Dynamic Properties Optimization Design Of The Suspension Spring System Under Full Vehicle Environment

As we know that the excessive levels of vibration in commercial vehicles, due to the excitation from the road irregularities, can lead to ride discomfort and cargo damage and safety problems. The automotive designers pay great attention to optimize the dynamic properties of the vehicle structure to reduce the levels of vibrations. The analysis models used for dynamic properties optimization have three ones, one degree of freedom, two degrees of freedom, and multi-degrees of freedom, in which the cab, frame, and cargo body are assumed to be the rigid body, and to be simplified as a concentric mass, and the complex coupling relations between components under the assembly environment of the full truck have been neglected. Therefore, the validity of results of the optimization may be limited, and it is necessary to develop the method for dynamic property optimization under the assembly environment of the full truck. To this end, this paper uses the model stiffness concept and presents the modal stiffness contributions of components to full truck and the modal stiffness sensitivity to identify which components are the key ones for controlling the modal frequencies considered. Based on the modal stiffness sensitivities, the method for the dynamic property optimization of the suspension spring system, the generalized inverse iterative, is presented.In order to describe efficiently modal properties of the full truck, a3D finite element of the full truck is established. In the model, the cab is modeled by the shell elements, and supporting elements of the cab is modeled with force elements with stiffness in the X, Y, Z direction and connected to the frame. The frame is a ladder structure consisting of two C channel rails with double layers connected by cross-members which are modeled with the shell elements. The suspension springs are modeled with force elements with stiffness at X, Y, Z direction and connected to the ground. The cargo body consists of sub frame, floor, right and left fender, which are modeled with the shell element connected to the frame. The full truck is divided into five components:Supporting springs of the cab (A), front and rear suspension springs (B), cab (C), frame (D), and cargo body (E).Under the assembly environment of the full truck, the natural frequencies and mode shapes are computed, and the modal stiffness contribution of five components as defined above to the full truck and corresponding modal stiffness sensitivities are also computed. From the results obtained, it can be seen that (1):for the first mode (full truck rolling)(fl=1.077Hz) the total modal stiffness is45.85and the contribution of B to full truck is39.95, the corresponding contribution rate is84.75%;(2):for the3rd mode (full truck vibrating along Y direction)(f3=2.78Hz), the total modal stiffness is305.76, corresponding contribution of B is280.70, contribution rate is91.80%;(3):for the4th mode (full truck pitch)(f4=3.37Hz), the total modal stiffness is450.95, corresponding contribution of B is373.90, contribution rate is82.93%.From the above analysis it can be seen that for controlling the1st,3rd, and4th modal frequencies the key component is the suspension spring stiffness and it is not necessary to modify the rest component parameters.By using the generalized inverse iterative, the dynamic property optimization is performed. After3iterative, the optimal results are obtained under the assembly environment of the full truck. The optimal results show that the root mean square (RMS) of acceleration response of the middle point of cab floor is reduced to2.5436from2.9354of the original design, that reduced13.65%. The results also show that the proposed method is effective.