How can I get UE4 API in a win32 DLL project?

Hi,guys,
I’m building a UE4 SDK , and I want to use the SDK in a win32 c++ dll which can provide APIs to use data from a Service process.
But I want to use the UE4 math API and FVector, FQuat,FRotator,etc in the dll and I can’t find the way to use the UE4 API in a win32 DLL Project because the dll of UE4 is too much.

Why UE4 can’t provide a main DLL just like Unity? Or maybe there is another way to get the API of UE4.

Who can help me find the way? Thanks a lot!