Research On Hydraulic Braking Energy Recovery System Of City Bus

Due to the particular work needs, city bus needs frequently brake and move, but during the braking process, huge energy is wasted (kinetic energy is transfered to heat and dissipated by the brake). If find a way to recovery the these energy, not only can reduce the fuel consumption, but also can make the engine work in fuel economic zone longer, thus improve fuel economy, reduce exhaust emission.Through analysis of research on existing hydraulic braking energy recovery of city bus, find that there are three questions. Firstly, in most research energy recovery system uses fixed displacement pump/motor, but fixed displacement pump/motor output torque changes along with the accumulator pressure, on one hand reduces the assigned brake toeque and the time that the recovery system participates in braking, on the other hand can also cause unstablity of braking. Secondly, there is no a given calculation method for system key component, always analyze through estimate data. Thirdly, little consideration on that bus drive condition influences on system parameter. Based on the above questions, this article take the Chengdu commonly used12meter long rear engine city bus as study object, designed a hydraulic braking energy recovery system based on the actual driving cycle. Main research content are as follows:(1) Through comparision among existing layout, connection position, connection way of recovery system and bus transmission system, brings out the system structure scheme, and carry out a control strategy based on the anlysis of the working feature of the recovery system.(2) Conduct a survey of Chengdu city bus drive condition, through anlysis of survey data, obtained the bus drving characteristics, and synthesize the drive cycle with six conditions.(3) Make an analysis and caculation on bus force condition and recyclable energy during braking. According to the driving characteristics, did a theoretical calculation and election for the system’s key components (parameters) pump/motors, accumulators, access gear ratio.(4) Established a simulation model of the corresponding transmission system with a hydraulic braking energy recovery system in AMESim, make simulations on energy consumption factors,factors that affect system performance, system energy saving performance under synthesis drive cycle and downhill(uphill) condition.(5) Bulid a brake energy recovery experiment platform that use a flywheel to simulate load, and did some related experiment.Results show that:firstly there exists a big difference between Chengdu bus driving condition and GB conditon, so to design the braking energy system based on GB conditon is not correcet. Secondly variable displacement pump/motor system can achieve a higher energy-saving effeciency than fixed displcement pump/motr. Thirdly the initial pressure, the volume of the accumulator, type of the pump/motor are the main factors that affect the energy-saving efficiency of the system, in a single braking conditions, when the initial pressure and volume of the accumulator are14.5Mpa and58L can get maximum energy-saving efficiency.Fourthly under the cycle conditions system can get an energy-saving efficiency of38.81%. Fifthly displacement of pump is the main factor that affects the recovery efficiency, but the volume of accumulator has little effect.