• Journal of Biosystems Engineering
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• 제40권2호
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• pp.95-101
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• 2015

Purpose: During the start-up period, the response time of a hydraulic system increases in the winter because of the increased oil viscosity caused by the cold weather. The problems of delayed tractor starting and excessive wear of the clutch disk occur for these reasons. Therefore, this study develops an analysis model using the commercial hydraulic analysis program AMESim to examine the characteristics of delays in power shuttle starting at different oil temperatures. Methods: In the experiment, a tractor was stationary on a flat surface with the engine running at a constant speed of 1,080 rpm. The forward lever was then pressed to activate the power shuttle at three different oil temperatures, and the pressure changes were measured. The pressure on the forward clutch control valve was measured by a pressure gauge installed on the hydraulic line supplied to the transmission from the main valve. An analysis model was also developed and verified with actual tests. Results: The trend of the simulated pressures of the power shuttle is similar to that of the measured pressures, and a constant modulation period was observed in both the simulation and test results. However, the difference found between the simulation and test results was the initial pressure required to overcome the initial force of the clutch spring. Conclusions: This study also examines the characteristics of the delayed startup of the power shuttle at different oil temperatures through simulations.

• Journal of Biosystems Engineering
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• 제28권3호
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• pp.187-198
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• 2003

This study was conducted to investigate the effect of design parameters of modulating valve and hydraulic clutch on the shift quality of a power shuttle transmission using a computer simulation. Computer simulation models of a hydraulic control system and a power shuttle drive train were developed and verified by an experimental power train in a laboratory. The software EASY5 was used for the modeling and simulation of the power shuttle transmission. Results of the study were summarized as follows: For a good shift quality. it is required to reduce the transient torque transmitted to the output shaft of the transmission as much as possible. This may be achieved by reducing the modulating time and clutch pressure. It was found that the design parameters most significantly affecting the modulating time and clutch pressure were the spring constant and displacement of a load piston of the modulating valve, and the spring constant and damping of the clutch piston. The modulating time decreased as the spring constant increased and increased as the displacement of the load piston decreased. The transient torque decreased as the modulating time increased. However their relationships were not always linear. As the damping decreased, both the modulating pressure and time decreased, which also resulted in a decrease in the transient torque. The spring constant of the clutch piston affected the modulating time and the peak transient torque. As the spring constant of the clutch increased, the peak transient torque decreased.

• 한국기계가공학회지
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• 제4권4호
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• pp.39-47
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• 2005

In this paper, a novel high power micropump using active check valves in place of conventional passive check valves employed at the inlet and outlet ports is presented. It actively controls open/close motion of check valves using piezoelectric actuator for expansion/contraction of pump chamber. A prototype micropump having an effective size of $17mm{\times}8mm{\times}11mm$ is fabricated. Frequency-dependent flow rate characteristics, bi-directional flow characteristics and load characteristics are experimentally investigated using a timing control method for valve closing motion. From the obtained experimental results, it is ascertained that optimal values of the phase shift compared to the voltage to drive pump chamber are $15^{\circ}$ for inlet check valve and $195^{\circ}$ for outlet. Based on the obtained results, a sheet-type active shuttle valve that has a unified valve-body for inlet and outlet check valves is proposed. A micropump with an effective size of $10mm{\times}10mm{\times}10mm$ is fabricated and the basic characteristics are experimentally investigated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1864-1869
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• 2003

A novel piezoelectric micropump using active check valves in place of conventional passive check valves in inlet and outlet has been proposed and investigated. It actively controls open/close motion of check valves using piezoelectric actuator for expansion/contraction of pump chamber. In this paper, bi-directional flow characteristics and load characteristics are experimentally investigated using an adequate timing control for valve closing motion with a prototype micropump fabricated with the effective size of $17{\times}8{\times}11mm^{3}$. From the experimental results, it is ascertained that optimal values of phase shift against voltage to drive pump chamber for realization of a miniaturized but powerful micropump, are $15^{\circ}$ in inlet check valve and $195^{\circ}$ in outlet. Based on the obtained results, a sheet-type active shuttle valve that has a unified valve-body for inlet and outlet check valves is proposed. A micropump with the effective size of $10{\times}10{\times}10mm^{3}$ is fabricated and basic characteristics are experimentally investigated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1572-1577
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• 2003

The powershift transmission have the advantage of easier operation and higher efficiency by using the hydraulic clutch and mechanical power transfer system. It is important to control the engaging pressure and time. The hydraulic control system is used for these controls of the modulator valve, the accumulator, the sump valve and etc. This study have made a simulator for verifying the pressure characteristic of the shuttle powershift transmission and developed the computer simulation model of the hydraulic components and system by using 'AMESim'. As a result, the design parameters which have an effect on the pressure modulation are verified to the spring stiffness of the modulator valve and the volume of the accumulator.

• 항공우주산업기술동향
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• 제9권1호
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• pp.158-164
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• 2011

항공우주용으로 개발되거나 활용 가능한 상업용 체크밸브사례가 조사되었다. 개발사례로 발사체용, 높은 수명이 요구되는 NASA의 SSME (Space Shuttle Main Engine) 및 지상 지원 시스템 퍼지 라인용과 국내에서 개발된 체크밸브가 있다. 상용품은 미국 주요 밸브개발업체의 제품을 상온용과 극저온용으로 분류하여 조사하였다. 또한 운용 온도, 운용 압력 및 크래킹 압력과 같은 주요 성능과 관련된 씰의 재질, 스프링 강성과 같은 설계 인자의 관계도 설명되었다. 이러한 단품 성능 이외에 채터 및 오염과 같은 운용상의 문제점과 일반적인 해결방안도 언급되었다. 또한 기타주의사항으로 필터, 피팅과 청정도 요구조건에 대하여도 조사되었다

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2013년도 춘계학술대회 논문집
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• pp.1359-1360
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• 2013

• 유공압시스템학회논문집
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• 제7권4호
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• pp.15-22
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• 2010

The typical hydraulic hoisting system of the rack-bar type sluice gate is composed of a hydraulic supply unit using an uni-directional pump, a direction control valve, a hydraulic motor, a counter balance valve, and flow control valves. Here, the hydrostatic transmission is applied to the hoisting system of rack-bar type sluice gate to simplify the operation of gate such that the upward and downward direction of gate is simply controlled by the direction of pump rotation. The new hydraulic hoisting system is composed of a bi-directional pump, a hydraulic motor, a counter balance valve, two check valves, two pilot-operated check valves, two relief valves and a shuttle valve. The characteristics of a suggested system are analyzed by computer simulations and experiments.

• 유공압시스템학회:학술대회논문집
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• 유공압시스템학회 2010년도 춘계학술대회
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• pp.86-92
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• 2010

The typical hydraulic hoisting system of the rack-bar type sluice gate is composed of a hydraulic supply unit using an uni-directional pump, a direction control valve, a hydraulic motor, a counter balance valve, and flow control valves. Here, the hydrostatic transmission is applied to the hoisting system of rack-bar type sluice gate to simplify the operation of gate such that the upward and downward direction of gate is simply controlled by the direction of pump rotation. The new hydraulic hoisting system is composed of a bi-directional pump, a hydraulic motor, a counter balance valve, two check valves, two pilot-operated check valves, two relief valves and a shuttle valve. The characteristics of a suggested system are analyzed by computer simulations and experiments.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.213-217
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• 2017

액체로켓엔진 고장에서 시동과정이 30% 이상을 차지하며 특히, 우주왕복선 주 엔진(Space Shuttel Main Engine, SSME)은 2%의 밸브위치 오차 또는 0.1초의 시간오차와 같은 작은 변화에도 급격하게 변화하는 매우 민감한 시스템으로 시동과정의 모델링이 중요하다. 하지만, 시동과정에서 비선형 질량 유량과 열전달 특성 때문에 많은 어려움이 발생한다. 본 논문에서는 이를 해결하기 위하여 부분적인 전산유체해석(Computational Fluid Dynamics, CFD) 방법을 사용하였으며 본 논문에서는 구성품의 모델링을 수행하여 정상상태에서 확인을 하였다.