Key Technologies Investigation Of Hydraulically Interconnected Suspension System With Pressure Self-Regulation For Buses

The passenger buses have the characteristics of wide operation range and strong road adaptability.With the rapid growth of the domestic tourism market,there is an increasing demand for passenger buses.But it is the fact that the passenger buses would have a higher risk of slipping and rollover due to their high center of gravity and heavy load,and also the motion sickness is prone to occur in mountainous areas.Thus,there are higher requirements for handling stability,safety,and ride comfort in bus market.In the meantime,the bus operators expect to obtain excellent vehicle performance under limited budgets.Overall,improving the handling stability,safety,and ride comfort of passenger buses at the lowest cost has great significance.The Hydraulically Interconnected Suspension(HIS)system is a feasible solution.According to the previous research,The HIS system with the roll interconnection configuration has nonlinear roll stiffness,which can effectively improve the handling stability and safety.The roll interconnection configuration decouples the roll and bounce mode,which contributes to equivalent ride comfort with the original vehicle,and it could be furtherly improved after optimization.At the same time,the passive HIS system can replace the original Anti-roll Bars(ARB)and shock absorbers,and the added cost is limited.However,the HIS system has the characteristics of multiple parameters and high design complexity,there are no complete theory for parameters tuning and investigation of comprehensive performance improvement,also,there is no detail applications made on passenger buses.Based on the above background,this dissertation focuses on a passenger bus and the HIS system with pressure selfregulation device is proposed and applicated in product level under the support of the National Natural Science Foundation of China(Grant No.51175157 and 51675152).The HIS system can solve the above market problems,the pressure self-regulation device in the system is proposed for the first time,and it can solve the instability issue of the vehicle body that arise during the productization,thus,improving the stability and reliability of the system.This dissertation takes passenger buses as the research object and aims to improve the handling stability,safety,and ride comfort.The indepth theoretical research and sufficient experimental verification have been conducted on the HIS system’s dynamic characteristics and tuning methods,providing an essential theoretical basis and engineering practice for its productization.The main research work and innovation points of this dissertation includes the following aspects:(1)The mechanical-hydraulic coupling vehicle dynamic model equipped with the HIS system has been built and validated with field tests.Firstly,based on the theorem of centroid and the moment of momentum,a dynamic model of the vehicle with 10 degrees of freedom is derived and established.Then,based on the fluid mechanics theory,the hydraulic model is established for the HIS system and components.And the HIS system model is then coupled with the 10-DOF vehicle model to obtain a mechanical-hydraulic coupling model.Finally,vehicle tests are conducted for the original vehicle and HIS vehicle,respectively.The test data verifies the model validity and builds a theoretical foundation for subsequent vehicle performance analysis and system parameter tuning.(2)The HIS system tuning method for handling stability has been proposed.Firstly,the evaluation indicators and methods of handling stability are investigated,and the selected evaluation parameters are determined.Then,based on the mechanicalhydraulic coupling model,the simulation analysis under the fishhook test condition is carried out,and the HIS system’s potential in improving handling stability is comprehensively analyzed from four dimensions: roll domain,lateral domain,vehicle trajectory,and tire forces.Finally,four key HIS system parameters are defined: roll stiffness,roll stiffness nonlinearity,roll stiffness front-to-rear axle distribution ratio,and roll damping.The sensitivity analysis of each parameter is carried out,and the design criteria are summarized,and the HIS system’s design procedure and tuning method are proposed.This provides a set of feasible methods for the HIS system parameter tuning design.(3)An optimized design method of the HIS system for improving ride comfort has been proposed.The optimization schemes from the suspension stiffness tuning,actuator optimization design,and accumulator layout optimization design are developed.Firstly,the mechanism of the additional vertical stiffness of the HIS system is analyzed,and the vertical stiffness of the suspension spring is adjusted and tuned,and the effect of improving ride comfort is simulated and analyzed.Then,the actuator’s design is optimized in terms of the friction of the actuator and the rubber bushing,and experiments verify the ride comfort improvement.Finally,a scheme of distributed arrangement for accumulators is proposed,and the system output characteristics of the centralized and distributed accumulator schemes are compared and analyzed using the verified AMESim simulation model.The simulation and test result verified the improvements in ride comfort by the optimization method proposed.(4)The mechanism of the unbalanced body motion from the view of actuator internal leakage has been investigated and the pressure self-regulation device to solve the unbalanced problem has been proposed.Firstly,the unbalanced body motion problem from the internal leakage mechanism of the actuator piston is analyzed,and there is no available solution to solve the problem by mere modifications of piston seals.Then,after a comprehensive analysis of the self-regulation pressure device’s performance and vehicle tests,an innovative design is proposed.Finally,the bench testing and vehicle testing of the pressure self-regulation device are carried out to verify its effectiveness.The pressure self-regulation device provides an effective solution to unbalanced body motion problem and can furtherly improve the stability and durability of the HIS system.(5)The static rollover,dynamic handling stability and ride comfort test of the bus fitted with the HIS system have been carried out.Firstly,based on the above parameter tuning and optimization method,a HIS system fit for the prototype bus is designed.Then,the static rollover test,dynamic handling stability test,and ride comfort test are carried out according to the national standards.Finally,the objective test results and subjective evaluation results of each test are analysed and the HIS system’s advantages over the original vehicle are discussed.The passenger buses’ all-around performance with the HIS system has been significantly improved according to the objective and subjective results.