Laminated thin plate end plate

Abstract

1. A laminated laminate end plate for a rotor comprising a number of adjacent laminates stacked together, each laminate having an identical shape including a central region symmetrical about a central axis and a number of spokes, each spoke extending radially outward from the central region, each spoke having a through hole at its tip, the laminates being stacked together and aligned to permit insertion of a bolt through a corresponding through hole in each laminate for each spoke.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to end plate designs for rotors, and more particularly to laminated end plate designs suitable for use in conjunction with flywheel rotors. [Background technology]

[0002] Modern energy storage rotors, which are applied in long term utility scale applications as well as short term power applications such as Uninterruptible Power Supply (UPS) settings, are typically constructed either with composite fiber wound rotors or from steel. Optimizing the cost of the rotor is a major goal when addressing the long term discharge applications encountered in such utility applications as well as in some commercial / industrial settings.

[0003] The cost of the flywheel rotor can make up in the range of 50% of the cost of the manufactured system. Other flywheel components then make up the other half of the system cost. Also, many of these system costs are proportional to the volume and / or mass of the rotor. Therefore, reducing the volume and mass of the rotor is of paramount concern in flywheel energy storage systems.

[0004] Monolithic steel rotors utilize standard steel processing (primary melting, secondary remelting refining steps, forging, quenching, and tempering) to achieve the desired shape and material mechanical properties set within the achievable design range. In general, rotor shapes can be characterized by a "shape factor", k. k = E / σV (Equation 1) where E is the stored kinetic energy, V is the total rotor volume, and σ is the rotor peak stress. The shape factor ranges from 0 to 1. Roughly speaking, the shape factor is an indicator of the effectiveness of the rotor's material utilization. A high shape factor is an indicator that the stress is distributed evenly throughout the rotor volume, which corresponds to good material utilization. As can be seen from the definition of the shape factor, the stored energy is directly proportional to the rotor peak stress. Thus, the practically usable peak stress defines how much energy can be stored in the rotor. The maximum peak stress can be limited by failure criteria in terms of the material's yield stress or ultimate stress, or it can be limited by cyclic fatigue constraints.

[0005] Typically, shape factors for large, multi-ton monolithic solid cylindrical rotors with substantial axial thicknesses of 6 to 20 inches are in the range of 0.55. For very thin disks analyzed assuming two-dimensional plane stress (zero axial stress), shape factors have been evaluated to be slightly above 0.6, representing approximately a 10% improvement in such thin disks compared to monolithic rotors.

[0006] To produce a rotor with the right energy capacity, the total volume (or mass) of the rotor must be set appropriately. The use of a laminated lamination construction of the rotor decouples the rotor size from the manufacturing process of the individual laminations. The size of a cylindrical rotor, symmetrical about a central axis, is determined by its axial length and its diameter, or its lateral length. This diameter is determined only by the available supply width of the material stock, i.e., the coil width. The axial dimension of a laminated lamination rotor is also defined by the number of laminations of the laminations. Thus, virtually any axial dimension of the rotor can be realized. The rotor dimensions that can be achieved with the laminated lamination approach are relatively unconstrained, in contrast to the dimensions achievable using solid forging, an alternative approach used in the manufacture of solid rotors.

[0007] Cold rolling is generally a process following the standard hot rolling process to further reduce the thickness of previously hot rolled plate material. The term cold rolling refers to the temperatures allowed in the process being lower than the temperature at which scale forms on the metal surface. Cold rolling is widely used throughout the metal fabrication industry with many alloys, treatments, and finish conditions used in products sold in coil or sheet form, and many metal combinations. Examples of materials are those used in many parts of automotive manufacturing, such as body panel parts that are easy to form, as well as high strength parts used in bumpers and structural panels. Silicon steels used in the electrical industry to build transformers, motors, and generators are also cold rolled to achieve the desired thickness, uniformity, and finish.

[0008] Cold rolled steels for major components such as automotive bumpers and structural panels are readily available in very high tensile strengths, for example up to 2000 MPa. Such materials are generally supplied in thicknesses of around 0.5 mm to 2.0 mm from leading global suppliers. Easily inspected with automated optical inspection systems, material quality is generally excellent; therefore, defects are generally absent within large panels. Furthermore, the quenching step for such thin materials allows for adequate cooling rates, and complete hardening of even low alloy steels is easily achieved, so very high strengths can be achieved using very basic carbon steel alloys.

[0009] As already mentioned, laminated steel rotors have several advantages in cost and performance over monolithic forged steel rotors. (1) Continuous processing of cold rolled steel is more economical than the individual processing required for monolithic rotors. Essentially, an extensive and continuous rolling process replaces a one-time forging step. (2) The thickness of a monolithic rotor is dictated by the hardenability of the steel alloy used. For a 6 inch thick rotor to achieve the same strength level as a 2 mm thick sheet, significantly more expensive steel alloys must be used. While monolithic forgings are limited in maximum thickness by hardenability limitations, rotors constructed of cold rolled sheets can be stacked into an assembled rotor at any required thickness because each sheet is individually quenched and tempered. (3) Laminated steel rotors also have an advantage in terms of defects present in the steel. As mentioned above, the cold rolling and inspection processes produce a very high quality material. Also, in flywheel rotors, the greatest stresses are in the in-plane radial and hoop (circumferential) directions. Defects oriented perpendicular to the radial or hoop directions will form cracks and propagate faster than defects parallel to the hoop and radial directions. The rolling process orients grains and any defects parallel to the rolling direction, which is optimal from a fatigue crack propagation standpoint. Monolithic forged rotors may have defects oriented parallel to the rotor axis, which is the weakest orientation for fatigue crack propagation in such structures.

[0010] Inspection of solid forgings is typically performed by ultrasonic (UT) testing by volume, and magnetic particle and / or dye penetrant testing for surface inspection. These are standardized testing processes, but are practically required since the inspection errors can vary widely. In contrast, inspection of cold-rolled material is largely automated on the production floor, with favorable results in terms of inspection costs and final product quality.

[0011] In applications intended for 10,000+ full amplitude stress cycles, each corresponding to a full depth cycle of a flywheel energy storage system, the stress amplitude is usually practically defined by cyclic fatigue. Cyclic fatigue life is defined by the presence (or absence) of defects and their subsequent propagation to a critical dimension that promotes failure as a crack. Crack propagation is a direct result of cycling the stress between predetermined minimum and maximum levels. Cold rolled sheet metal has inherent residual defects well positioned, which gives the sheet metal excellent resilience to cyclic fatigue.

[0012] US Patent No. 11,362,558, filed February 11, 2020, by Seth R. Sanders et al., discloses a flywheel rotor formed from several adjacent laminations stacked together. The invention also discloses end plates at one or both ends of the lamination stack. Various embodiments of end plates are disclosed in US Patent No. 11,362,558. However, further research and development has shown that the lamination approach used for the steel rotor disclosed in the patent can also be beneficial for steel end plates.

[0013] It is with respect to these and other considerations that the present invention has been made. Summary of the Invention

[0014] The present invention aims to manufacture an end plate for a flywheel rotor using laminated thin plates.

[0015] Certain embodiments are directed to an end plate design that supports at either end the stack of laminations that form the rotor. An embodiment of the end plate includes a central region and a number of spokes that extend radially outward from the central region. In one embodiment, each spoke has a hole that receives a bolt. In certain embodiments, a bolt passes through each rotor lamination and secures the lamination to the end plate. In one embodiment, the end plate itself is constructed from several laminations, each lamination having holes that align with the holes in the rotor laminations.

[0016] Another embodiment is directed to a laminated lamination end plate for a rotor comprising a number of adjacent laminations stacked on top of each other, each lamination having an identical shape including a central region symmetrical about a central axis and a number of spokes, each of which extends radially outward from the central region, each spoke having a through hole at its tip, the laminations being stacked on top of each other and aligned to allow for the insertion of a bolt into the corresponding through hole in each lamination for each spoke. [Brief description of the drawings]

[0017] Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings, in which like reference characters refer to like parts throughout the various views unless otherwise specified, in which:

[0018] [Figure 1] FIG. 1 is a schematic cross-sectional view of one embodiment of a flywheel energy storage system, also referred to as a flywheel unit.

[0019] [Figure 2A] FIG. 2A shows a sheet shape called a scalloped circle, which has a low stress area near the periphery through which a through hole can be inserted.

[0020] [Figure 2B] FIG. 2B shows in dashed lines the circular circumference of the sheet shape of FIG. 2A.

[0021] [Figure 3A] FIG. 3A shows one embodiment of an end plate where material is removed from around the outer diameter so that the end plate has spokes.

[0022] [Figure 3B] FIG. 3B shows in dashed lines the circular circumference of the central region of the endplate of FIG. 3A.

[0023] [Figure 4A] FIG. 4A shows an end plate made of laminated sheets.

[0024] [Figure 4B] FIG. 4B illustrates one embodiment of the end plate of FIG. 4A with an attachment mechanism for a stub shaft and a matching tag.

[0025] [Diagram 5] FIG. 5 shows one embodiment of a stub shaft attached to an end plate.

[0026] [Figure 6] FIG. 6 illustrates an embodiment of a fully assembled rotor suitable for use in a flywheel energy storage system.

[0027] These figures depict embodiments of the invention for purposes of example only, and from the following discussion, those skilled in the art will readily appreciate that alternative embodiments of the structures and methods shown herein may be used without departing from the spirit of the invention described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof and which show, by way of example, specific exemplary embodiments in which the invention may be practiced. However, the present invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will fully and thoroughly convey the scope of the invention to those skilled in the art. Among other things, the present invention may be embodied as a method, process, system, or device. Thus, the following detailed description should not be construed in a limiting sense.

[0029] Introduction A laminated rotor or end plate is constructed by stacking many laminations, each lamination in the stack having the same shape and the same orientation relative to the central axis. For example, a 300 mm thick rotor requires 150 laminations, each 2 mm thick. A 24 mm thick end plate requires 12 laminations, each 2 mm thick. As explained below, the thickness of the end plate may be slightly more than 24 mm if adhesive is used between the laminations. Thicknesses for larger designs currently underway are substantially larger, or up to about 75 mm for the largest yet planned.

[0030] In terms of resilience to single point defects, the entire laminate design can be organized so that adjacent laminae carry the extra load in the event of a single point defect, thus avoiding catastrophic failure.

[0031] In general, rotors constructed from laminated steel sheets can be less expensive than monolithic forged steel rotors and can provide greater stress amplitudes than monolithic forged steel rotors, which translates directly into improved performance per unit rotor cost and, therefore, improved system balance for the flywheel.

[0032] It can be understood that the shape of the laminated sheet rotor does not have to be circular, since the sheets can be manufactured by stamping, laser cutting, or any other suitable process. Using such processes to create any shape, the sheets can be made in any shape. Thus, rotors made of laminated sheets are not limited to circular contours or cylindrical shapes. It is the main object of the present invention to achieve an advantageous shape for a laminated sheet rotor and to provide the associated support elements.

[0033] definition As used herein, the following terms have the meanings indicated below.

[0034] As used herein, an energy storage system refers to a system that stores and releases energy. Energy storage systems are generally coupled to a power grid, allowing the grid to store and withdraw energy as needed.

[0035] As used herein, a flywheel energy storage system, flywheel unit or flywheel device, or flywheel, is an energy storage system that stores kinetic energy in a flywheel rotor. One or more flywheel units, when coupled together, comprise an energy storage system. Flywheel unit refers to the flywheel housing or enclosure and any rotor, motor / alternator, and other elements it houses, as well as power electronics elements that may be housed and attached to the flywheel enclosure.

[0036] A flywheel rotor or rotor as used herein is generally a spinning, rotationally symmetric mass such as a cylinder or disk, the main component of an energy storage system. The rotor is physically coupled, directly or indirectly, to a motor / alternator which is itself electrically coupled to a converter. The converter may be a single inverter that interfaces the motor / generator to a dc bus. This allows for the aggregation of multiple flywheels on the dc bus using a common high power inverter.

[0037] When power for storage is accepted, the rotor is driven, increasing the rotational speed of the flywheel rotor. The faster the flywheel rotor spins, the more energy is stored. When power is extracted, the flywheel rotor drives a motor / alternator.

[0038] Sheet metal, as used herein, generally refers to a thin, smooth, flat piece of material, typically steel, produced by a cold rolling process. Cold rolled steel is an obvious example of material that may be used for sheet metal, although other types of materials may be used, including plastics, aluminum, cement, glass, carbon fiber composites, other composites, and steel (other than cold rolled), among others. Sheet metal, as used herein, is cut into a shape and has two sides, a top and a bottom. Unless otherwise specified, sheet metal, as used herein, is circular or primarily circular in shape and may be characterized by two dimensions, an axial dimension and a radial or width dimension.

[0039] A lamination stack, as used herein, refers to a three-dimensional object constructed from multiple adjacent laminations stacked one on top of the next, such as a rotor or end plate. A lamination stack has two ends, a top end and a bottom end. Generally, the laminations are the same shape, positioned adjacent to each other, have the same rotational orientation relative to a central axis, and are joined or held together. For example, multiple circular laminations look like cylinders. Multiple rectangular laminations look like rectangular cuboids. The primary application of the lamination stack described herein is for flywheel energy storage, although the invention is not limited thereto. For example, rotors and end plates used in motors and other mechanical devices may utilize the invention.

[0040] A laminated lamination rotor, as used herein, refers to a rotor constructed from laminations, ie, as multiple adjacent laminations stacked one on top of the next.

[0041] A laminated lamination end plate, as used herein, refers to an end plate constructed from a laminate stack, ie, as multiple adjacent laminations stacked one on top of the next.

[0042] Flywheel Energy Storage System 1 is a schematic cross-sectional view of one embodiment of a flywheel energy storage system, also referred to as a flywheel unit 100. The flywheel unit 100 includes a flywheel rotor assembly 130, or simply a flywheel rotor 130, a motor and alternator 140 (also referred to as the motor / alternator 140 since both functions are generally performed by a single subsystem), a flywheel housing or enclosure 110, and a power electronics unit 120.

[0043] The motor / alternator 140 converts between electrical and mechanical energy so that energy can be stored in or drawn from the flywheel rotor 130. The motor / alternator 140 is sometimes referred to as a motor and alternator 140 since it combines the functions of a motor and an alternator. In one embodiment, the motor / alternator 140 is indirectly connected to the flywheel rotor 130 through a lower stub shaft 134 that is connected to a lower journal of the flywheel rotor 130 and also connected to a lower support bearing. An upper stub shaft 132 connects the flywheel rotor 130 and the upper bearing. In another embodiment, the flywheel rotor 130 incorporates a shaft that connects to the motor / alternator 140. The motor / alternator 140 is connected to the power electronics unit 120 through wires or other electrical connections that typically run from the flywheel housing 110 through a vacuum feedthrough.

[0044] The flywheel unit 100 further comprises a lifting magnet 150, also called a magnetic unloader, which at least partially levitates the mass of the flywheel rotor 130. The lifting magnet 150 is disposed above the flywheel rotor 130.

[0045] The power electronics unit 120 has a housing that encloses and houses electrical components including a power converter for converting either DC or AC input current to alternating current acceptable to the motor / alternator 140. The power electronics unit 120 may also include sensors, processors, memory, computer storage, and network adapters as required to provide communication, control, and status monitoring of the flywheel unit 100.

[0046] Although the flywheel housing 110 is shown enclosing a single flywheel rotor 130 and a single motor / alternator 140, in other embodiments a single housing may enclose multiple rotors and multiple motor / alternators.

[0047] Rotor thin plate shape A circular disk shaped sheet metal is a natural choice for a rotor and provides the most common symmetry, but other shapes are also practical and have substantial advantages. Because cold rolled sheet metal is typically supplied by manufacturers in coil form, shapes can be strategically selected to improve sheet metal material utilization. For example, a regular polygon with at least two sides or edges that match the as-supplied coil width will use a higher percentage of sheet metal material than a conventional circle.

[0048] FIG. 2A shows one embodiment of the shape of the laminations used to form the laminated lamination rotor. In this embodiment, each lamination is identical in shape and the shape is symmetrical about a central axis. This shape may also be referred to as rotationally symmetric. The lamination shape is generally circular, but has protrusions along its outer periphery or circumference. The protrusions may have through holes intended for placement of fastening or joining bolts to be inserted into the protrusions along the circumference of the lamination shape, which minimizes stresses associated with the through holes.

[0049] The laminations are joined together by a fastening mechanism. In certain embodiments, the fastening mechanism includes two or more tie rods or bolts that pass through the through holes. The fastening mechanism ensures that each lamination of the lamination has the same orientation relative to the central axis when the laminations are clamped. End plates further secure the laminations at one or both axial ends of the lamination. Although the embodiments of the shapes disclosed herein are all rotationally symmetric, the invention is not so limited and shapes that are not rotationally symmetric are also within the scope of the invention.

[0050] For reference, a circle relative to the inscribed square consumes π / 4 or about 0.785 percent of the available material. A regular octagon sharing a portion of each edge of a provided square consumes about 0.83 percent of the available material.

[0051] Manufacturing and joining methods for laminated thin plates Joining the laminations to each other in the lamination stack and to the stub shaft (or shaft) to provide bearing support imposes significant constraints on the shape design. The use of non-circular lamination shapes allows for advantageous use of joining techniques, as described below.

[0052] The sheets may be joined together by many possible means, including adhesive bonding, interference fitting onto a central shaft as is done in many electric machine rotor assemblies, welding by one of many possible welding processes, and retaining axial bolts.

[0053] A variety of adhesives may be used to bond the sheets together, including acrylic metal adhesives, cyanoacrylates, oxygen-free metal adhesives, and epoxy resins. The strongest adhesives to metal are known as epoxy resins, or simply epoxies.

[0054] In some cases, circumferential welding may be feasible, but welding generally imposes material degradation due to the heat affected zone of the weld. Laser welding is typically used on small electrical steel sheet laminations, but these light-duty welds are not intended for basic structural welding.

[0055] The use of a central shaft or axial retaining bolts requires through-holes, i.e. holes passing axially through each sheet of the lamination. Generally, for regions near the center of the rotor where the hoop and radial stresses are approximately equal (biaxial stress condition), the hoop stress in the required through-holes will be twice any prevailing principal stress. In regions away from the central region, for example on the periphery of a circular disk, the stresses are uniaxial in the hoop (circumferential) direction. In uniaxial stresses, a circular through-hole will cause a local stress concentration three times the prevailing stress. Thus, through-holes in circular sheet geometry are generally not practical for circular sheets.

[0056] However, the sheet shape does not have to be exactly circular, and there are many non-circular shapes that allow for a low stress region near the periphery where through holes can be introduced without a significant increase in stress compared to the overall normal stress in the bulk of the sheet, as depicted in Figures 2A and 3A.

[0057] FIG. 2A is an example of a lamination shape 200 that includes low stress areas near the periphery where through holes may be introduced, referred to herein as scalloped circles. Shape 200 has protruding "scallops" 202, each protruding slightly from the circular periphery or circumference. Shape 200 has eight evenly spaced scallops 202, although other embodiments may have more or less scallops. Under centrifugal loading, the scallops 202 are maintained at very low stress because they are areas that are effectively protected from general hoop stress. Thus, one or more through holes 204 can be easily introduced in one or more scallops without causing stress concentration issues. This approach allows laminations to be joined by axially oriented bolts. Additionally, axial bolts can be joined or fastened to the upper and lower end plates of the terminations that facilitate interconnection with the respective stub shafts at the top and bottom of the fully assembled rotor.

[0058] Although the protrusions of shape 200 are equidistant from one another and have a scalloped shape, the invention is not so limited, in other embodiments, the protrusions may not be equidistant from one another and the shape of the protrusions may have a shape other than a scallop.

[0059] The shape 200 has a through hole 204 in each scallop 202. Generally, during the manufacturing process, a structural retaining bolt is inserted through each through hole 204 to provide three-dimensional stiffness to the resulting assembled sheet lamination. One of the challenges in such an assembly is to avoid slippage under variable loading conditions as well as across operating conditions such as changing temperatures. Any slippage can lead to imbalance or, even worse, dynamic instability if the slippage provides significant damping to the rotating frame. Any of the associated outcomes of slippage are failure modes in nature. To prevent this slippage, the dimensions and tension of the retaining through bolts should be specified to maintain the proper compression surface contact load throughout the lamination at the proximal region of the through hole in the scallop or apex. After considering friction against slippage and calculating the required compression surface contact stress, the through bolt diameter, material, and tension level are calculated.

[0060] A convenient way to verify the tension level of a bolt is to simply measure the expansion in length of the bolt when it is under tension. This provides a direct measure of the strain and stress state of the bolt, as opposed to using traditional bolt torque specifications.

[0061] Another consideration is the use of permissible through-hole slot liners to mitigate wear of the bolt and sheet metal interface during bolt insertion and operation. Under repeated centrifugal loading, the through-hole bolts may become biased (repeatedly) within their respective clearance holes and become supported by the side walls of the clearance holes as they are centrifugal loaded. With repeated centrifugal loading and unloading, this repeated interaction with the side walls constitutes a wear process and may cause surface wear and subsequent loss of reliability of the bolt. Slot liners may be manufactured from softer metals such as aluminum or brass, or from organic materials. Slot liners can be manufactured as one-piece or slotted tubes. The latter may be manufactured, for example, by bending and forming the slot liner from a sheet of aluminum stock with a thickness of 0.1-1.0 mm.

[0062] 2B illustrates in dashed lines the circular circumference 206 of the sheet shape 200. Although the shape 200 is not perfectly circular due to the protruding scallops 202, the shape 200 may be understood to have a sheet circumference 206 that is the largest inscribed circle within the shape 200 without including material from any of the scallops 202. In this embodiment, each through hole 204 is generally outside the circumference 206, but generally inside the corresponding scallop 202.

[0063] End Plate Design In certain embodiments, for rotating systems that are constrained by two or more mechanical bearings during operation, rest, or shipping, the laminated thin plate rotor must be bonded to a pair of stub shafts to interface with the bearings. The following description focuses on one end of the laminated thin plate rotor, with the understanding that a similar bonding approach may be used for either or both ends of the laminated thin plate rotor.

[0064] Structural through bolts similar to those described above may be connected to the end plates. As used herein, the term end plate may be, among other things, a single solid piece, formed from multiple sheets, or assembled from several pieces. One purpose of the end plates is to provide a structurally sufficient connection near the periphery of the rotor between the axial through bolts that pass through the rotor. A second purpose is to provide a way for the central stub shaft to connect or join to the rotor.

[0065] In certain embodiments, solid circular end plates are used. The peak equivalent stress in a rotating disk occurs at the center. Some methods used to join cylindrical shafts or other strategically designed stub shafts to flat plates create stress concentrations in this peak stress region. Furthermore, as discussed above in consideration of the design of the laminar shape, the introduction of through holes in the circular end plates near the periphery creates severe localized stress concentrations. This stress concentration at the center and / or periphery limits the maximum speed of the rotor and therefore the energy storage capacity. The geometry of the rotor top and bottom end plates must be shaped to reduce stress on the shaft connections and connections to the structural through bolts.

[0066] In certain embodiments, a magnet-based offloading system, referred to herein as lifting magnets 150, provides a magnetic levitation force to the rotor to counteract the gravitational load that would be imposed on the system's bearings. It is desirable to maintain full density and circular symmetry in the area of ​​the ferromagnetic upper steel end plate for the flywheel rotor 130 to interact with the lifting magnets 150. Thus, the use of magnetic levitation imposes one constraint on the design of the upper end plate.

[0067] FIG. 3A shows an embodiment of an end plate 300 in which material is removed from around the outer diameter such that the plate has spokes 310. In the end plate 300, material is removed to create the spokes 310 that extend radially outward from a central region 320. Reducing the mass at the periphery of the end plate 300 effectively reduces the stress in the central region 320 and allows for attachment to the lower stub shaft 134. The end plate 300 may be attached to the stub shaft 132, 134 by a variety of mechanisms including a central hole 330, a bore, a bolt circle, or a weld to connect to the shaft, among others. Any number of spokes may be used in this design. In certain embodiments, the ends of the spokes 310 are connected to the adjacent lamination by directly connecting to the through bolts mentioned above. In certain embodiments, the lamination is supported by a top end plate and a bottom end plate. In other embodiments, there may only be a single end plate at the top or bottom of the lamination.

[0068] The central region 330 is typically made of solid ferromagnetic steel, like the lifting magnets 150, and interacts with the lifting magnets. Since the lifting magnets 150 are located at the top of the rotor 130, this constraint is only necessary for the upper end plates of the rotor 130. Thus, in certain embodiments, the central region of the lower end plates may not be made of ferromagnetic steel.

[0069] The spokes 310 may be tapered outward or dog-bone shaped so that there is more mass at the ends of the spokes than along their length. The ends of the spokes 310 may be connected via a rim around the outer diameter. By adding mass to the ends of the spokes, they can be designed to experience a radial displacement equivalent to the adjacent circular plate when subjected to centrifugal loads, thereby preventing stress concentrations at the spokes relative to the through bolted joints. The length and width of the spokes 310 are determined by the maximum allowable stress at the center of the plate and the area of ​​the unloading magnets used to lift the rotor.

[0070] In certain embodiments, the end plate 300 may have other characteristics. For example, U.S. Patent No. 11,362,558, filed February 11, 2020 by Seth R. Sanders et al., discloses end plates in several embodiments.

[0071] The use of monolithic solid steel end plates, i.e. end plates made from a single piece of steel, may not be optimal in terms of material cost, machining cost, and stress patterns. The end plate 300 embodiment made from solid steel requires the sacrifice or removal of a substantial amount of material in manufacture from other solid plates, either round or rectangular. Also, the manufacture requires significant machining and finishing steps. Also, as a part holding a one-piece solid steel spoke, residual centrifugal loads may still impose stress limitations in the center region.

[0072] In certain embodiments, central region 320 is generally circular. Figure 3B illustrates in dashed lines the circular circumference 340 of central region 320. Central region 320 is not perfectly circular due to the protruding spokes 310, but may be understood to have a circumference 340 that is the largest inscribed circle that can fit inside central region 320 and does not include any of the material of spokes 310.

[0073] Laminated thin plate end plate As shown in FIG. 4A, a laminated laminate end plate 400, also called an end plate 400, made of a plurality of laminated laminates 405, avoids many of the problems mentioned above. Most importantly, experience has shown that the machining cost of the end plate 400 is significantly reduced compared to a solid steel end plate of the same shape. For example, the spokes can be made using inexpensive laser machining equipment. Note that in the end plate 400, each laminate 405 is made integrally, i.e., from a single piece of steel or other material. Also, each laminate 405 is identical in shape and rotationally symmetric about a central axis A. Each laminate 405 has eight spokes 410 and a central region 420. In other end plate embodiments, the number of spokes is greater or less.

[0074] The laminations 405 have through holes 430 at the tip of each spoke 410. During the manufacturing process, the laminations 405 are stacked together such that the corresponding through holes 430 in each of the laminations 405 align with respect to the spokes 410 to allow a bolt to pass through the corresponding through hole 430 in each lamination. In certain embodiments, the bolt that passes through each through hole 430 in each lamination 405 also passes through the rotor lamination. In certain embodiments, the through holes 430 are threaded.

[0075] In certain embodiments, the end plate 400 has one or more intermediate through holes 440. Between each pair of spokes 410, the end plate 400 has an intermediate through hole 440. In other embodiments, there may be more or less intermediate through holes 440. In certain embodiments, the intermediate through holes 440 are threaded and receive eye bolts therethrough, allowing for lift-off during installation and maintenance, for example. To simplify the process of creating threads for each of the holes 440, nuts 445 may be inserted and secured within the holes 440 during the manufacturing process.

[0076] In one embodiment, a pattern is cut in the portion of the sheet metal that makes up the middle through hole 440 to accept a standard hex nut. The nut is bonded in place while allowing an adhesive to cure that is placed between each layer of end plate 300. With a stack of 12 2mm thick sheets, there may be a hex pattern laser cut into as many as 5 sheets, ensuring the nut is secured in place during lift-off.

[0077] 4B illustrates additional features that may be incorporated into end plate 400. Bolt circle 450 provides a method for joining end plate 400 to an adjacent structure or device, such as a stub shaft. For example, bolt circle 450 may be used to join end plate 400 to a stub shaft, such as upper stub shaft 132 or lower stub shaft 134, or stub shaft 500, described below. Other joining mechanisms besides bolt circles may be used for this purpose, including a single bolt, among others.

[0078] The end plate 400 may also include tags 460. The tags 460 may be used to align each of the end plate laminae 405 with one another during the manufacturing process. Alignment may be used to account for variations in thickness and other properties that may vary due to the rolling manufacturing process used to create the sheets. The tags 460 may be an integral part of one or more laminae 405, for example, by laser cutting, or may be affixed to one or more laminae 405, among other things. In certain embodiments, each sheet is rotated relative to adjacent sheets to maintain uniformity across the eight spokes in properties such as thickness.

[0079] As previously mentioned, manufacturing laminated sheet end plate 400 is more cost effective than manufacturing identically shaped solid end plates of comparable size and depth.

[0080] manufacturing process An example process for manufacturing the end plate 400 includes the following main steps.

[0081] Each lath is cut from a flat sheet of steel that has been rolled into a rectangle or other shape. The rolling process results in slight variations in the thickness of the material. For example, the center of the sheet may be slightly thicker than the edges. These thickness variations must be compensated for in subsequent manufacturing steps to create a single bonded end plate from several laths. Below is one process for creating laminated lath end plates that gives acceptable results:

[0082] 1. From this stock coil of rolled steel, cut one or more square sheets, each large enough to fit into an end plate lamination. A variety of methods may be used for cutting, including laser punching and shearing, among others.

[0083] 2. Laser cut or stamp each endplate sheet into a specified shape, such as the shape of endplate 300. This shape may optionally include a tag.

[0084] 3. Apply an adhesive, such as an epoxy, to each lamination. In certain embodiments, a film adhesive is used. This is an epoxy (similar to the fiberglass and carbon fiber materials of prepregs) that is premixed with a hardener and stored at low temperature until ready for use. The film adhesive is cut to shape and laminated to the steel lamination sheets to give uniform bond line properties. (The bond line is the thickness of the bond layer.) The laminations are then laminated together, tag-aligned (see FIG. 4B). The film adhesive, or other adhesive, may be applied after each lamination is added to the stack.

[0085] 4. Install nuts 445 into each intermediate through-hole 440.

[0086] 5. Apply plugs of Peek, Teflon, Delrin, or other suitable plastic, or other type of plug, to the top and bottom through holes 430 and intermediate through holes 440 in the laminate stack. This will prevent epoxy from entering the holes during subsequent processing. The use of polymers such as peek is also advantageous because it has a higher coefficient of temperature expansion than steel. As the epoxy cures in the platen press at elevated temperatures, the plugs expand to fill the holes tightly and prevent epoxy from entering. Upon cooling, the plugs shrink back and can be easily removed. Peek is one of the more advantageous materials due to its strength, frictional properties, and the fact that it does not bond with epoxy. As mentioned above, other polymer materials such as Teflon and Delrin are also suitable for this purpose.

[0087] 6. A platen press is used to apply the specified pressure and temperature profile for adhesive curing. The profile or program applied by the press controls the temperature according to the guidelines provided by the adhesive supplier. Cooling is performed in the platen press.

[0088] 7. Remove the plugs from the through holes 430, 440. If necessary, remove excess adhesive from the perimeter.

[0089] Generalized End Plate Design Most commonly, the end plates 300 and 400 have spokes, for reasons already discussed. In general, the present invention encompasses a rotationally symmetric end plate having a central region and spokes extending radially outward from the central region. A variety of spoke shapes and fastening mechanisms to the central region may be used. Furthermore, the spokes, as well as the central region, may be made of a variety of materials, including steel, plastics, and composites including carbon fiber, Kevlar, and fiberglass, among others. Additionally, the end plate may have one or more holes in the central region for the passage of bolts. Additionally, the spokes may have through holes at their tips for the passage of bolts that fasten the end plate to the rotor lamination.

[0090] 5 shows one embodiment of a stub shaft 500 that couples or attaches to an end plate, such as end plate 400. Stub shaft 500 is rotationally symmetric with flywheel 130. Stub shaft 500 has a cylindrical section 510 at the top and a bottom end called coupling section 515 for attachment to an end plate.

[0091] The link section 515 has one or more flanges 530 and a central region 520. At the bottom of the stub shaft 500, the flanges 530 are connected to the end plates via a bolt circle, such as bolt circle 450, a weld, or other form of mechanical attachment, such as a single threaded bolt. In certain embodiments, the central region 520 is conical in shape, allowing the central region 520 to flex, allowing the flanges 530 to move radially while maintaining sufficient axial stiffness. This design accommodates radial expansion and contraction of the rotor 130 at the connection with the end plate.

[0092] The stub shaft 500 may be provided with lateral bending compliance, which may be used to manage resonant modes as a suspension function in the flywheel unit 100. Designing such modal frequencies below the operating speed range is often a strategy to avoid exciting such resonances during normal operation.

[0093] FIG. 6 shows an embodiment of a fully assembled rotor 600 suitable for use in a flywheel energy storage system. The assembled rotor includes a stub shaft 610, two end plates 620, and a laminated lamination rotor 640. The end plates 620 are coupled to the top and bottom of the laminated lamination rotor 640. The laminated lamination rotor 640 is formed of a number of laminations, each of which is a scalloped circular shape, as shown in FIG. 2A. Each end plate 620 has eight spokes, each of which has a corresponding through hole at its tip through which a bolt is inserted. A portion of a motor / generator 650 is coupled to the bottom end of the laminated lamination rotor 640.

[0094] Upon reading this disclosure, those skilled in the art will appreciate further alternative structural and functional designs throughout the principles disclosed herein. Thus, while specific embodiments and applications have been illustrated and described, it should be understood that the disclosed embodiments are not limited to the precise structures and components disclosed herein. Various modifications, changes and variations that will be apparent to those skilled in the art may be made in the arrangement, operation and details of the methods and apparatus disclosed herein without departing from the spirit and scope as defined by the appended claims.

Claims

1. 1. A laminated lamination end plate for a rotor comprising a plurality of adjacent laminations laminated together, Each of the thin plates has the same shape, and the same shape is A central region symmetrical with respect to a central axis; a plurality of spokes extending radially outward from the central region and having through holes at their tips; An end plate, wherein the laths are stacked and aligned relative to one another to allow insertion of bolts through the corresponding through holes of each lath for each of the spokes.

2. The end plate of claim 1 , wherein a threaded nut is inserted into the through hole of each of the spokes.

3. 10. The end plate of claim 1 having eight spokes.

4. The end plate of claim 1 , wherein there is no through hole passing axially through the center of said central region.

5. The end plate of claim 1 , wherein the lamination is made of a material selected from the group consisting of steel, plastic, carbon fiber, composites, and cement.

6. The end plate of claim 1 , wherein each of the laminations is formed from a single piece of material.

7. The endplate of claim 1 , wherein the spokes of the sheet are formed by removing material from areas between adjacent spokes outside of the central region.

8. The end plate of claim 1 , wherein the uniform shape further comprises one or more intermediate through holes between each pair of adjacent spokes.

9. The end plate of claim 8 , wherein the central region is generally circular in shape and the intermediate through-hole is located circumferentially outside the central region.

10. The end plate of claim 1 , wherein at least one of the laminae includes a tag, the tag being used during a manufacturing process to align each of a plurality of adjacent laminae.

11. The end plate of claim 1 , wherein the uniform shape further includes a bolt circle in the central region that can be used to join the end plate to a stub shaft.

12. The end plate of claim 1 , wherein an adhesive is applied to each sheet during the manufacturing process.

Images