Friction Coefficient Ratio Research Articles

A Study on In-wheel Motor Control to Improve Vehicle Stability Using Human-in-the-Loop Simulation

In this study, an integrated motor control algorithm for an in-wheel electric vehicle is suggested. It consists of slip control that controls the in-wheel motor torque using the road friction coefficient and slip ratio; yaw rate control that controls the in-wheel motor torque according to the road friction coefficient and the yaw rate error; and velocity control that controls the vehicle velocity by a weight factor based on the road friction coefficient and the yaw rate error. A co-simulator was developed, which combined the vehicle performance simulator based on MATLAB/Simulink and the vehicle model of CarSim. Based on the co-simulator, a human-in-the-loop simulation environment was constructed, in which a driver can directly control the steering wheel, the accelerator pedal, and the brake pedal in real time. The performance of the integrated motor control algorithm for the in-wheel electric vehicle was evaluated through human-in-the-loop simulations.

Tribochemistry on Clutch Friction Material Lubricated by Automatic Transmission Fluids and the Link to Frictional Performance

Automatic transmissions (AT) for passenger cars are becoming more popular globally, including some countries that traditionally prefer manual transmissions. Some new friction modifiers for transmission fluid technologies have also emerged due to the downsizing trend of transmissions. In order to study the tribology and tribochemistry effects of some new automatic transmission fluid (ATF) additive formulations, both steel and wet-clutch friction materials were assessed by using surface analysis techniques. A variable speed friction test (VSFT) rig was used to study the antishudder properties in lock-up clutch tests and friction modifying mechanisms of ATFs. A test oil matrix containing basic ATF components was tested. The friction results were analyzed using both the linear-defined multiple parameter spider chart ATF evaluation (LSAE) method (Zhao et al., 2008, “A New Method to Evaluate the Overall Anti-Shudder Property of Automatic Transmission Fluids—Multiple Parameters Spider Chart Evaluation,” Proc. Inst. Mech. Eng., Part J: J. Eng. Tribol., 222(J3), pp. 459–470) and the friction coefficient ratio index method (Zhao et al., 2011, “Understanding Friction Behavior in Automatic Transmission Fluid LVFA Test: A New Positive Curve Parameter to Friction Coefficient Ratio Index Evaluation,” ASME J. Tribol., 133(2), p. 021802) (e.g., μ1/μ50 on the low-velocity friction apparatus (LVFA) μ-v curve results to compare the overall tribosystem and the snapshot friction performance during the test). Surface analysis results were obtained by using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and attenuated total reflectance Fourier transformed infrared spectroscopy (ATR FT-IR), and they are presented in this study to investigate the tribofilm compositions formed by different additive formulations. Some organic functional groups were found at the sample surfaces, such as –OH and O–C–O, and their presence is proposed to have a beneficial influence on the ATF friction performance. This paper discusses the surface analysis results of the test sample pieces, the possible links between specific functional groups and friction performance, and the proposed pathways of additive decompositions by using chemical bond dissociation energy comparisons.

Comparison of Braking Performance by Electro-Hydraulic ABS and Motor Torque Control for In-wheel Electric Vehicle

In this study, a slip control algorithm using motor torque control during the braking of the in-wheel electric vehicle was proposed and an anti-lock brake system (ABS) simulator was developed on the basis of the test results for electro-hydraulic ABS. The slip control algorithm using motor torque control limits the in-wheel motor torque according to road friction coefficient and slip ratio while the ABS prevents locking of the wheel by lowering or raising the brake pressure through solenoid valve control. A MATLAB/Simulink model and a CarSim vehicle model were developed, and the motor torque control and ABS simulator were applied to the MATLAB/Simulink-CarSim co-simulator and compared braking performance.

DEM Simulation of Micro-Macro Mechanical Behaviour of Granular Materials

The mechanical responses of granular materials are affected significantly by the properties of the individual particle. In order to establish the link between the micro and macro parameters, series of numerical biaxial simulations are carried out using two-dimensional discrete element method. The microscale mechanisms of mechanical behavior of granular materials are investigated through sensitivity analyses. The key influence of microscale parameters on the strength and deformation are discussed respectively. The peak strength depends on void ratio, friction coefficient and confining stress significantly. The elastic modulus is affected by friction coefficient, confining pressure and stiffness ratio, especially when the friction coefficient ranges from 0.1 to 0.3. The samples with different initial void ratio under the same loading condition can finally achieve the same critical state; the critical states at micro and macro scale are both independent of the initial void ratio.

Novel estimation of tyre-road friction coefficient and slip ratio using electrical parameters of traction motor for electric vehicles

The estimation of the friction coeffi cient and the slip ratio is crucial for advanced traction control or anti-brake control of electric vehicles. In this paper, dynamic behaviours of electrical parameters of the traction motor under road change are modelled and analysed. Novel estimation only using the measurements of the armature voltage and the current is proposed. The proposed method is much quicker than traditional methods, contributing to adjust the vehicle’s motion state more quickly and precisely. Further, it can eliminate the speed measuring devices of the wheel speed and the vehicle speed. Simulations verify the effectiveness.

Study on the friction and wear performance of carbon fabric/phenolic composites under oil lubricated conditions

Four kinds of carbon fabric reinforced phenolic resin composites were fabricated by the impregnation technique in the present study. And the effect of phenolic resin on friction and wear performance of the composites was investigated. Experimental results showed that the friction torque curves of the samples were very flat during the mixed asperity contact phase of the engagement except the sample with 30wt% resin content. The dynamic friction coefficient (μd) decreased with the increase of resin content, but the friction coefficient ratio increased. The wear rates of all samples did not exceed 1.30×10−5mm3/J, indicating excellent wear resistance of carbon fabric/phenolic composites. Meanwhile the composites were very friendly to the couple plate. The sample with 25wt% resin content possessed the best wear resistance due to the moderated combination between the carbon fibers and the matrix and good friction surface formation.

Molecular dynamics study of epoxy/clay nanocomposites: rheology and molecular confinement

To investigate the effect of nanoparticles on molecular confinement, epoxy/clay nanocomposites in 6 % wt were prepared by low shear mixer and ultrasonication methods. According to the XRD results, high energy sonication can significantly increase the intergallery space compared to that of the low shear mixer and, therefore, provide more interfacial area for polymer-particle interaction. Rheological measurements, including dynamic mechanical moduli, continuous relaxation spectrum and zero-shear viscosity, were carried out in the linear region to reveal the solid-like characteristics induced in the pure epoxy. The longest Rouse relaxation time, which was determined from the value of zero-shear viscosity, was employed to study the segmental friction. It is clear that the chain relaxation process was slowed by the polymer-particle interactions, which created very high monomeric friction. We introduce the ratio of monomeric friction coefficients (ζnano/ζepoxy) as the strength of immobilization to correlate the increasing elasticity, longer relaxation time and molecular confinement quantitatively. Because more monomers can be immobilized on a clay surface due to their strong affinity, the friction ratio increased to 359.48 for the sonicated sample, whereas weak polymer-particle affinity resulted in much lower growth, with a friction ratio of 2.11 for the low shear mixing method.

Screw extrusion of thermoplastics: II. Simulation of feeding zone of the single screw extruder

The technique of calculation of a feeding zone for a single screw extruder is developed taking into account the nonisothermal process and the actual boundary geometric conditions and speed conditions (the screw is rotated, the cylinder is fixed). An analysis of the influence of the screw geometry was performed and also of an effect of a ratio of friction coefficients of the processed material on the cylinder and worm, on a change in pressure and temperature of the processed material along the length of the feeding zone.

206 カーリングストーンの氷摩擦係数とカール比の測定(カーリング)

206 カーリングストーンの氷摩擦係数とカール比の測定(カーリング)

Tribomechanical calculation method of the lateral pressure coefficient for brittle dispersed materials

A calculation procedure is proposed to analyze the lateral pressure coefficient of brittle dispersed materials with account of the joint effect of the interparticle and external (wall or boundary) friction modes The measurement range of this coefficient is defined as the ratio of the interparticle friction coefficient to the external (boundary) friction one.

Study on Dynamic Minimum Thickness of Cut by Nanoscratch Testing

Nanoscratch tests showing clear ploughing behavior and stable chip formation was conducted to investigate the influence of friction coefficient on the minimum thickness of cut. A theoretical model accounting for the minimum thickness of cut is used to analyze the effects of the friction coefficient and force ratio. Results show that the minimum thickness of cut is strongly dependent on both friction coefficient and force ratio. Theoretical minimum thickness of cut can be obtained when adhesion friction plays a dominant role in the cutting process. Appropriate adjustments of processing parameters are hereby suggested to result in stable micro-machining process without ploughing, not only forming fine-thin continuous chip, but also achieving high surface quality. The role of friction coefficient on the minimum thickness of cut with δ (cutting depth/edge radius) is also discussed.

STUDY ON THE FORMATION MECHANISM OF TANGJIASHAN LANDSLIDE TRIGGERED BY WENCHUAN EARTHQUAKE USING DDA SIMULATION

Wenchuan earthquake, Ms 8.0 in magnitude and occurred on May 12, 2008 in Sichuan Province, China, triggered a lot of landslides, rock collapses, debris flow, etc. The Tangjiashan landslide, with its total volume 20.37 million m3, was the biggest and the most notable one for its effects. Based on the field geological investigation and the typical acceleration records of the main shock obtained in the period of the earthquake, numerical simulation of the whole sliding process of Tangjiashan landslide has been carried out by DDA method. It is shown that the Tangjiashan landslide was a high-speed landslide, behaved with nonlinear features in the whole sliding process. The total duration of the landslide was about 30 s while nearly all of their slipping displacements were carried out in the beginning 25 s, with the maximum sliding velocity about 30 m/s, and the average 15–17 m/s in the beginning 25 s. The crash of rock blocks induced a much higher stresses near the middle and lower parts of the landslide, with the maximum value of 6–7 MPa. The dynamic earthquake load caused an incessant deformation of the landslide, resulting in the reduction of mechanical parameters, especially the shear strength on the sliding surface and the ratio of friction coefficient on sliding surface in kinematical and static conditions are no more than 0.35. DDA simulation considering the displacement-based parameter reduction has been developed in the original DDA code, and its results primarily reflect the evolvement process of a landslide under strong seismic loads.

Activated ERK2 Is a Monomer in Vitro with or without Divalent Cations and When Complexed to the Cytoplasmic Scaffold PEA-15

The extracellular signal-regulated protein kinase, ERK2, fully activated by phosphorylation and without a His(6) tag, shows little tendency to dimerize with or without either calcium or magnesium ions when analyzed by light scattering or analytical ultracentrifugation. Light scattering shows that ~90% of ERK2 is monomeric. Sedimentation equilibrium data (obtained at 4.8-11.2 μM ERK2) with or without magnesium (10 mM) are well described by an ideal one-component model with a fitted molar mass of 40180 ± 240 Da (without Mg(2+) ions) or 41290 ± 330 Da (with Mg(2+) ions). These values, close to the sequence-derived mass of 41711 Da, indicate that no significant dimerization of ERK2 occurs in solution. Analysis of sedimentation velocity data for a 15 μM solution of ERK2 with an enhanced van Holde-Weischet method determined the sedimentation coefficient (s) to be ~3.22 S for activated ERK2 with or without 10 mM MgCl(2). The frictional coefficient ratio (f/f(0)) of 1.28 calculated from the sedimentation velocity and equilibrium data is close to that expected for an ~42 kDa globular protein. The translational diffusion coefficient of ~8.3 × 10(-7) cm(2) s(-1) calculated from the experimentally determined molar mass and sedimentation coefficient agrees with the value determined by dynamic light scattering in the absence and presence of calcium or magnesium ions and a value determined by NMR spectrometry. ERK2 has been proposed to homodimerize and bind only to cytoplasmic but not nuclear proteins [Casar, B., et al. (2008) Mol. Cell 31, 708-721]. Our light scattering data show, however, that ERK2 forms a strong 1:1 complex of ~57 kDa with the cytoplasmic scaffold protein PEA-15. Thus, ERK2 binds PEA-15 as a monomer. Our data provide strong evidence that ERK2 is monomeric under physiological conditions. Analysis of the same ERK2 construct with the nonphysiological His(6) tag shows substantial dimerization under the same ionic conditions.

Understanding Friction Behavior in Automatic Transmission Fluid LVFA Test: A New Positive Curve Parameter to Friction Coefficient Ratio Index Evaluation

The frictional characteristics of some basic additive systems used in automatic transmission fluids (ATFs) were assessed using a variable speed friction test machine. The test evaluates the coefficient of friction in unidirectional sliding contact over a range of speeds, loads, and temperatures. Tests were performed on a steel-versus-clutch friction material tribocouple, mainly to establish the link between the lubricant/surface interactions and additive system performance. A new parameter that measures the positive μ-v curve slope speed range was applied, together with friction coefficient ratio index, to show the antishudder property. It is suggested that this is a good complimentary method to the friction coefficient ratio index evaluation. Lubricant formulation is important to the overall friction performance. Both friction modifiers and detergents are shown to be important to the ATF antishudder performance. Oil absorption ability of the post-test friction material surface is proposed to be an important parameter to indicate the antishudder durability in the test. The detergent and antiwear agents are also suggested to be responsible for the decreased oil absorption and pore plugging of the friction material surface.

Microstructure and Wear Resistance of the Composite Coatings Fabricated on Titanium Alloys by Laser Cladding

In situ reaction synthesized TiB reinforced titanium matrix composites were fabricated using rapid non-equilibrium synthesis techniques of laser cladding. TiB/Ti composite coating was treated on Ti-6Al-4V surface using Ti and B powder mixture by laser cladding. Microstructure and dry sliding wear behavior of the in situ synthesized TiB/Ti composite coatings were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), energy-dispersive spectroscopy (EDS), hardness tester and friction and wear tester. The composite coatings consist of Ti, TiB and intermetallic compounds. The TiB reinforcement dispersed homogeneously in the composite coatings. The wear tests show that the friction coefficient and wear weight loss ratio of the coatings is lower than that of the Ti-6Al-4V alloy. The composite coating was reinforced by the in situ synthesized TiB ceramic particles. Based on the SEM observation, effects of scan speed on hardness and wear resistance of the laser cladding coatings were investigated and discussed.

Effect of Asymmetric Friction on Front End Curvature in Plate and Sheet Rolling Process

A formula of calculating curvature radius was deduced according to the theory of rolling, together with the characteristics of rolling process. Moreover, the simulation of producing process is represented. Simulating results indicate that the curvature radius could be reduced by increasing friction coefficient, friction coefficient ratio, reduction or roller radius, while it could be augmented by increasing the thickness of plate. Furthermore, increasing the thickness of plate would cause more effects on front end curvature, whereas reduction would do less. The result provides theoretic basis for eliminating the front end curvature in plate and sheet rolling process, and it is important to protect controlling equipment and reduce scrap as well.

Existence of oscillatory travelling wave solution of flood wave with viscosity

Using the shooting technique, we investigate the existence of oscillatory travelling wave solution of viscous flood wave in a wide rectangular channel with constant inclination. We prove the existence and uniqueness of an oscillatory travelling wave solution when the parameters of the viscous coefficient, frictional coefficient, inclination and altitudinal ratio satisfy certain conditions. Owing to the difficulty of analytical calculation, Matlab is used to compute the value of altitudinal ratio, and the structure of oscillatory travelling wave solution is also discussed.

Effects of Temperature on Microstructure and Tribological Performance of a-CN<sub>x</sub> Films Prepared by Pulsed Laser Deposition

a-CNx films were deposited onto silicon wafers at temperatures from RT up to 600 °C by using pulsed KrF excimer laser deposition. The composition, morphology and microstructure of the CNx films were characterized by X-ray photoelectron spectrum (XPS), scanning electron microscopy (SEM) and Raman spectrum. The tribological performance of the films was investigated using a ball-on-disk tribometer. With increasing the deposition temperature ranging from RT to 400 °C, the N content of films dropped from 36 at.% to 22 at.%, the ratio of N-sp3 C bonds, hardness and friction coefficient of the film decreased. Further increase of deposition temperature led to the lack of nitrogen and the increasing degree of order in ringed sp2 C=C bonds of the amorphous carbon film. The mechanical and tribological performances became worse. The film deposited at 300°C showed a low friction coefficient of 0.11 and a preferable wear resistance of 1.65×10–7 mm3 Nm–1 in humid air.

The Theoretical and Experimental of Tube Drawing With Floating Plug for Micro Heat-Pipes

ABSTRACTThis work presents a novel mathematical model, formed by modifying the conventional Slab Model, to predict the behaviors of tube drawing with a floating plug in the hollow copper tubes. FEM and experimentation are employed to verify the analytical solution. The model incorporates some parameters, including as die semi-angle, plug semi-angle, friction coefficient and wall thickness reduction ratio. The Self Lock Effect is simulated using FEM, and the effect is useful in estimating the critical drawing force. The results of this work reveal that the new model is more accurate than the conventional Slab Model especially at reduction ratios of up to 40%.

Turbulent Characteristics of a Flowfield over a Heated Riblet Surface

Experimental studies of a turbulent flowfield developing over the heated riblet surface were carried out in a low-speed wind tunnel. The instantaneous velocity fields were measured by using a particle image velocimetry (PIV) in a plane that was parallel to the riblet surface, and compared with those over a heated smooth surface. The reduction ratio of the skin friction coefficient over the heated riblet surface reached up to 8% for the riblet spacing of about 13 viscous wall units. This is almost the same spacing as that obtained for the non-heated condition. The streamwise and wall-normal turbulent intensities against the local time-mean velocity were decreased in their peak values for the heated riblet. The instantaneous fluctuating velocity fields obtained by subtracting the ensemble-averaged velocity from instantaneous velocity vectors revealed that the appearance of a lowspeed streaky structure became more intermittent over the riblet surface. This fact suggested a reduction in turbulence production in the near-wall region. Furthermore, it was also found that a perturbation of the spanwise velocity fluctuation was restricted near the riblet surface.