Carbon Fiber Monocoque Chassis Platform for Formula SAE and Formula SAE Electric Race Cars
Total Page：16
File Type：pdf, Size：1020Kb
Carbon Fiber Monocoque Chassis Platform for Formula SAE and Formula SAE Electric Race Cars Sponsored By: Ford Eimon [email protected] Michael Gonzalez [email protected] Michal Kramarz [email protected] Nathan Powell [email protected] Kevin Ziemann [email protected] We would like to extend a special thanks to the organizations who sponsored this project. None of this would have been possible without their support and generous donations. Aero SFC We’d also like to give our thanks to the 2016-2017 Cal Poly Racing team, for their dedication and endless hours of help with this project. You all make our dreams come true! 1 Table of Contents Introduction 19 Background Information 21 Design Requirements 24 Scheduling 28 Design Concepts 30 Lead Design Concept 31 General Car Layout 33 Concept Development 34 Geometry 35 Working Concept 36 Final Design 40 Nosecone Fairing and Impact Attenuator 40 Roll Hoops 41 Shoulder Harness Mounts 42 Firewall, Seatback and Headrests 42 System Integration 44 Platform Overview 44 Compromises 44 Suspension Subsystem Integration 45 Aerodynamic Subsystem Integration 50 Driver Ergonomics 51 E-Car Specific Subsystem Integration 54 C-Car Specific Subsystem Integration 59 2 Engine Mounting 61 Monocoque Heat Study 69 Stiffness 74 2016 Analysis Synopsis 75 Cross Section Emphasis 76 Torsion Tube Analysis 78 Final Stiffness Driven Geometry 84 Suspension Contribution 85 Full Chassis FEM Analysis 85 Results 88 Torsional Stiffness Testing 88 Suspension Stiffness Test Fixture Design 93 Hardpoints and Loads 95 Prior Failure Analysis 95 Load Categorizing 96 Design Considerations 98 Out of Plane Loads 98 Potting Sizing Trends 101 Bolt Patterns and Attachments 103 Insert Testing 105 Finalized Insert Design 108 Full Tab Testing 109 Failures 111 Impact Attenuator 113 3 Test Fixture 116 Mold Design 119 Preliminary Testing 119 Locating Features 121 Rocker Boss 121 Laminate Design 123 Core Selection 127 Staged-cure vs Single-cure Layup 127 SES Development 129 3-Point Bend Test 129 Perimeter Shear Test 130 Side Impact Structure 134 Front Bulkhead 135 Harness Attachements 146 Roll Hoop Attachements 141 SES Quirks and Limitations 142 Manufacturing 144 Plugs 144 Molds 153 Mold Repair 158 Rocker Boss 160 Test Layup 162 Layup 164 Core Forming Lessons Learned 171 4 Debulks 172 Cure 174 Post-Processing and Assembly 175 Drilling 185 Inserts 186 Temporary Aesthetics 188 Additional Touches 191 Fixes 195 Roll Hoops 198 Nosecone 199 AI/IA Plate 200 Seatback Mounting 202 Seatback/Firewall 203 Harness Mounts (Shoulder) 203 Vehicle Testing 205 Competition Results 207 Mass Props 210 Aesthetics 211 Recommendations 216 Conclusion 219 References 220 Extra Photos 221 Appendix 238 5 List of Figures Figure 1 The 2016 e-car undergoing testing. Figure 2 The team lining up a tub and a subframe for joining. Figure 3 The 2013 tub, Betty, in action. Figure 4 Catie enjoying the sun at the 2015 Lincoln competition Figure 5 J-lo during a testing session. Figure 6 Daisy in action as the e-car at FSAE Electric 2016 Figure 7 Overall team schedule with chassis dates included. Figure 8 Chassis manufacturing flowchart. The red lines indicate what will be done in parallel, once the first monocoque is laid up. Figure 9 Man-hour study conducted on monocoque manufacturing. Figure 10 Concept 1 for the monocoque. A basic nosecone shape is also included. Figure 11 Concept 2, the rough packaging layout. Although very simple, it was extraordinarily helpful in determining the final dimensions of the monocoque. Figure 12 Final monocoque concept presented at senior project CDR. Sharp corners are present in the model due to the inability to properly fillet the compound edges. Figure 13 Cutaway view showing driver layout sketch and integration with the battery box and e- drivetrain. Figure 14 Chassis assembly SolidWorks model. Figure 15 Cockpit swoopy, front roll hoop, and steering wheel. Figure 16 Pictures of rear rocker mounting and front boss Figure 17 Exploded view of nosecone/IA assembly. Figure 18 Fastener setup for AI plate. Figure 19 Front and rear roll hoops Figure 20 Roll hoop attachment assembly and bracket flat pattern Figure 21 Seatback/firewall panel (green) supported by the bonded seatback flange (carbon fiber texture). Figure 22 A side by side comparison between the combustion and electric vehicle platforms. Figure 23 Camber and toe deflection plotted as a function of changing pickup location on the chassis. Kinematics and loads from the 2016 c-car are used. Figure 24 Render of the front suspension geometry Figure 25 Render of the rear suspension geometry Figure 26 MDF fixture to locate chassis holes Figure 27 Aluminum fixture for control arm geometry Figure 28 2016 Nosecone and front wing. Air is forced down past the wing, separating the flow on the underside. The separation is shown as the dark blue area on the underside of the wing. Figure 29 The ergonomics rig in action. 6 Figure 30 Driver layout sketch used as a reference for the monocoque model. Figure 31 Finalized electric car packaging scheme. Image courtesy of the 2017 FSAE team. Figure 32 A view of both the external of the accumulator (left) and its insides (right). Figure 33 Renders of the E-Car with all subsystems packaged in the chassis. Figure 34 A view of the current drivetrain configuration. Figure 35 A cutout view of the e car packaging. Figure 36 A preliminary graphic to show how much access is available through the seatback to work on components of the engine during a test day. Figure 37 A cutaway of the c-car model gives a clear look at both the electronics packaging and the accessibility of the engine with the seatback removed. The electronics are the 4 boxes along the bottom of the chassis. From left to right they are the battery, the PDM, the ECU and the ACL. Figure 38 A sectional view of the car from the side also shows the location of the electronics in the c-car relative to the seatback and fuel tank. Figure 39 Roughly sketched ideas for mounting options for the engine in the rear of the monocoque. Figure 40 Dynamic engine loads due to eccentric rotating engine components at 10k rpm. The graph can be read counter-clockwise around each approximately closed loop as a full engine rotation beginning at piston TDC at the top of the graph. Figure 41 A plot of transmissibility ratio for different damping ratios and frequency ratio. For any damping ratio, a frequency ratio above 1.41 is necessary to have a transmissibility ratio that is less than 1. Figure 42 Visual representation along with specifications for the vibrations isolators used for mounting the engine in the formula car. Figure 43 Views of the engine upright and baseplates as the are positioned in the chassis. Bottom left: The rear base plate and uprights with the differential carriers included as well. Figure 44 Photos from Go-Pro footage of the car during testing. The top row shows the engine bucking forwards (front mounts in compression and rear mounts in tension), and the bottom row shows the engine bucking backwards (rear mounts in compression and front mounts in tension). The middle row shows the engine in its nominal, no load position. Figure 45 Side profile of the engine with the red line representing the location of the third engine mount from the top of the engine to the exhaust mounting bolt. Figure 46 Cut-out section of the rear most engine mount insert after competition. Figure 47 Sandwich panels cut to fit around the subframe and exhaust components. Figure 48 Panels enclosing the subframe. Figure 49 McMaster 595K16 temp-indicating sticker placed on a sandwich panel. Each white square will turn black once the corresponding temperature is reached. Figure 50 Approximate locations of temp-sticker placement on the car. Figure 51 Sticker near the oil pan showing exposure to 160-170°F. 7 Figure 52 Maxed-out stickers near the exhaust piping. Figure 53 Unaffected stickers that were protected by aluminum tape. Figure 54 Lateral load transfer distribution vs roll stiffness distribution for varying chassis stiffnesses. A chassis stiffness of 1500 ft-lb/degree achieves 88% of a rigid chassis. Figure 55 The radius decrease at the front of the cockpit can be easily seen as the chassis floor in the front of the vehicle is significantly higher than the chassis floor behind the front wheel. Figure 56 J-Lo (2015 e-car) chassis design Figure 57 A picture of the geometry and constraint method for the torsion tube analysis. The ends were allowed to deform radially. Figure 58 Convergence Graph of the torsion tube mesh. Figure 59 Picture of chassis with low (left) and high (right) cockpit sidewalls. Figure 60 FEA model and study results for the cockpit side profile torsional stiffness study. Figure 61 The above image shows the chassis of the 2015 electric vehicle, noted for the high specific stiffness. The high cockpit wall are characterized by a series of stressed bulkheads throughout the section. Figure 62 A view of the closeout curls on the cockpit opening on the torsion tube model. Figure 63 FEA model and study results for the top view cockpit profile torsional stiffness study. The red portions represent the approximate locations of max deflection Figure 64 A graph showing stiffness as a function of uniform core thickness. Figure 65 Finalized monocoque geometry. Figure 66 Chassis and suspension geometry imported into Ansys as a surface and wireframe. Figure 67 Contour plot of vertical deflection of the chassis model, with deformation scaled up to be clearly visible. The maximum deflection occurs at the front right upright, as expected. Figure 68 Proposed concept for new chassis fixturing table/torsion test rig for Cal Poly Racing.