Patent Publication Number: US-9843237-B2

Title: Electromechanical flywheel with evacuation system

Description:
PRIORITY CLAIM AND INCORPORATION BY REFERENCE 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/849,484 filed Mar. 23, 2013 which claims the benefit of U.S. Prov. Pat. App. No. 61/615,860 filed Mar. 26, 2012. 
     This application incorporates by reference, in their entireties and for all purposes: 1) U.S. patent application Ser. No. 13/849,484 filed Mar. 13, 2013, 2) U.S. Prov. Pat. App. No. 61/615,860 filed Mar. 26, 2012; 3) U.S. Pat. No. 6,884,039 to Woodard et al. filed Dec. 30, 2002; and 4) U.S. Pat. No. 6,175,172 to Bakholdin et al. filed Aug. 4, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     Known flywheels store kinetic energy, that is, the energy of motion. When called upon to release this energy, the flywheel slows as kinetic energy is depleted. Flywheels driving and driven by electric machines are also know. For decades, such electromechanical machines have been built and have achieved varying degrees of operational success. Widespread application has, however, eluded flywheel manufacturers as even the most advanced commercial machines suffer from significant operational limitations while exceeding the cost of better performing alternatives. Despite persistent efforts by a small flywheel manufacturing industry, modern electromechanical flywheels have found only narrow applications in a few niche markets and presently make no significant contribution to the developed world&#39;s energy supply. 
     Field of Invention 
     This invention relates to the electromechanical arts. In particular, an electromechanical flywheel includes an evacuation system for evacuating a flywheel mass enclosure. 
     Discussion of the Related Art 
     Electromechanical flywheels include machines operating under atmospheric conditions and machines operating under evacuated conditions. However, prior art vacuum systems have generally failed to establish and maintain desired vacuum conditions. 
     SUMMARY OF THE INVENTION 
     The present invention provides an electromechanical flywheel with an evacuation system. 
     In an embodiment, an electromechanical flywheel method of configuring rotating parts that is enabled by a variable geometry drag pump, the method comprising the steps of providing a flywheel mass made from a carbon composite; providing a rotor made from a metal; encircling the rotor with the mass; engaging the rotor and the mass via an interference fit therebetween; providing a variable geometry planar drag pump with a drag pump gap between a labyrinth ring and an end of the flywheel mass; and, during variable speed operation of the flywheel mass in an evacuated space, controlling the drag pump gap to limit the temperature rise of the flywheel mass. 
     And, in an embodiment, an electromechanical flywheel with a molecular drag pump comprises: a cylindrical motor-generator rotor surrounding a motor-generator stator; the motor-generator rotor encircled by and fixed to a cylindrical flywheel mass; a central axis about which the motor-generator rotor and flywheel mass rotate; a planar drag pump including a labyrinth ring with an annular working surface; the working surface in a plane about perpendicular to the central axis and centered on the central axis and; the working surface spaced apart from an end surface of the flywheel mass by a drag pump gap; and, an elevator that moves the working surface toward the flywheel mass end surface when the gap is larger than a first selected dimension and that moves the working surface away from the flywheel mass end surface when the gap is smaller than a second selected dimension. 
     In various embodiments, one or more of i) the labyrinth ring is located between the flywheel mass end surface and an elevator support located above the flywheel mass end surface; ii) three elevators are equally spaced around a circumference of the labyrinth ring; iii) the elevator includes an electromagnetic actuator, the actuator comprising an electrical coil surrounding a back iron arranged to magnetically attract a platen coupled via a link to the labyrinth ring for adjusting the gap; iv) the link passes through a hole centrally located in the back iron; v) the elevator includes a spring that encircles the link and urges the platen away from the back iron for increasing the gap; and vi) an evacuable housing encloses the flywheel mass. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described with reference to the accompanying figures. These figures, incorporated herein and forming part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art to make and use the invention. 
         FIG. 1  shows a block diagram of an electromechanical flywheel machine in accordance with the present invention. 
         FIG. 2  shows selected functions and equipment of the electromechanical flywheel machine of  FIG. 1 . 
         FIG. 3  shows a first embodiment of the electromechanical flywheel machine of  FIG. 1 . 
         FIG. 4A  shows a second embodiment of the electromechanical flywheel machine of  FIG. 1 . 
         FIG. 4B  shows a third embodiment of the electromechancial flywheel machine of  FIG. 1 . 
         FIGS. 4C-J  show drag pump embodiments for use with the electromechanical flywheel of  FIG. 1 . 
         FIG. 5A  shows rotor poles of an electromechanical flywheel machine of  FIG. 1 . 
         FIG. 5B  shows rotor poles and a stator of an electromechanical flywheel machine of  FIG. 1 . 
         FIG. 6  shows a lower bearing assembly and parts of an electromechanical flywheel machine of  FIG. 1 . 
         FIG. 7  shows an upper bearing assembly and parts of an electromechanical flywheel machine of  FIG. 1 . 
         FIG. 8  shows a fourth embodiment of the electromechanical flywheel machine of  FIG. 1 . 
         FIGS. 9A and 9B  show a first external pumping system of the electromechanical flywheel machine of  FIG. 1 . 
         FIGS. 9C and 9D  show a second external pumping system of the electromechanical flywheel machine of  FIG. 1 . 
         FIG. 9E  shows a third external pumping system of the electromechanical flywheel machine of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The disclosure provided in the following pages describes examples of some embodiments of the invention. The designs, figures, and descriptions are non-limiting examples of certain embodiments of the invention. For example, other embodiments of the disclosed device may or may not include the features described herein. Moreover, disclosed advantages and benefits may apply to only certain embodiments of the invention and should not be used to limit the disclosed inventions. 
       FIG. 1  shows an electromechanical flywheel machine  100 . Electrical interconnections  104  electrically couple an energy exchange block  102 , power electronics and controls  106 , and an electric power network  108 . 
     As used herein, unless otherwise stated, the term coupled refers to a direct or indirect connection such as 1) A connected directly to B and 2) C connected indirectly to E via D. 
     The energy exchange block  102  includes a spinning assembly  110  and a core assembly  112 . The spinning assembly includes a motor-generator rotor  114 , a flywheel mass  116 , and a hub  118 . The core assembly includes a motor-generator stator  120  and a motor-generator stator support  122 . In various embodiments, the rotor is shaft-less. And, in various embodiments, the spinning assembly is shaft-less. 
     Electrical interconnections  104  include any of electrical conductor connections, electrical interface devices, electrical transducers, and the like. Power electronics and controls  106  include any of silicon and/or semiconductor devices, analog and digital processors, and related interfaces including human interfaces. The electric power network  108  is 1) a source of electric power to the energy exchange block  102  in some embodiments, 2) a user of electric power from the energy exchange block in some embodiments, and 3) both a source and a user of electric power to and from the energy exchange block in some embodiments. 
       FIG. 2  shows selected electromechanical flywheel machine functions and equipment  200 . Energy storage  202  is central to flywheel operation. In electromechanical flywheels, energy storage and energy conversion  204  provide a means for converting kinetic energy to electrical power and/or converting electrical power to kinetic energy. Energy transfer  206  provides for electric power transfers between energy conversion equipment  220 ,  216  and an electric power network  108 . In various embodiments, an electrical switch such a circuit breaker  230  provides for connecting and disconnecting conductors enabling power transfer. In various embodiments, other electromechanical flywheel machine functions include any of several auxiliary support functions  208  described below. 
     Energy storage  202  utilizes the spinning assembly  110 . In various embodiments, a suspension system  210  supports the spinning assembly. Suspension equipment includes bearings or their equivalents  212  and in some embodiments a passive shutdown system  215  supports the spinning assembly in selected operating regimes such as shutdown. 
     Energy conversion  204  utilizes a means for converting kinetic energy into electrical power such as a generator or a motor-generator. A motor-generator  220  is shown. The motor-generator includes the rotor  114  and a stator  120  and provides a means for rotatably driving the spinning assembly  110  and for being rotatably driven by the spinning assembly. In various embodiments, power electronics  216  enable manipulation of electrical waveforms emanating from the motor-generator and/or the electric power network  108 . For example, in various embodiments, power electronics provide for frequency conversion in an AC to AC converter having an intermediate DC bus and power electronics provide for variable speed drive functions such as accelerating the rotational speed of the flywheel rotor. 
     In various embodiments, auxiliary support functions  208  are carried out by auxiliary support equipment described more fully below. Auxiliary support functions include housing  240 , safety  242 , vacuum  244 , cooling  248 , and man-machine interface  246 . 
     A control function  205  provides for one or more of monitoring, assessment, command, and control of other electromechanical flywheel functions. In particular, the control function enables electromechanical flywheel operation via supervision and/or control of one or more of the energy storage  202 , energy conversion  204 , energy transfer  206 , and auxiliary support  208  functions. 
       FIG. 3  shows a first electromechanical flywheel portion  300 . An energy exchange block  302  is enclosed by an inner housing  328  which is in turn enclosed by an optional outer housing  338 . 
     The energy exchange block  302  includes a spinning assembly  310  and a core assembly  312 . Included in the spinning assembly is a motor-generator rotor  314  and a flywheel mass encircling and coupled to the rotor  316 , a hub  318  coupled to the flywheel mass, and a moving suspension element  344 . In some embodiments, a sleeve such as a non-magnetic sleeve (e.g., non-magnetic metal alloys and super-alloys) is interposed between the rotor and the flywheel mass for, inter alia, backing the rotor and providing support to the rotor. The rotor, flywheel mass, hub, and moving suspension element are for rotation in synchrony about an axis x-x and in various embodiments the hub is attached to one or both of the rotor  350  and the flywheel mass  352 . Opposite the moving suspension element is a stationery suspension element  346  with a support such as a first wall of the inner housing  332 . Included in the core assembly  312  are a stator  320  and a stator support  322 . In some embodiments the stator support is coupled to a wall of the inner housing such as a second wall of the inner housing  334 . 
     Encircling the motor-generator stator  320  is the motor-generator rotor  314 . In various embodiments, the rotor  314  includes magnetic  354  and nonmagnetic  356  portions and, in some embodiments, the nonmagnetic portion is or includes blocking or matrix material supporting the magnetic portions. In an embodiment, the magnetic rotor portions are laminated structures. 
     In various embodiments the stator  320  includes a magnetic structure with one or more interengaged coils having electrically conductive windings capable of carrying variable currents and thereby varying the magnetic flux of the magnetic structure. In some embodiments, a first stator coil  364  encircles an imaginary y-y axis that is about perpendicular to the x-x axis. And, in some embodiments, a second stator coil  368  encircles the x-x axis. In an embodiment, a plurality of first stator coils encircle respective imaginary y-y axes and one or more second stator coils encircle the x-x axis, the first stator coils being armature coils and the second stator coils being field coils. 
     And, in an embodiment, the motor-generator  360  is a homopolar electric machine with the illustrated inside-out arrangement (rotor encircles stator) wherein a) a rotatable rotor similar to rotor  314  includes coil-less, laminated magnetic structures, b) wherein a stationery central stator similar to stator  320  includes laminated magnetic structures with coils for creating a magnetic flux in the magnetic structures and c) the rotor encircles the stator. 
       FIG. 4A  shows a second electromechanical flywheel portion  400 A. An energy exchange block  402  is enclosed by an inner housing  428  which is enclosed, or partially enclosed, in some embodiments, by an outer housing (not shown). 
     The energy exchange block  402  includes a spinning assembly  410  and a core assembly  412 . Included in the spinning assembly are a motor-generator rotor  414 , a flywheel mass encircling and coupled to the rotor  416 , a hub coupled to the flywheel mass  418 , a support pin for supporting the hub  496 , and a moving suspension assembly for supporting the hub  492 . Some embodiments include a sleeve such as a non-magnetic sleeve between the rotor and the flywheel mass. 
     In various embodiments, the flywheel mass  416  includes layers of different materials such as fiberglass in one or more types or grades and carbon fiber in one or more types or grades. U.S. Pat. No. 6,175,172 filed Aug. 4, 1997 and entitled HUB AND CYLINDER DESIGN FOR FLYWHEEL SYSTEM FOR MOBILE ENERGY STORAGE provides additional information about flywheel mass materials of construction. 
     U.S. Pat. No. 6,175,172 filed Aug. 4, 1997 and entitled HUB AND CYLINDER DESIGN FOR FLYWHEEL SYSTEM FOR MOBILE ENERGY STORAGE provides additional information about flywheel mass construction techniques and materials shown in  FIG. 4A  and the related description. This patent is incorporated in its entirety and for all purposes. 
     As shown, the flywheel mass includes three layers with a first layer  415  adjacent to the rotor, an intermediate layer  419 , and an outer layer  421 . In an embodiment, the intermediate and outer layers include carbon fiber materials and the inner layer includes fiberglass. In another embodiment, all three layers are substantially made from carbon fiber materials. In various embodiments, one or more layers are pre-stressed such as by winding fibers under tension to form substantially cylindrical shell(s) with inherent compressive stress. 
     The support pin, moving suspension assembly and hub are concentrically arranged and are for rotation in synchrony about an axis x-x. As seen, the support pin  496  is located in a gap  491  between upper and lower bearing carriers  490 ,  494 . Extending from the stator support  422  is an upper bearing carrier and supported from a first wall of the housing  432  is a lower bearing carrier. In an embodiment, elongation of the upper bearing carrier along the x-x axis  493  serves to rotatably restrain the support pin between the upper and lower bearing carriers. In this sense, the upper and lower bearing carriers provide a means to “capture” the spinning assembly  410  via the support pin and are useful for functions including passive shutdown. In various embodiments, the lower bearing carrier and the moving suspension assembly incorporate a first electromagnetic bearing. 
     A second electromagnetic bearing  451  is spaced apart from the upper and lower bearing carriers  490 ,  494 . The second electromagnetic bearing includes a fixed bearing stator  454  supported by the stator support  422  and electrical windings  452  for magnetizing the stator and a geometrically opposing rotor  456  coupled to the rotor. As shown, the mating faces of the electromagnet  498 ,  499  are parallel to the x-x axis such that electromagnetic bearing forces are perpendicular to the x-x axis. In other embodiments, angled electromagnetic bearing faces such as those described infra provide electromagnetic bearing force components along an axis parallel to the x-x axis and along an axis perpendicular to the x-x axis. 
     Included in the core assembly  412  is a stator  420  and a stator support  422  coupled to a second wall of the inner housing  434 . Encircling the motor-generator stator is the motor-generator rotor  414 . In various embodiments, the rotor includes magnetic and nonmagnetic portions (e.g., see  354 ,  356  of  FIG. 3 ) and, in some embodiments, the nonmagnetic portion is or includes blocking or matrix material supporting the magnetic portions. In an embodiment, the magnetic rotor portions are laminated structures. 
     In various embodiments, the stator  420  includes a magnetic structure with one or more interengaged coils having electrically conductive windings capable of carrying variable currents and thereby varying the magnetic flux of the magnetic structure. 
     In an embodiment, a stator such as a homopolar stator includes at least two peripheral rims and one smaller intermediate rim. The rims include a magnetic material such as iron and in various embodiments the rims are laminated structures with each laminate having a substantially annular shape. 
     As shown, the stator  420  includes three large diameter rims  464 ,  466 ,  470  and two smaller diameter rims  484 ,  488  such that substantially annular or somewhat doughnut shaped pockets  481  are formed between the large diameter and the small diameter rims. It is in these pockets that coils encircling the rotational axis x-x are placed to form field windings  482 ,  486 . In addition to the field coil(s), the stator also includes armature coils. 
     Armature coils  450  are interengaged with slots  483  in the periphery of the large rims  464 ,  466 ,  470  such that each armature coil will encircle an imaginary axis y-y that is substantially perpendicular to the axis of rotation x-x (see  FIG. 3 ). 
     For each stator rim, there is a plurality of mating rotor poles. As can be seen, the peripheral stator rims  464 ,  470  have axially spaced (x-x) mating rotor pole  462 ,  468  (shown in solid lines) and the central stator rim 466 has axially adjacent mating rotor poles  463 ,  469  (shown in broken lines). Rotor poles for adjacent rims (e.g.,  462 ,  463 ) are not only axially spaced (x-x), but they are also radially spaced such that a rotor pole for one rim is radially spaced by 90 electrical degrees from the closest rotor pole mating with an adjacent rim. 
     In various embodiments, internal vacuum pumps such as molecular drag pumps provide for moving molecules such as gas molecules away from the flywheel mass  416  and especially away from the flywheel mass periphery where the highest speeds are achieved. U.S. Pat. No. 5,462,402 FLYWHEEL WITH MOLECULAR PUMP is incorporated by reference herein in its entirety and for all purposes including its discussion of molecular drag pumps and their use in flywheel systems. 
     In an embodiment, a first or radial drag pump  4011  is formed by a first stationery labyrinth like ring  458  supported from the housing wall  434  which is closely spaced with respect to a vacuum pump surface of the flywheel mass  459 . In various embodiments grooves in the labyrinth ring provide for a pumping action  1453  in concert with the moving flywheel surface. In some embodiments, the groove is a spiral and in some embodiments the groove has a cross-sectional area that generally decreases along a forward flow path. 
     And, in some embodiments, a second or outer axial drag pump  4012  is formed by a labyrinth ring and a moving surface at a periphery of the flywheel mass  413 ; for example, a labyrinth located on or integral with the housing  428  and a periphery of the flywheel mass operating in close proximity to the labyrinth and establishing an evacuating flow  1455  in a direction about perpendicular to the direction of flow established by the first drag pump (peripheral labyrinth not shown). In various embodiments, such an alternative second drag pump is operable with the first drag pump to provide a two-stage drag pump. 
     In an embodiment, a supply region  467  and an exhaust region  487  are included within the vacuum barrier housing  428 . The supply region has a boundary defined at least in part by portions of a vacuum barrier housing, a hub exterior surface  417 , and a flywheel mass periphery  413 . The exhaust region has a boundary defined at least in part by portions of the vacuum barrier housing and the core assembly  412 . 
     In various embodiments, drag pump(s) include one or both of a) a  4011  first drag pump interposed between a first drag pump surface of the flywheel mass  459  and the second vacuum barrier housing wall  434  and b) a second drag pump  4012  interposed between a second drag pump surface of the flywheel mass  413  and a third vacuum housing wall  473  that is about perpendicular to the second vacuum housing wall. This first drag pump can be referred to as a radial drag pump and the second drag pump can be referred to as an outer axial drag pump. 
       FIG. 4B  shows a second drag pump utilizing a flywheel mass periphery  400 B. Here, the second vacuum pump is formed by a second stationery labyrinth ring  475  and a rotatable flywheel peripheral surface  477 . The labyrinth ring is coupled to a third housing wall  473 . Grooves in the labyrinth ring  476  are similar to those described above. In operation, the flywheel mass peripheral surface moves relative to the labyrinth ring and urges flow in a direction about perpendicular to the direction of flow of the first drag pump. 
     Multiple drag pumps can operate in parallel between a common supply and exhaust region. They can also be operated in series with one pump&#39;s exhaust in fluid communication with another pump&#39;s inlet. In the case of a multi-stage drag pump arrangement, flow travels from the second drag pump to the first drag pump. Here, gas in the supply region  467  enters a second pump intake  471  and travels to the second pump exhaust  478 . The second pump exhaust and the first pump inlet are fluidly coupled, for example by an interpump space such as a somewhat annular space in an upper corner of the vacuum housing  479 . Gas enters the first drag pump inlet  480  from the interpump space and travels to the first drag pump exit  485  where it empties into the exhaust region  487 . 
     In some embodiments, a third or inner axial vacuum pump  4013  for pumping  1457  is formed by a labyrinth similar to the one described above and fixed to peripheral stator parts (such as the large diameter stator rings  454 ,  464 ,  466 ,  470 , not shown for clarity) or fixed to geometrically opposed rotor poles ( 456 ,  462 ,  463 ,  469 ,  468 ). This third drag pump can be referred to as an inner axial drag pump. See for example the drag pump  822  of  FIG. 8 . In various embodiments, combinations of the first, second, and third drag pumps are used in serial and parallel operation. 
       FIGS. 4C-J  show molecular drag pump embodiments  400 C-J for use with the electromechanical flywheel of  FIG. 1 . In particular, the figures show portions of electromechanical flywheel assemblies including a drag pump with means for controlling a drag pump gap. 
     In electromechanical flywheels utilizing a drag pump, various operations and/or operating conditions may benefit from a means to control a drag pump gap. For example, where control of a gap between moving and stationary drag pump parts enhances electromechanical flywheel operation. 
       FIG. 4C  shows operation of a planar drag pump  4600  with variable geometry in an electromechanical flywheel. Two different operating configurations are shown. At left, a before axial contraction operating state is shown  4602 . At right, an after axial contraction operating state is shown  4604 . 
     Main flywheel parts typically include i) an upper support  4612  such as a housing, containment, or lid, ii) a stationary core assembly  4608  which may be supported by the support, and iii) a rotatable assembly  4609  including a flywheel mass and/or a rotor such as a motor-generator rotor  4606  that is rotatable about a central axis  4610 . 
     Drag pump parts typically include a non-rotating part and a rotating part. In the embodiment shown, the non-rotating part is a labyrinth ring or drag pump stator  4607  and the rotating part is the upper end of the flywheel mass or a structure at the upper end of the flywheel mass or drag pump rotor  4616 . As seen, these drag pump parts have opposed surfaces that lie in planes that are substantially perpendicular to the centerline  4610  such that a gap g 1 , p 1  exists between the stator and the rotor. 
       FIG. 4D  shows a drag pump labyrinth ring or stator, labyrinth side up.  FIG. 4E  shows a drag pump labyrinth ring or stator, labyrinth side down. As seen, the ring  4607  has a working surface or annular working surface such as a labyrinth side  4617 . The working surface may incorporate channels  4647  between sidewalls  4657  and in some embodiments the channels may follow a generally arc shaped radial path extending between a channel inlet such as a radial channel inlet  4647  and a channel outlet such as a radial channel outlet  4648 . The channel cross-sectional area at the inlet may be larger than the channel&#39;s corresponding outlet cross-sectional area and transition(s) in size may be generally smooth, for example to improve pumping performance or effectiveness. Notably, channel area variation may be due to channel height changes, channel width changes, or some combination of the two. 
     As shown in operating configurations  4602  and  4604 , the labyrinth ring  4607  has a working surface  4617  facing an upper end of the flywheel mass  4616  such that a gap g 1 , p 1  is provided between the drag pump rotor and the drag pump stator. This gap may be controlled and/or varied through the use of elevator(s)  4700  (see e.g.,  FIG. 4C ) that are coupled at one end to the support  4612  and at another end to a drag pump stator such as the labyrinth ring  4607 . 
     In some embodiments, it may be desirable to maintain a constant gap g 1 =p 1  over some operating range and/or despite changed operating condition(s). As mentioned above,  FIG. 4C  shows two different operating states. At left, a before axial contraction operating state is shown  4602  and at right, an after axial contraction operating state is shown  4604 . These two different operating states result in different drag pump stator locations or elevations that provide a constant gap g 1 =p 1 . For an exemplary embodiment, the table below shows a comparison of dimensions for the two states. 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 Dimension 
                 State 4602 
                 State 4604 
                 Comparison 
               
               
                   
                   
               
             
            
               
                   
                 Gap (ring face to 
                 g1 
                 p1 
                 g1 = p1 
               
               
                   
                 flywheel face) 
               
               
                   
                 Elevator length 
                 g2 
                 p2 
                 g2 &lt; p2 
               
               
                   
                 (support to ring) 
               
               
                   
                 Gap plus ring 
                 g3 
                 p3 
                 g3 = p3 
               
               
                   
                 thickness 
               
               
                   
                 Height of flywheel 
                 g4 
                 p4 
                 g4 &gt; p4 
               
               
                   
                 mass 
               
               
                   
                   
               
            
           
         
       
     
     The table above illustrates one operating mode of the variable geometry drag pump  400 C. This operating mode may be useful where a fixed gap g 1 , p 1  is desired but cannot be maintained over a flywheel operating range of interest absent some ability to vary geometry such as location of a drag pump stator relative to a stator support. For example, where drag pump performance depends on maintaining a constant or nearly constant gap between a drag pump rotor and a drag pump stator, variation in flywheel machine speed or temperature may be detrimental to drag pump performance. And, for example, where gap size increases/changes with wheel speed due to centrifugal stress in the flywheel mass which reduces flywheel mass length (see e.g. Poisson&#39;s ratio). And, for example, where gap size increases/changes with temperature due to thermal expansion of flywheel machine part(s) such as a housing (see e.g., housing  807 ). 
       FIG. 41  shows estimated drag pump pressure ratio variation with drag pump gap  4001 . In particular, as gap is diminished, pressure ratio increases and the effectiveness of the pump to move gas molecules is improved. 
       FIG. 4J  shows estimated wheel temperature variation with spin speed  400 J. Wheel temperature here refers to a temperature of a flywheel mass (e.g.,  4606 ) while spin speed refers to the angular velocity of the flywheel mass. 
     In the upper curve without variable drag pump geometry spin speed ranges from near zero to 30 thousand revolutions per minute (krpm) while the wheel temperature ranges from about 30 degrees C. to 150 degrees C. 
     In the lower curve where variable drag pump geometry maintains a substantially constant drag pump gap, from near zero to 30 krpm the corresponding wheel temperature variation ranges from about 30 degrees C. to about 38 degrees C. As seen here, variable drag pump geometry provides a substantial reduction in wheel temperature rise as wheel speed increases. 
     Limiting wheel temperature rise has obvious advantages including maintaining the integrity of and limiting the thermal expansion of heat sensitive flywheel mass and rotor components. For example, a carbon composite flywheel mass may be speed limited by rising temperature and the integrity of rotor to flywheel mass interference fit(s) may be jeopardized by rising temperature due, for example, to differences in thermal expansion rates. In an embodiment, a variable geometry drag pump enables use of a carbon composite wheel shrunk onto a metallic rotor in a high speed electromechanical flywheel where the flywheel mass operates in a vacuum. 
     Because the flywheel mass and rotor operate in an evacuated space which reduces available heat transfer coefficients, a reduction in wheel temperature rise may be essential to obtain desired speeds of operation given available heat removal rates. For example, in an embodiment, a variable geometry drag pump increases allowable operating speed. 
     Some details of exemplary elevator(s)  4700  will now be discussed in the context of an electromechanical flywheel that maintains a constant drag pump gap despite changed operating condition(s). 
     As shown in the embodiment of  FIG. 4E , a plurality of elevators  4700  is used. For example, where three elevators are used, they may be coupled to the non-working surface  4627  of the labyrinth ring  4607  at spaced apart or regular intervals (e.g., 120 degree intervals). In various embodiments, the elevators may be any of pneumatic, electric motor, gear, magnetic, electromagnetic, or other suitably actuated elevators. 
       FIGS. 4F-G  show radial cross-sections  400 E-G taken through a drag pump labyrinth ring  4607  and an elevator  4700  mounted thereon. The elevator is mounted at an upper labyrinth ring surface  4627  opposite the labyrinth working surface  4617 . Elevator body to support attachment features  4714  may provide a means for fixing the elevator to a support  4612 . 
     Here, the elevator shown  4700  is an electromagnetically actuated device. In various embodiments it includes one or more of a body  4702 , a link  4703 , a platen  4704 , a base  4705 , a base mandrel  4708 , a base rim  4712 , and an electrical coil  4710 . In various embodiments, the body, link, platen, base, base mandrel, base rim, and electrical coil are arranged coaxially about a central axis x 3 -x 3 . In various embodiments, these components provide means for moving or lifting the labyrinth ring  4607 . Particular embodiments are further described below. 
     A body mouth  4731  receives the platen  4704  such that the link  4703  passes through the base mandrel  4708  and interconnects with the labyrinth ring  4607 . A spring  4733  between the platen and the base  4705  encircles the link  4703  and tends to move or lift the platen away from the base. As the platen and labyrinth ring are interconnected by the link, action of the spring that lifts the platen also lifts the labyrinth ring. 
     Between the base mandrel  4708  and base rim  4712  is a base grove  4707  that receives the electrical coil  4710  such that the coil  4710  surrounds the mandrel  4708 . The base provides magnetic back iron and with the coil forms an electromagnet operable to attract the platen  4704 , compress the spring  4733 , and lower the labyrinth ring  4607 . 
     Notably, the drag pump gap g 1  may be controlled with or without feedback such as feedback from a gap or position sensor. For example, where position feedback is not used for adjusting the drag pump gap, actuator(s) such as elevator(s)  4700  may reposition the labyrinth ring  4607  with changing flywheel mass  4606  angular velocity such that the labyrinth ring moves to adjust or maintain a gap that tends to change (e.g., grow) with speed. In some embodiments, a lookup table or math formula may be used to control the actuator based on one or more of an indication of one or more of flywheel mass angular velocity, flywheel mass temperature, machine vibration, machine acoustic emission, machine electrical input, or machine electrical output. 
       FIG. 4H  shows an enlarged portion  400 H of  FIG. 4G  indicated by dashed lines in  FIG. 4G . Among other things, the figure shows selected embodiments that may use loop controls or not, open loop controls with or without the mentioned sensor, and closed loop controls with or without the mentioned sensor. Also shown are selected embodiments utilizing optional multipart links  4703 . 
     Operation of the electromagnet  4705 ,  4710  may be controlled by, inter alfa, sensing the position of the labyrinth ring  4607  with respect to the upper end of the flywheel mass  4616 . Various contact and non-contact sensors may be used such as i) potentiometer, ii) strain gauge, iii) acoustic, iv) electromagnetic wave including radio frequency wave, light wave, and coherent light wave, and v) other suitable sensors known to skilled artisans. 
     In an embodiment, an electromagnetic wave sensor such as a reflected light sensor  4751  is used. Here, a sensor emission  4761  through an opening or lens  4697  of the labyrinth ring  4607  is reflected  4763  back to a sensor surface  4752  from the flywheel mass upper surface  4616 . 
     In various embodiments, the sensor  4751  is interconnected  4753  via or with a terminal or circuit board  4741  that may be included with the elevator  4700 . And in various embodiments, one or more of sensor signal processing, coil  4710  signal processing, and coil power supply are provided by one or more of sensor electronics, circuit board electronics, or other electronics such as flywheel power electronics and controls  106 . 
     In an embodiment, the coil  4710  is operated by a coil controller that receives signals from the sensor  4751 . The coil controller provides power to the coil to reposition the labyrinth plate  4607  when sensor signals indicates a gap such as g 1  differs from a desired gap such as a predetermined gap. The coil controller may include one or more of circuit board  4741  electronics including a processor and flywheel power electronics and controls  106 . 
     Turning now to embodiments of the link  4703  interconnecting the platen  4704  and the labyrinth ring  4607 , the link may be extensible or not. Where the link is made from multiple parts, it may be configured and used to set the gap g 1  to an initial value. In various embodiments, this initial gap setting is made when the flywheel mass  4606  is at a standstill. 
     Multipart links may include variable length link assemblies. As shown, a threaded rod  4770  passes through the base  4705 . At a platen central neck  4733 , the rod threads engage mating neck threads. At a labyrinth ring  4607  socket  4772 , a head  4737  of the rod is rotatably retained. In this configuration, rotation of the rod in a first direction moves the labyrinth ring hanging from the rod closer to the platen  4704  while rotation of the rod in the opposite direction moves the labyrinth ring away from the platen. In some embodiments a nut  4771  threaded onto the rod between the base and the labyrinth ring provides a means for locking the rod against unwanted rotation when the nut is rotated to tightly meet with the base. 
     In selected embodiments, one or more of the following applies: 1) a gap g 1 , p 1  is maintained in a range of about 20 to 40 mil (1/1000th of an inch) or about 15 to 50 mil; 2) the elevator  4700  fits within a volume of about 2 to 6 cubic inches; 3) the platen  4704  to base  4705  magnetic gap is about 150 mil maximum and about 0 mil minimum; 4) coil power is in a range of about 0 to 15 watts; 5) spring  4733  parameters include about 0.24 OD, about 0.75 inch free length, about 0.17 inch max compression, and about 5.6 lbf/inch spring rate with spring force at minimum compression of about 2.1 lb and spring force at maximum compression of about 3.0 lb; 6) a flywheel mass  4606  height is in the range of about 1 to 6 feet or about 2 to 4 feet; 7) a flywheel  4606  outside diameter is in the range of about 1 to 3 feet; and 7) speed of flywheel mass rotation about axis  4610  is in the range of about 0 to 65,000 revolutions per minute. 
       FIG. 5A  shows a radially staggered arrangement of rotor poles in adjacent pole planes for a 2+2 pole single stage homopolar machine  500 A. Referring to rotor cross section  502  and rotor 514, a first pole  462  is located in a first pole plane Y 1  and an opposed pole  463  in located in the same plane. In a similarly clocked adjacent pole plane Y 2 , an adjacent plane pole  465  is between the Y 1  plane poles. Not shown in this cross section is the second pole in the Y 2  plane  464 . 
     The plane views  504 ,  506  of the pole planes Y 1 , Y 2  show the poles in each pole plane  462 ,  463  and  464 ,  465  are separated by a 90° geometric angle. In this 4 pole embodiment, the poles are similarly separated by 90 electrical degrees. 
     In various embodiments, a magnetic path extends between adjacent staggered poles. For example, as shown in the pole assemblies  508 ,  510 , magnetic path parts  466 ,  468  extend between pole pairs  462 ,  463  and  463 ,  464 . As shown here, two continuous magnetic paths are formed in a 4 pole machine rotor by magnetic path parts  462 - 466 - 465  and  463 - 468 - 464 . In some embodiments, each magnetic path part assembly  462 - 466 - 465  and  463 - 468 - 464  is “Z” shaped with the central members  466 ,  468  meeting adjoining members  462 ,  465  and  463 ,  464  at substantially right angles. Among other things, this structure preserves the capacity of the magnetic path. 
       FIG. 5B  shows a rotor and a stator for a three stage machine, each stage having four poles  500 B. Here, a view of rotor magnetic path part assemblies  560  is shown as if the normally cylindrical rotor structure is “unrolled” such that a planar surface is presented. The magnetic path part assemblies  520 ,  522 ,  523 ,  521  are arranged to create a lattice  569  with spaces between the parts  519 , the spaces being filled, in various embodiments, with non-magnetic material(s). 
     The lattice  569  is constructed such that a plurality of stages A, B, C is formed, each stage having 4 poles. For example, stage A has a North plane with a first full pole  557  and a second pole consisting of two half-poles  553 ,  555 . Stage A also has a South plane with two full poles  559 ,  561 . The North and South planes of Stage A therefore have a total of 4 complete poles. 
     Each stage includes four magnetic path part assemblies or rotor lattice parts. For example, Stage A includes magnetic path part assemblies  520 ,  522 ,  520 , and  522 ; Stage B includes magnetic path part assemblies  523 ,  521 ,  523 , and  521 ; and Stage C, like Stage A, includes magnetic path part assemblies  520 ,  522 ,  520  and  522 . In some embodiments, the path part assembly geometry differs primarily in part orientation when curvature is not considered. Here, for example, assembly  520  differs from assembly  522  by an 180° rotation about an axis parallel to the x-x axis, assembly  520  differs from assembly  523  by an 180° rotation about an axis perpendicular to the x-x axis, and assembly  522  differs from assembly  521  by an 180° rotation about an axis perpendicular to the x-x axis. 
     Also shown is a cross sectional view of a stator  562 . As seen, the stator has large  534 ,  536 ,  538 ,  540  and small  544 ,  546 ,  548  diameter rims centered on an x-x axis. First and second large diameter intermediate rims  536 ,  538  are interposed between large diameter peripheral rims  534 ,  540 . One small diameter rim is interposed between each pair of large diameter rims such that the rims are stacked in an order  534 ,  544 ,  536 ,  546 ,  538 ,  548 , and  540 . The rims are supported by a coupled stator support  532  that is supported via a wall  530 . 
     A plurality of armature windings eg . . .  571 ,  572  interengage a plurality of the large diameter rim peripheries eg. . .  574  via slots or a similar feature. Field windings  535 ,  537 ,  539  encircle the stator axis of rotation x-x with one field winding encircling each of the small diameter rims such that each field winding is between a pair of large diameter rims. 
     As can be seen, the lattice structure of the rotor  569  is arranged such that the first rim of the stator  534  corresponds to the North poles of stage A; the third rim of the stator  536  corresponds to the South poles of stage A and the South poles of stage B; the fifth rim of the stator corresponds to the North poles of stage B and the North poles of stage C; and, the seventh rim of the stator corresponds to the South poles of stage C. 
     In various embodiments, bearings are used to support the spinning assembly and the included flywheel mass  116 ,  316 ,  416 . Any combination of the bearings described herein that is sufficient to support the spinning assembly may be used. 
       FIG. 6  shows a lower bearing carrier and some related parts  600 . As shown in the upper half of the drawing, there is a hub  618  for coupling to a flywheel mass, a support pin  696  for supporting the hub  618 , a moving suspension assembly for supporting the hub  692 , and a lower bearing carrier  694 . The hub, support pin, and moving suspension assembly are fixedly coupled together (shown in  FIG. 6  in exploded diagram format for clarity). 
     In various embodiments, the moving suspension assembly  692  includes a moving suspension assembly electromagnetic bearing rotor  602 . In some embodiments, the bearing rotor is a laminated structure (as shown). In some embodiments, the bearing has a moving suspension assembly electromagnetic bearing face  603  oriented at an angle θ1=0° where the angle is defined by the face and an axis x 1 -x 1  parallel to the x-x axis. And, in some embodiments, the bearing has a face  603  oriented at an angle 0&lt;θ1&lt;90° (“angled face”) (as shown) providing electromagnetic bearing force components parallel to the x-x axis and parallel to an axis perpendicular to the x-x axis. 
     In various embodiments, the moving suspension assembly  692  includes a moving suspension assembly permanent magnet  604  and in some embodiments the permanent magnet is in addition to the electromagnetic bearing rotor  602 . And, in some embodiments, a moving suspension assembly magnet holder  606  provides a holder for either or both of the moving suspension assembly electromagnetic bearing rotor and the moving suspension assembly permanent magnet. 
     When the moving suspension assembly includes an electromagnetic bearing rotor  602 , the lower bearing carrier  694  includes a corresponding lower bearing carrier electromagnetic bearing stator  614  and a lower bearing carrier stator electrical coil  616  for magnetizing the stator. The stator is supported by a lower bearing carrier frame  612  which is in turn supported by a housing wall  632 . 
     In some embodiments, the bearing stator is a laminated structure (as shown). In some embodiments, the bearing has a lower bearing carrier electromagnetic bearing face  615  oriented at an angle θ2=0° where the angle is defined by the face and an axis x 2 -x 2  parallel to the x-x axis. And, in some embodiments, the bearing has a face  615  oriented at an angle 0&lt;θ2&lt;90° (“angled face”) (as shown) providing electromagnetic bearing magnetic force components parallel to the x-x axis and parallel to an axis perpendicular to the x-x axis. As will be appreciated by persons of ordinary skill in the art, the bearing faces  603 ,  615  interoperate such that a straight rotor face is matched with a straight stator face while an angled rotor face is matched with an angled rotor face. 
     Where a moving suspension assembly permanent magnet is used  604 , the lower bearing carrier includes a geometrically opposed permanent magnet  620 . In some embodiments a lower bearing carrier permanent magnet holder  619  supported from the lower bearing carrier frame  612  and supporting the permanent magnet. 
     In various embodiments, the lower bearing carrier  694  includes a lower bearing carrier landing bearing such as an antifriction bearing  622 . As shown, the landing bearing is supported from the lower bearing carrier frame  612 . In some embodiments, a damping material  624  provides a seating material for the landing bearing. 
       FIG. 7  shows an upper bearing carrier and some related parts  700 . As shown, the upper bearing carrier  790  includes a stationery plate  702  and a moving plate  704 . 
     The stationery plate  702  includes a coil space  706  in the form of a groove is on a side of the stationery plate facing the moving plate  730 . An electrical coil  722  for magnetizing a magnetic material surrounded by the coil  707  is included. 
     The moving plate  704  includes a spring space  708  and a mechanical bearing space  710 . The spring space  708  is formed where a reduced diameter section of the moving plate extends to the side of the plate facing the stationery plate  732  and a spring such as a coil spring  720  occupies this space. The bearing space  710  is a central cavity in a moving plate surface  734  opposite the moving plate surface facing the stationery plate  732 . As seen, operation of this electromagnet compresses the spring and tends to draw the plates together. 
     In various embodiments, the upper bearing carrier  790  includes an upper bearing carrier landing bearing such as an antifriction bearing  716 . As shown, the landing bearing is positioned in the moving plate cavity  710 . In some embodiments, a damping material  718  provides a seating material for the landing bearing. 
     As seen in  FIGS. 6 and 7 , the support pin  696  extends between the upper bearing carrier  790  and the lower bearing carrier  694 . Further, each of the upper bearing carrier landing bearing  716 , support pin  696 , moving suspension assembly  692 , lower electromagnetic bearing stator  614 , lower bearing carrier permanent magnet  620 , and lower bearing carrier landing bearing  622  is centered on the x-x axis such that when the moving plate  704  moves toward the lower bearing carrier  793 , the support pin upper and lower ends  728 ,  628  are engaged with respective upper and lower landing bearings  716 ,  622  and a central aperture of each landing bearing  726 ,  626 . 
       FIG. 8  shows another embodiment of an electromechanical flywheel  800 . A flywheel mass  831  surrounds and is coupled to a homopolar motor-generator rotor including a metallic liner  830 . As shown, the rotor includes rotor North rotor poles  824 ,  832 . Not shown are the South rotor poles; see stages A and B of  FIG. 5B  for a similar arrangement that locates the South rotor poles. 
     A stator support  811  is coupled to a motor-generator stator  828  and each of field windings  826  and armature windings  820  are interengaged with the stator in a manner similar to that described above. 
     Supporting the rotor  830  and flywheel mass  831  is a hub  846  that is in turn supported by a support pin  864  engaging and/or located between upper and lower bearing carriers  860 ,  862 . See  FIGS. 6 and 7  for details of similar bearing carriers. A first electromagnetic bearing  866  is located in the lower bearing carrier. A second electromagnetic bearing  870  is spaced apart from the first and second bearing carriers and includes a bearing stator  818 , a bearing rotor  818  and stator coils  814  for magnetizing the stator. 
     An electromechanical flywheel housing includes an inner vacuum barrier  812 . In some embodiments, an outer housing  807  supports the vacuum barrier. Suitable vacuum barrier materials include stainless steel and other materials known by skilled artisans to be suited to this purpose. 
     In various embodiments, the stator support  811  has a tubular structure and a coaxial tube  801  is located therein. As shown, the coaxial tube envelops a liquid coolant flow entering the stator support  802  and an annulus between the support structure inside diameter and the coaxial tube outside diameter  815  provides a flow path for coolant leaving the stator support  803 . Coolant traveling through the annulus absorbs heat from the stator  828  and is in various embodiments cooled in a cooler (not shown) before it is pumped (not shown) back into the flow entry  802 . 
     Heat pipes  808  provide stator cooling in some embodiments. As shown, each of a plurality of heat pipes has a heat absorbing first end in close proximity to the stator, such as in the stator armature winding slots (as shown)  872 . The heat rejecting end of the heat pipe is in close proximity to the vacuum barrier, such as in contact with vacuum barrier (as shown)  874  or in other embodiments cooled by the above mentioned liquid coolant flow. 
     As discussed in connection with  FIG. 4A  and  FIG. 4B , a drag pump utilizes stationery and moving surfaces operating in close proximity. As shown in  FIG. 8 , an inner axial drag pump is formed by a labyrinth similar to those described above and coupled to peripheral stator parts such as the large diameter stator rings  824 ,  828 ,  832  or fixed to geometrically opposed rotor poles  824 ,  828 ,  832 . For example, where the labyrinth is coupled to the stator, an adjacent moving surface is provided by the opposed rotor poles that move with the flywheel mass  831 . 
     Embodiments of the evacuation system described above, including embodiments discussed in connection with  FIG. 4  and  FIG. 8 , are augmented with gas removal trains with pumps. The gas removal trains are external to the vacuum barrier housing  428 . For example one or more pumps can be arranged in series or in parallel to take suction from a vacuum barrier housing exhaust port  489  in fluid communication with the vacuum barrier housing exhaust region  487 . 
       FIG. 9A  shows a first external pumping system with a branch gas removal device  900 A. A manifold  902  and a branch  911  fluidly couple the exhaust port  489  with a gas removal device  906 . A pumping system valve  908  is fluidly coupled to a mechanical vacuum pump  910  by a passageway  909 . The pumping system valve provides manifold isolation from a downstream connection or vent  912 . In various embodiments, a mechanical vacuum pump  910  is located downstream of the isolation valve. And, in some embodiments, a pressure sensor  904  is provided for manual viewing and/or automated operation. For example, a pressure feedback signal and/or controller  920  are used in some embodiments to operate the vacuum pump  910  when the sensed pressure is higher than a threshold vacuum level. 
       FIG. 9B  shows a first gas removal device  900 B. Embodiments of the gas removal device  906  include a housing or casing  913  with multiple chambers  912 ,  914  holding a plurality of pumps. In various embodiments, a gas removal device inlet  911  provides access to a getter type pump  925  in a first chamber that is separated from a sieve type pump  923  in a second chamber, the chambers being separated by a gas permeable structure  915  such as a perforated wall. 
     As is further discussed below, heating getter and sieve materials provides for enhanced activity and/or regeneration. An optional getter heater  916  and/or an optional sieve heater  918  with a corresponding control(s) and/or power supply(s)  917  provides this functionality. In some embodiments, the control  917  receives feedback from the pressure sensor  904  such that heater operation is a function of and/or influenced by pressure sensor measurements. 
     Flywheel machines with composite flywheel masses often evolve gasses including primarily water vapor and to a lesser extent hydrocarbons and other active gasses. Molecular sieves typically provide a majority of water vapor removal while getters typically provide a majority of active gas removal. 
     As persons of ordinary skill in the art will understand, getters provide for removal of gasses and in particular for removal of many active and inactive gasses other than water vapor. A getter is a deposit of reactive material placed inside a vacuum system, for completing and maintaining the vacuum. Gas molecules that strike the getter material combine with it chemically or by adsorption. 
     In flywheel systems designed to be exposed to air during maintenance, nonevaporative getters provide a getter pump solution. These getters work at high temperature and often consist of or include a special alloy such as zirconium. A desirable feature is that the alloy material(s) form a passivation layer at room temperature which disappears when heated. Common alloys have names of the form St (Stabil) followed by a number: St 707 is 70% zirconium, 4.6% vanadium and the balance iron, St 787 is 80.8% zirconium, 14.2% cobalt and balance mischmetal, St 101 is 84% zirconium and 16% aluminum. Heating these getter materials typically enhances their activity so they should not be heated if the system is not already in a good vacuum. 
     Sieves and in particular molecular sieves incorporate a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids. Molecules small enough to pass through the pores are adsorbed while larger molecules are not. It is different from a common filter in that it operates on a molecular level and traps the adsorbed substance. For instance, a water molecule may be small enough to pass through the pores while larger molecules are not, so water is forced into the pores which act as a trap for the penetrating water molecules, which are retained within the pores. Because of this, they often function as a desiccant. Often they consist of aluminosilicate minerals, clays, porous glasses, microporous charcoals, zeolites, active carbons, or synthetic compounds that have open structures through which small molecules, such as nitrogen and water can diffuse. Calcium oxide is a frequently used dessicant material. 
     Methods for regeneration of molecular sieves include heating under high vacuum. Temperatures typically used to regenerate water-adsorbed molecular sieves range from 130 ° C. to 250 ° C. Additional information on pumps including mechanical vacuum pumps, getter pumps, and sieve pumps can be found in U.S. Pat. No. 6,884,039 to Woodard et al. 
       FIG. 9C  shows a second external pumping system with an in-line gas removal system  900 C. A manifold  932  fluidly couples the exhaust port  489  with a first isolation valve  933  and a first passageway  935  couples the valve and a gas removal device  936 . In the first passageway and downstream of the isolation valve is a pressure sensor  934 . A mechanical vacuum pump  940  provides suction to the gas removal device via a second isolation valve  938  that is coupled therebetween via second and third passageways  937 ,  939 . A mechanical vacuum pump exhaust is coupled to a connection or vented  942 . In various embodiments, the pressure sensor  934  is provided for manual viewing and/or automated operation via a pressure feedback signal and/or controller  922  for operating the vacuum pump. For example, a pressure feedback signal and/or controller  922  are used in some embodiments to operate the vacuum pump  940  when the sensed pressure is higher than a vacuum pressure threshold level. 
       FIG. 9D  shows a second gas removal device  900 D. Embodiments of the gas removal device  936  include a housing  950  with multiple chambers  954 ,  956  holding a plurality of pumps. In various embodiments, a gas removal device inlet  955  provides access to a getter type pump  947  in a first chamber. The first chamber is separated from a sieve type pump  945  in a second chamber, the chambers being separated by a permeable structure  953  such as a perforated wall. Gas therefore enters through the getter chamber  954  and exits, via a gas removal device outlet  957 , after crossing the permeable structure and sieve chamber. 
     An optional getter heater  916  and/or an optional sieve heater  918  with a corresponding control(s) and/or power supply(s)  917  provides this functionality. In some embodiments, the control  917  receives feedback from the pressure sensor  934 . 
       FIG. 9E  shows a third external pumping system with an in-line gas removal system  900 E. A manifold  972  fluidly couples the exhaust port  489  with a first isolation valve  973  and a first passageway  975  couples the valve and a gas removal device  976 . A mechanical vacuum pump  980  provides suction to the gas removal device via a second isolation valve  978  that is coupled therebetween via second and third passageways  977 ,  979 . A second pressure sensor  971  is fluidly coupled to the second passageway and a mechanical vacuum pump exhaust is coupled to a connection or vented  982 . 
     A first signal line  984  couples the first pressure sensor  974  and a controller  917 . A second signal line  986  couples the second pressure sensor  971  and the controller. A third signal line  924  couples the controller and the mechanical vacuum pump. In various embodiments, a pressure sensor signal, such as a signal from the first pressure sensor  984 , is provided to the controller  917  and a controller control signal  924  is provided in turn for operating the mechanical vacuum pump when the sensed pressure exceeds a threshold vacuum pressure. 
     Embodiments of the gas removal device  976  include a housing  990  with multiple chambers  994 ,  996  holding a plurality of pumps. In various embodiments, a gas removal device inlet  995  provides access to a getter type pump  985  in a first chamber. The first chamber is separated from a sieve type pump  987  in a second chamber, the chambers being separated by a permeable structure  993  such as a perforated wall. Gas therefore enters through the getter chamber  994  and exits, via a gas removal device outlet  997 , after crossing the permeable structure and sieve chamber. 
     A sieve heater  918  with a corresponding control and power supply  917  provides this functionality in accordance with feedback from each of the pressure sensors  974  and  971 . Notably, either of the pressure sensors might be used to sense a pressure at the exhaust port  489  while isolation valve  973  is open. In some embodiments, reversal of the position in the passageway  975  of the first pressure sensor  973  and isolation valve  973  provides for exhaust port pressure sensing irrespective of the isolation valve being open or closed. In addition to redundancy, an added benefit of having pressure sensors to either side of the gas removal device  976  is measuring pressure drop across this device. Pressure drop information can be used to influence sieve heater control operation, rising differential pressures indicating an increasing need to operate the heater. 
     While the above gas removal device heaters for sieves and getters are schematically depicted as heaters within a respective pump chamber, skilled artisans will appreciate that embodiments having external heaters such as coils wrapping around a chamber could also be used. 
     In various embodiments, initial evacuation of the vacuum barrier housing is followed by operation of a gas removal device  906 ,  936 ,  976  as described above. Rising pressure at the exhaust port  489  indicates leaks and/or outgassing of parts exposed to the vacuum. When the pressure rises to a vacuum threshold level determined by flywheel design parameters such as flywheel mass temperature limits, the mechanical vacuum pump is operated and the passageway coupling the pump and the exhaust port  489  is opened to evacuate the vacuum barrier housing  428 . 
     In various embodiments, the sieve heater  918  is operated when one or more of rising exhaust port  489  pressure, sieve age, time since the last sieve regeneration, and operating time since the last sieve regeneration are used to signal sieve regeneration by operation of the sieve heater. Sieve regeneration typically requires blocking the exhaust port  489  with an isolation valve between the port and the gas removal device  906 ,  936 ,  976 . When this is done, sieve regeneration is accomplished by heating the sieve and by operation of the mechanical vacuum pump while isolation valves interposed between the mechanical pump and the gas removal device are open. 
     In various embodiments, the getter heater  916  is operated to regenerate the getter in a manner similar to that described for the sieve heater above. And in various embodiments, the getter heater  916  is operated while the exhaust port  489  is in fluid communication with the getter because getter heating improves getter performance. 
     In operation, a flywheel mass of the electromechanical flywheel is accelerated by the motor-generator during flywheel charging. During charging, energy is transferred to the motor-generator. During discharge, the motor-generator converts the kinetic energy of the flywheel into electrical energy as the flywheel mass is decelerated. Power electronics provide for conversion of network electric power in order to motor the motor-generator and the mechanically coupled flywheel mass. Power electronics also provide for conversion of motor-generator generated electric power into a waveform suited for use by the electrical network to which the electric power is transferred. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to those skilled in the art that various changes in the form and details can be made without departing from the spirit and scope of the invention. As such, the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and equivalents thereof.