A target-oriented conceptual process for the layout of vehicle-control systems leads to efficient product development. Enabling a target-oriented layout, a functional system description is necessary to define the system requirements, e.g., a maximum system torque or a defined minimum time constant. This paper introduces a novel approach to a systematic development of functional models for the quantification of the vehicle-control system requirements. The potential of the method is verified by applying it to the active roll stabilisation system (ARS).