Research On Regenerative Active Hydraulically Interconnected Suspension System With Closed Circuit Structure

As the key structure that maintains the stability of the sprung mass and cushions the impact of the road,the suspension system has a vital influence on the riding comfort and maneuver stability of the vehicle.Traditional suspension has always been the first choice for most vehicle designers due to its high cost-efficiency and reliability.However,it is well known that traditional suspensions are unable to meet the contradictory requirements of riding comfort and maneuvering stability on suspension performance.Among the existing advanced suspension technologies,both interconnected suspension and active suspension can improve the overall performance of off-road vehicles to a certain extent.On the one hand,interconnected suspension technology provides designers more flexibility to adjust the stiffness and damping for specific modalities through modal decoupling ways.On the other hand,active suspension system can directly control the force output of the suspension,and thus simultaneously improving vehicle driving comfort and maneuver stability.However,the constraints of energy supplying,and the contradiction between riding comfort and maneuver stability make it difficult for a standalone technology to fully meet the complex performance requirements of off-road vehicles.Semi-active suspension technology provides a compromise solution for control effect and energy consumption.Because it can achieve considerable performance improvements with lower energy consumption,semi-active suspensions have achieved rapid development in recent years.Moreover,with the integration of energy feeding technology,semi-active suspension can even realize the recovery of mechanical energy while suppressing vibration.Under the financial support of the National Natural Science Foundation of China,this paper aims to improve the comprehensive performance of off-road vehicle suspension systems.Through the cross integration of a variety of advanced suspension technologies,a closed-circuit-based Regenerative Active Hydraulically Interconnected Suspension(RAHIS)is proposed in this thesis.Compared with the existing active and semi-active suspension systems,RAHIS takes the advantages of regenerative suspension structure,which can greatly reduce the energy consumption when working in active mode,and can also improve vehicle performance through semi-active ways in the case of limited actuating power or magnitude.Besides,the interconnected structure itself has the merit of modal decoupling,which can ensure that the suspension performance is better than the traditional passive suspension even in the case of complete actuator failure.The main contents and innovations of this thesis are introduced as bellow:(1)The structure design and parameter matching of the vertical-roll collaborative control HIS oriented to the performance requirements of off-road vehicles.Based on the 7-degree-of-freedom vertical vibration model,a series of drop tests are conducted to identify the parameters of an actual off-road vehicle.Then,by studying the basic interconnection structure of the HIS system,and considering the performance requirements of the off-road vehicle,the structure of the vertical-roll HIS is proposed.The modeling method of key hydraulic components is derived,and an experiment using4-channel bench is conducted to verify the validity of the simulation model.Based on the simulation model,the parameter sensitivity of the HIS force feedback characteristics is analyzed.Finally,taking into consideration the original suspension configuration as well as the active control requirements,a parameter matching design on the HIS is carried out.Through numerical simulations,the performances of vehicles with and without HIS are analyzed.(2)Comprehensively considering the requirements of active control,semi-active control and energy regeneration,a novel regenerative hydraulic control unit is designed based on the closed-circuit structure,and the mechanical-hydraulic-circuit coupling mathematical model of the system is established.Compared with the existing hydraulic regenerative suspension,the proposed hydraulic control unit can not only recycle the vibration energy in passive way,but also control the suspension force(hydraulic pressure)in active and semi-active ways.The commonly seen damping discontinuity in the existing hydraulic regenerative structure is also eliminated.In order to improve the regeneration efficiency and provide a base for semi-active control,a boost/buck converter-based control circuit is designed to adjust the regenerative current of electric motor.Finally,the hydraulic control unit is integrated with the roll-vertical HIS to obtain the complete system structure of RAHIS.(3)Aiming at further improving the riding comfort and maneuver stability,a finite-frequency dynamic output-feedback H_?controller is proposed for the RAHIS with comprehensive consideration of the low-pass filter characteristics of hydraulic actuation and the sensitive frequency range of human body.The system control problem is formulated by transforming the dynamic equations into state equations.In the analysis of the control problem,many constraints that may exist in practical applications such as actuator failure,actuation saturation,suspension displacement limit are considered.A linear matrix inequity(LMI)method is proposed to design the finite-frequency dynamic output-feedback H_?controller,and the variable substitution method is adopted to transform the nonlinear coupled LMIs into linear decoupled LMIs.Furthermore,to facilitate the pressure tracking control,the output matrix of the H_?controller is modified,such that it can provide the time-derivative of the ideal pressure.Finally,the performance of the active suspension under different controller parameters,suspension parameters and road surface excitation conditions are analyzed from the following four perspectives:vibration transmissibility,transient response,energy consumption and regeneration potential.(4)In order to improve the economy of active suspension and reduce the number of sensors required for active suspension control,a vehicle state observer for active suspension is proposed based on H_?method.The observer needs only sprung and unsprung acceleration signals to realize accurate suspension state estimation.Compared with the Kalman observer,the H_? observer does not need to calculate the covariance matrix of the sensor noise,and can directly estimate the influence of the sensor noise on the observation accuracy.Through random road simulation,the observation performance under the influence of the uncertain system parameters and sensor noise is analyzed.(5)Considering the structural characteristics of the hydraulic control unit,a regeneration-oriented active and semi-active oil pressure tracking controller is proposed.A fast-converging adaptive radial basis function neural network(RBFNN)is used to estimate the time-varying parametric uncertainty in real time.Taking the advantage of the high sampling frequency of the electric circuit,the prescribed performance backstepping control method is used to improve the accuracy of pressure tracking in the case where the high-order derivative of the ideal pressure(target trajectory)cannot be obtained.Considering the additional actuation constraints of the semi-active mode,a decision tree is designed to ensure high-efficiency regeneration as well as vibration suppression.Finally,the pressure tracking controller is incorporated with the above-mentioned dynamic output-feedback H_?controller and vehicle state observer.Through numerical simulations,the performances of RAHIS under different working modes are analyzed,and the system's energy consumption and regeneration characteristics under different road conditions are further discussed.In summary,this thesis aims at improving the overall performance of off-road vehicles.Through the cross integration of a variety of advanced suspension technologies,a closed loop circuit-based RAHIS system is proposed.The RAHIS can meet the complex requirements of challenging driving environments on the suspension system,and thus greatly improve the overall performance of off-road vehicle.