| Hybrid driving is a new kind technology which is highly worthy of studying, it's invented because of the shortage of energy and serious environmental pollution. Cars have got a rapid development in the human world and also provided power for the social development. Because cars consume a lot of petroleum resources and it's exhaust emissions are pollutional to environmental, it also brings serious destroy to our common home earth. In the case, some governments and research institutions have spent lots of money and manpower on solving these problems. After a lot of studys, hybrid technology is successfully applied to cars. Compared with the traditional internal combustion engine, the main advantages of hybrid driving is adopting high power energy storage device (the flywheel, super capacitance, battery or hydraulic accumulator) which can provide extra energy, so can reduce demanded engine power, improve efficiency and reduce emissions.Electric hybrid vehicle is the most popular studies, and successfully goes into mass production. Electric hybrid vehicle equiped with engine and electric motor/motor generator can drive the vehicle and recover vehicle braking energy by using battery charging and discharging characteristics . But electric hybrid vehicle has some common shortcomings, for example, low specific power, low efficiency, high factoryprice which limit the development of cars.In this case, the hydraulic hybrid vehicle arises at the historic moment. The basic principle of hydraulic hybrid vehicle is that recovering the vehicle braking energy by pump/motor and storing hydraulic oil from oil tank to high pressure accumulator, also releasing hydraulic oil of high pressure accumulator and supporting auxiliary driving power when vehicle is started or accelerated. Engine only provides smaller power and can always works in high efficient area, which can reduce exhaust emissions and save energy. Also the life of friction slice has been increased. In the same circumstances, compared with electric hybrid vehicle, hydraulic hybrid vehicle can provide more auxiliary power, the hydraulic accumulator has faster velocity of charging and discharging energy than battery, hydraulic accumulator can recover more energy and also is more cheap.In the research project, we choose 8m3 concrete mixing truck as a prototype vehicle. We will redesign the vehicle by using hydraulic hybrid technology to optimize engine, improve vehicle driving ability and save petrol. Based on the comparison and analysis of various hydraulic hybrid system, we choose parallel hydraulic hybrid system as the final redesigned system. We design that the gear box is set before the torque coupler so as to recover more braking energy and get better driving abilities.Parallel hydraulic hybrid vehicle has good driving and braking energy recovery performance. Regenerative braking system is connected to the main transmission shaft by torque coupler and provides driving power together with engine. Engine working in high efficient area, recovering braking energy, improving the perfoermance of the vehicle's acceleration and climbing are the main functions of regenerative braking system. But there are a lot of difficulties to be solved in the course of parallel hydraulic hybrid vehicle researching. This paper made the following:(1) Analyzed the basic principle, advantages and disadvantages of several common mode of hydraulic hybrid vehicle, namely the series, parallel, mixed and direct wheel drving. Considering the manufacturing cost, recovering and driving performance, the final choice of hydraulic hybrid system mode is parallel. And also the main modules and typical working mode of parallel hydraulic hybrid vehicle were analyzed.(2) The hydraulic hybrid vehicle powertrain energy management strategies were studied and analysed. Designed a acceleration mode control strategy based on MAP figure which sumed up the advantages of logic threshold control strategy, optimal working curve control strategy and acceleration mode control strategy. The energy management strategy can make the engine to work in the best area. Also according to the control strategy, torque distribution is analyzed.(3) Chose 8m3 concrete mixing truck as a prototype vehicle. We chose the second parallel hydraulic hybrid system as the final designed scheme after lots of analysis and fixed parameters and model number of accumulator, pump/motor and torque coupler, which laid a foundation for the modification and test.(4) Modeling and simulation for the driveline and braking energy recovery system of parallel hydraulic hybrid heavy truck based on software AMESim. Also driving, acceleration, climbing and braking energy recovery performance were analyzed. The first parallel hydraulic hybrid system was modeled and simulated, and the simulation results were compared with the second scheme. Analyzed the advantages and disadvantages of the first scheme and the second paralle scheme.After the modeling and simulation of paralle hydraulic hybrid vehicle and ordinary vehicle, the simulation results confirm the correctness of theoretical analysis of hydraulic hybrid vehicle. This laid a theoretical foundation for the research of hydraulic hybrid vehicle. This paper tried to model hydraulic hybrid vehicle by using the software AMESim and got a lot. We can simulate the performance of vehicle's driving, acceleration, climbing, braking and energy recovery through the builded model, which provides a important tool for the research of hydraulic hybrid vehicle.
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