ANALYTICAL AND NUMERICAL AUTOMOTIVE SPRING-DAMPER MODULE SOLUTIONS by APM ENGINEERING & RESEARCH Background References Objectives This research was conducted by APM Engineering & Research suspension division Conclusion To improve automotive spring damper module design through fluid structure interaction and structural strength analysis where the quality of products and relative costs were optimum. Results 1. Altair Hyperworks Manual, 2011 2. SAE 1996, Spring design manual 3. John C Dixon 2007, The shock absorber handbook, Methods Fig 2: Stress analysis of coil spring An automotive spring damper module consists a pair of damper and coil spring integrated together to isolate road excitation and control resonance. It was designed to control ride and handling of a vehicle for the comfort and safety of its passengers. In order to design a comprehensive coil spring, acceptable stress level and desired spring stiffness must be taken into consideration. To minimize the weight, size and cost, engineers usually design springs to the highest stress level that will not result in significant long term “set”. On the other hand, a damper serve the purpose of limiting excessive suspension movement and to damp spring oscillations. For automotive applications, hydraulic damper is applied where that energy will converted to heat inside the viscous fluid. This research is focus on fluid and structure interaction of the damper as well as the imbedded coil spring force versus displacement characteristic. Fig 3: Force vs Displacement curve As conclusion, implementation of Radioss explicit dynamic solver significantly reduces the design duration of spring-damper module. Besides that, it also provides high accuracy results compared to actual experimental data. The prototype numbers were reduced and in other mean, the design costs of the spring damper module were also deduced. Radioss could be utilized to solve various complex engineering problems which is very beneficial. Fig 4: Damper cross section Illustration Fig 5: Fluid Structure Interaction (FSI) During the structural strength analysis of helical coil spring, the maximum principal and von Mises stress criterion were obtained to determine the maximum stress level (Figure 2). Secondly, the spring stiffness which contributes to the vehicle ride characteristic was correlated to experimental result. As seen from Figure 3, at least of 95% correlation has been achieved for this analysis. Fig 6: Force vs Displacement curve Fig 7: Force vs Velocity curve Rod Piston Washer Disc Orifice Figure 4 illustrates piston and its valve configuration of the designed damper. By simplified the analysis, the fluid space was discretized with 3D Hexa elements and solve through Radioss solver with ALE method. Velocity of the fluid when flow through the orifice and subsequently obstructed by the stacking disc will generate a reaction force where the force is the primary characteristic of the damper as shown in Figure 5. Interaction between the fluid and disc implies the fluid structure interaction analysis which is state of art solution in finite element and CFD research area. Figures 6 and 7 depicts the damping characteristic of the designed damper. With the simulation obtained characteristic curve, fine tuning process could be performed immediately prior to prototype stage. 1. Pre-processing • In this stage, highly accurate CAD model and good mesh generation were acquired. Relevant spring damper CAD model is displayed on Figure 1. • Materials and properties assignation for structural and fluid respectively. Load cases were also applied independently. • Applied boundary conditions to represent the actual behavior of the components and fluid. 2. Solver • Radioss explicit nonlinear dynamic scheme. • Arbitrary Lagrangian-Eulerian (ALE) for fluid structure interaction. 3. Post-processing • Stress level, spring stiffness and damper damping characteristic. • Experimental data correlations and component tuning. Fig 1: Spring-damper CAD model