The present invention relates to a method of controlling a power train of an automotive vehicle. The term "power train" is used herein to mean a power generating and delivery system which includes an engine and a transmission.
The power train of this kind is used for example as a drive system of an automotive vehicle. Until recently, it has been the common practice in controlling the power train to control an engine in a discrete manner from controlling a transmission as reported for example in an SAE technical paper 830423 published by Society of Automotive Engineering (SAE). In controlling an engine, an engine controller receives, as basic data, an engine revolution speed and an intake air flow rate, performs computations on these input data, and generates output data resulting from the computations in order to adjust fuel supply, ignition timing, exhaust gas recirculation rate, and intake air flow rate to optimal values, respectively. In controlling a transmission, a transmission controller receives, as basic input data, a vehicle speed and an engine load, performs computation on these input data, and generates output data resulting from the computations in order to shift the transmission to an optimal reduction ratio (a gear position) and adjust a slip in a torque converter to an optimal level. In controlling the engine, there are cases where an intake manifold vacuum or an intake pipe absolute pressure is used as an input data.
However, according to the control method as mentioned above, the input data for use in controlling the engine are different from the input data for use in controlling the transmission, and thus the engine and the transmission do not operate on integrated input data. Thus, when a plurality of means for generating input data, such as sensors, have less uniform characteristics or they age in different manners, the varying tendency of control characteristics of the engine and that of the transmission which are dependent upon the characteristics of the means are not uniform and less close with each other. In this case, since the engine control characteristics and the transmission control characteristics are not matched, even if variations in control characteristics of the engine and variations in control characteristics of the transmission are not substantially large, respectively, the fuel economy and the power performance of the power train as a whole are deteriorated greatly, resulting in a great deterioration in performance as compared to the initial performance. With the conventional control method, however, there are limits to enhancing or improving the control characteristics of the power train as a whole.