Study On Low Friction System Optimization Of Gasoline Engine And Its Effects On Energy-saving

The friction loss is one of the main reasons for engine energy loss, and the reductionof engine friction loss is important to save automobile energy. Low friction technology ofengine has become an important research direction of the major auto companies andresearch institutions. Through the combination of numerical simulation and experimentalmethods, the effect of detailed engine structure parameters on the friction loss wasanalysed. Through the combination of system tribology design and diamond-like carbonfilms deposition methods, the engine friction loss and fuel consumption was reduced.First, based on the hydrodynamic lubrication theory and multi-body system dynamics,the piston-cylinder system、piston ring-cylinder system and crankshaft-bearing systemtribological simulation analysis model was builded. On this basis, the engine tribologyengineering application analysis software was developed, which can analyze the frictionperformance parameters of the engine, such as the oil film pressure, minimum oil filmthickness and friction.The effects of the crank-connecting rod mechanism and cylinder structure parameterson the tribological properties were analysed. The analysis results are as follows: the effectof the piston skirt horizontal surface and longitudinal line on friction loss is significant, theprimary thrust side impact slightly larger. Reducing the lateral surface of the skirt portion,there isn’t significant effect on the oil film thickness; kepping a reasonable distancebetween the higest point and the piston pin centerline, the lateral motion of the piston canbe controlled, and the friction loss wii be reduced. The clearance between the pistons withcylinder bore has influence on the friction loss, but there is a significant effect on the oilfilm. The effects of the height and elasticity of piston ring on friction loss is significant,there is a change of the minimum film thickness in the mid-stroke, there isn’t a change ofthe minimum film thickness on the TDC. The effect of piston ring stretch reducing on theminimum film thickness is significant. The effect of bearing width、 diameter andcrankshaft bearing clearance on friction loss is significant, after changing the bearing structure,, the maximum film pressure rise with the speed reduction. The effect of thecylinder bore surface roughness on friction loss is significan.The next research content was tribological system optimization design for the CA4GAengine. The width of the piston skirts were reduced, the highest point of skirt profile linewas risen; the elasticity and height of the piston ring pack were reduced, the oil ringstructure was changed; the width of the crankshaft main bearings were reduced, theclearance of crankshaft bearings was increased. The tribological system optimizationdesign of cylinder included: reducing roughness of the cylinder bore; reducing distortion ofthe cylinder bore; increasing internal gas flow between the cylinder crankcase byventilation holes between cylinders, and analysis of the cylinder finite element structuralstrength was done. The design of the valve train tribological system optimization included:reducing valve spring preload and stiffness, and valve train dynamic analysis; chain guideslotted surface contact area to reduce the lubrication area;improving the chain structureand reducing the surface roughness; reducing the stiffness of the chain tensioner.The engine DLC films tappets、piston rings and piston pins were prepared by vacuummagnetron sputtering method, the performance of the DLC films were analyzed, DLCfilms can be significantly improving the hardness of the engine parts surface, appropriatetransition layer can make the binding force between the DLC films and the engine parts.In the fluid lubrication conditions, there is n’t effect of the friction coefficient of theengine DLC films parts; in the boundary lubrication and mixed lubrication conditions, itcan significantly reduce the friction coefficient of the engine parts, and the coefficient offriction is reduced as the load increases. The DLC films have no effect on the surfaceroughness of engine parts. But they can significantly improve wear resistance of engineparts surface. The motoring test bench was established to anaylsed valve train frictionlosses. The engine tappet deposited on the surface of the DLC film, it can significantlyreduce valve train friction losses in the rev range. It is10%lower on average.Based on the engine friction strip-down tests, the friction losses of low friction engineand the original engine were measured, the friction loss of the structural parameters of theengine parts and the DLC films were analysed. Under low load conditions, the width andprofile line of piston skirt have no effect on friction losses, the average reduction of the friction loss is about3.6%; bearing width and the change of the bearing clearance has littleeffect on the friction losses, average2.3%; The effect of tension and height of piston ringson engine friction losses is important, average12.3%. Integrated crank linkage systemtribology optimized design can significantly reduce friction losses. Increased ventilationholes between cylinders can effectively reduce engine friction losses. Reducing valvespring tension can reduce valve train average friction losses2.3%; the chain tensionerelastic have no effect on valve train friction losses; changed chain structure and the surfaceroughness can reduce valve train friction losses16.8%; chain guide surface lubricatedcontact area can reduce valve train friction losses about10%. Tribology valve train systemoptimized design, can significantly reduce the friction losses. Engine tribological systemcombining the optimization of the design and the DLC films technology can effectivelyreduce engine friction losses.Based on the performance test, the dynamic performance and fuel consumptionperformance of the low friction engine and the original engine was measured, and theeffect of engine friction loss on the fuel consumption was investigated. The test resultsshow that tribology structural optimization design and the diamond-like carbon (DLC)films can decrease mechanical friction loss of engine, it is decreased17.1%. The reducedfriction loss can effectively enhance engine performance, and the fuel consumption isdecreased2.5%.