Assessment of the technical condi-tion of an internal combustion en-gine by experimental parameters of pressure changes in the cylinder

Abstract Problem. During the operation of a car, it becomes necessary to determine the technical condition of its engine. This is due to the long-term operation of the car and the corresponding decrease in engine life, or there is a need to determine the technical condition of the engine before or after repair. Special attention for specialists is drawn to the complexity of assessing the technical condition of the main groups of internal combustion engine mechanisms, which are known to be the most valuable and are located in the middle of the engine. Access to them is very difficult or impossible without full or partial disassembly of the engine. And this is a common problem. Goal. The aim of the work is to evaluate the results of experimental studies to determine the technical condition of a car`s internal combustion engine by applying mathematical statistics methods. Methodology. To obtain experimental data, we used a developed digital diagnostic device with a program for processing digital information to reproduce the function of pressure in the engine cylinder at each degree of crankshaft rotation, with an error not exceeding 2 % in the test mode during cranking of the crankshaft by the starter. This paper summarizes the results of a multivariate experiment using the methods of mathematical statistics. Results. The theoretical law of distribution of the random value of compression for modern gasoline engines is obtained. Originality. For 2-valve engines and for 4-5-valve engines of modern cars, regression equations have been improved, which allow us to clarify the functional relationship between the random variable of compression and the crankshaft speed. Practical value. It has been experimentally established that the rate of increase in compression is significantly influenced not only by the technical condition of the cylinder-piston group, but also by the initial position of the piston and valves at the moment of start, therefore, the rate of increase in compression in the cylinder is proposed to be estimated as the difference between the maximum compression surge and the second one, which in serviceable cylinders does not exceed 0.25 MPa.