Hello, sorry for bumping this very old topic.
I'm also interested in knowing if it's possible to normalize _score values into the range 0,1.0 (where the top result has score 1.0).
The proposed solution floors scores above 1.0, but if I understood correctly the OP wanted to know if all scores could effectively be divided by max_score.
The reason this is interesting to me is: I don't know how to determine weights for functions in a function_score query. I.e. if a given query can produce _score values in an arbitrary range, how can I know if a weight of 1, 5, 100 or 50000 is effective?