• 제목/요약/키워드: Pressure modulation

검색결과 149건 처리시간 0.024초

파워시프트 변속기 유압클러치시스템의 해석적 연구 (An Analytical Investigation of a Hydraulic Clutch System of Powershift Transmission)

  • 이재천
    • 유공압시스템학회논문집
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    • 제6권1호
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    • pp.25-31
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    • 2009
  • This study presents an analytical model of hydraulic clutch system of a power shift transmission to analyze pressure modulation characteristics. A typical hydraulic clutch system was modeled by using AMESim in which the parameters of major components were measured for simulation. Test apparatus was established using the components of power shift and power shuttle clutches with instrumental equipment. The results of simulation and experiment were so close that the proposed analytical model in this study was validated. However the cylinder model analogized clutch dynamics need to be improved in future study. The effects of parameters of orifice diameter, accumulator stroke and oil temperature on pressure modulation were analyzed respectively. The results of parameter sensitivity analysis show that modulation time and set pressure can be easily adjusted by changing parameter values. It is also found that the hydraulic clutch system used in this study is so susceptible to oil temperature that cooling equipment is necessary.

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연소실내의 압력 변동에 따른 연료 분사구에서의 당량비 변동에 관한 수치해석 (Numerical Simulation on Equivalence Ratio Fluctuation at the Fuel Injection Hole with respect to Pressure Fluctuation in a Combustion Chamber)

  • 김현준;홍정구;신현동
    • 한국연소학회:학술대회논문집
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    • 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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    • pp.27-35
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    • 2006
  • It has been observed in experiments that combustion instability of low frequency (${\sim}$ 10Hz) results form the modulation of equivalence ratio at fuel injection hole when a pressure fluctuation propagates upwards along the channel of the burner under an unchoked fuel flow condition. In this study, a commercial program was used to determine how the fuel flow rate changed with respect to the pressure, velocity of the fuel flow and the mass fraction in a choked and an unchoked condition. The calculation focus on the upstream of the dump plane to know how the forced pressure with the fuel injection conditions affects the modulation of the equivalence ratio. Therefore, it is found that pressure fluctuation leads to oscillation of mass flow rate and then results in equivalence ratio modulation under the unchoked fuel flow condition.

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압력변동이 연료 분사구에서의 당량비 변동에 미치는 영향에 관한 수치 해석 (Numerical Simulation of the Effect of Pressure Fluctuation on the Modulation of Equivalence Ratio at the Fuel Injection Hole)

  • 김현준;홍정구;신현동
    • 대한기계학회논문집B
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    • 제31권3호
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    • pp.292-299
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    • 2007
  • In gas turbine technology, the flame stability is inherently greater in conventional diffusion type combustion over a wider range fuel to oxidizer ratio. However, premixed type combustion which has narrow flame stability region, is widely used due to environmental reason. It has been observed in experiments that combustion instability of low frequency (${\sim}10Hz$) results from the modulation of equivalence ratio at fuel injection hole when a pressure fluctuation propagates upwards along the channel of the burner under an unchoked fuel flow condition. In this study, a commercial program was used to determine how the fuel flow rate changed with respect to the pressure, velocity of the fuel flow and the mass fraction in a choked and an unchoked condition. The calculation focuses on the upstream of the dump plane to know how the forced pressure with the fuel injection conditions affects the modulation of the equivalence ratio. Therefore, it is found that pressure fluctuation leads to oscillation of mass flow rate and then results in equivalence ratio modulation under the unchoked fuel flow condition.

트랙터용 파워시프트 전.후진 클러치의 압력 모듈레이션 제어 (Pressure Modulation Control of Powershift Shuttle Clutch of Tractor)

  • 조재문;허준영;정병학;김경욱
    • 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.

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보행 혈압 측정과 심장 기능의 관계 (Relationship between ambulatory blood pressure monitoring and cardiac function)

  • 송영환
    • Clinical and Experimental Pediatrics
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    • 제52권7호
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    • pp.752-755
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    • 2009
  • It is well known that hemodynamic load is one of the most important determinants of cardiac structure and function. Circadian variations in blood pressure (BP) are usually accompanied by consensual changes in peripheral resistance and/or cardiac output. In recent years, reduction in circadian variations in BP and, in particular, loss of nocturnal decline of BP were observed in hypertensive patients with left ventricular hypertrophy (LVH). The patients with only a slight or no loss of nocturnal decline of BP were considered "non-dippers". Regression of LVH was observed after prolonged antihypertensive therapy. Restoration of the circadian rhythm of BP was also observed. However, the classification of patients into "dippers" and "non-dippers" is arbitrary and poorly standardized and repeatable, and in the recent studies, most hypertensive patients with LVH were "dippers". Therefore, we should be particularly cautious about the conclusions drawn using this index. On the other hand, reduced activity of low-pressure cardiopulmonary baroreceptors and impaired day-to-night modulation of autonomic nervous system activity were observed in patients with only LVH. Therefore, alterations in cardiac structure may impair BP modulation. On the other hand, the reverse can also be trueprimary alterations in BP modulation, through a persistently elevated afterload, can increase cardiac mass. Thus, the interrelationship between cardiac structure and BP modulation is complex. Hence, new and more specific methods of evaluating circadian changes in BP are needed to better clarify the abovementioned reciprocal influences.

On-Off 제어기를 이용한 가변추력 고체추진 기관의 압력제어 (Pressure Control of a Variable Thrust Solid Propulsion System Using On-Off Controllers)

  • 권순규;김영석;고상호;서석훈
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2011년도 제37회 추계학술대회논문집
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    • pp.942-948
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    • 2011
  • 고체추진기관은 구조가 비교적 간단하고 장기적 저장성이 우수한 반면에 일반적으로 추력의 조절등에 한계성을 가지고 있다. 본 논문에서는 구현의 용이함과 에너지 효율성이 좋은 on-off 제어기법을 이용한 가변추력 고체추진 기관의 압력 제어를 위한 제어기를 소개한다. 연소기 내 압력제어를위해 질량보존만을 고려한 추진기관의 연소기 내 압력변화 모델에 대하여 고전적인 비례-적분 제어기와 같은 연속적 제어 기법과 PWM, PWPFM과 같은 on-off 제어기를 설계하고 시뮬레이션을 통해 결과를 비교한다.

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개폐식 3방향 전자밸브의 펄스폭 변조 구동에 의한 압력제어 특성에 관한 연구 (A Study on the Pressure Control Characteristics of ON/OFF 3-way Solenoid Valve Driven by PWM Signal)

  • 정헌술
    • 대한기계학회논문집A
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    • 제21권3호
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    • pp.485-501
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    • 1997
  • Pressure control is possible driving a simple ON/OFF 3-way valve of hydraulic servo system by pulse width modulation signal. But the pressure varies according to the duty ratio and carrier frequency and repeated on-off action induces pressure fluctuation. So equations for mean pressure and ripple amplitude are theoretically derived as a function of on/off time, the system parameters which decide the pressure characteristics are arranged and they are verified by experimental study. As the result selection criteria for the major design parameters are established and the basic strategy to suppress the unnecessary fluctuation can be provided for a hydraulic pressure control system using these type of valves.

2방향 전자밸브 PWM압력제어특성의 실험적 비교연구 (Experimental Study on the PWM Pressure Control Characteristics of 2 Way Solenoid Valve)

  • 정헌술;박성진;김창완
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 1997년도 춘계학술대회 논문집
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    • pp.107-111
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    • 1997
  • Pressure control is possible by pulse width modulation signal driving a simple ON/OFF 2-way valve of hydraulic servo system. But it indices pressure fluctuation due to repeated on-off action and the pressure varies according to the duty ratio and carrier frequency. So mean pressure and ripple amplitude are arranged by experimental study as the driving signal change which decides the pressure characteristics. As the result selection criteria of the major design parameters may be established and the basic strategy to suppress the unnecessary flucturion may be provided for a hydraulic pressure control system.

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연소실 압력 변동이 버너내부의 당량비 변조에 미치는 영향 (An Effect of Pressure Fluctuations of a Combustion Chamber on the Modulation of Equivalence Ratio in the Channel of the Burner)

  • 홍정구;오광철;신현동
    • 대한기계학회논문집B
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    • 제31권2호
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    • pp.202-207
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    • 2007
  • In order to understand the phenomena of combustion instability, an experimental study was conducted at the moderate pressure and ambient temperature conditions. The flame behavior and the pressure fluctuations were measured in a dump combustor. Various types of combustion modes occurred in accordance with the equivalence ratio and the fuel supplying conditions. The fluctuation of pressure, heat release and equivalence ratio were measured by piezoelectric pressure sensor, high speed Intensified Charge Coupled Device (HICCD) camera and gas chromatography respectively. Two representative modes were self-excited pressure oscillations at the resonance of combustion chamber (200Hz) and instabilities related to the modulated fuel flow rate through the fuel holes (10Hz). It is found that, especially in an unchoked fuel flow condition, the modulation of the fuel flow rate affects the characteristics of flame behavior and pressure fluctuations in a lean premixed flame.

브레이크 압력 추정을 적용한 구동력 제어 (Traction Control with Brake Pressure Estimation)

  • 김세윤
    • 드라이브 ㆍ 컨트롤
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    • 제10권3호
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    • pp.1-6
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    • 2013
  • Traction control suppresses the spinning of the driven wheel during drive away or acceleration on slippery road condition. In this study, the estimation method of brake pressure hardly measured is proposed. The estimation method of brake pressure and the brake pressure control with pulse width modulation(PWM) are verified a good performance through experiment. Also, the vehicle simulation on slippery road conditions is validated the applicability of brake pressure control for traction control. The simulation results have showed that the brake pressure can be used the control variable for traction control.