 While clearly not the only patent relating to the hybrid electric vehicle, the patent was important based on 120+ subsequent patents directly citing it.The patent was issued in the U.S. and the system was not prototyped or commercialized.In 1988, Alfa Romeo built three prototypes of the Alfa 33 Hybrid, equipped with the tried and tested Alfasud boxer engine (1,500cc, 95 HP) combined with a three-phase asynchronous electric motor (16 HP, 6.1 kgm of torque) supplied by Ansaldo of Genoa.