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A laboratory method has been developed to rank the scuff resistance of piston ring coatings. This method employs a standard wear test apparatus with a specially designed sample holder. Scuff resistance of electrolytic chrome, thermal spray and physical vapor deposition (PVD) face coatings have been examined. Based on this method, examined PVD coatings produced the highest scuff resistance of all the tested face coatings.

Laboratory tests have shown that 40% glass-reinforced PPS is suitable for automotive underhood use where it comes into contact with used engine oil, gasoline/alcohol, gasoline/MTBE, water, water/ethylene glycol, hydraulic fluid, and transmission fluid at elevated temperatures. On exposure to water or water/ethylene glycol at 248° F (120° C) and 257°F (125°C), respectively, there is a sharp decline in mechanical strength in the first few weeks with little change thereafter. The residual strength of the 40% glass-reinforced PPS is comparable to, or better than other materials, such as phenolics, which have proved satisfactory in such usage. These results have been translated to successful applications in heavy duty diesel engines. Piston cooling nozzles and water pump impellers made of 40% glass-reinforced PPS have undergone successful engine component evaluations.

This paper examines the feasibility of using the boundary element method (BEM) and the Rayleigh integral to assess the sound radiation from engine components such as oil pans. Two oil pans, one cast aluminum and the other stamped steel, are used in the study. All numerical results are compared to running engine data obtained for each of these oil pans on a Cummins engine. Measured running-engine surface velocity data are used as input to the BEM calculations. The BEM models of the oil pains are baffled in various ways to determine the feasibility of analyzing the sound radiated from the oil pan in isolation of the engine. Two baffling conditions are considered: an infinite baffle in which the edge of the oil pan are attached to an infinite, flat surface; and a closed baffle in which the edge of the oil pan is sealed with a rigid structure. It is shown that either of these methods gives satisfactory results when compared to experiment.

The ability of a piston oil ring to conform to liner distortions during engine operation is directly related to its radial stiffness. The ability to conform is also very important for controlling lubricant oil consumption and emissions. This paper describes the procedure utilized to investigate the technical feasibility of using flexible high performance engineering plastics to replace metal as base material for oil rings. Bench tests and engines were used to select and evaluate different types of plastics for wear resistance and structural integrity. Engine test results indicated no structural failures but wear levels were found to be unacceptably high for use in durable heavy duty diesel engines.

High Velocity Oxygen Fuel sprayed face coatings have shown great promise for piston rings used for High Power Density Diesel Engines. Various coatings have been tested on both wear test rigs and in engines. A highly dense HVOF cermet coating was developed with reasonable crack resistance during service. The HVOF coated piston rings wore three to six times lower than chrome plating. Cylinder liner (counter face) wear was found to be one to three times higher than chrome. However, engine oil consumption and blow by were within normal values. The HVOF coating is considered to be an excellent replacement for chrome plating. The coating process is more environmentally friendly than the chrome plating process. Also, the coating has potentially lower or equivalent production cost when compared to chrome.

A number of wear resistant coatings has been developed using physical vapor deposition(PVD) process. However this coating process has not yet been widely used in the automotive industry. The purpose of this work was to evaluate thin PVD coatings such as diamond like carbon doped with tungsten (W-DLC), molybdenum-disulfide doped with aluminum (MoS2-Al), and chrome nitride (CrN). Some of these coatings were previously found to have low friction, high wear resistance, or both when tested in unlubricated conditions. In the present work, the experiments were conducted using a Cameron-Plint apparatus in lubricated conditions. The ring counterfaces used were Cr-plated and gas-nitrided compression rings. Our data also indicated that some PVD coatings with thicknesses in the same order of magnitude as the surface roughness of the liners did show some improvement in liner wear resistance. The suitability of thin coatings for liner applications needs additional study.

Diesel engine operation under high load conditions (>45 hp/cyl) may result in piston “debond” in which the Ni-resist ring carrier separates from the aluminum piston matrix leading to destruction of the piston. Historically, engine loads have increased to achieve higher power densities which together with more stringent emissions requirements have resulted in greatly increased stress levels in the piston. The higher stresses have resulted in debond failure. The design of the ring carrier will affect debond failure. Deformation of the ring carrier will initiate debond at the back of the insert at the junction with the piston matrix. The ring carrier cross-section must be made robust enough through proper design to achieve expected reliability. Another factor influencing ring carrier retention is the quality of the AlFin bond layer. Casting defects which arise from the AlFin bonding process, degrade the strength of the joint leading to failure.

This work evaluates the thermal and structural integrity of a heavy duty diesel piston using finite element analysis. The effects of aluminum, ductile iron, and superalloy piston materials; air gaps; and plasma-sprayed zirconia coating on piston temperature and stress, as well as on heat flux through the piston, are assessed. The coating lowered the heat flux through the piston 56 percent and caused other changes in the piston to have an insignificant effect on the heat flux. The air gaps had the least effect on heat flux with substantially lower safety margins than pistons without air gaps.