The crankshaft must effectively convert linear motion from the piston into rotational motion. In designing the crankshaft, its dimensions and strength were decided. The method to attach the crankshaft to the flywheel was also decided. A choice was made between keeping the engine lightweight and having heavy counterweights to reciprocate the piston. Aesthetics were not taken into consideration.
The crankshaft must resist failure due to bending or twisting. The center of mass is located at Point 1, where the piston applies its force. Although the dimensions of each of the two counterweights (Points 2 and 3) differ, the weight is distributed equally, helping to prevent bending and keep the piston balanced. The crankshaft is solid metal, with the exception of tapping at the end. The diameter is 1 inch at Point 1, which is the thickest diameter along the shaft. This helps to reinforce the shaft at its point of highest loading.
The crankshaft must be able to withstand bending at high loads at Point 1 from the piston/rod assembly. Torsion can also be expected along the axial direction. High temperatures and vibration rates must also be taken into consideration.
Methods of Performance Evaluation
A force can be applied at Point 1 until buckling or failure occurs. A torsion test can be performed on the crankshaft in the axial direction. The temperature effect can be tested by placing the parts in a furnace and performing the previously mention tests.
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