AUXILIARY COMPRESSOR AIR SUPPLY FOR AN AIRCRAFT

Abstract: Engine (10) shaft power provides a first input (16) for a differential gear box (18). This input (16) is additive in a gear box (18) to a second input (30) from an electric motor (32). The output (22) of the gear box (18) powers a rotor (24) of an auxiliary compressor (12) which produces compressed air for providing needed pneumatic services aboard the aircraft. Compressor rotor speed is sensed (sensor 40) and used for controlling operating current (via controller 42 and frequency converter 44) to the electric motor (32). Motor (32) is an electronically commutated brushless electric motor having a high torque output which is substantially linearly proportional to the input current.

Description: Technical Field This invention relates to an air supply system for an aircraft, comprising a propulsion engine having an output shaft, an air compressor separate from said engine having an inlet, an outlet and a rotor, said compressor being drivenly connected to the output shaft of the engine. Such a system is known from US-A-4 553 407. Background Art The operation of an aircraft requires the provision of a source of compressed air for pressurizing the cabin of the aircraft and providing other pneumatic services aboard the aircraft. The compressed air used for the pneumatic services has been obtained in different ways. One way is to design the engines of the aircraft in such a way that air can be bleed off from the compressors of the engines and used for the pneumatic services. It is also known to provide auxiliary compressors aboard aircraft and drive them directly or indirectly from the engine. Known direct drive systems utilize an auxiliary shaft which is connected at one end to the engine shaft and at its opposite end to the auxiliary compressor. Known indirect systems utilize a hydraulic pump which is driven by the engine shaft and which in turn drives a hydraulic motor which is connected to the auxiliary compressor. The efficient operation of advanced technology engines requires the passage of relatively low volumes of compressed air through the engines. Air cannot be bled from these engines for supplying the pneumatic services without severly affecting the function of these engines as the prime mover for the aircraft. If the engines are redesigned so that sufficient engine bleed air is available, the size, weight, and efficiency of the engines is compromised. Known systems for producing pneumatic services air aboard aircraft, as alternates to bleed air systems, have required compromises in operating efficiencies of the engines over a wide band of operating requirements. The known systems which comprise auxiliary air compressors coupled to the engine either require gear shifting transmissions, or are designed to handle worst case design conditions and operate in surge relief during some of the normal operating conditions. Known systems which comprise remotely powered compressors, driven either by hydraulic motors powered by the hydraulic system aboard the aircraft or electric motors powered by the electric system aboard the aircraft, take substantial amounts of power from the aircraft hydraulic or electrical systems, and are generally also chacterized by costly line losses of power. The system of the present invention applies recent technological advances in electric motors with the best features of known auxiliary compressor sytems, to produce a maximum efficiency system which does not require the mechanical complexity of gear shifting and/or slip couplings, and which does not experience substantial amounts of power waste. Disclosure of the Invention It is thus an object of the present invention to provide an air supply system as known from US-A-4 553 407, which may be efficiently used in an aircraft that is equipped with advanced technology high-bypass-ratio engines without the need for gear shifting and/or slip couplings. This is accomplished according to the invention in that the compressor is connected to the engine output shaft through differential gearing means having an output connected to the compressor rotor, a first input drivenly connected to the output shaft of the aircraft engine and a second input, an electric motor is drivingly connected to the second input; and means responsive to a condition of the compressor are provided for operating the electric motor in an amount sufficient to provide a predetermined desired amount of input drive to the differential gearing, for helping to drive the compressor rotor during periods of low output from the engine shaft, for the purpose of establishing a desired output from the air compressor. It should be noted that US-A-4 572 961 teaches a constant speed drive for driving an electrical generator comprising a differential having an output shaft drivingly connected to the generator, a first input shaft drivenly connected to the aircraft engine and a second input shaft drivenly connected to an electric motor. However, this publication does not suggest applying such a constant speed drive to an air supply system. Further preferred embodiments of the invention form the subject-matter of dependent claims 2-7. Brief Description of the Drawings Fig. 1 of the drawing is a schematic diagram of an embodiment of the present invention, such diagram including both legends and reference numerals; Fig. 2 is a top plan view of an example package design of a compressor, a differential gear box and a speed trim motor; Fig. 3 is an elevational view of the package shown by Fig. 2, looking toward the inlet of the compressor; Fig. 4 is an end elevational view of the package shown by Figs. 2 and 3, looking towards an end of the speed trim motor; and Fig. 5 is a schematic view of a differential gear box and its connection between the main engine shaft, the speed trim motor and the compressor rotor. Best Mode for Carrying Out the Invention Referring to Fig. 1, an aircraft propulsion engine 10 is shown by a block diagram. This engine 10 is a gas turbine engine. It comprises a compressor section, a combustion chamber section and a turbine section, in series. In accordance with the present invention, an auxiliary compressor 12, i.e. a compressor separate from the engine 10, is provided for generating the compressed air that is used for cabin pressurization, air conditioning, etc. Herein this compressed air will be sometimes referred to as the "pneumatic services air." In accordance with the invention, engine shaft power is used for driving the compressor 12 during relatively high power operation of the engine 10, e.g. during climb and cruise operation. As is known per se, a power take-off shaft 14 is provided which at one end is suitably connected to the turbine shaft of the engine 10, e.g. by meshing bevel gears. In accordance with the present invention, the shaft 14 provides a first input 16 into a differential gear box 18. Shaft 14 may include a one-way drive coupling 20. The differential gear box 18 has an output shaft 22 which is connected to the rotor 24 of the compressor 12. Compressor 12 includes an air inlet 26 and an air outlet 28. The outlet 28 is connected to deliver the effluent of the compressor 12 to the various pneumatic services, e.g. to the aircraft cabin for pressurization. Of course, the pneumatic services system will include various controls and conditioning components which are not a part of this invention. In accordance with the invention, the differential gear box 18 includes a second input 30. This input 30 includes a shaft which is driven by an electric motor 32, herein termed "the speed trim drive motor." The output shaft of motor 32 may include a one-way drive coupling 34. The electric motor 32 is an electronically commutated brushless electric motor. This type of motor is a known but relatively new development and it is the availability of this motor which has made the present invention feasible and advantageous. This type of motor owes its basic simplicity and absolute minimum of moving parts to a permanent magnet field assembly (e.g. Samarium cobalt magnets). The motor 12 is characterized by high linearity. The torque increases directly with input current, independent of speed or angular position. The motor can be constructed in many different configurations, each of which involves a small envelope, enabling the motor 32 to be fitted into a quite small space. By way of example, a motor of this type, capable of generating about 102 hp, can fit within an envelope measuring about 12 inches long by about 8 inches in diameter. All aircraft are provided with some sort of electrical power supply 36. In accordance with an aspect of the invention, the aircraft may include a starter generator 38 that is first used for intiating start rotation of the engine 10. Then, when engine 10 is operating, the starter/generator 38 will be coupled to the engine 10, to be driven thereby, and controlled to function as a generator. Of course, the present invention does not rely on the presence of this particular type of electrical power supply. Rather, the electrical power supply 36 may take any suitable form. It is only necessary that the aircraft include an electrical power supply 36 of some form. In accordance with an aspect of the invention, a device or sensor is associated with the compressor 12, to measure the output of the compressor 12. This device may be in the form of a shaft speed sensor 40 which measures the rotational speed of the output shaft 22 from the gear box 18. This also constitutes a measurement of the rotational speed of the compressor rotor 24. The sensor 40 produces a signal which is transmitted to a compressor speed controller 42. The compressor speed controller 42 may be in the form of a microprocessor which takes the signal from sensor 40 and compares it with model information. During periods of reduced power operation of the aircraft, e.g. descent with idle engine power, a droop in compressor speed is detected by the sensor 40. In response, the compressor speed controller 42 functions to operate a frequency converter 44 which is interconnected between the electrical power supply 36 and the speed trim drive motor 32. It may be desired to simply maintain operation of the compressor 12 at a constant speed, in which case the compressor speed controller 42 and the frequency converter 44 function to operate the speed trim drive motor 32 in a manner resulting in its input to the differential gear box 18, combined with the decreased power input from the engine shaft 14, providing a constant output rotation of the gear box shaft 22. Or, it may be desired to obtain a pattern of operation of the compressor 12 which is not constant, but which requires an input from the drive motor 32 in addition from the engine shaft power inputs 16. This selected operation of the compressor 12 may be provided by other command information that is processed in the compressor speed controller 42. The sensor 40 for detecting speed of rotation compressor rotor shaft, the compressor speed controller or microprocessor 42 and the frequency converter 44 are all elements which are known per se and are commercially available. Accordingly, these common elements of the system are merely shown in a schematic or block diagram form. The one-way drive couplings 20, 34 may be one-way overriding clutches of the type shown in U.S. Pat. No. 2,723,531 (elements 17, 24, 32, 34), granted November 15, 1955, to Leond R. Wosika et al. The one-way drive coupling 20 in shaft 16 functions to prevent the second input 30 into the differential gear box 18 from back driving the shaft 14. The one-way drive coupling 34 between motor 32 and gear box input 30 prevents a first input 16 from back driving the motor 32. The differential gear box 18 is per se not a part of the present invention; it involves known technology. Accordingly the differential gear box 18 is also shown in block diagram form in Fig. 1. The differential gear box 18 functions to produce an output shaft speed which is additive of the two input shaft speeds, or which is at least a function of the sum of the two inputs 16, 30. Fig. 5 sets forth the drive system in schematic form, minus right angle gearing, etc. The shaft 16 which is connected to the drive shaft of the main engine is shown connected to a rotary carrier 46. The carrier 46 carries a plurality of planet gears 48, each suitably mounted to rotate about an axis 50. The gears 48 mesh with a sun gear 52 and a ring gear 54. The sun gear 52 is connected to the compressor shaft 22. Ring gear 54 is a part of a rotating member 56 which includes a second ring gear section 58. The output shaft 30 of the speed trim drive motor 32 is connected to an output gear 60 which meshes with ring gear 58. Rotation of shaft 16 produces a rotation of the carrier 56 and the planet gears 48 carried thereby. Carrier movement of the gears 48 results in the gears 48 orbiting about the axis of ring gear 54 while at the same time rotating about their individual axes 50. As the gears 58 move they impart rotation to the sun gear 52 which in turn imparts rotation to the compressor shaft 22 and the compressor rotor 24. The gearing is designed so that when the trim motor 32 is operating it drives the member 56 in a direction causing it to impart a driving force on the gears 48 which is additive to the driving force from the shaft 16 and the carrier 46. This enables operation of the trim motor 32 in such a manner that the trim motor can be used for maintaining the drive speed of the shaft 22 and the rotor 40, during low power operation of the main engine. Figs. 2-4 disclose an advantages package design of the auxilliary compressor 12, the differential gear box 15 and the speed trim drive motor 32. This package is relatively small and can fit within space available adjacent the aircraft engine. Fig. 2 has been termed a top plan view, Fig. 3 has been termed a side elevational view, and Fig. 4 has been termed an end elevational view. This was done for the purpose of describing the orientation of the views shown by figs. 2-4. These views are orthographic projections. Of course, in an actual use installation, the positioning of the various components may vary. The shaft 16 may extend away from the main engine shaft in any one of a large number of positions. As stated above, the use of the plan view, side elevational view and end elevational view terminology was done merely to relate the views to each other. They do not denote the actual positioning of the package in the aircraft. This positioning may vary substantially. In the package views (Figs. 2-4) the shaft 16 is shown to be coaxially related to the output shaft of the speed trim drive motor 32. The compressor rotor shaft 22 is shown to extend at a right angle to the shafts 16, 30. It is well within the skill of a person having ordinary skill in the art, to design a differential gear box transmission which will operate like the transmission shown schematically by Fig. 5, but which has been input to output orientation of the axes that is shown by Figs. 2-4. In view of this fact, and in view of the fact that the invention does not depend upon the package design shown by Fig. 2-4 (i.e. the package design may vary from that shown), the details of construction of a suitable differential gear box is not considered to be a part of the present invention. The present invention is a system invention in which the differential gear box can exist in more than one form. The present invention makes it possible to operate advanced technology engines in an efficient manner because it is not necessary to design these engines so that they will have to supply substantial amounts of bleed air. The engines can be efficiently operated during climb and cruise maneuvers and sufficient shaft power will be available to by itself drive the compressor 12. The differential gear box 18 and the speed trim drive motor 32 are relatively small in size, and are relatively light weight in comparison to the advantages obtained by their use when the need arises. During periods of low power operation of the engines, e.g. descent maneuvers, the speed trim drive motor 32 provides a second input 30 to the differential gear box 18, which is additive to the first input 16, to produce a desired output 22 for driving the compressor rotor 24. An additional benefit of the system of the invention is that while the aircraft is on the ground, ground electrical power may constitute the electrical power supply 36. This would make it possible to use the compressor 12 to generate air conditioning air while the aircraft is on the ground and the engines 10 are not operating. The embodiment that has been illustrated and described represents an example of the invention. As should be apparent, various modifications in component make-up and arrangement can be made without departing from the scope of the claims. Accordingly, I am not to be limited by the details of the example embodiment, but only by the claims, interpreted in accordance with established principals of claim interpretation.

Claims: An air supply system for an aircraft, comprising: a propulsion engine (10) having an output shaft (14); an air compressor (12) separate from said engine (10) having an inlet (26), an outlet (28) and a rotor (24); said compressor (12) being drivenly connected to the output shaft (14) of the engine (10); characterized in that the compressor (12) is connected to the engine output shaft (14) through differential gearing means (18) having an output (22) connected to the compressor rotor (24), a first input (16) drivenly connected to the output shaft (14) of the aircraft engine (10) and a second input (30); an electric motor (32) is drivingly connected to the second input (30); and means (40-44) responsive to a condition of the compressor (12) are provided for operating the electric motor (32) in an amount sufficient to provide a predetermined desired amount of input drive to the differential gearing (18), for helping to drive the compressor rotor (24) during periods of low output from the engine shaft (14), for the purpose of establishing a desired output from the air compressor (12). An air supply system according to claim 1, characterized in that the first input (16) to the differential gearing means (18) comprises a shaft which includes a one-way drive coupling (20) arranged to prevent the second input (30) from back driving the first input (16). An air supply system according to claim 1 or 2, characterized in that the second input (30) comprises a shaft which includes a one-way drive coupling (34) for preventing the first input (16) from back driving the second input (30). An air supply system according to any one of the preceding claims, characterized in that the electric motor (32) is a variable speed motor. An air supply system according to claim 4, characterized in that the means (40-44) responsive to a condition of the compressor (12) for operating the electric motor (32) comprises control means (40) responsive to the speed of rotation of the compressor rotor (24) to produce a signal, and means (42,44) responsive to said signal for controlling the output speed of the electric motor (32). An air supply system according to any one of the preceding claims, characterized in that the electric motor (32) is of a type which produces an output torque that is substantially linearly proportional to the input current to the motor (32). An air supply system according to claim 6, characterized in that the electric motor (32) is a brushless permanent magnet motor.

Inventors: KENNEDY, NORMAN JAMES
Applicants: THE BOEING COMPANY
Application year: 1987
Main classification: B64D41
IPC codes: B64D41