Tribology of big-end-bearings

2014-03-20T12:50:01Z (GMT) by P.C. Mishra Homer Rahnejat
The parasitic frictional losses in an engine are estimated to account for 20% of the total engine losses. These include those due to piston assembly (45%), bearings (25%), pumping action (20%) and those attributed to the valve train system (10%). Thus, a quarter of all the parasitic losses are due to engine bearings, which include the main crankshaft support bearings (see chapter 18), big end bearing (see also chapter 19), and other camshaft and any rocker arm bearings. Though all these bearings are essentially hydrodynamic journal bearings, the nature of load application, construction and design is specific to each case. The main bearings have stationary bushings (see also chapter 18), while the bore of the big end bearing is oscillating and subjected to cyclic fluctuating loads from repetitive combustion pressure. The role of the big end bearing is to sustain the transmitted forces through the connecting rod, which are due to combustion pressure and inertial imbalance, as well as transmitting the torque to drive the crankshaft. If it malfunctions due to any reason, then this would lead to catastrophic engine failure. The understanding of journal bearing concept is essential for detailed analysis of big end bearings (see chapter 18).