• 한국산학기술학회논문지
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• 제17권6호
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• pp.687-692
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• 2016

엔진에 터보차져를 사용하게 되면 엔진의 출력도 향상되지만 동시에 엔진의 온도도 높아지게 된다. 특히 피스톤의 경우는 냉각이 문제가 된다. 이러한 문제를 해결하기 위하여 오일 젯을 사용하는데, 오일 젯은 오일을 피스톤의 밑 부분에 분사하여 피스톤을 냉각시키는 것이다. 오일 젯이 사용된다면, 오일의 분사로 인하여 오일 유량의 증가및 피스톤으로부터의 열전달에 의하여 높아진 오일 온도 문제를 해결하기 위하여 오일 펌프 용량 증대와 오일 쿨러의 사용이 필요하다. 그러나 용량 증대 오일 펌프와 오일 쿨러를 사용하면 엔진의 마찰 토크가 증가하는 원인이 된다. 본 연구에서는 오일 젯, 오일 쿨러 및 오일 펌프의 용량 증대로 인하여 엔진의 마찰 토크가 증가하는 정도에 대하여 연구하였다. 또한 각 부품의 사양을 변경함에 따라 마찰 토크가 얼마나 영향을 받는가도 측정되었다. 저속에서는 오일 펌프와 오일 쿨러에 의한 영향이 크고 고속에서는 오일 쿨러에 의한 영향이 큼을 알 수 있었다.

• Tribology and Lubricants
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• 제33권6호
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• pp.269-274
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• 2017

Currently, fuel efficiency becomes one of critical issues for automotive industries as concerns about environmental and energy problems grow. In an automatic transmission of an automobile, a drag torque due to a viscous drag of a fluid between friction and clutch plates is one of factors that degrade fuel economy. In this work, the drag torque characteristics of a wet clutch was experimentally investigated with respect to rotational speed, temperature of automatic transmission fluid (ATF), and gap between friction and clutch plates. The experimental results showed that drag torque increases to a certain level, and then decrease to the steady state value with increasing rotational speed. This behavior may be associated with two-phase flow of air and ATF at gap between friction and clutch plates. Also, it was found that the maximum drag torque value decreased as ATF viscosity decreases with increasing temperature. However, it was shown that the point at which the maximum drag torque occurs was not significantly affected by the ATF temperature. In addition, maximum drag torque was found to decrease as the gap between friction and clutch plates increased from 0.1 mm to 0.2 mm. Furthermore, it was observed that the generation of maximum drag torque was delayed as the gap increased. The outcomes of this work are expected to be helpful to gain a better understanding of drag torque characteristic of a wet clutch, and may therefore be useful in the design of wet clutch systems with improved performance.

• 한국기계가공학회지
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• 제20권3호
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• pp.40-46
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• 2021

An automatic transmission of automobiles enables comfortable driving experience with lower transmission shifting jerks. However, the assembly structure is more complicated and requires additional components with lower efficiency than the manual transmission system. Extensive research has been conducted to improve the overall transmission efficiency by optimizing each component of the automatic transmission assembly. This study focuses on enhancing the friction torque of double angular contact ball bearings used in automatic transmission. The friction torque of the bearing varies with the operating conditions such as the operational load and rotating speed. Since reducing the friction torque of the bearing tends to deteriorate the durability of the bearing, it is necessary to design the bearing having a minimum required friction torque by determining the durability life of an automatic transmission assembly, In this study, the theoretical life and friction torque of conventional and newly-developed bearings are calculated. The difference in the friction torque between the new and existing bearings are also evaluated.

• Tribology and Lubricants
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• 제14권2호
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• pp.26-34
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• 1998

This paper presents a high-speed performance analysis of ball bearings with ceramic balls under thrust loads. The sliding velocity profiles between a ball and raceways were obtained by the 3-D quasi-dynamic equations of motion including both centrifugal force and gyroscopic moment derived by vector matrix algebra. The friction at the contact areas was obtained by the Bair-Winer's non-Newtonian rheological model and the Hamrock-Dowson's central film thickness in EHL analysis. The nonlinear equations were solved by the Newton-Raphson method and the underrelaxation iterative method. The friction torques and ball behaviors with various loads, ball materials, and contact angles were predicted by this model. It was shown that the friction torque was sensitive to thrust load and contact angle, and that the friction torque and the pitch angle of the bearing with ceramic balls are smaller than those of the bearing with steel balls.

• Tribology and Lubricants
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• 제23권2호
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• pp.61-65
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• 2007

It is very important to connect machinery and maintain it. This is usually done by bolt joint. There are two ways in connecting the bolt joint : the angle method and the torque method. The torque method is a method that let the clamping force maintain. The underhead of the bolt's head and the thread friction are the main influences. This study focuses on how the clamping farce and friction coefficient change under the condition in vibrating the underhead of the bolt's head part. As a result, under vibration condition, we found out that the clamping farce increases, while the friction coefficient decreases.

• 대한기계학회논문집A
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• 제20권2호
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• pp.540-552
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• 1996

In this paper, a compensation method of disturbance using a disturbance observer is proposed for a force control of a pneumatic robot manipulator. The generated torque by a pneumatic actuator can be estimated based on the pressure signals. The inner torque control system is constructed by feeding back the generated torque to improve the dynamic characteristics of the actuator. In order to reduce the influence of disturbances comprising friction torque, parameter variations of plant and environment and so on, the reaction torque control system is constructed with a disturbance observer which estimates the disturbances based on the reference input to the inner torque control system and the reaction torque sensed with a forced sensor. From some simulations and experiments, it is confirmed that the proposed control system is effective to improve the robustness for the friction torque and the parameter change of object in the force control of a pneumatic robot manupulator.

• 한국유체기계학회 논문집
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• 제6권3호
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• pp.44-50
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• 2003

An experiment is conducted for measuring the performance of an air tool, which is operated at 100,000 RPM in an unloaded state with very low torque. A 551 kPa in gauge pressure is supply to the inlet of an air tool. An experimental apparatus is developed as a friction type dynamometer. Inlet total pressure, air flow rate, rotational speed and operating force are measured simultaneously. Torque, output power and specific output power are obtained with different rotational speeds. Those are compared with the experimental results which were obtained by a commercial dynamometer. However, no commercial dynamometers are available for measuring the torque above 30,000 RPM. In order to reduce the rotational speed, a reduction gear is applied between the air tool and the commercial dynamometer. Torque and power obtained by the commercial dynamometer show $55\%$ lower than those obtained by the developed friction type dynamometer, because the mass is added to the rotor of air tool for the braking system of the commercial dynamometer and power loss is generated by the reduction gear. From the compared results, the friction type dynamometer should be applied for measuring the performance of the air tool operating at low torque and high RPM.

• 한국지반환경공학회 논문집
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• 제24권1호
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• pp.51-60
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• 2023

수직 시추와 다르게 방향성 시추작업에서 발생하는 드릴스트링(drill string) 변형, 케이싱(casing) 마모, 키 씨팅(key seating) 등의 문제를 방지하기 위해서는 시추 궤도 내에서 발생하는 토크(torque)와 드래그(drag)가 최소화되어야 한다. 토크와 드래그의 크기는 시추 궤도 형태, 이수(mud), 드릴스트링의 종류 그리고 킥오프 지점(KOP, kick-off point)과 같은 매개변수들에 의해 결정되기 때문에 시추 궤도 설계 과정에서 고려하여 설계하여야 한다. 본 연구에서는 가장 일반적인 방향성 시추 궤도인 빌드-홀드(Build-hold) 형태의 시추 궤도에 킥오프 지점이 각기 다른 시추 궤도를 선정하였고, 분포하중 모델(analytical friction model)을 이용하여 각 구간내에서의 분포하중을 계산하여 궤도 전체에 대한 토크와 드래그를 계산하였다. 또한 매개변수에 따른 분석 값을 비교하여 분포하중이 최소로 발생하는 최적의 시추 궤도를 선정하였다. 분석결과 분포 하중을 최소화하기 위해서는 윤활성이 높은 이수를 사용, 궤도 형태에 따른 알맞은 킥오프 지점과 가능한 최소의 도그-래그를 지정하여 설계하는 것이 효과적임을 알 수 있었다. 이러한 결과는 분포하중을 최소화하기 위한 모든 방향성 시추 궤도 설계에 사용된다.

• 한국안전학회지
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• 제18권2호
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• pp.1-5
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• 2003

By using an approach developed to determine the torque-tension relationship for bolted joints, frictional properties of several typical bolted joints were studied experimentally. The specific property by bolted joints certify that the most significant influence of materials and bearing surface condition. Experiments on thread friction shows that prevailing torque nuts with distorted threads provide benefit for preventing self-loosening of the nut. Repeated tightening-loosening generally increases frictions in a bolted joint. It was noted that the data scatter of the experimental results of frictions in a belted joint may overshadow the influence of size. speed, and contact positions. The results from the experimental investigation will help to better design bolted joints.

• 한국지진공학회논문집
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• 제17권5호
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• pp.227-235
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• 2013

Friction energy dissipative devices have been increasingly implemented as structural seismic damage protecting systems due to their excellent seismic energy dissipating capacity and high stiffness. This study develops rotational friction energy dissipative devices and verifies experimentally their cyclic response. Based on the understanding of the differences between the traditional linear-motion friction behavior and the rotational friction behavior, the configuration of the frictional surface was determined by investigating the characteristics of the micro-friction behavior. The friction surface suggested in this paper consists of brake-lining pads and stainless steel sheets and is normally stressed by high-strength bolts. Based upon these frictional characteristics of the selected interface, the rotational friction energy dissipative devices were developed. Bolt torque-bearing force tests, rotational friction tests of the suggested friction interfaces were carried out to identify their frictional behavior. Test results show that the bearing force is almost linearly proportional to the applied bolt torque and presents stable cyclic response regardless of the experimental parameters selected this testing program. Finally, cyclic tests of the rotational friction energy dissipative devices were performed to find out their structural characteristics and to confirm their stable cyclic response. The developed friction energy dissipative devices present very stable cyclic response and meet the requirements for displacement-dependent energy dissipative devices prescribed in ASCE/SEI 7-10.