Cooling system for a mechanically and hydraulically powered hybrid vehicle

A cooling system (9) for a heavy road vehicle comprising a hybrid propulsion system (1), said hybrid propulsion system (1) comprising

• a first, mechanical propulsion system (12) comprising a mechanical drive train including an internal combustion engine (4) which provides a traction force to a first traction wheel (2a) via a gearbox (5),
• a second, hydraulic propulsion system (13) comprising a hydraulic pump unit (7) for powering a hydraulic motor (8a) in order to provide a traction force to a second traction wheel (6a), wherein said cooling system (9) further comprises a pump (14) and a first cooling circuit (18) including a gearbox cooling circuit (16), a hydraulic propulsion cooling circuit (17) and a first radiator (15) for cooling of a coolant flowing in the first cooling circuit, said radiator (15) being connected in series with and located upstream of the gearbox cooling circuit (16) and the hydraulic propulsion cooling circuit (17), characterized in that
• said hydraulic propulsion cooling circuit (17) and the gearbox cooling circuit (16) are connected in parallel, and wherein
• a temperature dependent thermostat (28) is positioned downstream said hydraulic cooling circuit (17), said temperature dependent thermostat being configured to increase the coolant flow through the gearbox cooling circuit (16) relative the coolant flow through the hydraulic propulsion coolant circuit (17) if a measured temperature of the coolant flow downstream said gearbox cooling circuit (16) exceeds a predetermined threshold temperature.