Patent Publication Number: US-2020290748-A1

Title: Ram air turbines and transmission systems

Description:
BACKGROUND 
     1. Field 
     This disclosure relates to ram air turbines and systems. 
     2. Description of Related Art 
     The primary function of a ram air turbine (RAT) is to provide alternate power to the aircraft at any flight phase during the aircraft&#39;s operational profile during emergency situations requiring the RAT. Depending on the specific RAT configuration and size, it will have a turbine, a gearbox, an electric generator or a hydraulic pump, or both a generator and a pump. Conventionally, a fluid filled, angled gearbox has been used to increase the turbine shaft speed into the generator. Typical gear ratios range from 1:1 to 1:2.5. As the turbine spins up, the full driveline spins with it. This adds inertia to the driveline which increases start time (especially at cold conditions where driveline bearing tare losses and gearbox fluid viscous losses are the highest). Additionally, since the gear ratio is fixed, the governing capability of the system is limited to the turbine. 
     Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved RATs and systems. The present disclosure provides a solution for this need. 
     SUMMARY 
     A ram air turbine (RAT) system can include a fluid circuit, a turbine, a shaft connected to the turbine to turn with the turbine, and a hydraulic pump connected (e.g., directly) to the shaft and connected to the fluid circuit to pump fluid within the fluid circuit. The hydraulic pump can be a variable displacement pump, for example (e.g., configured to govern a speed of the shaft and turbine). For example, the hydraulic pump can be a piston pump. Any other suitable pump is contemplated herein. 
     The system can further include a generator assembly operatively connected to the fluid circuit, wherein the generator assembly is configured to be driven by flow and/or pressure of the fluid in the fluid circuit. The generator assembly can include a hydraulic motor configured to be driven by flow and/or pressure within the circuit. The hydraulic pump can be configured to drive the hydraulic motor with the fluid in the fluid circuit. 
     The hydraulic motor can include a pump (e.g., configured to operate in reverse). The hydraulic motor can be a constant displacement pump (e.g., a gear pump). Any other suitable pump (e.g., a variable displacement pump) is contemplated herein. 
     The system can include a hydraulic loop connected to the fluid circuit, wherein one or more hydraulic systems are disposed in fluid communication with the hydraulic loop to be driven by flow and/or pressure in the fluid circuit. The hydraulic pump can be configured to drive the one or more hydraulic systems in fluid communication with the fluid in the fluid circuit. The hydraulic loop can connect upstream of the hydraulic motor and downstream of the hydraulic motor. 
     In accordance with at least one aspect of this disclosure, a ram air turbine (RAT) can include a turbine, a shaft connected to the turbine to turn with the turbine, and a hydraulic pump connected (e.g., directly) to the shaft and configured to connect to a fluid circuit to pump fluid within the fluid circuit. The hydraulic pump can be any suitable hydraulic pump as disclosed herein (e.g., described above). 
     In accordance with at least one aspect of this disclosure, a method can include turning a hydraulic pump of a ram air turbine (RAT) with a shaft of the RAT attached to a turbine of the RAT. The method can include pumping fluid with the hydraulic pump to generate fluid flow and/or fluid pressure in a fluid circuit. The method can include driving a generator with the fluid flow and/or fluid pressure. The method can include driving one or more hydraulic systems of an aircraft with the fluid flow and/or fluid pressure. The hydraulic pump used in the method can be a variable displacement pump configured to govern a speed of the RAT, for example. 
     These and other features of the embodiments of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a schematic diagram of an embodiment of a system in accordance with this disclosure; and 
         FIG. 2  is a schematic diagram of an embodiment of a system in accordance with this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, an illustrative view of an embodiment of a system in accordance with the disclosure is shown in  FIG. 100  and is designated generally by reference character  100 . Other embodiments and/or aspects of this disclosure are shown in  FIG. 2 . 
     A ram air turbine (RAT) system  100  can include a fluid circuit  101 , a turbine  103 , a shaft  105  connected to the turbine  103  to turn with the turbine  103 , and a hydraulic pump  107  connected (e.g., directly) to the shaft  105 . The hydraulic pump  107  can be connected to the fluid circuit  101  to pump fluid within the fluid circuit  101 . 
     The hydraulic pump  107  can be a variable displacement pump, for example. The use of a variable displacement pump can govern a speed of the shaft  105  and turbine  103  as a changing input speed into the variable displacement pump changes the output displacement. For example, the hydraulic pump  107  can be a piston pump. Any other suitable pump type (e.g., fix displacement) is contemplated herein as appreciated by those having ordinary skill in the art in view of this disclosure. 
     The system  100  can further include a generator assembly  109  operatively connected to the fluid circuit  101 . The generator assembly  109  can be configured to be driven by flow and/or pressure of the fluid in the fluid circuit  101 . The generator assembly  109  can include a hydraulic motor  111  configured to be driven by flow and/or pressure within the circuit  101 . The hydraulic pump  107  can be configured to drive the hydraulic motor  111  with the fluid in the fluid circuit  101 , for example. The hydraulic motor  111  can be connected to a generator  113  to turn the generator  113  when driven by fluid in the fluid circuit  101  to produce electrical energy. 
     The hydraulic motor  111  can include a pump (e.g., configured to operate in reverse). The hydraulic motor  111  can be a constant displacement pump (e.g., a gear pump). Any other suitable pump (e.g., a variable displacement pump) is contemplated herein. 
     Referring additionally to  FIG. 2 , a system  200  can additionally or independently include a hydraulic loop  215  connected to the fluid circuit  101 . One or more hydraulic systems  217  (e.g., any suitable an aircraft hydraulic systems) can be disposed in fluid communication with the hydraulic loop  215  to be driven by flow and/or pressure in the fluid circuit  101 . The hydraulic pump  107  can be configured (e.g., sized and/or speed set) to drive the one or more hydraulic systems  217  in fluid communication with the fluid in the fluid circuit  101  (e.g., in addition to driving the generator  113 ). As shown, in certain embodiments, the hydraulic loop  215  can connect upstream of the hydraulic motor  111  and downstream of the hydraulic motor  111  (e.g., an inlet upstream and an outlet downstream). While certain embodiments are shown having a hydraulic motor, it is contemplated that the shaft  105  can be mechanically connected to a generator (e.g., through a gearbox) while the hydraulic pump  107  governs a speed of the shaft, and thus the speed of the mechanically connected generator. Any other suitable arrangement is contemplated herein. 
     In accordance with at least one aspect of this disclosure, a ram air turbine (RAT) can include a turbine  103 , a shaft  105  connected to the turbine to turn with the turbine  103 , and a hydraulic pump  107  connected (e.g., directly) to the shaft  105  and configured to connect to a fluid circuit  101  to pump fluid within the fluid circuit  101 . The hydraulic pump  107  can be any suitable hydraulic pump  107  as disclosed herein (e.g., a variable displacement pump as described above). In certain embodiments, the RAT can include and/or be mechanically connected to a generator to mechanically turn the generator to produce electrical energy while the hydraulic pump is connected to a fluid circuit to govern a speed of the RAT and generator. Any other suitable features (e.g., one or more gear boxes) for the RAT are contemplated herein. 
     In accordance with at least one aspect of this disclosure, a method can include turning a hydraulic pump of a ram air turbine (RAT) with a shaft of the RAT attached to a turbine of the RAT. The method can include pumping fluid with the hydraulic pump to generate fluid flow and/or fluid pressure in a fluid circuit. The method can include driving a generator with the fluid flow and/or fluid pressure. The method can include driving one or more hydraulic systems of an aircraft with the fluid flow and/or fluid pressure. The hydraulic pump used in the method can be a variable displacement pump configured to govern a speed of the RAT, for example. The hydraulic motor of the generator assembly could also be a variable displacement pump type. In certain embodiments, one side can be fixed (e.g., a gear pump), and the other side can be variable. 
     In certain embodiments, a pump directly coupled to the turbine can create a hydraulic pump pressure which can drive a generator. In certain embodiments, this can allow governing of the generator (e.g., by using at least one variable displacement pump as the hydraulic pump and/or the hydraulic motor) and allow output that is in a narrower frequency band. For example, as disclosed above, the hydraulic pump can be a variable displacement pump, e.g., a piston pump, that can inherently cause governing. In certain embodiments, the speed can be set so that it operates at max displacement, for example. Certain embodiments can also allow direct drive of one or more hydraulic systems as well as driving the generator. Certain embodiments can prevent losses from otherwise having to convert hydraulic energy to electricity. 
     Embodiments can be used in aircraft, for example. Embodiments can replace the existing gear set with a hydrostatic transmission or be added to the RAT if a gearbox (e.g., an angled gearbox). A gearbox transmission can provide a secondary governing feature to the RAT system, for example. Embodiments can allow for a tighter output shaft speed range and thus, a tighter frequency band output from the generator. Embodiments can save weight by removing electrical devices and/or reducing electrical device size on the aircraft because electrical systems can be designed to operate in a narrower frequency band. Additionally, a portion of the hydraulic pump output can be routed to the aircraft hydraulic system. 
     As disclosed above, embodiments can utilize a hydrostatic transmission in the RAT. The hydrostatic transmission can be driven by the turbine shaft and the pump output can be routed to drive a generator and/or aircraft hydraulics. The hydrostatic transmission can replace the gearbox of existing RATs and can allow the generator to be placed essentially anywhere space allows within the RAT envelope. In the case of an electric RAT, the pump can act as another governor to help maintain a more constant output frequency. If a gearbox is not used and the hydrostatic pump is coupled to the turbine shaft, a planetary gear set can be added to increase or decrease the speed into the pump. 
     The use of a hydrostatic transmission on a RAT can provide tighter frequency band for electric RATs, allow electric devices to be smaller/lighter due to a narrow frequency band (e.g., within about 5% in certain embodiments), provide faster start-up by eliminating fluid viscous losses on gear set, allow for a smaller gearbox (e.g., 1:1 gear ratio) if still required for layout, provide hydraulic power to the aircraft, eliminate the gearbox entirely in certain cases, and allow relocation of the generator away from the turbine in a non-deploying portion of the RAT thereby reducing the moment of inertia during deployment and thus reducing deployment loads seen by the actuator and RAT structure. 
     Those having ordinary skill in the art understand that any numerical values disclosed herein can be exact values or can be values within a range. Further, any terms of approximation (e.g., “about”, “approximately”, “around”) used in this disclosure can mean the stated value within a range. For example, in certain embodiments, the range can be within (plus or minus) 20%, or within 10%, or within 5%, or within 2%, or within any other suitable percentage or number as appreciated by those having ordinary skill in the art (e.g., for known tolerance limits or error ranges). 
     Any suitable combination(s) of any disclosed embodiments and/or any suitable portion(s) thereof are contemplated herein as appreciated by those having ordinary skill in the art. 
     The embodiments of the present disclosure, as described above and shown in the drawings, provide for improvement in the art to which they pertain. While the subject disclosure includes reference to certain embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject disclosure.