A high solid hydroxyl polyester resin has been developed,which is used to prepare polyester-polyurethane top coatings for the city railway train,with high performance,such as high gloss,impact resistance,high hardness,good weathering resistance,low smoke toxicity and easy cleanness.

This paper introduces one of the methods——Smith overlapped control method, which is used in the automatic city railway train change_speed control,combining one kind of underway train tractive model,labor,the paper deduces the transfer function of the control system,and obtained the parameters of Smith control method,by experiments.