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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Transactions of the Korean Society of Automotive Engineers
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Journal DOI :
The Korean Society of Automotive Engineers
Editor in Chief :
Volume & Issues
Volume 14, Issue 6 - Nov 2006
Volume 14, Issue 5 - Sep 2006
Volume 14, Issue 4 - Jul 2006
Volume 14, Issue 3 - May 2006
Volume 14, Issue 2 - Mar 2006
Volume 14, Issue 1 - Jan 2006
Selecting the target year
Optimum Design of the Shock Absorber Position Using ADAMS and VisualDOC
Ok, Jin-Kyu ; Baek, Woon-Kyung ; Sohn, Jeong-Hyun ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 1~8
In this paper, an optimum design technology is developed to find an optimal position of the shock absorber using ADAMS and VisualDOC. A vehicle with a torsion-beam rear suspension is modeled by using ADAMS. Design variables for the optimal positioning of the shock absorber are defined considering the hard points of the chassis structure and design positioning are specified through the sensitivity analysis using a bump-crossing simulation. The objective function is defined as the joint reaction forces of the shock absorber connecting joints of the chassis structure. Sequential Quadratic Programming and Genetic Algorithms are used for this study. To validate the optimized design variables, pothole simulations are performed. GA showed better results than SQP algorithms for this design purpose.
Effect of Lock-up Control Strategy on Vehicle Fuel Economy
Kim, Woo-Seok ; Han, Chang-Ho ; Kim, Nam-Kyun ; Park, Kyung-Seok ; Park, Jin-Il ; Lee, Jong-Hwa ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 9~15
Experiments are conducted to compare fuel economy of FTP-75 mode on two different lock-up conditions; (A) Lock-up on at engine speed of 1,200(rpm) and above for 3rd & 4th gear, (B) Lock-up on at engine speed of 1400rpm and above for 4th gear only. As a result, case A had better fuel economy about 2.75(%) than case B for FTP-75 mode. Simulation(CRUISE, AVL) study is also carried out in order to estimate the effect of Lock-up control strategy for vehicle fuel economy. The fuel economy simulation result agrees with the measured fuel economy within error of 2(%). The improved Lock-up control strategy is proposed by simulation.
Creep Life Prediction of SUS 316L Stainless Steel
Yoon, Jong-Ho ; Hwang, Kyung-Choong ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 16~22
Stainless steel has widely been used in various industrial fields because it has high corrosion resistance. But, we have little design data about the creep life prediction of SUS316L stainless steel. Therefore, in this study, a series of creep tests and study on them under 16 constant stress and temperature combined conditions have been performed to get the creep design data and life prediction of SUS316L stainless steels and we have gotten the following results. First, the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy gradually decreases as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy is estimated about 10. And last, the creep rupture fractographs show the intergranular ductile fracture with many dimples.
A Tolerance Analysis Method for Spot-welded Deformable Auto Body Parts
So, Hyun-Chul ; Kim, Kuk-Saeng ; Yim, Hyun-June ; Jee, Hae-Seong ; Park, Bong-Jun ; Yoo, In-Suk ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 23~31
Tolerance analysis of auto body requires the consideration of its compliance because of potentially significant deformation during the spot-weld assembly process. In this paper, a relatively recent method for such analyses is briefly introduced as one can find in the literature. In this method, it is important to take into account of the covariance between the sources of variation as they are closely located, which is the case in most auto body assembly. However, it is often impossible to know such covariance, for example, when a new car is being developed. Therefore, a mechanics-based method is proposed in this paper to estimate the covariance among the sources of variation by finite element analyses and simple statistical computations. The proposed method is illustrated by applying it to a three-dimensional model of real front wheel housing.
A Vehicle Adaptive Cruise Control Design in Consideration of Human Driving Characteristics
Gu, Ja-Sung ; Yi, Kyong-Su ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 32~38
A vehicle adaptive cruise control strategy based on human drivers' driving characteristics has been investigated. Human drivers driving characteristics have been analyzed using vehicle test data obtained from 125 participants. The control algorithm has been designed to incorporate the driving characteristics of the human drivers and to achieve natural vehicle behavior of the controlled vehicle that would reduce the workload of the human driver. Vehicle following characteristics of the cruise controlled vehicle have been compared to real-world driving radar sensor data of human drivers using a validated vehicle simulator. and compare nominal cruise control and adaptive cruise control.
The Study about the Performance-Analysis of a Automotive Engine Cooling System
Shin, Chang-Hoon ; Lee, Seung-Hee ; Park, Warn-Gyu ; Jang, Gi-Lyong ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 39~48
An engine cooling system affects overall performances of an engine which has been recently requested higher power in more confined engine room. The design of efficient cooling system demands a great effort to effectively correlate with each components, such as water jacket, radiator, coolant pump, cooling fan, etc. Thus, the aim of this study is to provide the design tool of the cooling system in the early design stage by enabling for the designer to accurately predict the engine cooling performances. This user-friendly design tool has various ways to assemble each components and control the running condition with related database. The present design tool was simulated and compared with experimental data. As a result, the inlet and outlet temperature of the radiator agree very well with experiments. It was concluded that the present design tool could be effectively used for the design of the engine cooling system.
A Study on the Combustion Characteristics of Diesel Fuel Droplet with Additive Oxygenate and Paraffin
Kim, Bong-Seock ; Miyamoto, Noboru ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 49~56
The single droplet combustion characteristics of multicomponent fuel such as diesel-oxygenate and diesel-paraffin blends under high ambient temperature and atmospheric pressure were investigated in the study. The results of the study may be concluded as follows : In the combustion of diesel fuel droplet with additive of oxygenate and paraffin, the dimensionless droplet size of
was linearly decreased with time. A fuel droplet with low boiling temperature additives and in high boiling temperature diesel fuel evaporates and burns faster than usual diesel fuel. This rapid burning may result from so-called "micro-explosion" and its burning intensity varies with the types of additives. The results above may suggest that rapid evaporation of oxygenate additive in the middle stage of combustion can contribute much to combustion improvement of blended fuels. When compared to ordinary diesel fuel, neat oxygenate and paraffin fuels show blue flame during entire combustion which prove smokeless combustion.
Pastic Strain Ratio and Texture Evolution of Aluminum/Polypropylene/Aluminum Sandwich Sheets
Kim, Kee-Joo ; Jeong, Hyo-Tae ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 57~66
AA5182-polypropylene sandwich sheet was manufactured, and the mechanical properties evaluation was executed in order to identify
band that causes fabrication process problem and especially surface roughness. To identify formability, deformation behavior, plastic strain ratio (R-value) and pole figure were measured, and texture analysis was performed. In the case of sandwich sheet, the unstable deformation behavior has decreased. As well, for sandwich sheet, A1 skin could manage the most of load, and the elongation has improved about 45% more than that of A1 skin. The plastic strain ratio of A1 skin and sandwich panel, which indicates serration behavior, was obtained from instantaneous plastic strain ratio evaluation. Also, the planar anisotropy of sandwich sheet has decreased more than that of A1 skin. According to these results, the sandwich sheet produced lightening effect and could control unstable deformation characteristic, that is, surface roughness caused by
band. Furthermore, it was proved that the texture control of the rolling attachment of A1 skin is necessary to improve the formability of the sandwich panel.
Measurement of Interfacial Crack Length by Ultrasonic Scattering Compensation Depending on Thickness Variations of Bonded Dissimilar Components
Chung, Nam-Yong ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 67~75
In this paper, the compensation of ultrasonic scattering on interface crack depending on thickness variations of A1/Epoxy bonded dissimilar components was applied to improve measuring accuracy by using ultrasonic attenuation coefficient. The optimum conditions of theoretical value and experimental measuring accuracy by the ultrasonic method in A1/Epoxy bonded dissimilar components have been investigated. From the experimental results, the measurement method of interfacial crack lengths by using ultrasonic attenuation coefficient was proposed and discussed. After the ultrasonic scattering compensation depending on thickness variations of bonded dissimilar components was carried out, the measuring accuracy of interfacial crack length was improved by 5%.
Finite Element Analysis on Standing Wave Phenomenon of a Tire Considering Tread Pattern
Kim, Kee-Woon ; Jeong, Hyun-Sung ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 76~83
Each tire has a critical speed at which a standing wave phenomenon occurs along the circumferential direction. If the standing waves are formed, the tire temperature is rapidly increased and it leads to tire failure eventually. As the formation of the standing waves is closely related to the tire stiffness, the effect of the tread pattern needs to be studied numerically. The standing wave phenomenon of a tire model with tread pattern is predicted by an explicit finite element method. The critical speed of the tire with tread pattern is in a good agreement with the experiment and is
lower than that of the tire without tread pattern. The effects of the inflation pressure and the vertical load on the critical speed are also investigated by using the tire model with tread pattern.
The Limit Compression Ratio of Knock Occurring by
in the Heavy Duty Hydrogen-CNG Fueled Engine
Kim, Yong-Tae ; Lee, Jong-Tai ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 84~91
A heavy duty hydrogen-natural gas fueled engine can obtain stable operation at ultra lean conditions and reduce emissions extremely. Reduction of
in its engine is one of the most benefit. In this study, rate of hydrogen addition(
) and compression ratio(
) were investigated including performance of this engine. As results, it was found that phenomenon of pressure oscillation when increasing
, it means occurring knock. It consider that pressure oscillation was increased due to fast burning speed of hydrogen. Even if same compression ratio, pressure oscillation was remarkable increased according to increasing
. Therefore, limit compression ratio of knock occurring was reduced by increasing
Bending Collapse Characteristics of Hat Section Beam Filled with Structural Foam
Lee, Il-Seok ; Kang, Sung-Jong ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 92~99
Design capability for high safety vehicle with light weight is crucial to enhancing competitive power in vehicle market. The structural foam can contribute to restraining section distortion in body members undergoing bending collapse at vehicle crash. In this study, first, the validation of analysis model including structural foam model for simulating fracture behavior was discussed, and the bending collapse characteristics of five representative section types were analyzed and compared. Next, with changing the laminate foam shape, load carrying capability and absorbed energy were observed. The results suggests a design strategy of body members filled with laminate foam, leading to effectively elevating bending collapse characteristics with weight increase in the minimum.
Study on the Spray Behavior from Swirl and Fan Spray Type Gasoline Injectors Impinging on the Constant Temperature Flat Plate
Kim, Chong-Min ; Kang, Shin-Jae ; Kim, Man-Young ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 100~106
The behavior of spray impinging on the inclined constant temperature flat plate was experimentally investigated. To clarify the wall effect of a high pressure DISI injector, a relative angle of the inclined wall to a spray axis was varied. Spray penetration along the wall was observed optically and it was compared with that of a Fan spray type and Swirl type spray. To evaluate various spray motion quantitatively, a spray path penetration which describe the development of a spray tip along the wall was newly introduced. To observe the structure of an impinging spray, it was visualized by a controlled stroboscope light and its visualized image was captured on an CCD camera. Using the digital image of impinging spray
was extracted to clarify the structure of impinging spray. The main parameter of the relative position of the wall was the inclined angle which was defined as the angle was varied from
(vertical impingement) to
at the same condition.
A Study on the Simulation Model Verification for Performance Estimation of Torsion Beam Axle
Choi, Sung-Jin ; Park, Jung-Won ; Jeon, Kwang-Ki ; Lee, Dong-Jae ; Choi, Gyoo-Jae ; Park, Tae-Won ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 107~113
The torsion beam axle type is widely used in the rear suspension for small passenger cars due to low cost, good performance, etc. To develop the torsion beam axle, it is necessary to estimate the characteristics of rear suspension from the design process. The characteristics estimation of the torsion beam axle is performed using FEM, dynamic simulation and is verified the real test. In this study, the natural frequency and roll stiffness of the torsion beam axle were measured by FEM, and the reliability of the FE model was evaluated according to the comparison of test data. This study presents a unique method for the finite element modeling and analysis of the torsion beam axle. The results of the FEA were verified using test data.
Lean Combustion Characteristics with Hydrogen Addition in a LPG Fuelled Spark Ignition Engine
Oh, Seung-Mook ; Kim, Chang-Up ; Kang, Kern-Yong ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 114~120
The basic effects of hydrogen addition for engine performance and emission were investigated in single cylinder research engine. Seven commercial injectors were tested to choose a suitable injector for hydrogen injection prior to its engine implementation. The hydrogen fuel leakage and flow rate were evaluated for each injector and KN3-1(Keihin, CO.) showed the best performance for hydrogen fuel. At the higher excess air ratio(
, 2.0), the better combustion stability was found with hydrogen addition even though its effect was small at lower excess air ratio (
, 1.3). Stable operation of the engine was even guaranteed at
, if the amount of hydrogen gas was near 15% of total energy. In the lean region,
, thermal efficiency was improved slightly while it was not clearly observed at
, 1.3. It is considered that, in some cases, high temperature environment due to hydrogen combustion caused further heat loss to surroundings. Except for
, with larger amount of hydrogen addition, CO was reduced drastically but it was emitted more at the leaner region. Nitric oxides(NOx) was increased a little more with hydrogen addition at
, 1.3. However, at
its relative amount of emission was low. In addition, the amount of NOx was continuously decreased with hydrogen addition, but, at
the amount of NOx was lowered to 1/100 of that of
. THC emission was significantly increased as air/fuel ratio was raised to leaner region due to misfire and partial burn.
An Experimental Study on the Stratified Combustion Characteristics in a Direction Injection Gasoline Engine
Lee, Chang-Hee ; Lee, Ki-Hyung ; Lim, Kyoung-Bin ; Kim, Bong-Gyu ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 121~126
A gasoline-fueled stratified charge compression ignition (SCCI) engine with both direct fuel injection and intake temperature and compression ratio was examined. The fuel was injected directly by using the high temperature resulting from heating intake port. With this injection strategy, the SCCI combustion region was expanded dramatically without any increase in NOx emissions which were seen in the case of compression stroke injection. Injection timing during the intake temperature was found to be an important parameter that affects the SCCI region width. The effect of mixture stratification and the effect of fuel reformation can be utilized to reduce the required intake temperature for suitable SCCI combustion under each set of engine speed and compression ratio conditions.
Recyclability Estimation of Fuel Tank Module in Vechicle
Lee, Chul-Min ; Lee, Eun-Ok ; Kim, Ha-Su ; Lee, Jun-Su ; Kang, Hee-Yong ; Yang, Sung-Mo ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 127~135
We analyzed recyclability of the fuel tanks made from steel or aluminum alloy. For a comparison of the fuel tank recyclability, first we had analyzed the process of disassembly in a vehicle and evaluated its disassemblability. Then we evaluated the recyclability for reuse and withdrawal. The processes were more or less same owing to the similarity of fastening method of fuel tank and components. However, the fuel tank of the aluminum alloy was easier (about 5%) to disassembly than the fuel tank of steel. This could be attributed to the differences in weight of steel and aluminium. On light of the withdrawal and reuse, the fuel tank made up of steel needed to plate with zinc or lead due to its anti-corrosiveness. Hence, it required additional processes. In this paper, we were explaining the results of our on going research on the recyclability of fuel tanks made of steel and aluminum alloys. The differences that we found between the fuel tank made up of the aluminum alloy and steel were in their weight, recyclability, disassemblability, anticorrosive property, cost and productivity.
Performance Evaluation for Hydraulic Type Energy Regenerative System
Jung, Dong-Soo ; Kim, Hyong-Eui ; Kang, E-Sok ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 136~144
Vehicles usually have 3 types of speed pattern like acceleration, travel, and deceleration. It requires much driving energy from engine while accelerating, preserves much kinetic energy by inertia moment at travel speed, and releases the kinetic energy to the air while decelerating by the break system. If we accumulate the kinetic energy while decelerating and reuse the energy at the accelerating stage, then it can elevate the fuel efficiency, reduce the emission and improve the motive power. This paper proposes a hydraulic type energy regenerative system which converts the kinetic energy into hydraulic energy at the stage of deceleration and reuses it at the starting and accelerating stage of vehicles. The test equipment which has the field condition of city bus was prepared to evaluate the performance for energy regeneration. The test results show that both energy regeneration efficiency and fuel efficiency are improved significantly and the emission is reduced notably.
A Study of Unregulated Emission Reduction Characteristics by Diesel Oxidation Catalyst (DOC) for Light-Duty Diesel Engine
Kim, Ki-Ho ; Ahn, Gyun-Jae ; Kang, Keum-Won ; Lee, Seang-Wock ; Eom, Dong-Seop ; Lee, Tae-Young ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 145~150
Recently emission regulation on diesel vehicles is getting stringent and research on aftertreatment technology such as DPF and DOC has been carried out actively. Even though PM(Particulate matters) reduction efficiency in DOC is relatively low but the structure is simpler and very effective in the reduction of gas materials and unregulated materials. Therefore it has been applied to smaller diesel vehicles. The aims of this research is to investigate the emission reduction characteristics of DOC; DOC performance of regulated and unregulated material emission reduction. It results a Pt based catalyst demonstrated higher emission reduction efficiency than a Pt-V based catalyst in CVS-75 mode, and also the reduction efficiency of unidentified material was excellent.
A Study of the Driveability Improvement on the Electronic Throttle Control M/T Vehicle at Tip-in/out
Park, Kyoung-Seok ; Lee, Jong-Hwa ; Park, Jin-Il ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 151~157
The passenger car drivers want in general to feel good driveability, but they sometimes feel uncomfortable by shock and jerk phenomena when they push or release acceleration pedal with clutch on state. In this paper, the shock and jerk characteristics are studied on the vehicles controlled by the throttle-by-wire system. Experiments and simulations were carried out on two vehicles which show different control characteristics. The engine torque control characteristics was analyzed by measuring cylinder pressure. Various specification factors of the vehicles and the torque control logic of the engines were simulated through experimental data basis. The result shows the spring effect of the trans-axle in the drive-train is one of the most important factors of the shock-jerk phenomena and the engine torque control method is also responsible for the reducing the shock-jerk amplitude. In this paper a new control logic of the engine torque is suggested for the better driveablility on the tip-in/out event.
Development of Uni-Axial Bushing Model for the Vehicle Dynamic Analysis Using the Bouc-Wen Hysteretic Model
Ok, Jin-Kyu ; Yoo, Wan-Suk ; Sohn, Jeong-Hyun ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 158~165
In this paper, a new uni-axial bushing model for vehicle dynamics analysis is proposed. Bushing components of a vehicle suspension system are tested to capture the nonlinear and hysteric behavior of the typical rubber bushing elements using the MTS machine. The results of the tests are used to develop the Bouc-Wen bushing model. The Bouc-Wen model is employed to represent the hysteretic characteristics of the bushing. ADAMS program is used for the identification process and VisualDOC program is also used to find the optimal coefficients of the model. Genetic algorithm is employed to carry out the optimal design. A numerical example is suggested to verify the performance of the proposed model.
Effects of Parameters of Combustion and Fuel Injection System on Performance and Exhaust Emissions in a Diesel Engine
Lee, Joon ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 166~173
This study investigates a heavy duty diesel engine with swept vol. 12.6L, 4cycle-OHC type to verify the effects of the performance and exhaust gas emission according to the variable specifications of both swirl ratio and flow coefficient in inlet port, combustion bowl and fuel injection system. To meet the high BMEP and stringent exhaust emission standard, a turbocharger with wastegate and an intercooler were installed in the engine. Helical port, major design parameters for combustion chamber and electronic fuel injection pump with 1,000bar were reviewed and applied. Confirmation tests were also performed to meet the target value,
5.0g/kWh and PM 0.1g/kWh of Euro3 exhaust emission legislation. The results of this study show that not only is it effective to use a relatively bigger bowl size for controlling rapid burning condition due to the decreased in-bowl swirl, but also to use a concave cam with double injection rates to decrease
Evaluation of the Finite Element Modeling of Spot-Welded Region for Crash Analysis
Song, Jung-Han ; Huh, Hoon ; Kim, Hong-Gee ; Kim, Sung-Ho ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 174~183
The resistance spot-welded region in most current finite element crash models is characterized as a rigid beam at the location of the welded spot. The region is modeled to fail with a failure criterion which is a function of the axial and shear load at the rigid beam. The role of this rigid beam is simply to transfer the load across the welded components. The calculation of the load acting on the rigid beam is important to evaluate the failure of the spot-weld. In this paper, numerical simulation is carried out to evaluate the calculation of the load at the rigid beam. The load calculated from the precise finite element model of the spot-welded region considering the residual stress due to the thermal history during the spot welding procedure is regarded as the reference value and the value of the load is compared with the one obtained from the spot-welded model using the rigid beam with respect to the element size, the element shape and the number of imposed constraints. Analysis results demonstrate that the load acting on the spot-welded element is correctly calculated by the change of the element shape around the welded region and the location of welded constrains. The results provide a guideline for an accurate finite element modeling of the spot-welded region in the crash analysis of vehicles.
An Analytic Study on the Valve Rotation Behavior of an Internal Combustion Engine
Kim, Do-Joong ; Youn, Jae-Won ; Kim, Jin-Woung ; Song, Jin-Ook ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 184~193
Rotation of intake and exhaust valves are very closely related to the long term durability of automotive engines. If the valves do not rotate even at a rated engine speed, it causes the uneven wear of the valve seat and valve head contact area, which eventually shortens the engine life. A principle of valve rotation mechanism was presumed based on some findings from experiments, and computer programs were developed to simulate the valve rotation phenomena. In this study we investigated the valve rotation mechanism by using the computer simulation models.
An Effect of Roof-Fairing and Deflector System on the Reduction of Aerodynamic Drag of a Heavy-Duty Truck
Kim, Chul-Ho ;
Transactions of the Korean Society of Automotive Engineers, volume 14, issue 2, 2006, Pages 194~201
Roof-fairing and deflector system have been used on heavy-duty trucks to minimize aerodynamic drag force not only for driving stability of the truck but also for energy saving by reducing the required driving power of the vehicle. In this study, a numerical simulation was carried out to see aerodynamic effect of the drag reducing device on the model vehicle. Drag and lift force generated on the five different models of the drag reducing system were calculated and compared them each other to see which type of device is efficient on the reduction of driving power of the vehicles quantitatively. An experiment has been done to see airflow characteristics on the model vehicles. Airflow patterns around the model vehicles were visualized by smoke generation method to compare the complexity of airflow around drag reducing device. From the results, the deflector systems(Model 5,6) were revealed as a better device for reduction of aerodynamic drag than the roof-fairing systems(Model 2,3,4) on the heavy-duty truck and it can be expected that over 10% of brake power of an engine can be saved on a tractor-trailer by the aerodynamic drag reducing device at normal speed range(