Showing papers on "Slip ratio published in 2001"

Rate-dependent slip of Newtonian liquid at smooth surfaces.

Abstract: Newtonian fluids were placed between molecularly smooth surfaces whose spacing was vibrated at spacings where the fluid responded as a continuum. Hydrodynamic forces agreed with predictions from the no-slip boundary condition only provided that flow rate (peak velocity normalized by spacing) was low, but implied partial slip when it exceeded a critical level, different in different systems, correlated with contact angle (surface wettability). With increasing flow rate and partially wetted surfaces, hydrodynamic forces became up to 2--4 orders of magnitude less than expected by assuming the no-slip boundary condition that is commonly stated in textbooks.

Shear-Dependent Boundary Slip in an Aqueous Newtonian Liquid

Abstract: We report direct measurements of hydrodynamic drainage forces, which show clear evidence of boundary slip in a Newtonian liquid. The degree of boundary slip is found to be a function of the liquid viscosity and the shear rate, as characterized by the slip length, and is up to $\ensuremath{\sim}20\mathrm{nm}$. This has implications for confined biological systems, the permeability of microporous media, and for the lubrication of nanomachines, and will be important in the microcontrol of liquid flow. We also show that current theories of slip do not adequately describe the experimental data.

Conceptual and physical clarification of rate and state friction: Frictional sliding as a thermally activated rheology

Abstract: We observed slow frictional slip occurring at a constant shear stress below the nominal friction level and compared it with the time-dependent strengthening of the frictional interface, which was also tracked experimentally. It was found that slip velocity decreases as the interface strengthens due to aging, while it increases with the applied shear stress. These dependencies were both exponential and were of similar magnitudes, as implied by the framework law of rate- and state-dependent friction. In the spirit of the adhesion theory of friction the dependence of slip velocity on interface strength is understood to be the result of the change of the shear stress acting on frictional junctions due to the change of junction population, though the observed dependence was somewhat stronger than a simple model based on this idea predicts. By correcting the observed slip velocity for the effect of the change of the interface strength, we could obtain a unique relationship between stress and slip velocity, which may be readily compared with a standard rheological formulation. Thus the obtained relationship between stress and slip velocity showed a reasonable agreement with the absolute rate theory over a temperature range of 25-800°C for the present experimental condition (fine albite powder, 20 MPa normal stress, no pore water).

Numerical Simulation of the Two-Phase Flow in an Axially Stirred Vessel

Abstract: The two-phase flow field in an axially stirred vessel has been calculated using the commercially available CFD-code CFX4. The multi-fluid approach was used with separate k and e equations solved for each phase. The results were compared with experimental phase-Doppler anemometry data. Particular attention was given to the distribution of slip velocities in the tank. Qualitative agreement between calculations and experimental datawas obtained for the axial component of the slip and for the turbulence kinetic energy difference between the phases. The radial and tangential components of the slip vector were greatly under-predicted in the calculations. The drag was found to be most important of the investigated inter-phase momentum transfer terms. Four different drag models were tested and found to give very similar results. Finally, the importance of the slip velocity as well as the particle velocity for the mass transfer in stirred tanks was discussed.

Effect of texture and slip mode on the anisotropy of plastic flow and flow softening during hot working of Ti-6Al-4V

Abstract: The effect of crystallographic texture and slip mode on the plastic flow of Ti-6Al-4V with either a colony- or globular-alpha microstructure was determined by conducting isothermal, constant-strainrate, hot-compression tests on specimens cut at various orientations (rolling direction (RD), transverse direction (TD), 45 deg, and normal) from hot-rolled plate. Testing was performed using a fixed strain rate (0.1 s−1) and various temperatures below the beta transus. The flow curves from all of the experiments exhibited a peak flow stress followed by a large and a small amount of flow softening for the colony and globular microstructures, respectively. Although the flow softening response did not depend noticeably on test direction for a given microstructure and test temperature, the peak flow stress and development of sample ovality did. This orientation dependence was interpreted using both lower-bound (isostress-type) and upper-bound (isostrain, Taylor/Bishop-Hill) models to deduce the operative slip systems in the alpha phase. These analyses suggested that prism 〈a〉 and basal 〈a〉 slip are considerably easier than pyramidal 〈c+a〉 or 〈a〉 slip at hot-working temperatures. A comparison of the flow curves for the colony and globular alpha microstructures suggested that slip transfer across alpha/beta interfaces and loss of Hall-Petch boundary strengthening can account for a substantial portion of the flow softening observed during hot working.

Sliding integral proportional (SIP) controller for aircraft skid control

Abstract: The sliding, integral, and proportional controller for providing aircraft antiskid braking control includes a reference velocity subsystem, a velocity error ratio subsystem, and a main controller subsystem generating a control command output signal indicative of a command braking pressure. The main controller subsystem includes a one dimensional sliding mode controller subsystem to determine an estimated net wheel torque signal, an adaptive threshold subsystem for generating an adaptive threshold based upon the modified slip ratio signal and a clock signal, integral gain subsystems, a proportional controller subsystem, and a pressure limiter. A method for determining braking efficiency of an aircraft braking system independent of the specific conditions is also provided.

Performance enhancement of a sliding mode wheel slip controller by the yaw moment control

Abstract: A sliding mode wheel slip controller is the subject of this paper. The proposed wheel slip controller was based on a quarter-car model and a friction force observer was applied to ensure the robustness of the controller with respect to the estimation error. It was applied to a non-linear full vehicle model. This controller showed good longitudinal performance in tracking reference slip ratio regardless of modelling errors and disturbances. However, when cornering was combined with braking or there was a yaw moment disturbance due to a μ-split road, it was difficult to achieve the desired performance using this controller. In this case, lateral motion must be considered in maintaining the control of the vehicle. A yaw moment control method using the modified reference yaw rate was investigated. The effectiveness of this control theory was verified through simulations of emergency manoeuvres using a developed non-linear full vehicle Simulink model.

Optimal slip ratio estimator for traction control system of electric vehicle based on fuzzy inference

Abstract: In this paper we propose an optimal slip ratio estimation method based on fuzzy inference. One of the major advantages of electric vehicles is the quick and precise torque response of the electric motor, which realizes a novel traction control system. To prevent skidding, optimal slip ratio control has been successfully developed. It maintains the slip ratio at the optimum value that gives the maximum driving force. The remaining problem is how to generate the optimal slip ratio command sent to the controller. First we show that effective estimation of the optimal slip ratio is difficult to perform by the simple gradient method, which is a well-known optimization method. But various experimentally obtained data can be easily incorporated into fuzzy inference, and therefore its estimation performance can be easily improved by the accumulation of human experience. This is a major advantage in the nonlinear estimation of real road-tire characteristics. The effectiveness of the proposed estimation and control methods is confirmed by numerical simulation. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 56–63, 2001

Apparatus and method for identifying tires and apparatus and method for evaluating road surface conditions

Abstract: An apparatus for identifying tires comprising: a rotational speed detecting means; a first calculating means for calculating a vehicle speed; a second calculating means for calculating acceleration/deceleration of the vehicle; a third calculating means for calculating a slip ratio; a fourth calculating means for respectively obtaining moving averages of the acceleration/deceleration and the slip ratios of the vehicle; a fifth calculating means for obtaining linear regression coefficients and correlation coefficients of the moving-averaged acceleration/deceleration of the vehicle and the slip ratio; a sixth calculating means for calculating a tire identifying coefficient; and a tire identifying means for identifying tires which is presently mounted based on the tire identifying coefficient. Differences in tread rigidities of the tires can be automatically reflected for controlling the vehicle.

Measurements of viscosity, velocity slip coefficients, and tangential momentum accommodation coefficients using a modified spinning rotor gauge

Abstract: A selection of experimental viscosity and slip measurements are reported for He and Ar. The measured values have been made with a modified spinning rotor gauge (SRG-2; MKS Instruments, Inc.) where the sphere is coaxially rotated in the cylindrical tube housing. All of the experiments were conducted in the slip regime in accordance with the theory previously developed [S. K. Loyalka, J. Vac. Sci. Technol. A 14, 2940 (1996)]. The theoretical results from this previous article allow one to extract values of the viscosity, the velocity slip coefficient, and the tangential momentum accommodation coefficient from the experimentally obtained angular retardation data for each gas without a need for calibration of the system against a known gas viscosity. Since the existing manufactured SRGs mount horizontally with the rotor angular momentum vector oriented vertically, the required SRG modifications were necessarily limited to the interior of the mounting tube. Here, an insert was developed for the mounting tube in which was bored a short, vertically oriented, cylindrical hole in which the rotor could turn coaxially. Measurements made with this modified version of the SRG are compared with previous experimental results and a discussion of the errors associated with both wall and end effects is included.

Slip boundary condition on an idealized porous wall

Abstract: Slip boundary condition on a porous wall is investigated by considering a viscous flow near an idealized porous wall based on the Stokes’ approximation. The idealized porous wall is composed of a large number of parallel and equidistant thin semi-infinite plates. The flow is assumed to be a simple shear flow far from the plates and stagnant deep inside the channels of the plates. The slip velocity on the idealized porous wall is calculated by solving a Wiener–Hopf equation. From the streamline patterns shown, it is found that Moffatt’s infinite sequence of viscous eddies developed between the two adjacent plates. Pressure and shear stress distributions on the plates are shown and local flow near the edge of the plate is discussed. Laminar shear flow at the farfield unidirectional along the edges of the plates is also considered.

Design of Nonlinear Sliding Mode Controller with Pulse Width Modulation for Vehicular Slip Ratio Control

Abstract: For the control of anti-lock brake system (ABS), a longitudinal four-wheel vehicle model with brake actuator is described and a sliding mode controller with pulse width modulation (PWM) method has been developed for passenger vehicles. In our research, we introduced actuator dynamics in the system equation and derived the equivalent control input theoretically. We propose using the PWM method to compensate for the discrete nature of actuator dynamics by duty control. Stability of the PWM controller for sliding mode control (SMC) was theoretically checked. The effectiveness of the proposed control algorithms was confirmed by vehicle tests on an In-door test bench that was specially constructed for the purpose concerned.

Apparatus and method for estimating maximum road friction coefficient

Abstract: An apparatus and method that determines a maximum road friction coefficient for each wheel regardless of whether the tire is in a predetermined drive slip state, and whether the wheel is a driving wheel. The braking force of each wheel is calculated, and the longitudinal force of the tire of each wheel is calculated. Then, the driving force of the vehicle is calculated, and the lateral force of the tire of each wheel is calculated. Next, the reaction force of the road to each wheel is calculated, and the vertical load of each wheel is calculated. Finally, the ratio of variation in reaction force of the road to variation in composite slip ratio is calculated for each wheel. The sum of the ratio of the reaction force of the road to the vertical load, and the product of a predetermined coefficient and the ratio of variation in reaction force of the road to variation in composite slip ratios is calculated for each wheel as the maximum road friction coefficient.

Exploration of the slip phenomenon in the capillary flow of linear low-density polyethylene via electrical measurements

Abstract: The slip phenomenon and the electrification occurring in the capillary flow of a linear low-density polyethylene melt were studied in this work using dies made up of stainless steel and brass, respectively. The experiments were carried out in a torque driven capillary rheometer at a temperature of 200 °C and spanned the different flow regimes observed in capillary flow, including stable and unstable conditions. Flow enhancement or slip was generated in the brass die, as compared to the stainless steel one, after an appropriate cleaning treatment. The melt exhibited electrostatic charge and sharkskin distortions were eliminated during the processing with the brass die in the stable flow regime prior to the stick-slip. Electrification and elimination of sharkskin distortions on the extrudates were observed when the slip velocity was a significant part of the whole average melt velocity (more than 50% in this work). The observations in this work point to a tribological origin for the electrification of the melt. Finally, an electric charge of a different sign was measured on the extrudates obtained from the stainless steel and brass dies, respectively, during the stick-slip, which suggests a detachment mechanism for slip in this flow regime.

Control device for controlling front and rear wheel drive vehicle

Abstract: A vehicle control device for front and rear wheel drive vehicles, which have one wheel pair driven with an engine and the other pair driven with an electrical motor, and a torque converter with a lock-up mechanism controlling the engagement amount, has a lock-up control means changing the target slip amount to be set in accordance with driving conditions, a motor drive power setting means which sets the drive power distribution ratio of the motor and a compensation means which compensates the target slip amount according to the drive power distribution ratio set by the motor drive power setting means. The control device enables the setting of the optimum slip ratio of the torque converter to improve the fuel consumption, avoiding problems associated with: noise and vibration during the motor assisting.

Engine control system for improved driveability

Abstract: A vehicle and engine control system controls engine torque to maintain positive torque at a transmission input to minimize the transmission gears from separating. By maintaining a positive engine torque, operation of the transmission in or through the zero torque, or lash, zone, is minimized. This minimizes poor vehicle driveability that would otherwise result from operation in the lash zone. The control systems uses closed loop control based on a desired and actual turbine speed ratio, or slip ratio, to provide positive torque to the transmission.

Shear flow over a particulate or fibrous plate

Abstract: Simple shear flow over a porous plate consisting of a planar array of particles is studied as a model of flow over a membrane. The main objective is to compute the slip velocity defined with reference to the velocity profile far above the plate, and the drift velocity induced by the shear flow underneath the plate. The difference between these two velocities is shown to be proportional to the thickness of the plate. When the geometry of the particle array is anisotropic, the directions of the slip and drift velocity are generally different from the direction of the overpassing shear flow. An integral formulation is developed to describe flow over a plate consisting of a periodic lattice of particles with arbitrary shape, and integral representations for the velocity and pressure are developed in terms of the doubly-periodic Green’s function of three-dimensional Stokes flow. Based on the integral representation, asymptotic expressions for the slip and drift velocity are derived to describe the limit where the particle size is small compared to the inter-particle separation, and numerical results are presented for spherical and spheroidal particles of arbitrary size. The asymptotic results are found to be accurate over an extended range of particle sizes. To study the limit of small plate porosity, the available solution for shear flow over a plane wall with a circular orifice is used to describe flow over a plate with a homogeneous distribution of circular perforations, and expressions for the slip and drift velocity are derived. Corresponding results are presented for axial and transverse shear now over a periodic array of cylinders arranged distributed in a plane. Streamline pattern illustrations confirm that a negative drift velocity is due to the onset of eddies between closely-spaced particles.

Critical curves of plane Poiseuille flow with slip boundary conditions

Abstract: We investigate the linear stability of plane Poiseuille flow in 2D under slip boundary conditions. The slip s is defined by the tangential velocity at the wall in units of the maximal flow velocity. As it turns out, the critical Reynolds number depends smoothly on s but increases quite rapidly.

Estimating the minimum grip force required when grasping objects under impulsive loading conditions.

Abstract: As an aid to studying the efficiency of grip force scaling in the context of collisions, we present a simple cost-effective approach to estimating the slip ratio—that is, the minimum grip-to-load-force ratio needed to prevent object slippage. The grip apparatus comprises a sturdy load cell to measure grip force and two linear potentiometers to provide detailed description of finger movements. The slip ratio was estimated by plotting the magnitude of finger movement against the grip-to-load-force ratio at the time of impact. The slip ratio was dependent on the direction of loading, which stresses the importance of estimating slip ratios in a context similar to that of the experiment in which the efficiency of subjects’ behavior is to be assessed.

Apparatus and method for determining condition of road surface

Abstract: An apparatus for determining a condition of road surface comprising: rotational speed detecting means for periodically detecting rotational speeds of four tires of a vehicle; first computing means for computing a slip ratio from measurement values of the rotational speed detecting means; second computing means for obtaining a relational formula between the slip ratio and either the acceleration or deceleration of the vehicle; and friction coefficient judging means for judging a coefficient of friction occurring between a road and a tire on the basis of a slope of the relational formula obtained by the second computing means. The road friction coefficient can be judged with high accuracy in a short time using only the wheel rotational speed information of four wheels, whereby the performance and safety of a vehicle can be increased.

Apparatus and method for assessing condition of road surface

Abstract: An apparatus for assessing the condition of a road surface comprising rotational speed detecting means for periodically detecting rotational speeds of four tyres of a vehicle; first computing means for computing slip ratio from measurement values of the rotational speed detecting means; second computing means for obtaining a relational formula between the slip ratio and acceleration/deceleration of the vehicle; and friction coefficient judging means for judging a coefficient of friction occurring between a road and a tyre on the basis of a slope of the relational formula obtained by the second computing means The road friction coefficient mu can be judged with high accuracy in a short time by using only the wheel rotational speed information of four wheels Thus, the performance and safety of a vehicle can be increased

Device and method for determining coefficient of road surface friction

Abstract: PROBLEM TO BE SOLVED: To provide a device for determining a road surface friction coefficient capable of enhancing vehicle performance and safety by determining a coefficient of friction between a road surface and a tire based on rotation information of tire wheels. SOLUTION: This device comprises a rotational speed detecting means for regularly detecting a rotational speed of four wheel tires of a vehicle, a first computing means for calculating a slip ratio based on a value determined by the rotational speed detecting means, a second computing means for finding a relational expression showing the relation between the slip ratio and acceleration/deceleration of a vehicle, and a friction coefficient determining means for determining a coefficient of friction between a road and a tire based on the gradient in the relation found by the second computing means.

Estimating device of car body yaw rate

Abstract: PROBLEM TO BE SOLVED: To improve accuracy in estimating a yaw rate. SOLUTION: This estimating device comprises a steering angle sensor 1, wheel speed sensors 5a, 5b, 5c, and 5d, a longitudinal acceleration sensor 4, a lateral acceleration sensor 3, a tire model setting part TM, a real yaw rate variation calculating part ΔYRR, a wheel load calculating part FZmn, a tire slip angle calculating part αmn, a calculating part μ of a road surface friction coefficient, a tire lateral force calculating part CFmn, and a calculating part CFKx of correction coefficient of moment of front and rear wheels. An estimated yaw rate is determined based on a yaw rate correction coefficient and a tire lateral force. Thus, the tire lateral force including the road surface friction coefficient, a tire slip ratio, and the tire slip angle is determined in response to them, thereby determining the estimated yaw rate as a value matching with vehicle motion. COPYRIGHT: (C)2003,JPO

Calculating device of road surface friction coefficient

Abstract: PROBLEM TO BE SOLVED: To improve accuracy in determining a road surface friction coefficient. SOLUTION: This calculating device comprises a steering angle sensor 1, wheel speed sensors 5a, 5b, 5c, and 5d, a longitudinal acceleration sensor 4, a lateral acceleration sensor 3, a tire model setting part TM, a tire slip ratio calculating part SLPmn, a calculating part FGE of an estimated car body longitudinal acceleration, a tire slip angle calculating part αmn, a wheel load calculating part FZmn, a tire lateral force calculating part CFmn, an LGE, and a calculating part μ of a road surface friction coefficient. The calculating part μ of the road surface friction coefficient determines the road surface friction coefficient based on a deviation between a car body longitudinal acceleration and the estimated car body longitudinal acceleration and a deviation between a car body lateral acceleration and an estimated car body lateral acceleration. The road surface friction coefficient is not determined from the tire slip ratio, but sensor detecting values are compared with estimated values with respect to the car body longitudinal direction and the car body lateral direction, and the road surface friction coefficient can be accurately determined in respect to the deviation. COPYRIGHT: (C)2003,JPO

Vehicle movement control device

Abstract: PROBLEM TO BE SOLVED: To keep the traveling stability of a vehicle in a good condition even when the deviation of the actual yawing momentum to the target yawing momentum is particularly large. SOLUTION: A slide slip angle change speed β' of a center-of-gravity point as the actual yawing momentum of a vehicle having plural wheels is gained (S5), and the brake fluid pressure ΔP is acted on one of brakes of left and right rear wheels when an absolute value of the change speed β' is more than a predetermined value β0', to produce the yawing moment in a state that the more the absolute value of the change speed β' is, the more a value is, in the direction to reduce the absolute value of the change speed β' (S10-S12). Even during the control of the yawing moment, discrimination whether the slip control is necessary or not on the wheel applied the brake fluid pressure ΔP, continues (S1) and when the slip control is necessary the slip control for keeping a slip ratio within a proper range is executed by controlling the brake fluid pressure ΔP.

Brake apparatus for vehicle

Abstract: In a vehicle brake apparatus for executing ABS control to prevent a wheel from locking in such a manner that braking force is controlled so as to keep a slip ratio of a wheel at a target slip ratio so that an excessive drop of a wheel speed from a vehicle body speed is adjusted, an output current for driving a braking actuator is set to a current on which oscillating waves are superimposed during ABS control so that the wheel speed changes to show oscillating waves. Even if the wheel speed once drops to an extent that the slip ratio exceeds the target slip ratio, further decrease of the wheel speed is restricted and the wheel speed turns to an increase soon and this cycle is repeated. Accordingly, there occurs no excessive drop of the wheel speed due to the response delay so that sufficient braking force is generated.