  We derive Hardy type inequalities for a large class of sub-elliptic operators
that belong to the class of $\Delta_\lambda$-Laplacians and find explicit
values for the constants involved. Our results generalize previous inequalities
obtained for Grushin type operators $$ \Delta_{x}+
|x|^{2\alpha}\Delta_{y},\qquad\
(x,y)\in\mathbb{R}^{N_1}\times\mathbb{R}^{N_2},\ \alpha\geq 0, $$ which were
proved to be sharp.
