In utility model patents, how to express the functional features in independent claims?

the technical feature of limited functionality is the unity of function and technical solution-your technical solution (which can be covered exhaustively) realizes your function, that is, it is protected by patent. However, it is not within the scope of your patent protection to realize your function with other schemes, or to use your technical scheme for other functions (such as users).

you can't just describe the function and performance, it must be the subject that depends on the principle and function under the composition, structure and scheme. To give an inappropriate example: Einstein is admired by the world for his clever contribution, so he should be described by his deeds. Only when there is an entity can the function exist, and the combination of them is the technical feature of functional limitation.