Abstract:
A system and method of adaptively synchronizing the performance margin of a multi-engine system includes continuously, and in real-time, determining the performance margin of a first engine and the performance margin of the second engine. A difference between the performance margins of the first and second engines is calculated, and the first and second engines are controlled to attain a predetermined difference between the performance margins of the first and second engines.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the benefit of U.S. Provisional Application No. 61/804,836, filed Mar. 25, 2013. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention generally relates to performance analysis, and more particularly relates to a system and method for adaptively controlling performance margin synchronization in a multi-engine system. 
       BACKGROUND 
       [0003]    Helicopters typically have two engines that are connected through a combiner transmission to share the load of the rotor. It is desirable to share the load equally between the two engines so that the engines are more likely to deteriorate at the same (or similar) pace, and impart less stress to the combiner transmission. Helicopter engine controllers are typically configured to selectively implement one of a plurality load sharing control methods, and control logic that selects the control method. These control methods may include, for example, torque matching, a temperature matching, and a speed matching. With the torque matching method, measured engine torque is equalized, with the temperature matching method, measured engine temperatures are equalized, and with the speed matching method, measured engine speeds are equalized. 
         [0004]    Unfortunately, none of the above-described control methods can continuously produce identical or synchronized performance margins for the two engines. Performance margin is an engine condition indicator and, as is generally known, is defined as the difference between one or more performance parameters at rated power and the corresponding limits of the performance parameters. As may be readily understood, because performance margin is measured at max rated power, two engines can have very different performance margins even if the engines have similar performance characteristics at lower power. Moreover, each engine will typically exhibit its own unique performance deterioration characteristics. 
         [0005]    When the performance margin of an engine reaches zero, the engine is removed from the aircraft for repair, overhaul or replacement. Significant performance margin differences occur when a new or overhauled engine is installed with an engine that has already lost some performance margin. Thus, it is desirable to match the performance margins of both engines so that the engines can be simultaneously removed. However, the commonly used load sharing methods mentioned above do not ensure that the performance margins are matched. In particular, torque matching tends to cause the engine with a lower temperature margin to run hotter and increase the temperature margin split between the two engines. Temperature matching at part power does not guarantee that the temperature margins match at max rated power since the engines may have differently shaped temperature vs. torque characteristic curves. And speed matching at part power does not guarantee that the speed margins match at max rated power since the engines may have differently shaped speed vs. torque characteristic curves. 
         [0006]    When the performance margins of two engines are not matched, this can lead to reduced engine life, reduced aircraft availability, and increased maintenance costs. Moreover, helicopter engine controls are typically configured such that a pilot may manually select the control method to be used in order to attain maximum power from both engines. This can lead to increased pilot workload. For example, if one engine reaches the temperature margin limit before the other engine while operating in the torque matching mode, the pilot will need to switch to the temperature matching mode to allow the other engine to attain its maximum power. 
         [0007]    Hence, there is a need for a system and method of matching the performance margins of two engines. In doing so, the system and method will provide increased engine life, increased aircraft availability, reduced maintenance costs, and reduced pilot workload. The present invention addresses this need. 
       BRIEF SUMMARY 
       [0008]    In one embodiment, a method of adaptively synchronizing the performance margin of a multi-engine system includes continuously, and in real-time, determining the performance margin of a first engine and the performance margin of the second engine. A difference between the performance margins of the first and second engines is calculated, and the first and second engines are controlled to attain a predetermined difference between the performance margins of the first and second engines. 
         [0009]    In another embodiment, a system for adaptively synchronizing the performance margin of a multi-engine system includes a first engine, a second engine, a first engine controller, and a second engine controller. The first engine is configured to generate a first torque and has a determinable first engine performance margin. The second engine is configured to generate a second torque and has a determinable second engine performance margin. The first engine controller is coupled to, and is associated with, the first engine, and is configured to continuously, and in real-time, determine the first engine performance margin. The second engine controller is coupled to, and is associated with, the second engine, and is configured to continuously, and in real-time, determine the second engine performance margin. The first and second engine controllers are in operable communication with each other, and each is further configured to calculate a difference between the first engine performance margin and the second engine performance margin, and to control its associated engine to attain a predetermined difference between the first and second engine performance margins. 
         [0010]    Furthermore, other desirable features and characteristics of the system and method will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the preceding background. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
           [0012]      FIG. 1  depicts a functional block diagram of a portion of a multi-engine power train system for a rotary-wing aircraft; 
           [0013]      FIG. 2  depicts a functional block diagram of a feedback controller that may be implemented in the system of  FIG. 1 ; 
           [0014]      FIG. 3  graphically depicts the multi-engine power train system of  FIG. 1  operating with imbalanced performance margins; and 
           [0015]      FIG. 4  graphically depicts the multi-engine power train system of  FIG. 1  operating with balanced performance margins. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. 
         [0017]    Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description. In this regard, although embodiments are described herein as being implemented in a rotary-wing aircraft, such as a helicopter, it will be appreciated that the systems and methods described herein may be implemented in various other environments and applications that utilize a multi-engine output. Moreover, although embodiments are described herein as being implemented with two gas turbine engines, other numbers of engines greater than two could be used, and various other engine types, including diesel and combustion engines, may also be used. 
         [0018]    Referring first to  FIG. 1 , a functional block diagram of a portion of a multi-engine power train system  100  for a rotary-wing aircraft, such as a helicopter, is depicted. The power train includes two engines  102  (a first engine  102 - 1  and a second engine  102 - 2 ), a gear train  104 , and two engine controllers  106  (a first engine controller  106 - 1  and a second engine controller  106 - 2 ). It should be noted that although the system  100  of  FIG. 1  is depicted as including only two engines  102 , it could be implemented with more than this number of engines  102 , if needed or desired. 
         [0019]    The engines  102 , at least in the depicted embodiment, are implemented using gas turbine engines, and more particularly single-spool turbo-shaft gas turbine propulsion engines. Thus, each engine  102  includes a compressor section  108 , a combustion section  112 , and a turbine section  114 . The compressor section  108 , which may include one or more compressors  116 , draw air into its respective engine  100  and compresses the air to raise its pressure. In the depicted embodiment, each engine includes only a single compressor  116 . It will nonetheless be appreciated that each engine  102  may include one or more additional compressors. 
         [0020]    No matter the particular number of compressors  116  that are included in the compressor sections  108 , the compressed air is directed into the combustion section  112 . In the combustion section  112 , which includes a combustor assembly  118 , the compressed air is mixed with fuel supplied from a non-illustrated fuel source. The fuel and air mixture is combusted, and the high energy combusted air mixture is then directed into the turbine section  114 . 
         [0021]    The turbine section  114  includes one or more turbines. In the depicted embodiment, the turbine section  114  includes two turbines, a high pressure turbine  122  and a free power turbine  124 . However, it will be appreciated that the engines  102  could be configured with more or less than this number of turbines. No matter the particular number, the combusted air mixture from the combustion section  112  expands through each turbine  122 ,  124 , causing it to rotate an associated power shaft  126 . The combusted air mixture is then exhausted from the engines  102 . The power shafts  126  are each coupled to, and supply a drive torque to, the gear train  104 . 
         [0022]    The gear train  104  is coupled to receive the drive torque supplied from each of the engines  102 . The gear train  104 , which may include one or more gear sets, preferably includes at least a combiner transmission, which in turn supplies the combined drive torque to one or more rotors. 
         [0023]    The engine controllers  106  are each in operable communication with one of the engines  102 . In the depicted embodiment, for example, the first engine controller  106 - 1  is in operable communication with the first engine  102 - 1 , and the second engine controller  106 - 2  is in operable communication with the second engine  106 - 2 . Each engine controller  106  is configured, among other things, to control the operation of its associated engine  102  so as to minimize the performance margin difference between the engines  102 . To implement this functionality, the engine controllers  106  are each coupled to receive various control and performance data from its associated engine  102 . Thus, as  FIG. 1  further depicts, each engine  102  additionally includes a plurality of sensors  128 . Each of the sensors  128  is coupled to its associated engine controller  106  and is operable to sense an engine parameter and supply control and performance data representative of the sensed parameter to the engine controller  106 . It will be appreciated that the particular number, type, and location of each sensor  128  may vary. It will additionally be appreciated that the number and types of control and performance data supplied by the sensors  128  may vary depending, for example, on the particular engine type and/or configuration. In the depicted embodiment, however, at least a subset of the depicted sensors  128  supply control and performance data representative of, or that may be used to determine, engine inlet pressure, engine inlet temperature, engine speed, fuel flow, compressor discharge pressure, power turbine inlet temperature, engine torque, shaft horsepower, and thrust, to name just a few. 
         [0024]    The engine controllers  106  may be variously configured to implement the associated functionality. In the depicted embodiment, each engine controller  106  includes one or more processors  132  (for clarity, only one shown). The processors  132  are coupled to receive at least a portion of the control and performance data from the sensors  128  and are each configured, in response to these data, to continuously conduct performance analyses of its associated engine  102 . Moreover, each engine controller  106  also receives various sensor data, such as torque, turbine inlet temperature, and engine speed, from the other engine controller  106  via a data link  134  that interconnects the two engine controllers  106 . The processors  132  are additionally configured, based on the performance analyses, to control the operation of its associated engine  102  to minimize the difference between the performance margins of each engine  102 . To do so, the processors  132  are each configured to conduct continuous, real-time performance analyses of its associated engine  102  to thereby continuously determine, in real-time, the performance margin of its associated engine  102 . The processors  132  are additionally configured to implement identical feedback controllers that will shift the load between the engines  102  so that there is more load on the engine  102  with higher performance margin. One embodiment of the feedback controllers  200  are implemented in each of the processors  132  is depicted in  FIG. 2 , and will now be described in more detail. 
         [0025]    Before proceeding with the description, it is noted that the feedback controller  200  depicted in  FIG. 2  is the one implemented in the first engine controller  106 - 1 , and is thus associated with the first engine  102 - 1  (e.g., “Engine 1”). It will be appreciated that the feedback controller  200  implemented in the second engine controller  106 - 2 , and thus associated with the second engine (e.g., “Engine 2”) is an identical, “mirror-image,” copy of the one implemented in the first engine controller  106 - 1 . It is additionally noted that although the depicted feedback controller  200  is configured to implement a torque matching function, various other load matching functions may be implemented. For example, the feedback controller  200  may be configured to implement a load matching function based on temperature or speed, just to name a few. 
         [0026]    Turning now to the description of the feedback controller  200 , it is seen that the feedback controller  200  receives the control and performance data supplied by the sensors  128 . The control and performance data are supplied, at least in the depicted embodiment, to signal conditioning and BIT (built-in-test) logic, which provides appropriate signal conditioning and testing of the data supplied from the sensors  128 . At least a portion of the control and performance data are supplied to and processed by a continuous performance analysis (CPA) function  202 - 1 . The CPA function  202 - 1  is configured to conduct continuous, real-time performance analyses of the first engine  102 - 1 , and supply data representative of the instantaneous performance margin of the first engine  102 - 1 . As  FIG. 2  also depicts, the feedback controller  200  also receives, from a CPA function  202 - 2  in the feedback controller  200  of the second engine controller  106 - 2 , data representative of the instantaneous performance margin of the second engine  102 - 2 . 
         [0027]    Before proceeding further, it is additionally noted that the continuous, real-time performance analyses conducted by the CPA functions  202  may be implemented using any suitable algorithm capable of supplying instantaneous performance margins. Preferably, however, the continuous, real-time performance analyses are preferably conducted using the methodology described in U.S. Pat. No. 8,068,997, entitled “Continuous Performance Analysis System and Method,” and assigned to the assignee of the instant application. The entirety of this patent, which issued on Nov. 29, 2011, is hereby incorporated by reference. 
         [0028]    Returning now to the description of the feedback controller  200 , the instantaneous performance margins of each engine (MRG1, MRG2) are supplied to a first difference function  204 . The first difference function  204  determines a performance margin difference (MRG_DIFF) between the two engines  102 , and supplies the determined performance margin difference (MRG_DIFF) to a margin matching control function  206 . The margin matching control function  206  is configured, in response to the performance margin difference (MRG_DIFF), to generate and supply a torque bias signal (Q_BIAS). Though not depicted in  FIG. 2 , it should be noted that the instantaneous performance margins supplied from the CPA functions  202 - 1 ,  202 - 2  may be filtered to remove noise. If not adequately filtered, noise in the instantaneous performance margins can cause undesirable swings in the torque bias signal (Q_BIAS). It will be appreciated that the margin matching control function  206  may be implemented using any one of numerous types of controllers. In a particular preferred embodiment, the margin matching control function  206  is implemented as a proportion-plus-integral (PID) controller. This is because the proportional action provides relatively fast and measured correction, the integral action eliminates any steady state error of synchronization, and the derivative action provides anticipatory correction to avoid overshoot and hunting issues. 
         [0029]    No matter how the margin matching control function  206  is implemented, the torque bias signal (Q_BIAS), at least in the depicted embodiment, is supplied to a limiter  208 . The limiter  208 , as is generally known, is configured to limit the torque bias signal supplied from the margin matching control function  206 . In particular, it is configured to limit the torque bias signal to less than the maximum allowable torque split between the first and second engines  102 - 1 ,  102 - 2 . The limit values may vary, but are preferably chosen to limit stress to the gear train  104 . The limited torque bias signal (Q_BIAS_LMT) is supplied to a second difference function  212 . 
         [0030]    The second difference function  212  is coupled to receive, in addition to the limited torque bias signal (Q_BIAS_LMT), a torque matching error signal (Q_ERR). The torque matching error signal (Q_ERR) is supplied from a third difference function  214 , which receives, and determines the difference between, a first engine torque signal  216  and a second engine torque signal  218 . The determined difference is supplied as the torque matching error signal (Q_ERR). As may be appreciated, the first engine torque signal  216  is a signal representative of the instantaneous torque (Q1) being supplied by the first engine  102 - 1 , and the second engine torque signal  218  is a signal, supplied from the second engine controller  106 - 2 , representative of the instantaneous torque (Q2) being supplied by the second engine  102 - 2 . 
         [0031]    The output of the second difference function  212  is supplied to a torque matching function  222 . The torque matching function  222  is preferably configured to implement a conventionally known torque matching algorithm. It will be appreciated, however, that any one of numerous torque matching algorithms developed in the future could also be used. The torque matching function  222  supplies a speed control signal to the speed governor  224  in the first engine  102 - 1 , which in turn supplies a fuel control signal to a fuel control function  226 . The fuel control function  226 , which is implemented in the first engine controller  106 - 1 , supplies appropriate commands to appropriate control devices to meter an appropriate amount of fuel to the first engine  102 - 1 . 
         [0032]    From the above description it may be readily understood that when there is a non-zero performance margin difference between the first and second engines  102 - 1 ,  102 - 2 , the feedback controllers  200  use the determined performance margin difference (MRG_DIFF) to purposely create, within acceptable torque split limits, a load imbalance. The feedback controllers  200  are also configured to indirectly control load shifting via the torque matching function  222 . In particular, the feedback controllers  200  supply the limited torque bias signal (Q_BIAS_LMT) to the torque matching error signal (Q_ERR) such that both engines will settle into a desirable unbalanced load condition as long as performance margin difference exists between the two engines  102 . 
         [0033]    For completeness, a brief description of the operation of the system  100  implementing the feedback controllers  200  will be provided. Initially, it is assumed that the instantaneous performance margins (MRG1, MRG2) of the first and second engines  102 - 1 ,  102 - 2  are equal (or at least substantially equal). Such a situation may occur, for example, when both engines  102  are new. As a result, the performance margin difference (MRG_DIFF) will be zero and the limited torque bias signal (Q_BIAS_LMT) supplied to the second difference function  212  will also be zero. This will result in the first and second engines  102 - 1 ,  102 - 2  being controlled in accordance with a conventional torque matching control loop. If any divergence in the performance margins (MRG1, MRG2) of the first and second engines  102 - 1 ,  102 - 2  occurs, the feedback controllers  200  will implement immediate corrective action to drive the performance margin difference (MRG_DIFF) to zero in closed-loop fashion. 
         [0034]    For example, as graphically depicted in  FIG. 3 , the performance margin (MRG2) of the second engine  102 - 2  has decreased faster and becomes smaller relative to the performance margin (MRG1) of the first engine  102 - 1 . As a result, the performance margin difference (MRG_DIFF) will be non-zero and the limited torque bias signal (Q_BIAS_LMT) supplied to the second difference function  212  will also be non-zero. More specifically, the margin matching control function  206  associated with the first engine  102 - 1 , which has the higher performance margin, will supply a positive value for the torque bias signal (Q_BIAS) and the limited torque bias signal (Q_BIAS_LMT), such that it will reduce the torque error value (Q_ERR) before it is used in the torque matching function  222 . This operation has an equivalent effect of lowering the torque signal value of the first engine and thus causes the torque matching function  222  to increase the power and load share of the first engine  102 - 1 . The opposite will occur in the feedback controller  200  associated with the second engine  102 - 2 , which has the lower performance margin. Thus, a desirable torque split condition is purposely created as a result of the power imbalance of the first and second engines  102 . Because the first engine  102 - 1  (the higher performance margin engine) now has a greater power usage than the second engine  102 - 2  (the lower performance margin engine), the first engine  102 - 1  will degrade faster than the second engine  102 - 2 . As  FIG. 4  depicts, over time this will result in the performance margin differences of the two engines  102  converging to zero (e.g., MRG1=MRG2). Once the performance margins are matched, the feedback controllers  200  will continue to keep them matched until both engines  102  are fully degraded 
         [0035]    It should be noted that in some contexts, such as certain helicopter engine control systems, even though the engine with lower performance margin will bias its associated torque signal to a higher value, it will not decrease the engine power directly. This is because the torque matching control loops in some helicopter do not allow lowering the power of the high torque signal engine. Thus, the increased power to the engine with the higher performance margin will result in the speeds of both engines increasing, and further result in a power reduction from the speed governor of the lower performance margin engine. 
         [0036]    It is generally known that various parameters can be used as a measure of performance margin. For example, in the context of gas turbine engines, turbine inlet temperature and turbine speed can be used. Although multiple performance margin types could be used in the feedback controllers  200 , it is preferable to choose one margin type for synchronization, rather than switching among a plurality of different margin types. Different types of performance margins (e.g., temperature margin, speed margin, etc.) typically move in the same direction. Thus, if one performance margin type is in synch, then the other types are likely to be in synch (or at least closely in sync). Moreover, it is preferable to choose the performance margin type that reaches its performance limit more frequently and/or cause more engine removals. In the context of a helicopter, the turbine inlet temperature margin is typically chosen because it meets these criteria. 
         [0037]    The system and method described herein provides numerous significant benefits for various multi-engine systems, such as multi-engine helicopters. In particular, the system and method provides reduced maintenance cost, reduced pilot workload, increased engine life, and increased aircraft availability. Maintenance costs can be reduced since the removal of engines with small performance margins, which are often removed along with fully degraded engines, can be avoided, and because only a single maintenance test flight is needed after engine replacements. Pilot workload is reduced since the pilot does not need to manually switch from one load sharing method to another in order to get maximum power from both engines when one engine reaches a performance limit before the other. Engine life is increased since two engines with matched performance margins will experience lower maximum temperature and speed during transients than unmatched engines over their life span. As a result, the rate of damage to hot section life-limited components, which accelerates at higher engine speed and temperature, will be reduced. Moreover, the rate of performance degradation, which also accelerates at higher engine speed and temperature, is reduced due to slower surface oxidation or blade tip deformation. Aircraft availability is increased since aircraft downtime for fully degraded engine removal and replacement is reduced by 50 percent, since two maintenance events are reduced to just one. 
         [0038]    Those of skill in the art will appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. Some of the embodiments and implementations are described above in terms of functional and/or logical block components (or modules) and various processing steps. However, it should be appreciated that such block components (or modules) may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention. For example, an embodiment of a system or a component may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, look-up tables, or the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. In addition, those skilled in the art will appreciate that embodiments described herein are merely exemplary implementations. 
         [0039]    The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
         [0040]    The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal 
         [0041]    In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Numerical ordinals such as “first,” “second,” “third,” etc. simply denote different singles of a plurality and do not imply any order or sequence unless specifically defined by the claim language. The sequence of the text in any of the claims does not imply that process steps must be performed in a temporal or logical order according to such sequence unless it is specifically defined by the language of the claim. The process steps may be interchanged in any order without departing from the scope of the invention as long as such an interchange does not contradict the claim language and is not logically nonsensical. 
         [0042]    Furthermore, depending on the context, words such as “connect” or “coupled to” used in describing a relationship between different elements do not imply that a direct physical connection must be made between these elements. For example, two elements may be connected to each other physically, electronically, logically, or in any other manner, through one or more additional elements. 
         [0043]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.