Hydraulic hybrid electric vehicle transmission system and control method thereof

The invention provides a hydraulic hybrid electric vehicle transmission system, which belongs to the technical field of vehicle energy conservation and emission reduction. The vehicle transmission system, without a clutch or a gear box, is directly connected with a main reducer and a differential to drive the vehicle according to the stepless speed regulation characteristics of an electromotor and a hydraulic pump/motor to reduce the operation strength of a driver. A storage battery-electromotor is used as the main power source of the vehicle; a hydraulic accumulator-variable pump/motor is only used for recycling and reusing the brake energy of the vehicle; during acceleration, the hydraulic pump/motor supplies extra power; particularly in start process, the hydraulic pump/motor alone drives the vehicle to start moving, and the electromotor can always run in stable conditions. The impact of variable conditions on the circuit system is reduced, the load of the storage battery is remarkably lowered, the work performance of the storage battery-electromotor is promoted, the service life of the storage battery-electromotor is prolonged, and the continuous mileage of the electric vehicle is prolonged.