1. Introduction and motivation
Agricultural vehicles have to cope with working conditions which are more complex and demanding than those experienced by other ground vehicles, [10]. In fact, agricultural vehicles are essentially designed to work at low speed while providing large traction forces. Moreover, their ease of moving on uneven soil makes them suitable also for heavy trailers transportation. To ensure the maximum flexibility of use at each speed and to exploit the maximum engine power available in all working conditions, nowadays agricultural vehicles are often equipped with a so-called power-shift transmission. This kind of transmission has a large number of gears available (typically from 9 to 30) and it allows to perform a gearshift with no (or at least with a minimum) loss of power from the engine to the driving wheels.