Braking Speed Research Articles

Identifying the impact of the COVID-19 pandemic on driving behavior using naturalistic driving data and time series forecasting

Introduction: COVID-19 has disrupted daily life and societal flow globally since December 2019; it introduced measures such as lockdown and suspension of all non-essential movements. As a result, driving activity was also significantly affected. Still, to-date, a quantitative assessment of the effect of COVID-19 on driving behavior during the lockdown is yet to be provided. This gap forms the motivation for this paper, which aims at comparing observed values concerning three indicators (average speed, speeding, and harsh braking), with forecasts based on their corresponding observations before the lockdown in Greece. Method: Time series of the three indicators were extracted using a specially developed smartphone application and transmitted to a back-end platform between 01/01/2020 and 09/05/2020, a time period containing normal operations, COVID-19 spreading, and the full lockdown period in Greece. Based on the collected data, XGBoost was employed to identify the most influential COVID-19 indicators, and Seasonal AutoRegressive Integrated Moving Average (SARIMA) models were developed for obtaining forecasts on driving behavior. Results: Results revealed the intensity of the impact of COVID-19 on driving, especially on average speed, speeding, and harsh braking per 100 km. More specifically, speeds were found to increase by 2.27 km/h on average compared to the forecasted evolution, while harsh braking/100 km increased to almost 1.51 on average. On the bright side, road crashes in Greece were reduced by 49% during the months of COVID-19 compared to the non-COVID-19 period.

KLASSİK QAZMA BUCURQADLARININ ƏYLƏC SİSTEMLƏRİNİN TƏHLİLİ

The lowering and lifting of the drill strings during drilling is carried out using winches. One of the main elements of the winches is the braking system. The braking system of the drawworks is designed for: keeping the drill string suspended; power absorption during the descent of the string to the length of one candle with the highest permissible speed and complete braking at the end of the descent; smooth feed of the drill string as the well deepens while drilling. Braking devices used in drilling machines and mechanisms are divided into main and auxiliary ones according to their purpose.The main ones are designed to stop machines and mechanisms and are activated at the end of the movement with long interruptions in work, while auxiliary ones are for long-term braking in order to reduce the speed of movement. The brakes of classic drill bits consist of a main working belt-molded brake, as well as an auxiliary brake consisting of electromagnetic or hydrodynamic brakes. Key words: belt-molded brake, hydrodynamic brake, electromagnetic brake, electromagnetic ferro-dust brakes

Experimental evaluation of braking pad materials used for high-speed elevator

In this paper, an elevator safety gear braking testing rig was developed based on the disc-pad braking model in principles of energy equivalent and speed equivalent to evaluate the braking behavior of short carbon fiber (SCF) reinforced carbon/carbon (C/C) composite and Cu-based powder metallurgy (P/M) material. Note that the braking pressure and the initial braking speed were controlled between 10 MPa to 56 MPa and 3 m/s to 25 m/s respectively in the experiment, which covers the real braking conditions in high-speed elevator. Then friction behaviors of both braking materials were investigated. Especially, the dependence of the coefficient of friction (COF) on the braking pressure and initial braking speed were minutely studied. Interestingly, it was found the COFs increased with the initial braking speed, but decreased with the improved braking pressure. Besides, wear behaviors under different braking conditions for both materials were explored. Results showed the C/C composite pads were crushed at high initial braking speed (V ≧ 14 m/s) in this experiment, but the Cu-based P/M material could suffer higher initial braking speed, which suggested the Cu-based P/M material had more potential to be used as the braking material applied in high-speed elevator or even ultra-high speed elevator compared to C/C composite adopted in this paper.

Experimental study on braking and stability performance during low speed braking with ABS under critical road conditions

During braking with ABS (Anti-Lock Brake System), low braking initial speed causes to build-up and reduce brake pressure in longer time period due to extending application time of brake pressure and response time of solenoid valve. Also, the decision about speed and acceleration variations of wheel becomes very difficult due to weak speed signals arising from low speed. This results in lower braking torque than needed on the wheels. Therefore, effects of weak wheel speed signal become more pronounced in critical road conditions due to sudden changes in wheel speed. In this study, the effects of these problems occurring in low speed were investigated on both control and braking performance of ABS under critical road conditions. For this, ABS tests were carried out for low and high speeds on four different road types, which include slippery, wet and µ-jump tests (from wet to slippery and from slippery to wet). In this way, the results were compared to both vehicle speed and road type. The test results show that the low speed worsens braking stability, control and braking performance of ABS, regardless of road conditions. For this reason, it is proposed that ABS control algorithm must be divided in two parts as low and high speed control.

Calculation of the dependence of friction coefficient of locomotive composite ridge brake shoes on pressing force and braking speed

JSC “FRITEX” has developed non-asbestos ridge composite brake shoes UR 01-01 with a reduced coefficient of friction, which, in contrast to the cast iron ridge brake shoes currently used on locomotives, have high wear resistance and more stable frictional properties at high speeds. They are much lighter than traditional cast iron shoes, resulting in lower logistics costs and easier replacement by service departments. However, the new materials used for the production of the shoe, as well as its innovative design, which combines the two types of materials, require a detailed study of its frictional properties. For this, the braking modes of a locomotive equipped with UR 01-01 shoes were simulated in a full-scale unit of a brake mechanism on an inertial stand at fixed pressures and speeds. Based on the results of the experiments, the values of the friction coefficients of the brake shoes were determined and the dependence of the friction coefficient of the shoes on the pressing force and braking speed was established. The data obtained were used in braking calculations for an electric locomotive of the VL80 series, including the determination of the braking distance, holding a single locomotive by the parking brake on a slope, and ensuring the antiskid braking due to higher values of the friction coefficient of the UR 01-01 shoe at high speeds. The composite ridge brake shoe ensures compliance with the standard values of the braking distance, antiskid braking and slope parking for the VL80 series electric locomotive. In this case, the use of these composite shoes is possible without changes in the device of the lever transmission of the electric locomotive. It is necessary to conduct running brake tests to make approbation of obtained empirical dependence of the friction coefficient of new shoes on the pressing force and the braking speed of the locomotive and its widespread use in the calculation of brake systems.

Microstructure and tribological properties of PIP-SiC modified C/C–SiC brake materials

A combination method of precursor infiltration and pyrolysis (PIP), chemical vapor infiltration (CVI) and liquid silicon infiltration (LSI) was proposed to prepare PIP-SiC modified C/C–SiC brake materials. The SiC ceramic matrix pyrolyzed by polymethysilane (PMS) homogeneously dispersed in the fiber bundles region, which improved the plough resistance of local C/C region and the wear resistance of C/C–SiC brake materials. When the braking speed rises to 28 m/s, the fluctuation range of friction coefficient was limited to 0.026. The linear wear rate of the as-prepared composites was could be ~50% less than that of C/C–SiC, when the braking speed was above 15 m/s (for instance, the wear rate of 1.02 μm/(side·cycle) at 28 m/s less than 2.02 μm/(side·cycle) of traditional C/C– SiC). The fading ratio D of CoF under wet conditions was ~11%. The results showed that introducing PIP-SiC could stabilize the braking process and effectively prolong the service life of C/C–SiC brake materials.

Implications of sample size and acquired number of steps to investigate running biomechanics

Low reproducibility and non-optimal sample sizes are current concerns in scientific research, especially within human movement studies. Therefore, this study aimed to examine the implications of different sample sizes and number of steps on data variability and statistical outcomes from kinematic and kinetics running biomechanical variables. Forty-four participants ran overground using their preferred technique (normal) and minimizing the contact sound volume (silent). Running speed, peak vertical, braking forces, and vertical average loading rate were extracted from > 40 steps/runner. Data stability was computed using a sequential estimation technique. Statistical outcomes (p values and effect sizes) from the comparison normal vs silent running were extracted from 100,000 random samples, using various combinations of sample size (from 10 to 40 runners) and number of steps (from 5 to 40 steps). The results showed that only 35% of the study sample could reach average stability using up to 10 steps across all biomechanical variables. The loading rate was consistently significantly lower during silent running compared to normal running, with large effect sizes across all combinations. However, variables presenting small or medium effect sizes (running speed and peak braking force), required > 20 runners to reach significant differences. Therefore, varying sample sizes and number of steps are shown to influence the normal vs silent running statistical outcomes in a variable-dependent manner. Based on our results, we recommend that studies involving analysis of traditional running biomechanical variables use a minimum of 25 participants and 25 steps from each participant to provide appropriate data stability and statistical power.

Mathematical model for studying the braking distance of a car equipped with ABS in winter conditions

The article aims to develop a mathematical model for analytical studies of the braking process of a car equipped with an anti-lock braking system in order to identify the relationship between the stopping and braking distances of a car and pedestrian visibility in dark winter conditions, when headlights are contaminated with anti-icing materials. The mathematical model of the braking process of a car equipped with ABS was analyzed. Experimental studies of the braking process of a car with running and disabled ABSs were carried out on winter roads. The experimental studies of headlight contamination with chemical anti-icing materials (CAIM) and changes in luminous intensity were carried out in real road conditions in winter. The results are presented in the article. The results of the experimental studies of pedestrian visibility in dark conditions with contaminated headlights are presented. The adequacy of the mathematical model of the braking distance of a car with running and disabled ABSs in winter conditions was assessed. The trends characterizing the effect of headlight contamination on the pedestrian visibility in dark winter conditions are described. The results of the study are presented in tables, diagrams and equations. The values of the stopping distance were determined at different initial braking speed rates. The visibility distance for a car with contaminated headlights was determined in dark winter conditions.

The wet braking and recovery behaviors of the P/M pad mated with C/C–SiC disc for high-speed trains

C/C–SiC ceramic is a promising braking material in high-speed trains. The research on wet braking is necessary for its application. In this paper, braking tests of C/C–SiC disc mated with powder metallic (P/M) pads were conducted under dry, wet and recovery braking conditions at initial braking speed (IBS) of 14, 22, 33, 44, 55 m/s. Coefficient of friction (COF) and surface morphologies under different conditions were discussed: The instantaneous COF under wet condition was lower but the instantaneous COF curves became smoother than those under dry condition. The difference between two conditions went smaller as IBS increased. Under recovery condition, it cost 33 stops at 14 m/s to recover to 93.1% of the origin COF. Meanwhile, 8 stops were needed at 55 m/s, and the recovery rate was 98.9%. When the IBS increased, the number of the stop needed was fewer and the recovery rate was higher. The surface morphologies further showed the braking under wet condition resulted in a smoother surface with less ploughing grooves and the disappearance of the friction film. Under the recovery condition, the surface became rough again with grooves and the friction film formed again. The results indicate that the wear debris were washed away by the sprayed water and the formation of friction film was inhibited. In addition, water film subsequently lubricated the friction surface, which reduced COF at low IBS. As IBS increased, high temperature accelerated the dewatering and evaporation of water and thus lead to the decrement of the COF difference between wet and dry friction which, in turn accelerated the recovery process.

Design of adaptive sliding mode controller for ant-lock braking system using eddy current

When vehicle speed increases, stable and powerful brake system is required to ensure the safety of the vehicle and passengers. For high speed braking of vehicle, contactless eddy current brake (ECB) is developed and applied to antilock brake system (ABS). An adaptive sliding mode controller for ABS using eddy current is presented with a sliding mode observer (SMO). Using vehicle acceleration, wheel speeds, and braking torque, the vehicle velocity estimated by SMO. To control the system based on wheel slip, half-car model is developed by considering uncertainty of the road slope and aerodynamic drag force. According to the controller, the vehicle ABS model is built with MATLAB Simulink. The response of controller is compared in terms of braking time and stopping distance. The results indicate proposed controller algorithm achieves minimum braking time and minimum stopping distance on selected roads.

Design of adaptive sliding mode controller for ant-lock braking system using eddy current

When vehicle speed increases, stable and powerful brake system is required to ensure the safety of the vehicle and passengers. For high speed braking of vehicle, contactless eddy current brake (ECB) is developed and applied to antilock brake system (ABS). An adaptive sliding mode controller for ABS using eddy current is presented with a sliding mode observer (SMO). Using vehicle acceleration, wheel speeds, and braking torque, the vehicle velocity estimated by SMO. To control the system based on wheel slip, half-car model is developed by considering uncertainty of the road slope and aerodynamic drag force. According to the controller, the vehicle ABS model is built with MATLAB Simulink. The response of controller is compared in terms of braking time and stopping distance. The results indicate proposed controller algorithm achieves minimum braking time and minimum stopping distance on selected roads.

Estimation of Constant Speed Time for Railway Vehicles by Stochastic Gradient Descent Algorithm

While the investments in rail transportation systems continue without slowing down, various optimization issues come to the fore in order for the systems to work more efficiently. One of the most important of these issues is the optimization of the vehicle speed profile. Improvement in vehicle speed profile increases efficiency in operating traffic. Vehicle speed profile varies depending on the electrical-characteristic features of the vehicle, the distance between the stations and the line geometry. The vehicle's speed profile consists of several parts, such as acceleration, constant speed travel and braking zones. The constant speed in the constant velocity zone refers to the max operating speed, which is recommended for operation in the restricted area and remains within the limits. This part is critical in creating the speed profile of the vehicle. In this study, the estimation of the value of the constant speed time in the speed profile of the vehicles used in the city metro systems was made by using the Stochastic Gradient Descent method, which is one of the machine learning methods, and compared with various well-known methods. Coefficient of determination (R2) values were calculated as 0.9955 and 0.9951, respectively, with random sampling hold out and cross validation methods.

A fuzzy sliding mode control of anti-lock system featured by magnetorheological brakes: performance evaluation via the hardware-in-the-loop simulation

The aim of this work is to propose a new type of anti-lock braking system (ABS) using a magneto-rheological (MR) brake and validate its effectiveness by implementing a fuzzy logic sliding mode (FLSM) controller via the hardware-in-the-loop-simulation (HILS). Firstly, a quarter vehicle model integrated with the tire model is established to analyze control performance of MR brake during the braking process under different road conditions. Secondly, a disc type MR brake is designed on the basis of a mathematical model and the field-dependent braking torque is measured. Subsequently, in order to investigate the control performance of the proposed ABS, the software model is combined with the hardware configuration which is built by Matlab/Simulink. It is shown via HILS that the proposed ABS associated with the FLSM controller can provide high response speed and excellent braking control effect. In this work, control responses from the FLSM controller are also compared with those achieved from the conventional sliding mode controller in order to emphasize the significance of the control strategy to enhance ABS performances.

Role of titanium carbide and alumina on the friction increment for Cu-based metallic brake pads under different initial braking speeds

To understand the effect of abrasives on increasing friction in Cu-based metallic pads under different braking speeds, pad materials with two typical abrasives, titanium carbide (TiC) and alumina (Al2O3), were produced and tested using a scale dynamometer under various initial braking speeds (IBS). The results showed that at IBS lower than 250 km/h, both TiC and Al2O3 particles acted as hard points and exhibited similar friction-increasing behavior, where the increase in friction was not only enhanced as IBS increased, but also enhanced by increasing the volume fraction of the abrasives. However, at higher IBS, the friction increase was limited by the bonding behavior between the matrix and abrasives. Under these conditions, the composite containing TiC showed a better friction-increasing effect and wear resistance than the composite containing Al2O3 because of its superior particle-matrix bonding and coefficient of thermal expansion (CTE) compatibility. Because of the poor interface bonding between the matrix and Al2O3, a transition phenomenon exists in the Al2O3-reinforced composite, in which the friction-increasing effect diminished when IBS exceeded a certain value.

Evaluation of Alternative Messages and Sign Locations on Driver Response to a Dynamic Speed Feedback Sign on a Freeway Interchange Ramp

Research was undertaken to determine effective messaging strategies and sign positions for dynamic speed feedback signs (DSFS) when used for speed management at freeway ramp curves. A field evaluation was performed in this setting to assess the impacts of a DSFS on driver speed selection and braking characteristics while approaching and entering the curve. Three feedback messaging strategies were evaluated at three sign positions in advance of the curve. Compared with the existing site (without the DSFS), the DSFS reduced curve entry speeds and improved brake response across all test conditions, particularly for heavy trucks. Overall, considering the combination of both sign position and feedback messaging strategy, the greatest benefits to driver behavior were attained when the DSFS was positioned 255 ft upstream of the curve and the feedback message included the speed number alternating with a SLOW DOWN message. The inclusion of an advisory speed panel with the DSFS did not have a substantive impact on driver behavior. Based on the findings, the continued use of DSFS as a speed reduction treatment at freeway ramp curves is recommended. Specifically, the sign should be positioned to provide adequate time for drivers to perceive and react to the message, such that comfortable braking can be accommodated while approaching the curve. However, the sign should not be placed too far in advance of the curve, as drivers may be more likely to disregard such a premature warning message. Further evaluation of DSFS under various alternative ramp configurations is recommended.

Обґрунтування параметрів хибних теплових цілей для захисту літальних апаратів від керованих ракет з інфрачервоним самонаведенням

Стаття присвячена обґрунтуванню вимог до сучасних хибних теплових цілей для захисту літальних апаратів від керованих ракет з інфрачервоним самонаведенням. Так, для імітування просторових, енергетичних та траєкторних ознак повітряної цілі відстрілювання хибних теплових цілей виконується у вигляді комбінованих залпів, у яких хибні теплові цілі мають різну потужність інфрачервоного випромінювання, різні коефіцієнти лобового опору, завдяки чому швидкість гальмування зустрічним повітряним потоком у них різна, а часові інтервали відстрілювання окремих хибних теплових цілей у залпі підбираються таким чином, щоб амплітудні, спектральні та траєкторні селектори сучасних інфрачервоних головок самонаведення не змогли однозначно виконати селекцію. Підтверджено, що однією з основних характеристик хибних теплових цілей, яка визначає її ефективне застосування для захисту літальних апаратів від керованих ракет з інфрачервоним самонаведенням, є максимальна або пікова сила випромінювання у заданому діапазоні довжин хвиль. Також в статті розглянуто один з нових способів застосування хибних теплових цілей та вимоги до них. Зокрема, обґрунтовані вимоги до закону зміни інфрачервоного випромінювання у часі, необхідної сили інфрачервоного випромінювання, часу виходу на режим та досягнення ефективного рівня випромінювання, а також повного часу випромінювання.

Research on the Temperature Law of Brake Disc Based on Friction

The temperature characteristics of the brake disc will affect the material properties and stress characteristics and affect the safe operation of the train. In order to study the temperature distribution of the brake disc during the operation, a three-dimensional finite element contact model of the brake disc and the brake pad was established by software ABAQUS, applying the initial braking speed of 80 km/h. By analyzing the simulation results, it is found that in the process of the braking, the friction between the brake pad and the brake disc surface causes the temperature rising and forms a high-temperature zone in the middle of the brake disc surface. The temperature of the node belonging to the high temperature zone on the brake disc surface increases first and then decreases. The temperature of the brake disc along the axial direction decreases, and the temperature of the back of the disc increases continuously during the braking process.

Tribo-Brake Characteristics between Brake Disc and Brake Shoe during Emergency Braking of Deep Coal Mine Hoist with the High Speed and Heavy Load

The friction wear and thermal fatigue cracking of the brake shoe and friction-induced self-excited vibration (frictional flutter) of the disc brake can easily occur during emergency braking of a deep coal mine hoist with at high speed and with a heavy load. Therefore, tribo-brake characteristics between the brake disc and brake shoe during emergency braking of a deep coal mine hoist are investigated in the present study. Scaled parameters of the disc brake of a deep coal mine hoist are determined by employing the similarity principle. Friction tests between friction disc and brake shoe are carried out to obtain the coefficient of friction in the case of high speed and large specific pressure between the friction disc and brake shoe. Coupled thermo-mechanical finite element analyses of the brake disc and brake shoe are established to investigate temperature and stress fields of the brake disc and brake shoe during emergency braking, which is validated by the engineering failure case. Effects of braking parameters on flutter characteristics between the brake disc and brake shoe are explored by employing a double-degrees-of-freedom vibration mechanism model. The results show that the maximum temperature, equivalent Von Mises stress and contact pressure are all located at the average friction radii of contact surfaces of the brake disc and brake shoe during emergency braking. The cage crashing accident in the case of high speed and heavy load in a typical coal mine shows crack marks and discontinuous burn marks at central locations of brake shoe and brake disc surfaces, respectively, which indicates frictional flutter characteristics between brake disc and brake shoe. During emergency braking, flutter time duration decreases with increasing initial braking speed and damping parameter; the flutter amplitude and frequency of the disc brake increases with increasing normal braking load and stiffness, respectively.

On-orbit modal identification for vibration suppression of flexible aerospace structure using reaction wheel actuator

Flexible aerospace structure presents dynamic characteristics of low natural frequency and slow amplitude attenuation. Attitude adjustment or orbital maneuver for the spacecraft can excite the vibration of its flexible appendages/structures, which is prone to affect the normal operation of spacecraft. To address such problems, this paper introduces a feasible methodology by using reaction wheel (RA). The active feedback control strategy is established based on the relation of the measured bending moment and the wheel's rotating speed. The control law with a PD controller is adopted. The torque induced by the speed change of RA can be considered as an artificial damping to accelerate structural vibration attenuation. To guarantee the vibration suppression effectiveness and efficiency for engineering application, a modal identification approach using RA is proposed. The identification algorithm is designed by a vector fitting algorithm of rational polynomial combined with Fast Fourier Transform algorithm. The identified modal parameters are also utilized to design input shaper for the RA braking speed function, which is well verified to avoid undesired excitation. Both the numerical simulation and experimental research demonstrated the success of adopting reaction wheel as an actuator. For a full-scale solar array, the time required for vibration attenuation to the same amplitude is reduced from 602.8 sec to 162.4 sec.

Comparisons Between Braking Experiments and Longitudinal Train Dynamics Using Friction Coefficient and Braking Pressure Modeling in a Freight Train

Background: This paper describes the predictions and validation of the pneumatic emergency braking performance of a freight train consisting of a locomotive and 20 wagons, generally operated in Korea. It suggests the possibility of replacing the expensive and time-consuming train running tests with longitudinal train dynamic simulations. Methods: The simulation of longitudinal train dynamics of a freight train uses the time integration method of EN 14531. For reasonable simulation results, the characteristics of the train and brake equipment must be considered. For the train characteristics, specifications provided by the vehicle manufacturer are used. The braking characteristics are analyzed by friction coefficient tests and a braking pressure model. The friction coefficients of a locomotive and wagons are tested with a dynamo test bench and statistically expanded to account for variability. Freight trains should take into account the braking delay time. To reflect this in the simulation, the brake cylinder pressure pattern model uses pressures and exponential empirical equations measured at selective positions in a train of 50 vehicles. The simulation results are validated in comparison with those of the braking tests of a freight train consisting of 1 locomotive and 20 wagons. Results: The results of the longitudinal dynamics simulation show very similar results to the running test results based on the speed profile and braking distance. Conclusion: In particular, the statistical expansion method of the friction coefficient enables robust prediction of the distribution of the braking distance. The simulation can reduce or make up for costly and time-consuming repeated braking tests and reduce the risks that may arise during testing.