• Journal of Drive and Control
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• v.17 no.4
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• pp.46-53
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• 2020

In this paper, the development of a manually and continuously variable impact force control mechanism for hydraulic breakers was studied. Generally, a hydraulic breaker has one or two piston strokes. Hydraulic breakers, which have two strokes, have two valve-switching ports and make short and long piston strokes. The piston stroke valve controls the piston stroke by opening and closing a short stroke-switching port. The short piston stroke mode is used to break soft rock, concrete, or asphalt. This stroke control valve system is not popular for small hydraulic breakers mounted on 1 to 14-ton excavators. To preserve the carrier-like excavator, proper breaking force is needed, and it can be easily controlled by multiple piston stroke control valves. The easiest way to control these breakers is to use several switching ports and valves but they are not easy to install in small hydraulic breakers and are expensive. To use only one switching port and valve, a method can be used to change the open area of the switching port to delay valve switching. This method provides multiple piston strokes.

• Journal of Hydrogen and New Energy
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• v.20 no.5
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• pp.371-377
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• 2009

Backfire characteristics for hydrogen fueled free piston engine with uni-flow scavenging is investigated with different stroke, exhaust vlave openning timing and fuel-air equivalence ratio by using RICEM (Rapid Intake Compression Expansion Machine) for combustion research of free piston engine. As results, it is found that backfire can be occurred due to slow combustion of unhomogeneous mixture in the piston crevice volume or/and in the cylinder near piston head. And the more stroke of free piston H2 engine with uni-flow scavenging is short the more opening timing of exhaust valve have to be advanced to control backfire.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.114-120
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• 2000

Friction forces of piston rings for a typical SI engine were independently measured while excluding the effects of cylinder pressure, oil starvation and piston secondary motion using a floating liner system. Friction patterns, represented by the measured friction forces, were classified into five frictional modes with regard to the combination of predominant lubrication regimes(boundary, mixed and hydrodynamic lubrication) and stroke regions(mid-stroke and dead centers). The modes were identified on the Stribeck diagram of the dimensionless bearing parameter and friction coefficients which were evaluated at the mid-stroke and at the dead centers. And the frictional modes were estimated to the full operation range. The compression rings behave in the mode where hydrodynamic lubrication is dominant at the mid-stroke and mixed lubrication is dominant at the dead centers under steady operating conditions. However, the oil control ring behave in the mode where mixed lubrication is dominant throughout the entire stroke.

• Journal of Drive and Control
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• v.19 no.3
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• pp.1-8
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• 2022

In this paper, the design of automatic impact force control mechanism of hydraulic breaker was studied. The control mechanism uses the change of piston upper chamber pressure, when the hydraulic breaker impacts various strength rock. The piston stroke is controlled by rock strength sensing valve, piston stroke switching valve, and piston control valve. It is imperative to denote the area of each valve section, the spring constant of the spring. It provides convenience to users by automatically adjusting the appropriate striking force, according to the strength of the rock. Additionally, by increasing work productivity, it can contribute to reducing greenhouse gas emissions due to fuel efficiency reduction.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.274-282
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• 2013

In this paper, a linear motor stroke controller using a phase lag filter and a single phase PWM inverter with a current controller has been implemented. In order to control the cooling capability of a refrigerator or an air conditioner in which linear compressors are applied, the piston speed should be controlled. The piston speed control can be obtained by adjusting the frequency or the stroke of linear motors. Generally, the frequency is fixed, for example, as 60Hz and the stroke is adjusted. The dynamic performance of linear compressors depends on how accurately the stroke or the piston position is controlled by the current applied. A linear motor piston position controller with a current control loop is proposed and verified via some simulation studies.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.4
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• pp.212-218
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• 2013

In this paper, a linear motor piston amplitude estimator using phase lag filter has been implemented. In order to control the cooling capability of a refrigerator or an air conditioner in which liner compressors are applied, the piston speed should be controlled. The piston speed control can be obtained by adjusting the frequency or the stroke of linear motors. The dynamic performance of linear compressors depends on how accurately the stroke or the piston amplitude is estimated. A linear motor piston amplitude estimator using phase lag filter is proposed and the superior performance of our estimator is verified via some simulation studies.

• Journal of Hydrogen and New Energy
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• v.22 no.6
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• pp.794-799
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• 2011

In order to reduce the oil consumption for a 2 stroke free piston hydrogen fueled engine, the behaviors of residual lubricant oil of the cylinder wall surface were visualized and oil mass emitted into exhaust port was measured by using research engine with cross-head and eccentric crankshaft. As the results, it was shown that characteristics of residual lubricant oil such as oil thickness and distribution were remarkably different from a conventional 4 stroke engine. It was also analyzed that these tendencies relied on the configuration and installed position of the exhaust port, piston pin boss and so on.

• Journal of Hydrogen and New Energy
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• v.22 no.3
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• pp.299-304
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• 2011

A hydrogen fueled 2 stroke free-piston engine with reverse uni-flow scavenging have a advantageous structure for the backfire occurrence, but it can reduce thermal efficiency by the circuit-flow to go through a exhaust-port. In this research, varied boost pressure, SVOT and exhaust pressure are used in a 2stroke free-piston engine with hydrogen fueled for studying the possibility of increasing thermal efficiency of free-piston hydrogen engine. As a result, to increase thermal efficiency of free-piston are suitable to supply the mixture after port closed the exhaust rater than to use the scanvenging. And it was increased by the exhaust pressure, to achieve it must be used the lean-mixture at SVOT aBDC $34^{\circ}$.

• Journal of the Korean Society of Combustion
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• v.20 no.3
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• pp.13-20
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• 2015

The performance of a direct-injection diesel engine often depends on the strength of swirl or squish, the shape of combustion chamber, the number of nozzle holes, etc. This is natural because the combustion in the cylinder was affected by the mixture formation process. Since the available duration to make the mixture formation of air-fuel is very short, it is difficult to make complete mixture. Therefore, an early stage of combustion is violent, which leads to the weakness of noise and vibration. In this paper, the combustion process of a common-rail diesel engine was studied by employing two kinds of pistons. One has several cavities on the piston crown to intensify the squish during the compression stroke in order to improve the atomization of fuel, we call this multi cavity piston in this paper. The other is a toroidal single cavity piston, generally used in high speed diesel engines. To take photographs of flame and flaming duration, a four-stroke diesel engine was remodeled into a two-stroke visible single cylinder engine and a high speed video camera was used.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.88-93
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• 2003

The aim of this paper is to investigate the friction characteristics of piston assembly, which composed of ring pack and piston skirt. The friction force of piston assembly was measured by using the movable liner in the single cylinder engine, and the various parameters were tested. The friction force was suddenly increased at the expansion stroke due to higher cylinder pressure. The viscous friction was dominant at the mid stroke, but the boundary friction was dominant at the top and bottom dead centers. Through the experiment, we could validate previous theoretical study, and confirm that th e radial clearance and ring tension were very effective to reduce friction loss of piston assembly.