Study On Theory Of Onboard Measurement Of Wheel And Rail Forces

The measure of wheel/rail loads has great significance on vehicle dynamics, derailment mechanism, the theory of wheel/rail contact and the vehicle security monitor. Railway transportation is now developing towards high speed, heavy-loading, massive carry and high density. It also demands high precision and speed on the measure of wheel/rail loads. The instrumented wheelset is now the most direct and most precise technology of measuring the wheel/rail loads, which takes the wheel as the detecting sensor of wheel/rail loads and realizes continuous measurement of wheel/rail loads by measuring the strain on several places on the wheel plate. During the running of the vehicle, the wheel/rail loads is non-stationary because of the track irregularity and the plate strain which is produced by the wheel/rail loads is modulated by the wheel rolling angle. The accurance of the instrumented wheelset is influenced by the inequality of the wheel, the technics of sticking the strain gagues, rotate speed of the wheel, and the change of position of the wheel/rail contact point , and the measuring theory and data processing method of the wheel plate strain instrumented wheelset need further study.The paper looks back on the develop course of instrumented wheelset as well as its developing status domestic and oversea, and analyzes the stress distribution of wheelset plate under the wheel/rail loads, and proposes the measuring method of instrumented wheelset which can eliminates the influence of the wheel rotation, and studies the influence on the measuring precision of the wheel/rail contact point and the data processing method of instrumented wheelset. The detail and achievement is as below:1,proposing the measuring model of wheel/rail loads Through decades of development, the technology of instrumented wheelset has great use in vehicle dynamics experiment, but still has many problems in the continuous detecting of the wheel/rail loads. Nowadays, the continuous instrumented wheelset technology demands the plate strain produced by the wheel horizontal and vertical force follows the sine and cosine distribution after designing the measuring bridge. As it demands high wheel equality and technics of sticking the strain gages, however, the fact is most regions of the wheelset plates cannot meet the demands, and the high-order harmonic in the electrical bridge output could bring more measuring error. Another problem in instrumented wheelset is that it does not consider the influence on the measuring precision from the change of wheel/rail contact point. During the running of the vehicle, the contacting point between the wheelset and the track is changing near the rolling circle, especially in the pass of curve, switch and serpentine movement in which the contacting point is far away from the rolling circle. Nowadays, almost all the instrumented home dose not takes the change of contact point into consideration. The calibrating test and data processing all have the hypothesis that the contact point is on the rolling circle. So, as a matter of fact, it has great error.This paper analyzes the distribution rule of the wheelset plate strain influenced by the horizontal and vertical force and bending moment produced by the change of contact point based on the finite element analysis and experiment. Then it adopts several strain gages combination on the same radius to eliminate the high-order harmonic and studies the relationship between the order if harmonic component which needs to be eliminated and the amount of the electrical bridge as well as the phase difference among each electrical bridge which bring theoretical foundation to the improving of the measuring precision of the instrumented wheelset. On such basis, it sets up anon-linear equation sets of wheelset plate strain, wheel/rail loads and contact point.The paper studies the direct solution of the non-linear equation sets of the measuring model. As there is no analytical solution, so the only solution is to use Newton-Simpson iteration. This method needs to choose an initial value which influence the computing speed and precision and can lead to no convergence, and can has difficulty in error analyzing. This paper reduces the non-linear equation group reasonably, deduces the analytical solution and discusses the method of eliminating invalid solution.This paper again studies the method of reducing the non-linear equation group to linear equation group. By using principal component analysis, it gets the subspace of plate strain signal when each loads separately influence on it and through projection of measuring signal to each subspace, it sets up the linear equation group. Then we can choose reasonable strain gages' location according to the theory of stability of linear equation group and thus reduces the influence of the error of the strain measuring on the calculation of wheel/rail loads.As a matter of fact that equality of wheelset and plate gages' location can not meet the demand, this paper proposes new solution. Firstly, it confirm the horizontal and vertical force factor according to each steering angle and contact point location through the calibrating test, and then gets the best wheel rotated angle and contact point through Genetic Algorithm, finally get the horizontal and vertical force factor by checking the table and sets up the linear equation group of plate strain and wheel/rail loads on several radius. This method can effectively reduce the cost of the exploitation of instrumented wheelset as well as the researching time.2,When wheel/rail contact point location changes, the vertical force can bring a accessory bending moment which bring accessory strain on the wheelset plate and this is always a source of error of instrumented wheelset. Comparing to the strain produced by the horizontal and vertical force, the strain is lower which is produced by accessory bending moment. This paper proposes the detecting method of contact point based on the studying on the distribution rule of plate strain brought by the bending moment.Although the wheel/rail loads is the non-stationary signal, it is quite stationary in very short timestamp. This paper did the time-frequency analysis on the experiment data of rolling and vibration test rig and finally finds that it is feasible to use the short-time Fourier. When in the pure rolling, the wheelset plate strain is single frequency harmonic signal, and becomes modulation signal when it is added by track spectrum excitation. When in the serpentine movement, the wheelset plate strain is the overlap of several modulation signals. Analyzing the time-frequency characteristic of wheel plate under different conditions help to filter or reduce noise interference through using reasonable method of signal processing according to the time-frequency characteristic.