Experience in ensuring the strength of the supporting structures of locomotives and electric multiple units

To ensure fatigue strength of metal structures in mechanical engineering, various approaches are practiced. One of them allows for the appearance of cyclic stresses in details with amplitudes exceeding the fatigue limit. Typically, this approach is justified where the loads are fairly regular and ample opportunities for fatigue testing exists, but the requirement of a minimum metal consumption is critically important as well. Another approach to ensuring fatigue strength does not allow the possibility of cyclic stresses with amplitudes exceeding its endurance limit in the designed structure. With regard to the supporting elements of locomotives and electric multiple units (EMU) to ensure the fatigue resistance characteristics in Russia and the CIS countries, the second of these approaches has been implemented and successfully practiced for many years. Its purpose is to ensure the absence of fatigue damage in the parts of the carriage and the body during the designated service life. Relevant requirements for strength and dynamic qualities for these types of rolling stock, as well as the method of conducting dynamic strength tests are currently formalized in the standards. The article presents the main provisions of the methodology currently used on the railways of the Russian Federation and CIS countries to control the strength requirements of load-bearing structures of locomotives and EMUs, as well as the admission of these types of rolling stock to operation. Types of dynamic strength tests are described, strength

indicators are listed, methods for their determination are indicated. Today, this technique successfully solves the problem of the strength of load-bearing structures of traction rolling stock.

Ways to improve the efficiency of automatic control systems of pressing current collectors for railway service of high speeds

One of the limiting factors in increasing train speeds on railway transport is the quality of current collection. With increasing operation speeds, the dynamic loads on the current collector from the rolling stock increase and the aerodynamic impact

increases as well, which leads to an increase in the variation of the contact pressure, tearing off the current collector from the contact wire, arcing in contact and increased wear of the contact elements. A promising direction in addressing this issue is the use of automatic control systems, allowing to stabilize the amount of contact pressure. The article discusses the features of modern automatic control systems for pressing current collectors, its main disadvantages are indicated. Authors proposed new automatic control circuit for pressing a current collector, characterized by increased speed. A mathematical model of a current collector equipped with a high-speed automatic pressure control system is described. The results of the calculation of the parameters of the high-speed control system are presented, showing the possibility of its use in order to reduce the spread of the contact pressure of the current collector and improve the quality of the current collection at high speeds. Analysis of the characteristics of the transfer functions of

the regulator shows that the application of the PI controller algorithm is effective for stabilizing the contact pressure. Since the rod length of the pneumatic cylinder is limited, the regulator is able to maintain pressure for a limited time, after which the rod must be returned to its original position. The speed of the rod is limited by the characteristics of the actuator (electric motor). These features cause a significant variation in system parameters, such as the time constant and the duration of maintaining a stable depression, depending on the values of the controller coefficients kp and ki, which should be set taking into account the parameters of the current collector, operating conditions and type of contact suspension. For the considered current collector model, the optimal values of the controller coefficients are kp = 1.5 and ki = 1.0. Results of the calculations showed that the use of a rapid regulator based on a pneumatic cylinder in the carriage design reduces the standard deviation of the contact pressure to 37 % at speeds of up to 260 km/h.

On the rationing the parameters of asymmetric loading of all-purpose freight cars

Due to the presence in the operating fleet of freight cars with a base of over 10 m, as well as the practical impossibility of symmetrically placing loads with a weight corresponding to the nominal carrying capacity on open rolling stock, adjustments to the existing asymmetrical loading standards are necessary. To this end, it is  proposed to apply a comprehensive methodology for determining the allowable parameters of asymmetrical placement of freights, based on a combination of strength criteria of the bearing elements of cars, ensuring the normative level of dynamic qualiqualities and stability of the loaded car. The article provides an  example of determining the permissible parameters of the joint lateral and longitudinal displacement of the total center of gravity of the car (ЦТгр°), loaded to the nominal capacity. According to the results of the studies to determine the allowable values of longitudinal and lateral displacement ЦТгр° with unbalanced placement within the loading platform of the car, including the presence of a joint displacement, it was found that to improve the efficiency of using freight cars with an increased base, it is advisable to update the current offset standards of ЦТгр°. It is recommended to take the values of longitudinal displacement ЦТгр° for cars with a body base of 14.6 and 19.0 m respectively 1.46 and 2.11 m for freight with a total weight of 50 tons; 1.10 and 1.43 m for freight with a total weight of 60 tons; 0.22 and 0.28 m – for freight with a total weight of 67 tons. When placing freights with a total weight of over 67 tons with a height of center of gravity of 2.0 – 2.2 m on 4-axle freight cars with an axle load of 230.5 kN without limiting the permissible driving speeds, it is recommended to use a graphical method for determining the joint (longitudinal and transverse) displacement ЦТгр°. With an increase in the joint displacement parameters ЦТгр°, it will be necessary to limit the speed of the car in the curved sections of the track and to the lateral direction on the turnouts.

Determination of long-term permissible currents in wires of power supply systems of

Railways

In the standard for contact wires made from copper and its alloys, the values of  long-term permissible temperatures have significantly decreased. This requires recalculation of  previously valid values of long-term permissible currents. Authors

considered revised method for calculating the long-term permissible currents, based on a more rigorous consideration of the laws of heat transfer and experimental studies of the conditions of heating and cooling of shaped (contact) and stranded wires. Technique is based on heat balance conditions, using which the sources of greatest inaccuracies become such quantities as cooled surface area, influence of wind direction, meteorological conditions, laws of change in heat transfer coefficient, effect on additional heating of solar radiation. Deviations when these indicators are taken into account by existing methods can cause errors of 40 % or more. Formulas for calculating the actual outer surface of stranded and shaped wires are given. The inadmissibility of calculating the surface area of the wires by their reference diameter is noted. Updated law of the change in heat transfer coefficient for stranded and shaped wires, as well as the degree of its dependence on wind speed and cooled surface, is given based on a summary of extensive domestic and foreign research. It is shown that with the longitudinal direction of the wind, the reduction of this coefficient occurs to a lesser extent than has been assumed so far. Authors propose method for taking into account an increase in the heat transfer coefficient under meteorological conditions characteristic of ice formation. The heat transfer coefficient of shaped and stranded wires in no case can not be taken as for round pipes with smooth surface. Existing method of accounting for solar radiation, which influences the additional heating of wires, leads to an unjustified and repeated exaggeration of this effect, since previously only the radiation incident on the wire was taken into account in the calculations. According to the laws of heat transfer, the temperature of the irradiated body does not depend on the incident, but on the resulting radiation, defined as the difference between the radiations incident on the body and emitted by it in accordance with its temperature. A formula for accounting for such heat transfer is proposed. The above methodology and calculation formulas allow performing reasonable calculations to determine the long-term permissible currents of individual stranded and shaped wires, as well as the contact network as a whole.

Criterion for evaluating vehicle performance

The article proposes to evaluate the efficiency of an autonomous vehicle, taking into account not only the energy consumption for motion, but also the time of motion, i. e. both factors — efficiency and performance — should be taken into account. As a criterion for evaluating the efficiency of vehicles, authors propose the multiplication of efficiency on performance — the energy efficiency indicator (EEI). The best will be the vehicle with the highest EEI. The indicator should be calculated according to the specified technical characteristics of the vehicle laid down in the technical specifications. This criterion is suitable both for the evaluation of the vehicle during the design and during operation. At the same time, it is possible to evaluate and compare the EEI of technical vehicles not only of railway transport. The article presents the criterion values for water, rail and air transport. Proposed criterion makes it possible to evaluate the change in vehicle efficiency over time due to technical progress. Since 1953, the energy efficiency of

a diesel locomotive has increased almost 3 times. To calculate the operational energy efficiency, it is necessary to obtain data on the actual performance of the vehicle. On railway transport, this is data on train work in t·km, speed and fuel consumption. The EEI assessment based on operating data will show how correctly the organization of vehicle operation is built, how non-stationary modes of the power plant and specific modes of traction influence the overall performance of the vehicle, how well the vehicle is selected for these operating conditions.

Effect of measurement errors in determining the heat transfer coefficient of the enclosing structures of an isothermal car

When conducting thermal tests, the purpose of which is to determine the heat transfer coefficient of the body of an isothermal car K, the study of measurement errors affecting the accuracy of the obtained value plays an important role. The results of such experiments may contain various measurement errors that can introduce significant deviations into the resulting values of the desired coefficient. Obtaining accurate results when conducting this kind of experiments is impossible without a preliminary study of the causes that affect the final result. The article presents the types of measurement errors that affect the accuracy of determining the heat transfer coefficient of the body of an isothermal car when conducting thermal tests. It was noted that the magnitude of labor costs and energy losses during the further operation of this body significantly depends on the accuracy of the value of this coefficient. It was emphasized that one of the main types of random errors arising from measurements and compliance with the established procedure for conducting typical thermal tests is a voltage drop (“slump”) in the electrical network, leading to significant errors in the calculations of the heat transfer coefficient of the isothermal car body. The values of this coefficient are presented, which were obtained as a result of heat engineering tests performed using the equilibrium mode method and the express method. It is shown that the use of the express method to determine the heat transfer coefficient of the bodies of isothermal cars reduces the risk of random errors due to the minimum experiment duration (from 5.5 h), allows to obtain exact values of the desired coefficient (with an error not higher than 3 % of its value of long-term equilibrium method) and use this data for practical purposes.

Study of the characteristics of external noise of dual-powered electric locomotive

The article presents the results of tests of a freight dual-system electric locomotive 2EV120 when operating in stationary mode and moving at normalized speed. In the course of conducting experimental studies of the sound level of external noise during operation of a locomotive at a constant and alternating current, exceeding the regulatory requirements at individual observation points was found, and it was noticed that the operation of the traction transformer is the main source of increased noise, the main component of which is air in this case. It has been established that in the sound field formed around an electric locomotive operating in the parking lot, the distribution of sound levels is uneven. An example, given in the article, describes the distribution of sound levels when an electric locomotive is operated on alternating current before and after the application of noise protection measures. In the process of testing, a set of organizational and technical measures was developed, the implementation of which reduced the external noise of the electric locomotive 2EV120 as a whole to the regulatory requirements. In particular, to reduce the noise from the operation of the traction transformer, as one of the options, it is proposed to install a shielding device in its sub-body part, the minimum efficiency of which was 4.2 dBA. Analysis of the regulatory margin for external noise showed that its value at the observation point located opposite one of the operating traction transformers equipped with a shielding device is minimal. One of the reasons for this in this case is the sound energy penetrating through the body covering of a large area, generated by the work of the locomotive's internal equipment. In order to increase the regulatory margin when the 2EV120 electric locomotive is operating at a constant current, the authors propose the following: to strengthen the sound insulation capacity of the thin-walled body plating of the electric locomotive by installing a double-wall sound-insulating structure with sound-absorbing material inside it.

Damping of dynamic forces by materials used in the construction of ballast and ballastless railway tracks. Crushed stone

Strength properties of mineral materials used in the track operation, which are crushed stone and sand, do not depend on the ambient temperature (up to 500 °C) and humidity, but gradually degrade when its pore space becomes clogged with fines, oil products and plant residues. Polymeric materials used in the construction of railway tracks for damping dynamic loads, when exposed to significant stresses, are gradually destroyed. The main operating conditions that determine the performance of polymer products include the ambient temperature, its humidity, the presence of a chemically aggressive external effect and a stress fields. Cuts or scratches — stress concentrators on polymer products — significantly change the thermal dependence of its mechanical properties. Therefore, hemispherical grooves, cylindrical cuts in the central areas of pads, made to reduce wear in the peripheral areas, lead to a significant narrowing of the temperature range of the effective operation of these products. Granular media have strong non-linear properties, the main causes of which are microcracks, boundaries and areas of contact of the granules a well as physic-mechanical properties of substances that fill the pore space of crushed stone layer. Coefficient of energy absorption in a granular medium is directly proportional to the viscosity of the polymer layer between the granules. Filling the pore space of the crushed stone layer with sand and viscous-plastic medium (polymers, organic binders and materials based on them, solid polyurethane foam, water or oil products) leads to decrease in the strength of crushed stone prism. An increase in the ambient temperature, especially above 30 °C, reduces the elastic properties and structural viscosity of viscousplastic materials that fill the pore space of a crushed stone prism, thereby reducing its strength. But at the same time, the energy absorption coefficient of vibration in a wide frequency range sharply increases and the dynamic loads on the track gauge profile are decreased. Most often, cheap organic-based compositions are used as dynamic load absorbers in the crushed stone layer: synthetic resins, acrylic acid amide polymers, latexes, lignin sulfonates and bitumen. When filling the pore space of crushed stone, an adhesive interaction occurs between the polymer molecules and the surfaces of the granules. Polymer molecules fill not only the pore space, but also penetrate into the contact area of the granules, reduce friction and decrease the angle of internal friction of crushed stone and the adhesion index of the bulk material. However the operation of railways is associated with permanent deformation and destruction of the surface layers of the polymer. Multiple repetition of the deformation process leads to an increase in mechanical hysteresis losses, causing friction and wear of the polymer in contact with the granules. Therefore, one should not expect a long service life when using a polymeric material for hardening the ballast layer.

Comprehensive method for evaluating results of ultrasonic testing of parts and components of rolling stock when adjusting the sensitivity for different reflectors

Operation of railway rolling stock is accompanied by high costs of maintaining its operating condition throughout the entire period of operation. To improve the operation efficiency of rolling stock, methods and diagnostics tools have been developed, which are used both in its manufacture and in carrying out maintenance

and repairs, and as an independent technological process. Diagnostics allows to increase the availability factor and the probability of uptime of the rolling stock, reduce the complexity and cost of periodic maintenance of its nodes. The article proposes a new integrated method for estimating discontinuities in parts and units of railway rolling stock according to the amplitude — distance — diameter diagrams by the standardless method with the possibility of determining the type of discontinuity by the dual-frequency method of flaw-detection with a manual ultrasonic testing with a single-channel ultrasonic flaw detector. Developed method is most relevant in the control of cast parts of railway rolling stock, since castings can be equally likely to contain bulk (pores, shells, nonmetallic inclusions, etc.) and planar discontinuities (cracks of different origin; flocks; segregations that lead to violation continuity, etc.). Proposed method allows estimating the discontinuity by comparing the amplitude of the echo signal from it with the corresponding type of tuning reflector: if the discontinuity is planar as a result of using the two-frequency flaw-detection method, the comparison is carried out with the amplitude of the flat-bottomed cylindrical reflector; if the discontinuity is volumetric, then the comparison is made with the amplitude from the spherical reflector. The article describes the algorithm that was developed to automate the