Get search field content

How can I get the search field content? I want to integrate the search field content in the filename of the exporting csv-File on tabletools. But I am not able to get the content of the search field with fnSettings().oPreviousSearch:
http://live.datatables.net/icowul/11/edit#javascript,html,live
In this case there is a preset on the search field "Ger"
"oSearch": {"sSearch": "Ger"}
In the 2nd footer cell the current "Searchtext content" should be displayed but Datatables stop working as soon as adding fnSettings().oPreviousSearch

Regards

Mike