Mechanical Engineering ETDs

Ryan Robinson

Publication Date

2-9-2010

Abstract

Methodology to develop a baseline passive nonlinear damper and inerter for road race application to maximize vehicle lateral acceleration is developed here using optimization techniques. The method includes use of equations-of-motion for suspension models, assembly of equations in a computer model for simulation, identification of the objective function which maximizes lateral acceleration based on tire data, optimization of the objective function by varying damping and inertance, identification of mode shapes and root locus analysis. No closed form solution exists for an optimal linear or nonlinear damper which maximizes lateral acceleration. Consequently, numerical analysis is required to solve the problem. Several suspension models ranging from a quarter-suspension to a full-car suspension are examined to determine whether the simpler models are reasonable substitutes for higher order models. Fixed parameters required for the Simulink simulation, and thus the optimal damper, are from the 2007 UNM FSAE vehicle. Inertial forces from a data acquisition system are used to provide maneuver/handling input to the models. Tire data is analyzed using optimization to find the optimal vertical loading which maximizes lateral tire force. This optimization shows lateral force is maximized when inner and outer tire loads are equal, thus the objective function to be minimized is load transfer. Matlab Optimization Toolbox is then used to optimize the objective function by varying the linear/nonlinear damper rates followed by a separate optimization of the inerter. Root locus and mode shape identification are used to understand the results of the optimized system. The analysis indicates that a nonlinear damper attenuates lateral load transfer better than a linear design. It was also observed that the simpler models optimizations do not agree well with the full-car model due to over-simplified inputs and assumptions. The optimal inerter further increased lateral acceleration by decreasing load transfer.'

Keywords

Automobiles--Shock Absorbers--Design and construction, Damping (Mechanics), Lateral loads, Automobiles, Racing--Chassis.

Degree Name

Mechanical Engineering

Level of Degree

Masters

Department Name

Mechanical Engineering

First Committee Member (Chair)

Starr, Gregory

Second Committee Member

Ebrahimi, Nader

Document Type

Thesis

Language

English

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