• Tribology and Lubricants
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• 제27권3호
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• pp.134-139
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• 2011

The mechanical equipments which are exposed to impure environment undergo significant reductions in their own lifetimes. Several environmental test procedures have been developed to analyze these phenomena. Moreover in the industry to require shorter development duration, accelerated life testers artificially add test containments into machines. In this research JIS Z 8901 test powder was added into internal gear pumps which are used as oil pumps in vehicles and thus the effects of the addition on the degradation of the pumps were examined. Three kinds of contaminants were selected. Two of the contaminants are identical in particle size but different in the composition of the ingredients. The other pair have identical ingredients and composition but different particle size. The quantity of contaminants was also an interesting factor in this study. The results show that each JIS contaminant caused notable degradation in the discharge flow characteristic of pumps while friction torque degradation did not have any tendency. Finally leakage rates were deduced and equivalent wear volume ratios were calculated.

• Journal of Electrical Engineering and Technology
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• 제11권1호
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• pp.135-142
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• 2016

Generally, closed slots are adopted to reduce the water friction loss in both the stator and the rotor of water filling submersible motor due to the special environment of operation. One of the obvious differences between the traditional induction motors and water filling submersible motors is that the submersible motors only need relatively smaller starting torque. This paper aims to analyze the slot leakage reactance of water filling submersible motor during starting transient operation. An improved analytical method which considered the magnetic saturation of the slot bridge and the skin effect of rotor bars is proposed. The slot permeance factor which has a direct impact on the slot leakage reactance is calculated. Then finite element models with different stator slot types are constructed and search coils are introduced to measure the slot flux linkage. Moreover, the starting performances of the models with two typical stator slots are compared and the flux leakage characteristics are obtained. Finally, the results obtained by finite element method are very close to the results obtained by analytical method.

• 대한기계학회논문집A
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• 제28권9호
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• pp.1352-1358
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• 2004

The mechanical spring is one of widely used machine elements. Among various kinds, flat-type spring loaded by a rotating pin was studied. A flat spring was simplified to a cantilever beam, and numerical analysis was attempted. Since the loading pin rotates about a separate axis from the fixed spring or vice versa, the location, direction, and magnitude of the contact force including normal contact and friction loads vary accordingly. Meanwhile, the spring is deformed substantially as the relative motion progresses. Therefore, this problem needs to be formulated taking the follower loading characteristics and geometrical non-linearity into account. Derived nonlinear differential equation was solved to yield the spring deflection, contact force and the torque to rotate the pin, and the result was compared with a finite element solution. Also, the influences of principal design parameters were studied. The proposed methodology is expected to be useful for the design of pin-loaded flat spring and the prevention of mechanical failures in the form of yielding or fatigue failure of spring or severe wear of the components.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.852-858
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• 2007

This paper investigates the dynamic characteristics of a tilted HDD spindle system with fluid dynamic bearings (FDBs). Tilting motion of a HDD spindle system may be caused by improper manufacturing tolerance, such as imperfect cylindricity between shaft and sleeve of FDBs, imperfect perpendicularity between shaft and thrust as well as the gyroscopic moment of the unbalanced mass of the rotating part. Tilting motion may result in the instability of the HDD spindle system and it may increase the disk run-out to limit memory capacity. This research proposes a modified Reynolds equation for the coupled journal and thrust FDBs to include the variable film thickness due to the cylindricity and the perpendicularity. Finite element method is used to solve the Reynolds equation for the pressure distribution. Reaction forces and friction torque are obtained by integrating the pressure and shear stress, respectively. The dynamic behavior is determined by solving the equations of a motion of a HDD spindle system in six degrees of freedom with the Runge-Kutta method to study whirling and tilting motions. This research shows that the cylindricity and the perpendicularity increase the tilting angle and whirl radius of the rotor.

• Tribology and Lubricants
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• 제30권1호
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• pp.1-8
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• 2014

In this study, a three-pad gas foil journal bearing with a diameter of 40 mm and an axial length of 35 mm was modeled to predict the static and dynamic performances with regard to an increasing mechanical preload. The Reynolds equation for an isothermal and isoviscous ideal gas was coupled with a simple elastic foundation foil model to calculate the hydrodynamic pressure solution iteratively. In the prediction results, the journal eccentricity, journal attitude angle, and minimum film thickness decreased, but the friction torque increased with the preload. A quick comparison implied a lower load capacity but higher stability for a three-pad gas foil bearing compared to a one-pad gas foil journal bearing. The direct stiffness coefficients increased with the preload, but the cross-coupled stiffness coefficients decreased. The direct damping coefficient increased in the horizontal direction but decreased in the vertical direction as the preload increased. These model predictions will be useful as a benchmark against experimental test data.

• 한국기계가공학회지
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• 제14권5호
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• pp.22-27
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• 2015

Processing of low toughness graphite material requires high-speed machine tools and DLC coating. In this study, results of investigation of the tool wear and machining properties of the DLC coating according to the thickness, and the machining time of the tool used for the machining of graphite electrodes, were as follows. 1. DLC coating thickness shows a larger wear amount of the tool center in accordance with thickness; the wear amount of the tool increases in proportion to the machining time. 2. The difference between the amount of wear depending on the processing time shows edge portions larger than the tool wear amount in the center. This amount of wear of the tool edge is formed since the rotating torque is in contact with the graphite material surface significantly more than the central portion. 3. The thicker the DLC coating, the more the coating tool eliminated of the coating area by the interface between the cemented carbide tool being coated with an increased friction of the graphite material and the DLC coating area.

• 대한기계학회논문집A
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• 제24권5호
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• pp.1305-1313
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• 2000

In a co-rotating scroll compressor, both scrolls rotate on their fixed axes contrary to the conventional orbiting type scroll machine. This implies fixed locations and directions of the gas pressure force and sealing force. Because the tilting moment is mainly caused by interplay between the resultant force of above forces and bearing reaction force, the variation during one cycle is relatively small. Under real operation, this moment is balanced by the restoring moment created by the reaction between the baseplate and thrust bearing or between the scroll tip and baseplate. If these reactions become too large, greater torque is required due to increased friction in addition to the wear of mating parts. Consequently, appropriate study and minimization of tilting moment is important in the design of scroll machines. In this study, taking into account of the small variation of tilting moment during one cycle, we minimize the moment and thrust bearing reaction force by a properly designed back pressure chamber. As a result, for both the driving and driven scrolls, the tilting moment and the reaction force of thrust bearing can be minimized. And the stability is improved for all cases.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.304-311
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• 2001

This research numerically analyzes the dynamic characteristics of a coupled journal and thrust hydrodynamic bearing due to its groove location which has the static load due to the weight of a rotor in the axial direction and the dynamic load due to its mass unbalance in the radial direction. The Reynolds equation is transformed to solve a plain member rotating type of journal bearing(PMRJ), a grooved member rotating type of journal bearing (GMRJ), a plain member rotating type of thrust bearing (PMRT) and a grooved member rotating type of thrust bearing (GMRT). FEM is used to solve the Reynolds equations in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors, such as whirl radius or floating height of a rotor, are determined by solving its nonlinear equations of motion with the Runge-Kutta method. This research shows that the groove location affects the pressure distribution in the fluid film and consequently the dynamic performance of a HDD spindle system.

• 한국강구조학회 논문집
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• 제8권3호통권28호
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• pp.139-150
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• 1996

H/T(High Tension) bolt is generally being used in joining the members of steel structure. It has some difficulties in management such as an adequate fastening force and a selection of proper instrument for fastening. T/S(Torque Shear Type High Tension) bolt which is more convenient and easier than H/T bolt in quality control has recently been developed. T/S bolts are produced and widely used these days in domestic, but those have not a detail regulation for their on. Those are only being used according to the specification for the H/T bolts. In this study, we tried to confirm the soundness of T/S bolts by the fatigue test of the modified specimens. First, we measured the reduction rate of the initial axial force with time at bolts. Second, we investigated the slip forces of bolts when the test specimen is loaded in tension. Third, we implemented the fatigue tests. During the test, we measured the variation of the axial forces of bolts under the cyclic loading. Finally, we compared and analyzed the fatigue behavior of H/T and T/S bolt, by S-N curve diagrams that are obtained in this study.

• Advances in Automotive Engineering
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• 제1권1호
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• pp.21-39
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• 2018

Clutch energy is the thermal energy dissipated on the clutch disc, and it reaches its highest level during drive-off as a result of the difference between the angular speeds of the flywheel and clutch disc, and the torque transmitted. The thermal energy dissipated effects the clutch life. This study presents a new drive-off and thermal model to calculate the clutch energy for a rear wheel driven heavy-duty vehicle and to analyze the effects of clutch energy on temperatures of clutch pressure plate, flywheel and clutch housing. Three different driver profiles are used, based on the release of the clutch pedal in modulation zone: i) the pedal travels with the same speed all the way, ii) the travel speed of the pedal increases, iii) the travel speed of the pedal decreases. Vehicle test is performed to check the accuracy of the model. When compared to a simpler model that is widely used in the literature to calculate the clutch energy, the model used in this study calculates the clutch energy and angular speed behaviors of flywheel and transmission input shaft in better agreement with experimental results. Clutch wear and total clutch life are also estimated using the mean specific friction power.