The article presents three strategies for maintenance and repair of machines that control the pre-selected and justified parameters of the technical condition of the machine, as well as the costs of eliminating failures for these strategies and the possibility of reducing them. (Research purpose) The research purpose is to identify the most effective way to determine the residual life of machine parts. (Materials and methods) The article proposes a strategy for maintenance and repair of machines, in which a special place is occupied by ways of reducing the mechanical friction losses, increasing the efficiency of the machine and the service life of its parts. The article notes that in order to meet the service life, it is necessary to monitor their remaining life visually or using appropriate sensors. In order to determine the remaining resource in more accurately way, we suggested that it would be measured several times, preferably using different methods or devices. Authors designed a computer program that allows to estimate the remaining resource using an interval estimation of random values for a given probability of failure-free operation of the machine part. The plunger pairs of a high-pressure fuel pump were chosen as the object of research. As a diagnostic parameter that characterizes the technical condition of the pump, its starting cycle feed was used, the value of which was determined on different stands. (Results and discussion) Article presents the values of the average resources of the plunger pairs, their dispersion around the corresponding average values, and calculated their average residual resource as an interval estimate for a given probability of failure-free operation. (Conclusions) The research results have shown a possibility of using the residual resource as the basis of the proposed strategy for maintenance and repair of machines based on minimizing the residual resource of their parts. The most important unsolved task for this strategy remains the selection and justification of primary diagnostic sensors for assessing the residual life of machine parts.

The existing strategies of maintenance and repair are discussed and a new strategy based on the control of the residual life is presented. It is assumed that in the future, the main maintenance and repair operations will be focused on minimizing this residual life, i.e. on the increase in the service life. It is proved that this maintenance organization strategy for the maintenance and repair optimization allows minimizing the flow of random failures of components during operation and increasing their service life (for a group of the same components) to a maximum. The work on the selection and justification of the life parameters controlled in this strategy has been performed.

Modern machines are subject to progressive wear that occurs at different rates, which leads to unpredictable failures that reduce the reliability and durability of machines. The strategy of maintenance and repair is aimed at eliminating these problems. (Research purpose) The research purpose is in analyzing the basic principles of the strategy of maintenance and repair of agricultural machinery in order to ensure control of the technical condition of machine parts. (Materials and methods) When resource diagnostics is used, , the allowable value of the parameter is set in advance for a part . This value is the tolerance that corresponds to a certain wear rate of the part. The tolerance is set based on the condition that if the current value of the controlled resource parameter during the next diagnosis is less than the set value, then such a part at the current value of the wear rate can be finalized until the next inter-control check. Taking into account the wear rate of the same type of parts from the group when determining the allowable wear during their resource diagnostics becomes an urgent task. (Results and discussions) As a result of research, the article presents "Methodology for determining the main indicators of reliability of parts of agricultural machines with different wear rates" and "Methodology for determining the tolerance system of parts of agricultural machines with different wear rates". (Conclusions) The article presents the tolerance system that reduces the probability of failure of machine parts in operation. During resource diagnostics, those parts whose resource parameters exceed the tolerance are rejected.

Two basic functions of the machine, consumer and technical are given. Application the law of conservation of energy is shown in case of the description of an energy balance of an element of the machine. The expanded concept of technical condition in relation to the machine is this, parameters of technical condition are justified. Communications of technical condition with operability and working capacity and also communication of operability of an element of the machine with its efficiency are defined. The possibility of representation of technical condition in the form of сlass in object-oriented programming is revealed.

Two main functions of the machine are given, consumer and technical. The application of the law of conservation of energy in describing the energy balance of a machine element is shown. An extended concept of the technical condition is given in relation to the machine, the parameters of the technical condition are substantiated. The relationships between the technical condition and serviceability and serviceability, as well as the relationship between the serviceability of a machine element and its efficiency, have been determined. The possibility of representing a technical state in the form of a «Class» in object-oriented programming is revealed.