Optimization of Front Suspension Uprights on a Three-wheeled Electric Vehicle - Ecoist

Abstract: The master thesis was carried out as a part of the project Ecoist at Sirgomez Engineering AB, with the goal of reducing the complexity and mass of the current front suspension upright by designing a new upright from one piece, whilst also considering other aspects such as reliability and manufacturability. In order to achieve this, topology optimization was used. The inputs for the optimization needed from external programs were mainly two things; the loads acting on the upright and a generalized geometry allowing material to be removed. In order to generate the loads acting on the upright, a multibody model of the Ecoist vehicle was built in Adams/Car, consisting of several different subsystems. The full vehicle assembly was then used for a number of different dynamic drive cases, from which the reaction forces and moments acting on the upright were exported. From all those different load steps, one was chosen as representative for the worst case, which was then used in the optimization. The generalized geometry was created in Solidworks, using the old upright assembly as reference. The idea was to make it take up as much space as possible without interfering with the surrounding components. The important parts of the geometry, such as the contact surfaces and holes were kept the same, in order to be able to connect the adjacent parts without changing them. The topology optimization was then performed in Ansys Mechanical with key areas, such as the contact surfaces and holes, excluded from the optimization since they need to retain the same size and shape. The objective function was to minimize the mass whilst the only constraint was a predefined stress limit not to be exceeded of 125 MPa, half of the yield stress for an arbitrary linear elastic material (steel in this case). Afterwards, the optimized geometry had to be smoothed in SpaceClaim in order to obtain a useful geometry, since the optimization output featured undesirably rough surfaces and sharp edges. The final result is an upright geometry consisting of one piece rather than four pieces assembled by a number of screws. The new upright, proposedly made from aluminum alloy AlSi10Mg, has a mass of 0.9345 kg compared to the original upright assembly, which had a mass of 1.478 kg. This represents a decrease of mass with 36.8%.