Research On Key Technology Of Wheel/Rail Contact Status Measurment

The measure of wheel/rail loads is an important process of vehicle dynamics theory and practice, which has great significance on vehicle dynamics, derailment mechanism, wheel/rail contact theory and vehicle security measurement. As China’s railway transportation develops towards high speed and overloading, it asks higher precision and speed on the measure of wheel/rail loads. The instrumented wheelset, which is now the most direct and the most precise technology of the wheel/rail force measuring, takes the wheel as the detecting sensor of wheel/rail force and realizes continuous measurement of wheel/rail loads by measuring the strain on particular position of the wheel plate. As the vehicle running, the strain is produced by the wheel/rail force which is changing and non-stationary, and then modulated by the wheel steering angle. And therefore, there are a number of factors that can affect the accuracy of instrumented wheelset, such as:strain gauges sticking technics, wheel uniformity, vehicle speed (wheel rotate speed), position change of the wheel/rail contact point and some other interference factors. So it need further study on both measuring theory and data processing method of the wheel plate strain instrumented wheelset.This thesis reviewed the development history of instrumented wheelset and the international and domestic development present situation, analyzed the stress distribution of plate and axle under wheel/rail load, and put forward the general method of instrumented wheelset measurement and corresponding calculation methods, and designed the instrumented wheelset based on precision time measurement technique and wireless data transmission technology. The content and the results are as follows:1. Put forward the wheel/rail force measurement model regarding the whole wheelset as the detecting object.The instrumented wheelset widely used in the vehicle dynamics test still exists some places deficient, although the development of several decades. The current national standard scheme is based on two premise:1. The bridge radius contains only first harmonic output can be found.2. The bridge radius with no interferences between lateral force and vertical force can be found. For now, most wheelset especially straight plate can hardly achieve. In addition, national standard regards the wheelset’s rolling as nominal rolling circle, without considering that the position change of contact point can act on the output signal, which leads to lager measurement error. Based on the simulation analysis, this thesis analyzed the distribution regularity of strain caused by lateral force, vertical force and contact point position, eliminated the interference harmonic by several strain pieces arrangement in the position of the same radius on the plate and the same section of the axle. It is easy to realize for the wheel regarded as measuring object, which theoretically supports all types of instrumented wheelset, but not for straight plate. Also, it should be taken into consideration the installation of a specific type wheel.2. Put forward the estimation method of wheel/rail contact force based on modern signal theory.According to the experience, in any short time when vehicle is driving normally, there is certain continuity in this time on the value of state variable including lateral force, vertical force, contact point position and wheelset rotation angle which result in the output change of wheelset strain bridge. In other words, once the sampling time is short enough, it can be regarded the current state as the tiny change based on the state a moment before, and then it can be exported the change regularity and the recursion relation between lateral force, vertical force, contact point position and wheelset rotation angleThe thesis analyzed the characteristic of wheel/rail force signalnoise modulated by wheelset rolling, researched the time recursive discrete model of instrumented wheelset measuring system, and discussed the applicability of particle filter algorithm on various conditions.3^Designed the instrumented wheelsets based on precision time measurement technique and wireless data transmission technology.The strain measuring based on precise time measurement is different from Wheatstone bridge. Measuring the precision capacitors elapsed time of charge and discharge in order to calculate the strain value, has the characteristics of high stability, small gain error and low power consumption. This thesis was considerate the actual conditions in instrumented wheelset applications, researched the wireless strain acquisition system and confirmed it by measuring test.