• 전력전자학회논문지
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• 제13권3호
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• pp.171-178
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• 2008

본 논문에서는 압력예측기법과 직접 순시토크 제어기법을 통한 유압펌프용 SRM의 압력제어 구동시스템을 제안하였다. 일반적으로 유압 펌프 시스템은 유압센서의 응답성으로 인하여 제어시스템의 시지연이 비교적 길어지게 되며, 이러한 시간지연은 PI 또는 PID 제어 구조에서 장시간의 진동과 불안정화를 만들기 쉽다. 본 논문에서는 시간 지연문제를 해결하고 리플이 없는 압력제어를 위하여 스미스 예측기(simth predictor)를 통한 지연보상과 직접 순시토크제어기법(Direct Instantaneous Torque, 이하 DITC)을 적용하였다. 제안된 제어 방식은 펌프와 센서간의 기구적 문제에 의한 지연문제 해결과 안정성을 확보하고, 펌프 압력제어의 동특성을 향상시키며 전류(轉流, commutation) 구간에서 균일한 토크를 발생시켜 토크 리플을 억제하기 위함이다. 제안된 제어방식은 시뮬레이션과 실험을 통하여 효용성을 검증하였다.

• International Journal of Fluid Machinery and Systems
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• 제4권1호
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• pp.179-190
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• 2011

The swirling flow developing in Francis turbine draft tube under part load operation leads to pressure fluctuations usually in the range of 0.2 to 0.4 times the runner rotational frequency resulting from the so-called vortex breakdown. For low cavitation number, the flow features a cavitation vortex rope animated with precession motion. Under given conditions, these pressure fluctuations may lead to undesirable pressure fluctuations in the entire hydraulic system and also produce active power oscillations. For the upper part load range, between 0.7 and 0.85 times the best efficiency discharge, pressure fluctuations may appear in a higher frequency range of 2 to 4 times the runner rotational speed and feature modulations with vortex rope precession. It has been pointed out that for this particular operating point, the vortex rope features elliptical cross section and is animated of a self-rotation. This paper presents an experimental investigation focusing on this peculiar phenomenon, defined as the upper part load vortex rope. The experimental investigation is carried out on a high specific speed Francis turbine scale model installed on a test rig of the EPFL Laboratory for Hydraulic Machines. The selected operating point corresponds to a discharge of 0.83 times the best efficiency discharge. Observations of the cavitation vortex carried out with high speed camera have been recorded and synchronized with pressure fluctuations measurements at the draft tube cone. First, the vortex rope self rotation frequency is evidenced and the related frequency is deduced. Then, the influence of the sigma cavitation number on vortex rope shape and pressure fluctuations is presented. The waterfall diagram of the pressure fluctuations evidences resonance effects with the hydraulic circuit. The influence of outlet bubble cavitation and air injection is also investigated for low cavitation number. The time evolution of the vortex rope volume is compared with pressure fluctuations time evolution using image processing. Finally, the influence of the Froude number on the vortex rope shape and the associated pressure fluctuations is analyzed by varying the rotational speed.

• 한국자동차공학회논문집
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• 제14권4호
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• pp.32-38
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• 2006

A clutch hydraulic system for automotive manual transmissions transfers hydraulic pressure generated by driver's pedal manipulation to the clutch mechanism. The foot effort when the clutch pedal is pushed is different than that when the clutch is returned. The effort or load difference, called hysteresis, is caused by the friction produced between rubber seal and inner wall inside the hydraulic cylinder. This clutch pedal travel foot effort hysteresis is essential for a clutch hydraulic system design and analysis. The dynamic model for a clutch hydraulic system is developed and a simulation analysis is performed to estimate the fiction coefficient as a function of the cylinder pressure. The simulation result is then compared to the measurements obtained from a clutch hydraulic system tester to ensure the reliability of the dynamic model and the coefficients estimated. Also the estimated friction coefficients at various pressure values are compared to those reported by an independent study.

• 한국정밀공학회지
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• 제25권4호
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• pp.93-99
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• 2008

The clutch is a subcomponent of the transmission that is designed to engage and disengage power flow between the engine and the transmission. Recently, the engine power of automobile has been continuously increased because of customer's demand for the bigger one. As the engine power is increased, the vibration transmitted to the hydraulic clutch operating system has been increased. Therefore the demand for the reduction of clutch pedal vibration during the operation of the clutch system has been increased. This paper describes the pressure pulsation reduction characteristics of the damper cylinder which is applied to the hydraulic clutch operating system. And the purpose of this study is to confirm the availability of a simulation model and investigating the test results of hydraulic clutch operating system. The test results are compared with the simulation results. Therefore it may be concluded that the simulation model and test results will be very useful f3r the design of hydraulic clutch damper cylinder.

• 대한기계학회논문집A
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• 제34권9호
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• pp.1249-1255
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• 2010

초고압 시스템은 유압동력 발생장치, 충격압력 발생장치, 초고압부 오일 보충장치, 기동 및 제어반 등으로 일반적으로 구성된다. 유압동력 발생장치는 초고압 발생기에 유압원을 공급하고, 초고압 발생기에서는 공급되어진 유압원을 이용하여 초고압으로 압력을 증폭한다. 기동 및 제어반에서는 시스템을 운전하기 위한 전기모터, 밸브, 센서 등에 대한 제어 및 관찰을 하기 위해 사용된다. 본 연구에서는 초고압 압력을 발생시키기 위한 제어 방법을 서보밸브를 사용한 유량제어 방식에서 비례 릴리프 밸브를 사용한 압력제어 방법을 사용하여 연구하며, 초고압 압력 발생기의 압력을 가하는 주기와 유압동력 발생장치의 작동유의 온도 변화에 따라 충격압력을 발생시키는 성능이 변화하는 특성을 연구하는 것을 목적으로 한다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.209-214
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• 1999

Dynamic pressure is one of the major sources on noise emission in hydraulic axial piston pump. This paper reports an experimental study of dynamic pressure characteristics in the cylinder port of hydraulic axial piston pump. We investigated dynamic pressure with not only the effect of delivery pressure, rotational speed and temperature but also V-notches at the ends of the kidney ports in the valve plate. We experimented three valve plates with three type V-notches at the ends of the kidney ports, because V-notches of the valve plate is known of noise reduction. Finally, we hope this paper help to design of the valve plate in hydraulic axial piston pump.

• Journal of Power Electronics
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• 제9권5호
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• pp.800-808
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• 2009

This paper presents a practical method of pressure control for a hydraulic oil-pump system using an SR (Switched Reluctance) drive. For a 6Mpa grade hydraulic oil-pump, a 2.6kW SR drive is developed. In order to get high performance pressure dynamics in actual applications, a data based PID control scheme is proposed. The look-up table from a pre-measured data base produces an approximate current reference based on motor speed and oil-pressure. A PID controller can compensate for the pressure error. With the combination of the two references, the proposed control scheme can achieve fast dynamics and stable operation. Furthermore, a suitable current controller considering the nonlinear characteristics of an SRM (Switched Reluctance Motor) and practical test methods for data measuring are presented. The proposed control scheme is verified by experimental tests.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1936-1941
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• 2003

Characteristics of the high frequency and pulsatile flow investigated experimentally to understand the flow phenomena in the hydraulic system. In the study, I axis fatigue tester which are widely used for automobile filed are selected. 4 Pressure transducer, amplifier, A/D convertor are used to analyse and to obtain the pulsatle pressure waveform with high frequencies in hydraulic system. Matlab are used. to analyse the characteristics of frequency. Variation of pump input pressure and actuator acceleration frequency, pressure wave are measured with or without accumulators. For with accumulator, frequency amplitude of pressure are very lower than those of without accumulator due to absorbing function of accumulator. As the actuator acceleration frequency increased, effect of accumulator are very important to decrease the pulsatile pressure waveform with high frequencies.

• 한국정밀공학회지
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• 제18권1호
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• pp.74-81
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• 2001

Dynamic pressure is one of the major sources on noise emission in oil hydraulic piston pump. This paper reports an experimental study of dynamic pressure characteristics in the cylinder bore of oil hydraulic piston pump. We experimently measured dynamic pressure at BDC with delivery pressure, rotational speed and oil temperature. Because the V-grooves at the ends of the kidney ports with three types valve plates. We hope this paper help to design of the valve plate in oil hydraulic piston pump.

• Computers and Concrete
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• 제19권2호
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• pp.171-177
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• 2017

Water pressure test operation is used before the grouting to determine the rate of penetrability, the necessity and estimations related to grouting, by the penetration of water into the borehole. One of the parameters which have the highest effect is pressure of water penetration since the application of excessive pressure causes the hydraulic fracture to occur in the rock mass, and on the other hand, it must not be so small that prevents from seeing mechanical weaknesses and the rate of permeability. Mathematical modeling is used for the first time in this study to determine the optimum pressure. Thus, the joints that exist in the rock mass are simulated using cylindrical shell model. The joint surroundings are also modeled through Pasternak environment. To obtain equations governing the joints and the surroundings, energy method is used accompanied by Hamilton principle and an analytical solution method is used to obtain the maximum pressure. In order to validate the modeling, the pressure values obtained by the model were used in the sites of Seymareh and Aghbolagh dams and the relative error rates were measured considering the differences between calculated and actual pressures. Modeling in the sections of Seymareh dam showed 4.75, 3.93, 4.8 percent error rates and in the sections of Aghbolagh dam it rendered the values of 22.43, 5.22, 2.6 percent. The results indicate that this modeling can be used to estimate the amount of pressure for hydraulic fracture in water pressure test, to predict it and to prevent it.