An Analysis of Modal Damping Sources in a Reciprocating Engine

Effects of Viscous Friction and Non-Friction Damping Mechanisms in a Reciprocating Engine

“…The simple spring}mass systems shown in Figure 2 simulate the reciprocating piston and cross-head, while the pendulum test shown in Figure 3 mimics the rotating joints in the connecting rod and crankshaft. The materials and lubricated surfaces in these joints are maintained the same as they exist in the engine setups discussed in the two previous communications by Wank and Lim [1,2]. For each experimental group, three di!erent cases are examined.…”

“…The di!erence between the total damping in each joint and the viscous friction damping yields the non-friction damping from the lateral and tilting vibrations. Note that the total dampings in each joint for quasi-static and operating conditions were obtained in the early study [2].…”

“…For example, joints C, D and E that are basically revolute designs can roll with or without slip and at the same time vibrate transversely as shown in Figures 1(b) and 1(c), while the A and B ones that are of the cylindrical kind can actually slide and simultaneously translate and rotate dynamically normal to the bore axis as depicted in Figures 1(d)}1(f). In the classical rolling motion case, even though the damping e!ects of pure rolling and pure slipping are di$cult to separate out individually, its net vibratory energy dissipation due to simple shear resistance in the oil "lm can be obtained by performing a perturbation analysis about the mean geometry at a speci"c crank angle position [1,2]. Similarly, the e!ect of sliding perturbation on damping in the lubricated piston and cross-head due to viscous friction was also formulated earlier [1,2].…”

“…In the classical rolling motion case, even though the damping e!ects of pure rolling and pure slipping are di$cult to separate out individually, its net vibratory energy dissipation due to simple shear resistance in the oil "lm can be obtained by performing a perturbation analysis about the mean geometry at a speci"c crank angle position [1,2]. Similarly, the e!ect of sliding perturbation on damping in the lubricated piston and cross-head due to viscous friction was also formulated earlier [1,2]. However, the fundamental e!ects of lateral and tilting vibrations were not quanti"ed previously in spite of the appearance that they contribute to the total damping in the system possibly through oil "lm resistance to these types of motions and/or repetitive impacts between joint surfaces.…”

“…In a early experimental study by Wang and Lim [1], the torsional damping coe$cients in typical reciprocating engines were shown to vary with crank angle position (and thus time as well) similar to the predicted quasi-static natural frequency function but opposite to the e!ective mass moment of inertia trend. A second study [2] analyzed the major sources of modal damping, and concluded that the connecting rod}crank pin component contributed most signi"cantly to the variation observed. To further understand the underlying cause of damping variation, various form of dissipative mechanisms in a reciprocating engine are examined here.…”