Assurance Cases are increasingly being required for regulatory acceptance of Cyber-Physical Systems. However, the ever-increasing complexity of these systems has made the assurance cases development complex, labor-intensive and time-consuming. Assurance case fragments called patterns are used to handle the complexity. The state-of-the-art approach has been to manually select generic patterns from online catalogs, instantiate them with system-specific information, and assemble them into an assurance case. While there has been some work in automating the instantiation and assembly, a less researched area is the automation of the pattern selection process, which takes a considerable amount of the assurance case development time. To close this automation gap, we have developed an automated pattern selection workflow that handles the selection problem as a coverage problem, intending to find the smallest set of patterns that can cover the available system artifacts. For this, we utilize the ontology graphs of the system artifacts and the patterns and perform graph analytics. The selected patterns are fed into an external instantiation function to develop an assurance case. Then, they are evaluated for coverage using two coverage metrics. An illustrative autonomous vehicle example is provided, demonstrating the utility of the proposed workflow in developing an assurance case with reduced efforts and time compared to the manual development alternative.