A drive system for an engine arrangement, the drive system having a main axis and comprising: - a gear reduction mechanism having at least three separate and rotatable junction elements, the rotation speeds of the junction elements being interdependent but not having a fixed ratio the ones relative to the others, the gear reduction mechanism comprising an epicyclic gearing which includes: - a sun gear; - an annular gear; - planet gears meshing with both the sun gear and the annular gear and supported by a planet carrier; each of the sun gear, the annular gear and the planet carrier being connected to one of the junction elements (25, 21, 22); wherein, in the mounted position, among said junction elements: - a first junction element is connected to an engine crankshaft; - a second junction element is connected to an accessory pulley which is drivingly connected to an electric machine and at least one accessory; wherein, in a first operating phase of the drive system, the first junction element receives torque from the second junction element in a first operating phase of the drive system; - a free wheel which is connected to a non-rotating part of the engine arrangement in the mounted position, a third junction element among said junction elements being configured to be coupled to the free wheel in the first operating phase of the drive system, wherein, in the first operating phase, the free wheel is configured such that when the third junction element exerts torque on the free wheel in one direction, the free wheel is in an engaged state and stops the rotation of the third junction element, and when the third junction element exerts torque on the free wheel in the opposite direction, the free wheel is in a free state and allows rotation of the third junction element, characterized in that the third junction element is moveable in translation along said main axis between a first position, in the first operating phase, in which, in the mounted position, it is coupled to the free wheel, and another position, in an operating phase different from the first one, in which, in the mounted position, it is uncoupled from the free wheel. - a gear reduction mechanism having at least three separate and rotatable junction elements, the rotation speeds of the junction elements being interdependent but not having a fixed ratio the ones relative to the others, the gear reduction mechanism comprising an epicyclic gearing which includes: - a sun gear; - an annular gear; - planet gears meshing with both the sun gear and the annular gear and supported by a planet carrier; each of the sun gear, the annular gear and the planet carrier being connected to one of the junction elements (25, 21, 22); wherein, in the mounted position, among said junction elements: - a first junction element is connected to an engine crankshaft; - a second junction element is connected to an accessory pulley which is drivingly connected to an electric machine and at least one accessory; wherein, in a first operating phase of the drive system, the first junction element receives torque from the second junction element in a first operating phase of the drive system; - a sun gear; - an annular gear; - planet gears meshing with both the sun gear and the annular gear and supported by a planet carrier; each of the sun gear, the annular gear and the planet carrier being connected to one of the junction elements (25, 21, 22); wherein, in the mounted position, among said junction elements: - a first junction element is connected to an engine crankshaft; - a second junction element is connected to an accessory pulley which is drivingly connected to an electric machine and at least one accessory; - a first junction element is connected to an engine crankshaft; - a second junction element is connected to an accessory pulley which is drivingly connected to an electric machine and at least one accessory; wherein, in a first operating phase of the drive system, the first junction element receives torque from the second junction element in a first operating phase of the drive system; - a free wheel which is connected to a non-rotating part of the engine arrangement in the mounted position, a third junction element among said junction elements being configured to be coupled to the free wheel in the first operating phase of the drive system, wherein, in the first operating phase, the free wheel is configured such that when the third junction element exerts torque on the free wheel in one direction, the free wheel is in an engaged state and stops the rotation of the third junction element, and when the third junction element exerts torque on the free wheel in the opposite direction, the free wheel is in a free state and allows rotation of the third junction element, characterized in that the third junction element is moveable in translation along said main axis between a first position, in the first operating phase, in which, in the mounted position, it is coupled to the free wheel, and another position, in an operating phase different from the first one, in which, in the mounted position, it is uncoupled from the free wheel.