International Journal of Vehicle Systems Modelling and Testing (8 papers in press)
Unknown-input observer for vehicle lateral dynamics using a new sensor force technology
by Fatima Ezzahra Saber, Mohamed Ouahi, Abdelmjid Saka
Abstract: Robust estimation of a vehicle's dynamics states (steering angle and sideslip angle) is essential for vehicle handling and stability control. In the past, the estimation of a vehicle's lateral state with the measured steering angle has been proposed. In this paper, four unknown input observers are then designed using lateral tyre force measurements based on a non-linear vehicle model, to simultaneously estimate vehicle steering angle as unknown input and vehicle lateral state variables sideslip angle and yaw rate. All of the design conditions are formulated in terms of linear matrix inequalities, which can be solved efficiently. Simulation results through Matlab/Simulink software based on data of the CALLAS vehicle simulator are used to evaluate the performance of observers based on nonlinear unknown input observer.
Keywords: vehicle dynamics; unknown input observer; state estimation; driver assistance systems.
Transient thermal analysis of an interior permanent magnet synchronous in-wheel motor driving system
by Di Tan, Haitao Wang, Zhongyang Wang, Kun Yang, Fan Song, Hongxun Fu
Abstract: The integration of the in-wheel motor (IWM) driving system structure makes the space closed and narrow, and hence heat dissipation is difficult. Meanwhile, the pursuit of high power density of the IWM leads to the increase of the loss density and the temperature of the IWM. This seriously affects the safe operation of the motor and the vehicle. In this paper, an interior permanent magnet synchronous IWM driving system is taken as the research object. The electromagnetic and temperature field analysis model is developed based on the detailed structure of the IWM driving system. Then the transient thermal analyses under the rated and peak conditions are carried out through the magneto-thermal coupling method. The results show that, under the rated condition, when the IWM reaches a steady state, the highest temperature occurs on the copper wire of the stator winding, which is 111.8℃; under the peak condition, owing to the big loss generated by the motor overload operation, the maximum temperature of the motor has reached 170℃ during the simulation analysis of 60 s, which has exceeded the motor insulation level requirements 155℃. Therefore, a cooling design is necessary in order to ensure the normal operation of the IWM and the vehicle.
Keywords: in-wheel motor drive system; magneto-thermal coupling; transient thermal performance; loss density.
Design and analysis of a coupling mechanism with dual planetary gear sets for the power split hybrid electric vehicle
by Shaohua Wang, Sheng Zhang, Dehua Shi, Xiaoqiang Sun
Abstract: Hybrid electric vehicles (HEVs) are now used more and more widely, especially the power split HEVs. However, the fuel consumption of HEVs varies with the configuration of the power coupling device. In this paper, a novel power coupling mechanism with dual planetary gear sets is proposed, which is developed from an automotive transmission in the conventional vehicle. By analysing its power split characteristics, it is proved that two brakes are essential to be added into the power coupling mechanism. The addition of brakes enriches operation modes, which is effective to improve the system efficiency, though it would increase the complexity of the system. Characteristic parameters of the planetary gear sets are optimised. For accurate evaluations of the proposed configuration, a global optimisation control strategy is established based on the dynamic programming (DP) algorithm. Simulation results under different driving cycles show that the fuel consumption of HEV with the proposed power coupling mechanism is 6.89% and 8.30% lower than that of a benchmark vehicle. The proposed power coupling mechanism proves to be beneficial to improve HEV fuel economy.
Keywords: power split HEV; power coupling mechanism; DP algorithm; control strategies; fuel economy.
On the use of non-Gaussian models for statistical description of road micro-surface profiles
by Alexander Steinwolf, Matthias Wangenheim, Joerg Wallaschek
Abstract: When analysing parameters of vehicle-road interaction, such as contact forces and friction between the tyre and the pavement, the probability density function of random micro-surface is required. Since the asperity tops are being polished by slipping tyres more strongly than the valley bottoms, the surface height profiles become asymmetrical in shape. As a result, the probability distributions of micro-surface signals are often different from the Gaussian model. In this case, one needs a non-Gaussian probability density function model operating with the skewness and kurtosis, which can be calculated from road surface measurements. Previous solutions with the help of the Pearson and Johnson distributions take skewness and kurtosis into account, but the probability density equations obtained do not lend themselves for further implementation in analytical form. To overcome this difficulty, a non-Gaussian probability density function can be constructed from a few Gaussian sections with different mean values and standard deviations. Using such a piecewise Gaussian model for analytical derivations is no more complicated than using the Gaussian model. It is simply necessary to apply the classic Gaussian equation several times. An example of a skewed probability density function of the micro-surface of an asphalt concrete highway measured by a laser scanning system was adequately approximated by the tetra-Gaussian model consisting of four Gaussian sections.
Keywords: vehicle-road interaction; random micro-surface; probability density function; non-Gaussian; skewness; kurtosis.
Development and Vvalidation of an off-road rigid ring truck tyre model
by Zeinab El-Sayegh, Moustafa El-Gindy, Inge Johanson, Fredrik Oijer
Abstract: A rigid ring tyre model is developed using Matlab/Simulink to predict the in-plane and out-of-plane rigid tyre model characteristics of a truck tyre running over different terrains. The in-plane and out-of-plane tyre characteristics include traction, cornering and vertical stiffness. The terrains used include hard surface, flooded surface, snow, and several soils, such as dry and moist sand. The Matlab/Simulink tyre model is validated against previously computed and published tyre-terrain interaction results performed using an advanced simulation technique. The rigid ring tyre model is further implemented into a full vehicle model to evaluate the full vehicle response under several operating conditions.
Keywords: rigid ring tyre model; Matlab/Simulink; off-road; tyre-terrain interaction; traction; cornering; vertical stiffness.
An investigation of active safety control strategies for improving the lateral stability of car-trailer systems
by Lin Zhao, Yuping He
Abstract: This paper presents an evaluation of control strategies for improving the lateral stability of car-trailer systems. A linear stability analysis method is proposed for the evaluation. The strategies include active trailer differential braking, active trailer steering, and variable geometry approach. A linear three degrees of freedom (3-DOF) yaw-plane car-trailer model is generated for the controllers design, and a nonlinear 21-DOF yaw-roll car-trailer model is developed in CarSim to validate the stability control strategies by means of numerical simulations. To determine the stable motion boundary, eigenvalue analysis is conducted for identifying the vehicle critical speed. The linear quadratic regulator technique is applied to the design of controllers for active trailer braking, active trailer steering, and variable geometry strategies. It is revealed that the active trailer braking strategy is feasible and effective for improving the lateral stability of car-trailer systems. Simulation results demonstrate the effectiveness of the linear stability analysis method.
Keywords: car-trailer systems; active trailer braking; active trailer steering; variable geometry approach; linear quadric regulator; eigenvalue analysis; non-conservative forces; self-excited vibration; forced vibration.
Vehicle Centre of Mass, Roll-Centre and Pitch-Centre Height Estimation
by Theunis Botha, Schalk Els
Abstract: The location of a vehicle’s centre of mass is an important parameter as it has a determining effect on the dynamics of a vehicle. The height of the vehicle centre of mass from the roll and pitch centres have a large influence on the load transfer which occurs between wheels during braking and cornering manoeuvres. These vehicle parameters can vary significantly especially on off-road vehicles due to the large differences in laden and un-laden weight. This paper proposes an algorithm where suspension forces and inertial parameters are estimated in real time using inexpensive sensor measurements and an Unscented Kalman Filter. The algorithm is experimentally validated on an off-road vehicle performing various manoeuvres and driving over different terrains. The real time estimation of these parameters could contribute significantly to improving vehicle safety and control.
Keywords: Centre of gravity estimation, suspension force estimation, roll centre height
Development of a rolling truck tyre model using an automatic model regeneration algorithm
by Shahram Shokouhfar, Subhash Rakheja, Moustafa El-Gindy
Abstract: A three-dimensional finite element model of a rolling radial-ply truck tyre is developed to predict its vertical and cornering properties at relatively high speeds. The model includes a detailed representation of the tyre complex geometry and multi-layered composite structure including the carcass and belt plies, bead fillers and tread. LS-DYNA, a nonlinear finite element code, is used as the simulation tool. An algorithm is developed for efficient formulation of the model for parametric analyses. The validity of the proposed tyre model is demonstrated by comparing the predicted load-deflection, cornering and free vertical vibration characteristics with the reported experimental data. The simulation results revealed robust behaviour of the tyre model up to rolling speeds of 100 km/h. The verified tyre model is subsequently employed to study the influences of various operating parameters, namely, the inflation pressure, vertical load, rolling speed and road friction on the tyre vertical and cornering properties.
Keywords: rolling truck tyre models; multi-layered tyre structure; vertical tyre properties; cornering properties; parametric studies; finite element method; FEM; LS-DYNA; automatic model regeneration; truck tyres; tyre modelling; radial-ply tyres; carcass plies; belt plies; bead fillers; tyre tread; simulation; rolling speed; load deflection; free vertical vibration; tyre inflation pressure; vertical load; road friction; radial tyres.