Italian State Railway E.431

The E.431 was a three-phase electric express locomotive for the Northern Italian network that was developed after it became evident that the E.330 had insufficient adhesive weight. With an additional driving axle, it had the wheel arrangement 1-D-1, but still the same output of 1,900 kW. Two low-slung driving motors worked on a triangular rod and through coupling rods on all four driving axles. Each carrying axle formed a Zara bogie together with the adjacent driving axle. Anyway, this did not lead to good curve running characteristics due to the long driving wheel base.

Through pole switching and series-parallel control, a total of four continuous speeds could be realized. These were 37.5, 50, 75 and 100 km/h and while accelerating between the speed steps, excessive power had to be dissipated through resistors. These resistors were not cooled by a closed water circuit, but by soda solution that evaporated through a chimney into the environment and had to be refilled periodically. In the beginning, lighting was with gas lamps and electric lamps have only been added later.

The E.431 was mostly used on flat lines since it showed insufficient pulling power around 50 km/h. Since they were able to run in multiple with several types of electric locomotives, they were used for express trains with up to 20 cars, being assisted by another E.431 or any other type of compatible locomotives. They were used until the end of three-phase operation in Italy in 1976 and two were preserved.