• Journal of the Korea Convergence Society
• /
• v.8 no.10
• /
• pp.193-199
• /
• 2017

Mechanical tappet is used to reduce the cost and friction loss compared with hydraulic tappet. But the mechanical tappet doesn't have the ability to control the clearance between cams and valves and is selected by measuring the distance between valves and cams in order to minimize the clearance of valves by considering thermal expansion of valves. So, the valve clearance is nearly zero after fully warming-up periods, but there is valve clearance before warming-up. Especially at cold condition, the clearance is relatively large and can bring about some problems. In this study, the valve motions like lift, velocity, seating velocity and bouncing height were studied at various valve clearance conditions by experiment and analysis. As the valve clearance increases, the ramp area becomes shorten and it causes the valve train motion to have bad effects.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1997.04a
• /
• pp.218-223
• /
• 1997

유압장치의 핵심부품인 유압 제어밸브(hydraulic control valve)는 유압펌프 등에 의하여 가압된 유압유의 압력과 유량을 제어하고 유동방향을 변화시키는 주요기능을 수행한다. 특히, 대부분의 제어밸브는 스푸울(spool)과 슬리브(sleeve)를 기본구조로 채용하고 있다. 피스톤 형상인 스푸울이 슬리브내를 왕복운동하면 스푸울과 슬리브 사이의 간극(clearance)에서는 점성유체인 유압유의 윤활작용에 의하여 원주방향으로 비대칭인 유체압력이 발생한다. 이 결과로 스푸울에 측력(lateral force)이 작용하며, 조건에 따라서는 스푸울에 작용하며, 조건에 따라서는 스푸울에 작용하는 마찰력이 증대할 뿐만 아니라 스푸울과 슬리브의 내벽에 과도한 마멸(wear)을 유방시키기도 하여 제어밸브의 성능을 크게 저하시키기도 한다. 유압공학분야서는 이를 유체고착(hydraulic locking) 현상이라고 부른다. 본 논문에서는 항공기 Flap actuator의 Selector manifold에서 사용되는 스푸울 밸브의 성능에 큰 영향을 미칠 것으로 예상되는 스프울과 슬리브 사이 간극에서의 윤활특성을 이론적으로 조사하고자 한다.

• Journal of the Korean Institute of Gas
• /
• v.11 no.4
• /
• pp.1-6
• /
• 2007

This paper provides the effects on the leakage characteristics of the surface roughness of a valve stem in LPG automotive. The valve stem seal is to stop an oil leakage through a sealing gap between a valve stem and a valve stem seal. The sealing performance of two components is related to a leak safety and a long life of a valve stem and a valve stem seal. The experimental results show that the optimal surface roughness of a valve stem is to recommend as $0.4{\sim}0.5{\mu}m$ in a centerline average roughness, Ra and a uniformly distributed profile of the roughness. Basically the smooth surface and uniform profiles of the roughness may reduce an oil leakage between a valve stem and a valve stem seal.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.4 no.6
• /
• pp.97-108
• /
• 1996

A modeling technique is proposed for dynamic simulations of OHC valve trains with HLA(hydraulic lash adiuster). HLA is expressed by an air-oil mixture model considering HLA leak-down and aeraton effects. A compact nonlinear equation is derived which describe the short term dynamic behavior of the HLA. Valve spring is analyzed by a distributed parameter model including nonlinear characteristics in the spring surge phenomena. Global behavior of the remaining valve train is expressed by a lumped mass model. The experiental results prove that the simulation model developed here is accurate and useful for the dynamic simulations of OHC valve trains with HLA.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.14 no.4
• /
• pp.139-148
• /
• 2006

Valve train is one of the important noise sources in idling engines. Valve train noise comes mostly from two different impacts. One is the impact between cam and tappet at the beginning of the valve open period, which is an important source of impulsive noise of valve trains. The other is the impact between valve and valve seat at the closing of the valve open period. In case of mechanical lash adjusters, it is very difficult to control the initial impact. In this paper, we designed various types of cam profiles, especially in the opening ramp design, and investigated the effect of cam profiles on the magnitude of the initial impact. The effects that some cam design parameters have on the impulsive noise are also observed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2013.10a
• /
• pp.686-686
• /
• 2013

Automotive turbochargers have become common in gasoline engines as well as diesel engines. They are excellent devices to effectively increase fuel efficiency and power of the engines, but they unfortunately cause several noise problems. The noises are classified into mechanical noises induced from movement of a rotating shaft and aerodynamic noises by air flow in turbochargers. In addition to, there is a mechanical noise caused from movement of an actuator, electronically controlling a wastegate valve. It is called as valve rattle noise. The actuator is connected to a valve through a linkage. The noise occurs only if the valve is open, where the linkage is freely contact to neighbor structures without being constrained by any external forces. This condition allows impacts by the pulsation of exhaust gas, and the vibration from the impacts spreads out through turbine housing, causing the rattle noise. The noise is not in mechanical operating wastegate turbochargers because the linkage of an actuator is strongly connected by actuating force. For the electronic wastegate turbocharger, this paper proposed a test device to show the noise generating mechanism with a small vibration motor having an unbalanced shaft. It also shows how to reduce the noise - reduction of linkage clearances, inserting wave washers into a connection, and applying loose fitting in bushing embracing a valve lever to turbine housing.

• Journal of Advanced Navigation Technology
• /
• v.15 no.3
• /
• pp.441-448
• /
• 2011

It is very important that establishing the valve train equations and representing the behavior of the valve train parts. To maintain the specific efficiency of running engine, the cam profile of valve train has more specific influence on the adequate behavior of the valve train than a valve clearance, heat-resistance and durability of parts. The polynomial cam, the multipol cam and polydyne cam profie are widely used to represent cam behaviour. In this study, using polydyne cam design profile equations which is more adequate for representing high speed engine, the geometrical modeling and mathmatical variable analysis are established to analysis the valve behaviour.

• Journal of Aerospace System Engineering
• /
• v.13 no.4
• /
• pp.50-59
• /
• 2019

The design of the main control valve, which is the main component of the flap control system, was based on actual manufacturing experience on the basis of trial and error method. In this paper, a model-based part design method is proosed. The flap control system consists of a main control valve, fail-safe valve, solenoid valve, LVDT and force motor. The main control valve consists mainly of a spool and slot. The important design parameters of the main control valve are the slot width, overlap and clearance. AMESim is linked to the model and it analyzes the flow path of the main control valve. Applying the proposed design procedure, it was confirmed that the required performance was satisfied within the allowable machining error range.

• Journal of the Korean Society for Precision Engineering
• /
• v.19 no.12
• /
• pp.45-56
• /
• 2002

A pneumatic servo system requiring a fine gap control in a photo-electric sensor which is used for a LCD array detection device is introduced. The gap controlled by the pneumatic servo system remains within around 50~80 ${\mu}{\textrm}{m}$, and the system possesses an effect to eliminate undesirable particles on the LCD plate by blowing air out. The air flow rate is initially controlled by a servo valve and expanded by a booster valve, thus the controlled air pressure contributes to maintaining an appropriate gap between the LCD plate and photo-electric sensor An air floating plate of two degrees of freedom is designed and fabricated, and a fine tilting motion control is also implemented by assigning different gap commands. The pressure control and direct gap control are proposed, and each performance is verified experimentally.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.12
• /
• pp.1061-1069
• /
• 2010

In this study, a simplified axisymmetric model is proposed for the problem of compressible internal flow past a microgap. Using numerical and experimental methods, the phenomena of choked flows are observed; these flows are induced by the acceleration of subsonic flows past the narrow cross-section of an annular shape made by a microgap. The relation between mass flow rate and differential pressure is obtained, and by comparing the result with experimental results, the reliability of the numerical results is discussed. The generation of a supersonic jet flow and its diffraction are visualized by performing the numerical analysis of axisymmetric compressible Navier-Stokes equations. This investigation greatly extends the physical understanding of the axisymmetric compressible flow, which has a wide range of engineering applications, e.g., in the case of valves in automotive power systems.