Abstract:
A helical flow compressor used to supply gaseous fuel to a turbogenerator is equipped with an inlet throttling valve. The inlet throttling valve maintains the outlet pressure of the compressor at a preselected value.

Description:
This is a continuation of co-pending application. Ser. No. 09/295,238 filed Apr. 19, 1999, now abandon. 
    
    
     TECHNICAL FIELD 
     This invention relates to the general field of helical flow compressors and turbines and more particularly to an improved helical flow compressor/turbine integrated with a permanent magnet motor/generator. 
     BACKGROUND OF THE INVENTION 
     A helical flow compressor is a high-speed rotary machine that accomplishes compression by imparting a velocity head to each fluid particle as it passes through the machine&#39;s impeller blades and then converting that velocity head into a pressure head in a stator channel that functions as a vaneless diffuser. While in this respect a helical flow compressor has some characteristics in common with a centrifuigal compressor, the primary flow in a helical flow compressor is peripheral and asymmetrical, while in a centrifuigal compressor, the primary flow is radial and symmetrical. The fluid particles passing through a helical flow compressor travel around the periphery of the helical flow compressor impeller within a generally horseshoe shaped stator channel. Within this channel, the fluid particles travel along helical streamlines, the centerline of the helix coinciding with the center of the curved stator channel. This flow pattern causes each fluid particle to pass through the impeller blades or buckets many times while the fluid particles are traveling through the helical flow compressor, each time acquiring kinetic energy. After each pass through the impeller blades, the fluid particles reenter the adjacent stator channel where they convert their kinetic energy into potential energy and a resulting peripheral pressure gradient in the stator channel. 
     The multiple passes through the impeller blades (regenerative flow pattern) allows a helical flow compressor to produce discharge heads of up to fifteen (15) times those produced by a centrifugal compressor operating at equal tip speeds. Since the cross-sectional area of the peripheral flow in a helical flow compressor is usually smaller than the cross-sectional area of the radial flow in a centrifugal compressor, a helical flow compressor would normally operate at flows which are lower than the flows of a centrifugal compressor having an equal impeller diameter and operating at an equal tip speed. These high-head, low-flow performance characteristics of a helical flow compressor make it well suited to a number of applications where a reciprocating compressor, a rotary displacement compressor, or a low specific-speed centrifugal compressor would not be as well suited. 
     A helical flow compressor can be utilized as a turbine by supplying it with a high pressure working fluid, dropping fluid pressure through the machine, and extracting the resulting shaft horsepower with a generator. Hence the term “compressor/turbine” which is used throughout this application. 
     The flow in a helical flow compressor can be visualized as two fluid streams which first merge and then divide as they pass through the compressor. One fluid stream travels within the impeller buckets and endlessly circles the compressor. The second fluid stream enters the compressor radially through the inlet port and then moves into the horseshoe shaped stator channel which is adjacent to the impeller buckets. Here the fluids in the two streams merge and mix. The stator channel and impeller bucket streams continue to exchange fluid while the stator channel fluid stream is drawn around the compressor by the impeller motion. When the stator channel fluid stream has traveled around most of the compressor periphery, its further circular travel is blocked by the stripper plate. The stator channel fluid stream then turns radially outward and exits from the compressor through the discharge port. The remaining impeller bucket fluid stream passes through the stripper plate within the buckets and merges with the fluid just entering the compressor/turbine. 
     The fluid in the impeller buckets of a helical flow compressor travels around the compressor at a peripheral velocity which is essentially equal to the impeller blade velocity. It thus experiences a strong centrifugal force which tends to drive it radially outward, out of the buckets. The fluid in the adjacent stator channel travels at an average peripheral velocity of between five (5) and ninety-nine (99) percent of the impeller blade velocity, depending upon the compressor discharge flow. It thus experiences a centrifugal force which is much less than that experienced by the fluid in the impeller buckets. Since these two centrifugal forces oppose each other and are unequal, the fluid occupying the impeller buckets and the stator channel is driven into a circulating or regenerative flow. The fluid in the impeller buckets is driven radially outward and “upward” into the stator channel. The fluid in the stator channel is displaced and forced radially inward and “downward” into the impeller bucket. 
     The fluid in the impeller buckets of a helical flow turbine travels around the turbine at a peripheral velocity which is essentially equal to the impeller blade velocity. It thus experiences a strong centrifugal force which would like to drive it radially outward if unopposed by other forces. The fluid in the adjacent stator channel travels at an average peripheral velocity of between one hundred and one percent (101%) and two hundred percent (200%) of the impeller blade velocity, depending upon the compressor discharge flow. It thus experiences a centrifugal force which is much greater than that experienced by the fluid in the impeller buckets. Since these two centrifugal forces oppose each other and are unequal, the fluid occupying the impeller buckets and the stator channel is driven into a circulating or regenerative flow. The fluid in the impeller buckets is driven radially inward and “upward” into the stator channel. The fluid in the stator channel is displaced and forced radially outward and “downward” into the impeller bucket. 
     While the fluid is traveling regeneratively, it is also traveling peripherally around the stator-impeller channel. Thus, each fluid particle passing through a helical flow compressor or turbine travels along a helical streamline, the centerline of the helix coinciding with the center of the generally horseshoe shaped stator-impeller channel. While the unique capabilities of a helical flow compressor/turbine would seem to offer many applications, the low flow limitation has severely curtailed their widespread utilization. 
     Permanent magnet motors and generators, on the other hand, are used widely in many varied applications. This type of motor/generator has a stationary field coil and a rotatable armature of permanent magnets. In recent years, high energy product permanent magnets having significant energy increases have become available. Samarium cobalt permanent magnets having an energy product of near thirty megagauss-oersted (mgo) are now readily available and neodymium-iron-boron magnets with an energy product of over thirty megagauss-oersted are also available. Even further increases of mgo to over forty-five megagauss-oersted promise to be available soon. The use of such high energy product permanent magnets permits increasingly smaller machines capable of supplying increasingly higher power outputs. 
     The permanent magnet motor/generator rotor may comprise a plurality of equally spaced magnetic poles of alternating polarity or may even be a sintered one-piece magnet with radial orientation. The stator would normally include a plurality of windings and magnet poles of alternating polarity. In a generator mode, rotation of the permanent magnet motor/generator rotor causes the permanent magnets to pass by the stator poles and coils and thereby induces an electric current to flow in each of the coils. In the motor mode, electrical current is passed through the coils which will cause the permanent magnet motor/generator rotor to rotate. 
     An example of a helical flow compressor/turbine integrated with a permanent magnet motor/generator is described in U.S. patent application Ser. No. 08/730,946 filed Oct. 16, 1996 entitled Helical Flow Compressor/Turbine Permanent Magnet Motor/Generator, assigned to the same Assignee as this application and hereby incorporated by reference. 
     SUMMARY OF THE INVENTION 
     In the present invention, a helical flow compressor/turbine is integrated with a permanent magnet motor/generator to obtain fluid dynamic control characteristics that are otherwise not readily obtainable. The helical flow compressor/turbine permanent magnet motor/generator includes a helical flow compressor/turbine having multiple impellers mounted on a shaft rotatably supported by a pair of bearings within a compressor housing. A permanent magnet motor/generator stator is positioned around a permanent magnet motor/generator rotor disposed on the free end of the shaft supported within the compressor housing. The compressor housing includes a generally horseshoe shaped fluid flow stator channel operably associated with each row of impeller blades, a fluid inlet at one end of the generally horseshoe shaped fluid flow stator channel(s), and a fluid outlet at the other end of the generally horseshoe shaped fluid flow stator channel(s). 
     If operating conditions permit, the multiple impellers can be rotatably supported by a duplex pair of ball bearings at one end and a single ball bearing at the other end. If ambient operating temperatures are high, a compliant foil hydrodynamic fluid film journal bearing can be used at the high pressure (hotter) end in lieu of the single ball bearing. Still further, compliant foil hydrodynamic fluid film journal bearings can be used at both ends of the multiple impellers and a compliant foil hydrodynamic fluid film thrust bearing disposed around one of the impellers with the impeller acting as a thrust disk or around a stator channel plate and acting on opposite faces of adjacent impellers. A labyrinth seal may be utilized at the base of the impellers and a face or honeycomb seal may be used along the radial face of the impellers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus described the present invention in general terms, reference will now be made to the accompanying drawings in which: 
     FIG. 1 is an end view of a two stage helical flow compressor/turbine permanent magnet motor/generator of the present invention; 
     FIG. 2 is a cross sectional view of the helical flow compressor/turbine permanent magnet motor/generator of FIG. 1 taken along line  2 — 2 ; 
     FIG. 3 is a cross sectional view of the helical flow compressor/turbine permanent magnet motor/generator of FIG. 1 taken along line  3 — 3 ; 
     FIG. 4 is an enlarged sectional view of a portion of the low pressure stage of the helical flow compressor/turbine permanent magnet motor/generator of FIG. 3; 
     FIG. 5 is an enlarged sectional view of a portion of the high pressure stage of the helical flow compressor/turbine permanent magnet motor/generator of FIG. 3; 
     FIG. 6 is an enlarged sectional view of the helical flow compressor/turbine permanent magnet motor/generator of FIGS. 1-3 illustrating the crossover of fluid from the low pressure stage to the high pressure stage; 
     FIG. 7 is an enlarged partial plan view of the helical flow compressor/turbine impeller having straight radial blades and illustrating the flow of fluid therethrough; 
     FIG. 8 is an enlarged partial plan view of a helical flow compressor/turbine impeller having curved blades; 
     FIG. 9 is an exploded perspective view of a stator channel plate of the helical flow compressor/turbine permanent magnet motor/generator of FIGS. 1-5; 
     FIG. 10 is an enlarged sectional view of a portion of FIG. 4 illustrating fluid flow streamlines in the impeller blades and fluid flow stator channels; 
     FIG. 11 is a schematic representation of the flow of fluid through a helical flow compressor/turbine; 
     FIG. 12 is a cross sectional view of a three stage helical flow compressor/turbine permanent magnet motor/generator of the present invention; 
     FIG. 13 is a cross sectional view of an alternate three stage helical flow compressor/turbine permanent magnet motor/generator of the present invention; 
     FIG. 14 is a cross sectional view of a four stage helical flow compressor/turbine permanent magnet motor/generator of the present invention; 
     FIG. 15 is a cross sectional view of a portion of the four stage helical flow compressor/turbine permanent magnet motor/generator of FIG. 14 having labyrinth seals at the base of the impellers; 
     FIG. 16 is a cross sectional view of a portion of the four stage helical flow compressor/turbine permanent magnet motor/generator of FIG. 14 having a face or honeycomb seal along the radial face of an impeller; 
     FIG. 17 is a cross sectional view of a portion of the four stage helical flow compressor/turbine permanent magnet motor/generator of FIG. 14 illustrating an alternate compliant foil fluid film thrust bearing configuration; 
     FIG. 18 is a graphical representation of the operating conditions for a helical flow compressor/turbine permanent magnet motor/generator of the present invention; and 
     FIG. 19 is a cross sectional view of an inlet throttle valve for the helical flow compressor/turbine permanent magnet motor/generator of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A two stage helical flow compressor/turbine permanent magnet motor/generator  15  is illustrated in FIGS. 1-3 and includes a fluid inlet  18  to provide fluid to the helical flow compressor/turbine  17  of the helical flow compressor/turbine permanent magnet motor/generator  15  and a fluid outlet  16  to remove fluid from the helical flow compressor/turbine  17  of the helical flow compressor/turbine permanent motor/generator  15 . The helical flow machine is referred to as a compressor/turbine since it can function both as a compressor and as a turbine. The permanent magnet machine is referred to as a motor/generator since it can function equally well as a motor to produce shaft horsepower or as a generator to produce electrical power. 
     The helical flow compressor/turbine permanent magnet motor/generator  15  includes a shaft  20  rotatably supported by duplex ball bearings  21  and  31  at one end and single ball bearing  22  at the opposite end. The bearings are disposed on either side of low pressure stage impeller  24  and high pressure stage impeller  23  mounted at one end of the shaft  20 , while permanent magnet motor/generator rotor  27  is mounted at the opposite end thereof. The duplex ball bearings  21  and  31  are held by bearing retainer  28  while single ball bearing  22  is disposed between high pressure stator channel plate  32  and the shaft  20 . Both the low-pressure stage impeller  24  and high pressure stage impeller  23  include a plurality of blades  26 . 
     Low pressure stripper plate  37  and high pressure stripper plate  36  are disposed radially outward from low pressure impeller  24  and high pressure impeller  23 , respectively. The permanent magnet motor/generator rotor  27  on the shaft  20  is disposed to rotate within permanent magnet motor/generator stator  48  which is disposed in the permanent magnet housing  49 . 
     The low pressure impeller  24  is disposed to rotate between the low pressure stator channel plate  34  and the mid stator channel plate  33  while the high pressure impeller  23  is disposed to rotate between the mid stator channel plate  33  and the high pressure stator channel plate  32 . Low pressure stripper plate  37  has a thickness slightly greater than the thickness of low pressure impeller  24  to provide a running clearance for the low pressure impeller  24  between low pressure stator channel plate  34  and mid stator channel plate  33  while high pressure stripper plate  36  has a thickness slightly greater than the thickness of high pressure impeller  23  to provide a running clearance for the high pressure impeller  23  between mid stator channel plate  33  and high pressure stator channel plate  32 . 
     The low pressure stator channel place  34  includes a generally horseshoe shaped fluid flow stator channel  42  having an inlet to receive fluid from the fluid inlet  55 . The mid stator channel plate  33  includes a low pressure generally horseshoe shaped fluid flow stator channel  41  on the low pressure side thereof and a high pressure generally horseshoe shaped fluid flow stator channel  40  on the high pressure side thereof. The low pressure generally horseshoe shaped fluid flow stator channel  41  on the low pressure side of the mid stator channel plate  33  mirrors the generally horseshoe shaped fluid flow stator channel  42  in the low pressure stator channel plate  34 . The high pressure stator channel plate  32  includes a generally horseshoe shaped fluid flow stator channel  38  which minors the high pressure generally horseshoe shaped fluid flow stator channel  40  on the high pressure side of mid stator channel plate  33 . 
     Each of the stator channels includes an inlet and an outlet disposed radially outward from the channel. The inlets and outlets of the low pressure stator channel plate generally horseshoe shaped fluid flow stator channel  42  and mid helical flow stator channel plate low pressure generally horseshoe shaped fluid flow stator channel  41  are axially aligned as are the inlets and outlets of mid helical flow stator channel plate high pressure generally horseshoe shaped fluid flow stator channel  40  and high pressure stator channel plate generally horseshoe shaped fluid flow stator channel  38 . 
     The fluid inlet  18  extends through the high pressure stator channel plate  32 , high pressure stripper plate  36 , and mid stator channel plate  33  to the inlets of both of low pressure stator channel plate generally horseshoe shaped fluid flow stator channel  42  and mid helical flow stator channel plate low pressure generally horseshoe shaped fluid flow stator channel  41 . The fluid outlet  16  extends from the outlets of both the mid helical flow stator channel plate high pressure generally horseshoe shaped fluid flow stator channel  40  and high pressure stator channel plate generally horseshoe shaped fluid flow stator channel  38 , through the high pressure stripper plate  36 , and through the high pressure stator channel plate  32 . 
     The crossover from the low pressure compression stage to the high pressure compression stage is illustrated in FIG.  6 . Both of the outlets from the low pressure stator  5  channel plate generally horseshoe shaped fluid flow stator channel  42  and mid helical flow stator channel plate low pressure generally horseshoe shaped fluid flow stator channel  41  provide partially compressed fluid to the crossover  58  which in turn provides the partially compressed fluid to both inlets of mid helical flow stator channel plate high pressure generally horseshoe shaped fluid flow stator channel  40  and high pressure stator channel plate generally horseshoe shaped fluid flow stator channel  38 . 
     The impeller blades or buckets are best illustrated in FIGS. 7 and 8. The radial outward edge of the impeller  23  includes a plurality of low pressure blades  26 . While these blades  28  may be radially straight as shown in FIG. 7, there may be specific applications and/or operating conditions where curved blades may be more appropriate or required. 
     FIG. 8 illustrates a portion of a helical flow compressor/turbine impeller having a plurality of curved blades  44 . The curved blade base or root  45  has less of a curve than the leading edge  46  thereof The curved blade tip  47 , at both the root  45  and leading edge  46  would be generally radial. 
     The fluid flow stator channels are best illustrated in FIG. 9 which shows the mid  20  stator channel plate  33 . The generally horseshoe shaped stator channel  40  is shown along with inlet  55  and outlet  56 . The inlet  55  and outlet  56  would normally be displaced approximately thirty (30) degrees. Outlet  56  connects with crossover  58 . An alignment or locator hole  57  is provided in each of the low pressure stator channel plate  34 , the mid stator channel plate  33  and the high pressure stator channel plate  32  as well as stripper plates  37  and  36 . The inlet  55  is connected to the generally horseshoe shaped stator channel  40  by a converging nozzle passage  51  that converts fluid pressure energy into fluid velocity energy. Likewise, the other end of the generally horseshoe shaped stator channel  40  is connected to the outlet  56  by a diverging diffuser passage  52  that converts fluid velocity energy into fluid pressure energy. 
     The depth and cross-sectional flow area of fluid flow stator channel  40  are tapered preferably so that the peripheral flow velocity need not vary as fluid pressure and density vary along the fluid flow stator channel. When compressing, the depth of the fluid flow stator channel  40  decreases from inlet to outlet as the pressure and density increases. Converging nozzle passage  51  and diverging diffuser passage  52  allow efficient conversion of fluid pressure energy into fluid velocity energy and vice versa. 
     FIG. 10 shows the flow through the impeller blades and the fluid flow stator channels by means of streamlines  43 . On the other hand, FIG. 11 schematically illustrates the helical flow around the centerline of the impeller and fluid flow stator channel. The turning of the flow is illustrated by the alternating solid and open flow pattern lines in FIG.  11 . 
     In a helical flow compressor/turbine, fluid enters, the inlet port  18 , is accelerated as it passes through the converging nozzle passage  51 , is split into two (2) flow paths by stripper plate  37 , then enters the end of the generally horseshoe shaped fluid flow stator channels  41  and  42  axially adjacent to the low pressure impeller blades  26 . The fluid is then directed radially inward to the root of the impeller blades  26  by a pressure gradient, accelerated through and out of the blades  26  by centrifugal force, from where it reenters the fluid flow stator channel. During this time the fluid has been traveling tangentially around the periphery of the helical flow compressor/turbine. As a result of this, a helical flow is established as best shown in FIGS. 7,  10 , and  11 . 
     While the duplex ball bearings  21  and  31  are illustrated on the permanent magnet motor/generator end of the helical flow compressor/turbine and the single ball bearing  22  is illustrated at the opposite end of the helical flow compressor/turbine, their positions can readily be reversed with the single ball bearings  22  at the permanent magnet motor/generator end of the helical flow compressor/turbine and the duplex ball bearings  21  and  31  at the opposite end of the helical flow compressor/turbine. Likewise, as will become more apparent later, while the low pressure impeller  24  is shown at the permanent magnet motor/generator end of the helical flow compressor/turbine and the high pressure impeller  23  at the opposite end, their relative positions can also be readily reversed. 
     A three (3) stage helical flow compressor/turbine permanent magnet motor/generator  60  is illustrated in FIG.  12  and is in all respects generally similar to the two (2) stage machine except for the addition of a third impeller and items associated with the third impeller. Likewise, FIG. 14 illustrates a four (4) stage helical flow compressor/turbine permanent magnet motor/generator  80 . 
     The three (3) stage helical flow compressor/turbine permanent magnet motor/generator  60  of FIG. 12 includes low pressure stage impeller  61 , medium pressure stage impeller  62 , and high pressure stage impeller  63  all mounted at one end of the shaft  64 , while permanent magnet motor/generator rotor  65  is mounted at the opposite end thereof The permanent magnet motor/generator rotor  65  on the shaft  64  is disposed to rotate within permanent magnet motor/generator stator  66  that is disposed in the permanent magnet stator housing  67 . An inlet  75  is provided to the three (3) stage helical flow compressor/turbine permanent magnet motor/generator  60 . 
     The duplex ball bearings  21  and  31  are illustrated at the low pressure side of the helical flow compressor/turbine since this side will have a lower operating temperature than the high pressure side where the compliant foil hydrodynamic fluid film journal bearing is utilized. While ball bearings are suitable for many operating conditions of the helical flow compressor/turbine permanent magnet motor/generator, compliant foil hydrodynamic fluid film journal bearings are better suited for higher temperature operation. At higher ambient operating temperature, the expected operating life of a ball bearing may not be sufficient. 
     Low pressure stripper plate  68 , medium pressure stripper plate  69 , and high pressure stripper plate  70  are disposed radially outward from low pressure impeller  61 , medium pressure impeller  62 , and high pressure impeller  63 , respectively. The low pressure impeller  61  is disposed to rotate between the low pressure stator channel plate  71  and the first mid stator channel plate  72 ; the medium pressure impeller  62  is disposed to rotate between the first mid pressure stator channel plate  72  and the second mid pressure stator channel plate  73 ; while the high pressure impeller  63  is disposed to rotate between the second mid stator channel plate  73  and the high pressure stator channel plate  74 . Low pressure stripper plate  68  has a thickness slightly greater than the thickness of low pressure impeller  61  to provide a running clearance for the low pressure impeller  61  between low pressure stator channel plate  71  and the first mid stator channel plate  72 ; medium pressure stripper plate  69  has a thickness slightly greater than the thickness of medium pressure impeller  62  to provide a running clearance for the medium pressure impeller  62  between the first mid stator channel plate  72  and the second mid stator channel plate  73 ; while high pressure stripper plate  70  has a thickness slightly greater than the thickness of high pressure impeller  63  to provide a running clearance for the high pressure impeller  63  between the second mid stator channel plate  73  and high pressure stator channel plate  74 . 
     Generally horseshoe shaped fluid flow stator channels are disposed on either side of the low pressure impeller  61 , the medium pressure impeller  62  and the high pressure impeller  63 . Each of the fluid flow stator channels includes an inlet and an outlet disposed radially outward from the channel. 
     The crossover from the low pressure compression stage to the medium pressure stage and from the medium pressure compression stage to the high pressure compression stage would be as described with respect to the crossover between the low pressure stage to the high pressure stage in the two (2) stage helical flow compressor/turbine permanent magnet motor/generator. 
     An alternate three (3) stage helical flow compressor/turbine permanent magnet motor/generator  60  is illustrated in FIG.  13 . In this embodiment, the duplex ball bearings  21  and  31  are disposed at the permanent magnet motor/generator end of the shaft  64  and are positioned by a bearing retainer  29  within the permanent magnet stator housing  67 . Positioning the duplex bearings  21  and  31  at the end of the shaft  64  permits their operation in a much cooler environment. 
     The four (4) stage helical flow compressor/turbine permanent magnet motor/generator  20   80  of FIG. 14, having inlet  79 , includes low pressure stage impeller  84 , mid low pressure stage impeller  83 , mid high pressure stage impeller  82  and high pressure stage impeller  81 , all mounted at one end of the shaft  85  and each including a plurality of blades. Permanent magnet motor/generator rotor  86  is mounted at the opposite end of the shaft  85  and is disposed to rotate within permanent magnet motor/generator stator  87  which is disposed in the permanent magnet housing  88 . 
     Low pressure stripper plate  92 , mid low pressure stripper plate  91 , mid high pressure stripper plate  90 , and high pressure stripper plate  89  are disposed radially outward from low pressure impeller  84 , mid low pressure impeller  83 , mid high pressure impeller  82 , and high pressure impeller  81 , respectively. The low pressure impeller  84  is disposed to rotate between the low pressure stator channel plate  98  and the mid low pressure stator channel plate  97 ; the mid low pressure impeller  83  is disposed to rotate between the mid low pressure stator channel plate  95  and the middle stator channel plate  96 ; the mid high pressure impeller  82  is disposed to rotate between the middle stator channel plate  96  and the mid high pressure stator channel plate  97 ; while the high pressure impeller  81  is disposed to rotate between the mid high pressure stator channel plate  95  and the high pressure stator channel plate  94 . 
     It should be noted that the high pressure impeller  81  of the four (4) stage helical flow compressor/turbine permanent magnet motor/generator  80  is disposed at the permanent magnet motor/generator end of the helical flow compressor/turbine. Compliant foil hydrodynamic fluid film journal bearings  76  and  77  are disposed at either end of the impellers  84 ,  83 ,  82 , and  81  and the radial face of one of the impellers, illustrated as low pressure impeller  81 , serves as the thrust disk for double sided compliant foil hydrodynamic fluid film a thrust bearing  78 . 
     Generally horseshoe shaped fluid flow stator channels are disposed on either side of the low pressure impeller  81 , the mid low pressure impeller  83 , the mid high pressure impeller  82  and the high pressure impeller  84  which each include a plurality of blades. Each of the fluid flow stator channels include an inlet and an outlet disposed radially outward from the channel and the crossover from one compression stage to the next compression stage is as described with respect to the crossover between the low pressure stage to the high pressure stage in the two (2) stage helical flow compressor/turbine permanent magnet motor/generator. 
     In order to prevent leakage of fluid between the impellers, labyrinth seals  100  can be disposed between adjacent impellers  81  and  82 ,  82  and  83 , and  83  and  84  at the base of the stator channel plates  95 ,  96 , and  97  respectively, as illustrated in FIG.  15 . FIG. 16 illustrates a face or honeycomb seal  101  between an impeller  81  and stator channel plate  95 , for example. 
     An alternate double sided compliant foil hydrodynamic fluid film thrust bearing arrangement is illustrated in FIG.  17 . Instead of the double sided compliant foil hydrodynamic fluid film thrust bearing positioned on either side of an impeller as shown in FIG. 14, the arrangement in FIG. 17 shows the double sided compliant foil hydrodynamic fluid film thrust bearing  78  positioned on either side of the middle stator channel plate  96  with one side facing the mid low pressure impeller  83  and the other side facing the mid high pressure impeller  82 . 
     One particular application to which the helical flow compressor/turbine permanent magnet motor/generator is particularly well suited is to provide gaseous fuel to a turbogenerator. In order to start the turbogenerator, the helical flow compressor/turbine permanent magnet motor/generator may need to be run backwards as a turbine in order to reduce the upstream pressure of the gaseous fuel (typically supplied from a natural gas pipeline). The gaseous fuel header pressure has to be extremely low for ignition. 
     As the turbogenerator speed increases, the turbogenerator&#39;s compressor discharge pressure will increase and the gaseous fuel pressure in the header that feeds the combustor nozzle injectors needs to be maintained above the turbogenerator compressor discharge pressure. For example, if a natural gas pipeline pressure is twenty (20) psi gauge when you want to light-off the turbogenerator, the natural gas pressure will have to be reduced by about nineteen (19) psi when the turbogenerator is turning at low ignition speed. As the turbogenerator speed increases after ignition, the pressure that goes into the header can be increased, that is, the pressure needs to be reduced less. Ignition typically will occur while the helical flow compressor/turbine permanent magnet motor/generator is still turning backwards and reducing pressure. 
     In this type of application, the shaft bearings would normally need to operate in both a clockwise and a counterclockwise direction. For ball bearings this is no problem whatsoever. However, at the high pressure impeller end of the shaft, the temperatures maybe too great for a ball bearing to survive for any extended period of time, particularly if the ambient operating temperature is high. For higher temperatures, compliant foil hydrodynamic fluid film journal bearings can be utilized for longer life. 
     While a compliant foil hydrodynamic fluid film journal bearing is generally designed to operate in only one direction, there are such bearings that will run in both directions. An example of such a bearing is described in U.S. patent application No. 08/002,690 filed Jan. 5, 1998 entitled “Compliant Foil Fluid Film Radial Bearing” assigned to the same Assignee as this application and incorporated herein by reference. 
     Alternately, if it is desired to prevent rotation of the shaft in both directions, it is possible to provide an inlet throttle valve to prevent the helical flow compressor/turbine from operating as a turbine. A graphical representation of the operating conditions for a helical flow compressor/turbine is illustrated in FIG. 18, a plot of flow function percentage on the vertical axis versus compressor pressure ratio on the horizontal axis. Speed percentage lines from minus 46% (running as a turbine) to plus 100% (running as a compressor) are shown. Turbine load lines for various inlet pressures are also shown. 
     The inlet throttle valve  110  is schematically shown in cross section in FIG.  19 . The valve  110  includes diaphragm  112  disposed within a valve housing  114  having an end cap  116  at one end. The diaphragm  112  divides the interior of the housing into a compressor outlet pressure (P 2 ) chamber  118  and a compressor inlet pressure (P 1 ) chamber  120 . A spring  122  biases the diaphragm  112  towards the compressor outlet pressure chamber  120 . The compressor inlet pressure (P 1 ) is bled through the orifices  124  in the metering rod  126 . The differential pressure, namely the difference between P 1  and P 2 , positions the metering rod  126  within the valve housing throat  128  which controls the flow of gaseous fuel  130  into the helical flow compressor inlet  132 . The compressor outlet pressure P 2  is fed to chamber  118  via line  134 . 
     The valve  110  regulates the inlet flow to the helical flow compressor/turbine to maintain a minimum delta pressure across the helical flow compressor/turbine. When the pressure rise across the helical flow compressor/turbine is large, the throttle valve  100  will be wide open and not restrict the inlet pressure at all. When, however, the inlet pressure P 1  is greater than the outlet pressure P 2 , the throttle valve  110  will regulate the inlet pressure P 1  to the helical flow compressor/turbine to a value of 3 psig less than the outlet pressure P 2 . This forces the helical flow compressor/turbine to always operate in the area to the right of the Inlet Throttle line on FIG.  19 . Operating to the right of the Inlet Throttle line insures that the helical flow compressor/turbine will always operate as a compressor and never operate as a turbine, which means that the shaft will only rotate in a single direction. Alternately, a switching solenoid valve or a proportional valve can be utilized. 
     Positioning the pair of journal bearings around the multiple impellers of the helical flow compressor/turbine improves the shaft dynamics of the helical flow compressor/turbine permanent magnet motor/generator. While the ball or roller bearings are suitable for many applications, the higher temperature capability of compliant foil fluid film bearings can be used at the high pressure or hotter end of the helical flow compressor/turbine or at both ends of the helical flow compressor/turbine. This can greatly increase bearing life in high temperature operating environments. The thrust load can be taken by a compliant foil fluid film thrust bearing using one of the impellers as a thrust disk. With compliant foil fluid film bearings, an inlet throttle valve can be used to insure rotation in a single direction. 
     While specific embodiments of the invention have been illustrated and described, it is to be understood that these are provided by way of example only and that the invention is not to be construed as being limited thereto but only by the proper scope of the following claims.