Invariant differential operators for quantum symmetric spaces, I

This is the first paper in a series of two which proves a version of a theorem of Harish-Chandra for quantum symmetric spaces in the maximally split case: There is a Harish-Chandra map which induces an isomorphism between the ring of quantum invariant differential operators and the ring of invariants of a certain Laurent polynomial ring under an action of the restricted Weyl group. Here, we establish this result for all quantum symmetric spaces defined using irreducible symmetric pairs not of type EIII, EIV, EVII, or EIX. A quantum version of a related theorem due to Helgason is also obtained: The image of the center under this Harish-Chandra map is the entire invariant ring if and only if the underlying irreducible symmetric pair is not one of these four types.