  We consider mechanisms of directed transport in a ratchet model comprising,
besides the external freedom where transport occurs, a chemical freedom that
replaces the familiar external driving by an autonomous dynamics providing
energy input, and an internal freedom representing a functional mode of a motor
molecule. The dependence of the current on various parameters is studied in
numerical simulations of our model. In particular, we point out the role of the
internal freedom as a buffer between energy input and output of mechanical work
that allows a temporary storage of injected energy and can contribute to the
efficiency of current generation.
