NOVELTY - A power transmission system of a hybrid vehicle is provided to prevent circulation of energy and to allow the vehicle to be driven in a bifurcation region by connecting a first motor part to a third planetary gear and by a second motor part allowing the vehicle to be driven by transmitting the power to a driving shaft through a first planetary gear at the initial start of the vehicle. The second motor part renders the driving shaft operable with the power from the engine by supporting the ignited engine.    DETAILED DESCRIPTION - A power transmission system of a hybrid vehicle comprises a planetary gear unit(10), a driving motor unit(20), a clutch unit(30), and a controller(40). The planetary gear is installed in a transaxle housing(2) and includes first, second, and third planetary gears(12,14,16). The driving motor unit includes a first motor part(22) and a second motor part(24). The first motor part transmits the power to the third planetary gear. The second motor part transmits the power to a driving shaft(4) through the first planetary gear at the initial start of the vehicle, and supports an ignited engine(1) along with the first motor part, and drives the driving shaft with the power generated from the engine. In a critical velocity where the ratio of the electrical energy generated from a battery or a driving motor unit and the mechanical energy generated from the engine becomes zero, the clutch unit connected to the planetary gear unit regulates the power to allow the vehicle to be driven in a bifurcation region. The bifurcation region is a plus region. The control unit controls the driving motor unit and the clutch unit depending on the driving condition of the vehicle. The first planetary gear is directly installed to the engine and receives the power generated from the engine. The first motor part is connected to a third carrier(16c) of the third planetary gear, and the second motor part is installed to a first sun gear(12b) of the first planetary gear.Image 1/1