This invention relates to a method for detecting the opening of a throttle valve in a fully closed position in an internal combustion engine, which can detect the valve opening in an accurate and positive manner.
In conventional electronic fuel supply control systems, electronic suction air quantity control systems and other electronic control systems for internal combustion engines, the opening of a throttle valve arranged in the intake pipe of an engine, which forms a parameter indicative of the operating condition of the engine, is detected in the form of an electrical signal, and the electrical signal indicative of detected values of the valve opening is processed in an electronic control unit or like means, for use in respective controls. Particularly at engine idle, it is important for proper control of the engine operation to accurately determine whether or not the throttle valve is really in its proper fully closed position, i.e. in the idle opening position. To ensure accuracy of the determination, high detecting accuracy is required of a throttle valve opening sensor. Conventional throttle valve opening sensors include a type comprising a potentiometer directly coupled to the valve shaft of the throttle valve and a type comprising a vacuum intake port opening in the intake pipe at a location immediately upstream of the throttle valve in a fully closed position, a diaphragm actuatable by vacuum applied thereto through the vacuum intake port, and a potentiometer coupled to the diaphragm. According to these type sensors, the sensor output can be affected by the machining tolerances and assembling and mounting tolerances of the sensors, wear of the valve body and other sliding parts of the throttle valve, or other factors such as aging, making it difficult to always detect the valve opening of the throttle valve, particularly the idle opening, with accuracy.
To eliminate the above disadvantage, a method has been proposed by U.S. Pat. No. 4,359,894 to Ikeura et al., which is adapted to determine whether or not the throttle valve is in its proper fully closed position, by storing into a memory a lowest voltage value of an output signal of a throttle valve opening sensor, comparing the sum of the above lowest voltage value and a voltage value corresponding to the machining tolerances and assembling and mounting tolerances of the throttle valve or the insensitive output range of same with each of voltage values of the valve opening subsequently detected by the sensor, and storing a subsequently detected value into the memory as a new lowest voltage value when the subsequently detected value is determined to be lower than the previously stored value.
However, sometimes a value can be erroneously temporarily detected which is smaller than the actual throttle valve opening and also lower than the presently stored lowest voltage value, due to noises occurring in the supply line or processing system for the throttle valve opening signal or other disturbances. In such event, the above proposed method cannot avoid the disadvantage that the above false smaller detected value is stored into the memory as a lowest voltage value, i.e. a signal indicative of the fully closed position of the throttle valve.