1. In this mechanism, two co-axial pulleys with different diameters are fixed between the driving pulley and the idler pulley in a traditional timing transmitting system.

2. The transmission further comprises: gear change linkages (50, 50') connected between the driving pulley and the driven pulley for adjusting a gear ratio by axially translating each of the conical wheels constituting the driving pulley and the driven pulley; and a gear change actuator (60) connected to the gear change linkages (50, 50') for receiving a gear change input from the outside and actuating the gear change linkages (50, 50').