1. Field of the Invention
The present invention relates to a method and a device for regulating the air-fuel ratio and the ignition timing in an internal combustion engine, particularly in an automotive internal combustion engine of the spark ignition type.
2. Description of the Prior Art
Recent trends in internal combustion engines have been for cleaner engine emission and, from the viewpoint of fuel-economy, reduction of the specific fuel consumption.
The engine emission and specific fuel consumption of internal combustion engines are closely related to the air-fuel ratio supplied in the engines, as illustrated in FIG. 1 attached to the specification for illustrating the operation characteristics of the internal combustion engine.
In general, in order to attain both cleaner emission and reduced fuel consumption, it is advantageous to operate an internal combustion engine in the lean air-fuel mixture range. However, misfires tend to occur in the lean air-fuel mixture range. Individual variations in operating characteristics and deterioration of engines carburetors, and other parts make it impossible for engines to be operated in the range close to the misfire limit. Therefore, the usual practice is to operate an engine in the stable range with an air-fuel ratio which is richer by 2 than the misfire limit air-fuel ratio. However, operation of an engine in such a range is not desirable from the viewpoint of cleaner emission and fuel economy. This is an important problem in the operation of an internal combustion engine.
Other problems are that the optimum air-fuel ratio giving the best rate of fuel consumption can change, even under the same engine running conditions depending on ambient conditions such as the atmospheric pressure and temperature. Also, the ignition timing, which is closely related to the air-fuel ratio, affects the engine output and, accordingly, the rate of fuel consumption.
Now, the minimum rate of fuel consumption is attained at the lean air-fuel ratio range close to the misfire limit, as can be seen from the characteristic illustrated in FIG. 1. The variation in combustion, which is related to the air-fuel ratio, becomes eminently greater as the air-fuel ratio approaches the misfire limit.
The inventors noticed the fact that, since the variation of the combustion in cylinders causes vibration of the engine body due to the torque counter force of the cylinders, the variation of the combustion can be detected by that vibration.