of the secondary air supply as well as to avoid the generation of over lean or over rich mixture.

Abstract: An air intake side secondary air supply system for an internal combustion engine having an air intake system using a carburetor and an air intake side secondary air supply passage leading to the downstream of the carburetor, includes an oxygen concentration sensor producing an output signal whose level is substantially proportional to an oxygen concentration of the exhaust gas. A control means for controlling a duty ratio of opening and closing of an open/close valve disposed in the air intake side secondary air supply passage in accordance with a result of comparison between the level of the output signal of the oxygen concentration sensor and a level corresponding to a target air-fuel ratio. The target air-fuel ratio is up-dated in response to at least two parameters indicative of the engine operation.