A drive system for an engine arrangement, the drive system comprising an epicyclical gear reduction mechanism which has a main axis and which comprises: • a first main gear arranged to rotate about main axis, • a second main gear arranged to rotate about main axis in the same direction as the first main gear, • a first set of planet gears with planet gears meshing with the first main gear, • a second set of planet gears with planet gears meshing with the second main gear, • a planet carrier, supporting planet gears (23, 21) of the first and second planet gears (23, 21), the planet carrier being located, along the main axis, between the first main gear and the second main gear (22, 121); wherein each planet gear of the first set of planet gears is coupled to a planet gear of the second set of planet gears such that no relative rotation is possible between them, wherein, in the mounted position: • the first main gear is connected to an engine crankshaft, • the planet carrier is connected to at least one accessory pulley which is drivingly connected to an electric machine and preferably to at least one accessory; wherein the drive system further comprises a free wheel which is connected to a non-rotating part of the engine arrangement in the mounted position, wherein the second main gear is configured to be coupled, preferably via an intermediate junction element of the drive system, to the free wheel in a first operating phase of the drive system, wherein, in the first operating phase, the free wheel is configured such that when the second main gear (22, 121) exerts torque on the free wheel in one direction, the free wheel is in an engaged state and stops the rotation of the second main gear (22, 121), and when the second main gear (22, 121) exerts torque on the free wheel in the opposite direction, the free wheel is in a free state and allows rotation of the second main gear (22, 121). • a first main gear arranged to rotate about main axis, • a second main gear arranged to rotate about main axis in the same direction as the first main gear, • a first set of planet gears with planet gears meshing with the first main gear, • a second set of planet gears with planet gears meshing with the second main gear, • a planet carrier, supporting planet gears (23, 21) of the first and second planet gears (23, 21), the planet carrier being located, along the main axis, between the first main gear and the second main gear (22, 121); wherein each planet gear of the first set of planet gears is coupled to a planet gear of the second set of planet gears such that no relative rotation is possible between them, wherein, in the mounted position: • the first main gear is connected to an engine crankshaft, • the planet carrier is connected to at least one accessory pulley which is drivingly connected to an electric machine and preferably to at least one accessory; wherein the drive system further comprises a free wheel which is connected to a non-rotating part of the engine arrangement in the mounted position, wherein the second main gear is configured to be coupled, preferably via an intermediate junction element of the drive system, to the free wheel in a first operating phase of the drive system, wherein, in the first operating phase, the free wheel is configured such that when the second main gear (22, 121) exerts torque on the free wheel in one direction, the free wheel is in an engaged state and stops the rotation of the second main gear (22, 121), and when the second main gear (22, 121) exerts torque on the free wheel in the opposite direction, the free wheel is in a free state and allows rotation of the second main gear (22, 121). wherein each planet gear of the first set of planet gears is coupled to a planet gear of the second set of planet gears such that no relative rotation is possible between them, wherein, in the mounted position: • the first main gear is connected to an engine crankshaft, • the planet carrier is connected to at least one accessory pulley which is drivingly connected to an electric machine and preferably to at least one accessory; • the first main gear is connected to an engine crankshaft, • the planet carrier is connected to at least one accessory pulley which is drivingly connected to an electric machine and preferably to at least one accessory; wherein the drive system further comprises a free wheel which is connected to a non-rotating part of the engine arrangement in the mounted position, wherein the second main gear is configured to be coupled, preferably via an intermediate junction element of the drive system, to the free wheel in a first operating phase of the drive system, wherein, in the first operating phase, the free wheel is configured such that when the second main gear (22, 121) exerts torque on the free wheel in one direction, the free wheel is in an engaged state and stops the rotation of the second main gear (22, 121), and when the second main gear (22, 121) exerts torque on the free wheel in the opposite direction, the free wheel is in a free state and allows rotation of the second main gear (22, 121).