Braking Properties Research Articles

Оцінка ресурсу фрикційних поверхонь гальмівних дискових механізмів за показниками відносного зношення для легкових автомобілів

Modern development of vehicle designs requires paying great attention to braking properties, which will depend on the design parameters of the brake mechanisms. The article discusses a scheme where a disc brake is installed on the front wheels, and drum brakes are installed on the rear wheels. From the diagram of the distribution of forces that act on the vehicle during braking, the maximum friction forces for the front and rear axles were determined. A general formula was obtained for the braking distance of a vehicle, during which wear of the brake mechanism occurs. We used the results of the well-known theory of friction and wear by I.V. Kragelsky. The mathematical wear model was built for each friction pair. The wear model takes into account the design parameters of the vehicle, the wear resistance coefficient of materials, the initial braking speed of the vehicle, the mileage and braking distance. The main design parameters of the brake system are the friction radius, the kinematic rolling radius of the wheel, and the amount of drive pressure.
 To assess the service life of the brake mechanism, it was proposed to use such an indicator as the relative wear of associated parts. A formula has been obtained for calculating this indicator based on changes in geometric parameters and operating modes of the brake mechanism under operating conditions. A forecast was made of the service life of the brake mechanisms of the front and rear axles of passenger cars, which is proposed to be carried out according to the indicator of relative wear of friction surfaces. Graphic dependences of the distribution of relative wear of the friction surfaces of brake mechanisms for Chevrolet Aveo and Forza cars were constructed. It was shown using the example of Chevrolet Aveo passenger cars that the relative wear of the front axle brakes is maximum and it varies from 22.5 to 26.1%, and for the rear axle this figure varies from 21.0 to 22.5%. The service life of the brake disc is 4.44 times greater than the service life of the friction lining for the Chevrolet Aveo. For the Forza car this figure is 4.76. The results of the work can be used to estimate the residual life of brake mechanisms, taking into account operating conditions.

Influence of ferrochromium type on micro and macro tribology behavior of copper metal matrix composites

Ferrochromium, an important emerging abrasion component, is added to Cu metal matrix composites (Cu-MMCs) to enhance the high-energy braking properties of such composites. This study examined the microstructures, interfacial characteristics, and micro-tribology behaviors of two kinds of ferrochromium, and their effects on the braking performance of Cu-MMCs. The high-carbon ferrochromium (HCF) with higher hardness, consisting of (Cr,Fe)7C3 and (Cr,Fe)23C6-CrFe phases, formed a poor mechanical-diffusion mixed interface with the matrix and exhibited a low coefficient of friction (COF) in micro-friction tests. By cracking or crushing of HCFs, as well as third-body wear debris formed by HCFs, the COF in macro-friction tests was increased, helping Cu-MMCs maintain their braking performance at medium and high breaking energy densities (BEDs). The extra low-carbon ferrochromium (ELCF), consisting of a CrFe phase, generated a diffusion interface with the matrix, exhibited a greater COF, promoted the formation of a tribo-layer at high BED, and provided better wear resistance for Cu-MMCs. The wear mechanisms changed from plowing to severe plastic deformation-induced delamination and oxidation-induced delamination for Cu-MMCs with ELCF and HCF, respectively.

Braking force measurement errors on a stand with horizontal support discs

The authors have developed and are investigating the original design of a stand for testing the braking properties and suspension of wheeled vehicles, which provides the shape of the tyre contact spot with the support surface closest to real road conditions. The originality of the stand was confirmed by the decision to grant a patent for an invention of the Russian Federation. The advantages of implementing the proposed stand design, as well as disadvantages and ways to overcome them, are considered.

Априорно-аналитическое исследование свойств тормозного стенда с горизонтальными опорными дисками

The article presents an original stand designed and developed for testing the braking properties and suspension of wheeled vehicles, the tire contact patch with the supporting surface being provided maximally close to road conditions. The originality of the stand is confirmed by the decision to issue a patent of the Russian Federation for an invention. The advantages of using the proposed stand design, as well as the disadvantages and the ways to overcome them are considered.

Analysis of electromagnetic-thermal coupling braking properties of combined electromagnetic friction and shape memory alloy brake

To address the problems of severe heat generation and poor stability of traditional electromagnetic friction brakes, combined electromagnetic friction and shape memory alloy (SMA) braking method is proposed. This novel brake solves the traditional electric brake thermal decay problem based on the temperature sensing ability of SMA, which improves its working stability in a high-temperature environment. Based on Ampere’s law of magnetic field, the relationship between current and electromagnetic force was established, and the equation of electromagnetic force braking torque was derived. Based on the thermodynamic model of a SMA, the relationship between the frictional torque of SMA and parameters such as temperature, squeezing pressure, and structure size was established. The magnetic and thermal fields of this brake were analyzed by the finite element method to obtain the magnetic field distribution and the magnitude of electromagnetic force at different currents and to derive the temperature distribution of the brake at different currents. The brake was analyzed by the SMA squeezing pressure test platform and the braking performance test platform. The results show that the electromagnetic torque grows non-linearly with temperature, and the squeezing force generated by the SMA spring increases with temperature. When the current is 0.7 A, the braking torque generated by electromagnetism is 170.3 N m, while the maximum braking torque generated by the combination of electromagnetism and SMA is 212.6 N m, which is 20.4% higher than that of the traditional electromagnetic friction brake. This novel brake improves braking performance and ensures stable braking performance under temperature rise.

СИСТЕМНИЙ ПІДХІД ДО ОЦІНЮВАННЯ ЕКСПЛУАТАЦІЙНИХ ЯКОСТЕЙ СІЛЬСЬКОГОСПОДАРСЬКИХ ТРАКТОРІВ

Purpose of the study. Formation of a methodology for systematic evaluation of performance in agricultural tractors. Research methods. The methodological basis for evaluating the performance of agricultural tractors is the OECD Code 2. Code 2 of the OECD standardizes test methods. Determination of traction indicators for tractors is carried out by the method regulated by the SOU L. Pogorslyy UkrNDIPVT 71.2-37-046043090-017:2015. A measuring and registration complex is used. When evaluating the functional accuracy of the tractor, according to DSTU 7463:2013, indicators are analyzed that determine the traction class of the tractor, energy capabilities and aggregation. An analytical method and a comparative analysis with the results of experimental studies are used to form a scientific problem, determine the purpose and set the objectives of the study. The results of the study. The research results develop a methodology for a systematic approach to assessing the operational quality of agricultural tractors. Direction of research to improve the technical, economic and agro technical properties. New dependencies are proposed (they use the method of partial accelerations) for estimating the traction and energy performance of the tractor, handling and driving stability, and braking properties. A technique for estimating the dynamic properties of a tractor as part of a tillage unit in an unsteady mode of its movement on the rut is substantiated. Code 2 of the OECD standardizes the testing methodology for agricultural tractors regarding the evaluation of their performance under nominal technical condition. The results of the studies that are given in the article prove that the deviations of real functional parameters from the nominal ones significantly affect the performance of the tractor. Conclusions. According to the results of the research carried out, the classification of the performance of agricultural tractors was carried out according to their traction and agro technical properties. The research results made it possible to formulate the main theoretical and scientific-practical conclusions. A methodology for a systematic approach to assessing the performance of agricultural tractors has been formulated, based on the substantiated method of partial accelerations. Using the method of partial accelerations, the dependences of the effective power of the engine, the efficiency of the tractor, the mass and resistance of the agricultural machine aggregated with the tractor, the braking properties of the tractor, its controllability and driving stability on the rut are substantiated. Analytically proved and experimentally confirmed the instability of the traction force of the tractor, the resistance of the agricultural machine of the tillage unit, the dynamic performance of which exceeds the average values by 2.5-3.0 times. Keywords: tractor, system approach, operational properties, traction properties, controllability, braking properties.

МЕТОДИКА ВИПРОБУВАНЬ ЩОДО ОЦІНЮВАННЯ ЕКСПЛУАТАЦІЙНИХ ЯКОСТЕЙ СІЛЬСЬКОГОСПОДАРСЬКИХ ТРАКТОРІВ ЗА КОДЕКСОМ 2 ОЕСР

Purpose of the study is new provisions for testing agricultural tractors, evaluating their performance, which implement the OECD Code 2 Research methods. The testing of the tractor and its main elements is based on the method of partial accelerations, the basis of which is the solution of the inverse task of the dynamics: the acting forces are estimated from the acceleration. The method and means of measurement (developed in the L. Pogorilyy UkrNDIPVT Kharkiv branch) are effectively used in testing tractors and its main elements. The results of the study. The proposed express methods make it possible to reduce the time for testing and timely identify shortcomings in the operation of the systems being tested. The proposed express test method for the cylinder-piston group provides the ability to timely identify shortcomings in the operation of engines. It has been established that the most efficient operation of the tested unit is when the tractor is not fully loaded. The stability of the movement of the transport-technological unit is interconnected with its controllability, which is determined by the technical condition of the steering. The relationship between the investigated values of the angular accelerations of the steering wheel of the tractor and the aggregated machine is provided with a reliability of 95 %. To determine the braking properties, an indicator is proposed that characterizes the growth rate of the tractor deceleration during braking. To evaluate the quality of functioning of the hydraulic drive of the tractor mounted system in the case of unstable technical condition of its elements, it is necessary to start with the evaluation of the fluid flow in the hydraulic cylinder and end with the analysis of the flow in the bypass valve. Conclusions. Code 2 of the OECD normalizes the methodology for operational testing of agricultural tractors, on the basis of which in L. Pogorilyy UkrNDIPVT Kharkiv branch developed industry standards for assessing the traction and energy performance of tractors. It has been theoretically and experimentally proved that in the performance tests of tractors and its main elements, the method of partial accelerations is effective, which is based on the reverse transition from the vector sum in the space of forces that act on the tractor to the vector sum in the space of accelerations. This method allows you quickly assess the performance of tractors when coupled with mounted and trailed agricultural machines, as well as the technical condition of the main elements of the tractor design. Keywords: tractor, tests, OECD Code 2, main elements, malfunctions, express methods

Оцінка впливу стабільності характеристик гальмівних механізмів на процес гальмування транспортних засобів

The purpose of the article is to evaluate the influence of the stability of the characteristics of brake mechanisms on the process of braking of passenger vehicles. In the article, using the example of a mixed braking system of a passenger vehicle of segment C, an assessment was made of the influence of the stability of the characteristics of its braking mechanisms on the braking process. The results obtained allow us to conclude that with "cold" and "cooled" brake mechanisms of the vehicle, the values of the mathematical expectation of the friction coefficient and the dispersion of its values are approximately the same. The performed calculation shows that when the friction coefficient changes by 8-20%, the braking torque changes by 20-30%. In this case, the difference between the largest and smallest braking torque can be 50%. Given that the left and right brake mechanisms (due to various reasons) may have different coefficients of friction of the friction surfaces, then the unevenness of the braking forces on the rear axle of the vehicle under consideration can be up to 50%. In order to prevent advanced blocking of the rear wheels during vehicle braking in the event that the actual coefficient of distribution of braking forces between the axles deviates from the calculated value due to the instability of the brake mechanisms, it is necessary to ensure the fulfillment of the condition according to the dependence given in the work. The results obtained can be used in the design of braking systems and the assessment of the braking properties of vehicles, as well as in the examination of road accidents.The instability of the braking torques on the wheels does not have a significant effect on the reduction of the total braking force (braking efficiency) in the presence of amplifiers in the drive, but it significantly affects the stability of the vehicle during braking, since it causes a significant change in the coefficient of distribution of braking forces between the axles and the appearance of their onboard unevenness. The statistical analysis of the coefficients of friction of friction pairs (on the example of a passenger vehicle of segment C) showed their wide spread, which significantly affects the onboard and axial unevenness of the braking forces; for example, for friction linings DTM, the average difference between the friction coefficients on the left and right wheels is 0.17, and the standard deviation is ± 0.08. The difference in the coefficients of friction of friction pairs of different types of brake mechanisms, due to the use of friction linings from different manufacturers, can lead to a change in the coefficient of distribution of brake forces over a wide range.

Оптимізація інерційної маси гальмівного роликового стенда

The article deals with the issues of modeling conditions for obtaining diagnostic information when checking the braking properties of cars on a roller stand.As many studies show, roller stands of inertial type provide the most reliable information about the technical condition of the car. This concern, first of all, the parameters that determine the accuracy of simulation on the stand of real speed and thermal conditions. The accuracy of diagnosing the brake system of a car on an inertial test bench depends on many factors. One of the determining factors is the value of the reduced masses of rotating elements in the "car-stand" system: rollers, wheels and car transmission parts. The main design parameter of the inertial roller stand is the diameter of the roller. The reduced mass of the transmission can be determined by measuring the moments of inertia of its individual parts and bringing them to a given axis. But this is a laborious process and takes a lot of time. At the same time, the reduced mass of the transmission is also variable due to the wear of parts. Therefore, methods are required to determine the reduced mass of the transmission of a particular vehicle, regardless of the degree of wear of parts.To determine the reduced mass of the transmission, two modes of acceleration of the car on the stand are used: acceleration from the drive of the stand, while two wheels of the car rotate; acceleration from the stand drive, in which one wheel of the car rotates. The analysis of these modes is made and the equations for determination of the reduced mass of transmission are made.The analysis of changes in the moments of inertia of the wheel and rotating parts of the car, as well as the radius of the wheel is carried out. Based on this, the general variation of the reduced mass of the wheel and associated rotating parts of the vehicle is presented. This variation can have a significant impact on the accuracy of diagnosis. The optimal way to compensate for this uncertainty may be to increase the reduced mass of the stand so that the proportion of the reduced mass of the wheel and the associated rotating parts of the car is a small part and introduces an error no more than acceptable.

CONSTRUCTION OF FRICTION FEATURES OF FRICTION MOVEMENTS OF BRAKE MECHANISMS IN THE VIEW OF THIRD-ORDER POLYNOMIAL MODELS

The concepts of frictional characteristic of the brake mechanism and frictional characteristic of the friction pair of the brake mechanism, which are necessary for the calculation of the real braking properties of vehicles, are considered. An experimental device has been developed to determine the influence of such destabilizing factors as temperature, sliding speed and contact pressure on the mentioned characteristics. A method for obtaining polynomial models of the third order to determine the effect of temperature, sliding speed and contact pressure on the coefficient of friction in the friction pairs of brake mechanisms is proposed. The technique is suitable for cases when the second-order models inadequately describe the effect of these destabilizing factors on the coefficient of friction in the friction pairs of brake mechanisms.

ENSURING THE SAFETY OF ROAD ACCIDENTS

There is an analysis of the mechanism of accidents and it shows that improving road conditions and improving the speed and braking properties of the car, stability and controllability does not increase the active safety of road traffic. These measures only move the boundaries within which the driver can drive safely. The parameters of quality of car operation, which characterize the traffic safety, have been determined. The values of car operation quality parameters that correspond to different levels of traffic safety have been defined. In order that the proposed parameters of quality of car operation can be used to control the safety of traffic modes by drivers and traffic police, the computer must be used to calculate these parameters as a standard residual of the car. The studies carried out made it possible to single out three indicators of the quality of driving a car, which characterize the safety of the driving mode: maximum speed is the ratio of the average speed to the maximum, called the speed coefficient, the standart deviation of the vehicle's longitudinal acceleration from the average value, which is called acceleration noise in the theory of traffic flows. The above indicators of the quality of driving are measured from the moment of the start of the trip.

Comparison of braking properties of selected vehicle with different methods

The aim of this article was to perform a practical measurement of the braking properties of a selected Škoda Yeti vehicle on a wet and dry asphalt road and then evaluate and compare the measured data using a decelerograph and a mobile application mSTK. It is a new application for measuring driving dynamics, which was developed for the needs of technical inspection stations in Slovakia. The subject was the intensive braking of a Škoda Yeti passenger car with a fully compressed service brake from different velocities and on different surfaces. A total of 18 measurements were performed, of which 9 on the dry and 9 on the wet surface. This is a new alternative method for recording vehicle driving dynamics. The developed application in conjunction with modern smartphones can thus compete with the current decelographer, both in terms of technical parameters, measurement accuracy (total average deviation 2.11%) and ease of use. The results and data processed in this way are presented in the final part of the paper.

Investigation of functional characteristics of composites used for brake pads

The friction material used for the brake pads should have a low wear rate, outstanding thermal stability to hold the braking properties of the vehicle and coefficient of friction should constant under different operating conditions which include loads which applied, temperature, dry or wet braking environment and speed. Due to this reason, every newly developed friction material’s fabrication should undergo a series of experimental tests to evaluate the friction as well as wear properties. In this article a study of frictional and wear behavior of friction material for ecological brake pads of road vehicles discussed. In the formulation of the friction material shells as a filler, a small amount of metal, silicon carbide, graphite, resin and hexametiltetramine were used. The main objective of the paper refers to the investigation of the impact of the working regime on friction material’s tribological characteristics. In this sense, were studied the evolution of the coefficient of friction and the thermal field at the contact surface between the friction couplings, the influence of load on the friction coefficient at different speeds and the influence of load on wear rate at a constant speed. The knowledge of the functional properties of the newly developed friction material produced in the laboratory provides the possibility of pertinent assessments regarding the durability of the brake pads during operations, as well as on the quantity of wear products released into the atmosphere. The results concluded that as a filler material this species of shells may be used in the fabrication of brake pads for road vehicles.

ИССЛЕДОВАНИЕ ТОРМОЗНЫХ СВОЙСТВ КОЛЕСНОГО ФОРВАРДЕРА 8×8

The operating conditions of wheeled forwarders have been considered. The requirements for the efficiency of the braking system are described, as well as methods for testing the working and parking braking systems of wheeled forestry machines when operating on ups and downs of up to 50%. The most severe brake loading situations in terms of keeping the forwarder on a slope have been shown. A calculation scheme for determining the loads in the contact patch during the descent of a wheeled forwarder has been drawn up. The initial data necessary for calculating the braking system of the machine have been given. The results of calculations of reactions when the forwarder is located on a horizontal support surface and the calculation of reactions in the contact patch of the wheel during descent and ascent are given. The technical parameters of the braking system of the NAF TAP 7601 balancer axles used on the developed machine have been presented. The results of calculations of the braking properties of the forwarder in running order and at full weight on the descent (characterized by the parameters α = 40% and α = 50%, as well as on the ascent α = -50%) have been presented. The results of calculations of the required braking torque on the wheels of the machine, the maximum-realized braking torque for the adhesion of all wheels of the front and rear axles of the machine have been presented. The safety factor of braking mechanisms and the safety factor for adhesion have been given

The influence of the longitudinal dynamics of a passenger car on its braking properties

The influence of the longitudinal dynamics of a passenger car on its braking properties

ПОИСК РАЦИОНАЛЬНЫХ ТЕХНИЧЕСКИХ РЕШЕНИЙ ТЕПЛОВОЗА ДЛЯ ВОСТОЧНОГО ПОЛИГОНА

The purpose of the study is to search for rational engineering solutions for the main autonomous locomotive for the Eastern range of OAO Russian Railways.
 Research methods: methods of physical and field experiments, analytical methods for calculating the dynamics of the rolling stock. 
 Research results and novelty: it is established that the use of a four-axle truck of a diesel locomotive TEM7 does not allow to create a locomotive that meets all the requirements of OAO Russian Railways, and the design of truck TEM7 is irrational for mainline locomotives; it is proved that the one-sided arrangement of brake blocks leads to deterioration in the locomotive braking properties. The bearing and axial towline, despite the use of an asynchronous engine, has an unsprung mass 1.5 times greater than that of the previously produced domestic analogue with a collector engine and almost the same mass of the wheel-motor unit; dynamic moments in the drive due to the lack of elastic elements during prolonged operation can reach 56% of the traction torque, which worsens the traction properties of the locomotive. 
 Conclusion: it is advisable to carry out a design study of the drive variant with a support-frame asynchronous traction engine and an axial gearbox, as well as to conduct a technical and economic analysis and design study of a cheaper version of a diesel locomotive with sections on three two-axle bogies, maximally unified with electric locomotives, with a booster tanker module and AC-DC transmission with axial regulation of eight-pole collector motors with support-frame suspension.

ON THE QUESTION OF BRAKING ARTICULATED BUSES

The safe movement of a car and a road train is largely determined by its braking properties. The nature of the movement of the road train is fundamentally different from the movement of a single car. The difference can be explained by the presence of additional forces arising in the articulation of the links of the vehicle, as well as forces and moments acting on its individual links and the movement of the vehicle as a whole. Their effect is especially noticeable when braking a road train, which may be accompanied by folding links and loss of stability of the vehicle. As a result of the study, the optimal values of the brake force distribution coefficients for a fully loaded articulated bus are obtained, which provide both high braking efficiency and the stability of the articulated bus (AВ) during braking. The coefficients are determined taking into account the design features of the brake mechanisms and their geometric dimensions, providing the required braking performance. For the selected values of the braking force distribution coefficients along the axes of the AВ and the coefficients that take into account the design features of the braking mechanisms and their geometric dimensions, the braking distance during braking by the main or working braking system and the spare one satisfy the requirements of regulatory documents. With the selected asynchronous response of the brake drives of the bus and trailer, the steady deceleration of the АВ is slightly less than the standard.

INFLUENCE OF VEHICLE SUSPENSION PARAMETERS ON ITS BRAKING PROPERTIES

The paper focuses on the study of the performance of elastic and damping parameters of the car suspension. The problem of arising vibrations of the sprung and unsprung vehicle masses on the braking process is considered. The article presents theoretical models of vehicle braking taking into account the oscillations of the vehicle's sprung masses. The research results will make it possible to establish the relationship between the suspension parameters and the estimated parameters of braking properties, to supplement the "driver - car - road" system, and also to more accurately assess the active safety of vehicles associated with braking dynamics.

In-depth analysis of the results of an experimental study of the braking properties of a KAMAZ-740 engine with an engine brake under electronic control

As a result of an in-depth analysis, the dependences of the braking torque of a KAMAZ-740 diesel engine on the engine braking time were obtained in an analytical form, from which it was established that the initial braking torque when braking by an engine with an engine brake is 2 times higher than the initial braking torque when braking by an engine without an engine brake. But the braking torque when braking with an engine with an engine brake quickly decreases several times over time. This reduces the effectiveness of its use for service braking, therefore, to improve the engine brake, it is necessary to stabilize its braking torque due to the electronic control system. Keywords: analysis, engine braking properties, experimental research, electronic control

Graphene modified high-temperature resistant adhesive for bonding carbon/carbon composites: Microstructure characterization and properties study

Abstract A novel graphene modified high-temperature resistant adhesive for bonding carbon/carbon composites was developed. The effects of graphene content on the mechanical properties, thermal conductivities and braking properties of the carbon/carbon joints were studied. When the graphene content in the adhesive was 1.5 wt%, the specimens possessed the bonding strength of 13.2 MPa and the thermal conductivity of 23.89 W/(m•k), which were 63.09% and 145.03% higher than those of 0.0 wt%, respectively, and 24.38% and 64.53% higher than those of 5.0 wt%, respectively. The excellent properties were attributed to the uniform dispersion of graphene in the adhesive matrix, which could effectively reduce the stress concentration and provide a fast heat conductivity network chain. The adhesive properties also had an obvious influence on the braking performance. Finite element analysis considered that the main reason for the difference in braking performance was that the temperature and field distribution on the friction surface were affected by the thermal conductivity of the adhesive.