Research On Friction Condition Transition Mechanism Of Heavy Duty Diesel Engine Cylinder Liner-Piston Ring

In order to study the cylinder liner scuffing problems of heavy duty diesel engine, this dissertation focuses on the friction condition transiton (FCT) mechanism between piston ring and cylinder liner (PRCL) in terms of the FCT characterization methods and FCT rules. The following conclusions are drawn:Firstly, the FCT experimental methods and characterization methods are investigated. Through the varied loads, speeds, temperatures experiments as well as the starvation experiments, friction force is measured to judge the sensitivity of different experimental methods, then the starved lubrication experiments are optimized to analog the FCT process at the PRCL interface with the piston ring reciprocating liner test rig. Chaos theory is used to extract the transient features. It is based on the assumption that the chaos theory can characterize the nonlinear dynamic behavior of friction phenomenon. It allows for describing the dynamic behavior of the tribological process with the attractors in phase space. The attractors represent irregular behaviors of friction force in different strokes from chaos to order. It has three main patterns under starved lubrication conditions. As the projection of attractors on the phase space coordinate exceeds a limit, it indicates the onset and progression of scuffing. The autocorrelation function and profile dimension distribution are used to characterize the surface morphology. From lubricant starvation to the adhesive wear conditions, surface orientation gradually strengthens with the increasing amplitude of autocorrelation function. Moreover, the decreasing profile fractal dimensions in every direction indicate the fine or detailed structures constantly reduce. It can gain the relationship among the working conditions-friction condition-characteristic parameters-topographic features.Secondly, the FCT rules of PRCL are acquired. Through the starvation experiments, the influence of loads, temperatures and lubricants on FCT can be acquired with the characteristic parameters and topographic features method. Composited plated cylinder liner with the molybdenum-sprayed piston ring has the best anti-scuffing properties among the friction pairs. The lubricant temperature gap is existed between tribological surfaces (Chrome-plated cylinder liner and the CrN piston ring) and lubricant RP-4652D. For the lubrication problems near the PRCL top dead centre (TDC), it investigates friction force vs. sliding speed characteristics of lubricant under different loads and lubrication conditions. Minor speed change obviously varies the lubrication characteristic near TDC. When the load is10MPa, ZDDP additives reduce friction force at sliding speeds less than0.4mm/s. As the sliding speeds greater than0.4mm/s, the influence of ZDDP additives to the lubricating film shear characteristics become weakened. When the load is20MPa, ZDDP additives don’t obviously reduce friction force at slow sliding speed.Thirdly, when the grooves can’t supply the stored lubricant to the structure of the platform area, adsorption film/chemical reaction film/decomposition film will be gradually consumed until the asperities adhesion happen under the starvation condition. The adhesive wear areas have some common features,such as the weakened extreme pressure protection film, the transfered adhesive friction pair materials, the enhancement of surface morphology orientation feature, the reduced the fined complex structure with fractal dimension value closing to about1. It can design the gradient structures, keep the fined complex tribological surface and upgrade the compatibility between tribological surface and lubricant to improve the anti-adhesive properties of tribological surfaces and anti-scuffing perforemance of heavy duty diesel engineFinally, the dissertation systematically studies the transient mechanisms from mixed lubrication to scuffing wear of heavy duty diesel engine with the tribology, dynamics and materials science method. Scientific basis and theoretical supports are provided to the design and anti-scuffing control of the PRCL tribological surface. It is of considerable academic and engineering values to the PRCL samples develpoment and tribology theory.