Abstract
This work deals with an automatic power train for two-wheelers and it is carried out in the framework of the Italian MUSS project. Environmental issues are currently within the main topics on which vehicle design is focused. In this context, two wheelers have to face many challenges and one of them is to reduce the loss of efficiency in the power train. Motor-scooters are currently quite always equipped with CVT transmission with rubber belt. This kind of transmission can be very cheap to manufacture, it has good comfort performance but has a mechanical efficiency of just 80% – 85% in the best working conditions. In this work the study of an automatic transmission and its application to a small displacement motor-scooter are presented. In order to keep low manufacturing costs and a high comfort typical of the CVT, improving its efficiency at the same time, the studied system is based on a discrete ratio gear box with mechanical control. The transmission has gears and centrifugal clutches and free-wheels which mechanically control the gear shift. A dynamic model of the transmission and results of a typical acceleration manoeuvre are presented and discussed in the paper.
Keywords: automatic transmission, centrifugal clutch, free wheel, dynamic model, motor-scooter.