The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs.In this work,the thermal fatigue and wear of compacted graphite iron brake discs were investigat...The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs.In this work,the thermal fatigue and wear of compacted graphite iron brake discs were investigated,aiming to provide an experimental foundation for achieving a balance between their thermal and mechanical properties.Compacted graphite iron brake discs with different tensile strengths,macrohardnesses,specific heat capacities and thermal diffusion coefficients were produced by changing the proportion and strength of ferrite.The peak temperature,pressure load and friction coefficient of compacted graphite iron brake discs were analyzed through inertia friction tests.The morphology of thermal cracks and 3D profiles of the worn surfaces were also discussed.It is found that the thermal fatigue of compacted graphite iron discs is determined by their thermal properties.A compacted graphite iron with the highest specific heat capacity and thermal diffusion coefficient exhibits optimal thermal fatigue resistance.Oxidization of the matrix at low temperatures significantly weakens the function of alloy strengthening in hindering the propagation of thermal cracks.Despite the reduced hardness,increasing the ferrite proportion can mitigate wear loss resulting from low disc temperatures and the absence of abrasive wear.展开更多
Research into converting waste into viable eco-friendly products has gained global concern.Using natural fibres and pulverized metallic waste becomes necessary to reduce noxious environmental emissions due to indiscri...Research into converting waste into viable eco-friendly products has gained global concern.Using natural fibres and pulverized metallic waste becomes necessary to reduce noxious environmental emissions due to indiscriminately occupying the land.This study reviews the literature in the broad area of green composites in search of materials that can be used in automotive brake pads.Materials made by biocomposite,rather than fossil fuels,will be favoured.A database containing the tribo-mechanical performance of numerous potential components for the future green composite was established using the technical details of bio-polymers and natural reinforcements.The development of materials with diverse compositions and varying proportions is now conceivable,and these materials can be permanently connected in fully regulated processes.This explanation demonstrates that all of these variables affect friction coefficient,resistance to wear from friction and high temperatures,and the operating life of brake pads to varying degrees.In this study,renewable materials for the matrix and reinforcement are screened to determine which have sufficient strength,coefficient of friction,wear resistance properties,and reasonable costs,making them a feasible option for a green composite.The most significant,intriguing,and unusual materials used in manufacturing brake pads are gathered in this review,which also analyzes how they affect the tribological characteristics of the pads.展开更多
As the velocity of a train increases,the corresponding air pumping power consumption of the brake discs increases proportionally.In the present experimental study,a standard axle-mounted brake disc with circumferentia...As the velocity of a train increases,the corresponding air pumping power consumption of the brake discs increases proportionally.In the present experimental study,a standard axle-mounted brake disc with circumferential pillars was analyzed using a 1:1 scale model and a test rig in a wind tunnel.In particular,three upstream velocities were selected on the basis of earlier investigations of trains operating at 160,250,and 400 km/h,respectively.Moreover,3D steady computational fluid dynamics(CFD)simulations of the flow field were conducted to compare with the wind tunnel test outcomes.The results for a 3-car train at 180 km/h demonstrated:(1)good agreement between the air resistance torques obtained from the wind tunnel tests and the related numerical results,with differences ranging from 0.95%to 5.88%;(2)discrepancies ranging from 3.2 to 3.8 N·m;(3)cooling ribs contributing more than 60%of the air resistance torque;(4)the fast rotation of brake discs causing a significantly different flow field near the bogie area,resulting in 25 times more air pumping power loss than that obtained in the stationary brake-disc case.展开更多
A numerical program is built to simulate the performance of a spark ignited two-stroke free-piston engine coupled with a linear generator. The computational model combines a series of dynamic and thermodynamic equatio...A numerical program is built to simulate the performance of a spark ignited two-stroke free-piston engine coupled with a linear generator. The computational model combines a series of dynamic and thermodynamic equations that are solved simultaneously to predict the performances of the engines. The dynamic analysis performed consists of an evaluation of the frictional force and load force introduced by the generator. The thermodynamic analysis used a single zone model to describe the engine＇ s working cycle which includes intake, scavenging, compression, combustion and expansion, and to evaluate the effect of heat transfer based on the first law of thermodynamics and the ideal gas state equation. Because there is no crankshaft, a time based Wiebe equation was used to express the fraction of fuel burned in the combustion. The calculated results were validated by using the experimental data from another research group. The results indicate that the free-piston generator has some advantages over conventional engines.展开更多
A novel two-stroke boosted uniflow scavenged direct-injection gasoline (BUSDIG) engine has been proposed and designed in order to achieve aggressive engine downsizing and down-speeding for higher engine performance an...A novel two-stroke boosted uniflow scavenged direct-injection gasoline (BUSDIG) engine has been proposed and designed in order to achieve aggressive engine downsizing and down-speeding for higher engine performance and efficiency. In this paper, the design and development of the BUSDIG engine are outlined discussed and the key findings are summarized to highlight the progress of the development of the proposed two-stroke BUSDIG engine. In order to maximize the scavenging performance and produce sufficient in-cylinder flow motions for the fuel/air mixing process in the two-stroke BUSDIG engine, the engine bore/stroke ratio, intake scavenge port angles, and intake plenum design were optimized by three-dimensional (3D) computational fluid dynamics (CFD) simulations. The effects of the opening profiles of the scavenge ports and exhaust valves on controlling the scavenging process were also investigated. In order to achieve optimal in-cylinder fuel stratification, the mixture-formation processes by different injection strategies were studied by using CFD simulations with a calibrated Reitz–Diwakar breakup model. Based on the optimal design of the BUSDIG engine, one-dimensional (1D) engine simulations were performed in Ricardo WAVE. The results showed that a maximum brake thermal efficiency of 47.2% can be achieved for the two-stroke BUSDIG engine with lean combustion and water injection. A peak brake toque of 379 N·m and a peak brake power density of 112 kW·L^-1 were achieved at 1600 and 4000 r·min^-1, respectively, in the BUSDIG engine with the stoichiometric condition.展开更多
Air brake systems are critical equipment for railway trains, which affects the running safety of the trains significantly. To study air braking characteristics of long freight trains, an approach for simulating air br...Air brake systems are critical equipment for railway trains, which affects the running safety of the trains significantly. To study air braking characteristics of long freight trains, an approach for simulating air brake systems based on fuid dynamics theory was proposed. The structures and working mechanisms of locomotive and wagon air brakes are introduced, and mathematical models of the pipes, brake valves, reservoirs or chambers, cylinders, etc., are presented.Besides, the dynamic motions of parts in the main valve are considered. The simulation model of the whole air brake system is then formulated, and the solving method based on the finite-difference method is used. New efficient pipe boundary conditions without iterations are developed for brake pipes and branch pipes, which can achieve higher computational efficiency. The proposed approach for simulating the air brake system is validated by comparing with published measured data. Simulation results of different train formations indicate that models that consider the dynamic behavior of brake pipes are recommended for predicting the characteristics of long trains under service braking conditions.展开更多
With the continuous development of artillery,the disadvantages of hydraulic recoil brakes gradually appear.At the same time,the appearance of high-performance Nd Fe B permanent magnet makes it possible to apply electr...With the continuous development of artillery,the disadvantages of hydraulic recoil brakes gradually appear.At the same time,the appearance of high-performance Nd Fe B permanent magnet makes it possible to apply electromagnetic braking technology to recoil mechanism.In this paper,prototype tests of a certain artillery were carried out to verify the feasibility of the electromagnetic brake(EMB)and obtain the electromagnetic braking force.Due to the brittleness of Nd Fe B,in order to eliminate the worry about the safety of EMB,SHPB experiments of Nd Fe B were carried out.Then,based on the assumption of uniform crack distribution,the law of crack propagation and damage accumulation was described theoretically,and the damage constitutive model suitable for brittle materials was proposed by combining the Zhu-Wang-Tang(ZWT)equation.Finally,the numerical simulation model of the artillery prototype was established and through calculation,the dynamic mechanical characteristics of Nd Fe B in the prototype were analyzed.The calculation results show that the strength of Nd Fe B can meet the requirements of the use in the working process.From the perspective of damage factor,the damage value of the permanent magnet on the far right is larger,and the damage value of the inner ring gradually decreases to the outer ring.展开更多
In order to study the effect of two-stage injection on two-stroke diesel engines, a well characterized research engine equipped with electronically controlled common rail system and scavenging system was constructed. ...In order to study the effect of two-stage injection on two-stroke diesel engines, a well characterized research engine equipped with electronically controlled common rail system and scavenging system was constructed. Through analysis of combustion and emissions, two-stage injection shows its advantages. Compared with the standard injection, it produces less emissions, while compared with single early injection, it expands engine operation range. Further experiments were carried out to study the influence of several injection control parameters on two-stage injection. The fuel in the first injection is used for forming homogeneous mixture. The fuel in the second injection keeps combustion, and it is the main source of smoke emissions. NO_x is formed in both combustion process caused by these two injections, and there is an optimum fuel allocation ration to produce minimum NO_x. The cylinder pressure decreases, and the combustion is depressed with the increasing of scavenging pressure. By optimizing the injection control parameters of two-stage injection, NO_x and smoke can be reduced beyond 30% simultaneously.展开更多
A frequency compensation control method for the opposed-piston two-stroke folded-cranktrain（ OPFC） diesel engine＇s common rail system is presented as a result of the study of the loop-shaping theory. A common rail ...A frequency compensation control method for the opposed-piston two-stroke folded-cranktrain（ OPFC） diesel engine＇s common rail system is presented as a result of the study of the loop-shaping theory. A common rail working process and the classical frequency control theory are combined to construct a frequency restriction of common rail pressure. A frequency compensator is utilized to improve the robustness of multiplicative perturbations and disturbance. The loop-shaping method has been applied to design the common rail pressure controller of the OPFC diesel engine. Simulation and bench test results show that in the condition of perturbation that comes from the effect of injection,multi-injection,fuel pumping of a pre-cylinder,and instantaneous pressure fluctuation,the controller indicates high precision. Compared with the original controller,this method improves the control precision by 67. 3%.展开更多
The effects of different flow forms on an opposed-piston two-stroke（OPTS）gasoline-directinjection（GDI）engine was studied by analyzing the mixture formation and combustion.Swirl was broken and dissipated gradually ...The effects of different flow forms on an opposed-piston two-stroke（OPTS）gasoline-directinjection（GDI）engine was studied by analyzing the mixture formation and combustion.Swirl was broken and dissipated gradually and the turbulence kinetic energy（TKE）was small in the compression process;however,tumble was strengthened and the TKE was strong in the compression process.For swirl around X axis（the axis of cylinder）and tumble around Y axis（the vertical direction of injector）,droplets were attached to the cylinder liner by the centrifugal force and the mixture distribution was poor.For tumble around Zaxis（the direction of injector）,the wall film in cylinder liner was thin and mixture distribution was homogeneous.Results showed that since the injector were installed on the wall of the cylinder liner in the OPTS-GDI engine,the spray angle was small and the mixture formation time was short.The 45° oblique axis tumble ratio of 1 was reasonable for the mixture formation and combustion for an OPTS-GDI engine.展开更多
The present paper shows the development of a strategy for the calculation of the air brake forces of European freight trains. The model is built to upgrade the existing Politecnico di Torino longitudinal train dynamic...The present paper shows the development of a strategy for the calculation of the air brake forces of European freight trains. The model is built to upgrade the existing Politecnico di Torino longitudinal train dynamics(LTD) code LTDPoliTo, which was originally unable to account for air brake forces. The proposed model uses an empirical exponential function to calculate the air brake forces during the simulation, while the maximum normal force on the brake friction elements is calculated according to the indication of the vehicle braked weight percentage.Hence, the model does not require to simulate in detail the fluid dynamics in the brake pipe nor to precisely know the main parameters of the braking system mounted on each vehicle. The model parameters are tuned to minimize the difference between the braking distance computed by the LTDPoliTo code and the value prescribed by the UIC544-1 leaflet in emergency braking operations. Simulations are run for different configurations of freight train compositions including a variable number of Shimmns wagons trailed by an E402B locomotive at the head of the train, as suggested in a reference literature paper. The results of the proposed method are in good agreement with the target braking distances calculated according to the international rules.展开更多
Braking system performance is relevant for both railway safety and network optimization. Most trains employ air brake systems;air brake systems of freight trains mostly cannot achieve a synchronous application of brak...Braking system performance is relevant for both railway safety and network optimization. Most trains employ air brake systems;air brake systems of freight trains mostly cannot achieve a synchronous application of brake forces, which is usually customary for passenger trains. The paper generalizes a previous air brake pneumatic model to passenger trains and describes the needed modifications. Among them, the way the pressure reduces in the brake pipe is generalized. Moreover, this paper reports an analytical bi-dimensional function for calculating the nozzle diameter equivalent to the electro-pneumatic(EP) or the electronically controlled pneumatic(ECP)brake valve as a function of the wagon length and the time to vent the brake pipe locally. The numerical results of the new model are compared against several experimental tests of high-speed passenger trains of Trenitalia, namely ETR500 and ETR1000. The model is suitable to be integrated into the UIC software TrainDy, aiming to extend its computational field to passenger trains and to simulate the safety of trains during a recovery.展开更多
The wear patterns for drum-style automotive brakes tend to enlarge internal drum diameters. Such enlargement is most profound when used brake drums are machined to restore the metal friction surfaces. Specialized arc ...The wear patterns for drum-style automotive brakes tend to enlarge internal drum diameters. Such enlargement is most profound when used brake drums are machined to restore the metal friction surfaces. Specialized arc grinding machinery has been used to match replacement shoe-style brake friction materials to enlarged drums. The process of arc grinding removes friction material, thereby producing dust. When organic-style friction materials contained asbestos, use of arc grinding machinery posed an asbestos fiber exposure risk to operators and proximate personnel. The manufacturers of arc grinding machinery have incorporated local exhaust ventilation systems designed to capture and remove this dust at the point of grinding contact and propel this dust into collection bags or other systems. This research was designed to evaluate the dust capture and retention characteristics of a specific arc grinder product, when used to custom grind asbestos-containing brake friction materials. A Bear Model 1420 automotive brake shoe arc grinder was the subject of this study. During two separate but consecutive test sessions, newly relined sets of shoe-style automobile brake friction materials were precision ground. Both area and personal air samples were collected throughout each testing session. This work took place within a closed and unventilated metal building, with total interior volume of 2500 m<sup>3</sup>. Collected air samples were analyzed using phase contrast microscopy (PCM) and transmission electron microscopy (TEM). The results of analysis using PCM for personal samples (n = 6) ranged from <0.044 to 0.055 fibers per cc (f/cc) (mean 0.05). Follow-up analysis of these personal samples using TEM indicated asbestos-adjusted PCM exposures ranging from <0.0074 to 0.055 f/cc (mean ≤ 0.041). Area air samples, taken at distances ranging from 1.5 to 9 meters from the arc grinder (n = 12), showed asbestos-adjusted PCM concentrations ranging from <0.0075 to 0.041 f/cc (mean ≤ 0.017). The process of custom arc grinding shoe-style, asbestos-containing brake friction materials can cause exposure to airborne asbestos fibers. However, when done using properly equipped arc grinding machines, such exposures are not expected to exceed the current occupational exposure limits for asbestos of 0.1 f/cc 8-hour time-weighted average (TWA) or 1.0 f/cc 30-minute average.展开更多
Hybrid materials collected from organic and inorganic sources,which are traditionally used as brake lining materials,generally include fly ash,cashew shell powder,phenolic resins,aluminium wool,barites,lime powder,car...Hybrid materials collected from organic and inorganic sources,which are traditionally used as brake lining materials,generally include fly ash,cashew shell powder,phenolic resins,aluminium wool,barites,lime powder,carbon powder and copper powder.The present research focuses on the specific effects produced by fly ash and aims to provide useful indications for the replacement of asbestos due to the health hazards caused by the related fibers.Furthermore,the financial implications related to the use of large-volume use of fly ash,lime stone and cashew shell powder,readily available in most countries in the world,are also discussed.It is shown that many manufacturing and automotive industries,which are currently experiencing difficulties in meeting the increasing demand for brake lining material,may take advantage from the proposed solution.展开更多
ABS is an active safety system which showed a valuable contribution to vehicle safety and stability since it was first introduced. Recently, EVs with in-wheel-motors have drawn increasing attention owing to their grea...ABS is an active safety system which showed a valuable contribution to vehicle safety and stability since it was first introduced. Recently, EVs with in-wheel-motors have drawn increasing attention owing to their greatest advantages. Wheels torques are precisely and swiftly controlled thanks to electric motors and their advanced driving techniques. In this paper, a regenerative-ABS control RABS is proposed for all-in-wheel-motors-drive EVs. The RABS is realized as a pure electronic braking system called brake-by-wire. A coordination strategy is suggested to control RABS compromising three layers. First, wheels slip control takes place, and braking torque is calculated in the higher layer. In the coordinate interlayer, torque is allocated between actuators ensuring maximal energy recovery and vehicle stability. While in the lower layer, actuator control is performed. The RABS effectiveness is validated on a 3-DOF EVSimulink model through two straight-line braking manoeuvres with low and high initial speeds of 50 km/h and 150 km/h, respectively. Both regular and emergency braking manoeuvres are considered with ABS enabled and disabled for comparison. Simulation results showed the high performance of the proposed RABS control in terms of vehicle stability, brake response, stopping distance, and battery re-charging.展开更多
Brake systems are essential for the speed regulation or braking of a high-speed train.The vehicle dynamic performance under braking condition is complex and directly affects the reliability and running safety.To revea...Brake systems are essential for the speed regulation or braking of a high-speed train.The vehicle dynamic performance under braking condition is complex and directly affects the reliability and running safety.To reveal the vehicle dynamic behaviour in braking process,a comprehensive trailer car dynamics model(TCDM)considering brake systems is established in this paper.The dynamic interactions between the brake system and the other connected components are achieved using the brake disc-pad frictions,brake suspension systems,and wheel-rail interactions.The force and motion transmission from the brake system to the wheel-rail interface is performed by the proposed TCDM excited by track irregularity.In addition,the validity of TCDM is verified by experimental test results.On this basis,the dynamic behaviour of the coupled system is simulated and discussed.The findings indicate that the braking force significantly affects vehicle dynamic behaviour including the wheel-rail forces,suspension forces,wheelset torsional vibration,etc.The dynamic interactions within the brake system are also significantly affected by the vehicle vibration due to track irregularity.Besides,the developed TCDM can be further employed to the dynamic assessment of such a coupled mechanical system under different braking conditions.展开更多
Purpose–The brake controller is a key component of the locomotive brake system.It is essential to study its safety.Design/methodology/approach–This paper summarizes and analyzes typical faults of the brake controlle...Purpose–The brake controller is a key component of the locomotive brake system.It is essential to study its safety.Design/methodology/approach–This paper summarizes and analyzes typical faults of the brake controller,and proposes four categories of faults:position sensor faults,microswitch faults,mechanical faults and communication faults.Suggestions and methods for improving the safety of the brake controller are also presented.Findings–In this paper,a self-judgment and self-learning dynamic calibration method is proposed,which integrates the linear error of the sensor and the manufacturing and assembly errors of the brake controller to solve the output drift.This paper also proposes a logic for diagnosing and handling microswitch faults.Suggestions are proposed for other faults of brake controller.Originality/value–The methods proposed in this paper can greatly improve the usability of the brake controller and reduce the failure rate.展开更多
基金supported by the Science and Technology Innovation Development Project of Yantai(No.2023ZDX016)。
文摘The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs.In this work,the thermal fatigue and wear of compacted graphite iron brake discs were investigated,aiming to provide an experimental foundation for achieving a balance between their thermal and mechanical properties.Compacted graphite iron brake discs with different tensile strengths,macrohardnesses,specific heat capacities and thermal diffusion coefficients were produced by changing the proportion and strength of ferrite.The peak temperature,pressure load and friction coefficient of compacted graphite iron brake discs were analyzed through inertia friction tests.The morphology of thermal cracks and 3D profiles of the worn surfaces were also discussed.It is found that the thermal fatigue of compacted graphite iron discs is determined by their thermal properties.A compacted graphite iron with the highest specific heat capacity and thermal diffusion coefficient exhibits optimal thermal fatigue resistance.Oxidization of the matrix at low temperatures significantly weakens the function of alloy strengthening in hindering the propagation of thermal cracks.Despite the reduced hardness,increasing the ferrite proportion can mitigate wear loss resulting from low disc temperatures and the absence of abrasive wear.
文摘Research into converting waste into viable eco-friendly products has gained global concern.Using natural fibres and pulverized metallic waste becomes necessary to reduce noxious environmental emissions due to indiscriminately occupying the land.This study reviews the literature in the broad area of green composites in search of materials that can be used in automotive brake pads.Materials made by biocomposite,rather than fossil fuels,will be favoured.A database containing the tribo-mechanical performance of numerous potential components for the future green composite was established using the technical details of bio-polymers and natural reinforcements.The development of materials with diverse compositions and varying proportions is now conceivable,and these materials can be permanently connected in fully regulated processes.This explanation demonstrates that all of these variables affect friction coefficient,resistance to wear from friction and high temperatures,and the operating life of brake pads to varying degrees.In this study,renewable materials for the matrix and reinforcement are screened to determine which have sufficient strength,coefficient of friction,wear resistance properties,and reasonable costs,making them a feasible option for a green composite.The most significant,intriguing,and unusual materials used in manufacturing brake pads are gathered in this review,which also analyzes how they affect the tribological characteristics of the pads.
基金supported by the National Key Research and Development Program of China(2020YFA0710901)the National Natural Science Foundation of China(12002395)Natural Science Foundation of Hunan Province(Grant No.2023JJ30643).
文摘As the velocity of a train increases,the corresponding air pumping power consumption of the brake discs increases proportionally.In the present experimental study,a standard axle-mounted brake disc with circumferential pillars was analyzed using a 1:1 scale model and a test rig in a wind tunnel.In particular,three upstream velocities were selected on the basis of earlier investigations of trains operating at 160,250,and 400 km/h,respectively.Moreover,3D steady computational fluid dynamics(CFD)simulations of the flow field were conducted to compare with the wind tunnel test outcomes.The results for a 3-car train at 180 km/h demonstrated:(1)good agreement between the air resistance torques obtained from the wind tunnel tests and the related numerical results,with differences ranging from 0.95%to 5.88%;(2)discrepancies ranging from 3.2 to 3.8 N·m;(3)cooling ribs contributing more than 60%of the air resistance torque;(4)the fast rotation of brake discs causing a significantly different flow field near the bogie area,resulting in 25 times more air pumping power loss than that obtained in the stationary brake-disc case.
文摘A numerical program is built to simulate the performance of a spark ignited two-stroke free-piston engine coupled with a linear generator. The computational model combines a series of dynamic and thermodynamic equations that are solved simultaneously to predict the performances of the engines. The dynamic analysis performed consists of an evaluation of the frictional force and load force introduced by the generator. The thermodynamic analysis used a single zone model to describe the engine＇ s working cycle which includes intake, scavenging, compression, combustion and expansion, and to evaluate the effect of heat transfer based on the first law of thermodynamics and the ideal gas state equation. Because there is no crankshaft, a time based Wiebe equation was used to express the fraction of fuel burned in the combustion. The calculated results were validated by using the experimental data from another research group. The results indicate that the free-piston generator has some advantages over conventional engines.
基金financial support from the Engineering and Physical Sciences Research Council (EPSRC)
文摘A novel two-stroke boosted uniflow scavenged direct-injection gasoline (BUSDIG) engine has been proposed and designed in order to achieve aggressive engine downsizing and down-speeding for higher engine performance and efficiency. In this paper, the design and development of the BUSDIG engine are outlined discussed and the key findings are summarized to highlight the progress of the development of the proposed two-stroke BUSDIG engine. In order to maximize the scavenging performance and produce sufficient in-cylinder flow motions for the fuel/air mixing process in the two-stroke BUSDIG engine, the engine bore/stroke ratio, intake scavenge port angles, and intake plenum design were optimized by three-dimensional (3D) computational fluid dynamics (CFD) simulations. The effects of the opening profiles of the scavenge ports and exhaust valves on controlling the scavenging process were also investigated. In order to achieve optimal in-cylinder fuel stratification, the mixture-formation processes by different injection strategies were studied by using CFD simulations with a calibrated Reitz–Diwakar breakup model. Based on the optimal design of the BUSDIG engine, one-dimensional (1D) engine simulations were performed in Ricardo WAVE. The results showed that a maximum brake thermal efficiency of 47.2% can be achieved for the two-stroke BUSDIG engine with lean combustion and water injection. A peak brake toque of 379 N·m and a peak brake power density of 112 kW·L^-1 were achieved at 1600 and 4000 r·min^-1, respectively, in the BUSDIG engine with the stoichiometric condition.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51825504, 51735012, and 52072317)
文摘Air brake systems are critical equipment for railway trains, which affects the running safety of the trains significantly. To study air braking characteristics of long freight trains, an approach for simulating air brake systems based on fuid dynamics theory was proposed. The structures and working mechanisms of locomotive and wagon air brakes are introduced, and mathematical models of the pipes, brake valves, reservoirs or chambers, cylinders, etc., are presented.Besides, the dynamic motions of parts in the main valve are considered. The simulation model of the whole air brake system is then formulated, and the solving method based on the finite-difference method is used. New efficient pipe boundary conditions without iterations are developed for brake pipes and branch pipes, which can achieve higher computational efficiency. The proposed approach for simulating the air brake system is validated by comparing with published measured data. Simulation results of different train formations indicate that models that consider the dynamic behavior of brake pipes are recommended for predicting the characteristics of long trains under service braking conditions.
基金financially supported by the“National Natural Science Foundation of China”[Grant No.52105106]the“China National Postdoctoral Program for Innovative Talents”[Grant No.BX2021126]+2 种基金the“Jiangsu Province Natural Science Foundation”[Grant No.BK20210342]the“Jiangsu Planned Projects for Postdoctoral Research Funds”[Grant No.2021K008A]the“Nanjing Municipal Human Resources and Social Security Bureau”[Grant No.MCA21121]。
文摘With the continuous development of artillery,the disadvantages of hydraulic recoil brakes gradually appear.At the same time,the appearance of high-performance Nd Fe B permanent magnet makes it possible to apply electromagnetic braking technology to recoil mechanism.In this paper,prototype tests of a certain artillery were carried out to verify the feasibility of the electromagnetic brake(EMB)and obtain the electromagnetic braking force.Due to the brittleness of Nd Fe B,in order to eliminate the worry about the safety of EMB,SHPB experiments of Nd Fe B were carried out.Then,based on the assumption of uniform crack distribution,the law of crack propagation and damage accumulation was described theoretically,and the damage constitutive model suitable for brittle materials was proposed by combining the Zhu-Wang-Tang(ZWT)equation.Finally,the numerical simulation model of the artillery prototype was established and through calculation,the dynamic mechanical characteristics of Nd Fe B in the prototype were analyzed.The calculation results show that the strength of Nd Fe B can meet the requirements of the use in the working process.From the perspective of damage factor,the damage value of the permanent magnet on the far right is larger,and the damage value of the inner ring gradually decreases to the outer ring.
基金The National Basic Research Program of China(973 Program)(No.2001CB209208)The National Science Foundation of China(No.50136040)
文摘In order to study the effect of two-stage injection on two-stroke diesel engines, a well characterized research engine equipped with electronically controlled common rail system and scavenging system was constructed. Through analysis of combustion and emissions, two-stage injection shows its advantages. Compared with the standard injection, it produces less emissions, while compared with single early injection, it expands engine operation range. Further experiments were carried out to study the influence of several injection control parameters on two-stage injection. The fuel in the first injection is used for forming homogeneous mixture. The fuel in the second injection keeps combustion, and it is the main source of smoke emissions. NO_x is formed in both combustion process caused by these two injections, and there is an optimum fuel allocation ration to produce minimum NO_x. The cylinder pressure decreases, and the combustion is depressed with the increasing of scavenging pressure. By optimizing the injection control parameters of two-stage injection, NO_x and smoke can be reduced beyond 30% simultaneously.
基金Supported by the National Natural Science Foundation of China(51406013)
文摘A frequency compensation control method for the opposed-piston two-stroke folded-cranktrain（ OPFC） diesel engine＇s common rail system is presented as a result of the study of the loop-shaping theory. A common rail working process and the classical frequency control theory are combined to construct a frequency restriction of common rail pressure. A frequency compensator is utilized to improve the robustness of multiplicative perturbations and disturbance. The loop-shaping method has been applied to design the common rail pressure controller of the OPFC diesel engine. Simulation and bench test results show that in the condition of perturbation that comes from the effect of injection,multi-injection,fuel pumping of a pre-cylinder,and instantaneous pressure fluctuation,the controller indicates high precision. Compared with the original controller,this method improves the control precision by 67. 3%.
基金Supported by the National Natural Science Foundation of China(B2220110005)
文摘The effects of different flow forms on an opposed-piston two-stroke（OPTS）gasoline-directinjection（GDI）engine was studied by analyzing the mixture formation and combustion.Swirl was broken and dissipated gradually and the turbulence kinetic energy（TKE）was small in the compression process;however,tumble was strengthened and the TKE was strong in the compression process.For swirl around X axis（the axis of cylinder）and tumble around Y axis（the vertical direction of injector）,droplets were attached to the cylinder liner by the centrifugal force and the mixture distribution was poor.For tumble around Zaxis（the direction of injector）,the wall film in cylinder liner was thin and mixture distribution was homogeneous.Results showed that since the injector were installed on the wall of the cylinder liner in the OPTS-GDI engine,the spray angle was small and the mixture formation time was short.The 45° oblique axis tumble ratio of 1 was reasonable for the mixture formation and combustion for an OPTS-GDI engine.
文摘The present paper shows the development of a strategy for the calculation of the air brake forces of European freight trains. The model is built to upgrade the existing Politecnico di Torino longitudinal train dynamics(LTD) code LTDPoliTo, which was originally unable to account for air brake forces. The proposed model uses an empirical exponential function to calculate the air brake forces during the simulation, while the maximum normal force on the brake friction elements is calculated according to the indication of the vehicle braked weight percentage.Hence, the model does not require to simulate in detail the fluid dynamics in the brake pipe nor to precisely know the main parameters of the braking system mounted on each vehicle. The model parameters are tuned to minimize the difference between the braking distance computed by the LTDPoliTo code and the value prescribed by the UIC544-1 leaflet in emergency braking operations. Simulations are run for different configurations of freight train compositions including a variable number of Shimmns wagons trailed by an E402B locomotive at the head of the train, as suggested in a reference literature paper. The results of the proposed method are in good agreement with the target braking distances calculated according to the international rules.
文摘Braking system performance is relevant for both railway safety and network optimization. Most trains employ air brake systems;air brake systems of freight trains mostly cannot achieve a synchronous application of brake forces, which is usually customary for passenger trains. The paper generalizes a previous air brake pneumatic model to passenger trains and describes the needed modifications. Among them, the way the pressure reduces in the brake pipe is generalized. Moreover, this paper reports an analytical bi-dimensional function for calculating the nozzle diameter equivalent to the electro-pneumatic(EP) or the electronically controlled pneumatic(ECP)brake valve as a function of the wagon length and the time to vent the brake pipe locally. The numerical results of the new model are compared against several experimental tests of high-speed passenger trains of Trenitalia, namely ETR500 and ETR1000. The model is suitable to be integrated into the UIC software TrainDy, aiming to extend its computational field to passenger trains and to simulate the safety of trains during a recovery.
文摘The wear patterns for drum-style automotive brakes tend to enlarge internal drum diameters. Such enlargement is most profound when used brake drums are machined to restore the metal friction surfaces. Specialized arc grinding machinery has been used to match replacement shoe-style brake friction materials to enlarged drums. The process of arc grinding removes friction material, thereby producing dust. When organic-style friction materials contained asbestos, use of arc grinding machinery posed an asbestos fiber exposure risk to operators and proximate personnel. The manufacturers of arc grinding machinery have incorporated local exhaust ventilation systems designed to capture and remove this dust at the point of grinding contact and propel this dust into collection bags or other systems. This research was designed to evaluate the dust capture and retention characteristics of a specific arc grinder product, when used to custom grind asbestos-containing brake friction materials. A Bear Model 1420 automotive brake shoe arc grinder was the subject of this study. During two separate but consecutive test sessions, newly relined sets of shoe-style automobile brake friction materials were precision ground. Both area and personal air samples were collected throughout each testing session. This work took place within a closed and unventilated metal building, with total interior volume of 2500 m<sup>3</sup>. Collected air samples were analyzed using phase contrast microscopy (PCM) and transmission electron microscopy (TEM). The results of analysis using PCM for personal samples (n = 6) ranged from <0.044 to 0.055 fibers per cc (f/cc) (mean 0.05). Follow-up analysis of these personal samples using TEM indicated asbestos-adjusted PCM exposures ranging from <0.0074 to 0.055 f/cc (mean ≤ 0.041). Area air samples, taken at distances ranging from 1.5 to 9 meters from the arc grinder (n = 12), showed asbestos-adjusted PCM concentrations ranging from <0.0075 to 0.041 f/cc (mean ≤ 0.017). The process of custom arc grinding shoe-style, asbestos-containing brake friction materials can cause exposure to airborne asbestos fibers. However, when done using properly equipped arc grinding machines, such exposures are not expected to exceed the current occupational exposure limits for asbestos of 0.1 f/cc 8-hour time-weighted average (TWA) or 1.0 f/cc 30-minute average.
文摘Hybrid materials collected from organic and inorganic sources,which are traditionally used as brake lining materials,generally include fly ash,cashew shell powder,phenolic resins,aluminium wool,barites,lime powder,carbon powder and copper powder.The present research focuses on the specific effects produced by fly ash and aims to provide useful indications for the replacement of asbestos due to the health hazards caused by the related fibers.Furthermore,the financial implications related to the use of large-volume use of fly ash,lime stone and cashew shell powder,readily available in most countries in the world,are also discussed.It is shown that many manufacturing and automotive industries,which are currently experiencing difficulties in meeting the increasing demand for brake lining material,may take advantage from the proposed solution.
文摘ABS is an active safety system which showed a valuable contribution to vehicle safety and stability since it was first introduced. Recently, EVs with in-wheel-motors have drawn increasing attention owing to their greatest advantages. Wheels torques are precisely and swiftly controlled thanks to electric motors and their advanced driving techniques. In this paper, a regenerative-ABS control RABS is proposed for all-in-wheel-motors-drive EVs. The RABS is realized as a pure electronic braking system called brake-by-wire. A coordination strategy is suggested to control RABS compromising three layers. First, wheels slip control takes place, and braking torque is calculated in the higher layer. In the coordinate interlayer, torque is allocated between actuators ensuring maximal energy recovery and vehicle stability. While in the lower layer, actuator control is performed. The RABS effectiveness is validated on a 3-DOF EVSimulink model through two straight-line braking manoeuvres with low and high initial speeds of 50 km/h and 150 km/h, respectively. Both regular and emergency braking manoeuvres are considered with ABS enabled and disabled for comparison. Simulation results showed the high performance of the proposed RABS control in terms of vehicle stability, brake response, stopping distance, and battery re-charging.
基金supported by the National Natural Science Foundation of China(Nos.52205217 and U22A20181)the Natural Science Foundation of Sichuan(No.2022NSFSC1964).
文摘Brake systems are essential for the speed regulation or braking of a high-speed train.The vehicle dynamic performance under braking condition is complex and directly affects the reliability and running safety.To reveal the vehicle dynamic behaviour in braking process,a comprehensive trailer car dynamics model(TCDM)considering brake systems is established in this paper.The dynamic interactions between the brake system and the other connected components are achieved using the brake disc-pad frictions,brake suspension systems,and wheel-rail interactions.The force and motion transmission from the brake system to the wheel-rail interface is performed by the proposed TCDM excited by track irregularity.In addition,the validity of TCDM is verified by experimental test results.On this basis,the dynamic behaviour of the coupled system is simulated and discussed.The findings indicate that the braking force significantly affects vehicle dynamic behaviour including the wheel-rail forces,suspension forces,wheelset torsional vibration,etc.The dynamic interactions within the brake system are also significantly affected by the vehicle vibration due to track irregularity.Besides,the developed TCDM can be further employed to the dynamic assessment of such a coupled mechanical system under different braking conditions.
基金supported by the China Academy of Railway Sciences Foundation[Grant No.2021YJ244].
文摘Purpose–The brake controller is a key component of the locomotive brake system.It is essential to study its safety.Design/methodology/approach–This paper summarizes and analyzes typical faults of the brake controller,and proposes four categories of faults:position sensor faults,microswitch faults,mechanical faults and communication faults.Suggestions and methods for improving the safety of the brake controller are also presented.Findings–In this paper,a self-judgment and self-learning dynamic calibration method is proposed,which integrates the linear error of the sensor and the manufacturing and assembly errors of the brake controller to solve the output drift.This paper also proposes a logic for diagnosing and handling microswitch faults.Suggestions are proposed for other faults of brake controller.Originality/value–The methods proposed in this paper can greatly improve the usability of the brake controller and reduce the failure rate.
