Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
Shock absorbers are crucial components of a vehicle’s chassis responsible for the trade-off between stability, handling, and
passenger comfort. The aim of the thesis is to investigate the physical behavior of an advanced automotive racing shock
absorber, known as TTR, developed by Öhlins Racing AB. This goal is achieved by developing a detailed lumped parameter
numerical model of the entire TTR suspension in the advanced 1D simulation tool, AMESim.
The shock absorber is mainly composed of the main cylinder with through-rod piston design and the gas reservoir located at
the low pressure hydraulic line, which connects the compression and rebound sides. The mentioned sides are identical in terms
of the components which are a High Speed Adjuster, a Low Speed Adjuster, and a check valve mounted in parallel. The
adjusters are special hydraulic valves, which can be modified in terms of flow metering characteristics by means of external
accessible screws. Adjustment is done in a series of discrete numbers called ‘clicks’. A fixed orifice and a spring-loaded
poppet valve are responsible for controlling the piston low and high speed regions respectively.
The developed AMESim numerical model is capable of capturing the physics behind the real shock absorber damping
characteristics, under both static and dynamic conditions. The model is developed mainly using the standard AMESim
mechanical, hydraulic and hydraulic component design libraries and allows discovering the impact of each single hydraulic
component on the TTR overall behavior. In particular, the 1D model is presented in two levels of progressive physical
complexity in order to improve the dynamic damping characteristics. Several physical phenomena are considered, such as the
hydraulics volumes pressure dynamics, the contribution of external spring and pressure forces to the dynamic balance of the
moving elements, the static and viscous frictions, and the elastic deformations induced by solid boundaries pressure.
In this thesis, progressive model validation with different types of measurements is as well presented, covering the individual
hydraulic components models as well as the entire shock absorber model. The measurements have been performed on the flow
benches and dynamometers available at the Öhlins Racing measurements laboratory. These comparisons, deeply discussed in
the thesis, allow discovering the impact of specific physical effects on the low and high speed hydraulic valves static
performance and on the shock absorber dynamic behavior.
Numerical results show good agreement, especially at low and medium frequencies and symmetric ‘click’ adjustments on
compression and rebound sides. Further model development is necessary in the other areas, for example by considering more
complex models of the valve dynamics and fluid flow patterns, i.e. flow forces, together with more advanced models of the
sealing elements viscous friction, and thermal effects. Finally, the AMESim environments offered a good level of flexibility in
designing the TTR hydro-mechanical system, by allowing the user to choose between different levels of model complexity.
2012. , 78 p.
2012-06-15, A39 (MASS), Department of Management and Engineering, Linköping University, SE-581 83 Linköping , Sweden, 13:15 (English)