Patent Application
20120095661
The present invention relates to aircraft engine control systems. In particular, the invention relates to control systems for small aircraft engines.
Aircraft engines require highly reliable systems for control to ensure safe and efficient operation. Reliable control for more sophisticated gas turbine engines, and even some piston engines, is maintained, for example, by a Full Authority Digital Engine Control (FADEC). A FADEC receives cockpit commands in the form of a signal indicative of a performance level required from an engine. The FADEC also receives signals from a variety of sensors and other systems around the engine and the aircraft. The FADEC applies a set of control rules to the received signals and determines control signals to send to effectors on and around the engine. The control signals sent by the FADEC direct the effectors in such a way as to produce the required engine performance level. The FADEC performs this control function many times per second.
The primary mechanism by which the FADEC controls the engine is by controlling the amount of fuel flowing to a combustion area of the engine. In a gas turbine engine, for example, a Fuel Metering Unit (FMU) receives control signals from the FADEC that direct electro-mechanical effectors within the FMU to produce a required fuel flow rate. The FMU may also contain effectors that adjust stator vanes to alter the flow of air through the engine or bleed valves to control a compressor bleed air flow rate. The FMU often contains sensors, for example, an electro-mechanical position sensor, such as a Rotary Variable Differential Transformer (RVDT), monitoring the position of the effectors to provide signals to the FADEC as part of a feedback loop for more precise and responsive adjustment of the effectors. Signals to and from the FMU are typically analog and require heavy, shielded cables with large, heavy, shielded feed through connectors attached to the housing of the FMU to ensure the integrity of the analog signals. Like the FMU, the FADEC requires large, heavy, shielded feed through connectors attached to the housing of the FADEC to ensure the integrity of the analog signals. The FADEC is typically located somewhere on the engine to be close to the FMU to minimize the cable lengths between the FADEC and the FMU. However, the FADEC contains sophisticated electronics that generally cannot perform reliably if exposed to operating temperatures in and around the engine core. A cooling device attached to the FADEC, such as a cooling plate cooled by fuel flowing to the engine, can provide cooling for the FADEC. This leads to a tradeoff between the proximity of the FADEC to the FMU near the extremely hot engine core, and the cooling capacity and weight of the cooling device needed to protect the FADEC. As a result, the FADEC is typically mounted on or near the engine, but not close to the FMU and the engine core. The challenge presented by this tradeoff is particularly acute in small engines where the impact of extra cable weight is much greater as a fraction of the total engine weight than for a large engine.
Positioning the FADEC somewhere on or near the engine to minimize the cable lengths between the FADEC and the FMU forces a corresponding increase in cable lengths between the FADEC and the many sensors and systems on the airframe that provide signals to the FADEC. While such an increase in cable length, and the corresponding increase in cable weight, is a significant burden for a large engine on a large airframe, the increased weight represents an even greater relative burden for a small engine on a small airframe.
It is desirable to design a FADEC to control a large variety of engines. In use, an individual FADEC must be configured for the combination airframe and actual engine it will control. In addition, the FADEC performs complex calculations based, in part, on sensor input from the airframe. Each airframe type to which an engine may be attached will likely have different sensors, both in quantity and type, and will certainly have unique flight characteristics that require adjustment in the engine control calculations performed by the FADEC. The FADEC must be configured, or programmed, with control schedules for its specific engine/airframe combination. Storage memory for the control schedules for all foreseeable engine/airframe combinations for which the FADEC could be used can be allocated in the FADEC if the FADEC has sufficient data storage. A large engine can accommodate a large FADEC with room for such a large amount of data storage. Because the control schedules are stored and available in the FADEC, a single certification test can be performed for the FADEC software that covers all known engine/airframe combinations. Configuring a FADEC for such a large engine involves inserting a data entry plug into the FADEC that corresponds to the specific engine/airframe combination. The plug is typically large and sturdily constructed to handle the stresses associated with being mounted on the engine, thus requiring a large and sturdily constructed external socket on the FADEC as well. The data entry plug acts as a set of jumpers, directing the FADEC to the correct software for the desired airframe/engine combination.
In contrast, small engines cannot tolerate the extra weight of a FADEC large enough to store such a large amount of data, nor the size and weight of the data entry plug and the data entry plug socket. Configuration of small engines is done by loading a single software version into the FADEC for the specific engine/airframe combination. Each version of the software for the many unique engine/airframe combinations must be independently certified at considerable time and cost. This severely limits the number of small engine/airframe combinations to which a FADEC may be attached.
One embodiment of the present invention is a full authority digital engine controller (FADEC) for controlling an engine attached to an airframe. The FADEC includes an electronic engine controller (EEC) attached to the engine, an airframe data concentrator (ADC) attached to the airframe, and a digital data bus electrically connecting the ADC to the EEC. The ADC is electrically connected to a plurality of airframe sensors to convert the airframe sensor signals to airframe sensor digital data. The digital bus conducts the airframe sensor digital data to the EEC.
Full Authority Digital Engine Control (FADEC) systems for small aircraft engines are limited in their functionality by the need to minimize weight penalties associated with such control systems. The present invention significantly reduces such weight penalties by reducing the number, length and bulk of cables and cable connectors linking various components to the FADEC. In addition, by distributing the FADEC functions between the engine and the airframe, some of the weight and complexity of the typical engine-mounted FADEC is shifted from the engine to the airframe, which is better able to handle the weight and is a more benign environment, better suited to complex components. Finally, the reduced weight penalty and more suitable environment for a portion of the FADEC provide an opportunity to expand FADEC functionality to include features normally found only on large aircraft engines, such as configuration by data entry plug.
As illustrated in
In operation, airframe sensors 26 generate analog sensor signals which are transmitted to ADC 18. ADC 18 converts the analog sensor signals from airframe sensors 26 to airframe sensor digital data for transmission over digital bus 22. Cockpit display/control 24 also generates airframe sensor signals including, for example, throttle setting and airspeed set point. The electrical connection between cockpit display/control 24 and ADC 18 is either analog or digital. If analog, ADC 18 converts the analog signals from cockpit display/control 24 to airframe sensor digital data for transmission over digital bus 22. ADC 18 transmits the airframe sensor digital data over digital bus 22 to EEC 20. EEC 20 receives an analog sensor signal from engine sensor 30. EEC 20 generates a control signal by applying a set of control rules to the analog sensor signal received from engine sensor 30 and the airframe sensor digital data received over digital bus 22. EEC 20 transmits the control signal to effector 32 in FMU 28 to, for example, modulate the flow of fuel to engine 12, adjust stator vanes to alter the flow of air through the engine, or modulate the flow of compressor bleed air, thereby controlling engine 12.
Optionally, the analog sensor signal from engine sensor 30 is converted by EEC 20 to engine sensor digital data for transmission over digital bus 22. EEC 20 transmits the engine sensor digital data over digital bus 22 to ADC 18. Also, optionally, EEC 20 transmits other digital data, for example, an engine maintenance message or a calculated engine setting, over digital bus 22 to ADC 18. If the electrical connection between ADC 18 and cockpit display/control 24 is digital, ADC 18 transmits the digital data directly to cockpit display/control 24 for display. If the electrical connection between ADC 18 and cockpit display/control 24 is analog, ADC 18 converts the digital data to an analog signal before transmitting the converted analog signal to cockpit display/control 24 for display.
The distributed FADEC of the present invention provides several advantages. The use of digital bus 22 to transmit information between airframe 14 and engine 12 replaces numerous cables and cable connectors required to transmit analog airframe sensor information with a single digital data bus resulting in a reduction in weight associated with an engine control system. This weight reduction is particularly significant for small aircraft engines. In addition, by transferring some of the functionality of FADEC 16 off engine 12 to airframe 14, for example, analog-to-digital conversion of the airframe sensor signals, electronics associated with the conversion are in a more benign environment. The environment of engine 12 is typically fraught with high vibration and high temperatures, compared with the environment of airframe 14. Because the electronics need not be designed for high vibration and high temperature, the electronics are optionally less expensive, more readily available and contain additional functionality, for example, extra memory and smaller form factor.
Another advantage of the distributed FADEC of the present invention is retaining critical engine control on the engine itself. Any link between airframe 14 and engine 12, such as digital bus 22, is subject to disruption of data transmission. While the airframe sensor digital data is an important input to EEC 20 for proper control of engine 12, EEC 20 can still operate engine 12 without the airframe sensor digital data. EEC 20 can generate the control signal by applying the set of control rules to the analog sensor signal received from engine sensor 30, employing default values for airframe sensor digital data during disruption of digital bus 22. EEC 20 continues to transmit the control signal to effector 32 in FMU 28, thereby controlling engine 12. Because only non-critical functionality is moved off engine 12 to ADC 18, a higher level of safety is achieved by ensuring continued engine control and operation during a disruption of the link between engine 12 and airframe 14.
Although the embodiment of
For ease of illustration, the embodiment of
The embodiment of the present invention illustrated in
Beyond the significant weight reduction, the embodiment of
The embodiment of
Although the embodiment of
The embodiment described in reference to
FADEC 316 is configured by inserting data entry plug 342 into data entry plug socket 340. The electrical connections of data entry plug 342 direct ADC 326 to retrieve configuration data corresponding to the specific combination of engine 312 and airframe 314 from the control schedules stored within data storage device 338. ADC 326 retrieves the configuration data from data storage device 338 and transmits the configuration data over digital bus 322 to EEC 320. EEC 320 receives the transmitted configuration data and completes configuration of FADEC 316.
In addition to all of the advantages described above in reference to
The embodiment shown in
Further reduction in weight associated with the engine control system is achieved by incorporating EEC 420 within FMU 428, thereby reducing the amount of heavy, shielded cable required to connect EEC 420 to components within FMU 428, such as effector 432. Incorporating EEC 420 within FMU 428 also eliminates the need for a separate heavy protective housing normally surrounding a prior art FADEC and, along with it, the large, heavy, shielded feed-through connectors attached to the housing of such a prior art FADEC. Beyond the significant weight reduction, incorporating EEC 420 within FMU 428 provides the additional benefit of creating in FMU 428, a single, testable unit incorporating EEC 420 and effector 432. The ability to test and calibrate FMU 428 as a unit permits the use of lower cost, lower precision parts and allows for better tuning of the integrated unit, leading to better performance characteristics for control of fuel flow.
Another advantage of the distributed FADEC of the present invention is retaining critical engine control on the engine itself. Any link between airframe 414 and engine 412, such as digital bus 422, is subject to disruption of data transmission. While the airframe sensor digital data is an important input to EEC 420 for proper control of engine 412, EEC 420 can still operate engine 412 without the airframe sensor digital data. EEC 420 can generate the control signal by applying the set of control rules to the analog sensor signal received from engine sensor 430, employing default values for airframe sensor digital data during disruption of digital bus 422. EEC 420 continues to transmit the control signal to effector 432 in FMU 428, thereby controlling engine 412. Because only non-critical functionality is moved off engine 412 to ADC 418, a higher level of safety is achieved by ensuring continued engine control and operation during a disruption of the link between engine 412 and airframe 414.
Another advantage is obtained by transferring some of the functionality of FADEC 416 off engine 412 to airframe 414, for example, analog-to-digital conversion of the airframe sensor signals, electronics associated with the conversion are in a more benign environment. Because the electronics need not be designed for high vibration and high temperature, the electronics are optionally less expensive, more readily available and contain additional functionality, for example, extra memory and smaller form factor.
Finally, the reduced weight penalty and more suitable environment for the portion of the distributed FADEC on the airframe side provide an opportunity to expand FADEC functionality to include features normally found only on large aircraft engines, such as configuration by data entry plug. Because data storage device 438 is large enough to hold configuration tables for all foreseeable combinations and variations of engine 412 and airframe 414, a single certification for FADEC 416 covers all known engine 412 and airframe 414 combinations for which FADEC 416 may be used. This is in contrast to the prior art for small aircraft engine FADECs, where each version of the software for the many unique engine/airframe combinations or variation must be independently certified by the certifying authority. Also, because data entry plug 442 and data entry plug socket 440 are located in the benign environment of airframe 414, they need not be as large, heavy or sturdily constructed as comparable components are when mounted on a large engine.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
