As a general matter, if the engineer invented it off company time and did not use any materials, facilities, equipment, collaboration from co-workers, etc. to invent it, and the patent is not in the line of work the engineer is doing for the company, then no--the company should not have any rights to the patent. (Conversely, if the patent is for basically the same sort of things the engineer does for the company, and/or he used any company resources for it, it should belong to the company, even if invented after work hours, on weekends, etc.)The above could be broadened contractually--if the engineer signed a contract or agreement that anything he invents belongs to the company, that agreement would be enforceable.