• Title, Summary, Keyword: Drag torque

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Effects of Friction Plate Area and Clearance on the Drag Torque in a Wet Clutch for an Automatic Transmission (클러치 드래그 토크에 미치는 마찰재 면적 및 클리어런스의 영향)

  • Ryu, Jin Seok;Sung, In-Ha
    • Tribology and Lubricants
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    • v.30 no.6
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    • pp.337-342
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    • 2014
  • The reduction of drag torque is an important research issue in terms of improving transmission efficiency. Drag torque in a wet clutch occurs because of the viscous drag generated by the transmission fluid in a narrow gap (clearance) between the friction plate and a separate plate. The objective of this paper is to observe the effects of the friction plate area and the clearance on the drag torque using finite element simulation. The two-phase flow of air and oil fluid is considered and modeled for the simulation. The simulation analysis reveals that as the rotational speed increases, the drag torque generally increases to a critical point and then decreases sharply at a high speed regime. The clearance between the two plates plays an important role in controlling drag torque peak. An increase in the clearance causes a decrease in shear stress; thus, the drag torque also decreases according to Newton's law of viscosity. An observation of the effect of the area of contact between transmission fluid and friction plate shows that the drag torque increases with the contact area. The flow vectors inside the flow channel present clear evidence that the velocity of the fluid flows is faster with a larger friction plate, that is, in the case of a larger contact area. Therefore, the optimum size of the friction plate should be determined carefully, considering both the clutch performance and drag reduction. It is expected that the results from this study can be very useful as a database for clutch design and to predict the drag torque for the initial design with respect to various clutch parameters.

Experimental Assessment of Drag Torque of Wet Clutch (습식 클러치 드래그 토크 특성의 실험적 평가)

  • Kim, Hansol;Chung, Koo-Hyun
    • Tribology and Lubricants
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    • v.33 no.6
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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.

A Study on the Wet Clutch Pattern Design for the Drag Torque Reduction in Wet DCT System (습식 DCT의 드래그 토크 저감을 위한 클러치 패드 유로 설계)

  • Cho, Junghee;Han, Juneyeol;Kim, Woo-Jung;Jang, Siyoul
    • Tribology and Lubricants
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    • v.33 no.2
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    • pp.71-78
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    • 2017
  • The drag torque in the wet clutch system of a dual clutch transmission system is investigated because it is relatively high, up to 10 of the total output torque of the engine, even when the clutch is in the disengagement state with zero torque transfer. Drag torque results from the shear resistance of the DCTF between the friction pad and separator plate. To reduce the drag torque for ensuring fuel economy, the groove pattern of the wet clutch friction pad is designed to have a high flow rate through the pattern groove. In this study, four types of groove patterns on the friction pad are designed. The volume fraction of the DCTF (VOF) and hydrodynamic pressure developments in the gap between the friction pad and separator plate are computed to correlate with the computation of the drag torque. From the computational results, it is found that a high VOF and hydrodynamics increase the drag torque resulting from the shear resistance of the DCTF. Therefore, a patterned groove design should be used for increasing the flow rate to have more air parts in the gap to reduce the drag torque. In this study, ANSYS FLUENT is used to solve the flow analysis.

Effect of Angle and Density of Grooves between Friction Plate Segments on Drag Torque in Wet Clutch of Automatic Transmission (마찰재 그루브에 따른 습식 클러치 드래그 토크 변화 연구)

  • Ryu, Jin Seok;Sung, In-Ha
    • Tribology and Lubricants
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    • v.30 no.2
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    • pp.71-76
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    • 2014
  • As the importance of transmission efficiency to reducing fuel consumption and conserving the environment rapidly increases, reducing the drag torque in an automotive wet clutch is emerging as an important issue in the automotive industry. The drag torque in a clutch occurs from viscous drag generated by automatic transmission fluid in the narrow gap between separate friction plates. In this study, the drag torques in an automotive wet clutch are investigated with respect to the angle and density of the grooves between separate friction plates by three-dimensional finite element simulation of a single set of wet clutch disks considering the two-phase flow of air and oil. The simulation results shows that the drag torque generally increases with the rotational speed to a critical point and then decreases at the high-speed regime. The grooves between the plates plays an important role in reducing the drag peak, and the inclined angle of the grooves affects the oil flow. The grooves with an angle of $50^{\circ}$ shows the lowest drag torques at both low and high speeds. The flow vectors inside the $50^{\circ}$ grooves shows clear evidence that the fluid flows out more easily from the grooves compared with the flow vectors inside grooves with lower angles. The simulation results shows that increasing the number of grooves (density of grooves) decreases the drag torque.

Approximated Generalized Torques by the Hydrodynamic Forces Acting on Legs of an Underwater Walking Robot

  • Jun, Bong-Huan;Shim, Hyung-Won;Lee, Pan-Mook
    • International Journal of Ocean System Engineering
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    • v.1 no.4
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    • pp.222-229
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    • 2011
  • In this paper, we present the concept and main mission of the Crabster, an underwater walking robot. The main focus is on the modeling of drag and lift forces on the legs of the robot, which comprise the main difference in dynamic characteristics between on-land and underwater robots. Drag and lift forces acting on the underwater link are described as a function of the relative velocity of the link with respect to the fluid using the strip theory. Using the translational velocity of the link as the rotational velocity of the joint, we describe the drag force as a function of joint variables. Generalized drag torque is successfully derived from the drag force as a function of generalized variables and its first derivative, even though the arm has a roll joint and twist angles between the joints. To verify the proposed model, we conducted drag torque simulations using a simple Selective Compliant Articulated Robot Arm.

Drag Torque Prediction for Automotive Wheel Bearing Seals Considering Viscoelastic as Well as Hyperelastic Material Properties (초탄성 및 점탄성 물성을 고려한 자동차용 휠 베어링 실의 드래그 토크 예측)

  • Lee, Seungpyo
    • Tribology and Lubricants
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    • v.35 no.5
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    • pp.267-273
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    • 2019
  • Wheel bearings are important automotive parts that bear the vehicle weight and translate rotation motion; in addition, their seals are components that prevent grease leakage and foreign material from entering from the outside of the bearings. Recently, as the need for electric vehicles and eco-friendly vehicles has been emerging, the reduction in fuel consumption and $CO_2$ emissions are becoming the most important issues for automobile manufacturers. In the case of wheel bearings, seals are a key part of drag torque. In this study, we investigate the prediction of the drag torque taking into consideration the hyperelastic and viscoelastic material properties of automotive wheel bearing seals. Numerical analysis based on the finite element method is conducted for the deformation analyses of the seals. To improve the reliability of the rubber seal analysis, three types of rubber material properties are considered, and analysis is conducted using the hyperelastic material properties. Viscoelastic material property tests are also conducted. Deformation analysis considering the hyperelastic and viscoelastic material properties is performed, and the effects of the viscoelastic material properties are compared with the results obtained by the consideration of the hyperelastic material properties. As a result of these analyses, the drag torque is 0.29 Nm when the hyperelastic characteristics are taken into account, and the drag torque is 0.27 Nm when both the hyperelastic and viscoelastic characteristics are taken into account. Therefore, it is determined that the analysis considering both hyperelastic and viscoelastic characteristics must be performed because of its reliability in predicting the drag torque of the rubber seals.

A Study on the System Parameters to Reduce the Idle Gear Rattle (기어 래틀 저감을 위한 시스템 파라미터 연구)

  • 안병민;장일도;최은오;홍동표;정태진
    • Transactions of the Korean Society of Automotive Engineers
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    • v.6 no.3
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    • pp.88-96
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    • 1998
  • The rattle noise is the most significant in many kinds of manual gearbox nioses, which is generated at the idle stage of the engine operation. The main torsional vibrat- ion source of the driveline is the fluctuation of the engine torque. The gear rattle is impacts generating in the backlash of the free gear due to this torsional vibration. Many researchers reported the clutch torsional characteristic optimization method to reduce the idle gear rattle but only few of them give sufficient consideration to the system parameters like gear backlash, drag torque, system inertia, inertia distribution, engine torque fluctuation, idle engine rotation speed, and accessory load. In this paper, influence rate of system parameters on the gear rattle is presented and counterplans like backlash reduction, drag torque increase, inertia addition, inertia distribution modification and engine torque characteristic control are suggested.

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A Study on the Flow Path Position Design of Waviness Friction Pad for Drag Torque Reduction in Wet Type DCT (파형 습식클러치의 드래그 토크 저감을 위한 파형내 유로 위치 설정 설계 연구)

  • Cho, Junghee;Han, Juneyeol;Kim, Woojung;Jang, Siyoul
    • Tribology and Lubricants
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    • v.33 no.1
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    • pp.1-8
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    • 2017
  • Drag torque reduction in a wet clutch pack is a key aspect of the design process of the dual clutch transmission (DCT) system. In order to reduce the drag torque caused by lubricant shear resistance, recently developed wet clutch pack systems of DCT, as well as automatic transmission and other four-wheel drive (4WD) couplings, frequently utilize wavy wet clutch pads. Therefore, wavy shape of friction pad are made on the groove patterns like waffle pattern for the reduction of drag torque. Additionally, the groove patterns are designed with larger channels at several locations on the friction pad to facilitate faster outflow of lubricant. However, channel performance is a function of the waviness of the friction pad at the location of the particular channel. This is because the discharge sectional area varies according to the waviness amplitude at the location of the particular channel. The higher location of the additional channel on the friction pad results in a larger cross-sectional area, which allows for a larger flow discharge rate. This results in reduction of the drag torque caused by the shear resistance of DCTF, because of marginal volume fraction of fluid (VOF) in the space between the friction pad and separator. This study computes the VOF in the space between the friction pad and separator, the hydrodynamic pressure developed, and the shear resistance of friction torque, by using CFD software (FLUENT). In addition, the study investigates the dependence of these parameters on the location and waviness amplitude of the channel pattern on the friction pad. The paper presents design guidelines on the proper location of high waviness amplitude on wavy friction pads.

A Study on the Design Technique to Reduce the Rattle Vibration (래틀 진동을 위한 설계 기법 연구)

  • 안병민;장일도;홍동표;정태진
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.562-566
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    • 1997
  • The main torsional vibration source of the driveline is the fluctuation of the engine torque. The gear rattle is impacts generating in the backlash of the free gear due to this torsional vibration Optimization of the clutch torsional characteristic is one of the effective methods to reduce the idle gear rattle. Many researches have been reported on this problem but only few of them give sufficient consideration to the full clutch design parameters(stiffness, hysteresis torque, preload, first stage length) and drag torque This paper pays attention to the gear impact mechanism, clutch design parameters and drag torque to reduce the idle gear rattle with computer simulation.

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Structure Design and Experimental Appraisal of the Drag Force Type Vertical Axis Wind Turbine (수직축 항력식 풍력터빈의 구조설계 및 실험평가)

  • Kim Dong-Keon;Keum Jong-Yoon;Yoon Soon-Hyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.3
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    • pp.278-286
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    • 2006
  • Experiments were conducted to estimate the performance of drag force type vertical axis wind turbine with an opening-shutting rotor. It was operated by the difference in drag force generated on both sides of the blades. The rotational speed was measured by a tachometer in a wind tunnel and the tunnel wind speed was measured by using a pilot-static tube and a micro manometer. The performance test for a prototype was accomplished by calculating power, power coefficient, torque coefficient from the measurement of torque and rpm by a dynamometer controller. Various design parameters, such as the number of blades(B), blade aspect ratio(W/R), angle of blades$(\alpha)$ and drag coefficient acting on a blade, were considered for optimal conditions. At the experiment of miniature model, maximum efficiency was found at N=15, $\alpha=60^{\circ}$ and W/R=0.32. The measured test variables were power, torque, rotational speed, and wind speeds. The data presented are in the form of power and torque coefficients as a function of tip-speed ratio V/U. Maximum power was found in case of $\Omega=0.33$, when the power and torque coefficient were 0.14 and 0.37 respectively. Comparing model test with prototype test, similarity law by advance ratio for vertical axis wind turbine was confirmed.