| Owing to the advantages of high integration,strong bearing capacity,adjustable body height and nonlinear stiffness,hydro-pneumatic suspension can effectively improve the body vibration caused by bad road conditions,and has been widely used in various engineering vehicles and military vehicles.At present,the existing research on hydro-pneumatic suspension system mainly focus on the single control among the longitudinal,lateral,and vertical control objectives.Considering the influence of the variability of mining driving conditions and the nonlinearity of hydro-pneumatic suspension system itself on the comprehensive performance of mining dump truck,the existing designed control strategy is hard to satisfy the overall performance requirements in the longitudinal,lateral,and vertical directions,and even deteriorates the other performance of the system in the pursuit of a certain performance optimization.Therefore,longitudinal-lateralvertical coordinated(LLVC)control of the active hydro-pneumatic suspension for an engineering vehicle is deeply investigated in this paper through the methods of vehicle system modeling,simulation analysis and experimental research.This study is supported by the general program“Hydro-pneumatic suspension system of mining dump truck(hydraulic cylinder)” of the Major Technical Research Project,Jiangsu Province and “Research on key technologies of intelligent active hydro-pneumatic suspension system for engineering vehicles” of the Key Research and Development Program,Zhenjiang(GY2019031).Firstly,considering the accuracy of the vehicle model directly determines the response of the vehicle system with a hydro-pneumatic suspension at different driving conditions,and then affects the control performance of an active hydro-pneumatic suspension system,a passive hydropneumatic suspension system model is established.Furthermore,the hydro-pneumatic suspension characteristics are analyzed through simulation and the accuracy of the simulation model is verified experimentally on a test bench.On this basis,a vehicle simulation model is established according to the real vehicle test data.According to simulation and experimental results,the mapping relationship between driving conditions and dynamic performance requirements is analyzed,and the control objectives of the active hydro-pneumatic suspension under different road conditions are determined,which provides a basis for designing a vehicle LLVC controller under different driving conditions.Secondly,according to the essential feature that the LLVC control of the active hydropneumatic suspension is controlled by adjusting the target under different driving conditions,a road estimation method(including road displacement and road level estimation)for the active hydro-pneumatic suspension is proposed based on the theory of Unscented Kalman observation and spectral density estimation,and the influence of the vehicle speed and load on the accuracy of road identification is studied.Besides,the road displacement information under three different driving conditions is constructed based on wheel-track and wheel-base characteristics.The effectiveness of the designed road estimation method under the condition of time-varying parameters is verified by simulation analysis,which provides a prerequisite for the LLVC control of the active hydro-pneumatic suspension.Thirdly,on the basis of the mapping relationship(between driving conditions and dynamic performance requirements)and the road estimation method,the LLVC control strategy of the active hydro-pneumatic suspension system is studied.The model of the active hydro-pneumatic suspension system is established,the LLVC control architecture using the model predictive control(MPC)is constructed and a more detailed control logic is defined.Moreover,the reasonability of the MPC-based LLVC control strategy of the active hydro-pneumatic suspension is concretely demonstrated,through analyzing the vehicle dynamic response under the random road input based on the wheel-track and wheel-base characteristics.Taking three single objective MPC control strategies(longitudinal,lateral and vertical)as comparison objectives,the comprehensive performance simulation analysis of the active hydro-pneumatic suspension is carried out,and the superiority of the LLVC control is verified.Finally,according to the real-time simulation requirements of the controller,an electronic control unit(ECU)of the active hydro-pneumatic suspension,adopting LLVC control,is developed based on STM32F103VET6.The hardware in loop test platform is built based on the co-simulation of AMESim and Matlab,and the effectiveness of the suspension ECU system is verified.On this basis,the hardware in loop test of the active hydro-pneumatic suspension.using the MPC-based LLVC control,is carried out.Furthermore,the control performance under different driving conditions of the control strategy is verified,as well as the advantages for coordinating the longitudinal,lateral and vertical dynamic performance is validated.The results show that:(1)The road displacement and road level estimation can be estimated effectively by the unscented Kalman filter,and the comprehensive performance of the system can be improved by the active hydro-pneumatic suspension on the premise of cognizing the front-end road state so as to meet the dynamic performance requirements under different driving conditions.(2)The MPC-based LLVC controller of active hydro-pneumatic suspension can satisfy the dynamic performance requirements of the mining dump truck at mining road conditions.Under the C-class road,taking the handling stability of the active hydro-pneumatic suspension as the overall control objective,the dynamic tire loads of six wheels of the whole vehicle are reduced by25.8%,29.1%,30.6%,27.6%,29.9%,28.1%(with no-load)and 23.5%,26.2%,32.7%,32.9%,29.9%,28.4%(with full load),respectively,and the longitudinal,lateral and vertical accelerations of the vehicle body are not deteriorated simultaneously.Under the D-class road,taking the ride comfort and handling stability as the overall control objective,the longitudinal,lateral and vertical body accelerations are reduced by 19.1%,20.3%,19.7%(with no-load)and 18%,16.1%,16.8%(with full-load),respectively.Meanwhile,the dynamic tire loads of the wheels are reduced by20.5%,19.6%,14.2%,12.7%,12.3%,12.6%(with no-load)and 12.7%,12.4%,12.2%,10.8%,8.6%,10.3%(with full-load),respectively.Under the E-class road,taking the ride comfort as the overall control objective,the longitudinal,lateral and vertical accelerations under no-load and full load are optimized by 34.6%,31.4%,34.1%(with no-load)and 29.5%,29.4%,29.3%(with fullload),respectively.(3)Under different driving conditions,The MPC-based LLVC control of active hydro-pneumatic suspension can ensure the longitudinal,lateral and vertical coordinated motion of the vehicle,with the consideration of the longitudinal,lateral and vertical dynamic control effects.Furthermore,it can ensure that the suspension working space of the active hydropneumatic suspension is within a reasonable range.(4)Through the development,design and Hi L test of the MPC-based LLVC control of active hydro-pneumatic suspension,the controller is proved to have good real-time application conditions. |
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