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Simplified Tools and Methods for Chassis and Vehicle Dynamics Development for FSAE Vehicles

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Simplified Tools and Methods for Chassis and Vehicle Dynamics Development for FSAE Vehicles Simplified Tools and Methods for Chassis and Vehicle Dynamics Development for FSAE Vehicles A thesis submitted to the Graduate School of the University of Cincinnati in partial fulfillment of the requirements for the degree of Master of Science in the School of Dynamic Systems of the College of Engineering and Applied Science by Fredrick Jabs B.A. University of Cincinnati June 2006 Committee Chair: Randall Allemang, Ph.D. Abstract Chassis and vehicle dynamics development is a demanding discipline within the FSAE team structure. Many fundamental quantities that are key to the vehicle’s behavior are underdeveloped, undefined or not validated during the product lifecycle of the FSAE competition vehicle. Measurements and methods dealing with the yaw inertia, pitch inertia, roll inertia and tire forces of the vehicle were developed to more accurately quantify the vehicle parameter set. An air ride rotational platform was developed to quantify the yaw inertia of the vehicle. Due to the facilities available the air ride approach has advantages over the common trifilar pendulum method. The air ride necessitates the use of an elevated level table while the trifilar requires a large area and sufficient overhead structure to suspend the object. Although the air ride requires more rigorous computation to perform the second order polynomial fitment of the data, use of small angle approximation is avoided during the process. The rigid pendulum developed to measure both the pitch and roll inertia also satisfies the need to quantify the center of gravity location as part of the process. For the size of the objects being measured, cost and complexity were reduced by using wood for the platform, simple steel support structures and a knife edge pivot design. Via force balance methods, the addition of a known mass to the platform allows the computation of the center of gravity location. Measurement of the period of oscillation yields the respective inertia. Of note is the use of small angle approximations in the computation of the inertia; the magnitude of the oscillation should be kept minimal for best results. The newest, most relevant tire information available is only in a raw data format; for the design process this fact has been another barrier to integration. Data processing scripts were developed to organize the raw data and perform fittings to the PAC2002 tire model for steady state data; an i expansion function for usage in Matlab was written to allow use of the coefficients in subsequent simulations. Estimations of the vertical spring rate and loaded radius of the tires were also developed. To quantify the transient thermal response of the tires, scripts to graph and analyze the data were prepared. Lastly, procedures for the estimation of the relaxation length properties of the tires from the raw data were executed to quantify the dynamic response of the tire’s structure. With a working tire model that can be integrated in both Matlab and Adams simulations coupled with a full quantification of the vehicle’s inertias, the capability to perform valuable chassis development and vehicle dynamics work is much more accessible. ii iii Acknowledgements Thank you to my parents and family for their continued support of my work. A special thanks to Dr. Allemang for the freedom and support to pursue stimulating subjects and for the continued critical advice and feedback. Thanks to Jeff Kenney for having the interest and patience to listen to my crazy ideas. For all of the team members from Bearcat Motorsports that I have had the pleasure of knowing and interacting with over my years, I hope all of you have learned as much from me as I have learned from you. Keep discussing the ideas that drive you, and drive the dream that you build; don’t forget the logical and quantifiable reasons behind it all. Thanks to Dr. Wynn for being a good influence that sticks in my memory. iv Table of Contents Abstract .......................................................................................................................................................... i Acknowledgements ...................................................................................................................................... iv Table of Contents .......................................................................................................................................... v List of Figures ............................................................................................................................................... ix List of Tables ................................................................................................................................................ xi List of Symbols and Acronyms .................................................................................................................... xii 1. Introduction .............................................................................................................................................. 1 1.1. Formula SAE Competition .................................................................................................................. 1 1.2. Bearcat Motorsports .......................................................................................................................... 2 1.3. Chassis Terminology and Nomenclature ........................................................................................... 2 1.4. Systems Engineering Approach .......................................................................................................... 8 2. FSAE Regulations Background ................................................................................................................. 11 2.1. FSAE Regulation System Constraints ............................................................................................... 11 2.2. General Chassis Limitations ............................................................................................................. 12 2.3. Wheelbase and Track Width Restrictions ........................................................................................ 12 2.4. Suspension Functionality ................................................................................................................. 14 2.5. Brake System Restrictions ................................................................................................................ 15 2.6. Driveline Restrictions ....................................................................................................................... 15 3. FSAE Competition Events Background .................................................................................................... 18 3.1. Design Event..................................................................................................................................... 18 3.2. Cost Event ........................................................................................................................................ 20 3.3. Presentation Event ........................................................................................................................... 21 3.4. Skidpad ............................................................................................................................................. 21 3.5. Acceleration ..................................................................................................................................... 23 3.6. Autocross ......................................................................................................................................... 24 3.7. Endurance ........................................................................................................................................ 26 3.8. Fuel Economy ................................................................................................................................... 29 4. FSAE Chassis Design Background ............................................................................................................ 32 4.1. Qualitative Vehicle Performance Characteristics ............................................................................ 32 4.2. Vehicle Characteristics’ Influence upon Regulation Performance Metrics ..................................... 33 4.3. Quantified Vehicle Parameters ........................................................................................................ 37 v 4.3.1. Suspension Parameters ............................................................................................................. 37 4.3.2. Driveline Parameters ................................................................................................................ 38 4.3.3. Braking Parameters ................................................................................................................... 39 4.3.4. Aerodynamic Parameters ......................................................................................................... 40 4.4. Parameter Trending Effects towards Performance Metrics ............................................................ 40 4.5. Vehicle and Regulation Performance Metric Relationship .............................................................. 44 5. Chassis Development Tools .................................................................................................................... 46 5.1. System Parameters .........................................................................................................................
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