Nam-Jin Lee

Hardware-in-the-Loop Simulation for a Wheel Slide Protection System of a Railway Train

Abstract A wheel slide protection (WSP) system of a railway train has the role of reducing excessive wheel slide from brake applications in situations where wheel/rail adhesion is temporarily impaired. The mechanism of the WSP is complex and is related to highly nonlinear dynamics of the train. Hardware-in-the-loop simulation (HILS) for the WSP system can test various dangerous braking conditions which are not possible in actual train tests, and help to find appropriate parameters of the WSP system. This paper presents a HILS unit for the WSP system, which is composed of an actual WSP unit, two actual dump valves, a dSPACE module, and a personal computer with Linux operating system. The dSPACE module simulates railway train dynamics in real-time, which includes dynamic models of wheelsets, bogies, a carbody, and a mechanical brake, and also a dynamic model for creep force generation in wheel/rail contacts. The validity of the HILS system for WSP control is demonstrated by ways of off-line simulation studies and experimental tests using the HILS unit for the Korean tilting train, Hanvit 200.

The Effect of a Variable Disc Pad Friction Coefficient for the Mechanical Brake System of a Railway Vehicle

A brake hardware-in-the-loop simulation (HILS) system for a railway vehicle is widely applied to estimate and validate braking performance in research studies and field tests. When we develop a simulation model for a full vehicle system, the characteristics of all components are generally properly simplified based on the understanding of each component’s purpose and interaction with other components. The friction coefficient between the brake disc and the pad used in simulations has been conventionally considered constant, and the effect of a variable friction coefficient is ignored with the assumption that the variability affects the performance of the vehicle braking very little. However, the friction coefficient of a disc pad changes significantly within a range due to environmental conditions, and thus, the friction coefficient can affect the performance of the brakes considerably, especially on the wheel slide. In this paper, we apply a variable friction coefficient and analyzed the effects of the variable friction coefficient on a mechanical brake system of a railway vehicle. We introduce a mathematical formula for the variable friction coefficient in which the variable friction is represented by two variables and five parameters. The proposed formula is applied to real-time simulations using a brake HILS system, and the effectiveness of the formula is verified experimentally by testing the mechanical braking performance of the brake HILS system.

Smooth tilting motion control of a train using two hydraulic actuators

A hydraulic actuation system for a tilting train is usually composed of independent actuators to remove position errors due to bulk modulus of the hydraulic system. For the hydraulic control system using two independent cylinders, this paper presents the modeling of the hydraulic system, control logic, and simulation results of the hydraulic control system. Simulation results for motion responses of two cylinders using position commands calculated from tilting angles show the validity of the proposed hydraulic two-actuator system.

Experimental study on dynamic load measurement of a tilting mechanism of a railway vehicle using two hydraulic cylinders

A tilting train is primarily designed to achieve increased speed in a curved section without causing discomfort to passengers. Ensuring the safety of the tilting control system is one of the most important factors in such a train. This paper presents the development of a hydraulic tilting system that can measure the force in real time to find the cause of overcurrent occurring often in an actuator of a Korean tilting train. To smoothly realize tilting motion of the Korean tiling train using hydraulic actuators, the developed hydraulic tilting mechanism was designed such that synchronization control of two hydraulic cylinders installed in opposite directions was possible; furthermore, a cooling system was developed to ensure a test environment with an appropriate temperature. The actual force acting on the two hydraulic cylinders was measured and analyzed for various tilting speed of the Korean tilting train. The experimental results show that the hydraulic tilting actuator system developed for the Korean tilting train is valid. Furthermore, it is shown that two actuator loads are detected successfully acting on the hydraulic tilting system.

Wheel slide protection control using a command map and Smith predictor for the pneumatic brake system of a railway vehicle

ABSTRACT In railway vehicles, excessive sliding or wheel locking can occur while braking because of a temporarily degraded adhesion between the wheel and the rail caused by the contaminated or wet surface of the rail. It can damage the wheel tread and affect the performance of the brake system and the safety of the railway vehicle. To safeguard the wheelset from these phenomena, almost all railway vehicles are equipped with wheel slide protection (WSP) systems. In this study, a new WSP algorithm is proposed. The features of the proposed algorithm are the use of the target sliding speed, the determination of a command for WSP valves using command maps, and compensation for the time delay in pneumatic brake systems using the Smith predictor. The proposed WSP algorithm was verified using experiments with a hardware-in-the-loop simulation system including the hardware of the pneumatic brake system.

A control algorithm for WSP valves in a pneumatic brake system of a railway vehicle

In a railway vehicle, a WSP valve is a key component for the safety of the vehicle and the supplementation of brake operation in impaired track conditions. The WSP controller detects sliding of each wheelset and reduces pneumatic brake force of the sliding wheelset. Due to the working of the WSP system, the excessive sliding or a locking of wheels is prevented. On the WSP system operating, the WSP valve shall reduce an inner pressure of the brake cylinder sufficiently. But the WSP valve has its own time delay and response time because of the characteristics of the electro-magnet in the valve and air flow of a brake cylinder through pneumatic valves. Therefore it is necessary to develop a mathematical model to simulate and to improve the control algorithm of the WSP system with the valve model. In this study, the mathematical model of the WSP valve is to be built and control algorithm for WSP valve is to be introduced, and then the performance of the algorithm is to be verified through HILS for a pneumatic brake system.

Brake Force simulation of a High Speed Train Using a Dynamic Model

The brake system of a high speed train has a crucial role for the safety of the train. To develop a safe brake system of the high speed train, it is necessary to understand the braking principle and phenomena of the total brake system and its subsystems. In this paper, we have suggested a mathematical model which includes car dynamics, interactions between cars, adhesive forces, brake blending algorithm, and the dynamics of each brake devices. Also, we have proposed a ready-time compensation algorithm of eddy-current brake system and a brake control logic on electric-pneumatic blending. A simulation study has shown the proposed models and algorithms are effective on the braking of the train.

Creepage Model Analysis for a Tilting Train

Traction and braking of trains are due to the rolling contact of the wheel on the rail, and the rolling contact is fundamental to an understanding of the behavior of the railroad system. The way in which the forces are transmitted in the rolling contact is complex and highly nonlinear. This paper describes a rolling contact theory, a creepage model between wheel and rail, and a dynamic model of the tilting train Hanvit-200. The validity of the model is verified through simulation study using Simulink.

Braking control for wheel-slide protection using HILS

During the braking of a railway vehicle, excessive slide between wheel and rail can occur due to temporarily degraded adhesion by wet or contaminated rail surface. This can damage the wheel tread, and the damaged wheel affects seriously the safety and ride comfort of the railway vehicle. To prevent from excessive slide between wheel and rail, braking control using wheel-slide protection (WSP) logic is required. In this paper, we present an effective WSP logic to maximize the usage of adhesion force, and demonstrate experimentally the validity of it using a brake HILS (hardware-in-the-loop simulation) system developed in our laboratory.