Analysis On Coupling Characteristic Of Interconnected Suspension And Its Effect On Vehicle Performance

In recent years, fatal crashes due to vehicle rollovers have been frequently reportedaround the world, especially for four-wheel drive vehicles (4WDs) or sports utility vehicles(SUVs), typically having higher mass centers, which particularly vulnerable to rollover.The reasons for rollovers are complex, but well-designed suspension systems can greatlyreduce vehicular rollover propensity. However, modern vehicle suspensions are required toachieve a number of often conflicting objectives, such as the well-known trade-off betweenride comfort and handling stability. The structures of traditional suspensions keepunchanged after loading, but the vehicle’s driving conditions are ever-changing, so it isdifficult to achieve the desired results to use single suspension structure to deal withchanging driving conditions. More recently, research efforts have been focused onadvanced suspension systems to overcoming the inevitable compromise between ride andhandling encountered in conventional suspensions, such as active suspension andsemi-active suspension, which generally include variable or adjustable stiffness or dampingparameters. But there are some drawbacks associated with these active technologies, suchas increased cost, uncertain reliability, power consumption requirements and inherentcomplexity, for the reason, which have narrow application scope now. An approach toovercoming the ride-handling compromise via passive means is through the use ofhydraulically interconnected suspension (HIS) system, hence it is very meaningful tothoroughly and theoretically investigate HIS system.The calculation, analysis, simulation and matching works of the HIS system design anddevelopment is lunched combined with the concept/function development program of HISsystem. The thesis is carried out based on the idea of “Parts-System-Vehicle”, which includes three aspects: characteristic analysis of damping unit, coupling characteristicanalysis of interconnected suspension and its effect on vehicle performance.Characteristic analysis of damping unit. Damping unit is the essential component of aHIS system. Therefore, in this thesis, the flow-pressure of hydraulic cylinder subsystem,rebound valve subsystem, compression valve subsystem, damping valve subsystem,accumulator subsystem is analyzed and then the dynamic model of damping unit is builtbased on its structure and principle.Modeling and coupling characteristic analysis of HIS system. The mathematicalmodels of three HIS systems of different coupling configurations are deducted.Furthermore, three HIS systems of different coupling configurations are simulated inidealized suspension modes: bounce, roll, pitch, warp, to analyze the change of vertical force,roll moment, pitch moment, torsional moment and then the HIS systems nominal fluid flowdistribution are discussed. Also, the equations of the vertical, roll, pitch, torsion are given.The effect of coupling characteristic of HIS system on vehicle performance. On onehand, in this thesis, the four-wheel road surface model is investigated to build theroad-vehicle model, and then the HIS models are integrated into the vehicle model.Furthermore, the effects of the interconnection configurations on vehicle vertical and pitchvibration are analyzed based on random road input. On the other hand, the CarSim modelis built which is suitable for handling, braking and acceleration simulation, to analyze theeffects of the interconnection configurations on vehicle body gesture and torture. Theresults show the interconnection configurations have little influence on the vehicle verticalvibration but great influence on the vehicle pitch vibration, body gesture and torture.Hence, for a certain vehicle, the interconnection configuration should be chosenappropriately based on its operation condition and performance demand, to enhance the ridecomfort, vehicle gesture stability and reduce the body torque.