ANALYTICAL AND NUMERICAL AUTOMOTIVE SPRING-DAMPER MODULE SOLUTIONSby 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

RodPiston

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