Abstract:
A drive architecture comprises a rotor and a gearbox for driving the rotor. A pair of input gears provides rotational drive to the gearbox. A first recuperative cycle engine drives one of the pair of gears and a second engine drives the other of the pair of gears. The first recuperative cycle engine and the second engine are both gas turbine engines. A power takeoff from a drive shaft of the second engine supplies rotational drive to drive at least one component in the first recuperative cycle drive.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 62/019,478, filed Jul. 1, 2014. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This application relates to a combination of two distinct engine types which can be efficiently utilized to drive a rotor. 
         [0003]    Gas turbine engines are known and are used to drive a variety of aircraft. One known type of gas turbine engine is a so-called recuperated cycle engine. In such an engine, heat is captured and used to heat air downstream of a compressor prior to being delivered into a combustion section. 
         [0004]    Another type of gas turbine engine is a simple cycle engine wherein such preheating does not occur. 
         [0005]    Each type engine has its strengths. 
         [0006]    Gas turbine engines have been utilized to drive rotary wing aircraft, such as a propeller system for a helicopter. Typically, a pair of engines are placed on the helicopter. Under certain conditions, drive from both of the engines is required. However, under many standard operating conditions, only one of the engines is sufficient to provide adequate power. 
         [0007]    Pilots for such a rotary wing aircraft will often drive both engines as a safety measure. 
       SUMMARY OF THE INVENTION 
       [0008]    In a featured embodiment, a drive architecture comprises a rotor and a gearbox for driving the rotor. A pair of input gears provides rotational drive to the gearbox. A first recuperative cycle engine drives one of the pair of gears and a second engine drives the other of the pair of gears. The first recuperative cycle engine and the second engine are both gas turbine engines. A power takeoff from a drive shaft of the second engine supplies rotational drive to drive at least one component in the first recuperative cycle drive. 
         [0009]    In another embodiment according to the previous embodiment, the power takeoff from the second engine serves to provide rotational input to drive a compressor in the first recuperative cycle engine. 
         [0010]    In another embodiment according to any of the previous embodiments, air downstream of the compressor in the first recuperative cycle engine is directed through a heat exchanger downstream of a turbine section in the first recuperative cycle engine. The air is heated and is then returned into a combustor section, which is intermediate the compressor and the turbine section in the first recuperative cycle engine. 
         [0011]    In another embodiment according to any of the previous embodiments, air is tapped from the second engine downstream of a compressor in the second engine and passed into a second heat exchanger where it additionally provides heat to the air from the compressor in the first recuperative cycle engine before the air in the first recuperative cycle engine is returned to the combustion section. 
         [0012]    In another embodiment according to any of the previous embodiments, the air from the second engine is passed from a location downstream of a single compressor rotor and through the second heat exchanger. 
         [0013]    In another embodiment according to any of the previous embodiments, there are at least two compressor rotors in the compressor of the second engine. Air is passed into the second heat exchanger from the second engine at a location intermediate a first and second compressor rotor in the second engine. 
         [0014]    In another embodiment according to any of the previous embodiments, a bypass feature is provided on the tap from the second engine into the second heat exchanger with the bypass being provided with valving to selectively deliver air from the second engine to the second heat exchanger or bypass air back to the second engine. 
         [0015]    In another embodiment according to any of the previous embodiments, the drive shaft for the recuperative cycle engine also rotates a thrust propeller. 
         [0016]    In another embodiment according to any of the previous embodiments, the second engine is a reverse core engine wherein air is delivered along a path past a turbine section in the second engine, past a compressor in the second engine, and then turned into the compressor for the second engine. 
         [0017]    In another embodiment according to any of the previous embodiments, air downstream of the turbine section in the first recuperative cycle engine passes through a thrust nozzle. 
         [0018]    In another embodiment according to any of the previous embodiments, the thrust nozzle is a variable area nozzle. 
         [0019]    In another embodiment according to any of the previous embodiments, the power takeoff drives a generator to generate electricity. 
         [0020]    In another embodiment according to any of the previous embodiments, the generator provides power to a power electronic system which, in turn, drives the mechanical connection. 
         [0021]    In another embodiment according to any of the previous embodiments, a mechanical connection and a generator communicate with the power connection and with a shaft for the compressor in the second engine. 
         [0022]    In another embodiment according to any of the previous embodiments, the mechanical connection provides power to the shaft for the compressor and the second engine. 
         [0023]    In another embodiment according to any of the previous embodiments, the mechanical connection receives the rotary drive from the shaft of the compressor of the second engine. 
         [0024]    In another embodiment according to any of the previous embodiments, the power takeoff drives a generator to generate electricity. 
         [0025]    In another embodiment according to any of the previous embodiments, the generator provides power to a power electronic system which, in turn, drives the mechanical connection. 
         [0026]    In another embodiment according to any of the previous embodiments, a mechanical connection and a generator communicate with the power connection and with a shaft for the compressor in the second engine. 
         [0027]    In another embodiment according to any of the previous embodiments, the mechanical connection provides power to the shaft for the compressor and the second engine. 
         [0028]    In another embodiment according to any of the previous embodiments, the mechanical connection receives the rotary drive from the shaft of the compressor of the second engine. 
         [0029]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  shows a first schematic drive system for a rotary wing aircraft. 
           [0031]      FIG. 2A  shows a second embodiment. 
           [0032]      FIG. 2B  shows an alternative. 
           [0033]      FIG. 3  shows a third embodiment. 
           [0034]      FIG. 4  shows a feature that may be incorporated into the above-referenced embodiments. 
           [0035]      FIG. 5  shows another feature that may be incorporated into the embodiments. 
           [0036]      FIG. 6  shows an alternative embodiment. 
           [0037]      FIG. 7A  shows yet another alternative. 
           [0038]      FIG. 7B  shows yet another alternative. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    A rotary wing aircraft drive  20 , such as a propeller system for a helicopter, is illustrated in  FIG. 1 . A main rotor gearbox  22  drives the propeller system  20 . A pair of input drive gears  26  and  30  are shown schematically driving the gearbox  22 . Gear  26  is driven by a shaft  24  on an engine  18 . Gear  30  is driven by a shaft  28  which is part of an engine  19 . 
         [0040]    Engine  19  is a “reverse core” engine. Thus, an inlet duct  52  delivers air to a turning end  56 , where it is then delivered into a compressor  54 . The air is compressed in compressor  54 , delivered into a combustion section  58 , mixed with fuel and ignited. Products of this combustion pass downstream over a turbine rotor  60 , which drives the compressor rotor  54 . Downstream of the turbine rotor  60 , the products of combustion drive another turbine rotor  34  which drives the shaft  28 . Downstream of the turbine rotor  34 , the products of combustion are reversed through an exit duct  35 . 
         [0041]    The engine  18  has an inlet duct  17  delivering air into a compressor  32 . Compressor  32  delivers air into a combustion section  42 , where it is mixed with fuel and ignited. Products of this combustion drive a turbine rotor  44 , which, in turn, drives a shaft  46  to drive the compressor rotor  32 . 
         [0042]    Downstream of the turbine rotor  44 , the products of combustion drive another turbine rotor  35  to, in turn, drive the shaft  24  and a downstream shaft portion  36 , which drives a thrust propeller  38 . 
         [0043]    Engine  18  is a recuperative engine, while engine  19  is a simple cycle engine. A simple cycle engine has one instance of heat input without work being added or subtracted. The heat input typically is a combustor. A recuperative, or regenerative cycle recycles a fraction of the heat input by the combustor by transferring heat from the gas flow of products of combustion exiting the turbine to the air flow that exits the compressor and enters the combustor. The heat transfer device typically is a heat exchanger. 
         [0044]    In a regenerative cycle, the temperature of the air flow exiting the compressor is lower than the temperature of the gas flow exiting the turbine; hence, heat can be transferred from the gas flow to the air flow. This reduces the heat input required of the combustor. 
         [0045]    In a simple cycle, the temperature of the air flow exiting the compressor is higher than the temperature of the gas flow exiting the turbine; hence, heat cannot be transferred from the gas flow to the air flow of the simple cycle engine. However, heat can be transferred from the air flow of the simple cycle engine to the air flow of the regenerative cycle engine. Transferring heat from the air flow of the simple cycle engine intercools the air flow of the compressor of the simple cycle engine, lowering the compressor exit temperature of the airflow of the simple cycle. Controlling compressor exit temperature is advantageous when the ambient air inlet temperature of the compressor is high. The combination synergistically controls the inlet temperature of the combustor for each engine. 
         [0046]    As can be appreciated from the schematic of  FIG. 1 , air downstream of the compressor rotor  32  passes through a heat exchanger  40 , where it is heated by the products of combustion downstream of the turbine rotor  35 . The air may also pass to a heat exchanger  50  where it is heated by air from tap  62 , which has been heated in the compressor  54 . 
         [0047]    Thus, when the air returns from the heat exchanger  50  to the inlet to the combustor  42 , it has been preheated and, thus, the combustion is performed more efficiently. 
         [0048]    In addition, a gear  76  rotates with the compressor  32  and receives drive from a bevel gear  74 . Bevel gear  74  is driven by a gear  70 , driven by the shaft  28 . 
         [0049]    When the associated aircraft driven by the propeller system  20  is being driven in a condition where it does not need both engines, the engine  19  supplements power to engine  18  through the gear  74 . The gear and shaft combination  72 / 74  drive the gear  76  and supply power to the compressor  32 . This saves power that the turbine  44  would otherwise have to deliver to the compressor  32  and results in higher temperatures preheating the air in the heat exchanger  40 . As such, this cycle operates more efficiently. 
         [0050]      FIGS. 2A  and B show an engine system, wherein features generally identical to those of  FIG. 1  are simply identified by a number moved  100  higher. 
         [0051]    A difference is that the engine  119  now has two compressor rotors  180  and  182  and an intercooler  184  is passed through the heat exchanger  150 , rather than the air downstream of the entire compressor section being delivered into the combustion section. Otherwise, this combination operates in a manner similar to that of  FIG. 1 . 
         [0052]    In contrast, in  FIG. 2B , a portion  15  of the refrigerant downstream of the compressor stage  182  is tapped as the intercooler  184 , and is returned at  13  downstream of the compressor stage  180 . A portion of the air compressed at stage  182  does pass the stage  180 , and is then mixed with the returning fluid  13 . 
         [0053]      FIG. 3  shows an engine wherein features identical to FIGS.  2 A/B are identified by the number  200  added to the reference arrows in FIGS.  2 A/B. 
         [0054]    Here, the thrust propeller has been replaced by a thrusting nozzle  184 , which may be a variable nozzle, as is otherwise known. 
         [0055]      FIG. 4  shows the heat exchanger  350  and a feature which may be placed on the line  384  leading from the compressor section through the heat exchanger  350 . As shown, a shutoff valve  385  may be controlled in combination with the valve  386  to divert air through a line  387 , when it is not desired to achieve the intercooling. 
         [0056]    An appropriate control  387  controls the valves  385  and  386  and a worker of ordinary skill in the art would understand when to provide such control. 
         [0057]      FIG. 5  shows an embodiment wherein the connection between the engine is utilized to generate electrical power. As is shown, the gear  374  drives a shaft  372  which, in turn, drives a generator  375 . Generator  375  powers a power electronics  377  which can provide electrical power to a use  376 . The power electronics  377  drives a combined motor and mechanical connection  379  that passes rotational power to a shaft  380 , such that it can supply drive to the recuperative engine, as in the prior embodiments. 
         [0058]      FIG. 6  shows an embodiment, wherein the input gears  600  drives a shaft  602  to, in turn, drive a generator  679 . Generator  679  supplies power to the power electronics  677 . Motor and mechanical connection  680  receives power from the power electronics  677  to drive shaft  602 . The combination of  680 / 679  also is known in the art as a motor/generator. 
         [0059]    Downstream of the power electronics, another generator  681  generates electricity and supplies it back to the power electronics  677  and also drives a combined motor and mechanical connection  682 , which drives the shaft portion  683  to supply mechanical energy to the recuperative engine  618 . Another generator  681  generates electricity and supplies it back to the power electronics  677  and also drives the motor  682 , which drives the shaft portion  683  to supply mechanical energy to the recuperative engine  618 . Here again, a use  676  for generated electrical power is disclosed schematically. Mechanical power from engine  618  is converted to electrical power that is converted back to mechanical power to drive gear  600  that drivers gear  670  and shaft  628  of engine  619 . The combination of  682 / 681  also is known in the art as a motor/generator. 
         [0060]      FIG. 7A  shows an embodiment which may be incorporated into the embodiments of  FIG. 5  or  6 . A generator  706  receives power from the line  700  which may be the power electronics in the  FIG. 5  or  6  embodiment. It drives the mechanical connection  708  to supply power to a shaft  702 , which drives a compressor  704 . 
         [0061]      FIG. 7B  shows another embodiment wherein the compressors  808  and  810  rotate with a shaft  806  to, in turn, drive a mechanical connection  804  to generate electricity at generator  802  and supply that generator electricity though a line  800  back to the power electronics as in the  FIG. 5  or  6  embodiments. 
         [0062]    While a propeller system for a rotary wing aircraft is specifically disclosed, other gearbox applications for driving a rotor may benefit from these teachings. As an example, certain aircraft are provided with a lift fan, and a rotor for such a fan may well benefit from the drive architecture of this disclosure. 
         [0063]    Although a number of embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.