A three-function transmission system for a self-propelled vehicle with variable travel speed, comprising:
- a primary driving shaft;
- an output shaft;
- a variable speed drive with a belt, a controlled pulley and a driven pulley, flanges of the controlled pulley having a variable gap, the controlled pulley being carried by a corresponding pulley controlled shaft and the driven pulley being carried by a corresponding pulley driven shaft differently from the controlled pulley to the driven pulley, the pulley controlled shaft being fitted with a bearing, roller or ring able to rotate freely on the output shaft, such that the the controlled pulley is configured to be completely disengaged from the belt;
- a controlled reversal mechanism for reversing a direction of travel of the vehicle;
- and
- at least one three-function mechanical control device of the variable speed drive and the controlled reversal mechanism, the at least one mechanical control device being between the primary driving shaft and the output shaft;
- wherein the primary driving shaft transmits motion via the variable speed drive to an input shaft of the reversal mechanism, the input shaft being able to engage with the output shaft, in such a way as to allow the vehicle to travel forward or in reverse respectively, at a variable travel speed in at least one direction of travel, the variable speed drive and the reversal mechanism for reversing the direction of travel of the vehicle being controlled selectively from the mechanical control device,
- and the mechanical control device is configured to move angularly from a neutral position, either in a first direction in which the mechanical control device acts on a mechanical control device of the reversal mechanism and on the mechanical control device of the variable speed drive so as to allow, first of all, movement of the mechanical control device of the reversal mechanism into a forward travel position, then, second, a passage of the mechanical control device of the variable speed drive from a disengaged position into an engaged position depending on a selected travel speed, or in a second direction opposite to the first direction in which it acts on the mechanical control device of the reversal mechanism and on the mechanical control device of the variable speed drive in such a way as to allow, first of all, the movement of the mechanical control device of the reversal mechanism into a reverse travel position, then, second, a passage of the mechanical control device of the variable speed drive from the disengaged position into the engaged position, depending on a selected speed at which the vehicle backs up.