| As the main force of post disaster rescue,emergency rescue vehicles should have high mobility,good ride comfort and handling stability.However,passive suspension is widely used in the chassis of emergency rescue vehicles at home and abroad.The structural parameters of passive suspension are fixed and cannot be adjusted in real time according to the driving road conditions.When the emergency rescue vehicle runs in the area to be rescued with complex terrain environment,its driving performance is difficult to guarantee.Different from the passive suspension,the active suspension can obtain the body motion state according to the sensors installed on the body,and regulate the suspension actuator to output the corresponding force or displacement in real time according to the body motion state,so as to meet the requirements of different working conditions on the characteristics of the suspension system.In recent years,experts and scholars at home and abroad have conducted extensive research on active suspension control technology and achieved some research results,but their research results are mostly focused on two-axle passenger vehicles,and there is little research on multi-axle emergency rescue vehicles.Combined with the National Key R &D Project "Research on Key Technologies of Special Chassis and Suspension for High Mobility Emergency Rescue Vehicles(Including Fire Vehicles)"(Project No.2016YFC0802902),this paper makes an in-depth and systematic research on active suspension control technology in order to improve the handling stability and ride comfort of emergency rescue vehicles on unstructured roads.The main research work is as follows:(1)The feasibility of simplifying the single wishbone suspension 1/6 vehicle(the whole vehicle is a three-axle six-wheel vehicle)model to the classical two degree of freedom 1/6 vehicle model is demonstrated.The 1/6 vehicle model based on single wishbone suspension and the classical 2-DOF 1/6 vehicle model are established.Sinusoidal excitation is applied to the single-wishbone suspension model,and the results showed that within a sine cycle,the change of the kingpin’s inclination and the track was small;random road excitation was applied to the two models,and the results showed that the sprung mass acceleration difference of the two models and their root mean square values are small.Therefore,when building the vehicle model,the nonlinear influence caused by the geometry of the single wishbone suspension can be ignored,and the single wishbone suspension model can be simplified to the classical two degree of freedom 1/6vehicle model.(2)The control strategy of inertial control active suspension based on vehicle attitude deviation is studied.Aiming at the problems of complex decoupling process and strong model dependence in the existing active suspension control strategies,an inertial control active suspension control strategy based on vehicle attitude deviation is proposed.The attitude parameters of the vehicle body are measured online through the Inertial Measurement Unit,and the attitude deviation between the current time and the previous time of the vehicle body is calculated.The expansion and contraction of each suspension servo actuator cylinder required to eliminate the attitude deviation in the opposite direction is calculated,and the attitude of the vehicle body is adjusted and controlled by controlling the expansion and contraction of each cylinder.In order to realize the effective decoupling of the whole vehicle active suspension system,the multi-axle emergency rescue vehicle is equivalent to a three degree of freedom parallel mechanism by grouping and interconnecting the suspension units,and the expansion and contraction of each suspension servo actuator cylinder is obtained by solving the inverse position solution of the parallel mechanism.In order to verify the effectiveness of the control strategy,taking the three-axis emergency rescue vehicle as the research object,the position inverse solution and position forward solution of its equivalent three degree of freedom parallel mechanism are deduced,and the body attitude dynamic model,vehicle interconnected hydro-pneumatic suspension system model and random road model are established.Taking random road excitation as input,the simulation and analysis are compared with hydro-pneumatic suspension and sky-hook damper control active suspension.The simulation results show that the inertial control active suspension control strategy based on vehicle attitude deviation proposed in this paper can effectively stabilize the body attitude and improve the ride comfort of the vehicle at the same time.(3)The active suspension control strategy for envelope surface driving on the slope is studied.Aiming at the problem that the displacement output of the suspension servo actuator cylinder is saturated when the multi-axle emergency rescue vehicle is driving on the ramp or gully road,the active suspension control strategy for envelope surface driving on the slope is proposed on the basis of inertial control active suspension control strategy based on the vehicle attitude deviation.The control strategy filters out the part with low change frequency in the vehicle posture deviation,and only retains the part with high change frequency,so that the vehicle can drive along the envelope surface of the ramp or gully road,and so as to reduce the probability of the suspension servo actuator cylinder reaching the travel limit.In order to verify the effectiveness of the control strategy,the longitudinal slope random pavement and transverse slope random pavement are used as the system inputs for simulation and analysis.The simulation results show that the active suspension control strategy proposed in this paper can effectively reduce the probability of saturation of the displacement output of the suspension servo actuator cylinder when driving on a ramp.(4)The Internal Model Control method of electro-hydraulic servo actuator of active suspension is studied.Aiming at the problem that the traditional PID can not effectively deal with the time-varying parameters in the electro-hydraulic servo actuator position control system of active suspension,an Internal Model Control method is used.The linearized mathematical model of electro-hydraulic servo actuator position control system of active suspension is established,and the internal model controller is designed based on this model.In order to verify the control effect of internal model controller,comparative simulation and bench experiment with PID control are carried out.The simulation results show that the unit step response of the system under Internal Model Control is fast,stable and no overshoot,and the dynamic characteristics are better than PID control.When the system is subject to external interference,Internal Model Control can recover to the steady-state value more quickly and smoothly than PID control.The bench experiment results show that when the frequency of sinusoidal input signal changes,the tracking performance of the system based on PID control deteriorates significantly,while the tracking performance of the system based on Internal Model Control does not change significantly;when the load quality changes,the change amplitude of tracking error based on Internal Model Control is obviously less than that of PID control.The simulation and experiment results both show that the tracking response performance and robustness of the electro-hydraulic servo actuator position control system based on Internal Model Control are better than PID control.(5)The whole vehicle suspension system experiment platform was built and experiment.Based on the chassis of three-axle six-wheel crane,the electro-hydraulic servo control system of active suspension was designed,a vehicle suspension system experiment platform integrating active suspension system and hydro-pneumatic suspension system was built,and the experiments on pulse pavement,gravel pavement,longitudinal and transverse slope pavement are carried out.The experiment results on pulse road and gravel road show that compared with hydro-pneumatic suspension,the inertial control active suspension control strategy based on vehicle attitude deviation can effectively stabilize the body attitude and improve the vehicle ride comfort;the experiment results on longitudinal and transverse slopes show that the active suspension control strategy can make the vehicle drive along the slope envelope,and effectively reduce the probability of actuator displacement output saturation when driving on the slope. |
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