Showing papers on "Slip ratio published in 1995"

A non-slip boundary condition for lattice boltzmann simulations

Abstract: A non‐slip boundary condition at a wall for the lattice Boltzmann method is presented. In the present method unknown distribution functions at the wall are assumed to be an equilibrium distribution function with a counter slip velocity which is determined so that fluid velocity at the wall is equal to the wall velocity. Poiseuille flow and Couette flow are calculated with the nine‐velocity model to demonstrate the accuracy of the present boundary condition.

A fuzzy logic controller for an ABS braking system

Abstract: Anti-blocking system (ABS) brake controllers pose unique challenges to the designer: a) For optimal performance, the controller must operate at an unstable equilibrium point, b) Depending on road conditions, the maximum braking torque may vary over a wide range, c) The tire slippage measurement signal, crucial for controller performance, is both highly uncertain and noisy, d) On rough roads, the tire slip ratio varies widely and rapidly due to tire bouncing, and e) The braking system contains transportation delays which limit the control system bandwidth. A digital controller design was chosen which combines a fuzzy logic element and a decision logic network. The controller identifies the current road condition and generates a command braking pressure signal, based on current and past readings of the slip ratio and brake pressure. The controller detects wheel blockage immediately and avoids excessive slipping. The ABS system performance is examined on a quarter vehicle model with nonlinear elastic suspension. The parallelity of the fuzzy logic evaluation process ensures rapid computation of the controller output signal, requiring less time and fewer computation steps than controllers with adaptive identification. The robustness of the braking system is investigated on rough roads and in the presence of large measurement noise. This paper describes design criteria, and the decision and rule structure of the control system. The simulation results present the system's performance on various road types and under rapidly changing road conditions.

Pipe viscometry of foams

Abstract: This paper describes a method for extracting useful information from small‐scale pipe viscometer measurements of foam rheology. The rheology of a foamed polymer solution at a given temperature, pressure, and quality was determined in pipes of five diameters. The flow curves showed a marked dependence on the diameter of the pipe. The concept of apparent slip could be used to explain the phenomenon. The classical slip correction of Mooney was not applicable, but the method developed by Jastrzebski (based on the previous work of Oldroyd) provided a consistent means of apparent slip correction. The geometric interpretation of the two slip correction methods revealed the possible reason for the difference of their performance. The slip corrected measurements were interpreted in the framework of the volume equalization principle.

Effect of gap on the viscosity of monodisperse polystyrene melts: Slip effects

Abstract: The low shear rate slip behavior of monodisperse polystyrene melts was characterized with the parallel plate geometry in a torsional rheometer. It was found that all melts studied exhibited some slip behavior. Tool material of construction showed no appreciable effect. Results were analyzed according to deGennes’ theory of slip, and values of the characteristic slip dimension, b, were calculated for each molecular weight. The slip dimension was found essentially proportional to the molecular weight to the first power. A slider block and spring model is proposed in an attempt to explain slip phenomena in the low shear rate limit.

Mechanics of dip-slip faulting in an elastic half-space

Abstract: The mechanics of dip-slip faulting is examined using a model of a crack in a plane strain elastic half-space loaded by remote stresses: vertical stresses are equal to the overburden and horizontal stresses are the sum of a constant (c) times the overburden and a depth-independent term σtect, which may be compressive or tensile. Opening is allowed in response to local tension, and slip on closed regions is governed by Mohr-Coulomb conditions. Because regions of opening and slip, in general, must be determined as part of the solution, relative displacements and stress intensity factors are calculated by iterative solution of integral equations. If the fault is not too shallow (h/L > 0.3, where h is the depth of the upper end of the slip zone and L is the length along dip) and the Coulomb stress (the shear stress minus the friction coefficient ƒ times the effective normal stress) is of one sign over most of the fault, simple approximations suffice. Use of these approximations and the criterion that the energy release rate equals a critical value demonstrates that updip propagation is unstable if the slip zone length exceeds a minimum value. For typical values of ƒ dip angle, and c, the slip zone will be locked below a certain depth. In general, the depth at which the Coulomb stress changes sign underestimates the locking depth, but the magnitude of the difference decreases as the depth of the sign change approaches the lower end of the slip zone. For shallow slip zones, h/L < 0.3, slip induces changes in both shear and normal stresses on the slip surface. For reverse (normal) slip, this coupling reduces (increases) the compressive normal stress and amplifies (diminishes) slip near the upper end of the slip zone surface. For extensional loading (σtect < 0), opening can occur for shallow embedded zones and, more prominently, for surface breaking zones. Although the shear stress drop is nonuniform in this model, calculations reveal that unless fault opening occurs, the surface displacement is well-approximated by that due to a uniform shear stress drop equal to the average.

Slip flow of polybutadiene through fluorinated dies

Abstract: Wall surface energy affects the flow of polymer melts in extrusion dies. The aim of the present study is to demonstrate and characterise the flow regimes with slip that are specific to low-energy walls. The polymer used is a polybutadiene (PB) of high molar mass. The dies considered are two-dimensional with either steel walls or walls covered with a fluorinated (PTFE) deposit. Flow curves are drawn for each of the dies and compared. The appearance of the extrudate corresponding to the various flow regimes is observed. Additional results are obtained by various techniques such as flow visualisation and local velocity measurement with a Doppler velocimeter, and stress determination by means of birefringence. For PTFE dies, two stable slip regimes are observed, for low and high levels of stress, separated by a transition zone. The second slip regime, corresponding to higher levels of stress, is characterised by extremely low friction at the wall. The occurrence of slip produces major modifications in the velocity and stress fields, as well as in the appearance of the extrudate, which shows a crack-free surface.

Direct measurements of slip in sheared polymer solutions

Abstract: We report direct measurements of slip flow during and after plane-Couette shearing of poly(styrene) solutions between glass surfaces. Slip is studied by visualizing the microscopic motions of micron-sized silica spheres suspended in the solutions. Slip velocities as large as 4 μm s −1 are observed during shear, and recoil displacements of as much as 80 μm are observed at the glass surfaces after the driving surface stops moving. Significant slip is observed when the Weissenberg number $\lambda\dot{\gamma}$ exceeds 0.5 or so, where λ is the relaxation time and $\dot{\gamma}$ the shear rate. The magnitude of the slip correlates strongly with the fluid's birefringence, indicating that slip is induced by polymer stress or orientation. Away from the centre of the sample, toward the free edges, a secondary flow is observed, which appears to be driven by a normal-stress imbalance at these edges.

Control system for internal combustion engines

Abstract: A control system for an internal combustion engine adjusts at least one predetermined control parameter such that a rate of combustion variation calculated based on a detected state of combustion of the engine becomes equal to a desired rate of combustion variation, which is dependent on operating conditions of the engine A state of engagement of a lock-up clutch connected to the engine and a slip ratio of a torque converter connected to the same are detected The desired rate of combustion variation is corrected in dependence on at least one of the detected state of engagement of the lock-up clutch and the detected slip ratio of the torque converter

Extrude distortion in the capillary/slit extrusion of a molten polypropylene

Abstract: Experiments were carried out in both sliding plate and capillary rheometers with a polypropylene resin to determine the conditions for the onset of slip, surface, and gross melt fracture. It was found that there was no distinction between surface and gross melt fracture, which is commonly observed in the case of polyethylenes. Furthermore, the flow curves determined by using capillaries having various diameters are diameter independent implying the absence of slip. However, experiments with slit dies having rough surfaces suggest wall slip. Further analysis has shown that the effect of viscous heating masks the detection of slip from the diameter-dependency of the flow curves. The effect of a thin layer of fluoropolymer (Teflon PA, DuPont) on the critical shear stress for the onset of wall slip and melt fracture, as well as on the relationship between the wall shlip and the shear stress, were also examined. It was found that the presence of such layers increases the slip velocity, while it decreases the critical shear stress for the onset of slip.

Estimation of the wall slip velocity in the capillary flow of potato granule pastes

Abstract: The slip velocity of potato granule pastes as a function of wall shear stress was determined in capillary flow at several temperatures and aqueous concentrations. The Mooney technique was used together with a variation of the method in which the shear rate for each die was subtracted from that for a no‐slip flow, approximated using rough dies. General agreement between the two methods was found, despite some unrealistic results in applying the Mooney technique. A critical wall shear stress for slip was found, consistent with published results for other materials. The exponent in the wall shear stress–slip velocity power law was consistently higher than that in the wall shear stress–apparent wall shear rate relationship. This is in keeping with the observation that the ratio of slip flow rate to total flow rate fell with increasing wall shear stress.

Anti-skid control device

Abstract: PROBLEM TO BE SOLVED: To improve the accuracy of the brake control of a vehicle when a wheel rides over a step SOLUTION: A control device starts the anti-skid control by controlling a wheel cylinder pressure adjusting means based on the comparison of the detected value of the wheel rotation acceleration/deceleration with the threshold and the comparison of the detected value of the slip ratio with the threshold in applying the brake Tire pneumatic pressure detecting means 1a-1d to detect the tire pneumatic pressure of each wheel, and a road surface condition judging means 7 to judge the road surface condition from the detected value of the tire pneumatic pressure adjusting means are provided When it is judged from the road surface condition judging means that the wheel crosses over the step, the thresholds of the wheel rotation acceleration/deceleration and the slip ratio are changed to the thresholds to cross over the step different from the threshold for the flat road from the time point of judgment to the elapse of the prescribed time to make it difficult to start the anti-skid control COPYRIGHT: (C)1997,JPO

System for determining side slip angle

Abstract: A system for controlling the yaw rate of a vehicle is provided. The system includes a facility for measuring the yaw rate, the lateral acceleration and the reference velocity of the vehicle. The velocity of the side slip angle of the vehicle is determined according to the equation: ##EQU1## where β is the velocity of the side slip angle, atrans is the lateral acceleration, ν is the reference velocity, γ is the yaw rate, ν is the time derivative of the reference velocity, and β is a side slip angle. The velocity of the side slip angle determining mechanism includes a mechanism for setting the value of the time derivative of the reference velocity to zero, and a mechanism for determining the side slip angle by integrating the velocity of the side slip angle.

Dynamic Analysis of Off-Road Vehicles

Abstract: This paper deals with the simulation of off-road robots while taking into account the mechanical behavior of the locomotion system and its interaction with its environment. This interaction is studied and discussed for different behaviors of wheel-soil contact. The analysis considers phenomena of slips, of soil shear deformations, of soil compaction and wheel elastic deformation. Wheel-soil contact models are expressed by analytical relationships which link each contact force components (radial, longitudinal and lateral forces) to relative displacements (radial displacement, longitudinal slip ratio and side slip angle). These laws are then coupled to the dynamic equations of the mechanical system in order to characterize the behavior of the whole system. These models are implemented on a graphic simulation system which provides a basic tool for the design of the mechanical system, for the path planning and for the definition of control schemes.

Extrudate Distortion in the Capillary/Slit Extrusion of a Molten Polypropylene

Abstract: Experiments were carried out in both sliding plate and capillary rheometers with a polypropylene resin to determine the conditions for the onset of slip, surface and gross melt fracture. It was found that there was no distinction between surface and gross melt fracture, which is commonly observed in the case of polyethylenes. Furthermore, the flow curves determined by using capillaries having various diameters are diameter independent implying the absence of slip. However, performing experiments with slit dies having rough surfaces suggested the presence of wall slip. Further analysis has shown that the effect of viscous heating masks the detection of slip from the diameter-dependency of the flow curves. The effect of presence of a thin layer of fluoropolymer (Teflon® PA, Du Pont) on the critical shear stress for the onset of wall slip and melt fracture as well as on the relationship between the wall slip and the shear stress were also examined. It was found that the presence of such layers increases the slip velocity while it decreases the critical shear stress for the onset of slip.

A simple traction control for tracked vehicles

Abstract: This paper introduces a simple traction control for a tracked vehicle (STCTV). This STCTV uses a zero-order sliding surface with time varying boundary layer thickness. This approach is proven to guarantee that the slip ratio converges to any predefined value asymptotically via Lyapunov stability theory. Simulation results confirm that STCTV allows the tracked vehicle to maintain maximum tractive force available in a frozen snow.

The Moving Contact Line of a Droplet on a Smooth Solid

Abstract: The slip velocity near the contact line of a liquid drop is considered to be generated by the shear stress induced by a non-uniform interaction potential in the liquid. Near the contact line, this interaction potential differs from that in a semi-infinite liquid and depends upon the distance x to the leading edge. Einstein's equation is used to relate the slip velocity to the force acting upon a molecule located on the solid surface. The equation derived for the slip velocity at the leading edge on the basis of these dynamical considerations coincides with that obtained previously by the author by considering that the force is generated by the gradient of the chemical potential. However, the slip velocity decays to zero as x -4 in the latter case and as x -3 in the former.

Control system for motor vehicles equipped with a torque converter and a lock-up clutch

Abstract: In a control system for controlling motor vehicles in such a manner that the drive force of the vehicle is determined by the accelerator pedal stroke and the vehicle speed, the fuel consumption is minimized by appropriately selecting the gear ratio of the power transmission system under each current operating condition. In particular, the present invention accounts for the slip ratio of the lock-up clutch as well as the transmission efficiency of the torque converter by noting the fact that the lock-up clutch operates under semi-tight conditions as well as under tight and loose conditions.

Anti-skid control method

Abstract: A method is provided that provides optimum anti-skid control when the vehicle is turning. If a vehicle enters a turning motion, the maximum frictional resistance corresponds to a larger slip ratio; therefore, in this method, the slip threshold is gradually increased to provide the optimum anti-skid control.

Control device of continuously variable transmission

Abstract: PURPOSE:To secure the braking distance by reducing the minimum transmission ratio in the region to control the engine brake transmission ratio to the prescribed value where the wheel speed of the driving wheels is reduced from the vehicle speed by the prescribed ratio to rapidly return the wheel speed to the target value when the detected value of the wheel speed deceleration is over the prescribed value. CONSTITUTION:The working hydraulic pressure is supplied from a hydraulic control device to the respective chambers 20a, 20b of a cylinder chamber 20 of a driving pulley 16 to change the width of a V-shaped pulley groove of the driving pulley 16, and change the radius at the contact position of a V-belt with the driving pulley 16, and achieve the desired pulley ratio between the pulleys 16, 26 to provide the transmission ratio between the input and the output. The minimum transmission ratio in the range to control the transmission ratio of each engine brake range is set to the value where the wheel speed of the driving wheels is reduced from the detected vehicle speed by the prescribed ratio. The braking force to the driving wheels by the engine brake is secured in the range where the slip ratio of the driving wheels is not excessive to secure the best braking distance.

Braking force control device and method thereof

Abstract: To provide optimal braking force control using braking operation data, an ECU in a brake force control system detects a braking operation according to fluctuation components of wheel rotation. That is, the ECU calculates the wheel acceleration and sets a reference load level for the braking operation according to a road surface coefficient of friction at the wheel tire. When the amplitude of the wheel acceleration increases and exceeds the reference load level, the braking load is determined to be heavy. If the braking load is heavy, the ECU decreases the brake oil pressure of the wheel being detected. In this way, the slip ratio can be controlled around a peak road surface coefficient of friction.

Wheel slip control device

Abstract: PURPOSE:To suppress the lateral difference in braking force based on the lateral difference in tire inflation pressure by the slip control of lateral wheels, and ensure the stability of a vehicle at vehicle braking. CONSTITUTION:In a braking force control device for approaching the actual slip ratio of each wheel 1 at vehicle braking to a target slip ratio by controlling the respective rotations of lateral wheels 1 through a wheel rotation control device 4 by a controller 5, a tire pressure sensor 2 detects the respective tire pressures of the lateral wheels 1. On the basis of the relation that the lower the tire pressure, the more the braking force generated in each wheel 1 is increased, the controller 5 sets the target slip ratio in the wheel lower in tire pressure of the lateral wheels 1 lower than the higher wheel, whereby the lateral difference in braking force based on the lateral difference in tire pressure is suppressed, and the stability of the vehicle at vehicle braking is ensured.

Traction controller for four-wheel drive vehicle

Abstract: PURPOSE: To properly control driving force or traverse force of four wheels, and to improve anti-spin stability by controlling a brake pressure on the basis of a brake pressure instruction signal from a center differential gear and a control unit and controlling an engine output on the basis of an instruction signal from the control unit. CONSTITUTION: A control unit 40 is provided with a four-wheel slip ratio computing means 42, which computes actual slip ratios for four wheels on the basis of signals of wheel speed of the four wheels and a signal from a front/rear G sensor, and a target slip ratio setting means 43, which determines a target slip ratio for front/rear wheels according to a running condition while always setting a slip ratio for the rear wheel to be lower than that for the front wheel. The control unit 40 is also provided with a traction controlling action determining means 44, which determines a traction controlling action when at least one of the slip ratios for four wheels exceeds the target ratio, and a four-wheel brake pressure computing means 45, which individually computes a target brake pressure for each of the four wheels in the traction controlling action so as to output an instruction signal for the predetermined brake pressures or for the target brake pressure to a four wheel brake pressure controller 25.

Front and rear wheel drive vehicle, and road surface mu detecting device

Abstract: PURPOSE: To automatically achieve the starting assist by an electric motor when a vehicle is started on the road surface of low μ with excellent responsiveness in a front and rear wheel drive vehicle to drive either of the front and rear wheels by the engine and drive the other by the electric motor. CONSTITUTION: A μ detecting device 15 consists of a means 15a to detect the driving force of a wheel 1 to be driven by an engine 3, a means to detect the slip ratio of the wheel 1, and a means 5c to detect μ of the road surface based on the correlation between the driving force and the slip ratio. When the detected μ is below the prescribed value, a switch circuit 9 is turned on by a control means 10 in the next starting, and an electric motor 5 is started to achieve the starting assist.