Rails: Plus sign in GET-Request replaced by space

In Rails 3 (Ruby 1.9.2) I send an request

 Started GET "/controller/action?path=/41_+"

But the parameter list looks like this:

 {"path"=>"/41_ ",
   "controller"=>"controller",
   "action"=>"action"}

Whats going wrong here? The -, * or . sign works fine, its just the +which will be replaced by a space.