Abstract:
A variable pitch propulsor system with a propeller pitchlock system having a pitchlock solenoid valve located in communication with a pitchlock pressure circuit to selectively actuate pitchlocking in response to a controller. The pitchlock solenoid valve includes an electro-mechanical device which is normally closed but may be commanded to electrically open and dump the pitchlock pressure which causes actuation of the pitchlock system. The pitchlock solenoid provides a mechanism which will selectively pitchlock the propulsor system; permits a built in test routine to determine the condition of the pitchlock system through a commanded propeller pitchlock sequence; requires no mechanical link between the rotating and non-rotating propeller components to initiate pitchlock; is independent of engine and gearbox configurations; and can initiate pitchlock remotely with a signal from a remote location.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to propulsor systems, and more particularly to a pitchlocking system that may be selectively commanded to pitchlock without a mechanical link between the rotating and non-rotating propeller components.  
         [0002]     In typical variable pitch propulsor systems, a plurality of propulsor blades, each pivotably mounted for movement about its longitudinal axis relative to a rotary hub driven by an aircraft engine, are operatively connected to a mechanical or hydromechanical blade pitch change system disposed within the hub assembly. These blade pitch change actuation systems typically include a pitchlock for maintaining blade pitch in the event of a malfunction such as a loss in the system&#39;s hydraulic supply.  
         [0003]     Conventional pitch lock systems often incorporate a pitch lock screw to provide a locking mechanism which prevents the blades from moving to a lower blade angle in addition to a separate ballscrew mechanism which is backdriven to rotationally drive the pitchlock screw.  
         [0004]     Disadvantageously, as the pitchlock condition occurs through a mechanical link between the rotating and non-rotating propeller components bearings and a drive are required to transmit the control signal to the pitchlock screw, increasing complexity and reducing reliability.  
         [0005]     Accordingly, it is desirable to provide a variable pitch propulsor system with an uncomplicated and light weight pitchlocking system that may be selectively commanded to pitchlock through a propeller control.  
       SUMMARY OF THE INVENTION  
       [0006]     A variable pitch propulsor system according to the present invention provides a pitchlocking system in which the propeller blade loads, (ie. twisting moments), are transmitted about a blade centerline, through blade pins and reacted by a yoke assembly as an axial load. The yoke assembly includes an actuator piston that is hydraulically capable of outputting a force which overcomes the blade loads and position the blades to some desired operating angle. The pitchlocking system locks the propeller actuator at an axial location which corresponds to a current blade pitch angle should the actuator piston no longer hold or react the loads from the blades. The pitchlock system locks the actuator and prevents a decrease in blade angle when there is a hydraulic condition where the coarse pitch pressure cannot support the blade loads. The propeller is then pitchlocked and operates at that fixed pitch condition.  
         [0007]     A pitchlock solenoid valve is located in communication with a pitchlock pressure circuit to selectively actuate pitchlocking in response to a controller. The pitchlock solenoid valve includes an electro-mechanical device which is normally closed but may be commanded to electrically open to dump the pitchlock pressure which causes actuation of the pitchlock system. The pitchlock solenoid provides a mechanism which will selectively pitchlock the propulsor system; permits a built in test routine to determine the condition of the pitchlock system through a commanded propeller pitchlock sequence; requires no mechanical link between the rotating and non-rotating propeller components to initiate pitchlock; is independent of engine and gearbox configurations, i.e., in-line and offset gearboxes; and can initiate pitchlock remotely with a signal from an electronic control or the flight deck if so desired  
         [0008]     The present invention therefore provides a variable pitch propulsor system with an uncomplicated and light weight pitchlocking system that may be selectively commanded to pitchlock through a propeller control. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0010]      FIG. 1  is a general perspective view an exemplary gas turbine turboprop engine embodiment for use with the present invention;  
         [0011]      FIG. 2A  is a sectional view of a turboprop system illustrating the electronic/hydraulic control system along a hub axis of rotation;  
         [0012]      FIG. 2B  is an expanded partial sectional view of a pitch change system valve illustrated in  FIG. 2A ;  
         [0013]      FIG. 3  is an expanded view of a ballscrew, ballscrew ballnut, and pitchlock nut in a pitchlock condition;  
         [0014]      FIG. 4A  is an expanded sectional view of the pitchlock system in a normal operating position;  
         [0015]      FIG. 4B  is an expanded sectional view of the pitchlock system in a first initiated position;  
         [0016]      FIG. 4C  is an expanded sectional view of the pitchlock system in a second initial pitchlock load reaction position;  
         [0017]      FIG. 4D  is an expanded sectional view of the pitchlock system in a peak pitchlock load reaction position;  
         [0018]      FIG. 5  is a schematic view of a pitchlock communication system;  
         [0019]      FIG. 6A  is a sectional view of a turboprop system illustrating another electronic/hydraulic control system along a hub axis of rotation; and  
         [0020]      FIG. 6B  is an expanded partial sectional view of a pitch change system illustrated in  FIG. 6A . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]      FIG. 1  illustrates a general perspective view of a propeller system  20  driven by a gas turbine engine (illustrated schematically at  22 ). The engine  22  rotates a turbine output shaft  24  at a high speed to drives a gear reduction gearbox (illustrated somewhat schematically at  26 ) which decrease shaft rotation speed and increase output torque. The gearbox  26  drives a propeller shaft  28  which rotates a hub assembly  30  and a plurality of propeller blades  32  which extend therefrom. The hub axis A is substantially perpendicular to a plane P which is defined by the propeller blades  32 .  
         [0022]     Referring to  FIG. 2A , a sectional view of the propeller system  20  is illustrated. A main pump  36 , for actuating the various mechanism disclosed herein, provides hydraulic pressure. The main pump  36  provides a pressure indicated generally by the appropriately shaded areas and more specifically by the P subscript  designations, wherein PC is coarse pitch pressure, P F  is fine pitch pressure, and P PL  is pitchlock pressure.  
         [0023]     The main pump  36  provides fluid pressure to the transfer bearing  38  through a servo valve  42 . A feathering solenoid and protection valve  44  and a high pressure relief valve  45  are also preferably located between the main pump  36  and the transfer bearing  38 . The pitchlock solenoid  43  is located in communication with the pitchlock pressure P PL  line.  
         [0024]     From the transfer bearing  38 , pitchlock pressure P PL  is communicated to a pitchlock system  46 , while the coarse pitch pressure P c  and the fine pitch pressure P F  are supplied to a pitch change system  48  having a pitch change actuator  53 . The pitch change actuator  53  is preferably mounted along the hub axis A forward of a yoke assembly  50 . Generally, by selectively communicating coarse pitch pressure P c  and fine pitch pressure P F  to the pitch change system  48 , speed governing, synchrophasing, beta control, feathering and unfeathering of the propeller blades  32  is hydraulically provided.  
         [0025]     Preferably, a pitch change yoke is located between a coarse pitch actuator chamber PC and a fine pitch actuator chamber PF defined within the pitch change actuator  53 . The chambers PC, PF are respectively supplied with coarse pitch pressure P c  and fine pitch pressure P F  from a coarse pitch pressure communication circuit PC c  and fine pitch pressure communication circuit PF C  (illustrated somewhat schematically) such that the pitch change actuator piston  49  is selectively driven by differential pressure therebetween. It should be understood that the hydraulic pressure system disclose herein is illustrated somewhat schematically as various pressure communication circuits may be utilized with the present invention.  
         [0026]     The pitch change actuator piston  49  translates along axis A to drive a yoke assembly  50 . The yoke assembly  50  is attached to a blade pin  51  which extends from each propeller blade  32  to control the pitch thereof. The yoke assembly  50  is mounted to the blade pin  51  about a pivot axis P which is offset from a blade axis B about which each propeller blades pitches.  
         [0027]     The pitchlock system  46  interacts with the pitch change system  48  in response to differential pressure between pitchlock pressure P PL  and coarse pitch pressure P c . The pitchlock system  46  generally includes a pitchlock piston  52 , a pitchlock ballscrew screw  54 , a pitchlock nut  56 , ballscrew ballnut  58  located generally along the hub axis A from forward to aft relative to dome assembly  60  which forms a portion of the hub assembly  30 .  
         [0028]     A ballscrew bearing support assembly  62  is mounted to a pitchlock piston load tube  63  about a pitchlock transfer tube  65  which communicates the pitchlock pressure P PL  to the pitchlock piston  52 . The pitchlock piston  52  is located to separate a pitchlock piston coarse pitch pressure chamber  52 C from a pitchlock piston pitchlock pressure chamber  52 P. The pitchlock piston coarse pitch pressure chamber  52 C is supplied with coarse pitch pressure PC from the coarse pitch pressure communication circuit PC c  and the pitchlock piston pitchlock pressure chamber  52 P is supplied with pitchlock pressure P PL  from the pitchlock pressure communication circuit PPL c . The pitchlock pressure P PL  is equivalent to the supply pressure P s  to generally balance the pitchlock piston  52  therebetween. It should be understood that the pitchlock pressure P PL  will be greater than the coarse pitch pressure P c  by a predetermined amount such that the pitchlock piston  52  is actuated in response to a predetermined difference therebetween.  
         [0029]     The pitchlock ballscrew screw  54  is back driven within the ballscrew ballnut  58  under normal operating conditions. The pitchlock ballscrew screw  54  rotationally translates relative to the ballscrew ballnut  58 . The pitchlock ballscrew screw  54  includes a continuous ballscrew ball track groove  64  with a helix angle that matches the helix angle of the pitchlock nut  56 , and the ballscrew ballnut  58 . The ballscrew screw  54  is mounted within the pitchlock nut  56  and the ballscrew ballnut  58  to rotationally axially advance or retreat over the full travel of the actuator yoke assembly  50 .  
         [0030]     A ballscrew screw flange  66  is located at a forward end segment of the pitchlock ballscrew screw  54 . The ballscrew screw flange  66  is spaced away from an axially fixed actuator dome cover  68  during normal operation by a pitchlock gap. Should a hydraulic pressure failure occur, the pitchlock gap is closed when the ballscrew screw flange  66  contacts the actuator dome cover  68  to lock the propeller blades  32  in their last pitch position. The ballscrew screw flange  66  is capable of reacting the full actuator fine pitch hydraulic pressure output and resulting blade load under failure conditions.  
         [0031]     Opposite the ballscrew screw flange  66 , an aft end segment  67  of the pitchlock ballscrew screw  54  is mounted within the ballscrew bearing support assembly  62 . The ballscrew bearing support assembly  62  is mounted to the pitchlock piston load tube  63 . The ballscrew bearing support assembly  62  moves axially with the pitchlock piston load tube  63  and provides a ground relative to which the pitchlock ballscrew screw  54  rotates. That is, the pitchlock ballscrew screw  54  rotates within the ballscrew bearing support assembly  62  and the ballscrew bearing support assembly  62  is axially translatable with the pitchlock piston load tube  63  in response to actuation of the pitchlock piston  52  that supports the pitchlock piston load tube  63 .  
         [0032]     The ballscrew ballnut  58  mates with the pitchlock ballscrew screw  54 . The ballscrew ballnut  58  includes a continuous mating ballnut ball track groove  72  with a helix angle equivalent to that of the ballscrew ball track groove  64 . The ballnut ball track groove  72  provides the other half of the ball track for the supporting ball bearings  74 . The ballscrew ballnut  58  provides both the stationary contact surface for the ball bearings  74  as well as ball bearing containment and ball bearing crossovers.  
         [0033]     The ballscrew ballnut  58 , during normal operation, is mounted within an actuator yoke bore  76  and axially translates with the yoke assembly  50  until the ballscrew screw flange  66  contacts the axially fixed actuator dome cover  68  in response to some pitchlock input signal. At this point, when the actuator yoke  50  loads exceed a biasing force provided by a ballscrew ballnut spring  78 , the ballscrew ballnut  58  will axially slide within the actuator yoke bore  76  until pitchlock nut threads  86  of the pitchlock nut  56  contact the ballscrew ball track groove  64  to pitchlock the pitchlock ballscrew screw  54  and react the aerodynamic blade loads.  
         [0034]     The pitchlock nut  56  defines an external mounting thread  80  which corresponds to an internal thread  82  of the actuator yoke bore  76 . The pitchlock nut  56  preferably includes a shoulder flange  84  which positions the pitchlock nut  56  relative the actuator yoke assembly  50 . It should be understood that other attachments such as bolts or the like may alternatively be utilized.  
         [0035]     The pitchlock nut  56  includes internal pitchlock nut threads  86  that preferably provides a toroidal profile ( FIG. 3 ) with the same helix angle as the ballscrew ball track groove  64  such that the pitchlock nut threads  86  mate therewith. The toroidal profile of the pitchlock nut threads  86  provide a clearance relative to the ballscrew ball track groove  64  ( FIG. 3 ) such that under normal propeller operation the ballscrew ball track groove  64  and the pitchlock nut threads  86  do not contact. When the propeller is commanded to pitchlock and the resulting blade loads are transferred through the pitchlock nut  56  into the pitchlock ballscrew screw  54 , the lead angle is configured such that the pitchlock ballscrew screw  54  cannot back drive in the pitchlock nut  56  and the propeller pitchlocks.  
         [0036]     The ball bearings  74  provide the dynamic interface between the ballscrew ballnut  58  and the pitchlock ballscrew screw  54 . The ball bearings  74  travel in the mating ball grooves of the ballscrew ball track groove  64  and the ballnut ball track groove  72  when the ballscrew ballnut  58  and pitchlock ballscrew screw  54  move relative to each other. The circuit of ball bearings  72  may be diverted within ball track cross-overs located in the ballscrew ballnut  58 . The cross-overs provide recirculation and unrestricted travel of the ballscrew ballnut  58  relative to the pitchlock ballscrew screw  54 . Because the ball bearings  74  roll in the ballscrew ball track groove  64  and the ballnut ball track groove  72 , the friction losses are minimized allowing the pitchlock ballscrew screw  54  to be backdriven within the ballscrew ballnut  58 .  
         [0037]     A timing keyway  88  is located in both the pitchlock nut  56  and the ballscrew ballnut  58  within which a lock  91  fits. Because the ballscrew ballnut  58  and pitchlock nut  56  fit about the common pitchlock ballscrew screw  54 , the threads must be properly timed. The timing keyway  88  times the ballnut ball track groove  72  and the pitchlock nut threads  86 . The timing keyway  88  also provides an anti-rotation feature for the ballscrew ballnut  58 . That is, to impart the resulting rotational load on the pitchlock ballscrew screw  54 , the ballscrew ballnut  58  itself must be rotationally held to ground.  
         [0038]     The ballscrew ballnut spring  78  provides an axial preload on the ballscrew ballnut  58  relative to the pitchlock nut  56  to ensure that under normal operating conditions, the pitchlock baliscrew screw  54  operates through the ball bearings  74 . When the propeller is commanded to pitchlock and the resulting blade loads acting through the actuator yoke assembly  50  against the pitchlock ballscrew screw  54  exceed the ballscrew ballnut spring  78 , the ballscrew ballnut spring  78  begins to collapse which permits the ballscrew ballnut  58  to translate ( FIGS. 4A-4D ) axially along the hub axis A and transfer the loads to the pitchlock nut threads  86 .  
         [0039]     The pitchlock nut threads  86  are designed to accept high axial loads through the tangential ball track groove flanks with a radial ball bearing seat for normal ballscrew screw  54  operation. The thread profile of the pitchlock nut threads  86  preferably resemble that of an ACME thread which provides a large bearing surface and a non-back driving interface. The thread profile of the pitchlock nut threads  86  are configured such that ball bearings  74  only contact on the radial ball bearing seat of the continuous ballscrew ball track groove  64 , while the ACME style pitchlock nut threads  86  only contact on the flanks of the continuous ballscrew ball track groove  64  such that minimal deleterious effect to the track groove and normal ball bearing movement results.  
         [0040]     Referring to  FIG. 4A , the pitchlock system  46  is illustrated in a normal operational position in which the pitchlock gap is maintained and differential pressure between the coarse pitch pressure P c  and the fine pitch pressure P F  operate to effectuate movement of the pitch change actuator piston  49  and resulting pitch change to the propeller blades  32  ( FIG. 2A ).  
         [0041]     The pitchlock pressure P PL  is communicated to the pitchlock system  46  to counteract the coarse pitch pressure P c  and pitchlock spring, balance the pitchlock piston  52  and maintain the pitchlock gap. The ballscrew screw  54  is mounted within the pitchlock nut  56  and the ballscrew ballnut  58  to rotationally advance or retreat over the full travel of the actuator yoke assembly  50  in response to movement of the pitch change actuator piston  49  through the differential pressure between the coarse pitch pressure P c  and the fine pitch pressure P F .  
         [0042]     Referring to  FIG. 4B , when the propeller system is commanded to pitchlock such as by a decrease in the coarse pitch pressure P c  which may result from a loss of hydraulic pressure, or by dumping of the pitchlock pressure P PL , the pitchlock system  46  is mechanically initiated by the pitch lock spring.  
         [0043]     Once the hydraulic pressure on the pitchlock piston  52  is removed, the pitchlock piston  52  and pitchlock piston load tube  63  are biased (to the left in the figure) by a set of pitchlock springs  90 . As the pitchlock piston load tube  63  strokes, the ballscrew bearing support assembly  62  ( FIGS. 2A and 2B ) which is mounted thereto also strokes to drive the pitchlock ballscrew screw  54  toward the axially fixed actuator dome cover  68  and close the pitchlock gap. The load from the pitchlock springs  90  loads the pitchlock ballscrew screw  54  against the axially fixed actuator dome cover  68 . Contact with the axially fixed actuator dome cover  68  generates a torsional and an axial resistance which grounds the pitchlock ballscrew screw  54 .  
         [0044]     Referring to  FIG. 4C , aerodynamic forces provide propeller blade loads which drives the pitch change system  48  and attached pitch change actuator piston  49  towards the fine pitch direction. The load driven through the ballscrew ballnut  58  and into pitchlock ballscrew screw  54  changes the contact angle (i.e. direction) through the ball bearings  74 . The load from piston springs  90  holds the pitchlock ballscrew screw  54  against the axially fixed actuator dome cover  68  while the bias from the pitch change actuator piston  49  being driven towards fine pitch results in a force which attempts to back-drive the pitchlock ballscrew screw  54 . However, the resistant torsional loads between the ballscrew screw flange  66  and the fixed actuator dome cover  68  are greater than the force which is attempting to back-drive through the pitchlock ballscrew screw  54  such that the ballscrew ballnut spring  78  begin to collapse ( FIG. 4D ).  
         [0045]     Referring to  FIG. 4D , the ballscrew ballnut spring  78  begins to collapse due to decreased pitch load. The load from piston springs  90  maintains the pitchlock ballscrew screw  54  against the axially fixed actuator dome cover  68  while the bias from the pitch change actuator piston  49  being driven towards fine pitch attempts to back-drive the pitchlock ballscrew screw  54  and drive the ballscrew ballnut  58  therewith (note separation between the pitchlock nut  56  and the ballscrew ballnut  58 ). The pitch load continues to decrease enough to further collapse the ballscrew ballnut spring  78  such that the ACME style pitchlock nut threads  86  contact the flanks of the continuous ballscrew ball track groove  64  until the lead angle results in a lock-up condition to thereby pitchlock the propeller system. Notably, no mechanical link is required between the rotating and non-rotating propeller components to initiate pitchlock.  
         [0046]     When the pitchlock pressure P PL  is restored, the coarse pitch pressure P c  is balanced and the bias from the piston springs  90  is overcome such that the pitchlock piston  52 , the pitchlock piston load tube  63 , attached ballscrew bearing support assembly  62  and pitchlock ballscrew screw  54  returns to their normal operational position ( FIG. 4A ). Commensurate therewith, the ballscrew ballnut spring  78  repositions the ballnut  58  as the load on the ballscrew is removed such that the pitchlock gap returns ( FIG. 4A ) and normal operation again is available.  
         [0047]     Preferably, a pitchlock solenoid valve  44  ( FIG. 2A ) is located in communication with the pitchlock pressure P PL  circuit to selectively actuate pitchlocking in response to a controller (illustrated schematically at C). The pitchlock solenoid valve  44  is preferably an electro-mechanical device which is normally closed. When the pitchlock solenoid valve  44  is commanded to electrically open in response to the controller C, the valve  44  ports the pitchlock pressure P PL  to return pressure (low) which causes the pitchlock piston  53  to stroke and initiate pitchlock as described above with reference to  FIGS. 4A-4C .  
         [0048]     Referring to  FIG. 5 , the pitchlock solenoid valve  44  is additionally or alternatively operated by a remotely located controller C′ such that pitchlock may be commanded from a location separate from a vehicle V within which the pitchlock system is located. Such an arrangement advantageously provides for remotely commanded pitchlock from a flight deck or the like.  
         [0049]     Referring to  FIG. 6A , a sectional view of another the pitchlock system  46 B which interacts with the pitch change system  48  in response to differential pressure between pitchlock pressure P PL  and coarse pitch pressure P c  is illustrated. The pitchlock system  46 B is generally as described above such that only components which are different than that described above are discussed in detail. The pitchlock ballscrew screw  54 B of the pitchlock system  46 B generally includes a pitchlock screw  100  and a ballscrew screw  102  interconnected through a universal joint  104  arranged in a generally linear manner. That is, the pitchlock ballscrew screw  54 B is articulately through separate components which are mounted together through the universal joint  104 . The pitchlock screw  100  and the ballscrew screw  102  are located along the hub axis A in a sequential manner such that the pitchlock system  46 B may have a longer axial length than the pitchlock system  46  but the pitchlock system  46 B allows torque to be transmitted from the ballscrew to pitchlock screw with out generating side loads.  
         [0050]     Referring to  FIG. 6B , the ballscrew screw  102  is pinned to a universal joint ring  106  of the universal joint  104  in two places 180° apart at universal pins  108 A (one shown). A sliding clearance fit is provided between the universal pins  108 A and apertures  110  in the ballscrew screw  102  that receive the pins  108 . Likewise, the pitchlock screw  100  is pinned to the universal joint ring  106  in two places at universal pins  108 B (one shown) to provide a similar sliding fit 90° in relation to the ballscrew pins  108 A. This arrangement allows torque to be transmitted from the ballscrew  100  to the pitchlock screw  102  with out generating side loads. Without this type of connection side loads may be generated which may increase friction in the system. It should be understood that various pitchlock systems will benefit from the present invention.  
         [0051]     It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.  
         [0052]     It should be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit from the instant invention.  
         [0053]     Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.  
         [0054]     The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.