http://www.icsv12.ist.utl.pt/papers/paper.php?id=717
http://www.freepatentsonline.com/6546328.html
http://www.freepatentsonline.com/EP1221603.html
http://www.sae.org/technical/papers/ground_vehicle/SI - a lot of tech papers (including about wavelets in knock-sensing), but not free.