Abstract: Arrangement and method of operating a variable drive unit with a selector switch for the preselection of a long-term speed and a control unit which allows for the continuous operation of a continuously variable power split transmission only at reduction ratios (.phi..sub.continuous) having a certain minimum interval (.phi..sub.min) from the reduction ratio at the shift points between the speed ranges in the mechanical branch of the transmission and the control unit changes the speed of the internal combustion engine in order to reach speeds lying within the minimum interval and controlled by changing the engine speed while maintaining reduction ratio of the transmission instant.

Abstract: Arrangement and method for operating a drive unit for motor vehicles, particularly for agricultural and construction machinery, with a controllable internal combustion engine (2), a continuously variable hydromechanical power split transmission (6) and a control device (3) which in order to start and to operate the vehicle at low speeds and under load, at first reduces the rotational speed of the internal combustion engine to less then the nominal speed, reaches a first speed by reducing the delivery volume of the adjusting pump (13) of the hydrostatic branch (15), a further increased speed by increasing the rotational speed of the internal combustion engine and as a result the further increase in the vehicle speed by controlling the transmission ratio of the hydrostatic-mechanical power split transmission (6) is achieved.

Abstract: A hydrostatic-mechanical power-distribution transmission with infinitely variable gear ratio in the hydrostatic branch and several ratios in the mechanical branch, which downstream of the coupling gear has shiftable planetary reduction gears for the purpose of reducing the power contribution of the hydrostatic branch in the starting range.