The present invention pertains generally to an elevated guideway for a magnetically levitated (MAGLEV) vehicle. More particularly, the present invention pertains to a hybrid MAGLEV guideway module that can be supported by vertical columns to construct an elevated MAGLEV guideway. The present invention is particularly, but not exclusively, useful as a MAGLEV guideway module for use in a MAGLEV vehicle system which uses a linear synchronous motor (LSM) and an electro-dynamic system (EDS) for propulsion, levitation and lateral stability.
Magnetic levitation systems, often called MAGLEV systems, typically take advantage of an electromagnetic interaction between components that are mounted on a vehicle, and components that are mounted on a stationary guideway. The consequence of this interaction is to levitate the vehicle over the guideway. Because the vehicle does not physically contact the guideway during its travel over the guideway, energy losses associated with contact friction are greatly reduced.
One particular system that utilizes the electromagnetic interaction between guideway-mounted components and vehicle-mounted components is disclosed in co-pending, co-owned U.S. patent application Ser. No. 10/330,733 which was filed on Dec. 27, 2002 and is titled “Magnetic Levitation and Propulsion System.” U.S. patent application Ser. No. 10/330,733 (hereinafter the '733 application) is hereby incorporated by reference in its entirety herein. As disclosed in the '733 application, a system for levitating and propelling a vehicle along a stationary guideway includes a linear synchronous motor (LSM) having a component mounted on the vehicle (e.g. a linear array of permanent magnets) and a component mounted on the guideway (e.g. a polyphase winding on an iron core). In combination, these LSM components interact with each other to generate electromagnetic forces for two purposes. For one, the forces act to levitate the vehicle. For another, they act to propel the vehicle along the guideway. It happens that the strength of these LSM forces are strongly dependent on the size of the LSM gap (i.e. the distance between the vehicle-mounted LSM component and the guideway-mounted LSM component).
As further disclosed in the '733 application, the gap between LSM components can be maintained by an electrodynamic system (EDS) having a component that is mounted on the vehicle (e.g. a magnet array), and a component that is mounted on the guideway (e.g. a conductive sheet which is also sometimes called a Litz track). Specifically, the EDS generates electromagnetic forces during movement of the vehicle relative to the guideway that react with the levitation forces created by the LSM. In particular, the forces generated by the EDS maintain the LSM gap within a predetermined operational range. Maintenance of the LSM gap then stabilizes the LSM, and allows the LSM to operate efficiently within a pre-selected range of vehicle speeds.
As implied above, the guideway is an important part of the MAGLEV system. Typically, it is desirable to use a modular guideway design to facilitate guideway construction and simplify the delivery and assembly of the guideway. Functionally, all portions of the guideway must be capable of supporting the weight of the MAGLEV vehicle under all operational conditions. For example, in addition to normal operation, the guideway must also support the MAGLEV vehicle during a power outage or system failure. Further, for applications in high-density urban areas, it is often desirable to elevate the guideway. For these applications, it is desirable that elevated portions of the guideway be lightweight in order to reduce the size and cost of the guideway supporting structures. Moreover, in frigid climates, large guideway structures can cast relatively long shadows which can cause undesirable ice buildups on adjacent roads and roofs. Thus, for some MAGLEV system applications, the size, profile and weight of a guideway structure are all important design considerations.
Other factors that can be important in designing a MAGLEV guideway are the dimensional tolerances of the guideway components and the dimensional stability of the guideway. As indicated above, it is desirable to maintain the gap(s) between vehicle-mounted, and guideway-mounted LSM components within a pre-selected operational range. This, in turn, dictates that relatively tight tolerances be held with regard to the position of guideway-mounted LSM and EDS components and that the modular guideway components fit together closely. Moreover, the specified guideway dimensions must be stable over the life of the guideway and these dimensions must be maintained under typical MAGLEV system loading conditions. More specifically, guideway structures typically require one or more substantially flat surfaces that extend uniformly along the length of the guideway. Applications of these flat guideway surfaces include, but are not limited to, a landing surface for receiving the station/emergency wheels of a MAGLEV vehicle during a vehicle descent, and a structure on which LSM and EDS components can be mounted.
In light of the above, it is an object of the present invention to provide relatively light-weight guideway modules for an elevated MAGLEV guideway and methods for their manufacture. It is another object of the present invention to provide lightweight MAGLEV guideway components that are manufactured to close dimensional tolerances, and that maintain their structural integrity under typical MAGLEV system loading conditions. Yet another object of the present invention is to provide MAGLEV guideway components and methods for their manufacture which are easy to use, relatively simple to implement, and comparatively cost effective.
The present invention is directed to a MAGLEV guideway module that can be supported by vertical columns to create a section of an elevated MAGLEV guideway. Each guideway module includes an elongated beam that is made of lightweight, pre-stressed concrete. Functionally, the guideway modules are integrated to form an elevated levitation track that supports the operational electromagnetic guideway components and the weight of a MAGLEV vehicle.
In greater structural detail, each guideway module includes an elongated beam, such as a box beam, which has a first end and a second end. Also, each guideway module defines a longitudinal axis that extends between its first and second ends in the direction of elongation. In use, the first end is attached to a vertical column and is mated with the second end of an adjacent guideway module. For each guideway module, a portion (e.g. a lower portion) or all of the beam is made of a molded, pre-stressed concrete. Specifically, each beam is typically pre-stressed in a direction that is substantially parallel to the beam's longitudinal axis.
In a first embodiment of the invention, each module includes a concrete transverse deck that is monolithically cast with the box beam. In detail, the transverse deck includes first and second cantilevers that each extend from the beam in opposite directions, with the first cantilever extending to a first deck edge and the second cantilever extending to a second deck edge. Together, the cantilevers and the beam establish a substantially flat deck surface that runs from the first end to the second end of the module, and extends between the first deck edge and the second deck edge. The deck itself is not necessarily pre-stressed.
In one aspect of the invention, metal hardware embedments are cast into the surface of the concrete module to facilitate the attachment of levitation components to the concrete module. Each embedment can then be accurately machined after the concrete has fully cured, to ensure accurate positioning and alignment of the levitation components. Importantly, this can be done in spite of any concrete shrinkage and distortion that may occur during concrete curing. For example, as an alternative to the monolithically cast concrete transverse deck described above, metal overhangs can be attached to the pre-stressed box beam for the same purpose.
In a particular embodiment, the guideway modules are configured for use in a MAGLEV system which uses both an LSM and an EDS system to levitate, propel and laterally stabilize a MAGLEV vehicle over and along the guideway. For this embodiment, the module includes a mounting system for attaching LSM windings and LSM iron laminations to each concrete cantilever (or, alternatively, metal overhangs attached to the box beam). For the cantilevers, the LSM components are typically mounted on a respective cantilever surface that is located opposite the deck surface (e.g. underneath the deck surface).
In addition, the beam can be formed with two notches for use in mounting a pair of substantially flat, EDS conductive tracks to the beam. Each notch is sized to receive a portion of a respective EDS conductive track and a clamp assembly is provided to maintain the track in the notch and secure the track to the beam. Each notch extends from the first module end to the second module end and is positioned and aligned on the module to orient a respective EDS conductive track substantially parallel to the deck surface of the module. More specifically, the notches are located on opposite sides of the beam. With this cooperation of structure, the two EDS conductive sheets extend from the beam in opposite directions and in a common plane. As an alternative to notches formed in the concrete beam, the embedments described above can be used to attach the EDS conductive track to the beam.
A method for manufacturing a guideway module in accordance with the present invention includes the step of providing a steel form molding system for shaping the guideway module. In detail, the molding system has a beam portion and, optionally, a deck portion. Next, a plurality of cambered or straight pre-stressing cables are placed in the form of the molding system and are aligned to be substantially parallel to the beam's intended longitudinal axis. Once the cables are positioned in the form, they are then anchored at one end and pulled from the other end to provide the needed axial tension. With the cables in tension, the lightweight concrete is poured into the beam portion of the form and allowed to cure. The tension on the cables is then released, resulting in a precast, pre-stressed beam. After the beam has been cast, lightweight concrete can then be poured into the deck portion of the steel form and bonded with the beam. The result is a precast pre-stressed deck and beam structure that is ready for installation of the MAGLEV components after approximately 28 days of curing. Unlike a guideway that is entirely constructed at a guideway site, the use of a shop-assembled precast, pre-stressed lightweight concrete module allows for dimensional tolerances to be effectively controlled.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
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For the guideway 10, a portion (e.g. a lower portion) or all of the beam 16 for each levitation module 12a-c is made of a molded, pre-stressed concrete.
For the guideway 10,
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For the embodiments described above, the concrete used to form the beam 16, 16′, 16″ and deck 18, 18′ can be a steel fiber reinforced concrete (SFRC). Typically, selected sections of the cast structures are pre-stressed using stressed cables 27 as described above. On the other hand, conventional metal reinforcement (i.e. rebar) is not typically necessary when the SFRC material is used. For the SFRC material, continuous micro-stitching properties of the randomly distributed steel fibers result in a significant increase in the material's flexural strength. For some test samples, a maximum ultimate flexural bending stress of approximately 23 Mpa (3,335 psi) and an ultimate minimum compressive strength of approximately 72.3 Mpa (10,480 psi) was attained. In one implementation, an SFRC material having an allowable flexural bending stress of about 10.3 Mpa (1500 psi) is used. Typically, structures cast with SFRC are strong in fatigue compression, flexural bending, ductility and impact resistance. In addition, the use of the SFRC in place of conventional reinforced concrete can significantly enhance the magnetic performance of the magnetic levitation components.
While the particular Modular Guideway for a Magnetic Levitation Vehicle and Method for Manufacturing a Guideway Module as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.