IMPROVED VEHICLE SUSPENSION CONTROL ARM MODEL USING EXPERIMENTAL DEFLECTION MEASUREMENTS
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Abstract
The suspension system plays an important role in automobile performance, safety and noise level reduction. In a suspension system, a control arm is a crucial component. The control arms have different shapes depending upon the model and the purpose of the vehicle. The control arm having a wishbone or ‘A’ shape carries the maximum load from the shocks helping the wheels to maintain their geometry with the road and thus resulting in a steady ride and good handling. After absorbing the impact that the road has on the wheels the control arm either absorbs it or deflects it to the coils of the suspension depending on the type of suspension. The control arm being a vital component of the vehicle suspension system, it becomes necessary to study the mechanical behavior under varying load conditions. This thesis describes an improved vehicle suspension control arm finite element model supported by deflections recorded from experiments. It also presents the strength and compliance analysis of a suspension control arm using the load cell output from an Instron 4400- Universal Testing Machine (UTM). Initially stress analysis is done on the control arm model in SolidWorks to get a measure of the stresses and deflections induced in a control arm. Accordingly the test rig is also designed in SolidWorks which helps model the control arm on the UTM. The experimental test rig was manufactured and made ready for testing. The control arm is then fixed in the setup at two inboard ends and the outboard ball joint has an attachment for application of the load through combination of mechanical connectors. The load is applied to the ball joint of the control arm through a tapered hole in the attachment to the load cell. Displacement results for the load applied are recorded by UTM. Data from UTM is transferred to the external computer through use of General Purpose Instrument Bus (GPIB). The graphs for Force-Elongation and Stress-Strain are plotted and presented from the results. These results are in accordance with the theoretical curves. The strength and the compliance for the control arm is then analyzed from the plotted curves and recorded values. Internal deflections of the control arm (metal deflection not including the deflection of the rubber bushing) are measured with a dial indicator mounted on the metal at one end of the control arm and measured at the other end for loading in both directions i.e. longitudinal and lateral directions. Also the displacements from FEA model of control arm are measured. Careful improvements or mesh refinements to the model were made until the experimental results matched the FEA results to a predefined accuracy in order to get an improved vehicle suspension control arm model. Lastly, the model was done for the lower front control arm of an Acura MDX sport utility vehicle (SUV) for the 2007-2015 model years.