The new Milwaukee Streetcar system has been in the planning, design and construction phases for over 10 years and on November 2, 2018, operations with a combined overhead contact system and streetcar battery power commenced ushering in a new era of growth for the City of Milwaukee. Many challenges in the design and construction of the overhead contact line and power system were encountered during this time period including budgetary constraints, multiple pole location changes, underground obstacles, low clearance bridges, alignment changes, utility conflicts, and changing vehicle requirements. The line was originally designed for pantograph operation but soon adapted for pole/pantograph current collection and then changed back to pantograph only current collection during the final design. The original design consisted of underground feeder cables to supplement a 4/0 contact wire but eventually not utilized due to budgetary constraints. Instead, a larger 350 kcmil contact wire was used with no paralleling feeder cables. The added weight of a 350 kcmil wire with wind, ice and low temperatures created high forces in the overhead contact system (OCS) leading to challenges in pole and foundation design where compliance to the National Electrical Safety Code (NESC) was required. The OCS style originally proposed and finally constructed used an inclined pendulum suspension (IPS) system that was constant tensioned with rotating springs deemed by the installing contractor superior to balance weights. The pendulum system was chosen as it is simple, lightweight, less visually obtrusive, and more economical than other suspension systems such as stitch and steady arm that are being used on other streetcar or light rail systems. IPS has provided Milwaukee with an excellent operating overhead contact system. Buildings along the route that were not historic structures were utilized where possible for span wire attachment but in many locations long bracket arms up to 40 feet long had to be used requiring special designs to keep the size of the pipes standard with the rest of the system. Challenges arose at low bridge underpasses where the contact wire had to be below required code height and special precautions had to be undertaken. Other areas such as the St. Paul Lift Bridge proved challenging as well where special electrically interlocked OCS devices were initially designed to de-energize the overhead wires and is further discussed with the reasoning for their use. This paper outlines the phases of design, the changes to the design that occurred over time, the challenges encountered to the OCS design, the method of design, and the final disposition of the design for construction. It further outlines the construction of the system and problems encountered with poles, foundations, bracket arms, traction power substations, contact wire, feeder cables, and winter conditions affecting the integrity of these structures and how some of these problems were solved.

Overhead Contact Systems for electric transit vehicles utilize catenary or single contact wire suspended from cantilevers, bracket arms or span wires. For single contact wire, inclined pendulum suspension provides optimal performance for pantograph or trolley pole current collectors, though it is under-utilized in the United States. Typical suspension for single contact wire consists of direct suspension hangers or stitch suspension with steady arms where stagger is achieved by pulling off the contact wire with the hanger (direct suspension) or steady arms (stitch suspension). This results in the full weight of the contact wire in the span length being supported by the stitch or line insulator. This rigid point of attachment results in a heavy, stiff suspension leading to current collector bouncing, arcing and premature contact wire wear as the upward movement of the wire is restricted and a hard spot is created. It also results in excessive sag at elevated temperatures and contributes to an increased angle at the support span approach. Inclined pendulums can be utilized in constant tension systems or variable tensioned systems where they impart a semi-constant tensioning into the line and keep the wire tension relatively stable over a particular temperature range. The expansion/contraction of the contact wire is taken up in the inclination of the pendulums where they rise or fall so that the tension and sag in the contact wire remains relatively consistent. In addition, they provide less resistance to uplift of the current collectors at the suspension point so that rising of the contact wire occurs as the collector approaches and passes under it. The vertical angle of the contact wire approaching the span support is kept to minimum levels and collector performance during hot weather conditions tends to remain trouble free. Further, the energy wave set up in the wire from the moving collector is not grossly reflected at the suspension point as with direct suspension thus allowing the collector to pass through smoothly without bounce or loss of continuous contact. This paper describes the benefits of inclined pendulums in constant and variable tensioned systems such as creating a semi-constant tensioning effect, preventing current collector bounce and premature contact wire wear at the supports by reducing the uplift resistance on current collectors. It also provides the least visual obtrusiveness of all the suspension systems. In addition, this paper will present the associated costs of the inclined pendulum suspensions.

Advanced active suspension systems has attracted considerable attention in modern railway vehicle designs in recent years. The purpose of the suspension is to attenuate the vehicle vibrations due to various rail excitations. With active suspensions it is aimed to improve the performance in some cases, while not making it worse in others. The performance-related objectives can be approximately translated in different norm bounds on certain transfer functions or impulse responses. In this paper, a multi-objective problem is formulated as a non-convex and non-smooth optimization problem for a full-car railway vehicle modelled with seventeen-degrees-of-freedom (17 DOF) and excited by random rail inputs. The controller order restricted to be less than or equal to the passive system model order. For a range of orders, controllers are synthesized by using the HIFOO toolbox.

With the development of high-speed rail technology, the interaction between wheel and track becomes more serious, which threatens the running stability, riding quality and safety of the vehicle. Due to the selected stiffness and damping parameters, conventional passive suspensions cannot fit in with the diverse conditions of the railway. Additionally, among these vibrations contains a large amount of energy, if this vibrational energy can be recycled and used for the active suspension to control, it will be a good solution compared to the conventional passive suspensions. Many energy-harvesting shock absorbers have been proposed in recent years, the most popular design is the electromagnetic harvester including linear electromagnetic shock absorbers, rotational electromagnetic shock absorbers, the mechanical motion rectifier (MMR), and the hydraulic electromagnetic energy-regenerative shock absorber (HESA). With different energy converting mechanisms, the complicated effects of the inertia and nonlinear damping behaviors will severely impact the vehicle dynamic performance such as the ride comfort and road handling. In the past few years, engineers and researchers have done relevant researches on HESA which have shown that it has good effects and proposed several suspension energy regeneration solutions for applying to car. This paper presents a novel application of HESA into a bogie system for railway vehicles comparing to the conventional suspension systems. HESA is composed of hydraulic cylinder, check valves, accumulators, hydraulic motor, generator, pipelines and so on. In HESA, the high-pressure oil which is produced by shock absorber reciprocation could be exported to drive the hydraulic motor, so as to drive the generator to generate electricity. In this way, HESA regenerate the mechanical vibrational energy that is otherwise dissipated by the traditional shock absorber as heat energy. Because the bogie has two sets of suspension systems, a dynamic model of bogie based on AMESim is established in order to clarify the influence of the dynamic characteristics effect and the energy harvesting efficiency when installing the HESA into different sets of the bogie. Then, set the HESA model into each suspension system of the bogie and input with the corresponding characteristic excitation, the influence of the dynamic characteristics and the energy harvesting efficiency are analyzed and compared. The simulation results show that the system can effectively reduce the vibration of the carriage, while maintaining good potential to recycle vibratory energy. Based on the results of the simulation, the relationships as well as differences between the first suspension system and second suspension system have been concluded, which are useful for the design of HESA-Bogie. Moreover, comparing the energy harvesting efficiency discrepancy between the two suspension systems, the potential of energy harvesting of a novel railway vehicle bogie system with HESA has been evaluated and then the best application department has been found, which indicates the theoretical feasibilities of the HESA-bogie to improve the fuel economy.

Thermoplastic elastomers (TPE’s) are increasingly being used in rail service in load damping applications. They are superior to traditional elastomers primarily in their ease of fabrication. Like traditional elastomers they offer benefits including reduction in noise emissions and improved wear resistance in metal components that are in contact with such parts in the railcar suspension system. However, viscoelastic materials, such as the railroad bearing thermoplastic elastomer suspension element (or elastomeric pad), are known to develop self-heating (hysteresis) under cyclic loading, which can lead to undesirable consequences. Quantifying the hysteresis heating of the pad during operation is therefore essential to predict its dynamic response and structural integrity, as well as, to predict and understand the heat transfer paths from bearings into the truck assembly and other contacting components. This study investigates the internal heat generation in the suspension pad and its impact on the complete bearing assembly dynamics and thermal profile. Specifically, this paper presents an experimentally validated finite element thermal model of the elastomeric pad and its internal heat generation. The steady-state and transient-state temperature profiles produced by hysteresis heating of the elastomer pad are developed through a series of experiments and finite element analysis. The hysteresis heating is induced by the internal heat generation, which is a function of the loss modulus, strain, and frequency. Based on previous experimental studies, estimations of internally generated heat were obtained. The calculations show that the internal heat generation is impacted by temperature and frequency. At higher frequencies, the internally generated heat is significantly greater compared to lower frequencies, and at higher temperatures, the internally generated heat is significantly less compared to lower temperatures. However, during service operation, exposure of the suspension pad to higher loading frequencies above 10 Hz is less likely to occur. Therefore, internal heat generation values that have a significant impact on the suspension pad steady-state temperature are less likely to be reached. The commercial software package ALGOR 20.3TM is used to conduct the thermal finite element analysis. Different internal heating scenarios are simulated with the purpose of obtaining the bearing suspension element temperature distribution during normal and abnormal conditions. The results presented in this paper can be used in the future to acquire temperature distribution maps of complete bearing assemblies in service conditions and enable a refined model for the evolution of bearing temperature during operation.

Vehicle/Track Interaction (VTI) Safety Standards aim to reduce the risk of derailments and other accidents attributable to the dynamic interaction between moving vehicles and the track over which they operate. On March 13, 2013, the Federal Railroad Administration (FRA) published a final rule titled “Vehicle/Track Interaction Safety Standards; High-Speed and High Cant Deficiency Operations” which amended the Track Safety Standards (49 CFR Part213) and the Passenger Equipment Safety Standards (49 CFR Part 238) in order to promote VTI safety under a variety of conditions at speeds up to 220 mph. Among its main accomplishments, the final rule revises standards for track geometry and enhances qualification procedures for demonstrating vehicle trackworthiness to take advantage of computer modeling. The Track Safety Standards provide safety limits for maximum allowable track geometry variations for all nine FRA Track Classes — i.e., safety “minimums.” These limits serve to identify conditions that require immediate attention because they may pose or create a potential safety hazard. While these conditions are generally infrequent, they define the worst conditions that can exist before a vehicle is required to slow down. To promote the safe interaction of rail vehicles with the track over which they operate (i.e. wheels stay on track, and vehicle dynamics do not overload the track structure, vehicle itself, or cause injury to passengers), these conditions must be considered in the design of suspension systems. In particular, rail vehicle suspensions must be designed to control the dynamic response such that wheel/rail forces and vehicle accelerations remain within prescribed thresholds (VTI safety limits) when traversing these more demanding track geometry conditions at all allowable speeds associated with at particular track class. To help understand the differences in performance requirements (design constraints) being placed on the design of passenger equipment suspensions throughout the world, comparisons have been made between FRA safety standards and similar standards used internationally (Europe, Japan, and China) in terms of both allowable track geometry deviations and the criteria that define acceptable vehicle performance (VTI safety limits). While the various factors that have influenced the development of each of the standards are not readily available or fully understood at this time (e.g., economic considerations, provide safety for unique operating conditions, promote interoperability by providing a railway infrastructure that supports a wide variety of rail vehicle types, etc.), this comparative study helps to explain in part why, in certain circumstances, equipment that has been designed for operation in other parts of the world has performed poorly, and in some cases had derailment problems when imported to the U.S. Furthermore, for specific equipment that is not specifically designed for operation in the U.S., it helps to identify areas that may need to be addressed with other appropriate action(s) to mitigate potential safety concerns, such as by ensuring that the track over which the equipment is operating is maintained to standards appropriate for the specific equipment type, or by placing operational restrictions on the equipment, or both. In addition to these comparisons, an overview of the new FRA qualification procedures which are used for demonstrating vehicle trackworthiness is provided in this paper. These procedures, which include use of simulations to demonstrate dynamic performance, are intended to give guidance to vehicle designers and provide a more comprehensive tool for safety assessment and verification of the suitability of a particular equipment design for the track conditions found in the U.S.

Currently, the onboard applications of many electronic devices that could benefit rail operation are hindered by the lack of availability of electrical power in freight cars. Although the locomotives, of course, have available sources of power, the freight cars usually don’t have any. The systems presented in this paper are meant to provide a solution for distributed power in freight trains. Although ideas like Timken’s generator roller bearing or solar panels exist, the railroads have been slow in adopting them for different reasons, including cost, difficulty of implementation, or limited capabilities. The solutions presented in this paper are vibration-based electromechanical energy harvesting systems. With size and shape similar to conventional shock absorbers, these devices are designed to be placed in parallel with the suspension elements, possibility inside the coil spring, maximizing underutilized space. As the train goes down the track, the suspension will accommodate the imperfections and its relative displacement will be used as the input for the harvesting systems. The first prototype generation used a linear generator, with the advantage of no need for a mechanical transformation of the input. They have proven that they could work but present some limitations in terms of power and efficiency. The second generation of prototypes is built around a rotating generator. The linear input motion is transformed into rotation by a ball screw. The possibility of including a gearbox to increase the speed is the key to greatly improve performances. The latest built prototype has shown during lab tests that it is capable of providing up to 75W RMS with displacements and velocities that resemble the relative motion across a vehicle suspension.

A model for dynamic analysis of the track stiffness distribution on the impact of track transition is developed with vehicle element and track element. The vehicle element model has a total of 26 DOFs, in which 10 DOFs are used to describe the vertical movement of the car body, and 16 DOFs are associated with the rail displacements. The track element includes rail, rail fastening and pad, ballast and subgrade. By means of Lagrange equation, numerical method for coupling the moving wheel and the rail with explicit formula is presented and the associated finite element formulations are obtained. As an application, influences of four kinds of transition patterns, i.e., abrupt change, step by step change and linear change as well as cosine change for track stiffness distributions in track transition, on dynamic behavior of the vehicle and the track are investigated. The computational results show that the transition pattern of the track stiffness has great influence on the dynamic behavior of the vehicle and the track and smoothing of the track stiffness distribution can significantly reduce the wheel/rail interaction forces and the vertical rail accelerations. From abating wheel/rail impact and improving traffic operation’s point of view, the cosine change is the best, the linear change is the better and the abrupt change is the worst in the four kinds of the transition pattern of the track stiffness. However, the transition patterns of the track stiffness have nearly no influences on the vertical vehicle accelerations due to the excellent behaviour of vibration isolation resulting from the primary and the secondary suspension system of the vehicle.

As track geometry degrades, and in particular as track surface and cross-level (as defined by a Track Quality Index or TQI) degrades, railway vehicles going over that degraded track experience increased vertical dynamic behavior and increased vehicle/track interaction. This in turn translates into increased wheel/rail dynamic forces as well as increased energy (fuel) consumption. While this concept has been known for many years, there has been limited study of the direct relationships between the degree of track degradation (as quantified by a Track Quality Index type parameter) and the magnitude of the dynamic force and energy consumption increase. This paper presents a recent study on the dynamic effects of track surface geometry degradation, which has direct impact on maintenance practices, policies, and economics. Specifically, this paper presents the results of a series of analyses looking at the effect of increased track geometry degradation, as measured by a track geometry inspection vehicle, and quantified by a Track Quality Index (TQI). The effects examined include loss of energy and wasted fuel due to dissipation of energy in the vehicle suspension, as well as the increase in dynamic vertical force at the wheel/rail interface. The analyses used over 100 miles of US main line (Class 1) railroad track geometry data for a broad range of track conditions (and corresponding Track and Surface Quality Indices); together with a sophisticated multi-degree of freedom vehicle dynamics model to develop a relationship between track condition and dynamic effects. The results are a series of non-linear relationships between track condition, as defined by TQI, and energy loss in the suspension system, i.e. energy dissipation. A second set of non-linear relations was also developed between track condition, as defined by TQI, and dynamic force multiplier, i.e. the ratio of dynamic force to static wheel/rail load. The paper presents these results in both mathematical and graphical form.

New types of vehicle and track elements are presented, by means of the finite element method, to establish a model for dynamic analysis of vehicle-track-subgrade coupling systems. The associated stiffness matrix, mass matrix and damping matrix for these two types of elements are deduced. Computational software is coded with Matlab. As an application example, dynamic behavior of track transition is investigated by the vehicle and the track elements. The influencing factors for the simulation include train speed, subgrade stiffness, and irregularity angles of track transition as well as the transition pattern. The computational results show that 1) Abrupt changes of the subgrade stiffness influence vertical acceleration of the rail and the wheel/rail contact force, and this influence increases with increases in train speed, 2) Both the irregularity angles of the track transition and the abrupt changes of the subgrade stiffness have significant effects on rail vertical acceleration and the wheel/rail contact force, with the peak value in this situation being greater than that generated by irregularity angles of the track transition or the abrupt changes of the subgrade stiffness, 3) Train speed, abrupt changes of the subgrade stiffness, and track transition irregularity angles have minor influences on the vertical acceleration of the vehicle due to the excellent behavior of vibration isolation resulting from the primary and the secondary suspension systems of the vehicle, 4) Transition pattern for irregularity of track transition has significant influences on the vehicle acceleration and the wheel/rail contact force, and the cosine transition is a much better indicator than the linear transition, and 5) Influences of the directions the train is moving on the dynamic behavior of the vehicle and the track are relatively insignificant.

Analytical results indicate that there is a wide variation in roll and lateral behavior on curves at unbalance speeds, for passenger car suspensions in use today. This paper categorizes passenger car types and analyzes behavior under the action of quasi-static lateral forces such as can occur on curves. Understanding this behavior can be important in providing guidelines for developing new designs that operate at relatively high unbalance speeds while still retaining safe operation, good ride quality and other performance related to suspension system design. The approach taken is to develop equations of motion in terms of the physical parameters that must be known in order to determine carbody roll and lateral motions due to lateral loads and laterally offset component weights. These equations are then rearranged in terms of parameters that characterize quasistatic and dynamic performance in a form that facilitates making general statements about the comparative influence of categories of cars on carbody roll and lateral motions, and the resultant increase in wheel unloading, as functions of lateral load. Results are presented for ranges of cars in each category. Roll and lateral motions of existing designs can be estimated by using the physical parameters of the existing design to calculate the parameters used in the equations presented in the paper and then using those equations to calculate estimates of the roll and lateral motions. For contemplated new designs either physical parameters can be selected and motions calculated, or values of the parameters used in the equations presented in the paper that result in desirable levels of roll and lateral motions can be used as trial values for initial and later iterations of the design. The analytical approach has been subjected to limited correlation with static lean test results with good agreement found.

The relative significance of vehicle dynamics on the dynamic component of wheel-rail interface vertical forces caused by relatively short wavelength track perturbations is estimated, based on a simple dynamic model, for a range of suspension design types. The results indicate the relative importance of suspension design on track damage. This study is analytical. However, it provides a basis for testing to ensure that the influence of suspension design on track-induced vertical loads is better documented and understood.

For wagons with three-piece bogies, the suspension dynamic characteristics are largely dependent on the friction condition of the wedge dampers. The influence of changes in wedge friction conditions on the dynamic wheel load is investigated. Comprehensive wagon-track modelling has been developed for the analysis. Simulations show that a small friction coefficient on the wedge contact surfaces can lead to the severe resonance of suspension system, causing large dynamic wheel loads and high levels of wheel unloading while with a large friction coefficient, suspension resonance is restricted, leading to smaller dynamic wheel loads.