습식클러치의 동적 동력전달 거동 연구

장시열(Siyoul Jang),김도환(DoHan Kim),김명식(Myongsik Kim),최완(Wan Choi),장영기(Younggi Jang),한관수(Gwansoo Han),장재덕(Jaeduk Jang) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11

Wet clutch is widely used for the power flow distribution in various mechanical systems. Especially, in the automatic transmission system wet clutch is adapted in the forms of multi disc clutch and lock-up clutch subsystems. Wet clutch is made of soft paper based friction material and metal plate for the mating friction performance and it is operated under high hydraulic pressure for the clutch engagement. All of the engagements are working under the ATF environment that has the function of less frictional contact behaviors. In this study, the contact deformation, surface roughness, porosity behaviors of paper based friction material and the centrifugal effects of ATF during the engagement process are studied.

Monochromatic Image Analysis of Elastohydrodynamic Lubrication Film Thickness by Fringe Intensity Computation

Siyoul Jang 대한기계학회 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.11

Point contact film thickness in elastohydrodynamic lubrication (EHL) is analyzed by image processing method for the images from an optical interferometer with monochromatic incident light. Interference between the reflected lights both on half mirror Cr coating of glass disk and on super finished ball makes circular fringes depending on the contact conditions such as sliding velocity, applied load. viscosity-pressure characteristics and viscosity of lubricant under ambient pressure. I n this situation the film thickness is regarded as the difference of optical paths between those reflected lights, which make dark and bright fringes with monochromatic incident light. The film thickness is computed by numbering the dark and bright fringe orders and the intensity (gray scale image) in each fringe regime is mapped to the corresponding film thickness. In this work, we developed a measuring technique for EHL film thickness by dividing the image patterns into two typical types under the condition of monochromatic incident light. During the image processing, the captured image is converted into digitally formatted data over the contact area without any loss of the image information of interferogram and it is also interpreted with consistency regardless of the observer's experimental experience. It is expected that the developed image processing method will provide a valuable basis to develop the image processing technique for color fringes, which is generally used for the measurement of relatively thin films in higher resolution.

A Study on the Measurement for the Nano Scale Film Formation of Ultra Low Aspect Ratio

Siyoul Jang,Hyungsang Kong 한국트라이볼로지학회 2004 한국트라이볼로지학회 학술대회 Vol.39 No.-

The measurement of ultra low aspect ratio fluid film thickness is very crucial technique both for the verification of lubrication media characteristics and for the clearance design in many precision components such as MEMS, precision bearings and other slideways. Many technologies are applied to the measurement of ultra low aspect ratio fluid film thickness (i.e. elastohydrodynamic lubrication film thickness). In particular, in-situ optical interferometric method has many advantages in making the actual contact behaviors realized with the experimental apparatus. This measurement method also does the monitoring of the surface defects and fractures happening during the contact behavior, which are delicately influenced by the surface conditions such as load, velocity, lubricant media as well as surface roughness. Careful selection of incident lights greatly enhances the fringe resolutions up to~1.0 nanometer scale with digital image processing technology. In this work, it is found that coaxial aligning trichromatic incident light filtering system developed by the author can provide much finer resolution of ultra low aspect ratio fluid film thickness than monochromatic or dichromatic incident lights, because it has much more spectrums of color components to be discriminated according the variations of film thickness. For the measured interferometric images of ultra low aspect ratio fluid film thickness it is shown how the film thickness is finely digitalized and measured in nanometer scale with digital image processing technology and space layer method. The developed measurement system can make it possible to visualize the contact deformations and possible fractures of contacting surface under the repeated loading condition.

Monochromatic Image Analysis of Elastohydrodynamic Lubrication Film Thickness by Fringe Intensity Computation

Jang, Siyoul The Korean Society of Mechanical Engineers 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.11

Point contact film thickness in elastohydrodynamic lubrication (EHL) is analyzed by image processing method for the images from an optical interferometer with monochromatic incident light. Interference between the reflected lights both on half mirror Cr coating of glass disk and on super finished ball makes circular fringes depending on the contact conditions such as sliding velocity, applied load, viscosity-pressure characteristics and viscosity of lubricant under ambient pressure. In this situation the film thickness is regarded as the difference of optical paths between those reflected lights, which make dark and bright fringes with monochromatic incident light. The film thickness is computed by numbering the dark and bright fringe orders and the intensity (gray scale image) in each fringe regime is mapped to the corresponding film thickness. In this work, we developed a measuring technique for EHL film thickness by dividing the image patterns into two typical types under the condition of monochromatic incident light. During the image processing, the captured image is converted into digitally formatted data over the contact area without any loss of the image information of interferogram and it is also interpreted with consistency regardless of the observer's experimental experience. It is expected that the developed image processing method will provide a valuable basis to develop the image processing technique for color fringes, which is generally used for the measurement of relatively thin films in higher resolution.

Transient Elastohydrodynamic Lubrication Film Thickness in Sliding and Rolling Line Contacts

Siyoul Jang 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.5

The contact behavior between cam and follower is greatly influenced by the kinematics and dynamics of the whole valve train system. This is the reason that both shape and thickness of the fluid film in the contact gap are mainly determined by applied loads and relative contact speeds as well as the curvatures of contacting elements. Most of the studies about lubricant film behavior between cam and follower have been performed without a consideration of transient effects in the contact gap. For the computational difficulties of transient effects, most contact conditions such as relative contacting speeds have been regarded as quasi-steady state during the whole operating cycle. In this work, in order to obtain stable convergence, a multigrid multi-level method is used for the computation of load capacity in the lubricant film. Nonlinear valve spring dynamics are also considered in the same way as Hanachi’s. From the computational results, transient EHL film thicknesses under the conditions of different contact geometries are computed for a pushrod type valve train system during an engine cycle. Several results show the squeeze film effect, which is generally not found with conventional EHL computations of the cam and follower contact. The results are also compared with those by the Dowson-Hamrock (D-H) formula, which does not consider the dynamic film effect. Without the dynamic film effect as in D-H’s formula, the minimum film thickness is highly dependent on the entraining lubricant velocity, whereas the minimum film thickness including the squeeze film effect is dependent on the applied loa

Elliptical EHL Contacts under Dynamic Loading Conditions in HERB Drive

Siyoul Jang,Kyoung Kuhn Park,Wandoo Kim,Ho Jee Moon 한국트라이볼로지학회 2002 한국트라이볼로지학회 학술대회 Vol.2002 No.10

Ball reducer (HERB Drive: High Efficient Wave Rolling Ball Drive) with waved grooves has many advantages over other types of reducers for high-reduction ratio, low noise and low energy loss, etc. The mechanism of force transmission is very similar to that of cam and follower in automobile valve train system especially in contact behaviors. In this study, we have investigated the traces of contact between ball and outer ring, and the dynamic contact behaviors of elastohydodynamic lubrication (EHL) with a certain reduction ratio. In order to verify the contact behaviors between ball and outer ring for the critical endurance life, the contact velocity and load are computed for a cycle. During some intervals of a cycle, the contact velocity reverses its direction very suddenly. It is expected that changing the contact direction causes undesirable endurance performance because EHL films frequently collapse at the moment of velocity reversal. From the computational investigation in this work, we hope to predict similar contact damages in other machinery due to this kind of contact behaviors, which is very typical in many contact phenomena.

표면구조패턴에서의 탄성유체윤활유막 형성 연구

Siyoul Jang,Kil Min Moon,Eungji Ha,Sahoon Hong,Kwan Ho Ryu,Jun-Kui Yang 한국트라이볼로지학회 2012 한국트라이볼로지학회 학술대회 Vol.2012 No.4

Analysis of the Effects of Bore Clearance Due to Skirt Profile Changes on the Piston Secondary Movements

Jang, Siyoul Korean Tribology Society 2002 KSTLE International Journal Vol.3 No.2

Clearance movements of engine piston are very related to the piston impact to the engine block as well as many tribological problems. Some of the major parameters that influence these kinds of performances are piston profiles, piston offsets and clearance magnitudes. In our study, computational investigation is performed about the piston movements in the clearance between piston and cylinder liner by changing the skirt profiles and piston offsets. Our results show that curved profile and more offset magnitude to thrust side have better performance that has low side impact during the engine cycle.

고온 고전단 변형률 속도 조건에서 멀티그레이드 윤활유의 유막두께 형성 측정 연구

장시열(Siyoul Jang),김재홍(Jaehong Kim),배대윤(D. Y. Bae),유성춘(S. C. Yoo),이병옥(B. Rhee) 한국트라이볼로지학회 2005 한국트라이볼로지학회 학술대회 Vol.2005 No.11

It is important to decide the minimum film thickness and viscosity of a multigrade lubricant in a contact surface between engine composition articles. By carrying out acceleration, deceleration, and sliding-rolling ratio movement, it is experimented that film formation variations in the contact surface are measured. In order to exactly investigate the variations of a multigrade lubricant film thicknesses. optical interference images are continuously taken by high resolution CCD camera, the friction torques in a contact surface measured simultaneously as well.

탄성변형을 고려한 엔진베어링의 동적 거동에 대한 연구

장시열(Siyoul Jang),박계민(Gaemin Park) 한국트라이볼로지학회 2004 한국트라이볼로지학회 학술대회 Vol.39 No.-

The engine bearing transmits the powers from cylinder to crankshaft with small clearance between con-rod and crankpin. The minimum oil film thickness is a significant parameter in the operation of bearing. The contact pressure of bearing should be considered for the reason that elastic deformation of bearing be caused by contact pressure of bearing. There are important factors which are maintaining of minimum oil film thickness, expecting of the length of maximum and minimum oil film thickness with changing of the loads to keep running normally. Furthermore, this study is very crucial to develop the design of engine bearing and crankshaft system.