Assessment of a semi-Hertzian method for determination of wheel–rail contact patch

Wheel–rail contact calculations are essential for simulating railway vehicle dynamic behavior. Currently, these simulations usually use the Hertz contact theory to calculate normal forces and Kalker's ‘FASTSIM’ program to evaluate tangential stresses. Since 1996, new methods called semi-Hertzian have appeared: 5 Kik, W. and Piotrowski, J. A fast approximate method to calculate normal load at contact between wheel and rail and creep forces during rolling. Paper presented at the 2nd Mini-conference on Contact Mechanics and Wear of Rail/Wheel Systems. July29–31, Budapest.  [Google Scholar] 7 Ayasse, J. B., Chollet, H. and Maupu, J. L. 2000. Paramètres caractéristiques du contact roue-rail. Rapport de Recherche INRETS n225, ISSN 0768–9756 (in French) [Google Scholar] (STRIPES). These methods attempt to estimate the non-elliptical contact patches with a discrete extension of the Hertz theory. As a continuation of 2 Ayasse, J. B and Chollet, H. 2005. Determination of the wheel–rail contact patch in semi-Hertzian conditions. Vehicle System Dynamics, 43(3) [Google Scholar], a validation of the STRIPES method for normal problem computing on three test cases is proposed in this article. The test cases do not fulfill the hypothesis required for the Hertz theory. Then, the Kalker's FASTSIM algorithm is adapted to STRIPES patch calculus to perform tangential forces computation. This adaptation is assessed using Kalker's CONTACT algorithm.     

PantoCat statement of method

The pantograph–catenary dynamic interaction analysis program (PantoCat) addresses the need for a dynamic analysis code able to analyse models of the complete overhead energy collecting systems that include all mechanical details of the pantographs and the complete topology and structural details of the catenary. PantoCat is a code based on the finite element method, for the catenary, and multibody dynamics methods, for the pantograph, integrated via a co-simulation procedure. A contact model based on a penalty formulation is selected to represent the pantograph–catenary interaction. PantoCat enables models of catenaries with multiple sections, including their overlap, the operation of multiple pantographs and the use of any complex loading of the catenary or pantograph mechanical elements including aerodynamic effects. The models of the pantograph and catenary are fully spatial being simulated in tangential or curved tracks, with or without irregularities and perturbations. User-friendly interfaces facilitate the construction of the models while the post-processing facilities provide all quantities of interest of the system response according to the norms and industrial requirements.     

Incorporating insights from signal optimization into reservation-based intersection controls

Reservation-based intersection control for autonomous vehicles has the potential to make greater use of intersection capacity. Indeed, previous studies on the first-come-first-served (FCFS) policy (which prioritizes vehicles by order of their reservation request) have shown improvements over optimized signals. However, in certain situations, such as asymmetric intersections, FCFS easily performs worse than signals. To address this issue, we propose two new reservation policies, WEIGHTED and PHASED. WEIGHTED weights vehicle delay by signal timings, and PHASED simulates a signal but allows red phase turning movements that will not cause a collision. We test these policies on a city network and an arterial bottleneck intersection subnetwork and show that PHASED performs better than WEIGHTED in some scenarios, and vice versa. Furthermore, we show that using a combination of PHASED and WEIGHTED can perform better than using either one alone for the entire network. Results show that these policies provide effective and easily implemented alternatives to FCFS for reservations.     

Development of active front wheel steering control system keeping stable region in driving phase diagram

This paper presents a new active steering control system based on driving phase diagram (β _fr ?δ _f diagram). In order to make state variables to follow those of nominal vehicle model that was developed under no consideration of disturbance, Quadratic Programming Problem (QPP) is formulated, where time varying objective function minimizes the differences between nominal and actual parameters. The steering characteristic in active steering control system changes when the vehicle faces disturbance such as crosswind and flat tire, and driver tries to counteract it after recognizing the change. The proposed method defines a stability region on β _fr ?δ _f diagram. In order to make β _fr and δ _f remain in the stability region, a new model predictive controller is proposed. While conventional controllers are restrictive to satisfy the β _fr ?δ _f diagram based stability condition, the proposed controller ensures solution space and also plays a direct role to minimize the evaluation function in the constrained optimal control problem.     

Gain scheduled linear quadratic tracking system tuned optimally by covariance matrix adaption evolutionary strategy for automotive engine coldstart control

In this paper, a gain scheduled linear quadratic tracking system (LQTS) tuned optimally by an evolutionary strategy (ES) is devised to reduce the total tailpipe hydrocarbon (HC) emissions of an automotive engine over the coldstart period. As the engine’s behavior during coldstart operations is nonlinear, the system dynamics is clearly analyzed and represented by a number of separate linear models generated based on a coldstart model verified by experimental data. An independent LQTS is then implemented for each of these linear models. In this way, several control laws are created, and the corresponding gains are calculated for each of the independent control laws. ES is then used to tune the adjustable parameters of LQTSs to calculate the control inputs, namely air/fuel ratio (AFR) and spark timing (Δ), such that the resulting exhaust gas temperature (T _exh) and engine-out HC emissions (HC _raw) be close to a set of optimum profiles. This enables the controller reduce the cumulative tailpipe hydrocarbon emissions (HC _cum) to the highest possible extent. To demonstrate the acceptable performance of the proposed controller, an optimal controller derived from the Pontryagin’s minimum principle (PMP) is also taken into account. Based on the results of the conducted comparative study, it is shown that the proposed control technique has a very good performance, and also, can be easily used for real-time applications, as it consumes a remarkably trivial computational time for calculating the controlling commands.     

System power loss optimization of electric vehicle driven by front and rear induction motors

Power loss optimization aiming at the high-efficiency drive of front-and-rear-induction-motor-drive electric vehicle (FRIMDEV) as an effective way to improve energy efficiency and extend driving range is of high importance. Different from the traditional look-up table method of motor efficiency, power loss optimization of the dual- motor system based on the loss mechanism of induction motor (IM) is proposed. First of all, based on the power loss characteristic of FRIMDEV from battery to wheels, the torque distribution optimization model aiming at the minimum system power loss is put forward. Secondly, referring to d-q axis equivalent model of IM, the power loss functions of the dual-IM system are modeled. Then, the optimal torque distribution coefficient (β _o) between the two IMs is derived, and the theoretical switching condition (T _sw) between the single- and dual-motor-drive mode (SMDM and DMDM) is confirmed. Finally, a dual-motor test platform is developed. The derived torque distribution strategy is verified. The influence of motor temperature on β _o and T _sw are tested, and the correction models based on temperature difference are proposed. Based on the system power loss analysis, it can be confirmed that, under low load conditions, the SMDM takes priority over the DMDM, and the controller of the idling motor should be shut down to avoid the additional excitation loss. While under middle to high load conditions, even torque distribution (β _o = 0.5) is preferred if the temperature difference between the two IMs is small; otherwise, β _o should be corrected based on dual-motor temperatures. The theoretical T _sw derived without dealing with temperature difference is a function only of motor speed, while temperature difference correction of it should be conducted in actual operations based on motor resistance changing with temperature.