Drive device and method for moving a vehicle part

Process for adjusting a motor vehicle part between at least two positions, the motor vehicle part being driven by an electric motor, furthermore a pulse signal being generated proportionally to the rotary motion of the electric motor and being supplied to a control unit for controlling the electric motor, the instant of input of each signal to the control unit being acquired and at certain extrapolation instants between two such input instants, the current force acting on the motor vehicle part being estimated from at least some of these measured instants and ultimately this estimate being used as the criterion in the decision whether the electric motor is turned off or reversed or not, upon the input of a new pulse signal, the measured value of the current period duration of the motor revolution being determined from the difference relative to at least one earlier pulse signal measured value, an estimate of the current period duration being determined at each extrapolation instant with consideration of the current measured period duration and at least one of the previous measured period durations, furthermore the estimated current rpm change being determined from the estimated period durations, and the estimate of the current force acting on the motor vehicle part being determined from the estimated changes of rpm.