急曲線部を走行する鉄道車両においては, 車輪に大きな横圧が作用し, 出口側の緩和曲線部では軌道の平面のねじれも加わり, 外軌側の車輪のフランジはレールに乗り上がり易くなる. 本研究では, このような場合を想定し, 急曲線を低速で通過する車両の走行安全性を検討することを目的とした数値解析シミュレーション法の開発を行い, 主要なパラメータが車輪のレールへの乗り上がりに対してどのような影響を与えるかを二三の解析例で示した. その結果曲線に沿った車両の回転運動による左右レールの相対移動速度差を解析上無視することはできないこと, 低速走行時に静止輪重のアンバランスが大きな値に保持され, さらに車輪・レール間の摩擦係数がある大きな値に達する場合は, 車輪がレールに完全に乗り上がり, 脱輪に至ること等が明らかになった.

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This paper presents the laboratory experimental results in relation to tangent force between a wheel and a rail under different environmental conditions. In the experiments, we used two types of cylindrical test specimens (with / without fine unevenness on contact surface) assuming actual wheels, and investigated the relation of tangent force to the cases of with / without fine unevenness on contact surface under the conditions of different environmental temperature and relative humidity. Consequently, under the conditions of without fine unevenness on the contact surface of a test specimen, it showed that there is a tendency in the tangent force which turned out low whence relative humidity is over 60%, regardless of environmental temperature. However, on the conditions which have fine unevenness on the contact surface of a test specimen, we could not observe the effect of environmental temperature and relative humidity on the tangent force. In addition, running stability analysis of railway vehicle was carried out for the cases of with / without fine unevenness on wheel tread of railway vehicle under the condition of different relative humidity. As a result, it was shown that the critical hunting velocity under the condition of without fine unevenness becomes low while increasing relative humidity.

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最近の社会的な事故を調べてみると、グレイゾーンで発生する事故が多いことに気づく。本論では、このグレイゾーンを把握しリスク低下のための対応方法を提案することが、リスク工学の主たる課題であるという観点に立つ。初めにグレイゾーンを考慮した安全保証型と危険回避型のシステム設計の分類の重要性を説き、グレイゾーンを減少させリスクを低下させるための学習メカニズムを提案する。特に危険回避型では2つの学習によってグレイゾーンの縮小化が可能となることを示す。後半では、グレイゾーンに不可避部分があることから、むしろそれを積極的に利用してリスクを低下させる方法として、規則の記述方法への活用と、数理的なモデルに基づく高信頼性モニタリングの設計方法について述べる。

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鉄道において,安全への投資はもっとも重要な経営施策であり,列車脱線事故の根絶に向けた各種の取り組みが鋭意進められている.効果的な脱線防止対策を実施するには脱線現象の理解が不可欠で,これまで実際の事故を教訓として,実験,解析の両面から精力的に研究が行われてきた.本稿ではまず,鉄道車両の脱線の中で特に注意を要する乗り上がり脱線を取り上げ,そのメカニズムを解説する.次に,脱線に対する安全性の評価手法を紹介し,その現状と課題について述べる.本稿に紹介する評価手法は,約半世紀に渡って適用され十分な実績を積んだものであるが,信頼性の観点からみるとやや曖昧な部分が残っている感は否めない.鉄道にはレールと車輪間の摩擦をはじめとする不確定な要素が数々あるため,評価には一定の安全率を見込んだ目安値を用いている.また,計測,データ処理の各段階で誤差が生じ,さらに扱う周波数成分が同じでなければ,同じ目安値を適用しても評価結果は異なったものとなる.基本的な現象の解明を進めるとともに,これらの点に信頼性の視点を導入し,評価手法の標準化を図ることが今後の課題の一つと考えられる.

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In this study, uncertainties of aerodynamic force, gravitational force, excessive centrifugal force and lateral vibration induced inertial force acting on the train cars are investigated based on the measured data. A performance function is then proposed based on the reliability theory and the safety indexes are assessed when the train operation regulations are performed. The code calibration is carried out to obtain an acceptable safety index and a formula with partial factors is proposed to calculate critical wind speeds of overturning. Finally, the safety indexes for several train operation conditions are assessed based on the critical wind speed of overturning predicted by three formulas. It is found that the safety indexes obtained by the proposed formula are nearly constant values, while those by the conventional formula show different values for different train operation conditions.

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It’s generally known that tangential force of wheel/rail interface which depends on a change of coefficient of friction between wheel and rail has a big influence on a steady lateral force of railway vehicle. According to our past researches, regardless of an attack angle, tangential force coefficient becomes smaller in the case with fine unevenness than in the case without fine unevenness on the surface by means of a two-disk rolling contact machine. In particular, a tangential force coefficient is more affected by the situation of with /without fine unevenness under low relative humidity condition. The conditions under low relative humidity are almost the same as the conditions that a coefficient of friction of wheel/rail is high. In this paper, in order to reduce steady lateral force during a railway vehicle passing curve, we proposed a new wheel tread profile with providing one streak of fine unevenness, called ‘Micro-ribbed wheel tread profile’ on a wheel tread away from a flange. We verified a validity of this wheel tread profile by applying a numerical analysis and a running test in RTRI. As a result, we confirmed that the Micro-ribbed wheel tread profile is effective to reduce the steady lateral force of the outside wheel/rail interface when the railway vehicle is passing curve under high coefficient of friction between wheel and rail.

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This paper describes a consideration of the difference in wheel/rail tangential contact force characteristics between in running tests and in laboratory experiments. To improve the accuracy of vehicle dynamics analysis, it is important to obtain the relationship between the tangential contact force coefficient and the slip ratio under realistic conditions. Since these characteristics cannot be obtained by numerical analysis, running tests on commercial lines and laboratory experiments using a twin-disk rolling machine are carried out. On the other hand, under conditions of high slip ratios, these characteristics differ between cases where the tangential contact force coefficient between wheel/rail remains contact and cases where the tangential contact force coefficient decreases. In this study, focusing on the state of the coefficient of friction between wheel/rail, a 3D-MBD model which can simulate vehicle behavior during braking was constructed on the SIMPACK commercial software, and these different reasons and their relationships were discussed. The result clarified that the difference in these characteristics is due to whether the friction coefficient on the contact surface is constant or fluctuating during the measurement by numerical analysis. That is, the characteristics measured in laboratory experiments can be modeled by Kalker’s rolling contact theory with a constant friction coefficient, and the characteristics measured in running tests can be modeled by combining the characteristics obtained by the Kalker’s theory under the conditions of different friction coefficients at each running distance.

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