Grounding of pneumatic sensor parameters for control of the technical state of the cylindro- piston motor group

Abstract

In the work the analysis of the existing market of diagnostic devices offered in Ukraine for the determination of the technical state of the cylinder-piston group of automotive tractor engines has been performed, the urgency of the improvement of existing and the creation of new methods and technical means by modeling the processes of measurement and selection and justification of their rational parameters has been identified. Imperfection of known models results in the search and implementation in diagnostic diagnostic machines of diagnostic tools that do not always meet the established requirements for the quality of control measurements of state parameters and are not certified. The paper analyzes the technical means and methods for determining the technical condition of automotive internal combustion engines, proposed an improved design of the pneumatic tester (face tester) on the basis of a single measuring device. The calculations of the pneumatic characteristics of the tester for diagnosing the technical condition of the cylinder-piston group are made, the constuctive-regime parameters of the device are calculated: the second flow rate and the air flow rate in the pneumatic scheme of the tester, the dependence of the reduced area of the leakage gap on the throttle area. It is established that, to improve the accuracy of measurement of the diagnostic parameter and reduce the probability of diagnostic error, the design of the pneumatic tester should be performed according to the scheme with one measuring device. The common methods for diagnosing a cylinder-piston group of internal combustion engines are, today, predominantly the integral nature of the assessment of the technical condition and do not allow to identify the cause of a specific malfunction. Due to the imperfection of existing methodological approaches and technical means for measuring the value of diagnostic parameters, errors in diagnostic measurements are very often occurring, which causes the receipt of engine repairs from an incompletely exhausted resource. This condition necessitates the carrying out of scientific researches on improvement of methods and technical means of diagnosing a cylinder-piston engine group. From the point of view of the thermodynamics of the processes occurring in the given pneumatic scheme of the tester, the thermodynamic theory of the flow of gases and vapors from the reservoir of unlimited capacity was used in the calculations, which is a kind of conditional capacity (reference pressure chamber), in which the initial parameters of the working fluid remain unchanged throughout the expiration process. Based on this, a mathematical model was developed, which allowed us to state that the calculated pneumatic characteristics of the tester are nonlinear. The second flow rate and air velocity through the throttle hole in the critical pressure drop zone is nonlinear, and in the critical zone the second flow rate and air velocity remain constant and do not depend on the pressure drop on the throttle. When using the proposed design scheme of the pneumatic tester with a diameter of 1 mm throttle orifice and air pressure in the support chamber P1=0.5 MPa at β =P2/P1= 0.67 the area of the equivalent gap (the total reduced leakage area) f2 is equal to the area of the throttle opening f1. The feasibility of the diagnosis of the Chu pneumatischer with a diameter of 1mm choke when the pressure of the air in the chamber a reference pressure of 0.5 MPa, the internal combustion engine with such a technical state, when a conditional total area of the leakage f2 exceeds the area of the throttle f1 is not more than twice. Otherwise, use a larger diameter throttle or increase the pressure P1. Based on this, it is proposed to complete the pneumatic chokes with different hole diameters: 0,6; 0,8; 1,0;1.2 mm. The level of nominal, permissible and limit values of the diagnostic parameter for a particular engine are determined by the diameter of the throttle hole, the diameter of the engine cylinder and the pressure drop on the throttle. The proposed method of calculation allows analytically simulate the effect of various additional design and operating parameters of the pneumatic tester on the accuracy and reliability of the diagnostic information.