THE FORMATION OF THE PATTERNS OF THE INCREASE OF TRIBOLOGICAL CHARACTERISTICS OF CYLINDER-PISTON GROUP
The operation of cylinder-piston group is accompanied by an unequal distribution of load and wear in contact point of the piston rings and the piston with cylinder liner. At the same time, one of the main causes of wear of piston rings when the engine is running is their simultaneous movement in the longitudinal and radial directions relative to piston grooves under the influence of friction forces on the surface of piston grooves and cylinder liners, inertia, elasticity of piston rings and gas pressure in the space behind the rings. Analysis of the nature of the external loading of cylinder-piston group details shows that to optimize the operation of the cylinder-piston group of internal combustion engine it is necessary to adjust basic tribological parameters of friction parts, including dynamic load bearing capacity of the support profile of the cylinder liner and the piston ring, friction force, the gap in the coupling, etc., to the operating conditions of cylinder-piston group (character of external loads, kinematics and thermal fields). Consideration of the cylinder liner - piston ring tribosystem as a dynamic model with two degrees of freedom allowed establishing that the reduction of the wear will be ensured only by maintaining the external friction of the coupling surfaces. It can be achieved provided that the shear strength of the thin surface layer is less than that of the base material. At the same time, one of the factors determining the amount of wear is the difference between the strength of the adhesive bond and the strength of the underlying layers. The practical implementation of this effect can be realized by engagement of a solid anti-friction material with a high load-bearing capacity, low shear resistance and resistance to high temperatures. Solving of the equations of motion of the tribological system by replacement of characteristic coefficients and the coefficients of the linear decomposition on the parameters of the real factors operating in a dynamic cylinder liner - piston ring system, taking into account the properties of the materials of the friction surfaces confirms that the reduction of the friction force and wear can be carried out by the reduction of the modulus of elasticity of materials of contacting surfaces and improvement of their geometric parameters.