• 한국자동차공학회논문집
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• 제9권4호
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• pp.184-192
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• 2001

Cam/tappet wear is one of the critical concerns in valve train deign. Maximum contact stress and minimum oil film thickness between the cam and tappet are usually checked for the estimation of wear characteristics. If the two extreme cases arise simultaneously, there is a strong possibility of cam/tappet wear. In this paper, effects of valve train layout on the wear characteristics were studied. Especially for swinging arm type valve trains, initial geometric layout must be very carefully defined to avoid wear problems. The study was performed fur an end pivot type OHC valve train, which had severe wear problems. Analysis results show that some geometric parameter affect very sensitively on the wear characteristics. Experiments were also performed for the original and modified valve trains, which strongly support the analysis results.

• 한국자동차공학회논문집
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• 제5권2호
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• pp.111-119
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• 1997

The operating characteristics of the check valve in the clutch piston of an automatic transmission have a great effect on the shifting performance. This paper addresses the modeling, dynamic analysis, and optimization of the check valve. It was found that the vortex causes a pressure drop, which is related to the rotating speed of the clutch piston, oil volume discharged from the check valve, and valve geometry. Maximizing the oil volume discharged, geometry of the check valve is optimized. The results can be used to design an improved check valve which provides a suitable oil pressure curves for achieving smoother shifting.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.68-69
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• 2003

• International Journal of Automotive Technology
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• 제8권6호
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• pp.697-704
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• 2007

Recently, a variable valve timing system has been widely adopted in internal combustion engine in order to improve the fuel economy and torque at low engine speed. In addition, it is known that varying valve timing according to the various engine operations could reduce exhaust gas, especially NOx, because of residual gas by valve overlap. In this study, to improve the low exhaust gas and fuel economy at part load condition, the residual gas and back flow of exhaust gas due to valve overlap were calculated computationally. Moreover, the characteristics of engine performances and NOx formations were investigated with the experiment of combination of intake and exhaust valve timing condition. Under these various valve operating conditions, the effects of both the positive valve overlap and negative valve overlap(valve underlap) were examined simultaneously. Finally, the characteristics of cyclic THC emission were analyzed by using Fast Response FID(FR-FID) in the cylinder, intake port and exhaust port positions. Besides, the effect of the different gradients of the valve timing change on engine performance was investigated and an optimum control strategy was suggested.

• 한국기계가공학회지
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• 제20권4호
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• pp.73-79
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• 2021

The objective of this study is to prevent or decrease condensation on the surface of aluminum butterfly valves used in high humidity air conditions. We proposed a new valve with an anti-condensation device, a heat resistance medium, instead of a conventional valve. We, then, compared the surface temperature distribution between the proposed and conventional valves using experimental and analytical methods. The size of the evaluated valve is 100A and fluid conditions are 35℃/RH 75% in the air outside the valve and 5℃ in the cooling water inside the valve. The experimental results show that the surface temperature of the proposed valve is 23~42% higher than that of a conventional valve, thereby exhibiting an anti-condensation effect. As a result, we observed the complete prevention of condensation on a gear box mounted to the proposed valve, showing surface temperature distribution above the dew point temperature of air. The analytical results are in agreement with the trends in experimental results.

• 대한기계학회논문집
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• 제19권2호
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• pp.443-450
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• 1995

An analysis of the dynamics of a mechanical monoleaflet heart valve prosthesis in the closing phase is presented. Employing the moment equilibrium principles on the occluder motion and the squeeze film dynamics of the fluid between the occluder and the guiding strut at the instant of impact, the velocity of the occluder tip and the impact force were computed. The dynamics of fluid being squeezed between the occluder and the guiding struts is accounted for by Reynold's equation. The effect of the fluid being squeezed between the occluder and the guiding strut was to reduce the velocity of the occluder tip at the instant of valve closure as well as dampen the fluttering of the occluder before coming to rest in the fully closed position. The squeeze film fluid pressure changed rapidly from a high positive value to a relatively large negative value in less than 1 msec. The results of this study may be extended for the analysis of cavitation inception, mechanical stresses on the formed elements and valve components as well as to estimate the endurance limits of the prosthetic valves.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 춘계학술대회 논문집
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• pp.843-844
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• 2009

• Journal of Advanced Marine Engineering and Technology
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• 제38권8호
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• pp.961-967
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• 2014

In onshore and offshore plant engineering, a broad use of pipe system have been achieved and accordingly related technologies has been developed especially in the field of flow control valves. The aim of this study is to suggest the quadruple offset butterfly valve for bi-directional applications which show equivalent operating torque characteristics of the triple offset butterfly valve. Seat design parameters for the quadruple offset butterfly valve are determined by the proposed method utilizing both ANOVA (analysis of variance) and the orthogonal array. Through additive model considering the effect of design parameters on seating torque, mean estimation is performed and thus its optimization results are verified by design of experiment results. The insight obtained from the present study is beneficial for valve design engineers to develop reliable and integrated design of the quadruple offset butterfly valve.

• Journal of Chest Surgery
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• 제23권4호
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• pp.622-639
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• 1990

The use of aortic valve homograft has been developed since 1962 when Ross and Barratt - Boyes independently replaced a diseased aortic valve with an orthotopically inserted homograft valve. And also surgical treatment of complex congenital cardiac malformations utilizing homograft extracardiac conduit has been tried with better result than any other prosthetic material. The present study was undertaken to clarify the safety tissue viability, sterility, after following our protocol of procurement of heart, dissection of aortic and pulmonic homograft, sterilization, cryopreservation, thawing and dilution, and transplantation on experimental animal, sheep. Tissue viability of valve and great artery was assessed by tissue culture. Sterility was evaluated by bacterial and fungal culture. The method used was proven no deleterious effect on the integrity of the valve. Tissue culture of valve tissue before, and after cryopreservation process resulted that active fibroblast growth was observed from homograft sterilized with antibiotics. And culture of the transplanted homograft from sacrificed animal showed active fibroblast growth. Pathologic examination of implanted valve tissue from sacrificed sheep showed mild calcification and minor change, but there were moderate and severe calcification of wall of great arteries.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.174-177
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• 2003

The automatic temperature control valve is used to control the flow rate of heating water in the large apartment complex and buildings. It is important to have simillar heating flow rate in the apartments, even though the apartment is top or bottom floors. To achieve those purposes, the automatic flow-temperature control valve was developed. The perfromance of this control valve is effected by the catridge shape and spring length. The flow capacity of this control valve is obtained with the different shape of catridges and with change of spring length.