A device for transmitting torque between a drive member and a driven member for vehicles, said system consisting of automatic clutch means (1) disposed within a drive-system and control means (2) operable in a driver's cab,
- said automatic clutch means (1) comprising:
- a drive member (3);
- a driven member (7);
- a shaft (4) rigidly connected to or integrally formed with the drive member (3) and having a substantially regular prismatic section (5) concentric therewith;
- a hub (6) connected to or integrally formed with the driven member (7) and mounted concentrically on said shaft (4) by means of bearings (8,9), said regular prismatic section (5) being positioned within the hub (6);
- a synchronous cage (10) rotatably supported at its axial ends on the shaft (4) between an inner surface of the hub (6) and said regular prismatic section (5), and having openings (11) evenly distributed around a circumference of the synchronous cage (10), the number of said openings (11) being the same as that of side surfaces of said regular prismatic section (5);
- a torque-transmitting element (12) provided in each said opening (11) with a clearance therebetween, and movable on a respective side surface of said regular prismatic section (5) between a first position (I) near one end of respective arched space defined between the inner surface of the hub (6) and the side surface of said regular prismatic section (5) and a second position (II) near the other end of said arched space, each torque-transmitting element (12) being dimensioned so that when it is in a middle position (III) between said first position (I) and second position (II), the hub (6) is in disengagement with the shaft (4) and no torque is transmitted between the shaft (4) and the hub (6), and when it is in said first position (I) or said second position (II), the hub (6) is in engagement with the shaft (4) and torque is transmitted between the shaft (4) and the hub (6) through the torque-transmitting element (12);
- means for holding each torque-transmitting element (12) in said middle position (III) when said shaft (4) rotates at a speed lower than its idle speed or does not rotate, each said torque-transmitting element (12) entering said first position (I) due to inertia lag behind the shaft (4) when the drive member (3) starts to rotate in a positive direction (14);
- means for restricting each torque-transmitting element (12) in said middle position (III) when the speed of the drive member (3) becomes lower than that of the driven member (7) only in said positive direction;
- and
- means for enforcing the synchronous cage (10) to temporarily rotate along with said hub (6) so as to force each torque-transmitting element (12) to move from said middle position (III) to one of said first position (I) or said second position (II);
- wherein said control means (2) controls the operation of said enforcing means.