This paper presents a framework for schedule integration of time-triggered systems tailored to the automotive domain. In-vehicle networks might be very large and complex and hence obtaining a schedule for a fully synchronous system becomes a challenging task since all bus and processor constraints as well as end-to-end-timing constraints have to be taken concurrently into account. Existing optimization approaches apply the schedule optimization to the entire network, limiting their application due to scalability issues. In contrast, the presented framework obtains the schedule for the entire network, using a two-step approach where for each cluster a local schedule is obtained first and the local schedules are then merged to the global schedule. This approach is also in accordance with the design process in the automotive industry where different subsystems are developed independently to reduce the design complexity and are finally combined in the integration stage. In this paper, a generic framework for schedule integration of time-triggered systems is presented. Further, we show how this framework is implemented for a FlexRay network using an Integer Linear Programming (ILP) approach which might also be easily adapted to other protocols. A realistic case study and a scalability analysis give evidence of the applicability and efficiency of our approach.