Design And Study On A Novel Hydraulic-electrical Regenerative Suspension System For Vehicles

Vehicle suspension system is an important componet connecting carbody and wheels.To ensure vehicle ride comfort,it is developed to attenuate the shock and vibration caused by uneven road.A traditional suspension reduces vibration usually though dissipating the vibration energy in form of heat,by damping valves in its shock absorber.As one of advanced suspensions,energy regenerative suspension can not only restrain carbody vibration effectively,but also recover part of vibration energy.With the promotion of energy conservation and emission reduction,energy regenerative suspension development has become a hot issure in automobile industry and has a wide application prospect.This paper proposes a novel hydraulic-electricity energy regenerative suspension system(HERS).It can convert suspension reciprocating linear motion into a hydraulic motor unidirectional rotation through a hydraulic rectification circuit,and then the hydraulic motor drive a generator to output electrical energy.Based on the structure and working principle,simulations and prototype testing are developed to validate the feasibility of the system,and some useful researches and trials on the working performance of the HERS are also carried out.This paper mainly includes the following aspects:(1)A novel hydraulic-electrical energy regenerative suspension system has been designed.Its structural characteristics and working principle are analyzed.And based on mathematical models of components,the expression of the hydraulic cylinder output force is derived,and a differential equation is established to describe vibration of a carbody-wheel dual mass system with the regenerative suspension.By calculating energy dissipation of traditional passive suspensions in the vehicle driving,the potential of the energy regenerative suspension is analyzed,and the energy regenerative characteristics of the suspension system are discussed.Referring to stiffness and damping characteristics of traditional passive suspensions,major components parameters are obtained by analyzing working parameters of the regenerative suspension.(2)The hydraulic-electrical energy recovery unit(HERU)proves feasible,and its external characteristics have been studied.In AMESim software,the HERU is modeled.Then it is demonstrated that the unit can work by simulations preliminarily.Based on that,according to the structure of the HERU,a prototype is manufactured and tested on a test bench.It is confirmd that the energy recovery scheme and the simulation model are available.Output characteristics and efficiency of the HERU are also obtained by the testing results.(3)The working performance of the HERS has been studied in 1/4 vehicle vibration system.1/4 vehicle with the HERS system installed is modeled in AMESim.With sinusoidal and random road excitation signals,the HERS is compared with a traditional passive suspension on damping performance,taking carbody vertical acceleration,suspension travel and wheel dynamic load as objects of investigation.By analyzing the time domain response of the generator output power and rotational speed,there is‘power dead time’affecting the energy recovery of the HERS system.To alleviate this problem,two methods are proposed: to decrease the hydraulic motor displacement or the minimum working speed of the generator.Based on results of time domain simulation response of the 1/4 vehicle model,the frequency response function of the HERS system is estimated by the H1 frequency response function estimation method and the mean root square value ratio method.Finally,the HERS system is mounted to a complete vehicle model in AMESim,which is travelling on a class C road.The performance of the regenerative suspension for vehicle riding is further confirmed.(4)Sensitivity analysis and optimization of main hydraulic parameters that influence vibration reduction and energy regeneratation are carried out.Based on simulations of the 1/4 vehicle model with the HERS system,the bypass protective valve is validated to prevent the hydraulic motor from overspeed.Hydraulic parameters effect on the regenerative suspension working performance is analyzed,such as the piston rod diameter,accumulator volume and precharge pressure.On the platform of ISIGHT,with AMESim combined,the sensitivity of these hydraulic parameters to the mean square root value of the carbody vertical acceleration and the average recovery power is obtained.Considering the carbody vertical acceleration as constraints,these hydraulic parameters are optimized to obtain a maximum average recover power.(5)Semi-active control and anti-roll of the HERS system are studied.To control the regenerative suspension,a variable hydraulic motor is adopted,and its displacement is set as controlled variable.Synthesizing vibration reduction and energy regeneration,a modified skyhook damping algorithm is presented for the semi-active regenerative suspension.The algorithm is verified by simulations based on Simulink and AMESim.To improve vehicle roll stability,based on the relationship between the suspension stiffness and the vehicle roll angle,an anti-roll scheme is proposed.Utilizing a 2/2port solenoid valve,the hydraulic circuit between the two accumulators is switchable.With the vale closed,the hydraulic cylinder is connected to a single accumulator,and the stiffness of the HERS increases,which is be beneficial to decrease vehicle roll.