Y.S. Kong

Topological and Topographical Optimization of Automotive Spring Lower Seat

The design of a suspension system emphasizes weight reduction in this high-computation technology era. Understanding that the reduction of suspension mass can lead to cost and material reduction is important; moreover, the riding performance of the vehicle should be improved. Topology and topography structure optimization for the spring lower seat is performed to reduce the weight of a passenger car spring lower seat design under stress and structure compliance constraints. Topology optimization is performed to identify the density of the required elements, whereas topography optimization is utilized to strengthen the structure of the lower seat by applying bead parameters in the model. Based on topology optimization, the mass of the model is improved by a reduction of 36.5%. Topography optimization is subsequently performed to fine-tune the topology-optimized model. Beads are added to the model to strengthen the stiffness of the structure. The topography-optimized model has successfully increased compliance by 27% compared with the sole topological optimized design. With the combination of topology and topography optimization techniques, the weight of coil spring lower seat has been successfully reduced while preserving the strength. Suitable sheet materials are proposed to match the optimized coil spring lower seat design.

Ride quality assessment of bus suspension system through modal frequency response approach

The ride dynamic characteristics of an urban bus were investigated through simulations with suspension component characteristics and were validated through field measurements. It was performed on highway road at a constant forward speed. A random vibration bus model with two parallel tracks of terrain profile was synthesized with superposition between the left and right sides as well as time delay between front and rear. The bus frequency response model was introduced with embedded modal extraction data to enhance computation efficiency. The simulation results of the bus model were derived in terms of acceleration PSD and frequency-weighted root mean square acceleration along the vertical axes at three locations, namely, driver side, middle, and rear passenger side, to obtain the overall bus ride performance. Another two sets of new leaf spring design were proposed as suspension parameter analysis. The simulation approach provides reasonably good results in evaluating passenger perception on ride and shows that the proposed new spring design can significantly improve the ride quality of the driver and passengers.

Observing the Durability Effects of a Formula Student Electric Car using Acceleration and Strain Signals

This paper presents the durability analysis of suspension system from an electric Formula Student race car using strain and acceleration signals. To have outstanding performance in a competition, the Formula Student car was required to have light weight but safe design. To evaluate the suspension design of the vehicle, strain and acceleration signals were collected under a vehicle double lane change event according to the ISO 3888 testing procedure. Strain signals were measured on the wheel carrier and lower control arm of the Formula Student car. Meanwhile, tri-axis accelerations were measured on the wheel and chassis of the vehicle during the testing. In addition, the wheel displacement relative to vehicle chassis was measured using laser sensors. The fatigue life of the lower arm and wheel carrier were predicted using the measured strain signals. Due to limited instrument, a quarter car model was simulated using wheel displacement signals to obtain spring force signals for fatigue estimation. The simulation model was validated using the measured chassis acceleration signal. Ride and whole-body vibration of the vehicle were also assessed using the measured acceleration signals. Through this analysis, the durability effects of the Formula Student car suspension system were identified. The Formula Student car suspension design could be improved through understanding the vibration behaviour.

Suspension parametric analysis of conventional bus through finite element modal simulation

Vehicle dynamic response of urban bus for common manoeuvres enhancing purpose has been investigated. Nowadays, increasing concerns on human driver comfort and emerging demands on suspension systems for off-road vehicles call for an effective vehicle ride dynamics model. This study devotes an analytical effort in developing a comprehensive vehicle ride dynamics simulation model. A bus simulation model which consists of two sets of different parabolic leaf springs and shock absorbers, front and rear axle, one dimensional tyres, anti-roll bars and simplified bus body with assumption the chassis is rigid has been built in finite element (FE) environment. Modal analysis is further to be performed in order to calculate the mode shapes and associated frequencies. Subsequently, suspension parameters analysis has been conducted to identify the sensitivity of every component towards the vehicle vibration behaviour. The related suspension parameters in the sensitivity analysis are parabolic leaf spring stiffness, anti-roll bars bending moment, and shock absorber damping characteristics respectively. The mode shapes and natural frequencies change due to the suspension parameters modification could be obviously visualized through finite element method. The visualization capabilities of the mode shape would provide an insight understanding of vehicle vibration behaviour in which is generally complex. The developed vehicle ride dynamics model could serve as an effective and efficient tool for predicting vehicle ride vibrations, to seek designs of primary and secondary suspensions, and to evaluate the roles of various operating conditions.

Fatigue Life Prediction of Leaf Spring through Multi Mean S-N Approach

Parabolic leaf spring is a suspension component for heavy vehicles where spring itself experiences repeated cyclic loading under operating condition. Fatigue life of the parabolic leaf spring is vital since the deflection of the spring is large and continuous. To determine the fatigue life of the parabolic leaf spring, material properties input to the design is important. The objective of this study is to predict the fatigue life of a parabolic leaf spring based on two different material grades which are SAE 5160 and SAE 51B60H under constant amplitude loading through various mean stress method. SAE 51B60H is the material with slightly higher carbon, manganese and chromium content compared to material SAE 5160. Chemical composition differences between SAE 5160 and SAE 51B60H have significant effects on the mechanical properties and fatigue life. In this analysis, finite element method together with multi mean curve stress life (S-N) approach has been implemented to estimate the fatigue life of the spring. Goodman, Gerber and Interpolate mean stress correction method were adopted to correct the damage calculation for mean stress. The results show that interpolate and Goodman method predict the fatigue life of the material with higher accuracy. On the other hand, material SAE 51B60H yields higher fatigue life compared to material SAE 5160.