Mirko Rinchi

A railway vehicle multibody model for real-time applications

Hardware in the loop (HIL) techniques are widely used for fast prototyping of control systems, electronic and mechatronic devices. In the railway field, several mechatronic on board subsystems are often tested and calibrated following the HIL approach. The accuracy of HIL tests depends on how the simulated virtual environment approximates the physical conditions. As the computational power available on real-time hardware grows, the demand for more complex and realistic models of railway vehicles for real-time application increases. In past research activities, the authors worked on the implementation of simplified real-time models for several applications and in particular for an HIL test rig devoted to the type approval of wheel slide protection systems. The activity has then been focused on the development of a three-dimensional model of the dynamics of a railway vehicle for more complex applications. The paper summarises the features and the results of the study.

Odometric estimation for automatic train protection and control systems

The paper summarises the main features concerning the definition of an efficient odometry algorithm to be used in modern automatic train protection and control (ATP/ATC) systems. The availability of a reliable speed and travelled distance estimation is essential for the efficiency and the safety of the whole system. The first essential step in odometric subsystem design is the choice of the sensors, whose output signals will be used for velocity estimation. Then a suitable procedure fusing sensor signals has to be defined as a function of number and type of sensors and accuracy and safety targets. In the paper, the main features of an innovative solution will be summarised and its performance will be presented, in terms of precision in speed and travelled distance estimation.

A TEST RIG FOR EVALUATING ODOMETRY ALGORITHMS

Odometry is a fundamental task to perform in modern systems for monitoring and control of trains. However, odometry becomes difficult to perform when wheel/rail adhesion is not good and the train is braking or accelerating. To improve the performance of odometry systems, the use of sensors in addition to axle-mounted encoder-type sensors (such as longitudinal accelerometers and radar Doppler sensors) is being tested on prototype onboard systems. This paper describes work being conducted by researchers of TRENITALIA S.p.A. and the Section of Applied Mechanics of the University of Florence for the design and realization of a test rig for odometry techniques.

Design of a Semi Active Differential to Improve the Vehicle Dynamics

Suppressing or limiting the differential action of the differential mechanism is the mostly adopted technique to avoid the skidding of a driving wheel of a vehicle riding on a poorly adherent surface. The devices carrying out this function unbalance the traction force distribution in the differential, generating a yaw torque acting on the vehicle as a secondary effect. If the unbalancing action is electronically controlled, this yaw torque can be used to affect the attitude of car as a torque vectoring technique.In this paper, a purpose built differential is presented and its technical features are highlighted, including the electrohydraulic actuation. Moreover, its torque vectoring capabilities are discussed, basing on the numerical simulation campaign performed deploying this device in a 7 DOFs model of a race car with low ground effect.The results of these simulations are compared with the behavior of the same vehicle equipped with a common passive locking differential, to show that the proposed one and its control logic (which relies on only measurable inputs) are able of improving the handling of the vehicle, in terms of both vehicle stability and linearity with the driver’s inputs. Therefore, this system could be considered as a completion of the common ESC (“Electronic Stability Control) systems to control the vehicle attitude when using the brake system is an inefficient solution.Copyright

Analysis of Braking Performance for the Definition of Emergency Braking Intervention in ATP Systems

This paper describes how a traffic management system is generally based on a set of supervision curves relating the permitted velocity of the train to the running distance, in order to ensure the respect of speed restrictions on the line by intervention of an emergency braking in case of train velocity exceeding the permitted one. The basic braking model defines a deceleration profile, which represents the train nominal braking performance, used to determine the stopping distance and to compare it with the available distance. This deceleration profile value has to be reduced using properly defined safety coefficients. The paper describes the method that allows one to calculate the safety coefficient as a function of the safety target (in terms of probability of failure). The method is based on the braking performance probability distribution estimation, expressed as the ratio between the real and the nominal deceleration. This study permits one to evaluate the probability that the real deceleration is smaller than the one used in the basic braking model and then that the real stopping distance is longer than the one calculated by the braking model. This model can then be used to tune the value of the safety margin in order to obtain a certain probability of system failure. The numerical procedure used to simulate the braking performance is based on the Monte Carlo method, which is a method for iteratively evaluating a deterministic model using sets of random numbers as inputs. This method is often used when the model is complex, nonlinear, or involves several parameters.

Optimization of Special Freight Wagons with Small Wheel Diameter

This paper describes how better integration and interoperability between rail and road transportation is a key factor in reducing pollution and increase railway freight traffic. Development of special freight wagons like “SAADKMS” for the transportation of trucks by railway is a successful solution that is meeting an increasing consensus and popularity among many European countries. In order to accelerate truck loading on wagons and reduce the limitation of normal clearance (structure/vehicle/loading gauges) it is necessary to reduce the wheel diameter as much as possible. This is not a drawback-free solution since an excessive reduction of wheel diameter involves many troubles concerning the stability of the vehicle, maximum axle load, wear of bearings and rolling surfaces of rails and axles. Also designing the braking system is very complicated because the reduced number of encumbrances available makes the placement of internal disks on the axles difficult. In order to solve these problems a very original solution concerning wheelset, wheel profiles and more general bogie design have been applied in the development of “SAADKMS” freight wagons so the resulting vehicle is very different from the conventional one. As a matter of fact, many past experiences and know-how for conventional freight wagons are not applicable for this kind of application, so numerical simulations are very important to deeply understand the behavior of the system and propose criteria for further optimization. The authors of this paper have developed models on commercial multibody software in order to simulate the behavior of the “SAADKMS” freight wagon in different conditions (stability, steering performances). Also important results such as position of the contact point or wear-number are shown to be useful parameters for further optimization of the rolling surface profiles.

ACTIVE CONTACT FORCE CONTROL OF PANTOGRAPH

In the past 52 years, many researchers have investigated the problem of optimum current pick-up in high-speed running railways. There is the requirement of maintaining almost constant contact force between pantograph and catenary, thus avoiding losses of contact involving mechanical, electric, and electromagnetic negative consequences, such as excessive wear, insufficient current pick-up, and high electromagnetic interference. One of the proposed solutions to this problem is to design servo-actuated pantographs and regulate relevant variables, such as the contact force, during operation. Since 1993, researchers of the University of Florence have proposed solutions for the placement of sensors and actuators on existing pantographs for high-speed operations as well as their control with the purpose of regulating the contact force at a desired optimum level. After the development of simulation models to evaluate performance and robustness of some control techniques for a servoactuated pantograph, an experimental campaign is currently being conducted on a symmetric pantograph mounted on a train at rest interacting with a standard 3 kV direct-current overhead line. This paper describes simulation and experimental results obtained with the servoactuated pantograph.