Study of Connecting Rod for High BMEP Engines

Engine up rating is not unusual in these days as the need is felt for more energy output from the same volume of the cylinder. This has increased the brake mean effective pressures in the internal combustion engines. The power train components are highly loaded as the peak firing pressures are required to be on the higher side. The connecting rod of such a highly loaded engine was designed with bmep of 2.3 MPa. To overcome the initial failures of the connecting rods it was realized that the critical design review was essential. Classical calculations and FEM studies revealed the stresses in the critical sections. The failures were overcome by the improvements in the geometry of the specific zones. The machining process improvements were necessary to reduce the stress concentration at the bottom of the blind drills. To avoid the rotation of the small bearing bush the surface finish of the connecting rod, the parent bore was improved by burnishing to get better profile metal ratio. The gripping force was improved by use of liquid nitrogen during the assembly of the bush. The durability trials on the improved components showed the increase in the factor of safety from 1.26 to 1.42 and the improvements were also proven to be satisfactory from the field trials.