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Roller bearings of aircraft turbo engines are operated under high-speed conditions of over 2 million DN. If contact force between rollers and the raceway is insufficient, then relative slip between the roller and raceways occurs and speed of the cage decreases. This condition may induce skid damage in the raceway. Large operating radial clearance can cause skid damage, but their analytical correlations have rarely been studied. In this study, cage slip ratio was quantified according to clearance changes in various operating conditions and geometric parameters, and causes of cage slip were analyzed using the simplified dynamic model. The design methodology will be proposed to select the proper operating clearance in consideration of cage slip and fatigue life.

Purpose The purpose of this study is to investigate the adhesion characteristics of the wheel–rail under water and large sliding conditions. This is carried out by conducting a series of tests on a full-scale roller rig. The measured data provides an experimental base for conducting further theoretical research. Design/methodology/approach The influence of the slip ratio, rolling speed and the axle load on the adhesion coefficient between the wheel and the rail is analyzed under wet conditions using a full-scale roller rig. Findings From the research, it is found that the adhesion coefficient–slip ratio curve varies from the traditional theoretical description under water and large sliding conditions. Moreover, it is also observed that after the adhesion coefficient reaches the saturation point, the adhesion coefficient does not decrease, but continues to increase as the slip ratio increases. Originality/value The adhesion improvement phenomenon in this paper may provide new ideas for designing anti-skid control and braking system mechanisms for trains. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0236/

The present paper introduces a tire/road friction prediction tool based on modelling the tire/road contact as dynamic, viscoelastic, rough, and lubricated. The tool takes into account a considerable part of influent parameters related to tire, road, contaminant, and contact operating conditions:\ud \ud For the tire, the tool takes into account its geometry and rubber material behaviour.\ud \ud For the road, the texture is taken into account via the surface topography.\ud \ud At the contact interface, dry or wet conditions are taken into account through the lubricant depth, viscosity, and density.\ud \ud The operating conditions are taken into account through the normal load, speed, and slip ratio of the tire.\ud \ud The real novelty of this tool lies in its ability to reproduce the complete curve of the tire/road friction coefficient as a function of the slip rate. The validation of the tool is initially done through parametric studies by analyzing the trends of the results, then by performing braking tests on a passenger car at various speeds on different wet roads with different textures. The tool correctly ranks the peak friction and the sliding friction on these various road surfaces.

Since the beginning of their production, pneumatic tires have experienced tremendous improvements in structure and materials, becoming the dominant design in the world tires market. Nevertheless, relying upon pressurized air, they are affected by maintenance and security issues that can lead to fatal accidents. Therefore, tire-makers are investigating new tire designs, called Airless or Non-Pneumatic, with the aim of removing air-related problems. The research about such tires is still at an early stage, especially if compared to the one conducted on the pneumatic ones. In this paper, the development of a methodology capable of studying the mechanical behavior of a Non-Pneumatic Tire (NPT) by means of experimental data and numerical approach is illustrated. The experimental activities consisted of a scanner acquisition of the NPT and a footprint analysis for the calculation of the radial stiffness and contact patch pressure distribution. Moreover, the Digital Image Correlation (DIC) technique was applied to carry out a more specific study about the spoke’s deformation. From the acquired 3D model, a calculation of the NPT vertical deflection with finite element analysis (FEA) was performed—validating the model and then submitting it to a steady state analysis—that allows the simulation of a steady state rolling tire with the possibility to replicate different values of slip ratio. The results of the experimental activities are in good agreement with the ones obtained with FEA, further validating the developed methodology.

Purpose The purpose of this paper is to study the influence of the cage dynamic unbalance on the dynamic performances in cylindrical roller bearings. Design/methodology/approach The dynamic analysis model which considering cage dynamic unbalance is presented, and the relationship between the cage dynamic unbalance and the cage stability, the cage slip ratio and the cage skew angle is investigated. Findings Cage dynamic unbalance has a great effect on the cage stability. The cage dynamic unbalance which in an axial excursion affects the cage characteristics is greater than that only in the radial direction. The cage slip ratio and the cage skew increases with the cage dynamic unbalance, especially with the axial excursion. The non-metal cage is more sensitive to the cage dynamic unbalance than that of the metal cage. Originality/value The analytical method and model can be applied by the bearing engineering designers.

Electric vehicles have been the focus of the automotive industry in recent years. However, relatively small driving range of electric vehicles makes it not be broadly adopted in the market. Regenerative braking is one of the most effective ways to extend the endurance of electric vehicles. To sufficiently utilise the regenerative braking of electric vehicles and explore the potential of the electric motor plugging braking capability to simplify the braking system structure and reduce the cost, a new braking strategy based on the driver's braking intention and motor working characteristics is proposed. Driver's braking intention is classified as the emergency braking and the normal braking. In the case of normal braking, model predictive control (MPC) is used to express driver's braking intention. By adjusting the weight of the MPC cost function, different braking intentions can be achieved. This strategy is able to achieve as much as possible braking energy recovery without violating the driver's braking intention. In the case of the emergency braking, the sliding mode based optimal slip ratio control is adopted and it is able to obtain the shortest braking distance. In order to validate the effectiveness of the proposed approach, numerical simulations on a quarter-vehicle braking model are tested.

Based on dynamic analysis of rolling bearings, the nonlinear dynamic differential equations of a cylindrical roller bearing with a trilobe-raceway were established and solved by the GSTIFF (gear stiff) integer algorithm with a variable step. The influences of structural parameters and the tolerance of the trilobe-raceway, working conditions of the bearing, and the outer ring installation method on cage slip characteristics were investigated. The results show that: (i) The cage slip ratio and bearing rating life of a cylindrical roller bearing with a trilobe-raceway would reduce when the low-radius (radius of the outer raceway contour at the lowest point) and D-value (difference value between the high and low points of the outer raceway contour) decrease, and the former (low-radius) contributes more significantly. (ii) The cage slip ratio of a cylindrical roller bearing with a trilobe-raceway rises with the increase of the bearing speed, and decreases with the increase of the radial force; the variation range increases with the increase of the low-radius. (iii) When the installation angle of the outer ring increases in a period, the cage slip ratio remains unchanged while the bearing rating life rises up a little. Therefore, when installing a cylindrical roller bearing with a trilobe-raceway, the location of the maximum radius shall be under that of the radial force to improve the bearing rating life. (iv) With the increase of the roundness of the base circle where the radius of the lowest points of the trilobe-raceway contour locates, the cage slip ratio rises gradually and the bearing rating life decreases. Keywords: Bearing rating life, Cage slip ratio, Dynamics, Raceway contour, Trilobe-raceway

Wheeled mobile robots (WMRs) often suffer from the longitudinal slipping when moving on the loose soil of the surface of the moon during exploration. Longitudinal slip is the main cause of WMRs' delay in trajectory tracking. In this paper, a nonlinear extended state observer (NESO) is introduced to estimate the longitudinal velocity in order to estimate the slip ratio and the derivative of the loss of velocity which are used in modelled disturbance compensation. Owing to the uncertainty and disturbance caused by estimation errors, a multi-objective controller using the mixed H2/H∞ method is employed to ensure the robust stability and performance of the WMR system. The final inputs of the trajectory tracking consist of the feedforward compensation, compensation for the modelled disturbances and designed multi-objective control inputs. Finally, the simulation results demonstrate the effectiveness of the controller, which exhibits a satisfactory tracking performance.

When rock tunnel boring machines (TBMs) advance into rock with high strength and hardness, serious cutter wear can result, which greatly obstructs construction efficiency and safety. In this work, disc cutter wear evolution under the action of hard rock is investigated by theoretical analysis and experimental methods. Based on a mechanics analysis of the contact area between the disc cutter and rock, the relationship is determined between the slip ratio of disc cutter and the penetration and cutting coefficient of TBM. And on this basis, the wear mechanism of the cutter ring surface material is specifically analyzed to propose a new theory model for cutter wear evolution. To develop and apply this model further, a series of wear simulation tests are performed to validate this model and establish an application model for a specific project. The application model’s effectiveness is preliminarily verified by project data obtained on site. This study provides a new feasible method for real-time prediction of disc cutter wear conditions and a basis for optimizing the boring parameters and prolonging the life of disc cutters used with rock TBMs.

This paper aims to investigate the slip ratio of induction motor at different working condition of pumping gasoline. An experiment platform is set up to do the contrast experiment. The results show that a peak of slip ratio about 22% occurs at speed of 675r/min, when gasoline is pumped under the minimum opening of nozzle. But this phenomenon doesn’t appear at pumping testing fluid D80. The slip ratio of pumping testing fluid D80 is no more than 8%, while that of pumping gasoline is at the range of 9.5% to 22%. Though explanations are given to explain some phenomenon, the reason why a peak occurs at pumping gasoline needs more investigation.

Efficient slip and slide control systems are crucial in railway transportation since maximization of adhesion utilization and minimization of operating costs mainly depend on performance of such control systems. In order to improve adhesion characteristics, slip and slide control systems should hold the slip ratio at its optimum value which is determined considering vehicle velocity and environmental conditions. On the other hand, calculation of slip ratio with high accuracy is a quite challenging problem because of the difficulties in obtaining vehicle longitudinal velocity. This article proposes a novel method for robust estimation of railway vehicle velocity which uses only the angular velocity of the wheels. To this end, linear matrix inequality (LMI) approach is used to synthesize a robust estimator established on a longitudinal vehicle model with dynamic friction properties. The developed estimator is tested for extreme scenarios and the results are discussed regarding the international standards for vehicle velocity measurement in slip/slide control systems.

This paper presents a numerical analysis on steering performance including tractive parameters and lug effects. To explore the difference between the turning and straight conditions of steering, a numerical sand model for steering is designed and appropriately established by the discrete element method on the basis of triaxial tests. From the point of mean values and variation, steering traction tests are conducted to analyze the tractive parameters including sinkage, torque and drawbar pull and the lug effects resulting from type, intersection and central angle. Analysis indicates that steering motion has less influence on the sinkage and torque. When the slip ratio exceeds 20%, the steering drawbar pull becomes increasingly smaller than in the straight condition, and the increase of steering radius contributes to a decline in mean values and a rise in variation. The lug effect of central angle is less influenced by the steering motion, but the lug intersection is able to significantly increase the steering drawbar pull along with the variation reduced. However, the lug inclination reduces the steering drawbar pull along with the variation raised in different degrees.

Tire footprint properties have important effects on tire-road contact pressure distribution and, consequently, on the general performance of the tire when it is in contact with the road. Most of the research conducted in this area is related to the tire performance under static loading conditions. Past studies show that the slip ratio of the tire plays a significant role on tire footprint characteristics. In this study, to account for the effect of the tire footprint characteristics on the tire performance, a finite element tire model with detailed tread pattern (similar to the tire 205/55R16 used for testing and modeling) has been developed using ABAQUS software. The model has been validated using the experimental methods for both footprint dimensions and vertical stiffness values. The comparison of the results from experiment and simulation show a satisfying agreement within 3.6% error. The model has next been used to simulate tire-road interaction for both, static loading conditions and slippage. The results for the footprint properties of the tire with applied normal load of 4 kN for slip ratio of 10%, 15%, 20%, 35%, and 40% are presented. The footprint characteristics of the tire have been parametrized in order to describe the changes in the tire-road contact patch properties under different operational conditions. The parameters with the greatest effect on tire traction performance have been identified and the relationships between these parameters and the tire performance have been presented.

Through the analysis of driving stability of the vehicle on combined horizontal and vertical curves (CHVC), the safety model based on vehicle-road coordination was established with the critical state of accident as the limited condition. The influence of various factors on the design parameters such as the minimum radius and the maximum slope length were discussed. The safety model showed that the minimum radius of CHVC was proportional to the driving speed and road gradient, but inversely proportional to the value of the superelevation and crosswise affixing coefficient. Besides, the maximum slope length of CHVC was proportional to the road rolling resistance coefficient and slip ratio, but it was inversely proportional to driving speed, road gradient, and vehicle type. Furthermore, the maximum slope length was less affected by the superelevation. In addition, in order to improve the safety level of mountainous roads, this paper discussed the threshold value of the design index of CHVC considering the actual operating speed of the vehicle.

The flow pattern of gas-liquid two-phase flow has a great influence on the water holdup measurement by capacitor sensor. In this paper, the idea of flow pattern regularization is proposed. The complex flow pattern of gasliquid two-phase flow is forcibly changed into the swirling flow pattern with regularized phase distribution by using the hydrocyclone. The structure of the hydrocyclone is designed by means of flow pattern observation to ensure better separation effect and less pressure loss, and the stability of the swirling flow is analyzed. Based on the hydrocyclone-capacitor sensor, the water volume fraction information is converted into liquid film thickness and water holdup information. The experimental results indicate that the sensor has a good resolution to the water volume fraction. A new model of the slip ratio in the swirling flow is presented. Based on the slip ratio in the swirling flow, the water volume fraction can be acquired, realizing the measurement of water volume fraction within 10%. The mean absolute error is 0.244%.

Soil–wheel interaction under cornering and slip conditions (SWICS) has a significant impact on the steering performance of off-road vehicles. In order to analyze the six-dimensional wheel forces in SWICS, a SWICS model based on the analytical method and the discrete element method (DEM) is developed in this paper. First, the modeling process of SWICS using the analytical method was detailed to predict the six-dimensional wheel forces in SWICS. The SWICS was then modeled using the DEM, which involved the following steps: (a) establishment of tire geometry, (b) selection of particle parameters, (c) parameter calibration, and (d) particle generation. Finally, DEM simulations were carried out for different slip angles and slip ratios under three loads, and the results were compared with those of the analytical model. The results show that the SWICS DEM model in this paper maintains a good fit with the analytical model, validating the efficiency of the DEM model and the parameter calibration method. The slip angle has a great influence on the lateral force, overturning moment, and aligning moment and a smaller impact on the normal force, drawbar pull, and rolling resistance moment. The slip ratio promotes an increase in the drawbar pull and rolling resistance moment but reduces the value of the lateral force and aligning moment. The research in this paper provides a DEM modeling approach and an analysis method for solving mechanical problems with different dimensions in SWICS, which will help improve the performance of off-road vehicles.

Due to the noise of sensing equipment, the tire states, such as the sideslip angle and the slip ratio, cannot be accurately observed under the conditions with small acceleration, which results in the inapplicability of the time domain data based tire-road friction coefficient (TRFC) estimation method. In order to overcome this shortcoming, frequency domain data fusion is proposed to estimate the TRFC based on the natural frequencies of the steering system and the in-wheel motor driving system. Firstly, a relationship between TRFC and the steering system natural frequency is deduced by investigating its frequency response function (FRF). Then the lateral TRFC is determined by the steering natural frequency which is only identified using the information of the assist motor current and the steering speed of the column. With spectral comparison between the steering and driving systems, the data fusion is carried out to get a comprehensive TRFC result, using the different frequency information of the longitudinal and lateral value. Finally, simulations and experiments on different road surfaces validated the correctness of the steering system FRF and the effectiveness of the proposed approach.

To investigate the rotation vibration dynamics of the pulleys and the tension arms, and to estimate the vibrations of the belts and the slip ratio between the belt and the pulleys in the engine front-end accessory drive systems, a systematic modelling and analytical method is proposed for engine front-end accessory drive systems; this can be used for modelling engine front-end accessory drive systems with different layouts and different numbers of tensioners, including automatic and fixed tensioners. In the modelling, the rotational pulleys are classified as fixed-axis pulleys and moveable-axis pulleys (such as the pulley in the tensioner). Moreover, the belt spans are classified as the belt spans between the two fixed pulleys, and the belt spans adjacent to the pulley of a tensioner. The equations of motion for each type of pulley and the tension calculation equations for each type of belt span are developed. In this way, the equations of motion for all the pulleys and the tensioner arms can be obtained easily, irrespective of the layout of the tensioners. To obtain the dynamic rotational vibration responses of an engine front-end accessory drive system by the conventional Runge–Kutta method, high-efficiency algorithms or methods are also proposed for calculating the tangent-point coordinates between a belt and the adjacent pulleys and the belt length of the contact arc on one pulley. The proposed modelling and analysis methods are validated by modelling different layouts of the engine front-end accessory drive systems with different types and numbers of tensioners, and also by comparisons between the calculated dynamic vibration responses of the pulleys and the belts and the real experimental data.

Magic Formula (MF) tyre model is widely used for the analysis of tyre behavior in different driving situations. The model is mostly used to fit the simulation and experimental data slip curves. As there are many modifications of the MF, this paper presents a literature analysis of MF application and fitting techniques. A short review of other empirical tyre models was also made. At the end, a simple least squares minimisation technique was used to fit the experimental data of longitudinal tyre performance on ice. Measurements were performed with the inner drum test rig in the laboratory. In general, the fitting showed a very good accuracy.

After the reference of straight line stability control strategy of four-wheel drive vehicle, this paper proposes a control algorithm combining the sliding mode variable structure and optimization control method. The control algorithm is mainly divided into the upper generalized moment calculation based on the sliding mode variable structure controller and the lower torque distribution controller based on the optimization algorithm, also including the slip rates controller based on PID algorithm to ensure the straight line stability control. This paper establishes the combined model based on the CarSim and MATLAB, and tests to verify the validation of the control strategy through the four-wheel drive vehicle test-bed based on RT_LAB. The simulation and experimental results show that when the tire-road friction coefficient is low, the control strategy can not only make the vehicle tire slip rates stay near the optimal slip ratio, at the same time through the yawing moment adjustment, ensure the yaw angle of vehicle not beyond 0.5 deg/s, so the method can effectively ensure the straight line stability of four wheel drive vehicle.

This paper presents a boundary perturbation method of the Brinkman-extended Darcy model to investigate the flow in corrugated microannuli cylindrical tubes with slip surfaces. The stationary random model is used to mimic the surface roughness of the cylindrical walls. The tube is filled with a porous medium. We shall consider the two cases where corrugations are either perpendicular or parallel to the flow, and particular attention is given to the effect of the phase shift. The effects of the corrugations on the flow rate and pressure gradient are investigated as functions of wavelength, the permeability of the medium, the radius ratio and the slip parameter. Particular surface roughnesses are examined as special cases of stationary random surface. It is found that the effect of the partial slip is significant on the corrugation functions. The limiting cases of Stokes and Darcy’s flows and no-slip case are discussed.

Knowledge of the current tyre–road friction coefficient is essential for future autonomous vehicles. The environmental conditions, and the tyre–road friction in particular, determine both the braking distance and the maximum cornering velocity and thus set the boundaries for the vehicle. Tyre–road friction is difficult to estimate during normal driving due to low levels of tyre force excitation. This problem can be solved by using active tyre force excitation. A torque is added to one or several wheels in the purpose of estimating the tyre–road friction coefficient. Active tyre force excitation provides the opportunity to design the tyre force excitation freely. This study investigates how the tyre force should be applied to minimise the error of the tyre–road friction estimate. The performance of different excitation strategies was found to be dependent on both tyre model choice and noise level. Furthermore, the advantage with using tyre models with more parameters decreased when noise was added to the force and slip ratio.

The friction between wheel and track is usually called adhesion force, and it is the critical factor for the movement of trains. On one hand, excessive driving force of a train may lead to insufficient utilization of the adhesion effect and cause wasted energy; on the other hand, insufficient driving force of a train brings inefficient train operation. To balance the issues of energy consumption, operational efficiency, and security, it is necessary to control a train to obtain its maximal adhesion force, particularly in the cases of fast acceleration and emergency braking. However, since engineering experiments indicate a complex nonlinear relationship between the adhesion force and the slip ratio of a train, such a control problem is difficult and challenging, particularly when the optimal slip ratio is unknown. Facing this problem, this paper proposes a novel control method based on the modification of the famous super-twisting sliding mode algorithm, and rigorous mathematical analysis is given to guarantee the ultimate boundedness of the proposed algorithm. Furthermore, by considering four different control scenarios, detailed control and estimation algorithms are both proposed. Simulation result verifies that the proposed control strategy can control the train to obtain its maximum adhesion force.

Anti-lock Braking System (ABS) is a crucial part in electric vehicle. It is an uncertain and nonlinear system. In this paper a Sliding Mode Control (SMC) technique with PID sliding surface is used to maintain the slip ratio, at 0.2 of ABS system. The mathematical representation of a quarter vehicle model that emphasizes essential characteristics of the whole vehicle was implemented in this research. The model was developed using Simulink and the proposed SMC technique was tested and validated. In addition, the sliding mode enforcement was ensured via stability analysis. The simulation results have shown good agreement and acceptable response of the ABS system

Perturbation solutions for the velocity and electric potential of a time periodic magnetohydrodynamic slip flow in a microchannel with sinusoidal wall corrugations are obtained using perturbation method. The effects of wall corrugations, slip length, Hartmann number and the frequency of the electric potential on the flow are analyzed theoretically and graphically. The results show that velocity and electric potential are significantly disturbed by wall roughness and that there exists a phase lag between the velocity and the electric potential. The velocity profile is characterized by the ratio of momentum diffusion time scale to the period of the applied electric field. The phase lag increases with frequency, slip length and decreases with Hartmann number, the wavenumber and phase difference of the wall corrugations. However, for a sufficiently small frequency, the phase lag is almost nonexistent. The effect of the phase difference of the wall corrugations on the phase lag becomes unimportant when the wavenumber is larger than 2. The velocity amplitude increases with slip length and decreases with frequency, wavenumber and phase difference. However, the phase difference becomes unimportant for sufficiently large wavenumber. When the frequency is large enough, the velocity amplitude is not influenced by slip length.

The motion of air and water is characterised in a downflow co-current column reactor. The velocity of the bubble swarm relative to that of the bulk water is determined using a new approach for the computation of the slip velocity in a CFD simulation using a modified drift flux model and incorporating the data obtained from the CFD modeling. The validity of the numerical model is confirmed by comparing the simulation results with those of experimental. The average slip velocity is found to be approximately 3.3 cm/s in the down-comer co-current column, which is lower than those prevailing in counter-current columns. It is concluded that in a bubbly flow regime lower slip velocity improves the bubble particle collection efficiency.

An analytical model is presented for pressure-driven two-fluid flow between two parallel flat plates rotating about an axis perpendicular to the plates. The aim is to determine the lubricating effects due to a near-wall low-viscosity depletion layer on the axial as well as transverse flows in a rotating channel. It is found that the primary and secondary flow fields may be affected differently by the system rotation, the thickness of the depletion layer, and the viscosity ratio. For a very thin depletion layer, the wall lubrication reduces to a Navier slip condition, where the slip length is found to be the same as the one for a non-rotating channel at the leading order, while the higher-order slip length is a function of a complex rotation parameter. The Fahraeus–Lindqvist effect in a rotating environment is also examined.

To characterize the effect of pipe inclination, low viscosity, flow rate and inlet water cut on annular flow pattern, a low viscosity oil-water two-phase annular flow in horizontal and slightly inclined (+1°, +3° and +5°) pipes with diameter of 20 mm has been experimentally investigated. A modified VOF model based on the CFD software package FLUENT was used to predict the in-situ oil fraction and pressure drop. The experimental data indicate that annular flow appears at a medium-high water cut. The slip ratio increases with flow rate increase but decreases with increasing water cut. The changes are more significant as the degree of inclination increases. Pressure drop is strongly dependent on flow rate, as it increases rapidly as inlet flow rate increase. Good agreement between the experimental data and calculated results of slip ratio and pressure drop was obtained.

Driving electric vehicles by electric motors can result in many unique advantages for dynamic control of electric vehicles. With the superior fast and accurate torque control performance of electric motors, electric vehicles, in particular, can achieve higher levels of safety and handling performance. A simple, effective and efficient anti-skid control method specified for electric vehicles is proposed in this paper by considering the real-world resistance factors. This method is developed on the basis of sensing and regulating a newly defined parameter, namely the ratio of the drive motor torque to the angular acceleration of the wheels, both of which can be easily obtained for electric motors. The monotonic relationship between the slip ratio and the ratio of the drive motor torque to the angular acceleration of the wheels is proved under both acceleration conditions and deceleration conditions, by considering the real-world resistance factors. The simulations and the experimental results show that the ratio of the drive motor torque to the angular acceleration of the wheels can be efficiently used, instead of the slip ratio, in anti-skid control. The results indicate that electric vehicles can achieve high-performance vehicle motion control with more flexible and simplified configurations by using in-wheel electric motors.

Traction control, which can be performed by different types of chassis control system, plays an important role in vehicle motion control. Since the propulsive force is actually produced by the friction between the tyre and road, information on the tyre–road friction is crucial for traction control. In this paper, a robust and effective tyre–road friction coefficient identification algorithm for straight acceleration is proposed, and a coordinative traction control method is designed by integrated usage of gear shifting control, engine control and braking control. For different driving conditions, the tyre forces were observed by a sliding-mode observer or calculated from the states of the vehicle directly, and the tyre–road friction coefficients were estimated by the recursive least-squares method or calculated from the linear characteristics between the friction coefficient and the slip ratio consequently. Based on the estimated tyre–road information, a practical and systematic coordinative traction control algorithm was designed to integrate shifting control, engine torque control and braking pressure control. Finally, the proposed methods are verified by both simulations and road tests. The results show that the estimation algorithms can identify the variation in the road conditions with considerable accuracy and response speed, and the controller successfully adjusted the slip ratios of the driving wheels in the stable region with good performances on different types of road.

This paper presents the comparison between two braking methods for a two-wheel front driven Electric Vehicle maximizing the energy recovery on the Hybrid Energy Storage System. The first method consists in controlling the wheels slip ratio while braking using a robust sliding mode controller. The second method will be based on ECE R13H constraints for an M1 passenger vehicle. The vehicle model used for simulation is a simplified five degrees of freedom model. It is driven by two 30 kW permanent magnet synchronous motor (PMSM) recovering energy during braking phases. Several simulation results for extreme braking conditions will be performed and compared on various road type surfaces using Matlab/Simulink®. For an initial speed of 80 km/h, simulation results demonstrate that the difference of energy recovery efficiency between the two control braking methods is beneficial to the ECE constraints control method and it can vary from 3.7% for high friction road type to 11.2% for medium friction road type. At low friction road type, the difference attains 6.6% due to different reasons treated in the paper. The stability deceleration is also discussed and detailed.

For the purpose of regenerative braking control in hybrid and electrical vehicles, recent studies have suggested controlling the slip ratio of the electric-powered wheel. A slip tracking controller requires an accurate slip estimation in the overall range of the slip ratio (from 0 to 1), contrary to the conventional slip limiter (ABS) which calls for an accurate slip estimation in the critical slip area, estimated at around 0.15 in several applications. Considering that it is not possible to directly measure the slip ratio of a wheel, the problem is to estimate the latter from available online data. To estimate the slip of a wheel, both wheel speed and vehicle speed must be known. Several studies provide algorithms that allow obtaining a good estimation of vehicle speed. On the other hand, there is no proposed algorithm for the conditioning of the wheel speed measurement. Indeed, the noise included in the wheel speed measurement reduces the accuracy of the slip estimation, a disturbance increasingly significant at low speed and low torque. Herein, two different extended Kalman observers of slip ratio were developed. The first calculates the slip ratio with data provided by an observer of vehicle speed and of propeller wheel speed. The second observer uses an original nonlinear model of the slip ratio as a function of the electric motor. A sinus tracking algorithm is included in the two observers, in order to reject harmonic disturbances of wheel speed measurement. Moreover, mass and road uncertainties can be compensated with a coefficient adapted online by an RLS. The algorithms were implemented and tested with a three-wheel recreational hybrid vehicle. Experimental results show the efficiency of both methods.

Electro-osmosis has the potential to reduce concentration polarisation (CP) because it induces the movement of fluid in the vicinity of membrane, thus improving mixing within the boundary layer and enhancing mass transfer. Computational Fluid Dynamics (CFD) is used to simulate steady and unsteady electro-osmotic flow (EOF) in 2D spacer-filled channels, using the Helmholtz-Schmoluchowski slip velocity approximation. The results show that mass transfer enhancement due to EOF is larger in spacer-filled channel than in empty channels. For the steady EOF, the simulation results show that uniform slip velocity reduces the development of stagnant and high concentration regions near spacer filaments when the slip velocity direction is away from the spacer. For unsteady EOF in spacer-filled channels, the simulation results show that an oscillating slip velocity has the potential to induce vortex shedding. This occurs when a resonant slip velocity frequency is used for Reynolds numbers near the transition from steady to unsteady flow. EOF induced vortex shedding due to the resonant slip velocity results in significant increase in maximum wall shear stress along the membrane, therefore potentially delaying the onset of fouling. The data also shows that at the same permeate flux, EOF at the resonant slip velocity frequency results in a significantly lower Power number (a proxy for pumping energy) than the case without EOF.

Heavy aircraft main landing gear tyres skid immediately after touchdown as result of the high slip ratio between the tyres and runway, which lead to tyre wear and smoke. In this paper, the tyre wear is modelled on the Archard theory using ANSYS mechanical transient, to reveal the wheel’s dynamic and the tyre tread wear. The wheel’s dynamic and the amount of wear are calculated for initially static and for pre-spun wheels in order to find the effectiveness of the technique of pre-spinning the wheel, as suggested by many patents since the early days of airplane use, in order to eliminate aircraft landing wear and smoke.

A method is presented for the online prediction of the terrain-shearing parameters for a wheeled Unmanned Ground Vehicles (UGVs) traversing on an unknown terrain. The method uses a trained multiple-output least squares support vector machine (LS_SVM) to map engineering data and predict the terrain-shearing parameters such as cohesion, internal friction angle and shear deformation modulus without requiring information on wheel sinkage. The predicted terrain-shearing parameters can be used to predict vehicle drawbar pull which can be used for trafficability prediction, traction control and performance optimization. Experiments were performed using a single-wheel soil bin to measure the sinkage, drawbar pull and torque for a griddle net wheel under different slip ratio. An additional experiment was performed under a continuous slip ratio from 0.2 to 0.6 with a wheel load of 50 N to validate the method. The experimental results show that the multiple output LS_SVM model can accurately predict the terrain-shearing parameters using the slip ratio, torque and wheel load without the need of wheel sinkage.

Slip ratio can be readily measured in an adiabatic two-phase flow experiment. However, in the flow boiling experiments, as the phase velocities keep varying, the estimation of slip ratio becomes difficult. In the absence of reliable methodology, the slip ratio for boiling flows is either taken simply as unity or deduced from void fraction experiments. It is noticed in literature that the experimental results reveal the effects of pressure and mass flux on void fraction and hence slip ratio. In the present work, numerical simulations to estimate slip ratio are carried out based on a well established wall boiling model. The computationally obtained void fraction values for subcooled boiling conditions in the vertical tube are verified with the available experimental data. The effect of operating variables, such as the tube diameter, the inlet mass flux and the degree of subcooling, on the variation of slip ratio is presented. The results show that the values of slip ratio vary along the length of the tube. A new correlation is proposed relating slip ratio with the thermodynamic quality, implicitly taking into account the effect of length and the operating conditions.

Longitudinal slip efficiency of driving wheels of off road vehicles is function of not only slip of all driving wheels but also their gross traction force. In this work, the slip efficiency was ascertained for a mechanical front wheel drive (MFWD) tractor in a tillage practice. Front and rear driving wheels of the MFWD tractor performed in unequal traction circumstances (size, inflation pressure, and dynamic vertical load) and soil cone indices. Obtained results indicated that the slip efficiency nonlinearly dropped from 0.94 to 0.74 as simultaneous augmentation of slip ratio of the rear wheels to that of the front wheels (0.72-0.87) along with ratio increment of gross traction force of the rear wheels to that of front wheels (1.81-4.93). These conditions occurred, when draft force requirements of implement augmented from 8.58 to 25.85 kN. Hence, it can be pointed out that the maximum slip efficiency as well as overall power efficiency of the MFWD tractor in tillage practices would be achieved at the same slip in accordance with the same gross traction force of the front and rear wheels. To do this for, specific tire type (radial or bias ply), automatic slip control of the wheels by implementing wheel slip control system would be beneficial, especially in case of lower slip than 0.2 for achievement of maximum tractive efficiency. It must be noted that adjustment of inflation pressure of the tires is also advantageous followed by ballast weight application in this realm.

In order to study the characteristics of 3D gas-liquid interfaces, flow pattern transitions, and void fraction in mini tubes, virtual multi-vision experiments and numerical simulations are conducted in a 5.16 mm horizontal tube with air as the dispersed phase and water as the continuous phase. Air and water flow velocities range from 0.024 to 12.330 m/s and from 0.039 to 0.942 m/s, respectively. A simple setup is adopted to capture images synchronously from two orthogonal views with a prism. 3D gas-liquid interfaces of bubbly, slug, and annular flows in horizontal mini tubes are reconstructed in Matlab based on the captured images. Flow pattern transitions and void fractions with 3D interfaces are comprehensively investigated both experimentally and numerically. The numerical results fit well with experimental data in terms of 3D interfaces, cross-sectional and volumetric void fractions. The results show that three flow patterns (bubbly, slug, and annular) are observed experimentally and numerically. The increases in both bubble size and interfacial fluctuation are the main reasons for flow pattern transitions. Two peaks are observed in the Probability Density Functions figures for intermittent flows, while only one peak is obtained for annular flow. The volumetric void fraction fits well with the homogenous model when the gas quality is lower than 0.8, while the slip ratio is around 1. The velocity difference between the two phases increases dramatically at a higher gas quality, leading to a lower void fraction than the predicted value by the homogenous model. The results agree well with empirical correlations with a mean average deviation about 10%, which validates the experimental and numerical methods in the present work.

This paper investigates the fluidelastic instability of a rotated triangular tube array subjected to two-phase crossflow considering the effect of the slip ratio of air-phase and water phase. We first established a Computational Fluid Dynamics model to determine the two-phase flow parameters. Then, a dynamic model of the tube motion while considering the effect of the slip ratio of the air phase and the water phase was developed. The eigenvalue problem of fluidelastic instability of the tube bundles for five void fraction conditions was studied. The results indicate that the slip ratio of the air phase and water phase is an important factor to predict the threshold of fluidelastic instability of a rotated triangular tube array in the transverse direction. The critical velocities of fluidelastic instability of the tube bundles obtained from the separated flow model are much lower those obtained from the Homogeneous Equilibrium Model.

This paper is concerned with the improvement of vehicle stability during braking. A disturbance observer (DO) in conjunction with sliding mode control (SMC) has been proposed for anti-lock braking system (ABS). DO is used to estimate and compensate the effect of uncertainty and disturbance from the system. The SMC provides robust control for the nonlinear ABS system to track the desired slip ratio. The objective of DO is to maintain the desired slip ratio for different runway surfaces and different runway transition i.e. change in slip ratio. The controller is verified using MATLAB/Simulink.

The collision avoidance system is the present state-of-the-art hardware/software integration for preventing an impending collision. The developed algorithm functions in two stages. It first warns the driver and if the driver fails to respond in time, it applies the brakes automatically to avoid the collision or reduce its severity. This paper deals with the development of a suitable mathematical model for Collision Avoidance System. Analysis and Simulation of the mathematical model has been done in MATLAB®. Simulation studies with On–Off and Fuzzy Logic Controller are compared and usefulness of Fuzzy Inference System (FIS) has been established. With two fuzzy inputs namely (slip ratio and rate of change of slip ratio) and one output (fraction of Brake Pressure required), optimum braking force is achieved. An iterative method is used to optimize the FIS controller. A new definition of critical distance has also been developed for optimization of the assessment of critical distance.

Purpose – The purpose of this paper is to study a woodworking machine, in which a linear induction motor (LIM) is applied to feed the wood to be processed into the cutting saw. The LIM is optimally designed and the whole drive system is controlled by a programmable logic controller (PLC) to meet the industrial demands. Design/methodology/approach – Since the operation range is short, the LIM mainly works at the transient state of quick start and quick brake. Hence, the thrust force with a large slip ratio (hereafter called the starting thrust) is one of the most important issues in the LIM design. Finite element method is used to optimize the starting thrust while taking a specific variable voltage variable frequency (VVVF) drive into account. Findings – The LIM system directly drives the machine workbench where the wood is placed, eliminating the requirement of manpower to push the wood through the cutting saw, hence, greatly reduces the operation hazard. It has a higher reliability and longer service life than the conventional drive system employing a rotary motor with a ball screw mechanism. Originality/value – The LIM is an attractive candidate for the woodworking machine application, which can replace the complicated and relatively low-efficiency mechanism of rotary motor and ball screw. High starting thrust can be achieved by optimizing the LIM design, whilst the specific VVVF control is essential to ensure a good drive performance. The PLC is competent for both human-machine interface (HMI) and control of the inverter-fed LIM system, and is of high reliability in industrial environment.

Planetary rovers on rough terrain are likely to encounter hazards such as rocks as well as loose soil or regolith that causes the wheels to slip and potentially get stuck. These missions need autonomous navigation for avoiding these hazards. The slippage of the wheels depends dynamically on the wheel properties, soil mechanical properties, speed and pose of the rover. In this paper, we investigate the path finding problem for a planetary rover on rough sandy terrain. Insights from terramechanics, ie. the wheel soil interaction model, is used to determine path cost to be used for the A ∗ algorithm, which is used on a sample grid to determine the best path. The proposed model incorporates the slippage required to develop drawbar pull to climb up a slope, as well as steering angle needed to counter lateral force. The path thus found is evaluated based on the slip ratio and steering angle required to traverse it.

To improve the vehicle stability of an electric vehicle (EV) with four in-wheel motors, the authors investigate the use of a non-linear control allocation scheme based on model predictive control (MPC) for EVs. Such a strategy is useful in yaw stabilisation of the vehicle. The proposed allocation strategy allows a modularisation of the control task, such that an upper level control system specifies a desired yaw moment to work on the EVs, while the control allocation is used to determine control inputs for four driving motors by commanding appropriate wheel slips. To avoid unintended side effects, skidding or discomforting the driver in critical driving condition, the MPC method, which permits us to consider constraints of actuating motors and slip ratio, is proposed to deal with this challenging problem. An analytical approach for the proposed controller is given and applied to evaluate the handing and stability of EVs. The experimental results show that the designed MPC allocation algorithm for motor torque has better performance in real time, and the control performance can be guaranteed in the real-time environment.

As an indispensable tool for astronauts on lunar surface, the lunar roving vehicle (LRV) is of great significance for manned lunar exploration. An LRV moves on loose and soft lunar soil, so the mechanical property of its wheels directly affects the mobility performance. The wheels used for LRV have deformable and mesh pattern, therefore, the existing mechanical theory of vehicle wheel cannot be used directly for analyzing the property of LRV wheels. In this paper, a new mechanical model for LRV wheel is proposed. At first, a mechanical model for a rigid normal wheel is presented, which involves in multiple conventional parameters such as vertical load, tangential traction force, lateral force, and slip ratio. Secondly, six equivalent coefficients are introduced to amend the rigid normal wheel model to fit for the wheels with deformable and mesh-pattern in LRV application. Thirdly, the values of the six equivalent coefficients are identified by using experimental data obtained in an LRV’s single wheel testing. Finally, the identified mechanical model for LRV’s wheel with deformable and mesh pattern are further verified and validated by using additional experimental results.

In this paper, a resonance frequency-based tire–road friction coefficient (TRFC) estimation method is proposed by considering the dynamics performance of the in-wheel motor drive system under small slip ratio conditions. A frequency response function (FRF) is deduced for the drive system that is composed of a dynamic tire model and a simplified motor model. A linear relationship between the squared system resonance frequency and the TFRC is described with the FRF. Furthermore, the resonance frequency is identified by the Auto-Regressive eXogenous model using the information of the motor torque and the wheel speed, and the TRFC is estimated thereafter by a recursive least squares filter with the identified resonance frequency. Finally, the effectiveness of the proposed approach is demonstrated through simulations and experimental tests on different road surfaces.

Three different torque control algorithms are compared and evaluated for rear wheel drive electric vehicle (EV COMS) with in-wheel motors on split-mu road. The performance of direct yaw moment control, slip ratio control and integral control of both direct yaw moment and slip ratio control are studied by applying these control algorithms to electric vehicle for a straight motion on a split-mu road. The split-mu road disturbs the straight motion and vehicle will deviate from straight path with some error. In simulation, driver model is applied and driver effort of steering wheel angle eliminates this error in all the three cases. The simulation results show that the integral torque control schemes exhibit better performance as compared to direct yaw moment control and slip ratio control as it needs very little driver effort for vehicle straight motion. The three torque control schemes are also compared experimentally on a split-mu road using EV COMS. The desired yaw rate is set to zero in the software and the vehicle trajectory with reference to the desired straight path is recorded and compared. The integral control showed little deviation of test vehicle yaw rate from the desired zero yaw rate as compared to the other two control algorithms.

This study proposes a novel approach to evaluating and controlling the traction force of a wheel directly driven by an electric motor on different road surfaces. Instead of slip ratio measurements, the database of the motor called the current-RPM-torque database can evaluate the traction force of the wheel. The feedback of the measured current and the rotational speed can assist the autonomous traction controller synthesized from this database by the neural network approach when one traction wheel of the vehicle is traveling on different kinds of road surfaces. The adequate gains which are the training data for the neural network control synthesis have to satisfy the assigned specifications in time domain for different slip ratios. This paper also finds that the adequate gains mainly depend on slip ratio slope rather than slip ratio. Based on a scenario similar to real situations, the simulated results in this study show that it is feasible to evaluate and control the traction force through the motor database by the feedback of the current and the RPM.

Wheeled exploration robots (WERs) used for applications such as planetary exploration have to traverse loose terrain, often, during which time they may suffer longitudinal slip and side slip owing to the interaction between their rigid wheels and the loose soil. Longitudinal slip and side slip are the main causes for WERs delay or deviate from the ideal trajectory. But the presented work is indeed focused on longitudinal slip. By analyzing and simplifying the wheel–soil interaction terramechanics model for this case, the algorithm for an adaptive fuzzy control law based on slip ratio optimization is designed to optimize the tractive efficiency and minimize energy consumption. Its stability is proved, and conditions for control parameters are derived. Analytical and simulation results demonstrate that the proposed control system significantly improves the mobile performance of the WER.

Measurement of tyre longitudinal slip-ratio is often estimated from three independent measurements devices namely wheel rotation speed, vehicle speed and tyre rolling radius. This produces an expensive measurement system to indirectly determine the slip-ratio. This paper presents a method by which the slip-ratio is determined from a video camera using digital image correlation techniques. The camera, mounted in such a way that the contact patch region is captured, enables the system to measure the tyre tread speed and ground speed at the contact patch. The slip-ratio is then determined from these two measurements.