The Austrian, who has previously had spells at SpVgg Unterhaching (2007-10) and most recently VfR Aalen (2011-13) begins work in Bavaria on Monday.
'An experienced coach'
"We're pleased to be able to present an experienced coach," said Sporting Director Thomas Linke. "We're sure that under Ralph's leadership we'll find some success."
Ingolstadt, who sit bottom of the Bundesliga 2, face a tricky trip to VfL Bochum 1848 on Sunday under the guidance of caretaker coach Michael Henke.