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Table of Content

    25 September 2014, Volume 42 Issue 9
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    Mechanical Engineering
    Burnishing-Induced Ultra-Fine Grained Pure Iron Surface Layer and Its Corrosion Resistance
    Li Ning Xia Wei Zhao Jing Li Feng-lei
    2014, 42(9):  1-6.  doi:10.3969/j.issn.1000-565X.2014.09.001
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    In the investigation,by means of a new surface self-nanocrystallization technique named SPRB ( SeverePlasticity Roller Burnishing) ,a gradient ultra-fine grain ( UFG) surface layer of a minimum grain size of about 300nmwas fabricated on pure iron.Then,the microstructure and the corrosion behavior of UFG surface layer wereanalyzed by means of TEM,XRD,SEM and electrochemical methods.The results show that ( 1) the outermost layerhardness of UFG iron is improved by more than 1.6 times in comparison with that of coarse grain ( CG) iron; ( 2) astrongly basal-textured grain orientation forms on the UFG surface and its micro strain is ( 0.313 ±0.017) %; ( 3) in 3.5% NaCl solution,the open circuit corrosion potential of UFG Fe is 24mV more than that of CG Fe in the positivedirection,and the corrosion current density decreases from 2.371 × 10－5 A/cm2 of CG Fe to 7.547 × 10－8 A/cm2 of UFG Fe; ( 4) in 6% FeCl3 solution,the pitting rate of UFG Fe is about half as much as that of CG Fe; ( 5) thecorrosion resistance of UFG Fe is remarkably improved in comparison with that of CG Fe; and ( 6) the corrosion resistanceimprovement of UFG Fe is attributed to the surface grain refinement and the formation of the strongly basaltexturedgrain orientation.

    Calibration Method of Systematic Odometry Errors of Mobile Robot
    Zhang Tie Chen Wei- hua Zou Yan- biao Ma Qiong- xiong
    2014, 42(9):  7-11.  doi:10.3969/j.issn.1000-565X.2014.09.002
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    In order to improve the localization accuracy and to reduce the systematic errors,a calibration method ofsystematic odometry errors is proposed for the mobile robot with a low accuracy of motion control model,and anexperiment is designed to correct the system parameters,namely,the left and right wheel diameters and the wheel-base.This calibration method takes into account the position and orientation errors caused by three main systematicerror sources,namely,the inequality between left and right wheel diameters,the uncertainty of wheelbases and thedifference between the average actual wheel diameter and the nominal wheel diameter.This calibration method alsoconsiders the influences of the systematic errors on the linear motion and the rotation motion of the mobile robot,and uses the experimental data of linear motion and rotation motion to correct the systematic parameters.Experi-mental results demonstrate that the corrected diameters are closer to their actual values with smaller systematicerrors and higher localization accuracy,and the experiment is simple and easy to handle.

    Crack Initiation and Propagation Laws of Graphite Specimen Subjected to Edge- Indentation
    Zhang Shi- wei Wan Zhen- ping Ou Yuan- xian Xu Pei- jie Tang Yong
    2014, 42(9):  12-17.  doi:10.3969/j.issn.1000-565X.2014.09.003
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    In order to reveal the cutting process of graphite materials and the forming mechanism of machined sur-faces,the crack initiation and propagation laws of a graphite specimen subjected to edge- indentation are investigated.The results show that (1) cracks initiate suddenly and propagate rapidly when the indentation loading increases to acritical value; (2) initial cracks spread toward the inside of specimens,and then propagate toward the indentationsurface gradually and reach the indentation surface finally,which occurs along an arc- shaped propagation path; and(3) as the interior angle of indenter and the edge- indentation thickness increase,the cracks spread farther towardthe inside of specimens and the depth and width of concavities forming on the specimen surface become greater.Inaddition,cutting experiments indicate that the crack initiation and propagation laws of the graphite specimen sub-jected to edge- indentation can be used to describe the material removal and the machined surface formation.

    Design of High- Frequency Narrow- Pulsed Inverter Power Supply for Micro- Arc Oxidation
    Yang Kai Cao Biao Ding Li Yang Guang Huang Zeng- hao
    2014, 42(9):  18-23.  doi:10.3969/j.issn.1000-565X.2014.09.004
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    In order to enhance the arc controllability during the MAO (Micro- Arc Oxidation) process,a high- fre-quency narrow- pulse inverter power supply for micro- arc oxidation is designed in the perspective of pulse energycontrol.This power supply adds an impedance matching circuit to the main circuit of the source on the basis of a tra-ditional two- stage inverter structure.Thus,rapidly releasing and storing of energy in the circuit and load is realizedunder the variable polarity mode.Then,a cooperative control strategy is presented to carry out DC/pulsed/ variablepolarity pulsed modes,and the corresponding operation patterns for the main circuit are also described.Finally,theload characteristic of the proposed power supply is analyzed and the availability of the equivalent model of the loadcharacteristic is verified by comparing simulation and experimental waveforms.Experimental results demonstrate that,for the proposed power supply,both increasing the pulse frequency (up to 20kHz) and decreasing the pulse width(low to 20μs) help to realize the precise control of pulse energy and enhance the energy utilization of the system,andboth the porosity and surface roughness of the coating obtained in the high- frequency narrow- pulse mode are lower.

    Analysis on High Power Density Gear Transmission Efficiency Considering Tooth Friction
    Feng Hai- sheng Wang Li- qin Zheng De- zhi Zhao Xiao- li Dai Guang- hao
    2014, 42(9):  24-29.  doi:10.3969/j.issn.1000-565X.2014.09.005
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    In order to investigate the effect of tooth friction on the transmission efficiency of high power density gear,a method to predict the gear transmission efficiency and to analyze its dynamic characteristic is proposed onthe basis of virtual prototype technology.In this method,a flexible multi- body dynamic model of gear,rotation shaftand bearing is built when the flexibile deformation of gear and rotation shaft as well as the time- varying mesh stiff-ness of gear are taken into account.Then,the dynamic characteristics and the efficiency of gear transmission sys-tem are obtained by means of dynamic equations of prototype,and the effects of the tooth friction coefficient on theefficiencies and the dynamic characteristics of spur,helical and double helical gear transmission systems are alsoanalyzed.The results show that both the contact stress and the dynamic tangential friction force increase when thetooth friction coefficient increases,and that,at a high rotation speed,the contact stress of double helical gear is theleast in comparison with those of helical and spur gears,and its efficiency is higher than that of other gears.

    Motion Control Method of Spatial Surface Grinding for Knives and Scissors
    Jiao Qing- song Li Di Wang Shi- yong Kong Xiang- hong
    2014, 42(9):  30-34,40.  doi:10.3969/j.issn.1000-565X.2014.09.006
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    In order to realize the surface grinding of complicated and specially- shaped knives and scissors,a multi- axismotion control method is proposed for spatial surface grinding.Based on the characteristics of surface grinding andhorizontal surface grinder,the functional relationship between machining parameters and process parameters isestablished.The machining parameters include radial feed,axial feed and rotation angle,and the process parame-ters includes grinding depth of top surface,grinding depth of bottom surface and grinding width.Then,the jointcontrol of one rotational axis and two translational axes is realized by taking into account surface projection rules．Based on the proposed control method,a computer numerical control (CNC) system is developed,which supportsthe mixed 2D graphic and parametric user programming.Finally,the CNC system is employed to develop a proto-type of numerical control surface grinder,and grinding experiments are performed by using the surface grinder.Theresults show that the surface grinder is able to manufacture various kinds of knives and scissors and is superior to ahydraulic surface grinder in terms of efficiency and quality.

    Fatigue Strength Probability Distribution Inference Based on Monte Carlo Simulation Method
    Hu Yun Liu Shao- jun Liao Ya- shi Ding Sheng
    2014, 42(9):  35-40.  doi:10.3969/j.issn.1000-565X.2014.09.007
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    When a reliability analysis is performed according to the stress- strength interference theory,the fatiguestrength probability distribution needs to be obtained at an arbitrary fatigue life based on the existing fatigue experi-ment data of material.In this paper,a simulation method of fatigue strength probability distribution is proposedunder the condition that the fatigue life follows a lognormal distribution.In this method,a P- S- N curve at an arbi-trary survival probability with a finite life is reconstructed according to two known P- S- N curves,and then thefatigue strength probability distribution at an arbitrary fatigue life is inferred by means of the Monte Carlo simulationmethod.Finally,analyses on 20Cr2Ni4A are performed.It is found that the reconstructed P- S- N curve is highlyprecise,the fatigue strength probability distribution follows normal distribution and the simulation results accordwell with the equality principle and the fatigue strength degradation theory.The above results show that the pro-posed method is effective.

    Structural Reliability- Based Optimization Design Using PSO- DE Hybrid Algorithm
    Jong Chanhyok Meng Guang- wei Li Feng Zhou Li- ming Kong Yongsu
    2014, 42(9):  41-45,75.  doi:10.3969/j.issn.1000-565X.2014.09.008
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    In order to enhance the efficiency of structural reliability- based optimization design,a PSO- DE hybridalgorithm is proposed on the basis of search features of the particle swarm optimization (PSO) and differential evo-lution (DE) algorithms.This algorithm overcomes the premature convergence of basic PSO algorithm.Moreover,by combining the PSO- DE hybrid algorithm with the structural reliability- based optimization theory,an optimization model is established to minimize the structure mass under the constraint of structural system failure probability.Caseanalyses show that,in comparison with the basic PSO algorithm,the proposed PSO- DE hybrid algorithm improves the convergence rate and the computational accuracy,and the algorithm is easy to implement with strong robustness.

    Multidimensional Micro Transmission Platform Design and RPY Angle- Based Movement Characteristic Analysis
    Lin Chao Cai Li- zhong Ji Jiu- xiang Liu Lei
    2014, 42(9):  46-52.  doi:10.3969/j.issn.1000-565X.2014.09.009
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    In order to meet the requirement of degree of freedom and long distance in the precision manufacturing field,a micro transmission platform with six degrees of freedom is designed on the basis of spatial mechanism.This platform is driven by piezoelectric ceramic and oriented by flexible hinge.Aiming at the small output displacement of piezoelectric ceramic,a bridge mechanism is designed to enlarge its output displacement,and the wire cuttingmethod is employed to accomplish a one- time processing of transmission platform.Thus,a one- piece transmissionplatform with long distance is obtained.Moreover,a supplemented and corrected RPY (Roll- Pitch- Yaw) anglepose description method is put forward by means of the homogeneous coordinate transformation,and then it is usedto analyze the motional characteristics of the transmission platform.Consequently,a kinematics model of microtransmission platform is established according to the virtual work principle and the coordinate transformation theory,and thus the mapping relationship between the moving displacement of transmission platform and the driving dis-placement of piezoelectric ceramics is obtained.Besides,the static stiffness in six directions of micro transmissionplatform and their change rules are also arrived at.Finally,a finite element simulation on the one- piece transmi-ssion platform is performed by using the software ANSYS12.0,and an experimental platform is put up to carry outthe corresponding experiments.As a result,the correctness of the proposed theoretical model and the rationality ofthe proposed platform are verified by means of the comparative analysis among theoretical,simulation and experi-mental results.

    Shape Control of Parts Formed by Means of Flexible 3D Stretch- Bending Technology
    Gao Song Liang Ji- cai Teng Fei Chen Guang- yi Wei Zhi- yong
    2014, 42(9):  53-58.  doi:10.3969/j.issn.1000-565X.2014.09.010
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    In this paper,the flexible 3D stretch- bending (FSB) process is investigated,and the mathematicalexpressions of the formed parts are put forward.Then,a method to adjust the flexible fundamental units (FFU)and a calculation algorithm of clamp stretch- bending trajectories are proposed by analyzing the deformation processin the horizontal and vertical directions.By considering the multipoint control of the FFU envelop shape,theadjustment parameters of multi- points dies (MPD) are defined,and the geometric relationship between the FFUand the workpiece is established.Moreover,an interpolation method based on cubic B- spline is presented todescribe the envelop shape of MPD.Based on the above- mentioned geometric relationship and MPD adjustmentparameters,the arc stretch- bending trajectories of the clamp are calculated.Finally,3D stretch- bending experi-ments of the L- section aluminum profile are conducted.The results show that the formed part is of a measured con-tour error of less than 0.7%,which indicates that the proposed methods are practical.

    Electronics, Communication & Automation Technology
    Edge Detection Based on Edge Intensity Accumulation in Scale- Space
    Hu Yue- ming Chen Ze- wu Chen An Gao Hong- xia
    2014, 42(9):  59-64.  doi:10.3969/j.issn.1000-565X.2014.09.011
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    In order to reduce such effects of interference as microscopic structure,noise and weak edge on theimage edge detection and to improve the positional accuracy of the detection,an edge detection method is proposedon the basis of edge intensity accumulation characteristic in scale- space.This method selects the optimal scale oftarget edges by comparing the average edge intensity of target object at different scales,and then filters out all thejamming edges at the optimal scale according to the difference of edge intensity accumulation values of edge pointsin scale- space.Experimental results show that the proposed method can effectively restrain all the above interferenceswith slight smoothing,and thus the stability and positional accuracy of target edges is improved.

    GK Clustering Model Based on Optimal Initial Clustering Center of AFS
    Wang Li- na Chen Xiao- hong
    2014, 42(9):  65-69.  doi:10.3969/j.issn.1000-565X.2014.09.012
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    Gustafson- Kessel (GK) clustering algorithm can be used to search for hyper ellipsoid,plane and lineardata effectively,but it is still sensitive to initial clustering center and easy to fall into a local optimum.In order tosolve this problem,this paper presents an improved GK clustering algorithm,which adopts the artificial fish- swarm(AFS) algorithm to initialize clustering centers according to the similarity between clustering and searching food offish school.Then,this algorithm is employed to perform a simulation based on artificial data and IRIS data.Theresults show that the improved algorithm can find the clustering structure of datasets effectively,and it possesses abetter classification performance than GK clustering algorithm.

    Differential Image Localization Method for IC PEM
    Lin Xiao- ling Lian Jian- wen Zhang Xiao- wen Yao Ruo- he
    2014, 42(9):  70-75.  doi:10.3969/j.issn.1000-565X.2014.09.013
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    When the bias voltage is low,PEM (Photon Emission Microscopy) failure signal is weak and is easy tobe influenced by noise,which results in a poor quality of PEM image.In order to solve this problem,a signal- noisemodel of PEM image is established,and a differential image localization algorithm is designed to improve the PEMprecision.First,this algorithm acquires two groups of images with different failure signal strengths by adjusting thebias voltage.Then,the average differential image of these two group images is calculated and dealt with by meansof mean filter and image binarization,thus obtaining a statistical image.Finally,IC failure points can be effectivelylocated according to the statistical image.Physical analysis demonstrates the accuracy of IC PEM based on the pro-posed differential image localization algorithm.

    A Low Computational Complexity Channel Estimation Algorithm for Time- Variant Channels
    Huang Min Li Bing- bing Sun Ru- qin
    2014, 42(9):  76-81.  doi:10.3969/j.issn.1000-565X.2014.09.014
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    For the orthogonal frequency- division multiplexing (OFDM) systems in time- variant channels,traditionalestimation methods are of poor estimation performance and high computational complexity.In order to solve theseproblems,we propose a channel estimation method named as DD- LMMSE (Dual- Diagonal Linear Minimum MeanSquare Error).In this method,a system model is constructed on the basis of expansion model (BEM) and the esti-mated coefficients of BEM are obtained by performing the diagonal LMMSE twice,and thus achieving the channelimpulse response (CIR) in time domain.Simulation results show that,whether in slowly time- variant or rapidlytime- variant channels,the proposed method has better performance and lower computational complexity.

    An Improved Interacting Multiple Model Algorithm Based on Multi- Sensor Information Fusion Theory
    Zhou Wei- dong Liu Meng- meng Yang Yong- jiang
    2014, 42(9):  82-89.  doi:10.3969/j.issn.1000-565X.2014.09.015
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    In the classical interacting multiple model (IMM) algorithm,because of the Gaussian approximation tothe likelihood function and the confusion of probability density function and probability mass function,the obtainedmode probabilities are only the approximations of probability mass,which is a suboptimal result in the sense ofBayes.In order to solve this problem,a reweighted IMM algorithm is proposed based on the correlation among theestimation errors of mode- conditioned filters and the multi- sensor optimal information fusion criterion.In this algo-rithm,the mode probabilities are updated by calculating the cross- covariance matrix of estimation errors,and thenthe filtering results are fused according to the optimal information fusion theory.Theoretical analysis and simulationresults indicate that the estimation accuracy of the proposed algorithm is significantly improved in comparison withthose of the classical IMM algorithm and other IMM- related algorithms which ignore the error correlation.

    Robust Flight Control Law Design of Unmanned Aerial Vehicle Based on Baseline- Augmented Control Structure
    Yang Yi Chen Xin Li Chun- tao
    2014, 42(9):  90-95,101.  doi:10.3969/j.issn.1000-565X.2014.09.016
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    Flying unmanned aerial vehicles can be easily affected by such uncertain factors as disturbance andunmodeled dynamics.In order to solve this problem,a new robust flight control law design method is proposed.Based on the framework of a baseline controller and an augmented compensator,the baseline controller uses arobust servomechanism LQR control method so as to provide the basic command to track the control input.Then,by using the ideal closed loop system of the baseline controller as a reference model,the augmented compensator onthe basis of robust model- reference adaptive control algorithm is constructed,so that the adverse effect caused bybounded disturbance and unmodeled dynamics is reduced.Theoretical analysis demonstrates that the proposedcontrol law is able to ensure the closed- loop system of being stable and the output tracking error of being bounded inthe presence of bounded disturbance and unmodeled dynamics.The comparative nonlinear simulation resultsdemonstrate that the proposed control system is able to reject various kinds of disturbances,indicating that the pro-posed system is effective and robust.

    Design and Processing of Spherical Inflatable Antenna
    Huang He Guan Fu- ling Feng Shang- sen
    2014, 42(9):  96-101.  doi:10.3969/j.issn.1000-565X.2014.09.017
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    The analysis,design and manufacture of spherical inflatable antenna have become hot research issuesboth at home and abroad,and the demands on mass production and processing research are urgent.From the per-spective of design and process,this paper proposes an analytical method for the initial profile design of inflatableantenna reflector and the design of membrane pieces,and presents design methods for the pasting molds of reflectorand sphere as well as for the cutting line and mold.Moreover,the processes and procedures of spherical inflatableantenna are illustrated.Performance test results show that the proposed process and procedure is feasible,efficientand reliable.

    Automotive Engineering
    Investigation into Mean Crush Force of Single- Cell Thin- Walled Rectangle Section Beam
    Tian Sheng
    2014, 42(9):  102-106,146.  doi:10.3969/j.issn.1000-565X.2014.09.018
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    The energy absorption ability of a car rail during crash depends on the mean crush force of the rail.Themean crush force research helps to know the rail impact performance and reduce the potential defect at conceptdesign stage.However,as for the mean crush force,there is a considerable discrepancy among tests,simulationsand fitting results in literatures.In order to solve this problem,this paper analyzes the relationships between themean crush force and such parameters as the beam shape,beam thickness and mechanical properties of material bycombining physical tests with simulations.Then,a series of single- cell thin- walled rectangle section beams areemployed to carry out tests and simulations,and a new formula of mean crush force is deduced for the beams on thebasis of minimization principle of range,maximum deviation and standard deviation.The calculation results showthat the deduced formula achieves a fitting value which is closer to the simulation value than that in literatures,andit can meet the concept design requirement of frontal rail.

    A Novel Driving System for Rang- Extended Electric Vehicle
    Luo Yu- tao Jiang Cui- na Liang Wei- qiang Lin Xiao- wei
    2014, 42(9):  107-113.  doi:10.3969/j.issn.1000-565X.2014.09.019
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    In order to improve the dynamic performance and the fuel economy of HEV (Hybrid Electric Vehicle)and to simplify the structure of driving system,a novel multi- mode driving system is proposed for REEV (Rang-Extended Electric Vehicle).Then,all the operating modes and the power flow distribution of the proposed systemare analyzed,and the performances of engine,motor and battery are obtained through a bench test.On this basis,a dynamic model of such key power components as engine,main motor,auxiliary motor and the battery and a vehi-cle simulation model are established by using the Matlab/Simulink software,and the dynamic performance and thefuel economy of the vehicle are simulated.The results show that,as compared with the Volt system,the proposedsystem improves the dynamic performance significantly,increases the maximum speed by 37.5% and decreases thefuel consumption by 24.8%.

    Design of a Novel Electric Clutch Actuator for Hybrid Vehicles
    Wu Hai- kang Zhong Zai- min Yu Zhuo- ping Wang Xin- jian
    2014, 42(9):  114-121.  doi:10.3969/j.issn.1000-565X.2014.09.020
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    This paper analyzes the functional requirements of the electric diaphragm spring clutch actuator in thefixed shaft transmission for hybrid vehicles.Then,a design to apply a two- way overreach clutch to the clutchactuator is proposed,which is used to realize positive high efficiency driving and the reverse self- locking function atthe same time.Moreover,the authors describe both the working principle of the proposed clutch actuator and themechanical structure of its prototype,and analyze the principles in great detail of how the two- way overreach clutchrealizes the reverse self- locking and the positive high efficiency driving function.Finally,the feasibility of theproposed clutch actuator is verified by experiments,and its shortcomings and corresponding solutions are alsoexpounded.

    Effects of Gas Dissolution and Precipitation in Ring Cavity on Hydro- Pneumatic Suspension Characteristics
    Zhang Wei Zhang Wen- ming Zhao Xuan Chen Qiang Li Xin- long
    2014, 42(9):  122-128.  doi:10.3969/j.issn.1000-565X.2014.09.021
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    In the single chamber- type hydro- pneumatic suspension of construction vehicles,some gas flows into ringcavity with liquid,and the gas dissolution and precipitation in the ring cavity can affect the suspension performanceto some extent.In order to reveal the effect mechanism,a nonlinear mathematical model of hydro- pneumaticsuspension is established on the basis of gas volume in the ring cavity.In this model,a co- simulation method isused to solve nonlinear equations so as to analyze the effect of the gas dissolution and precipitation in the ring cavityon the pressure.Furthermore,an equally- proportional hydro- pneumatic suspension test bench is set up to verify theco- simulation results.Comparison between the co- simulation and experimental results indicates that (1) the pro-posed model can accurately describe the effect of the gas dissolution and precipitation in ring cavity on the suspen-sion performance and the effect should not be ignored in the design and application of this kind of suspension;(2) the gas solubility and the external stimulation play an important role in the effect; and (3) the gas dissolutionand precipitation have a small effect on the suspension spring quality but have strong effects on the impact,vibra-tion strength and durability of internal structure of the hydro pneumatic suspension.

    A Measurement Method of Vehicle Center of Gravity Based on Dynamic Braking Model
    Zhang Li- bin Yue Hong- wei Liu Yi- cai Li Fu- qi
    2014, 42(9):  127-133.  doi:10.3969/j.issn.1000-565X.2014.09.022
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    The center of gravity (CG) height of a vehicle is an important indicator that affects the stability,smooth-ness and security of the vehicle.Too much CG height of a vehicle may lead to a serious traffic accident.In order tosolve this problem,a dynamic method measuring CG of a vehicle is proposed on the basis of a dynamic brakingmodel.This method utilizes a plate- type test bench to estimate the height of CG of a vehicle according to measuredaxle mass and brake force.Then,a dynamic detection system of the CG position of a vehicle is established,and areal vehicle experiment is performed to verify the proposed method.It is found that the detection value of the pro-posed method is closer to the actual one in the driving process of the vehicle.Meanwhile,the proposed method isemployed to obtain the CG height of three different types of vehicles.The results show that the proposed method ishigher in measurement accuracy and efficiency,and suitable for the measurement of the CG of vehicles of any type.

    A Series- Parallel Hydraulic Hybrid System and Its Control Strategy
    2014, 42(9):  134-139.  doi:10.3969/j.issn.1000-565X.2014.09.023
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    The whole vehicle performance depends on the topological structure and the control strategy of hybridpower system.In this paper,a series- parallel hydraulic hybrid system is proposed on the basis of ground torquecoupling mode.This kind of hydraulic hybrid system is suitable for the working condition of urban public traffic.Inorder to meet the instantaneous power requirement of vehicles and achieve the optimal global economy,an energymanagement strategy is proposed for the whole vehicle.Then,to simplify the system structure,the progressivelyhierarchical control method is adopted according to the hybrid system theory.Finally,through the Matlab/Simu-link/Statflow co- simulation,a forward model of the whole vehicle is established and the fuel economy and thedynamic performance of a whole vehicle are analyzed under the ECE city driving cycle.The results show that theproposed system and strategy can significantly improve the engine output characteristic and effectively increase thefuel economy and the instantaneous dynamic performance of the whole vehicle.

    Simulation and Experimental Research on Performance of Decompression Engine Brake
    Gong Jin- ke Wang Yun- ke Jia Guo- hai
    2014, 42(9):  140-146.  doi:10.3969/j.issn.1000-565X.2014.09.024
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    In order to investigate the decompression engine brake performance,a mesh model is established withthe help of the software CFD (Computational Fluid Dynamics) according to the analysis on its working process.Then,a 3D simulation of the working process of the transient decompression engine brake is performed by means ofthe dynamic mesh technology,and the simulation results are verified by experiments.The results show that (1) thehigher the rotating speed of engine is,the better its braking performance will be; (2) the larger the decompressionvalve opening is,the higher the brake power peak will be; (3) however,the maximum decompression valve openingis limited by compression clearances and piston movement rules; and (4) at a certain rotating speed,each decom-pression valve opening corresponds to an optimal decompression valve advance angle,which causes an optimal bra-king performance.Besides,the optimal valve advance angle decreases as the decompression valve opening increases.

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