• Journal of the Korean Institute of Intelligent Systems
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• v.10 no.6
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• pp.597-604
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• 2000

본 연구에서는 전기자동차에 사용되는 전자식 차동 시스템의 신경망 모델을 제안한다. 차량이 곡선도로를 따라 주행할 경우 내측 바퀴와 외측 바퀴의 회전속도가 서로 달라야 진동이나 뒤틀림 없이 완만한 선회 주행을 할 수 있다. 전기자동차는 그 구조적 특성상 각각의 바퀴가 독립된 구동원을 갖는다. 이 때문에 일반 엔진 차량의 기어식 차동장치를 대신할 전자식 차동장치가 요구된다. 이러한 차동장치는 차량의 구조뿐만 아니라 차량의 주요 파라미터인 조향각 및 속도에 따라서 비선형적인 관계를 가지고 있어서 해석하기가 쉽지 않다. 따라서 이와 같은 비선형적인 관계 모델을 학습 능력을 가진 신경망에 의하여 모델링 함으로써 제어에 적용할 수 있다. 이를 실현하기 위해 제작한 전기자동차로 곡선도로를 주행하여 다양한 곡률과 주행속도에 따른 내측 외측 바퀴의 회전속도 데이터를 획득하고, 데이터의 비선형 특성을 고려한 차동 속도 제어기의 구조를 설계한다. 이 제어기에 적합한 모델은 신경망을 이용하여 실측 데이터를 학습시킴으로써 차동기능을 수행할 수 있는 제어기를 구현한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.5
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• pp.62-70
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• 2015

A liquid rocket engine system can cause rapid pressure and temperature variations during the startup period. Thus the startup analysis is required to reduce time and expense for successful development of liquid rocket engine through the startup prediction. In this study, a startup analysis simulator is developed for a staged combustion cycle engine powerpack. This simulator calculates propellant flow rates using pressure and flow rate balances. In addition, a rotational speed of turbopump is obtained as a function of time by mathematical modeling. A startup analysis result shows that the time to reach a steady-state and a rotational speed at the steady-state are 1.3 sec and 27,500 rpm, respectively. Moreover it can indicate proper startup sequences for stable operation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1529-1535
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• 2011

Improvement of the thermal efficiency in operation and maintenance of low- and medium-speed engines is a kind of never-ending requirement in the maritime power plant business. For the purpose of improving engine management efficiency, a principal factor that represents the fitness of the engine should be identified. Gas pressure, gas temperature, and vibration have all been used as this factor. However, they have limitations in terms of response speed and diagnosis accuracy. The EFR (engine fitness ratio) is suggested as a new diagnostic factor in this paper. The EFR is defined as the ratio of particular frequencies in the frequency domain and represents the fitness of an engine. It is calculated from the fluctuation pattern of the crankshaft angular speed. The EFR was verified using an experimental method for a low-speed engine and an analytic method for a medium-speed engine.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.765-770
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• 2020

The turbochargers used widely in diesel and gasoline engines are effective devices to reduce fuel consumption and emissions. In this study, the isentropic turbine efficiency of the steady flow in a twin-scroll turbocharger for the passenger vehicle gasoline engine was analyzed. The cold gas test bench was designed and made. The pressure and temperature of the inlet and exit of the turbine were measured at 60,000, 70,000, 90,000, and 100,000rpm under the steady-state flow. The isentropic turbine efficiency was calculated. The efficiency was the range of 0.53 to 0.57. The BSR and expansion ratio were changed from 0.71 to 0.84 and from 1.24 to 1.72, respectively. The isentropic turbine efficiency decreased with increasing BSR and expansion ratio. The operation of only scroll A or B was compared with that of the twin-scroll turbine. The isentropic efficiency of using only scroll B was higher than those of only scroll A at 60,000rpm. The isentropic efficiency of using only scroll A was higher than those of only scroll B at 100,000rpm. Therefore, the twin-scroll turbine used in this study is operating effectively in the wide speed range.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.688-694
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• 2008

A rotordynamic analysis is performed for a high thrust class liquid rocket engine turbopump considering the dynamic characteristics of ball bearings and pump noncontact seals. Complex eigenvalue problems are solved to predict the rotating natural frequencies and damping ratios as a function of rotating speeds. Synchronous rotor mass unbalance response and time transient response analyses are also performed to figure out the rotor critical speed and the onset speed of instability. From the numerical analysis, it is found that the rear bearing stiffness is most important parameter for the critical speed and instability because the 1st mode is turbine side shaft bending mode. The pump seal effect on the critical speed is enlarged as the rear bearing stiffness decreases and the front bearing stiffness increases.

• Journal of the KSME
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• v.53 no.2
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• pp.30-34
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• 2013

기어는 사람에 의해 사용된 가장 중요한 기계 중의 하나이며, 회전하는 두 축 사이에 운동과 동력을 전달하고 회전 방향과 속도를 변경하는 역할을 한다. 기어는 우리가 손에 차는 시계나 벽시계뿐만 아니라 자동차, 기차, 선박, 비행기에서 엔진의 동력을 전달하여 바퀴나 혹은 프로펠러를 돌리기 위해 사용된다. 또한 장난감, 복사기, 팩스, 풍력발전기에 사용하는 등 그 용도가 다양하다. 이 글에서는 기어의 역사를 간단히 살펴보고 기어의 진동 소음에 관련된 연구 주제에 대해 기술한다.

• Proceedings of the KAIS Fall Conference
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• 2010.05b
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• pp.1163-1165
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• 2010

가솔린 기관의 체적 효율은 흡기 장치의 효율의 척도로 표현된다. 현재 체적효율은 4행정 가솔린 엔진의 흡기장치의 특성과 공연비 제어를 위한 중요한 파라미터로 사용되고 있다. 체적 효율은 이론적으로 실린더로 흡입 가능한 양에 대한 실제로 실린더로 흡인한 공기량의 비율이다. 체적효율은 엔진회전 속도와 흡기다기관 부압에 따라 결정되는 종속변수이다. 체적 효율은 정상상태와 과도상태와 같은 엔진의 모든 운전조건을 시험하는데 한계와 제약이 매우 크다. 이 논문에서는 선형 알고리즘을 사용하여 체적 효율의 파라미터를 규명하여 선형 다항식 모델을 개발한다. 그리고 실험으로 구한 체적효율 데이터와 다항식 모델을 비교하고 객관적인 타당성을 평가 하였다.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.202-203
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• 2011

본 논문에서는 자동차가 전기모터로 주행하다가 배터리가 방전되면 엔진으로 구동할 수 있도록 연결해 주는 클러치 시스템에 적용된 BLDC 모터의 위치제어기를 제안한다. 클러치 시스템에 사용되는 BLDC 모터의 구동은 Hall 센서로부터 검출된 회전자 위치정보를 이용하여 위치제어를 수행하였다. PHEV 시스템에서는 클러치를 엔진과 전기모터로 연결해야 하므로 정확하고 빠른 위치제어를 위해 위치제어기를 적용하였고, 클러치 연결 시 진동을 최소화하기 위해 속도제어기를 사용하여 엔진의 속도와 클러치 모터의 속도를 동기가 되도록 하였다. 또한 위치제어를 하기 전에 클러치의 초기위치를 맞춰 줘야 하므로 모터의 위치정보를 이용하여 속도제어기와 전류제어기로 모터를 일정한 위치로 이동시켰다. BLDC 모터의 전압제어를 위한 PWM 방법은 기존의 바이폴라 PWM 보다 전류리플이 적은 유니폴라 효과를 내는 새로운 바이폴라 PWM 방법을 사용하였다. 제안된 알고리즘은 시뮬레이션과 실험을 통해 검증하였다.

• Journal of ILASS-Korea
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• v.16 no.3
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• pp.126-133
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• 2011

In HCCI Engine, combustion is affected by change of compression speed corresponding to engine speed. The purpose of this study is to investigate the mechanism of influence of engine speed on HCCI combustion characteristics by using numerical analysis. At first, the influence of engine speed was shown. And then, in order to clarify the mechanism of influence of engine speed, results of kinetics computations were analyzed to investigate the elementary reaction path for heat release at transient temperatures by using contribution matrix. In results, as engine speed increased, in-cylinder gas temperature and pressure at ignition start increased. And ignition start timing was retarded and combustion duration was lengthened on crank angle basis. On time basis, ignition start timing was advanced and combustion duration was shortened. High engine speed showed higher robustness to change of initial temperature than low engine speed. Because of its high robustness, selecting high engine speed was efficient for keeping stable operation in real engine which include variation of initial temperature by various factors. The variation of engine speed did not change the reaction path. But, as engine speed increased, the temperature that each elementary reaction would be active became high and reaction speed quicken. Rising the in-cylinder gas temperature of combustion start was caused by these gaps of temperature.

• Restorative Dentistry and Endodontics
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• v.31 no.3
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• pp.179-185
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• 2006

This study was conducted to evaluate canal configuration after shaping by $ProTaper^{TM}$ with various rotational speed in J-shaped simulated resin canals. Forty simulated root canals were divided into 4 groups, and instrumented using by $ProTaper^{TM}$ at the rotational speed of 250, 300, 350 and 400 rpm. Pre-instrumented and post-instrumented images were taken by a scanner and those were superimposed. Outer canal width, inner canal width, total canal width, and amount of transportation from original axis were measured at 1, 2, 3, 4, 5, 6, 7 and 8 mm from apex. Instrumentation time, instrument deformation and fracture were recorded. Data were analyzed by means of one-way ANOVA followed by Scheffe's test. The results were as follows 1. Regardless of rotational speed, at the $1{\sim}2mm$ from the apex, axis of canal was transported to outer side of a curvature, and at 3~6 mm from the apex, to inner side of a curvature. Amounts of transportation from original axis were not sienifcantly different among experimental groups except at 5 and 6 mm from the apex. 2. Instrumentation time of 350 and 400 rpm was significantly less than that of 250 and 300 rpm (p<0.01). In conclusion the rotational speed of $ProTaper^{TM}$ files in the range of $250{\sim}400rpm$ does not affect the change of canal configuration, and high rotational speed reduces the instrumentation time. However appearance of separation and distortion of Ni-Ti rotary files can occur in high rotational speed.