Design, Development of bush load simulator for luxuary car manufactures | Daily News


Research at SLIIT:

Design, Development of bush load simulator for luxuary car manufactures

Figure 1: Computer Aided Engineering (CAE) model of the bush load
Figure 1: Computer Aided Engineering (CAE) model of the bush load

Modern luxury vehicle customers have stringent demands regarding ride comfort and vehicle stability and these factors greatly influence the perceived quality of the vehicle.

To achieve a comfortable ride, the suspension system needs to be soft to absorb vibrations generated from road imperfections. On the other hand, to improve vehicle stability, the suspension system must be stiff to maintain a constant contact between road and tire. So, designing a suspension system is a shear compromise between ride comfort and stability. As a technique, increasing the damping of the rubber bushings of the vehicle suspension system is widely employed. Damping is the physical effect that restraining the vibration motion by means of energy dissipation.

Rubber bushes in the suspension system play a vital role in controlling and reducing vibrations. However, not all suspension bushes are made for vibration and noise attenuation, Rubber bushes that are designed to reduce vibrations and improve comfort are called comfort bushes. These bushes generally have high damping co-efficients to absorb vibration energy and low stiffness to isolate the vehicle from external vibrations. To increase damping, these bushes have fluid chambers on either side which are connected together by small channels, and fluid flow between them during compression and expansion providesdampening (Fig 3).

Due to the complex design of the bush, it is very difficult to derive an accurate theoretical representation of its behaviour. Currently, designing and validating bushes is done using a trial and error approach where each bush iteration is assembled in the vehicle and tested at the vehicle proving grounds. However, performing these real vehicle experiments are expensive and time-consuming. Thus, developing a bush test-rig that replicates the real enviroment for the bush loads would be beneficial.

There can be staic loads that comes onto a rubber bush such as forces due to self weight, force due to breaking with a constant deceleration and force due to acceleration with a constant acceleration. On top of this, there can be cyclic loads that can come onto a bush such as force due to centrifugal action of mass imbalance of a rotating tyre. Situation is very critical if there is an radial misalignment which again creates a cyclic load when rotating. This is a major problem particularly in hot countries like Dubai, Australia and USA where the day time temperatures are very high and at the night, the temperature drops down is something badly wrong in the car which could end up in garages when in reality there would be no problem with the car.

Therefore it is vital to design the suspension sub-syem where it can absorbe these cyclic loads under different static loading conditions (light accelerations and decelerations). Due to complex geometries, multi physics environment and non linear behaviour in the bush, it is very difficult to develop a valid theoretical model.. Hence the performance of the bushes are tested in real cars at the proving grounds. In this context,a testrig has been desinged and developed by set of undergraduates together with Bentley CAE Research Unit at Faculty of Engineering, SLIIT. The unit is conducting research and development work for Bentley Motors Ltd, UK and for other local institutes where the said unit is headed by Senior Lecturer, Dr Malika Perera of the Faculty of Engineering of SLIIT.

The testrig is capable in simulating the range of preloads (static loads) and cyclic loads that could be there in the Car during all its operating conditions. Therefore the bush can be tested in the testrig rather than the car which can save lot of money for the car manufacturer.

In developing the testrig (Fig 1 & 2), a commercially available multibody dynamics software MSCAdmas was used. This is a virtual prototyping software where it can calculate all the forces on the structures. Those forces were used to calculate the durability of the testrig. Hence the final product is optimised and also the durability is garanteed for 10 years of oepration without any structural failures. The final product was validated against experimental data obtained from a real car test data provided by Bentley Motor Ltd, UK (due to confidantiality the exact numbers are not plotted in the figure, Fig 4).

The Industry-University collaborating model used here is similar to the approach that all the high end universities all over the world are using to uplift their teaching and research into a different height. It is proud to announce that SLIIT has such a colloborations with a world leading car manufacture so that the students can gain international experience by participating in these projects available locally at SLIIT. Bentley CAE Research Unit at SLIIT is interested in supporting the local industries further by introducing the state of the art technology on the same lines as they have already rendered to international industries.



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