Abstract:
A braking system for a high speed, high load rotor operating in a vacuum and suspended by a magnetic field such as in a flywheel energy storage device includes a pair of calipers disposed on opposed sides of the rotor for actuating a pair of annular friction discs into engagement with opposed sides of the rotor. Each caliper includes a mounting ring on its outer edge and an inner shallow annular groove in which it disposed one of the friction discs. A circulating fluid under pressure is directed into each annular groove for urging each friction disc into engagement with one of the opposed surfaces of the rotor for safely bringing the rotor to a stop such as in an emergency. The circulating fluid removes the heat generated by the braking action, while the controlled pressure applied by the discs also controls the position of the rotor when static such as during initialization.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to a braking system for a high speed, high load rotating system, such as a flywheel energy storage device, which also dissipates energy generated during braking. 
       BACKGROUND OF THE INVENTION 
       [0002]    Disc brakes are commonly used in various applications such as in vehicles for slowing or stopping the vehicle. Disc brakes are also connected to the output shaft of a prime mover, such an internal combustion engine, for measuring the output power as in a dynamometer. Disc brakes are also increasingly being used in high energy storage devices employing a rotating flywheel for controlling the speed of rotation of the flywheel. In these types of applications, the disc brake engages a moving rotor for controlling the speed, or even stopping, the rotor. 
         [0003]    In a high speed flywheel energy storage device, the flywheel rotor is often magnetically suspended and operates at very high speeds. These types of flywheel rotors typically have a composite composition and are the product of extensive design and development efforts and are expensive. Stopping a rotor such as for an emergency requires the application of a large torque on the rotor resulting in the generation of large amounts of heat which can damage or destroy the rotor and other energy storage device components. An emergency may arise because of a loss of cryostat cooling, a loss of vacuum within which the flywheel rotor operates, or the loss of the energy storage device&#39;s computer control system. In any of these cases, it is of the utmost importance to safely and quickly bring the flywheel rotor to a complete stop so as to avoid damaging the system or injuring operating personnel. In addition, for safety and operating purposes, it is essential that the rotor be precisely located vertically and laterally within the energy storage device particularly during initiation of the operation of the flywheel energy storage device using magnetic bearings. To date, the inability to safely stop a high speed, high energy magnetically suspended flywheel rotor in an energy storage device and to consistently and precisely position the rotor within the energy storage device have limited the use of these types of devices in commercial environments and applications. 
         [0004]    One embodiment of the present invention addresses the aforementioned limitations of the prior art by providing a safe and efficient braking system for a high speed, high load rotor magnetically suspended in a flywheel energy storage device and also provides the capability for consistently and accurately positioning the rotor within the energy storage device particularly at initiation of operation of the device. 
       SUMMARY OF THE INVENTION 
       [0005]    The brake mechanism of the present invention includes a pair of annular brake pads disposed adjacent opposed surfaces of a flywheel rotor. The brake friction surfaces, which are kept apart by springs during normal flywheel operation, contact the full annular surface area of both sides of the rotor when the brake is applied. By applying pressure to the lower half of the brake caliper, a lifting force is provided which, when precisely controlled, allows the static flywheel rotor to be suspended at the desired height for chilling the superconducting bearing cryostat and setting the magnetic suspension height of the flywheel rotor before commencing rotor spinning. The brake mechanism also laterally restricts movement of the flywheel rotor when not in motion for precise positioning of the rotor within the brake mechanism. During brake applications, cooling water or hydraulic fluid is forced under pressure through the caliper&#39;s passages, providing a clamping force and removing the heat generated by the engagement of the friction materials. The present invention is capable of operating with water which has inefficient hydraulic fluid characteristics because the inventive brake mechanism provides a large braking force area of application and is capable of accommodating the lower pressure requirements of water. In the event the rotor drifts out of its permitted vertical envelope, an external system not part of the present invention applies braking on the spinning rotor. In the event vibration causes the rotor to leave its predetermined safe lateral envelope of operation, the annular brake pads apply a radially inward force on the rotor for maintaining the required rotor lateral positioning. The brake calipers may be replaced as a “cartridge” and can be replaced as necessary without affecting any other part or component of the flywheel system. The frictional components of the brake mechanism can be easily replaced as an assembly such as where system requirements dictate that the friction components be a one time use item such as when used in an emergency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The appended claims set forth those novel features which characterize the invention. However, the invention itself, as well as further objects and advantages thereof, will best be understood by reference to the following detailed description of a preferred embodiment taken in conjunction with the accompanying drawings, where like reference characters identify like elements throughout the various figures, in which: 
           [0007]      FIG. 1  is a perspective, partially cutaway view of a braking system for high speed and power rotating machinery in accordance with the principles of the present invention; 
           [0008]      FIG. 2  is an exploded perspective view of the brake system of the present invention; 
           [0009]      FIG. 3  is a vertical sectional view of the brake system of the present invention; 
           [0010]      FIG. 4  is a partial, enlarged sectional view of a portion of the brake system shown in  FIG. 3 ; and 
           [0011]      FIG. 5  is a partial sectional view of the brake system of the present invention illustrating the taper of the rotor and the upper and lower brake pads. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]    Referring to  FIG. 1 , there is shown a perspective, partially cutaway view of a brake system  10  in accordance with the principles of the present invention.  FIGS. 2 and 3  are respectively exploded perspective and vertical sectional views of the brake system  10 .  FIGS. 4 and 5  are partial, enlarged sectional views of portions of the brake system  10  shown in  FIG. 3 . 
         [0013]    The brake system  10  of the present invention includes a brake disc rotor  18  attached to a main shaft  27  as well as to a rotating body  50  by means of a retainer plate  16  and plural threaded bolts  28  concentrically disposed in a spaced manner about aligned center apertures in each of the retainer plate, brake disc rotor and main shaft. The brake disc rotor  18  is preferably comprised of a high strength, annular heat resistant composite material, such as carbon-carbon, and is disposed between first and second annular brake disc pads  14  and  23 . Each of the first and second brake disc pads  14  and  23  includes respective plural spaced projections, or teeth,  29   a  and  29   b  disposed about the outer periphery of the brake disc pad. Each of the plural projections  29   a  and  29   b  of the first and second brake disc pads  14  and  23  engage a respective recess, or dog,  21  on the outer periphery of a ring  30  fixedly positioned between the first and second brake disc pads. The recesses  21  are arranged in a spaced manner about ring  30 . The first and second brake disc pads  14 ,  23  are prevented from rotating by engagement of their respective teeth  29   a  and  29   b  with the spaced peripheral recesses  21  in ring  30 . When pressure is not applied to the first and second caliper half housings  13  and  25 , plural coil springs  19  disposed about the brake disc rotor  18  in a spaced manner maintain the first and second brake disc pads  14  and  23  in spaced relation from the brake disc rotor  18 . The plural resilient, coil springs  19  are in the form of resilient members which function as displacement means by engaging and urging the first and second brake disc pads  14  and  23  in a direction away from the brake disc rotor  18 . 
         [0014]    First and second caliper halves respectively include a first caliper half housing  13  and first fluid bladder, or moveable member,  15  and a second caliper half housing  25  and second fluid bladder, or moveable member,  22 . While brake system  10  is described herein as including first and second caliper half housings  13  and  25 , the present invention is not limited to this configuration as it may also be in the form of a single integrated structure or may be comprised of more than two outer housings. The term “bladder” is used herein to designate structure which forms a portion of a hollow structure, or cavity, as described in detail below. Each of the first and second fluid bladders  15  and  22  is in the form of an annular disc preferably comprised of stainless steel, titanium or carbon fibers. Each of the first and second fluid bladders  15  and  22  is attached about its respective outer periphery to the first and second caliper half housings  13  and  25  by means of recesses  21  disposed on ring  30 . The first and second fluid bladders  15  and  22  are also attached about their inner peripheries to the first and second caliper half housings  13  and  25  by means of respective retainer rings  17  and  20 . Retainer rings  17  and  20  act as a seal by means of a clamping force to prevent the escape of hydraulic fluid from the cavities formed between the first and second fluid bladders  15  and  22  and the first and second caliper half housings  13  and  25 , respectively. While the first and second fluid bladders  15 ,  22  are described as being in the form of annular discs, these moveable members could also be in the form of virtually any annular structure responsive to an increase in hydraulic pressure for applying a mechanical force to an adjacent brake pad. 
         [0015]    First paired outlet and inlet fluid fittings  11  and  12  direct hydraulic fluid under pressure into and out of the annular channel  13   a  in the first caliper half housing  13 , while second paired inlet and outlet fluid fittings  26  and  24  direct hydraulic fluid into and out the annular channel  25   a  in the second caliper half housing  25 . The outlet and inlet fluid fittings  11 ,  12  and  24 ,  26  are preferably coupled to a closed fluid system (not shown for simplicity) to allow the fluid to be recirculated through the brake system  10 , but may also operate with an open, noncirculating fluid system. The outlet and inlet fluid fittings  11 ,  12  and  24 ,  26  are preferably displaced 180° from one another on the first and second caliper half housings  13  and  25 , respectively. The aforementioned cavities discussed above are formed within the first and second annular recesses  13   a ,  25   a  between the first caliper half housing  13  and the first fluid bladder  15  and between the second caliper half housing  25  and the second, fluid bladder  22 , respectively. 
         [0016]    During brake application, hydraulic fluid is pumped continuously under pressure from the inlet fittings  12  and  26  respectively into the annular channel  13   a  of the first caliper half housing  13  as well as into the annular channel  25   a  of the second caliper half housing  25 . Hydraulic pressure forces the first and second fluid bladders  15  and  22  against the first and second brake disc pads  14  and  23 , respectively, so as to overcome the opposing pressure of springs  19  which creates friction against the brake disc rotor  18 . Heat generated by friction between the first and second brake disc pads  14  and  23  and the brake disc rotor  18  is transmitted to and absorbed by the hydraulic fluid within the first and second fluid bladders  15  and  22 . The heated hydraulic fluid is directed out of the first and second fluid bladders  15  and  22  via the first and second outlet fittings  11  and  24 , respectively, and the heat is dissipated by an external system not part of this invention. It is in this manner that heat is safely and efficiently removed from the brake system during operation. Significantly, the fluid provided under pressure to the brake system  10  has a dual function. It is used to mechanically actuate the brake and to thermally remove heat from the brake. 
         [0017]    When the brake disc rotor  18  is at rest, such as prior to initialization of operation, the brake disc rotor engages and is supported in a secure manner by the second brake disc pad  23 . As shown in the partial sectional view of  FIG. 5 , the upper surface  23   a  of the second brake disc pad  23  is tapered downwardly in proceeding radially inwardly to provide a self-centering function for the brake disc rotor  18  when at rest as well as when braking action is applied to the brake disc rotor. Similarly, the lower surface  14   a  of the first brake disc pad  14  is tapered upwardly in proceeding radially inwardly to also provide a self-centering function for the brake disc rotor when at rest as well as when braking action is applied to the brake disc rotor  18 . The angle of taper is preferably less than 1°. It is in this manner that the brake disc rotor  18  is restrained in movement vertically and horizontally, or laterally, prior to operation as well as during operation to ensure that it stays within precisely defined positioning criteria. 
         [0018]    The disclosed embodiment provides an improved brake for stopping or controlling the speed of a magnetically suspended flywheel rotor in a high energy storage device which is also capable of safely and efficiently removing heat generated during braking of the rotor. 
         [0019]    The disclosed embodiment also provides a braking system for safely stopping a magnetically suspended high speed rotor in an energy storage device under vacuum which is also capable of consistent and accurate positioning of the rotor vertically and laterally during initialization of operation within the energy storage device. 
         [0020]    The disclosed embodiment further provides a friction braking for a magnetically suspended, high energy flywheel rotor in an energy storage machine wherein the brake pad calipers can be easily removed and replaced as an assembly without affecting or involving any other component of the energy storage machine. 
         [0021]    The disclosed embodiment still further provides an improved disc brake wherein the spinning rotor is engaged on opposed surfaces by a pair of annular discs for maximum braking surface engagement. 
         [0022]    While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the relevant arts that changes and modifications may be made without departing from the invention in its broader aspects. For example, while the present invention has been describe primarily in terms of use with a flywheel rotor in an energy storage device, the inventive braking system is also applicable for use in virtually any system incorporating high speed or high power rotating machinery, such as in dynamometer measuring systems. In addition, while the invention has been described for use with a magnetically suspended flywheel rotor, the inventive brake system can equally as well be used with a flywheel rotor suspended either electromagnetically or by superconductors or by means of mechanical bearings. Finally, while the axis of the spinning rotor is shown in the various figures as aligned generally vertically, a rotor used with the braking system of the present invention may have virtually any orientation. Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. The manner set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.