  Weyl's idea on scale invariance was resurrected by Cheng in 1988. The
requirement of local scale invariance leads to a completely new vector field,
which we call the ``Cheng-Weyl vector field''. The Cheng-Weyl vector field
couples only to a scalar field and the gravitational field naturally. It does
not interact with other known matters in the standard model of particle
physics. In the present work, the (generalized) Cheng-Weyl vector field coupled
with the scalar field and its cosmological application are investigated. A
mixture of the scalar field and a so-called ``cosmic triad'' of three mutually
orthogonal Cheng-Weyl vector fields is regarded as the dark energy in the
universe. The cosmological evolution of this ``mixed'' dark energy model is
studied. We find that the effective equation-of-state parameter of the dark
energy can cross the phantom divide $w_{de}=-1$ in some cases; the first and
second cosmological coincidence problems can be alleviated at the same time in
this model.
