阅读说明：本技术 用于操作联接至飞行器螺旋桨的燃气涡轮发动机的方法和系统 (Method and system for operating a gas turbine engine coupled to an aircraft propeller ) 是由 J.查哈尔 C.利希奥 D.麦格拉思 G.辛嘉罗 于 2020-01-17 设计创作，主要内容包括：本文描述了用于操作联接到飞行器螺旋桨的燃气涡轮发动机的方法和系统。从飞行器的动力杆接收螺旋桨推力反向的请求。确定螺旋桨的叶片角度。当叶片角度超过阈值时,阻止螺旋桨的反向推力。当叶片角度低于阈值时,基于请求允许螺旋桨的反向推力。(Methods and systems for operating a gas turbine engine coupled to an aircraft propeller are described herein. A request for propeller thrust reversal is received from a power rod of the aircraft. The blade angle of the propeller is determined. When the blade angle exceeds a threshold value, reverse thrust of the propeller is prevented. When the blade angle is below a threshold, reverse thrust of the propeller is allowed upon request.)

1. A method for operating a gas turbine engine coupled to an aircraft propeller, the method comprising:

receiving a request for reverse thrust of a propeller from a power rod of an aircraft;

obtaining the blade angle of the propeller;

blocking reverse thrust of the propeller when the blade angle exceeds a threshold; and

when the blade angle is below a threshold, reverse thrust of the propeller is allowed upon request.

2. The method of claim 1, further comprising: obtaining an aircraft state indicative of whether the aircraft is on the ground or in flight; allowing the reverse thrust when the aircraft state indicates that the aircraft is on the ground; and blocking the reverse thrust when the aircraft state indicates that the aircraft is in flight.

3. The method of claim 1, wherein inhibiting the reverse thrust includes setting an output power of the engine to a minimum level of the engine.

4. The method of claim 1, wherein the threshold value corresponds to a minimum blade angle at which the propeller can provide reverse thrust.

5. The method of claim 1, wherein receiving a request for reverse thrust comprises receiving a position of the power rod from at least one sensor.

6. The method of claim 5, wherein the position of the power lever is below ground idle.

7. The method of claim 5, wherein allowing the reverse thrust comprises: determining a power demand of the engine based on the position of the power lever, and controlling an output power of the engine based on the power demand.

8. The method of claim 7, wherein controlling the output power of the engine comprises: a fuel flow to the engine is determined based on the power demand, and a fuel flow request is output to a torque motor for controlling the fuel flow to the engine.

9. The method of claim 1, wherein obtaining a blade angle of the propeller comprises: the blade angle is obtained from the propeller control.

10. The method of claim 1, wherein the aircraft propeller is a first aircraft propeller and the blade angle is a first blade angle, the method further comprising: obtaining a second blade angle of the second aircraft propeller, and wherein allowing reverse thrust comprises: allowing reverse thrust when the first and second blade angles are below a threshold, and preventing reverse thrust comprises: blocking reverse thrust when at least one of the first and second blade angles exceeds a threshold.

11. A system for operating a gas turbine engine coupled to an aircraft propeller, the system comprising:

a processing unit; and

a non-transitory computer readable memory having stored thereon program instructions executable by a processing unit for:

receiving a request for reverse thrust of a propeller from a power rod of an aircraft;

obtaining the blade angle of the propeller;

blocking reverse thrust of the propeller when the blade angle exceeds a threshold; and

when the blade angle is below a threshold, reverse thrust of the propeller is allowed upon request.

12. The system of claim 11, wherein the program instructions are further executable by the processing unit to: obtaining an aircraft state indicative of whether the aircraft is on the ground or in flight; allowing the reverse thrust when the aircraft state indicates that the aircraft is on the ground; and blocking the reverse thrust when the aircraft state indicates that the aircraft is in flight.

13. The system of claim 11, wherein blocking the reverse thrust includes setting an output power of the engine to a minimum level of the engine.

14. The system of claim 11, wherein the threshold value corresponds to a minimum blade angle at which the propeller can provide reverse thrust.

15. The system of claim 11, wherein receiving a request for reverse thrust comprises receiving a position of the power rod from at least one sensor.

16. The system of claim 15, wherein the position of the power lever is below ground idle.

17. The system of claim 15, wherein allowing the reverse thrust comprises: determining a power demand of the engine based on the position of the power lever, and controlling an output power of the engine based on the power demand.

18. The system of claim 17, wherein controlling the output power of the engine comprises: a fuel flow to the engine is determined based on the power demand, and a fuel flow request is output to a torque motor for controlling the fuel flow to the engine.

19. The system of claim 11, wherein obtaining a blade angle of the propeller comprises: the blade angle is obtained from the propeller control.

20. The system of claim 11, wherein the aircraft propeller is a first aircraft propeller and the blade angle is a first blade angle, the program instructions being further executable by the processing unit to: obtaining a second blade angle of the second aircraft propeller, and wherein allowing reverse thrust comprises: allowing reverse thrust when the first and second blade angles are below a threshold, and preventing reverse thrust comprises: blocking reverse thrust when at least one of the first and second blade angles exceeds a threshold.

Technical Field

The present disclosure relates generally to gas turbine engines and, more particularly, to controlling engine operation.

Background

For propeller driven aircraft, the control system may adjust the blade angle of the propeller blades to cause a transition from forward thrust to reverse thrust during landing. The transition from forward thrust to reverse thrust requires the propeller blades to transition through an operating region known as "disking" or blade angle of minimum rotational resistance, where the engine is typically operated at low power. The pilot uses the feedback of the angular position of the propeller blades to determine when to apply increased engine power upon landing. However, if increased engine power is applied prematurely when transitioning from forward thrust to reverse thrust during landing, positive thrust may be generated rather than reverse thrust.

Therefore, improvements are needed.

Disclosure of Invention

In one aspect, a method for operating a gas turbine engine coupled to an aircraft propeller is provided. The method comprises the following steps: receiving a request for reverse thrust of a propeller from a power rod of an aircraft; obtaining the blade angle of the propeller; blocking reverse thrust of the propeller when the blade angle exceeds a threshold; and allowing reverse thrust of the propeller based on the request when the blade angle is below a threshold.

In another aspect, a system for operating a gas turbine engine coupled to an aircraft propeller is provided. The system includes a processing unit and a non-transitory computer readable memory having program instructions stored thereon. The program instructions are executable by the processing unit to: receiving a request for reverse thrust of a propeller from a power rod of an aircraft; obtaining the blade angle of the propeller; blocking reverse thrust of the propeller when the blade angle exceeds a threshold; and allowing reverse thrust of the propeller based on the request when the blade angle is below a threshold.

Drawings

Reference is now made to the accompanying drawings, in which:

FIG. 1 is a schematic illustration of an exemplary gas turbine engine and propeller in accordance with an illustrative embodiment;

FIG. 2A is a schematic diagram showing a system for controlling the operation of the engine and propeller of FIG. 1, according to an illustrative embodiment;

FIG. 2B is a schematic diagram showing the system of FIG. 2A with a propeller controller and an engine controller in accordance with an illustrative embodiment;

FIG. 2C is a schematic diagram showing the system of FIG. 2C with dual channels in accordance with an illustrative embodiment;

FIG. 3A is a flowchart of a method for controlling operation of an engine in accordance with an illustrative embodiment;

FIG. 3B is a flowchart showing another embodiment of a method for controlling operation of an engine in accordance with an illustrative embodiment;

FIG. 4 is a block diagram of an exemplary computing device for controlling operation of an engine and/or propeller according to an illustrative embodiment.

It will be noted that throughout the drawings, like features are indicated by like reference numerals.

Detailed Description

FIG. 1 illustrates an aircraft power plant 100 for an aircraft of the type preferably provided for use in subsonic flight, the aircraft power plant 100 generally comprising an engine 110 and a propeller 120, the power plant 100 generally comprising, in series flow communication, the propeller 120 attached to a shaft 108 and through which ambient air is propelled, a compressor section 114 for pressurized air, a combustor 116 in which the compressed air is mixed with fuel and ignited for generating an annular flow of hot combustion gases, and a turbine section 106 for extracting energy from the combustion gases, the propeller 120 converting rotational motion of the shaft 108 from the engine 110 to provide propulsive force (also referred to as thrust) to the aircraft, the propeller 120 comprising two or more propeller blades 122, the blade angle of the propeller blades 122 may be adjusted, the blade angle may be referred to as β angle, angle of attack, or blade pitch.

Referring to FIG. 2A, a system 200 for operating the power plant 100 is shown according to an embodiment, in which a control system 210 receives a power lever request from a power lever 212 of an aircraft under the control of a pilot of the aircraft, the power lever request indicating the type of thrust required by the power lever 212, the power lever request indicating the position of the power lever 212, several power lever positions may be selected, including those that are (1) the maximum forward thrust (MAX FWD) typically used during takeoff, (2) the flight idle (F L T ID L E) that may be used during approach in flight or during ground taxi, (3) the ground idle (GND L E) that the propeller 120 is rotating but providing very low thrust, (4) the maximum reverse thrust (MAX REV) typically used at landing to slow the aircraft.

Control system 210 receives additional inputs related to the operation of propeller 120, engine 110, and/or the aircraft. In the illustrated embodiment, the control system 210 receives the blade angle of the propeller 120. In some embodiments, control system 210 receives an aircraft status indicating whether the aircraft is on the ground or in flight. The additional inputs may vary depending on the actual implementation.

Generally, the control system 210 is configured to control the engine 110 and the propeller 120 based on the received input. Control system 210 controls engine 110 by outputting an engine request to an engine actuator 216 for adjusting engine fuel flow, and controls propeller 120 by outputting a propeller request to a propeller actuator 214 for adjusting a blade angle of propeller 120. The engine actuator 216 and/or the propeller actuator 214 may each be implemented as a torque motor, a stepper motor, or any other suitable actuator. Control system 210 determines an engine request and a propeller request based on the received inputs. The propeller actuator 214 may control hydraulic oil pressure to adjust the blade angle based on the propeller request. The engine actuator 216 may regulate the flow of fuel to the engine 110 based on the engine request. Although the control system 210 is shown separate from the power plant 100, this is for illustrative purposes.

The control system 210 receives a request for reverse thrust of the propeller 120 from a power rod 212 of the aircraft. The control system 210 is configured to control the engine 110 to prevent reverse thrust of the propeller 120 by preventing an increase in engine output power when the blade angle of the propeller 120 exceeds a reverse thrust blade angle threshold. Control system 210 is configured to allow reverse thrust of propeller 120 based on the power rod request by allowing an increase in engine output power when the blade angle is below a reverse thrust blade angle threshold. Blocking reverse thrust refers to preventing the engine 110 from providing output power based on the output power required by the power rod 212. In some embodiments, preventing reverse thrust includes setting the output power of engine 110 to a minimum level for engine 110. Allowing reverse thrust refers to allowing the engine 110 to provide output power based on the output power required by the power rod 212. By allowing and blocking reverse thrust based on the position of the blade angle, this may prevent the propeller 120 from accidentally providing positive thrust if increased engine power is applied prematurely when transitioning from forward thrust to reverse thrust. The corresponding blade angle for the reverse thrust blade angle threshold may vary depending on the actual implementation.

Referring to fig. 2B, a control system 210 is shown according to an embodiment. In this embodiment, propeller controller 252 controls propeller 120, and engine controller 254 controls engine 110. Propeller controller 252 determines and outputs a propeller request, and engine controller 254 determines and outputs an engine request. In this embodiment, propeller controller 252 receives inputs (e.g., power lever requests, blade angles, aircraft states, and/or any other suitable inputs) and is in electronic communication with the engine controller to provide one or more of the received inputs to engine controller 254. In some embodiments, engine controller 254 additionally or alternatively receives inputs (e.g., power lever requests, blade angles, aircraft states, and/or any other suitable inputs). In some embodiments, engine controller 254 provides one or more of the received inputs to propeller controller 252. In some embodiments, propeller controller 252 may determine a blade angle of propeller 120 and provide the blade angle to engine controller 254. In an alternative embodiment, the functions of propeller controller 252 and engine controller 254 may be implemented in a single controller.

To further illustrate the allowance and prevention of reverse thrust, an example of a transition from forward thrust to reverse thrust will now be described. When the power lever 212 requests forward thrust, the control system 210 controls the blade angle of the propeller 120 and the output power of the engine 110 based on the power lever request. For example, when the aircraft is in flight and the power lever position is set at or above the flight idle position, propeller controller 252 controls the blade angle above the forward thrust blade angle threshold to maintain a constant propeller speed at the propeller speed target and engine controller 254 controls engine output based on the power lever position. When the propeller speed is higher than the target, the propeller blade angle increases, which causes the propeller 120 to expel more air and thus reduce the propeller speed. When the propeller speed is below target, the propeller blade angle is reduced, which results in the propeller 120 expelling less air and thus increasing the propeller speed. Controlling the propeller 120 to maintain a constant speed at the propeller speed target may be referred to as speed control. Engine output power may be determined from a schedule based on the power lever position. Controlling engine output power based on power lever position may be referred to as power control.

When the power lever position moves below the ground idle position to request reverse thrust, propeller controller 252 determines the blade angle of propeller 120 from a blade angle schedule based on the power lever request (e.g., power lever position), and engine controller 254 sets the engine output power to a low power state (e.g., minimum power level of engine 110). Propeller controller 252 controls the blade angle to obtain a reverse blade angle that is directly related to the power lever position.

Engine controller 254 may further use the aircraft state to allow or prevent thrust. In some embodiments, engine controller 254 allows reverse thrust when the blade angle of propeller 120 is below a reverse thrust blade angle threshold and the aircraft state indicates that the aircraft is on the ground. In some embodiments, engine controller 254 blocks reverse thrust when the blade angle is above a reverse thrust blade angle threshold or when the aircraft state indicates that the aircraft is in flight.

Referring to fig. 2C, in some embodiments, each of propeller controller 252 and engine controller 254 includes two channels a and B. For each of the controllers 252, 254, the channel A, B is a redundant channel, and one of the channels (e.g., channel a) is selected to be active while the other channel is still in standby (e.g., channel B). The channel is configured to generate and output an engine request or a propeller request when the channel is in an active state, and not generate and output an engine request or a propeller request when the channel is in a standby state. When a channel is in standby, it is functional and can take over control when needed. If it is determined that the currently active channel or one of the actuators 214, 216 is malfunctioning or inoperative, the currently active channel may be deactivated and the standby channel activated. Similarly, if during operation an input to the currently active channel is erroneous or non-existent, the currently active channel may be deactivated and one of the standby channels activated.

In the illustrated embodiment, each channel A, B of propeller controller 252 receives a power lever request from at least one sensor 224 (e.g., a two-coil rotary variable differential transformer, where one coil provides a power lever request to channel a and the other coil provides a power lever request to channel B). Each channel A, B of propeller controller 252 also receives the blade angle of the propeller from at least one sensor 224 (e.g., a dual coil rotary variable differential transformer, where one coil provides the blade angle to channel a and the other coil provides the blade angle to channel B). Propeller actuator 214 (e.g., a dual input pitch change mechanism actuator) adjusts the blade angle based on the propeller request from the active channel of propeller controller 252. In this example, the engine controller 254 receives blade angle and power lever requests from the propeller controller 254. An engine actuator 216 (e.g., a dual input torque motor) regulates fuel flow to the engine 110 based on an engine request from an active channel of the engine controller 254.

Referring to FIG. 3A, a flow chart of a method 300 for operating an engine, such as engine 110, is shown. Method 300 may be performed by control system 210 and/or engine controller 254. At step 302, a request for reverse thrust of the propeller 120 is received from the power rod 212 of the aircraft. Receiving the request for reverse thrust may include receiving a position of the power rod 212 from at least one sensor associated with the power rod 212. Receiving a request for reverse thrust may include receiving a request for reverse thrust from propeller controller 252. At step 304, the blade angle of the propeller 120 is obtained. Obtaining the blade angle of the propeller 120 may include receiving the blade angle of the propeller 120 from the propeller controller 252. At step 306, reverse thrust of the propeller 120 is prevented when the blade angle exceeds a reverse thrust blade angle threshold. At step 308, reverse thrust of the propeller 120 is allowed when the blade angle is below the reverse thrust blade angle threshold. The reverse thrust blade angle threshold may correspond to a minimum blade angle at which the propeller may provide reverse thrust. In some embodiments, allowing reverse thrust includes determining a power demand of the engine 110 based on the power lever request (e.g., based on the position of the power lever 212) and controlling the output power of the engine 110 based on the power demand. Controlling the output power of the engine 110 may include determining a fuel flow rate of the engine 110 based on the power demand and outputting a fuel flow rate request to the engine actuator 216 to control the fuel flow rate to the engine 110.

Referring additionally to FIG. 3B, another embodiment of a method 300 for operating an engine, such as engine 110, is shown. In some embodiments, the method 300 includes: a power lever request is received from the power lever 212 and an aircraft state is obtained indicating whether the aircraft is on the ground or in flight. In some embodiments, method 300 blocks reverse thrust when the aircraft status indicates that the aircraft is in flight and/or when the blade angle exceeds a reverse thrust blade angle threshold, and method 300 allows reverse thrust based on a reverse thrust request when the aircraft status indicates that the aircraft is on the ground and when the blade angle is below the threshold.

Each request for reverse thrust, blade angle of the propeller, and/or aircraft state may be received from a respective measurement device that includes one or more sensors. In some embodiments, the request for reverse thrust, blade angle of the propeller, and/or aircraft state is obtained via existing components as part of engine control and/or operation. For example, the request for reverse thrust, blade angle of the propeller, and/or aircraft state may be provided from one of an engine controller, a propeller controller, or an aircraft computer. The request for reverse thrust, blade angle of the propeller, and/or aircraft state may be obtained dynamically in real time, may be obtained regularly according to any predetermined time interval, or may be obtained irregularly.

At step 352, the method 300 includes determining whether the aircraft is on the ground or in flight based on the aircraft state. If the aircraft is in flight, then at step 354, a power request for the engine 110 is determined based on the power lever request, which is used for forward thrust. In step 356, fuel flow to the engine 110 is controlled based on the power request. At step 352, if it is determined that the aircraft is on the ground, the method 300 proceeds to step 358.

At step 358, method 300 includes determining whether the power lever request indicates that the position of power lever 212 is between the ground idle position and the flight idle position. If the position of the power lever 212 is between the ground idle position and the flight idle position, then at step 360, the power request of the engine 110 is determined to correspond to the minimum power of the engine 110. At step 358, if the position of power lever 212 is not between the ground idle position and the flight idle position, method 300 proceeds to step 362.

At step 362, the method 300 includes determining whether the power lever request indicates that the position of the power lever 212 is below a ground idle position. If the power lever is not below the ground idle position, then at step 354, a power request for the engine 110 is determined based on the power lever request (e.g., power lever position), which is used for forward thrust. At step 362, if the power lever is below the ground idle position, the method 300 proceeds to step 364.

At step 364, method 300 includes determining whether the blade angle is below a reverse thrust blade angle threshold. If the blade angle is not below the reverse thrust blade angle threshold, then at 360, the power request of the engine 110 is determined to correspond to the minimum power of the engine 110. If the blade angle is below the reverse thrust blade angle threshold, then at step 366, a power request for the engine 110 is determined based on the power lever request for reverse thrust (e.g., power lever position).

In some embodiments, the systems and methods described herein may be used with an aircraft that includes two powerplants. For example, each power plant may be implemented in accordance with power plant 100. Thus, the systems and methods described herein may be used to operate a first engine coupled to a first propeller and to operate a second engine coupled to a second propeller. In some embodiments, step 304 of fig. 3A includes obtaining a first blade angle of the first propeller and a second blade angle of the second propeller. In some embodiments, at step 306 of FIG. 3A, reverse thrust is prevented when at least one of the first blade angle and the second blade angle exceeds a reverse thrust blade angle threshold. In some embodiments, reverse thrust is prevented when the aircraft state indicates that the aircraft is in flight and/or when at least one of the first blade angle and the second blade angle exceeds a reverse thrust blade angle threshold. In some embodiments, at step 308 of fig. 3A, reverse thrust is allowed when the first blade angle and the second blade angle are below a reverse thrust blade angle threshold. In some embodiments, reverse thrust is allowed when the aircraft state indicates that the aircraft is on the ground and when the first blade angle and the second blade angle are below a reverse thrust blade angle threshold. A first engine controller associated with a first engine may perform the method 300 for allowing and preventing reverse thrust of the first engine, and a second engine controller associated with a second engine may perform the method 300 for allowing and preventing reverse thrust of the second engine. Alternatively, in some embodiments, each power plant of a multi-power plant aircraft may independently implement method 300 and/or include control system 210.

In some embodiments, the systems and/or methods described herein may be used with the systems and/or methods described in U.S. patent application No. 16/159,970, the contents of which are incorporated herein by reference.

The systems and methods described herein may be used to prevent and allow forward thrust. In some embodiments, control system 210 receives a request for forward thrust from power rod 212. The control system 210 may be configured to control the engine 110 to prevent forward thrust when the blade angle of the propeller 120 is below a forward thrust blade angle threshold. Control system 210 may be configured to allow forward thrust based on the power rod request when the blade angle exceeds a forward thrust blade angle threshold. The corresponding blade angle of the forward thrust blade angle threshold may vary depending on the actual implementation.

Referring to fig. 4, an example of a computing device 400 is shown. The control system 210 may be implemented with one or more computing devices 400. For example, each of propeller controller 252 and engine controller 254 may be implemented by a separate computing device 400. Computing device 400 includes a processing unit 412 and a memory 414, memory 414 having stored therein computer-executable instructions 416. The processing unit 412 may include any suitable device configured to implement the method 300 such that, when executed by the computing device 400 or other programmable apparatus, the instructions 416 may result in the functions/acts/steps performed as part of the method 300 being performed as described herein. Processing unit 412 may include, for example, any type of general purpose microprocessor or microcontroller, a Digital Signal Processing (DSP) processor, a Central Processing Unit (CPU), an integrated circuit, a Field Programmable Gate Array (FPGA), a reconfigurable processor, other suitable programmed or programmable logic circuitry, or any combination thereof.

Memory 414 may include any suitable known or other machine-readable storage medium. Memory 414 may include non-transitory computer-readable storage media such as, but not limited to: an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. The memory 414 may comprise any type of suitable combination of computer memory, either internal to the device or external to the device, such as Random Access Memory (RAM), Read Only Memory (ROM), Compact Disc Read Only Memory (CDROM), electro-optical memory, magneto-optical memory, Erasable Programmable Read Only Memory (EPROM), and Electrically Erasable Programmable Read Only Memory (EEPROM), ferroelectric RAM (fram), and the like. Memory 414 may comprise any storage device (e.g., an apparatus) adapted to retrievably store machine-readable instructions 416 that are executable by processing unit 412. It is noted that the computing device 400 may be implemented as part of a Fully Authorized Digital Engine Control (FADEC) or other similar device, including an Electronic Engine Control (EEC), an engine control unit (EUC), an electronic propeller control, a propeller control unit, and so forth.

The methods and systems for operating an engine described herein may be implemented by a high level procedural or object oriented programming language, or a scripting language, or a combination thereof, to communicate with or facilitate the operation of a computer system (e.g., computing device 400). Alternatively, the method and system for operating an engine may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code implementing the methods and systems for operating the engine may be stored on a storage medium or device, such as a ROM, magnetic disk, optical disk, flash drive, or any other suitable storage medium or device. The program code can be read by a general-purpose or special-purpose programmable computer for configuring and operating the computer when the storage medium or device is read by the computer to perform the steps described herein. Embodiments of the method and system for operating an engine may also be considered to be implemented by a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer readable instructions which cause a computer, or more specifically the processing unit 412 of the computing device 400, to operate in a specific and predefined manner to perform the functions described herein, such as those described in the method 300.

Computer-executable instructions may take many forms, including program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Generally, the functionality of the program modules may be combined or distributed as desired in various embodiments.

The above description is intended to be exemplary only, and those skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Still other modifications that fall within the scope of the invention will be apparent to those skilled in the art from a reading of this disclosure.

Aspects of the methods and systems for operating an engine may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. While particular embodiments have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. The scope of the appended claims should not be limited to the embodiments set forth in the examples, but should be accorded the broadest reasonable interpretation consistent with the description as a whole.