Vibration　analysis　has　been　proved　to　be　an　effective　and　powerful　tool　for　the　condition　monitoring　and　fault　diagnosis　of　rolling　bearings.　During　the　past　decades,　the　conventional　envelope　analysis　has　been　one　of　the　main　approaches　in　vibration　signal　processing.　However,　the　envelope　analysis　is　based　on　stationary　assumption,　thus　it　is　not　applicable　to　the　fault　diagnosis　of　bearings　under　rotating　speed　variation　conditions.　This　constraint　limits　the　bearing　diagnosis　in　industrial　applications.　In　recent　years,　order　tracking　methods　based　on　time-frequency　representation　have　been　proposed　for　bearing　fault　detection　under　speed　variation　operating　conditions.　However,　the　methods　are　only　applicable　for　offline　bearing　fault　detection.　Aiming　at　the　shortcomings　of　the　current　tacholess　order　tracking　techniques,　an　online　tacholess　order　tracking　method　is　proposed　in　this　paper.　The　proposed　method　is　on　the　basis　of　extracting　the　instantaneous　tachometer　information　from　the　collected　vibration　signal　itself　continuously,　and　resampling　the　original　signal　with　equal　angle　increment.　The　envelope　order　spectrum　is　used　for　bearing　fault　identification.　The　effectiveness　of　the　proposed　method　has　been　validated　by　both　simulated　and　experimental　bearing　vibration　signals.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.