Modelling and Testing - Analysis and Optimisation: Bushings

Elastomer bushings are used in vehicle chassis applications to contribute to self-steering effects and vehicle handling behaviour within the limits of the elastic-kinematic design of vehicle suspensions. Moreover, they have been more and more frequently adopted to improve ride comfort as well. A known issue with elastomer bushings is that their properties, like stiffness and damping characteristics, may change considerably over their operational lifetime due to numerous influences and may show adverse effects compared with their initial design configuration.

The project addresses the relationships that are responsible for the change of the static and dynamic behaviour of rubber bushings over the course of time and as a matter of diverse (thermal, chemical and geometrical) influences. To achieve a preferred and robust design of the suspension system, regarding the selection of the appropriate design and rubber compounds of convenient bushings, and in this way to restrain their limits of tolerance, the properties of both the components and their rubber compounds are analysed. Based on comprehensive experimental test results of the full component and of the rubber compounds, a design concept for an elastomer chassis bushing is proposed that aims to better preserve its functional properties with respect to time, high temperatures and operational loads.

Further, effects and interactions of varying bushing properties over time are examined regarding the dynamic behaviour of the chassis in the comfort-relevant frequency range from 0 to 30 Hz, as well as objective criteria for overall vehicle assessment concerning dynamics and ride comfort.

Suspension Design Optimisation

The kinematic layout of a suspension system determines the positioning of the wheel during wheel travel or steering and has a major impact on the vehicle handling behaviour. The same applies to elasto-kinematics, which describes the movement of the wheel as a result of external forces. The wheel performs a spatial movement, and usually, there is more than one kinematic target. Therefore, the design of the wheel suspension requires a lot of experience or many manual iterative loops in order to approach the desired targets. If the elasto-kinematic objectives are considered as well, an inexperienced chassis developer quickly reaches the limits. It becomes obvious to apply an optimization algorithm for the determination of the hardpoints. This may yield an advantage in time as well as an increase in the quality of the results.

First, different kinematic and elasto-kinematic objectives and various possibilities for determining an appropriate target function for the optimisation are analysed. Several optimization examples are studied to determine suitable optimization algorithms for suspension kinematics optimization. In addition to kinematics and elasto-kinematics objectives, further optimization targets are considered. For example, how the use of Carry-Over Parts, which have an invariable geometry, can be considered in the suspension optimization process. Different approaches are developed.

The second aim is to optimise the robustness of the suspension system regarding component tolerances.

Finally, the maximum forces occurring in the links of the suspension system are minimized within an optimization process. As a result, the weight of the individual axle components can be reduced. Furthermore, an acoustic insulation potential is given because elastic bushings can be designed softer in order to achieve the respective compliance targets of the suspension system.

Modelling, Testing, and Analysis of Wheel Suspensions

To achieve superior ride comfort and vehicle handling, a detailed knowledge of the dynamic behaviour and characteristics of a modern suspension is required. In order to understand the effects of these characteristics on full vehicle level, they may evaluated on subsystem level first. For this reason, the project focuses on the development of a consistent process for the quasi-static and dynamic suspension characterization on a subsystem test rig.

An appropriate multi-body simulation model is developed considering a reasonable compromise between efforts in parameterisation and resulting accuracy. The models allow the validation of the measurement results on the full vehicle and subsystem level and, finally, to evaluate the new approach. Also, a new method to identify synthetic excitation spectra for a suspension test rig from full vehicle tests when running over uneven roads, is proposed.

Figure 1: Analysis and testing of elastomer bushings

References

Kemna, Jens, Johannes Edelmann, and Manfred Plöchl. "Influences on long-term behaviour of elastomer chassis bushings considering their geometric design and rubber compounds., opens an external URL in a new window" Polymer Testing 65 (2018): 69-77.

Mutter, Fabian. "Eine effiziente Achskonzeptentwicklung durch Verwendung von Optimierungsmethoden, opens an external URL in a new window." PhD thesis, Technische Universität Wien, 2018.

Angrosch, Bernhard, Manfred Plöchl, and Werner Reinalter. "Suspension design by means of numerical sensitivity analysis and optimisation., opens an external URL in a new window" International journal of vehicle design 65, no. 1 (2014): 52-72.

Zauner, Christoph, Johannes Edelmann, and Manfred Plöchl. "Modelling, validation and characterisation of high-performance suspensions by means of a suspension test rig., opens an external URL in a new window" International Journal of Vehicle Design 79, no. 2-3 (2019): 107-126.

Researchers

• Jens Kemna
• Fabian Mutter
• Christoph Zauner
• Bernhard Angrosch

Project Partners

• Porsche
• Magna Steyr