Background
The UCI Formula SAE Internal Combustion Racing car for the 2020-2021 year had an interference problem between the rear left chassis tube and the driving chain from the engine. First Finite Element Analysis (FEA) simulations were conducted by using SolidWorks 2021, shown in figure 1, to verify and note the overall torsional rigidity of the chassis before any design modifications were performed to resolve the interference problem.
Knowing the overall torsional rigidity of the chasis is a key information to optimzing chassis frame. If a chassis frame is extremely stiff, then there's a high chance that the chassis frame can also be heavy, which can jeoprodize the vehciles performance. There needs to be a balance between stiffness and lightweighness.
Also, Torsional Rigidity or Stiffness is one of the crucial test performed to verify that the racecar chassis meets the Formula SAE 2020-2021 Rules & Regulations to ensure the racecar is properly built and safe to operate on the track.
Figure 1: Torsional Rigidity FEA simulation on the UCI Formula SAE Internal Combustion Racing 2020-2021 racecar chassis.
To resolve the interference issue, the solution was to replace the rear left tube with the interference problem with two steel triangular plates to allow for the engine drive chain to freely move.
Goals
The goal was to eliminate the chain and chassis interference with minimally invasive work on the chassis and engine for manufacturing and cost reasons. The implemented design had to meet a Factor of Safety (FoS) of 2.5 to ensure that the part does not fail under loading. The implemented design required little to no effect on the torsional rigidity of the chassis. This was mportant as the replaced tube was an engine mount and cannot fail without compromising the safety of the driver and performance of the vehicle.
The method used could not increase the weight of the car more than a pound over the original weight. The simulation had to model the forces as they are expected, and needed ti have a corresponding validation process that can be done in the laboratory. If the suggested design failed, there was a need to redesign a new solution that meets the stated goals and requirements.
Process
A total of four different chassis assembly torsional rigidity simulation tests were performed on the chassis structure to measure the torsional rigidity. The first test was performed with the tube that had the interference issue, shown in figure 2. This is the specific tube that made contact with the drive chain from the engine. Test was conducted to show a baseline rigidity needed to maintain with the new design solution.
Figure 2: Displaying the specific location and tube which interfered with the drive chain from the engine.
By following a similar setup shown in figure 3 diagram as a guide to measure torsional rigidity; fixating the rear of the chassis, while placing equal force but opposite in direction where the front wheels are positioned to create a torsional moment along the chassis frame.
Figure 3: Torsional rigidity chassis setup configuration guide. (Diagram from Race Car Vehicle Dynamics)
Utilized SolidWorks FEA Static Simulation, configured the chassis CAD model by first excluding any small beams that are not connected with the chassis structure tubes. These components were chassis tabs, shown in figure 4, which is positioned at the bottom of the front of the chassis, along with the steering mounts shown in figure 5.
Figure 4: The excluded tabs highlighted in light blue, which are located at the bottom of the front of the chassis.
Figure 5: The excluded steering mounts highlighted in light blue, which are located front of the driver.
Then by fixating the rear of the chassis to eliminate any translation movements, shown in figure 6 and 7, followed by correctly placing where the forces need to be input shown in figure 8 and 9, to create a torsional moment along the chassis frame.
Figure 6: Displaying the locations where fixcture was applied in green color (left side).
Figure 7: Displaying the locations where fixcture was applied in green color (right side).
Figure 8: Displaying the location of the downward 300 N force applied to the front of the chassis to create torsioinal moment along the chassis.
Figure 9: Displaying the location of the upward 300 N force applied to the front of the chassis to create torsioinal moment along the chassis.
The maximum displacement was formulated from the first analysis to be about 1.275 mm, shown in figure 10, and the maximum stress was about 7355 psi, shown in figure 11.
Figure 10: Displacement result for the standard torsional rigidity of the chassis with the yellow interference tube included.
Figure 11: Stress result for the standard torsional rigidity of the chassis with the yellow interference tube included.
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