Showing papers on "Slip ratio published in 1997"

Wrinkle‐like slip pulse on a fault between different materials

Abstract: Pulses of slip velocity can propagate on a planar interface governed by a constant coefficient of friction, where the interface separates different elastic materials. Such pulses have been found in two-dimensional plane strain finite difference calculations of slip on a fault between elastic media with wave speeds differing by 20%. The self-sustaining propagation of the slip pulse arises from interaction between normal and tangential deformation that exists only with a material contrast. These calculations confirm the prediction of Weertman [1980] that a dislocation propagating steadily along a material interface has a tensile change of normal traction with the same pulse shape as slip velocity. The self-sustaining pulse is associated with a rapid transition from a head wave traveling along the interface with the S wave speed of the faster material, to an opposite polarity body wave traveling with the slower S speed. Slip occurs during the reversal of normal particle velocity. The pulse can propagate in a region with constant coefficient of friction and an initial stress state below the frictional criterion. Propagation occurs in only one direction, the direction of slip in the more compliant medium, with rupture velocity near the slower S wave speed. Displacement is larger in the softer medium, which is displaced away from the fault during the passage of the slip pulse. Motion is analogous to a propagating wrinkle in a carpet. The amplitude of slip remains approximately constant during propagation, but the pulse width decreases and the amplitudes of slip velocity and stress change increase. The tensile change of normal traction increases until absolute normal traction reaches zero. The pulse can be generated as a secondary effect of a drop of shear stress in an asperity. The pulse shape is unstable, and the initial slip pulse can change during propagation into a collection of sharper pulses. Such a pulse enables slip to occur with little loss of energy to friction, while at the same time increasing irregularity of stress and slip at the source.

Wall slip in polymer melts

Abstract: We present a review of the recent characterizations of the flow behaviour of high-molecular-weight polymer melts, with special emphasis on situations in which slip at the wall appears. These characterizations are based on direct measurements of the local velocity of the fluid, in the immediate vicinity of the solid wall, through near-field velocimetry techniques. The results demonstrate the importance of polymer molecules anchored on the solid surface, either by strong adsorption or by chemical grafting, and entangled with the bulk polymer, to produce a strong friction at low shear rates and to lead to a shear rate threshold above which strong slip at the wall and low friction develop. The evolution of the shear rate threshold and of the flow characteristics (the length of the extrapolation of the velocity profile to zero, the critical slip velocity for the onset of strong slip, ...) with the molecular parameters of the system (the molecular weights of the bulk and surface chains, and the surface density of anchored chains) is analysed and compared with the predictions of recent theoretical models.

Wall slip in the capillary flow of molten polymers subject to viscous heating

Abstract: The traditional way of determining the slip velocity of molten polymers is the classic Mooney technique, which utilizes experimental data obtained from a capillary rheometer. However, measurements of the rheological properties of polymer melts in capillary flow at high shear rates are often complicated by viscous heating, which is not taken into account by this method. A data analysis procedure based on a mathematical model for nonisothermal capillary flow of molten polymers is developed. Conduction, convection, and viscous heating are included, together with the effect of wall slip. The technique provides detailed velocity and temperature fields in the die, and can be used to determine the slip velocity at high shear rates corrected for the effect of viscous heating. It is tested for the capillary flow of several polymers, including polystyrene, polypropylene, high-density, and linear low-density polyethylenes.

Influence of grafting density on wall slip of a polymer melt on a polymer brush

Abstract: We have investigated the shear flow of a polydimethylsiloxane (PDMS) melt on a PDMS brush of well-controlled density. As the shear rate, , is increased, we show the existence of a slip transition from a weak slip regime, where the extrapolation length of the velocity profile, b, is a constant b0, to a strong one, where sticks to its value at the transition . We discuss the influence of the grafting density Σ on b0 and . We compare our results with a recent microscopic model.

The effect of die materials and pressure-dependent slip on the extrusion of linear low-density polyethylene

Abstract: The flow of linear low-density polyethylene through stainless-steel slit dies occurred at shear rates approximately 12% higher than in identical α-brass dies at the same wall shear stresses, indicating near-wall slip. The flow curves were independent of gap spacing. We show through the slip theory of Hill and co-workers [J. Rheol. 34, 891–918 (1990)] that a measurable gap dependence of the flow curve is not a necessary consequence of wall slip; the flow curves for both stainless steel and α-brass dies can be fit with the same rheological parameters, with a difference in the work of adhesion accounting for the differences in the flow curves. X-ray photoelectron spectroscopy revealed differences in the chemistry of brass surfaces with different pretreating, corresponding to small differences in flow curves. Fluorocarbon-coated die surfaces showed no more slip than stainless steel, while the flow curve with gold-coated surfaces followed stainless steel at intermediate stress and brass at high stress.

Attitude control device for vehicle

Abstract: PROBLEM TO BE SOLVED: To satisfy attitude control together with vehicle braking in a high level while avoiding spin by providing a cooperative control means correcting posture control and adding brake control distribution to it according to the stepping pressure of a brake pedal, and adding regulation to the cooperative means at detecting spin of a vehicle. SOLUTION: A vehicle body sideslip angle is computed out of vehicle body speed computed from respective wheel speed detected by wheel speed sensors 6,... together with lateral acceleration by a lateral G sensor 7, yaw rate by a yaw rate sensor 8, and steering angle by a steering angle sensor 9. From these, the slip ratio, the slip angle, the load factor, and the road surface friction coefficient of each tire 23 are computed, deviation quantities from a target yaw rate and a target sideslip angle are computed based on these, and intervention judgement of posture control is executed. According to the judged result, braking force of each wheel 21 is computed so as to converge the turning posture of a vehicle toward the target running direction. The degree of brake control to promote spin is reduced, and hence the spin is avoided. COPYRIGHT: (C)1998,JPO

Anomalous flow profile due to the curvature effect on slip length

Abstract: Einzel, Panzer, and Liu [Phys. Rev. Lett. 64, 2269 (1990)] suggest that the slip boundary condition for a fluid moving near a wall is modified by the radius of curvature of the surface. Using particle simulations of a microscopic flow between concentric cylinders we qualitatively confirm their prediction and point out that the effect is seen in a limiting case derived by Maxwell [Nature (London) 16, 244 (1877)].

Traction control of electric vehicle based on the estimation of road surface condition-basic experimental results using the test EV "UOT Electric March"

Abstract: The most distinct advantage of an electric vehicle is in its quick and precise torque generation. The authors propose two novel traction control techniques of electric vehicles: model-following control; and optimal slip ratio control. Their effectiveness is demonstrated by using the "UOT Electric March" test vehicle.

Flow and load characteristics of microbearings with slip

Abstract: The fluid mechanics and operating characteristics of bearings that support rotating surfaces in micromachines are different from their larger cousins. The present study analyzes microbearings represented as an eccentric cylinder rotating in a stationary housing. The flow Reynolds number is assumed small, the clearance between shaft and housing is not small relative to the overall bearing dimensions, and there is slip at the walls due to non-continuum effects. The two-dimensional governing equations are written in terms of the streamfunction in bipolar coordinates and an infinite-series solution is obtained. For high values of the eccentricity and low slip factors the flow may develop a recirculation region. The force and torque on the load-bearing inner cylinder increase with increasing eccentricity and decrease with increasing slip.

The "Slip Law" of the Free Surface

Abstract: A “slip law” connects the excess velocity or “slip” of a wind-blown water surface, relative to the motion in the middle of the mixed layer, to the wind stress, the wind-wave field, and buoyancy flux. An inner layer-outer layer model of the turbulent shear flow in the mixed layer is appropriate, as for a turbulent boundary layer or Ekman layer over a solid surface, allowing, however, for turbulent kinetic energy transfer from the air-side via breaking waves, and for Stokes drift. Asymptotic matching of the velocity distributions in inner and outer portions of the mixed layer yields a slip law of logarithmic form, akin to the drag law of a turbulent boundary layer. The dominant independent variable is the ratio of water-side roughness length to mixed layer depth or turbulent Ekman depth. Convection due to surface cooling is also an important influence, reducing surface slip. Water-side roughness length is a wind-wave property, varying with wind speed similarly to air-side roughness. Slip velocity is typically 20 times water-side friction velocity or 3% of wind speed, varying within a range of about 2 to 4.5%. A linearized model of turbulent kinetic energy distribution shows much higher values near the surface than in a wall layer. Nondimensional dissipation peaks at a value of about eight, a short distance below the surface.

Braking force controller

Abstract: PROBLEM TO BE SOLVED: To prevent any driving force being produced in a brake operation from occurring, and also to deter the lowering of braking effectiveness during the practice of control over an automatic braking system, pertaining to this braking force controller to be mounted on an electric vehicle. SOLUTION: When a slip ratio S of a wheel exceeds the specified threshold value S0 (time t3 ), automatic braking system control is started into started into operation. During the practice of this automatic braking system, in a state that the slip ratio S is more than the threshold value S0 (terms (t3 , t4 ), (t5 , t6 ), (t7 , t8 ), hydraulic braking force FL and regenerative braking force FG both are reduced to some extent. In a state that the slip ratio S is less than the threshold value S0 (terms t4 , t5 ), (t6 , t7 ), the regenerative braking force FG is kept in constant, whereas the hydraulic braking force FL is gently increased. If the regenerative braking force FG is reduced up to zero (time t9 ), subsequently, a reduction in this regenerative braking force FG is prohibited. Therefore, this regenerative braking force FG will in no case come to a negative value at all.

Gear shift control device of automatic transmission with estimation of tire grip limit

Abstract: A gear shift control device of an automatic transmission of a vehicle, including: a means for estimating a target shift stage for harmonizing rotation speed and power output of engine of the vehicle; a means for estimating slip angle of at least one of the pair of drive wheels; a means for estimating slip ratio of the at least one drive wheel which would be caused thereon by the automatic transmission being shifted to the target shift stage; a means for estimating tire grip of the at least one drive wheel based upon the estimated slip angle and the estimated slip ratio; a means for judging if the estimated tire grip of the at least one drive wheel is in a grip range predetermined therefor; and a means for executing gear shift of the automatic transmission when the target shift stage is different from a current shift stage with the estimated tire grip being within the predetermined grip range.

Stability control device of vehicle for relieving drive wheels from side slipping

Abstract: A behavior control device of a vehicle having a means for estimating slip ratio of a pair of left and right drive wheels; a means for estimating lateral force acting at the vehicle body due to its turn running to provide a factor representative of the lateral force; and a means for estimating a target braking force to be generated in one of a pair of front driven wheels serving at the outside of the turn when the vehicle is a rear drive vehicle or one of a pair of rear driven wheels serving at the inside of the turn when the vehicle is a front drive vehicle, based upon the slip ratio and the factor; so that the brake system of the vehicle brakes the front driven wheel serving at the outside of the turn or the rear driven wheel serving at the inside of the turn to generate the target braking force.

Wheel decompression judging device for vehicle

Abstract: PROBLEM TO BE SOLVED: To judge the decompression of the follower wheels and driving wheels certainly despite eventual slipping condition of the driving wheel (s). SOLUTION: A driving wheel slip amount calculating means M4 calculates the slip amount KIDD of each driving wheel as the difference between the left and right follower wheel speed difference FID and the left and right driving wheel speed difference RID, while a torque calculating means M5 calculates the torque TQDW of the driving wheel. A slip ratio presuming means M6 presumes the change characteristics of the slip amount KIDD for changing TQDW using the minimum square method. A deviation calculating means M7 calculates the deviation CKID of the follower wheel speed difference FID and driving wheel speed difference RID while the driving wheels are not in slippage in the form of intercept of the driving wheel slip amount KIDD under the condition that the driving wheel torque is zero in the graph showing the change characteristics. A wheel decompression judging means M8 compares the deviation CKID with its reference value and judges decompression from the diametric difference of the follower wheels and driving wheels.

Modeling separation in rarefied gas flows

Abstract: In this paper, we study rarefied internal gas flows subject to strong adverse pressure gradients and separation in the slip flow regime (Knudsen number Kn < 0.1), with the objective of investigating the validity of continuum-based slip models under separation. Such conditions are encountered in typical components of Micro-Electro-Mechanical Systems (MEMS) and in low pressure/vacuum applications. Solutions of compressible Navier-Stokes equations subject to various velocity slip and temperature jump boundary conditions are compared against predictions of direct simulation Monte Carlo (DSMC) method, employing variable hard sphere (VHS) model. Sudden changes of the flow conditions in backwards-fac ing step geometry result in significant variations of the mean-free path of the gas molecules, with corresponding variations in the wall shear stress affecting the slip velocity directly. Unlike the straight channel flow, significant cross-flow variations are obtained. In addition, the change of characteristi c length scale from the inlet channel height to larger height downstream presents extra difficulties in choosing the proper scaling.

Traction force control of an electric vehicle in 2ws-4wd mode using fuzzy reasoning

Abstract: This paper is concerned with the design of traction force control of an electric vehicle in 2WS–4WD mode using fuzzy reasoning. The electric vehicle is in a motor–in–wheel system, and the traction force in each wheel can be determined independently. The yaw moment is regulated by the motor torque to improve the handling and stability of the vehicle as well as the skidding of lyres. The input variables in the fuzzy control rules are treated as the error of yaw ratio and its time difference, and the slip ratio. The simulation results show that the proposed traction force control improves the performance more than the traction force without control.

Turbulent Dispersion of Heavy Particles With Nonlinear Drag

Abstract: The analysis of Reeks for particle dispersion in isotropic turbulence is extended so as to include a nonlinear drag law. The principal issue is the evaluation of the inertial time constants, β - α 1 , and the mean slip. Unlike what is found for the Stokesian drag, the time constants are functions of the slip velocity and are anisotropic. For settling velocity, V T, much larger than root-mean-square of the fluid velocity fluctuations, u 0, the mean slip is given by V T. For V T → 0, the mean slip is related to turbulent velocity fluctuation by assuming that fluctuations in βα are small compared to the mean value. An interpolation formula is used to evaluate βα and V T in regions intermediate between conditions of V T → 0 and V T >> u 0. The limitations of the analysis are explored by carrying out a Monte-Carlo simulation for particle motion in a pseudo turbulence described by a Gaussian distribution and Kraichnan's energy spectrum.

Braking force control device for vehicle

Abstract: PURPOSE:To improve the braking performance on a bad road by judging it to be a bad road when the slip ratio is larger than a target slip ratio and deceleration of the vehicle body is larger than a prescribed value, and reserving control to change the slip rate to the target slip ratio in this case. CONSTITUTION:A anti-lock control device 11 as a braking force control device is provided with brake hydraulic control valves 18 - 21 to regulate brake liquid pressure based on control signals from a controller 17 to which signals from a G sensor 12, a steering angle sensor 22, and speed sensors 13 - 16 of respective wheels are input. At controlling respective brake hydraulic control valves 18 - 21, when the slip ratio of respective wheel are larger than a target slip ratio, braking force is controlled with this controller 17 so as to change the slip ratio to the target slip ratio. Further, when the slip ratio is larger than the target slip ratio and deceleration of a vehicle body is larger than a prescribed value, it is judged to be a bad road, in this case, the above-stated anti-lock control is reserved so that the slip ratio is larger than the target slip ratio and the wheels are put in tendency of lock.

Gear shift control device of automatic transmission for variable stage upshift against wheel slip

Abstract: A gear shift control device of an automatic transmission of a vehicle, including a slip angle estimator for estimating a slip angle of at least one of a pair of drive wheels; a slip ratio estimator that estimates the slip ratio of the one drive wheel; a determiner that determines an upshift of the automatic transmission when the absolute value of the estimated slip ratio is greater than a threshold value; and a upshift executor for executing the upshift automatic transmission according to the upshift determined by the determiner, wherein the determiner determines the upshift to be of a greater number of stage within an available range against the absolute value of the estimated slip ratio according as the absolute value of the estimated slip angle is greater.

Initial correction factor computing apparatus and apparatus utilizing the same

Abstract: An apparatus for computing correction factors for correcting the output from a rotational frequency mechanism which is adapted to detect the rotational frequency of a tire fixed to a vehicle, and a slip percentage calculating apparatus and a tire pressure decrease detecting apparatus which utilize such a computing apparatus. In response to the operation of an initialization switch during an experimental linear coasting of a vehicle, the rotational frequency of a tire is detected. An initial correction factor is determined on the basis of this rotational frequency. This initial correction factor is stored in E2PROM. When the vehicle travels normally, the rotational frequency is initially corrected on the basis of the initial correction factor (at S2). The slip percentage is calculated on the basis of the initially corrected rotational frequency (at S3). A judgement value required to detect a decrease in the tire pressure is corrected on the basis of the slip ratio (at S9). Since an initial correction factor representative of only a relative difference between the effective rolling radii of the tires is obtained, the initial difference is eliminated accurately from the rotational frequency.

Vehicle driving force control device

Abstract: PROBLEM TO BE SOLVED: To prevent the increase in an exhaust gas temperature through continuous operation of drive power control at a high load area and to protect an exhaust catalyst, in a vehicle driving force control device to control an engine output through cut of fuel injection. SOLUTION: A vehicle driving force control device comprises the slip ratio computing means to compute the slip ratio of a drive wheel; and a drive power control permission deciding means to permit control of a drive power when a computed slip ratio exceeds a slip control threshold. Since the slip control threshold is set to a high value when a shift lever is selected to the slip control threshold, Drive power control hardly occurs continuously at a high load region. This constitution prevents the increase of an exhaust temperature and prevents incurring of the heat loss of an exhaust catalyst and the occurrence of deterioration thereof.

Slip velocity characteristics in the riser of circulating fluidised bed

Abstract: Experiments were carried out in a conventional circulating fluidised bed to measure the axial pressure profile and total pressure drop, which covered a wide range of operating conditions. Material belonging to the Geldart A (fine material) as well as the Geldart B (course material) categories have been used in the present work. Slip velocity is determined from the total pressure drop and noticed that the slip velocity is much higher than the free fall velocity of single particle for Geldart A type material, while it is approximately equal to the free fall velocity of single particle for the Geldart B type materials. A model is developed for slip velocity taking into account all the hindrance effects: particle-particle, and particle-wall, and particle agglomeration. Predictions of the present model are validated with the data due to present study and the data reported in the literature.

Vehicle behavior control device with wheel slip control device

Abstract: PROBLEM TO BE SOLVED: To limit the upper limit of desired braking force for behavior control and the upper limit of the rate of change thereof in such a way that hunting does not result from interference with antiskid control. SOLUTION: In 81, a desired before-limit slip ratio S1 * is calculated from a desired before-limit braking force F0 * and the braking drive rigitity factor KS of wheels, and if, in 82, S1 * is determined to be greater than a maximum controllable slip ratio Smax , in 84 a desired after-limit slip ratio S2 * is limited to Smax and the upper limit of a desired after-limit braking force determined by multiplying S2 * by KS is limited to a slip-controllable maximum value. In 85, the deviation ΔS* of S2 * from the previous desired slip ratio S0 * is regarded as the desired rate of change of slip, and if in 86 ΔS* is determined to be faster than a set value ΔS0 a desired slip ratio S* is determined according to the direction of change of the desired slip ratio determined in 87, so that in 89, 90 the rate of change of the desired slip ratio S* is not greater than ΔS0 Therefore, the upper limit of the rate of change of the desired braking force calculated by multiplying S* by KS can be limited.

Anti-skid control device using acceleration gradient

Abstract: An anti-skid control device for braking a vehicle safely and quickly comprises a wheel speed sensor, a computer and an actuator for controlling brake fluid pressure in a wheel cylinder. The computer calculates, based on the wheel speed detected by the sensor, a wheel slip ratio relative to a road surface, a wheel speed acceleration and a gradient of the wheel speed acceleration, and controls the actuator so that it increases, decreases or holds the brake fluid pressure according to the data calculated. The brake fluid pressure is decreased to avoid locking of the wheel when the slip ratio exceeds a predetermined value, the wheel speed acceleration is below a predetermined value and the gradient of the wheel speed acceleration becomes lower than the predetermined level. In this manner, the brake fluid pressure is not decreased unnecessarily, and a desirable anti-skid control is achieved for braking the vehicle quickly and safely.

Vehicle with idling speed controller

Abstract: PROBLEM TO BE SOLVED: To enable opening of throttle to be corrected without changing engine speed at switching non-engagement and engagement of a clutch. SOLUTION: This idling speed controller is provided with a throttle control means 1 which calculates opening of driving force throttle so that the vehicle runs by a target driving force calculated from a throttle opening AP and a vehicle speed V, a memory 4 which memorizes opening of drive idle throttle and opening of non-drive idle throttle, and a slip ratio detection means 6 which monitors a slip ratio of hydraulic torque converter, detects a first slip ratio value when clutch begins to be engaged or a second slip ratio value of clutch at engagement release initiation, and outputs the detection signal to the throttle control unit 1. When the slip ratio is detected by the slip ratio detection means 6, the opening of non-drive idol throttle or the opening of the drive idle throttle is drawn out from the memory 4 and output to a throttle TH.