| Problems of high wear rate of wheels and low service life of tread trimmers had occurred on intercity EMUs with a designed speed of 200 km/h,when operating on an intercity line in China,which worsened the wheel-rail profile matching,reduced the stability of vehicle operation and greatly increased the operation cost.In this thesis,through the field monitoring tests and numerical simulations,the wear characteristic of wheels of the above mentioned intercity EMUs was quantified.A wheel wear model considering the action of tread trimmer-wheel and wheel-rail was developed and used to systematically investigate the effect of the tread trimmer on the wheel wear.The optimum working scheme of the tread trimmer was determined under different stopping station spacing.The main work and conclusions are as follows.First of all,the development processes and related research results of the tread trimmer were investigated,involving materials,technologies,mechanics,performance,using and side effects in this thesis.Existing wheel wear prediction models and related researches were reviewed.It was pointed out that working scheme of the tread trimmer needs to be optimized and the existing wheel wear prediction model did not take into account the lack of wear caused by the tread trimmer.An intercity EMU(the first car to the fourth car used LMA wheel profile and the fifth car to the eighth car used LM wheel profile)was investigated in the field tests.The high hardness tread trimmers consecutively operating in the high-pressure way was used during the first reprofiling period.The low hardness tread trimmers intermittently operating in the low-pressure way was used during the second re-profiling period.It is found in the analysis of wheel wear characteristics that there is no essential difference in the wear performance of LM and LMA wheel profiles under the same working scheme of the tread trimmer.However,different working schemes of the tread trimmer have great influence on wheel wear.Specifically,the wheel wear rate in the second re-profiling period is significantly lower than the first reprofiling period.The average wear rates of LM and LMA profiles at wheel nominal rolling circle(NRC)decrease from 0.200 mm and 0.216 mm per 10,000 km to 0.101 mm and 0.079 mm per 10,000 km,respectively.Based on the monitoring results of wheel wear,an estimation method for wheel wear rate was put forward to quantify the contributions of tread trimmer-wheel and wheel-rail contact.It is found that the wear rates of the LM wheel’s NRC caused by tread trimmer-wheel contact are 0.122 mm and 0.023 mm per 10,000 km in the first and second re-profiling period,respectively,and the wear rate caused by wheel-rail contact is0.078 mm per 10,000 km.This means that the main reasons for the high wheel wear rate of the above-mentioned intercity EMU are the frequent high-pressure action and the excessive material hardness of tread trimmers.In order to further investigate the effects of tread trimmers on wheel profile evolution,the wheel wear model which based on the vehicle system dynamics model was developed.The wear model contained tread trimmer-wheel contact model and the material wear model,which can consider the tread trimmer-wheel action and wheel-rail action.The wheel wear caused by the tread trimmer-wheel contact and wheel profile evolution were simulated using the wear model during the first re-profiling period.The results show that the wheel wear caused by the tread trimmer from simulation agrees with the measurement,showing the lowest wear distribution near NRC and the highest on both sides.Wheel profiles from simulation agree well with the measured average wheel profiles in the range of-50～52 mm.For instance,the wear rates of measurement and simulation at wheel NRC are 0.200 mm and 0.209 mm per10,000 km,respectively,with a difference of only 4.50%.It shows that the established model can accurately predict the wheel wear performance of intercity EMUs.Based on the wheel wear model,the influences of working pressure,working mode and material hardness of tread trimmer on wheel wear were systematically investigated.Considering the change of working pressure in the range of 0-0.7 MPa,when the pressure of tread trimmers is applied in a uniform way,there is a non-contact area around the NRC between the contact surfaces of the tread trimmer and the wheel under low working pressure.The range of the non-contact area gradually decreases as the working pressure increases,and disappears completely when the pressure reaches 0.5 MPa.The non-contact area also decreases as the working pressure increases when the pressure of tread trimmers is applied in the mode of left deflection and right deflection.Therefore,for wheel wear caused by the tread trimmer,there is a minimum value near the NRC and a peak value at both ends of NRC.The wear distribution shows a hump shape,and the maximum wear increases with an increase of working pressure,which increases the depth of the hump.The influences of continuous and intermittent operating modes on wheel wear are compared using working pressure of 0.3 MPa.The tread trimmer works for 20 s and does not work for 5 s,10 s,15 s,20 s and 25 s periodically under intermittent operating modes.It is found that the wheel wear caused by the tread trimmers decreases significantly with an increase of non-working time,and the wear under the non-working time of 25 s is 48.99% lower than that of the continuous operation.According to the high and low hardness tread trimmers used in the field,the effect of the material hardness on wheel wear is analyzed by using the corresponding wear rates which are determined by field monitoring tests.It is found that the wheel wear caused by the low hardness tread trimmer is 56.59% lower than that of high hardness under the same working pressure.When the wheel wear caused by tread trimmers decreases,the dominant factor affecting wheel profile evolution is from tread trimmer-wheel contact to the wheel-rail contact.The change of dominant factors has a significant impact on the wheel profile evolution.Considering the difference of station spacing on different lines,the influence of tread trimmers on wheel wear was further investigated under 23.98 km,40 km and 60 km stopping station spacing.With an increase of the stopping station spacing,the contact gap between the tread trimmer and the wheel surface increases,and the working pressure of the tread trimmer should be increased to restrain the development of the gap.Therefore,it is suggested to adopt0.30 MPa working pressure at 23.98 km stopping station spacing,adopt 0.49 MPa working pressure at 40 km and 60 km stopping station spacing.From the perspective of the ideal wear rate of wheel,the optimal working schemes of the tread trimmer under 23.98 km,40 km and60 km stopping station spacing are proposed.Ultimately,the main work of the thesis was summarized and a prospect was made. |
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