Consider The Fretting Fatigue Of Mixed-lubricated Connecting Rod End Bushings

The connecting rod small head bushing is one of the key components of diesel engines.With the diesel engine strengthening indicators continue to improve,the performance of its components put forward higher requirements.In the engine work process,the piston pin in the cylinder burst pressure and reciprocating inertia force under the action of bending deformation,the bottom edge of the bushing and the piston pin rough contact,resulting in rod small head bearing lubrication performance deterioration.At the same time,the bushing with a high bending load parts will produce a very small amplitude of relative sliding,micro-action fatigue damage accumulated to a certain extent,the contact surface will sprout cracks,so that the small head of the connecting rod premature failure.Therefore,considering the mixed lubrication characteristics of the connecting rod small head bearing to carry out research on the micro-motion fatigue characteristics of the bushing,and then to improve lubrication to reduce the micro-motion fatigue damage of the bushing,is an effective means to improve the reliability and durability of diesel engines.Taking a horizontal two-cylinder diesel engine connecting rod small head bearing as the research object,the motion characteristics and mixed lubrication performance of the connecting rod small head bearing are analyzed to reveal the mechanism of micro-motion fatigue on the mating surface of the bushing;the research on micro-motion fatigue characteristics of the connecting rod small head bushing is carried out to predict the location of micro-motion cracks on the mating surface of the small head bottom hole and the bushing,and the location of cracks on the mating surface is verified through the connecting rod fatigue test;combined with the causes of micro-motion fatigue of the connecting rod small head bushing,the micro-motion fatigue of the bushing is investigated by using a combination of the two-cylinder bearing and the bushing.Combined with the causes of micro-movement fatigue,the bushing surface profile design was adopted to optimize the lubrication performance of the connecting rod small head bearing while reducing the micro-movement fatigue damage on the mating surface of the bushing.The main findings of the study are as follows.(1)In the second cycle of the engine,the connecting rod small head bearing is only in the fluid lubrication state near 793°CA and 1384°CA,i.e.the time when the exhaust stroke and suction stroke connecting rod oscillation angle is at its maximum;at1095°CA burst pressure,the total frictional power consumption and rough contact frictional power consumption reaches its maximum,the bearing is in boundary lubrication,and the position near 140°～210° of the circumferential edge of the bushing on both sides and piston pin rough contact,resulting in poor bearing lubrication,which is also the main reason for micro-movement of the connecting rod small head bushing.(2)During engine operation,micro-movement cracks appear in the axial-14 mm,circumferential 140°～150° area of the bottom hole of the connecting rod small head and the edge of the bushing mating surface;to meet the design requirements of the interference fit,reduce the friction coefficient and the amount of interference,can reduce the probability of micro-movement cracks sprouting on the contact edge of the bushing mating surface;12 connecting rods of the connecting rod fatigue test,33% of which did not appear cracks on the bushing mating surface.25% of the cracks appeared in the circumferential direction 140°～150°,which is consistent with the theoretical analysis of the crack emergence position.(3)Double curve,parabolic and exponential bushings make the deformation of the piston pin match the surface of the bushing,effectively reducing the rough contact between the piston pin and the bottom rib of the bushing,improving the lubrication performance of the small head bearing of the connecting rod,and reducing the probability of micro-motion cracks on the edges of the small head bottom hole and the mating surface of the bushing.