Single-mode Hybrid Shunt Hybrid System Development And Technology Of Thermal Equilibrium

As the fear of environment pollution as well as the energy crisis, the pressure for the reduction of fuel consumption and exhaust emissions becomes a new challenge for all vehicle manufacturers. Developing the electrified vehicle power-train becomes the main trend of present vehicle technology. Among the various power-trains for hybrid electric vehicle, the planetary gear power split hybrid system, which is also known as series/parallel hybrid, has been widely regarded as the most promising hybrid configuration. Power split hybrid systems are more beneficial because they have the advantages of both series and parallel types, and enable the e-CVT function. The key development technology of power split hybrid system includes the power split configuration design, electric motor system, hybrid transmission thermal management technology and the control algorithm, which are studied in this thesis.Power circulation characteristics of the basic power split modes are analyzed, and the performance in the transmission configuration design is estimated according to the power-train efficiency and torque output ability, which can be used to guide the development of power split system. Design regulations for single mode and two mode hybrid systems and the application of shifting elements are summarized. Dual clutch technology, electric motor speed decouple technology, fixed gear driving mode, etc. are used to perfect the operating modes of power split system. Several single mode and two mode hybrid systems are designed, and the recommended single mode system has a highly flexible configuration, which is especially practical for improving the torque output ability and the high vehicle speed power-train efficiency. A new single mode hybrid system which utilizes an innovative four-shaft power split device based on the Ravigneaux compound planetary gear set is introduced. This hybrid configuration is the first single mode power split production with compound power split mode, which is also the first three-degree-of-freedom hybrid system. Torsional vibration analysis method for power split hybrid power-train is studied. Parametric power-train vibration model is built to optimize the resonant frequency through the torsional damper stiffness match.Control strategy development is a key step of the power split hybrid transmission design, which can be used to verify the power-train performance and supply the load cycle for all the mechanical parts design. The control strategy includes driving power interpretation, driving mode management and torque balance technology. As to all kinds of the planetary gear power split system, the torque balance technology is the necessary technology. Torque balance modes of different driving modes are studied to decouple the control parameters of the power split hybrid system. Control strategy of the compound power split system is developed to simulate the performance under different standard load cycles. Simulation data is also applied to guide and check the design of all the mechanical parts. The loss power spectrum of electric motors and power-train is used to develop the transmission thermal balance management system and confirm the oil flow and pressure requirement of the hydraulic system.Thermal balance management system is mainly used to keep the thermal balance status of the hybrid transmission, which includes the thermal power calculation, hydraulic system principle design and the hydraulic parts design. The thermal energy of the hybrid transmission is mainly from the electric motor loss power and the power-train friction loss power. Therefore, the thermal management technology can be considered as a control technology based on the system control strategy. The two electric motors rotate in the oil mist and are fully oil-cooled through the direct spray cooling mode. ATF oil is injected directly onto the cable ends of the motor stators to absorb the motor loss power. A high pressure oil circulation is needed to supply pressure oil for brake elements. So a multi-function integrated hydraulic system is designed including the cooling circulation and high pressure control elements. The integrated hydraulic system is practical to simplify the transmission structure and the layout of oil channels in the transmission housing.The hydraulic system design of full hybrid transmission is different from that of conditional automatic transmission, because in some driving modes the combustion engine can be stopped. Because of this reason, a new oil supply system of two oil pumps is designed. A first oil pump is located below the output-gear and becomes driven by that shaft, so it can be running even when the combustion engine stands still. A second pump is defined as an assistante one driven by a small electric motor which is only activated at reverse vehicle speed and when the flow rate from the first pump is not enough. The rotating speed of electric pump is controlled to compensate the required oil flow and ensure the necessary oil flow for motor cooling and power-train lubrication. Self-adapted pressure regulation circuit is designed for the brake element engagement via solenoid valves which only happens in the electric driving mode and the overspeed mechanical point driving mode. Otherwise the oil pressure is controlled around the low cooling-lubrication level. The pressure control circulate can be used to decrease the power consumption of hydraulic system.Dimensions of the hydraulic valves are design by theoretical calculation. Finite element techonolgy is applied to check the channel leakage of hydraulic block and optimize the layout of connecting bolts. Oil flow distribution model is established to distribute the oil flow and to observe the flow and pressure characteristic under different oil temperature and different driving modes. Dynamic simulation model of the whole hydraulic system is built to investigate the function of hydraulic principle, valve dimensions and characteristics of oil flow and pressure with ITI-SimulationX. Simulation results indicate the hydraulic system is practical and the element design parameters can reach the design requirement.Bench test and hybrid vehicle test are made to check the hybrid system function and the performance of hydraulic system. A special hydraulic test bench is built to test the oil flow and pressure characteristics. The hydraulic test results indicate the output cooling flow and pressure control principle are practical, which reach the requirement of the first prototype production. Full load bench test is designed to check whether the cooling oil flow for electric motors and planetary gear is enough or not. Test data is recorded and used to modify the oil distribution calculation results. The cooling flow for two motors and planetary is adjusted according to the test results. Vehicle test is carried out to check the real performance of the power split hybrid system and the thermal status of the transmission. Vehicle test results indicate the hybrid system can complete all the design functions and driving modes, and temperature level of the hybrid transmission is in the good condition.In recent years, more and more attention is paid to the research of power split hybrid transmission, which has become one important direction of vehicle power-train development. Unfortunately, so far there is no this kind of hybrid transmission. The key technologies of power split hybrid transmission are studied in this thesis, which can be used to guide the similar hybrid transmission development.