The study actuality is connected with a problem of high mechanical losses due to friction in naturally aspirated high-speed low-cylinder four-stroke diesel engines. The research aims to check the efficiency of application of an experimental piston with rigid skirt that according to preliminary data provides the decrease of mechanical losses in the cylinder-piston group. The check method consists in comparison of benchmarks of a serial piston and an experimental one. Following indices are accepted as benchmarks: the piston friction force and mechanical losses formed by its work; the temperatures in characteristic zones of the piston; the temperatures of cylinder wall and motor oil caused by the piston friction; the moment of resistance to turning of crankshaft of installation with piston in the cylinder. The comparison is made by means of both modeling and experiments on a model installation designed on the base of 1Ch 85/80 (TMZ-450D) low-sized diesel engine. The comparison objects are a serial piston of diesel engine and an experimental piston with improved rigidity of skirt provided by special stiffening ribs joining the skirt wall with piston bosses. The results of modeling show the advantage of the experimental piston over serial one by signs of decrease of mechanical losses by 4%, of skirt wear by 33%, of temperatures of combustion chamber center and piston top edge accordingly by 5 and 10%. The experimental check allows to establish that the experimental piston with other equal conditions of turning without compression, combustion and cooling provides the decrease in the moment of resistance to turning by 3%, in temperatures of cylinder wall by 9% and motor oil by 6%. The results of comparative modeling and experiment highlight the certain prospect of substitution of serial piston for the experimental one, which is caused by possibility of significant decrease of temperature of the piston top and mechanical losses.

During designing, calculation and further development of an engine it is necessary to take into account all the values that define its lifetime. In variable modes of tractor diesel engine, the stress level of piston changes over time, which leads to the appearance of cracks on the edge of combustion chamber. It especially applies to the semi-open combustion chambers. The appearance and growth of crack to a critical length often leads to failure of the combustion chamber edge. In this regard, the selection of failure criteria of pistons in operation is an urgent task. The durability assessment should be made on the criteria of the thermal fatigue strength that could be divided into three groups: the deformation criteria, the deformation and kinetic criteria, the energy criteria. Deformation criteria is the most widely used. Taking into account the active loading in conditions of uniaxial tension, the damage accumulation related to the material plastic deformation, or the peak deformation criterion is determined. Along with experimental methods consuming time and money, the other reliability assessment methods based on the numerical calculations, such as finite element method become common use. The fatigue material properties when loading a small number of cycles are determined by the Coffin-Manson equations in the form introduced by J. Morrow for the amplitudes of elastic and plastic deformations, depending on the number of cycles to failure. The analysis of the works of various authors shows that the crack growth process is not fully considered. The lack of theoretical approach to determining the remaining lifetime demands the improvement of calculation method which should take into account the temperature difference on the surface of piston, gas pressure and piston geometric dimensions affecting the stress concentration.

The attention to statistical methods of quality control is driven by their reliability in case of the small sample volumes in comparison with continuous control. The article shows the reasons of delaying of introduction of statistical methods in the enterprises of technical service of agroindustrial complex. The value of statistical quality control of test and measurement processes is pointed out. It is confirmed by the standardized requirements to the quality management and by the assessment of impact of this control on failures of products in operation. The use of statistical control allows to stabilize in more short timeframes the production on high-quality level. The analysis of standards and technic specifications for machinery production shows that the acceptance rules for machinery generally indicate the sample volume equal to 2% of batch of machines. This is only 1 machine of daily batch of 50 machines. At that, the risk of the fact that a consumer will receive defective products is 26%. The control of a single machine in the sample shows the imperfection of acceptance rules. Despite the availability of regulations on statistical quality control, it has not become widely used in practice in the field of domestic agricultural and automotive engineering and technical services. It is necessary to determine the problems of statistical quality control of test and measurement processes and the ways of its implementation; to establish the reasons for the lack of attention to statistical quality control. It is required to substantiate the ways for its widespread use in the technical service and production. As research techniques, it is proposed to apply the information retrieval, statistical methods of data collection, analogy methods and morphological analysis.

Reduction of harmful effects of agricultural machinery on the ecosphere is an important task; its solution requires extensive use of emission reducing devices. Compliance with up-to-date legal requirements causes the cost increase of systems of diesel exhaust gases aftertreatment. This applies especially the systems that require an additional reagent feeding into exhaust system. The cost factor determines the study aim that is the creation of prototype of alternative aftertreatment system for selected engine type with the possibility of rapid adaptation to other types of the same power class. The article considers the operating principles of a storage-type system of catalytic reduction of nitrogen oxides, the design features of the system for tractor engine. An important advantage of this system is the fact that there is no need for additional reagent. The experimental studies of converter prototype as part of series-production engine were conducted on the engine test bench. In addition, the tests of samples of catalyst bricks with different types of catalytic coating were carried out. As a result of testing and selection of optimal catalytic coating, the new fuel supply system with increased performance is obtained and the converter design recommended for agricultural machinery is modified. The storage catalytic converter system allows to reduce the nitrogen oxides emissions by 40-50 %. With such efficiency of the system, its cost is noticeably lower than the cost of the system of selective catalytic reduction. The proposed design allows to adapt the storage system to engines of any power class without change in systems and control algorithms. The optimal field of application of storage systems is determined.

The expediency of use of analogy of wheel and track movers interaction with the supporting surface is established. The research aim is to implement the possibility of simulation of power parameters of a track mover with rubber-covered caterpillars using the positions designed for movers of wheeled vehicles. It is suggested to determine an axial force in plane of contact area of track mover through the sum of products of normal responses and adhesion coefficients on slipping and idling sections of elements of contact area. The normal response in each section should be determined taking into account the variable diagram of specific normal responses. Without slipping of elements, a rectangular diagram is assumed; with full slipping, a triangle one with right angle on the rear part of contact area is assumed. A diagram is a trapezoidal in case of the intermediate slipping. It is recommended to calculate the adhesion coefficient of elements of contact area in the sliding section through the descending elliptical dependence as a function of the relative normal response on slipping section of contact area. The low value is equal to the static friction coefficient of elements without slipping, the high value is equal to the coefficient of sliding friction with full slipping. It is recommended to calculate adhesion coefficient of the idling section through the ascending elliptical dependence as a function of the relative normal response on slipping section of contact area. The low value is equal to zero without slipping, the high value is equal to the static friction coefficient in the transition to full slipping of extreme rear element. The calculated values of the axial force coefficient for track mover of John Deere 8300RT tractor with 1.91 radians of central angle of contact area are well coherent with the actual data of drawbar tests of John Deere 8310RT, 8335RT and 8360RT tractors carried out in the University of Nebraska-Lincoln. The proposed simulation algorithm of power parameters of track mover could be useful when choosing the rational traction modes of tractors operation in different operating conditions.