Abstract:
A torque converter for converting torque between an input shaft and an output shaft includes an impeller operably connected to the input shaft and rotatable therewith. The torque converter further includes a turbine operably connected to the output shaft and rotatable therewith. A fluid flow system directs a flow of motive fluid through the impeller and through the turbine to drive rotation of the output shaft relative to the input shaft. A lockup mechanism is engageable to urge rotation of the output shaft at an output shaft rotational speed identical to an input shaft rotational speed. A switching module controls an actuation system to urge engagement of the lockup mechanism.

Description:
BACKGROUND 
     The subject matter disclosed herein relates to the art of rotary wing aircraft and, more specifically to a torque converter for a rotary wing aircraft powered by a piston engine. 
     Some configurations of rotary wing aircraft, or rotorcraft, require the capability to allow for torque slip and freewheeling of the drive system, allowing the engine speed to be essentially independent of drive system speed to prevent stall or damage of the engine under certain operating conditions. These conditions include, but are not limited to, engine startup, increasing or decreasing drive system speed regardless of engine speed, stopping drive system output with the engine running, and autorotation maneuvers of the rotorcraft. Turbine engine powered rotorcraft typically do not require additional components to allow for torque slip as the turbine engine design inherently includes a torque slip capability. A freewheel unit is still necessary to allow for autorotation and engine shut down. 
     Piston engine powered rotorcraft require both additional torque slip and freewheel devices for operation. Typically, such rotorcraft utilize belt drives, which are effective at low power levels, but eventual wear requires regular inspection and replacement of the belts. Larger rotorcraft, operating at higher power levels, have used wet clutches with friction discs to allow for torque slip, but these configurations are prone to overheating and wear. 
     BRIEF DESCRIPTION 
     In one embodiment, a torque converter for converting torque between an input shaft and an output shaft includes an impeller operably connected to the input shaft and rotatable therewith. The torque converter further includes a turbine operably connected to the output shaft and rotatable therewith. A fluid flow system directs a flow of motive fluid through the impeller and through the turbine to drive rotation of the output shaft relative to the input shaft. A lockup mechanism is engageable to urge rotation of the output shaft at an output shaft rotational speed identical to an input shaft rotational speed. A switching module controls an actuation system to urge engagement of the lockup mechanism. 
     In another embodiment, a drive system includes an engine, a gearbox operably connected to the engine, and a torque converter operably connected to the engine via an input shaft and operably connected to the gearbox via an output shaft. The torque converter includes an impeller operably connected to the input shaft and rotatable therewith and a turbine operably connected to the output shaft and rotatable therewith. A fluid flow system directs a flow of motive fluid through the impeller and through the turbine to drive rotation of the output shaft relative to the input shaft. A lockup mechanism is engageable to urge rotation of the output shaft at an output shaft rotational speed identical to an input shaft rotational speed. A switching module controls an actuation system to urge engagement of the lockup mechanism. 
     In yet another embodiment, a helicopter includes an airframe and a drive system. The drive system includes a piston engine, a gearbox operably connected to the engine, and a torque converter operably connected to the engine via an input shaft and operably connected to the gearbox via an output shaft. The torque converter includes an impeller operably connected to the input shaft and rotatable therewith and a turbine operably connected to the output shaft and rotatable therewith. A fluid flow system directs a flow of motive fluid through the impeller and through the turbine to drive rotation of the output shaft relative to the input shaft. A lockup mechanism is engageable to urge rotation of the output shaft at an output shaft rotational speed identical to an input shaft rotational speed. A switching module controls an actuation system to urge engagement of the lockup mechanism. A rotor assembly is operably connected to the drive system. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic view of an embodiment of a helicopter; 
         FIG. 2  is a schematic view of an embodiment of a drive system for a helicopter; 
         FIG. 3  is a schematic view of another embodiment of a drive system for a helicopter; 
         FIG. 4  is a schematic view of yet an embodiment of a drive system for a helicopter; 
         FIG. 5  is a schematic view of still another embodiment of a drive system for a helicopter; and 
         FIG. 6  is a schematic view of another embodiment of a drive system for a helicopter. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION 
     Shown in  FIG. 1  is schematic view of an embodiment of an aircraft, in this embodiment a helicopter  10 . The helicopter  10  includes an airframe  12  with an extending tail  14  and a tail rotor  16  located thereat. While the embodiment of a helicopter  10  described herein includes an extending tail  14  and tail rotor  16 , it is to be appreciated that the disclosure herein may be applied to other types of rotor craft as well as helicopters  10  of other configurations. A main rotor assembly  18  is located at the airframe  12  and rotates about a main rotor axis  20 . The main rotor assembly  18  is driven by a drive shaft  22  connected to a power source, for example, an engine  24  (in this embodiment a piston engine) by a gearbox  26 . Located between the engine  24  and the gearbox  26 , and operably connected to both, is a locking hydraulic torque converter (LHTC)  28 . The LHTC  28  allows for torque slip and freewheel between the engine  24  and gearbox  26  such that the gearbox  26  and main rotor assembly  18  rotational speeds can vary from the engine  24  rotational speed under selected operating conditions such as engine startup, shutdown, and autorotation. While shown in the context of a single rotor helicopter  10 , it is understood that aspects can be used in coaxial rotor craft such as the X2® helicopter by Sikorsky Aircraft Corporation. 
       FIG. 2  illustrates a schematic layout of an embodiment of an LHTC  28 . The LHTC  28  is generally located between the engine  24  and the gearbox  26  at an LHTC housing  30 . The LHTC  28  is connected to the engine  24  via input shaft  32  and is connected to the gearbox  26  via an output shaft  34 . The input shaft  32  is connected to an impeller  36 , which is capable of driving a turbine  38  connected to the output shaft  34 . A stator  40  section is located between the impeller  36  and the turbine  38  and directs a motive fluid, such as hydraulic fluid  42 , between the impeller  36  and the turbine  38 . In the embodiment of  FIG. 2 , stator  40  directs hydraulic fluid  42  discharged from turbine  38  back into the intake of impeller  36 . The input shaft  32  and the output shaft  34  are arranged such that they are capable of substantially independent rotation about an LHTC axis  44 . While in the embodiment of  FIG. 2 , the input shaft  32  and output shaft  34  share a common axis of rotation; it is understood that in other embodiments the input shaft  32  and output shaft  34  axes may be offset and/or nonparallel. A lockup mechanism  46 , in some embodiments including friction discs  48 , includes an input lockup  50  connected to the input shaft  32  and an output lockup  52  connected to the output shaft  34 . When the lockup mechanism  46  is energized, and the input lockup  50  is engaged with the output lockup  52 , the input shaft  32  and output shaft  34  are driven at a common speed. 
     The LHTC  28  is operated via a hydraulic control system  54  dedicated to the LHTC  28 . The hydraulic control system  54  includes a fluid reservoir  56  located in the LHTC housing  30 , along with a fluid pump  58  to maintain system pressure and to urge hydraulic fluid  42  to various components of the LHTC  28 . The hydraulic control system may further include a filter/pressure relief valve schematically represented at  57  ( FIG. 2 ). While in the embodiment of  FIG. 2 , the fluid reservoir  56 , filter/valve  57 , and fluid pump  58  are located within the LHTC housing  30 , it is understood that in other embodiments the fluid reservoir  56 , filter/valve  57 , and fluid pump  58  may be located external of the LHTC housing  30  to accommodate another drive system arrangement. The flow of hydraulic fluid  42  is directed and controlled by a switching module  60  receiving operational commands from systems such as a flight control system  76 . The switching module  60  is operably connected to the fluid pump  58  and having hydraulic lines  62  connected to the lockup mechanism  46  and the impeller  36  as required by the system operation. The hydraulic control system  54  further includes a fluid cooler  64  including, in some embodiments, a heat exchanger  66  and a blower  68 . In operation, hydraulic fluid  42  is urged from the fluid reservoir  56  by the fluid pump  58 , and flowed toward the fluid cooler  64 . Depending on fluid temperature, the hydraulic fluid  42  may be flowed through the fluid cooler  64 , or through a bypass valve  70 , thus bypassing the fluid cooler  64 . From the fluid cooler  64  (or the bypass valve  70 ), the hydraulic fluid  42  flows to the switching module  60  and to the impeller  36  and/or lockup mechanism  46 . While not required in all aspects, the hydraulic control system  54  can be integral to the LHTC  28 , such as within a common housing (not shown) as might occur in a field replaceable unit. 
     Illustrated in  FIG. 3  is operation of the LHTC  28  during helicopter  10  operations such as engine  24  startup, ground idle of the helicopter  10 , and/or slow down or stop of main rotor assembly  18  rotation while engine  24  is on. Torque applied at the input shaft  32  is greater than torque at the output shaft  34 , and rotational speed S I  of the input shaft  32  is greater than the rotational speed S O  of the output shaft  34 . The rotational speed S O  may be greater than or equal to zero. During this operation mode, rotor brake  72  is engaged to slow or stop rotation of the output shaft  34 . The impeller  36  pumps the hydraulic fluid  42  into the turbine  38  to transfer torque from input shaft  32  to output shaft  34 . The rotational speed transferred from input shaft  32  to output shaft  34  slips because of the reaction torque applied by the rotor brake  72 . This operation results in a large amount of heat in the hydraulic fluid  42 , such that maximum cooling by the fluid cooler  64  is used. However, in other aspects, cooling can be achieved by other mechanisms consistent with the type of fluid  42  used. To reduce heat generation and torque output generated by the flow of hydraulic fluid  42  through the turbine  38 , a turbine bypass  74  may be positioned along the flow of hydraulic fluid  42  created by the impeller  36  pumping hydraulic fluid  42  into the turbine  38  to reduce the hydraulic pressure applied to turbine  38 . Reducing heat generation and torque output for this operation reduces the required cooling capacity of the fluid cooler  64  and reaction torque required by the rotor brake  72 , respectively. 
     In  FIG. 4 , the rotor brake  72  is disengaged, but torque slip still occurs between the output shaft  34  and the input shaft  32 . This equates with operation to bring the main rotor assembly  18  up to full speed while preventing stall of the engine  24 . Hydraulic fluid  42  is pumped from the impeller  36  into the turbine  38  creating hydraulic pressure that drives rotation of the turbine  38  and the output shaft  34  since the rotor brake  72  is disengaged. The lockup mechanism  46 , however, is not engaged, thus allowing torque slip between the output shaft  34  and the input shaft  32 , such that speed and torque at the input shaft  32  is greater than speed and torque at the output shaft  34 . 
       FIG. 5  illustrates operation of the LHTC  28  during normal flight operation of the helicopter  10 . When the output shaft  34  speed converges on the input shaft speed  32 , hydraulic fluid  42  is urged to the lockup mechanism  46  to drive the input lockup  50  into engagement with the output lockup  52 . While the lockup mechanism  46  to drive the input lockup  50  into engagement with the output lockup  52  is shown to be energized by the hydraulic fluid  42 ; it is understood that in other embodiments the lockup mechanism  46  may be energized by other means such as electric actuation or speed and/or torque activated passive mechanisms. With the lockup mechanism  46  engaged, the rotation of the output shaft  34  is driven by the input shaft  32  and the speed S O  of the output shaft  34  equals the speed S I  of the input shaft  32 . Hydraulic fluid  42  is still pumped through the impeller  36 , but the hydraulic fluid  42  does not drive the turbine  38 . While shown as urging the input lockup  50  against the output lockup  52 , it is understood that the output lockup  52  may be urged against the input lockup  50  or both the input lockup  50  and the output lockup  52  may be mutually urged together. 
     Shown in  FIG. 6  is operation of the LHTC  28  during conditions, such as autorotation or engine  24  shutdown. In this mode, the locking mechanism  46  is disengaged, thus allowing the output shaft  34  to rotate at a higher speed than the input shaft  32  to reduce parasitic drag in the turbine  38  by hydraulic fluid  42  flowing therethrough, the turbine bypass  74  may be used to redirect the hydraulic fluid  42 . In other embodiments, the output shaft  34  may include a mechanical free wheel clutch thus eliminating the necessity for the lockup mechanism  46  to be disengaged during conditions, such as autorotation and engine  24  shutdown. 
     The shown LHTC  28  is an independent component of the helicopter  10 , rather than integrated into the gearbox  26 , and utilizes an independent hydraulic control system  54 , rather than gearbox  26  to drive the LHTC  28 . Further the LHTC  28  provides its own cooling system in the form of fluid cooler  64 . Isolating the LHTC  28  from the gearbox  26  in this manner adds safety in that it allows the LHTC  28  to continue operations even if other components, such has the gearbox  26 , have failures of their lubrication system. Further, this independence allows greater flexibility in incorporating the LHTC  28  as an add-on component to an existing helicopter  10 , by installing the LHTC  28  between the engine  24  and the gearbox  26 . However, it is understood that the LHTC  28  or portions thereof can be integrated into the gearbox  26  in aspects of the invention. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. For instance, aspects can be used with propeller assemblies and/or fans where blade pitch control and compactness of design may be useful. Further, while described in terms of use on a rotor craft, it is understood that aspects can be used with other drive trains in other contexts, such as in generators, ships, and cars. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.