Modeling the Average and Instantaneous Friction Coefficient of a Disc Brake on the Basis of Bench Tests.

Wojciech Sawczuk,Armando Miguel Rilo Cañás,Dariusz Ulbrich,Jakub Kowalczyk

doi:10.3390/ma14164766

Abstract

This article presents the results of tests conducted on the average and instantaneous friction coefficients of railway vehicle disc brakes. The tests were carried out independently of various states of wear on the friction linings and the brake disc. The requirements of the International Union of Railways (UIC) regarding the approval of brake linings for use were taken into account. Based on many years of research using a brake bench to test railway disc brakes, the authors developed multiple regression models for the average friction coefficient and fluctuations (tolerances) in the instantaneous friction coefficient and achieved 870 results. The models proposed three types of variables: the input braking parameters (speed, pressure, and mass to be braked), operational parameters (the wear on the friction linings and the brake disc), and design parameters (perforations in the form of holes on the disc surface). The above two models were validated on the basis of 384 brakes, and in subsequent stages a further evaluation was performed. The coefficients were determined to be, respectively, 0.99 for the model of the average friction coefficient and 0.71 for the model of tolerance (fluctuations) of the instantaneous friction coefficient.

Highlights

Due to the increasing speed of passenger and freight trains, the friction disc brake has become the basic braking device
An analysis of changes in the instantaneous coefficient of friction presented in Figure 4 stated that in some braking combinations, the μa values were lower than the minimum required value of the instantaneous friction coefficient contained in [44]
Based on the research and analysis, the following conclusions can be drawn: The bench tests of the railway friction disc brake showed that, for some braking conditions and degree of wear on the brake components, the friction coefficient dropped and did not meet the requirements of the UIC 541-3 card

Summary

Introduction

Due to the increasing speed of passenger and freight trains, the friction disc brake has become the basic braking device. The main advantage is the constant value of the friction coefficient in the entire braking speed range compared to the classic block brake. Despite the many advantages of this braking system, it is difficult to control the wear on the disc-lining friction pair because the discs are mounted on the axle between the wheels of a wheelset. It is possible to stop a train in any condition, even when there is ice on the contact line, an obstruction on the track, or something in the brake causing a reduction in the friction coefficient [1,2]. For passengers on high-speed trains, fluctuations in the friction coefficient translate into changes in braking deceleration, which can be unpleasant

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