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Peugeot XU7 Connecting Rod

The connecting rod undergoes a complex motion, which is characterized by inertia loads tha t induce bending stresses. In view of the objective of this study, which is optimization of the connecting rod, it is essential to determine the magnitude of the loads acting on the connecting rod. In addition, significance of bending stresses caused by inertia loads needs to be determined, so that we know whether it should be taken into account or neglected during the optimization. Nevertheless, a proper picture of the stress variation during a loading cycle is essential from fatigue point of view and this will require FEA over the entire engine cycle.

All connecting rods function in internal combustion engine environments and are subjected to high rate cyclic loading requiring exacting tolerances and fits to mating components, such as the crankshaft and piston head. Until the advent of the crackable P/F connecting rod cap end, all connecting rod cap ends were sawn or machined apart to enable inclusion of a bearing and attachment to the crankshaft. The cost of sawing and machining the cap end to meet tolerances in finish and fit were a considerable portion of the manufacturing cost and sawing required that the internal diameter of the rod cap end account for the “kerf” of the sawn area in the shape of the “hole” (it was formed slightly out-of-round). A “crackable” rod cap end provides the advantages of lower cost to separate the cap end, the surfaces of the cracked ends mate better and more accurately when reassembled after machining and the tolerances of the cap end internal diameter can be closely held to a perfectly circumferential circle. From the conventional method of splitting connecting rods with twenty steps, the fracture splitting method reduced the process to ten steps, all essentially machining, honing or drilling steps. Connecting rod manufacture is a high volume, price sensitive application with strict performance, design and durability requirements. Process or material improvements leading to lower costs result in large scale cost savings. Annual North American production is approximately 100 million rods.

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