| I Piston type internal combustion engine came out in the 1860 s. It was perfect and optimize on and on continuously. The technology of engine had been very maturity. Automobile as the important and most widespread transportation vehicle in daily life, it became the most dissipative source of engine market. The 15% of total burning energy of engine was loss in mechanical motion, most of which was loss in friction. Frictional power consumption of piston-cylinder sleeve system was account for nearly 50% in the whole engine. This article considered the largest usage amount of engines. Friction of piston-cylinder sleeve system was reduced very small, it would have greater effects on reducing energy consumption and improving the environment. So this article made the research emphasis on anti-drag and wear-resisting of piston-cylinder sleeve system.Most species in the biosphere had evolved and formed anti-drag & wear-resisting structures in surface. This article would select the bionic based, of which moving conditions were like piston-cylinder sleeve system. This article would aim at decreasing friction、wear and heat dissipation、increasing lubrication of piston-cylinder sleeve system. So it designed bionic strunctures on piston skirt. The reliability and stability of engine were advance.Earthworm shuttled in the soil, it was the same as piston doing reciprocation motion in the cylinder, both of that were solid-solid contact between soft matter and hard matter. Shell was erosion in the sediment, it was the same as the movement of piston and cylinder, both of that solid-solid contact and lubricant in the contact surface. This article select the earthworm and shell as the bionic based, and processed the anti-drag and wear-resisting structures of them in the piston skirt surface for decreasing fiction & abrasion and friction heat.First this article adopted reverse engineering technology to model the standard piston. Based on parameters of piston-rod assembly of experimental engine, it done dynamics and thermodynamics model analysis. Referenced ECE 15-mode test cycle and research results before, and accorded to research emphasis of this article, it select three mode test cycles as analytical foundation later. The computed results were boundary conditions in the thermal-structural coupling finite element analysis, then got the stress、strain and deformation of the worst severe operation conditions.Based on thermal-structural coupling finite element analysis results of standard piston and anti-drag structures of bionic based, it designed two bionic forms in the piston skirt, that were cross stripe and vertical groove. Cross stripe refered to earthworm and designed along piston circumference, nearly the top of piston, which had the max stress, the bigger dimensions of depth、width and spaces of stripe. Based on orthogonal array, it made three levels and three factors test plan. The three factors were stripe configuration、stripe depth and stripe width, and every factors included three levels. Vertical groove refered to scapharca subcrenata and designed penetration piston axial. Based on orthogonal array, it made three levels and three factors test plan. The three factors were groove configuration、groove depth & width and groove space, and every factors included three levels.The both groups were done thermal-structural coupling analysis, then max stress of every part of pistons were comparative between bionic and standard pistons. Cross stripe bionic piston: coring in stripe had best loaded stress on the part, which was far from bionic structure and had high temp; stripe made concentrated stress smaller on the part, which was near bionic structure and stress concentration. Vertical groove bionic piston: narrow stripe between two wide stripes、big depth & width、middle space had best loaded stress on the part, which was far from bionic structure and had high temp; groove、big depth & width、middle space made concentrated stress smaller on the part, which was near bionic structure and stress concentration. Max stress of every part of two groups bionic pistons had been made range analysis. Cross stripe bionic piston: the influence of factors form big to small successively were stripe configuration、stripe depth、stripe width; optimal combination was stripe、stripe depth from bottom to top was 0.5、0.6、0.7、0.8 mm and 0.6、0.7、0.8、0.9 mm、stripe width from bottom to top was 0.5、0.6、0.7、0.8 mm and 0.7、0.8、0.9、1 mm. Vertical groove bionic piston: the influence of factors form big to small successively were groove configuration、groove depth & width、groove space; optimal combination was groove and narrow stripe between two wide stripes、groove depth & width was 1 mm、groove space was 12o.Based on working conditions of piston, it made low frequency fatigue life prediction plans. Manson and Coffin came forward computing method, which adopted calculate cycle indexes of start-run-stop. The regression analysis could find out the inherent law between three levels& three factors and fatigue life of every part of bionic pistons. Cycle indexes compared of standard and cross stripe bionic piston: the fatigue lives of every bionic pistons were longer than standard piston, average lifetime of bionic piston was 8.8 percent higher than standard piston;a line of stripe a line of hole and stripe depth & width from top to bottom as 0.8、0.7、0.6、0.5mm made max deformation smaller and fatigue life longer; in regression analysis, the biggest influence to fatigue life was stripe width, next was stripe depth, shallow & wide stripe could ensure stiffness better and loaded concentrated stress、heat dispersal、reduced friction. Cycle indexes compared of standard and vertical groove bionic piston: the fatigue lives of every bionic pistons were longer than standard piston, average lifetime of bionic piston was 7.8 percent higher than standard piston; groove、groove depth & width as 0.8 mm、groove space as 10o&12o made max deformation smaller and fatigue life longer; in regression analysis, the biggest influence to fatigue life was stripe width, next was groove space about piston top and groove configuration about middle & bottom piston, from relation between factors and fatigue life we could see groove、groove depth & width as 0.8 mm、groove space as 12o were best.It used average reynolds equation calculating oil film thickness、lubricating oil pressure、normal pressure、friction of standard and bionic piston skirt, then made contrastive analysis. Lubrication of every cross stripe bionic piston skirt was better than standard piston, coring in stripe made oil film thickness bigger, when pressure area of oil film of bionic piston was 80 to 86 percent of standard piston the normal pressure was least, when pressure area of oil film of bionic piston was 81 to 84 percent of standard piston the friction was least, when stripe depth & width(or diameter) was 0.8 to 0.9 mm in skirt upper and stripe depth & width(or diameter) was 0.7 to 0.8 mm in skirt bottom the lubrication was best. Lubrication of every vertical groove bionic piston skirt was better than standard piston, groove depth & width as 0.8 mm and space as 10 o made the oil film thickness bigger, when pressure area of oil film of bionic piston was 74 to 87 percent of standard piston the normal pressure was least, when pressure area of oil film of bionic piston was 74 to 85 percent of standard piston the friction was least, when groove in skirt upper and narrow stripe between two wide stripes in skirt bottom the lubrication was best.It set up durable engine test-bed, and made contrast test between standard and bionic piston. Durabletest-bed spent too much time, so in each group it select three bionic pistons, which were the optimal structure in every simulated analysis, and made two times experiments. Test results as follows: wear of cross stripe bionic piston was average 79.5 percent smaller than standard piston; wear of vertical groove bionic piston was average 40.9 percent smaller than standard piston. Detected maximum temperature of piston top, cross stripe bionic piston was average 9.5 percent smaller than standard piston; vertical groove bionic piston was average 6.4 percent smaller than standard piston.Surface roughness detected after experiments, cross stripe bionic piston was average 60.1 percent smaller than standard piston; vertical groove bionic piston was average 47.6 percent smaller than standard piston.Testing results of test-bed was accordance with results of analogue simulation, so simulation method was exactly verify farther.Based on results of simulation and test-bed, bionic structure was made mechanism analysis. Cross stripe bionic piston, stripe could transmit small stress along longitudinal skirt, the holes of a line of stripe a line of hole made big stress concentrating skirt surface and small stress dispersing inside skirt, coring in stripe transmit small stress to big stress area inside skirt; vertical groove bionic piston, groove could transmit small stress around skirt circumference, when stress was greater than 54 MPa wide groove could collect stress to reduce rounding big stress at skirt bottom, when stress was less than 27 MPa holes and narrow groove could spread small stress but not collect big stress. The two bionic structures both could oil storage、store scraps、reduce friction, bionic cross stripe could interdict lengthways scratch of skirt and stop it extend and influence the fatigue life of piston; bionic vertical groove could reduce the abrasion area around skirt circumference. |
PDF Full Text Request