Research On Interconnected Hydro-pneumatic Suspension Systems For Heavy Multi-axle Off-road Vehicle

Interconnected hydro-pneumatic suspension (IHS) systems could achieve anti-roll,axles balance and many other features by the interaction forces among differentsuspensions. It can excellently coordinate the vehicle ride comfort and handling stabilitycompared with the traditional non-interconnected suspension systems by tuning thestiffness and damping of the suspension according to the working conditions automatically.IHS systems can improve the vehicle driving performance effectively, so it has animportant application prospects for improving vehicle driving performances.This dissertation is based on the college and enterprise joint project: the developmentof heavy off-road vehicle controllable hydro-pneumatic suspension systems. It proposed adesign layout of IHS systems aiming to coordinate the vehicle ride comfort and handlingstability. IHS systems could achieve anti-roll, axles balance，rigid latch and many otherfeatures. In the dissertation, IHS systems model was built based on modularizationmodeling method. The characteristics of stiffness and damping are analyzed by combiningwith the mathematical simulation and bench test. Driver-vehicle-road close-loop systemsare proposed by combining the eight wheels random road excitations model and genericsingle point preview optimal driver model of multi-axle truck. The IHS forces are asexternal input for the full vehicle dynamic models. The effects of IHS design parameters tothe ride comfort and handling stability are analyed in Matlab/Simulink virtual environment.And the real vehicle rough road and bump road tests on gravel and asphalt road for the IHSheavy off-road vehicle are implemented to validate the effectiveness of IHS systems. Themain study contents are as follows:(1) IHS systems which can anti-roll motion and balance axel load are designed for8×8heavy and high maneuverability off-road vehicle so as to consider the high mass center,low rollover threshold, complicate working condition and special use (maybe used for theweapon system platform) et al. The mathematical models of hydraulic components are builtaccording to different types of damping manifolds and based on modularization modelingmethod. The modeling of high-pressure pipeline considers the pressure loss caused by theoil compressibility and flow-ripple, so that the built model is more reliable and precise. Theeffects of IHS design parameters to the suspension stiffness and damping are studied basedon the built model in Matlab/Simulink environment.(2) The full vehicle dynamic model including vertical, lateral and longitudinal motionis built based on Lagrange equations in consideration of inconsistency between the fullvehicle mass center and vehicle body mass center. The single point preview optimal drivermodel of two axles is more mature at present，but the multi-axle driver model is still veryfew studied. In response to this problem, a generic single point preview optimal drivermodel of multi-axle truck is introduced according to linear2DoF vehicle model. Thisdriver model can be used for different number of axle vehicle by setting the parameters.Handling performance and stability simulation test of the8×8heavy and highmaneuverability off-road vehicle with IHS systems are carried out according to GB/T6323-1994, QC/T480-1999and international ISO standard. The tests are includingsteady and transient simulation. The setting parameters and conditions of multi-axle vehiclehandling stability tests are presented(3) The IHS forces from nonlinear mathematical model are as external input for the fullvehicle dynamic models. The ride comfort is studied in time domain and frequency domainunder random road and speed bump road excitation. The simulation results clearly indicatethat the IHS systems can improve the vehicle ride comfort compared with the independenthydro-pneumatic suspension. The real road tests are also carried out to evaluate ridecomfort of the8×8heavy and high maneuverability off-road vehicle equipped with IHSsystems, and the experiment results indicates that the proposed IHS system is working welland feasible.