  We study compactifications of eleven-dimensional supergravity on Calabi-Yau
threefolds times a circle, with a duality twist along the circle a la
Scherk-Schwarz. This leads to four-dimensional N=2 gauged supergravity with a
semi-positive definite potential for the scalar fields, which we derive
explicitly. Furthermore, inspired by the orientifold projection in string
theory, we define a truncation to N=1 supergravity. We determine the D-terms,
Kaehler- and superpotentials for these models and study the properties of the
vacua. Finally, we point out a relation to M-theory compactifications on
seven-dimensional manifolds with G2 structure.
