Generalizations of the Kovalevskaya case and quaternions
  This paper provides a detailed description of various reduction schemes in rigid body dynamics. Analysis of one of such nontrivial reductions makes it possible to order the cases already found and to obtain new generalizations of the Kovalevskaya case to e(3). We note that the above reduction allows one to obtain in a natural way some singular additive terms which were proposed earlier by D.N. Goryachev. 
Ivan A. Bizyaev, Alexey V. Borisov, Ivan S. Mamaev
nlin.SI