Annotation. Development of agriculture in the conditions of market relations is accompanied by aggravation of the problem of efficiency of use of machinery. In this connection, the task of scientists is to increase the actual volume of work performed by tractor units, reducing the cost per unit of production. The high cost of tractors, lack of personnel, reduction of technical equipment of farms and the increase in the volume of products produced in the agro-industrial complex, natural and climatic conditions impose special requirements on technical service to maintain tractors in working conditions. The working state of tractors is the state at which values of parameters, which characterize the ability to execute the given functions, correspond to the normativereference and design documents. During operation of tractors in agriculture under the influence of various factors their parts and units wear. The indicator determining the value of wear is the residual resource of aggregates and units. In the article, the questions of influence of residual resources of basic aggregates and systems of tractors on frequency of failures of various groups of complexity are considered. Experimental research on determination of dependencies of residual resources of tractor units and frequency of failures of different groups of complexity, on the basis of which the rules of replacement of the unit whose resource is exhausted, is carried out, i.e. is replaced with a full of the resource (new) or on the aggregate after overhaul.

Abstract. The article determines the weight and power of the tractor, as well as the width of the seeder and the operational speed of the tractor-seeder unit based on the new method. Using multi-cycle, multi-parameter calculations, it is revealed that the seeding operation quality could be achieved with a single combination of optimal values of the tractor weight and power, which are almost the same even within different environmental conditions. The main influence on the optimal value of the tractor weight and engine power is caused by a specific traction resistance of the seeder. For the seeder specific traction resistances ranging from 3.2 to 5.2 kN·m -1 , the optimal value of the tractor weight for seeding operations with a DMC-implement (chisel-shaped openers) is in the range from 80 to 120 kN. The required rational power varies from 200 hp up to 310 hp. The optimal seeder width is 12 m, the optimum speed of the unit is 12 km·h -1 . The nomograph is proposed for seeders with a different working width, with a different type of working elements and, accordingly, with a different traction resistance. The optimum values of the main parameters of the tractor revealed by the proposed graph will ensure minimum total energy costs for seeding, by reducing the energy costs of the lost crop. Increasing the operational speed of the seeding units leads to an increase in required power of the tractor engine, while maintaining the value of its weight.Key words: tractor, weight, power, optimization, total energy costs, mathematical model, seeder. IntroductionThe considerable attention in foreign and domestic scientific literature is paid to increase in the efficiency of use of tractors and tractor-implement units. For assessment of the efficiency of tractors and units different indicators are used -productivity, fuel usage on 1 hectare, given expenses and other indicators [1][2][3][4][5]. These indicators do not consider the influence of parameters of the equipment (technology) on the created harvest. Therefore, scientists pay considerable attention to studying of interaction of a running gear of tractors with the soil and to influence of soil compaction on the created harvest [6][7][8][9][10][11][12][13][14][15]. Operating conditions of tractors and their influence on the indicators of efficiency are investigated [16; 17]. There is a need of a system approach for justification of the parameters of tractors taking into account their influence on the created harvest.On the basis of many years of research, we developed a system mathematical model of atractor and an implement has been developed using the energy optimization criterion -total energy costs. Numerous pilot studies proved adequacy of the mathematical model of different tractor-implement units [18][19][20]. Total energy costs, in addition to direct and indirect energy costs, include the energy of the crop lost due to incorrectly selected parameters and operating modes of implements, which occupies from 40 to 80 % of the total energy costs in various operations and ...

Abstract. The modern stage of development of agrarian production is characterized as a transition period in market relations. In turn market relations are characterized by crisis situations, especially at the beginning of formation of structure of economic activity of enterprises of agro-industrial complex. Increase of efficiency of tractors is directly connected with estimation of their condition and development of measures on maintenance of performance of agricultural works without refusal of tractor units, and also substantiation of volume of works of the planned period, providing working State of the equipment. Technical condition and techno-economic indicators of machines in the process of operation are constantly changing. These changes are caused by constant increase of wear of machine parts, violation of dimension circuits and conditions of contact in part mates. As a result, the technique goes from working state to non-working, which is accompanied by the emergence of tractor failures of various groups of complexity. The challenge is to prevent these failures. For this purpose the technique of estimation of a condition of tractors which consists in determination of level of ability to perform works is developed. The level of ability of the tractor to perform the work-the degree of compliance of the tractor status parameters with nominal values. Experimental researches on definition of dependences of level of ability of the tractor to performance of works and indicators of their reliability on the basis of which are received permissible and limit values of levels for the basic kinds of agricultural works.

The article is devoted to the substantiation of the main parameters of the tractor (tractor weight and engine power) and the unit for plowing. For calculations, we used the energy mathematical model of arable units according to the optimization criterion -total energy costs, taking into account the influence of the tractor and aggregate parameters on the formed crop of grain crops. Calculations using the systemic energy mathematical model of arable units have shown that for a specific combination of operating conditions of the units there is an optimal combination of the tractor weight, engine power, implement width, which remain stable, when most of the main parameters of the system -"tractor -implement -operator -field -soil -crop" (TIOFSC), as well as environmental factors change. The optimal weight of the tractor for plowing, when changing most of the factors of the "TIOFSC" system, changes slightly and remains in the range 130-160 kN, usually 160 kN. A larger value of the tractor weight corresponds to a larger value of the specific traction resistance of the plow of more than 50 kN•m -2 . Power requirements range from 450 to 590 hp. Tractors with less power are effective with less seasonal load on the unit (less than 250 hectares). The optimal working width of the tillage unit varies from 4.20 to 5.25 m, more often it is in the region of 4.55 m. The decrease in the rational working width is associated with an increase in the resistivity of the plow and an increase in the depth of plowing. The optimal speed can vary from 10 to 12 km•h -1 , more often within 11 km•h -1 . The value of rational speed is associated with a change in the physical and mechanical properties of the soil

Topicality of the research: the value of the research is caused by the need to optimize main parameters of an agricultural tractor during its operation, taking into account their influence on the crop and the actual absence of such optimization methods. Purpose of the study: the purpose of the work is to develop an energybased mathematical model of a tractor-implement unit (later-'unit') to identify the optimal parameters of the tractor, the width of the implement and the speed of the unit, which increase the efficiency in terms of energy costs. Research methods: the main research method is mathematical modeling based on system analysis, field experiments and computational simulations. Results of the research: the paper describes the proposed structure of the system under study, a justified criterion for optimizing the tractor parameters, and some interdependencies of the proposed energy-based mathematical model parameters. As a result of use of the theory of similarity and the organization of six-factorial experiment, dependence of the maximum pressure of a wheel of the tractor on the soil is received. It is revealed that with increase in the wheel size, the width of its profile decreases in a vertical load on the wheel, the maximum pressure of the wheel on the soil decreases. It is found that in the structure of total energy costs the major part is accounted for by the energy of the crop lost due to the impact of machinery and the optimality of the unit parameters (from 40 to 80 % depending on the type of operation, equipment used, operating conditions of units). Value: the proposed method of optimization of the main parameters of the tractor and unit will be useful in justifying the mass of the tractor and the power of its engine, both at the design stage of tractors and operations. The practical use of the research results benefits in a reduction of the total energy costs. The magnitude of reducing energy costs depends on the used tractors, agricultural machines and the conditions of their operation.