In a model-driven development context, the refinement of a Real Time Operating System (RTOS) independent design model of a real-time application to a RTOS specific implementation model is a non-trivial task. Indeed, the different design choices made to guarantee the application timing properties are not always implementable on the target RTOS. In this paper, we propose a pattern-based approach to perform the refactoring of the real-time design model when a deployment problem appears. This refactoring guarantees the deployment of the refactored design model and the respect of its timing properties. This paper explains in details two examples of patterns which are the Equal Priority Merge Pattern (EPMP) and the Distinct Priority Merge Pattern (DPMP). The automation of the proposed approach allows showing its applicability on a robotic case study.