Abstract:
A turbine pump assembly has a turbine, a centrifugal pump, and a passive electrical speed control system. The turbine has a peak efficiency at a first speed that is lower than a second speed at which the centrifugal pump is operating at a peak power requirement. A rocket thrust vector control system is also disclosed.

Description:
BACKGROUND 
       [0001]    This application relates to a turbine pump assembly, and more particularly to a passive overspeed controlled turbine pump assembly. 
         [0002]    Rockets are maneuvered by vectoring the rocket engine thrust direction. A thrust vector control system often relies on hydraulic rams to displace the engine nozzle angle. Such hydraulic rams require high pressure hydraulic fluid pumping systems, capable of providing very high flow rates. This hydraulic flow is typically generated by a Turbine Pump Assembly (TPA), which may be powered by a fluid propellant provided by the main engine turbo-pump assembly. 
         [0003]    A traditional TPA comprises a turbine and a hydraulic pump. Typically, the turbine operates at very high rotational speeds, such as 115,000 rpm, while the hydraulic pump operates at lower speeds, such as 6100 rpm. A gear reduction system is incorporated between the hydraulic pump and the turbine to accommodate the different operating speeds. 
         [0004]    A traditional TPA further includes a Turbine Speed Control Valve Assembly to control the fluid flowing to the turbine, and thus the turbine rotational speed. The output power of the turbine is proportional to the mass flow rate of the propellant through the valve. In traditional systems, this valve assembly comprises a spring and a fly weight governor assembly. As the turbine spins, the fly weight governor assembly also rotates. As the fly weight governor rotates, a centripetal force is applied to arms of the fly weight governor, proportional to the rotational speed of the turbine. When the turbine and fly weight governor reach a particular speed, the fly weight governor arms push against the spring, causing the valve to partially close. As the turbine spins faster, the valve is pushed further closed. When the turbine reaches a desired speed, the fly weight governor forces are balanced against the spring force, with the valve open just far enough to maintain the turbine speed. 
         [0005]    If additional load is applied to the TPA by the hydraulic system, the turbine will decelerate. When the turbine slows down, the centripetal force acting on the fly weight governor arms is reduced, allowing the spring to push the valve further open, allowing more propellant to flow into the turbine, causing the turbine to speed back up to the desired speed. This system is well developed, but also complex and expensive. 
       SUMMARY 
       [0006]    A turbine pump assembly has a turbine, a centrifugal pump, and a passive electrical speed control system. The turbine has a peak efficiency at a first speed that is lower than a second speed at which the centrifugal pump is operating at a peak power requirement. A rocket thrust vector control system is also disclosed. 
         [0007]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of an embodiment. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a perspective view of a turbine pump assembly. 
           [0009]      FIG. 2  shows a cross section of the turbine pump assembly of  FIG. 1 . 
           [0010]      FIG. 3  shows a partial view of a portion of the turbine pump assembly of  FIG. 1 . 
           [0011]      FIG. 4  shows a partial view of a portion of the turbine pump assembly of  FIG. 1 . 
           [0012]      FIG. 5  shows a graph of speed and power of the turbine pump assembly of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring to  FIG. 1 , a turbine pump assembly (TPA) system  20  includes a turbine  22  and a centrifugal pump  24 . The TPA  20  may be powered by a propellant, such as hydrogen gas, provided by the main engine turbo-pump assembly  29  (shown in  FIG. 2 ). Other propellants are contemplated, such as oxygen, methane, helium, or nitrogen, for example. The centrifugal pump  24  allows the TPA  20  to be much smaller than the traditional system that utilizes a hydraulic pump. 
         [0014]    Both the turbine  22  and centrifugal pump  24  are capable of operating at very high speeds, and thus are configured to rotate on a single shaft  26 , as shown in  FIG. 2 . In one example, the operating speed of the turbine  22  and centrifugal pump  24  is between 90,000 rpm and 140,000 rpm. The turbine  22  drives the centrifugal pump  24  through the shaft  26 . Hydraulic fluid from the centrifugal pump  24  is communicated to an engine nozzle  27  (shown schematically) to displace a rocket engine nozzle angle relative to a rocket core axis. The operation of the engine nozzle  27  and how the angle is adjusted are known. 
         [0015]    Although disclosed as part of a rocket engine nozzle control, this disclosure may have application in other systems. 
         [0016]    Since the turbine  22  and centrifugal pump  24  both operate at high speeds, and thus can operate on the same shaft  26 , a gear reduction between the turbine  22  and the centrifugal pump  24  is not required. This configuration results in fewer moving parts in the overall system than a traditional TPA. The higher speeds of the single shaft  26  also prohibit the use of the fly weight governor used in traditional systems. 
         [0017]    A speed control valve  28  controls the amount of propellant that goes to the turbine  22  from a main engine turbo-pump assembly  29  (shown schematically) through a turbine gas inlet port  30 . When propellant is supplied to the turbine gas inlet port  30 , propellant flows through the speed control valve  28  and to the turbine  22 , causing the turbine  22  to rotate. As the mass flow rate of the propellant increases, the speed of the turbine  22  will increase. The speed control valve  28  controls the speed of the turbine  22  by varying the mass flow rate of the propellant. 
         [0018]      FIG. 3  shows the rotating components of the TPA  20 . A generator  32  is arranged along the shaft  26  between the turbine  22  and the centrifugal pump  24 . In one embodiment, the generator  32  is a high speed permanent magnet generator. In the illustrated embodiment, the generator  32  comprises permanent magnets  31  that rotate with the shaft  26 , and generate a current in a stationary coil  33 . The permanent magnet generator  32  generates alternating current power proportional to the rotational speed of the turbine  22 . This alternating current power is passively rectified by a passive rectifier  34  (shown in  FIG. 1 ) into direct current power proportional to the rotational speed of the turbine  22 , which is then used to control the speed of the turbine  22 . 
         [0019]      FIG. 4  shows the turbine speed control valve assembly  28 , which provides passive electrical proportional turbine speed control. In the illustrated embodiment, the direct current power from the passive rectifier  34  is sent to a valve control solenoid  36 . The solenoid  36  produces an electromagnetic force applied to a valve control solenoid plunger  38 , which exerts an axial force that is proportional to the direct current power that is flowing in the windings of solenoid  36 . Because the direct current power is proportional to the speed of the turbine  22 , the axial force produced by solenoid  36  is also proportional to the speed of the turbine  22 . This axial force exerted by the plunger  38  pushes against a valve spool  40 , which pushes against a valve opening spring  42 . In another embodiment, a linear motor or electromechanical actuator may be used to displace the valve spool  40 . In the shown example, the axial force exerted by plunger  38  causes the valve spool  40  to shift to the left, compressing the valve opening spring  42  and decreasing the mass flow rate of the propellant entering the turbine  22  through the turbine inlet port  30 . 
         [0020]    As the turbine  22  spins faster, more alternating current power is generated at the permanent magnet generator  32 , creating more direct current power rectified by the passive rectifier  34 . As direct current power in the valve control solenoid  36  increases, the electromagnetic force applied to the valve control solenoid plunger  38  increases. The increased electromagnetic force results in an increased axial force exerted by the plunger  38 . The increased axial force exerted by the plunger  38  pushes the valve spool  40 , which pushes the spring  42  to push the valve  28  further closed, which decreases the mass flow rate of propellant entering the turbine  22 , thus decreasing the speed of the turbine  22 . When the turbine  22  reaches a desired speed, the axial force generated by the valve control solenoid  36  is balanced with the spring force of spring  42 , such that the valve  28  is open just far enough to maintain a desired speed of the turbine  22 . 
         [0021]    As the speed of the turbine  22  decreases, the electromagnetic force applied to the valve control solenoid plunger  38  decreases, causing the valve spool  40  to shift in the opposite direction, decompressing the valve opening spring  42 . When the valve opening spring  42  is decompressed, the mass flow rate of propellant entering the turbine  22  through turbine gas inlet port  30  increases. The desired mass flow rate and turbine speed depend on the requirements of a particular system. Details of the passive electrical speed control system are found in co-pending U.S. patent application Ser. No. _____, entitled “Passive Electrical Proportional Turbine Speed Control System” filed on even date herewith. Details of a circuit breaker control valve are found in co-pending U.S. patent application Ser. No. _____, entitled “Pneumatic Circuit Breaker Based Self Resetting Passive Overspeed Control Valve for TPA” filed on even date herewith. 
         [0022]    If the passive electrical proportional turbine speed control system becomes damaged, the solenoid  36  may stop providing an axial force to the valve spool  40 . When no axial force is applied to the valve spool  40 , the spring  42  will decompress, causing the valve  28  to fully open, which allows the turbine  22  to accelerate to undesirable speeds. 
         [0023]    Passive overspeed protection can be accomplished by designing the turbine  22  such that the peak efficiency of the turbine  22  occurs at a rotational speed that is below the peak power requirement of the centrifugal pump  24 , as shown in  FIG. 5 . Curve  50  shows the power capability of turbine  22 . Curve  52  shows the required power of the centrifugal pump  24 . The peak efficiency point  54  of turbine power curve  50  shows the rotational speed at which the turbine  22  will produce the most power. As the rotational speed of turbine  22  increases beyond the peak efficiency  54 , efficiency of the turbine  22  is reduced due to incidence losses, blockage, and leakage. Incidence losses occur because the fluid incidence angle at an inlet of the turbine  22  causes an aerodynamic blockage in turbine blade passages, decreasing the efficiency of the turbine  22 , and thus the output power of the turbine  22 . At point  56 , where the turbine efficiency drops to zero, the blades of the turbine  22  are completely stalled. 
         [0024]    As the speed of the centrifugal pump  24  increases, its input power requirement increases. At the intersection of curves  50 ,  52 , the rotating group, comprising turbine  22 , centrifugal pump  24 , shaft  26  and permanent magnet generator  32 , will reach its maximum aerodynamic rotational speed  58 . In one embodiment, the peak efficiency  54  of the turbine  22  occurs at a lower rotational speed than the intersection  58 . In one embodiment, the peak efficiency  54  of the turbine  22  occurs at about 80,000 rpm, and the maximum aerodynamic rotational speed  58  of the rotating group is about 110,000 rpm. 
         [0025]    The design of the turbine  22  such that its peak efficiency  54  at a speed lower than a speed of the peak power requirement of the centrifugal pump  24  protects the TPA  20  from becoming damaged in the event of damage to the passive electrical proportional turbine speed control system. In one embodiment, this design is accomplished by incorporating a feature into a disk of the turbine  22  that causes the turbine efficiency to decrease beyond a predetermined speed. In another embodiment, an angle of attack in the turbine  22  is designed such that the turbine efficiency decreases beyond a predetermined speed. In another embodiment, a chord length of a disk of turbine  22  is designed such that the turbine efficiency decreases beyond a predetermined speed. In yet another embodiment, a disk of the turbine  22  is designed such that the blades deform (twist) at high speeds, thereby negatively altering the blade incidence angles. In this embodiment, as the speed of the turbine  22  increases beyond a predetermined speed, the turbine disk will deform due to a higher radial load, which decreases the efficiency of the turbine  22 . 
         [0026]    In further embodiments, the centrifugal pump  24 , permanent magnet generator  32  and shaft  26  are designed such that the rotating group operates at the maximum aerodynamic rotational speed  58 . 
         [0027]    Although the different examples have a specific component shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
         [0028]    Furthermore, the foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.