Layered Independent Modeling And Control Of Off Road Vehicle Based On 1/4 Suspension

The main purpose of suspension system is to improve the operating stability and ride comfort of a vehicle. The researches on how to improve a full vehicle vibration feature, construct a new suspension type and speed up the vibration reduction are the primary ways to improve the overall performance of the vehicle. In recent years, with the development of computer and controlling technology, the active suspension method was increasingly developed sophisticated. The active suspension could be obtained to deal well with the contradiction between the handling stability and ride comfort. It was applied for real-time control of a vehicle so as to achieve an optimal performance.In the course of this paper, the real driving road conditions of SUV were considered. A traditional vehicle model with fourteen degree of with vertical and in-road lateral excitations were adopted. The fourteen degree of freedoms include four vertical and lateral wheel motions, the vertical motion of suspension center, the lateral motion of suspension center, the pitch angle motion of suspension center, the roll angle and yaw angle motions of suspension center, as well as the vertical motion of driver system. Consider the vertical direction should be the main control objective of the active suspension in practical application, the lateral vibration would be acted as the uncontrolled units. According to the actual demands, the fuzzy control was adopted to control the active suspension.In order to improve the ride comfort and driving stability of a SUV, a hierarchical independent model and control method were proposed based on parallel quarter suspensions. Based on the controlling objectives of a center control layer and the bottom layers, the coupling relationship between the vehicle model and the quarter suspensions was derived. The SIMULINK of the MATLAB software was used to establish a traditional vehicle model with fourteen degrees of freedoms and the overall vehicle simulation module, which adopted hierarchical independent model and control. The control comparisons were made between the traditional full vehicle model with fourteen degrees of freedoms and the hierarchical independent model. The vehicle body vertical acceleration, lateral acceleration, pitch angle acceleration, yaw angular acceleration, roll angle acceleration, four wheel suspension accelerations, four suspension travels, four tire deformations and vertical acceleration of driver were executed respectively. The comparison results showed that the vertical vibration of the hierarchical independent control had been improved obviously more than the traditional full vehicle control. The maximum values of the vertical, pitch and roll accelerations were reduced by 29%,71% and 50% respectively. The maximum acceleration values of suspension sprung mass about wheel 1 to wheel 4 were reduced by 20%,22.4%,50% and 50% respectively. Moreover, the maximum values of suspension travels about wheel 1 to wheel 4 were decreased by 60%,25%, 33% and -30%. Last but not the least, the maximum vertical acceleration of the driver system reduced by 33%. Consider the lateral direction had not been controlled in the models, the lateral and yaw angle vibrations were not improved.In conclusion, due to the presentation of the hierarchical independent modeling and control, the controlled variables of four quarter suspensions could be resolved simultaneously so that the online calculation time would be decreased and sample frequency would be increased. Therefore, the detailed vibration control would be fulfilled for road excitations so as to improve the ride comfort and driving stability of SUV effectively.