Tridimensional analyses of mechanical suspension for autovehicles.

Spanu, Alina ; Stoenescu, Adrian ; Anghel, Florina 等

Abstract: The paper is focused on the problem of mechanical condition design for the coachwork, taking into account the force developed by the independent suspension for each wheel of a car, with direct application and results for the Fiat Panda. We have designed a 3D model for the suspension system and we have studied the internal tensions that could cause its functional disorder and even the breaking. Finally, we have designed a special part that could improve the stiffness of the car coachwork.

Keywords: 3D car modeling, 3D car analysis, car suspension

1. INTRODUCTION

The paper focuses mainly on the influence of the car suspension system over the coachwork taking into account different types of road. The car displacement on the road as well as on the highway, with great values of speed are being influenced by some external and internal factors such as the road profile, which could not be theoretically established before, the torsion couple acting on the transmission shaft, the dynamic influence over ball joints and the wheel balance. All these reasons specified before could lead to vibrations and shaking movements, as well as great values for forces and mechanical couples caused by mechanical sprung and unsprung masses (Law & McComas, 2005).

The sprung mass is the mass of the vehicle supported on the springs, while the unsprung mass is loosely defined as the mass between the road and the suspension springs. In order to solve these technical issues, we have made a mathematical model for computing the dynamic values for speed and displacement of sprung and unsprung masses and much more the time in which the movement could be dampened (Kalhori, 2001).

The quarter-car model of the wheels, sprung and unsprung masses, suspension components with three different functional design conditions were developed in (Stein & Mucka, 2003). The first choice and the simplest one is the passive suspension where it is used only the spring and the damper. The second choice is a semi-active suspension where a damper with variable damping constant is required. The main disadvantage is that the energy dissipates only and the time constant is very large. The last one is the active suspension where energy source was added and then the ride properties (passenger comfort, car stability and road friendliness) could be improved significantly. The last mathematical model has considered the passenger too, so that we presented the influence of vibrations to human body and the suitable design for the comfort level (Miner, 2005).

2. 3D MODEL FOR THE CAR COACHWORK

The main goal of our work was to established the tensions and displacements acting on the coachwork as a consequence of the force which loaded the car suspension system. As it can be seen in fig. 1 the assembly of the coachwork has eight components:

[FIGURE 1 OMITTED]

Superior Beam, Central Body, Wheel Surface, Inferior Beam, Main Inferior Beam, Central Beam, Stiff Beam and Stiff Damp.

The 3D assembly was designed only for the front left side. As we can see in fig. 1, it has a very complex shape, so that we had to measure some characteristic points in order to have a realistic model of the Fiat Panda car.

2.1. 3D models for each part of assembly

For instance, we can see one of these parts in fig. 2 with its main profile points.

The most important surface in fig.2 is the green one because here will be put the surface on which will act the force given by the spring of the car suspension. After its representation as a surface using CATIA V5 R14 soft, we have added material with the thickness 1mm and we have designed the mesh for computing with finite element method. In fig. 3 we showed the mesh of this part.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Fig. 4 represents the mesh of the surface on which is loaded the force given by the car suspension.

We have done the same thing for all the eight components of the assembly. We represented the mesh surface for the entire assembly in fig. 5.

2.2. 3D analysis for the assembly

Using the 3D model for the assembly, we have made the analysis of tension and profile displacement with a force acting straight to the direction computed with the mathematical model for the suspension. The force components are: [F.sub.x]=235.964N; [F.sub.y]=235.564N; [F.sub.z]=6791.814N. As we can infer from the fig.7 the great values of tension should be found on the surface where the force is acting, as well as on the surfaces where the assembly is restrained with clamp and where the welding have been done (Patrascu, 2004).

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

3. CONCLUSIONS

The paper gives a useful method for the 3D analysis of tensions and displacements of the coachwork taking into account the force computed for the independent wheel car suspension with the mathematical model. We may observe the critical surfaces, especially for the welding, so that we can improve the mechanical structure in order to avoid the critical functional conditions and even the breaking. For instance, we have designed a new part of the assembly that increases the structure stiffness.

The future work is going will focus on improving the structure stiffness and the mathematical model for computing the real value of the force.

4. REFERENCES

Kalhori, V. (2001). Modelling and Simulation of Mechanical Cutting, PhD Thesis, Lulea University of Technology, Department of Mechanical Engineering, Sweden, pp. 5-27.

Law, A.M. & McComas, M.G. (2001). How To Build Valid and Credible Simulation Models, Proceedings of the 2001 Winter Simulation Conference, B. A. Peters, J. S. Smith, D. J. Medeiros, and M. W. Rohrer, eds.

Miner, W.D. (2005). A Tool Wear Comparative Study in Turning Versus Computer Simulation in 1018 Steel, MS Thesis, Brigham Young University, pp. 5-20.

Movahhedy, M., Gadala, M.S., & Altintas, Y. (2000). Simulation of the orthogonal metal cutting process using an arbitrary Lagrangian-Eulerian finite-element method, Journal of Materials Processing Technology 103 (2000): 267-275.

Patrascu, G. (2004). 3D Simulation of Turning Process using FEM Software, Proceedings of the International Conference on Manufacturing Systems ICMaS 2004, Constantin, I., Ghionea, A., Constantin, G. (Ed.), pp. 297-300, ISBN 973-27-1102-7, Bucharest, 2004 October, Editura Academiei Romane, Bucharest

Stein, G., J., Mucka, P. (2003) Theoretical Investigations of a linear planar model of a passenger car with seated people, in Proceedings of the Institution of Mechanical Engineers, Vol. 217, Part D, of Journal of Automobile Engineering 2003.