FIELD OF THE INVENTION
The invention relates to a method for controlling a drive train of a motor vehicle and to a drive train control system.
In conventional transmission control systems for motor vehicles, the transmission ratio of the transmission is set automatically as a function of the position of the accelerator pedal and of the speed of travel by using stored maps. Instead of using the position of the accelerator pedal as such, it is also possible to use a signal of a so-called electronic accelerator pedal (E-Gas for short) or some other variable derived from the engine torque demanded by the driver. In this case, various driving parameters and operating states of the motor vehicle are taken into account as is described in International Publication WO 97/01051. The respective gear to be selected or--in the case of continuously variable transmissions--the transmission ratio to be set is selected by control circuits operating by fuzzy logic methods. This logic describes expert knowledge gained from experience in the form of what is referred to as a basic set of rules. These rules are then used for regulating operations or control operations of the motor-vehicle transmission. The fuzzy logic circuit produces control signals, which, among other things, define the transmission ratio of the transmission and, in the case of automatic step-change transmissions, the gear to be selected.
Published, Non-Prosecuted German Patent Application DE 196 37 210 A1 discloses a conventional integrated drive train control system for a motor vehicle. The drive train control system interprets the position of the accelerator pedal and of the brake pedal as a wheel torque desired by the driver. It has a calculating device which receives the positions of the accelerator pedal and the brake pedal and which produces central control parameters for the drive unit and for those units of the drive train that exert a decelerating effect.
There are driving situations in which it would be expedient if actuation of the brakes by the driver were assisted by the drive train of the motor vehicle, when traveling downhill for example. This can, for example, be accomplished by the suppression of upshifts specified by a map, i.e. by retaining the existing transmission ratio.
European Patent Application EP 0 531 154 A2 discloses a transmission control system, with which the transmission ratio, which is determined as a function of the position of the accelerator pedal and of the speed of travel by using stored maps, can be corrected. For this purpose, a correction factor is determined by a fuzzy unit as a function of the driver's desire for braking, of the tractive resistance and of the current transmission ratio, and is added to the corresponding map value.