Hydromechanical Transmissions Research Articles

ACTIVE MONITORING OF COMPLEX ELEMENTS OF HYDROMECHANICAL TRANSMISSIONS
 OF MOBILE MACHINES

The issues of active monitoring and diagnosing the technical condition of a mobile machine equipped with a hydromechanical
 transmission are reflected. The factors influencing the decrease in machine efficiency and the deterioration
 of transmission performance are considered. It is noted that the main processes contributing to the loss of performance
 of a hydromechanical transmission are friction and wear of the working surfaces of parts and their interfaces;
 fatigue processes in parts subject to variable loads; aging of materials The causes of defects and the nature of their
 manifestation in hydromechanical transmissions are given, as well as measures for continuous and active monitoring of
 faults in automatic transmissions. It is noted that in order to carry out active monitoring of automated mechanical and
 hydromechanical transmissions that have complex elements of gear interaction, it is necessary to obtain interdependencies
 between diagnostic parameters and criteria for assessing the technical condition in order to implement this information
 in monitoring and diagnostic algorithms for mobile applications.

Гидромеханические трансмиссии лесотранспортных машин: технологическая связь с воздействием на почвенно-растительную среду

Reducing the negative impact on the forest soil and vegetation environment of wheeled propellers of biaxial articulated forest transport vehicles, along with changing the parameters of the propellers themselves, can be effectively carried out by redistributing the power flow in the hydromechanical transmission. In order to ensure high traction performance and cross-country capability through single obstacles (root systems) in the conditions of a cutting area, it is necessary to take into account the rational parameters of the components and assemblies of the hydromechanical transmission based on new scientifically sound technical solutions. A review of the designs of hydromechanical transmissions of domestic and foreign-made forest transport vehicles revealed their advantages and disadvantages that affect the effectiveness of their use in the conditions of forest exploitation. The primary transportation of trees, which occupies a significant volume during logging, is effectively handled by forest transport vehicles with high energy saturation. The use of a promising torque converter design as part of a hydromechanical transmission unit for the separate drive of the drive axles of wheeled articulated timber vehicles will compensate for the effect of external forces and reactions to the wheel mover, as well as minimize the phenomenon of power circulation in a closed loop "wheel mover – bearing surface", which will contribute to an increase in traction performance. The technological relationship from the use of different powertrain designs is characterized by moderate differentiation (p < 0.05) according to the criteria of impact on the soil environment, based on the use of the median method in the statistical analysis of similarities and differences. Future research will answer the following questions: how will the level of loss of useful power in the hydromechanical transmission of a wheeled forest transport vehicle equipped with a new torque converter change in conditions of constantly changing external influences? How and how closely will the transmission parameters with the new torque converter affect the performance and patency of the forest transport vehicle, taking into account the characteristics of the soil and plant environment?

Energy and Fuel Consumption of a New Concept of Hydro-Mechanical Tractor Transmission

Tractors equipped with hydro-mechanical transmissions (HMTs) typically deliver excellent fuel-saving performance but are expensive. To improve the fuel economy of cheaper tractors, the authors of this study have designed an HMT for a tractor that uses a simple, single planetary gear to merge the power and analyze its consumption of energy and fuel. First, we introduce the principle of transmission of the HMT and formulate a model to calculate its speed, torque, and efficiency. Second, we analyze the parasitic power of the HMT and simulate its characteristics of efficiency. Finally, we compare the efficiency of transmission and fuel consumption of HMTs with a single planetary gear and Simpson planetary gears. The results showed that parasitic power was obtained when the displacement of the variable pump was negative and the maximum ratio of hydrostatic power in each range was 45–46%. The highest efficiency of the proposed HMT in ranges RL (low range) and RH (high range) were 87% and 89%, respectively. It has a simpler structure than the HMT with Simpson planetary gears and consumes lower amounts of energy and fuel. These attributes make it suitable for use as a transmission system for large- and medium-power tractors with a continuously variable transmission.

Исследование надёжности гидромеханических коробок передач городских автобусов в условиях эксплуатации

The article considers the problem of reliability of hydromechanical gearboxes of city buses with the terms of replacement of transmission oils regulated by the manufacturer, which negatively affect operational efficiency and efficiency in real conditions. The motor transport company has collected and processed information statistics on failures, malfunctions and repair activities in the part of hydromechanical gearboxes of city buses, which has been accumulated during operation. Reliability studies of hydromechanical gearboxes of city buses have been carried out. The list of considered hydromechanical gearboxes of city buses for research is summarized. Mathematical expressions are presented for calculating the values of reliability and durability indicators, namely, the main parameters are calculated - the number of failures or malfunctions, the average time to failure, the average resource, the standard deviation, the coefficient of variation, and the failure flow parameter. The key graphs of reliability and durability indicators of the analyzed hydromechanical transmissions of city buses are shown. Schedules for the distribution of nonfailure operating time, the allocation of resources before repair, as well as changes in the probability of repair of hydromechanical gearboxes of city buses are compiled. The scientific and technical groundwork for further promising research in this area is outlined.

Design procedures for hybrid hydromechanical transmissions

Hybrid hydromechanical transmissions are particularly suitable for heavy vehicle and have the potential to provide better efficiencies than other hybrid architectures. However, their study must be carried out with care, since there are many possible transmission configurations and there is not one superior to the others for all applications. The particular complexity of these transmissions requires that design be treated as an optimization problem.In this paper, the optimization procedures of the “non-optimal” type are compared with the “optimal” ones, which are more precise than the former, but much heavier in terms of calculation time. The former consist of two sections. The first one is dedicated to the simultaneous optimization of the layout and components of the non-hybrid hydromechanical transmission; the second one is dedicated to the accumulator only, which can be optimized by means of simple physical laws or by means of a “Design of Experiments “procedure.The “optimal” procedures, on the other hand, proceed with the sizing of the entire hybrid transmission through a mathematical programming problem that can be single or multi-objective. It will be demonstrated that the DOE “non-optimal” procedure provides results very close to those derived from the “optimal” procedures, with considerable savings in calculation times.

АВТОМАТИЧЕСКИЕ ТРАНСМИССИИ: О СВЯЗИ КАВИТАЦИОННЫХ РЕЖИМОВ ГИДРОТРАНСФОРМАТОРА И ВЫСОКОЧАСТОТНЫХ РЕЗОНАНСНЫХ КРУТИЛЬНЫХ КОЛЕБАНИЙ МЕХАНИЧЕСКИХ КОМПОНЕНТОВ

Based on the analysis of foreign publications, a number of new scientific results are presented in the field of hydrodynamics of working fluid flows in torque converters (TC) of automatic hydromechanical transmissions (AHMT), including cavitation in TC, which were obtained using the new CFD (Computational Fluid Dynamics) technology as part of research to reduce the vibroacoustic loading of AHMT. CFD modelling methods have shown that cavitation in a TC, along with the creation of noise and vibration, significantly degrades its characteristics (in the example given, the transformation coefficient is by 18.1 %, efficiency is by 5.8 %, turbine torque is by 20.3 %), and also creates high-frequency oscillations in a wide range that can resonate with the natural frequencies of the AHMT components. The influence of structural and operational factors on cavitation is investigated. The greatest cavitation occurs on the blades of the TC stator in stop mode when the car accelerates from a standstill. The results of CFD modelling are in good agreement with experimental data. CFD technology has become an effective tool for optimizing the design of an automotive TC, its blade system, flow part, visualization of internal flows, study of the mechanism of occurrence and impact of cavitation. The analysis of methods of attenuation of cavitation is carried out, including the selection and maintenance of the value of the TC recharge pressure. The presented provisions in Russian are published for the first time.

Effect of iron addition on the structure and properties of copper-based friction powder material used under friction conditions with lubrication

Machines and mechanisms contain units responsible for their movement and stopping, and such units use friction materials. These units include oil-cooled brakes, hydromechanical transmissions, and clutches. They use mainly copper-based friction materials providing the high coefficient of friction and wear resistance. These materials feature by effective heat dissipation since a large amount of heat is released in these areas for a short period of time. The paper presents the results of studies into the effect of iron addition into a frictional powder material based on BrO6 and BrO12 bronze on its structure, mechanical and tribotechnical properties. It was shown that the introduction of iron contributes to an increase in the coefficient of friction from 0.034 to 0.055 for the BrO6-based friction material and from 0.042 to 0.073 for the BrO12-based friction material. It was determined that the ultimate compression strength of the BrO12-based friction material is 340 MPa without iron addition, 310 MPa at 10 vol.% of iron, and 180 MPa at 50 vol.% of iron. This is due to the fact that the iron content of more than 30 vol.% results in the change of the frame structure of the material to the matrix one having a sintering temperature higher than the temperature used in the paper for friction material sintering. It was found that for the BrO6-based friction material there are both rounded and elongated inclusions in the copper phase up to 2.5 μm in size with the iron content of 30–50 %. In the BrO12-based material there are more iron inclusions in the copper phase and their size are much larger, the length of inclusions reaches 20 μm, and the iron content in them is 49–73 %.

MODERN TRENDS OF DESIGN, RESEARCH AND USE OF HYDRAULIC MACHINES IN DRIVES OF MECHANISMS AND TRANSMISSIONS (REVIEW ARTICLE)

The work is devoted to an overview of modern trends in the design, research and use of hydraulic machines in the drives of mechanisms and transmissions. The analysis of the use of hydromechanical transmissions has been carried out. The advantages and disadvantages of hydromechanical transmissions in comparison with mechanical ones are described. A brief overview of modern approaches to the design of new products, taking into account the existing information technologies, is carried out. We have analyzed modern software products designed to support the project at different stages of the product life cycle. It has been found that at the present time the appearance of individual variants of highly specialized software with a modern interface for synthesizing the structure of a designed product does not make it possible to solve the problems of synthesis and structural analysis of hydro-mechanical transmissions. A review of the analysis of operational factors affecting the fault tolerance and operating parameters of hydrostatic transmissions in general and hydromechanical transmission in particular is carried out. We have also considered the examples of technical solutions that allow to reduce the number of failures associated with the influence of one factor or another, as well as allow to reduce its influence on the parameters of the mechanism. The analysis of sources with information on the study of the parameters of hydrostatic transmissions using field tests or the mathematical apparatus developed by the authors is carried out. The ways of solving problems arising at the stages of design research are outlined. Keywords: design, hydrostatic transmission, hydromechanical transmission, influence of operational factors, synthesis

Hydromechanical Transmissions of Heavy-Duty Trucks

Hydromechanical Transmissions of Heavy-Duty Trucks

Novations in creation and ensuring the competitiveness of BELAZ quarry machinery

The development tasks of OJSC “BELAZ” – Management Company of Holding “BELAZ-HOLDING”, are defined, which consist in using and introducing the latest achievements in the field of technical sciences and innovative technologies created on their basis into the design and production processes of mining equipment; development of new competitive products and promising sales markets, diversification of exports. Together with scientific organizations, studies have been carried out that have allowed us to develop new and improve existing methodological approaches to solving urgent problems in all problematic areas of creating modern mining dump trucks especially and in excess of extra heavy lifting capacity. OJSC “BELAZ” is the only manufacturer and supplier of dump trucks with a carrying capacity of 450–500 tons. As a result of research on the creation of such machines, the model of a short-base maneuverable dump truck with a rigid frame of a special design was first recommended, which reduces the center of gravity and loading height of a mining dump truck, designed according to the 4 × 4 scheme (two drive axles) with double axle busbar and the use of existing tires with a maximum carrying capacity of 104 tons. The proposed and comprehensively tested new layout solutions give reason to believe that the development of dump trucks with a carrying capacity of up to 600 tons is a reality when mastering the production of tires with a carrying capacity of more than 110 tons. А new generation of dump trucks with hydromechanical transmissions is designed; work is underway to create robotic complexes for the mining industry. Particular attention is paid to computerization, digitalization and environmental friendliness of mining equipment, ensuring the reliability of technology by creating and applying new structural materials and technologies for large parts and systems.

Modeling of the dynamics of switching stages of hydromechanical gears based on the Lagrange equations with indefinite multipliers

A procedure is proposed for modeling automobile hydromechanical transmissions, based on representing them in the form of multi-mass mechanical systems and applying the Lagrange equations with indefinite multipliers to derive the equations of motion of concentrated masses. Keywords hydromechanical transmission, clutches, gear shifting, mathematical model, Lagrange equations with indefinite multipliers. harb_60@tut.by

Combined Torque Converter for Mining Machines

Transmissions of many technological and transport machines for mining enterprises are equipped with hydro-mechanical transmissions (HMT) with torque converters. HMTs have a number of positive properties. But a significant drawback of traditional automotive single-stage (single-turbine) torque converters is their relatively narrow torque ratio, which most often makes 2 or 3. Multi-stage torque converters in which two or three turbines are simultaneously connected to the output shaft demonstrate higher converting properties. The toque ratio of multi-stage hydraulic torque converters makes 4-6 or more. The drop in the efficiency in the range of large ratios and the lack of hydraulic coupling mode is one of the disadvantages of multistage torque converters. In order to overcome these shortcomings, the design of a combined torque converter is proposed. It combines modes of operation with one and two active turbines, as well as modes of hydraulic coupling and blocking. The main turbine of a combined torque converter is of the centrifugal type. The combination of single-stage and two-stage operation modes is achieved through the use of a composite pump wheel, one part of which can be used as a second centrifugal turbine. Two clutches are provided to control the torque converter.

Past, present, future of agricultural tractors

The development of tractor design is closely related to its technological updating, improving environmental performance and increasing usability. Study of this problem in a historical context shows the unity in approaches of various agricultural tractor manufacturers to tractor design aimed at increased productivity and reduced operation costs in accordance with the requirements for agronomic and environmental performance. The main task of the first-generation tractors was to develop traction for agricultural work with maximum productivity and cost-effectiveness. Solution of these problems required further development of the tractor theory and the idea of the processes quality, and ensured the optimization of design and performance. As a result, the designs of tractors from different manufacturers developed in the same direction. Modern tractors are equipped with electronically controlled turbocharged diesel engines and have systems reducing toxicity of the exhaust gases. Power transmission of the tractors is implemented either with a robotic gearbox without interrupting the power flow, or in a continuously variable format, which ensures a more optimized operating mode. While for small-traction-class tractors stepless power transmission is provided with a mechanical variable speed gear, the rest of the tractors require electronicallycontrolled hydromechanical transmissions. As the capacity of power stations grows and an extensive power grid based on renewable energy resources is developed, the demand for electric tractors is to be increased. Tractors with hybrid power plants are likely to be produced at the transitional stage of development. They have the advantages of controlling processes in the machine and tools, the ability to provide agricultural implements with electric power for carrying out their work processes and ensuring their active drive to develop traction as well.

Reverse rotation stator of torque converter in automotive powertrain system

Global economy demonstrates a steady elevated demand for heavy mobile equipment for construction and mining enterprises. At the same time wheel loaders, the total annual world output of which is about 160-170 thousand units are in high demand. Many wheel buckets and forklifts are equipped with hydro-mechanical transmissions containing a torque converter and a manual gearbox with hydraulic control. The positive properties of self-regulating torque converters are particularly favorable for equipment operating under stress. The transmission is equipped with a gear due to insufficient transforming properties of the torque converter. In order to improve the dynamic properties of self-propelled machines, designers increase the number of stages in gearboxes. However, multi-stage boxes complicate the hydro-mechanical transmission and its control system. One of the ways to improve the hydro-mechanical gears of mobile machines is to fully utilize the motor and tractor torque converters by using the opposite rotation of the torque converter reactor in the forward and reverse modes of the transmission. The article discusses circuit solutions for a hydro-mechanical transmission with a single-stage torque converter without a multi-stage gearbox, intended for use in transmissions of wheeled transport and loading and other self-propelled machines.

Low-Level Control of Hybrid Hydromechanical Transmissions for Heavy Mobile Working Machines

Fuel efficiency has become an increasingly important property of heavy mobile working machines. As a result, Hybrid Hydromechanical Transmissions (HMTs) are often considered for the propulsion of these vehicles. The introduction of hybrid HMTs does, however, come with a number of control-related challenges. To date, a great focus in the literature has been on high-level control aspects, concerning optimal utilization of the energy storage medium. In contrast, the main topic of this article is low-level control, with the focus on dynamic response and the ability to realize requested power flows accurately. A static decoupled Multiple-Input-Multiple-Output (MIMO) control strategy, based on a linear model of a general hybrid HMT, is proposed. The strategy is compared to a baseline approach in Hardware-In-the-Loop (HWIL) simulations of a reference wheel loader for two drive cycles. It was found that an important benefit of the decoupled control approach is that the static error caused by the system’s cross-couplings is minimized without introducing integrating elements. This feature, combined with the strategy’s general nature, motivates its use for multiple-mode transmissions in which the transmission configuration changes between the modes.

Formation of the friction surface of a friction material based on copper depending on the amount of tin under lubrication conditions

The paper presents the study results of the surface wear of a friction material based on copper, operating under boundary friction. These materials are used for the manufacture of friction discs in hydromechanical transmissions, oil-cooled brakes. It was found that the frame composition of the friction material (tin content in bronze) is defined as the mechanism of material wear, its working conditions, as well as the effectiveness of running-in and the possibility of increasing the load-speed characteristics. The growth of tin content from 6 to 12% contributes to an increase in the strength of the material, while keeping its pore structure, which is an additional source of lubricant in the process of friction interaction.

Continuous formulation of the layout of a hydromechanical transmission

In this paper, an analytical formulation of the layouts of three-shaft hydromechanical transmissions is presented. The formulation was obtained starting from the Willis equation for the planetary gears. Its graphical representation results in a polar plot dependent only on the angular coordinate: by varying the latter between 0 and 2π, all the transmission layouts can be continuously described. In this way, the layout, together with the transmission ratios of the gears and the displacements of the hydraulic machines, can enter as a degree of freedom in the problem of mathematical optimization of the hydromechanical transmissions. The potential of this analytical formulation will be shown by studying the case of a transmission for a forklift of 75 kW.

Investigation of the driven disks of hydromechanical transmission BELAZ with the new LZ_G-Base oil and the friction materials FM-15 and MK-5

At the mining dump trucks BELAZ with lifting capacity from 30 to 90 tons, loaders and bulldozers, special vehicles BELAZ for metallurgical production (slag trucks, heavy vehicles), aerodrome tractors, as well as for dump trucks and vehicles for underground works of the brand “MoAZ” are used hydromechanical transmissions OJSC “BELAZ” is the managing company of the holding “BELAZ-HOLDING”. The most important element of the hydromechanical transmission, which limits its service life and reliability, are the friction clutches for switching the stages and blocking the hydraulic transformer. The disks of friction clutches sustain significant static and dynamic loads, their surfaces are exposed to high specific thermal energy and intensive wear. During the tests it was established that for the sintered powdered friction material based on copper MK-5 (commercially used in the hydromechanical gearbox) it’s possible to increase the friction coefficient, decrease the stopping time and the wear rate by using the transmission oil LZ_G-Base. The sintered powdered friction material FM-15 has initially increased tribotechnical properties in comparison with material MK-5. The investigations of tribotechnical properties of sintered powder materials is currently being given to much attention. However, these studies do not consider the influence of lubricants on the operation of the sintered powder friction materials. The application of oil of type (LZ_G-Base) which is developed on Lubrizol technologies and G-Base base oils during operation of the sintered friction material FM-15 increases its tribotechnical properties by 10…15%. The conducted investigations of the driven discs for the hydromechanical transmissions BELAZ with the new gear oil LZ_G-Base and the friction materials FM-15 and MK-5 have showed that the tribotechnical characteristics are increased and the wear rate of the discs is decreased.

Energy analysis of dual-flow hydromechanical gears

Two-flow hydromechanical transmissions are becoming increasingly common in the construction of modern land transport and traction machines (tractors, automobile and high-speed crawler vehicles). This is mainly due to the desire to increase the efficiency of transmission. In order to select a dual-flow hydromechanical transmission scheme in relation to specific operating conditions, it is necessary to know the advantages and disadvantages of various schemes, their potential capabilities. The evaluation of the operation of each circuit can be made on the basis of their kinematic, power, and energy analysis. The results of the kinematic and force analysis of two-flow hydromechanical gears were previously developed by the authors of this article. In energy analysis, the following estimated parameters were used to compare the performance of the transmission: г|ГМП - efficiency of transmission; РМ - power factor in the mechanical branch of the transmission; РН - power factor on the pump wheel of the torque converter; РТ - the power factor on the turbine wheel of the torque converter. The paper considers 12 schemes of two-flow hydrome-chanical gears with a differential link at the input and output with mixed gear coupling, the results of their energy analysis are given. For each of the schemes considered, analytical dependencies of the estimated parameters on the internal parameters of the hydromechanical transmission were obtained, which were used as the characteristic k of the planetary gear set, the power transfer ratio йгт of the torque converter, and the kinematic gear ratio игмп of the hydromechanical transmission. The results of calculations performed on a computer using the external characteristic of a specific torque converter are obtained and presented in graphical form. The obtained results can be used in developing recommendations for the choice of a two-flow hydromechanical transmission scheme.

PLOTTING OF EXTERNAL CHARACTERISTIC OF A TORQUE CONVERTER WITH COUNTER-ROTATING MODE OF TURBINE WHEEL IN DOUBLE-FLOW HYDROMECHANICAL TRANSMISSION OF AN INDUSTRIAL TRACTOR

Double-flow hydromechanical transmissions are widely used in industrial tractors and high-speed tracked vehicles. The main advantage of this transmission is a higher value of the maximum efficiency compared to a single-flow hy-dromechanical transmission. Considered is the double-flow hydromechanical transmission of the industrial tractor D8L «Caterpillar» and the results of its bench experimental studies are presented. In this transmission, the torque converter operates in a certain rotational speed range of the driven shaft in the counter-rotating mode of the turbine wheel. In the domestic and foreign literature there are no external characteristics of torque converters with the mode of turbine wheel anti-rotation. It was not possible to obtain such external characteristics of the torque converter experimentally so far. This is due to the complexity of providing a test-bench with anti-rotation mode of the turbine wheel of the torque converter. This mode is realized only in a double-flow hydromechanical transmission. However, with its experimental test-bench studies, existing techniques did not allow plotting of an external characteristic of the for the turbine wheel counter-rotating mode. At experimental test-bench researches of a torque converter only it is also impossible to provide the mode of counter rotation of a turbine wheel. In this paper, a method is given for plotting of external characteristic of a torque converter with turbine wheel anti-rotation mode, if an external characteristic of a double-flow hydromechanical transmission is known. The validity and reliability of the proposed approach to the plotting of the external characteristic of the torque converter with turbine wheel counter rotation mode is confirmed by the results of bench experimental studies of the double-flow hydromechanical transmission and the torque converter of the industrial tractor D8L Caterpillar.