Thanks for your answer.
I hope this is not necessary, because the string is transfered via POST and is not an URL.
I have to use my own data-format, with delimeters Ascii 17 and 18 between the data-sets and I was so glad, that in my tests every byte seems to be allowed with the transfer.
So URL-Encoding is not the right choice. If it is only the '=' I could escape that, but I first want to find out here what is the best way.