Modelling the influence of velocity on wet friction-element friction in clutches

Purpose This study aims to establish a friction coefficient model relative to the rotation speed of a wet clutch engagement, which can predict friction coefficient under different stages of slipping velocity and different load pressures. In particular, the model has been improved by accounting the speed effect for the perdition of wet friction-element boundary friction, which is significant for understanding the friction mechanisms and for supporting the development of more efficient and related products. Design/methodology/approach This research investigated the mechanism of wet friction in a wet clutch engagement. A mixed friction model is established based on the asperity model and Newton’s law of viscosity. To obtain a friction coefficient computed by the model, the normal load shared by both asperities and lubrication fluid needs to be determined. Therefore, rough surface contact mechanism is analysed; a surface topography model is established; and surface parameters are obtained by means of surface topography measurement and reconstruction. Finally, verification of the mixed friction model is achieved. Findings Friction will be generated by both the asperity contact and the lubrication film shear relative to the rotation speed. And, the higher the relative speed, the larger the shearing power of lubrication film. It is caused by decrease in contact area of asperity. Surface morphology of a sintered bronze friction disk was obtained by a Laser-Micro-Test. The predicted results by the established model show that the total friction coefficient slightly reduced and then increased suddenly with speed. The surface topography model is responsible for the nonlinear behaviour of the asperity friction. Results of the simulation model are in agreement with those of the wet clutch engagement experiments. Originality/value This research is original and it is supported by the national defence project. The wet friction element which is applied on tracked vehicles is analysed for the first time. Through the model, the trend of the friction coefficient can be more accurately predicted. The problem of the wet friction plate modelling difficult is solved by using the mixed friction model.

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Modeling and experimental research on engaging characteristics of wet clutch

Industrial Lubrication and Tribology ◽

10.1108/ilt-12-2017-0383 ◽

2019 ◽

Vol 71 (1) ◽

pp. 94-101 ◽

Cited By ~ 1

Author(s):

Yanzhong Wang ◽

Yuan Li ◽

Yang Liu ◽

Wei Zhang

Keyword(s):

Contact Surface ◽

Hydrodynamic Lubrication ◽

Load Capacity ◽

Lubricating Oil ◽

Centrifugal Effect ◽

Element Analysis ◽

Content Type ◽

Clutch Engagement ◽

Wet Clutch ◽

Engagement Process

PurposeTo gain in-depth understandings of engaging characteristics, the purpose of this paper is to improve the model of wet clutches to predict the transmitted torque during the engagement process.Design/methodology/approachThe model of wet clutch during the engagement process took main factors into account, such as the centrifugal effect of lubricant, permeability of friction material, slippage factor of lubricant on contact surface and roughness of contact surface. Reynolds’ equation was derived to describe the hydrodynamic lubrication characteristics of lubricant film between the friction plate and the separated plate, and an elastic-plastic model of the rough surfaces contact based on the finite element analysis was used to indicate the loading force and friction torque of the contact surface.FindingsThe dynamic characteristics of wet clutch engagement time, relative speed, hydrodynamic lubrication of lubricating oil, rough surface contact load capacity and transfer torque can be obtained by the wet clutch engagement model. And the influence of the groove shape and depth on the engaging characteristics is also analyzed.Originality/valueThe mathematical model of the wet clutch during the engagement process can be used to predict the engaging characteristics of the wet clutch which could be useful to the design of the wet clutch.

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Effect of surface topography associated with arbitrary velocity direction on the lubrication film thickness in elliptical contacts

Industrial Lubrication and Tribology ◽

10.1108/ilt-09-2016-0206 ◽

2018 ◽

Vol 70 (2) ◽

pp. 444-452 ◽

Cited By ~ 2

Author(s):

Wei Pu ◽

Jiaxu Wang ◽

Guangwu Zhou ◽

Ke Xiao ◽

Junyang Li

Keyword(s):

Surface Roughness ◽

Film Thickness ◽

Surface Topography ◽

Surface Velocity ◽

Content Type ◽

Lubrication Film ◽

Wide Range ◽

Lubricating Property ◽

Inclined Angle ◽

Effect Of Surface

Purpose The purpose of this study is to describe and observe the effect of surface topography associated with arbitrary directions of rolling and sliding velocities on the performance of lubricating films in elliptical contacts. Design/methodology/approach The most recently published mixed elastohydrodynamic (EHL) model by Pu and Zhu is used. Three different machined rough surfaces are discussed and the correlated inclined angle of surface velocity varies from 0° to 90° in the analyzed cases. These cases are carried out in a wide range of speeds (five orders of magnitude) while the simulated lubrication condition covers full-film and mixed EHL down to the boundary lubrication. Findings The results indicate that the variation of the average film thickness corresponding to different entrainment angles is distinct from those without considering surface roughness. In addition, the surface topography appears to have an immense effect on the lubrication film thickness in the exceptive situation. Originality/value This paper has not been published previously. Surface roughness has attracted much attention for many years owing to the significant influence on lubricating property. However, previous studies mainly focus on the counterformal contact with the same direction between surface velocity and principal axis of the contact zone. Little attention has been paid to the specific condition with the arbitrary direction of rolling and sliding velocities found in hypoid gears and worm, and some other components. The purpose of this study is to describe and observe the effect of surface topography associated with arbitrary directions of rolling and sliding velocities on the performance of lubricating films in elliptical contacts based on the most recently published mixed EHL model by Pu and Zhu.

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Analysis of influencing factors on transient temperature field of wet clutch friction plate used in marine gearbox

Industrial Lubrication and Tribology ◽

10.1108/ilt-08-2016-0181 ◽

2018 ◽

Vol 70 (2) ◽

pp. 241-249 ◽

Cited By ~ 6

Author(s):

Tengjiao Lin ◽

Zi-ran Tan ◽

Ze-yin He ◽

Hong Cao ◽

He-sheng Lv

Keyword(s):

Temperature Field ◽

Friction Coefficient ◽

Sliding Friction ◽

Moment Of Inertia ◽

Transient Temperature ◽

Content Type ◽

Transient Temperature Field ◽

Wet Clutch ◽

Sliding Friction Coefficient ◽

Friction Plate

Purpose This paper aims to introduce the moment of inertia of the driving and driven end of the clutch into the analysis of the transient temperature field of a friction plate and studied the influencing factors on that, especially to a marine gearbox. Design/methodology/approach A three-dimensional transient heat transfer analysis model of a wet clutch friction plate used in a marine gearbox is developed, and the transient characteristics of the temperature field during engagement are analyzed with taking account of the influence factors such as the sliding friction coefficient, engaging revolving speed, moment of inertia and applied engagement pressure. Findings The paper found out that the hot spot appears on the surface of the friction plate, taking account of the effect of radial slots and spiral groove. To avoid damage to the friction plate as a result of overheating, the appropriate sliding friction coefficient, lower engaging revolving speed and reasonable selection of applied engagement pressure curve can ensure a favorable heating situation of the friction plate. The reasonable structural design for the clutch with a bigger moment of inertia of driving end and smaller moment of inertia of driven end can reduce the engaging time effectively and decrease the peak temperature of the friction plate. Originality/value This paper fulfils a method to study the transient temperature field of a wet clutch friction plate, especially used in a marine gearbox.

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Numerical Simulation of Engagement of a Wet Clutch With Skewed Surface Roughness

Journal of Tribology ◽

10.1115/1.1402178 ◽

2001 ◽

Vol 124 (2) ◽

pp. 305-312 ◽

Cited By ~ 22

Author(s):

H. Gao ◽

G. C. Barber ◽

M. Shillor

Keyword(s):

Surface Roughness ◽

Friction Coefficient ◽

Weibull Distribution ◽

Height Distribution ◽

Asperity Contact ◽

Friction Characteristic ◽

Friction Materials ◽

Wet Friction ◽

Torque Response ◽

Wet Clutch

The engagement of a wet clutch with skewed surface roughness was investigated. A Weibull asperity height distribution rather than a Gaussian one was utilized in the asperity contact pressure model. The combined effects of surface roughness and skewness on the friction coefficient were studied for new, run-in and glazed wet friction materials. The results show that the engagement time predicted by the Weibull distribution is greater than that obtained using the Gaussian distribution. A torque spike at the beginning of engagement occurs using the Weibull distribution by taking the skewness into account. A positively sloped curve of friction coefficient versus velocity can reduce the torque increase near the end of the engagement. The strain value at the end of engagement obtained by including the skewness is lower than that predicted by excluding it. The surface topography and the friction characteristics change with the engagement wear and thermal glazing. The torque response and the phase plane are presented for the run-in and the glazed wet friction materials as a function of surface roughness, skewness, and friction characteristic.

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Frictional Torque Transfer Behaviors of Friction Pads in Wet Clutch Engagement

Volume 15: Advances in Multidisciplinary Engineering ◽

10.1115/imece2015-53032 ◽

2015 ◽

Cited By ~ 1

Author(s):

Siyoul Jang

Keyword(s):

Friction Coefficient ◽

Direct Contact ◽

Hydrodynamic Lubrication ◽

Static Friction ◽

Design Parameters ◽

Frictional Torque ◽

Kinetic Friction ◽

Static Friction Coefficient ◽

Clutch Engagement ◽

Wet Clutch

For stable frictional torque transfer, wet clutch pads have the functional requirements of a high traction and a low wear rate with positive μ-V frictional characteristics. However, because of the intrinsic negative μ-V frictional characteristics of a friction material that has a static friction coefficient greater than its kinetic friction coefficient, the frictional torque transfer has unstable vibrations during the clutch-pad engagement. To reduce the vibration mode during the engagement of wet clutch pads, the kinetic friction coefficient should be made greater than the static friction coefficient through modifications in the design parameters as well as in the characteristics of the friction materials. To obtain positive μ-V frictional characteristics, it is important to manipulate the static-friction coefficient, which largely develops in the boundary lubrication stage during the clutch-pad engagement. The formation of the boundary film is described by slip boundary conditions and hydrodynamic lubrication films. It also includes the elastic deformation of the wet pad material due to the contact pressure. The wet clutch pad material is made of a porous structure through which the lubricant can easily spread when the applied load and sliding speed are imposed. The lubrication and the direct contact of the surfaces are simultaneously considered for a frictional torque transfer that lasts for less than one second, depending on the working conditions. In this study, some of the computational results with a measured μ-V friction coefficient covering both the static and kinetic friction during the wet-clutch engagement are obtained for the lubrication and the direct-contact pressures.

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Study on high-temperature wear and mechanism of Al-Si/graphite composites prepared by the die-casting process

Industrial Lubrication and Tribology ◽

10.1108/ilt-10-2019-0454 ◽

2020 ◽

Vol 72 (10) ◽

pp. 1153-1158 ◽

Cited By ~ 1

Author(s):

Yafei Deng ◽

Xiaotao Pan ◽

Guoxun Zeng ◽

Jie Liu ◽

Sinong Xiao ◽

...

Keyword(s):

Friction Coefficient ◽

Wear Rate ◽

Peer Review ◽

Die Casting ◽

Casting Machine ◽

Injection Pressure ◽

Casting Process ◽

Matrix Alloy ◽

Content Type ◽

The Matrix

Purpose This paper aims to improve the tribological properties of aluminum alloys and reduce their wear rate. Design/methodology/approach Carbon is placed in the model at room temperature, pour 680°C of molten aluminum into the pressure chamber, and then pressed it into the mold containing carbon felt through a die casting machine, and waited for it to cool, which used an injection pressure of 52.8 MPa and held the same pressure for 15 s. Findings The result indicated that the mechanical properties of matrix and composite are similar, and the compressive strength of the composite is only 95% of the matrix alloy. However, the composite showed a low friction coefficient, the friction coefficient of Gr/Al composite is only 0.15, which just is two-third than that of the matrix alloy. Similarly, the wear rate of the composite is less than 4% of the matrix. In addition, the composite can avoid severe wear before 200°C, but the matrix alloy only 100°C. Originality/value This material has excellent friction properties and is able to maintain this excellent performance at high temperatures. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2019-0454/

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An improved nonlinear model considering relative velocity for the friction behavior between untwisted glass-fiber tow and roller

Textile Research Journal ◽

10.1177/00405175211030877 ◽

2021 ◽

pp. 004051752110308

Author(s):

Yang Liu ◽

Zhong Xiang ◽

Xiangqin Zhou ◽

Zhenyu Wu ◽

Xudong Hu

Keyword(s):

Friction Coefficient ◽

Glass Fiber ◽

Relative Velocity ◽

Friction Model ◽

Woven Fabric ◽

Test Results ◽

Application Process ◽

Friction Behavior ◽

Improved Model

Friction between the tow and tool surface normally happens during the tow production, fabric weaving, and application process and has an important influence on the quality of the woven fabric. Based on this fact, this paper studied the influence of tension and relative velocity on the three kinds of untwisted-glass-fiber tow-on-roller friction with a Capstan-based test setup. Furthermore, an improved nonlinear friction model taking both tension and velocity into account was proposed. According to statistical test results, firstly, the friction coefficient was found to be positively correlated with tension and relative velocity. Secondly, tension and velocity were complementary on the tow-on-roller friction behavior, with neither being superior to the other. Thirdly, an improved model was found to present well the nonlinear characteristics between friction coefficient and tension and velocity, and predicational results of the model were found to agree well with the observations from Capstan tests.

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A novel technique for modeling friction behavior in knitted fabric simulation

International Journal of Clothing Science and Technology ◽

10.1108/ijcst-01-2017-0006 ◽

2017 ◽

Vol 29 (6) ◽

pp. 776-792

Author(s):

Vajiha Mozafary ◽

Pedram Payvandy

Keyword(s):

Friction Coefficient ◽

Uniform Distribution ◽

Friction Force ◽

Experimental Result ◽

Knitted Fabric ◽

Friction Behavior ◽

Content Type ◽

Novel Technique ◽

Fabric Structure ◽

Fabric Surface

Purpose Fabric-object friction force is a fundamental factor in cloth simulation. A large number of parameters influence the frictional properties of fabrics such as fabric structure, yarn structure, and inherent properties of component fibers. The purpose of this paper is to propose a novel technique for modeling fabric-object friction force in knitted fabric simulation based on the mass spring model. Design/methodology/approach In this technique, unlike other studies, distribution of friction coefficient over the fabric surface is not uniform and depends on the fabric structure. The main reason for considering non-uniform distribution is that in various segments of fabric, contact percent of fabric-object is different. Findings The proposed technique and common methods based on friction coefficient uniform distribution are used to simulate the frictional behavior of knitted fabrics. The results show that simulation error values for proposed technique and common methods are 2.7 and 9.4 percent as compared with the experimental result, respectively. Originality/value In the existing methods of the friction force modeling, the friction coefficient of fabric is assumed uniform. But this assumption is not correct because fabric does not have an isotropic structure. Thus in this study, the friction coefficient distribution is considered based on fabric structure to achieve more of realistic simulations.

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