Material property variations and defects of carbon/carbon brake disks monitored by ultrasonic methods

Several ultrasonic techniques were applied to carbon/carbon brake disks for the evaluation of spatial variations in material properties that are attributable to the manufacturing process. In a carbon/carbon brake disk manufactured by a combination of pitch impregnation and vapor infiltration methods, the spatial variation of ultrasonic velocity was measured and found to be consistent with the nonuniform densification behavior in the manufacturing process. Low frequency (e.g. 1–5 MHz) through-transmission scans were used for mapping out the material property inhomogeneity. These results were compared with that obtained by dry-coupling ultrasonics. A good correlation was found between ultrasonic velocity and material density on a set of small blocks cut out of the disk. Pulse-echo C-Scans (10–25 MHz) were used to image near-surface material property anomalies associated with certain steps in the manufacturing process. Ultrasonic velocities in the in-plane directions were affected more by the relative contents of fabric and chopped fiber, and less by the void content.     

无机房电梯的一种平层标识救援方法

某建筑物安装有一台无机房电梯,因受现场条件限制．原有的曳引钢丝绳平层标识达不到应急救援的要求,故综合现场实际情况。提出了一种在限速器钢丝绳上设置平层标识的新方法．通过采用该方法．使得整改后满足了应急救援要求。     

车用多功能湿式多盘制动器

介绍了车用多功能湿式多盘制动器的优点和过去车用各种制动器的缺点。较详细介绍了当前车辆使用的湿式多盘制动器的现状、种类、特点、结构和工作原理。     

闸瓦销辊锻咬入条件分析

就闸瓦销的外形特征,分析了自由咬入时,模具及辊轮参数的合理性。     

制动盘早期磨损失效分析

对失效的汽车制动盘进行了扫描电镜分析、化学成分分析、金相检验和硬度检测等。结果表明，制动盘属于早期磨粒磨损失效。对进口和国产的制动盘及制动片进行了对比分析，讨论了材质及摩擦付匹配对制动盘使用性能的影响。制动盘磨损性能的影响因素不仅与制动盘材质有关，更主要是与摩擦片的材质与摩擦副匹配有关。     

Pedestrian crossing situations: Quantification of comfort boundaries to guide intervention timing

Introduction

Technical systems that warn or brake for vehicle–pedestrian encounters reduce injuries more effectively the earlier an intervention is initiated. However, premature intervention can irritate drivers, leading to system deactivation and, consequently, no injury reduction whatsoever. It has been proposed that no intervention should be initiated as long as attentive drivers are within their comfort zones. This study aims at quantifying driver comfort boundaries for pedestrian crossing situations to offer guidance for the appropriate timing of interventions.

Methods

Sixty two volunteers drove through an intersection on a test track at 30 and 50 km/h. A pedestrian dummy was launched from behind an obstruction towards the driving path of the approaching car. Brake onset indicated discomfort. Time to collision (TTC), longitudinal and lateral distance were measured at brake onset.

Results

TTC was independent of driving speed ranging from 2.1 to 4.3 s with a median of 3.2 s. Longitudinal distance ranged from 19 to 48 meters with an apparent difference between driving speeds. Lateral distances differed slightly, but significantly between driving speeds. The median was 3.1 m (3.2 m for 30 km/h and 2.9 m for 50 km/h) and values ranged from 1.9 to 4.1 m. Lateral distance in seconds ranged from 1.9 to 4.3 s with a median value of 3.1 s (3.2 s for 30 km/h and 3.0 s for 50 km/h).

Discussion

TTC was independent of driving speed, trial order and volunteer age. It might be considered suitable to intervene in situations where, for example, 90% of drivers have exceeded their comfort boundary, i.e. when drivers have already initiated braking. This percentile value translates to intervention at a TTC of 2.5 s (95% confidence 2.4–2.7 s). The study was limited to Swedish nationals, fully aware drivers, and two driving speeds, but did not investigate behavioural changes due to system interaction.

Conclusion

This study showed that TTC at brake onset was a suitable measure for the quantification of driver comfort boundaries in pedestrian crossing situations. All drivers applied their brakes prior to 2.1 s TTC.     

Clean hydrogen for mobility – Quo vadis?

Achieving complete combustion of fossil fuels has long been thought of as a sufficient remedy for tackling vehicular emissions and the ensuing environmental effects. However, thanks to the increasing awareness around the climate change, the global dialogue has now shifted to realizing a carbon-free economy, which has set stricter curbs on the energy source that can power the future mobility. Therefore, the idea of “clean combustion” requires rethinking. Of the many choices for alternative clean fuels that are both energy-efficient and environment-friendly, hydrogen has always been eyed as the best clean alternative there is. This article reviews various available approaches to utilizing hydrogen for mobility applications with a discussion of their relative merits and shortcomings. In addition to well-discussed methods like fuel cell electric vehicles, hydrogen-based IC engines, and dual-fuel operation with hydrogen, this review also assesses the technical and economic feasibilities of using hydrogen in e-fuels and their implications for our existing infrastructure and future energy demands.     

6102BQ柴油机排放特性的研究

摘要本文研究了6102BQ型柴油机排气中有害气体和微粒的排放特性.测量了不同喷油提前角时的发动机十三工况废气比排放量,并对微粒排放量的评价方法进行了探讨,认为目前参照我国十三工况法进行试验和计算比较合适.按照十三工况法进行了微粒排放试验,着重研究改变喷油提前角对No_x、微粒质量和微粒成份的影响.试验结果表明:当喷油提前角从21°CA减少到18°CA时,NO_x排放量明显减少,十三工况比排放量降低27.5%、微粒质量浓度平均增加9.1%,微粒中碳的含量随提前角减少而增加.     

一起电梯溜车伤人事故的分析

结合一起电梯溜车伤人事故,对制动器检测开关和接触器等部件进行分析,并进一步探讨制动器控制电路的设计和制动器的维护保养,从而预防制动器故障和事故。     

一种湿式安全型中央制动器

制动器是工程车辆的关键部件,对车辆运行的安全起着决定性作用.不同功用的制动器,其结构也不相同,介绍一种适用于恶劣环境,特别是可在煤矿井下高瓦斯环境中使用的,具有隔爆性能的湿式安全型中央制动器,对其结构特点、工作原理和制动力矩特性进行分析,为设计同类型制动器提供参考,也为使用和维护这种制动器提供理论依据.