Abstract:
Nozzle control apparatus for an axial flow air turbine having an inlet nozzle for air entering the turbine and an associated turbine inlet housing for channeling air flowing to the inlet nozzle for at least partially blocking air flow from the turbine inlet housing to the turbine inlet nozzle. The nozzle control apparatus uses an axially movable annular slider member that is biased to its open position by an annular spring and is moved axially by bleed air pressure exerted on a portion of the annular slider member.

Description:
BACKGROUND OF THE INVENTION 
     Axial flow air turbines can have various uses. One significant use is in an air drive unit incorporated in modern day wide-body aircraft such as the Boeing 747, 767 and 777 aircraft to augment engine driven hydraulic pumps during peak demand periods. The air drive unit also serves to provide hydraulic power during emergency conditions when one or more of the primary engine driven hydraulic pumps are inoperative. An air drive unit includes a turbine gearbox assembly, a modulating valve, a hydraulic pump, and other ancillary components such as a muffler, ducting, controller, and clamps. The turbine gearbox assembly contains the axial flow air turbine, inlet volute, nozzle, exhaust diffuser, gearbox assembly, and hydraulic pump interface. 
     In operation, engine bleed air flows through the inlet volute and turbine nozzle and drives the axial flow turbine. The turbine power generated by the engine bleed air is transmitted to the hydraulic pump interface through the gearbox. The gearbox allows the turbine to rotate at a much higher speed than the hydraulic pump, thus maximizing turbine efficiency without adversely effecting pump life. It is generally desirable to operate the turbine at nearly constant speed during all operational conditions. Since the engine bleed air pressure and hydraulic load vary during operation, a method for controlling the flow entering the turbine is required for stable, constant speed operation. Flow control currently is typically exerted in one of the following two ways: 
     1. Bleed air is metered by a modulating valve located upstream of the air turbine inlet volute. This system of control typically utilizes a fixed area nozzle to accelerate air into the axial flow turbine. 
     2. Bleed air is modulated by variable inlet guide vanes which serve as a variable geometry nozzle to accelerate air into the axial flow turbine. With this method the turbine speed is maintained constant by varying the nozzle area under varying power conditions. 
     The first system, utilizing a modulating valve, is far simpler than the second, utilizing variable inlet guide vanes. Only one moving part is typically utilized in an air modulating valve, whereas variable inlet guide vanes necessitate synchronized rotation of every nozzle vane. In addition to the actuating mechanism, each of the typically more than twenty nozzle vanes in a variable inlet guide vane system must contain suitable bearing surfaces, a timing gear, and precision shafts. Consequently initial cost of a system employing variable geometry is far greater than that of a system employing a modulating valve. In addition, the reliability of a variable inlet guide vane system is inherently lower than systems employing a modulating valve for turbine control due to the increased complexity and the increased number of parts. 
     The benefit of using a variable inlet guide vane system is reduced air consumption at normal operating conditions, especially at the sea level take-off condition. At this condition, maximum power must be delivered by the air drive unit to quickly retract the landing gear. At the same time, maximum engine thrust is required, and maximum engine bleed pressure is available. Since engine bleed air is taken directly from the engine compressor, which reduces the available engine thrust, it is desirable to minimize the bleed air consumption when maximum engine thrust is required. 
     The air drive unit can produce the required power at the sea level take-off condition by utilizing the high pressure supply air and using a small nozzle area to accelerate the flow into the turbine. This approach minimizes the required engine bleed flow rate, and is thus the most desirable in terms of engine performance. However, a primary role of air drive units is to provide power during emergency conditions. The emergency requirement that typically sizes the machine is a low pressure (typically 25%-50% of the sea level take-off pressure), high power condition. To produce high power at low pressure requires a large nozzle area and consequently high bleed air flow consumption. 
     Since the nozzle area in a variable inlet guide vane system can be controlled, the area is minimized for the sea level take-off condition to minimize bleed air consumption, and maximized for low pressure emergency conditions to produce the required power. Systems employing a modulating valve, however, normally use a fixed area nozzle. Since the low pressure emergency condition requires the largest nozzle area of all operational conditions, the fixed nozzle area in these systems is sized for this requirement. As a result, during the sea level take-off condition, and most operational conditions, systems employing a modulating valve for flow control have a much larger nozzle area than required. As a result, these systems consume more bleed air than similar variable inlet guide vane systems at the same condition (up to 40% more at the sea level take-off condition). 
     The inlet nozzle air control apparatus invention for an axial flow air turbine solves the problem of excessive air consumption in fixed nozzle systems without the added complexity and cost of a variable inlet guide vane system. Use of the inlet nozzle air control apparatus invention results in optimal flow consumption at two design points, as opposed to the single optimal design point of a fixed area nozzle, and performance equivalent to that of a variable inlet guide vane system at those design points, with far less complexity since only one additional moving part is required. The reduced complexity means improved reliability with equivalent performance. This invention can be successfully employed whenever optimal performance of an axial flow turbine is required at more than one operating condition. 
     The inlet nozzle air control apparatus invention offers automatic (self actuated) optimal nozzle area selection, with minimal complexity. This allows an axial flow turbine to operate optimally, thus reducing air flow consumption, at more than one design condition. This inlet nozzle air control apparatus invention allows multi point design optimization at a fraction of the cost of variable inlet guide vane systems, and with far greater reliability. Thus, simplicity and cost comparable to the fixed nozzle, modulating valve controlled system, and performance comparable to the complex variable inlet guide vanes controlled system is achieved using the inlet nozzle air control apparatus invention. 
     SUMMARY OF THE INVENTION 
     This invention relates to axial flow turbines and more particularly to axial flow turbines having increased flexibility. 
     Accordingly, it is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that increases the flexibility of the axial flow turbine. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that permits optimal performance of the axial flow turbine. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that permits optimal performance of the axial flow turbine at more than one turbine operating condition. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that permits optimal performance of the axial flow turbine at a plurality of turbine operating design points. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that permits optimal performance of the axial flow turbine at at least two turbine operating design points. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that reduces air consumption. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that permits a reduced nozzle area. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that is reliable. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has few parts. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has only one moving part. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that is simple in its operation. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that is easy to operate. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has reduced complexity. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has reduced weight. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has reduced maintenance. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that is easy to manufacture. 
     It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has a low manufacturing cost. 
     These and other objects will be apparent from the invention that includes inlet nozzle air control apparatus for an axial flow air turbine having an inlet nozzle for air entering the turbine and an associated turbine inlet housing for channeling air to the inlet nozzle comprising means for at least partially blocking air flow from the turbine inlet housing to the turbine inlet nozzle and control means associated with the air flow blocking means for controlling the operation of the blocking means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be hereinafter more fully described with reference to the accompanying drawings in which: 
     FIG. 1 is a perspective sectional view of a portion of an axial flow turbine with the inlet nozzle air control apparatus invention installed and in the non-blocking position; 
     FIG. 2 is a view of a portion of the structure set forth in FIG. 1 taken in the direction  2 — 2  thereof; 
     FIG. 3 is a view of the structure set forth in FIG. 2 with the inlet nozzle air control apparatus invention in the blocking position; and 
     FIG. 4 is a perspective view of a portion of the structure set forth in FIGS.  1  through  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, the inlet air control apparatus invention is illustrated and is designated generally by the number  10 . The inlet nozzle air control apparatus  10  is illustrated installed in a conventional axial flow air turbine that is designated generally by the number  12 . It will be appreciated that a number of parts that would normally be part of the complete axial flow air turbine have been omitted from the figures that illustrate the axial flow turbine  12  for clarity and since they are not necessary for an understanding of the invention. 
     The air turbine  12 , as illustrated, has an air turbine inlet housing  14  with a hollow curved tubular shaped interior  16  with an annular exit  18 , an adjacent annular shaped turbine entrance nozzle  20  that has an inner annular entrance area  22  and an outer annular entrance area  24  that are separated by a circular ring  25  and an air turbine rotor  26  with its circumferentially located blades  28  that are located adjacent to the inlet nozzle  20 . The air turbine inlet housing  14  has an outer portion  30  and inner portions  32  and  34 . The portions  30 ,  32 , and  34  are secured together in a conventional manner to form the air turbine inlet housing  14  with the interior  16 . 
     The inner portion  34  has an outer circumferential recess  36 . This recess  36  is partially closed by an inner cylindrical surface  38  on the inside of inner portion  32  and by the inner surface  40  on the outer end  42  of the inner portion  32 . The circumferential recess  36  houses a generally ring shaped slider member  44  that is movable axially in the direction of the axis of rotation A of the rotor  26 . 
     A circumferential spring  46  is located adjacent to the slider member  44  in position to normally bias the slider member  44  into its open position. The slider member  44  has a forward cylindrical closure portion  48  that is sized and shaped to slide axially back and forth within the cylindrical shaped slot  50  that exists between the inlet housing inner portions  32  and  34 . This slot  50  is located directly adjacent to the annular exit portion  18  of the inlet housing  14  and also, as is apparent in FIG. 2, this slot  50  is located substantially opposite the inlet housing exit portion  18  from the circular separator ring  25  located in the annular entrance area  22  of the entrance nozzle  20 . 
     In addition to the cylindrical closure portion  48 , the slider member  44  also has an adjacently located cylindrical portion  52  that is smaller in diameter than the cylindrical closure portion  48 . The inner end surface  54  provides a resting surface for one end  56  of the spring  46 . The other end  58  of the spring  46  rests on the wall  60  of the recess  36  in the outer circumferential surface of the inlet housing portion  34 . The fact that the end  58  of the spring  46  rests on the wall  60  and the other end rests on the surface  54  of the movable slider member  44  is the reason why the slider member  44  is biased by the spring  46  to its open or rearward position as illustrated in FIGS. 1 and 2. 
     A port  62  is provided in the outer end  42  of the inner portion  32  that is threaded to receive the hose fitting  64  that is in turn connected to the hose or conduit  66 . This hose or conduit  66  is in turn connected to the source of compressed air  68  that in the preferred embodiment would be aircraft engine bleed air. This arrangement permits compressed air to pass from the source of compressed air  68  through the hose  66 , through the fitting  64  that is secured in the port  62  and into the circumferential recess  36  where it exerts pressure on the cylindrical surface  70  of the slider member  44  that can overcome the spring force that is exerted by the end of the spring  56  on the cylindrical surface  54  of the slider member  44 . 
     The force of compressed air on the cylindrical surface  70  of the slider member  44  can compress the spring  46  and cause the slider member  44  to have to move to the left so that its closure portion  48  passes through the slot  50  and into the annular exit portion  18  of the air turbine inlet housing  14  so that the closure portion  48  of the slider member  44  blocks air flow from the exit portion  18  of the inlet housing  14  into the inner annular entrance area  22  of the turbine entrance nozzle  20  as illustrated in FIG.  3 . When the slider member  44  is in this position, it is clear that its closure portion  48  essentially only permits air to flow from the exit portion  88  of the air turbine inlet housing  14  into the outer entrance area  24  of the turbine entrance nozzle  20 . 
     A vent  72  is provided from the recess  36  through inner portion  34  of the inlet housing  14  to its interior surface  74 . This vent  72  vents the area of the recess  36  that is occupied by the spring  46  to the outside ambient air. It will also be apparent that a series of sealing rings are provided to be in contact with the slider member  44 . In this connection, the inner portion  34  of the inlet housing  14  has circumferentially located seals  76  and  78  and the inner portion  32  of the inlet housing  14  has a sealing ring  80 . The seals  76  and  80  are located to contact and seal the closure portion  48  of the slider member  44  and the other seal  78  is located in the cylindrical surface of the recess  36  in position to contact the slider member  44 . 
     FIG. 4 illustrates in greater detail the previously described slider member  44  and the return spring  46  that are important parts of the air inlet control apparatus invention  10 . As illustrated, the slider member  44  has the cylindrical closure portion  48  that is a hollow cylinder. The cylindrical closure portion  48  is also connected to an adjacently located larger diameter hollow cylinder  52  that is sized and shaped to be located around the circular return spring  46  with the end  58  of the spring  46  resting on the wall surface  60 . 
     The inlet nozzle air control apparatus  10  is manufactured in the following manner. In order to manufacture the inlet nozzle air control apparatus  10 , only relatively minor changes are necessary to the axial flow air turbine  12 . Basically, the only changes are to the air turbine inlet housing  14 . In this connection, the inner portion  34  of the inlet housing  14  is suitably cast and/or machined to provide the outer circumferential recess  36  and the inner portion  32  of the inlet housing  14  is suitably cast and machined to provide the surfaces  38  and  40  so that when these parts  32  and  34  are assembled they provide the closed recess  36  for the slider member  44  and the circular slot  50  for the cylindrical closure portion  48  of the slider member  44 . The inner portions  32  and  34  of the air turbine inlet housing  14  are also suitably machined to accept the sealing rings  76 ,  78 , and  80 . 
     The slider member  44  is typically machined from aluminum using conventional machinery and techniques. The spring  46  is manufactured in a conventional manner from standered spring steel. The circular seals  71 ,  78  and  80  are conventional seal rings or piston rings. The assembly of the inlet nozzle air control apparatus  10  is accomplished during assembly of the turbine inlet housing  14 . Prior to the inner portions  32  and  34  being installed the seals  76 ,  78  and  80  are installed and then when the portions  32  and  34  are installed the cylindrical slider member  44  and the cylindrical spray are installed in the recess  36 . Also, the fitting  64  of the conduit  66  is threaded into the threaded hole  62  so that pressurized air can be supplied through the conduit  66  to move the slider member  44 . 
     The air inlet control apparatus invention  10  is used in the following manner. As previously indicated, the air turbine inlet nozzle vanes  28  contain a cylindrical element  25  that separates the inlet nozzle flow area  20  into an outer flow area  24  and an inner flow area  22 . The cylindrical slider member  44  which is incorporated in the adjacent portion of the inlet housing  14  is movable axially from the normally open position as illustrated in FIGS. 1 and 2 to the closed position as illustrated in FIG.  3 . When the slider member  44  is in the open position, air flow passes through the both the inner and outer sections  22  and  24  of the turbine entrance nozzle  20 . When the slider member  44  is in the closed position, flow can only pass through the outer section  24  of the entrance nozzle  20 . 
     The slider member  44  is activated by the ambient to bleed air pressure differential since the vent  72  is exposed to ambient air and the port  62  is exposed to pressurized bleed air through the conduit  66 . The slider member  44  is normally in the open position due to the force exerted by the spring  46  and hence the slider member  44  allows full air flow into the air turbine inlet nozzle  20  through both the inner and outer sections  22  and  24  of the nozzle  20 . The slider member  44  is held in this position by the force of the return spring  46 . The pressure differential at which the slider member  44  strokes is controlled by the spring  46  pre-load. Thus, when the pressure differential exceeds the set point pressure determined by the spring  46 , the slider member  44  closes, and air flows only through the outer nozzle area  24 . The outer nozzle area  24  is sized to produce the maximum required power when high bleed air pressure is available to minimize bleed air consumption. The pressure set point is chosen by selecting the appropriate spring  46  such, that all operational requirements are met. 
     Although the invention has been described in considerable detail with reference to a certain preferred embodiment, it will be understood that variations or modifications may be made within the spirit and scope of the invention as defined in the appended claims.