Vol 14, No 2 (2020)

To provide an analysis of the thermodynamic processes occurring in a heat engine and its efficiency the indicator diagrams are used. The diagrams are constructed in the dimensional values of the parameters of the working fluid: volume, entropy, pressure, temperature, and other parameters. Exceptions include, for example, experimental studies and thermodynamic calculations performed, when designing a Laval nozzle for jet engines. These studies are based on the Similarity Theory. The paper shows graphoanalytical calculation of the efficiency of the idealized cycle of a heat engine in dimensionless working body parameters. Research methods using dimensionless parameters - similarity criteria are a characteristic feature of the Similarity Theory. In addition to the dimensionless indicator diagram, an energy dimensionless diagram of a circular closed loop of a heat engine was developed and described. The energy diagram depicts the thermodynamic processes of the exchange of heat and mechanical work between the working fluid and the environment in the dimensionless coordinates of heat and mechanical work. It is shown in the paper that the use of an energy dimensionless diagram is the simplest and most obvious graphoanalytical method for determining the efficiency of a heat engine. With regard to the analysis of the operation of a heat engine, the importance of using the Similarity Theory is determined by the fact that the only analytical, graphic or experimental study of a heat-specific engine with the least difficulties can be extended to the study of an infinite number of thermodynamically similar engines. For example, in the proposed work, the dimensionless calculation of the idealized Otto engine cycle is performed.

The article considers a single-mass vibration protection system with an executive electromechanical device. The relevance of the research direction and the current state of its knowledge are presented. It is proved that in comparison with the controlled elements of viscous resistance, the controlled stiffeners provide the best quality of vibration protection. The prospects for the use of controlled electromechanical stiffeners are emphasized. The paper considers an actuator in the form of a linear DC motor. Examples of the use of active vibration protection systems with linear electric machines are given. In particular, an example of using as suspension of the vehicle is provided. The advantages and most significant drawbacks of such suspensions, which hinder their mass introduction, are indicated. The design scheme of a single-mass oscillatory system with parallel installation of a viscous friction element and a stiffener is presented. It is substantiated that, taking into account the accepted assumptions, the presented scheme is equivalent to vehicle suspensions. It is proposed to use a magnetorheological vibration damper as a controlled element of viscous resistance. The analysis of the state of the issue of active vibration protection systems with magnetorheological vibration dampers is given. The structure of closed by vibration acceleration of vibroprotection system protected object is developed. There are presented the mathematical models of its functionally necessary elements: vibration sensor, vibration protection system along the disturbance and control channel, linear DC motor. A technique for synthesizing a correction device that provides the desired resonant properties of a closed system is proposed. The results of simulation modeling of an active vibration protection system with a regulator synthesized according to the proposed technique and a regulator, the structure of which was obtained in the author’s previous works, are presented. Based on the obtained results, the conclusions on the presented materials are drawn and recommendations on the use of regulators are formulated.

Nowadays, self-propelled jib cranes equipped with telescopic jib equipment are widely used in construction, loading, unloading and installation works. Accidents of self-propelled jib cranes caused by a sudden break of a cargo rope, as well as spontaneous unloading of cargo, can be attributed to the main causes of accidents of hoisting cranes. This reason can be considered as one of the most dangerous, since sudden release of the load is characterized by unpredictability, independence from the skill of the operator and the transience of the impact. The aim of the work is to study the loading of telescopic boom equipment during sudden load removal and to propose measures to prevent or reduce the consequences of accidents caused by this type of loading. The railway crane “Sokol 80.01M” was selected as the object of study. The method of numerical experiment, carried out in the module of complex dynamic and kinematic analysis of SolidWorks Motion mechanisms was used as a research method. As a result of numerical simulation of instantaneous load removal, balancing of the telescopic boom on the sliding plates and shock interactions of the boom sections were established. The following parameters were determined: the time dependence of the sliding support reactions, the magnitude of shock interactions, and the time dependence of the boom head vibrations. It is proposed to use on a self-propelled jib cranes the “Method to increase the safety and security system of a jib crane”, which, in addition to protecting the crane from overload and from collisions of its boom or load-lifting body with various obstacles (coordinate protection), due to the presence of pyro-cartridges and their control subsystem, ensure the prevention of accidents in the event of a sudden removal of the load from the boom, as well as the protection of the hoisting machine when exposed to random external factors, damage reduction with irreversible loss of stability of the crane. The most rational parameters of the emergency power device for boom equipment were established: the time of action of the squib; the action coefficient of the squibs, the initial force of the squibs, the charge force of the emergency power device on the boom equipment.

The vehicles equipped with electromechanical transmission due to the development of traction electric drive, as well as on-board electric energy storage became very prospective. However, at the stage of such vehicles design the difficulties associated with evaluating the energy efficiency of the developed vehicles, in particular, with the evaluation of the efficiency of traction electric vehicles arise. In this work, the authors propose a method for evaluating the efficiency of traction electric motors of newly developed electromechanical transmissions of transport vehicles, based on the construction of an empirical dependence approximating statistical data on the characteristics of existing electric motors. The data on electric motors from a number of manufacturers used in vehicle transmissions was studied for approximation. The article discusses the application of the developed method to design an algorithm for controlling the transmission of a wheeled vehicle, aimed at increasing its energy efficiency. The efficiency of the algorithm is confirmed by simulation of the dynamics of the vehicle, the initial data for the simulation were obtained during the traction-dynamic calculation. The developed simulation model together with the method of evaluating the efficiency of the electric motor made it possible to carry out a comparative assessment of the developed gearshift control algorithm and the gearshift approach, which does not take into account the dependence of the energy losses of the electric machine on the operating mode in cases of urban and mixed driving cycles. As criteria for assessing the effectiveness of the application of the developed law of control of an electromechanical transmission, the amount of energy spent on movement along a given cycle and the number of gear shifts on the route were used. The obtained results confirm the effectiveness of using the developed algorithm in the conditions of vehicle movement in an urban environment.

Starting a cold diesel engine, in the Arctic, with minimum temperatures below -60 ° C, presents significant difficulties due to: low temperature of the air charge; increased resistance to cranking the crankshaft and moving other kinematically related parts (pistons, parts of the gas distribution mechanism; etc.) due to the increased viscosity of the oil, deterioration of fuel atomization conditions, enhanced heat transfer to the cylinder wall, loss of part of the air charge. This article is devoted to solving the urgent problem associated with the development of a theoretical framework that provides comprehensive simulation of the starting mode of a diesel engine at low ambient temperatures when using start-up facilitators. The article proposes a mathematical model of a diesel engine, based on thermal mechanics (thermodynamics of open systems), which reflects the main features of an internal combustion engine (ICE) as a system that converts energy over time. The system of equations of the mathematical model is based on the laws of conservation of energy, mass, equations of motion of solid links and includes differential equations of the rate of change of temperature and density of the working fluid in the cylinder and in the engine crankcase, ideal gas equation of state, as well as differential equations of change of angular velocity and angle of rotation of engine shaft. The mathematical model is tested on the example of a 1CH9.5 / 8.0 diesel engine. The article presents graphs of changes in the angular velocity, pressure and temperature in the cylinder, as well as the results of calculating the engine pre-start operation at various low ambient temperatures in comparison with the results of full-scale experiments conducted in the refrigerating chamber.

In the context of an ever-increasing complication of both the construction of building machines and mechanisms and the conditions of their operation, the issues of achieving reliability and durability of the main welded joints are actualized, since the quality of the welded joint determines the operability of the assembly and the machine as a whole. In this regard, ensuring satisfactory weldability and obtaining a better welded joint are necessary conditions of increased strength for welded structures on which the working bodies of construction machinery, as well as mechanisms and their assembly units are mounted. The article addresses the key issues of improving the reliability of welded structures of building machines. Special attention is paid to the problems of strengthening hazardous areas, as well as the restoration of such zones in the welded structures of construction machinery. As an example, the article considers the frame of a forklift truck equipped with a hydraulic manipulator. Particular emphasis is placed on the fact that when calculating the distances between welds, it is necessary to take into account its dependence on the welding conditions and the parameters of the frame structures of construction machines. The stress-strain state of the frame was evaluated by modeling the state of the structure in various situations. Using finite element analysis programs, it was found that it is possible to reduce local stresses that exceed the tensile strength of the material and cause the risk of microcracks due to the welding of overlays with short seams in a checkerboard pattern, as well as finding the optimal parameters of the welds taking into account the stress concentration. It was also established during the study that the greatest influence on the value by stress concentration factors is exerted by the radius of the transition from the base metal to the weld metal. An increase in the transition radius from 0.1 mm to 1.0 mm makes it possible to reduce the value of the stress concentration coefficient.