analytical and numerical automotive spring-damper module
TRANSCRIPT
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