Machine element or mechanism – Elements – Flywheel – motion smoothing-type
Reexamination Certificate
1998-06-12
2001-02-06
Luong, Vinh T. (Department: 3682)
Machine element or mechanism
Elements
Flywheel, motion smoothing-type
C074S608000, C074S609000, C464S101000
Reexamination Certificate
active
06182531
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to flywheel containment systems, and more particularly to light-weight, low cost containment systems designed to accommodate high-energy composite flywheel failures.
BACKGROUND OF THE INVENTION
The principle of flywheel energy storage is that a spinning wheel stores mechanical energy, energy that can be put in or taken out of the spinning wheel with the use of a motor or generator. The amount of energy stored in a flywheel depends on the mass of the rotor, the configuration of the rotor, and how fast the rotor is spinning. Specifically, the energy storage varies as a function of the rotational moment of inertia of the rotor and the square of the rotational speed of the rotor.
Flywheel energy storage depends on mechanical parts rotating in a precise relationship to electrical and other mechanical components. A major problem in these systems is the safety of the people and the property in the local area during the catastrophic failure of the rotating system. Historically, flywheels have been made of steel for the purpose of smoothing the flow of energy in the rotating machines. Steel flywheels, when stressed to failure by overspeed, will fracture into several large pieces. The inertial forces on the failed parts cause the parts to move radially outward away from the machine, at speeds proportional to the rotating speed of the flywheel before failure. This expulsion of energy can be extremely dangerous and destructive.
A new generation of flywheels is now being produced from composite materials (fiber and plastic) to take advantage of the composite material's inherent strengths which are much greater than steel. As a result, composite flywheels fail at much higher energy levels in quite a different manner than their steel counterparts. Instead of fracturing into pie-shaped pieces in the manner of steel flywheels, composite material flywheels fail such that a composite ring of circumferentially wrapped fibers extend as if the fibers were a viscous liquid. Although some fiber breakage occurs to initiate the expansion, the spinning mass of fibers remains grossly intact, while the plastic that binds the fibers together experiences complete failure.
Containment vessels for this type of composite material in failure have taken the form of very strong, rigid vessels. The practicality of making rigid vessels in large scale production is low and the space required for installation is prohibitive. These types of thick, rigid containment vessels have other disadvantages as well. First, containment vessels of this nature tend to be extremely heavy, and as such, are expensive and difficult to handle. Additionally, they cause the failed flywheel material fragments to divert their energy in the axial direction, since the rigid wall stops fragment expansion in the radial direction. Thus, this requires that containment vessels of this design utilize very heavy top and bottom end caps at the axial ends of the vessel, in order to contain diverted flywheel material fragments.
Another approach to safety in rotating materials, such as flywheels, is to overdesign and control the quality of the systems to the point that failure is exceedingly unlikely. This design philosophy is utilized in jet engine construction. Ideally, from a purely safety standpoint, this is the most desirable construction approach. However, if flywheels are to be widely utilized in diverse engineering applications, they cannot be as expensive to produce as jet engines.
Due to their superior strength qualities, flywheels constructed of composite materials may fail at speeds four to five times higher than that which was achievable using traditional steel flywheels. Thus, there is a continuing need for a relatively low cost, lightweight flywheel vessel that can contain flywheels that operate at energy levels on the order of twenty-five times higher than that produced by steel flywheels. Prior art physical mechanisms that have relied primarily on friction, local buckling, and pure tensile loading, have not proved to be sufficient since they cannot withstand the strain rate produced by the high speed event of the above-described type of failure. The material and configuration utilized in these types of prior art containment systems have not been able to change shape fast enough to avoid ultimate failure of the material.
SUMMARY OF THE INVENTION
The present invention discloses a containment device for retaining projected high energy material fragments that are produced during the catastrophic failure of a high energy rotary mechanism, such as aa composite flywheel. The containment device contains an approximately circular-shaped outer ring that is designed to be unyielding and not to experience direct contact with flywheel material fragments during a flywheel failure. Positioned axially along the inner periphery of the outer ring are a plurality of juxtapositioned, shaped elements that are configured and positioned to produce hollow cells. These shaped elements are adapted of a material and are configured and positioned in such a way as to possess sufficient ductility to adequately flatten through non-destructive plastic deformation and contain the high energy material fragments of a failed flywheel. The hollow cells formed by the shaped elements plastically deform (or bend) at a rate fast enough to prevent the elements from experiencing ultimate tensile failure (rupture) or localized compression failure (buckling). The shaped elements attach to the interior of the outer ring in a manner that forms an inner ring layer.
In a preferred embodiment of the present invention, the outer ring and shaped inner elements have an axial height that is greater than that of the flywheel itself. The shaped inner elements have midsections that are designed to plastically deform in the radially outward direction in response to impact from failed flywheel fragments in a manner that creates a concave interior surface. This concave surface then acts to prevent axial dispersion of diverted flywheel material fragments. The plastic deformation of the shaped inner elements occurs quickly enough to significantly extend the total impact time interval and thus reduce the peak force that must be absorbed by the elements. Therefore, the strength and thickness (and correspondingly, the weight and cost) of the material required to prevent ultimate failure of the shaped elements are dramatically reduced.
In one embodiment of the present invention, the inner elements are each formed in an S-shaped configuration. The two bends which form the S-shape of each inner element are oriented in the axial direction. These elements are juxtapositioned along the inner periphery of the outer ring in an overlapping arrangement to form an inner ring layer. In this design, one region of each S-shaped element contacts the inner wall of the outer ring and another region of each S-shaped element contacts an adjacent S-shaped element.
In an alternate embodiment, the shaped inner elements are similarly configured, but each contains more than two bends to form a more complex shape. This embodiment is capable of absorbing higher energy levels than the first described embodiment, but is more expensive to produce due to the increased forming requirements. Still another alternate embodiment utilizes a single shaped inner element that contains a plurality of axially aligned bends and folds such that this single inner element is configured to form a similar shape to the combination of all of the S-shaped elements in the original embodiment.
A containment device constructed in accordance with the present invention can thus be produced that is lightweight for relatively low cost, which is capable of containing composite flywheels during catastrophic failure, and that operates at energy levels on the order of twenty-five times higher than that produced by steel flywheels. The use of a containment system design that is based upon plastic deformation and high energy absorbing, hollow cell configurations, allows containment of high energy flywhe
Gabrys Jonathan W.
Gallagher Patrick
Christensen O'Connor Johnson & Kindness PLLC
Luong Vinh T.
The Boeing Company
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