Problems of Reducing Friction Losses of a Piston-Ring-Cylinder Configuration in a Combustion Piston Engine with an Increased Isochoric Pressure Gain

Currently, there is a tendency to increase the mean workable pressure in internal combustion engines, to reduce their cylinder volume and the number of cylinders in a balanced manner, depending on the vehicle's class and weight in order to improve the thermal and mechanical efficiency of the engine. An increased engine torque at a slight angular velocity results in an increase in the mean value of the unit pressure distribution of the piston rings, especially the upper sealing ring in the initial period of the expansion stroke, which limits the slip effect affecting the ability to form an oil film. The essence of validity of increasing the isochoric degree of pressure gain is the use of vehicles at low speeds with a high torque. Such selection of parameters ensures good motion dynamics at low fuel consumption.

The use of sliding surfaces shape asymmetry significantly affects the course of the distribution of oil film on the cooperating working surfaces and the amount of oil scraped in selected directions depending on the direction of the piston movement resulting from the realized engine stroke. The value of the minimum thickness of the oil film and the period of its occurrence in the engine cycle depend on the geometry of the asymmetry of the shape of the sliding surfaces. Regardless of individual parameters describing a given shape, one can assume that this modification will significantly affect the value of the minimum thickness of the oil film with the simultaneous increase in the isochoric degree of pressure gain. The article presents the legitimacy of applying the asymmetry of the shape of the sealing rings’ sliding surfaces in the aspect of the impact of the increased isochoric degree of pressure gain on individual parameters determining the ability to form an oil film in the entire engine work cycle by the sliding surfaces of the piston rings on the cylinder bearing surface.