Study On Height Adjustment Under Dynamic Condition And Posture Chasing Control Of Laterally Interconnected Air Suspension

With the development of modern automotive technology,the application of air suspension on vehicles is widely used,and in order to improve the characteristic of air suspension one step further,many derived structures based on ordinary air suspension are proposed,one of which is laterally interconnected air suspension.The adjacent air spring in the front or rear axle is connected by pneumatic pipelines which is different from ordinary air suspension,when the pressure in the connected air spring is unbalance the gases exchange which can effectively improve vehicle ride comfort.However its laterally interconnected structure is conflicted with traditional height adjustment charging &discharging strategy,which will cause vehicle with laterally interconnected air suspension not to achieve height adjustment function.It is unwise for laterally interconnected structure to give up height adjustment function.Therefore,this paper is focusing on solving this defect,and an effective control for whole vehicle height adjustment studied.First of all,height adjustment charging &discharging system which is suitable for vehicle with laterally interconnected air suspension was redesigned,and then the mathematical model of each component and the whole vehicle dynamic model were built based on related theory to determine the control variables in the system.And considering the unsprung mass displacement caused by road excitement which affects the accuracy during the height adjustment process resulted in the built of the four-wheel road excitement model.Secondly,height adjustment modes were designed based on the adjusted height of air spring that match the target vehicle,and then control method was added to solve the problem of overshooting and oscillation during height adjustment process.In addition to ensure posture stability during the height adjustment process,the function of each controller was decoupled so as to form a new kind of posture chasing control strategy.To verify the efficiency of the posture chasing control strategy,front and rear controllers were designed based on the height requirement of parking condition and simulation was conducted.The simulation result shows that the front controller was in collaboration with the rear controller.Also,the problem of overshooting was alleviated,and the body posture kept stable.Thirdly,the test bench of laterally interconnected air suspension was built based on modified prototype,and the designed height adjustment and posture chasing control strategy was implement by D2 P,which can then be connected to the bench.On the basis,the height adjustment test on parking condition was conducted.The test results also shows that the height adjustment control strategy is effective,which can meet the demand of height adjustment.Finally,the objective of control system was redefined according to the requirement of height adjustment under dynamic condition,and then front and rear controllers were designed based on validated chasing control system.Considering that the front controller has important influence on the characteristics of overall system,and its actual effect under dynamic condition was verified by the previous built test bench.From the test we can know the measured height signal with noise interference under dynamic condition as the input would disturb system to judge,determining the air mass deviation in the air spring as the control input,at the same time front and rear controllers inputs and control rules were modified.The simulation results show that the control strategy can switch body height quickly under the incentive disturbance while the root mean square of sprung mass acceleration during height adjusting compare to initial height has no signs of deterioration which retain the suspension damping performance,and the body posture keep stable.