Chassis Design Principles And Analysis Milliken Pdf 13
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William F. Millikens handling research is fundamental to modern automobile design, and his definitive books on vehicle dynamics provide engineers and racers with practical understanding of chassis design for maximum performance. Equations of Motion is the story of Millikens lifetime of experimentation and innovation in vehicle stability and control.
This study explains a coherent flow for designing, manufacturing, analyzing, and testing a tunable anti-roll bar system for a formula student racecar. The design process starts with the analytical calculation for roll stiffness using constraining parameters such as CG (Center of Gravity) height, total mass, and weight distribution in conjunction with suspension geometry. Then, the material selection for the design i.e. Aluminum 7075 T6 is made based on parameters such as density and modulus of rigidity. A MATLAB program is used to iterate deflection vs load for different stiffness and shaft diameter values. This is then checked with kinematic deflection values in Solidworks geometry. To validate with the material deflection, finite element analysis is performed on ANSYS workbench. Manufacturing accuracy for the job is checked using both static analysis in lab settings and using sensors on vehicles during on-track testing. The error percentage is found to be 4% between the target stiffness and the one obtained from static testing. Parameters such as moment arm length, shaft diameter and length, and deflection were determined and validated. This paper shows the importance of an anti-roll bar device to tune the roll stiffness of the car without interfering with the ride stiffness.
Vehicles are generally classified into two types on-road and off-road vehicles. This research is focused on on-road vehicles specifically formula student racecar. Formula Student is an international design competition where students design, build an open-cockpit race car and compete in various static and dynamic events. Each team in Formula Student is broadly categorized in suspension, aerodynamics, powertrain, chassis, and electrical departments. This research operates under suspension department workflow while coordinating with other departments. The designing of a Formula Student car is carried with a single goal in mind i.e., to achieve the best lap time possible. Every other design concept and goal is sketched out using the former as the central idea. Suspension design plays a vital role in the complete designing process as it determines how the input from other systems such as powertrain and aerodynamics reach the ground level and helps in the achievement of goals. The suspension system controls the dynamics of the tire, which ultimately affects the amount of grip of the car to the ground that is responsible for the overall control of the racecar. This system is designed to control the basic motions of the vehicle in 3-Dimensional space that are lateral, vertical, and longitudinal forces acting on a car, also the control of roll and the moments on those axes. The position where these forces are acting on the racecar is shown in Fig. 1.
After determining the torque applied, the additional roll stiffness required (N-m/degree) is compared with the torque achieved at the anti-roll bar (also the resisting moment by Newton's third law) that is calculated to be at 10 chassis roll. Subsequently, the motion ratio and length of the shaft are iterated using MATLAB code to equate it to the required value (additional roll stiffness at a given axle). Then, the length of the moment arm is fixed for each iteration. After that, the overall concept of the project including the tunability and the system which is designed for different stiffness setups by utilizing variable-discrete length mounting holes. Lastly, the length of the anti-roll bar shaft is constrained due to cockpit dimensions; hence it is used as the input dimension. These are the steps involved in designing the shaft geometry. After this, the material used for this project is selected to be Al 7075-T6. The material required for this project was purchased from Perfect Metalworks, Bangalore, with a material certification bill.
As the highlight of this research is tunability in the component, the moment arm (Fig. 5) was modeled with 4 different mounting points (holes) to accommodate a different range of roll stiffness aimed earlier. To hold the structure in place, supporting flanges were designed with press-fit tolerance for deep groove ball bearings (as depicted in Fig. 6), as the device is supposed to undergo torsion and angular deflection. Finally, a shaft structure is extruded with the required dimensions, and then an assembly is made in the software (as shown in Fig. 7) according to packaging constraints in the chassis and with systems in its proximity. The same assembly is used for FEA analysis in ANSYS. All dimensions are in mm.
For measuring the effect of the anti-roll bar on vehicle motion, the wheel travel data was logged in the lap run and was compared for both cases. As the anti-roll bar provides additional stiffness to the chassis, the vehicle remains more stable and becomes less "sloppy" in the corners, hence this change is reflected in the wheel travel data plots. The anti-roll bar not only decreases the amount of body roll while cornering but also helps to maintain the stability of the vehicle while a single wheel goes into a bump due to track elevations and unevenness. When a wheel passes over some uneven surface, the anti-roll bar pushes the other wheel in a bump and, as a result, lowers both the wheels. The change in wheel travel is measured using a linear potentiometer, which is mounted parallel to the damper on the rocker/bell crank. The motion of the wheel is transferred to the potentiometer via a rocker. Also, while designing the suspension geometry, the motion ratio was checked constantly and kept as constant as possible, and the changes were kept to be minimized linearly. This helps to visualize the motion of the wheel better as the vehicle takes a lap.
The anti-Roll bar plays a cardinal role in a Formula Student race car, and it is a device that improves agility, stiffness, driveability, and stability without adding much weight. This research demonstrated the design, analysis, manufacturing, and testing procedure for such components. The parts designed were thoroughly scrutinized for their effectiveness, and the results were satisfactory. To analyze the results of the research, FEA was carried out on ANSYS, static testing was done in laboratory conditions and to determine the effect of the designed component on the vehicle system on-track testing was also carried out for which the results were logged using sensors such as potentiometers. Hence based on the above results, it could be concluded that this research was carried out successfully with desired outcomes, which are within a range of acceptable values and errors. It could also be emphasized from the track testing data that the designed component desirably improves the vehicle characteristics. Despite being advantageous, it has limitations due to it being heavier in nature. In future studies on anti-roll bar, better and lighter materials like carbon fiber and others can be researched upon. Moreover, strain gauges can be used to accurately verify the stress induced in the shaft and moment arms with FEA. The future scope for the calculation and verification of this research can be an extensive comparison between FEA analysis, experiment results, and analytical calculation by utilizing different meshing parameters such as mesh sizing methods, type of transition, and quality to further optimize the FEA process and also to reduce the error between the three calculating methods. Hence converging the results to greater accuracy.
RVD2 builds on RVD1, exploringadvanced techniques such as quasistatic vehicle analysis. Oscillations of the sprung and unsprungmasses are investigated with a focus on ride comfort, and the design andanalysis of suspensions are covered. Thecourse has more open-ended material and higher expectations of independentstudent learning, with several paper reviews, in-class presentations and projectsthroughout the semester. 2b1af7f3a8