Advancing high-speed train gearbox durability:enhanced bearing load and contact stress through transition from helical to herringbone gears

High-speed trains typically utilize helical gear transmissions,which significantly impact the bearing load capacity and fatigue service performance of the gearbox bearings.This paper focuses on the gearbox bearings,establishing dynamic models for both helical gear and herringbone gear transmissions in high-speed trains.The modeling particularly emphasizes the precision of the bearings at the gearbox's pinion and gear wheels.Using this model,a comparative analysis is conducted on the bearing loads and contact stresses of the gearbox bearings under uniform-speed operation between the two gear transmissions.The findings reveal that the helical gear transmission generates axial forces leading to severe load imbalance on the bearings at both sides of the large gear,and this imbalance intensifies with the increase in train speed.Consequently,this results in a significant increase in contact stress on the bearings on one side.The adoption of herringbone gear transmission effectively suppresses axial forces,resolving the load imbalance issue and substantially reducing the contact stress on the originally biased side of the bearings.The study demonstrates that employing herringbone gear transmission can significantly enhance the service performance of high-speed train gearbox bearings,thereby extending their service life.

Safety evaluation for railway vehicles using an improved indirect measurement method of wheel–rail forces

The wheel-rail force measurement is of great importance to the condition monitoring and safety evaluation of railway vehicles. In this paper, an improved indirect method for wheel-rail force measurement is proposed to evaluate the running safety of railway vehicles. In this method, the equilibrium equations of a suspended wheelset are derived and the wheel-rail forces are then be obtained from measured suspension and inertia forces. This indirect method avoids structural modifications to the wheelset and is applicable to the long-term operation of railway vehicles. As the wheel-rail lateral forces at two sides of the wheelset are difficult to separate, a new derailment criterion by combined use of wheelset derailment coefficient and wheel unloading ratio is proposed. To illustrate its effectiveness, the indirect method is applied to safety evaluation of rail- way vehicles in different scenarios, such as the cross wind safety of a high-speed train and the safety of a metro vehicle with hunting motions. Then, the feasibility of using this method to identify wheel-rail forces for low-floor light rail vehicles with resilient wheels is discussed. The values identified by this method is compared with that by Simpack simulation for the same low-floor vehicle, which shows a good coincidence between them in the time domain of the wheelset lateral force and the wheel-rail vertical force. In addition, use of the method to determine the high-frequency wheel-rail interaction forces reveals that it is possible to identify the high-frequency wheel-rail forces through the accelerations on the axle box.

Influence of equipment excitation on flexible carbody vibration of EMU

To study the vibration transmission character istics of a flexible carbody and its suspended equipment, a vertical mathematical model of highspeed electric multiple unit was established with equipment excitation considered. And the dynamic unbalance and impact turbulence excita tion from equipment were taken into account in a single stage and twostage vibration isolation system, respectively. Results show that the excitation transferred to carbody increases with suspension stiffness but decreases with the equipment mass increasing; the vibration transmission can be reduced by increasing the equipment mass or reduce the suspension stiffness. To avoid vibration resonance, the dynamic unbalance frequency of equipment should be out of the possible range of the carbody flexible modes, and a small stiffness should be applied to reduce the impact tur bulence. A small stiffness, however, would result in a large movement of the equipment which is limited by the static deflection requirement, while a great stiffness will transfer high frequency vibration. Therefore, a preferred stiffness should make the suspension frequency of equipment a bit greater than the first bending mode of carbody. Additionally, a 3D rigidflexible coupled dynamics model was built to verify the mathematical analysis, and they show good agreements. Results show that a twostage isolation could reduce the excitation transmission and make the vibration of carbody and equipment acceptable.

Factors that associated with TB patient admission rate and TB inpatient service cost: a cross-sectional study in China

Background:China has recently adopted the“TB designated hospital model”to improve the quality of tuberculosis(TB)treatment and patient management.Considering that inpatient service often results in high patient financial burden,and therefore influences patient adherence to treatment,it is critical to better understand the TB patient admission rate and TB inpatient service cost,as well as their influential factors in this new model.Methods:Quantitative and qualitative studies were conducted in two cities,Hanzhong in Shaanxi Province and Zhenjiang in Jiangsu Province,in China.Quantitative data were obtained from a sample survey of 533 TB patients and TB inpatient records from 2010–2012 in six county designated hospitals.Qualitative information was obtained through interviews with key stakeholders(40 key informant interviews,14 focus group discussions)and reviews of health policy documents in study areas.Both univariate and multivariate statistical analyses were applied for the quantitative analysis,and the thematic framework approach was applied for the qualitative analysis.Results:The TB patient admission rates in Zhenjiang and Hanzhong were 54.8 and 55.9%,respectively.Qualitative analyses revealed that financial incentives,misunderstanding of infectious disease control and failure of health insurance regulations were the key factors associated with the admission rates and medical costs.Quantitative analyses found differences in hospitalization rate existed among patients with different health insurance and patients from different counties.Average medical costs for TB inpatients in Jurong and Zhenba were 7,215 CNY and 4,644 CNY,which was higher than the 5,500 CNY and 3,800 CNY limits set by the New Rural Cooperative Medical System.No differences in medical cost or length of stay were found between patients with and without comorbidities in county-level hospitals.Conclusions:TB patient admission rates and inpatient service costs were relatively high.Studies of related factors indicated that a package of interventions,including health education programs,reform of health insurance regulations and improvement of TB treatment guidelines,are urgently required to ensure that TB patients receive appropriate care.