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Application To Railway Pneumatic Suspensions

As the railway industry evolves in response to globalization, digitalization and climate change, it faces new challenges. In order to solve them, the technology used in rail transport must develop too. However, as products change, they must meet stringent national and international safety requirements. Many of these products are pneumatic components and systems to control various functions on passenger and freight trains.

Application to Railway Pneumatic Suspensions

To overcome the latest industry challenges successfully, rail OEMs must implement effective, future-proof pneumatic systems that meet all railway standards. Railway compliant pneumatic components must fulfill the highest safety requirements and toughest industry demands across a wide range of applications.

Pressures between 2 and 10 Bar and nominal voltages of 24 to 110 V DC for pneumatic components usually apply. The drop-out voltage must be higher than 10% of the nominal voltage, especially in braking applications, and only negligible leakage is allowed at low temperatures.

Since the air brake was invented more than 150 years ago, compressed air has played a major role in the railway industry. Today, pneumatic components are used in a wide range of applications in both passenger and freight vehicles. For successful product development, OEMs must implement pneumatic applications that meet the highest safety requirements and industry demands. Outlined below are a few of the many applications and compliant solutions.

The potential of a direct operated poppet valve is often underestimated, but 3/2 poppet valves specifically designed for the railway industry prove their advantage on toilet and water applications. The valves control different functions of vacuum toilets, fresh water supply and grey water applications on trains, combining a compact size with high reliability and assuring comfort at all times.

Frank Gevers is director, railway, fluid control and pneumatics at Emerson. With a degree in mechanical engineering from the University of Applied Sciences, Cologne, he has been involved in the railway industry for nearly 15 years.

The secondary suspension connects the body of the car with the bogie and aids comfort of passengers by isolating the vehicle from vibrations transmitted from the track. Commonly part of secondary suspensions, the air spring works to reduce lower frequency range accelerations in the body of the train. The role of the secondary suspension is mainly to act as a pneumatic suspension and is even used in freight trains.

The UM Pneumatic Systems module is used for simulation of pneumatic suspensions of coaches. The module allows including the main elements of pneumatic suspension into a multibody model of a vehicle for dynamic modeling. The following pneumatic elements are used in the suspensions:

GMT Rubber can offer a wide range of air spring systems from our existing range or air bellows and auxiliary springs. We also supply additional secondary rubber springs for extra suspension protection, in the event of any air leaks and ensure high passenger comfort whatever the application. We specialise in developing and manufacturing air suspensions for railway vehicle bogies. Still, you may wish to weigh up the air suspension advantages and disadvantages and speak to one of our experienced engineers to design a bespoke air spring system to meet the requirements of your commercial vehicles.

Since the concept of active suspensions appeared, its large possible benefits has attracted continuous exploration in the field of railway engineering. With new demands of higher speed, better ride comfort and lower maintenance cost for railway vehicles, active suspensions are very promising technologies. Being the starting point of commercial application of active suspensions in rail vehicles, tilting trains have become a great success in some countries. With increased technical maturity of sensors and actuators, active suspension has unprecedented development opportunities. In this work, the basic concepts are summarized with new theories and solutions that have appeared over the last decade. Experimental studies and the implementation status of different active suspension technologies are described as well. Firstly, tilting trains are briefly described. Thereafter, an in-depth study for active secondary and primary suspensions is performed. For both topics, after an introductory section an explanation of possible solutions existing in the literature is given. The implementation status is reported. Active secondary suspensions are categorized into active and semi-active suspensions. Primary suspensions are instead divided between acting on solid-axle wheelsets and independently rotating wheels. Lastly, a brief summary and outlook is presented in terms of benefits, research status and challenges. The potential for active suspensions in railway applications is outlined.

Over the last half-century, railway vehicles have developed in a way that more and more electronics, sensors and controllers are applied along with the traditional mechanical structures to meet the new demands for higher speed, better ride quality and stricter safety requirement. A number of digital technologies in railway engineering have been developed and put in practical use in sub-systems including train management, communication, traction and braking systems. In contrast, only a limited number of active control solutions have been introduced to improve the dynamics of the railway vehicle. Tilting trains, as one of the successful applications, have shown great benefits, which encouraged further explorations of active suspensions over last two decades.

Since the suspension of railway vehicles is a complicated system aimed at achieving different functions, active suspension technologies with different functions and configurations have been developed in various forms. Major reviews were published in 1983, 1997, 2003 and 2007 [1,2,3,4]. Many new theories and implementations emerged in the last decade, however. Therefore, in this work, a systematic state-of-the-art review is presented including recent studies on active suspension. In Sect. 2, the general concepts are explained, and a classification of active suspension is introduced. Based on the classification, the different actuation solutions are introduced. Since tilting train can be regarded as a quite mature technology and little development has been made since 2009 [5], it is only briefly introduced in Sect. 3. Emphasis is put on active secondary and primary suspensions that are described in Sects. 4 and 5, respectively. Finally, Sect. 6 provides a summary and an outlook to future trends and research needs.

A successful implementation of LQG was described by Gong et al. [46], where it was combined with preview control. It is shown that LQG control is effective in control of both rigid and elastic modes together over a wide frequency range. An interesting application was studied by Leblebici and Türkay [47]. Here, a lumped track model was introduced, and it was proven through simulations that the LQG control can effectively counteract bounce and pitch motions of the car-body. A quarter car model with nonlinear suspensions was studied by Nagarkar et al. [48] where NSGA II was used to optimize PID and LQR control parameters with a multiple objective problem compromising ride comfort, suspension space and control force. Sugahara et al. [40] compared sky-hook damping and LQG control both by simulation and test on a full-scale model. It is shown that LQG control works better when the natural frequency of the first bending mode of the car-body is far from the bogie one while the sky-hook damping improves the response when these two are close to each other. A similar approach was applied by Pacchioni et al. [42]. Here, it is shown that with a careful choice of the gains similar effects can be produced by sky-hook and LQG. Nevertheless, as discussed by Sugahara et al. [39], LQG control can be a precise control but it can suffer from unmodeled uncertainty or even dynamics that can cause a drastic decrease in the controller performances.

In 2001, the commercial operation of Series E2 and E3 Shinkansen trains started using fully active lateral suspension. In these vehicles, pneumatic actuators are implemented on the end cars and the green car (first class car). Semi-active suspensions have been installed in all cars [79]. \(H_\infty \) control is adopted to eliminate the yaw and roll car-body vibrations. After that, the fully active suspension was further explored and developed in the project Fastech 360, aimed at developing higher speed trains. The test trains 360S and 360Z had electromagnetic actuators with high bandwidth installed [80], while electro-mechanical actuators are applied in Series E5 and E6 in 2011 and 2013 [81].

Firstly, five modes were considered: two rigid modes and three elastic modes [51]. A weighting function for disturbance suppression (\(W_s\)) was chosen separately for each considered mode. A combination of linear and 20 stack piezoelectric actuators was used. The tasks were split between the two different actuators types. Linear actuators were used to control the two rigid modes while the piezoelectric ones were used to suppress the three elastic modes. Subsequently, the usage of pneumatic actuators in parallel with the air spring was considered [52]. Despite rigid body modes were effectively suppressed, the control performance became worse near the elastic vibration modes due to the nonlinearity of the electric-pneumatic valve. Lastly, air suspensions were directly used to control the first and second rigid modes and the first bending mode [53]. The air spring was controlled by adjusting the air pressure, and accelerometers were placed at the edges and the centre of the 1:6 scaled vehicle. Satisfactory results were obtained for the 1:6 scaled vehicle and for a simulated full-size vehicle. Here, a careful model of the pressure valve should be considered.

Also, fault tolerance design and analysis, especially for the actuation systems, is very important because safe operation is an aspect which the industry is most concerned about. The development of affordable safe and reliable solutions which yield excellent maintainability and availability solutions is therefore critical. This is a topic deserving more research work in the future, also taking benefit from examples and best practices from other technology fields, aircraft industry in particular, to ensure the safety and improve the reliability of railway vehicles with mechatronic suspensions, for instance adopting backups or redundant structures. 041b061a72

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