An electric motor of the inner rotor type having a stator (10, 20) and a rotor (90), - the uprights (10, 20) a number of 3N poles (11, 21) with windings and the rotor (90) opposing pole pieces, and a yoke (12, 22) connecting the poles (11, 21) to each other, comprising, where N is an integer greater than 1, - the rotor (90) having a plurality of permanent magnets (92) that form alternately a total of 2N North and South poles on its surface, as well as with - an air gap between the pole pieces and the rotor (90), and - an open groove (14, 24) between the respective leading and trailing portions of the adjacent pole pieces of successive circumferentially poles (11, 21) and wherein the said rotor (90) opposite surfaces of the pole pieces have an arcuate section and an adjoining rectilinear portion and the circular portion with the leading portion of the respective ...